JP3068920B2 - Polyethylene heat-shrinkable laminated 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 laminated film, and more particularly to a heat-shrinkable laminated film made of a specific ethylene-based copolymer and having excellent suitability for a packaging machine.

[0002]

2. Description of the Related Art Conventionally, as a heat-shrinkable film, a stretched film of polyvinyl chloride, polypropylene, polyethylene or the like has been known. Among them, polyethylene-based heat-shrinkable films have heat sealing properties and are practically used from the viewpoint of low cost, and in recent years ethylene and α-
Polyethylene-based heat-shrinkable films using linear low-density copolymers with olefins (hereinafter simply abbreviated as linear low-density polyethylene) have attracted attention because of their excellent impact resistance, heat seal strength, and the like. It is expected to be used in many fields.

[0003]

The present inventors have previously proposed a heat-shrinkable film mainly containing a specific ethylene-α-olefin copolymer (JP-A-62-20122).
No. 9). By implementing the method of this proposal, it was possible to obtain a film having a small thickness unevenness and a good low-temperature shrinkage as compared with a film obtained by inflation. When used in packaging machines, half-fold automatic packaging machines, etc.), the packaging speed of the packaging machines has been remarkably increased in recent years, so that there is a problem that heat sealing failure (partially not sealed) which has not occurred conventionally occurs. is there. When wrapping with an automatic wrapping machine, heat sealing is generally performed by fusing with a heat knife. However, the poor sealing phenomenon refers to the case where peeling of the sealing part occurs in the shrinking process or when large tension is applied to the film (package Is bulky, etc.), the seal portion becomes stringy and is not cut beautifully, a pinhole is generated in the seal portion, and in an extreme case, it is not sealed at all. Also, when the fusing resin adheres to the edge of the heat knife or the heat knife receiving base, the same sealing failure as described above occurs.

[0004]

Means for Solving the Problems The inventors of the present invention have studied in more detail to solve the above-mentioned defective sealing, and have confirmed the following. That is, by increasing the packaging speed, the time required for shrinkage in the shrinkage tunnel is also shortened, and when the solidification of the melted resin does not proceed within that short time, a part of the melted resin is separated and pinholes are removed. Or in extreme cases, complete peeling of the seal. Also, when the film has a weak stiffness (small tensile elasticity), wrinkles are likely to be formed during film running, so that the film folded portion at the portion to be melt-sealed increases, and pinholes are generated. To be more. Further, when the slipperiness of the film is poor and the running property in the packaging machine is insufficient, or when the packaged object is bulky, a greater tension is applied to the fusing seal portion, and the fusing resin is solidified before the fusing resin is solidified. A part of the seal part is pulled apart to increase the number of pinholes. Furthermore, when the viscosity of the fusing resin is low, the fusing resin easily adheres to the cutting edge of the heat knife or the heat knife holder, and pinholes are generated in the seal portion, the film is not cut, or in extreme cases. May not be sealed at all.

The inventors of the present invention have conducted intensive studies on the lamination structure of the film and various raw material resins in order to solve the above-mentioned problems and provide a heat-shrinkable film having good suitability for a packaging machine. Use a resin with a low melt index, a high total heat of fusion, and a heat-absorbing area ratio higher than the melting point and a certain range or more in order to increase the cooling and solidification rate during fusing sealing. In addition, it has been found that by using a resin having a higher melt index than the intermediate layer and having the same properties as the intermediate layer, a heat-shrinkable film having good suitability for a packaging machine can be obtained, and the present invention has been achieved. .

That is, according to the present invention, the intermediate layer has a density of 0.5.
910 to 0.930 g / cm ³ , melt index is 0.1 to 0.8 g / 10 min, and in the melting curve by DSC, after holding at 190 ° C. for 30 minutes, the temperature was lowered at a rate of 10 ° C./min. ℃, then the heating rate 1
The linear low density in which the total heat of fusion in the melting curve obtained when the temperature is raised at 0 ° C./min is 135 mJ / mg or more, and the endothermic area above the main peak temperature (melting point) is 12% or more of the total endothermic area. At least one layer composed of a composition mainly composed of polyethylene (A), a melt index of 0.8 to 5.0 g / 10 min, and a total heat of fusion in a melting curve of 135 to 160 mJ / mg. And a laminated film containing, as the innermost layer and the outermost layer, a layer composed of a composition mainly composed of linear low-density polyethylene (B) having an endothermic area not lower than the main peak temperature of 12% or more of the total endothermic area. Wherein the thickness of the intermediate layer with respect to all layers is 60% or more, and the tensile modulus is 3000 kg / c.
m ² or more, relates polyethylene heat-shrinkable laminated film excellent in packaging machines suitability biaxially oriented, wherein the area shrinkage of 20% or more at 90 ° C..

