JP2001055406A - Production of methacrylic resin board for sanitary use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably and readily producing a methacrylic resin board excellent in moldability for sanitary use, and further excellent in crack resistance of hardly causing a crack in a test for a practical use, comprising alternately repeating the contact of the resin board with a high temperature water and the drying thereof. SOLUTION: A syrup obtained by adding 0.1-0.5 pts.wt. polyfunctional monomer copolymerizable with a methyl methacrylate-based monomer, and 0.01-0.30 pts.wt. chain transfer agent, to 100 pts.wt. syrup comprising 0.5-3.5 pts.wt. linear methyl methacrylate-based polymer having >=1,000,000 viscosity average molecular weight, 5-25 pts.wt. methyl methacrylate-based polymer having 50,000-300,000 viscosity average molecular weight, and 71.5-94.5 pts.wt. methyl methacrylate- based monomer, and the obtained syrup is poured in a cell and polymerized to provide the objective methacrylic resin board for a sanitary use.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a methacrylic resin plate suitable for sanitary use such as a bathtub and a washbasin.

[0002]

2. Description of the Related Art Resin materials are frequently used in sanitary articles such as bathtubs and washbasins. As these resin materials, FRP made of unsaturated polyester has been often used, but unsaturated polyester-based materials have drawbacks such as yellowing over time and susceptibility to damage. For this reason, recently, a methacrylic resin-based sanitary material having characteristics of being hardly yellowed and being hardly damaged has been proposed and put into practical use.

[0003] To give a specific example, JP-A-8-3224 discloses that, based on 100 parts by weight of a methacrylic monomer,
A syrup is prepared by dissolving 5 to 50 parts by weight of a methacrylic resin having a viscosity average molecular weight of about 10,000 to about 300,000,
A production method has been proposed in which the syrup is injected into a cell and polymerized. Also, JP-A-9-31109 discloses that
In a method for producing an acrylic resin plate in which an acrylic monomer is mixed with a mercaptan, a polyfunctional monomer, and a radical polymerization initiator, and the mixed solution is injected into a cell and polymerized, a polyfunctional monomer having a specific structure is used. 0.1 to the mercaptan amount
There has been proposed a method for producing an acrylic resin plate characterized by adding about 1.0 mol, and it is known that a methacrylic resin plate excellent in moldability for any of sanitary products can be obtained.

[0004]

As a method for forming a methacrylic resin plate used for sanitary applications, vacuum forming, pressure forming and the like are used. In these methods, the resin itself is stretched by molding, and the thickness of the molded product is considerably reduced.
Further, the stretched methacrylic resin exerts a force for returning to the shape before molding. Therefore, when exposed to an environment where contact with high-temperature water and drying after draining are alternately repeated, such as in a bathtub, cracks occur in the stretched portion. This phenomenon is the same in the methacrylic resin plate obtained by the method described in JP-A-8-3224 or JP-A-9-31109.

Accordingly, the present invention provides a methacryl for sanitary methacrylic material having excellent heat resistance, excellent moldability for sanitary use, and no cracks in practical tests in which contact and drying with high temperature water are alternately repeated, ie, excellent crack resistance. Resin board,
As a result of intensive studies for the purpose of finding a stable and easy production method, a linear methyl methacrylate polymer having a viscosity average molecular weight of 1,000,000 or more and a viscosity average molecular weight of 5 to 3
When the syrup obtained by allowing both of the methyl methacrylate-based polymer to be present in the methyl methacrylate-based monomer is polymerized by injecting the syrup into a cell, the sanitary garment having excellent crack resistance that satisfies the above-mentioned object is used. The present inventors have found that a methacrylic resin plate for use can be manufactured, and have completed the present invention.

