JP2014193580A - Laminated body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminate having an excellent water resistance and provided with a coating layer containing anion-modified cellulose nanofibers on a substrate.
SOLUTION: In a laminate in which a coating layer containing cellulose nanofibers and a metal salt is provided on a substrate, the cellulose nanofibers are anion-modified (carboxymethylated or carboxylated) cellulose nanofibers and metal salts Is a trivalent metal salt.
[Selection figure] None

Description

The present invention relates to a laminate in which a layer containing cellulose nanofibers and a metal salt is provided on a substrate.

  When the cellulosic material is treated in the presence of 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as TEMPO) and sodium hypochlorite which is an inexpensive oxidant, Carboxyl groups can be efficiently introduced onto the surface of cellulose microfibrils (Patent Documents 1 and 2). Moreover, a carboxymethyl group can be introduce | transduced into a cellulose by making it react with a monochloroacetic acid or sodium monochloroacetate after making a cellulose raw material into merceres (patent documents 3 and 4).

Cellulose introduced with a carboxyl group (—COOH) or a carboxymethyl group (—CH ₂ COOH) is negatively charged in the solvent and exhibits anionic properties (hereinafter referred to as “anion-modified cellulose raw material”). Sometimes.).

  It is known that when such an anion-modified cellulose raw material is treated in a solvent using a mixer or the like, an anion-modified cellulose nanofiber dispersion can be easily obtained (Patent Documents 1, 2 and 4). .

Anion-modified cellulose nanofibers are made from cellulose and are excellent in biodegradability. Moreover, since it is a hydrophilic material, it can be blended with various water-soluble polymers and can be used for modification of various water-soluble polymers. Furthermore, by providing a coating layer containing anion-modified cellulose nanofibers on various base materials (paper, nonwoven fabric, film, etc.), it can be used for packaging materials, substrate members, separation membranes, regenerative medical materials, etc. that have unprecedented functions. Efforts to apply are being made.

JP 2008-001728 A JP 2010-235679 A JP-A-10-251301 JP 2011-195738 A

  However, the packaging material provided with the coating layer containing the anion-modified cellulose nanofiber, the substrate member, etc. are in contact with water or in a high humidity atmosphere, the anion-modified cellulose nanofiber absorbs moisture, and the packaging material, There has been a problem that the quality of the substrate member is greatly impaired.

Then, an object of this invention is to provide the laminated body which provided the coating layer which has an anion modified cellulose nanofiber on the base material which has the outstanding water resistance.

The present invention provides the following [1] to [5].
[1] In a laminate in which a coating layer containing cellulose nanofibers and a metal salt is provided on a substrate, the cellulose nanofibers are anion-modified cellulose nanofibers and the metal salt is a trivalent metal salt A laminate characterized by the following.
[2] The laminate according to [1], wherein the trivalent metal salt is any one of potassium alum, ammonium alum, and aluminum chloride.
[3] The anion-modified cellulose nanofiber is a cellulose nanofiber introduced with a carboxymethyl group, and the degree of carboxymethyl substitution per glucose unit of cellulose is 0.01 to 0.50. The laminated body as described in 1]-[2].
[4] The anion-modified cellulose nanofiber is a cellulose nanofiber introduced with a carboxyl group, and the amount of the carboxyl group is 0.5 mmol / g with respect to the absolute dry mass of the cellulose nanofiber introduced with a carboxyl group. It is -2.0 mmol / g, The laminated body as described in [1]-[2] characterized by the above-mentioned.
[5] The trivalent metal salt is contained in an amount of 0.1 to 2.0 chemical equivalents relative to the carboxyl group or carboxymethyl group of the anion-modified cellulose nanofiber [1] to [4] ] The laminated body as described in.

ADVANTAGE OF THE INVENTION According to this invention, the laminated body which provided the coating layer containing an anion modified cellulose nanofiber on the base material which has the outstanding water resistance can be provided.

Hereinafter, the present invention will be described in detail. In the present specification, “to” includes values at both ends.
1. Cellulose nanofibers In the present invention, anionic cellulose nanofibers are cellulose fibers having an average fiber length of 50 to 5000 nm and an average fiber width of 1 to 1000 nm, obtained by defibrating an anion-modified cellulose raw material.

