JP2000334764A - Injection molding method and apparatus for thermoplastic resin molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method and an apparatus for producing a thermoplastic resin molded article capable of stably and continuously supplying inert gas to a thermoplastic resin under relatively low pressure to infiltrate the same in the thermoplastic resin. SOLUTION: In an injection molding method for a thermoplastic resin molded article having a gas impregnation process for supplying gas held to a gaseous state at the normal temp. under atmospheric pressure to the molten resin in the cylinder 11 of an injection molding machine 1 from the gas supply port 5 provided to a screw to impregnate the resin with the gas and an injection molding process for plasticizing and metering the obtained gas impregnated resin to inject the same in a mold cavity to obtain a molded article, the gas is introduced into the supply passage 6 provided in the screw from the inflow port 11 provided to the rear part 32 of the screw and supplied to the thermoplastic resin from the gas supply port 5 in the screw on this side of the leading end part thereof while the pressure of the molten resin of the part 4 to which the supply port faces is always held to a state lower than the pressure of the gas supplied from the gas supply port to be infiltrated in the thermoplastic resin. An injection molding apparatus using this injection molding method is also provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thermoplastic resin molded article, particularly a thermoplastic resin foam molded article or a thermoplastic resin molded article having a high melt viscosity and which is difficult to melt-mold, and an injection method used in this production method. It relates to a molding device.

[0002]

2. Description of the Related Art As a method of obtaining a thermoplastic resin foam by injection molding, a gaseous inert gas such as carbon dioxide or nitrogen gas serving as a foaming agent is impregnated in a molten resin to be injected at normal temperature and normal pressure. There is a way. As a method for impregnating the molten resin with the inert gas as described above, 1) a method of previously impregnating a raw material resin in a solid state before being charged into a cylinder under a high pressure, and 2) US Pat. No. 5,158,986
As described in the specification, there is a method of impregnating a resin in a molten state in a cylinder.

However, the method 1) of impregnating the raw material resin in the solid state with a gas can obtain a thermoplastic resin foam, but a gas in a gaseous state at normal temperature and normal pressure, particularly an inert gas, is used. In order to completely impregnate the gas into the resin, it is necessary to stop the supply of the resin to the molding machine and impregnate the gas in the pressure-resistant chamber, for example, since the affinity with the resin is low. It takes several tens of hours to reach the state, and there is a problem that it is difficult to implement industrially.

On the other hand, as disclosed in US Pat. No. 5,158,986, a method of impregnating a resin in a molten state in a cylinder is performed by rotating a resin pellet or the like supplied from a material supply port while rotating a screw in the cylinder. While feeding the carbon dioxide gas from the gas supply port provided in one place of the cylinder during the plasticization and measurement to the measuring section at the tip of the cylinder by retracting the screw, Since the resin is in a high pressure state, it is very difficult to inject the gas unless the pressure of the supplied gas is higher than the pressure of the molten resin.
However, when a high-pressure gas is used, the apparatus itself must have a pressure-resistant structure that can withstand the high-pressure gas, and there has been a problem that the manufacturing cost increases sharply.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems associated with the production of foamed molded articles or resin molded articles made of thermoplastic resin having a high melt viscosity, and to obtain a gaseous state at normal temperature and normal pressure. Provided is a method for producing a thermoplastic resin molded article, which can stably and continuously supply and impregnate a gas, particularly an inert gas, to a thermoplastic resin at a relatively low pressure, and an injection molding apparatus used in the production method. It is in.

[0006]

Means for Solving the Problems In order to achieve the above object, an injection molding method for a thermoplastic resin molded product according to the first aspect of the present invention (hereinafter referred to as "the molding method of the first aspect") is as follows.
The resin melted in the cylinder of the injection molding machine
A gas impregnation process in which a gas in a gaseous state is supplied and impregnated at normal temperature and normal pressure from a gas supply port provided in a screw, and the obtained gas impregnated resin is plasticized and measured, and then injected into a mold cavity and molded. An injection molding step of obtaining a product, the injection molding method of a thermoplastic resin molded product comprising:
From the inlet provided behind the screw, through the supply path provided inside the screw, from the gas supply port inside the screw in front of the tip, the molten resin pressure at the part facing the gas supply port, always from the gas supply port The supply was impregnated while keeping the pressure lower than the pressure of the supplied gas.

