JP2003039545A - Method for manufacturing expanded resin sheet, expanded resin sheet and embossing roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for continuously forming irregularities on an expanded resin sheet as per the pattern of an embossing roll and an expanded resin sheet which shows high cushioning properties and permeability to air and is suitably used as a cushioning material. SOLUTION: This method for manufacturing the expanded resin sheet comprises the steps to extrude a resin sheet containing a foaming agent in the form of a sheet through a T-die 5, then continuously solidify the sheet between the embossing roll 8 and a cooling roll 9 positioned opposite to the former and form an embossment. In addition, the method is characterized in that the internal pressure of a recessed part 19 of the embossing rolls is reduced. That is, the internal pressure of the recessed part 19 of the embossing roll 8 is reduced at a position where the molten resin extruded in the form of a sheet is brought into contact with the embossing roll 8 and the internal reduced pressure of the recessed part 19 of the embossing roll 8 is preferably restored to a normal pressure level at a position where the solidified sheet is released from the embossing roll 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a foamed resin sheet, and in particular, a molten resin containing a foaming agent is extruded into a sheet form from a die, and the embossing roll and a cooling roll facing it are continuously fed. The present invention relates to a method for producing a foamed resin sheet which is solidified to form an embossed shape. Further, the present invention relates to a foamed resin sheet having a plurality of independent protrusions on one surface. Furthermore, the present invention relates to an embossing roll for imparting a concavo-convex shape to a sheet-shaped molded product.

[0002]

2. Description of the Related Art Foamed resin sheets are widely used as cushioning materials for protecting various articles and heat insulating materials in the field of construction. When used as a cushioning material, a foamed resin sheet having an uneven surface is often used, and it is preferable to form a deep uneven shape in order to obtain good cushioning properties. As one method for forming a deep uneven shape, there is known a method in which a flat foamed resin sheet is melt-molded in advance and cut and then vacuum-formed by heating each sheet.

Further, Japanese Patent Laid-Open No. 7-24913 discloses that
In a roll forming method in which a resin foam sheet is compressed with an embossing roll and a pinch roll, and shaped, in the embossing roll, a large number of recesses and air vent holes at the bottom of the recesses are provided, and the embossing roll and the pinch roll are formed. A roll forming method for a resin foam sheet is described, which comprises compressing the resin foam sheet to a thickness of 1/4 or less by a clearance. According to the method, when the foam flows into the recess, the air existing in the recess is discharged from the air vent hole, and the molding is performed as the mold.

[0004]

However, as described above, in the case of vacuum-forming by heating one by one, the productivity is lower than that in the case of continuous molding. Further, when a hydrocarbon gas such as butane is used as a foaming agent, the gas forming bubbles during extrusion molding is absorbed again in the resin during storage and foams again during reheating. Sometimes. That is, depending on the type of the foaming agent, a problem is likely to occur in reproducibility of moldability during embossing.

Further, according to the method disclosed in Japanese Patent Laid-Open No. 7-24913, since the thickness is compressed to ¼ or less, the content of bubbles is reduced by the amount of compression, resulting in poor cushioning. I have a problem. In addition, there are cases where it is desired to give air permeability to the foamed resin sheet depending on the application, but it is difficult to give air permeability with such a high compression rate.

The present invention has been made in order to solve the above problems, and provides a method for continuously forming a concavo-convex shape as an embossing roll on a foamed resin sheet. Further, the present invention provides a foamed resin sheet having an emboss with excellent air permeability. Further, the present invention provides an embossing roll that is preferably used in the above manufacturing method.

[0007]

[Means for Solving the Problems] The above-mentioned problems are solved by extruding a molten resin containing a foaming agent into a sheet form from a die and continuously solidifying it between an embossing roll and a cooling roll facing the embossing roll to form an embossed shape. A method for manufacturing a foamed resin sheet to be formed, which is achieved by providing a method for manufacturing a foamed resin sheet, characterized in that the pressure inside the recess of the embossing roll is reduced. By reducing the pressure in the recess of the embossing roll, the molten resin can be easily filled in the recess, and the product sheet can be provided with an uneven shape as the embossing roll has.

