JP2005239769A - Acrylic polymer fine particle and production method therefor, and plastisol composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide acrylic polymer fine particles which can uniformly and easily be dispersed in an organic solvent, and to obtain a plastisol composition having largely improved flowability. <P>SOLUTION: The acrylic polymer fine particles having fine particles having a volume-average particle diameter of ≤100 μm as primary particles, is characterized by having a contact angle of ≥90 degree to water. A method for producing the acrylic polymer fine particles comprises adding a monomer having a solubility of ≤0.03 mass % in 20°C water or a compound comprising alkylsiloxane units to a polymer dispersion, and then drying the polymer dispersion to recover the polymer. The plastisol composition contains the acrylic polymer fine particles. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an acrylic polymer fine particle having a hydrophobic surface and a method for producing the same. The present invention also relates to a plastisol composition obtained by dispersing the acrylic polymer fine particles in a plasticizer or the like.

  Acrylic polymer fine particles having a very small particle diameter have been increasingly used in various industrial fields including plastisol. Since the fine particles are usually obtained by polymerization in an aqueous medium such as emulsion polymerization or fine suspension polymerization, the surface of the particles is hydrophilic. Such properties are suitable when re-dispersed in water and used like re-emulsified powder. However, for example, in applications that are used by being dispersed in an organic medium such as plastisol, the wettability to the medium is low and it is extremely difficult to use. Furthermore, when fine particles having low wettability are dispersed in an organic medium, not only is the dispersion difficult to disperse, but the obtained dispersion has a structural viscosity, resulting in inconveniences such as poor fluidity.

  Hereinafter, the case where such fine particles are used in plastisol will be described in detail. Pasty materials obtained by dispersing thermoplastic polymer particles in a plasticizer are collectively referred to as plastisol. In particular, plastisols using vinyl chloride polymers are widely used in various industrial fields as vinyl chloride sols. In recent years, a plastisol (hereinafter abbreviated as “acrylic sol”) using an acrylic polymer has also been proposed, and has attracted attention as a material excellent in environmental compatibility, such as being less toxic gas at the time of incineration unlike vinyl chloride sol.

  There have been a number of specific proposals regarding the constitution of polymers that can be used as acrylic sols and their applications. For example, the structure of the polymer described in Patent Document 1 can provide a practically well-balanced performance, and can be cited as a typical prior art in this field. In addition to Patent Document 1, for example, Patent Document 2, Patent Document 3, Patent Document 4 and the like can be cited as prior art of acrylic sol.

  The polymer fine particles proposed in each of these patent documents are all prepared by spray-drying a polymer latex obtained by emulsion polymerization to form a powder. Therefore, hydrophilic functional groups, emulsifiers and the like are present on the surface of the polymer fine particles, and the state is extremely high in hydrophilicity. Therefore, when it is dispersed in an organic medium such as a plasticizer such as plastisol, the dispersibility is extremely low. Specifically, (1) when mixing the fine particles and the plasticizer, the fine particles are difficult to adapt to the plasticizer and take a long time for uniform mixing. (2) The thixotropy of the obtained dispersion (plastisol) is high. Problems such as poor fluidity arise. The problem (1) cannot be solved by taking time and effort, but the problem (2) is very difficult to solve unless the properties of the fine particles are modified.

As described above, in the conventionally proposed acrylic polymer fine particles, the particle surface is not sufficiently hydrophobized, and therefore has high thixotropy when dispersed in an organic medium and requires fluidity. It is very difficult to apply to the field.
International Publication No. 00/01748 Pamphlet JP-A-7-233299 Japanese Patent Laid-Open No. 8-3411 JP-A-8-295850

  An object of the present invention is to prepare acrylic polymer fine particles that can be produced by a polymerization method using an aqueous medium such as emulsion polymerization and fine suspension polymerization, and that can be easily uniformly dispersed in an organic medium, and such fine particles are simple and good It is to provide a method that can be manufactured. It is a further object of the present invention to provide a plastisol composition with significantly improved flowability.

