JPS6129268B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a low-temperature shrinkable film suitable for low-temperature sleeve shrink packaging and a method for producing the same. Films made of low-density polyethylene or ethylene-vinyl acetate copolymers are inexpensive, easy to form, and have appropriate physicochemical properties.
It is widely used for general packaging. Further, by specially selecting the conditions during extrusion film formation of the above resin, heat shrinkability is imparted, and this is increasingly used for shrink wrapping such as sleeve shrink wrapping. Conventionally, such shrinkable films made of low-density polyethylene or ethylene-vinyl acetate copolymer are usually made by extrusion molding using the inflation method, and stretching is performed at the same time as molding, so the temperature is 110°C.
100
It hardly shrinks below ℃. Therefore, when such shrinkable films are used to package items that have been wrapped with general packaging films such as low-density polyethylene, or where the packaging of the items is printed. In the case of integrated shrink wrapping, the shrink film is heated to a temperature of about 110° C. or higher to cause the shrink wrapping to shrink, which has the disadvantage that the shrink film is fused to the interior general packaging film or the printed surface. In addition, when shrink-wrapping foods such as sausages, the food may be damaged by heat, and when shrink-wrapping products with poor heat resistance, such as foam products, the product may foam or become deformed. It had the disadvantage of doing things like that. Recently, a so-called low-temperature shrinkable film, which is produced by stretching a low-density polyethylene film in the longitudinal direction and rapidly shrinks at 80 to 100°C, has been commercially available as a shrinkable film that does not have the above-mentioned drawbacks. However, when the low-temperature shrinkable film made of such low-density polyethylene is used for integrated shrink-wrapping, there is a drawback that if the object to be packaged has corners, the film at the corners may be torn during shrink-wrapping. Further, when a strong impact is applied to this integrated shrink package, the heat-sealed portion ruptures and the film at the corners is torn in the stretching direction of the film. In an attempt to eliminate the drawbacks of the low-temperature shrinkable film made of low-density polyethylene mentioned above, the present inventor focused on and studied ethylene-vinyl acetate copolymer instead of low-density polyethylene, and as a result, was able to complete the present invention. Ivy. That is, the low-temperature shrinkable film of the present invention is a laminated stretched film in which a plurality of ethylene-vinyl acetate copolymer films are adhered or adhered and stretched in at least one direction, and the stretched laminated film is At a heating temperature where the thermal shrinkage rate in the direction is 100℃ or less
30% or more, and the method for manufacturing the low-temperature shrinkable film of the present invention is to produce a laminated film in which a plurality of ethylene-vinyl acetate copolymer films are superimposed and adhered or bonded together, and 90
Heat to a stretching temperature of 1.5 to 1.5 °C in at least one direction.
It is characterized by being stretched 4.0 times. Therefore, the ethylene used in the present invention
Vinyl acetate copolymer has a melt index of 0.3
~2.0 preferably 0.3~5, density 0.925~0.942g/
cm ² , vinyl acetate content 5-15% by weight, preferably 5
~10% by weight. A plurality of films made of such ethylene-vinyl acetate copolymer are closely attached or adhered to form a laminated film, and the laminated film is stretched in at least one direction to form a laminated stretched film. As long as two or more films of approximately the same thickness are laminated together, the laminated film may be simply pressed together to make a close contact, or it may be bonded with an adhesive, but the softening of the film It is preferable to use pressure bonding in this state.
Further, the laminated stretched film may be a laminated film stretched in either the longitudinal direction or the width direction, or in both directions. This laminated stretched film has a heat shrinkage rate of 30% or more in the stretching direction at a heating temperature of 100° C. or less. Heat to a heating temperature higher than 100℃
Films with a heat shrinkage rate of 30% or more have the drawbacks mentioned above, and films with a heat shrinkage rate of less than 30% have poor adhesion to the packaged items, especially when performing sleeve-integrated shrink wrapping. This is because the finish of the sleeve hole becomes poor. In the present invention, a film having a heat shrinkage rate of 40% or more in the stretching direction at a heating temperature of 80 to 100°C is optimal. Such a low-temperature shrinkable film is produced by heating a laminated film of ethylene-vinyl acetate copolymer to a stretching temperature of 60 to 90°C, preferably 70 to 80°C, and stretching the film at least 1.5 to 4.0 times in one direction, preferably 1.5 to 3.0 times. Obtained by double stretching. The laminated film may be made by laminating multiple films and sticking or adhering them together, but in particular, the ethylene-vinyl acetate copolymer is extruded into a tube shape, air is injected into the tube to expand it, and the tube is expanded. When a laminated film is made by overlapping two films by passing them through a pair of pressure and take-off rolls while gradually folding them flat, the laminated film is produced without air bubbles between the films, and without wrinkles or sagging. This is preferable because it is possible to easily form a laminated film that is strongly adhered or adhered to each other in a softened state and can be stretched uniformly. In addition, the stretching temperature when stretching this laminated film is set in the range of 60 to 90°C, because if the stretching temperature is lower than 60°C, uniform stretching will not be possible, resulting in a film with uneven thickness and breakage during stretching. Also, if the stretching temperature is higher than 90°C, the heat shrinkage rate at heating temperatures of 100°C or less will be low, and the surface will become