Methacrylic resin composition

Abstract

Provided is a methacrylic resin composition containing: a methacrylic resin; and coated particles in which silica composite oxide particles are coated with silica, wherein the methacrylic resin composition can improve the transparency and abrasion resistance of a molded body and more satisfactorily achieve a balance between the transparency and the abrasion resistance.

Description

Technical Field

[0001] The present invention relates to a methacrylic resin composition and a molded article thereof.

Background Art

[0002] For the purpose of enhancing the transparency and scratch resistance of a lamp cover for vehicles, a mode in which a thermoplastic resin (methacrylic resin) and silica composite oxide particles are blended in a resin composition as a material for the lamp cover is known (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the resin composition disclosed in Patent Document 1 above, although it is possible to improve the transparency and scratch resistance of the lamp cover and to improve the balance between them, there is still room for further improvement in the compatibility between transparency and scratch resistance.

Means for Solving the Problems

[0005] As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by containing predetermined particles in the resin composition, and have completed the present invention.

[0006] Therefore, the present invention provides the following [1] to [9]. 〔1〕 A methacrylic resin, Coated particles in which silica composite oxide particles are coated with silica, and A methacrylic resin composition containing the same. 〔2〕 The methacrylic resin composition according to 〔1〕, wherein the silica composite oxide is a silica-titania composite oxide. 〔3〕 The methacrylic resin composition according to 〔1〕 or 〔2〕, wherein the median diameter of the coated particles is 0.4 μm to 2.0 μm. 〔4〕 The methacrylic resin composition according to any one of 〔1〕 to 〔3〕, wherein the refractive index of the coated particles when irradiated with light having a wavelength of 589 nm at 25 °C is 1.474 to 1.494. 〔5〕 The methacrylic resin composition according to any one of 〔1〕 to 〔4〕, wherein the content of the coated particles is 0.001 part by mass to 5 parts by mass with respect to 100 parts by mass of the methacrylic resin. 〔6〕 The methacrylic resin composition according to 〔5〕, wherein the content of the coated particles is 0.06 part by mass to 0.6 part by mass with respect to 100 parts by mass of the methacrylic resin. 〔7〕 The methacrylic resin composition according to any one of 〔1〕 to 〔6〕, wherein the methacrylic resin contains 85% by mass or more of monomer units derived from methyl methacrylate. 〔8〕 A methacrylic resin composition containing a methacrylic resin and inorganic particles, wherein a molded article having a width of 75 mm, a length of 90 mm, and a thickness of 3 mm obtained by molding the methacrylic resin composition satisfies the following formulas (1) to (3). Haze 0 <4 (1) Haze 7 <4 (2) Haze 25 / Haze 7 <3.2 (3) (In the above formulas (1) to (3), Haze 0 represents the haze (%) of the molded article in a completely dry state. Haze 7 represents the haze (%) of the molded article after being kept in a completely dry state and then immersed in pure water at 80 °C for 7 days. Haze 25 represents the haze (%) of the molded article after being kept in a completely dry state and then immersed in pure water at 80 °C for 25 days.) A molded article containing the methacrylic resin composition according to any one of [1] to [8].

Advantages of the Invention

[0007] According to the methacrylic resin composition of the present invention, when used particularly as a material for a lamp cover for a vehicle, the transparency and scratch resistance of the lamp cover can be further improved, and the balance between transparency and scratch resistance can be made better.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be specifically described. The present invention is not limited to the specific embodiments shown below, and can be appropriately changed without departing from the object of the present invention.

[0009] 1. Methacrylic resin composition The methacrylic resin composition of the present embodiment contains a methacrylic resin and coated particles in which silica composite oxide particles are coated with silica. Hereinafter, it will be specifically described.

[0010] (1) Methacrylic resin The methacrylic resin contained in the methacrylic resin composition of the present embodiment is a polymer having monomer units derived from monomers having a methacrylic group.

[0011] Examples of the methacrylic resin include a methacrylic homopolymer containing only monomer units derived from an alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms, and monomer units derived from an alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms in an amount of 85% by mass or more and less than 100% by mass, and monomer units derived from a vinyl monomer copolymerizable with an alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms in an amount exceeding 0% by mass and 15% by mass or less.

[0012] Here, the "alkyl methacrylate having an alkyl group with 1 to 4 carbon atoms" is a compound represented by CH2=CH(CH3)COOR (where R is an alkyl group with 1 to 4 carbon atoms). The "vinyl monomer copolymerizable with the alkyl methacrylate having an alkyl group with 1 to 4 carbon atoms" is a monomer that is copolymerizable with the alkyl methacrylate having an alkyl group with 1 to 4 carbon atoms and has a vinyl group.

[0013] Examples of the alkyl methacrylate having an alkyl group with 1 to 4 carbon atoms include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, sec-butyl methacrylate, and isobutyl methacrylate. The alkyl methacrylate having an alkyl group with 1 to 4 carbon atoms is preferably methyl methacrylate. The alkyl methacrylate may be used alone or in combination of two or more.

[0014] Examples of the vinyl monomer copolymerizable with the alkyl methacrylate having 1 to 4 carbon atoms in the alkyl group include, for example, cyclohexyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, monoglycerol methacrylate, etc. (however, alkyl methacrylates having 1 to 4 carbon atoms in the alkyl group are excluded), acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, monoglycerol acrylate, etc., unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride, etc. or their acid anhydrides, nitrogen-containing monomers such as acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, diacetone acrylamide, dimethylaminoethyl methacrylate, etc., epoxy group-containing monomers such as allyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, etc., styrene-based monomers such as styrene, α-methylstyrene, etc.

[0015] In this embodiment, the alkyl methacrylate is preferably methyl methacrylate, and the methacrylic resin composition of this embodiment preferably contains 85% by mass or more of monomer units derived from methyl methacrylate.

[0016] In this embodiment, the difference between the refractive index of the methacrylic resin when irradiated with light of wavelength 589 nm at 25°C and the refractive index of the coating particles is preferably 0.03 or less, more preferably 0.02 or less, and even more preferably 0.01 or less. It is particularly preferable that the refractive indices of the methacrylic resin and the coating particles are the same. If the difference in the refractive indices of the methacrylic resin and the coating particles is made smaller, especially 0.03 or less, the transparency of the molded body can be made higher, and thus a molded body excellent in both transparency and scratch resistance can be obtained.

