JP2000229343A - Method for injection compression molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve flatness, sink, strain, and others by a method in the injection molding of a thermoplastic resin, after the resin in a specified ratio to the volume of a mold cavity being injected, compression is started, and when the volume of the resin has arrived at a specified ratio to the volume of the cavity, mold clamping force is decreased gradually. SOLUTION: In a mold, in order to open its cavity sufficiently, a movable side piece 11 the side of which can slide by a spring 10 is formed in a fixed side mold 9. A thermoplastic resin 15 passes through a sprue 13 and a gate 11 to be injected into the cavity opened in excess of a prescribed size t1. The injection amount of the resin 15 is set to be 1.09-1.2 times as large as the volume of the cavity. When the temperature of the resin 15 is at least its solidification temperature, mold clamping force is increased, and the resin 15 is compressed promptly to be packed in the cavity. When the specific volume of the resin 15 in the cavity is 1.005-1.07 times as large as that of a molding, the mold clamping force is decreased gradually to keep the compression.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection compression molding method, and more particularly to a method for molding a light guide plate used in a surface light emitting device of a liquid crystal monitor having a maximum thickness of 4 mm or more or a thickness variation of 15 inches or more. About.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices (hereinafter referred to as "liquid crystal") have been increasing in size, and their applications have been expanded from display of a notebook personal computer to liquid crystal monitors in place of CRT monitors, and have begun to appear on the market. The size of the liquid crystal monitor is 15 to 18 inches, which is larger than that of the conventional liquid crystal, and high brightness is required for a CRT monitor. In the conventional notebook personal computer, the cold cathode tube of the light source of the light guide plate of the surface emitting device used for the liquid crystal is one light, the diameter is about 2 mm, the number is one, and the thickness of the light guide plate is about 2 mm. The obtained luminance is sufficiently ensured. However, in the case of a CRT monitor, the brightness is insufficient in this case, and the cold cathode tube has a diameter of 2-3 mm.
A light guide plate is also required to have a thickness of 4 to 9 mm in order to require a book and guide the light effectively.

[0003] Most of the surface-emitting display devices of liquid crystal monitors that are currently on the market are obtained by cutting a transparent plate formed by sheet molding and polishing the cut end to a mirror surface by polishing with a buff or the like. . In this case, the work of cutting out and polishing the plate is troublesome, and it is very difficult to reduce the cost and mass-produce. Therefore, an injection molding method that can produce a light guide plate product in one step is conceivable.However, in injection molding, when it becomes large and thick, sink and warpage caused by the difference in cooling rate and shrinkage rate between the inside and outside of the thick part are considered. Occurs. In addition, in order to suppress this sink mark, we will apply a high pressure,
The molded product is distorted. If the distortion in the molded product is large, the light from the light source does not enter straight, and the surface light emission of the light guide plate causes uneven brightness. If the injection speed is reduced and molded to reduce this distortion, the resin is cooled and solidified when the molten resin comes into contact with the mold, the resin stops without flowing, and at that point, the overall distortion due to the filling pressure Becomes larger on the contrary. Also, in particular, the light guide plate injects the resin by the side gate method, but the larger the size, the longer the flow distance, so if the injection speed is slowed down, the resin on the mold surface solidifies during filling and the flow mark Tends to occur. In order to prevent the flow mark, the mold temperature must be sufficiently high, and therefore, the molding cycle becomes long, and a light guide plate of 4 to 9 mm by injection molding has not been put to practical use at present. In order to solve this problem of injection molding, injection compression molding as disclosed in JP-A-55-39355, JP-A-52-14657 and the like can be considered. In injection compression molding, an extra mold cavity is opened for compression and injection is performed, and the mold is clamped while compressing, or resin is injected into the mold cavity, and the mold is expanded by the injection pressure and compressed. This is a method of performing mold clamping. However, in practice, the quality of the molded product is greatly affected by the opening amount of the mold, the amount of the injected resin and the mold clamping force, and the sample obtained by injection compression molding has a worse sample than that obtained by the conventional injection molding. It turns out to happen. In another known technique, Japanese Patent Application Laid-Open No. 9-76310, the amount of extra opening for compression is 0.5 to 2% of the maximum thickness.
It is. Further, Japanese Patent Application Laid-Open No. 60-110419 discloses that the opening amount of a mold at the time of injection filling is kept in a range of 0.5 to 3.0 mm. But required,
In order to prevent sink marks, distortion, and warpage, this method alone produces flow marks if the resin temperature and mold clamping force are not devised, leaving mechanical distortion in the mold, especially in the parting line, resulting in non-defective products. It turned out that it could not be collected. In addition, in injection compression molding, the relationship between how much the mold cavity is opened and the amount of the injection resin to be opened is important, but the relationship is unknown. In addition, Japanese Patent Publication No. 4-60016 describes that the pressure is reduced once during cooling, then the pressure is increased over a plurality of times, and the pressure is reduced again. At this point, the resin expands to release the pressure, and then is pressurized again. Then, the expanded resin is subjected to pressure contraction. Japanese Patent Application Laid-Open No. Hei 5-31774 proposes a method of performing compression molding by lowering the mold clamping force during holding pressure or cooling. In this method, the mold is opened with the resin pressure and the resin amount from the mold-clamped state. In this method, distortion near the gate remains and the entire distortion is uniform, but the absolute distortion amount is large. This is not preferable in the field of optical components. In addition, the mold clamping force is reduced immediately after the filling, but in this case, the transferability of the originally intended mold is deteriorated because the pressure is weakened.

