JPH1080932A - Injection molding method using resin mixed with foaming agent and injection mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a silver streak, a sinkmark or a warp from being generated on the surface of moldings, if a wall thickness is reduced by controlling the surface temperatures of an injection mold on the face side through which moldings are visible, without the use of a high pressure air injection device, so that the surface temperatures are kept close to a glass transition temperature level during the period from the start of packing a resin to the end of packing it. SOLUTION: The adherence between the face of an injection mold on the visible face side of moldings and a molten resin material is improved to make the formation of a solidified layer hardly develop by controlling the temperatures of the injection mold on the visible face side of the moldings to a vicinity of a glass transition temperature level (Tg point) during the period from the start of filling the molten resin material into the injection mold to the end of filling the resin. That is, a high frequency heating-type temperature controller 8 is built, as a heating means, into the back of the front 7 side, kept in contact with the visible face of the moldings, in the injection molds 5, 6. Further, the injection molds 5, 6 are used and the surface 7 temperatures of the injection mold 6 on the visible face side of the moldings are thermally controlled by the temperature controller 8 so to the vicinity of the Tg point during the period from the start of filling the molten resin to the end of filling it. After the completion of filling the molten resin, the surface 7 of the injection mold 6 on the visible face side of the moldings is cooled to obtain the moldings.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injection-molding a plastic molded article using a resin mixed with a foaming agent. ) And an injection molding die.

[0002]

2. Description of the Related Art In plastic injection molding, for example, when a molded product 1 as shown in FIG.
A dent state (hereinafter referred to as “sink”) occurs on the visible surface side. Conversely, when a molded product having a large thickness is injection molded, there is a problem that the molded product is deformed. For this reason, when a molded product having a rib or a boss on the back surface is injection-molded, it is extremely difficult to obtain a molded product having excellent appearance.

Therefore, a technique called gas counter pressure method has been proposed as a technique for preventing the above-mentioned sink marks and deformation in the integral molding of thick ribs and bosses and the thick molding. In this gas counter pressure molding method, the inside of the resin is foamed with a foaming agent, and the internal pressure at the time of the foaming is intended to prevent sink and deformation of the surface of the molded product.

[0004]

However, this technique is
In practice, it is necessary to make the thickness of the molded product as thick as possible and to have strength by the surface thickness itself, so that there is a disadvantage that the weight of the molded product becomes heavy. In addition, in the case of such thick molded products or molded products on which ribs, bosses, etc. are arranged, if a foaming agent is mixed with the resin in order to prevent sink marks and deformation that occur at this time, the molded product will have a defect called silver. There is a drawback that many occur.

It is said that the cause of this silver is a phenomenon of resin peeling from the resin surface. Therefore, as a measure for preventing silver, it is a necessary condition for molding to apply air pressure inside the mold. However, in order to apply air pressure to the inside of the mold, it becomes a very complicated structure in which a sealing material must be installed as a mold structure to prevent gas leakage for each protruding pin of each molded product. The costs are soaring, and furthermore, it is troublesome to take measures against gas leakage, and the overall life is short. Further, even in the nozzle structure of the injection molding machine, there is a disadvantage that a special device must be used in order to prevent air from flowing back into the mold. Further, when the gas counter pressure method is performed, there is a disadvantage that high-pressure air injection equipment is required.

[0006]

DISCLOSURE OF THE INVENTION A method of injection molding using a resin mixed with a foaming agent according to the present invention and this injection molding die solve these problems, and provide a surface of a molded article with sink marks, deformation or the like. It is characterized in that a molded article having no appearance of silver and superior in appearance can be obtained. The present inventors have conducted extensive studies on molds, and as a result, have solved the conventional problems associated with foam molding by maintaining the mold temperature on the visible side of the molded product from the start to the completion of filling. Was. The solution is as follows.

