JP3788193B2 - Method for producing a plastic bubble sheet comprising a two-layer film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an advantageous method for producing a plastic bubble sheet made of a laminated film.
[0002]
[Prior art]
A plastic bubble sheet obtained by laminating a cap film having a large number of cap-shaped bulges and a flat back film on the bottom surface of the cap is widely used as a cushioning material for packaging and as a heat insulating material. The plastic used as the material is most often polyethylene. This is because polyethylene is inexpensive and has high processability.
[0003]
Depending on the application, gas barrier properties may be required for the plastic foam sheet. For example, in order to withstand changes in temperature and pressure during use and maintain a buffering force, air must be prevented from escaping through the bubble wall. In order to meet such a requirement, a gas barrier plastic layer such as nylon or polyester is present inside polyethylene as a material for the bubble sheet.
[0004]
As shown in FIG. 1, the buffer composite disclosed in Japanese Utility Model Publication No. 1-99615, which is an example thereof, uses a polyamide or ethylene-vinyl alcohol copolymer layer as a gas barrier layer (A1, B1). Laminate via polyolefin layers (A2, B2) and adhesive layers (A3, B3), and prepare a cap film (A) and a back film (B) using these laminates. A bubble sheet having bubbles (C) is formed by bonding. In this air bubble sheet, the gas barrier layer faces the cap film and the back film, but when the gas barrier plastic has low adhesion, an adhesive layer (not shown) is sandwiched between them. Select.
[0005]
Another example of the buffer composite disclosed in Japanese Utility Model Laid-Open No. 1-99616 is that at least one of the cap film and the back film constituting the thermoplastic resin / gas barrier resin layer / thermoplastic resin / gas barrier. It has a five-layer structure of a functional resin layer / thermoplastic resin.
[0006]
If the production of such a known gas barrier foam sheet is attempted by a production method in which a cap film is prepared using a conventional vacuum forming roll, the productivity cannot be increased, and the gas barrier resin and the thermoplastic resin are not improved. Some combinations with resins have been found to be difficult to manufacture. The reason for this is that plastics with gas barrier properties generally have a high melting point, while polyethylene and the like laminated together have a low melting point and the extrusion temperature of the laminated material is high. It means that you have to take heat away until it solidifies.
[0007]
Another problem is that in a multi-layer configuration of three or more layers and a maximum of five layers, the lamination itself is complicated and an advantageous technique such as coextrusion cannot be used. Needless to say, this increases the manufacturing cost. Further, no matter how thin each layer is, there is a limit, so the bubble sheet is composed of an extremely thick material as a whole. Considering disposal after use, the thickness of the material film of the bubble sheet should be as thin as possible if the same level of cushioning performance or heat insulation performance can be achieved. From the viewpoint of manufacturing cost, it is advantageous if it is thin.
[0008]
Another characteristic often required for plastic foam sheets is their waist. In order to increase the stiffness of the bubble sheet, it is necessary to use a highly rigid material with the same film thickness or to increase the thickness of the material film. As can be easily understood from the above, it is disadvantageous to make the material film thicker and cannot be adopted.
[0009]
[Problems to be solved by the invention]
The object of the present invention is to improve the low productivity associated with the conventional method of producing a plastic bubble sheet made of a laminated film, enjoy a high productivity not inferior to that of a single-layer film, and An object of the present invention is to provide a method for producing a bubble sheet composed of a thin material film.
[0010]
[Means for Solving the Problems]
As shown in FIG. 2, the method for producing a plastic foam sheet comprising a double-layer film of the present invention that achieves this object comprises a plastic film that is melted by an extruder (1) and melt-extruded from a T-die (3). A cap film (7) having a large number of bulges by vacuum suction is prepared by bringing it into contact with a rotating vacuum forming roll (5) having a large number of depressions on the surface. The plastic bubble sheet (9) is melted in 2) and melt-extruded from the other T-die (4) as a back film (8) and pressed against the cap film by the pressure roll (6). In the method of manufacturing
Using two extruders and two laminated T dies connected to them, one extruder melts a plastic with a relatively high melting point, and the other extruder melts a plastic with a relatively low melting point Then, each molten plastic is supplied to two laminated T dies, and the temperature of the two laminated T dies is kept at a low temperature as long as the high melting point plastic can be processed. Extruded as a laminated film of a plastic and a low-melting plastic, and one extruded laminated film was vacuum-molded by placing the high-melting-point plastic on the side in contact with the vacuum forming roll, and the other was made into a cap film the laminated film as a back film, to characterized in that it is performed by positioning the low melting point of the plastic on the side fused to the cap film .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
As described above, as shown in FIG. 3, the cap film (7) and the back film (8) are formed as a laminate of two layers of plastics having different melting points, and a high melting point plastic (71) is formed on the outside. Is obtained, and a bubble sheet in which a low melting point plastic (72) is located inside is obtained . The temperature to be applied to the laminated T-die varies depending on factors such as the melting point of the high melting point plastic, the thickness of the extruded film, the distance from the die lip to the vacuum forming roll, but those skilled in the art will refer to the examples described later. In addition, an appropriate range could be determined by performing some experiments if necessary.
[0012]
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 and positioned as the outermost layer of the laminated film. A polyethylene film is suitable as the plastic film having a low melting point located in the innermost layer.
[0013]
When the objective is a bubble sheet that does not require gas barrier properties and is strong, polypropylene is preferably used as the plastic having a high melting point. Also in this case, a polyethylene film is also suitable as a plastic film having a low melting point located in the innermost layer.
[0014]
For the formation of a laminated film, co-extrusion using a laminated T-die was adopted as the most preferable from the viewpoint of efficiency. If necessary to ensure adhesion between layers, an appropriate adhesive may be used. As a means of using an adhesive in coextrusion, known means such as blending an adhesive polymer having a polar group added to polyethylene by a method such as graft polymerization on the side of a low melting point plastic, typically polyethylene. Can be used.
[0015]
【The invention's effect】
If a plastic bubble sheet is produced by the method of the present invention, the cap film and the back film of the plastic in contact with the vacuum forming roll and the pressure roll have a high melting point, and the sides to be fused to each other have a low melting point. The resin temperature for coextrusion may be low as long as the high melting point plastic can be processed, and the plasticity is maintained at the time when the cap is formed in contact with the vacuum forming roll. If it is at a low temperature close to such a limit, the high melting point plastic is immediately solidified when the cap is molded by the vacuum forming roll, so it is easy to remove the mold from the molding roll, and the molding can be performed at high speed. it can. On the other hand, since the low melting point plastic side can be sufficiently fused at that temperature, the two films necessary for forming the bubble sheet are surely fused.
[0016]
Since the film of the air bubble sheet thus produced is usually two layers for both the cap film and the back film, it is much thinner than the conventional multi-layer film air bubble sheet of 3 layers or more and 5 layers. can do.
[0017]
[Example 1]
Nylon (NY) and low-density polyethylene (PE) were coextruded (melting points were 210 ° C. and 115 ° C., respectively) to produce a gas bubble plastic foam sheet. The cap has a staggered arrangement with a diameter of 10 mm, a height of 4 mm, and a pitch of 11.5 mm. The film thicknesses are as follows:
Cap film NY layer 7 μm + PE layer 23 μm = 30 μm
Back film NY layer 5 μm + PE layer 15 μm = 20 μm
The temperature of the T-die was 250 ° C., and the take-up speed of the product bubble sheet could be up to 150 m / min. This is a 70% increase over the line speed when using only PE to produce a bubble sheet of the same film thickness.
[0018]
[Example 2]
Polypropylene (PP) and low density polyethylene (PE) were combined (PP has a melting point of 170 ° C. and PE has a melting point of 115 ° C. as described above), and a stiff cell sheet was produced. The cap size is the same as in Example 1. 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 = 20 μm
The strength of the waist of this bubble sheet is a value of 430 kgf · mm in a cantilever type test, and when trying to achieve the same waist strength with PE alone, for example, the thickness of cap film 50 μm + back film 35 μm Need.
[Brief description of the drawings]
FIG. 1 is an enlarged cross-sectional view showing a layer structure of an example of a plastic foam sheet made of a multilayer film according to the prior art.
FIG. 2 is a cross-sectional view of the main part of the apparatus showing the production of a plastic bubble sheet made of a multilayer film by the method of the present invention.
FIG. 3 is an enlarged cross-sectional view corresponding to FIG. 1, showing an example of a plastic bubble sheet made of a multilayer film manufactured by the method of the present invention.
[Explanation of symbols]
A1, B1 Gas barrier layer A2, B2 Polyethylene layer A3, B3 Adhesive layer A Cap film B Back film C Air bubbles 1, 2 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

