JPH0349827B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD This invention relates to heat-shrinkable packaging. Recently, there has been a rise in the use of exterior packaging to improve the appearance of packaged goods, tight packaging to avoid direct impact on the contents, label packaging that serves both to protect glass bottles or plastic containers and to display the product, and other packaging products that require less transportation space. Exteriors of packaging products, labels for various molded products, cap stickers, etc. are widely used for the purpose of bundling, etc. Plastic films used for these purposes are required to have anisotropic heat shrinkability, heat sealability, printability, and the like. Conventionally, films made of polyvinyl chloride, polyethylene irradiated with electron beams, etc. have been used to achieve the above objectives, and biaxially oriented polypropylene films have been used as light packaging materials such as instant cutlet ramen containers. . However, while the above-mentioned polyvinyl chloride film has good heat shrinkability, it has poor heat sealability and requires the use of adhesives, and is also undesirable because it causes corrosion and environmental problems due to chlorine gas generated when waste is incinerated. . In addition, in the case of the polyethylene film mentioned above, transparency and gloss are insufficient, and vertical and
It is difficult to obtain films with different heat shrinkage rates in the lateral direction. Furthermore, biaxially oriented polypropylene film has a low heat shrinkage rate at low temperatures, so it must be heat-shrinked at high temperatures.In this case, the temperature of the packaged items also rises, causing problems such as deterioration of the packaged items, coloring, and damage to the exterior. This may cause deformation of the material or the container itself, making it difficult to obtain a tight packaging material with a good appearance. The inventor completed this invention as a result of intensive research to solve the above problems and meet market demands. That is, this invention provides a propylene/α-olefin copolymer containing 1.5 to 20% by weight of α-olefin having 2 to 10 carbon atoms (excluding 3 carbon atoms), and a propylene/α-olefin copolymer containing 1.5 to 20% by weight copolymerizable α- with at least two different carbon numbers
An α-olefin copolymer obtained by copolymerizing olefins, in which the content of one type of α-olefin is 21 to 79% by weight, and the propylene constituent unit is 50% by weight. A film made of a mixed resin containing the above, in either the horizontal or vertical direction of the film.
A heat shrinkable film whose heat shrinkage rate at 120°C is at least twice the heat shrinkage rate in the other direction and whose heat shrinkage rate in the other direction is 15% or less, and the specific shrinkage rate of the film is 90%. This is a heat-shrinkable packaging body characterized in that the outside of a solid object is partially or completely covered in an adhesive manner in a state of shrinkage of less than %. The thickness of the film used in this invention is 10 to 500.
It ranges from 10 to 250 microns when called a normal film, and from 250 to 500 microns when called a normal sheet. In this specification, composite sheets are collectively referred to as composite films, without distinguishing between films and sheets. Among the mixed resins forming the film, the propylene/α-olefin copolymer is a copolymer of propylene and α-olefin having 2 to 10 carbon atoms (excluding 3 carbon atoms). And α in this copolymer
- The content of the olefin component is 1.5 to 20% by weight, preferably 3.6 to 20% by weight based on the total copolymerization components. If the content of the α-olefin component is less than 1.5% by weight, the low-temperature shrinkage rate will decrease. , on the contrary 20% by weight
If the temperature is too high, the heat resistance will be insufficient. Among the above-mentioned propylene-based polymers, polypropylene has a melt index (measurement temperature: 230°C, unit: g/10 minutes, hereinafter abbreviated as MI) of 0.5 to 10, preferably 1.0 to 7. Also propylene α-
The MI of the olefin copolymer is 0.1-20, preferably
It is 1.5-9. Other resins that form the film have a carbon number of 2 or more
The α-olefin copolymer consisting of at least two arbitrary types of 10 (excluding 3 carbon atoms) is one of them.
The alpha-olefin content of the seeds is 21-79% by weight. The MI of the above α-olefin copolymer is 0.5
-20, preferably 1.0-10. In order to make the propylene structural unit in the mixed resin 50% by weight or more, the mixing ratio of the propylene polymer in the mixed resin should be 55 to 99% by weight based on the total mixed resin.
Preferably 54-95% by weight, particularly preferably 55-90%
Weight%. The mixing ratio of propylene polymer is
If it is less than 50% by weight, the film becomes too stiff to be used in automatic packaging machines, and the temperature at which shrinkage starts becomes high, and the resulting heat shrinkage rate also decreases. On the other hand, if the mixing ratio exceeds 99% by weight,
