JP2019035016A - Methacrylic resin composition, molded body, and optical member - Google Patents

Abstract

To provide a methacrylic resin composition which has high heat resistance, has highly controlled birefringence, and is excellent in light transmittance, color tone, transparency and injection moldability. A methacrylic resin composition contains a methacrylic resin including at least a structural unit derived from an N-substituted maleimide monomer in its main chain, has a melt viscosity on the conditions of a glass transition temperature of higher than 120°C and 160°C or lower, a resin temperature of 270°C and a shear rate of 1000 secof 250 pa seconds or less, and has an absolute value of a photoelastic coefficient of 1×10paor less, where in a solution in which the resin composition is dissolved in chloroform in 20 mass to volume percentage, light transmittance measured on the conditions of a light path length of 100 mm and a wavelength of 470 nm is 94% or more, light transmittance measured on the condition of a wavelength of 700 nm is 96% or more, and the solution contains predetermined fatty acid ester and predetermined phosphorus-based antioxidant having a trivalent phosphorus element and a predetermined melting point.SELECTED DRAWING: None

Description

  The present invention relates to a methacrylic resin composition, a molded body, and an optical member.

In recent years, a planar light emitting device having an edge light type backlight unit is used in applications such as a television, a monitor for a personal computer, a car navigation system monitor, a mobile phone, and a PDA, and is often required to be thinner.
A light guide plate which is a member constituting an edge light type backlight unit in a planar light emitting device plays a role of guiding light from a light source such as an LED disposed on a side surface to the front.
For light guide plates used in backlight units, use of transparent resin materials such as acrylic resins, cyclic polyolefin resins, and polycarbonate resins because of their high light transmittance, relatively low cost, and availability. Is being considered.

  In particular, in order to realize a thinner backlight unit, development of a methacrylic resin having excellent injection moldability, higher light transmittance, and more excellent birefringence characteristics and a composition thereof is progressing. .

In the edge light system, since the light transmission distance in the light guide plate is relatively long, the light loss in the light guide plate is large. In order to prevent light loss, the resin used and the molded product obtained therefrom have higher light transmission. It is required that the transmittance difference is small in the transmittance and visible light region (wavelength range is 400 to 750 nm).
When the light transmittance decreases, the brightness of the light guide plate decreases, brightness unevenness or color unevenness occurs, and when the transmittance difference is large, for example, the light transmittance in a short wavelength region of about 470 nm. If it is low, there is a high concern that the transmitted light will be yellowish.
In addition, as the output of the light source is increased, the amount of heat generated by the light source is increased, and the light guide plate is also required to have heat resistance. In addition, the light guide molded article has birefringence. When expressed, there is a problem that the polarized light generated by the polarized light source passes through the light guide and the polarization characteristics are disturbed to approach random polarized light. In order to solve these problems, it has been proposed to increase the light utilization efficiency by using a light guide plate made of a resin having a small phase difference and a small photoelastic coefficient.

  Therefore, for polycarbonate resins with relatively good heat resistance, studies on low birefringence were made. On the other hand, for methacrylic resins with higher light transmittance and excellent birefringence characteristics, the introduction of a cyclic structural unit into the main chain, etc. Improvement of heat resistance and further improvement of birefringence characteristics are actively studied.

For example, in a methacrylic resin, Patent Document 1 proposes a thermoplastic resin having a structural unit derived from a maleimide monomer in the main chain and excellent in heat resistance and birefringence and a molded product thereof. ing.
Certainly, although the resin disclosed in Patent Document 1 has excellent heat resistance and low phase difference and low photoelastic coefficient, it is mainly designed for film use. The color tone of a thick molded article and the light transmittance at a long optical path length are not sufficient, and there is room for further improvement.

Patent Document 2 discloses an optical member prepared using a methacrylic resin having a structural unit derived from an N-alkylmaleimide and / or N-cycloalkylmaleimide monomer and having a specific weight average molecular weight. However, it is disclosed that its color tone and light transmittance in a long optical path are good and can be used for an optical member such as a light guide.
However, the optical member obtained in Patent Document 2 is polymerized without intentionally using N-aromatic substituted maleimide such as colored phenylmaleimide as a monomer, so that its color tone and transmittance at a long optical path length are obtained. In some cases, the birefringence characteristics were insufficiently improved. When used as a light guide plate constituting an edge light type backlight unit, birefringence characteristics (for example, phase difference, photoelastic coefficient) and thin-wall injection moldability are achieved along with further improvement of light transmittance in a long optical path. There is room for improvement.

  On the other hand, such a thin light guide plate having a long optical path length is generally prepared conventionally by an injection molding method. However, for example, when trying to obtain a thin molded article having a relatively long flow length by injection molding with a thickness of 1 mm or less, it is impossible to melt the resin or resin composition and fill the entire mold. Molding in a form that leaves distortion, cracking, etc. may occur when removing the molded product filled in the mold from the mold, and surface defects such as silver streaks will occur in the molded product There are problems such as. Further, in order to obtain a molded product having a small in-plane retardation value, molding at a higher temperature is being adopted, and further improvement in injection molding stability is required.

  For example, in Patent Document 3, a methacrylic resin composition having a structural unit derived from a maleimide monomer in the main chain containing a specific release agent as its composition is used. In Patent Document 4, a specific organic phosphorus compound is used. A methacrylic resin composition having a structural unit derived from a maleimide monomer in the main chain included in the composition has been disclosed, and while exhibiting good releasability in the preparation of a thin-walled injection molded article, it has improved color tone and heat resistance. It is said that an excellent injection molded body can be obtained.

  However, in order to use it as a light guide plate for a planar light emitting device having an edge light type backlight unit, it is required to obtain a molded body having a smaller in-plane phase difference, and therefore a higher melting temperature (for example, It is employed to perform injection molding at a temperature exceeding 270 ° C. and at a higher mold temperature (for example, a temperature exceeding 100 ° C.). In the methods described in Patent Document 3 and Patent Document 4, there is room for improvement in injection molding stability including mold release in injection molding under these high temperature conditions and light transmittance, and an edge light type backlight unit In order to prepare a light guide plate for a planar light emitting device having the above, there is room for further improvement.

International Publication No. 2011/149088 Japanese Patent Laid-Open No. 2016-210963 Japanese Patent Laid-Open No. 2006-169282 Japanese Patent Laying-Open No. 2006-169283

  Therefore, it can be used suitably for the manufacture of high-quality optical components, especially light guide plates constituting edge light type backlight units, etc., which has high heat resistance, highly controlled birefringence, and high light beams in a long optical path. There is still a need for a methacrylic resin composition having transmittance and excellent color tone, transparency and injection moldability.

  Accordingly, an object of the present invention is to provide a methacrylic resin composition and a molded body having high heat resistance, highly controlled birefringence, high light transmittance in a long optical path, and excellent color tone, transparency and injection moldability. And providing an optical member.

  In order to solve the above-described problems, the present inventors have prepared methacrylic resin having a cyclic structural unit in the main chain and conditions for preparing a resin composition (for example, polymerization method, polymerization condition, devolatilization method, addition of additives) The method, pellet granulation conditions, etc.) were examined in more detail. As a result, in the methanol reprecipitation method which is a devolatilization method adopted in Patent Documents 1, 3 and 4, it is for the production of a reaction by-product between the remaining monomer and methanol, or Compared with a polymer obtained by other devolatilization methods (for example, a method using a twin-screw extruder for devolatilization, a method of devolatilization using a thin film evaporator, etc.) It has been found that there is room for improvement in light transmittance at a long optical path length.

  On the other hand, in Patent Document 2, which employs a suspension polymerization method as the polymerization method, a colored hydrolysis by-product derived from an N-substituted maleimide monomer is produced during polymerization, or a foreign substance derived from a suspension aid to be used. In addition, since the polymer obtained is a particulate material, when an antioxidant or a release agent is blended to prepare a composition, it is melt kneaded again using an extruder or the like. It has been found that there may be problems such as a decrease in light transmittance at a long optical path length and a decrease in the compounding effect of the release agent.

  As a result of further intensive studies, the present inventors also applied to optical components having high heat resistance, highly controlled birefringence, and excellent color tone and transparency, in particular, light guide plates constituting edge light type backlight units. In order to prepare a methacrylic resin composition having a high light transmittance in a long optical path, it is possible to recover a polymer through a devolatilization step from a polymerization solution containing a polymer obtained after solution polymerization. The structure of the unreacted N-substituted maleimide monomer in the polymerization solution to be subjected to the devolatilization step, particularly the concentration of the N-aromatic substituted maleimide monomer in the solution is a specific concentration or less, and its structure As a high-concentration chloroform solution, a methacrylic resin composition having a very high transmittance can be prepared by recovering a polymer by performing a devolatilization operation using a devolatilizer having no rotating part as And Akira.

  In addition, by setting the melt viscosity of a methacrylic resin composition having a relatively high glass transition temperature to a specific range in the shear rate region corresponding to the injection molding region, a thin-walled injection molding like a light guide plate It has also been found that an injection molded body having a low retardation value can be obtained.

  Furthermore, in order to obtain a thin injection molded plate having a small in-plane retardation value using this methacrylic resin composition, injection molding is continuously performed using a mold set at a high temperature at a high resin temperature. Even when it is performed, a specific release agent and a specific phosphorus antioxidant are used in combination, and a methacrylic resin composition to which a specific amount is added is prepared in advance and used, so that stable and high-quality injection can be achieved. It has been found that a molded plate can be obtained.

That is, the present invention is as follows.
[1] A methacrylic resin composition comprising a methacrylic resin containing at least a structural unit derived from an N-substituted maleimide monomer in the main chain,
(A) The glass transition temperature is more than 120 ° C and not more than 160 ° C,
(B) the melt viscosity is 250 pa · sec or less under the conditions of a resin temperature of 270 ° C. and a shear rate of 1000 sec ⁻¹ ;
(C) The absolute value of the photoelastic coefficient is 1 × 10 ⁻¹² pa ⁻¹ or less,
(D) About the solution which melt | dissolved this resin composition in chloroform by 20 mass to volume percentage, the light transmittance measured on the conditions of optical path length 100mm and wavelength 470nm is 94% or more,
(E) About the solution which melt | dissolved this resin composition in 20 mass to volume percentage in chloroform, the light transmittance measured on conditions with an optical path length of 100 mm and a wavelength of 700 nm is 96% or more,
(F) 0.05 to 0.2 parts by mass of at least one fatty acid ester selected from glycerin fatty acid ester, diglycerin fatty acid ester, and sorbitan fatty acid ester is contained with respect to 100 parts by mass of the methacrylic resin,
(G) It is characterized by containing 0.01 to 0.2 parts by mass of a phosphorus antioxidant having a melting point of 100 to 250 ° C. and having a trivalent phosphorus element with respect to 100 parts by mass of the methacrylic resin. A methacrylic resin composition.
[2] About a solution in which the resin composition is dissolved in chloroform at a mass percentage of 20% by mass, the light transmittance measured under conditions of an optical path length of 100 mm and a wavelength of 470 nm is 96% or more, and an optical path length of 100 mm; The methacrylic resin composition according to [1], wherein the light transmittance measured under a wavelength of 700 nm is 98% or more.
[3] Using a resin flow length measuring mold having a spiral flow path having a thickness of 1 mm and a width of 10 mm, injection molding is performed under the conditions of a cylinder temperature of 270 ° C., a mold temperature of 100 ° C., and an injection pressure of 125 MPa. The methacrylic resin composition according to [1] or [2], wherein the flow length (spiral flow length) is 150 mm or more.
[4] The phosphorus element content in the methacrylic resin composition is 5 to 200 ppm by mass,
^{In 31} P-NMR measurement, the ratio (P3 / P5) of the integral value (P3) of the spectral peak attributed to trivalent phosphorus to the integrated value (P5) of the spectral peak attributed to pentavalent phosphorus is 0.2 to The methacrylic resin composition according to any one of [1] to [3], which is 2.0.
[5] The methacrylic resin composition according to any one of [1] to [4], which contains 0.005 to 0.1 part by mass of a hindered phenol-based antioxidant with respect to 100 parts by mass of the methacrylic resin. .
[6] The methacrylic resin according to any one of [1] to [5], wherein the methacrylic resin is 100% by mass and the structural unit derived from an N-substituted maleimide monomer is contained by 5 to 40% by mass. The methacrylic resin composition described.
[7] The structural unit derived from the N-substituted maleimide monomer includes both a structural unit derived from an N-aromatic substituted maleimide monomer and a structural unit derived from an N-alicyclic substituted maleimide monomer. The methacrylic resin composition according to any one of [1] to [6].
[8] The methacrylic resin composition according to any one of [1] to [7], which is for injection molding.
[9] The methacrylic resin composition according to any one of [1] to [8], which is for an optical member.

[10] A molded article comprising the methacrylic resin composition according to any one of [1] to [9].
[11] An optical member comprising the molded article according to [10].
[12] The optical member according to [11], which is a light guide plate.

  According to the present invention, a methacrylic resin composition having high heat resistance, highly controlled birefringence, high light transmittance in a long optical path, excellent color tone, transparency, and injection moldability, a molded body, and An optical member can be provided.

  Hereinafter, although the form for implementing this invention (henceforth "this embodiment") is demonstrated in detail, this invention is not limited to the following description, In the range of the summary Various modifications can be made.

(Methacrylic resin composition)
The methacrylic resin composition of the present embodiment includes a methacrylic resin and, if necessary, includes other thermoplastic resins and additives.

-Methacrylic resin-
The methacrylic resin in this embodiment includes at least a structural unit derived from an N-substituted maleimide monomer as a structural unit derived from a methacrylic acid ester monomer and a structural unit having a ring structure in the main chain.

  Hereinafter, each monomer structural unit will be described.

-Structural unit derived from methacrylic acid ester monomer-
First, a structural unit derived from a methacrylic acid ester monomer will be described.
The structural unit derived from a methacrylic acid ester monomer is formed from, for example, a monomer selected from the following methacrylic acid esters. Examples of the methacrylate ester include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, and methacrylic acid. Cyclopentyl, cyclohexyl methacrylate, cyclooctyl methacrylate, tricyclodecyl methacrylate, dicyclooctyl methacrylate, tricyclododecyl methacrylate, isobornyl methacrylate, phenyl methacrylate, benzyl methacrylate, 1-phenylethyl methacrylate, methacrylic acid Examples include 2-phenoxyethyl, 3-phenylpropyl methacrylate, 2,4,6-tribromophenyl methacrylate, and the like.
These monomers may be used alone or in combination of two or more.
Of the above methacrylic acid esters, methyl methacrylate and benzyl methacrylate are preferred in that the obtained methacrylic resin is excellent in transparency and weather resistance.
The structural unit derived from a methacrylic acid ester monomer may contain only 1 type, or may contain 2 or more types.