Further, the light guide plate is required to have a light exit surface, a reflection surface, and a light entrance surface, and a gate cannot be used directly on this surface, so that the gate becomes a side gate. Each surface of the light guide plate will be described with reference to the cross-sectional view of FIG.
Is a light emitting surface 3 and the opposite surface is a reflecting surface 4. The surface facing the cold cathode tube 5 is the light incident surface 6. The cold cathode tube 5 is provided with a reflector 8 on the opposite side of the light guide plate so that light can effectively enter the light guide plate. On the reflective surface side, a reflective sheet 7 is generally used. Between the liquid crystal panel 2 and the light guide plate 1, a prism sheet for adjusting brightness or a diffusion sheet for diffusing, called a bef, is sometimes sandwiched. Side gates are commonly used on one of the remaining two sides. In this case, when the resin is injected, the resin is biased toward the mold cavity near the gate. In order to compress this and spread the resin over the entire cavity, especially the relationship between this mold opening amount, changing resin temperature, and mold clamping force,
The flow distance of the resin after the injection and the influence of the resulting distortion due to the flow become important.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems existing in the prior art, and particularly has the problems of flatness, sink mark, distortion, and the like, which are problems with thick and large optical components.
An object of the present invention is to provide a method of manufacturing a thick large-sized optical component that solves the problem of cracks.

[0006]

SUMMARY OF THE INVENTION According to the present invention, when a thermoplastic resin is injection-molded, the mold cavity is opened in an extra thickness direction and the volume of the cavity is increased by 1.
Inject the resin in an amount of 09 times or more and 1.20 times or less, further start the compression of the mold while the molten resin in the cavity is at or above the solidification temperature to fill the resin into the mold cavity, When the volume of the resin becomes 1.005 times or more and 1.07 times or less of the volume of the cavity, the mold clamping force is reduced, and the resin is further compressed with the reduced mold clamping force or a weaker clamping force. After cooling and solidifying, the mold is opened and a molded product is taken out to obtain an injection compression molding method.

[0007] This is because the mold cavity is opened sufficiently in the thickness direction, the injection pressure is reduced as much as possible, the distortion due to the resin pressure and the injection pressure is reduced as much as possible, and the compression stroke is largely divided into two steps. Spread the resin into the cavity with a uniform pressure in the step, reduce the mold clamping force in the next step, and once reduce the mold clamping force so as not to apply the distortion due to the mold clamping force, to eliminate optical defects due to distortion. By improving, a desired molded product can be obtained.

Hereinafter, the present invention will be described in detail. The thermoplastic resin of the present invention is classified into an amorphous thermoplastic resin and a crystalline thermoplastic resin. Specific examples of the amorphous thermoplastic resin of the present invention, polystyrene, polyvinyl chloride, acrylic resin, styrene resin, polyarylate, modified polyphenylene ether resin, polycarbonate resin, polyetherimide, polyether sulfone, It is a thermoplastic plastic material such as polysulfone or a blend of one or more of these plastic materials.

The styrenic resin of the present invention is a homopolymer or a copolymer containing styrene as an essential component, and a polymer blend obtained by obtaining these polymers from other resins. The styrenic resin of the present invention is polystyrene or AB
It is preferably S resin. The polystyrene of the present invention is a styrene homopolymer or a rubber-reinforced polystyrene in which rubber is distributed in a resin phase.

The modified polyphenylene ether resin of the present invention is a resin obtained by melt-kneading polyphenylene ether, and a polymer alloy or polymer composite obtained by mixing and melting polyphenylene ether with another composition. The acrylic resin of the present invention includes, for example, a resin mainly composed of methyl methacrylate. Specifically, a homopolymer of methyl methacrylate, or methyl methacrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, butyl acrylate, acrylonitrile, acrylic acid, methacrylic acid, vinyl pyridine, vinyl morpholine, vinyl pyridone tetrahydro Furfuryl acrylate, N, N-dimethylaminoethyl acrylate,
N, N-dimethylacrylamide, 2-hydroxyacrylate, ethylene glycol monoacrylate, glycerin monoacrylate, maleic anhydride, styrene,
Alternatively, a copolymer of at least one of copolymerizable monomers such as α-methylstyrene, a heat-resistant acrylic resin, a low-hygroscopic acrylic resin, an impact-resistant acrylic resin, and the like are included. The impact-resistant acrylic resin is obtained by blending an acrylic resin with impact resistance, and is obtained by blending an acrylic resin with a rubber elastic body.
It is disclosed in JP-A-3-58554, JP-A-55-94917, JP-A-61-32346 and the like. Briefly, a multi-stage polymer produced by a multi-stage sequential polymerization method in which an elastic layer and an inelastic layer are alternately formed around an acrylic polymer core material. These acrylic resins may be used alone or as a polymer blend. Further, the polymerization method is not particularly limited.

