JPH08295850A - Acrylic sol - Google Patents

Abstract

PURPOSE: To obtain an acrylic sol not evolving a hydrogen chloride gas during incineration, excellent in compatibility with a plasticizer, film forming properties and storage stability. CONSTITUTION: This acrylic sol comprises (I) an acrylic polymer particle consisting of constituent units composed of (a-1) a specific (meth)acrylate unit excellent in compatibility with a plasticizer, (b-1) a prescribed methacrylate unit having low compatibility with a plasticizer and (b-2) a specific unsaturated carboxlic acid unit and having the constitution ratio of the component (a-1) decreasing from the central part toward the outermost part of the acrylic polymer particle (I) in multiple stages or continuously and the constituent ratios of the components (b-1) and (b-2) increasing from the central part toward the outermost part of the acrylic polymer particle in multiple stages of continuously, (II) a plasticizer and (III) a filler.

Description

Detailed Description of the Invention

[0001]

The present invention relates to acrylic polymer particles,
The present invention relates to an acrylic plastisol composed of a plasticizer and a filler, and an acrylic organosol obtained by adding an organic solvent to the acrylic plastisol.

[0002]

2. Description of the Related Art Plastisols which are widely used in the industry at present are composed mainly of vinyl chloride sol obtained by dispersing polyvinyl chloride powder and a filler in a plasticizer.
Depending on the application, those containing a pigment, heat stabilizer, foaming agent, diluent, etc. are common. This plastisol is used in various fields such as automobiles, carpets, wallpaper and floors.

On the other hand, from the viewpoint of environmental problems, PVC-related products which generate hydrogen chloride gas during incineration not only cause destruction of the ozone layer and acid rain, but also seriously damage the incinerator, and are called dioxin. Since it has a serious problem of generating harmful substances, the appearance of plastisol instead of vinyl chloride sol has been awaited in various commercial fields.

In response to this requirement, as a plastisol which does not generate hydrogen chloride gas at the time of incineration, Japanese Patent Publication No. 55-1617.
No. 7 publication proposes an acrylic sol composition. This is because acrylic polymer particles of uniform composition are used.When a general-purpose plasticizer such as dioctyl phthalate is used, the solubility in the particles is high and the viscosity of the acrylic sol increases within a few minutes after mixing. Therefore, it cannot be applied practically and cannot be used in practice. In order to improve the coating stability and storage stability of the acrylic sol, it has been proposed to copolymerize a monomer component having low solubility with an acrylic polymer, which is the surface of the coating film after curing. In addition, there is a problem that the plasticizer easily bleeds out. As described above, in the conventional acrylic sol, although hydrogen chloride gas is not generated during incineration, practical properties such as coating properties and storage stability such as not increasing viscosity during storage cannot be satisfied at present.

Further, in JP-A-6-25365,
A plastisol characterized by using a styrene polymer having a good compatibility with a plasticizer as a core layer and a copolymerized polymer of methyl methacrylate, an unsaturated carboxylic acid and an unsaturated alcohol having an incompatibility with the plasticizer as a shell layer. Is disclosed. However, when the core layer and the shell layer have a multilayer structure composed of two types of monomer units having different compatibility with the plasticizer,
The cured coating film formed under the gelling condition of high temperature and short time heating is essentially lacking in compatibility with the plasticizer and
Since the polymer having a shell structure also lacks in compatibility, a layer separation phenomenon easily occurs in the polymer, resulting in brittleness. In particular, in the case of forming bubble cells during film formation with a foaming agent, the gelled film becomes significantly defective, resulting in a coating film having extremely insufficient flexibility as compared with a PVC sol product. Further, in such a plastisol, a phosphoric acid ester system is used as a plasticizer, and a good cured coating film can be formed only under limited conditions such that an ester part has an aromatic ring, Inexpensive plasticizers such as dioctyl phthalate and diisononyl phthalate, which are widely used in PVC sol, cannot be used because bleed-out of the plasticizer occurs on the coating film.

Therefore, as a measure against the bleeding out of the plasticizer, the present inventors tried a plastisol in which a polymer having a high compatibility with the plasticizer was blended in the core portion, but the polymer swelled / dissolved by the plasticizer, Since the sol viscosity increases, the long-term dispersion stability is insufficient, and it is not yet sufficiently satisfactory.