[0017] The refractive index of the methacrylic resin can be measured by any suitable conventional measurement method such as the critical angle method, V-block method, and immersion method.

[0018] As a method for producing a methacrylic resin, an alkyl methacrylate having an alkyl group with 1 to 4 carbon atoms and, if necessary, a vinyl monomer copolymerizable with the alkyl methacrylate having an alkyl group with 1 to 4 carbon atoms are used as monomer components, and a bulk polymerization method, solution polymerization method, suspension polymerization method, emulsion polymerization method, etc. can be used. Among them, the bulk polymerization method is preferred.

[0019] Since the bulk polymerization method does not use a polymerization stabilizer, a methacrylic resin with better appearance can be obtained. Also, unlike the case of suspension polymerization, the polymerization temperature is higher than 100°C, and as a result, the syndiotacticity of the methacrylic resin tends to decrease, so the fluidity of the methacrylic resin further increases. When performing continuous bulk polymerization, for example, a partial polymer obtained by continuously supplying the above monomer components and, if necessary, a polymerization initiator, a chain transfer agent, etc. into a reaction vessel and retaining them in the reaction vessel for a predetermined time can be continuously withdrawn, so that the methacrylic resin can be efficiently polymerized and produced.

[0020] In the production of the methacrylic resin contained in the methacrylic resin composition of the present invention by the bulk polymerization method, the polymerization temperature is preferably 110 to 190°C.

[0021] In the above method for producing a methacrylic resin, for example, additives such as a polymerization initiator and a chain transfer agent may be used. As the polymerization initiator, for example, a radical initiator can be used.

[0022] Examples of radical initiators include azo compounds such as azobisisobutyronitrile, azobisdimethylvaleronitrile, azobiscyclohexanenitrile, 1,1'-azobis(1-acetoxy-1-phenylethane), dimethyl 2,2'-azobisisobutyrate, 4,4'-azobis-4-cyanovaleric acid; organic peroxides such as benzoyl peroxide, lauroyl peroxide, acetyl peroxide, caprylyl peroxide, 2,4-dichlorobenzoyl peroxide, isobutyl peroxide, acetylcyclohexylsulfonyl peroxide, tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, tert-butyl peroxyneoheptanoate, tert-butyl peroxy-2-ethylhexanoate, 1,1-di(tert-butylperoxy)cyclohexane, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(tert-hexylperoxy)-3,3,5-trimethylcyclohexane, diisopropyl peroxydicarbonate, diisobutyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, di-n-butyl peroxydicarbonate, bis(2-ethylhexyl) peroxydicarbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, tert-amyl peroxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutyl peroxy-ethylhexanoate, 1,1,2-trimethylpropyl peroxy-2-ethylhexanoate, tert-butyl peroxyisopropyl monocarbonate, tert-amyl peroxyisopropyl monocarbonate, tert-butyl peroxy-2-ethylhexyl carbonate, tert-butyl peroxyallyl carbonate, tert-butyl peroxyisopropyl carbonate, 1,1,3,3-tetramethylbutyl peroxyisopropyl monocarbonate, 1,1,2-trimethylpropyl peroxyisopropyl monocarbonate, 1,1,3,3-tetramethylbutyl peroxyisononanoate, 1,1,2-trimethylpropyl peroxy-isononanoate, tert-butyl peroxybenzoate, etc.

[0023] The polymerization initiator may be used alone as only one type, or two or more types may be used.

[0024] The polymerization initiator can be selected according to the types of methacrylic resin to be synthesized, raw material monomers to be used, etc. As the radical initiator, a polymerization initiator having a half-life within 1 minute at the polymerization temperature is preferable.

[0025] In this embodiment, the chain transfer agent may be any of monofunctional and polyfunctional chain transfer agents. Specific examples of the chain transfer agent include, for example, alkyl mercaptans such as n-propyl mercaptan, isopropyl mercaptan, n-butyl mercaptan, tert-butyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, 2-ethylhexyl mercaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan; aromatic mercaptans such as phenyl mercaptan and thiocresol; mercaptans having 18 or less carbon atoms such as ethylene thioglycol; polyhydric alcohols such as ethylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, and sorbitol; compounds obtained by esterifying a hydroxyl group with thioglycolic acid or 3-mercaptopropionic acid, 1,4-dihydronaphthalene, 1,4,5,8-tetrahydronaphthalene, β-terpinene, terpinolene, 1,4-cyclohexadiene, hydrogen sulfide, and the like. The chain transfer agent may be used alone as only one type, or two or more types may be used.

[0026] The type and amount of the chain transfer agent can be appropriately selected according to the types of methacrylic resin to be synthesized, monomer components to be used, etc. As the chain transfer agent, n-octyl mercaptan or n-dodecyl mercaptan is preferable.

[0027] In addition to the above monomer components, polymerization initiator, chain transfer agent, etc., for example, a release agent, a rubber-like polymer such as butadiene and styrene-butadiene rubber (SBR), a heat stabilizer, an ultraviolet absorber, etc. may be used.

[0028] Here, the release agent is a component used to improve the moldability of the methacrylic resin composition. The heat stabilizer is a component used to suppress the thermal decomposition of the methacrylic resin. The ultraviolet absorber is a component used to suppress the deterioration of the methacrylic resin due to ultraviolet rays.

[0029] In this embodiment, the release agent is not particularly limited. Examples of the release agent include higher fatty acid esters, higher aliphatic alcohols, higher fatty acids, higher fatty acid amides, and higher fatty acid metal salts. Note that the release agent may be used alone as only one kind, or may be used in combination of two or more kinds.

[0030] The amount of the release agent used is preferably 0.01 to 1.0 part by mass, and more preferably 0.01 to 0.50 part by mass, based on 100 parts by mass of the methacrylic resin. When the methacrylic resin composition of the present invention contains two or more kinds of methacrylic resins, "100 parts by mass of the methacrylic resin" means the total amount of the two or more kinds of methacrylic resins.

