JPH0747609B2 - Method for producing acrylic polymer particles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing acrylic polymer particles.

(Problems to be Solved by the Related Art and Invention) Conventionally, for example, by mixing methyl methacrylate with acrylic polymer particles to swell in a clay form, shaping and polymerizing it to form a molded article, It is especially popular in the field of dental materials. Examples of the acrylic polymer particles used for this purpose include a pearl polymer of methyl methacrylate, and the clay-like composition prepared by using the particles exhibits a clay-like shape only when swelling occurs. In addition to the inconvenience that the moldable pot life is extremely short and the materials must be mixed for each molding, it is virtually impossible to mold a large molded body. Had. Further, in the specification of West German Patent Application No. 2850916, a highly crosslinkable pearl-like polymer which hardly swells after being mixed with a monomer is described. However, in this polymer, when the amount of the liquid monomer to be added is small, it is in the form of powder, and when the amount is increased, it suddenly changes to a liquid state, and there is a problem that the polymer particles settle due to the difference in specific gravity. However, there is a problem that the moldability is not sufficient. Further, as the above-mentioned improved technology, U.S. Patent No.
4,396,476 describes that a cross-linked polymer particle and a non-cross-linked polymer particle are used in combination and these particles and a monomer are mixed to mold a dental material. However, in this case, the non-crosslinked polymer is dissolved in the monomer to increase the viscosity,
Although it has the advantage that the cross-linked polymer particles can be prevented from settling and the workability is improved, it has the drawback that sufficient mechanical strength of the molded product cannot be obtained.

Therefore, the present invention has the drawback that the working life seen in the case of the non-crosslinked polymer particles is extremely short,
It is an object of the present invention to provide a method for producing polymer particles, which can simultaneously solve the sedimentation of particles, the poor mechanical strength of a molded product, and the like that occur in the case of crosslinked polymer particles.

(Means for Solving the Problems) The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, by preparing specific acrylic polymer particles based on a novel production method, the object of the present invention has been achieved. Therefore, the present invention has been completed.

That is, according to the present invention, the above-mentioned object is a method for producing acrylic polymer particles having an average particle size of 1 to 100 µm by a suspension polymerization method, wherein 1 to 50% by weight of a polyfunctional (meth) acrylic acid ester and methacrylic acid are used. A monomer mixture of 99 to 50% by weight of a monofunctional monomer consisting of methyl acid alone or methyl methacrylate and another copolymerizable vinyl monomer is polymerized to obtain a monomer mixture. When the conversion of the polymer reached 30 to 95%, 100 parts by weight of the monomer mixture was used, and methyl methacrylate alone or a monomer composed of methyl methacrylate and another copolymerizable vinyl monomer was used. It can be achieved by a method for producing acrylic polymer particles in which 50 to 500 parts by weight of a functional monomer is added and polymerization is substantially completed.

Hereinafter, the present invention will be described in detail.

For the production of the acrylic polymer particles according to the present invention, for example, the suspension polymerization method described in the above-mentioned prior art or Japanese Examined Patent Publication No. Sho 62-6210 is employed. It is preferable to use partially saponified PVA as the dispersion stabilizer, and further, a monomer mixture containing water and an initiator in which partially saponified PVA is dissolved is formed into fine droplets by high-speed shear stirring. It can be said that a method in which the polymer is dispersed in water and then charged in a polymerization vessel is particularly preferable because it can narrow the particle size distribution in order to obtain polymer particles having an average particle size in the range of 1 μ to 100 μ.

The acrylic polymer particles according to the present invention contain a crosslinked polymer having a specific structure. Therefore, non-crosslinked polymer particles are used to show (meth) acrylic acid ester (acrylic acid ester and methacrylic acid ester. The same applies hereinafter. .) And, in some cases, the disappearance of the plasticity of the composition due to the swelling / dissolution of polymer particles, which is observed when a composition for molding is mixed with an initiator, a polymerization inhibitor, a dye and a pigment, in a short time. However, it is believed that the plasticity of the composition can be maintained for a much longer period of time.

