JP7112403B2 - Methacrylic resin cast plate and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a methacrylic resin cast plate having excellent flame retardancy and a method for producing the same.

Methacrylic resins containing methyl methacrylate (MMA) units as a main component are excellent in properties such as transparency, colorability, moldability, weather resistance and surface hardness, and are used in various applications. Applications of methacrylic resins are expanding, and flame retardancy is required depending on the application. Patent Documents 1 to 3 disclose a methacrylic resin composition or a methacrylic resin sheet having improved flame retardancy by adding an organic phosphorus compound (preferably a halogen-containing organic phosphorus compound) as a flame retardant to a methacrylic resin. (Claim 1 of Patent Document 1, Claim 1 of Patent Document 2, Claim 1 of Patent Document 3).

JP 2015-74740 A JP-A-6-100712 JP 2011-46835 A Japanese Patent Publication No. 46-30297

However, when a flame retardant is added to a methacrylic resin containing MMA units as a main component, heat resistance tends to decrease due to the plasticizing action of the flame retardant, so the amount of the flame retardant added is limited. Therefore, it is difficult to increase flame retardancy by increasing the amount of flame retardant added.
Conventionally, as a method for producing a methacrylic resin cast plate, a syrup containing a methacrylic resin such as polymethyl methacrylate (PMMA) and one or more monomers containing MMA is prepared, and MMA is added to this syrup. There is a method of adding one or more kinds of monomers to obtain a raw material mixture, and performing cast polymerization of the obtained raw material mixture. However, when syrup is used, the amount of terminal double bonds, which are starting points for thermal decomposition, tends to increase in the resulting methacrylic resin, which may deteriorate thermal decomposition resistance and reduce flame retardancy. .
Patent Document 4 discloses that a flame-retardant methacrylic resin can be produced by polymerizing MMA or a monomer mixture containing MMA as a main component in the presence of an organic acid, even with a relatively small amount of flame retardant added. (page 1, right column). It is believed that the addition of an organic acid during polymerization reduces the amount of terminal double bonds, which are starting points for thermal decomposition, and improves the thermal decomposition resistance of the methacrylic resin. However, simply reducing the amount of terminal double bonds in methacrylic resins to improve thermal decomposition resistance does not solve the problem of the limit of flame retardancy improvement due to the limitation of the amount of flame retardant added. The effect cannot be said to be sufficient.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a methacrylic resin cast plate having excellent heat resistance and flame retardancy and a method for producing the same.

The present invention provides the following [1] to [5] methacrylic resin cast plates and methods for producing the same.
[1] A methacrylic resin cast plate made of a resin composition containing a methacrylic resin (A) made of a methyl methacrylate-(meth)acrylic acid copolymer and an organic phosphorus compound (B),
The organophosphorus compound (B) is represented by the following formula (I),
Based on the total of the methacrylic resin (A) and the organic phosphorus compound (B), the amount of methyl methacrylate units is 68 to 74% by mass, the amount of (meth) acrylic acid units is 6 to 9% by mass, and the organic phosphorus compound ( The amount of B) is 19 to 24% by mass,
A methacrylic resin casting plate that does not contain a methyl methacrylate polymer that is not copolymerized with (meth)acrylic acid.
P(=O)(-O-R-X) ₃ (I)
(Wherein, R represents an alkylene group having 1 to 6 carbon atoms, and X represents a chlorine atom or a bromine atom.)

[2] The methacrylic resin casting plate according to [1], wherein the organic phosphorus compound (B) is represented by the following formula (II).

[3] The methacrylic resin casting board according to [1] or [2], wherein the methacrylic resin (A) is a non-crosslinked resin.
[4] The methacrylic resin cast board according to any one of [1] to [3], which has a deflection temperature under load of 75° C. or higher according to JIS K 7191 B method.
[5] A raw material mixture containing 68 to 74% by mass of methyl methacrylate, 6 to 9% by mass of (meth)acrylic acid, 19 to 24% by mass of an organic phosphorus compound (B), and a radical polymerization initiator was prepared without using syrup. The method for producing a methacrylic resin cast plate according to any one of [1] to [4], wherein the cast polymerization is performed on the methacrylic resin cast plate.

