JPH0576423B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to improvements in heat-shrinkable laminated packaging materials having heat sealability. (Prior Art) Heat-shrinkable plastic films such as polyolefin films and polyamide films are widely used as heat-shrinkable packaging materials for foods and other products. Depending on the type of item being packaged, packaging materials may be required to have properties such as pinhole resistance, cold resistance, and gas barrier properties. Although it is often used as a film, nylon-based film tends to stretch and its gas barrier properties deteriorate due to moisture absorption, so nylon film is laminated with a moisture-proof sealant film on both sides of this base film. is used. When heat-shrink packaging foods, etc., the items to be packaged are generally filled into bags made of heat-shrinkable packaging material that are made in advance using the gassho pasting method, tape sealing method, envelope pasting method, etc., and then degassed. ,
After being sealed by heat sealing, the package is heat-shrinked in hot air or hot water to form an adhesive package. As a heat-shrinkable laminated packaging material having such heat-sealing properties, for example,
Some of these are disclosed in Japanese Patent Application Laid-open No. 47986 and Japanese Patent Application Laid-open No. 15981/1983. (Problems to be Solved by the Invention) However, such multilayer films are made by laminating a sealant film with almost no heat shrinkability on one or both sides of a heat-shrinkable base film, or by laminating a sealant film on the base film. After the films are laminated, they are stretched. In such a multilayer film, the sealant layer has poor heat shrinkability, so a sufficient heat shrinkage rate cannot be obtained during heat shrink packaging, and voids are likely to occur inside the tight package, resulting in poor packaging tightness. Not only is the appearance damaged due to insufficient water retention, but also condensation forms in the voids, causing bacterial growth. Even if heat shrink treatment is performed under higher temperature conditions to compensate for the above-mentioned drawbacks, not only is it still not possible to obtain a satisfactory finished appearance, but depending on the type of item being packaged, the heat shrinkage during shrink wrapping may This may cause deterioration in the quality of the packaged items. In addition, when shrink wrapping is attempted using a multilayer film in which a heat-shrinkable sealant film is laminated on only one side of a heat-shrinkable base film, the heat-sealed portion must be placed in a clasped manner; In order to obtain seal strength, it is necessary to increase the thickness of the sealant film or widen the seal width, which poses a problem that the seal portion becomes unsightly. (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides heat-shrinkable laminated packaging having heat-sealability, which is formed by laminating heat-shrinkable sealant films on both sides of a heat-shrinkable base film. The material provides a satisfactory finished appearance during heat shrink packaging. The heat-shrinkable base film used in the present invention is stretched in the longitudinal and transverse directions at a stretching ratio of 1.5 to 7.0 times, and has a hot water shrinkage rate of 15 to 50% at 95°C, preferably 20 to 50%. % heat shrinkable films are used, such as nylon 6, nylon 6-6, nylon 6-10, nylon 6-6/6 copolymer, nylon 6-12, nylon 11, nylon
Polyamide resins such as 12, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyvinyl chloride resins, polyacrylonitrile resins, polystyrene resins, polyolefin resins such as polypropylene, polyvinyl alcohol resins, and ethylene/vinyl acetate copolymers. EVOH (hereinafter referred to as EVOH), a mixture thereof, or a resin containing these as main components is formed into a film, which is biaxially stretched in the longitudinal and transverse directions by at least 1.5 times, preferably 1.5 to 7.0 times, and 95 Examples include films that have been heat-shrinkable so that the hot water shrinkage rate at °C is 15 to 50%, preferably 20 to 50%, but the film is not limited to these. Furthermore, these films may be provided with a coating layer or a printing layer of polyvinylidene chloride resin, EVOH resin, or the like. The heat-shrinkable sealant film used in the present invention may be any heat-shrinkable sealant film having a melting point lower than that of the heat-shrinkable base film, such as a linear low-density polyethylene film (hereinafter referred to as L-LDPE film). ),
Low-density polyethylene film (hereinafter referred to as LDPE film), polypropylene film, ionomer resin, a mixture of these resins, or these resins with polyester elastomer,
A film mainly composed of a resin blended with a small amount of other polymers such as ethylene vinyl acetate copolymer resin is
Biaxially stretched 1.5 times, preferably 1.5 to 7.0 times at 95℃
More preferably, the hot water shrinkage rate is 10-50%.
