JP2016199638A - Polyolefin-based heat shrinkable film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin-based heat shrinkable film having enhanced adhesiveness with an ink and capable of being suitably used for a high speed automatic packaging machine while maintaining properties such as high tensile elastic modulus, high thermal shrinkage percentage, high tear strength, fusion cutting sealability and shrinkage in time equal to conventionally used polyolefin-based heat shrinkable film.SOLUTION: A resin by mixing a propylene-α-olefin copolymer and an acid modified polyolefin with a ratio of 90:10 to 0:100 is used for a surface layer of a film, and difference of melting peak temperatures of each polymer is set at 20°C or less.SELECTED DRAWING: None

Description

  The present invention relates to a polyolefin-based heat-shrinkable packaging material for overlap, and more specifically, a polyolefin-based heat-shrinkable film having improved adhesion to ink, and a polyolefin-based heat-shrinkable film that has been conventionally used The present invention relates to a polyolefin-based heat-shrinkable film having high tensile elastic modulus, high heat shrinkage, high tear strength, low shrinkage with time, and high-speed automatic packaging suitability.

  Conventionally, polyolefin shrink films such as polypropylene and polyethylene have been preferred as heat shrinkable packaging materials in terms of cost and ease of disposal after use. Is inactive, so it uses chlorinated PP ink or polyamide nitrile varnish ink that has low adhesion to general-purpose ink and high cost but good adhesion to polyolefin heat-shrinkable film. Has been.

As a means for modifying a plastic film, there is generally known a method of activating the surface by corona discharge treatment, plasma treatment, flame treatment, coating or the like. Since the compatibility is lowered, a problem that the sealing strength is lowered when fusing and sealing is likely to occur.
In addition, a method of adding an acid-modified polyolefin resin to the surface layer is also known (Patent Document 1). However, when this method is used for shrink film, the fusing seal strength is hardly reduced, but depending on the conditions, other physical properties may be reduced, and the suitability for high-speed automatic packaging machines used for shrink wrapping will be drastically reduced. There was a problem.

JP2013-82190A

  In view of the above situation, the present invention maintains a balance of properties such as high tensile elastic modulus, high thermal shrinkage, high tear strength, fusing sealability and small shrinkage over time, which are equivalent to those of polyolefin heat-shrinkable films that have been used in the past. In addition, the present invention provides a polyolefin heat-shrinkable film that can be suitably used for high-speed automatic packaging and has improved adhesion to ink.

As a result of intensive studies, the present inventors have made a surface layer of a resin obtained by mixing a propylene-α-olefin copolymer and an acid-modified polyolefin at a predetermined ratio, and the difference in melting peak temperature as a polymer is within a certain range. By adopting the above, it was found that the problem could be solved, and the present invention was completed.
That is, the present invention
1) A polyolefin-based biaxially stretched heat-shrinkable film, wherein at least one surface layer is a mixed resin of a propylene-α-olefin copolymer and an acid-modified polyolefin resin in a weight ratio of 90:10 to 0: 100. A biaxially stretched polyolefin heat-shrinkable film having a value of [(melting peak temperature of propylene-α-olefin copolymer) − (melting peak temperature of acid-modified polyolefin resin)] of 20 ° C. or less,
2) The polyolefin biaxially stretched heat-shrinkable film according to (1), wherein the melting peak temperature of the propylene-α-olefin copolymer is 125 to 150 ° C.
3) The polyolefin biaxially stretched heat-shrinkable film according to (1) or (2), wherein the layer containing the acid-modified polyolefin has a thickness of 0.1 to 5 μm.

  The polyolefin-based heat-shrinkable film of the present invention has a balance of properties such as high tensile elastic modulus, high heat-shrinkage, high tear strength, fusing sealability and small shrinkage over time, which are the same as the conventional polyolefin-based heat-shrinkable films. It is suitable for high-speed automatic packaging and has improved adhesion to ink. Thus, printing can be performed using general-purpose ink while being a shrink film that can be used in a high-speed automatic packaging machine.

