JP6532125B2 - Polyethylene-based crosslinked shrink film - Google Patents

Description

  The present invention relates to a polyethylene-based crosslinked shrink film excellent in shrink wrap finish, which is used for shrink wrap materials.

  Heretofore, polyvinyl chloride-based shrink films, polypropylene-based shrink films, polyethylene-based non-crosslinked shrink films, polyethylene-based crosslinked shrink films and the like have been known as heat-shrinkable packaging materials.

Among them, polyethylene-based crosslinked shrink film does not generate harmful hydrogen chloride gas at the time of packaging work or waste incineration like polyvinyl chloride-based shrink film, and polypropylene-based shrink film, polyethylene-based uncrosslinked It is widely used for shrink packaging such as food, cosmetics, medicine, stationery, etc. because it has the feature of being superior in shrink packaging finish compared with shrink film. However, with the films described in Patent Documents 1 to 4 disclosed, the margin ratio of bag making is made larger than usual due to the bag making conditions of the packaging machine such as when packaging a small container with an electrostatic seal packaging machine. If the bag has to be made larger than usual in order to eliminate corner wrinkles as much as possible, the shrink wrap does not finish tight, and the fit between the shrinked film and the package is insufficient. In addition, there has been a problem that wavelike wrinkles are generated on the top surface portion of the shrink package due to insufficient shrinkage, and sufficient shrink package finish can not be obtained. The margin ratio of bag making as referred to herein is represented by (bag film circumferential length-circumferential length of package) / peripheral length of package x 100 (%), and is usually 10 to 20. Although it is about%, when set relatively large to about 30 to 70%, the above-described poor shrink wrap finish was observed.

Although the film described in Patent Document 5 containing a specific low density polyethylene is disclosed in order to improve the shrinkage finish at the above-mentioned high bag manufacturing margin, the film described in Patent Document 1 is significantly superior to the film described in Patent Document 1. Although it can exhibit shrink finish, it has not been able to satisfy the severe shrink package finish requirements when packaging high-grade products such as cosmetics and drugs.

The film disclosed in Patent Document 6 has a concern that production stability may be impaired if it is intended to satisfy the strict shrink-wrapping finish requirements when packaging high-class products such as cosmetics and medicines. Specifically, in the core layer material system of EVA and low density polyethylene, EVA having a high vinyl acetate content (more than 15% by weight) is required to satisfy high packaging finish requirements, and extrusion molding processing in production In the process, the thermal degradation of the high vinyl acetate content EVA causes frequent occurrence of gelation, which causes the inhibition of the stretching stability. In order to use EVA having a low vinyl acetate content (less than 15% by weight) which is resistant to heat degradation and to meet high packaging finishing requirements, ethylene-methyl acrylate copolymer or ethylene-butyl acrylate co-weight is used Although it is necessary to combine the combination, in this case, it takes a long time to replace the raw materials when producing many varieties of different raw material systems with the same production machine, and there is a concern that it causes the yield loss due to production loss. It was In addition, it was difficult to meet the strict shrink-wrapping finish requirements without using EVA.

Unexamined-Japanese-Patent No. 5-84826 JP-A-5-162270 Japanese Patent Application Laid-Open No. 8-169093 Japanese Patent Application Laid-Open No. 10-250012 JP 2014-223808 A Japanese Patent Laid-Open No. 2-283445

An object of the present invention is to provide a polyethylene-based crosslinked shrink film capable of satisfying the strict shrink-wrapping finish requirements for packaging high-class products such as cosmetics and drugs, and which does not impair the productivity. It is said that.

