JP2008302565A - Manufacturing method and manufacturing apparatus for plastic bubble sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plastic bubble sheet in which many sealed air cells are formed by molding a melt-extruded plastic film with a vacuum forming roll to make a cap film with many caps and gluing another melt-extruded flat plastic film as a back film on the bottom of the caps and which, when used as a cushioning material, is little of leaving the marks of the caps corresponding to the shape of the caps on the other object having been put into contact and is improved in slipping properties. <P>SOLUTION: By putting a film (2) for the cap film, or the film for the cap film and a film (3) for the back film into contact with one or more temperature controlling rolls (7A, 8A; 7B, 8B) in the course of from T-dies (4A, 4B) and a vacuum forming roll (5), the film temperature is maintained higher than that provided by natural cooling. In the meantime, the low molecular weight substances contained in the plastic material are removed and the bubble sheet is formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an improvement in a method and an apparatus for producing a plastic foam sheet, and when used as a cushioning material, there is no trace of a cap remaining on a contacted partner, and the secondary processing has been improved due to improved slipperiness. Provided is a plastic bubble sheet that can be easily packaged with increased accuracy.

Plastic bubbles, which are made of plastic, typically polyethylene, especially low-density polyethylene, and in which many caps are formed by vacuum forming and flat back films are bonded together to form many sealed air chambers Sheets (hereinafter simply referred to as “bubble sheets”) are mainly used in the field of cushioning packaging, and some are also used as heat insulating materials.

This type of bubble sheet generally uses one or two extruders and two T-dies, and one of the molten plastic films coming out of them is used as a cap film and the other as a back film. A film for a cap film is formed into a cap film by a vacuum forming roll having a large number of dents for vacuum forming and vacuum suction means, and a film for a back film is pasted on the back surface, that is, the bottom surface of the cap as a back film. The product is manufactured by a procedure in which the product is obtained by removing the produced plastic foam sheet from the vacuum forming roll with a peeling roll after being completely integrated with a pressure roll.

At this time, the molten plastic film exiting the T-die reaches the vacuum forming roll as it is and is processed. In plastic processing of plastics, it goes without saying that the resin temperature is generally preferably as low as necessary. Since the film is cooled slightly while traveling in the air and the temperature is lowered, the temperature of the T-die is set slightly higher than the melting temperature in view of it.

The applicant has developed a “cooling and heating method” in which the cap film is once cooled and stretched in the production of a bubble sheet made of polyethylene, especially LDPE, and then heated again to restore plasticity and then turn to molding. Has been implemented. Thereby, the intensity | strength of a film can be raised and a rigid (strong back) bubble sheet can be manufactured. The above-described conventional technique for directly sending a film from a T-die to a vacuum forming roll is referred to as a “direct method” in contrast to the cooling and heating method.

In recent years, new materials, such as LLDPE or polyethylene using a metallocene catalyst, have emerged as a material for the bubble sheet, and products having sufficient strength can be obtained without being stretched. Therefore, the adoption of the direct method, which consumes less energy than the cooling heating method, has come to attract attention again.

On the other hand, in the use as a cushioning material, which is the largest application of the bubble sheet, there may be a case where a “grain mark” corresponding to the shape of the bubble sheet cap is left on the partner with which the bubble sheet is in contact. Was demanded. The generation of grain marks is significant on the side where the top of the cap is in contact, but also on the back film side. Even if the grain mark is generated, if it wipes off and disappears, there is no problem. However, it often remains, and the value of the package is impaired.

Another problem with bubble sheets is low slip between the bubble sheets and between the bubble sheets and other objects. This problem is a specific disadvantage, especially when performing secondary processing such as cutting on long and wide air bubble sheets, resulting in low work efficiency and poor dimensional accuracy of the resulting product. Appear.

The inventor found that the above two problems are more conspicuous in the product by the “direct method” than the product in which the “cooling heating method” is selected as the manufacturing method of the bubble sheet. Paying attention to the fact that the problem is reduced compared to the direct method, the history until the molten plastic film that has exited the T-die is processed by the vacuum forming roll has an effect on the generation of grain marks and the slipperiness. I thought I might give it. In other words, rather than the history that plastic film is extruded and processed as soon as possible, it exists as a molten film in the air at a high temperature for a certain period of time. He had the expectation that the cause would be removed. As a result of the test, it was confirmed that this expectation was met and the present invention was achieved.

