JPH10286840A - New molding method of synthetic resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the favorable external appearance of an injection molded article by a method wherein the pouring of a synthetic resin is performed after a gaseous body, the solubility of which in the synthetic resin is a specified times as much as the solubility of an air and/or a nitrogen in the synthetic resin, is forced through the synthetic resin pouring port and/or from the neighborhood of a sprue. SOLUTION: As a medium in a mold cavity, a gaseous body, the solubility of which in a synthetic resin is three or more times as much as the solubility of an air and/or a nitrogen in the synthetic resin, is employed. Under the state that a nozzle 15 is brought into contact with the sprue bushing 14 of a mold 9, a synthetic resin is injected from a sprue 10 through runners 11 and gates 12 in a mold cavity 13. At the inference between the sprue bushing 14 and the mold 9, a fine hole 19, through which not the synthetic resin but the gaseous body can pass, is provided so as to force the gaseous body force through the fine hole 19 and a passage 17 in the mold. At the fluid end parts of the synthetic resin in a mold cavity 13, fine holes 18, through which the gaseous body can pass, are provided, The gaseous body is forced in the mold through the passage 17 just before an injection molding. After that, the synthetic resin is injected for molding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for molding a synthetic resin.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for omitting post-processing such as painting of synthetic resin injection molded articles. That is, there is an extremely strong demand for eliminating coatings or reducing the number of coatings in order to reduce manufacturing costs, recycle molded articles, and reduce environmental destruction due to solvent evaporation during coating. In particular, there is a strong demand for omitting the subsequent processing for synthetic resin housings of electric equipment, electronic equipment, office equipment, and the like. Further, various optical components that accurately reproduce the mold surface are required.

[0003] A thermoplastic resin is injected into a mold cavity and molded to improve the reproducibility in imparting the shape state of the mold surface to the molded product, reduce the appearance of weld lines, and improve the appearance of the molded product. Can usually be achieved to some extent by selecting molding conditions such as increasing the resin temperature and the mold temperature, and increasing the injection pressure. Among these factors, the mold temperature has the greatest influence, and it is preferable to increase the mold temperature. However, the higher the mold temperature, the longer the cooling time required for cooling and solidifying the plasticized resin, and the lower the molding efficiency.

[0004] A method of repeating heating and cooling of a mold by alternately flowing a heat medium and a cooling medium and attaching the holes for heating and cooling to the mold, respectively, is known as Plastic Technology.
gy, June, p. 151 (1988). WO 93/06980 and the like disclose a molding method for improving mold surface reproducibility by using a mold in which the mold wall surface is covered with a substance having a small thermal conductivity, that is, a thin heat-insulating layer. Further, for a mold in which the mold wall surface is covered with a thin heat-insulating layer and the surface of which is further covered with a thin metal layer, U
SP3734449, USP 5302467 and USP
No. 5,388,803.

[0005]

The mold surface reproducibility can be improved by setting the mold temperature high, heating the mold surface immediately before molding, or covering the mold surface with a heat insulating layer. However, air and the like in the mold cavity are not sufficiently discharged due to the shape of the molded product and molding conditions, and air and the like remain between the molded product and the surface of the mold (this is hereinafter referred to as an air trap). An unsightly pox mark (hereinafter referred to as an air trap mark) is often formed. This is more likely to occur when the mold surface is heated and the adhesion to the resin increases.The higher the mold surface temperature, the thicker the heat insulation layer in the heat insulation layer coating mold, the more air traps are generated. It will be easier. In many cases, the occurrence of an air trap cannot be prevented even if the mold is sufficiently ventilated, and this solution is required.

Further, when the mold is not sufficiently degassed or when the degassing cannot be performed due to the structure of the mold, an unsightly weld line is easily noticeable in the molded product. Further, in the so-called counter pressure method in which the mold cavity is maintained in a pressurized state with a gas body at a pressure higher than the atmospheric pressure, so-called counter pressure method, gas degassing tends to be insufficient, and weld lines and the like tend to be conspicuous.

Furthermore, molded parts such as Fresnel lenses, lenticular lenses, recording disks, light guide plates, and light diffusion sheets have sharp irregularities on the surface thereof, and optical parts and the like which require mold surface reproducibility at the acute angles. In molding, the reproducibility of the mold surface at a sharp convex portion (a sharp concave portion on the surface of a mold) is poor in a general injection-molded product, and its improvement is required. Further, in general injection molding, reduction of the conspicuousness of a weld line, improvement of glossiness, and the like have always been required.