[0007] The injection molding apparatus for a thermoplastic resin molded product according to the second aspect of the present invention (hereinafter referred to as "the molding apparatus of the second aspect") is capable of melting and kneading the molten resin by the rotation of a screw in a cylinder. An injection molding apparatus made to supply a gas in a gaseous state at normal temperature and normal pressure from a gas supply port provided in a screw to impregnate the gas,
The pressure of the molten resin includes a low-pressure portion forming portion that is a lower-pressure portion than the pressure of the gas supplied from the gas supply port in the screw, and the low-pressure portion forming portion or the screw inside the vicinity thereof includes a gas facing the low-pressure portion. A check valve for preventing the molten resin from entering the gas supply passage in the screw from the supply port is provided, and a gas inlet into the screw is provided behind the screw.

According to the first aspect of the present invention, in the gas impregnating step, the gas supply port is provided at a portion in front of the screw tip (downstream side) and in front of the hopper (side of the hopper), and the pressure of the molten resin at the portion facing the gas supply port is constantly adjusted. Then, the gas is impregnated while maintaining the pressure lower than the pressure of the gas supplied from the gas supply port, and then an injection molded product is obtained in an injection molding process. In order to carry out this method, the molding apparatus according to claim 2 is provided with a low-pressure portion forming portion that can always keep the pressure of the molten resin in a portion facing the gas supply port lower than the gas pressure supplied from the gas supply port. With the provided screw, from the gas supply port facing the low-pressure portion formed by the low-pressure portion forming portion, to provide a check valve to prevent the molten resin from entering the gas supply path in the screw, when measuring the molten resin, In addition, even when the screw moves during the injection molding, the gas can be stably supplied.

That is, in the molding apparatus according to the second aspect, the resin check valve for preventing the molten resin from entering between the cylinder and the screw from the gas supply port provided in front of the screw tip to the gas supply path into the screw is provided. Is provided. The resin check valve is located inside the screw and is provided near the gas supply port, and is, for example, a spring type. Usually, the surface of the gas supply port is closed by a taper pin with the force of the spring, and the gas supply port is closed.The gas supply port is opened when the inflow gas pressure from the screw internal supply path is larger than the biasing force of the spring, Gas impregnates the molten resin between the cylinder and the screw from the gas supply port, while the molten resin tries to flow backward from the gas supply port, it is closed by the tapered pin structure and can prevent entry into the gas supply path (backflow). It has been.

The thermoplastic resin used in the present invention is not particularly limited. For example, a resin having a high melt viscosity, which is difficult to melt-mold such as melt extrusion, a resin which is easily decomposed thermally, a low-boiling additive or Examples include hard-to-mold resins containing additives that are easily decomposed by heat.

Examples of resins which are difficult to melt-mold by melt extrusion or the like due to high melt viscosity include resins for engineering plastics such as ultra-high molecular weight polyethylene, ultra-high polymerization degree polyvinyl chloride, polytetrafluoroethylene and polyimide. No. Examples of resins that are easily thermally decomposed include biodegradable resins such as polylactic acid and polyhydroxybutyrate, polyvinyl chloride having a high degree of chlorination, and polyacrylonitrile. If necessary, an appropriate foaming agent may be added to these resins.

The gas in a gaseous state at normal temperature and normal pressure is not particularly limited as long as it does not react with the resin and does not adversely affect the resin such as deteriorating the resin. Examples include inorganic gases such as nitrogen, argon, neon, helium, and oxygen, and organic gases such as chlorofluorocarbon and low molecular weight hydrocarbons. Among these gases, inorganic gases are preferred because they have a low adverse effect on the environment and do not require gas recovery, have high solubility in difficult-to-mold resins, have a large plasticizing effect on the resins, and are released directly into the atmosphere. Carbon dioxide is preferred from the viewpoint that it hardly causes any harm. Note that such a non-reactive gas may be used alone, or two or more non-reactive gases may be used in combination.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described in detail with reference to the drawings. 1 to 6 show one embodiment of an injection molding apparatus according to the present invention.

