JPH0349826B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a shrink wrap made of film. Recently, there has been an increase 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 methods that reduce transportation space.
For the purpose of bundling the packaged items, etc.,
Various molded label sheets, cap stickers, etc. are widely used. 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 package with good appearance. The inventor completed this invention as a result of intensive research to solve the above problems and meet market demands. That is, the present invention provides a film made of a propylene/α-olefin copolymer in which the content of α-olefin having 4 to 10 carbon atoms is 12 to 20% by weight based on the total copolymerization components, and A heat-shrinkable composite film whose heat shrinkage rate at 120°C in one direction is at least twice that of the other direction, and whose heat shrinkage rate in the other direction is 15% or less; This is a shrink wrap made of a film, characterized in that the outside of a solid object is partially or completely covered in a contracted state with a specific shrinkage degree of 90% or less. The thickness of the film used in this invention is 10 to 500.
The thickness 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, sheets are collectively referred to as films, without making any distinction between films and sheets. The propylene-α-olefin copolymer that forms the film is composed of propylene and α-olefin having 4 to 10 carbon atoms.
It is a copolymer with olefin. The content of the α-olefin component in this copolymer is 12 to 20% by weight, preferably 3.6 to 20% by weight based on the total copolymer components.
20% by weight, and if the α-olefin content is less than 12% by weight, the low-temperature shrinkability tends to decrease;
If it exceeds 20% by weight, heat resistance will be insufficient. propylene·
The α-olefin copolymer has a melt index (measurement temperature: 230° C., unit: g/10 minutes, hereinafter abbreviated as MI) of 0.5 to 15, preferably 1.0 to 10. Additives such as antistatic agents, lubricants, and antiblocking agents can be mixed into the film to improve automatic packaging properties and the slipperiness of objects to be packaged. 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.
As the lubricant, higher fatty acid amide type, higher fatty acid ester type, wax type, metal soap, etc. are generally used. As anti-blocking agents, inorganic additives such as silica, calcium carbonate, magnesium silicate, calcium phosphate, nonionic surfactants, anionic surfactants, incompatible organic polymerization agents (e.g. polyamide, polyester,
Polycarbonate, etc.) are used. These additives are mixed in an amount of 0.005 to 5% by weight, preferably 0.1 to 3% by weight, based on the resin component. In addition to the above additives, pigments, dyes, violet ray absorbers, etc. can be added depending on the purpose.One feature of the film used in this invention is that it can be used in either the horizontal or vertical direction. 120 of
Heat shrinkage rate at °C (JIS-K-6782, 12 °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 is at least twice the heat shrinkage rate in the longitudinal direction. In addition, when the above-mentioned film is formed into a circular shape and is coated on an object to be packaged and then heat-shrinked to make it adhere tightly to the object, 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 axial 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 object and comes into close contact with the packaged object, but the upper and lower ends of the film cylinder shrink vertically and close to the top of the packaged object. , is shorter than the lower edge, 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, the heat shrinkage rate in the transverse direction is preferably large, usually 2.0 to 40 times the heat shrinkage rate in the longitudinal direction, and specifically preferably 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 above-mentioned film is produced by stretching mainly in the transverse direction in the usual T-die method or inflation method, or by stretching and heat setting under specific conditions. 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 preferred range is 6.0 to 12 times, and 7.0 to 13 times if even greater heat shrinkability in the lateral direction is required. In addition, the stretching temperature is 800~160℃,
Preferably it is 90-140°C. The film stretched as above continues to
Reduce the temperature to 120℃, preferably below 80℃, or
Or rapidly cooled to 0℃, preferably around 10℃,
While maintaining the above-mentioned stretched state or maintaining the state where the dimensions have changed by about ±10%, the film is left for 2 to 10 seconds until it reaches room temperature. This cooling after stretching is
This may be done 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 film used in this invention not only has heat shrinkability, but also has superior high-speed ultrasonic sealability compared to general polyolefin films. Of course, it goes without saying that thermal bonding by a thermal method such as ordinary hot plate sealing, multi-point sealing, fusing sealing, etc., and bonding using a connecting agent are possible. The heat-shrinkable film obtained as above is
