JP2001072705A - Vinyl acetate/(meth)acrylate copolymer, preparation thereof, and adhesive composition using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an emulsion excellent in the initial adhesion and viscosity characteristics, by emulsion-polymerizing a vinyl acetate monomer, a (meth) acrylate monomer and a monomer copolymerizable therewith with a polyvinyl alcohol as an emulsion stabilizer in the presence of a gel fraction inhibitor to regulate a specific gel fraction. SOLUTION: An emulsion comprises a copolymer emulsion which has a gel fraction of 0-30 wt.% and is obtained by emulsion-polymerizing 100 pts.wt. of a monomer mixture containing 1-70 wt.% of vinyl acetate monomer, 30-95 wt.% of a (meth)acrylate monomer and 0-30 wt.% of a monomer copolymerizable therewith; 1-10 pts.wt. of a gel fraction inhibitor; and 0.1-10 pts.wt. of an emulsion stabilizer such as a polyvinyl alcohol, using a polymerization initiator and a pH adjuster. Examples of the gel fraction inhibitor include 2,2,4-trimethyl-1,3-pentanediol, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-concentration and stable vinyl acetate which is excellent in initial adhesive strength and viscosity characteristics and can be widely used in fields requiring adhesive and coating functions such as adhesives, pressure-sensitive adhesives and binders. The present invention relates to a (meth) acrylate copolymer emulsion adhesive composition and a method for producing the same, and a method for producing a vinyl acetate / (meth) acrylate copolymer emulsion used for the composition.

[0002]

2. Description of the Related Art In recent years, water-based emulsions have been increasingly used as adhesives and coating resins in place of conventional solvent-based resins, reflecting recent environmental problems and increasing awareness of occupational health. Among them, acrylic resins and vinyl acetate / ethylene copolymer resins can be copolymerized with a wide range of glass transition temperatures and various functional monomers. Have been. For example, an acrylic resin emulsion obtained by emulsion polymerization in the presence of a surfactant, and a vinyl acetate / ethylene copolymer resin emulsion (and a copolymer emulsion of this and an ethylenically unsaturated compound) using polyvinyl alcohol as a protective colloid are known. However, in the former, the initial adhesive strength and the viscosity characteristics are poor, so the addition of a thickener or the like is indispensable, and there are few examples used for adhesives except for adhesives (pressure-sensitive adhesives). In the latter, commercially available ones have inferior initial adhesiveness and are too low in viscosity as an adhesive, and are generally used by adding a solvent such as toluene to improve initial adhesiveness and viscosity characteristics. ing. In addition, generally 50%
It has a high gel fraction as described above.

On the other hand, a vinyl acetate homopolymer emulsion using polyvinyl alcohol as a protective colloid, which has been widely used in the past, has excellent viscosity characteristics and initial adhesion performance, but has a limited glass transition temperature range. There is a disadvantage that the range of use is limited depending on the type and the like. In order to improve these points, various attempts have been made to polymerize an acrylic monomer in the presence of polyvinyl alcohol. For example, a method of polymerizing in the presence of a chain transfer agent (US Pat. No. 4,265,796), a method of using allyl alcohol or allyl halide and a low molecular weight aliphatic alcohol (UK Patent No. 12788).
No. 13), a method of using a surfactant substantially or using an amino alcohol having a surface active ability (US Pat. No. 4,670,505) has been proposed. According to these methods, the gel fraction is low, and a stable emulsion may be obtained.However, since a compound having surface activity is used in combination, initial adhesive strength and viscosity characteristics are inferior, and as an adhesive, The fact is that there is difficulty.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned problems of the prior art and to provide an initial adhesive property equal to or higher than that of a conventional vinyl acetate resin emulsion using polyvinyl alcohol as a protective colloid. Vinyl acetate (meta) with viscosity characteristics and a wide range of glass transition temperatures, with a wide range of applications and excellent initial adhesion and viscosity characteristics
It is an object to provide an acrylic ester copolymer emulsion, a method for producing the same, and an adhesive composition using the same.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve this problem, and as a result, in the presence of a gel fraction inhibitor, polyvinyl alcohol was used as an emulsion stabilizer, and a surfactant was used. A vinyl acetate / (meth) acrylic acid ester having a low gel fraction obtained by emulsion-copolymerizing vinyl acetate, (meth) acrylic acid ester and a monomer copolymerizable therewith at a specific ratio without using the same. The present invention has been found that by using a polymerized emulsion as a main component, a high-concentration and stable emulsion adhesive having excellent initial adhesiveness and viscosity characteristics can be obtained by suppressing the gel fraction of the entire composition below a specified level. Was completed.

