Methacrylic resin casting plate

Abstract

To provide a methacrylic resin cast plate which has no poor appearance such as sink, and is excellent in ethanol resistance.SOLUTION: A methacrylic resin plate is formed of a methacrylic resin composition containing a non-crosslinked methyl methacrylate-based polymer (P) and a crosslinked methyl methacrylate-based polymer (C), wherein a weight average molecular weight of the non-crosslinked methyl methacrylate-based polymer (P) is 500,000 to 1,500,000, a content of the non-crosslinked methyl methacrylate-based polymer (P) is 6-15 mass%, a content of the crosslinked methyl methacrylate-based polymer (C) is 94-85 mass%, a storage elastic modulus (E') at 200°C in a rubbery flat region when dynamic viscoelasticity measurement is performed is 3 MPa or more, a peak value of tanδ is 1.55 or less, and a peak temperature of the tanδ is 130°C or higher.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a methacrylic resin casting plate.

Background Art

[0002] Methacrylic resins are excellent in transparency, colorability, moldability, weather resistance, surface hardness, etc., and are widely used in various fields as signboards, decorative materials, lighting covers, automotive parts, and glazing materials. In recent years, due to the above-mentioned properties such as transparency, this resin has been used for acrylic partitions for preventing droplet infection that can be easily installed at reception windows and counters in facilities such as stores, companies, nurseries, kindergartens, schools, and hospitals. In the methacrylic resin plate used for this application, since droplets, hand dirt, dust, etc. adhere, it is necessary to disinfect it regularly with a disinfectant such as ethanol.

[0003] Generally, although methacrylic resins have relatively good chemical resistance and oil resistance, since they are thermoplastic resins, they tend to be relatively weak against organic solvents such as ethanol. In particular, since stress applied during processing remains in the processed parts such as cutting, polishing, and thermo-bending, they tend to be weaker against organic solvents than other parts. Therefore, if an organic solvent repeatedly touches the processed part of the methacrylic resin plate, or if the methacrylic resin plate including the processed part is immersed in an organic solvent, cracks or whitening may occur in the processed part of the resin plate.

[0004] Generally, the solvent resistance is improved by using a methacrylic resin composition containing a crosslinked methyl methacrylate (MMA) polymer. As a method for manufacturing a resin plate containing a crosslinked MMA polymer, there is a method of casting polymerization of a polymerizable raw material containing a plurality of monomers including MMA and a crosslinking agent, or a polymerizable raw material obtained by adding a crosslinking agent and one or more monomers including MMA as necessary to a syrup containing a non-crosslinked MMA polymer and one or more monomers including MMA.

[0005] For example, Patent Document 1 discloses a method for manufacturing a methacrylic resin casting plate excellent in solvent resistance, in which a polymerizable raw material obtained by adding a crosslinking agent and a polymerization initiator to a prepolymerized syrup is subjected to cast polymerization, and the degree of polymerization of the trunk polymer crosslinked by the crosslinking agent is set to a specific viscosity [η] of 0.05 to 0.15 (l / g) (Claim 1). In Patent Document 1, in the section of [Examples], "solvent resistance" is measured by dropping a solvent styrene while applying a stress of 140 kg / cm 2 to the sample and measuring the breaking time of the sample.

[0006] Patent Document 2 discloses a method for manufacturing a methacrylic resin casting plate excellent in solvent resistance, in which 99.5 to 60% by weight of one or more monomers containing MMA is subjected to cast polymerization in the presence of 0.5 to 40% by weight of a crosslinking agent represented by a specific chemical formula (Claim 1). In Patent Document 2, in the section of [Examples], "solvent resistance" is evaluated by the light transmittance when immersed in organic solvents such as benzene and acetone.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] As described above, the solvent resistance is improved by using a methacrylic resin composition containing a crosslinked MMA polymer. However, when polymerizing a polymerizable raw material containing MMA and a crosslinking agent, gelation is accelerated and polymerization shrinkage tends to proceed rapidly. In this case, a transfer defect of the mold surface called "sink mark" may occur at the peripheral edge of the plate where polymerization is likely to be delayed. Transfer defects of the mold surface lead to a decrease in productivity, which is not preferable. This problem is likely to occur when the addition amount of the crosslinking agent increases. For example, Patent Document 3 describes the problem that "when the usage amount of the crosslinking agent in the syrup exceeds 25% by weight, sink marks caused by curing occur in the molded product." Therefore, in order to enhance the solvent resistance, it is not preferable to use a large amount of the crosslinking agent as in Patent Document 2.

[0009] In a methacrylic resin cast plate used for applications such as an acrylic partition for preventing droplet infection, it is preferable to have good ethanol resistance such that no appearance defects such as cracks and whitening occur even when ethanol is repeatedly used for a long period without using a large amount of a crosslinking agent.

[0010] The present invention has been made in view of the above circumstances, and an object thereof is to provide a methacrylic resin cast plate that has no appearance defects such as sink marks and is excellent in ethanol resistance.

Means for Solving the Problems

[0011] As a result of intensive studies to solve the above problems, the present inventors have found that by optimizing the weight average molecular weight (Mw) and content of the non-crosslinked methyl methacrylate (MMA) polymer contained in the methacrylic resin cast plate, and the dynamic viscoelasticity of the methacrylic resin cast plate, it is possible to suppress the occurrence of sink marks during casting polymerization and provide a methacrylic resin cast plate having good ethanol resistance, thereby completing the present invention.

