JPH1044203A - Injection molding method for molding with uneven thickness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of appearance defects such as warping caused by molding strains, weld lines, silver streaks by heating the metal mold surface forming the surface of a molding at a higher temperature than the softening temperature in advance by high frequency induction heating and then molding it by the injection molding. SOLUTION: Copper tubes composed of mutually isolated fine wires are densely shaped along a single layer spiral form, and solidified to be fixed to form a flat plate by using partially heat-resistant resin, in an inductor. The inductor is disposed close to the surface of a metal mold cavity before a thermoplastic resin is injected for molding, to heat the metal mold by a high frequency electric source. Thereafter, the inductor is drawn from the metal mold and then the metal mold is closed to start injection-molding. By this method, a molding product having a thickness ratio b/a of 1/30-1/2, and the thickness of 0.1-5mm at the thin part of the molding product, in particular a flat plate molding product with uneven thickness having 10 inches or longer diagonal length, for instance, can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injection-molding various kinds of thermoplastic resin uneven molded articles, and to the molded articles. In particular, it is suitable for injection molding of a light guide plate for a side-light type surface illumination device (backlight) of an uneven thickness type.

[0002]

2. Description of the Related Art Injection molding of various thermoplastic resins is performed by injecting a molten resin into a mold cavity, applying pressure to the cavity through the molten resin of the spool by holding pressure until the gate is cooled and solidified, and applying a gate. Usually, a method of obtaining a molded product in a mold after solidification is performed. In general, in the filling and holding pressure steps in such injection molding, pressure distribution occurs in the cavity due to the flow resistance and cooling of the molten resin, and uneven cooling is likely to occur. It is remarkable in a thin-walled molded product of 1 mm or less, and when the flow distance from the gate to the flow end is long, poor filling occurs. In the method of injection molding a thin-walled thin-walled molded product having a thin-walled portion having a thickness of 1 mm or less, usually, the injection molding speed is increased, the injection molding pressure or holding pressure is increased, or the mold temperature is increased. Or a method using a resin having good fluidity has been used, but the method is not sufficient.

When the injection molding speed is increased, the temperature of the molten resin becomes extremely high due to the heat generated by the shearing of the molten resin, and silver streaks may occur. Since the frictional resistance with the resin is increased, the molded product is warped or a flow mark is generated. In addition, when the injection molding pressure or the holding pressure is increased, the molten resin is rapidly cooled (the cooling rate is high) particularly in the thin portion of the molded product, so that the residual stress increases, and the molded product is reduced. Undesirably, deformation or warpage easily occurs. Also, by using a resin having good fluidity, the fluidity in a thin portion is improved to some extent, but in order to obtain a sufficient effect, it is necessary to reduce the molecular weight of the resin, and the mechanical strength is reduced and cracks and Crazing and the like easily occur, which is not preferable.

[0004] In the above method, increasing the mold temperature is a very effective means. However, conventionally, generally, a method for controlling the mold temperature (heating and cooling) by providing a heating and cooling hole in the mold respectively and alternately flowing a heat medium and a coolant through the hole is performed. Usually, a mold is made of steel, and is many times larger in weight and capacity than a molded product, and requires a large amount of heat and time for heating and cooling. That is, there is a problem in industrial production.

Further, a method of heating the mold surface to a temperature higher than the heating deformation temperature of the thermoplastic resin by adopting a high frequency induction heating method is disclosed in Japanese Patent Publication No. 58-40504, Japanese Patent Publication No. 62-58287, and Japanese Patent Publication No. Although disclosed in Japanese Patent Application Laid-Open No. 3-45687 and the like, it does not relate to the method for molding an uneven thickness thin molded article according to the present invention.

[0006]

According to the present invention, the ratio b / a of the thick portion a to the thin portion b is 1/30 using a thermoplastic resin.
The thickness of the thin part of the molded product is from 0.1 mm to 5
In the method of injection-molding an uneven thickness molded product having a thickness of 0.1 mm, if the flowability of the molten resin in the mold is insufficient, a molded product having a predetermined shape cannot be obtained, It is necessary to increase the injection molding speed or increase the injection molding pressure than usual in order to obtain a molded product with a shape of, and the resulting molded product is warped or has poor appearance such as weld lines or silver streaks There is a problem that occurs. There is also a method in which holes for heating and cooling are provided in a mold for the purpose of increasing fluidity, and a molded product is obtained by flowing a cooling medium during cooling of a heat medium during molding.However, the mold is usually made of steel. Heating and cooling require a large amount of heat and a lot of time as compared with the molded product. That is, there is a problem in industrial production.

