JPH06210730A - Heat-shrinkable laminated film and production thereof - Google Patents

Abstract

PURPOSE:To obtain a polypropylene type heat-shrinkable laminated film low in heat shrinkage starting temp. and having a wide heat shrinkage proper temp. range and suitable as a shrinkable packing film excellent in tear resistance, low temp. stretchability, low temp. heat sealability and impact resistance. CONSTITUTION:Polypropylene is used as a resin for a core layer and a straight chain low density polyethylene resin is used as a resin for both outer layers and outer layers 2 composed of the straight chain low density polyethylene resin are provided on both surfaces of the core layer 1 composed of a polypropylene resin by a co-extrusion three-layered T-die to produce a co- extrusion laminated film having a three-layered structure. This co-extrusion laminated film is uniaxially stretched by 2-5 times at stretching temp. of 100 deg. or lower by a uniaxial stretching machine to obtain a uniaxially stretched film with a thickness of about 30mum.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention provides a shrinkage having a low heat shrinkage initiation temperature, a wide heat shrinkage proper temperature range, and excellent tear resistance, low temperature stretchability, low temperature heat sealability, and impact resistance. The present invention relates to a polypropylene-based heat-shrinkable laminated film suitable for use as a packaging film and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a polypropylene heat-shrinkable film, for example, a polypropylene single-layer tube is biaxially stretched at a high magnification (for example, 6 times in the horizontal direction and 6 times in the vertical direction).
A biaxially stretched film thinned to 15 to 25 μm has excellent transparency and rigidity, and is used in the field of individual commercial packaging. However, this polypropylene single-layer biaxially stretched film has a problem that it cannot be used as a shrink wrapping film for a weight of 1 kg or more because of its poor impact resistance.

A uniaxially stretched polypropylene single-layer tube is liable to tear, and is not only inferior in heat sealability and impact resistance, but also has a high heat shrinkage initiation temperature.
Moreover, the shrinkage rate tends to increase sharply as the temperature rises, and when trying to complete the shrinkage in a short time by passing through the shrink tunnel at high speed, uneven shrinkage, wrinkles, or perforations occur. Therefore, it is not suitable as a shrink wrapping film.

Further, as described in JP-A-1-317765, 2 to 4 carbon atoms are formed on both surfaces of a base layer made of polypropylene resin and hydrogenated hydrocarbon having a softening point in the range of 80 to 125 ° C. A shrinkable film in which a heat-sealable upper layer such as an α-olefin resin having an atom is laminated is proposed.

[0005]

However, this shrinkable film is not commercially available because a shrinkable film having sufficient adhesion between layers cannot be obtained by coextrusion and the resin used is expensive. There is a problem that it does not hold. The present invention solves the above-mentioned drawbacks of the prior art, has a low thermal contraction start temperature, does not sharply increase the contraction rate as the temperature rises, and has a wide thermal contraction proper temperature range. Even when passing through the tunnel at high speed, uneven contraction,
A commercial polypropylene-based heat-shrinkable laminated film that can achieve uniform shrinkage without causing wrinkles and holes, is resistant to tearing, and has excellent low-temperature heat-sealing properties, impact resistance, and transparency. The purpose of the present invention is to provide a method for producing the heat-shrinkable laminated film.

[0006]

The method for producing a heat-shrinkable laminated film according to the first aspect of the present invention comprises at least three outer layers made of a linear low-density polyethylene resin provided on both sides of a core layer made of a polypropylene resin. A co-extruded laminated tube or laminated film having a layered structure at a temperature of 100 ° C. or less
It is a method of stretching to 5 times.

In the present invention 1, the polypropylene-based resin forming the core layer may be a homopolymer, but in terms of elasticity and adhesiveness to the outer layer made of a linear low-density polyethylene resin, it may be combined with ethylene. Random copolymers and block copolymers are preferred.

