JP2022138994A - Methacrylic resin cast plate - Google Patents

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

The present invention relates to a methacrylic resin cast board.

Methacrylic resins are excellent in transparency, colorability, moldability, weather resistance, surface hardness, etc., and are widely used in various fields such as signboards, decorative materials, lighting covers, automobile parts, and glazing materials. . In recent years, due to the above-mentioned properties such as transparency, this resin has been used as an acrylic partition for droplet infection prevention that can be easily installed at reception desks and reception counters in facilities such as stores, companies, nursery schools, kindergartens, schools, and hospitals. It's meant to be used. A methacrylic resin plate used for this purpose needs to be regularly disinfected with a disinfectant solution such as ethanol because droplets, fingerprints, dust, and the like adhere to the plate.

In general, methacrylic resins have relatively good chemical resistance and oil resistance, but because they are thermoplastic resins, they tend to be relatively weak against organic solvents such as ethanol. In particular, a portion that has undergone processing such as cutting, polishing, and thermal bending retains the stress applied during processing, so it tends to be weaker than other portions against organic solvents. Therefore, if the processed portion of the methacrylic resin plate is repeatedly exposed to an organic solvent, or if the methacrylic resin plate including the processed portion is immersed in an organic solvent, cracks or whitening may occur in the processed portion of the resin plate.

Solvent resistance is generally improved by using a methacrylic resin composition containing a crosslinked methyl methacrylate (MMA) polymer. As a method for producing a resin plate containing a crosslinked MMA-based polymer, a polymerizable raw material containing a plurality of types of monomers including MMA and a cross-linking agent, or a non-crosslinked MMA-based polymer and one or more types of MMA are used. A method of cast-polymerizing a polymerizable raw material obtained by adding a cross-linking agent and, if necessary, one or more monomers containing MMA to a syrup containing a monomer.

For example, in Patent Document 1, as a method for producing a methacrylic resin cast plate having excellent solvent resistance, a polymerizable raw material obtained by adding a cross-linking agent and a polymerization initiator to a prepolymerized syrup is cast-polymerized, and the cross-linking agent is used. A production method is disclosed in which the degree of polymerization of the crosslinked trunk polymer is 0.05 to 0.15 (l/g) in terms of intrinsic viscosity [η] (claim 1).
In Patent Document 1, in the section [Examples], "solvent resistance" is measured by dropping solvent styrene while applying a stress of 140 kg/cm ² to the sample and measuring the rupture time of the sample. .

In Patent Document 2, as a method for producing a methacrylic resin cast plate having excellent solvent resistance, in the presence of 0.5 to 40% by weight of a cross-linking agent represented by a specific chemical formula, one or more types including MMA (Claim 1).
In Patent Document 2, in the section [Examples], "solvent resistance" is evaluated by light transmittance when immersed in organic solvents such as benzene and acetone.

Japanese Patent Publication No. 6-70098 Japanese Patent Publication No. 44-020626 JP-A-61-108630

As described above, solvent resistance is improved by using a methacrylic resin composition containing a crosslinked MMA polymer. However, when a polymerizable raw material containing MMA and a cross-linking agent is polymerized, gelation tends to be accelerated and polymerization shrinkage tends to proceed quickly. In this case, there is a case where the transfer failure of the mold surface called "sink" occurs at the periphery of the plate where the polymerization is likely to be delayed. Improper transfer of the mold surface leads to a decrease in productivity, which is not preferable. This problem tends to occur when the amount of the cross-linking agent added is large. For example, Patent Literature 3 describes a problem that "if the amount of the cross-linking agent used in the Shiratsubu exceeds 25% by weight, the molding will have sink marks during curing". Therefore, it is not preferable to use a large amount of a cross-linking agent as in Patent Document 2 in order to improve solvent resistance.

Methacrylic resin cast plates used for applications such as acrylic partitions to prevent droplet infection do not use a large amount of cross-linking agents and do not cause appearance defects such as cracks and whitening even after repeated use of ethanol for a long period of time. It preferably has good ethanol resistance.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a methacrylic resin cast board free from appearance defects such as sink marks and having excellent ethanol resistance.

As a result of intensive research conducted by the present inventors to solve the above problems, the weight average molecular weight (Mw) and content of the non-crosslinked methyl methacrylate (MMA) polymer contained in the methacrylic resin cast plate, And by optimizing the dynamic viscoelasticity of the methacrylic resin cast plate, it is possible to suppress the occurrence of sink marks during cast polymerization and to provide a methacrylic resin cast plate having good ethanol resistance. We have completed the present invention.

The present invention provides the following methacrylic resin cast plates of [1] to [5].
[1] Consisting of a methacrylic resin composition containing a non-crosslinked methyl methacrylate polymer (P) and a crosslinked methyl methacrylate polymer (C),
The non-crosslinked methyl methacrylate polymer (P) has a weight average molecular weight of 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 dynamic viscoelasticity measurement was performed, the storage elastic modulus (E') in the rubbery flat region was 3 MPa or more at 200°C, the tan δ peak value was 1.55 or less, and the tan δ peak temperature was 130°C. A methacrylic resin casting board which is the above.

