JP2005254818A - Method for molding resin-molded object and mold used for this method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve transferability by reducing the formation incidence of a cooling-solidified layer on the surface of a molten resin injection-packed into a cavity and realize high productivity by diminishing the generation of a weld-mark, a cold resin mark, a flow mark or the like. <P>SOLUTION: In the method for molding a resin molded object, a thermoplastic resin at a temperature above a transfer starting temperature is introduced into a cavity part constituted of a mold maintained at a temperature below the transfer starting temperature. Further, the thermoplastic resin, near the surface of the mold, the temperature of which drops below the transfer starting temperature due to the cooling of the resin by the mold, is injection-molded by the mold whose heat capacity of the surface part of the cavity part side is set so as to allow the thermoplastic resin to again rise to a temperature exceeding the transfer starting temperature after the packing of the thermoplastic resin in the cavity part. In this injection molding, the mold with a thin sheet member 2 having a low coefficient of thermal conductivity member which shows a lower coefficient of thermal conductivity than that of the thin sheet body 1, fitted to the back of the thin sheet body 1 constituting the cavity part, can be used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for molding a resin molded product and a mold used in the method. It is useful to mold a resin molded product having a fine concavo-convex structure on the surface according to the present invention. For example, according to the present invention, (1) a light guide plate used for a backlight of a liquid crystal display device, (2) a Fresnel lens sheet or lenticular lens sheet used for a screen of a liquid crystal projection television, a projector, etc. Lens sheets such as Fresnel lens sheets can be molded.

  In general, a molded product having a fine concavo-convex structure on the surface is formed by an injection molding method using a thermoplastic resin. An example of such a molded article is a light guide used for a backlight of a liquid crystal display device.

  Hereinafter, a conventional method for forming a light guide plate will be described. FIG. 7 shows a configuration of an illumination device used for a backlight of a liquid crystal display device. As shown in FIG. 7, the illuminating device is disposed on the light source 11 such as a cold cathode tube, the light guide plate 12 disposed so that the incident end face 12 a is positioned in the vicinity of the light source 11, and the surface of the light guide plate 12. The diffusion sheet 13 and the reflection sheet 14 disposed on the side of the light guide plate 12 opposite to the diffusion sheet 13 are configured. In the illuminating device having such a configuration, light from the light source 11 enters the light guide plate 12 from the incident end surface 11a, and the light incident on the light guide plate 12 is reflected by the surfaces of the diffusion sheet 13 and the reflection sheet 14. The light is transmitted in the direction opposite to the incident end face 12a. In the meantime, a part of the light exits from the surface of the light guide plate 12 to the outside of the light guide plate 12, passes through the diffusion sheet 13, and exits the illumination device as diffused light, whereby uniform illumination light is obtained.

  Conventionally, in the above illumination device, in order to obtain uniform diffused light, a pattern having a dense distribution such as dots is printed on the back surface (surface on the reflection sheet 14 side) of the light guide plate, or uneven processing is performed, A textured pattern or a prism-like dense distribution is processed.

  When a light guide plate is formed by injection molding, the processing of a pattern having a dot-like dense distribution on the light guide plate is generally a mold in which a concave / convex pattern opposite to a desired concave / convex pattern is formed in a predetermined region. It is done using.

  Due to the cooling solidified layer generated when the molten resin injected and filled into the cavity by the injection molding method is rapidly cooled in contact with the cavity surface, the transfer property is reduced to the light guide plate as in the optical recording medium substrate. It causes problems such as abnormal light emission, reduced intensity, deformation, poor appearance, and flow marks.

  Next, a conventional method for forming a lens sheet will be described. When manufacturing a lens sheet such as a Fresnel lens sheet or a lenticular lens sheet having a large area, a heated flat plate mold is brought into contact with the resin plate and pressed to apply the uneven lens surface of the lens mold surface to the resin mold. It is common to transfer it. However, this method has a problem that the molding cycle is long and the productivity is not high. Therefore, recently, a technique has been developed in which an ultraviolet curable resin is applied to a lens mold, a resin plate is placed on the lens mold, and ultraviolet rays are irradiated to form a lens using the ultraviolet curable resin.