In the present invention 1, the linear low-density polyethylene resin forming both outer layers has a density of 0.910.
Those having a density of g / cm ³ or less are preferably used. When the density exceeds 0.910 g / cm ³ , at least a three-layer structure is obtained by co-extruding a core layer made of a polypropylene resin with outer layers made of a linear low-density polyethylene resin laminated on both sides with good adhesiveness. Molding tubes or laminated films tends to be difficult.

In the present invention 1, the layer thickness ratio in a coextruded laminated tube or laminated film having a three-layer structure in which an outer layer made of a linear low-density polyethylene resin is provided on both sides of a core layer made of a polypropylene resin has a layer thickness ratio of 1 It is preferably in the range of / 1/1 to 1/4/1. When the layer thickness ratio of the core layer is less than 1/1/1, the heat resistance of the shrinkable laminated film obtained tends to be low, and conversely, when it exceeds 1/4/1, it is obtained. The shrinkable laminated film tends to tear and the heat sealability tends to deteriorate.

The thickness of the heat-shrinkable laminated film obtained in the present invention 1 is not particularly limited, but it is preferably 10 to 120 μm, preferably 25 to 70 μm in view of various conditions in the above heat shrinkage.

An outer layer made of a linear low-density polyethylene resin having a three-layer structure, in which an outer layer made of a linear low-density polyethylene resin is provided on both surfaces of a core layer made of a polypropylene resin, has an adhesive property. It may be a layer,
A four-layer structure or more may be formed by further providing a layer of a linear low-density polyethylene resin having adhesiveness on the three-layer structure.

In order to mold the heat-shrinkable laminated film of the present invention using the above-mentioned polyporoprene-based resin and the linear low-density polyethylene resin, first, the polyporoprene-based resin and the linear low-density resin are used. Polyethylene resin and the like are melt-kneaded in separate extruders and coextruded into a laminated tube or a laminated film by a tubular method, a T-die method or the like, and an unstretched at least three-layer structure coextruded unstretched tube or Make a film.

The resulting unstretched tube or film having at least a three-layer structure has a core layer made of polypropylene resin and outer layers made of a linear low-density polyethylene resin provided on both sides of the core layer. Even if it is extruded, it is laminated with the layers well adhered.

Then, the unstretched coextruded stretched tube or film having at least a three-layer structure is appropriately selected from known uniaxial and biaxial stretching methods such as a roll stretching method, a tubular stretching method and a tenter stretching method. It is stretched 2 to 5 times at a stretching temperature of 100 ° C. or less to obtain a heat-shrinkable laminated film.

In the method for producing a heat-shrinkable film of the present invention 1, it is important that the stretching conditions are a stretching temperature of 100 ° C. or lower and a stretching ratio of 2 to 5 times. When the stretching temperature exceeds 100 ° C., the heat shrinkable laminated film obtained has a high heat shrinkage initiation temperature, and the heat shrinkage proper temperature range is narrowed accordingly.

When the draw ratio is less than 2 times, the heat shrinkable laminated film obtained does not have a sufficient heat shrinkage force. On the contrary, when it exceeds 5 times, the heat shrinkable laminated film is obtained. The film tends to tear. That is, by adopting these stretching conditions, the obtained heat-shrinkable laminated film has a low heat-shrinking start temperature, a wide heat-shrinking proper temperature range, is less likely to tear, and has suppressed the occurrence of a whitening phenomenon. Be done.

The heat-shrinkable laminated film of the present invention 2 has at least a three-layer structure in which an outer layer made of a linear low-density polyethylene resin is provided on both surfaces of a core layer made of a polypropylene resin. Is a copolymer with ethylene, and the linear low-density polyethylene resin has a density of 0.910 or less, and is obtained by stretching a coextruded laminated tube or laminated film 2 to 5 times.

In the second aspect of the present invention, the polypropylene-based resin forming the core layer is excellent in elasticity and adhesiveness to the outer layer made of a linear low-density polyethylene resin, so that a random copolymer or block with ethylene is used. Copolymers and the like are used.

