JPH0931393A - Water-based coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-based coating composition which has excellent pigment dispersion, has satisfactory adhesion especially to plastic substrates, and gives a film excellent in drying properties, water resistance, heat resistance, and alcohol resistance. SOLUTION: This composition comprises a combination of a water-compatible acrylic resin with a carboxyalkylcellulose nitrate in which the number of nitrate substituents and that of carboxyalkyl ether substituents are 0.2 or larger and 0.05 or larger, respectively, per anhydrous glucose unit.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an aqueous coating composition capable of forming a coating film having particularly good coating film adhesion to a plastic substrate and excellent water resistance and alcohol resistance. . In addition to plastic paint,
Applications that require water resistance, alcohol resistance, etc., for example,
The present invention relates to a water-based paint composition applicable to functional inks, paper coatings, thermal papers, leather paints, fiber processing, magnetic paints, conductive pastes and the like.

[0002]

2. Description of the Related Art Conventionally, cellulose esters such as nitrocellulose and cellulose acetate butyrate have been used in paints, plastic paints, printing inks, paper coatings, fiber processing, magnetic paints, conductive pastes, etc. in view of their drying property and heat resistance. It is used as a functional coating material.

However, since a large amount of organic solvent is used for cellulose ester such as nitrocellulose or cellulose acetate butyrate as a coating material or the like, there is a possibility that vaporization solvent may cause air pollution and deterioration of working environment. In order to prevent this, we are trying to protect the environment by installing recovery equipment, recycling equipment, etc., but there is a problem that equipment investment is large. In addition, the water-based cellulose acetate butyrate has a problem in that it is physically unstable such that it is hydrolyzed during storage to increase its viscosity.

On the other hand, aqueous cellulose derivatives such as carboxymethyl cellulose, methyl cellulose, and hydroxyethyl cellulose are used as thickeners, but there is a problem that pigment dispersibility and coating film water resistance are very poor. . To solve these problems,
Nitric acid esters of carboxyalkyl cellulose have been proposed (JP-A-5-39301 and JP-A-5-3).
9302 publication etc.). For example, JP-A-5-39301
In the publication, it is described that the nitrate of carboxyalkyl cellulose is mixed with water and a minimum necessary organic solvent and a neutralizing agent, and by using it as an aqueous material, it is possible to improve the drying property, heat resistance and the like. There is. However,
The mixed solution of the nitrate ester of carboxyalkyl cellulose, water, an organic solvent and a neutralizing agent has a practical problem that the solid content in the coating is low.

On the other hand, since the water-based emulsion type paint and the water-based resin paint do not contain any organic solvent or the amount thereof is small, there is a fear of causing air pollution like the organic solvent type paint. It is excellent in that it does not exist. However, emulsion type paints and water-based resin paints cannot be said to have sufficient water resistance due to the influence of the emulsifier contained in the system, and their alcohol resistance and adhesiveness are not always satisfactory.

[0006]

DISCLOSURE OF THE INVENTION According to the present invention, by combining a nitrate ester of carboxyalkyl cellulose with an acrylic water-based resin, pigment dispersibility is excellent, good adhesion to a plastic substrate is exhibited, and drying property is excellent. Another object of the present invention is to provide an aqueous coating composition which forms a coating film having excellent water resistance, heat resistance and alcohol resistance.

[0007]

Means for Solving the Problems As a result of intensive research to solve the above-mentioned problems, the present inventors have found that pigment dispersibility and adhesion are improved by combining a specific carboxyalkyl cellulose nitrate ester and an acrylic water-based resin. It was found that a water-based coating composition excellent in water resistance, drying property, heat resistance and alcohol resistance was obtained, and the present invention was completed.

