JPH11314253A - Gas injection mold of thermoplastic resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas injection mold capable of molding a partially hollow injection-molded product having no sink or warpage without generating surface gloss irregularity and lowering productivity and a method for producing the partially hollow injection-molded product by using this mold. SOLUTION: In a gas injection mold constituted of a cavity mold 1, a core mold 2 and a product cavity part 3 and having a resin gate, a gas gate and a resin sump part 6, a gas discharge mechanism 12 is provided between the product cavity part 3 and the resin sump part 6 and a molten resin is injected and charged into the product cavity part 3 from the resin gate and gas is subsequently introduced into the molten resin under pressure from the gas gate and, before the resin sump part 6 is perfectly filled with the molten resin, the gas introduced under pressure is discharged from the gas discharge mechanism 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection molding method capable of stably performing a gas injection molding of a molded article having a high appearance without gloss unevenness or sink marks without lowering industrial productivity. The present invention relates to a molding die and a method for producing a thermoplastic resin molded article having a hollow portion using the same.

[0002]

2. Description of the Related Art When manufacturing an injection molded article of a thermoplastic resin, if there is a difference in wall thickness depending on a part of the molded article, a difference in shrinkage rate between a thick part and a thin part causes a surface of the thick part to have a sink mark. Deformation such as warpage is likely to occur. As a means for preventing the occurrence of such sink marks and the like, there is a method in which a gas is press-fitted into a thick portion to make a partially hollow product. The method of injection molding while forming a hollow portion by press-fitting a gas in this way is collectively referred to as a gas injection molding method.

[0003] In the gas injection molding method of a thermoplastic resin, an inert gas is injected into a molten resin injected into a mold to form a hollow portion inside the molded product, and a hollow portion is formed inside the molten resin. In this method, a uniform gas pressure is applied to the surface of the mold cavity to obtain a molded product without deformation such as sink marks and warpage. Here, conventionally, a technique of providing a resin pool near the final filling portion of the molten resin to improve the hollow ratio has been adopted,
At that time, the hollow ratio was maintained by sufficiently applying a gas holding pressure.

However, in such a conventional gas injection molding method, when a gas is injected, a thick portion (gas channel portion) having a large volume shrinkage, which serves as a passage of the gas, and a glossy surface on the upper surface of the gas channel portion. Due to unevenness, satisfactory product quality could not be obtained. That is,
When the gas is press-fitted into the gas channel portion, the gas is held at a high pressure, and thus is pressed against the mold more strongly than the other portions. For this reason, there is a disadvantage that the transferability is improved only in that portion, and as a result, transfer unevenness and gloss unevenness occur on the entire product.

Therefore, it is necessary to control the gas pressure so that the gas channel portion and the other portions come into contact with the mold at the same pressure to maintain uniform transferability. In addition, the initial conditions such as gas injection timing, gas volume, mold compression speed, etc. must be changed in various ways to find optimal conditions and implement them precisely, requiring a great deal of labor and significantly increasing productivity. It was low.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a mechanism capable of forming a partially hollow injection-molded article free from sink marks and warpage without eliminating gloss unevenness on the surface of the product and without reducing industrial productivity. It is an object of the present invention to provide a gas injection molding die having the above and a gas injection molding method using the same.

[0007]

As a result of diligent studies, the present inventor has found that the above problem can be solved by providing a gas discharge mechanism between a gas gate of a gas injection mold and a resin reservoir. The present invention has been reached.

That is, the present invention comprises a cavity mold, a core mold, and a product cavity formed between the cavity mold and the core mold and filled with a molten resin. A gas injection molding die of a thermoplastic resin having a resin reservoir provided in a final filling portion of the resin, wherein a gas discharge mechanism is provided between the gas gate and the resin reservoir. Provide an injection mold.

Further, according to the present invention, the resin reservoir is a final filling portion of the molten resin and is provided outside the product cavity, and the gas discharge mechanism is provided between the resin reservoir and the product cavity. The gas injection molding die is provided between the molds.

The present invention also relates to a method for producing a thermoplastic resin molded article having a hollow portion, wherein the method comprises the following steps (a) to (c) using the gas injection mold. Provided is a method for producing a thermoplastic resin molded product, which is characterized by performing injection molding. (A) an injection filling step of injecting and filling a molten resin into a product cavity from a resin gate; (b) a gas injection step of injecting a gas from a gas gate into the molten resin; and (c) releasing the gas injected in the gas injection step. Gas release process released by mechanism

In the present invention, in the gas releasing step, the gas is released before the molten resin is completely filled in the resin reservoir of the gas injection molding die. Provided is a method for producing a plastic resin molded article.

