JPH09216258A - Resin molding method and molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent development of a sink mark in the rear surface of a boss even if a thickness of a boss is set 2/3 or more of the thickness of a basal plate in order to enhance a screw intensity of the boss. SOLUTION: When a thermal deformation temperature or a crystallization temperature of the center layer of a molten resin enclosed with a die for forming A surface of a resin molding having a roughly parallel A and B surfaces, a die for forming B surface thereof and a die for forming a boss and charged in cavities 2, 3 having a movable pin for forming a boss center hole becomes ±40 deg.C, a movable pin 5 moved back from a scheduled position of the center hole beforehand is moved forward to the scheduled position of the center hole, so that a resin in the cavity is given a dwelling effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding method and a molded product for molding a resin molded product having a boss.

[0002]

2. Description of the Related Art A resin shaping technique in which a molten resin is injected into a cavity of a mold and cooled and solidified has a feature that a molded product having irregularities and a complicated shape can be produced in a relatively short cycle. Above all, an injection molding technique for injecting a molten resin into a cavity at a relatively high pressure is widely used.

Taking advantage of the above characteristics, resin molded products are often provided with inserts, outserts, screws, holes, notches, etc. A boss 3P having a protrusion-like thickness may be provided. Since the shape of the boss 3P is engraved in the molding die 1b in advance as indicated by reference numeral 3 in FIG. 11 as a boss cavity, there are the following problems.

[0004]

The tapping torque that can be withstood by the boss 3P when attaching parts or the like to the boss 3P is generally 3 to 15 kgf · cm or more, although the required level varies depending on the purpose such as home electric appliances and automobile parts. is necessary. The magnitude of the torque is determined by the screw diameter and the boss hole diameter if the resin is the same, and the torque becomes larger as the boss hole diameter is smaller than the screw diameter.

Depending on the size and weight of the parts to be attached,
The size of the screw required for the boss and the screw-in strength are determined, and thus the wall thickness of the boss is uniquely determined. However, the boss thickness is 2 / of the plate thickness
When the wall thickness exceeds 3, the sink marks 6 remarkably appear on the appearance of the product as shown in FIG.

The reason why the sink marks 6 appear remarkably on the product appearance as described above is that when a molded product having the boss 3P is molded.
This is because the presence of the boss causes the resin in the thickened portion of the substrate to have a relatively low cooling rate, so that the sink mark 6 is generated in the last solidified portion. Actually, as a result of measuring the resin pressure at the bottom of the boss and the resin pressure at the part without the boss, the resin pressure at the part without the boss shows that the pressure rises sharply at the end of the injection process and gradually decreases as the cooling progresses. Has been confirmed. However, the resin pressure at the bottom of the boss where sink marks are generated on the opposite surface 3a of the boss shows the same tendency as the portion without the boss until the end of the injection process, but the resin pressure sharply decreases with the progress of cooling, It has been confirmed that sink marks 6 are already generated when the molded product is in the mold, depending on the boss shape and molding conditions.

In order to maintain the strength of the boss while suppressing the occurrence of such sink marks, it is necessary to increase the thickness of the substrate of the molded product to a certain level or more, which reduces the weight and cost of the product. It is a big barrier.

The present invention has been made in view of the above problems, and in order to improve the screwing strength of the boss, even if the thickness of the boss is set to exceed 2/3 of the plate thickness of the substrate, the back surface of the boss is reduced. It is an object of the present invention to provide a molding method and a resin molded product that do not cause sink marks.

[0009]

The first aspect of the present invention is to enclose a mold for forming an A surface of a resin molded product having AB surfaces that are substantially parallel to each other, and a mold for forming a B surface and a boss. The thermoplastic resin is injection-molded into the cavity space that has the movable pin for forming the boss center hole, and the center layer of the molten resin filled in the cavity has a thermal deformation temperature or crystallization temperature of ± 40.
When the temperature reaches ℃, the movable pin that had been retracted from the boss center hole planned position in advance is advanced to the boss center hole planned position to give a pressure holding effect to the resin in the cavity and suppress the occurrence of sink marks. The resin molding method is characterized in that

The gist of the second invention is that the parallel A
A boss center hole surrounded by a mold for forming an A surface of a resin molded product having a B surface, a mold for forming a B surface and a boss outer periphery, and a boss-shaped mold portion for molding a boss end surface slidable therewith Injection molding of the thermoplastic resin in the cavity space that has the fixing pin for use, and when the center layer of the molten resin filled in the cavity reaches the heat distortion temperature or crystallization temperature ± 40 ° C, A resin molding method, characterized in that the boss-shaped mold part that has been retracted from the boss end face planned position is advanced to the boss end face planned position, and a pressure holding effect is given to the resin in the cavity to suppress the occurrence of sink marks. is there.