To form a crosslinked polymer, a polyfunctional (meth) acrylic acid ester is used in combination with methyl methacrylate or a monofunctional monomer composed of methyl methacrylate and another copolymerizable vinyl monomer. Multifunctionality (meta)
The amount of acrylic ester used is in the range of 1 to 50% by weight, preferably 2 to 30% by weight, most preferably 5 to 20% by weight. When the amount used is less than 1% by weight, the swelling phenomenon of the polymer particles becomes remarkable, the plasticity of the composition disappears in a short time and the pot life becomes short, which is not preferable, while the amount used exceeds 50% by weight. In such a case, although the pot life is much longer, the mechanical strength of the molded product obtained by polymerizing and curing the composition becomes extremely poor, and the appearance of the molded product is deteriorated, which is not preferable.

Examples of the polyfunctional (meth) acrylic acid ester include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol (meth) acrylate, 1,4 butanediol di ( (Meth) acrylate, neopentyl glycol di (meth)
Acrylate, 1,6 hexanediol di (meth) acrylate, 1,9 nonanediol di (meth) acrylate,
Trimethylolpropane tri (meth) acrylate, bisphenol A dimethacrylate, 2,2-bis [P-
(Meth) acryloxydiethoxy) phenyl] propane and the like. In particular, a combination of neopentyl glycol dimethacrylate and methyl methacrylate is preferable for transparency.

Examples of the vinyl-based monomer copolymerizable with methyl methacrylate include (meth) acrylic acid ester derived from alcohol having an alkyl group having 2 to 17 carbon atoms, cyclohexyl (meth) acrylate, ( Meta)
Benzyl acrylate, phenyl (meth) acrylate,
(Meth) acrylic acid, N-alkyl (meth) acrylamide, styrene, acrylonitrile and the like can be mentioned.

The above-mentioned polyfunctional (meth) acrylic acid ester and methyl methacrylate, and in some cases the copolymerizable vinyl monofunctional monomer are mixed, and an organic peroxide such as benzoyl peroxide or laurolyl peroxide is used as an initiator. Oxide, or azo-based initiator such as azobisisobutyronitrile is dissolved in a required amount, for example, partially saponified PVA is dissolved in water and dispersed by a high-speed shear stirrer, and then dispersed in a polymerization container. The liquid is introduced, and if necessary, suspension polymerization is started while stirring under a N ₂ gas atmosphere. During the course of this polymerization, with respect to 100 parts by weight of the monomer that has already started the polymerization, 50
~ 500 parts by weight, preferably 100 to 300 parts by weight of methyl methacrylate alone, or a monofunctional monomer consisting of methacrylic acid and other copolymerizable vinyl monomers (in some cases, an initiator, (A chain transfer agent or the like may be added in advance) as it is, or preferably, as described above, dispersed in an aqueous solution containing partially saponified PVA and added,
It is particularly important in the present invention to employ a method of further advancing the polymerization to substantially complete the polymerization to obtain acrylic polymer particles. Furthermore, when the addition of the monofunctional monomer to the monomer that has begun polymerization, the polymer conversion rate of the monomer that has already begun polymerization is 30 to 95%, preferably 60. Need to be in the range of ~ 90%.

The acrylic polymer particles obtained by the production method according to the present invention can be mixed with a (meth) acrylic acid ester and, in some cases, an initiator, a polymerization inhibitor, a dye, a pigment, etc. to form a molding composition. In this case, the composition is characterized in that it can maintain plasticity for a long period of time and that the cured product obtained by polymerizing and curing the composition has excellent mechanical strength. However, if the amount of the monofunctional monomer added during the polymerization is less than 50 parts by weight with respect to 100 parts by weight of the monomer that has already started the polymerization,
The composition does not exhibit clay-like plasticity and is only powdery or liquid, and the handleability and moldability of the composition are poor, which is not preferable. On the other hand, if it exceeds 500 parts by weight, the plasticity of the composition cannot be maintained for a long period of time, which is not preferable.