<Raw material>
The cellulose raw material is wood-derived kraft pulp or sulfite pulp, powdered cellulose obtained by pulverizing them with a high-pressure homogenizer, a mill, or the like, or microcrystalline cellulose powder purified by chemical treatment such as acid hydrolysis. In addition to these, cellulosic materials derived from plants such as kenaf, hemp, rice, bacus, and bamboo can also be produced. However, if a large amount of hardwood-derived lignin remains in the cellulosic raw material, there is a risk of inhibiting the oxidation reaction of the raw material. Therefore, in the present invention, the cellulosic raw material obtained by the method for producing chemical pulp is preferred. . In order to further remove lignin, it is more preferable to subject the cellulosic raw material thus obtained to a known bleaching treatment.

In addition, the cellulose raw material described above, which has been refined with a high-speed rotating type, colloid mill type, high-pressure type, roll mill type, ultrasonic type dispersing device, wet high-pressure or ultra-high pressure homogenizer, etc. may be used as the cellulose raw material. it can.
<Anion modification of cellulose raw material>
In the present invention, an anion-modified cellulose can be obtained by anion-modifying the above cellulose raw material by using a known method exemplified below, and an example thereof is as follows. be able to.
(1) Carboxymethylation Using the above cellulose raw material as a starting material, 3 to 20 times by weight of a lower alcohol, specifically methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, A tertiary butanol or the like alone or a mixture of two or more kinds and water is used. The mixing ratio of the lower alcohol is 60 to 95% by weight. As the mercerizing agent, 0.5 to 20 times moles of alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide is used per glucose residue of the bottoming material. A bottoming raw material, a solvent, and a mercerizing agent are mixed and subjected to mercerization treatment at a reaction temperature of 0 to 70 ° C., preferably 10 to 60 ° C., and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times mol per glucose residue, a reaction temperature of 30 to 90 ° C., preferably 40 to 80 ° C., and a reaction time of 30 minutes to 10 hours, preferably 1 hour. Perform etherification reaction for ~ 4 hours.

In the present invention, it is preferable that the degree of carboxymethyl substitution per glucose unit of anion-modified cellulose is 0.01 to 0.50. By introducing a carboxymethyl substituent into cellulose, the celluloses are electrically repelled. For this reason, the cellulose which introduce | transduced the carboxymethyl substituent can be nano-defibrated easily. In addition, when the carboxymethyl substituent per glucose unit is smaller than 0.01, it is not possible to sufficiently nano-defibrate. On the other hand, if the carboxymethyl substituent per glucose unit is larger than 0.50, it may swell or dissolve, and may not be obtained as a nanofiber.

  The degree of carboxymethyl substitution can be measured by the following method.

About 2.0 g of sample is precisely weighed and placed in a 300 ml stoppered Erlenmeyer flask. Add 100 ml of nitric acid methanol (1 ml of anhydrous methanol and 100 ml of special concentrated nitric acid) and shake for 3 hours to convert sodium carboxymethyl cellulose (Na-CMC) to carboxymethyl cellulose (H-CMC). The absolute dry H-CMC 1.5-2.0 g is precisely weighed and put into a 300 ml stoppered Erlenmeyer flask. Wet H-CMC with 15 ml of 80% methanol, add 100 ml of 0.1 N NaOH and shake at room temperature for 3 hours. Back titrate excess NaOH with 0.1 N H2SO4 using phenolphthalein as indicator. The following formula: [{100 × F ′-(0.1N H 2 SO 4 (ml)) × F} / (absolute dry mass of H-CMC (g))] × 0.1 = A carboxyl methyl substitution degree = 0. 162A / (1-0.058A)
A: Amount of 1N NaOH required to neutralize 1 g H-CMC (ml)
F ′: 0.1N H 2 SO 4 factor F: 0.1 N NaOH factor

(2) Carboxylation Carboxylation by oxidizing the above cellulose raw material in water using an oxidizing agent in the presence of a compound selected from the group consisting of N-oxyl compounds and bromides, iodides or mixtures thereof Oxidized cellulose having a group introduced into cellulose can be obtained.