The present inventors arrived at the present invention as a result of earnest studies to solve such problems.
That is, the present invention provides 35 to 70 parts by weight of EVA (hereinafter referred to as EVA (A)) having a vinyl acetate content of 5 to 15% by weight and an MI of 0.3 to 3.0 g / 10 min, and a density of 0.865 to 0 25 to 65 parts by weight of a polyethylene-based elastomer (hereinafter referred to as a polyethylene-based elastomer (B)) having an .885 g / cm ³ MI and 0.5 to 4.0 g / 10 min, and a density of 0.895 to 0.910 g / cm ³ A core layer mainly composed of a resin composition comprising 0 to 40 parts by weight of ultra low density polyethylene (hereinafter referred to as ultra low density polyethylene (C)) having a MI of 0.5 to 4.0 g / 10 min, 80 to 95 parts by weight of linear low density polyethylene (hereinafter referred to as linear low density polyethylene (D)) having a density of 0.915 to 0.930 g / cm ³ and an MI of 1.0 to 3.0 g / 10 min , Density 0.8 5~0.885g ^/ cm 3, a polyethylene-based elastomer is a MI0.5~4.0g / 10 min (hereinafter referred to as polyethylene-based elastomer (E)) and the main component a resin composition comprising 5 to 20 parts by weight Providing a polyethylene-based crosslinked shrink film obtained by cross-linking by electron beam irradiation of 20 to 60 kGy and performing stretching processing 3 to 6 times simultaneously in both longitudinal and transverse directions; Preferably, the density of the polyethylene elastomer (B) in the core layer main component and the polyethylene elastomer (E) in both surface layer main components is 0.865 to 0.879 g / cm ³ , 35 to 45 kGy It is cross-linked by electron beam irradiation, and it is characterized by having an MFR of 7 to 25 g / 10 min under a load condition of 250 ° C. and 21.6 kg. There is provided a Riechiren based crosslinking shrink film.
Furthermore, the present invention provides the following methods [1] to [4].
[1] A polyethylene-based crosslinked shrink film having a laminated structure of at least three or more layers having a core layer mainly composed of the following (a) composition and both surface layers mainly composed of the following (b) composition: A manufacturing method,
A step of obtaining an unstretched film having a laminated constitution of at least three or more layers having (a) a core layer containing the composition as a main component and (b) both surface layers containing the composition as a main component by melt coextrusion;
Irradiating the unstretched film with an electron beam of 20 to 60 kGy to obtain a crosslinked unstretched film;
A production method comprising the step of simultaneously biaxially stretching the crosslinked unstretched film at a stretch ratio of 3 to 6 times in each of the longitudinal and lateral directions .
(A) Ethylene-vinyl acetate copolymer (hereinafter referred to as EVA) 35 to 70 having a vinyl acetate content of 5 to 15% by weight and a melt index (hereinafter referred to as MI) of 0.3 to 3.0 g / 10 min. Parts by weight, density 0.865 to 0.885 g / cm ³ , MI 0.5 to 4.0 g / 10 min 25 to 65 parts by weight of a polyethylene elastomer, density 0.895 to 0.910 g / cm ³ , and MI 0 Resin composition comprising 0 to 40 parts by weight of ultra-low density polyethylene of 0.5 to 4.0 g / 10 min
(B) 80 to 95 parts by weight of linear low density polyethylene having a density of 0.915 to 0.930 g / cm ³ , an MI of 1.0 to 3.0 g / 10 min, and a density of 0.865 to 0.885 g / cm ^{3. A} resin composition comprising 5 to 20 parts by weight of a polyethylene elastomer having an MI of 0.5 to 4.0 g / 10 min.
[2] The polyethylene-based polymer according to [1], wherein the density of the polyethylene-based elastomer in the composition of (a) and the composition of (b) is 0.865 to 0.879 g / cm ³ Method of producing a crosslinked shrink film.
[3] The method for producing a polyethylene-based crosslinked shrink film according to [2], wherein an electron beam of 35 to 45 kGy is irradiated in the step of obtaining the crosslinked unstretched film.
[4] The polyethylene-based crosslinked shrink film according to [2], wherein the melt-flow rate of the crosslinked polyethylene-based shrink film under a load condition of 250 ° C. and 21.6 kg is 7 to 25 g / 10 min. Manufacturing method.

The cross-linked polyethylene-based shrink film of the present invention is optionally made of a specific EVA having excellent conformability required for high shrinkage finish, a specific polyethylene-based elastomer excellent in low-temperature shrinkage and tear resistance, and as required. A core layer comprising a resin composition containing an ultra low density polyethylene excellent in tear resistance and stretch stability as a core layer, and a specific linear low density polyethylene excellent in transparency, slipperiness and heat resistance, , A layer consisting mainly of a resin composition consisting of a specific polyethylene-based elastomer excellent in low-temperature shrinkability is laminated as both surface layers, electron beam irradiation, stretching, so that severe shrink-wrapping finish without impairing productivity The effect of satisfying the demand is achieved.

Hereinafter, the present invention will be described in detail.
Of the resin compositions used as the main component of the core layer in the present invention, EVA (A) has a vinyl acetate content of 5 to 15% by weight, and an MI of 0.3 to 3.0 g / 10 min. And 35 to 70 parts by weight as a resin composition of the core layer main component. It is preferable to blend those in the above-mentioned range in order to function mainly to impart features excellent in conformity to the irregular shape required for high shrinkage finish.