As the polycarbonate resin of the present invention, a polymer derived from a divalent phenolic compound represented by bisphenol A is used. The method for producing the polycarbonate resin is not particularly limited, and a resin produced by any of the phosgene method, the transesterification method, and the solid-state polymerization method can be used. The cyclic polyolefin resin of the present invention is a polymer having a cyclic olefin skeleton in a polymer chain or a copolymer containing these, such as nobornene or cyclohexadiene, and belongs to an amorphous thermoplastic resin.
The manufacturing method is not particularly limited.
For example, cyclic polyolefin resins mainly containing nobornene are disclosed in JP-A-60-168708, JP-A-62-252406, and JP-A-62-252406.
JP, JP-A-2-133413, JP-A-63-163
145324, JP-A-63-264626, JP-A-1-240517, JP-B-57-88.
Resins described in JP-A No. 15 can be used.

Specific examples of the crystalline thermoplastic resin of the present invention include high-density polyethylene, low-density polyethylene,
Thermoplastic plastic materials such as linear low-density polystyrene, polypropylene, syndiotactic polystyrene, polyethylene terephthalate, polybutylene terephthalate, wholly aromatic polyester, polyacetal, polyamide resin, polyetheretherketone, polyetherketone, and the like. A blend in which one or more plastic materials are mixed, and a blend in which an amorphous thermoplastic resin and a crystalline thermoplastic resin are mixed.

The shape of the thermoplastic resin material in the present invention is not particularly limited, and any of granular, pellet and powder forms can be used. Among the thermoplastic resins in the present invention,
Acrylic resin, polycarbonate resin, and cyclic olefin resin, which are transparent resins, are preferred. Further, in the present invention, a composition containing a thermoplastic resin obtained by adding a desired additive to the thermoplastic resin as required and as necessary may be used.
Additives include heat stabilizers, antioxidants, UV absorbers,
Surfactants, lubricants, fillers, flame retardants, pigments, dyes, optical brighteners, impact modifiers, polymer additives, fillers,
Glass fibers, carbon fibers, inorganic fibers, peroxides, organic crosslinked polymer beads, inorganic beads, glass beads, silicon beads, and the like.

Particularly, optical components are used as a light guide plate material for a liquid crystal monitor, a light diffusing material is used as a stabilizer such as organic crosslinked polymer beads or inorganic beads, and a UV absorber, an antioxidant,
A composition containing a thermoplastic resin in which a heat stabilizer is added to an acrylic resin, a polycarbonate resin, or a cyclic olefin resin, which is a transparent resin, may be used. The injection compression molding machine used in the present invention is not particularly limited, and an ordinary in-line type injection compression molding machine with a horizontal clamping type is used.
If necessary, a vented injection compression molding machine having a vent in the middle of the heating cylinder may be used. As a program,
Since the mold clamping force is divided into at least two stages, it is preferable that the mold clamping control can be programmed in multiple stages.

The processing temperature conditions in the melting and injection molding of the thermoplastic resin in the present invention are not particularly limited, but in the case of an amorphous resin such as an acrylic resin, a styrene resin, a polycarbonate resin, a cyclic olefin resin, etc. The glass transition temperature of the resin is preferably + 250 ° C or lower. In the case of a crystalline resin such as polyethylene terephthalate and polybutylene terephthalate, the melting point of the thermoplastic resin +
200 ° C. or lower is preferred. The processing temperature condition is the temperature of the resin in the heating cylinder. If there is no substantial difference, the set temperature of the injection molding machine can be substituted. In the case of an amorphous resin, if the processing temperature is higher than the glass transition temperature + 250 ° C., thermal decomposition of the resin itself occurs, and the moldability becomes unstable due to this factor, which is not preferable. More preferably, the glass transition temperature +20
0 ° C. or less. In the case of a crystalline resin, the melting point is more preferably + 150 ° C. or lower. The glass transition temperature of the amorphous resin and the melting point of the crystalline resin are determined according to JIS K 712.
1 and can be measured using DSC or DTA.