[0012]

Embodiments of the present invention will be described below.

(1) Mold for Gas Injection Molding A mold used for injection molding of a thermoplastic resin usually comprises two sets of a concave mold (cavity mold) and a convex mold (core mold). When they are combined, a product cavity portion in which the molten resin is filled and a product is molded is formed. Therefore, the mold for gas injection molding of the present invention,
Basically, it is composed of a cavity mold, a core mold and a product cavity.

The cavity mold and the core mold are generally divided into a fixed side and a movable side. The fixed side is fixed to a fixed side die plate of a molding machine, and the movable side is attached to a movable side die plate. In many ordinary dies, the fixed side is a cavity type and the movable side is a core type in many cases. The cavity mold and the core mold are formed from a metal material such as an alloy such as stainless steel containing iron or iron as a main component, an aluminum alloy, a nickel alloy, a zinc alloy, and a copper alloy.

The mold is provided with a resin gate for injecting molten resin into the product cavity. Then, the movable side is advanced, the cavity mold and the core mold are closed and the mold is closed, and the product cavity formed between the two molds is filled with a thermoplastic resin injected from the resin gate. , The product is molded. After injection molding, retract the movable side to open the cavity mold and core mold,
Take out the molded product. The position of the resin gate can be appropriately determined according to the design of a desired molded product, and the number of gates is not limited to one in the mold, but may be two or more to form a multipoint gate.

The gas injection mold according to the present invention is provided with a gas gate in addition to the resin gate. Hereinafter, a gas injection molding die according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an example of the mold of the present invention. In FIG. 1, 1 is a cavity mold, 2 is a core mold, 3 is a product cavity portion formed between the cavity mold and the core mold and filled with molten resin, 4 is a resin gate, and 5 is a gas gate.

In gas injection molding, the cavity mold 1 is used.
And the core mold 2 are closed and clamped, and then the molten resin is injected from the resin gate 4 to fill the product cavity 3 formed between the cavity mold 1 and the core mold 2 and then the gas gate 5 A gas is pressed into the molten resin so that a hollow portion is formed inside the molded product. The gas may be any gas that is inert to the thermoplastic resin used, for example, nitrogen gas or the like.

Since the injected gas flows in the direction of low resistance to the gas, the cooling rate is low and the melt viscosity is low. Introduced selectively. The product part which becomes such a gas passage is called a gas channel (8 in FIG. 1).

Since the gas channel depends on the resin gate position, the gas gate position, the shape and the thickness of the molded article, and the like, usually these are taken into consideration so that the desired gas channel is formed in the molded article. Do the design. The position of the gas gate can be appropriately determined according to the design of the gas channel of a desired molded product, and the number of gates can be provided not only at one point but also at two or more points in the mold.

As a method of injection molding by injecting a gas, there are a short shot method and a full shot method. In the short shot method, injection is stopped in a short shot state without completely filling the molten resin in the injection step, and then gas is injected, and then the product cavity is extruded by gas pressure while extruding the molten resin to an unfilled portion. Fill.

In the full shot method, after the product cavity is fully filled with the molten resin in the injection step, the injection of the resin is stopped, and then pressurized gas is injected, and the volume shrinkage due to the cooling shrinkage of the resin is reduced to the gas pressure. To make it hollow. Since the volume shrinkage of the gas channel portion in the molded article is large, the press-fitted gas hollows the gas channel portion.

In any of the methods, in a process in which the molten resin filled in the product cavity portion may contract in volume due to cooling and cause sink marks or the like, a gas is injected into the gas channel to reduce the volume of the resin in the volume contraction portion. And pressurize the molded product by applying a uniform gas pressure from the interior of the molded product to the cavity surface, thereby deforming sink marks, warpage, etc. A molded article free from defects can be obtained.

The molten resin in the gas channel flows by the pressurized gas and is filled in the product cavity. The gas is introduced into the product part where the volume contraction is large, but since the gas is kept at a high pressure, it not only compensates for the shrinkage in the gas channel and hollows it out, but also to the basic thick part around the gas channel. Extrudes molten resin.

