JP4858410B2 - Light guide plate - Google Patents

Description

  The present invention relates to a light guide plate made of a copolymer that is excellent in transparency, heat resistance, and scratch resistance, and in particular has a low birefringence and excellent optical isotropy.

  In recent years, transparent resins have been used for optical lenses, prisms, mirrors, optical disks, optical fibers, and liquid crystal displays, as well as applications as molding materials that require normal transparency, such as conventional automotive parts, lighting equipment, and electrical parts. It has come to be widely used for higher performance optical materials such as sheets, films and light guide plates.

  Conventionally, polymethyl methacrylate (hereinafter referred to as “PMMA”) and polycarbonate (hereinafter referred to as “PC”) have been mainly used as these resins for optical materials, but PMMA has a problem of low heat resistance. Has a large birefringence, which is an optical strain, and has a problem that optical anisotropy occurs in the molded product.

  In particular, an optical disk is an example of an optical resin application that requires high optical performance. Since optical recording using a laser can record, store and reproduce high-density information, improvement and development of optical discs are being actively promoted. An optical disc is basically composed of a transparent substrate and various recording media coated thereon.

  The current state of the art in optical discs is to mold an optical disc with a low birefringence by devising molding conditions for a PC having a large birefringence. The optical disk thus obtained is widely used for CDs (compact disks) whose tolerance limit of birefringence is relatively gentle, low recording density DVDs (digital multipurpose disks), MOs (magneto-optical disks), and the like. Yes.

  However, the recent increase in the density of recorded information is accompanied by a reduction in the wavelength of the laser used and an increase in the NA (numerical aperture) of the optical lens system. In particular, in DVDs, the use of short wavelength light (blue laser) with a laser wavelength of about 350 to 410 nm and an NA value of 0.6 or more is studied, and in a PC containing an aromatic group in the molecule, the birefringence is large. Since the light transmittance in the short wavelength region is lowered, the limit of use has been pointed out. Moreover, since PC has low surface hardness and poor scratch resistance, it has a problem that it cannot be read.

  Furthermore, recently, the demand for a light guide plate for a backlight of a liquid crystal display device of a transparent resin is increasing. The light guide plate for backlight has a function of propagating and diffusing light rays incident from a predetermined direction of the light guide plate and emitting them to the liquid crystal cell side. As a backlight system, an edge light system in which a light source is arranged at the edge of a light guide plate is mainly employed in order to reduce the thickness of a liquid crystal display device. In such an edge light method, since the light transmission distance in the light guide plate is relatively long, the light loss in the light guide plate increases, and in order to prevent this, the material used for the light guide plate has high light transmittance. Is required.

  Further, the light guide plate is often used in applications requiring heat resistance, such as a backlight for a vehicle-mounted meter panel, an operation panel, a back lighting device such as a tail lamp, and a liquid crystal display device for a car navigation system. Further, in the future, for the liquid crystal display device capable of displaying a more uniform image, a more highly optically uniform material having a small birefringence is required for the light guide plate.

  For this reason, the materials used for the light guide plate are required to have high heat resistance, light transmittance, and low birefringence (optical isotropy).

  In view of such a situation, a cyclic polyolefin (hereinafter referred to as COC) using a polycyclic norbornene-based monomer has been developed as an optical transparent resin that solves the above problems. These have heat resistance, low birefringence, and light transmittance at a short wavelength. However, a transition metal catalyst is used as a polymerization catalyst for COC, but if the transition metal remains, it causes coloring and a decrease in transparency. Further, the production of the cyclic polyolefin requires a hydrogenation reaction, and a transition metal catalyst is also used for the hydrogenation reaction. For this reason, not only the coloring and transparency due to the remaining transition metal are lowered, but also such a hydrogenation reaction has a problem of increasing the production cost.

Patent Documents 1 and 2 disclose a method using a copolymer having a specific 6-membered cyclic acid anhydride unit and an aromatic vinyl compound unit. However, since the copolymer specifically described in the same publication also contains a considerable amount of aromatic vinyl compound groups, the birefringence obtained and the light transmittance in the short wavelength region are required to be advanced in recent years. There was a problem that the characteristics could not be sufficiently satisfied.
JP-A-60-133004 (page 1-2, known example) JP 63-264613 (page 1-2, known example)

  The present invention has been made to solve the above problems. Accordingly, an object of the present invention is to provide a light guide plate having excellent transparency, heat resistance and scratch resistance, and extremely excellent in low birefringence (optical isotropy).