  As a result of intensive studies on the above problems, the inventors of the present invention can easily achieve uniform dispersion in an organic medium by hydrophobizing the surface of fine particles and setting the contact angle to water to 90 degrees or more. It has been found that it can be used for applications, and in particular, in the case of plastisol, it has been found that the viscosity characteristics are remarkably changed and the fluidity is dramatically improved, and the present invention has been achieved.

  That is, the present invention is an acrylic polymer fine particle having a fine particle having a volume average particle size of 100 μm or less as a primary particle, and having a contact angle with water of 90 ° or more. .

  Furthermore, the present invention is a method for producing acrylic polymer fine particles having the above-mentioned characteristics, wherein an acrylic monomer is polymerized in an aqueous medium to prepare a polymer dispersion, and water at 20 ° C. Of acrylic polymer fine particles having a step of adding a monomer (or a compound comprising an alkylsiloxane unit) having a solubility in 0.03% by mass or less to this, and then drying the polymer dispersion to recover the polymer Is the method.

  Furthermore, the present invention is a plastisol composition comprising the above acrylic polymer fine particles.

  In the present invention, since the acrylic polymer fine particles have specific properties (specific contact angle with water), even fine particles produced by a polymerization method using an aqueous medium such as emulsion polymerization or fine suspension polymerization are organic. Uniform dispersion on the medium is easy. Moreover, the manufacture can be carried out easily and satisfactorily. In particular, by using these acrylic polymer fine particles, dramatic wettability and fluidity improvement effects can be obtained in applications where fine particles are dispersed in an organic medium such as plastisol. Such improved wettability can reduce the energy and time required for mixing. Moreover, the improvement of wettability can give high fluidity to the dispersion, and various processing methods that have not been conventionally available become possible. Therefore, the industrial significance of the present invention and the effect on global environmental conservation are significant.

  In the present invention, the acrylic polymer fine particles are composed of primary particles having a volume average particle diameter of 100 μm or less. Polymer particles with larger particle diameters are generally produced by suspension polymerization, but these can be dispersed in an organic medium because hydrophilic components such as dispersants and emulsifiers can be easily washed by washing treatment after polymerization. There is no problem even in applications that are used. On the other hand, polymer fine particles having a particle diameter of 100 μm or less are mostly produced by fine suspension polymerization or emulsion polymerization. The fine particles obtained are extremely difficult to clean because of their small size, and it is almost impossible to sufficiently remove emulsifiers and dispersants at the industrial level.

  In the present invention, the volume average particle diameter of the primary particles is further preferably 10 μm or less, and particularly preferably 2 μm or less. In general, fine particles having a small particle diameter require a large amount of an emulsifier and a dispersant to be added during polymerization in the production process, and the surface is likely to become hydrophilic. At the same time, the smaller the particle size, the larger the total surface area of the particles and the more susceptible to wettability. Therefore, the effect obtained by hydrophobizing the particle surface becomes more remarkable as the particle diameter is smaller. Specifically, fine particles having a volume average particle size of 10 μm or less are often produced by fine suspension polymerization, and in this case, since a large amount of dispersant is contained, the effect of hydrophobization is particularly great. Furthermore, fine particles having a volume average particle diameter of 2 μm or less are often produced by emulsion polymerization, and since they contain a lot of highly hydrophilic emulsifiers, the effect of hydrophobization becomes even greater.

  Moreover, about the minimum of the volume average particle diameter of a primary particle, 500 nm or more is preferable. This is to maintain the dispersion stability of the particles in the aqueous polymerization by hydrophobizing.

