JPH05124095A - Compressed air molding method with undercut of synthetic resin plate - Google Patents

Abstract

PURPOSE:To provide a molded product of deep drawing with an undercut having a uniform plate thickness distribution by clamping a synthetic resin plate, which is heated previously with a parting part of a recessed mold being opened, after pre-blowing and by molding with compressed air finally. CONSTITUTION:Moulds 2,3 are fixed on the table 6 of a compressed air molding machine, and the undercut part 2 of a parting mould is opened. A synthetic resin plate 1 softened previously by heating is clamped with a plug frame 8 for compressed air and is pre-blown. After the blow height being extended, for example, to 0.5-1.5 times of an opening size, the mould is closed to conduct the final compressed air molding. When the mould is cooled, the undercut part 2 of the parting mould is opened to take out the product. In this way, the tolerance of plate thickness for the product with a large undercut form can be made remarkably uniform to improve the product strength greatly. When the product is used for a lighting cover, the uniformity at its periphery affords a uniform distribution of brightness without transparency of a lamp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for obtaining covers for lighting, industrial parts, and cases for low-current-related parts by heating a synthetic resin plate and forming it under pressure by a male mold having an undercut.

[0002]

2. Description of the Related Art Conventionally, a thermoforming method for obtaining a molded article having an undercut from a synthetic resin plate is generally a vacuum forming method and a pressure forming method. Due to the mold structure, there were restrictions on the equipment of the undercut opening / closing mechanism, the size of the product, and the undercut shape. In addition, although this method is also widely used by pressure molding using a male mold, the mere straight molding method has a problem that the protruding corner portion becomes thin and the shape of the undercut is also limited.

Further, as a method for improving these problems,
There is a reentrant molding method utilizing a protruding nose shown in Japanese Examined Patent Publication No. 46-41827, but this is a method that requires complicated die equipment. Moreover, it is limited to a rectangular shape.

[0004]

In deep-drawing thermoforming having an undercut shape from a synthetic resin plate, the tolerance of the plate thickness of the product is apt to widen, and especially the tip of the protruding corner part in the product accompanied by high drawing or Due to the thinness, the corners of the rectangular products have a thickness distribution that cannot be practically used in terms of strength, and in the case of the light diffusing covers for illumination, there is a problem of seeing through the lamp image in terms of optical properties. From the above, the conventional compressed air molding method has a limited expansion rate of the molding area, and thus the undercut shape is also limited. The present invention is capable of maintaining a more uniform plate thickness distribution even in deep drawing with undercut, which is remarkably highly stretched by a method devised in view of these points, and is extremely easy to design a die. It can handle a wide variety of product shapes.

[0005]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present inventors have paid attention to the increase in the thickness of the inside of the female mold in the straight pressure forming, and as a result of diligent study, as a result, The present invention has been completed by devising a fixing method.

That is, according to the present invention, in a compressed air molding method using a female mold in which the outer dimension of the molded product is wider than the opening, the split mold portion of the female mold is previously opened to preheat and blow the heated synthetic resin plate. After that, the mold is clamped, and finally the product is subjected to pneumatic molding, which is a pneumatic molding method with an undercut.

In the conventional molding having an undercut, a straight pressure molding method using a female mold is easy, but when compressed by a conventional pre-integrated female mold, the contact portion with the inner surface of the mold is cooled and the sheet stretches. The protruding portion beyond the undercut, which is delayed due to the interruption, becomes extremely thin.

By the improved clamp frame according to the present invention, the split die protrusion is opened and the heating sheet is clamped to perform pre-tension blow, whereby cooling due to contact with the die on the protrusion can be prevented. By being stretched in advance, the wall thickness of the molded product can be made more uniform.

Generally, in a thermoforming method of a synthetic resin plate, uniforming of the wall thickness by pre-expansion blow has been carried out by a male molding method, but in the case of a female mold shape having an undercut like the main molding, This is a completely new molding method made possible only by improving the split mold structure and clamping method on the undercut side. The thermoforming machine used in the present invention is a general pressure and pressure forming machine including a table and a clamp, or a vacuum and pressure forming machine including a table, a clamp and a plug.

In the present invention, the split mold portion of the female mold is previously opened and the heated synthetic resin plate is pre-expanded and blown, and then the mold is clamped to perform the pneumatic molding. The opening conditions of the split mold portion differ depending on the shape of the product, but it is sufficient that a gap is provided so that the synthetic resin plate does not contact the split mold during pre-expansion blow. Normally, the blow height during pre-blow is 0.5 to 1.5 times the opening size, so
Within this range, a gap is secured so that the synthetic resin plate does not contact the split mold.

