JP2005326761A - Light guide with excellent optical properties - Google Patents

Abstract

Provided is a light guide made of an acrylic resin composition having sufficient light resistance, little yellowing, and excellent optical characteristics.
[MEANS FOR SOLVING PROBLEMS] An acrylic resin composition comprising 0.0005 to 0.3 parts by mass of an alkyl methoxycinnamate UV absorber based on 100 parts by mass of an acrylic resin obtained using methyl methacrylate as a main component. Light body.
[Selection figure] None

Description

  The present invention relates to a light guide excellent in optical characteristics. More specifically, the present invention relates to a light guide made of an acrylic resin composition containing an alkyl methoxycinnamate UV absorber.

  2. Description of the Related Art Conventionally, as a light source device used for a thin signboard, a display device, a back light source of a liquid crystal display device, and the like, a backlight device that emits light by entering light into a light guide is known. In recent years, edge-light type backlight devices have become mainstream. The edge light system is a system in which a light source such as a cold cathode tube or a hot cathode tube is disposed on the end face of a light guide, and light is emitted in an arbitrary shape or pattern.

  This type of light source device is required to have higher luminance and be more compact (light and thin). As a material of the light guide in such a light source device, a material having as little transmission loss as possible such as absorption, scattering and reflection of light in the light guide is desirable, and a transparent resin having high light transmittance is suitable. Therefore, at present, acrylic resins obtained with methyl methacrylate as a main component are often used. Specifically, the acrylic resin is molded into an arbitrary shape, or the resin plate itself is used as a light guide. It is used. Since the cold cathode tube serving as the light source emits ultraviolet rays due to its mechanism, the transparent resin constituting the light guide is also required to have light resistance. In this respect, acrylic resin is excellent as a light guide material.

  On the other hand, with the increasing demand for large-sized and high-brightness display devices that use light guides, the number of cold-cathode tubes used is often increased and the tube current value is increased. As a result, the amount of ultraviolet rays from the light source increases, and the acrylic resin light guide that does not contain a light resistance improver may cause a problem of yellowing during use.

In order to improve light resistance, a light guide made of an acrylic resin composition containing an ultraviolet absorber has been proposed. As the ultraviolet absorber, for example, benzotriazole-based, benzophenone-based, and salicylic acid-based ones have been proposed (for example, see Patent Document 1).
JP 2001-195914 A

  However, many of the ultraviolet absorbers disclosed in Patent Document 1 also absorb the lower limit side (370 to 400 nm) of the visible light region when an amount that sufficiently exhibits ultraviolet absorbing ability is added. Therefore, for example, when the light guide is used in an edge light type device, the transmitted light often appears yellow when the optical path length of the light guide is increased.

  The present invention has been made to solve such a problem. That is, an object of the present invention is to provide a light guide made of an acrylic resin composition having sufficient light resistance, little yellowing, and excellent optical characteristics.

  As a result of intensive studies to achieve the above object, the present inventors have found that a light guide made of an acrylic resin composition containing a specific amount of a specific ultraviolet absorber exhibits an excellent effect, and the present invention. It came to complete.

  That is, the present invention relates to an acrylic resin composition containing 0.0005 to 0.3 parts by mass of an alkyl methoxycinnamate UV absorber with respect to 100 parts by mass of an acrylic resin obtained using methyl methacrylate as a main component. It is a light guide.

  In the present invention, since the light guide is configured using an acrylic resin composition containing a specific amount of a specific ultraviolet absorber, the light guide has sufficient light resistance and yellowing is not caused. It has few optical properties. The light guide of the present invention having such excellent characteristics is very useful particularly when the optical path length of the light guide is relatively long.

  The acrylic resin used in the present invention is obtained by polymerizing methyl methacrylate (hereinafter referred to as “MMA”) as the main component of the monomer. Specifically, MMA is preferably 50% by mass or more out of 100% by mass of the monomer constituting the resin. For example, polymethyl methacrylate, which is a homopolymer of MMA, or a copolymer obtained by copolymerizing MMA 50% by mass or more with other unsaturated monomers 50% by mass or less can be used. The amount of MMA is more preferably 80% by mass or more, and particularly preferably 90% by mass or more, out of 100% by mass of the monomer constituting the resin.