  In the present invention, the contact angle of the acrylic polymer fine particles with respect to water is 90 degrees or more. If the contact angle is less than 90 degrees, the polymer has high hydrophilicity and poor wettability with respect to an organic medium such as a plasticizer and is difficult to disperse in the organic medium. In addition, the fluidity after dispersion is poor and the dispersion becomes extremely thixotropic. Further, the contact angle is preferably 120 degrees or more. When preparing plastisols, various plasticizers are generally used as the organic dispersion medium. However, if the contact angle is 120 degrees or more, the fluidity is improved particularly when a highly versatile plasticizer such as dialkyl phthalate is used. Is done.

  This contact angle is a value obtained by measurement by the following method. First, polymer fine particles are filled into a flat plate-shaped mold, and press molding is performed at a temperature of 60 ° C. under a pressure of 20 MPa to produce a flat test body in which the fine particles are compacted. And the contact angle with respect to a pure water is measured using a commercially available contact angle measuring apparatus with respect to this flat plate at 25 +/- 5 degreeC environment.

  It is preferable that at least the surface layer of the acrylic polymer fine particles contains a hydrophobic organic compound or a polymer obtained by copolymerizing a hydrophobic monomer. Here, the hydrophobic property means that the solubility in water at 20 ° C. is 0.03 mass% or less. By using a material having such a low solubility, the contact angle described above can be easily realized. Here, the former hydrophobic organic compound is typically a hydrophobic monomer, the case where it is not polymerized corresponds to the former, and the case where it is copolymerized corresponds to the latter. In particular, a state in which a hydrophobic monomer is copolymerized is preferable because the component is fixed and changes with time are reduced.

  Specific examples of the hydrophobic organic compound and the hydrophobic monomer include 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, stearyl (meth) acrylate, isobornyl ( Examples include alkyl (meth) acrylates such as (meth) acrylate. However, the present invention is not limited to these. These monomers may be copolymerized or may exist in the state of non-copolymerized monomers (hydrophobic organic compounds).

  The location where the hydrophobic organic compound or the polymer formed by copolymerization of the hydrophobic monomer exists may be at least the surface layer of the polymer fine particles. When it exists only in the inside rather than the surface layer, the surface properties of the particles are substantially not affected, and the effect of obtaining the contact angle as described above becomes small. However, as long as there is no harmful effect, these may be present not only on the surface layer but also inside the particles.

  In plastisol compositions, if a large amount of polymer formed by copolymerization of hydrophobic organic compounds and hydrophobic monomers is present in the interior of the fine particles, the storage stability may decrease, so they exist only on the surface layer. It is preferable to do. In particular, acrylic plastisol compositions are conventionally known to use fine polymer particles having a core / shell structure. In this case, a hydrophobic organic compound or a hydrophobic monomer is copolymerized. It is preferable from the viewpoint of maintaining storage stability that the polymer is present on the surface of the particle with a sufficiently thin thickness with respect to the thickness of the shell.

  The copolymerization ratio of the hydrophobic monomer is not particularly limited, but the preferable lower limit is 0.1% by mass (% by mass with respect to the total amount of monomers giving the polymer), and the reason is not limited to the type of the hydrophobic monomer, and the high contact angle. It is easy to get. Moreover, a preferable upper limit is 5 mass% because the polymerization stability in an aqueous medium is good and the productivity is high.

  Moreover, it is also preferable that the component which consists of an alkylsiloxane unit exists in the at least surface layer of acrylic polymer microparticles. The presence of such components on the surface layer allows the fine particles to have a sufficiently high contact angle with water. The alkylsiloxane unit refers to one having 1 to 3 alkyl groups and 1 to 3 oxygen atoms bonded to a silicon atom (however, the total number of alkyl groups and oxygen atoms is 4). This component may be, for example, a compound comprising an alkylsiloxane unit alone or a polyalkylsiloxane compound comprising a plurality of alkylsiloxane units as monomer units. In particular, polysiloxane compounds are preferred because they are difficult to dissipate due to volatilization and the like. Specifically, polydialkylsiloxane compounds are preferable, and polydimethylsiloxane is particularly preferable. These are easily available industrially and can be easily added to an aqueous medium.