If the vinyl acetate content of EVA (A) is less than 5%, the conformability required for high shrinkage finish is insufficient, and if it exceeds 15%, thermal degradation in the melt extrusion process is caused. It is not preferable because it induces the generation of a gel and lowers the stretching stability. If the MI is less than 0.3 g / 10 min, it is not preferable because the motor load at the time of extrusion increases, and if it exceeds 3.0 g / 10 min, the drawability and heat resistance decrease, and the pinholes and the It is not preferable because seal opening occurs. In addition, if the composition in the resin composition used as the main component of the core layer is less than 35 parts by weight, the conformity to the atypical shape required for high shrinkage finish becomes insufficient, and if it exceeds 70 parts by weight, low temperature shrinkability It is not preferable because the tear resistance is insufficient.

Among the resin compositions used as the main component of the core layer of the present invention, the polyethylene elastomer (B) has a density of 0.865 to 0.885 g / cm ³ and an MI of 0.5 to 4.0 g / 10 min. And copolymerization weight of ethylene with one or more α-olefins selected from the group consisting of butene-1, pentene-1, hexene-1, heptene-1, octene-1, 4-methylpentene-1. It is composed of unity and is compounded in 25 to 65 parts by weight as a resin composition of the core layer main component, and mainly functions to impart low temperature shrinkability and tear resistance, so it is preferable to blend the resin and the range resin .

A polyethylene-based elastomer (B) having a density of less than 0.865 g / cm ³ is not preferable because the tensile modulus of the film is lowered and the running property on the packaging machine is lowered, and it exceeds 0.885 g / cm ³ And low temperature shrinkage, which is not preferable. If the MI is less than 0.5 g / 10 min, it is not preferable because the motor load at the time of extrusion increases, and if it exceeds 4.0 g / 10 min, the stretching processability and the heat resistance decrease, and the pinholes and the It is not preferable because seal opening occurs. Less than 25 parts by weight as the composition in the resin composition used as the main component of the core layer is not preferable because low temperature shrinkage and tear strength decrease, and it is not preferable when it exceeds 65 parts by weight, the heat resistance of the film in the shrinking tunnel. It is not preferable because the nature is reduced.

Among the resin compositions used as the main component of the core layer of the present invention, ultra low density polyethylene (C) has a density of 0.895 to 0.910 g / cm ³ and an MI of 0.5 to 4.0 g / 10 min. A co-polymer of ethylene with one or more α-olefins selected from the group consisting of butene-1, pentene-1, hexene-1, heptene-1, octene-1, 4-methylpentene-1; It is composed of a polymer and is blended in an amount of 0 to 40 parts by weight as the resin composition of the core layer main component, and mainly functions to reinforce tear resistance and stretch stability, so it is preferable to blend one in the above range.

Ultra low density polyethylene (C) having a density of less than 0.895 g / cm ³ is not preferable because the tensile modulus of the film becomes low and the running property on the packaging machine becomes a factor of reduction, and 0.885 g / cm ^When it exceeds ³ , it is not preferable because it inhibits low temperature shrinkability. If the MI is less than 0.5 g / 10 min, it is not preferable because the motor load at the time of extrusion increases, and if it exceeds 4.0 g / 10 min, the stretching processability and the heat resistance decrease, and the pinholes and the It is not preferable because seal opening occurs. If it exceeds 40 parts by weight as the composition in the resin composition used as the main component of the core layer, it is not preferable because the low temperature shrinkage is inhibited.

Among the resin compositions used as the main component of both surface layers of the present invention, linear low density polyethylene (D) has a density of 0.915 to 0.930 g / cm ³ and an MI of 1.0 to 3.0 g / 10. And one or more .alpha.-olefins selected from the group consisting of butene-1, pentene-1, hexene-1, heptene-1, octene-1, 4-methylpentene-1. Containing 80 to 95 parts by weight as a resin composition of both surface layers as the main component of the resin and mainly imparts slipperiness, heat resistance and transparency, It is preferable to mix | blend.

A linear low density polyethylene (D) having a density of less than 0.915 g / cm ³ is not preferable because the slipperiness decreases, and it is not preferable because it exceeds the heat sealability if it exceeds 0.930 g / cm ³ . If the MI is less than 1.0 g / 10 min or more than 3.0 g / 10 min, the transparency is unfavorably reduced. If it is less than 80 parts by weight as the resin composition of the main component of both surface layers, the heat resistance in the shrinking tunnel is lowered, and if it exceeds 95 parts by weight, the low temperature shrinkability is unfavorably lowered.

