MXPA06010393A - Low migration, low odour offset inks or varnishes - Google Patents

Abstract

An offset printing ink or varnish uses as a solvent at least one water-insoluble ester of a polycarboxylic acid with an alcohol having at least 4 carbon atoms.

Description

INKS OR VARNICES FOR OFFSET WITH LOW EMISSION OF SMELLS AND LOW MIGRATION Field of the Invention The present invention relates to novel inks with low emission of odors and low migration which are useful for printing in offset lithography, especially printing in offset lithography with paper feeding.

BACKGROUND OF THE INVENTION Offset lithography with paper feeding is the dominant printing process for the printing of folding boxes for many purposes, including for use as food packaging. However, where an ink should be used in food packaging, it is essential, from the point of view of consumer acceptance, that the ink should not contaminate the food or transmit an artificial odor to it. In addition, there is a growing trend in legislation to prescribe very low levels of contaminants in food and other material that could affect public health. Pollution, in this context, can result from the migration of components from an ink to the food product or other packaged material or from the undesirable odors transmitted to the material packed by the ink. Therefore, there is a need for an ink for printing which can be used for offset lithography with paper feeding and which allows little or no migration of its components while being essentially odorless or has little odor. The nature of the offset lithography process also involves severe restrictions on the ink formulation, as explained in The Printing Ink Manual by R.H. Leach et al [Fifth edition (1993) pages 342-346] and compliance with all these requirements is not an easy task. One of the main odorous components of offset inks is the solvent used. In the nature of offset lithography it is observed that the solvent must be organic and insoluble in water. Many solvents that have these properties are not only highly odorous but also many of these are toxic to a greater or lesser degree. Therefore, the selection of solvents for this purpose is extremely restricted. The North American Patent No. 6,613,813 attempts to overcome these problems through the use, inter alia, of a solvent comprising an ester of a multivalent alcohol with a fatty acid. The composition may optionally contain a multifunctional allyl ester of a multivalent organic acid; however, the function of these esters is to improve the drying process by undergoing oxidant drying, preferably to serve as a substantial part of the solvent system. While the solution proposed in the North American Patent? O. 6,613,813 is effective, the Examples of the patent seem to suggest that an additional drying agent is necessary to achieve the required drying in a reasonable time. It has now been discovered that a class of compounds based on polycarboxylic acids are useful as solvents for inks for offset printing and are capable of producing a variety of improvements over known inks of the US Patent. 6,613,813, which include equivalent or less odor, equivalent or less migration, and equivalent or improved stability in the printing house. In this way, the present invention consists of an offset printing ink or varnish, particularly useful in offset lithography printing with paper feeding, characterized in that the solvent comprises at least one water-insoluble ester of a polycarboxylic acid with an alcohol monohydric having at least 4 carbon atoms. As the oxidizing drying process and the byproducts generated by it are an important source of odor development in finished prints, careful selection of raw materials is necessary. The dryers as well as the raw materials with oxidizing drying potential that are used in offset inks with conventional paper feed should preferably be excluded. A good resistance to rubbing of the printing work can be achieved by using the inks of the present invention in combination with a water-based overprint varnish (OVP, for its acronym in English) . The composition of inks or varnishes for offset lithography printing, including offset lithography printing with paper feeding, is very well known and is described in considerable detail in, for example, The Printing Ink Manual (supra) pages 342-452 and the North American Patents? o. 5,382,282,? O. 5,725,646 y? O. 6,489,375. In general terms, a lithographic printing ink must have a low surface tension, it must be water repellent, it must be capable of emulsifying with a wetting solution and, for offset lithography with conventional paper feeding, it must be able to dry without radiation. These very particular requirements are met by the careful formulation and selection of the various components and it is well known in the printing ink industry.

Description of the Invention The solvent used in the ink or varnish composition of the present invention is a water-insoluble ester of a polycarboxylic acid with an alcohol having at least 4 carbon atoms. The polycarboxylic acid may be aromatic or aliphatic, although it is preferably aromatic and must have more than one carboxylic acid group. Preferably, the acid has from 2 to 4, more preferably 3, carboxylic acid groups. Examples of polycarboxylic, aromatic acids include: trimellitic acid, phthalic acid, isophthalic acid, terephthalic acid, 1,2,3-benzenetricarboxylic acid, 1,2,4-benzenecarboxylic acid, 1,3-benzenetricarboxylic acid, 1 , 2,3,4-benzenetracarboxylic acid, 1,2,3,5-benzenetracarboxylic acid, 1,2,4,5-benzenetracarboxylic acid, 1,3,5-naphthalenetricarboxylic acid, 1,3,6-naphthalenetriacetic acid, acid 6-carboxy-1- (carboxymethyl) -2-naphthalene-propionic acid, 1,4,5,8-naphthalene-tetracarboxylic acid, 3,3 ', 4,4'-biphenyltetracarboxylic acid and 3,4,9,10-perylene-tetracarboxylic acid. Of these, trimellitic acid is preferred.