That is, using a thermoplastic resin, the ratio b / a of the thick portion a to the thin portion b is 1/30 to 1/2, and the thickness of the thin portion of the molded product is 0.1 mm to 5 mm. It is necessary to solve the above problems in a method of injection-molding an uneven thickness molded product.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve these problems, and as a result, in a method of injection-molding an uneven thickness molded product, a high-frequency induction heating method is used to heat a metal mold cavity. Using the principle of
It is possible to selectively heat the surface layer of the mold, and it is also possible to rapidly heat and cool the surface of the mold, without causing appearance defects such as warpage due to molding distortion or weld lines and silver streaks. We have found that we can obtain uneven thickness molded products and completed it.

That is, in the present invention, the ratio b / a of the thick part a to the thin part b is 1/30 to 1/2 using a thermoplastic resin.
In the method of injection-molding an uneven thickness molded product having a thin portion with a thickness of 0.1 to 5 mm, the surface of a mold on which a molded product surface is to be formed is softened in advance by the thermoplastic resin. It is characterized by high-frequency induction heating above the temperature and injection molding. Furthermore, the thickness of the thin portion of the molded product is particularly 0.1
mm to 1 mm, wherein the thermoplastic resin is a methacrylic resin or a polycarbonate resin.

Further, the b / a ratio obtained by the above method is made of a thermoplastic resin, and is 1/30 to 1/2,
In addition, the thickness of the thin-walled portion of the molded product is 0.1 mm to 5 mm, and a sidelight type surface lighting device used for a large-sized liquid crystal display device or the like comprising the molded product ( (Backlight) light guide plate.

Hereinafter, the present invention will be described in detail. The present invention makes it possible to mold while maintaining the plasticity by setting the mold surface temperature to the softening temperature of the thermoplastic resin or higher,
As described above, it is possible to obtain an uneven thickness molded product without causing warpage due to molding distortion, or appearance defects such as weld lines and silver streaks.

Further, by adopting a high-frequency induction heating method as a means for heating the mold surface, the productivity was successfully improved. This is described below. It is impossible to release the molded product from the mold while keeping the surface of the mold at or above the softening temperature of the thermoplastic resin.To obtain the desired molded product without deformation, cool the mold and cool the molded product. It is necessary to release the mold from the mold while cooling and solidifying the thermoplastic resin at a temperature lower than the softening temperature of the thermoplastic resin. However, the mold for injection molding is usually made of steel which is several times larger in volume and capacity than the shape of the molded product, and requires a large amount of heat and time for heating and cooling. That is, there is a problem in industrial production in obtaining the above-mentioned molded product. Molding by such a method requires a molding cycle of 40 to 60 minutes.
Therefore, if the principle of high-frequency induction heating is used for heating, the surface layer of the mold can be selectively heated, and the mold surface can be rapidly heated and cooled. In other words, if the vicinity of the mold surface is selectively heated by high-frequency induction heating, the vicinity of the mold surface can be rapidly heated and cooled, so that injection molding can be performed without prolonging the molding cycle. Is maintained at a temperature equal to or higher than the softening temperature of the thermoplastic resin, so that the thermoplastic resin is hardly cooled during the flow in the mold. Therefore, the ratio b /
A flat plate whose a is 1/30 to 1/2 and the thickness of the thin portion of the molded product is 0.1 mm to 5 mm, especially a diagonal length of which is 10 inches or more When molding an uneven thickness molded article, it can be molded without increasing the injection molding speed and injection molding pressure more than necessary, so that the flow resistance at the time of injection molding is small and the orientation distortion hardly occurs. Warpage does not easily occur in the thin portion of the uneven thickness molded product having a thin thickness of 0.1 mm to 1 mm.
In addition, since no shear heat is generated due to an extremely rapid decrease in the flow resistance of the molten resin, a molded article free from appearance defects such as silver streaks can be obtained. Further, it is possible to obtain a molded article free from flow marks and gloss unevenness and having excellent surface smoothness and gloss.