Further, when the addition time of the monofunctional monomer added during the polymerization, the polymer conversion of the monomer that has already started the polymerization is less than 30%, the molding composition does not show plasticity However, the composition is in the form of powder or liquid and is inferior in handleability and moldability of the composition. On the other hand, when the addition time is over 95% of the polymer conversion rate of the monomer that has already started the polymerization, the composition exhibits plasticity for a long period of time,
It is easy to handle and mold, but the composition is polymerized.
It is not preferable because the mechanical strength of the cured product becomes extremely poor.

Here, the polymer conversion rate in the present invention is determined by sampling a suspension during polymerization, adding a fixed amount of n-hexane, and further shaking the mixture, and mixing the hexane layer of the supernatant with an unreacted unit amount by gas chromatography analysis. It can be determined by a method of quantitative analysis of the body.

Then, the polymerization reaction is advanced to substantially complete the polymerization reaction. As used herein, "substantially completing the polymerization reaction" generally means completion of the polymerization reaction in suspension polymerization, and the polymerization rate
The reaction may be terminated at about 97%. Therefore, depending on the case, it is also possible to employ a method in which the unreacted monomer is driven out of the system by further heating the temperature and performing steam distillation.

The average particle size of the acrylic polymer particles obtained by the above method is measured by, for example, a sedimentation type particle size distribution measuring device. The average particle size needs to be in the range of 1 μ to 100 μ, and more preferably 30 μ or less. If the average particle size is less than 1 μ, the kneading workability of the composition is complicated, time is required, and the moldability is deteriorated, which is not preferable. On the other hand, if it exceeds 100 μ, the moldability of the composition tends to be poor, and the appearance of the molded article tends to deteriorate, such being undesirable.

The acrylic polymer particles obtained by the above method are (meth) acrylic acid esters that are liquid at room temperature, especially methyl methacrylate alone, methyl methacrylate and a small amount of polyfunctional (meth) acrylic acid ester. Or a mixture of methyl methacrylate, other copolymerizable vinyl-based monomer and polyfunctional (meth) acrylic acid ester, and optionally an initiator, a polymerization inhibitor, a dye, a pigment, a UV sensitizer. Etc. can be mixed and used as a molding composition. Since it depends on the properties of the acrylic polymer particles, it cannot be uniformly expressed. However, for 100 parts by weight of the acrylic polymer particles, 25 to 25 parts of the (meth) acrylic acid ester that is a liquid at room temperature is used. By mixing 150 parts by weight, preferably 25 to 100 parts by weight, a clay-like to paste-like plastic body that is easy to handle and can be provided for molding.

As the molding method, for example, casting, compression molding, transfer molding, injection molding or the like can be adopted. Further, by using dyes and pigments, various uniformly colored molded products can be obtained.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples. All parts and percentages used in the examples are parts and percentages by weight.

Example 1. 90 parts of methyl methacrylate (MMA), 10 parts of neopentyl glycol dimethacrylate (NPGDM) and 0.07 part of lauroyl peroxide are partially saponified PVA (Kuraray Poval, P
VA-420) was added to 200 parts of water in which 0.5% was dissolved, and dispersed with a high-speed shearing type stirrer. A round-bottom separable flask of No. ₂ was equipped with a stirrer, a condenser with a bulb, and an N ₂ gas introduction tube, charged with 0.6 kg of the above-mentioned dispersion liquid, heated to 70 ° C. in an oil bath, and heated to 90 ° C.
Polymerization proceeded for a minute. At this time, while sampling the contents, MMA 150 parts, n-octyl mercaptan 0.3 parts,
Add 0.07 part of laurolyl peroxide to 300 parts of water in which 0.5% of partially saponified PVA (Kuraray Poval, PVA420) is dissolved, add 0.9 kg of dispersion liquid dispersed by a high-speed shear stirrer to a flask, and polymerize at 70 ° C for 180 minutes. Further, the internal temperature was raised to 100 ° C. and kept for 60 minutes to complete the polymerization.

