COATING AGENT, ADHESIVE, AND COATED PRODUCT

Abstract

The present invention provides a coating agent having a reduced methanol content, an adhesive including the coating agent and excellent in coating performance and adhesiveness, and a coated product including the coating agent and excellent in water resistance and alcohol resistance. The present invention relates to a coating agent comprising a modified vinyl alcohol polymer (A), the modified vinyl alcohol polymer (A) comprising a structural unit derived from a derivative (a) of an ethylenically unsaturated dicarboxylic acid in a content (X) of 0.05 mol % or more and 10 mol % or less, having a degree of saponification of 80.0 mol % or more and 99.9 mol % or less, having a methanol content of less than 3.0 mass % as measured by headspace gas chromatography, and having an amount of 0.1 ppm or more and less than 2,000 ppm of a component insoluble in a 90 C., 5 mass % aqueous solution.

Claims

1. A coating agent, comprising a modified vinyl alcohol polymer (A), the modified vinyl alcohol polymer (A) comprising a structural unit derived from a derivative (a) of an ethylenically unsaturated dicarboxylic acid in a content (X) of 0.05 mol % or more and 10 mol % or less, having a degree of saponification of 80.0 mol % or more and 99.9 mol % or less, having a methanol content of less than 3.0 mass % as measured by headspace gas chromatography, and having an amount of 0.1 ppm or more and less than 2,000 ppm of a component insoluble in a 90 C., 5 mass % aqueous solution.

2. The coating agent according to claim 1, wherein the derivative (a) of an ethylenically unsaturated dicarboxylic acid is a monoester, a diester, or an anhydride of an ethylenically unsaturated dicarboxylic acid.

3. The coating agent according to claim 1, wherein at least a part of the structural unit derived from the derivative (a) of an ethylenically unsaturated dicarboxylic acid is a structural unit represented by the following formula (I), ##STR00003## wherein R.sup.1 is a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms, and R.sup.2 is a metal atom, a hydrogen atom, or a linear or branched alkyl group having 1 to 8 carbon atoms, and the following formula (Q) is satisfied,
0.05Y/X<0.98 (Q), wherein X is the content of the structural unit derived from the derivative (a) of an ethylenically unsaturated dicarboxylic acid, and Y is the content of the structural unit represented by the formula (I).

4. The coating agent according to claim 1, further comprising a crosslinking agent (B).

5. The coating agent according to claim 1, further comprising a filler (C).

6. An adhesive comprising the coating agent according to claim 1.

7. A coated product made by coating a substrate with the coating agent according to claim 1.

8. The coated product according to claim 7, being a thermal recording material.

9. The coated product according to claim 7, being base paper for release paper.

10. The coated product according to claim 7, being a greaseproof paper.

11. The coated product according to claim 7, being an inkjet recording material.

Description

EXAMPLES

[0118] The present invention will be described in more detail by way of Examples. It should be noted that the present invention is in no way limited to the Examples given below, and the present invention can be implemented in various modifications within the technical idea of the present invention by a person with common knowledge in the art. In the following Examples and Comparative Examples, part means part by mass, and % means mass %, unless otherwise specifically stated.

[0119] [Viscosity-Average Degree of Polymerization of Modified PVA (A)]

[0120] The viscosity-average degree of polymerization of the modified PVA (A) was measured following JIS K 6726: 1994. Specifically, when the degree of saponification was less than 99.5 mol % in the modified PVA (A), the modified PVA (A) was saponified until the degree of saponification became 99.5 mol % or more, and was measured for the viscosity-average degree of polymerization (P) by the following equation using the intrinsic viscosity [n] (liter/g) measured in water at 30 C.

P=([]10.sup.4/8.29).sup.(1/0.62)

[0121] [Degree of Saponification of Modified PVA (A)]

[0122] The degree of saponification of the modified PVA (A) was determined following the method described in JIS K 6726: 1994.

[0123] [Content (X) of Structural Unit Derived from Derivative (a) of Ethylenically Unsaturated Dicarboxylic Acid]

[0124] The content (X) was calculated from a spectrum of the modifying species by .sup.1H-NMR spectral analysis.

