JP4400063B2 - Method and apparatus for producing plastic foam sheets with controlled wall thickness distribution - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a plastic foam sheet having a controlled wall thickness distribution, and also to an apparatus used to carry out the method. In the present invention, the term “film” is used to include a film having a thickness suitable to be referred to as “sheet”. The term “vacuum forming” includes “vacuum and pneumatic forming”. Therefore, “vacuum suction” covers both simple vacuum suction and “vacuum suction + pressure air”. Similarly, the “vacuum source” is not limited to the vacuum pump but includes “vacuum pump + pressure chamber”. However, for the sake of simplicity, the following describes a mode in which only vacuum suction is performed.
[0002]
[Prior art]
A plastic bubble sheet (hereinafter referred to as “bubble sheet”), which is formed by vacuum forming a plastic film such as polyethylene to form a cap film having a large number of caps, and bonding a flat back film to the bottom of the cap It is used in various fields including the beginning.
[0003]
With this type of bubble sheet, it is inevitable that the thickness of the cap film varies depending on the part due to the vacuum forming mechanism, and the side wall and top surface of the stretched cap are thinner than the flat part, and the ridge part is It becomes thinner. For example, in the case of a cylindrical cap having a diameter of 10 mm and a height of 4 mm, a typical thickness distribution has a ratio as shown in FIG.
[0004]
The preferred cap thickness distribution varies depending on the application of the bubble sheet. An air bubble sheet used as an underlay when packaging fresh food such as shrimp in a styrene foam tray is required to have a soft air bubble and be flexible. In this case, the thickness distribution of the cap portion of the bubble sheet is preferably as small as possible depending on the location of the thickness.
[0005]
On the other hand, if it is an air bubble sheet used as an insole for canned cookie confectionery, the strength of the air bubbles is not particularly limited, but a loose air bubble sheet is preferred for the convenience of packaging work. In this case, as the wall thickness distribution, a rather biased bubble sheet is used.
[0006]
Since the cap sheet and the back film are both thick (0.2 to 1.0 mm), and the foam sheet produced in a rigid body is often used as a structural material, It is desirable that the wall thickness be as uniform as possible. That is, it is desirable that not only the thickness of the cap portion is substantially uniform, but also the difference in thickness between the cap portion and the bonded portion of the back film on the bottom surface is small.
[0007]
[Problems to be solved by the invention]
In this way, even though the thickness distribution of each part of the bubble sheet varies according to the application and customer needs, there has been a technology to manufacture the bubble sheet by adjusting the thickness distribution accordingly. I didn't. An object of the present invention is to satisfy such a blank of the bubble sheet manufacturing technology and to manufacture a plastic bubble sheet in which the thickness distribution of each part is adjusted within a limited range. .
[0008]
[Means for Solving the Problems]
One embodiment of the apparatus for producing a plastic foam sheet having a regulated thickness distribution according to the present invention that achieves the above object is characterized by the structure and function of a vacuum forming roll. That is, as shown in FIG. 2, a vacuum forming roll (1) for forming a cap film having a large number of cap-shaped cavities (11) having vacuum suction holes at the bottom and rotatably supported, and a cap film A flat die (2) for discharging a film for use, a flat die (3) for discharging a back film, and a pressure roll (4) for bonding the back film to a cap film as essential components, a vacuum source In a plastic bubble sheet manufacturing apparatus to which (not shown) is connected, each cavity of the vacuum forming roll has a vacuum suction hole (12) at the substantially center of the bottom surface, and a vacuum suction hole ( 13), and the start timing of vacuum suction for cap molding performed through these vacuum suction holes ,
1) First, the vacuum suction hole at the center of the bottom surface, followed by the vacuum suction hole at the corner of the bottom surface, or
2) First, vacuum suction holes at the corners of the bottom surface, then vacuum suction holes at the center of the bottom surface
It is characterized in that it can be selected from either of the above.