In the present invention 2, the linear low-density polyethylene resin forming both outer layers has a density of 0.910.
A material having a density of g / cm ³ or less is used. Since the density is 0.910 g / cm ³ or less, at least a three-layer structure in which an outer layer made of a linear low-density polyethylene resin is laminated on both surfaces of a core layer made of a polypropylene resin by co-extrusion with extremely high adhesiveness Laminated tubes or films can be formed.

[0020]

The method for producing a heat-shrinkable laminated film of the present invention is a coextrusion laminate having at least a three-layer structure in which an outer layer made of a linear low-density polyethylene resin is provided on both surfaces of a core layer made of a polypropylene resin. By forming a tube or a laminated film, even if coextruded, the layers are laminated in a state where the layers are well adhered, and the laminated tube or laminated film is 2 to 5 times at a temperature of 100 ° C. or lower. By stretching at a ratio of 1, the heat shrinkage start temperature is low, and the heat shrinkage proper temperature range is wide without shrinkage rate rapidly increasing with temperature rise, even when passing through the shrink tunnel at high speed. Uneven shrinkage, wrinkles,
It is possible to obtain a heat-shrinkable laminated film in which uniform shrinkage can be achieved without generation of perforations and the like, it is hard to tear, and the occurrence of a whitening phenomenon is suppressed, and the outer layer is made of a linear constant density polyethylene resin. Therefore, it has excellent low-temperature heat sealability at 120 ° C or less, and also has excellent adhesive strength between at least three-layer structure after stretching, and since the core layer is made of polypropylene resin, impact resistance strength is improved. A heat-shrinkable laminated film having excellent tear strength and heat resistance can be obtained, and a polypropylene-based heat-shrinkable laminated film having such excellent performance can be produced on a commercial basis.

The heat-shrinkable laminated film of the present invention 2 has at least a three-layer structure in which an outer layer made of a linear low-density polyethylene resin is provided on both sides of a core layer made of a polypropylene resin. Is a copolymer with ethylene, and the linear low-density polyethylene resin has a density of 0.910 or less. The shrinkage start temperature is low, and the shrinkage rate does not increase sharply as the temperature rises, and the appropriate temperature range for heat shrinkage is wide. Even when passing through a shrink tunnel at high speed, shrinkage unevenness, wrinkles, perforations, etc. Uniform shrinkage can be achieved without occurrence, tearing is difficult, and low temperature heat sealability, impact resistance and transparency are remarkably excellent.

[0022]

EXAMPLES The present invention will be described below with reference to examples. Example 1 As a resin for the core layer, polypropylene (manufactured by Mitsui Oil Co., Ltd., trade name "Hipol F650", density: 0.910, MF
R: 6.0) and a linear low-density polyethylene resin (trade name "Ultox 1030L" manufactured by Mitsui Oil Co., Inc., density: 0.910, MI: 1.
6), a three-layer co-extrusion T-die in which outer layers 2 and 3 made of linear low-density polyethylene resin are provided on both surfaces of a core layer 1 made of polypropylene resin as shown in FIG. A coextrusion laminated film having a structure (outer layer / core layer / outer layer layer pressure ratio of 1/4/1 and total thickness of 90 μm) was produced.

This coextruded laminated film having a three-layer structure was uniaxially stretched by a uniaxial stretching machine at a stretching temperature of 95 ° C. to obtain a uniaxially stretched film having a thickness of 30 μm. The performance evaluation shown in Table 1 was performed on this uniaxially stretched film.

The appearance of the film was evaluated by visually observing the appearance of the uniaxially stretched film. The breaking strength, breaking elongation, tear strength, and seal strength were measured in the longitudinal direction according to JIS Z-1702.

Regarding the heat shrinkage ratio, each film was put in a gap open at a predetermined temperature for 5 minutes, taken out and brought to room temperature, and then the shrinkage ratio in the lengthwise direction was measured.
Regarding the appropriate shrinkage temperature range, a shrink tunnel was used to examine an average temperature range when a 325 × 270 × 140 mm carton case was sleeve-wrapped with each film having a thickness of 40 μm. An appropriate temperature range for heat shrinkage is defined as a range in which shrinkage is insufficient at a temperature lower than this range and perforation is caused at a high temperature.