  The method for producing the acrylic polymer fine particles of the present invention is not particularly limited. In particular, an acrylic monomer is polymerized in an aqueous medium to prepare a polymer dispersion, a hydrophobic compound (hydrophobic monomer, etc.) is added thereto, and then the polymer dispersion is dried to recover the polymer. The method is preferred. This is because according to this method, the hydrophobic compound can be efficiently introduced into the particle surface layer. Furthermore, a method in which a hydrophobic monomer is emulsified with an emulsifier and water and supplied to the reaction system is preferable. In the case of emulsion polymerization, the hydrophobic monomer has a low diffusion rate in an aqueous medium, and thus the polymerization rate tends to decrease. However, the decrease in polymerization rate can be avoided by increasing the surface area of the monomer by emulsifying in advance. Because.

  When a hydrophobic monomer is copolymerized, auxiliary agents such as a chain transfer agent can be used in combination.

  When using a compound having an alkylsiloxane unit, in particular, an acrylic monomer is polymerized in an aqueous medium to prepare a polymer dispersion, a compound comprising an alkylsiloxane unit is added thereto, and then the polymer dispersion A method of drying the polymer to recover the polymer is preferred. This is because this method can efficiently introduce a compound having an alkylsiloxane unit into the particle surface layer. Furthermore, a method of supplying dialkoxydialkylsilane and / or a hydrolyzate thereof, polydialkylsiloxane and / or a hydrolyzate thereof to the reaction system under acidic or alkaline conditions is preferable. These compounds easily form a polysiloxane skeleton by condensation reaction under acidic or alkaline conditions, and efficiently produce a compound having a polysiloxane skeleton on the surface of polymer fine particles when drying an aqueous dispersion of the polymer. This is because the surface can be hydrophobized.

  The structure of the acrylic polymer fine particles is not particularly limited. In particular, the portion other than the surface layer may be, for example, a uniform particle with respect to the polymer composition or molecular weight, or a core-shell structure or multistage structure composed of polymer layers having different compositions, or a continuous polymer composition. It is also possible to take a gradient type structure that changes to When acrylic polymer fine particles are used for plastisol, a core-shell structure is particularly preferable, and this can improve the storage stability and film formability of the plastisol composition. Moreover, you may comprise by the thermoplastic acrylic polymer which does not have a crosslinked structure, and you may comprise by the acrylic polymer which has a crosslinked structure and does not show thermoplasticity. In plastisol applications, it is preferable to use a thermoplastic acrylic polymer from the viewpoint of film formability, and the gel fraction is preferably 90% or less.

  The acrylic polymer usually refers to a polymer in which most of the monomers constituting the polymer are acrylates or methacrylates. Therefore, for example, a polymer in which silicone resin or fluorine resin occupies most does not apply.

  Examples of monomers that can be used to obtain acrylic polymers include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) ) (Meth) acrylates of linear alkyl alcohols such as acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate; (meth) of cyclic alkyl alcohols such as cyclohexyl (meth) acrylate Acrylates: methacrylic acid, acrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, methacrylic acid 2-succinoloyloxyethyl-2-methacryloyloxyethyl succinic acid, methacrylic acid 2-malenoyloxyethyl-2 -Methacryloy Carboxyl group-containing monomers such as ruoxyethylmaleic acid, methacrylic acid 2-phthaloyloxyethyl-2-methacryloyloxyethylphthalic acid, methacrylic acid 2-hexahydrophthaloyloxyethyl-2-methacryloyloxyethylhexahydrophthalic acid; Sulfonic acid group-containing monomers such as allylsulfonic acid; Phosphoric acid group-containing (meth) acrylates such as 2- (meth) acryloyloxyethyl acid phosphate; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) Hydroxyl group-containing (meth) acrylates such as acrylate; Carbonyl group-containing (meth) acrylates such as acetoacetoxyethyl (meth) acrylate; N-dimethylaminoethyl (meth) acrylate, N-diethylamino Amino group-containing (meth) acrylates such as ethyl (meth) acrylate; and the like.

