JP2000109784A - Emulsion type adhesive or adhesive composition, and pressure sensitive adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an adhesive or an adhesive composition excellent in properties of hardly causing whitening even if the adhesive or the adhesive composition is dipped in water or absorbs moisture by constituting the adhesive or the adhesive composition of an emulsion obtained by regulating a mean particle diameter of dispersed particles and so as to have a narrow distribution of the particle diameters. SOLUTION: This adhesive (composition) is composed of an emulsion having <=0.3, preferably 0.01-0.28 μm weighted mean particle diameter of dispersed particles, and 1.0-1.5, preferably 1.0-1.4, more preferably 1.0-1.3, most preferably 1.0-1.15 ratio of the weighted mean particle diameter to an arithmetical mean particle diameter (weighted mean particle diameter/arithmetical mean particle diameter), and providing a film containing preferably >=40, more preferably 45-90, most preferably 50-85 wt.% toluene-insoluble component. A polymer composed of a constituent monomer consisting essentially of an alkyl (meth)acrylate, a polymer composed of a constituent monomer consisting essentially of ethylene and a vinyl ester-based monomer, or the like, is cited as the dispersed particle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an emulsion-type pressure-sensitive adhesive, an adhesive composition, and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition. The present invention relates to a pressure-sensitive adhesive and a composition for providing an adhesive excellent in hardly whitening performance (hereinafter, referred to as whitening resistance) and a pressure-sensitive adhesive sheet.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of environmental hygiene and the like, emulsion-type adhesives have been used in place of organic solvent-type adhesives and adhesives (hereinafter, adhesives and adhesives are collectively referred to as adhesives). Agents are becoming widely used. However, emulsion-type adhesives generally tend to have lower water resistance than solvent-type adhesives. For this reason, when used under the condition of being exposed to water or moisture, an organic solvent type adhesive is often used. In particular, when an emulsion-type adhesive is used as an adhesive for an adhesive sheet using a transparent substrate or as an adhesive for bonding a transparent material, it is whitened by immersion in water or absorbing moisture. Has the problem of being damaged.

Conventionally, as a method for improving the whitening resistance of an emulsion type adhesive, a method of reducing the diameter of the dispersed particles of the emulsion, a method of increasing the crosslink density of the adhesive, a surfactant, etc. Methods for reducing the amount of the hydrophilic compound used are known.

For example, a particle size of 0.001 to 0.009 μm
Pressure-sensitive adhesive composition comprising a colloidal acrylic emulsion and a crosslinking agent (JP-A-62-297372), an aqueous emulsion having an average particle size of 100 nm (0.1 μm) or less and having a crosslinked structure is essential. Pressure-sensitive adhesive composition comprising an acrylic copolymer having an average particle size of 0.3 μm or less and a gel fraction of 40% by weight or more (JP-A-7-26229) and the like have been proposed.

[0005] In the art, simply referring to the particle size or the average particle size usually refers to the weight average particle size, and since these publications do not particularly describe the meaning of the average particle size, they are described in the above publications. Particle size or average particle size,
All are considered to be used in the meaning of the weight average particle size. It is known to reduce the average particle size of the dispersed particles of the emulsion in order to improve water resistance, as in the examples of the above-mentioned known documents, but none of them has yet sufficiently achieved the whitening resistance improving effect. .

[0006]

DISCLOSURE OF THE INVENTION The present invention has been studied in order to obtain an adhesive composition and a pressure-sensitive adhesive sheet having excellent whitening resistance.

[0007]

Means for Solving the Problems The present inventors control the average particle size of the dispersed particles of the emulsion and, when the distribution of the particle size is controlled to be narrow, control the dispersion of the emulsion. The present invention was completed by finding that a pressure-sensitive adhesive having as a main component has good whitening resistance.

That is, in the first invention of the present application, the ratio of the weight average particle diameter to the arithmetic average particle diameter (weight average particle diameter / arithmetic average particle diameter) is 1 when the weight average particle diameter of the dispersed particles is 0.3 μm or less. A pressure-sensitive adhesive composition comprising an emulsion having a viscosity of from 0.0 to 1.5 (hereinafter, referred to as the present composition).
It is about.

The second invention according to the present invention relates to the adhesive composition according to the first invention, wherein the emulsion formed from the emulsion has a toluene-insoluble content of 40% by weight or more. It is.

In a third aspect of the present invention, in the first aspect, the dispersed particles comprise the following monomers (a), (b) and (c) and a copolymer having the following constituent monomers and constituent ratios. The present invention relates to a characteristic adhesive composition. (A) Alkyl acrylate or alkyl methacrylate monomers 45 to 9 having an alkyl group having 4 to 12 carbon atoms
7% by weight (b) 0.1-10% by weight of α, β-unsaturated carboxylic acid monomer (c) 2.9-% radical polymerizable monomer having a cyclic structure other than (a) and (b) 30% by weight

In a fourth aspect of the present invention, in the first aspect, the emulsion contains 0.05 to 5 parts by weight of a nonionic surfactant with respect to 100 parts by weight of the polymer forming dispersed particles. And a pressure-sensitive adhesive.