[0008]

SUMMARY OF THE INVENTION The present invention solves these problems and provides a method for molding a molded article having excellent mold surface reproducibility and good appearance. That is, according to the present invention, (1) in a molding method in which a synthetic resin is injected into a mold cavity and molded, the solubility of the gas body in the synthetic resin during molding is 3 times the solubility of air and / or nitrogen in the synthetic resin. (2) a method of molding a synthetic resin, which comprises injecting a synthetic resin into the mold after press-fitting a gas body that is twice or more from the vicinity of a synthetic resin injection port and / or a sprue, and then molding the synthetic resin. The above (1) or (1) or (2), wherein the molding method of the synthetic resin of the above (1), which is carbon dioxide gas or a gas containing carbon dioxide gas as a main component, and (3) the molding method of injecting and molding the synthetic resin is an injection molding method. (2) a method of molding a synthetic resin; (4) a heated mold of carbon dioxide containing a vapor of a liquid in which carbon dioxide is easily dissolved and / or a carbon dioxide containing the liquid dispersed in atomized fine particles. (2) or press-fit into the mold cavity The present invention provides (3) a method for molding a synthetic resin.

The present invention further includes the following molding method. (A) The method of molding a synthetic resin according to the above (1), (2), (3) or (4), wherein the molding method is a molding method selected from the following low pressure molding methods. (A) Gas-assisted injection molding, (b) Liquid-assisted injection molding, (c) Oligomer-assisted injection molding, (d) Injection compression molding, (e) Extrusion compression molding, (B) Atmospheric pressure in mold cavity with gas Over 10
The above (1), which is formed by satisfying a pressure of not more than MPa,
(2) The method for molding a synthetic resin according to (3), (4) or (A). (C) The method of molding a synthetic resin according to the above (1), (2), (3), (4), (a) or (b), wherein the mold cavity is filled with a gas at atmospheric pressure. (D) Claims (1), (2), (3), which are used in combination with a molding method selected from the following mold surface reproducibility improving molding methods:
(4) The method for molding the synthetic resin according to (a), (b) or (c). (A) a molding method using a heat-insulating layer-coated mold, (b) a molding method in which the mold surface is subjected to high-frequency induction heating immediately before molding, (c) a molding method in which a heated gas body is blown into a mold cavity immediately before molding,
(D) A molding method in which a heat medium and a cooling medium are alternately flowed in a mold to form a molding. Hereinafter, the present invention will be described in detail.

The synthetic resin molded by the molding method of the present invention is a thermoplastic resin usable for general injection molding and the like, such as polyolefin such as polyethylene and polypropylene, polystyrene, styrene-acrylonitrile copolymer, rubber-reinforced polystyrene, and styrene. Styrene resins such as methyl methacrylate copolymer and ABS resin; methacrylic resins such as polymethyl methacrylate and methyl methacrylate-styrene copolymer; polyamides, polyesters, polycarbonates and vinyl chloride resins.

The molding method of the present invention can be used particularly well for polystyrene, rubber-reinforced polystyrene, styrene-
Non-crystalline resin selected from acrylonitrile copolymer, ABS resin, styrene resin such as styrene-methyl methacrylate copolymer, methacrylic resin such as polymethyl methacrylate, rubber reinforced polymethyl methacrylate, and polycarbonate. Is a resin in which various fillers are blended.

Good molded articles molded by the molding method of the present invention are generally used synthetic resin injection molded articles such as housings for light electric equipment, electronic equipment, office equipment, various automobile parts, various daily necessities, and various industrial parts. It is. Particularly preferred are housings for electronic equipment, electric equipment, office equipment, etc., which are injection molded with a multipoint gate, resulting in a large number of weld lines. In addition, a good mat-like molded product, a good patterned grain molded product, a good lenticular lens formed using a transparent synthetic resin, a lens such as a Fresnel lens, a recording disk, a light guide plate, a good high transmission, a high It is an injection molded product of various optical components such as a diffusion plate. These molded articles molded by the method of the present invention have improved mold surface reproducibility, improved glossiness, reduced noticeability of weld lines, sharp edge reproducibility of the mold surface, and fine mold surface. The reproducibility of the unevenness is improved, and the above-mentioned various molded products can be obtained favorably.
These injection molded products are molded by a general injection molding method, but a synthetic resin is applied to the surface of the mold during molding, such as gas-assisted injection molding, liquid-assisted injection molding, oligomer-assisted injection molding, injection compression molding, or extrusion compression molding. Combination with low pressure injection molding, in which the pressing pressure is low and / or the flow rate of the synthetic resin in the mold is slow, can be used favorably. In the low-pressure injection molding, the resin pressure is low, so that an air trap or the like easily appears, and the weld line is also conspicuous, so that the present invention can be used favorably.

