JPS6139339B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel heat-shrinkable film. The present invention relates to a heat-shrinkable polyethylene film having excellent properties such as shrink-wrappability and transparency, and a packaging method using the film. Conventionally, polyethylene heat-shrinkable films with a relatively high heat shrinkage rate in the longitudinal direction have been used for shrink wrapping using the sleeve wrap method.In particular, polyethylene heat-shrinkable films that are highly uniaxially stretched and oriented have a large cohesive force and are transparent. It has excellent properties and is suitable. However, the appropriate shrinkage temperature range is narrow for polyethylene heat-shrinkable films that are highly uniaxially stretched and oriented.
In addition to requiring a high-performance shrinking furnace, if the packaged item has a complex shape or sharp corners, the film is likely to melt or break. There are two ways to solve this problem during shrink packaging: crosslinking polyethylene and using high-density polyethylene, which has a high melting point and strength, but the former requires expensive crosslinking equipment and has poor heat sealability. In the latter case, crystallization is promoted during heat shrinkage, resulting in a new problem that the transparency of the film is significantly reduced. Therefore, the present inventors have developed a method for shrink packaging without sacrificing the advantages of uniaxially highly stretch-oriented polyethylene heat-shrinkable film, such as easy heat-shrinkability, high cohesive strength, easy heat-sealability, and transparency. As a result of extensive research into whether there is a way to improve the shrink wrapping properties of the sleeve wrap method, we found that in order to improve the shrink wrapping properties, i.e. to widen the appropriate shrink temperature range, and to prevent film melting and bag tearing, the shrink wrapping temperature (100℃ to 200℃) ) and found that it is important to increase the elongation at the shrinkage temperature, and by blending polyethylene with a polymer that has a large elongation at the shrinkage temperature, we created a polyethylene heat-shrinkable film with very good shrink wrapping properties. Ta. That is, the present invention uses 95 to 50% by weight of polyethylene with a density of 0.930 g/cm ³ or less and a density of 0.920 g/cm ³ or less.
A novel heat-shrinkable product made by uniaxially stretching a film of a blend of 5 to 50% by weight of a polyolefin resin containing 20% by weight or more of ethylene-propylene rubber with an elongation E ₁₅₀ of 500% or more at 150°C. This is a shrink sleeve packaging method characterized by wrapping an object to be packaged with a film and the novel heat-shrinkable film described above. In the present invention, the polymer blended to give polyethylene a large elongation at the shrinkage temperature is an ethylene-propylene rubber having a density of 0.920 g/cm ³ or less and an elongation _E150 value of 500% or more at 150°C. The polyolefin resin contains 5 to 50% by weight of the polyolefin resin based on 95 to 50% by weight of polyethylene. Note that if the amount of the polyolefin resin added to the polyethylene is less than 5% by weight, it will not be possible to impart the elongation at the shrinkage temperature necessary to improve the shrink wrapping properties of the polyethylene film, and If this is the case, the advantages of polyethylene film, such as easy heat-sealability and transparency, will be significantly reduced. The elongation _E150 value in the present invention, that is, the elongation at 150°C, was determined in accordance with JISK6761. Specifically, a test piece was punched out using a JIS No. 3 dumbbell from a press sheet with a wall thickness of 1 mm, and stretched at a tensile speed of 200 mm/min by autographing at 150°C. The resulting elongation at the break point was divided by the previously measured distance between the gauge lines. In the present invention, a polyolefin resin containing 20% by weight or more of ethylene-propylene rubber is selected from polyolefin resins having a density of 0.920 g/cm ³ or less and an E ₁₅₀ value of 500% or more as the resin to be blended with polyethylene. The reason for this is that the polyolefin resin does not impair the advantages of heat-shrinkable polyethylene film, such as easy heat-sealability, easy heat-shrinkability, and transparency. , polybutene-
Polyolefin resins having an E ₁₅₀ value of 500% or more can be blended. E ₁₅₀ value is less than 0.920g/ ^cm3 with polyethylene density.
