JP2007197520A - Water-based coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based coating composition which contains a water-soluble polymer comprising a cellulose composite material and a cellulose derivative and has excellent pigment storage stability. <P>SOLUTION: This water-based coating composition is characterized by containing (A) &ge;0.1% of a cellulose composite material comprising fine crystalline cellulose and sodium carboxymethylcellulose or xanthan gum, and (B) &ge;0.2% of water-soluble polymer comprising a cellulose derivative in a (A)/(B) solid content ratio of 1/9 to 7/3, and having viscosity of 2,500 to 10,000 mPa s. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to an aqueous coating composition containing a water-soluble polymer comprising a cellulose composite and a cellulose derivative. More specifically, the present invention relates to viscosity and long-term storage stability of a pigment while reducing the blending amount of a thickener. The present invention relates to a water-based coating composition having properties.

There are many known coating compositions characterized by containing cellulose so far, such as Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4. In Patent Document 1, there is a description of a coating composition containing microcrystalline cellulose. However, unless the addition amount in the coating composition is increased, the desired peelability cannot be obtained. Further, in Patent Document 2 and Patent Document 3, micronized cellulose or microcrystalline cellulose is used as a dispersion stabilizer, but there is no description that the blending amount can be reduced due to the synergistic effect of viscosity by the combined use with a water-soluble polymer. . Patent Document 4 describes the dispersion stability of low crystalline cellulose pigments, but cellulose alone has no thickening synergistic effect and has to be increased in amount, and the cost of the final coating is increased. There was a problem. On the other hand, hydroxyethylcellulose and sodium carboxymethylcellulose are widely used as stabilizers for water-soluble cellulose. However, in order to stabilize the dispersion of pigments, the viscosity must be increased and the viscosity will increase too much. There were problems such as a significant decrease in coating performance. Further, there are problems such as easy decay during long-term storage, a decrease in viscosity with time, and precipitation of pigments. Thus, it has not been known to produce a synergistic effect of viscosity by combining the cellulose composite and water-soluble cellulose, to reduce the blending amount of the stabilizer, and to stabilize the pigment.
Japanese Patent Laid-Open No. 58-13660 JP-A-5-163445 JP-A-5-279576 JP 2001-247812 A

  The present invention relates to an aqueous coating composition containing a cellulose composite composed of microcrystalline cellulose and sodium carboxymethyl cellulose / xanthan gum and a water-soluble polymer composed of a cellulose derivative, and both are used in combination at a specific ratio. Thus, the present invention provides a water-based paint composition capable of exhibiting a sufficient viscosity and dispersion stability of a pigment while reducing the total amount of the blended amount, by finding that the viscosity is dramatically increased by a synergistic effect. .

That is, the present invention is as follows.
(1) (A) A cellulose composite composed of microcrystalline cellulose and carboxymethylcellulose sodium or xanthan gum is 0.1% or more of the total amount of the aqueous coating composition, and (B) a water-soluble polymer composed of a cellulose derivative is 0.1%. An aqueous coating composition containing 2% or more, having a solid content ratio of (A) and (B) of 1/9 to 7/3 and having a viscosity of 2500 to 10,000 mPa · s.
(2) The water-based coating composition according to claim 1, wherein the water-soluble polymer is hydroxyethyl cellulose or carboxymethyl cellulose sodium.

  The aqueous coating composition of the present invention contains a cellulose composite and a water-soluble cellulose composed of a cellulose derivative at a specific ratio, so that the dispersion stability of the pigment is good while reducing the blending amount of the thickener. Yes, it does not cause surface layer separation or bottom sedimentation, and has excellent storage stability.

Hereinafter, the present invention will be described in detail.