As in the case of less than 50% by weight, the shrinkage onset temperature is high and the heat shrinkage rate is low, making it impractical. The resin of the above film contains antistatic agents, lubricants,
Additives such as anti-blocking agents can be mixed to improve automatic packaging and the slipperiness of the packaged items. Examples of antistatic agents include ethylene oxide adducts of alkylamines, ethylene oxide adducts of alkylamides, betaine type antistatic agents, monoglycerides of other fatty acid esters, and polyoxyethylene alkyl phenyl ethers. Commonly used soaps include fatty acid amide-based soaps, higher fatty acid ester-based soaps, wax-based soaps, and metal soaps. Anti-blocking agents include inorganic additives such as silica, calcium carbonate, magnesium silicate, and calcium phosphate, nonionic surfactants, anionic surfactants, and incompatible organic polymers ( For example, polyamide, polyester, polycarbonate, etc.) are used. These additives are mixed in an amount of 0.05 to 5% by weight, preferably 0.1 to 3% by weight, based on the resin component. In addition to the above additives, pigments, dyes, ultraviolet absorbers, etc. can be added depending on the purpose. One feature of the film used in this invention is that it has a 120
Heat shrinkage rate at °C (JIS-K-6782, 120 °C, 15
The dry heat free shrinkage rate (per minute) is at least twice the heat shrinkage rate in the other direction, and the heat shrinkage rate in the other direction is 15% or less. The heat shrinkage rate may be greater in either the transverse direction or the longitudinal direction, but in the commonly used sequential biaxial stretching, longitudinal stretching is performed using stretching rolls, followed by transverse stretching using a tenter. In terms of film production, it is preferable that the heat shrinkage rate in the transverse direction is at least twice the heat shrinkage rate in the longitudinal direction. In addition, when the above-mentioned film is formed into a cylindrical shape and is coated on an object to be packaged, and then heat-shrinked to make it adhere tightly to the object to be packaged, it is preferable for the film to have a larger heat shrinkage rate in the lateral direction as described above in terms of cutting the film. . Therefore, the case where the lateral heat shrinkage rate is large will be explained below. If the heat shrinkage rate in the transverse direction of the film is less than 2 times the heat shrinkage rate in the longitudinal direction, that is, if the heat shrinkage rate in the longitudinal direction is more than 0.5 times the heat shrinkage rate in the transverse direction, this film is Appearance deteriorates when used as an exterior. For example, heat seal the film in the axial direction with the vertical direction as the horizontal direction and the horizontal direction as the circumferential direction to create a film cylinder with the same length as the height of the packaged item, and then cover the packaged item with this film cylinder. When the film cylinder is heat-shrinked, the film cylinder shrinks horizontally along the outer circumferential surface of the packaged item and comes into close contact with the packaged item, but the upper and lower ends of the film cylinder shrink vertically and shrink over the packaged item. It is shorter than the lower end, and furthermore, the lower edge has a zigzag shape, resulting in a poor appearance. In particular, when a cylinder of printed film is used, the printed pattern is distorted at the upper and lower edges, degrading the appearance. As understood from the above explanation, the thermal shrinkage rate in the longitudinal direction is preferably small, and is generally 15% or less. On the other hand, it is preferable that the heat shrinkage rate in the transverse direction is large, but it is usually 2.0 to 40 times the heat shrinkage rate in the longitudinal direction, and specifically, it is preferable that the heat shrinkage rate is 15 to 80%. The larger the unevenness of the outer shape of the packaged object, the higher the lateral heat shrinkage rate is required. The film of the present invention is manufactured by appropriately setting stretching conditions in a conventional film manufacturing method. The longitudinal stretching ratio in film production is
It is 1.0 to 2.0 times, preferably 1.0 to 1.5 times, that is, longitudinal stretching may be omitted. Further, the stretching temperature is 70 to 160°C, preferably 80 to 140°C. The stretching ratio in the transverse direction is 5.0 to 16 times, preferably
The preferable range is 6.0 to 12 times, and 7.0 to 13 times if even higher heat shrinkability in the transverse direction is required. Further, the stretching temperature is 80 to 160°C, preferably 90 to 140°C. The film stretched as above continues to