[0006]

The present invention provides a linear methyl methacrylate polymer having a viscosity average molecular weight of 1,000,000 or more.
5 to 3.5 parts by weight, 5 to 25 parts by weight of a methyl methacrylate polymer having a viscosity average molecular weight of 50,000 to 300,000, and 100 parts by weight of a syrup comprising 71.5 to 94.5 parts by weight of a methyl methacrylate monomer, A syrup containing 0.1 to 0.5 parts by weight of a polyfunctional monomer copolymerizable with a methyl methacrylate-based monomer and 0.01 to 0.30 parts by weight of a chain transfer agent is injected into a cell and polymerized. This is a method for producing a methacrylic resin plate for sanitary.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The viscosity average molecular weight of the present invention is 1
A linear methyl methacrylate polymer of 100,000 or more is a polymer obtained by copolymerizing a monomer mixture containing a methyl methacrylate monomer or a comonomer copolymerizable with the methyl methacrylate monomer.

[0008] Specific examples of comonomers copolymerizable with methyl methacrylate monomer include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, cyclohexyl acrylate, Acrylic esters such as phenyl acrylate; methacrylic esters such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, isononyl methacrylate, cyclohexyl methacrylate, and phenyl methacrylate Methacrylic acid, maleic anhydride, styrene, cyclohexylmaleimide, acrylonitrile and the like. Two or more of these comonomers can be used in combination.

[0009] These comonomers are appropriately selected according to the molding conditions and the intended use of the obtained resin plate. When particularly high crack resistance is required, the amount of the comonomer may be reduced. The amount of the comonomer in the monomer mixture of the methyl methacrylate monomer and the comonomer may be used in a range of 10% by weight or less, and is preferably 5% by weight or less. More preferably, a methyl methacrylate monomer may be used without using the comonomer.

[0010] The viscosity average molecular weight of a linear methyl methacrylate polymer having a viscosity average molecular weight of 1,000,000 or more obtained by copolymerizing a monomer mixture containing a methyl methacrylate monomer or a comonomer copolymerizable with the methyl methacrylate monomer M can be determined from the following equation 1 by determining the intrinsic viscosity [η] using an Ubbelohde viscometer.

[0011] lnM = {ln [η] -ln (4.8 × 10 ⁻⁵ )} / 0.8 (Equation 1)

[0012] The higher the viscosity average molecular weight M of the linear methyl methacrylate polymer obtained by copolymerizing a monomer mixture containing a methyl methacrylate monomer or a comonomer copolymerizable with the methyl methacrylate monomer, the higher the crack resistance, the higher the crack resistance. The property is improved and 1,000,000 or more is good. By adding a methacrylic resin having a molecular weight in this range, the crack resistance of the obtained resin plate after processing can be improved.

The linear methyl methacrylate-based polymer is used in an amount of 0.5 to 3.5 parts by weight based on 100 parts by weight of the syrup. If the amount is less than 0.5 parts by weight, the crack resistance of the molded product is reduced. If it is more than 3.5 parts by weight, the moldability deteriorates.

The method for dissolving the linear methyl methacrylate polymer having a viscosity average molecular weight of 1,000,000 or more in a methyl methacrylate monomer may be produced by a conventionally known method. For example, a radical polymerization initiator is added to a monomer mixture containing a methyl methacrylate monomer and a comonomer copolymerizable with the methyl methacrylate monomer, and heated to partially polymerize a part thereof, whereby a methyl methacrylate monomer or a methacrylic monomer is added. It is obtained as a comonomer solution that can be copolymerized with the acid methyl monomer. It may be used as it is or may be diluted to a predetermined concentration. Further, the linear methyl methacrylate polymer having a viscosity average molecular weight of 1,000,000 or more obtained by suspension polymerization, emulsion polymerization or the like may be dissolved in the methyl methacrylate monomer.

In the present invention, the methyl methacrylate polymer having a viscosity average molecular weight of 50,000 to 300,000 is obtained by copolymerizing a monomer mixture containing a methyl methacrylate monomer or a comonomer copolymerizable with the methyl methacrylate monomer. It is a polymer.

