Release-paper base paper and method for producing same, and release paper

Abstract

Release paper base paper includes a substrate; and a coating agent containing a modified polyvinyl alcohol (A) and sodium acetate, the substrate coated with the coating agent, wherein the modified polyvinyl alcohol (A) has 0.005 mol % or more and less than 10 mol % of double bonds derived from unsaturated carboxylic acid or a derivative thereof (B) in side chains, has 1.4 mol % or more and 2.0 mol % or less of 1,2-glycol bond, units, and is water soluble, and a content of the sodium acetate relative to the modified polyvinyl alcohol (A) is 0.01 mass % or more and 10 mass % or less. The release paper base paper of the present invention is excellent in sealing properties for silicone. Use of the release paper base paper allows acceleration of curing of silicone in a release layer and improvement in adhesion between the substrate and the release layer.

Claims

1. A release paper base paper, comprising: a substrate coated with a coating agent, wherein the coating agent comprises a modified polyvinyl alcohol (A) and sodium acetate, wherein the modified polyvinyl alcohol (A) has 0.005 mol % or more and less than 10 mol % of double bonds derived from unsaturated carboxylic acid or at least one selected from the group consisting of unsaturated carboxylic acid anhydride, unsaturated carboxylic acid ester and unsaturated carboxylic acid salt, has 1.4 mol % or more and 2.0 mol % or less of 1,2-glycol bond units, and is water soluble, and a content of the sodium acetate relative to the modified polyvinyl alcohol (A) is 0.01 mass % or more and 10 mass % or less.

2. The release paper base paper according to claim 1, wherein the modified polyvinyl alcohol (A) has a viscosity-average degree of polymerization of 400 or more and less than 5000 and has a degree of saponification of 70.0 mol % or more and 99.9 mol % or less.

3. The release paper base paper according to claim 1, wherein the modified polyvinyl alcohol (A) further has ethylene units in a main chain and a content of the ethylene units is 1 mol % or more and 10 mol % or less.

4. A release paper, comprising: the release paper base paper according to claim 1; and a release layer formed on a surface of the release paper base paper.

5. The release paper according to claim 4, wherein the release layer comprises addition-type silicone (D) and platinum (E), and 0.001 part by mass or more and 0.05 part by mass or less of the platinum (E) is present based on 100 parts by mass of the addition-type silicone (D).

6. A method of producing the release paper base paper according to claim 1, comprising: (i) obtaining the modified polyvinyl alcohol (A) by reacting the unsaturated carboxylic acid or a derivative thereof (B) with a polyvinyl alcohol (C); (ii) obtaining the coating agent by dissolving the modified polyvinyl alcohol (A) obtained in (i) and the sodium acetate in water; and (iii) coating the substrate with the coating agent obtained in (ii).

7. The production method according to claim 6, wherein, in (i), the modified polyvinyl alcohol (A) is obtained by reacting the unsaturated carboxylic acid or a derivative thereof (B) with the polyvinyl alcohol (C) in powder form having an average particle diameter from 50 to 500 μm.

8. The production method according to claim 6, wherein the coating agent obtained in (ii) has a pH of 3.0 or more and 7.0 or less.

9. The production method according to claim 6, wherein the modified polyvinyl alcohol (A) is in powder form and the powder has a yellow index of less than 40.

Description

EXAMPLES

(1) Although an even more detailed description is given below to the present invention with reference to Examples, the present invention is not at all limited to Examples below. In Examples below, “%” and “parts” respectively mean “mass %” and “parts by mass” unless otherwise specified.

(2) [Viscosity-Average Degree of Polymerization of PVA]

(3) The viscosity-average degree of polymerization of the PVA was measured by a method in accordance with JIS-K 6726: 1994. Specifically, when the degree of saponification was less than 99.5 mol %, the PVA was saponified to have a degree of saponification of 99.5 mol % or more and the viscosity-average degree of polymerization (P) was obtained by an equation below using the limiting viscosity [η] (liter/g) measured at 30° C. in water.
P=([η]×10.sup.4/8.29).sup.(1/0.62)
[Degree of Saponification of PVA]

(4) The degree of saponification of the PVA was obtained by the method described in JIS-K 6726: 1994.