Either lower the temperature to 120°C or lower, preferably 80°C or lower, or rapidly cool it to 0°C, preferably around 10°C to maintain the above stretched state or maintain the state with a dimensional change of about ±10%. While doing so, leave it for 2 to 10 seconds until it reaches room temperature. Cooling after stretching is performed by air cooling, cooling rolls, cooling belts, or a combination thereof. The surface layer of the stretched film obtained as described above is subjected to surface activation treatment such as corona discharge treatment, discharge treatment in various gas atmospheres, acid treatment, flame treatment, etc., and printing and metal vapor deposition as necessary. can be processed. The heat-shrinkable film obtained as described above is formed into a cylindrical shape with the longitudinal direction as its axis and heat-sealed, and the film cylinder is coated on the object to be packaged and then heated to heat-shrink the outer surface. Make sure it is in close contact with the In the case of hot air, the conditions for heat shrinking are 160 to 280°C for 2 to 10 seconds, and the film temperature at that time is preferably 80 to 150°C. Note that the relationship between heating temperature and time is determined by the wind speed and blowing angle of the hot air. Of course, the heating method and heating conditions described above may be other methods than hot air. The degree of heat shrinkage of the above-mentioned film is such that the heat-shrinked film adheres partially or completely to the outer surface of the packaged object, and the packaged object adheres tightly to the extent that the packaged object does not shift even when an external force is applied. It is sufficient. That is, in this invention, the actual heat shrinkage rate under restraint that occurs when the film covered with the packaged item is heated and heat-shrinked during packaging, and the film is heated at the same heating temperature and time as during packaging. The ratio (percentage) to the free heat shrinkage rate when freely heat-shrinked below is defined as the specific shrinkage degree, and this specific shrinkage degree is set to 90% or less, preferably 70% or less. The above-mentioned specific shrinkage of 90% or less has an important meaning because damage to the packaged object is reduced when the package is subjected to impact such as dropping or hitting. If the specific shrinkage rate exceeds 90%, the outer film will not be able to cushion the impact when the package receives an impact, and the packaged item may be damaged by the impact. Note that even if the shrink wrapper has holes or openings partially in the outer film, the effects of the present invention will not be diminished. Items to be packaged include glass or plastic bottles, containers made of paper, plastic, metal, and other materials, metal rod-shaped bodies such as the legs of desks, chairs, etc., or spherical bodies, and agricultural products such as root vegetables and fruits. can be given. The shrink wrapper according to the present invention not only improves its commercial value by printing product names, advertisements, cautionary notes, etc. on the outer film, but also prevents the packaged items from being damaged or broken by impact. Examples of the present invention will be described below. Example 1 A mixture of 75 parts by weight of propylene-ethylene copolymer (ethylene content 4.5% by weight) with MI2.5 and 25 parts by weight of butene-ethylene copolymer (ethylene content 60% by weight) with MI2 A composition was prepared by adding 0.35 parts by weight of glycerin ester of stearic acid, 0.8 parts by weight of an alkylamine type antistatic agent, 0.1 parts by weight of erucic acid amide, and 0.4 parts by weight of calcium carbonate. The composition was melt-extruded to produce an unstretched film (thickness 600μ), which was then stretched 1.3 times in the machine direction at 122°C, then stretched 9 times in the transverse direction at 125°C, and held in this tensioned state for 5 seconds for 2 4 in relaxation state of %
After heat fixing for seconds and further cooling to 25°C, it was removed from the clip, and one side was subjected to corona discharge treatment to obtain a heat-shrinkable film with a thickness of 50 μm.
Heat shrinkage rate of the film of Example 1 (JIS-K-
6782, dry heat free shrinkage rate at 120°C for 15 minutes) was 8.9% in the machine direction and 65.0% in the transverse direction. The above heat-shrinkable film was made into a cylindrical shape, and the overlapping surfaces at the ends were heat-sealed with a heater having serrations to create a film tube with a diameter of 58 mm and a length of 38 cm open at the top and bottom. Insert a 55mm and 35cm long yam, then heat at 230℃.
The film tube was shrunk by applying hot air treatment for 5 seconds. The specific shrinkage of the film at this time was 12% in the transverse direction, and a shrink-wrapped body was obtained in which the film adhered to the yam and the film surface was taut.
The degree of breakage of the yams was tested by dropping one package and 10 packages obtained by bundling the yams in two places with polypropylene bands from a height of 1 m onto a concrete floor. For comparison, similar drop tests were conducted on yams with specific shrinkage of 95% (Comparative Example 1), yams before heat shrinkage treatment (Comparative Example 2), and yams that were not wrapped at all (Comparative Example 3). The first result of the drop test
Shown in the table.

