KR100302128B1 - Polystyrene resin compound for injection molding - Google Patents

Abstract

The present invention relates to a resin composition for injection molding, wherein 70% to 90% of the first styrene composition comprising 6% to 8% of the rubber having a particle diameter of 3 to 5 μm and 7% to a rubber having a particle diameter of 1 to 3 μm. The second styrene composition, which contains 9%, is 9.4-29%, and the remainder is composed of heat stabilizer and silicone oil, respectively, and improves fluidity characteristics by appropriately mixing the styrene resin composition containing rubber having particles of different sizes. Therefore, there is an effect of improving the weld line and appearance characteristics accordingly.

[Index]

Polystyrene, Injection Molding, Resin Composition, Styrene, Fluidity, Weldline

Description

Polystyrene-based resin composition for injection molding {POLYSTYRENE RESIN COMPOUND FOR INJECTION MOLDING}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to resin compositions for injection molding, and more particularly, to injection molding resins in which external defects, such as weld lines, are reduced when injection molding of a TV case, thereby eliminating post-processing treatments such as coating.

In general, polystyrene produced by radical polymerization of styrene using an initiator such as an organic peroxide has characteristics of excellent transparency, small specific gravity, and excellent electrical and high frequency insulation due to the non-linear nature of the structure, but the softening temperature is low and hard. There is a drawback to being well broken.

The styrene resin has a low melting point viscosity and a low viscosity in a relatively low temperature range, so that the molding temperature is wide, and transparency and moldability are excellent.

Therefore, high impact polystyrene (High Impact PS), acrylonitrile, butadiene, which improves the breakdown point of polystyrene by blending synthetic rubber (5- 20%) with general purpose polystyrene (GPPS) polymerized with styrene only ABS resin, a shock-resistant thermoplastic made of styrene, is widely used as a case for home electric and electronic products.

The flowability of each resin is about the ratio of the flow length and the thickness of the molded article (L / t) in general resin (GP-PS) 230-250, high impact resin (HI-PS) 220-230, ABS resin 190 -ABS resins have excellent liquidity characteristics in order of 200, but because ABS resins are more expensive than general resins or high impact resins, high impact resins are used for home appliances such as TV cases.

Since the high impact resin is generally inferior in fluidity, weld lines occur in the molded article during injection molding, and there is a problem in that a coating treatment is required as a separate post-processing treatment for aesthetic treatment of the product.

In general, the weld line refers to the formation of a slender solid line formed in a part where the molten resin flows through the mold and joins the resin, which means that the molten resin is not completely joined at the point where the molten resin joins each other. It is a main cause of occurrence, and weld lines are also generated by other resins such as moisture, volatile matter, and a release agent used during injection molding.

In particular, the weld line is generated when there are holes or two or more gates in the molded part. In order to perform injection molding, a gate for passing resin is required, and as the molded part grows in size or complexity, the number of gates is 2 Since more than one gate is needed, it is easy to generate weld lines, and even if molten resin is supplied to one gate, weld lines are generated even if there are insert parts or holes along the way or the thickness of the molded article is different. do.

FIG. 1 is a schematic view for explaining a process of forming a weld line, and FIG. 1A illustrates a melt line at a portion where molten resin is supplied into a cavity from two gates 10 and 12 and the molten resin is joined to each other. 14) is formed.

At this time, even though the molten resin is joined, the weld line is not formed at a portion close to the gates 10 and 12, but a weld line is formed at a portion far from the gates 10 and 12. As the cooling proceeds, the joined resin is not completely fused by the low temperature at the part away from the gate, thereby forming a weld line.

1B illustrates that even when molten resin is supplied through one gate 12 when the hole 18 is provided inside the molded article, the molten resin is sorted around the hole 18 and then welded again. Line 16 is formed.

Such weld lines inevitably occur in high impact resins containing butadiene rubber in order to improve impact properties, particularly in the case of high impact resins, thereby reducing the strength of the molded article. In addition, since the appearance quality of the molded product is lowered, there is a problem such as adding a painting operation to paint to remove the weld line after the injection process is finished.

The present invention has been made to solve the above problems, and an object thereof is to provide an improved injection molding polystyrene resin composition to minimize the generation of weld lines during injection molding by increasing the flow characteristics during melting. .

1A is a schematic diagram illustrating a process of forming a weld line;

1B is a schematic diagram illustrating another formation process of the weld line.

* Description of the symbols for the main parts of the drawings *

12 gate 16 weld line

18: Hall

Polystyrene resin composition according to the present invention for achieving the above object, characterized in that made by mixing the first and second styrene composition including rubber having a different particle size.

At this time, the first styrene composition is characterized in that it comprises 6-8% of the rubber having a particle diameter of 3 to 5 ㎛.

