WO2005030468A1

WO2005030468A1 - Thick flat-plate molded product and method of producing the same

Info

Publication number: WO2005030468A1
Application number: PCT/JP2004/014710
Authority: WO
Inventors: Masahiko Hayashi; Kazunori Ueki; Fumihiro Naruse
Original assignee: Zeon Corporation
Priority date: 2003-09-30
Filing date: 2004-09-29
Publication date: 2005-04-07
Also published as: KR20060088550A; TW200526392A; CN1860013A; CN100482442C; JPWO2005030468A1

Abstract

A rectangular thick flat-plate molded product, produced by injection molding, including a thermoplastic resin and a method of producing the molded product are provided. In the molded product, the difference between the maximum thickness and the minimum thickness is equal to or smaller than 3% of the thickness of the central portion, the thickness from the central portion to a peripheral edge is uniform and even, a fine recess-ridge pattern on the surface of a metal die can be accurately transferred to the product, and the molded product can be suitably used as an optical material. In the method of producing the molded product by injection molding, a metal die is heated so that the temperature of at least a pair of two opposed end sides of a rectangular cavity of the metal die is maintained higher by 2°C or more than the maximum temperature of the central portion of the cavity of the metal die.

Description

Technical Field of the Invention

The present invention relates to a thick plate molded product and a method for producing the same. More specifically, the present invention is directed to a thick flat plate that is uniform in thickness from the center to the periphery, accurately transfers fine irregularities on the mold surface, and can be suitably used as an optical material. The present invention relates to a molded article and a method for producing the same. Background art

Injection molded products are widely used from general-purpose to precision applications such as daily necessities, automobile parts, home appliances parts, electronic parts, and optical equipment. The quality of injection molded products and the quality of productivity largely depend on the quality of molds. Production of injection molding dies requires advanced technology in all aspects, such as machining accuracy, uniform quality, and productivity. At first glance, the light diffusion plate and the light guide plate of the liquid crystal display device are flat plates having a simple shape, but in practice, they require extremely strict flatness and are required to have no thickness unevenness. It is not easy to produce an injection molded product with a uniform thickness even with a simple shape such as a flat plate, and various attempts have been made to produce an injection molded product with a uniform thickness. I have.

For example, as an injection molding method to reduce the galling of the mold and uneven thickness of the molded product due to the deviation of the parallelism of the platen and the change of the tie bar elongation, the parallelism of the fixed platen and the movable platen is set at A method has been proposed in which the temperature is adjusted in advance while being heated to a temperature corresponding to the platen temperature, and the platen is maintained at the temperature at which the parallelism is adjusted during injection molding (Patent Document 1). However, in injection molding, the mold deforms due to the force of the mold clamping pressure and injection pressure, etc., especially in the case of large molded products, it is difficult to achieve parallelism only by temperature control. is there. In addition, it has a fixed-side assembly and a movable-side assembly as injection molding dies that can increase the dimensional accuracy and surface roughness accuracy of magneto-optical disc bases and the like, and increase the packing density of molded products. Before the molten resin material injected into the cylinder solidifies, push up the force sleeve and press the center hole A mold has been proposed in which the formation of a mold and the sealing of the disk cavity portion are performed simultaneously, and then the movable-side assembly is raised to recompress the primary compact (Patent Document 2). However, it is difficult to reduce the thickness unevenness of large rectangular shaped articles by such means. In addition, the force S that can suppress the bending of the mold due to the molding pressure is possible, and as a mold that can suppress the occurrence of burrs due to the generation of a large gap on the parting surface, Injection molding dies have been proposed in which a plurality of ejector spaces are provided in accordance with the number and arrangement of cavities so as to suppress the radius (Patent Document 3). However, such a method is effective for multi-cavity dies, but cannot be applied to large-sized single-cavity dies.

[Patent Document 1] Japanese Patent Application Laid-Open No. H10-3223887 (Page 2, FIG. 1-2)

[Patent Document 2] Japanese Patent Application Laid-Open No. 6-2700208 Kimitaka β (Page 2-3, Figure 1)

[Patent Document 3] Japanese Patent Application Laid-Open No. 10-44 1997 β (No. 2, FIG. 1)

The present invention relates to a thick flat molded article which can transfer a fine uneven pattern on a mold surface accurately and has a uniform thickness from a central portion to a peripheral edge, and can be suitably used as an optical material, and its production. It is intended to provide a method.