[Table] As seen in Table 1 above, Example 1 had significantly fewer breakages than Comparative Examples 1 and 2, indicating that the close-tight packaging was highly effective. Example 2 A film tube with a diameter of 42 mm and a length of 80 cm was created using the same heat-shrinkable film as in Example 1.
This film tube is placed over a truncated conical container with a bottom diameter of 40 mm, a head diameter of 30 mm, and a height of 80 mm at a rate of 100 pieces per minute, and then treated with hot air at 210°C for 5 seconds to shrink the film tube and adhere tightly to the container. I let it happen. The specific shrinkage of the film at this time was 46% in the transverse direction. For comparison, similar packages were obtained for a biaxially shrinkable polypropylene film (Comparative Example 4) and a shrinkable polyvinyl chloride film (Comparative Example 5). The heat shrinkage rate (JIS-K-6782, 120°C x 15 minutes) of the film of Comparative Example 4 was
The heat shrinkage rate of the film of Comparative Example 5 was 7.0% in the longitudinal direction and 29.0% in the transverse direction. Evaluations of the workability, appearance, etc. of the films of Example 2 and Comparative Examples 4 and 5 are shown in Table 2.

【table】

[Table] As seen in Table 2 above, the film of Example 2 was easy to cover even if there was some resistance when covering the film tube with the container, but Comparative Example 4
The film tube was difficult to cover because the tube was bent over. Furthermore, in Example 2, the film did not rise much after shrink wrapping, and there was no odor during heat sealing. Example 3 In Example 1 above, various polymers were used,
A heat-shrinkable film having a total thickness of 70 μm was obtained, and one side of this film, which had been subjected to corona discharge treatment, was printed using printing ink for polypropylene (trade name: PP-ST, manufactured by Toyo Ink Co., Ltd.). These films were rolled into a cylindrical shape and the end joints were ultrasonically sealed to create a film tube with a diameter of 62 mm and a length of 80 mm.
100mm and approximately the center of the height is 50mm in diameter and 10mm in width.
Cover a cylindrical container with an annular recess of mm, 230
℃ for 5 seconds to shrink the film tube. The distance between the bottom of the annular recess of the container and the shrink film in the annular recess after heat shrinkage (0 if it is in close contact with the annular recess), the presence or absence of wrinkles in the heat seal part, the adhesion status, and the heat seal strength are shown in Table 3 below. Shown below. In addition, in the above Example 3, the specific shrinkage degree when the film was in close contact with the annular recess was 34%. Furthermore, the types of resins are as follows.

