JP2007291230A - Light guide plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate which shows few defects caused by burrs or warpage at molding, enables good transfer of micro-asperity and shows reduced defects such as cracks, backward warpage, etc., in an environmental test. <P>SOLUTION: The light guide plate comprises a methacrylic resin composed of a methyl methacrylate monomer and at least one other vinyl monomer copolymerizable with methyl methacrylate. The methacrylic resin comprises a polymer (A) whose weight average molecular weight determined by gel permeation chromatography (GPC) is 65,000-350,000 and a polymer (B) whose weight average molecular weight is 5,000-100,000. The methacrylic resin has a weight average molecular weight of 60,000-300,000 and a molecular weight distribution (Mw/Mn) of 2.2-7.0, and the polymer (A) and the polymer (B) composing the methacrylic resin satisfy a prescribed relation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a light guide plate suitable for a display device that has few appearance defects due to burrs, flow marks, and warpage during molding, improves the transfer of fine irregularities, and reduces defects such as cracks and back warpage in environmental tests. About.

  In recent years, the demand for light guide plates for display devices has increased with the increase in personal computers, liquid crystal monitors, and liquid crystal televisions. FIG. 1 shows an example of a light guide plate for a display device. In general, a light guide plate for a display device is a part of a backlight unit installed on the back side of the display unit 1. A light source is received from a light source 3 installed on the end face of the light guide plate 2 (the light source 3 is provided with a reflector 4 for effectively putting light into the light guide plate), and the light is guided to the back surface. There is a function of effectively emitting light to the display device side using the reflection plate 5 installed and the reflection sheet 6 installed on the surface other than the light source surface. In order to emit light more effectively, the light exit surface facing the display unit 1 and / or the reflective surface facing the reflection plate 5 may be given a fine uneven shape or lens shape. Furthermore, an optical sheet 7 such as a diffusion sheet, a prism sheet, or a polarizing sheet may be provided between the light guide plate 2 and the display unit 1.

  Personal computers, monitors, and liquid crystal televisions as display devices including liquid crystals are desired to be light in weight, and measures to reduce the thickness of members including liquid crystals are being taken, and the demand for reducing the thickness of light guide plates is also increasing. In particular, when the light source 1 in FIG. 1 is changed from a cold cathode tube to an LED, the light incident surface of the light guide plate can be made thin because the light output size from the light source is small. When the thickness of the light guide plate is reduced, warpage occurs due to the environment, and there is a problem that interference fringes are generated when the liquid crystal is touched. In the first place, when the light guide plate is molded, particularly when it is molded by injection molding, there is a problem that if the fluidity is low, the resin does not flow to the end or must be filled at a high pressure. Strain is generated by filling with high pressure, and warping occurs when the strain is relaxed by the environment. Therefore, it is necessary to mold the light guide plate with a resin having higher fluidity as the resin.

In addition, there is a problem that burrs are generated because the mold clamping force (clamping force) is insufficient for the filling pressure during filling. The burr cracks while moving or setting the light guide plate and damages the light guide plate, or sticks to the light guide plate due to static electricity, resulting in poor volatile point. Furthermore, the burr is caught and the light guide plate cannot be set. In addition, in the conventional thick light guide plate, there are many flow mark defects due to jetting during filling (resin moves closer to the gate after the mold is cooled) and air entrainment near the gate. .
Several materials are known for solving such problems. (For example, see Patent Documents 1, 2, and 3)
However, the contents of Patent Documents 1 and 2 are only about describing the relationship between the molecular weight and other vinyl monomers copolymerizable with methyl methacrylate. In the light guide plate, in order to achieve high fluidity, the molecular weight or heat resistance must be reduced, and a light guide plate satisfying warpage and deformation in an environmental test cannot be obtained.

In the method based on micro-crosslinking using the polyfunctional monomer described in Patent Document 3, it is very difficult to control the polyfunctional monomer, and if it is too much, the mixing uniformity is lowered and the appearance of the molded product is lowered. It is very difficult to maintain a stable quality by saying that the effect is lost.
Since the number of light guide plates is very small, some existing techniques are known when they are further expanded and considered as a highly fluid methacrylic resin as optics. (For example, Patent Documents 4 and 5)
The contents of Patent Documents 4 and 5 are high molecular weight or low molecular weight methacrylic resins that impart flowability with a low molecular weight methacrylic resin, impart mechanical strength with high molecular weight, and impart processability in a mixed state. However, it has been found that the contents described in Patent Document 4 are only about the relationship of molecular weight, and as such, high fluidity and mechanical strength cannot be satisfied. Patent Document 5 describes a technique in which a low molecular weight methacrylic resin is copolymerized with another vinyl monomer copolymerizable with a large amount of methyl methacrylate. It turns out to be insufficient to improve.

JP-A-9-31134 Japanese Patent Laid-Open No. 10-265530 Japanese Patent No. 3454072 Japanese Patent Publication No. 1-2865 JP-A-4-277545

  The present invention provides a light guide plate for a display device that has few defects due to burrs and warping during molding, has good transfer of fine irregularities, and has reduced defects such as cracks and back warp in environmental tests.

