JPH1058493A - Injection molding method for synthetic resin molding, and mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a sink mark in a cavity where a rear face is peeled so as to improve a commodity value by injecting to charge molten synthetic resin, then introducing compressed fluid between a mold of an opposite side to a mold for forming an appearance surface and the molten synthetic resin so as to peel it. SOLUTION: When a male mold 12 is joined with a female mold 11, a cavity of the same shape as a molding 1 is formed between both the molds 11 and 12. A predetermined quantity of a molten synthetic resin is injected to be filled in the cavity from a runner via a nozzle and sprue 14 of the mold 11. A valve is opened immediately after injection of the resin is finished, and pressurized compression fluid (air) is introduced into the cavity from a compression pump via a compression fluid channel 18. The compression air is fed between the unsolidified resin in the cavity and a cavity forming surface of the mold 12 to form an air gap 19. The molten resin is entirely continuously urged to the mold 11 side for forming an appearance surface. A sink mark is freely generated on a rear surface, and not generated at the apperance surface 2 side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method and a mold for molding a synthetic resin molded article such as a cabinet of an AV apparatus. More specifically, the present invention relates to an injection molding method and a mold for preventing sink marks and transfer unevenness occurring during injection molding from appearing on the appearance of a molded product.

[0002]

2. Description of the Related Art In general, a method of injection molding a plastic product using a mating die is a well-known technique. Many of the mating dies used in the injection molding are a female mold that forms the front side of the molded article and a male mold (also called a core mold) that forms the back side (or inside) of the molded article. The female mold is formed by engraving the pattern on the front surface side of the molded product, and the male mold is formed by engraving the pattern on the rear surface side of the molded product.

[0003] When a mating mold composed of a female mold and a male mold is combined, a space having the same shape as the molded product, that is, a cavity is formed between the two molds. After the resin is injected and filled, and cooled and solidified to a predetermined temperature in the cavity, the union of the two molds is released and separated, so that a molded product molded in the cavity can be taken out.

According to the injection molding means using such a mating die, even products having complicated shapes can be mass-produced uniformly and at low cost, so that they are widely used in the manufacture of cabinets and the like of many AV equipment. ing.

[0005] However, in the injection molding means, when the injection-filled molten synthetic resin is cooled in the cavity, the cooling of the thick portion is delayed more than that of the other portions. In addition, there is a problem that a depression due to shrinkage due to a delay in cooling, that is, so-called sink occurs.

In addition, in the injection molding means, it is necessary that the pattern on the surface of the injection molded article formed in the mold be accurately and uniformly transferred to the injection-filled molten synthetic resin. To this end, while increasing the injection pressure for injecting the molten synthetic resin into the cavity, the filled molten synthetic resin is substantially evenly distributed on each part of the mold surface until the injected and filled molten synthetic resin is cooled and solidified. So that it can be pressed
An extra molten synthetic resin is injected for so-called holding pressure. If the pressure is not maintained, not only transfer unevenness occurs in the completed molded product, but also large sink marks occur.

Recently, the number of cabinets for AV equipment and the like manufactured by injection molding of a molten synthetic resin has increased, but the surface of the cabinet of AV equipment, that is, the appearance surface is A-shaped.
Since it is an important factor that determines the commercial value of the V equipment, a sink that has a sink mark or uneven transfer on the appearance is called a defective appearance and reduces the commercial value. for that reason,
Injection molding methods have been developed for removing appearance defects of AV equipment in various ways.

There is a gas assist method as one injection molding method for preventing sink marks. An invention of a molding method using this gas assist method is disclosed in Japanese Patent Publication No. 5-44234 (Japanese Patent Application No. 63-240469). According to the disclosed invention, a molten synthetic resin is injected into a cavity, and at the same time, a gas space is formed in the molten synthetic resin by injecting a high-pressure gas into a portion corresponding to a thick portion of a product, and a molten space is formed in the space. Even after the injection of the synthetic resin is completed, high-pressure gas is continuously injected and so-called secondary pressure is applied to the molten synthetic resin to obtain a hollow molded article having high strength and without sink marks.