Hereinafter, the present invention will be described in detail.
The biaxially stretched heat-shrinkable film of the present invention is a single layer or multilayer film, and the layer forming at least one side thereof is composed of a mixed resin of a propylene-α-olefin copolymer and an acid-modified polyolefin resin. It is.
The mixing ratio of the propylene-α-olefin copolymer and the acid-modified polyolefin resin in the mixed resin is 90:10 to 0: 100 by weight. If the compounding ratio of the acid-modified polyolefin is less than 10, ink adhesion cannot be obtained, which is not preferable.
The blending ratio of 0: 100 indicates that the acid-modified polyolefin resin is used alone, and this is not a problem. However, when it is desired to further improve the suitability for a high-speed automatic packaging machine, the weight ratio is 90:10. It is desirable to set to -5: 95.

Examples of the copolymer of propylene and α-olefin used in the present invention include propylene-ethylene, propylene-butene copolymer, and propylene-ethylene-butene terpolymer, and at least one selected from these. Resins composed of more than seeds can be mentioned. In consideration of the balance between heat resistance, high elastic modulus, heat shrinkage characteristics and transparency, a crystalline propylene-α-olefin random copolymer is preferably used.
The propylene-α-olefin copolymer preferably has a melting peak temperature measured by DSC in the range of 125 to 150 ° C, and more preferably 125 to 145 ° C.

  The acid-modified polyolefin-based resin is a resin obtained by graft-polymerizing a polyolefin resin with an unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid or the like. The acid-modified polyolefin resin used in the present invention preferably has a melting peak temperature measured by DSC in the range of 120 to 170 ° C.

In order to satisfy the high-speed packaging suitability in addition to the heat resistance, high elastic modulus, heat shrinkage properties, transparency and fusing sealability of the film, the acid-modified polyolefin resin is determined from the melting peak temperature of the propylene-α-olefin copolymer used. The value obtained by subtracting the melting peak temperature is set to 20 ° C. or less. That is, the value of [(melting peak temperature of propylene-α-olefin copolymer) − (melting peak temperature of acid-modified polyolefin resin)] needs to be 20 ° C. or less, and desirably the value is −25 to 20 Within the range of ° C.
When the difference in melting points exceeds 20 ° C., high-speed packaging tends to be particularly difficult.

The melting peak temperature of the present application is measured by DSC (Differential Scanning Calorimeter), and after weighing about 10 mg of sample, it is sealed in an aluminum pan, and under a 40 ml / min nitrogen stream with a differential calorimeter. The temperature is raised from room temperature to 230 ° C. at a temperature rising rate of 40 ° C./min, held at 230 ° C. for 10 minutes, and then cooled to room temperature at 10 ° C./min. Then, the temperature of the main peak top was made into melting peak temperature by the melting curve obtained at the temperature increase rate of 10 degree-C / min.

The biaxially stretched heat-shrinkable film of the present invention may be a single layer or a multilayer, but it is preferably a multilayer structure, and at least one surface layer is composed of a propylene-α-olefin copolymer and an acid-modified polyolefin resin. A resin mixed at a predetermined blending ratio or an acid-modified polyolefin resin alone is used. In addition, a scrap of a mixture of a propylene resin, a propylene homopolymer, and an ethylene resin can be reused as long as the object of the present invention is not hindered.

The thickness of the polyolefin-based heat-shrinkable film of the present invention may be appropriately selected according to the use, but is preferably about 6 to 35 μm from the viewpoint of effectively expressing shrink finish and high-speed packaging suitability.

The thickness of the layer containing the acid-modified polyolefin resin in the film of the present invention is preferably in the range of 0.1 to 5 μm, more preferably 0.5 to 3.0 μm. When the layer containing the acid-modified polyolefin resin is 5 μm or more, packaging suitability and optical characteristics are likely to deteriorate.

