JP2007190878A - Method of injection molding for thermoplastic resin product, and mold for use in the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injection molding method for a thermoplastic resin, associated with the injection of a fluid such as carbon dioxide, which excels in transferring property and glossiness and enables to save the consumption of the fluid. <P>SOLUTION: While providing a seal mechanism 5 on the composition surface of a fixed mold 2 and a movable mold 3 which encloses a cavity 4, a mold preparing an impregnation fluid recovery means for collecting the impregnation fluid from the inside of the cavity which has flowed out through the composition surface between this seal mechanism 5 and the cavity 4 is used to perform the mold bundle of the mold at first. The cavity 4 is filled up with a resin next. Next, for example, carbon dioxide as a fluid for reforming a visible surface is impregnated between the visible surface of the product in the cavity 4 and the surface of the cavity 4 touching with this visible surface. Next, the resin pressure is raised and the visible surface is stuck to the surface of the cavity 4, and the injection molding is finalized through the preservation of a pressure and cooling. The collected fluid is used again. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a thermoplastic resin injection molding method and a mold used therefor, and more specifically, to improve transferability and glossiness on the visible surface of a product, or to improve the visible surface. The present invention relates to a thermoplastic resin injection molding method and a mold used therefor.

  Generally, injection molding of a thermoplastic resin is one in which a molten resin is filled in a mold cavity and cooled in the mold to obtain a molded product. In this injection molding, the mold is made of resin. Since it is kept at a temperature lower than the solidification temperature of the resin before filling, the solidification of the resin proceeds from the moment when the molten resin is filled into the cavity, and a so-called solidified layer called a skin layer. Is formed on the surface. In particular, the flow front of the molten resin is transferred to the surface of the molded product by phantom flow, but solidification progresses even in this part and it is pressed against the cavity surface with low pressure. This causes molding defects such as flow unevenness and jetting. For this reason, in the prior art, a method is adopted in which the melting temperature of the resin, the mold temperature, and the like are set high to suppress the solidification of the resin and improve the transfer.

  However, in this method, although transferability to a molded product is improved, there is a problem that sink and warp are likely to occur in the molded product due to non-uniform solidification shrinkage of the resin, which makes control difficult. Moreover, the economical problem that a shaping | molding cycle becomes long and the cost of a molded article becomes high generate | occur | produces.

  In order to solve this problem, there has been proposed a method of temporarily heating the mold cavity surface in the injection molding process using the heat of the heater, oil, pressurized hot water, or the molten resin itself. However, in this method, although transferability is improved, special equipment is required, and the molding cycle becomes long, resulting in economic problems.

  As a method for improving transferability while solving the above problems, in Japanese Patent Laid-Open No. 10-128783, in an injection molding process, an inert gas such as carbon dioxide is injected into a mold cavity before filling with a resin in advance. There has been proposed a method of injecting resin into an injection mold. However, in this method, since the resin flows while carbon dioxide gas or the like is dissolved in the resin, the flow is unstable, and appearance defects such as flow unevenness due to uneven flow velocity occur. In addition, since the pressurized cavity space is filled with resin, the molded product tends to be unfilled, and it is difficult to control gas exhaust. Furthermore, since the mold to be used needs to maintain the pressure of the injected carbon dioxide gas, a seal structure must be installed in the entire mold. For this reason, a mold structure that can withstand a high injection pressure of carbon dioxide gas is required, and the problem is that the mold cost is increased.

  Furthermore, in order to solve the above problem, the present inventors disclosed in Japanese Patent Laid-Open No. 2002-52583 that carbon dioxide gas is dissolved in the grown skin layer on the product visible surface immediately after filling the molten resin into the mold. A forming method was proposed. In this method, when the shape of the product is simple, it is possible to mold a product excellent in good transferability without requiring a seal structure in the mold. However, when a product having a complicated shape or depth is formed, a defect in which transferability is not improved or a defect in transfer unevenness occurs. This is considered because carbon dioxide gas leaks from the combination part of the members in the mold, and as a result, the carbon dioxide gas cannot uniformly contact the skin layer surface. As a countermeasure, sealing is provided by providing packing or the like in the combination part in the mold, but the mold has a complicated structure, which is an obstacle to cost reduction in mold manufacture.

