JPH11129305A - Molding method of resin molded article and mold employed therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve transferability, reduce the occurrence of weld marks, cold resin marks, flow marks, etc., and achieve high productivity by lessening the formation of cool-curable layers on the molten resin surface filled in the cavity. SOLUTION: Thermoplastic resin having an equal or higher temperature than a transfer initiation temperature is introduced into a cavity defined by a mold retained at an equal or lower temperature than a transfer initiation temperature, and injection molding is carried out through the use of a mold having a set heat capacity in the surface part of the cavity side in order for thermoplastic resin in the proximity of the surface of a mold lowered to an equal or lower temperature than a transfer initiation temperature cooled by the mold to rise to a temperature beyond the transfer initiation temperature again after thermoplastic resin is filled in the cavity part. For the injection mold, a mold can be used which includes a sheet plate member 2 provided with a low heat conduction member having lower heat conduction than that of the sheet plate main body 1 on the rear surface of the sheet plate main body 1 forming the cavity part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a resin molded product and a mold used for the method. It is useful to mold a resin molded product having a fine uneven 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 screen of a liquid crystal projection television,
Lens sheets such as a Fresnel lens sheet or lenticular lens sheet used for a projector, a Fresnel lens sheet for condensing, and (3) a substrate of an optical recording medium for optically reproducing or recording / reproducing information such as images. Etc. can be molded.

[0002]

2. Description of the Related Art In general, a molded article having a fine uneven structure on its surface is formed by an injection molding method using a thermoplastic resin. Examples of such a molded product include a substrate of an optical recording medium. Optical recording media such as optical discs were compact discs (C
D) and laser disks (LD) became commercially available after the commencement of marketing. At present, studies are being made on the development of an optical disk that is thinner than conventional CDs and LDs and that has a large capacity data such as moving image information of about 2 hours digitally recorded on a CD-size transparent resin molded substrate. As a method for molding these large-capacity optical disks, from the viewpoint of mass productivity and cost, the substrate is formed by injection molding using a transparent resin and transferring pits or grooves on the surface of the stamper mounted on the mold. A molding method is generally used.

In the injection molding process of an optical recording medium substrate, a molten resin is injected and filled into a cavity of a mold, and in a pressure-holding process, the sprue or runner is melted through the molten resin until the gate is completely cooled and solidified. The shape of the mold is transferred by applying pressure to the mold. After the gate is solidified, the resin in the mold is cooled and solidified to obtain a molded product (optical recording medium substrate).

[0004] The molten resin injected and filled into the cavity by the above-mentioned injection molding method is rapidly cooled when it comes into contact with the cavity surface, and the cavity is filled with the molten resin while a cooled solidified layer is formed. The cooling and solidifying layer thus formed has poor transferability, generates weld marks and cold marks that occur at the junction of the filled molten resin and causes abnormal light emission, and the strength at the weld marks and cold marks. It causes deterioration, quality deterioration due to deformation due to residual stress, poor appearance due to deformation, and generation of flow marks.

Next, a conventional method of forming a light guide plate will be described. FIG. 9 illustrates a structure of a lighting device used for a backlight or the like of a liquid crystal display device. As shown in FIG. 9, the lighting device includes a light source 11 such as a cold-cathode tube, a light guide plate 12 arranged such that an incident end face 12 a is located near the light source 11, and a light guide plate 12 arranged on a surface of the light guide plate 12. And a reflection sheet 14 disposed on the side of the light guide plate 12 opposite to the diffusion sheet 13. In the illumination device having such a configuration, light from the light source 11 enters the light guide plate 12 from the incident end face 11 a, and the light incident into the light guide plate 12 is reflected by the surfaces of the diffusion sheet 13 and the reflection sheet 14. Are transmitted in the direction opposite to the incident end face 12a. In the meantime, some light is transmitted from the surface of the light guide plate 12 to the light guide plate 1.
2, the light passes through the diffusion sheet 13 and goes out of the lighting device as diffused light, so that illumination light with uniform luminance can be obtained.

Conventionally, in the above-mentioned lighting apparatus, in order to obtain uniform diffused light, the back surface of the light guide plate (the surface on the reflection sheet 14 side).
A pattern having a sparse / dense distribution such as a dot shape is printed, unevenly processed, embossed, or a pattern having a sparse / dense distribution in the shape of a prism is processed.

When a light guide plate is formed by an injection molding method, processing of a pattern having a sparse and dense distribution of dots on the light guide plate generally involves forming a concavo-convex pattern opposite to a desired concavo-convex pattern in a predetermined region. This is performed using a mold.