[0009]
Another aspect of the apparatus for producing a plastic bubble sheet having a controlled wall thickness distribution according to the present invention is characterized in that a plug-assist type pre-forming roll is provided and disposed in the front stage of the vacuum forming roll. That is, as shown in FIG. 3, a vacuum forming roll (1) for forming a cap film having a large number of cap-shaped cavities (11) having vacuum suction holes at the bottom and rotatably supported, and a cap film The first flat die (2) for discharging the film for use and the second flat die (3) for discharging the back film and the pressure roll (4) for bonding the back film to the cap film are essential. In an apparatus for producing a plastic bubble sheet, which is a component and connected to a vacuum source (not shown), the front of the vacuum forming roll (1) protrudes with a position and shape corresponding to the cavity (11), A preforming roll (5) having a plug (51) capable of blowing hot air from the tip and supported rotatably is disposed, Wherein the film cap film discharged from the flat die (2) is constructed to reach the forming roll through the preforming roll.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The method for producing a bubble sheet having an adjusted wall thickness distribution according to the present invention, which is performed using a vacuum forming roll having two types of vacuum suction holes (12, 13) capable of performing vacuum suction at different timings, is a plastic film. Forming a cap film having a large number of caps by vacuum forming, and attaching a back film, which is a flat plastic film, to the bottom surface of the cap to obtain a molded product having a large number of sealed air chambers Although it is a manufacturing method of a sheet | seat, there exist two aspects by the timing of vacuum suction. One of them is that vacuum suction for forming a cap starts from suction through a vacuum suction hole (12) provided at substantially the center of the bottom surface of the cavity, and then vacuum suction holes (13) provided at the corners of the bottom surface of the cavity. By performing the suction through the nozzles in this order, a molded product having a thin ridge portion of the cap is obtained.
[0011]
The cap molding pattern in this case is as shown in FIG. That is, the film for cap film (6A) is first drawn to the bottom surface by suction from the vacuum suction hole (12) provided at substantially the center of the cavity bottom surface, where it is cooled and fixed in shape (FIG. 4A). Next, by suction from the vacuum suction hole (13) at the corner, the remaining corner portion is drawn into the cavity and molded, but since the periphery is fixed, only that portion is stretched and thinned. (FIG. 4B). The cap obtained in this way gives a foamy bubble sheet, although the compressive strength of the cap is low.
[0012]
The second aspect of the method for producing a bubble sheet having a controlled thickness distribution according to the present invention, which is performed using a vacuum forming roll having two types of vacuum suction holes (12, 13), is for forming a cap. The vacuum suction is started from the suction through the vacuum suction hole (13) provided at the corner of the bottom surface of the cavity, and then the suction through the vacuum suction hole (12) provided at the substantially center of the bottom surface of the cavity is added thereto. By performing , a molded product having a small difference in thickness over the entire cap is obtained.
[0013]
The cap molding pattern in this case is as shown in FIG. That is, the film for cap film (6A) is first drawn toward the corner of the bottom by suction from the vacuum suction hole (13) provided at the corner of the bottom of the cavity, and cooled to fix the shape (FIG. 5A). Next, by suction from the vacuum suction hole (12) provided at substantially the center of the bottom surface, the center portion of the bottom surface is drawn to the cavity and molded. Rather, the wall thickness becomes uniform as a whole (FIG. 5B). The cap obtained in this way gives a bubble sheet that has a relatively high compressive strength of the cap but is not too stiff.
[0014]
The method of producing a plastic foam sheet having a controlled thickness distribution according to the present invention, which is performed using a molding apparatus having a preforming roll, also forms a cap film having a large number of caps by vacuum forming of the plastic film. A plastic foam sheet manufacturing method comprising a step of bonding a back film, which is a flat plastic film, to a bottom surface of a cap to obtain a molded product having a large number of sealed air chambers. By forming a film for a cap film discharged from a preforming roll into an intermediate film having a protrusion close to a plug shape, and forming a cap by vacuum forming this protruding portion with a cavity of a vacuum forming roll, The difference in wall thickness between the cap part and the bottom part of the cap film Wherein the obtaining again moldings.
[0015]
The cap molding pattern in this case is as shown in FIG. That is, in the film for cap film (6A), in the preformed roll (5), the part in contact with the plug (51) planted there is almost regulated by the top of the plug, but the other part is the roll. It approaches the surface and becomes an intermediate film (6B) with a half-molded shape. At this time, by blowing hot air at an appropriate temperature from the hot air nozzle (52) provided in the plug, the intermediate film (6B) is transferred to the vacuum forming roll (1) while maintaining the plasticity of the cap film film. In this manufacturing apparatus, the plug (51) and the cavity (11) correspond in shape and position, and the intermediate film (6B) is further formed by the vacuum forming roll (1) to complete the cap shape. To do.