  Other unsaturated monomers copolymerizable with MMA include, for example, methacrylic acid esters other than MMA such as ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, and phenyl methacrylate; methyl acrylate, ethyl acrylate Acrylic acid esters such as butyl acrylate, cyclohexyl acrylate and phenyl acrylate; unsaturated acids such as methacrylic acid and acrylic acid; styrene, α-methylstyrene, acrylonitrile, methacrylonitrile, maleic anhydride, phenylmaleimide, Examples thereof include cyclohexylmaleimide. Two or more kinds of other unsaturated monomers copolymerizable with MMA can be used as necessary. Moreover, the copolymer may have a glutaric anhydride unit and a glutarimide unit as needed.

  As other unsaturated monomers copolymerizable with MMA, alkyl acrylates such as methyl acrylate are particularly preferable. By copolymerizing an appropriate amount of alkyl acrylates, fluidity during molding, heat decomposability and the like are improved, and molding processability is improved. However, the amount of alkyl acrylates is preferably set to such an extent that heat resistance and transmittance do not decrease so much. Specifically, the amount of alkyl acrylates is preferably 20% by mass or less, more preferably 15% by mass or less, and particularly preferably 10% by mass or less, in 100% by mass of the monomer constituting the resin.

  From the viewpoint of low water absorption, it is also preferable to use styrene as another unsaturated monomer. However, the amount of styrene is preferably set to such an extent that the transmittance and light resistance do not decrease so much. Specifically, the amount of styrene is preferably 25% by mass or less, more preferably 15% by mass or less, and particularly preferably 10% by mass or less, in 100% by mass of the monomer constituting the resin.

  Further, other unsaturated monomers copolymerizable with MMA include, for example, allyl methacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,6. Polyfunctional monomers such as polyfunctional methacrylates such as hexanediol diacrylate and neopentyl glycol dimethacrylate and polyfunctional acrylates may be used. However, the amount of these polyfunctional monomers is preferably set to such an extent that the fluidity of the resin during molding does not deteriorate so much. Specifically, the amount of the polyfunctional monomer is preferably 5% by mass or less, more preferably 1% by mass or less, out of 100% by mass of the monomer constituting the resin. Note that this is not the case when a molding method that does not greatly affect the fluidity of the resin during molding, such as cast polymerization, is employed.

  There is no restriction | limiting in particular in the manufacturing method of acrylic resin, Various polymerization methods conventionally known, for example, solution polymerization, suspension polymerization, emulsion polymerization, block polymerization, cast polymerization etc. can be used. In particular, when an acrylic resin is produced as a molding material, for example, from the viewpoint of avoiding contamination by foreign matters, for example, JP-A-58-88701, JP-A-2000-26507, JP-A-2000-53712, It is preferable to use the continuous bulk polymerization method described in JP-A No. 2000-159818. In the production of the acrylic resin, for example, an azo compound, a peroxide, a mercaptan compound, a terpenoid compound, or the like can be appropriately used as a polymerization initiator or a molecular weight regulator.

  The acrylic resin composition used in the present invention can be obtained by adding an alkyl methoxycinnamate UV absorber to the acrylic resin described above. The content of the alkyl methoxycinnamate UV absorber is 0.0005 parts by mass or more, preferably 0.003 parts by mass or more, more preferably 0.003 parts by mass with respect to 100 parts by mass of the acrylic resin from the viewpoint of improving light resistance. 005 parts by mass or more. Further, from the viewpoint of transparency, it is 0.3 parts by mass or less, preferably 0.15 parts by mass or less, more preferably 0.1 parts by mass or less with respect to 100 parts by mass of the acrylic resin.

  As the alkyl methoxycinnamate ultraviolet absorber, the following general formula (1)

(Wherein R represents an alkyl group)
Is preferred. R in the general formula (1) is particularly preferably an alkyl group having 1 to 10 carbon atoms.