  As a result of intensive studies to solve the above problems, the present inventors have found that a material comprising a specific copolymer having an unsaturated carboxylic acid alkyl ester unit and a glutaric anhydride unit has excellent transparency and heat resistance. The present invention has been found as being useful as a molding material for a light guide plate having scratch resistance and extremely excellent low birefringence (optical anisotropy).

That is, the present invention
[1] (i) Unsaturated carboxylic acid alkyl ester unit, (ii) The following general formula (1)

(In the above formula, R ¹ and R ² represent the same or different hydrogen atoms or alkyl groups having 1 to 5 carbon atoms.)
A copolymer having a glutaric anhydride unit represented by: or (iii) a copolymer having an unsaturated carboxylic acid unit in the unit (i) or (ii), or the unit (i), (ii) A copolymer having (iv) other vinyl monomer units in addition to the units (i), (ii) and (iii), and having an absolute value of birefringence of 1.0 × 10 ⁻ A light guide plate made of a copolymer of ⁴ or less,
[2] The light guide plate according to [1], wherein the content of (ii) glutaric anhydride units in the copolymer is 5 to 60% by weight,
[3] The light guide plate according to [1] or [2], wherein the copolymer has a pencil hardness of 4H or more.
[4] The light guide plate according to any one of [1] to [3], wherein the copolymer has a glass transition temperature of 120 ° C. or higher.
[5] The light guide plate according to any one of [1] to [4], wherein the unsaturated carboxylic acid unit (iii) has a structure represented by the following general formula (2):

(However, R ³ represents hydrogen or an alkyl group having 1 to 5 carbon atoms)
[6] The light guide plate according to any one of [1] to [5], wherein the unsaturated carboxylic acid alkyl ester unit (i) has a structure represented by the following general formula (3): Is.

(However, R ⁴ represents hydrogen or an alkyl group having 1 to ⁵ carbon atoms, and R ⁵ represents an aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms, or a hydroxyl group or halogen having a number of 1 to ⁵ carbon atoms. A C1-C6 aliphatic or alicyclic hydrocarbon group substituted with

  As described above, the light guide plate made of the copolymer of the present invention has high transparency, heat resistance, and scratch resistance, and is particularly excellent in low birefringence (optical isotropy).

  Hereinafter, the optical material for a light guide plate of the present invention will be specifically described.

  The optical material for a light guide plate of the present invention comprises (i) an unsaturated carboxylic acid alkyl ester unit, (ii) the following general formula (1)

(In the above formula, R ¹ and R ² represent the same or different hydrogen atoms or alkyl groups having 1 to 5 carbon atoms.)
A copolymer having a glutaric anhydride unit represented by: (iii) a copolymer having an unsaturated carboxylic acid unit in the above unit, or the above (i), (ii) unit or the above (i), (ii) And (iii) a copolymer having (iv) another vinyl monomer unit in addition to the unit (iii).

The copolymer used in the present invention must have an absolute value of birefringence of 1.0 × 10 ⁻⁴ or less, preferably 0.7 × 10 ⁻⁴ or less, and most preferably 0.5 ×. 10 ⁻⁴ or less. The lower limit of the birefringence is not particularly limited, and the ideal birefringence is 0, but is usually 0.01 × 10 ⁻⁴ or more.

  The absolute value of the birefringence referred to here is a non-oriented film of 100 ± 5 μm thickness obtained by the casting method and uniaxially stretched 1.5 times at the glass transition temperature according to ASTM D542. It is the absolute value of the birefringence obtained by measuring the retardation at 405 nm and dividing by the thickness.

  The method for producing the copolymer used in the present invention is not particularly limited as long as it has the above birefringence, but can basically be produced by the method shown below. That is, an unsaturated carboxylic acid monomer and an unsaturated carboxylic acid alkyl ester monomer that give the glutaric anhydride unit (ii) represented by the general formula (1) by the subsequent heating step, and the other vinyls In the case of containing a monomer unit (iv), a vinyl monomer giving the unit is copolymerized to obtain a precursor polymer (A), and then the precursor polymer (A) is converted into a suitable catalyst. It can be produced by heating in the presence or absence of (i) dealcoholization and / or (b) intramolecular cyclization reaction by dehydration. In this case, typically, the carboxyl group of the unsaturated carboxylic acid unit (iii) of 2 units is dehydrated by heating the precursor polymer (A), or the adjacent unsaturated carboxylic acid unit (iii) And 1 unit of the glutaric anhydride unit (ii) is generated by elimination of the alcohol from the unsaturated carboxylic acid alkyl ester unit (i).

