JPH11129366A - Plastic cellular sheet and apparatus for producing same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the low product dimensional accuracy caused by the extension and contraction at a time of secondary processing, in a long product of a plastic cellular sheet having a large number of hermetically closed cells formed thereto, by arranging respective cells zigzag so as to position them on straight lines in relation to a longitudinal direction. SOLUTION: A molding roll 4 subjects the plastic film extruded from one T-die 3a to vacuum molding to provide a large number of depressions to form a cap film CF. A press roll 5 presses the back film BF being the flat plastic film extruded from other T-die 3b to the cap film CF on the molding roll 4 to fuse both films to form a cellular sheet 1A. The formed cellular sheet 1A is taken over by a taking-over means 6. Herein, a large number of the depressions 41 of the molding roll 4 are arranged on a large number of straight lines along the periphery of the roll to be present zigzag.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a plastic foam sheet, and also relates to an apparatus for producing the foam sheet.

[0002]

2. Description of the Related Art A film made of plastic represented by polyethylene and provided with a large number of recesses (called a "cap film") and a flat film (called a "back film") are bonded together. Produced sheets with a large number of closed cells are widely used primarily as cushioning material for packaging. There are various grades of bubble size depending on the application.
Some plastic films (called "liner films") are laminated to form a three-layer structure.
Many of these plastic foam sheets are shipped in the form of long rolls and are subjected to secondary processing such as cutting, punching, and folding in the longitudinal and / or width directions.

[0003] There are various demands for the dimensional accuracy of such a secondary processed product depending on the application. For example, the inner surface of a paper envelope with this foam sheet lining is manufactured and sold as a "buffer envelope" with a function to protect the contents. If the accuracy is low, the end of the bubble sheet is separated from the paper in the envelope or protrudes into the folded portion, thereby deteriorating the commercial value. A bubble sheet to be used as an insole or overlay for a can serving as a container for confectionery must be cut or punched with high precision because the function is incomplete if it is too small and it will not fit in the can if it is too large.

[0004] However, it has been difficult to increase the dimensional accuracy of the secondary processed foam sheet. In pursuit of the reason, when the bubble sheet is drawn out from a long roll and subjected to secondary processing, the tension applied to the bubble sheet changes variously due to the relationship between the take-up speed of the pinch roll and the resistance to feeding. It was found that the bubble sheet expands and contracts accordingly.

[0005]

SUMMARY OF THE INVENTION A first object of the present invention is to improve the low product dimensional accuracy caused by expansion and contraction during secondary processing, which is inevitable in conventional plastic foam sheets, and to achieve the required accuracy. It is an object of the present invention to provide a plastic foam sheet that can easily obtain a secondary processed product having the following.

A second object of the present invention is to provide an apparatus suitable for producing such a plastic foam sheet.

[0007]

As shown in FIG. 1, a plastic foam sheet according to the present invention is obtained by laminating a cap film provided with a number of depressions on a plastic film and a back film which is a flat plastic film. In a long product of a plastic foam sheet (1A) in which a number of closed air bubbles are formed, each air bubble (2)
However, it is characterized in that it is arranged in a staggered manner located on a straight line in the longitudinal direction.

As shown in FIG. 2, the conventional product is an air bubble sheet (1B) in which air bubbles (2) arranged in a staggered manner are arranged in a straight line in the width direction. The staggered arrangement is an arrangement that must be selected in order to increase the density of bubbles per unit area and obtain a sufficient buffer capacity. In the conventional arrangement of FIG. 2, since a bubble portion which is relatively easily deformed due to a tensile stress and a bonded portion which is relatively hard to deform exist in a zigzag, stress dispersion occurs when a tensile stress is applied in the longitudinal direction. Easy to stretch in the longitudinal direction even with slight tensile stress. In contrast, in the staggered bubble sheet according to the present invention, as shown in FIG.
Since the bubble portion and the bonded portion are arranged in series with respect to the longitudinal stress, and the spacing of the bubbles on the straight line in the longitudinal direction is narrow, it is difficult for stress dispersion to occur, and the elongation also occurs for the same tensile stress. Is small.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The plastic foam sheet of the present invention can be manufactured in the same manner as a conventional product, except for the arrangement of bubbles. That is, as a material, a common polyethylene, a polyolefin such as polypropylene, an ethylene-vinyl acetate copolymer, nylon, and other various plastics can be used. The bubbles typically have a low columnar shape, which can be easily manufactured in a vacuum forming mold, but any shape such as a prism having a round pillar or a rounded vertex can be selected. Its dimensions can also be selected from a wide range,
The most demanding dimensions are diameter D of 6 to 50 mm and height of 2 to 3
0 mm, and the arrangement pitch is (1.1 to 1.
5) D, (1.0 to 1.5) D in the width direction.