The same weight of n-hexane was added to the above-mentioned sampled contents, shaken and stirred sufficiently, and the polymer conversion ratio of the monomer was determined by gas chromatography analysis of the upper n-hexane layer. It was 75%.

After separating the obtained polymer fine particles and washing with water several times,
It dried at 80 degreeC and obtained the polymer microparticles. The average particle size of the polymer particles was 18μ.

A monomer mixture consisting of 70 parts of the polymer fine particles, 27 parts of MMA, 3 parts of NPGDN, 0.09 part of azobisisobutyronitrile (AIBM) was put into a closed tabletop kneader (manufactured by Irie Shokai; PNV-1), and A clay-like composition was obtained by mixing and kneading for 5 minutes. This composition was placed in a mold heated to 110 ° C.,
By compression molding at a pressure of 30 kg / cm ² , 150 mm square and thickness 3
A transparent molded product of mm was obtained. This composition was placed in a sealed container, stored at 23 ° C. for 1 week, and then compression-molded in the same manner to obtain a transparent molded product, which had a long pot life. The Izod impact strength without notch of the molded product was 22 kg · cm / cm.

Example 2. MMA (98 parts), NPGDM (2 parts) and lauroyl peroxide (0.07 part) were added to 200 parts of water in which 0.5% of partially saponified PVA was dissolved, and the mixture was dispersed with a high-speed shearing stirrer. The same equipment was used and the polymerization was allowed to proceed at 70 ° C for 120 minutes.
At this time, the polymer conversion rate of the monomer was 72%. next
MMA 150 parts, n-octyl mercaptan 0.3 parts, lauroyl peroxide 0.07 parts water in which 0.5% of partially saponified PVA is dissolved.
0.9 kg of a dispersion liquid dispersed in 300 parts was charged, polymerization was performed at 70 ° C. for 180 minutes, the internal temperature was further raised to 100 ° C., and the temperature was maintained for 60 minutes to complete the polymerization. The average particle size of the polymer particles obtained by washing with water and drying was 15μ.

70 parts of these polymer particles, 27 parts of MMA, 3 parts of NPGDM, AIBN0.0
A clay-like composition was obtained by mixing and kneading a 9-part monomer mixture solution. This composition is put into a mold heated to 110 ° C and compression-molded at a pressure of 30 kg / cm ² to obtain 150 mm.
A transparent molded product with a square thickness of 3 mm was obtained. This composition was placed in a sealed container, stored at 23 ° C. for 1 week, and compression-molded in the same manner to obtain a transparent molded product. The notched Izod impact strength of the molded product is 25 kgcm / cm.
Met.

Example 3. 80 parts of MMA, 10 parts of ethyl acrylate, 10 parts of NPGDM and 0.07 part of lauroyl peroxide were dispersed in 200 parts of water in which 0.5% of partially saponified PVA was dissolved, and 0.6 kg of this dispersion was used in the same apparatus as in Example 1. Then, the polymerization was carried out at 70 ° C. for 90 minutes. At this time,
The polymer conversion rate of the monomer was 73%. Then MMA150
Part, n-octyl mercaptan 0.3 part, lauroyl peroxide 0.07 part were dispersed in 300 parts of water in which 0.5% of partially saponified PVA was dissolved, and 0.9 kg of a dispersion liquid was charged, followed by polymerization at 70 ° C. for 180 minutes,
Furthermore, the internal temperature was raised to 100 ° C. and maintained for 60 minutes to complete the polymerization. The average particle size of the polymer particles obtained by washing with water and drying was 19μ.