The conditions under which the method according to the present invention effectively exerts performance on a product may be deep drawing with a molding area expansion rate of more than about 100%. It is a method to demonstrate the performance in. The molding area expansion ratio here is the following formula (1)
It is a value represented by. ((Product surface area after molding / area of original plate before molding) -1) x 100 (1)

The method according to the present invention is also characterized in that in the shape of the undercut, a remarkable expansion effect of the projected area after molding to the opening can be obtained, and the outermost dimension ratio of the molded article to the opening dimension is 1 Although the performance can be effectively exhibited at 2 times or more, it is effective as a deep drawing molded product having an undercut shape with an outermost dimension ratio of 1.3 to 2.0 times as a region of a product shape which is preferable as an actual product. The opening dimension here is the minimum dimension (FIG. 1: d ₀ ) due to undercut, and the outermost dimension is the maximum dimension (FIG. 1: d ₁ ) of the product projection.

The synthetic resin plate applied to the present invention is a thermoplastic synthetic resin plate, such as acrylic resin, vinyl chloride resin,
A plate material such as ABS resin, polycarbonate, polystyrene, polypropylene, or polyethylene may be used as long as it can be deep-drawn. Further, these thermoplastic synthetic resin plates may contain processing aids such as plasticizers and lubricants, colorants, and various fillers for the purpose of reinforcement.

The molding temperature of these thermoplastic synthetic resin plates is generally in the range of 130 to 200 ° C., but in the case of general-purpose acrylic resin plates, ABS resin plates, polystyrene resin plates and polypropylene resin bodies, they are usually used. , 150-
At 180 ° C., a better molded product can be obtained.

The method of the present invention will be described below with reference to the drawings. The outermost dimension (d ₁ ) of the molded product is the opening dimension (d ₁ ) of the product.
₀ ) Wider, circular shaped undercut molds for lighting covers (2, 3) are placed on a table (6) of a normal pressure molding machine.
Fixed to. Next, the split mold undercut portion (2) is opened, and the synthetic resin plate (1) that has been heated and softened in advance is clamped by the compressed air plug frame (8) to pre-blow. (Second
Figure). After expanding the blow height to about 0.5 to 1.5 times the opening size, the mold is closed and the final pressure molding is performed (Fig. 3). After cooling, split mold undercut (2)
Crack and take out the molded product (9). (Fig. 4).

[0016]

EXAMPLES Examples will be shown below to more specifically explain the method of the present invention, but the present invention is not necessarily limited to these examples. The molded products were evaluated according to the following criteria.

Plate Thickness Tolerance: Plate thickness distribution in the region of the molded product excluding the undercut portion.

Tolerance ratio: Expressed by the ratio of the maximum value and the minimum value of the plate thickness distribution, the larger the ratio, the poorer the uniformity. If this value exceeds 3.0, the uniformity is judged to be poor.

Appearance: Visually judged by the following criteria. ⊚: Good ◯: Partially uneven, but almost good ×: Poor color at corners and poor.

Example 1 Product opening size (d ₀ ) 470 mm, outermost size (d ₁ )
A 660 mm circular undercut mold for a lighting cover is used, and this is fixed to a table of an ordinary pressure molding machine to open the undercut portion. As a synthetic resin plate, an acrylic resin plate which was previously softened by heating at 160 ° C. (Sumitex Chemical Industry Co., Ltd., Sumipex E-059, thickness 3.0)
(mm) was clamped with a plug frame for compressed air and pretension blown.
(Fig. 2). After expanding the blow height to about 500 mm, the mold was closed and the final pressure molding was performed. (Fig. 3)
After cooling, the undercut portion was broken to obtain a molded product. (4th
As shown in Table 1, the obtained molded product had a uniform plate thickness distribution and a good appearance.

Examples 2 to 3 The opening dimension (d ₀ ) of the product is reduced and the outermost dimension ratio is shown in Table 1.
Molding was carried out under the same conditions as in Example 1 except that those shown in FIG. As shown in Table 1, the obtained molded product had a uniform plate thickness distribution and a good appearance.

Example 4 Example 4 was carried out except that the outermost dimensional ratio was as shown in Table 1 and an acrylic resin plate (Sumipex E-059, manufactured by Sumitomo Chemical Co., Ltd., thickness 5.0 mm) was used as the synthetic resin plate. Molding was performed under the same conditions as in Example 1. The obtained molded products are shown in Table 1.
As shown in (1), the plate had a uniform thickness distribution and had a good appearance.

Example 5 An ABS resin plate (made of plastic in a cylinder, natural) was used as a synthetic resin plate, and molding was performed under the conditions shown in Table 1. As shown in Table 1, the obtained molded product had a uniform plate thickness distribution and a good appearance.