That is, the present invention uses polyvinyl alcohol as an emulsion stabilizer in the presence of a gel fraction inhibitor, without using a surfactant, a) 1-70% by weight of a vinyl acetate monomer, b) ( (Meth) acrylic acid ester monomers 30 to 95
C) acetic acid having a gel fraction of 0 to 30% by weight obtained by emulsion polymerization of c) vinyl acetate and / or (meth) acrylate with 0 to 30% by weight of a copolymerizable monomer. A vinyl / (meth) acrylate copolymer emulsion and a method for producing the same.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As a gel fraction inhibitor, any one can be used as long as it can obtain the above gel fraction and can obtain the characteristics of the present invention.
4-trimethyl 1,3-pentanediol, 2,2,4
-Trimethyl 1,3-pentanediol monoisobutyrate and 2,2,4-trimethyl 1,3-pentanediol diisobutyrate, which may be used alone or in combination of two or more. it can. Further, in the emulsion adhesive composition of the present invention, it is preferable that not only the specific copolymer emulsion as the main component does not use a surfactant, but also the composition does not contain a surfactant.

[0008] It is not clear how the gel fraction and the substantial absence of surfactants function to improve initial adhesion, viscosity characteristics and emulsion stability. One of the factors that determine the initial adhesion is considered to be the good filling of the emulsion particles during compression. Emulsions with a low gel fraction can be more densely packed due to easier deformation of the particles, and spherical large particles of several μm or more can be easily obtained, and thus often have a broad particle size distribution. It is considered that this effect is further enhanced. Also, the ability to form relatively large spherical particles means that the surface area of the particles can be reduced,
Increases resistance to mechanical and chemical external forces.
That is, it is considered that the emulsion is mechanically and chemically stable.

The aqueous solution of polyvinyl alcohol itself has excellent viscosity characteristics and wet tack, but when emulsion polymerization is carried out using a surfactant as an emulsion stabilizer, these characteristics are impaired. The viscosity characteristics of the emulsion obtained by emulsion polymerization without using a surfactant are close to those of a concentrated solution of polyvinyl alcohol, which is considered to form so-called protective colloids that adsorb to the particles. When emulsion polymerization is carried out in combination with a surfactant, since the surfactant is adsorbed on the particles instead of polyvinyl alcohol, reducing this thickening effect impairs the viscosity characteristics and wet tack of the obtained emulsion. Presumed cause.

When a surfactant is added later to the emulsion of the present invention for the preparation of an adhesive composition or the like, the adverse effect is less than when it is added as a stabilizer during emulsion polymerization. In particular, when an emulsion obtained by emulsion polymerization using a surfactant is mixed, when the mixing ratio is within the range of the present invention, adverse effects are relatively small. This means that, in the case of a surfactant added later in the composition, the degree of replacement by eliminating the protective colloid differs depending on the manner of addition. Therefore, it is not desirable to add a surfactant later, except in the case where the surfactant is used as a stabilizer, as in the case of an emulsifier contained in an emulsion polymerized using a surfactant.

In the present invention, the copolymerization ratio of vinyl acetate is 1 to 70%, preferably 5 to 50% (% is% by weight, hereinafter the same in the copolymerization ratio). If the copolymerization ratio is 1% or less, the effect of the gel fraction inhibitor preferably used in the present invention cannot be obtained. When the copolymerization ratio exceeds 70%, the characteristics of the present invention with respect to the conventional vinyl acetate homopolymer emulsion cannot be exhibited.

