HK1233689B - Leather or leather article and method for producing same, hexavalent chromium treatment agent, method for treating hexavalent chromium in crude leather or crude leather article - Google Patents

Description

Leather or leather products and methods for their manufacture, hexavalent chromium treatment agents, and methods for treating hexavalent chromium in raw leather or raw leather products

Technical Field

The present invention relates to leather or leather products with reduced hexavalent chromium content, methods for producing the same, a hexavalent chromium treatment agent, methods for producing the same, and methods for treating hexavalent chromium in raw leather or raw leather products. More specifically, the present invention relates to a hexavalent chromium treatment agent comprising a compound containing a 1,2,3-trihydroxyphenyl group, and leather or leather products treated with the same.

Background Art

Leather products are used in a variety of products, including watch straps and handbags. In particular, the appearance of leather enhances the product's value and increases consumer satisfaction. Furthermore, since these products utilize a structure where the leather directly contacts the skin, the tactile feel of the leather further enhances the product's added value.

To produce such leather products, it is first necessary to produce large sheets of leather. To produce leather, the skins of animals to be used in leather products, such as crocodiles and cows, are obtained. In their original state, they are too durable to be used, so they are tanned. This treatment imparts heat resistance and durability, allowing leather to be produced from the skins. The leather thus obtained is then colored to a desired color or the surface shape is trimmed to produce a sheet of leather. To use this to make leather products, it is cut into the desired shape and attached to a core material using an adhesive to produce the leather product. The methods used to produce such leather products are well known.

Tanning is a method of treating hides to obtain durable leather. There was a time when tannin collected from plants was used, but the heat resistance, softness and elasticity of this treatment were insufficient. Therefore, chrome tanned leather with high heat resistance, softness and elasticity using chrome tanning agents (basic chromium sulfate) has recently become mainstream. Chrome tanned leather has the greatest economic importance, accounting for over 90% of the world. By embedding a hydrated chromium complex between the carboxyl groups of glutamic acid and aspartic acid in the collagen peptide skeleton, it is possible to obtain durable and soft leather. The method of chrome tanning is well known and widely known, for example, it is described on the website of the Japan Leather Technology Association, a non-profit organization.

In addition, as a tanning method, for example, Patent Document 1 discloses a method for tanning leather and skin, characterized in that the leather and skin are treated with a tanning agent containing deglycosylated iridoids and/or deglycosylated cleo-iridoids instead of a tanning agent containing genipin.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent No. 5302327 (page 4, paragraph 0016)

Patent Document 2: Japanese Patent Application Laid-Open No. 2008-231388

Summary of the Invention

Problems to be solved by the invention

High-quality leather or leather products with excellent heat resistance, softness, and elasticity are typically obtained through chrome tanning. The chrome tanning agent used for chrome tanning contains chromium, and a large amount of chromium remains in the leather or leather products tanned using this agent. While this residual chromium content varies depending on the chrome tanning method used in each country, the total chromium content in the leather or leather product, as determined by fluorescent X-ray analysis, is typically 5,000 ppm or greater, with some containing 6,000 ppm or greater, and others containing 7,000 ppm or greater. Depending on the method and the leather or leather product, it can also reach 10,000 ppm or greater.

The chromium in chrome tanning agents is trivalent, but hexavalent chromium is sometimes generated during the manufacturing process of leather or leather products due to heating, bonding and other processes. In addition, hexavalent chromium mixed into the chrome tanning agent as an impurity may sometimes be mixed into leather or leather products. When testing whether leather or leather products contain hexavalent chromium, in addition to the hexavalent chromium contained in the process, trivalent chromium will be oxidized to hexavalent chromium in the leather or leather products due to light, heat, high temperature and humidity, etc., so sometimes the result of containing hexavalent chromium is obtained. Although trivalent chromium is harmless, hexavalent chromium is harmful. When it comes into contact with the skin and mucous membranes, it can induce skin cracking, allergies and other diseases. In severe cases, it can cause dermatitis and tumors, so it has a great impact on the human body. Hexavalent chromium, even in small amounts, has all the harmful risks of carcinogenicity, mutagenicity, and reproductive toxicity. Due to its toxicity, it is also treated as a banned substance.

The EU regulation on hexavalent chromium in leather or leather products was published in the Official Journal of the European Union on March 26, 2014, as Regulation (EU) No. 301/2014 (Regulation (EU) No. 301/2014). According to this regulation, from May 1, 2015, leather products and products containing leather in skin-contacting parts are restricted from containing chromium (IV) oxide in an amount of 3 mg/kg (3 ppm) or more per dry weight of the leather and leather parts, taking into account the effects on the human body (particularly skin irritation). It should be noted that this regulation states that the EN ISO 17075 standard method is the only currently available international analytical method for the quantitative determination of hexavalent chromium in leather or leather products (Regulation (6)).

Patent Document 1 describes suppressing the formation of hexavalent chromium by using a specific tanning agent. However, leather products are typically produced by a variety of companies and blended together. Consequently, numerous companies perform leather tanning, and it is unrealistic to simply produce products that use a specific tanning agent in their respective tanning processes.

In Example 2 of Patent Document 2, it is described that an aqueous solution of ascorbic acid is added dropwise to tanned leather to render hexavalent chromium harmless. Ascorbic acid has a high reducing power and is also excellent in safety and quick-acting properties. However, ascorbic acid is prone to decomposition, so when stored in a solvent-dissolved state, the possibility of inactivation is high, and therefore there is a risk that it cannot be used on-site. In addition, an aqueous solution of ascorbic acid has water repellency and is difficult to penetrate into the interior of leather or leather products with high fat solubility. Moreover, it has a high solubility in water and is therefore easily lost from the leather or leather products due to sweat and moisture in the atmosphere (e.g., dew, rain). Therefore, ascorbic acid is difficult to remain in the leather or leather products, and there is a risk that the hexavalent chromium in the leather or leather products will be dissolved into the environment and exposed to people due to sweat and moisture in the atmosphere, making it impossible to stably maintain the reducibility of hexavalent chromium over a long period of time. In particular, hexavalent chromium oxidized from trivalent chromium in leather or leather products cannot be rendered harmless with ascorbic acid.

Furthermore, chrome-tanned leather generally involves a heating step, and therefore requires a treatment agent that can maintain its reducing power even when exposed to heat so that it can be used during the leather production process.

The present invention provides a heat-resistant hexavalent chromium remover that can remain in leather or leather products for extended periods of time, even when hexavalent chromium is present, and stably reduces the hexavalent chromium to, for example, trivalent chromium, rendering it harmless. The invention also provides leather or leather products that use the same to reduce the hexavalent chromium content to a level that does not fall within the restrictions set forth in Regulation (EU) No. 301/2014. The present invention also provides leather or leather products having a hexavalent chromium content of less than 3 ppm, preferably less than 2 ppm for greater safety, as measured in accordance with ISO 17075:2008-02. The lower limit is 0 ppm.

In the present invention, leather before treatment with the hexavalent chromium treatment agent of the present invention is also referred to as raw leather or raw leather products, and leather after treatment is also referred to as leather or leather products. The total chromium content of the leather or leather product, as determined by fluorescent X-ray analysis, remains unchanged before and after treatment with the treatment agent and is generally 5,000 ppm or greater, but may also contain 6,000 ppm or greater, 7,000 ppm or greater, and may even contain 10,000 ppm or greater depending on the production method.

Solutions for solving problems

The hexavalent chromium treatment agent of the present invention contains at least an organic compound (A) represented by Chemical Formula 1. The organic compound (A) has a reducing property capable of reacting with hexavalent chromium to reduce it to trivalent chromium, contains C atoms, O atoms, and H atoms, and has a hydroxyl group on a central carbon having single and double bonds between the three carbon atoms.

In formula (1), ^R1 , ^R2 , ^R3 , ^R4 , and ^R5 are each independently a substituent consisting of C, H, or O, preferably a carbonyl group containing an unsaturated bond, but not including reactive functional groups such as aldehyde or carboxyl groups. Furthermore, they preferably do not include nitrogen-containing groups such as amino or isocyanate groups, or sulfur-containing groups such as sulfate groups. ^R1 or ^R2 may optionally bond with any of ^R3 , ^R4 , or ^R5 to form a ring. It should be noted that, in the present invention, the hexavalent chromium treatment agent is sometimes also referred to as a hexavalent chromium remover.

The organic compound (A) preferably has the structure represented by the above formula (1) and a hydroxyl group, and does not have a reactive functional group such as an aldehyde group or a carboxyl group in its structure.

The hexavalent chromium treatment agent preferably comprises the organic compound (A) and an organic compound (B), wherein the organic compound (B) has a structure represented by the aforementioned chemical formula 1, which is reducible to react with hexavalent chromium to reduce it to trivalent chromium, and does not have a hydroxyphenyl group, an aldehyde group, or a carboxyl group. Furthermore, the organic compound (B) preferably does not have functional groups such as amino groups, nitrogen-containing groups such as isocyanate groups, or sulfur-containing groups such as sulfate groups.

The leather or leather product of the present invention comprises at least an organic compound (A) and trivalent chromium. The organic compound (A) has the structure shown in Chemical Formula 1, which is reducible to hexavalent chromium and reduces it to trivalent chromium, and a hydroxyphenyl group, and does not contain oxygen-containing groups such as aldehyde and carboxyl groups. The inclusion of the organic compound (A) allows the leather or leather product to have a hexavalent chromium content of less than 3 ppm, preferably less than 2 ppm, as measured in accordance with ISO 17075:2008-02. The trivalent chromium content varies depending on the leather or leather product and is not particularly limited, but is typically at least 4000 ppm, and may sometimes contain at least 4500 ppm.

Examples of the organic compound (A) or (B) include the following compounds (chemical formulas (2) to (14)) and their derivatives. In the present invention, a mixture thereof is preferably used.

·Pyrogallol

Propyl gallate

Tannic acid

1,2,4-Trihydroxybenzene

Phloroglucinol

Resorcinol

Hydroquinone

Catechol

2,3-Dihydroxynaphthalene

2,7-Dihydroxynaphthalene

1,4,9,10-Anthracenetetrol

·ascorbic acid

Tocopherol

The leather or leather products of the present invention preferably contain a hexavalent chromium treatment agent. The method for making it contain the hexavalent chromium treatment agent is preferably to use a hexavalent chromium treatment liquid in which the hexavalent chromium treatment agent is diluted in water, an organic solvent or a mixed solvent thereof to immerse the leather or leather products or to apply the leather or leather products. The method for making it contain a hexavalent chromium removal agent is preferably to use a hexavalent chromium treatment liquid in which the hexavalent chromium removal agent is diluted in a hexane or heptane solvent as an organic solvent to immerse the leather or leather products or to apply the leather or leather products. The hexavalent chromium treatment agent is also preferably the aforementioned formula (14). As a method for making it contain the hexavalent chromium treatment agent, the leather may also contain the hexavalent chromium treatment agent in order to dissolve it in an adhesive used in the production of leather products and obtain a harmless leather product.

The leather product is preferably a leather strap for a watch.

Effects of the Invention

The hexavalent chromium treatment agent of the present invention has a quick-acting effect in leather or leather products, remains stably for a long time, has a long-term reducing effect, and has excellent heat resistance. Therefore, when used, the treatment agent can render leather or leather products containing hexavalent chromium harmless and can suppress the generation of hexavalent chromium over a long period of time. In addition, the hexavalent chromium treatment agent remains in the treated leather or leather products, so even if hexavalent chromium is generated during use by customers after manufacturing, it can be removed, thereby allowing continued harmlessness. As a result, harmless leather can be provided, allowing leather, which is readily available from a variety of leather manufacturing companies, to be commercialized and used in a freely designed, high-value product.

Leather products obtained using this material do not contain harmful hexavalent chromium, which can cause skin cracking, allergies, and, in severe cases, dermatitis and tumors. Therefore, products that are friendly to the human body and the environment can be provided.

According to the present invention, it is possible to obtain leather or leather products in which harmful hexavalent chromium is rendered harmless until the functions and purposes of the leather or leather products are achieved.

The leather or leather product of the present invention does not release harmful hexavalent chromium over a long period of time even when exposed to sweat and atmospheric moisture (e.g., dew and rain). Therefore, it is possible to provide a product that is friendly to the human body and the environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an image taken with a digital camera showing the coloring properties of cowhide leather used in Example 34. FIG.

FIG. 2 is an image taken with a digital camera showing the coloring properties of cowhide leather used in Example 35. FIG.

DETAILED DESCRIPTION

Hereinafter, the present invention will be described in detail.

The hexavalent chromium treatment agent of the present invention contains an organic compound that reacts with harmful hexavalent chromium to chemically transform into a harmless compound. For example, the compound can reduce hexavalent chromium to render it harmless to trivalent chromium.

Generally, known reducing agents include lithium aluminum hydride, sodium borohydride, hydrazine, dibutylaluminum hydride, oxalic acid, formic acid, etc. However, there are various problems when using these representative reducing agents.

