JPH07178751A - Square injection-molded article of thermoplastic resin and its manufacture - Google Patents

Abstract

PURPOSE:To provide a square injection-molded article of a thermoplastic resin and its manufacturing method, by which a loading of an injection-molding machine is reduced by lowering the injection pressure, and forming defects are reduced. CONSTITUTION:For a square injection-molded article 1 of a thermoplastic resin, thicker parts 2 which extend to respective corners from the center 3 of a square are provided, and the width of the thicker part is radially extended from the. center in such a manner that the thicker part may expand to both sides of the outer periphery from the corner by a width of approx. l/10 of the length of one edge. For the manufacturing method, one point 3 at the center of a square is made a gate, and at the same time, the thicker parts 2 which extend to respective corners from the center are provided. Then, a square flat plate 1 of a thermoplastic resin is injection-formed by selecting a forming condition so that the reaching periods of time of the resin to respective corners and the outer peripheries of respective edges may become the same. By this method, the resin can be evenly filled to the outer periphery including the corners, and forming defects such as burr or warp, etc., residual distortion, unevenness in gloss or luster, unfilled part, etc., can be prevented from generating. In addition, since the resin can be evenly filled to the outer periphery including the corners, a loading of an injection-molding machine can be reduced by lowering the injection pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectangular flat thermoplastic resin injection molded article made of a thermoplastic resin, which is mainly used as a lid, and a method for producing the same.

[0002]

2. Description of the Related Art For example, a rectangular flat plate made of a thermoplastic resin such as plastic is often used for a cover of an electric washing machine or a cover of a record player. This rectangular flat plate is produced by a method of injection molding by filling a thermoplastic resin from a central one-point gate for a certain period of time.

[0003]

However, the rectangular flat plate injection-molded by the central one-point gate as described above is
Since the thickness is as thin as a few mm, there is a problem that molding defects such as burrs and warps, residual strain, uneven gloss and gloss, unfilled parts, etc. are likely to occur and it is difficult to eliminate these. . Moreover, for example, if it is attempted to eliminate the unfilled portion, it is necessary to increase the injection pressure and also to provide an appropriate resin reservoir, which complicates the mold design and further increases the load on the injection molding machine. The problem arises.

The present invention is to solve the above-mentioned problems and to reduce the injection pressure to reduce the load on the injection molding machine.
It is an object of the present invention to provide a thermoplastic resin rectangular injection molded article and a method for producing the same in which molding defects are reduced.

[0005]

To this end, the thermoplastic resin square injection-molded article of the present invention is provided with a thick portion extending from the center of the square to each corner, and the thick portion has a thickness of about 1 / the side length.
It is characterized in that it is radially widened from the center so as to spread from the corner to both sides of the outer periphery with a width of 10. Further, the manufacturing method is such that one square center point is used as a gate, a thick portion extending from the center to each corner is provided, and molding conditions are set so that the resin arrival time at each corner and each side outer circumference is almost the same. It is characterized in that a rectangular flat plate of thermoplastic resin is selected and injection-molded.

[0006]

In the thermoplastic resin square injection molded article and the manufacturing method thereof according to the present invention, a thick portion extending from the center of the square to each corner is provided, and one point in the center of the square serves as a gate, and each corner and each side outer periphery. Since the molding conditions are selected so that the arrival time of the resin is almost the same time, and the rectangular plate of thermoplastic resin is injection-molded, the resin can be uniformly filled in the outer periphery including the corners, and burrs, warps, etc. It is possible to prevent defective molding, residual distortion, uneven gloss / gloss, and unfilled parts. Moreover, since the resin can be uniformly filled in the outer periphery including the corners, the injection pressure can be reduced and the load on the injection molding machine can be reduced.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view for explaining one embodiment of a thermoplastic resin rectangular injection molded product and a method for producing the same according to the present invention. FIG. 1 (a) is a front view, (b) is a side view, and (c) is A-. FIG. 3 is a sectional view taken along the line A ′, where 1 is a rectangular flat plate, 2 is a thick portion, 3 is a central gate portion, and 4 is a tip of the thick portion.

In FIG. 1, a rectangular flat plate 1 is a general-purpose resin such as an olefin resin or a styrene resin, or a thermoplastic resin such as an engineering plastic such as polycarbonate under a predetermined molding condition from a central gate portion 3 to a central one-point gate. And injection molding is performed. Thick part 2
Has a thickness t1 (> t) with respect to the thickness t of the rectangular flat plate 1 and is radially provided from the center of the rectangular shape to each corner. When injection molding a rectangular flat plate, the thick part 2
If a flat plate with a uniform thickness is used, the filling time of each corner (the arrival time of the resin) is delayed compared to the outer circumference of each side, but by providing the thick portion 2 as in the present invention, The arrival time of the resin on the outer periphery of each side can be made substantially the same. As a result, unfilled portions and residual strain can be reduced, and molding defects such as burrs and warps, and uneven gloss and gloss can be reduced.