  As an unsaturated carboxylic acid monomer used in this case, the following general formula (4)

(However, R ³ represents hydrogen or an alkyl group having 1 to 5 carbon atoms)
Preferred examples thereof include maleic acid, and a hydrolyzate of maleic anhydride, among which acrylic acid and methacrylic acid are preferable, and methacrylic acid is more preferable in view of excellent thermal stability. These can be used alone or in combination. In addition, the unsaturated carboxylic acid monomer represented by the general formula (4) gives an unsaturated carboxylic acid unit having a structure represented by the general formula (2) when copolymerized.

  Preferred examples of the unsaturated carboxylic acid alkyl ester monomer include those represented by the following general formula (5).

(However, R ⁴ represents hydrogen or an alkyl group having 1 to ⁵ carbon atoms, and R ⁵ represents an aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms, or a hydroxyl group or halogen having a number of 1 to ⁵ carbon atoms. A C1-C6 aliphatic or alicyclic hydrocarbon group substituted with

  Among these, an acrylate ester and / or a methacrylic ester having an aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms or the hydrocarbon group having a substituent is particularly preferable. The unsaturated carboxylic acid alkyl ester monomer represented by the general formula (5) gives an unsaturated carboxylic acid alkyl ester unit having a structure represented by the general formula (3) when copolymerized.

  Preferable specific examples of the unsaturated carboxylic acid alkyl ester monomer include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, (meth ) T-butyl acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, chloromethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate , (Meth) acrylic acid 3-hydroxypropyl, (meth) acrylic acid 2,3,4,5,6-pentahydroxyhexyl and (meth) acrylic acid 2,3,4,5-tetrahydroxypentyl Of these, methyl methacrylate is most preferably used. These can be used alone or in combination of two or more thereof.

  In the production of the copolymer (A) used in the present invention, other vinyl monomers may be used as long as the birefringence of the copolymer falls within the scope of the present invention. Preferred specific examples of other vinyl monomers include vinyl cyanide monomers such as acrylonitrile, methacrylonitrile, ethacrylonitrile, allyl glycidyl ether, maleic anhydride, itaconic anhydride, N-methylmaleimide, N-ethylmaleimide, N-cyclohexylmaleimide, acrylamide, methacrylamide, N-methylacrylamide, butoxymethylacrylamide, N-propylmethacrylamide, aminoethyl acrylate, propylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethyl methacrylate Aminopropyl, cyclohexylaminoethyl methacrylate, N-vinyldiethylamine, N-acetylvinylamine, allylamine, methallylamine, N-methylallylamine, 2-iso Ropeniru - oxazoline, 2-vinyl - oxazoline, 2-acryloyl - oxazoline and 2-styryl - like can be mentioned oxazoline, they alone to can be used two or more kinds. Aromatic vinyl such as styrene, α-methyl styrene, o-methyl styrene, p-methyl styrene, o-ethyl styrene, p-ethyl styrene and pt-butyl styrene, p-glycidyl styrene, p-amino styrene Since the use of monomers containing aromatic rings such as N-phenylmaleimide and phenylaminoethyl methacrylate is generally in the direction of increasing the birefringence, it is preferable not to use it. Therefore, it is necessary to limit the birefringence of the copolymer (B) within the range of the present invention.

  As for the polymerization method of the original polymer (A), basically known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc. by radical polymerization can be used, but there are fewer impurities. Particularly preferred are solution polymerization, bulk polymerization and suspension polymerization.

  Moreover, it is preferable that the raw polymer (A) is produced at a polymerization temperature of 90 ° C. or less in terms of colorless transparency after the heat treatment, and a more preferable polymerization temperature is 80 ° C. or less, particularly preferably 70 ° C. or less. It is. The lower limit of the polymerization temperature is not particularly limited as long as the polymerization proceeds, but is usually 50 ° C. or higher, preferably 60 ° C. or higher from the viewpoint of productivity considering the polymerization rate. The polymerization time is not particularly limited as long as it is a time sufficient to obtain a necessary polymerization rate, but is preferably in the range of 60 to 360 minutes, particularly preferably in the range of 90 to 180 minutes from the viewpoint of production efficiency.