As a result of diligent research to solve these problems, the appearance of burrs, flow marks, and warpage during molding while maintaining heat resistance by using methacrylic resins with two different molecular weights and polymer compositions. It has been found that a light guide plate for a display device can be produced which can reduce defects, improve the transfer of fine irregularities, and reduce defects such as cracks and back-warping in environmental tests. That is, the present invention
[1] A methacrylic resin composed of at least one methyl methacrylate monomer and another vinyl monomer copolymerizable with methyl methacrylate, the methacrylic resin being gel permeation chromatography ( GPC) includes a polymer (A) having a weight average molecular weight of 65,000 to 350,000 and a polymer (B) having a weight average molecular weight of 50,000 to 100,000. The weight average molecular weight is 60,000 to 300,000, the molecular weight distribution (Mw / Mn) is 2.2 to 7.0, and the constituting polymer (A) and polymer (B) are the following (1) to ( 5. A light guide plate characterized by using a methacrylic resin satisfying the relationship 5).
The amount of other vinyl monomer units copolymerizable with methyl methacrylate in the polymer (A) and the polymer (B) is the amount in the polymer (A): AMa wt%
Amount in polymer (B): BMa wt%,
Further, the amount of the polymer (A) is AM wt%, the amount of the polymer (B) is BM wt%,
When the weight average molecular weight of the polymer (A) is Mwa and the weight average molecular weight of the polymer (B) is Mwb,
Mwb + 0.5 × 10 ⁴ ≦ Mwa (1)
0 ≦ BMa <AMa <20 (2)
2 ≦ AMa × (AM / 100) + BMa × (BM / 100) ≦ 20 (3)
AM: BM = 50: 50 to 95: 5 (4)
5 ≦ (Mwa / Mwb) × (AM / BM) (5)
[2] The method according to [1], wherein a methacrylic resin obtained by two-stage polymerization by any one of a bulk polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method or two methods is used. Light guide plate.
[3] According to [1] and [2], at least one surface of the light guide plate is formed with fine unevenness or lens shape having a 10-point average roughness of less than 200 μ based on JIS-B0601. The light guide plate according to any one of the above.
[4] The light guide plate according to any one of [1] to [3], wherein a maximum thickness of the light guide plate is 1.5 mm or less.
[5] The lead according to any one of [1] to [4], wherein the methacrylic resin contains 0.5 ppm to 5 wt% of fine particles having an average particle size of 0.01 μm to 50 μm. Light board.
[6] The light guide plate according to any one of [1] to [5], wherein the light guide plate is obtained by injection molding.
[7] The light guide plate according to any one of [1] to [6], wherein the light source used is an LED.

  According to the present invention, a light guide plate suitable for a display device having few appearance defects due to burrs, flow marks and warpage during molding, improving the transfer of fine irregularities, and reducing defects such as cracks and back warpage in environmental tests. Is obtained.

  The present invention is described in further detail below. The methacrylic resin used for the light guide plate in the present invention is composed of methyl methacrylate and other vinyl monomers copolymerizable with methyl methacrylate. Other vinyl monomers copolymerizable with methyl methacrylate include alkyl methacrylates having 2 to 18 alkyl groups, alkyl acrylates having 1 to 18 carbon atoms in alkyl groups, acrylic acid, methacrylic acid, and the like Of α, β-unsaturated acid, maleic acid, fumaric acid, itaconic acid and other unsaturated group-containing divalent carboxylic acids and alkyl esters thereof, aromatic vinyl compounds such as styrene, α-methylstyrene, and nucleus-substituted styrene, Vinyl cyanide compounds such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, N-substituted maleimide, etc., ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, Tetraethylene glycol di (meth) acrylate etc. Esterification of both hydroxyl groups of ethylene glycol or its oligomer with acrylic acid or methacrylic acid: Hydroxyl ester of two alcohols such as neopentyl glycol di (meth) acrylate and hexanediol dimethacrylate with acrylic acid or methacrylic acid A product obtained by esterification of a polyhydric alcohol derivative such as trimethylolpropane or pentaerythritol with acrylic acid or methacrylic acid: a polyfunctional monomer such as divinylbenzene may be used alone or in combination of two or more. Can be used. Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like are preferably used from the viewpoints of light resistance, heat stability, heat resistance, and fluidity. , Methyl acrylate, ethyl acrylate, and n-butyl acrylate are particularly preferable.

The methacrylic resin used for the light guide plate in the present invention comprises a polymer (A) and a polymer (B), and the average molecular weight measured by each GPC is 65,000 to 350,000 for the polymer (A). The polymer (B) is from 50,000 to 100,000. From the viewpoint of mechanical strength, the average molecular weight of the polymer (A) is 650,000 or more. It is 350,000 or less from the viewpoint of fluidity. Preferably it is 68,000-250,000. Considering that the polymer becomes liquid and becomes a foamed state at the time of molding, the average molecular weight of the polymer (B) is required to be not less than 50,000. It is necessary to be 100,000 or less from the viewpoint of fluidity. Preferably it is 60,000 to 80,000.
The weight average molecular weight measured in the present invention is measured by gel permeation chromatography. Prepare a calibration curve from the elution time and the weight average molecular weight in advance using a standard methacrylic resin that has a narrow molecular weight distribution and a known weight average molecular weight and is available as a reagent. From the calibration curve, calculate the weight average molecular weight and number of each sample. The average molecular weight can be measured.

  As a polymerization initiator for producing the polymer (A) and the polymer (B) in the present invention, when using free radical polymerization, di-t-butyl peroxide, dilauroyl peroxide, t-butyl peroxide are used. Peroxides such as oxy-2-ethylhexanoate, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, Common azo-based radical polymerization initiators such as azobisisobutyronitrile, azobisisovaleronitrile, 1,1-azobis (1-cyclohexanecarbonitrile) can be used. You may use the above together. A combination of these radical initiators and an appropriate reducing agent may be used as a redox initiator. These initiators are generally used in the range of 0.001 to 1 wt% with respect to the monomer mixture.