Comparative Example 1 A molded product was obtained in the same manner as in Example 1 except that the outermost dimensional ratio was 2.06. The molded product thus obtained had uniform thickness as shown in Table 1. Was inferior, and the color of the corner was weak and the appearance was poor.

COMPARATIVE EXAMPLE 2 The undercut mold used in Example 1 was used to perform molding using Sumipex E-059 as in Example 1 without pretensioning. Although the molding operation was possible, the outermost peripheral part of the product was remarkably thin at the time of mold release after cooling, and some parts were damaged.

COMPARATIVE EXAMPLE 3 The undercut mold used in Example 2 was used to perform molding using Sumipex E-059 as in Example 2 without pretensioning. Although the molding operation was possible, the outermost peripheral part of the product was remarkably thin at the time of mold release after cooling, and some parts were damaged.

Comparative Example 4 The undercut mold used in Example 2 was used to perform molding without using pre-stretching, using Sumipex E-059 (thickness: 5.0 mm) as in Example 3. Although the molding operation was possible, the appearance was inferior, with the color unevenness in the center and thin peripheral areas of the product.

Comparative Example 5 An ABS resin plate was used in the same manner as in Example 3 except that the undercut mold used in Example 2 was not pretensioned. Although the molding operation was possible, the appearance was inferior, with the color unevenness in the center and thin peripheral areas of the product.

[0029]

[Table 1]

[0030]

By obtaining a product shape with a large undercut by the molding method according to the present invention, the plate thickness tolerance of the product is remarkably uniformed and the strength of the product is remarkably improved.
When used as a lighting cover, it is possible to obtain a good product having good uniformity in the peripheral portion, no transparency of the lighting lamp, and a substantially uniform luminance distribution.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a molding apparatus showing a pressure molding step according to the present invention.

FIG. 2 shows a vertical cross-sectional view of a molding apparatus showing a pressure molding step according to the present invention.

FIG. 3 is a vertical sectional view of a molding apparatus showing a pressure molding step according to the present invention.

FIG. 4 is a vertical sectional view of a molding apparatus showing a pressure molding step according to the present invention.

[Explanation of symbols]

1. Synthetic resin plate 2. Split mold undercut part 3. Split mold 4. Split mold attaching / detaching jig 5. Split mold attaching / detaching jig 6. Table attached to the pneumatic molding machine 7. Plug attached to the pneumatic molding machine 8. Box and plug frame for compressed air blow 9. Pneumatic molded product 10. Pressurized air for compressed air blow

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] December 2, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

Example 1 Product opening size (d ₀ ) 550 mm, outermost size (d ₁ )
A 660 mm circular undercut mold for a lighting cover is used, and this is fixed to a table of an ordinary pressure molding machine to open the undercut portion. As a synthetic resin plate, an acrylic resin plate which was previously softened by heating at 160 ° C. (Sumitex Chemical Industry Co., Ltd., Sumipex E-059, thickness 3.0)
(mm) was clamped with a plug frame for compressed air and pretension blown.
(Fig. 2). After expanding the blow height to about 500 mm, the mold was closed and the final pressure molding was performed. (Fig. 3)
After cooling, the undercut portion was broken to obtain a molded product. (4th
As shown in Table 1, the obtained molded product had a uniform plate thickness distribution and a good appearance.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

Comparative Example 4 The undercut mold used in Example 2 was used to perform molding without using pre-stretching, and using Sumipex E-059 (thickness: 5.0 mm) as in Example 4 . Although the molding operation was possible, the appearance was inferior, with the color unevenness in the center and thin peripheral areas of the product.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

[0029]

[Table 1]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI technical display location B29C 51/38 7421-4F // B29L 22:00 4F (72) Inventor Osamu Tsukamoto Kadoma City, Osaka Prefecture 7-1 Fukadacho Kamwa Plus Chikku Co., Ltd. (72) Inventor Shoji Makimura 7-1 Fukadacho, Kadoma-shi, Osaka Kawa Plus Chikku Co., Ltd.

Claims (3)

[Claims] 1. In a compressed air molding method using a female mold in which an outer dimension of a molded product is wider than an opening, a split mold portion of the female mold is preliminarily opened to preheat and blow a heated synthetic resin plate, A compressed air forming method with an undercut, which is obtained by clamping and finally performing pressure forming. 2. The method of pressure molding according to claim 1, wherein the method is applied to deep drawing where the molding area expansion ratio of the molded product is 250% or more. 3. The method of pressure forming according to claim 1, wherein the outermost dimension of the cross section of the molded product is 1.2 to 2.0 times the opening dimension and is applied to deep drawing.