JP2007284465A - Method for producing methacrylic resin molded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a methacrylic resin molded product having excellent impact resistance even when the amount of an added impact modifier is small and further excellent transparency. <P>SOLUTION: The method for producing the methacrylic resin molded product is carried out as follows. A radically polymerizable monomer (A) consisting essentially of methyl methacrylate is pre-mixed with a multi-stage polymerization copolymer (B) obtained by carrying out at least one stage of polymerization and containing a rubber-like copolymer having a cross-linked structure to prepare a polymerizable mixture (P). The resultant polymerizable mixture (P) is then mixed with a radical polymerization initiator to polymerize a part of the polymerizable mixture (P). Thereby, a syrup is prepared. The obtained syrup is cured by a cast polymerization method for casting the syrup into a mold and polymerizing the syrup. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a methacrylic resin molded article.

Methacrylic resin molded products have excellent transparency and surface gloss, good weather resistance, mechanical properties, etc., so they are used in a wide range of fields such as lighting fixtures, signboards, various building materials, sound insulation boards, and various displays. ing.
However, methacrylic resin molded products are not necessarily sufficient in terms of impact strength (impact resistance), but rather fragile, and improvement in impact resistance is desired.
Against this background, various proposals regarding methacrylic resin molded products have been made so far.

As a method for improving the impact resistance of a methacrylic resin molded product, for example, the following method is disclosed.
(1) By a casting method of an impact resistant composition obtained by mixing about 4 to 90% by mass of a multistage polymer including an elastomer layer and about 10 to 96% by mass of a rigid thermoplastic polymer such as methacrylic resin. A manufacturing method is disclosed. As one example, a method is described in which a composition in which 50 parts by mass of a multistage polymer is dispersed in 50 parts by mass of methyl methacrylate is cast polymerized (see Patent Document 1).
(2) Hard to rubbery copolymer having a crosslinked structure and an average particle size of 0.1 to 1 μm in 100 parts by mass of methyl methacrylate resin or methyl methacrylate resin containing 50% by mass or more of methyl methacrylate unit A methacrylic resin cast plate in which 2 to 30 parts by mass of a graft copolymer obtained by graft polymerization of a resin component is dispersed as an amount of a rubbery copolymer is disclosed (see Patent Document 2).
(3) 5 to 50 parts by mass of a methyl methacrylate polymer having a viscosity average molecular weight of 10,000 to 200,000 is dissolved in 100 parts by mass of a monomer having methyl methacrylate as a main component, and 1 to 50 parts by mass of a multilayer structure elastic body. A method for producing a methacrylic resin cast plate in which syrup in which a part is dispersed is injected into a cell and polymerized is disclosed (see Patent Document 3).
Japanese Patent Publication No.55-27576 Japanese Patent No. 2648179 Japanese Patent No. 3508251

However, although the methacrylic resin molded product obtained by the methods (1) to (3) is excellent in impact resistance, it is necessary to add a large amount of impact modifier in order to develop impact resistance.
Moreover, in the method of the Example as described in (1), the viscosity of a composition is too high and injection | pouring to a casting_mold | template etc. is difficult.
In the methods described in (2) and (3), the multilayer structure elastic body is dispersed in the syrup containing the partial polymer. However, due to the presence of the partial polymer in the syrup, the multilayered elastic body is difficult to disperse as the particle size at the primary particle level, and thus there is a problem that it is difficult to obtain transparency due to poor dispersion. Furthermore, the compatibility between the monomer (radically polymerizable monomer) part constituting the partial polymer and the rubber-like copolymer in the multilayer structure elastic body is poor, so that it is difficult to obtain strength. There is also.

  An object of the present invention is to provide a method for producing a methacrylic resin molded article that is excellent in impact resistance and excellent in transparency even if the amount of impact modifier added is small.

  The method for producing a methacrylic resin molded article of the present invention comprises a multi-stage process comprising a radically polymerizable monomer (A) having methyl methacrylate as a main component and a rubbery copolymer having a crosslinked structure obtained by at least one stage of polymerization. A polymerized copolymer (B) is mixed in advance to prepare a polymerizable mixture (P), and the polymerizable mixture (P) and a radical polymerization initiator are mixed to form a part of the polymerizable mixture (P). Is a production method in which syrup is prepared by polymerizing and then cured by a casting polymerization method in which the syrup is poured into a mold and polymerized.

