JPS6021052B2 - Thermoforming method for packaging containers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for aging and forming packaging containers in which composite sheets of thermoplastics are laminated, heated and formed under vacuum and/or pressure.

BACKGROUND OF THE INVENTION It is widely practiced to manufacture packaging containers by heating a single layer sheet of thermoplastic and forming it under vacuum and/or pressure.

Furthermore, in order to satisfy the wide variety of performances required for packaging containers, it has become common practice to heat composite sheets and mold them under vacuum and/or pressure instead of single-layer sheets. Multiple single-layer sheets are stacked, heated, vacuumed and/or
Alternatively, it has been proposed to obtain a packaging container of a composite sheet by simultaneously fusing single-layer sheets together with pressure molding.

However, since the temperature suitable for vacuum and/or pressure molding and the temperature for bonding single-layer sheets together are generally different, it is impossible to satisfy molding and fusing at the same time. In particular, by stacking two or more stretched sheets and heating them,
This difference is significant during vacuum and/or pressure forming, and at temperatures high enough to completely fuse the stretched sheets together, the stretched sheets lose most of their stretching effect, their strength and transparency are significantly reduced, and they become virtually invisible. Only molded products of the same quality as those produced by laminating non-stretched sheets, heating, vacuum and/or pressure molding can be obtained. In addition, instead of the expensive double-stretched sheets, uniaxially stretched sheets are stacked so that their stretching directions are perpendicular to each other, heated, and vacuum and/or pressure-formed, making them essentially the same as the double-stretched sheets. A method has been proposed for obtaining packaging containers having these characteristics at low cost.

However, as in the case of using a biaxially oriented sheet, at a temperature high enough to completely fuse the uniaxially oriented sheets, the uniaxially oriented sheet loses most of its stretching effect, and its strength, stiffness, and transparency are significantly reduced. Substantially the same quality as that obtained by laminating unstretched sheets, heating, vacuum and/or pressure molding can be obtained.

The present invention provides a composite sheet consisting of two types of thermoplastic layers having different melting points or softening points, in which at least one layer constituting the composite sheet is stretched in a uniaxial direction. The plastic layers with a low melting point or low softening point are stacked so that their surfaces are in contact with each other and the stretching directions are perpendicular to each other, and the plastic layers are stacked at a temperature higher than the melting point or softening point of the plastic layer with a low melting point or low softening point. The composite sheets are heated at a temperature lower than the melting point or softening point of the high-melting point or high-softening point plastic, molded under vacuum and/or pressure, and simultaneously fused or pressed together to form a substantially biaxial This is a method to inexpensively produce aged molded products with the same performance as molded products obtained from stretched sheets.

The melting point or softening point in the present invention refers to the temperature at which the plastic becomes completely liquid when heated at a constant rate, and the softening point is the temperature at which the plastic begins to deform (Test Method Melting Point ASTM -2117, softening point D 1525).

The present invention also uses a composite sheet that is composed of two types of thermoplastic plastic layers having different melting points or softening points, and in which at least one layer constituting the composite sheet is stretched in two directions. Among the thermoplastic plastic layers, the surfaces of the low melting point or low softening point layers are stacked so that they are in contact with each other. Two types of composite sheets with substantially different performance are created by heating the plastic at the melting point of the plastic or at a temperature lower than the softening point, forming the composite sheets under vacuum and/or pressure, and simultaneously fusing or pressing the composite sheets together. This is a method for producing a matured shaped product with mutually complementary properties without losing the double-stretching effect. The thermoplastics used in the composite sheet of the present invention include thermoplastics for stretched films such as high-density polyethylene, polypropylene, polypynychloride, polyvinylidene chloride, polystyrene, polyethylene terephthalate, nylon, and ethylene vinyl acetate copolymer. Examples include copolymers such as polymers, which may be used alone or in combination with each other.

As the uniaxially stretched composite sheet used in the present invention, two types of thermoplastic plastics having different melting points or softening points were selected from among the above-mentioned thermoplastics, depending on the performance required of the packaging container manufactured by the method of the present invention. , a composite sheet manufactured by a coextrusion method, an extrusion coating method, a dry lamination method, etc., is stretched by 1.1 times to 10 times by a general stretched film stretching method.
Various composite sheets are used, such as ones that have been stretched to about twice the original size, or those made by extrusion coating a thermoplastic film that has been stretched to about 1.1 times to 1 pm with other low-melting point thermoplastics. be done.

The stretching ratios of the two types of plastics constituting the uniaxially stretched composite sheet may be the same or different. There is no problem even if it is a stretched one.

Further, the composite sheet to be used may be one in which two types of plastics are stacked to form two layers, or one in which a high melting point plastic is the center and low melting point plastics are stacked on both sides to form three layers. The biaxially stretched composite sheet used in the present invention is a composite sheet in which two types of thermoplastic plastics having different melting points or softening points are stretched biaxially in all directions in the same manner as the single-stretched composite sheet. The stretching ratios of the two types of thermoplastic plastics constituting the composite sheet may be the same or different, or only one layer may be stretched. Various composite layers can be used, such as a composite of two or three layers, similar to the single-stretch composite sheet. As a method for ripening the stacked composite sheets according to the present invention, any method such as a vacuum or pressure molding method or a matched die molding method may be used, and a plug or the like may be used in combination as appropriate.

