JP6097184B2 - adhesive - Google Patents

Description

The present invention relates to an adhesive having high water resistance and adhesion after bonding and having excellent durability over a long period of time.

Conventionally, a film such as a heat ray reflective film or an optical film is used by adhering to a base material such as resin, metal, glass, etc., and such an adhesive includes EVA, acrylic resin, polyurethane. Such a solvent-type adhesive containing a material and an organic solvent is used.
However, such an adhesive has a problem in water resistance after bonding, and has a problem in durability after a long period of time. In recent years, it has been desired to reduce the use of organic solvents from the viewpoint of environmental impact. From a solvent-type adhesive that uses an organic solvent as a solvent, a water-dispersed adhesive that uses water as a dispersion medium. Conversion to is desired.

As such a water-dispersed pressure-sensitive adhesive, an aqueous dispersion of particles made of acrylic resin and polyurethane is also used, but there is a problem that adhesion to a substrate is poor.
On the other hand, for example, Patent Document 1 describes using a polyvinyl acetate emulsion composition as an adhesive material.
However, polyvinyl alcohol uses polyvinyl alcohol as a protective colloid in the polyvinyl acetate emulsion, and there is a problem in water resistance due to the high hydrophilicity of this polyvinyl alcohol.

Japanese Patent Publication No. 51-20213

An object of the present invention is to provide an adhesive having high water resistance and adhesion after bonding and having excellent durability over a long period of time.

The present invention is an adhesive in which polyvinyl acetal fine particles are dispersed in an aqueous dispersion medium, and the polyvinyl acetal fine particles are made of a polyvinyl acetal resin having an ionic functional group, and have a volume average particle diameter of 10 to 500 nm, and The adhesive has a volume particle size distribution CV value of 40% or less.
The present invention is described in detail below.

In addition to using a polyvinyl acetal resin as a dispersoid, the inventor gives a specific functional group to the resin, and sets the volume average particle diameter and the CV value of the volume average particle diameter within a predetermined range. Thus, the inventors have found that the water resistance and adhesion after bonding are high, and that it is possible to realize excellent durability over a long period of time, and the present invention has been completed.

The adhesive of the present invention contains polyvinyl acetal fine particles made of a polyvinyl acetal resin having an ionic functional group.

The ionic functional group is at least one selected from the group consisting of a carboxyl group, a sulfonic acid group, a sulfinic acid group, a sulfenic acid group, a phosphoric acid group, a phosphonic acid group, an amino group, and a salt thereof. Functional groups are preferred. Of these, carboxyl groups, sulfonic acid groups, and salts thereof are more preferable, and sulfonic acid groups and salts thereof are particularly preferable.

The content of the ionic functional group in the polyvinyl acetal resin is preferably 0.01 to 1 mmol / g. When the content of the ionic functional group is less than 0.01 mmol / g, the dispersibility of the fine particles is lowered, and when it exceeds 1 mmol / g, the adhesive strength may be lowered when a coating is formed. More preferably, it is 0.05-0.5 mmol / g. More preferably, it is 0.2-0.4 mmol / g.

The degree of acetalization of the polyvinyl acetal resin is preferably in the range of 40 to 80 mol% in terms of the total acetalization degree regardless of whether a single aldehyde or a mixed aldehyde is used. If the total degree of acetalization is less than 40 mol%, the resulting polyacetal resin becomes water-soluble and an adhesive composed of an aqueous dispersion may not be formed. When the total degree of acetalization exceeds 80 mol%, the hydrophobicity becomes too strong, and it may be difficult to obtain a stable dispersion. More preferably, it is 55-75 mol%.

In particular, the polyvinyl acetal resin is preferably obtained by acetalizing polyvinyl alcohol having a polymerization degree of 200 to 5000 and a saponification degree of 80 mol% or more. Polyvinyl acetal resins having the above polymerization degree and saponification degree are excellent in the preparation of adhesives, coating properties of the resulting adhesives, adhesiveness, and film-forming properties when dried, and also the strength and flexibility of the formed coating film It will be excellent.

When the degree of polymerization is less than 200, mechanical strength and adhesive strength are reduced when a coating is formed. If the degree of polymerization exceeds 5000, the solution viscosity becomes abnormally high during the acetalization reaction, making the acetalization reaction difficult. The degree of polymerization is more preferably 800-4500.
On the other hand, if the saponification degree is less than 80 mol%, the acetalization reaction becomes difficult because of poor solubility in water, and the acetalization reaction itself becomes difficult because the amount of hydroxyl groups is small. In particular, the saponification degree is more preferably 85 mol% or more.