  In the method for producing a methacrylic resin molded article of the present invention, the amount of the multistage polymerization copolymer (B) used is preferably 4 to 30 parts by mass in 100 parts by mass of the polymerizable mixture (P).

  According to the method for producing a methacrylic resin molded article of the present invention, a methacrylic resin molded article having excellent impact resistance and transparency can be produced even if the amount of the impact modifier added is small.

The method for producing a methacrylic resin molded article of the present invention comprises a multi-stage process comprising a radically polymerizable monomer (A) having methyl methacrylate as a main component and a rubbery copolymer having a crosslinked structure obtained by at least one stage of polymerization. A polymerized copolymer (B) is mixed in advance to prepare a polymerizable mixture (P), and the polymerizable mixture (P) and a radical polymerization initiator are mixed to form a part of the polymerizable mixture (P). Is a production method in which syrup is prepared by polymerizing and then cured by a casting polymerization method in which the syrup is poured into a mold and polymerized.
Hereinafter, the manufacturing method of the present invention will be described by dividing it into a step of preparing a polymerizable mixture (P), a step of preparing syrup, and a casting polymerization step.

<Process for preparing polymerizable mixture (P)>
In the step of preparing the polymerizable mixture (P), a multistage polymerization comprising a radically polymerizable monomer (A) mainly composed of methyl methacrylate and a rubbery copolymer having a crosslinked structure obtained by at least one stage of polymerization. A copolymer (B) is previously mixed to prepare a polymerizable mixture (P).
In this invention, since the radically polymerizable monomer (A) which has methyl methacrylate as a main component is used, it is excellent in the dispersibility of a multistage polymerization copolymer (B). Thereby, it is estimated that the transparency of the methacrylic resin molded product is improved.

・ Radically polymerizable monomer (A)
In the present invention, the radical polymerizable monomer (A) contains methyl methacrylate as a main component.
Here, the “radical polymerizable monomer” refers to a monomer (monomer) capable of radical polymerization.
The “main component” means a monomer contained in 50% by mass or more of all monomers contained in the radical polymerizable monomer (A).

As the radical polymerizable monomer (A), methyl methacrylate is essential, and in addition to this, monomers that can be copolymerized therewith include ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, Methacrylic acid esters other than methyl methacrylate such as phenyl methacrylate and benzyl methacrylate; Acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate; Unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and itaconic acid Acid; maleic anhydride, acid anhydrides such as itaconic anhydride; maleimide derivatives such as N-phenylmaleimide and N-cyclohexylmaleimide; 2-hydroxyethyl acrylate, 2-hydroxy Hydroxy group-containing monomers such as loxyethyl methacrylate and 2-hydroxypropyl methacrylate; vinyl esters such as vinyl acetate and vinyl benzoate; vinyl chloride, vinylidene chloride or derivatives thereof; nitrogen-containing single quantities such as methacrylamide and acrylonitrile Examples: Epoxy group-containing monomers such as glycidyl acrylate and glycidyl methacrylate; aromatic compounds having an ethylenically unsaturated bond in the molecule such as styrene and α-methylstyrene.
The radical polymerizable monomer (A) other than methyl methacrylate may be used alone or in combination of two or more.

In the present invention, the radical polymerizable monomer (A) is used in combination with methyl methacrylate alone or with methyl methacrylate and another monomer copolymerizable therewith, but methyl methacrylate alone is preferred.
The amount of the radical polymerizable monomer (A) used is preferably 70 to 96 parts by mass in 100 parts by mass of the polymerizable mixture (P). If it is 70 parts by mass or more, the transparency of the resulting methacrylic resin molded product is improved, and if it is 96 parts by mass or less, impact resistance is improved.

