JP2002307471A - Method for molding thermoplastic resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To economically provide a method for transferring a state of the surface of a mold to a molding precisely without using a complex apparatus and a complex mold by preventing solidification and viscosity rise of a thermoplastic resin in a resin packing process in the injection molding of the resin. SOLUTION: The thermoplastic resin incorporated with a filler is melted, packed in a cooling mold filled with carbon dioxide at a pressure which dissolves at least 0.1 wt.% of carbon dioxide in the resin, and molded with the solidification temperature of the surface of the resin lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding method for transferring a surface state of a mold to the surface of a molded article at a high level in molding a thermoplastic resin.

[0002]

2. Description of the Related Art In molding a thermoplastic resin, the temperature of a mold is usually kept sufficiently lower than the temperature at which the molding resin solidifies. This is necessary for cooling a resin material having extremely low thermal conductivity from a molten state to a temperature at which it can be taken out as a molded product in a short time. Further, in order to transfer a mold surface state to a molded article to a high degree, it is necessary to press a resin having a low viscosity into a mold with a high pressure.

However, when the mold temperature is lower than the solidification temperature of the resin, the resin filling and the solidification of the resin proceed simultaneously, and the resin contacting the mold near the resin flow front (flow front) is It is rapidly cooled to increase the viscosity and solidifies while being pressed against the mold surface at a low pressure. Therefore, it is difficult to transfer the mold surface state to a molded product at a high level. For this reason, normal injection molding tends to cause poor appearance such as uneven gloss, weld lines, flow marks, and jetting, and poor transfer of fine pits in precision molded products such as optical discs, and short shots in thin parts. There is also.

In order to enhance the transferability of the mold surface, it is necessary to prevent or minimize the solidification of the resin during the resin filling step.

[0005] In injection molding of a thermoplastic resin and the like, it has always been required to economically enhance the mold surface transferability without increasing the molding cycle time. Various methods have been proposed as means for improving the mold surface transferability. For example, there are the following methods.

(1) A method of repeating heating and cooling of the mold surface by alternately flowing a heat medium and a coolant through the mold (Plastic)
Technology, VOL. 34 (June), 1
50 (1988)). (2) A method of selectively heating the mold surface by high-frequency induction heating immediately before molding (US Pat. No. 4,439,492). (3) A method in which an insulating layer and a conductive layer are provided on a mold surface, and the conductive layer is energized and heated (Polym. Eng. Sci., V
ol. 34 (11), 894 (1994), etc.). (4) Method of radiantly heating the mold surface (synthetic resin, Vo
l. 42 (1), 48 (1996), etc.). (5) A heat insulating layer coating method (USP) in which a mold surface is coated with a heat insulating layer, and the mold surface is molded while heating the mold surface with the heat of the molding resin itself.
5362226, WO97 / 04938, etc.).

[0007] A report by BH Kim (Polym. Plast. Technol. En.)
g. , Vol. 25 (1), 73 (1986))
The method of (1) to (4), in which the mold surface is heated by external energy such as electricity just before molding, is an active control method. Is referred to as a passive control method.

[0008] Both the active control method and the passive control method are methods of molding while heating the mold surface during injection molding. That is, this is a molding method in which the mold surface is heated to a temperature not lower than the solidification temperature of the resin when the injected molten resin is pressed against the mold wall surface, thereby improving the mold surface transferability.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of transferring a surface state of a mold to a molded article by preventing the resin from solidifying or increasing in viscosity during a resin filling step in molding a thermoplastic resin. Is to provide economically.

[0010]

The present inventors have studied to solve the above-mentioned problems, and as a result, the present invention is completely different from the conventionally considered method of improving the mold surface transferability by heating the mold surface. The present inventors have found that the mold surface state can be highly transferred to a molded article by the method, and have completed the present invention. That is, the present invention includes the following inventions.

(1) In a molding method in which a molten thermoplastic resin mixed with a filler is filled in a mold and molded, the solubility of the resin at the solidification temperature in the resin is at least twice that of air and / or nitrogen. Is filled into the mold cavity,
Next, the resin is filled in the mold cavity, and the resin is molded while the solidification temperature of the resin surface in contact with the mold is lowered during the resin filling step.

(2) The molding method according to (1), wherein the gas is carbon dioxide.

(3) In the above (1) or (2),
A molding method wherein the filler is glass fiber.

The present invention is a method for achieving the object by a mechanism completely different from the conventional molding mechanism for improving the mold surface transferability, and has found a method for obtaining a remarkable effect by a new idea different from the conventional art. This has led to the present invention.

The following is a description of known documents that are somewhat relevant to the present invention.