When lithium aluminum hydride is used, the chemical reagent is a powdered, strong reducing agent. However, it reacts violently with water to produce hydrogen, making it flammable and dangerous. Leather and leather products are often exposed to skin (sweat) and rain, so such flammable materials are not durable.

When using sodium borohydride, the chemical reagent is slightly hygroscopic and easily decomposes due to moisture, so it must be sealed and stored. For aqueous solutions generated by moisture such as sweat and rain, since the chemical reagent is a decomposition product, it shows strong alkalinity. Therefore, it has adverse effects on the skin (skin), mucous membranes, etc. Since it decomposes under acidic and neutral conditions to produce hydrogen, it must be stored in an alkaline solution, so it is impossible to contain sodium borohydride in leather or leather products. Since it decomposes in water and produces hydrogen, it is also difficult to handle.

Hydrazine is a colorless liquid with a pungent odor similar to ammonia. It produces white smoke when in contact with air, making it difficult to handle. It is easily soluble in water, has strong reducing properties, and is easily decomposed and flammable, making it difficult to handle.

When dibutylaluminum hydride is used, the chemical reagent is a colorless liquid, but is not resistant to moisture and must be stored and used in an inert gas atmosphere, making it difficult to use in ordinary air.

In the case of oxalic acid, the chemical binds strongly to calcium ions in the blood, making it toxic and designated as a non-pharmaceutical highly toxic substance under the Poison and Exploitably Toxic Substances Control Act. Using such a toxic substance on leather or leather products is not suitable for the intended purpose and is not durable.

When using formic acid, liquid formic acid solutions and vapors are harmful to the skin and eyes, sometimes causing irreversible damage to the eyes. Furthermore, inhalation can cause damage such as pulmonary edema, making it unsuitable for long-term use. Furthermore, considering the potential for adverse effects on the liver and kidneys from chronic exposure and the potential for allergens, this product does not meet the objectives of the present invention and is unsuitable for long-term use.

Based on these facts, the applicant conducted extensive research and experiments on hexavalent chromium treatment agents that can be used for leather or leather products, discovered which compounds meet the purpose, and completed the present invention.

The organic compounds (A) and (B) contained in the hexavalent chromium treatment agent of the present invention have the ability to treat hexavalent chromium and clearly possess the basic property of rendering it harmless. When leather or leather products treated with the organic compounds come into contact with the skin, they do not cause skin cracking or other effects and are non-toxic. Furthermore, (A) and (B) are preferably compounds that do not decompose each other due to their respective reducing properties and do not react or affect each other. The organic compounds preferably have the basic skeleton represented by the aforementioned chemical formula (1), and are preferably stable compounds containing C, H, and O atoms.

The organic compound represented by the aforementioned chemical formula (1) does not contain functional groups such as aldehyde or carboxyl groups. Furthermore, it preferably does not contain nitrogen-containing groups such as amino or isocyanate groups, or sulfur-containing groups such as sulfate groups. Such functional groups are reactive and therefore pose a risk of unintended reactions when leather or leather products are used, making them unsuitable for the hexavalent chromium remover of the present invention. This organic compound reacts with hexavalent chromium to form a compound that is not detected as hexavalent, thereby rendering the hexavalent chromium harmless.

[Organic compound (A)]

The organic compound (A) has a structure represented by the aforementioned chemical formula (1) and a hydroxyphenyl group represented by the following chemical formula (15). By having this functional group, it also has a fast-acting property in leather or leather products, is stably retained for a long time, has a reducing effect for a long time, and has excellent heat resistance. Therefore, the generation of hexavalent chromium can be suppressed for a long time. In addition, by being contained in leather or leather products, it is not easily decomposed by moisture such as sweat and rain. Although the reason for such an excellent effect is unclear, collagen, which is usually the main component of leather, is chemically cross-linked and stabilized by tanning. It is speculated that the hydroxyphenyl group possessed by the organic compound (A) has a high interaction with the collagen, so it can be retained for a long time. On the other hand, it is not completely absorbed into the collagen, and becomes like an island part of a sea-island structure, which is absorbed into the collagen with a degree of freedom of reduction. Since it is used for leather or leather products, the organic compound (A) is preferably a compound with high safety and low environmental load.

In the chemical formula (15), ^Ra is a monovalent group or a divalent group. As a monovalent group, a hydrogen atom, a hydrocarbon group or an oxygen-containing group can be mentioned. As a divalent group, a divalent hydrocarbon group or a divalent oxygen-containing group can be mentioned. Among them, when it is a hydrogen atom, a monovalent hydrocarbon group, a divalent hydrocarbon group or a hydroxyl group, it is more compatible with leather or leather products, so it is preferred. ^Ra is independent of each other and can be the same or different. ^Ra optionally adjacent groups are bonded to each other to form an aromatic ring or an aliphatic ring. In addition, ^Ra is optionally bonded to ^Ra of other hydroxyphenyl groups. It is preferred that all ^Ra are not hydrogen atoms at the same time. In order to have a faster effect, stability and long-term better reducibility in leather or leather products, dihydroxyphenyl or trihydroxyphenyl is more preferred, and 1,2,3-trihydroxyphenyl is more preferred.

The hydrocarbon group is preferably a hydrocarbon group having 1 to 20 carbon atoms, and specifically includes an alkyl group having 1 to 20 carbon atoms, an arylalkyl group having 7 to 20 carbon atoms, an aryl group (aryl) or a substituted aryl group (aryl) having 6 to 20 carbon atoms. For example, methyl, ethyl, n-propyl, isopropyl, allyl (allyl), n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, n-pentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, 3-methylpentyl, 1,1-diethylpropyl, 1,1-dimethylbutyl, 1-methyl-1-propylbutyl, 1,1-propylbutyl, 1,1-dimethyl-2-methylpropyl, Examples of hydrocarbon groups (e.g., alkoxy groups) include 1-methyl-1-isopropyl-2-methylpropyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, norbornyl, adamantyl, phenyl, o-tolyl, m-tolyl, p-tolyl, xylyl, isopropylphenyl, tert-butylphenyl, naphthyl, biphenyl, terphenyl, phenanthryl, anthracenyl, benzyl, and cumyl. Examples of hydrocarbon groups (e.g., alkoxy groups) include groups containing oxygen-containing groups such as methoxy, ethoxy, and phenoxy. Examples of hydrocarbon groups include groups containing unsaturated carboxylic acid esters such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and (5-norbornene-2-yl) esters (when the unsaturated carboxylic acid is a dicarboxylic acid, it may be a monoester or a diester).

As the oxygen-containing group, a hydroxyl group can be mentioned.

Examples of the organic compound (A) include: the aforementioned chemical formulas (2) to (12) and (14);

Phenol, o-cresol, m-cresol, p-cresol, 2,3-dimethylphenol, 2,5-dimethylphenol, 3,4-dimethylphenol, 3,5-dimethylphenol, 2,4-dimethylphenol, 2,6-dimethylphenol, 2,3,5-trimethylphenol, 3,4,5-trimethylphenol, 2-tert-butylphenol, 3-tert-butylphenol, 4-tert-butylphenol, BHT (butylated hydroxytoluene), BHA (butylated hydroxyanisole), 2-phenylphenol, 3-phenylphenol, 4-phenylphenol, 3,5-diphenylphenol, 2-naphthylphenol, 3-naphthylphenol , 4-naphthylphenol, 4-tritylphenol, 2-methylresorcinol, 4-methylresorcinol, 5-methylresorcinol, 4-tert-butylcatechol, 2-methoxyphenol, 3-methoxyphenol, 2-propylphenol, 3-propylphenol, 4-propylphenol, 2-isopropylphenol, 3-isopropylphenol, 4-isopropylphenol, 2-methoxy-5-methylphenol, 2-tert-butyl-5-methylphenol, thymol, isothymol, 1-naphthol, 2-naphthol, 2-methyl-1-naphthol, 4-methoxy-1-naphthol, 7-methoxy-2-naphthol;

Dihydroxynaphthalenes such as 1,5-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, and 2,6-dihydroxynaphthalene;

Tetrahydroxynaphthalenes such as 1,3,6,8-tetrahydroxynaphthalene;

3-Hydroxy-naphthalene-2-carboxylic acid methyl ester, 9-hydroxyanthracene, 1-hydroxypyrene, 1-hydroxyphenanthrene, 9-hydroxyphenanthrene, bisphenol fluorene, phenolphthalein;

Benzophenone derivatives such as 2,3,4-trihydroxybenzophenone and 2,2’,3,4-tetrahydroxybenzophenone;

Tannins such as catechol tannins, pyrogallol tannins, gallic tannins, gallic acid tannins, and brown algae polyphenols (phlorotannin);

Flavonoids such as anthocyanins, rutin, quercetin, fisetin, daidzein, hesperidin, chrysin, flavonol, and hesperetin;

Catechin, gallocatechin, catechin gallate, epicatechin, epigallocatechin, epicatechin gallate, epigallocatechin gallate, proanthocyanidins, theaflavins and other catechins;

Curcumin, xylan;

Rhododendrol [4-(p-hydroxyphenyl)-2-butanol];

Acylated rhododendrols such as acetyl rhododendrol, hexanoyl rhododendrol, octanoyl rhododendrol, dodecanoyl rhododendrol, tetradecanoyl rhododendrol, hexadecanoyl rhododendrol, octadecanoyl rhododendrol, 4-(3-acetoxybutyl)phenyl acetate, 4-(3-propionyloxybutyl)phenyl propionate, 4-(3-octanoyloxybutyl)phenyl octanoate, and 4-(3-hexadecanoyloxybutyl)phenyl palmitate;

Rhododendron alkyl ethers such as 4-(3-methoxybutyl)phenol, 4-(3-ethoxybutyl)phenol, and 4-(3-octyloxybutyl)phenol;

Rhododendronol glycosides such as rhododendronol-D-glucoside (α or β form), rhododendronol-D-galactoside (α or β form), rhododendronol-D-xyloside (α or β form), and rhododendronol-D-maltoside (α or β form);

α-tocopherol, β-tocopherol, γ-tocopherol, δ-tocopherol, etc.

In addition, derivatives thereof such as compounds having an alkoxy group and esters thereof are also mentioned. Specifically, for example, pyrogallol-1,3-dimethyl ether, pyrogallol-1,3-diethyl ether, and 5-propylpyrogallol-1-methyl ether are mentioned.

Examples of the organic compound (A) include compounds having the structure (1,2,3-trihydroxybenzene, 1,2,3-Trihydroxybenzene skeleton) represented by the chemical formula (2) and derivatives thereof. Such compounds have a hexavalent chromium removal function.

As derivatives thereof, there are derivatives having substituents such as hydrocarbon groups or oxygen-containing groups at positions 4, 5, and 6 of the compound represented by the aforementioned chemical formula (2). Preferred substituents include hydrocarbon groups having 1 to 20 carbon atoms, alkoxy groups having 1 to 20 carbon atoms, and esters having 1 to 20 carbon atoms, and more preferably hydrocarbon groups having 1 to 10 carbon atoms, alkoxy groups having 1 to 20 carbon atoms, and esters having 1 to 10 carbon atoms. These groups are as described above. It should be noted that the same applies to the derivatives of the compounds described below. For example, there are gallic acid esters such as the compound represented by the aforementioned chemical formula (3), compounds represented by the aforementioned chemical formula (4) having multiple structures of the aforementioned chemical formula (2) in one molecule, and derivatives of such compounds. Examples include tannins such as catechol-based tannins, pyrogallol-based tannins, gallic acid tannins, and brown algae polyphenols.

Thus, when introducing substituents at positions 4, 5, and 6, substituents suitable for respective methods of use can be introduced. For example, when the compound is dissolved in an ester solvent for use, an ester group can be introduced to improve compatibility.

In the present invention, the organic compound (A) preferably comprises (i) an ester of gallic acid and (ii) at least one compound selected from tannic acid and its derivatives, and more preferably comprises (i) an ester of gallic acid and (ii) tannic acid.

Because gallic acid esters have a relatively low molecular weight, they are thought to be susceptible to seepage from leather or leather products. However, since they have a partial structure of tannic acid, they maintain their reducing power while interacting appropriately with tannic acid and its derivatives, making them less susceptible to seepage. They also possess reducing power in leather or leather products, and their rapid effect is high. Although their reducing power does not reach the level of ascorbic acid, it is higher than that of tannic acid. Therefore, even after ascorbic acid decomposes and loses its reducing power, it still exerts its reducing power for a long time (afterwards, it can reduce the chromium ions oxidized to hexavalent ions again). In leather or leather products, gallic acid esters are also resistant to moisture such as sweat and rain and are less likely to decompose.

Tannic acid and its derivatives are large and have long been used in tanning processes. They have good affinity for collagen and other substances in leather and leather products, making them less susceptible to oozing out and maintaining their reducing power in leather and leather products for extended periods. Consequently, they can suppress the formation of hexavalent chromium for a longer period. Furthermore, tannic acid and its derivatives are less irritating to humans (skin), making them highly safe. While their reducing power is delayed compared to ascorbic acid and gallic acid esters, they have good affinity for leather and leather products and are less susceptible to decomposition. Therefore, compared to ascorbic acid and gallic acid esters, they can maintain their reducing power until the leather product achieves its function and purpose.