A film having a heat-sealing property of 15 to 50% may be used, but a film having a heat-shrinkable property comparable to that of the heat-shrinkable base film is more preferably used. Furthermore, a heat-shrinkable sealant film made of L-LDPE is particularly preferred since it has excellent pinhole resistance and heat sealing strength. The heat-shrinkable base film used in the present invention usually has a thickness of 5 to 50 μm, and practically 10 to 50 μm thick.
A thickness of ~35 μm is preferred. In addition, a sealant film with a thickness of 10 to 50 μm is normally used, but since the sealant film according to the present invention is laminated on both sides of the base film, the heat-sealed part must be attached to an envelope. Therefore, the thickness of the sealant film may be relatively thin, and even a thickness of 10 to 30 μm can be suitably used. The type and thickness of the sealant film should be determined based on the performance required of the packaging material, such as pinhole resistance, gas barrier properties, and heat seal strength, as well as the characteristics of the base film used, based on the type and capacity of the packaged items. and is not limited to the above range. The heat-shrinkable laminated packaging material according to the present invention can be obtained by laminating the heat-shrinkable base film and the heat-shrinkable sealant film by a conventional laminating method, such as extrusion lamination or dry lamination. I can do it.
The extrusion lamination is a method in which a thermoplastic resin that can be formed into a film by melt extrusion is extruded through a thin slit of a T-die of an extruder, laminated on a base film, and then cooled and solidified. The dry lamination is a method in which an organic solvent-based adhesive such as a urethane adhesive is applied to a base film, the solvent is evaporated and removed by drying, and then a sealant film is laminated by heating and pressure bonding. The processing conditions during the lamination are appropriately selected depending on the combination of the base film and sealant film to be laminated. (Functions and Effects) The heat-shrinkable laminated packaging material according to the present invention obtained as described above can be heat-sealed in the sealant layer, and a sealant film with excellent heat-shrinkability is laminated thereon. It has excellent heat shrinkability without impairing the heat shrinkability of the material film. Furthermore, since the laminated packaging material of the present invention has a heat-shrinkable sealant film with excellent heat-sealability laminated on both sides of the base film, it can be made into bags by an envelope pasting method or the like, and can be made by a conventional method. A beautiful close-fitting package with high tightness can be obtained. In particular, those whose heat-shrinkable base film is a heat-shrinkable nylon film and L-LDPE sealant films are laminated on both sides of this film have excellent pinhole resistance, cold resistance, gas barrier properties, etc. It is an extremely superior heat-shrinkable packaging material that is almost unaffected by outside air humidity.
Since the heat sealing strength of LDPE sealant film is excellent, it is possible to reduce the thickness of the sealant layer and narrow the overlap width during lap sealing, resulting in a beautiful appearance of the sealed part. Therefore, the packaging material according to the invention is suitable for shrink-wrapping meat packages, cheese and various other articles. Moreover, the laminated packaging material according to the present invention is
It is made by laminating a base film and a sealant film, each of which has been made heat-shrinkable by stretching, and the films forming each layer are stretched under the optimum stretching conditions, and then the heat-shrinking treatment conditions are adjusted to the conditions for practical use. However, since it is possible to combine films with similar heat shrinkage rates, there is no possibility that internal distortions, etc. that would cause a decrease in the heat shrinkage rate of the packaging material and the occurrence of curls, etc., would occur before and after the heat shrinkage treatment. Also from this point of view, it is possible to obtain a beautiful tight-fitting package with high tightness. Furthermore, the laminated packaging material according to the present invention is made by laminating a base film and a sealant film, each of which has been made heat-shrinkable by stretching, as described above, and can be laminated with the printed surface inside. Compared to the case where both materials are laminated by a coextrusion method and then stretched, the printed appearance is better, and it is advantageous in that the printed surface can be prevented from peeling off or falling off due to friction, oil, water, etc. Furthermore, a single film has simpler manufacturing equipment and easier quality control than a multilayer film produced by coextrusion, making it suitable for mass production. It is also possible to easily obtain a laminated packaging material with predetermined properties such as heat shrinkability, barrier properties, heat sealability, puncture resistance, etc. as needed. It is practically superior to those with . (Example) Next, the present invention will be specifically explained, but the present invention is not limited thereto. In addition, the measuring method of the main characteristics measured in the present invention is as follows. Hot water shrinkage rate: The packaging material to be measured is approximately 20cm x 20
After cutting into cm pieces and conditioning the humidity at 20°C and 65% RH for 24 hours, accurately measure the vertical and horizontal dimensions of the film (the measured value is designated as A). This sample
After completely immersing the sample in hot water at 95℃ for 10 seconds (however, nylon film with sealant laminated on both sides is immersed in 100℃ for 5 minutes), remove it from the sample, remove moisture adhering to the surface of the sample by filtration, and heat the sample at 20℃. Leave it at 65% RH for 24 hours and accurately measure the vertical and horizontal dimensions of the film (the measured value is designated as B). The hot water shrinkage rate is calculated using the following formula. Hot water shrinkage rate (%) = (A-B/A) x 100 Heat seal strength: 20% of packaging material to be measured
℃, 65% RH for 24 hours, cut the samples into 25 mm x 300 mm, overlap them so that the sealant film sides are facing each other, and put this sample into a cylinder with a diameter of 50 mm.
