JPH0234779B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD This invention relates to heat-shrinkable packaging. Recently, packaging has been developed to improve the appearance of packaged items, tight packaging to avoid direct impact on the contents, label packaging that serves both to protect the glass bottle or plastic container and to display the product, and to reduce the space required for transportation. 2. Description of the Related Art Exterior packaging, label stickers for various molded products, cap stickers, etc. are widely used for the purpose of bundling articles. The plastic films used in these applications are anisotropic, heat-shrinkable,
It is required to have heat sealability, printability, etc. 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 discoloration and coloring of the packaged items, 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 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 comprises a propylene polymer and
Copolymerizing at least two types of copolymerizable α-olefins having different numbers of carbon atoms, each having from 2 to 10 carbon atoms (excluding 3 carbon atoms), to obtain one type of α-olefin among the at least two types of α-olefins. Content is 29
A mixed resin containing 50% by weight or more of propylene structural units in a mixture with ~71% by weight of an α-olefin copolymer is used as a base layer, and a surface layer of an olefin resin with a melting point of 150°C or less is formed on at least one side of the base layer. A heat-shrinkable composite film having a heat shrinkage rate at 120°C in either the transverse or longitudinal direction of the composite film that is at least twice the heat shrinkage rate in the other direction. , a heat-shrinkable packaging body 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 composite film used in this invention is 10~
500 microns, and when it is called a normal film, the surface layer thickness is 0.2 to 20 microns,
The thickness of the base layer is 10 to 200 microns, and when it is called a normal sheet, the thickness of the surface layer is generally 1 to 30 microns and the thickness of the base layer is 250 to 500 microns. In this specification, composite sheets are collectively referred to as composite films, without distinguishing between films and sheets. Among the mixed resins forming the base layer of the composite film, propylene polymers include isotactic polypropylene and propylene with carbon atoms of 2 to 10 carbon atoms.
It is a copolymer with α-olefin (excluding 3 carbon atoms). The content of α-olefin component in this copolymer is 0.5 to 20% of the total copolymer components.
% by weight, preferably from 3.6 to 20% by weight. Among the above propylene-based polymers, the melt index of polypropylene (measurement temperature 230°C, unit g/10 minutes, hereinafter abbreviated as MI) is 0.5 to 10,
Preferably it is 1.0-7. Also propylene α
- The MI of the olefin copolymer is 0.1-20, preferably 1.5-9. The other resin forming the base layer of the composite film, an α-olefin copolymer consisting of at least two types of carbon atoms of 2 to 10 (excluding 3 carbon atoms), contains one type of α-olefin. The amount is 21-79
Weight%. of the above α-olefin copolymer
MI is 0.5-20, preferably 1.0-10. In order to make the propylene constituent unit in the mixed resin 50% by weight or more, the mixing ratio of the propylene polymer in the mixed resin should be 50 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 composite 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, the shrinkage onset temperature will be high and the heat shrinkage rate will be low, as in the case of less than 50% by weight. Next, the surface layer provided on at least one side of the base layer has a melting point of 150°C or lower, preferably 147°C or lower, more preferably 135°C or lower, and 3°C or higher than the melting point of the resin of the base layer, preferably 5
It is an olefin resin with a temperature of ~80℃, and these olefin resins include polyethylene, ethylene/α-olefin copolymer, propylene/α-
Olefin copolymer, polybutene-1, butene
Examples include α-olefin copolymer, hexene/α-olefin copolymer, and the like. The copolymers exemplified above, such as ethylene/α-olefin copolymers, have ethylene as a main component, α-olefin has 3 to 10 carbon atoms, and the type and content of α-olefin vary depending on the copolymer. was selected so that its melting point would be 150°C or less. Examples of the above-mentioned copolymers include terpolymers containing three types of olefin components, such as propylene-ethylene-butene-1 copolymers. Further, the olefin resin of the surface layer may be any mixed resin of the above-mentioned polymers. Note that the melting point is a value measured with a differential calorimeter, and in the case of a mixed resin, it can be determined from the main peak. In this invention, by providing the above surface layer and further stretching, it is heat-sealed at a temperature lower than the melting point of the olefin resin, and when pressure is applied during heat-sealing, the heat-sealing temperature is lower than the melting point of each resin. , strong heat sealing strength can be obtained. If the melting point of the surface layer resin exceeds 150℃,
Heat-sealability deteriorates, and shrinkage occurs during heat-sealing, making wrinkles more likely to occur. Additives such as an antistatic agent, a lubricant, and an antiblocking agent can be mixed with the resin of the composite film to improve the automatic packaging property and the slipperiness of the packaged object. 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, polyoxyethylene alkyl phenyl ethers, and lubricants include: Common soaps include higher fatty acid amide, higher fatty acid ester, wax, 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,
In addition to the above additives, pigments, dyes, ultraviolet absorbers, etc. can be added depending on the purpose. One of the features of the composite film used in this invention is that it can be used in either the horizontal or vertical direction.