The mold described in the present invention is generally used for molding synthetic resins such as iron or steel containing iron as a main component, aluminum or an alloy containing aluminum as a main component, zinc alloys such as ZAS, and beryllium-copper alloys. It is a metal mold used. In particular, a mold made of a steel material such as S55C and S45C can be used favorably. The gas body to be pressed into the mold cavity of the present invention is a gas body in which the solubility of the gas body in the synthetic resin at the time of molding is at least three times the solubility of air and / or nitrogen in the synthetic resin, and is preferably at least four times. , More preferably 5
It is more preferable that the solubility is greater than twice and the solubility is higher. The solubility at the time of molding refers to the solubility of the synthetic resin under the molding pressure near the solidification temperature of the synthetic resin. Further, the gas body is selected from the constraints of not deteriorating the resin, being inexpensive, and having no great environmental destruction. The solubility of the gas in the synthetic resin is measured by a pressure drop method, and is measured in an equilibrium state at the solidification temperature of the resin and the gas pressure used.

The gaseous body which is press-fitted into the mold cavity of the present invention and has a solubility of the gaseous body in the synthetic resin at the time of molding at least three times that of air and / or nitrogen in the synthetic resin is carbon dioxide, hydrocarbon or the like. , Halides and the like are preferred, and particularly preferred is carbon dioxide or a gas containing carbon dioxide as a main component. 2 if gas solubility is high
Mixtures of more than one species can be used. A gas body in which air is mixed with carbon dioxide gas can be used in the present invention as long as its solubility is three times or more. In the case of a mixed gas of carbon dioxide and air, the carbon dioxide is preferably 50% by volume or more,
It is more preferably at least 70% by volume, particularly preferably at least 90% by volume, most preferably at least 95% by volume, and more preferably as close as possible to 100% by volume. Gas bodies at various temperatures can be used. Atmospheric temperature gas and heated gas can be used favorably. In the case of a heated gas body, a mixed gas of a liquid vapor and a carbon dioxide gas that easily dissolves the carbon dioxide gas can be used favorably.

The carbon dioxide gas dissolves well in the synthetic resin and becomes a good plasticizer to improve the flowability of the synthetic resin. Next, the amount of carbon dioxide dissolved in each synthetic resin, the decrease in the glass transition temperature (hereinafter abbreviated as Tg) of the synthetic resin due to the dissolution of carbon dioxide, and the like will be described with reference to the drawings. 5 to 14 show reports described in various documents. In other words, FIGS. 279 (1989), FIG. 7, FIG. 8, FIG. 9, FIG. App
l. Polym. Sci. , Vol. 30 p. 401
9 (1985), FIG. 11 and FIG. Poly
m. Sci. , Vol. 30 p. 2633 (198
From FIG. 5), FIG. Membrane Sci. ,
Vol. 5P. 63 (1979). C (cm ³ CO ₂ (STP) / cm ³ polymer) indicating the amount of carbon dioxide dissolved in each resin in the figure
Is the capacity of carbon dioxide dissolved in the resin at 35 ° C. and 20 atm.

FIGS. 5 and 6 show the amounts of carbon dioxide gas and nitrogen gas dissolved in polystyrene (PS), respectively. Carbon dioxide has a dissolution amount of about 10 times that of nitrogen gas, and the plasticizing effect is low. large. 7 and 8 show the amount of carbon dioxide dissolved in polystyrene, and FIG. 9 shows the amount of reduction in Tg due to the dissolution of carbon dioxide. Polystyrene can easily reduce Tg by dissolving carbon dioxide gas.

FIGS. 10 and 11 are graphs showing the amount of carbon dioxide dissolved in polymethyl methacrylate (PMMA) and polyvinylidene fluoride (PVF ₂ ) polymer alloys and the decrease in Tg due to the dissolution of carbon dioxide. Tg can be reduced by gas dissolution. FIGS. 12 and 13 show the amounts of dissolved carbon dioxide in polycarbonate (PC) and polysulfone, respectively.