The volume of the mold cavity in the present invention refers to the volume according to the inner dimensions of the mold, regardless of whether the mold shrinkage rate is expected or not. Further, the behavior of the mold and the resin in the present invention will be described with reference to FIGS. The points are as follows. In other words, by injecting the mold after opening the mold cavity to a sufficient size, the distortion due to the injection and the increase in the resin pressure due to the movement of the injected resin in the narrow mold are reduced, and the thermoplastic resin is reduced. While the temperature is higher than the glass transition temperature, compression is performed to minimize the distortion of the resin surface in contact with the mold, and after filling the mold cavity with resin, the mold clamping force is reduced to reduce distortion due to compression. Compression. Referring to the drawings, FIG. 2 shows a state in which the mold cavity is excessively opened by a sufficient width t1. FIG. 3 shows a state where the thermoplastic resin is injected into the state of the mold shown in FIG. FIG. 3 shows a state in which the thermoplastic resin injected by compression is filled in the mold cavity which is excessively opened. FIG. 4 shows a state immediately before the compression is weakened, and t2 is a state in which the cavity is still opened by t2 at that time. The mold structure shown in FIGS. 2 to 4 can be compression-molded by providing a movable side piece 11 whose side surface slides by a spring 10 in order to open a mold cavity in the fixed side mold 9 excessively. . In the state of FIG. 3, the thermoplastic resin 15 passes through the sprue 13 and the gate 11,
It exists in the mold cavity which is excessively opened by t1 in the dumpling state, the injection pressure may be low, and the stress on the mold surface is small, so that the increase in the pressure inside the resin is low and the distortion is small. Since the thickness is large, the amount of resin in the mold cavity is large, but since the volume of the mold cavity is large, the injected resin does not receive an excessive pressure and the distortion is small. The mold and resin change from FIG. 3 to FIG. 4 by the process of filling the extra open cavity with resin by compression. At this time, the resin must be at or above the solidification temperature, and if it is lower than the solidification temperature, a fine circular pattern called so-called hesitation, in which the resin spreads on the resin surface, is generated, and the appearance is not good. Here, the fact that the temperature of the resin is equal to or higher than the solidification transition temperature is not the temperature of the resin on the surface of the mold but the temperature inside the resin. Since the mold is lower than the solidification temperature of the resin, the molten resin comes into contact with the mold and simultaneously forms a solidified layer called a skin layer.

The solidification temperature in the present invention indicates a glass transition temperature in the case of an amorphous resin and a melting point in the case of a crystalline resin, and can be measured by the method described above. For this reason, it is necessary here to increase the mold clamping force and quickly compress the resin while the resin is at or above the solidification temperature to fill the extra open cavity with the resin. Further, by performing the step of compressing while weakening the mold clamping force in FIG. 4, the mechanical distortion of the mold clamping force caused by cooling can be reduced. During this process, if the mold clamping force is equal to or weaker than the previous mold clamping force, mechanical force is applied to the corners and sides where the resin force in the mold cavity gathers, and distortion is likely to occur newly This is not good because it causes cracks.
If no mold clamping force is applied, cooling shrinkage will occur and sinks will easily occur, which is not good. It is preferable that the mold clamping force is weakened in accordance with the cooling shrinkage of the resin. In particular, in the case of a thick wall, the influence becomes large because the area of the corner or the side is large.

In the present invention, the amount by which the mold cavity is first opened extra, that is, t1 in FIG. 2 is preferably 3 to 30% with respect to the maximum thickness of the molded product. If less than 3%, when the molten resin flow front reaches the mold,
Since it is pressed by a metal mold with a large tree finger pressure, even if it compresses, it cannot be fully relaxed and distortion remains, which is not preferable. If it is greater than 30%, in the case of a horizontal type clamping mechanism, the resin flows due to gravity, which makes it difficult to control the resin and causes the resin to be unbalanced and generate burrs. In addition, a shift occurs between the mold and the resin, and a mark remains on the molded product. Further, since the compression stroke becomes too long, it takes a long time to compress and the resin cools, so that a flow mark is easily generated, which is not good. More preferably, it is 5 to 20%.

The injection amount of the resin in the present invention is not less than 1.09 times and not more than 1.2 times the volume of the mold cavity. This volume is the injection amount when the volume of the molded product becomes substantially equal to the volume of the mold cavity when the room temperature is reached after the completion of molding. As the injection amount, a volume can be obtained in advance by measuring the temperature, pressure and specific volume (PVT) of a constant weight, and the value can be used.

The PVT measurement is not particularly limited and can be obtained by a known method. As for the specific volume at the time of injection, the temperature is the injection temperature, and the pressure is the specific volume at 1 atm.
For example, the specific volume at 25 ° C. and 1 atm of the acrylic resin prepared by PVT measurement is 0.83 cm ³ / g,
When the injection temperature is 240 ° C., the PVT measurement is 250 ° C.
It is a specific volume of 1 atm, which is 0.93 cm ³ / g, and the injection amount is 1.12 times the volume of the mold cavity. If the injection amount is smaller than 1.09 times, the molding temperature is lowered, resulting in a short circuit, which is not preferable. If the ratio is more than 1.2 times, the thickness of the finally obtained molded article becomes large, so that the resin temperature must be increased, which is not good because resin burning and decomposition occur. Preferably it is 1.09 times or more and 1.2 times or less.

In the present invention, the start of compression is as follows.
It is preferable to perform the operation when the completion is at least 100% and less than 100%.
If it is less than 90%, the injection continues even if the resin is filled in the open mold cavity, so that the shape becomes the same as that of the normal pressure holding in injection molding, which is not preferable because distortion occurs. 100% injection
After completion, a change occurs between the movement of the resin due to the injection and the movement of the resin due to the compression, and thus a switching pattern or hesitation occurs, which is preferable. More preferably,
This is when the completion is 95% or more and less than 100%.