The content of the structural unit derived from the methacrylic acid ester monomer is not particularly limited, but the methacrylic resin is 100% by mass, preferably 60 to 95% by mass, more preferably 60 to 92% by mass. It is.
When it is within this range, since the high optical properties inherent to the methacrylic resin can be maintained, a more preferable improvement effect can be obtained.

-Structural unit derived from N-substituted maleimide monomer-
The structural unit derived from an N-substituted maleimide monomer is a structural unit derived from an N-aromatic substituted maleimide monomer represented by the following formula (1) and / or an N-fat represented by the following formula (2). It may be at least one selected from structural units derived from a cyclic substituted maleimide monomer, and is preferably composed of both structural units represented by the following formula (1) and the following formula (2).

In Formula (1), R ¹ represents any of an arylalkyl group having 7 to 14 carbon atoms and an aryl group having 6 to 14 carbon atoms, and R ² and R ³ each independently represent a hydrogen atom or a carbon number. One of an alkyl group having 1 to 12 and an aryl group having 6 to 14 carbon atoms is shown.
When R ² is an aryl group, R ² may contain a halogen atom as a substituent.
R ¹ may be substituted with a substituent such as a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a nitro group, or a benzyl group.

In formula (2), R ⁴ represents any one of a hydrogen atom, a cycloalkyl group having 3 to 12 carbon atoms, and an alkyl group having 1 to 18 carbon atoms, and R ⁵ and R ⁶ are each independently a hydrogen atom. Or an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 14 carbon atoms.

Specific examples will be shown below.
Examples of the monomer that forms the structural unit represented by the formula (1) include N-phenylmaleimide, N-benzylmaleimide, N- (2-chlorophenyl) maleimide, N- (4-chlorophenyl) maleimide, N -(4-bromophenyl) maleimide, N- (2-methylphenyl) maleimide, N- (2-ethylphenyl) maleimide, N- (2-methoxyphenyl) maleimide, N- (2-nitrophenyl) maleimide, N -(2,4,6-trimethylphenyl) maleimide, N- (4-benzylphenyl) maleimide, N- (2,4,6-tribromophenyl) maleimide, N-naphthylmaleimide, N-anthracenylmaleimide, 3-methyl-1-phenyl-1H-pyrrole-2,5-dione, 3,4-dimethyl-1-phenyl-1H- Roll-2,5-dione, 1,3-diphenyl -1H- pyrrole-2,5-dione, 1,3,4-triphenyl -1H- pyrrole-2,5-dione, and the like.
Among these monomers, N-phenylmaleimide and N-benzylmaleimide are preferable because the obtained methacrylic resin has excellent heat resistance and optical properties such as birefringence.
These monomers may be used alone or in combination of two or more.

Examples of the monomer that forms the structural unit represented by the formula (2) include N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, N-isopropylmaleimide, Nn-butylmaleimide, N-isobutylmaleimide, Ns-butylmaleimide, Nt-butylmaleimide, Nn-pentylmaleimide, Nn-hexylmaleimide, Nn-heptylmaleimide, Nn-octylmaleimide, N-lauryl Maleimide, N-stearylmaleimide, N-cyclopentylmaleimide, N-cyclohexylmaleimide, 1-cyclohexyl-3-methyl-1H-pyrrole-2,5-dione, 1-cyclohexyl-3,4-dimethyl-1H-pyrrole-2 , 5-dione, 1-cyclohexyl-3-phenyl-1H-pillow 2,5-dione, and 1-cyclohexyl-3,4-diphenyl -1H- pyrrole-2,5-dione can be cited.
Among these monomers, N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, and N-cyclohexylmaleimide are preferable because the weather resistance of the methacrylic resin is excellent. N-cyclohexylmaleimide is particularly preferable because of its excellent hygroscopicity.
These monomers can be used alone or in combination of two or more.

In the methacrylic resin of this embodiment, the monomer that forms the structural unit represented by the formula (1) and the monomer that forms the structural unit represented by the formula (2) are used in combination. This is preferable because highly controlled birefringence characteristics can be exhibited.
Structure derived from the N-alicyclic substituted maleimide monomer represented by the formula (2) of the content (A1) of the structural unit derived from the N-aromatic substituted maleimide monomer represented by the formula (1) The molar ratio (A1 / A2) to the unit content (A2) is preferably more than 0 and 15 or less, more preferably more than 0 and 10 or less. When the molar ratio (A1 / A2) is in this range, the methacrylic resin of this embodiment maintains transparency, does not cause yellowing, and does not impair environmental resistance, and has good heat resistance and good Expresses photoelastic properties.

The content of the structural unit derived from the N-substituted maleimide monomer is not particularly limited, but the methacrylic resin is 100% by mass, preferably 5 to 40% by mass, more preferably 11 to 35% by mass. It is a range.
When it is within this range, the methacrylic resin can obtain a more sufficient heat resistance improving effect, and more preferable effects of improving weather resistance, low water absorption, and optical properties. It should be noted that the content of the structural unit derived from the N-substituted maleimide monomer being 40% by mass or less reduces the reactivity of the monomer component during the polymerization reaction and increases the amount of unreacted monomer. This is effective in preventing deterioration in physical properties of the methacrylic resin.

The methacrylic resin having a structural unit derived from an N-substituted maleimide monomer in the present embodiment can be copolymerized with a methacrylic acid ester monomer and an N-substituted maleimide monomer as long as the object of the present invention is not impaired. It may contain structural units derived from other monomers.
For example, other copolymerizable monomers include aromatic vinyl; unsaturated nitrile; cyclohexyl group, benzyl group, or acrylic acid ester having an alkyl group having 1 to 18 carbon atoms; unsaturated carboxylic acid of glycols Examples include esters; glycidyl compounds; unsaturated carboxylic acids and the like.

Examples of the aromatic vinyl include styrene, α-methylstyrene, divinylbenzene, and the like.
Examples of the unsaturated nitrile include acrylonitrile, methacrylonitrile, ethacrylonitrile and the like.
Examples of the acrylate ester include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, and butyl acrylate.
The unsaturated carboxylic acid esters of glycols include ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, butanediol dimethacrylate, hexanediol dimethacrylate, neopentyl. Examples include glycol dimethacrylate.
Examples of the glycidyl compound include glycidyl acrylate and allyl glycidyl ether.
Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and half-esterified products or anhydrides thereof.
The structural unit derived from the other copolymerizable monomer may have only one type, or may have two or more types.

The content of structural units derived from these other copolymerizable monomers is preferably 0 to 20% by mass, and 0.05 to 15% by mass, based on 100% by mass of the methacrylic resin. Is more preferable, and it is still more preferable that it is 0.1-10 mass%.
When the content of the structural unit derived from another monomer is within this range, it is preferable because the processability and mechanical properties of the resin can be improved without impairing the original effect of introducing a ring structure into the main chain.

  As a method for producing a methacrylic resin having a structural unit derived from an N-substituted maleimide monomer in the main chain in this embodiment, a solution polymerization method can be employed.

Hereinafter, a method for producing a methacrylic resin having a structural unit derived from an N-substituted maleimide monomer by radical polymerization using a solution polymerization method (hereinafter sometimes referred to as “maleimide copolymer”). This will be specifically described.
As a polymerization mode in the production method in the present embodiment, for example, any of a batch (also referred to as batch method) polymerization method, a semi-batch (also referred to as semi-batch method) polymerization method, and a continuous polymerization method can be used.

  In the present embodiment, a method in which a part of the monomer is charged into the reactor before the start of polymerization, the polymerization is started by adding a polymerization initiator, and then the remainder of the monomer is supplied, so-called semi-batch weight. Legal methods can be preferably used.

In the semi-batch polymerization method, the total mass of all monomers (methacrylic acid ester, N-substituted maleimide, and any other monomer) donated to the polymerization is measured after 30 minutes from the start of addition of the polymerization initiator. It is preferable to add 5 to 35% by mass of a methacrylic acid ester monomer as 100% by mass. In other words, 65 to 95% by mass of 100% by mass of the total mass of all monomers donated to the polymerization is charged into the reactor before the start of polymerization, and methacrylic acid is added after 30 minutes from the start of addition of the polymerization initiator. It is preferable to add the remaining 5-35% by mass of the ester monomer.
The amount of the methacrylic acid ester monomer to be added is more preferably 10 to 30% by mass, with the total mass of all the monomers donated to the polymerization as 100% by mass.

What is necessary is just to select suitably the start time of the additional addition of a monomer, the speed of additional addition, etc. according to a polymerization conversion rate.
In addition to methacrylic acid ester monomers, N-substituted maleimide monomers and other monomers are included within the range that does not hinder the effects of the present invention and increase the conversion rate of N-substituted maleimide monomers. An additional monomer mixture may be added.

  By adopting the semi-batch polymerization method as described above, it becomes possible to increase the conversion rate of the unreacted N-substituted maleimide monomer at the latter half of the polymerization, and to improve the light transmittance of the molded product having a long optical path length. It is preferable because it is excellent in that it is easy to control the molecular weight distribution of the resulting polymer, and a resin having fluidity suitable for injection molding and a composition of the resin can be obtained.

The polymerization solvent to be used is not particularly limited as long as the solubility of the maleimide copolymer obtained by polymerization is increased and the viscosity of the reaction solution can be appropriately maintained for the purpose of preventing gelation.
Specific examples of the polymerization solvent include aromatic hydrocarbons such as toluene, xylene, ethylbenzene, and isopropylbenzene; ketones such as methyl isobutyl ketone, butyl cellosolve, methyl ethyl ketone, and cyclohexanone; polar solvents such as dimethylformamide and 2-methylpyrrolidone. Can be used.
Moreover, you may use together alcohol, such as methanol, ethanol, and isopropanol, as a polymerization solvent in the range which does not inhibit the melt | dissolution of the polymerization product at the time of superposition | polymerization.

  The amount of solvent at the time of polymerization is not particularly limited as long as the polymerization proceeds and the copolymer or used monomer does not precipitate during production and can be easily removed. When the total amount is 100 parts by mass, it is preferably 10 to 100 parts by mass. More preferably, it is 25-100 mass parts, More preferably, it is 40-100 mass parts, More preferably, it is 50-100 mass parts.

In this embodiment, when the amount of solvent during polymerization is 100 parts by mass when the total amount of monomers to be blended is 100 parts by mass, polymerization is performed while appropriately changing the solvent concentration during polymerization. A method can also be preferably used.
More specifically, 40-60 mass parts is mix | blended in the superposition | polymerization initial stage, the remaining 60-40 mass parts is mix | blended in the middle of superposition | polymerization, and finally the total amount of the monomer to mix | blend is 100 mass parts. In this case, a method of adjusting the amount of solvent to be in the range of 100 parts by mass or less can be exemplified.
By adopting this method, the polymerization conversion rate can be increased, the molecular weight distribution can be controlled, the injection moldability is excellent, and the light transmittance is high even when a molded product having a long optical path length is prepared. Is preferable because a resin and a resin composition are obtained.

  In solution polymerization, it is important to reduce the dissolved oxygen concentration in the polymerization solution as much as possible. For example, the dissolved oxygen concentration is preferably 10 ppm or less. The dissolved oxygen concentration can be measured using, for example, a dissolved oxygen meter DO meter B-505 (manufactured by Iijima Electronics Co., Ltd.). As a method for lowering the dissolved oxygen concentration, a method of bubbling an inert gas in the polymerization solution, and an operation of releasing the pressure after pressurizing the container containing the polymerization solution with an inert gas to about 0.2 MPa before the polymerization are repeated. A method such as a method and a method of passing an inert gas in a container containing a polymerization solution can be appropriately selected.

  The polymerization temperature is not particularly limited as long as the polymerization proceeds, but is preferably 70 to 180 ° C, more preferably 80 to 160 ° C. More preferably, it is 90-150 degreeC, More preferably, it is 100-150 degreeC. From the viewpoint of productivity, the temperature is preferably 70 ° C. or higher, and is preferably 180 ° C. or lower in order to suppress side reactions during polymerization and obtain a polymer having a desired molecular weight and quality.

  The polymerization time is not particularly limited as long as the required degree of polymerization can be obtained at the required conversion rate, but from the viewpoint of productivity and the like, it is preferably 2 to 15 hours, More preferably, it is 3-12 hours, More preferably, it is 4-10 hours.

As the polymerization initiator, any initiator generally used in radical polymerization can be used. For example, cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide Organic peroxidation such as oxide, t-butylperoxyisopropyl carbonate, t-amylperoxy-2-ethylhexanoate, t-amylperoxyisononanoate, 1,1-di (t-butylperoxy) cyclohexane 2,2′-azobis (isobutyronitrile), 1,1′-azobis (cyclohexanecarbonitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), dimethyl-2,2′- Azo compounds such as azobisisobutyrate; You can.
These may be used alone or in combination of two or more.
The addition amount of the polymerization initiator may be 0.01 to 1 part by mass, preferably 0.05 to 0.5 part by mass, when the total amount of monomers used for polymerization is 100 parts by mass. is there.

As a method for adding the polymerization initiator, the polymerization initiator is added into the reactor while gradually decreasing the addition amount per unit time, and the polymerization of the monomer proceeds. A method is preferred in which polymerization is continued almost simultaneously with the addition of the monomer by increasing the amount of the polymerization initiator added per unit time.
In this case, the polymerization initiator may be added continuously or intermittently. When the polymerization initiator is intermittently added, the addition amount per unit time is not considered for the time not added.

In the present embodiment, the type and addition amount of the polymerization initiator, so that the ratio of the total amount of radicals generated from the polymerization initiator to the total amount of unreacted monomers remaining in the reaction system is always below a certain value, and It is preferable to appropriately select the polymerization temperature and the like.
By adopting these methods, it is possible to suppress the production amount of oligomers and low molecular weight substances in the later stage of polymerization, or to suppress the overheating at the time of polymerization, thereby achieving the stability of the polymerization.

During the polymerization reaction, if necessary, a chain transfer agent may be added for polymerization.
As the chain transfer agent, a chain transfer agent used in general radical polymerization can be used, for example, n-butyl mercaptan, n-octyl mercaptan, n-decyl mercaptan, n-dodecyl mercaptan, 2-ethylhexyl thioglycolate and the like. Mercaptan compounds; halogen compounds such as carbon tetrachloride, methylene chloride and bromoform; unsaturated hydrocarbon compounds such as α-methylstyrene dimer, α-terpinene, dipentene and terpinolene;
These may be used alone or in combination of two or more.
These chain transfer agents may be added at any stage as long as the polymerization reaction is in progress, and are not particularly limited.
The addition amount of the chain transfer agent may be 0.01 to 1 part by mass, preferably 0.05 to 0.5 part by mass, when the total amount of monomers used for polymerization is 100 parts by mass.