(5) [Amount of Double Bonds Introduced into Modified PVA (A)]

(6) The modified PVA (A) was subjected to measurement of the amount of the double bonds introduced into the modified PVA (A) using .sup.1H-NMR. The amount of the double bonds is an amount of the double bonds based on the total monomer units in the modified PVA (A).

(7) [Content of 1,2-Glycol Bond Units in PVA]

(8) A modified PVA (A) obtained in each Example below was added to a methanol solution of sodium hydroxide and kept at 60° C. for 5 hours for resaponification of the modified PVA (A). At this time, the amount of sodium hydroxide was 0.1 mol relative to 1 mol of vinyl alcohol units in the modified PVA (A). The PVA thus obtained was subjected to Soxhlet extraction with methanol for 1 week to obtain a purified PVA having a degree of saponification of 99.9 mol % or more.

(9) The purified PVA obtained in the above method was dried under reduced pressure at 90° C. for 2 days, to completely remove the methanol. The purified PVA was then dissolved in dimethyl sulfoxide-d.sub.6 to make a 0.1 mass % solution, and several drops (approximately 0.1 ml) of trifluoroacetic acid were added to the solution to measure .sup.1H-NMR. The content of 1,2-glycol bond units (monomer units bonded by 1,2-glycol bond) contained in the purified PVA was calculated from a peak (integral value a) from 3.2 to 4.0 ppm derived from methine protons in the vinyl alcohol units and a peak (integral value β) at 3.25 ppm derived from one methine proton in the 1,2-glycol bond units in accordance with an equation (I) below. At this point, the content of the 1,2-glycol bond units in the modified PVA (A) does not change before and after the resaponification, and thus the value obtained by the equation (I) below becomes the content of the 1,2-glycol bond units in the modified PVA (A).
Content of 1,2-Glycol Bond Units in PVA (mol%)=100×β/α  (I)

Example 1

(10) [Production of Modified PVA (A)]

(11) To a separable flask, 400 parts by mass of dimethyl sulfoxide (DMSO), 100 parts by mass of a PVA, as the PVA (C), having a viscosity-average degree of polymerization of 500, having a degree of saponification of 88.2 mol %, and a content of 1,2-glycol bond units of 1.6 mol % were added and subjected to a raise in temperature to 105° C. while stirring to obtain a homogeneous solution. To the homogeneous solution, 44 parts by mass methyl methacrylate as the compound (B) and 1.1 parts by mass of phenothiazine were added and stirred to homogeneity. After becoming homogeneous, 1.8 parts by weight of zinc nitrate hexahydrate was added as a transesterification catalyst for reaction for 5 hours and then left for cooling to room temperature. To the reaction solution, 100 parts by mass of DMSO was added for dilution, followed by dropping of 1000 parts by mass of methanol to precipitate a modified PVA. The precipitated modified PVA was washed twice with 1000 parts by mass methanol and then vacuum dried to obtain a modified PVA (A).

(12) The modified PVA (A) thus obtained was subjected to .sup.1H-NMR measurement to find out that the content of the double bonds was 1.00 mol %. The viscosity-average degree of polymerization was 500, the degree of saponification was 87.1 mol % and the content of the 1,2-glycol bond units was 1.6 mol %. The results are shown in Table 1.

(13) [Yellow Index (YI) of Powder of Modified PVA (A)]

(14) The yellow index (YI) of powder of the modified PVA (A) was measured by removing powder of less than 100 μm and more than 1000 μm from powder of the modified PVA (A) thus obtained using sieves (mesh size of 100 μm and 1000 μm) and then using a color meter (SM-T-H1 manufactured by Suga Test Instruments Co., Ltd.). The yellow index was a value measured and calculated in accordance with JIS-Z 8722: 2009 and JIS-K 7373: 2006. As a result, the powder of the modified PVA (A) had a yellow index (YI) of 18. The result is shown in Table 2.