ADVANTAGE OF THE INVENTION According to this invention, the methacrylic-resin casting board excellent in heat resistance and flame retardance can be provided.

The present invention will be described in detail below. In this specification, "methacryl" and "acryl" are collectively referred to as "(meth)acryl".
The methacrylic resin cast plate of the present invention is a methacrylic resin (A) made of a methyl methacrylate-(meth)acrylic acid copolymer containing methyl methacrylate (MMA) units and (meth)acrylic acid units and the following formula ( It is a methacrylic resin casting plate containing an organic phosphorus compound (B) represented by I) and containing no methyl methacrylate polymer which is not copolymerized with (meth)acrylic acid. In the methacrylic resin cast plate of the present invention, the amount of MMA units is 68 to 74% by mass and the amount of (meth)acrylic acid units is 6 to 74% by mass, based on the total of the methacrylic resin (A) and the organic phosphorus compound (B). 9% by mass, and the amount of the organic phosphorus compound (B) is 19-24% by mass.
P(=O)(-O-R-X) ₃ (I)
(Wherein, R represents an alkylene group having 1 to 6 carbon atoms, and X represents a chlorine atom or a bromine atom.)

(Methacrylic resin (A))
The methacrylic resin (A) is a copolymer having methyl methacrylate (MMA) units and (meth)acrylic acid units. The methacrylic resin (A) having a (meth)acrylic acid unit has a high heat distortion temperature and is excellent in heat resistance, and is also excellent in flame retardancy because it is quickly carbonized when in contact with a flame and is difficult to burn. Therefore, by using the methacrylic resin (A), it is possible to provide a methacrylic resin cast board having excellent heat resistance and flame retardancy even with a relatively small amount of flame retardant added.
The heat resistance of a resin (composition) can be measured by, for example, the load deflection temperature (HDT) according to JIS K 7191 B method. The deflection temperature under load (HDT) of the methacrylic resin cast plate of the present invention is preferably 70°C or higher, more preferably 75°C or higher. Heat deflection temperature (HDT) is the heat distortion temperature.
(Meth)acrylic acid units are methacrylic acid (MAA) units and/or acrylic acid (AA) units, and since the deflection temperature under load (HDT) of the methacrylic resin (A) increases, the methacrylic acid (MAA) units more preferred.

From the viewpoint of transparency, the amount of MMA units in the methacrylic resin (A) is 68 to 74% by mass, preferably 68 to 72% by mass, based on the total amount of the methacrylic resin (A) and the organic phosphorus compound (B). be. From the viewpoint of improving heat resistance, flame retardancy, and releasability, the amount of (meth)acrylic acid units in the methacrylic resin (A) with respect to the total amount of the methacrylic resin (A) and the organic phosphorus compound (B) is 6 to 9% by mass, preferably 7 to 9% by mass, more preferably 7.5 to 8.5% by mass.
If the amount of MMA units is less than 68% by mass, the transparency may be insufficient. If the amount of MMA units exceeds 74% by mass, the amounts of (meth)acrylic acid units and organic phosphorus compound (B) may be insufficient, resulting in insufficient heat resistance and flame retardancy. If the amount of (meth)acrylic acid units is less than 6% by mass, the heat resistance may be insufficient. If the amount of (meth)acrylic acid units exceeds 9% by mass, the releasability may deteriorate.