Specific examples of the comonomer include acrylic esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, cyclohexyl acrylate, and phenyl acrylate. Methacrylates such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, isononyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate; methacrylic acid, maleic anhydride, styrene , Cyclohexylmaleimide, acrylonitrile and the like. Furthermore, ethylene glycol diacrylate, ethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol methacrylate, neopentyl glycol dimethacrylate, neopentyl glycol diacrylate, hexanediol diacrylate, hexanediol dimethacrylate, nonanediol diacrylate, Nonanediol dimethacrylate, trimethylolpropane triacrylate,
Polyfunctional monomers having two or more radically polymerizable groups in the molecule, such as trimethylolpropane dimethacrylate, bis (2-methacryloyloxyethyl) phthalate, and allyl methacrylate. Two or more of these comonomers can be used in combination.

The comonomer is appropriately selected according to the molding conditions of the obtained resin plate and the intended use. When particularly high crack resistance is required, the amount of the comonomer may be reduced or the amount of the polyfunctional monomer having two or more radically polymerizable groups therein may be increased. When particularly high moldability is required, the amount of the comonomer may be increased or the amount of the polyfunctional monomer having two or more radically polymerizable groups therein may be reduced. The amount of the comonomer is 0.5 to 1
5% by weight is preferred. Less than 0.5% by weight or 15
If the amount is more than the percentage by weight, the moldability and the crack resistance of the molded product deteriorate, which is not preferable. The comonomer amount is more preferably 0.5 to 12% by weight.

The viscosity average molecular weight of the methyl methacrylate polymer having a viscosity average molecular weight of 50,000 to 300,000 can be determined by the above (Equation 1). Its viscosity average molecular weight is between 50,000 and 300,000. If it is smaller than 50,000, the crack resistance of the molded product is deteriorated, and if it is larger than 300,000, the moldability is deteriorated. By adding a methacrylic resin having a molecular weight in this range, workability during thermoforming of the obtained resin plate can be improved.

The amount of the methyl methacrylate polymer having a viscosity average molecular weight of 50,000 to 300,000 is based on 100 parts by weight of the syrup.
Used in the range of 5 to 25 parts by weight. If the amount is less than 5 parts by weight, the crack resistance of the molded product is reduced. On the other hand, if it is more than 25 parts by weight, the syrup has too high a viscosity to make it difficult to handle, and at the same time, moldability deteriorates.

As a method for dissolving the methyl methacrylate polymer having a viscosity average molecular weight of 50,000 to 300,000 in a methyl methacrylate monomer, a conventionally known method may be used. For example, a methyl methacrylate-based monomer may have the viscosity average molecular weight of 5 to 3
A method of dissolving 100,000 methyl methacrylate polymer is exemplified. As a form of the methyl methacrylate-based polymer having a viscosity average molecular weight of 50,000 to 300,000 in order to be easily dissolved in a methacrylic monomer, it is preferable to use the form of a powder, a pellet, or the like in the form of particles having an average size of 10 mm or less. .

The methyl methacrylate monomer dissolving the linear methyl methacrylate polymer having a viscosity average molecular weight of 1,000,000 or more and the methyl methacrylate polymer having a viscosity average molecular weight of 50,000 to 300,000 is mainly composed of methyl methacrylate monomer. Is a monomer mixture containing a comonomer copolymerizable with a methyl methacrylate monomer described below.

Specific examples of the copolymerizable comonomer include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, cyclohexyl acrylate, phenyl acrylate and the like. Acrylic esters: methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-methacrylic acid 2-
Methacrylic esters such as ethylhexyl, isononyl methacrylate, cyclohexyl methacrylate, and phenyl methacrylate; and methacrylic acid, maleic anhydride, styrene, cyclohexylmaleimide, and acrylonitrile. Two or more of these comonomers can be used in combination. Among them, it is particularly preferable to use acrylic acid esters as one component.

The amount of the comonomer that can be copolymerized is not limited, but is a methyl methacrylate monomer from 71.5 to 94.5.
It is particularly preferred that the amount be 0.5 to 15 parts by weight per part by weight. If the amount is small, the moldability deteriorates, and if the amount is large, the crack resistance of the molded product deteriorates.