Therefore, the volume shrinkage of the resin in the basic thick portion is compensated by extruding the resin in the gas channel to the surroundings. That is, the volume shrinkage of the resin is not compensated for by the resin in the injection cylinder in the pressure holding step of the molding machine, but can be compensated for by extruding the resin in the gas channel by gas pressure and fully filling the resin. The molten resin in the gas channel is also pushed out to the tip by the gas.

<Resin Reservoir> The resin mold for gas injection molding of the present invention is provided with a resin reservoir at a portion corresponding to the final filling portion of the molten resin. When the gas is injected after injection of the molten resin, the gas flows in the gas channel, that is, in the direction of the thick portion having a large volume shrinkage, and forms a hollow portion. Usually, the resin extruded by the gas flows into the gas channel. When the gas channel is designed close to the final filling part of the molten resin, which is the end of the product, the resin extruded to the tip by the gas accumulates at the tip because the gas flows first and fills the cavity. As a result, a hollow portion may not be formed in all the gas channels without hollowing only that portion.

In this case, a resin reservoir is separately provided in the final filling portion of the molten resin as a place where the resin can be evacuated so that the resin at the tip of the gas channel pressed by the gas does not prevent hollowing. This makes it possible to form a hollow portion in all of the gas channels, thereby increasing the hollow ratio.

In FIG. 1, reference numeral 6 denotes a resin reservoir. When molten resin is injected and injected from the resin gate 4 and then gas is injected from the gas gate 5, the injected molten resin gradually pushes the product cavity portion 3 and is pushed by the gas to hit the end of the product. The molten resin flows toward the final filling section 7. On the other hand, the injected gas passes through the gas channel portion 8 in the molten resin and advances toward the final filling portion 7 of the molten resin while hollowing the gas channel portion 8.

Here, if a resin pool is provided in the final filling section, the molten resin that has been accumulated in the final filling section 7 due to being pressed by gas pressure does not stay in the final filling section 7, Is pushed out to the resin reservoir 6 outside the product cavity, the gas can reach the final filling portion 7 without being hindered by the resin, and the gas can be hollowed up to the final filling portion.

As shown in the example of FIG.
It is preferable that the final filling portion 7 of the molten resin is provided outside the product cavity portion 3. That is, for example, an overflow tab or the like is connected to the outside of a portion corresponding to the end of the product in the product cavity of the mold to form a resin reservoir. In the product formed by this, a resin pool is formed outside the end of the product,
By cutting it off, it is possible to obtain a final product in which no resin pool remains. In this case, as shown in FIG. 1, depending on the design of the mold, a mold in which a product cavity portion and a resin reservoir portion are integrated so that a product and a resin reservoir outside the product can be molded in the same mold. It can also be used.

The configuration of the resin reservoir is not limited to this. For example, a mold can be designed so that a resin reservoir is formed inside a product. In this case, a resin pool is formed at the end of the gas channel inside the product.

<Gas Release Mechanism> The gas injection mold according to the present invention has a gas release mechanism for releasing gas at a predetermined stage in the gas injection process between the gas gate and the resin reservoir. It is characterized by having been provided. By discharging the pressurized gas at a predetermined stage of the injection molding process, the gas pressure in the gas channel is controlled, and the pressure on the mold cavity surface is made uniform to eliminate transfer unevenness and gloss unevenness. Can be.

FIG. 2 is an enlarged view of the vicinity of the resin reservoir in FIG. 1 and shows an example of a gas release mechanism. In FIG. 2, 1
Reference numeral 0 denotes a hollow portion, and reference numeral 11 denotes an unfilled portion where the resin is accumulated. In this example, a shooting pin 12 is used as a gas release mechanism, and when the molten resin is filled into the resin reservoir 6 in a certain amount, the pin is shot and discharged again to release the gas.

The gas can be released at any stage before the completion of the gas injection step, but after the molten resin starts to be filled into the resin reservoir 6 and before it is completely filled. Is preferred. If the resin pool is not completely filled with the molten resin, the gas pressure will be directed to the filling direction, and the resin in the gas channel will not be pressed against the surrounding mold more than necessary. If the gas is released, transfer unevenness and gloss unevenness hardly occur as a whole. On the other hand, when the molten resin is completely filled in the resin reservoir, only the gas channel portion is strongly pushed by the surrounding mold due to the gas pressure, so that uneven transfer and uneven gloss occur. Therefore, even if the gas is released after the molten resin is completely filled in the resin reservoir, it is not possible to prevent transfer unevenness and gloss unevenness from occurring.