  In the present invention, the preferred ratio of these monomer mixtures used in the production of the precursor polymer (A) is that the monomer mixture is 100% by weight, and the unsaturated carboxylic acid monomer is 15 to 50% by weight. %, More preferably 20 to 45% by weight, the unsaturated carboxylic acid alkyl ester monomer is preferably 50 to 85% by weight, more preferably 55 to 80% by weight, and other vinyl monomers copolymerizable therewith. When using a monomer, the preferable ratio is 0 to 35 weight%.

  When the amount of the unsaturated carboxylic acid monomer is less than 15% by weight, the production amount of the glutaric anhydride unit represented by the general formula (1) by heating the precursor polymer (A) decreases, There exists a tendency for the heat resistance improvement effect to become small. On the other hand, when the amount of the unsaturated carboxylic acid monomer exceeds 50% by weight, a large amount of the unsaturated carboxylic acid unit tends to remain after the cyclization reaction by heating of the original polymer (A), and it is colorless. There is a tendency for transparency and retention stability to decrease.

  The method for producing a copolymer containing glutaric anhydride units by heating the precursor polymer (A) in the present invention and performing an intramolecular cyclization reaction by (i) dehydration and / or (b) dealcoholization, Although there is no restriction | limiting in particular, The method manufactured through the heated extruder which has a vent, and the method manufactured in the apparatus which can heat-devolatilize in nitrogen stream or under a vacuum are preferable. The temperature for the devolatilization by the above method is not particularly limited as long as it is a temperature at which an intramolecular cyclization reaction occurs due to (i) dehydration and / or (b) dealcoholization, but preferably in the range of 180 to 300 ° C. In particular, a range of 200 to 280 ° C. is preferable. In addition, the time for heating and devolatilization at this time is not particularly limited, and can be set as appropriate according to the desired copolymer composition, but is usually preferably in the range of 1 minute to 60 minutes.

  Furthermore, in the present invention, when the precursor polymer (A) is heated by the above method or the like, one or more of acid, alkali and salt compounds may be added as a catalyst for promoting the cyclization reaction to glutaric anhydride. it can. The addition amount is not particularly limited, and is suitably about 0.01 to 1 part by weight per 100 parts by weight of the original polymer (A). There are no particular restrictions on the types of these acids, alkalis, and salt compounds, and examples of the acid catalyst include hydrochloric acid, sulfuric acid, p-toluenesulfonic acid, phosphoric acid, phosphorous acid, phenylphosphonic acid, and methyl phosphate. It is done. Examples of the basic catalyst include metal hydroxides, amines, imines, alkali metal derivatives, alkoxides, ammonium hydroxide salts and the like. Furthermore, examples of the salt-based catalyst include metal acetates, metal stearates, metal carbonates, and the like. These catalysts can be added singly or in combination as long as the object of the present invention is not impaired.

The content of the glutaric anhydride unit represented by the general formula (1) in the copolymer used in the present invention is 5 in the copolymer in order to obtain a birefringence within the scope of the present invention. It is preferably -60% by weight, more preferably 5-50% by weight, still more preferably 10-45% by weight, and most preferably 20-40% by weight. When the glutaric anhydride unit is less than 5% by weight, the effect of improving heat resistance is small, and a sufficient low birefringence index tends not to be obtained. In general, an infrared spectrophotometer is used for quantification of the glutaric anhydride unit. Glutaric anhydride units, absorption of 1800 cm ^-1 and 1760 cm ^-1 are characteristic, be distinguished from unsaturated carboxylic acid unit (1700 cm ^-1) and an unsaturated carboxylic acid alkyl ester unit (1730 cm ^-1) it can.

The amount of unsaturated carboxylic acid units contained in the copolymer used in the present invention is 0 to 10% by weight, more preferably 0 to 5% by weight. Furthermore, it is most preferable in terms of colorless transparency that the unsaturated carboxylic acid unit is not substantially contained. When the unsaturated carboxylic acid unit exceeds 10% by weight, colorless transparency and residence stability tend to be lowered. The unsaturated carboxylic acid alkyl ester monomer is preferably 40 to 95% by weight, more preferably 50 to 95% by weight, still more preferably 55 to 90% by weight, and particularly preferably 60 to 80% by weight. The other copolymerizable vinyl monomer is preferably 0 to 35% by weight. In addition, for quantification of each component contained in the copolymer used in the present invention, a method by 1H-NMR can be used together with the method by the infrared spectrophotometer described above. For example, in the case of a copolymer consisting of a glutaric anhydride unit, methacrylic acid, and methyl methacrylate, the attribution of the spectrum is 0.5 to 1.5 ppm. The peak of methacrylic acid, methyl methacrylate, and glutaric anhydride ring compound 11. The hydrogen of α-methyl group, the peak of 1.6 to 2.1 ppm is hydrogen of methylene group of the polymer main chain, the peak of 3.5 ppm is hydrogen of carboxylic acid ester of methyl methacrylate (—COOCH ₃ ), The peak of 4 ppm can determine the copolymer composition from hydrogen of carboxylic acid of methacrylic acid and the integral ratio of the spectrum.