  On the other hand, a relatively small Fresnel lens sheet, lenticular lens sheet, and the like are manufactured by an injection molding method using a synthetic resin. When a lens sheet is molded by an injection molding method, processing of the lens surface is generally performed using a mold in which a concavo-convex pattern opposite to the desired concavo-convex pattern is formed.

  Due to the cooling solidified layer that is generated when the molten resin injected and filled into the cavity by the injection molding method comes into contact with the cavity surface and is rapidly cooled, the lens sheet has reduced transferability, abnormal light emission, reduced strength, deformation, It causes problems such as appearance defects and flow marks.

  In the above-described conventional injection molding method, in order to suppress the generation of a cooling solidified layer that causes a decrease in transferability, generally molding such as increasing the temperature of the molten resin or increasing the filling speed. It is conceivable to take measures such as changing the conditions or controlling the mold temperature using a cooling / heating cycle temperature controller. However, in this method, the light transmittance decreases due to thermal deterioration or yellowing of the resin due to the extension of the molding cycle, so that the molded product that is in a high temperature state during molding is forcibly released from the mold. As a result, a problem arises in that the yield of the molded product is reduced due to deformation of the molded product, which is not sufficient as a countermeasure.

On the other hand, in order to reduce the temperature unevenness of the stamper, Patent Document 1 discloses a technique in which the stamper is brought into close contact with the mold using a magnet, and Patent Document 2 discloses that the stamper is brought into close contact with the mold by a viscous thin film. Techniques for making them disclosed are disclosed. In these methods, the entire transfer surface of the stamper in the mold can be uniformly cooled and the transfer property can be made uniform. However, the cooling and solidification layer of the filled resin can be reduced. The transferability cannot be improved. Furthermore, Patent Document 3 discloses a technique for coating a back surface of a stamper used for injection molding of a compact disk or the like with a material having a thermal conductivity of 7 × 10 ⁻² cal / cm · sec · ° C. or less. Document 4 discloses a technique for delaying the initial cooling of the thermoplastic material during molding by installing a heat insulating mold insert on the back surface of the stamper. However, the techniques described in these publications are supplied from the molten resin to the stamper because of insufficient consideration of the relationship between the physical properties of the resin used for injection molding and the heat capacity of the mold including the stamper. The heat immediately escaped to the mold, and the generation of the cooled solidified layer could not be suppressed, and sufficient transferability could not be realized.

JP-A-3-26616 Japanese Patent Laid-Open No. 4-224921 Japanese Patent Laid-Open No. 62-180541 JP-A-7-178774

  The molding method of the resin molded product of the present invention has been made to solve the above-mentioned problems, and improves transferability by reducing the formation of a cooling solidified layer on the surface of the molten resin injected and filled in the cavity. An object of the present invention is to provide a molding method that realizes high productivity by reducing the occurrence of weld marks, cold resin marks, flow marks, and the like. Moreover, the metal mold | die of this invention is used for the shaping | molding method of the resin molded product of the said invention.

  In the molding method of the resin molded product of the present invention that solves the above-described problems, a thermoplastic resin having a temperature equal to or higher than the transfer start temperature is introduced into a cavity portion constituted by a mold that is held at a temperature equal to or lower than the transfer start temperature. Then, after the thermoplastic resin in the vicinity of the mold surface cooled to the temperature below the transfer start temperature after being cooled by the mold is filled with the thermoplastic resin in the cavity, the temperature again exceeds the transfer start temperature. Injection molding is performed using a mold in which the heat capacity of the surface portion on the cavity portion side is set so as to rise. In this specification, the transfer start temperature refers to the tangent to the graph of the phase transition region and the rubbery flat region when the relationship between the temperature of the thermoplastic resin used for molding and the longitudinal elastic modulus (storage modulus) is measured. This is the temperature obtained by the intersection with the tangent of the graph.

  It is useful to mold a resin molded product having a fine concavo-convex structure on the surface according to the present invention. For example, a light guide plate, a lens sheet, etc. can be formed by the method of the present invention. Also, the present invention can form a substrate of an optical functional product having an optical waveguide pattern.