[0008] The cooling solidified layer 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 is transferred to the light guide plate similarly to the optical recording medium substrate. This causes problems such as reduction in light emission, abnormal light emission, reduction in intensity, deformation, poor appearance, and generation of flow marks.

Next, a conventional method of 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-shaped lens mold is brought into contact with a resin plate, and the pressure is applied to the uneven lens surface of the lens mold surface by the resin mold. It is common to transfer to However, this method requires a long molding cycle,
There is a problem that 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 thereon, and ultraviolet rays are irradiated to form a lens using the ultraviolet-curable resin.

On the other hand, relatively small-sized Fresnel lens sheets, lenticular lens sheets, 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 a lens surface is generally performed using a mold having a concave / convex pattern opposite to a desired concave / convex pattern on the lens surface.

[0011] As in the case of the optical recording medium substrate, the transferability of the molten resin injected into the cavity by the injection molding method to the lens sheet is increased by the cooling solidified layer generated when the molten resin is rapidly cooled in contact with the cavity surface. This causes problems such as reduction in light emission, abnormal light emission, reduction in intensity, deformation, poor appearance, and generation of flow marks.

[0012]

In the above-mentioned conventional injection molding method, in order to suppress the generation of a cooling solidified layer which causes a decrease in transferability, the temperature of the molten resin is generally increased. It is conceivable to take measures such as changing the molding conditions such as increasing the filling rate or controlling the mold temperature using a cooling / heating cycle temperature controller. However, in this method, the light transmittance is reduced due to the thermal deterioration or yellowing of the resin due to the extension of the molding cycle. At times, the molded product in a high-temperature state is forcibly released from the mold, thereby deforming the molded product, thereby causing a problem that the yield is reduced, which is not sufficient as a measure.

On the other hand, in order to reduce the temperature unevenness of the stamper, Japanese Patent Application Laid-Open No. 3-26616 discloses a technique in which a stamper is brought into close contact with a mold using a magnet. There is disclosed a technique in which a stamper is brought into close contact with a mold using a viscous thin film. According to these methods, the entire transfer surface of the stamper in the mold can be uniformly cooled, and the transferability of the optical recording medium substrate can be made uniform. Cannot be reduced, and transferability cannot be improved. Further, Japanese Patent Application Laid-Open No. 62-180541 discloses that 7 × 10 ⁻² cal / cm · sec ·
A technique for coating a substance having a thermal conductivity of not more than 0 ° C. is disclosed. JP-A-7-178774 discloses that a heat-insulating mold insert is provided on the back surface of a stamper, and the initial temperature of the thermoplastic material during molding is reduced. A technique for delaying cooling is disclosed. However, the techniques described in these publications have 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, and therefore have a higher density than CD or LD. If the techniques described in these publications are applied to the molding of recent optical discs having pits or grooves with finer shapes, for example, the heat supplied to the stamper from the molten resin escapes to the mold immediately. In addition, it was not possible to suppress the formation of the cooling solidified layer, and it was not possible to realize sufficient transferability.

The method of molding a resin molded article according to the present invention has been made to solve the above-mentioned problems, and the transfer property can be reduced by reducing the formation of a cooled and solidified layer on the surface of the molten resin injected and filled in the cavity. It is an object of the present invention to provide a molding method capable of improving weldability, reducing the occurrence of weld marks, cold resin marks, flow marks, and the like, and realizing high productivity. The mold of the present invention is used in the method of molding a resin molded product of the present invention.

[0015]

According to the present invention, there is provided a method for molding a resin molded article, comprising: converting a thermoplastic resin having a temperature equal to or higher than a transfer start temperature to a metal held at a temperature equal to or lower than a transfer start temperature; Introduced into the cavity formed by the mold, the thermoplastic resin near the surface of the mold cooled to a temperature equal to or lower than the transfer start temperature after being cooled by the mold, after the cavity portion is filled with the thermoplastic resin, Injection molding is again performed using a mold in which the heat capacity of the surface portion on the cavity side is set so as to rise to a temperature exceeding the transfer start temperature again. In the present specification, the transfer start temperature refers to a tangent line of a graph of a phase transition region and a rubber-like flat region when a relationship between a temperature of a thermoplastic resin used for molding and a longitudinal elastic modulus (storage elastic modulus) is measured. Means the temperature determined by the intersection with the tangent line in the graph.

According to the present invention, it is useful to mold a resin molded article having a fine uneven structure on the surface. For example,
A light guide plate, a lens sheet, a substrate of an optical recording medium, and the like can be formed by the method of the present invention. Further, the present invention can also form a substrate of an optical functional product having an optical waveguide pattern.

