JPWO2019059179A1 - Light guide plate for vehicle display - Google Patents

Abstract

The present invention contains a methacrylic resin (A) containing a structural unit derived from 99% by mass to 100% by mass of methyl methacrylate and a structural unit derived from 0% by mass to 1% by mass of an acrylic acid ester, and has an optical path length. The transmittance of the wavelength of 450 nm when converted to 180 mm is 65% or more, the glass transition temperature of the midpoint evaluated by the temperature rise measurement of 10 ° C./min by DSC is 118 to 124 ° C., and the residual methacrylic acid The present invention provides a light guide plate for a vehicle display device in which the amount of methyl is 1.0% by mass or less.

Description

The present invention relates to a light guide plate of a vehicle display device. More specifically, the present invention relates to a light guide plate having high heat resistance, high transmittance, and high shaping rate.

In recent years, the size of liquid crystal display devices mounted on vehicles has increased, and the physical properties required for light guide plates have also become more sophisticated. In particular, as the size increases, the optical path becomes longer and higher transparency is required, while the heat resistance originally required for vehicles is also required.
The methacrylic resin used as a raw material for the light guide plate has been used for the light guide plate for vehicles because of its high transparency and good moldability. Resins having improved heat resistance by copolymerization or cyclization reaction have been proposed, but the transparency is insufficient, and a material satisfying both heat resistance and transparency has been required.
Patent Documents 1 and 2 describe a methacrylic resin composition used for an optical member such as a polarizer, but its translucency has room for improvement as a light guide plate used for a vehicle display device.

WO2014 / 00205 JP-A-2017-048344

The present invention has been made in view of the above background, and an object of the present invention is to provide a light guide plate having high heat resistance, high transmittance, and high shaping rate.

As a result of repeated studies to achieve the above object, the present inventors have completed the present invention including the following aspects.

[1]
A methacrylic resin (A) containing a structural unit derived from 99% by mass to 100% by mass of methyl methacrylate and a structural unit derived from 0% by mass to 1% by mass of an acrylic acid ester.
When the optical path length is converted to 180 mm, the transmittance of the wavelength of 450 nm is 65% or more.
The glass transition temperature at the midpoint evaluated by the temperature rise measurement of 10 ° C./min by DSC is 118 to 124 ° C.
A light guide plate for a vehicle display device in which the amount of residual methyl methacrylate is 1.0% by mass or less.
[2]
The light guide plate of the vehicle display device according to [1], wherein the melt flow rate measured by crushing the light guide plate is 5 g / 10 minutes or more and 40 g / 10 minutes or less.
[3]
The light guide plate of the vehicle display device according to [1] or [2], which contains 0.01 to 1 part by mass of a lubricant with respect to 100 parts by mass of the methacrylic resin (A).
[4]
A monomer mixture containing 98.6% by mass to 100% by mass of methyl methacrylate and 0% by mass to 1.4% by mass of an acrylic acid ester is polymerized by radical polymerization to obtain 99% by mass to 100% by mass of methyl methacrylate. A step of obtaining a methacrylic resin (A) containing a structural unit derived from it and a structural unit derived from 0% by mass to 1% by mass of an acrylic acid ester, and a methacrylic resin (A) obtained by heat devolatile in an inert gas atmosphere. A method for producing a methacrylic resin (A), which comprises a step of removing an unreacted monomer from the reaction mixture containing () to reduce the amount of residual methyl methacrylate to 1.0% by mass or less.
[5]
The method for producing a methacrylic resin (A) according to [4], wherein the inert atmosphere is a nitrogen atmosphere.
[6]
The method for producing a methacrylic resin (A) according to [4] or [5], wherein the heat devolatilization is performed using a twin-screw extruder and the cylinder heating temperature of the twin-screw extruder is 200 to 230 ° C.

Hereinafter, the light guide plate of the present invention and the methacrylic resin (A) which is a raw material of the light guide plate will be described. In the present invention, various physical properties related to the methacrylic resin (A) can be found by analyzing the light guide plate of the present invention. Items that cannot be analyzed in the state of the light guide plate can be analyzed by crushing the light guide plate.

The light guide plate of the present invention and the methacrylic resin (A) used for the light guide plate contain 99% by mass or more of structural units derived from methyl methacrylate. In the methacrylic resin (A), the content of the structural unit derived from methyl methacrylate is preferably 99.1% by mass or more, more preferably 99.2% by mass or more, still more preferably 99.3% by mass or more. ..

Structural units other than the structural unit derived from methyl methacrylate include, for example, methyl acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and 2-ethyl (meth) acrylate. (Meta) acrylic acid alkyl esters such as hexyl (excluding methyl methacrylate); acrylic acid aryl esters such as phenyl acrylate; acrylic acid cycloalkyl esters such as cyclohexyl acrylate and norbornenyl acrylate; styrene, α- A structural unit derived from a vinyl-based monomer having only one polymerizable carbon-carbon double bond in one molecule such as an aromatic vinyl compound such as methylstyrene; acrylamide; methacrylicamide; acrylonitrile; methacrylonitrile; Can be mentioned. Among these, a structural unit derived from a (meth) acrylic acid ester is preferable from the viewpoint that a resin that is easily copolymerized and has high transparency can be obtained.

The content of the structural unit other than the structural unit derived from methyl methacrylate is preferably 1% by mass or less, more preferably 0.5% by mass or less, and most preferably 0.1% by mass or less.
In particular, the content of the structural unit derived from the acrylic acid ester is 0% by mass to 1% by mass, preferably 0.9% by mass or less, more preferably 0.8% by mass or less, and even more preferably 0. It is 0.7% by mass or less. When the content of the structural unit derived from the acrylic acid ester exceeds 1% by mass, the glass transition temperature of the methacrylic resin (A) decreases.

The light guide plate of the present invention and the methacrylic resin (A) used for the light guide plate have a triplet display syndio tacticity (rr) of preferably 53% to 58%, more preferably 54% to 57%. Is. If the syndiotacticity is too large, the glass transition temperature of the methacrylic resin becomes higher than 124 ° C., while the molding processing temperature becomes high and foaming is likely to occur. On the other hand, if the syndiotacticity is too small, the glass transition temperature is lower than 118 ° C., resulting in a resin having low heat resistance.

Here, the syndio tacticity (rr) of the triplet display will be described. In the chain of structural units (doubles, diads) in the polymer molecule, those having the same configuration are called meso, and the opposite ones are called racemo, which are referred to as m and r, respectively. The ratio of the two chains (doubles, diad) of the chain of three consecutive structural units (triple, triad) being both racemo (denoted as rr) is the syndiotacticity of triplet display. City (rr) (hereinafter, simply referred to as "Syngio Tacticity (rr)").