[0031] In this embodiment, the heat stabilizer is not particularly limited. Examples of the heat stabilizer include hindered phenol-based heat stabilizers, phosphorus-based heat stabilizers, and organic disulfide compounds. Among these, organic disulfide compounds are preferred. Note that the heat stabilizer may be used alone as only one kind, or may be used in combination of two or more kinds.

[0032] The amount of the heat stabilizer used is preferably 1 to 2000 mass ppm with respect to 100 parts by mass of the methacrylic resin. In order to produce a molded article from the methacrylic resin composition, when molding the methacrylic resin composition (more specifically, the methacrylic resin composition after devolatilization), the molding temperature may be set higher for the purpose of enhancing the molding efficiency. In such a case, when a heat stabilizer is blended, the resin composition can be molded more effectively.

[0033] Examples of the ultraviolet absorber include benzophenone-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, malonic ester-based ultraviolet absorbers, and oxalanilide-based ultraviolet absorbers. The ultraviolet absorber may be used alone as only one kind, or may be used in combination of two or more kinds. Among these, benzotriazole-based ultraviolet absorbers, malonic ester-based ultraviolet absorbers, and oxalanilide-based ultraviolet absorbers are preferable.

[0034] The amount of the ultraviolet absorber used is preferably 5 to 1000 mass ppm with respect to 100 parts by mass of the methacrylic resin contained in the methacrylic resin composition.

[0035] (2) Coated particles The methacrylic resin composition of the present embodiment contains coated particles in which silica composite oxide particles are coated with silica.

[0036] The "silica composite oxide particles" are particulate substances that can be the core of the "coated particles" of the present embodiment. Here, the "silica composite oxide" refers to an oxide in which a part of the silicon (Si) element in silica is replaced by another element, in other words, an oxide in which silicon and another element together form a uniform structure.

[0037] The structure of such a silica composite oxide can be analyzed by TEM-EDX (Transmission Electron Microscope-Energy Dispersive X-ray spectrometry), X-ray absorption fine structure (XAFS) spectrum, or the like.

[0038] The above-mentioned "other elements" refer to elements other than silicon and oxygen, and are not particularly limited as long as they can form oxide particles with a uniform structure together with silicon.

[0039] Examples of the above-mentioned "other elements" include elements from Group 2 to Group 14 of the periodic table. Preferably, the "other elements" are titanium, zirconium, aluminum, zinc, chromium, manganese, magnesium, cerium, boron, iron, indium, and tin. More preferably, the "other elements" are titanium, zirconium or aluminum, and even more preferably titanium.

[0040] Specific examples of the above-mentioned silica composite oxide particles include silica-titania composite oxide particles, silica-zirconia composite oxide particles, and silica-alumina composite oxide particles.

[0041] The above-mentioned silica composite oxide particles are preferably silica-titania composite oxide particles or silica-zirconia composite oxide particles, and more preferably silica-titania composite oxide particles.

[0042] In this embodiment, the shape of the silica composite oxide particles is not particularly limited. The silica composite oxide particles can be, for example, substantially spherical, rectangular parallelepiped-shaped, or pulverized with a plurality of corners. The shape of the silica composite oxide particles is preferably substantially spherical, and more preferably truly spherical.

[0043] In this embodiment, the average primary particle diameter of the silica composite oxide particles is usually 0.1 μm or more and 2.0 μm or less, preferably 0.2 μm or more and 2.0 μm or less, more preferably 0.3 μm or more and 2.0 μm or less, and even more preferably 0.4 μm or more and 2.0 μm or less.

[0044] Here, the average primary particle diameter of the silica composite oxide particles can be measured, for example, by reading from an observation image of the particles using a scanning electron microscope. If the average primary particle diameter of the silica composite oxide particles is within the above range, a molded article excellent in both scratch resistance and transparency can be produced. Here, the primary particle means the particle that is the smallest unit constituting the silica composite oxide particles.

[0045] The average particle diameter (diameter) of the silica composite oxide particles is usually 0.1 μm or more and 2.0 μm or less, preferably 0.2 μm or more and 2.0 μm or less, more preferably 0.3 μm or more and 2.0 μm or less, and still more preferably 0.4 μm or more and 2.0 μm or less.

[0046] The average particle diameter of the silica composite oxide particles can be measured, for example, by the laser diffraction scattering method. By setting the average particle diameter of the silica composite oxide particles within the above range, both the scratch resistance and transparency of the molded article formed from the methacrylic resin composition of the present embodiment can be improved.

[0047] In this specification, the average particle diameter means the median diameter (d50) (hereinafter referred to as the median diameter).

[0048] In the present embodiment, the refractive index of the silica composite oxide particles (refractive index when irradiated with light of wavelength 589 nm at 25°C) is preferably 1.47 or more and 1.60 or less, more preferably 1.47 or more and 1.52 or less, and still more preferably 1.47 or more and 1.50 or less.

[0049] The refractive index of the silica composite oxide particles can be adjusted to any suitable refractive index by changing the composition ratio of silicon and other elements in the silica composite oxide particles.

[0050] Note that the refractive index of the silica composite oxide particles can be measured by any suitable conventionally known method such as the immersion method.

[0051] If the refractive index of the silica composite oxide particles is within the above range, the transparency of the molded article formed from the methacrylic resin composition of the present embodiment can be further enhanced.

[0052] The silica composite oxide particles can be produced by any suitable known production method such as the flame melting method, the flame hydrolysis method, the sol-gel method, etc.

[0053] The coated particles of the present embodiment have a form in which the surface of the silica composite oxide particles already described is coated with silica.

[0054] Here, the "coating" includes not only the mode in which the entire surface of the silica composite oxide particles is completely covered with silica, but also the mode in which only a part of the surface of the silica composite oxide particles is covered with silica.

[0055] The thickness of the layer composed of silica (hereinafter referred to as the surface silica layer) that can constitute the surface of the coated particles of the present embodiment is not particularly limited.