In addition, the second styrene composition is characterized in that it comprises 7-9% of the rubber having a particle diameter of 1 to 3 ㎛.

And 70-90% of the first styrene composition and 9.4-29% of the second styrene composition, and the remainders are heat stabilizers and silicone oils, respectively.

According to the present invention, by appropriately mixing the styrene resin composition comprising a rubber having a different particle size has the effect of improving the fluidity characteristics, thereby improving the weld line and appearance characteristics.

In general, when including particles of synthetic rubber included in polystyrene resin, when large rubber particles or small rubber particles are used, these rubber particles are interspersed with butadiene fibers inside the polystyrene matrix. When the impact is applied to the molded article, the stress is concentrated in the fibrous structure, so that fine crazing occurs and thus the shock tends to be absorbed. However, as described above, when the size of rubber particles included in polystyrene is large or small, a large amount of rubber particles may generally reduce fluidity during injection molding in proportion to their usage.

Therefore, it is most desirable to use less rubber particles and to enhance impact resistance, and for this reason, when only one type of rubber particles included in polystyrene is used, either large or small, these rubber particles are evenly dispersed in the polystyrene. It becomes difficult to distribute. However, when the two sizes of rubber particles are used, the rubber particles are well mixed with each other to satisfy the impact resistance and fluidity of the polystyrene, thereby improving the moldability during injection molding. It will be able to improve the appearance characteristics.

Hereinafter, the present invention will be described in detail according to preferred embodiments.

EXAMPLE

The 1st styrene composition is a styrene composition which mix | blended 7% of the rubber which has an average particle diameter of 3-5 micrometers with styrene, and the 2nd styrene composition is a styrene composition which mix | blended 8% of the rubber which has an average particle diameter of 1-2 micrometers with styrene.

The first and second styrene compositions are mixed according to the composition shown in Table 1 below, and the mixed compositions are then tested at a cylinder temperature of 190-220 ° C and a mold temperature of 50 ° C with an injection pressure of 100 tons. As shown in Figure 1b was prepared by filling the molten resin using a gate in a mold having an insert hole in the center.

division First styrene composition Second styrene composition Heat stabilizer Silicone oil Swelling index Example 1 99.8 0 0.2 0 11 Example 2 90.0 9.4 0.4 0.2 9 Example 3 80.0 19.0 0.6 0.4 7 Example 4 70.0 28.6 0.8 0.6 6 Example 5 60.0 38.2 1.0 0.8 5

Here, Example 1 is to use only the first styrene composition, Examples 2 to 5 is to increase the content of the second styrene composition little by little, the crosslinking degree is increased by mixing the styrene composition with different rubber particle size swelling You can see that the index is decreasing.

Thus, the test results of each of the test pieces having different mixing ratios as shown in FIG. 1B are shown in Table 2 below.

division Weld line (mm) Polish stain Gas generation amount (%) Length width Example 1 10.0 0.5 35 △ 2.417 Example 2 4.0 0.1 55 ◎ 1.502 Example 3 3.0 0.2 63 0 1.524 Example 4 3.0 0.4 64 △ 1.890 Example 5 3.0 0.5 70 X 2.141

Here, in Example 1, while the length and width of the weld line are long and wide, Examples 2 to 5 including the second styrene composition are gradually reduced in length and width of the weld line, and the second styrene composition contains a lot of the second styrene composition. In Example 5, the width of the weld line is widened again.

In addition, the glossiness tends to be better in Example 2-5 than in Example 1, and the staining tends to be bad in Example 5, which contains a lot of the second styrene composition.

In these examples, the amount of gas generated was measured after losing 30 minutes at 230 ° C. for the amount of reduction, which can be seen in Examples 2 and 3 to be the least represented.

As can be seen from the above examples, the appearance effect of the molded article during injection molding was improved by appropriately mixing the first polystyrene composition including the large rubber particle size and the second polystyrene composition including the small rubber particle size.

In these examples, the first and second polystyrene compositions are simply mixed, but when they are mixed with each other and extruded to proceed with injection, they are more closely acted between the large rubber and the small rubber particles to further improve the appearance effect of the molded article. It will be possible.

As described above, according to the present invention, the injection molding is performed by mixing a polystyrene composition containing large rubber particles and a polystyrene composition containing small rubber particles with each other, thereby improving the appearance of the molded article.

Claims (1)

The first styrene composition comprising 6-8% of the rubber having a particle size of 3-5 μm 70-90%, the second styrene composition comprising 7-9% of the rubber having a particle size of 1-3 μm 9.4-29 %, And the remaining heat stabilizer, polystyrene composition for injection molding comprising a silicone oil.