In injection molding of a foaming resin containing a foaming agent or water, a pressurized gas body is injected into a mold cavity prior to resin filling in order to eliminate surface defects such as swirl marks on the surface of the molded product due to foaming gas. And pressurizing and molding the so-called counter pressure method. In this method, gas pressure is applied to the mold cavity in advance to prevent bubbles generated by foaming gas or vaporized moisture from exploding at the flow front of the molten resin flowing through the mold cavity and causing surface defects. In this case, the gas may be any one that does not cause oxidative degradation of the resin. In general, air is used, and all inert gas can be used in this molding method. This counter pressure method is a method used for injection molding of a foaming agent-containing resin or a resin that is insufficiently dried. However, when the air enters the gap between the molten resin and the mold and hinders transfer, or when the gaseous body is air, the part where the air is compressed by the resin in the cavity becomes a state of high oxygen concentration at high temperature, resulting in oxidative deterioration of the resin. It can be said that only the problem of causing the mold transfer or the like occurs, and there is no effect of improving the mold surface transferability. For this reason, in order to transfer the mold surface state to the molded product to a high degree, there are also methods such as opening the mold slightly during resin filling to release air in the cavity, and reducing the pressure inside the mold by a vacuum pump. It is used.

Japanese Unexamined Patent Publication (Kokai) No. 62-231715 discloses a method of molding a water-containing polymer alloy using a counter pressure method for injection molding. The gas body for pre-pressurizing the mold cavity is air or nitrogen. And inert gas bodies such as carbon dioxide, but do not suggest the concept of the present invention.

Further, Japanese Unexamined Patent Publication (Kokai) No. 61-213111 discloses a reaction injection molding in which two kinds of monomers are mixed and injected (Reaction Injection Molding).
Regarding ng), a method is described in which the mold cavity is replaced with carbon dioxide at atmospheric pressure and then molded to reduce voids generated when air is entrapped in the resin during resin filling. However, the reaction injection molding in which the mold temperature is higher than the temperature of the raw material in which two or more types of monomers are mixed, and the injection molding of the thermoplastic resin of the present invention are completely different fields, and the resin molding during the resin filling step is different. It does not disclose a method for improving a mold surface transferability defect caused by solidification.

On the other hand, J.I. Appl. Polym. Sc
i. , Vol. 30, 2633 (1985), it is known that when carbon dioxide is absorbed by a resin, it acts as a plasticizer for the resin and lowers the glass transition temperature. It has not been widely applied to processing. As a few application examples,
German Patent DE 4314869 discloses that a glass transition temperature is lowered by dissolving supercritical carbon dioxide and hydrocarbons in a bioabsorbable polyester in a high-pressure vessel.
A method of molding a resin at a low temperature of about 0 ° C. is disclosed. However, this method lowers the glass transition temperature of the entire resin, so it is necessary to use a mold temperature lower than usual for the reduction of the glass transition temperature for molding, and improper transfer due to solidification during the resin filling step. There is no effect to prevent.

The present invention focuses on the gas inside the mold cavity, which has been conventionally considered to inhibit the transfer of the mold surface. The mechanism by which the effect is exhibited is considered as follows.

In the injection molding, the resin always flows in a laminar flow in the mold cavity, and when it comes into contact with the cooled mold wall, a solidified layer is formed at the interface, and the resin to be filled later is placed inside the solidified layer. And flows forward to reach a resin flow front end (flow front), and then flow toward a mold wall surface, called a fountain flow. If the mold cavity is filled with resin after filling the mold cavity with a specific gaseous substance such as carbon dioxide at an appropriate gas pressure, the gaseous body is absorbed at the flow front of the flowing resin or enters the interface between the mold and the resin and enters the resin surface. Dissolve in layer. The gas dissolved in the resin acts as a plasticizer and selectively lowers the solidification temperature only on the resin surface or lowers the melt viscosity of the resin. If the solidification temperature is lowered only for the thin resin surface layer and the solidification temperature is equal to or lower than the mold surface temperature, no solidification occurs during the resin filling step, and the mold surface transferability of the molded product can be significantly improved. The gas dissolved in the resin surface layer diffuses into the resin with time, and the solidification temperature of the resin surface layer rises. Therefore, the surface layer solidifies within the usual resin cooling time and can be taken out as a product.

As a result, it becomes possible to perform molding while lowering the solidification temperature of the resin surface in contact with the mold during the resin filling step, and the present invention has been achieved.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The resin used in the present invention is a thermoplastic resin that can be used for general injection molding and the like. An amorphous thermoplastic resin, a thermoplastic polymer alloy containing an amorphous resin as a main component, or a part of the crystalline thermoplastic resin having a low crystallinity can be preferably used. Polystyrene, styrene-acrylonitrile copolymer, rubber-reinforced polystyrene,
Styrene-methyl methacrylate copolymer, ABS resin, styrene-based resin such as styrene-methyl methacrylate-butadiene copolymer, polymethyl methacrylate,
Modified polyphenylene ether blended with methacrylic resin such as methyl methacrylate-styrene copolymer, polyvinyl acetate, polycarbonate, polyphenylene ether or polystyrene, polysulfone, polyether sulfone, polyetherimide, polyarylate, polyamideimide, polyvinyl chloride, chloride Vinyl-
Vinyl chloride resins such as an ethylene copolymer and a vinyl chloride-vinyl acetate copolymer can be used particularly favorably. Further, there are blends of these resins, resins in which some crystalline resins are blended with these amorphous resins, and resins in which various fillers such as inorganic and organic substances are blended.