・ Multi-stage copolymer (B)
In the present invention, the multistage polymerization copolymer (B) is obtained by at least two stages of polymerization, and includes a rubbery copolymer having a crosslinked structure obtained by at least one stage of polymerization.
The multistage polymerization copolymer (B) is not particularly limited as long as it has a rubbery copolymer having a crosslinked structure obtained by at least one-stage polymerization, and the rubbery copolymer having a crosslinked structure. Even if it is obtained by two-stage polymerization consisting of a polymer and a graft copolymer, it can be obtained by three-stage polymerization using a first stage polymerization to make a rigid copolymer based on methyl methacrylate. Alternatively, it may be obtained by four or more stages of polymerization in which a hard copolymer and a rubbery copolymer are alternately provided and the last stage is a hard graft copolymer.
Further, in the production method of the present invention, the radical polymerizable monomer (A) can be easily impregnated into the rubber-like copolymer, so that it is estimated that the impact resistance of the methacrylic resin molded article is improved. . Therefore, the usage-amount of a multistage polymerization copolymer (B) can be decreased. Furthermore, since the usage-amount of a multistage polymerization copolymer (B) can be decreased, the increase in the viscosity of polymeric mixture (P) is suppressed, and dispersion time is shortened and productivity improves.
Preferable examples of the rubbery copolymer include generally used diene rubbers, acrylic rubbers, silicone rubbers, and silicone / acrylic composite rubbers. Of these, acrylic rubber is preferred from the viewpoint of weather resistance and transparency. The amount of these rubbery copolymers used is preferably 30 to 90 parts by mass in 100 parts by mass of the multistage polymer (B).

(Acrylic rubber)
Suitable acrylic rubbers include, for example, acrylate-based polymers having 4 to 10 carbon atoms in the alkyl group such as butyl acrylate and 2-ethylhexyl acrylate, and copolymers of the acrylate esters with the acrylate esters. Examples thereof include copolymers with possible monomers.
Examples of the copolymerizable monomer include styrene monomers such as styrene and α-methylstyrene; methacrylic acid esters such as methyl methacrylate and ethyl methacrylate; and alkyl groups such as methyl acrylate and ethyl acrylate having 1 carbon atom. Acrylic acid ester having ˜8 and different from the acrylic acid ester having 4-10 carbon atoms in the alkyl group; vinylcyan compound such as (meth) acrylonitrile; ethylene glycol di (meth) acrylate, allyl (meth) acrylate, Examples thereof include polyfunctional polymerizable compounds having two or more ethylenically unsaturated bonds in the molecule such as divinylbenzene and 1,3-butylene di (meth) acrylate. Especially, the said polyfunctional polymerizable compound which can form a crosslinked structure is preferable.
As the copolymerizable monomer, one kind may be used alone, or two or more kinds may be used in combination, and it is particularly preferable that at least one kind of the polyfunctional polymerizable compound is contained.
The amount of the polyfunctional polymerizable compound used is preferably 5 parts by mass or less, more preferably 0.01 to 3 parts by mass in 100 parts by mass of the rubbery copolymer. If it is 5 parts by mass or less, an appropriate crosslinking density is obtained in the rubber-like copolymer, and impact resistance is improved.
“(Meth) acrylate” means one or both of “acrylate” and “methacrylate”.

In addition, from the viewpoint of transparency of the methacrylic resin molded product, the multistage polymerization copolymer (B) including a rubbery copolymer having a crosslinked structure obtained by at least one polymerization of the refractive index of the methacrylic resin molded product. It is preferable to adjust the refractive index of the polymer of the radical polymerizable monomer (A) so as to be the same as the refractive index of the polymer.
The acrylic rubber may be obtained by multistage polymerization of two or more stages. Moreover, the polyalkyl (meth) acrylate type | system | group composite rubber | gum which contains 2 or more types of monomer units (copolymer) and has two or more glass transition temperatures may be sufficient.

The polymerization method and polymerization conditions for polymerizing the acrylic rubber are not particularly limited, and usual emulsion polymerization, soap-free emulsion polymerization, and the like can be used.
The polymerization initiator for polymerizing the acrylic rubber is not particularly limited, and water-soluble persulfuric acid such as potassium persulfate, sodium persulfate, ammonium persulfate; diisopropylbenzene hydroperoxide, p-menthane hydroper Redox polymerization initiators containing organic peroxides such as oxides, cumane hydroperoxides, t-butyl hydroperoxides, etc., or combinations of the above organic peroxides with one or more reducing agents, etc. Can be used.
When polymerizing acrylic rubber, the emulsifier used is not particularly limited, and alkali metal salts of higher fatty acids such as disproportionated rosin acid, oleic acid and stearic acid; sulfonic acids such as dodecylbenzene sulfonic acid One or more alkali metal salts and the like can be added.
Further, the particle diameter of the acrylic rubber particles dispersed in the rubber latex can be controlled by using a method in which the rubber latex obtained by polymerization is enlarged using an acid or a salt.

