Shrink film and multilayer shrink film

Abstract

To provide a shrink film and a multilayer shrink film having excellent transparency and strength while enhancing heat shrinkability even when a polyethylene having a low degree of crystallization is used.SOLUTION: There is provided a shrink film which comprises a first polyethylene having a density of 0.910 to 0.930 g / cm3, a second polyethylene having a density of 0.890 g / cm3 or more and less than 0.910 g / cm3, silica dioxide having an average particle diameter of 0.1 μm or less and a glycerin fatty acid ester, contains the first polyethylene and the second polyethylene in a mass ratio of 80:20 to 60:40, contains 0.5 to 5 pts.mass of silica dioxide based on 100 pts.mass of the total of the first polyethylene and the second polyethylene and contains 0.5 to 3 pts.mass of the glycerin fatty acid ester. A multilayer shrink film has the shrink film.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a shrink film and a multilayer shrink film.

Background Art

[0002] Conventionally, as a heat-shrinkable packaging material, a shrink film (heat-shrinkable film) mainly composed of a polyethylene-based resin is known. The shrink film for packaging can package a plurality of products simultaneously regardless of the shape and size of the object to be packaged. In addition, since the polyethylene-based shrink film has transparency, the obtained packaged product can be easily visually inspected for quality.

[0003] As such a shrink film, Patent Document 1 discloses a multilayer polyethylene-based stretch shrink film having an intermediate layer mainly composed of a mixture of two types of linear low-density polyethylene, and an innermost layer and an outermost layer mainly composed of a mixed composition of high-pressure polyethylene, an ethylene-α-olefin copolymer, and linear low-density polyethylene, and obtained by blending at least two or more surfactant compositions.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Generally, polyethylene with high transparency has low crystallinity and low heat shrinkage rate. On the contrary, polyethylene with low transparency has high crystallinity and high heat shrinkage rate. Since there are many types of such polyethylene with low transparency but high crystallinity and high heat shrinkage rate on the market, the range of material selection is wide. However, since there are few types of polyethylene with high transparency and high heat shrinkage rate, the range of material selection is narrow. Therefore, conventionally, special polyethylene suitable for the shrink film has been used for polyethylene-based shrink films having high transparency and high heat shrinkage rate. Therefore, there has been a demand for a technique of using polyethylene having high transparency but low crystallinity and low heat shrinkage rate for shrink films.

[0006] The present invention has been made in view of the problems of such conventional techniques. The object of the present invention is to provide a shrink film and a multilayer shrink film excellent in transparency and strength while enhancing heat shrinkability even when using polyethylene with low crystallinity.

Means for Solving the Problems

[0007] The shrink film according to the first aspect of the present invention includes a first polyethylene having a density of 0.910 to 0.930 g / cm 3 , a second polyethylene having a density of 0.890 g / cm 3 or more and less than 0.910 g / cm 3 , silicon dioxide having an average particle diameter of 0.1 μm or less, and glycerin fatty acid ester. The shrink film contains the first polyethylene and the second polyethylene in a mass ratio of 80:20 to 60:40, contains 0.5 to 5 parts by mass of silicon dioxide with respect to a total of 100 parts by mass of the first polyethylene and the second polyethylene, and contains 0.5 to 3 parts by mass of glycerin fatty acid ester.

[0008] The multilayer shrink film according to the second aspect of the present invention includes the above shrink film.

Effects of the Invention

[0009] According to the present invention, even when using polyethylene with low crystallinity, it is possible to provide a shrink film and a multilayer shrink film that enhance heat shrinkability while being excellent in transparency and strength.

Mode for Carrying Out the Invention

[0010] Hereinafter, the shrink film and the multilayer shrink film according to the present embodiment will be described in detail.

[0011] The shrink film according to the present embodiment contains a first polyethylene having a density of 0.910 to 0.930 g / cm 3 and a second polyethylene having a density of 0.890 g / cm 3 or more and less than 0.910 g / cm 3 As described above, polyethylene with a low density has high transparency but has a property of low heat shrinkage rate due to low crystallinity. Therefore, in the shrink film of the present embodiment, by mixing the second polyethylene with a low density and the first polyethylene with a density higher than that of the second polyethylene, in addition to transparency, the heat shrinkability is enhanced.

[0012] The first polyethylene is polyethylene having a density of 0.910 to 0.930 g / cm 3 As the first polyethylene, it is preferable to use low-density polyethylene (LDPE) having a density of 0.910 to 0.930 g / cm 3 Examples of such first polyethylene include Sumitomo Chemical Co., Ltd.'s high-pressure method low-density polyethylene, Sumika Sen (registered trademark) F-208-3 (density 0.924 g / cm 3 ), ENEOS NUC Co., Ltd.'s LDPE for film, NUC8230 (density 0.928 g / cm 3 ).