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, when a thick flat molded product is manufactured by injection molding of a thermoplastic resin, the thickness of the peripheral portion of the thick flat molded product is reduced in the central portion. Therefore, when a thick flat molded product is used as a light guide plate of a liquid crystal display device, striped portions with different brightness, such as a bright line and a ゃ嗲 band, occur at the periphery of the screen. Also, by heating the edges of the mold for injection molding to keep the temperature higher than the center of the mold, the difference between the thickness of the peripheral part and the thickness of the center of the thick flat molded product is reduced, and When a flat molded product was used as a light guide plate of a liquid crystal display device, it was found that bright lines and dark bands did not occur at the periphery of the screen, and based on this finding, the present invention was completed.

That is, the present invention

(1) A rectangular thick flat molded product containing a thermoplastic resin produced by an injection molding method, Gap value = {(τ _ΜΑΧ _{-τ ΜΙΝ} ) / T _CENTER } XI 00

(However, in the above formula, τ _ΜΑΧ is the maximum thickness of the flat molded product, T _MIN is the minimum thickness of the flat molded product, and T _CENTER is the thickness of the center of the flat molded product.)

A thick flat plate molded product having a gap value of 3% or less, (2) a thick flat molded product according to item 1, wherein the gap value is 1% or less,

(3) The thick flat molded article according to paragraph 1 or 2, wherein the thickness of the central part is 3 to 5 Omm,

(4) The thick flat plate molded product according to any one of (1) to (3), wherein the thermoplastic resin is a resin having an alicyclic structure.

(5) The thick plate molded article according to any one of (1) to (3), wherein the thermoplastic resin is a metharyl resin or an alkyl (meth) acrylate monoaromatic compound.

(6) The light guide plate of the liquid crystal display device, the thick flat plate molded product according to any one of paragraphs 1 to 5 and 1 or

(7) When manufacturing a thick flat molded article of a thermoplastic resin by the injection molding method, the temperature of at least one pair of two opposite sides of the rectangular cavity of the injection molding die is determined by the temperature of the mold cavity. 7.Manufacturing the thick flat plate molded article according to any one of paragraphs 1 to 6, characterized in that the mold is heated so that the temperature is maintained at least 2 ° C higher than the maximum temperature at the center. Method,

Is to provide.

Further, as a preferred embodiment of the present invention,

(8) During one molding cycle, the heat medium passing through the heat medium flow path in the mold is switched to a high-temperature heat medium and a low-temperature heat medium, and the temperature of the center of the mold cavity at the time of injection is changed. 7. The method of manufacturing a thick flat plate product according to claim 6, wherein the temperature of the center of the mold cavity during cooling is lowered.

Can be mentioned. Brief Description of Drawings

FIG. 1 is a schematic cross-sectional view of a thick flat plate molded product manufactured by an injection molding method. Fig. 2 is an explanatory view of a screen of a liquid crystal display device, Fig. 3 is an explanatory view of a central part of a thick flat molded product, and Fig. 4 is an embodiment of a method of heating the edge of a cavity in the method of the present invention. FIG. In the figure, reference numeral 1 denotes a central portion, 2 denotes an edge, 3 denotes a bright line, 4 denotes a dark zone, 5 denotes a cavity, and 6 denotes a bar heater. BEST MODE FOR CARRYING OUT THE INVENTION

The thick flat molded product of the present invention is a rectangular flat molded product of a thermoplastic resin produced by an injection molding method, wherein the difference between the maximum thickness and the minimum thickness is 3% or less of the thickness of the central portion. It is more preferably 2% or less, particularly preferably 1% or less. There is no particular limitation on the target to which the thick flat plate molded article of the present invention and the method for producing the same are applied, but a large thick flat plate molding requiring strict flatness on the surface of a light guide plate, a light diffusion plate, a reflection plate, or the like. The present invention can be suitably applied to a product, but can be particularly preferably applied to a light guide plate of a liquid crystal display device.