  In the method for molding a resin molded product according to the present invention, the thin plate body having the first surface constituting the cavity portion is mounted on the cavity portion side, and the second surface, which is the surface facing the first surface, A low thermal conductivity member having a thermal conductivity smaller than that of the thin plate body is provided, and when a thermoplastic resin having a temperature equal to or higher than the transfer start temperature is introduced into the cavity, the transfer start temperature is equal to or lower than the transfer start temperature. After the thermoplastic resin in the vicinity of the mold surface cooled to a temperature lower than the transfer start temperature after being cooled by the mold having the temperature is filled with the thermoplastic resin in the cavity, the temperature again exceeds the transfer start temperature. A molding die for a resin molded product is used in which a thin plate member having a set heat capacity is mounted on the cavity side so as to rise.

  In order to shorten the time required for one cycle of injection molding, the thermal conductivity of the thin plate body is in the range of 30 to 100 kcal / m · hr · ° C. and the thickness is 0 as the molding die of the resin molded product. The heat conductivity of the low thermal conductivity member is in the range of 0.2 to 0.5 kcal / m · hr · ° C., and the thickness is 0.05 to 0.3 mm. It is preferable to use one having a thin plate member that is within the range. As the molding die for the light guide plate, it is preferable to include a low thermal conductivity member having the above-described thermal conductivity and thickness, and a thin plate member having the above-described thermal conductivity and thickness. Moreover, as a molding die for a lens sheet or an optical recording medium substrate, the thermal conductivity of the thin plate body is in the range of 30 to 100 kcal / m · hr · ° C., and the thickness is in the range of 0.3 to 0.6 mm. A low thermal conductivity member having a thin plate member having a thermal conductivity of 0.2 to 0.5 kcal / m · hr · ° C. and a thickness of 0.05 to 0.3 mm. Is preferred.

  According to the present invention, a resin molded product can be molded with high transferability. Therefore, for example, if a light guide plate, a lens sheet, and the like are molded according to the present invention, the desired performance can be realized even when the conventional method cannot transfer the image as the design is insufficient. In addition, since appearance defects such as weld lines do not occur in resin molded products, it is possible to obtain high-quality resin molded products that do not emit abnormal light, and there is no warping in high temperature or high humidity environments, so it is reliable. It is possible to obtain a highly molded resin molded product. Moreover, since it can transfer with a low internal pressure, it can shape | mold with a smaller molding machine conventionally, and can reduce cost. Furthermore, according to the present invention, it is possible to obtain a highly reliable substrate in which deformation due to residual stress is small.

  An example of the cross-sectional structure of the molding die of the resin molded product according to the present invention is shown in FIG. 1A, and an example of the planar structure is shown in FIG. This mold is attached to an injection molding machine and used for injection molding of resin molded products such as a light guide plate and a lens sheet. The metal mold 1 according to the present invention is provided with a thin plate member 2 in which one main surface constitutes a part of a cavity. The thin plate member 2 includes a thin plate main body 3 and a low thermal conductivity member 4, and one main surface (first surface) of the thin plate main body 3 forms a part of the cavity, and the main surface forms a part of the cavity. The low thermal conductivity member 4 is provided on another main surface (second surface) different from the surface. The back plate 5 of the mold 1 is engraved to a depth corresponding to the thickness of the thin plate member 2, and the thin plate member 2 is attached thereto. Here, the “main surface” refers to two opposing surfaces having a large area among the six surfaces constituting the thin plate member.

  Hereinafter, the reason why transferability is improved and generation of weld marks, cold resin marks, flow marks, and the like is reduced by the method for molding a resin molded product of the present invention will be described. Here, a case where a light guide plate is formed using polymethyl methacrylate resin will be described as an example.