(15) [Evaluation of Water Solubility of modified PVA (A)]

(16) The modified PVA (A) thus obtained was dissolved in water at 98° C. to prepare a 4 mass % aqueous solution. The aqueous solution was visually inspected to evaluate in accordance with the following evaluation criteria. The result is shown in Table 2. A: It was dissolved at 98° C. B: An insoluble matter was found in the solution at 98° C.
[Preparation of Release Paper Base Paper]

(17) A 6 mass % aqueous solution of the modified PVA (A) was prepared and sodium acetate was added to the aqueous solution to have the content of the sodium acetate relative to the modified PVA (A) of 1.3 mass % to obtain a coating agent. Glassine paper having an air permeability of 100 seconds was coated with the coating agent using a wire bar to have the amount of coating of approximately 1 g/m.sup.2 in dry mass. After coating, it was dried at 100° C. for 5 minutes to obtain coated paper. The coated paper thus obtained was subjected to treatment twice at 70° C. and 400 kg/cm.sup.2 in a super calender to obtain release paper base paper.

(18) [pH of Coating Agent]

(19) The pH of the coating agent used for preparation of the release paper base paper was measured. Since a lower pH means the coating liquid to be a stronger acidic solution, it causes a problem of corrosion of the coating machine. The result is shown in Table 2.

(20) [Coating Stability]

(21) The coating agent used for preparation of the release paper base paper was diluted with water to have the modified PVA (A) at a concentration of 2 mass %. The diluted aqueous solution was stirred at 20° C. and 200 rpm to observe the presence of fibrils produced in the aqueous solution for evaluation of coating stability. The result is shown in Table 2. A: No fibrils were produced. B: Fibrils were produced.
[Evaluation of Air Permeability of Release Paper Base Paper]

(22) The air permeability of the release paper base paper was measured using a smoothness and air permeability tester of Oken method in accordance with JIS-P 8117: 2009 to be used as an index of sealing properties for silicone. The result is shown in Table 2.

(23) [Evaluation of Silicone Curability]

(24) Using LTC1056L produced by Dow Corning bray Co., Ltd. as the addition-type silicone (D) and SRX212 as the platinum catalyst, the release paper base paper thus obtained was coated by a blade coater with a coating liquid mixed to have a ratio of the addition-type silicone (D) to the platinum (E) at 100/0.007 for a coating amount of 1.5 g/m.sup.2 in terms of solid content. A silicone layer was thus formed on the release paper base paper. It was then heat treated at 110° C. to measure the time until the silicone was cured. In this context, the time until the silicone was cured means time (seconds) taken until no peeling at all found in the silicone layer while the silicone layer was strongly rubbed 10 times with a finger at predetermined time intervals. The result is shown in Table 2.

(25) [Evaluation of Adhesion of Release Layer]

(26) Using LTC1056L produced by Dow Corning Toray Co., Ltd. as the addition-type silicone (D) and SRX212 as the platinum catalyst, the release paper base paper thus obtained was coated by a blade coater with a coating liquid mixed to have a ratio of the addition-type silicone (D) to the platinum E) at 100/0.009 for a coating amount of 1.5 g/m.sup.2 in terms of solid content. It was then heat treated at 110° C. for 90 seconds to obtain release paper with a release layer (silicone layer) formed on the release paper base paper. The release paper thus obtained was evaluated by the following indices. The result is shown in Table 2. A: After leaving in the conditions of 40° C. and 90% RH for 1 week, the silicone layer was strongly rub bed with a finger. As a result, the silicone layer did not peel. After leaving in the same conditions for another 1 week, the silicone layer was strongly rubbed with a finger. As a result, the silicone layer did not peel. B: After leaving in the conditions of 40° C. and 90% RH for 1 week, the silicone layer was strongly rubbed with a finger. As a result. the silicone layer did not peel. However, after leaving in the same conditions for another 1 week. the silicone layer was strongly rubbed with a finger and the silicone layer was peeled. C: After leaving in the conditions of 40° C. and 90% RH for 1 week, the silicone layer was strongly rubbed with a finger. As a result, the silicone layer was peeled.

