JP2008013676A - Polyvinyl acetal resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyvinyl acetal resin which can give a coating solution having such excellent applicability that coating unevenness due to film thickness fluctuation and film break during coating do not occur. <P>SOLUTION: The polyvinyl acetal resin is one synthesized by the acetalization of a polyvinyl alcohol with an aldehyde, wherein the degree of polymerization is 300-3,000, the polydispersity index (Mw/Mn) as measured by gel permeation chromatography (GPC) is 5.0-10.0, and the complex modulus G' at a shear stress of 220 Pa is 0.2-0.9 Pa when measured in a resin solution obtained by dissolving the polyvinyl acetal resin in methyl ethyl ketone and having solution viscosity of 3,700 mPa s as measured with a Brookfield viscometer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polyvinyl acetal resin capable of obtaining a coating solution having excellent coating properties.

  Polyvinyl butyral resin is suitably used in various fields that require a coating process because of its good solubility in various solvents and excellent dispersibility of metals and inorganic powders.

  However, when a general polyvinyl acetal resin is adjusted to a specific viscosity for coating, an attempt to increase the coating speed in order to increase productivity may cause coating unevenness due to film thickness variation, or In addition, there is a problem in that air bubbles are involved between the support and the coating solution to be applied, resulting in problems such as film breakage of the coating solution and a decrease in coating productivity.

Japanese Patent Publication No.43-4924

  The present invention provides a polyvinyl acetal resin capable of obtaining a coating solution having excellent coating properties without causing coating unevenness due to film thickness fluctuation or film breakage during coating.

  The polyvinyl acetal resin of the present invention is a polyvinyl acetal resin synthesized by acetalization reaction between polyvinyl alcohol and an aldehyde, having a polymerization degree of 300 to 3000 and a molecular weight dispersity (Mw / M) by gel permeation chromatography (GPC). Mn) is 5.0 to 10.0, and a complex elastic modulus G at a shear stress of 220 Pa in a resin solution obtained by dissolving the polyvinyl acetal resin in methyl ethyl ketone and having a solution viscosity by a B-type viscometer of 3700 mPas. 'Is 0.2 to 0.9 Pa.

  When the degree of polymerization of the polyvinyl acetal resin of the present invention is small, the film strength obtained from the coating solution using the polyvinyl acetal resin is reduced. On the other hand, when the polymerization degree is large, the degree of polymerization is obtained from the coating solution using the polyvinyl acetal resin. Since a film thickness becomes thin too much, it is limited to 300-3000, and 400-2000 are preferable.

  Moreover, when the molecular weight dispersity (Mw / Mn) by the gel permeation chromatography (GPC) in the polyvinyl acetal resin of the present invention is small, the film breaks during coating of the coating solution obtained using the polyvinyl acetal resin. On the other hand, if it is large, coating unevenness occurs during the coating of the coating solution obtained using the polyvinyl acetal resin, so it is limited to 5.0 to 10.0, and preferably 5.0 to 8.0. In addition, the molecular weight dispersity (Mw / Mn) by the gel permeation chromatography (GPC) in polyvinyl acetal resin means what was measured using the gel permeation chromatography developed with tetrahydrofuran. In addition, Mw means a weight average molecular weight and Mn means a number average molecular weight.

  Then, in a resin solution obtained by dissolving the polyvinyl acetal resin of the present invention in methyl ethyl ketone, the complex elastic modulus G ′ at a shear stress of 220 Pa when adjusted so that the solution viscosity by a B-type viscometer is 3700 mPas is 0 Limited to 2 to 0.9 Pa.

  When the complex elastic modulus G ′ of the resin solution is low, film breakage occurs when the coating solution obtained using the polyvinyl acetal resin is applied. On the other hand, when the complex elastic modulus G ′ is high, the resin solution is obtained using the polyvinyl acetal resin. This is because coating unevenness occurs when the coating solution is applied.

  Here, the complex elastic modulus G ′ of the resin solution is measured in the following manner. First, a polyvinyl acetal resin is dissolved in methyl ethyl ketone to prepare a resin solution. At this time, the resin viscosity of the resin solution is adjusted to 3700 mPas with a B-type viscometer.

  Then, the viscoelasticity of the resin solution is measured using a rheometer under the conditions of a frequency of 1 Hz and a shear stress of 0.1 to 1000 Pa, and a complex elastic modulus G ′ when the shear stress is 220 Pa can be obtained. In addition, as a rheometer, what is marketed by the brand name "Gemini150" from BOHLIN INSTRUMENTS can be used, for example.

