JP3335038B2 - Polyethylene heat-shrinkable co-extruded film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyethylene-based heat-shrinkable coextruded film, and more particularly to a polyethylene-based heat-shrinkable coextruded film having excellent suitability for high-speed packaging machines.

[0002]

2. Description of the Related Art Conventionally, as a heat-shrinkable packaging material, polyvinyl chloride-based film, polyethylene-based film, polypropylene-based film and the like have been known. However, polyethylene is preferred because of its low cost and ease of disposal after use. Polyolefin-based heat-shrinkable films such as polypropylene and the like are preferably used. Above all, a polyethylene-based heat-shrinkable film is noted for its excellent impact resistance and heat seal strength, and is expected to be used in many fields.

[0003]

However, when a polyethylene heat-shrinkable film is packaged as a packaging material by an automatic packaging machine, it can be packaged when the packaging speed is relatively slow, but the packaging speed is significantly increased. In recent years, a heat sealing trouble due to a running trouble or a shift in cut pitch, which has not conventionally occurred, may occur. The high-speed packaging machine suitability is related to the magnitude of the waist of the film, and the waist of the film is expressed by using the tensile modulus of the film as an index. It is considered that the running trouble and the shift of the cut pitch at the time of high-speed packaging occur due to the weakness of the packaging material film, that is, the low tensile modulus of the packaging material film. Therefore, there is a demand for a packaging material having excellent impact resistance of a polyethylene-based heat-shrinkable film and a high tensile modulus suitable for high-speed packaging.

On the other hand, JP-A-2-196832 and JP-A-5-262899 disclose a heat-shrinkable film using a cyclic olefin resin. But,
The heat-shrinkable film described in JP-A-2-196832 has a high elastic modulus, but is extremely inferior to a polyethylene-based heat-shrinkable film in terms of impact resistance. The heat-shrinkable film described in the publication cannot obtain a high tensile modulus because the cyclic olefin-based resin has a glass transition temperature of 30 ° C. or lower, and is inferior in high-speed packaging machine suitability.

[0005]

Means for Solving the Problems The present inventors have intensively studied for a heat-shrinkable film which has solved the above-mentioned disadvantages, and as a result, have reached the present invention. That is, the present invention relates to a linear low-density polyethylene (A) having a density of 0.900 to 0.930 g / cm ³ and a melt index of 0.3 to 5.0 g / 10 min. 10 to 50% by weight of a cyclic olefin resin (B) having a glass transition temperature of 50 ° C. or higher, which is an ethylene-cyclic olefin random copolymer comprising a copolymer of olefin and a cyclic olefin.
Having a density of 0.900 to 0.930 g /
cm ³ , melt index 0.5 to 3.0 g / 10
Heat-shrinkable co-extruded polyethylene film having a tensile modulus of 4000 kg / cm ² or more as the innermost layer and the outermost layer, each of which comprises a layer mainly composed of a linear low-density polyethylene (C). , And the film is 1 to 10M
An object of the present invention is to provide a polyethylene-based heat-shrinkable coextruded film which has been subjected to electron beam crosslinking at a rad dose.

Hereinafter, the present invention will be described in detail. The linear low-density polyethylene (A) used in the present invention has a temperature of 25 ° C.
Is 0.900 to 0.930 g / cm ³ ,
A melt index having a characteristic value of 0.3 to 5.0 g / 10 min is used, and more preferably a density of 0.1 to 5.0 g / 10 min.
Those having a characteristic value of 910 to 0.925 g / cm ³ and a melt index of 0.5 to 3.0 g / 10 minutes are used. If the density is less than 0.900 g / cm ³ , the tensile modulus is undesirably reduced, and the density is less than 0.930 g / cm ^3.
If it exceeds cm ³ , the low-temperature shrinkage is insufficient, which is not preferable. Further, those having a melt index of less than 0.3 g / 10 min are not preferred because the motor load at the time of melt extrusion is increased, and those having a melt index exceeding 5.0 g / 10 min are not preferred because the stability in the stretching step is deteriorated. . The α-olefin copolymerized with ethylene of the linear low-density polyethylene is selected from the group consisting of butene-1, pentene-1, hexene-1, heptene-1, octene-1, and 4-methylpentene-1. It is preferable that one or two or more kinds are selected.

