JP2000071277A - Method for foaming injection holding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of a swirl mark, a silver streak, and a sink mark by using a mold in which an insulating layer of specified heat conductivity and of specified thickness is formed on the inner surface of a cavity mold. SOLUTION: A mold is used in which an insulating layer 0.002 cal/cm.sec. deg.C or below in heat conductivity and 0.001-3 mm in thickness is formed on the inner surface of a cavity mold, preferably on both inner surfaces of the cavity mold and core mold. The insulating layer prevents the cooling of an injected expandable resin and, while the resin is injected and pressed to a mold cavity surface, keeps the temperature of the mold cavity surface (insulating layer surface) brought into contact with the resin to exceed the solidification temperature of the resin. By the installation of the insulating layer, the rapid cooling of the injected expandable resin is prevented to keep its fluidity so that the surface defects of the obtained foamed molding can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-foamed surface,
Moreover, the present invention relates to a foam injection molding method for a foam molded article having a highly foamed inside. More specifically, especially for exterior appearance, light weight, high heat insulation etc. are required for automobile door panels, hoods, fenders and other outer plates, door linings, pillars and other interior parts,
Further, the present invention relates to a foam injection molding method suitable for molding inner and outer wall materials in a housing field, floor materials in a bathroom, and the like.

[0002]

2. Description of the Related Art Hitherto, in order to improve the appearance of a foam molded product, it has been known that the foam molded product has a non-foamed surface and a highly foamed inside. Specifically, there is known a foam injection molding method in which a heat-plasticized foamable resin is injected into a mold cavity pressurized with compressed air in advance, the pressure is reduced after completion of the injection, and then the volume of the mold cavity is enlarged. (Japanese Patent Publication No. 51-27266). Also, during or immediately after injection of the foaming resin, the mold cavity is reduced,
While completely filling the mold cavity with foaming resin,
There is known a foam injection molding method in which a solidified layer in contact with a mold cavity surface and a molten layer therein are cooled to a mixed state, and then the mold cavity is expanded to the volume of a molded product (Japanese Patent Application Laid-Open No. 8-300392). ).

According to the above conventional foam injection molding method, foaming resin injected into a mold cavity is suppressed from foaming until a solidified layer is formed on the surface of the foaming resin. It is said that the generation of swirl marks (foaming gas traces) and silver (silver streaks) on the product surface can be prevented.

[0004]

However, according to the findings of the present inventors, the above conventional foam injection molding method has the following problems.
It is useful for reducing the occurrence of swirl marks and silver,
The appearance of the obtained foam molded product is not satisfactory enough to be commercialized as it is. There is also a problem that a pock-like sink is likely to occur on the surface of the obtained foam molded article.

[0005] It is an object of the present invention to improve the appearance of a foamed molded product whose surface is non-foamed and whose interior is highly foamed.

[0006]

The cause of the surface defect of the foam molded article obtained by the conventional foam injection molding method is caused by the foam generated from the flow front of the foamed resin when the foamable resin is injected. When gas is confined between the inside of the mold cavity and the foamable resin surface that has started to solidify by contacting the cooled mold cavity inner surface, or when the mold cavity is expanded to the volume of the molded product, It is considered that the solidified layer is separated from the inner surface of the mold cavity without being able to follow the movement of the inner surface of the mold cavity, and foaming gas or air enters between the solidified layer and the inner surface of the mold cavity.

[0007] The present invention is to eliminate the cause of the above-mentioned surface defects, inject foamable resin into the mold cavity,
After the foamable resin is pressed against the surface of the mold cavity, the volume of the mold cavity is expanded to the volume of the molded product to form a foam molded product. 002 cal / cm · s
An object of the present invention is to provide a foam injection molding method characterized by using a mold provided with a heat insulation layer of ec · ° C or less with a thickness of 0.001 to 3 mm.

[0008] Usually, the mold cavity surface is maintained at a temperature much lower than the solidification temperature. Although the temperature of the mold cavity may be instantaneously raised to a temperature higher than the solidification temperature due to the contact of the injected foamable resin, Is kept below the solidification temperature. Therefore, in the case of the conventional foam injection molding, the surface of the foamable resin is cooled to a temperature equal to or lower than the solidification temperature immediately after injection, and the foaming gas generated from the flow front of the foamable resin starts to solidify. Easily trapped between the conductive resin surface and the mold cavity inner surface. In addition, when the foamable resin is pressed against the mold cavity surface, the adhesion between the foamable resin surface and the mold cavity surface is weakened by the solidified layer on the foamable resin surface. It is considered that a solidified layer having a thickness is formed, and expansion due to foaming becomes difficult.