  As described above, the copolymer having the above composition can be obtained by appropriately setting the temperature, time and the like for heating and devolatilizing the original polymer (A).

  Further, the intrinsic viscosity of such a copolymer is not particularly limited, but the intrinsic viscosity measured at 30 ° C. in a dimethylformamide solution in an Ubbelohde type viscosity system is preferably 0.1 to 0.7 dl / g, More preferably, it is 0.3-0.6 dl / g.

  The copolymer used in the present invention has excellent heat resistance with a glass transition temperature of 120 ° C. or higher, and in a preferred embodiment, has extremely excellent heat resistance of 130 ° C. or higher. The upper limit is not particularly limited as long as it can be used as a light transmitting material, but a material having a temperature of about 160 ° C. can be obtained. In addition, the glass transition temperature here is a glass transition temperature (Tg) measured using a differential scanning calorimeter (DSC-7 type manufactured by Perkin Elmer).

  Moreover, it has been found that the copolymer used in the present invention has high surface hardness (pencil hardness) and excellent scratch resistance. Therefore, it is particularly suitable as a base material for a substrate or a protective layer of an optical disk through which a laser beam is transmitted and which reads a precise information record. In a preferred embodiment of the present invention, particularly a copolymer having a glutaric anhydride unit content in a preferred range, the pencil hardness is 4H or more, and in a particularly preferred embodiment, it is 5H or more. The pencil hardness was measured according to JIS-K-5401 using a 50 mm × 50 mm × 0.5 mm molded product obtained by press molding the copolymer at a glass transition temperature + 100 ° C.

  In a preferred embodiment, the copolymer used in the present invention has a total light transmittance (50 mm × 50 mm × 0.5 mm molded product obtained by press molding the copolymer at a glass transition temperature + 100 ° C. The total light transmittance measured according to 6714) is 85% or more, and in a more preferred embodiment, it is 88% or more, and in a particularly preferred embodiment, it has an excellent light transmittance of 90% or more. It is possible to exhibit sufficient performance as an optical material. In addition, the transmittance of ultraviolet light having a wavelength of 350 to 410 nm, which is a short wavelength region, is excellent at 85% or more in a preferable embodiment, and at 88% or more in a particularly preferable embodiment. Light transmittance at a wavelength in this region is necessary for writing and reading with a short-wavelength laser beam when used for an optical disk, but the optical material for light transmission made of a copolymer used in the present invention is used for an optical disk. In some cases, it is possible to exhibit excellent performance. The transmittance of ultraviolet light in the short wavelength region can be measured with an ultraviolet-visible spectrophotometer.

  The optical material for light transmission of the present invention is composed of the above copolymer, and further, hindered phenol-based, benzotriazole-based, benzophenone-based, benzoate-based, and cyanoacrylate-based in the range not impairing the object of the present invention. UV absorbers and antioxidants, higher fatty acids, acid esters and acid amides, lubricants and plasticizers such as higher alcohols, montanic acid and salts thereof, esters thereof, half esters thereof, stearyl alcohol, stellar amide and ethylene Release agents such as waxes, anti-coloring agents such as phosphites and hypophosphites, halogen flame retardants, phosphorus and silicone non-halogen flame retardants, nucleating agents, amines, sulfonic acids, Add additives such as polyether-based antistatic agents, pigments and other colorants. It can be. In particular, when used for an optical disk substrate or a protective film, an additive that does not absorb light in the wavelength region of the laser beam used is preferable.

  Such additives can be blended by a known method. For example, the copolymer used in the present invention and other necessary additives may be premixed or supplied to an extruder or the like without being premixed. It is possible to melt and knead at 350 ° C.

  As described above, the optical material for a light guide plate of the present invention has excellent heat resistance, transparency and other characteristics, and particularly has a low birefringence (optical isotropy) and excellent scratch resistance. Accordingly, the light guide plate of the present invention is particularly excellent in that it has a low birefringence.