The syndiotacticity (rr) (%) displayed in triplets is 0.6 when ^{1 1} H-NMR spectrum is measured in deuterated chloroform at 30 ° C. and TMS is 0 ppm from the spectrum. The area (X) in the region of ~ 0.95 ppm and the area (Y) in the region of 0.6 to 1.35 ppm were measured, and the values were calculated by the formula: (X / Y) × 100.

The light guide plate of the present invention and the methacrylic resin (A) used for the light guide plate have a weight average molecular weight (hereinafter, referred to as “Mw”) of preferably 40,000 to 80,000, more preferably 50,000 to 70,000. The light guide plate obtained when the Mw is 40,000 or more tends to be excellent in impact resistance and toughness. When it is 80,000 or less, the moldability of the methacrylic resin is enhanced, so that the thickness of the obtained light guide plate tends to be uniform and the surface smoothness tends to be excellent.

The light guide plate of the present invention and the methacrylic resin (A) used for the light guide plate have a ratio of Mw to a number average molecular weight (hereinafter referred to as “Mn”) (Mw / Mn: hereinafter, this value is referred to as “molecular weight distribution”. ) Is preferably 1.2 to 2.5, and more preferably 1.5 to 2.0. When the molecular weight distribution is 1.2 or more, the fluidity of the methacrylic resin is improved, and the obtained light guide plate tends to have excellent surface smoothness, and when the molecular weight distribution is 2.5 or less, the obtained light guide plate has excellent surface hardness. It becomes a tendency. In addition, Mw and Mn are values which converted the chromatogram measured by gel permeation chromatography (GPC) into the molecular weight of standard polystyrene.

The light guide plate of the present invention and the methacrylic resin (A) used for the light guide plate are measured in accordance with JIS K7210 under the condition of 230 ° C. and a load of 3.8 kg, and the melt flow rate is preferably 1 g / 10 min. As described above, it is more preferably 5 to 40 g / 10 minutes, still more preferably 8 to 30 g / 10 minutes.

The glass transition temperature at the midpoint evaluated by the DSC of the light guide plate of the present invention and the methacrylic resin (A) used for the light guide plate by a temperature rise measurement of 10 ° C./min is preferably 118 ° C. or higher, more preferably 119 ° C. or higher. , More preferably 120 ° C. or higher. The upper limit of the glass transition temperature of the methacrylic resin is usually 124 ° C. or lower, preferably 123 ° C. or lower, and more preferably 122 ° C. or lower. The glass transition temperature can be controlled by adjusting the monomer composition, molecular weight, syndiotacticity (rr), and the like. When the glass transition temperature is in this range, deformation such as heat shrinkage of the obtained light guide plate is unlikely to occur, and it is easy to suppress thermal decomposition of the resin during molding of the light guide plate. The glass transition temperature of the light guide plate of the present invention can be measured by the method described in Examples using a sample obtained by crushing and powdering the light guide plate.

The acetic acid-equivalent acid value of the light guide plate and the methacrylic resin (A) used in the light guide plate of the present invention is preferably 40 ppm or less, more preferably 30 ppm or less, still more preferably 20 ppm or less from the viewpoint of good heat resistance decomposition. Is. When the acid value in terms of acetic acid is high, not only the heat-decomposability is inferior, but also gel or the like may be generated by reacting with other compounds at the time of molding, which may cause a defect in the molded product, which is not preferable.
The evaluation of the acid value is a value calculated as the amount of acetic acid contained in the weight of the methacrylic resin (A) after converting the acid value of JIS K0070: 1992 into the amount of acetic acid instead of the KOH conversion. Specifically, it may be measured by the method described in the examples.

The air atmosphere of the light guide plate of the present invention and the methacrylic resin (A) used for the light guide plate, the thermogravimetric retention measured at a constant temperature of 290 ° C. and a time of 20 minutes is preferably 75% or more from the viewpoint of heat resistance decomposition. 80% or more is more preferable, and 85% or more is most preferable.
To measure the thermogravimetric retention rate, use a thermogravimetric measuring device (manufactured by Shimadzu Corporation, TGA) to apply methacrylic resin (A) in an air atmosphere at a flow rate of 50 ml / min in dry air from 50 ° C to 290 ° C. After raising the temperature at 20 ° C./min, the thermogravimetric reduction may be measured under the condition of holding at 290 ° C. for 20 minutes in an air atmosphere. The heat-resistant decomposition property can be evaluated by the following formula based on the weight (X2) when the weight (X1) at 50 ° C. is used as a reference (retention rate 100%) and the product is held at 290 ° C. for 20 minutes. It can be said that the higher the weight retention rate, the higher the heat decomposition property.
Weight retention rate (%) = (X2 / X1) x 100 (%)

The light guide plate of the present invention and the methacrylic resin (A) used for the light guide plate preferably have an insoluble content of 1% by mass or less when dissolved in chloroform. The insoluble content when dissolved in chloroform can be measured by the method described in Examples using a sample obtained by crushing a light guide plate and powdering it. The insoluble content can be reduced to 1% by mass or less by not copolymerizing the polyfunctional monomer in the production of the methacrylic resin (A).

The method for producing the methacrylic resin (A) used for the light guide plate of the present invention is not limited, but is from the viewpoints that there is little coloring, the acid value in terms of acetic acid is small, the heat-resistant decomposition property is good, and the productivity is good. Therefore, the radical polymerization method is preferable.
The radical polymerization method is preferably bulk polymerization performed without a solvent from the viewpoint of obtaining a methacrylic resin (A) having a low impurity concentration. In particular, from the viewpoint of productivity, continuous bulk polymerization is preferable. From the viewpoint of suppressing the occurrence of silver streaks and coloring in the molded product, it is preferable to carry out the polymerization reaction with a low amount of dissolved oxygen. Further, the polymerization reaction is preferably carried out in an atmosphere of an inert gas such as nitrogen gas.

The polymerization initiator used in the radical polymerization method for producing the methacrylic resin (A) is not particularly limited as long as it generates reactive radicals. For example, t-hexylperoxyisopropyl monocarbonate, t-hexylperoxy2-ethylhexanoate, 1,1,3,3-tetramethylbutylperoxy2-ethylhexanoate, t-butylperoxypivalate. , T-Hexylperoxypivalate, t-Butylperoxyneodecanoate, t-Hexylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, 1 , 1-bis (t-hexyl peroxy) cyclohexane, benzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, lauroyl peroxide, 2,2'-azobis (2-methylpropionitrile), 2, Examples thereof include 2'-azobis (2-methylbutyronitrile) and dimethyl 2,2'-azobis (2-methylpropionate). Of these, t-hexyl peroxy2-ethylhexanoate, 1,1-bis (t-hexyl peroxy) cyclohexane, and dimethyl 2,2'-azobis (2-methylpropionate) are preferable.