The methacrylic resin (A) can contain one or more monomeric units other than MMA units and (meth)acrylic acid units. Other monomers include alkyl methacrylates other than MMA and other copolymerizable unsaturated monomers that can be used in combination with alkyl methacrylates. The number of carbon atoms in the alkyl group of the alkyl methacrylate other than MMA is preferably 2-20, more preferably 2-12. Such alkyl methacrylates include ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, and cyclohexyl methacrylate. is mentioned. Other copolymerizable unsaturated monomers that can be used with alkyl methacrylates include acrylic acids such as methyl acrylate, ethyl acrylate, propyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, and cyclohexyl acrylate. Alkyl; hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxy-3-chloropropyl (meth)acrylate; (meth)acrylic acid metal salts; vinyl-based monomers such as vinyl chloride, vinyl acetate, and vinyltoluene; acrylonitrile; acrylamide; styrene-based monomers such as styrene and α-methylstyrene;
However, since the methacrylic resin (A) contains other monomer units, the amount of MMA units and (meth)acrylic acid units, which are active ingredients, is relatively small, so the amount of other monomer units is Less is better. The content of other monomer units in the methacrylic resin (A) is preferably 10% by mass or less, more preferably 5% by mass or less.

The methacrylic resin (A) may be a non-crosslinked resin or a crosslinked resin. In general, a crosslinked resin has a higher deflection temperature under load (HDT) than a non-crosslinked resin, and tends to be less prone to thermal deformation. In the methacrylic resin cast plate of the present invention, the methacrylic resin (A) is preferably a non-crosslinked resin that does not contain polyfunctional monomer units because secondary molding with heat is facilitated. Since the methacrylic resin (A) contains MMA units and (meth)acrylic acid units, even if it is a non-crosslinked resin, it has a sufficiently high heat deflection temperature (HDT) and excellent heat resistance.

The viscosity average degree of polymerization of the methacrylic resin (A) is not particularly limited, and is preferably 2,000 to 70,000, more preferably 10,000 to 50,000.
The weight average molecular weight (Mw) of the methacrylic resin (A) is not particularly limited, and is preferably 200,000 to 7,000,000, more preferably 1,000,000 to 5,000,000 from the viewpoint of mechanical strength and transparency.

The methacrylic resin cast plate of the present invention can contain other methacrylic resins other than the methacrylic resin (A). However, methyl methacrylate polymer not copolymerized with (meth)acrylic acid shall not be included in a proportion that can be regarded as a contaminant component. Methyl methacrylate polymers not copolymerized with (meth)acrylic acid, such as methyl methacrylate homopolymers and methyl methacrylate-methyl acrylate copolymers, are combined with the methacrylic resin (A) essential in the present invention. In comparison, the deflection temperature under load (HDT) is low and the heat resistance is not good, so it is difficult to achieve high heat resistance and flame retardancy when used.

(Organic phosphorus compound (B))
The organophosphorus compound (B) is a flame retardant represented by the following formula (I). 1 type(s) or 2 or more types can be used for an organic phosphorus compound (B).
P(=O)(-O-R-X) ₃ (I)
(Wherein, R represents an alkylene group having 1 to 6 carbon atoms, and X represents a chlorine atom or a bromine atom.)
R is selected from the group consisting of methylene, ethylene, propylene, butylene, pentylene, and hexylene. When R has 3 or more carbon atoms, R may have a linear structure or a branched structure.

Tris(2-chloro-1 -methylethyl) is preferred. Commercially available flame retardants represented by formula (II) include "CR570" manufactured by Daihachi Chemical Industry Co., Ltd., and the like.

In general, when a flame retardant is added to a methacrylic resin containing MMA units as a main component, the plasticizing action of the flame retardant tends to lower the heat resistance, so the amount of the flame retardant to be added is limited. In the methacrylic resin cast plate of the present invention, the amount of the organic phosphorus compound (B) is 19 to 24% by mass, preferably 20 to 23% by weight, based on the total of the methacrylic resin (A) and the organic phosphorus compound (B). is. If the amount of the organic phosphorus compound (B) is less than 19% by mass, the flame retardancy of the methacrylic resin cast plate may be insufficient. The heat resistance of the methacrylic resin cast plate may be insufficient due to the plasticizing action of the compound (B). In the present invention, by using a methacrylic resin (A) containing MMA units and (meth)acrylic acid units and having excellent heat resistance and flame retardancy, the amount of the organic phosphorus compound (B) is relatively small 19 to 24 mass %, it is possible to provide a methacrylic resin cast board having excellent heat resistance and flame retardancy.