Further, the gist of the third invention is that the parallel A
A boss center hole is formed which is surrounded by a mold for forming an A surface of a resin molded product having a B surface, a mold for forming a B surface and a boss outer periphery, and a boss-shaped mold portion for forming a boss end surface slidable therewith. Injection molding of thermoplastic resin in the cavity space equipped with movable pins for use, and when the center layer of the molten resin filled in the cavity reaches the heat distortion temperature or crystallization temperature ± 40 ° C, The boss-shaped mold part and the movable pin that have been retracted from the boss end surface planned position and the boss center hole planned position are advanced to the boss end surface planned position and the boss center hole planned position, and a pressure holding effect is given to the resin in the cavity. The resin molding method is characterized by suppressing the occurrence of sink marks.

Furthermore, in the present invention, in each of the above inventions, the injection molding of the amorphous thermoplastic resin is performed, and after filling the cavity with the molten resin, the movable pin and / or the movable pin and / or the time delay represented by the following mathematical formula 3 are given. A resin molding method is characterized in that the boss-shaped mold portion is projected.

[0013]

(Equation 3)

Further, in the present invention, in each of the above inventions, the crystalline thermoplastic resin is injection-molded, and the movable pin and / or the boss is injected with a time delay represented by the following formula 4 after the molten resin is filled in the cavity. A resin molding method is characterized in that the shaped mold portion is projected.

[0015]

(Equation 4)

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, since the center hole of the boss is formed by a movable pin, or a mold for forming the B surface and the boss outer periphery and a boss-shaped mold portion for forming a boss end surface slidable therewith. Since the boss mold is composed of the movable pin or the boss when the center layer of the molten resin filled in the cavity reaches the heat deformation temperature (hereinafter referred to as HDT) or the crystallization temperature ± 40 ° C. The shape die is preferably projected into the cavity by the operation of the ejector to give a pressure holding effect to the resin in the cavity, so that the sink mark does not occur at the position 3a corresponding to the boss on the surface A.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an apparatus for carrying out the molding method according to the first aspect of the present invention, and FIGS.
2 is a schematic cross-sectional view of an apparatus for explaining the molding method according to the invention of FIG. 3 is a schematic cross-sectional view of another apparatus for carrying out the molding method according to the first invention, and FIGS. 4 (a) and 4 (b) are for explaining a molding method using the apparatus shown in FIG. 2 is a schematic sectional view.

2 and 4, 2P is a product substrate having two parallel surfaces AB, and 3P is a boss protruding from the B surface. In FIG. 1, 1 is a mold device, and 1a is a mold for forming the A surface, which is a fixed mold in this example. 1b is a mold for forming the B surface and the boss 3P, which is a movable mold in this example. The cavity 2 and the boss cavity 3 of the product substrate are formed by these two molds. Reference numeral 4 is a mounting plate, 7 is an ejector plate, and 5 is a movable pin having one end fixed to the ejector plate 7 for forming a boss hole.

In order to carry out the molding method according to the first aspect of the invention using the above apparatus, as shown in FIG. 2 (a), a molten resin is injected into a mold apparatus by an injection molding machine (not shown). , The cavity 2 and the boss cavity 3 of the substrate are pressure-filled. The movable pin 5 is held in the retracted state until it is filled with the molten resin and the central layer is cooled to the HDT or the crystallization temperature. When the cooling step of the molding cycle progressed and the central layer reached the HDT or crystallization temperature ± 40 ° C.
As shown in (b), the ejector plate 7 causes the movable pinch 5 to protrude while pushing up the resin in the cavity, and exerts a pressure holding effect on the resin in the cavity to suppress the occurrence of sink marks.

In FIG. 3 showing another apparatus for carrying out the molding method according to the first aspect of the present invention (the same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted). 5 is a holding sleeve 5 whose one end is fixed to the mounting plate 4.
It is slidably inserted in b. The holding sleeve 5
b is a flange-shaped mounting space 5c with a larger diameter
It is being fixed via the flange 5d.