  The result of having measured the relationship between the temperature of a polymethylmethacrylate resin (Kuraray Parapet HR-1000LC) and a longitudinal elastic modulus is shown in FIG. As shown in FIG. 2, when the relationship between the temperature of the polymethyl methacrylate resin and the longitudinal elastic modulus is measured (bending mode), and the temperature dependence of the storage elastic modulus is obtained, there is a temperature at which the slope of the graph changes greatly. The temperature is the transfer start temperature as used herein. As shown in FIG. 2, the transfer start temperature of the polymethyl methacrylate resin (Kuraray Parapet HR-1000LC) obtained by the intersection of the tangent of the graph of the phase transition region and the tangent of the graph of the rubber-like flat region is 128 ° C. It is.

The time after injection when the temperature of the mold is set to 85 ° C. and the temperature of the polymethyl methacrylate resin injected into the cavity (the measurement result shown in FIG. 2) is set to 280 ° C. (Second) and the temperature of the surface of the polymethyl methacrylate resin in contact with the mold are shown in FIG. 3 by the result of simulation by unsteady heat conduction analysis using MARC (manufactured by MARC). Here, as shown in FIG. 4, the thickness of the molded product is 3 mm, the thickness of the mold (made of carbon steel) is 25 mm, and the thickness of the thin plate body (made of nickel) is 0. Simulation is performed as 3 mm. The thermal conductivity of nickel in the thin plate body is 79.2 kcal / m · hr · ° C. The uneven structure formed on the surface of the thin plate main body has a height of 13 μm and a pitch of 30 μm. The filling time is 1.4 seconds, the molding cycle is 60 seconds, and the heat conduction coefficient on the cooling water side is 1.0 × 10 ⁻³ cal / mm ² · sec · ° C.

  Here, (a) of FIG. 3 is a simulation result when the thin plate member is not attached to the mold, and when polymethyl methacrylate resin having a temperature equal to or higher than the transfer start temperature is introduced into the cavity portion. The polymethyl methacrylate resin in the vicinity of the surface of the mold is cooled by a mold having a temperature not higher than the transfer start temperature, drops to a temperature not higher than the transfer start temperature, and does not exceed the transfer start temperature as it is. As described above, when the polymethyl methacrylate resin in the vicinity of the surface of the mold falls below the transfer start temperature, a cooling solidified layer is formed on the resin in the cavity. After the resin is filled in the cavity, pressure is applied to the resin in the cavity in the pressure-holding step, and the uneven pattern is transferred to the polymethyl methacrylate resin to obtain a molded product (light guide plate). At this time, since the cooling solidified layer formed on the polymethyl methacrylate resin near the surface of the mold is pushed into the concavo-convex pattern by pressure from the inside, orientation distortion, cooling distortion, etc. occur, and the weld mark, cold resin mark, A flow mark occurs.

  On the other hand, (b) and (c) of FIG. 3 show the time (seconds) after injection in the case of following the molding method of the resin molded product of the present invention and the temperature of the surface in contact with the polymethyl methacrylate resin mold. The result of simulating the relationship is shown. FIG. 3B shows a thermal conductivity of 0.126 kcal on one surface of a nickel thin plate body having a thermal conductivity of 79.2 kcal / m · hr · ° C. and a thickness of 0.3 mm. / M · hr · ° C., a polyethylene terephthalate low thermal conductivity member having a thickness of 0.1 mm is attached, and the same condition as in (a) is used, using a mold to which this thin plate member is attached. FIG. 3C shows the result of simulating the relationship between the time (seconds) after injection and the temperature by simulating in FIG. 3, except that the thickness of the low thermal conductivity member is 0.15 mm. It is the result of simulating on the same conditions as the case of (b).

  As shown in FIGS. 3 (b) and 3 (c), in the molding method of the resin molded product of the present invention, the mold is introduced into a cavity portion constituted by a mold held at a temperature not higher than the transfer start temperature. After the thermoplastic resin in the vicinity of the mold surface, which has been cooled by the mold and has fallen from a temperature higher than or equal to the transfer start temperature to a temperature lower than or equal to the transfer start temperature, is filled with the thermoplastic resin in the cavity, the transfer start temperature again. A mold is used in which the heat capacity of the surface portion on the cavity side is set so that the temperature rises above the temperature. When a molded product such as a light guide plate is molded using such a mold, a cooling solidified layer is formed in the vicinity of the mold surface by the resin temperature being equal to or lower than the transfer start temperature immediately after injection filling. Thereafter, when the resin temperature again exceeds the transfer start temperature, the cooling solidified layer that causes orientation strain, cooling strain, and the like disappears. As a result, the occurrence of weld marks, cold resin marks, flow marks, etc. can be suppressed.