  The polyvinyl acetal resin is synthesized by acetalization reaction between polyvinyl alcohol and aldehyde. Specifically, in general, water, alcohol, a mixed solution of water and alcohol, and dimethyl sulfoxide (DMSO) Etc., by reacting polyvinyl alcohol and aldehyde in the presence of an acid catalyst.

  Polyvinyl alcohol is usually obtained by saponifying polyvinyl acetate, and simultaneously performing saponification and acetalization of polyvinyl acetate to obtain a polyvinyl acetal resin all at once from polyvinyl acetate, Alternatively, polyvinyl alcohol obtained by saponifying polyvinyl acetate may be once taken out and reacted with aldehyde.

  As the aldehyde, any aldehyde that can be acetalized, such as formaldehyde, acetaldehyde, butyraldehyde, and propylaldehyde, may be used, but n-butyraldehyde and acetaldehyde are preferable. In addition, an aldehyde may be used independently or 2 or more types may be used together.

  The acid catalyst is not particularly limited, and either an organic acid or an inorganic acid can be used. Examples thereof include acetic acid, paratoluenesulfonic acid, nitric acid, sulfuric acid, and hydrochloric acid. In order to stop the above synthesis reaction, alkali neutralization is usually performed. Examples of the alkali used in this case include sodium hydroxide, potassium hydroxide, ammonia, sodium acetate, sodium carbonate, hydrogen carbonate. Sodium, potassium carbonate, potassium hydrogencarbonate, etc. are mentioned.

  And in order to obtain the polyvinyl acetal resin of this invention, after mixing the polyvinyl alcohol which has 2 or more types of different polymerization degrees, it is preferable to make these polyvinyl alcohol and aldehyde carry out the acetalization reaction.

  In this way, polyvinyl alcohol having two or more different degrees of polymerization and aldehyde are reacted, or crosslinkable monomers such as polyfunctional aldehyde and polyfunctional isocyanate are added in an amount of 0.001 to 0.02 mol% based on the total amount of aldehyde. The polyvinyl acetal resin of the present invention can be obtained by introducing a partial intermolecular cross-linking structure by acetalization reaction of polyvinyl alcohol containing an acetoacetyl group having self-crosslinking property and an aldehyde. Can do.

  Examples of the polyfunctional aldehyde include glutaraldehyde, and examples of the polyfunctional isocyanate include toluene 2,4-diisocyanate, 1,6-diisocyanate hexane, isoformyl diisocyanate, and diphenylmethane diisocyanate. Can be mentioned.

  Further, as a composition component of the polyvinyl acetal resin, the ratio of the remaining acetyl group is 0 in both cases where the acetal group is counted as one side chain and when the acetal group is counted as two acetalized hydroxyl groups. It is preferably ˜25 mol%, and the ratio of the remaining hydroxyl group is preferably 17 to 35 mol% from the viewpoint of solubility in various solvents and coating suitability.

  In addition, if the amount of the aldehyde remaining in the polyvinyl acetal resin of the present invention and the total amount of the aldehyde dimer compound are large, an inherent odor is emitted. From the viewpoint of environmental hygiene, the total weight of the polyvinyl acetal resin It is preferably 300 ppm or less.

  In order to use the polyvinyl acetal resin thus obtained as a coating solution, it can be obtained by dissolving the polyvinyl acetal resin in a solvent suitable for the application. Moreover, it can also mix | blend with another material according to a use.

  The support for applying the coating solution obtained using the polyvinyl acetal resin is not particularly limited, and examples thereof include polyethylene terephthalate, polycarbonate, polyethylene, polyvinyl acetal, cellulose ester, cellulose triacetate, nitrocellulose, and polyethylene naphthalate. Examples thereof include a synthetic resin film such as phthalate, a metal plate such as glass, paper, and an aluminum plate.

  Since the polyvinyl acetal resin of the present invention has the configuration as described above, it is possible to obtain a coating solution having excellent coating properties without causing coating unevenness due to film thickness fluctuations or film breakage during coating. it can.

(Example 1)
10 parts by weight of polyvinyl alcohol having a degree of polymerization of 300 and 98 mol% saponification, 75 parts by weight of polyvinyl alcohol having a degree of polymerization of 500 and 98 mol% of saponification, and 15 of polyvinyl alcohol having a degree of polymerization of 800 and 98 mol% of saponification A resin solution was prepared by heating and dissolving in 700 parts by weight of distilled water. While maintaining the resin solution at 20 ° C., 29 parts by weight of 35% by weight hydrochloric acid was added to the resin solution, 14 parts by weight of aldehyde was added.

  Next, the resin solution was cooled to 12 ° C., and 64 parts by weight of butyraldehyde was added to the resin solution. After the polyvinyl butyral resin was precipitated in the resin solution, it was held for 30 minutes, and then 108 parts by weight of hydrochloric acid was added to the resin solution, heated to 30 ° C. and held for 10 hours.

