JPH0542600A - Shrinkable sheet - Google Patents

Abstract

PURPOSE:To obtain a shrinkable sheet which is superior in the secondary processability and possesses water absorbing properties and heat shrinkability, by a method wherein thermoplastic molding is performed of polyalkylene oxide into a sheetlike state and the same is oriented after the same is made into a crosslinked polyalkylene oxide sheet by applying ionizing radiation to the sheetlike polyalkylene oxide. CONSTITUTION:Polyethylene oxide or an ethylene oxide copolymer singly or blended polyalkylene oxide is processed into a sheetlike state by making use of a single shaft extruder. Then ionizing radiation such as electron rays or gamma rays are applied to the sheet by an electron ray irradiation device and the polyalkylene oxide is insolubilized by crosslinking the same. Then the same is oriented in a uniaxial or biaxial direction by flat orientation or tubular orientation. With this construction, in the case where heat shrinkable processing is performed by coating foodstuffs with this, a shrinkable coated body can be formed as water absorbing properties are kept on. To use for which water absorbing properties are not required, shrinkable processing not by heat becomes possible by bringing an article into contact with water after the article is coated with the title sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer sheet having a property of shrinking by heat or moisture, a packaging material,
The present invention provides a sheet useful as a material for covering electric wires, a material for labels, and the like.

[0002]

2. Description of the Related Art In recent years, the degree of utilization of water-absorbing polymer products represented by disposable paper diapers has increased. The water-absorbent polymer is selectively imparted with properties relating to water regulation such as high water-absorption and water retention depending on its use. As the water-absorbent polymer, polyvinyl alcohol type, polyacrylic acid type and the like are known, and the powder and fibrous form are well known. However, these forms of water-absorbent polymer have poor secondary processability such as stretching and compounding, and are difficult to fix by themselves, so that they may be dispersed and retained on a fibrous base material such as paper or nonwoven fabric. It is currently being used as For this reason, it is inferior in handleability as a packaging material and a covering material, and a satisfactory material has not been obtained yet. On the other hand, heat-shrinkable films and sheets are widely used as packaging materials and coating materials for food packaging and labels, etc., but these apply heat, so in the case of refrigerated / frozen food packaging, etc. There are problems that the temperature rises and it deteriorates, and that it requires a quenching process again after shrinkage processing due to refrigeration / freezing.

[0003]

To solve these problems, the present invention provides a thermoplastic molded sheet which has heat-shrinkability in addition to water absorption and is suitable as, for example, a food shrink-wrapping material. In addition, particularly when water absorption is not required, it is possible to shrink with water without applying heat, and to provide a sheet that can be suitably used for packaging foods that dislike heating, and the like. Is a shrinkable sheet obtained by thermoplastically molding into a sheet shape and stretching a crosslinked polyalkylene oxide sheet irradiated with ionizing radiation.

The present invention will be described in detail below. In addition, in the following description, the “sheet” may be in the form of a tube other than a flat plate, and includes a thin film. The polymer used in the sheet of the present invention is polyalkylene oxide, and polyethylene oxide or ethylene oxide copolymer can be used alone or in a blend. Examples of the component copolymerized with ethylene oxide include alkylene oxides such as propylene oxide and butylene oxide, and / or vinyl ethers such as vinyl methyl ether and vinyl ethyl ether.

The molecular weight of the polymer is 10,000 to 500,
000 can be used. If it is less than 10,000, the secondary workability is poor, and if it exceeds 500,000, thermoplastic molding becomes difficult. Polymer is used alone, filler,
You may add additives, such as a crosslinking agent, a plasticizer, and a coloring agent. Molding is carried out by thermoplastic molding. As a molding means, the same method as a generally known polymer such as polyethylene or polyvinyl chloride can be adopted, and it can be molded into a sheet or tube by extrusion molding, calendar molding or the like.

Since the polyalkylene oxide is water-soluble, the sheet is crosslinked and insolubilized by irradiation with ionizing radiation. As the ionizing radiation, an electron beam, γ-ray, X-ray or the like is used. The dose of the ionizing radiation varies depending on the sheet thickness, the subsequent stretching conditions, etc., but the absorbed dose is preferably in the range of 5 to 50 Mrad. When it is less than 5 Mrad, the strength may be insufficient and a part of the water-soluble portion may remain, and when it is more than 50 Mrad, it is practically disadvantageous and the stretching becomes difficult. The preferred range is 5 to 20 Mrad. Irradiation can be performed separately before and after stretching.

Following the crosslinking, the sheet is uniaxially or biaxially stretched under the stretching conditions of a stretching temperature of 45 to 60.
C. and the draw ratio is preferably in the range of 4 to 6 times in one direction. The stretching method is preferably flat stretching using a tenter or the like, but tubular stretching in which the tube is expanded by internal pressure can also be used.

The sheet of the present invention is suitable for applications where it is desirable to have shrinkability and water absorption, such as food packaging.
By coating a food sheet or the like with this sheet and subjecting the sheet to a heat shrinking treatment by a usual method, a shrinkage-coated body can be obtained while maintaining water absorption, and a freshness-retaining effect is obtained by absorbing drip coming out from the food. Further, when used for coating electric wires, electric parts, optical fiber cables, etc., it is possible to absorb moisture from the outside and prevent the moisture from entering the inside. In addition, particularly when it is used for an application that does not require water absorption, when the article is coated and then brought into contact with water, shrinkage occurs together with water absorption, and shrinkage processing can be performed without applying heat. Therefore, it is suitable for shrink wrapping of foods such as refrigerated / frozen foods that may be deteriorated by heat. Also, since it is not necessary to apply heat, it can be applied to living organisms where heat shrink processing could not be applied until now, for example, it can be used for both cooling and fixing such as compresses for bruise and bandages for burns. I can.

[0009]

[Example] Polyethylene oxide was mixed with a single screw extruder to obtain T
Extrusion was carried out under the condition that the die temperature was 90 ° C., and a cast sheet having a thickness of 200 μm was collected. The sheet was irradiated with an electron beam irradiation device at an acceleration voltage of 200 kV and an absorbed dose of 10 Mrad, and then sequentially biaxially stretched at a temperature of 55 ° C. in the longitudinal direction by 4 times and in the width direction by 4 times. By heating this sheet to 55 ° C, it is possible to obtain about 40 in each of the longitudinal and width directions.
Shrinked by%. The sheet after shrinkage also retained water absorption. When the stretched sheet was immersed in water, it instantly shrank by about 40% in each of the longitudinal direction and the width direction.

[0010]

INDUSTRIAL APPLICABILITY The sheet of the present invention is water-absorbing and heat-shrinkable and is obtained by efficient thermoplastic molding, and is dispersed and retained on a fibrous base material like conventional water-absorbing products. There is no need to let them do it. The resulting sheet is heat-shrinked to wrap the article in a state of retaining water absorption,
Since it can be covered, moisture can be absorbed after packaging and covering, and effects such as protection of contents can be achieved. Further, in the case of a use which does not require water absorption, it is possible to perform shrink wrapping / coating, etc. without applying heat by bringing it into contact with water.

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Claims (1)

[Claims] 1. A shrinkable sheet obtained by thermoplastically molding into a sheet shape and stretching a crosslinked polyalkylene oxide sheet irradiated with ionizing radiation.