JP2006264149A - Mold for injection molding and manufacturing method of optical member using the mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mold for injection molding which can obtain a large-sized optical member, such as a light diffusion plate, free from local deformation such as sink marks with a shortened molding cycle and reduction in the amount of a wasted resin, and to provide a manufacturing method of the optical member using the mold. <P>SOLUTION: The mold for injection molding has a first runner of the nozzle side of an injection molding machine and a second runner of the mold cavity side, the first runner having a heating means to keep the resin inside the runner in a molten state and the second runner having a cooling means to cool and solidify the resin inside the runner. The method of manufacturing the optical member by injection molding of a thermoplastic resin uses the above mold having the first runner of the nozzle side of the injection molding machine and the second runner of the mold cavity side, the first runner is heated to keep the resin inside the runner in a molten state, and the second runner is cooled to solidify the resin inside the runner. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an injection mold and a method for manufacturing an optical member using the mold. More specifically, the present invention has a hot runner and a cold runner, shortens the molding cycle, reduces the amount of resin to be discarded, and can obtain an optical member free from local deformation such as sink marks. The present invention relates to a mold and a method for producing an optical member using the mold.

Liquid crystal display devices that utilize the property of liquid crystals that change the arrangement of molecules when a voltage is applied are widely used in personal computers, thin televisions, in-vehicle panels, portable information terminals, and the like. 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-sized liquid crystal display device that requires high luminance.
In both the sidelight system and the direct system, an optical member made of a thermoplastic resin performs an important function. In the direct system, a light diffusion plate is used. In a direct-type liquid crystal display device, a plurality of light sources such as cold-cathode tubes are arranged on the back of the device casing, and incident light is diffused by a light diffusion plate to convert it into planar light with uniform luminance. If necessary, a reflection plate is provided behind the cold cathode tube, gradation printing is performed on the back surface of the light diffusion plate, and a condensing sheet, a diffusion sheet, and the like are stacked 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, to have sufficient strength without warping, and to reduce luminance unevenness.
As a material for the light diffusing plate, a molded product of a thermoplastic resin containing a light diffusing agent is often used, but only the thermoplastic resin may be used to devise the shape of the surface of the molded product. 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 productivity is not high. According to the injection molding method, the number of post-processing steps is small and a light diffusing plate can be manufactured in a short time. However, in the conventional method of injecting molten thermoplastic resin from the side gate on the side of the cavity, Injection molding of the light diffusing plate is technically difficult. When a large number of pinpoint gates are provided on the light incident surface of the light diffusing plate, a large light diffusing plate can be manufactured by an injection molding method. When a mold having a hot runner and a pinpoint gate is used, a large light diffusion plate can be efficiently injection-molded in a short molding cycle, but when the obtained light diffusion plate is mounted on a liquid crystal display device, There has been a problem in that the image quality of the display screen is degraded due to the occurrence of sink marks and unevenness in the vicinity of the pinpoint gate trace on the liquid crystal display screen.

  The present invention relates to an injection mold that can shorten a molding cycle, reduce the amount of resin to be discarded, and obtain a large optical member such as a light diffusing plate without local deformation such as sink marks, and the mold. It is made for the purpose of providing the manufacturing method of the optical member to be used.

As a result of intensive research to solve the above problems, the present inventors have combined a hot runner and a cold runner, the first runner on the injection molding machine nozzle side is the hot runner, and the second on the mold cavity side. By using a cold runner as a runner, the molding cycle is shortened, the amount of resin to be discarded is reduced, there is no generation of burnt foreign matter in the molded product, and there is a sink near the pinpoint gate mark when it is installed in a liquid crystal display device. The inventors have found that it is possible to produce a large light diffusing plate without unevenness of brightness due to or deformation, and have completed the present invention based on this finding.
That is, the present invention
(1) An injection mold having a first runner on the injection molding machine nozzle side and a second runner on the mold cavity side, and the first runner keeps the resin in the runner in a molten state. An injection mold characterized in that the second runner has cooling means for cooling and solidifying the resin in the runner, and
(2) In the method of manufacturing an optical member by injection molding of a thermoplastic resin, an injection mold having a first runner on the injection molding machine nozzle side and a second runner on the mold cavity side is used. A method for producing an optical member, characterized in that the runner is heated to keep the resin in the runner in a molten state, and the second runner is cooled to solidify the resin in the runner.
Is to provide.