In the present invention, at least one linear low-density polyethylene (A) used as a main component of the intermediate layer
Having a density of 0.910 to 0.930 g / cm ³ and a melt index of 0.1 to 0.8 g / 10 min, more preferably a density of 0.915 to 0.9
25 g / cm ³ , melt index 0.2-0.7 g
Those having characteristic values of / 10 minutes are used. If the density is less than 0.910 g / cm ³ , the tensile modulus is low, which is not preferable. If the density is more than 0.930 g / cm ³ , the low-temperature shrinkage is insufficient, which is not preferable. If the melt index is less than 0.1 g / 10 min, the load on the motor during melt extrusion is increased, and workability is deteriorated. Absent. The linear low-density polyethylene (A) has a total heat of fusion of 135 mJ / mg or more in a melting curve measured by DSC, and an endothermic area not less than the main peak temperature must be 12% or more of the total endothermic area. is there. If the condition is not satisfied, the cooling and solidifying rate of the blown resin is low, and good blown sealability cannot be obtained. It is necessary that the thickness of the intermediate layer with respect to all the layers is 60% or more. When the thickness of the intermediate layer is less than 60%, excellent fusing sealing properties cannot be exhibited.

[0008] The linear low-density polyethylene (B) used as a main component in the innermost layer and the outermost layer has a melt index of 0.8 to 5.0 g / 10 min. Heat of fusion 135-160mJ
/ Mg in which the endothermic area above the main peak temperature is 12% or more of the total endothermic area. If the melt index is less than 0.8 g / 10 minutes, the transparency is reduced due to the roughening of the film surface, which is not preferable. If the melt index exceeds 5.0 g / 10 minutes, the heat seal strength is reduced and the stretchability is deteriorated. Is also undesirable because it has a bad effect. Further, if the total heat of fusion is less than 135 mJ / mg, good fusing sealability cannot be obtained, and if it exceeds 160 mJ / mg, the transparency is undesirably reduced.

The above linear low-density polyethylenes (A) and (B) are linear copolymers of ethylene and α-olefin, and the α-olefin copolymerized with ethylene is not particularly limited. Absent. For example, those having 4 to 12 carbon atoms, butene-1, pentene-1, hexene-1, heptene-1, octene-1,4-methylpentene-1, decene-1, undecene-1, dodecene-1, etc. However, α-olefins having 4 to 8 carbon atoms are more preferably used. These linear copolymers (A) and (B) of ethylene and α-olefin can be easily obtained by a low-to-medium pressure method using a so-called Ziegler-Natta type catalyst. 50-32270
JP, JP-A-49-35345, JP-A-55-35345
Techniques disclosed in JP-A-780004, JP-A-55-86804, JP-A-54-154488, and the like can be used. The resin composition used in each of the above layers may be used alone or in combination of two or more. Further, as long as the object of the present invention is not hindered, high-pressure polyethylene and ethylene-vinyl acetate copolymer may be used. Polyolefin resins such as coalesced, ionomer, and ethylene-propylene copolymers can be mixed and used. The laminated film of the present invention is a polyolefin-based resin other than the linear low-density polyethylene resins (A) and (B) as long as the thickness of each layer is satisfied in addition to the intermediate layer, the innermost layer, and the outermost layer. One or more intermediate layers made of resin may be included. Examples of the polyolefin resin used for such an intermediate layer include linear low-density polyethylene resins other than the above-mentioned linear low-density polyethylene resins (A) and (B);
Examples include polyolefin resins such as high-pressure polyethylene and ethylene-propylene copolymer, and one or more types can be appropriately selected and used within a range that does not interfere with the object of the present invention.

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.
This is particularly effective for the innermost layer and the outermost layer. The production and stretching of the raw film for stretching used in the present invention can be performed by a known method. Hereinafter, a case of three-layer laminated tubular film forming and stretching will be described as an example.