φ, size 10mm width x 300mm length, seal with a bar sealer set at the specified temperature, gauge pressure 1Kg/cm ² , sealing time 1 second, and seal at 20℃, 65%RH for 24 hours.
Humidify for a period of time and sample to a width of 15 mm. This sample was attached to the chuck of Tensilon by pulling a different film from inside the seal, and it was attached to the chuck of Tensilon.
Pull at a speed of 1 minute, and read the strength using the Tensilon chart. Pinhole resistance: Pinhole resistance is expressed as puncture resistance. Fix the film in a frame with an inner diameter of 60 mm,
Place a hemispherical needle tip with a radius of curvature of 0.5 mm in the center of this circle perpendicularly to the film surface, and
Apply force at a speed of mm/min to determine the maximum resistance until it breaks.
Expressed in kg. Oxygen gas barrier property: Oxygen gas barrier property is
It is expressed as oxygen gas permeability measured by MOCON (OX-TRAN100 type oxygen gas permeability measuring device) manufactured by Modern Controls, Inc. in the United States in accordance with ASTM D-1434. Measurement conditions DRY: Measured in a dry state using a sample left in an absolute dry desiccator for 24 hours or more WET: Measured in a wet state after being immersed in water for 24 hours Example 1 Simultaneously biaxially stretched 15 μm thick nylon 6 (second
The heat-shrinkable film shown in Table (A)) was simultaneously biaxially stretched as a heat-shrinkable sealant on both sides with a specific gravity of 0.92 and a thickness of
15μm single-sided corona treatment (wetting tension 40 dynes/cm)
heat-shrinkable linear low-density polyethylene (hereinafter referred to as
(abbreviated as L-LDPE) film (Table 2-(F)) so that the corona-treated sides were facing each other, and applied laminating adhesive AD-503/made by Toyo Morton Co., Ltd.
Using CTA-10=90/10, dry lamination was performed at about 70°C, and after aging at 35 to 40°C for 2 days, the physical properties were evaluated and the results are shown in Table 1. Using the obtained laminated film, it was made into a cylinder shape by a wrap seal with a wrap width of 2 mm, and the bottom part was sealed with a seal width of 2 mm.
mm round seal length 300mm, folded diameter 165mm
A bag with a round bottom was made, filled with irregularly shaped roast ham of 25 cm in length, degassed, the opening sealed with a flat seal with a seal width of 2 mm, and then heated to 95°C.
After 5 minutes of boiling water shower treatment,
A heat bath treatment was performed at ℃ for 10 minutes. the result,
Although the contents were amorphous, the laminated film portion of the bag adhered extremely tightly and did not form any voids, so no condensation occurred and the appearance was extremely beautiful. Comparative Example 1 An unstretched L-LDPE film (product name: Kojin L-Ace, Kojin Co., Ltd.) with a specific gravity of 0.92, a thickness of 15 μm, and one side corona treated (wetting tension 40 dynes/cm) was used as a sealant instead of a heat-shrinkable sealant. Made, 2nd
A double-layered heat-sealable heat-shrinkable packaging material was produced in exactly the same manner as in Example 1, except for observing Table 1-()). The physical properties were evaluated and the results are shown in Table 1. As is clear from the results of Example 1 and Comparative Example 1 above, the product in which biaxially stretched heat-shrinkable sealant films are laminated on both sides has better hot water shrinkage than the product in which non-shrinkable sealant films are laminated. It was extremely expensive. Example 2 Weight ratio of nylon 6/nylon 6-6 is 85/15
A polyamide copolymer (trade name: Novamit, manufactured by Mitsubishi Kasei Corporation) was extruded into a tube shape at 250 to 260°C to obtain a tube-shaped unstretched film with a diameter of 66 mm and a thickness of 14.5 μm. This unstretched film was simultaneously biaxially stretched at 75 to 80℃ using the tubular stretching method, opened, and then heated at 150℃ using a tenter.