As shown in FIG. 3, the apparatus of the present invention for producing the above plastic foam sheet is an extruder (not shown) for melting and extruding plastic, and two T dies. (3a, 3b), a plurality of dents connected to vacuum suction means for forming a cap film (CF) by forming a large number of dents by vacuum forming a plastic film extruded from one T-die (3a). Roll (4) provided with a back film (BF), which is a flat plastic film extruded from the other T die (3b), is pressed against the cap film (CF) on the forming roll (4). Press roll (5) for fusing and fusing to form a foam sheet, and take-up means (6) for drawing off the formed foam sheet (1A). In the device made, a number of depressions of the molding roll (4) (41) is disposed on a plurality of straight line along the circumference of the roll, and characterized in that it exists in a staggered manner.

[0011] Any technique known in the art can be arbitrarily applied to the above-mentioned bubble sheet manufacturing apparatus. For example,
As shown in FIG. 3, a cooling roll (for cooling the film once) from the T die (3b) for extruding the back film (BF) to the press roll (5) for fusing with the cap film (CF). 8) and a reheating roll (9) for reheating the cooled film to restore the heat fusibility, and the back film (BF) is extruded between the two rolls (8, 9). In this embodiment, the rotational speeds of both rolls are set so as to receive a slight stretching in the direction. This embodiment is implemented when a plastic sheet such as low-density polyethylene is used as a material, and the foam sheet product has a certain rigidity, that is, when a so-called "tough" product is obtained. The present invention can also be employed.

The reason why the conventional plastic foam sheet generally arranges the bubbles as shown in FIG. 2 is due to the convenience of manufacturing the device. That is, the method of providing a cavity in a vacuum forming roll for manufacturing a cap film has heretofore traditionally been performed manually using a drilling machine. The work involves fixing the material whose cross section forms a part of an arc with the dimensions of the roll surface divided into several parts, making holes in the cavities for it, and shifting the tool in the axial direction at regular intervals. It is a repetition of the work of drilling holes.

However, with the recent advance in machining technology, the use of an NC-controlled machining center has made it possible to perform high-precision drilling work based on a position determined by a computer without manual work. became.
The vacuum forming roll, which is a feature of the apparatus of the present invention, has thus realized the arrangement of bubbles shown in FIG.

Providing cavities for molding bubbles on a straight line in the circumferential direction makes it easy to arbitrarily select the number of cavities provided in one round, even or odd. According to the method of manufacturing the conventional device described above,
Since the target is a material whose circumferential surface is divided into several parts (usually 8 to 24), it is difficult to manufacture unless an even number of cavities are arranged in the circumferential direction. It was close to

Although this is not a problem in an apparatus for producing a bubble sheet having relatively small bubbles,
The problem is exacerbated in the production of vacuum forming rolls with large bubbles. For example, when arranging cavities having a diameter of 30 mm on a vacuum forming roll having an outer diameter of about 300 mm, the circumference is about 942 mm.
If we try to do it (pitch 40mm), it will be an odd number of 23.5, so we have to select 24.
As a result, the distance between the bubbles is reduced to 9.2 mm. If cavities are provided on the circumferential straight line by using an NC control drilling machine as in the present invention, it is possible to reduce the number of cavities to 24 (23 spaces) (the interval between bubbles is 10.9 mm).
Therefore, the degree of design freedom is higher.

[0016]

EXAMPLE A cavity having a diameter of 10 mm and a depth of 4 mm was formed on a vacuum forming roll having an outer diameter of 300 mm and a length of 1200 mm at a pitch of 11.49 mm on the circumference and a pitch of 10.0 mm in the axial direction.
Four cavities were provided so that the row of cavities existed over 110 cavities in the axial direction, that is, about 1100 mm. This makes the cavity arrangement of a conventional vacuum forming roll 90 °.
It has been converted.

Using this vacuum forming roll, a bubble sheet was manufactured using a common low-density polyethylene material and an apparatus having a set of rolls for cooling and reheating as shown in FIG.
Make a cut on both ears, and make the width 1200mm x length 20
A roll of 0 m bubble sheet was made.