  Examples of commercially available alkyl methoxycinnamate ultraviolet absorbers include trade name PARSOL MCX (2-methoxyhexyl 4-methoxycinnamate) manufactured by Roche Vitamin Japan Co., Ltd.

  In order to further improve the durability, the acrylic resin composition may contain a hindered amine stabilizer (hereinafter referred to as “HALS”). In this case, the HALS content is usually 0.0001 parts by mass or more, preferably 0.001 parts by mass or more, and more preferably 0.003 parts by mass or more with respect to 100 parts by mass of the acrylic resin. Moreover, from a viewpoint of cost and transparency, it is 0.1 mass part or less normally, 0.05 mass part or less is preferable and 0.03 mass part or less is more preferable. When based on 100 parts by mass of the alkyl methoxycinnamate UV absorber, the HALS content is usually 100 parts by mass or less, preferably 80 parts by mass or less, and more preferably 50 parts by mass or less.

  The acrylic resin composition can contain various additives as required. Examples of the additive include organic crosslinked fine particles such as siloxane crosslinked resin particles, styrene crosslinked resin particles, and acrylic crosslinked resin particles; inorganic fine particles such as glass particles, talc, calcium carbonate, and barium sulfate (light diffusing agent). Antistatic agents such as sodium alkyl sulfonate, sodium alkyl sulfate, stearic acid monoglyceride, polyether ester amide; Antioxidants such as hindered phenols; Flame retardants such as phosphate esters; Palmitic acid And a lubricant such as stearyl alcohol. Two or more additives may be used as necessary.

  As a method for preparing the acrylic resin composition, various conventionally known methods can be used. For example, a bead-like, pellet-like, or pulverized acrylic resin obtained by polymerization in advance is mixed with an alkyl methoxycinnamate UV absorber and, if necessary, HALS or other additives using a Henschel mixer, etc. There is a method in which the mixture is melt-kneaded using a single-screw or twin-screw extruder or various kneaders, and pelletized again. Further, for example, methoxy cinnamon is added to a syrup composed of a monomer or a monomer mixture constituting an acrylic resin, or a polymer or copolymer obtained by polymerizing a part thereof and a monomer or a monomer mixture. There is a method in which an alkyl alkyl UV absorber and, if necessary, HALS and other additives are mixed, and the mixture is subjected to bulk polymerization in a continuous or batch manner to form a pellet or plate.

  In the case of producing an acrylic resin composition in the form of a pellet, as described above, from the viewpoint of avoiding contamination by foreign substances when kneading an alkyl methoxycinnamate UV absorber and other additives, It is desirable to knead within a series of processes of the continuous bulk polymerization method described in 58-88701, JP-A 2000-26507, JP-A 2000-53712, JP-A 2000-159818, and the like.

  Pellet-shaped acrylic resin composition is molded into any shape (plate, wedge shape, etc.) using various known molding methods such as extrusion, injection molding, press molding, etc., and used as a light guide it can. Moreover, it is also possible to use the acrylic resin composition polymerized and molded into an arbitrary shape such as a plate shape by cast polymerization as the light guide.

  Since the light guide of the present invention is excellent in optical characteristics and light resistance, it can be suitably used particularly as a light guide plate for backlight. Furthermore, it can be very suitably used as a light guide plate for a backlight of a liquid crystal display device having a diagonal inch number of the screen of 14 inches or more (particularly 20 inches or more).

  Examples of the present invention will be described below, but the present invention is not limited thereto. In the following descriptions, “parts” and “%” are based on mass. Methyl methacrylate is referred to as “MMA”, and methyl acrylate is referred to as “MA”. Moreover, each evaluation was implemented with the following method.

(Color evaluation)
Since it is difficult to confirm the color tone at a normal light guide plate thickness (about 2 mm), a resin plate having a thickness of 5 mm or more and an optical path length of 200 mm was used as a test piece. Specifically, first, a resin plate was prepared by injection molding, extrusion molding, or cast plate, and this was cut as necessary to prepare a test piece having the above size. Further, the end face of this test piece was polished. The transmitted color with an optical path length of 200 mm of this test piece was visually determined according to the following evaluation criteria.
“◯”: Almost no coloring is observed.
“Δ”: There is some coloring.
"X": Coloring is recognized.

