JPS6331732A - Thermoforming of vessel and the like - Google Patents

Abstract

PURPOSE:To eliminate the generation of a warpage after forming to smoothen and unify a vessel and prevent the generation of deformation such as a recess or the like, by a method wherein a crystalline thermoplastic resin sheet, not oriented substantially, is pinched and pressed under a condition that a heating surface, specified in the surface roughness thereof, is isolated from the surface of a forming mold, while the sheet is abutted against the heating surface by pressure air from the side of the surface of the forming mold and is heated at a temperature lower than the melting point of the resin of the sheet. CONSTITUTION:A crystalline thermoplastic resin sheet or the like 1, not oriented substantially, is introduced between the heating surface 13 of a hot plate 11, arranged above the sheet, and the surface 16 of the forming mold of a forming template 15, arranged below the sheet, and is pinched and pressed under a condition that the sheet is isolated from them at least by the height of 1 mm of a projection 16a. Subsequently, the pressure air of about 0.5-3.0 kg/cm<2> is supplied from a through hole 18 through the cavity 17 of the forming template 15 to abut the sheet 1 or the like against the heating surface 13 having the surface roughness 3S or less to heat it. The temperature of the heating surface 13 in this case is made lower than the melting point of the sheet 1 or the like. Subsequently, air is blown through the pressure air blow-off port 14 of the hot plate 11 and is sucked from the cavity 17 of the forming template 15 to force the sheet 1 or the like into the cavity having the surface roughness 4S or less and mold a vessel or the like, thereafter, the vessel or the like is cooled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the manufacture of containers by thermoforming from substantially non-oriented crystalline thermoplastic resin sheets or films (hereinafter referred to as "sheets, etc." including films). The present invention relates to a thermoforming method for containers, in which when a large number of containers are formed, the sheets are molded in a state where residual stress is small so as not to cause warping.

[Prior Art] Thermoplastic resin sheets and the like are formed into containers of various shapes by thermoforming methods such as vacuum forming, pressure forming, vacuum and pressure forming, etc., and are used as packaging materials for foods, medicines, various equipment parts, etc. Widely used.

When molding containers from relatively thin sheets, etc. using these thermoforming means, the thin thermoplastic resin sheet, etc. is sandwiched between a heating plate and a mold plate, and while being heated by the heating plate, air is compressed. BACKGROUND OF THE INVENTION Multi-cavity containers are formed by thermoforming means such as molding.

[Problems to be solved] However, in the molding of this type of containers, due to the temperature difference between the heating plate side and the molding plate side, the heating plate side of the sheet etc. shrinks significantly after molding, and the sheet etc. 1 Figure 3(a)
As shown in the figure, the disadvantage is that the heating plate is greatly warped, making it difficult to work and handle the subsequent filling process of the containers 2 or sealing process, as well as reducing the commercial value of the final product. There is.

Therefore, in order to prevent the sheet etc. from warping after forming,
It is also possible to send the formed sheet etc. to the next process in a tensioned state, but in this case, due to the stress of warping, the containers 2 may have dents or the like as shown in Figure 3(b). It has the disadvantage of causing deformation and significantly reducing commercial value.

These drawbacks are particularly noticeable in crystalline thermoplastic resins such as polypropylene and polyester, which poses the problem of restricting their use in fields where the excellent properties of crystalline resins can be fully utilized. Was.

Although Utility Model Publication No. 59-41060 discloses a device for forming a stretched sheet of thermoplastic resin, that is, an oriented sheet, it does not mention anything about the method for forming a non-oriented sheet, which is the object of the present invention. No, again.
In the molding of non-oriented sheets, Utility Model Publication No. 59-4106
If the periphery of the heating plate is made convex as in No. 0, there is a problem in that it may lead to molding defects such as raindrops and wrinkles.

The present invention has been made in view of the above-mentioned problems, and has substantially the same or better heating properties and moldability of non-oriented sheets, etc. as conventional methods, and also prevents the occurrence of warpage in the sheets etc. after molding. The purpose of the present invention is to provide a method for thermoforming containers, which makes the containers flat and uniform without causing any deformation such as dents in the molded containers.