The cellulose composite composed of microcrystalline cellulose and carboxymethylcellulose sodium or xanthan gum used in the cellulose composite of the present invention is obtained by, for example, dissolving insoluble fine cellulose obtained by acid hydrolysis of pulp with water-soluble carboxymethylcellulose sodium or It is obtained by uniformly mixing xanthan gum to a homogeneous slurry and drying it. Known cellulose composites can be used, and specifically those described in JP-A No. 54-54169 can be used.
The composition of microcrystalline cellulose and carboxymethylcellulose sodium or xanthan gum is preferably in the range of 50 to 95% by weight of microcrystalline cellulose and 50 to 5% by weight of carboxymethylcellulose sodium or xanthan gum.

  The sodium carboxymethyl cellulose used in the cellulose composite of the present invention is not particularly limited, but the degree of substitution of the carboxymethyl group is 0.2 to 1.5, the degree of polymerization is 200 to 500, and the viscosity of the 2% by weight aqueous solution is The thing of about 10-1000 mPa * s is preferable.

  The xanthan gum used in the cellulose composite of the present invention may also be used for general purposes. The xanthan gum has a molecular structure equivalent to cellulose, in which glucose residues are linked in a straight chain with β-1,4-glucoside bonds. With a main chain of α-D-mannose, β-D-glucuronic acid, β-D-mannose linked to every other glucose residue in the main chain as a side chain preferable. The trisaccharide preferably has an acetyl group and a pyruvate group bonded, and preferably has a number average molecular weight of about 1,000,000 or more.

  Carboxymethylcellulose sodium or xanthan gum in the cellulose composite used in the present invention quickly disperses the cellulose particles in the dried cellulose composite and serves as a protective colloid for the cellulose particles to prevent their aggregation and sedimentation There is. Furthermore, in order to promote dispersion of cellulose particles in water, dextrins such as roasted dextrin and hydrolyzed starch, sugars such as xylose, glucose, fructose and trehalose, emulsifiers such as sucrose fatty acid ester and glycerin fatty acid ester, linoleic acid, Oils and fats such as linolenic acid and oleic acid can be freely blended as a disintegrant.

Furthermore, when this cellulose composite is mechanically stirred in water, it is dispersed in cellulose particles having an average particle size of 20 μm or less, preferably 10 μm or less, more preferably 5 μm or less, and has a characteristic of forming a stable suspension. As described above, when the cellulose composite of the present invention is subjected to an appropriate shearing force in water, fine crystalline cellulose particles are uniformly dispersed in water and become an excellent dispersion stabilizer. Carboxymethylcellulose sodium or xanthan gum promotes the dispersion of fine cellulose particles in water, enhances the function as a protective colloid, and further increases the dispersion stability of the cellulose particles. Furthermore, fine cellulose particles form a three-dimensional network in the coating composition, and can take in pigments and prevent sedimentation.
The blending amount of the cellulose composite composed of microcrystalline cellulose and carboxymethylcellulose sodium / xanthan gum used in the present invention is suitably about 0.1 to 10% by weight. When the blending amount is less than 0.1% by weight, sufficient storage stability of the pigment is not exhibited. When the blending amount exceeds 10% by weight, the cellulose particles are difficult to disperse due to the thickening effect, and the precipitation of the cellulose particles is recognized. It is done.

Hydroxyethyl cellulose or carboxymethyl cellulose / sodium is used as the water-soluble polymer comprising the cellulose derivative used in the present invention. Hydroxyethyl cellulose may be used for general purposes. For example, hydroxyethyl cellulose is produced by reacting wood pulp with sodium hydroxide to obtain alkali cellulose and adding ethylene oxide. At this time, the average number of substituted moles used as an indicator that the cellulose substituent is substituted with a hydroxyethyl group may be 1.5 to 2.5. Also, carboxymethylcellulose sodium may be used for general purposes. For example, it is produced by immersing wood pulp in an aqueous sodium hydroxide solution and mixing sodium monochloroacetate. At this time, a carboxymethyl group having a degree of substitution of 0.2 to 1.5, a degree of polymerization of 200 to 500, and a 2% by weight aqueous solution having a viscosity of about 10 to 1000 mPa · s is used.
The blending amount of hydroxyethyl cellulose or carboxymethyl cellulose / sodium is suitably about 0.2 to 1.0% by weight. If the blending is less than 0.2% by weight, the bottom surface of the pigment tends to settle, and if it exceeds 1.0% by weight, handling during preparation becomes difficult due to the thickening effect.