The 1-hour half-life temperature of such a polymerization initiator is preferably 60 to 140 ° C, more preferably 80 to 120 ° C. The polymerization initiator used for producing the methacrylic resin (A) has a hydrogen extraction ability of preferably 20% or less, more preferably 10% or less, still more preferably 5% or less. Such a polymerization initiator may be used alone or in combination of two or more. The amount of the polymerization initiator used is preferably 0.0001 to 0.02 parts by mass, more preferably 0.001 to 0.01 parts by mass, still more preferably, with respect to 100 parts by mass of the monomer subjected to the polymerization reaction. Is 0.005 to 0.007 parts by mass.

The hydrogen abstraction ability can be known from the technical data of the polymerization initiator manufacturer (for example, the technical data of Nippon Oil & Fats Co., Ltd. "Hydrogen extraction ability of organic peroxide and initiator efficiency" (created in April 2003)). .. Further, the hydrogen extraction ability can be measured by a radical trapping method using an α-methylstyrene dimer, that is, an α-methylstyrene dimer trapping method. The measurement is generally performed as follows. First, the polymerization initiator is cleaved in the coexistence of α-methylstyrene dimer as a radical trapping agent to generate a radical fragment. Among the generated radical fragments, the radical fragment having a low hydrogen abstraction ability is added to the double bond of the α-methylstyrene dimer and captured. On the other hand, a radical fragment having a high hydrogen abstraction ability abstracts hydrogen from cyclohexane to generate a cyclohexyl radical, and the cyclohexyl radical is added to the double bond of α-methylstyrene dimer and trapped to produce a cyclohexane trapping product. Therefore, the ratio (molar fraction) of radical fragments having high hydrogen abstraction ability to the theoretical amount of radical fragment generation, which is obtained by quantifying cyclohexane or cyclohexane capture product, is defined as hydrogen abstraction ability.

Chain transfer agents used in the radical polymerization method for the production of the methacryl resin (A) include n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, 1,4-butanedithiol, and 1,6-hexanedithiol. , Ethylene glycol bisthiopropionate, butanediol bisthioglycolate, butanediol bisthiopropionate, hexanediol bisthioglycolate, hexanediol bisthiopropionate, trimethylpropanthris- (β-thiopropio) Nate), alkyl mercaptans such as pentaerythritol tetraxthiopropionate and the like. Of these, monofunctional alkyl mercaptans such as n-octyl mercaptan and n-dodecyl mercaptan are preferable. These chain transfer agents may be used alone or in combination of two or more.

The amount of the chain transfer agent used is preferably 0.1 to 1 part by mass, more preferably 0.15 to 0.8 part by mass, and further preferably 0 with respect to 100 parts by mass of the monomer subjected to the polymerization reaction. .2 to 0.6 parts by mass, most preferably 0.2 to 0.5 parts by mass. The amount of the chain transfer agent used is preferably 2500 to 10000 parts by mass, more preferably 3000 to 9000 parts by mass, and further preferably 3500 to 6000 parts by mass with respect to 100 parts by mass of the polymerization initiator. When the amount of the chain transfer agent used is within the above range, the obtained methacrylic resin (A) tends to have good molding processability and high mechanical strength.

The temperature during the polymerization reaction is preferably 90 to 120 ° C, more preferably 95 to 115 ° C, and even more preferably 98 to 110 ° C. When the polymerization temperature is 120 ° C. or lower, the productivity tends to be improved due to the improvement of the polymerization rate, the reduction of the viscosity of the polymerization solution, and the like. Further, when the polymerization temperature is 120 ° C. or lower, the polymerization rate can be easily controlled, the formation of by-products is suppressed, and a methacrylic resin having a desired glass transition temperature can be obtained. The temperature during the polymerization reaction can be controlled by the temperature of the jacket of the reactor and the polymerization conversion rate.
The time of the polymerization reaction is preferably 0.5 to 4 hours, more preferably 1.5 to 3.5 hours, still more preferably 1.5 to 3 hours. In the case of a continuous flow reactor, the time of such a polymerization reaction is the average residence time in the reactor. When the temperature at the time of the polymerization reaction and the time of the polymerization reaction are within the above ranges, the methacrylic resin (A) having excellent transparency can be produced with high efficiency.

The polymerization conversion rate in the radical polymerization method for producing the methacrylic resin (A) is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and further preferably 35 to 65% by mass. When the polymerization conversion rate is 20% by mass or more, the remaining unreacted monomer can be easily removed, the obtained methacrylic resin is less likely to foam, and the appearance of the obtained molded product tends to be good. When the polymerization conversion rate is 80% by mass or less, the viscosity of the polymerization solution tends to be low and the productivity tends to be improved.

The radical polymerization may be carried out using a batch reactor, but it is preferable to carry out the radical polymerization using a continuous flow reactor from the viewpoint of productivity. In the continuous flow reaction, for example, a polymerization reaction raw material (a mixed solution containing a monomer, a polymerization initiator, a chain transfer agent, etc.) is prepared under a nitrogen atmosphere, and the mixture is supplied to the reactor at a constant flow rate, and the supply thereof. Drain the liquid in the reactor at a flow rate corresponding to the amount. As the reactor, a tubular reactor that can bring the state close to a plug flow and / or a tank type reactor that can bring the state close to complete mixing can be used. Further, the continuous flow type polymerization may be carried out with one reactor, or the continuous flow type polymerization may be carried out by connecting two or more reactors. In the present invention, it is preferable that at least one of them employs a continuous flow type tank reactor. The amount of liquid in the tank reactor at the time of the polymerization reaction is preferably 1/4 to 3/4, more preferably 1/3 to 2/3 with respect to the volume of the tank reactor. The reactor is usually equipped with a stirrer. Examples of the stirring device include a static stirring device and a dynamic stirring device. Examples of the dynamic stirring device include a max blend type stirring device, a stirring device having a grid-like blade rotating around a vertical rotating shaft arranged in the center, a propeller type stirring device, a screw type stirring device, and the like. Of these, the Max Blend type agitator is preferably used from the viewpoint of uniform mixing.