  In order to adjust the molecular weights of the polymer (A) and the polymer (B) in the present invention, a chain transfer agent generally used can be used in the case of producing by radical polymerization. Examples of the chain transfer agent include n-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, 2-ethylhexyl thioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris (thioglycolate), pentaerythritol tetrakis (thioglycolate). Etc.) are preferably used. Generally, it is used in the range of 0.001 to 1 wt% with respect to the monomer mixture. The chain transfer agent used for the polymer (A) and the polymer (B) may be the same or different. Regarding the amount of the chain transfer agent of the polymer (A) and the polymer (B), the polymer (B) having a low molecular weight is used more frequently, and the polymer (A) or the polymer (B) is polymerized alone. The molecular weight is set based on the molecular weight of the polymer thus obtained, and the amount of the molecular weight modifier used therefor can be determined.

The amount of other vinyl monomer units copolymerizable with methyl methacrylate in the polymer (A) and the polymer (B) constituting the methacrylic resin in the present invention is the amount in the polymer (A).・ AMa wt%
Amount in polymer (B): BMa wt%,
Further, the amount of the polymer (A) is AM wt%, the amount of the polymer (B) is BM wt%,
When the weight average molecular weight of the polymer (A) is Mwa and the weight average molecular weight of the polymer (B) is Mwb,
Mwb + 0.5 × 10 ⁴ ≦ Mwa (1)
0 ≦ BMa <AMa <20 (2)
2 ≦ AMa × (AM / 100) + BMa × (BM / 100) ≦ 20 (3)
AM: BM = 50: 50 to 95: 5 (4)
5 ≦ (Mwa / Mwb) × (AM / BM) (5)
Need to hold.

Formula (1) shows the magnitude relationship between the weight average molecular weights of the polymer (A) and the polymer (B). From the viewpoint of the effect of improving fluidity, the polymer (A) is always more than the polymer (B). It must be larger than 50,000. Preferably it is 10,000 or more, More preferably, it is 20,000 or more.
Formula (2) represents each quantity of the vinyl monomer which can be polymerized to the methyl methacrylate of a polymer (A) and a polymer (B), and is 0 <= BMa <AMa <20. A vinyl monomer must be copolymerized with the polymer (A). Since the polymer (A) has a higher molecular weight than the polymer (B), the fluidity is poor. Therefore, the relationship between AMa and BMa of the polymer (A) and the polymer (B) is higher in fluidity when AMa is larger than BMa. This is particularly effective for fluidity at higher shares such as during injection molding than at low shares such as melt flow rate. However, AMa needs to be less than 20 wt% from the heat resistance point of methacrylic resin. Further, the polymer (B) may be a polymer based on a methyl methacrylate monomer alone. Since the polymer (B) has a low molecular weight, a large number of chain transfer agents are used to adjust the molecular weight, and the lower the molecular weight, the larger the amount of polymer bound to the terminal by the chain transfer agent. For this reason, the heat resistance as thermal decomposability is stronger at low molecular weight. Methacrylic resin is said to have low heat resistance in the sense of thermal decomposition because it decomposes monomers from the polymer end called the zipper effect, and in order to prevent this, copolymerizable vinyl monomers are copolymerized. It is known to do. However, it is known that a polymer having a chain transfer agent at the end hardly causes thermal decomposition of the polymer end. Preferably 0 ≦ BMa <AMa ≦ 15, and more preferably 0 ≦ BMa <AMa ≦ 10.

Formula (3) in the present invention is the amount of other vinyl monomers that can be polymerized to the average methyl methacrylate monomer present in the methacrylic resin comprising the polymer (A) and the polymer (B) ( wt%), and 2 ≦ AMa × (AM / 100) + BMa × (BM / 100) ≦ 20. It must be 2 or more in terms of heat resistance and fluidity in the sense of thermal decomposition. 20 or less is required in terms of heat resistance in the sense of thermal deformation. Preferably, 2 ≦ AMa × (AM / 100) + BMa × (BM / 100) ≦ 13, and more preferably 2 ≦ AMa × (AM / 100) + BMa × (BM / 100) ≦ 10.
Formula (4) for satisfying the methacrylic resin in the present invention represents the ratio of the polymer (A) and the polymer (B) in the methacrylic resin, and AM: BM = 50: 50 to 95: 5. It is. From the viewpoint of strength, the ratio of the polymer (A) needs to be 50 wt% or more. It is necessary to be 95% or less from the viewpoint of fluidity. More preferably, AM: BM = 60: 40 to 92: 8, and still more preferably AM: BM = 65: 35 to 92: 8.

Moreover, Formula (5) in this invention is a relational expression which considered both the weight average molecular weight of the polymer (A) which comprises methacrylic resin, and a polymer (B), and the existing quantity. When the formula (5) is smaller than 5, two cases can be considered. One is when the weight average molecular weight ratio is large and the abundance ratio is small. In this case, it is necessary to increase the abundance ratio from the point of mechanical strength and satisfy the formula (5). The second is a case where the weight average molecular weight ratio is small even if the abundance ratio is large. In this case, it is necessary to increase the weight average molecular weight ratio and satisfy the formula (5) in terms of fluidity effect. Preferably, Formula (5) is 7 or more.
The weight average molecular weight of the methacrylic resin comprising the polymer (A) and the polymer (B) according to the present invention is 60,000 to 300,000. From the viewpoint of mechanical strength, the weight average molecular weight needs to be 60,000 or more. It is necessary to be 300,000 or less from the viewpoint of fluidity and workability. Preferably it is 6.5-250,000, More preferably, it is 6.5-200,000. The molecular weight distribution is preferably 2.2 to 7.0.

Here, the molecular weight distribution is the ratio of the weight average molecular weight to the number average molecular weight (weight average molecular weight / number average molecular weight) measured by GPC, and this ratio needs to be 2.2 or more from the viewpoint of fluidity. It is. The swell becomes too large, and the solidified layer that is cooled and solidified from the mold called the skin layer when filling the mold in injection molding is formed too early, and the fluid thickness of the resin cannot be secured, resulting in poor fluidity. In order to prevent this, it is necessary to be 7.0 or less. More preferably, it is 2.3-6.
The methacrylic resin used in the light guide plate for a display device obtained in the present invention may be a combination of a plurality of methacrylic resin compositions of the present invention having different compositions, or may be combined with an existing methacrylic resin. As a combination method, they may be used by blending, or may be heated, melted and mixed once by an extruder and pelletized.