FIG. 14 is a graph showing the amount of Tg reduction due to dissolution of carbon dioxide in each synthetic resin. The decrease in Tg due to the dissolved amount of carbon dioxide is almost the same except for polycarbonate. Polycarbonate is Tg by dissolving carbon dioxide
Is particularly large. The pressure of the gas filled in the mold cavity is a pressure higher than the atmospheric pressure, preferably the atmospheric pressure,
Alternatively, the pressure is selected from atmospheric pressure to 10 MPa. The pressure of the gas described in the present invention is indicated by absolute pressure. That is, 0.1
MPa substantially corresponds to the atmospheric pressure. The pressure of the gas is selected and used depending on the type of molding method, the type of gas used, and the like. Minimize the amount of gas used in one process,
In order to simplify the mold seal and the structure of the gas supply device, it is preferable that the temperature is as low as possible within a necessary range.
a is practical. When the pressure is increased, problems tend to occur such that the force for opening the mold cannot be ignored, and the sealing of the mold becomes difficult.

When polystyrene is used as the resin and carbon dioxide gas is used as the gas, the carbon dioxide gas is dissolved at a solidification temperature of 100 ° C. at a pressure of about 1.5 MPa and 1% by weight. on the other hand,
In the combination of polystyrene and nitrogen, only 0.1% by weight or less of nitrogen dissolves under the same conditions, and the presence of nitrogen at the interface between the mold and the resin lowers the transfer state of the mold surface state to the molded product. Become. If nitrogen remains on the weld line, the weld line becomes more conspicuous, and if it remains on the general part as an air trap, a trace of pox remains.

In the present invention, after a gas is injected into the mold cavity from near the synthetic resin injection port and / or sprue of the mold, the synthetic resin is injected into the mold cavity and molded. In the present invention, the synthetic resin injection port of the mold is an injection port for injecting the synthetic resin into the mold, generally refers to a sprue of the mold, and the vicinity of the sprue refers to a gas passage provided near the sprue. The passage leads to a sprue or runner. Synthetic resin is generally injected into a mold cavity through a sprue, a runner, and a gate. In the case of a direct gate, the tip of the sprue becomes the gate. In the present invention, it is preferable to press-fit the gas from the nozzle side of the sprue. However, the present invention includes press-fitting the gas from the runner side of the sprue in the middle of the sprue. Gates are gates such as pinpoint gates, side gates, fan gates, etc.
Various gates such as a single-point gate, a multi-point gate, a gate from a cold runner, and a gate from a hot runner can be used.

According to the present invention, the air in the mold cavity is filled with a gas (hereinafter, referred to as a specific gas) having a solubility of the gas in the synthetic resin at least three times as high as the solubility of air and / or nitrogen in the synthetic resin. It is an economical way to replace The air in the mold cavity should be reduced to 100
There is a need for an economical method of substituting close to%, and the present invention is a method that answers this. Injection molding is most characterized in that a mold having a complicated shape is obtained by one molding, and therefore, generally, the mold cavity of the injection molding has a complicated shape. In order to sufficiently replace the air in the complex mold cavity with the gas, a method of directly injecting the gas into the mold cavity from the mold parting surface is generally used. Requires a gas body. That is, although the molding cycle time of injection molding is generally about 60 seconds, the replacement with the injected gas body has required a replacement time of 5 to 10 seconds. Adding a displacement time of 5 to 10 seconds means an increase of the molding cycle time by 8 to 17%, which is a very large reduction in productivity. In addition, in order to directly inject a gas body into the mold cavity, it is necessary to uniformly inject from a plurality of resin flowing ends of the mold cavity,
The mold processing cost becomes large.

When the solubility of the gas in the mold cavity in the synthetic resin is 10 times that of air, if the mold cavity is replaced by 100% with the gas, the mold cavity is reduced to 1/10 atm and injected. The same effect as that obtained by molding can be obtained.
Replacing the mold cavity with 90% of the gas and 10% of air has the same effect as injection molding at a reduced pressure of 1/5 atm. For this reason, it is preferable to replace the gas with a gas whose solubility in the synthetic resin is at least three times as high as the solubility of air and / or nitrogen in the synthetic resin at the time of molding to as close to 100% as possible. The following shows an economical method for performing body substitution.