[0012] The present invention provides a methacrylic resin cast plate according to the following [1] to [5]. [1] It is composed of a methacrylic resin composition containing a non-crosslinked methyl methacrylate polymer (P) and a crosslinked methyl methacrylate polymer (C). The weight average molecular weight of the non-crosslinked methyl methacrylate polymer (P) is 500,000 to 1,500,000, the content of the non-crosslinked methyl methacrylate polymer (P) is 6 to 15% by mass, the content of the crosslinked methyl methacrylate polymer (C) is 94 to 85% by mass, When performing dynamic viscoelasticity measurement, the storage elastic modulus (E') in the rubbery plateau region is 3 MPa or more at 200 °C, the peak value of tanδ is 1.55 or less, and the peak temperature of tanδ is 130 °C or more, a methacrylic resin casting plate.

[0013] [2] The methacrylic resin casting plate of [1], when the cut end face of the laser-cut methacrylic resin casting plate is wiped with ethanol 1200 times or more at 20 to 25 °C, no crack with a length of 0.5 mm or more occurs. [3] The methacrylic resin casting plate of [1], when the cut end face of the cut methacrylic resin casting plate is flame polished and then wiped with ethanol 1200 times or more at 20 to 25 °C, no crack with a length of 0.5 mm or more occurs. [4] The methacrylic resin casting plate of [1], when the cut end face of the cut methacrylic resin casting plate is buff polished and then wiped with ethanol 1200 times or more at 20 to 25 °C, no crack with a length of 0.5 mm or more occurs. [5] The methacrylic resin casting plate of [1], when the laser-cut methacrylic resin casting plate is immersed in ethanol for 24 hours at 20 to 25 °C, no crack with a length of 0.5 mm or more occurs.

Advantages of the Invention

[0014] According to the present invention, it is possible to provide a methacrylic resin casting plate having no appearance defects such as sink marks and excellent ethanol resistance.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described in detail. In this specification, "methacryl" and "acryl" may be collectively referred to as "(meth)acryl". The same applies to "(meth)acrylic acid" and (meth)acryloyl. In this specification, "crack" shall include crazes and cracks.

[0016] [Methacrylic resin casting plate] The methacrylic resin casting plate of the present invention is composed of a methacrylic resin composition containing an uncrosslinked methyl methacrylate (MMA) polymer (P) and a crosslinked methyl methacrylate (MMA) polymer (C). In the methacrylic resin casting plate of the present invention, the weight average molecular weight (Mw) of the uncrosslinked MMA polymer (P) is 500,000 to 1,500,000, the content of the uncrosslinked MMA polymer (P) is 6 to 15% by mass, and the content of the crosslinked MMA polymer (C) is 94 to 85% by mass. When the dynamic viscoelasticity measurement is carried out on the methacrylic resin casting plate of the present invention, the storage elastic modulus (E') in the rubbery plateau region is 3 MPa or more at 200 °C, the peak value of tanδ is 1.55 or less, and the peak temperature of tanδ is 130 °C or more.

[0017] Generally, by using a methacrylic resin composition containing a crosslinked MMA polymer, the solvent resistance is improved. However, when polymerizing a polymerizable raw material containing MMA and a crosslinking agent, gelation is accelerated and polymerization shrinkage tends to proceed rapidly. In this case, a transfer defect of the mold surface called "sink mark" may occur at the peripheral portion of the plate where polymerization is likely to be delayed. This problem is likely to occur when the addition amount of the crosslinking agent increases. In this specification, "sink mark" refers to a transfer defect of the mold surface caused by the resin peeling off from the mold surface such as the glass surface due to polymerization shrinkage or the like during polymerization. For example, when the mold surface is a mirror surface, "sink mark" is a non-mirror surface portion where the mirror surface is not transferred well.

[0018] The inventors have optimized the weight average molecular weight (Mw) and content of the non-crosslinked MMA-based polymer (P) contained in the methacrylic resin casting plate, and the dynamic viscoelasticity of the methacrylic resin casting plate, so that even if a large amount of crosslinking agent is not used and ethanol is repeatedly used for a long time, a methacrylic resin casting plate having good ethanol resistance without appearance defects such as cracks and whitening can be provided. In the present invention, since it is not necessary to use a large amount of crosslinking agent, sink marks caused by polymerization shrinkage when using a crosslinking agent can be effectively suppressed. The inventors have also found that by optimizing the weight average molecular weight (Mw) of the non-crosslinked MMA polymer (P), sink marks caused by polymerization shrinkage when using a crosslinking agent can be suppressed, and the ethanol resistance of the methacrylic resin casting plate can be improved. Due to the above-described effects, according to the present invention, it is possible to provide a methacrylic resin casting plate that has no appearance defects such as sink marks and is excellent in ethanol resistance.

[0019] According to the present invention, it is possible to provide a methacrylic resin casting plate in which no crack having a length of 0.5 mm or more occurs when the cut end face of a laser-cut methacrylic resin casting plate is wiped with ethanol 1200 times or more at 20 to 25°C. According to the present invention, it is possible to provide a methacrylic resin casting plate in which no crack having a length of 0.5 mm or more occurs when the cut end face of a cut methacrylic resin casting plate is flame polished and then wiped with ethanol 1200 times or more at 20 to 25°C. According to the present invention, it is possible to provide a methacrylic resin casting plate in which no crack having a length of 0.5 mm or more occurs when the cut end face of a cut methacrylic resin casting plate is buff polished and then wiped with ethanol 1200 times or more at 20 to 25°C. According to the present invention, it is possible to provide a methacrylic resin casting plate in which no crack having a length of 0.5 mm or more occurs when a laser-cut methacrylic resin casting plate is immersed in ethanol for 24 hours at 20 to 25°C. For the specific methods of the above four ethanol resistance tests, refer to the section of [Examples] described later.

[0020] By the dynamic thermomechanical property analysis method (DMTA method), a DMTA curve showing the relationship between temperature and storage modulus can be obtained. Refer to FIG. 1 of International Publication No. 2015-122174, etc. In the DMTA curve, when the glass transition point (Tg) is exceeded, the storage modulus decreases significantly. However, thereafter, a rubbery plateau region appears where the storage modulus does not change significantly even when the temperature is increased. The rubbery plateau region is a region where the polymer molecular chains move but do not completely melt. Thereafter, when the temperature is further increased and the flow region is entered, the storage modulus decreases significantly again.