This is formed into a cylindrical shape with the longitudinal direction as its axis and heat-sealed, and the film cylinder is coated on the packaged item and then heated to cause heat shrinkage and bring it into close contact with the outer surface of the packaged item. 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 70 to 150°C. 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 is in close contact with the outer surface of the packaged object partially or completely, and the packaged object is not damaged even if 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 placed on 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 is defined as the specific shrinkage degree, and this specific shrinkage concentration is set to 90% or less, preferably 7% or less. It is important that the specific shrinkage is 90% or less because it reduces damage to the packaged product when it is subjected to impacts such as drops and hits. 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 rods such as the legs of desks and chairs, or spheres, 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 0.35 parts by weight of glycerin ester of stearic acid, 0.8 parts by weight of an alkylamine-type antistatic agent, and 0.1 parts by weight of erucic acid amide were added to a propylene-butene-1 copolymer with an MI of 4.5 (butene-1 content: 19% by weight). A composition was prepared in which parts by weight were added. The composition was melt extruded to form an unstretched film (thickness:
530μ), then stretched 1.1 times in the longitudinal direction at 114°C, then stretched 9.5 times in the transverse direction at 120°C, cooled to 60°C in this tensioned state, and then stretched at a relaxation rate of 1.5%.
The mixture was cooled to room temperature in 4 seconds. Furthermore, one side was subjected to corona discharge treatment to obtain a heat-shrinkable film with a thickness of 50 μm. The heat shrinkage rate (JIS-K-6782, dry heat free shrinkage rate at 120°C for 15 minutes) of the film of Example 1 was 5.7% in the machine direction and 61.0% 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 using a heater with 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 200℃.
The film tube was shrunk by applying hot air treatment for 5 seconds. The specific shrinkage of the film at this time was 15% in the transverse direction, and a shrink-wrapped body was obtained in which the film was in close contact with 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 mm was created using the same heat-shrinkable film as in Example 1.
This film tube was placed over a truncated conical vessel with a bottom diameter of 4 mm, a head diameter of 30 mm, and a height of 80 mm at a rate of 100 pieces per minute.
The film tube was shrunk by hot air treatment at 210° C. for 5 seconds and brought into close contact with the container. The specific shrinkage of the film at this time was 48% in the lateral direction.
It was hot. 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] 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, a heat-shrinkable film with a total thickness of 60 μm was obtained using various polymers with different melting points, and one side of this film treated with corona discharge was
Printing ink for polypropylene (product name PP-ST,
(manufactured by Toyo Ink Co., Ltd.). . These films are rolled into a cylindrical shape and the end portions are ultrasonically sealed to create a film tube with a diameter of 62 mm and a length of 80 mm. The film tube was placed over a cylindrical container having an annular recess approximately 50 mm in diameter and 10 mm in width in the center, and subjected to hot air treatment at 230°C 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-sealed portion, the adhesion condition, and the heat-seal strength are shown in Table 3 below. In the above example, the specific shrinkage rate when the film was in close contact with the annular recess was 35%. 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, and 〇 indicates that the adhesion is sufficient and no wrinkles occur. 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 and B do not come up and adhere, but the films of resins C and D 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
It was placed on the outside of a mm cylindrical shaped vessel, and then hot air at 220°C was blown for 5 seconds to cause heat shrinkage. 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.

Claims (1)

[Scope of Claims] 1. Propylene α containing 12 to 20% by weight of α-olefin having 4 to 10 carbon atoms based on the total copolymerization components.
- A film made of an olefin copolymer,
The heat shrinkage rate at 120°C in either the transverse or longitudinal direction of the film 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, and the outside of the solid object is partially or completely covered in a contracted state with a specific shrinkage of 90% or less. Shrink wrapping. 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.
Shrink wrapping made from the film described in Section 2. 3. A shrink-wrapped body made of a film according to claim 1 or 2, wherein at least one side of the film is subjected to a corona discharge treatment and printing is applied to that side.