That is, according to the present invention, a nitrate ester of carboxyalkyl cellulose having a degree of substitution of a nitrate ester group per anhydroglucose unit of 0.2 or more and a degree of substitution of a carboxyalkyl ether group of 0.05 or more, and an acrylic type The present invention relates to an aqueous coating composition for plastics, which is characterized by combining an aqueous resin. The nitric acid ester of carboxyalkyl cellulose used in the present invention means carboxyalkyl cellulose such as carboxymethyl cellulose and carboxyethyl cellulose treated with a known nitric acid esterification mixed acid, for example, nitric acid esterification mixed acid composed of sulfuric acid / nitric acid and water. The degree of substitution of the nitrate ester group contained in the nitrate ester of carboxyalkyl cellulose is 0.2 or more, and the degree of substitution of the carboxyalkyl ether group is 0.05 or more.
It refers to the aqueous cellulose derivatives disclosed in Japanese Patent No. 39301 and Japanese Patent Application Laid-Open No. 5-39302. When the nitrate ester group substitution degree is less than 0.2, the pigment dispersibility becomes insufficient, and when the carboxyalkyl ether group substitution degree is less than 0.05, the solubility in water becomes insufficient and the organic solvent used is A large amount is required.

Preferably, the degree of substitution of the nitrate ester group is
It is 0.5 or more and 2.5 or less, and the degree of carboxyalkyl ether group substitution is 0.3 or more and 2.0 or less. More preferably, the degree of substitution with the nitrate ester group is 0.8 or more and 2.1.
And the degree of carboxyalkyl ether group substitution is
It is 0.5 or more and 1.6 or less. The carboxylate contained in the nitrate of carboxylalkyl cellulose used in the present invention is neutralized. Neutralized means that all or part of the hydrogen ions of the carboxyl group are replaced with one or a combination of two or more ions of an alkali metal ion, an ammonium ion or a monobasic organic amine to form a salt. Say that

The alkaline metal ions used for neutralizing the carboxyl groups contained in the nitrate of carboxyalkyl cellulose are, for example, lithium, sodium,
An ion of an element of Group 1 of the Periodic Table such as potassium and rubidium, and a monobasic organic amine means, for example, one amino group in a molecule such as ethylamine, propylamine, butylamine, triethylamine and diethylethanolamine. Means an ion of an organic compound containing. Other metal element ions and dibasic or more polybasic organic amine ions cause excessive interaction between molecules, resulting in insufficient solubility in water or a mixed solvent with an organic solvent. become. Of these, ammonium ion and triethylamine ion are preferable.

As the organic solvent used in the present invention, alcohols, polyhydric alcohols, polyhydric alcohol derivatives, ketones, esters, ethers, carbonates and the like may be used alone or in combination of two or more. Different solvents can be used. Examples of alcohols include methanol, ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonyl alcohol, n.
-Decanol, n-undecanol or isomers thereof, cyclopentanol, cyclohexanol and the like. Alcohols having 1 to 6 alkyl carbon atoms are preferable.

The polyhydric alcohols include ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1, 2-cyclohexanediol, 1,7
-Heptanediol, 1,8-octanediol, 1,
Examples thereof include 9-nonanediol, 1,10-decanediol, glycerin, pentaerythritol and the like.

Derivatives of polyhydric alcohol include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol isopropyl ether, ethylene glycol monobutyl ether, ethylene glycol isobutyl ether, propylene glycol monomethyl ether, propylene. Glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, cellosolve acetate, etc., or solvent pocket book edited by the Society of Synthetic Organic Chemistry (September 20, 1990, Ohmsha) No. 47
Examples thereof include polyhydric alcohols and their derivatives described on pages 9 to 575.

Examples of ketones include acetone, methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diisopropyl ketone, cyclopentanone and cyclohexanone. Examples of the esters include methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, amyl acetate, lactate ester, butyrate ester, diisopropyl glutarate, dibutyl phthalate, dioctyl phthalate, and ε-caprolactone, ε- Examples thereof include cyclic esters such as caprolactam.

As the ethers, diethyl ether,
Examples include isopropyl ether, n-butyl ether, tetrahydrofuran, tetrahydropyran, 1,4-dioxane and the like. Examples of the carbonates include dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, ethylene carbonate and the like.

In the water-based coating composition of the present invention, the acrylic water-based resin to be used may be a conventionally known emulsion, colloidal dispersion, water-soluble one or more kinds in combination. The conventionally known acrylic water-based resin that can be combined is not particularly limited, but as an example, as the emulsion-based resin,
Acrylic emulsion, acrylic-styrene emulsion, acrylic-acrylonitrile emulsion,
There are acrylic-polyurethane emulsions, acrylic-alkyd emulsions, epoxy-acrylic emulsions, and the like, and water-soluble synthetic polymer compounds such as polyacrylic acid, polyacrylamide, and the like. Preferred are acrylic emulsions, acrylic-styrene emulsions, and acrylic-acrylonitrile emulsions.