  The weight ratio of the water-soluble polymer comprising the cellulose composite of the present invention and the cellulose derivative must be in the range of 1/9 to 7/3. Preferably, it is 2/8 to 6/4, and more preferably 3/7 to 5/5. When the ratio of the cellulose composite to the water-soluble polymer is smaller than 1/9, the cellulose particles are few, so the three-dimensional network structure formed by the cellulose particles is weakened, the protective colloid function for the pigment is reduced, and the pigment Sedimentation is likely to occur. On the other hand, when this ratio exceeds 7/3, since there are few water-soluble cellulose particles, the viscosity sufficient to stabilize the pigment cannot be obtained, and water separation tends to occur. Further, the viscosity of the aqueous coating composition is usually 2500 to 10,000 mPa · s. If it is 2500 mPa · s or less, sagging occurs during the formation of the coating film, and if it exceeds 10,000 mPa · s, it may cause roughness of the coating film surface or clogging during spraying. The viscosity in the coating composition is appropriately selected depending on the application of the coating. For example, when obtaining a viscosity of 2500 mPa · s, 1.0% is required for the cellulose composite and 0.4% is required for the hydroxyethyl cellulose when stabilizing with either the cellulose composite or hydroxyethyl cellulose. On the other hand, the amount that can be reduced when stabilizing by combining cellulose composite and hydroxyethyl cellulose depends on the ratio of cellulose composite and hydroxyethyl cellulose, but when the total amount of thickener is 0.3% at maximum, That is, in a system in which 0.1% of the cellulose composite and 0.2% of hydroxyethyl cellulose are blended, the amount of hydroxyethyl cellulose can be reduced by 50%, and long-term storage stability can be improved. The addition amount of the water-soluble polymer composed of the cellulose composite and the cellulose derivative is in a range not exceeding 10,000 mPa · s, and the effect of reducing the addition amount of the water-soluble polymer composed of the cellulose derivative increases as the viscosity increases.

  The following water-soluble resin can be used for the water-based coating composition of the present invention. For example, aqueous acrylic resin, aqueous reaction curable acrylic resin, aqueous acrylic urethane paint, aqueous urethane resin, aqueous acrylic urethane resin, aqueous vinyl chloride resin, aqueous vinyl acetate resin, aqueous epoxy resin, aqueous alkyd resin Commonly used materials such as aqueous polyamide resins and aqueous cellulose resins can be used.

  The aqueous coating composition of the present invention can contain a pigment, specifically, titanium oxide, white lead, basic lead sulfate, basic lead silicate, zinc white, zinc sulfide, antimony trioxide, calcium. White pigments such as composites, calcium carbonate, barium sulfate, alumina white, silica, diatomaceous earth, kaolin, talc, organic bentonite, white carbon and other extender pigments, carbon black, yellow lead, molybdenum red, red iron oxide, yellow iron oxide, Coloring pigments such as iron black, ocher, senna, amber, green clay, mars violet, cadmium yellow, cadmium red, cadmium bon red, cadmium bon yellow, ultramarine blue, and bitumen can be used alone or in combination of two or more. In addition, wetting agents, pigment dispersants, emulsifiers, thickeners, anti-settling agents, anti-skinning agents, anti-sagging agents, leveling agents, leveling agents, anti-blocking agents, antioxidants, UV rays Absorber, radical scavenger, curing accelerator, surfactant, light resistance improver, preservability improver, filler, defoamer, plasticizer, desiccant, preservative, fragrance, pearl agent, lame agent, drug Etc. can be included. Examples of the method for forming a coating film include air spray coating, airless spray coating, electrostatic coating, electrodeposition coating, powder coating, curtain flow coating, and roll coating.