[Methacrylic resin cast plate]
The methacrylic resin cast plate of the present invention may optionally contain one or more optional components other than those described above. Specific examples of optional components will be described later.
The thickness of the methacrylic resin cast plate of the present invention is appropriately designed according to the application, preferably 1 to 20 mm, more preferably 1 to 10 mm. If the thickness is less than 1 mm, it may crack when it is removed from the mold, and if it exceeds 20 mm, foaming may occur during polymerization.

[Manufacturing method of methacrylic resin cast plate]
The method for producing the methacrylic resin cast plate of the present invention is not particularly limited, and includes 68 to 74% by mass of methyl methacrylate (MMA), 6 to 9% by mass of (meth)acrylic acid, and 19 to 24% by mass of an organic phosphorus compound (B). % and a radical polymerization initiator (hereinafter also simply referred to as a polymerization initiator) is preferably cast-polymerized without using syrup, which will be described later.
The raw material mixture can contain one or more monomers other than those described above. Other monomers include alkyl methacrylates other than MMA and other copolymerizable unsaturated monomers that can be used in combination with alkyl methacrylates. For specific examples and usage amounts, refer to the section of (methacrylic resin (A)).

Conventionally, as a method for producing a methacrylic resin cast plate, a syrup in which a methyl methacrylate polymer is dissolved in one or more monomers containing MMA is prepared, and one or more monomers containing MMA are added to the syrup. There is a method in which a polymer is added to obtain a raw material mixture, and the resulting raw material mixture is subjected to cast polymerization. The syrup may be a prepolymerized syrup in which a polymer obtained by prepolymerizing one or more monomers containing MMA in the presence of a polymerization initiator is dissolved in unreacted monomers. Diluted syrup obtained by further adding one or more monomers such as MMA to the prepolymerized syrup, and beads, pellets, powders, crushed shapes obtained by separately polymerizing one or more monomers including MMA There is a dissolved syrup obtained by dissolving a methacrylic resin such as MMA in one or more monomers including MMA.
Since it is possible to reduce the amount of terminal double bonds that are the starting point of thermal decomposition and improve the thermal decomposition resistance of the methacrylic resin (A), in the present invention, a raw material mixture containing a plurality of types of monomers without using syrup is preferably directly cast-polymerized.

The polymerization initiator is not particularly limited, and 2,2'-azobis(isobutyronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis( 2,4-dimethylvaleronitrile), 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-di(t-butylperoxy)cyclohexane, acetylcyclohexyl sulfonyl peroxide , isobutyryl peroxide, cumyl peroxyneodecanoate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, dimyristyl peroxycarbonate, di-(2-ethoxyethyl) peroxydicarbonate, di -(Methoxyisopropyl)peroxydicarbonate, di-(2-ethylhexyl)peroxydicarbonate and the like. 1 type(s) or 2 or more types can be used for a polymerization initiator.
The amount of polymerization initiator to be added is not particularly limited, and is preferably 0.018 to 0.05 g per 1 kg of the total amount of MMA, (meth)acrylic acid and organic phosphorus compound (B). If the amount added is less than the lower limit, the polymerization reaction may not proceed well, and if it exceeds the upper limit, the polymerization reaction may run out of control.

