JPS62263019A - Method of press molding thermoplastic synthetic resin sheet - Google Patents

Abstract

PURPOSE:To obtain a molded item, the releasability and mold form reproducibility of which are excellent and which has uniform thickness and favorable external appearance, by a method wherein press molding is performed under the state that a covering layer with required bed-like elasticity is provided on the surface of at least either one of a female mold and a male mold. CONSTITUTION:Covering layers 3 are formed by strongly and adheringly pasting a fibrous or porous bed-like elastic flexible sheet 4 having a surface part, which can be impregnated with liquid material, through proper heat resistant adhesive 5 on the surfaces of molds 1 an 2 in the state that liquid silicone rubber is applied to the surface part of the sheet 4 in order to form a silicone rubber-impregnated and cured layer 6 on the surface part. Favorable bed-like elastic flexible sheet 4 is fibrous material or continuous cell type foamed synthetic resin sheet, the surface part of which is porous, or the like. Material with the surface having raised fiber layer such as cut pile or the like is especially suitably employed as the bed-like elastic flexible sheet 4. A thermoplastic synthetic sheet 7, which is heated in advance, up to its thermoforming temperature, is provided between the male mold 1 and the female mold 2, on both of which the covering layers 3 are coveredly formed, so as to be formed under pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a press molding method for various thermoplastic synthetic resin sheets, that is, a resin sheet heated to a thermoforming temperature is sandwiched between male and female molds, The present invention relates to an improvement in a press molding method in which molding is performed by holding under a predetermined pressure.

Conventional technology The press molding method, which is known as one of the thermoforming methods for thermoplastic synthetic resin sheets, has a shorter molding cycle than other methods such as vacuum molding and pressure forming, and is suitable for molding large molded products. It is particularly suitable for molding acrylic resin sheets and glass fiber reinforced thermoplastic synthetic resin sheets because it is suitable for molding materials with high rigidity at thermoforming temperatures.

However, one of the inherent problems with the press molding method is that unless pressure is applied uniformly to the entire sheet, it is not possible to create a molded product with high dimensional accuracy that accurately reproduces the mold shape. In practice, it is extremely difficult to make the molding gap between the male and female molds uniform and exactly match the predetermined thickness of the molded product.

Conventionally, as a solution to these problems,
Japanese Patent Publication No. 53-11976 proposes a method of press molding with a highly flexible rubber sheet spread on one side of male and female molds. This method is effective to some extent in solving the above problems, but if the mold shape is complex or has a concave surface with a relatively small curvature, the rubber sheet itself may not cover the mold surface sufficiently. There was a problem in that the adhering state could not be followed, resulting in poor reproducibility of the mold shape of the molded product.

It is also common practice to cover the mold surface with flannel cloth to give it a cushioning effect and then press mold it, but in this case, the fuzz on the surface of the flannel cloth gets eaten into the sheet surface during press molding. There were problems such as the molded product having poor mold releasability and the appearance of flanges on the surface of the molded product.

Furthermore, thermoplastic synthetic resin sheets for press molding usually have a polyethylene protective film attached to the surface, and are often subjected to press molding with this protective film attached, but in this case, When using the above-mentioned conventional techniques, there was a problem in that the surface protective film sometimes adhered to the flannel cloth, neoprene rubber sheet, etc. covering the mold surface.

Purpose of the Invention In view of the prior art as described above, the present invention provides a press for a thermoplastic synthetic resin sheet that has excellent mold releasability and mold shape reproducibility, and is capable of producing molded products with uniform thickness and good appearance. The purpose is to provide a molding method.

Means to Solve the Problems As a result of various experiments and research, this invention was developed by attaching a fiber sheet or a foamed synthetic resin sheet to the mold surface to provide cushioning properties, and then impregnating and hardening silicone rubber on the surface. If it is made of a molded material, it is possible to correct the unevenness of the molding gap between the male and female molds during press molding, maintain a good surface texture with excellent reproducibility of the mold shape, and maintain good mold releasability. This was completed by performing press molding with excellent molding accuracy and discovering the scales.

According to the present invention, when press-molding a thermoplastic synthetic resin sheet by sandwiching it between male and female molds under heating, the surface of at least one of the male and female molds is coated with fibers that can be impregnated with a liquid. A flexible or porous elastic sheet is attached, and a liquid silicone rubber is applied to at least the surface of the sheet and impregnated and cured to form a coating layer, and in this coating layer formed state, the press molding is performed. The gist of the present invention is a method for press-molding a thermoplastic synthetic resin sheet, which is characterized by performing the following steps.