In the present invention, the polymer (A) monomer composition and the weight average molecular weight range and the polymer (B) monomer composition and weight average molecular weight range are each one polymer. May be plural. In the case of multiple, for example, when there are two or more copolymers in the polymer (A) composition and weight average molecular weight range, the composition is that the average monomer composition is the composition of the polymer (A). The average weight average molecular weight is the weight average molecular weight of the polymer (A). The same applies to the polymer (B). Since the light guide plate of the present invention uses the above resin, it can be easily molded.
The method for producing a methacrylic resin composition in the present invention is not particularly limited, and specifically,
1. The polymer (A) or the polymer (B) is polymerized in advance, and the specified amount of the monomer obtained for polymerizing the remaining polymer (B) or polymer (A) is already obtained. A method in which the polymer (B) or the polymer (A) is added and mixed, and then the polymerization reaction is carried out to control the respective ratios and molecular weights for production.
2. A method of polymerizing a polymer (A) or a polymer (B) in advance, and then adding a raw material composition mixture of the polymer (B) or the polymer (A) at once or sequentially.
3. The method of blending and manufacturing what polymerized the polymer (A) and the polymer (B) separately beforehand is mentioned. Particularly preferably, Is easy to control the composition of each of the copolymer (A) and the copolymer (B), and as a polymerization method therefor, any of bulk polymerization, solution polymerization, suspension polymerization method or emulsion polymerization method can be used. preferable.
More preferably, either a suspension polymerization method or an emulsion polymerization method with little waste due to switching is preferable.

  The methacrylic resin used for the light guide plate in the present invention includes dyes, pigments, heat stabilizers such as hindered phenols and phosphates, benzotriazoles, 2-hydroxybenzophenones, salicylic acid phenyl esters, etc. UV absorbers, phthalate ester, fatty acid ester, trimellitic acid ester, phosphate ester, polyester and other plasticizers, higher fatty acids, higher fatty acid esters, higher fatty acid mono-, di- or triglycerides Mold release agent, higher fatty acid ester, polyolefin type lubricant, polyether type, polyether ester type, polyether ester amide type, alkyl sulfonate, alkylbenzene sulfonate, etc. antistatic agent, phosphorus type, phosphorus / Chlorine, phosphorus / bromine flame retardant, reflected light In order to prevent glare, organic light diffusing agents such as methyl methacrylate / styrene polymer beads, inorganic light diffusing agents such as barium sulfate, titanium oxide, calcium carbonate, talc, and acrylics obtained by multistage polymerization as reinforcing agents System rubber or the like may be used. When these additives are blended, it can be carried out by a known method. For example, a method in which an additive is dissolved in a monomer mixture in advance and polymerized is used.

The methacrylic resin in the present invention may be used alone or in combination with another resin. In the case of mixing, blending may be performed by heating and melting and mixing with an extruder, an injection molding machine, or the like, or a plurality of pellets heated and mixed with an extruder may be blended and used. The additives mentioned above may be blended and mixed at this time.
The light guide plate of the present invention preferably has fine irregularities or lens shapes on at least one surface. You may have the dot shape by which the pattern was designed in order to light-emit light uniformly on the reflective surface side. In addition, a prism, lenticular lens, pyramid type, fly-eye lens, or other lens shape is provided on the reflecting surface or the outgoing light surface so that the display device can emit light in the normal direction as much as possible. The lens shape may be given. A prism lens may be formed on the reflecting surface side, and dots, a satin pattern, or fine irregularities may be formed on the outgoing light side. The size is preferably as small as possible. Specifically, it is preferable that the 10-point average roughness based on JIS-B0601 is a fine unevenness or lens shape within 200 μm. These can be measured using a commercially available contact type or non-contact type surface roughness meter.

The light guide plate in the present invention preferably has a maximum thickness of 1.5 mm or less. The light guide plate should be thin to reduce weight. When the maximum thickness is greater than 1.5 mm, not only is it heavy, but the cooling time at the time of molding becomes long, and sinking problems occur.
The light guide plate in the present invention preferably contains 0.5 ppm to 5 wt% of fine particles having an average particle diameter of 0.01 μm to 50 μm in the methacrylic resin. The light guide plate guides light while being internally reflected repeatedly inside the light guide plate, and with a certain probability, the light is scattered by being hit by the minute irregularities on the reflection surface or the outgoing light surface, and the light is emitted from the outgoing surface. However, most of the light is repeatedly attenuated in internal reflection, and the amount of light emitted from the emission surface is reduced. In order to prevent this, the presence of the fine particles to be scattered inside the light guide plate makes it possible to scatter light during repeated internal reflections and to emit light to the light guide output surface. The type of fine particles is not particularly limited, and may be inorganic materials such as calcium carbonate, titanium oxide (rutile type, anatase type) alumina, silica, barium sulfate, talc, mica, acrylic type, MS type, styrene type beads, organic silicone. Organic fine particles such as system beads may also be used. These may be used alone or several kinds of fine particles may be used in combination. The shape of the fine particles is not particularly specified, but is preferably as spherical as possible. The average particle size of the fine particles is preferably 0.01 μm to 50 μm. More preferably, it is 0.01 micrometer-30 micrometers, More preferably, it is 0.01 micrometer-10 micrometers. The particle size distribution of the fine particles is not particularly limited, but if the particle size distribution is large, the in-plane chromaticity difference becomes large, so that the particle size distribution should be as small as possible. The average particle size and particle size distribution are determined by dissolving the light guide plate molded product in a solvent that can dissolve methacrylic resins such as dichloromethane, acetone, and THF, but not the contained particles, filter, wash, dry, and measure the weight. Further, the fine particles are immersed again in a solvent, and the particle size and particle size distribution can be measured using a Coulter counter using a commercially available laser light source.