Further, as a means for preventing sink marks, an invention of an injection molding method disclosed in Japanese Patent Publication No. 61-9126 (Japanese Patent Application No. 58-115254) is also known. According to this known invention, when a molded product has a flat appearance surface and a convex portion or a thick portion on the rear surface, when the molten synthetic resin is cooled and solidified, the molded product is provided on a rear surface side mold at a position corresponding to the convex portion. By sending compressed air to the convex or thick part through the through hole and pushing it from the back side to the front side, even if the concave part due to pressure occurs at the end of the convex part, it corresponds to the convex part This is a method in which sink marks are not generated on the side of the appearance surface.

[0010]

In the above prior art, in order to avoid sink marks and transfer unevenness, techniques such as increasing the injection pressure and holding pressure and making the molded product as thin as possible have a thickness that is as small as possible. Although some measures have been taken by using this material, its size and shape are actually limited by design and function, and the maximum pressure for injecting molten synthetic resin is limited by the size of the injection molding equipment. Actually, sink marks and transfer unevenness cannot be completely prevented. In addition, since extra molten synthetic resin must be injected in order to increase the holding pressure, there is a problem that the number of materials used increases.

In addition, in the injection molding using the gas assist method, a certain degree of sink can be prevented, but there is a problem that transfer unevenness is apt to occur due to a biased pressing point. In addition, in the injection molding method in which pressure is applied to the convex part and the convex part is pressed toward the surface, the molten synthetic resin must be pressed at a high pressure until cooling and solidification is completed. In other words, the so-called roughening occurs in which the molten synthetic resin sticks to the cavity side of the mold, making it difficult to release the molded product with the knockout pins, which not only results in poor productivity, but also causes traces of the knockout pins. There is a problem that it tends to remain. At the same time, there is a problem that the shape of the molded product is restricted in order to prevent the leakage of the compressed air.

Therefore, in the conventional injection molding method,
There are problems that must be solved to completely prevent sink marks and transfer unevenness and to improve productivity without being restricted by the shape and size of the molded product.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, a method of injection molding a synthetic resin molded article according to the present invention comprises the steps of: An injection molding method for molding a molded product, wherein after injection of the molten synthetic resin, a compressed fluid is injected between the mold and the molten synthetic resin on the side opposite to the mold that forms the appearance surface. To peel off.

The mold is a mating mold for molding an injection-molded product, and has a fluid injection portion for injecting a compressed fluid into a mold opposite to the mold forming the appearance surface. That is.

According to the injection molding method of the present invention, when the molten synthetic resin injected into the cavity is cooled and solidified, the compressed fluid is placed between the molten synthetic resin and the mold opposite to the mold forming the appearance surface. Injecting and peeling, the peeled space allows the sink phenomenon that occurs in the thick part to be freely absorbed, and the sink is positively generated on the back side of the molded article that does not substantially appear, and The space formed by the injection of the compressed fluid uniformly presses the molten synthetic resin against the mold on the side of the appearance surface, thereby eliminating uneven transfer on the entire appearance side. On the side of the appearance, a good finish is obtained without sink marks and transfer unevenness.

Further, since the mold of the present invention only has a fluid injection section for injecting a compressed fluid into one of the molds, if the fluid injection section is formed at a required position in a conventional mold,
This makes it possible to produce a molded article free of sink marks or transfer unevenness on the appearance surface side.

[0017]

Next, an injection molding method according to the present invention and a mold used therein will be described in detail with reference to the drawings. As a preferred embodiment, for example,
A molded product such as a cabinet of an AV device will be described.

FIG. 1A is a cross-sectional view schematically showing an entire mold 10 to which the injection molding method of the first embodiment according to the present invention is applied, and FIG. It shows a molded product formed by the mold. This molded article 1 is, for example,
It is like a lid member of a cabinet, and has a face 2 that comes out on the front side, and a back face 3 that is on the back side and is integrally formed with a projection 4 such as a boss for coupling with another member. . The projections 4 and the edges 5 and 6 of the molded product 1 are thick portions, and generally cause sink marks on the appearance surface 2 side.