The raw material mixture preferably contains a chain transfer agent. By using a chain transfer agent, the amount of terminal double bonds in the methacrylic resin (A) can be reduced, and the thermal decomposition resistance of the methacrylic resin (A) can be improved. Examples of chain transfer agents include terpinolene; styrene dimers such as α-methylstyrene dimer; mercaptans such as n-octylmercaptan and n-dodecylmercaptan; thioglycolic acid or esters thereof; β-mercaptopropionic acid such as β-mercaptopropionic acid, methyl β-mercaptopropionate, and octyl β-mercaptopropionate, and esters thereof; Among them, terpinolene and the like are preferable because they have a mild chain transfer action and can effectively reduce the amount of terminal double bonds in the methacrylic resin (A).
The amount of the chain transfer agent to be added is not particularly limited, and is preferably 0.015 to 0.03 g per 1 kg of the total amount of MMA, (meth)acrylic acid and organic phosphorus compound (B). If the amount added is less than the lower limit, the polymerization reaction may not proceed well, and if it exceeds the upper limit, the polymerization reaction may run out of control.

Since the heat decomposition resistance of the methacrylic resin (A) is improved, the amount of terminal double bonds in the methacrylic resin cast plate containing the methacrylic resin (A) is preferably 0.10 mol% or less, more preferably 0.09 mol%. Below, it is particularly preferably 0.088 mol % or less. Since the terminal double bond serves as a starting point for thermal decomposition, the smaller the amount of the terminal double bond, the higher the heat resistance (thermal decomposition resistance), which is preferable. The amount of terminal double bonds can be reduced by conducting direct polymerization without syrup, preferably by using a chain transfer agent.

The raw material mixture may optionally contain one or more optional components other than those described above. Other optional components include resins other than the methacrylic resin (A); release agent; UV absorber; antioxidant; dispersant; coloring agents such as pigments and dyes; Design materials such as resin granules and natural stone granules are included. However, as described above, a methyl methacrylate polymer not copolymerized with (meth)acrylic acid is not used as another resin.

Cast polymerization can be carried out by known methods. The mold consists of a pair of plates such as tempered glass, chromium plated plate, or stainless steel plate and a soft vinyl chloride resin gasket, and a pair of endless belts running in the same direction at the same speed. A mold or the like that is composed of a surface to be pressed and gaskets that run at the same speed as both endless belts on both sides of the surface. Polymerization of the raw material mixture is preferably carried out in two stages, primary curing at 40 to 90° C. and subsequent secondary curing at 110 to 130° C., from the viewpoint of increasing the rate of polymerization.

[Secondary molded product]
The methacrylic resin cast plate (primary molded product) of the present invention can be processed into any three-dimensional shape by secondary molding. The secondary forming method includes vacuum forming, pressure forming, and the like. After heating the methacrylic resin casting plate in advance to an appropriate temperature using a heating furnace or the like, vacuum, compression, air, mechanical pressure, or a combination thereof is used to conform the methacrylic resin casting plate to the mold, It can be processed into a desired shape. The secondary molding temperature is preferably 150°C or higher, more preferably 180°C or higher.

Since the methacrylic resin cast plate of the present invention is made of a methacrylic resin composition, it has inherent properties of methacrylic resin such as transparency, colorability, moldability, weather resistance and surface hardness. Since the methacrylic resin cast plate of the present invention contains a methacrylic resin (A) containing methyl methacrylate (MMA) units and (meth)acrylic acid units and an organic phosphorus compound (B), an organic phosphorus compound that is a flame retardant Even if the amount of (B) added is relatively small, excellent heat resistance and flame retardancy are obtained.
In the present invention, since the amount of the costly flame retardant used can be relatively reduced, it is possible to provide a low-cost methacrylic resin cast board excellent in heat resistance and flame retardancy.
The methacrylic resin cast plate of the present invention can be used for any purpose, and can be preferably used for building materials that require flame retardancy.

Examples and comparative examples according to the present invention will be described.
[Evaluation items and evaluation methods]
(Amount of residual monomer)
The resulting methacrylic resin cast plate was dissolved in methylene chloride and reprecipitated with an excess amount of methanol, and the supernatant was subjected to gas chromatography to determine the amount of residual monomer. It should be noted that a low residual monomer content indicates that the polymerization was completed as desired. The amount of residual monomers should be less than 1.0% by mass.