Heat-setting was performed for 10 seconds to obtain a heat-shrinkable film with a thickness of 15.5 μm. The heat shrinkage rate of this film is
Shown in Table (B). A heat-shrinkable L-LDPE sealant film (trade name: Kojin BO-LS, manufactured by Kojin Co., Ltd., Table 2-(F)) was laminated on both sides of this heat-shrinkable film in the same manner as in Example 1. The physical properties of the laminated packaging material obtained were evaluated, and the results are shown in Table 1. Comparative Example 2 Double-sided layered packaging was carried out in exactly the same manner as in Example 2, except that an unstretched L-LDPE film (trade name: Kojin L-Ace, manufactured by Kojin Co., Ltd., Table 2-()) was used as the sealant film. The material was prepared. The physical properties were evaluated and the results are shown in Table 1. As can be seen from the results of Example 2 and Comparative Example 2 above, even if the same heat-shrinkable film is used as the base material, if the sealant film laminated on both sides is not heat-shrinkable, the heat-shrinkability of the laminated film will be However, in the case of the heat-shrinkable sealant film laminated, the heat-shrinkability decreased only slightly. Example 3 One side corona treatment (wetting tension 40 dynes/
cm) heat-shrinkable polypropylene film (product name: KOHJIN KORAP, manufactured by Kojin Co., Ltd., Table 2-
A laminated packaging material was produced in exactly the same manner as in Example 1 except that (G)) was used, and its physical properties were evaluated. The results are shown in Table 1. As described above, it has been found that a heat-shrinkable film in which heat-shrinkable sealants are laminated on both sides exhibits excellent heat-shrinkability even when the heat-shrinkable sealant is a polypropylene film. Example 4 A biaxially stretched heat-shrinkable polypropylene film (product name: KOHJIN KORAP, manufactured by Kojin Co., Ltd.) with a thickness of 20 μm was corona treated on both sides (wetting tension 39 dynes/cm), and one side was treated with polypropylene. A small polka dot pattern was gravure printed using blue ink, and a biaxially stretched heat-shrinkable L-LDPE film (product name: Kojin BO-) with a thickness of 15 μm was printed on both sides.
The corona-treated surfaces (wet tension: 40 dyne/cm) of LS, manufactured by Kojin Co., Ltd. (Table 2-(F)) were laminated using the same dry laminating adhesive as in Example 1, and heated at 40°C. It was left at room temperature for 2 days. There were no particular problems during printing. The properties of the obtained laminated packaging material are shown in Table 1. In addition, this laminated packaging material was made into a cylinder shape using a wrap seal with a wrap width of 2 mm using an automatic bag making machine, and a round bottom bag with a length of 300 mm and a fold diameter of 165 mm was made by sealing the bottom with a round seal with a seal width of 2 mm. No particular troubles occurred. As described above, the laminated packaging material of this example not only had excellent heat shrinkability and pinhole resistance, but also had sufficient suitability for printing and bag making processing. The reason for this is believed to be the synergistic effect of the good heat shrinkability and processability of the polypropylene layer of the base material and the heat shrinkability and pinhole resistance of the sealant layer. Comparative Example 3 Specific gravity 0.92, simultaneously biaxially stretched as a sealant.
Except that a heat-shrinkable L-LDPE film (product name: Kojin BO-LS, Table 2-(E)) with a thickness of 30 μm and a corona-treated surface on one side (wetting tension 40 dynes/cm) was laminated on only one side. A laminated film was produced in exactly the same manner as in Example 1. The physical properties of the obtained film were measured and the results are shown in Table 1. As can be seen from this result, the heat shrinkability of the obtained laminated shrinkable film is not much different from that of the heat-shrinkable L-LDPE film laminated on both sides (Example 1), but since it is laminated on one side, This is a gassho pasting method, and the seal strength is significantly lower than that of a double-sided laminated product (envelope pasting). Also, the gas barrier property is
In the case of WET conditions: There was a drawback that the gas permeability increased significantly because the nylon layer absorbed moisture. Reference example 1 Heat-shrinkable polyester film (product name: Diafoil, thickness 12 μm,
Made by Diafoil Co., Ltd., a biaxially stretched LDPE film (Table 2-(D)) with a thickness of 30 μm (Table 2-(H)) was laminated on one side as a sealant layer in the same manner as in Example 1. A laminated film was prepared. The physical properties of the obtained film were measured and the results are shown in Table 1. Reference example 2 Low-density polyethylene with a melting point of 111.5℃ and a density of 0.920 at 25℃ (product name: UBE HF019, Ube Industries, Ltd.)
