JPS6282018A - Thermoforming method for thermoplastic resin molded article - Google Patents

Abstract

PURPOSE:To enable peeling of a protective film after molding by obtaining a molded article having a glossy surface whose surface properties are smooth, by performing vacuum or air-pressure forming in a state that the protective film is stuck to a material sheet by making use of the same composed of a double layer film of a low density polyethylene film and ethylene.vinyl acetate copolymer film. CONSTITUTION:As for a thermoforming method for a thermoplastic resin molded article, at the time of thermoforming of a molded article by a vacuum or air-pressure forming method by making use of a thermoplastic resin sheet as a material, a protective film composed of a laminated material of a low-density polyethylene film and ethylene.vinyl acetate copolymer film is stuck beforehand at least to the surface of the same with which the material comes into contact, and the thermoforming is performed by heating and softening the material sheet as it is in a sticking state of the protective film. As the molding material sheet, the thermoplastic resin composed e.g. of polymethyl methacrylate or polyvinyl chloride is used. As the protective film, the ethylene.vinyl acetate copolymer film and the low-density polyethylene film are unified by laminating them.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a thermoforming method for thermoplastic resin molded products, particularly when a predetermined molded product is obtained using a thermoplastic resin sheet as a material by vacuum forming or pressure forming. The present invention relates to a thermoforming method.

BACKGROUND ART In thermoforming as described above, thermoplastic resin sheets such as polymethyl methacrylate, polycarbonate, acrylonitrile-butadiene-Φ styrene copolymer, polyvinyl chloride, etc. are generally used as the molding material sheet. When these material sheets are handled with their surfaces exposed, their surfaces are often easily scratched during the handling process, which is likely to impair their aesthetic appearance and reduce their commercial value.

For this reason, protective paper or a protective film is usually attached to the surface. Therefore, the above-mentioned protective paper is generally made of a paper material such as kraft paper coated with a water-soluble adhesive, and the protective film is mainly made of a polyethylene film coated with a live pipe agent, or a polyethylene film coated with a live pipe agent. A two-layer film made by integrating ethylene/vinyl acetate copolymer films into a laminated form is used.

However, when thermoforming a molded article by vacuum forming or pressure forming using a synthetic resin sheet pasted with a protective film as described above, in the conventional technology, the protective film must be peeled off before molding. I didn't get it. The reason for this is that the thermoforming described above has a relatively high tM (15
This is because heating at a temperature of 0 to 200[deg.] C. changes the physical properties of the film itself, promotes adhesion, etc., making it extremely difficult to peel off the protective film after molding.

Problems to be Solved by the Invention However, in conventional thermoforming methods, thermoforming is performed with the protective film peeled off in advance, so for example, polycarbonate, acrylonitrile, butadiene, etc. require preliminary drying before molding. When molding a styrene copolymer sheet or the like as a material, scratches caused during the pre-drying process may remain on the molded product, and if the heat-softened thermoplastic resin sheet comes into contact with the molding die, the outside of the sheet may be damaged. There are disadvantages in that the surface of the molded product has minute irregularities called bumps, causing the molded product to have a rough surface, and furthermore, the molded product is easily scratched during trimming. In particular, when the thermoplastic resin sheet is transparent, this surface quality defect causes diffused reflection in reflected and transmitted light, which significantly reduces the appearance of the product. It was requested.

Means for Solving the Problems The present inventors focused on the fact that thermoforming is possible when the protective film is a polymer film, and after repeating numerous experiments and research on various protective films, found that Using a protective film consisting of two layers of low-density polyethylene film and ethylene/vinyl acetate copolymer film,
When this is attached to a material sheet and vacuum or pressure molded, the surface of the molded product will not have scratches or the above-mentioned spots, and a molded product with an extremely smooth and glossy surface will be obtained. The present invention was completed based on the discovery that the protective film can be peeled off even afterwards.