Ethylene-propylene rubber showing 500% or more
The most suitable method for blending polyolefin resins containing 20% by weight or more is to mix pellets using a drum tumbler or Henschel mixer, and then knead and granulate them using an extruder for granulation. For polyolefin resins having good compatibility, it is also possible to mix pellets using a drum tumbler or Henschel mixer and then directly feed the mixture into an extruder for raw film. The raw film before stretching is processed by normal film manufacturing methods, such as inflation film processing method or T
A flat film processing method using a die is used, and the uniaxial stretching method can be a normal inter-roll stretching method or a pressure roll method, but a blended film containing two or more types of resins as in the present invention is stretched. In this case, the pressure roll method is most suitable because it provides uniform stretching, no stretching breakage, and significantly improves the transparency of the film itself.In particular, the film stretched at a pressure roll temperature of 100℃ or less is easily heatable It has shrinkability and is suitable for shrink sleeve packaging. Next, the shrink sleeve packaging method of the present invention is to use 95 to 50% by weight of polyethylene with a density of 0.930 g/cm ³ or less and an elongation E ₁₅₀ at 150°C with a density of 0.920 g/cm ³ or less.
Ethylene-propylene rubber that is more than 500%
Packaging items with a new heat-shrinkable film made by uniaxially stretching a film made of a blend of 5-50% by weight of a polyolefin resin containing 20% by weight or more by passing it between pressure rolls. Compared to conventional shrink sleeve packaging using polyethylene heat-shrinkable film, shrink sleeve packaging using the characteristic shrink sleeve packaging method has a wider range of appropriate shrinkage temperatures in the shrink oven, so it is possible to create tight shrink sleeves by using higher temperatures or longer passage time in the oven. Even when packaging is performed, the film is not fused or the bag is torn, and packaging can be done with a good finish. Therefore, the commercial value of the packaged items has also been significantly improved. As mentioned above, the heat-shrinkable film of the present invention has excellent advantages of polyethylene heat-shrinkable film, namely easy heat-shrinkability, high cohesive strength, easy heat-sealability,
A heat-shrinkable film with excellent shrink-wrappability, that is, a narrow range of appropriate shrinkage temperatures, and improved film fusing and bag breakage during shrink-wrapping without impairing transparency, etc., and packaging objects with the heat-shrinkable film. This is a shrink sleeve packaging method that provides a packaged product with a good finish. Next, the present invention will be explained by examples, but the present invention is not limited in any way by these examples. Example 1 Polyethylene (Sumikasen) with a density of 0.923g/ ^cm3
101-1 manufactured by Sumitomo Chemical Industries) 90% by weight, density
Elongation E ₁₅₀ at 150℃ is 500% at 0.920g/cm3 or ^less
A mixture of 10% by weight of the above ethylene-propylene rubber polyolefin resin (Esplen 814M.I. = 0.83, density = 0.90g/cm ³ , manufactured by Sumitomo Chemical Industries, Ltd.) in a tumbler was mixed in an extruder with a diameter of 65 mmφ. A raw film having a thickness of 0.2 mm and a width of 600 mm was obtained. This raw film was passed between pressure rolls (diameter 260 mm, surface length 700 mm) at 80°C and stretched four times in the longitudinal direction to obtain a heat-shrinkable film having a thickness of 0.05 mm and a width of 500 mm. The thermal shrinkage rate of this film at 120° C. was 56% in the longitudinal direction and 8% expansion in the lateral direction, and the shrinkage stress in the longitudinal direction was 35 Kg/cm ² . Using this film, three cardboard boxes (weight 5 kg) each containing electrical products, measuring 20 cm long, 30 cm wide, and 15 cm wide, were assembled and wrapped using the sleep wrap method. , the furnace passage time was varied widely and shrink wrapping was carried out. Packaging results first
As shown in the table, even under high heat shrink wrapping conditions,
The film will not be fused, the bag will not break, or the transparency will decrease.
The three cardboard boxes were tightly bound with sufficient binding force, and the opening of the sleeve also had a beautiful packaging finish with no wrinkles or fusion. Example 2 Polyethylene (Sumikasen) with a density of 0.923g/ ^cm3
101-1 Sumitomo Chemical) 80% by weight, 0.920
Ethylene-propylene rubber polyolefin resin with elongation E ₁₅₀ at 150°C of 500% or more at g/cm ³ or less (Bieuron BR2700M.1 = 2, density =
A raw film having a thickness of 0.10 mm and a width of 600 mm was obtained by the same method as in Example 1 from a mixture of 20% by weight of 0.91 (manufactured by Mitsui Petrochemical) mixed in a tumbler. This raw film was stretched 2.0 times in the longitudinal direction using a six-roll longitudinal stretching machine heated to 70°C to obtain a heat-shrinkable film with a thickness of 0.05 mm and a width of 450 mm.