[2] When the cut end face of the laser-cut methacrylic resin cast plate is wiped with ethanol at 20 to 25 ° C. 1200 times or more, no cracks with a length of 0.5 mm or more are generated, [1] Methacrylic resin casting board.
[3] After the cut end surface of the cut methacrylic resin cast plate is flame-polished, when it is wiped with ethanol at 20 to 25 ° C. for 1200 times or more, no cracks with a length of 0.5 mm or more are generated. 1] methacrylic resin casting plate.
[4] After buffing the cut end face of the cut methacrylic resin cast plate, when wiping with ethanol at 20 to 25 ° C. for 1200 times or more, no cracks with a length of 0.5 mm or more are generated. 1] methacrylic resin casting plate.
[5] The methacrylic resin casting of [1], wherein no cracks having a length of 0.5 mm or more occur when the laser-cut methacrylic resin casting plate is immersed in ethanol at 20 to 25° C. for 24 hours. board.

According to the present invention, it is possible to provide a methacrylic resin cast board that is free from appearance defects such as sink marks and has excellent ethanol resistance.

The present invention will be described in detail below.
In this specification, "methacryl" and "acryl" may be collectively referred to as "(meth)acryl". The same applies to "(meth)acrylic acid" and (meth)acryloyl. As used herein, "crack" includes crazes and cracks.

[Methacrylic resin casting board]
The methacrylic resin cast plate of the present invention comprises a methacrylic resin composition containing a non-crosslinked methyl methacrylate (MMA) polymer (P) and a crosslinked methyl methacrylate (MMA) polymer (C). .
In the methacrylic resin cast plate of the present invention,
The weight average molecular weight (Mw) of the non-crosslinked MMA polymer (P) is 500,000 to 1,500,000,
The content of the non-crosslinked MMA polymer (P) is 6 to 15% by mass,
The content of the crosslinked MMA polymer (C) is 94-85% by mass.
The methacrylic resin cast plate of the present invention has a storage elastic modulus (E′) in the rubbery flat region of 3 MPa or more at 200° C. and a peak value of tan δ of 1.55 when subjected to dynamic viscoelasticity measurement. and the peak temperature of tan δ is 130° C. or higher.

Solvent resistance is generally improved by using a methacrylic resin composition containing a crosslinked MMA polymer. However, when a polymerizable raw material containing MMA and a cross-linking agent is polymerized, gelation tends to be accelerated and polymerization shrinkage tends to proceed quickly. In this case, there is a case where the transfer failure of the mold surface called "sink" occurs at the periphery of the plate where the polymerization is likely to be delayed. This problem tends to occur when the amount of the cross-linking agent added is large.
As used herein, the term "sink marks" refers to poor transfer defects on the mold surface caused by peeling of the resin from the mold surface such as a glass surface due to polymerization shrinkage or the like during polymerization. For example, if the mold surface is a specular surface, the "sink" is a non-specular portion where the specular surface was not transferred well.

The present inventors have optimized the weight-average molecular weight (Mw) and content of the non-crosslinked MMA polymer (P) contained in the methacrylic resin casting plate, and the dynamic viscoelasticity of the methacrylic resin casting plate. By doing so, it is possible to provide a methacrylic resin cast board having good ethanol resistance that does not cause appearance defects such as cracks and whitening even when ethanol is repeatedly used for a long period of time without using a large amount of a cross-linking agent. Found it.
In the present invention, since it is not necessary to use a large amount of a cross-linking agent, it is possible to effectively suppress sink marks caused by polymerization shrinkage when a cross-linking agent is used.
The present inventors have also found that by optimizing the weight average molecular weight (Mw) of the non-crosslinked MMA polymer (P), the shrinkage caused by polymerization shrinkage when using a crosslinking agent can be suppressed, and the methacrylic resin can be injected. It was found that the ethanol resistance of the template can be improved.
Owing to the above effects, according to the present invention, it is possible to provide a methacrylic resin cast board which is free from appearance defects such as sink marks and has excellent ethanol resistance.

According to the present invention, a methacrylic resin that does not cause cracks having a length of 0.5 mm or more when the cut end face of a laser-cut methacrylic resin cast plate is wiped with ethanol at 20 to 25 ° C. for 1200 times or more. Cast plates can be provided.
According to the present invention, after flame polishing the cut end surface of the cut methacrylic resin cast plate, when wiping with ethanol at 20 to 25 ° C. for 1200 times or more, cracks with a length of 0.5 mm or more do not occur. A methacrylic resin cast plate can be provided.
According to the present invention, after buffing the cut end surface of the cut methacrylic resin cast plate, when wiping with ethanol at 20 to 25 ° C. for 1200 times or more, no cracks with a length of 0.5 mm or more do not occur. A methacrylic resin cast plate can be provided.
According to the present invention, there is provided a methacrylic resin cast plate in which no cracks having a length of 0.5 mm or more occur when the laser-cut methacrylic resin cast plate is immersed in ethanol at 20 to 25° C. for 24 hours. can do.
For specific methods of the above four types of ethanol resistance tests, see the section [Examples] below.