In the present invention, the multi-stage copolymer (B) latex is, for example, a rubbery copolymer consisting of at least one selected from the above-mentioned diene rubbers, acrylic rubbers, silicone rubbers, silicone / acrylic composite rubbers, and the like. It can be obtained by adding one or more copolymerizable monomers to the combined latex and graft polymerization.
Such a copolymerizable monomer is not particularly limited as long as it does not contain an epoxy group, a glycidyl group, an isobornyl group, an allyl group, and a hydroxyl group and can be copolymerized with a rubbery copolymer. . Specific examples include alkyl methacrylates such as methyl methacrylate and ethyl methacrylate; alkyl esters of acrylic acid such as ethyl acrylate and n-butyl acrylate; aromatic vinyl such as styrene, α-methyl styrene and various halogen-substituted and alkyl-substituted styrenes. An unsaturated nitrile such as acrylonitrile or methacrylonitrile;
These copolymerizable monomers can also be used as a monomer mixture with a chain transfer agent or the like. The monomer mixture can be used for multistage graft polymerization having one or two or more polymerization steps as necessary from the viewpoint of the balance between dispersibility and impact strength.
In addition, when a copolymerizable monomer containing any of an epoxy group, a glycidyl group, an isobornyl group, an allyl group and a hydroxyl group is used, the dispersibility of the resulting multistage polymerization copolymer (B) in latex Is unfavorable because it decreases.
The amount of the copolymerizable monomer used for the graft polymerization of the multistage polymerization copolymer (B) is preferably 10 to 70 parts by mass in 100 parts by mass of the multistage polymerization copolymer (B). When it is 70 parts by mass or less, impact resistance is improved, and when it is 10 parts by mass or more, fusion between primary particles is weakened, and dispersibility is improved.

In addition, suitable antioxidant, an additive, etc. can be previously added to a multistage polymerization copolymer (B) latex as needed.
Moreover, the collection method of a multistage polymerization copolymer (B) is not specifically limited, It can collect | recover by well-known spray drying, acid coagulation, salt coagulation, etc.
By these methods, it is usually possible to design a multistage polymerization copolymer (B) having an average primary particle diameter of 150 to 800 nm. If the particle size is designed to be small, a methacrylic resin molded product having good transparency can be easily obtained, and if the particle size is designed to be large, a methacrylic resin molded product having excellent viscosity characteristics and dispersibility can be easily obtained. Particularly preferably, the average primary particle diameter is 200 to 500 nm, and thereby, transparency, viscosity characteristics, dispersion time, and dispersibility in a methacrylic resin molded article are excellent. In addition, when using in the field | area which does not require transparency, even the particle diameter of about 800 nm can be used effectively.

  It is preferable that the usage-amount of a multistage polymerization copolymer (B) shall be 4-30 mass parts in 100 mass parts of polymeric mixtures (P). If it is 30 parts by mass or less, pouring into a mold becomes easy, and further, a methacrylic resin molded product having excellent transparency is easily obtained. On the other hand, if it is 4 parts by mass or more, the impact resistance is improved, and the surface impact is 3 times or more compared to that not containing the multistage copolymer (B).

  The polymerizable mixture (P) is prepared by, for example, charging the component (A) and a chain transfer agent as necessary into a flask equipped with a stirring bar, a cooling tube, etc. While stirring at a stirring speed of 5 to 500 rpm, the component (B) is added, and preferably mixed for 0.5 to 24 hours. Thereby, the multistage polymerization copolymer (B) can be sufficiently dispersed in the polymerizable mixture (P).

Chain transfer agent When preparing the polymerizable mixture (P), a chain transfer agent may be added for the purpose of adjusting the average molecular weight.
The chain transfer agent can be selected from those usually used for radical polymerization, and preferably a mercaptan chain transfer agent such as an alkyl mercaptan having 2 to 20 carbon atoms, a mercapto acid, thiophenol or a mixture thereof. It is. More preferred is a mercaptan having a short chain length of an alkyl group such as n-octyl mercaptan or n-dodecyl mercaptan.

<Step of preparing syrup>
In the step of preparing syrup, syrup is prepared by mixing the polymerizable mixture (P) obtained in the previous step and the radical polymerization initiator and polymerizing a part of the polymerizable mixture (P).
The preparation of syrup is not particularly limited, and for example, the temperature of the polymerizable mixture (P) is increased, a radical polymerization initiator is added thereto, and a suitable solid content (mass%) is appropriately obtained. It can be carried out by heating and prepolymerization.
Although superposition | polymerization temperature changes with kinds of the said radical polymerization initiator, it is preferable to carry out at 10-150 degreeC.