At this time, the inside of the recess of the embossing roll is depressurized at the position where the molten resin extruded in the form of a sheet is brought into contact with the embossing roll, and the position of the embossing roll is depressurized at the position where the solidified sheet is peeled from the embossing roll. It is preferable to release the above because the shaping and the releasing can be smoothly performed.

Further, at this time, the embossing roll comprises a fixed inner ring and a rotatable outer ring, the inner ring is connected to a pressure reducing device, and the outer ring is formed from an embossed concave portion formed on the outer peripheral surface thereof. It is preferable to have a through hole to the inner peripheral surface, and to decompress the inside of the recess via the through hole from a pressure reducing groove formed in a part of the outer peripheral surface of the inner ring.

The above problem can also be solved by providing a foamed resin sheet having a plurality of independent projections on one surface and having air permeability from the one surface to the other surface in the flat portion. It Such a foamed resin sheet has excellent cushioning properties due to independent protrusions and has good air permeability, and thus is useful as a cushioning material for packaging fresh foods, for example, fruits and vegetables. Further, at this time, it is preferable that the foamed resin sheet is made of a thermoplastic synthetic resin and starch, from the viewpoint of environmental protection because the cushioning material is easily biodegraded.

Further, the above-mentioned problem is composed of a fixed inner ring and a rotatable outer ring, wherein the inner ring is connected to a pressure reducing device, and the outer ring is formed from an embossed concave portion formed on the outer peripheral surface thereof to the inner peripheral surface. It is also achieved by providing an embossing roll which has a through hole and which can reduce the pressure in the concave portion through the through hole from the pressure reducing groove formed in a part of the outer peripheral surface of the inner ring. This embossing roll is useful because it can give an uneven shape as the embossing roll has on the surface of the product.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The molten resin containing a foaming agent used in the present invention is not particularly limited, and various thermoplastic synthetic resins can be used. For example, polyolefins such as polyethylene and polypropylene, polystyrene, polyester, and the like can be exemplified. Among them, polyolefin, particularly polyethylene is preferable because it has excellent flexibility.

In particular, in addition to the above-mentioned thermoplastic synthetic resin, it is preferable to contain a carbohydrate, especially starch, because the foamed resin sheet obtained has biodegradability. Since many cushioning materials are discarded after packaging, transportation, or display, it is extremely useful that the foamed resin sheet has biodegradability. The type of starch used is not particularly limited, but it is preferable to use modified starch because it is easy to melt-mold. The amount of starch is not particularly limited, but is preferably 5 to 100 parts by weight, and more preferably 10 to 50 parts by weight, based on 100 parts by weight of the thermoplastic synthetic resin.

Further, in order to improve the melt moldability of the added carbohydrate, it is preferable to contain a plasticizer. The type of plasticizer is not particularly limited, but a hydrophilic plasticizer, specifically water or alcohol, is suitable. From the viewpoint of easy handling and safety, various polyols such as ethylene glycol, polyethylene glycol and glycerin are particularly preferable. The content of the plasticizer is not particularly limited, but starch 10
An amount of 10 to 100 parts by weight is suitable for 0 part by weight.

The molten resin of the present invention contains a foaming agent,
The type is not particularly limited. It may be a volatile foaming agent composed of a substance having a boiling point equal to or lower than the melt molding temperature,
It may be a decomposing type foaming agent composed of a substance that decomposes to generate a gas at a high temperature. Examples of the volatile foaming agent include aliphatic hydrocarbons such as propane, butane, pentane and hexane, and inert gases such as carbon dioxide gas, nitrogen and argon. Examples of the decomposition-type foaming agent include organic compounds such as hydrazine compounds, guanidine compounds and triazine compounds, and inorganic compounds such as metal azodicarboxylate salts. A suitable amount of the aliphatic hydrocarbon used is 0.2 to 5 parts by weight per 100 parts by weight of the thermoplastic synthetic resin.

It is preferable that the molten resin of the present invention further contains bacterial cells capable of decomposing carbohydrates, such as lactic acid bacteria, since the biodegradability is further improved. In addition, it is also suitable to mix inorganic fine particles as a foam nucleation material in order to cause uniform foaming when foaming. Examples of such inorganic fine particles include talc, calcium carbonate, calcium oxide, kaolin, alumina and the like. The blending amount is not particularly limited, but a suitable blending amount is the thermoplastic synthetic resin 100.
It is about 2 to 20 parts by weight with respect to parts by weight.