In the present invention, (meth) acrylic esters used by copolymerizing with vinyl acetate include methyl acrylate, ethyl acrylate, n-butyl acrylate,
Alkyl acrylates such as isobutyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, methyl methacrylate, ethyl methacrylate,
Methacrylates such as butyl methacrylate, hexyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, acetoacetoxyethyl methacrylate, and the like, and one or more selected from these groups. Several types can be used together, and the total weight fraction thereof is used in the range of 30 to 95% of the total monomer weight. If necessary, ethylene, acrylic acid, methacrylic acid, maleic anhydride, itaconic acid, vinyl chloride, acrylamide, N-substituted acrylamide derivatives, acrylonitrile copolymerizable with vinyl acetate and (meth) acrylic esters. , Vinyl esters such as vinyl propionate and vinyl versatate, and styrene may be copolymerized in the range of 0 to 30% by weight of the total monomers as long as the effects of the present invention are not impaired.

The polyvinyl alcohol used as an emulsion stabilizer in the emulsion of the present invention is generally produced by hydrolyzing commercially available polyvinyl acetate.
Degree of hydrolysis (degree of saponification) of 60 to 100 mol%, degree of polymerization of 3
Those having a number of 00 to 2500 are preferably used. In addition, a so-called modified polyvinyl such as a product obtained by copolymerizing a small amount of ethylene with vinyl acetate and hydrolyzing it, a product obtained by introducing a carboxyl group, a sulfone group, an alkyl ether group, an acetoacetyl group or the like, or a product modified by diacetone acrylamide or the like. What is called alcohol can also be used as needed. Polyvinyl alcohol is used as an aqueous solution having an appropriate concentration capable of acting as an emulsion stabilizer according to a conventional method of emulsion polymerization. In the present invention, the amount of polyvinyl alcohol used as an emulsion stabilizer is 0.1 to 10 parts by weight, preferably 0.5 to 6.0 parts by weight, based on 100 parts by weight of all monomers.

Effective compounds found by the inventors of the present invention as gel fraction inhibitors include 2,2,4-
There are trimethyl 1,3-pentanediol, 2,2,4-trimethyl 1,3-pentanediol monoisobutyrate, and 2,2,4-trimethyl 1,3-pentanediol diisobutyrate. These need to be present in the emulsion at the time of polymerization, and as an addition method, added before the polymerization, mixed with the monomer, or separately, intermittently or continuously during the polymerization. A method of adding, for example, is used. The appropriate amount to be added varies depending on the monomer composition and the method of addition.
When 1 to 10 parts by weight is used with respect to 0 parts by weight, a desired gel fraction can be obtained. It is not clear what effect these compounds have on gel fraction suppression. In emulsion polymerization in the presence of polyvinyl alcohol, there is a theory that a monomer is graft-polymerized to polyvinyl alcohol to form a gel component, and that if the molecular weight itself becomes extremely large, a gel component is formed.

Since these gel fraction inhibitor compounds have a structure of a secondary alcohol and an ester thereof similar to polyvinyl alcohol, these compounds (in the present invention, instead of chain transfer to polyvinyl alcohol) are used. It is presumed that chain transfer to the gel fraction inhibitor) occurs to suppress grafting or increase in molecular weight. Conventionally, it is generally believed that grafting onto polyvinyl alcohol is a condition for emulsification stabilization. When (meth) acrylic acid esters are mainly used, this grafting does not occur, so that only polyvinyl alcohol is emulsified. The idea that a stable emulsion cannot be obtained when used as a stabilizer was the mainstream in the art. However, conventionally, in the emulsion polymerization mainly using (meth) acrylates without using the gel fraction inhibitor of the present invention, only the polyvinyl alcohol is used as the emulsion stabilizer, and the gel fraction as in the present invention is used. These myths are erroneous due to the fact that low emulsions have not been obtained, and the fact that very stable emulsions can only be obtained using the gel fraction inhibitors found by the present inventors. Proven to be.

In the presence of these gel fraction inhibitors,
As the polymerization initiator used for producing the vinyl acetate / (meth) acrylate copolymer emulsion of the present invention, a water-soluble peroxide such as hydrogen peroxide or persulfate which is generally widely used is used. be able to. Also,
If necessary, a redox catalyst system using a reducing agent such as tartaric acid, sulfite, thiosulfate, ferric oxide, or Rongalite may be used. Buffer agents such as carbonates and acetates can be used as pH adjusters. As the polymerization method, an emulsion polymerization method in which a monomer is polymerized in an aqueous solution of polyvinyl alcohol (PVA) in the presence of these initiators, auxiliaries, and a pH adjuster is preferably used. Or a method of continuously or intermittently supplying, a method of continuously supplying as a mixed solution with an aqueous PVA solution, a so-called power feed method or a seed polymerization method in which a monomer mixing ratio is continuously changed, or the like. Accordingly, it is also possible to provide a composition distribution in the particles as required. Polymerization initiator, auxiliary,
pH adjusters and the like may be added all at once before polymerization,
A method may be used in which the monomer is added after a part of it is added, or the monomer is added intermittently, intermittently added, or continuously dropped.