There are cases where the appearance surface 2 is simply formed on a flat surface and cases where various decorative patterns or characters are applied. In any case, in consideration of commercial value, sink marks, transfer unevenness, etc. are considered. The surface must not be deformed by the On the other hand, the back surface 3 is a place that is not directly visible from the outside, and is a part that is allowed even if there is some sink or deformation.

A mold 10 for molding such a molded article 1
Is a so-called mating die, which is basically a female die 11 for forming the appearance surface 2 of the molded product 1 and a male (also called core) die for forming the back surface 3 of the molded product 1. The cavity C corresponding to the shape of the molded product 1 is formed between the two by combining the two dies.

On the surface constituting the cavity C of the female mold 11, for example, various decorative patterns or characters are engraved as necessary, and a sprue 14 connected to the cavity C is provided. A frame 11a is attached, and the support frame 11a is fixed to an injection molding device (not shown). The molten synthetic resin is injected into the cavity C from the runner 13 of the injection molding device via the sprue 14.
The molten synthetic resin injected from the runner 13 has a function of being injected at a relatively low injection pressure and at a high injection speed via the nozzle 13a.

The surface forming the cavity C of the male mold 12 is formed in a shape corresponding to the back surface 3 side of the molded article 1, and a fluid flow path 18 penetrating from the back surface side to the cavity C is formed. I have. The compressed fluid flow path 18 is, for example, a path for guiding the compressed air to the plane portion of the cavity C. The compressed fluid flow path 18 has a small hole or a narrow slit shape (about 30 μmm) that allows only the compressed air to flow without sending the molten synthetic resin. Is formed. Then, the fluid injection section 2 is
0 is connected.

The fluid injection section 20 is provided with a compression pump 15
, A piping section 16 and a valve 17 provided in the middle of the piping section 16, and a free end of the piping section 16 is connected to the fluid flow path 18.

The compression pump 15 is a pump that outputs a compressed fluid, for example, a pump that outputs compressed air having a pressure of 5 to 50 kg / cm ² . The opening and closing of the valve 17 used is controlled by an appropriate control device.

The male mold 12 is movably supported by a mold driving mechanism generally used in the related art. A part of the mold driving mechanism is a support member 21 attached to an injection molding device (not shown), and a plurality of plungers 21a provided to protrude from the support member 21.
Thereby, the male mold 12 is slidably supported in the direction of the female mold 11.

When the mating mold having the above configuration is set in a predetermined injection molding apparatus, and the male mold 12 is integrated with the female mold 11,
As shown in FIG. 1, a cavity (cavity) C having the same shape as the molded article 1 to be molded is formed between the female mold 11 and the male mold 12. At this point, the valve 17 is closed and no compressed fluid is supplied.

With respect to the cavity C, a runner 13 of the injection molding apparatus is connected to the female mold 1 via a nozzle 13a.
A predetermined amount of molten synthetic resin is injected and filled through one sprue 14. In this case, the injection is performed at a low pressure with a short shot, and the injection time is set to, for example, about 1.2 seconds.

As for the temperature of the mold, for example, the temperature of the female mold 11 is maintained at 65 ° C., and the temperature of the male mold 12 is maintained at 78 ° C. That is, the mold on the appearance side is maintained at a lower temperature than the mold on the back side. By increasing the temperature of the mold on the back side in this way, the circumference of the molten synthetic resin with respect to the back side is improved.

The molten synthetic resin injected and filled into the cavity C immediately starts to cool and solidify. However, as soon as the injection of the molten synthetic resin is completed, the valve 17 is opened and the compression pump 15 is opened.
Compressed air, which is an example of a compressed fluid pressurized to a predetermined pressure, for example, 18 kg / cm ² , is injected into the cavity C for a predetermined time through the pipe 16 and the compressed fluid flow path 18. The injection time at this time is, for example, about 15 seconds, but the injection time is arbitrarily set depending on the size of the molded article 1 and the like.

When the compressed air is injected, the cavity C
Since the inside is already filled with the molten synthetic resin, as shown in FIG. 2, the injected compressed air flows between the unsolidified molten synthetic resin and the cavity forming surface of the male mold 12 in the cavity C. As a result, the molten synthetic resin is separated from the cavity forming surface of the male mold 12 to form a gap 19 having a predetermined pressure. Then, due to the presence of the gap 19, the molten synthetic resin is formed into the female mold 11 forming the appearance surface.
You can continue to press the entire side.