[0125] [Content (Y) of Structural Unit Represented by Formula (I)]

[0126] The content (Y) was calculated from a signal detected at 6.8 to 7.2 ppm in .sup.1H-NMR spectral analysis using a dimethyl sulfoxide solvent.

[0127] [Methanol Content in Modified PVA (A)]

[0128] The methanol content in the modified PVAs (A) of Examples and Comparative Examples was determined by headspace gas chromatography in the manner described below.

<Creation of Standard Curve>

[0129] Three aqueous solutions of known methanol contents are prepared using isopropanol as an internal standard. A standard curve is created by measuring these aqueous solutions with a gas chromatography device (GC-2010, manufactured by Shimadzu Corporation) installed with a headspace sampler (Turbo Matrix HS40, manufactured by Parkin Elmer).

<Measurement of Methanol Content in Modified PVA (A)>

[0130] Distilled water is taken into a 1,000 mL-graduated flask by filling it to a marked line, and 0.1 mL of isopropanol as an internal standard solution is added with a graduated pipette. The mixture is then thoroughly stirred. This solution will be called solvent. Thereafter, 500 mg of each of the modified PVAs (A) of Examples and Comparative Examples is weighed out as a sample into a vial container for headspace gas chromatography measurement, and, after putting a stir bar, the solvent is charged into the vial container in a measured amount of 10 mL using a volumetric pipette. After placing and securely locking a cap on the vial container, the vial container is placed on a hot stirrer, and the modified PVA (A) sample is dissolved under heat. The modified PVA (A) is subjected to headspace gas chromatography measurement after visually confirming that the modified PVA (A) has completely dissolved. The methanol content in the modified PVA (A) is determined from the standard curve previously created.

[0131] [Amount of Component Insoluble in 90 C., 5 Mass% Aqueous Solution]

[0132] A 500-mL flask fitted with an agitator and a reflux condenser is placed in a 20 C. water bath. 285 g of distilled water is charged into the flask, followed by stirring at 300 rpm. 15 g of each of the modified PVAs (A) of Examples and Comparative Examples is weighed out and is gradually charged into the flask. As soon as all the modified PVA (A) (15 g) is charged into the flask, the water bath temperature is increased to 90 C. over a time period of about 30 minutes. After the temperature reaches 90 C., the modified PVA (A) is further dissolved while stirring the mixture for 60 minutes at 300 rpm. The mixture is then filtered through a metal filter with 63-pm openings to trap undissolved, remaining particles (undissolved particles). The filter is thoroughly washed with 90 C. hot water to remove the solution on the filter. The filter is then dried for 1 hour with a heating drier at 120 C. The mass of the undissolved particles thus collected is determined as the amount of a component insoluble in the aqueous solution.

[0133] [Particle Size Distribution]

[0134] The modified PVAs (A) obtained in Examples and Comparative Examples were measured for particle size distribution using the dry sieving method described in JIS Z 8815: 1994. Each of the modified PVAs (A) obtained in Examples and Comparative Examples was sieved through a sieve (filter) with 1.00-mm openings, and the mass of the modified PVA (A) having passed through the sieve was measured. The proportion (mass %) of the modified PVA (A) particles having passed through the sieve was then calculated from the mass of the modified PVA (A) before sieving. In a similar fashion, each of the modified PVAs (A) obtained in Examples and Comparative Examples was sieved through a sieve (filter) with 500-m openings, and the mass of the modified PVA (A) having passed through the sieve was measured. The proportion (mass %) of the modified PVA (A) particles having passed through the sieve was then calculated from the mass of the modified PVA (A) before sieving. The opening complies with the nominal opening W of JIS Z 8801-1: 2006.