[0056] The thickness of the surface silica layer can be adjusted to any suitable thickness in consideration of the balance between the transparency and the scratch resistance of the molded article formed from the methacrylic resin composition of the present embodiment.

[0057] The thickness of the surface silica layer is preferably, for example, 1 nm to 30 nm, and more preferably 3 nm to 15 nm.

[0058] The thickness of the surface silica layer can be adjusted, for example, by adjusting the ratio of the amount of the raw material of the surface silica layer to the specific surface area of the silica composite oxide particles.

[0059] Also, the thickness of the surface silica layer can be determined, for example, by calculation based on the charged composition ratio of the raw materials, and further can also be determined by observation with a transmission electron microscope.

[0060] Here, the observation by a transmission electron microscope can be performed by, for example, embedding the coating particles of the present embodiment in an acrylic resin, an epoxy resin, and then polishing by any conventionally known suitable polishing method to expose the cross-section of the coating particles.

[0061] The median diameter (diameter) of the coating particles is usually 0.1 μm or more and 2.0 μm or less (0.1 μm to 2.0 μm), preferably 0.2 μm or more and 2.0 μm or less (0.2 μm to 2.0 μm), more preferably 0.3 μm or more and 2.0 μm or less (0.3 μm to 2.0 μm), and even more preferably 0.4 μm or more and 2.0 μm or less (0.4 μm to 2.0 μm).

[0062] The median diameter of the coating particles can be measured, for example, by a laser diffraction scattering method.

[0063] By setting the median diameter of the coating particles within the above range, both the scratch resistance and transparency of the molded body formed from the methacrylic resin composition of the present embodiment can be improved.

[0064] In the present embodiment, the refractive index of the coating particles (refractive index when irradiated with light of wavelength 589 nm at 25°C) is preferably 1.470 or more and 1.600 or less (1.470 to 1.600), more preferably 1.474 or more and 1.520 or less (1.474 to 1.520), and even more preferably 1.474 or more and 1.494 or less (1.474 to 1.494).

[0065] The refractive index of the coating particles can be measured by any conventionally known suitable method such as an immersion method using light of wavelength 589.3 nm (sodium D line), for example.

[0066] If the refractive index of the coating particles is within the above range, the transparency of the molded body formed from the methacrylic resin composition of the present embodiment can be further enhanced.

[0067] In this embodiment, the coated particles obtained by coating the surface of the silica composite oxide particles with silica can be produced, for example, by a method in which tetraethyl silicate is dropped into a liquid in which the silica composite oxide particles are dispersed in an alkaline alcohol solution, and the hydrolyzate of tetraethyl silicate is deposited on the surface of the silica composite oxide particles.

[0068] The coated particles thus produced are further subjected to a heat (calcination) treatment to remove moisture, organic substances, etc. contained in the particles. The temperature of this heat treatment is not particularly limited. From the viewpoint of suppressing sintering between particles and improving monodispersity, the temperature of the heat treatment is preferably 900°C to 1200°C, more preferably 950°C to 1100°C. Also, the time required for the heat treatment is not particularly limited. The heat treatment time is preferably 30 minutes to 10 hours.

[0069] When, for example, silica particles with a median diameter of 1 μm or less are heat-treated at a temperature of 1000°C or higher, the particles may sinter together and the monodispersity of the particles may decrease. However, if the surface of the silica composite oxide particles is coated with chemically inert silica like the coated particles of this embodiment, even if heat-treated at a temperature of 1000°C or higher, the monodispersity of the particles can be improved.

[0070] The content of the coated particles contained in the methacrylic resin composition of this embodiment is preferably 0.001 part by mass or more and 5 parts by mass or less (0.001 part by mass to 5 parts by mass), more preferably 0.01 part by mass or more and 5 parts by mass or less (0.01 part by mass to 5 parts by mass), still more preferably 0.01 part by mass or more and 1 part by mass or less (0.01 part by mass to 1 part by mass), and particularly preferably 0.03 part by mass or more and 0.45 part by mass or less (0.03 part by mass to 0.45 part by mass) with respect to 100 parts by mass of the methacrylic resin. The content of the coated particles in the methacrylic resin composition can be measured, for example, using the ICP - AES method.

[0071] Also, the compounding concentration of the coated particles when melt-kneading the methacrylic resin and the coated particles may be used as the content. The value of the compounding concentration and the value of the content are generally the same. From the viewpoint of accuracy, the content of the coated particles is preferably measured by the ICP-AES method.

[0072] By setting the content of the coated particles to 0.001 part by mass or more, a molded body of a methacrylic resin composition having high scratch resistance can be obtained. Also, by setting the content of the coated particles to 5 parts by mass or less, a molded body having high transparency can be obtained.

[0073] If the content of the coated particles is within the above range, both the scratch resistance and transparency of the molded body formed from the methacrylic resin composition of the present embodiment can be improved, and furthermore, the water resistance can be improved.

[0074] (3) Other components The methacrylic resin composition of the present embodiment may further contain other components as necessary in addition to the methacrylic resin and the coated particles already described. Examples of other components include, for example, ultraviolet absorbers, antioxidants, release agents, antistatic agents, and flame retardants.

[0075] Examples of ultraviolet absorbers include benzophenone-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, malonic ester-based ultraviolet absorbers, and oxalanilide-based ultraviolet absorbers.

[0076] Examples of antioxidants include phenolic antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants.

[0077] Examples of release agents include higher fatty acid esters, higher aliphatic alcohols, higher fatty acids, higher fatty acid amides, higher fatty acid metal salts, and fatty acid derivatives.

[0078] Examples of the antistatic agent include conductive inorganic particles, tertiary amines, quaternary ammonium salts, cationic acrylate derivatives, and cationic vinyl ether derivatives.

[0079] Examples of the flame retardant include cyclic nitrogen compounds, phosphorus-based flame retardants, silicon-based flame retardants, cage-like silsesquioxanes or their partially cleaved structures, and silica-based flame retardants.

[0080] 2. Method for producing methacrylic resin composition Examples of the method for producing the methacrylic resin composition of the present embodiment include a method of kneading the above methacrylic resin, coated particles, and, if necessary, the above other components (ultraviolet absorber, antioxidant, release agent, antistatic agent, flame retardant, etc.) by any conventionally known suitable method. In the present embodiment, the conditions for kneading are not particularly limited. The conditions for kneading can be any suitable conditions in consideration of the selected components, their amounts, properties, etc.