After completion of the polymerization, if necessary, remove volatile components such as unreacted monomers. The removal method is not particularly limited, but heat devolatile is preferable. Examples of the devolatile method include a balanced flash method and an adiabatic flash method. The volatilization temperature by the adiabatic flash method or the equilibrium flash method is preferably 200 to 270 ° C, more preferably 220 to 260 ° C. The time for heating the resin by the adiabatic flash method is preferably 0.3 to 5 minutes, more preferably 0.4 to 3 minutes, and even more preferably 0.5 to 2 minutes. When devolatile in such a temperature range and heating time, it is easy to obtain a methacrylic resin (A) having less coloring and a low acid value in terms of acetic acid. The removed unreacted monomer can be recovered and used again in the polymerization reaction. The yellow index of the recovered monomer may be increased by the heat applied during the recovery operation or the like. It is preferable that the recovered monomer is purified by an appropriate method such as distillation or adsorption purification by a column to reduce the acid value and yellow index in terms of acetic acid.

Further, the resin mixture of the polymer and the unreacted monomer obtained after the polymerization can be continuously transferred from the reactor to a twin-screw extruder equipped with a vent. Subsequently, equilibrium flushing or adiabatic flushing can be performed at the twin-screw extruder inlet, followed by devolatile with a twin-screw extruder vent. The atmosphere for adiabatic flushing is preferably an inert gas atmosphere. Examples of the inert gas include nitrogen, carbon dioxide, argon and the like. More preferably, it is a nitrogen gas atmosphere. In an atmosphere containing oxygen, oxidative deterioration progresses in the extruder, making it difficult to obtain a highly transparent light guide plate. The inert gas can be introduced from the vicinity of the shaft seal portion of the extruder with a vent.

The pressure of the resin melt immediately before the flash in the heat insulating flash is preferably 1.5 to 3.0 MPa, more preferably 2.0 to 2.5 MPa. If it is less than 1.5 MPa, the flush becomes insufficient and the residual monomer tends to increase. On the contrary, if it exceeds 3.0 MPa, it tends to be difficult to obtain stable production.

The twin-screw extruder used in the present invention preferably includes a vent. The vent is preferably a vacuum vent or an open vent. At least one vent is provided on the downstream side of the polymer inflow portion. The pressure in the vacuum vent is preferably 30 Torr or less, more preferably 15 Torr or less, further preferably 9 Torr or less, and most preferably 6 Torr or less. When the pressure in the vacuum vent is within the above range, the volatilization efficiency is good, and the unreacted monomer, dimer, trimer and the like remaining in the methacrylic resin (A) can be reduced.

The screw of the twin-screw extruder is preferably a twin-screw screw in the same direction. Compared to the case of a single shaft, the shear energy given to the resin is large and the degree of surface renewal is large, so that volatilization can be performed efficiently, so that the remaining unreacted monomers, dimers, trimers, etc. can be reduced. .. Further, the screw configuration preferably has a kneading segment portion of 5% or more with respect to the total length of the screw. Examples of the kneading segment include a rotor segment, a forward feed kneading disc, a reverse feed kneading disc, and a mixing gear.

The average residence time when the methacrylic resin (A) passes through the screw of the twin-screw extruder is preferably 180 seconds or less. If the average residence time is long, the resin deteriorates and is easily thermally decomposed, and the heat resistance of the light guide plate that can be obtained is lowered or foamed.

The cylinder heating temperature of the twin-screw extruder is preferably 200 to 225 ° C, more preferably 210 to 225 ° C. If the temperature is lower than 200 ° C., it takes time to volatilize, and the volatilization tends to be insufficient. When the volatilization is insufficient, the molded product may have an appearance defect such as silver streak. On the contrary, when the temperature exceeds 225 ° C., the amount of the terminal double bond in the methacrylic resin (A) increases, the acid value in terms of acetic acid increases, and it becomes difficult to secure the thermostable decomposition property. In addition, the production of the above-mentioned dimers and trimers may increase. In addition, the transmittance at the wavelength of 450 nm is reduced.

The resin temperature immediately after passing through the twin-screw extruder and exiting the die is preferably 200 to 230 ° C, more preferably 210 to 230 ° C. If it is too low, the strands will become unstable, and if it is too high, the amount of terminal double bonds in the obtained methacrylic resin (A) will increase, and the acid value in terms of acetic acid will increase, making it difficult to ensure thermostable decomposition. Become.

The methacrylic resin (A) can be made into pellets, granules, powders or the like for convenience of storage, transfer, molding and the like. Pellets can be obtained, for example, by extruding the methacrylic resin (A) into a strand shape in the above-mentioned extruder and cutting the methacrylic resin (A) extruded into a strand shape with a pelletizer.

The methacrylic resin (A) used in the light guide plate of the present invention is preferably composed of only the methacrylic resin, but when actually obtained as the methacrylic resin (A), a trace amount of other optional components due to the production conditions are present. May exist. Other optional components resulting from this production condition include unreacted monomers, dimers, trimers, chain transfer agents and the like. In the present specification, the methacrylic resin (A) is referred to as a methacrylic resin (A) for convenience, including those containing these other optional components.

The methacrylic resin (A) used in the light guide plate of the present invention preferably contains 1% by mass or less of the above-mentioned other optional components in the methacrylic resin (A).
In the methacrylic resin (A) used for the light guide plate of the present invention, the amount of residual methyl methacrylate in the residual unreacted monomer is 1% by mass or less, preferably 0.8 in the methacrylic resin (A). It is mass% or less, more preferably 0.6 mass% or less.
The remaining monomer can be measured by the method described in Examples.

A lubricant and / or an antioxidant can be added to the methacrylic resin (A) used for the light guide plate of the present invention to be used as the methacrylic resin composition (B). That is, the methacrylic resin composition (B) can contain the methacrylic resin (A) and a lubricant and / or an antioxidant.
The amount of the lubricant or the antioxidant used in the present invention is preferably 0.01 to 1 part by mass and more preferably 0.05 to 0.5 part by mass with respect to 100 parts by mass of the methacrylic resin (A).

Examples of the lubricant include stearic acid, behenic acid, stearic acid amide, methylene bisstearoamide, hydroxystearic acid triglyceride, paraffin wax, ketone wax, octyl alcohol, hydrogenated oil and the like.

The antioxidant is effective in preventing oxidative deterioration of the resin by itself in the presence of oxygen. For example, phosphorus-based antioxidants, hindered phenol-based antioxidants, thioether-based antioxidants, and the like can be mentioned. These antioxidants may be used alone or in combination of two or more. Among them, phosphorus-based antioxidants and hindered phenol-based antioxidants are preferable, and the combined use of phosphorus-based antioxidants and hindered phenol-based antioxidants is more preferable, from the viewpoint of the effect of preventing deterioration of optical properties due to coloring.
When a phosphorus-based antioxidant and a hindered phenol-based antioxidant are used in combination, the amount of the phosphorus-based antioxidant used: the amount of the hindered phenol-based antioxidant used is 1: 5 to 2: by mass ratio. 1 is preferable, and 1: 2 to 1: 1 is more preferable.