[0007]

DISCLOSURE OF THE INVENTION According to the present invention, it is possible to use a general-purpose dialkyl phthalate plasticizer which is inexpensive and industrially advantageous, such as dioctyl phthalate and diisononyl phthalate, without generating hydrogen chloride gas during incineration. In addition, under room temperature conditions, the dispersion stability with respect to the plasticizer is good and there is little change in viscosity. Under high temperature conditions, it dissolves and gels easily, and there is no bleed out of the plasticizer, and a cured film with good flexibility is obtained. The aim is to provide a plastisol which can be formed.

[0008]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that the composition ratio of a specific monomer unit changes in multiple steps or continuously from the central part of the particle toward the outermost part. It has been found that the above problems can be solved by using acrylic polymer particles having a mold structure, and the present invention has been completed. That is, the present invention is
In an acrylic sol containing an acrylic polymer particle (I), a plasticizer (II) and a filler (III), the acrylic polymer particle (I) is a structural unit of the particle from the central part to the outermost part. The acrylic sol has a ground-type structure in which the composition ratio of is varied in multiple stages or continuously.

The acrylic sol of the present invention will be described in detail below. The acrylic sol of the present invention comprises acrylic polymer particles (I), a plasticizer (II) and a filler (III). The acrylic polymer particles of the component (I) are composed of at least a (meth) acrylate unit (a-1) having good compatibility with a plasticizer and a methacrylate unit (b-1) having a low compatibility with a plasticizer and methyl. Methacrylate, at least one methacrylate unit selected from benzyl methacrylate (b-1), and at least one carboxylic acid unit selected from methacrylic acid, acrylic acid, itaconic acid, crotonic acid (b-2), these, It has a gradient type structure in which the constitutional ratio of the constitutional units of (1) changes in multiple stages or continuously from the central part of the particle toward the outermost part. Specifically, the constituent ratio of the (meth) acrylate unit (a-1) is reduced in multiple steps or continuously from the central part of the acrylic polymer particle (I) to the outermost part,
(b-1) and the unsaturated carboxylic acid unit (b-2) composition ratio increases from the central part of the acrylic polymer particle (I) to the outermost part in multiple steps or continuously Have. With such a structure, it is possible to obtain an acrylic sol capable of forming a cured coating film by diffusing and gelling the plasticizer by heating at 100 ° C. or higher.

Although the molecular weight of the acrylic polymer particles as the component (I) of the present invention varies depending on the use, it is preferably 10,000 to 2,000,000 in terms of weight average molecular weight. When the weight average molecular weight is less than 10,000, the obtained acrylic polymer particles tend to be easily dissolved in the plasticizer, and the weight average molecular weight is 2,000,00.
This is because if it is larger than 0, it tends to be difficult to produce acrylic polymer particles by emulsion polymerization.

The particle diameter of the component (I) is preferably 0.1 to 100 μm for primary particles and / or secondary particles obtained by aggregating the primary particles, from the viewpoint of the balance between heat film forming property and storage stability. The thickness is preferably 3 to 30 μm. If this particle size is too large, the plasticizer tends to be poorly diffused during heating and film formation, and complete gelation tends not to occur. If the particle size is too small, the storage stability of the acrylic sol tends to be insufficient. Therefore, it is preferable to optimize the particle size according to the required performance.

Acrylic polymer particles (I) used in the present invention
The method for producing is not particularly limited as long as the particle structure has a structure in which the constitutional ratio of constitutional units of a specific monomer changes from the central part to the outermost part in multiple stages or continuously. However, acrylic polymer particles (I)
The emulsion polymerization method is particularly preferable from the viewpoint of efficiently obtaining an emulsion containing The obtained emulsion containing the acrylic polymer particles (I) is coagulated and dried by, for example, a spray drying method or an acid or salting out to obtain the acrylic polymer particles (I) of the present invention.

Acrylic polymer particles (I) used in the present invention
The (meth) acrylate unit (a-1) constituting the is a component having a high affinity with a plasticizer, and specific examples thereof include ethyl methacrylate, n-butyl methacrylate, i-
Examples thereof include butyl methacrylate, sec-butyl methacrylate, Tert-butyl methacrylate, cyclohexyl methacrylate, ethylhexyl methacrylate, ethyl acrylate, n-butyl acrylate, sec-butyl acrylate, and tert-butyl acrylate. These may be used alone or in combination of two or more.