  It is also possible to crosslink the polymer as necessary. In this case, a polyfunctional monomer may be used in combination. Specifically, polyfunctional (meta) such as (poly) ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, etc. ) Acrylates can be preferably used.

  Further, for example, acrylamide and derivatives thereof such as diacetone acrylamide, N-methylol acrylamide, N-methoxymethyl acrylamide, N-ethoxymethyl acrylamide, N-butoxymethyl acrylamide, and the like; furthermore, styrene and derivatives thereof, vinyl acetate, urethane-modified acrylate It is also possible to use special monomers such as epoxy-modified acrylates and silicone-modified acrylates.

  However, it is not limited to the monomer illustrated above.

  The method for producing the acrylic polymer fine particles is not particularly limited as long as it is a method capable of obtaining primary particles of 100 μm or less. For example, primary particles of 100 μm or less can be obtained in an aqueous medium by an emulsion polymerization method, a soap-free polymerization method, a fine suspension polymerization method, or the like. Also, there is no particular limitation on the method of drying the obtained polymer aqueous dispersion and recovering the polymer as a powder. For example, a spray drying method (spray drying method) or a wet coagulation method can be used.

  The properties and structure of the powder are not limited. For example, a large number of primary particles obtained by polymerization may be aggregated to form aggregated particles (secondary particles), or higher order structures may exist. However, in the case of plastisol use, it is preferable that the primary particles are not firmly bonded to each other and are loosely aggregated. This is because fine and uniform dispersion of the primary particles in the plasticizer is easily achieved.

  The acrylic polymer fine particles of the present invention are preferably used in a plastisol composition. As described above, plastisol is a paste-like material in which polymer fine particles are dispersed in a plasticizer. Here, if the polymer fine particles are well dispersed in the plasticizer without agglomerating, and maintain a fine and homogeneous dispersed state, it becomes a plastisol composition having a low viscosity, a high fluidity and excellent workability, Furthermore, the coating film obtained by heating this also becomes smooth and rich in gloss. The acrylic polymer fine particles having a hydrophobized surface according to the present invention are particularly suitable for exhibiting the above-described properties because of good wettability and good dispersibility with respect to a plasticizer.

  The plasticizer used for the plastisol composition is not particularly limited. For example, dibutyl phthalate, dihexyl phthalate, dioctyl phthalate, diisononyl phthalate, diisodecyl phthalate, etc .; alkyl phthalates such as butyl benzyl phthalate; alkyl aryl phthalates; diaryl phthalates; dibenzyl phthalates; Diaryl; or phosphate esters such as triaryl phosphates such as tricresyl phosphate, trialkyl phosphates and alkylaryl phosphates; and aliphatic dibasic esters such as adipine dibutyl; ethers such as dibutyl glycol adipate Examples thereof include polyesters, plasticizers, soybean oil plasticizers such as epoxidized soybean oil, and the like. These plasticizers can be used alone or in combination of two or more plasticizers. In particular, dialkyl phthalates such as diisononyl phthalate are preferable because they have particularly good wettability with the polymer fine particles of the present invention. The blending amount of the plasticizer is preferably 40 to 300 parts by mass, more preferably 50 to 200 parts by mass with respect to 100 parts by mass of the acrylic polymer fine particles.

  For plastisol composition, calcium carbonate, aluminum hydroxide, pearlite, clay, colloidal silica, mica powder, quartz sand, diatomaceous earth, kaolin, talc, bentonite, glass powder, aluminum oxide, fly ash, shirasu balloon, if necessary You may mix | blend fillers, such as. The purpose, type, amount, etc. of the filler are arbitrary. Further, the filler may be subjected to a surface treatment or the like.