  An object of the present invention is to provide a complicated method for molding a product having excellent transferability by filling a mold with a molten resin and then infiltrating a fluid layer such as carbon dioxide into a skin layer on the visible surface of the product. Injection molding method capable of reducing (improving) appearance defects such as transfer failure and transfer unevenness without using a mold having a complicated structure even when forming a product shape with a large depth and depth, and this method It is providing the metal mold | die used for.

In order to achieve the above object, according to the first aspect of the present invention, in the thermoplastic resin product injection molding method, after filling the cavity with the thermoplastic resin, the visible surface modification between the visible surface and the cavity surface of the product is performed. A quality fluid is injected, and then the resin pressure is increased to bring the visible surface into close contact with the cavity surface, and the process is completed through pressure holding and cooling.
According to the present invention, since the fluid permeates the skin layer and reforms, it is possible to improve transferability and glossiness by pressing again on the cavity surface, or to modify with a fluid using a visible surface.

Furthermore, in the invention according to claim 2, in the method of injection molding of a thermoplastic resin product, a sealing mechanism is provided on the joint surface between the fixed side mold and the movable side mold surrounding the cavity, and between the sealing mechanism and the cavity. In addition, using a mold provided with an injection fluid recovery means for recovering the injection fluid from the cavity that has flowed out through the joint surface, the mold is first clamped, and then the resin is added to the cavity. Then, the visible surface modification fluid is injected between the visible surface of the product in the cavity and the cavity surface in contact with the visible surface, and then the resin pressure is increased to adhere the visible surface to the cavity surface. And is completed through pressure holding and cooling.
According to the present invention, by providing the sealing mechanism on the joining surface of the mold, when the fluid is injected, the fluid can be prevented from escaping via the joining surface, and the injected gas body recovery means can The remaining fluid is recovered, and in the next molding step, the recovered fluid is used again, so that economic efficiency can be achieved.

Furthermore, in the invention according to claim 3, in the injection molding method according to claim 1 or 2, the fluid is carbon dioxide or supercritical carbon dioxide, or the carbon dioxide or the supercritical carbon dioxide is dyed. Or it is the fluid which mixed 1 type or multiple types, such as a coating material, an antistatic agent, organic powder, inorganic powder, electroconductive powder, or a reactive monomer.
According to this invention, the fluid mixture suitable for the purpose can be injected to color the visible surface of the product or to impart antistatic properties.

Furthermore, in the invention according to claim 4, in the injection molding method according to claim 2 or 3, immediately after the resin is filled in the cavity, the skin layer on the visible surface of the grown product and the cavity surface in contact therewith By injecting a fluid for reforming in between and retreating the skin layer by a small amount, the growth of the skin layer was temporarily stopped, the fluid injected during this time was permeated into the skin layer, the resin pressure was increased again, and the fluid permeated. The skin layer is brought into close contact with the cavity surface, and is completed through pressure holding and cooling.
According to the present invention, since the fluid can penetrate the entire skin layer only by the pressure of the fluid, the molding process can be easily controlled and the molding time can be shortened.

Furthermore, in the invention according to claim 5, in the injection molding method according to claim 2 or 3, immediately after the resin is filled in the cavity, the movable side mold is backed up by a small amount so that the visible surface of the product and the visible surface of the product are visible. By forming a small amount of space between the cavity surfaces that contact the surface, the growth of the skin layer is temporarily stopped on the visible surface, and then a fluid is injected into the space to infiltrate the gas body into the skin layer, and the resin is again formed. The skin layer into which the fluid has penetrated by increasing the pressure is brought into close contact with the cavity, and is completed through pressure holding and cooling.
According to the present invention, it is not necessary to increase the pressure of the fluid to be injected more than necessary, and the fluid can uniformly penetrate the entire visible surface.