Therefore, when these compounds are included, they have high permeability into leather or leather products, allowing them to remain in the leather or leather products for a long time, enabling long-term and stable reduction. Furthermore, polyphenols have strong reducing properties, which can cause browning and discoloration. However, these compounds are absorbed into the leather or leather products before discoloration occurs, making them less susceptible to fading and discoloration, and minimizing the risk of damaging the color tone and texture of the leather or leather products, making them preferred.

In the aforementioned chemical formula (2), hydroxyl groups are present at positions 1, 2, and 3. However, compounds having a skeleton having hydroxyl groups introduced at positions 1, 2, and 4 (the aforementioned chemical formula (5)) or a skeleton having hydroxyl groups introduced at positions 1, 3, and 5 (the aforementioned chemical formula (6)) also exhibit the same effects. Furthermore, derivatives also exhibit the same effects.

In the aforementioned chemical formula (2), three hydroxyl groups are introduced into one aromatic ring. However, compounds having one hydroxyl group or two hydroxyl groups also have the function of removing hexavalent chromium. Examples of such skeletons include phenol, BHT, compounds of the aforementioned chemical formulas (7), (8), and (9), and their derivatives.

Compounds composed of multiple aromatic rings and containing hydroxyl groups also have the same effect. Examples include compounds containing one or more hydroxyl groups on a naphthalene ring. For example, compounds containing two hydroxyl groups include those represented by the aforementioned chemical formula (10) and chemical formula (11). Derivatives of such compounds also have the same hexavalent chromium removal function as the aforementioned compounds.

Compounds containing three linked aromatic rings and hydroxyl groups introduced at one or more arbitrary positions on anthracenes also exhibit similar functionality. Examples of such compounds include the compound represented by the aforementioned chemical formula (12). Furthermore, their derivatives also exhibit hexavalent chromium removal functionality.

Examples of the compound represented by the aforementioned chemical formula (1) include compounds having a long-chain alkyl group and a condensed ring. Such compounds have a higher organic property and a lower water solubility. However, on the other hand, their affinity for organic solvents increases, and thus they have the advantage of being soluble in hydrocarbon solvents. Examples of such compounds include the compound represented by the aforementioned chemical formula (14).

Preferred compounds of the chemical formula (1) include catechins and catechin derivatives such as catechin, gallocatechin, catechin gallate, epicatechin, epigallocatechin, epicatechin gallate, epigallocatechin gallate, proanthocyanidins, and theaflavins. These catechins have excellent safety and high reducing power in leather or leather products.

[(B) Organic compounds]

The organic compound (B) has the structure shown in the aforementioned chemical formula (1), but does not have the hydroxyphenyl group shown in the aforementioned chemical formula (15). Since it does not contain the hydroxyphenyl group, it is difficult to penetrate into leather or leather products. However, since it has the structure shown in the chemical formula (1), it can appropriately reduce the hexavalent chromium located on the surface of the leather or leather products to trivalent chromium, rendering it non-toxic. Therefore, by using the compound (B), it is possible to quickly and effectively suppress the dissolution of hexavalent chromium ions dissolved in water such as sweat and rain into the environment and exposure to humans. Examples of the organic compound (B) include compounds having heterocyclic rings. Examples of heterocyclic rings include furans, chromenes, isochromenes, and xanthenes. Examples of such derivatives include compounds having the structure shown in the aforementioned chemical formula (13), derivatives thereof, isoascorbic acid, derivatives thereof, and 4-hydroxyfuran-2(5H)-one. Such compounds have the function of removing hexavalent chromium.

The derivatives of ascorbic acid are not particularly limited, and examples thereof include ascorbic acid esters, ascorbic acid phosphates, ascorbic acid sulfates, ascorbyl glucoside (2-O-α-D-glucopyranosyl-L-ascorbic acid), ascorbyl glucosamine, and dehydroascorbic acid.

Examples of the derivatives of erythorbic acid include erythorbic acid esters and the like.

In the present invention, the organic compound (B) is preferably at least one compound selected from ascorbic acid and isoascorbic acid, more preferably ascorbic acid. This compound is easily decomposed, so it is impossible to achieve the effect for a long time, and it is easy to ooze out from leather or leather products, but it has low irritation to people (skin), excellent safety, high reducing power, and high quick-acting property. Therefore, the treatment agent containing this compound (B) is brought into contact with leather or leather products, so as to effectively prevent the dissolution of hexavalent chromium ions into the environment and exposure to people in advance. In addition, it is particularly possible to quickly detoxify the surface, so that symptoms such as skin cracking and allergies can be appropriately suppressed. This compound (B) does not react or is incompatible with the organic compound (A), nor does it decompose due to this compound (A), so it can be appropriately mixed into the treatment solution. In addition, since the reducing power is strong, by including this compound, it is possible to prevent the browning and discoloration caused by the organic compound (A). Moreover, it is highly decomposable, so it is not easy to color, and does not damage the color tone and texture of the leather or leather products, so it is preferred.

Thus, if the compound includes the basic skeleton represented by the above chemical formula (1) in its molecule, hexavalent chromium can be rendered harmless and removed.

[Amount ratio of organic compounds (A) and (B)]

In the hexavalent chromium treatment agent of the present invention, there are no particular restrictions on the organic compounds (A) and (B), as long as the effects of the present invention are achieved. However, the weight percent ratio ((A):(B)) is preferably 50-90:10-50, more preferably 50-80:20-50, and even more preferably 50-70:30-50 (wherein the total of A and B is 100 weight percent). Although organic compound (A) exhibits excellent rapid effects, it has difficulty penetrating into leather or leather products, and thus cannot achieve long-term stability. Therefore, the amount of organic compound (A) is preferably equal to or less than that of (B). On the other hand, if the amount is less than 10 weight percent, there is a risk that hexavalent chromium on the surface of the leather or leather product may not be properly reduced to trivalent chromium and rendered non-toxic.

In the case of the hexavalent chromium treatment agent containing (i) the ester of gallic acid, (ii) at least one compound selected from tannic acid and its derivatives, and the organic compound (B), there is no limitation as long as the effects of the present invention are achieved. The weight percent ratio ((i):(ii):(B)) is preferably 1-20:30-89:10-50, more preferably 3-17:33-77:20-50, and even more preferably 5-15:35-65:30-50 (wherein the total of (i), (ii), and (B) is 100 weight percent). The amount ratio of the organic compound (A) is as described above. As the organic compound (B) is incompatible with compounds (i) and (ii), is not absorbed into compound (ii), and can appropriately reduce the surface of leather or leather products, ascorbic acid and/or isoascorbic acid are preferred. Compounds (i) and (ii) primarily function to reduce hexavalent chromium within the leather or leather products. Ascorbic acid, propyl gallate and tannic acid meet the international safety standards for the concentrations used in leather or leather products for carcinogenicity, skin sensitization and skin irritation as specified in the OECD Guidelines for the Testing of Chemicals. Compound (i) has a high reducing power but is relatively easy to decompose. On the other hand, compound (ii) has compound (i) as a partial structure, so compound (i) can be obtained by decomposing compound (ii), but its reducing power is delayed compared to the esters of ascorbic acid and gallic acid. Therefore, it is preferred that the amount of compound (ii) is greater than that of compound (i). In addition, compound (i) is also pointed out to have a slightly greater risk of allergic reaction to humans (skin) than compound (ii) and organic compound (B), and in comparison, it also has a risk of coloration, so it is preferably used in an amount less than that of compound (ii) and organic compound (B). When the amount of compound (ii) is less than 1% by weight, the hexavalent chromium in the leather or leather product cannot be quickly detoxified, and there is a risk that the amount left to be treated with the organic compound (B) or the untreated hexavalent chromium ions will dissolve on the surface after the organic compound (B) is inactivated. Polyphenols have strong reducing properties, so there is a concern that they may turn brown or fade. However, when used in these amount ratios, they are more suitably easily absorbed into the leather or leather product before fading, making them less likely to fade or discolor, and substantially not damaging the color tone or texture of the leather or leather product, and are therefore preferred. In addition, if these amount ratios are used, they are easily soluble in both water and organic solvents, and are therefore preferred. This treatment solution can provide long-term reliability, and is therefore preferred.

Next, a method for obtaining leather or leather products using a hexavalent chromium remover and a hexavalent chromium treatment method will be described.

The leather or leather product of the present invention can be obtained using a production method comprising contacting a raw leather containing hexavalent chromium or a raw leather product containing hexavalent chromium with a hexavalent chromium treatment agent. The leather or leather product obtained by this production method has a hexavalent chromium content of less than 3 ppm as measured in accordance with ISO 17075:2008-02, and the total chromium content of the leather or leather product, as determined by fluorescent X-ray analysis, is typically 5000 ppm or greater.

The leather or leather product of the present invention is not particularly limited. Examples include leather or leather products obtained by chrome tanning cowhide, sheepskin, goat skin, pigskin, horsehide, deerskin, kangaroo skin, ostrich skin, crocodile skin, lizard skin, snake skin, bird skin, fish skin, and the like, or processed products thereof. Examples of processed products include shoes, clothing, hats, gloves, belts, wallets, business card holders, watch straps, purses, sofas, cushions, cushion covers, book covers, pen holders, mobile phone cases, personal organizers, key cases, car interiors, eyeglass cases, and tool boxes.

The hexavalent chromium treating agent of the present invention can be used to render hexavalent chromium harmless in leather obtained by chrome tanning or leather products during the leather making process.

An example of a treatment method in a leather making process is shown below. Usually, raw hides peeled from animals are used, and after removing fat, protein, etc. from the hides, they are provided in tanning processes such as chrome tanning. Thereafter, they are washed, dehydrated in a drum, and processed with a roller coater to obtain leather (for example, leather sheets). In the present invention, for example, a hexavalent chromium treatment agent is placed in the drum to detoxify the hexavalent chromium. In addition, countless holes are opened in the roller coater, and for example, the hexavalent chromium treatment agent is blown together with water from the holes, so that detoxification can also be performed. As the hexavalent chromium treatment agent in these cases, it is preferred to use a treatment liquid consisting only of water or a treatment liquid containing water and an alcohol having 1 to 3 carbon atoms, which will be described later.

Alternatively, the hexavalent chromium treatment agent may be brought into contact with untreated raw leather for products (e.g., leather sheets, also referred to as raw leather in the present invention) to render it non-toxic.

For leather products, purchased leather sheets are cut into the desired shape and bonded to a core material or to each other using an adhesive, stitching, etc., to obtain the desired leather product. It should be noted that untreated leather products are also referred to as raw leather products in the present invention.

For example, in the case of a watch band, leather cut into a band shape is adhered to the front and back surfaces of a core material using an adhesive, and then heated to obtain a watch band.

In addition, depending on the product, the surrounding area is sewn to give it a textured finish.

When manufacturing leather products, leather sheets that have been tanned using chromium contain chromium. Most of this chromium is trivalent chromium, but during storage, importation, transportation, sales, and handling, the leather sheets are subjected to physical stresses (e.g., light, heat, high temperature and humidity), sometimes generating harmful hexavalent chromium. When raw leather sheets are made to contain hexavalent chromium and then processed to obtain leather products, leather products (such as watch bands) containing harmful hexavalent chromium can be obtained. Therefore, it is ideal to pre-detoxify leather sheets that have been tanned using chromium using the hexavalent chromium remover of the present invention.

The hexavalent chromium remover can be used to render the leather sheet harmless before or after cutting it into a specific size.

Hexavalent chromium can be rendered harmless by contacting raw leather containing hexavalent chromium or raw leather products containing hexavalent chromium with a hexavalent chromium treatment agent. The contact method is not particularly limited as long as it achieves the effects of the present invention; examples include spraying, spreading, dipping, coating, or immersion. Organic compounds (A) and (B), particularly compound (B), have strong reducing power on the surface of raw leather or raw leather products, so direct contact with the hexavalent chromium treatment agent can also treat hexavalent chromium. To achieve long-term reduction by penetrating deeper into the leather or leather products, the hexavalent chromium remover is preferably dissolved in a single solvent, such as water, alcohols with 1 to 3 carbon atoms (propanol, isopropyl alcohol (IPA), methanol, and ethanol), butanol, acetone, methyl ethyl ketone (MEK), toluene, xylene, N,N-dimethylformamide (DMF), hexane, or heptane; a mixed solvent of water and the organic solvent; or a volatile organic solvent containing a mixture of multiple organic solvents to prepare a treatment solution for treatment. As a solvent, it is preferred to use at least one solvent selected from water, alcohols having 1 to 3 carbon atoms, hexane and heptane. It is more preferred to use two or more solvents because a suitable treatment liquid can be obtained. Although hydrocarbon solvents such as toluene have excellent permeability to leather or leather products, most of them are harmful to humans, so it is best to avoid their use as much as possible. In addition, the leather sheet or the cut leather sheet is sprayed with the treatment liquid, applied with a pen or brush, wiped with cloth, or immersed in water, so that the leather contains the hexavalent chromium remover. The surface of leather or leather products is very delicate and easily damaged, so it is preferred to apply it by spraying or blowing. By doing so, the hexavalent chromium is rendered harmless and harmless leather can be obtained.