The cyclic olefin resin (B) used in the present invention is an ethylene-cyclic olefin random copolymer composed of a copolymer of ethylene and a cyclic olefin, and has a glass transition temperature of 50 ° C. or higher, preferably 70 ° C. What is more than ° C is used. If the glass transition temperature is lower than 50 ° C., a high tensile modulus cannot be obtained, which is not preferable.

[0008] The cyclic olefin resin (B) used in the present invention generally contains 5 structural units derived from ethylene.
In an amount of 2-90 mol%, preferably 55-80 mol%,
Known ones containing structural units derived from cyclic olefins in an amount of 10 to 48 mol%, preferably 20 to 45 mol% can be used. The cyclic olefin used, for example, bicyclo [2.2.1] hept-2-ene derivatives, tetracyclo [4.4.0.1 ^2.5 .1 ^7.10] -3- dodecene derivatives, hexacyclo [6.6.1.1 ^3.5 .1 ^10.13 .0 ^2.7 .0 ^9.14 ]-
4-Heptadecene derivative, octacyclo [8.8.0.1 ^2.9 .
1 ^4.7 .1 ^11.18 .1 ^13.16 .0 ^3.8 .0 ^12.17 ] -5-Docosene derivative,
Pentacyclo ^{[6.6.1.1 3.6 .0 2.7 .0 9.14]} -4- hexadecene derivative, heptacyclo -5 Eikosen derivatives, heptacyclo -5 Hen'eikosen derivatives, tricyclo [4.3.0.1
^2.5] -3-decene derivatives, tricyclo [4.3.0.1 ^2.5] -3-undecene derivatives, pentacyclo [6.5.1.1 ^3.5 .0 ^2.7.
0 ^9.13] -4-pentadecene derivatives, penta cyclopentadiene decadiene derivative, pentacyclo [7.4.0.1 ^2.5 .1 ^9.12 .0
^8.13 ] -3-pentadecene derivative, pentacyclo [8.7.0.1.
3.6.1 ^10.17 .1 ^12.15 .0 ^2.7 .0 ^11.15] -4-eicosene derivatives, Nonashikuro ^{[10.9.1.1 4.7 .1 13.20 .1 15.18 .O} 3.8 .0
^2.10 .0 ^12.21 .0 ^14.19] -5-pentacosene derivatives, pentacyclo ^{[8.4.0.1 2.3 .1 9.12 .0 8.13]} -3- hexadecene derivative, pentacyclo ^{[8.8.0.1 4.7 .1 11.18 .1 13.15 .0} 3.8 .0
^12.17 ] -5-Hyneecocene derivative, nonacyclo [10.10.1.
1 ^5.8 .1 ^14.21 .1 ^15.19 .0 ^2.11 .0 ^4.9 .0 ^13.22 .0 ^15.20] -5-hexacosenoic derivatives, 1,4 methanol: Synthesis of 1,4,4, 9a- tetrahydrofluorene derivatives, 1,4-methanol 1 , 4,4a, 5,10,10a −
Hexahydroanthracene derivatives, cyclopentadiene-acenaphthylene adducts and the like can be exemplified. Cyclic olefin resins are described, for example, in JP-A-60-1687.
08, JP-A-61-120816, JP-A-61-115912, JP-A-61-115916
JP, JP-A-61-271308, JP-A-61-271308
-272216, JP-A-62-252406, JP-A-62-252407, and the like.

In the present invention, the amount of the linear low-density polyethylene (A) used as one component of the intermediate layer is 50 to 90% by weight, preferably 55 to 85% by weight,
More preferably, it is 60 to 80% by weight, and the mixing amount of the cyclic olefin resin (B) used as the other component is 50 to 10% by weight, preferably 45 to 15% by weight, more preferably 40 to 20% by weight. % By weight. If the mixing amount of the linear low-density polyethylene (A) is less than 50% by weight, transparency, glossiness and impact resistance are unfavorably reduced, and if it exceeds 90% by weight, the tensile modulus is undesirably reduced. .