The gel fraction referred to in the present invention means a value measured by the following method. The emulsion is freeze-dried in an eggplant-shaped flask and the nonvolatile content is measured. Next, an extraction operation was performed three times with acetone at room temperature (the extract was vacuum-dried = acetone-soluble matter was measured), and then the extraction residue was extracted three times in a 70 ° C hot water bath (extraction). Lyophilized product = water-soluble content), and the residue was incinerated at 600 ° C. The residue weight (ash content) was measured.
It is obtained by the following formula. If it is known in advance that no inorganic filler has been added, the incineration operation may be omitted (in this case, the ash content = 0). The above steps are schematically shown below. Freeze drying (non-volatile) → acetone extraction → acetone soluble → warm water extraction (70 ° C) → water soluble acetone / water insoluble → 600 ° C incineration → ash [Equation 1] Note: Soluble (+) indicates acetone-soluble + water-soluble.

The adhesive composition of the present invention may optionally contain
Calcium carbonate, aluminum hydroxide. It may contain an inorganic filler such as clay and talc, and an organic filler such as starch and flour. When an organic filler is used, this is excluded from the calculation of the nonvolatile content and the gel content in the calculation of the gel content. If necessary, a polyfunctional isocyanate compound such as polymethylene polyphenyl polyisocyanate (crude MDI), a polyfunctional aziridine compound, a polyfunctional epoxy compound, a polyfunctional oxazoline compound, a silane coupling agent, or the like may be included as a crosslinking agent. good. Of these, those having a molecular weight exceeding 10,000 are treated as organic polymer compounds and are involved in the calculation of the gel fraction and the calculation of the composition ratio of the main component and the total organic polymer. As well as fillers are excluded from these.

[0019]

Examples and Comparative Examples The present invention will be described below with reference to examples. The gel fraction was measured for each example by the method described in the text above. The glass transition temperature was measured using a differential thermal analyzer (DSC), after heating the sample to 150 ° C., rapidly cooling it to −70 ° C., and then increasing the temperature at a rate of 5 ° C./min.
C. and the temperature at which the specific heat transition started was read.
Further, the same operation was repeated for the same sample, and the average value of the temperatures at which two changes in specific heat were started was defined as the glass transition temperature. The viscosity characteristics were measured at 30 ° C. using a Brookfield viscometer at a viscosity of 1 rpm and 10 rpm (unit: m
Pa · s). In addition, evaluation was also made according to the state at the time of application with a hand roll.

The initial adhesive performance was 7.5 as a test piece.
cm, 2.5 cm wide, 4 mm thick commercially available MDF (medium density fiberboard), and each emulsion was coated on one side with 150-2
Immediately after applying 00 g / m ^2, 2.5 cm of the length of the test pieces were superimposed so as to overlap each other, and 8 kgf / c was applied.
Immediately after pressing at m ² for a predetermined time, a bending load was applied at a speed of 30 cm / min to the center (overlapping portion) of the 7.5 cm span immediately at a rate of 30 cm per minute, and evaluation was made by a so-called bending adhesion test in which the bending load at the time of breaking was measured. . This test was performed in a room adjusted to 20 ° C. and a relative humidity (RH) of 65%. The mechanical stability of the emulsion was evaluated by using a cone-plate viscometer, when a shear rate of 10,000 cm ^-1 was given for 1 minute, by the presence or absence of generation of aggregates and breakage of the emulsion.