The light guide plate in the present invention is preferably obtained by injection molding. Injection molding is preferable because it can be molded freely by changing the shape of the mold, such as mirror surfaces, fine irregularities, and shaping of surfaces such as lenses and ribs and bosses for attachment. Injection molding also uses injection compression molding and low-pressure molding (a method commonly called pressure-holding molding and flow molding), and on the mold side, the mold is heated with ultrasonic waves, and the mold is heated and cooled. It is also preferable to use these two lines in combination with a mold such as a mold using a heat insulating layer.
The light source used for the light guide plate in the present invention is preferably an LED. Since the cold cathode tube cannot have a tube diameter of 1 mmΦ or less because of its structure, the thickness of the light incident surface of the light guide plate cannot be reduced. Since the LED light source is a point light source, its light output area is small, so that the thickness of the light guide plate can be reduced. Since the LED is basically a point light source, a dark portion is generated between the LED unless a large number of LEDs are arranged. However, by combining the above-described inclusion of fine particles in the light guide plate, the light guided from the LEDs is immediately scattered and the dark part between the LEDs can be erased, and the number of LEDs can be reduced.
The light guide plate in the present invention is suitably used for a display device.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
1. Measurement of weight average molecular weight of methacrylic resin Tosoh Corporation Gel Permeation Chromatography (HLC-8120 + 8020) column and Tosoh TSK Super HH-M (2) + Super H2500 (1) are arranged in series and the detector is RI As a measurement sample, 0.2 g of methacrylic resin was dissolved in 20 cc of a THF solvent, and the elution time and strength were measured at an injection amount of 10 ml and a development flow rate of 0.3 ml / min. The weight average molecular weight was determined based on a calibration curve using 11 monodispersed methacrylic resins with known weight average molecular weights as standard samples. The weight average molecular weight of the mixture was determined by subtracting the weight average molecular weight of any single substance from the weight average molecular weight of the mixture to obtain the weight average molecular weight and the ratio of the remaining simple substance of the mixture.
2. Measurement of Melt Flow Rate Using a Toyo Seiki melt indexer F-B01, the melt flow rate was measured under conditions of 230 ° C. and a load of 3.8 kg according to the conditions of ISO 1133 cond 13.
3. Evaluation of heat resistance (measurement of VICAT softening temperature)
A test piece having a thickness of 4 mm was prepared with a 30-t press molding machine, and the VICAT softening temperature was determined according to the conditions of ISO 306 B50.

4). Evaluation of moldability of light guide plate 4-1. Using a thin light guide plate Sumitomo Heavy Industries molding machine SG-260, at a barrel temperature of 280 ° C., a 10 inch (4: 3) thickness of 1 mm, a half width at the center of the long side, and a thickness of 1 mm fan gate are provided on the core surface. A linear prism with an apex angle of 100 ° and a pitch of 150 μm is provided in parallel with the flow direction, a mold surface with a fine irregular shaped satin pattern on the cavity surface, and a mold with the remaining surface as a mirror surface is prepared. Molding was performed at a speed of 200 cc / sec and a holding pressure of 50 MPa under molding conditions of 40 sec.
4-2. Using a thick light guide plate Toshiba Machine IS-550, at a barrel temperature of 270 ° C, a fan gate of 15 inch (4: 3) 6 mm thick, 1/4 width and 4 mm thick at the center of the long side is provided on the mold surface. A mold having a fine rectangular parallelepiped shape with a height of 28 μm and a 60 μm square on one side and the remaining surface as a mirror surface is prepared, and the mold temperature is 85 ° C., the molding speed is 100 cc / sec, and the holding pressure is 50 MPa under the molding conditions of 40 sec. Molded.

5). Measurement of burr amount of light guide plate 4-1. And the maximum length of the burr | flash which generate | occur | produced in the light-guide plate obtained by 4-2 was measured using the caliper which can be measured to 0.01 mm.
6). Evaluation of saddle shape of light guide plate 6-1. Thin-walled light guide plate The mold of the thin-walled light guide plate and the prism part of the light-guide plate were measured for the height of the prism of the mold and the height of the light-guide plate using a contact type 3D roughness meter Surfcom manufactured by Tokyo Seimitsu. Prism height) / (mold prism height) was determined and used as the transfer rate.
6-2. Thick light guide plate Thick light guide plate die and light guide plate fine rectangular parallelepiped-shaped portion were measured in the same manner as in 6-1, and the length of the top side holding the 28 μm height of the rectangular parallelepiped was obtained. Long side length) / (mold long side length) was determined as the transfer rate.
7). Environmental test evaluation of light guide plate 4-1. And the fan gate of the light guide plate obtained in 4-2 is cut with a cutter, and the surface with the gate is polished with an Asahi Megalo plasticity, and then the light guide plate is hung to 75 ° C. and a relative humidity of 90%. It was placed in a thermo-hygrostat for 500 hours, and the amount of warpage and cracks were evaluated.
After the evaluation test, the amount of warpage was cooled to 25 ° C at the same humidity in the machine, and after taking out, on the surface plate with the edge warped upward, set the edge warpage amount to the lower side with a clearance gauge of 0.1 mm. Measured against