Therefore, one object of the present invention is based on the knowledge obtained by the inventor, and when used as a cushioning material in a bubble sheet, leaves marks corresponding to the shape of the cap on other objects that the bubble sheet is in contact with. The other purpose is to provide a product with improved slipperiness.

FIG. 1 shows a manufacturing method for obtaining the foam sheet of the present invention that achieves the above two objects at once, that is, a plastic foam sheet that does not leave a trace of a cap on the contacted partner and has improved slipperiness. As shown in this figure, the plastic film melt-extruded from the T-die is molded with a vacuum forming roll having a large number of dents to form a cap film having a large number of caps. In the method for producing a plastic bubble sheet, comprising a flat plastic film melt-extruded from a T-die of the present invention as a back film and forming a number of sealed air chambers, a film (2) for a cap film, or A film for a cap film and a film for a back film (3) are combined into a T-die (4A, 4B). The vacuum forming roll after leaving the film temperature higher than the temperature given by natural cooling by coming into contact with one or more temperature control rolls (7A, 8A; 7B, 8B) It is sent to (5).

The production apparatus of the present invention for carrying out this production method includes an extruder (not shown) for melt-extruding plastic, a T-die (4A) for extruding a cap film (2), and a back film film ( 3) T-die (4B) for extruding, vacuum forming roll (5) having a large number of dents and vacuum suction means for forming the extruded cap film into a cap film by vacuum forming, back film In an apparatus for producing a plastic foam sheet comprising as essential components a pressure roll (6) for affixing a cap film to the bottom surface of a cap film and a winding means for winding up the produced plastic foam sheet (1) , A path from the T-die (4A) for the cap film to the vacuum forming roll (5), or a cap One or two or more temperature control rolls (7A) on both the path from the T-die for the film to the vacuum forming roll and the path from the T-die (4B) for the back film to the vacuum forming roll (5) , 8A; 7B, 8B), and the film temperature of the film for the cap film from the T-die or the film for the cap film and the film for the back film was kept higher than the temperature achieved by natural cooling. After that, it is configured to be sent to a vacuum forming roll.

According to the present invention, if a bubble sheet is produced by adjusting the temperature of a film for a cap film, or both a film for a cap film and a film for a backfill, the resulting product is used as a cushioning material, After contact with another object for a long time, the mark of the cap is not left on the other object, or the remaining mark is remarkably reduced, so that there is no practical problem. The problem of cap particle marks was particularly seen in plastic products, painted products, etc., so attention had to be paid to such contact with other objects, but the bubble sheet of the present invention Such considerations are not necessary for products.

As described above, the improvement in the slipperiness of the air bubble sheet product brings about the advantage that the workability is greatly improved in the secondary processing such as cutting, punching, folding, bag making, heat sealing and the like. The improvement of the sliding property is also useful for improving the accuracy of the product. For example, even in a simple operation of cutting, the accuracy of the cutting width is 7% with respect to the target within ± 5% in a product with poor sliding. Such a situation sometimes occurs, but with the product of the present invention, the target is sufficiently cleared, and a better result of ± 3% or so can be obtained.

Although the inventor has not yet fully elucidated the mechanism of action by which the production method of the present invention can provide a bubble sheet with less trace of caps and improved slipperiness, it is included in the material plastic as a leading factor. It is possible to eliminate the low molecular weight substances. That is, while the molten plastic film exiting the T-die is kept at a temperature higher than the naturally applied temperature before being formed by the vacuum forming roll, the low molecular weight is removed from the surface of the molten plastic film. Due to the volatilization of the substance, the low molecular weight substance no longer remains on the plastic surface constituting the product bubble sheet, or only a small amount remains, and it does not come into contact with other objects in the use of the bubble sheet. However, it is a mechanism that the surface is less affected.