In order to carry out the molding method according to the first invention using the above apparatus, as shown in FIG. 4 (a), molten resin is injected into a mold apparatus by an injection molding machine (not shown),
The cavity 2 and the boss cavity 3 of the substrate are pressure-filled. The movable pin 5 is held in the retracted state until it is filled with the molten resin and the center layer is cooled to the HDT or the crystallization temperature ± 40 ° C. The cooling process of the molding cycle progresses,
When the temperature of the central layer falls below the flow stop temperature or the crystallization temperature, as shown in FIG. 4B, the movable pin 5 is pushed up by the ejector plate 7 while pushing up the resin in the cavity, and the resin in the cavity is projected. It suppresses the occurrence of sink marks by giving a pressure holding effect to the.

Here, the reason why the cylindrical holding sleeve 5b is provided on the outer periphery of the movable pin 5 is to prevent the molten resin from directly adhering to the movable pin 5 by the holding sleeve 5b.
Movable pin 5 provided by ejector plate 7
This is to effectively transmit the pressure holding effect due to the protrusion of the tip.

If the molded product formed as described above is taken out from the molding dies 1a and 1b, a resin molded product having a boss can be obtained. As described above, this resin molded product suppresses the occurrence of sink marks because the protrusion of the movable pin 5 provides a pressure holding effect as the resin pressure at the bottom of the boss decreases in the cooling step.

It is preferable to use an ejector plate as a mechanism for pushing the movable pin as shown in each of the above-mentioned embodiments because the structure is simple and the operation is reliable, but it is also possible to use a fluid pressure cylinder device such as hydraulic pressure or pneumatic pressure. is there.

FIG. 5 is a schematic sectional view of an apparatus for carrying out the molding method according to the second invention, and FIGS. 6A and 6B are apparatuses for explaining the molding method using the apparatus shown in FIG. 2 is a schematic sectional view of FIG. In FIGS. 5 and 6, 1 is a mold device, 1
a is a mold for forming the A surface, which is a fixed mold in this example. 1
c is a die for forming the B surface and the outer periphery of the boss 3P, which is a movable die in this example. Reference numeral 8 denotes a boss-shaped die portion for forming a boss end surface that is slidable on the die for forming the surface B and the outer periphery of the boss 3P, and one end thereof is fixed to the ejector plate 7. 5a is a fixing pin for forming the boss center hole, one end of which is the B surface and the boss 3
It is fixed to the end surface of the die 1c for forming the P outer circumference via a mounting plate 4. A cavity 2 and a boss cavity 3 for the product substrate are constituted by the three molds 1a, 1c and 8.

In order to carry out the molding method according to the second aspect of the invention using the above apparatus, as shown in FIG. 6 (a), molten resin is injected into a mold apparatus by an injection molding machine (not shown). , The cavity 2 and the boss cavity 3 of the substrate are pressure-filled. The boss-shaped mold part 8 is held in a retracted state by the ejector plate 7 until it is filled with the molten resin and the center layer is cooled to the HDT or the crystallization temperature. When the cooling step of the molding cycle progresses and the central layer reaches HDT or the crystallization temperature ± 40 ° C., the boss-shaped mold portion 8 is pushed by the ejector plate 7 to push the resin in the cavity as shown in FIG. 6B. The resin is kept raised while it is projected to give a pressure-holding effect to the resin in the cavity to suppress the occurrence of sink marks.

If the molded product formed as described above is taken out from the molding dies 1a, 1b, a resin molded product having a boss can be obtained. As described above, this resin molded product suppresses the occurrence of sink marks because the protrusion of the boss-shaped mold portion 8 provides a pressure-holding effect as the resin pressure at the bottom of the boss decreases in the cooling step.

FIG. 7 is a schematic sectional view of an apparatus for carrying out the molding method according to the third invention, and FIGS. 8A and 8B are apparatuses for explaining the molding method using the apparatus shown in FIG. 2 is a schematic sectional view of FIG. Further, FIG. 9 is a schematic cross-sectional view of another apparatus for carrying out the molding method according to the third invention, and FIG.
(B) is a schematic sectional view of an apparatus for explaining a molding method using the apparatus shown in FIG. 9.

In FIGS. 7 and 8, 1 is a mold device, 1a
Is a mold for A-side molding, which is a fixed mold in this example. 1c
Is a die for forming the B surface and the outer periphery of the boss 3P, which is a movable die in this example. Reference numeral 5 is a movable pin for forming a boss center hole, 8 is a boss-shaped mold portion for forming a boss end face that is slidable on the surface B and the mold 1c for forming the outer periphery of the boss 3P, and one end is a movable pin for the ejector plate 7. It is fixed together with 5. 3 above
Cavity 2 of product substrate by one mold 1a, 1c, 8
And the boss cavity 3 is configured.