According to the present invention, prior to injecting the synthetic resin into the mold cavity, a gas body is press-fitted from the synthetic resin injection port of the mold and molded so that the injected gas body is injected later. The resin is pressed, and the air remaining in the mold cavity by the gas body is discharged to the outside of the mold to be molded. That is, if the vicinity of the sprue, the runner, and the gate of the mold is sufficiently replaced with a gas, the gas in direct contact with the synthetic resin is always the gas. The time for replacing the air in the mold should be a time for sufficiently replacing the vicinity of the sprue, the runner, and the gate of the mold, which is an extremely short time. In order to replace the sprue portion shown in FIGS.
5 and the sprue bush 14 contact for a very short time (0.1
(About 2 seconds).

According to the present invention, carbon dioxide or the like in the mold cavity dissolves in the synthetic resin surface layer at the flow front of the synthetic resin flowing through the mold cavity to plasticize the surface layer, thereby improving the mold surface reproducibility of the molded product. How to improve. This method has a more satisfactory effect as the pressure of carbon dioxide or the like in the mold cavity is increased. However, filling the mold cavity with high pressure gas requires safety precautions. Particularly in Japan, pressures of 1.1 MPa or more are strictly regulated by the High Pressure Gas Control Law. The present invention also provides a molding method that provides a mold surface reproducibility effect at a lower mold cavity gas pressure. That is, according to the present invention, a heated carbon dioxide gas containing a vapor of a liquid that easily dissolves the carbon dioxide gas and / or a carbon dioxide gas containing the liquid dispersed in atomized fine particles are pressed into a mold cavity of a cooled mold and molded. This is a molding method. The liquid described here is a liquid having a boiling point equal to or higher than the mold temperature, in which carbon dioxide is dissolved in water or higher at atmospheric pressure or higher. Preferably, it is a liquid that easily dissolves in a synthetic resin. The amount of dissolved carbon dioxide is large, and a good solvent for the synthetic resin and a plasticizer for the synthetic resin can be used favorably. Generally, ketones such as acetone and methyl ethyl ketone, alcohols such as ethyl alcohol, polar solvents such as dimethylformamide, dimethylacetamide and N-methylpyrrolidone can be used favorably. When the synthetic resin is a crystalline synthetic resin, a solvent that easily dissolves the amorphous phase of the synthetic resin can be used favorably.

The method of the present invention comprises the steps of: heating heated carbon dioxide gas containing a liquid vapor which easily dissolves carbon dioxide gas and / or carbon dioxide gas containing the liquid dispersed in atomized fine particles; To cover the mold surface with a thin layer of a liquid containing a large amount of carbon dioxide having a plasticizing effect of the synthetic resin on the cooled mold surface by dew condensation or the like. This is a method in which the synthetic resin surface layer is impregnated with a large amount of carbon dioxide gas to improve the mold surface reproducibility of the molded product. That is, a method in which a liquid containing a large amount of carbon dioxide gas is present on the surface of the mold to supply a sufficient amount of carbon dioxide gas to the surface of the synthetic resin with the low-pressure carbon dioxide gas in the mold cavity. The synthetic resin flows through the mold cavity during molding by a so-called “Fontain Flow”, and a solidified layer is formed immediately after contacting the mold surface, but a thin liquid having a thickness within a range where the synthetic resin solidified layer does not slip on the mold surface. Need to be coated. Generally 0.1 μm to 10 μm
The range of the degree is preferable. It is preferable that the concentration of the liquid in the carbon dioxide gas is adjusted to a concentration that allows the thickness of the thin layer liquid to be injected into the mold cavity. In the present invention, the cooled mold is a cooled mold used for injection molding of a synthetic resin, and the mold temperature is equal to or lower than the boiling point of the liquid contained in carbon dioxide gas,
And it is preferably selected from 0 ° C to 100 ° C, more preferably from 10 ° C to 80 ° C. The heated carbon dioxide gas is a carbon dioxide gas heated to a temperature higher than the boiling point of the liquid contained in the carbon dioxide gas by at least 20 ° C.
It is selected from a temperature exceeding 0 ° C and 300 ° C or less, and more preferably from 120 ° C to 250 ° C.

FIGS. 1 to 4 show an apparatus for injecting a gas having a high solubility in a synthetic resin according to the present invention. 1 and 2 show an apparatus for injecting gas from a nozzle connected to an injection cylinder of an injection molding machine. In FIG. 1, a nozzle 2 connected to an injection cylinder 1 has a needle valve 4 for opening and closing a nozzle tip 3, and a central portion of the needle valve 4 has a passage 5 through which a gas passes. It is linked to
Immediately before the injection molding of the synthetic resin, a gas body is pressed into the mold from the passage 5 and then the synthetic resin is injected and molded.