Further, according to this method, the influence of thermal expansion, shrinkage, etc. of the whole mold is eliminated, the dimensional accuracy of the molded product is increased, and the appearance is not uneven. The material of the mold used in the present invention is preferably a magnetic material because an induction heating phenomenon can be caused by high frequency. The frequency in the high-frequency induction heating method used in the present invention ranges from 1 KHz to 1 KHz in that the thickness of the heated portion of the mold surface can be controlled.
The range of MHz is particularly preferred.

The softening temperature in the present invention is defined by JIS K
Method B of 7207 (Bending stress applied to test piece 4.6 kgf
/ Cm ² ) is defined as a temperature 10 degrees lower than the deflection temperature under load of the thermoplastic resin measured by the method specified in ( ² ). In the present invention, the temperature of the mold surface needs to be equal to or higher than the softening temperature defined in this way. Further, the softening temperature needs to be changed depending on the thermoplastic resin used.

Further, the molding method according to the present invention will be described with reference to the drawings. As shown in FIG. 1, an inductor for high-frequency induction heating is installed between the fixed mold and the movable mold. FIG. 2 shows a time-dependent change in the temperature distribution of the mold when the inductor is sandwiched between the movable mold and the fixed mold and a high frequency is transmitted in the sandwiched state. At this time, the mold was not cooled by the cooling water. It can be confirmed that the temperature rises only at the mold surface (points A and B), and the temperature inside the mold (points C and D) hardly rises due to high-frequency induction heating.
If the vicinity of the mold surface is selectively heated by high-frequency induction heating, the vicinity of the mold surface can be rapidly heated and cooled, enabling injection molding without prolonging the molding cycle, and the mold surface is thermoplastic during injection molding. Since the resin is kept at a temperature higher than the heating deformation temperature, the thermoplastic resin is hardly cooled during cooling of the mold, and can be injection molded without increasing the injection speed and injection pressure more than necessary. A molded product having no appearance defects such as generation of silver streaks due to shear heat generation and yellowing, that is, no flow mark or uneven gloss, and excellent smoothness and gloss can be obtained.

The uneven thickness molded article in the present invention means a flat-plate shaped article having a wedge-shaped cross section, and may have a surface with fine irregularities. FIG. 4 shows a typical cross-sectional shape. The thermoplastic resin in the present invention, methacrylic resin, polycarbonate resin, polystyrene, rubber-reinforced polystyrene, AS resin, acrylonitrile butadiene-styrene copolymer, polyethylene, polypropylene, nylon, modified polyphenylene ether, etc. , Methacrylic resin or polycarbonate resin is suitable.

Further, the thickness ratio b / a of the molded product obtained by the above molding method is 1/30 to 1/2, and the thickness of the thin portion of the molded product is from 0.1 mm to 5 mm, An uneven thickness molded product having a thickness of preferably 0.1 to 1 mm has no appearance defect, and is used for an uneven thickness thin type (wedge-shaped) sidelight type surface illumination device (backlight) used as a light source for a liquid crystal display device or the like. Suitable for light guide plate.

Based on recent demands for large-sized and thin-walled liquid crystal display devices and the like, similar demands have been made for backlights, and light guide plates are required to be large-sized, thin and have stable quality. In particular, a wedge shape in which the diagonal size is 10 inches or more, the thickness ratio b / a is 1/30 to 1/2, and the thickness of the thin-walled molded product is 0.1 mm to 5 mm. It is very difficult to form a light guide plate while suppressing the occurrence of excessive molding distortion and weld lines. If excessive molding distortion remains in the molded product, it may cause warpage,
When the light guide plate is incorporated in the backlight, it is not preferable because cracks and deviation in luminance balance occur. However, the backlight light guide plate according to the present invention can meet these requirements.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Various evaluation methods in this case were based on the following methods. (1) Delpet ^R 80NH: a methacrylic resin manufactured by Asahi Kasei Corporation. Heat deformation temperature: 100 ° C., melt flow rate: 5.9 g / 10 minutes. (2) Measurement of Weight The weight is measured with an electromagnetic balance FA-6000 manufactured by Kensei Industry Co., Ltd. Measure with an accuracy of 0.05 g. (3) Measurement of amount of warpage After molding the molded article shown in FIG. 3, it was aged in a gear oven at 70 ° C. for 48 hours, left in a constant temperature room at 23 ° C. × 50% RH for 24 hours, and then left in the constant temperature room. Measure according to the following procedure.