On the other hand, when a mold provided with a heat insulating layer as in the present invention is used, from the start of injection of the foamable resin to the pressing with the mold cavity surface, the entire foamable resin in the mold cavity is In particular, the temperature of the foamable resin surface can be maintained at a temperature exceeding its solidification temperature. For this reason, even if foaming gas enters between the foaming resin and the mold cavity surface during the injection process, since the foaming resin surface is rich in fluidity, it is easily discharged with the flow. Become. Further, when the foamable resin is pressed against the mold cavity surface, the foamable resin surface is easily adapted to the mold cavity surface, and high adhesion is obtained. It is considered that this improvement in the adhesion at the same time provides a certain degree of adhesion of the foamable resin surface to the mold cavity surface. For this reason,
In the present invention, when the mold cavity is enlarged, the surface of the foaming resin follows the movement of the mold cavity surface such that the surface of the foaming resin is pulled by the mold cavity surface, and the space between the foaming resin surface and the mold cavity surface is moved. It is considered that the mold cavity can be enlarged without peeling off while maintaining the adhesion between the two. In addition, when the mold cavity is enlarged, the foamable resin surface is appropriately adhered to the mold cavity surface and is pulled in the direction of increasing the volume, so that the inside of the foamable resin is easily negatively charged, and the foaming inside the foamable resin is easily performed. Is promoted, and it is considered that a highly foamed molded article is easily obtained.

[0010] The foaming resin surface in the mold cavity is pressed against the mold cavity surface with high adhesion as described above to suppress foaming. Also,
In the present invention, it is considered that the solidified layer on the surface at the time when the foamable resin is brought into pressure contact with the mold cavity surface is in a state where there is little or almost no solidified layer. For this reason, after the foamable resin is pressed against the mold cavity surface, it is appropriately cooled while maintaining the pressed state to form a minimum necessary solidified layer, thereby hindering the followability of the movement of the mold cavity surface. Without foaming of the surface when the volume of the mold cavity is increased, swirl marks and silver can be prevented.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The foamable resin used in the present invention is a thermoplastic resin to which a foaming agent has been added.

As the thermoplastic resin, thermoplastic resins used in general injection molding can be widely used. Examples thereof include styrene polymers and their copolymers, polyolefins such as polypropylene and polyethylene, polyamides, polyesters, vinyl chloride resins, polycarbonates, methacrylic resins, polyvinyl alcohols, and the like.
In addition to these foaming agents, these thermoplastic resins include, for example, coloring agents (dyes and pigments), softeners, lubricants, antistatic agents,
Various additives such as an ultraviolet absorber and a resin reinforcing material can also be added. As the resin reinforcement, various fibers such as glass fiber and carbon fiber, rubber, talc, calcium carbonate,
Examples include inorganic powders such as kaolin.

Examples of the foaming agent include inorganic foaming agents such as ammonium carbonate and sodium bicarbonate, and organic foaming agents such as azo compounds, sulfohydrazide compounds, nitroso compounds and azide compounds. As the azo compound, for example, azodicarbonamide (AD
CA), 2,2-azoitibutyronitrile, azohexahydrobenzonitrile, diazoaminobenzene and the like. Examples of the sulfohydrazide compound include:
For example, benzenesulfohydrazide, benzene-1,3-
Disulfohydrazide, diphenylsulfone-3,3-disulfohydrazide, diphenyloxide-4,4-disulfohydrazide and the like can be mentioned. As the nitroso compound, for example, N, N-dinitrosopentamethylenetetramine (DNPT) ), N, N-dimethyl terephthalate and the like. Examples of the azide compound include terephthal azide and P-tert-butyl benzazide.

The amount of the foaming agent added to the thermoplastic resin is as follows:
Although it differs depending on the type of the foaming agent, it is generally 0.5
To 10 parts by weight.

In the present invention, a mold capable of expanding and reducing the volume of the mold cavity while injecting and filling a molten foamable resin into the mold cavity (a mold capable of injection compression).
Is used. Usually, such a mold is constituted by a cavity mold (female mold) and a core mold (male mold), and the design surface (outer surface) of the foam molded product is formed by the cavity mold.