In addition, the uniaxially stretched composite sheets to be stacked are generally of the same type (same or different) in order to obtain substantially the same effect as two bag-stretched composite sheets by stacking one koji-stretched composite sheet orthogonally to each other. Composite sheets of different types (same or different stretching ratios) are also used.

In addition, biaxially stretched composite sheets are generally manufactured by stacking different types of composite sheets to complement each other's performance, but for the purpose of manufacturing thick sheets at low cost, sheets of the same type are also used. be done. There is no limit to the number of the above-mentioned uniaxially stretched or biaxially stretched composite sheets that can be stacked.

Example 1 Commercially available polypropylene (Mitsui Toatsu Kogyo ■) from the first extruder
(product name: “Mitsui Noblen”, brand name: “JS-G”)
A commercially available ethylene-vinyl acetate copolymer (manufactured by Sumitomo Chemical Co., Ltd., trade name "Ebatate", brand name "D2") was extracted from the second extruder.
02r) were respectively supplied to the same T-die to obtain a coextruded two-layer composite sheet of two types and two layers, one layer of polypropylene and the other layer of ethylene-acetate-picopolymer.

This is uniaxially stretched to about twice the size, and the thickness is about 25 mm as shown in Figure 1.
Uniaxially stretched composite sheets 2 and 2' having excellent strength, stiffness, and transparency were obtained, which consisted of a polypropylene layer 6 or 6' having a zero thickness and an ethylene-vinyl acetate copolymer layer 5 or 5' having a thickness of 10A.

A sheet made by stacking 2 and 2' so that their stretching directions are perpendicular to each other is heated to about 160 q0 and pressure-formed using air at a pressure of about 5 k9/ground to a depth of about 2 ft. , vertical 1
A thermoformed rectangular parallelepiped product with 5 ribs and about 100 ribs in width was obtained.

This thermoformed product retains the strength, stiffness, and transparency of sheets 2 and 2', and has excellent properties in the two-koji direction, with sheets 2 and 2' completely fused together; 2'
Instead, a polypropylene sheet made from the above-mentioned "Mitsui Noprene" and "JS-G" is stretched to about twice the length in both the length and width, and an OPP sheet with a thickness of about 500 r is produced at a lower cost than by heating and pressure forming. was completed. Example 2 A commercially available biaxially oriented polypropylene film with a thickness of about 60 layers (
The above Evatate D202r (manufactured by Toyobo Aya) was extrusion coated to a thickness of about 10 mm and about 250 mm, and as shown in Figure 2, it was coated with a polypropylene layer 8 or 8' and an ethylene-vinyl acetate copolymer layer 7 or 7'. Biaxially stretched composite sheets 3 and 3' having excellent strength, stiffness, and transparency were obtained.

3 and 3' stacked sheets 1 are heated to about 1600C and air-formed using pressurized air of about 5k9 to form a sheet with a depth of about 1 inch, a length of about 200 ribs, and a machine of about 15 inches. A rectangular shaped aged product was obtained.

This thermoformed product preserves the strength, stiffness, and transparency of 3 and 3', and has a thickness of approximately 140 ridges with 3 and 3' completely fused, making it extremely difficult to manufacture commercially. What?
Therefore, instead of an OPP sheet with a thickness of about 140 ridges, which is not commercially available, a thick aged product was obtained using a thin OPP sheet as a raw material.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a laminated sheet in which single-track stretched composite sheets according to the present invention are laminated, and FIG. 2 is a cross-sectional view of a laminated sheet in which biaxially stretched sheets according to the present invention are laminated. 1...superimposed composite sheet, 2, 2'...uniaxially stretched composite sheet, 3,3'...2 uniaxially stretched composite sheet,
5, 5', 7, 7'...Low melting point thermoplastic plastic, 6, 6', 8, 8'......High melting point thermoplastic plastic. Next r diagram Next Z diagram

Claims (1)

[Claims] 1. A composite sheet comprising a monoaxially or biaxially stretched thermoplastic layer and a thermoplastic layer bonded to one side of the thermoplastic layer and having a melting point or softening point lower than that of the thermoplastic layer. Two or more sheets of low melting point or low softening point thermoplastic plastic layers are stacked so that the surfaces of the low melting point or low softening point thermoplastic plastic layers are in contact with each other, and the melting point or softening point of the low melting point or low softening point thermoplastic plastic layer is above A thermoforming method for packaging containers, which involves heating to a temperature lower than the melting point or softening point of the high melting point or high softening point thermoplastic layer, forming the composite sheet under vacuum and/or pressure, and simultaneously fusing or pressing the composite sheets together. . 2. The method of thermoforming a packaging container according to claim 1, wherein two composite sheets each having a thermoplastic layer stretched in a uniaxial direction are superimposed so that the stretching directions of the layers are perpendicular to each other.