  By the way, in order to prevent the cooling and solidifying layer from being formed, there is a technique in which only the surface of the mold on the cavity side is heated by radiant heat using an infrared heater or the like. However, this technique has a temporary effect in preventing the formation of a cooled solidified layer, but the surface on the cavity side of the mold must be heated for each cycle of injection molding. There is a disadvantage that the time required for the cycle becomes long.

  On the other hand, if molding is performed using a mold in which a thin plate member is attached to the cavity, as in the mold used in the molding method of the resin molded product of the present invention, the central portion of the resin in the cavity The temperature is not much different from the case where molding is performed using a mold not provided with a thin plate member. FIG. 5 shows the simulation results of the relationship between the time (seconds) after injection and the temperature of the surface of the polymethyl methacrylate resin in contact with the mold shown in FIG. 3, obtained by extending the time axis. The curve of (d) shown in FIG. 5 represents the temperature of the central portion of the resin in the cavity, and the temperature of the central portion is substantially the same regardless of the presence or absence of the thin plate member and the thickness thereof.

  When the light guide plate is to be molded according to the present invention, if the light guide plate has a concavo-convex pattern on the surface, the main surface constituting the cavity portion of the thin plate member is formed on the surface of the light guide plate. Concave / convex reverse to the concavo-convex pattern is provided. In addition, if the light guide plate to be molded has a textured surface, the surface of the thin plate member constituting the cavity portion is textured. Furthermore, if the light guide plate to be molded is printed with a dot-like pattern, the main surface constituting the cavity portion of the thin plate member remains a mirror surface (plane).

  If the light guide plate to be molded has a concavo-convex pattern or texture on both the front and back surfaces, a thin plate member may be provided on both sides of the mold cavity. If the concavo-convex pattern or texture is only on one side of the light guide plate, a thin plate member may be provided on one side of the cavity (surface with the concavo-convex pattern or texture), and the other surface may remain a mirror surface. You may provide (in this case, the surface of one thin-plate member is a mirror surface).

Even when a lens sheet is molded by the molding method of the resin molded product of the present invention, the transferability is improved, and the occurrence of weld marks, cold resin marks, flow marks, and the like is reduced. As shown in FIG. 6, this means that the thickness of the molded product is 2 mm, the thickness of the mold (made of carbon steel) is 25 mm, and the thickness of the thin plate body (made of nickel). The thickness was set to 0.3 mm, and the thickness of the low thermal conductivity member made of polyethylene terephthalate was set to 0.1 mm. Here, the temperature of the mold is set to 85 ° C., and the polymethyl methacrylate resin injected and filled into the cavity has the measurement result shown in FIG. 2, and this temperature is set to 280 ° C. The filling time is 1.4 seconds, the molding cycle is 60 seconds, and the heat conduction coefficient on the cooling water side is 1.0 × 10 ⁻³ cal / mm ² · sec · ° C.

  When the lens sheet is to be molded according to the present invention, the main surface constituting the cavity portion of the thin plate member is provided with irregularities opposite to the irregular pattern of the lens to be formed on the lens sheet. If the lens sheet to be molded has concave and convex lens surfaces on both the front and back surfaces, a mold having the structure shown in FIG. 1 may be provided on both surfaces of the cavity. If the uneven lens surface is only on one side of the lens sheet, the mold having the structure shown in FIG. 1 may be provided only on one side of the cavity, and the other surface may be a mirror surface.

  Even when the substrate of the optical recording medium is molded by the molding method of the resin molded product of the present invention, the transferability is improved and the occurrence of weld marks, cold resin marks, flow marks and the like is reduced.

  Examples of the method for mounting the thin plate member on the mold include a method of vacuum adsorption, a method of bonding with an adhesive, and a method of fixing using a magnet.