[0081] Specifically, the methacrylic resin composition of the present embodiment can be produced by adding a predetermined amount of coated particles and, if necessary, the above other selected components to 100 parts by mass of the prepared methacrylic resin, mixing them, and then melt-kneading using any conventionally known suitable extruder (e.g., twin-screw extruder).

[0082] The conditions for melt-kneading can be, for example, setting the temperature between the raw material inlet and the outlet of the extruder to 200°C to 270°C.

[0083] After melt-kneading as described above, for example, extruding in a strand form from the extruder, cooling with water to solidify, and cutting to a desired length with a strand cutter, a pellet-shaped methacrylic resin composition can be obtained.

[0084] 3. Molded body The methacrylic resin composition of this embodiment can be formed into a molded article of any shape by molding it by any conventionally known and suitable molding method (the method for manufacturing the molded article will be described later). That is, the molded article of this embodiment contains the methacrylic resin composition already described.

[0085] In this embodiment, the size such as the shape and thickness of the molded article is not particularly limited. The thickness of the molded article is preferably 0.5 mm or more and 8 mm or less, more preferably 1 mm or more and 6 mm or less, and even more preferably 1 mm or more and 4 mm or less. By setting the thickness of the molded article within the above range, a molded article excellent in transparency can be obtained.

[0086] Also, using the methacrylic resin composition of this embodiment, a layer constituting a laminate can be formed. That is, the molded article of this embodiment includes a laminate including a layer containing the methacrylic resin composition already described.

[0087] A molded article of this embodiment, which is a molded article having a width of 75 mm, a length of 90 mm, and a thickness of 3 mm, obtained by molding a methacrylic resin composition containing a methacrylic resin and inorganic particles satisfies the following formulas (1) to (3). Haze 0 <4 (1) Haze 7 <4 (2) Haze 25 / Haze 7 <3.2 (3)

[0088] In the above formulas (1) to (3), Haze 0 represents the haze (%) when the molded article is in a completely dry state. Haze 7 represents the haze (%) after the molded article is in a completely dry state and then immersed in pure water at 80°C for 7 days. Haze 25 represents the haze (%) after the molded article is in a completely dry state and then immersed in pure water at 80°C for 25 days.

[0089] Here, the "inorganic particles" may include particles containing an inorganic material that satisfies the above requirements, in addition to the coated particles already described.

[0090] Also, the absolutely dry state means that the molded body is dried by leaving it standing in an environment of a temperature of 80°C and a pressure of 100 mmHg or less for 120 hours or more, and the amount of change in the weight of the molded body is less than 0.05% compared to the weight 120 hours before, and the amount of change in the haze of the molded body is less than 5% of the haze 120 hours before.

[0091] (1) Haze and its measurement method In the present embodiment, the haze of the molded body can be measured in accordance with JIS K 7136 (corresponding to ISO14782, Plastics - Determination of haze for transparent materials) applicable to objects with a haze of 40% or less. Specific description is given below.

[0092] First, the haze refers to the percentage of transmitted light that has deviated from the incident light by 0.044 rad (2.5°) or more due to forward scattering among the transmitted light passing through the test piece which is the molded body of the present embodiment.

[0093] In the present embodiment, the haze can be measured by any conventionally known suitable device. Examples of the device for measuring the haze include a device equipped with a stable light source, a connecting optical system, an integrating sphere having an opening, and a photometer. The photometer is preferably composed of a light receiver, a signal processing device, and a display device or a recorder.

[0094] For the measurement of the haze, a plurality of test pieces cut out from the molded body formed from the above methacrylic resin composition are used. The size of the test piece is not limited as long as it is large enough to cover the inlet opening and the compensation opening of the integrating sphere.

[0095] First, before the measurement of the haze, the test piece is conditioned for 15 minutes under the conditions of a temperature of (23 ± 2)°C and a relative humidity of (50 ± 10)% in accordance with ISO291.

[0096] Next, the device used for measurement is installed in an atmosphere maintained at a temperature of (23 ± 2)°C and a relative humidity of (50 ± 10)% as required, and sufficient time is allowed to reach thermal equilibrium before measurement.

[0097] Next, the test piece is installed in the device, the light beam of the incident light transmitted through the test piece is observed, and the haze (%) is calculated by the following formula. Formula: Haze = [(τ4 / τ2) - τ3(τ2 / τ1)] × 100

[0098] In the above formula, τ1 represents the light beam of the incident light, τ2 represents the total light beam transmitted through the test piece, τ3 represents the light beam diffused by the device, τ4 represents the light beam diffused by the device and the test piece.

[0099] (2) Evaluation of scratch resistance The scratch resistance of the molded body of this embodiment can be evaluated based on the change in haze (refractive index) before and after the scratch resistance test.

[0100] (Scratch test) When evaluating the scratch resistance of the molded body, a scratch test is performed by rubbing the surface of the molded body with steel wool.

[0101] First, the molded body used for the test is left standing under high temperature and reduced pressure as described above to make it in a completely dry state.

[0102] Specifically, for example, the molded body can be made in a completely dry state by leaving it standing in an oven at a temperature of 80°C while reducing the pressure to 85 mmHg to 90 mmHg using a vacuum pump.

[0103] Next, the molded body in a completely dry state is left standing in an environment at a temperature of 80°C and a relative humidity of 35% for 13 days to bring it to an equilibrium state.

[0104] Incidentally, prior to the abrasion test, the initial haze of the molded body is measured in advance in accordance with JIS K7136 as described above.

[0105] Next, an abrasion test is carried out. Specifically, the surface of the molded body is pressed with steel wool (grade: #0000) under a load of 14 kPa, and is rubbed by reciprocating 11 times at a speed of 15 cm / second in a direction perpendicular to the extending direction of the fibers constituting the steel wool, thereby causing abrasion. Subsequently, the haze of the molded body after the abrasion test is measured in accordance with JIS K7136 as described above.