FIG. 1 is a schematic cross-sectional view of a thick plate molded product manufactured by an injection molding method. When a thick flat plate molded product is manufactured by the injection molding method, a molded product having a thicker edge 2 at the center 1 than at the center 1 is obtained. When such a molded product is used as a light guide plate of a liquid crystal display device, a linear bright line 3 with high luminance, as schematically shown in FIG. The appearance of a dark band 4 with a weak band, etc., degrades the image quality. By using the thick flat plate molded product of the present invention in which the difference between the maximum thickness and the minimum thickness is 3% or less of the thickness at the center as the light guide plate of the liquid crystal display device, the appearance quality without bright lines or dark bands is obtained. Good screen can be obtained.

In the present invention, the central portion of the thick flat molded product is the intersection of the diagonal lines of the rectangular thick flat molded product. If the thick flat plate product is not an accurate rectangular shape, the intersection of the diagonals of the rectangle formed by extending each side of the shape shall be the center. At this time, each side is extended to form a rectangle so that the total area of the part supplemented by the extension of each side and the part removed is minimized. FIG. 3 is an explanatory view of the center of a thick flat plate molded product. As shown in the three examples in this figure, in each example, a rectangle is formed by extending each side as shown by a dotted line, and for example, each side is not extended as shown by a dashed line in the center figure. In the thick flat plate molded product of the present invention, the thickness of the central portion is preferably 3 to 50 mm, more preferably 5 to 20 mm. Flat plate molded products with a thickness of less than 3 mm at the center have optical inconveniences such as bright lines and dark bands even if the difference between the maximum thickness and the minimum thickness exceeds 3 ° / ₀ of the thickness at the center. It is unlikely to occur. It is not advisable to manufacture thick flat plate molded products with a central part thickness exceeding 5 Omm by injection molding method because it takes a long time to cool

The thermoplastic resin used in the present invention is not particularly limited. For example, a resin having an alicyclic structure, a methacrylic resin, a polycarbonate, a polystyrene, an acrylonitrile-styrene copolymer resin, an estero (meth) acrylate I ^ aroma Group vinyl compound copolymers, preferably methyl methacrylate-styrene copolymer resin, ABS resin, polyether sulfone, and the like. Among these, a resin having an alicyclic structure, a methacrylic resin and a (meth) acrylic acid ester-aromatic vinyl conjugated copolymer can be preferably used, and have an alicyclic structure. Resins can be particularly preferably used.

The resin having an alicyclic structure has good fluidity S of the molten resin, so it can accurately transfer the fine irregularities on the mold cavity surface, and has extremely low hygroscopicity. It is excellent, does not warp a thick flat molded product, and has a small specific gravity, so that a large thick flat molded product can be reduced in weight.

Examples of the resin having an alicyclic structure include a polymer resin having an alicyclic structure in a main chain or a side chain. A polymer resin having an alicyclic structure in its main chain can be particularly preferably used because of its good mechanical strength and heat resistance. The alicyclic structure is preferably a saturated cyclic hydrocarbon structure, and its carbon number is preferably 4 to 30, more preferably 5 to 20, and more preferably 5 to 15. It is even better. The proportion of the repeating unit having an alicyclic structure in the polymer resin having an alicyclic structure is preferably 50% by weight or more, more preferably 0% by weight or more, and 90% by weight. More preferably, it is the above.

Examples of the resin having an alicyclic structure include ring-opening polymers or ring-opening copolymers of nonolebornene monomers or hydrogenated products thereof, caropolymers or addition copolymers of norbornene monomers. Or their hydrogenated carohydrates, monocyclic cyclic olefins Polymer of monomer or hydrogenated product thereof, polymer of cyclic conjugated diene monomer or hydrogenated product thereof, polymer or copolymer of vinyl alicyclic hydrocarbon monomer or hydrogen thereof Examples of the additive include a hydrogenated product of an unsaturated bond portion containing an aromatic ring of a vinyl aromatic hydrocarbon-based monomer or polymer. Among these, hydrogenated products of the norbornene-based monomer polymer and hydrogenation power of the unsaturated bond portion containing the aromatic ring of the vinyl aromatic hydrocarbon-based polymer are mechanical Since it has excellent strength and heat resistance, it can be used particularly preferably.

Examples of the methacrylic resin include those containing preferably at least 80 mol% of a repeating unit derived from methynole methacrylate based on all repeating units. Among them, 230 in accordance with ASTM D1238. C, the melt flow rate measured under a load of 37. 3 kg, methacryloyl resin of 0.5 to 20 g Z l 0 min is preferred.