In the present invention, a combination in which the gas used is well dissolved in the resin is preferable. When carbon dioxide is used as the gas, a resin having a higher affinity for carbon dioxide and a higher solubility of carbon dioxide has a greater effect. Further, in the present invention, a resin having a poor appearance of a molded product among various difficult-to-process resins has a large effect.

The solidification temperature of the resin described in the present invention is a temperature at which a molten thermoplastic resin solidifies in a mold, a glass transition temperature for an amorphous resin, and a crystallization start temperature for a crystalline resin. In the case of the incompatible polymer alloy, it is the glass transition temperature or the crystallization start temperature of the resin constituting the sea having the sea-island structure. Here, the crystallization start temperature of the crystalline resin is determined by heating the resin to a molding temperature using a differential calorimeter, melting the resin, and cooling the resin at a rate of 20 ° C./min. The temperature allowed first.

In the present invention, the gas filling the mold cavity has a high solubility in a thermoplastic resin,
A gas having a solubility of at least twice that of air and / or nitrogen at the solidification temperature of the resin and having a plasticizing effect on the resin. That is, the gas body is a gas body that exists in the mold cavity, is absorbed by the resin surface during the resin filling step, and lowers the solidification temperature of the resin surface in contact with the mold. In the case of air or a gaseous substance having a solubility of about nitrogen in a resin, the transfer of the mold surface is only inhibited in the cavity, as is conventionally known. is necessary. In addition, it is selected from restrictions such as not deteriorating the resin, no danger to the mold and molding environment, and being inexpensive. As long as the gas has high solubility, a mixture of two or more gases can be used.

Specifically, carbon dioxide, methane, ethane,
Hydrocarbons such as propane, and fluorocarbons in which hydrogen has been partially substituted with fluorine or the like, and the most suitable one is selected depending on the thermoplastic resin used. Among them, carbon dioxide can be used best not only in terms of safety, price, ease of handling, etc., but also dissolves well in resin and becomes a plasticizer,
The effect of lowering the solidification temperature of the resin is also great.

Next, the drawings showing the amount of dissolved carbon dioxide, which is the gaseous substance most preferably used in the present invention, in each resin, and the decrease in the glass transition temperature (hereinafter abbreviated as Tg) of the resin due to the dissolution of carbon dioxide, etc. It will be described using FIG.

FIGS. 1 to 10 show reports described in various documents. That is, FIG. 1 and FIG.
96 (JSPP'96 Tech. Papers), 2
3 to FIG. 6 and FIG. Ap
pl. Polym. Sci. , Vol. 30,4019
(1985), FIG. 7 and FIG. Appl. Po
lym. Sci. , Vol. 30, 2633 (198
From FIG. 5), FIG. Membrane Sci. , V
ol. 5, 63 (1979).

FIGS. 1 and 2 show the amounts of carbon dioxide and nitrogen dissolved in polystyrene. Carbon dioxide has about 10 times the amount of nitrogen dissolved.

FIGS. 3 and 4 show the amount of carbon dioxide dissolved in polystyrene containing a liquid plasticizer, and FIG. 5 shows the amount of reduction in Tg due to dissolution of carbon dioxide. Polystyrene can easily lower Tg by dissolving carbon dioxide.

FIGS. 6 and 7 show the amount of carbon dioxide dissolved in polymethyl methacrylate and polyvinylidene fluoride polymer alloy, and the amount of decrease in Tg due to the dissolution of carbon dioxide. Can be.

FIGS. 8 and 9 show the amounts of carbon dioxide dissolved in polycarbonate and polysulfone.

FIG. 10 is a graph showing T by dissolving each resin in carbon dioxide.
It is the figure which showed the g reduction amount collectively. The decrease in Tg due to dissolution of carbon dioxide is almost the same except for polycarbonate. Polycarbonate is Tg by dissolving carbon dioxide
Is particularly large.

As the gas pressure filled in the mold cavity becomes higher, a larger amount of gas is dissolved in the resin as the pressure becomes higher.
The solidification temperature is lower, and solidification during the resin filling step can be prevented even at a low mold temperature. In practice, the required gas pressure is determined by the required mold surface transferability, the type of resin and gas body, and the mold temperature.Use a gas body with high solubility and raise the mold temperature. If set, sufficient transferability can be obtained at a low gas pressure.

