JP4457344B2 - Manufacturing method of light diffusion plate - Google Patents

Description

  The present invention relates to a method for manufacturing a light diffusing plate. More specifically, the present invention relates to a light diffusing plate that can efficiently produce a large-quality light diffusing plate by using an injection molding machine having a small mold clamping force and reducing the number of post-processing steps. It relates to a manufacturing method.

Liquid crystal display devices utilizing the property of liquid crystal that the arrangement of molecules changes when voltage is applied are widely used in portable information terminals, in-vehicle panels, personal computers, and the like. In the future, liquid crystal display devices are expected to replace CRT display devices (CRTs) as the size and performance of liquid crystal display devices increase. Since the liquid crystal itself does not emit light, the liquid crystal display device requires an external light source, and the sidelight method in which the light source is arranged on the side edge of the liquid crystal display device and the direct light method in which the light source is arranged on the back of the liquid crystal display device are practical It has become. In the sidelight method, the device unit can be made thin, but since the luminance is low, the direct method is suitable for a large liquid crystal display device that requires luminance.
In a direct liquid crystal display device, a light source such as a plurality of fluorescent tubes is disposed on the back of the device housing, and incident light is diffused by a light diffusing plate to convert it into planar light with uniform luminance. If necessary, a reflection plate is provided behind the fluorescent tube, gradation printing is performed on the back surface of the light diffusion plate, and a light collecting sheet, a diffusion sheet, etc. are installed on the front surface of the light diffusion plate. The light diffusing plate is required to have a good balance between light transmittance and light diffusibility, no warping, and sufficient strength.
As a material for the light diffusing plate, a molded article of a thermoplastic resin molding material containing a light diffusing agent is used. Examples of the light diffusion plate molding method include an extrusion molding method, a casting method, and an injection molding method. According to the extrusion molding method, a raw material sheet for a light diffusing plate can be efficiently produced, but post-processing for making the light diffusing plate takes time and waste of material is generated. According to the casting method, a light diffusing plate having high strength and no optical distortion can be obtained, but the productivity is not high. According to the injection molding method, the number of post-processing steps can be reduced, and a light diffusion plate can be manufactured in a short time. However, in the conventional method of injecting a molten thermoplastic resin molding material from the side gate on the side of the cavity, a large size is required. The manufacture of the light diffusing plate is not only technically difficult, but also requires a large injection molding machine with a large mold clamping force, so an economic disadvantage is also expected.
JP-A-5-281403 JP-A-6-107881 JP-A-8-327806 WO01 / 32774

  The present invention uses an injection molding machine with a small mold clamping force, reduces the number of post-processing steps, and can efficiently manufacture a light diffusion plate having a large size, a small amount of warpage change, and a good quality. It is made for the purpose of providing the manufacturing method of a diffusion plate.

As a result of intensive studies to solve the above problems, the present inventors, as a mold, have a fixed mold plane with a value calculated by a specific expression expressed as a function of the cavity area and depth. It has been found that by injecting a molten resin molding material from eight gates, it is possible to efficiently manufacture a large-quality light diffusion plate using an injection molding machine having a small clamping force. The present invention has been completed based on the findings.
That is, the present invention
(1) In a method of manufacturing a light diffusing plate for a liquid crystal display device by injection molding of a thermoplastic resin molding material containing a light diffusing agent, a mold having a hot runner with a valve gate is used, and the main surface of the cavity of the mold is When the diagonal length is 400 mm or more, the depth is 0.1 to 5 mm, the cavity area is Smm ² , the cavity depth is tmm, and the number of gates is 8 (1)
8 ≧ [S / (t + 4)] × 10 ⁻⁴ (1)
It satisfies the relationship, around the eight diagonal lines of intersection of the divided regions into a rectangular, in the case where the radius is a circle is 0.1 times the length of a diagonal line, drawn on the fixed planar, all rectangular regions Manufacture of a light diffusing plate for injection molding of the molding material using a mold having one gate each outside the circle and centered in the lateral direction of the fixed mold plane Method,
(2) The method of manufacturing a light diffusing plate according to (1) above, wherein one gate is present in the rectangular region near the outside of the circle and from the center in the short direction of the fixed mold plane,
(3) The method for producing a light diffusing plate according to (1) or (2) above, wherein the gate arrangement is a line-symmetric or point-symmetric arrangement,
(4) The method for producing a light diffusing plate according to any one of (1) to (3), wherein the mold is provided with a vacuum hole.
(5) The method for producing a light diffusing plate according to any one of (1) to (4) above, wherein the thermoplastic resin molding material contains a resin having an alicyclic structure as the thermoplastic resin, and (6) (1) to (5), wherein the thermoplastic resin molding material contains a copolymer of an aromatic vinyl monomer and a (meth) acrylic acid alkyl ester monomer having a lower alkyl group as the thermoplastic resin. ) Manufacturing method of the light diffusing plate according to any one of
Is to provide.
Furthermore, as a preferred embodiment of the present invention,
(7) The method for producing a light diffusing plate according to any one of (1) to (6) above, wherein the pressure in the cavity at the start of injection is reduced to 50 kPa or less by reducing the pressure from the vacuum drawing hole,
(8) The method for producing a light diffusing plate according to the above (5) or (7), wherein the resin having an alicyclic structure is a norbornene polymer,
(9) The method for producing a light diffusing plate according to the above (5) or (7), wherein the resin having an alicyclic structure is a vinyl alicyclic hydrocarbon polymer, and
(10) The above (1) to (1), wherein the light diffusing agent is at least one selected from the group consisting of a polystyrene polymer, a polysiloxane polymer, or a fine particle comprising a crosslinked product thereof, calcium carbonate, silica, and talc. 9) The method for producing a light diffusing plate according to any one of items
Can be mentioned.