As a method of knowing the timing of such gas release, for example, a method of installing a pressure sensor 13 in the resin reservoir 6 and sensing the pressure can be adopted. After finding the filling condition, a method of releasing gas according to the condition may be adopted. For example, when the internal pressure of the resin reservoir is 10 to 5
It is preferable to release gas when the pressure becomes about 00 kg / cm ² , more preferably about 50 to 200 kg / cm ² .

The gas releasing mechanism is provided at the connection between the final filling portion 7 of the molten resin and the resin reservoir 6 at the end of the product cavity in FIG. As described above, the gas release mechanism is preferably provided at the end of the gas channel, that is, at the connection from the product cavity to the resin reservoir corresponding to the end of the product to be the final filling portion of the molten resin. However, the present invention is not limited to this, and it can be provided at any position between the gas gate 5 and the resin reservoir 6. For example, it can be provided at an arbitrary position of the gas channel 8 in the product cavity 3.

The structure of the gas releasing mechanism is not limited to the one using the above-described shooting pin. For example, an on-off valve for releasing gas may be provided at an arbitrary position in the product cavity 3. Further, a thin portion may be provided in the vicinity of the final filling portion of the molten resin so as to be designed to burst when gas is injected at a certain pressure or more, so that the gas can be released as a result. In addition, there is a method in which the gas channel portion communicating with the resin reservoir portion in the mold is sheared to release the gas in the gas channel.

<Thermoplastic resin> Examples of the thermoplastic resin that can be injection-molded by the gas injection mold of the present invention include polyolefin resins, polyamide resins, polycarbonate resins, polyester resins and the like. Of these, polyolefin resins are often used for unpainted exterior parts and are useful.

Examples of the polyolefin resin include ethylene homopolymers such as low pressure polyethylene, medium pressure polyethylene, high pressure polyethylene, and linear low density polyethylene;
Or an ethylene-based resin such as an ethylene-propylene copolymer; a polypropylene homopolymer such as a stereoregular polypropylene, or a propylene-based resin such as a propylene-ethylene copolymer; a stereoregular poly-1-butene, a stereoregular poly Other α-olefin-based resins such as -4-methyl-1-pentene; and the like.

Among these, it is preferable to use an ethylene resin such as an ethylene homopolymer or an ethylene / propylene copolymer, and a propylene resin such as a propylene homopolymer or a propylene / ethylene copolymer.

The thermoplastic resin used in the present invention includes:
Other additives such as an inorganic filler and a rubber component may be blended as required. Specifically, examples of the inorganic filler include calcium oxide, magnesium oxide, silica, titanium oxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, basic magnesium carbonate, calcium carbonate, barium sulfate, talc, clay, and mica. Whisker, such as zeolite, zeolite, fibrous potassium titanate, fibrous magnesium oxalate, and fibrous aluminum borate; carbon fiber; glass fiber; The amount of the inorganic filler is generally 1 to 60 parts by weight, preferably 20 to 6 parts by weight, per 100 parts by weight of the thermoplastic resin.
When the amount is 0 parts by weight, the effects of the present invention can be remarkably exhibited.

As rubber components, ethylene-propylene copolymer rubber (EPM), ethylene / 1-butene copolymer rubber, ethylene / propylene / 1-butene copolymer rubber, ethylene / propylene / non-conjugated diene copolymer rubber (EPD)
M), polyolefin-based rubber such as ethylene / 1-butene / non-conjugated diene copolymer rubber, ethylene / propylene / 1-butene / non-conjugated diene copolymer rubber, and styrene-based rubber such as styrene / butadiene copolymer. be able to. Among these rubber components, it is preferable to use a polyolefin rubber such as an ethylene / propylene copolymer rubber (EPM) and an ethylene / propylene / non-conjugated diene copolymer rubber (EPDM). These rubber components are 100
Mooney viscosity (ML _{1 + 4} ) measured at 10 ° C.
Those having a range of 200, preferably 30 to 150 are used. The amount of the rubber component is generally 1 to 40 parts by weight, preferably 10 to 40 parts by weight, per 100 parts by weight of the thermoplastic resin.
When the amount is part by weight, the effects of the present invention can be remarkably exhibited.