The lower limit of the pressure is determined by the plasticizer effect of the gas dissolved in the resin, and is the pressure at which the resin dissolves in the resin in an equilibrium state at a solidification temperature of 0.1% by weight, preferably 0.5% by weight. Dissolution pressure. The solubility of the gas used in the resin is a value measured by a pressure drop method. Even if the pressure or the atmospheric pressure is lower than this, when a highly soluble gas such as carbon dioxide is used, it is possible to obtain an effect of improving transferability equal to or higher than that when the cavity is depressurized by a vacuum pump. When using at low pressure,
It is preferable to replace the cavity with a specific gas as much as possible.

The upper limit of the pressure is not particularly limited.
If the pressure is too high, the force to open the mold cannot be ignored, and problems such as difficulty in sealing the mold are likely to occur. Therefore, 15 MPa or less is practical.
Preferably it is 10 MPa or less. In order to minimize the amount of gas used in one process and to simplify the structure of the mold seal and the gas supply device, the gas pressure is preferably as low as possible within the range where the required effects can be obtained.

It is preferable that the air remaining in the mold when the mold is closed be replaced with a gas used during or after completion of the mold clamping. However, when the gas pressure used exceeds 1 MPa,
The effect of air is almost negligible.

After filling the resin, the gas pushed out of the cavity is released to atmospheric pressure. The release of the gas is performed after the cavity is filled with the molten resin. After the resin is filled, it is desirable to apply a sufficient pressure to the resin in the cavity until the surface of the molded product is solidified in order to transfer the surface state of the mold to the molded product. In particular, when transferring a point-like dent shape on the mold surface, it is necessary to press the resin against the mold against the gas pressure inside the dent, in which case it is higher than normal molding It is desirable to mold with resin pressure.

The gas dissolved in the resin gradually diffuses into the air if the molded article is left in the air after the resin is molded. No bubbles are generated in the molded article due to the radiation, and the mechanical performance of the molded article after the radiation is the same as that produced by the ordinary molding method.

It is preferable that a device for supplying and discharging a gas body to and from the cavity, a gas pipe and a mold take measures to prevent liquefaction of the gas body. This is because at a temperature at which liquefaction of the gas occurs, not only a high gas pressure cannot be obtained, but also when the liquefied gas comes into contact with the resin in the cavity, a large amount of gas dissolves into the resin, and after the gas pressure is released, the surface of the molded product is released. This is to cause foaming and cause poor appearance. As measures to prevent liquefaction, the gas body is heated by a heater to maintain the temperature of the gas body flow path and mold above the critical temperature of the gas body, and the gas body is pushed out of the cavity during resin filling. In order to prevent a large pressure increase due to the above, a pressure release valve capable of maintaining the gas pressure in the cavity and the pipe in an arbitrary range, and a gas reservoir in which a gas can flow backward from the cavity are provided. However, it is not preferable to increase the temperature of the gas body excessively in order to prevent liquefaction of the gas body, because the gas amount in the cavity decreases due to expansion of the gas body.

Normally, in order to make the mold hermetically sealed by molding by a counter pressure method or the like, the parting surface and each plate are sealed with an O-ring, and movable pins such as protruding pins communicating with the cavity are also formed with an O-ring. A method of sealing or covering the entire protruding plate portion to which the protruding pin is fixed to be airtight is adopted. When an O-ring is used to seal the ejection pin, it is necessary to insert the O-ring between the two plates and then pass the ejection pin. At this time, if the O-ring is damaged by the edge of the tip of the protruding pin, or if the pin insertion resistance is large, the O-ring is twisted, and reliable sealing performance cannot often be secured. On the other hand, when sealing is performed with a rubber packing having a U-shaped cross section in the radial direction (hereinafter referred to as U packing), the insertion resistance at the time of inserting the protruding pin is small, and it is easily formed without being damaged or twisted at the edge of the pin tip. The mold can be assembled, and a highly reliable sealing property can be obtained.

When the movable pin is sealed with packing, the pressurized gas body that has entered the gap around the pin between the cavity and the packing is confined in the gap by resin filling.
If the surface of the molded product is cooled and separates from the surface of the mold, the molded product may flow into the cavity, dent the surface of the molded product that is not sufficiently solidified, or expand and deform the molded product when the mold is opened. When such a problem occurs, the mold is provided with a groove or a hole capable of discharging the pressurized gas entering the gap around the pin from the path other than the cavity to the outside of the mold, and after being filled with the resin, is pushed out of the cavity. It is desirable to exhaust the gas at the same time as the exhausted gas. FIG. 12 shows an example of the structure of a mold capable of discharging a pressurized gas body out of the mold from a path other than the cavity.