Among the resin compositions used as the main components of both surface layers of the present invention, the polyethylene elastomer (E) has a density of 0.865 to 0.885 g / cm ³ and a MI of 0.5 to 4.0 g / 10 min. And one or more α-olefins selected from the group consisting of butene-1, pentene-1, hexene-1, heptene-1, octene-1, 4-methylpentene-1 with ethylene. It is preferably composed of a copolymer and is blended in an amount of 5 to 20 parts by weight as the resin composition of both surface layer main components, and mainly functions to impart low temperature shrinkage, so that it is preferable to blend those within the above range.

A polyethylene-based elastomer (B) having a density of less than 0.865 g / cm ³ is not preferable because the slipperiness is reduced, and when it exceeds 0.885 g / cm ³ , the low-temperature shrinkability is not preferable. . When MI is less than 0.5 g / 10 min or more than 4.0 g / 10 min, the transparency is unfavorably reduced. Less than 5 parts by weight as the composition in the resin composition used as the main component of both surface layers is not preferable because low temperature shrinkability is reduced, and more than 20 parts by weight is not preferable because slipperiness is reduced.

If both surface layers and / or core layers are in a range that does not interfere with the object of the present invention, the core layer main component resin composition is mixed in both surface layers, and both surface layers are mixed in the core layer. The main component resin composition can be mixed and used. By this, various physical properties can be adjusted according to the required characteristics, and it is also possible to mix and use recycled resins such as trims and extras.

The layer structure of the present invention is a layer structure of at least three layers, for example, B / A / B, B / A + B / B three-layer structure, B / A + B / A / A + B / B, B / A / A + B / A five-layer configuration such as A / B etc. may be mentioned. Among them, the layer configuration provided with the A + B layer is suitable because it is easy to adjust various physical properties and to mix and use the recycled resin. The layers other than the core layer and both surface layers are not particularly limited as long as the objects of the present invention are not impaired.

The thickness ratio of each layer of the present invention is not particularly limited, but the thickness ratio of the core layer is preferably in the range of 40 to 80% with respect to the total thickness. If the thickness ratio of the core layer is less than 40%, the performance of highly shrink-wrapping finish is deteriorated, and it is not preferable. If it exceeds 80%, the tensile elastic modulus of the film is lowered, and the runnability in the packaging machine is easily reduced It is not preferable because The total thickness of the film is also not particularly limited, but is preferably 7 to 35 μm for heat-shrinkable packaging material applications.

Additives such as lubricants, antiblocking agents, antistatic agents, antifogging agents, antioxidants, etc. should be suitably used for the purpose of providing their respective effective actions, as long as the objects of the present invention are not impaired. Can.

The crosslinking treatment in the present invention is performed by irradiating the film with an electron beam in the range of 20 to 60 kGy, and more preferably in the range of 35 to 45 kGy. If it is less than 20 kGy, it is not preferable because heat resistance and stretching processability decrease and pinholes and seal opening occur at the time of fusion seal, and if it exceeds 60 kGy, fusion cutting property is unfavorably lowered.

In the present invention, after electron beam crosslinking treatment in the range of 20 to 60 kGy, MFR (hereinafter referred to as MFR ^H ) under load conditions of 250 ° C. and 21.6 kg of the film obtained by stretching is 7 to 25 g / 10 min. It is preferable to be in the range of MFR ^H changes depending on the combination of the raw material type and the dose, but if it is less than 7 g / 10 min, it is not preferable because the melt cutting property tends to decrease, and if it exceeds 25 g / 10 min, the heat resistance and heat resistance in the heat-shrink tunnel This is not preferable because the melt-cut sealability is likely to be reduced under the condition that high-speed packaging of a bulky package.

In the present invention, the crosslinking degree of each layer obtained by the crosslinking treatment is preferably equivalent to each other. If the degree of crosslinking and the melt viscosity of each layer are too different, the transparency tends to be reduced, which is not preferable.
The addition of a cross-linking aid, cross-linking inhibitor, etc., adjustment of acceleration voltage, etc. for the purpose of matching the degree of cross-linking of each layer may be carried out without any problem as long as the purpose of the present invention is not impaired. .