While pulling the foamed sheet product once rolled with a pinch roll, slit it to a width of 100 mm with a round blade slitter in the direction along the flow, that is, in the longitudinal direction, and then with a guillotine blade at intervals of 200 mm. Cut in the width direction of an automatic cutter with a length of 200 mm
A rectangular cut product having a width of 100 mm was obtained.

The variation in the dimension in the longitudinal direction of 100 products was examined and found to be within ± 2.3%.
When the same cutting device was used to process a bubble sheet having the same bubble size and pitch but the conventional bubble arrangement, ie, the arrangement shown in FIG. 2, it was not easy to reduce the variation to ± 5% or less.

[0020]

According to the plastic foam sheet of the present invention, the longitudinal expansion is small in the secondary processing of a long product by selecting the arrangement of the bubbles different from the conventional product. A processed product having high dimensional accuracy can be obtained. Therefore, it is possible to easily meet demands requiring high dimensional accuracy, such as the above-mentioned buffer envelope lining and confectionery can rugs.
The fact that the elongation in the longitudinal direction is small naturally means that the contraction in the width direction is also small.

[0021] The above effects also lead to the merit that, when the required accuracy is not high, there is no need to use a high-precision apparatus for the secondary processing, or special attention or skill is not required. Specifically, products that had been punched can be switched to cutting,
This has the advantage of eliminating the need for punching dies.

When the bubble sheet is pulled by a pinch roll, the conventional arrangement of the bubbles causes the rolls to successively cross the rows of the bubbles arranged in a line in the width direction, and as a result, contact occurs. Intermittent and rattling occurs. With the bubble arrangement according to the present invention, the roll rides on one of the longitudinally aligned sets of every other bubble,
Contact is continuous and there is no backlash. This also contributes to reducing the variation caused by the tension caused by the pinch roll, and consequently improving the dimensional accuracy.

The vacuum forming roll, which characterizes the apparatus, allows a high degree of design freedom and enables the production of a foam sheet product of the desired cell size and arrangement.

[Brief description of the drawings]

FIG. 1 is a plan view showing the arrangement of bubbles in a plastic foam sheet of the present invention.

FIG. 2 is a plan view showing the arrangement of bubbles in a conventional plastic bubble sheet.

FIG. 3 is an explanatory view showing the configuration of a conventional plastic foam sheet manufacturing apparatus.

FIG. 4 is a plan view showing an arrangement of forming recesses in a forming roll forming a part of the apparatus of FIG. 3;

[Explanation of symbols]

 1A Plastic foam sheet of the present invention 1B Conventional plastic foam sheet L Longitudinal direction W Width direction 2 Bubbles 3a One T die (for cap film) 3b The other T die (for back film) 4 Vacuum forming roll 41 Depression for forming Reference Signs List 5 press roll 6 take-up roll 7 roll 8 cooling roll 9 reheating roll CF cap film BF back film

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI // B29K 23:00 105: 04 B29L 9:00

Claims (4)

[Claims] 1. A long product of a plastic foam sheet in which a plastic film provided with a number of dents in a plastic film and a back film which is a flat plastic film are bonded together to form a number of closed cells. A plastic bubble sheet, wherein each bubble is arranged in a staggered manner located on a straight line in the longitudinal direction. 2. A cylindrical body having low air bubbles, using polyethylene as a plastic, and having a diameter D of 6 to 50 m.
m, the height is 2 to 30 mm, and the arrangement pitch is (1.1 to 1.5) D in the longitudinal direction and (1.0 to 1.5) in the width direction.
1.5) The plastic foam sheet according to claim 1, which is D. 3. An extruder for melting and extruding plastic, two T dies, and a plastic film extruded from one of the T dies for forming a cap film by vacuum forming a plurality of recesses to form a cap film. A forming roll provided with a number of dents connected to the vacuum suction means, and a back film as a flat plastic film extruded from the other T-die are pressed and fused on the cap film on the forming roll to form an air bubble. In a device essentially formed from a press roll for forming a sheet and a take-off means for drawing off the formed foam sheet, a number of depressions of the forming roll are arranged in a number of straight lines along the circumference of the roll. And a staggered plastic foam sheet manufacturing apparatus. 4. A cooling roll for cooling a film once during a period from a T-die for extruding a back film to a press roll for fusing with a cap film, and a heat-fusing property by reheating the cooled film. 5. The bubble sheet manufacturing apparatus according to claim 4, further comprising a reheating roll for recovery, wherein the rotation speed of both rolls is set so that the back film is slightly stretched in the extrusion direction between the two rolls.