Examples of a method for recovering a polymer from a polymerization solution obtained by solution polymerization include a method for recovering a polymerization product by separating a polymerization solvent and unreacted monomers via a step called a devolatilization step. .
Here, the devolatilization step refers to a step of removing volatile components such as a polymerization solvent, a residual monomer, and a reaction by-product under heating and reduced pressure conditions.

  In this embodiment, it is important to control the content of the unreacted N-substituted maleimide monomer contained in the polymerization solution containing a methacrylic resin to be used in the devolatilization step to a certain concentration or less.

Specifically, as the content of the N-substituted maleimide monomer contained in the polymerization solution subjected to the devolatilization step, when the entire polymerization solution is 100% by mass, the remaining N-substituted maleimide monomer The total amount is preferably 2000 mass ppm or less, more preferably 1500 mass ppm or less, and still more preferably 1000 mass ppm or less. When N-aromatic substituted maleimide such as N-phenylmaleimide is used as N-substituted maleimide, the content thereof is 1000 mass ppm or less, more preferably 800 mass ppm or less, and still more preferably 600 mass ppm or less. It is.
When the concentration of the N-substituted maleimide remaining in the polymerization solution containing the methacrylic resin used in the devolatilization step is within this range, the unreacted N-substituted maleimide is used as the structural unit in the heated devolatilizer. It is preferable because it can suppress generation of a reaction by-product having a low molecular weight and coloring property and a heat-modified product of N-substituted maleimide, and a methacrylic resin having high light transmittance can be obtained.

  On the other hand, in a state where the concentration of the N-substituted maleimide monomer contained in the polymerization solution is high, the N-substituted maleimide monomer is supplied to the devolatilization step, devolatilized at a high temperature and under a high reduced pressure, and in the recovered polymer. In the method of reducing the content of the remaining N-substituted maleimide monomer, a methacrylic resin having a structural unit derived from an N-substituted maleimide monomer having a high light transmittance in a wide wavelength region tends not to be obtained. Therefore, it is difficult to achieve the object of the present invention.

  As a method for obtaining the residual concentration of the N-substituted maleimide monomer remaining in the polymerization solution containing the methacrylic resin to be subjected to the devolatilization step, for example, a part of the polymerization solution is collected and weighed, and this sample is put in chloroform. Dissolve to prepare a 5% by mass solution, add n-decane as an internal standard substance, and use N-substituted maleimide monomer remaining in the sample using gas chromatography (GC-2010, manufactured by Shimadzu Corporation). It can obtain | require by measuring the density | concentration of. As more specific measurement conditions, those described in the examples described later can be used.

  The method for controlling the residual concentration of the N-substituted maleimide monomer remaining in the polymerization solution containing the methacrylic resin to be subjected to the devolatilization step within the preferable range of the present embodiment is not particularly limited. In order to increase the conversion rate of the monomer, the polymerization time is increased as much as possible, or the polymerization is performed by changing the addition rate of the polymerization initiator in accordance with the unreacted monomer concentration in the polymerization solution; Polymerization while appropriately changing the solvent concentration during the polymerization; Additional addition of another monomer having high reactivity with the N-substituted maleimide monomer remaining in the latter half of the polymerization; α-terpinene at the end of the polymerization, etc. , A method of adding a compound having high reactivity with N-substituted maleimide; a part of the monomer is charged into the reactor before the start of polymerization, and the polymerization is started by adding a polymerization initiator; Supply the rest of the body That method (so-called semi-batch polymerization method); or the like method can be exemplified in. Of these, the semi-batch polymerization method is preferable.

As an apparatus used for the devolatilization step in the present embodiment, it is important to use a devolatilizer having a heat exchanger and a decompression vessel as main components and having no rotating part as its structure.
Specifically, a devolatilization tank with a decompression unit attached to a decompression vessel having a size capable of devolatilization with a heat exchanger disposed thereon, and a gear pump for discharging a polymer after devolatilization It is possible to employ a devolatilizing device composed of a discharging device such as the above.
The devolatilization apparatus is a heat exchanger in which a polymerization solution is disposed and heated at the top of a decompression vessel, for example, a multi-tubular heat exchanger, a plate fin heat exchanger, a flat plate type flow path and a flat plate type having a heater. After preheating by using a heat exchanger or the like, it is supplied to a devolatilization tank under heating and reduced pressure to separate and remove the polymerization solvent, unreacted raw material mixture, polymerization by-product, and the copolymer.

In the present embodiment, it is preferable to use a flat plate type heat exchanger having a flat plate type flow path and a heater as the heat exchanger disposed on the upper part of the decompression vessel. More preferably, it is a flat plate type heat exchanger having a flat plate-type flow path having a laminated structure having a plurality of slit-shaped flow paths having a rectangular cross section on the same plane and a heater.
The polymerization solution supplied to the devolatilizer is sent from the center of the heat exchanger to the slit channel and heated. The heated polymerization solution is supplied from a slit-like channel into a vacuum container under reduced pressure integrated with a heat exchanger, and is flash-evaporated.
Such a devolatilization method is sometimes referred to as flash devolatilization. In the present invention, it is hereinafter also referred to as flash devolatilization.
It is also possible to employ a method in which two or more devolatilizers described above are installed in series and devolatilized in two or more stages.

The temperature range to be heated by the heat exchanger attached to the devolatilizer may be 100 ° C. or higher and 300 ° C. or lower, preferably Tg + 100 ° C. to Tg + 140 ° C., more preferably Tg + 110 ° C. to Tg + 140 ° C. . The temperature range of the heated / heated devolatilization tank may be 100 ° C. or higher and 300 ° C. or lower, preferably Tg + 100 ° C. to Tg + 140 ° C., more preferably Tg + 110 ° C. to Tg + 140 ° C. When the temperature of the heat exchanger and the devolatilization tank is within this range, it is effective for preventing an increase in residual volatile matter, and this is preferable because the thermal stability and product quality of the resulting methacrylic resin are improved.
The degree of vacuum in the devolatilization tank may be in the range of 5 to 300 Torr, and more preferably in the range of 10 to 200 Torr. When the degree of vacuum is 300 Torr or less, the unreacted monomer or the mixture of the unreacted monomer and the polymerization solvent can be separated and removed efficiently, and the thermal stability and quality of the resulting thermoplastic copolymer are improved. It does not decline. Industrial implementation is easier when the degree of vacuum is 5 Torr or more.
The average residence time in the devolatilization tank is 5 to 60 minutes, preferably 5 to 45 minutes. It is preferable for the average residence time to be in this range since it can be devolatilized efficiently and coloring and decomposition due to thermal modification of the polymer can be suppressed.

The polymer recovered through the devolatilization process is processed into a pellet form in a process called a granulation process.
In the granulation process, the molten resin is extruded into a strand by using at least one unloading granulator selected from a gear pump, a single screw extruder, a twin screw extruder, etc. having a perforated die as an incidental facility, and cold It is processed into pellets by the cutting method, aerial hot cutting method, underwater strand cutting method, and underwater cutting method.

In the present embodiment, in order to obtain a highly controlled methacrylic resin composition, the composition in a molten state at a high temperature can be quickly cooled and solidified so as not to be exposed to air as much as possible. It is preferable to employ a grain system.
In that case, the molten resin temperature should be lowered as much as possible, the residence time from the perforated die outlet to the cooling water surface should be minimized, and the cooling water temperature should be as high as possible. It is more preferable to perform granulation.

For example, the molten resin temperature is preferably 220 to 280 ° C, more preferably 230 to 270 ° C, and the residence time from the porous die outlet to the cooling water surface is preferably within 5 seconds, more preferably within 3 seconds. The temperature of the cooling water is preferably 30 to 80 ° C, more preferably 40 to 60 ° C.
By carrying out in the range of these molten resin temperatures and cooling water temperatures, a methacrylic resin and a composition thereof with less coloring and a low moisture content can be obtained.

About content of the monomer which remains in the methacrylic resin after a devolatilization process, it is so preferable from a viewpoint of thermal stability or product quality that it is small. Specifically, the content of the methacrylic acid ester monomer is preferably 3000 mass ppm or less, more preferably 2000 mass ppm or less. The total content of the N-substituted maleimide monomer is preferably 200 ppm by mass or less, more preferably 100 ppm by mass or less.
Moreover, as content of the polymerization solvent which remains, 500 mass ppm or less is preferable, More preferably, it is 300 mass ppm or less.

-Other thermoplastic resins-
When preparing the methacrylic resin composition of the present embodiment, other thermoplastic resins may be blended for the purpose of adjusting the birefringence and improving flexibility without impairing the purpose of the present embodiment. it can.
Examples of other thermoplastic resins include polyacrylates such as polybutyl acrylate; polystyrene, styrene-methyl methacrylate copolymer, styrene-butyl acrylate copolymer, styrene-acrylonitrile copolymer, and acrylonitrile-butadiene-styrene. Aromatic vinyl resins such as styrene polymers such as block copolymers; and further, for example, JP 59-202213 A, JP 63-27516 A, JP 51-129449 A, Acrylic rubber particles having a three- to four-layer structure described in Japanese Utility Model Laid-Open No. 52-056150; a rubbery polymer disclosed in Japanese Patent Publication No. 60-17406 and Japanese Patent Laid-Open No. 8-245854; Methacrylic rubber-containing graph obtained by multistage polymerization as described in 2014-002491 Copolymer particles; and the like.
Among these, from the viewpoint of obtaining good optical properties and mechanical properties, the surface layer of the graft portion made of a composition compatible with the styrene-acrylonitrile copolymer or the methacrylic resin prepared in the present embodiment is used. The rubber-containing graft copolymer particles are preferably used.

  As the average particle diameter of the acrylic rubber particles, methacrylic rubber-containing graph copolymer particles, and rubbery polymers, the impact strength and optical characteristics of the film obtained from the methacrylic resin composition of the present embodiment, etc. From the viewpoint of increasing the thickness, it is preferably 0.03 to 1 μm, more preferably 0.05 to 0.5 μm.

  The content of the other thermoplastic resin is preferably 0 to 50 parts by mass, more preferably 0 to 25 parts by mass when the methacrylic resin is 100 parts by mass.

-Additives-
When the methacrylic resin composition according to the present embodiment is used for preparing a light guide plate by injection molding, the injection molding conditions are higher at higher temperatures and higher shear as the light guide plate is made thinner and more complex in recent years. Even in the case of severe conditions such as below, it is important to stably perform injection molding, and in addition, it is important to suppress coloring of the light guide plate due to higher output of the light source.
Therefore, the methacrylic resin composition according to the present embodiment includes a phosphorus antioxidant and a release agent, and more preferably includes a hindered phenol antioxidant.
In addition, the methacrylic resin composition according to the present embodiment may contain other additives within a range that does not significantly impair the effects of the present embodiment.
Hereinafter, these additives will be described in detail.

--Fatty acid ester (release agent)-
The methacrylic resin composition in the present embodiment contains at least one fatty acid ester selected from glycerin fatty acid ester, diglycerin fatty acid ester, and sorbitan fatty acid ester as a release agent in order to improve injection molding processability. To do.
By containing at least one fatty acid ester selected from glycerin fatty acid ester, diglycerin fatty acid ester, and sorbitan fatty acid ester in its composition, the mold adhesion of the injection molded body during injection molding and the accompanying surface defects are suppressed. In addition, a molded article having a good appearance can be obtained. These mold release agents have an effect as an internal lubricant during melt-kneading during injection molding, and have good appearance with less haze due to gas adhesion etc. by suppressing resin decomposition during melting Can be provided continuously.
They also have good compatibility with methacrylic resins, have little effect on the transmittance of the molded product with a long optical path length, and suppress exudation when the resulting molded product is placed at high temperatures. It is also effective for the purpose of use, and it can be preferably used because it does not cause fogging or the like in the molded article even when used for a long time at a high temperature.

Examples of the glycerin fatty acid ester, diglycerin fatty acid ester, and sorbitan fatty acid ester used for this purpose include caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, Mono- or di-fatty acid esters of fatty acids such as arachidic acid, behenic acid, lignoceric acid, serotic acid, montanic acid, melissic acid, linoleic acid and oleic acid.
Among these, glycerin monostearate, diglycerin monostearate, sorbitan monostearate, glycerin monobehenate, glycerin-12-hydroxy monostearate and the like are particularly preferable.
Among these, glycerin monostearate can be particularly preferably used in order to minimize the influence on the light transmittance in a molded product having a long optical path length.
These can be used alone or in combination of two or more. When two or more types are used in combination, the combination is not particularly limited, but a combination in which at least one type is a glycerin fatty acid ester is particularly preferable because it can achieve both mold release properties and injection molding stability during high temperature molding. The combination may be a combination of two or more glycerin fatty acid esters.

  The addition amount of these fatty acid esters is in the range of 0.05 to 0.2 parts by mass, preferably 0.08 to 100 parts by mass with respect to 100 parts by mass of the methacrylic resin, from the viewpoint of suppressing resin degradation and improving processability. It is 0.18 mass part, More preferably, it is the range of 0.10-0.15 mass part. Within this range, it is preferable because the deterioration of transparency in the case of a molded product can be suppressed without causing mold contamination during injection molding, and the original release properties can be effectively exhibited.

  The timing for adding these release agents is the addition to the polymerization solution containing the polymer after polymerization, the addition to the polymer in a molten state after devolatilization, and the pellets obtained after devolatilization and granulation, and again. Examples include addition during melt extrusion and granulation. When preparing the methacrylic resin composition of the present embodiment, among these, a mold release agent may be added to the polymerization solution containing the polymer after polymerization, or to the polymer in a molten state after devolatilization. preferable. As a method of adding to a polymer in a molten state after devolatilization, for example, a method of adding using a polymer mixer or an in-line mixer is also preferable.

-Phosphorous antioxidant-
The methacrylic resin composition in the present embodiment contains a phosphorus antioxidant having a melting point in the range of 100 to 250 ° C. and having a trivalent phosphorus element.
When the methacrylic resin composition in the present embodiment is used for, for example, injection molding to prepare a light guide plate having a relatively thin flow distance, a higher temperature is required to improve optical properties such as workability and birefringence. In many cases, the resin composition is molded together with a release agent such as a fatty acid ester, and it is necessary to further improve the thermal stability of the resin composition. Therefore, from the viewpoint of improving thermal stability during processing and preventing bleeding out of the antioxidant itself to the surface of the molded body, the phosphorus-based antioxidant has a trivalent phosphorus element, and its melting point is It needs to be in the range of 100-250 ° C. The melting point of the phosphorus antioxidant is preferably in the range of 120 to 200 ° C, more preferably in the range of 140 to 200 ° C.