[0021] When dynamic viscoelasticity measurement is carried out, the fact that the storage modulus (E’) in the rubbery plateau region is 3 MPa or more at 200 °C means that a crosslinked structure having ethanol resistance in which cracks or fractures with a length of 0.5 mm or more do not occur in the above four kinds of ethanol resistance tests is generated. As shown in FIG. 1 of International Publication No. 2015-122174, etc., in the methacrylic resin casting plate, 200 °C is the reference temperature on the high-temperature side of the rubbery plateau region. When dynamic viscoelasticity measurement is carried out, the fact that the peak value of tanδ is 1.55 or less and the peak temperature of tanδ is 130 °C or more means that the amount and molecular weight of the non-crosslinked MMA-based polymer (P) with low ethanol resistance are within the range of the amount and molecular weight that do not prevent the crosslinked MMA-based polymer (C) from forming and maintaining a crosslinked structure having ethanol resistance.

[0022] [Method for manufacturing methacrylic resin casting plate] The methacrylic resin casting plate of the present invention can be produced, for example, by a production method including step (1) of preparing a syrup (S) containing one or more monomers (M) containing methyl methacrylate (MMA) and a non-crosslinked methyl methacrylate (MMA)-based polymer (P), step (2) of adding one or more monomers (M3) containing methyl methacrylate (MMA) and one or more crosslinking agents (M4) to the syrup (S) to obtain a polymerizable raw material, and step (3) of carrying out cast polymerization of the obtained polymerizable raw material.

[0023] The Mw of the non-crosslinked MMA-based polymer (P) can be adjusted to a desired range by appropriately selecting the polymerization conditions and adjusting the degree of polymerization when polymerizing the raw material monomers of the non-crosslinked MMA-based polymer (P). By appropriately selecting the composition of the polymerizable raw materials and the casting polymerization conditions, the storage elastic modulus (E') of the rubbery flat region of the methacrylic resin cast plate, the peak values of tanδ, and the peak temperature can be adjusted to a desired range.

[0024] (Step (1)) As a method for preparing the syrup (S), the prepolymerization method is preferred because a syrup (S) containing a non-crosslinked MMA-based polymer (P) having a weight average molecular weight (Mw) of 500,000 to 1,500,000 can be easily produced. The syrup (S) obtained by this method is a prepolymerized syrup (S1) containing a non-crosslinked linear MMA-based polymer (P1) obtained by prepolymerizing one or more monomers (M1) containing MMA in the presence of a polymerization initiator and one or more unreacted monomers (M1). After prepolymerization, one or more monomers (M1) such as MMA may be further added and diluted as necessary.

[0025] As a method for preparing the syrup (S), in addition to the above prepolymerization method, there is a polymer dissolution method. The syrup (S) obtained by this method is a dissolved syrup (S2) obtained by dissolving a non-crosslinked linear MMA-based polymer (P2) polymerized using one or more monomers containing MMA in one or more monomers (M2) containing MMA. However, since it is very time-consuming and laborious to dissolve a non-crosslinked MMA-based polymer (P) having a weight average molecular weight (Mw) of 500,000 to 1,500,000 in one or more monomers (M2) containing MMA, the prepolymerization method is preferred over the polymer dissolution method.

[0026] The non-crosslinked MMA-based polymer (P) may be any of a homopolymer of MMA, a copolymer of MMA and one or more other alkyl methacrylates, and a copolymer of one or more alkyl methacrylates containing MMA and one or more other copolymerizable unsaturated monomers.

[0027] The number of carbon atoms of the alkyl group of the alkyl methacrylate used as a raw material for the non-crosslinked linear MMA-based polymer (P) is preferably 1 to 20, more preferably 1 to 12. Examples of such alkyl methacrylates include MMA, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, and cyclohexyl methacrylate.

[0028] As other copolymerizable unsaturated monomers that can be used in combination with the alkyl methacrylate as a raw material for the non-crosslinked linear MMA-based polymer (P), there are alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, and cyclohexyl acrylate; 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 of (meth)acrylic acid; vinyl monomers such as vinyl chloride, vinyl acetate, and vinyltoluene; acrylonitrile; acrylamide; styrene-based monomers such as styrene and α-methylstyrene; maleic anhydride, etc.

[0029] The concentration of the non-crosslinked MMA-based polymer (P) in the syrup (S) is not particularly limited, and is preferably 5% by mass or more. If the concentration of the polymer (P) in the syrup (S) is less than 5% by mass, the polymerization shrinkage in step (3) becomes large, and there is a risk of sink marks. If the viscosity of the syrup (S) is too high, it is difficult to add and mix monomers such as MMA for dilution to the syrup (S), and it becomes difficult to defoam the polymerizable raw material obtained in the next step and inject it into the mold. From the viewpoint of optimizing the viscosity of the syrup (S), the concentration of the polymer (P) in the syrup (S) is preferably 40% by mass or less, more preferably 30% by mass or less, and particularly preferably 20% by mass or less.

[0030] The weight average molecular weight (Mw) of the non-crosslinked linear MMA-based polymer (P) is 500,000 to 1,500,000. By setting the Mw of the non-crosslinked MMA polymer (P) within this range, sink marks caused by polymerization shrinkage when using a crosslinking agent can be effectively suppressed, and the ethanol resistance of the methacrylic resin casting plate can be improved. If Mw is less than 500,000, the ethanol resistance of the resulting methacrylic resin casting plate may be insufficient. If Mw is 1,500,000 or more, the viscosity of the syrup (S) becomes high, making it difficult to add and mix monomers such as MMA for dilution with respect to the syrup (S), and there is a risk that the defoaming treatment of the polymerizable raw material obtained in the next step and the injection into the mold will become difficult. The Mw of the non-crosslinked linear MMA-based polymer (P) is preferably 700,000 to 1,200,000, more preferably 700,000 to 1,000,000.