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

In order to shorten the time required for one cycle of the injection molding, the heat conductivity of the thin plate body should be 30 to 100 kcal / m · hr · ° C.
And the thickness is in the range of 0.03 to 0.6 mm, and the thermal conductivity of the low thermal conductivity member is 0.2 to 0.5 kc.
al / m · hr · ° C. and a thickness of 0.05 to
It is preferable to use one provided with a thin plate member having a range of 0.3 mm. It is preferable that the mold for forming the light guide plate includes 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. Further, as a molding die for a lens sheet or an optical recording medium substrate, the heat conductivity of the thin plate body is 30 to 100 kca.
1 / m · hr · ° C. and a thickness of 0.3 to 0.6
mm and the thermal conductivity of the low thermal conductivity member is 0.1 mm.
It is preferable to provide a thin plate member having a thickness of 2 to 0.5 kcal / m · hr · ° C. and a thickness of 0.05 to 0.3 mm.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 (a) shows an example of a sectional structure of a molding die for a resin molded product according to the present invention, and FIG. 1 (b) shows an example of a planar structure thereof. This mold is attached to an injection molding machine and used for injection molding of resin molded products such as a light guide plate, a lens sheet, and an optical recording medium substrate. The mold 1 according to the present invention is provided with a thin plate member 2 whose one main surface forms a part of the cavity. The thin plate member 2 is composed of 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 a cavity and a main part forming 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 carved to a depth corresponding to the thickness of the thin plate member 2, and the thin plate member 2 is mounted thereon. Here, the "principal surface" is two opposing surfaces having a large area among the six surfaces constituting the thin plate member.

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

FIG. 2 shows the measurement results of the relationship between the temperature and the longitudinal modulus of the polymethyl methacrylate resin (Kuraray parapet HR-1000LC). As shown in FIG. 2, when the relationship between the temperature and the longitudinal elastic modulus of the polymethyl methacrylate resin is measured (bending mode) and the temperature dependence of the storage modulus is obtained, there is a temperature at which the slope of the graph changes greatly. The temperature is the transfer start temperature referred to in the present specification. As shown in FIG. 2, a polymethyl methacrylate resin (Kuraray's Parapet HR) determined by the intersection of the tangent of the graph of the phase transition region and the tangent of the graph of the rubbery flat region
The transfer start temperature of (−1000 LC) is 128 ° C.

When the temperature of the mold was set at 85 ° C. and the temperature of the polymethyl methacrylate resin (obtained the measurement results shown in FIG. 2) injected and filled in the cavity was set at 280 ° C. The relationship between the time (seconds) and the temperature of the surface of the polymethyl methacrylate resin in contact with the mold was determined by MAR.
FIG. 3 shows a result obtained by a simulation based on an unsteady heat conduction analysis using C (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. 3 mm. The thermal conductivity of nickel of the thin plate body is 79.2 kcal / m · hr · ° C. The uneven structure formed on the surface of the thin plate body has a height of 13 μm and a pitch of 30 μm. Also, the filling time is 1.4.
The molding cycle is 60 seconds, and the heat transfer coefficient on the cooling water side is 1.0 × 10 ⁻³ cal / mm ² · sec · ° C.

Here, FIG. 3A shows a simulation result in the case where the thin plate member is not mounted on the mold, and the polymethyl methacrylate resin having a temperature higher than the transfer start temperature is introduced into the cavity. Then, the polymethyl methacrylate resin near the surface of the mold is cooled by the mold having a temperature equal to or lower than the transfer start temperature and falls to a temperature equal to or lower than the transfer start temperature, and does not directly exceed the transfer start temperature. As described above, the polymethyl methacrylate resin near the surface of the mold becomes lower than the transfer start temperature,
A cooling solidified layer is formed on the resin in the cavity. After the cavity is filled with the resin, pressure is applied to the resin in the cavity in a pressure-holding step, and the concavo-convex pattern is transferred to the polymethyl methacrylate resin to obtain a molded product (light guide plate). At this time, the cooling solidified layer formed on the polymethyl methacrylate resin near the surface of the mold is pressed into the concave / convex pattern by the pressure from the inside, so that orientation distortion, cooling distortion, etc. occur, and a weld mark, a cold resin mark, Flow marks and the like occur.