The intermediate layer may be mixed with other resins, for example, high pressure polyethylene, ethylene-vinyl acetate copolymer, ionomer, propylene-butene copolymer, etc., within a range not to impair the object of the present invention. Can be used.

In the present invention, the intermediate layer does not necessarily have to be a single layer, but may be formed as two or more layers as necessary. For example, a layer made of a resin having a high gas barrier property for the purpose of improving the gas barrier property. Can be another intermediate layer. The thickness of the intermediate layer needs to be 30% or more of the whole, and if it is less than 30%, the desired high tensile modulus cannot be obtained.

The linear low-density polyethylene (C) used in the innermost layer and the outermost layer of the present invention has a density of 0.900 to 0.900.
0.930 g / cm ³ , melt index 0.5 to
Those having a characteristic value of 3.0 g / 10 min are used, and more preferably the density is 0.910 to 0.925 g / cm.
^{3. A} melt index having a characteristic value of 0.8 to 2.0 g / 10 minutes is used. 0.900g density
/ Cm ³ less than what is not preferable because the sliding resistance is reduced, 0.930 g / cm ³ and exceeds the undesirable to lower the transparency and gloss. Further, those having a melt index of less than 0.5 g / 10 minutes are not preferred because the transparency and gloss are reduced, and those having a melt index exceeding 3.0 g / 10 minutes are not preferred because the heat seal strength is reduced.
The linear low-density polyethylene (C) may be the same as the linear low-density polyethylene (A) used for the intermediate layer.

The thickness of the innermost layer and the outermost layer made of linear low-density polyethylene (C) is at least 1 μm or more, and more preferably 2 μm or more. When the thickness of the innermost layer and the outermost layer is less than 1 μm,
It is not preferable because transparency, glossiness and heat seal strength decrease.

The innermost layer and the outermost layer may be, for example, an ethylene-vinyl acetate copolymer, an ethylene-α-olefin copolymer, a propylene-butene copolymer, or an ionomer, as long as the object of the present invention is not hindered. And polybutene can be used. In addition, if desired, additives such as a lubricant, an antiblocking agent, an antistatic agent, and an antifogging agent can be appropriately used for the purpose of providing their respective effective functions, particularly when added to the innermost layer and the outermost layer. ,It is valid.

According to the present invention, there is further provided a polyethylene-based heat-shrinkable coextruded film which is cross-linked with an electron beam at a dose of 1 to 10 Mrad, preferably 3 to 7 Mrad. If the dose is less than 1 Mrad, no improvement in heat resistance can be obtained, and if it is more than 10 Mrad, the heat sealability is undesirably reduced. The polyethylene-based heat-shrinkable co-extruded film cross-linked under such conditions can have a high shrink tunnel temperature at the time of shrink-wrapping in order to improve heat resistance, so that a clean packaging finish can be obtained. Therefore, for example, it is suitable when beautifully shrink-wrapping a package having a complicated shape such as a cosmetic bottle.

Next, a method for producing the film of the present invention will be described.
The method for producing the stretched film of the present invention using the resin described above can be carried out by a known method. Hereinafter, a case of three-layer laminated annular film-forming stretching will be described as an example.
First, a mixed composition comprising the linear low-density polyethylene (A) and the cyclic olefin-based resin (B) is applied to an intermediate layer,
The linear low density polyethylene (C) is melt-kneaded by three extruders so as to be the innermost layer and the outermost layer, respectively.
It is co-extruded annularly from a three-layer annular die and quenched and solidified without stretching to produce a tubular unstretched film.

The obtained tubular unstretched film is supplied to, for example, a tubular stretching apparatus as shown in FIG. A gas pressure is applied inside the tube at a temperature lower than the degree to cause simultaneous biaxial orientation by expansion and stretching. The stretching ratio is not necessarily the same in the vertical and horizontal directions, but in order to obtain physical properties such as excellent strength and shrinkage ratio, it is at least 2 times, preferably at least 2.5 times, more preferably at least 3 times in any direction. It is preferable to stretch the film. The film taken out of the stretching device can be annealed as desired, and this annealing can suppress natural shrinkage during storage.