8). Evaluation of performance of light guide plate 8-1 Evaluation of thin light guide plate 4-1. 6. The surface with the fan gate of the light guide plate obtained in step 7 above. In order to receive light from this surface, a light source in which Nichia LEDs are arranged in a horizontal row is installed, the surface with the prism is the reflective surface side, and the reflectance is 98% on the reflective surface side. A reflective film made of foamed polyethylene terephthalate is provided, and the same foamed polyethylene terephthalate reflective film is pasted on the surface other than the light source. A linear prism film shaped with a UV curable acrylic resin was provided on the acrylic film, and the backlight unit for the display device was turned on. The average luminance of the entire surface of the outgoing light surface 30 minutes after lighting and the luminance ratio of the maximum dark portion and the maximum bright portion were measured by a Konica Minolta luminance meter CA-1000 in 10 × 10 divisions.
8-2. Performance evaluation of thick light guide plate 4-2. 4. The surface with the fan gate of the light guide plate obtained in step 5 above. In order to receive light from this surface and the opposite surface, a light source in which three rows of Nichia LEDs are arranged in a zigzag pattern is installed, and the surface with minute irregularities on the rectangular parallelepiped is the reflective surface side. A reflective film made of foamed polyethylene terephthalate having a reflectance of 98% was provided on the side, and the same foamed polyethylene terephthalate reflective film was pasted on the surface other than the surface with the light source, and the backlight unit for the display device was turned on. The average luminance of the entire outgoing light surface 30 minutes after lighting and the luminance ratio of the dark part and the bright part were measured by a Konica Minolta luminance meter CA-1000 in 20 × 20 divisions.

[Production of methacrylic resin]
[Resin 1]
In a 60 L reactor, 1956 g of methyl methacrylate, 17 g of lauryl peroxide, 160 g of 2-ethylhexyl thioglycolate (the above is the raw material of the polymer (B)), 26000 g of deionized water, 65 g of calcium triphosphate, 39 g of calcium carbonate, sodium lauryl sulfate 0.39 g was added and stirred and mixed, and suspension polymerization was performed at a reaction temperature of 80 ° C. for 150 minutes, and a small amount of the polymer was taken out. It was measured by gel permeation chromatography and confirmed to be a polymer (B) having a weight average molecular weight of 0.68 million. Sixty minutes later, 18257 g of methyl methacrylate and 835 g of methyl acrylate, 48 g of lauryl peroxide, and 54.34 g of n-octyl mercaptan, which are raw materials for the polymer (A), were charged into the reactor, and then suspended at 80 ° C. for 90 minutes. Polymerization was continued, followed by aging at 92 ° C. for 60 minutes to substantially complete the polymerization reaction, then cooled to 50 ° C., charged with mineral acid, washed and dehydrated and dried to obtain a bead-like methacrylic resin. This bead-like polymer was measured by gel permeation chromatography, and as shown in Table 1, calculated using the result of the weight average molecular weight of the previous polymer (B), the weight average molecular weight was 77,000 and the ratio was Was 91 wt% of the polymer (A) and the polymer (B) having a weight average molecular weight of 0.68 million and a ratio of 9 wt%.
The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized.

[Resin 2]
As raw materials for the polymer (B), 6212 g of methyl methacrylate, 32 g of methyl acrylate, 51.2 g of lauryl peroxide, 105.6 g of 2-ethylhexyl thioglycolate, 13865 g of methyl methacrylate and methyl acrylate as the raw materials of the polymer (A) Polymerization and measurement were carried out in the same manner as in Resin 1 using 1001 g, lauryl peroxide 22.4 g, and n-octyl mercaptan 41 g to obtain Resin 2 in Table 1. The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized.

[Resin 3]
In a 60 L reactor, 20123 g of methyl methacrylate and 1067 g of methyl acrylate as raw materials for the polymer (A), 53.3 g of lauryl peroxide, 91.7 g of n-octyl mercaptan, 26000 g of deionized water, 65 g of calcium triphosphate, calcium carbonate 39 g and 0.39 g of sodium lauryl sulfate were added, and the reaction temperature of the reactor was suspended and polymerized at 80 ° C. for 150 minutes, followed by aging at 92 ° C. for 60 minutes to complete the polymerization reaction and then to 50 ° C. After cooling, the mineral acid was added, washed and dehydrated and dried to obtain a bead-like methacrylic resin. This bead polymer was measured by gel permeation chromatography to obtain Resin 3 in Table 1. The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized.

[Resin 4]
A bead-like methacrylic resin was obtained in the same manner as Resin 3 except that 20108 g of methyl methacrylate and 1067 g of methyl acrylate, 53.3 g of lauryl peroxide, and 106.7 g of n-octyl mercaptan were used as raw materials for the polymer (A). . This bead polymer was measured by gel permeation chromatography to obtain Resin 4 in Table 1. The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized.

[Resin 5]
A bead-like methacrylic resin was obtained in the same manner as Resin 3 except that 17383 g of methyl methacrylate and 3840 g of methyl acrylate, 53.3 g of lauryl peroxide, and 58.7 g of n-octyl mercaptan were used as raw materials for the polymer (A). . This bead polymer was measured by gel permeation chromatography to obtain Resin 5 shown in Table 1. The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized.

