JP2001322162A - Method for manufacturing cellular plastic sheet comprising multilayered film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a cellular sheet which is composed of a thin film and has a high productivity and gas-barrier properties or stiffness wherein a melt-extruded plastic film is brought into contact with a rotating vacuum molding roll having a large number of recesses on its surface to prepare, by vacuum suction, a cap film having a large number of swells, and a melt-extruded flat plastic film, as a back film, is fused to the bottom surface of a cap. SOLUTION: At least a cap film (7), preferably both of the cap film (7) and a back film (8) are formed into a laminated material comprising two or more layers having different melting points, while plastics of high melting point are located on the side of the laminated material where the plastics come into contact with a vacuum molding roll and a pressure roll, while plastics having low melting point are located on the side of the laminated material where the plastics are fused to each other, whereby a cellular plastic sheet comprising multilayered film is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an advantageous method for producing a plastic foam sheet using a laminated film as a material.

[0002]

2. Description of the Related Art A plastic foam sheet obtained by laminating a cap film having many cap-shaped bulges and a flat back film on the bottom surface of a cap is widely used as a cushioning material for packaging and as a heat insulating material. Have been. The most common plastic material is polyethylene. This is because polyethylene is inexpensive and has high processability.

In some applications, gas barrier properties are required for plastic foam sheets. For example, in order to withstand changes in temperature and pressure during use and maintain the buffering force, it is necessary to prevent air from escaping through the walls of the bubbles. In order to respond to such a demand, as a material of the foam sheet, a layer of a plastic having a gas barrier property such as nylon or polyester is present inside polyethylene.

As one example, the cushioning composite material disclosed in Japanese Utility Model Laid-Open No. 1-99615 uses a polyamide or ethylene-vinyl alcohol copolymer layer as a gas barrier layer (A1, B1) as shown in FIG. This is laminated via a layer of polyolefin, especially polyethylene (A2, B2) and a layer of adhesive (A3, B3), and a cap film (A) and a back film (B) are prepared using this laminated material. Are bonded together to form a bubble sheet having bubbles (C). In this bubble sheet, the gas barrier layers are opposed to each other in the cap film and the back film. However, when the gas-barrier plastic has low fusion-bonding property, an adhesive layer (not shown) is interposed therebetween. Choose

Another example is Japanese Utility Model Laid-Open No. 1-99616.
Has a five-layer structure of thermoplastic resin / gas barrier resin layer / thermoplastic resin / gas barrier resin layer / thermoplastic resin. It has become.

If the production of such a known gas barrier foam sheet is attempted by a production method of preparing a cap film using a conventional vacuum forming roll, the productivity cannot be improved, and the gas barrier resin is not improved. Depending on the combination of and the thermoplastic resin, it has been experienced that production is even difficult. The cause is that plastics with gas barrier properties generally have a high melting point, while polyethylene and other materials laminated with it have a low melting point and the extrusion temperature of the laminated material is high, so low-melting materials in vacuum forming rolls are sufficient. This means that heat must be removed until it solidifies.

Another problem is that in a multi-layer configuration of three or more layers and up to five layers, the lamination itself is complicated and an advantageous method such as co-extrusion cannot be used. This, of course, increases manufacturing costs. Also, no matter how thin each layer is, there is a limit, so that the bubble sheet is composed of an extremely thick material as a whole. Considering disposal after use, if the same level of buffering performance or heat insulating performance can be exhibited, it is desirable to reduce the thickness of the material film of the bubble sheet as much as possible. From the viewpoint of manufacturing cost, it is convenient if the thickness is small.

Another property often required of plastic foam sheets is that they be rigid. In order to increase the rigidity of the bubble sheet, a material having the same film thickness and high rigidity is used, or the thickness of the material film is increased. As can be easily understood from the above, thickening the material film is disadvantageous and cannot be adopted.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the low productivity associated with the prior art method of producing plastic foam sheets from laminated films and to provide an inferior product to monolayer films. An object of the present invention is to provide a method for producing a foam sheet made of a thin material film while enjoying high productivity.

[0010]

According to the method for producing a plastic foam sheet comprising a multilayer film of the present invention which achieves this object, as shown in FIG. 2, the extruder (1) melts the T-die (3). The plastic film melt-extruded from the above is brought into contact with a rotating vacuum forming roll (5) having a large number of depressions on the surface, and a cap film (7) having a large number of bulges is prepared by vacuum suction. The bottom surface is melted by another extruder (2), and a plastic film melt-extruded from another T-die (4) is used as a back film (8) and pressed against a cap film by a pressure roll (6) to be fused. In the method for producing a plastic foam sheet (9) by using the method as shown in FIG.
As a laminate of two or more layers of plastics having different melting points, a high melting point plastic (71) is positioned on the side in contact with the vacuum forming roll, and a low melting point plastic is positioned on the side fused to the back film. (72) is positioned and implemented.

[0011]

DETAILED DESCRIPTION OF THE INVENTION In many cases, a back film (8)
Also, it is desirable to form two or more layers of plastic laminates having different melting points. As is easily understood from the above, in this embodiment, the high melting point plastic (8
1) is positioned, and the low melting point plastic (82) is positioned on the side to be fused to the cap film. The plastic foam sheet manufactured in this manner has a layer configuration shown in FIG.

When a gas barrier property is desired, a plastic film selected from a polyester resin, nylon and an ethylene-vinyl acetate copolymer is preferably used as a plastic film having a high melting point positioned as the outermost layer of the laminated film. . As the plastic film having a low melting point located in the innermost layer, a polyethylene film is appropriate.

If the purpose is to provide a foam sheet that does not require gas barrier properties and is strong, polypropylene is preferably used as a plastic having a high melting point. Also in this case, a polyethylene film is suitable as a plastic film having a low melting point to be positioned as the innermost layer.