First, the molded product is placed on a metal platen, and then a 200 cm weight is placed on a corner having a gate with a 5 cm square cube. At this time, the gap formed between the molded product and the surface plate at the points a and b of the molded product is measured with a dial gauge.

[0021]

Example 1 As a thermoplastic resin, Delpet ^R 80N was used.
H, a normal S-45C steel material is used as a mold, and a thick part a shown in FIG. 3 is 2.5 mm and a thin part b is shown in FIG. 3 by an SG100 type injection molding machine manufactured by Sumitomo Heavy Industries, Ltd.
Was 1.0 mm.

The inductor is formed by densely forming a copper tube having a sectional area of 10 mm ³ consisting of fine wires insulated from one another in a spiral shape, and partially fixing and solidifying it in a flat plate shape using heat-resistant silicon resin. The injection molding conditions are shown in Table 1. The cylinder temperature was set such that the temperature of the molten resin was 250 ° C.

Before the injection molding of Delpet ^R 80NH, the above-mentioned inductor is brought close to the position 5 mm from the surface of the mold cavity, the mold is heated by a high frequency power supply of 25 KHz and 30 KW for 6 seconds, and then the inductor is removed from the mold. Then, the mold is closed and injection molding is started. The mold surface temperature at the time of filling the resin was 118 ° C. Injection was performed at a filling speed shown in Table 1 for 3 seconds, a holding pressure of 30 kgf / cm ² was applied for 1 second, and after cooling for 30 seconds, the molded product was taken out.
The entire molding cycle was 50 seconds.

[0024]

Comparative Example 1 Injection molding was performed under the same conditions as in Example 1 except that the step of sandwiching the inductor between the molds was not performed. The mold surface temperature at the time of filling the resin was 58 ° C. In both Example 1 and Comparative Example 1, the weight of the molded article was measured with the accuracy of 0.05 g using the scale of (2), and divided by the weight of the molded article which had been fully filled in advance, and then filled. The results are shown in Table 1 below.

[0025]

EXAMPLE 2 Dell thermoplastic resin Pet ^R 80 N
Using H, a normal S-45C steel material was used as a mold, and the same uneven thickness type flat plate as in Example 1 was formed by an SG100 type injection molding machine manufactured by Sumitomo Heavy Industries, Ltd. The inductor has a cross-sectional area 1 consisting of fine wires insulated from each other.
A copper tube of 0 mm ³ is densely formed in a spiral shape to form a mold, and a heat-resistant silicon resin is partially used to fix and solidify it in a flat plate shape.

The injection molding conditions are shown in Table 1. The cylinder temperature was set such that the temperature of the molten resin was 250 ° C. Before the injection molding of Delpet ^R 80NH, the above-mentioned inductor was brought close to a position 5 mm from the surface of the mold cavity, and a high frequency power supply of 25 KHz and 30 KW was used.
The mold is heated for a second, and then the inductor is pulled out from between the molds, and the mold is closed to start injection molding. The mold surface temperature at the time of filling the resin was 118 ° C. Injection was performed for 3 seconds at a filling speed shown in Table 1, a holding pressure of 50 kgf / cm ² was applied for 1 second, and after cooling for 30 seconds, a molded product was taken out. The entire molding cycle was 50 seconds.

[0027]

Comparative Example 2 Injection molding was performed under the same conditions as in Example 2 except that the step of sandwiching the inductor between the molds was not performed. The mold surface temperature at the time of filling the resin was 58 ° C. In both Example 2 and Comparative Example 2, the weight of the molded article was measured with the scale of (2) with an accuracy of 0.05 g, and divided by the weight of the molded article which had been fully filled in advance. The results are shown in Table 1 below.

[0028]

Example 3 As a thermoplastic resin, Delpet ^R 80N
Using H, a normal S-45C steel material was used as a mold, and the same uneven thickness type flat plate as in Example 1 was formed by an SG100 type injection molding machine manufactured by Sumitomo Heavy Industries, Ltd. The inductor has a cross-sectional area 1 consisting of fine wires insulated from each other.
A copper tube of 0 mm ³ is densely formed in a spiral shape to form a mold, and a heat-resistant silicon resin is partially used to fix and solidify it in a flat plate shape.