  The thermoplastic resin used in the method of the present invention is not particularly limited, and examples thereof include polymethyl methacrylate, polycarbonate, polystyrene, polypropylene, polyethylene terephthalate, polyvinyl chloride, thermoplastic elastomer, and copolymers thereof. .

  Hereinafter, the present invention will be described in detail by way of examples. First, the Example of the shaping | molding method of a light-guide plate is demonstrated.

(Examples 1-2)
As the thin plate main body, a nickel thin plate having a thermal conductivity of 79.2 kcal / m · hr · ° C., a thickness of 0.3 mm, and a size of 250 mm × 220 mm was used. On the cavity side surface of the thin plate main body, an isosceles prism-shaped uneven pattern having a pitch of 50 μm and a height of 25 μm is arranged. On the parting surface (surface opposite to the cavity) side of the thin plate body, the thermal conductivity is 0.3 kcal / m · hr · ° C., the thickness is 0.1 mm, and the size is 220 mm × 170 mm. A certain polyimide film (low thermal conductivity member) is bonded. In addition, the mold on which the thin plate member is mounted has a thickness of 0.3 mm and a size of 250 mm × 220 mm so as to correspond to a thin plate made of nickel which is a thin plate body, from the parting surface of the mold. Furthermore, it is engraved so as to have a thickness of 0.1 mm and a size of 220 mm × 170 mm so as to correspond to a polyimide film which is a low thermal conductivity member. A light guide plate could be molded by an injection molding method using a polymethylmethacrylate resin using a mold equipped with this thin plate member under the conditions shown in Table 1.

  When the internal pressure at which the prism shape was transferred was measured under the condition of the cylinder temperature of 270 ° C. using the above mold, it was 38 MPa.

(Comparative Example 1)
As a member constituting the cavity, a nickel thin plate having a thermal conductivity of 79.2 kcal / m · hr · ° C., a thickness of 0.3 mm, and a size of 250 mm × 220 mm was used (low thermal conductivity). The rate member is not provided.) On the cavity side surface of the thin plate main body, an isosceles prism-shaped uneven pattern having a pitch of 50 μm and a height of 25 μm is arranged. The mold on which this member is mounted has a size of 250 mm × 220 mm, and is carved from the parting surface of the mold by a thickness corresponding to a nickel plate. Using this mold, the same polymethyl methacrylate resin as in Examples 1 and 2 was used, and a light guide plate was molded by an injection molding method under the conditions shown in Table 1.

(Comparative Example 2)
Using the same mold as in Comparative Example 1, using the same polymethylmethacrylate resin at higher cylinder temperature and higher mold temperature than in Examples 1 and 2, and under the conditions shown in Table 1, injection molding The light guide plate was molded by this method.

(Comparative Example 3)
Table 1 shows the same polymethylmethacrylate resin, using the same mold as in Comparative Example 1, setting the medium temperature of the mold temperature controller to 100 ° C. until holding pressure, and 85 ° C. during cooling. Depending on conditions, a light guide plate was formed by injection molding.

  Among the comparative examples described above, in Comparative Example 1, the height of the prism was low and the transferability was low. When Comparative Examples 2 and 3 were used, the transferability was improved, but the molding cycle became longer. When the internal pressure at which the prism shape was transferred was measured under the condition of the cylinder temperature of 270 ° C. using the mold of Comparative Example 1, it was 55 MPa.

(Examples 3 to 9)
As the thin plate main body, a nickel thin plate having a thermal conductivity of 79.2 kcal / m · hr · ° C., a thickness of 0.3 mm, and a size of 250 mm × 220 mm was used. On the cavity side surface of the thin plate main body, an isosceles prism-shaped uneven pattern having a pitch of 50 μm and a height of 25 μm is arranged. On the parting surface (surface opposite to the cavity) side of the thin plate body, a polyimide film (low thermal conductivity member) having a thermal conductivity of 0.3 kcal / m · hr · ° C. and a size of 220 mm × 170 mm Is glued. Here, the thickness of the polyimide film was changed as shown in Table 2. Using the same polymethyl methacrylate resin as in Examples 1 and 2 using the above mold, a light guide plate was molded by an injection molding method under the conditions shown in Table 2. The measurement of the height of the prism of the obtained light guide plate, the appearance observation, and the warpage measurement by the environmental test were performed. The environmental test was performed by leaving the light guide plate in an environment of 65 ° C. × 90% RH for 300 hours, and the warpage of the light guide plate after 300 hours was measured with a chikness gauge.