On the other hand, FIGS. 3 (b) and 3 (c) show the time (seconds) after injection and the surface of the polymethyl methacrylate resin in contact with the mold when the method of molding a resin molded article of the present invention is used. It shows the result of simulating the relationship with temperature. FIG. 3B shows that the thermal conductivity is 79.2 kc.
al / m · hr · ° C. and a heat conductivity of 0.12 on one surface of a nickel thin plate body having a thickness of 0.3 mm.
A low thermal conductivity member made of polyethylene terephthalate having a thickness of 6 mm / m · hr · ° C. and a thickness of 0.1 mm is attached, and a mold on which the thin plate member is attached is used.
FIG. 3C shows the result of simulating the relationship between the time (second) after injection and the temperature by performing a simulation under the same conditions as in FIG. 3A. FIG. 3C shows the thickness of the low thermal conductivity member. Is the result of a simulation under the same conditions as in the case of (b) except that is set to 0.15 mm.

As shown in FIGS. 3B and 3C,
In the method for molding a resin molded article of the present invention, the transfer is started from a temperature higher than the transfer start temperature by being introduced into the cavity formed by the mold held at a temperature equal to or lower than the transfer start temperature, and cooled by the mold. After the thermoplastic resin in the vicinity of the surface of the mold, which has been cooled to a temperature lower than the temperature, is filled with the thermoplastic resin, the surface portion on the cavity portion side is again heated to a temperature exceeding the transfer start temperature. Use a mold with a heat capacity of When a molded product such as a light guide plate is molded using such a mold, the resin temperature becomes equal to or lower than the transfer start temperature immediately after injection filling, whereby a cooled solidified layer is formed near the surface of the mold, Thereafter, when the resin temperature exceeds the transfer start temperature again, the cooled solidified layer causing alignment distortion, cooling distortion and the like disappears. As a result, the occurrence of weld marks, cold resin marks, flow marks, and the like is suppressed.

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 in order to prevent the formation of a cooled solidified layer. However, although this technique has a prima facie effect in preventing the formation of a cooling solidified layer, the surface on the cavity side of the mold must be heated every cycle of injection molding.
There is a disadvantage that the time required for one cycle of injection molding is long.

On the other hand, if molding is performed using a mold having a thin plate member mounted in a cavity portion, such as a mold used in the method for molding a resin molded product of the present invention, the resin in the cavity is formed. The temperature at the center does not change much compared to the case where molding is performed using a mold to which no thin plate member is attached.
FIG. 5 shows a simulation result of the relationship between the time (second) 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.
Shown in The curve (d) shown in FIG. 5 represents the temperature at the center of the resin in the cavity. The temperature at the center is almost the same regardless of the presence or absence of the thin plate member and the thickness of the thin plate member.

When a light guide plate is to be formed according to the present invention, if the light guide plate has an uneven pattern on its surface, the main surface constituting the cavity portion of the above-mentioned thin plate member is formed on the surface of the light guide plate. The concavities and convexities opposite to the concavo-convex pattern to be formed are provided. If the light guide plate to be molded has a textured surface, the main surface constituting the cavity of the thin plate member is textured. Furthermore, if the light guide plate to be molded has a dot-like pattern printed thereon, the principal surface of the cavity of the thin plate member remains a mirror surface (flat surface).

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

According to the method for molding a resin molded article of the present invention, even when a lens sheet is molded, transferability is improved, and the occurrence of weld marks, cold resin marks, flow marks, etc. is reduced. This means that, as shown in FIG. 6, the thickness of the molded product is 2 mm, the thickness of the mold (made of carbon steel) is 25 mm, and the thin plate body (made of nickel).
The thickness was 0.3 mm, and the thickness of the low thermal conductivity member made of polyethylene terephthalate was 0.1 mm, and the results were simulated in the same manner as in the light guide plate molding method described above. Here, the temperature of the mold is set to 85 ° C., and the polymethyl methacrylate resin injected and filled into the cavity has obtained the measurement results shown in FIG. 2, and this temperature is set to 280 ° C. The filling time was 1.4 seconds, the molding cycle was 60 seconds, and the heat transfer coefficient on the cooling water side was 1.
0 × 10 ⁻³ cal / mm ² · sec · ° C.

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

According to the method for molding a resin molded article of the present invention, even when a substrate of an optical recording medium is molded, transferability is improved,
The occurrence of weld marks, cold resin marks, flow marks, and the like is reduced. This means that, as shown in FIG. 7, the thickness of the molded product is 0.6 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 uneven structure formed on the surface of the thin plate body has a height of 0.1 μm and a pitch of 1.4 μm. The temperature of the mold is set at 85 ° C., and as a resin to be injected and filled into the cavity, an acrylic resin composed of 90% by weight of methyl methacrylate and 10% by weight of methyl acrylate (Kuraray Parapet HR)
-1000 LC. (Transfer start temperature: 128 ° C.), and this temperature is set to 280 ° C. The filling time was 1.4 seconds, the molding cycle was 60 seconds, and the heat transfer coefficient on the cooling water side was 1.
0 × 10 ⁻³ cal / mm ² · sec · ° C.