The degree of carboxymethyl substitution can be measured by the following method:
About 2.0 g of sample is precisely weighed and placed in a 300 ml stoppered Erlenmeyer flask. Add 100 ml of nitric acid methanol (1 ml of anhydrous methanol and 100 ml of special concentrated nitric acid) and shake for 3 hours to convert sodium carboxymethyl cellulose (Na-CMC) to carboxymethyl cellulose (H-CMC). The absolute dry H-CMC 1.5-2.0 g is precisely weighed and put into a 300 ml stoppered Erlenmeyer flask. Wet H-CMC with 15 ml of 80% methanol, add 100 ml of 0.1 N NaOH and shake at room temperature for 3 hours. Back titrate excess NaOH with 0.1 N H2SO4 using phenolphthalein as indicator. The following formula:
[{100 × F ′ − (0.1N H 2 SO 4 (ml)) × F} / (absolute dry mass of H-CMC (g))] × 0.1 = A
Carboxymethyl substitution degree = 0.162A / (1-0.058A)
A: Amount of 1N NaOH required to neutralize 1 g H-CMC (ml)
F ′: 0.1N H 2 SO 4 factor F: 0.1 N NaOH factor is used to calculate the degree of carboxyl methyl substitution.

(1-2) Carboxylation (oxidation)
A carboxyl group was introduced by oxidizing the cellulose raw material in water using an oxidizing agent in the presence of a compound selected from the group consisting of an N-oxyl compound and a bromide, iodide or a mixture thereof. Cellulose (hereinafter also referred to as “oxidized cellulose”) can be obtained.

  The N-oxyl compound refers to a compound that can generate a nitroxy radical. As the N-oxyl compound, any compound can be used as long as it promotes the target oxidation reaction. For example, the compound shown by the following general formula (Formula 1) is mentioned.

(In Formula 1, R1 to R4 represent the same or different alkyl groups having about 1 to 4 carbon atoms.)
Of the substances represented by Formula 1, 2,2,6,6-tetramethyl-1-piperidine-oxy radical (hereinafter referred to as TEMPO) is preferable.

Further, the N-oxyl compound represented by any one of the following formulas 2 to 5, that is, the hydroxyl group of 4-hydroxy TEMPO was etherified with alcohol or esterified with carboxylic acid or sulfonic acid to impart moderate hydrophobicity. A 4-hydroxy TEMPO derivative or 4-acetamido TEMPO having an appropriate hydrophobicity by acetylating the amino group of 4-amino TEMPO is preferable because it is inexpensive and can provide uniform oxidized cellulose.

(In formulas 2 to 4, R is a linear or branched carbon chain having 4 or less carbon atoms.)
Furthermore, an N-oxyl compound represented by the following formula 6, that is, an azaadamantane-type nitroxy radical, is preferable because it can efficiently oxidize a cellulose-based raw material in a short time and is less likely to break the cellulose chain.

(In Formula 6, R5 and R6 represent the same or different hydrogen or a C1-C6 linear or branched alkyl group.)
The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of forming cellulose into nanofibers. For example, 0.01 to 10 mmol is preferable, 0.01 to 1 mmol is more preferable, and 0.05 to 0.5 mmol is more preferable with respect to 1 g of the absolutely dry cellulosic material.

  Bromide is a compound containing bromine, examples of which include alkali metal bromides that can dissociate and ionize in water. Further, an iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide used can be selected as long as the oxidation reaction can be promoted. The total amount of bromide and iodide is, for example, preferably from 0.1 to 100 mmol, more preferably from 0.1 to 10 mmol, and even more preferably from 0.5 to 5 mmol, with respect to 1 g of an absolutely dry cellulose raw material.

  As the oxidizing agent, known ones can be used, and for example, halogen, hypohalous acid, halous acid, perhalogen acid or salts thereof, halogen oxide, peroxide and the like can be used. Of these, sodium hypochlorite is preferable because it is inexpensive and has a low environmental impact. The appropriate amount of the oxidizing agent used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, further preferably 1 to 25 mmol, and 3 to 10 mmol with respect to 1 g of the cellulosic raw material. Most preferred.

  The cellulose oxidation process allows the reaction to proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature may be a room temperature of about 15 to 30 ° C. As the reaction proceeds, a carboxyl group is generated in the cellulose, so that the pH of the reaction solution is reduced. In order to advance the oxidation reaction efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 9 to 12, preferably about 10 to 11. The reaction medium is preferably water because it is easy to handle and hardly causes side reactions.

  The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of oxidation, and is usually 0.5 to 6 hours, for example, about 0.5 to 4 hours.

  The oxidation reaction may be performed in two stages. For example, oxidized cellulose obtained by filtration after the completion of the first stage reaction is oxidized again under the same or different reaction conditions, so that the cellulose is not subject to reaction inhibition by the salt produced as a by-product in the first stage reaction. A carboxyl group can be efficiently introduced into the system raw material.