The mixing ratio is 5 to 99 parts by weight of nitrate esters of carboxyalkyl cellulose in terms of solid content weight ratio,
The water-based resin is 1 to 95 parts by weight. Preferred are 5 to 50 parts by weight of nitrate esters of carboxyalkyl cellulose and 50 to 95 parts by weight of water-based resin. The water-based coating composition of the present invention may contain a pigment and / or a dye depending on the purpose of use. As the pigment, titanium oxide,
Coloring pigments such as iron oxide, carbon black, phthalocyanine blue, phthalocyanine green, watchan red, quinacridone yellow, extender pigments such as barium sulfate, calcium carbonate, clay, aluminum paste, magnetic iron oxide, barium titanate, gold, silver, etc. One kind or a combination of two or more kinds of the functional pigments and the like can be used. Known dyes such as methylene blue, malachite green, rhodamine, and alizarin can be used as the dye.

In addition, if necessary, a dispersant, a thickener,
Various additives commonly used in the paint industry such as defoaming agents, leveling agents and antifreezing agents can be added in conventional amounts. An example of the method for preparing the water-based coating composition of the present invention will be described. The nitrate ester of carboxyalkyl cellulose is weighed in a closed container equipped with a stirrer, and water is added in a specified amount. Next, a specified amount of organic solvent is added and stirred to make the system uniform. Next, a neutralizing agent is added, and the mixture is stirred and heated to be completely dissolved to obtain an aqueous solution of a carboxyalkyl cellulose nitrate ester. A predetermined amount of acrylic water-based resin is added to this aqueous solution, and the mixture is thoroughly mixed and stirred to prepare the desired water-based coating composition. If necessary, pigments and additives are added.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to Examples. The evaluation method in the present invention is as follows. <Adhesiveness> On the surface of the coating film, 11 cuts are made at intervals of 1 mm in length and width to make 100 cross-cuts, and after sticking cellophane adhesive tape on this, the adhesive tape is rapidly cut. The state of the coating film after peeling is observed and evaluated according to the following evaluation criteria.

◯: No peeling is recognized. ×: There is peeling around the notch on the cross board. <Alcohol resistance> After dropping a drop of methanol on the surface of the coating film, it is determined whether or not whitening occurs. ◯: No change Δ: Slightly whitening ×: Whitening <Pigment dispersibility> Mixing was performed so that the pigment concentration was 20% by weight and the resin concentration was 80% by weight, and the mixture was dispersed for 1 hour with a paint shaker. The obtained coating material was applied on a polystyrene plate so that the dry film thickness was 30 to 50 μm, and dried at 60 ° C. for 1 hour. The coated plate was measured for gloss at 60 ° -60 ° with a variable angle gloss meter manufactured by Suga Test Instruments Co., Ltd.

<Heat-resistant blocking resistance> A coating material is applied to high-quality paper so that the dry film thickness is 30 to 50 μm, and 60
It was dried at ° C for 1 hour. Next, stack the coated surfaces together, and
A load of 5 g / cm ² was applied, the plate was left in an oven set to a predetermined temperature for 30 minutes, the blocking state of the coated surface was evaluated, and the temperature at which no blocking occurred was determined.

[0022]

[Production Example 1] 100 g of carboxymethyl cellulose (degree of carboxymethyl ether group substitution = 0.7) and 3 liters of a mixed acid consisting of sulfuric acid / nitric acid / water = 58.8 / 20.2 / 21.0% by weight were added to 5 liters. Put in reaction vessel, 5
The nitrification reaction is carried out with stirring at ℃ for 1 hour. The product was deoxidized with a centrifuge and immediately washed with a large amount of water to obtain 100 g of carboxymethyl cellulose nitrate.