Next, the method for producing the film of the present invention is shown. The method for producing the film of the present invention using the above-mentioned resin can be carried out by a known method of simultaneous biaxial stretching in the longitudinal and transverse directions, and the stretching ratio is preferably 3 to 6 in both longitudinal and transverse directions. If it is less than 3 times, it is not preferable because the heat resistance failure due to the decrease of the modulus and the expansion of the formed film in the contraction tunnel is large, and the appearance defect of the vertical streaks seen after the contraction packaging occurs. When it exceeds, tear strength will fall and it is unpreferable.
Hereinafter, the case of three-layer lamination annular film formation stretching is taken as an example, and will be specifically described. First, a layer mainly composed of a resin composition containing EVA (A), polyethylene-based elastomer (B) and, if necessary, ultra low density polyethylene (C) as core layer, linear low density polyethylene (D), Melt-kneading with an extruder of 3 units so that a layer composed mainly of a resin composition consisting of a polyethylene-based elastomer (E) will be both surface layers, co-extrusion cyclically from a three-layer annular die, once without stretching The solution is quenched and solidified to produce a tubular unstretched film. Subsequently, the electron beam is irradiated to the both sides of a tube-like unstretched film by irradiation conditions of 20-60 kGy with an electron beam irradiation apparatus, and a crosslinked tube-like unstretched film is produced. The obtained crosslinked tubular unstretched film is supplied to a tubular stretching device, and is highly orientable in a temperature range, for example, a temperature lower than 10 ° C. below the melting point of the core layer resin, preferably 15 ° C. below the melting point A gas pressure is applied to the inside of the tube at a low temperature to cause simultaneous biaxial orientation at a stretching ratio of 3 to 6 times in both longitudinal and lateral directions by expansion and stretching. The film removed from the stretching apparatus can be heat treated or annealed as desired, which can suppress natural shrinkage during storage.

EXAMPLES Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.
The methods of measurement and evaluation in Examples and Comparative Examples were performed as follows.
1. Film thickness: It measured according to JIS-Z1709.
2. Thickness ratio: It measured by observing the cross section of a film with a microscope. 3. Haze: Measured according to JIS-K7105.
4. MI: It measured on 190 degreeC and 2.16 kg load conditions according to JIS-K7210.
5. MFR ^H : It measured on 250 degreeC and 21.6 kg load conditions according to JIS-K7210.
6. Tensile modulus of elasticity: Measured according to JIS-Z7127.
7. 100 ° C. heat shrinkage rate: After immersing a film cut into a square of 100 mm in length and width in a glycerin bath at 100 ° C. for 10 seconds, the film is quenched in water, and the length in each direction is measured. The thermal contraction rate of TD was calculated.

(1)
Thermal contraction rate (%) = 100-A
(However, A indicates the longitudinal or transverse length (mm) after quenching.)

8. Shrink-packing finish: 30% vertical and 100% horizontal bag room for commercial lotion pump container with L-type sealed half-cut automatic packing machine (model: ASL-260) manufactured by International Sanko Co., Ltd. The film was prepackaged at a rate condition and retained for 10 seconds in a shrink tunnel set to a temperature limit of 5 ° C. of the film, and five samples were randomly selected from package samples after passing through the tunnel and evaluated according to the following criteria.
<Evaluation criteria>
:: There is sufficient tightness between the shrink film and the package, and there are almost no corners of the package sample or small wrinkles.
Δ: The shrink film and the package have a tight feeling, but the corners of the package sample and the small wrinkles are slightly noticeable.
X: The feeling of tightness between the shrink film and the package is insufficient, or the corner corners of the package sample and small wrinkles are clearly noticeable. Alternatively, the film may run poorly at the time of packaging, causing damage to the appearance and the like.
9. Melt-off sealability, electrostatic sealability: A box of 15 cm sides is packaged at a packaging speed of 40 pcs / min with an overlap automatic packaging machine (model: HP-20SA) manufactured by Hanagata Co., Ltd. Hold for 5 seconds in the shrinking tunnel set to a temperature limit of 5 ° C, randomly select 10 pieces from the package sample after passing through the tunnel, and cut the sealability of the horizontal seal and the electrostatic sealability of the vertical seal below It was evaluated on the basis of
<Fusing sealability-Evaluation criteria>
○: No pinhole or seal opening was observed in the fused seal portion of the package sample.
X: Pin holes or seal opening can be observed in the fused and sealed portion of the package sample. Alternatively, melting can not be performed unless the seal temperature is raised to 230 ° C. or higher.
<Electrostatic sealability-Evaluation criteria>
○: The electrostatic seal portion of the package sample is not opened but is sealed cleanly.
X: Opening is seen in the electrostatic seal part of a package sample.