It is also conceivable to treat commercially available leather products containing hexavalent chromium. In this case, the leather products are removed from a watch or other similar device and treated with a treatment solution containing the hexavalent chromium treatment agent, such as by spraying, applying with a brush, wiping the surface with a cloth, or immersing the leather in the treatment solution to allow the leather to be treated.

In the present invention, this treatment liquid is also one embodiment of the hexavalent chromium treatment agent of the present invention.

The organic compound (A) contained in the hexavalent chromium treatment liquid is not particularly limited, but is preferably contained in an amount of about 0.01 to 10.0 (weight %), more preferably about 0.1 to 7.0 (weight %), even more preferably about 0.3 to 5.0 (weight %), even more preferably about 0.5 to 3.0 (weight %), and even more preferably about 0.5 to 2.0 (weight %), based on 100 (weight %) of the treatment liquid. This amount is particularly preferred because it minimizes discoloration or fading of leather or leather products.

The organic compounds (A) and (B) contained in the hexavalent chromium treatment solution are not particularly limited, but are preferably contained in a total amount of about 0.01 to 10.0 (weight %), more preferably about 0.1 to 7.0 (weight %), even more preferably about 0.3 to 5.0 (weight %), even more preferably about 0.5 to 3.0 (weight %), and even more preferably about 0.5 to 2.0 (weight %), based on 100 (weight %) of the treatment solution. These amounts are particularly preferred because they minimize fading or discoloration of leather or leather products.

The hexavalent chromium treatment agent formed from the treatment liquid preferably has permeability into leather or leather products. An organic solvent is preferred because the treatment liquid is relatively fat-soluble, allowing for optimal permeation. Containing water and an alcohol having 1 to 3 carbon atoms is particularly preferred because it provides enhanced safety and ease of handling, and allows for permeation without impairing the design characteristics of the leather or leather product, such as color, tone, and texture, or causing discoloration or browning.

The hexavalent chromium treatment agent formed from the treatment liquid is not particularly limited as long as the effects of the present invention are achieved. However, from the perspective of rapid penetration into leather or leather products and rendering them harmless, the kinematic viscosity at 25°C is preferably 0.001 (cSt) or higher and less than 5 (cSt), more preferably 0.01 (cSt) or higher and less than 4.5 (cSt), even more preferably 0.05 (cSt) or higher and less than 4.3 (cSt), and even more preferably 0.1 (cSt) or higher and less than 4.0 (cSt). Japanese Patent Application Laid-Open No. 2008-272552 describes a treatment agent (aqueous solution) for treating hexavalent chromium-contaminated soil, containing ascorbic acid and having a viscosity of 5 cP or higher and thickened with a thickener. As described in this publication, a treatment agent with a viscosity of less than 5 cP has excessive soil permeability, resulting in uneven penetration into the soil. Therefore, treatment agents with a viscosity of less than 5 cP are not useful for treating hexavalent chromium in soil. Since collagen, which is a main component of leather or leather products, is chemically cross-linked and stabilized, a treatment agent having a viscosity of 5 cP or more may not penetrate the leather or leather products, which is not preferred.

The solvent used in the treatment liquid is preferably water alone in order to avoid damaging the design characteristics of the leather or leather product, such as color, tone, and texture, and preventing discoloration or browning, especially when treating leather or leather products having design characteristics.

Organic compound (B) is generally water-soluble, but organic compound (A) is generally hydrophobic due to its phenyl group. Therefore, considering the proper dissolution of organic compound (A) and, by extension, organic compound (B), the solvent used in the treatment liquid preferably contains a polar solvent, although this may cause discoloration compared to non-polar solvents. Alcohols with 1 to 3 carbon atoms are more preferred. IPA is even more preferred from the perspectives of high workability, minimal deterioration of the design characteristics of the leather or leather product, such as color matching, hue, and texture, fading, and browning, excellent compatibility with other solvents, and excellent solubility in a variety of organic compounds. Furthermore, water is preferably included because it provides high safety and can easily dissolve organic compound (B). When the treatment liquid contains water and alcohol, the weight % ratio (water: alcohol) is preferably 20 to 80: 20 to 80, more preferably 30 to 70: 30 to 70. Since the organic compounds (A) and (B) can be suitably dissolved and mixed, and the leather or leather product can be treated without damaging the design, fading, and browning of the color matching, hue, and texture, the total amount of the two is 100% by mass. If the solvent is only water, the leather or leather product has water repellency, which is hydrophobic (fat soluble) and therefore there is a risk of not being penetrated. However, if it is a treatment liquid containing water and an alcohol having 1 to 3 carbon atoms, it does not damage the design and has suitable volatility, so it can penetrate into deeper parts of the leather or leather product, so it is preferred. In addition, when the amount ratio of the alcohol is greater than 80% by weight, if the flash point of the alcohol is considered, there is a risk of becoming the cause of fire in the factory, so it is not preferred. When IPA is used as the alcohol, the alcohol content is preferably 60% by weight or less, taking the flash point into consideration. On the other hand, if the alcohol content is less than 20% by weight, the solubility in leather or leather products may not be improved.

When ascorbic acid and/or isoascorbic acid are used as the organic compound (A), these compounds are difficult to dissolve in polar solvents other than water due to their high water solubility. When gallic acid esters and/or tannic acid derivatives are used as the organic compound (B), these compounds are relatively highly hydrophobic and therefore difficult to dissolve in water. In particular, gallic acid esters and/or tannic acid derivatives are difficult to dissolve in non-polar solvents. It should be noted that tannic acid is amphiphilic.

When the solvent used as the treatment liquid is intended to better maintain the long-term reducibility of leather or leather products, non-polar organic solvents are preferred compared to water. Since no coloring components are extracted and the volatility is high, the color change is smaller than that of other non-aqueous solvents. Therefore, it is more preferred to include at least one solvent selected from hexane and heptane. Since the drying speed is also fast and the operability is also good, hexane is further preferred. These solvents have good volatility, can suitably dissolve the organic compound (A) that is hydrophobic in comparison in a short time, and can suitably penetrate into the leather or leather products that are fat-soluble in comparison, so they are preferred. However, the solvent is only an organic solvent with high volatility and flammability. Therefore, especially in the case of a large amount of solvent required for the method of treating hexavalent chromium by immersion, there is a risk of becoming the cause of fire in the factory, so the operation needs to be careful. In addition, since non-polar organic solvents are difficult to dissolve the organic compound that is hydrophilic in comparison, it is necessary to appropriately select the organic compound that can be used. If the impact on design is considered, the contact surface of the treatment liquid is preferably the back of the leather or leather product. At this time, it is preferred to treat the surface of the leather or leather products with a treatment solution containing only water or water and a polar solvent. In addition, when the organic compound (A) is relatively water-soluble, if the compatibility with hexane and/or heptane is considered, although it is not easy to dissolve the organic compound (A) compared to water, it is preferred to use an alcohol with 1 to 3 carbon atoms. Since it has little effect on the leather or leather products and can obtain safety and operability, it is more preferred to use IPA. A mixed solvent of a non-polar solvent and the alcohol has little effect on the leather or leather products, so it can penetrate into the deeper parts of the leather or leather products, and can be used for a variety of leather or leather products, and can obtain high productivity, so it is preferred. Furthermore, IPA is less volatile than hexane, heptane, etc., so even if the solvent evaporates during the operation, the treatment agent will not be precipitated, and the operation can be carried out for a long time. In addition, it is preferred because various organic compounds can be dissolved by making a mixed solvent. When the treatment liquid contains an alcohol having 1 to 3 carbon atoms and hexane and/or heptane, the weight percent ratio (alcohol:hexane and/or heptane) is preferably 20-90:10-80, more preferably 35-85:15-65. This has little effect on the leather or leather product and allows for relatively good dissolution and mixing of the organic compounds (A) and (B), and therefore is further preferably 45-80:20-55 (where the total amount of the two is 100% by weight). Using an alcohol ratio greater than 90% by weight does not pose a quality problem, but there is a risk of discoloration on the surface of the leather or leather product.

The leather or leather product thus treated contains the hexavalent chromium remover of the present invention. If harmless chromium is converted to harmful hexavalent chromium after treatment of the leather or leather product containing the hexavalent chromium remover, the hexavalent chromium can be rendered harmless using the hexavalent chromium remover contained in the leather or leather product. In other words, the leather or leather product treated with the hexavalent chromium remover can maintain a stable harmless state even after production.

In addition, when manufacturing leather products, sometimes adhesives are used to stick leather to the front and back of a core material different from the leather (mostly resin, etc.). The adhesive is made to contain the hexavalent chromium remover and used for bonding, so that the hexavalent chromium can be rendered harmless. When the adhesive contains the hexavalent chromium remover and is used for an article, the hexavalent chromium remover is present between the leather on the surface and the leather on the back. Due to this effect, there is an advantage that pollution does not spread, such as the movement of hexavalent chromium between the front and back. It is especially effective when using tanned leather in which the leather on the surface contains a large amount of chromium and the leather on the back does not use chromium. By doing so, there is an effect of preventing hexavalent chromium from penetrating to the part on the back that comes into contact with the skin.

The hexavalent chromium remover contains at least an organic compound represented by Chemical Formula 1. The organic compound has reducing properties capable of reacting with hexavalent chromium to reduce it to trivalent chromium. The organic compound contains C atoms, O atoms, and H atoms. The central carbon having single and double bonds between the three carbon atoms has a hydroxyl group.

R ¹ -C(-R ² )=C(-OH)-C(-R ³ )(-R ⁴ )-R ⁵ ...(1)

(R ¹ , R ² , R ³ , R ⁴ , and R ⁵ are each independently a substituent composed of C, H, or O, and contain a carbonyl group having an unsaturated bond, but do not have a functional group such as an aldehyde group or a carboxyl group.)

The organic compound is the aforementioned compound (chemical formulas (2) to (14)) or a derivative thereof, or a mixture thereof.

Leather products contain hexavalent chromium remover.

The method of adding the hexavalent chromium remover is to immerse the leather in or apply the hexavalent chromium treatment solution prepared by diluting the hexavalent chromium remover in water, an organic solvent, or a mixed solvent thereof.

The method of adding the hexavalent chromium remover is to immerse the leather in or apply the hexavalent chromium treatment solution prepared by diluting the hexavalent chromium remover in an organic solvent such as hexane or heptane.

Leather products can be obtained by using a method in which a hexavalent chromium remover is incorporated into the leather product.

The hexavalent chromium remover has the chemical formula (14).

The method for making the leather contain the hexavalent chromium remover is to dissolve the hexavalent chromium remover in the adhesive and then make the leather contain the hexavalent chromium remover.

The leather products are leather straps for watches.

The leather or leather product contains at least an organic compound (A) and trivalent chromium. The organic compound (A) has a structure represented by the aforementioned chemical formula 1 and has a reducing property capable of reacting with hexavalent chromium to reduce it to trivalent chromium, and has a hydroxyphenyl group and does not have an aldehyde group or a carboxyl group. The hexavalent chromium content measured in accordance with ISO 17075:2008-02 is less than 3 ppm.

The hexavalent chromium treatment agent contains at least an organic compound (A) having a structure represented by the chemical formula 1 having a reducing property that reacts with hexavalent chromium to reduce it to a trivalent state, and a hydroxyphenyl group, and having no aldehyde group or carboxyl group; and an organic compound (B) having a structure represented by the chemical formula 1 having a reducing property that reacts with hexavalent chromium to reduce it to a trivalent state, and having no hydroxyphenyl group, aldehyde group, or carboxyl group.

The hexavalent chromium treatment agent comprises at least an organic compound (A): having a structure represented by Chemical Formula 1, which has reducing properties and reacts with hexavalent chromium to reduce it to trivalent chromium, and a hydroxyphenyl group, and having no aldehyde group or carboxyl group; and at least two or more solvents selected from the group consisting of water, alcohols having 1 to 3 carbon atoms, hexane, and heptane, and having permeability to leather or leather products.

A method for treating hexavalent chromium contained in raw leather or a raw leather product comprises contacting the raw leather containing hexavalent chromium or the raw leather product containing hexavalent chromium with a hexavalent chromium treating agent.

A method for producing leather or leather products having a hexavalent chromium content of less than 3 ppm as measured in accordance with ISO 17075:2008-02 comprises the step of contacting raw leather containing hexavalent chromium or raw leather products containing hexavalent chromium with a hexavalent chromium treatment agent.

Example

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

As the compound represented by the above chemical formula (1), compounds represented by the above chemical formulas (2) to (14) are prepared.

The evaluation is as follows.

(1) Kinematic viscosity (cSt)

The kinematic viscosity of the hexavalent chromium treatment liquid was measured at 25.0° C. using an Ubbelohde viscometer and a mixed solvent of IPA and water (1 vol:1 vol) as a solvent.

(2) Total chromium content (ppm)

The total chromium content in leather or leather products was measured using an energy dispersive X-ray fluorescence analyzer (JSX-3202EV ELEMENT ANALYZER manufactured by JEOL Ltd.).