  When an injection mold having a runner that combines the hot runner and the cold runner of the present invention is used, a large optical member such as a light diffusing plate can be disposed of in a short molding cycle, and the amount of runners to be discarded is economical. Can be manufactured. In addition, because it has a cold runner on the mold cavity side, the temperature of the mold cavity does not rise near the gate, and local deformation and sink marks occur due to insufficient cooling near the gate in the molded product. There is no. Furthermore, since the molten resin that has accumulated and deteriorated in the hot runner is solidified in the cold runner, there is little mixing of burnt foreign substances into the molded product, and the yield of large optical members is improved.

The injection mold of the present invention is an injection mold having a first runner on the injection molding machine nozzle side and a second runner on the mold cavity side, and the first runner is in the runner. It has heating means for keeping the resin in a molten state, and the second runner has cooling means for cooling and solidifying the resin in the runner.
FIG. 1 is an explanatory view of one embodiment of an injection mold according to the present invention. The mold according to this aspect includes a fixed-side mounting plate 1, a fixed-side template 2, a movable-side template 3, and a movable-side mounting plate 4. The fixed runner plate 1 is provided with a first runner 5 on the injection molding machine nozzle side, the fixed mold plate 2 is provided with a second runner 6 on the mold cavity side, and the movable mold plate 3 is provided with a mold cavity. 7 is provided. The fixed side attachment plate is attached to the fixed side die plate of the molding machine, and the fixed side mold plate slides on a guide pin (not shown).
The first runner is heated by the heating means provided on the fixed side mounting plate, and the resin in the first runner is kept in a molten state. The second runner is cooled by the cooling means provided on the stationary side template, and the resin in the second runner is cooled and solidified. The molten resin injected from the nozzle of the injection molding machine flows into the first runner 5 from the sprue 8 and pushes out the molten resin already retained in the first runner while pushing the gate 9 of the first runner. Then, it flows into the second runner 6, which is a gap, and further fills the mold cavity 7 via the gate 10 of the second runner. In the mold of this aspect, resin reservoirs 11 are provided at both ends of the second runner. When the resin in the second runner and the resin in the mold cavity are cooled and solidified, the mold opens, the resin in the second runner part is taken out between the fixed side mounting plate and the fixed side mold plate, and the fixed side mold plate The molded product is taken out between the movable mold plate and the movable side template.
In the present invention, a sprue is also included in the runner.
The length of the second runner is preferably 0.1 times or more and 0.9 times or less, and more preferably 0.2 times or more and 0.8 times or less with respect to the entire length of the runner. If it is larger than 0.9 times, the molding cycle is prolonged and the number of runners is increased too much. If it is smaller than 0.1 times, sink marks and local deformation may occur in the vicinity of the pinpoint gate trace.

In the mold of the present invention, the heating means of the first runner is not particularly limited. For example, the heater embedded in the fixed side mounting plate, the external heating by the oil-based heat medium flow path provided on the fixed side mounting plate, The internal heating etc. which provide a heating body in the center can be mentioned. Among these, heating with a heat medium can be suitably used because of good temperature controllability. In the mold of the present invention, the cooling means for the second runner is not particularly limited, and examples thereof include an aqueous heat medium flow path and an oily heat medium flow path provided on the stationary side plate. The fixed mold plate provided with the second runner is preferably controlled at the same temperature as the movable mold plate provided with the mold cavity. The lower the mold cavity temperature, the faster the cooling and solidification of the molten resin and the shorter the molding cycle. However, in consideration of the transferability of the mold cavity surface and the occurrence of distortion of the molded product, the mold cavity It is preferable to select the temperature.
Since the first runner is heated and the resin in the first runner is kept in a molten state, the injection mold according to the present invention requires less runner material to be discarded than the cold runner, and the injection time. By reducing the injection amount, the capacity of the injection molding machine can be used effectively. Further, when injection molding is performed using a hot runner, the temperature near the gate of the hot runner becomes higher than the mold cavity temperature, so that the molded product is not sufficiently cooled, and local deformation and sink marks are likely to occur. The mold of the present invention cools the fixed side mold plate provided with the second runner, so that the mold cavity surface can be kept at a constant temperature and has optical characteristics free from distortion and local deformation. An excellent molded product can be produced.