In the film of the present invention, additives such as a lubricant, an antiblocking agent, an antistatic agent, an antifogging agent, an antioxidant, and a nucleating agent can be appropriately used for the purpose of providing each effective action. Any layer other than the layer containing the acid-modified polyolefin resin can be used without particular limitation as long as it is a polyolefin resin. More preferably, the melting peak temperature measured by DSC is in the range of 125 to 145 ° C., for example, propylene-ethylene copolymer, propylene-butene copolymer, which is a copolymer of propylene and α-olefin, And a resin composed of at least one selected from propylene-ethylene-butene terpolymers. Among these, a crystalline propylene-α-olefin random copolymer is preferably used in consideration of the balance between heat resistance, high elastic modulus, heat shrinkage characteristics and transparency.

The biaxially stretched polyolefin heat-shrinkable film of the present invention can be obtained by performing longitudinal and lateral biaxial stretching by a known method using the above-described resin.
Hereinafter, the case of three-layer laminated annular film-forming stretching will be described as an example.
First, a resin in which a propylene-α-olefin copolymer and an acid-modified polyolefin are mixed is melt-kneaded by three extruders so that both surface layers and an ethylene-based resin become an inner layer, and then cyclically formed from a three-layer annular die Coextruded and then rapidly cooled and solidified without stretching to produce a tubular unstretched film.
The obtained tubular unstretched film is supplied to a tubular stretching apparatus, and is in a highly orientable temperature range, for example, at a temperature lower than 10 ° C below the melting point of the core layer resin, preferably lower than 15 ° C below the melting point. The tube is expanded and stretched by applying a gas pressure to the inside of the tube at a temperature, and the longitudinal and lateral stretch ratios are set to 3 times or more to cause simultaneous biaxial orientation. The film taken out from the stretching apparatus can be subjected to heat treatment or annealing as necessary, thereby suppressing natural shrinkage during storage.
The 120 ° C. heat shrinkage rate of the obtained film is preferably 20% to 60%, more preferably 30% to 50%, from the viewpoint of effectively expressing the shrink finish.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.
In addition, each physical property measurement shown in a present Example was based on the following method.
1. Ink Adhesion Evaluation Method Ink (# Dainichi Seika Kogyo Co., Ltd., Ramic SR739R Indigo M3 Kai) is diluted with a diluent (Daiichi Seika Kogyo Co., Ltd.) so that the Zaan Cup # 3 has 16.00-16.50 seconds The solution was diluted with Lamic SR No. 3 solvent) and coated such that the coating amount after drying was 3 g / m 2. Drying was carried out by natural drying for 24H, and cellophane tape (manufactured by Nichiban Co., Ltd., 15 mm width) was applied for 10 cm and rubbed until air was removed.
Thereafter, the cellophane tape is peeled off vigorously. If the amount of ink peeled is 0%, the evaluation is 5, if it is 10%, the evaluation is 4, if it is 11-60%, the evaluation is 3, 61-99%, the evaluation is If it was 2, 100%, it evaluated as the evaluation 1.
2. Fusing seal strength: TP-701-B manufactured by Tester Sangyo Co., Ltd., using a 0.5R seal bar, measured after fusing and sealing at a fusing temperature of 220 and 240 ° C. according to JISZ 1707.
3. Tear strength: Measured with a light load tear tester manufactured by Toyo Seiki in accordance with JIS-P8116.
4). Tensile modulus: measured according to JIS-Z7127.
5. 120 ° C. heat shrinkage rate: Films cut into 100 mm squares in the vertical and horizontal directions were immersed in a glycerin bath at 100 ° C. for 10 seconds, then rapidly cooled in water, measured in length and horizontal directions, and heat of MD and TD. Shrinkage was calculated. 5. Wetting index: measured according to JIS-K6768.
6). Haze: Measured according to JIS-K7105.
7). Gloss (60 °): Measured according to JIS-Z7105.
8). High-speed automatic packaging suitability: Automatic packaging machine manufactured by Tokiwa Industries Co., Ltd. (model: NEO type, pillow packaging machine), tunnel (model: Kyowa Denki-2400B), liquor pack (285 mm x 195 mm x) at 156 ° C x 3.5 sec. 195 mm) was packed at a speed of 40 and 25 m / min, and the running property was evaluated.
A: Packaging at a speed of 40 m / min with no opening of the fusing seal portion and stable packaging.
○: If the packaging speed is 25 m / min, the fusing seal part does not open at all, and the packaging can be performed stably.
X: Opening of the fusing seal part occurs, and stable packaging is not possible.