0.5 to 3.5 parts by weight of a linear methyl methacrylate polymer having a viscosity average molecular weight of 1,000,000 or more, and 5 to 25 parts by weight of a methyl methacrylate polymer having a viscosity average molecular weight of 50,000 to 300,000.
Parts by weight, methyl methacrylate monomer 71.5-9
A syrup consisting of 4.5 parts by weight has a viscosity average molecular weight of 1
It is obtained by a method in which a linear methyl methacrylate polymer having a molecular weight of 100,000 or more and a methyl methacrylate polymer having a viscosity average molecular weight of 50,000 to 300,000 are dissolved in a methyl methacrylate monomer by the above method and then mixed. Alternatively, a viscosity average molecular weight of 10
It is also possible to simultaneously produce a linear methyl methacrylate polymer having a molecular weight of 50,000 or more and a methyl methacrylate polymer having a viscosity average molecular weight of 50,000 to 300,000 by preliminary polymerization.

The polyfunctional monomers copolymerizable with the methyl methacrylate monomer include ethylene glycol diacrylate, ethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, and neopentyl. Glycol diacrylate, hexanediol diacrylate, hexanediol dimethacrylate, nonanediol diacrylate,
Polyfunctional monomers having two or more radically polymerizable groups in a molecule such as nonanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane dimethacrylate, bis (2-methacryloyloxyethyl) phthalate, and allyl methacrylate It is. Two or more of these polyfunctional monomers can be used in combination. In particular, neopentyl glycol dimethacrylate and neopentyl glycol diacrylate are preferably used as one component.

The amount of the polyfunctional monomer copolymerizable with the methyl methacrylate monomer is 0.1 to 0.5 part by weight based on 100 parts by weight of the syrup. If the amount is less than 0.1 part by weight, a sufficient crosslinked structure is not obtained, and the crack resistance of the molded product is reduced. If the amount is more than 0.5 part by weight, the crosslinked structure becomes too dense and the moldability deteriorates.

Examples of the chain transfer agent to be added to the syrup include alkyl mercaptans such as lauryl mercaptan, octyl mercaptan and butyl mercaptan; thioglycolic acid esters such as thioglycolic acid-2-ethylhexyl and ethyl thioglycolate; Octyl mercaptopropionate, β-mercaptopropionic acid, etc.
-Mercaptopropionic acid and esters thereof; aromatic mercaptans such as thiophenol and p (t-butyl) thiophenol. Of these, alkyl mercaptans are preferred. Two or more of these chain transfer agents can be used in combination. Among them, it is preferable to contain 80% by weight or more of alkyl mercaptans from the viewpoint of crack resistance.

[0028] The amount of the chain transfer agent is 0.01 to 0.30 parts by weight. If it is less than 0.01 parts by weight, the moldability deteriorates,
If the amount is more than 0.3 parts by weight, the crack resistance of the molded product deteriorates. When the molar ratio of the alkyl mercaptan and the polyfunctional monomer copolymerizable with the methyl methacrylate-based monomer in the chain transfer agent is from 1.5 to 3.5, moldability,
Excellent crack resistance.

[0029] A polyfunctional monomer copolymerizable with the methyl methacrylate-based monomer and the chain transfer agent are added to the syrup, and a radical polymerization initiator is added to the syrup when the syrup is subjected to polymerization. As the radical polymerization initiator, a usual polymerization initiator used for producing a methacrylic resin plate can be used. For example, lauroyl peroxide, benzoyl peroxide, di-t-butyl peroxide, t-butyl peroxy 2-ethylhexanoate, t-butyl peroxy isobutyrate, t-butyl peroxy pivalate, t-butyl peroxy benzoate, t-butyl peroxy Peroxide initiators such as oxyacetate, diisopropylperoxydicarbonate, disecbutylperoxydicarbonate; 2,2 ′ azobisisobutyronitrile, 2,2 ′ azobis (2,4-dimethylvaleronitrile) And azo initiators such as known compounds; and known redox initiator systems in which a peroxide initiator is combined with a reducing compound such as an amine or a mercaptan as a main component.