It is of the utmost importance in the molding method of the present invention that the timing of reducing the clamping force in the present invention, that is, the reduction of the clamping force in the state of FIG. As a result of research, it has been found that if the switching is performed too fast, the transfer of the mirror surface is deteriorated, and if the switching is performed too late, mechanical distortion occurs at corners and sides, causing luminance unevenness and cracks. In addition, when taken out after being cooled and solidified, the central portion of the side surface expands into a convex lens shape, which is not preferable as an optical component, particularly, a light guide plate which receives light from the side surface. further,
After the open mold cavity is filled with resin, it is important to reduce the mold clamping force. Until the mold is filled, high mold clamping force is used to give priority to the formation of the shape of the molded product, and thereafter, the effect of the mold clamping force changes from the shape stability of the molded product to mechanical distortion on the corners and sides . Therefore, by reducing the mold clamping force, the mechanical strain on the resin that continues to solidify is reduced, and the volume of the resin expands due to the previous resin pressure. It can be eased once. Also,
These are greatly related to the volume and volume shrinkage, and in the region where volume shrinkage is going to be positively performed, the mold clamping force is increased to maintain the shape of the molded product including sink marks and warpage.
When the transferability of the mold is positively performed and the volume shrinkage rate becomes low, the mold clamping force remains as mechanical strain, so that the mold clamping force is weakened to reduce the mechanical strain.

That is, when the specific volume of the thermoplastic resin in the mold cavity is 1.005 to 1.07 times the molded product, the mold clamping force is weakened. If it is smaller than 1.005 times, the above-mentioned clamping force remains without being fully relieved, which is not good. 1.07
If it is more than twice, the transferability of the mold is poor, and the surface of the molded product is not good. Preferably it is 1.008 times or more and 1.065 times or less, more preferably 1.01 to 1.06 times. The relationship of the specific volume of the thermoplastic resin in the mold cavity relative to the molded product is such that the volume of the thermoplastic resin in the mold cavity is
Since the open mold cavity is full, it can be obtained by observing the opening amount of the mold cavity, that is, the amount t2 in FIG.

The pressure for initial compression, the pressure at the time of weakening, the injection speed, and the injection pressure are not particularly limited, and are set within the range of the mold clamping force in ordinary injection compression molding. Further, the mold clamping force in the present invention is 10 MPa
It is better to start compression with the above clamping force. Particularly preferably, it is 20 MPa or more, and more preferably 30 MPa or more. Further, the pressure may be increased stepwise in accordance with the movement of filling the mold cavity with the resin. The mold clamping force is preferably weakened by a mold clamping force of 30% or more and 90% or less of the preceding clamping force. When the pressure is increased stepwise when compression is first started, the mold clamping force when the pressure is fully increased is 30% or more and 90% or more.
% Or less. More preferably, it is 50% or more and 80% or less. It is preferable that the mold clamping force is reduced, and thereafter, the compression is continued at a constant level with the reduced mold clamping force or further reduced. After weakening the mold clamping force,
If the mold clamping force is increased, the resin is distorted again and remains, which is not good. Preferably, after the mold clamping force is weakened, in order to prevent sink marks from occurring, it is preferable to continue the compression with the mold clamping force having a compression speed higher than the volume contraction speed. After the mold clamping force is weakened, the compression may be continued in a plurality of stages by reducing the mold clamping force as long as the pressure is not increased.

The amount of opening of the mold cavity in the present invention may be provided with a sensor for detecting the position of the tie bar of the movable mold, or the distance between the fixed mold and the fixed mold is detected by a dial gauge. Alternatively, the signal obtained from these may be reflected in the mold clamping force to control the mold clamping force by the mold opening amount. The mold in the present invention is not particularly limited, and a mold used in general injection molding is used. However, since the mold opening amount is widened, burrs may be generated between the movable side and the fixed side mold. is there. Therefore, it is preferable to use a mold having an intaglio structure in which the structure of the fixed mold and the movable mold forming the gate portion can slide in the opening and closing direction of the molding machine. However, due to the thermal expansion of the mold, the inro part may collide with the mold, causing the mold to be chipped, thereby causing burrs. In order to prevent this, it is more preferable that the side surface on the core side of the mold cavity be a separate piece and slide using a spring. This mold structure is preferable because the distance between the molds and the mold clamping force can be controlled by a spring force, and no excessive pressure is applied to the resin.

It is preferable that the mold cavity in the present invention is filled with carbon dioxide gas. Air existing in the mold cavity is difficult to escape at the time of injection, and resin injection or air entrainment occurs due to application of the injection speed and injection pressure of the resin. In injection compression molding, the parting line surface (hereinafter referred to as the PL surface) is open. However, even if the mold cavity is excessively opened, resin leakage does not occur. Due to the swinging structure, there is a problem that it is difficult for air to escape. Especially in the case of thick and large molded products, since the mold cavity is deep, it is difficult for air in the mold cavity to escape, and the problem is remarkable. Only known gas escape allows air to escape from the deep mold cavity well. I can't do things.
By filling the mold cavity with carbon dioxide gas, resin burn is prevented. Further, since carbon dioxide gas is easily dissolved in the resin, entrainment hardly occurs. Further, when the mold is filled with carbon dioxide gas, the transferability of the mold is improved, so that it is particularly preferable to fill the carbon dioxide gas.