[Resin 6]
In a 60 L reactor, 20138 g of methyl methacrylate and 1067 g of methyl acrylate as raw materials for the polymer (A), 53.3 g of lauryl peroxide, 76.8 g of n-octyl mercaptan, 26000 g of deionized water, 65 g of calcium triphosphate, calcium carbonate 39 g and 0.39 g of sodium lauryl sulfate were added, and the reaction temperature of the reactor was suspended and polymerized at 80 ° C. for 150 minutes, followed by aging at 92 ° C. for 60 minutes to complete the polymerization reaction and then to 50 ° C. After cooling, the mineral acid was added, washed and dehydrated and dried to obtain a polymer (A) bead-like methacrylic resin. Next, in another 60 L reactor, 21335 g of methyl methacrylate and 1067 g of methyl acrylate, 53.3 g of lauryl peroxide, 99.2 g of n-octyl mercaptan, 26000 g of deionized water, calcium triphosphate as raw materials for the polymer (B) 65 g, calcium carbonate 39 g, and sodium lauryl sulfate 0.39 g were added, and the reaction temperature of the reactor was suspended and polymerized at 80 ° C. for 150 minutes, followed by aging at 92 ° C. for 60 minutes to complete the polymerization reaction. After cooling to 50 ° C., a mineral acid was added, washed and dehydrated and dried to obtain a polymer (B) bead-like methacrylic resin.
Each bead polymer was measured by gel permeation chromatography, and the resin (A) and polymer (B) resins shown in Table 1 were obtained.
Each of these beads was weighed in an amount of 50 wt% as shown in Table 1, blended with a tumbler, and then kneaded and extruded at 240 ° C. with a twin screw extruder for pelletizing.

[Resin 7]
6212 g of methyl methacrylate, 32 g of methyl acrylate, 51.2 g of lauryl peroxide, 105.6 g of 2-ethylhexyl thioglycolate as raw materials for polymer (B), 11133 g of methyl methacrylate and methyl acrylate as raw materials for polymer (A) Polymerization and measurement were conducted in the same manner as in Resin 1 using 3734 g, lauryl peroxide 22.4 g, and n-octyl mercaptan 41 g to obtain Resin 7 in Table 1. The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized.

[Resin 8]
As raw materials for polymer (B), 5934 g of methyl methacrylate, 307 g of methyl acrylate, 51.2 g of lauryl peroxide, 105.6 g of 2-ethylhexyl thioglycolate, 14150 g of methyl methacrylate and methyl acrylate as raw materials for polymer (A) Polymerization and measurement were carried out in the same manner as in Resin 1 using 717 g, lauryl peroxide 22.4 g, and n-octyl mercaptan 41 g to obtain Resin 8 in Table 1. The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized.

[Resin 9]
As raw materials for the polymer (B), 6285 g of methyl methacrylate, 32 g of methyl acrylate, 51.2 g of lauryl peroxide, 30.8 g of n-octyl mercaptan, 13855 g of methyl methacrylate and 1001 g of methyl acrylate as raw materials for the polymer (A) Polymerization and measurement were carried out in the same manner as in Resin 1 using 22.4 g of lauryl peroxide and 52.3 g of n-octyl mercaptan to obtain Resin 9 in Table 1. The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized.

[Resin 10]
As raw materials for polymer (B), 9315 g of methyl methacrylate, 48 g of methyl acrylate, 76.81 g of lauryl peroxide, 158.4 g of 2-ethylhexyl thioglycolate, 10895 g of methyl methacrylate and methyl acrylate as raw materials for polymer (A) Polymerization and measurement were performed in the same manner as in Resin 1 using 786 g, lauryl peroxide 17.6 g, and n-octyl mercaptan 32.3 g, and Resin 10 in Table 1 was obtained. The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized.

[Resin 11]
4075 g of methyl methacrylate, 21 g of methyl acrylate, 34.1 g of lauryl peroxide, 136.54 g of 2-ethylhexyl thioglycolate as raw materials for polymer (B), 16056 g of methyl methacrylate and methyl acrylate as raw materials for polymer (A) Polymerization and measurement were performed in the same manner as in Resin 1 using 939 g, lauryl peroxide 42.7 g, and n-octyl mercaptan 30.38 g to obtain Resin 11 in Table 1. The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized.

[Resin 12]
As raw materials for polymer (B), 3222 g of methyl methacrylate, 875 g of methyl acrylate, 34.14 g of lauryl peroxide, 136.5 g of 2-ethylhexyl thioglycolate, 16909 g of methyl methacrylate and methyl acrylate as raw materials for polymer (A) Polymerization and measurement were carried out in the same manner as in Resin 1 using 85 g, 42.7 g of lauryl peroxide and 30.38 g of n-octyl mercaptan, and Resin 12 shown in Table 1 was obtained. The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized.

[Resin 13]
A bead-like methacrylic resin was obtained in the same manner as Resin 3 except that 20913 g of methyl methacrylate and 277 g of methyl acrylate, 53.3 g of lauryl peroxide, and 84.3 g of n-octyl mercaptan were used as raw materials for the polymer (A). . This bead polymer was measured by gel permeation chromatography to obtain a resin 13 shown in Table 1. The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized.

