JPH0258099B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a novel knotless film and a method for producing the same. More specifically, the present invention provides a knotless film suitable as a packaging material, which has excellent cushioning and heat insulation properties, is easy to tear, and is easily heat-sealable, and which can be easily manufactured. It's about how to do it. Conventional technology Conventionally, in order to provide effective tearability, films that are easy to tear have been stretched at high temperatures and high magnifications to increase their molecular orientation, and made of resin compositions with high strength and stiffness as materials. Measures such as foaming itself have been taken. The film created in this way is difficult to melt at low temperatures and has poor thermal conductivity, making it extremely difficult to heat seal, and therefore it is used as a packaging material only in extremely limited fields where heat sealing is not required. It has not been. Therefore, in order to impart heat-sealing properties to such easily tearable films, methods have been adopted, such as coating or laminating a low melting point resin composition. However, with this method, a uniform continuous film is formed on the film surface, which inhibits tearability, and it is necessary to make cuts or broken lines at the tear points, which inevitably increases costs. . Problems to be Solved by the Invention The object of the present invention is to overcome the drawbacks of the conventional heat-sealable film, and to create a film that is suitable as a packaging material, has excellent cushioning and heat insulation properties, and is easy to tear. It is an object of the present invention to provide a so-called notchless film which is easy to heat seal and does not require cutting or broken lines. Means for Solving the Problems As a result of intensive research, the present inventors provided a heat-sealable resin layer containing air bubbles with a predetermined thickness on the surface of a thermoplastic foam sheet, and stretched it in a uniaxial direction. Then, the inventors discovered that the above object could be achieved by forming the heat-sealable resin layer into a network structure, and based on this knowledge, the present invention was accomplished. That is, the present invention provides a heat-sealable resin layer having a network structure on at least one side of a thermoplastic foam film stretched in a uniaxial direction, and the amount of the resin is 2 to 8 c.c. per 1 m ² of the foam film. This film has a heat-sealable resin layer containing air bubbles on at least one side of a thermoplastic foam sheet, and the amount of the resin is equal to or greater than the amount after stretching. It can be easily obtained by forming a foamed film with a thickness of 2 to 8 c.c. per m ² and then stretching this composite sheet in a uniaxial direction to form the heat-sealable resin layer into a network structure. . The resin used for the thermoplastic foam sheet in the present invention (resin for sheet) can be stretched when made into a film, such as polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-propylene-butene copolymer, etc. Examples include thermoplastic resins. On the other hand, the resin used for the heat-sealing resin layer (heat-sealing resin) must have a lower melting point than the resin for the sheet and be highly compatible with the resin. Examples include low-melting thermoplastic resins such as ethylene-vinyl acetate copolymer, modified polypropylene, ionomer resin, low-density polyethylene, and linear polyethylene. In the present invention, first, a heat-sealable resin layer containing air bubbles is provided on one or both sides of a thermoplastic foam sheet. Methods for providing this heat-sealable resin layer include, for example, a method of co-extrusion molding a foaming agent-containing sheet resin composition and a foaming agent-containing resin composition for heat-sealing, A method such as lamination can be used. As the foaming agent, a chemical foaming agent or a physical foaming agent can be used. As a chemical blowing agent,
For example, ammonium carbonate, sodium bicarbonate, inorganic decomposable blowing agents such as azide compounds, azodicarboxamide, azobisisobutyronitrile, diazoaminobenzene, N,N'-dinitropentamethylenetetramine, N,N'- dimethyl-N,
Examples of organic blowing agents include N'-dinitroterephthalamide, benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, and p,p'-oxybenzenesulfonyl hydrazide. Examples of physical blowing agents include pentane, neopentane, Examples include hexane, isohexane, heptane, isoheptane, benzene, toluene, methylene dichloride, trichlorofluoromethane, dichlorotetrafluoroethane, and the like. These blowing agents may be used alone or in combination of two or more. Next, the composite sheet in which the heat-sealable resin layer containing air bubbles is provided on one or both sides of the thermoplastic foam sheet is uniaxially stretched. By this stretching process, the molecules are oriented in one direction, and the partition walls of the bubbles are cut in the heat-sealable resin layer, so that the heat-sealable resin layer becomes mesh-like. Regarding the thickness of this heat-sealable resin layer, the amount of resin is 2 to 8 c.c., preferably 4 to 8 c.c., per 1 m ² of the expanded film after stretching.