[0016]
Since the intermediate film (6B) existing on the preforming roll (5) is formed in the process as described above, there are a part located on the plug and a part located between the plugs and approaching the roll. The wall thickness of the latter is rather thin at this stage. That is, the portion of the cap film that is bonded to the back film is formed relatively thin. Next, the portion located on the plug is slightly stretched by vacuum forming, and as a result, the cap film is bonded to the back film with a substantially uniform thickness throughout. Therefore, the difference in the thickness of each part in the air bubble sheet product is much higher than the conventional product shown in FIG.
[0017]
In the case of carrying out the bubble sheet manufacturing method in which the preform roll is baton-touched to the vacuum forming roll, the conventional vacuum forming roll is usually sufficient. Of course, a vacuum forming roll provided with the two types of vacuum suction holes described above may be used, and thereby the above-described effects can be obtained.
[0018]
[Example 1]
Using the apparatus shown in FIG. 2, a bubble sheet was manufactured using low-density polyethylene as a material. A vacuum forming roll having a diameter of 10 mm and a depth of 4 mm and having vacuum suction holes arranged at equal intervals in the center and corners of the bottom surface at a pitch of 11.5 mm in a staggered manner was used. According to the first aspect described above, that is, a cap film was formed by vacuum suction first from substantially the center of the bottom surface of the cavity of the vacuum forming roll, and a back film was attached thereto.
[0019]
The thickness of each part of the product bubble sheet was measured, and the following values were obtained.
Cap side wall: 45 μm
Top surface of cap (bottom surface of cavity): 30 μm
Cap edge (cavity corner): 7 μm
Back film single part: 30 μm
Bonding part of cap film and back film: 85μm
[0020]
[Example 2]
The apparatus shown in FIG. 2 was also used to produce a bubble sheet having the same specifications using the same low-density polyethylene as in Example 1 as a material. According to the second aspect described above, that is, a cap film was formed by suction first from a vacuum suction hole provided at the corner of the bottom of the cavity of the vacuum forming roll, and a back film was attached thereto.
[0021]
The thickness of each part of the product bubble sheet was measured, and the following values were obtained.
Cap side wall: 40 μm
Cap top surface (bottom surface of cavity): 20 μm
Cap edge (cavity corner): 15 μm
Back film single part: 30 μm
Bonding part of cap film and back film: 85μm
[0022]
[Example 3]
Using the apparatus shown in FIG. 3, a thick bubble sheet was produced using polypropylene as a material. The apparatus was prepared by arranging a preforming roll having the same diameter as that of the vacuum forming roll used in Examples 1 and 2. In this preforming roll, plugs having a diameter of 8 mm and a height of 25 mm and having a nozzle for blowing hot air at the center were arranged in a staggered manner at a pitch of 11.5 mm. While the cap film was warmed by gently blowing hot air at a temperature of 120 ° C. from the plug nozzle of the preforming roll, an intermediate film was prepared and transferred to a vacuum forming roll as it was to perform vacuum forming. The vacuum suction was performed at the same time without providing a time lag between the two types of suction holes.
[0023]
The product bubble sheet is rigid. The thickness of each part was measured and the following values were obtained.
Cap side wall: 0.5mm
Cap top (cavity bottom): 0.3 mm
Back film single part: 0.35mm
Laminating part of cap film and back film: 0.8mm
[0024]
【The invention's effect】
If a bubble sheet having a wall thickness distribution adjusted according to the technique of the present invention is manufactured, a bubble sheet having a wall thickness adjusted in each part within a certain limit, which has been impossible in the past, is obtained. Depending on the properties required for the product foam sheet, it is possible to produce a desired foam sheet such as a cap with high compressive strength but flexible, or a cap that is not strong but easy to handle. Made possible by the present invention.
[0025]
In the embodiment using a pre-formed roll, since a relatively small difference in the thickness of each part of the bubble sheet is obtained, when targeting a bubble sheet as a structural material that is a thick rigid product, There is an advantage that a product with improved strength per unit weight can be produced.
[Brief description of the drawings]
FIG. 1 is a conceptual cross-sectional view relatively showing a thickness distribution of each part of a cap in a conventional plastic bubble sheet.