As a crosslinking method, after preparing a tubular unstretched film, an electron beam is irradiated from both sides of the tube with an electron beam at a dose of 1 to 10 Mrad by an electron beam irradiation device.
Thereafter, tube stretching is performed in the same manner as described above to obtain a crosslinked polyethylene-based heat-shrinkable coextruded film.

[0019]

FIG.

[0020]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. In addition, each physical property measurement shown in this example was based on the following methods. Haze Measured according to JIS-K6714. Gloss (60 °) Measured according to JIS-Z8741. Tensile modulus Measured according to JIS-K7127. Impact strength Measured according to JIS-P8134. Suitability for high-speed packaging machine Using an automatic packaging machine (model PW-R2, pillow packaging machine) manufactured by Tokiwa Industry Co., Ltd., 150 cups / min of cup ramen (about 36
m / min), and the state of packaging was observed.

Example 1 Linear low-density polyethylene having a density of 0.920 g / cm ³ and a melt index of 1.0 g / 10 min was used as an inner layer and an outer layer. Cyclic olefin copolymer having a glass transition point of 80 ° C. by weight (APL650, manufactured by Mitsui Petrochemical Co., Ltd.)
9) Using a 15% by weight mixed composition as an intermediate layer, three extruders melt and knead each at 170 ° C. to 240 ° C., and the thickness ratio of each layer is inner layer: intermediate layer: outer layer = 1: 5: 1. The extrusion rate of each extruder was set so that
Co-extruded downward from the layered die. The formed three-layered tube is taken out by cooling it by passing it through a water bath on the outside while sliding the outer surface of a cylindrical cooling mandrel in which cooling water circulates, and has a diameter of 75 mm and a thickness of 320 μm. An unstretched film was obtained. This tubular unstretched film is guided to the tubular biaxial stretching apparatus shown in FIG. 1 and stretched at 90 to 110 ° C. four times each in the vertical and horizontal directions,
A polyethylene heat-shrinkable co-extruded film having a thickness of about 20 μm was obtained. Next, after the stretched film was treated with hot air at 75 ° C. for 10 seconds in a tube annealing apparatus,
Cooled to room temperature, folded and wound. The stability during stretching was good, there was no vertical movement of the stretching point and no swing of the stretching tube, and no uneven stretching state such as necking was observed. As shown in Table 1, the obtained stretched film has excellent transparency and gloss, and has a high tensile modulus and impact strength. And had good suitability for high-speed packaging machines.

Example 2 The same raw material formulation as in Example 1 except that the mixing ratio of the intermediate layer in Example 1 was changed to 55% by weight of linear low-density polyethylene and 45% by weight of cyclic olefin copolymer. A polyethylene heat-shrinkable co-extruded film was produced by the above method. The obtained stretched film is excellent in transparency and gloss as shown in Table 1, and has high tensile modulus and impact strength. And had good suitability for high-speed packaging machines.

Example 3 Linear low-density polyethylene having a density of 0.920 g / cm ³ and a melt index of 1.0 g / 10 was used as an inner layer and an outer layer, and had a density of 0.916 g / cm ³ and a melt index of 1 Example 2 A mixed composition of 70% by weight of a linear low-density polyethylene of 0.2 g / 10 minutes and 30% by weight of a cyclic olefin copolymer having a glass transition point of 80 ° C. (manufactured by Mitsui Petrochemical Co., Ltd.) was used as an intermediate layer. A polyethylene heat-shrinkable co-extruded film was produced in the same manner as in Example 1. The obtained stretched film is excellent in transparency and gloss as shown in Table 1, and has a high tensile modulus and impact strength.
There was no heat sealing trouble, and it had good suitability for high-speed packaging machines.