As shown in FIG. 1, this injection molding apparatus A
Comprises an injection molding machine 1 and a gas injection device B.
The injection molding 1 includes a cylinder 2 and a screw 3.

As shown in FIGS. 2 and 3, the screw 3 has a low-pressure portion forming portion 31 in front of the distal end (downstream side) of the screw 3, and the low-pressure portion forming portion 31 has a screw groove more than other portions. The gap with the cylinder 2 is made larger than other portions by increasing the depth of the low pressure portion forming portion 31.
A low-pressure section 4 is formed between the cylinder and the cylinder 2 where the pressure of the molten resin is lower than the gas pressure in the gaseous state at normal temperature and normal pressure supplied into the cylinder 2.

That is, the gap between the inner wall surface of the cylinder and the outer wall surface of the screw is large, and the pressure of the molten resin is lower than the pressure of the gas supplied from the gas supply port.
Is formed in a part of the screw.

The screw 3 has a low pressure portion forming portion 31
A gas supply port 5 is opened in the
Is provided with a gas inlet 11 for guiding gas from the gas injection device B, as shown in FIGS.
The gas inlet 11 communicates with the gas supply port 5 via the gas supply path 6.

A check valve 7 for preventing molten resin from entering the gas supply passage 6 in the screw from the gas supply port 5 facing the low pressure part 4 is provided in the screw in the low pressure part forming part 31 or in the vicinity thereof. I have.

As shown in FIGS. 5 and 6, the check valve 7 is provided with a casing 19 and a valve body (shut-off valve) 7.
1 and a spring 8 provided with a spring 8,
There is no particular limitation as long as the gas supply port is opened when the gas pressure becomes higher than the molten resin pressure. It is preferable to use a spring type or ball check type that ensures operation, but also a type that detects the pressure of the molten resin and opens the electromagnetic valve when the molten resin pressure becomes lower than a preset gas pressure. I do not care. In addition, the material of the check valve is not specified as long as it has heat resistance of 200 ° C. or higher, but metal, particularly stainless steel is preferable in terms of strength, heat resistance, slidability, and workability. .

The casing 19 is provided therein with a gas flow path 61 connecting the gas supply port 5 and the gas supply path 6 (see FIG. 3), and has a valve body 72, a valve shaft 73, a spring 8 Is housed so as to be able to advance and retreat in the direction of the gas supply port 5. The gas flow path 61 has a large-diameter portion 62 in which the spring 8 of the valve body 72 is accommodated and a gas passage 61 connected to the large-diameter portion 62 extending from the gas supply passage 6 toward the gas supply port 5. A large-diameter small-diameter portion 63 and a large-diameter portion 65 that expands in a trumpet shape from the small-diameter portion 63 are sequentially provided.

Normally, as shown in FIG. 5, the valve body 71 urged by the spring 8 in the direction of the right arrow has a trumpet-shaped enlarged portion 75 formed by the enlarged portion 65 of the casing 19 (that is, the enlarged gas flow path). The gas is supplied to the gas supply passages 6 and 61. When the gas is supplied to the gas supply paths 6 and 61, the pressure is applied to the back surface of the enlarged diameter portion 75 of the valve main body. 8, the gas is advanced toward the gas supply port 5 side, and the gas passes through the gas supply path 61 and further passes through the gas supply port 5 to the molten resin between the cylinder and the screw as shown in FIG. It is impregnated.

The screw 3 has a rear portion 32,
A gas inlet 11 for introducing gas from the gas injection device B is provided, and a seal box 12 is provided around the periphery to prevent gas leakage, as shown in FIG. The seal box 12 is provided with a seal member 19 so as to seal the gas inlet 11 and is in surface contact with the outer periphery of the screw.

A gas flow path pipe 16 from the gas injection device B is attached to the seal box 12, and gas flows from a sealed portion in the seal box 12 through the gas inlet 11 as described above to the gas supply paths 6 and 61. To. The seal box 12 is fixed to the unit 13 of the injection molding machine 1 by a connection arm 14 so that the position of the seal box 12 does not deviate from the gas inlet 11 with respect to the forward and backward movement and rotation of the screw 3.