In the mold of the present invention, the gate of the first runner is preferably a pinpoint gate or a valve gate to prevent leakage of the molten resin when the mold is opened. In the mold of the present invention, the second runner is not particularly limited, and examples thereof include a pinpoint gate, an edge gate, a fan gate, a submarine gate, a ring gate, a disk gate, a tab gate, and a film gate. Among these, a large number of pinpoint gates can be provided for a large molded product, and the degree of freedom in arrangement is large and the processing of gate traces is easy, so that it can be suitably used. Also, in the pinpoint gate, the flow of the molten resin is throttled and the pressure drop occurs due to the viscous resistance of the resin, and the energy loss due to the pressure drop is converted into heat and used for heating the resin. Residual stress can be reduced.
When injection molding is performed using the mold of the present invention, when the molten resin staying in the first runner flows through the second runner, a boundary layer having a zero velocity is first formed on the outer wall of the runner. . The boundary layer immediately transfers heat to the outer wall and the temperature drops, and in this state the boundary layer becomes quite thick. As a result, a considerable part of the molten resin that has accumulated and deteriorated in the first runner is solidified in the second runner and is not sent to the mold cavity. Obtainable. If necessary, a resin reservoir is provided at both ends of the second runner, and the resin staying in the molten state in the first runner is led to the resin reservoir to be cooled and solidified, and a mold of molten resin with a long thermal history The amount of inflow into the cavity can be reduced. The cylinder of the injection molding machine can prevent the deterioration of the molten resin by nitrogen gas replacement, but the hot metal runner is not easy to replace the nitrogen gas, so the molten resin gold retained in the first runner By preventing the flow into the mold cavity, a high-quality molded product can be obtained.

In the method for producing an optical member of the present invention, in the method for producing an optical member by injection molding of a thermoplastic resin, the injection molding machine has a first runner on the nozzle side and a second runner on the mold cavity side. Using a mold, the first runner is heated to keep the resin in the runner in a molten state, and the second runner is cooled to solidify the resin in the runner. According to the method of the present invention, it is possible to economically manufacture an optical member that is free from sink marks and local deformations and is less contaminated with burnt foreign matters, in a short molding cycle, with a reduced amount of runner parts to be discarded. it can. The method of the present invention can be particularly suitably applied to the production of large optical members such as a light diffusing plate of a direct type backlight and a lighting curtain. Further, the present invention can be applied to a light guide plate for a sidelight type backlight, a Fresnel lens for a rear projection TV, and the like.
The thermoplastic resin used in the method of the present invention is not particularly limited, and examples thereof include resins having an alicyclic structure, methacrylic resin, polycarbonate, polystyrene, acrylonitrile-styrene copolymer resin, (meth) acrylic acid ester-aromatic vinyl compound. A copolymer, preferably methyl methacrylate-styrene copolymer resin, ABS resin, polyethersulfone and the like can be mentioned. Among these, a resin having an alicyclic structure, a methacrylic resin, and a (meth) acrylic acid ester-aromatic vinyl compound copolymer can be preferably used, and a resin having an alicyclic structure is particularly preferably used. be able to. Resin with alicyclic structure has good flowability of molten resin, so it can fill the mold cavity with low injection pressure using pin gate or film gate, and has extremely low hygroscopicity, so dimensional stability The optical member can be reduced in weight because the light diffusion plate does not warp and the specific gravity is small. In addition, when a resin having an alicyclic structure is used in the production method of the present invention, weld lines are less likely to occur than other resins.
Examples of the resin having an alicyclic structure include polymer resins having an alicyclic structure in the main chain or side chain. A polymer resin having an alicyclic structure in the main chain can be particularly preferably used because it has good mechanical strength and heat resistance. The alicyclic structure is preferably a saturated cyclic hydrocarbon structure, and the carbon number thereof is preferably 4 to 30, more preferably 5 to 20, and further preferably 5 to 15. . The ratio 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 70% by weight or more, and 90% by weight or more. More preferably.