In the present invention, at least the inner surface of the cavity mold, preferably both the inner surface of the cavity mold and the inner surface of the core mold, have a thermal conductivity of 0.002 cal / cm · sec.
A mold provided with a heat insulating layer of c · ° C. or less with a thickness of 0.001 to 3 mm is used. This heat insulating layer prevents cooling of the injected foamable resin, and the mold cavity surface (heat insulating layer surface) in contact with the foamable resin until the foamable resin is injected and pressed against the mold cavity surface. Is maintained at a temperature exceeding the solidification temperature of the foamable resin. By providing this heat-insulating layer, as described above, the quenching of the injected foamable resin is prevented, and the fluidity thereof is maintained. it can. If the thermal conductivity of the heat insulating layer is too high or the thickness is too thin, rapid cooling of the foamable resin cannot be sufficiently prevented, and defects on the surface of the obtained foamed molded product are likely to occur. On the other hand, if the heat insulating layer is too thick, it is difficult to cool the foamable resin, and the molding cycle is likely to be delayed.

The upper limit of the temperature exceeding the solidification temperature maintained by the surface of the heat-insulating layer in contact with the foamable resin until the foamable resin is injected and pressed against the mold cavity surface is lower than the decomposition temperature of the foamable resin. However, if the temperature is excessively high, the molding cycle is delayed.
It is preferably 0 ° C. or lower.

The solidification temperature is the temperature at which the molten resin solidifies. The glass transition temperature for an amorphous resin, the crystallization start temperature for a crystalline resin, and the sea-island structure for an incompatible polymer alloy. Refers to the glass transition temperature or the crystallization onset temperature of the resin constituting the sea. The crystallization start temperature of the crystalline resin is determined by using a differential calorimeter to heat and melt the resin, and then cooling the resin at a rate of 20 ° C./min. I do.

The provision of the heat insulating layer is described in, for example,
As shown in Japanese Patent No. 62172, this can be performed by forming a polyimide film. Further, in order to prevent the surface of the heat-insulating layer from being damaged and to facilitate graining or matting, the surface of the heat-insulating layer may be plated.

In the present invention, first, a molten foamable resin is injected into the mold cavity of the mold, and the foamable resin is pressed into contact with the entire surface of the mold cavity. The method of injecting the foamable resin includes a method of performing the injection on a mold that has been clamped and a method of performing the injection on a mold that has been slightly opened.

In the case of injection into a closed mold, the foaming resin is pressed against the mold cavity surface by filling the inside of the mold cavity with the foaming resin, similarly to the usual injection molding. be able to. In particular, if overfilling is performed by injecting an excessive amount of foaming resin into the mold cavity volume, the foaming resin is strongly pressed against the mold cavity surface,
This is preferable because the state of adhesion between the foamable resin and the mold cavity surface is improved.

In the case of injecting into the opened mold, an insufficient amount of foaming resin is filled to fill the opened mold cavity, and the volume of the mold cavity is reduced during or immediately after the injection. By reducing and compressing, the foamable resin can be pressed against the mold cavity surface. The injection amount of the foaming resin is preferably 70 to 95% by volume of the volume of the mold cavity in the slightly opened state.

As described above, the temperature of the surface of the heat insulating layer in contact with the foamable resin is higher than the solidification temperature until the foamable resin is injected and pressed against the mold cavity surface. The surface of the foaming resin in the mold cavity is pressed against the mold cavity surface with high adhesion without generating an excessive solidified layer, to suppress foaming and to the mold cavity surface when the next mold cavity volume expansion. And the following ability is surely obtained.

After the foamable resin is pressed against the surface of the mold cavity, the volume of the mold cavity is increased to the volume of the molded product.
The pressurized state inside the foamable resin maintained at a temperature equal to or higher than the foaming temperature is released, and foaming is performed to a predetermined molded product volume. Preferably, after injection into the mold cavity of the closed mold and filling or after injection into the mold cavity of the slightly opened mold to reduce the mold cavity volume by a predetermined amount, 0.1
After cooling for 5 seconds while maintaining the press-contact state between the foaming resin and the mold cavity surface, the volume of the mold cavity is expanded to the volume of the molded product. Forming the minimum required solidified layer on the surface of the foaming resin by allowing the cooling time in the pressed state between the time when the foaming resin is pressed against the entire mold cavity surface and the time when the mold cavity volume is expanded And foaming on the surface when the mold cavity is enlarged can be easily suppressed.

After expanding the volume of the mold cavity to the volume of the molded product as described above, the foamed molded product is taken out after further performing necessary cooling. The obtained foamed molded product has a non-foamed surface and an internal foamed one, so that a lightweight and thick foamed molded product can be obtained. The expansion ratio of this foam molded article is preferably 1.2 to 5 times in order to obtain a foam molded article having a good surface.