(Amount of terminal double bond)
The resulting methacrylic resin cast plate was subjected to ¹ H-NMR measurement to determine the amount of terminal double bonds.
(Weight average molecular weight)
Two KF-806L columns were connected to a Viscoteck max305 GPC apparatus, tetrahydrofuran was used as an eluent, and Mw in terms of standard PMMA was measured at 40° C. using an RI detector.

(Load deflection temperature (HDT))
Deflection temperature under load (HDT) was measured according to JIS K 7191 B method. The load was 0.45 MPa.
(Flame retardance)
Five test pieces were allowed to stand in an environment of 23° C./50% relative humidity (RH) for 48 hours, and then evaluated for flame retardancy according to the UL94V test. A flame of a gas burner was applied to the lower end of the vertically held test piece for 10 seconds, and the flame of the gas burner was separated from the test piece (first flame contact). After the flame on the test piece disappeared, the flame of the gas burner was again applied to the lower end of the test piece for 10 seconds in the same manner as the first time, and the flame of the gas burner was separated from the test piece (second flame application). The flaming combustion duration after the end of flame contact was confirmed for each of the first and second flame contact. In addition, for the second flame contact, the total time of flaming combustion duration and non-flaming combustion duration after the end of flame contact, the total flaming combustion time of the five test pieces, and the amount of combustion droplets (drip) Checked for presence. According to the standard, it was evaluated in four grades of V-0, V-1, V-2, and non-standard. Flame retardancy increases in the order of nonstandard, V-2, V-1, and V-0.

[Examples 1 to 8]
(1) Preparation of raw material mixture Methyl methacrylate (MMA), methacrylic acid (MAA) (containing 250 ppm of methoquinone as a stabilizer), methyl acrylate (MA), and an organic phosphorus compound represented by the above formula (II) ( B1) (“CR570” manufactured by Daihachi Chemical Industry Co., Ltd.) was mixed at the compounding ratio shown in Table 1. For this mixture, 0.15 g / kg of 2,2'-azobis-2,4-dimethylvaleronitrile ("V-65" manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, and 1 , 1-di(t-butylperoxy)cyclohexane (NOF Co., Ltd. "Perhexa C") was added at 0.25 g/kg. Furthermore, 0.01 g/kg of terpinolene as a chain transfer agent and 0.16 g/kg of a release agent (“Zerec UN” manufactured by DuPont) were added. The amount of polymerization initiator, chain transfer agent, and release agent added is the amount added per 1 kg of the mixture before addition of these components. These raw materials were thoroughly mixed to obtain a raw material mixture, which was defoamed by a known method.
(2) Preparing the mold A soft vinyl chloride resin gasket (outer diameter 6.5 mmφ) is sandwiched between two pieces of tempered glass (20 cm × 25 cm × 5 mm thick), and in this state the two pieces of tempered glass are clamped from the outside. did. The obtained glass cell was used as a mold. The separation distance between the two sheets of tempered glass was set to 4 mm.
(3) Casting polymerization The obtained raw material mixture was injected into the mold. This mold was placed in a vacuum dryer, the pressure was reduced to 8 kPa, and the pressure was maintained for 5 minutes. Next, the mold was placed in a water bath whose temperature was controlled at 67° C. and held for 3 hours for primary curing. Further, it was placed in an oven heated to 125° C. and held for 2 hours for secondary curing. After completion of heating, the mold was removed from the oven and allowed to cool to room temperature (20-25°C), after which a molded methacrylic resin casting plate (3.1 ± 0.1 mm thick) was removed from the mold. A test piece having a length of 127 mm, a width of 13 mm, and a thickness of 3.1 mm was cut out from the obtained methacrylic resin cast plate and subjected to evaluation.