Furthermore, in the invention described in claim 6, in the injection molding method described in claim 5, the fluid is injected simultaneously with a small amount of retraction of the movable side mold.
According to the present invention, the molding time can be shortened.

Furthermore, in the invention according to claim 7, in the injection molding method according to any one of claims 2 to 6, the cavity and the product visible surface side are formed immediately after filling the resin into the mold cavity. The pressure of the fluid in the cavity injected between the skin layers is controlled.
According to this invention, the optimum fluid pressure can be selected according to the shape and material of the molded product.

Furthermore, in the invention according to claim 8, in the injection molding method according to any one of claims 2 to 7, the fluid that has flowed out from the joint surface of the mold is recovered, and this is again performed in the next molding. The recovered fluid is used.
According to the present invention, fluid consumption can be saved.

Further, in the invention described in claim 9, in the injection molding mold for thermoplastic resin products, a sealing mechanism is provided on the joint surface between the fixed mold and the movable mold surrounding the cavity, An injection fluid recovery means for recovering the injection fluid from the cavity that has flowed out to the joint surface is provided between the cavities.
According to the present invention, it is possible to accurately control the pressure of the fluid, and it is possible to prevent wasteful disposal of the fluid remaining in the mold.

Immediately after resin is filled in a mold cavity with a seal structure, a void is formed by injecting fluid such as skin layer modification or dye between the cavity and the skin layer that forms the visible surface, or by retreating the mold Then, the growth of the skin layer is stopped, and then, for example, carbon dioxide or the like for softening the skin layer is injected into the voids, and then the resin pressure is increased to bring the skin layer into close contact with the cavity surface again. By cooling and solidifying while applying pressure, the following effects are obtained.
1. Regardless of the product shape, carbon dioxide or the like can be injected uniformly between the mold cavity and the skin layer forming the visible surface. As a result, it is possible to obtain a product with a good appearance that is free from transfer defects and transfer unevenness regardless of the product shape.
2. Since the pressure of carbon dioxide or the like in the cavity can be set to a desired value by the pressure control means provided with the fluid recovery means, high-quality transfer can be obtained according to the product shape and material.
In the case of a mixed fluid of carbon dioxide and a dyeing agent, the surface of the molded product can be dyed uniformly.
3. Economical injection molding is possible by collecting and reusing carbon dioxide remaining in the mold with the fluid recovery means.

  In the injection molding method of the present invention, a sealing mechanism is provided on the joint surface of a mold in injection molding of a thermoplastic resin. The seal mechanism is formed so as to surround the periphery of the cavity, and a fluid recovery means and a gas pressure control means are provided between the seal mechanism and the cavity. The fluid injection port is provided in a resin filling port or a mold on the visible surface side. Fluid injection is spread over the entire visible surface by forcing injection between the visible surface and the cavity surface. Alternatively, a small amount of the movable mold is retracted to form a gap between the skin layer on the visible surface and the cavity surface, and a fluid is injected into the gap. For example, when carbon dioxide is injected, the fluid is applied to the skin layer. Penetrates and softens skin layer. In addition, when the resin pressure is increased, the skin layer is again softened and is closely adhered to the cavity surface, and then subjected to pressure holding and cooling to obtain a product with extremely excellent transferability and glossiness. be able to.