  According to the light diffusing plate manufacturing method of the present invention, an injection molding machine with a small mold clamping force is used, the post-processing steps are reduced, and a large-sized, small amount of warpage change and a good quality light diffusing plate are efficiently produced. Can be manufactured automatically.

In the method for producing a light diffusing plate of the present invention, in the method for producing a light diffusing plate for a liquid crystal display device by injection molding of a thermoplastic resin molding material containing a light diffusing agent, a plurality of gates are provided on a fixed mold plane. The cavity is molded using a mold having a substantially rectangular main surface and a diagonal length of 400 mm or more and a depth of 0.1 to 5 mm. The number of the plurality of gates is expressed by the following formula (1), where the cavity area is Smm ² , the cavity depth is tmm, and the number of gates is N.
N ≧ [S / (t + 4)] × 10 ⁻⁴ (1)
And 2 ⁿ , 2 ⁿ −2 or 2 ⁿ +2 (n is an integer of 2 to 5).
A light diffusing plate having a rectangular diagonal length of less than 400 mm can be injection-molded using a conventional side-gate mold, and thus the method of the present invention is not particularly required. The depth of the mold cavity substantially matches the thickness of the obtained light diffusion plate. The depth of the cavity is preferably 0.5 to 3 mm. A light diffusing plate having a thickness of less than 0.1 mm is likely to have insufficient strength because it is thin and the content of a light diffusing agent for obtaining necessary light diffusibility increases. The thickness of the light diffusion plate is 5 mm or less, and sufficient strength and light diffusibility can be obtained.
Further, if the number of gates is less than [S / (t + 4)] × 10 ⁻⁴ , the flow of the molten resin molding material is unreasonable, and complete filling may not be achieved, or the molded product may remain distorted. By setting the number of gates to 2 ⁿ , 2 ⁿ −2 or 2 ⁿ +2 (n is an integer of 2 to 5), the molten resin molding material can be made to flow uniformly and injection-molded with good balance. n is 2 to 5, that is, the number of gates is 2 or more and 34 or less. When the number of gates is 62, the runner configuration of the mold becomes complicated, and it may be difficult to perform stable injection molding.
It is preferable that the mold has a vacuum drawing hole. By providing the vacuum drawing hole, it is possible to reduce the occurrence of appearance defects due to air remaining during molding.
FIG. 1 is an explanatory view of one embodiment of a mold used in the method of the present invention. The mold shown in this figure has four gates A, B, C, and D on a fixed mold plane 1 and is provided with a vacuum drawing hole E. The vacuum pulling hole can also be provided in a movable mold. The mold according to this embodiment is a substantially rectangular shape having a main surface of the cavity of 303.4 mm in length and 405.2 mm in width, and therefore, the length of the diagonal line is 506.2 mm. The depth of the cavity is 1.0 to 2.0 mm although not shown. By injection molding using this mold, a light diffusion plate of 302.5 mm × 404 mm × 1.0-2.0 mm can be obtained.
In the present invention, the number of gates needs to satisfy the formula (1). For example, in the mold of the embodiment shown in FIG. 1, when the cavity size is 303.4 mm × 405.2 mm × 1.5 mm,
[(303.4 × 405.2) / (1.5 + 4)] × 10 ⁻⁴ = 2.24
Therefore, the number of gates 4 satisfies the above formula (1).

2 (a) shows two gates, FIG. 2 (b) shows four gates, FIG. 2 (c) shows six gates, FIG. 2 (d) shows eight gates, and FIG. 2 (e) shows sixteen gates. The positional relationship is shown. In the figure, ● represents the sprue position, ○ represents the gate position, and the straight line represents the runner. 2 (a) to 2 (e), the lengths of the runners from the sprue to the gates are all the same, and the injected molten resin molding materials are all runners at the same distance in the plurality of gates. Since the cavity is filled after flowing, the molded product can be obtained uniformly and without distortion. In this way, by providing a plurality of gates, the flow distance of the molten resin molding material fed from each gate into the cavity is shortened, so that the molten resin molding from one side gate into the cavity. Compared to the case of injecting the material, the molding material pressure can be lowered, and a large light diffusion plate can be injection molded using a small injection molding machine having a small clamping force.
In addition, when the distance of the runner from the sprue to each gate is not the same, for example, by adjusting the diameter of the runner, the flow state of the molten resin molding material at each gate is substantially equal, A light diffusing plate without optical distortion can be formed.
In the method of the present invention, the mold preferably has a hot runner. There is no restriction | limiting in particular in the heating system of a hot runner, For example, any of the external heating system which heats a runner manifold, and the internal heating system which provides a heating body in the center of a runner can be used. In the external heating method, the temperature of the resin molding material in the runner is uniform, and the pressure loss in the flow of the molding material is small. The internal heating method has good thermal efficiency. When a hot runner is used, the runner material can be saved, the injection time can be shortened, and the capacity of the molding machine can be effectively utilized by reducing the injection amount. Further, the mold runner take-out mechanism and its peripheral devices are not required. In addition, the mold opening and closing distance can be shortened to shorten the cycle time, and since the molten resin molding material has reached the gate, it can be filled with low pressure and a molded product with less optical distortion can be obtained. Can do. When a pinpoint gate is used, a molded product can be obtained almost in a state close to a finished product, and post-processing steps can be greatly shortened. When using a hot runner, it is preferable to open and close the gate with a needle valve. The needle valve can be surely sealed, and a good molded product in which the gate trace is not noticeable can be obtained.