The carbon dioxide gas in the present invention is a gas containing 50% or more of carbon dioxide.
It may be a 100% gas, a liquid, or a gas containing the state of an individual. The conditions for filling the carbon dioxide gas in the present invention are not particularly limited, and the method for introducing the carbon dioxide gas may be from the PL surface, or the carbon dioxide gas may be injected from outside the mold into a gap in the mold cavity. In order to reliably fill the mold cavity, high-pressure carbon dioxide gas is continuously injected from the PL surface of the mold cavity into the mold cavity before the injection, until the start of the injection, or until the end of the injection. The injection pressure of carbon dioxide gas is preferably 0.2 to 5 MPa. More preferably, it is 1 to 3 MPa. In the case of injection compression molding, the PL surface is usually open, and the injection pressure of carbon dioxide gas injected into the mold cavity does not increase. In this case, open PL
By inserting an O-ring into the O-ring and crushing the O-ring during compression, it is possible to make it difficult for carbon dioxide gas to leak. Further, a groove may be dug inside the O-ring to surely introduce carbon dioxide into the mold cavity.

In the present invention, the gate seal is not particularly limited, but may be a gate seal mechanically in a mold or a nozzle of a molding machine. As a method of mechanically sealing a gate, a known method of performing a gate seal including a gate cut by displacing a mold piece near a gate from the outside with a hydraulic pressure or a method of performing a gate seal using a valve gate is also known. good. As a method of mechanically sealing the nozzle, a valve-type nozzle or a nozzle of a shut-off mechanism may be used. Of course, a gate seal of a type in which the resin is cooled and solidified is also possible.

The molded article of the present invention has a maximum thickness of 4 mm or more, particularly preferably a maximum thickness of 5 mm or more and an image area of 60 mm or more.
It is preferable for a thick large molded product having a size of 0 cm ² or a maximum length of 300 mm or more. The shape of the liquid crystal monitor light guide plate in the present invention is a rectangular parallelepiped or uneven wedge shape,
There are no particular limitations on both sides, such as a chopstick shape, a shape obtained by removing an ellipsoid from a rectangular parallelepiped, and a maximum thickness of 4 mm or more, particularly preferably a maximum thickness of 5 mm or more, and an image area of 600 cm ² or a diagonal length. This is particularly preferable for a 15-inch liquid crystal monitor light guide plate. Also, its surface is
It may be a mirror surface or a fine pattern. The shape may have ribs and standing walls. If there are ribs or standing walls, their height is not included in the maximum thickness.

The light guide plate has a large influence on its brightness and uniformity due to sink marks and distortion. Further, as the light guide plate shape, all six surfaces may be mirror surfaces, and the surface on which light enters may be a mirror surface on which light exits and / or the opposite surface is formed with fine irregularities. Is also good. The fine pattern is a geometrical shape such as a prism, a lens, a rectangular parallelepiped, a cube, a cone, a triangular prism, an elliptical cone, or the like, or an irregular shape such as a satin shape. May be. By changing the arrangement, regularity, shape, and size of the fine pattern formed on the light guide plate, the performance as surface light emission can be controlled. For this reason,
The shape may be the same in the aggregate,
A mixture of a plurality of shapes may be used, and the sizes thereof may be different. Further, it is preferable that the ratio between the shape height of the constituent units and the arrangement pitch is (height / pitch) = 0.2 to 500. This relationship may change arbitrarily within this range in the vertical or horizontal direction.

[0031]

Hereinafter, the present invention will be described more specifically with reference to examples. The thermoplastic resin used for molding is an acrylic resin (Delpet 80NH manufactured by Asahi Kasei) and is in the form of pellets before molding. The solidification temperature of this resin is J
It was 100 ° C. as measured by DSC (7 series manufactured by PerkinElmer) based on IS K7121.

The molding machine is a mold clamping force 300 manufactured by Komatsu Ltd.
t of IP-1050 was used. The shut-off mechanism of the nozzle part attached to this molding machine was used as a seal for supplying resin. In addition, the opening amount of the mold was determined by using a tie bar position detection mechanism attached to the machine. For the volume of the resin, a PVT resin property measuring device manufactured by GNOMIX was used. In brief, this machine is a system in which a resin is put into mercury by a bellows method using mercury, and the specific volume of the resin is obtained by a change amount of the bellows when a temperature and a pressure are applied. The mold is a light guide plate mold 1 in which the mold cavity is a 6-mirror surface having a thickness of 6 mm, a length of 324 mm, and a width of 243 mm, and the other is a mold cavity having a thickness of 6 m.
m, length 324mm, width 243mm, 324mm × 24
One surface of 3 mm has a fine shape, and the remaining five surfaces are mirror-finished light guide plate molds 2. As shown in FIG. 5, the fine shape means that the light guide plate molded product 16 has a height a of 32 μm, the arrangement pitch b is constant at 250 μm in the vertical direction, and the arrangement pitch b is 710 from both ends to the center in the horizontal direction. ~ 190μ
The rectangular parallelepiped shape units sequentially changing in the range of m are arranged.