  In addition, if necessary, pigments such as titanium oxide and carbon black, further diluents such as mineral terpenes and mineral spirits, further antifoaming agents, antifungal agents, deodorants, antibacterial agents, surfactants, lubricants, ultraviolet rays Absorbers, fragrances, foaming agents, leveling agents, adhesives and the like can be freely blended.

  The acrylic plastisol composition of the present invention can be widely used in fields of application where a conventional vinyl chloride sol has been used. Specifically, automotive undercoats, automotive body sealers, automotive mastic adhesives, tile carpet backing materials, cushion floors, wallpaper, steel plate paints, toys, gloves, food samples, shoes, building materials, various adhesives, various sealers, Gaskets, waterproof sheets, automobile inner layer skin materials, canvas, table cloths, synthetic leather, erasers, screen printing paints, and the like. However, the application is not particularly limited.

  Hereinafter, the present invention will be specifically described according to examples.

[Preparation of polymer fine particles (A1)]
100 g of pure water is put into a 300 ml four-necked flask equipped with a thermometer, nitrogen gas introduction tube, stirring rod, dropping funnel, and cooling tube, and nitrogen gas is thoroughly bubbled for 30 minutes to dissolve dissolved oxygen in the pure water. Replaced. Next, after stopping the aeration of nitrogen gas, the temperature was raised to 80 ° C. while stirring at 200 rpm. When the internal temperature reached 80 ° C., 0.05 g of potassium persulfate (manufactured by Kirk) dissolved in 2.0 g of pure water was added all at once.

  Next, as the first drop, monomer [methyl methacrylate (Mitsubishi Rayon Co., Ltd., trade name Acryester M) 90 g, n-butyl methacrylate (Mitsubishi Rayon Co., Ltd., trade name Acryester B) 10 g] and emulsifier [Dioctyl A mixed solution in which sodium sulfosuccinate (trade name: Perex OTP, manufactured by Kao Corporation, 1.0 g per 100 g of total monomer) was uniformly dissolved was added dropwise at a rate of 20 g / hr, followed by stirring at 80 ° C. for 1 hour. To obtain a polymer latex.

  After cooling this polymer latex to room temperature, it was spray-dried at an inlet temperature of 150 ° C., an outlet temperature of 60 ° C., and an atomizer speed of 25000 rpm using a spray dryer (L8 type, manufactured by Okawara Chemical Co., Ltd.). Fine particles (A1) were obtained.

[Preparation of polymer fine particles (A2)]
First, the first dropping was performed in the same manner as in the case of the polymer fine particles (A1), and stirring was continued at 80 ° C. for 1 hour. Next, 2.0 g of 2-ethylhexyl acrylate (manufactured by Mitsubishi Chemical Corporation, trade name 2-ethylhexyl acrylate) and an emulsifier (sodium dioctylsulfosuccinate, 1.0 g per 100 g of total monomer) were uniformly dissolved as a hydrophobic monomer. The mixed solution was added, and the stirring was continued at 80 ° C. for 1 hour to obtain a polymer latex. This polymer latex was spray-dried in the same manner as in the case of the polymer fine particles (A1) to obtain polymer fine particles (A2).

[Preparation of polymer fine particles (A3) to (A5)]
In place of the hydrophobic monomer (2-ethylhexyl acrylate) of the polymer fine particle (A2), the polymer fine particle (A3) is a C12-C13 alkyl methacrylate (trade name Acryester SL, manufactured by Mitsubishi Rayon Co., Ltd.). For fine particles (A4), cyclohexyl methacrylate (Mitsubishi Rayon Co., Ltd., trade name Acryester CH) was used as the hydrophobic monomer, and for polymer fine particles (A5), methacrylic acid (Mitsubishi Rayon Co., Ltd.) was used as the hydrophobic monomer. Except for, polymer fine particles (A3) to (A5) were prepared in the same manner as in the case of the polymer fine particles (A2).