Examples 1 to 8 The following examples show the performance when an emulsion obtained by a production method particularly effective in the present invention is used as it is as an adhesive. Tables 1 and 2 show the composition and procedure of the emulsion used in Examples 1 to 8. In the following table, PVA117 and 'PVA217 indicate polyvinyl alcohol manufactured by Kuraray Co., Ltd., and gel fraction inhibitor A is 2,2,4-trimethyl 1,3
-Pentanediol monoisobutyrate B is 2,2,4-trimethyl 1,3-pentanediol diisobutyrate C is 2,2,4-trimethyl 1,3-pentanediol. Incidentally,% in the table indicates% by weight.

[0022]

[0023]

The components (1) to (1) (liter) in the above table
The mixture was placed in a four-necked flask equipped with a stirrer, a Dim funnel, a thermometer, and a dropping funnel, and heated to 90 ° C. with stirring to keep the temperature until the polyvinyl alcohol was completely dissolved. Thereafter, the liquid temperature was lowered to 80 ° C., ammonium persulfate was added, and dropping of the monomer mixture was started immediately. After the entire amount of the monomer mixture was dropped over about 2 hours and 30 minutes, stirring was continued for 30 minutes while maintaining the internal temperature at 80 ° C to 85 ° C. Then, after adding ammonium persulfate, 8
After heating to 5 ° C. and continuing stirring for 30 minutes,
After cooling to ℃, the desired emulsion was obtained.

In the following, the synthesis formula and the synthesis procedure of Example 9 are shown.

Each of the components (1) to (3) shown in Table 3 above was equipped with a 1 L capacity stirrer, Dim funnel, thermometer and dropping funnel.
The flask was placed in a one-necked flask, and heated to 90 ° C. while stirring to keep the polyvinyl alcohol completely dissolved. Thereafter, the liquid temperature was lowered to 70 ° C., ammonium persulfate was added, and dropping of the monomer mixture was started immediately. The whole amount of the monomer mixture was dropped over about 3 hours while maintaining the liquid temperature during the dropping at 75 ° C. or lower, and then the liquid temperature was lowered to 70 ° C.
Stirring was maintained for 1 hour at -75 ° C. Thereafter, ammonium persulfate was added, and the mixture was further stirred for 1 hour while maintaining the liquid temperature at 70 to 75 ° C, and then cooled to 30 ° C to obtain a desired emulsion. With respect to the emulsions obtained in Examples 1 to 9, the emulsions obtained in Examples were used as they were as adhesives. The performance of the obtained adhesive is shown in Table 5 together with other examples.

Comparative Examples 1 and 2 The following examples are examples in which emulsion polymerization was carried out without using a gel fraction inhibitor and synthesis examples in which a surfactant was used together with polyvinyl alcohol. The synthetic formulation and procedure are shown below. Note: Surfactant Revenol WZ: polyoxyethylene nonylphenyl ether ammonium sulfonate: manufactured by Kao

Put (1) in the above table into a four-necked flask equipped with a 1 L capacity stirrer, Dim funnel, thermometer, and dropping funnel, and heat to 90 ° C. with stirring until polyvinyl alcohol is completely dissolved. Insulated.
Thereafter, the liquid temperature was lowered to 80 ° C., ammonium persulfate was added, and dropping of the monomer mixture was started immediately. After dropping the entire amount of the monomer mixture over about 2 hours and 30 minutes,
Stirring was continued for 30 minutes while maintaining the internal temperature at 80 ° C to 85 ° C.
Thereafter, ammonium persulfate was added, followed by heating to 85 ° C., and stirring was continued for 30 minutes, and then cooled to 30 ° C. to take out a polymerization emulsion. Comparative Example 1 produced a large amount of aggregates during the reaction, so that no other performance tests were performed except for measuring only the gel fraction. The performance of the emulsions obtained in Comparative Examples 1 and 2 is shown in Table 5 together with other examples.

Comparative Examples 3 and 4 Two commercial products are shown as examples of the emulsion having no specific constitution of the present invention. Showa Kobunshi ethylene-vinyl acetate copolymer resin emulsion AD-68 (Comparative Example 3),
Sumitomo Chemical Co., Ltd. ethylene-vinyl acetate-acrylate copolymer emulsion SF-475 (Comparative Example 4) 2
The species were measured for gel fraction, glass transition temperature, and performance tests. These are examples having very high gel fractions. The performance test results are shown in Table 5 together with other examples.