  Further, by injecting while continuously or intermittently increasing the fluid injection pressure, even if the fluid is finally injected at a high pressure, the skin layer immediately after filling will not be adversely affected. Alternatively, the gap can be gradually formed between the mold cavity and the skin layer immediately after filling. In order to form this gap, the cavity surface of the movable side mold or the fixed side mold facing the visible surface is partially retracted slightly, and in accordance with this, the fluid is placed between the cavity surface and the visible surface of the molded product. The fluid may be injected after the recession is stopped and the gap is formed. In addition, by providing a sealing mechanism on the joint surface of the mold, carbon dioxide or the like can be reliably injected into the gap between the mold cavity on the product visible surface side and the molten resin. In addition, even a product having a complicated shape or a product having a deep shape can easily obtain a good molded product free from transfer defects or transfer unevenness. Furthermore, by controlling the pressure of carbon dioxide or the like injected into the cavity by the fluid pressure control means, the transferability can be freely changed, and a product having the intended transferability can be obtained. In addition, when carbon dioxide or the like is partially injected excessively due to the influence of the product shape, the excess fluid can be discharged and the pressure can be kept constant. Further, by moving the fluid recovery means to recover carbon dioxide remaining in the cavity and reusing it in the next molding, it is possible to save fluid consumption and reduce the molding cost. it can.

FIG. 3 shows a mold seal structure generally used in a gas counter pressure method or the like. In the gas counter pressure method, an inert fluid such as nitrogen, air, or carbon dioxide must be injected into the mold cavity and sealed before filling the mold cavity with molten resin. It is necessary to install a sealing material on all mating surfaces between the parts to be constructed. In particular, since many ejector pins are generally installed on the movable mold side corresponding to the non-visible surface side of the product, it is necessary to install as many sealing materials as the number of ejector pins. It is very difficult to seal the corresponding side.
On the other hand, in the present invention, when the seal structure is installed only on the side corresponding to the product visible surface side, it can be implemented very easily and at low cost. Even if the product visible surface side is reversed, the seal structure may be installed only on the side corresponding to the product visible surface side. However, in the present invention, this sealing mechanism may basically be either a fixed side mold or a movable side mold.

  The thermoplastic resin used in the present invention is, for example, a styrene resin (for example, polystyrene, butadiene / styrene copolymer, acrylonitrile / styrene copolymer, acrylonitrile / butadiene / styrene copolymer, etc.), ABS resin, polyethylene, Polypropylene, ethylene-propylene resin, ethylene-ethyl acrylate resin, polyvinyl chloride, polyvinylidene chloride, polybutene, polycarbonate, polyacetal, polyphenylene oxide, polyvinyl alcohol, polymethyl methacrylate, saturated polyester resin (for example, polyethylene terephthalate, polybutylene terephthalate, etc. ), Biodegradable polyester resins (for example, hydroxycarboxylic acid condensates such as polylactic acid, diol and dibutyl such as polybutylene succinate) Condensates of rubonic acid, etc.) Polyamide resin, polyimide resin, fluororesin, polysulfone, polyethersulfone, polyarylate, polyetheretherketone, liquid crystal polymer, etc. Examples include resins in which various fillers are mixed. Among these thermoplastic resins, styrene resins and ABS resins are preferable.

The fluid used in the present invention uses carbon dioxide or carbon dioxide in a supercritical state as a fluid that dissolves in the resin in order to improve transferability and glossiness.
In addition, the fluid used for mixing with the dye or the modifier in the present invention is not limited as long as it is a fluid that dissolves on the resin surface, but carbon dioxide having the highest solubility or carbon dioxide in a supercritical state is used. desirable.
Further, the chromosome or modifier used in the present invention is an organic powder or inorganic powder that imparts functionality such as coloring, abrasion resistance, conductivity, hardness, luminance, coating, spectral properties, antistatic effect to the resin surface. As long as it is a body, a conductive powder, a conductive inhibitor, or a reactive monomer, it does not matter. Specifically, as a dye that colors the resin surface and imparts spectral characteristics, nitro dye, methine dye, quinoline dye, aminonaphthoquinone dye, coumarin dye, preferably anthraquinone dye, tricyanovinyl dye, azo dye, dinitrodiphenylamine The group which consists of organic powders, such as these, and those combinations, Furthermore, the group which consists of inorganic powders, such as silver white, ivory black, peach black, lamp black, carbon black, and those combinations, etc. can be mentioned.