FIG. 8 shows an example of a sectional structure of a molding die for an optical recording medium substrate according to the present invention. In FIG. 8, reference numeral 6 denotes a thin plate body on which grooves or pits are formed, and reference numeral 7 denotes a low thermal conductivity member. A thin plate member is constituted by the thin plate body 6 and the low thermal conductivity member 7, and one main surface of the thin plate member becomes a part of the cavity. Reference numeral 8 denotes an outer peripheral side holding ring, and 9
Denotes an inner peripheral side holding ring, which is a die component member 1.
0 is attached. On the main surface constituting the cavity of the thin plate member, a concavo-convex pattern opposite to the concavo-convex pattern of pits or grooves to be formed on the optical recording medium substrate is provided. The mold on which the pits or grooves are not provided may have a mirror surface, but it is preferable to provide the mold having the structure shown in FIG. 8 on both sides of the cavity in order to further improve transferability.

As a method of mounting the thin plate member on the mold,
Examples thereof include a method of vacuum suction, a method of bonding with an adhesive, and a method of fixing with a magnet. If it is a mold for molding an optical recording medium, a fixing method using an outer peripheral side press ring and an inner peripheral side press ring conventionally used, a vacuum suction on the outer peripheral side and an inner peripheral side press ring are used. Combined fixation methods can also be used.

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

[0036]

The present invention will be described below in detail with reference to examples. First, an example of a method for forming a light guide plate will be described.

(Examples 1 and 2) As a thin plate main body, a nickel 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 thin plate was used. On the cavity side surface of the thin plate body, the pitch is 50 μm and the height is 25 μm.
An isosceles prism-like concave / convex pattern of m 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, thickness 0.1mm, size 220m
A polyimide film (low thermal conductivity member) measuring mx 170 mm is adhered. The mold on which the thin plate member is mounted has a thickness of 0.3 mm from the parting surface of the mold so as to correspond to a nickel thin plate which is a thin plate body.
mm and a size of 250 mm x 220 mm, and a thickness of 0.1 mm and a size of 2 so as to correspond to a polyimide film which is a low thermal conductivity member.
It is engraved to 20 mm x 170 mm.
The light guide plate was able to be formed by injection molding under the conditions shown in Table 1 using polymethyl methacrylate resin by using a mold equipped with the thin plate member.

The internal pressure at which the prism shape was transferred was measured at a cylinder temperature of 270 ° C. using the above-mentioned mold, and was found to be 38 MPa.

(Comparative Example 1) A member constituting a cavity has a thermal conductivity of 79.2 kcal / m · hr · ° C., a thickness of 0.3 mm, and a size of 250 mm × 2.
A nickel thin plate having a thickness of 20 mm was used (a low thermal conductivity member was not provided). On the cavity side surface of the thin plate body, the pitch is 50 μm and the height is 25 μm
Are arranged in an isosceles prism shape. The mold to which this member is attached is 250 mm in size.
× 220 mm, the depth of which is carved from the parting surface of the mold by the thickness corresponding to the nickel plate. Using this mold, a light guide plate was molded by the injection molding method under the conditions shown in Table 1 using the same polymethyl methacrylate resin as in Examples 1 and 2.

(Comparative Example 2) Using the same mold as in Comparative Example 1, the same polymethyl methacrylate resin was used at a higher cylinder temperature and a higher mold temperature than in Examples 1 and 2. Under the conditions shown in 1, the light guide plate was formed by an injection molding method.

(Comparative Example 3) Using the same mold as in Comparative Example 1, the medium temperature of the mold temperature controller was maintained at 100 until the pressure was maintained.
A light guide plate was molded by an injection molding method under the conditions shown in Table 1 using the same polymethyl methacrylate resin at a temperature of 85 ° C. during cooling.

[0042]

[Table 1]

In Comparative Example 1 among the above Comparative Examples, the height of the prism was low and the transferability was low. In the case of Comparative Examples 2 and 3, the transferability was improved, but the molding cycle was longer. The internal pressure at which the prism shape was transferred was measured using the mold of Comparative Example 1 at a cylinder temperature of 270 ° C. and found to be 55 MPa.