As shown in FIG. 6, the mold structure is of a side gate type, the sprue 17 has a length of 130 mm, the sprue diameter on the gate 18 side is 12 mm, and the gate 18 has a width of 30 m.
m, a fan gate having a thickness of 3 mm was used. The mold structure for compression is such that the movable cavity 21 on the side surface of the movable mold 19 is slid by the spring 20 so that the mold cavity can be opened extra. In detail, the gate 18 has an intaglio structure between the gate 18 and the fixed-side mold 21, and the resin does not leak from the gate 18 even if the mold cavity is opened extra and injected. (Measurement of flatness): About 324 mm x 243 mm plane of the molded product, 324 m vertically from 1 mm inside from the end
The thickness at each of a total of 81 points, 9 points of 8 equal parts on the m side and 9 points of 8 equal parts in the 243 mm width direction, is measured with a three-dimensional roughness meter (Mitsutoyo Seimitsu's three-dimensional roughness meter MACROCORD
AE122), and the difference between the maximum value and the minimum value was calculated to determine the flatness. (Measurement of sink mark): Gate 24 of light guide plate molded product 23 obtained as shown by the thick line in FIG. 7 with a surface roughness meter (3-D roughness meter R-600 manufactured by Mitutoyo Seimitsu) according to JIS-B0601. The surface shape between the 20 mm portions at the side end was measured. (Measurement of distortion): The distortion was examined by making a polarizing plate orthogonal by 90 ° using a strain meter. A molded product was placed between polarizing plates, and the distortion was measured. As shown in FIG. 8, the measuring method is such that the polarizing directions of the upper and lower polarizers 25 are orthogonal to each other, and the light guide
Are arranged in parallel, and light is emitted from the white light source 27 from below. The luminance is observed from a position 70 cm directly above using a luminance meter 28 (CS-1000 manufactured by Minolta). If there is no distortion, the sample is dark, but if the sample is distorted, the polarization of light changes as it passes through the sample, making it whiter and brighter. The luminance was measured, the maximum value and the minimum value of the luminance were obtained, and the degree of distortion and distortion unevenness were examined. (Measurement of crack after environmental test): 60 ° C., 90 RH%
The molded article is suspended for 100 hours in a constant temperature and high humidity
The number of cracks after 0 hour was measured. (Measurement of transferability): The shape of the molded product was measured for a part where the shape of the concaves and convexes of the mold was known using a surface roughness meter (3-D roughness meter R-600 manufactured by Mitutoyo Seimitsu) according to JIS-B0601. Sought its maximum height. Then, the ratio to the maximum height of the shape of the mold was determined as the transfer rate. (Practical measurement of luminance) A surface emitting device as shown in FIG.
4 mm in diameter from the two long sides of the light guide plate 31
The light guide plate mold I is molded on the reflective sheet 30 side by printing a white circle having a diameter of 1.6 mm and a pitch of 2.5 mm on the surface of the reflective sheet by screen printing. Then, the molded product of the light guide plate mold II is shown in FIG. 9 by using a luminance meter 32 (CS-1000 manufactured by Minolta) to measure the surface luminance of the light emitting surface with the fine uneven surface facing the reflective sheet 30 side. Point X near gate 33 shown and 20 points from point X
The luminance at the Y point separated by cm was measured, and the luminance difference was measured. The cold cathode tube 29 was a 4 mm diameter cold cathode tube manufactured by Harrison Electric Co., and was evaluated at an input voltage of 7V.

[0034]

[Example 1] Cylinder temperature 240 ° C, mold temperature 60
C., filling time: 5 seconds, and the gate seal closed the nozzle shut-off mechanism after the injection was completed to seal the supply of the resin. The mold used was a mold 1 for a light guide plate having six mirror surfaces. The mold cavity is opened with a force of 285 t and the opening amount is 1 mm (maximum mold cavity thickness 6.
(16.6% extra opening for 0 mm). Next, carbon dioxide gas was injected into the extra open mold cavity from the PL surface at a pressure of 2 MPa from 2 seconds before injection of the acrylic resin. Acrylic resin was injected in an amount of 1.12 times the volume of the original mold cavity, and when the injection was completed 99%, the mold clamping force was increased to 28%.
Compressed at 5t. The injection of carbon dioxide gas was terminated at the same time as the completion of the injection. After the mold cavity is filled with the resin, when the opening amount of the mold cavity is 0.3 mm (1.05 times the volume of the mold cavity), the mold clamping force is reduced to 150 t, and compression is continued. Cool and solidify for 75 seconds, then. The mold was opened and removed. At this time, the time from the start of injection until the mold was opened and taken out was 2 minutes.

[0035]

Embodiment 2 The first mold clamping force in Embodiment 1 was 195
After that, the mold was molded under the same conditions as in Example 1.

[0036]

Comparative Example 1 A light guide plate mold 1 having six mirror surfaces was used. The molding conditions were as follows: cylinder temperature 240 ° C, mold temperature 60
Injection was performed at a temperature of 300 ° C., a pressure of 300 t, a closed state, an injection speed of 80 cc / sec, a filling time of 5 seconds, a dwell time of 20 seconds, and a dwell pressure of 20 MPa. The opening amount of the mold was 0 mm, and injection was started when the fixed mold and the movable mold were completely in close contact with each other. The shut-off mechanism of the nozzle was closed after the dwell was completed. Two minutes after the start of the injection, the mold was opened and the molded product was taken out.

[0037]

[Comparative Example 2] The same conditions as in Comparative Example 1 were measured except that the dwell time was 10 seconds and the dwell pressure was 10 MPa.