-Radical polymerization initiator Examples of the radical polymerization initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (2 , 4-dimethyl-4-methoxyvaleronitrile), etc .; organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-hexyl peroxypivalate; etc .; by combination of the organic peroxide and amines Examples thereof include redox polymerization initiators.
These radical polymerization initiators may be used alone or in combination of two or more.
It is preferable that the usage-amount of a radical polymerization initiator shall be 0.005-5 mass parts with respect to 100 mass parts of polymeric mixtures (P).

The syrup further includes the radical polymerizable monomer (A); ethylene glycol di (meth) acrylate, 1,2-propylene glycol di (meth) acrylate, 1,3-butylene glycol di, depending on the purpose. Alkanediol di (meth) acrylates such as (meth) acrylate and 1,6-hexanediol di (meth) acrylate; diethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, triethylene glycol (meth) acrylate, Polyoxyalkylene glycol di (meth) acrylates such as tetraethylene glycol di (meth) acrylate and polyethylene glycol di (meth) acrylate; polyfunctional polymerization having two or more ethylenically unsaturated bonds in the molecule such as divinylbenzene It is also possible to add compounds.
These addition amounts are preferably 0.01 to 5 parts by mass with respect to the polymerizable mixture (P).

As solid content of syrup obtained by superposition | polymerization, it is preferable that it is 4.1-70 mass% in syrup, It is more preferable that it is 5-50 mass%, Especially preferably, it is 5-35 mass%. In particular, when the solid content of syrup is 35% by mass or less, pouring into a mold becomes easy.
The viscosity of syrup is preferably 100 to 10,000 mPa · s.

<Cast polymerization process>
In the present invention, a methacrylic resin molded article is produced by curing by casting polymerization method in which the prepared syrup is poured into a mold and polymerized, and then peeled off from the mold.
In the casting polymerization step, the syrup (preferably syrup from which dissolved air has been removed by decompression or the like) is cured in a mold by a polymerization reaction. This makes it difficult for foreign matter or the like to enter. Further, the curability is enhanced as compared with other polymerization methods, and good impact resistance is obtained.
The casting polymerization method is not particularly limited. For example, (1) the syrup is poured into a mold in which the peripheral portions of two opposed inorganic glass plates or metal plates are sealed with a gasket and heated. Cell casting method, or (2) Two stainless steel endless belts facing each other running at the same speed in the same direction, and a space (mold) in which both end portions of the stainless steel endless belt are sealed with a gasket, A suitable method is a method in which the syrup is continuously poured from the upstream and heated to continuously polymerize.
As the heating method, for example, the mold can be heated and polymerized by heating with warm water at 30 to 90 ° C. and cured.
Thereafter, in order to further improve the curability, heat treatment at 90 to 150 ° C. can be performed with a far infrared heater or the like in an air atmosphere. And it cools by ventilation etc. as needed.
The material of the gasket is preferably polyvinyl chloride, and more preferably soft polyvinyl chloride.
The thickness of the produced methacrylic resin molded product is preferably 0.2 to 150 mm. When it is 0.2 mm or more, impact resistance is good, and when it is 150 mm or less, cracks and the like at the time of cutting of the methacrylic resin molded product are hardly generated, and workability is good.

In the methacrylic resin molded product to be produced, an antireflection film or an antistatic layer can be formed on the surface of the methacrylic resin molded product as necessary.
Furthermore, in the production method of the present invention, a release agent, a colorant, an ultraviolet absorber, a heat stabilizer, an antistatic agent, a filler and the like can be appropriately added in any convenient step.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. Each measurement method and evaluation method in this example are shown below.

(1) Measurement of particle diameter of polymer in latex The obtained latex was diluted with distilled water, and 50% number was obtained using a laser diffraction scattering type particle size distribution measuring device (LA-910, manufactured by Horiba, Ltd.). The average particle size was measured.