Example 1
As shown in Table 1, a vinyl acetate content of 10% by weight, 65 parts by weight of EVA (A1) with an MI of 2.0 g / 10 min, a density of 0.870 g / cm ³ , a polyethylene based elastomer with an MI of 1.0 g / 10 min (B1) the resin composition consisting of 35 parts by weight as a core layer, density 0.920g / cm ^3, MI1.0g / 10 min linear low density polyethylene (D1) 90 parts by weight, density 0.870 g / cm ^3, 10 parts by weight of a polyethylene-based elastomer (E1) having a MI of 1.0 g / 10 min is used as both surface layers, and after melt-kneading with three extruders, extrusion of each extruder so that the thickness ratio becomes 1/5/1 The amount was set and co-extruded downward with a 3-layer annular die. While sliding the outer surface of the cylindrical cooling mandrel inside of which the cooling water was circulating, the outside was cooled and pulled through a water tank to obtain an unstretched film, while the formed three-layer tube was slid on the inside. Electron beam irradiation is performed on both sides of this tube-shaped unstretched film under an irradiation condition of 38 kGy using an electron beam irradiation apparatus manufactured by Nisshin High Voltages, and then a crosslinked tube-like unstretched film is tubular biaxially stretched It introduce | transduced into the apparatus and it extended | stretched 5 times in length and width each at 90-110 degreeC, and obtained the lamination | stacking biaxial stretching film of film thickness 15 micrometers.
There is no trouble at the time of production, and the obtained film is excellent in high shrink-wrapping finish, and the tightness between the shrink-film and the package is sufficient, and there are almost no corners or corner wrinkles at the four corners A beautiful shrink wrap was obtained. In addition, the properties such as haze, tensile modulus, heat shrinkage at 100 ° C., melt-cut sealability, and electrostatic seal were also good.

Example 2
As shown in Table 1, a vinyl acetate content of 15% by weight, 50 parts by weight of EVA (A2) with an MI of 1.0 g / 10 min, a density of 0.870 g / cm ³ , a polyethylene based elastomer with an MI of 1.0 g / 10 min (B1) Resin composition consisting of 25 parts by weight of ultra low density polyethylene (C1) 25 parts by weight with a density of 0.905 g / cm ³ and MI 0.8 g / 10 min is used as a core layer, irradiation dose is 40 kGy, draw ratio is 4 times in length and width A laminated biaxially stretched film with a film thickness of 15 μm was obtained in the same manner as in Example 1 except for using the above.
There is no trouble at the time of production, and the obtained film is excellent in high shrink-wrapping finish, and the tightness between the shrink-film and the package is sufficient, and there are almost no corners or corner wrinkles at the four corners A beautiful shrink wrap was obtained. In addition, the properties such as haze, tensile modulus, heat shrinkage at 100 ° C., melt-cut sealability, and electrostatic seal were also good.

Example 3
As shown in Table 1, a vinyl acetate content of 6% by weight, 45 parts by weight of EVA (A3) having a MI of 0.3 g / 10 min, a density of 0.875 g / cm ³ , and a polyethylene-based elastomer having a MI of 3.0 g / 10 min (B2) A resin composition comprising 55 parts by weight is used as a core layer, and the density is 0.920 g / cm ³ , 90 parts by weight of linear low density polyethylene (D1) having a MI of 1.0 g / 10 min, and the density is 0.875 g / cm ³ Example 1 except that 10 parts by weight of a polyethylene-based elastomer (E2) having a MI of 3.0 g / 10 min was used as both surface layers, the thickness ratio was 1/6/1, the irradiation dose was 35 kGy, and the draw ratio was 4 times in length and width. A laminated biaxially stretched film with a film thickness of 15 μm was obtained in the same manner as in the above.
There is no trouble at the time of production, and the obtained film is excellent in high shrink-wrapping finish, and the tightness between the shrink-film and the package is sufficient, and there are almost no corners or corner wrinkles at the four corners A beautiful shrink wrap was obtained. In addition, the properties such as haze, tensile modulus, heat shrinkage at 100 ° C., melt-cut sealability, and electrostatic seal were also good.

Example 4
As shown in Table 1, a vinyl acetate content of 15% by weight, an EVA (A2) of 50 parts by weight with an MI of 1.0 g / 10 min, a density of 0.885 g / cm ³ , and an MI of 1.0 g / 10 min of a polyethylene-based elastomer (B3) A resin composition consisting of 50 parts by weight is used as a core layer, and the density is 0.920 g / cm ³ , 85 parts by weight of linear low density polyethylene (D1) having a MI of 1.0 g / 10 min, the density 0.885 g / cm ³ A film was prepared in the same manner as in Example 1, except that 15 parts by weight of a polyethylene elastomer (E3) having a MI of 1.0 g / 10 min was used as both surface layers, the thickness ratio was 1/4/1, and the irradiation dose was 35 kGy. A laminated biaxially stretched film with a thickness of 15 μm was obtained.
There is no trouble at the time of production, and the obtained film is excellent in high shrink-wrapping finish, and the tightness between the shrink-film and the package is sufficient, and there are almost no corners or corner wrinkles at the four corners A beautiful shrink wrap was obtained. In addition, the properties such as haze, tensile modulus, heat shrinkage at 100 ° C., melt-cut sealability, and electrostatic seal were also good.