In order to carry out the molding method according to the third invention using the above apparatus, as shown in FIG. 8 (a), molten resin is injected into a mold apparatus by an injection molding machine (not shown),
The cavity 2 and the boss cavity 3 of the substrate are pressure-filled. The boss-shaped mold part 8 is held in a retracted state by the ejector plate 7 until it is filled with the molten resin and the center layer is cooled to the HDT or the crystallization temperature. When the cooling step of the molding cycle progresses and the central layer reaches the HDT or the crystallization temperature ± 40 ° C., the ejector plate 7 is used to move the boss-shaped mold portion 8 and the movable pin 5 into the cavity as shown in FIG. 8B. While pushing up the resin, the resin in the cavity is given a pressure-holding effect to suppress the occurrence of sink marks.

In FIG. 9 showing another apparatus for carrying out the molding method according to the third aspect of the present invention (the same parts as those in FIG. 7 are designated by the same reference numerals and their explanations are omitted). 5 is a holding sleeve 5 whose one end is fixed to the mounting plate 4.
It is slidably inserted in b. The holding sleeve 5
b is fixed to the mounting plate 4 via a flange 5d. The ejector plate 7 has a double structure including an inner plate 7a and an outer plate 7b. One end of a boss-shaped mold portion 8 is fixed to the inner plate 7a and one end of a movable pin 5 is fixed to the outer plate 7b.

In order to carry out the molding method according to the third aspect of the invention using the above apparatus, as shown in FIG. 10 (a), molten resin is injected and injected into the mold apparatus by an injection molding machine (not shown). , The cavity 2 and the boss cavity 3 of the substrate are pressure-filled. The movable pin 5 and the boss-shaped mold 8 are held in a retracted state until they are filled with the molten resin and the central layer is cooled to the HDT or the crystallization temperature. The cooling process of the molding cycle progresses, and the central layer is HDT or crystallization temperature ± 40 ° C.
10B, the ejector plate 7 causes the movable pin 5 and the boss-shaped mold portion 8 to both project while pushing up the resin in the cavity, thereby retaining the pressure in the resin in the cavity. To suppress the occurrence of sink marks.

Here, the reason why the cylindrical holding sleeve 5b is provided on the outer periphery of the movable pin 5 is that the ejector plate 7 prevents the molten resin from directly adhering to the movable pin 5 and is given by the ejector plate 7. This is for effectively transmitting the pressure holding effect due to the protrusion of the tip of the movable pin 5.

If the molded product formed as described above is taken out from the molding dies 1a and 1b, a resin molded product having a boss can be obtained. As described above, this resin molded product suppresses the occurrence of sink marks because the movable pin 5 and the boss-shaped mold portion 8 project a pressure-holding effect as the resin pressure at the bottom of the boss decreases in the cooling step. ing.

It is preferable to use the ejector plate as the mechanism for pushing the boss-shaped mold portion 8 as described above because the structure is simple and the operation is reliable, but it is also possible to use a fluid pressure cylinder device such as hydraulic pressure or pneumatic pressure. .

In each of the embodiments described above, when the thermoplastic resin used is an amorphous resin, the resin is injection-molded, and the molten resin is filled in the cavity, and then is represented by the following mathematical formula. It is preferable to project the movable pin and / or the boss-shaped mold portion with a time delay.

[0037]

(Equation 5)

In the above formula 5, HDT (T _h ) is measured by JIS K7196 and corresponds to the heat distortion temperature.

In each of the embodiments described above, when the thermoplastic resin used is a crystalline resin, injection molding of the resin is performed, and the time expressed by the following mathematical formula after the molten resin is filled in the cavity It is preferable to project the movable pin and / or the boss-shaped mold portion with a delay.

[0040]

(Equation 6)

In the above equation 6, the crystallization temperature (T _CR )
Is measured according to JIS K7121.

[0042]

EXAMPLES The following two types of molding materials A and B were melted and injection-molded using the above-mentioned various mold apparatuses, and the obtained samples were evaluated. All sample dimensions are vertical 200mm, horizontal 500
mm, substrate thickness 3 mm, boss wall thickness 1.8 mm. Molding material A: ABS resin 1001 as an amorphous thermoplastic resin (manufactured by Mitsubishi Rayon Co., Ltd.) Specific gravity; 1.05 Thermal conductivity; 2.9 × 10 ^-4 cal / sec / ° C.cm Specific heat; 0.33 cal / ° C · g Flow stop temperature; 97 ° C Molding material B: Polybutylene terephthalate (PBT) resin N1000 (manufactured by Mitsubishi Rayon Co., Ltd.) as a crystalline thermoplastic resin Specific gravity; 1.42 Thermal conductivity 5.5 × 10 ⁻⁴ cal / sec / ° C.cm specific heat; 0.30 cal / ° C.g crystallization temperature; 225 ° C. injection molding machine ... IS-50EP (manufactured by Toshiba Machine Co., Ltd.)

Example 1 The molding material A was supplied to the mold apparatus shown in FIG. 1 and injection molding was performed under the molding conditions of a cylinder temperature of 220 ° C., a mold temperature of 60 ° C. and an injection time of 20 seconds. When 25 seconds had passed, the movable pin was projected, and the mold was opened with a cooling time of 30 seconds after molding. The amount of sink marks of the obtained sample is shown in Table 1.

Example 2 The molding material B was supplied to the mold apparatus shown in FIG. 1 and injection molding was carried out under the molding conditions of a cylinder temperature of 260 ° C., a mold temperature of 80 ° C. and an injection time of 20 seconds. After 10 seconds, the movable pin was projected and the mold was opened with a cooling time of 30 seconds after molding. The amount of sink marks of the obtained sample is shown in Table 1.

Example 3 The molding material A was supplied to the mold apparatus shown in FIG. 7, and injection molding was carried out under the molding conditions of a cylinder temperature of 220 ° C., a mold temperature of 60 ° C. and an injection time of 20 seconds. When 25 seconds had passed, the movable pin and the boss-shaped mold were projected, and the mold was opened with a cooling time of 30 seconds after molding. The amount of sink marks of the obtained sample is shown in Table 1.

Example 4 The molding material B was supplied to the mold apparatus shown in FIG. 7, and injection molding was carried out under the molding conditions of a cylinder temperature of 260 ° C., a mold temperature of 80 ° C. and an injection time of 20 seconds. When 10 seconds had passed, the movable pin and the boss-shaped mold were projected, and the mold was opened with a cooling time of 30 seconds after molding. The amount of sink marks of the obtained sample is shown in Table 1.

Comparative Example 1 The molding material A was supplied to the mold apparatus shown in FIG. 11, and injection molding was performed under the molding conditions of a cylinder temperature of 220 ° C., a mold temperature of 60 ° C. and an injection time of 20 seconds. The mold was opened with a cooling time of 30 seconds after molding. The amount of sink marks of the obtained sample is shown in Table 1.

Comparative Example 2 The molding material B was supplied to the mold apparatus shown in FIG. 11, and injection molding was performed under the molding conditions of a cylinder temperature of 260 ° C., a mold temperature of 80 ° C. and an injection time of 20 seconds. The mold was opened with a cooling time of 30 seconds after molding. The amount of sink marks of the obtained sample is shown in Table 1.

[0049]

[Table 1]

Table 1 shows the amount of sink marks in each of the examples and the comparative examples, which are different from each other in the molding method.
The amount of sink marks was measured using a surface roughness meter Surfcom (manufactured by Tokyo Seimitsu Co., Ltd.), and an average value of n = 5 was used as a representative value.

From these results, it is clear that the molding method and molded product of the present invention are extremely effective as means for suppressing sink marks.

[0052]

EFFECTS OF THE INVENTION The molding method of the resin molded product and the molded product of the present invention are such that when the center layer of the molten resin filled in the cavity reaches the heat deformation temperature or the crystallization temperature ± 40 ° C., the movable pin is By advancing to the planned position of the boss center hole and / or advancing the boss-shaped mold part to the planned position of the boss end surface to give a pressure holding effect to the resin in the cavity, the position corresponding to the boss on the A surface, that is, the boss It is possible to suppress the occurrence of sink marks on the back surface. Therefore, since it is not necessary to increase the thickness of the molded product substrate, the product quality can be improved, and the product can be reduced in weight and cost.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an apparatus for carrying out a molding method according to a first invention.

FIG. 2 is a schematic cross-sectional view of a device for explaining a molding method using the device shown in FIG.

FIG. 3 is a schematic sectional view of another apparatus for carrying out the molding method according to the first invention.

4 is a schematic cross-sectional view of an apparatus for explaining a molding method using the apparatus shown in FIG.

FIG. 5 is a schematic sectional view of an apparatus for carrying out the molding method according to the second invention.