A dynamic thermo-mechanical property analysis (DMTA method) provides a DMTA curve showing the relationship between temperature and storage modulus. See FIG. 1 and the like of International Publication No. 2015-122174. In the DMTA curve, the storage modulus drops significantly above the glass transition point (Tg), but after that, a rubber-like flat region appears where the storage modulus does not change significantly even when the temperature is raised. A rubbery plateau is an area where the polymer chains move but do not completely melt. After that, when the temperature is further increased to enter the flow region, the storage modulus is greatly reduced again.

When the dynamic viscoelasticity measurement was performed, the storage elastic modulus (E') in the rubber-like flat region was 3 MPa or more at 200°C. Alternatively, it means that a crosslinked structure having ethanol resistance that does not cause breakage is generated.
Incidentally, as shown in FIG. 1 of International Publication No. 2015-122174, 200° C. is the reference temperature on the high temperature side of the rubber-like flat region in the methacrylic resin cast plate.
When the dynamic viscoelasticity measurement is performed, the peak value of tan δ is 1.55 or less and the peak temperature of tan δ is 130° C. or more, which indicates that the non-crosslinked MMA polymer (P) having low ethanol resistance It means that the amount and molecular weight are within a range that does not prevent the crosslinked MMA-based polymer (C) from forming and maintaining a crosslinked structure having ethanol resistance.

[Method for producing methacrylic resin cast plate]
The methacrylic resin cast plate of the present invention is, for example, a syrup ( step (1) of providing S);
A step (2) of adding one or more monomers (M3) containing methyl methacrylate (MMA) and one or more crosslinking agents (M4) to syrup (S) to obtain a polymerizable raw material;
It can be produced by a production method including the step (3) of cast-polymerizing the obtained polymerizable raw material.

The Mw of the non-crosslinked MMA-based polymer (P) can be set to a desired value by appropriately selecting polymerization conditions and adjusting the degree of polymerization when the raw material monomers of the non-crosslinked MMA-based polymer (P) are polymerized. Range can be adjusted.
By appropriately selecting the composition of the polymerizable raw material and the casting polymerization conditions, the storage elastic modulus (E') of the rubber-like flat region of the methacrylic resin casting plate, the peak value of tan δ, and the peak temperature can be adjusted to desired ranges. can be adjusted to

(Step (1))
As a method for preparing the syrup (S), a prepolymerization method is preferable because the syrup (S) containing the non-crosslinked MMA 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 non-crosslinked linear MMA-based polymer ( A prepolymerized syrup (S1) comprising P1) and one or more unreacted monomers (M1).
After the preliminary polymerization, if necessary, one or more monomers (M1) such as MMA may be further added for dilution.

As a method for preparing the syrup (S), there is a polymer dissolution method in addition to the prepolymerization method described above. The syrup (S) obtained by this method comprises a non-crosslinked linear MMA-based polymer (P2) polymerized using one or more monomers containing MMA, and one or more monomers containing MMA. It is a dissolved syrup (S2) obtained by dissolving the polymer (M2).
However, dissolving 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 is very troublesome and time consuming. Therefore, the prepolymerization method is preferable to the polymer dissolution method.

The non-crosslinked MMA-based polymer (P) is an MMA homopolymer, a copolymer of MMA and at least one other alkyl methacrylate, or at least one alkyl methacrylate containing MMA and at least one other may be any copolymer with a copolymerizable unsaturated monomer.

The number of carbon atoms in the alkyl group of the alkyl methacrylate used as the starting material for the non-crosslinked linear MMA polymer (P) is preferably 1-20, more preferably 1-12. 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 methacrylic acid. cyclohexyl and the like.

Other copolymerizable unsaturated monomers that can be used in combination with alkyl methacrylate as raw materials for the non-crosslinked linear MMA polymer (P) include methyl acrylate, ethyl acrylate, propyl acrylate, acrylic Alkyl acrylates such as 2-ethylhexyl acid, lauryl acrylate, and cyclohexyl acrylate; 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxy-3 (meth)acrylate. -Hydroxyalkyl (meth)acrylates such as chloropropyl; (meth)acrylic acid; (meth)acrylic acid metal salts; vinylic monomers such as vinyl chloride, vinyl acetate, and vinyltoluene; acrylonitrile; Styrenic monomers such as α-methylstyrene; and maleic anhydride.

The concentration of the non-crosslinked MMA 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) may increase and sink marks may occur.
If the viscosity of the syrup (S) is too high, it will be difficult to add and mix a monomer such as MMA for dilution into the syrup (S), and the defoaming treatment of the polymerizable raw material obtained in the next step and injection into the mold will be difficult. it gets harder. 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. is.