The injection molding conditions are shown in Table 1. The cylinder temperature was set so that the temperature of the molten resin became 250 ° C. Before the injection molding of Delpet ^R 80NH, the above-mentioned inductor was brought close to a position 5 mm from the surface of the mold cavity, and a high frequency power supply of 25 KHz and 30 KW was used.
The mold is heated for a second, and then the inductor is pulled out from between the molds, and the mold is closed to start injection molding. The mold surface temperature at the time of filling the resin was 118 ° C. Injection was performed for 3 seconds at a filling speed shown in Table 1, a holding pressure of 70 kgf / cm ² was applied for 1 second, and after cooling for 30 seconds, a molded product was taken out. The entire molding cycle was 50 seconds.

[0030]

Comparative Example 3 Injection molding was performed under the same conditions as in Example 3 except that the step of sandwiching the inductor between the molds was not performed. The mold surface temperature at the time of filling the resin was 58 ° C. In each of Example 3 and Comparative Example 3, the weight of the molded article was measured with the accuracy of 0.05 g using the scale of (2), and divided by the weight of the molded article which had been fully filled in advance, and then filled. The results are shown in Table 1 below.

[0031]

Example 4 As a thermoplastic resin, Delpet ^R 80N
Using H, a normal S-45C steel material was used as a mold, and the same uneven thickness type flat plate as in Example 1 was formed by an SG100 type injection molding machine manufactured by Sumitomo Heavy Industries, Ltd. The inductor has a cross-sectional area 1 consisting of fine wires insulated from each other.
A copper tube of 0 mm ³ is densely formed in a spiral shape to form a mold, and a heat-resistant silicon resin is partially used to fix and solidify it in a flat plate shape.

The injection molding conditions are shown in Table 2. The cylinder temperature was set such that the temperature of the molten resin was 250 ° C. Before the injection molding of Delpet ^R 80NH, the above-mentioned inductor was brought close to a position 5 mm from the surface of the mold cavity, and a high frequency power supply of 25 KHz and 30 KW was used.
The mold is heated for a second, and then the inductor is pulled out from between the molds, and the mold is closed to start injection molding. The mold surface temperature at the time of filling the resin was 118 ° C. Injection was performed at a filling speed of 100 mm / s for 3 seconds, a holding pressure of 70 kgf / cm ² was applied for 1 second, and after cooling for 30 seconds, the molded product was taken out.
The entire molding cycle was 50 seconds.

The obtained molded product had no warp or weld line and was most suitable for use as a light guide plate.

[0034]

Comparative Example 4 Injection molding was performed under the same conditions as in Example 4 except that the step of sandwiching the inductor between the molds was not performed. The mold surface temperature at the time of filling the resin was 58 ° C. In both Example 4 and Comparative Example 4, the molded product was aged in a gear oven at 70 ° C. for 48 hours, left in a constant temperature room at 23 ° C. × 50% RH for 24 hours, and then the amount of warpage was determined by the method (3). The measurement was performed, and the presence or absence of a weld line was observed by visual observation. The results are shown in Table 2.

[0035]

EXAMPLE 5 Del thermoplastic resin Pet ^R 80 N
Using H, a normal S-45C steel material was used as a mold, and the same uneven thickness type flat plate as in Example 1 was formed by an SG100 type injection molding machine manufactured by Sumitomo Heavy Industries, Ltd. The inductor has a cross-sectional area 1 consisting of fine wires insulated from each other.
A copper tube of 0 mm ³ is densely formed in a spiral shape to form a mold, and a heat-resistant silicon resin is partially used to fix and solidify it in a flat plate shape.

The injection molding conditions are shown in Table 2, and the cylinder temperature was set such that the temperature of the molten resin became 250 ° C. Before the injection molding of Delpet ^R 80NH, the above-mentioned inductor was brought close to a position 5 mm from the surface of the mold cavity, and a high frequency power supply of 25 KHz and 30 KW was used.
The mold is heated for a second, and then the inductor is pulled out from between the molds, and the mold is closed to start injection molding. The mold surface temperature at the time of filling the resin was 118 ° C. Injection was performed at a filling speed of 100 mm / s for 3 seconds, a holding pressure of 70 kgf / cm ² was applied for 1 second, and after cooling for 25 seconds, the molded product was taken out.
The entire molding cycle was 45 seconds.

The obtained molded product had no warp or weld line and was most suitable for use as a light guide plate.