The fifth invention of the present application relates to a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to claim 1 on a surface of a transparent substrate.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

(1) Definition of Average Particle Size and Particle Size Distribution In the present application, the weight average particle size and the arithmetic average particle size are described in, for example, the Chemical Dictionary (published by Kyoritsu Shuppan Co., Ltd.). ⁴ / Σnd ³ ) and (Σnd / Σ
(In both formulas, n represents the number of particles, and d represents the particle size (diameter).) The ratio of the weight average particle size to the arithmetic average particle size (weight average particle size / arithmetic average particle size) is hereinafter referred to as a particle size distribution. The average particle size and the particle size distribution in the present application are measured by a laser diffraction / scattering type particle size distribution analyzer LA-910 manufactured by HORIBA or ELS-8 manufactured by Otsuka Electronics.
00 was measured. The weight average particle size and the arithmetic average particle size in the present application are obtained as volume-based average particle size and number-based average particle size, respectively, in LA-910 manufactured by HORIBA.

(2) Weight Average Particle Size and Particle Size Distribution In the composition of the present invention, the dispersed particles have a weight average particle size of 0.3 μm.
Hereinafter, an emulsion having a particle size distribution of 1.0 to 1.5 is used as a component. The emulsion as a component of the composition of the present invention has a weight average particle size of the dispersed particles of 0.0
It is preferably from 0.1 to 0.28 μm, and from 0.05 to
Those having a thickness of 0.26 μm are more preferred. The reason is,
Those having a weight average particle size of 0.28 μm or less have better whitening resistance, and those having a weight average particle size of 0.26 μm or less have particularly good whitening resistance. This is because production of the adhesive composition may be difficult.

The emulsion which is a component of the composition of the present invention preferably has a particle size distribution of dispersed particles of 1.0 to 1.4, more preferably 1.0 to 1.3, and more preferably 1 to 1.3. It is most preferable that the ratio is from 0.0 to 1.15. The reason is that those having a particle size distribution of 1.4 or less have better whitening resistance, and those having a particle size distribution of 1.3 or less have particularly good whitening resistance. It is because it becomes the best.

The composition of the present invention comprises an emulsion in which the dispersed particles have a weight average particle size of 0.3 μm or less and a particle size distribution of 1.0 to 1.5. An emulsion having dispersed particles that do not meet the above-mentioned conditions of the weight average particle diameter or the particle size distribution is added in an amount of less than 10% by weight of all the particles for the purpose of adjustment. There may be. The addition of an emulsion in an amount of 10% by weight or more of particles that do not meet the conditions should be avoided because the whitening resistance is poor. The content ratio of the added particles that do not correspond to the conditions of the weight average particle size or the particle size distribution can be confirmed by a particle size-frequency graph obtained by the particle size distribution measuring device.

(3) Toluene-Insoluble Content The emulsion in the composition of the present invention preferably has a toluene-insoluble content (hereinafter, referred to as a gel fraction) of a film obtained by drying the emulsion of not less than 40% by weight. 45-
Those having 90% by weight are more preferred, and those having 50 to 85% by weight are even more preferred. That is, the gel fraction is 4
When it is 0% by weight or more, the whitening resistance is good, and
When the content is not less than 5% by weight, the whitening resistance is better, and
When the content is 0% by weight or more, the whitening resistance is more excellent.
Further, when the gel fraction is 90% by weight or less, the adhesive strength or the adhesive strength becomes large, and when the gel fraction is 85% by weight or less, the effect becomes remarkable. The gel fraction can be measured, for example, by the method described in Examples described later.

(4) Structure of Dispersion Particles of Emulsion The structure of the dispersion particles of the emulsion in the present composition is not particularly limited, and alkyl acrylate or alkyl methacrylate (hereinafter, these are collectively referred to as alkyl (meth) acrylate). (Hereinafter referred to as an acrylic polymer), a polymer having ethylene and a vinyl ester monomer as a main constituent monomer (hereinafter referred to as an ethylene-vinyl ester polymer). ), A polymer having a conjugated diene-based monomer or a monomer copolymerizable with the conjugated diene-based monomer as a main constituent monomer (hereinafter, referred to as a conjugated diene-based polymer). it can.

Examples of the vinyl ester monomer include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl laurate, vinyl versatate, and the like. Of these, vinyl acetate is a preferred monomer. . As the conjugated diene monomer, butadiene,
Examples include isoprene, chloroprene, and isobutylene.