Example 4 90 parts of MMA, 10 parts of NPGDM, and 0.07 part of lauroyl peroxide were added to 200 parts of water in which 0.5% of partially saponified PVA was dissolved and dispersed by a high-speed shearing type stirrer, and 0.6 kg of this dispersion was used. The same equipment was charged and the polymerization was allowed to proceed at 70 ° C for 100 minutes.
At this time, the polymer conversion rate of the monomer was 45%. next
MMA 150 parts, n-octyl mercaptan 0.3 parts, lauroyl peroxide 0.07 parts water in which 0.5% of partially saponified PVA is dissolved.
0.9 kg of a dispersion liquid dispersed in 300 parts was charged, polymerization was carried out at 70 ° C. for 180 minutes, and the internal temperature was further raised to 100 ° C. and maintained for 60 minutes to complete the polymerization. The average particle size of the polymer particles obtained by washing with water and drying was 18μ.

70 parts of these polymer particles, 27 parts of MMA, 3 parts of NPGDM, AIBN0.0
A clay-like composition was obtained by mixing and kneading a 9-part monomer mixture solution. This composition was placed in a mold heated to 110 ° C. and compression-molded at a pressure of 30 kg / cm ² to obtain a transparent molded product having a 150 mm square and a thickness of 3 mm. This composition was placed in a sealed container, stored at 23 ° C. for 1 week, and then compression-molded in the same manner to obtain a transparent molded product. The Izod impact strength without notch of the molded product was 18 kg · cm / cm.

Comparative Example 1. Water in which 100 parts of MMA, 0.07 part of lauroyl peroxide, and 0.2 part of n-octyl mercaptan were dissolved in 0.5% of partially saponified PVA 2
1.5 kg of a dispersion liquid dispersed in 00 parts was charged, polymerization was carried out at 70 ° C. for 30 minutes, and the internal temperature was further raised to 100 ° C. and maintained for 60 minutes to complete the polymerization. The average particle size of the polymer particles obtained by washing with water and drying was 20μ.

70 parts of these polymer particles, 27 parts of MMA, 3 parts of NPGDM, AIBN0.0
A monomer mixture consisting of 9 parts was mixed and kneaded. A clay-like composition was obtained by kneading for about 10 minutes. At this time, the composition is put into a mold and compression-molded at a pressure of 30 kg / cm ² to obtain 15
A 0 mm square transparent molded product with a thickness of 3 mm was obtained. However, when this composition was placed in a sealed container and stored at 23 ° C. for 1 day, it changed into a hard elastic composition that was no longer clay-like. Compression molding was carried out in the same manner, but the prescribed molded product could not be obtained due to insufficient filling.

Comparative Example 2. 40 parts of MMA, 60 parts of NPGDM and 0.07 part of lauroyl peroxide were made into 200 parts of water in which 0.5% of partially saponified PVA was dissolved, and 0.6 kg of this dispersion was charged in the same apparatus as in Example 1 and heated at 90 ° C. at 70 ° C. Polymerization proceeded for a minute. At this time, the polymer conversion rate of the monomer is 73
%Met. Next, MMA 150 parts, n-octyl mercaptan 0.
Partly saponified PVA with 3 parts lauroyl peroxide 0.07 parts
0.9 kg of a dispersion liquid dispersed in 300 parts of 0.5% water was charged, the polymerization was allowed to proceed at 70 ° C. for 180 minutes, the internal temperature was further raised to 100 ° C., and the temperature was maintained for 60 minutes to complete the polymerization. The average particle size of the polymer particles obtained by washing with water and drying was 17μ.

70 parts of these polymer particles, 27 parts of MMA, 3 parts of NPGDM, AIBN0.0
A soft clay-like composition was obtained by mixing and kneading a 9-part monomer mixture solution. This composition is put into a mold heated to 110 ° C and compression molded at a pressure of 30 kg / cm ^2.
A transparent molded product having a 150 mm square and a thickness of 3 mm was obtained. However, the unnotched Izod impact strength of this molded product is 8.5k.
It was brittle with g · cm / cm.