[0031] Regarding the degree of polymerization, weight average molecular weight (Mw), and content of the non-crosslinked MMA-based polymer (P) that can suppress sink marks during casting polymerization while ensuring the ethanol resistance of the methacrylic resin casting plate, the peak value and peak temperature of tanδ in the dynamic viscoelastic properties can be used as indicators. In the methacrylic resin casting plate of the present invention, it is necessary that the peak value of tanδ is 1.55 or less and the peak temperature of tanδ is 130°C or more. When the peak value of tanδ exceeds 1.55 or the peak temperature of tanδ is less than 130°C, even if the type and amount of the crosslinking agent are designed to be the preferred types and amounts described in this specification, the ethanol resistance of the resulting methacrylic resin casting plate may be insufficient. The peak value of tanδ is preferably 0.35 or more and 1.55 or less. The peak temperature of tanδ is preferably 130°C or more and 200°C or less.

[0032] Instead of the syrup (S) containing MMA and the non-crosslinked MMA-based polymer (P), a syrup or gel containing a partially crosslinked MMA-based gel polymer can also be used. This syrup or gel is obtained by adding a crosslinking agent to the dissolved syrup (S2) and performing prepolymerization, and contains a non-crosslinked MMA-based polymer (P), a crosslinked MMA-based polymer (C), and one or more monomers containing MMA.

[0033] (Step (2)) In step (2), one or more monomers (M3) including methyl methacrylate (MMA), one or more crosslinking agents (M4), and a polymerization initiator are added to the syrup (S) to obtain a polymerizable raw material. As the monomer (M3), in addition to MMA, one or more other alkyl methacrylates and / or one or more other copolymerizable unsaturated monomers can be used as needed. The addition of the monomer (M3) may also serve as the addition of the monomer (M1) that is carried out as needed after prepolymerization. Examples of other alkyl methacrylates and other copolymerizable unsaturated monomers that can be used as the monomer (M3) are the same as the examples of the raw material monomers of the non-crosslinked MMA-based polymer (P).

[0034] As the crosslinking agent (M4), a monomer having two or more (meth)acryloyl groups in the molecule is preferably used. The molecular weight of the crosslinking agent (M4) is not particularly limited and is preferably 400 or less. For example, ethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, (1,3-butanediol di(meth)acrylate), 1,4-butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and neopentyl glycol di(meth)acrylate are preferred.

[0035] When a crosslinking agent having a molecular weight exceeding 400 is used, the molecular weight between crosslinking points of the obtained crosslinked MMA-based polymer (C) becomes large, and the ethanol resistance of the obtained methacrylic resin casting plate may be insufficient. The molecular weight between crosslinking points of the crosslinked MMA-based polymer (C) is affected by the molecular weight and amount of the monomer (M3) and the crosslinking agent (M4), and the amount of the non-crosslinked MMA-based polymer (P). The molecular weight between crosslinking points of the crosslinked MMA-based polymer (C) can be indicated by the storage elastic modulus (E’) in the rubbery plateau region of the methacrylic resin casting plate. In the present invention, it is necessary that the storage elastic modulus (E’) in the rubbery plateau region is 3 MPa or more at 200 °C. If the storage elastic modulus (E’) in the rubbery plateau region is 3 MPa or more at 200 °C, it can be said that a crosslinked structure is formed in which cracks with a length of 0.5 mm or more do not occur in the above four ethanol resistance tests. The storage elastic modulus (E’) in the rubbery plateau region is preferably 3 MPa or more and 200 MPa or less at 200 °C.

[0036] The polymerization initiator is not particularly limited, and examples thereof include 2,2’-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2’-azobis(2,4-dimethylvaleronitrile), acetylcyclohexylsulfonyl peroxide, isobutyryl peroxide, cumyl peroxyneodecanoate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, dimyristyl peroxydicarbonate, di-(2-ethoxyethyl) peroxydicarbonate, di-(methoxyisopropyl) peroxydicarbonate, and di-(2-ethylhexyl) peroxydicarbonate.

[0037] In step (2), a chain transfer agent and / or an ultraviolet absorber can be added as necessary. Examples of the chain transfer agent include styrene dimers such as α-methyl-styrene dimer; mercaptans such as n-octyl mercaptan, n-dodecyl mercaptan, and thiophenol; thioglycolic acid or its esters such as thioglycolic acid, ethyl thioglycolate, and butyl thioglycolate; β-mercaptopropionic acid and its esters such as β-mercaptopropionic acid, methyl β-mercaptopropionate, and octyl β-mercaptopropionate; and terpinolene. Examples of the ultraviolet absorber include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole.

[0038] In step (2), if necessary, one or more other additives can be added. Examples of other additives include other resins of different types, antioxidants, dispersants, fillers, resin granules, pigments, dyes, pattern materials such as natural stone granules, and mold release agents.

[0039] The blending ratio of the raw materials is not particularly limited. The total amount of the raw materials other than the polymerization initiator, chain transfer agent, ultraviolet absorber, and other additives is set to 100 parts by mass. The amount of the syrup (S) is designed such that the content of the non-crosslinked MMA-based polymer (P) in the polymerizable raw material is 6 to 15% by mass. If the content of the polymer (P) in the polymerizable raw material is less than 6% by mass, the polymerization shrinkage during casting polymerization becomes large, and there is a risk of sink marks occurring in the resulting methacrylic resin cast plate. If this content exceeds 15% by mass, the amount of the components soluble in the solvent increases. Therefore, even if the type and amount of the crosslinking agent (M4) are designed to be the preferred types and amounts described in this specification, the ethanol resistance of the resulting methacrylic resin cast plate may be insufficient.