The thermal shrinkage rate of this film at 120℃ is 52% in the longitudinal direction and 12% in the lateral direction, and the shrinkage stress is
It was 31Kg/ ^cm2 . This film was used to wrap a 30 cm square cardboard box using the sleeve wrap method, and as in Example 1, the shrink wrapping conditions were varied widely to carry out shrink sleeve wrapping. The packaging results are shown in Table 1. Even under high-heat shrink packaging conditions, the film did not melt, break, or reduce transparency, and the packaging was tight and beautiful with no wrinkles or fusion at the sleeve opening. A packaging finish was obtained. Comparative Example 1 A polyethylene film (Sumikasen F101-1, thickness 0.2 mm, width 600 mm) with a density of 0.923 g/cm ³ obtained by the usual inflation molding method was processed using the same equipment and conditions as in Example 1. Stretched and thickened
A heat-shrinkable film with a size of 0.05 mm and a width of 500 mm was obtained. The thermal shrinkage rate of this film at 120° C. was 60% in the longitudinal direction, 9% expansion in the lateral direction, and the shrinkage stress in the longitudinal direction was 65 Kg/cm ² . This film was packaged in exactly the same way as in Example 1, in a hot air shrink oven,
Shrink wrapping was performed under shrink conditions. Packaging results first
As shown in the table, the suitable shrinkage temperature range was narrower than in Examples 1 and 2, and the film was fused and the bag was torn under high heating shrink packaging conditions. The physical properties of the film are values measured by the following measuring method. The heat shrinkage rate was determined by immersing a square test piece of 50 mm on each side, with its four sides parallel to both the length and width of the film, in a glycerin bath heated to 120°C for 5 seconds, and measuring the dimensions in both directions after cooling. Shrinkage rate (%) = film size before shrinkage - film size after shrinkage / film size before shrinkage x 100. Measurements were performed on 10 test pieces, and the average value was expressed. Shrinkage stress was measured by making a test piece with a width of 10 mm and a length of 50 mm in the longitudinal direction from a heat-shrinkable film, setting this test piece in the clamp of a strain gauge type shrinkage stress measuring device, and placing it in a glycerin bath heated to 120°C. to
Measurements were taken after immersion for 30 seconds. The value is the average value of 5 test pieces. As described above, the heat-shrinkable film of the present invention is an excellent polyethylene-based heat-shrinkable film that has easy heat-shrinkability, high cohesive strength heat-sealability, and excellent transparency, and has a wide range of suitable shrinkage temperatures. Moreover, if the film is used to wrap the packaged item and shrink sleeve wrapping is performed, it is possible to obtain a packaged item with a good packaging finish over a wide range of conditions. 【table】

Claims (1)

[Claims] 1. 95 to 50% by weight of polyethylene with a density of 0.930 g/cm ³ or less and elongation at 150°C with a density of 0.920 g/cm ³ or less
Polyolefin resin 5 containing 20% by weight or more of ethylene-propylene rubber with E ₁₅₀ of 500% or more
A novel heat-shrinkable film made by uniaxially stretching a film of a compound containing ~50% by weight. 2 Elongation at 150℃ with 95-50% by weight of polyethylene with a density of 0.930g/ ^cm3 or less and a density of 0.920g/ ^cm3 or less
Polyolefin resin 5 containing 20% by weight or more of ethylene-propylene rubber with E ₁₅₀ of 500% or more
2. A novel heat-shrinkable film according to claim 1, which is obtained by uniaxially stretching a film of a blend consisting of ~50% by weight by passing between pressure rolls. 3 Elongation at 150℃ with 95-50% by weight of polyethylene with a density of 0.930g/ ^cm3 or less and a density of 0.920g/cm3 ^or less
Polyolefin resin 5 containing 20% by weight or more of ethylene-propylene rubber with E ₁₅₀ of 500% or more
1. A method for packaging a shrink sleeve, characterized in that an article to be packaged is wrapped with a heat-shrinkable film formed by uniaxially stretching a film of a compound containing up to 50% by weight by passing between pressure rolls.