[0026]

EXAMPLES First, molding conditions common to each of Examples and Comparative Examples are shown below.

Molding machine: Maximum mold clamping force 125 ton, cylinder set temperature 210 ° C. Mold: Mold capable of injection compression and having a valve gate,
Mold temperature 80 ° C ・ Foam molded product: 150 mm long, 150 mm wide, 5 mm thick plate ・ Thermoplastic resin: polystyrene (“Stylon H8662” manufactured by Asahi Kasei Kogyo Co., Ltd.), melt flow rate 5 g / 10 min according to JIS K7210 (200 , 5 kg), glass transition temperature about 100 ° C ・ Blowing agent: Master batch “ES-2” manufactured by Eiwa Chemical Industry Co., Ltd.
06 ”・ Foamable resin: 3% by weight of the above foaming agent is added to the above thermoplastic resin

Example 1 Bubble injection molding was performed using a mold coated with a polyimide having a thickness of 0.12 mm as a heat insulating layer on both the cavity mold surface and the core mold surface.

The initial thickness of the mold cavity is set to 2.3 mm, and after injecting the foamable resin, the thickness of the mold cavity is immediately reduced to 2.0 mm and compressed. After cooling under the condition, the mold cavity thickness is 5
mm and cooled for 30 seconds to take out a foam molded article. The temperature of the mold cavity surface upon completion of the reduction of the mold cavity volume was 130 ° C.

Observation of the foamed product taken out with the naked eye revealed no swirl marks, silver or sink marks. The surface was non-foamed and the inside was highly foamed.

Example 2 The mold of Example 1 was clamped (mold cavity thickness = 2.0).
mm), the mold cavity is injection-filled with a foaming resin of 110% by volume of the mold cavity volume, kept for 0.3 seconds and cooled, and then the mold cavity thickness is increased to 5 mm. After cooling for 2 seconds, the foam molded article was taken out. The temperature of the mold cavity surface upon completion of the injection was 130 ° C.

As in Example 1, no swirl mark, silver and sink marks were observed in the obtained foamed molded product.
The surface was non-foamed and the inside was highly foamed.

Comparative Example 1 Using a mold having no heat-insulating layer, foam injection molding was carried out in the same manner as in Example 1 to obtain a foam molded article. The temperature of the mold cavity surface when the mold cavity volume reduction was completed was 110 ° C.

Although the swirl mark and silver were not observed in the obtained foamed molded product, sink marks were present on the entire surface and the appearance was poor.

[0035]

As described above, the present invention can prevent the occurrence of swirl marks and silver, and at the same time, can prevent sink marks and can easily obtain a foam molded article excellent in appearance. Can be done.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masato Kuramitsu 1-3-1 Yoko, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture F-term in Asahi Kasei Kogyo Co., Ltd. 4F202 AA03 AA13 AA15 AA24 AA28 AA29 AB02 AH17 AH48 AH49 AJ02 AJ03 AJ13 AR20 CA11 CA23 CB01 CD22 CK11 CL01 4F206 AA03 AA13 AA15 AA24 AA28 AA29 AB02 AH17 AH48 AH49 AJ02 AJ03 AJ13 AR20 JA04 JL02 JM02 JM04 JM05 JN11 JN21 JN25 JN32 JQ81 JT05

Claims (5)

[Claims] 1. A foamed resin is injected into a mold cavity, and the foamable resin is pressed against the surface of the mold cavity. Then, the volume of the mold cavity is expanded to the volume of the molded product to form a foam molded product. In the foam injection molding method, at least the inner surface of the cavity mold has a thermal conductivity of 0.002 cal / c.
A foam injection molding method characterized by using a mold provided with a heat insulating layer of m · sec · ° C or less with a thickness of 0.001 to 3 mm. 2. The foam injection molding according to claim 1, wherein the foaming resin is pressed against the surface of the mold cavity by overfilling the foaming resin into the mold cavity of the clamped mold. Method. 3. A mold cavity of the opened mold,
By injecting an insufficient amount of foaming resin to fill the opened mold cavity and reducing the volume of the mold cavity during or immediately after injection, it is possible to press the foaming resin against the mold cavity surface. The foam injection molding method according to claim 1, wherein: 4. The foam injection molding method according to claim 1, wherein a mold having a heat insulating layer provided on both the inner surface of the cavity mold and the inner surface of the core mold is used. 5. The expansion ratio of the obtained foamed molded product is 1.2.
The foam injection molding method according to any one of claims 1 to 4, wherein the ratio is up to 5 times.