Examples of polycarboxylic, aliphatic acids include: dicarboxylic acids, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, tartronic acid, malic acid and tartaric acid; tricarboxylic acids, such as citric acid, acetylcitric acid, 2-hydroxy-2-methylpropane-1,2,3-tricarboxylic acid, pentane-1,3,5-tricarboxylic acid, 1,3-propanetricarboxylic acid and 7- methyl-l, 7, 9-decanotricarboxílico; and tetracarboxylic acids, such as 1,2,3,4-butanetetracarboxylic acid, cyclopentane-1,2,3,4-tetracarboxylic acid, 2,3,4,5-tetracarboxytetrahydrofuran and acid 1,1,12,12- dodecanotetracarboxílico. The monohydric alcohol with which these polycarboxylic acids form esters has at least 4 carbon atoms and preferably from 4 to 20, more preferably from 4 to 18 and even more preferably from 6 to 10, carbon atoms. Examples of these alcohols include: butanol, sec-butanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nonadecanol, icosanol, hexan -2-ol, 2, 3-dimethylbutan-2-ol, 3-methyl-pentan-1-ol, 3,3-dimethylbutan-2-ol and 2, 3, 3-trimethylbutan-2-ol. A particularly preferred polycarboxylic acid ester solvent according to the present invention is that sold under the trade name Uraplast 525 ™ by DSM Resins bv. This is a trialkyl trimellitate of low viscosity based on alcohols of 8 to 10 carbon atoms. It has previously been used as a plastir. Other suitable solvents include tridecyl trimellitate, tributyl citrate and acetyl tributyl citrate. In order that the polycarboxylic acid ester and the monohydric alcohol must be able to function as a solvent, it is usually important that their molecular weight be within a specific range. In general, a molecular weight of at least 250 and more preferably at least 300 is preferred, the molecular weight, preferred, maximum is 1000. In this manner, the molecular weight is preferably 250 to 1000, more preferably 300 to 1000 and even more preferably from 500 to 800. Although the polycarboxylic acid ester can be used as the sole solvent in the compositions of the present invention, it may be necessary, in order to achieve the correct rheological properties, to also include another solvent. This other solvent, if present, does not preferably exceed 60% of the total solvent that is present in the composition. More preferably, from 45% to 90%, still more preferably from 50% to 80% and most preferably from 55% to 65%, by weight of the solvent comprises the polycarboxylic acid ester. If another solvent is present, any solvent conventionally used in lithographic inks can be used, provided it does not have an oxidative drying potential and does not tend to migrate from the dry ink. Examples of these other solvents include triglycerides of aliphatic carboxylic acids of 8 to 20 carbon atoms, for example, coconut oil, such as that sold under the tradename Kokosol by Lechner and Crebert. The solvent, or mixture of solvents, used in the present invention preferably has a melting point such that it is liquid at the temperature at which the printing ink or varnish is to be used. This usually means that it must be liquid at the temperature of the printing press and preferably at room temperature, for example at temperatures above 10-15 ° C. However, in some cases, for example if the printing ink or varnish is to be used only in a hot atmosphere, it may be possible for the solvent to be solid at these temperatures, provided that it melts at a somewhat higher temperature, for example approximately 25 ° C. The resin component in a lithographic ink or varnish composition functions, inter alia, as a film former for bonding the varnish and the pigment and, when the ink or varnish is dried, attaching the same to the receiving substrate. The resin component also contributes to the hardness, gloss, adhesion and flexibility properties of an ink and must be compatible with the solvent component of the varnish. In conventional oleoresin systems, the resin component commonly comprises a first component or a hard resin component and a second resin component which is typically an alkyl or polyester resin, but which may also comprise various other compositions and resins. Hard resins which are usable in the lithographic inks or varnishes of the present invention include, for example, natural or processed resins such as rosins, rosin esters, modified maleic resins, modified fumaric resins of rosin, dimerized and polymerized rosins, phenolic resins , modified phenolic resins of rosin, terpenes, polyamides, cycled rubber, acrylics, hydrocarbons and modified hydrocarbons. Also included among the available resins are those identified in The Printing Ink Manual, supra, the essence of which is incorporated herein by reference. The lithographic inks of the present invention will usually include at least one pigment, the nature of which is not critical to the present invention and which can be selected from any of those pigments well known to those skilled in the art. Alternatively, the ink may include an extender. The varnishes will not normally include any pigment or extender in their composition. In addition, other additives, such as antioxidants, waxes, anti-staining compounds, lithographic additives and rheology modifiers, may be present if desired. These are likewise well known to those skilled in the field. The invention is further illustrated by the following non-limiting Examples.