The methacrylate unit (b-1) constituting the acrylic polymer particles (I) used in the present invention is a component having low compatibility with the plasticizer, and specific examples thereof include methyl methacrylate and benzyl methacrylate. Any one or both of these can be used. As the unsaturated carboxylic acid unit which is the component (b-2),
Specific examples include methacrylic acid, acrylic acid, itaconic acid, and crotonic acid, and these can be used alone or in combination of two or more kinds.

Acrylic polymer particles (I) used in the present invention
In order to form the above-mentioned ground structure, the monomer mixture (Ia) containing the (meth) acrylate component (a-1), the methacrylate component (b-1) and the unsaturated carboxylic acid The monomer mixture (Ib) containing the components is preferably polymerized while changing the blending ratio thereof in multiple stages or continuously.

As the monomer mixture (Ia), in addition to the component (a-1), an unsaturated carboxylic acid component (a-2) may be mixed as a component having good compatibility with the plasticizer. In addition, in order to adjust the balance of compatibility with the plasticizer and storage stability,
Component (a-1) component and monomer component (a-2) other than component (a-)
3) may be mixed.

Specific examples of the unsaturated carboxylic acid as the component (a-2) include (meth) acrylic acid, itaconic acid,
At least one unsaturated carboxylic acid selected from crotonic acid and the like can be mentioned.

The component (a-1) and the component (a-) which are the component (a-3).
2) Specific examples of monomers other than the component include 1 to 1 carbon atoms.
Thirteen alcohols (meth) acrylate, acrylonitrile, (meth) acrylamide, N-dimethylacrylamide, N-dimethylmethacrylamide, N-dimethylaminoethylmethacrylate, N-diethylaminoethylmethacrylate, vinyl acetate, styrene, α-methylstyrene. , (Meth) acrylic acid, crotonic acid, itaconic acid, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, ethylene glycol dimethacrylate, divinylbenzene, glycidyl methacrylate, allyl methacrylate and the like. These may be used alone or in combination of two or more.

The ratio of these components (a-1), (a-2) and (a-3) is (a-1) / (a- from the viewpoint of flexibility of the cured coating film.
2) / (a-3) = 50 to 100/0 to 40/0 to 40 (% by weight) is preferable. Particularly preferably, (a-
1) / (a-2) / (a-3) = 70-90 / 0-5 / 0-5
(% By weight).

As the monomer mixture (Ib),
In addition to the component (b-1), an unsaturated carboxylic acid unit (b-2) may be mixed as a component having low compatibility with the plasticizer. Also,
Monomer units (b-) other than the component (b-1) and the component (b-2) are used for the purpose of adjusting the balance between the compatibility with the plasticizer and the storage stability.
You may mix and use 3).

Specific examples of the component (b-2) include at least one selected from methacrylic acid, acrylic acid, itaconic acid and crotonic acid.

Further, specific examples of the component (b-3) include (meth) acrylate of alcohol having 1 to 13 carbon atoms, acrylonitrile, (meth) acrylamide, N-dimethylacrylamide, N-dimethylmethacrylamide, N-.
Dimethylaminoethyl methacrylate, N-diethylaminoethyl methacrylate, vinyl acetate, styrene,
Examples thereof include α-methylstyrene, (meth) acrylic acid, crotonic acid, itaconic acid, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, ethylene glycol dimethacrylate, divinylbenzene, glycidyl methacrylate, allyl methacrylate and the like. These may be used alone or in combination of two or more.

The ratio of these components (b-1), (b-2), and (b-3) is (b-1) / (b-2) in terms of storage stability of the acrylic sol. /(B-3)=60.5 to 99.5
/0.5 to 10/0 to 29.5 (% by weight) is preferable. Particularly preferably, (b-1) / (b-2) / (b-
3) = 75 to 99/1 to 5/0 to 20 (% by weight).

In the acrylic polymer particles (I) of the present invention, the mixing ratio of the monomer mixture (Ia) and the monomer mixture (Ib) varies depending on the selection of the mixed monomers, but the compatibility with the plasticizer, Considering the target performance of acrylic sol such as film-forming property and storage stability, (Ia) / (Ib) = 30
/ 70 to 70/30 is preferable.

The plasticizer which is the component (II) of the present invention is not particularly limited, but it is a dialkyl phthalate type having a high dissolving power such as dioctyl phthalate, diisononyl phthalate, diisodecyl phthalate and diundecyl phthalate which are commonly used in vinyl chloride sol. Plasticizers can be used. Particularly, dioctyl phthalate, diisononyl phthalate and the like are inexpensive and industrially preferable.