As phosphorus-based antioxidants, 2,2-methylenebis (4,6-dit-butylphenyl) octylphosphite (manufactured by ADEKA; trade name: ADEKA STAB HP-10), tris (2,4-dit-) Butylphenyl) phosphite (manufactured by BASF; trade name: IRGAFOS168), 3,9-bis (2,6-di-tert-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa 3,9 -Diphosphaspiro [5.5] Undecan (manufactured by ADEKA; trade name: ADEKA STAB PEP-36) and the like are preferable.

As hindered phenolic antioxidants, pentaerythrityl-tetrakis [3- (3,5-dit-butyl-4-hydroxyphenyl) propionate] (manufactured by BASF; trade name IRGANOX1010), octadecyl-3- ( 3,5-Dit-butyl-4-hydroxyphenyl) propionate (manufactured by BASF; trade name IRGANOX1076) and the like are preferable.

In addition to lubricants and antioxidants, the methacrylic resin composition (B) according to the present invention includes fillers, thermal deterioration inhibitors, light stabilizers, mold release agents, polymer processing aids, antistatic agents, and flame retardant agents. , Dyeing pigments, light diffusing agents, organic dyes, matting agents, phosphors, UV absorbers and other additives that may be incorporated into ordinary resins may be included.

Examples of the filler include calcium carbonate, talc, carbon black, titanium oxide, silica, clay, barium sulfate, magnesium carbonate and the like. The amount of the filler that can be contained in the methacrylic resin composition of the present invention is preferably 3% by mass or less, more preferably 1.5% by mass or less, still more preferably 0% by mass.

The heat deterioration inhibitor can prevent the heat deterioration of the resin by capturing the polymer radicals generated when exposed to high heat under a substantially oxygen-free state.
Examples of the heat deterioration inhibitor include 2-t-butyl-6- (3'-t-butyl-5'-methyl-hydroxybenzyl) -4-methylphenyl acrylate (manufactured by Sumitomo Chemical Co., Ltd .; trade name: Sumilyzer GM). 2,4-dit-amyl-6- (3', 5'-dit-amyl-2'-hydroxy-α-methylbenzyl) phenylacrylate (manufactured by Sumitomo Chemical Co., Ltd .; trade name Sumilyzer GS) and the like are preferable.

A light stabilizer is a compound that is said to have a function of capturing radicals mainly generated by oxidation by light. Suitable light stabilizers include hindered amines such as compounds having a 2,2,6,6-tetraalkylpiperidine skeleton.

Examples of the release agent include higher alcohols such as cetyl alcohol and stearyl alcohol; and glycerin higher fatty acid esters such as stearic acid monoglyceride and stearic acid diglyceride. In the present invention, it is preferable to use higher alcohols and glycerin fatty acid monoester in combination as a release agent. When the higher alcohols and the glycerin fatty acid monoester are used in combination, the ratio is not particularly limited, but the amount of the higher alcohols used: the amount of the glycerin fatty acid monoester used is 2.5: 1 to 3 by mass ratio. 5: 1 is preferable, and 2.8: 1-3.2: 1 is more preferable.

The polymer processing aid is a polymer compound having an average degree of polymerization of 3,000 to 40,000, preferably 60% by mass or more of methyl methacrylate unit and 40% by mass of a vinyl-based monomer unit copolymerizable therewith. It consists of% or less. Specific examples thereof include the Metabren-P series manufactured by Mitsubishi Rayon and the Pararoid series manufactured by Dow Chemical.
Examples of the flame retardant include organic halogen-based flame retardants such as tetrabromobisphenol A, decabromodiphenyl oxide, and brominated polycarbonate; non-halogen flame retardants such as antimony oxide, aluminum hydroxide, zinc borate, and tricresyl phosphate. And so on.
Examples of the antistatic agent include stearoamide propyldimethyl-β-hydroxyethylammonium nitrate and the like. Examples of the dyeing pigment include titanium oxide and red iron oxide.

As the organic dye, a compound having a function of converting ultraviolet rays into visible light is preferably used.

Examples of the light diffusing agent and the matting agent include glass fine particles, polysiloxane-based crosslinked fine particles, crosslinked polymer fine particles, talc, calcium carbonate, barium sulfate and the like.

Examples of the phosphor include a fluorescent pigment, a fluorescent dye, a fluorescent white dye, a fluorescent whitening agent, and a fluorescent bleaching agent.
Examples of the ultraviolet absorber include benzophenones, benzotriazoles, triazines, benzoates, salicylates, cyanoacrylates, oxalic acid anilides, malonic acid esters, formamidines and the like. These can be used alone or in combination of two or more. Among these, benzotriazoles and oxalic acid anilides are preferable.

Thermal deterioration inhibitor, light stabilizer, lubricant, mold release agent, polymer processing aid, antistatic agent, flame retardant, dye pigment, which can be contained in the methacrylic resin composition (B) used for the light guide plate of the present invention. The total amount of the light diffusing agent, the organic dye, the matting agent, the phosphor and the ultraviolet absorber is preferably 1% by mass or less, more preferably 0.5% by mass or less, still more preferably 0.3% by mass or less. Most preferably, it is 0.1% by mass or less.

The methacrylic resin composition (B) used for the light guide plate of the present invention preferably contains 97% by mass or more, more preferably 98% by mass or more, and 99% by mass or more of the methacrylic resin (A) of the present invention. Is even more preferable.

The light guide plate of the present invention can be obtained by heat-melt molding the methacrylic resin (A) by a method such as injection molding or injection compression molding. In heat melt molding, pellet-shaped methacrylic resin (A) is preferably used.

The mold for molding the light guide plate of the present invention by injection molding preferably has a degassing mechanism. The content of the methyl methacrylate monomer remaining on the light guide plate can be reduced, and the heat resistance of the light guide plate can be improved.

The methacrylic resin (A) is preferably dried before molding. Examples of the drying method include a hot air drying method, a dehumidifying drying method, a vacuum drying method, and a low oxygen drying method. By reducing the water content by drying before molding, molding defects such as silver streaks can be reduced.

Further, it is preferable to remove defective cut products and resin powder from the methacrylic resin pellets before molding. Defective cut products include long resin pieces obtained as a result of failing to cut the strands. The resin powder is a powder formed by rubbing chips or pellets generated when the strands are cut. The method for removing defective cut products and resin powder is not particularly limited. For example, a centrifugation method, a sieving method and the like can be mentioned.