  Specifically, it can be used for a light guide plate for a backlight of a liquid crystal display device.

  In addition, because of excellent heat resistance and transparency, and low birefringence (optical isotropy), light guide plates for backlights for liquid crystal display devices, backlights for meter panels, operation panels, etc., lighting devices for tail lamps, etc. Can be suitably used.

  Hereinafter, the configuration and effects of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples. Prior to the description of each example, various physical property measurement methods employed in the example will be described.

(1) Glass transition temperature (Tg)
Using a differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer), the measurement was performed at a temperature increase rate of 20 ° C./min in a nitrogen atmosphere.

(2) 1H-NMR
Each sample dissolved in deuterated dimethyl sulfoxide solvent was measured using a 400 MHz nuclear magnetic resonance apparatus (NMR) manufactured by JEOL Ltd.

(3) Intrinsic viscosity The intrinsic viscosity at 30 ° C. of the obtained copolymer was measured using dimethylformamide as a solvent.

(4) Total light transmittance About 50 mm × 50 mm × 0.5 mm molded product obtained by press molding at glass transition temperature + 100 ° C. using a direct reading haze meter manufactured by Toyo Seiki Co., Ltd. according to JIS-K-5401. The total light transmittance (%) at 23 ° C. was measured to evaluate the transparency.

(5) Light transmittance in short wavelength region 360 of a molded product of 50 mm × 50 mm × 0.5 mm obtained by press molding in the above (4) using an ultraviolet-visible spectrophotometer (UV-1600PC) manufactured by Shimadzu Corporation The transmittance at 405 nm was measured.

(6) Birefringence index An ellipsometer (Otsuka) according to ASTM D542 is obtained by uniaxially stretching a non-oriented film of about 100 μm (100 ± 5 μm) obtained by the casting method at a glass transition temperature of 1.5 times. An LCD cell gap inspection apparatus RETS-1100 manufactured by Denki Co., Ltd. was used to irradiate laser light at an angle of 90 ° with respect to the film sample surface at 23 ° C., and the retardation (Re) of transmitted light at 405 nm. It was measured. Moreover, the thickness (d) at 23 degreeC of the said stretched film was measured using the Mitsutoyo Digimatic indicator, and birefringence ((DELTA) n) was computed by the following formula based on these.
Δn = Re (nm) / d (nm)

(7) Pencil Hardness The pencil hardness of a molded product of 50 mm × 50 mm × 0.5 mm obtained by press molding in the above (4) was measured according to JIS-K-5401.

[Reference Example 1] Production of copolymer containing glutaric anhydride unit (1) Production of raw polymer (A-1) A stainless steel autoclave having a capacity of 5 liters and equipped with a baffle and a fudra-type stirring blade was charged with methacrylic acid. Methyl acid / acrylamide copolymer suspending agent (prepared by the following method: 20 parts by weight of methyl methacrylate, 80 parts by weight of acrylamide, 0.3 part by weight of potassium persulfate and 1500 parts by weight of ion-exchanged water were added to the reactor. The inside of the charged reactor is replaced with nitrogen gas and kept at 70 ° C. The reaction is continued until the monomer is completely converted into a polymer, and is obtained as an aqueous solution of methyl acrylate and acrylamide copolymer. Was used as a suspending agent) and a solution in which 0.05 part was dissolved in 165 parts of ion-exchanged water was supplied, stirred at 400 rpm, and the system was replaced with nitrogen gas. . Next, the following mixed substances were added while stirring the reaction system, and the temperature was raised to 70 ° C. The time when the internal temperature reached 70 ° C. was set as the start of polymerization, and kept for 180 minutes to complete the polymerization. Thereafter, the reaction system was cooled, the polymer was separated, washed, and dried according to the usual method to obtain a bead-shaped precursor polymer (A-1). The polymerization rate of this original polymer (A-1) was 98%.
Methacrylic acid 30 parts by weight Methyl methacrylate 70 parts by weight t-dodecyl mercaptan 0.6 parts by weight 2,2′-azobisisobutyronitrile 0.4 parts by weight