[0007] 1. When injection molding a plastic molded product using a resin mixed with a foaming agent, the surface temperature of the mold in contact with the visible surface of the molded product should be controlled near the glass transition temperature of the resin from the start to the completion of resin filling. Injection molding using a resin mixed with a foaming agent that does not generate sink marks, deformation or silver in the molded product. 2. Injection molding using a resin mixed with a foaming agent is provided on the mold side in contact with the visible surface of the molded product, from the start of resin filling to the completion thereof, a heating means capable of heating the resin to near the glass transition temperature. Molds for.

As described above, in the present invention, without using a special device such as a high-pressure air injection device as seen in the gas counter pressure method, the visible surface of the molded product is measured from the time when the resin is filled until the completion of the filling. By controlling the mold temperature on the side near the glass transition temperature of the resin (hereinafter referred to as "Tg point"), mixing a foaming agent with a conventional plastic material and injection molding, the boss-rib integrated structure, Even in a thin molded product, a foam molded product excellent in appearance without silver, sink mark, deformation or the like on the molded product surface can be obtained, and the object of the present invention has been achieved.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the temperature of a mold on the visible surface side of a molded article is controlled near the Tg point of the resin from the start of filling of the molten resin material into the mold until the completion of the filling. The adhesion between the resin surface and the mold surface on the visible side of the molded product is improved, and the formation of a solidified layer is hardly developed. As a result, the bubbles inside the resin burst at the front of the resin and are stretched between the mold surface on the visible side of the molded product and create silver on the surface of the molded product. Since the mold temperature is near the Tg point, the resin pushed up to the mold surface by the resin pressure is retransferred to the mold surface to eliminate the silver factor.

Further, regarding the sink marks, the foam layer 3 is formed uniformly at the center of the ribs 2 and the bosses 4 in FIG. Does not occur. As for the warpage, FIG.
The foamed layer 3 is uniformly formed on the molded article 1 of the above, the foaming pressure is uniformly applied to the entire molded article 1, and no warpage occurs. Further, features of the present invention will be apparent in the following examples.

[0011]

Example 1 Foaming was performed using dies 5 and 6 shown in FIG. The molds 5 and 6 incorporate a high-frequency heating type temperature controller 8 as a heating means on the back side of the surface 7 in contact with the visible surface of the molded article, and the heating means can control the surface 7 near the Tg point. . Using the molds 5 and 6, first, the high-frequency heating type temperature controller 8 controls the temperature of the surface 7 of the mold 6 on the visible side of the molded product from the start of resin filling to the completion of filling to 110 ° C. After completion, the surface 7 of the mold 6 on the visible side of the molded product was cooled to obtain a molded product.

The material is a high-impact polystyrene (SEHI-119 manufactured by Idemitsu Petrochemical Co., Ltd.) mixed with 5 wt% of a foaming agent (master batch compound polystyrene ES-206 manufactured by Eiwa Kasei Kogyo Co., Ltd.), and an injection molding machine (Toshiba Machine Co., Ltd.) The molding conditions were measured using the actual resin temperature (HL-10 manufactured by Anritsu Keiki Co., Ltd.).
0) at 240 ° C. and a filling time of 2.0 seconds. as a result,
There was no silver on the visible side of the molded article. Further, as shown in the AA 'cross-sectional view of FIG. 2 (FIG. 2), the foamed layer 3 was confirmed inside the entire boss 4, and no sink was confirmed on the surface of the rib 2.

[0013]

Comparative Example 1 Molding was performed in the same manner as in Example 1, except that the shape was the same as that shown in FIG. Other conditions were the same as in Example 1. As a result, silver was widely generated on both the visible surface and the back surface of the molded product. No foam layer 3 was found inside the boss 4, and sink was found on the surface of the rib 2.