[0030] In addition, as long as the characteristics of the resin of the present invention are not impaired, known additives such as antioxidants, ultraviolet absorbers, mold release agents, dyes, pigments, inorganic fillers and the like are used depending on the application. Can also be added. As the release agent, it is preferable that a phosphate ester having a specific structure represented by the following formula 2 be added to the release agent in an amount of 50% by weight or more.

{R _1- (R ₂ O) _n } _m -P (O)-(OH) _3-m (Formula 2) (where R ₁ and R ₂ are alkyl groups having 1 to 20 carbon atoms) Wherein m is 1 or 2, and n is a number average of 0 to 100.)

The syrup is injected into a cell and polymerized by a known so-called cell casting method. That is, as the cell, for example, a cell composed of two glass plates or metal plates, a soft sealing material and a clamp can be used, and a continuous cell using two stainless steel continuous belts can also be used. The thickness of the cell is selected so as to obtain a desired resin plate, but is generally in the range of 1 to 30 mm. As a heating method in the polymerization, heating is performed by a known method, for example, a heat source such as hot air, hot water, or an infrared heater. The polymerization conditions are appropriately selected depending on the type and amount of the initiator used and the composition of the monomer mixture.
The polymerization is carried out at 0 to 120 ° C for 1 to several tens of hours. After the polymerization is completed, the frame is released to obtain a methacrylic resin plate.

[0033]

Industrial Applicability According to the present invention, a sanitary product having excellent heat resistance, excellent moldability for sanitary use, and no cracking in practical tests in which contact and drying with high temperature water are alternately repeated, that is, excellent crack resistance. A methacrylic resin plate can be stably and easily produced. Since the resin plate obtained by the present invention has a low tensile strength at the time of thermoforming and a high elongation at break, a deep drawn molded product such as a bathtub can be easily molded. That is, the resin plate obtained according to the present invention has good processability for processing into sanitary products such as bathtubs and wash bowls. Further, in a practical test in which a product obtained by molding is alternately contacted with high-temperature water and dried alternately, no cracks are generated, that is, it has excellent crack resistance and good durability.

[0034]

The present invention will be specifically described below with reference to examples.
Parts in Examples and Comparative Examples represent parts by weight. Also,
The physical property measurement and test methods performed in the examples are as follows.

Viscosity average molecular weight: The intrinsic viscosity [η] was determined using an Ubbelohde viscometer, and the viscosity average molecular weight M was determined from the following equation. lnM = {ln [η] -ln (4.8 × 10 ⁻⁵ )} /
0.8

[0036] Tensile test: The distance between the marked lines is 15 mm and the sample thickness is 5 mm according to JIS K-7113.
A JIS No. 2 test piece was used, and the test piece was preheated to 160 ° C., and a tensile test was performed at a crosshead speed of 500 mm / min to determine the elongation at break.

Crack resistance: 280 mm × 280 mm bottom, 70 m depth in vacuum forming device with built-in slide type infrared heater
m, set a rectangular mold having a shape with a radius of curvature R of 5 mm at the boundary between the bottom and the side, heat to a surface temperature of 180 ° C., vacuum form the sheet, and furthermore, glass fiber mat and unsaturated polyester resin Backing by hand lay-up method. Warm water at 90 ° C for 5 minutes
On the day, a durability cycle test consisting of two days of drying, in which water was removed and left at room temperature, was performed. Judgment was made based on whether cracks occurred within 6 weeks. The sample having a crack within 6 weeks was evaluated as x, and the sample without cracks was evaluated as ○.