Example 5
As shown in Table 1, a vinyl acetate content of 15% by weight, 35 parts by weight of EVA (A2) of 1.0 g / 10 min MI, a density of 0.875 g / cm ³ , a polyethylene-based elastomer of MI 3.0 g / 10 min (B2) A resin composition consisting of 35 parts by weight, a density of 0.905 g / cm ³ and an MI of 0.8 g / 10 min, and 30 parts by weight of ultra low density polyethylene (C1) as a core layer, a density of 0.920 g / cm ³ and an MI of 1.0 g 90 parts by weight of linear low density polyethylene (D1) which is 10 minutes, a density of 0.875 g / cm ³ , 10 parts by weight of polyethylene elastomer (E2) of MI 3.0 g / 10 minutes as both surface layers, and the thickness ratio A laminated biaxially stretched film with a film thickness of 15 μm was obtained in the same manner as in Example 1 except that the irradiation dose was 45 kGy, and the draw ratio was 4 × 4.
There is no trouble at the time of production, and the obtained film is excellent in high shrink-wrapping finish, and the tightness between the shrink-film and the package is sufficient, and there are almost no corners or corner wrinkles at the four corners A beautiful shrink wrap was obtained. In addition, the properties such as haze, tensile modulus, heat shrinkage at 100 ° C., melt-cut sealability, and electrostatic seal were also good.

Comparative Example 1
As shown in Table 2, 35 parts by weight of low density polyethylene (F1) having long chain branching manufactured by a high pressure method having a density of 0.920 g / cm ³ and an MI of 0.3 g / 10 min, a density of 0.885 g / cm ^{3 A} linear low density resin having a density of 0.920 g / cm ³ and an MI of 1.0 g / 10 min, with a resin composition consisting of 65 parts by weight of a polyethylene elastomer (B3) having an MI of 1.0 g / 10 min. A laminated film having a film thickness of 15 μm was prepared in the same manner as in Example 1 except that polyethylene (D1) was used as both surface layers, the thickness ratio was 1/4/1, the irradiation dose was 40 kGy, and the draw ratio was 4 times. An axial stretched film was obtained.
There were no troubles during production, and the obtained film had sufficient tightness between the shrink film and the package, but the corners and corner wrinkles of the four corners were slightly noticeable, and the shrink finish was insufficient. It was a thing.

Comparative example 2
As shown in Table 2, 40 parts by weight of low density polyethylene (F1) having long chain branching manufactured by a high pressure method having a density of 0.920 g / cm ³ and an MI of 0.3 g / 10 min, a density of 0.885 g / cm ^{3 A} linear low density resin having a density of 0.920 g / cm ³ and an MI of 1.0 g / 10 min, with a resin composition comprising 60 parts by weight of a polyethylene elastomer (B3) having an MI of 1.0 g / 10 min. 85 parts by weight of polyethylene (D1), density 0.885 g / cm ³ , 15 parts by weight of polyethylene elastomer (E3) with MI 1.0 g / 10 min are used as both surface layers, irradiation dose is 40 kGy, draw ratio is 4 times A laminated biaxially stretched film with a film thickness of 15 μm was obtained in the same manner as in Example 1 except for the above.
There were no troubles during production, and the obtained film had sufficient tightness between the shrink film and the package, but the corners and corner wrinkles of the four corners were slightly noticeable, and the shrink finish was insufficient. It was a thing.

Comparative example 3
As shown in Table 2, a vinyl acetate content of 21%, 70 parts by weight of EVA (A4) with MI 2.5 g / 10 min, a density of 0.870 g / cm ³ , a polyethylene-based elastomer (B1) 30 with MI 1.0 g / 10 min. The film thickness is 15 μm in the same manner as in Example 1 except that the resin composition consisting of parts by weight is used as a core layer, the thickness ratio is 1/6/1, the irradiation dose is 40 kGy, and the draw ratio is 4 × 4. A laminated biaxially stretched film was obtained.
The obtained film was excellent in high shrink-wrapping finish, had a sufficient tightness between the shrink-film and the package, and had almost no corners or corner wrinkles at the four corners. On the other hand, due to the heat deterioration of EVA during production, punctures of stretch bubbles frequently occur, and the stretch stability is insufficient.