EXAMPLES 1-4 Preparation of Inks The components shown in the following Table 1 were combined as described below to produce inks suitable for use in offset litho printing with paper feeding.

Table 1 Coconut oil and approximately half of Uraplast 525MR were added to a reaction vessel, stirred and heated to 180 ° C. Then Tergraf ND 2030MR and Tergraf 902MR were added, making sure that the temperature did not fall below 160 ° C. The mixture was heated to 180 ° C and maintained at that temperature for 60 minutes. Approximately the other half of the total amount of Uraplast 525MR was then added and the mixture allowed to cool to 160 ° C. The gelling agent was then added with rapid stirring and the entire varnish was heated to 180 ° C and maintained at that temperature for 30 minutes. The external cooling then reduced the temperature to 110 ° C and the varnish was discharged from the reaction vessel. The pigment (s) and other solid components (except polyethylene wax) were dispersed in the varnish and the mixture was completely combined with a triple roller mill. The polyethylene wax was then added and the mixture was again passed through the triple roll mill for deaeration. The viscosity and tack were adjusted, before deaeration, by the addition of small amounts of the trialkyl trimellitate, to provide the final composition shown in Table 1.

EXAMPLE 5 Ink preparation The following components were mixed to form a magenta ink, following essentially the same procedure described in Examples 1-4. The amounts are parts by weight.

EXAMPLE 6 Ink Preparation The following components were mixed to form a magenta ink, following essentially the same procedure described in Examples 1-4. The amounts are parts by weight.

EXAMPLE 7 Preparation of the ink The following components were mixed to form a magenta ink, following essentially the same procedure described in Examples 1-4. The amounts are parts by weight.

EXAMPLE 8 Ink Preparation The following components were mixed to form a magenta ink, following essentially the same procedure described in Examples 1-4. The amounts are parts by weight.

EXAMPLE 9 Preparation of varnish The following components were mixed to form a varnish, following essentially the same procedure described in Examples 1-4. The amounts are parts by weight.

EXAMPLES 10-13 Ink Preparation The components listed in Table 2 were mixed to form inks, following essentially the same procedure described in Examples 1-4. The amounts are parts by weight.

Table 2 EXAMPLE 14 Preparation of the printed material The test prints were produced in a Heidelberg MOMR 4-color printing press that included a unit for the application of water-based overprint varnishes. The printing speed was between 7000-9000 sheets / hour, using a humectant solution containing 6-9% by volume of isopropanol. The printing was carried out with standard optical densities, yellow = 1.35, magenta = 1.50, cyan = 1.40 and black = 1.80, using FujiMR plates and Astral 'PremiumMR blankets. The substrate used was Invercote GMR, which is a standard substrate for packaging. The prints were produced using a water-based overprint varnish. The rub tests were performed after 24 hours and all the printing inks of the present invention had satisfactory results.

EXAMPLE 15 Robinson Test The odor and stain caused by the inks of the present invention were subjected to the well-known Robinson test. This is a test originally devised by The Technical Committee of the International Office of Cocoa and Chocolate to determine if the odors of packaging materials are transferred to cocoa and chocolate products. It is now also more generally used to verify if the odor and stain are probably transferred from the packaging materials used in the food industry. The test was carried out as follows: A petri dish containing approximately 25 g of chocolate with freshly grated milk was placed in a clean storage jar with a capacity of 1 liter. 16 representative round samples (9 cm in diameter), the total area of the 16 samples was 1017 cm2) of the packaging material to be evaluated were placed in the jar, so that the sample and the chocolate were not in contact with each other. One jar, the "white model", similar in all respects, but without any sample and a jar with a non-printed substrate, were also prepared. The jars were closed with a lid. Then they were stored for 24 hours in an odorless, dark place at 23 ° C. A panel of tasters then compared the smell and then the taste of the chocolate in each sample jar with the chocolate on the white model. The results were evaluated in the following scale: 0 = no difference in odor / taste 1 = barely noticeable smell / taste difference 2 = noticeable change in odor / taste 3 = significant change in smell / taste 4 = intense change in smell / taste Four-color prints (Black, Cyan, Magenta, Yellow) were produced by printing as described in Example 14 and then tested. The sets of inks used were: Set A, standard offset inks, Irocart ProcessMR inks, a set of conventional paper feed offset inks currently available from Sun Chemical that contain dryers: Set B, Irocart GN Low He ink OR a set of conventional paper feed inkset inks currently available from Sun Chemical that are formulated for low odor emission and low staining; Set C, the inks of Examples 1-4; and Set D, the ink of Example 7, and the black, cyan and yellow inks that were prepared in the same manner as that of Example 7. The results are shown in Table 3 below. Table 3 It can be seen from these results that the compositions of the present invention (Examples 1 and 7) provided a printed material having a comparable or better odor and a comparable or lower stain than that of the product of US Patent No. 6,613,813.