Example 1 20 ppm of 2,2 ′ azobisisobutyronitrile was added to methyl methacrylate and prepolymerized at 70 ° C.
A methyl methacrylate monomer solution containing 5% by weight of a polymer having a viscosity average molecular weight of 1.5 million was obtained. 15 parts by weight of a methyl methacrylate monomer solution (hereinafter referred to as prepolymerized syrup) of a linear methyl methacrylate polymer having a viscosity average molecular weight of 1.5 million and 65.5 methyl methacrylate monomer.
Methyl methacrylate-based polymer 1 having a viscosity average molecular weight of 140,000 and obtained by suspension polymerization comprising 99.2% by weight of methyl methacrylate and 0.8% by weight of methyl acrylate.
5 parts by weight, 4.5 parts by weight of 2-ethylhexyl acrylate, 0.18 of neopentyl glycol dimethacrylate
Parts by weight, 0.06 parts by weight of lauryl mercaptan, 2,
0.1% by weight of 2 'azobisisobutyronitrile, phosphanol RS710 manufactured by Toho Chemical Co., Ltd. as a release agent
0.01 parts by weight were mixed. At this time, the molar ratio of the polyfunctional monomer to the mercaptan was 2.5. After degassing the mixed solution, the mixture was poured into a 5 mm thick cell composed of two glass plates and a gasket made of vinyl chloride resin, and then cooled to 65 ° C.
For 4 hours and then at 120 ° C. for 1 hour. The elongation at break of the obtained plate in a tensile test was 750%. The result of the crack resistance test was ○.

Examples 2 to 4 and Comparative Examples 1 and 2 The same procedure as in Example 1 was carried out except that the amounts of the syrup, the crosslinking agent and the serial transfer agent were changed to those shown in Table 1. Table 2 shows the evaluation results.

[0040]

[Table 1]

[0041]

[Table 2]

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08J 5/18 CEY C08J 5/18 CEY C08L 33/12 C08L 33/12 (72) Inventor Masashi Mori Ehime 5-1, Sokaicho, Niihama-shi Sumitomo Chemical Co., Ltd. F-term (reference) 4F071 AA33 AF23 AH03 BA09 BB01 BC01 4J002 BC071 BC072 BG061 BG062 BG071 BG101 BG102 BH021 BH022 EA046 EF046 EH076 EH106 EV27 EV046 EF046 EH146 EL146 EL067 EV067 4J011 AA05 GA05 NA25 NA26 NB04 PA34 PA38 PA69 PB30 PC08

Claims (7)

[Claims] Claims 1. A linear methyl methacrylate polymer having a viscosity average molecular weight of 1,000,000 or more, 0.5 to 3.5 parts by weight, and a methyl methacrylate polymer having a viscosity average molecular weight of 50,000 to 300,000.
5 parts by weight, methyl methacrylate-based monomer 71.5-9
To 100 parts by weight of a syrup composed of 4.5 parts by weight, 0.1 to 0.5 parts by weight of a polyfunctional monomer copolymerizable with a methyl methacrylate-based monomer and 0.01 to 0.5 parts by weight of a chain transfer agent
A method for producing a methacrylic resin plate for sanitary, in which a syrup containing 0.30 parts by weight is injected into a cell and polymerized. 2. The method for producing a sanitary methacrylic resin plate according to claim 1, wherein the linear methyl methacrylate polymer having a viscosity average molecular weight of 1,000,000 or more is a homopolymer of methyl methacrylate. 3. A methyl methacrylate polymer having a viscosity average molecular weight of 50,000 to 300,000 is a copolymer of a methyl methacrylate monomer and an acrylate, and the acrylate content is 0.5% by weight or more. The method for producing a methacrylic resin plate for sanitary according to claim 1, wherein: 4. A methyl methacrylate-based monomer of 71.5 to
Acrylic ester is 0.5 to 10 in 94.5 parts by weight.
The method for producing a sanitary methacrylic resin plate according to claim 1, wherein the methacrylic resin plate is contained in parts by weight. 5. The sanitary methacrylic resin plate according to claim 1, wherein the polyfunctional monomer copolymerizable with the methyl methacrylate monomer is neopentyl glycol diacrylate or neopentyl glycol dimethacrylate. Production method. 6. The method for producing a methacrylic resin sheet for sanitary according to claim 1, wherein the alkyl mercaptan is contained in an amount of 80% by weight or more in 0.01 to 0.30 part by weight of the chain transfer agent. 7. The method according to claim 1, wherein the molar ratio of the polyfunctional monomer copolymerizable with the methyl methacrylate monomer and the alkyl mercaptan in the chain transfer agent is from 1.5 to 3.5. Of producing a methacrylic resin plate for sanitary use.