Note that JSX3000 Series Standard Sample 1, JSX3000 Series Standard Sample 2, and JSX3000 Series Energy Calibration Standard Sample, manufactured by JEOL Ltd., were used as reference samples. Measurements were performed using Plastic D3 connected to a JSX starter in accordance with the JEOL Ltd. Quick Manual (EY07007-J00, J00EY07007G, August 2007 edition).

(Reference Example 1)

(Confirmation of reactivity to hexavalent chromium)

A 1/60 mol/l aqueous solution of potassium dichromate (chromium is hexavalent) is measured and placed in a 10 ml container. The compound represented by the aforementioned chemical formula (2) is added in an amount four times the molar content of the hexavalent chromium, and stirred at room temperature. The color of the solution changes from orange to purple-red.

The total Cr content of the obtained solution was quantified by ICP emission spectrometry.

The sample was heated and decomposed with sulfuric acid and nitric acid, dissolved in dilute nitric acid and fixed to volume. The total Cr content in the solution was determined by ICP emission spectrometry (apparatus: SPS3000, manufactured by SII NanoTechnology Inc.).

Quantitative analysis of hexavalent chromium using ion chromatography

The sample was diluted 1000-fold with ultrapure water. Vibration was performed for 20 minutes, and the mixture was filtered through a cation exchange filter (OnGuard 2H, manufactured by ThermoFisher Scientific). The treated solution was quantified using ion chromatography. A solution treated in the same manner without the sample was used as a blank.

Ion chromatography conditions

Device: Dionex ICS-3000

Sample injection volume: 10μl

Eluent: 15 mM potassium hydroxide

Separation column: 2mmφ*250mm IonPac AS23

Column temperature: 35°C

Detector: Conductivity meter

Analysis results Total chromium content 1st time: 1720μg/g 2nd time: 1720μg/g

Average value: 1720 μg/g

Hexavalent chromium content: Below the first detection limit Below the second detection limit

From the above results, it was found that the hexavalent chromium was treated with the organic compound (A), and the initial hexavalent chromium (total chromium content) was rendered harmless.

(Reference Example 2-1)

0.5 g of a 1/60 mol/l aqueous dichromic acid solution was added dropwise to 0.6 g of Toyo filter paper No. 131 to contaminate the filter paper with hexavalent chromium. The contaminated medium was dried at room temperature (about 25° C.).

A hexavalent chromium treatment solution was prepared by dissolving 0.3 g of the compound represented by chemical formula (2) in 10 g of pure water. 1 g of this treatment solution was then applied to a hexavalent chromium contaminated medium with a brush and dried at room temperature.

This sample was submitted to an ISO 17075:2008-02 certified organization for measurement of hexavalent chromium content. The results showed no hexavalent chromium, indicating undetectable levels below the detection limit (2 ppm). It should be noted that the detection limit is also referred to as the determination limit in this invention.

From the above results, it can be seen that the use of the compound represented by chemical formula (2) can render the polluted medium contaminated with hexavalent chromium harmless.

Reference: When the contaminated medium was measured according to ISO17075:2008-02, hexavalent chromium was detected at 830 ppm.

(Reference Example 2-2)

0.5 g of a 1/60 mol/l aqueous dichromic acid solution was added dropwise to 0.6 g of Toyo filter paper No. 131 to contaminate the filter paper with hexavalent chromium. The contaminated medium was dried at room temperature (about 25° C.).

A hexavalent chromium treatment solution was prepared by dissolving 0.3 g of the compound represented by chemical formula (2) in 10 g of pure water. 1 g of this treatment solution was then applied to a hexavalent chromium-contaminated medium with a brush and dried at 120°C, which is higher than the heating temperature assumed for leather product manufacturing.

The sample was submitted to an ISO 17075:2008-02 certified organization for measurement of hexavalent chromium content. The result showed that hexavalent chromium was absent and undetectable, below the detection limit.

From the above results, it is clear that even when a heating process considered in the production of leather products is used, the compound represented by the chemical formula (2) can be used to render a polluted medium contaminated with hexavalent chromium harmless.

(Reference Example 2-3)

0.5 g of a 1/60 mol/l aqueous dichromic acid solution was added dropwise to 0.6 g of Toyo filter paper No. 131 to contaminate the filter paper with hexavalent chromium. The contaminated medium was dried at room temperature (about 25° C.).

A hexavalent chromium treatment solution was prepared by dissolving 0.3 g of the compound represented by chemical formula (2) in 10 g of pure water. 1 g of this treatment solution was then applied to a hexavalent chromium-contaminated medium with a brush and dried at 120°C, which is higher than the heating temperature assumed for leather product manufacturing.

In order to determine whether the product subsequently heated is also in a harmless state, an accelerated test is performed by applying a heat history at 120°C for 2 hours.

The sample was submitted to an ISO 17075:2008-02 certified organization for measurement of hexavalent chromium content. The result showed that hexavalent chromium was absent and undetectable, below the detection limit.

The above results show that even when a heating process, which is considered in the production of leather products, the compound represented by the chemical formula (2) can be used to render a polluted medium contaminated with hexavalent chromium harmless, and this effect is sustained.

(Reference Examples 3-1 to 3-3)

The same tests as in Reference Examples 2-1 and 2-3 were conducted except that the compound represented by Chemical Formula (4) was used instead of the compound represented by Chemical Formula (2). As a result, hexavalent chromium was below the detection limit in all cases and was not detected.

From the above results, it can be seen that the compound represented by Chemical Formula (4) has the same effect as the compound represented by Chemical Formula (2).

(Reference Examples 4-1 to 4-3)

The same tests as in Reference Examples 2-1 to 2-3 were conducted except that 10 g of ethanol was used instead of 10 g of pure water. As a result, hexavalent chromium was below the detection limit in all cases and was not detected.

From the above results, it is understood that hexavalent chromium can be treated with a long-term durability by dissolving in an ethanol solvent for coating.

(Reference Examples 5-1 to 5-3)

The same tests as in Reference Examples 2-1 to 2-3 were conducted, except that 10 g of a mixed solvent containing 20 parts by weight of toluene, 40 parts by weight of MEK, 15 parts by weight of acetone, and 5 parts by weight of DMF was used instead of 10 g of pure water. The results showed that hexavalent chromium was below the detection limit in all cases and was not detected.

From the above results, it is understood that hexavalent chromium can be treated with a long-term durability by dissolving in an ethanol solvent for coating.

(Reference Examples 6-1 to 6-3 and 7-1 to 7-3)

The same tests as in Reference Examples 4-1 to 4-3 and Reference Examples 5-1 to 5-3 were conducted except that the compound represented by Chemical Formula (3) was used instead of the compound represented by Chemical Formula (2). As a result, hexavalent chromium was below the detection limit in all cases and was not detected.

From the above results, it can be seen that the compound represented by Chemical Formula (3) has the same effect as the compound represented by Chemical Formula (2).

(Reference Examples 8-1 to 8-3, 9-1 to 9-3, 10-1 to 10-3, 11-1 to 11-3, 12-1 to 12-3, 13-1 to 13-3, 14-1 to 14-3, 15-1 to 15-3, 16-1 to 16-3)

The same tests as in Reference Examples 5-1 to 5-3 were conducted except that the compounds represented by Chemical Formulas (5) to (13) were used. As a result, hexavalent chromium was below the detection limit in all cases and was not detected.

From the above results, it can be seen that the compounds represented by chemical formulas (5) to (13) can also treat hexavalent chromium in a similar manner and have a sustained effect.

(Reference Examples 17-1 to 17-3 and 18-1 to 18-3)

The same tests as in Reference Examples 4-1 to 4-3 were conducted except that the compound represented by Chemical Formula (14) was used instead of the compound represented by Chemical Formula (2) and that hexane and heptane were used as solvents. The results showed that hexavalent chromium was below the detection limit and could not be detected in all cases.

From the above results, it can be seen that the compound represented by Chemical Formula (14) has the same effect as the compound represented by Chemical Formula (2).

(Reference Examples 19-1 to 19-3)

The same tests as in Reference Examples 5-1 to 5-3 were conducted except that a mixture of 50 parts by weight of each of the compounds represented by Chemical Formula (4) and Chemical Formula (6) was prepared as the compound and 0.3 g of this mixture was used. The results showed that hexavalent chromium was below the detection limit in all cases and was not detected.

The above results demonstrate that even mixing multiple compounds can effectively treat and render hexavalent chromium harmless. Furthermore, since multiple compounds can be mixed, treatment can be performed by mixing an appropriate combination of hexavalent chromium treatment agents based on usage conditions, such as differences in solubility in solvents.

(Example 20)

There are many adhesives for bonding leather sheets, core materials, etc. on the market. Experiments were conducted to confirm whether the function of the hexavalent chromium treatment agent can be maintained even if a hexavalent chromium treatment agent is mixed therein. In this embodiment, HIGHBON4250 manufactured by Hitachi Chemical Polymers Co., Ltd. was prepared. 0.3 g of the compound represented by chemical formula (2) was dissolved in 10 g of the adhesive, and the result was that it dissolved easily. In addition, it remained in liquid form even after being stored at room temperature for 30 days, and its function as an adhesive did not change. The results show that the hexavalent chromium treatment agent can be mixed in the adhesive. It is believed that this is because the hexavalent chromium treatment agent does not have reactive functional groups such as aldehyde, amino, and carboxyl groups, and therefore does not react specifically with the adhesive components and remains stable.

Using this adhesive stored at room temperature for 30 days and the freshly mixed adhesive, crocodile leather was bonded to the front surface of a plastic core material and cowhide leather to the back surface to create watch straps. All watch straps adhered well, resulting in leather products with excellent appearance and no issues as watch straps.

The hexavalent chromium content of the finished watch straps was measured according to ISO-17075:2008-02. The results showed that hexavalent chromium was below the detection limit (2 ppm) in all cases, indicating that no hexavalent chromium was detected, indicating that the watch straps were harmless. Similarly, similarly produced leather watch straps were stored at 60°C for 500 hours and analyzed using the ISO17075:2008-02 method. The results showed that hexavalent chromium was not detected in all cases (below the detection limit of 2 ppm), indicating that the watch straps were harmless.

These results demonstrate that the hexavalent chromium treatment agent can be incorporated into commercially available adhesives for leather, resulting in harmless leather products containing no hexavalent chromium. Hexavalent chromium was not detected even after further heating (below the detection limit of 2 ppm), demonstrating that the agent maintains a stable, harmless state even under heat.

(Examples 21-1 to 21-12 and Reference Examples 21-13 to 21-18)

A chrome-tanned leather sheet was prepared. Crocodile leather and cow leather were used as the leather material. The leather was cut into the size used for watch bands and used as the raw material.

Three treatment solutions containing the three compounds represented by chemical formula (2), chemical formula (4), and chemical formula (13) were prepared by dissolving 0.3 g of each in 10 g of ethanol. The treatment solutions were applied to leather by spraying and dried at room temperature to obtain treated leather sheets.

Next, 0.3 g of the three compounds represented by Chemical Formula (2), Chemical Formula (4), and Chemical Formula (13) were dissolved in 10 g of an adhesive (HIGHBON 4250) to prepare three adhesives containing these compounds. Using these adhesives, three different types of crocodile and cow leather were applied to each of the three adhesives, resulting in a total of 18 watch bands. The watch bands made from crocodile leather were divided into two types: those for aging evaluation and those for water flow evaluation.

[Maturation evaluation]

The obtained watch bands (18 types of alligator and cow) were aged at 60° C. for 500 hours to obtain watch bands for evaluation.

The hexavalent chromium content of each watch strap was measured according to ISO17075:2008-02. The results showed that hexavalent chromium was below the detection limit (2 ppm) in all the watch straps, and was not detected, indicating that it was harmless.

[Flow Evaluation]

Nine types of watch bands made of crocodile leather were immersed in running water immediately after production without aging, allowing tap water (Tokyo) to fully permeate. These bands were then aged at 60°C for 500 hours to obtain watch bands for evaluation.

The hexavalent chromium content of each watch band was measured according to ISO 17075:2008-02. The results showed that the hexavalent chromium content in the watch bands obtained using the compounds represented by chemical formula (2) and chemical formula (4) was below the detection limit (2 ppm), indicating that the hexavalent chromium was not detected and was harmless. On the other hand, the hexavalent chromium content in the watch bands obtained using the compound represented by chemical formula (13) was not detected.

The model numbers of the watch straps of this product are 59-S52979 (manufactured by Citizen Watch Co., Ltd.) for the ox and 59-T50736 (manufactured by Citizen Watch Co., Ltd.) for the crocodile.

The above results indicate that the use of the organic compound of the present invention can provide a harmless watch band (leather product) that is free of hexavalent chromium. It is understood that the compound represented by chemical formula (13), while having a high reducing power, is readily soluble in water. Therefore, there is a risk that the compound, when exposed to sweat or atmospheric moisture (e.g., dew or rain), may readily flow away, exposing humans to harmful hexavalent chromium and potentially releasing hexavalent chromium into the environment.