The compound other than the thermoplastic synthetic resin may be compounded in advance with the thermoplastic synthetic resin to prepare a so-called masterbatch and then compounded. By doing so, the compounding work becomes easy, and a homogeneous molded product is easily obtained.

The present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of the entire molding apparatus of the present invention.
2 is a sectional view taken along the line AA ′ of FIG. 1, and FIG. 3 is a sectional view taken along the line BB ′ of FIG.

A thermoplastic synthetic resin is charged from a resin charging section 2 of the extruder 1. At the same time, starch, inorganic fine particles, plasticizer, etc. can be added. When the foaming agent used is a decomposing type foaming agent, it is also possible to add it at the same time. The resin charged into the extruder 1 is melt-kneaded. When the foaming agent used is a volatile foaming agent, it is melt-kneaded and then charged into the extruder 1 through the foaming agent charging port 3. Further, when lactic acid bacteria are charged, the lactic acid bacteria are charged in the form of a solution from the lactic acid bacteria charging port 4 on the further downstream side. The melting temperature varies depending on the type of thermoplastic synthetic resin used, but is 150 when polyethylene is used.
An example is about 250 ° C.

The molten foamed resin sheet 6 extruded in a sheet form from the T die 5 at the tip of the extruder 1 passes between the infrared heaters 7 for keeping the heat, and between the embossing roll 8 and the cooling roll 9 facing it. Sent in. Since the molding is performed immediately after extrusion, the amount of heat required by the infrared heater 7 is not so high and may not be used depending on the case. The cooling roll 9 is hollow and allows cooling water to flow inside, and rotates in the direction along the sheet flow. The expansion ratio of the melt-foamed resin sheet is not particularly limited, but it can be expanded to a ratio of about 10 to 50 times. The foamed resin sheet 10 in which an uneven shape is formed between both rolls and solidified is peeled from the embossing roll 8 when passing through the peeling roll 11 rotating in the direction along the sheet flow, and the belt is hung on the rotating shaft. Structure take-up machine 12
To be taken over. The foamed resin sheet 10 that has passed through the take-up machine 12 is cut by a cutter 13, and product sheets 14 are continuously manufactured.

The embossing roll 8 comprises an inner ring 16 fixed to the shaft 15 and an outer ring 17 rotatable with respect to the shaft 15. The outer ring 17 has an embossed shape formed on its outer peripheral surface 18 and has a plurality of recesses 19. All recesses 19
A through hole 21 is provided from to the inner peripheral surface 20. The outer surface of the inner ring 16 is covered with rubber 22, and the outer ring 17
It is slidable on the inner peripheral surface 20. A substantially rectangular decompression groove 23 is formed on the surface of the inner ring 16, and a decompression hole 24 communicating with the shaft 15 is provided from the bottom surface of the decompression groove 23 so that the inside of the decompression groove 23 can be decompressed. The cooling roll 9 is filled with the cooling water 25, and is introduced from the cooling water introduction pipe 26 and led out from the cooling water discharge pipe 27 to circulate the cooling water 25.

The molten foamed resin sheet 6 guided between the embossing roll 8 and the cooling roll 9 is the embossing roll 8
The pressure reduction groove front end portion 28 of the inner ring 16 is located near the position where On the downstream side of this position, the through hole 21 of the outer ring 17 is located on the pressure reducing groove 23, so that the inside of the recess 19 is depressurized, and as a result, the molten foamed resin is easily filled inside the recess 19. In order to fill the inside of the recess 19 with the molten foamed resin, it is not necessary to strongly compress the molten foamed resin in contact with the portion other than the recessed portion 19, so that the foamed resin sheet is not unnecessarily compressed, and the foaming ratio is increased. It is possible to obtain a foamed resin sheet having a large size.