[Means for Solving Problems and Effects] In order to achieve the above object, the method for thermoforming containers of the present invention includes introducing a substantially non-oriented crystalline thermoplastic resin sheet or film between a heating plate and a molding plate. , surface roughness is 3
The above-mentioned sheet or film is sandwiched and pressed with at least 11 layers or more separated between the two surfaces by a heating surface of S or less and a mold surface, and the sheet or film is brought into contact with the heating surface by compressed air from the mold surface side. After heating the resin to a temperature below the melting point of the resin, air is compressed from the heating surface to the surface of the mold to form containers.

According to the method of the present invention, most of the non-oriented crystalline thermoplastic resin sheet does not come into contact with the mold surface during heating, and most of the sheet does not come into contact with the heating surface during cooling, so that it does not contact the heating plate side. The temperature difference with the mold surface side can be reduced,
The sheet will not warp.

[Examples] Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall view of an example of a molding apparatus for carrying out the present molding method, and FIGS. 2(a) to 2d) are explanatory diagrams of the molding method including sectional views of essential parts of the molding apparatus.

First, in FIGS. 1 and 2, a description of the molding process will be given. 10 shows the entire hot plate pressure bonding type air pressure forming apparatus;
11 is a compressed air heating plate; 15 is a mold plate; these heating plate 11 and mold plate 15 face each other in the vertical direction;
It is also designed to be movable up and down. A heat source 12 such as a heater is embedded in the heating plate 11, and the surface of the heating plate 11 is
The heating surface 13 that comes into contact with the sheet etc. 1 and heats it has a surface roughness of 3S or less. The heating surface 13 is usually provided with a large number of small pressurized air blowing holes 14 for blowing out air corresponding to the cavity portions 17 of the mold plate 15, which will be described later. In this case, the heating temperature by the heating plate 11 is
The temperature is below the melting point of.

The mold plate 15 has a convex portion 16a having a width and a notch of 1 mg or more, which is continuously formed on the outer peripheral edge of the mold surface 16 facing the heating plate 11, so that the mold surface 16 has a thickness of 1 mm or more. The four portions 16b are formed to have a depth of . Convex portion 16
The height of a, that is, the depth of the recess 16b is 1 mm to 1 mm.
The range is 0 m dew, preferably 1.5 lm to 6.0 m dew.
The range was m■.

The convex portion 16a is formed integrally with the mold plate 15, and
It can also be formed by providing it separately as a frame or a spacer and attaching it to the molding plate 15 later.

It is also possible to operate the frame body and the like independently of the forming plate by a separate drive device. This molding template 1
The temperature in step 5 is usually 30°C to 80°C.

The cavity portion 17 forming containers is provided in multiple stages in the recessed portion 16b. A through hole 1 is provided at the bottom of this cavity portion 17.
8 is provided, for example, to supply compressed air when heating the sheet,
This allows for vacuum suction or degassing during molding.

Although a metal mold is generally used as the molding plate 15, it may also be a mold made of other materials, such as a resin mold. A part or all of the surface may be made of resin.

Note that if the heating plate 11 is placed below, the temperature difference between it and the mold plate 15 cannot be made very small during sheet heating, so it is preferable to place it above as in the above embodiment.

Next, an example method will be explained with reference to FIGS. 2(a) to 2d).

■ A substantially non-oriented crystalline thermoplastic resin sheet 1 is introduced between the heating surface 13 of the heating plate 11 disposed above and the mold surface 16 of the mold plate 15 disposed below (Fig. 2). (see (a)).

■ Operate the heating plate 11 and molding plate 15 to form the sheet etc.
Press down. In this case, the part to be formed of the sheet etc. 1 is pressed while being separated from the mold surface 16 by the depth of the recess 16b, that is, the height of the convex part 16a (1 am north). For forming, pressurized air of about 0.5 kg/c to 3.0 kg/c layer 2 is supplied from the through hole 18 through the cavity 17 of the plate 15, and the sheet 1 etc. is heated on a heated surface with a surface roughness of 3S or less. 13 and heat it (
(See FIG. 2(b)), the temperature of the heating surface 13 at this time is below the melting point of the sheet etc. 1.