[0013] The second polyethylene has a density of 0.890 g / cm 3 or more and 0.910 g / cm 3It is polyethylene with a density less than. As the second polyethylene, linear low-density polyethylene (LLDPE) with a density of 0.890 g / cm 3 or more and less than 0.910 g / cm 3 is preferably used. Examples of such second polyethylene include, for example, linear low-density polyethylene, Exceed (registered trademark) VL102 (density 0.908 g / cm 3 ) manufactured by Sumitomo Chemical Co., Ltd., and metallocene catalyst LLDPE, Yumelite (registered trademark) 0520F (density 0.904 g / cm 3 ) manufactured by Ube Maruzen Polyethylene Co., Ltd.

[0014] In the shrink film of the present embodiment, the mass ratio of the first polyethylene to the second polyethylene is preferably 80:20 to 60:40. When the first polyethylene is 80 to 60 parts by mass and the second polyethylene is 20 to 40 parts by mass, a shrink film having both transparency and heat shrinkability can be obtained.

[0015] The shrink film of the present embodiment contains silicon dioxide with a very small particle size in addition to the first polyethylene and the second polyethylene. Silicon dioxide with a very small particle size imparts the effect of thixotropy (lowering viscosity) when processing polyethylene, so that it becomes possible to process polyethylene at a low temperature and shorten the cooling time to the melting point. In addition, it is considered that the silicon dioxide improves crystallization by supplementing the role as a nucleating agent. Therefore, by adding fine particles of silicon dioxide to the first polyethylene and the second polyethylene, it becomes possible to improve the heat shrinkage rate of the obtained shrink film.

[0016] The average particle size of the silicon dioxide is preferably 0.1 μm or less, and more preferably 0.05 μm or less. The average particle size of the silicon dioxide can be measured by observing it using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) for the shrink film.

[0017] The silicon dioxide is preferably fumed silica obtained by vaporizing silicon chloride and then synthesizing silica fine particles by a gas-phase reaction in a high-temperature hydrogen flame. Examples of such silicon dioxide include hydrophilic fumed silica manufactured by Nippon Aerosil Co., Ltd., AEROSIL (registered trademark) 200, dry silica (fumed silica) manufactured by Tokuyama Corporation, Reolosil (registered trademark) QS102, and amorphous hydrophilic fine powder silica manufactured by Asahi Kasei Wacker Silicone Corporation, HDK (registered trademark) N20.

[0018] In the shrink film of the present embodiment, the content of silicon dioxide is preferably 0.5 to 5 parts by mass with respect to a total of 100 parts by mass of the first polyethylene and the second polyethylene. When the content of silicon dioxide is 0.5 part by mass or more, as described above, it becomes possible to improve the heat shrinkage rate of the obtained shrink film. Further, when the content of silicon dioxide is 5 parts by mass or less, it becomes possible to ensure the transparency of the obtained shrink film.

[0019] The shrink film of the present embodiment contains glycerin fatty acid ester in addition to the first polyethylene, the second polyethylene, and silicon dioxide. The glycerin fatty acid ester is considered to act as an internal lubricant for polyethylene and assist in linearizing the polymer in the amorphous part during stretching. Therefore, even when using the second polyethylene with high transparency and low crystallinity, a decrease in the heat shrinkage rate of the obtained shrink film can be suppressed.

[0020] The glycerin fatty acid ester is preferably glycerin monostearate. Examples of such glycerin fatty acid esters include Rikemal (registered trademark) S-100 manufactured by Riken Vitamin Co., Ltd., and Leodol (registered trademark) MS-60 manufactured by Kao Corporation.

[0021] In the shrink film of the present embodiment, the content of glycerin fatty acid ester is preferably 0.5 to 3 parts by mass with respect to a total of 100 parts by mass of the first polyethylene and the second polyethylene. When the content of glycerin fatty acid ester is 0.5 parts by mass or more, as described above, it becomes possible to improve the heat shrinkage rate of the obtained shrink film. Further, when the content of glycerin fatty acid ester is 3 parts by mass or less, it becomes possible to ensure the strength of the obtained shrink film.