FIG. 2 is a cross-sectional view of an essential part showing a first embodiment of an apparatus for producing a plastic foam sheet having an adjusted wall thickness distribution according to the present invention.
FIG. 3 is a cross-sectional view of the main part corresponding to FIG. 2, showing a second embodiment of the apparatus for producing a plastic foam sheet having a controlled wall thickness distribution according to the present invention.
FIG. 4 is a view for explaining one embodiment of a plastic bubble sheet manufacturing method using the apparatus of FIG. 2;
FIG. 5 is a view for explaining another aspect of the plastic bubble sheet manufacturing method using the apparatus of FIG. 2;
[Explanation of symbols]
1 Vacuum forming roll 11 Cavity 12 Vacuum suction hole (almost center of bottom surface)
13 Vacuum suction hole (bottom corner)
2 First Flat Die 3 Second Flat Die 4 Pressure Roll 5 Preliminary Roll 51 Plug 52 Hot Air Nozzle 6A Cap Film Film 6B Intermediate Film

Claims (4)

A cap film having a large number of caps is formed by vacuum forming of a plastic film, and a back film, which is a flat plastic film, is bonded to the bottom surface of the cap to obtain a molded product having a large number of sealed air chambers. A method for producing a plastic foam sheet, which has a large number of cap-shaped cavities with vacuum suction holes at the bottom and is rotatably supported for vacuum forming rolls for forming cap films and discharging film for cap films A manufacturing apparatus comprising a first flat die and a second flat die for discharging a back film, and a pressure roll for bonding the back film to a cap film as essential components, and a vacuum source connected thereto. a method for use, the vacuum suction for molding the cap Starting from the suction through the vacuum suction hole provided at the center of the bottom of the cavity, and subsequently adding suction through the vacuum suction hole provided at the corner of the bottom of the cavity, the ridge portion of the cap is thin. A method for producing a plastic foam sheet characterized by obtaining a molded article. A cap film having a large number of caps is formed by vacuum forming of a plastic film, and a back film, which is a flat plastic film, is bonded to the bottom surface of the cap to obtain a molded product having a large number of sealed air chambers. A method for producing a plastic foam sheet, which has a large number of cap-shaped cavities with vacuum suction holes at the bottom and is rotatably supported for vacuum forming rolls for forming cap films and discharging film for cap films A manufacturing apparatus comprising a first flat die and a second flat die for discharging a back film, and a pressure roll for bonding the back film to a cap film as essential components, and a vacuum source connected thereto. a method for use, the vacuum suction for molding the cap By starting with suction through the vacuum suction holes provided at the corners of the bottom of the cavity and subsequently adding suction through the vacuum suction holes provided at substantially the center of the bottom of the cavity, the thickness of the entire cap is increased. A method for producing a plastic foam sheet, characterized in that a molded product having a small difference is obtained. A vacuum forming roll for forming a cap film that has a large number of cap-shaped cavities with vacuum suction holes at the bottom and is rotatably supported, a first flat die and a back film for discharging the film for the cap film In a plastic foam sheet manufacturing apparatus comprising a second flat die to be discharged and a pressure-bonding roll for attaching a back film to a cap film as an essential component and connected to a vacuum source, the first stage of the vacuum forming roll In addition, a cap that protrudes with a position and shape corresponding to the cavity and has a plug that can blow hot air from the tip thereof, and a preliminarily formed roll that is rotatably supported is arranged, and the cap is discharged from the first flat die. Constructed so that the film for the film reaches the forming roll through the preforming roll Apparatus for producing a plastic foam sheet having an adjusted thickness distribution, characterized in that the. A cap film having a large number of caps is formed by vacuum forming of a plastic film, and a back film, which is a flat plastic film, is bonded to the bottom surface of the cap to obtain a molded product having a large number of sealed air chambers. In the method for producing a plastic bubble sheet, an intermediate having a projection close to a plug shape by using the apparatus described in claim 3 and forming a film for a cap film discharged from a first flat die by a preforming roll. The film is formed into a film, and the protrusion is vacuum formed by a cavity of a vacuum forming roll to form a cap, thereby obtaining a molded product having a small difference in wall thickness between the cap portion and the bottom portion of the cap film. For producing a plastic foam sheet having a distributed thickness distribution.

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