To further explain this invention based on the attached drawings, in FIG. 1, (1) is a male mold, and (2) is a corresponding female mold. The predetermined 111 layers (3) are coated. As shown in FIG.
) on the surfaces of molds (1) and (2) in advance with an appropriate heat-resistant adhesive (
5), and then apply liquid silicone rubber to the sheet (
4), an impregnated hardened layer (6) of the silicone rubber is formed on at least the surface portion of the silicone rubber.

The Dan-Ayu flexible sheet (4) is made of fibrous materials such as knitted fabrics, woven fabrics, non-woven fabrics made of natural fibers, synthetic fibers, inorganic fibers, etc., and flocked sheets with the above-mentioned short fibers flocked on the surface. ,
Alternatively, an open-cell foamed synthetic resin sheet whose surface portion is porous can be suitably used. Among fibrous materials, it is particularly preferable to use materials with a raised fiber layer on the surface, such as flannel or cut pile fabric, from the viewpoint of excellent elasticity and impregnability with liquid silicone rubber. .

Further, as the foamed synthetic resin sheet, open-cell polyurethane foam, polystyrene foam, etc. are preferably used from the viewpoint of heat resistance.

On the other hand, the liquid silicone rubber impregnated hardening layer (6) not only improves the surface condition of the elastic sheet (4), but also contributes to improving the reproducibility of the mold shape and improving the mold releasability. Therefore, it is not necessarily necessary to impregnate the entire thickness of the elastic sheet (4), but it is necessary and sufficient to form the impregnation at least only on the surface portion thereof.

In this invention, a thermoplastic synthetic resin sheet (7) of a predetermined thickness is placed in advance between the male mold (1) and the female mold (2) on which the coating layer (3) (3) having the above structure is formed. Needless to say, the material is heated to a thermoforming temperature, sandwiched, and pressurized to form the material. Here, the mold shape reproducibility, appearance,
The quality of molding accuracy such as thickness uniformity is determined by the above coating layer (3).
It is also dominantly influenced by the hardness of If it is too soft or too hard, good results will not be obtained. The suitable hardness of the coating layer (3) varies depending on the shape of the molded product, the thickness of the resin sheet material, etc., so consider the relationship with these factors, and select the material and thickness of the flexible sheet, and the thickness of the silicone rubber impregnated cured layer. The hardness of the silicone rubber impregnated cured layer (6) should be adjusted as appropriate by such methods as appropriate, but generally good results can be obtained if the hardness of the silicone rubber impregnated cured layer (6) is between 30 and 80 degrees in terms of rubber hardness.

In addition, the drawing shows a coating layer (
3), but if the resin sheet to be molded is thick, the mold shape is simple and the molding magnification is low, etc., either the female mold (1) or the male mold (2) may be used. A coating layer may be provided only on the surface of the mold.

Effects of the Invention In this invention, press molding is performed with a coating layer having the required elasticity provided on the surface of at least one of the female mold and the male mold, so that the molding gap between the two molds is reduced. Even if there is some variation in the mold, it is possible to perform good molding without causing wrinkles, etc. 1 Furthermore, since the finishing accuracy of the mold is not particularly strictly required, its production can be facilitated. .

In addition, the above-mentioned coating layer is made by pasting a flexible sheet on the mold surface,
Since it is formed by impregnating and curing liquid silicone rubber, it can be made to fit exactly and reliably along the mold surface. Therefore, even if the mold shape is complex and has a concave portion with a relatively small curvature, good mold shape reproducibility of the molded product can be achieved.

Of course, since the above-mentioned coating layer has a cured layer impregnated with silicone rubber on at least the surface portion, it is suitable for molded products.

It has good l1Il type properties, and even when a thermoplastic synthetic resin sheet with a polyethylene protective film attached to its surface is directly molded, there is no fear of adhesion and demolding can be easily and reliably performed.

Furthermore, since the surface of the coating layer is covered with the silicone rubber impregnated cured layer, the surface of the molded product can be finished in a smooth and glossy state.