  In addition, as a modifying material that modifies the resin surface and imparts high brightness, wear resistance and surface hardness, inorganic powders such as mica titanium, titanium oxide, gold powder, calcium carbonate, or fluorine particles can be used. . Further, as a modifier for coating the resin surface and imparting conductivity, zinc powder, silver powder, nickel powder, powders obtained by coating inorganic powder such as mica or sericite with a highly conductive metal, and those Examples include groups consisting of combinations. In addition, as a modifier that causes a binding or cross-linking reaction with the resin surface and expresses elastic properties, chemical resistance and various functions on the surface, proteins, polypeptides, nucleotides, drugs, or acrylic acid, ethylene, styrene, Examples thereof include a group consisting of reactive monomers such as isobutyl vinyl ether, methyl acetate, vinyl chloride, propylene, amino acid ester, polyphenol and silicone, and combinations thereof.

  Examples of the antistatic agent include water-soluble surfactants, polyoxyalkylene ethers, polyoxyethylene derivatives, sorbitan fatty acid esters, medium-purity monoglyceride stearin, polyethylene glycol distearate, and combinations thereof. It is done. Moreover, you may use the group which consists of a combination of the said organic powder, an inorganic powder, and an antistatic agent as a modifier. Hereinafter, examples and comparative examples of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these examples, and may be a combination of these examples.

  FIG. 1 shows a case where the present invention is applied to a molding method and a mold for the purpose of improving transferability and glossiness. In FIG. 1, reference numeral 1 denotes a mold. The mold 1 includes a fixed side mold 2 and a movable side mold 3, and a cavity 4 is formed when the mold is clamped.

A seal mechanism 5 is provided on the joint surface 1a so as to surround the cavity 4. The seal mechanism 5 forms a seal material mounting groove 5a in the fixed mold 2 and a rubber is formed in the mounting groove 5a. It is the structure which assembled the sealing material 5b made from.
6 is a gate of the cavity 4, 7 is a sprue following the gate 6, and 8 is a screw type resin filling machine for filling the cavity 4 from the sprue 7 via the gate 6.
Reference numeral 9 denotes a fluid injection port provided in the cavity surface of the fixed mold 2 in the cavity 4, 10 denotes a fluid injection pipe connected to the fluid injection port 9, and 11 denotes a fluid injection unit connected to the fluid injection pipe 10. , 12 is a fluid generator connected to the fluid injection unit 11 via a pipe 13.

  14 is a fluid recovery means provided in the stationary mold 2 so as to be disposed between the cavity 4 and the seal mechanism 5. The fluid recovery means 14 opens a recovery port 14a on the joint surface 1a. 4 is composed of a control pin 14b which is incorporated in the recovery port 14a so as to freely enter and exit, and a sealing O-ring 14c of the control pin 14b. The pressure of the fluid can be controlled by entering and exiting the control pin 14b. The high-pressure fluid generator is configured to retreat and open the discharge port 14d of the recovery port 14a so that the fluid that has flowed out (leaked) from the cavity 4 via the joint surface 1a via the recovery pipe 15 is shown in FIG. It can collect | recover in 12 and control for using at the time of the next shaping | molding can be performed. That is, the fluid recovery means 14 does not abandon the remaining fluid once used when adjusting the degree of skin surface modification, etc. by adjusting the pressure of the fluid injected into the cavity 4. In addition, it is used for economic efficiency by reusing.

  The fluid injection system shown in FIG. 1 was manufactured in-house, and a molding machine (manufactured by Nippon Steel Works; J220E2-P-2M) with a clamping force of 220 t was used as the injection molding machine. Impact-resistant polystyrene (PS Japan, Inc .; AGI02) was used as the resin. The molded product A had the shape shown in FIG. 2 (vertical 148 mm, horizontal 210 mm, depth 15 mm, product thickness 2 mm). Since the used mold 1 has the fixed mold 2 on the product visible surface side, the fluid injection mechanism is incorporated in the fixed mold 2 as shown in FIG. Further, the eject pin 3a of one movable side mold 3 is not provided with a seal structure.

An injection molding method and a mold according to the present invention will be described with reference to FIGS. First, as shown in FIG. 1, the molds of the fixed mold 2 and the movable mold 3 are clamped. Next, the resin melted from the injection molding machine 8 at a molding machine heater temperature of 230 ° C. is placed in the mold cavity 4 set to an injection pressure of 60 MPa, a filling time of 0.6 sec, and 40 ° C. (material S45C, nested mold, product visible). The surface side cavity surface is filled in a 2000th mirror finish. Immediately after filling with the molten resin, as shown in FIG. 3, carbon dioxide set at 20 MPa is injected from the fluid injection unit 11 between the skin surface and the cavity in contact with the skin surface via the pipe 10. When carbon dioxide is injected into the entire product visible surface side, the valve 10a of the pipe 10 is closed, and an electromagnetically driven pressure control movable mold installed in the mold is used to adjust the pressure to an appropriate pressure that can provide high transfer. The mold part (gas body recovery means 14) is operated so that the pressure of carbon dioxide injected between the cavity and the skin layer is 14 MPa, and is controlled uniformly. After adjusting to the desired pressure, the movable mold part for pressure control is operated and returned to its original state, the resin pressure is increased to 90 MPa, carbon dioxide is dissolved in the skin surface, and the skin surface is softened while holding the pressure. Then, the skin surface was again brought into close contact with the cavity surface for 7 seconds to perform molding. The excessive amount of carbon dioxide injected between the cavity and the skin layer by the operation of the movable mold part for pressure control is transferred to the fluid discharge pipe 15 via the pressure control discharge circuit 15a in FIG. It returned to the high pressure fluid generator 12, and it utilized as the carbon dioxide injected in the next process.
The molded product obtained by this method had a good appearance with no defective transfer or uneven transfer. The surface gloss of this molded product was measured using (GLOSS CHECKER; IG-310 manufactured by HORIBA. Ltd). As a result, the glossiness on the visible side of the molded product was 90.

In the second embodiment, in order to prevent the air discharged from the cavity 4 during resin filling from being hindered by the seal mechanism 5 and the pressure in the cavity 4 and the filling resin pressure from being increased more than prescribed, As shown in FIG. 5, an air reservoir 16 is formed in the mold 2, and the air discharged from the cavity 4 is temporarily accommodated in the air reservoir 16, so that the air from the cavity 4 described above is stored. In this example, the discharge can be performed and the increase in the resin pressure is prevented.
In addition, although the said Example 1, 2 is an example which improves transferability and glossiness using a carbon dioxide, the operation example when utilizing various fluids for the modification | reformation etc. of the visible surface of a molded article Is performed through the same process as the carbon dioxide injection method described above.

[Comparative Example 1]
The mold of Example 1 was molded under the same conditions using the same apparatus as that shown in FIG. 1 except that the seal mechanism 5 and the fluid recovery means 14 were not provided. As a result, since carbon dioxide leaks from the mold joint surface 1a, the pressure of the injected carbon dioxide does not readily increase, so that the penetration of carbon dioxide into the skin surface does not proceed, and the product has transferability and glossiness. Was slightly better than when carbon dioxide was not injected, but was inferior to that of Example 1, and the glossiness was 70.

  The third embodiment is an example in which the seal mechanism 5 is provided in the movable mold 3 as shown in FIG. 6 and the example in which the seal mechanism 5 is provided in the fixed mold 2 as shown in FIG. . As described above, any seal mechanism 5 may be used, but it is preferable that the seal mechanism 5 is provided on the stationary mold 2 that is not movable.

Explanatory drawing of the fluid injection | pouring system for implementing this invention, a molding machine, and a metal mold | die. It is explanatory drawing of the shape of the molded article used in the Example of this invention, Comprising: (a) is a front view, (b) is AA 'sectional view taken on the line. Explanatory drawing at the time of fluid injection. Explanatory drawing at the time of fluid pressure control and fluid collection | recovery. Explanatory drawing of the metal mold | die which provided the air pocket. Explanatory drawing of a metal mold | die structure when a sealing mechanism is installed in the stationary mold. Explanatory drawing of a metal mold | die structure when the seal mechanism is installed in the movable mold. Explanatory drawing of the sealing structure of a general metal mold | die.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mold 2 Fixed side mold 3 Movable side mold 4 Cavity 5 Seal mechanism 6 Gate 7 Sprue 8 Screw type resin filling machine 9 Fluid inlet 10 Fluid injection pipe 11 Fluid injection unit 12 High pressure fluid generator 13 Pipe 14 Fluid recovery Means 15 Recovery piping 16 Air reservoir

Claims (9)

  After filling the cavity with the thermoplastic resin, inject the visible surface modification fluid between the visible surface and the cavity surface of the product, and then increase the resin pressure to bring the visible surface into close contact with the cavity surface for pressure holding and cooling The thermoplastic resin product injection molding method completed through.   A sealing mechanism is provided at the joint surface between the fixed mold and the movable mold surrounding the cavity, and the injected fluid from the cavity flowing out through the joint surface is collected between the seal mechanism and the cavity. First, the mold is clamped and then the resin is filled in the cavity, and then the visible surface of the product in the cavity and the cavity where the visible surface is in contact A method for injection molding of a thermoplastic resin product, in which a visible surface modification fluid is injected between the surfaces, and then the resin pressure is increased to bring the visible surface into close contact with the cavity surface, followed by pressure holding and cooling.   The fluid is carbon dioxide or supercritical carbon dioxide, or the carbon dioxide or the supercritical carbon dioxide, a staining agent, a coating material, an antistatic agent, an organic powder, an inorganic powder, a conductive powder, a reactive monomer, or the like. The injection molding method according to claim 1, wherein the fluid is a fluid obtained by mixing one or more of the above.   Immediately after filling the cavity with resin, the skin layer grows by retreating a small amount of the skin layer by injecting a modifying fluid between the skin layer on the visible surface of the grown product and the cavity surface in contact with the skin layer. 4. The fluid according to claim 2, wherein the fluid injected during this time is permeated into the skin layer, the resin pressure is increased again, the skin layer into which the fluid permeates is brought into close contact with the cavity surface, and the process is completed through pressure holding and cooling. Injection molding method.   Immediately after filling the resin in the cavity, the movable side mold is backed by a small amount to form a minute gap between the visible surface of the product and the cavity surface where the visible surface is in contact, so that the skin layer grows once on the visible surface. Stop, then inject fluid into this gap to infiltrate the gas body into the skin layer, increase the resin pressure again to bring the skin layer infiltrated with fluid into close contact with the cavity, and complete after holding and cooling The injection molding method according to claim 2 or 3.   The injection molding method according to claim 5, wherein fluid is injected simultaneously with a small amount of retraction of the movable side mold.   The injection molding method according to any one of claims 2 to 6, wherein the pressure of the fluid in the cavity injected between the skin and the skin layer forming the product visible surface side is controlled immediately after the resin is filled in the mold cavity. .   The injection molding method according to any one of claims 2 to 7, wherein the fluid flowing out from the joint surface of the mold is recovered, and the recovered fluid is used again in the next molding.   A sealing mechanism is provided on the joint surface between the fixed mold and the movable mold surrounding the cavity, and an injection fluid for recovering the injection fluid from the cavity flowing out to the joint surface between the seal mechanism and the cavity A mold for injection molding of thermoplastic resin products provided with a collection means.

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