The (meth) acrylic acid alkyl ester-aromatic vinyl conjugate copolymer is obtained by copolymerizing an aromatic vinyl compound and a (meth) acrylic acid alkyl ester compound having a lower alkyl group.

Examples of the aromatic vinyl compound include styrene, permethylstyrene, m-methinorestylene, methynolestyrene, o-chloronostyrene, and p-chlorostyrene. These may be used alone or in combination of two or more.

Examples of the (meth) acrylic acid alkyl ester compound having a lower alkyl group include an alkyl group having 1 to 4 carbon atoms, preferably an alkyl ester of (meth) acrylic acid having an alkyl group having 1 to 2 carbon atoms, Specific examples include methyl methacrylate, methyl methacrylate, methyl acrylate, and ethyl acrylate. These may be used alone or in combination of two or more.

The proportion of each component constituting the copolymer is in the range of 95 to 5% by weight of the aromatic vinyl compound and 5 to 95% by weight of the (meth) acrylic acid / realkyl ester compound having a lower alkyl group. . Above all, from the viewpoint of optical properties, molded raw material, etc., the aromatic vinyl conjugate is 60 to 20 weight by weight. /. The content of the (meth) acrylic acid alkyl ester compound having a lower alkyl group is preferably in the range of 80 to 40% by weight.

The glass transition temperature TTg of the thermoplastic resin used in the present invention is at least 80 ° C, and preferably 90 to 250 ° C. Glass transition temperature T g conforms to JISK 7 121 Measured by differential scanning calorimetry (DSC).

When the thick flat plate molded product of the present invention is used as a light guide plate, the above-mentioned resin may be used, if necessary, with other polymers, various compounding agents or fillers alone or in combination of two or more. it can. Other polymers include rubbers or resins such as polybutadiene and polyacrylate.

Compounding agents include compounding agents such as antioxidants, ultraviolet spring absorbers, light stabilizers, near infrared absorbers, coloring agents such as dyes and pigments, lubricants, plasticizers, antistatic agents, and fluorescent brighteners. No. Further, the light guide plate is not necessarily required to be transparent, and light scattering ability can be imparted by blending fine particles comprising a polystyrene-based polymer, a polysiloxane-based polymer, or a crosslinked product thereof.

The above-mentioned other polymers, various compounding agents or fillers can be used alone or in combination of two or more, and the amount of their combination is appropriately selected within a range and a range that does not impair the object of the present invention. It is usually 0 to 5 parts by weight, preferably 0 to 3 parts by weight, based on 100 parts by weight of the plastic resin.

In the method of manufacturing a thick flat molded product of the present invention, when manufacturing a thick flat molded product of a thermoplastic resin by an injection molding method, at least one pair of two opposite ends of a rectangular cavity of an injection mold. Heat the mold so that the side temperature is maintained at least 2 ° C above the maximum temperature in the center of the mold cavity. The temperature at the center of the cavity refers to the temperature at the center of the mold that comes into contact with the center of the thick flat plate product. In addition, the temperature of the two opposite sides refers to the temperature of the two sides of the mold that comes into contact with the thick plate molded product. If there is a temperature distribution at the two ends, the lowest temperature must be maintained at least 2 ° C higher than the highest temperature in the center of the cavity. FIG. 4 is an explanatory view showing one embodiment ′ of a method of heating the edge of the cavity in the method of the present invention. In this figure, a bar-shaped heater 6 made of a heating resistor is embedded in a pair of two opposite long sides of a mold cavity 5. By adjusting the voltage applied to the rod-shaped heater, the temperature at the end of the cavity can be controlled. In the embodiment shown in FIG. 4, two opposite long sides of the mold cavity are heated. However, a bar-shaped heater is embedded in the other two sides, and the two pairs of the cavity are opposed to each other. You can also heat the four edges. In the method of the present invention, the end of the cavity There is no particular limitation on the method of heating the side. For example, a heating medium flow path is provided near the end of the cavity in the mold, and heating can be performed by passing a high-temperature heating medium. In the method of the present invention, by making the temperature of at least one pair of opposed two ends of the mold cavity higher than the temperature of the center of the cavity, the peripheral portion of the thick flat plate molded product is prevented from being thickened. It is possible to obtain a thick flat plate molded product having a small thickness unevenness and excellent flatness. When the thick flat plate is a light guide plate, a fine prism pattern for diffusing light is provided on the light exit surface, and fine projections for controlling the direction of light reflection are provided on the reflective surface. In many cases, patterns are provided. The molten resin sent from the gate into the cavity flows through the cavity and reaches the edge, filling the cavity. However, the temperature of the molten resin drops while flowing in the cavity, and the transfer of fine irregularities on the mold tends to be incomplete at the edges of the cavity. According to the method of the present invention, by increasing the temperature of the edge of the cavity where the temperature of the molten resin is likely to decrease to be higher than the maximum temperature at the center of the cavity, it is possible to enhance the transferability of the fine uneven pattern of the mold. .