Next, the filling effect by providing the thick portion 2 will be described. Now, regarding a flat plate having a uniform thickness without the thick portion 2, that is, when t1 = t, when the thermoplastic resin is filled from the central gate portion 3, the resin is circular toward the outer periphery of each side. Spread to. Therefore, the filled resin first reaches the closest point from the center of the outer circumference of each side, gradually expands to both sides, and finally reaches each corner. As is clear from this, unfilled portions are likely to occur at the corners, and the resin density is not uniform along each side, so the gloss and luster are also uneven and prone to deterioration. Further, in order to prevent the unfilled portion from being generated in the corner, it is necessary to apply a sufficient injection pressure and continue the filling for a while even after the resin reaches the center of each side. Therefore, the pressure becomes high in the center of each side, which may cause molding defects such as burrs unless the mold is tightly tightened.

On the other hand, when the thick portion 2 is provided with t1> t, the filling speed increases in the thick portion 2, so that the larger t1 is, the faster the resin reaches the corner. Even at the boundary of the thick portion 2, the thick portion 2 pulls the filling portion to speed up the filling, and conversely, the central portion becomes slightly slower. That is, if t1 is increased, the arrival time of the resin at the corner can be made faster than that at the central portion of each side, and the value of t1 is set so that the arrival time of the resin becomes substantially the same at the outer circumference of each side and the corner. You can choose. At this time, the thick portion 2
Since the resin is pulled toward the thick portion 2 where the filling is fast at the boundary with, the resin as a whole expands in a shape similar to the outer shape of the rectangular flat plate.

Next, the results of analysis of the thermoplastic resin square injection-molded article of the present invention and the manufacturing method thereof using the finite element method by setting a specific model will be described. FIG. 2 is a diagram showing melt viscosity data of acrylonitrile-butadiene-styrene resin (ABS resin; TFX-410), FIG.
Is a diagram for explaining analysis conditions and results, FIGS. 4, 6 and 8 are diagrams showing a resin filling flow pattern, and FIGS. 5, 7 and 9 are diagrams showing a pressure distribution during resin filling. .

The dimensions of the model are as follows:
mm × 500 mm, the thickness of the rectangular flat plate is 2 mm, 3 mm,
The width w was 4 mm and the width w at the outer periphery of the thick portion was 50 mm (1/10 of the side length). The resin used is ABS resin (TFX-
410) was used. FIG. 2 shows the melt viscosity data of the resin, which has a density of 1.02 g / cm ³ , a specific heat of 2.4 × 10 ⁷ erg / g · ° K, and a thermal conductivity of 1.8 ×.
The molding conditions were 10 ⁴ erg / sec · cm · ° K, the filling time was 5 seconds, the resin temperature was 240 ° C., and the mold temperature was 40 ° C.

Thickness of square flat plate t = 2 mm, 3 mm, 4 m
For each of m, the analysis results are obtained for the case where the thickness t1 of the thick portion 2 is the same, the case where the values are selected so that the arrival times of the sides and the corners are the same, and the case where the thickness t1 is made larger than that. Is summarized in [Table 1].

[0014]

[Table 1] When the resin flows in through the central one-point gate, the arrival time to the center of the flat plate, the center of each side of the outer circumference, and the position of each corner shown in FIG. 3 and the resin pressure at that time are analyzed. Like thickness t = 2.0m
When the thickness is m, filling of the corner is slow when the thick portion is eliminated (t1 = 2.0 mm), and when t1 = 2.2 mm, the corner and other outer circumferences are filled almost at the same time, and further t1 =
Increasing to 2.5 mm will speed up corner filling. Similarly, when the thickness t = 3.0 mm, t1 = 3.
6 mm and t = 4.0 mm, t1 = 5.5 mm
When set to, the corner and other outer circumferences are filled almost at the same time, and when the value of t1 is smaller than that, the filling of the corner is delayed,
The larger the size, the faster the corner filling.

That is, when the thicker portion is gradually thickened with respect to the thickness of the rectangular flat plate and the analysis is performed, filling of the corner becomes faster, and conversely, filling of the outer periphery becomes slower. It is possible to easily select the thickness of the thick portion in which the other outer peripheries are filled almost simultaneously.

Condition 1 as a flow pattern at the time of resin filling
FIG. 4 shows an example of the case, FIG. 6 shows an example of the case of Condition 2, and FIG. 8 shows an example of the case of Condition 3. FIG. 5 shows an example of the case of condition 1 as the pressure distribution at the time of resin filling, FIG. 7 shows an example of the case of condition 2, and FIG. 9 shows an example of the case of condition 3. Is. Of these, FIG. 6 showing a flow pattern under Condition 2,
As is clear from comparison between FIG. 7 showing the pressure distribution and other figures, both the flow pattern and the pressure distribution form a shape similar to the outer shape of the substantially rectangular flat plate.