Therefore, in the thermoforming method for thermoplastic resin molded products according to the present invention, when thermoforming a molded product using a thermoplastic resin sheet as a material by vacuum or pressure forming, the material sheet is brought into contact with at least the mold in advance. A protective film made of a laminate of a low-density polyethylene film and an ethylene/vinyl acetate copolymer film is attached to the surface, and the material sheet is heated and softened while the protective film is attached to perform thermoforming. It is characterized by the fact that

The material sheet for the above-mentioned molding is a thermoplastic resin conventionally commonly used for vacuum or pressure molding, such as polymethyl methacrylate, polycarbonate,
Those made of acrylonitrile/butadiene/styrene resin, polyvinyl chloride, etc. are used.

As a protective film, a low-density polyethylene film with a thickness of about 40 to 100 μ (density 0.910 to 0.925) is used.
An ethylene/vinyl acetate copolymer film with a thickness of about 20 to 50 μm is laminated and integrated on both sides or at least one side of the molded product. Especially when considering the surface texture of the molded product, the overall thickness is about 100 to 150 μm. It is preferable to use the created protective film. The thickness ratio of low density polyethylene film (LDPE) and ethylene vinyl acetate copolymer film (EVA) is LDPE/EVA-2/1.
It is common to use something of a certain degree.

By the way, there are limitations to the use of low-density polyethylene as a base material for the protective film, compared to the use of other thermoplastic resins. This is because the protective film can be easily peeled off without causing unnecessary breakage when the protective film is peeled off. By the way,
When a high-density polyethylene film is used, the reduction in elongation rate makes it extremely difficult to peel off the protective film after molding, as shown in Example 1 below.

On the other hand, the adhesive layer for attaching the protective film is not limited to ethylene/vinyl acetate copolymer film, but other adhesives such as rubber, resin materials, acrylic, etc. can be used. This is based on the fact that it has better adhesion or adhesion to the molding material sheet than in conventional molding materials, as well as easy peelability from the surface of the molded product after molding. Therefore, the f.

As the ilm, one having a vinyl acetate content of 5 to 15% is preferably used. That is, the vinyl acetate content is 5
If it is less than 15%, the adhesive strength to the material sheet will be weak and there is a risk that the protective film will peel off when handling the material sheet, and if it exceeds 15%, the adhesive strength will be too high when the material sheet is heated and molded. This is because it cannot be peeled off from the surface.

As shown in FIG.
) is laminated by coextrusion or lamination, etc., to one side (in the case of Figure 1 (a)) or both sides (in the case of Figure 1 (a)) of a molding material sheet (2) made of thermoplastic resin. ), the film is attached using the adhesive force of the ethylene/vinyl acetate film (1b).

After that, as shown in FIG. 2, the molding sheet (2)
Hold the protective film (1) in the clamp (4) of the molding machine with the adhesive side facing the inside of the mold (3),
After heating to the thermoforming temperature with a heater (5), the material sheet (1) is pressed against the inner surface of the mold by vacuum suction inside the mold or compressed air supplied from outside the mold to form a predetermined shape. It is used to form molded products. Note that during this molding, it is desirable to keep the mold in advance at a temperature of about 80 to 90°C, since this allows the surface texture of the molded product to be finished even better.

Effects of the Invention As described above, this invention provides the following advantages when thermoforming a molded article using a thermoplastic resin as a material by vacuum or pressure forming method.
A protective film is pasted on one side of the material sheet in advance, and the protective film is heat-formed in the pasted state without being peeled off, so there is no drying process before molding the material sheet, and there is no need to set it on the molding machine. Not only can it prevent scratches on the surface due to external force during the handling process before molding, such as the handling process, but also during molding, a protective film is interposed between the mold and the material sheet. Therefore, the protective film acts as a cushion layer and can prevent minute irregularities on the inner surface of the mold from being formed on the surface of the molded product, or from creating irregularities due to residual air. Therefore, it is possible to obtain a molded product having an extremely smooth and glossy surface without scratches or so-called bumps on the surface of the molded product. Furthermore, since the protective film layer remains on the surface of the molded product, it is possible to prevent the surface from being scratched during storage and handling of the molded product. When using the protective film, despite the thermoforming process, the elongation rate of the low-density polyethylene film does not decrease significantly, and the peel strength of the ethylene/vinyl acetate film does not increase significantly. As a result, the adhesive can be easily and cleanly peeled off from the surface of the molded product without leaving any residue of the adhesive component.