[0038]

Comparative Example 5 Injection molding was performed under the same conditions as in Example 5 except that the step of sandwiching the inductor between the molds was not performed. The mold surface temperature at the time of filling the resin was 58 ° C. In each of Example 5 and Comparative Example 5, the molded product was aged in a gear oven at 70 ° C. for 48 hours, left in a constant temperature room at 23 ° C. × 50% RH for 24 hours, and then the amount of warpage was determined by the method (3). The measurement was performed, and the presence or absence of a weld line was observed by visual observation. The results are shown in Table 2.

[0039]

Embodiment 6 As a thermoplastic resin, Delpet ^R 80N is used.
Using H, a normal S-45C steel material was used as a mold, and the same uneven thickness type flat plate as in Example 1 was formed by an SG100 type injection molding machine manufactured by Sumitomo Heavy Industries, Ltd. The inductor has a cross-sectional area 1 consisting of fine wires insulated from each other.
A copper tube of 0 mm ³ is densely formed in a spiral shape to form a mold, and a heat-resistant silicon resin is partially used to fix and solidify it in a flat plate shape.

The injection molding conditions are shown in Table 2. The cylinder temperature was set so that the temperature of the molten resin was 250 ° C. Before the injection molding of Delpet ^R 80NH, the above-mentioned inductor was brought close to a position 5 mm from the surface of the mold cavity, and a high frequency power supply of 25 KHz and 30 KW was used.
The mold is heated for a second, and then the inductor is pulled out from between the molds, and the mold is closed to start injection molding. The mold surface temperature at the time of filling the resin was 118 ° C. Injection was performed at a filling speed of 100 mm / s for 3 seconds, a holding pressure of 100 kgf / cm ² was applied for 1 second, and after cooling for 30 seconds, the molded product was taken out. The entire molding cycle was 50 seconds.

The obtained molded product had no warp or weld line and was most suitable for use as a light guide plate.

[0042]

Comparative Example 6 Injection molding was performed under the same conditions as in Example 6, except that the step of sandwiching the inductor between the molds was not performed. The mold surface temperature at the time of filling the resin was 58 ° C. In both Example 6 and Comparative Example 6, the molded product was aged in a gear oven at 70 ° C. for 48 hours, left in a constant temperature room at 23 ° C. × 50% RH for 24 hours, and then the amount of warpage was determined by the method (3). The measurement was performed, and the presence or absence of a weld line was observed by visual observation. The results are shown in Table 2.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

According to the present invention, an uneven thickness thin molded product can be economically injection molded, and the obtained uneven thickness thin molded product has a good appearance and is suitable as a light guide plate.

[0046]

[Brief description of the drawings]

[0047]

FIG. 1 is a conceptual diagram of an embodiment of the present invention.

[0048]

FIG. 2 shows an example of a temperature distribution of a mold in the apparatus shown in FIG.

[0049]

FIG. 3 is a conceptual diagram of a molded product used in the present embodiment.

[0050]

FIG. 4 is a sectional view of an uneven thickness molded product.

[0051]

[Explanation of symbols]

 A, B, C, D Measuring position of mold temperature a Thick part of molded product b Thin part of molded product

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29K 101: 12 B29L 11:00

Claims (5)

[Claims] 1. Using a thermoplastic resin, the ratio b / a of the thick part a to the thin part b is 1/30 to 1/2, and the thickness of the thin part of the molded product is 0.1 to 5 mm. In a method of injection-molding a certain uneven molded product, a mold surface on which a molded product surface is to be formed is subjected to high-frequency induction heating in advance to a temperature higher than a softening temperature of the thermoplastic resin and injection-molded. Injection molding method for meat molded products. 2. The molded article according to claim 1, wherein said thin portion has a thickness of O.D. 2. The injection molding method according to claim 1, wherein the distance is 1 mm to 1 mm. 3. The method according to claim 1, wherein the thermoplastic resin is a methacrylic resin or a polycarbonate resin.
Injection molding method. 4. An uneven thickness molded article made of a thermoplastic resin and molded by the injection molding method according to claim 1, wherein b / a
Characterized by a ratio of 1/30 to 1/2, and a thickness of the thin-walled molded product is from 0.1 mm to 5 mm. 5. A light guide plate for a sidelight-type surface illumination device (backlight), comprising the unevenly molded product according to claim 4.