  The method for producing the water-based coating composition of the present invention is not particularly limited. For example, a cellulose composite and a water-soluble polymer are added to water and then dispersed in advance using a homogenizer with high shearing force and other components. It is preferable to mix.

EXAMPLES Next, although an Example demonstrates this invention further in detail, these do not restrict | limit the scope of the present invention. In addition, the average particle diameter of the cellulose particle in an Example and a comparative example, the viscosity of a coating composition, the water separation rate, and the sedimentation rate were measured as follows.
<Average particle size>
(1) Put a sample in a solvent in methanol and apply ultrasonic waves for 1 minute.
(2) A value at which the integrated volume was 50% was read by a laser diffraction scattering apparatus (LA-910, manufactured by Horiba, Ltd.) and used as an average particle diameter.
<Viscosity (mPa · s)>
・ Using a B-type viscometer (manufactured by Tokyo Keiki), rotor No. 3 was used to read the value at 60 rpm.
<Water separation rate (%)>
Weigh 50 g of sample into a glass sample bottle of 30 mmφ. This sample was left in a thermostatic chamber at 25 ° C. for 30 days. The water separation rate (%) was expressed by dividing the height (mm) of the boundary between the upper liquid surface of the sample, the water separation layer, and the suspension layer by the distance (mm) between the upper liquid surface and the bottom surface of the sample.
<Settling rate (%)>
Weigh 50 g of sample into a glass sample bottle of 30 mmφ. This sample was left in a thermostatic chamber at 25 ° C. for 30 days. The sedimentation rate (%) was expressed by dividing the height (mm) of the sediment layer by the distance (mm) between the upper liquid surface and the bottom surface of the sample.
Example 1

(1) Preparation of cellulose composite composed of microcrystalline cellulose and carboxymethylcellulose / sodium Commercially available DP pulp (average polymerization degree 850) was cut and hydrolyzed at 105 ° C. for 30 minutes under 1% hydrochloric acid. The obtained acid-insoluble residue was filtered and washed with pure water to obtain cake-like cellulose. It added so that the ratio of the solid content weight of carboxymethylcellulose and sodium might become 1/9 with respect to the solid content of this cellulose, and kneading and grinding were performed with the kneader. Subsequently, it was dried with hot air and pulverized with a hammer mill to obtain a dry powder of a cellulose composite composed of microcrystalline cellulose and carboxymethyl cellulose / sodium. The average particle size of this dry powder was 8.1 μm.
(2) Preparation of aqueous coating composition Aqueous coating composition using hydroxyethyl cellulose (SP600, manufactured by Daicel Chemical Industries), titanium oxide (TIPAQUA T-60, manufactured by Ishihara Sangyo), and water for the dry powder of the above cellulose composite. Adjusted. In 40 parts by weight of water, 5 parts by weight of a 2% by weight cellulose composite (solid content) dispersed in water at 25 ° C. in advance using a homogenizer (TK homoxer, manufactured by Special Machine Chemical Co., Ltd.) at 6000 rpm for 15 minutes 0.1 wt% in terms of conversion) and 15 parts by weight of hydroxyethyl cellulose (0.3 wt% in terms of solid content) previously dissolved in warm water at 80 ° C. under the same dispersion conditions using a homogenizer were added. Further, 40 parts by weight of titanium oxide was added, mixed and dispersed, and then filled in a polytank to obtain a coating composition. The viscosity of this coating composition was 3200 mPa · s. Thereafter, it was allowed to stand at 25 ° C. for 30 days, but separation of water on the surface and sediment on the bottom surface were not observed, and the homogeneous state immediately after production was maintained.
Example 2

(3) Preparation of cellulose composite composed of microcrystalline cellulose and xanthan gum Using the wet cake of Example 1, xanthan gum (bis) Top, San-Eigen F.F.I) and dextrin (Sandex, Sanwa Starch) were added to make a prototype in the same manner as in Example 1 to obtain a dry powder of cellulose composite. The average particle size at the time of dispersion of this dry powder was 7.5 μm.