The acetalization method is not particularly limited, and a conventionally known method can be used. Examples thereof include a method of adding various aldehydes to the aqueous solution of polyvinyl alcohol in the presence of an acid catalyst such as hydrochloric acid.

The aldehyde used for the acetalization is not particularly limited. For example, formaldehyde (including paraformaldehyde), acetaldehyde (including paraacetaldehyde), propionaldehyde, butyraldehyde, amylaldehyde, hexylaldehyde, heptylaldehyde, 2-ethylhexylaldehyde, Examples include cyclohexyl aldehyde, furfural, glyoxal, glutaraldehyde, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, β-phenylpropionaldehyde and the like. Of these, acetaldehyde or butyraldehyde is preferable in terms of productivity and property balance. These aldehydes may be used alone or in combination of two or more.

The existence form of the ionic functional group may be directly present in the polyvinyl acetal resin structure, or may be present in the graft chain of the polyvinyl acetal resin containing a graft chain (hereinafter also simply referred to as a graft copolymer). May be.
In particular, when an ionic functional group is present in the graft chain, the main chain skeleton of the polymer is maintained as polyvinyl acetal, so that the original excellent mechanical properties of the polyvinyl acetal resin are not deteriorated. When it is done, high adhesive strength can be expressed. Moreover, it is possible to prevent the introduced ionic functional group from being altered.

The method for producing a polyvinyl acetal resin in which an ionic functional group is directly present in the polyvinyl acetal resin structure is not particularly limited. For example, the modified polyvinyl alcohol raw material having the ionic functional group is reacted with an aldehyde to be acetalized. Examples thereof include a method, a method of preparing a polyvinyl acetal resin and then reacting it with a compound having another functional group that has reactivity with the functional group of the polyvinyl acetal resin.

The method for producing the graft copolymer is not particularly limited. For example, the polymerizable monomer containing the ionic functional group is placed in the presence of a hydrogen abstraction polymerization initiator in an environment where polyvinyl acetal is present. And radical polymerization.
The said polymerization method is not specifically limited, For example, conventionally well-known polymerization methods, such as solution polymerization, emulsion polymerization, suspension polymerization, block polymerization, are mentioned.
The solvent used for the solution polymerization is not particularly limited, and examples thereof include ethyl acetate, toluene, dimethyl sulfoxide, ethanol, acetone, diethyl ether, tetrahydrofuran, and a mixed solvent thereof.

The hydrogen abstraction polymerization initiator is not particularly limited, but is preferably a t-butyl peroxy peroxide, such as t-butyl peroxypivalate, t-butyl peroxy-2-ethylhexanoate, t-butyl perhexyacetate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxylaurate, t-butyl peroxyisopropyl nomocarbonate, t-butyl peroxyneopenta Noate, t-butylperoxyneodecanate, t-butylperoxy-2-ethylhexyl monocarbonate, 2,2-di (t-butylperoxy) butane, 1,1-di (t-butylperoxy) ) Cyclohexane, t-butyl peroxybenzoate and the like can be used.

The graft chain of the graft copolymer is preferably composed of a polymer of (meth) acrylic monomers. Thereby, the said ionic functional group can be efficiently introduced into the polyvinyl acetal resin. Therefore, the polyvinyl acetal fine particles can exhibit high dispersion stability even in a dispersion medium containing water as a main component.
Specifically, it is preferable to form a graft chain using a (meth) acrylic monomer having an ionic functional group.

Examples of the (meth) acrylic monomer having an ionic functional group include (meth) acrylic acid, (meth) acrylamide, aminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, and 2-sulfoethyl (meth). Acrylate, 3-sulfopropyl (meth) acrylate, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloyloxyethyl acid phosphate, phenyl (2- (meth) acryloyloxyethyl) phosphate, 3 -(Meth) acryloyloxypropylphosphonic acid, sodium (meth) acrylate, potassium (meth) acrylate, 2-sodium sulfoethyl (meth) acrylate, 2-potassium sulfoethyl (meth) acrylate, 3-sodium sulfo Propyl (meth) acrylate, 3-Potassium nitrosium sulfopropyl (meth) acrylate.