[0014]

COMPARATIVE EXAMPLE 2 The molding was performed in the same manner as in Example 1 except that the mold surface temperature on the visible surface side of the molded product was kept at 110 ° C. from the start of resin filling. Other conditions were the same as in Example 1. As a result, although the presence of silver and sink marks was not confirmed in the molded product, deformation occurred. That is, if the mold surface temperature on the visible side of the molded article is not cooled after the completion of the resin filling, the molded article is deformed.

[0015]

Comparative Example 3 Molding was performed in the same manner as in Example 1 except that the mixing ratio was reduced to 2 wt% of the foaming agent with respect to the resin. As a result, no silver was confirmed in the molded product. However, the length of the foamed layer 3 inside the boss 4 was about 60 mm, and sink was confirmed in a portion where the foamed layer was not confirmed.

[0016]

[Embodiment 2] A molded article 1 of the entire molded article as shown in FIG.
Example 1 was performed using a mold having a molded product shape of 0.8 mm.
Molding was carried out in the same manner as described above. As a result, the foamed layer 3 was formed uniformly inside the molded product, and sink marks and silver were not confirmed. In addition, a scale is installed on the end surface of the molded product and the end surface,
When the gap was measured at the center of the molded article by a gap gauge, the maximum gap was 0.2 mm.

[0017]

Comparative Example 4 A molded product was molded in the same manner as in Example 2 without mixing a foaming agent. Other conditions were the same as in Example 2. As a result, sink marks were confirmed. In addition, when the warpage was measured in the same manner as in Example 2, the maximum gap was 1.5 mm.

[0018]

Comparative Example 5 The shape of the molded product was the same as in Example 2, the mold surface temperature on the visible side of the molded product was 75 ° C., and the other conditions were the same as in Example 2. As a result, silver was generated on both the visible surface and the back surface of the molded product, and sink was confirmed on the surface of the boss 4. Further, the measurement was carried out in the same manner as in Example 2. The maximum gap was 1.7 mm, and no good product was obtained. That is, if the foamed layer 3 is not formed uniformly inside the molded article, the warpage increases. In addition, sinks also occur on the surface of the boss 4.

[0019]

As described above, according to the present invention, the mold surface temperature on the visible side of the molded product is controlled to be in the vicinity of the Tg point from the start of resin filling to the completion of filling without using a high-pressure air injection device. Thereby, the adhesion between the mold surface on the visible side of the molded product and the resin is improved, and thus, even if the thickness is reduced, generation of silver on the surface of the molded product can be prevented. In particular, even in a thin molded product having a wall pressure of about 0.8 mm, a foam molded product excellent in appearance can be obtained without sink marks and warpage.

[Brief description of the drawings]

FIG. 1 is a view showing the formation of a foam layer in a molded article molded by controlling the mold temperature according to the present invention.

FIG. 2 is a cross-sectional view (cross-sectional view taken along line AA ′ of FIG. 1) showing the length of a boss foam layer of a molded product formed by controlling the mold temperature according to the present invention.

FIG. 3 is a cross-sectional view of a thin-walled molded product formed by mold temperature control according to the present invention.

FIG. 4 is an explanatory view of a mold according to the present invention.

FIG. 5 is a cross-sectional view of a conventional foam molded article having a rib shape.

[Explanation of symbols]

 Reference Signs List 1 Molded product 2 Rib 3 Foam layer 4 Boss 5, 6 Die 7 Surface in contact with visible surface 8 High frequency heating type temperature controller

Claims (2)

[Claims] When a plastic molded product is injection-molded using a resin mixed with a foaming agent, the surface temperature of a mold in contact with the visible surface of the molded product from the start to the completion of resin filling is determined by the glass transition temperature of the resin. A method of performing injection molding using a resin in which a foaming agent that does not generate sink marks, deformation, or silver is mixed into a molded product by controlling the molded product to be close to the molded product. 2. A resin mixed with a foaming agent, which is provided with a heating means capable of heating the resin to a temperature close to the glass transition temperature from the start to the completion of filling of the resin, on the mold side in contact with the visible surface of the molded product. A mold for injection molding using.