In the method of the present invention, the method for controlling the temperature of the mold is not particularly limited. For example, it is possible to control the mold temperature to be constant by passing a heat medium having a constant temperature through the flow path of the heat medium in the mold. Alternatively, in one cycle of injection molding, high-temperature heat medium and low-temperature heat medium are switched and liquid is passed, and during injection, the mold temperature is raised to increase the fluidity and transferability of the molten resin. During cooling, the mold temperature can be lowered, shortening the molding cycle and improving productivity. If the mold temperature is controlled to be constant, that temperature will be the highest temperature in the center of the cavity.If the hot medium and the low-temperature medium are passed through by switching, the center of the cavity during one molding cycle Is the highest temperature in the center of the cavity.

In the method of the present invention, the temperature of at least one pair of two opposite sides of the mold cavity is higher than the maximum temperature of the central part of the cavity by 2 ° C or more, more preferably 3 to 30 ° C, more preferably Is maintained at 5-20 ° C high. If the difference between the temperature at the edge of the mold cavity and the maximum temperature at the center of the cavity is less than 2 ° C, the effect of reducing the thickness unevenness of the thick flat molded product and the fine uneven pattern of the knob type Effect of accurately transferring „

WO 2005/030468

May not be sufficiently expressed. If the difference between the temperature at the edge of the mold cavity and the maximum temperature at the center of the mold is too large, the molding cycle may be extended and productivity may be reduced.

In the present invention, at a resin temperature of usually Tg + 100 (° C) to Tg + 200 (° C), preferably Tg + 150 (.C) to Tg + 200 (° C), Tg—50 (° C), preferably at a mold temperature of Tg-30 (° C) to Tg (° C). The above Tg is the glass transition temperature (unit: C) of the thermoplastic resin used. Example

Hereinafter, the power s for explaining the present invention in more detail with reference to examples, the present invention is not limited by these examples.

In the examples and comparative examples, the thick plate molded products were evaluated by the following methods.

(1) Gap value

The intersection of the diagonal lines of the light guide plate is set at the center, and on a straight line parallel to the short side passing through the center, from the end of the light guide plate by 0.1 mm, a non-contact three-dimensional measuring device [Mitaka Optical Co., Ltd. Measure the thickness using NH-1 3] and calculate the gap value by the following formula.

Gap value = {(T _MAX -T _MIN ) ZT _CENTER } XI 00

In the above equation, T _MAX represents the maximum thickness of the light guide plate, T _MIN represents the minimum thickness of the light guide plate, and T _CENTER represents the thickness of the central portion of the light guide plate.

(2) Transfer rate

With the intersection of the diagonal lines of the light guide plate with short side 276.4 mm and long side 34 4.0 mm as the center, on a straight line parallel to the short side passing through the center, from the center, 69.1 mm from the center, 103.6 mm, 132 mm At 13 points and 138.2 mm at 0.5 mm pitch up to 138 mm, the height (hm) of the columnar protrusion was measured using an ultra-depth microscope [Keyence Corporation, VK-9500], and each point was transcribed by the following formula. The ratio is calculated, and the average and standard deviation are calculated from the calculated values.

Transfer rate = (h / ht) X 100 (%)

However, h _t is the theoretical height of the cylindrical protrusion which is calculated from the mold (μπι), gold Equal to the depth of the cylindrical cavity of the mold cavity.

(3) Appearance quality

A cold-cathode fluorescent lamp, Lison Toshiba Lighting Co., Ltd., MBSM24 JN10W 370NLU] is attached to each of the two long sides of the light guide plate to assemble a liquid crystal display device. Inspection of appearance quality by paying attention to the belt Example 1

As a thermoplastic resin, a norbornene-based polymer [Nippon Zeon Co., Ltd., ZE ONOR 106 OR, glass transition temperature 100 ° C], which is a kind of resin having an alicyclic structure, is used as an injection molding machine [Toshiba Machine ( Co., Ltd., IS 350GS, screw diameter 70 mm, clamping force 3,430 kN] were used to manufacture a 17-inch light guide plate by injection molding.