Further, when the methacrylic resin (A) is transferred to the hopper of the molding machine, it is preferable to maintain the temperature of the methacrylic resin composition or the methacrylic resin pellets at, for example, 70 ° C. or higher. When transferred at a high temperature, it may be possible to suppress the formation of resin powder due to moisture absorption during transfer and rubbing between pellets.

The light guide plate of the present invention has a transmittance of 65% or more, more preferably 70% or more, still more preferably 75% or more at a wavelength of 435 nm in terms of an optical path length of 180 mm. When converting to an optical path length of 180 mm, it is converted using Lambert-Beer's law. If the light guide plate has irregularities, the correct transmittance cannot be measured. Therefore, the irregularities on the surface are polished and smoothed for measurement.

The light guide plate of the present invention is used for an in-vehicle display device installed in a vehicle. Examples of display devices include speed displays, liquid crystal display devices for back monitors and navigation, and decorative display devices such as switches, buttons, and emblems.

Since the light guide plate of the present invention has high transparency, it is possible to exhibit high performance as a light guide plate regardless of the size. On the other hand, a light guide plate having a maximum optical path length of 150 mm or more is preferable from the viewpoint of being able to take advantage of the high transparency.

When the light guide plate of the present invention is used, a concave-convex shape for light guide may be formed on the back surface of the plate by a known method such as fusion, adhesion, coating, printing, injection molding, and processing by laser light. Light incident from the end surface of the plate can be reflected or refracted in the uneven shape and emitted to the front surface of the plate. Examples of the uneven shape include a perfect circle or elliptical dot pattern, a line pattern such as a rectangle or a V-groove, a hemispherical lens-shaped unevenness, and a grain pattern. These uneven shapes cannot be unconditionally defined because the optimum structure differs depending on the size and thickness of the light guide plate, but the width is 1 to 600 μm, the length is 2 to 1200 μm, the height or depth is 1 to 500 μm, and the adjacent uneven shapes. The distance between the shapes is preferably 2 to 10000 μm. If the uneven shape is too large, it will be visually recognized and the quality of the display will be deteriorated, and if it is too small, it will be difficult to process and the productivity will be lowered. Further, if the distance between the adjacent uneven shapes is narrower than 2 μm, it becomes difficult to independently form the adjacent uneven shapes, and molding defects are likely to occur. If it is wider than 10000 μm, the number of uneven portions cannot be increased. Since the uneven portion has a function of emitting light, the limitation on the number of the uneven portion causes a limitation of the utilization rate, which is the ratio of the light effectively emitted from the light incident on the end surface of the light guide plate. These uneven shapes may be the same shape in one light guide plate, may be formed by combining different shapes, or patterns having the same shape but different sizes may be arranged. Further, the interval and size of the unevenness may be modulated according to the distance from the light source arranged adjacent to the end face of the light guide plate.

Further, instead of forming the uneven shape, a white reflective material may be printed on the back surface of the light guide plate. The size of the white reflector is preferably 500 μm to 5000 μm. If it is smaller than 500 μm, it becomes difficult to print the white reflective material by existing screen printing or the like. If it is larger than 5000 μm, the white reflective material is visually recognized even when viewed through a diffusion sheet or the like, and the quality of the display deteriorates. The distance between the reflectors is preferably 1000 to 5000 μm. If the interval is narrower than 1000 μm, adjacent white reflective materials may overlap each other in screen printing or the like, resulting in a defect. If it is wider than 5000 μm, the dark part between the white reflective materials will be visible even when viewed through a diffusion sheet or the like, and the quality of the display will deteriorate. Further, the spacing and size of the white reflector may be modulated according to the distance from the light source arranged adjacent to the end face of the light guide plate. Further, a prism or an arcuate line-shaped convex portion may be formed on the surface (front surface of the plate) from which the light of the light guide plate is emitted by the same means. When used as a backlight, a reflective sheet may be arranged on the back side of the light guide plate, and a diffusion sheet and / or a prism sheet may be appropriately arranged on the front side of the light guide plate.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. The physical property values and the like were measured by the following methods.

(Weight average molecular weight (Mw), number average molecular weight (Mn), molecular weight distribution)
The chromatogram was measured by gel permeation chromatography (GPC) under the following conditions, and the value converted to the molecular weight of standard polystyrene was calculated. The baseline is that the slope of the peak on the high molecular weight side of the GPC chart changes from zero to plus when viewed from the earliest retention time, and the slope of the peak on the low molecular weight side changes from minus to zero when viewed from the earliest retention time. It is a line connecting the points that change to.
GPC device: manufactured by Tosoh Corporation, HLC-8320
Detector: Differential refractive index detector Column: Two TSKgel SuperMultipore HZM-M manufactured by Tosoh Corporation and SuperHZ4000 connected in series were used.
Eluent: Tetrahydrofuran Eluent flow rate: 0.35 ml / min Column temperature: 40 ° C
Calibration curve: Created using data of 10 standard polystyrene points

(Shinji Ikari City (rr) with triplet display)
A ¹ H-NMR spectrum of a methacrylic resin was measured using a nuclear magnetic resonance apparatus (ULTRA SHIELD 400 PLUS manufactured by Bruker) using deuterated chloroform as a solvent at room temperature and 64 times of integration. From the spectrum, the area (X) of the region of 0.6 to 0.95 ppm and the area (Y) of the region of 0.6 to 1.35 ppm when TMS was set to 0 ppm were measured, and then the triplets were measured. The displayed syndiotacticity (rr) was calculated by the formula: (X / Y) × 100.

(Polymerization conversion rate), (Amount of residual methyl methacrylate monomer)
As a column on the gas chromatograph, GL Sciences Inc. The INERT CAP 1 (df = 0.4 μm, 0.25 mm I.D. × 60 m) was connected, and the analysis was performed under the following analysis conditions, and the calculation was performed based on the analysis. The contained volatile matter can be measured for each type based on the retention time.
<Analysis conditions>
injection temperature: 250 ° C
detector temperature: 250 ° C
Column temperature conditions:
Initial temperature: 60 ° C
Initial temperature holding time: 5 minutes Heating rate: 10 ° C / min Maximum temperature: 250 ° C
Maximum temperature retention time: 10 minutes

(Glass transition temperature Tg)
The sample obtained by crushing the light guide plate is first heated to 230 ° C. using a differential scanning calorimetry device (manufactured by Shimadzu Corporation, DSC-50 (product number)) in accordance with JIS K7121, and then to room temperature. After cooling, the DSC curve was measured under the condition that the temperature was raised from room temperature to 230 ° C. at 10 ° C./min for the second time. The midpoint glass transition temperature obtained from the DSC curve measured at the time of the second temperature rise was defined as the glass transition temperature in the present invention.