(2) Copolymer (B-1)
The bead-shaped precursor polymer (A-1) obtained by (1) was depressurized to 250 ° C. and 2.6 kPa using a square vacuum constant temperature dryer (DP-32 manufactured by Yamato Scientific Co., Ltd.) A vacuum heat treatment was performed for 30 minutes to obtain a copolymer (B-1) containing a glutaric anhydride unit. The results obtained copolymer (B-1) was analyzed using an infrared spectrophotometer, absorption peaks were observed at 1800 cm ^-1 and 1760 cm ^-1, glutaric acid in the copolymer (B-2) It was confirmed that an anhydride unit was formed. Further, this copolymer was dissolved in deuterated dimethyl sulfoxide, and 1H-NMR was measured at room temperature (23 ° C.), and the spectrum was assigned to a peak of 0.5 to 1.5 ppm with methacrylic acid, methyl methacrylate and Hydrogen of α-methyl group of glutaric anhydride ring compound, peak of 1.6 to 2.1 ppm is hydrogen of methylene group of polymer main chain, peak of 3.5 ppm is carboxylate ester of methyl methacrylate (—COOCH ₃ ), The peak at 12.4 ppm was taken as the carboxylic acid hydrogen of methacrylic acid. When the copolymer composition was determined from the integral ratio of the spectrum, it was 76% by weight of methyl methacrylate (MAA) units, 20% by weight of glutaric anhydride (GAH) units, and 4% by weight of methacrylic acid (MAA) units. In addition, this copolymer (B-1) had an intrinsic viscosity of 0.47 dl / g and a Tg of 151 ° C.

  Various physical properties of the copolymer were measured. The stretched film for measuring the birefringence is prepared by preparing a 20% by weight THF solution of the above resin, obtaining an unoriented film by the casting method, and increasing the unoriented film by 1.5 times at the glass transition temperature of each resin. Uniaxially stretched to produce a stretched film. Various physical properties measured are shown in Table 1.

[Reference Example 2]
Using the same base polymer (A-1) as in Reference Example 1 and subjecting it to a vacuum heat treatment at 280 ° C. for 30 minutes by the same production method as in Reference Example 1 (2), a copolymer (B-2) is obtained. It was. Results The copolymer (B-2) was analyzed using an infrared spectrophotometer, absorption peaks were observed at 1800 cm ^-1 and 1760 cm ^-1, glutaric anhydride in the copolymer (B-2) It was confirmed that the unit was formed. Further, this copolymer was dissolved in deuterated dimethyl sulfoxide, 1H-NMR was measured at room temperature (23 ° C.), and the copolymer composition was determined from the integral ratio of the spectrum. The glutaric anhydride unit was 27% by weight, and the methacrylic acid unit was 0% and was not detected. In addition, this copolymer (B-2) had an intrinsic viscosity of 0.418 dl / g and a Tg of 153 ° C. Various physical properties of the obtained copolymer (B-2) were measured in the same manner as in Reference Example 1. Various physical properties measured are shown in Table 1.

[Reference Example 3]
Except that 15 parts by weight of methacrylic acid and 85 parts by weight of methyl methacrylate were used as the monomer mixture, the base polymer (A-3) was obtained at a polymerization rate of 97% by the same production method as in Reference Example 1. Was subjected to vacuum heat treatment at 250 ° C. for 2 hours by the same production method as in Reference Example 1 (2) to obtain a copolymer (B-3). Result of this copolymer (B-3) was analyzed using an infrared spectrophotometer, absorption peaks were observed at 1800 cm ^-1 and 1760 cm ^-1, glutaric anhydride in the copolymer (B-3) It was confirmed that the unit was formed. Further, this copolymer was dissolved in deuterated dimethyl sulfoxide, 1H-NMR was measured at room temperature (23 ° C.), and the copolymer composition was determined from the integral ratio of the spectrum. The glutaric anhydride unit was 15% by weight and the methacrylic acid unit was 0% and was not detected. In addition, this copolymer (B-3) had an intrinsic viscosity of 0.41 dl / g and a Tg of 135 ° C. Various physical properties of the obtained copolymer (B-3) were measured in the same manner as in Reference Example 1. Various physical properties measured are shown in Table 1.

[Comparative Reference Example 1]
Except for using 30 parts by weight of methacrylic acid, 50 parts by weight of methyl methacrylate and 20 parts by weight of styrene as the monomer mixture, 97% of the original polymer (A-1-1) was produced by the same production method as in Reference Example 1. This was used to obtain a copolymer (B-1-1) by the same production method as in Reference Example 1 (2). The copolymer (B-1-1) was analyzed using an infrared spectrophotometer, absorption peaks were observed at 1800 cm ^-1 and 1760 cm ^-1, in the copolymer (B-1-1) It was confirmed that a glutaric anhydride unit was formed. Further, this copolymer was dissolved in deuterated dimethyl sulfoxide, and 1H-NMR was measured at room temperature (23 ° C.) to determine the copolymer composition. As a result, 55% by weight of methyl methacrylate unit and glutaric anhydride unit were determined. They were 20% by weight, 21% by weight of styrene (ST) units, and 4% by weight of methacrylic acid units. In addition, this copolymer (B-1-1) had an intrinsic viscosity of 0.47 dl / g and a Tg of 148 ° C.