The amount of the plasticizer (II) used in the present invention is
50 to 100 parts by weight of acrylic polymer particles (I)
It is preferably 500 parts by weight. If the amount of the plasticizer used is less than 50 parts by weight with respect to 100 parts by weight of the component (I), the viscosity of the acrylic sol may be high and the coating may not be possible. If the content of the agent is too large, the gelled cured coating tends to bleed out the plasticizer.

The filler (III) used in the present invention is not particularly limited as long as it is a component capable of imparting the hiding property by increasing the amount of the acrylic sol and coloring it. Specific examples thereof include calcium carbonate, paraita, clay, colloidal silica, mica powder, diatomaceous earth, kaolin, talc, pentonite, glass powder, sand, aluminum oxide, aluminum hydroxide, antimony trioxide, titanium dioxide, carbon. Examples include black, metallic soap, dyes, pigments, and the like. Particularly preferred are calcium carbonate, titanium dioxide and the like for the purpose of increasing the amount of the acrylic sol.

The proportion of the component (III) used in the present invention is 5 based on 100 parts by weight of the acrylic polymer particles (I).
It is preferably from 0 to 500 parts by weight. When the amount used is less than 50 parts by weight based on 100 parts by weight of the acrylic polymer particles, various performances of the acrylic sol tend to be difficult to develop, and when it is more than 500 parts by weight,
The viscosity of the acrylic sol tends to be too high.

The acrylic sol of the present invention includes the above (I) to
In addition to component (III), an organosol can be prepared by adding, for example, mineral turbene as a diluent. Further, various additives such as an adhesion promoter, a leveling agent, an anti-tacking agent, a release agent, an antifoaming agent, a foaming agent, a surfactant, an ultraviolet absorber, a lubricant, a flame retardant, and a fragrance are added depending on the purpose. can do.

The acrylic sol of the present invention can be applied in various applications, such as brush coating method, spray coating method, dip coating method, knife coating method, roll coating method, curtain flow coating method and electrostatic coating method. It can be used as a coating material used or a molding material used in a dip molding method, a cast molding method, a slush molding method, a rotation molding method, or the like.

The cured coating film obtained by gelling with the acrylic sol of the present invention has a gel forming temperature of 70 to 260 ° C.
Within the range, the treatment time can be formed within the range of 30 seconds to 90 minutes, and the conditions in this range may be appropriately selected depending on the composition of the acrylic sol. Further, depending on the application, the obtained cured coating film may be subjected to printing, embossing or foaming treatment.

The acrylic sol of the present invention is used for paints, inks,
It can be applied to adhesives, pressure-sensitive adhesives, sealing agents, etc., and also to molded products such as sundries, toys, industrial parts, and electric parts. Further, for example, when applied to paper or cloth, artificial leather, rug, medical treatment, waterproof sheet, etc. can be obtained, and when applied to a metal plate, a corrosion-resistant metal plate can be obtained.

[0033]

EXAMPLES The present invention will be described in detail below with reference to examples. However, the part in an Example shows a weight part.

[Evaluation method]

<Sol Performance> Viscosity change: The viscosity (25 ° C.) / Initial viscosity (25 ° C.) after standing for 6 days was measured by an E-type viscometer manufactured by Tokyo Keiki Co., Ltd. ○… <2.0 △… 2.0 to 3.0 × ...> 3.0 Storage stability; Acrylic sol was prepared and allowed to stand at 25 ° C. for 6 days, and then coated on a substrate to evaluate coatability. did. ○: Coating is possible △: Coating is difficult due to thickening due to partial gelling ×: Gelation progresses, thickening is severe and coating is impossible

<Coating film performance> Non-bleed-out property: 10 ° C. after forming a cured coating film
The surface of the coating film after being kept for 1 week was evaluated by touch with a finger. ◯: No bleed-out ×: With bleed-out Coating uniformity: The state of the cured coating after baking at 200 ° C. for 45 seconds was visually evaluated. Good coating film with good heat fusion of the polymer and smooth coating film with unevenness due to partial poor heat fusion of the polymer. Poor coating film with poor heat fusion bonding of the polymer and flexibility. After forming a cured coating film, fold it 180 degrees,
The state of the coating film was visually evaluated. ○: No crack ×: Crack

[Example 1] [Preparation of monomer mixture (A1)] 120 parts of isobutyl methacrylate, 60 parts of butyl acrylate, 120 parts of methyl methacrylate, polyoxyethylene nonylphenyl ether (manufactured by Kao Corporation; trade name: Emulgen 90)
5) Mixing 6.0 parts of monomer mixture (A1) 306
Parts were prepared.