Further, preferably, when the rotation of the screw 3 is stopped, the gas-impregnated molten resin between the cylinder and the screw is prevented from flowing back to the resin supply hopper side due to gas pressure. A check ring 10 (see FIG. 3) is attached to the front side, that is, to the side (hopper side) of the gas supply port 5.
This check ring 10 is suitably used for preventing resin backflow, particularly when the gas pressure from the gas supply port is high.

Since the injection molding apparatus A is configured as described above, when the raw resin is supplied from the raw material supply port 15, the raw resin is melted and kneaded by the rotation of the screw 3 while the raw resin is melted and kneaded. Sent to the tip. The melt-kneaded resin is sent to the pressure release section, that is, the low pressure section 4 via the check ring 10. At that time, gas injection device B
The gas sent from the tank enters the seal box 12 via the pipe 16, and flows into the gas inlet 11, the gas supply path 6,
The resin is impregnated through the check valve 7 and the gas supply port 5.

Then, as the plasticized molten resin is sent to the tip of the cylinder 2 one after another, the screw 3 gradually moves backward according to the amount of the sent resin as shown in FIG. A fixed amount of molten resin is measured at the tip of the cylinder 2.

In this way, the gas-impregnated molten resin after the plasticization measurement is injected into an injection mold (not shown) to obtain a molded product. As described above, according to the injection molding apparatus A, that is, according to the molding method of the first aspect using the molding apparatus of the second aspect, the molten resin can be uniformly impregnated with the gas in a short time. It is possible to provide a uniform and fine foamed molded product with high productivity.

(Example 1) Using the injection molding apparatus shown in Fig. 1, a device capable of supplying gas from inside the screw was installed to obtain a thermoplastic resin molded product. The pellet resin was charged into the hopper 17 and supplied to the plasticizer from the raw material supply port 15. The screw 3 was rotated (weighed) to measure the resin. During the plasticization, the gas was supplied from the gas injection device B to the molten resin at a pressure of 6 MPa through the pipe 16, the seal box 12, the gas inlet 11, the gas supply path 6, the check valve 7, and the gas supply port 5. .

[Resin impregnation step] In the above method, polypropylene resin (Montel PF814, manufactured by JPO Co., Ltd.) is used as a molding material, and a measuring resin is discharged from the tip 18 of the injection molding apparatus shown in FIG. The gas impregnated state was confirmed. The plasticization was performed at a temperature of 200 ° C. in the plasticizer. The discharged molding material is foamed uniformly,
No difference in the gas impregnation state between the weighed resins was observed.

[Injection molding step] Using the above-mentioned gas-impregnated molding material, a resin to be discharged is filled in a mold cavity with about half the volume of the gas-impregnated molding material. After cooling, the mold was opened and taken out as a molded product. Plasticizer temperature 200 ° C, resin filling speed 20
Injection molding was performed at 0 mm / sec, a mold temperature of 50 ° C., and a cooling time of 60 seconds.

The shape of the molded product is a cup shape, approximately φ1
Using a mold having a shape of 00 mm, a height of 130 mm, and a thickness of 8 mm, a molded body having a corresponding size was obtained. The molded article was smooth, the average expansion ratio was 2.2 times, and the error of the expansion ratio in each part of the product was within 5%, and a uniform foamed article could be obtained.

[0032]

The method of injection molding a thermoplastic resin molded article according to the present invention is characterized in that a molten resin in a molten state in a cylinder of an injection molding machine is fed from a gas supply port provided in a screw at room temperature.
A gas impregnating step of supplying and impregnating a gas in a gaseous state at normal pressure, and an injection molding step of plasticizing and measuring the obtained gas impregnated resin and then injecting it into a mold cavity to obtain a molded product. An injection molding method of a plastic resin molded article,
The gas, through the supply path provided in the screw from the inlet provided behind the screw, from the gas supply port in the screw in front of the tip, the molten resin pressure of the portion facing the gas supply port, always, Since the gas is supplied and impregnated while maintaining the pressure lower than the pressure of the gas supplied from the gas supply port, it does not require a long time for gas impregnation as in the related art, and is stably and continuously at a relatively low pressure. Gas can be supplied, and high productivity can be obtained, and a uniform and fine high-performance (insulation, cushioning, lightweight) foamed molded article can be provided at low cost by injection molding.