Comparative Example 3. 90 parts of MMA, 10 parts of NPGDM, and 0.07 part of lauroyl peroxide were added to 200 parts of water in which 0.5% of partially saponified PVA was dissolved, and dispersed with a high-speed shearing stirrer. 0.6 kg of this dispersion was charged into the same apparatus as in Example 1, and polymerization was allowed to proceed at 70 ° C. for 60 minutes.
At this time, the polymer conversion rate of the monomer was 14%. next
MMA 150 parts, n-octyl mercaptan 0.3 parts, lauroyl peroxide 0.07 parts water in which 0.5% of partially saponified PVA is dissolved.
0.9 kg of a dispersion liquid dispersed in 300 parts was charged, polymerization was carried out at 70 ° C. for 240 minutes, the internal temperature was further raised to 100 ° C., and the temperature was kept for 60 minutes to complete the polymerization. The average particle size of the polymer particles obtained by washing with water and drying was 13μ.

70 parts of these polymer particles, 27 parts of MMA, 3 parts of NPGDM, AIBN0.0
When 9 parts of the monomer mixture was mixed and kneaded, it was in the form of a moist powder and did not form a clay. This composition 11
It was placed in a mold heated to 0 ° C. and compression-molded at a pressure of 30 kg / cm ^{2. The} central part became transparent, but the periphery was in a white filling failure state, and a molded product could not be obtained.

Comparative Example 4. 90 parts of MMA, 10 parts of NPGDM, and 0.07 part of lauryl peroxide were added to 200 parts of water in which 0.5% of partially saponified PVA was dissolved and dispersed with a high-speed shearing stirrer, and 0.6 kg of this dispersion liquid was used.
The same equipment as described above was charged, and polymerization was allowed to proceed at 70 ° C for 300 minutes. The polymer conversion rate of the monomer at this time was 97%. Then MM
A150 parts, n-octyl mercaptan 0.3 parts, lauroyl peroxide 0.07 parts partially saponified PVA 0.5% water 30
0.9 kg of a dispersion liquid dispersed in 0 parts was charged, polymerization was carried out at 70 ° C. for 180 minutes, the internal temperature was further raised to 100 ° C., and the temperature was kept for 60 minutes to complete the polymerization. The average particle size of the polymer particles obtained by washing with water and drying was 19μ.

70 parts of these polymer particles, 27 parts of MMA, 3 parts of NPGDM, AIBN0.0
A clay-like composition was obtained by mixing and kneading a 9-part monomer mixture solution. This composition was placed in a mold heated to 110 ° C. and compression-molded at a pressure of 30 kg / cm ² to obtain a transparent molded product having a 150 mm square and a thickness of 3 mm. However, the Izod impact strength without notch of this molded product is 11 kg ・ cm / c.
It was as small as m and was brittle.

(Effects of the Invention) According to the present invention, molding in which acrylic polymer particles obtained by the method of the present invention and (meth) acrylic acid ester, and in some cases, an initiator, a polymerization inhibitor, a dye and a pigment are mixed. By forming a composition for use in the composition, the composition exhibits a clay-like shape and can be formed into a molded article by compression molding / transfer molding, injection molding or the like at a relatively low pressure, and the clay-like composition is exhibited, that is, the pot life. Is long and the molded product has excellent mechanical strength, so that a large molded product can be manufactured.

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Claims (1)

[Claims] 1. A method for producing acrylic polymer particles having an average particle size of 1 to 100 μm by a suspension polymerization method, wherein 1 to 50% by weight of a polyfunctional (meth) acrylic acid ester and methyl methacrylate alone or methacrylic acid are used. Monofunctional monomer consisting of methyl and its copolymerizable vinyl monomer
When a monomer mixture consisting of 99 to 50% by weight is polymerized and the polymer conversion rate of the monomer mixture reaches 30 to 95%, methacrylic acid is added to 100 parts by weight of the monomer mixture. Monofunctional monomer consisting of methyl alone or methyl methacrylate and other copolymerizable vinyl monomers 50 ~
A method for producing acrylic polymer particles, which comprises adding 500 parts by weight to substantially complete the polymerization.