Graft ratio in the polyvinyl acetal resin grafted with the polymerizable monomer containing the ionic functional group (the unit of the polymerizable monomer containing the ionic functional group with respect to the unit comprising the polyvinyl acetal in the graft copolymer) The ratio is not particularly limited as long as the content of the ionic functional group in the polyvinyl acetal resin is within the above suitable range, but is preferably 0.001 to 100% by weight. By using it as the said range, when it uses as a dispersoid of an adhesive agent, the adhesive strength of the film | membrane obtained and softness | flexibility can be made compatible.
In the present invention, the “graft ratio” represents the ratio of units composed of a polymerizable monomer containing an ionic functional group to units composed of polyvinyl acetal in the graft copolymer, for example, by the following method. Can be evaluated. The obtained resin solution is dried at 110 ° C. for 1 hour, dissolved in methanol, and the methanol solution is added dropwise to water, and then separated into an insoluble portion and a soluble portion by centrifugation. The insoluble matter obtained at this time is used as a graft copolymer. About the obtained graft copolymer, the weight of the unit which consists of the unit which consists of a unit which consists of polyvinyl acetal, and the polymeric monomer containing an ionic functional group by NMR can be converted, and it can calculate using following formula (1). .

In addition, when a polyvinyl acetal resin in which the ionic functional group is present in the graft chain is used, in addition to the (meth) acrylic monomer having the ionic functional group, another (meth) acrylic monomer is simultaneously added. It may be used.
Examples of the other (meth) acrylic monomers include monofunctional (meth) acrylic acid alkyl esters, monofunctional (meth) acrylic acid cyclic alkyl esters, and monofunctional (meth) acrylic acid aryl esters. .

Examples of the monofunctional (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, and isobutyl. (Meth) acrylate, t-butyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) ) Acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, isotetradecyl (meth) acrylate, 2-isocyanatoethyl methacrylate and the like.
Examples of the monofunctional (meth) acrylic acid cyclic alkyl ester include cyclohexyl (meth) acrylate and isobornyl (meth) acrylate.
Examples of the monofunctional (meth) acrylic acid aryl ester include phenyl (meth) acrylate and benzyl (meth) acrylate.
In the present specification, the (meth) acrylic acid is a generic term for acrylic acid and methacrylic acid, and the (meth) acrylate is a generic term for acrylate and methacrylate.

The graft ratio of other (meth) acrylic monomers in the graft copolymer (ratio of units composed of other (meth) acrylic polymers to units composed of polyvinyl acetal in the graft copolymer) depends on the application. However, it is preferably 900% by weight or less. By using it as the said range, when it uses as a dispersoid of an adhesive agent, the adhesive strength of the film | membrane obtained and softness | flexibility can be made compatible.
In the present invention, “the graft ratio of other (meth) acrylic monomers” represents the ratio of units composed of other (meth) acrylic polymers to units composed of polyvinyl acetal in the graft copolymer, For example, it can be evaluated by the following method. The obtained resin solution is dried at 110 ° C. for 1 hour, then dissolved in xylene, separated into an insoluble part and a soluble part, and the insoluble part is used as a graft copolymer. About the obtained graft copolymer, the weight of the unit which consists of polyvinyl acetal and the unit which consists of another (meth) acrylic-type polymer by NMR can be converted, and it can calculate using following formula (2).

The molecular weight of the polyvinyl acetal resin having an ionic functional group is not particularly limited, but the number average molecular weight (Mn) is 10,000 to 400,000 and the weight average molecular weight (Mw) is 20,000 to 800,000. And it is preferable that these ratios (Mw / Mn) are 2.0-40. When Mn, Mw, and Mw / Mn are within such ranges, when used as a dispersoid of an adhesive, it is possible to achieve both the adhesive strength and flexibility of the resulting film.

The polyvinyl acetal fine particles have a volume average particle diameter having a lower limit of 10 nm and an upper limit of 500 nm. If the volume average particle diameter is less than 10 nm, it is substantially difficult to prepare. If the volume average particle diameter exceeds 500 nm, the sedimentation rate of the fine particles in the dispersion is increased, and a stable dispersion cannot be obtained. The preferable lower limit of the volume average particle diameter is 20 nm, the preferable upper limit is 400 nm, the more preferable lower limit is 30 nm, and the more preferable upper limit is 300 nm.
The volume average particle size of the polyvinyl acetal fine particles can be measured using a laser diffraction / scattering particle size distribution measuring device or the like.