Example 2

(27) A modified PVA (A) was produced in the same manner as in Example 1 other than changing the type of PVA (C) and the amount of the compound (B) as shown in Table 1 and using 1.9 parts by mass of sodium acetate instead of the zinc nitrate hexahydrate as the transesterification catalyst. The production conditions of the modified PVA (A) are shown in Table 1, and the analysis results are shown in Tables 1 and 2. Then, a coating agent was obtained in the same manner as in Example 1 other than changing the amount of the sodium acetate as shown in Table 2. The evaluation results of the coating agent are shown in Table 2. The performances of the release paper base paper and the release paper were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Example 3

(28) [Production of Modified PVA (A)]

(29) To a reactor provided with a stirrer, a reflux condenser tube, a nitrogen introduction tube, and a reactant addition port, 100 parts by mass of a PVA, as the PVA (C), having a viscosity-average degree of polymerization of 1000, having a degree of saponification of 99.5 mol %, having an amount of ethylene modification of 6 mol %, and having a content of the 1,2-glycol bond units of 1.7 mol % and 400 parts by mass of DMSO were added to prepare a solution at a concentration of 20 mass %. To the solution, 65 parts by mass of 3,3-methyl dimethylpentenoate as the compound (B) and 0.4 part by mass of tetramethylammonium methyl carbonate as the catalyst were added and subjected to a raise in temperature to 100° C. under a nitrogen flow and heat stirring for 130 minutes. The solution was then dropped into methanol, and the polymer was isolated and vacuum dried at 40° C. overnight to obtain the modified PVA (A). The analysis results of the modified PVA (A) thus obtained are shown in Tables 1 and 2.

(30) A coating agent was then obtained in the same manner as in Example 1 other than changing the amount of the sodium acetate as shown in Table 2. The evaluation results of the coating agent are shown in Table 2. The performances of the release paper base paper and the release paper were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Example 4

(31) [Production of Modified PVA (A)]

(32) A solution was prepared by dissolving 100 parts by mass of a PVA powder (average particle diameter of 500 μm), as the PVA (C), having a viscosity-average degree of polymerization of 1000, having a degree of saponification of 99.5 mol %, having an amount of ethylene modification of 6 mol %, and having a content of the 1,2-glycol bond units of 1.7 mol %, 2.63 parts by mass of fumaric acid as the compound (B), and 0.2 part by mass of propyl gallate as the compound (F) in 150 parts by mass of methanol, and was poured into a flask and mixed to swell the PVA powder, followed by removal of methanol by pressure reduction. It was then heat treated while stirring at 85° C. for 1 hour, at 90° C. for 1 hour, and at 120° C. for 4 hours for reaction to obtain a modified PVA (A). The modified PVA (A) thus obtained was subjected to reprecipitation purification and the amount of the double bonds was calculated, and it was 0.19 mol %. The results are shown in Table 1.

(33) A coating agent was then obtained in the same manner as in Example 1 other than changing the amount of the sodium acetate as shown in Table 2.

(34) The evaluation results of the coating agent are shown in Table 2. The performances of the release paper base paper and the re lease paper were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Examples 5 through 11, Comparative Examples 1 through 6

(35) A modified PVA (A) was produced in the same manner as in Example 4 other than changing the type of PVA (C) and the type and the amount of the compound (B) as shown in Table 1. The production conditions of the modified PVA (A) are shown in Table 1, and the analysis results are shown in Tables 1 and 2. A coating agent was then obtained in the same manner as in Example 1 other than changing the amount of the sodium acetate as shown in Table 2. The evaluation results of the coating agent are shown in Table 2. The performances of the release paper base paper and the release paper were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Example 12

(36) A solution was prepared by dissolving 100 parts by mass of PVA powder, as the PVA (C), having a viscosity-average degree of polymerization of 1700, having a degree of saponification of 99.5 mol %, having an amount of methyl acrylate modification of 5 mol %, and having a content of the 1,2-glycol bond units of 1.7 mol %, 5.90 parts by mass of 2-hydroxyethyl methacrylate as the compound (B) and 0.2 part by mass of propyl gallate as the compound (F) in 150 parts by mass of methanol, and was poured into a flask and mixed to swell the PVA powder, followed by removal of methanol by pressure reduction. It was then heat treated while stirring at 85° C. for 1 hour, at 90° C. for 1 hour, and at 120° C. for 4 hours for reaction to obtain a modified PVA (A). The modified PVA (A) thus obtained was subjected to reprecipitation purification, and the amount of the double bonds was calculated and it was 0.09 mol %. The results are shown in Table 1.