It is necessary that the thickness be within the range of 6 c.c. If the amount of the resin is less than 2 c.c., no heat sealing effect can be obtained, while if it exceeds 8 c.c., tearability will be impaired. Further, the stretching ratio is usually selected within the range of 4 to 7 times. When a heat-sealable resin layer that does not contain air bubbles is provided on the surface of a thermoplastic foam sheet, the resin layer does not become mesh-like even when stretched at a high magnification, so the resulting film cannot be heat-sealed. Although this is possible, the tearability is impaired and it cannot be easily torn, so it is necessary to add cuts and broken lines. In contrast, in the film of the present invention obtained as described above, the heat-sealable resin layer has a network structure, so the tearability is not impaired and the cuts can be easily made without the need for broken lines. Tearable and heat sealable. Next, an example of the present invention will be explained with reference to additional drawings. Figures 1 and 2 are cross-sectional views showing the structure of an example of a composite foam sheet for producing the knotless film of the present invention. FIG. 3 is a perspective view of a notchless film obtained by uniaxially stretching the composite sheet. In the figure, numeral 3 represents air bubbles contained in the heat-sealable resin layer 1, numeral 4 represents air bubbles in the thermoplastic foam sheet 2, and 1' represents the heat-sealable resin layer in the form of a mesh. EXAMPLES Next, the present invention will be explained in more detail with reference to Examples. The thicknesses of the thermoplastic foam sheet and the heat-sealable resin layer in the composite foam sheet were measured by observing the cross section of the composite foam sheet using a reading microscope PRM-3 (manufactured by Pika Seiko Co., Ltd.). Moreover, for each thickness of the film after stretching, the value obtained by dividing the corresponding thickness of each of the composite foam sheets by the stretching ratio was used. Example 1 100 parts by weight of ethylene-propylene copolymer (manufactured by Chitsuso Co., Ltd., Chitsuso Polypro F-8277) with MFI 7.0 was mixed with azodicarboxamide blowing agent master pellets (manufactured by Sankyo Kasei Co., Ltd., Cellmic). MB-3013,
A thermoplastic resin composition for foamed sheets (hereinafter referred to as sheet resin) containing 20% ADCA] and an ethylene-vinyl acetate copolymer [manufactured by Nippon Unicar Co., Ltd., DQDJ-1830H]. , VA content
10%] 100 parts by weight and azodicarboxamide blowing agent master pellets [manufactured by Sankyo Kasei Co., Ltd., Cellmic]
A low melting point resin composition with heat sealing properties (hereinafter referred to as sealing resin) made by adding 3 parts by weight of MB-3013 (containing 20% ADCA) and 0.01 part by weight of ultramarine blue was added in separate extruders. The mixture is kneaded, then introduced into a feedblock to join the T-
By a coextrusion molding method in which the laminated sheet materials are extruded through a die, a two-type, three-layer composite foam sheet with a sealing resin layer on the surface was obtained. The total thickness of this composite foam sheet was 0.75 mm, and the sealing resin layer was 0.025 mm, the foam sheet layer was 0.70 mm, and the sealing resin layer was 0.025 mm. Next, the composite foam sheet thus obtained was stretched in the transverse uniaxial direction in an atmosphere at 110°C to obtain a composite foam stretched film with a thickness of 0.15 mm that can be easily torn in the transverse direction. Ta. When the surface layer of this composite foam stretched film was observed under a microscope, it was observed that the air bubbles in the laminated surface foam layer (sealing resin layer) were torn by the stretching process, and the surface layer had become a mesh-like film. . When this material was subjected to ordinary heat sealing, adhesive strength within the practical range was obtained. The transverse right angle tear strength of this composite expanded stretched film is 2.1 Kg/cm.
