JPS6011612B2 - Differential pressure molding method for thermoplastic resin sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming cup-shaped containers, trays, caps, packings, etc. by vacuum forming and pressure forming.

Conventionally, a wide thermoplastic resin sheet extruded with a T-die is vacuum-formed or pressure-formed in a direction perpendicular to the extrusion direction to obtain cups, egg trays, and the like.

However, with this method, if a polyolefin resin such as polypropylene or polyethylene is used as the sheet material, only a drawing ratio of 1 or less can be obtained, and not only polyolefin but also impact-resistant polystyrene,
Even if polyvinyl chloride is used, which has relatively good differential pressure molding, the wall thickness at the corners of the product will be thin, so only products with a tapered part and a rounded corner design can be used. Not only is there a disadvantage that it cannot be obtained, but also in the molding method, in order to obtain a product with as good wall thickness distribution as possible,
There are drawbacks such as the need for pre-blowing, plug assist, and the use of complicated techniques such as using compressed air and vacuum in combination. The present invention was made for the purpose of improving the drawbacks of the above-mentioned conventional molding method, and involves fixing the periphery of a sheet obtained by cutting an extruded thermoplastic resin rod perpendicular to the extrusion direction. The present invention provides a method for molding a cup or the like, characterized in that the sheet is then heated to a temperature in the range from the softening point of the thermoplastic resin material to 400° C. and molded under differential pressure. More specifically, the residual strain stored in the rod during extrusion disappears when the sheet is heated above the softening point of the thermoplastic resin material.
When this occurs, deformation of the sheet occurs.

When using a sheet obtained by cutting an extruded rod perpendicularly to the extrusion direction, the deformation of the sheet can be achieved by preforming it like an injection blow-molded parison, as shown in Figure 1b (described later). The present invention provides a differential pressure molding method in which compressed air is blown into the recesses of the preformed sheet, or a vacuum mold is used as a mold to perform molding under reduced pressure. The following resins can be mentioned as thermoplastic resins that can be used as materials for the sheet used in the method of the present invention.

Crystalline resin> Low density polyethylene, high density polyethylene, polypropylene, polyolefin such as ethylene-pynylacetate copolymer, polyacetal, polyamide such as nylon 6, nylon 6,6, nylon 6, lu nylon 11, nylon 12, polyethylene Thermoplastic polyesters such as terephthalate and polybutylene terephthalate, saponified products of ethylene-vinyl acetate copolymers, polycarbonates, etc.

<Amorphous resin> Polypynyl chloride, impact-resistant polystyrene, etc.

A heat stabilizer, pigment, filler, glass fiber, etc. may be added to this. The cross-sectional shape of the thermoplastic resin rod to be extruded may be any polygon such as circular, elliptical, triangular, square, rectangular, pentagonal, hexagonal, or octagonal, but the strain distribution of the sheet should also be taken into account. A circular shape is most preferable.

Furthermore, depending on the shape of the desired product, the obtained sheet may be cut as shown in FIG. 6a. If possible, the rod-shaped object may be cut as shown in FIG. 6b. The extrusion pressure of the rod-shaped product is 20 k9/min or more, preferably 100 to 350
It is k9/.

Furthermore, if the extruded rod-shaped product is rolled using a shrinking die at a temperature from above the softening point to below the melting point of the resin, a product with a higher drawing ratio can be obtained. The cutting of the rod-like object is carried out by force cutting with a knife bar, cutting with a saw, etc., and the thickness of the cut sheet is 0.1 to 20 mm, preferably 2 mm.
~7 side. As a method for forming the sheet of the present invention, a conventional differential pressure forming method, that is, air pressure forming, vacuum forming, or a forming method using a combination of both can be used.

Pressure air pressure is 0.1 to 12k9/G, vacuum pressure is 6
50 side Hg or less, preferably 100 side Hg or less.
Of course, auxiliary means such as pre-blow and plug assist can also be used. If the sheet temperature exceeds 400 degrees Celsius, there is a risk that the resin will decompose. The most preferred embodiment of the invention is
In the case of a thin wall with a thickness of less than 1 skin, the sheet with its surroundings fixed is heated above its melting point, and the sheet is deformed by eliminating the residual strain of the sheet itself, and when the deformation reaches the maximum, it is deformed. 0.1 to 7k9 in the depression caused by
/Mold by blowing in compressed air or using a combination of compressed air and vacuum.

If the sheet wall thickness is two ribs or more, the heating of the sheet is slowed down to raise the temperature of the sheet, and in addition to the deformation due to the release of the strain mentioned above, deformation due to sagging due to the sheet's own weight during chick melting is also caused. Shape. In addition, when forming a sheet in a solid state with a temperature above the softening point and below the melting point,
Blow molding is performed using compressed air of 3 to 12 k9/g of crucian carp using a heated plug as an auxiliary means as disclosed in 48 Keitei. Of course, a vacuum may also be used. In the case of molding in this solid state, if the sheet material is polypropylene, a product that is more transparent and stronger than a product molded at a temperature above the melting point can be obtained. For reference, the preform body produced by heating a high-density polyethylene sheet (Figure 1 a) without fixing it is shown in Figure 1 b, and the periphery of the sheet with a diameter of 5 mm and a wall thickness of 2 is fixed. The correlation between the preform height of the sheet and the standing time when the sheet is left at a constant temperature without heating is shown in FIGS. 2a and 2b for a high-density polyethylene sheet and a polyvinyl chloride sheet, respectively. Next, an apparatus for carrying out the method of the present invention will be explained with reference to FIG.

In Fig. 3, 1 is an upper chamber made of aluminum, 2 is a lower chamber made of European steel, 3, 3 is a band heater, 4 is a bimetal, 5 is a compressed air inlet, 6 is a thermometer, 7 is a seat, and 8 is a It is a mold.