After the valve 17 is closed and the flow of the compressed air is stopped, the molten synthetic resin is cooled and solidified while being pressed entirely by the female mold 11 side. Although the molten synthetic resin shrinks during the cooling and solidification process, the female mold 11
The side is kept in close contact with the male mold 12 forming the back surface side, and a gap 19 is present. Therefore, mass compensation by shrinkage is performed by the gap 19.

Therefore, the transfer from the female mold 11 is reliably performed without unevenness on the appearance surface 2 side of the molded article 1, and the sink is freely generated on the back surface facing the gap 19. The protruding portion 4 of the molded product 1 and the thick portions 5 and 6 on both edges.
Almost no sink marks occur on the side of the appearance surface 2 corresponding to.

Further, since the cavity 19 having a predetermined pressure is formed in the cavity C, an additional extra space is required for applying a holding pressure after the usual injection molding process, that is, after injection filling of the molten synthetic resin. Since there is no need for a step of injecting the molten synthetic resin and the molding can be performed at a low pressure, even if the molding surface 2 of the molded article 1 is decorated with a grain or the like, there is a low probability of occurrence of graining and the molded article is released. And the time required for molding (molding cycle time) can be shortened.

The second embodiment shown in FIGS. 3 and 4 shows a mold for molding a relatively large molded product. In the case of a large molded product, as a matter of course, the mold itself becomes large, the inside of the cavity is widened, and the contact area with the molten synthetic resin is widened, but it does not cause sink on the appearance surface. And transfer so as not to cause transfer unevenness.
The same parts as those in the first embodiment will be described with the same reference numerals.

That is, the female mold 1 for forming the appearance of the molded product
1, a sprue 14 is provided, and a plurality of compressed fluid flow paths 18 reaching the cavity C are provided in the male mold 12 which forms the back side of the molded product. These compressed fluid passages 18 are formed in small holes or narrow slits as in the first embodiment, and are basically formed at predetermined intervals. It is preferable to provide a plurality of compressed fluid passages 18 in a place where a large number of projections having a simple structure are formed, in order to make the compressed fluid easily turn substantially evenly.

A fluid injection section 20 similar to that of the first embodiment is connected to each of the compressed fluid flow paths 18 in a branched or distributed state. The fluid injection section 20 is composed of a compression pump 15, a pipe section 16, and a valve 17 provided in the middle of the pipe section 16, and the opening and closing of the valve 17 is controlled by appropriate control means. It is.

Also in the second embodiment, as shown in FIG. 4, after the molten synthetic resin is injected and filled into the cavity C from the sprue 14, the valve 17 is opened to release the compressed air, which is one of the compressed fluids. Since the molten synthetic resin injected from each of the compressed fluid flow paths 18 into the cavity C at a predetermined pressure for a predetermined time, and the injection-filled molten synthetic resin is peeled off from the wall surface of the male mold 12 on the side of the cavity C, a gap 19 is formed therebetween. is there.

In this case, the void 19 formed on the back side of the molded product is in full communication with the entire surface except for the convex portion of the molded product. While continuing to press against the female mold 11 side, it also plays a role in creating a trigger for sinkage due to cooling and solidification of the molten synthetic resin. Therefore, the molten synthetic resin has a void 1
On the side facing 9, sinks are generated freely, so that sinks hardly occur on the side of the female mold 11 forming the appearance surface. At the same time, on the appearance surface, accurate transfer without unevenness is performed on the contact surface with the female mold 11.

[0039]

[Experimental Example 1] Using the above-mentioned mold (the number of slits in the compressed fluid flow path 18 = 10), a cabinet 2 as shown in FIG.
2 was injection molded under the following conditions.