(Light resistance evaluation as a light guide plate)
A resin plate was prepared by injection molding, extrusion molding, or cast plate, and was cut as necessary to prepare a test piece having a size of 30 mm × 5 mm × 200 mm. Both end surfaces (5 mm × 200 mm) of this test piece were mirror-polished, and cold-cathode tubes (Harrison Electric Co., Ltd., HMBSM2JD86E256YS / AX) were arranged on the both end surfaces after polishing, and a total of 4 lamps were arranged. The lamp plate and the resin plate were surrounded by two cold cathode fluorescent lamps arranged on both end faces. Then, a lighting exposure test was performed continuously for 2000 hours at a voltage of 12 V and a tube current of 8 mA. The appearance of the end face of the test piece after the test was visually observed according to the following evaluation criteria.

The judgment criteria are as follows.
“◯”: Almost no coloring is observed.
“Δ”: There is some coloring.
"X": Coloring is recognized.

[Example 1]
Nitrogen gas was introduced into the monomer mixture consisting of 98% MMA and 2% MA to make dissolved oxygen 0.5 ppm. For 100 parts of this monomer mixture, 0.23 parts of n-octyl mercaptan as a molecular weight regulator and 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane 0.003 as a radical polymerization initiator Parts (Nippon Yushi Co., Ltd., trade name Perbutyl 355) were mixed. This mixture was continuously fed into the fully mixed reactor while stirring and mixing, and the polymerization was carried out at a polymerization temperature of 135 ° C. with an average residence time of 3.0 hours.

  Subsequently, the reaction mixture was continuously withdrawn from the reactor, and 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane (perbutyl 355) 0. 002 parts were added and this was supplied to a plug flow reactor equipped with a static mixer. The inner wall temperature of the reactor was 150 ° C., and the average residence time was 30 minutes. Next, the reaction mixture is continuously supplied to the vent extruder type extruder from the outlet of the reactor at 220 ° C., and volatiles mainly composed of unreacted monomers are separated and removed at 270 ° C. and pelletized. A pellet-shaped acrylic resin (A-1) was obtained.

  To 100 parts of this acrylic resin (A-1), 2-methoxyhexyl 4-methoxycinnamate (trade name PARSOLMCX, hereinafter referred to as “MCX”, manufactured by Roche Vitamin Japan) as an alkyl methoxycinnamate UV absorber 0.08 part was added and mixed, and pelletized with an extruder (30 mm, biaxial, resin temperature 250 ° C.). The obtained pellets were injection molded by using an injection molding machine (IS220 manufactured by Toshiba Machine Co., Ltd.) under the conditions of a cylinder temperature of 270 ° C. and a molding cycle of 120 seconds, and test pieces were produced and evaluated. As a result, the test piece of this example was made of a resin excellent in transparency, color tone, and light resistance, and was suitable for use as a light guide.

[Example 2]
Instead of 0.23 part of n-octyl mercaptan as a molecular weight regulator, 0.17 part of n-butyl mercaptan was used, and 1,1-bis (tert-butylperoxy) 3,3,5- In place of 0.003 part and 0.002 part of trimethylcyclohexane (perbutyl 355), dimethyl-2,2′-azobis (2-methylpropionate) (Wako Pure Chemicals V-601, purity 99%) 0.007 A pellet-like acrylic resin (A-2) was obtained in the same manner as in Example 1 except that the parts (0.004 part, 0.003 part) were used.

  To 100 parts of this acrylic resin (A-2), MCX 0.05 part as an alkyl methoxycinnamate UV absorber was added and mixed, and pelletized and injection-molded in the same manner as in Example 1 for testing. Pieces were made and evaluated. As a result, the test piece of this example was made of a resin excellent in transparency, color tone, and light resistance, and was suitable for use as a light guide.