Example 4 The unstretched film having a thickness of 320 μm obtained in Example 3 was subjected to a crosslinking treatment at a dose of 5 Mrad using an electron beam irradiation apparatus (manufactured by Nissin High Voltage). Next, a polyethylene-based heat-shrinkable co-extruded film was produced from the tubular unstretched film in the same manner as in Example 1. The obtained stretched film is excellent in transparency and gloss as shown in Table 1, and has a high tensile modulus and impact strength.
There was no heat sealing trouble, and it had good suitability for high-speed packaging machines. Further, in order to improve the heat resistance by the crosslinking treatment, even if the temperature setting of the shrinking tunnel was set high, the film was hardly burnt (whitening or blurring due to melting), and a beautiful packaging finish was obtained.

Comparative Example 1 As shown in Table 1, linear low-density polyethylene having a density of 0.920 g / cm ³ and a melt index of 1.0 g / 10 min was used as an inner layer and an outer layer. Linear low-density polyethylene: A polyethylene heat-shrinkable co-extruded film was produced in the same manner as in Example 1 using 100% by weight as an intermediate layer. The obtained stretched film is
As shown in Table 1, it has excellent transparency, glossiness, and impact strength. In packaging evaluation using a pillow packaging machine, if the packaging speed is 50 pcs / min (about 12 m / min), it is suitable for a packaging machine. The packaging speed was 150
When the rate was increased to 10 m / min (approximately 36 m / min), a running trouble due to meandering of the film and a heat sealing trouble due to a shift in cut pitch frequently occurred because the tensile modulus was low.

Comparative Example 2 A linear low-density polyethylene having a density of 0.920 g / cm ³ and a melt index of 1.0 g / 10 min was used as the surface layer, and the same linear low-density polyethylene as the surface layer was 40% by weight. A heat-shrinkable co-extruded film was produced in the same manner as in Example 1 using a mixed composition of 60% by weight and a cyclic olefin copolymer having a glass transition point of 80 ° C. (manufactured by Mitsui Petrochemical Co., Ltd.) as an intermediate layer. did. The obtained stretched film is shown in Table 1.
As shown in Table 2, the tensile modulus was high, and the packaging evaluation by the pillow packaging machine showed good suitability for packaging machinery. However, the transparency and glossiness were poor, and the impact strength was extremely poor.

[0027]

[Table 1]

[0028]

The film of the present invention in which the innermost layer and the outermost layer are composed of a linear low-density polyethylene resin and the intermediate layer is composed of a specific proportion of a linear low-density polyethylene resin and a cyclic olefin resin is a conventional polyethylene film. Packaging material that has a higher tensile modulus than system-based heat-shrinkable film, and has excellent suitability for high-speed packaging machines even when packaging with a high-speed automatic packaging machine without running troubles or heat sealing problems due to shifts in cut pitch. It is. Further, the film cross-linked with an electron beam improves heat resistance, and thus is particularly suitable for beautifully shrink-wrapping a package having a complicated shape.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a tubular biaxial stretching apparatus used in Examples.

[Explanation of symbols]

 1 Unstretched film 2 Low speed nip roll 3 High speed nip roll 4 Preheater 5 Main heater 6 Cooling air ring 7 Folding roll group

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-262899 (JP, A) JP-A-2-196832 (JP, A) JP-A-58-175635 (JP, A) JP-A-55-175635 118859 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1/00-35/00 C08J 5/18

Claims (2)

(57) [Claims] (1) a density of 0.900 to 0.930 g / cm;
³ , 50 to 90% by weight of linear low density polyethylene (A) having a melt index of 0.3 to 5.0 g / 10 min;
A cyclic olefin resin (B), which is an ethylene-cyclic olefin random copolymer comprising a copolymer of ethylene and a cyclic olefin, and which has a glass transition temperature of 50 ° C. or higher.
A layer comprising 10 to 50% by weight and having a density of 0.900
0.930 g / cm ³ , melt index 0.5
Linear low-density polyethylene (C) up to 3.0 g / 10 min
A layer composed of a composition containing as a main component an innermost layer and an outermost layer, and a tensile modulus of elasticity of 4000 kg / cm ² or more;
Polyethylene heat-shrinkable co-extruded film. 2. A polyethylene heat-shrinkable co-extruded film obtained by subjecting the polyethylene heat-shrinkable co-extruded film according to claim 1 to electron beam crosslinking at a dose of 1 to 10 Mrad.