(37) A coating agent was then obtained in the same manner as in Example 1 other than changing the amount of the sodium acetate as shown in Table 2. The evaluation results of the coating agent are shown in Table 2. The performances of the release paper base paper and the release paper were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Example 13

(38) [Production of Modified PVA (A)]

(39) In a flask, 100 parts by mass of PVA powder, as the PVA (C), having a viscosity-average degree of polymerization of 1000, having a degree of saponification of 99.5 mol %, and having an amount of ethylene modification of 6 mol %, 1.77 parts by mass of itaconic acid as the compound (B), and 0.2 part by mass of propyl gallate as the compound (F) were placed. After mixing, it was heat treated while stirring directly in solid form at 85° C. for 1 hour, at 90° C. for 1 hour, and at 120° C. for 4 hours for reaction to obtain a modified PVA (A). The modified PVA (A) thus obtained was subjected to reprecipitation purification, and the amount of the double bonds was calculated to find out that the amount of the double bonds was 0.12 mol %, the degree of saponification was 99.3 mol %, the viscosity-average degree of polymerization was 1000, and the amount of ethylene modification was 6 mol %. The results are shown in Table 1.

(40) A coating agent was then obtained in the same manner as in Example 1 other than changing the amount of the sodium acetate as shown in Table 2. The evaluation results of the coating agent are shown in Table 2. The performances of the release paper base paper and the release paper were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 7

(41) A mixture was made by mixing 100 parts by mass of a PVA, as the PVA (C), having a viscosity-average degree of polymerization of 1000, having a degree of saponification of 99.5 mol %, having a content of the 1,2-glycol bond units of 1.7 mol %, and having an amount of ethylene modification of 6 mol % and 0.30 part by mass of maleic anhydride. It was then placed in a batch mixer set at 200° C. and 100 rpm for melt kneading for 5 minutes. The mixture thus obtained turned yellow and was a gel insoluble even in water. Therefore, the subsequent preparation of release paper base paper was not performed.

Comparative Example 8

(42) A modified PVA (A) was produced in the same manner as in Example 1 other than changing the type of PVA (C) and the amount of the compound (B) as shown in Table 1 and not using the transesterification catalyst. The production conditions of the modified PVA (A) are shown in Table 1, and the analysis results are shown in Tables 1 and 2. A coating agent was then obtained in the same manner as in Example 1 other than changing the amount of the sodium acetate as shown in Table 2. The evaluation results of the coating agent are shown in Table 2. The performances of the release paper base paper and the release paper were evaluated in the same manner as in Example 1. The results are shown in Table 2.