(2) Measurement of acetone insoluble fraction of multistage polymerization copolymer (B) About 0.5 g of the multistage polymerization copolymer (B) sample and 50 cc of acetone were added to a 200 ml eggplant type flask. It was set in a condenser and refluxed at a temperature of 65 ° C. for 4 hours. The sample solution after cooling was added to a centrifugal sedimentation tube (cell) and separated by a centrifuge to collect a sample insoluble in acetone. The setting conditions of the centrifuge were as follows: rotation speed: 14000 rpm, time: 30 minutes, and ambient temperature: 4 ° C.
Next, the sample collected in the centrifugal sedimentation tube (cell) is heated by a water bath in the centrifugal sedimentation tube (cell) to evaporate acetone contained in the sample. Was dried. Thereafter, the weight of the centrifugal sedimentation tube (cell) is measured, and the acetone insoluble amount (g) is obtained by subtracting the weight of the centrifugal sedimentation tube (cell) that has been measured in advance, from the following formula (I) The acetone insoluble fraction (gel content, mass%) was determined.
Acetone insoluble fraction (gel content, mass%) = acetone insoluble amount (g) / sample weight before dissolution (g) × 100

(3) Measurement of solid content of syrup About 5 g of syrup is precisely weighed and dissolved in about 100 g of chloroform. This solution is dropped into about 1000 g of hexane to solidify the polymer, and then filtered and dried. And weighed and determined by the following formula.
Solid content (mass%) = polymer mass after solidification / drying (g) / syrup mass (g) × 100

(4) Viscosity evaluation The viscosity of a B-type viscometer at 20 ° C. was measured at 6 rpm. The results are shown in Table 1.

(5) Evaluation of impact resistance According to JIS K 7211, the impact resistance was evaluated by calculating 50% fracture energy (J) in a Dupont falling weight test and measuring the surface impact strength. In addition, it measured so that a hard-coat surface might turn into a striking surface. The results are shown in Table 1.

(6) Evaluation of transparency The transparency was evaluated by measuring the total light transmittance and the haze value using a haze meter (manufactured by Color Research Laboratory, HR-100) in an atmosphere at 23 ° C.

(Production Example 1)
Production of multistage copolymer (B-1):
116 mass parts of pure water was put into a 5 L flask equipped with a stirring rod and a cooling tube, and heated to 80 ° C. while stirring at a rotation speed of 150 rpm in a nitrogen atmosphere. Dissolved by dissolving 0.000075 parts by mass of disodium ethylenediaminetetraacetic acid, 0.000025 parts by mass of ferrous sulfate and 0.25 parts by mass of sodium formaldehyde sulfoxylate in 1.9 parts by mass of pure water. The liquid was added. Next, 13.94 parts by mass of methyl methacrylate, 9.99 parts by mass of n-butyl acrylate, 1.06 parts by mass of styrene, 0.75 parts by mass of 1,3-butylene dimethacrylate, 0.094 parts by mass of allyl methacrylate, t- 0.044 parts by mass of butyl hydroperoxide, polyoxyethylene alkyl (12-15) ether phosphate (trade name: RS-610, manufactured by Toho Chemical Industry Co., Ltd., hereinafter referred to as “RS-610”) 0 1/10 out of 95 parts by mass of the mixed solution was dropped over 4 minutes and held for 15 minutes, and then the remaining mixed solution 9/10 was dropped over 108 minutes and held for 40 minutes. The eye was polymerized.
Subsequently, a solution obtained by dissolving 0.125 parts by mass of sodium formaldehyde sulfoxylate in 1.91 parts by mass of pure water was added all at once, and after maintaining for 15 minutes, 30.939 parts by mass of n-butyl acrylate and 6.563 parts by mass of styrene. Part, 1,3-butylene dimethacrylate 0.094 parts by mass, allyl methacrylate 0.656 parts by mass, cumene hydroperoxide 0.106 parts by mass, RS-610 0.6 parts by mass over 180 minutes The solution was added dropwise and held for 105 minutes to carry out the second stage polymerization.
Subsequently, a solution obtained by dissolving 0.125 parts by mass of sodium formaldehyde sulfoxylate in 1.91 parts by mass of pure water was added all at once, and after maintaining for 15 minutes, 35.63 parts by mass of methyl methacrylate and 1.88 parts by mass of methyl acrylate , T-butyl hydroperoxide 0.064 parts by mass and n-octyl mercaptan 0.113 parts by mass is added dropwise over 120 minutes, held for 60 minutes, the third stage polymerization is performed, multistage polymerization Copolymer (B-1) latex was obtained. The number average particle diameter of the multistage polymerization copolymer (B-1) in the latex was 280 nm.
The obtained multistage polymerization copolymer (B-1) latex was sprayed with fine droplets using an atomizer with a rotational speed of 25000 rpm using a spray dryer, and dried at a hot air inlet temperature of 150 ° C. A multistage polymerization copolymer (B-1) was obtained. The acetone insoluble fraction of the obtained multistage polymerization copolymer (B-1) was 90.0% by mass.