The rear end portion 29 of the pressure reducing groove of the inner ring 16 is located near the position where the foamed resin sheet 10 contacts the peeling roll 11. On the downstream side of this position, the through hole 21 of the outer ring 17 is disengaged from above the pressure reducing groove 23, whereby the pressure reduction is released.
As a result, the foamed resin sheet 10 is attached to the embossing roll 8
Can be easily peeled off. Further, since only the portion covered with the foamed resin is depressurized and the other portions are not depressurized, air from the outside does not directly flow into the depressurization groove 23 through the through hole 21. The outer peripheral surface of the inner ring 16 is covered with the rubber 22 except for the pressure reducing groove 23, and the inner peripheral surface 20 of the outer ring 17 comes into contact with and slides.
The degree of pressure reduction inside the pressure reducing groove 23 does not unnecessarily decrease.

The embossing roll of the present invention as described above can be used for various embossing sheets. It is particularly useful for molding foamed resin sheets, but moldings other than that are also possible. The embossed shape can be changed as appropriate by changing the surface shape of the embossing roll.

The manufacturing method described above is suitable for manufacturing a foamed resin sheet having independent protrusions, because the shape of the recess can be transferred as a mold even with an embossing roll having independent recesses. Is. At this time,
Since the resin is not pushed into the recess by compression but is pulled into the recess by depressurization, a foamed resin sheet having a high expansion ratio and excellent cushioning properties can be manufactured. At the same time, the breathability of the sheet tends to be good.

The preferred form of the foamed resin sheet of the present invention is
A foamed resin sheet having a plurality of independent protrusions on one surface and allowing ventilation from one surface to the other surface in a flat portion. Excellent cushioning is achieved by forming independent protrusions. At this time, since there is little variation in the shape of the protrusion, it can be used as a cushioning material having uniform performance depending on the location. The height of the protrusion is preferably 30% or more, and more preferably 50% or more with respect to the total thickness of the sheet. Also, instead of a closed cell structure,
It is useful as a cushioning material for packaging fresh foods, for example, fruits and vegetables, since it is easy to have a structure mainly having an open cell structure and has good air permeability. Suitable expansion ratio is 2
It is 0 to 60 times, and more preferably 30 to 50 times. The thick protruding portion contributes to cushioning, while the flat portion is thin and has open cells, resulting in excellent breathability. The ratio of the closed cell structure to the open cell structure can be appropriately adjusted depending on the production conditions, and it is also possible to produce a sheet having an open cell structure depending on the application.

Conventionally, several kinds of cushioning materials for packing fruits and vegetables, for example fruits, have been known. For example, in the method of individually wrapping fruits with a tubular net, it is possible to prevent contact between fruits arranged on the left and right, but usually contact between fruits in the vertical direction cannot be prevented. , It is necessary to use a buffer sheet separately. As such a cushioning sheet, when a net-like sheet made by knitting a string-like body of foamed resin is used, cushioning properties are not sufficient, for example, in the case of fruits having stems such as apples, The stem may damage the fruit in the upper row. On the other hand, a so-called air cap obtained by heat-sealing a flat film and a concavo-convex film still has insufficient air permeability even if a needle hole is formed in the flat portion, and the emission of water, ethylene gas, etc. is insufficient. And the fruits were easy to damage.

The foamed resin sheet of the present invention has excellent cushioning properties and air permeability, and is extremely useful as a cushioning material when packaging fruits and vegetables. Further, at this time, when a carbohydrate such as starch is contained, the water absorption, water retention and biodegradability are also excellent. In addition, since carbohydrate has a smaller combustion energy than polyolefin, the energy released during combustion is small and the furnace is less damaged during incineration.

[0029]

EXAMPLES The present invention will be further described below with reference to examples. The compounding ratio of the raw materials charged into the extruder for producing the melt-foamed resin sheet in the present invention is as follows.・ Polyethylene 50 parts by weight ・ Polyethylene masterbatch with modified starch 35
Parts by weight (starch / polyethylene = 60/40 (weight ratio))-Glycerin containing lactic acid bacteria 10 parts by weight-Polyethylene masterbatch containing talc 5 parts by weight (talc / polyethylene = 90/10 (weight ratio))-Butane 0.7 parts by weight Department

Using the above raw materials, a foamed resin sheet was prepared using the apparatus shown in FIG. The polyethylene, the polyethylene masterbatch containing modified starch and the polyethylene masterbatch containing talc were charged into the extruder 1 from the resin charging section 2 of the extruder 1 and melt-kneaded. After melt-kneading, butane was injected through the foaming agent charging port 3, and lactic acid bacterium-containing glycerin was injected through the lactic acid bacteria charging port 4 on the downstream side. The set temperature of the cylinder of the extruder 1 is 180 ° C. in the melt-kneading region immediately downstream of the resin charging unit 2, 150 ° C. in the foaming agent charging port 3, 130 ° C. in the lactic acid bacterium charging port 4, and the T die 5 from the downstream. Were set to 80 ° C.