For the formation of a laminated film, coextrusion is most preferred from the viewpoint of efficiency. If necessary to ensure the adhesion between the layers, an appropriate adhesive can be used.
As means for using an adhesive in coextrusion, known means such as blending an adhesive polymer obtained by giving a polar group to polyethylene by graft polymerization or the like on the side of low melting point plastic, typically polyethylene. Can be used.

[0015]

If a plastic foam sheet is produced by the method of the present invention, the cap film or the back film, in a preferred embodiment both the vacuum forming rolls or the pressure rolls, and in the preferred embodiment the plastic in contact with both are in contact. Because of the high melting point and the low melting point on the side that fuses with each other, the resin temperature of co-extrusion is limited to the point where high melting point plastic can be processed, and plasticity is maintained at the time of forming a cap in contact with a vacuum forming roll. May be as low as possible. At low temperatures near such limits,
Since the high melting point plastic is immediately solidified when the cap is formed by the vacuum forming roll, it can be easily separated from the forming roll and can be formed at a high speed. On the other hand, the low-melting-point plastic side can be sufficiently fused at that temperature, so that the two films necessary for forming the bubble sheet are reliably fused.

Since the thickness of the film of the foam sheet manufactured in this manner is usually two in both the cap film and the back film, the film thickness is more than that of the conventional multilayer film foam sheet having three or more layers and as many as five layers. Can be much thinner.

[0017]

Example 1 Nylon (NY) and low-density polyethylene (PE) were coextruded (melting points 210 ° C. and 115 ° C., respectively) to produce a plastic foam sheet having gas barrier properties. Cap diameter is 10mm, height is 4m
In a zigzag arrangement with a pitch of 11.5 mm. The film thicknesses are as follows: Cap film 7 μm NY layer + 23 μm PE layer = 3
0 μm Back film NY layer 5 μm + PE layer 15 μm = 2
The temperature of the 0 μm T-die was 250 ° C. and the take-off speed of the product foam sheet could be up to 150 m / min. this is,
This is a value that is 70% higher than the line speed when a bubble sheet having the same film thickness is manufactured using only PE.

[0018]

Example 2 Combination of polypropylene (PP) and low density polyethylene (PE) (the melting point of PP is 170 ° C.,
PE had the same melting point as above (115 ° C.), and a stiff foam sheet was produced. The size of the cap is the same as in the first embodiment. The film thicknesses are as follows: Cap film PP layer 15 μm + PE layer 15 μm =
30 μm back film PP layer 10 μm + PE layer 10 μm =
The stiffness of this bubble sheet is 430 kgf · mm in a cantilever type test. To achieve the same stiffness with PE alone, for example, the thickness of the cap film is 50 μm + the back film is 35 μm. Need to be.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view showing a layer configuration of an example of a plastic foam sheet made of a multilayer film according to a conventional technique.

FIG. 2 is a cross-sectional view of a main part of the apparatus, showing the production of a plastic foam sheet comprising a multilayer film according to the method of the present invention.

FIG. 3 is an enlarged cross-sectional view corresponding to FIG. 1, showing an example of a plastic foam sheet made of a multilayer film manufactured by the method of the present invention.

[Description of Signs] A1, B1 Gas barrier layer A2, B2 Polyethylene layer A3, B3 Adhesive layer A Cap film B Back film C Bubble 1, Extruder 3, 4 T die 5 Vacuum forming roll 6 Pressure roll 7 Cap Film 71 High melting point plastic 72 Low melting point plastic 8 Back film 81 High melting point plastic 82 Low melting point plastic 9 Plastic bubble sheet

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) B29K 55:00 B29K 55:00 67:00 67:00 77:00 77:00 B29L 7:00 B29L 7: 00 9:00 9:00 24:00 24:00 F-term (Reference) 4F100 AK01A AK01B AK01C AK01D AK04B AK04C AK07A AK07D AK41A AK41D AK48A AK48D AK69A AK69D BA04 BA06 BA10A BA10D BA26A BA26B BA26C BA26E BAD DD JA04B JA04C JA04D JD02A JD02D JK01 JL01 4F208 AA03 AA19 AA24 AA29 AE02 AE07 AE10 AF01 AG01 AG03 AG05 AG06 MA01 MB02 MB22 MB28 MB29 MD02 MG04 MG22 MJ09

Claims (4)

[Claims] 1. A plastic film melt-extruded from a T-die is brought into contact with a rotating vacuum forming roll having a large number of depressions on its surface, and a cap film having a large number of bulges is prepared by vacuum suction. In a method of manufacturing a plastic foam sheet by pressing a bottom surface of a plastic film melt-extruded from another T-die as a back film onto a cap film by a pressure roll and fusing the same, at least the cap film is formed of two layers or More than that, it is configured as a laminated material of plastics with different melting points, with the high melting point plastic positioned on the side that contacts the vacuum forming roll, and the low melting point plastic positioned on the side fused to the back film. Characteristic plastic foam sheet made of multilayer film Manufacturing method. 2. The back film is also formed as a laminated material of two or more layers of plastics having different melting points, wherein the high melting point plastic is located on the side in contact with the pressure roll, and the side to be fused to the cap film. 2. The production method according to claim 1, wherein the method is carried out by placing a low-melting-point plastic on the substrate. 3. A gas barrier plastic film selected from a polyester resin, nylon and an ethylene-vinyl alcohol copolymer is used as a plastic film having a high melting point located in the outermost layer of the laminated film. 2. The production method according to claim 1, wherein the method is carried out by using a polyethylene film as the low-plastic. 4. The method according to claim 1, wherein polypropylene is used as the plastic having a high melting point located in the outermost layer of the multilayer film, and polyethylene is used as the plastic having a low melting point located in the innermost layer.