[0040] The amount of one or more monomers (M3) is preferably 6.2 to 12 parts by mass, more preferably 7 to 10 parts by mass, based on 100 parts by mass in total of the polymerizable monomer and monomer units. The amount of one or more crosslinking agents (M4) is preferably 2.5 to 25 parts by mass, more preferably 4.5 to 20 parts by mass. The amount of the chain transfer agent is preferably 0 to 0.5 parts by mass. The amount of the polymerization initiator is preferably 0.05 to 3 g per 1 kg of the total amount of the raw materials other than the polymerization initiator, chain transfer agent, ultraviolet absorber, and other additives. The amount of the ultraviolet absorber is preferably 0 to 2 g per 1 kg of the total amount of the raw materials other than the polymerization initiator, chain transfer agent, ultraviolet absorber, and other additives.

[0041] (Step (3)) In step (3), the liquid polymerizable raw material obtained in step (2) is poured into a mold and subjected to casting polymerization. The injection molding can be carried out by a known method. Examples of the mold include a mold composed of a pair of plate-like bodies such as tempered glass, a chromium-plated plate, or a stainless steel plate and a soft vinyl chloride gasket, and a mold composed of the opposing surfaces of a pair of endless belts running at the same speed in the same direction and a gasket running at the same speed as the two endless belts at both side edges thereof.

[0042] The polymerizable raw material is preferably polymerized and cured in two or more stages by changing the temperature. The two-stage polymerization can be carried out as follows. First, a mold filled with the polymerizable raw material in the internal space portion is immersed in a water bath preferably temperature-controlled to about 55 to 85°C and held for about 1 to 20 hours to perform the first-stage polymerization and curing. Next, the mold is placed in a hot air drying furnace and heated preferably at a temperature of about 80°C for about 2 to 15 hours, and then preferably at a temperature of about 120 to 130°C for about 3 to 15 hours to carry out the second-stage polymerization and curing to drive the reaction. As described above, a methacrylic resin casting plate made of a methacrylic resin composition containing an uncrosslinked MMA-based polymer (P) and a crosslinked MMA-based polymer (C) is produced. The flat resin plate, which is a primary molded product thus obtained, may be secondary molded into an arbitrary three-dimensional shape by a known method such as vacuum molding and pressure air molding.

[0043] As described above, according to the present invention, it is possible to provide a methacrylic resin casting plate having no appearance defects such as sink marks and excellent ethanol resistance. Since the methacrylic resin casting plate of the present invention is made of a methacrylic resin composition, it can have the properties inherent in methacrylic resins such as transparency, colorability, moldability, weather resistance, and surface hardness.

[0044] [Applications] The methacrylic resin casting plate of the present invention can be suitably used for applications such as acrylic partitions for preventing droplet infection. The thickness of the methacrylic resin casting plate of the present invention is not particularly limited, and in applications such as acrylic partitions for preventing droplet infection, it is preferably 3 to 5 mm.

Examples

[0045] Examples and comparative examples according to the present invention will be described. [Evaluation items and evaluation methods] (Weight average molecular weight (Mw) and molecular weight distribution ((Mw) / (Mn)) of non-crosslinked methyl methacrylate (MMA) polymer (P)) 5 g of syrup (S) was extracted with 200 ml of chloroform, filtered, and methanol was added to the collected filtrate to form a precipitate. This precipitate was dried under vacuum, and 0.12 g of the obtained dried product was dissolved in 20 ml of tetrahydrofuran to obtain a measurement sample. Using "LC-9A" manufactured by Shimadzu Corporation as a molecular weight measuring device, and using "GPC-802", "HSG-30", "HSG-50" manufactured by Shimadzu Corporation and "Shodex A-806" manufactured by Showa Denko K.K. as columns, the molecular weight was measured by the GPC (gel permeation chromatography) method. Note that Mw and Mn are values in terms of polystyrene.

[0046] (Content of non-crosslinked methyl methacrylate (MMA) polymer (P)) 1 g of syrup (S) was dried using an infrared heater ("IB-30" manufactured by CHYO), the mass of the obtained dried product was measured, the solid content concentration of the syrup (S) was determined, and the content of the non-crosslinked MMA polymer (P) in the casting plate was determined from the content of the syrup (S) in the polymerizable raw material and the solid content concentration of the syrup (S). In the casting plate, it was extracted with chloroform, filtered, methanol was added to the collected filtrate to form a precipitate, this precipitate was dried using an infrared heater ("IB-30" manufactured by CHYO), the mass of the obtained dried product was measured, and the content of the non-crosslinked MMA polymer (P) in the casting plate was determined.

[0047] (Appearance) The appearance of the manufactured or prepared resin plate (acrylic resin casting plate or acrylic resin extrusion plate) was visually observed and evaluated according to the following criteria. Good (○): No sink marks are visible. Defective (×): Sink marks are visible.

[0048] (Dynamic viscoelasticity) The dynamic viscoelasticity of the manufactured or prepared resin plate (acrylic resin casting plate or acrylic resin extrusion plate) was measured in accordance with JIS K7244-1 and JIS 7244-4. First, the resin plate was cut to obtain samples with a length of 20 mm, a width of 1.5 mm, and a thickness of 2 mm. The measurement was carried out using a dynamic viscoelasticity measuring device ("Rheogel-E4000" manufactured by UBM). A sinusoidal vibration with a set frequency and amplitude was applied to the sample under heating, and the stress response generated at that time was detected to obtain the phase difference between the dynamic stress waveform and the dynamic displacement waveform. Based on the arithmetic expressions of linear viscoelasticity theory, data such as the storage modulus (E') and tanδ were plotted against the temperature in the measurement region to obtain a DMTA curve, etc. The main measurement conditions were set as follows. From this, the storage modulus (E') at 200°C in the rubbery plateau region was obtained. Also, the peak value and peak temperature of tanδ were obtained. <Measurement conditions> Measurement frequency: 1 Hz, Load: 1 kg, Measurement mode: Temperature dependence, Measurement temperature: 30 to 250°C, Heating rate: 3°C / min.