[0106] (Calculation of Δ haze) Based on the haze of the molded body before and after the abrasion test measured as described above, Δ haze (unit: %), which is the amount of change in haze before and after the abrasion test, is calculated.

[0107] Here, in the methacrylic resin composition of the present embodiment, when the content of the coating particles is a parts by mass with respect to 100 parts by mass of the content of the methacrylic resin, the value calculated by the following formula is defined as the Δ haze threshold value (unit: %). Formula: -1.43×ln(a) - 0.7

[0108] In the methacrylic resin composition of the present embodiment, if the content of the coating particles is higher, usually, the value of Δ haze in the molded body becomes smaller. Therefore, the Δ haze threshold value is a reference value for more substantially evaluating the abrasion resistance of the molded body in consideration of the content of the coating particles.

[0109] In the present embodiment, when the value of Δ haze is below the Δ haze threshold value, it is evaluated that the abrasion resistance of the molded body is effectively improved even if the content of the coating particles is small.

[0110] More specifically, in the present embodiment, when the Δ haze / Δ haze threshold is 1.00 or more, it is evaluated that "the scratch resistance is not improved", and when the Δ haze / Δ haze threshold is less than 1.00, it is evaluated that "the scratch resistance is improved", and when the Δ haze / Δ haze threshold is 0.80 or less, it is evaluated that "the scratch resistance is further improved".

[0111] Therefore, in the present embodiment, the Δ haze / Δ haze threshold of the molded body is preferably less than 1.00, more preferably 0.80 or less, and even more preferably 0.71 or less.

[0112] In the present embodiment, the initial haze of the molded body is preferably less than 4%, more preferably 2.4% or less, and even more preferably 2.0% or less.

[0113] Also, in the present embodiment, the Δ haze of the molded body is preferably 3.88% or less, more preferably 3.40% or less, and even more preferably 2.32% or less.

[0114] (3) Evaluation of water resistance The water resistance of the molded body of the present embodiment can be evaluated based on the change in haze before and after the water resistance test.

[0115] In the present embodiment, the "water resistance of the molded body" refers to the resistance to the "deterioration of the haze of the molded body" over time due to contact with water (including moisture in the air), that is, the resistance to the "decrease in transparency of the molded body".

[0116] In this specification, the haze of the molded body subjected to the water resistance test is denoted as "Haze x ". Here, X represents the number of days that the molded body in the absolutely dry state is immersed in pure water at 80°C, and Haze 0 represents the haze of the initial molded body in the absolutely dry state that is not immersed in pure water.

[0117] In this embodiment, the water resistance test of the molded body can be carried out by immersing the molded body in a dry state in pure water at 80°C for X days to make it in a water-absorbed state, and then measuring the haze of the molded body in the water-absorbed state according to JIS K7136 as described above.

[0118] The methacrylic resin contained in the molded body usually reaches an equilibrium water absorption rate (water-absorbed state) by being immersed in pure water at 80°C for 7 days. When the water absorption rate of the methacrylic resin reaches equilibrium, the amount of water in the molded body increases. Therefore, the refractive index of the coated particles (inorganic particles) changes due to water absorption, and consequently, the difference in refractive index between the methacrylic resin and the coated particles (inorganic particles) may also change.

[0119] Therefore, the water resistance of the molded body is evaluated preferably by three indexes: Haze 0 (the initial haze without immersion in pure water), Haze 7 (the haze after immersion in pure water for 7 days), and Haze 25 (the haze after immersion in pure water for 25 days) / Haze 7 .

[0120] If both Haze 0 and Haze 7 are less than 4%, the difference in refractive index between the methacrylic resin and the coated particles (inorganic particles) contained in both the molded body in a dry state and the molded body in a water-absorbed state is small, and it can be said that the transparency is high regardless of the amount of water in the molded body. Therefore, it can be evaluated that the water resistance of the molded body is excellent. Also, if Haze 25 / Haze 7 is less than 3.2, it can be said that the change in refractive index of the coated particles (inorganic particles) over time due to water absorption is small. Therefore, it can be evaluated that the water resistance of the molded body is excellent.

[0121] Therefore, Haze 25 / Haze 7 is preferably less than 3.2, more preferably 2.2 or less, and even more preferably 1.9 or less.

[0122] Also, in this embodiment, Haze0 is preferably less than 4%, more preferably 1.4% or less, and even more preferably 1.1% or less.

[0123] Furthermore, Haze 7 is preferably less than 4%, more preferably 3.7% or less, and even more preferably 2.1% or less.

[0124] Furthermore, Haze 25 is preferably less than 4.2%, more preferably 4.0% or less, and even more preferably 3.3% or less.

[0125] 4. Method for manufacturing a molded article Examples of the method for manufacturing the molded article of the present embodiment include, for example, a method of molding the methacrylic resin composition already described using any conventionally known and suitable molding machine. The method for manufacturing the molded article of the present embodiment is not particularly limited. Examples of the method for manufacturing the molded article of the present embodiment include an extrusion molding method and an injection molding method.

[0126] Since a molded article having a complex shape can be obtained, as the method for manufacturing the molded article of the present embodiment, for example, it is preferable to use an injection molding method in which an injection molding machine is used as the molding machine and the methacrylic resin composition is injected into the mold of the molding machine for molding.

[0127] Hereinafter, the method for manufacturing the molded article of the present embodiment will be described by taking the manufacturing method by the injection molding method as an example.

[0128] The method for manufacturing the molded article of the present embodiment includes a step of preparing a methacrylic resin composition and a step of forming a molded article by injection molding the prepared methacrylic resin composition. Hereinafter, each step will be specifically described.

[0129] (1) Step of preparing a methacrylic resin composition This step is to prepare a methacrylic resin composition for use in an injection molding machine. Since the "methacrylic resin composition" has already been described as above, a detailed description thereof will be omitted.

[0130] In this embodiment, when manufacturing a molded body by an injection molding method, from the viewpoint of further improving the manufacturing efficiency, the methacrylic resin composition is preferably in the form of pellets as already described. The shape, size, etc. of the pellet-shaped methacrylic resin composition can be set within an arbitrarily suitable range in consideration of the injection molding apparatus to be used and the conditions to be applied.