The heat shrinkage rate at 120°C is more than twice the heat shrinkage rate in the other direction. 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 composite film is formed into a cylindrical shape, coated on an object to be packaged, and heat-shrinked to make it adhere tightly to the object, the one with a higher heat shrinkage rate in the lateral direction is better for cutting the film. preferable. Therefore, the case where the lateral heat shrinkage rate is large will be explained below. If the heat shrinkage rate of the composite film is less than twice 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 composite film is Appearance deteriorates when used and packaged. For example, a composite film is heat-sealed 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 this film cylinder is attached to the packaged item. When the film cylinder is coated and 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 shrink over 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 printed composite film cylinder is used, the printed pattern is distorted at the upper and lower edges, degrading the appearance. As understood from the above description, the thermal shrinkage rate in the longitudinal direction is preferably small, and is generally 1% 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 composite film is manufactured by appropriately setting the stretching conditions in a normal composite film manufacturing method. That is, an unstretched composite film is produced by coextruding the surface layer and the base layer from one die, or by extruding and laminating the surface layer on the top surface on which the base layer has been extruded.
Stretching this unstretched film at least in the transverse direction,
Preferably, the stretching is carried out sequentially or simultaneously in the machine direction and the transverse direction. Alternatively, the base layer may be extruded, stretched longitudinally if necessary, and then the surface layer extruded, laminated, and then stretched laterally, or the base layer and surface layer may be extruded separately, and both may be longitudinally stretched. It is also possible to use a method in which the film is laminated at the same time and further stretched in the transverse direction. When laminating the base layer and the surface layer, an adhesive may be used if necessary. The longitudinal stretching ratio in the production of the composite film is 1.0 to 2.0 times, preferably 1.0 to 1.5 times,
That is, stretching in the longitudinal direction may be omitted in some cases. Further, the stretching temperature is 70 to 160°C, preferably 80 to 140°C. The stretching ratio in the transverse direction is 6.0 to 16 times, preferably
The preferred range is 6.5 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 80~160℃,
Preferably it is 90-140°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 composite 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. Vapor deposition can be processed. The heat-shrinkable composite 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 an object to be packaged and then heated and heat-shrinked. Make sure it is in 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 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 above heating method and heating conditions 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, the degree of heat shrinkage of the film is 90% or less, preferably 70% or less of the free heat shrinkage rate of the film at the heating temperature and time for heat shrinking. The percentage of the shrinkage rate of the packaging film to the heat shrinkage rate is defined as the specific shrinkage degree. 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 and chairs, 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 As a base layer, 75 parts by weight of propylene-ethylene copolymer (ethylene content 4.5% by weight) with MI2.5,
A mixture of MI2 with 25 parts by weight of butene-ethylene copolymer (ethylene content 60% by weight), 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, A composition containing 0.4 parts by weight of calcium carbonate was prepared. In addition, as a surface layer, 100 parts by weight of MI5 propylene-butene-1 copolymer (butene-1 content 20% by weight), calcium carbonate 0.15
Part by weight, glycerin ester of stearic acid 0.3
A composition containing 0.2 parts by weight of oleic acid amide and 0.2 parts by weight was prepared. The above base layer and surface layer compositions were melt-extruded using two extruders to produce a three-layer sandwich-like unstretched composite film (thickness: 600μ) consisting of a surface layer on both sides and a base layer in the center. It was stretched 1.3 times in the machine direction at 120°C, then stretched 9 times in the transverse direction at 125°C, heat-set in this tensioned state for 5 seconds, in a 2% relaxed state for 4 seconds, and then cooled to 25°C. Thereafter, it was removed from the clip and one side was subjected to corona discharge treatment to obtain a heat-shrinkable composite film with a thickness of 50 μm (base layer 44 μm). The above heat-shrinkable composite 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 an open top and bottom and a diameter of 58 mm and a length of 38 cm. Insert a yam with a diameter of 55 mm and a length of 35 cm, then
The film tube was shrunk by hot air treatment at 230°C for 55 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. One package and a package containing 10 packages were dropped from a height of 1 m to test the degree of breakage of the yams. For comparison, similar drop tests were conducted on yams with specific shrinkage of 90% (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 composite film as in Example 1, and this film tube had a bottom diameter of 40 mm and a head diameter of 30 mm.