[0022] Since glycerin fatty acid ester acts as an internal lubricant as described above, if the blending amount is excessive, the processability may decrease and the tensile strength of the obtained shrink film may also decrease. However, by adding silicon dioxide after setting the content of glycerin fatty acid ester to 3 parts by mass or less, the thixotropy of silicon dioxide assists the action as an internal lubricant during film processing. Therefore, due to these synergistic effects, the entanglement of polyethylene molecules is loosened, and the linearization of the polymer in the amorphous part during stretching is assisted, so that a decrease in the heat shrinkage rate of the obtained shrink film can be suppressed.

[0023] In addition to the above components, the shrink film of the present embodiment may contain additives. As the additives, lubricants, antioxidants, ultraviolet absorbers, antistatic agents, antifogging agents, flame retardants, colorants, etc. can be used. These components may be used alone or in combination of two or more.

[0024] The thickness of the shrink film of the present embodiment is not particularly limited, but is preferably, for example, 50 μm to 150 μm. When the thickness is 50 μm or more, the strength of the shrink film can be increased. Further, when the thickness is 150 μm or less, the heat shrinkability of the shrink film can be increased.

[0025] The shrink film of this embodiment preferably shrinks in at least one direction when heated. Specifically, the shrink film preferably shrinks in at least one of the MD (Machine Direction) and TD (Traverse Direction) when heated.

[0026] The shrink film of this embodiment may be single-layer. Also, it may be a multilayer shrink film formed by laminating the shrink film of this embodiment with other films. Specifically, the multilayer shrink film of this embodiment includes at least the above-mentioned shrink film. Also, the multilayer shrink film may be formed by laminating a plurality of layers of the above-mentioned shrink film. Further, the multilayer shrink film may be formed by laminating the above-mentioned shrink film with other shrink films. The other shrink film is not particularly limited, and for example, a polyolefin-based shrink film can be mentioned.

[0027] The manufacturing method of the shrink film of this embodiment is not particularly limited. For example, first, a resin composition is prepared by melt-kneading the above-mentioned resin components. Melt-kneading can be performed using known kneading machines such as an extruder, a Banbury mixer, a kneader, and a roll mill. When kneading the first polyethylene and the second polyethylene with a kneading machine, silicon dioxide, glycerin fatty acid ester, and other additives can be added. Also, silicon dioxide, glycerin fatty acid ester, and other additives may be processed in the state of a masterbatch in advance. Then, when kneading the first polyethylene and the second polyethylene with a kneading machine, the resin composition may be prepared by adding and kneading the masterbatch.

[0028] And the obtained resin composition is formed into a film shape by, for example, an inflation (tubular) molding method or a T-die film extrusion molding method, whereby the shrink film of this embodiment can be obtained.

[0029] Thus, the shrink film of this embodiment contains a first polyethylene having a density of 0.910 to 0.930 g / cm 3 , a second polyethylene having a density of 0.890 g / cm 3 or more and less than 0.910 g / cm 3 , silicon dioxide having an average particle diameter of 0.1 μm or less, and glycerin fatty acid ester. And the shrink film contains the first polyethylene and the second polyethylene in a mass ratio of 80:20 to 60:40. Further, the shrink film contains 0.5 to 5 parts by mass of silicon dioxide and 0.5 to 3 parts by mass of glycerin fatty acid ester with respect to a total of 100 parts by mass of the first polyethylene and the second polyethylene.

[0030] In the shrink film of this embodiment, a polyethylene having low transparency but high crystallinity and high heat shrinkage rate, and a polyethylene having high transparency but low crystallinity and low heat shrinkage rate are used. And since many types of these polyethylenes are commercially available, the range of material selection can be widened. Further, in the shrink film, in addition to the two types of polyethylenes, a predetermined amount of silicon dioxide and glycerin fatty acid ester are added to enhance the heat shrinkability and strength. As a result, the shrink film of this embodiment can obtain high heat shrinkability, transparency and strength even when using a polyethylene with low crystallinity.

[0031] In the shrink film of this embodiment, the first polyethylene may be low density polyethylene, and the second polyethylene may be linear low density polyethylene. By using such first polyethylene and second polyethylene, a shrink film excellent in heat shrinkability, transparency and strength can be obtained.

[0032] The thickness of the shrink film of this embodiment may be 50 μm to 150 μm. Thereby, a shrink film particularly excellent in heat shrinkability can be obtained.

[0033] The multilayer shrink film of the present embodiment includes a shrink film. By laminating the above-described shrink film and another shrink film, a multilayer shrink film having the characteristics of each layer can be obtained.

Examples

[0034] Hereinafter, the present embodiment will be described in more detail with reference to Examples and Comparative Examples, but the present embodiment is not limited to these Examples.