EXAMPLE 16 Migration Test The prints were prepared as described in Example 14 using the inks of Examples 1-4 or-for the inks of Example 8-using a Prüfbau ™ standard laboratory test printer. In all cases, the impressions were individually placed in a petri dish and 1 g of clean Tenax ™ (an absorbent used to simulate dry and / or greasy foods available from Akzo Nobel) was placed on the back of each print. After 10 days at 40 ° C, the Tenax ™ was extracted in diethyl ether and analyzed using GC-MS (Gas Chromatography-Mass Spectrometry). The materials analyzed were Uraplast 525MR, Citrofol BIMR, coconut oil and the solvent used in the US Patent No. 6,613,813, of which its trade name is Radia 7187MR. None was found within the detection limits of the analysis. The invention has been described in terms of preferred embodiments thereof, but is more widely applicable as will be understood by those skilled in the art. The scope of the invention is limited only by the following claims.

Claims (18)

1. CLAIMS 1. An ink or varnish for offset printing, characterized in that the solvent comprises at least one water-insoluble ester of a polycarboxylic acid with an alcohol having at least 4 carbon atoms.
2. 2. An offset printing ink or varnish according to claim 1, characterized in that from 45% to 90% by weight of the solvent comprises an ester of a polycarboxylic acid with an alcohol having at least 4 carbon atoms.
3. 3. An offset printing ink or varnish according to claim 2, characterized in that from 50 to 80% by weight of the solvent comprises an ester of a polycarboxylic acid with an alcohol having at least 4 carbon atoms.
4. 4. An offset printing ink or varnish according to claim 2, characterized in that from 55% to 65% by weight of the solvent comprises an ester of a polycarboxylic acid with an alcohol having at least 4 carbon atoms.
5. 5. An ink or varnish for offset printing according to any of the preceding claims, characterized in that the alcohol has from 4 to 20 carbon atoms.
6. 6. An offset printing ink or varnish according to claim 5, characterized in that the alcohol has from 6 to 10 carbon atoms.
7. 7. An ink or varnish for offset printing according to any of the preceding claims, characterized in that the polycarboxylic acid has 2 to 4 carboxylic acid groups.
8. An ink or varnish for offset printing according to claim 7, characterized in that the polycarboxylic acid has 3 or 4 carboxylic acid groups.
9. 9. An ink or varnish for offset printing according to any of the preceding claims, characterized in that the polycarboxylic acid is an aromatic polycarboxylic acid.
10. 10. An ink or varnish for offset printing according to claim 9, characterized in that the polycarboxylic acid is a benzenepolycarboxylic acid.
11. 11. An ink or varnish for offset printing according to claim 10, characterized in that the benzenepolycarboxylic acid is trimellitic acid.
12. 12. An offset printing ink or varnish according to claim 11, characterized in that the ester is an ester of trimellitic acid with one or more aliphatic alcohols of 8 to 10 saturated straight carbon atoms.
13. 13. An ink or varnish for offset printing according to claim 11, characterized in that the ester is tridecyl trimellitate.
14. 14. An ink or varnish for offset printing according to claim 11, characterized in that the ester is an ester of citric acid or acetylcitric acid.
15. 15. An ink or varnish for offset printing according to claim 14, characterized in that the ester is the butyl ester.
16. 16. An ink or varnish for offset printing according to any of the preceding claims, characterized in that the solvent additionally comprises at least one triglyceride of aliphatic carboxylic acids of 8 to 20 carbon atoms.
17. 17. An ink or varnish for offset printing according to claim 16, characterized in that the triglyceride is a triglyceride of aliphatic carboxylic acids of 10 to 18 carbon atoms.
18. 18. An ink or varnish for offset printing according to claim 17, characterized in that the triglyceride is coconut oil.