Although it does not specifically limit as a phosphorus antioxidant which has a trivalent phosphorus element and melting | fusing point is 100-250 degreeC, Phosphite ester (henceforth "phosphites"), phosphonites, etc. Can be used. For example, a commercially available phosphorus-based antioxidant may be used. For example, Irgaphos (registered trademark) 168 (Irgafos 168: Tris (2,4-di-t-butylphenyl) phosphite, manufactured by BASF, melting point 180 to 190 ° C. ), Irgafos 12: Tris [2-[[2,4,8,10-tetra-t-butyldibenzo [d, f] [1,3,2] dioxaphosphin-6-yl] oxy ] Ethyl] amine, manufactured by BASF, melting point 190 to 210 ° C., Adekastab (registered trademark) HP-10 (ADKSTAB HP-10: 2,2′-methylenebis (4,6-di-tert-butylphenyl) octyl phosphite : ADEKA Corporation, melting point 146-152 ° C), ADK STAB PEP36 (ADKSTAP PEP36: screw (2, -Di-t-butyl-4-methylphenyl) pentaerythritol diphosphite: manufactured by ADEKA Corporation, melting point 234-240 ° C., ADK STAB PEP36A (ADKSTAB PEP36A: bis (2,6-di-t-butyl-4-) Methylphenyl) pentaerythritol diphosphite: manufactured by ADEKA Corporation, melting point 234-240 ° C., Sumilyzer (registered trademark) GP (Sumilizer GP: (6- [3- (3-t-butyl-4-hydroxy-5-methyl) Phenyl) propoxy] -2,4,8,10-tetra-t-butyldibenz [d, f] [1,3,2] dioxaphosphine, manufactured by Sumitomo Chemical Co., Ltd., melting point 128 ° C.), GSY P101 (tetrakis ( 2,4-di-tert-butyl-5-methylphenyl) 4,4'-biphenylenediphosphonite Sakai Kagaku include a melting point of about 100 ° C.) and the like.
These may be used alone or in combination of two or more.

As content of phosphorus antioxidant, it is 0.01-0.2 mass part with respect to 100 mass parts of methacrylic resin, Preferably it is 0.05-0.2 mass part, More preferably, it is 0.00. It is the range of 1-0.2 mass part.
Within this range, the thermal stability can be improved, and defects such as silver streaks are formed on the surface of the molded product due to a decrease in the light transmittance of the injection molded product and decomposition products derived from phosphorus antioxidants. And there is little risk of contamination of the mold during molding.

  In addition, when using a compound that acts as both a phosphorus-based antioxidant and a phenol-based antioxidant (for example, a compound containing both a phosphite structure and a hindered phenol structure in the molecule), a phosphorus-based antioxidant and It is considered that each of the phenolic antioxidants is contained.

--Hindered phenolic antioxidants--
The methacrylic resin composition in the present embodiment preferably contains a hindered phenolic antioxidant in addition to the above phosphorus antioxidant.
There is no restriction | limiting in particular as a hindered phenolic antioxidant to be used, Commercially available phenolic antioxidant may be used, for example, Irganox (trademark) 1010 (Irganox 1010: pentaerythritol tetrakis [3- ( 3,5-di-t-butyl-4-hydroxyphenyl) propionate], manufactured by BASF), Irganox 1076 (Irganox 1076: octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) Propionate (manufactured by BASF), Irganox 1330 (Irganox 1330: 3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-t-butyl-a, a ′, a ″-(mesitylene- 2,4,6-triyl) tri-p-cresol, manufactured by BASF), Irganox 3114 (Irgan x3114: 1,3,5-tris (3,5-di-t-butyl-4-hydroxybenzyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trione, BASF Irganox 3125 (Irganox 3125, manufactured by BASF), Adekastab AO-60 (pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], manufactured by ADEKA) Adekastab AO-80 (3,9-bis {2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxyoxy] -1,1-dimethylethyl} -2,4 8,10-tetraoxaspiro [5.5] undecane, manufactured by ADEKA), Cyanox 1790 (Cyanox 1790, Cyanox) Technic), Sumilizer GA-80 (Sumilizer GA-80, manufactured by Sumitomo Chemical), Sumilizer GS (Sumilizer GS: 2- [1- (2-hydroxy-3,5-di-tert-pentylphenyl) ethyl acrylate] -4,6-di-tert-pentylphenyl, manufactured by Sumitomo Chemical Co., Ltd., Sumilizer GM: 2-tert-butyl-4-methyl-6- (2-hydroxy-3-tert-butyl-5-acrylate) Methylbenzyl) phenyl, and Sumitomo Chemical Co., Ltd.).
Among these commercially available hindered phenol antioxidants, Irganox 1076, Adekastab AO-60, Adekastab AO-80, Irganox 1010, Sumilizer GS, and the like are preferable from the viewpoint of imparting thermal stability to the resin.
These may be used alone or in combination of two or more.

The content of the hindered phenol-based antioxidant is preferably 0.1 parts by mass or less, more preferably 0.01 to 0.1 parts by mass, and still more preferably with respect to 100 parts by mass of the methacrylic resin. Is 0.02-0.08 parts by mass.
If it is within this range, the thermal stability can be improved, there is no concern that the light transmittance of the injection-molded product is reduced and defects such as silver streaks are formed on the surface of the molded product, and bleed out during molding. There is little risk of contamination of the mold due to such problems.

The timing for adding these hindered phenolic antioxidants and phosphorus antioxidants is a method of adding to a monomer mixed solution before polymerization, a method of adding to a polymerization solution containing a polymer after polymerization, and after devolatilization. Examples include a method of adding to a polymer in a molten state, a method of adding pellets obtained after devolatilization and granulation, and adding again when melt extrusion and granulation.
When preparing the methacrylic resin composition of the present embodiment, among these, from the viewpoint of suppressing the thermal deterioration of the methacrylic resin and the formation of coloring by-products in the devolatilization step performed at higher temperatures. In addition, it is preferable to add an antioxidant to the polymerization solution containing the polymerized product after polymerization, and more preferably, a method of additionally adding an antioxidant during granulation after being subjected to the devolatilization step may be adopted. Particularly preferred.
At that time, the antioxidant added to the polymerization solution containing the polymer and the antioxidant added at the time of granulation are the same or different, and are not particularly limited as long as the effects of the present invention are not impaired. There is no.

--UV absorber ---
The methacrylic resin composition of the present embodiment can contain an ultraviolet absorber in its composition as long as the object of the present invention is not impaired.
Although it does not specifically limit as an ultraviolet absorber, It is preferable that it is an ultraviolet absorber which has the maximum absorption wavelength in 280-380 nm, For example, a benzotriazole type compound, a benzotriazine type compound, etc. can be used preferably.

  Although there is no restriction | limiting in particular as a benzotriazole type compound, For example, when a commercial item is illustrated, Kemisorb (trademark) 2792 (made by Chemipro Kasei), Adekastab (trademark) LA31 (made by ADEKA Corporation), Tinuvin (trademark) 234 (manufactured by BASF).

  Although there is no restriction | limiting in particular as a benzotriazine type compound, When a commercial item is illustrated, for example, Kemisorb102 (made by Chemipro Kasei), LA-F70 (made by ADEKA), LA-46 (made by ADEKA), Tinuvin 405 (Made by BASF), Tinuvin 460 (made by BASF), Tinuvin 479 (made by BASF), Tinuvin 1577FF (made by BASF), etc. can be used.

  The UV absorber is preferably a benzotriazole-based compound or a benzotriazine-based compound having a molecular weight of 400 or more from the viewpoint of compatibility with the resin and volatility during heating, and heating during extrusion of the UV absorber itself. From the viewpoint of inhibiting decomposition by benzotriazine, a benzotriazine-based compound is particularly preferable.

Further, the melting point (Tm) of the ultraviolet absorber is preferably 80 ° C. or higher, more preferably 100 ° C. or higher, further preferably 130 ° C. or higher, and more preferably 160 ° C. or higher. More preferred.
In addition, the UV absorber preferably has a weight reduction rate of 50% or less, more preferably 30% or less when the temperature is increased from 23 ° C. to 260 ° C. at a rate of 20 ° C./min. It is more preferably 15% or less, still more preferably 10% or less, still more preferably 5% or less.

These ultraviolet absorbers may be used alone or in combination of two or more.
By using two types of ultraviolet absorbers having different structures in combination, ultraviolet rays in a wide wavelength region can be absorbed.

  The blending amount of the ultraviolet absorber is not particularly limited as long as it is an amount that does not hinder heat resistance, moist heat resistance, thermal stability, transparency and moldability, and exhibits the effects of the present invention. The amount is preferably 0.001 to 0.1 parts by mass with respect to 100 parts by mass, preferably 0.001 to 0.08 parts by mass or less, more preferably 0.001 to 0.05 parts by mass, Still more preferably, it is 0.001-0.03 mass part. Within this range, it is possible to suppress coloration and performance deterioration due to ultraviolet rays while minimizing the change in color tone due to the ultraviolet absorber.

--Light stabilizer--
When the methacrylic resin composition of the present embodiment is used for an optical member such as a light guide plate, a light stabilizer can be included in the composition as long as the object of the present invention is not impaired.
Examples of the light stabilizer include hindered amine light stabilizers.
Examples of the hindered amine light stabilizer include bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, N, N-bis (3-aminopropyl) ethylenediamine, 2,4-bis [N- And butyl-N- (1,2,2,6,6-pentamethyl-4-piperidyl) amino] -6-chloro-1,3,5-triazine condensate.
The amount of the light stabilizer is not particularly limited as long as it is an amount that does not hinder heat resistance, moist heat resistance, thermal stability, transparency and molding processability and exhibits the effects of the present invention. It is preferable that it is 0.001-0.05 mass part with respect to 100 mass parts of resin, More preferably, it is the range of 0.001-0.03 mass part. Within this range, the balance as the molded article for the light guide plate, the balance of injection moldability, etc. is excellent.

-Other additives-
In particular, when the methacrylic resin composition of the present invention is used for forming a light guide plate, a masking agent such as a fluorescent brightening agent and a bluing agent can be optionally used as necessary.
Other additives are not particularly limited. For example, stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate; paraffinic process oil, naphthenic process oil, aromatic process oil, paraffin And softeners / plasticizers such as organic polysiloxanes and mineral oils; antistatic agents; or mixtures thereof.

  Hereinafter, the characteristics of the methacrylic resin composition of the present embodiment will be described in detail.

-Glass transition temperature-
The glass transition temperature (Tg) of the methacrylic resin composition in this embodiment is more than 120 ° C. and 160 ° C. or less.
If the glass transition temperature (Tg) of the methacrylic resin composition exceeds 120 ° C., necessary and sufficient heat resistance can be obtained more easily as a recent lens molded body and a film molded body optical film for a liquid crystal display.
The glass transition temperature (Tg) is more preferably 125 ° C. or higher, and further preferably 130 ° C. or higher, from the viewpoint of dimensional stability and durability under the use environment temperature.
On the other hand, when the glass transition temperature (Tg) of the methacrylic resin composition exceeds 160 ° C., the temperature at the time of melt processing must be set to a considerably high temperature, which tends to cause thermal decomposition of the resin, etc. It may be difficult to obtain a good product.
The glass transition temperature (Tg) is preferably 150 ° C. or lower for the reasons described above.
The glass transition temperature (Tg) can be determined by measuring in accordance with JIS-K7121. Specifically, it can measure using the method described in the Example mentioned later.

-Weight average molecular weight (Mw)-
The methacrylic resin composition of the present embodiment preferably has a weight average molecular weight (Mw) in terms of polymethyl methacrylate measured by a gel permeation chromatography (GPC) measurement method of 90,000 to 180,000, More preferably, it is 100,000-170,000, More preferably, it is 120,000-160,000.
When the weight average molecular weight (Mw) is in this range, the balance between mechanical strength and moldability is excellent, which is preferable.
In addition, the weight average molecular weight of a methacrylic-type resin composition can be measured by the method of the below-mentioned Example description.

-Molecular weight distribution-
In addition, regarding the ratio among the Z average molecular weight (Mz), the weight average molecular weight (Mw), and the number average molecular weight (Mn) as parameters representing the molecular weight distribution, in the methacrylic resin composition in the present embodiment, the fluidity Mw / Mn is preferably 2.0 to 3.0, more preferably 2.1 to 2.9, and 2.1 to 2.7 in consideration of the balance between mechanical strength and mechanical strength. More preferably; Mz / Mw is preferably 1.6 to 3.0, more preferably 1.6 to 2.8, and even more preferably 1.7 to 2.7. preferable.
In particular, in the methacrylic resin composition in the present embodiment, when Mz / Mw is in this range, an increase in the gel-like material in the molded body accompanying an increase in the proportion of the high molecular weight material is suppressed, and It tends to be a composition having a good balance between properties and impact resistance, and is particularly preferred for the purpose of obtaining a thin injection molded article.
In addition, about the Z average molecular weight of a methacrylic resin composition, and a number average molecular weight, it can measure by the method of the below-mentioned Example description.

In this embodiment, as a method for preparing the resin composition having the molecular weight distribution as described above, two or more methacrylic resins having the same kind of ring structure in the main chain and having different weight average molecular weights and molecular weight distributions are used. It can also be prepared.
The range of the weight average molecular weight (Mw) of the methacrylic resin used when preparing a composition by mixing two or more methacrylic resins is arbitrarily selected from the range of 70,000 to 500,000, respectively. Good.
When the weight average molecular weight (Mw) is low (hereinafter referred to as “low molecular weight component”), the weight average molecular weight is preferably in the range of 70,000 to 150,000, and more preferably 80,000 to More preferably, it is in the range of 150,000.
In the case of a material having a high weight average molecular weight (Mw) (hereinafter referred to as “high molecular weight component”), the weight average molecular weight is preferably in the range of 200,000 to 500,000, particularly 220,000 to More preferably, it is in the range of 400,000.
The mixing ratio of the low molecular weight component and the high molecular weight component in the present embodiment is not particularly limited as long as the above molecular weight distribution characteristics can be satisfied.

  In the present embodiment, the method of mixing two or more methacrylic resins having different weight average molecular weights (Mw) is not particularly limited, but 2 polymers having different weight average molecular weights obtained by the polymerization reaction described above are used. It is possible to employ a method in which a solution containing at least seeds is mixed in a liquid phase, and then prepared using a devolatilization apparatus composed of a heat exchanger and a vacuum vessel.

  In addition, about the Z average molecular weight of a methacrylic resin and a methacrylic resin composition, a weight average molecular weight, and a number average molecular weight, it can measure by the method of the below-mentioned Example description.

-Melt viscosity-
As the melt viscosity of the methacrylic resin composition having a ring structure in the main chain of the present embodiment, the melt viscosity is 250 pa · sec or less at a resin temperature of 270 ° C. and a shear rate of 1000 sec ⁻¹ , 50 to It is preferably in the range of 200 pa · sec, and more preferably in the range of 50 to 170 pa · sec. When the melt viscosity is within this range, high-quality injection molding is achieved without causing problems such as burrs, silver streaks, and warpage as the molded product while reducing residual stress strain and thermal strain generated in the injection molded product. Since a body is obtained, it is preferable.