The injection molding apparatus for a thermoplastic resin molded article of the present invention is characterized in that a gas in a gaseous state at normal temperature and pressure is supplied to a molten resin melt-kneaded by rotation of a screw in a cylinder from a gas supply port provided in the screw. An injection molding apparatus adapted to be supplied and impregnated with the gas, comprising a low-pressure part forming part in which the pressure of the molten resin is lower than the pressure of the gas supplied from the gas supply port in the screw, The low-pressure part forming part or the screw inside the vicinity thereof is provided with a check valve for preventing molten resin from entering the gas supply path in the screw from the gas supply port facing the low-pressure part,
Behind the screw, a gas inlet communicating with the gas supply port is provided, and since a device related to gas supply is a screw portion, it is not necessary to make the entire device a pressure-resistant structure. In addition to the above, the cost of the molding can be reduced, and similarly to the above-described injection molding method, a uniform and fine foam molded article or a molded article of a difficult-to-mold material can be provided with high productivity.

[0034]

[Brief description of the drawings]

FIG. 1 is a side view schematically showing one embodiment of an injection molding apparatus according to the present invention.

FIG. 2 is a schematic side sectional view showing an overall outline of an injection molding machine of the injection molding apparatus of FIG. 1 and showing a gas inflow path inside a screw.

FIG. 3 shows details of a gas supply port to a molten resin.
FIG. 3 is an enlarged view of a check valve 7 and a vicinity of a low-pressure section in FIG. 2.

FIG. 4 is an enlarged view of the vicinity of a gas inlet 11 in FIG. 2 for illustrating details of a gas inlet into the screw; FIG. 4A is a schematic side cross-sectional view of a rear part of the screw;
(B) is a schematic front sectional view.

FIG. 5 is an enlarged view of the check valve of FIG. 3 and is a cross-sectional view showing a state where the valve is closed and gas supply is closed.

6 is an enlarged view of the check valve of FIG. 3 and is a cross-sectional view showing a state where the valve is opened and gas is supplied.

[Explanation of symbols]

 Reference Signs List A injection molding apparatus B gas injection apparatus 1 injection molding machine 2 cylinder 3 screw 31 low-pressure part forming part 32 screw rear part 4 low-pressure part 5 gas supply port 6 gas supply path 61 gas supply path 7 check valve 71 valve body (pin) 8 Spring 10 Check ring 11 Gas inlet 12 Seal box

Claims (2)

[Claims] A gas impregnating step of impregnating a molten resin in a molten state in a cylinder of an injection molding machine by supplying a gaseous gas at normal temperature and normal pressure from a gas supply port provided in a screw; An injection molding step of injecting the gas-impregnated resin into the mold cavity after plasticizing and measuring the obtained gas-impregnated resin to obtain a molded product, the method comprising: Through the supply path provided in the screw from the inflow port provided in the screw, from the gas supply port in the screw in front of the tip, the molten resin pressure of the portion facing the gas supply port, is always supplied from the gas supply port An injection molding method of a thermoplastic resin molded product, wherein the resin is supplied and impregnated while keeping the pressure lower than the gas pressure. 2. A gas in a gaseous state is supplied to a molten resin kneaded by rotation of a screw in a cylinder at a normal temperature and a normal pressure from a gas supply port provided in the screw to impregnate the molten resin. An injection molding apparatus, comprising a low-pressure portion forming portion in which the pressure of the molten resin becomes a lower-pressure portion than the pressure of the gas supplied from the gas supply port in the screw, and the low-pressure portion forming portion or in the vicinity of the screw inside the screw. Is provided with a check valve for preventing the molten resin from entering the gas supply path in the screw from the gas supply port facing the low pressure portion, and a gas inlet communicating with the gas supply port is provided behind the screw. Injection molding apparatus for thermoplastic resin molded products.