[Example 3]
The test piece was prepared in the same manner as in Example 2 except that the amount of MCX, which is an alkyl methoxycinnamate UV absorber, was changed to 0.03 parts and a resin plate was produced by extrusion instead of injection molding. Prepared and evaluated. In extrusion molding, a screw extruder having a screw diameter of 45 mm, a single shaft, and a vented sheet extruder is used. The lip width of the T die is 200 mm, the lip interval is 6 mm, three horizontal polishing rolls are used, and the extrusion temperature is 240. The roll temperature was 95 ° C, 100 ° C, 110 ° C from the T die side. The test piece of this example was made of a resin excellent in transparency and color tone, and was suitable for use as a light guide.

[Example 4]
For 100 parts of a monomer mixture composed of 94% MMA and 6.0% neopentyl glycol dimethacrylate, a polymerization initiator (Nippon Yushi Co., Ltd., trade name perhexyl PV, 10 hour half-temperature 53.2 ° C.) 0.32 part, MCX 0.05 part as an alkyl methoxycinnamate UV absorber was added and mixed. The mixture was degassed with a suction bottle and poured into a polymerization cell (prepared by sealing the periphery of a pre-cleaned 60 cm × 40 cm square tempered glass surface with a vinyl chloride gasket). This cell was heated at 76 ° C. for 1 hour and then heat treated at 130 ° C. for 1 hour to polymerize the mixed solution to obtain a resin plate having a 5 mm thick crosslinked structure. A test piece was prepared from this resin plate and evaluated. The test piece of this example was made of a resin excellent in transparency, color tone, and light resistance, and was suitable for use as a light guide.

[Example 5]
Further, 2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazadispiro as a hindered amine stabilizer (HALS) with respect to 100 parts of the acrylic resin (A-2) [5. 1.11.2] -Heneicosane-20-propanoic acid dodecyl ester / tetradecyl ester mixture (manufactured by Clariant Japan Co., Ltd., trade name Hostabin N24, hereinafter referred to as “N24”) except that 0.01 part was added. Test pieces were prepared and evaluated in the same manner as in Example 3. As a result, the test piece of transparency and this example was made of a resin excellent in transparency, color tone, and light resistance, and was suitable for use as a light guide.

[Comparative Example 1]
In place of alkyl methoxycinnamate UV absorber, 0.05 part of 2,4-dihydroxybenzophenone (trade name Seasorb 100, hereinafter referred to as "SEASORB", manufactured by Cypro Kasei Co., Ltd.), a benzophenone ultraviolet absorber A test piece was prepared and evaluated in the same manner as in Example 2 except that it was used. The test piece of this comparative example had a stronger tendency to be colored than Examples 1 to 5, and was inferior in light resistance.

[Comparative Example 2]
2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5 [(hexyl) oxy] -phenol which is a triazine ultraviolet absorber instead of an alkyl methoxycinnamate ultraviolet absorber A test piece was prepared and evaluated in the same manner as in Example 2 except that 0.05 part (Ciba Specialty Chemicals Co., Ltd., trade name: Tinuvin 1577FF, hereinafter referred to as “1577”) was used. The test piece of this comparative example had a stronger tendency to be colored than Examples 1 to 5, and was inferior in light resistance.

[Comparative Example 3]
A test piece was prepared and evaluated in the same manner as in Example 1 except that the amount of MCX, which is an alkyl methoxycinnamate UV absorber, was changed to 0.0002 part. The test piece of this comparative example was inferior to Examples 1-5 in light resistance.

[Comparative Example 4]
A test piece was prepared and evaluated in the same manner as in Example 2 except that the amount of MCX, which is an alkyl methoxycinnamate UV absorber, was changed to 0.5 part. The test piece of this comparative example had a stronger tendency to color than Examples 1-5.

  The evaluation results of Examples 1 to 5 and Comparative Examples 1 to 4 are summarized in Table 1 below.

Claims (1)

  A light guide comprising an acrylic resin composition containing 0.0005 to 0.3 parts by mass of an alkyl methoxycinnamate UV absorber with respect to 100 parts by mass of an acrylic resin obtained using methyl methacrylate as a main component.