Furthermore, as the melt viscosity of the methacrylic resin composition having a ring structure in the main chain of the present embodiment, the ratio of the melt viscosity at 250 ° C. to the melt viscosity at 290 ° C. at a shear rate of 1000 sec ⁻¹ is 3. It is preferably 0 or less. Within this range, a high-quality injection-molded product can be obtained without causing problems such as burrs, silver streaks, and warpage as the molded product while reducing residual stress strain and thermal strain generated in the molded product. This is preferable because it becomes easier.

The melt viscosity in the present invention can be measured using, for example, a twin capillary rheometer manufactured by Rosand. More specifically, it can be measured by the method described in the examples.
As the orifice to be used, a long die having a length of 16 mm, a diameter of 1 mm, and a die inflow angle of 90 ° is used, and a short die having a length of 0.25 mm, a diameter of 1 mm, a die Measurement is performed at a desired measurement temperature and shear rate using an inflow angle of 90 °.

-Photoelastic coefficient-
The absolute value of the photoelastic coefficient C _R of the methacrylic resin composition having a main chain in the ring structure of the present embodiments are to 1.0 × 10 ^-12 Pa ^-1 or less, 0.6 × 10 ^-12 Pa ^{-1 Or} less, more preferably 0.3 × 10 ⁻¹² Pa ⁻¹ or less.
The photoelastic coefficient is described in various documents (see, for example, Chemical Review, No. 39, 1998 (published by the Academic Publishing Center)) and is defined by the following formulas (ia) and (ib). It is. As the value of photoelastic coefficient C _R is close to zero, it can be seen that change in birefringence due to an external force is small.
C _R = | Δn | / σ _R (ii)
| Δn | = | nx−ny | (i−b)
(Where C _R is the photoelastic coefficient, σ _R is the tensile stress, | Δn | is the absolute value of birefringence, nx is the refractive index in the stretching direction, and ny is the direction perpendicular to the stretching direction in the plane] The refractive index is shown respectively.)
If the absolute value of the photoelastic coefficient C _R of the methacrylic resin composition of the present embodiment is 1.0 × 10 ⁻¹² Pa ⁻¹ or less, even in an injection molded product having a relatively thin thickness and a long optical path length. In addition, an optical member having a high light transmittance and less luminance unevenness can be obtained even when used as a light guide plate.
Specifically, the photoelastic coefficient C _R can be obtained by the method described in Examples below.

-Light transmittance in chloroform solution-
In general, a methacrylic resin composition is used, and a molded product obtained by injection molding has its molding conditions (cylinder temperature, mold temperature, injection speed, holding pressure, mold material, test piece mold shape in mold, sprue, It is widely known to show the light transmittance of a molded body after being influenced by various factors such as a flow path design of a runner or the like.
Therefore, the present inventors thought that it is better to obtain a light transmittance in a solution state by obtaining a solution of the composition when the light transmittance inherent in the resin composition is to be obtained.
At that time, as a result of intensive studies to make the evaluation reflecting the original characteristics of the resin composition as much as possible, a concentration of 20 mass to volume was adopted as the concentration, and the quartz cell length at the time of measuring the light transmittance was 100 mm. By adopting this long optical path cell, it was found that the evaluation that well reflects the transmittance characteristics inherent in the resin composition is possible.

That is, the methacrylic resin composition of the present embodiment has a light transmittance of 94.94 when measured in the condition of an optical path length of 100 mm and a wavelength of 470 nm when prepared in a 20 mass to volume percent chloroform solution. It is 0% or more, preferably 95.0% or more, more preferably 96.0% or more.
In addition to the light transmittance described above, the light transmittance when the composition is prepared in a 20 mass to volume percent chloroform solution is a light transmittance obtained by measurement under conditions of an optical path length of 100 mm and a wavelength of 700 nm. It is 96.0% or more, preferably 97.0% or more, more preferably 98.0% or more.
By satisfying these, when the methacrylic resin composition obtained in the present embodiment is used as an optical member such as a light guide plate, even when a light guide plate is prepared by injection molding under a wide range of conditions, higher light transmission is achieved. When using as a light guide plate, a light guide plate with high luminance and less color unevenness can be obtained.

As a method of measuring the light transmittance of the resin composition in a chloroform solution, a mass to volume percentage (hereinafter referred to as w / v%) is 20 w / v% (that is, 10 g of a sample is dissolved in chloroform and 50 mL of Solution prepared at such a ratio as to be a solution) and can be measured and determined using an ultraviolet-visible spectrophotometer.
More specifically, the light transmittance can be determined by the method described in the examples described later.

-Phosphorus element content and phosphorus element valence determination-
The methacrylic resin composition of the present embodiment is added with at least a phosphorus-based antioxidant that is an organic phosphorus compound having a melting point of 100 to 250 ° C. and having a trivalent phosphorus element, such as phosphites and phosphonites. Contains as an agent. It is known that phosphites and phosphonites, which are trivalent organic phosphorus compounds, are generally easily oxidized by applying heat in the presence of oxygen and are also prone to hydrolysis. It is known that acidic P—OH and PH═O protons are generated by hydrolysis and react directly with oxygen and hydroperoxide to form pentavalent organophosphorus compounds. Therefore, the methacrylic resin composition of the present embodiment may include a pentavalent phosphorus element in which the trivalent phosphorus element in the phosphorus antioxidant is changed by oxidation, hydrolysis, or the like during the manufacturing process.
Therefore, the methacrylic resin composition of this embodiment contains trivalent and pentavalent phosphorus elements.

It is preferable that content of the phosphorus element of the methacrylic resin composition of this embodiment is 5-200 mass ppm, More preferably, it is 10-180 mass ppm, More preferably, it is 20-150 mass ppm. Here, the content of phosphorus element means the content of all phosphorus elements contained in the methacrylic resin composition, and the oxidation number is not limited.
When the phosphorus element content is less than 5 ppm by mass, the heat and oxygen decomposition of the methacrylic resin composition having a high glass transition temperature as in the present embodiment and mold contamination during injection molding are sufficiently suppressed. There is a fear that you can not.
Further, when the phosphorus element content exceeds 200 ppm by mass, the volatile matter that is produced when melt kneading is performed at a high temperature using a methacrylic resin composition having a high glass transition temperature as in this embodiment. Decomposition products are present in a large amount in the composition, and cooling rolls and mold dirt during injection molding increase, and a large amount of streaks and silver streaks are generated on the surface of the resulting molded product. There is a fear.
The content of the phosphorus element contained in the methacrylic resin composition can be measured using an X-ray fluorescence analyzer, for example, obtained by SQX order analysis using Rigaku X-ray fluorescence: ZSX Primus II. Can do.

Whether or not the organophosphorus compound contained in the methacrylic resin composition contains an organophosphorus compound having a trivalent phosphorus element as its constituent element is attributed to trivalent phosphorus in ³¹ P-NMR measurement. It can be confirmed from the spectrum peak.
More specifically, for example, using a Fourier transform nuclear magnetic resonance apparatus (AVANCE III 500HD Prodigy) manufactured by Bruker Biospin, observation frequency: 202 MHz, number of integration: 50000 times, flip angle of detection pulse: 30 °, delay time: It can be determined by performing measurement under the conditions of 2 seconds, pulse program: zg30, measurement temperature: room temperature, solvent used: CDCl ₃ , internal standard substance: hexamethylphosphoric triamide.
For more specific conditions for preparing the measurement sample solution, the methods described in the examples described later can be used.

Further, in the ³¹ P-NMR measurement of the methacrylic resin composition of the present embodiment, the integral value (P3) of the spectrum peak attributed to trivalent phosphorus with respect to the integral value (P5) of the spectrum peak attributed to pentavalent phosphorus. The ratio (P3 / P5) is preferably 0.2 to 2.0, more preferably 0.4 to 1.8, and still more preferably 0.6 to 1.8.
When the ratio (P3 / P5) is less than 0.2, decomposition by heat or oxygen cannot be sufficiently suppressed when injection molding is performed at a high temperature using the methacrylic resin composition of the present embodiment. In addition, the formation of aggregated foreign substances may occur due to the influence of the generated decomposition products and oxidation products, which may cause streaks and silver streaks on the surface of the injection molded product.
In addition, when the ratio (P3 / P5) exceeds 2.0, decomposition products and oxidation products generated due to high temperature and long stay during injection molding increase, and streaks and Silver streaks are generated, and the product quality may be deteriorated.
The proportion of this embodiment (P3 / P5) can be determined from the spectral peaks obtained using the ³¹ P-NMR.

-Spiral flow length (SFD)-
The methacrylic resin composition of the present embodiment uses a resin flow length measuring mold having a spiral flow path having a thickness of 1 mm and a width of 10 mm, a cylinder temperature of 270 ° C., a mold temperature of 100 ° C., and an injection pressure of 125 MPa. The flow length (spiral flow length) measured by performing injection molding at is preferably 150 mm or more, more preferably 170 mm or more, and further preferably 190 mm or more.
When the spiral flow length (SFD) is in the above range, it is excellent in fluidity and is suitably used for molding an injection molded body with a thin wall or a mold having a long flow distance for use in an optical member such as a light guide plate. be able to.
The upper limit value of the spiral flow length (SFD) is not particularly limited, but is usually about 300 mm.
Spiral flow length (SFD) is a resin having an Archimedes spiral flow path with a thickness of 1.0 mm and a width of 10 mm under the predetermined conditions of cylinder temperature, mold temperature, cooling time and injection pressure in an injection molding machine. It can be measured by injection molding using a flow length measuring mold.

(Method for producing methacrylic resin composition)
The method for producing the methacrylic resin composition of the present embodiment is not particularly limited as long as a composition satisfying the requirements of the present invention can be obtained.
Further, when the methacrylic resin composition of the present embodiment is used for an optical member application such as a light guide plate, the polymerization reaction step, liquid-liquid is used for the purpose of keeping the light transmittance high and reducing foreign matters. In any one or more of the separation step, the liquid-solid separation step, the devolatilization step, the granulation step, and the molding step, for example, a sintered filter, a pleat filter, and / or a filtration accuracy of 1.5 to 20 μm. It is also a preferred method to prepare by adding a leaf disk type polymer filter or the like to the filtration device.

Regardless of which method is selected, when producing a methacrylic resin composition, it is preferable to reduce oxygen and moisture as much as possible.
For example, the dissolved oxygen concentration in the polymerization solution in the solution polymerization is less than 300 ppm in the polymerization step, and in the preparation method using an extruder or the like, the oxygen concentration in the extruder is less than 1% by volume. It is preferable to be less than 0.8% by volume.
It is recommended that the water content of the methacrylic resin is adjusted to preferably 1000 ppm by mass or less, more preferably 500 ppm by mass or less.
Within these ranges, it is relatively easy and advantageous to prepare a composition that satisfies the requirements of the present invention.

For example, when adopting a manufacturing method using an extruder, the pelletized methacrylic resin as a raw material is heated under reduced pressure or dehumidified air and sufficiently dried in advance to remove moisture as much as possible. And preferably used.
At that time, when various antioxidants and additives described later are blended, it is preferable to blend these various antioxidants and additives themselves after sufficiently reducing the amount of water contained therein.
Furthermore, in order to reduce oxygen contamination in the extruder as much as possible and prevent oxidation of the composition in the molten state, an inert gas such as nitrogen gas is allowed to flow into the extruder and a vented extruder is used. It is preferable to carry out while evacuating under reduced pressure.

In the present embodiment, in order to obtain a highly controlled methacrylic resin composition, the composition in a molten state at a high temperature can be quickly cooled and solidified so as not to be exposed to air as much as possible. It is preferable to employ a grain system.
For this purpose, for example, a watering hot cut method, a cold cut method, an underwater strand cut method, an underwater cut method, and the like are preferable. A cut method is more preferable.
In that case, the molten resin temperature should be lowered as much as possible, the residence time from the perforated die outlet to the cooling water surface should be minimized, and the cooling water temperature should be as high as possible. It is more preferable to perform granulation.
For example, the molten resin temperature is preferably 220 to 280 ° C, more preferably 230 to 270 ° C, and the residence time from the porous die outlet to the cooling water surface is preferably within 5 seconds, more preferably within 3 seconds. The temperature of the cooling water is preferably 30 to 80 ° C, more preferably 40 to 60 ° C.

  Hereinafter, the characteristics of the molded body of this embodiment will be described in detail.

-In-plane phase difference Re-
In the molded body of the present embodiment, the absolute value of the phase difference Re in the in-plane direction is preferably 10 nm or less. Here, the in-plane direction phase difference Re is a value obtained by converting to a thickness of 1 mm.
The absolute value of the in-plane direction phase difference Re is more preferably 8 nm or less, further preferably 6 nm or less, and particularly preferably 4 nm or less.
In general, the absolute value of the in-plane direction phase difference Re is an index representing the magnitude of birefringence. The molded body according to this embodiment is sufficiently small with respect to the birefringence of an existing resin (for example, PMMA, PC, triacetylcellulose resin, cyclic olefin resin, etc.), and an optical component that requires low birefringence as an optical material. It is suitable for applications such as a lens and a light guide plate.
On the other hand, when the absolute value of the in-plane phase difference Re exceeds 10 nm, it means that the refractive index anisotropy is high, and it may not be used for applications requiring low birefringence as an optical component.

-Color tone (YI value)-
The molded product of this embodiment preferably has a YI (yellowness index) value of 1 or less at an optical path length of 1 mm, more preferably 0.8 or less, and even more preferably 0.6 or less.
When the YI value at an optical path length of 1 mm is in the above range, a color tone suitable for a molded article for optical applications can be obtained.
The YI value can be measured according to JIS K 7373 using a color difference meter (SD5000, manufactured by Nippon Denshoku Co., Ltd.). More specifically, it can be measured by the method described in Examples below.

-Light transmittance in the thickness direction-
The molded product of this embodiment preferably has a light transmittance of 90% or more at an optical path length of 1 mm, more preferably 91% or more, and still more preferably 92% or more.
When the light transmittance at an optical path length of 1 mm is in this range, transparency suitable for a molded article for optical applications can be obtained.
In addition, light transmittance can be measured based on JISK7361-1 using a Hayes meter (Nippon Denshoku make, NDH5000W). More specifically, it can be measured by the method described in Examples below.

-Manufacturing method of molded body-
When the methacrylic resin composition of the present embodiment is used to obtain a molded body, injection molding and injection compression molding can be applied.