[Synthesis Example 1]

[0135] For copolymerization, an apparatus was used that had a reflux condenser, a raw-material supply line, a reaction-solution eject line, a thermometer, a nitrogen inlet, and stirring vanes, together with a polymerization container (continuous polymerization device; hereinafter, polymerization vessel) equipped with a reflux condenser, a raw-material supply line, a thermometer, a nitrogen inlet, and stirring vanes. Vinyl acetate (VAM; 876 L/hr), methanol (MeOH; 157 L/hr), a 20% methanol solution (12.9 L/hr) of monomethyl maleate (MMM) as a modifying species being the derivative (a) of an ethylenically unsaturated dicarboxylic acid, and a 2% methanol solution (13.6 L/hr) of 2,2-azobis(4-methoxy-2,4-dimethylvaleronitrile) (AMV) were continuously supplied into the polymerization vessel using a metering pump. The polymerization solution was continuously ejected from the polymerization vessel in such a way as to maintain a certain liquid level in the polymerization vessel. The polymerization rate of vinyl acetate was adjusted to be 43% in the polymerization solution ejected from the polymerization vessel. The polymerization solution was retained in the polymerization vessel for 4 hours. The polymerization solution ejected from the polymerization vessel had a temperature of 63 C. The polymerization solution ejected from the polymerization vessel was exposed to methanol vapor to remove unreacted vinyl acetate. A methanol solution of vinyl ester copolymer (PVAc; concentration: 35%) was thus obtained.

[0136] Water and methanol were added in desired amounts to the methanol solution of vinyl ester copolymer to prepare a raw saponification solution, specifically, a vinyl ester copolymer/methanol solution (concentration: 32 mass %) having a water content of 1.5 mass %. A sodium hydroxide/methanol solution (concentration: 4 mass %) as a saponification catalyzing solution was then added so that the molar ratio of sodium hydroxide to the vinyl acetate unit in the vinyl ester copolymer was 0.01. The raw saponification solution and the saponification catalyzing solution were mixed using a static mixer to obtain a mixture. The mixture was placed and kept on a belt under 40 C. temperature conditions for 18 minutes to promote a saponification reaction. The gel from the saponification reaction was pulverized, and impregnated with a washing solution having a methanol/methyl acetate ratio of 35/65 (volume ratio). The solution was then removed using a centrifugal dehydrator to obtain a polymer. The polymer (600 kg/hr; a resin component) was continuously supplied into a drier that had been adjusted to have a controlled inner temperature that brings the resin to 105 C. The polymer was retained in the drier for 6 hours on average. The polymer was then pulverized so as to pass through a filter with 1.00-mm openings. The modified PVA (A) (PVA-1) was thus obtained. The modified PVA (A) had a viscosity-average degree of polymerization of 1,700 and a degree of saponification of 88.0 mol %. The modifying contents (X) and (Y) were 0.4 mol % and 0.04 mol %, respectively, as measured by .sup.1H-NMR spectral analysis, and the ratio (Y/X) was 0.10. The proportion of modified PVA (A) particles that passed through a filter with 1.00-mm openings was 99.0 mass %, and the proportion of modified PVA (A) particles that passed through a filter with 500-pm openings was 56.0 mass %, with respect to all the modified PVA (A). The methanol content in the PVA (A) was calculated to be 0.9 mass % by headspace gas chromatography described above, and the amount of a component insoluble in the aqueous solution (Amount of water-insoluble component) was 700 ppm as measured by the method described above. The analysis results for PVA-1 are presented in Table 2.

[Synthesis Examples 2 to 8]

[0137] PVA-2 to PVA-8 were obtained in the same manner as for the method for producing PVA-1 of Synthesis Example 1, except that the conditions were changed to those described in Table 1. The analysis results for the modified PVAs (A) are presented in Table 2.