  In addition, the cellulose raw material may be appropriately subjected to alkali treatment before the oxidation step to change the crystal form to the II type. Ordinary cellulose is a type I crystal, but if it contains a type II crystal, the oxidant easily enters and the reaction efficiency is improved.

  It is preferable to set conditions so that the amount of carboxyl groups of oxidized cellulose is 0.5 to 2.0 mmol / g with respect to the absolute dry mass of cellulose. The amount of the carboxyl group can be adjusted by adjusting the oxidation reaction time, adjusting the oxidation reaction temperature, adjusting the pH during the oxidation reaction, adjusting the addition amount of the N-oxyl compound, bromide, iodide, or oxidizing agent.

  The obtained oxidized cellulose is preferably washed.

The amount of carboxyl groups was prepared by preparing 60 ml of 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose or cellulose nanofibers, adding 0.1M hydrochloric acid aqueous solution to pH 2.5, and then adding 0.05N sodium hydroxide. The electrical conductivity was measured by dropping the aqueous solution until the pH reached 11, and the amount was calculated from the amount of sodium hydroxide (a) consumed in the neutralization step of the weak acid where the change in electrical conductivity was slow, using the following formula: can do:
Amount of carboxyl group [mmol / g oxidized cellulose or cellulose nanofiber] = a [ml] × 0.05 / mass of oxidized cellulose or cellulose nanofiber [g].

<Defibration of anion-modified cellulose>
A dispersion containing the anion-modified cellulose obtained above is prepared, and the anion-modified cellulose is fibrillated in the dispersion to form nanofibers. “Nanofiber” means that cellulose is processed into cellulose fibers having an average fiber width of 1-1000 nm, preferably 2-150 nm, and an average fiber length of 50-5000 nm, preferably 0.1-5 μm. . When the anion-modified cellulose is a cellulose having a carboxyl group introduced, the obtained cellulose fiber is preferably 2 to 5 nm in width and about 1 to 5 μm in length, or 2 to 300 nm in width and about 100 to 500 nm in length. is there. A dispersion is a liquid in which the anion-modified cellulose is dispersed in a dispersion medium. From the viewpoint of ease of handling, the dispersion medium is preferably water.

  In order to disentangle anion-modified cellulose and disperse it in a dispersion medium, a strong shearing force is applied to the dispersion using a high-speed rotating type, colloid mill type, high pressure type, roll mill type, ultrasonic type device, etc. It is preferable. In particular, in order to efficiently obtain anion-modified cellulose nanofibers, it is preferable to use a wet high pressure or ultrahigh pressure homogenizer capable of applying a pressure of 50 MPa or more to the dispersion and applying a strong shearing force. The pressure is more preferably 100 MPa or more, and further preferably 140 MPa or more. By this treatment, the anion-modified cellulose is fibrillated to form anion-modified cellulose nanofibers, and the anion-modified cellulose nanofibers are dispersed in the dispersion medium.

  The anion-modified cellulose concentration in the dispersion used for the treatment is 0.1% (w / v) or more, preferably 1 to 50% (w / v), more preferably 1 to 10% (w / v). preferable. It may be 2 to 10% (w / v), or 3 to 10% (w / v).

2. Trivalent metal salt In the present invention, the trivalent metal salt contained in the coating layer provided on the substrate is a sulfate such as aluminum, iron (trivalent), boron, or chromium (trivalent). , Nitrates, ammonium salts, chlorides and the like can be exemplified but are not particularly limited. Among these, potassium aluminum sulfate, which is approved for use as a food additive from the viewpoint of safety. It is preferable to use aluminum ammonium sulfate, ammonium iron (III) citrate, or ferric chloride. In addition, these trivalent metal salts can be used for additives and packaging materials related to foods and pharmaceuticals.

  The addition amount of the trivalent metal salt is 0.1 to 3.0 chemical equivalents of the trivalent metal salt with respect to the carboxyl group or carboxymethyl group of the anion-modified cellulose nanofiber constituting the coating layer. Is important, preferably 0.2 to 2.0, more preferably 0.5 to 1.5. Even if the amount of the compound added exceeds 3.0 as a chemical equivalent, no more water-resistant effect can be obtained, whereas if it is less than 0.1, a sufficient effect cannot be obtained.