In the method of the present invention, a cold runner can be provided in the mold. The cold runner has a demerit that the sprue runner part becomes waste material compared to the hot runner. However, the mold can be manufactured at a relatively low cost, and by using a pinpoint gate or a submarine gate as the gate, the molded product can be automatically cut, and the cut trace can be made small and inconspicuous.
In the method of the present invention, the size of the gate of the fixed mold plane is not particularly limited, and can be appropriately selected according to the size of the molded product and the number of gates. Usually, the diameter is about 0.8 to 4 mm. It is more preferable that the diameter is 1 to 3 mm. If the gate diameter is less than 0.8 mm, it takes a long time to fill the resin molding material, or if the filling speed is increased, the molten resin molding material may generate heat at the gate and deteriorate. When the diameter of the gate part exceeds 4 mm, the gate trace is conspicuous, and there is a possibility that it takes time for post-processing.
In the present invention, the following three types of molds having different gate arrangements can be suitably used.
The mold according to the first aspect is a diagonal line of a region obtained by dividing a cavity having a substantially rectangular main surface into 2 ⁿ , 2 ⁿ -2 or 2 ⁿ +2 (n is an integer of 2 to 5) rectangles having substantially the same shape. When a circle with a radius of 0.1 times the length of the diagonal line is drawn on the fixed mold plane, the outer side of the circle and the short direction of the fixed mold plane are drawn in all rectangular regions. This is a mold in which one gate exists from the center of each.
FIG. 3 is an explanatory view of one embodiment showing the arrangement of gates in the mold of the first embodiment used in the present invention, and shows the gate position of a mold having eight gates. The substantially rectangular cavity main surface 1 is divided into eight rectangles 2 having substantially the same shape, as indicated by a virtual dotted line in the figure. The division into 2 ⁿ (n = 3) rectangles is preferably performed such that the aspect ratio of the divided rectangles is closest to 1. By dividing the rectangular shape so that the aspect ratio of the divided rectangle is closest to 1, the flow distance of the molten resin molding material in the cavity can be shortened and molded in a good state. Centered at the intersection of diagonal lines a and b of each divided rectangle 2 and outside the circle 3 whose radius is 0.1 times the length of the diagonal line, and in the short direction of the fixed plane In addition, one gate 6 is provided for each. In this case, each gate 6 is preferably line-symmetric with respect to the dotted lines c and d as the central axis.

FIG. 4 is an explanatory view of another aspect showing the arrangement of gates in the mold according to the first aspect, and shows the gate position of a mold having eight gates. The substantially rectangular cavity main surface 1 is divided into eight rectangles 2 having substantially the same shape, as indicated by a virtual dotted line in the figure. Centered at the intersection of diagonal lines a and b of each divided rectangle 2 and outside the circle 3 whose radius is 0.1 times the length of the diagonal line, and in the short direction of the fixed plane In addition, one gate 6 is provided from the outside in the longitudinal direction. Also in this case, the gates 6 are preferably symmetrical with respect to the dotted lines c and d.
Next, the mold according to the second aspect is a diagonal line of a region obtained by dividing a substantially rectangular cavity into 2 ⁿ , 2 ⁿ -2 or 2 ⁿ +2 (n is an integer of 2 to 5) rectangles having substantially the same shape. When a circle whose center is the intersection and whose radius is 0.1 times the length of the diagonal is drawn on a fixed plane, there is one gate in the circle, and each outermost It is preferable that at least two gates exist outside the circle in a substantially rectangular inner region formed by connecting the centers of the gates in the circle. More preferably, the gate in the circle is present in a circle whose radius is 0.05 times the length of the diagonal line.
The position of the gate outside the circle is not particularly limited, but if the length of the diffuser plate in the short direction is usually L, the distance from the center line in the short direction is within 0.1L, preferably 0.05L. Is within. With such a gate arrangement, appearance defects due to remaining air are less likely to occur.

FIG. 5 is an explanatory diagram of one embodiment showing the arrangement of gates in the mold of the second embodiment, and shows the gate position of the mold having eight gates and two gates outside the circle. The substantially rectangular cavity main surface 1 is divided into eight rectangles 2 having substantially the same shape, as indicated by a virtual dotted line in the figure. A gate (not shown) is provided in each circle 3 whose radius is 0.1 times the length of the diagonal line, centered on the intersection of the diagonal lines a and b of each rectangle 2 divided. Gates 4a and 4b are provided in a substantially rectangular inner region (shaded portion) formed by connecting the centers of the outermost gates with a dashed line 5. Each gate is preferably symmetrical with respect to the dotted lines c and d. By providing the gate outside the circle in this way, the molten resin molding material is more uniformly filled in the cavity, and a light diffusion plate with less warpage variation and no optical distortion is molded. Can do.
In the present invention, as a mold according to the third aspect, a cavity having a substantially rectangular main surface is made into 2 ⁿ , 2 ⁿ −2 or 2 ⁿ +2 (n is an integer of 2 to 5) rectangles having substantially the same shape. When a circle whose center is at the intersection of the diagonal lines of the divided area and whose radius is 0.1 times the length of the diagonal line is drawn on the fixed plane, it is outside the circle in at least one rectangular area, It is possible to use a mold in which one gate exists each from the center in the short direction of the fixed mold plane, and one gate exists inside each circle in the remaining rectangular area.