TABLE-US-00001 TABLE 1 Wash- ing con- ditions Compo- sition of washing Saponification conditions solution Drying conditions Polymerization conditions PVAc/ Meth- Aver- Modifying species meth- anol/ age Modi- Concen- Polymer- Reten- anol Water methyl Resin reten- fied tration ization tion solution content NaOH acetate temper- tion PVA VAM MeOH AMV (mass rate time (mass (mass (molar (volume ature time type (L/hr) (L/hr) (L/hr) Type .sup.1) %) (L/hr) (%) (hr) %) %) ratio) ratio) ( C.) (hr) Synthesis PVA-1 876 157 13.6 MMM 20 12.9 43 4 32 1.5 0.01 35/65 105 6 Example 1 Synthesis PVA-2 926 76 9 MMM 20 13.4 35 4 30 1.5 0.01 35/65 105 6 Example 2 Synthesis PVA-3 963 47 3 MMM 20 11 30 6 25 1.5 0.01 50/50 105 6 Example 3 Synthesis PVA-4 955 18 6 DMM 20 12 30 6 25 1.5 0.015 20/80 105 6 Example 4 Synthesis PVA-5 981 1 4 MA 50 35 25 8 25 1.5 0.10 20/80 105 6 Example 5 Synthesis PVA-6 810 220 4 40 4 32 1.5 0.008 35/65 105 6 Example 6 Synthesis PVA-7 963 47 3 MMM 20 11 30 6 25 1.5 0.01 100/0 105 6 Example 7 Synthesis PVA-8 963 47 3 MMM 20 11 30 6 25 1.5 0.01 100/0 120 4 Example 8 .sup.1) MMM: monomethyl maleate DMM: dimethyl maleate MA: maleic anhydride

TABLE-US-00002 TABLE 2 Modified PVA (A) Particle size distribution Particles Particles Amount of passing passing Modi- Saponi- Modi- Modi- Meth- water- through through fied fication Degree of fying fying anol insoluble 1.00-mm 500-m PVA (A) degree polymer- content (X) content (Y) content component openings openings type (mol %) ization (mol %) (mol %) Y/X (mass %) (ppm) (mass %) (mass %) Synthesis PVA-1 88.0 1700 0.4 0.04 0.10 0.9 700 99.0 56.0 Example 1 Synthesis PVA-2 88.0 2400 0.5 0.05 0.10 1.5 1700 99.0 56.0 Example 2 Synthesis PVA-3 88.0 3200 0.4 0.03 0.08 1.3 1200 97.0 49.0 Example 3 Synthesis PVA-4 98.0 3500 0.4 0.09 0.23 0.9 40 96.0 44.0 Example 4 Synthesis PVA-5 96.0 3500 4.0 0.81 0.20 0.8 30 99.5 98.5 Example 5 Synthesis PVA-6 88.0 1700 1.5 10 99.0 56.0 Example 6 Synthesis PVA-7 88.0 3200 0.4 0.03 0.08 4.1 500 73.0 3.5 Example 7 Synthesis PVA-8 88.0 3200 0.4 0.07 0.18 1.1 >5000 99.0 56.0 Example 8

Example 1

[0138] (Preparation of Coating Agent)

[0139] Kaolin (product name: UW90; manufactured by Engelhald Corporation (today's BASF)) as the filler (C) was dispersed in water so that the concentration would be 40%, and the resulting mixture was mixed in a home blender for 10 minutes to prepare a dispersion. A coating agent was prepared by mixing the dispersion, an aqueous PVA-1 solution, and a crosslinking agent at a solid content ratio of 32 parts by mass of PVA-1 included in the aqueous solution to 60 parts by mass of kaolin as the filler (C) to 8 parts by mass of a polyamide-epichlorohydrin resin (WS4020, manufactured by SEIKO PMC CORPORATION) as the crosslinking agent (B). The concentration of PVA-1 in the coating agent was 5.8 mass %. The methanol content in the coating agent measured in the manner described below was 0.05 mass %.

[0140] (Production of Thermal Recording Material)

[0141] Commercially-available thermal paper (manufactured by KOKUYO Co., Ltd.; with no overcoat layer) was coated with the coating agent in an amount of 3.5 g/m.sup.2 in terms of solid content using a curtain coater. This was followed by drying at 50 C. A thermal recording material including an overcoat layer formed of the coating agent was thus produced as a coated product. After the thermal recording material was stored at 40 C. and 50% RH for 2 days, the water resistance and alcohol resistance thereof were evaluated in the manner descried below. The results are presented in Table 3.

[0142] [Methanol Content in Coating Agent]

[0143] The methanol content in the coating agent was determined by headspace gas chromatography in the manner described below.