A coating composition was obtained by performing the same operation as in Example 1 except that this cellulose composite was used in the same composition as in Example 1. The viscosity of this coating composition was 3100 mPa · s. Thereafter, it was allowed to stand at 25 ° C. for 30 days, but separation of water on the surface and sediment on the bottom surface were not observed, and the homogeneous state immediately after production was maintained.
Example 3

In the blend composition of Example 2, sodium carboxymethylcellulose (Serogen FS-C, manufactured by Daiichi Kogyo Seiyaku) was used instead of hydroxyethylcellulose. That is, in 40 parts by weight of water, 5 parts by weight of a 2% by weight cellulose composite (0.1% by weight in terms of solid content) and 15% by weight of 2% by weight of carboxymethyl cellulose / sodium (0.3% by weight in terms of solid content) Add Furthermore, 40 parts by weight of titanium oxide was added, and the other operations were performed in the same manner as in Example 2 to obtain a coating composition. The viscosity of this coating composition was 3000 mPa · s. Thereafter, it was allowed to stand at 25 ° C. for 30 days, but separation of water on the surface and sediment on the bottom surface were not observed, and the homogeneous state immediately after production was maintained.
Comparative Example 1

In the formulation composition of Example 1, without using hydroxyethyl cellulose, 20 parts by weight of cellulose composite of 2% by weight (0.4% by weight in terms of solid content) was used. A paint composition was obtained. The viscosity of the coating composition after adjustment was 1100 mPa · s. Thereafter, when it was allowed to stand at 25 ° C. for 30 days, no separation of water on the surface was observed, but sediment on the bottom surface was observed. The sedimentation rate of this sample was 8%.
Comparative Example 2

In the blending composition of Example 1, in 40 parts by weight of water, 15 parts by weight of a 2% by weight cellulose composite (0.3% by weight in terms of solid content) and 5 parts by weight of 2% by weight of hydroxyethyl cellulose (in terms of solid content: 0. 1% by weight). Further, 40 parts by weight of titanium oxide was added, and the other operations were performed in the same manner as in Example 1 to obtain a coating composition. The viscosity of the coating composition was 1500 mPa · s. Then, when left at 25 ° C. for 30 days, surface water separation and bottom sediment were observed. This sample had a water separation rate of 3% and a sedimentation rate of 5%.
Comparative Example 3

  In the formulation composition of Example 1, without using the dry powder of the cellulose composite, 20 parts by weight of 2% by weight of hydroxyethyl cellulose (0.4% by weight in terms of solid content) was used, and other operations were the same as in Example 1. To obtain a coating composition. The viscosity of the coating composition after adjustment was 2700 mPa · s. Thereafter, when left at 25 ° C. for 30 days, no sedimentation was observed, but water separation was observed on the surface. The water separation rate of this sample was 15%.

It is suitably used in the field of water-based paints containing a water-soluble polymer comprising a cellulose composite and a cellulose derivative.

Claims (2)

(A) A cellulose composite composed of microcrystalline cellulose and carboxymethylcellulose sodium or xanthan gum is 0.1% or more of the total amount of the aqueous coating composition, and (B) a water-soluble polymer composed of a cellulose derivative is 0.2% or more. A water-based coating composition characterized in that the solid content ratio of (A) and (B) is 1/9 to 7/3 and has a viscosity of 2500 to 10,000 mPa · s. The water-based coating composition according to claim 1, wherein the water-soluble polymer is hydroxyethyl cellulose or carboxymethyl cellulose sodium.