In the present invention, the dispersed particles of the emulsion are preferably made of an acrylic polymer because it is easy to obtain an adhesive having excellent transparency, and the polymer is preferably selected from the following (a), (b) and ( Those comprising a copolymer containing c) as a constituent monomer are preferred because a tacky adhesive having particularly excellent transparency is easily obtained. (A) Alkyl (meth) acrylate having an alkyl group having 4 to 12 carbon atoms (b) α, β-unsaturated carboxylic acid (hereinafter referred to as unsaturated carboxylic acid) (c) Other than (a) and (b) Radical polymerizable monomer having a cyclic structure (hereinafter, referred to as a cyclic structure-containing monomer)

Examples of the alkyl (meth) acrylate having an alkyl group having 4 to 12 carbon atoms include n-butyl (meth) acrylate, i-butyl (meth) acrylate, n-hexyl (meth) acrylate, and n-octyl ( (Meth) acrylate, i-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-
Nonyl (meth) acrylate, i-nonyl (meth) acrylate, n-decyl (meth) acrylate, n-lauryl (meth) acrylate, and the like can be used, and one or more of these can be used. Of these, alkyl (meth) acrylates having an alkyl group having 4 to 9 carbon atoms are preferable because of good polymerizability and the resulting adhesive has high adhesive strength or adhesive strength.

As the unsaturated carboxylic acid, acrylic acid,
Examples thereof include methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, cinnamic acid, and maleic anhydride, and one or more of these can be used. Of these, acrylic acid and methacrylic acid are preferred because they are inexpensive and the resulting adhesive has good performance.

Among the ring structure-containing monomers, examples of the radical polymerizable monomer having an aromatic ring include styrene, vinyl toluene, divinyl toluene, α-methyl styrene, paramethyl styrene, chlorostyrene, and vinyl dibenzyl chloride. And benzyl (meth) acrylate. Among them, styrene is preferable because it is inexpensive and the performance of the obtained adhesive is good. Examples of the radically polymerizable monomer having an aliphatic ring include cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, and the like. Of these, cyclohexyl (meth) acrylate is relatively inexpensive and the viscosity obtained is relatively low. It is preferable because the performance of the adhesive is good.

The preferred constituent ratios of the constituent monomers in the above copolymer are as follows. Each of the alkyl (meth) acrylate having an alkyl group having 4 to 12 carbon atoms, the unsaturated carboxylic acid, and the ring structure-containing monomer is 45 to 9
7% by weight, 0.1 to 10% by weight, 2.9 to 30% by weight, preferably 55 to 95% by weight, 0.2 to 8% by weight, 4.8 to 25% by weight More preferred,
More preferably, the content is 65 to 92% by weight, 0.5 to 5% by weight, and 7.5 to 20% by weight.

When the content of the alkyl (meth) acrylate having an alkyl group having 4 to 12 carbon atoms is less than 45% by weight, the adhesive strength, cohesive strength and tack of the obtained adhesive can be balanced. It may be difficult, and if it exceeds 97% by weight, the cohesive force of the adhesive may be insufficient. When the content of the unsaturated carboxylic acid is less than 0.1% by weight, the cohesive strength, adhesive strength and whitening resistance of the obtained adhesive may be insufficient, and when it exceeds 10 parts by weight, tack and adhesive strength may be obtained. , Whitening resistance may be reduced. When the content of the ring structure-containing monomer is less than 2.9 parts by weight, the whitening resistance of the obtained adhesive may be insufficient, and when it exceeds 30 parts by weight, the tack and the adhesive strength may be reduced. There is.

The copolymer comprising an alkyl (meth) acrylate having an alkyl group having 4 to 12 carbon atoms, an unsaturated carboxylic acid and a monomer having a ring structure may be optionally copolymerized with these constituent monomers. Other polymerizable monomers are used in combination. Examples of other monomers include alkyl having 1 to 3 carbon atoms such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and i-propyl (meth) acrylate. (Meth) acrylate, (meth) acrylonitrile, α
-A cyano group-containing vinyl monomer such as chloroacrylonitrile, 2-hydroxyethyl (meth) acrylate,
Hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate,
Hydroxyl-containing vinyl monomers such as glycerol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol-polypropylene glycol copolymer mono (meth) acrylate, and monoethyl itaconate Monoalkyl esters of unsaturated dicarboxylic acids such as esters, monobutyl fumarate and monobutyl maleate; unsaturated carboxylic acids such as acrylamide, methacrylamide, N-methylolacrylamide, N-methoxymethylacrylamide and N-methoxybutylacrylamide Acid amides and their N-substituted compounds, unsaturated alcohols such as allyl alcohol, vinyl acetate, glycidyl (meth) acrylate, vinyl chloride, vinylidene chloride And the like. Also, 2-hydroxyethyl (meth) acrylate, glycidyl (meth)
By copolymerizing a crosslinkable monomer such as acrylate, (meth) acrylamide and N-methylolacrylamide, the gel fraction of the adhesive can be adjusted.
The copolymerization ratio of the crosslinkable monomer is preferably set to 20% by weight or less of the constituent monomer.