(MFR)
The melt flow rate (MFR) of the methacrylic resin and the sample obtained by crushing the light guide plate was measured at 230 ° C. and a load of 3.8 kg in accordance with JIS K7210.

(Evaluation of heat-resistant decomposition by thermogravimetric retention)
For a sample obtained by crushing a methacrylic resin and a light guide plate, a thermogravimetric analyzer (manufactured by Shimadzu Corporation, TGA-50 (product number)) was used to create a dry air flow rate of 50 ml / min in an air atmosphere from 50 ° C. to 290. After raising the temperature to 20 ° C./min, the thermogravimetric decrease was measured under the condition of holding at 290 ° C. for 20 minutes in an air atmosphere. Based on the weight (X1) at 50 ° C. as a reference (retention rate 100%) and the weight (X2) when the product was held at 290 ° C. for 20 minutes, the heat degradability was evaluated by the following formula.
Weight retention rate (%) = (X2 / X1) x 100 (%)

(Acetic acid equivalent acid value)
The acid value was measured by dissolving the resin sample in chloroform and titrating with an aqueous potassium hydroxide solution according to the method described in JIS-K0070-1992, and the value obtained by subtracting the acid value of chloroform alone was taken as the acid value. ..
Using the following formula (I), the value obtained by converting the obtained acid value into acetic acid was used.
Acetic acid equivalent acid value (ppm) = (acid value / 1000) x (60/56) x 1000000 (I)
The meanings of the numerical values in the formula (I) are as follows.
1000: Convert milligrams to grams 60: Molecular weight of acetic acid 56: Molecular weight of potassium hydroxide 1000000: Converted to ppm units

(Filling evaluation at the time of injection molding)
The thicknesses of the four corners of the injection-molded light guide plate were measured, and if all four points were 0.4 mm ± 0.05, the evaluation was A, and the others were evaluated as B.

(Insoluble matter when dissolved in chloroform)
After pulverizing the light guide plate with a pulverizer, 1 g was added to 50 mL of chloroform, and the mixture was stirred at room temperature for 12 hours. The obtained solution was filtered through a 0.45 μm membrane filter, the filter was vacuum dried at 60 ° C. for 1 hour or more, and then the weight of the residue remaining on the filter was measured to measure the insoluble matter.

(Transmittance at 450 nm)
After polishing the end face of the obtained light guide plate, use the long side direction (optical path length 180 mm) of the front and back mirror surface processed parts without a pattern on the surface, and use an ultraviolet visible near infrared spectrophotometer (manufactured by JASCO Corporation, product number: With V-670), the transmittance at a wavelength of 450 nm and an optical path length of 180 mm was measured.

(Production Example 1-1) (Production of methacrylic resin [A-1])
The inside of the autoclave equipped with a stirrer and a sampling tube was replaced with nitrogen. To this, 100 parts by mass of purified methyl methacrylate, 0.0115 parts by mass of 2,2'-azobis (2-methylpropionitrile (hydrogen extraction capacity: 1%, 1 hour half-life temperature: 83 ° C.)), and 0.504 parts by mass of n-octyl mercaptan was added and stirred to obtain a raw material solution. Nitrogen was sent into the raw material solution to remove dissolved oxygen in the raw material solution.
The raw material liquid was put into a tank reactor connected to the autoclave by piping up to 2/3 of the capacity. The temperature was maintained at 100 ° C., and the polymerization reaction was first started by a batch method. When the polymerization conversion rate reaches 45% by mass, the raw material liquid is supplied from the autoclave to the tank reactor at a flow rate having an average residence time of 120 minutes, and the reaction liquid is supplied at a flow rate corresponding to the supply flow rate of the raw material liquid. It was taken out from the tank reactor, maintained at a temperature of 100 ° C., and switched to a continuous flow type polymerization reaction. After switching, the polymerization conversion rate in the steady state was 45% by mass.

The reaction solution extracted from the tank reactor in a steady state was supplied to a multi-tube heat exchanger to heat it so that the internal temperature was 230 ° C. at a flow rate having an average residence time of 2 minutes. Next, nitrogen gas was introduced from the back vent section, the heated reaction solution was introduced into the volatilization twin-screw extruder, and the reaction solution was adiabatic flushed at 230 ° C. The volatile matter was removed, and the cylinder heating temperature was set to 210 ° C., and the volatile matter was passed through three front vents to remove the remaining volatile matter containing the unreacted monomer as a main component. After that, a mixture of stearyl alcohol and stearyl monoglyceride (weight ratio 3: 1) was added as a lubricant from the tip of the twin-screw extruder to 100 parts by mass of the methacrylic resin so as to be 0.1 phr. Extruded into strands from the die. The temperature of the strands immediately after leaving the die was 220 ° C. After discharging from a twin-screw extruder into a strand shape, cooling with water, and cutting with a pelletizer, the pellet shape has a Mw of 55,000, a molecular weight distribution of 1.79, and a syndiotacticity (rr) of 55.4%. Then, a methacrylic resin [A-1] having an MFR of 10 g / 10 min, a glass transition temperature of 120 ° C., and a content of a structural unit derived from methyl methacrylate was 100% by mass was obtained. The acid value of the methacrylic resin [A-1] was 21 ppm, and the weight retention rate was 81%.

(Manufacturing Example 1-2) (Manufacturing of methacrylic resin [A-2])
Using a mixture of 99 parts by mass of methyl methacrylate and 1 part by mass of methyl acrylate instead of 100 parts by mass of methyl methacrylate in Production Example 1-1, the amount of n-octyl mercaptan was changed from 0.504 parts by mass to 0.490 parts by mass. A pellet-shaped methacrylic resin [A-2] was obtained in the same manner as in Production Example 1-1 except for the modification. The methacrylic resin [A-2] has a Mw of 56500, a molecular weight distribution of 1.78, a syndiotacticity (rr) of 54.9%, an MFR of 10 g / 10 min, a glass transition temperature of 119 ° C., and The content of the structural unit derived from methyl methacrylate was 99.3% by mass, the content of the structural unit derived from methyl acrylate was 0.7% by mass, the acid value was 23 ppm, and the weight retention rate was 82%. ..

(Manufacturing Example 1-3) (Manufacturing of methacrylic resin [A-3])
Using a mixture of 94 parts by mass of methyl methacrylate and 6 parts by mass of methyl acrylate instead of 100 parts by mass of methyl methacrylate in Production Example 1-1, the amount of n-octyl mercaptan was changed from 0.504 parts by mass to 0.390 parts by mass. A pellet-shaped methacrylic resin [A-3] was obtained in the same manner as in Production Example 1-1 except for the modification. Mw of methacrylic resin [A-3] is 70,000, molecular weight distribution is 1.83, syndiotacticity (rr) is 52.9%, MFR is 9.4 g / 10 min, and glass transition temperature is 111 ° C. The content of the structural unit derived from methyl methacrylate is 95.5% by mass, the content of the structural unit derived from methyl acrylate is 4.5% by mass, the acid value is 20 ppm, and the weight retention rate is 69%. there were.