(Examples 3 to 9) As a thin plate body, a nickel 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 thin plate was used. On the cavity side surface of the thin plate body, the pitch is 50 μm and the height is 25 μm.
An isosceles prism-like concave / convex pattern of m 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 ·
A polyimide film (low thermal conductivity member) having a temperature of 220 ° C. and a size of 220 mm × 170 mm is adhered.
Here, the thickness of the polyimide film was changed as shown in Table 2. The light guide plate was molded by the injection molding method under the conditions shown in Table 2 using the above-mentioned mold and the same polymethyl methacrylate resin as in Examples 1 and 2. The measurement of the height of the prism of the obtained light guide plate, the appearance observation, and the warpage measurement by an environmental test were performed. Environmental test was conducted on 65 light guide plates.
30 hours in an environment of 90 ° C. × 90% RH.
After 0 hour, the warpage of the light guide plate was measured with a chiness gauge.

[0045]

[Table 2]

When the thickness of the thin plate body is 0.1 to 0.6 mm and the thickness of the low thermal conductivity member is 0.05 to 0.3 mm as in Examples 3 to 9, the transfer of the prism is performed. A molded product having high reliability, no appearance defects such as weld lines, and high reliability was obtained. Further, even under a high temperature and high humidity environment, warpage hardly occurred.

Next, an example of a method for forming a lens sheet will be described.

(Examples 10 to 11) As a thin plate body, the thermal conductivity was 79.2 kcal / m · hr · ° C., the thickness was 0.3 mm, and the size was 250 mm × 220 mm.
Was used. On the cavity side surface of the thin plate body, a Fresnel lens pattern having an effective area of 220 mm × 166 mm, a pitch of 500 μm, and a height gradually changing from 25 to 80 μm from the center to the outer periphery is arranged. On the parting surface (surface opposite to the cavity) side of the thin plate main body, the thermal conductivity is 0.3 kcal / m · hr · ° C. and the thickness is 0.
A polyimide film (low thermal conductivity member) having a size of 1 mm and a size of 220 mm × 170 mm is adhered. A lens sheet was able to be formed by injection molding under the conditions shown in Table 3 using polymethyl methacrylate resin by using a mold equipped with the thin plate member.

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

(Comparative Example 4) A member constituting the cavity has a thermal conductivity of 79.2 kcal / m · hr · ° C, a thickness of 0.3 mm, and a size of 250 mm × 2.
A nickel thin plate having a thickness of 20 mm was used (a low thermal conductivity member was not provided). On the cavity side surface of the thin plate body, a Fresnel lens pattern having an effective area of 220 mm × 166 mm, a pitch of 500 μm, and a height gradually changing from 25 to 80 μm from the center to the outer periphery is arranged. The mold to which this member is attached is 250 mm x 220 mm in size,
The depth is carved from the parting surface of the mold by the thickness corresponding to the nickel plate. Using this mold, the same polymethyl methacrylate resin as in Examples 10 to 11 was used to mold a lens sheet by an injection molding method under the conditions shown in Table 3.

(Comparative Example 5) Using the same mold as in Comparative Example 4, the same polymethyl methacrylate resin was used at a higher cylinder temperature and a higher mold temperature than in Examples 10 and 11. Under the conditions shown in No. 3, a lens sheet was formed by an injection molding method.

(Comparative Example 6) Using the same mold as in Comparative Example 4, the medium temperature of the mold temperature controller was maintained at 100 until the pressure was maintained.
A lens sheet was molded by an injection molding method under the conditions shown in Table 3 using the same polymethyl methacrylate resin at 85 ° C. and 85 ° C. during cooling.

[0053]

[Table 3]

In Comparative Example 4 among the above Comparative Examples, the height of the Fresnel lens pattern was low and the transferability was low. In the case of Comparative Examples 5 and 6, transferability was improved, but the molding cycle was longer. The internal pressure at which the Fresnel lens pattern was transferred was measured using the mold of Comparative Example 4 at a cylinder temperature of 270 ° C.
Pa.

(Examples 12 to 18) As a thin plate body, the thermal conductivity was 79.2 kcal / m · hr · ° C., the thickness was 0.3 mm, and the size was 250 mm × 220 mm.
Was used. On the cavity side surface of the thin plate body, a Fresnel lens pattern having an effective area of 220 mm × 166 mm, a pitch of 500 μm, and a height gradually changing from 25 to 80 μm from the center to the outer periphery 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. and the size is 2 kcal / m · hr · ° C.
A polyimide film (low thermal conductivity member) measuring 20 mm × 170 mm is adhered. Here, the thickness of the polyimide film was changed as shown in Table 4. Using the above-mentioned mold, the same polymethyl methacrylate resin as in Examples 10 to 11 was used to mold a lens sheet by an injection molding method under the conditions shown in Table 4. The height of the Fresnel lens pattern of the obtained lens sheet was measured, the appearance was observed, and the warpage was measured by an environmental test. The environmental test was performed by leaving the lens sheet in an environment of 65 ° C. × 90% RH for 300 hours, and measuring the warp of the lens sheet after 300 hours with a chiness gauge.