In FIG. 2, 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 6 is provided at the tip of the nozzle, and a space 7 formed by the nozzle body 2 and the outer nozzle 6 is a passage 8.
Through a gas source. When the outer nozzle 6 comes into contact with the mold lightly, the space 7 is connected to the mold cavity, and in this state, the gas is pressed into the mold from the space 7. Next, the injection cylinder 1 moves forward strongly and the outer nozzle 6
When the outer nozzle 6 is strongly pressed against the mold, the outer nozzle 6 retreats and is pressed against the nozzle body 2 so that the connection between the space 7 and the mold is cut off. In this state, the synthetic resin is injected into the mold from the injection cylinder 1.

FIGS. 1 and 2 can also be used for nozzles for gas-assisted injection molding. Conversely, various nozzles used for gas assist injection molding can be favorably used in the present invention.
In the method of the present invention, gas-assisted injection molding can be favorably used.
That is, this is a molding method in which the specific gas body of the present invention is press-fitted into the mold from the gas body passage of the nozzle, then the synthetic resin is press-fitted, and then the gas body forming the gas channel is press-fitted.
A specific gas body that fills the mold cavity and a gas body that is injected into resin to form a gas channel in the molded article are alternately switched from the same passage and press-fitted.

FIGS. 3 and 4 show an apparatus for press-fitting a specific gas body from near the sprue of the mold. In FIG. 3, the nozzle 15 comes into contact with the sprue bush 14 of the mold 9 and the synthetic resin is injected into the mold cavity 13 through the sprue 10, the runner 11, and the gate 12. Sprue bush 14
And the main body of the mold 9 are fixed by bolts. At the interface, there is a pore 19 through which a gas body can pass but a synthetic resin cannot pass. Pressed into the mold. It is preferable that a pore 18 through which a gas can pass is provided in the mold mating surface at the synthetic resin flowing end of the mold cavity 13.

In FIG. 4, the nozzle 15 contacts the sprue bush 14 of the mold 9 and the synthetic resin
Mold cavity 13 through runner 11 and gate 12
Injected into. The mating surface of the sprue bush 14 and the main body of the mold 9 has a pore 16 through which a gas can pass but a synthetic resin cannot pass, and the gas press-fitted through the passage 17 is pressed into the mold through the pore 16. You. Mold cavity 1
At the flow end of the synthetic resin 3, pores 18 through which gas can pass are provided.
Is preferably provided on the mold mating surface.

Using a mold shown in FIGS. 3 and 4, a gas body is pressed into the mold through the passage 17 immediately before injection molding of the synthetic resin, and then the synthetic resin is injected to be molded. The present invention can be favorably used in combination with various existing molding methods for improving mold surface reproducibility. When the gas pressure in the mold cavity is low, particularly when the specific gas pressure is less than 1.1 MPa, it can be used favorably. Specific gas pressure is 1.1M
When the pressure is Pa or more, the pressure is strictly regulated by the High Pressure Gas Control Law from the viewpoint of safety, and it is preferable that the pressure be less than 1.1 MPa. (A) a molding method using a heat-insulating layer-coated mold, (b) a molding method in which the mold surface is subjected to high-frequency induction heating immediately before molding, (c) a molding method in which a heated gas body is blown into a mold cavity immediately before molding,
(D) A molding method in which a heat medium and a coolant are alternately flowed into a mold and a method of high-frequency induction heating of the mold surface immediately before molding are disclosed in JP-B-58-40504 and US Pat. No. 4,340,055.
1, the method described in the specification such as US Pat. No. 4,439,492.

A method of blowing a heated gas body into a mold cavity immediately before molding to heat the mold surface is disclosed in Japanese Patent Publication No. 45-22 / 1972.
No. 020, JP-A-6-170943, JP-A-8-24
No. 4072, which are described in each publication. Heating and cooling holes are attached to the mold, and the heating medium is alternately
A method of repeating heating and cooling of a mold by flowing a coolant can also be used. In this case, steam is particularly suitable for the heat medium, and water is suitable for the refrigerant.

