JPS6230900B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyethylene non-crosslinked shrink film for sleeve wraps using a polyethylene resin most suitable for use as a shrink film for sleeve wraps. More specifically, the present invention relates to a non-crosslinked polyethylene shrinkable film for sleeve wraps that utilizes the characteristics of non-crosslinked polyethylene film to have excellent heat sealability and is advantageous in terms of packaging material cost. One form of integrated packaging using shrink film is
There is a method called sleeve wrap packaging, in which the contents are packaged in an integrated manner with openings on both sides by sealing the front and back without sealing both sides, and then shrinking the contents (for example, (See Food Packaging Technology Handbook, edited by Japan Packaging Technology Association, published by Japan Productivity Center, pp. 317-318). However, when carrying out the sleeve wrap packaging using the conventional non-crosslinked polyethylene shrink film, a number of problems occurred. For example, if a biaxially balanced film (a film whose heat shrinkage rate in the axial direction and the heat shrinkage rate in the perpendicular direction are similar to each other) is used for sleeve wrap packaging,
After the shrinkage is completed, the openings on both sides become excessively large, and sometimes only the corners of both sides are covered, resulting in a disadvantage that the cohesiveness and protection of the contents are significantly reduced. In addition, extreme uniaxial films (heat shrinkage in the direction perpendicular to the film axis of -20% or more, i.e. 20
If a film that stretches more than 30% is used for sleeve wrap packaging, the dimensions of the openings on both sides will become smaller, but when multiple contents are packaged together, the film will bite into the gaps between the individual packages, reducing cohesiveness. There were also problems such as the film becoming punctured in the tunnel, the heat-sealed portion peeling off, and the thickness of the film corresponding to the corners of the package becoming extremely thin. Furthermore, even if the above trouble is not fatal,
The openings on both sides are irregular in shape, blocking, wrinkles, etc. are formed, which not only impairs the appearance of the packaging, but also tends to cause tears from the blocking portions when the package is handled. Furthermore, when crosslinked films are used for sleeve wrap packaging, it is easy to control the shaping and bundling of both sides, but the crosslinking effect significantly reduces heat sealability, making it difficult to suit high-speed packaging operations.
Furthermore, there was a disadvantage in terms of film price. In order to improve the shortcomings of these conventional methods, the present inventors investigated polyethylene shrink films having various shrinkage characteristics as films for sleeve wraps.
Only films with appropriate heat shrinkage stress values are
They discovered the fact that it satisfies the various performances required for sleeve wraps, and arrived at the present invention. A film suitable as a shrink film for sleeve wraps has a heat shrinkage rate in the film axial direction, that is, the direction in which the film travels in the sleeve wrap packaging method (hereinafter abbreviated as the film axial direction), and a heat shrinkage rate in the direction perpendicular to the film axial direction. It was vaguely recognized that setting the value of heat shrinkage rate (heat shrinkage rate perpendicular to the film) appropriately was sufficient, but if the appropriate range of heat shrinkage rate and heat shrinkage stress was not met, then the necessary and sufficient conditions were not met. By discovering this fact, the present invention was completed. That is, the present invention is a film made of a polyethylene resin with a melting index of 1.0 g/10 minutes or less,
A polyethylene non-crosslinked shrinkable film for sleeve wraps, which has a heat shrinkage rate of 70% or more in the film axial direction, a heat shrinkage rate of 5% or less in the film perpendicular direction, and a film axial heat shrinkage stress of 10 g/mm ² or more and 30 g/mm ² or less. . The present invention will be explained in detail below. The non-crosslinked film described in the present invention refers to a film crosslinked by radiation such as alpha rays, electron beams, and ultraviolet rays, and a thermoplastic linear film that does not have a network chemical structure crosslinked by a chemical crosslinking agent. It is a film made up of molecules. The polyethylene resin used in the present invention is required to have film portion strength, seal portion strength, and cold resistance due to the nature of its use. And the melting index (ASTM−
D1238) polyethylene resin of 1.0 g/10 min or less, low density polyethylene with a resin density of 0.917 to 0.927 g/ ^cm2 , ethylene vinyl acetate copolymer with a vinyl acetate content of 1 to 20% by weight, ethyl acrylate content ethylene ethyl acrylate copolymer with a content of 1 to 20% by weight, an ethylene methyl methacrylate copolymer with a methyl methacrylate content of 1 to 20% by weight, an unsaturated carboxylic acid content of 1 to 20% by weight, and an unsaturated carboxylic acid. Ionomer resins (metal salts of ethylene/α-β unsaturated carboxylic acid copolymers) having a metal salt ratio of 1 to 60% are preferred. On the other hand, polypropylene and polyvinyl chloride have poor cold resistance and heat sealability, high-density polyethylene has poor sealing impact strength, and polystyrene resin has high rigidity and poor packaging workability, so the present invention is not suitable. I can't say that. Furthermore, for the purpose of the present invention, it is preferable to incorporate a lubricant, a light stabilizer, an antistatic agent, etc. into the polyethylene resin depending on the usage. The reason why the melting index of the polyethylene resin in the present invention is set to 1.0 g/10 minutes or less is a necessary condition not only for imparting various strengths to the film but also for imparting the shrinkage characteristics described below to the film. That is, the polyethylene non-crosslinked shrinkable film for sleeve wrap of the present invention has a heat shrinkage rate of 70% or more in the axial direction of the film, a heat shrinkage rate of 5% or less in the direction perpendicular to the film, a heat shrinkage stress of 10 or more in the film axial direction, and a heat shrinkage rate of 30 g/ The condition is that it is less than ^m2 . The heat shrinkage rate described here is the heat shrinkage rate obtained by immersing the film in an ethylene glycol heating medium at 120℃ for 20 seconds in accordance with JIS-Z1709, and the heat shrinkage stress is the heat shrinkage rate in accordance with ASTM-D1637. This is a value calculated by extrapolating the corresponding thermal shrinkage stress from the thermal deformation behavior in an empty bath during heating and heating. The film axial heat shrinkage rate is a fundamental factor for shrinkage films for sleeve wraps, and if sleeve wrap packaging is performed using a film with this value of less than 70%, the openings on both sides of the package will expand. It is customary. If the length of the outer cover film on both sides is set too long before tunnel processing, the size of the openings on both sides can be maintained at an appropriate value, but the shrinkage film on both ends may protrude from both sides or become folded. This will damage the packaging finish and appearance. When sleeve wrap packaging is carried out using a film with a heat shrinkage rate of 5% or more in the direction perpendicular to the film, the openings on both sides of the package expand, similar to the results described above, resulting in a package with poor finished appearance. In addition, even if the film satisfies the conditions of 70% or more heat shrinkage in the film axial direction and 5% or less in the perpendicular direction, a film with a heat shrinkage stress in the film axial direction exceeding 30 g/mm ² is prohibited. If used, the dimensions of the openings on both sides will be reduced, but excessive thermal shrinkage stress will cause film tearing in the latter half of the shrink tunnel or near the exit, thinning of the film at the corners after shrink wrapping, and unwrapping. Packaging defects such as poor cohesiveness due to the film being bitten between objects frequently occur. Similarly, the heat shrinkage stress in the film axis direction is 10g/
If a film with a diameter of less than mm ² is used, packaging defects such as enlargement of openings on both sides, partial blocking of films, and wrinkles are found. In other words, the heat shrinkage stress in the film axis direction is 10g/mm ²
If a film of less than 100 ml is used, packaging defects such as enlargement of the openings on both sides, partial blocking of the films, and wrinkles may be found. That is, whether the heat shrinkage stress in the axial direction of the film is too high or too low, packaging defects occur. From the above results, the most excellent basic film performance for a non-crosslinked shrink film for sleeve wraps made of polyethylene resin is a heat shrinkage rate of 70% or more in the axial direction of the film, a heat shrinkage rate of 5% or less in the perpendicular direction of the film, and It has been found that the shrinkage stress is 10 g/mm ² or more and 30 g/mm ² or less, and films made of polyethylene resin with a melting index of 1.0 g/10 minutes or less, which corresponds to these conditions, are prone to film tearing and shrink wrapping after shrink wrapping. Thinner corner film,
This is an excellent product that does not cause defects such as peeling of the heat-sealed portion, deterioration in cohesiveness due to the film being bitten into gaps between the individual objects to be packaged, partial blocking of the films with openings on both sides, and wrinkles. That is, when three specimens were wrapped in sleeve wrap using the polyethylene non-crosslinked shrink film for sleeve wrap of the present invention that satisfies all of the above conditions, a good packaging form was obtained as shown in FIG. On the other hand, if a film is used which has an excessive heat shrinkage rate in the perpendicular direction and insufficient heat shrinkage stress in the film axial direction, the protection of the contents will be reduced and the opening area ratio will be too large, as shown in FIG. Furthermore, if a film with excessive heat shrinkage coefficient and heat shrinkage stress in the film axial direction is used, defects such as thinning of the film at the corner portions and digging of the film into solid gaps will occur as shown in FIG. Furthermore, even if the heat shrinkage rate in the film axial direction and in the perpendicular direction to the film is appropriate, if the shrinkage stress in the film axial direction is insufficient, the film will block at the opening as shown in Figure 4, which is undesirable. . An inflation method or a T-die method is applied to the film manufacturing method according to the present invention. The film described in the present invention can be produced by appropriately setting the extrusion temperature, stretching ratio, and stretching speed to provide basic performance. In addition, it is a fact that the opening area ratio (opening area to the total area of the side surface with openings) after sleeve wrap shrink wrapping is preferably 0.3 or more and 0.6 or less from the viewpoint of content protection, handling workability, and packaging appearance. discovered. Examples of films forming preferred packaging forms will be shown below, and comparative examples will be shown showing examples of films forming less preferred packaging forms. Examples and Comparative Examples Three rectangular parallelepipeds were wrapped in sleeve wrap using polyethylene resin films having the melting index, film heat shrinkage rate, and film axial heat shrinkage stress shown in Table 1. The opening area ratio, opening shaping properties, etc. at that time are listed in Table 1. 【table】

[Brief explanation of the drawing]

Figure 1A is a perspective view showing a shrink-wrapped body in which three solids are sleeve-wrapped and shrink-wrapped using the film of the present invention, B is a front view showing the opening of the shrink-wrapped body, and Figure 2B is a comparison. FIG. 3A is a perspective view of a shrink wrapper showing another comparative example; B is a front view thereof; FIG.
Figure A is a perspective view of a shrink wrapper showing another comparative example, and Figure B is a front view thereof.

Claims (1)

[Claims] 1 A film made of polyethylene resin with a melting index of 1.0 g/10 minutes or less, with a heat shrinkage rate of 70% or more in the axial direction of the film, and a heat shrinkage rate of 5 in the perpendicular direction of the film.
% or less, and the film axial heat shrinkage stress is 10g/
^1. A non-crosslinked polyethylene shrinkable film for sleeve wraps, characterized in that it has a weight of 30 g/mm ² or more and 30 g/mm 2 or less.