  Usually, the injection molding method consists of (1) an injection process in which the resin is melted and the temperature-controlled mold cavity is filled with the molten resin, and (2) pressure is applied in the cavity until the gate is sealed, and the injection process is performed. A pressure-holding step of injecting a resin corresponding to the amount of the molten resin that has been brought into contact with the mold and cooled and contracted; (3) a cooling step of holding the molded product until the resin is cooled after releasing the pressure-holding; 4) Opening the mold and taking out the cooled molded product.

At this time, the molding temperature is preferably in the range of Tg + 100 ° C. to Tg + 180 ° C., preferably in the range of Tg + 110 ° C. to Tg + 160 ° C., based on the glass transition temperature of the methacrylic resin composition. Here, the molding temperature refers to the control temperature of the band heater wound around the injection nozzle.
The mold temperature is in the range of Tg-70 ° C to Tg, preferably in the range of Tg-50 ° C to Tg-20 ° C, based on the glass transition temperature (Tg) of the methacrylic resin composition. preferable.

The injection speed can be appropriately selected depending on the thickness and dimensions of the injection molded product to be obtained. For example, it can be appropriately selected from the range of 200 to 1000 mm / second.
Further, the pressure for holding pressure can be appropriately selected within the range of 30 to 120 MPa.
Here, the pressure for holding pressure is a pressure held by a screw for further feeding the molten resin from the gate after filling with the molten resin.

Injection compression molding means that the mold is opened slightly in advance at the start of injection molding, the molten resin is filled into the mold at high speed and low pressure, and then the mold clamping pressure is increased at high speed to keep the entire surface of the resin uniform. This is an injection molding method to which a compression / holding step for pressing is added, and it becomes possible to mold a molded article excellent in surface characteristics and optical characteristics.
When it is intended to obtain an injection molded body having a thinner thickness, for example, a thickness of less than 1 mm and a diagonal dimension exceeding 100 mm, a molded body having excellent optical properties and color tone can be obtained by adopting injection compression molding. Since it is obtained, it is especially preferable.

  Moreover, when using the injection-molded body obtained by using the methacrylic resin composition of the present invention as a light guide plate, those having fine irregularities on the surface thereof are also included. Providing such fine irregularities is preferable because it is not necessary to separately provide a reflective layer by printing or the like. The fine irregularities are not particularly limited, but are irregularities such as a rectangular parallelepiped, a cylindrical shape, an elliptical column, a triangular prism, a spherical surface, an aspherical surface, and an irregular shape such as a satin shape or a hairline shape, Concavities and convexities in which the structural unit is not clear, or a combination thereof, and also the structural units in which the structural unit is clear but the shape, in particular, the size is changing. Examples of the shape of the unevenness include a height of the shape or a recess of 0.1 to 500 μm, and an example of the pitch distance between the unevenness is 10 to 1000 μm.

The molded body comprising the methacrylic resin composition of the present invention can be suitably used for applications such as household items, OA equipment, AV equipment, battery electrical parts, lighting equipment, and optical members in automobiles.
As an optical member in household goods, OA equipment, AV equipment, battery electrical equipment parts, lighting equipment, etc., for example, a light guide plate, a display front plate, a touch panel used for a display such as a smartphone, a PDA, a tablet PC, and a liquid crystal television, Is a lens for smartphones, tablet PC cameras, etc., optical lens components such as head mounted displays and liquid crystal projectors, such as prism elements, waveguides, lenses, especially small thin walled optical lenses, optical fibers, optical fiber coating materials A lens, a Fresnel lens, a phase plate provided with a microlens array, an optical cover component, and the like.
Examples of optical members in automobiles include in-vehicle display light guide plates; in-vehicle instrument panels; car navigation front panels, combiners, optical cover parts and other optical components for head-up displays; in-vehicle camera lenses, light guide bars, and the like. .
In addition to the above, there are also parts for display devices for digital signage that send information to a thin display connected to a network for the purpose of advertising, advertising, etc. in places such as camera focusing plates, outdoors, storefronts, public institutions, transportation, etc. It can be preferably used.

  Among them, the molded body made of the methacrylic resin composition of the present invention has high heat resistance, highly controlled birefringence, high light transmittance, small retardation value, and excellent color tone and transparency. It can be suitably used for an optical member having a long optical path length such as a light guide plate.

  Hereinafter, the contents of the present invention will be specifically described with reference to Examples and Comparative Examples. In addition, this invention is not limited to the following Example.

(1. Determination of remaining amount of N-substituted maleimide monomer)
Part of the analysis target (polymerized solution after polymerization or bead polymer) is collected and weighed, this sample is dissolved in chloroform to prepare a 5% by mass solution, and n-decane is added as an internal standard substance. And gas chromatography (Shimadzu Corporation GC-2010) were used for measurement under the following conditions.
Detector: FID
Column used: ZB-1
Measurement conditions: After holding at 45 ° C. for 5 minutes, the temperature is raised to 300 ° C. at a temperature rising rate of 20 ° C./min.
Then hold for 15 minutes

(2. Structural unit analysis)
Unless otherwise specified, each structural unit in the methacrylic resin compositions produced in the examples and comparative examples described below is about methacrylic resin and methacrylic resin composition by ¹ H-NMR measurement and ¹³ C-NMR measurement. Each structural unit was identified and its abundance was calculated. The measurement conditions for ¹ H-NMR measurement and ¹³ C-NMR measurement are as follows.
・ Measurement equipment: DPX-400 manufactured by Blue Car Co., Ltd.
Measurement solvent: CDCl ₃ or d6-DMSO
・ Measurement temperature: 40 ℃

(3. Glass transition temperature)
Based on JIS-K7121, the glass transition temperature (Tg) (degreeC) of the methacrylic resin composition was measured.
First, 4 pieces (about 4 places) of about 10 mg each were cut out as test pieces from a sample that was conditioned (left at 23 ° C. for 1 week) under standard conditions (23 ° C., 65% RH).
Next, a differential scanning calorimeter (Diamond DSC manufactured by PerkinElmer Japan Co., Ltd.) was used under a nitrogen gas flow rate of 25 mL / min. Temperature (primary temperature increase), held at 200 ° C. for 5 minutes to completely melt the sample, then cooled to 10 ° C./minute from 200 ° C. to 40 ° C., held at 40 ° C. for 5 minutes, Of the DSC curve drawn during the temperature rise (secondary temperature rise) again under the above temperature rise conditions, the stepwise change partial curve at the time of the secondary temperature rise and the respective base line extension lines are equidistant in the vertical axis direction. The intersection (intermediate glass transition temperature) with a certain straight line was measured as the glass transition temperature (Tg) (° C.). Four points were measured per sample, and the arithmetic average of four points (rounded off after the decimal point) was taken as the measured value.

(4. Molecular weight and molecular weight distribution)
The weight average molecular weight (Mw), number average molecular weight (Mn), and Z average molecular weight (Mz) of the methacrylic resin compositions produced in Examples and Comparative Examples described later were measured using the following apparatuses and conditions.
-Measuring apparatus: Tosoh Corporation gel permeation chromatography (HLC-8320GPC)
·Measurement condition:
Column: One TSK guard column SuperH-H, two TSK gel Super HM-M, and one TSK gel Super H 2500 were connected in series in this order.
Column temperature: 40 ° C
Developing solvent: tetrahydrofuran, flow rate: 0.6 mL / min, 2,6-di-t-butyl-4-methylphenol (BHT) was added at 0.1 g / L as an internal standard.
Detector: RI (differential refraction) detector Detection sensitivity: 3.0 mV / min Sample: 0.02 g of methacrylic resin composition in 20 mL of tetrahydrofuran Injection amount: 10 μL
Standard sample for calibration curve: The following 10 polymethyl methacrylates (manufactured by Polymer Laboratories; PMMA Calibration Kit MM-10) having different molecular weights but known monodispersed weight peak molecular weights were used.
Weight peak molecular weight (Mp)
Standard sample 1 1,916,000
Standard sample 2 625,500
Standard sample 3 298,900
Standard sample 4 138,600
Standard sample 5 60,150
Standard sample 6 27,600
Standard sample 7 10,290
Standard sample 85,000
Standard sample 9 2,810
Standard sample 10 850
Under the above conditions, the RI detection intensity with respect to the elution time of the methacrylic resin composition was measured.
Based on each calibration curve obtained by measurement of the standard sample for the calibration curve, the weight average molecular weight (Mw), the number average molecular weight (Mn), and the Z average molecular weight (Mz) of the methacrylic resin composition are obtained. The value was used to determine the molecular weight distribution (Mw / Mn) and (Mz / Mw).

(5. Melt viscosity)
The methacrylic resin compositions obtained in Examples and Comparative Examples described later were dried at 80 ° C. for 24 hours, and then measured under the following conditions.
Device name: Twin capillary rheometer (Rosand)
Orifice: Long die Length: 16mm Hole diameter: 1mmφ Incident angle 90 °
Short die Length: 0.25mm Hole diameter: 1mmφ Incident angle 90 °
Measurement temperature: 270 ° C
Holding time in the cylinder until the start of measurement: 9 minutes Shear rate at the time of measurement: Measured by sequentially changing to the following 8 levels within the range of 8000 to 40 sec ⁻¹ (8 levels: 8000, 4000, 2000, 1000, 400, 200, 100, 40 sec ⁻¹ ). Among the obtained results, a value at 1000 sec ⁻¹ close to the shear rate region at the time of injection molding was used for evaluation.

(6. Light transmittance in solution)
The methacrylic resin composition obtained in the examples and comparative examples described later is 20 w / v% (that is, a solution prepared in such a ratio that a 10 g sample is dissolved in chloroform to form a 50 mL solution). A chloroform solution was used as a measurement sample. Using a UV-visible spectrophotometer (manufactured by Shimadzu Corporation, UV-2500PC), measuring wavelength 380-780 nm, slit width 2 nm, 10 cm optical path length cell with viewing angle 10 °, auxiliary illuminant C, reference object: chloroform The transmittance was measured.
The transmittance (%) at a wavelength of 470 nm and a wavelength of 700 nm was recorded.

(7. Photoelastic coefficient)
The methacrylic resin compositions obtained in Examples and Comparative Examples were used as measurement samples by using a vacuum compression molding machine as a press film.
As specific sample preparation conditions, using a vacuum compression molding machine (manufactured by Shinfuji Metal Industry Co., Ltd., SFV-30 type), preheating at 260 ° C. under reduced pressure (about 10 kPa) for 10 minutes, After compressing at about 10 MPa for 5 minutes and releasing the reduced pressure and the press pressure, it was transferred to a cooling compression molding machine and solidified by cooling. The obtained press film was cured for 24 hours or more in a constant temperature and humidity chamber adjusted to 23 ° C. and a humidity of 60%, and then a test specimen (thickness: about 150 μm, width: 6 mm) was cut out.
The photoelastic coefficient C _R (Pa ⁻¹ ) was measured using a birefringence measuring device described in detail in Polymer Engineering and Science 1999, 39, 2349-2357.
The film-shaped test piece was similarly arrange | positioned so that it might become 50 mm between chuck | zippers on the film tension apparatus (made by Imoto Seisakusho) installed in the constant temperature and humidity chamber. Next, the apparatus was arranged so that the laser beam path of the birefringence measuring apparatus (manufactured by Otsuka Electronics, RETS-100) was positioned at the center of the film, and the strain rate was 50% / min (between chucks: 50 mm, chuck moving speed: The birefringence of the test piece was measured while applying an extensional stress at 5 mm / min.
From the relationship between the absolute value of birefringence (| Δn |) and the tensile stress (σ _R ) obtained from the measurement, the slope of the straight line is obtained by least square approximation, and the photoelastic coefficient (C _R ) (Pa ⁻¹ ) is obtained. Calculated. For the calculation, data with an extensional stress between 2.5 MPa ≦ σ _R ≦ 10 MPa was used.
C _R = | Δn | / σ _R
Here, the absolute value (| Δn |) of birefringence is a value shown below.
| Δn | = | nx−ny |
(Nx: refractive index in the stretching direction, ny: refractive index in the direction perpendicular to the stretching direction in the plane)

(8. Spiral flow; SFD)
Using an “EC100SX” injection molding machine manufactured by Toshiba Machine Co., Ltd., a spiral flow of Archimedes having a thickness of 1.0 mm and a width of 10 mm under conditions of a cylinder temperature of 270 ° C., a mold temperature of 100 ° C., and a cooling time of 7 seconds. The spiral flow length (mm) was measured under the condition that the injection pressure was 125 MPa using a mold having a path.

-Evaluation with injection molded plate-
(9. Phase difference Re in the in-plane direction of the injection molded product)
Using the “AUTO SHOT Model 15A” injection molding machine made by FANUC CORPORATION, flat plate mold (product dimensions: short side; 45 mm × long side; 60 mm × thickness; 1 mm; gate type: installed on the long side with a fan gate) ), 50 shots of injection molding were performed under the conditions of a cylinder temperature of 270 ° C., a mold temperature of 110 ° C., a cooling time of 60 seconds, and a cycle time of 70 seconds to prepare a thin injection molded plate.
Among the obtained injection-molded plates, the last five obtained were placed in a constant temperature and humidity chamber adjusted to 23 ° C. and humidity 60%, and a phase difference measuring device (KOBRA-21ADH) manufactured by Oji Scientific Instruments Co., Ltd. Was used to measure the phase difference Re in the in-plane direction at a wavelength of 589 nm.
As the measurement position, in addition to the center part of the flat plate sample, 4 points were added 10 mm inside from the long side end face part and 10 mm inside from the short side end face part, respectively, and the total position was 5 points per sheet. The phase difference Re was measured. Similarly, measurement was performed for each of five injection-molded plates, and the average value of a total of 25 absolute values was used as the phase difference Re value.

(10. Color tone (YI) and light transmittance in thickness direction of injection molded product)
The above-mentioned 9. The YI value and light transmittance in the thickness direction (optical path length 1 mm) were measured for the injection-molded plate obtained by the preparation of the described injection-molded plate.
The YI value in the thickness direction was measured in a wavelength range of 380 to 780 nm using a color difference meter (Nippon Denshoku Co., Ltd., SD5000) in accordance with JIS K 7373.
The light transmittance in the thickness direction was measured according to JIS K7361-1 using a haze meter (NDH5000W, manufactured by Nippon Denshoku Co., Ltd.).

(11. Injection moldability: releasability)
The above-mentioned 9. In the injection molding plate preparation described above, injection molding was performed with the cylinder temperature changed to 290 ° C, and the evaluation was based on the rate of occurrence of defects in 100 shots (cracking on the molded product during mold sticking and / or mold release). went.
A case where the incidence was less than 5% was determined as “◯”, a case where it was 5% to 20% was determined as “Δ”, and a case where the occurrence rate exceeded 20% was determined as “x”.