  Various physical properties of the obtained copolymer (B-1-1) were measured in the same manner as in Reference Example 1. Various physical properties measured are shown in Table 1.

[Comparative Reference Examples 2 and 3]
The same physical properties were measured using polymethyl methacrylate resin (Sumitex MG manufactured by Sumitomo Chemical Co., Ltd.) and polycarbonate resin (AD5503 manufactured by Teijin Chemicals). The stretched film for measuring the birefringence is prepared by preparing a 20% by weight chloroform solution of the above resin and obtaining an unoriented film by the casting method. Uniaxially stretched to produce a stretched film. Various physical properties measured are shown in Table 1.

  From the results of Reference Examples 1 to 3 and Comparative Reference Examples 1 to 3 in Table 1, it can be seen that the copolymer of the present invention is excellent in heat resistance and light transmittance and also in short wavelength light transmittance. Furthermore, it is possible to provide an optical material for light transmission that is extremely excellent in low birefringence (optical isotropy), has high surface hardness, and has excellent scratch resistance.

  On the other hand, as shown in Comparative Reference Example 1, when a styrene unit is present in the copolymer, the birefringence increases and the optical isotropy is inferior. Moreover, it turns out that the transmittance | permeability of short wavelength light and surface hardness are also inadequate. Furthermore, as shown in Comparative Reference Examples 2 and 3, the PMMA resin has insufficient heat resistance, and the PC resin does not have sufficient birefringence and short-wavelength light transmittance, resulting in high optical characteristics. It is understood that the surface hardness is inferior.

[Example 1]
Copolymer B-1 described in Reference Example 1 is injection-molded to produce a molded product of 200 mm × 120 mm × 3 mm. Further, as shown in the schematic cross-sectional view shown in FIG. 1, the diffusion sheet (3), the light guide plate (1) Then, a light guide plate made of a reflection sheet (4) was prepared, and a light source (2) and a reflector (5) were installed on the light guide plate to confirm light guide properties. As a result, it turned out that it was excellent in transparency and light guide property, and useful as a light-guide plate.

2 is a side cross-sectional view of a light guide plate produced in Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light guide plate 2 ... Light source 3 ... Diffusing sheet 4 ... Reflective sheet 5 ... Reflector

Claims (6)

(i) unsaturated carboxylic acid alkyl ester unit, (ii) the following general formula (1)

(In the above formula, R ¹ and R ² represent the same or different hydrogen atoms or alkyl groups having 1 to 5 carbon atoms.)
A copolymer having a glutaric anhydride unit represented by: or (iii) a copolymer having an unsaturated carboxylic acid unit in the unit (i) or (ii), or the unit (i), (ii) A copolymer having (iv) other vinyl monomer units in addition to the units (i), (ii) and (iii), and having an absolute value of birefringence of 1.0 × 10 ⁻ A light guide plate made of a copolymer of ⁴ or less. The light guide plate according to claim 1, wherein the content of (ii) glutaric anhydride units in the copolymer is 5 to 60% by weight. The light guide plate according to claim 1 or 2, wherein the copolymer has a pencil hardness of 4H or more. The light guide plate according to claim 1, wherein the copolymer has a glass transition temperature of 120 ° C. or higher. The light guide plate according to any one of claims 1 to 4, wherein the unsaturated carboxylic acid unit (iii) has a structure represented by the following general formula (2).

(However, R ³ represents hydrogen or an alkyl group having 1 to 5 carbon atoms) The light guide plate according to any one of claims 1 to 5, wherein the unsaturated carboxylic acid alkyl ester unit (i) has a structure represented by the following general formula (3).

(However, R ⁴ represents hydrogen or an alkyl group having 1 to ⁵ carbon atoms, and R ⁵ represents an aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms, or a hydroxyl group or halogen having a number of 1 to ⁵ carbon atoms. A C1-C6 aliphatic or alicyclic hydrocarbon group substituted with

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