Co., Ltd.) at 200 to 250℃ and polyethylene terephthalate with an intrinsic viscosity of 0.7 at 287℃ using an extruder. , and the ratio of the thickness of the inner and outer layers is 1:
The inside of the film is indirectly water-cooled by extruding the film into a 66 mm diameter internal mandrel, which is installed directly below the die and is cooled with 30°C water, and at the same time, By jetting high-speed cold air, the film is cooled from the outside surface with a diameter of 66 mm and a thickness of 234 μm.
Crystallinity of polyethylene terephthalate part is 18%
A laminated unstretched film was obtained. This unstretched film was simultaneously biaxially stretched by the tubular method. The stretching conditions were based on the biaxial stretching conditions of polyethylene terephthalate, first preheated to 70°C with hot air, then the temperature at the starting point of stretching was 107°C, the first 1/3 of the stretching zone was 105 to 108°C, and then the interval of
After finishing the stretching with a continuous descending gradient from 104 to 75℃, it is cooled at room temperature, with a diameter of 200 mm and a thickness of
A biaxially stretched laminated film of 41 μm was obtained and further heat-set at 80° C. for 10 seconds. The properties of this laminated film were evaluated and shown in Table 1. As can be seen from the results of Reference Example 1 and Reference Example 2, the heat shrinkability of the film of Reference Example 2 that was stretched after coextrusion was different from that of the film that was laminated after stretching the heat-shrinkable film layer and the sealant film layer separately. The ratio was considerably lower than that of the film of Reference Example 1, and a phenomenon in which the film curled significantly in the direction of the polyethylene terephthalate layer when it was heat-shrinked was observed. From these phenomena, it seems that the polyethylene layer serving as the sealant layer had almost no residual shrinkage even though it was stretched together with the polyethylene terephthalate layer, thereby reducing the original shrinkage force of the polyethylene terephthalate layer. (Effects of the Invention) As explained above, according to the present invention, heat-shrinkable sealant films are laminated on both sides of a heat-shrinkable base film, which provides excellent heat-shrinkability and heat-sealability. A laminated packaging material can be obtained. In particular, in the heat-shrinkable packaging material according to the present invention, the following unique effects can be obtained compared to those that are laminated and then stretched, or those that are laminated with an unstretched film and a stretched film. (1) Higher heat shrinkability suitable for sealed shrink packaging can be obtained. (2) Before and after heat shrinkage treatment, there is no reduction in the heat shrinkage rate of the packaging material or internal distortion that causes curling, etc., and it is possible to obtain a highly tight and beautiful adhesive package. can. (3) A printing layer or the like can be provided between the layers, and the appearance of the printing is better than that in which the printing is stretched after lamination, and peeling and falling off of the printed surface can be prevented.

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Claims (1)

[Claims] 1. A heat-shrinkable laminated packaging material having heat-sealability, which is formed by laminating heat-shrinkable sealant films on both sides of a heat-shrinkable base film. 2. The heat-shrinkable sealant film has a melting point lower than that of the heat-shrinkable base film, and has a heat shrinkage rate of 10 to 50% in the longitudinal direction and in the lateral direction, respectively.
The heat-shrinkable laminated packaging material according to claim 1, which is a polyolefin film. 3. The heat-shrinkable base film according to claim 1, wherein the heat-shrinkable base film is a polyamide film or a polypropylene film having a heat shrinkage rate of 15 to 50% in the longitudinal and lateral directions, respectively. Shrinkable laminated packaging material. 4. Claim 1, wherein the heat-shrinkable base film is made of a biaxially stretched polyamide film, and the heat-shrinkable sealant film is made of a biaxially stretched linear low-density polyethylene film. heat-shrinkable laminated packaging material.