[0131] (2) Step of forming a molded body by injection molding the methacrylic resin composition This step is to form a methacrylic resin composition into a molded body by an injection molding machine. Specifically, this step is performed by melting the methacrylic resin composition and injecting it into the cavity of the mold provided in the injection molding machine for filling and molding, then cooling, and finally peeling and removing the molded body formed from the methacrylic resin composition from the mold.

[0132] More specifically, the molded body can be manufactured by putting the pellet-shaped methacrylic resin composition into the cylinder from the hopper provided in the injection molding machine, melting it while rotating the screw, then retracting the screw to fill a predetermined amount of the methacrylic resin composition into the cylinder, advancing the screw to inject the melted methacrylic resin composition into the cavity of the mold at a predetermined injection temperature and a predetermined injection speed while applying pressure, holding the pressure for a certain period until the mold is sufficiently cooled, and then opening the mold, peeling it, and taking it out.

[0133] In this embodiment, the conditions for manufacturing the molded body can be set as appropriate and are not particularly limited. In this embodiment, for example, the temperature inside the cylinder of the injection molding machine is set to about 200°C to 270°C, the holding pressure is set to about 80 MPa, the mold temperature is set to about 60°C, and the cooling time is set to about 45 seconds. By performing injection molding under these conditions, a molded body with a desired shape can be manufactured.

[0134] In this embodiment, the temperature inside the cylinder of the injection molding machine is preferably 200°C to 270°C, and more preferably 220°C to 260°C.

[0135] In this embodiment, the holding pressure (MPa) in the injection molding machine is preferably 10 MPa to 100 MPa, and more preferably 20 MPa to 90 MPa.

[0136] In this embodiment, the mold temperature (°C) of the injection molding machine is preferably 30°C to 80°C, and more preferably 50°C to 70°C.

[0137] In this embodiment, the cooling time (seconds) is the time for cooling the molten methacrylic resin composition filled in the cavity in the mold while maintaining the pressure with the mold. The cooling time is preferably 20 to 150 seconds, and more preferably 30 to 60 seconds.

[0138] 5. Use of the Molded Body The molded body of this embodiment has high transparency and scratch resistance, and further has excellent water resistance. Therefore, it can be suitably used, for example, as a lamp cover for vehicles such as automobiles and motorcycles.

[0139] Examples of lamp covers for vehicles include covers for headlights, tail lights, stop lights, turn signals, fog lights, side marker lights, and reverse lights.

Examples

[0140] Hereinafter, the present invention will be described more specifically by way of examples. The present invention is not limited to the examples.

[0141] <Measurement of median diameter of inorganic particles> The median diameter of the inorganic particles (silica composite oxide particles and coated particles) was measured by the laser diffraction scattering method (unit: μm).

[0142] <Measurement of refractive index nD of inorganic particles> The refractive index nD of the inorganic particles was measured by the immersion method using light with a wavelength of 589.3 nm (sodium D line).

[0143] <Measurement of transparency of molded body> The transparency of the molded body was measured by measuring the haze of the molded body at 23°C according to JIS K7136 (unit: %).

[0144] The inorganic particles used in the examples and comparative examples are shown in Table 1 below.

[0145]

Table 1

[0146] <Production of methacrylic resin A> In a polymerization reactor equipped with a stirrer, a mixture of 97.5 parts by mass of methyl methacrylate and 2.5 parts by mass of methyl acrylate, 0.016 parts by mass of 1,1-di(tert-butylperoxy)cyclohexane, and 0.16 parts by mass of n-octyl mercaptan were continuously supplied respectively, and a polymerization reaction was carried out at 175°C with an average residence time of 43 minutes.

[0147] Next, the reaction solution (partial polymer) flowing out from the polymerization reactor was preheated, and then the reaction solution was supplied to a devolatilization extruder to vaporize and recover the unreacted monomer components, and pellet-shaped methacrylic resin A was obtained.

[0148] The obtained methacrylic resin A had a monomer unit derived from methyl methacrylate at 97.5% by mass and a monomer unit derived from methyl acrylate at 2.5% by mass, and had a melt flow rate (MFR) of 2 g / 10 min measured according to JIS K7210 (ISO 1133).

[0149] [Example 1] <Production of Methacrylic Resin Composition (Melt Kneading)> The above-produced methacrylic resin A and SiTi07488-S, which is a coated particle with a content of 0.03 parts by mass based on 100 parts by mass of methacrylic resin A, were charged as raw materials and mixed. Then, a twin-screw extruder (model: TEX30SS-30AW-2V, manufactured by Japan Steel Works, Ltd.) was used to melt-knead under the following kneading conditions, extruded into strands, cooled with water and solidified, and cut with a strand cutter to obtain a pelletized methacrylic resin composition. The inorganic particles (coated particles) and their addition amounts are shown in Table 2.

[0150] (Conditions for Melt Kneading) Regarding the temperature of the extruder, for the eight heaters arranged at intervals from the raw material inlet to the outlet, they were set at 200°C, 200°C, 210°C, 220°C, 230°C, 240°C, 240°C, and 250°C in order from the raw material inlet side. The screw rotation speed and the raw material feeding rate are as follows. Screw rotation speed: 200 rpm Raw material feeding rate: 14 kg / h

[0151] <Production of Molded Body (Injection Molding)> The obtained pelletized methacrylic resin composition was molded into a flat plate with a length of 150 mm × width of 90 mm × thickness of 3.0 mm using an injection molding machine (EC130SXII-4A, manufactured by Toshiba Machine Co., Ltd.) under the following molding conditions to obtain a molded body.

[0152] (Conditions for Injection Molding) Regarding the temperature inside the cylinder, for five heaters arranged at intervals from the raw material inlet to the outlet, the temperatures were set to 60°C, 230°C, 240°C, 250°C, and 250°C respectively, starting from the raw material inlet side. Other molding conditions are as follows. Injection speed: 90 mm / second Maximum injection pressure: 200 MPa Holding pressure: 80 MPa Mold temperature: 60°C Cooling time: 45 seconds

[0153] The obtained molded body was left standing in an oven at 80°C for 16 hours, and then gradually cooled to 40°C over 4 hours, and the abrasion resistance was evaluated as follows.