  In the range where the thickness of the thin plate body is 0.1 to 0.6 mm as in Examples 3 to 9 and the thickness of the low thermal conductivity member is 0.05 to 0.3 mm, the transferability of the prism is high. There was no appearance defect such as a weld line, and a highly reliable molded product was obtained. Further, even under a high temperature and high humidity environment, almost no warping occurred.

  Next, an embodiment of a lens sheet molding method will be described.

(Examples 10 to 11)
As the thin plate main body, a nickel thin plate having a thermal conductivity of 79.2 kcal / m · hr · ° C., a thickness of 0.3 mm, and a size of 250 mm × 220 mm was used. A Fresnel lens pattern having an effective area of 220 mm × 166 mm, a pitch of 500 μm, and a height that gradually changes from 25 to 80 μm from the center to the outer periphery is disposed on the cavity side surface of the thin plate body. On the parting surface (surface opposite to the cavity) side of the thin plate body, the thermal conductivity is 0.3 kcal / m · hr · ° C., the thickness is 0.1 mm, and the size is 220 mm × 170 mm. A certain polyimide film (low thermal conductivity member) is bonded. A lens sheet was able to be molded by an injection molding method under the conditions shown in Table 3 using a polymethylmethacrylate resin using a mold equipped with this thin plate member.

  When the internal pressure at which the Fresnel lens pattern was transferred was measured under the condition of the cylinder temperature of 270 ° C. using the above mold, it was 45 MPa.

(Comparative Example 4)
As a member constituting the cavity, a nickel thin plate having a thermal conductivity of 79.2 kcal / m · hr · ° C., a thickness of 0.3 mm, and a size of 250 mm × 220 mm was used (low thermal conductivity). The rate member is not provided.) A Fresnel lens pattern having an effective area of 220 mm × 166 mm, a pitch of 500 μm, and a height that gradually changes from 25 to 80 μm from the center to the outer periphery is disposed on the cavity side surface of the thin plate body. The mold on which this member is mounted has a size of 250 mm × 220 mm, and is carved from the parting surface of the mold by a thickness corresponding to a nickel plate. Using this mold, the same polymethyl methacrylate resin as in Examples 10 to 11 was used, and a lens sheet was molded by an injection molding method under the conditions shown in Table 3.

(Comparative Example 5)
Using the same mold as in Comparative Example 4, using the same polymethylmethacrylate resin at higher cylinder temperature and higher mold temperature than in Examples 10 and 11, and under the conditions shown in Table 3, injection molding A lens sheet was molded by this method.

(Comparative Example 6)
Using the same mold as in Comparative Example 4, the medium temperature of the mold temperature controller is set to 100 ° C. until holding pressure, and 85 ° C. during cooling. Depending on conditions, a lens sheet was molded by an injection molding method.

  Among the above comparative examples, in Comparative Example 4, the Fresnel lens pattern has a low height and low transferability. When Comparative Examples 5 and 6 were used, the transferability was improved, but the molding cycle became longer. The internal pressure at which the Fresnel lens pattern was transferred under the condition of the cylinder temperature of 270 ° C. using the mold of Comparative Example 4 was 70 MPa.

(Examples 12 to 18)
As the thin plate main body, a nickel thin plate having a thermal conductivity of 79.2 kcal / m · hr · ° C., a thickness of 0.3 mm, and a size of 250 mm × 220 mm was used. A Fresnel lens pattern having an effective area of 220 mm × 166 mm, a pitch of 500 μm, and a height that gradually changes from 25 to 80 μm from the center to the outer periphery is disposed on the cavity side surface of the thin plate body. On the parting surface (surface opposite to the cavity) side of the thin plate body, a polyimide film (low thermal conductivity member) having a thermal conductivity of 0.3 kcal / m · hr · ° C. and a size of 220 mm × 170 mm Is glued. Here, the thickness of the polyimide film was changed as shown in Table 4. Using the same polymethyl methacrylate resin as in Examples 10 to 11 using the above mold, a lens sheet was molded by an injection molding method under the conditions shown in Table 4. Measurement of the height of the Fresnel lens pattern of the obtained lens sheet, appearance observation, and warpage measurement by an environmental test were performed. The environmental test was performed by leaving the lens sheet in an environment of 65 ° C. × 90% RH for 300 hours, and the warpage of the lens sheet after 300 hours passed was measured with a chikness gauge.