The heat-insulating layer coating mold method is described in WO 93/06980.
This is a molding method using a mold in which a heat-insulating layer is coated on a surface forming a mold cavity of a metal mold. A heat-insulating-layer-coated mold covered with a heat-insulating layer made of a heat-resistant polymer is preferable, and a heat-insulating-layer-coated mold having a thin metal layer on the heat insulating layer surface can also be used. The present invention is suitable for molding various types of optical components such as Fresnel lens, lenticular lens, recording disk, light guide plate, etc., which require sharp corners, and diffusion plates, which require fine and sharp mold surface irregularities. ing. In these moldings, it is necessary that the synthetic resin sufficiently penetrates deep into the concave portion on the surface of the mold, but in many cases, the synthetic resin cannot penetrate deeply due to the gas trapped in the concave portion. In the present invention, the trapped gas is absorbed by the synthetic resin, and the synthetic resin can penetrate into the recess. Furthermore, the fluidity of the synthetic resin is improved by the absorbed gas, and the synthetic resin is more likely to enter deep into the concave portion, and the mold surface reproducibility is improved. When carbon dioxide is used as the gas, the softening temperature of the synthetic resin that has absorbed carbon dioxide is lowered, and the fluidity is improved.

When injection molding is performed by filling the mold cavity with a specific gas at atmospheric pressure, the effect of eliminating traces of air traps generated on the surface of the molded product is remarkable. The air trap is more likely to be generated as the mold surface temperature when the synthetic resin comes into contact is higher, and is more likely to be generated when the mold surface temperature is equal to or higher than (the softening temperature of the synthetic resin−20 ° C.). 1
0 ° C.) or more, and the effect of the present invention is remarkable in such a case. The present invention can be favorably used when the mold surface is heated to a temperature of (softening temperature of synthetic resin −20 ° C.) or higher by high frequency induction heating or the like immediately before molding. Furthermore, on the mold wall surface of the main mold made of metal, 0.1-0.1
When a mold coated with a heat insulating layer having a thickness of 2 mm is used, and when a metal layer having a thickness of 1/3 or less of the thickness of the heat insulating layer is used on the surface of the heat insulating layer, the mold is injected into the mold. Since the molding is performed while heating the mold surface with the heat of the synthetic resin, an air trap is easily generated, and in this case, the effect of the present invention is remarkable.
The mold surface temperature immediately after the synthetic resin contacts the mold surface described in the present invention means a mold surface temperature before the synthetic resin contacts the mold surface and a solidified layer is formed. In a mold in which a metal layer is present on a heat insulating layer, the mold surface temperature once drops, but immediately rises and then falls (generally, the temperature falls within 0.1 seconds, preferably within 0.05 seconds). Rises), and the increased mold surface temperature is the immediately following mold surface temperature.

In the present invention, an injection molding method, which is generally called a counter pressure method, in which a mold cavity is pressurized with the gas of the present invention in advance and then molded, is particularly effective. The present invention is also effective in an injection molding method in which the gas pressure in the mold cavity at the start of injection is close to the atmospheric pressure, and molding is performed while increasing the gas pressure in the mold cavity with the injected resin. In the method of molding by increasing the pressure of the gas body in the mold cavity as described above, a mold structure in which the gas body in the mold cavity is sealed with an O-ring or the like is used. When a mold having a gas body sealing structure is used and the mold cavity is maintained at atmospheric pressure or at a pressure exceeding 10 MPa or less with the gas body of the present invention and synthetic resin is injected, the specific gas body is compressed by the injected synthetic resin. You. If the gas does not escape outside the mold cavity, the gas pressure increases as the resin injection proceeds. If the pressure exceeds a certain level, provide a safety valve so that the gas pressure does not increase any more. When the gas pressure increases, the amount of gas dissolved in the synthetic resin increases, and the synthetic resin is plasticized and softened by the dissolved gas, thereby improving the mold surface reproducibility of the molded product. In a general injection-molded product, the mold surface reproducibility at the resin flow end portion where the injection pressure is poor is lower than the mold surface reproducibility near the gate. The above-described molding method of the present invention improves the reproducibility of the mold surface at the resin flow end.