The resulting carboxymethyl cellulose nitrate ester has a carboxymethyl ether group substitution degree of 0.
7, the degree of substitution of nitrate ester group was calculated from the nitrogen content,
It was 1.0. 15 g of the obtained carboxymethyl cellulose nitrate ester, 54.7 g of ion-exchanged water, and 25.5 g of n-butyl cellosolve as an organic solvent were put in a separable flask and stirred. Next, 4.8 g of 28% ammonia water was added as a neutralizing agent and stirred while stirring.
Completely dissolved while heating at 0 ° C, solid content 15% by weight
To obtain an aqueous solution composition.

[0024]

[Production Example 2] 100 g of carboxymethyl cellulose (degree of carboxymethyl ether group substitution = 0.5) and 3 liters of a mixed acid consisting of sulfuric acid / nitric acid / water = 62.6 / 25.0 / 12.4% by weight were added to 5 liters. Put in reaction vessel, 5
The nitrification reaction is carried out with stirring at ℃ for 1 hour. The product was deoxidized with a centrifuge and immediately washed with a large amount of water to obtain 120 g of carboxymethyl cellulose nitrate.

The obtained carboxymethyl cellulose nitrate has a carboxymethyl ether group substitution degree of 0.
5, the nitrate ester group substitution degree was 2.0 as determined from the nitrogen content. The obtained carboxymethyl cellulose nitrate ester (15 g), ion-exchanged water (56.1 g), and n-butyl cellosolve (25.5 g) as an organic solvent were placed in a separable flask and stirred. Next, add 3.4 g of triethylamine as a neutralizing agent and stir 8
Completely dissolved while heating at 0 ° C, solid content 15% by weight
To obtain an aqueous solution composition.

[0026]

Example 1 100 parts by weight of the aqueous solution composition obtained in Production Example 1, Polytron Z430 (manufactured by Asahi Kasei Corporation: solid content = 46%: acrylic acrylonitrile emulsion)
After 293 parts by weight, 28 parts by weight of ethanol, and 22 parts by weight of n-butyl cellosolve were placed in a container and mixed by stirring, 39 parts by weight of carbon black was further dispersed with a paint shaker to obtain an aqueous coating composition. The obtained coating composition was applied on a polystyrene plate so that the dry film thickness was 30 to 50 μm, and dried at 60 ° C. for 1 hour, and the coating film performance was evaluated.

As a result, the coating film gloss value was 80%, and the adhesion was:
○, alcohol resistance: ○, heat resistant blocking temperature 90 ° C
Met.

[0028]

Example 2 105 parts by weight of the aqueous solution composition obtained in Production Example 1, 295 parts by weight of Polytron E390M (manufactured by Asahi Chemical Industry Co., Ltd .: solid content = 49%: acrylic emulsion), 28 parts by weight of ethanol, n-butyl cellosolve. After 22 parts by weight was placed in a container and mixed by stirring, 39 parts by weight of carbon black was further dispersed by a paint shaker to obtain an aqueous coating composition. The obtained coating composition was applied on a polystyrene plate so that the dry film thickness was 30 to 50 μm, and dried at 60 ° C. for 1 hour, and the coating film performance was evaluated.

As a result, the coating film gloss value was 80%, and the adhesion was:
○, alcohol resistance: ○, heat resistant blocking temperature 90 ° C
Met.

[0030]

Example 3 105 parts by weight of the aqueous solution composition obtained in Production Example 1, 295 Polytron F2430 (manufactured by Asahi Chemical Industry Co., Ltd .: solid content = 49%: acrylic / styrene emulsion)
By weight, 28 parts by weight of ethanol and 22 parts by weight of n-butyl cellosolve were placed in a container and mixed by stirring, and 39 parts by weight of carbon black were further dispersed by a paint shaker to obtain an aqueous coating composition. The obtained coating composition was applied on a polystyrene plate so that the dry film thickness was 30 to 50 μm, and dried at 60 ° C. for 1 hour, and the coating film performance was evaluated.

As a result, the coating film gloss value was 83%, and the adhesion was:
○, alcohol resistance: ○, heat resistant blocking temperature 80 ° C
Met.