[0049] [Processing method] (Laser cutting) The manufactured or prepared resin plate (acrylic resin casting plate or acrylic resin extrusion plate) was cut using "Spirit GLS 100W" manufactured by ComNet as the laser, under the conditions of 80% power control and a processing speed of 2 m / min to obtain laser processing samples with a length of 100 mm, a width of 30 mm, and a thickness of 3 mm.

[0050] (Polishing) The resin plate (acrylic resin casting plate or acrylic resin extrusion plate) that was manufactured or prepared was cut using an electric saw to obtain two samples with a length of 100 mm, a width of 30 mm, and a thickness of 3 mm. Flame polishing was performed on the cut end face of one sample to obtain a first mirror-finished sample. Specifically, with the main surface of the sample horizontal, using a commercially available flame polishing machine, a thin flame the size of a pencil lead was brought close to the cut end face. When the color of the cut end face began to change, while maintaining the distance between the cut end face and the flame, the flame was slid horizontally at a speed of approximately 3 to 5 m / min, and the cut end face was melted by the heat of the flame. After the melted cut end face cooled and solidified, it became a mirror surface. The distance between the cut end face and the flame and the moving speed of the flame were designed within the range where deterioration such as combustion or deformation of the sample did not occur.

[0051] After the cut end face of the other sample was polished to some extent with sandpaper, buff polishing was performed on this cut end face to obtain a second mirror-finished sample. Specifically, buff polishing was performed as follows using a commercially available buff polishing machine. Using #600 grit sandpaper wetted with water, the saw marks on the cut end face of the sample were removed. As the buff, a cotton buff with a diameter of 100 to 300 mm and a thickness of 25 to 30 mm was used. With the buff with the abrasive attached applied to the cut end face, the buff was rotated at a rotational speed of 1000 to 1500 rpm, and mirror finishing was performed while checking the flatness of the cut end face. The force of pressing the buff against the cut end face and the rotational speed of the buff were designed within the range where buff burning due to overheating did not occur.

[0052] [Ethanol resistance test] For each processed sample (specifically, the laser processed sample and the first and second mirror finished samples), the ethanol resistance test was carried out by the following two methods respectively. The processed end face is the cut end face (100 mm × 3 mm) in the laser processed sample and the mirror finished end face (100 mm × 3 mm) in the mirror finished sample. In the following two tests, as the ethanol, anhydrous ethanol with a purity of 99.5 mass% or more was used.

[0053] (Ethanol wiping test) A cellulose nonwoven fabric (manufactured by Asahi Kasei Corporation, "Benkot M-3") was immersed in a container containing ethanol to make the nonwoven fabric contain ethanol. The nonwoven fabric containing ethanol was held by hand with one processed end face (100 mm × 3 mm) of the processed sample facing up, and the nonwoven fabric containing ethanol was brought into contact with this processed end face. In this state, the nonwoven fabric was reciprocated within a range of about 50 mm in length. One reciprocating movement was counted as two wipings, and every 50 reciprocating movements (100 wipings), the used nonwoven fabric was immersed in a container containing ethanol to replenish the nonwoven fabric with ethanol. This test was repeatedly performed at room temperature of 20 - 25°C visually until cracks with a length of 0.5 mm or more were confirmed on the processed end face. The number of wipings up to the turn immediately before the turn when cracks were confirmed was determined. Evaluation was carried out according to the following criteria. Excellent (◎): The number of wipings is 1500 or more. Good (○): The number of wipings is 1200 or more and less than 1500. Fair (△): The number of wipings is 900 or more and less than 1200. Poor (×): The number of wipings is less than 900. In Table 1, the numbers described in the evaluation column of the ethanol wiping test represent the number of wipings.

[0054] (Ethanol immersion test) One processed end face (100 mm × 3 mm) of the processed sample was facing up, and the processed sample was placed in a container containing ethanol so that this processed end face was completely immersed, and it was left at 23°C for 24 hours. Then, the processed sample was taken out from the container, and visually, the presence or absence and number of cracks on the main surface (100 mm × 30 mm) with a large area, which is the non-processed surface, and the processed end face (100 mm × 3 mm) were confirmed. Also, the presence or absence of whitening on the main surface with a large area, which is the non-processed surface, and the processed end face was confirmed. Evaluation was carried out according to the following criteria.

[0055] <Crack> Excellent (○): No cracks are visible. Good (○△): One or more and less than six cracks with a length less than 0.5 mm were observed. Acceptable (△): Six or more but less than ten cracks with a length of less than 0.5 mm were observed. Acceptable (▲): Ten or more cracks with a length of less than 0.5 mm were observed. Defective (×): Cracks with a length of 0.5 mm or more but less than 1.0 mm were observed. Extremely defective (××): Cracks with a length of 1.0 mm or more were observed. In Tables 1 and 2, the numbers described in the evaluation column of the ethanol immersion test represent the number of cracks.

[0056] <Whitening> Good (○): No whitening was observed. Acceptable (△): Partial whitening was observed. Defective (×): Overall whitening was observed.

[0057] [Material] The materials used are as follows. <Crosslinking agent> NPG: Neopentyl glycol dimethacrylate, BG: 1,3-Butanediol dimethacrylate. <Polymerization initiator> AIBN: 2,2’-Azobis(isobutyronitrile), V-65: 2,2’-Azobis(2,4-dimethylvaleronitrile). <Chain transfer agent> TPL: Terpinolene.