[Preparation of Monomer Mixture (B1)] 550 parts of methyl methacrylate, 7.2 parts of methacrylic acid, and 6 parts of sodium dialkylsulfosuccinate (manufactured by Kao Corporation; trade name: Perex OTP) are mixed to prepare a monomer component ( B1) 563.2 parts was prepared.

[Production of Acrylic Polymer Particles (6 Division Drop Polymerization)] Pure water 1294 was placed in a 5-liter four-necked flask.
Parts, polyoxyethylene nonyl phenyl ether (manufactured by Kao Corporation; trade name: Emulgen 910), 7.8 parts, and potassium persulfate, 1.8 parts, were added, and the mixture was placed in a nitrogen atmosphere at 13
The temperature was raised to 70 ° C. with stirring at 0 rpm. Next, a monomer mixture prepared by mixing 5/12 amount of the monomer mixture (A1) prepared in advance and 1/12 amount of the monomer mixture (B1) was dropped into the flask over 30 minutes, and held for 30 minutes, The first stage emulsion polymerization was performed. Next, using the particles polymerized in the first step as seed particles, emulsion polymerization was carried out by repeating dropping and holding from the second step to the sixth step under the conditions shown in Table 1 and holding for 1 hour. Further, the temperature was raised to 80 ° C. and maintained for 1 hour, then emulsion polymerization was completed to obtain a milky white emulsion (solid content 40.1%).

[0040]

[Table 1]

The obtained emulsion was spray-dried (manufactured by Okawara Kakoki Co., Ltd .; trade name: L-8 type) with a chamber inlet temperature of 120 ° C. and a chamber outlet temperature of 80.
C., atomizer rotation number was set to 25000 rpm, spray drying was carried out to obtain powder, and acrylic polymer particles having an average particle diameter of 18 .mu.m were obtained. Then, as a result of observing the obtained particles with an electron microscope (manufactured by JEOL Ltd.), primary particles of 1 μm or less aggregated to form spherical particles of about 18 μm. Next, to 100 parts of the obtained acrylic polymer particles, 80 parts of dioctyl phthalate and calcium carbonate (manufactured by Takehara Chemical Industry Co., Ltd .; trade name: Neolite SP) 70
And 20 parts of mineral tarpen were added to obtain an acrylic sol.

As a result of evaluating the physical properties of this sol, the initial viscosity was 3200 cps, and the viscosity (25 ° C.) after standing at 25 ° C. for 6 days was 3900 cps, and the storage stability was practically sufficient. This sol was applied to a tin plate with a knife coater to a thickness of 50 μm and heated at 200 ° C. for 45 seconds to cause gelation, and a uniform cured coating film was obtained. The cured coating film had no bleeding of the plasticizer even after being kept at 10 ° C. for 1 week, and the compatibility with the plasticizer was good. Further, this cured coating film had sufficient flexibility without cracking even when bent 180 degrees.

[Examples 2 and 3, Comparative Examples 1 to 4] Example 1
Six kinds of acrylic polymer particles shown in Table 2 were obtained by the same method as described above.

[0044]

[Table 2]

The abbreviations in the table are as follows. iBMA: Isobutyl Methacrylate nBMA: Normal Butyl Methacrylate nBA: Normal Butyl Acrylate EMA: Ethyl Methacrylate MMA: Methyl Methacrylate MAA: Methacrylic Acid AA: Acrylic Acid Next, as in Example 1, except that diisononyl phthalate is used as a plasticizer. Then, an acrylic sol and a cured coating film were obtained using the acrylic sol. The results of these evaluations are shown in Table 3.

[Comparative Example 5] Monomer mixture (A1) 1 /
Polymerization was carried out in the same manner as in Example 1 except that a monomer mixture in which 6 amounts and 1/6 amount of the monomer mixture (B1) were mixed was uniformly dropped from the first stage to the sixth stage, Acrylic sol was prepared by obtaining polymer particles having no gradient type composition structure. Then, in the same manner as in Example 1, the obtained acrylic sol and a cured coating film were obtained using the acrylic sol. The evaluation results are shown in Table 3.