Although the present invention has been described by injection molding, it can be widely applied to a molding method in which a synthetic resin is injected into a mold cavity.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following main mold, heat insulating layer, synthetic resin and the like are used. Mold: A mold for injection molding made of steel (S55C) with a molded product size of 100 mm x 100 mm and a thickness of 2
mm, and has a mold cavity for molding a molded article having a 30 mm × 30 mm hole in the center. The gate is a side gate at the center of the side, and a weld line is formed on the molded product on the opposite side of the hole from the gate. A nest forming the mold cavity of the main mold is prepared. The nested surface forming the mold surface is mirror-like. Heat insulation layer: A polyimide varnish (trade name, manufactured by Toray Nice # 3000, manufactured by Toray Industries, Inc.) is applied on the surface of the mold nest, heated at 160 ° C., and the application and heating are repeated to a predetermined thickness, and then 290 Heat to 100 ° C
% Imidation to form a 50 μm thick polyimide layer.
The polyimide layer is polished to a mirror surface. Synthetic resin: Rubber reinforced polystyrene, Styrone 495
(Trade name, manufactured by Asahi Kasei Kogyo Co., Ltd.) Carbon dioxide: carbon dioxide with a purity of 99% or more A synthetic resin is injection-molded using a mold coated with a heat insulating layer and a mold not coated with a heat insulating layer. Resin temperature 240 ° C,
At a mold temperature of 30 ° C., injection molding is performed when the mold cavity is filled with air and when the mold cavity is filled with carbon dioxide gas. The replacement of the mold cavity with carbon dioxide is performed by injecting 1 MPa of carbon dioxide for 3 seconds from the outer nozzle shown in FIG. 1MPa mold cavity with carbon dioxide
When the pressurized state is maintained, an O-ring is attached to the parting surface of the mold to form a seal structure. The mold cavity is connected to the outside via a safety valve, and a part of the carbon dioxide gas injected with air. Is released from the mold to replace the mold cavity with carbon dioxide gas. Table 1 shows the results of the injection molding.

From the results, it can be seen that the glossiness is significantly improved by injecting carbon dioxide gas into the mold cavity for 3 seconds and filling the mold cavity with carbon dioxide gas. Further, the weld line of the injection molded article filled with carbon gas becomes less noticeable.

[0039]

[Table 1]

[0040]

According to the method of the present invention, the appearance of an injection molded article can be improved. In particular, it can be favorably used for injection molding of synthetic resin having poor appearance such as recycled resin, which is required in recent years.

[Brief description of the drawings]

FIG. 1 is a view showing a cross section of a part directly related to the present invention of an injection molding machine nozzle for carrying out the present invention.

FIG. 2 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. 3 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. 4 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. 5 is a graph showing the amount of carbon dioxide dissolved in polystyrene.

FIG. 6 is a diagram showing the amount of nitrogen gas dissolved in polystyrene.

FIG. 7 is a graph showing the amount of carbon dioxide dissolved in polystyrene.

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

FIG. 9 is a graph showing the amount of decrease in Tg due to dissolution of carbon dioxide in polystyrene.

FIG. 10 is a graph showing the amount of carbon dioxide dissolved in a PMMA / PVF ₂ polymer alloy.

FIG. 11 is a graph showing the amount of decrease in Tg by dissolving carbon dioxide in a PMMA / PVF ₂ polymer alloy.

FIG. 12 is a graph showing the amount of dissolved carbon dioxide in polycarbonate.

FIG. 13 is a graph showing the amount of carbon dioxide dissolved in polysulfone.

FIG. 14 is a diagram showing a decrease in Tg due to dissolution of carbon dioxide in each synthetic resin.

[Explanation of symbols]

 Reference Signs List 1 injection cylinder 2 nozzle 3 nozzle tip 4 needle valve 5 passage 6 outer nozzle 7 space 8 passage 9 mold 10 sprue 11 runner 12 gate 13 mold cavity 14 sprue bush 15 nozzle 16 pore 17 passage 18 pore 19 pore

Claims (4)

[Claims] In a molding method in which a synthetic resin is injected into a mold cavity and molded, the solubility of a gas body in the synthetic resin at the time of molding is at least three times the solubility of air and / or nitrogen in the synthetic resin. A method for molding a synthetic resin, comprising: injecting a gas body from a mold near a synthetic resin injection port and / or a sprue, and then injecting and molding a synthetic resin. 2. The method for molding a synthetic resin according to claim 1, wherein the gas body is carbon dioxide gas or a gas body containing carbon dioxide gas as a main component. 3. The method for molding a synthetic resin according to claim 1, wherein the molding method for injecting and molding the synthetic resin is an injection molding method. 4. A heated carbon dioxide gas containing a vaporized liquid of a carbon dioxide gas easily dissolvable and / or a carbon dioxide gas containing the liquid dispersed in atomized fine particles is pressed into a mold cavity of a cooled mold and molded. The method of molding a synthetic resin according to claim 2 or 3.