(43) TABLE-US-00001 TABLE 1 PVA (C) Viscosity- Ethylene Average Average Degree of 2,1-Glycol Modification Particle Compound (B) Degree of Saponification Amount Amount Degree of parts by Polymerization (mol %) (mol %) (mol %) (μm) Type mass*.sup.3) Example 1 500 88.2 1.6 — *1) Methyl Methacrylate 44 Example 2 1700 98.5 1.8 — *1) Methyl Methacrylate 67 Example 3 1000 99.5 1.7 6 *1) 3,3-Methyl 65 Dimethylpentenoate Example 4 1000 99.5 1.7 6 500 Fumaric Acid 2.63 Example 5 1700 96.5 1.4 2 600 Fumaric Acid 2.63 Example 6 2400 88.7 1.7 — 500 Fumaric Acid 2.63 Example 7 1000 99.5 1.7 6 500 Citraconic Acid 2.95 Example 8 1000 99.5 1.7 6 500 Itaconic Acid 1.77 Example 9 1000 99.5 1.7 6 500 Itaconic Acid 11.8 Example 10 1000 99.5 1.7 6 500 Itaconic Acid 0.30 Example 11 800 72 1.6 — 200 Itaconic Acid 0.60 Example 12 1700 99.5 1.7 (5)*.sup.4) 100 2-Hydroxyethyl 5.90 Methacrylate Example 13 1000 99.5 1.7 6 500 Itaconic Acid 1.77 Comparative 1700 98.5 1.8 — — — — Example 1 Comparative 800 72.0 1.6 — — — — Example 2 Comparative 1000 99.5 1.3 6 500 Itaconic Acid 0.30 Example 3 Comparative 1000 99.5 1.7 6 500 Itaconic Acid 11.8 Example 4 Comparative 1000 99.5 1.7 6 500 Itaconic Acid 1.77 Example 5 Comparative 800 72 2.2 — 200 Itaconic Acid 0.60 Example 6 Comparative 1000 99.5 1.7 6 *2) Maleic Anhydride 0.30 Example 7 Comparative 1000 99.5 1.7 6 *1) Itaconic Acid 1.77 Example 8 Modified PVA (A) Viscosity- Ethylene Double Average Degree of 2,1-Glycol Modification Bond Degree of Saponification Amount Amount Amount Polymerization (mol %) (mol %) (mol %) (mol %) Example 1 500 87.1 1.6 — 1.00 Example 2 1700 95.0 1.8 — 3.50 Example 3 1000 98.3 1.7 6 1.20 Example 4 1000 99.3 1.7 6 0.19 Example 5 1700 96.4 1.4 2 0.13 Example 6 2400 88.5 1.7 — 0.12 Example 7 1000 99.3 1.7 6 0.18 Example 8 1000 99.3 1.7 6 0.08 Example 9 1000 99.1 1.7 6 0.53 Example 10 1000 99.5 1.7 6 0.01 Example 11 800 72.0 1.6 — 0.05 Example 12 1700 99.5 1.7 (5)*.sup.4) 0.09 Example 13 1000 99.3 1.7 6 0.12 Comparative — — — — — Example 1 Comparative — — — — — Example 2 Comparative 1000 99.5 1.3 6 0.01 Example 3 Comparative 1000 99.1 1.7 6 0.53 Example 4 Comparative 1000 99.3 1.7 6 0.08 Example 5 Comparative 800 72.0 2.2 — 0.05 Example 6 Comparative No Evaluation Possible due to Gelation Example 7 Comparative 1000 99.5 1.7 6 <0.005 Example 8 *1) PVA (C) and Compound (B) were Reacted in Solution. *2) PVA (C) and Compound (B) were Melt Kneaded. *.sup.3)Amount based on 100 parts by mass of PVA (C). *.sup.4)Amount of Methyl Acrylate Modification.

(44) TABLE-US-00002 TABLE 2 Performance Evaluation of Release Performance Paper Evaluation Modified Coating Agent Base Paper of Release Paper PVA (A) Na Air Silicone Water Acetate Coating Permeability Curability YI Solubility (mass %) pH Stability (sec) (sec) Adhesion Example 1 18 A 1.3 6.5 A  1,600 60 A Example 2 21 A 1.0 6.3 A 100,000< 60 A Example 3 11 A 1.1 6.5 A  65,000 60 A Example 4 11 A 6.0 4.4 A 100,000< 60 A Example 5 12 A 5.9 4.3 A 100,000< 60 A Example 6 20 A 5.0 4.1 A 100,000< 60 A Example 7 11 A 5.6 4.2 A 100,000< 60 A Example 8 10 A 1.2 4.5 A 100,000< 60 A Example 9 13 A 4.8 4.2 A 100,000< 60 B Example 10  7 A 0.9 4.3 A 100,000< 80 B Example 11 16 A 1.0 4.3 A  2,700 120  A Example 12 24 A 1.1 6.6 A 100,000< 60 A Example 13 17 A 1.2 4.6 A 100,000< 60 A Comparative  7*.sup.5) A 0.01 6.8 A 100,000< 120< C Example 1 Comparative 13*.sup.5) A 0.08 6.8 A  3,000 120< C Example 2 Comparative  7 A 0.9 4.3 B 100,000< 60 A Example 3 Comparative 13 A 0.008 2.8 A 100,000< 60 A Example 4 Comparative 10 A 12.0 4.8 A 100,000< 80 C Example 5 Comparative 17 A 1.2 4.4 A  2,700 120  C Example 6 Comparative — B — — — — — — Example 7 Comparative  7 A 0.5 6.2 A 100,000< 120< C Example 8 *.sup.5)YI of PVA (C).