The emulsion of the present invention is prepared by (1) a batch charging method in which all of the monomers are charged into a reaction vessel at a time and polymerization is performed, and (2) a prepolymerization is performed by charging a part of the monomers into the reaction vessel. Then, a monomer addition method in which the remaining monomers are polymerized while being continuously added, (3) the monomers are emulsified in advance, a part of the monomers is preliminarily polymerized, and then the remaining emulsified product is continuously formed. (4) Emulsion addition method to promote polymerization by addition
A polymer emulsion of small particles (hereinafter, referred to as a seed), which has been polymerized in advance, is charged into a reaction vessel, and monomers are added thereto as they are or emulsified and polymerized to form new dispersed particles. It can be obtained by polymerizing the above monomers by various emulsion polymerization methods such as seed polymerization method (emulsion latex handbook, p. 279 (issued by Taisei Co., Ltd. in 1975)) for growing seed particles.

In these emulsion polymerization methods, a chain transfer agent can be appropriately used. Examples of the chain transfer agent include a lipophilic chain transfer agent such as dodecyl mercaptan and a hydrophilic chain transfer agent such as mercaptopropionic acid. The dispersed particles in the emulsion of the present invention are produced using these chain transfer agents, and using the above-mentioned crosslinkable monomer as a constituent monomer of the copolymer forming the dispersed particles. The case is preferable because the whitening resistance of the obtained adhesive becomes particularly good.

When the seed polymerization method is used among the above emulsion polymerization methods, an emulsion composed of dispersed particles having a desired particle size can be easily obtained, and the particle size distribution is 1.0 to 1. 15 (1.0-1.
It is preferable because 1) and particularly a small emulsion can be easily produced and an adhesive having good whitening resistance can be obtained. further,
Another advantage is that the amount of grit produced during emulsion polymerization is reduced.

When the dispersed particles of the present invention are obtained by using a seed polymerization method, a portion of the dispersed particles grown around the seed (hereinafter, also referred to as “shell”).
Preferably comprises a copolymer having the structure described in the third invention. Although the structure of the seed is not particularly limited, α,
It is preferable to include a β-unsaturated carboxylic acid monomer, and that at least one type of monomer other than the α, β-unsaturated carboxylic acid monomer is the same as the monomer constituting the shell. Is more preferred. When the shell is made of a copolymer having the structure described in the third invention and the seed is made of a copolymer not having the structure described in the third invention, the weight-average particle diameter of the seed is determined by the dispersion particles obtained after the seed polymerization. Is preferably 1/10 to 1 / 1.2 of the weight average particle size. Adhesives obtained from such dispersed particles have particularly good whitening resistance. Further, it is preferable that the entire structure including the seed and the shell satisfy the condition described in the third invention.

When the composition of the present invention is a pressure-sensitive adhesive composition, the above copolymer has a glass transition temperature of -20 ° C.
Or less, more preferably -30 ° C or less. When the glass transition temperature of the copolymer exceeds -20 ° C, the tack as an adhesive tends to be insufficient.

(5) Nonionic Surfactant As the composition of the present invention, the emulsion contains 0.05 to 5 parts by weight of a nonionic surfactant per 100 parts by weight of a polymer forming dispersed particles. It is preferably contained, more preferably 0.3 to 5 parts by weight, even more preferably 0.5 to 5 parts by weight.
An emulsion containing 0.05 parts by weight or more of a nonionic surfactant has good stability, and improves the whitening resistance of the composition of the present invention. If the content exceeds 5 parts by weight, the whitening resistance may deteriorate. The nonionic surfactant may be added at the time of polymerization of various monomers during the preparation of the emulsion, may be added after the polymerization, a part may be added at the time of polymerization, and the rest may be added after the polymerization. Good. When the nonionic surfactant is a reactive surfactant, it is effective that the entire amount is added during polymerization. Examples of the nonionic surfactant include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenol ethers, sorbitan higher fatty acid esters, polyoxyethylene sorbitan higher fatty acid esters, polyoxyethylene higher fatty acid esters, and glycerin higher fatty acid. Esters and the like, for example, emulsifiers, dispersants, defoamers, thickeners, lubricants, film-forming auxiliaries, fiber auxiliaries, detergents, antistatic agents, leveling agents, wetting agents, leveling improvers Among them, non-ionic ones can be selected.

In the composition of the present invention, a toluene-insoluble matter,
Preferred conditions for the composition of the dispersed particles of the emulsion and the content of the nonionic surfactant are respectively described in claim 2 and
As described in Claims 3 and 4, it is more preferable that two of these three conditions are satisfied at the same time, and those that satisfy all three conditions have particularly good whitening resistance and adhesive strength. It is more preferable because it is large. The composition of the present invention has an ionic emulsifier, a dispersant, an antifoaming agent, a thickener, a lubricant, a film-forming auxiliary, a fiber auxiliary, a cleaning agent, an antistatic agent, a leveling agent, depending on the application. Common additives such as wetting agents and leveling improvers can be used in combination. The composition of the present invention
The combination with an anionic surfactant is preferred because the stability is good.