poor due to adhesion to the rolls during stretching, making it easier to break. It is. In addition, the stretching ratio is set to 1.5 to 4.0 times because if the stretching ratio is less than 1.5 times, it will not be possible to obtain a product with the desired heat shrinkage rate, and if the stretching ratio exceeds 4.0 times, it will tend to tear in the stretching direction. This is because when used as a shrink wrapping film, it has the disadvantage of tearing during shrink wrapping or when an impact force is applied to the packaged item. To stretch a laminated film, the laminated film heated to the stretching temperature is stretched in the longitudinal direction between a pair of delivery pinch rolls rotating at a low circumferential speed and a pair of take-up pinch rolls rotating at a high circumferential speed. This method is preferable because the equipment is simple and there is no product loss, but stretching may be performed in the width direction or in both the longitudinal and width directions using a tenter stretching machine. In particular, as mentioned above, if a laminated film extruded into a tube shape and folded flat is uniformly heated to the stretching temperature and stretched in the next successive process without cooling, the laminated film can be heated easily and without waste. can. The low-temperature shrinkable film obtained in this way has a heat shrinkage rate of 30°C in the stretching direction at a heating temperature of 100°C or less.
% or more, the tensile strength in the stretching direction is 400 Kg/ ^cm2 or more, the elongation is 250% or less, the Elmendorf tear strength is 120 Kg/cm or more, and the heat sealing strength (sealing conditions are a heat bar seal method with a pressure of 3 Kg). / ^cm2 ,
Temperature: 170°C, 1 second) is 1.30 kg/10 mm width or more, impact strength is 3000 kg/cm/cm or more, haze (haze is 5% or less), and has desirable properties as a shrink wrapping film. The low temperature yielding film of the present invention usually has a yield of 0.04~
A thickness of about 0.12 mm is used, and 0.04 to 0.06
Those stretched in one direction of mm are used for sleeve shrink wrapping, and those stretched in one direction of 0.06 to 0.12 mm are used for bundled shrink wrapping. Also, those stretched in both directions are used for pillow shrink packaging. Next, examples and comparative examples of the present invention will be described. Example 1 An ethylene-vinyl acetate copolymer with a melt index of 0.6, a density of 0.930 g/cm ² and a vinyl acetate content of 7% by weight was molded into a 178 mmφ (7 inchφ) annular mold.
It is extruded into a tube shape at a temperature of 160℃, air is forced into the tube to expand it, and the tube is gradually folded into a flat shape and taken up by a pair of pressing and pulling rolls with a linear pressure of 20 kg/cm and a circumferential speed of 10 m/min. A two-layer laminated film with a length of 0.1 mm (total thickness of the folded film) and a width of 850 mm was manufactured. Next, the laminated film was passed through two preheating rolls (heating temperature: 80°C, circumferential speed: 10 m/min), a stretching roll (heating temperature: 70°C, circumferential speed: 20 m/min), and a cooling roll (cooling temperature: approximately 20°C, circumferential speed). 20m/min) using a roll stretching device arranged close to each other in this order,
The film was transferred in contact with each roll in an S-shape, and the raised portions at both ends were cut and removed in the length direction. Thus, the lengthwise stretched thickness
A low-temperature shrinkable film consisting of uniformly stretched laminated stretched films with a width of 0.05 mm and a width of 750 mm was fabricated.
In addition, even if it was produced continuously for a long time, it did not break during stretching. The physical properties of the above-mentioned low-temperature shrinkable film were as shown in Table 1. Using this low-temperature shrinkable film, four toilet paper rolls 12 are wrapped in a low-density polyethylene film 11 as shown in FIG.
A total of 20 sets were arranged in two tiers between 1 and 22 and tightened with polypropylene bands 23 and 24 in a criss-cross pattern to make a packaged item. Next, the low temperature shrinkable film 26 of the present invention is applied.
Cut to a length of 1020mm, overlap two films of 750mm x 1020mm, and heat seal both ends in the width direction (750mm) using the heat bar sealing method (pressure 3Kg/cm ² , time 1 second, temperature 170℃). Step 25 was carried out to form a cylindrical film, and the object to be packaged was placed in it and passed through a heat shrink tunnel (hot air at about 120° C.) for about 11 seconds to shrink the film in close contact with the object to be packaged. The temperature of the film never exceeded 100°C. The shrink film 26 closely adhered to the object to be packaged, the sleeve hole 27 had a good finish, and no fusion occurred between the shrink film 26 and the low density polyethylene film 11 wrapping the toilet paper roll. Also, the shrink film 26 at the corners of the trays 21 and 22 is approximately
Although the film was thinner, reaching a thickness of 20μ, no film tearing occurred. This shrink wrap (weighing 15 kg) was dropped from a height of 3 m onto concrete ground at a temperature of 23°C with the tray surface facing up and down, but the film did not tear at all. Comparative Example 1 A commercially available low-temperature shrinkable film with a thickness of 50μ made of a low-density polyethylene film stretched in the length direction (this film is a single layer film and not a laminated film as in the present invention) was obtained, and this was made into a 750mm film.
When the shrink film was cut to 1020 mm and tested under the same conditions as Example 1, it was found that the shrink film adhered tightly to the packaged object and the sleeve hole had a good finish. No fusion with the density polyethylene film occurred. However, the shrink film at the corner of the tray was torn by about 5 mm, and in a 3 m drop test, part of the film was torn by about 10 cm in the length direction, and most of the heat-sealed parts on the sides of the shrink wrap were broken. Broken. The physical properties of the commercially available low-temperature shrink film were as shown in Table 1.

