JP2881468B2 - Method for eliminating scratches on thermoplastic synthetic resin molded products - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for eliminating a flaw which is generated at a corner portion due to a mold hit when a thermoplastic synthetic resin sheet is thermoformed.

[Prior Art] In general, the production of a molded article from a thermoplastic synthetic resin sheet is performed by pneumatically molding a material sheet by a vacuum molding method, a pressure molding method, or a combination of these methods. In such a molding method, a material sheet is formed into a desired shape by heating a material sheet to a thermoforming temperature in advance by a heater and bringing the material sheet into close contact with a molding die.

[Problems to be Solved by the Invention] However, in the conventional molding method, the shape of the mold becomes complicated, and as the molding magnification increases, the contact of the resin sheet with the mold at the time of molding becomes severe. There is a drawback in that a scratch is generated at a contact portion, that is, a corner portion of the molded article. When the resin sheet for molding is transparent, this corner portion surface defect causes irregular reflection in reflected light and transmitted light, thereby significantly reducing the appearance and commercial value, and its improvement is strongly demanded. I was about to.

Conventionally, in order to improve such problems, various on-site work considerations such as controlling the heating temperature of the resin sheet, the mold temperature relative to the resin sheet, and the molding pressure have been made. However, at present, no fundamental solution to the above problem has been found.

[Means for Solving the Problems] The present inventors have repeated various experiments. After the thermoforming of the resin sheet, the surface temperature of the contact portion of the resin sheet is 20 to 40 higher than the thermal deformation temperature of the molded product. It has been found that when hot air is blown so as to increase the temperature by ℃, the scratches on the mold contact portion are removed, and the present invention has been completed.

That is, in the method for eliminating scuffs of a plastic synthetic resin molded article according to the present invention, after the thermoplastic synthetic resin sheet is thermoformed into a desired shape, the surface temperature of the molded article at the contact portion is lower than the thermal deformation temperature of the molded article by 20%. It is characterized by blowing hot air up to 40 ° C higher.

In the above method, a typical example of the thermoforming method is a pneumatic forming method such as vacuum forming, compressed air forming, and combined use of compressed air and vacuum.

As a material of the thermoplastic synthetic resin sheet used for molding, generally, for example, a vinyl chloride resin, a methyl methacrylate resin, a polycarbonate resin and the like can be mentioned.
The thickness of the resin sheet is about 0.5 to 5 mm.

Then, after the resin sheet is heated to a thermoforming temperature by a heater, the resin sheet is arranged on a molding die and thermoformed. In this case, the resin sheet hits the mold, and a scratch is generated at a contact portion, that is, a corner portion of the molded product. Therefore, the surface temperature of the flaw is determined by the heat deformation temperature T ° C (ASTM D-94) of the molded article.
Blow hot air at 20-40 ° C higher If the surface temperature of the flaw is less than T ° C. + 20 ° C., it is difficult to erase the flaw.
If the temperature exceeds 40 ° C., the molded article is deformed or foamed. Therefore, the surface temperature of the scratched part is T ° C + 20 to 40 ° C.
Is limited to

[Effects of the Invention] The present invention provides a method for thermoforming a thermoplastic synthetic resin sheet as described above, so that the surface temperature of the molded product at the contact portion is 20 to 40 ° C higher than the thermal deformation temperature of the molded product. Since the hot air is blown, the flaws generated at the mold contact portion can be softened and smoothed by the hot air and removed. Thus, according to the method of the present invention, it is possible to eliminate the flaws on the molded article by a very simple method, and to prevent irregular reflection of reflected light and transmitted light.

In addition, it is not necessary to consider the work on site as in the conventional method described at the beginning of this document, and the molding workability is greatly improved, and a molded product having excellent quality can be provided with a high yield.

[Embodiment] Next, an embodiment of the present invention will be described with reference to the accompanying drawings.

Referring to FIG. 1, a pair of upper and lower clamps (2) are attached to the edge of a 3 mm thick vinyl chloride resin sheet (1) prepared in advance.
After the sheet (1) was heated to the thermoforming temperature, the sheet (1) was pressed from below with a forming die (4) to perform ridge forming. Thus, height 700 mm × width 400
A molded product (5) having a size of mm × 70 mm in height was obtained. This molded product (5)
As a result of observation of the appearance of the sample, the occurrence of scratches due to the contact of the mold was observed at the contact portion, that is, the corner portion (5a).

Then, the molded product (5) is removed from the mold (4), and the second
As shown in the figure, from the corner (5a) of the molded product (5)
Use a hot air gun (6) from a distance of 30mm, and
The surface temperature of a) is 20 to 4 higher than the thermal deformation temperature of vinyl chloride resin.
Hot air was blown to increase the temperature by 0 ° C. The name of the hot air gun (6) is K. LEISK
TER KAGISWIL, model is LEISTER CH
IBLI), and the hot air blowing temperature at the tip is
450 ° C. Temperature was measured with a thermocouple.

After the blowing of the hot air, the state of the scratches on the corners (5a) was visually observed, and it was determined whether or not the scratches were erased by blowing the hot air. The results are shown in the table below.

In addition, using a methyl methacrylate resin sheet and a polycarbonate resin sheet as sheets,
By repeating the same operation as above, it was determined whether or not the flaw was erased by blowing hot air. The results of the determination are also shown in the table below.

As is clear from this table, by blowing hot air onto the contact part of the molded product so that its surface temperature is 20 to 40 ° C higher than the thermal deformation temperature of the molded product, the flaws on the molded product are effectively reduced. Be erased.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show an embodiment of the present invention, and FIG. 1 is a vertical sectional view of a molding die, and FIG. 2 is a vertical sectional view of a molded product. (1) Sheet, (2) (3) ... Upper and lower pair of clamps, (4) ... Mold, (5) ... Molded product, (5a) ...
Corner, (6)… hot air gun.

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Claims (1)

(57) [Claims] (1) After thermoforming a thermoplastic synthetic resin sheet into a desired shape, hot air is blown onto a contact portion of the molded product such that the surface temperature thereof is higher by 20 to 40 ° C. than the thermal deformation temperature of the molded product. A method for erasing scratches on a thermoplastic synthetic resin molded article, characterized by comprising: