JP2003145695A - Method for manufacturing polyethylenic heat-shrinkable film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polyethylenic low temperature heat-shrinkable film used in the packaging of DVD or video, excellent in low temperature shrinkage, not generating wrinkles especially in the corners or sides of the film and good in packaging finish. SOLUTION: Two surface layers comprising a polyethylene resin with a density of 0.905-0.960 g/cm<3> and a core layer comprising a mixed resin of 2-30% of a petroleum resin and 98-70% of a polyethylenic resin with a density of 0.870-0.935 g/cm<3> are co-extruded and the extrudate is irradiated with electron beam of 10-100 kGy and stretched longitudinally and laterally by 3-10 times to manufacture the polyethylenic biaxially stretched heat-shrinkable film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyethylene-based low-temperature heat-shrinkable film used for packaging DVDs and videos, which has excellent low-temperature shrinkability, and has no wrinkles on corners or sides, and has a finished package. It relates to a good polyethylene-based low temperature heat-shrinkable film and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, packaging of DVDs and video software has been
Polyvinyl chloride-based shrink films have been used because of their wide shrinkage temperature range, good workability, no wrinkles on the corners and sides, and good packaging finish. However, it does not have good heat-sealing properties, there are quality problems such as smelling, environmental problems such as dioxins, and it has good heat shrinkability as a substitute for polyvinyl chloride shrink film, low cost, no environmental problems, polyethylene, etc. There is a strong desire to use the above polyolefin film. Therefore, for example, a polypropylene resin is used for the inner and outer layers, a polyethylene resin is used for the core layer, and a biaxially stretched film is used, a polyolefin resin is used for the inner and outer layers, and a polyolefin resin with a lower density than the inner and outer layers is used for the core layer, and after crosslinking Stretched films, polyethylene-based resins for the inner and outer layers, and cross-linked stretched films using ethylene / vinyl acetate copolymer for the core layer have been developed.

However, these films, for example, a biaxially stretched film in which polypropylene resin is used for the inner and outer layers and polyethylene resin is used for the core layer, have a heat shrinkage ratio close to that of the polypropylene shrink film and have low temperature shrinkability. There are drawbacks such as not being sufficient and the finish being poor. In addition, a polyolefin resin for the inner and outer layers, a polyolefin resin having a lower density than the inner and outer layers for the core layer, or a film stretched after crosslinking using ethylene / vinyl acetate copolymer has improved low-temperature shrinkability, but shrinks. It has drawbacks such as narrow temperature range and poor fusing cutability.

[0004]

Therefore, an object of the present invention is to use polyethylene for low temperature heat shrinkage which is used for packaging DVDs and videos, has excellent low temperature shrinkability, and in particular has no wrinkles on corners and sides and has a good packaging finish. To provide a film. Another object of the present invention is to provide a polyethylene-based low temperature heat-shrinkable film having a wide shrinking temperature range and good melt-cutting property.

[0005]

Means for Solving the Problems As a result of intensive research to solve these problems, the present inventors have found that by blending a petroleum resin and a low density polyethylene resin in the core layer,
The inventors have found that these problems can be solved and have completed the present invention. The present invention includes the following inventions.

(1) Density 0.905 to 0.960 g / c
m³Two surface layers made of polyethylene resin and stone
Oil resin 2 to 30 mass%, density 0.870 to 0.935g
/ Cm ³Of polyethylene resin 98-70% by mass
A core layer made of resin is co-extruded to obtain 10 to 100 kGy.
After irradiating with an electron beam, stretch in the longitudinal and transverse directions 3 to 10 times
Polyethylene biaxially stretched heat shrinkable film characterized by
Method of manufacturing film.

(2) The polyethylene resin of the core layer is a mixture of a polyethylene resin having a density of 0.920 to 0.935 g / cm ^{3 and} a polyethylene resin having a density of 0.870 to 0.915 g / cm ^3. The method for producing a polyethylene-based biaxially stretched heat-shrinkable film according to item (1).

The present invention further includes the following inventions. (3) The proportion of the polyethylene-based resin having a density of 0.920 to 0.935 g / cm ^{3 in} the core layer is 5 to 20% by mass based on the polyethylene-based resin in the core layer. A method for producing the described polyethylene-based biaxially stretched heat-shrinkable film. (4) The polyethylene according to any one of items (1) to (3), wherein the polyethylene resin (the total of the surface layer and the core layer) excluding petroleum resin has an average density of 0.910 g / cm ³ or less. Method for producing a biaxially stretched heat-shrinkable film.

(5) A polyethylene-based biaxially stretched heat-shrinkable film produced by the method described in any one of the above items (1) to (4). (6) Heat shrinkage at 100 ° C. is 35% or more in both length and width, 90
The polyethylene-based biaxially stretched heat-shrinkable film according to the item (5), which has a heat shrinkage at 20 ° C. of 20% or more in both length and width.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The core layer of the heat shrinkable film of the present invention comprises petroleum resin and a density of 0.870 to 0.935 g / cm ^3.
It is made of a mixed resin of polyethylene resin. The petroleum resin used here is an alicyclic saturated hydrocarbon, and is obtained by hydrogenating a polymer of a C9 fraction obtained during petroleum refining. Petroleum resin is mainly used for stabilizing the film-forming property. D
In order to obtain a good finish in VD packaging, it is necessary to increase the heat shrinkage rate at low temperatures, but for this purpose, polyethylene having a low melting point of 110 ° C. or lower is usually used. However, the lower the melting point, the more unstable the film formation and the inability to stretch. However, by adding an appropriate amount of petroleum resin, stable film formation becomes possible.

The addition of petroleum resin can strengthen the rigidity of the film. The film made mainly of polyethylene has a low rigidity and is inferior in workability at the time of packaging as compared with the polypropylene-based film, but by adding a petroleum resin as in the present invention, the rigidity becomes strong and Workability is improved. Another advantage of adding a petroleum resin is improving the transparency of the film. Since DVDs are directly exposed to consumers at stores, it is important to improve transparency and gloss.

The content of petroleum resin in the core layer is 2 to 30% by mass, preferably 10 to 20% by mass. If the content of the petroleum resin is less than 2% by mass, the stretching point may fluctuate, the film formation may not be stable, and uneven thickness of the film may occur.
Problems such as breakage of thin parts and uneven shrinkage occur. If the amount of the petroleum resin compounded is 2% by mass or more, stable film formation is possible, but if it is intended to further reduce the uneven thickness, it is preferably 10% by mass or more. Further, when the content of the petroleum resin is more than 30% by mass, discharge variation occurs, uneven thickness of the raw fabric (sheet before stretching) occurs, and stretching becomes difficult. The blending amount of the petroleum resin is 30% by mass or less, but 20% by mass or less is preferable in consideration of stretchability.

[0013] core layer of a heat shrinkable film of the present invention has a density polyethylene resin 0.870g / cm ³ ~0.935g / cm ³ is used. If the density of the polyethylene-based resin is less than the lower limit, raw material forming failure occurs, and if it exceeds the upper limit, stretching is possible but the heat shrinkage rate becomes insufficient. The polyethylene resin may be one kind or a plurality of resins having different densities, but the density of each resin is 0.870 g /
It must be in the range of cm ^{3 to} 0.935 g / cm ³ .

Among them, the polyethylene resin of the core layer may be a mixture of a polyethylene resin having a density of 0.920 to 0.935 g / cm ^{3 and} a polyethylene resin having a density of 0.870 to 0.915 g / cm ^3. It is preferable in that the shrinkage temperature range is widened. Furthermore, the density is 0.920 to 0.935 g /
The proportion of the polyethylene resin of cm ³ is 5 to 20% by mass in the polyethylene resin of the core layer, and the density is 0.870 to 0.9.
It is particularly preferable for the stable film formation that the proportion of the polyethylene resin of 15 g / cm ³ is 95 to 80% by mass in the polyethylene resin of the core layer.

The proportion of polyethylene resin in the core layer is 7
It is 0 to 98% by mass, preferably 80 to 90% by mass.
If the proportion of the polyethylene-based resin is less than the lower limit, discharge fluctuations occur and stretching becomes difficult. If the upper limit is exceeded, the stretching point will fluctuate, causing uneven thickness of the film.

As the polyethylene resin for the core layer, low density polyethylene (density 0.910 to 0.935) prepared by the high pressure method is used.
g / cm ³ ), linear low-density polyethylene (density 0.9
10 to 0.935 g / cm ³ ), linear ultra low density polyethylene (density 0.870 to 0.910 g / cm ³ ), low density polyethylene using a metallocene catalyst (density 0.
910 to 0.935 g / cm ³ ), ultra low density polyethylene using metallocene catalyst (density 0.870 to 0.9
10 g / cm ³ ) is used. The above-mentioned polyethylene-based resin also includes a copolymer resin copolymerized with another monomer as long as the physical properties aimed at by the present invention are not impaired. The amount of comonomer depends on the type and other conditions,
It is possible to use up to about 20% by mass of the total mass of the monomers. Types of comonomers include butene-1, hexene
-1, octene-1, 4-methylpentene-1 and the like are used.

The surface layer of the heat shrinkable film of the present invention has a density of 0.905 g / cm ³ or more, preferably 0.910.
It is made of polyethylene resin of 0.930 g / cm ³ .
If the density of the polyethylene-based resin is less than the lower limit, the tubular method may cause blocking on the inner surface of the bubble during stretching and unstable drawing due to poor slip between the outer surface and the touch-preventing ring. In the tenter method, stickiness to the roll and unchucking occur. If the density of the polyethylene-based resin is too high, no particular problem will occur, but the heat shrinkage rate will be low and the low temperature shrinkable film will be unsatisfactory.
The resin configurations of the two surface layers may be the same or different.

The polyethylene resin having a density of 0.905 g / cm ³ or more used for the surface layer of the heat-shrinkable film of the present invention includes low density polyethylene (density 0.9
10 to 0.940 g / cm ³ ), high density polyethylene (density 0.940 to 0.960 g / cm ³ ), linear low density polyethylene (density 0.910 to 0.940 g / c)
m ³ ), linear ultra-low density polyethylene (density 0.905
˜0.910 g / cm ³ ), low density polyethylene using a metallocene catalyst (density 0.910 to 0.940 g /
cm ³ ), and ultra-low density polyethylene (density 0.905 to 0.910 g / cm ³ ) using a metallocene catalyst. The above-mentioned polyethylene-based resin also includes a copolymer resin copolymerized with another monomer as long as the physical properties aimed at by the present invention are not impaired. Although the amount of the comonomer depends on the type and other conditions, it can be used up to about 20% by mass of the total weight of the monomers. The types of comonomer include butene-1, hexene-1, octene-1, 4
Methylpentene-1 or the like is used.

The layer ratio of the surface layer to the core layer is not particularly specified, but in the case of a film having a three-layer structure of surface layer / core layer / surface layer, the thickness ratio of each layer is 2: 1: 2-1 :. Within the range of 10: 1, a good sheet without uneven thickness can be obtained.

To the resin for the core layer or the surface layer, in order to impart necessary properties, additives usually used in plastics processing, that is, lubricants, antistatic agents, antiblocking agents, antioxidants and the like may be used. .

To produce the heat-shrinkable film of the present invention,
A mixture of two surface layers made of polyethylene resin having a density of 0.905 g / cm ³ or more, and 2 to 30 mass% of petroleum resin and 98 to 70 mass% of polyethylene resin having a density of 0.870 to 0.935 g / cm ^3. A resin core layer is coextruded, irradiated with an electron beam of 10 to 100 kGy, and then stretched 3 to 10 times in the machine and transverse directions. As a manufacturing method, either a tubular method or a tenter method may be used, but the tubular method is preferable from the viewpoint of longitudinal and lateral balance of heat shrinkage.

The heat-shrinkable film of the present invention needs to be irradiated with an electron beam before stretching. Stretching is possible without irradiating the electron beam, but not only does the film become very unstable and has a large thickness variation, the finished film does not have heat resistance and becomes a film that easily punctures during packaging. .
The electron beam irradiation dose is required to be 10 to 100 kGy, preferably 30 to 70 kGy. Electron beam irradiation dose is 1
If it is less than 0 kGy, stretching is unstable and a thick and thick film is obtained. If it exceeds 100 kGy, stretching is stable,
Although the thickness unevenness is small and the required heat shrinkage ratio is obtained, the film does not have the durability to use because of its poor melt-cut seal cut property during packaging. For electron beam irradiation, in the case of a tubular method sheet, the sheet is made into a flat tape shape from both sides of the sheet, and in the case of a tenter method sheet,
It is preferable to irradiate from one side of the sheet.

The heat-shrinkable film of the present invention thus produced has an excellent heat-shrinkage ratio at low temperatures, and has a heat-shrinkage ratio of 100 ° C. of 35% or more in both length and width and a heat shrinkage ratio of 90 ° C. of 20% or more in both length and width. It becomes an ultra-low temperature shrinkable film having a rate. When the heat shrinkage rate satisfies these values, it is possible to obtain an excellent product in which no wrinkles are left on the sides and corners during DVD packaging. In order to obtain such an ultra-low temperature shrinkable film, in addition to the above-mentioned conditions, the average density of polyethylene-based resins (total of surface layer and core layer) excluding petroleum resin is 0.910.
It is effective to use g / cm ³ or less.

[0024]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

<Calculation Method of Average Density> The calculation method of average density in Examples and Comparative Examples is as follows. For example, 20 parts by mass of LLDPE1 (density 0.915 g / cm ³ ) and 5 parts of LLDPE2 (density 0.905 g / cm ³ ).
0 parts by mass, LLDPE3 (density 0.885 g / cm ³ )
When is 30 parts by mass, it is calculated as follows. Average density = 0.915 × 0.2 + 0.905 × 0.5 +
0.885 x 0.3 = 0.901

Example 1 70 parts by mass of a polyethylene resin having a density of 0.905 g / cm ³ (Atein 4203 manufactured by Dow Chemical Co.) in the core layer, and a polyethylene resin having a density of 0.930 g / cm ³ (Dow Rex manufactured by Dow Chemical Co.) 2042A) 10 parts by mass, 10 parts by mass of a polyethylene resin (DFDB1088 manufactured by Nippon Unicar Co., Ltd.) having a density of 0.885 g / cm ³ , and 10 parts by mass of a petroleum resin (Arcon P-125 manufactured by Arakawa Chemical Co., Ltd.) are kneaded to form a surface layer. A polyethylene resin having a density of 0.912 g / cm ³ (Atein 4201 manufactured by Dow Chemical Co., Ltd.) was used for extrusion with a ring die, followed by rapid cooling to obtain a tube having a thickness of 450 μm. This tube was folded, and an electron beam of 50 kGy was irradiated from the front and back using an electron beam irradiation device. This tube is 6 times in length and 5 in width by the standard method.
Biaxial stretching was performed twice to obtain a three-layer film having a thickness of 15 μm. The heat shrinkage percentage of this film at 100 ° C. was 40%. When a shrink wrap of a DVD case was carried out using this film, the evaluation point was 4, and a beautiful finish was obtained.

Example 2 45 parts by mass of a polyethylene-based resin having a density of 0.905 g / cm ³ (Atein 4203 manufactured by Dow Chemical Co., Ltd.) and a polyethylene-based resin having a density of 0.930 g / cm ³ (Dow Rex manufactured by Dow Chemical Co., Ltd.) were used for the core layer. 2042A) 15 parts by mass, 30 parts by mass of a polyethylene resin (DFDB1088 manufactured by Nippon Unicar Co., Ltd.) having a density of 0.885 g / cm ³ , and 10 parts by mass of a petroleum resin (Arcon P-125 manufactured by Arakawa Chemical Co., Ltd.) are kneaded to form a surface layer. A polyethylene resin having a density of 0.912 g / cm ³ (Atein 4201 manufactured by Dow Chemical Co., Ltd.) was used for extrusion with a ring die, followed by rapid cooling to obtain a tube having a thickness of 450 μm. This tube was folded, and an electron beam of 50 kGy was irradiated from the front and back using an electron beam irradiation device. This tube is 6 times in length and 5 in width by the standard method.
Biaxial stretching was performed twice to obtain a three-layer film having a thickness of 15 μm. The heat shrinkage percentage of this film at 100 ° C. was 46%. When a shrink wrap of a DVD case was carried out using this film, the evaluation point was 4.5 points.

Example 3 65 parts by mass of a polyethylene resin having a density of 0.905 g / cm ³ (Atein 4203 manufactured by Dow Chemical Co., Ltd.) and a polyethylene resin having a density of 0.930 g / cm ³ (Dow Rex manufactured by Dow Chemical Co., Ltd.) were used for the core layer. 2042A) 10 parts by mass and petroleum resin (Arcon P-125 manufactured by Arakawa Chemical Co., Ltd.) 25 parts by mass are kneaded, and a polyethylene resin having a density of 0.912 g / cm ³ (Atein 4201 manufactured by Dow Chemical Co., Ltd.) is used for the surface layer. Then, it was extruded with an annular die and rapidly cooled to obtain a tube having a thickness of 450 μm. This tube was folded, and an electron beam of 50 kGy was irradiated from the front and back using an electron beam irradiation device. This tube is 6 times in length and 5 in width by the standard method.
Biaxial stretching was performed twice to obtain a three-layer film having a thickness of 15 μm. The stretching was somewhat unstable. 100 of this film
The heat shrinkage rate at ° C was 51%. Using this film to shrink-wrap DVD cases,
The evaluation score was 5 and a beautiful finish was obtained without wrinkles.

Comparative Example 1 70 parts by mass of a polyethylene resin having a density of 0.905 g / cm ³ (Atein 4203 manufactured by Dow Chemical Co., Ltd.) and a polyethylene resin having a density of 0.930 g / cm ³ (Dow Rex manufactured by Dow Chemical Co., Ltd.) were used for the core layer. 2042A) 10 parts by weight, the polyethylene resin (manufactured by Nippon Unicar Company Limited DFDB1088 density 0.885 g / cm ³⁾ 20 parts by weight were kneaded, polyethylene resin density of 0.912 g / cm ³ on the surface layer (Dow Chemical Company Atein 4201) was used, and a tube having a thickness of 450 μm was obtained by extrusion with an annular die and rapid cooling. This tube was folded, and an electron beam of 50 kGy was irradiated from the front and back using an electron beam irradiation device.
This tube was biaxially stretched 6 times in the longitudinal direction and 5 times in the lateral direction by a conventional method, but the stretching point was not stable, and a three-layer film with poor thickness deviation was obtained.

Comparative Example 2 45 parts by mass of a polyethylene resin having a density of 0.905 g / cm ³ (Atein 4203 manufactured by Dow Chemical Co.) and a polyethylene resin having a density of 0.930 g / cm ³ (Dow Rex manufactured by Dow Chemical Co., Ltd.) were used for the core layer. 2042A) 10 parts by mass, 10 parts by mass of a polyethylene resin (DFDB1088 manufactured by Nippon Unicar Co., Ltd.) having a density of 0.885 g / cm ³ , and 35 parts by mass of a petroleum resin (Arcon P-125 manufactured by Arakawa Chemical Co., Ltd.) are kneaded to form a surface layer. A polyethylene resin (Atein 4201 manufactured by Dow Chemical Co., Ltd.) having a density of 0.912 g / cm ³ is used as the material and is extruded with a ring die to be rapidly cooled to obtain a thickness of 4
A 50 μm tube was obtained. Fold this tube,
An electron beam of 50 kGy was irradiated from the front and back using an electron beam irradiation device. This tube was biaxially stretched 6 times in the longitudinal direction and 5 times in the lateral direction by a conventional method, but could not be stretched.

Comparative Example 3 90 parts by mass of a polyethylene-based resin (Engage EG8150 manufactured by Dow Chemical Co., Ltd.) having a density of 0.868 g / cm ³ and 10 parts of petroleum resin (Arcon P-125 manufactured by Arakawa Chemical Co., Ltd.) in the core layer.
Kneading parts by mass, the surface layer has a density of 0.912 g / cm ³
Polyethylene resin (Atein 42 manufactured by Dow Chemical Co., Ltd.
No. 01) was used and the mixture was extruded with a ring die and rapidly cooled.

Comparative Example 4 90 parts by mass of a polyethylene resin (E807F manufactured by Nippon Polyolefin Co., Ltd.) having a density of 0.950 g / cm ³ and 10 parts by mass of a petroleum resin (Arcon P-125 manufactured by Arakawa Chemical Co., Ltd.) were kneaded in the core layer. , Polyethylene resin with a density of 0.912 g / cm ^{3 on} the surface layer (Atein 4201 manufactured by Dow Chemical Co.)
Was extruded with an annular die and rapidly cooled to obtain a tube having a thickness of 450 μm. Fold this tube and use the electron beam irradiation device from the front and back to 50 kGy
Was irradiated with an electron beam. This tube is vertically 6 by standard method.
The film was biaxially stretched twice and five times horizontally to obtain a three-layer film having a thickness of 15 μm. The heat shrinkage rate of this film at 100 ° C is 1
It was 0%. Shrink wrapping of a DVD case was carried out using this film, but the evaluation point was 1.5 and the finish was poor.

Comparative Example 5 70 parts by mass of a polyethylene resin having a density of 0.905 g / cm ³ (Atein 4203 manufactured by Dow Chemical Co., Ltd.) and a polyethylene resin having a density of 0.930 g / cm ³ (Dow Rex manufactured by Dow Chemical Co., Ltd.) were used for the core layer. 2042A) 10 parts by mass, 10 parts by mass of a polyethylene resin (DFDB1088 manufactured by Nippon Unicar Co., Ltd.) having a density of 0.885 g / cm ³ , and 10 parts by mass of a petroleum resin (Arcon P-125 manufactured by Arakawa Chemical Co., Ltd.) are kneaded to form a surface layer. Polyethylene resin with a density of 0.895 g / cm ³ (Affinity PF1140 manufactured by Dow Chemical Co.)
Was extruded with an annular die and rapidly cooled to obtain a tube having a thickness of 450 μm. Fold this tube and use the electron beam irradiation device from the front and back to 50 kGy
Was irradiated with an electron beam. This tube is vertically 6 by standard method.
The film was biaxially stretched twice and five times horizontally, but slippage with the touch stop ring was poor and stable stretching could not be performed.

Comparative Example 6 70 parts by mass of a polyethylene resin having a density of 0.905 g / cm ³ (Atein 4203 manufactured by Dow Chemical Co.) and a polyethylene resin having a density of 0.930 g / cm ³ (Dow Rex manufactured by Dow Chemical Co., Ltd.) were used for the core layer. 2042A) 10 parts by mass, 10 parts by mass of a polyethylene resin (DFDB1088 manufactured by Nippon Unicar Co., Ltd.) having a density of 0.885 g / cm ³ , and 10 parts by mass of a petroleum resin (Arcon P-125 manufactured by Arakawa Chemical Co., Ltd.) are kneaded to form a surface layer. A polyethylene resin having a density of 0.912 g / cm ³ (Atein 4201 manufactured by Dow Chemical Co., Ltd.) was used for extrusion with a ring die, followed by rapid cooling to obtain a tube having a thickness of 450 μm. This tube was folded and irradiated with an electron beam of 5 kGy from the front and back using an electron beam irradiation device. This tube was biaxially stretched 6 times in the longitudinal direction and 5 times in the lateral direction by a conventional method, but the stretching point was unstable and stable stretching could not be performed.

Comparative Example 7 70 parts by mass of a polyethylene resin having a density of 0.905 g / cm ³ (Atein 4203 manufactured by Dow Chemical Co.) in the core layer, and a polyethylene resin having a density of 0.930 g / cm ³ (Dow Rex manufactured by Dow Chemical Co.) 2042A) 10 parts by mass, 10 parts by mass of a polyethylene resin (DFDB1088 manufactured by Nippon Unicar Co., Ltd.) having a density of 0.885 g / cm ³ , and 10 parts by mass of a petroleum resin (Arcon P-125 manufactured by Arakawa Chemical Co., Ltd.) are kneaded to form a surface layer. A polyethylene resin having a density of 0.912 g / cm ³ (Atein 4201 manufactured by Dow Chemical Co., Ltd.) was used for extrusion with a ring die, followed by rapid cooling to obtain a tube having a thickness of 450 μm. This tube was folded, and 120 kGy of electron beam was irradiated from the front and back using an electron beam irradiation device. This tube was biaxially stretched 6 times in length and 5 times in width by a conventional method to obtain a three-layer film having a thickness of 15 μm. The heat shrinkage percentage of this film at 100 ° C. was 40%. Shrink wrapping of a DVD case was carried out using this film, but the cutability of the fusing seal was poor, and stable wrapping was not possible.

90 ° C. and 100 ° C. of the film thus obtained
The heat shrinkability, the packaging finish, and the stretchability of the film were measured and evaluated according to the following criteria. The results are shown in Tables 1 and 2. <Heat shrinkage of film at 90 ° C and 100 ° C> 100 mm
Cut out from the center and both ends of the film to a dimension of × 100 mm. Put this film in a basket made of wire mesh and 1
Immerse in a glycerin bath at 00 ° C. for 30 seconds. The basket is immersed in cooling water, and the heat shrinkage is calculated by the following formula. Heat shrinkage (%) = [(dimension before immersion-dimension after immersion)
/ (Dimension before immersion)] × 100

It should be noted that general polypropylene heat-shrinkable films are 10 to 15% at 100 ° C., polyethylene crosslinked heat-shrinkable films are 20 to 30%, and polyvinyl chloride heat-shrinkable films are around 40%. The heat shrinkability of the film at 90 ° C. was measured in the same manner as at 100 ° C. except that the temperature of the glycerin bath was 90 ° C. In addition, the general polypropylene heat shrink film is 5 to 7% at 90 ° C,
10 to 15 for polyethylene-based crosslinked heat shrink film
%, About 35% for a polyvinyl chloride-based heat-shrinkable film.

<Evaluation Method of Packaging Finish> A commercially available DVD case is wrapped with a film having six air vent holes, three sides are seal-cut with a hot blade, and the resultant is passed through a shrink tunnel manufactured by KE system at 140 ° C. for 5 seconds. . The packaging finish was evaluated on a scale of 5 from the tightness after shrinkage and the presence or absence of wrinkles on the corners and sides, and the average value of 6 times was shown. 5: No wrinkles on corners and sides, good tightness 4: Good wrinkle on corners, 1 side, but good tightness 3: Corner, 2 wrinkles on sides, good tightness 2: Corners, sides There are four wrinkles on the surface, but the tightness is good 1: The tightness is poor

<Stretchability of Film> Stretchability was evaluated by the time from the start of stretching to the break. ◎: Stretching is possible for 10 hours or more ○: Stretching is possible for 3 hours or more and less than 10 hours Δ: Breaking for 30 minutes or more and less than 3 hours x: Breaking for less than 30 minutes

[0040]

[Table 1]

[0041]

[Table 2]

In each table, "part" means part by mass. From the table, it is clear that the heat-shrinkable film of the present invention has a heat shrinkage ratio at a relatively low temperature of 90 ° C. and 100 ° C. comparable to that of a vinyl chloride-based heat-shrinkable film, and can be tightly packed without wrinkles on the corners and sides. is there.

[0043]

As is clear from the above results, the heat-shrinkable film obtained by the method of the present invention is a heat-shrinkable film suitable for packaging flat objects to be packaged such as DVDs and videos, especially at low temperatures. A polyethylene ultra-low temperature heat-shrinkable film with excellent shrinkability, with no wrinkles on the corners and sides and good packaging finish. Further, it is a heat-shrinkable film which is excellent in transparency, has a strong elasticity, and has good workability during packaging. Furthermore, it is a film with good fusing and seal-cutting properties.

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Claims (4)

[Claims] 1. A density of 0.905 to 0.960 g / cm ^3.
Two surface layers made of polyethylene resin, petroleum resin 2 to 30% by mass, density 0.870 to 0.935 g / c
A core layer made of a mixed resin of 98 to 70% by mass of m ³ polyethylene resin is coextruded, irradiated with an electron beam of 10 to 100 kGy, and then stretched 3 to 10 times in the longitudinal and transverse directions. A method for producing a polyethylene-based biaxially stretched heat-shrinkable film. 2. The polyethylene resin of the core layer has a density of 0.
The method for producing a polyethylene biaxially stretched heat-shrinkable film according to claim 1, which is a mixture of a polyethylene resin having a density of 920 to 0.935 g / cm ^{3 and} a polyethylene resin having a density of 0.870 to 0.915 g / cm ^3. . 3. A polyethylene-based biaxially stretched heat-shrinkable film produced by the method according to claim 1. 4. The polyethylene-based biaxially stretched heat-shrinkable film according to claim 3, wherein the heat shrinkage at 100 ° C. is 35% or more in both length and width and the heat shrinkage rate at 90 ° C. is 20% or more in both length and width.