The composition of the present invention has a solid content of 30 to 30%.
It is preferably 70% by weight, more preferably 45 to 65% by weight. The viscosity measured by a B-type viscometer at 25 ° C. and 12 rpm is 50 to 2000.
Those having a pH of 0 cps are preferred, and those having a pH of 2 to 9 are preferred.

(6) Use of adhesive composition Since the present composition forms a film having excellent transparency and whitening resistance, it is suitable for adhesive adhesion of a transparent adherend. Can be used. Specific applications include adhesives for polarizing plates, liquid crystal displays, optical components, watch components, composites, laminated glass, double-glazed glass, and the like.

Further, for the same reason, it can be suitably used for producing an adhesive sheet using a transparent substrate. As the material of this transparent substrate, cellophane, polypropylene, polyethylene, polyester, fluororesin, polystyrene,
Examples include polyimide, polyacetate, polyvinyl chloride, glass, acrylic resin, methacrylic resin, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, liquid crystal polymer, polyether sulfone, ethylene vinyl alcohol resin, urea melamine resin, and the like.

The adhesive sheet having a transparent substrate includes an adhesive label, an adhesive tape, a special adhesive film and the like. Specific examples of applications for adhesive labels include trademark labels, quality labels,
For product display such as content display label, returnable label, name plate, etc., for weighing label, hand label, price display such as price tag / regular tag, instruction manual label, inspection certificate label, warranty label, tamper-proof label, power distribution diagram label, For explanation / warranty of scale plate labels, PL law warning labels, etc., for stickers (for windows, vehicles, stores, etc.), marks / decorative labels, stamps, stickers, patches, posters, multilayer labels, etc. , Form labels, computer labels, POS labels, process / inventory management labels, etc., double-sided / single-sided tag labels, address labels, home delivery slip labels, etc., seals, cap seals, etc. For information and signs such as sealing, information sign labels, traffic sign labels, facility sign labels, toiletry related labels,
For recycling home appliance labels, OA equipment labels, etc., and other index labels (for stationery, video cassettes,
For floppy disks, etc.), for color sample labels, for toys (stickers), for teaching materials, and for labeling products with the possibility of condensation. Specific examples of the application of the adhesive tape include name plate tapes, tapes for metal building materials, tapes for automobiles, surface protection, semiconductor manufacturing process tapes, tapes for transporting electronic components, tapes for protection and masking, and fixing and bonding. For electrical and electronic equipment such as tapes, tapes for electrical insulation, binding and repair tapes, conductive tapes, EP
S (foamed polystyrene bead fused products) For display and sealing on cases, for general masking such as painted masking tape, curing masking tape, etc., for sealing and packaging such as cardboard packaging tape, office use, and other automotive decorative tapes. Applications include photolithography tapes, splicing tapes, and general binding and fixing applications such as double-sided tape, cellophane tape, and OPP tape. Specific examples of the application of the special adhesive film include outdoor durable films such as outdoor advertising films, automotive stripes, marking films, etc., general wall mounting such as posters, interior films, and interior materials, elevator interior films, counter decoration films, and furniture decoration films. For interior decoration such as vehicle interior film, vending machine decoration film, cash corner decoration film, table decoration film, etc., for short-term decoration such as wind display film, sticker, marking film, etc., for internally illuminated signboard such as outdoor durable transparent film, for buildings For solar shading and scattering prevention film, for reflective film for security (for automobiles, shoes, helmets, etc.), for use as a window film to be applied to automobiles while wetting with water or soapy water, other, prism, hologram film, Animal film, Is the use of such an optical film.

[0039]

Conventionally, it has been attempted to improve the whitening resistance by reducing the particle size of the dispersed particles of the emulsion constituting the adhesive composition and reducing the amount of the surfactant contained in the composition. . These means are to make the particles forming the adhesive layer tightly packed (the volume of the interstices between the particles is reduced), and to make the interface existing on the surface of the adhesive layer or the interstices between the particles. This is based on the idea that by reducing the amount of the activator, it becomes difficult for the adhesive to absorb water, thereby preventing whitening.

On the other hand, the inventors of the present invention concluded that the emulsion dispersed particles having a small particle size and a uniform size (small particle size distribution) were slightly different from the water absorption of the adhesive. Regardless, it was found that the whitening resistance was good.
Although the reason cannot be determined, it is considered that the whitening phenomenon is caused not by mere water absorption but by uneven refractive index due to uneven water absorption of the adhesive layer. It is presumed that the pressure-sensitive adhesive obtained from the composition of the present invention, which is small and is composed of an emulsion having a small particle size distribution, has a small non-uniformity of water absorption. Further, when the emulsion is obtained by seed polymerization, the whitening resistance of the adhesive becomes particularly good because the particle size distribution of each dispersed particle becomes more uniform. It is presumed that the non-uniformity of water absorption of the layer becomes smaller.