(Production Example 2)
Production of multi-stage copolymer (B-2):
In a 5 L flask equipped with a stirrer and a condenser tube, 100 parts by mass of pure water and sodium dialkylsulfosuccinate (trade name: Perex OT-P, manufactured by Kao Corporation, hereinafter referred to as “OT-P”) 0 .008 parts by weight, methyl methacrylate 2.788 parts by weight, n-butyl acrylate 2 parts by weight, styrene 0.212 parts by weight, allyl methacrylate 0.0188 parts by weight, 1,3-butylene dimethacrylate 0.15 parts by weight Then, nitrogen substitution was performed, and the mixture was heated to 80 ° C. with stirring at a rotation speed of 150 rpm in a nitrogen atmosphere. A solution obtained by dissolving 0.05 part by mass of potassium persulfate in 5 parts by mass of pure water was added all at once, and held for 60 minutes to carry out the first stage polymerization.
Subsequently, a solution obtained by dissolving 0.1 part by mass of potassium persulfate in 5 parts by mass of pure water was added all at once, and 40 parts by mass of pure water, 47.44 parts by mass of n-butyl acrylate, 10.06 parts by mass of styrene, , 3-butylene dimethacrylate 0.144 parts by mass, allyl methacrylate 0.575 parts by mass, OT-P 0.36 parts by mass of nitrogen-substituted mixed solution was added dropwise over 280 minutes, and then maintained for 120 minutes. Stage polymerization was carried out.
Then, 35.625 parts by mass of methyl methacrylate, 1.875 parts by mass of methyl acrylate, and 0.113 parts by mass of n-octyl mercaptan were added dropwise over 120 minutes, and then maintained for 120 minutes to maintain the third stage. Polymerization of the eyes was carried out to obtain a multistage polymerization copolymer (B-2) latex. The number average particle diameter of the multistage polymerization copolymer (B-2) in the latex was 417 nm.
The obtained multistage polymerization copolymer (B-2) latex was sprayed with fine droplets using an atomizer with a rotational speed of 25000 rpm using a spray dryer, and dried at a hot air inlet temperature of 150 ° C. A multistage polymerization copolymer (B-2) was obtained. The acetone insoluble fraction of the obtained multistage polymerization copolymer (B-2) was 76.2% by mass.

Example 1
To a flask equipped with a stirrer and a cooling tube, 88.65 parts by mass of methyl methacrylate and 0.1 part by mass of n-dodecyl mercaptan were added, and the multistage polymerization copolymer (B -1) 11.35 parts by mass was added and stirred for 4 hours to obtain a polymerizable mixture (P-1).
The obtained polymerizable mixture (P-1) was substituted with nitrogen, heated to 60 ° C., 0.1 part by mass of 2,2′-azobis (2,4-dimethylvaleronitrile) was added, and the solid content was Polymerization was performed by heating until the content became 24% by mass to obtain syrup.
To the obtained syrup, 0.32 parts by mass of t-hexylperoxypivalate was added and stirred for 5 minutes to obtain mixed syrup having a viscosity of 2700 mPa · s.
After the dissolved air was removed by vacuum, the mixed syrup was poured into a 2 mm thick mold formed by a gasket and two tempered glasses. Next, this was heated in a warm water atmosphere at 78 ° C. for 45 minutes and then in an air atmosphere at 130 ° C. for 45 minutes and cured by a casting polymerization method to obtain a methacrylic resin molded article.
The 50% fracture energy of this methacrylic resin molded product was 2.1 J.

(Example 2)
In Example 1, the amount of methyl methacrylate was changed to 96 parts by mass, the amount of the multistage polymerization copolymer (B-1) was changed to 4 parts by mass, and polymerization was performed by heating until the solid content was 15.2% by mass. A methacrylic resin molded product was obtained in the same manner as in Example 1 except that syrup was prepared.
The 50% fracture energy of this methacrylic resin molded product was 1.5 J.

(Example 3)
In Example 1, the amount of methyl methacrylate was changed to 98 parts by mass, the amount of the multistage polymerization copolymer (B-1) was changed to 2 parts by mass, and polymerization was performed by heating until the solid content became 13.2% by mass. A methacrylic resin molded product was obtained in the same manner as in Example 1 except that syrup was prepared.
The 50% fracture energy of this methacrylic resin molded product was 1.2 J.