First, the linear low-density polyethylene (A) of ethylene and α-olefin is mixed with an intermediate layer, and ethylene and α-olefin are mixed.
The linear low-density polyethylene (B) with olefin is melt-kneaded by three extruders so as to form inner and outer layers, co-extruded into a tube from a three-layer annular die, quenched once without stretching, and then solidified into a tube. Make a stretched film. The obtained tubular unstretched film is supplied to, for example, a tubular stretching apparatus as shown in FIG. 1, and a temperature range in which a high degree of orientation is possible, for example, the melting point of the intermediate layer resin is 10 ° C. or less, preferably 15 ° C. or less A gas pressure is applied inside the tube at a low temperature to cause simultaneous biaxial orientation by expansion and stretching. The stretching ratio is not necessarily the same in both the vertical and horizontal directions, but in order to obtain physical properties such as excellent strength and shrinkage, it is at least 2 times, preferably at least 2.5 times, more preferably at least 3 times in any direction. It is preferable that the film is stretched as described above. The film taken out of the stretching device can be annealed as desired, and this annealing can suppress natural shrinkage during storage.

[0012]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples. In addition, various measurements shown in this example were based on the following methods. 1) Total heat of fusion A sample of 8 to 10 mg was weighed, sealed in an aluminum pan, and then subjected to a differential scanning calorimeter (model DSC-10 manufactured by Seiko Denshi Co., Ltd.).
0) at room temperature to 190 ° C. in a nitrogen stream of 30 ml / min.
Temperature, hold at this temperature for 30 minutes, then
/ Min to room temperature. Thereafter, using a melting curve obtained at a heating rate of 10 ° C./min, the heat of fusion was calculated from the area of the endothermic peak.

2) Endothermic area ratio From the above melting curve, the ratio of the area above the main peak temperature (melting point) to the total endothermic area is indicated by%.

3) Thickness of each layer The thickness of each layer of the laminate was measured by observing a cross section of the film with a microscope.

4) Haze The ratio of the scattered light transmittance to the parallel light transmittance was indicated by% using an integrating sphere light transmittance measuring device in accordance with JIS-K6714.

5) Area Shrinkage A film cut into a square of 10 cm in length and width was immersed in a glycerin bath at a predetermined temperature for 10 seconds, and calculated by the following equation.

[0017]

[Equation 1] Area shrinkage = 100−A × B where A and B are the lengths and widths after immersion (unit is c
m).

6) Tensile modulus MD (longitudinal), TD (horizontal) from film sample
Each test piece is taken so as to have a width of 15 mm and a length of 300 mm, and the thickness is measured. Next, the test piece was gripped by a universal tensile tester manufactured by Orientec Co., Ltd. and the interval was 50 m.
m, pulling speed 40 mm / min, recording paper speed 500
It was measured under the conditions of mm / min and 2 kg of full scale, and was calculated by the following equation.

[0019]

(Equation 2) Here, P: full-scale strength (kg) S: cross-sectional area of the film (cm ² ) ΔL: distance from L1 to L2 in the load-deformation curve shown in FIG. 2 (mm) L: grip distance between test pieces

7) Fusing sealability Half-fold automatic packaging machine (Model AT-500) manufactured by Kyowa Electric Co., Ltd.
Is supplied with a half-fold film having a width of 400 mm and a height of 23.5 c.
lunch box (200 cm, width 15.5 cm, height 5.6 cm)
g) were continuously packaged at a rate of 25 pieces / min., and the non-defective rate was measured. The non-defective rate in the sealing temperature range of 220 ° C. to 250 ° C. was 100%.
% And less than 80% were evaluated as Δ, and less than 80% were evaluated as x. In addition, the standard of the non-defective product rate was defined as a non-defective product having no threading in the seal portion after shrink wrapping and having no pinhole of 1 mm or more. In addition, the margin ratio of the preliminary packaging was set to 13% both vertically and horizontally.