  Examples of the resin having an alicyclic structure include a ring-opening polymer or a ring-opening copolymer of a norbornene monomer or a hydrogenated product thereof, an addition polymer or an addition copolymer of a norbornene monomer, or Those hydrogenated products, polymers of monocyclic olefin monomers or hydrogenated products thereof, polymers of cyclic conjugated diene monomers or hydrogenated products thereof, vinyl alicyclic hydrocarbon monomers Or a hydrogenated product thereof, a polymer of a vinyl aromatic hydrocarbon monomer, or a hydrogenated product of an unsaturated bond part containing an aromatic ring of the copolymer. Among these, hydrogenated products of norbornene-based monomer polymers and hydrogenated products of unsaturated bonds containing aromatic rings of vinyl aromatic hydrocarbon-based monomer polymers have mechanical strength and heat resistance. Since it is excellent in property, it can be used especially suitably.

The methacrylic resin is excellent in transparency, tough and hardly cracked, so that it can be suitably used as an optical member. Examples of the methacrylic resin include a methacrylic resin molding material containing 80% or more of a methyl methacrylate polymer defined in JIS K 6717. Among the methacrylic resins specified in this standard, methacrylic resins having a specified classification code 100-120 having a Vicat softening point temperature of 96 to 100 ° C. and a melt flow rate of 8 to 16 have suitable fluidity and strength, and thus are suitable. Can be used.
The (meth) acrylic acid alkyl ester-aromatic vinyl compound copolymer is obtained by copolymerizing an aromatic vinyl monomer and a (meth) acrylic acid alkyl ester monomer having a lower alkyl group.
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.
In the method of the present invention, the resin molding material can be injection-molded by containing other polymers, various compounding agents or fillers singly or in combination, if necessary. Examples of the other polymer include rubbers or resins such as polybutadiene and polyacrylate.

  Examples of the compounding agents include antioxidants, ultraviolet absorbers, light stabilizers, near infrared absorbers, coloring agents such as dyes and pigments, lubricants, plasticizers, antistatic agents, fluorescent whitening agents, and the like. . In addition, when a light diffusing agent is blended in the light diffusing plate obtained by the production method of the present invention, fine particles comprising a polystyrene-based polymer, a polysiloxane-based polymer or a cross-linked product thereof, a fluorine-based resin, barium sulfate, Calcium carbonate, silica, talc and the like can also be used. Among these, the fine particles made of polystyrene polymer, polysiloxane polymer, or cross-linked products thereof are particularly suitable because they have good dispersibility, excellent heat resistance, and no yellowing during molding. be able to.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
Example 1
99 parts by weight of a resin having an alicyclic structure [Nippon Zeon Co., Ltd., ZEONOR 1060R] and 1 part by weight of silicone resin fine particles [GE TOSHIBA Silicone Co., Ltd., Tospearl 120, average particle size of 2.0 μm] are mixed. A light diffusion plate pellet was prepared by extruding into a strand using an axial extruder and cutting with a pelletizer. A light diffusing plate was molded from the light diffusing plate pellet using an injection molding machine (clamping force 8,338 kN).
Injection molding was performed using a mold having a first runner and a second runner shown in FIG. The mold cavity dimensions are 600 mm in length, 1,020 mm in width, and 2.0 mm in depth, 8 at a position indicated by a circle so that molten resin is supplied approximately evenly and no gas residue is generated inside the molded product. The pinpoint gate 10 is provided. Molten resin is supplied from the injection molding machine to the sprue 8 indicated by ◎, and the hot nozzle indicated by ● is the hot runner (first runner), the temperature of the hot runner manifold is set to 260 ° C, and the temperature of the hot runner nozzle is set to Maintained at 240 ° C. From the hot nozzle shown by ● to the gate 10 shown by ○ is a cold runner (second runner), the length of all runners is 3,190 mm, the length of the cold runner is 2,220 mm, and the temperature of the cold runner is Maintained at 85 ° C. The light diffusion plate was injection molded at a cylinder temperature of 280 ° C., an injection speed of 130 mm / s, a holding pressure of 100 MPa, and a mold cavity temperature of 85 ° C. Molding was possible in a molding cycle of 105 seconds, and 100 light diffusion plates were injection molded.
When the obtained light diffusing plate was visually observed, no sink marks or local deformation were observed in the vicinity of the pinpoint gate trace. Among 100 sheets of light diffusion plate, burnt foreign matter was observed on 2 sheets. The weight of the cold runner resin to be discarded was 80 g per light diffusion plate.