[0154] (Evaluation of the abrasion resistance of the molded body) A scratch test was conducted by scratching the surface of the molded body using steel wool. First, the molded body used for measurement was left standing in an environment at a temperature of 80°C and a pressure of 100 mmHg or less until it reached a completely dry state. Specifically, the molded body was placed in an oven with the temperature set to 80°C while reducing the pressure to 100 mmHg or less, for example, to about 85 mmHg to 90 mmHg, using a vacuum pump, thereby achieving a completely dry state.

[0155] Thereafter, it was left standing in an environment at a temperature of 80°C and a relative humidity of 35% for 13 days. Then, #0000 steel wool was pressed against the surface of the molded body at a load of 14 kPa, and the surface was scratched by rubbing it 11 times in a direction perpendicular to the extending direction of the fibers of the steel wool at a speed of 15 cm / second.

[0156] As described above, the haze of the molded body before and after the scratch test was measured in accordance with JIS K7136, and the change amount of haze (Δhaze (unit: %)) before and after the abrasion test was calculated.

[0157] Here, when the content of the coating particles is a mass part with respect to 100 mass parts of the methacrylic resin, "-1.43×ln(a) - 0.7" is defined as the Δhaze threshold value (unit: %).

[0158] When the Δ haze is below the Δ haze threshold value, it means that even with the addition of a small amount of coated particles, the scratch resistance of the molded body is efficiently improved.

[0159] Therefore, when the Δ haze / Δ haze threshold value is 1.00 or more, it is evaluated as "the scratch resistance is not improved (×: not acceptable)", and when the Δ haze / Δ haze threshold value is less than 1.00, it is evaluated as "the scratch resistance is improved (〇: good)", and when the Δ haze / Δ haze threshold value is 0.80 or less, it is evaluated as "the scratch resistance is further improved (◎: excellent)". When the Δ haze is 10% or more, since the scratch resistance is extremely poor, regardless of the Δ haze threshold value, it was judged as (×: not acceptable). The results are shown in Table 2.

[0160] [Examples 2 to 10] As shown in Table 2, except for changing the inorganic particles (coated particles) and their addition amounts, molded bodies were produced in the same manner as in Example 1, and the scratch resistance was evaluated. The results are shown in Table 2 below.

[0161] [Comparative Examples 1 to 9] As shown in Table 2, except for changing the inorganic particles (silica composite oxide particles) and their addition amounts, molded bodies were produced in the same manner as in Example 1, and the scratch resistance was evaluated. The results are shown in Table 2 below.

[0162] [Comparative Example 10] Except for not adding inorganic particles, a molded body was produced in the same manner as in Example 1, and the scratch resistance was evaluated. The results are shown in Table 2 below.

[0163]

Table 2

[0164] Regarding the molded bodies according to Examples 1 to 10 and Comparative Examples 3, 6, 9, and 10, the water resistance was evaluated as follows.

[0165] (Evaluation of the water resistance of the molded body) First, a flat molded body was produced by cutting it into a strip shape with a width of 75 mm, a length of 90 mm, and a thickness of 3 mm.

[0166] Next, the obtained molded body was dried until it reached a completely dry state. Specifically, the molded body was placed in an oven at a temperature of 80°C while reducing the pressure to 100 mmHg or less using a vacuum pump, and it was dried for 24 days while observing the weight change of the molded body to achieve a completely dry state. Here, the weight change of the molded body from the 19th day to the 24th day (120 hours) was less than 0.05% for all molded bodies, and the change amount of haze was less than 5%. Therefore, it was determined that the molded body reached the "completely dry state" on the 24th day.

[0167] The molded body in the completely dry state was immersed in pure water at 80°C for 7 days or 25 days to make it in a water-absorbed state, and then a water resistance test was conducted to measure the haze at 23°C in accordance with JIS K7136 (unit: %).

[0168] The water resistance of the molded body was evaluated using three indicators: Haze 0 (the initial haze before immersion in pure water), Haze 7 (the haze after immersion in pure water for 7 days), and Haze 25 (the haze after immersion in pure water for 25 days) / Haze 7 . The results are shown in Table 3 below.

[0169]

Table 3

Claims

1. A methacrylic resin composition containing coated particles in which silica composite oxide particles are coated with silica, wherein a molded article having a width of 75 mm, a length of 90 mm, and a thickness of 3 mm formed from the methacrylic resin composition satisfies the following formulas (1) to (3). Haze 0 < 4 (1) Haze 7 < 4 (2) Haze 25 / Haze 7 < 3.2 (3) (In the above formulas (1) to (3), Haze 0 represents the haze (%) when the molded article is in a completely dry state. Haze 7 represents the haze (%) when the molded article is in a completely dry state and then immersed in pure water at 80°C for 7 days. Haze 25 represents the haze (%) when the molded article is in a completely dry state and then immersed in pure water at 80°C for 25 days.)

2. The methacrylic resin composition according to claim 1, wherein the silica composite oxide is a silica - titania composite oxide.

3. The methacrylic resin composition according to claim 1 or 2, wherein the median diameter of the coated particles is 0.4 μm to 2.0 μm.

4. The methacrylic resin composition according to any one of claims 1 to 3, wherein the refractive index of the coated particles when irradiated with light having a wavelength of 589 nm at 25°C is 1.474 to 1.

494.

5. The methacrylic resin composition according to any one of claims 1 to 4, wherein the content of the coated particles is 0.001 part by mass to 5 parts by mass with respect to 100 parts by mass of the methacrylic resin.

6. The methacrylic resin composition according to claim 5, wherein the content of the coated particles is 0.06 part by mass to 0.6 part by mass with respect to 100 parts by mass of the methacrylic resin.

7. The methacrylic resin composition according to any one of claims 1 to 6, wherein the methacrylic resin contains 85% by mass or more of monomer units derived from methyl methacrylate.

8. A molded article containing the methacrylic resin composition according to any one of claims 1 to 7. ​

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