[Comparative Example 6] 1251 parts of pure water and polyoxyethylene nonylphenyl ether (manufactured by Kao Corporation; trade name: Emulgen 91) were placed in a 5-liter four-necked flask.
0) 8.5 parts and 1.0 part of potassium persulfate were added, and the temperature was raised to 70 ° C. in a nitrogen atmosphere while stirring at 150 rpm. In this, 140 parts of n-butyl methacrylate, 41.4 parts of n-butyl acrylate, 40 parts of ethyl methacrylate, 20 parts of methyl methacrylate, sodium dialkyl sulfosuccinate (manufactured by Kao Corporation; The total amount of the monomer mixture (A6) obtained by mixing 5 parts of trade name: Perex OTP) was added dropwise over 2 hours, and the mixture was kept for 1 hour to polymerize the seed particles.
Next, as the outermost monomer mixture, 445 parts of methyl methacrylate, 6 parts of methacrylic acid, and sodium dialkylsulfosuccinate (Kao Corporation; trade name: Perex, a monomer mixture (B5) containing 5 parts of TP were mixed for 2 hours. The mixture was added dropwise, kept for 2 hours, heated to 80 ° C. and kept for 1 hour to complete the seed polymerization to obtain an emulsion containing polymer particles having a core / shell type two-layer structure. The acrylic polymer particles obtained by pulverizing in the same manner as in Example 1 were mixed with the same plasticizer as in Example 1 to prepare an acrylic sol.

The obtained acrylic sol had good storage stability, but the gelled film was opaque and did not become a completely uniform film, and the layer was partially peeled off. In addition, the gelled film is 180
When it was bent many times, small cracks were generated and the flexibility was insufficient.

[0049]

[Table 3]

In Comparative Example 1, since the total amount of the monomer component (A) was small, the storage stability of the acrylic sol was good, but the gelled cured coating film bleeded out of the plasticizer. In Comparative Example 2, since the total amount of the monomer component (B) is small and the plasticizer resistance of the acrylic polymer particles is insufficient, the acrylic polymer particles start to dissolve at room temperature and the viscosity of the acrylic sol increases. , Storage stability became poor. Comparative Example 3 is MMA in the monomer component (A).
Since the amount of is too large, the compatibility between the acrylic polymer particles and the plasticizer was insufficient, and the gelled cured coating film bleeded out of the plasticizer. Further, in Comparative Example 4, since the amount of MMA in the monomer component (B) was too small, the acrylic polymer particles started to dissolve at room temperature, the viscosity of the acrylic sol increased, and the storage stability became poor.

As described above, the acrylic sol of the present invention is
It does not generate hydrogen chloride gas at the time of incineration and can be used for practical plastisol and organosol by using general-purpose inexpensive and industrially advantageous plasticizers such as dioctyl phthalate and diisononyl phthalate, and its industrial significance. Is large.

Claims (2)

[Claims] 1. Acrylic polymer particles (I), plasticizer (II)
In the acrylic sol containing the filler (III) and the acrylic polymer particles (I), the acrylic polymer particles (I) are granulated such that the constituent ratio of the constituent units changes from the central part to the outermost part in multiple stages or continuously. An acrylic sol having a gentle structure. 2. Acrylic polymer particles (I) are ethyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, sec-butyl methacrylate, ter.
at least one (meth) acrylate unit (a-1) selected from t-butyl methacrylate, cyclohexyl methacrylate, ethylhexyl methacrylate, ethyl acrylate, n-butyl acrylate, sec-butyl acrylate and tert-butyl acrylate,
At least one methacrylate unit (b-1) selected from methyl methacrylate and benzyl methacrylate, and at least one unsaturated carboxylic acid unit selected from methacrylic acid, acrylic acid, itaconic acid, and crotonic acid
(b-2) and at least the (meth) acrylate unit (a-1) is contained in the acrylic polymer particles (I).
From the central part of the acrylic polymer particles (I) toward the outermost part in a multi-step or continuous manner, and the ratio of the methacrylate unit (b-1) and the unsaturated carboxylic acid unit (b-2) is the center of the acrylic polymer particle (I). The acrylic sol according to claim 1, wherein the amount increases in multiple stages or continuously from the part to the outermost part.