Further, the reason why the corner pressure is not 0 under the conditions 2 and 8 in [Table 1] is that the corner arrival time is 0.1 seconds earlier than the side arrival time, and the pressure rises during this time. As the thickness value is smaller, the value in condition 2 is larger.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, in the above example, the present invention was applied to a square flat plate of 500 mm × 500 mm, but as an embodiment of the present invention, a frame plate,
Even for molded products with attached bosses, holes, notches, etc.
If the development drawing shows a substantially square, rectangular, or polygonal flat plate, similarly, by providing a thick portion that radially expands in the slow filling direction from a single gate in the center of the molded product. It is possible to shorten the arrival time of the resin to each corner portion so that the arrival time of the resin to the outer periphery of each side is almost the same. It can also be adjusted by changing the thickness of the thick portion according to the difference in filling time. Therefore, it is possible to control the resin to reach the outer circumference at the same time by providing the thick portion toward the corner where the filling is delayed when the thickness is uniform. Furthermore, although the thick portion that radially expands from the center is provided, it is possible to form a thick portion that extends from the center to the corner with a constant width because the filling into the corner is accelerated. There is no end.

[0019]

As is apparent from the above description, according to the present invention, a thick wall portion radially extending from the center of the rectangle to each corner is provided, and one point of the center of the rectangle is used as a gate, and each corner is formed. And since the rectangular flat plate of the thermoplastic resin is injection-molded by selecting the molding conditions so that the arrival time of the resin to each side outer circumference is almost the same, it is possible to uniformly fill the outer circumference including the corners with the resin. It is possible to prevent molding defects such as burrs and warpage, residual strain, uneven gloss and gloss, and unfilled parts. Moreover, since the resin can be uniformly filled in the outer periphery including the corners, the injection pressure can be reduced and the load on the injection molding machine can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of a thermoplastic resin rectangular injection molded product and a method for producing the same according to the present invention.

FIG. 2 is a diagram showing melt viscosity data of acrylonitrile-butadiene-styrene resin (ABS resin; TFX-410).

FIG. 3 is a diagram for explaining analysis conditions and results.

FIG. 4 is a diagram showing a flow pattern of resin filling.

FIG. 5 is a diagram showing a pressure distribution during resin filling.

FIG. 6 is a diagram showing a flow pattern of resin filling.

FIG. 7 is a diagram showing a pressure distribution during resin filling.

FIG. 8 is a diagram showing a flow pattern of resin filling.

FIG. 9 is a diagram showing a pressure distribution during resin filling.

[Explanation of symbols]

1 ... Square flat plate, 2 ... Thick part, 3 ... Central gate part, 4 ... Tip of thick part

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[Procedure amendment]

[Submission date] February 6, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of a thermoplastic resin rectangular injection molded product and a method for producing the same according to the present invention.

FIG. 2 is a diagram showing melt viscosity data of acrylonitrile-butadiene-styrene resin (ABS resin; TFX-410).

FIG. 3 is a diagram for explaining analysis conditions and results.

FIG. 4 is a halftone image in which a resin-filled flow pattern is displayed on a display.

FIG. 5 is a halftone image in which a pressure distribution during resin filling is displayed on a display.

FIG. 6 is a halftone image showing a resin filling flow pattern on a display.

FIG. 7 is a halftone image in which a pressure distribution during resin filling is displayed on a display.

FIG. 8 is a halftone image showing a resin filling flow pattern on a display.

FIG. 9 is a halftone image in which a pressure distribution during resin filling is displayed on a display.

[Explanation of Codes] 1 ... Square flat plate, 2 ... Thick portion, 3 ... Central gate portion, 4 ... Thick portion tip

Claims (4)

[Claims] 1. A thermoplastic resin square injection-molded article, characterized in that a thick portion extending from the center of the square to each corner is provided. 2. The thermoplastic resin according to claim 1, wherein the thick portion is radially widened from the center so as to spread from the corner to both sides of the outer periphery with a width of about 1/10 of the side length. Square injection molded product. 3. A rectangular central point is used as a gate, a thick portion extending from the center to each corner is provided, and molding conditions are selected so that the arrival time of the resin to each corner and the outer periphery of each side is almost the same. A method for producing a thermoplastic resin square injection molded article, which comprises subjecting a thermoplastic resin square flat plate to injection molding. 4. Molding conditions include filling time, resin temperature,
The method for producing a thermoplastic resin square injection molded article according to claim 1, wherein a mold temperature is selected.