Injection of the gas into the cavity can be performed by using a mold structure generally used for venting the cavity. A slit provided on a parting surface on the outer periphery of the cavity, a gap between a mold insert and a protrusion pin, Degassing pins and nests made of porous sintered bodies can be used. When replacing the cavity with a gas body near the atmospheric pressure, an economical method is required that replaces the air in the cavity with as little gas as possible and as little as 100% as much as possible. A method of blowing a gas body is suitable. Prior to filling the cavity with the resin, the gas body is injected from the vicinity of the mold sprue and molded, so that the gas body is pushed by the resin and the gas body discharges the air remaining in the cavity to the outside of the mold. It will be molded. That is, if the vicinity of the sprue, runner, and gate of the mold is sufficiently replaced with a gas, the gas that comes into contact with the resin is always the injected gas.

FIG. 11 shows a nozzle for injecting a gas for pressurizing the cavity from the sprue portion of the mold. In FIG. 11, a nozzle 2 connected to an injection cylinder 1 has a needle valve 4 for opening and closing a nozzle tip 3. An outer nozzle 5 is provided at the nozzle tip, and a space 6 formed by the nozzle body 2 and the outer nozzle 5 is connected to a gas source through a passage 7. When the outer nozzle 5 contacts the mold lightly, the space 6 is connected to the cavity, and in this state, the gas is pressed into the mold from the space 6. Next, when the injection cylinder 1 moves forward and the outer nozzle 5 is strongly pressed against the mold, the spring pressing the outer nozzle 5 against the mold is compressed, the nozzle body 2 moves forward, and the connection between the space 6 and the mold is established. Will be shut off. In this state, the mold is filled with resin from the injection cylinder 1.

According to the present invention, there is also provided a method of filling a mold cavity with a mold cavity at a pressure as low as about 1 MPa from the atmospheric pressure, and then compressing the cavity with a molten resin and molding while increasing the gas pressure. included. Using a mold with a structure in which the gas body in the cavity is sealed with an O-ring or the like,
When the cavity is filled with a gas and filled with a resin at a pressure as low as about 1 MPa from the atmospheric pressure, the gas is compressed by the resin, and the gas pressure increases as the filling of the resin proceeds. When the gas pressure increases, the amount of gas dissolved in the resin increases, the resin is plasticized by the dissolved gas, and the fluidity improves,
High mold surface transferability can be obtained. In general injection-molded products, the mold surface transferability at the resin flow end where the injection pressure is poor is lower than that near the gate, but the above method can improve the mold surface transfer at the flow end.

The same effect is also effective for transferring a fine concave portion on the surface of a mold. In general, in a fine concave portion, the resin often cannot enter the interior sufficiently due to solidification during resin flow or air trapped in the concave shape, but in the present invention, the trapped gas is absorbed by the resin. Therefore, it hardly hinders the filling of the resin, the solidification temperature of the resin is reduced by the plasticizer effect of the absorbed gas, and the fluidity is increased, so that the resin can be filled all the way into the recess.

Further, the present invention also provides another molding method which provides a mold surface reproducibility effect at a lower gas pressure in the cavity. That is, there is also included a molding method in which a liquid that becomes a plasticizer dissolved in a resin is present at an interface where a mold and a molten resin come into contact with each other, thereby lowering the solidification temperature of the resin surface during the molding process. Choose an appropriate plasticizer,
By coating the mold surface with an appropriate thickness, the mold surface reproducibility of the molded product is improved.

The present invention also includes a molding method in which carbon dioxide or the like containing a liquid vaporized substance and / or atomized fine particle dispersion in which carbon dioxide or the like is easily dissolved is pressed into a cavity of a cooled mold and molded. included. The liquid described here has a large amount of dissolved carbon dioxide, and is a liquid that is well soluble in resin when the boiling point is equal to or higher than the mold temperature. A good solvent and plasticizer for the resin, which has a large amount of dissolved carbon dioxide, can be used favorably. Generally, water, ketones such as acetone and methyl ethyl ketone, alcohols such as ethyl alcohol, and various polar solvents can be used.

Liquid vapor which easily dissolves carbon dioxide and the like;
When carbon dioxide containing the liquid dispersed in the form of atomized fine particles is injected into the cavity of the cooled mold, the cavity surface has a plasticizing effect of the resin due to dew condensation and contains a large amount of carbon dioxide and the like. It is also possible to improve the mold surface transferability of the molded product by coating the resin being molded with a thin layer of liquid and pressing the resin being molded onto the surface to impregnate the resin surface layer with a large amount of carbon dioxide. That is, a method in which a sufficient amount of carbon dioxide is supplied to the resin surface only by supplying low-pressure carbon dioxide into the cavity by allowing a liquid containing a large amount of carbon dioxide to exist on the mold surface.

The thickness of the thin liquid on the surface of the mold must be within a range that does not cause the resin solidified layer to slip on the surface of the mold when the resin is filled, and is generally preferably in the range of about 0.1 μm to 10 μm. It is preferable that the concentration of the liquid in the carbon dioxide be adjusted to a concentration that allows the thickness of the thin liquid to be injected into the cavity.