(12. Injection moldability: retention stability A)
The above-mentioned 9. In the injection molding plate preparation described above, after 40 shots, the injection molding cycle time was changed from 70 seconds to 240 seconds, the number of moldings was changed to 10 shots, injection molding was performed, and the state of occurrence of silver streaks on the molding plate surface was determined. It was observed visually.
The case where no silver streaks occurred in any of the 10 samples was determined as “◯”. The case where silver streaks occurred in 1 to 3 injection-molded plates in the sample was determined as “Δ”. The case where silver streaks occurred in four or more injection-molded plates in the sample was determined as “x”.

(13. Injection moldability: retention stability B)
The above-mentioned 9. In the preparation of the injection-molded plate described, after 40 hours, the molten resin composition is held in the cylinder, and after 1 hour, molding is resumed, 10-shot injection molding is performed, and the occurrence of foreign matter in the molded plate is checked. It was observed visually.
A case where no colored foreign matter was observed in any of the 10 samples was determined as “◎”. A case where foreign matter was observed on one or less of the 10 samples was determined as “◯”. A case where colored foreign matters were observed on 2 to 4 molded plates in 10 samples was determined as “Δ”. The case where foreign matter was observed in 5 or more of 10 samples was determined as “x”.

[material]
It shows below about the raw material used in the Example and comparative example which are mentioned later.
[[Monomer]]
・ Methyl methacrylate (MMA): Asahi Kasei Corporation ・ N-Phenylmaleimide (phMI): Nippon Shokubai Co., Ltd. ・ N-cyclohexylmaleimide (chMI): Nippon Shokubai Co., Ltd. ・ Styrene: Asahi Kasei Chemicals [[Start of polymerization Agent]]
1,1-di (t-butylperoxy) cyclohexane: NOF Corporation "Perhexa C"
[[Chain transfer agent]]
-N-octyl mercaptan: manufactured by Kao Corporation [[hindered phenol-based antioxidant]]
A-1; Irganox 1076 (manufactured by BASF)
A-2; Irganox 1010 (manufactured by BASF)
・ A-3: Sumilyzer GS (manufactured by Sumitomo Chemical Co., Ltd.)
[[Phosphorus antioxidant]]
・ P-1; Irgaphos 168 (melting point: 180 to 190 ° C., manufactured by BASF)
P-2: ADK STAB PEP36 (melting point: 234-240 ° C., manufactured by ADEKA Corporation)
P-3; ADK STAB HP-10 (melting point: 146 to 152 ° C., manufactured by ADEKA Corporation)
-P-4; Sumilizer GP (melting point 128 ° C., manufactured by Sumitomo Chemical Co., Ltd.)
-P-5; ADK STAB 1500 (liquid at room temperature (25 ° C); manufactured by ADEKA Corporation)
[[Release agent]]
R-1; Riquemar H-100 (glycerin monostearate; manufactured by Riken Vitamin Co.)
R-2: Riquemar S71-D (diglycerin monostearate; manufactured by Riken Vitamin Co., Ltd.)
R-3: Rheodor AS-10V (sorbitan monostearate; manufactured by Kao Corporation)
R-4: Exepearl PE-MS (pentaerythritol monostearate; manufactured by Kao Corporation)

[Example 1]
Methyl methacrylate (hereinafter referred to as MMA) 450.7 kg, N-phenylmaleimide (hereinafter referred to as phMI) 39.6 kg, N-cyclohexylmaleimide (hereinafter referred to as chMI) 59.3 kg, chain transfer agent n-octyl mercaptan 0.33 kg and mXy 450.0 kg were weighed and added to a 1.25 m ³ reactor equipped with a temperature control device using a jacket and a stirring blade, and stirred to obtain a mixed monomer solution.
The contents of the reactor were bubbled with nitrogen for 1 hour at a rate of 30 L / min to remove dissolved oxygen.
Thereafter, steam was blown into the jacket to raise the solution temperature in the reactor to 124 ° C., and while stirring at 50 rpm, 0.23 kg of 1,1-di (t-butylperoxy) cyclohexane was dissolved in 1.82 kg of mXy. Polymerization was initiated by preparing a polymerization initiator solution and adding this solution at a rate of 1 kg / hour. Further, the initiator solution was 0.5 kg / hour 0.5 hours after the start of polymerization, 0.42 kg / hour after 1 hour, 0.35 kg / hour after 2 hours, 0.14 kg / hour after 3 hours, and 0.14 kg / hour after 4 hours. The addition rate was decreased to 13 kg / hour, and the addition was stopped 7 hours after the start of polymerization.
During polymerization, the temperature of the solution in the reactor was controlled at 124 ± 2 ° C. by adjusting the temperature with a jacket.
After 15 hours from the start of polymerization, a polymerization solution containing a methacrylic resin having a ring structure in the main chain was obtained.
As a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 630 ppm by mass of phMI and 1250 ppm by mass of chMI.
In this polymerization solution, 0.15 parts by mass of Irgaphos 168 (P-1) and 0.05 parts by mass of ADK STAB PEP36 (P) as phosphorus antioxidants with respect to 100 parts by mass of the polymer contained in the solution. -2) as a hindered phenol-based antioxidant, 0.05 parts by mass of Irganox 1076 (A-1) was added with stirring.
Filtration was performed by passing the polymerization solution containing this antioxidant through a filter made of SUS316L metal fiber and having a filtration accuracy of 2 μm.
In order to recover the polymer from the polymerization solution, as a device used in the devolatilization step, a flat plate heat exchanger having a flat slit type flow path and a heat medium flow path and a SUS heat medium jacket having an internal volume of about 0.3 m ³ are provided. A devolatilization apparatus composed of a vacuum container (hereinafter referred to as a devolatilization tank) and an additive feed apparatus was used.
A solution containing a polymer obtained by polymerization is supplied to a heat exchanger installed at the top of a vacuum vessel at a rate of 30 liters / hour, heated to 260 ° C., and then an internal temperature of 260 ° C. and a degree of vacuum of 30 Torr. Was supplied to a devolatilization tank heated and reduced in pressure and subjected to devolatilization (hereinafter also referred to as “flash devolatilization”).
To the polymer after devolatilization, 0.1 part by mass of glycerin monostearate (R-1) is added as a fatty acid ester from 100 parts by mass of the polymer from the additive supply device installed at the bottom of the devolatilization tank. The mixture was mixed and pressurized with a gear pump, extruded from a strand die, cooled with water, and pelletized to obtain methacrylic resin composition pellets.
As a result of confirming the composition of the obtained pellet-like polymer, the structural units derived from MMA, phMI, and chMI monomers were 81.3 mass%, 7.9 mass%, and 10.8 mass%, respectively. there were. The weight average molecular weight was 141,000, Mz / Mw was 1.54, Mw / Mn was 2.24, the glass transition temperature was 135 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 170 Pa · s. Other physical properties are shown in Table 2.

[Example 2]
MMA 341.0 kg, phMI 39.3 kg, chMI 59.7 kg, chain transfer agent n-octyl mercaptan 0.28 kg, metaxylene 247.0 kg (hereinafter referred to as mXy), weighed the temperature control device by the jacket and the stirring blade The mixture was added to the 1.25 m ³ reactor provided and stirred to obtain a mixed monomer solution.
Next, 123.0 kg of mXy was weighed and added to tank 1.
Further, 110.0 kg of MMA and 80.0 kg of mXy were weighed and stirred in the tank 2 to obtain a monomer solution for addition.
Bubbling with nitrogen is performed for 1 hour for the contents of the reactor at a rate of 30 L / min, and bubbling with nitrogen is performed for 30 minutes for each of tank 1 and tank 2 for 10 minutes to remove dissolved oxygen. did.
Thereafter, steam was blown into the jacket to raise the temperature of the solution in the reactor to 124 ° C., while stirring at 50 rpm, 0.35 kg of 1,1-di (t-butylperoxy) cyclohexane was dissolved in 4.652 kg of mXy. Polymerization was started by adding the polymerization initiator solution at a rate of 1 kg / hour, and mXy was added from tank 1 at 30.75 kg / hour for 4 hours.
During polymerization, the temperature of the solution in the reactor was controlled at 124 ± 2 ° C. by adjusting the temperature with a jacket.
Then, from 4 hours to 6 hours later, a monomer solution containing MMA was added from tank 2 at a rate of 95 kg / hour.
Furthermore, the initiator solution decreased the addition rate to 0.25 kg / hour after 4 hours of polymerization, 0.75 kg / hour after 4 hours, and 0.5 kg / hour after 6 hours. The addition of the solution was stopped, and the polymerization was further continued for 3 hours to obtain a polymerization solution containing a methacrylic resin having a cyclic structural unit in the main chain.
As a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 360 mass ppm of phMI and 590 mass ppm of chMI.
In this polymerization solution, 0.1 part by mass of Irgaphos 168 (P-1) and 0.1 part by mass of ADK STAB HP-10 are used as phosphorus antioxidants with respect to 100 parts by mass of the polymer contained in the solution. (P-3) was added as a hindered phenol-based antioxidant with 0.03 parts by mass of Irganox 1076 (A-1) under stirring.
Filtration was performed by passing the polymerization solution containing the antioxidant through a filter made of SUS316L metal fiber and having a filtration accuracy of 2 μm.
In order to recover the polymer from the polymerization solution, as a device used in the devolatilization step, a flat plate heat exchanger having a flat slit type flow path and a heat medium flow path and a SUS heat medium jacket having an internal volume of about 0.3 m ³ are provided. A devolatilization apparatus composed of a decompression vessel (hereinafter referred to as a devolatilization tank) was used.
A solution containing a polymer obtained by polymerization is supplied to a heat exchanger installed at the top of a vacuum vessel at a rate of 30 liters / hour, heated to 260 ° C., and then an internal temperature of 260 ° C. and a degree of vacuum of 30 Torr. Was supplied to a devolatilization tank heated and reduced in pressure to perform devolatilization.
To the polymer after devolatilization, 0.1 part by mass of glycerin monostearate (R-1) is added as a fatty acid ester from 100 parts by mass of the polymer from the additive supply device installed at the bottom of the devolatilization tank. Then, the pressure was increased with a gear pump from the lower part of the devolatilization tank, extruded from a strand die, cooled with water, and pelletized to obtain a methacrylic resin composition pellet.
As a result of confirming the composition of the obtained pellet-like polymer, the structural units derived from MMA, phMI, and chMI monomers were 82.0% by mass, 7.1% by mass, and 10.9% by mass, respectively. there were. The weight average molecular weight was 145,000, Mz / Mw was 1.75, Mw / Mn was 2.44, the glass transition temperature was 135 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 135 Pa · s. Other physical properties are shown in Table 2.

[Example 3]
First, the amount of monomers charged into the reactor was changed to MMA 291.5 kg, phMI 44.0 kg, and chMI 104.5 kg, respectively. A methacrylic resin composition pellet was obtained in the same manner as in Example 2 except that the product and the addition amount shown in Table 1 were changed.
As a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 500 ppm by mass of phMI and 1160 ppm by mass of chMI.
As a result of confirming the composition of the obtained pellet-like polymer, the structural units derived from MMA, phMI, and chMI monomers were 73.0% by mass, 8.0% by mass, and 19.0% by mass, respectively. there were. The weight average molecular weight was 133,000, Mz / Mw was 1.78, Mw / Mn was 2.39, the glass transition temperature was 151 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 220 Pa · s. Other physical properties are shown in Table 2.

[Example 4]
First, the amount of monomers charged into the reactor was changed to 381.3 kg of MMA, 52.2 kg of phMI, and 16.5 kg of chMI, respectively, and a phosphorus antioxidant, a hindered phenol antioxidant, and a fatty acid ester to be added were added. A methacrylic resin composition pellet was obtained in the same manner as in Example 2 except that the product and the addition amount shown in Table 1 were changed.
As a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 640 mass ppm of phMI and 310 mass ppm of chMI.
As a result of confirming the composition of the obtained pellet-like polymer, the structural units derived from MMA, phMI, and chMI monomers were 87.5% by mass, 9.5% by mass, and 3.0% by mass, respectively. there were. The weight average molecular weight was 151,000, Mz / Mw was 1.65, Mw / Mn was 2.29, the glass transition temperature was 123 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 121 Pa · s. Other physical properties are shown in Table 2.

[Example 5]
First, the amount of chain transfer agent added to the reactor was changed to 0.39 g, and the phosphorus antioxidant, hindered phenol antioxidant, and fatty acid ester to be added and the products and addition amounts shown in Table 1 A methacrylic resin composition pellet was obtained in the same manner as in Example 2 except that the above was changed.
In addition, as a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 320 mass ppm of phMI and 580 mass ppm of chMI.
As a result of confirming the composition of the obtained pellet-like polymer, the structural units derived from MMA, phMI, and chMI monomers were 82.0% by mass, 7.1% by mass, and 10.9% by mass, respectively. there were. The weight average molecular weight was 95,000, Mz / Mw was 1.62, Mw / Mn was 2.18, the glass transition temperature was 134 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 60 Pa · s. Other physical properties are shown in Table 2.

[Example 6]
First, the amounts of monomers charged into the reactor were changed to MMA 204.2 kg, phMI 5.5 kg, chMI 187.0 kg, and styrene 53.3 kg, respectively, and a phosphorus antioxidant and a hindered phenol antioxidant added. A methacrylic resin composition pellet was obtained in the same manner as in Example 2 except that the fatty acid ester was changed to the product and addition amount shown in Table 1.
In addition, as a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 50 mass ppm of phMI and 1260 mass ppm of chMI.
When the composition of the obtained pellet-like polymer was confirmed, the structural units derived from the monomers MMA, phMI, chMI and styrene were 55.3% by mass, 1.0% by mass and 34.0%, respectively. It was mass% and 9.7 mass%. The weight average molecular weight was 130,000, Mz / Mw was 1.71, Mw / Mn was 2.33, the glass transition temperature was 150 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 158 Pa · s. Other physical properties are shown in Table 2.

[Example 7]
A methacrylic resin composition pellet was obtained in the same manner as in Example 1 except that the phosphorus antioxidant and fatty acid ester used were changed to the products and addition amounts shown in Table 1.
In addition, as a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 400 mass ppm of phMI and 620 mass ppm of chMI.
As a result of confirming the composition of the obtained pellet-like polymer, the structural units derived from MMA, phMI, and chMI monomers were 81.3 mass%, 7.9 mass%, and 10.8 mass%, respectively. there were. The weight average molecular weight was 141,000, Mz / Mw was 1.54, Mw / Mn was 2.24, the glass transition temperature was 135 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 170 Pa · s. Other physical properties are shown in Table 2.