Other additives include pigments and pigment dispersants for coloring, and antioxidants, antistatic agents, light stabilizers, ultraviolet absorbers, and neutralizing agents to be added for further improving the performance. Metal corrosion inhibitors, lubricants, flame retardants, nucleating agents, dispersants, processability stabilizers, flow improvers and the like.

(2) Method for producing thermoplastic resin molded article In the present invention, a thermoplastic resin molded article having a hollow portion is produced by performing gas injection molding using the above-mentioned gas injection molding die. Can be.

<Preparation of Raw Materials> Raw materials are prepared by adding additives to the above-mentioned thermoplastic resin as necessary and mixing them well. Mixing is performed by using a conventional kneader, for example, a single-screw or twin-screw extruder, a Banbury mixer, a super mixer, a roll, a Brabender plastograph,
The kneading is preferably performed by kneading using a kneader or the like, and more preferably using an extruder, particularly a twin-screw extruder. The kneading conditions can be appropriately selected according to the resin used, but generally, the kneading is carried out under normal pressure at 180 to 260 ° C, preferably 190 to 230 ° C.

<Gas Injection Molding> The production method of the present invention is characterized by performing gas injection molding including the following steps (a) to (c). (A) an injection filling step of injecting and filling a molten resin into a product cavity from a resin gate; (b) a gas injection step of injecting a gas from a gas gate into the molten resin; and (c) releasing the gas injected in the gas injection step. Gas release process released by mechanism

(A) Injection and filling step In the injection and filling step, the cavity mold and the core mold of the mold of the present invention are closed (mold clamping), and the product is adjusted by the above-described method into the product cavity formed therein. The raw material thermoplastic resin is injected and filled from the resin gate. The molding conditions in this case are not particularly limited and can be appropriately selected depending on the size and thickness of the target molded product, but the resin temperature is 180 to
It is preferable that the temperature is 250 ° C. and the mold temperature is about 20 to 60 ° C. The injection pressure is preferably 100 to 1500 k.
g / cm ² , more preferably 300 to 900 kg / cm ²
It is about.

(B) Gas Injection Step In the gas injection step, gas is injected into the molten resin filled in the product cavity, following the injection filling step. The gas is introduced into a predetermined gas channel,
The molten resin in the gas channel is extruded to the surroundings.

[0048] Although the pressure of the gas to be pressed at this time is not particularly limited, it is preferably 500 kg / cm ² or less, more preferably 100 to 200 kg / cm ² approximately.

Regarding the timing for injecting the gas, it is preferable that the injection of the molten resin is completed and the injection pressure of the molding machine is lowered, and at the same time, the gas is injected and the resin is caused to flow at the gas pressure. If a long time elapses until the gas is injected after the injection pressure drops, it takes too much time until the resin reflows due to the gas pressure, and a flow mark may be generated.

(C) Gas Release Step In the gas release step, the gas injected in the gas injection step is released by a gas release mechanism.

In the example of FIG. 2 described above, by the injection filling step and then the gas injection step, the product 9 having the hollow portion 10 is formed, and at the same time, the molten resin in the gas channel extruded by the gas is removed. Then, the resin is filled from the final filling section 7 into the resin storage section 6. As the filling of the resin reservoir 6 progresses, the pressure sensor 13 detects the gas pressure in the resin reservoir before the filling is completed, and can know the timing of releasing the gas.

Next, the gas is released by shooting the shooting pin 12 into the connecting portion between the resin reservoir 6 and the final filling portion 7 and pulling it out again.

After the resin is cooled, the cavity mold and the core mold are opened, and the molded product is taken out of the mold as in the case of ordinary injection molding.

(3) Use of Thermoplastic Resin Molded Product The thermoplastic resin molded product obtained by the production method of the present invention is not particularly limited as long as it has a hollow portion. Parts, instrument panels, console boxes, assist grips,
Automobile interior parts such as side moldings.

[0055]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. The evaluation of the physical properties in the following Examples and Comparative Examples was performed by the following methods.