6 is a schematic cross-sectional view of an apparatus for explaining a molding method using the apparatus shown in FIG.

FIG. 7 is a schematic sectional view of an apparatus for carrying out the molding method according to the third invention.

FIG. 8 is a schematic cross-sectional view of an apparatus for explaining a molding method using the apparatus shown in FIG.

FIG. 9 is a schematic cross-sectional view of another device for carrying out the molding method according to the third invention.

10 is a schematic cross-sectional view of an apparatus for explaining a molding method using the apparatus shown in FIG.

FIG. 11 is a cross-sectional view of a conventional resin molding die device.

FIG. 12 is a diagram showing sink marks of a conventional resin molded product.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold device 1a Mold for forming A surface 1b Mold for forming B surface and boss 1c Mold for forming B surface and boss outer periphery 2 Mold for substrate 2P Product substrate 3 Boss cavity 3a Corresponding to boss for A surface Position 3P Boss 4 Mounting plate 5 Movable pin 5a Fixed pin 5b Holding sleeve 5c Mounting cylinder 5d Flange 6 Sink 7 Ejector plate 7a Inner plate 7b Outer plate 8 Boss shaped part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Aroyoshi Ogame 3816 Noborito, Tama-ku, Kawasaki-shi, Kanagawa Mitsubishi Rayon Co., Ltd. Tokyo Technical and Information Center

Claims (8)

[Claims] 1. A cavity space provided with a mold for forming an A surface of a resin molded product having substantially parallel AB surfaces, and a movable pin for forming a boss center hole surrounded by a B surface and a boss forming mold. The thermoplastic resin was injection-molded inside, and when the center layer of the molten resin filled in the cavity reached the heat deformation temperature or crystallization temperature ± 40 ° C, it was previously retracted from the planned boss center hole position. A resin molding method characterized in that the movable pin is advanced to a predetermined position of the boss center hole to exert a pressure holding effect on the resin in the cavity to suppress the occurrence of sink marks. 2. A mold for forming an A surface of a resin molded product having AB surfaces substantially parallel to each other, a mold for forming a B surface and a boss outer periphery, and a boss-shaped mold portion for molding a boss end surface slidable therewith. A thermoplastic resin is injection-molded into a cavity space surrounded by and having a fixing pin for forming a boss center hole, and the center layer of the molten resin filled in the cavity has a heat deformation temperature or a crystallization temperature of ± 40. When the temperature reaches ℃, advance the boss-shaped mold part that had been retracted from the boss end face planned position in advance to the boss end face planned position, and give a pressure holding effect to the resin in the cavity to suppress the occurrence of sink marks. And a resin molding method. 3. A mold for forming an A surface of a resin molded product having AB surfaces that are substantially parallel to each other, a mold for forming a B surface and a boss outer periphery, and a boss-shaped mold portion for forming a boss end surface slidable therewith. A thermoplastic resin is injection-molded into a cavity space surrounded by and having a movable pin for forming a boss center hole, and the center layer of the molten resin filled in the cavity has a heat deformation temperature or a crystallization temperature of ± 40. When the temperature reaches ℃, advance the boss-shaped mold part and the movable pin that have been retracted from the boss end surface planned position and the boss center hole planned position in advance to the boss end surface planned position and the boss center hole planned position, A resin molding method, wherein a pressure holding effect is applied to the resin to suppress the occurrence of sink marks. 4. When advancing the movable pin to a predetermined position of the boss center hole, the movable pin is projected from a holding sleeve provided at the boss center position of the boss forming mold or the B surface and the boss outer peripheral forming mold. The resin molding method according to claim 1 or 3, wherein the resin molding method is carried out. 5. The resin molding method according to claim 1, wherein the movable pin and / or the boss-shaped mold part is moved forward and backward by moving the ejector plate. 6. Amorphous thermoplastic resin is injection-molded,
The movable pin and / or the boss-shaped mold part is projected with a time delay represented by the following mathematical formula 1 after the molten resin is filled in the cavity, and the movable pin and / or the boss-shaped mold part are projected. Resin molding method. [Equation 1] 7. A crystalline thermoplastic resin is injection molded,
The movable pin and / or the boss-shaped mold part is projected with a time delay represented by the following mathematical formula 2 after the molten resin is filled in the cavity, and the movable pin and / or the boss-shaped mold part are projected. Resin molding method. [Equation 2] 8. A resin molded product molded by using the resin molding method according to any one of claims 1 to 7.