[Production Example 1] Preparation of prepolymerized syrup (S1) 500 g of methyl methacrylate (MMA) was charged into a 1 L pressure-resistant reaction vessel, and heating was started. When the temperature reached 110° C., 0.015 parts by mass of azobisisobutyronitrile (AIBN) as a polymerization initiator was added and mixed with 100 parts by mass of MMA, and the mixture was held for 40 minutes. Thereafter, 500 g of MMA at room temperature (20 to 25° C.) was added and cooled to terminate the polymerization reaction. Thus, a prepolymerized syrup (S1) having a viscosity of 7 poise and containing a methyl methacrylate homopolymer not copolymerized with methacrylic acid was obtained. The viscosity was measured using a B-type viscometer (NDJ-5S rotational viscometer, rotation speed: 12 rpm, rotor: L-type No. 2).

[Comparative Examples 1 to 8, 11]
Prepolymerized syrup (S1), methacrylic acid (MAA) (containing 250 ppm of methoquinone as a stabilizer), and an organic phosphorus compound (B1) represented by the above formula (II) ("CR570" manufactured by Daihachi Chemical Industry Co., Ltd.) were mixed at the compounding ratio shown in Table 2. To this mixture, 0.01 g/kg of terpinolene as a chain transfer agent and 0.16 g/kg of a release agent (“Zerec UN” manufactured by DuPont) were added. The amount of chain transfer agent and release agent added is the amount added per 1 kg of the mixture before addition of these components. These raw materials were thoroughly mixed to obtain a raw material mixture in which 10% by mass of methyl methacrylate homopolymer was dissolved in a mixed monomer of MMA and methacrylic acid (MAA). The resulting raw material mixture was defoamed by a known method. Using the obtained raw material mixture, casting polymerization was performed in the same manner as in Examples 1 to 8 to obtain a methacrylic resin casting plate, and a test piece was cut out and subjected to evaluation.
[Comparative Examples 9, 10, 12, 13]
A methacrylic resin cast plate was obtained and tested in the same manner as in Examples 1 to 8, except that the blending ratio of MMA, MAA, and the organic phosphorus compound ((B1) or (RB2)) was changed as shown in Table 2. A piece was cut out and provided for evaluation.
The organic phosphorus compound (RB2) is a comparative organic phosphorus compound (triphenyl phosphate; “CR733S” manufactured by Daihachi Chemical Industry Co., Ltd.) having a structure other than that of formula (I).

[Evaluation results]
Examples 1 to 8 contain a methacrylic resin (A) containing methyl methacrylate (MMA) units and methacrylic acid (MAA) units and an organic phosphorus compound (B) represented by formula (II), A methacrylic resin cast plate containing no methyl methacrylate polymer, which is not copolymerized with acrylic acid, was produced. Each of the obtained methacrylic resin cast plates has an amount of MMA units of 68 to 74% by mass and an amount of MAA units of 6 to 9% by mass based on the total amount of the methacrylic resin (A) and the organic phosphorus compound (B). %, and the amount of the organophosphorus compound (B) was 19-24% by mass. In each of Examples 1 to 8, even if the amount of the organophosphorus compound (B) added as a flame retardant is relatively small, the deflection temperature under load (HDT) is as high as 70°C or higher, preferably 75°C or higher, and the heat resistance is high. It was possible to produce a methacrylic resin cast board having excellent flame retardancy, with an evaluation result of V-0 in the UL94V test.
The methacrylic resin cast plate obtained in Example 2 had a terminal double bond content as low as 0.087 mol %. Moreover, Mw was 3.7 million. Since the amount of the chain transfer agent used is the same in other examples, it is considered that the levels are the same.

In Comparative Examples 1 to 7, methacrylic resin cast plates containing methyl methacrylate homopolymers not copolymerized with methacrylic acid (MAA) were produced. When comparing Examples and Comparative Examples in which the amounts of methacrylic acid and the organophosphorus compound (B) are the same (for example, comparing Example 1 and Comparative Example 1), methyl methacrylate (MMA) is replaced with methacrylic acid Comparative examples using prepolymerized syrups containing methyl homopolymer showed a decrease in deflection temperature under load (HDT) (a decrease in heat resistance) and/or a decrease in flame retardancy of the methacrylic resin cast plate. Especially in Comparative Examples 1 to 5, the flame retardancy was poor.
The methacrylic resin cast plate obtained in Comparative Example 2 had a terminal double bond content of 0.112 mol %, which was higher than in Example 2. Moreover, Mw was 3.6 million. Since the amount of chain transfer agent used is the same in other comparative examples, it is considered that the levels are the same.