3. Base material The base material used in the laminate of the present invention includes paper, laminated paper, non-woven fabric made of paper and / or synthetic fibers, glass, polyethylene film, polypropylene film, polyolefin film such as polypropylene film, polyethylene terephthalate film, etc. Examples of the polyester film are not limited thereto.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
[Example 1]
(Manufacture of anion-modified pulp)
To a stirrer that can mix pulp, add 200 g of dry pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) and 88 g of dry hydroxide of sodium hydroxide, and add water so that the pulp solid concentration is 15%. It was. Then, after stirring for 30 minutes at 30 ° C., the temperature was raised to 70 ° C., and 117 g of sodium monochloroacetate (in terms of active ingredient) was added. After reacting for 1 hour, the reaction product was taken out, neutralized and washed to obtain an anion-modified cellulose (cellulose having a carboxymethyl group introduced) having a carboxymethyl substitution degree of 0.05 per glucose unit.
(Preparation of anion-modified nanofiber dispersion)
The oxidized pulp was adjusted to 1.0% (w / v) and treated 10 times with an ultrahigh pressure homogenizer (20 ° C., 140 MPa) to obtain an anion-modified cellulose nanofiber dispersion. Prepare a 1% (w / v) aqueous solution of trivalent metal salt (potassium aluminum sulfate 12 hydrate), add 5 ml to 95 ml of cellulose nanofiber dispersion, and gently stir with a stirrer for 2 hours. Aggregates of crosslinked nanofibers were obtained. The agglomerates were centrifuged at 5000 rpm for 15 minutes using a centrifuge and dehydrated. Thereafter, it was re-diluted to 200 ml with water, and centrifugation and dehydration were performed twice in the same manner. The obtained precipitate was adjusted to 0.3% (w / v), and a uniform dispersion was obtained by stirring for 30 minutes at 3000 rpm with a homogenizer.

(Create laminate)
The dispersion was coated and dried on a PET film (thickness 38 μm) with an applicator so that the coating amount after drying was 0.3 g / m ² . The contact angle of the obtained laminate was measured. For the measurement of the contact angle, 1100 DAT (Dynamic Absorption Tester) manufactured by Fibro was used, and the contact angle at 1 second after dropping of pure water was compared.

[Example 2]
A laminate was obtained in the same manner as in Example 1 except that the trivalent metal salt was changed to ammonium alum.

[Example 3]
(Manufacture of anion-modified pulp)
Add 500 g of bleached unbeaten kraft pulp (whiteness 85%) derived from coniferous trees (absolutely dry) to 500 ml of an aqueous solution in which 780 mg of TEMPO (Sigma Aldrich) and 75.5 g of sodium bromide are dissolved, until the pulp is uniformly dispersed Stir. An aqueous sodium hypochlorite solution was added to the reaction system to 6.0 mmol / g to initiate the oxidation reaction. During the reaction, the pH in the system was lowered, but a 3M sodium hydroxide aqueous solution was sequentially added to adjust the pH to 10. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system no longer changed. The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was sufficiently washed with water to obtain oxidized pulp (pulp introduced with carboxyl groups). The pulp yield at this time was 90%, and the time required for the oxidation reaction was 90 minutes.

(Preparation of anion-modified nanofiber dispersion, creation of laminate)
A laminate was obtained in the same manner as in Example 1 except that the trivalent metal salt was changed to aluminum chloride.

[Comparative Example 1]
A laminate was obtained in the same manner as in Example 1 except that the trivalent metal salt was not added.

Claims (5)

In a laminate in which a coating layer containing cellulose nanofibers and a metal salt is provided on a substrate, the cellulose nanofibers are anion-modified cellulose nanofibers, and the metal salt is a trivalent metal salt. Laminated body. The laminate according to claim 1, wherein the trivalent metal salt is any one of potassium alum, ammonium alum, and aluminum chloride. The anion-modified cellulose nanofiber is a cellulose nanofiber introduced with a carboxymethyl group, and the degree of carboxymethyl substitution per glucose unit of cellulose is 0.01 to 0.50. 2. The laminate according to 2. The anion-modified cellulose nanofiber is a cellulose nanofiber introduced with a carboxyl group, and the amount of the carboxyl group is 0.5 mmol / g to 2. with respect to the absolutely dry mass of the cellulose nanofiber introduced with the carboxyl group. It is 0 mmol / g, The laminated body of Claims 1-2 characterized by the above-mentioned. 5. The laminate according to claim 1, comprising 0.1 to 3.0 chemical equivalents of the trivalent metal salt with respect to the carboxyl group or carboxymethyl group of the anion-modified cellulose nanofiber. body.