It was equivalent to that of a foamed stretched film with only a resin layer for sheets. Example 2 Composite foaming was carried out in exactly the same manner as in Example 1, except that modified polypropylene resin [Tafmer XR-107L, manufactured by Mitsui Petrochemicals, Ltd.] was used instead of the ethylene-vinyl acetate copolymer in Example 1. A stretched film was obtained. When the performance of this film was investigated in the same manner as in Example 1, the transverse right angle tear strength of the film was
The heat sealability was 2.2Kg/cm, and the heat sealability was also practically satisfactory. Example 3 Instead of the ethylene-vinyl acetate copolymer in Example 1, an ionomer made by crosslinking ethylene-methacrylic acid copolymer with zinc [manufactured by Mitsui Polychemical Co., Ltd., Himilan 1650, MFR 1.5, SpGr] was used.
A composite expanded stretched film was obtained in exactly the same manner as in Example 1, except that 0.94] was used, and the same tests were conducted. As a result, the transverse right angle tear strength of the film was 2.4 kg/cm, without compromising ease of tearing.
Practical heat seal strength was obtained. Example 4 Ethylene-propylene-butene copolymer with MFI 8.5 [Chitsuso Polypro XF-7500, manufactured by Chitsuso Corporation]
Add 100 parts by weight of azodicarboxamide blowing agent master pellets (manufactured by Sankyo Kasei Co., Ltd., Cellmic MB-
3013, containing 20% ADCA] A sheet resin containing 3 parts by weight, and low-density polyethylene containing 8% hexane [manufactured by Nippon Unicar Co., Ltd., NUC]
−8505, MI 0.8, SpGr 0.923] A sealing resin made by adding 0.1 part by weight of azobisisobutyronitrile, 0.1 part by weight of sodium bicarbonate, and 0.01 part by weight of ultramarine is kneaded in separate extruders. and then lead it to the feedblock and merge it with the T-
A composite foam sheet of two types and three layers, with the sealing resin layer on the surface, was obtained by a coextrusion molding method in which the laminated sheet material was extruded through a die. This composite foam sheet was made into a composite foam stretched film in the same manner as in Example 1, and its performance was determined. As in Example 1, the surface layer was a mesh film, and its heat sealability reached a practical level. Ori,
The right angle tear strength was 2.1 kg/cm, which was equivalent to that of the uncoated foam sheet layer. Example 5 60 parts by weight of ethylene-propylene copolymer with MFI 7.0 [Chitsuso Polypro F-8277] and ethylene-vinyl acetate copolymer [Nippon Unicar Co., Ltd.]
(manufactured by Sankyo Kasei Co., Ltd., Cellmic MB-
3013, containing 20% ADCA] Resin for foamed sheets with the addition of 3 parts by weight, and linear polyethylene containing 10% hexane [manufactured by Mitsui Petrochemicals Co., Ltd.]
Urtozetsu 3520, MI 2.3, SpGr 0.929〕100
0.1 part by weight of azobisisobutyronitrile,
A sealing resin containing 0.1 part by weight of sodium bicarbonate and 0.01 part by weight of ultramarine blue was kneaded in separate extruders, and a composite foam sheet was formed by coextrusion through a feed block and a T-die. A composite foam sheet with two types and three layers was obtained. This composite foam sheet was made into a composite foam stretched film in the same manner as in Example 1, and its performance was determined. As in Example 1, the resin layer for the sheet was a mesh-like coating, and the right angle tear strength of the film was determined. teeth
It was 2.0Kg/cm. Moreover, the sealing strength of this composite expanded stretched film was practically effective. Example 6 In the same manner as in Example 1, a composite foam sheet of two types and two layers, a foam sheet layer and a sealing resin layer, was formed by co-extrusion molding and stretched in the transverse uniaxial direction to form a composite with a thickness of 0.15 mm. A foamed stretched film was obtained. The transverse right angle tear strength of this film was 2.1 kg/cm, which was exactly the same as that of Example 1. Regarding heat sealability, when the sealing resin surfaces are bonded together, it is exactly the same as in Example 1, but when the sealing resin surface is in contact with the foamed base film surface, the sealing strength does not reach a practical level. It was in a state where it could be easily peeled off. Comparative Example 1 100 parts by weight of ethylene-propylene copolymer (manufactured by Chitsuso Co., Ltd., Chitsuso Polypro F-8277) with an MFI of 7.0 was added
A sheet resin containing 3 parts by weight of MB-3013) was molded into a foamed sheet with a thickness of 0.75 mm by T-die extrusion. This foam sheet was stretched in the transverse uniaxial direction in the same manner as in Example 1, and the thickness was 0.15 mm.