  In the range where the thickness of the thin plate body is 0.1 to 0.6 mm and the thickness of the low thermal conductivity member is 0.1 to 0.3 mm as in Examples 12 to 18, the Fresnel lens pattern is transferred. Highly reliable molded products without appearance defects such as weld lines were obtained. Further, even under a high temperature and high humidity environment, almost no warping occurred.

It is a figure which shows the mounting state to the metal mold | die of the thin plate member in this invention. It is a figure which shows the result of having measured the relationship between the temperature of a polymethylmethacrylate resin, and a longitudinal elastic modulus. It is a figure which shows the result of having calculated | required the relationship between the time (second) after injection | emission, and the temperature of the surface which touches the metal mold | die of a polymethylmethacrylate resin by the simulation by unsteady heat conduction analysis using MARC. It is a figure which shows the conditions of the simulation about the light-guide plate which obtained the result of FIG. It is the figure which expressed the simulation result of FIG. 3 extending the time axis. It is a figure which shows the conditions of the simulation about a lens sheet. It is a figure which shows the structure of the illuminating device using a light-guide plate.

Explanation of symbols

1 Mold 2 Thin plate member 3 Thin plate body 4 Low thermal conductivity member 5 Back plate

Claims (8)

A thermoplastic resin having a temperature equal to or higher than the transfer start temperature is introduced into a cavity formed of a mold held at a temperature equal to or lower than the transfer start temperature, and is cooled by the mold to be lowered to a temperature equal to or lower than the transfer start temperature. The heat capacity of the surface portion on the cavity side was set so that the thermoplastic resin near the surface of the mold was again raised to a temperature exceeding the transfer start temperature after the cavity portion was filled with the thermoplastic resin. A method for molding a resin molded product, which comprises injection molding using a mold. The thin plate main body, the first surface of which forms the cavity portion, is mounted on the cavity portion side, and the second surface, which is the surface facing the first surface, has a heat smaller than the thermal conductivity of the thin plate main body. The method for molding a resin molded product according to claim 1, wherein a mold having a thin plate member provided with a low thermal conductivity member having conductivity is used. The method for molding a resin molded product according to claim 1 or 2, wherein the resin molded product is a light guide plate. The method for molding a resin molded product according to claim 1 or 2, wherein the resin molded product is a lens sheet. A thin plate main body having a first surface constituting a cavity portion is mounted on the cavity portion side, and a second surface, which is a surface opposite to the first surface, has a thermal conductivity smaller than that of the thin plate main body. When a thermoplastic resin having a temperature equal to or higher than the transfer start temperature is introduced into the cavity portion, the transfer start temperature is cooled by a mold having a temperature equal to or lower than the transfer start temperature. A thin plate member whose heat capacity is set so that the thermoplastic resin near the surface of the mold, which has been lowered to the following temperature, rises again to a temperature exceeding the transfer start temperature after the cavity portion is filled with the thermoplastic resin. A mold for resin molded products, characterized in that is mounted on the cavity side. The thin plate body has a thermal conductivity of 30 to 100 kcal / m · hr · ° C., a thickness of 0.3 to 0.6 mm, and a low thermal conductivity member having a thermal conductivity of 0.2 to The molding die for a resin molded product according to claim 5, which has a thickness in the range of 0.5 kcal / m · hr · ° C and a thickness in the range of 0.05 to 0.3 mm. The molding die for a resin molded product according to claim 5 or 6, wherein the resin molded product is a light guide plate. The molding die for a resin molded product according to claim 5 or 6, wherein the resin molded product is a lens sheet.

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