When taking a typical polyethylene as a material for the bubble sheet and considering its molecular weight distribution, it is inevitable that a substance having a low molecular weight is contained to a greater or lesser extent even if there is a difference depending on the polymerization method. Such low molecular weight materials act like a kind of solvent, as will be readily understood. If the molecular weight is low, it is easy to move inside the polymer, so that it tends to come out on the surface by bleeding, and the influence is considered to be increased in film products.

The effect on slipperiness can be considered similarly. The low molecular weight substance appearing on the film surface has the effect of wetting the film surface of the bubble sheet, and inhibits slippage between the bubble sheets and between the bubble sheet and other objects.

When the molten plastic film exiting the T-die is quickly cooled, the low molecular weight material is fixed to the film surface and transferred to the product. This is the reason why the remaining problems are large in the conventional air bubble sheet products by the direct method. On the other hand, the problem with bubble sheet products using the cooling and heating method is alleviated because the low molecular weight substances are volatilized and removed as a result of the film being heated again to a high temperature prior to processing with the vacuum forming roll. It is done. According to the present invention, the melt-extruded plastic film is kept at a high temperature by a heating roll, and during that time the volatilization of the low molecular weight substance is promoted, and then cooled to a low temperature suitable for vacuum forming to process the cap formation. Thus, low molecular weight substances that cause traces are highly removed.

The above relationship can be conceptually expressed as a graph in FIG. In the conventional direct system from the T-die to the vacuum forming roll, the film is naturally cooled. In the cooling heating method, the temperature once decreases and then increases again. On the other hand, in the case of the present invention, as shown by the solid line, the high temperature after extrusion is maintained for a relatively long time. If it is intended to sufficiently obtain the effect of maintaining a high temperature, it is possible to select a heating temperature higher than the extrusion temperature. Here, as shown in the figure, the solid lines typically show three types of temperature, that is, the temperature of the film extruded from the T-die is increased (A), maintained (B), or gradually cooled (C). And there may be combinations and variations thereof, and “temperature regulation” as used in the present invention encompasses these.

As can be easily understood from the above description, the operation of heating and maintaining the temperature of the melt-extruded film is preferably performed not only on the film for the cap film but also on the film for the back film. . However, in the case of performing only one of them, the film for the cap film should be targeted. This is because the trace residue produced when the cap touches another object is more severe than the trace residue produced when the back film touches the other object.

The film should be heated by a heating roll, and cooling is preferably by a cooling roll, but cooling can also be by natural cooling. However, if the temperature is lowered to a level suitable for vacuum forming by natural cooling, it is often necessary to pass a long pass through the film. Therefore, it is advantageous to avoid the manufacturing apparatus from becoming excessively large by employing other means such as cooling with an air knife arranged immediately before the vacuum forming roll.

Low density polyethylene “Petrocene” (Tosoh) is used as a material, and the apparatus having the configuration shown in FIG. 1, that is, one high temperature roll and one low temperature roll, one for cap film and one for back film, respectively. An air bubble sheet was manufactured using the apparatus arranged in the above manner. Both the high temperature roll and the low temperature roll had an outer diameter of 20 cm, and the surface temperatures were 140 ° C. and 115 ° C., respectively, through a heat medium or cooling water. The temperature of the T-die is 230 ° C, and the surface temperature of the vacuum forming roll is 78 ° C. Therefore, in this case, the melted polyethylene film is gradually cooled and then cooled and sent to a vacuum forming roll.

In this apparatus, between the die lip and the pressure roll on the vacuum forming roll, the cap film passes through a path of 60 cm and the back film passes through a path of 40 cm, and the required time between them is about 0.7 seconds. is there. The obtained bubble sheet is a product having the following specifications.
Cap film: 35 μm
Back film: 20μm
Cap: Staggered arrangement with diameter 10mm, height 4mm, pitch 11.5mm

[Remaining test]
A 10 cm × 10 cm piece was cut out from this bubble sheet, placed on a polystyrene plate slightly larger than that with a cap on the bottom, and a steel plate weighing 500 g was placed on the bubble sheet and a load was applied. It was allowed to stand at room temperature, and it was examined how the trace of the cap remained on the polystyrene plate. For comparison, the same test was performed using the same polyethylene as a material and a bubble sheet of the same specification manufactured by a conventional direct method. After 3 months, the polystyrene plate of the comparative example clearly left a trace of the cap and did not disappear even after wiping, but the trace of the cap substantially did not remain on the polystyrene plate to which the bubble sheet of the present invention was in contact.