In the mold according to the first aspect and the mold according to the third aspect, the number of gates that are outside the circle and one each from the center in the short direction of the fixed mold plane is not particularly limited. However, the target circle is selected within the range of one circle or all circles, but for each circle, there is one gate each outside the center in the short direction of the fixed plane. The presence of the light diffusion plate is more preferable because it is more uniformly filled in the cavity and a light diffusion plate without uniform optical distortion can be obtained.
In addition, there is no particular restriction on the position of the fixed mold plane from the center in the short direction of the fixed mold plane, and it is appropriate depending on the cavity area, the total number of gates and the number of gates positioned outside the circle, etc. A proper position may be selected as appropriate.
Furthermore, in the mold according to the first aspect and the mold according to the third aspect, the gate existing on the outer side of each circle is outside or centered in the longitudinal direction from the center in the short direction of the fixed mold plane. It is preferable that it exists more because poor appearance due to air remaining hardly occurs. The position in the longitudinal direction outside or from the center is not particularly limited, and an appropriate position may be appropriately selected according to the cavity area, the total number of gates, the number of gates located outside the circle, and the like.
With such a gate arrangement, appearance defects due to remaining air are less likely to occur.
In the present invention, as shown in FIGS. 3, 4 and 5, all the gates arranged in the fixed mold plane are uniformly filled with a molten resin molding material in the cavity, and are uniform and optical. From the point of obtaining a light diffusing plate without any significant distortion, it is preferable that it is line symmetric or point symmetric.

When the vacuum hole is provided in the method of the present invention, the material of the vacuum hole is not particularly limited, but pure iron, iron-copper alloy, iron-carbon alloy, iron-carbon-copper alloy, iron-carbon- Sintered metals such as copper-nickel alloy, iron-carbon (copper infiltration) alloy, iron-nickel alloy, iron-carbon-nickel alloy, austenitic stainless steel, martensitic stainless steel, bronze alloy Is preferred. The hole diameter of the vacuum drawing hole can be selected according to the fluidity of the resin molding material to be used. When the flowability of the molding material is relatively good, the hole diameter is preferably about 0.02 to 0.05 mm, and when the flowability is relatively poor, the hole diameter is 0.1 to 0.2 mm. It is preferable that
In the case of providing a vacuum hole in the method of the present invention, the number of vacuum holes is usually 1 or more. When there are two gates, it is preferably located in the middle, and when there are four gates, there are four. It is preferable to be in the center of a rectangle formed by the gates. FIG. 6 is an explanatory view of the vacuum hole position of the mold having eight gates shown in FIG. 3 or FIG. In the figure, ◯ indicates the gate position, and ◎ indicates the vacuum hole position. Since the three rectangles shown in the figure are formed by virtually connecting the gates with a dashed line, a vacuum suction hole is provided in the center of each rectangle. In the cavity, when the molten resin molding material flows from each of the four opposing gates of the rectangle toward the inside of the rectangle, the air inside the rectangle flows out from the vacuum suction hole, so that the molding material completely passes through the cavity. The molded product with good dimensional accuracy can be obtained. The air outside the rectangle can be released by providing a gas vent on the outer periphery of the mold. In the method of the present invention, the pressure in the cavity at the start of injection is preferably 50 kPa or less, and more preferably 35 kPa or less. When the pressure in the cavity at the start of injection exceeds 50 kPa, filling of the molten resin molding material into the cavity becomes insufficient, and gas burning may occur.
The main surface of the mold cavity used in the method of the present invention is substantially rectangular. Depending on the structure of the liquid crystal display device, the mold cavity is provided with some irregularities on the outer periphery of the rectangle, but the method of the present invention can be applied by assuming that the mold cavity is rectangular as a whole. FIG. 7 shows three examples of the cavity main surface of the mold.

There is no particular limitation on the thermoplastic resin used in the method of the present invention, for example, polyethylene, propylene-ethylene copolymer, polystyrene, aromatic vinyl monomer and (meth) acrylic acid alkyl ester monomer having a lower alkyl group And a copolymer, terephthalic acid-ethylene glycol-cyclohexanedimethanol copolymer, polycarbonate, acrylic resin, resin having an alicyclic structure, and the like. Among these, a copolymer of an aromatic vinyl monomer and a (meth) acrylic acid alkyl ester monomer having a lower alkyl group or a polymer resin having an alicyclic structure has good fluidity. Since the weld strength is large, it is preferable in that a large light diffusing plate can be obtained efficiently, and the polymer resin having an alicyclic structure has a small deformation due to moisture absorption, so that a large light diffusing plate with little warpage is obtained. It is further preferable in that it can be performed. A compound in which a light diffusing agent is blended with a resin having an alicyclic structure has both high permeability and high diffusibility required for a light diffusing plate, and has good chromaticity, so that it can be suitably used.
The copolymer of the aromatic vinyl monomer and the (meth) acrylic acid alkyl ester monomer having a lower alkyl group used in the method of the present invention has an aromatic vinyl monomer and a lower alkyl group. An aromatic vinyl copolymer obtained by copolymerizing a (meth) acrylic acid alkyl ester monomer.
Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, m-methylstyrene, p-methylstyrene, o-chlorostyrene, p-chlorostyrene, and the like. You may use these individually or in combination of 2 or more types.
Examples of the (meth) acrylic acid alkyl ester monomer having a lower alkyl group include (meth) acrylic acid alkyl esters having an alkyl group having 1 to 4 carbon atoms, preferably an alkyl group having 1 or 2 carbon atoms. Specific examples include methyl methacrylate, ethyl methacrylate, methyl acrylate, and ethyl acrylate. You may use these individually or in combination of 2 or more types.
The proportion of each component constituting the copolymer is such that the aromatic vinyl monomer is 95 to 5% by weight and the (meth) acrylic acid alkyl ester monomer having a lower alkyl group is 5 to 95% by weight. It is a range. Among these, from the viewpoint of optical properties, moldability, etc., the aromatic vinyl monomer is 60 to 20% by weight, and the (meth) acrylic acid alkyl ester monomer having a lower alkyl group is 80 to 40% by weight. A range is preferred.