Example 2 A thickness of 30 μm was obtained in the same manner as in Example 1 except that the layer thickness ratio of outer layer / core layer / outer layer of the three-layer structure coextrusion laminated film was 1 / 0.5 / 1. A uniaxially stretched film was obtained.
The same performance evaluation as in Example 1 was performed on the obtained uniaxially stretched film. The results are shown in Table 1.

Example 3 Uniaxial thickness of 30 μm was obtained in the same manner as in Example 1 except that the layer thickness ratio of outer layer / core layer / outer layer of the three-layer structure coextrusion laminated film was set to 1/5/1. A stretched film was obtained. The same performance evaluation as in Example 1 was performed on the obtained uniaxially stretched film. The results are shown in Table 1.

Comparative Example 1 A uniaxially stretched film having a thickness of 30 μm was obtained in the same manner as in Example 1 except that a single film of polypropylene resin was produced instead of the coextruded laminated film having a three-layer structure. The same performance evaluation as in Example 1 was performed on the obtained uniaxially stretched film. The results are shown in Table 1.

Comparative Example 2 As a resin for both outer layers, a linear low density polyethylene resin (manufactured by Mitsui Oil Co., Ltd. under the trade name "Ultox 2020") is used.
L ”, density: 0.920, MI: 2.1) except that a uniaxially stretched film having a thickness of 30 μm was obtained in the same manner as in Example 1. The same performance evaluation as in Example 1 was performed on the obtained uniaxially stretched film. The results are shown in Table 1.

[0030]

[Table 1]

As is clear from Table 1, in all the examples of the present invention, the heat shrinkage initiation temperature was low, the heat shrinkage proper temperature range was wide, and the low temperature heat sealability, tensile strength, tear strength, and extensibility were good. While the film appearance and the like are excellent, in the case of Comparative Example 1, under the same stretching conditions as in the Example, whitening occurs and the film cannot be stretched. Adhesiveness is not enough.

[0032]

EFFECT OF THE INVENTION Since the method for producing a heat-shrinkable laminated film of the present invention 1 is constructed as described above, the heat-shrinkage start temperature is low, and the shrinkage rate can be rapidly increased as the temperature rises. Since it has a wide temperature range suitable for heat shrinkage, even when passing through a shrink tunnel at high speed, uniform shrinkage can be achieved without uneven shrinkage, wrinkles, perforations, etc. A polypropylene-based heat-shrinkable laminated film excellent in impact resistance and transparency can be manufactured on a commercial basis.

Since the heat-shrinkable laminated film of the present invention 2 is constructed as described above, the heat-shrinkage initiation temperature is particularly low, and the shrinkage rate does not sharply increase as the temperature rises. Wide appropriate temperature range, even when passing through a shrink tunnel at high speed, uniform shrinkage can be achieved without uneven shrinkage, wrinkles, perforations, etc., and it is difficult to tear.
It is remarkably excellent in low-temperature heat-sealing property, impact resistance and transparency, and can be suitably used as a shrink wrapping film.

[0034]

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a coextrusion laminated film having a three-layer structure for producing a heat-shrinkable laminated film of the present invention.

[Explanation of symbols]

 1 core layer 2 and 3 outer layer

Claims (2)

[Claims] 1. A coextruded laminated tube or laminated film having at least a three-layer structure in which an outer layer made of a linear low-density polyethylene resin is provided on both surfaces of a core layer made of a polypropylene resin, and the temperature is set to 100 ° C. or lower. A method for producing a heat-shrinkable laminated film, which comprises stretching the film by 2 to 5 times. 2. A polypropylene-based resin core layer having an outer layer of linear low-density polyethylene resin on both sides, and at least a three-layer structure, wherein the polypropylene-based resin is a copolymer with ethylene. And a linear low-density polyethylene resin having a density of 0.910 or less, which is obtained by stretching a coextruded laminated tube or laminated film 2 to 5 times, and a heat-shrinkable laminated film.