[0032]

Example 4 100 parts by weight of the aqueous solution composition obtained in Production Example 2, Polytron Z430 (manufactured by Asahi Kasei Kogyo Co., Ltd .: solid content = 46%: acrylic acrylonitrile emulsion)
After 293 parts by weight, 28 parts by weight of ethanol, and 22 parts by weight of n-butyl cellosolve were placed in a container and mixed by stirring, 39 parts by weight of carbon black was further dispersed with a paint shaker to obtain an aqueous coating composition. The obtained coating composition was applied onto a polystyrene plate so that the dry film thickness was 30 to 50 μm, and dried at 60 ° C. for 1 hour, and the coating film performance was evaluated.

As a result, the coating film gloss value was 80% and the adhesion was:
○, alcohol resistance: ○, heat resistant blocking temperature 90 ° C
Met.

[0034]

Example 5 105 parts by weight of the aqueous solution composition obtained in Production Example 2, 295 parts by weight of Polytron F2430 (manufactured by Asahi Chemical Industry Co., Ltd .: solid content = 49%), 28 parts by weight of ethanol, n
-Butyl cellosolve (22 parts by weight) was placed in a container and mixed with stirring, and 39 parts by weight of carbon black was further dispersed with a paint shaker to obtain an aqueous coating composition. The obtained coating composition was applied onto a polystyrene plate to give a dry film thickness of 30 to
It was applied so as to have a thickness of 50 μm and dried at 60 ° C. for 1 hour, and the coating film performance was evaluated.

As a result, the coating film gloss value was 82%, and the adhesiveness was:
○, alcohol resistance: △, heat resistant blocking temperature 80 ° C
Met.

[0036]

Example 6 105 parts by weight of the aqueous solution composition obtained in Production Example 2, 295 parts by weight of Polytron E390M (manufactured by Asahi Chemical Industry Co., Ltd .: solid content = 49%), 28 parts by weight of ethanol, n
-Butyl cellosolve (22 parts by weight) was placed in a container and mixed with stirring, and 39 parts by weight of carbon black was further dispersed with a paint shaker to obtain an aqueous coating composition. The obtained coating composition was applied onto a polystyrene plate to give a dry film thickness of 30 to
It was applied so as to have a thickness of 50 μm and dried at 60 ° C. for 1 hour, and the coating film performance was evaluated.

As a result, the coating film gloss value was 81% and the adhesion was:
○, alcohol resistance: △, heat resistant blocking temperature 90 ° C
Met.

[0038]

Comparative Example 1 100 parts by weight of an acrylic-styrene emulsion (acrylic / styrene = 55/45, solid content = 40%) and 10 parts by weight of carbon black were dispersed by a paint shaker, and the obtained composition was applied to a polystyrene plate. It was coated on the above so that the dry film thickness would be 30 to 50 μm, and dried at 60 ° C. for 1 hour, and the coating film performance was evaluated.

As a result, the coating film gloss value was 40% and the adhesion was:
×, alcohol resistance: ×, heat resistant blocking temperature 40 ° C
Met.

[0040]

Comparative Example 2 100 parts by weight of an aqueous polyurethane resin (acrylic polyurethane emulsion, solid content = 35.6%) and 9 parts by weight of carbon black were dispersed with a paint shaker, and the obtained composition was placed on a polystyrene plate. , So that the dry film thickness is 30 to 50 microns, and apply 60
The coating film performance was evaluated by drying at 1 ° C. for 1 hour.

As a result, the coating film gloss value was 32% and the adhesion was:
○, alcohol resistance: ×, heat resistant blocking temperature 40 ° C
Met.

[0042]

EFFECTS OF THE INVENTION The water-based coating composition of the present invention is mainly used in the field of plastic coating, and has excellent adhesion to a plastic substrate and improves the drying property, alcohol resistance and heat blocking resistance of the coating film. In addition to the field of plastic paints, it can also be used for other paints, printing inks, paper coatings, film processing paints, thermal paper, leather paints, textile processing, magnetic coatings and functional coating materials such as conductive pastes.

Claims (1)

[Claims] 1. A combination of an acrylic water-based resin and a nitrate ester of carboxyalkyl cellulose having a degree of substitution of nitrate ester group of 0.2 or more and a degree of substitution of carboxyalkyl ether group of 0.05 or more per anhydrous glucose unit. A water-based coating composition characterized by the above.