Example 4
In Example 1, the multistage polymerization copolymer (B-1) was changed to the multistage polymerization copolymer (B-2) produced in Production Example 2, and the mixture was stirred for 30 minutes to obtain a polymerizable mixture (P-4). A methacrylic resin molded article was obtained in the same manner as in Example 1 except that it was prepared.
The 50% fracture energy of this methacrylic resin molded product was 2.3 J.

(Example 5)
In Example 1, the amount of methyl methacrylate was changed to 68 parts by mass, the amount of the multistage polymerization copolymer (B-1) was changed to 32 parts by mass, and polymerization was carried out by heating until the solid content became 35% by mass. A methacrylic resin molded product was obtained in the same manner as in Example 1 except that was prepared.
When the mixed syrup was poured into the mold, the viscosity of the mixed syrup had increased so that it could not be measured with a B-type viscometer.
The 50% fracture energy of this methacrylic resin molded product was 15.0 J.

(Comparative Example 1)
To a flask equipped with a stir bar, 96.0 parts by mass of a partially polymerized methyl methacrylate (viscosity 1000 mPa · s, polymerization rate 20% by mass) and 0.1 part by mass of n-dodecyl mercaptan are added and stirred at a rotation speed of 500 rpm. Then, 4.0 parts by mass of the multistage polymerization copolymer (B-1) obtained in Production Example 1 was added and stirred for 4 hours. Subsequently, 0.32 parts by mass of t-hexyl peroxypivalate was added and stirred for 5 minutes to obtain mixed syrup having a viscosity of 2800 mPa · s.
After the dissolved air was removed by vacuum, the mixed syrup was poured into a 2 mm thick mold formed by a gasket and two tempered glasses. Next, this was heated for 45 minutes in a 76 ° C. warm water atmosphere and then in a 130 ° C. air atmosphere for 45 minutes to obtain a methacrylic resin molded article.
The 50% fracture energy of this methacrylic resin molded product was 1.3 J.

(Comparative Example 2)
88.65 parts by mass of the dried beads produced by suspension polymerization using methyl methacrylate / methyl acrylate = 95/5 (mass ratio), and the multistage polymerization copolymer (B-1) obtained in Production Example 1 ) 11.35 parts by mass were mixed and melt kneaded at 230 ° C. in an extruder to be pelletized. A flat plate (methacrylic resin molded product) having a thickness of 3 mm was molded from the pellets by an injection molding machine.
The 50% fracture energy of this methacrylic resin molded product was 0.6J.

As shown in Table 1, it was confirmed that the methacrylic resin molded articles produced in Examples 1 to 5 had good impact resistance even when the amount of the impact modifier added was small.
Moreover, when the total light transmittance and haze value of the methacrylic resin molded product were measured and the transparency was evaluated, it was confirmed that Example 2 was superior to Comparative Example 1 in transparency.

On the other hand, the 50% breaking energy of Comparative Example 1 using a partially polymerized methyl methacrylate was lower than that of Example 2 using the radical polymerizable monomer (A).
Further, the 50% fracture energy of Comparative Example 2 subjected to injection molding was lower than that of Example 1 using the casting polymerization method.

Since the methacrylic resin molded product obtained by the production method of the present invention is excellent in impact resistance and transparency, for example, window glass, signboards, lighting fixture covers, optical parts, automobile-related parts, portable face plates, liquid crystal It is useful as a resin molded product used for various applications such as covers and sound insulation walls.

Claims (2)

  A radical polymerizable monomer (A) mainly composed of methyl methacrylate and a multi-stage polymerization copolymer (B) containing a rubbery copolymer having a crosslinked structure obtained by at least one-stage polymerization are mixed in advance. A polymerizable mixture (P) is prepared, the polymerizable mixture (P) and a radical polymerization initiator are mixed, a part of the polymerizable mixture (P) is polymerized to prepare syrup, and the syrup is used as a template. A method for producing a methacrylic resin molded article that is cured by a casting polymerization method in which it is poured into a polymer. The method for producing a methacrylic resin molded article according to claim 1, wherein the amount of the multistage polymerization copolymer (B) used is 4 to 30 parts by mass in 100 parts by mass of the polymerizable mixture (P).