Furthermore, the coating layer according to the present invention can be easily formed to have a uniform thickness as a whole, has good fixing properties to the mold surface, and can improve the molding accuracy of the molded product. There is no problem of peeling. In other words, when applying liquid silicone rubber directly to the mold surface to improve mold releasability, the silicone rubber flows and the thickness of the applied film must be judged visually, resulting in a uniform coating. It is extremely difficult to form a coating film with a certain thickness. In addition, metal molds such as aluminum or wooden molds are generally used as molds, but when applying silicone rubber directly to these molds, it is difficult to ensure sufficient adhesion. Therefore, there is a risk of peeling during molding. On the other hand, according to the embodiment of the present invention, a fibrous or porous resilient sheet that can be impregnated with a liquid is applied to the mold surface, and liquid silicone rubber is impregnated and cured thereon. Therefore, the thickness of the coating layer can be made uniform over the entire surface, and it can be adhered sufficiently firmly to the mold surface, and there is no fear of peeling during molding.

Examples Example 1 Cotton flannel standard 1 was applied to the surfaces of both female and male molds made of wooden molds.
No. 00 cotton flannel was pasted with a stone adhesive, and liquid silicone rubber (manufactured by Toshiba Silicone Corporation, product name: T) adjusted to an accuracy of 40 poise (temperature 25°C) was applied to the surface.
SE39X series, product number: TSE399) was applied at a coating amount of 8°6 g/100 c#l and impregnated and cured.

The hardness of the coating layer thus formed was approximately 30 degrees in terms of rubber hardness.

Next, using both male and female molds on which the above-mentioned coating layer was formed, a thickness of 2
．． 0mm polycarbonate resin sheet (manufactured by Tsutsunaka Plastic Industry Co., Ltd., product name: Polyriki Ace, product number: E
CK100) was heated in an oven with a furnace temperature of 190°C for 5 minutes, then placed between the two molds and closed.
Press molding was carried out for 2 minutes by applying a pressure of /at. As a result, a bowl-shaped molded product with a diameter of 300 max and a radius of curvature of 400 m was obtained.

However, this molded product had a uniform thickness throughout, excellent reproducibility of the mold shape, and was of high quality with good gloss on the entire surface and no wrinkles.

Example 2 A coating layer similar to that in Example 1 was formed only on the surface of the male mold, and a high-density polyethylene protective film with a thickness of 40 μm was attached to the surface as a synthetic resin sheet to be molded. Using a polycarbonate resin sheet with a thickness of 2.0 m, the same press molding operation as in Example 1 was performed with the protective film side facing the male die.

The molded product thus obtained had excellent molding accuracy as in Example 1, and the surface of the molded product was free! 4! ! The protective film remained attached to the entire surface even after the application.

Example 3 In place of the brocade flannel used in Example 1, a 1.0 mm thick foamed polyurethane sheet with quick-reading cells was used, and the other conditions were the same as in Example 1, except that an impregnated hardened layer of silicone rubber was applied to the surfaces of both male and female molds. A coating layer having the following properties was formed.

Then, when the polycarbonate resin sheet was press-molded in the same manner as in Example 1, a bowl-shaped molded product of good quality, which was no different from that in Example 1, could be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a mold portion showing a state in which the press molding method of the present invention is carried out, and FIG. 2 is a cross-sectional view showing the structure of a coating layer that is adhered and formed on the surface of the mold. (1)...male type, (2)...female type, (3)...coating layer, (4)...repellent sheet, (5)...adhesive, (6)...Silicone rubber impregnated hardened layer, (7
)...Thermoplastic synthetic resin sheet. Above Figure 1 Figure 2

Claims (3)

[Claims] (1) When press-molding a thermoplastic synthetic resin sheet by sandwiching it between male and female molds under heating, the surface of at least one of the male and female molds is coated with a fibrous or porous material that can be impregnated with a liquid. A resilient sheet is attached, and a liquid silicone rubber is applied to at least the surface of the sheet and impregnated and cured to form a coating layer, and the press molding is performed in the state in which the coating layer is formed. A press molding method for a thermoplastic synthetic resin sheet. (2) A method for press-molding a thermoplastic synthetic resin sheet according to claim 1, wherein the elastic flexible sheet is a fibrous sheet such as a knitted fabric, a woven fabric, a nonwoven fabric, or a flocked fabric. (3) A method for press-molding a thermoplastic synthetic resin sheet according to claim 1, wherein the elastic flexible sheet is an open-cell foamed synthetic resin sheet.