(1) Uneven gloss The appearance of the obtained molded article was visually observed for the difference between the general part and the gas channel part, and evaluated according to the following criteria. ：: The general portion and the gas channel portion have the same appearance, and the boundary cannot be determined. Δ: There is sink mark, but the appearance of the gas channel is slightly improved. X: The gas channel portion and the general portion can be clearly distinguished. (2) Sinking The appearance of the obtained molded article was visually observed and evaluated according to the following criteria. ：: No sink marks are observed. Δ: The glossiness is slightly good, but sink marks are observed in the gas channel portion. ×: Sink is clearly seen in the gas channel portion.

<Example 1, Comparative Examples 1-2> As a thermoplastic resin, a polyolefin resin was used as a base and rubber was 30% by weight.
Gas injection molding was performed using a molding material containing 10% by weight of talc and talc as a raw material. The mold used was that shown in FIGS.

First, the cavity mold 1 and the core mold 2 are closed,
Raw materials melt-kneaded into the product cavity 3 were injected and injected from the resin gate 4. The resin temperature was 240 ° C., the mold temperature was 50 ° C., and the injection pressure was 1200 kg / cm ² .

Next, nitrogen gas was injected from the gas gate at a gas pressure of 130 kg / cm ² . Thereafter, after the filling of the molten resin into the resin reservoir 6 and before the resin is completely filled (when the residual pressure becomes about 10 kg / cm ² ), the shooting pin 12 is shot into the connecting portion and quickly. The gas was released to release the gas. After the resin had cooled, the cavity mold and the core mold were opened, and the molded product was taken out.

The resulting molded article was observed for uneven gloss and sink marks on the surface, and evaluated according to the above criteria. Table 1 shows the results.

<Comparative Example 1> A molded product was formed in the same manner as in Example 1 except that the gas was released by firing a shooting pin after the molten resin was completely filled in the resin reservoir 6. Table 1 shows the evaluation results.

<Comparative Example 2> A molded product was formed in the same manner as in Example 1 except that the process of releasing gas by firing a shooting pin was not performed. Table 1 shows the evaluation results.

<Comparative Example 3> Example 1 was repeated except that the resin pool was not provided, the molten resin was filled in the product cavity, the gas was press-fitted, and then the gas was released by shooting with a shooting pin.
A molded article was molded in the same manner as described above. Table 1 shows the evaluation results.

[0064]

[Table 1]

[0065]

According to the gas injection molding die of the present invention, a partially hollow molded article having no deformation such as sink marks and warpage can be produced with high industrial productivity without causing transfer unevenness and gloss unevenness. Can be molded.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an example of a gas injection mold according to the present invention.

FIG. 2 is an enlarged view of the vicinity of a resin reservoir in the gas injection mold of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cavity type 2 ... Core type 3 ... Product cavity part 4 ... Resin gate 5 ... Gas gate 6 ... Resin pool part 7 ... Final filling part of molten resin 8.・ Gas channel 9 ・ ・ ・ Product 10 ・ ・ ・ Hollow part 11 ・ ・ ・ Resin pool unfilled part 12 ・ ・ ・ Gas release mechanism 13 ・ ・ ・ Pressure sensor

Claims (4)

[Claims] 1. A resin mold comprising a cavity mold, a core mold, and a product cavity formed between the cavity mold and the core mold and filled with a molten resin. A gas injection molding die of a thermoplastic resin having a resin reservoir provided in the gas injection molding, wherein a gas discharge mechanism is provided between the gas gate and the resin reservoir. Mold. 2. The method according to claim 2, wherein the resin reservoir is a final filling portion of the molten resin and is provided outside the product cavity, and the gas discharge mechanism is provided between the resin reservoir and the product cavity. The mold for gas injection molding according to claim 1, wherein the metal mold is provided in a mold. 3. A method for producing a thermoplastic resin molded article having a hollow portion, wherein the steps (a) to (c) shown below are performed using the mold for gas injection molding according to claim 1 or 2. A method for producing a thermoplastic resin molded article, characterized by performing gas injection molding containing the same. (A) an injection filling step of injecting and filling a molten resin into a product cavity from a resin gate; (b) a gas injection step of injecting a gas from a gas gate into the molten resin; and (c) releasing the gas injected in the gas injection step. Gas release process released by mechanism 4. The gas discharging step according to claim 3, wherein the discharging of the gas is performed before the molten resin is completely filled in the resin reservoir of the gas injection molding die. A method for producing a thermoplastic resin molded product.