The upper limit of the CV value of the volume average particle diameter of the polyvinyl acetal fine particles is 40%. When the CV value exceeds 40%, fine particles having a large particle diameter exist, and a stable dispersion cannot be obtained by the precipitation of the large particle diameter particles.
The preferable upper limit of the CV value is 35%, the more preferable upper limit is 32%, and the more preferable upper limit is 30%. The CV value is a numerical value indicated by a percentage (%) of a value obtained by dividing the standard deviation by the average particle diameter.

It does not specifically limit as a method of manufacturing the said polyvinyl acetal microparticles | fine-particles, For example, after obtaining the polyvinyl acetal resin which has an ionic functional group, it can manufacture by granulating the said polyvinyl acetal resin.

Examples of a method for obtaining the polyvinyl acetal resin having an ionic functional group include, for example, a method of reacting an aldehyde with the modified polyvinyl alcohol raw material having an ionic functional group to acetalize, and after producing a polyvinyl acetal resin, the polyvinyl acetal A method of reacting with a compound having another functional group reactive to the functional group of the resin, and grafting a polymerizable monomer containing the above ionic functional group onto the polyvinyl acetal resin using a hydrogen abstraction initiator And the like.
Especially, the mechanical properties inherent to the polyvinyl acetal resin are not deteriorated, high mechanical properties can be expressed when formed into a coating, and the introduced functional group is not altered. The grafting method is particularly preferred.

The polyvinyl acetal resin can be made into particles by dissolving the polyvinyl acetal resin having an ionic functional group in an organic solvent, adding water little by little, and removing the organic solvent by heating and / or decompressing. Or a method of removing an organic solvent by heating and / or decompressing as necessary after adding a solution in which a polyvinyl acetal resin having an ionic functional group is dissolved in a large amount of water, and having an ionic functional group Examples thereof include a method in which the polyvinyl acetal resin is heated at a temperature equal to or higher than the glass transition temperature of the polyvinyl acetal resin having an ionic functional group and kneaded with a kneader or the like, and water is added little by little under heat and pressure.

Examples of the organic solvent include tetrahydrofuran, acetone, toluene, methyl ethyl ketone, ethyl acetate, alcohols such as methanol, ethanol, butanol, and isopropyl alcohol.

The adhesive of the present invention contains an aqueous dispersion medium.
The aqueous dispersion medium may contain water as a main component, or may be a mixed solvent of water and an organic solvent. When the organic solvent is contained, if the amount of the organic solvent is too large, the storage stability of the adhesive is lowered. Therefore, the content of the organic solvent in the adhesive is preferably 40% by weight or less. More preferably, it is 30% by weight or less.

Examples of the organic solvent used in the aqueous dispersion medium include alcohols such as methanol, ethanol, butanol, and isopropyl alcohol, tetrahydrofuran, acetone, toluene, methyl ethyl ketone, and ethyl acetate.

The water content in the adhesive of the present invention is 40 to 1000 parts by weight with respect to 100 parts by weight of the polyvinyl acetal fine particles. If the amount of water is too small, the solid content concentration becomes too high and the dispersibility is lowered, or the viscosity of the adhesive becomes too high and the coatability is lowered. If the amount is too large, the concentration of the solid content decreases, so that the film obtained after coating may be non-uniform.
The adhesive of the present invention has sufficient dispersion stability, but a dispersant may be added separately as long as the adhesive strength of the resulting coating is not deteriorated.

The adhesive of the present invention may contain additives such as an antioxidant, a light stabilizer, a surfactant, a flame retardant, an antistatic agent, a moisture-resistant agent, a heat ray reflective agent, and a heat ray absorbent, as necessary. Good.
The antioxidant is not particularly limited, and examples of the phenol-based antioxidant include 2,6-di-tert-butyl-P-cresol (BHT) (Sumitomo Chemical Co., Sumirider BHT), tetrakis- [ Methylene-3- (3′-5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane (manufactured by Ciba Geigy, Irganox 1010) and the like. The minimum with preferable content of the said antioxidant is 0.01 weight part, and an upper limit is 5.0 weight part.

According to the present invention, an adhesive having high water resistance and adhesion after bonding and excellent durability over a long period can be obtained.