Example 1 A linear low-density polyethylene resin which is a copolymer of ethylene having the properties shown in Table 1 and 4-methylpentene-1 as a comonomer was used as an intermediate layer. A linear low-density polyethylene resin which is a copolymer of ethylene and octene-1 having such properties is used as an inner / outer layer in three extruders (for an intermediate layer, an innermost layer, and an outermost layer) at 170 ° C. The mixture was melt-kneaded at 240 ° C., the extruding amount from each extruder was set assuming the thickness ratio shown in Table 1, and co-extruded downward from a three-layer annular die kept at 240 ° C. The formed three-layered tube is cooled and taken off by sliding the outer surface of a cylindrical cooling mandrel through which a cooling water circulates, while sliding the outer surface of the outer tube through a water bath.
An unstretched film having a thickness of 320 μm and a thickness of 320 μm was obtained. The thickness of each layer was adjusted by adjusting the screw rotation speed and the take-up speed of the extruder. This tubular unstretched film was guided to the tubular biaxial stretching apparatus shown in FIG. 1 and stretched at 95 to 105 ° C. four times vertically and horizontally to obtain a laminated biaxially stretched film. Next, the stretched film was treated with hot air at 75 ° C. for 10 seconds using a tube annealing device, 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. The obtained stretched film had a thickness configuration as shown in Table 1, was excellent in transparency and low-temperature shrinkability, and had a high tensile modulus. Further, the continuous actual packaging evaluation of the lunch box was carried out by a half-fold automatic packaging machine, and it was found that there was no defect in the sealing portion and the packaging machine had good suitability in a wide temperature range.

Example 2 A heat-shrinkable laminated film was produced in the same manner as in Example 1 using the resin composition shown in Table 1. The obtained stretched film was excellent in transparency and low-temperature shrinkability, and had a high tensile modulus. Further, as in Example 1, the suitability for the packaging machine was excellent.

Example 3 A heat-shrinkable laminated film was produced in the same manner as in Example 1 using the resin composition shown in Table 1. Although 5000 ppm of stearic acid monoglyceride was added as an antifogging agent to the inner and outer layers, the film was excellent in transparency, low-temperature shrinkage, high in tensile modulus, and excellent in suitability for a packaging machine.

Comparative Example 1 As shown in Table 1, the intermediate layer had a melt index of 2.0.
g / 10 minutes of linear low-density polyethylene, the same linear low-density polyethylene resin as that used for the inner and outer layers of Example 1 was used for the inner and outer layers, and extruded under the same conditions as in Example 1. Cool and take off, about 75mm in diameter and 320 in thickness
A layered unstretched film raw material of μm was obtained. The thickness of each layer was adjusted by adjusting the screw rotation speed and the take-up speed of the extruder. This tubular unstretched film was guided to the tubular biaxial stretching apparatus shown in FIG. 1 in the same manner as in Example 1, and stretched four times in each of length and width at 95 to 105 ° C. to obtain a laminated biaxially stretched film. Next, the stretched film was heated with hot air at 75 ° C. for 1 hour using a tube annealing apparatus.
After treating for 0 seconds, the mixture was cooled to room temperature, folded and wound. There was no problem in the stability during stretching, and the obtained film was excellent in transparency and low-temperature shrinkability, but had a small tensile modulus. When this film was placed on a packaging machine and evaluated for packaging suitability, adhesion of resin to the fusing seal bar and stringing were slightly improved, but pinholes were easily generated and the sealing property was insufficient.

Comparative Examples 2 and 3 The intermediate layer of Comparative Example 2 had a total heat of fusion of 13 in the melting curve.
The linear low-density polyethylene of 2.0 mJ / mg and not more than 135 mJ / mg is used, and the intermediate layer of Comparative Example 3 has an endothermic area ratio of not less than the melting point in the melting curve of 11.0% and not more than 12%. A linear low-density polyethylene was used, and the heat-shrinkable laminated film was obtained in the same manner as in Example 1 by using the same linear low-density polyethylene as in Example 1 for both the inner and outer layers in Comparative Examples 2 and 3. The resulting heat-shrinkable films were both excellent in transparency and low-temperature heat-shrinkability in Comparative Examples 2 and 3, but had low tensile modulus. In the actual packaging test using the packaging machine, pinholes were liable to occur in the seal portion in both cases, and the sealability was insufficient.

Comparative Example 4 The intermediate layer uses the same linear low-density polyethylene as in Example 1, and the inner and outer layers have a melt index of 0.6 g / 10 min, and a range of 1.0 to 5.0 g / 10 min. A heat-shrinkable laminated film was obtained in the same manner as in Example 1 by using a linear low-density polyethylene which was not described above. The obtained film was excellent in low-temperature shrinkability and large in tensile elasticity, and showed good fusing sealability in an actual packaging test using a packaging machine, but was inferior in transparency.