The resin having an alicyclic structure has an alicyclic structure in the main chain and / or side chain, and contains an alicyclic structure in the main chain from the viewpoint of mechanical strength, heat resistance, etc. Is preferred.
Examples of alicyclic structures include saturated cyclic hydrocarbon (cycloalkane) structures and unsaturated cyclic hydrocarbon (cycloalkene) structures. From the viewpoint of mechanical strength and heat resistance, cycloalkane structures and cycloalkene structures are exemplified. A structure is preferable, and a cycloalkane structure is most preferable among them. The number of carbon atoms constituting the alicyclic structure is not particularly limited, but is usually 4 to 30, preferably 5 to 20, more preferably 5 to 15 in the mechanical strength, The properties of heat resistance and moldability of the light diffusing plate are highly balanced and suitable.
The proportion of the repeating unit having an alicyclic structure in the resin having an alicyclic structure may be appropriately selected according to the purpose of use, but is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90%. % By weight or more. When the ratio of the repeating unit having an alicyclic structure is too small, the heat resistance is lowered, which is not preferable. In addition, repeating units other than the repeating unit which has an alicyclic structure in resin which has an alicyclic structure are suitably selected according to the intended purpose.
Specific examples of the resin having an alicyclic structure include, for example, (1) a ring-opening polymer of a norbornene-based monomer and a ring-opening copolymer of a norbornene-based monomer and another monomer capable of ring-opening copolymerization thereof, And norbornene polymers such as addition products of these hydrogenated products, norbornene monomers and addition copolymers of norbornene monomers with other monomers copolymerizable therewith; (2) monocyclic cycloolefins Polymer and hydrogenated product thereof; (3) cyclic conjugated diene polymer and hydrogenated product thereof; (4) polymer of vinyl alicyclic hydrocarbon monomer and hydrogenated product thereof, vinyl aromatic monomer And vinyl alicyclic hydrocarbon-based polymers such as hydrogenated products of the aromatic ring portion of the polymer. Among these, from the viewpoints of heat resistance, mechanical strength, and the like, norbornene-based polymers and vinyl alicyclic hydrocarbon-based polymers are preferable, and ring-opening polymer hydrogenated norbornene-based monomers of norbornene-based monomers. More preferred is a hydrogenated product of the aromatic ring portion of the polymer.

The light diffusing agent used in the present invention may be an organic light diffusing agent or an inorganic light diffusing agent. Examples of the organic light diffusing agent include a polymer capable of forming transparent fine particles in a thermoplastic resin or a cross-linked product thereof. Specifically, the polymer or the cross-linked product is formed into a plate-like molded product having a thickness of 1 mm. The total light transmittance is preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more. When the total light transmittance is too low, the light transmittance of the obtained light diffusion plate is lowered due to light loss inside the polymer. The total light transmittance here is generally visible light of 400 to 700 nm. For example, when the light beam to be transmitted and diffused has a wavelength other than this, the above light transmittance at the target wavelength. It is preferable to have. The refractive index of the organic light diffusing agent has a lower limit of n ₁ / n ₂ or n ₂ / n ₁ when the refractive index n ₁ of the thermoplastic resin is n ₂ and the refractive index of the organic light diffusing agent is n _2. The upper limit is preferably 1.01, more preferably 1.015, particularly preferably 1.025, and the upper limit is preferably 1.3, more preferably 1.2. Further, n ₂ is preferably 1.4 to 1.8, more preferably 1.42 to 1.72. When this refractive index ratio is too low, the light diffusibility of the obtained light diffusing plate becomes low. When the refractive index ratio is too high, the light transmittance of the obtained light diffusion plate is lowered. This refractive index is a value at a wavelength according to the purpose of use. The refractive index varies depending on the type of polymer used, but the value can be adjusted by, for example, the amount of monomer containing a phenyl group. The greater the amount of monomer containing a phenyl group, the higher the refractive index of the polymer.
Such organic light diffusing agents include: (1) vinyl monomers such as styrenes and acrylonitriles; (meth) acrylics such as methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate. Homopolymers or copolymers such as acid ester monomers; (2) the above monomers and diethylene glycol di (meth) acrylate copolymerizable therewith, 1,3-butylene glycol di (meth) acrylate, divinylbenzene, etc. And a copolymer with a polyfunctional monomer, (3) a polysiloxane polymer, and (4) a fluorine resin.