<Creation of Standard Curve>

[0144] Three aqueous solutions of known methanol contents are prepared using isopropanol as an internal standard. A standard curve is created by measuring these aqueous solutions with a gas chromatography device (GC-2010, manufactured by Shimadzu Corporation) installed with a headspace sampler (Turbo Matrix HS40, manufactured by Parkin Elmer).

<Measurement of Methanol Content in Coating Agent>

[0145] 10 mg of the coating agent is weighed out and charged into a vial container. After placing and securely locking a cap on the vial container, the coating agent is subjected to headspace gas chromatography measurement. The methanol content in the coating agent is determined from the standard curve previously created.

[0146] [Evaluation of Water Resistance]

[0147] The thermal recording material was cut to produce a 2 cm5 cm strip. A drop of water was placed on the surface with the overcoat layer formed of the coating agent, and then the surface was rubbed in one direction with an index finger until the liquid turned white. The water resistance of the thermal recording material was evaluated according to the following criteria based on the number of strokes needed to turn the liquid white.

[0148] A: The liquid does not turn white after 50 strokes or more.

[0149] B: The liquid turns white after 20 strokes or more and less than 50 strokes.

[0150] C: The liquid turns white after less than 20 strokes.

[0151] [Evaluation of Alcohol Resistance]

[0152] The thermal recording material was cut to produce a 2 cm5 cm strip. The surface with the overcoat layer formed of the coating agent was gently wiped with absorbent cotton saturated with ethanol and was then dried. The alcohol resistance of the thermal recording material was evaluated according to the following criteria based on the coloring condition.

[0153] A: Coloring is hardly observed.

[0154] B: Black dots attributable to coloring are observed in some parts.

[0155] C: Black dots are observed all over the surface.

Examples 2 to 5 and Comparative Examples 1 to 3

[0156] Coating agents and thermal recording materials were produced in the same manner as in Example 1, except that the type and the amount of the modified PVAs (A) used and the amount of the crosslinking agent (B) were changed according to the conditions as described in Table 3. The methanol content of the coating agents and the water resistance and alcohol resistance of the thermal recording materials were evaluated in the same manner as in Example 1. The results are presented in Table 3.

TABLE-US-00003 TABLE 3 Coating agent Crosslinking Modified PVA (A) agent (B) Filler (C) Evaluation of coated Amount Amount Amount Methanol product (parts by (parts by (parts by content Water Alcohol Type mass) mass) mass) (mass %) resistance resistance Example 1 FVA-1 32 8 60 0.05 A B Example 2 PVA-2 30 10 60 0.08 A B Example 3 PVA-3 29 11 60 0.06 A A Example 4 PVA-4 30 10 60 0.04 A A Example 5 PVA-5 33 7 60 0.03 A A Comparative PVA-6 32 8 60 0.08 C C Example 1 Comparative PVA-7 32 8 60 0.18 A A Example 2 Comparative PVA-8 32 8 60 0.05 B B Example 3

[0157] Because an unmodified PVA was used in Comparative Example 1, the water resistance and alcohol resistance of the resulting thermal recording material were insufficient. As the methanol content in the modified PVA (A) was high in Comparative Example 2, the resulting coating agent had a high methanol content and was environmentally unfriendly in that methanol evaporated in the coating step. In Comparative Example 3, the amount of a component insoluble in the aqueous solution was too high in the modified PVA (A) to achieve sufficient water resistance of the thermal recording material.

Example 6

(Preparation of Adhesive)

[0158] Kaolin (product name: UW90; manufactured by Engelhald Corporation (today's BASF)) as the filler (C) was dispersed in water so that the concentration would be 25%. Subsequently, citric acid and PVA-1 were added to the dispersion, followed by heating under stirring and then stirring at 90 C. for a given time period to dissolve PVA-1. A crosslinking agent was added to the resulting liquid mixture at a solid content ratio of 0.1 parts by mass of citric acid to 12 parts by mass of PVA-1 to 37 parts by mass of kaolin as the filler (C) to 1.2 parts by mass of a boric acid as the crosslinking agent (B). An adhesive was thus prepared. The concentration of PVA-1 in the adhesive was 7.0 mass %. The methanol content in the adhesive measured in the manner described below was 0.04 mass %.