(Manufacturing Example 1-4) (Manufacturing of methacrylic resin [A-4])
A methacrylic resin [A-4] was obtained in the same manner as in Production Example 1-1 except that the cylinder heating temperature of the devolatilized twin-screw extruder was set from 210 ° C. to 250 ° C. The methacrylic resin [A-4] has a Mw of 55,000, a molecular weight distribution of 1.79, a syndiotacticity (rr) of 55.4%, an MFR of 11 g / 10 min, a glass transition temperature of 119 ° C., and The content of the structural unit derived from methyl methacrylate was 100% by mass, the acid value was 40 ppm, and the weight retention rate was 74%.

(Production Example 1-5) (Production of methacrylic resin [A-5])
A methacrylic resin [A-5] was obtained in the same manner as in Production Example 1-1 except that air was introduced instead of introducing nitrogen gas into the back vent of the devolatilized twin-screw extruder. The methacrylic resin [A-5] has a Mw of 55,000, a molecular weight distribution of 1.79, a syndiotacticity (rr) of 55.4%, an MFR of 11 g / 10 min, a glass transition temperature of 119 ° C., and The content of the structural unit derived from methyl methacrylate was 100% by mass, the acid value was 49 ppm, and the weight retention rate was 71%.

(Manufacturing Example 1-6) (Manufacturing of methacrylic resin [A-6])
The temperature during polymerization was changed from 100 ° C to 140 ° C, and 2,2'-azobis (2-methylpropionitrile 0.0115 parts by mass to 0.072 parts by mass, and n-octyl mercaptan 0.490 parts by mass). A methacrylic resin [A-6] was obtained in the same manner as in Production Example 1-2 except that the amount was changed from 0.480 parts by mass. The methacrylic resin [A-6] had a Mw of 57,000 and a molecular weight distribution. At 1.81, the syndiotacticity (rr) is 50.5%, the MFR is 10 g / 10 min, the glass transition temperature is 116 ° C., and the content of structural units derived from methyl methacrylate is 99.3% by mass. The content of the structural unit derived from methyl acrylate was 0.7% by mass, the acid value was 22 ppm, and the weight retention rate was 82%.

(Manufacturing Example 1-7) (Manufacturing of methacrylic resin [A-7])
A methacrylic resin [A-7] was obtained in the same manner as in Production Example 1-6 except that the amount of n-octyl mercaptan was changed from 0.480 parts by mass to 0.220 parts by mass. The methacrylic resin [A-7] has an Mw of 84,000, a molecular weight distribution of 1.81, a syndiotacticity (rr) of 50.5%, and an MFR of 2.7 g / 10 min at a glass transition temperature of 117 ° C. The content of the structural unit derived from methyl methacrylate is 99.3% by mass, the content of the structural unit derived from methyl acrylate is 0.7% by mass, the acid value is 24 ppm, and the weight retention rate is 80%. there were.

(Examples 1 and 2, Comparative Examples 1 to 5)
Using methacrylic resins [A-1] to [A-7], an ultra-high speed injection molding machine (SE-180LGP, manufactured by Sumitomo Heavy Industries, Servo 15G), 9.7 inches (180 mm x 160 mm), thickness 0. The light guide plate was injection-molded by a light guide body mold (manufactured by Kuraray) having a pattern on the other regions, with 4 mm and 180 mm × 25 mm being mirror-finished on the front and back. The molding conditions were a cylinder temperature of 300 ° C., a mold temperature of 85 ° C., and an injection speed of 800 mm / sec.
Table 1 shows the evaluation results of the obtained light guide plate. When the methacrylic resin [A-7] was used, the filling was insufficient and the transmittance at 450 nm could not be measured.

From Comparative Example 1, it became clear that it is important that the structural unit derived from methyl methacrylate is 99% by mass or more in order to realize a glass transition temperature of 118 ° C. or more.
From Comparative Example 2, it became clear that the cylinder heating temperature (200 to 230 ° C.) is important in order to obtain sufficient transmittance at a wavelength of 450 nm.
From Comparative Example 3, it was clarified that it is important to carry out the volatilization in an atmosphere of an inert gas such as nitrogen in order to obtain a sufficient transmittance at a wavelength of 450 nm.
From Comparative Example 4, although the transmittance at a wavelength of 450 nm is the same as that of Example 2, the glass transition temperature is low, and it is preferable to set the polymerization temperature to 90 to 120 ° C. in order to realize a glass transition temperature of 118 ° C. or higher. It became clear.

Claims (6)

A methacrylic resin (A) containing a structural unit derived from 99% by mass to 100% by mass of methyl methacrylate and a structural unit derived from 0% by mass to 1% by mass of an acrylic acid ester.
When the optical path length is converted to 180 mm, the transmittance of the wavelength of 450 nm is 65% or more.
The glass transition temperature at the midpoint evaluated by the temperature rise measurement of 10 ° C./min by DSC is 118 to 124 ° C.
A light guide plate for a vehicle display device in which the amount of residual methyl methacrylate is 1.0% by mass or less. The light guide plate of the vehicle display device according to claim 1, wherein the melt flow rate measured by crushing the light guide plate is 5 g / 10 minutes or more and 40 g / 10 minutes or less. The light guide plate of the vehicle display device according to claim 1 or 2, wherein the lubricant is contained in an amount of 0.01 to 1 part by mass with respect to 100 parts by mass of the methacrylic resin (A). A monomer mixture containing 98.6% by mass to 100% by mass of methyl methacrylate and 0% to 1.4% by mass of acrylic acid ester is polymerized by radical polymerization to obtain 99% by mass to 100% by mass of methyl methacrylate. A step of obtaining a methacrylic resin (A) containing a structural unit derived from it and a structural unit derived from 0% by mass to 1% by mass of an acrylic acid ester, and a methacrylic resin (A) obtained by heat devolatile in an inert gas atmosphere. A method for producing a methacrylic resin (A), which comprises a step of removing an unreacted monomer from the reaction mixture containing () to reduce the amount of residual methyl methacrylate to 1.0% by mass or less. The method for producing a methacrylic resin (A) according to claim 4, wherein the inert atmosphere is a nitrogen atmosphere. The method for producing a methacrylic resin (A) according to claim 4 or 5, wherein the heat devolatilization is performed using a twin-screw extruder, and the cylinder heating temperature of the twin-screw extruder is 200 to 230 ° C.