(Examples 22-1 to 22-12 and Reference Examples 22-13 to 22-18)

A chrome-tanned leather sheet was prepared. Crocodile and cow leather were used as the leather material. The leather was cut into sizes used for watch bands and used as the raw material. The leather was then immersed in a 1/60 mol/l potassium dichromate aqueous solution to contaminate it with hexavalent chromium. This contamination increased the hexavalent chromium content in the leather sheet by approximately 70 ppm.

Three treatment solutions containing the three compounds represented by chemical formula (2), chemical formula (4), and chemical formula (13) were prepared by dissolving 0.3 g of each in 10 g of ethanol. The treatment solutions were applied to leather by spraying and dried at room temperature to obtain treated leather sheets.

Next, 0.3 g of the three compounds represented by Chemical Formula (2), Chemical Formula (4), and Chemical Formula (13) were dissolved in 10 g of an adhesive (HIGHBON 4250) to prepare three adhesives containing these compounds. Using these adhesives, a total of 18 watch bands were prepared using three different types of crocodile and cow leather. These were aged at 60°C for 500 hours to obtain watch bands for evaluation.

The hexavalent chromium content of each watch strap was measured according to ISO17075:2008-02. As a result, hexavalent chromium was not detected in any of the watch straps, falling below the detection limit (2 ppm) and indicating that the content was harmless.

Next, the aged watch band was immersed in running water to allow the tap water to fully permeate, and aged at 80° C. for 500 hours to obtain a watch band for evaluation.

The hexavalent chromium content of each watch band was measured in accordance with ISO 17075:2008-02. The hexavalent chromium content in the watch bands obtained using the compounds represented by chemical formula (2) and chemical formula (4) was below the detection limit (2 ppm). On the other hand, no hexavalent chromium was detected in the watch band obtained using the compound represented by chemical formula (13).

The model of the watch strap of this product is 59-S52979 for cattle and 59-T50736 for crocodile.

The above results indicate that the use of the organic compound of the present invention can provide a harmless watch band (leather product) that is free of hexavalent chromium. It is understood that the compound represented by chemical formula (13), while having a high reducing power, is inactivated by running water and therefore has difficulty maintaining its reducing power over a long period of time. This suggests that the compound represented by chemical formula (13) is susceptible to decomposition.

(Examples 23-1 to 23-12 and Reference Examples 23-13 to 23-18)

A chrome-tanned leather sheet was prepared. Crocodile leather and cow leather were used as the leather material. The leather was cut into the size used for watch bands and used as the raw material. The leather was then immersed in a 1/60 mol/l potassium dichromate aqueous solution to contaminate it with hexavalent chromium.

Three treatment solutions containing these compounds were prepared by dissolving 0.3 g of each of the three compounds represented by Chemical Formula (2), Chemical Formula (4), and Chemical Formula (13) in 10 g of a mixed solvent containing 20 parts by weight of toluene, 40 parts by weight of MEK, 15 parts by weight of acetone, and 5 parts by weight of DMF. These treatment solutions were then applied to leather by spraying and dried at room temperature to obtain treated leather sheets.

Next, 0.3 g of the three compounds represented by Chemical Formula (2), Chemical Formula (4), and Chemical Formula (13) were dissolved in 10 g of an adhesive (HIGHBON 4250) to prepare three adhesives containing these compounds. Using these adhesives, a total of 18 watch bands were prepared using three different types of crocodile and cow leather. These were aged at 60°C for 500 hours to obtain watch bands for evaluation.

The hexavalent chromium content of each watch strap was measured according to ISO17075:2008-02. As a result, hexavalent chromium was not detected in any of the watch straps, falling below the detection limit (2 ppm) and indicating that the content was harmless.

Next, the aged watch band was immersed in running water to allow the tap water to fully permeate, and aged at 80° C. for 500 hours to obtain a watch band for evaluation.

The hexavalent chromium content of each watch band was measured in accordance with ISO 17075:2008-02. The hexavalent chromium content in the watch bands obtained using the compounds represented by chemical formula (2) and chemical formula (4) was below the detection limit (2 ppm). On the other hand, no hexavalent chromium was detected in the watch band obtained using the compound represented by chemical formula (13).

The model of the watch strap of this product is 59-S52979 for cattle and 59-T50736 for crocodile.

The above results show that the use of the organic compound of the present invention can provide a harmless watch band (leather product) that does not contain hexavalent chromium. It is known that the compound represented by chemical formula (13), although having a high reducing power, is inactivated by running water and therefore has difficulty maintaining its reducing power for a long period of time.

(Examples 24-1 to 24-12 and Reference Examples 24-13 to 24-18)

A chrome-tanned leather sheet was prepared. Crocodile leather and cow leather were used as the leather material. The leather was cut into the size used for watch bands and used as the raw material. The leather was then immersed in a 1/60 mol/l potassium dichromate aqueous solution to contaminate it with hexavalent chromium.

Three treatment solutions containing the three compounds represented by chemical formula (2), chemical formula (4), and chemical formula (13) were prepared by dissolving 0.3 g of each in 10 g of pure water. The treatment solutions were applied to leather by spraying and dried at room temperature to obtain treated leather sheets.

Next, 0.3 g of the three compounds represented by Chemical Formula (2), Chemical Formula (4), and Chemical Formula (13) were dissolved in 10 g of an adhesive (HIGHBON 4250) to prepare three adhesives containing these compounds. Using these adhesives, a total of 18 watch bands were prepared using three different types of crocodile and cow leather. These were aged at 60°C for 500 hours to obtain watch bands for evaluation.

The hexavalent chromium content of each watch strap was measured according to ISO17075:2008-02. As a result, hexavalent chromium was not detected in any of the watch straps, falling below the detection limit (2 ppm) and indicating that the content was harmless.

Next, the aged watch band was immersed in running water to allow the tap water to fully permeate, and aged at 80° C. for 500 hours to obtain a watch band for evaluation.

The hexavalent chromium content of each watch band was measured in accordance with ISO 17075:2008-02. The hexavalent chromium content in the watch bands obtained using the compounds represented by chemical formula (2) and chemical formula (4) was below the detection limit (2 ppm). On the other hand, no hexavalent chromium was detected in the watch band obtained using the compound represented by chemical formula (13).

The model of the watch strap of this product is 59-S52979 for cattle and 59-T50736 for crocodile.

The above results indicate that the use of the organic compound of the present invention can provide a harmless watch band (leather product) that is free of hexavalent chromium. It is understood that the compound represented by chemical formula (13), while having a high reducing power, is inactivated by running water, making it difficult to maintain its reducing power for a long period of time. It should be noted that since the leather sheet is immersed in an aqueous solution of potassium dichromate, which penetrates into the interior, the aqueous solution of the compound represented by chemical formula (13) also penetrates into the leather sheet.

(Examples 25-1 to 25-4)

A chrome-tanned leather sheet was prepared. Crocodile leather and cow leather were used as the leather material. The leather was cut into the size used for watch bands and used as the raw material. The leather was then contaminated with hexavalent chromium using a 1/60 mol/l potassium dichromate aqueous solution.

A treatment solution containing a hexavalent chromium treatment agent was prepared by dissolving 0.3 g of the compound represented by chemical formula (14) in 10 g of hexane, and a treatment solution containing a hexavalent chromium treatment agent was prepared by dissolving 0.3 g in 10 g of heptane. These treatment solutions were applied to leather by spraying and dried at room temperature to obtain two types of treated leather sheets. It was found that hexane and heptane not only have good penetration into leather but also do not extract coloring components, resulting in less color change than other non-aqueous solvents. In particular, hexane has a fast drying rate and good workability.

Next, using an adhesive (HIGHBON 4250), crocodile leather and cow leather, a total of four types of watch bands were obtained, and these were aged at 60° C. for 500 hours to obtain watch bands for evaluation.

The hexavalent chromium content of each watch strap was measured according to ISO17075:2008-02. As a result, hexavalent chromium was not detected in any of the watch straps, falling below the detection limit (2 ppm) and indicating that it was harmless.

The model of the watch strap of this product is 59-S52979 for cattle and 59-T50736 for crocodile.

The above results show that the use of a hexavalent chromium treatment agent can provide a harmless watch band (leather product) that does not contain hexavalent chromium.

It is also known that, in particular, by using hexane or heptane as a solvent and a highly organic hexavalent chromium treatment agent represented by chemical formula (14), a harmless watchband treated with hexavalent chromium with minimal changes in color and leather texture can be obtained.

Reference: When 0.3 g of the compound represented by chemical formula (2) was dissolved in 10 g of IPA to prepare a hexavalent chromium treatment agent, and large amounts of the compound were repeatedly applied, the color gradually changed (faded). Although this does not present a problem in actual use, the solvent and hexavalent chromium treatment agent described in Example 25 are preferred, especially when producing products requiring color.

(Example 26)

The hexavalent chromium-containing watchbands described in Comparative Examples 1 and 2 were prepared and made of crocodile and cow leather (model numbers: 59-S52979 for cow and 59-T50736 for crocodile).

A treatment liquid containing a hexavalent chromium treatment agent was prepared by dissolving 0.3 g of the compound represented by chemical formula (14) in 10 g of hexane, and a treatment liquid containing a hexavalent chromium treatment agent was prepared by dissolving 0.3 g of the compound represented by chemical formula (14) in 10 g of hexane.

A commercially available watch band was immersed in the two obtained hexavalent chromium treatment agents to allow them to penetrate, and then dried to obtain a watch band.

The hexavalent chromium content of each watch strap was measured according to ISO17075:2008-02. As a result, hexavalent chromium was not detected in any of the watch straps, falling below the detection limit (2 ppm) and indicating that it was harmless.

From the above results, it is understood that the use of a hexavalent chromium treatment agent can provide a harmless watch band (leather product) that does not contain hexavalent chromium.

Furthermore, it was found that, in particular, by using hexane or heptane as a solvent and a highly organic hexavalent chromium treatment agent represented by Chemical Formula (14), a product containing hexavalent chromium was subsequently impregnated, thereby obtaining a harmless watchband treated with hexavalent chromium with minimal changes in color and leather texture. Moreover, compared to heptane, hexane has good volatility and a short treatment time, so it has excellent treatment capacity and exhibits significant performance. In addition, heptane and hexane penetrate leather significantly faster than water, and therefore have advantages over water, which also has little color change. When using hydrocarbon solvents, such as Chemical Formula (4) and Chemical Formula (13), they do not dissolve and therefore cannot achieve the desired effect. However, when using the structure of Chemical Formula (14) or its derivatives, it can be dissolved by using a long-chain alkyl group with 10 or more carbon atoms (16 carbon atoms in Chemical Formula 14). Thus, the hexavalent chromium treatment function can be obtained from this embodiment, and the hexavalent chromium treatment agent most suitable for leather products with little change in the texture of the leather including the color and touch, and the treatment method using the same, are provided.

(Example 27)

A chrome-tanned leather sheet was prepared. Crocodile leather and cow leather were used as the leather material. The leather was cut into the size used for watch bands and used as the raw material. The leather was then contaminated with hexavalent chromium using a 1/60 mol/l potassium dichromate aqueous solution.

A treatment liquid (W) containing an organic compound (B) was prepared by dissolving 0.3 g of the compound represented by the chemical formula (13) in 10 g of pure water.

Furthermore, 0.15 g of the compound represented by chemical formula (4) and 0.15 g of the compound represented by chemical formula (3) were dissolved in 10 g of each of the mixed solutions of IPA and hexane at a ratio of 8:2, 7:3, and 5:5 (a total of 0.30 g) to prepare three treatment solutions containing a hexavalent chromium treatment agent (8:2, 7:3, and 5:5). The kinematic viscosity of the treatment solution with a ratio of IPA to hexane of 5:5 was approximately 1.1 (cSt).

The surface of the leather is coated with a cloth containing a treatment liquid (W) and dried. Treatment liquids of 8:2, 7:3, and 5:5 are applied from the back using a sprayer and dried. It can be seen that the 8:2, 7:3, and 5:5 treatment liquids sprayed from the back have good penetration power. They are mixed with not only IPA but also hydrocarbon hexane, so they have little impact on the leather and can be used for most leathers. In addition, since the impact is small, it is possible to fully apply the amount that completely penetrates the surface of the leather, which is good. In addition, compared with hexane, the solubility of the compounds represented by the chemical formula (4) and the chemical formula (3) of IPA is high. Therefore, even if the solvent of the treatment liquid evaporates slightly during the operation, the hexavalent chromium treatment agent will not be precipitated, and it can be used well for a long time. It can be seen that by mixing a hydrocarbon non-polar solvent and a polar solvent such as alcohol, the function of the hydrocarbon to reduce the impact on the leather and the function of the polar solvent to increase the solubility of the hexavalent chromium treatment agent can be taken into account, and a treatment liquid with good production convenience can be obtained. In addition, it can be seen from this embodiment that in order to add a non-polar solvent to the polar solvent to reduce the impact on the leather, the content of the non-polar solvent relative to the polar solvent is more than 20wt% (in the test using a treatment liquid of 9:1, although it is within the range where there is no problem in terms of quality, a small amount of white can be seen on the surface).