Comparative Example 1
A light diffusing plate was injection-molded in the same manner as in Example 1 using a mold having a hot runner shown in FIG.
The cavity size of the mold is the same as that of Example 1, molten resin is supplied from an injection molding machine to a sprue indicated by ◎, and eight valve gates are provided at positions indicated by ●. The total length of the runner is 3,090 mm. The temperature of the hot runner manifold was maintained at 260 ° C, and the temperature of the hot runner nozzle was maintained at 240 ° C. The light diffusion plate was injection molded at a cylinder temperature of 280 ° C., an injection speed of 130 mm / s, a holding pressure of 80 MPa, and a mold cavity temperature of 85 ° C. Molding was possible in a molding cycle of 70 seconds, and 100 light diffusion plates were injection molded. The temperature of the mold cavity near the gate rose to 130 ° C.
When the obtained light diffusing plate was visually observed, local deformation and sink marks were found near the pinpoint gate trace. Burning foreign materials were observed on 10 out of 100 light diffusion plates.
Comparative Example 2
A light diffusing plate was injection-molded in the same manner as in Example 1 using a mold having a cold runner shown in FIG.
The cavity size of the mold is the same as that of the first embodiment, and has eight pinpoint gates at the positions indicated by ◯. The length of all runners was 3,090 mm, the length of the cold runner was 704.8 mm, and the temperature of the cold runner was maintained at 85 ° C. The light diffusion plate was injection molded at a cylinder temperature of 280 ° C., an injection speed of 130 mm / s, a holding pressure of 100 MPa, and a mold cavity temperature of 85 ° C. Molding was possible in a molding cycle of 130 seconds, and 100 light diffusion plates were injection molded.
When the obtained light diffusing plate was visually observed, no sink marks or local deformation were observed near the pinpoint gate trace. Burning foreign materials were observed on one of the 100 light diffusion plates. The weight of the resin in the cold runner portion to be discarded was 140 g per light diffusion plate.
The results of Example 1 and Comparative Examples 1 and 2 are shown in Table 1.

  As shown in Table 1, the first runner on the injection molding machine nozzle side is heated to keep the resin in the runner in a molten state, and the second runner on the mold cavity side is cooled to solidify the resin in the runner. In Example 1 made, compared with Comparative Example 2 using a cold runner, the molding cycle is short, the amount of runners to be discarded is small, the appearance of the light diffusing plate is equally good, and the occurrence of burnt foreign matter is also generated. Almost the same amount. In Comparative Example 1 using a hot runner, the molding cycle is short and no runner to be discarded is generated, but the mold cavity temperature rises near the gate, and local deformation and sinking can occur near the gate trace of the molded product, Many burnt foreign substances are also generated.

  When an injection mold having a runner that combines the hot runner and the cold runner of the present invention is used, a large optical member such as a light diffusing plate can be disposed of in a short molding cycle, and the amount of runners to be discarded is economical. Can be manufactured. Further, since the cold runner is provided on the mold cavity side, the temperature of the mold cavity does not rise near the gate, and local deformation and sink marks are not generated in the molded product. Furthermore, since the molten resin that has accumulated and deteriorated in the hot runner is solidified in the cold runner, there is little mixing of burnt foreign substances into the molded product, and the yield of large optical members is improved.

It is explanatory drawing of the one aspect | mode of the injection die of this invention. It is explanatory drawing of the hot runner metal mold | die used in the comparative example 1. It is explanatory drawing of the cold runner metal mold | die used in the comparative example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixed side mounting plate 2 Fixed side mold plate 3 Movable side mold plate 4 Movable side mounting plate 5 First runner 6 Second runner 7 Mold cavity 8 Sprue 9 First runner gate 10 Second runner gate 11 Resin pool

Claims (2)

  An injection mold having a first runner on the injection molding machine nozzle side and a second runner on the mold cavity side, the first runner having a heating means for keeping the resin in the runner in a molten state. An injection mold, wherein the second runner has a cooling means for cooling and solidifying the resin in the runner.   In the method of manufacturing an optical member by injection molding of a thermoplastic resin, an injection mold having a first runner on the injection molding machine nozzle side and a second runner on the mold cavity side is used, and the first runner is heated. Then, the resin in the runner is kept in a molten state, the second runner is cooled, and the resin in the runner is solidified.

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