In order to manufacture a cup-shaped container using this apparatus, a sheet 7 as shown in FIG. The periphery is sandwiched between the upper and lower chambers 1 and 2. At this time, it is preferable to hold the sheet 7 with its extrusion direction side (the extruded side when the rod-shaped object is extruded) facing in the opposite direction to the mold 8 side. and upper and lower chambers 1
. After that, or during the process when the strain is not completely eliminated, or after taking into account the deformation due to the sheet's own weight after the strain is eliminated, compressed air is blown into the recesses caused by the deformation, and the sheet is stretched out until it comes into close contact with the mold 8. After that, a cup-shaped container can be obtained by cooling. In this case, if a vacuum mold is used as the mold 8, molding can be performed using both compressed air and vacuum. Of course, it is also possible to perform vacuum forming by reducing the pressure without using compressed air. 50) in an extruder (L/D28) with a heating temperature of 230°C and an inner diameter of 100 legs.
Melt and mix the rice bran using
9/ It was extruded with a pressing force of 1.9 mm, and then cooled with water.

This round bar was cut with a mirror perpendicular to the extrusion direction to obtain a circular sheet with a wall thickness of 2 as shown in FIG. 1a. With the side surface A of this circular sheet in the extrusion direction facing the opposite direction from the mold 8 side as shown in the third figure, the outer periphery IW cape width of this sheet is placed between the upper and lower chambers 1 and 2, and the heater 3 , 3 for 12 minutes at 150°C to cause deformation (preform) by eliminating distortion, then blowing Shoku of lk9/lump G for 30 seconds from the blowing port 5, then turning off the power to the heaters 3 and 3. After the mold 8 was left to stand until the temperature reached room temperature, the upper and lower chambers 1 and 2 were opened and the product c with a drawing ratio of 1.3 was taken out. The appearance of this product c is shown in Fig. 1c. <Example
2-5> Change the shape of the mold 8, set the heating temperature and time as shown in the following table, and make other products d-g in the same manner as in Example 1.
I got it.

The appearance of these products is shown in Figures 1d-g. table For reference, the wall thickness distribution of product c is shown in Fig. 4.

<Example 6> An extrusion-molded round rod of polyvinyl chloride having a diameter of 5 m was cut perpendicularly to the extrusion direction using a mirror to obtain a circular sheet with a thickness of 2 ribs.

This circular sheet is sandwiched between the upper and lower chambers 1 and 2 with the extrusion direction side facing away from the mold side as shown in the third figure, and heated with a heater 5 at 20030° C. for 2 minutes to deform by eliminating strain. After this, compressed air of 2 kg/l is blown in for 30 seconds, then the power to the heater 5 is turned off, and the temperature of the mold is left to reach room temperature, and then the upper and lower chambers,
2 was opened to obtain a cup with an aperture ratio of 1.3. <Example 7
> Extruded polypropylene with a diameter of 5 mm (melting point 1
A round birch (64°C) was cut perpendicular to the extrusion direction using a mirror to obtain a circular sheet with a wall thickness of 1.5 mm.

The circumference of this circular sheet is fixed, and then the sheet is
When the temperature reached 0.000, the sheet was pressed down with a plug at 140° C., and compressed air of 10 k9/ground was further blown into the sheet to shape it, and then cooled to obtain a transparent cup with a drawing ratio of 0.5. This cup had significantly superior transparency and rigidity compared to a cup that was air-formed by heating to a temperature above the melting point (21,000 ℃). As mentioned above, according to the present invention, "the periphery of the sheet obtained by cutting an extruded thermoplastic resin rod perpendicular to the extrusion direction is fixed, and then this sheet is cut into a thermoplastic resin material. This is a method of differential pressure forming by heating to a temperature above the softening point of the sheet and below 400 qo, which deforms the sheet by eliminating its internal strain, making it possible to make the wall thickness uniform and the resulting product Compared to the pot method, it has the advantage of less residual strain and less thermal deformation.

Furthermore, a product having an aperture ratio of 1 or more can also be obtained. Note that if the offering is subjected to cross-rolling, low-temperature deformation can be made even more effective. In addition, there is an advantage that there is no need to use a complicated molding method to obtain a product with a good wall thickness distribution.

[Brief explanation of drawings]

Figure 1a is a sheet according to the present invention, Figure 1b is a preform state of the sheet thermally deformed by strain relief, Figures c to g are external views showing the product obtained by implementing the present invention, Figure 2a
,b are diagrams showing the relationship between temperature retention time and thermal deformation height using constant temperature room temperature as a parameter for low-density polyethylene sheets and polyvinyl chloride sheets, respectively.
The figure is a partially cutaway cross-sectional view showing the device used as an embodiment of the present invention, FIG. 4 is a wall thickness distribution diagram of the product shown in FIG. 1g,
FIG. 6 is an explanatory view showing the manufacturing state of the sheet according to the invention, and FIGS. 6a and 6b are cross-sectional views of the sheet according to the invention. In Fig. 3, 1, 2...Chamber for holding the sheet, 3...Heater, 5...Compressed air inlet, 7...Sheet, 8
... Mold, 10... Twill-like object. Many diagrams, many 2 diagrams, many 9 diagrams, many 9 diagrams, many diagrams, many diagrams

Claims (1)

[Claims] 1. The periphery of the sheet obtained by cutting an extruded thermoplastic resin rod perpendicular to the extrusion direction is fixed, and then this sheet is heated at a temperature of at least the softening point temperature of the thermoplastic resin of the sheet material and at most 400 degrees Celsius. A differential pressure molding method for a thermoplastic resin sheet, which is characterized by heating to a temperature and performing differential pressure molding.