JP2002530504A - Polystyrene resin composition for injection molding - Google Patents

Abstract

  (57) [Summary] The present invention relates to a polystyrene resin composition for injection molding, comprising a mixture of first and second styrene compositions containing rubbers of different particle sizes, wherein the first styrene composition has a particle diameter of 3 to 5 μm. The second styrene composition contains 6 to 8% of rubber and 7 to 9% of rubber having a particle size of 1 to 3 μm. As a result, the rubber particles having a large size and the rubber particles having a small size come into intimate contact with each other after the injection molding, so that the appearance of a molded product can be improved by suppressing the occurrence of a welding line.

Description

DETAILED DESCRIPTION OF THE INVENTION

TECHNICAL FIELD [0001] The present invention relates to a polystyrene resin composition for injection molding, and more particularly to a post-processing step such as a coating process by reducing external defects such as a welding line formed during injection molding. The present invention relates to a polystyrene-based resin composition for injection molding for omitting the above.

BACKGROUND ART In general, polystyrene is an organic peroxide.
It is produced by radical polymerization of styrene using an initiator such as.

[0003] The polystyrene thus obtained has a linear structure, is excellent in transparency, has a low specific gravity, and has excellent properties in electrical and high-frequency insulation. However, it has a low softening temperature and is hard and easily broken. There are drawbacks.

[0004] Polystyrene resins have a low melting point viscosity in a relatively low temperature range, the degree of viscosity decrease with temperature decrease is slow, the molding temperature range is wide, and transparency and molding characteristics are excellent.

[0005] Therefore, high impact polystyrene (H
(High Impact PS) resin and ABS resin are widely used. High impact polystyrene (HIPS) resin is a general-purpose polystyrene (Ge
Neural Purpose PS) resin is obtained by compounding 5 to 20% of synthetic rubber, thereby improving the fragility of polystyrene. It is a thermoplastic resin.

The flow length L of each resin and the building thickness of a molded product (buildin)
The ratio (L / t) of gthickness / t is 230-250 for general-purpose polystyrene (GPPS) resin and 220-230 for high-impact polystyrene (HIPS) resin.
, ABS resin is 190 to 200.

Accordingly, although the fluidity of the resin is superior in the order of the ABS resin, the GPPS resin, and the HIPS resin, the price of the ABS resin is higher than that of the general-purpose polystyrene (GPPS) resin or the high-impact polystyrene (HIPS) resin. High impact polystyrene (HIPS) resin is widely used for general home appliances such as a vision case.

However, since the HIPS resin is inferior in fluidity, a welding line is formed in a molded product at the time of injection molding, and a coating process must be performed as another post-processing process after the injection molding.

The term “welding line” means that a thin solid line is formed at a portion where two branched and fused resins meet in a mold. The main cause of the welding line is that the low temperature at the front end of the two resins makes it impossible for the two branched and melted resins to be completely mixed at the confluence point. A welding line may also be formed depending on the release agent used during molding.

[0010] Injection molding requires a gate through which resin passes. When a molded product is large or complicated, two or more gates are required. In this case, a welding line is easily formed. On the other hand, even if molten resin is supplied to one gate,
Weld lines also occur when there are inserts or holes in the part or when the building thickness of the part is different.

FIGS. 1A and 1B are schematic views for explaining a process of forming a welding line. As shown in FIG. 1A, a molten resin forms two gates 12 and 14. The welding line is formed at a portion where the two branched portions of the resin are fed into the cavity and merge.

At this time, even if the branched and molten resins are merged, a welding line is not formed in a portion close to the gates 12 and 14, and a welding line is formed in a portion far away from the gates 12 and 14. This is because, at a position apart from the two gates 12 and 14, the molten resin cooled through the mold and cooled to a low temperature cannot be completely fused, and the welding line 16 is formed.

On the other hand, as shown in FIG. 1B, when there is a hole 18 inside the molded product, even if the molten resin is supplied through one gate 12, the molten resin is branched around the hole 18. Thereafter, when they merge again, a welding line 16 is formed.

[0014] Such a welding line is inevitably generated due to a decrease in fluidity when butadiene is added to the HIPS resin in order to improve impact strength and fluidity. Such a welding line not only reduces the strength of the molded product, but also lowers the appearance quality level of the molded product, so it is necessary to perform painting work to make the welding line invisible after the injection process did not become.

DISCLOSURE OF THE INVENTION [0015] The present invention has been devised to solve the above-described problems, and enhances the fluidity of a resin composition during melting to minimize the occurrence of a welding line during injection molding. It is an object of the present invention to provide a polystyrene resin composition for injection molding to be converted.

The polystyrene resin composition for injection molding according to the present invention for achieving the above object is characterized by mixing first and second styrene compositions containing rubbers having different particle sizes. .

Here, the first styrene composition contains 6 to 8% of a rubber having a particle diameter of 3 to 5 μm, and the second styrene composition contains a rubber of 7 to 9 having a particle diameter of 1 to 3 μm.
%.

Further, the polystyrene-based resin composition may contain the first styrene composition in an amount of 70 to 90.
% And 9 to 29% of the second styrene composition, and a heat stabilizer and silicone oil.