The dimensions of the molded product are 276.4 mm on the short side, 344.0 mm on the long side, and 8.0 mm in thickness. Adjacent to the surface of the cavity on the movable side of the mold, which is the light exit surface of the light guide plate, is a prism pattern with a folded surface of an isosceles triangle with a base of 50 Aim and a vertex angle of 140 degrees as a prism pattern that diffuses light The unit prisms were provided perpendicular to the long sides with the lower ends in contact with each other. The surface of the cavity on the fixed side of the mold, which is the reflecting surface of the light guide plate, has a hole that forms a cylindrical protrusion with a diameter of 80μπι and a height of 80Aim, and a pitch between the two long sides of the cavity, 1 30μπι. , And up to a pitch of 300 im near the long side. Adjacent to the two long sides of the mold cavity, one 800W bar heater was embedded. Also, a fan gate was set up on one short side of the cavity.

Using the above injection molding machine and mold, the molding temperature was 270 ° C, the mold temperature was 85 ° C, the temperature near the long side of the mold was 95 ° C, the injection time was 5 seconds, and the holding pressure was 15 MPa after injection. After 10 seconds of heat, the light guide plate was injection molded in 120 seconds of cooling, 5 seconds of removal, and 140 seconds of molding cycle. The mold temperature is adjusted by keeping the temperature of the hot water passing through the flow path in the mold at 80 ° C, and the temperature near the long side of the mold is controlled by controlling the voltage applied to the rod heater. Keep at 95 ° C. The maximum temperature at the center of the mold cavity was 85 ° C, and the temperature at the long side of the cavity was 95 ° C. The maximum thickness of the obtained light guide plate was 8.01 lmm, the minimum thickness was 7.995 mm, the thickness at the center was 8.001 mm, and the gap value was 0.20%. The average transfer rate was 89.5% and the standard deviation was 0.34%. When the appearance quality was evaluated using this light guide plate, there was no bright line or dark band on the screen of the liquid crystal display device, and the appearance quality was good and the screen was dark.

Example 2

During the removal 5 seconds, the injection 5 seconds, and the holding pressure 10 seconds, pass 90 ° C hot water through the flow path inside the mold, and cool down at 25 ° C through the flow path inside the mold during 10 O seconds. Injection molding of the light guide plate was performed under the same conditions as in Example 1 except that water was passed. The highest temperature in the center of the mold cavity-90 ° C, the temperature on the long side of the cavity was 95 ° C.

The maximum thickness of the obtained light guide plate was 8.018 mm, the minimum thickness was 7.989 mm, the thickness at the center was 8.005 mm, and the gap value was 0.36%. The average transfer rate was 93.7% with a standard deviation of 0.18%. When the appearance quality was evaluated using this light guide plate, there was no bright line or dark zone on the screen of the liquid crystal display, and the appearance quality was good.

Example 3

Same as Example 1 except that a methacrylic resin [Asahi Kasei Corporation, Delpet 80NH] was used as the thermoplastic resin instead of the resin having an alicyclic structure, and the molding temperature was set to 260 ° C. Under the conditions, the light guide plate was injection molded.

The maximum thickness of the obtained light guide plate was 8.025 mm, the minimum thickness was 7.994 mm, the thickness at the center was 8.015 mm, and the gap value was 0.39%. The average transfer rate was 80.3% and the standard deviation was 1.50%. When the appearance quality was evaluated using this light guide plate, there were no bright lines or dark bands on the screen of the liquid crystal display device, and the appearance quality was good.

Example 4

As the thermoplastic resin, instead of the resin having an alicyclic structure, an ester of methacrylic acid mono-aromatic vinylinole compound was used; f Nittetsu Chemical Co., Ltd., Estyrene MS-600] Injection molding of the light guide plate was performed under the same conditions as in Example 1.