[Preparation of polymer fine particles (A6) and (A7)]
The addition amount (2.0 g) of the hydrophobic monomer (2-ethylhexyl acrylate) of the polymer fine particles (A2) was changed to 1.0 g for the polymer fine particles (A6) and 4.0 g for the polymer fine particles (A7). Except for the above, polymer fine particles (A6) and (A7) were prepared in the same manner as in the case of the polymer fine particles (A2).

[Preparation of polymer fine particles (A8)]
First, the 1st dripping was performed similarly to the case of polymer fine particles (A1), and stirring was continued at 80 ° C. for 1 hour to obtain a polymer latex. After cooling this polymer latex to room temperature, 2.0 g of dimethyldimethoxysilane (manufactured by Shin-Etsu Silicone Co., Ltd., trade name KBM22) is added as a hydrophobic monomer, and immediately, the polymer fine particles (A1) are added using a spray dryer. Spray drying was performed in the same manner as in the case to obtain polymer fine particles (A8).

[Measurement of primary particle size]
The primary particle size of the polymer fine particles was determined by measuring the particle size of the polymer latex before producing the polymer fine particles using a spray dryer. Specifically, it was carried out using a laser light scattering particle size distribution measuring apparatus LA-910W manufactured by HORIBA, Ltd. and using deionized water as a dispersion medium.

[Measurement of contact angle]
The fine polymer particles (A1) to (A8) obtained as described above were press-molded under the conditions of a load of 20 MPa and 60 ° C. to obtain a flat test body in which the particles were compactly packed. The contact angle formed by pure water with respect to this test specimen was measured using a contact angle measuring device (Kyowa Interface Science Co., Ltd. CA-X150) in an environment of 25 ± 5 ° C. The measurement was performed 8 times for the same specimen, and the average value was calculated among 6 points where the maximum and minimum values were discarded. In addition, when water droplets were absorbed by the specimen and measurement was not possible, it was described as “impossible to measure”. The measurement results are shown in Table 1.

[Examples 1 to 6 and Comparative Examples 1 and 2: Preparation of a plastisol composition]
100 parts by mass of diisononyl phthalate as a plasticizer per 100 parts by mass of each polymer fine particle shown in Table 2 was added and defoamed with a vacuum mixer (ARV-200 manufactured by Sinky Corporation) for 10 seconds at atmospheric pressure. Thereafter, the pressure was reduced to 20 mmHg and mixed for 50 seconds) to obtain a uniform plastisol composition. For the obtained plastisol composition, the following items were evaluated. The evaluation results are shown in Table 2.

[viscosity]
Within 1 hour after preparing the plastisol composition, using an EMD type viscometer (manufactured by Toki Sangyo Co., Ltd., EMD type viscometer, cone angle 3 degrees), measurement temperature 25 ° C., shear rate 10 s ⁻¹ Viscosity was measured at 2 points (rotation speed 5 rpm) and shear rate 100 s ⁻¹ (rotation speed 50 rpm) (unit: mPa · s), and evaluated according to the following criteria.
“◎”: The viscosity at a shear rate of 10 ⁻¹ is less than 1500 mPa · s.
“◯”: The viscosity at a shear rate of 10 ⁻¹ is 1500 mPa · s or more and less than 2000 mPa · s.
“X”: The viscosity at a shear rate of 10 ⁻¹ is 2000 mPa · s or more.

[TI value]
As a thixotropy index, the TI value was calculated as follows from the above two viscosity measurement results. TI value = (viscosity at a shear rate of 10 s ⁻¹ ) / viscosity at a shear rate of 100 s ⁻¹ )
Here, the higher the TI value, the stronger the thixotropy and the poorer the fluidity, and the lower the TI value, the lower the thixotropy and the better the fluidity. Specifically, evaluation was performed according to the following criteria.
“◎”: TI value is less than 1.5.
“◯”: TI value is less than 2.0.
“×”: TI value is 2.0 or more.