Next, using an adhesive (HIGHBON 4250), three types of crocodile leather with surface and back treatments, and three types of cow leather with surface and back treatments, a total of six watch bands were prepared. These were aged at 60°C for 500 hours to obtain watch bands for evaluation.

The hexavalent chromium content of each watch strap was measured according to ISO17075:2008-02. As a result, hexavalent chromium was not detected in any of the watch straps, falling below the detection limit (2 ppm) and indicating that it was harmless.

Next, the aged watch band was immersed in running water to allow the tap water to fully permeate, and aged at 80° C. for 500 hours to obtain a watch band for evaluation.

The hexavalent chromium content of each watch band was measured in accordance with ISO 17075:2008-02. As a result, the hexavalent chromium content of each watch band was below the detection limit (2 ppm).

The model of the watch strap of this product is 59-S52979 for cattle and 59-T50736 for crocodile.

The above results demonstrate that the use of a hexavalent chromium treatment agent can produce a harmless watch band (leather product) that remains free of hexavalent chromium. Furthermore, the hexavalent chromium treatment agent maintains its reducing power and renders the leather product harmless, even when exposed to sweat and atmospheric moisture, without dissolving harmful hexavalent chromium over a long period of time.

Separately, the treatment solution for treating the back side of the leather was diluted with the same solvent (IPA/hexane) as used previously, producing treatment solutions diluted 2x, 3x, 5x, 10x, and 30x. Similarly, the surfaces of crocodile and cow leather contaminated with hexavalent chromium were treated with treatment solution (W) as described above, and the back side was sprayed with the treatment solution (2x, 3x, 5x, 10x, and 30x) and dried.

Next, using an adhesive (HIGHBON 4250), crocodile leather and cow leather, a total of 30 types of watch bands were obtained, and these were aged at 60° C. for 500 hours to obtain watch bands for evaluation.

The hexavalent chromium content of each watch strap was measured according to ISO17075:2008-02. As a result, hexavalent chromium was not detected in any of the watch straps, falling below the detection limit (2 ppm) and indicating that it was harmless.

The model of the watch strap of this product is 59-S52979 for cattle and 59-T50736 for crocodile.

From the above, it is understood that the appropriate concentration of the hexavalent chromium treatment agent in the solvent is 0.01 g or more per 10 g of the solvent, in order to achieve the desired effect.

(Comparative Examples 1 and 2)

As shown in Example 20, a leather sheet obtained from chrome-tanned leather was prepared. Crocodile and cow leather were used as the leather type. This leather was cut into the size used for a watch band and used as the raw material. This leather was bonded to a plastic core material using the same adhesive (HIGHBON 4250) as in Example 20 to produce a watch band. The model numbers of the bands for these products were 59-S52979 for cow and 59-T50736 for crocodile. Since the resulting watch bands risk converting to hexavalent chromium if heated, they were not aged at 60°C, but rather measured for hexavalent chromium content in the product using the ISO 17075:2008-02 method in its optimal state. Despite favorable conditions, hexavalent chromium was detected at 8 ppm for crocodile and 3 ppm for cow.

In addition, the total chromium content of each watch strap was analyzed using a fluorescent X-ray analyzer, and the results showed that the chromium content in crocodile was 7141 ppm and that in cattle was 16362 ppm.

(Comparative Examples 3-1 to 3-3, 4-1 to 4-3, 5-1 to 5-3)

The same experiments as in Reference Examples 2-1 and 2-3 were carried out except that 1,2,3-cyclohexanetriol, α-cyclodextrin, and D-(+)-glucose were used instead of the compound represented by Chemical Formula (2).

The results showed that hexavalent chromium showed high values of 830 ppm or higher in all cases. These results indicate that even compounds with carbon-based hydroxyl groups, similar in structure, consisting of only three carbon atoms (C, H, and O) and lacking aldehyde or carboxyl groups, cannot treat hexavalent chromium unless they possess the specific structure of the present invention.

(Comparative Examples 6-1 to 6-3)

Confirmation of the reactivity of hexavalent chromium.

A 1/60 mol/l aqueous solution of potassium dichromate (chromium is hexavalent chromium) was measured and placed in a 10 ml container. 1 g of 1,2,3-cyclohexanetriol, α-cyclodextrin, and D-(+)-glucose were added thereto respectively, and stirred at room temperature.

As a result, for all solutions, chromium did not change from a valent state to hexavalent, and the characteristic ion color did not change. This fact demonstrates that even compounds with carbon-based hydroxyl groups, with similar skeletons consisting of only three types of carbon, hydrogen, and oxygen, and lacking aldehyde or carboxyl groups, cannot treat hexavalent chromium unless they possess the specific structure of the present invention.

In the above examples and comparative examples, the term "coating with hexavalent chromium" refers to coating with a brush, sprayer, or sponge roller, etc. In the leather industry, cattle are called calves, and in the experiments of the present invention, cattle refers to calves.

(Example 28)

The hexavalent chromium-containing watchbands described in Comparative Examples 1 and 2 were prepared from crocodile and cow leather (model numbers: 59-S52979 for cow and 59-T50736 for crocodile). The hexavalent chromium content was 8 ppm for crocodile and 3 ppm for cow.

0.5 g of the compound represented by Chemical Formula (3), 2.5 g of the compound represented by Chemical Formula (4), and 2.0 g of the compound represented by Chemical Formula (13) were mixed and dissolved in 500 g of a mixed solution of water and IPA (50 wt %:50 wt %) to obtain a hexavalent chromium treatment solution. The kinematic viscosity of the treatment solution was 3.7 (cSt).

Each watch band was immersed in the resulting hexavalent chromium treatment agent to allow penetration. The mixture was dried to produce two types of watch bands. The hexavalent chromium content of each band was immediately measured according to ISO 17075:2008-02. The results showed that all hexavalent chromium levels were below the detection limit (2 ppm), indicating no harmful effects.

The bands were then aged at 60°C for 500 hours to produce watch bands for evaluation. Hexavalent chromium content was measured for each band according to ISO 17075:2008-02. The hexavalent chromium content was below the detection limit (2 ppm), indicating harmlessness. Furthermore, total chromium content in each band was analyzed using a fluorescent X-ray analyzer. The results showed approximately 7,000 ppm for crocodile and approximately 16,000 ppm for cattle.

Next, the aged watch bands were immersed in running water, allowing the tap water to penetrate thoroughly. They were aged at 80°C for 500 hours to obtain watch bands for evaluation. The hexavalent chromium content of each band was measured according to ISO 17075:2008-02. The results showed that hexavalent chromium was below the detection limit (2 ppm) in all bands, indicating no harmful effects.

It can be seen that the hexavalent chromium treatment agent, because it contains the compounds represented by chemical formulas (3) and (4), has high permeability into leather or leather products, can be retained in the leather or leather products for a long time, and can be reduced stably over a long period of time. It is known that the compound is easily absorbed into the leather or leather products before fading, is not easy to fade or discolor, and has a low risk of damaging the color tone and texture of the leather or leather products.

Furthermore, it was found that the inclusion of the compound represented by chemical formula (13) enabled rapid detoxification of the surface, and suitably suppressed symptoms such as skin cracking and allergies. It was also found that the compound was suitably compatible with the compounds represented by chemical formulas (3) and (4), which are polyphenols, and could prevent browning and discoloration. Due to its high decomposability, it was not easily discolored, and did not damage the color tone or texture of leather or leather products.

Furthermore, it was found that the use of water and IPA as solvents resulted in excellent miscibility, which helped prevent fires in factories and provided high safety. Furthermore, it was found that the solvent could penetrate deep into the leather strap with appropriate volatility without compromising design.

(Example 29)

Two types of leather straps were obtained by the same method as in Example 28, except that 0.5 g of the compound represented by chemical formula (3) in Example 28 was replaced by 0.75 g, 2.5 g of the compound represented by chemical formula (4) was replaced by 3.0 g, and 2.0 g of the compound represented by chemical formula (13) was replaced by 1.25 g.

After the leather watch strap was produced, the hexavalent chromium content was measured according to ISO 17075:2008-02. The hexavalent chromium content was below the detection limit (2 ppm).

Then, aging was performed in the same manner as in Example 28. The hexavalent chromium content of the obtained watch band was measured in accordance with ISO 17075:2008-02, and the hexavalent chromium content was below the detection limit (2 ppm).

Next, running water treatment was performed in the same manner as in Example 28. The hexavalent chromium content of the obtained watch band was measured in accordance with ISO 17075:2008-02, and the hexavalent chromium content was below the detection limit (2 ppm).

(Example 30)

Two types of leather straps were obtained by the same method as in Example 28, except that 0.5 g of the compound represented by chemical formula (3) was changed to 0.25 g, 2.5 g of the compound represented by chemical formula (4) was changed to 3.75 g, and 2.0 g of the compound represented by chemical formula (13) was changed to 1.0 g, by using the hexavalent chromium treatment solution obtained in Example 28.

After the leather watch strap was produced, the hexavalent chromium content was measured according to ISO 17075:2008-02. The hexavalent chromium content was below the detection limit (2 ppm).

Then, aging was performed in the same manner as in Example 28. The hexavalent chromium content of the obtained watch band was measured in accordance with ISO 17075:2008-02, and the hexavalent chromium content was below the detection limit (2 ppm).

Next, running water treatment was performed in the same manner as in Example 28. The hexavalent chromium content of the obtained watch band was measured in accordance with ISO 17075:2008-02, and the hexavalent chromium content was below the detection limit (2 ppm).

(Example 31)

A hexavalent chromium treatment solution was obtained by the same method as in Example 28, except that the hexavalent chromium treatment solution obtained in Example 28 was changed from the amount ratio of water and IPA in the mixed solution of 50 wt %:50 wt % to 60 wt %:40 wt %.

After the leather watch strap was produced, the hexavalent chromium content was measured according to ISO 17075:2008-02. The hexavalent chromium content was below the detection limit (2 ppm).

Then, aging was performed in the same manner as in Example 28. The hexavalent chromium content of the obtained watch band was measured in accordance with ISO 17075:2008-02, and the hexavalent chromium content was below the detection limit (2 ppm).

Next, running water treatment was performed in the same manner as in Example 28. The hexavalent chromium content of the obtained watch band was measured in accordance with ISO 17075:2008-02, and the hexavalent chromium content was below the detection limit (2 ppm).

(Comparative Example 7)

A watchband was prepared using crocodile and cow leather in the same manner as in Example 28. The leather had been previously contaminated with hexavalent chromium by immersing it in a 1/60 mol/l aqueous potassium dichromate solution. This contamination increased the hexavalent chromium content in the leather by approximately 70 ppm.

5.0 g of the compound represented by Chemical Formula (13) was mixed and dissolved in 500 g of a mixed solution of water and IPA (50 wt %:50 wt %) to obtain a solution.

Each watch band was immersed in the resulting solution to allow penetration. The solution was then dried to obtain a watch band. The hexavalent chromium content of each band was immediately measured according to ISO 17075:2008-02, and the result showed that the hexavalent chromium content was below the detection limit (2 ppm).

The samples were then aged at 60° C. for 500 hours to obtain watch bands for evaluation. The hexavalent chromium content of each band was measured according to ISO 17075:2008-02, and the hexavalent chromium content was below the detection limit (2 ppm).

Next, the aged watch bands were immersed in running water, allowing the tap water to fully penetrate. They were aged at 80°C for 500 hours to obtain watch bands for evaluation. The hexavalent chromium content of each band was measured according to ISO 17075:2008-02, and no hexavalent chromium was detected.

Comparison of Examples 28-31 with Comparative Example 7 demonstrates that the hexavalent chromium treatment agent is fast-acting, capable of stably and long-term retention in the watchband, rendering it non-toxic. Furthermore, the treated watchbands exhibit no long-term release of hexavalent chromium, even when exposed to moisture such as sweat and rain, making them both human- and environmentally friendly.

(Example 32)

A watch strap was prepared in the same manner as in Example 28 using crocodile and cow leather.

3.0 g of the compound represented by Chemical Formula (4) and 2.0 g of the compound represented by Chemical Formula (13) were mixed and dissolved in 500 g of a mixed solution of water and IPA (50 wt %:50 wt %) to obtain a hexavalent chromium treatment solution.

The resulting hexavalent chromium treatment agent was sprayed onto the surface of the watchband and dried at room temperature. Two types of leather watchbands were obtained. The hexavalent chromium content of each watchband was immediately measured according to ISO 17075:2008-02, and the results showed that the hexavalent chromium content was below the detection limit (2 ppm).

Then, aging was performed in the same manner as in Example 28. The hexavalent chromium content of the obtained watch band was measured in accordance with ISO 17075:2008-02, and the hexavalent chromium content was below the detection limit (2 ppm).

(Example 33)

A watch strap was prepared in the same manner as in Example 28 using crocodile and cow leather.

2.5 g of the compound represented by Chemical Formula (3) and 2.5 g of the compound represented by Chemical Formula (13) were mixed and dissolved in 500 g of a mixed solution of water and IPA (50 wt %:50 wt %) to obtain a hexavalent chromium treatment solution.