Claims (3)

A plastic film melt-extruded from a T-die is brought into contact with a rotating vacuum forming roll having a number of depressions on the surface, and a cap film having a number of bulges is prepared by vacuum suction. In the method of producing a plastic foam sheet by pressing a plastic film melt-extruded from the T-die of the die as a back film and pressing the cap film with a pressure roll to cause fusion
Using two extruders and two laminated T dies connected to them, one extruder melts a plastic with a relatively high melting point, and the other extruder melts a plastic with a relatively low melting point Then, each molten plastic is supplied to two laminated T dies, and the temperature of the two laminated T dies is kept at a low temperature as long as the high melting point plastic can be processed. Extruded as a laminated film of a plastic and a low-melting plastic, and one extruded laminated film was vacuum-molded by placing the high-melting-point plastic on the side in contact with the vacuum forming roll, and the other was made into a cap film the laminated film as a back film, to characterized in that it is performed by positioning the low melting point of the plastic on the side fused to the cap film Manufacturing method for a plastic bubble wrap having a two-layer film. Use a gas barrier plastic selected from polyester resin, nylon and ethylene-vinyl alcohol copolymer as the high melting point plastic located in the outer layer of the laminated film, and use polyethylene as the low melting point plastic located in the inner layer The manufacturing method according to claim 1. The production method according to claim 1, wherein polypropylene is used as the plastic having a high melting point positioned in the outer layer of the laminated film, and polyethylene is used as the plastic having a low melting point positioned in the inner layer.

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