The organic light diffusing agent needs to maintain the shape as fine particles in the light diffusing plate. If the shape cannot be maintained during molding, a light diffusing plate having uniform light diffusibility cannot be obtained as will be described later. Therefore, a crosslinked product is preferable. Those that can be crosslinked at the time of polymerization, such as a copolymer copolymerized by adding a polyfunctional monomer, are preferably crosslinked to obtain particles. Fine particles that are cross-linked by a method such as ultraviolet irradiation after being polymerized into a particle shape after polymerization or after polymerization into a particle shape can also be used.
Specific examples include cross-linked polymethyl methacrylate, cross-linked polystyrene, cross-linked sodium polyacrylate, cross-linked silicone, cross-linked methyl methacrylate-styrene copolymer, and cross-linked polydimethylsiloxane.
Among the above organic light diffusing agents, fine particles comprising a polystyrene polymer, a polysiloxane polymer, or a cross-linked product thereof are suitable.
The method of making the polymer used in the present invention into fine particles is not particularly limited, but can be formed into particles by suspension polymerization or the like. For example, if a monomer containing a polyfunctional monomer is subjected to suspension polymerization, such as copolymerization of styrene and divinylbenzene, crosslinked polymer fine particles can be obtained, and after polymerization, washed and dried, using a wind micron separator, etc. If classified, crosslinked fine particles having a desired particle size distribution can be obtained.
Examples of the inorganic light diffusing agent that can be used in the present invention include inorganic fine particles that can form transparent fine particles in a thermoplastic resin. Specific examples include silica, silica alumina, alumina, aluminum hydroxide, magnesium hydroxide, talc, glass flakes, glass beads, sodium silicate, calcium carbonate, barium carbonate, and titanium oxide. Among these inorganic light diffusing agents, calcium carbonate, silica, and talc are preferable because of excellent transparency. These inorganic light diffusing agents can be used singly or in combination of two or more, or can be used in combination with a transparent organic light diffusing agent.
In addition, when the inorganic light diffusing agent is blended by melting and kneading a thermoplastic resin using, for example, a twin-screw kneader, the inorganic light is used in order to avoid deterioration of the color tone of the resin composition due to wear of cylinders and screws. Among the diffusing agents, it is preferable to use one having a low hardness, such as talc.

The particle diameter of the organic light diffusing agent and / or inorganic light diffusing agent used in the present invention is not particularly limited, but the lower limit of the average particle diameter is preferably 0.3 μm, more preferably 0.5 μm, and particularly preferably 1 μm. The upper limit is preferably 30 μm, more preferably 20 μm, and particularly preferably 15 μm. If it is too small, the light diffusibility of the light diffusing plate of the present invention increases, but the light transmittance decreases.If it is too large, the light transmittance increases, but the light diffusing property decreases, and the surface smoothness of the light diffusing plate further decreases. It may decrease or unevenness may occur.
The organic light diffusing agent and / or inorganic light diffusing agent used in the present invention is more preferable as it contains more spherical ones. The spherical shape means that the minor axis / major axis of the fine particle is preferably 0.6 to 1.0, more preferably 0.8 to 1.0, particularly preferably 0.9 to 1.0, and has a corner. I say something that is not. The short diameter means the smallest diameter of one fine particle, and the long diameter means the largest diameter of the same fine particle. In the present invention, the proportion of spherical fine particles in the fine particles used is preferably 80% or more, more preferably 90% or more, and particularly preferably 95% or more. What is necessary is just to measure based on the image | video of a micrograph about the short diameter, long diameter, an average particle diameter, and the presence or absence of an angle | corner. If there are many non-spherical ones, the dispersion tends to be non-uniform at the time of molding, and it becomes difficult to obtain a uniform light-diffusing molded article having orientation.
In addition, the organic light diffusing agent and / or the inorganic light diffusing agent used in the method of the present invention do not need to be one kind, for example, for the purpose of adjusting light transmittance and light diffusibility, or for the purpose of adjusting to the use environment, A plurality of types of organic light diffusing agents and / or inorganic light diffusing agents may be used in combination.
The amount of the organic light diffusing agent and / or inorganic light diffusing agent in the molding material varies depending on the optical path length of the target light diffusing plate. For example, the light diffusion plate having a thickness of 1 mm is usually 0.8 to 20% by weight, and the light diffusion plate having a thickness of 2 mm is usually 0.1 to 10% by weight. This is because when the optical path length is short (thickness is thin), sufficient light diffusibility cannot be obtained unless a large amount of organic light diffusing agent and / or inorganic light diffusing agent is blended. On the other hand, when the optical path length is long (thickness is large), even if a small amount of organic light diffusing agent and / or inorganic light diffusing agent is blended, the light transmittance is lowered. This is because it must be reduced.