The weight average molecular weight (Mw) of the non-crosslinked linear MMA polymer (P) is 500,000 to 1,500,000. By setting the Mw of the non-crosslinked MMA polymer (P) within this range, it is possible to effectively suppress sink marks caused by polymerization shrinkage when a crosslinking agent is used, and to improve the ethanol resistance of the methacrylic resin cast plate. can be done.
If the Mw is less than 500,000, the resulting methacrylic resin cast plate may have insufficient ethanol resistance. If the Mw is 1,500,000 or more, the viscosity of the syrup (S) increases, making it difficult to add and mix a monomer such as MMA for dilution into the syrup (S), and defoaming the polymerizable raw material obtained in the next step. and can be difficult to pour into the mold.
Mw of the non-crosslinked linear MMA polymer (P) is preferably 700,000 to 1,200,000, more preferably 700,000 to 1,000,000.

The degree of polymerization, weight average molecular weight (Mw), and content of the non-crosslinked MMA polymer (P), which can suppress sink marks during casting polymerization while ensuring the ethanol resistance of the methacrylic resin cast plate, are dynamically The tan δ peak value and peak temperature in the viscoelastic properties can be used as indicators. The methacrylic resin cast plate of the present invention must have a tan δ peak value of 1.55 or less and a tan δ peak temperature of 130° C. or higher.
When the tan δ peak value is more than 1.55 or the tan δ peak temperature is less than 130 ° C., the type and amount of the cross-linking agent are designed to the preferred types and amounts described herein, the obtained methacrylic The ethanol resistance of the resin cast plate may be insufficient.
The peak value of tan δ is preferably 0.35 or more and 1.55 or less.
The peak temperature of tan δ is preferably 130°C or higher and 200°C or lower.

A syrup or gel containing a partially crosslinked MMA gel polymer can be used instead of the syrup (S) containing MMA and a non-crosslinked MMA polymer (P). This syrup or gel is obtained by adding a cross-linking agent to the dissolved syrup (S2) and prepolymerizing it. and the above monomers.

(Step (2))
In step (2), one or more monomers (M3) containing methyl methacrylate (MMA), one or more crosslinking agents (M4), and a polymerization initiator are added to the syrup (S) to polymerize. obtain sexual raw materials.
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 necessary. The addition of the monomer (M3) may be combined with the addition of the monomer (M1) after prepolymerization, if necessary. Examples of other alkyl methacrylates and other copolymerizable unsaturated monomers that can be used as the monomer (M3) are the same as those of the raw material monomers for the non-crosslinked MMA polymer (P). is.

A monomer having two or more (meth)acryloyl groups in the molecule is preferably used as the cross-linking agent (M4). The molecular weight of the cross-linking 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, neopentyl glycol di(meth)acrylate and the like are preferred.

If a cross-linking agent having a molecular weight of more than 400 is used, the resulting cross-linked MMA polymer (C) will have a large molecular weight between cross-linking points, and the resulting methacrylic resin cast plate may have insufficient ethanol resistance. .
The molecular weight between cross-linking points of the cross-linked MMA polymer (C) is affected by the molecular weights and amounts of the monomer (M3) and the cross-linking agent (M4), and the amount of the non-cross-linked MMA polymer (P).
The molecular weight between cross-linking points of the cross-linked MMA-based polymer (C) can be indexed by the storage elastic modulus (E′) in the rubber-like flat region of the methacrylic resin cast plate. In the present invention, it is necessary that the storage elastic modulus (E') in the rubbery flat region is 3 MPa or more at 200°C. If the storage elastic modulus (E′) in the rubber-like flat region is 3 MPa or more at 200° C., a crosslinked structure that does not generate cracks of 0.5 mm or more in length in the above four types of ethanol resistance tests is considered to be generated. I can say
The storage elastic modulus (E') in the rubbery flat region is preferably 3 MPa or more and 200 MPa or less at 200°C.

The polymerization initiator is not particularly limited, and 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 peroxycarbonate, di-(2-ethoxyethyl) peroxydicarbonate , di-(methoxyisopropyl)peroxydicarbonate, and di-(2-ethylhexyl)peroxydicarbonate.

In step (2), a chain transfer agent and/or an ultraviolet absorber can be added as required. Chain transfer agents include styrene dimers such as α-methyl-styrene dimer; mercaptans such as n-octylmercaptan, n-dodecylmercaptan, and hyophenol; thioglycolic acid, ethyl thioglycolate, and butyl thioglycolate; β-mercaptopropionic acid and its esters such as β-mercaptopropionic acid, β-methyl β-mercaptopropionate and octyl β-mercaptopropionate; terpinolene and the like. UV absorbers include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole and the like.

In step (2), one or more other additives can be added, if desired. Other additives include other resins of different types, antioxidants, dispersants, fillers, resin particles, pigments, dyes, patterning materials such as natural stone particles, and release agents.