[0159] [Methanol Content in Adhesive]

[0160] The methanol content in the adhesive was determined by headspace gas chromatography in the manner described below.

<Creation of Standard Curve>

[0161] Three aqueous solutions of known methanol contents are prepared using isopropanol as an internal standard. A standard curve is created by measuring these aqueous solutions with a gas chromatography device (GC-2010, manufactured by Shimadzu Corporation) installed with a headspace sampler (Turbo Matrix HS40, manufactured by Parkin Elmer).

<Measurement of Methanol Content in Adhesive>

[0162] 10 mg of the adhesive is weighed out and charged into a vial container. After placing and securely locking a cap on the vial container, the adhesive is subjected to headspace gas chromatography measurement. The methanol content in the adhesive is determined from the standard curve previously created.

[0163] [Evaluation of Coating Performance]

[0164] The adhesive was manually applied onto a sheet of A4 kraft paper using a wire bar #6. The coated surface was observed to evaluate the coating performance according to the following criteria.

[0165] A: The coated surface is free of defects.

[0166] B: The coated surface shows a few appearance defects such as a bump.

[0167] C: The coated surface shows a lot of appearance defects such as a bump.

[0168] [Evaluation of Adhesiveness]

[0169] The adhesive was manually applied onto a sheet of A4 kraft paper using a wire bar #6. To the A4 kraft paper was attached another sheet of A4 kraft paper, and, 10 seconds later, the two sheets of paper were separated by hand. The adhesive force was evaluated according to the following criteria. The larger a broken portion of the sheets of paper is, the higher the adhesiveness is.

[0170] A: 60% or more of the sheets of paper was broken.

[0171] B: 20% or more and less than 60% of the sheets of paper was broken.

[0172] C: Less than 20% of the sheets of paper was broken.

Examples 7 to 11 and Comparative Examples 4 to 6

[0173] Adhesives were produced in the same manner as in Example 6, except that the type and the amount of the modified PVA (A) used, the amount of the crosslinking agent (B), the amount of the filler (C), and whether or not a polyvinyl acetate emulsion is added were changed according to the conditions as described in Table 4. The methanol content, coating performance, and adhesiveness of the adhesives were evaluated in the same manner as in Example 6. The results are presented in Table 4.

TABLE-US-00004 TABLE 4 Adhesive Polyvinyl Crosslinking acetate Modified PVA (A) agent (B) Filler (C) emulsion Amount Amount Amount Amount Methanol Evaluation of adhesive (parts by (parts by (parts by (parts by content Coating Type mass) mass) mass) mass) (mass %) performance Adhesiveness Example 6 PVA-1 12 1.2 37 0 0.04 A B Example 7 PVA-2 10 1 37 0 0.06 A B Example 8 PVA-2 10 1 37 30 0.07 A A Example 9 PVA-3 7 0.7 37 0 0.05 A A Example 10 PVA-4 10 1 60 0 0.03 A A Example 11 PVA-5 13 1.3 60 0 0.02 A A Comparative PVA-6 12 1.2 60 0 0.08 C C Example 4 Comparative PVA-7 12 1.2 60 0 0.15 A A Example 5 Comparative PVA-8 12 1.2 60 0 0.04 C B Example 6

[0174] Because an unmodified PVA was used in Comparative Example 4, the coating performance and adhesiveness of the resulting adhesive were insufficient. As the methanol content in the modified PVA (A) was high in Comparative Example 5, the resulting coating agent had a high methanol content and was environmentally unfriendly in that methanol evaporated in the coating step. In Comparative Example 6, the amount of a component insoluble in the aqueous solution was too high in the modified PVA (A) to achieve sufficient coating performance of the adhesive.

INDUSTRIAL APPLICABILITY

[0175] Including the modified PVA (A) having a reduced methanol content and a reduced amount of a component insoluble in the aqueous solution, the coating agent and adhesive of the present invention are excellent in coating performance and adhesiveness. Coated products made by coating a substrate with the coating agent are excellent in water resistance and alcohol resistance.