In this way, when the sheet, etc. 1 is heated by the heating plate 11, the air in the recess 16b of the mold surface 16 functions as a heat insulating layer, so that the sheet, etc. 1 is heated quickly, and the sheet, etc. The temperature difference between the surface side and the mold surface side can be reduced. Further, since the surface roughness of the heating surface 13 is 3S or less, there is no occurrence of rough surface transfer, rain drop phenomenon, etc., and the transparency, gloss, surface properties, etc. of the sheet etc. 1 are not impaired.

■ Next, from the compressed air outlet 14 of the heating plate 11, 2,0
While blowing out compressed air of about Kg/cm2 to 8/OKg/cm2, the cavity part 17 of the mold plate 15 is
Air is taken in (natural exhaust may be used), and a sheet or the like is press-fitted into a cavity 17 having a surface roughness of 4S or less, formed into a container, and cooled (see FIG. 2(C)).

In this case, since the surface roughness of the cavity portion 17 is set to 4S or less, sufficient degassing during molding can be achieved, and the transparency, gloss, and surface properties of the molded product, i.e., containers, can be maintained in good condition. I can do what I did. Further, since the air in the recess 16b of the mold surface 16 acts as a heat insulating layer, cooling during molding can be performed quickly and the temperature difference between both sides of the sheet etc. 1 can be reduced.

(2) Thereafter, the heating plate 11 and the mold plate 15 are operated to separate them, and the molded containers are taken out from the cavity portion 17 (see FIG. 2(d)) and cooled.

Next, specific examples and comparative examples will be shown.

Specific example: A non-oriented polypropylene resin film (haze 2%) with a thickness of 150 g is 10 m wide x 40 m long x 15 m deep
A thin-walled container was formed using a hot plate heating and pressure forming apparatus having a 12 (4×3) individual mold for semi-cylindrical containers. Under the conditions of a heating plate temperature of 135°C and a mold temperature of 30°C, the sheet was sandwiched between the heating surface of the heating plate and the mold surface of the mold with a distance of 5 cm, and air pressure of 1.0 kg/cm2 was applied from the mold side. After pressing the sheet against the heating plate and heating it, 6,0 degrees from the heating plate side.
A container molded sheet with excellent transparency and gloss in the container portion was obtained by molding under a molding pressure of Kg/cm2. As a result, no warpage was observed in the sheet. The molding cycle was 40 mm/min.

Comparative Example: The same procedure as in Example was carried out except that a flat mold was used and the heating surface and mold surface were not separated. The obtained molded sheet curled significantly upward in the sheet flow direction, and the molding cycle was 31 shots/min. Furthermore, when this sheet was sealed flat with a cover material to prevent it from curling, a dent occurred on the side of the official cover.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible, and for example, a forming method such as vacuum forming can be used.

[Effects of the Invention] As described above, according to the molding method of the present invention, when molding a non-oriented sheet, the sheet does not warp or the containers undergo deformation such as dents. , it is possible to obtain high-quality molded products with good workability. Also,
It is also possible to speed up the molding cycle by improving heating and cooling efficiency during heating and cooling.

[Brief explanation of the drawing]

FIG. 1 is an overall view of an example of a molding apparatus for carrying out the present molding method, FIGS. b) is a diagram showing an example of molding by a conventional method.

Claims (5)

[Claims] (1) A substantially non-oriented crystalline thermoplastic resin sheet or film is introduced between the heating plate and the mold plate, and the distance between the two surfaces is at least 1 mm or more between the heating surface with a surface roughness of 3S or less and the mold surface. The sheet or film is clamped in an isolated state, and the sheet or film is brought into contact with the heating surface by air pressure from the mold surface side, heated to below the melting point of the resin, and then heated from the heating surface side to the mold surface side. A method for thermoforming containers, which is characterized by forming containers by compressing air. (2) A method for thermoforming containers according to claim 1, characterized in that the molding is performed with a heating plate disposed on the upper side. (3) Containers according to claim 1 or 2, which are molded using a mold plate in which a continuous convex portion with a width of 1 mm or more is formed on the periphery of the mold surface. Thermoforming method. (4) Claims 1, 2, or 3 characterized in that the molding is performed using a heating plate with a uniformly flat heating surface.
Thermoforming method for containers described in Section 1. (5) A method for thermoforming containers according to claim 1, 2, 3 or 4, characterized in that the molding is carried out using a molding plate whose cavity portion has a surface roughness of 4S or less. .