The mixing ratio of raw materials is not particularly limited. The total amount of raw materials other than the polymerization initiator, chain transfer agent, ultraviolet absorber, and other additives is 100 parts by mass.
The amount of syrup (S) is designed so that the content of the non-crosslinked MMA 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, polymerization shrinkage during casting polymerization may increase, and sink marks may occur in the obtained methacrylic resin casting plate. If this content exceeds 15% by mass, the amount of components soluble in the solvent increases, so the type and amount of the cross-linking agent (M4) may be designed to the preferred types and amounts described herein. Otherwise, the resulting methacrylic resin cast plate may have insufficient ethanol resistance.

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, with respect to a total of 100 parts by mass of polymerizable monomers and monomer units. is.
The amount of one or more crosslinkers (M4) is preferably 2.5 to 25 parts by weight, more preferably 4.5 to 20 parts by weight.
The amount of chain transfer agent is preferably 0 to 0.5 parts by weight.
The amount of the polymerization initiator is preferably 0.05 to 3 g per 1 kg of the total amount of raw materials other than the polymerization initiator, chain transfer agent, ultraviolet absorber and other additives.
The amount of the UV absorber is preferably 0 to 2 g per 1 kg of the total amount of raw materials other than the polymerization initiator, chain transfer agent, UV absorber and other additives.

(Step (3))
In step (3), the liquid polymerizable raw material obtained in step (2) is injected into a mold for cast polymerization.
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 gasket, and a pair of endless belts running in the same direction at the same speed. Examples include a mold or the like composed of a face and both endless belts and gaskets running at the same speed on both sides thereof.

The polymerizable raw material is preferably polymerized and cured in two or more stages while changing the temperature. A two-stage polymerization can be carried out as follows. First, the mold in which the polymerizable raw material is injected into the inner space is preferably immersed in a water bath whose temperature is controlled to about 55 to 85° C. and held for about 1 to 20 hours to perform the first stage of polymerization and curing. be able to. Next, the mold is placed in a hot air drying furnace, preferably heated at a temperature of about 80° C. for about 2 to 15 hours, and then preferably heated at a temperature of about 120 to 130° C. for about 3 to 15 hours. A second stage of polymerization curing that drives the reaction can be performed.
As described above, a methacrylic resin cast board is produced from a methacrylic resin composition containing the non-crosslinked MMA polymer (P) and the crosslinked MMA polymer (C).
The flat resin plate, which is the primary molded article thus obtained, may be secondary molded into an arbitrary three-dimensional shape by a known method such as vacuum molding or pressure molding.

INDUSTRIAL APPLICABILITY As described above, the present invention can provide a methacrylic resin cast board which is free from appearance defects such as sink marks and has excellent ethanol resistance.
Since the methacrylic resin cast plate of the present invention is made of a methacrylic resin composition, it can have properties inherent to methacrylic resins, such as transparency, colorability, moldability, weather resistance, and surface hardness.

[Use]
The methacrylic resin cast 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 cast plate of the present invention is not particularly limited, and is preferably 3 to 5 mm for applications such as acrylic partitions for preventing droplet infection.

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 vacuum-dried, 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, "GPC-802", "HSG-30", "HSG-50" manufactured by Shimadzu Corporation and "Shodex A-806" manufactured by Showa Denko K.K. was used to measure the molecular weight by the GPC (gel permeation chromatography) method. Mw and Mn are polystyrene conversion values.

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

(exterior)
The appearance of the produced or prepared resin plate (methacrylic resin cast plate or methacrylic resin extruded plate) was visually observed and evaluated according to the following criteria.
Good (○): No sink marks were observed.
Poor (x): Sink marks are observed.

(dynamic viscoelasticity)
The dynamic viscoelasticity measurement of the manufactured or prepared resin plate (methacrylic resin cast plate or methacrylic resin extruded plate) was performed according to JIS K7244-1 and JIS 7244-4.
First, a resin plate was cut to obtain a sample having a length of 20 mm, a width of 1.5 mm, and a thickness of 2 mm. Measurement was performed 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 elevated temperature, and the stress response generated at that time was detected, and the phase difference between the dynamic stress waveform and the dynamic displacement waveform was obtained. A DMTA curve or the like was obtained by plotting each data such as the storage modulus (E') and tan δ against the temperature in the measurement region using an arithmetic expression based on the linear viscoelastic theory. In addition, the main measurement conditions were set as follows. From this, the storage elastic modulus (E') of the rubbery flat region at 200°C was obtained. Also, the peak value of tan δ and the peak temperature were obtained.
<Measurement conditions>
Measurement frequency: 1Hz,
Load: 1kg,
Measurement mode: temperature dependent,
Measurement temperature: 30-250°C,
Temperature rising conditions: 3°C/min.

[Processing method]
(laser cutting)
The manufactured or prepared resin plate (methacrylic resin cast plate or methacrylic resin extruded plate) is cut using Comnet's "Spirit GLS 100W" as a laser under the conditions of power control of 80% and processing speed of 2m/min. A laser-processed sample having a length of 100 mm, a width of 30 mm, and a thickness of 3 mm was obtained.

(polishing)
A manufactured or prepared resin plate (methacrylic resin cast plate or methacrylic resin extruded plate) was cut with an electric saw to obtain two samples of length 100 mm, width 30 mm, and thickness 3 mm.
The cut end face of one sample was flame-polished to obtain a first mirror-finished sample.
Specifically, with the main surface of the sample lying down, a thin flame the size of a pencil lead is brought close to the cut end surface using a commercially available flame polisher, and when the color of the cut end surface begins to change, the cut end surface and the flame The flame was slid laterally at a speed of approximately 3 to 5 m/min while keeping the distance, and the cut end face was melted by the heat of the flame. The melted cut end surface became a mirror surface after being cooled and solidified. The distance between the cut end face and the flame and the movement speed of the flame were designed within a range in which deterioration such as burning or deformation of the sample did not occur.

After the cut end face of the other sample was polished with sandpaper to some extent, the cut end face was buffed to obtain a second mirror-finished sample.
Specifically, buffing was performed using a commercially available buffing machine as follows. The serrations on the cut edge of the sample were removed using #600 grit sandpaper moistened with water. A cotton buff having a diameter of 100 to 300 mm and a thickness of 25 to 30 mm was used as the buff. A buff to which an abrasive was applied was applied to the cut end face, and the buff was rotated at a rotational speed of 1000 to 1500 rpm, and mirror finishing was performed while checking the surface condition of the cut end face. The force with which the buff is pressed against the cut end surface and the rotation speed of the buff were designed within a range in which buff burn due to overheating does not occur.

[Ethanol resistance test]
Each processed sample (specifically, the laser-processed sample and the first and second mirror-finished samples) was tested for ethanol resistance by the following two methods. The processed end face was a cut end face (100 mm×3 mm) for the laser-processed sample, and a mirror-finished end face (100 mm×3 mm) for the mirror-finished sample.
In the following two tests, absolute ethanol with a purity of 99.5% by mass or more was used as ethanol.

(Ethanol wiping test)
A nonwoven fabric made of cellulose (“BEMCOT M-3” manufactured by Asahi Kasei Co., Ltd.) was immersed in a container containing ethanol to impregnate the nonwoven fabric with ethanol.
Hold a nonwoven fabric impregnated with ethanol in your hand, place one processed end face (100 mm × 3 mm) of the processed sample upward, bring the nonwoven fabric impregnated with ethanol into contact with this processed end face, and in this state, stretch the nonwoven fabric to a length of about 50 mm. Moved back and forth within range. One back-and-forth movement was counted as two wipings, and the non-woven fabric used for every 50 reciprocating movements (100 times of wiping) was immersed in a container containing ethanol to replenish ethanol to the non-woven fabric. This test was repeated at a normal temperature of 20 to 25° C. until a crack having a length of 0.5 mm or more was visually observed on the processed end face. The number of times of wiping up to the time immediately before the time when cracks were confirmed was obtained. Evaluation was made according to the following criteria.
Excellent (⊚): The number of times of wiping is 1500 times or more.
Good (◯): The number of times of wiping is 1200 times or more and less than 1500 times.
Acceptable (Δ): The number of times of wiping is 900 times or more and less than 1200 times.
Poor (x): The number of times of wiping is less than 900 times.
In Table 1, the numbers in the evaluation column of the ethanol wiping test represent the number of times of wiping.

(Ethanol immersion test)
One processed end surface (100 mm × 3 mm) of the processed sample was placed upward, and the processed sample was placed in a container containing ethanol so that this processed end surface was completely immersed, and allowed to stand at 23° C. for 24 hours. After that, the processed sample was taken out from the container, and the presence and number of cracks on the main surface (100 mm×30 mm) and the processed end surface (100 mm×3 mm) with a large area, which were non-processed surfaces, were visually confirmed. In addition, the presence or absence of whitening on the main surface having a large area, which is the unprocessed surface, and the processed end surface was confirmed. Evaluation was made according to the following criteria.

<crack>
Excellent (○): No cracks were observed.
Good (◯Δ): 1 or more but less than 6 cracks having a length of less than 0.5 mm were observed.
Acceptable (Δ): 6 or more but less than 10 cracks having a length of less than 0.5 mm were observed.
Good (▴): 10 or more cracks with a length of less than 0.5 mm were observed.
Poor (x): A crack having a length of 0.5 mm or more and less than 1.0 mm was observed.
Very poor (xx): A crack with a length of 1.0 mm or more was observed.
In Tables 1 and 2, the numbers in the evaluation column of the ethanol immersion test represent the number of cracks.

<Whitening>
Good (○): Whitening is not observed.
Acceptable (Δ): Whitening was observed partially.
Poor (x): Whitening was observed on the entire surface.