COMPARATIVE EXAMPLE 5 An emulsion prepared by mixing the emulsion of Example 1 and the emulsion of Comparative Example 3 at a ratio of 7/3 (Example 10) and 5/5 (Comparative Example 5) was used. It is an example for clarifying the effect of the ratio on the initial bonding performance. The performance test results are shown in Table 5 together with other examples.

Comparative Example 6 As an example of a polymer emulsion having excellent initial adhesion performance, a vinyl acetate resin homopolymer emulsion VW-415 manufactured by Honen Corporation was used. Table 5 shows the performance test results. As shown in Table 5, the emulsion adhesive of the present invention has at least the same initial adhesion and viscosity characteristics as the emulsion of Comparative Example 6, but the conventional vinyl acetate copolymer emulsion is inferior in initial adhesion performance. You can see that.

[0032] Note 1: * 1 5 pbw of DBP (dibutyl phthalate) was added for the initial adhesion test. Note 2: Tg value of Test Example 7 is +60 without DBP and (+30) is the value with 4% DPB added.

[0033]

[0034] Note: Commercial emulsion is a commercial ethylene-vinyl acetate copolymer emulsion Commercial emulsion is a commercial ethylene-vinyl acetate-acrylic copolymer emulsion Commercial emulsion is a commercial vinyl acetate homopolymer emulsion

[0035]

As described above, the emulsion adhesive of the present invention has excellent initial adhesiveness and viscosity characteristics which are not available in conventional emulsion adhesives, and has a wide range of glass transition temperatures. It can bond a wide range of materials by a wide range of processing methods. The present invention also provides a method for producing such an excellent emulsion adhesive.

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Claims (6)

[Claims] 1. Use of polyvinyl alcohol as an emulsion stabilizer in the presence of a gel fraction inhibitor, without using a surfactant, a) 1-70% by weight of a vinyl acetate monomer, b) (meth) acrylic acid 30 to 95% by weight of ester monomer, c)
Vinyl acetate / (meth) having a gel fraction of 0 to 30% by weight obtained by emulsion polymerization of 0 to 30% by weight of a copolymerizable monomer with vinyl acetate and / or (meth) acrylic acid ester Acrylic ester copolymer emulsion. 2. The method according to claim 2, wherein the gel fraction inhibitor is 2,2,4-trimethyl-1,3-pentanediol, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate,
The vinyl acetate / (meth) acrylate copolymer emulsion according to claim 1, wherein the emulsion is at least one member selected from 2,4-trimethyl 1,3-pentanediol diisobutyrate. 3. Use of polyvinyl alcohol as an emulsion stabilizer in the presence of a gel fraction inhibitor, without using a surfactant, a) 1-70% by weight of a vinyl acetate monomer, b) (meth) acrylic acid 30 to 95% by weight of ester monomer, c)
D) vinyl acetate. Obtained by emulsion polymerization of vinyl acetate and / or (meth) acrylic acid ester with 0 to 30% by weight of a copolymerizable monomer, and having a gel fraction of 0 to 30% by weight. A (meth) acrylate copolymer emulsion is a main component, the proportion of d) in the organic compound in the whole composition is 50 to 100% by weight, and the gel fraction in the whole composition is 0 to 100% by weight. An adhesive composition which is contained in a range of 30% by weight and has a solid content of 40 to 85%. 4. The adhesive composition according to claim 3, wherein the adhesive composition does not contain a surfactant. 5. Use of polyvinyl alcohol as an emulsion stabilizer in the presence of a gel fraction inhibitor, without using a surfactant, a) 1-70% by weight of a vinyl acetate monomer, b) (meth) acrylic acid 30 to 95% by weight of ester monomer, c)
Emulsion polymerization of vinyl acetate and / or (meth) acrylic acid ester with 0 to 30% by weight of a copolymerizable monomer is characterized by having a gel fraction of 0 to 30% by weight. ) A method for producing an acrylic ester copolymer emulsion. 6. A gel fraction inhibitor comprising 2,2,4-trimethyl-1,3-pentanediol, 2,2,4-trimethyl1,3-pentanediol monoisobutyrate,
The method for producing a vinyl acetate / (meth) acrylic acid ester copolymer emulsion according to claim 5, which is one or more kinds selected from 2,4-trimethyl 1,3-pentanediol diisobutyrate.