[0035] [Production of Shrink Film] Shrink films of Examples 1 to 14 and Comparative Examples 1 to 7 were produced with the raw materials and compounding amounts shown in Tables 1 to 3. When producing the shrink film of each example, the following raw materials were used. · First polyethylene: manufactured by Sumitomo Chemical Co., Ltd., high-pressure low-density polyethylene, Sumika Sen (registered trademark) F-208-3, density 0.924 g / cm 3 · Second polyethylene: manufactured by Sumitomo Chemical Co., Ltd., linear low-density polyethylene, Exceed (registered trademark) VL102, density 0.908 g / cm 3 · Silicon dioxide: manufactured by Nippon Aerosil Co., Ltd., hydrophilic fumed silica, AEROSIL (registered trademark) 200 · Glycerin fatty acid ester: manufactured by Riken Vitamin Co., Ltd., glycerin monostearate, Rikemal (registered trademark) S-100 · Lubricant: zinc stearate · Antioxidant: manufactured by BASF Japan Ltd., hindered phenol-based antioxidant, Irganox (registered trademark) 1010

[0036] Specifically, first, the raw materials were weighed in the compounding amounts shown in Tables 1 to 3, and then the first polyethylene and the second polyethylene were kneaded using an extruder. Further, silicon dioxide, glycerin fatty acid ester, lubricant, and antioxidant were added and kneaded thoroughly. Then, the obtained kneaded product was formed into a film by the inflation molding method to obtain the shrink films of each example. The thickness of the shrink films of Examples 1 to 14 and Comparative Examples 1 to 7 was 50 μm to 150 μm.

[0037] [Table 1]

[0038] [Table 2]

[0039] [Table 3]

[0040] [Evaluation] The heat shrinkability, transparency, and strength of the shrink films of each example obtained as described above were evaluated.

[0041] For the heat shrinkability, in accordance with Japanese Industrial Standard JIS Z1709 (Film for Shrink Packaging), the shrinkage rates in both the MD direction and the TD direction were measured. The heating condition of the test piece was immersion in an oil bath at 100°C for 20 seconds. And it was considered qualified when the heat shrinkage rate in the MD direction was 45% or more and the heat shrinkage rate in the TD direction was 20% or more.

[0042] For the transparency, the haze value was measured in accordance with JIS K7136 (Method for Determining Haze of Transparent Plastics). And it was considered qualified when the haze value was 20% or less.

[0043] The strength was measured for the tensile strength in the MD direction in accordance with JIS Z1702 (Polyethylene film for packaging). When the tensile strength was 60 MPa or more, it was considered qualified. The test methods and reference values for heat shrinkability, transparency, and strength are summarized in Table 4.

[0044]

Table 4

[0045] As shown in Tables 1 to 3, it can be seen that the shrink films of Examples 1 to 14 are excellent not only in heat shrinkability and transparency but also in tensile strength.

[0046] On the other hand, for the shrink film of Comparative Example 1 in which the mass ratio of the first polyethylene to the second polyethylene is 59:41 and the blending amounts of silicon dioxide and glycerin fatty acid ester are large, all of heat shrinkability, transparency, and tensile strength were inferior. For the shrink films of Comparative Examples 2 to 4 in which the blending amounts of silicon dioxide and glycerin fatty acid ester are large, transparency and tensile strength were inferior. Also, for the shrink films of Comparative Examples 5 to 7 in which the blending amounts of silicon dioxide and glycerin fatty acid ester are small, heat shrinkability was inferior.

[0047] Although the present embodiment has been described above, the present embodiment is not limited to these, and various modifications are possible within the scope of the gist of the present embodiment.

Claims

1. The first polyethylene having a density of 0.910 to 0.930 g / cm ３ and, The density is 0.890 g / cm ３ or more and less than 0.910 g / cm ３ a second polyethylene, and Silicon dioxide with an average particle diameter of 0.1 μm or less, glycerin fatty acid ester, and including the first polyethylene and the second polyethylene in a mass ratio of 80:20 to 60:40, a shrink film containing 0.5 to 5 parts by mass of the silicon dioxide and 0.5 to 3 parts by mass of the glycerin fatty acid ester with respect to a total of 100 parts by mass of the first polyethylene and the second polyethylene.

2. The shrink film according to Claim 1, wherein the first polyethylene is low density polyethylene and the second polyethylene is linear low density polyethylene.

3. The shrink film according to Claim 1 or 2, wherein the thickness of the shrink film is 50 μm to 150 μm.

4. A multilayer shrink film comprising the shrink film according to Claim 1 or 2.

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