  After completion of the reaction, the polyvinyl butyral resin in the resin solution was washed with distilled water, and sodium hydroxide was added to the polyvinyl butyral resin dispersion after washing to adjust the pH of the polyvinyl butyral resin dispersion to 7. Thereafter, the polyvinyl butyral resin dispersion was kept at 60 ° C. for 10 hours and then cooled. The pH of the polyvinyl butyral resin dispersion at this time was 6.5.

  Subsequently, the polyvinyl butyral resin dispersion was washed with 100 times the amount of distilled water with respect to the solid content, and the polyvinyl butyral resin dispersion was held at 50 ° C. for 5 hours, and then 10 times the amount of distilled water. The product was washed with water, dehydrated and dried to obtain a polyvinyl butyral resin A.

  The obtained polyvinyl butyral resin A has a polymerization degree of 525, a residual hydroxyl group amount of 22 mol%, a residual acetyl group amount of 1.5 mol%, and a molecular weight dispersity (Mw / Mn) by GPC of 5.4. there were. Further, a polyvinyl butyral resin A was dissolved in methyl ethyl ketone so that the solution viscosity by a B-type viscometer was 3700 mPas to prepare a resin solution.

  Next, using a rheometer (trade name “Gemini 150” manufactured by BOHLIN INSTRUMENTS), the viscoelasticity of the resin solution was measured under conditions of a frequency of 1 Hz and a shear stress of 0.1 to 1000 Pa. The complex elastic modulus G ′ of was 0.8 Pa.

(Example 2)
As polyvinyl alcohol, 10 parts by weight of polyvinyl alcohol having a polymerization degree of 300 and a saponification degree of 98 mol% and 90 parts by weight of polyvinyl alcohol having a polymerization degree of 500 and a saponification degree of 98 mol% were used together with 64 parts by weight of butyraldehyde. A polyvinyl butyral resin B was obtained in the same manner as in Example 1 except that 0.005 part by weight of glutaraldehyde was added.

  The obtained polyvinyl butyral resin B had a polymerization degree of 480, a residual hydroxyl group amount of 22 mol%, a residual acetyl group amount of 1.5 mol%, and a molecular weight dispersity (Mw / Mn) by GPC of 5.6. It was. Further, when polyvinyl butyral resin B was dissolved in methyl ethyl ketone so that the solution viscosity by a B-type viscometer was 3700 mPas, a resin solution was prepared, and the viscoelasticity of the resin solution was measured in the same manner as in Example 1. The complex elastic modulus G ′ at a stress of 220 Pa was 0.6 Pa.

(Comparative Example 1)
A polyvinyl butyral resin C was obtained in the same manner as in Example 1 except that 100 parts by weight of polyvinyl alcohol having a polymerization degree of 500 and a saponification degree of 98 mol% was used as the polyvinyl alcohol.

  The obtained polyvinyl butyral resin C had a degree of polymerization of 500, a residual hydroxyl group amount of 22 mol%, a residual acetyl group amount of 1.5 mol%, and a molecular weight dispersity (Mw / Mn) by GPC of 5.4. It was. Moreover, when polyvinyl butyral resin C was dissolved in methyl ethyl ketone so that the solution viscosity by a B-type viscometer was 3700 mPas, a resin solution was prepared, and the viscoelasticity of the resin solution was measured in the same manner as in Example 1. The complex elastic modulus G ′ at a stress of 220 Pa was 0.1 Pa.

  Using the polyvinyl butyral resin obtained as described above, a coating solution was prepared in the following manner.

(Preparation of coating solution)
30 parts by weight of polyvinyl butyral resin and 70 parts by weight of diethyl ketone were supplied to a ball mill and stirred and mixed for 24 hours to obtain a coating solution.

(Preparation of coated film)
The coating solution was applied onto a polyester substrate using an automatic bar coater so that the thickness after drying was 10 μm and dried. The coating films obtained in Examples 1 and 2 had no coating unevenness. On the other hand, some coating unevenness was confirmed in the coating film obtained in Comparative Example 1.

Claims (1)

Polyvinyl acetal resin synthesized by acetalization reaction of polyvinyl alcohol and aldehyde, having a polymerization degree of 300 to 3000 and a molecular weight dispersity (Mw / Mn) by gel permeation chromatography (GPC) of 5.0 to 10 The complex elastic modulus G ′ at a shearing stress of 220 Pa in a resin solution obtained by dissolving the polyvinyl acetal resin in methyl ethyl ketone and having a solution viscosity of 3700 mPas by a B-type viscometer is 0.2 to 0.00. Polyvinyl acetal resin characterized by being 9 Pa.