[Examples 1 and 2 and Comparative Examples 1 to 8]
Evaluation was performed using the prepared resin as shown in Table 2. The light guide plate was evaluated with a thin light guide plate. The results are shown in Tables 3 and 4.
Since both Examples 1 and 2 have good fluidity, the length of burrs generated during molding is short and almost no burrs are generated. Moreover, the amount of warpage after the environmental test is small, and cracks are not generated. Also, more than 80% of the transferability of the prism is filled and transferred.
On the other hand, since the fluidity of Comparative Example 1 was low, burrs were generated in the molded product for a long time, molding distortion was generated in the molded product, and a large warp occurred after the environmental test, which was not good. Since the comparative example 2 has a low molecular weight, the fluidity is high, the molding strain is suppressed, and warping after the environmental test hardly occurs. However, since the fluidity was too good, the generation of burrs could not be suppressed, and innumerable fine cracks were generated around the light guide plate after the environmental test. In Comparative Example 3, the heat resistance is low and therefore the fluidity is improved. As in Comparative Example 2, burrs are generated, and further, the vicinity of the gate shrinks after the environmental test, resulting in a bad U-shaped deformation. It became. Moreover, since the comparative example 4 did not satisfy | fill Formula (5) and fluidity | liquidity was low, the molding distortion generate | occur | produced in the molded article and the big curvature generate | occur | produced after the environmental test. Comparative Example 5 is a case where AMa is larger than 20 and does not satisfy the formula (2). In this case, the heat resistance is lowered and the shape is deformed after the environmental test. There was also a large amount of burrs. In Comparative Example 6, when BMa and AMa are equal in Formula (2), the MFR is not different from that in Example 2, but the flowability is poor when injection molding is performed, and the burr is in Examples 1 and 2. It was worse than that, and the warping amount was also bad. Comparative Example 7 is a case where Equation (5) is not satisfied because Mwa / Mwb is small. At this time, since the fluidity was low, a large amount of molding distortion remained, resulting in a large amount of warpage after the environmental test. Moreover, since fluidity | liquidity was bad, the amount of burr | flash generation increased. Comparative Example 8 is a case where AM / BM is small and does not satisfy the formula (5). In this case, the fluidity is high and the heat resistance is good, so the amount of warpage after the environmental test was good, but the molding was It was a bad result that countless cracks occurred around the product.
In both Examples 1 and 2, the prism shape could be reproduced by 80% or more, and as a result, the average luminance was high. On the other hand, Comparative Examples 2, 3, 5, and 8 with high fluidity showed good results in the transferability, average luminance, and luminance ratio of the prism, but Comparative Examples 1, 4, 6, and 7 with poor fluidity showed prisms. The shape transferability was poor, the average brightness was low, and the brightness ratio was poor.

[Examples 3 and 4, Comparative Examples 9 and 10]
Evaluation was performed using the prepared resin as shown in Table 2. The light guide plate was evaluated with a thick light guide plate. In Example 4, when pelletizing resin 8, 100 ppm of polyorganosiloxane was added and pelletized, and then a light guide plate was prepared. It was 2 micrometers when the average particle diameter of the particle | grains contained in the light-guide plate was measured. The results are shown in Tables 3 and 4.
In Examples 3 and 4, the length of burrs generated during molding was short, and almost no burrs were generated. Moreover, the amount of warpage after the environmental test is small, and cracks are not generated.
On the other hand, in Comparative Example 9, the occurrence of burrs was small, but due to the low fluidity, the amount of warpage after the environmental test was large. Further, Comparative Example 10 resulted in a very long burr generated during molding.
In Examples 3 and 4, both fine uneven shapes were transferred by 70% or more and the average luminance was high. Further, Example 4 had a high luminance ratio and a small difference between light and dark due to the LED array. became. On the other hand, Comparative Example 9 did not satisfy the formula (2), so that the fluidity was low, molding distortion occurred in the molded product, and a large warp occurred after the environmental test. Comparative Example 10 did not satisfy the formula (3), and the warping in the environmental test was small because the softening temperature of the resin was high. However, the cooling strain was generated due to the temperature difference from the mold, and after the environmental test A crack occurred. Further, the transferability was insufficient and the average luminance and luminance ratio were poor.

It is the schematic of the display apparatus for demonstrating this invention.

Explanation of symbols

1. Display unit 2. 2. Light guide plate Light source 4. Reflector 5. Reflector 6. Reflective sheet 7. Optical sheet

  The present invention is used for mobile telephones, liquid crystal monitors, liquid crystal televisions and the like, indoor and outdoor signs, billboards for advertisements and postings, indirect lighting fixtures, taillights, in-vehicle lighting and other optical parts for vehicles, etc., and maintains the appearance quality. However, the present invention relates to a high-performance light guide plate with little change over time.

Claims (7)

A methacrylic resin composed of at least one methyl methacrylate monomer and another vinyl monomer copolymerizable with methyl methacrylate, the methacrylic resin being gel permeation chromatography (GPC) Including the polymer (A) having a weight average molecular weight of 650,000-350,000 and the polymer (B) having a weight average molecular weight of 50,000-100,000, the weight average molecular weight of the methacrylic resin Of the polymer (A) and the polymer (B) are the following (1) to (5), and the molecular weight distribution (Mw / Mn) is 2.2 to 7.0. A light guide plate using a methacrylic resin satisfying the relationship.
The amount of other vinyl monomer units copolymerizable with methyl methacrylate in the polymer (A) and the polymer (B) is the amount in the polymer (A): AMa wt%
Amount in polymer (B): BMa wt%,
Further, the amount of the polymer (A) is AM wt%, the amount of the polymer (B) is BM wt%,
When the weight average molecular weight of the polymer (A) is Mwa and the weight average molecular weight of the polymer (B) is Mwb,
Mwb + 0.5 × 10 ⁴ ≦ Mwa (1)
0 ≦ BMa <AMa <20 (2)
2 ≦ AMa × (AM / 100) + BMa × (BM / 100) ≦ 20 (3)
AM: BM = 50: 50 to 95: 5 (4)
5 ≦ (Mwa / Mwb) × (AM / BM) (5)   2. The light guide plate according to claim 1, wherein a methacrylic resin obtained by two-stage polymerization using any one of a bulk polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, or two methods is used. .   The at least one surface of the light guide plate is formed with fine irregularities or a lens shape having a 10-point average roughness of less than 200 µ based on JIS-B0601. Light guide plate.   The light guide plate according to claim 1, wherein a maximum thickness of the light guide plate is 1.5 mm or less.   5. The light guide plate according to claim 1, wherein the methacrylic resin contains 0.5 ppm to 5 wt% of fine particles having an average particle diameter of 0.01 μm to 50 μm.   The light guide plate according to claim 1, wherein the light guide plate is obtained by injection molding.   The light guide plate according to claim 1, wherein the light source used is an LED.

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