In the present invention, various injection molding methods can be favorably used. In general, low-pressure injection molding methods such as gas-assisted injection molding, liquid-assisted injection molding, and injection compression molding, which are considered to be inferior in mold surface transferability, can be used favorably. Further, injection molding including low-speed filling with a flow front flow rate of the resin of 200 mm / sec or less, particularly 100 mm / sec or less, can also be favorably used. This includes various cases such as a case where the flow speed of the resin temporarily becomes low, a case where the flow stops momentarily, and a case where the flow is entirely low. According to the present invention, since the solidification of the resin at the time of filling the resin can be prevented, a difference in partial mold surface transferability due to a difference in resin flow speed called a hesitation mark found in gas assist injection molding is also small. Become.

Further, in the present invention, it can be used in combination with the existing mold surface transferability improving method for increasing the mold surface temperature described above. In these molding methods, since the mold temperature is high, the resin and the mold are easily brought into close contact with each other at the time of filling the resin, and when air in the cavity is trapped between the resin and the mold,
Often a depression is formed on the resin surface. In combination with the present invention, not only the dent defect on the resin surface is improved, but also high mold surface transferability can be obtained at a lower mold temperature, and the heating efficiency can be increased.

Further, the present invention can provide a molded article having both high mold surface transferability and high mechanical properties by combining with a method of applying vibration to the resin during the resin filling step. As a method of applying vibration to the resin, a method of vibrating the resin in the injection cylinder (Polym. Plas.
t. Technol. Eng. , 17 (1), 11 (1
981)), a method of vibrating the mold (forming process '97
(JSPP '97 Tech. Papers), 18
5, (1997)), and a method of vibrating a pressurized gas in a cavity (Plattics World, Jul.
y, 8 (1997)). In particular, in the combination of the present invention with the method of exciting the pressurized gas in the cavity,
Since the transfer inhibition by the nitrogen gas used conventionally can be prevented, a high combined effect can be obtained.

[0056]

EXAMPLES The effects of the present invention will be more specifically described below with reference to examples and comparative examples.

The resin used in the injection molding was rubber-reinforced polystyrene (manufactured by Asahi Kasei Corporation, trade name: Stylon 40).
0), 20% glass fiber-filled ABS resin (manufactured by Asahi Kasei Corp., trade name: Stylac ABS R240A), methacrylic resin (manufactured by Asahi Kasei Corp., trade name: Delpet 80)
NH) and polycarbonate (trade name: Panlite L1225, manufactured by Teijin Chemicals Ltd.).

Carbon dioxide having a purity of 99% or more was used as the gas.

As a molding machine, SG50 manufactured by Sumitomo Heavy Industries, Ltd. was used.

The molded product is a square flat plate having a thickness of 2 mm and a length and width of 100 mm. FIG. 12 shows the structure of the mold, and FIG. 13 shows the structure of the gas supply device. 12A is a cross-sectional view of the whole mold, FIG. 12B is a cross-sectional view of the mold on the moving side, and FIG. 12A is a cross-sectional view of AA ′ in FIG. 12A, and FIG. FIG. 3D is a detailed sectional view of the sealing portion of the extension pin.

On the surface of the mold, half of the surface of the cavity on the moving side was matte-treated, and the other surfaces were mirror-finished. 8m diameter at center of molded product
m direct gate, sprue length is 58m
m, the diameter of the nozzle touch portion was 3.5 mm. Depth of 0.0 for gas supply and release around the mold cavity
A gap 8 having a width of 5 mm, a gas passage groove 9, and a hole 10 communicating from the gas passage groove 9 to the outside of the mold are provided and connected to a gas supply device. 11 and the cavity was made airtight. The protrusion pins 12 were sealed by inserting a U packing 15 between the cavity block 13 and the backup plate 14. The MPR series manufactured by Nippon Valqua Industries was used for the U packing. The hole 10 communicating with the outside of the mold has a protruding pin 12
Around the space and between the cavity block 13 and the backup plate 14, so that the gas in the gap can be released simultaneously with the completion of the resin filling.

In the gas supply device, a cylinder 16 filled with liquefied carbon dioxide was kept at 40 ° C. and used as a gas supply source of about 12 MPa. The gas passes through a heater 17 from a cylinder 16 and is regulated to a predetermined pressure by a pressure reducing valve 18.
It is stored in a gas reservoir 19 having an internal volume of 100 cm ³ kept at a temperature of ° C. Gas supply to the mold cavity is performed by the gas reservoir 19.
The opening is performed by opening the supply solenoid valve 20 and simultaneously closing the release solenoid valve 21, so that the gas reservoir and the cavity are connected during resin filling. Simultaneously with the completion of the resin filling, the supply electromagnetic valve 20 is closed and the release electromagnetic valve 21 is opened to release the gas body from the mold. When compressing the gas in the cavity and increasing the pressure by filling the molten resin, after supplying the gas, the supply electromagnetic valve 20 is closed at the same time as the resin filling is started, and the release electromagnetic valve 21 is opened at the end of the resin filling. Unnecessary pressure rise during resin filling is prevented by releasing gas from the pressure release valve 22.