[0038]

Comparative Example 3 Injection compression molding was performed in Example 1 while keeping the mold clamping force at 285 t.

[0039]

Example 3 A mold was formed in the same manner as in Example 1 except that a mold was used for the light guide plate 2 having a fine pattern on one surface and mirror surfaces on the remaining five surfaces.

[0040]

Comparative Example 4 Molding was performed in the same manner as in Comparative Example 1 except that a mold for a light guide plate having a fine pattern on one surface of the mold and mirror surfaces on the remaining five surfaces was used. Example, flatness of the comparative example, sink, distortion,
Table 1 shows the results of measuring cracks and transferability after the environmental test. In all of Examples 1 to 3, the difference between the maximum value and the minimum value of the thickness in each portion in the evaluation of flatness is small, and the flatness is high. No sink marks have occurred. The distortion is also the maximum value,
A molded product having a small minimum value and a small required distortion is obtained as an optical component. No crack was generated due to moisture absorption after the environmental test. As for the practical luminance, a light guide plate having no difference in luminance is obtained. The transfer of the mold was significantly improved as compared with Comparative Example 4. Comparative Examples 1, 2, and 4 have poorer planarity than Examples 1 to 3. In addition, sink marks have occurred. Many cracks are generated, which is not preferable as a light guide plate product. Many practical brightness differences occur,
Uniform surface emission is not good for a light guide plate. In Comparative Example 3, which is injection compression molding, the flatness, sink mark, and practicality could be improved as compared with other Comparative Examples. However, compared to the Examples, the distortion, particularly the minimum value, was high, and further cracks were generated, which is not preferable. . Regarding the transfer of the mold, the transfer rate of Comparative Example 4 was less than 50%, and the transfer was not sufficiently performed.

[0041]

[Table 1]

[0042]

According to the injection compression molding method of the present invention, the flatness of an optical molded product, for example, a surface light emitting device used for a liquid crystal monitor or the like can be improved, sink marks and cracks can be eliminated, and the amount of distortion can be greatly reduced. In addition, the transferability of the mold is good, and the performance of the optical component in practical use can be improved.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a surface light emitting device using a liquid crystal panel and a light guide plate.

FIG. 2 is a conceptual diagram of a cross section of a mold in a state in which a mold cavity is further opened by t1.

FIG. 3 is a conceptual diagram of a cross section of a resin and a mold when the resin is injected by opening a mold cavity by an extra amount of t1.

FIG. 4 is a conceptual diagram of a cross section of the resin and the mold when the mold cavity is compressed to an extra open state by t2.

FIG. 5 is a conceptual diagram of fine irregularities of the light guide plate formed by the light guide plate mold 2 used in the embodiment of the present invention.

FIG. 6 is a conceptual diagram of a cross section of the structure of a mold used in an embodiment of the present invention.

FIG. 7 is a schematic diagram of a measurement position of a sink mark amount in the embodiment of the present invention.

FIG. 8 is a conceptual diagram of a distortion measuring method according to the embodiment of the present invention.

FIG. 9 is a conceptual diagram of luminance measurement during practical use in an embodiment of the present invention.

[Explanation of symbols]

 1, light guide plate 2, liquid crystal panel 3, light exit surface 4, reflection surface 5, cold cathode tube 6, light entrance surface 7, reflection sheet 8, reflector 9, movable mold 10, spring 11, movable frame 12, fixed Side mold 13, sprue 14, gate 15, thermoplastic resin 16, molded product of light guide plate 17, sprue 18, gate 19, movable mold 20, spring 21, movable piece 22, fixed mold 23, light guide plate Molded product 24, Gate 25, Polarizer 26, Light guide plate molded product 27, White light source 28, Luminance meter 29, Cold cathode tube 30, Reflective sheet 31, Light guide plate molded product 32, Luminance meter 33, Gate 34, Reflector

Claims (5)

[Claims] In injection molding of a thermoplastic resin, a mold cavity having a volume of 1.09 times or more and 1.20 times or less with respect to the volume of the mold cavity is formed with the mold cavity being excessively opened in the thickness direction. Injecting the resin, further starting the compression of the mold while the molten resin in the cavity is at or above the solidification temperature, filling the resin in the mold cavity, and further reducing the volume of the resin to the volume of the cavity. 1.005 times or more 1.07
When it becomes less than double, the mold clamping force is weakened, the compression is continued further with the weakened mold clamping force or a weaker mold clamping force, and after cooling and solidification, the mold is opened and the molded product is taken out. Injection compression molding method. 2. A molded article molded by the injection compression molding method according to claim 1, having a maximum thickness of 4 mm or more and a projected area of 600 mm ² or more or a maximum length of the molded article of 300 m.
Injection compression molding method characterized by being a thick large-sized molded product having a thickness of at least m. 3. The injection compression molding method according to claim 1, wherein the mold cavity is filled with carbon dioxide gas before injection molding. 4. The injection compression molding method according to claim 1, wherein the thermoplastic resin is a transparent resin such as an acrylic resin, a polycarbonate resin, or a cyclic polyolefin resin. 5. The injection compression molding method according to claim 1, wherein the molded product according to claim 2 is a light guide plate for a liquid crystal monitor made of a composition containing the thermoplastic resin.