In the conventional method of improving the whitening resistance by preventing the adhesive from absorbing water, it has been suggested that the amount of the surfactant contained in the composition should be reduced. However, it has been found that the present invention preferably contains a specific surfactant, and it is presumed that the whitening resistance is improved because the water absorption becomes more uniform. In other words, even if the adhesive absorbs water to some extent, if the water absorption occurs uniformly throughout the adhesive,
It is considered that whitening hardly occurs. However, when the degree of water absorption is excessive, even when water is uniformly absorbed, whitening also occurs, and the adhesive performance is impaired by the water absorption. The adhesive obtained from the composition of the present invention has good whitening resistance to not only water but also water containing a surfactant.

[0042]

EXAMPLES The present invention will be described more specifically with reference to the following examples. In the following description, “part” means “part by weight” and “%” means “% by weight”. In addition, production of test adhesive film,
The gel fraction, adhesive strength, holding power, tack, and whitening resistance (visual and haze values) were measured by the following methods.

1) Preparation of Sample of Gel Fraction An adhesive was applied on release paper so that the thickness of the adhesive film obtained after drying was about 100 μm, and then heated at 100 ° C. in a hot air circulation type dryer. After drying for 1 hour, a pressure-sensitive adhesive film as a sample was prepared. Toluene extraction 0.5 g of the pressure-sensitive adhesive film obtained above was
The sample was immersed in the solution for 1 week. This toluene solution was filtered with filter paper and dried at 100 ° C. for 3 hours to obtain a residue. The gel fraction was calculated by the following equation using the residue as a gel component. Gel fraction (% by weight) = residual dry weight (g) /0.5×1
00

2) Preparation of Test Adhesive Film A composition was applied to the surface of a 25 μm-thick polyethylene terephthalate film so that the thickness of the adhesive layer after drying was 20 μm, and then applied to a hot-air circulation dryer. And dried at 100 ° C. for 120 seconds to produce an adhesive film. For evaluation of the following items, an adhesive film prepared by this method was used.

3) Adhesive Strength A stainless steel plate was used as the adhesive film and the adherend under the conditions of 23 ° C. and 65% RH under JIS Z-
The 180-degree peel strength was measured according to 0237, and defined as the adhesive strength.

4) Holding force The above adhesive film was bonded to a stainless steel plate with an adhesive area of 25 m.
It was pasted so as to have a size of mx 25 mm, a time of 1 kg was applied under a load of 1 kg at 40 ° C, and the time until the film was peeled off was measured. In the case where it was held even after 180 minutes, the holding time was set to 180 minutes or more, and the value obtained by measuring the width of deviation from the initial attaching position was also shown.

5) Tack The above adhesive film was measured in an atmosphere of 23 ° C. and 65% RH according to the ball rolling method of JIS Z-0237.

6) Whitening Resistance (Visual) The above adhesive film was immersed in water at 20 ° C. for 3 days, and the degree of whitening of the film was visually evaluated. The evaluation result is 5
Shown in stages. ：: The coated part is also transparent and the boundary with the non-coated part is unknown. ：: The coated part is almost transparent but the boundary with the non-coated surface is slightly visible. ：: The coated part is slightly white. Worked part shows white ×: Coated part shows strong white

7) Whitening Resistance (Haze Value) The pressure-sensitive adhesive film evaluated for whitening resistance was used as a test piece, and the haze value was measured with a haze meter (# 80 COLOR M manufactured by Nippon Denshoku Co., Ltd.).
EASURING SYSTEM). The larger the haze value, the worse the degree of whitening.

The meanings of the abbreviations of the monomers and chain transfer agents used are as follows. HA; 2-ethylhexyl acrylate BA; butyl acrylate St; styrene CHA; cyclohexyl acrylate CHMA; cyclohexyl methacrylate MA; methyl acrylate MMA; methyl methacrylate EA; ethyl acrylate AN; acrylonitrile VAc; vinyl acetate GMA; glycidyl methacrylate HEA; Ethyl acrylate HEMA; 2-hydroxyethyl methacrylate N-MAM; N-methylol acrylamide AMD; acrylamide AA; acrylic acid MAA; methacrylic acid DM; dodecyl mercaptan MPA; mercaptopropionic acid

(Example 1) In a reaction vessel equipped with a stirrer, thermometer, cooler, nitrogen inlet tube and two dropping funnels,
50 parts of water was charged and the temperature was raised to 80 ° C. 3 parts of sodium polyoxyethylene nonylphenyl ether sulfate and 27 parts of water were added to a monomer mixture (composed of a monomer or a monomer and a chain transfer agent) having the composition shown in Table 1 to emulsify.
The obtained emulsion and 8 parts of a 5% aqueous solution of ammonium persulfate as a polymerization initiator were added to each of 4 parts from separate dropping funnels.
Emulsion polymerization was carried out by dropping continuously into the flask over time. Two hours after the completion of the dropwise addition, the system was cooled to terminate the polymerization. Aqueous ammonia was added to the obtained copolymer emulsion to prepare liquid adhesive compositions shown in Table 6.