The transferability of the mold surface state was evaluated by measuring the surface gloss of the mirror surface portion, observing with an optical microscope, and measuring the surface roughness of the satin portion. The surface gloss was measured using a variable angle glossmeter manufactured by Suga Test Instruments, trade name: UGV-5K, and the surface roughness was measured using Tokyo Seimitsu, trade name: Surfcom 575A.

Example 1 A mold having a cavity surface temperature of 70 ° C. was filled with carbon dioxide at a pressure of 5.0 MPa.
The rubber-reinforced polystyrene at a resin temperature of 220 ° C. was filled at filling times of 0.6 seconds and 2.4 seconds, the pressure in the cylinder was maintained at 35 MPa for 10 seconds, and after cooling for 20 seconds, the molded product was taken out. The carbon dioxide filled in the mold was released to the atmosphere at the same time as the resin filling was completed.

As a result of measuring the surface gloss of the obtained molded article, it was confirmed that the surface gloss was excellent regardless of the filling time (60 ° specular gloss = 101 for all).

Example 2 A molded product was obtained in the same manner as in Example 1 except that the pressure of carbon dioxide filling the mold was 2.5 MPa.

As a result of measuring the surface gloss of the obtained molded article, it was confirmed that the surface gloss was excellent regardless of the filling time (60 ° specular gloss = 88 in all cases).

Example 3 The mold cavity surface temperature was set to 8
A molded product was obtained in the same manner as in Example 2 except that the temperature was 0 ° C.

As a result of measuring the surface gloss of the obtained molded article, it was confirmed that the surface gloss was excellent regardless of the filling time (60 ° mirror gloss = 108 for all).

Example 4 ABS filled with 20% glass fiber
Using resin, cavity surface temperature 88 ° C, resin temperature 24
A molded product was obtained in the same manner as in Example 1, except that the temperature was set to 0 ° C. and the holding pressure was set to 70 MPa. As a result of measuring the surface gloss of the obtained molded article, it was confirmed that the surface gloss was excellent (60-degree specular gloss = 99 and 100) regardless of the filling time.

When the surface of the molded product was observed with a microscope at a magnification of 100 times, glass fiber was hardly exposed on the surface, and the surface was smooth.

Example 5 A mold having a cavity surface temperature of 80 ° C. was filled with carbon dioxide at a pressure of 5.0 MPa.
A methacrylic resin having a resin temperature of 240 ° C. was charged for a charging time of 0.6 second, the pressure in the cylinder was maintained at 80 MPa for 10 seconds, and after cooling for 20 seconds, the molded product was taken out. The carbon dioxide filled in the mold was released to the atmosphere at the same time as the resin filling was completed. Surface roughness R _max of satin part of obtained molded product
Was 12.0 μm.

Example 6 Cavity surface temperature 120 ° C.
After filling carbon dioxide to a pressure of 5.0 MPa and filling a polycarbonate at a resin temperature of 300 ° C. for a filling time of 0.6 seconds, holding the resin pressure in a cylinder at 120 MPa for 10 seconds, and cooling for 20 seconds, The molded article was taken out. The carbon dioxide filled in the mold was released to the atmosphere at the same time as the resin filling was completed.

The surface roughness R of the satin portion of the obtained molded article
_max was 11.5 μm.

Comparative Example 1 A molded product was obtained in the same manner as in Example 1 except that the mold was opened to the atmosphere without connecting a gas supply device.

As a result of measuring the surface gloss of the obtained molded product, the surface gloss was inferior at 60 ° specular gloss = 61 at a filling time of 0.6 seconds and at 60 ° specular gloss = 48 at a filling time of 2.4 seconds. , It was confirmed that it depends on the filling time.

Comparative Example 2 A molded product was obtained in the same manner as in Example 1 except that nitrogen was used as a gas to fill a mold.

As a result of measuring the surface gloss of the obtained molded article, the surface gloss was inferior to that of Comparative Example 1 (mirror gloss = 46 at a filling time of 0.6 seconds = 46, 60 degrees at a filling time of 2.4 seconds). Specular gloss = 40) was confirmed.

Comparative Example 3 A molded product was obtained in the same manner as in Example 4, except that the mold was opened to the atmosphere without connecting a gas supply device.

As a result of measuring the surface gloss of the obtained molded article, the surface gloss was inferior: 60 ° specular gloss = 85 at a filling time of 0.6 seconds, and 60 ° specular gloss = 62 at a filling time of 2.4 seconds. , It was confirmed that it depends on the filling time.

When the surface of the molded product was observed with a microscope, a large number of glass fibers and irregularities were found on the surface.