The resulting hexavalent chromium treatment agent was sprayed onto the surface of the watchband and dried at room temperature. Two types of leather watchbands were obtained. Immediately after treatment, the hexavalent chromium content of each watchband was measured according to ISO 17075:2008-02, and the results showed that the hexavalent chromium content was below the detection limit (2 ppm).

Then, aging was performed in the same manner as in Example 28. The hexavalent chromium content of the obtained watch band was measured in accordance with ISO 17075:2008-02, and the hexavalent chromium content was below the detection limit (2 ppm).

Next, running water treatment was performed in the same manner as in Example 28. The hexavalent chromium content of the obtained watch band was measured in accordance with ISO 17075:2008-02, and the hexavalent chromium content was below the detection limit (2 ppm).

(Example 34)

Using cowhide leather whose colorability had been confirmed, a study on surface treatment was conducted. As shown in FIG1 , when the leather was immersed in a mixed solution of water and IPA (50 wt %:50 wt %), a red coloring material was eluted.

This leather was used to produce a leather watchband in the same manner as in Comparative Examples 1 and 2. Note that the leather had been previously contaminated with hexavalent chromium by immersing it in a 1/60 mol/l aqueous potassium dichromate solution. This contamination resulted in an increase in the hexavalent chromium content of the leather by approximately 70 ppm.

A hexavalent chromium treatment solution was obtained in the same manner as in Example 28, except that the mixed solution of water and IPA was replaced with water alone. This treatment solution was applied to a leather watchband by spraying and dried at room temperature to obtain a treated leather sheet.

Visual inspection of the watch strap revealed no fading or discoloration on the leather surface, and no loss of color tone or texture.

(Example 35)

Using cowhide leather whose colorability had been confirmed, a study on surface treatment was conducted. As shown in FIG2 , when the leather was immersed in a mixed solution of water and IPA (50 wt %:50 wt %), a green colored material was eluted.

Using this leather, a leather watchband treated with a hexavalent chromium treatment solution was produced in the same manner as in Example 34.

Visual inspection of the watch strap revealed no fading or discoloration on the leather surface, and no loss of color tone or texture.

(Example 36)

The hexavalent chromium-containing watchbands described in Comparative Examples 1 and 2 were prepared from crocodile and cow leather (model numbers: 59-S52979 for cow and 59-T50736 for crocodile). The hexavalent chromium content was 8 ppm for crocodile and 3 ppm for cow.

0.3 g of the compound represented by Chemical Formula (3) and 0.7 g of the compound represented by Chemical Formula (4) were mixed and dissolved in 100 g of a mixed solution of water and IPA (50 wt %:50 wt %) to obtain a hexavalent chromium treatment solution.

Each watch band was immersed in the obtained hexavalent chromium treatment agent to allow it to penetrate, and then dried to obtain two types of watch bands.

The samples were then aged at 60° C. for 500 hours to obtain watch bands for evaluation. The hexavalent chromium content of each band was measured according to ISO 17075:2008-02, and the hexavalent chromium content was below the detection limit (2 ppm).

Next, the aged watch bands were immersed in running water, allowing the tap water to penetrate thoroughly. They were aged at 80°C for 500 hours to produce watch bands for evaluation. The hexavalent chromium content of each band was measured according to ISO 17075:2008-02, and the results showed that hexavalent chromium was below the detection limit (2 ppm). Furthermore, the total chromium content of each aged band was analyzed using a fluorescent X-ray analyzer, revealing approximately 7,000 ppm for crocodile and approximately 16,000 ppm for cattle.

Claims (38)

1. A type of leather comprising at least an organic compound (A) and trivalent chromium, said organic compound (A) having the structure shown in chemical formula (1) which has reducing properties to trivalent chromium by reaction with hexavalent chromium, and a hydroxyphenyl group and lacking an aldehyde group and a carboxyl group. The content of hexavalent chromium, as measured according to ISO 17075:2008-02, is less than 3 ppm. The organic compound (A) comprises: (i) esters of gallic acid; and (ii) at least one compound selected from tannic acid and its derivatives. ^R1 , ^R2 , ^R3 , ^R4 and ^R5 are each independently a substituent composed of C, H and O; ^R1 or ^R2 may be selectively bonded to any one of ^R3 , ^R4 or ^R5 to form a ring. 2. The leather according to claim 1, wherein the total chromium content determined by fluorescence X-ray diffraction is 5000 ppm or more. 3. The leather according to claim 1, wherein the compound (ii) is tannic acid. 4. The leather according to claim 1, further comprising: Organic compound (B) having the structure shown in the chemical formula (1) which has the reducing property of reacting with hexavalent chromium to reduce it to trivalent chromium and does not have hydroxyphenyl, aldehyde and carboxyl groups. 5. The leather according to claim 4, wherein the organic compound (B) is at least one compound selected from ascorbic acid, derivatives of ascorbic acid, isoascorbic acid, and derivatives of isoascorbic acid. 6. A leather article comprising at least an organic compound (A) and trivalent chromium, said organic compound (A) having the structure shown in chemical formula (1) which has reducing properties to trivalent chromium by reacting with hexavalent chromium, and having a hydroxyphenyl group and lacking an aldehyde group and a carboxyl group. The content of hexavalent chromium, as measured according to ISO 17075:2008-02, is less than 3 ppm. The organic compound (A) comprises: (i) esters of gallic acid; and (ii) at least one compound selected from tannic acid and its derivatives. ^R1 , ^R2 , ^R3 , ^R4 and ^R5 are each independently a substituent composed of C, H and O; ^R1 or ^R2 may be selectively bonded to any one of ^R3 , ^R4 or ^R5 to form a ring. 7. The leather product according to claim 6, wherein the total chromium content determined by fluorescence X-ray diffraction is 5000 ppm or more. 8. The leather article according to claim 6, wherein the compound (ii) is tannic acid. 9. The leather article according to claim 6, further comprising: Organic compound (B) having the structure shown in the chemical formula (1) which has the reducing property of reacting with hexavalent chromium to reduce it to trivalent chromium and does not have hydroxyphenyl, aldehyde and carboxyl groups. 10. The leather article according to claim 9, wherein the organic compound (B) is at least one compound selected from ascorbic acid, derivatives of ascorbic acid, isoascorbic acid, and derivatives of isoascorbic acid. 11. The leather article according to claim 6, wherein it is a leather strap for watchmaking. 12. A hexavalent chromium treatment agent for leather or leather articles, comprising at least: Organic compound (A) having the structure shown in chemical formula (1) which has the reducing power to reduce hexavalent chromium to trivalent chromium and a hydroxyphenyl group but does not have an aldehyde or carboxyl group; and Organic compound (B) has the structure shown in chemical formula (1) which has the reducing property of reacting with hexavalent chromium to trivalent chromium and does not have hydroxyphenyl, aldehyde and carboxyl groups. The organic compound (A) comprises: (i) esters of gallic acid; and (ii) at least one compound selected from tannic acid and its derivatives. ^R1 , ^R2 , ^R3 , ^R4 and ^R5 are each independently a substituent composed of C, H and O; ^R1 or ^R2 may be selectively bonded to any one of ^R3 , ^R4 or ^R5 to form a ring. 13. The hexavalent chromium treatment agent for leather or leather products according to claim 12, wherein the organic compound (B) is at least one compound selected from ascorbic acid, derivatives of ascorbic acid, isoascorbic acid, and derivatives of isoascorbic acid. 14. The hexavalent chromium treatment agent for leather or leather articles according to claim 12 or 13, comprising the organic compound (A) and organic compound (B) in a weight ratio of 50-90:10-50, wherein the total of A and B is set to 100 by weight. 15. The hexavalent chromium treatment agent for leather or leather articles according to claim 12 or 13, wherein it is an aqueous solution containing only water as a solvent. 16. The hexavalent chromium treatment agent for leather or leather articles according to claim 12 or 13, further comprising an alcohol having 1 to 3 carbon atoms. 17. The hexavalent chromium treatment agent for leather or leather articles according to claim 16, further comprising water. 18. The hexavalent chromium treatment agent for leather or leather articles according to claim 12 or 13, further comprising water and an alcohol having 1 to 3 carbon atoms. The water and alcohol are in a weight ratio of 20–80:20–80, wherein the total amount of both is set at 100% by mass, and... The organic compound (A) and organic compound (B) are dissolved in the water and alcohol. 19. The hexavalent chromium treatment agent for leather or leather articles according to claim 12 or 13, further comprising at least one solvent selected from hexaane and heptane. 20. The hexavalent chromium treatment agent for leather or leather products according to claim 19, further comprising an alcohol having 1 to 3 carbon atoms. 21. The hexavalent chromium treatment agent for leather or leather products according to claim 12 or 13, further comprising an alcohol having 1 to 3 carbon atoms, and hexane and/or heptane. The alcohol is in a weight ratio of 20–80:20–80 with hexane and/or heptane, wherein the total amount of both is set at 100% by mass, and... The organic compounds (A) and (B) are dissolved in the alcohol, as well as in hexane and/or heptane. 22. The hexavalent chromium treatment agent for leather or leather articles according to claim 15, which is permeable to leather or leather articles. 23. The hexavalent chromium treatment agent for leather or leather products according to claim 15, wherein the kinematic viscosity at 25°C is 0.001 cSt or higher and less than 5 cSt. 24. The hexavalent chromium treatment agent for leather or leather articles according to claim 12, wherein the compound (ii) is tannic acid. 25. The hexavalent chromium treatment agent for leather or leather articles according to claim 12 or 24, comprising said compound (i), compound (ii) and organic compound (B) in a weight percentage ratio of 1-20:30-89:10-50, wherein the total of (i), (ii) and (B) is set to 100 by weight. 26. A method for treating hexavalent chromium contained in coarse leather, comprising: contacting the coarse leather containing hexavalent chromium with a leather hexavalent chromium treatment agent according to any one of claims 12 to 25. 27. A method for treating hexavalent chromium contained in coarse leather, comprising: contacting the coarse leather containing hexavalent chromium with the leather treatment agent for leather according to any one of claims 12 to 25 by spraying, spreading, dipping, coating or impregnating it. 28. The method for treating hexavalent chromium contained in coarse leather according to claim 26 or 27, wherein the total chromium content in the coarse leather, as determined by fluorescence X-ray diffraction, is 5000 ppm or more. 29. A method for manufacturing leather, comprising: a step of contacting coarse leather containing hexavalent chromium with a hexavalent chromium treatment agent as described in any one of claims 12 to 25. The content of hexavalent chromium, as measured according to ISO 17075:2008-02, is less than 3 ppm. 30. The method for manufacturing leather according to claim 29, wherein the total chromium content in the leather, as determined by fluorescence X-ray diffraction, is 5000 ppm or more. 31. A method for treating hexavalent chromium contained in a coarse leather article, comprising: contacting the coarse leather article containing hexavalent chromium with a hexavalent chromium treatment agent for leather articles according to any one of claims 12 to 25. 32. A method for treating hexavalent chromium contained in a coarse leather article, comprising: contacting the coarse leather article containing hexavalent chromium with the hexavalent chromium treatment agent for leather articles according to any one of claims 12 to 25 by spraying, spreading, dipping, coating or impregnating the coarse leather article containing hexavalent chromium. 33. The method for treating hexavalent chromium contained in coarse leather products according to claim 31 or 32, wherein the total chromium content in the coarse leather products, as determined by fluorescence X-ray diffraction, is 5000 ppm or more. 34. A method for manufacturing leather articles, comprising: a step of contacting a coarse leather article containing hexavalent chromium with a hexavalent chromium treatment agent for leather articles according to any one of claims 12 to 25. The content of hexavalent chromium, as measured according to ISO 17075:2008-02, is less than 3 ppm. 35. The method for manufacturing leather articles according to claim 34, wherein the total chromium content in the leather articles, as determined by fluorescence X-ray diffraction, is 5000 ppm or more. 36. A hexavalent chromium treatment agent for leather or leather articles, comprising at least: Organic compound (A) having the structure shown in chemical formula (1) which has the reducing power to reduce hexavalent chromium to trivalent chromium and a hydroxyphenyl group but does not have an aldehyde or carboxyl group; and At least two solvents selected from water, alcohols having 1 to 3 carbon atoms, hexane, and heptane. The organic compound (A) comprises: (i) esters of gallic acid; and (ii) at least one compound selected from tannic acid and its derivatives. This hexavalent chromium treatment agent is penetrable to leather or leather products. ^R1 , ^R2 , ^R3 , ^R4 and ^R5 are each independently a substituent composed of C, H and O; ^R1 or ^R2 may be selectively bonded to any one of ^R3 , ^R4 or ^R5 to form a ring. 37. The hexavalent chromium treatment agent for leather or leather products according to claim 36, further comprising an organic compound (B): having the structure shown in the chemical formula (1) having reducing properties to reduce hexavalent chromium to trivalent chromium by reaction and not having hydroxyphenyl, aldehyde and carboxyl groups. 38. The hexavalent chromium treatment agent for leather or leather articles according to claim 36 or 37, wherein the kinematic viscosity at 25°C is 0.001 cSt or higher and less than 5 cSt.