[Consideration of each example]
Example 1 is an example using polymer fine particles (A2) having a surface coated by polymerizing 2-ethylhexyl acrylate which is a hydrophobic monomer. It can be seen that the polymer fine particles (A2) have a high contact angle with water and are difficult to wet with water. In other words, the wettability was good with respect to the hydrophobic medium, and in fact, it could be well dispersed with respect to the plasticizer (diisononyl phthalate), and the viscosity and thixotropy of the resulting plastisol composition were low. That is, an extremely good plastisol composition having excellent fluidity was obtained.

  Examples 2-3 are examples in which polymer fine particles (A3) and (A4) were used, and each fine particle was polymerized and coated using an arbitrary hydrophobic monomer instead of 2-ethylhexyl acrylate. . The solubility (water, 20 ° C.) of any hydrophobic monomer is less than 0.03 mass%. In this case, both the viscosity and thixotropy of plastisol were low, but it can be seen from this result that the effect is particularly remarkable when 2-ethylhexyl acrylate or C12-C13 alkyl methacrylate is used.

  Examples 4 and 5 are examples using polymer fine particles (A6) and (A7), and each fine particle is an example in which the amount of 2-ethylhexyl acrylate, which is a hydrophobic monomer, is decreased or increased. . In either case, an extremely good plastisol composition having low viscosity and thixotropy of plastisol and excellent fluidity was obtained.

  Example 6 is an example using polymer fine particles (A8), in which dimethyldimethoxysilane, which is a hydrophobic monomer, is used to coat the particle surface with cyclic polydimethylsiloxane, which is a kind of alkylsiloxane. is there. An extremely good plastisol composition having low viscosity and thixotropy of plastisol and excellent fluidity was obtained.

  Comparative Example 1 is a case where polymer fine particles (A1) obtained without adding a hydrophobic monomer were used. In this case, the viscosity was not as low as that obtained in Examples 1 to 4, but was high. Moreover, it was confirmed that the TI value, which is an index of fluidity, is high and hardly flows, that is, it is a plastisol composition having various workability and workability.

  Comparative Example 2 is a case in which polymer fine particles (A5) obtained by adding and polymerizing methacrylic acid as a hydrophilic monomer are used. In this case, the viscosity was not as low as that obtained in Examples 1 to 4, but was high. Moreover, it was confirmed that the TI value, which is an index of fluidity, is high and hardly flows, that is, it is a plastisol composition having various workability and workability.

Claims (7)

  An acrylic polymer fine particle having a fine particle having a volume average particle diameter of 100 μm or less as a primary particle, the contact angle with water being 90 degrees or more.   The acrylic polymer fine particles according to claim 1, wherein an organic compound having a solubility in water at 20 ° C of 0.03 mass% or less is present on the surface layer of the polymer fine particles.   2. The acrylic polymer fine particle according to claim 1, wherein a polymer obtained by copolymerizing a monomer having a solubility in water at 20 ° C. of 0.03 mass% or less is present on the surface layer of the polymer fine particle.   The acrylic polymer fine particle according to claim 1, wherein a compound comprising an alkylsiloxane unit is present on the surface layer of the polymer fine particle.   A method for producing the acrylic polymer fine particles according to claim 3, wherein an acrylic monomer is polymerized in an aqueous medium to prepare a polymer dispersion, and the solubility in water at 20 ° C is 0.03 mass. A method for producing acrylic polymer fine particles, which comprises a step of adding a monomer of not more than 1% to this, and then drying the polymer dispersion to recover the polymer.   A method for producing the acrylic polymer fine particles according to claim 4, wherein an acrylic monomer is polymerized in an aqueous medium to prepare a polymer dispersion, and a compound comprising an alkylsiloxane unit is added thereto. Then, a method for producing acrylic polymer fine particles, comprising a step of drying the polymer dispersion and recovering the polymer.   A plastisol composition comprising the acrylic polymer fine particles according to any one of claims 1 to 4.