[0058] [Production Example 1] Preparation of prepolymerized syrup (S1) A prepolymerized syrup (S1) containing an uncrosslinked linear MMA-based polymer (P1) was obtained as follows. 2,2’-Azobisisobutyronitrile (AIBN) as a polymerization initiator was added to MMA as a monomer (M), and the mixture was heated with stirring until the weight average molecular weight (Mw) of the polymer reached about 800,000. Then, it was cooled to room temperature (20 - 25°C), and additional MMA was added for dilution to produce a prepolymerized syrup (S1) containing 8% by mass of the uncrosslinked MMA-based polymer (P1) (Mw = about 800,000).

[0059] [Production Example 2] Preparation of Dissolved Syrup (S2) A dissolved syrup (S2) containing an uncrosslinked linear MMA-based polymer (P2) was obtained as follows. To a monomer mixture consisting of 95 parts by mass of methyl methacrylate (MMA) and 5 parts by mass of methyl acrylate, 0.1 part by mass of a polymerization initiator (2,2'-azobis(2-methylpropionitrile)) and 0.16 part by mass of a chain transfer agent (n-octyl mercaptan) were added and dissolved to obtain a raw material solution. 100 parts by mass of ion-exchanged water, 0.03 part by mass of sodium sulfate, and 0.46 part by mass of a suspension dispersant were mixed to obtain a mixed solution. Into a pressure-resistant polymerization tank, 210 parts by mass of the above raw material solution and 420 parts by mass of the above mixed solution were charged, and while stirring under a nitrogen atmosphere, the temperature was set to 70°C to initiate a polymerization reaction. After 3 hours from the start of the polymerization reaction, the temperature was raised to 90°C, and stirring was continued for 1 hour to obtain a dispersion of bead-shaped copolymer. The bead-shaped copolymer was taken out from this dispersion to obtain an uncrosslinked linear MMA-based polymer (P2). The obtained uncrosslinked linear MMA-based polymer (P2) had a weight average molecular weight (Mw) of about 130,000 and a molecular weight distribution (Mw / Mn) of 1.8. While stirring MMA as the monomer (M), the uncrosslinked linear MMA-based polymer (P2) obtained above was added, and the mixture was heated to 60°C and stirred for 90 minutes. Then, it was cooled to room temperature (20 - 25°C) to obtain a dissolved syrup (S2) containing 30% by mass of the uncrosslinked MMA-based polymer (P2) (Mw = about 130,000).

[0060] [Production Example 3] Preparation of Prepolymerized Syrup (S3) A prepolymerized syrup (S3) containing 15% by mass of an uncrosslinked MMA-based polymer (P1) (Mw = about 800,000) was produced in the same manner as in Production Example 1, except that no additional MMA was added.

[0061] [Examples 1 to 3, Comparative Examples 1, 3 to 12] In Examples 1 to 3 and Comparative Examples 1 and 3 to 12, a plurality of materials were mixed with the composition shown in Tables 1 to 3 to prepare a polymerizable raw material. In these tables, the unit of the blending amount of raw materials other than the polymerization initiator and the chain transfer agent is "mass%", and the total amount of raw materials other than the polymerization initiator and the chain transfer agent is 100 mass%. The blending amounts of the polymerization initiator and the chain transfer agent are shown as the addition amount [g] per 1 kg of the total amount of raw materials other than the polymerization initiator and the chain transfer agent. After subjecting the obtained polymerizable raw material to defoaming treatment, it was poured into a mold composed of a pair of reinforced glasses and a soft vinyl chloride gasket. Primary curing (pre-polymerization) and secondary curing (post-polymerization) were carried out at the temperatures and times shown in Tables 1 to 3. Then, after cooling to near the temperature of the primary curing, a methacrylic resin casting plate with a length of 1250 mm, a width of 2500 mm, and a thickness of 3 mm was taken out from the mold. The main production conditions and evaluation results are shown in Tables 1 to 3.

[0062] [Comparative Example 2] Using a 50 mmφ sheet extruder, an uncrosslinked MMA-based polymer (P2) was melt-kneaded under the condition of a cylinder temperature of 250 °C to obtain a 3 mm-thick methacrylic resin extruded plate. The evaluation results are shown in Table 1.

[0063] [Table 1]

[0064] [Table 2]

[0065] [Table 3]

[0066] [Summary of Results] (Examples 1 to 3) The methacrylic resin casting plates obtained in Examples 1 to 3 were free of sink marks and had good appearance. The casting plates obtained in these Examples contained 6 to 15% by mass of an uncrosslinked MMA polymer (P) with an Mw of 500,000 to 1,500,000 and 94 to 85% by mass of a crosslinked MMA polymer (C). The casting plates obtained in these Examples had a storage modulus (E’) in the rubbery plateau region of 3 MPa or more at 200 °C, a peak value of tanδ of 1.55 or less, and a peak temperature of tanδ of 130 °C or more.

[0067] In addition, in the dynamic viscoelasticity measurement of Example 3, the storage modulus (E’) at high temperature was very high, and when it exceeded 150 °C, the safety device operated and the measurement became impossible. Therefore, in this Example, the peak temperature of tanδ was regarded as 150 °C or more. In this Example, the storage modulus (E’) was regarded as a value exceeding the storage modulus (E’) of Example 2 where the peak temperature of tanδ was 141.4 °C, and was regarded as 5.00 MPa or more. In this Example, the peak value of tanδ was regarded as a value lower than the peak value of tanδ of Example 2 where the peak temperature of tanδ was 141.4 °C, and was regarded as 1.30 or less. All of the casting plates obtained in Examples 1 to 3 had good ethanol resistance.