(Example 2) Using the same apparatus as in Example 1, 50 parts of water and 0.1 part of sodium lauryl sulfate were charged into a reaction vessel and the temperature was raised to 80 ° C. To a monomer mixture having the composition shown in Table 1, 1 part of sodium lauryl sulfate and 2 parts of water
The mixture was emulsified by adding 7 parts and polymerized and adjusted in the same manner as in Example 1 to obtain a pressure-sensitive adhesive composition.

Examples 3 to 10 The composition of the monomer mixture was as shown in Table 1, and the type and amount of the emulsifier to be charged into the reaction vessel and the type and amount of the emulsifier used for emulsification of the monomer mixture were shown in Table 2. The polymerization and adjustment were carried out in the same manner as in Example 1 except that the pressure-sensitive adhesive composition was changed as shown in Example 1 to obtain a pressure-sensitive adhesive composition.

[0054]

[Table 1]

[0055]

[Table 2]

Examples 11 to 14 To the copolymer emulsion of Example 4 were added and mixed the types and amounts of nonionic surfactants shown in Table 3 to prepare pressure-sensitive adhesive compositions.

[0057]

[Table 3]

(Examples 15 to 20) The composition of the monomer mixture was as shown in Table 4, and the type and amount of the emulsifier charged in the reaction vessel and the type and amount of the emulsifier used for emulsifying the monomer mixture were shown in Table 4. A copolymer emulsion was obtained in the same manner as in Example 1, except that the pressure-sensitive adhesive composition was added and mixed with a type and amount of a nonionic surfactant shown in Table 4 to obtain an adhesive composition. It was adjusted. Both Rheolate 255 and Adekanol UH-420 are thickeners composed of nonionic polymer derivatives, and are trade names of Rhox and Asahi Denka Kogyo, respectively.

[0059]

[Table 4]

Examples 21 to 24 are examples in which a pressure-sensitive adhesive composition was produced by a seed polymerization method. (Example 21) (1) Synthesis of seed A In a reaction vessel equipped with a stirrer, a thermometer, a cooler, a nitrogen inlet tube, and two dropping funnels, 81.4 parts of water and 0.1% of sodium dodecylbenzenesulfonate were added. Prepare 9 copies 6
The temperature was raised to 0 ° C. A monomer mixture consisting of 45.0 parts of BA, 45.0 parts of MMA and 10.0 parts of MAA was added to 0.72 parts of sodium dodecylbenzenesulfonate and 2 parts of water.
1.1 parts were added and emulsified. The obtained emulsion and 3.0 parts of a 10% aqueous solution of ammonium persulfate as a polymerization initiator were respectively continuously dropped into the reaction vessel from different dropping funnels over 3 hours to carry out emulsion polymerization. After further aging for 30 minutes from the end of the dropping, the system was cooled to terminate the polymerization. When the particle size and the particle size distribution of the obtained seed A were measured by LA-910 manufactured by HORIBA,
The weight average particle size was 0.078 μm, and the particle size distribution was 1.28. (2) Seed polymerization Using the same apparatus as in Example 1, water 44.2 was introduced into the reaction vessel.
Parts and seed A, the weight average particle size of the final product was 0.2 μm.
m and the temperature was raised to 80 ° C. Set the DM amount to 0.
To a monomer mixture having the same composition as in Example 4 except that the amount was changed to 05 parts, 3 parts of sodium polyoxyethylene nonylphenyl ether sulfate and 27 parts of water were added and emulsified. The resulting emulsion and 8 parts of a 5% aqueous solution of ammonium persulfate as a polymerization initiator were continuously dropped into the reaction vessel over 4 hours from different dropping funnels to carry out emulsion polymerization. Two hours after the completion of the dropwise addition, the system was cooled to terminate the polymerization. Aqueous ammonia was added to the obtained copolymer emulsion, and a nonionic surfactant of the same type and amount as in Example 14 was further added and mixed to obtain a liquid adhesive composition shown in Table 8. Was. The amount of seed used is the emulsion latex handbook (published by Taiseisha in 1975)
It was calculated by the equation described on page 280.

Example 22 In a monomer mixture, DM
A pressure-sensitive adhesive composition was obtained in the same manner as in Example 21 except that was not used.

Example 23 Seed A was prepared except that sodium dodecylbenzenesulfonate used in the synthesis of seed A was replaced with the same amount of sodium lauryl sulfate.
Seed B was synthesized in the same manner as described above. The weight average particle size of the obtained seed B was 0.132 μm, and the particle size distribution was 1.
34. A pressure-sensitive adhesive composition was obtained in the same manner as in Example 21 except that seed polymerization was performed using this seed B instead of seed A.