An antioxidant may be added to the thermoplastic resin molding material used in the method of the present invention in order to prevent oxidative degradation and thermal degradation during molding. Moreover, in order to improve the light resistance etc. of a molded article, a light resistance stabilizer can be added.
Examples of the antioxidant include a phenol-based antioxidant, a phosphorus-based antioxidant, and a sulfur-based antioxidant. These antioxidants can be used individually by 1 type, or can be used in combination of 2 or more type. Among these, phenolic antioxidants, particularly alkyl-substituted antioxidants can be suitably used. The addition amount of the antioxidant is preferably 0.01 to 2 parts by weight, and more preferably 0.02 to 1 part by weight with respect to 100 parts by weight of the thermoplastic resin.
Examples of the light resistance stabilizer include hindered amine light resistance stabilizer (HALS) and benzoate light resistance stabilizer. These light-resistant stabilizers can be used alone or in combination of two or more. Among these, hindered amine light resistance stabilizers can be particularly preferably used. The addition amount of the light-resistant stabilizer is preferably 0.01 to 2 parts by weight, more preferably 0.02 to 1 part by weight, with respect to 100 parts by weight of the thermoplastic resin, and 0.05 to 0. More preferably, it is 0.5 parts by weight.
If necessary, other additives can be added to the molding material. Other additives include, for example, stabilizers such as heat stabilizers, ultraviolet absorbers and near infrared absorbers; resin modifiers such as lubricants and plasticizers; colorants such as dyes and pigments; antistatic agents, light Examples include a diffusing agent.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
Production Example 1 (Production of norbornene polymer)
500 parts by weight of dehydrated cyclohexane, 0.82 part by weight of 1-hexene, 0.15 part by weight of dibutyl ether, and 0.30 part by weight of triisobutylaluminum are thoroughly dried at room temperature and placed in a stainless steel pressure-resistant container purged with nitrogen. After mixing, while maintaining the temperature at 45 ° C., 170 parts by weight of tricyclo [4.3.0.1 ^2.5 ] deca-3,7-diene (dicyclopentadiene, hereinafter abbreviated as “DCP”), 8- ethylidene - tetracyclo [4.4.0.1 ^2.5 .1 ^7.10] - dodeca-3-ene (. ethylidene tetracyclododecene, hereinafter, abbreviated as "ETD") and 30 parts by weight, tungsten hexachloride (0. (7 wt% toluene solution) and 30 parts by weight were continuously added over 2 hours for polymerization. To the polymerization solution, 1.06 part by weight of butyl glycidyl ether and 0.52 part by weight of isopropyl alcohol were added to deactivate the polymerization catalyst and stop the polymerization reaction.
Next, 270 parts by weight of cyclohexane is added to 100 parts by weight of the reaction solution containing the obtained ring-opening polymer, and further 5 parts by weight of a nickel-alumina catalyst [manufactured by JGC Chemical Co., Ltd.] is added as a hydrogenation catalyst. The mixture was heated to 200 ° C. with stirring under pressure of 5 MPa and then reacted for 4 hours to obtain a reaction solution containing 20% by weight of a DCP / ETD ring-opening polymer hydrogenated product. After removing the hydrogenation catalyst by filtration, 0.1 parts by weight of pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-) as a phenolic antioxidant per 100 parts by weight of the hydrogenated product. 4-hydroxyphenyl) propionate] was added to and dissolved in the resulting solution. Next, using a cylindrical concentrator / dryer [manufactured by Hitachi, Ltd.], an extruder in which the hydrogenated product is melted while removing cyclohexane and other volatile components from the solution at a temperature of 270 ° C. and a pressure of 1 kPa or less. Were extruded into strands, cooled and pelletized to recover the pellets. This hydrogenated ring-opened polymer had a weight average molecular weight (Mw) of 35,000, a hydrogenation rate of 99.9%, and a glass transition temperature (Tg) of 100 ° C.

Example 1
99 parts by weight of the DCP / ETD ring-opening polymer hydrogenated product obtained in Production Example 1 and 1 part by weight of fine particles composed of a crosslinked product of a polysiloxane polymer [GE Toshiba Silicone Co., Ltd., Tospearl 120] were mixed, Extruded into a strand shape using a twin screw extruder [Toshiba Machine Co., Ltd., TEM-35B], and cut with a pelletizer to produce a pellet for a light diffusion plate.
Using this light diffusion plate pellet, a light diffusion plate was molded with an injection molding machine [Sodick, TR450EH, screw / plunger diameter φ50 mm, maximum clamping force 450 t]. The mold has a cavity in which eight gates are arranged as shown in FIG. 3 on a fixed mold plane. The cavity has a length of 320 mm, a width of 426 mm, a diagonal length of 533 mm, and a depth of 1. Variable to 5 mm or 2.0 mm. The mold has 8 hot runner type valve gates [Mitsubishi Materials Co., Ltd.] having a diameter of 2 mm at the position shown in FIG. 3 on the fixed mold plane, and 10 mm in diameter at the position shown in FIG. Three vacuum holes for sintered metal are provided.
The injection molding conditions were a cylinder temperature of 275 ° C., a hot runner temperature of 275 ° C., a mold temperature of 78 ° C., an injection speed of 100 mm / s, and a cooling time of 30 seconds. At the same time as the mold was clamped by the low pressure clamping force, pressure reduction was started, the pressure in the cavity was reduced to 10 kPa or less, and injection was started 1 second after the mold clamping was completed.
When the depth of the cavity was 1.5 mm and molding was performed with a mold clamping force of 350 t, a good molded product was obtained. The molded article had no appearance of air remaining and had a good appearance.
Even when the cavity depth was 2.0 mm and the mold clamping force was 350 t, a good molded product was obtained.
From the above results, it was confirmed that a light diffusing plate having a thickness of 1.5 mm or more in a 20-inch mold can be molded with a clamping force of 350 t.
The obtained light diffusion plate was placed in a constant temperature and humidity chamber (60 ° C., 90% RH) for 117 hours, and the subsequent warpage change was measured using a three-dimensional measuring machine [Mitutoyo Corporation, Microcode BH504]. It was 0.05 mm.
Instead of FIG. 3, a molded product is obtained in the same manner as described above except that a die in which eight gates each having one gate are arranged in a fixed mold plane is used in each circle in FIG. Produced. In molding with a mold clamping force of 350 t, residual air was observed, and the appearance was slightly inferior to the molded product.
Example 2
In Example 1, a molded product was produced in the same manner as in Example 1 except that a mold having 8 gates arranged on a fixed mold plane as shown in FIG. 4 was used instead of FIG. In molding with a mold clamping force of 350 t, no air residue was observed, and a molded product having a good appearance was obtained.
Even when the cavity depth was 2.0 mm and the mold clamping force was 350 t, a good molded product was obtained.
From the above results, it was confirmed that a light diffusing plate having a thickness of 1.5 mm or more in a 20-inch mold can be molded with a clamping force of 350 t.
The obtained light diffusion plate was placed in a constant temperature and humidity chamber (60 ° C., 90% RH) for 117 hours, and the subsequent warpage change was measured using a three-dimensional measuring machine [Mitutoyo Corporation, Microcode BH504]. 0.08 mm.
Example 3
Implementation was performed except that a copolymer of methyl methacrylate and styrene [Nippon Steel Chemical Co., Ltd., Estylene MS-600] was used instead of the hydrogenated DCP / ETD ring-opening polymer obtained in Production Example 1. In the same manner as in Example 1, a light diffusion plate pellet was produced, and a molded product was produced by injection molding. In molding with a mold clamping force of 350 t, no air residue was observed, and a molded product having a good appearance was obtained.
Even when the cavity depth was 2.0 mm and the mold clamping force was 350 t, a good molded product was obtained.
From the above results, it was confirmed that a light diffusing plate having a thickness of 1.5 mm or more in a 20-inch mold can be molded with a clamping force of 350 t.
The obtained light diffusion plate was placed in a constant temperature and humidity chamber (60 ° C., 90% RH) for 117 hours, and the subsequent warpage change was measured using a three-dimensional measuring machine [Mitutoyo Corporation, Microcode BH504]. 0.22 mm.