Comparative Example 4 A molded product was obtained in the same manner as in Example 5 except that the mold was opened to the atmosphere without connecting a gas supply device.

The surface roughness R of the matte portion of the obtained molded product
_max was 8.2 μm.

Comparative Example 5 A molded article was obtained in the same manner as in Example 6, except that the mold was opened to the atmosphere without connecting a gas supply device.

The surface roughness R of the satin portion of the obtained molded article
_max was 7.4 μm.

Tables 1 and 2 summarize the results of the examples and comparative examples.

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[Table 1]

[0088]

[Table 2]

[0089]

According to the present invention, it is possible to economically transfer the surface state of a mold to a molded product at a high level. No post-process is required, and the cost of parts can be greatly reduced. In addition, since it is not possible to uniformly transfer the fine mold surface state to the molded product, the productivity of flat lenses and the like that were molded by press molding, which has low productivity compared to injection molding, has been significantly increased, and a new It can be expected to have the effect of creating application fields for injection molding.

Examples of the molded article that can be favorably molded by the molding method of the present invention include resin injection molded articles such as optical equipment parts, housings for light electric equipment, electronic equipment, office equipment, various automobile parts, various daily necessities, and the like. Can be Injection molding with multi-point gate,
As a result, the present invention is suitable for improving the appearance of housings of electronic equipment, electric equipment, office equipment, etc., in which a large number of weld lines are generated, matte molded products, and patterned grain molded products. In addition, lenses such as lenticular lenses and Fresnel lenses molded using a transparent synthetic resin, recording disks such as optical disks,
It is also suitable for injection molded products of various optical components such as a light guide plate and a diffusion plate which are liquid crystal display components. These molded articles molded by the method of the present invention have improved mold surface reproducibility, improved gloss, reduced appearance defects due to weld lines, improved sharp edge reproducibility of the mold surface, and fine mold surface irregularities. Not only has the effect of improving the reproducibility of the resin, but also reduces the internal strain near the surface of the molded product that occurs during the resin filling process, reduces birefringence, improves chemical resistance, and reduces plating orientation by reducing the orientation of the compounded rubber. There are also effects such as improvement. By filling high-pressure gas in the cavity, generation of gas from the melt front generated during the resin filling step is suppressed, so that mold contamination is reduced and the mold release force of the molded product is reduced. Such effects are expected.

[Brief description of the drawings]

FIG. 1 is a diagram showing the amount of carbon dioxide dissolved in polystyrene.

FIG. 2 is a diagram showing the amount of nitrogen gas dissolved in polystyrene.

FIG. 3 is a graph showing the amount of carbon dioxide dissolved in polystyrene.

FIG. 4 is a diagram showing the amount of carbon dioxide dissolved in polystyrene.

FIG. 5 is a graph showing the amount of decrease in Tg due to dissolution of carbon dioxide in polystyrene.

FIG. 6 is a graph showing the amount of carbon dioxide dissolved in a PMMA / PVF2-based polymer alloy.

FIG. 7 is a graph showing a decrease in Tg due to dissolution of carbon dioxide in a PMMA / PVF2-based polymer alloy.

FIG. 8 is a graph showing the amount of carbon dioxide dissolved in polycarbonate.

FIG. 9 is a diagram showing the amount of carbon dioxide dissolved in polysulfone.

FIG. 10 is a diagram showing a decrease in Tg due to dissolution of carbon dioxide in each synthetic resin.

FIG. 11 is a view showing a cross section of a part directly related to the present invention of an injection molding machine nozzle embodying the present invention.

FIG. 12 is a view showing a cross section of a part directly related to the present invention of a mold for carrying out the present invention.

FIG. 13 is a diagram showing a structure of a gas supply device for implementing the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injection cylinder 2 Nozzle 3 Nozzle tip 4 Needle valve 5 Outer nozzle 6 Space 7 Passage 8 Gap 9 Gas passage groove 10 Hole leading out of mold from gas passage groove 11 O-ring 12 Protruding pin 13 Cavity block 14 Backup plate 15 U Packing 16 cylinder 17 heater 18 pressure reducing valve 19 gas reservoir 20 supply solenoid valve 21 release solenoid valve 22 pressure release valve

Claims (3)

[Claims] 1. A molding method in which a molten thermoplastic resin blended with a filler is filled in a mold and molded, wherein the resin has a solubility in the resin at a solidification temperature of at least twice that of air and / or nitrogen. A certain gas body is filled in a mold cavity, and then the resin is filled in the mold cavity.During the resin filling step, molding is performed while lowering the solidification temperature of the resin surface in contact with the mold. Molding method of thermoplastic resin. 2. The gas body according to claim 1, wherein said gas body is carbon dioxide.
Molding method of thermoplastic resin. 3. The method according to claim 1, wherein the filler is glass fiber.
Alternatively, the thermoplastic resin molding method according to 2.