<Example 1>
As a propylene-α-olefin copolymer, a propylene-ethylene random copolymer having a melting peak temperature of 143 ° C. (manufactured by “233DR” Prime Polymer Co., Ltd.) and an acid-modified polyolefin having a melting peak temperature of 141 ° C. (“ As shown in Table 1, a resin blended with Modic P644V (manufactured by Mitsubishi Chemical Corporation) at a blending weight ratio of 80:20 was used. For the other layer, only 233DR was used, and this was melt-kneaded with two extruders and co-extruded downward with a multilayer annular die. The formed tube was cooled by passing through a water tank while the outside was slid on the outer surface of a cylindrical cooling mandrel in which cooling water circulated, and an unstretched film was obtained.
This tubular unstretched film was guided to a tubular biaxial stretching apparatus, and stretched 4.5 × 4.0 times in the longitudinal and lateral directions to obtain a multilayer biaxially stretched film having a film thickness of 20 μm.

<Example 2>
A multilayer biaxially stretched film of Example 2 was obtained in the same manner as in Example 1 except that the blending weight ratio of the two resins was changed to 40:60.

<Example 3>
A multilayer biaxially stretched film of Example 3 was obtained in the same manner as in Example 1 except that the blending weight ratio of the two resins was changed to 0: 100 in Example 1.

<Example 4>
In Example 1, instead of “Modic P644V” as the acid-modified polyolefin, “Modic P575” having a melting point of 162 ° C. was used, and the blending weight ratio of the two resins was changed to 20:80. The multilayer biaxially stretched film of Example 4 was obtained.

<Example 5>
A multilayer biaxially stretched film of Example 5 was obtained in the same manner as in Example 4 except that the blending weight ratio of the two resins was changed to 0: 100 in Example 4.

<Comparative Example 1>
A multilayer biaxially stretched film of Comparative Example 1 was obtained in the same manner as in Example 1 except that no acid-modified polyolefin was blended.

<Comparative example 2>
In Example 1, instead of “Modic P644V” as the acid-modified polyolefin, the same procedure as in Example 1 was performed except that “Modic F534A” having a melting point of 120 ° C., and the single-layer biaxially stretched film of Comparative Example 2 was used. Obtained.

For the films of Examples 1 to 5 and Comparative Examples 1 and 2 obtained by the above method, ink adhesion, fusing seal strength, tear strength, tensile elastic modulus, 120 ° C. heat shrinkage, haze, gloss, high-speed automatic packaging Suitability was evaluated. The results are shown in Table 2. ("-" Indicates items that were not tested.)
The films of Examples 1 to 5 exhibited desirable physical properties for both ink adhesion and other items.
Among them, Examples 1, 2, 4, and 5 were particularly excellent in high-speed packaging suitability.

The heat-shrinkable packaging material of the present invention is a general-purpose ink while having properties such as fusing sealability, tensile elastic modulus, heat shrinkage rate, tear strength, and small shrinkage with time equivalent to those of conventional polyolefin heat-shrinkable films. Since it is suitable for high-speed automatic packaging, it can be suitably used for packaging beverages such as sake packs, foods such as cup ramen, and many other items.

Claims (3)

A polyolefin-based biaxially stretched heat-shrinkable film, wherein at least one surface layer is a mixed resin of a propylene-α-olefin copolymer and an acid-modified polyolefin resin in a weight ratio of 90:10 to 0: 100, A biaxially stretched polyolefin heat-shrinkable film having a value of [(melting peak temperature of propylene-α-olefin copolymer) − (melting peak temperature of acid-modified polyolefin resin)] of 20 ° C. or less. 2. The polyolefin biaxially stretched heat-shrinkable film according to claim 1, wherein the propylene-α-olefin copolymer has a melting peak temperature of 125 to 150 ° C. 3. The polyolefin biaxially stretched heat-shrinkable film according to claim 1 or 2, wherein the layer containing the acid-modified polyolefin has a thickness of 0.1 to 5 µm.