The molten foamed resin sheet 6 having a thickness of about 6 mm extruded from the T die 5 was guided between the embossing roll 8 and the cooling roll 9. Emboss roll 8 has a diameter of 15m
Columnar recesses 19 having a depth of m and a depth of 5 mm were two-dimensionally formed at equal intervals, and the clearance between the embossing roll 8 and the cooling roll 9 was 4 mm.

The foamed resin sheet 10 thus obtained has a shape as shown in FIG. 4, the flat portion 30 has a thickness of 3 mm, the cylindrical protrusions 31 have a diameter of 15 mm and a height of 5 mm. The surface shape of was clearly transferred. The expansion ratio of the entire sheet was about 40 times. When the mouth was put on the sheet and the air was blown, it was confirmed that the flat portion 30 could be ventilated from the front surface to the back surface. On the other hand, on the upper surface 32 of the protrusion 31, a continuous skin layer was formed, and it was confirmed that this portion did not vent. It is not clear why only the upper surfaces 32 of the protrusions 31 cannot be ventilated, but such a structure provides high air bubble strength at the protrusions and good cushioning properties, while at the same time providing air permeability for the entire seat. Can have.

[0033]

According to the molding method of the present invention, there is provided a method for continuously forming a concavo-convex shape as an embossing roll on a foamed resin sheet. Further, there is provided a foamed resin sheet which is excellent in cushioning property and air permeability and is preferably used as a cushioning material. When the foamed resin sheet contains a carbohydrate such as starch, it is excellent in biodegradability, water absorption and water retention and is particularly suitable for packaging fruits and vegetables.

[Brief description of drawings]

FIG. 1 is a schematic view of an entire molding apparatus of the present invention.

FIG. 2 is a cross-sectional view taken along the line A-A ′ of FIG.

FIG. 3 is a sectional view taken along line B-B ′ of FIG.

FIG. 4 is a perspective view of a foamed resin sheet obtained in an example.

[Explanation of symbols]

1 extruder 5 T die 8 embossing roll 9 Cooling roll 19 recess 21 through holes 23 Decompression groove

Claims (6)

[Claims] 1. A method for producing a foamed resin sheet, in which a molten resin containing a foaming agent is extruded from a die into a sheet shape and continuously solidified between an embossing roll and a cooling roll facing the embossing roll to form an embossed shape. The method for producing a foamed resin sheet, wherein the pressure inside the recess of the embossing roll is reduced. 2. The pressure in the recess of the embossing roll is reduced at a position where the molten resin extruded into a sheet shape is brought into contact with the embossing roll, and the reduced pressure state in the recess of the embossing roll is removed at a position where the solidified sheet is separated from the embossing roll. The method for producing a foamed resin sheet according to claim 1, which is released. 3. An inner ring having an embossing roll fixed thereto,
A rotatable outer ring, the inner ring is connected to a pressure reducing device, the outer ring has a through hole from an embossed recess formed on the outer peripheral surface to the inner peripheral surface, and a part of the outer peripheral surface of the inner ring The method for manufacturing a foamed resin sheet according to claim 1, wherein the inside of the recess is depressurized from the depressurization groove formed on the substrate through the through hole. 4. A foamed resin sheet having a plurality of independent protrusions on one surface and having air permeability from one surface to the other surface in a flat portion. 5. The foamed resin sheet according to claim 4, which comprises a thermoplastic synthetic resin and a carbohydrate. 6. A fixed inner ring and a rotatable outer ring, wherein the inner ring is connected to a pressure reducing device, and the outer ring has a through hole from an embossed concave portion formed on the outer peripheral surface to the inner peripheral surface. And an embossing roll capable of reducing the pressure in the recess through the through hole from a pressure reducing groove formed in a part of the outer peripheral surface of the inner ring.