In Comparative Example 8, a methacrylic resin cast board containing a homopolymer of methyl methacrylate not copolymerized with MAA and containing more than 24 parts by mass of the organophosphorus compound (B) was produced. This methacrylic resin cast board contained a large amount of flame retardant, so it had good flame resistance. was inadequate.
In Comparative Examples 9 and 10, as in Examples 1 to 8, a methacrylic resin (A) containing methyl methacrylate (MMA) units and methacrylic acid (MAA) units and an organic phosphorus compound represented by formula (II) ( A methacrylic resin casting board was prepared containing B) and containing no methyl methacrylate homopolymer copolymerized with MAA. However, since the blending amount of the organic phosphorus compound (B) was less than 19 parts by mass, the flame retardancy was poor.
In Comparative Example 11, a methacrylic resin cast board containing a methyl methacrylate homopolymer not copolymerized with MAA was produced. This methacrylic resin cast plate was poor in flame retardancy. Furthermore, since the compounding amount of methacrylic acid (MAA) was increased to more than 9 parts by mass, the releasability of the methacrylic resin casting plate was also poor.
In Comparative Example 12, a methacrylic resin cast plate containing a methyl methacrylate polymer not copolymerized with (meth)acrylic acid was produced without using a prepolymerized syrup, but the flame retardancy was poor.
In Comparative Example 13, a methacrylic resin cast board was produced using an organic phosphorus compound having a structure other than formula (I), but the flame retardancy was poor.

The present invention is not limited to the above-described embodiments and examples, and design changes can be made as appropriate without departing from the gist of the present invention.

This application claims priority based on Japanese Patent Application No. 2017-155614 filed on August 10, 2017, and the entire disclosure thereof is incorporated herein.

Claims (5)

A methacrylic resin cast plate made of a resin composition containing a methacrylic resin (A) made of a methyl methacrylate-(meth)acrylic acid copolymer and an organic phosphorus compound (B),
The methacrylic resin (A) is a non-crosslinked resin having a terminal double bond content of 0.10 mol% or less,
The organophosphorus compound (B) is represented by the following formula (I),
Based on the total of the methacrylic resin (A) and the organic phosphorus compound (B), the amount of methyl methacrylate units is 68 to 74% by mass, the amount of (meth) acrylic acid units is 6 to 9% by mass, and the organic phosphorus compound ( The amount of B) is 19 to 24% by mass,
A methacrylic resin casting plate that does not contain a methyl methacrylate polymer that is not copolymerized with (meth)acrylic acid.
P(=O)(-O-R-X) ₃ (I)
(Wherein, R represents an alkylene group having 1 to 6 carbon atoms, and X represents a chlorine atom or a bromine atom.) 2. The methacrylic resin cast board according to claim 1, wherein the organic phosphorus compound (B) is represented by the following formula (II).

3. The methacrylic resin cast plate according to claim 1 , which has a deflection temperature under load of 75[deg.] C. or higher according to JIS K 7191 B method. 68 to 74% by mass of methyl methacrylate, 6 to 9% by mass of (meth)acrylic acid, 19 to 24% by mass of organic phosphorus compound (B), a radical polymerization initiator, and methyl methacrylate, (meth)acrylic acid, and 4. The method according to any one of claims 1 to 3 , wherein a raw material mixture containing 0.015 to 0.03 g of a chain transfer agent per 1 kg of the organic phosphorus compound (B) is cast-polymerized without using syrup. A method for producing a methacrylic resin cast plate. 5. The method for producing a methacrylic resin cast plate according to claim 4, wherein the chain transfer agent is terpinolene.