Type of synthetic resin: PS (94HB grade) Molten synthetic resin temperature: 225 ° C. Temperature of mold 11 on the appearance side at the time of injection: 65 ° C. Temperature of mold 12 on the back side at the time of injection: 78 ° C. Injection time: 1.2 seconds Compressed air pressure: 18 kg / cm ² Compressed air injection time: 15 seconds Molding cycle time: 45 seconds

[0041]

[Experimental Example 2] Using the same mold as in Experimental Example 1, FIG.
Was injection-molded under the following conditions.

Synthetic resin: ABS Compressed air pressure: 35 kg / cm ² Other conditions are the same as in Example 1.

In each of Experimental Examples 1 and 2, almost no sink marks, uneven transfer, and uneven surface were observed on the side of the surface of the cabinet 22 as a molded product. The molding cycle time when no compressed air was used was about 50 seconds, but the molding cycle time was reduced to 45 seconds by using compressed air.

Although only a few compressed fluid channels 18 are shown in the illustrated embodiment, the compressed air is entirely applied to the back side of the molded product, ie, between the male mold 12 and the molten synthetic resin. In order to perform uniform and uniform injection, it is desirable to provide several tens of compressed fluid flow paths depending on the size and shape of the molded product.

[0045]

As described above, in the injection molding method for a synthetic resin molded product according to the present invention, the mold is provided between the mold opposite to the mold forming the appearance surface and the molten synthetic resin. By injecting a compressed fluid into the molded product and peeling it off, in a thick portion such as a rib, a boss, or an edge provided on the back surface of the molded product, sink marks caused by delay in cooling and solidification are formed in the separated void portion on the back surface. It can be generated freely, thereby giving rise to an excellent effect that almost no sink marks are generated on the appearance surface side, and the quality of the injection molded article can be improved and the commercial value can be increased.

After the molten synthetic resin is injected and filled in the cavity of the mating mold, a compressed fluid is injected between the molten synthetic resin and the mold opposite to the mold forming the appearance surface. By exfoliating, the molten synthetic resin is pressed against the mold side that forms the appearance surface with the compressed fluid, so that the transfer on the appearance surface side can be performed evenly, thereby improving the quality and by injecting the compressed fluid. In addition, since there is no need to inject an extra resin for holding pressure and use less material, there is an excellent effect that it can be provided at low cost.

[Brief description of the drawings]

FIG. 1A is an explanatory view schematically showing a main part of an injection molding apparatus of a first embodiment for carrying out a molding method according to the present invention, and FIG. 1 is a schematic cross-sectional view of a synthetic resin molded product to be manufactured.

FIG. 2 is a schematic sectional view of a main part of the injection molding apparatus.

FIG. 3 is a sectional view schematically showing a main part of the injection molding apparatus according to a second embodiment of the present invention.

FIG. 4 is a schematic sectional view of a main part of the injection molding apparatus according to the second embodiment.

FIG. 5 is a perspective view of one example of a molded article formed by the molding method according to the present invention.

[Explanation of symbols]

1: molded product, 2: appearance surface, 3: back surface, 4: protrusion, 5, 6: thick part, 10: injection molding device, 11:
Female mold (mold to form appearance), 12: male mold (mold to form back surface), 13: runner, 13a: nozzle, 14: sprue, 15: compression pump, 16: piping, 17: Valve, 18: compressed fluid flow path, 19: air gap, 20: fluid injection part, 21: support member, 22: cabinet (molded product), C: cavity.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toshihide Endo 4-6-2 Muromachi, Nihonbashi, Chuo-ku, Tokyo Inside Ryoka Kogyo Co., Ltd.

Claims (3)

[Claims] 1. An injection molding method for molding an injection-molded product by injection-filling a molten synthetic resin into a cavity of an assembling mold, wherein the mold is formed by injection-filling the molten synthetic resin and then forming a form surface. A method of injection molding a synthetic resin molded product, comprising injecting a compressed fluid between a mold opposite to the mold and the molten synthetic resin so as to be separated. 2. The injection molding method of a synthetic resin molded product according to claim 1, wherein after the molten synthetic resin is injected and filled, the molten synthetic resin is molded without applying pressure. 3. A mating mold for molding an injection-molded product, comprising a fluid injection part for injecting a compressed fluid into a mold opposite to a mold forming a presentation surface. Mold to do.