Examples of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1
In a reaction vessel equipped with a thermometer, a stirrer, a nitrogen introduction tube, and a cooling tube, polyvinyl acetal resin (polymerization degree 800, acetalization degree [butyralization degree] 65 mol%, hydroxyl group amount 33.8 mol%, acetyl group amount 1.2 mol%) 25 parts by weight, 1 part by weight of 2-sodium sulfoethyl methacrylate and 100 parts by weight of dimethyl sulfoxide were added, and polyvinyl butyral and 2-sodium sulfoethyl methacrylate were dissolved while stirring. Next, nitrogen gas was blown for 30 minutes to replace the inside of the reaction vessel with nitrogen, and then the inside of the reaction vessel was heated to 85 ° C. while stirring. After 30 minutes, 0.5 parts by weight of t-butylperoxy-2-ethylhexanoate as a polymerization initiator was diluted with 5 parts by weight of dimethyl sulfoxide, and the resulting polymerization initiator solution was placed in the reactor. Over 3 hours. Thereafter, the mixture was further reacted at 85 ° C. for 3 hours. After cooling the reaction solution, it was precipitated in water three times and then sufficiently dried to obtain a polyvinyl acetal resin composed of a polyvinyl acetal resin grafted with 2-sodium sulfoethyl methacrylate. It was 0.1 mmol / g when the quantity of the ionic functional group contained in the obtained polyvinyl acetal resin was measured by NMR.
Next, 10 parts by weight of the obtained polyvinyl acetal resin was dissolved in 150 parts by weight of methanol, and the solution was added dropwise to 300 parts by weight of water. Next, the liquid temperature was kept at 30 ° C., and the methanol was volatilized by stirring while reducing the pressure. Then, the solution was concentrated until the solid content became 20% by weight to prepare an adhesive in which polyvinyl acetal fine particles were dispersed.

(Example 2)
100 parts by weight of polyvinyl alcohol having a degree of polymerization of 800 and a degree of saponification of 99 mol% and 1 mol% of acrylic acid as a copolymer is added to 1000 parts by weight of pure water and dissolved by stirring at a temperature of 90 ° C. for about 2 hours. I let you. The solution was cooled to 40 ° C., 80 parts by weight of 35% by weight hydrochloric acid was added thereto, the liquid temperature was lowered to 4 ° C., 70 parts by weight of n-butyraldehyde was added, and this temperature was maintained and acetal was maintained. The reaction product was precipitated by the reaction. Thereafter, the liquid temperature was maintained at 30 ° C. for 3 hours to complete the reaction, and after neutralization, washing with water and drying, a white powder of polyvinyl acetal resin was obtained. When the obtained polyvinyl acetal resin was measured using NMR, the degree of butyralization was 67 mol%, the amount of hydroxyl group was 32 mol%, the amount of acetyl group was 1 mol%, and the ionic functional group contained in the resin. The amount of was 0.15 mmol / g.
Next, using the obtained polyvinyl acetal resin, an adhesive in which polyvinyl acetal fine particles were dispersed was produced in the same manner as in Example 1.

(Example 3)
The same operation as in Example 1 was performed except that the polyvinyl acetal resin having a polymerization degree of 3300, a butyralization degree of 67 mol%, a hydroxyl group content of 32 mol%, and an acetyl group content of 1 mol% was obtained. Polyvinyl acetal resin fine particles comprising a grafted polyvinyl acetal resin were obtained. It was 0.15 mmol / g when the quantity of the ionic functional group contained in the obtained resin was measured by NMR.
Using the obtained polyvinyl acetal resin, an adhesive in which polyvinyl acetal fine particles were dispersed was prepared in the same manner as in Example 1.

(Comparative Example 1)
30 parts by weight of polyvinyl alcohol as a solute was added to 100 parts by weight of water, and then heated and dissolved at 90 ° C. for 30 minutes to prepare an adhesive.
In Comparative Example 1, polyvinyl alcohol was dissolved in water, and particles made of polyvinyl alcohol were not formed.

(Comparative Example 2)
30 parts by weight of methyl methacrylate was used as an oil phase component, and 100 parts by weight of water and 0.3 part by weight of sodium lauryl sulfate were dissolved to prepare an aqueous phase component. The oil phase component and the aqueous phase component are emulsified with a homogenizer, heated to 70 ° C. with stirring, and when 70 ° C. is reached, 0.3 part by weight of potassium persulfate is added, and a polymerization reaction is carried out for 12 hours. An adhesive in which particles made of resin were dispersed was produced.