【table】

[Table] The thermal contraction rate 〓- indicates that the material expands when heated.
As is clear from the above examples, the low-temperature shrinkable film of the present invention is made of an ethylene-vinyl acetate copolymer film, and this film is made up of two films that are closely attached or bonded together. The combination of the above-mentioned copolymer's good elongation effect during heating and the reinforcing effect of the weak points in each film by laminating the two films makes it possible to reduce the strength of the film at the corners of the packaged object during shrink wrapping. This will prevent tearing. Furthermore, the low-temperature shrinkable film of the present invention uses an ethylene-vinyl acetate copolymer, and two films of this copolymer are closely attached or bonded and stretched in the longitudinal direction. The combination of the effect of the combination and the lamination effect of the two films results in uniform stretching and good low-temperature shrinkability even when stretched at a relatively low temperature and at a low magnification, which results from increasing the stretching magnification. A reduction in heat-sealing strength and vertical tearing are prevented, and a shrink-wrapped body made of such a film is prevented from tearing or tearing of the heat-sealed part and the film itself when subjected to a strong impact such as falling from a high place. It is possible.

[Brief explanation of the drawing]

1 and 2 are perspective views for explaining an example of use of the low-temperature shrinkable film of the present invention, and FIG. 1 is a perspective view of an interior body of a toilet paper roll;
FIG. 2 is a partially cutaway perspective view of an integrated packaging body in which the inner body shown in FIG. 1 is integrated and packaged using the low-temperature shrinkable film of the present invention. DESCRIPTION OF SYMBOLS 11...Low density polyethylene film, 12...Toilet paper roll, 13...One set of wrapped toilet paper, 21, 22...Tray, 2
3, 24...Polypro band, 25...Heat seal, 2
6...Low temperature shrinkable film of the present invention, 27...Sleeve hole.

Claims (1)

[Scope of Claims] 1. A laminated stretched film formed by adhering or adhering a plurality of ethylene-vinyl acetate copolymer films and stretching in at least one direction, wherein the laminated stretched film is heat-shrinkable in the stretching direction. A low-temperature shrinkable film characterized by a shrinkage rate of 30% or more at a heating temperature of 100°C or less. 2. The ethylene-vinyl acetate copolymer has a melt index of 0.3 to 20, preferably 0.3 to 5, and a vinyl acetate content of 5 to 15% by weight, preferably 5 to 10% by weight. low temperature shrinkable film. 3 The heat shrinkage rate of the laminated stretched film in the stretching direction is 80
The low-temperature shrinkable film according to claim 1 or 2, which has a shrinkage of 40% or more at a heating temperature of ~100°C. 4. A laminated film in which a plurality of ethylene-vinyl acetate copolymer films are laminated and adhered to each other is heated to a stretching temperature of 60 to 90°C, and stretched 1.5 to 4.0 times in at least one direction. A method for producing a low-temperature shrinkable film. 5 Ethylene-vinyl acetate copolymer is extruded into a tube shape, air is forced into the tube to expand it, and the tube is gradually folded into a flat shape while being passed through a pair of pressing and pulling rolls to form two sheets of ethylene.
5. The method for producing a low-temperature shrinkable film according to claim 4, wherein the film is a laminated film made of vinyl acetate copolymer films adhered to each other. 6. The method for producing a low-temperature shrinkable film according to claim 4 or 5, wherein the laminated film heated to the stretching temperature is stretched in the longitudinal direction between pinch rolls having different circumferential speeds. 7. The method for producing a low-temperature shrinkable film according to claim 4, 5 or 6, wherein the stretching temperature is 70 to 80°C and the stretching ratio is 1.5 to 3.0.