According to the present invention, by mixing styrene compositions containing rubbers of different particle sizes, the fluidity characteristics are improved, and as a result, the appearance of a molded product is improved by suppressing the occurrence of welding lines. be able to.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Generally, when synthetic rubber particles are included in a polystyrene resin, only rubber particles having a large particle size or rubber particles having a small particle size are simply used. These rubber particles are scattered in the fiber structure of butadiene existing inside the polystyrene cloth, and when an impact is applied to the molded product, stress is concentrated on the fiber structure, and fine crazing (crazing) occurs. Shock can be absorbed.

However, when a large amount of rubber particles having a large particle size or a small particle size are used as the rubber particles contained in the polystyrene, the fluidity at the time of injection molding should be proportional to the amount of the rubber particles used. Become.

Therefore, it is necessary to reduce the amount of rubber particles used as much as possible to enhance the impact resistance. If only one of the large and small rubber particles is used as the rubber particles contained in the polystyrene, it becomes difficult to uniformly distribute the rubber particles in the polystyrene.

On the other hand, when both the rubber particles having a large particle size and the rubber particles having a small particle size are used, the rubber particles are uniformly mixed, and both the impact resistance and the fluidity of polystyrene are satisfied. Can be. Thereby, the moldability at the time of injection molding is improved, and the appearance characteristics of the molded product are improved.

Hereinafter, the present invention will be described in detail with reference to the following preferred embodiments. 1. Examples 1 to 5 In the first styrene composition, 7% of rubber having an average particle diameter of 3 to 5 μm was blended with styrene, and in the second styrene composition, 8% of rubber having an average particle diameter of 1 to 2 μm was mixed with styrene. Was blended. The first and second styrene compositions and other additives were mixed at the mixing ratio shown in Table 1.

[0025] The mixed composition was heated at an injection machine cylinder temperature of 190 to 220 ° C, a mold temperature of 50 ° C,
A test piece was manufactured by injection molding under the conditions of an injection pressure of 100 tons. These test pieces had a size of 450 mm × 250 mm, and were melt-filled using a single gate in a mold having an insert hole 18 formed at the center shown in FIG. 1B.

[0026]

[Table 1]

In Example 1, the polystyrene resin composition was obtained by using only the first styrene composition. In Examples 2 to 5, the polystyrene resin composition gradually reduced the content of the second styrene composition. Obtained by increasing. Here, by increasing the mixing ratio of the styrene composition containing rubbers having different particle sizes, the degree of crosslinking (cross) was increased.
It can be seen that the expansion index decreases as the linking ratio increases. Table 2 shows test results for test pieces manufactured using the two compositions at different compounding ratios and having the shape shown in FIG. 1 (b).

[0028]

[Table 2]

In the first embodiment, the welding line has a long length and a wide width. In Examples 2 to 5 including the second styrene composition, the length and width of the welding line were reduced,
In Example 5, in which a large amount of the styrene composition was included, the width of the welding line was widened again. The gloss characteristics of Examples 2 to 5 are better than those of Example 1. The unevenness characteristics of Example 5 containing a large amount of the second styrene composition were not good. The amount of gas generated is
Expressed by the weight loss of the test piece measured after allowing the test piece to stay at 230 ° C. for 30 minutes,
In Example 2 and Example 3, the amount of generated gas was small.

As can be seen from the above examples, a composition in which a first styrene composition containing a rubber having a large particle size and a second styrene composition containing a rubber having a small particle size are mixed at a predetermined ratio is used. Thereby, the appearance quality of the molded article at the time of injection molding can be improved.

In the above embodiment, there is a risk that the first and second polystyrene compositions may be misunderstood simply as being simply mixed. However, in practice, the mixture is mixed and then subjected to injection molding to reduce the particle size. The large rubber and the rubber particles having a small particle size are in close contact with each other, so that the appearance quality of the molded product is further improved.

As described above, the present invention relates to injection molding a composition obtained by mixing a polystyrene composition containing a rubber having a large particle size and a polystyrene composition containing a rubber having a small particle size. This has the effect of improving the appearance of the molded article.

Although the preferred embodiment of the present invention has been described, the present invention is not limited to this.
Various changes and modifications can be made by those skilled in the art without departing from the technical concept and the protection scope of the present invention described in the claims.

[Brief description of the drawings]

FIG. 1A is a schematic diagram showing a process of forming a welding line, and FIG. 1B is a schematic diagram showing another process of forming a welding line.

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Claims (4)

[Claims] 1. A polystyrene resin composition for injection molding obtained by mixing first and second styrene compositions containing rubbers having different particle sizes. 2. The first styrene composition contains A% of a rubber having a particle diameter of 3 to 5 μm, and the second styrene composition contains B% of a rubber having a particle diameter of 1 to 3 μm. The polystyrene resin composition for injection molding according to claim 1, which comprises: 3. The polystyrene resin composition for injection molding according to claim 2, wherein A is 6 to 8, and B is 7 to 9. 4. The polystyrene-based resin composition contains 70 to 90% of the first styrene composition, 9 to 29% of the second styrene composition, a heat stabilizer and silicone oil. 3. The polystyrene resin composition for injection molding according to 2.