[Slidability test]
Cut out two pieces of 15cm x 30cm from the upper air bubble sheet, fix one piece with the cap facing upward, wrap a steel wire around one side of the other piece, and tie a string at both ends to connect to a spring balance It is. The bubble sheets were stacked and a spring balance was pulled with a 500 g steel plate placed thereon, and the value displayed on the spring balance was read when the bubble sheet slipped and moved. For comparison, the same slip property test was carried out using a bubble sheet produced by a conventional manufacturing method as in the case of the trace remaining test. The read values were as follows: Example: 467 g, comparative example: 871 g

The side view which shows an example of the manufacturing apparatus of the bubble sheet according to this invention. The temperature change of the film for a cap film and / or the film for a back film between the T-die and the vacuum forming roll realized in the method for producing a bubble sheet according to the present invention is compared with the conventional production method. Illustrated conceptual graph.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Plastic foam sheet 2 Film for cap films 3 Back film films 4A, 4B T-die 5 Vacuum forming roll 6 Pressure rolls 7A, 8A Temperature control (high temperature) rolls 7B, 8B Temperature control (low temperature) roll

Claims (6)

A plastic film melt-extruded from a T-die is molded with a vacuum forming roll having a large number of dents to form a cap film having a large number of caps, and a flat surface melt-extruded from another T-die on the bottom of the cap. In a method for producing a plastic air bubble sheet comprising attaching a plastic film as a back film to form a large number of sealed air chambers, a film for a cap film (2), or a film for a cap film and a back film The film (3) is brought into contact with one or more temperature control rolls (7A, 8A; 7B, 8B) when coming out of the T-die (4A, 4B). Keep higher than the temperature given by proper cooling and then send to vacuum forming roll (5) Wherein, without leaving a trace of the cap to contact the other party, and manufacturing method for obtaining a plastic bubble sheet slipperiness is improved (1). 2. The operation of keeping the film temperature higher than that given by natural cooling by means of a temperature control roll is carried out by increasing, maintaining or slowly cooling the temperature of the film extruded from the T-die. Manufacturing method. The manufacturing method of Claim 2 which cools the film which maintained temperature high with the air knife provided near the vacuum forming roll. Two temperature control rolls, a high temperature roll (7A) and a low temperature roll (7B) for the film for the cap film, or a high temperature roll (7A, 8A) for the film for the cap film and the film for the back film, and Two low-temperature rolls (7B, 8B) are used, and the film extruded from the T-die is brought into contact with the high-temperature roll, and the temperature of the film is increased, maintained, or gradually cooled, and given by natural cooling. The manufacturing method according to claim 1, which is carried out after being kept at a temperature higher than the temperature to be cooled and then cooled to a low temperature roll and sent to a vacuum forming roll. The manufacturing method in any one of Claims 1-4 implemented using low density polyethylene as a plastic material. Extruder for melt extrusion of plastic, T-die (4A) for extruding cap film (2), T-die (4B) for extruding back film (3), and vacuum for extruding cap film Vacuum forming roll (5) having a large number of dents and vacuum suction means for forming a cap film by molding, a pressure roll (6) for attaching a back film to the bottom surface of the cap film cap, and manufacturing Path from the T-die (4A) for the cap film to the vacuum forming roll (5) in the plastic bubble sheet manufacturing apparatus having a winding means for winding the plastic bubble sheet (1) as an essential component. , Or path from T-die for cap film to vacuum forming roll and back One or two or more temperature control rolls (7A, 8A; 7B, 8B) are provided on both the path from the film T-die (4B) to the vacuum forming roll (5), and the film exits from the T-die. The film temperature for the cap film, or the film for the cap film and the film for the back film is kept higher than the temperature reached by natural cooling and then sent to the vacuum forming roll. A manufacturing apparatus for obtaining a plastic bubble sheet that does not leave a trace of a cap on the contacted partner and has improved slipperiness.

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