[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.

[Production Example 1] Preparation of prepolymerized syrup (S1) A prepolymerized syrup (S1) containing a non-crosslinked linear MMA polymer (P1) was obtained in the following manner.
2,2'-Azobisisobutyronitrile (AIBN) as a polymerization initiator was added to MMA as the monomer (M) and heated with stirring until the weight average molecular weight (Mw) of the polymer was about Polymerization was carried out until it reached 800,000. After that, it is cooled to room temperature (20 to 25° C.), diluted by adding additional MMA, and prepolymerized syrup containing 8% by mass of non-crosslinked MMA polymer (P1) (Mw = about 800,000). (S1) was produced.

[Production Example 2] Preparation of Dissolving Syrup (S2) A dissolving syrup (S2) containing a non-crosslinked linear MMA polymer (P2) was obtained in the following manner.
A monomer mixture consisting of 95 parts by mass of methyl methacrylate (MMA) and 5 parts by mass of methyl acrylate, a polymerization initiator (2,2'-azobis (2-methylpropionitrile) 0.1 parts by mass and chain transfer An agent (0.16 parts by mass of n-octyl mercaptan) was added and dissolved to obtain a raw material liquid.
100 parts by mass of ion-exchanged water, 0.03 parts by mass of sodium sulfate, and 0.46 parts by mass of a suspension dispersant were mixed to obtain a mixed liquid.
A pressure-resistant polymerization tank was charged with 210 parts by mass of the raw material liquid and 420 parts by mass of the mixed liquid, and the temperature was raised to 70° C. while stirring in a nitrogen atmosphere to initiate a polymerization reaction. After 3 hours from the initiation of the polymerization reaction, the temperature was raised to 90° C. and stirring was continued for 1 hour to obtain a bead-like copolymer dispersion. A bead-like copolymer was taken out from this dispersion to obtain a non-crosslinked linear MMA polymer (P2). The obtained non-crosslinked linear MMA 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 non-crosslinked linear MMA polymer (P2) obtained above was added, heated to 60° C., and stirred for 90 minutes. Thereafter, the mixture was cooled to room temperature (20 to 25° C.) to obtain a dissolved syrup (S2) containing 30% by mass of the non-crosslinked MMA polymer (P2) (Mw=approximately 130,000).

[Production Example 3] Preparation of prepolymerized syrup (S3) In the same manner as in Production Example 1, except that no additional MMA was added, a non-crosslinked MMA polymer (P1) (Mw = about 800,000) was added. An amount of 15% by weight of prepolymerized syrup (S3) was produced.

[Examples 1 to 3, Comparative Examples 1, 3 to 12]
In each of Examples 1 to 3 and Comparative Examples 1 and 3 to 12, a plurality of materials were mixed according to the composition shown in Tables 1 to 3 to prepare polymerizable raw materials. In these tables, the unit of the amount of raw materials other than the polymerization initiator and the chain transfer agent is "% by mass", and the total amount of the raw materials other than the polymerization initiator and the chain transfer agent is 100% by mass. The amounts of the polymerization initiator and the chain transfer agent to be blended are indicated by the amount [g] added per 1 kg of the total amount of raw materials other than the polymerization initiator and the chain transfer agent.
After defoaming the obtained polymerizable raw material, it was poured into a mold composed of a pair of tempered glass and a soft vinyl chloride gasket. Primary curing (prepolymerization) and secondary curing (postpolymerization) were performed at the temperatures and times shown in Tables 1 to 3. Then, after cooling to around the primary curing temperature, a methacrylic resin cast plate of 1250 mm long, 2500 mm wide and 3 mm thick was taken out from the mold.
Main manufacturing conditions and evaluation results are shown in Tables 1 to 3.

[Comparative Example 2]
Using a 50 mmφ sheet extruder, the non-crosslinked MMA polymer (P2) was melt-kneaded at a cylinder temperature of 250° C. to obtain a 3 mm thick methacrylic resin extruded plate.
Table 1 shows the evaluation results.

[Summary of results]
(Examples 1-3)
The methacrylic resin cast plates obtained in Examples 1 to 3 had no sink marks and had a good appearance. The cast plates obtained in these Examples contain 6 to 15% by mass of a non-crosslinked MMA polymer (P) having an Mw of 500,000 to 1,500,000, and 94 to 85 mass% of a crosslinked MMA polymer (C). %. The cast plates obtained in these Examples had a storage elastic modulus (E') in the rubbery flat region of 3 MPa or more at 200°C, a tan δ peak value of 1.55 or less, and a tan δ peak temperature of It was 130°C or higher.