Comparative example 4
As shown in Table 2, a vinyl acetate content of 15% by weight, 50 parts by weight of EVA (A2) with an MI of 1.0 g / 10 min, a density of 0.875 g / cm ³ , a polyethylene based elastomer with an MI of 3.0 g / 10 min (B2) A resin composition consisting of 35 parts by weight, a density of 0.905 g / cm ³ , and an MI of 0.8 g / 10 min. 15 parts by weight of ultra low density polyethylene (C1) is used as a core layer, and a density of 0.920 g / cm ³ , MI 1.0 g 70 parts by weight of linear low density polyethylene (D1) which is 10 min, density 0.875 g / cm ³ , 30 parts by weight of polyethylene elastomer (E2) with MI 3.0 g / 10 min as both surface layers, and irradiation dose A laminated biaxially stretched film with a film thickness of 15 μm was obtained in the same manner as in Example 1 except that 65 kGy was used.
The obtained film has poor running during packaging, and scratches and the like enter to damage the appearance, and it can not be melted unless the sealing temperature is raised to 230 ° C. or higher, and the easily melted sealability is also inferior. The

Comparative example 5
As shown in Table 2, a vinyl acetate content of 6% by weight, 80 parts by weight of EVA (A3) with an MI of 0.3 g / 10 min, a density of 0.870 g / cm ³ , a polyethylene-based elastomer with an MI of 1.0 g / 10 min (B1) A laminated biaxially stretched film with a film thickness of 15 μm was obtained in the same manner as in Example 1 except that the resin composition consisting of 20 parts by weight was used as a core layer, the irradiation dose was 35 kGy, and the draw ratio was 4 × 4. .
The obtained film is poor in low temperature shrinkability, so the tightness between the shrink film and the package is sufficient, but the corners and corner wrinkles of the four corners are slightly noticeable, and the shrink finish is insufficient. In addition, since the tear resistance is poor, packaging defects in which the film tears from the needle hole for removing air in the bag in the shrinkage tunnel frequently occur.

The heat-shrinkable packaging material of the present invention is a polyethylene-based crosslinked shrink film capable of satisfying the strict shrink-wrapping finish requirements for packaging high-grade products such as cosmetics and drugs, and which does not impair productivity. It can be suitably used as

Claims (4)

Following (a) a core layer mainly composed of the composition, and (b) below composition having at least three or more layers structure having both surface layers mainly composed of, method of manufacturing the port Riechiren based crosslinking shrink film And
A step of obtaining an unstretched film having a laminated constitution of at least three or more layers having (a) a core layer containing the composition as a main component and (b) both surface layers containing the composition as a main component by melt coextrusion;
Irradiating the unstretched film with an electron beam of 20 to 60 kGy to obtain a crosslinked unstretched film;
A production method comprising the step of simultaneously biaxially stretching the crosslinked unstretched film at a stretch ratio of 3 to 6 times in each of the longitudinal and lateral directions .
(A) Ethylene-vinyl acetate copolymer (hereinafter referred to as EVA) 35 to 70 having a vinyl acetate content of 5 to 15% by weight and a melt index (hereinafter referred to as MI) of 0.3 to 3.0 g / 10 min. Parts by weight, density 0.865 to 0.885 g / cm ³ , MI 0.5 to 4.0 g / 10 min 25 to 65 parts by weight of a polyethylene elastomer, density 0.895 to 0.910 g / cm ³ , and MI 0 Resin composition comprising 0 to 40 parts by weight of ultra-low density polyethylene of 0.5 to 4.0 g / 10 min
(B) 80 to 95 parts by weight of linear low density polyethylene having a density of 0.915 to 0.930 g / cm ³ , an MI of 1.0 to 3.0 g / 10 min, and a density of 0.865 to 0.885 g / cm ^{3. A} resin composition comprising 5 to 20 parts by weight of a polyethylene elastomer having an MI of 0.5 to 4.0 g / 10 min. Wherein the density of the polyethylene-based elastomer in the composition of the composition prior to Symbol (a) and (b) is a 0.865~0.879g / cm ^3, a polyethylene-based cross-shrink according to claim 1, wherein How to make a film. In the step of obtaining the crosslinked unstretched film, and then irradiating an electron beam of 35～45KGy, manufacturing method of polyethylene crosslinked shrink film of claim 2 wherein. Of the polyethylene crosslinking shrink film, 250 ° C., a melt flow rate at 21.6kg load condition, and wherein it is 7~25g / 10 min, a manufacturing method of polyethylene crosslinked shrink film of claim 2, wherein .