[0056]

[Table 4]

When 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 A highly reliable molded product having high pattern transferability and no appearance defects such as weld lines was obtained. Further, even under a high temperature and high humidity environment, warpage hardly occurred.

Next, an embodiment of a method for forming an optical recording medium substrate will be described. Here, using an injection molding machine (SIM-4749 manufactured by Techno Plus Co., Ltd.), the outer diameter is 120 mm.
An optical disk substrate having a thickness of 0.6 mm and a thickness of 0.6 mm was injection molded. The transferability was evaluated by forming a film of platinum by sputtering on the surface of the optical disk substrate on which the grooves were formed, and measuring the shape of the grooves using a scanning tunneling microscope (SAM3100, manufactured by Seiko Instruments Inc.). Was. The depth of the groove is determined from the measurement result of the shape of the groove, and the value obtained by dividing this value by the value of the groove depth of the thin plate body is defined as the transfer rate.

(Examples 19 to 21) The thin plate body had a thermal conductivity of 79.2 kcal / m · hr · ° C., a thickness of 0.3 mm, an outer diameter of 128 mm and an inner diameter of 3 mm.
A 7 mm nickel donut-shaped disc-shaped thin plate was used. The pitch on the cavity side surface of the thin plate body is 0.7
A spiral groove having a diameter of 12 μm and a depth of 12 μm is formed in a range of a radius of the thin plate body from 25 mm to 55 mm. 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., a thickness of 0.1 mm, and a polyimide donut-shaped disk film (low thermal conductivity member) having a size of 128 mm in outer diameter and 38 mm in inner diameter are bonded.
This thin plate member is mounted on a mold as shown in FIG. In FIG. 8, reference numeral 6 denotes a thin plate main body having a groove formed therein, reference numeral 7 denotes a low thermal conductivity member, reference numeral 8 denotes an outer peripheral side press ring, and reference numeral 9 denotes an inner peripheral side press ring. 10 is attached. Injection molding of the substrate of the optical recording medium was performed by using an acrylic resin composed of 90% by weight of methyl methacrylate and 10% by weight of methyl acrylate (PARAPET HR-1000LC manufactured by Kuraray) under the conditions shown in Table 5. The substrate was molded with. Table 5 shows the results of the transfer rate of the substrate. In addition, the substrates formed in each of the above-mentioned examples showed little deformation.

(Comparative Examples 7 to 9) As a member constituting the cavity, the thermal conductivity was 79.2 kcal / m · hr · ° C.
With a thickness of 0.3 mm and an outer diameter of 128
A nickel-shaped donut-shaped disk-shaped thin plate having an inner diameter of 37 mm and an inner diameter of 37 mm was used (a low thermal conductivity member was not provided). A spiral groove having a pitch of 0.7 μm and a depth of 12 μm is formed on the cavity-side surface of the thin plate body in a range of a radius of the thin plate body from 25 mm to 55 mm. This thin plate body is made in the same manner as in FIG.
The outer ring and the inner ring were mounted on a mold. In injection molding of the substrate of the optical recording medium, the above-mentioned acrylic resin was used to mold the substrate by the injection molding method under the conditions shown in Table 5. Table 5 shows the results of the transfer rate of the substrate.

[0061]

[Table 5]

[0062]

According to the present invention, a resin molded article can be molded with high transferability. Therefore, for example, when a light guide plate, a lens sheet, an optical recording medium substrate, and the like are molded according to the present invention, desired performance is realized even when transfer is insufficient due to a conventional method and performance as designed is not obtained. be able to. In addition, since appearance defects such as weld lines do not occur in the resin molded product, it is possible to obtain a high quality resin molded product without abnormal light emission, and since there is no warpage in a high temperature or high humidity environment, reliability is improved. It is possible to obtain a resin molded product having high property. In addition, since transfer can be performed with a low internal pressure, molding can be performed with a smaller molding machine than before,
Cost can be reduced. Further, according to the present invention, a highly reliable substrate with little deformation due to residual stress can be obtained. Thus, a substrate such as an optical disk on which a large amount of data such as moving image information can be recorded can be formed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a state in which a thin plate member is mounted on a mold according to the present invention.

FIG. 2 is a diagram showing a result of measuring a relationship between a temperature and a longitudinal elastic modulus of a polymethyl methacrylate resin.