【table】

[Table] The wrinkles in the heat seal part in Table 3 above are as follows:
Heat-seal with a hot plate for 2 seconds at 130℃ and a pressure of 2Kg/cm ² , and visually observe and evaluate the degree of wrinkles that occur in the area. The degree of wrinkles caused by poor heat sealing is limited to the extent that wrinkles occur, △ indicates that wrinkles are observed but the level is practically usable, and 〇 indicates that the adhesion is sufficient and there are no wrinkles. be. The adhesion status of the heat-sealed portion was evaluated by observing the situation in which the heat-sealed portion peeled or waved due to the application of tension due to shrinkage stress after heat shrinkage. As can be seen in Table 3 above, in the annular recess at the center, the films of resins A, B, and C do not stick together because the film floats up, but those of resins D and E completely adhere to each other. In particular, the heat-sealed portion of the film tube may not be sufficiently heat-shrinked because two films are stacked on top of each other, and depending on the type of resin, it may not be possible to obtain a package that is in close contact with the film. Example 4 Films with different horizontal/vertical heat shrinkage ratios at 120°C were produced by changing the stretching ratio in the transverse direction in Example 1 above, and the films were heat-sealed to form a film with a diameter of 72 mm and a length of 100 mm. I created a film tube. This film tube is
35mm, bottom diameter 40mm, lower half maximum diameter 70mm, height 100
Cover the outside of a cylindrical container with a diameter of
It was thermally shrunk by blowing hot air on it for 5 seconds. Table 4 shows the results of measuring the lifting distance of the lower end of the film from the bottom of the irregularly shaped container and the variation range of the lifting distance on the circumferential surface of the container.

[Table] As shown in Table 4, when the horizontal heat shrinkage rate is twice or more than the vertical heat shrinkage rate, the film hardly lifts up even if it is heat-shrinked. Examples 5 to 7 Heat-shrinkable films were manufactured using various resins having different compositions in the same manner as in Example 3 above, and the same tests were conducted. The composition of the above resin is shown in Table 5.
The test results are also shown in Table 6.

【table】

【table】

[Table] As shown in Table 6 above, in Examples 5 to 7, the adhesion of the annular recess in the center was good and the appearance of the heat-sealed part was also good, but in Comparative Examples 6 and 7, the stiffness was poor. This resulted in poor workability, and lifting was observed in the annular recess at the center, resulting in insufficient adhesion.
Furthermore, in Comparative Examples 6 and 7, wrinkles occurred in the heat-sealed portion due to insufficient heat resistance. Note that the specific shrinkage degree of the above example was 34%.

Claims (1)

[Claims] 1 α having 2 to 10 carbon atoms (excluding 3 carbon atoms)
- Propylene/α-olefin copolymer containing 1.5 to 20% by weight of olefin and having 2 to 10 carbon atoms
An α-olefin copolymer obtained by copolymerizing at least two copolymerizable α-olefins with different numbers of carbon atoms (excluding those with 3 carbon atoms), the content of one of which is 21 ~79% by weight
A film made of a mixed resin containing 50% by weight or more of propylene constitutional units in a mixture with an α-olefin copolymer of The heat shrinkage rate in the other direction is more than twice,
With a heat shrinkable film whose heat shrinkage rate in the other direction is 15% or less, the specific shrinkage rate of the film is 90%.
1. A heat-shrinkable package characterized in that the outside of a solid object is partially or completely covered in a tightly adhered manner in the following contracted state. 2. Claim 1, wherein the heat shrinkage rate in the transverse direction of the film is at least twice the heat shrinkage rate in the longitudinal direction.
Heat-shrinkable packaging as described in section. 3. The heat-shrinkable package according to claim 1 or 2, wherein at least one side of the film is subjected to corona discharge treatment and printing is applied to that side.