[0068] (Comparative Example 1) The methacrylic resin casting plate obtained in Comparative Example 1 was free of sink marks and had good appearance. The casting plate obtained in this Comparative Example was an uncrosslinked plate composed of 100% by mass of an uncrosslinked MMA polymer (P) with an Mw of 500,000 to 1,500,000. The casting plate obtained in this Comparative Example had a storage modulus (E’) in the rubbery plateau region of less than 3 MPa at 200 °C, and a peak value of tanα exceeding 1.55. The casting plate obtained in this Comparative Example had poor ethanol resistance.

[0069] (Comparative Example 2) The methacrylic resin extruded sheet prepared in Comparative Example 2 had no sink marks and had a good appearance. The extruded sheet prepared in this comparative example was a non-crosslinked sheet composed of 100% by mass of a non-crosslinked MMA-based polymer (P) with an Mw of 500,000 to 1,500,000. The extruded sheet prepared in this comparative example had a storage elastic modulus (E') in the rubbery plateau region of less than 3 MPa at 200 °C, a peak value of tan α exceeding 1.55, and a peak temperature of tan α of less than 130 °C. The extruded sheet prepared in this comparative example had extremely poor ethanol resistance on the processed end face and also had poor ethanol resistance on the main face, which was the non-processed end face.

[0070] (Comparative Examples 3, 5 to 9) The methacrylic resin cast sheets obtained in Comparative Examples 3, 5 to 9 had no sink marks and had good appearances. The cast sheets obtained in these comparative examples contained 6 to 15% by mass of a non-crosslinked MMA-based polymer (P) with an Mw of 500,000 to 1,500,000 and 94 to 85% by mass of a crosslinked MMA-based polymer (C). In these comparative examples, the amount of the crosslinking agent used was less than that in Examples 1 to 3. The cast sheets obtained in these comparative examples had a storage elastic modulus (E') in the rubbery plateau region of less than 3 MPa at 200 °C and a peak value of tan α exceeding 1.55. In Comparative Examples 6 to 9, the peak temperature of tan δ was less than 130 °C. The cast sheets obtained in these comparative examples had poor ethanol resistance or were inferior to those in Examples 1 to 3.

[0071] (Comparative Example 4) The methacrylic resin cast sheet obtained in Comparative Example 4 had no sink marks and had a good appearance. The cast sheet obtained in this comparative example had an Mw of the non-crosslinked MMA-based polymer (P) of less than 500,000 and a content of the non-crosslinked MMA-based polymer (P) of more than 15% by mass. In this comparative example, the amount of the crosslinking agent used was less than that in Examples 1 to 3. The cast sheet obtained in this comparative example had a storage elastic modulus (E') in the rubbery plateau region of less than 3 MPa at 200 °C, a peak value of tan α exceeding 1.55, and a peak temperature of tan δ of less than 130 °C. The casting plate obtained in this comparative example had extremely poor ethanol resistance on the machined end face, and also had poor ethanol resistance on the main face which is the non-machined end face.

[0072] (Comparative Examples 10 and 11) In the methacrylic resin casting plates obtained in Comparative Examples 10 and 11, the content of the non-crosslinked MMA polymer (P) with Mw of 500,000 to 1,500,000 was less than 6% by mass, and the content of the crosslinked MMA polymer (C) was 94% by mass or more. The methacrylic resin casting plates obtained in these comparative examples had sink marks and poor appearance.

[0073] (Comparative Example 12) In Comparative Example 12, since no additional MMA was added during the preparation of the syrup (S), the resulting polymerizable raw material had a high viscosity, making it difficult to inject into the mold and impossible to produce a plate.

Claims

1. It consists of a methacrylic resin casting plate containing an uncrosslinked methyl methacrylate polymer (P) and a crosslinked methyl methacrylate polymer (C). It consists of a polymerized cured product of a polymerizable raw material containing an uncrosslinked methyl methacrylate polymer (P), one or more monomers containing methyl methacrylate, one or more crosslinking agents, and a polymerization initiator. The amount of the crosslinking agent is 2.5 to 25 parts by mass with respect to a total of 100 parts by mass of the polymerizable monomer and monomer units. The molecular weight of the crosslinking agent is 400 or less. The weight average molecular weight of the uncrosslinked methyl methacrylate polymer (P) is 500,000 to 1,500,000. The content of the uncrosslinked methyl methacrylate polymer (P) is 6 to 15% by mass. The content of the crosslinked methyl methacrylate polymer (C) is 94 to 85% by mass. When dynamic viscoelasticity measurement is carried out, the storage elastic modulus (E') in the rubbery plateau region is 3 MPa or more at 200 °C, the peak value of tanδ is 1.55 or less, the peak temperature of tanδ is 130 °C or more, and it is a methacrylic resin casting plate which is a laser-cut plate.

2. The methacrylic resin casting plate according to claim 1, wherein when the cut end face of the laser-cut methacrylic resin casting plate is wiped with ethanol 1200 times or more at 20 to 25 °C, cracks with a length of 0.5 mm or more do not occur.

3. The methacrylic resin casting plate according to claim 1, wherein when the cut end face of the cut methacrylic resin casting plate is flame polished and then wiped with ethanol 1200 times or more at 20 to 25 °C, cracks with a length of 0.5 mm or more do not occur.

4. The methacrylic resin casting plate according to claim 1, wherein when the cut end face of the cut methacrylic resin casting plate is buff polished and then wiped with ethanol 1200 times or more at 20 to 25 °C, cracks with a length of 0.5 mm or more do not occur.

5. The methacrylic resin casting plate according to claim 1, wherein when the laser-cut methacrylic resin casting plate is immersed in ethanol for 24 hours at 20 to 25 °C, cracks with a length of 0.5 mm or more do not occur.

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