Examples Example 1 A polycarbonate resin sheet with a thickness of 1.5 mm was used as a molding material sheet, and a protective film consisting of various two-layer films shown in Table 1 below was placed on both sides (vinyl acetate content of EVA film was 10%). Under the conditions of 60℃ x 2kg/cm, the pressure is +ji L.

After heating and softening this protective film pasting material sheet to 190°C, the mold temperature was 90°C and the development magnification was 1. S(
A box-shaped molded product was formed by a vacuum forming method under the molding conditions of a. After cooling, the peelability of the protective film covering the surface of the molded product was examined, and the condition of the surface of the molded product after peeling was visually inspected. The results are shown in Table 1.

In the table, HDPE means high-density polyethylene, LDPE means low-density polyethylene, and EVA means ethylene-vinyl acetate copolymer. The same applies to Table 2 and below.

[Margin below] Table 1 Example 2 A polymethyl methacrylate resin sheet with a thickness of 2.0 mm was used as the molding material sheet, a protective film was attached only to one side, and the heating temperature of the material sheet was set to 175°C.
Box-shaped molded products were molded using various protective film-applied material sheets in the same manner as in Example 1, except that the mold temperature was 80° C. and the pressure molding method was employed.

The peelability and surface appearance of the protective film in the molded article thus obtained were similar to the results of Example 1 shown in Table 1.

Based on the results of Examples 1 and 2 above, when a two-layer film of a low-density polyethylene film and an ethylene/vinyl acetate copolymer film is used as a protective film, it is possible to heat it while it is attached to a material sheet. It was confirmed that molding was possible and that the protective film could be peeled off after 11 days.

Example 3 A material sheet made of the same polycarbonate resin as in Example 1 was used, and two types of protective films with different base layer materials were bonded to one side of the sheet (sheet temperature: 60°C, pressure: 2 kg/co+). After the adhesive was pasted, it was once softened by heating at 190°C, and then cooled. The peel strength and elongation of the protective film before and after heating were determined by DI, and the results were as shown in Table 2 below.

[Margin below] According to the results in the above table, by using a low-density polyethylene film for the base layer of the protective film, the elongation of the protective film after heating is significantly reduced compared to when using a high-density polyethylene film. It was found that because of the small size, the film can be easily peeled off from the surface of the molded product without unnecessarily breaking or tearing the film.

Example 4 Next, several types of protective films were prepared in which the vinyl acetate content in the ethylene/vinyl acetate polymer film was varied, and these were made of polycarbonate resin in the same manner as in Example 3. Paste it on the material sheet,
After heating and cooling, the peel strength of the protective film was examined.

The results were as shown in Table 3 below.

[Margins below] Table 3: 5 mm 25 mm 5 mt
It was confirmed that it is preferable to use a content in the range of 15%.

[Brief explanation of drawings]

Figures 1 (a) and (b) are cross-sectional views showing the state in which the protective film is attached to the material sheet, Figure 2 is a cross-sectional view showing the state during heat treatment immediately before thermoforming, and Figure 3 is when the material is shaped into a thermospherical shape. FIG. (1)...protective film, (1a)...low density polyethylene film, (2a)..., (3)...molding mold and more

Claims (2)

[Claims] (1) When thermoforming a molded product using a thermoplastic resin sheet as a material by vacuum or pressure forming, a low-density polyethylene film and an ethylene/vinyl acetate copolymer film are preliminarily applied to at least the surface of the material sheet that will be in contact with the mold. 1. A method for thermoforming a thermoplastic resin molded article, comprising: adhering a protective film made of a laminate of the same, and thermoforming the material sheet by heating and softening the material sheet while the protective film is attached. (2) The method for thermoforming a thermoplastic resin molded article according to claim 1, wherein the ethylene/vinyl acetate copolymer film has a vinyl acetate content of 5 to 15%.