FIG. 3 is a diagram showing a result obtained by simulating a relationship between a time (second) after injection and a temperature of a surface of a polymethyl methacrylate resin in contact with a mold by a transient heat conduction analysis using MARC.

FIG. 4 is a diagram illustrating simulation conditions for the light guide plate obtained with the results of FIG. 3;

FIG. 5 is a diagram showing the simulation result of FIG. 3 with the time axis extended.

FIG. 6 is a diagram showing simulation conditions for a lens sheet.

FIG. 7 is a diagram showing simulation conditions for an optical recording medium substrate.

FIG. 8 is a diagram showing an example of the structure of a mold for molding an optical recording medium using the present invention.

FIG. 9 is a diagram showing a configuration of a lighting device using a light guide plate.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 thin plate member 3, 6 thin plate body 4, 7 low thermal conductivity member 5 back plate 8 outer peripheral holding ring 9 inner peripheral holding ring 10 mold constituent member

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G02B 6/00 331 G02B 6/00 331 G11B 3/70 G11B 3/70 A 7/26 511 7/26 511 // B29L 11: 00 17:00 (31) Priority claim number Japanese Patent Application No. 9-232041 (32) Priority date Hei 9 (1997) August 28 (33) Priority claim country Japan (JP) (72) Inventor Takao Hosokawa Ibaraki 41 Miyukigaoka, Tsukuba-shi

Claims (13)

[Claims] 1. A thermoplastic resin having a temperature equal to or higher than a transfer start temperature is introduced into a cavity formed by a mold maintained at a temperature equal to or lower than a transfer start temperature, and cooled by the mold to transfer the transfer start temperature. The thermoplastic resin near the surface of the mold that has dropped to the following temperature, after the cavity is filled with the thermoplastic resin, again rises to a temperature exceeding the transfer start temperature, so that the surface portion of the cavity portion side A method for molding a resin molded product, comprising performing injection molding using a mold having a predetermined heat capacity. 2. A thin plate body, the first surface of which forms a cavity portion, is mounted on the cavity portion side, and the second surface, which is a surface facing the first surface, has a heat conduction of the thin plate body. 2. The method for molding a resin molded product according to claim 1, wherein a mold provided with a thin plate member provided with a low thermal conductivity member having a thermal conductivity smaller than the thermal conductivity is used. 3. The method of molding a resin molded product according to claim 1, wherein the resin molded product is a light guide plate. 4. The method for molding a resin molded product according to claim 1, wherein the resin molded product is a lens sheet. 5. The method according to claim 1, wherein the resin molded product is an optical recording medium substrate. 6. A thin plate 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, is provided with a thermal conductivity of the thin plate body. A low thermal conductivity member having a small thermal conductivity is provided, and when a thermoplastic resin having a temperature equal to or higher than the transfer start temperature is introduced into the cavity portion, it is cooled by a mold having a temperature equal to or lower than the transfer start temperature. The heat capacity of the thermoplastic resin near the surface of the mold, which has been lowered to a temperature equal to or lower than the transfer start temperature, is increased so that the temperature rises again to a temperature higher than the transfer start temperature after the cavity is filled with the thermoplastic resin. A molding die for a resin molded product, wherein the set thin plate member is mounted on the cavity side. 7. The heat conductivity of the thin plate body is 30 to 100 kc.
al / m · hr · ° C., and the thickness is 0.03 to
It is in the range of 0.6 mm, the thermal 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 in the range of 0.05 to 0.3 mm. Claim 6
A molding die for the resin molded product described in the above. 8. The molding die according to claim 6, wherein the resin molded product is a light guide plate. 9. The heat conductivity of the thin plate body is 30 to 100 kc.
al / m · hr · ° C., and the thickness is 0.03 to
It is in the range of 0.6 mm, the thermal 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 in the range of 0.05 to 0.3 mm. Claim 8
A molding die for the light guide according to the above. 10. The molding die for a resin molded product according to claim 6, wherein the resin molded product is a lens sheet. 11. The heat conductivity of the thin plate body is 30 to 100 k.
cal / m · hr · ° C., and the thickness is 0.3 to
It is in the range of 0.6 mm, the thermal 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 in the range of 0.05 to 0.3 mm. Claim 1
0. A molding die for the lens sheet according to 0. 12. The molding die for a resin molded product according to claim 6, wherein the resin molded product is an optical recording medium substrate. 13. The heat conductivity of the thin plate body is 30 to 100 k.
cal / m · hr · ° C., and the thickness is 0.3 to
It is in the range of 0.6 mm, the thermal 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 in the range of 0.05 to 0.3 mm. Claim 1
3. A molding die for an optical recording medium substrate according to 2.