(Comparative Example 3)
100 parts by weight of polyvinyl alcohol having a polymerization degree of 1000 and a saponification degree of 99 mol% was added to 1000 parts by weight of pure water, and the mixture was stirred and dissolved at a temperature of 90 ° C. for about 2 hours.
The solution was cooled to 40 ° C., 80 parts by weight of 35% by weight hydrochloric acid was added thereto, the liquid temperature was lowered to 4 ° C., 70 parts by weight of n-butyraldehyde was added, and this temperature was maintained and acetal was maintained. The reaction product was precipitated by the reaction.
Thereafter, the liquid temperature is maintained at 30 ° C. for 3 hours to complete the reaction, and after neutralization, washing with water and drying by a conventional method, the degree of butyralization is 68 mol%, the hydroxyl amount is 31 mol%, and the acetyl group amount is 1 mol%. A certain polyvinyl acetal resin powder was obtained.
Next, using the obtained polyvinyl acetal resin, an adhesive in which polyvinyl acetal fine particles were dispersed was produced in the same manner as in Example 1.

(Comparative Example 4)
10 parts by weight of polyvinyl butyral resin having no ionic functional group as a solute (degree of polymerization 800, degree of acetalization 68 mol%, hydroxyl content 31 mol%, acetyl group content 1 mol%) is dissolved in 100 parts by weight of toluene and bonded. An agent was prepared.
In Comparative Example 4, the polyvinyl butyral resin was dissolved in toluene, and particles made of the polyvinyl butyral resin were not formed.

(Evaluation method)
The performance of the obtained adhesive was evaluated by the following method. The results are shown in Table 1.

(1) Measurement of particle size The volume average particle size and volume particle size distribution of the resin fine particles contained in the adhesive were measured using a laser diffraction / scattering particle size distribution measuring device (LA-950, manufactured by Horiba, Ltd.). .

(2) Evaluation of water resistance The obtained adhesive was wet-coated using a bar coater on a 1.5 cm × 6 cm glass plate, respectively, so that the film thickness was 300 μm. Then, it was dried at 80 ° C. for 30 minutes. After the obtained adhesive was poured for 30 minutes with running water, the water resistance was evaluated by observing the ratio of the remaining area of the adhesive (the ratio of the remaining area to the area where the film was formed).
○: Remaining area is 50% or more Δ: Remaining area is 5% or more and less than 50% ×: Remaining area is less than 5%

(3) Adhesion evaluation Adhesive tape (manufactured by Sekisui Chemical Co., Ltd., cello tape (registered trademark) No. 252) is pasted on the surface of the film-formed glass plate prepared in “(2) Water resistance evaluation”. The tape was gently removed after 10 minutes. The adhesiveness was evaluated by observing the remaining area ratio of the adhesive (the ratio of the remaining area to the area where the film was formed).
◎: Residual area is 70% or more ○: Residual area is 50% or more and less than 70% △: Residual area is 30% or more and less than 50% ×: Residual area is less than 30%

(4) Durability Evaluation The obtained adhesive was wet coated on a 1.5 cm × 6 cm glass plate using a bar coater so that the film thickness was 300 μm. Then, it was dried at 80 ° C. for 30 minutes. The resulting adhesive was visually observed for changes in the adhesive after 100 hours at 50 ° C. in a constant temperature oven. The case where yellowing was observed was evaluated as “◯”, and the case where yellowing was not observed was evaluated as “x”.
○: Yellowing ×: No yellowing

According to the present invention, it is possible to provide an adhesive having high water resistance and adhesion after bonding and having excellent durability over a long period of time.

Claims (5)

An adhesive in which polyvinyl acetal fine particles are dispersed in an aqueous dispersion medium,
The said polyvinyl acetal microparticles | fine-particles consist of polyvinyl acetal resin which has an ionic functional group, The volume average particle diameter is 10-500 nm, CV value of volume particle diameter distribution is 40% or less, The adhesive agent characterized by the above-mentioned. The ionic functional group is at least one functional group selected from the group consisting of a carboxyl group, a sulfonic acid group, a sulfinic acid group, a sulfenic acid group, a phosphoric acid group, a phosphonic acid group, an amino group, and a salt thereof. The adhesive according to claim 1, wherein The adhesive according to claim 1 or 2, wherein the polyvinyl acetal resin is a graft copolymer including a graft chain having an ionic functional group. The adhesive according to claim 3, wherein the graft chain is made of a polymer of a (meth) acrylic monomer. The adhesive according to claim 1, 2, 3 or 4, wherein the content of the ionic functional group of the polyvinyl acetal resin is 0.01 to 1 mmol / g.