The film tube was placed over a truncated conical container of 80 mm in height and 80 mm in height at a rate of 100 pieces per minute, and subjected to hot air treatment at 210° C. for 5 seconds to shrink the film tube and bring it into close contact with the container.
The specific shrinkage of the film at this time was 39% in the transverse direction. For comparison, similar packages were obtained for a biaxially shrinkable polypropylene film (Comparative Example 4) and a uniaxially shrinkable polyvinyl chloride film (Comparative Example 5). 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, various polymers with different melting points were used as the surface layer, and the total thickness was 70μ (base layer thickness
A heat-shrinkable three-layer film of 60μ) was obtained, and one side of the three-layer film that had been subjected to a corona discharge treatment was printed using printing ink for polypropylene (trade name PP-ST, manufactured by Toyo Ink Co., Ltd.). These films are rolled into a cylindrical shape and the end joints are ultrasonically sealed to create a film tube with a diameter of 62 mm and a length of 80 mm. 50mm diameter and width approximately in the center
Place it over a cylindrical container with a 10mm annular recess,
The film tube was heat-shrinked by hot air treatment at 230°C for 5 seconds. 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-mentioned Example 3, the degree of specific shrinkage when the film was in close contact with the annular recess was 35%. Furthermore, the types of surface layer resin are as follows. Name MI A Isotactic polypropylene 2.5 B Propylene/ethylene copolymer (ethylene content: 0.4% by weight) 4.0 C Propylene/ethylene copolymer (ethylene content: 3.0% by weight) 2.5 D Propylene/ethylene copolymer (ethylene content: 3.0% by weight) 3.0 E Propylene-butene copolymer (butene-1 content 17% by weight) 5.0 F Propylene-ethylene-butene copolymer (ethylene content 6% by weight, butene-1 content 13% by weight) ) 7.0

[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. △ means that wrinkles are observed, but it is at a level that can be put to practical use, and 〇 means 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, the annular recess in the center of the surface layer resins A, B, and C causes the film to rise and not adhere, but the surface layer resins D, E, and F completely adhere to the annular recess. do. In particular, the heat-sealed portion of the film tube may not be sufficiently heat-shrinked when two layers are stacked on top of each other, and depending on the type of surface layer resin, it may not be possible to obtain a tightly-fitting package. Example 4 Composite 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 heat-sealing the films to obtain a film with a diameter of 72 mm and a length of 100 mm. I created a film tube. This film tube has a head diameter of 35 mm, a bottom diameter of 40 mm, a maximum diameter of the lower half of 70 mm, and a height of
Cover the outside of a 100mm cylindrical container, then 220mm
It was thermally shrunk by blowing hot air at ℃ 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.

Claims (1)

[Scope of Claims] 1 A propylene-based polymer is copolymerized with at least two types of copolymerizable α-olefins having different carbon numbers, each having 2 to 10 carbon atoms (excluding 3 carbon atoms). α-olefin containing 29 to 71% by weight of one α-olefin among the species α-olefin
A composite film having a base layer of a mixed resin containing 50% by weight or more of propylene structural units in a mixture with an olefin copolymer, and a surface layer of an olefin resin having a melting point of 150° C. or less on at least one side of the base layer, A heat-shrinkable composite film in which the heat shrinkage rate at 120°C in either the transverse direction or the longitudinal direction of the composite film is at least twice the heat shrinkage rate in the other direction, and the specific shrinkage degree of the film 1. 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 90% or less. 2. The heat-shrinkable package according to claim 1, wherein the heat shrinkage rate of the composite film in the transverse direction is at least twice the heat shrinkage rate in the longitudinal direction. 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. 4 Among the mixed resins forming the base layer of the film,
Propylene polymers include isotactic polypropylene and α-olefins having 2 to 10 carbon atoms.
The heat-shrinkable package according to any one of claims 1 to 3, which is a propylene/α-olefin copolymer containing 2.5 to 40% by weight.