Example 24 In the synthesis of seed A, seed A was changed except that the amount of dodecylbenzenesulfonic acid charged in the reaction vessel was changed from 0.9 part to 14.4 parts.
Seed C was synthesized in the same manner as in Example 1. The weight average particle size of the obtained seed C was 0.040 μm, and the particle size distribution was 1.
28. A pressure-sensitive adhesive composition was obtained in the same manner as in Example 21, except that seed polymerization was performed using this seed C instead of seed A.

(Comparative Examples 1 and 2) Except that the composition of the monomer mixture, the type and amount of the emulsifier charged in the reaction vessel, and the type and amount of the emulsifier used for emulsification of the monomer mixture were as shown in Table 5. In the same manner as in Example 1, a copolymer emulsion was obtained, and a kind and amount of a nonionic surfactant shown in Table 5 were added later to prepare a pressure-sensitive adhesive composition.

[0065]

[Table 5]

(Comparative Example 3) Using the same apparatus as in Example 1, 50 parts of water and 0.05 part of sodium dodecylbenzenesulfonate were charged into the reactor, and the temperature was raised to 80 ° C. To the monomer mixture having the composition shown in Table 5, 0.5 part of sodium dodecylbenzenesulfonate and 27 parts of water were added and emulsified. The obtained emulsion and the same polymerization initiator as in Example 1 were continuously dropped into the flask over 4 hours to carry out emulsion polymerization. Every hour from the start of the dropping, 0.1 part of sodium dodecylbenzenesulfonate was added to the flask three times in total. The obtained emulsion was treated in the same manner as in Example 1 to prepare a pressure-sensitive adhesive composition.

For each of the pressure-sensitive adhesive compositions of Examples 1 to 24 and Comparative Examples 1 to 3, the results of analyzing the weight average particle diameter and particle diameter distribution of the dispersed particles, the gel fraction after drying, and the like, Tables 6 to 9 show the results of evaluating the performance.

[0068]

[Table 6]

[0069]

[Table 7]

[0070]

[Table 8]

[0071]

[Table 9]

As can be seen from Tables 6 to 9, the weight average particle size is 0.3 μm or less and the particle size distribution is 1.0 to 1.5.
All of the pressure-sensitive adhesive compositions of Examples 1 to 24 were excellent in whitening resistance and also excellent in pressure-sensitive adhesive performance. In the present composition, among the three preferable conditions regarding the toluene-insoluble matter, the composition of the dispersed particles of the emulsion, and the content of the nonionic surfactant, at least two of Examples 3 to 9 satisfy only one at a time. Example 1, Example 2, Example 1
7. The whitening resistance was better as compared with Example 18 and the like. Examples 10 to 1 satisfying the three conditions
Sample No. 6 had even better whitening resistance. Then, the compositions of Examples 21 to 24 obtained by the seed polymerization method and having both the weight average particle size and the particle size distribution in the preferable ranges have excellent balance between the whitening resistance and the adhesive performance, and all are particularly favorable. Was something.

The present invention is not limited to the specific examples described above, but various conditions can be changed within the scope of the present invention depending on the purpose and application.

[0074]

The adhesive composition of the present invention forms an adhesive having excellent whitening resistance. Therefore, the composition of the present invention is extremely suitable for applications such as adhesives for adherends having transparency and pressure-sensitive adhesive sheets using transparent substrates.

Claims (5)

[Claims] 1. The dispersed particles have a weight average particle size of 0.3 μm or less, and the ratio of the weight average particle size to the arithmetic average particle size (weight average particle size / arithmetic average particle size) is 1.0 to 1.5. A pressure-sensitive adhesive or adhesive composition comprising an emulsion as a component. 2. The pressure-sensitive adhesive or adhesive composition according to claim 1, wherein the emulsion has a toluene-insoluble content of 40% by weight or more in a film formed from the emulsion. 3. The dispersed particles are composed of a copolymer having the following constituent monomers and constituent ratios described in (a), (b) and (c). Pressure-sensitive adhesive or adhesive composition. (A) Alkyl acrylate or alkyl methacrylate monomers 45 to 9 having an alkyl group having 4 to 12 carbon atoms
7% by weight (b) 0.1-10% by weight of α, β-unsaturated carboxylic acid monomer (c) 2.9-% radical polymerizable monomer having a cyclic structure other than (a) and (b) 30% by weight 4. The emulsion according to claim 1, wherein the emulsion contains 0.05 to 5 parts by weight of a nonionic surfactant based on 100 parts by weight of the polymer forming the dispersed particles. The pressure-sensitive adhesive or the adhesive composition according to claim 1. 5. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to claim 1 on a surface of a transparent substrate.