Comparative Example 1
From the pellet for the light diffusing plate manufactured in Example 1, using a die having a side gate with a cold runner and a cavity having a length of 229 mm, a width of 305 mm, a diagonal length of 381 mm, and a depth of 1.5 mm, A light diffusion plate was molded.
The injection molding conditions were a cylinder temperature of 275 ° C., a mold temperature of 78 ° C., an injection speed of 100 mm / s, a mold clamping force of 350 t, and a cooling time of 30 seconds. A good molded product was obtained.
When the mold was replaced with a mold having a cold runner / side gate and having a length of 244 mm, a width of 325 mm, a diagonal length of 406 mm, and a depth of 1.5 mm, and molding was performed under the same conditions, complete filling was not achieved. .
From this result, it can be seen that the conventional method using a mold having a cold runner / side gate is limited to a 15-inch light diffusion plate, and injection molding of a 16-inch light diffusion plate is difficult.
Comparative Example 2
A light diffusion plate was molded in the same manner as in Example 1 except that the cavity depth was 1.5 mm and the number of gates was two as shown in FIG. In molding with a mold clamping force of 350 t, unfilled portions remained at the four corners of the light diffusion plate, and a good molded product could not be obtained.

  According to the method of the present invention, a large-sized light diffusing plate with good quality can be manufactured with high productivity. This light diffusion plate is suitably used for a liquid crystal display device.

It is explanatory drawing of the one aspect | mode of the metal mold | die used for this invention method. It is explanatory drawing which shows the positional relationship of a some gate. It is explanatory drawing of the one aspect | mode which shows arrangement | positioning of the gate in this invention. It is explanatory drawing of another aspect which shows arrangement | positioning of the gate in this invention. It is explanatory drawing which shows arrangement | positioning of the gate of the reference example of this invention . It is explanatory drawing of the vacuum drawing hole position of a metal mold | die. It is an example of the cavity main surface of a metal mold | die. It is explanatory drawing which shows arrangement | positioning of the gate of the metal mold | die used in the comparative example 2.

Explanation of symbols

1 Fixed mold plane (cavity main surface)
2 Divided rectangles 3 Circles centered on the intersection of diagonal lines 4a, 4b Gate 5 Dotted lines 6 Gates A, B, C, D Gate E Vacuum holes a, b Diagonal lines c, d Dotted lines

Claims (6)

In a method of manufacturing a light diffusing plate for a liquid crystal display device by injection molding of a thermoplastic resin molding material containing a light diffusing agent, a mold having a hot runner with a valve gate is used, and the main surface of the cavity of the mold is substantially rectangular. When the diagonal length is 400 mm or more, the depth is 0.1 to 5 mm, the cavity area is Smm ² , the cavity depth is tmm, and the number of gates is 8 on the fixed mold plane, the formula (1)
8 ≧ [S / (t + 4)] × 10 ⁻⁴ (1)
It satisfies the relationship, around the eight diagonal lines of intersection of the divided regions into a rectangular, in the case where the radius is a circle is 0.1 times the length of a diagonal line, drawn on the fixed planar, all rectangular regions Manufacture of a light diffusing plate for injection molding of the molding material using a mold having one gate each outside the circle and centered in the lateral direction of the fixed mold plane Method.   2. The method of manufacturing a light diffusing plate according to claim 1, wherein one gate is present in the rectangular region near the outside of the circle and from the center in the short direction of the fixed mold plane.   The method of manufacturing a light diffusing plate according to claim 1 or 2, wherein the gates are arranged in line symmetry or point symmetry.   4. The method for manufacturing a light diffusing plate according to claim 1, wherein the mold is provided with a vacuum drawing hole.   The method for producing a light diffusing plate according to any one of claims 1 to 4, wherein the thermoplastic resin molding material contains a resin having an alicyclic structure as the thermoplastic resin. 6. The thermoplastic resin molding material according to claim 1, comprising a copolymer of an aromatic vinyl monomer and a (meth) acrylic acid alkyl ester monomer having a lower alkyl group as the thermoplastic resin. A method for producing a light diffusing plate according to claim 1.

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