Comparative Example 5 The intermediate layer used was the same linear low-density polyethylene as in Example 2. The inner and outer layers had a total heat of fusion of 121 mJ in the melting curve.
/ Mg, and a heat-shrinkable laminated film was obtained in the same manner as in Example 1 using a linear low-density polyethylene not in the range of 135 to 160 mJ / mg. The obtained film was a film excellent in transparency and low-temperature shrinkability,
In the actual packaging test using a packaging machine, the tensile elasticity was somewhat inferior, and resin adhesion to the heat knife and adhesion of the film to the heat knife holder were observed. Was very unstable.

Comparative Example 6 The intermediate layer uses the same linear low-density polyethylene as in Example 1, and the inner and outer layers have a total heat of fusion in the melting curve of 162.4.
A heat-shrinkable laminated film was obtained in the same manner as in Example 1 using a linear low-density polyethylene having a mJ / mg of 160 mJ / mg or more. The stability in the stretching step was poor, and the obtained film was inferior in transparency and low-temperature shrinkage. In actual packaging tests with a packaging machine, wrinkles were likely to be formed in the seal portion, and some pinholes were observed.

Comparative Example 7 The same linear low-density polyethylene as in Example 1 was used except that the thickness of the intermediate layer was 50% of the total thickness. A heat-shrinkable laminated film was obtained in the same manner as in Example 1. The resulting film is transparent,
Although the film was excellent in low-temperature shrinkability, some pinholes were observed in the seal portion, and the sealability was insufficient.

[0030]

[Table 1]

[0032]

The polyethylene-based heat-shrinkable laminated film of the present invention is made of a material that satisfies the specific conditions as a raw material for each layer, so that it is excellent in transparency and low-temperature shrinkage, and is further blown. The present invention provides a shrinkable film excellent in suitability for a packaging machine because a raw material capable of rapidly cooling and solidifying a blown resin at the time of sealing and obtaining a high tensile modulus is used.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining a tubular biaxial stretching device used in Examples.

FIG. 2 shows a graph for calculating a tensile modulus in an embodiment.
5 is a schematic diagram for explaining a load-deformation curve.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-18347 (JP, A) JP-A-3-215034 (JP, A) JP-A-63-173641 (JP, A) JP-A-1- 304938 (JP, A) JP-A-1-301251 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1/00-35/00 B29C 61/00-61/10 B65D 65/00-65/46

Claims (3)

(57) [Claims] 1. A polyethylene-based heat-shrinkable laminated film having a density of 0.910 to 0.930 g as an intermediate layer.
/ Cm ³ , melt index 0.1-0.8 g / 1
0 minutes, and in a melting curve by a differential scanning calorimeter (hereinafter abbreviated as DSC), after holding at 190 ° C. for 30 minutes, the temperature was lowered to 20 ° C. at a rate of 10 ° C./min.
A line having a total heat of fusion of 135 mJ / mg or more in the melting curve obtained when the temperature is increased at a rate of temperature increase of 10 ° C./min, and an endothermic area at or above the main peak temperature (melting point) of 12% or more of the total endothermic area. At least one layer composed of a composition mainly composed of the low-density polyethylene (A) in the form of a mixture and having a density of 0.910 to 0.930 g / cm ³ and a melt index of 0.8 to 5.0 g / 10 min. And a linear low-density polyethylene (B) having a total heat of fusion in the melting curve in the range of 135 to 160 mJ / mg and an endothermic area not lower than the main peak temperature being 12% or more of the total endothermic area. A polyethylene-based heat-shrinkable laminated film comprising a layer made of a composition as an innermost layer and an outermost layer. 2. The intermediate layer has a thickness of 60% or more with respect to all layers, and has a tensile modulus of 3000 kg / cm ² or more,
2. The polyethylene-based heat-shrinkable laminated film according to claim 1, wherein the area shrinkage at 20C is 20% or more. 3. The heat-shrinkable polyethylene-based laminate according to claim 1, wherein the linear low-density polyethylenes (A) and (B) contain ethylene and an α-olefin having 4 to 8 carbon atoms as main components. the film.