[Comparative Example 1]
A methacrylic resin having a structural unit derived from an N-substituted maleimide monomer was prepared by a solution polymerization method and a methanol reprecipitation method according to Production Example 3 and Example 3 described in JP-A-2016-169282.
More specifically, a SUS polymerization reactor (capacity 0.5 L) equipped with a stirring device, a temperature sensor, a cooling pipe, a nitrogen gas introduction nozzle, an initiator solution introduction nozzle, and a polymerization solution discharge nozzle was used, and the pressure was Slight pressure was applied, and the reaction temperature was controlled at 130 ° C. with an oil bath.
In the polymerization reactor, MMA 576 g, phMI 61 g, chMI 83 g, methyl isobutyl ketone 480 g, and chain transfer agent n-octyl mercaptan 0.31 g were mixed, and then replaced with nitrogen gas to prepare a raw material solution. Further, 8.63 g of Perhexa C (manufactured by NOF Corporation; concentration 75 wt%) was dissolved in 91.37 g of methyl isobutyl ketone, and then substituted with nitrogen gas to prepare an initiator solution.
The raw material solution was introduced from the raw material solution introduction nozzle at 8.25 mL / min using a pump. The initiator solution was introduced from the initiator solution introduction nozzle at 0.08 mL / min using a pump.
After 30 minutes, the polymer solution was discharged from the polymerization solution discharge nozzle at a constant flow rate of 500 mL / hr using a pump.
The polymer solution was collected separately in the initial flow tank for 1.5 hours after discharge. The polymer solution was collected for 1.5 hours after 1.5 hours from the start of discharge.
As a result of evaluating the residual amount of N-substituted maleimide contained in the recovered polymer solution, it contained 42000 mass ppm of phMI and 22000 mass ppm of chMI.
The recovered polymer solution and methanol as an extraction solvent were simultaneously supplied to a homogenizer, and emulsified, dispersed and extracted.
The separated and precipitated polymer was collected and dried under vacuum at 130 ° C. for 2 hours to obtain the desired methacrylic resin.
Using a Henschel mixer, with respect to 100 parts by mass of the obtained methacrylic resin, 0.15 parts by mass of Irgaphos 168 (P-1) and 0.05 parts by mass of Adekastab PEP36 (P -2) and 0.1 part by mass of glycerin monostearate (R-1) were mixed to prepare a mixture.
The obtained mixture was supplied to a twin screw extruder with a 15 mmφ vent (manufactured by Technobel; KZW15-45MG) and melt kneaded. As operating conditions, the lower part of the extruder and the die set temperature of 230 ° C. were used.
When the composition of the obtained resin composition was confirmed, the structural units derived from MMA, phMI, and chMI monomers were 77.3 mass%, 10.6 mass%, and 12.1 mass%, respectively. . The weight average molecular weight was 141,000, Mz / Mw was 1.48, Mw / Mn was 1.79, the glass transition temperature was 137 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 251 Pa · s. Other physical properties are shown in Table 2.

[Comparative Example 2]
A methacrylic resin containing a structural unit derived from an N-substituted maleimide monomer was prepared by suspension polymerization according to Example 1 described in JP-A-2016-210963.
More specifically, 2 kg of water, 65 g of tricalcium phosphate, 39 g of calcium carbonate, and 0.39 g of sodium lauryl sulfate were charged into a container having a stirrer equipped with four inclined paddle blades to obtain a mixed solution (a). .
Next, 26 kg of water was charged into a 60 liter reactor equipped with a stirrer equipped with three receding blades, the temperature was raised to 80 ° C., and then the mixed solution (a), MMA 17.03 kg, chMI 4.57 kg, styrene 1 .33 kg, 41 g of lauroyl peroxide as an initiator, and 49 g of n-octyl mercaptan as a chain transfer agent were charged into the reactor. Subsequently, suspension polymerization was carried out at about 75 ° C. About 120 minutes after the introduction of the polymerization raw materials such as monomers, the temperature was increased at a rate of 1 ° C./min to achieve a polymerization temperature of 93 ° C., and then the polymerization was continued for 180 minutes to complete the polymerization reaction. .
Next, after cooling to 50 ° C., 20% by mass of sulfuric acid was added to dissolve the suspending agent.
Next, the polymerization solution was passed through a 1.68 mm mesh sieve to remove abnormal polymer, and the resulting slurry containing the polymer was dehydrated to recover a bead-like polymer.
In addition, as a result of evaluating the amount of N-substituted maleimide contained in the recovered bead polymer, 4200 mass ppm of chMI was contained.
The collected bead polymer was repeatedly washed with water and dehydrated, and then dried in a drying oven at 80 ° C. for 12 hours.
Using a tumbler mixer previously substituted with nitrogen, 0.15 parts by mass of Irgaphos 168 (P-1) and 0.05 parts by weight as a phosphorus-based antioxidant with respect to 100 parts by mass of the obtained bead polymer. A part by weight of ADK STAB PEP36 (P-2) and 0.1 part by weight of glycerin monostearate (R-1) were mixed to prepare a mixture.
The obtained mixture was supplied to a 58 mmφ vented twin screw extruder and melt kneaded. As operating conditions, the lower part of the extruder and the die set temperature of 270 ° C., the rotation speed of 200 rpm, the degree of vacuum at the vent part was 200 Torr, and the discharge rate was 20 kg / hour.
The melt-kneaded resin composition is extruded into a strand through a perforated die, introduced into a cooling bath filled with cooling water preheated to 50 ° C., cooled and solidified, cut with a cutter, and pelletized methacrylic A system resin composition was obtained.
When the composition of the obtained resin composition was confirmed, the structural units derived from MMA, chMI, and styrene monomers were 74.6% by mass, 19.6% by mass, and 5.8% by mass, respectively. . The weight average molecular weight was 159,000, Mz / Mw was 1.42, Mw / Mn was 1.76, the glass transition temperature was 137 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 246 Pa · s. Other physical properties are shown in Table 2.

[Comparative Example 3]
Polymerization was performed in the same manner as in Example 1 to obtain a polymerization solution containing an antioxidant.
As a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 620 ppm by mass of phMI and 1220 ppm by mass of chMI.
This polymerization solution was supplied to a concentrating device consisting of a tubular heat exchanger and a vaporization tank preliminarily heated to 170 ° C., and the concentration of the polymer contained in the solution was increased to 70% by mass.
The obtained polymerization solution was supplied to a thin film evaporator having a heat transfer area of 0.2 m ² and devolatilized.
In this case, the temperature in the apparatus was 280 ° C., the supply amount was 30 L / hr, the rotation speed was 400 rpm, and the degree of vacuum was 30 Torr. Add 3 parts by mass of glycerin monostearate (R-1) from the additive supply device installed at the bottom of the devolatilization tank, pressurize it with a gear pump, extrude it from a strand die, cool with water, pelletize, methacrylic resin composition Product pellets were obtained.
As a result of confirming the composition of the obtained pellet-like polymer, the structural units derived from MMA, phMI, and chMI monomers were 81.3 mass%, 7.9 mass%, and 10.8 mass%, respectively. there were. The weight average molecular weight was 136,000, Mz / Mw was 1.54, Mw / Mn was 1.94, the glass transition temperature was 135 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 162 Pa · s. Other physical properties are shown in Table 2.

[Comparative Example 4]
The solvent to be used is changed to methyl isobutyl ketone, and the addition amount of the chain transfer agent charged into the reactor is changed to 0.15 g, and the phosphorus antioxidant, hindered phenol antioxidant and fatty acid ester to be added are added. A methacrylic resin composition pellet was obtained in the same manner as in Example 2 except that the product and the addition amount shown in Table 1 were changed.
As a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 320 mass ppm of phMI and 550 mass ppm of chMI.
As a result of confirming the composition of the obtained pellet-like polymer, the structural units derived from MMA, phMI, and chMI monomers were 82.0% by mass, 7.1% by mass, and 10.9% by mass, respectively. there were. The weight average molecular weight was 218,000, Mz / Mw was 1.88, Mw / Mn was 2.67, the glass transition temperature was 135 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 270 Pa · s. Other physical properties are shown in Table 2.

[Comparative Example 5]
A methacrylic resin composition pellet was obtained in the same manner as in Example 1 except that the phosphorus antioxidant and fatty acid ester used were changed to the products and addition amounts shown in Table 1.
As a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 620 ppm by mass of phMI and 1220 ppm by mass of chMI.
As a result of confirming the composition of the obtained pellet-like polymer, the structural units derived from MMA, phMI, and chMI monomers were 81.3 mass%, 7.9 mass%, and 10.8 mass%, respectively. there were. The weight average molecular weight was 141,000, Mz / Mw was 1.54, Mw / Mn was 2.24, the glass transition temperature was 135 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 170 Pa · s. Other physical properties are shown in Table 2.

[Comparative Example 6]
A methacrylic resin composition pellet was obtained in the same manner as in Example 2 except that the phosphorus antioxidant and fatty acid ester used were changed to the products and addition amounts shown in Table 1.
As a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 360 mass ppm of phMI and 590 mass ppm of chMI.
As a result of confirming the composition of the obtained pellet-like polymer, the structural units derived from MMA, phMI, and chMI monomers were 81.3 mass%, 7.9 mass%, and 10.8 mass%, respectively. there were. The weight average molecular weight was 141,000, Mz / Mw was 1.54, Mw / Mn was 2.24, the glass transition temperature was 135 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 170 Pa · s. Other physical properties are shown in Table 2.

[Comparative Example 7]
A methacrylic resin composition pellet was obtained in the same manner as in Example 2 except that the phosphorus antioxidant and fatty acid ester used were changed to the products and addition amounts shown in Table 1.
As a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 350 mass ppm of phMI and 590 mass ppm of chMI.
As a result of confirming the composition of the obtained pellet-like polymer, the structural units derived from MMA, phMI, and chMI monomers were 81.3 mass%, 7.9 mass%, and 10.8 mass%, respectively. there were. The weight average molecular weight was 141,000, Mz / Mw was 1.54, Mw / Mn was 2.24, the glass transition temperature was 135 ° C., and the melt viscosity at a shear rate of 1000 sec ⁻¹ was 170 Pa · s. Other physical properties are shown in Table 2.

As is clear from Tables 1 and 2, the methacrylic resin compositions of the examples have high heat resistance, highly controlled birefringence, and are excellent in light transmittance, color tone, transparency, and injection moldability.
On the other hand, in the methacrylic resin compositions of Comparative Examples 1 to 7, an increase in birefringence, an increase in photoelastic coefficient, a decrease in light transmittance at a long optical path length, an injection molding property (release property and / or retention stability). ) Was worsened.

The methacrylic resin composition of the present invention has high heat resistance, excellent birefringence, and in addition, excellent injection moldability.
The molded article for optical components obtained using the methacrylic resin composition of the present invention is, for example, a light guide plate, a display front plate, a touch panel, and a smartphone used for displays such as smartphones, PDAs, tablet PCs, and liquid crystal televisions. Lenses for tablet PC cameras, etc., optical lens components such as head mounted displays and liquid crystal projectors, for example, prism elements, waveguides, lenses, especially optical lenses with small and thin wall thickness, optical fibers, optical fiber coating materials, lenses, Examples include a Fresnel lens, a phase plate provided with a microlens array, and an optical cover component.
In addition, as automobile parts, light guide plates for in-vehicle displays; in-vehicle instrument panels; optical parts for head-up displays such as car navigation front panels, combiners, optical cover parts; in-vehicle camera lenses, light guide bars, etc. In addition, it is particularly preferably used for parts for display devices for digital signage that send information to a thin display connected to a network for the purpose of advertising, advertising, etc. in places such as camera focusing plates, outdoors, stores, public institutions, transportation, etc. it can.

Claims (12)

A methacrylic resin composition comprising a methacrylic resin containing a structural unit derived from at least an N-substituted maleimide monomer in the main chain,
(A) The glass transition temperature is more than 120 ° C and not more than 160 ° C,
(B) the melt viscosity is 250 pa · sec or less under the conditions of a resin temperature of 270 ° C. and a shear rate of 1000 sec ⁻¹ ;
(C) The absolute value of the photoelastic coefficient is 1 × 10 ⁻¹² pa ⁻¹ or less,
(D) About the solution which melt | dissolved this resin composition in chloroform by 20 mass to volume percentage, the light transmittance measured on the conditions of optical path length 100mm and wavelength 470nm is 94% or more,
(E) About the solution which melt | dissolved this resin composition in 20 mass to volume percentage in chloroform, the light transmittance measured on conditions with an optical path length of 100 mm and a wavelength of 700 nm is 96% or more,
(F) 0.05 to 0.2 parts by mass of at least one fatty acid ester selected from glycerin fatty acid ester, diglycerin fatty acid ester, and sorbitan fatty acid ester is contained with respect to 100 parts by mass of the methacrylic resin,
(G) It is characterized by containing 0.01 to 0.2 parts by mass of a phosphorus antioxidant having a melting point of 100 to 250 ° C. and having a trivalent phosphorus element with respect to 100 parts by mass of the methacrylic resin. A methacrylic resin composition.   About the solution which melt | dissolved this resin composition in chloroform by 20 mass to volume percentage, the light transmittance measured on condition of optical path length 100mm and wavelength 470nm is 96% or more, and optical path length 100mm and wavelength 700nm. The methacrylic resin composition according to claim 1, wherein the light transmittance measured under conditions is 98% or more.   Using a resin flow length measurement mold having a spiral flow path with a thickness of 1 mm and a width of 10 mm, injection molding is performed under the conditions of a cylinder temperature of 270 ° C., a mold temperature of 100 ° C., and an injection pressure of 125 MPa, and the flow length The methacrylic resin composition according to claim 1 or 2, wherein (spiral flow length) is 150 mm or more. The phosphorus element content contained in the methacrylic resin composition is 5 to 200 ppm by mass,
^{In 31} P-NMR measurement, the ratio (P3 / P5) of the integral value (P3) of the spectral peak attributed to trivalent phosphorus to the integrated value (P5) of the spectral peak attributed to pentavalent phosphorus is 0.2 to The methacrylic resin composition according to any one of claims 1 to 3, which is 2.0.   The methacrylic resin composition according to any one of claims 1 to 4, comprising 0.005 to 0.1 parts by mass of a hindered phenol-based antioxidant with respect to 100 parts by mass of the methacrylic resin.   The methacrylic resin according to any one of claims 1 to 5, wherein the methacrylic resin contains 5 to 40% by mass of a structural unit derived from an N-substituted maleimide monomer based on 100% by mass of the methacrylic resin. -Based resin composition.   The structural unit derived from the N-substituted maleimide monomer includes both a structural unit derived from an N-aromatic substituted maleimide monomer and a structural unit derived from an N-alicyclic substituted maleimide monomer. The methacrylic resin composition according to any one of 1 to 6.   The methacrylic resin composition according to any one of claims 1 to 7, which is used for injection molding.   The methacrylic resin composition according to any one of claims 1 to 8, which is used for an optical member.   A molded body comprising the methacrylic resin composition according to any one of claims 1 to 9.   An optical member comprising the molded body according to claim 10.   The optical member according to claim 11, wherein the optical member is a light guide plate.