In addition, in the dynamic viscoelasticity measurement of Example 3, the storage elastic modulus (E') at high temperature was very high, and when the temperature exceeded 150°C, the safety device operated and the measurement became impossible. Therefore, in this example, the peak temperature of tan δ was considered to be 150° C. or higher. In this example, the storage modulus (E') was regarded as a value exceeding the storage modulus (E') of Example 2 in which the tan δ peak temperature was 141.4°C, and was regarded as 5.00 MPa or more. In this example, the tan δ peak value was considered to be lower than the tan δ peak value of Example 2, in which the tan δ peak temperature was 141.4° C., and was considered to be 1.30 or less.
All of the cast plates obtained in Examples 1 to 3 had good ethanol resistance.

(Comparative example 1)
The methacrylic resin cast plate obtained in Comparative Example 1 had no sink marks and had a good appearance. The cast plate obtained in this comparative example was a non-crosslinked plate comprising 100% by mass of a non-crosslinked MMA polymer (P) having an Mw of 500,000 to 1,500,000. The cast plate obtained in this comparative example had a storage modulus (E′) in the rubbery flat region of less than 3 MPa at 200° C. and a peak value of tan α of more than 1.55. The cast plate obtained in this comparative example had poor ethanol resistance.

(Comparative example 2)
The methacrylic resin extruded plate prepared in Comparative Example 2 had no sink marks and had a good appearance. The extruded plate prepared in this comparative example was a non-crosslinked plate comprising 100% by mass of a non-crosslinked MMA polymer (P) having an Mw of 500,000 to 1,500,000. The extruded plate prepared in this comparative example has a storage modulus (E′) in the rubbery flat region of less than 3 MPa at 200° C., a tan α peak value of more than 1.55, and a tan α peak temperature of 130° C. was less than
In the extruded plate prepared in this comparative example, the ethanol resistance of the processed end surface was extremely poor, and the ethanol resistance of the main surface, which was the unprocessed end surface, was also poor.

(Comparative Examples 3, 5 to 9)
The methacrylic resin cast plates obtained in Comparative Examples 3 and 5 to 9 had no sink marks and had a good appearance. The cast plates obtained in these comparative examples contain 6 to 15% by mass of a non-crosslinked MMA polymer (P) having an Mw of 500,000 to 1,500,000, and 94 to 85 mass% of a crosslinked MMA polymer (C). %. In these comparative examples, the amount of the cross-linking agent used was less than in Examples 1-3.
The cast plates obtained in these comparative examples had a storage modulus (E′) in the rubbery flat region of less than 3 MPa at 200° C. and a peak value of tan α of more than 1.55. In Comparative Examples 6 to 9, the tan δ peak temperature was less than 130°C.
The cast plates obtained in these comparative examples had poor ethanol resistance or were inferior to those of Examples 1-3.

(Comparative Example 4)
The methacrylic resin cast plate obtained in Comparative Example 4 had no sink marks and had a good appearance. In the cast plate obtained in this comparative example, the Mw of the non-crosslinked MMA polymer (P) was less than 500,000, and the content of the non-crosslinked MMA polymer (P) was more than 15% by mass. . In this comparative example, the amount of cross-linking agent used was less than in Examples 1-3.
The cast plate obtained in this comparative example has a storage elastic modulus (E′) in the rubbery flat region at 200° C. of less than 3 MPa, a tan α peak value of more than 1.55, and a tan δ peak temperature of It was less than 130°C.
In the cast plate obtained in this comparative example, the ethanol resistance of the processed end face was extremely poor, and the ethanol resistance of the main surface, which was the unprocessed end face, was also poor.

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

(Comparative Example 12)
In Comparative Example 12, no additional MMA was added during the preparation of the syrup (S), so the polymerizable raw material obtained had a high viscosity and was difficult to pour into a mold, making plate making impossible.

Claims (5)

Consisting of a methacrylic resin composition containing a non-crosslinked methyl methacrylate polymer (P) and a crosslinked methyl methacrylate polymer (C),
The non-crosslinked methyl methacrylate polymer (P) has a weight average molecular weight of 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 dynamic viscoelasticity measurement was performed, the storage elastic modulus (E') in the rubbery flat region was 3 MPa or more at 200°C, the tan δ peak value was 1.55 or less, and the tan δ peak temperature was 130°C. A methacrylic resin casting board which is the above. The methacrylic resin according to claim 1, wherein no cracks having a length of 0.5 mm or more occur when the cut end surface of the laser-cut methacrylic resin cast plate is wiped with ethanol at 20 to 25° C. 1200 times or more. system resin casting board. According to claim 1, when the cut end face of the cut methacrylic resin cast plate is flame-polished and then wiped with ethanol at 20 to 25° C. for 1200 times or more, no cracks having a length of 0.5 mm or more occur. The methacrylic resin cast board described. After buffing the cut end surface of the cut methacrylic resin cast plate, when wiping with ethanol at 20 to 25 ° C. for 1200 times or more, no cracks with a length of 0.5 mm or more are generated. The methacrylic resin cast board described. The methacrylic resin casting plate according to claim 1, wherein no cracks having a length of 0.5 mm or more occur when the laser-cut methacrylic resin casting plate is immersed in ethanol at 20 to 25°C for 24 hours. .