The maximum thickness of the obtained light guide plate is 8.052 mm, the minimum thickness is 7.978 mm, the center Has a thickness of 8.040 mm and a gap value of 0.92. /. Met. The average transfer rate was 82.4% and the standard deviation was 1.82%. When the appearance quality was evaluated using this light guide plate, there was no bright line or dark zone on the screen of the liquid crystal display, and the appearance quality was good. Comparative Example 1

The light guide plate was injection-molded under the same conditions as in Example 1 except that the rod heater embedded adjacent to the two long sides of the mold cavity was removed and heating was not performed from the long side. . The maximum temperature at the center of the mold cavity was 85 ° C, and the temperature at the long side of the cavity was 85 ° C.

The maximum thickness of the obtained light guide plate was 8.102 mm, the minimum thickness was 7.808 mm, the thickness at the center was 8.005 mm, and the gap value was 3.67%. The average value of the transfer rate was 84.9%, and the standard deviation was 11.98%. When the appearance quality was evaluated using this light guide plate, bright lines and dark bands appeared near the long side of the screen of the liquid crystal display device, and the appearance quality was poor.

Table 1 shows the results of Examples 1 to 4 and Comparative Example 1.

Table 1

Mold temperature (.C) Gap value Transfer rate (%)

Thermoplastic resin Appearance quality Highest in the center Longest side (%) Average standard deviation

Example: 85 85 Π 9 Π 89.5 0.34 Minpaku Hna Example 2 Alicyclic structure 90 95 0.36 93. 7 0.18 Good Example 3 Methacryl 85 95 0.39 80. 3 1. 50 Good

CO Methacrylate monoaromatic

Example 4 85 95 0.92 82.4 1.82 Good Bull compound copolymer

'' Comparative Example 1 Alicyclic structure 85 85 3.67 84.9 11.98 Light line, dark zone

As can be seen in Table 1, bar heaters are embedded adjacent to the two long sides of the mold cavity, and the temperature near the long side of the mold cavity is the maximum temperature at the center of the mold cavity. The light guide plates of Examples 1 to 4 which were kept higher than those of Example 1 showed good performance with little unevenness of thickness and unevenness of the transfer rate of the columnar projections, no bright lines or dark bands on the LCD screen. Have. In particular, the performance of the light guide plates of Examples 1 and 2 using a resin having an alicyclic structure is excellent. In contrast, the light guide plate of Comparative Example 1, in which the edge of the mold cavity was not heated, had a large unevenness in thickness and a large variation in the transfer rate of the columnar protrusions, and the liquid crystal display screen had a clear line. And a dark band appears. Industrial applicability

The thick flat plate molded product of the present invention has a small thickness unevenness, has good flatness, and has an excellent appearance quality without a bright line or a dark band on a screen by being used as a light guide plate of a liquid crystal display device. Obtainable. According to the method of the present invention, by heating the end of the cavity of the injection molding die and raising the temperature of the end to be higher than the temperature of the center of the cavity, thickness unevenness is reduced and flatness is improved. A thick flat plate product can be easily manufactured.

Claims

The scope of the claims

1. For a rectangular thick flat molded product containing a thermoplastic resin manufactured by the injection molding method, the following formula is used.

5 Gap value = {(T _MAX -T _MIN ) / T _CENTER } XI 00

(However, in the above formula, τ _ΜΑΧ indicates the maximum thickness of the flat molded product, Τ _ΜίΝ indicates the minimum thickness of the flat molded product, and T _CENTER indicates the thickness of the center of the flat molded product, respectively.)

A thick flat molded product characterized by having a gap value of 3% or less.

2. The thick flat molded product according to claim 1, wherein the gap value is 1% or less.

10- 3. The thickness at the center is

The thick flat molded product according to claim 1 or 2, wherein the thickness is 3 to 50 mm.

4. The thick plate molded article according to any one of claims 1 to 3, wherein the thermoplastic resin is a resin having an alicyclic structure.

5. The thick plate molded article according to any one of claims 1 to 3, wherein the thermoplastic resin is a metharyl resin or a (meth) acrylic acid alkyl ester-an aromatic aromatic compound copolymer.

6. The thick flat plate molded product according to any one of claims 1 to 5, which is a light guide plate of a liquid crystal display device.

7. When manufacturing a thick flat molded product of thermoplastic resin by the injection molding method, the temperature of at least one pair of two opposite sides of the rectangular cavity of the injection mold 20 is set at the center of the mold cavity. 7. The method for producing a thick plate molded article according to claim 1, wherein the mold is heated so that the temperature is maintained at least 2 ° C. higher than the maximum temperature of the part.