A foamed film that was easy to tear in the transverse direction was obtained. The perpendicular tear strength in the transverse direction of this foamed stretched film was measured to be 2.1 Kg/cm, which is exactly the same strength as in Example 1. However, the heat sealability of this foamed stretched film was poor, and it peeled off without any resistance, meaning that no practical strength could be obtained. Comparative Example 2 Example 1 except for the blowing agent composition in the low melting point resin composition having heat sealability in Example 1.
A similar test was conducted, but the transverse right angle tear strength of the resulting composite expanded stretched film was 5.3 kg/cm, indicating that not only the tearability of the expanded expanded film was impaired, but also the laminated ethylene and acetic acid The vinyl copolymer coating could not be easily torn even if the foam-stretched base film was destroyed. Comparative Example 3 The ethylene-vinyl acetate copolymer in the sealing resin of Example 1 was replaced with an ionomer resin (Himilan 1650), and the sealing resin layer was formed by coextrusion molding in the same manner as in Example 1. It was molded to a thickness of 0.05 mm, twice the thickness of the sealing resin layer of Example 3, and this composite foam sheet was stretched in the transverse uniaxial direction in the same manner as in Example 3 to obtain a composite foam film. The transverse right angle tear strength of this film was 3.8, and when the sealing resin layer was observed under a microscope, it was found that the bubbles in the sealing resin foam layer were not destroyed and the film was not mesh-like but completely sponge-like. Ta. Although this composite foam film has no problems with heat sealability, it is quite resistant to tearing by hand, although it is not impossible, and it is necessary to make "slits" or "dashed lines" in order to tear it easily. This was not suitable for the purpose of the present invention. The above results are summarized in the table below.

【table】

[Table] Effects of the Invention The knotless film of the present invention has a uniaxially stretched thermoplastic foam film on one or both sides.
It is equipped with a heat-sealable resin layer having a mesh structure, and has excellent cushioning and heat insulation properties.
In addition, it is easy to heat seal and tear easily, so it can be easily torn by hand without making cuts or broken lines, and it is so smooth that you can hardly tell that it foams from its appearance. Since it can be processed such as printing without any problems, it is extremely useful as a packaging material.

[Brief explanation of drawings]

1 and 2 are a cross-sectional view and a perspective view of an example of a composite foam sheet used for manufacturing the notchless film of the present invention, and FIG. FIG. 3 is a perspective view of a res film. In the figure, reference numeral 1 is a heat-sealable resin layer containing air bubbles, 2 is a thermoplastic foam sheet, and 1' is a heat-sealable resin layer having a mesh shape.

Claims (1)

[Scope of Claims] 1 A heat-sealable resin layer having a network structure is provided on at least one side of a thermoplastic foam film stretched in a uniaxial direction, and the amount of the resin is 1.
An easily tearable knotless film provided with a thickness of 2 to 8 c.c. per m ² . 2. A heat-sealable resin layer containing air bubbles is provided on at least one side of the thermoplastic foam sheet to a thickness such that the resin amount is 2 to 8 c.c. per 1 m ² of the stretched foam film, and then this composite A method for producing an easily tearable knotless film, which comprises uniaxially stretching a sheet to form the heat-sealable resin layer into a network structure.