JP3272554B2 - Multilayer polyethylene stretch shrink film and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer polyethylene stretch shrink film. More specifically, the present invention is a multi-layer polyethylene stretch shrink film excellent in automatic packaging suitability and deformation recovery property, which is suitable mainly as a film for stretch packaging or shrink packaging used for pre-packaging of retail goods, particularly for foods, and the same. It relates to a manufacturing method.

[0002]

2. Description of the Related Art In recent years, the demand for stretch films for food packaging of meat, seafood, vegetables, fruits, prepared foods and the like has been further increased with the expansion of supermarkets and convenience stores. Conventionally, films made of plasticized polyvinyl chloride have been widely used as the above stretch film.However, since a large amount of plasticizer is used, the amount of permeation of water vapor is increased, and loss or deterioration of the packaged object is caused. In addition to the drawbacks such as being easy to occur and the plasticizer being easily transferred to the package and contaminating, harmful hydrogen chloride gas is generated at the time of film forming or cutting of the film during packaging, and also at the time of incineration of waste. Have safety and health issues and pollution issues.

[0003] For this reason, development of films replacing plasticized polyvinyl chloride has been actively made with ethylene resins such as polyethylene and ethylene-vinyl acetate copolymer, or polybutadiene resins. However, although films obtained from polyethylene resins or polybutadiene resins have no problem with safety and health and pollution, they are not yet satisfactory as stretch films. For example, if a low-density polyethylene unstretched film is stretched for stretch packaging, a necking phenomenon occurs, and the elastic recovery is small, so that a beautiful packaging finish cannot be obtained. Further, the film strength is low and the transparency is not sufficient. In order to solve these drawbacks, attempts have been made to set a high degree of stretching orientation by biaxial stretching. However, for example, in the case of low-density polyethylene, there are technical problems such as tearing during processing, and the resulting film However, since the effective molecular orientation is not performed, the film strength is weak, and the heat shrinkage does not appear unless the temperature is high near the melting point. In addition, crystalline 1,
2-Polybutadiene-based, ethylene-vinyl acetate copolymer-based films obtained by adding anti-fogging agents and pressure-sensitive adhesives to these are also reported. However, these films do not exhibit heat shrinkage, and these films are used. When used and wrapped, there is a drawback that the film tends to be torn at corners of the tray due to low film strength.

[0004] In recent years, along with the diversification of packaged articles, those that can be heat-sealed and those that also have heat shrinkability have been developed.
Due to the spread of automatic packaging machines, the suitability for automatic packaging and the change in the distribution process have led to a demand for a packaging material that does not lose the film tension on the tray surface even when transported in a stacked box state or the like.

[0005] The present inventors have previously solved the drawbacks of the above-mentioned stretch film, and in order to meet these demands, a polyethylene-based resin has been used, which has heat shrinkability and stretchability, and is made of a hot plate. A multi-layer polyethylene-based stretch shrink film which can be heat-sealed, does not peel off the seal portion even when moisture adheres, and has a good finish in shrink wrapping has been proposed (JP-A-3-215034).
issue).

[0006]

However, even in the above-mentioned multilayer polyethylene stretch shrink film, the type of automatic wrapping machine or the lateral stretchability required when wrapping a tray having a low strength such as a paper tray is required. Or, the folding property and the low-temperature heat sealing property were not always satisfactory.
In addition, a resin having a relatively low melting point is generally used as a resin used for improving low-temperature heat sealability, and the effect of improving low-temperature sealability is exhibited according to the amount of the resin added. It was a drawback, and it was difficult to achieve conflicting characteristics.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to a film having excellent suitability for an automatic packaging machine having excellent low-temperature heat-sealing properties, particularly without the drawbacks of folding property, lateral stretching property, reduced film slip property and blocking. As a result of intensive studies to develop, specific linear low-density polyethylene 2
A multilayer film having an innermost layer and an outermost layer mainly composed of an intermediate layer containing a seed mixture as a main component, a specific high-pressure process polyethylene, an ethylene-α-olefin copolymer, and a linear low-density polyethylene mixed composition. The inventors have found that the present invention can be adapted to the purpose, and have completed the present invention.

That is, in the present invention, the intermediate layer is composed mainly of the following linear low-density polyethylene (A) and the following linear low-density polyethylene (D), and the innermost layer and the outermost layer are the following high-pressure method (B). 15 to 50% by weight of polyethylene, 60 to 20% by weight of an ethylene-α-olefin copolymer of the following (C) and a linear low-density polyethylene of the following (D) as main components, and a linear low-density of the following (D) Polyethylene is composed of a composition in which the maximum amount added to each layer is 30% by weight, and 10 to 30% by weight is added to all layers.
% Or more, and the thickness of the innermost layer and the outermost layer is 1 μm each.
m or more, and the thickness of the intermediate layer is 60% or more of the entire layer, and the thickness of the innermost layer and the outermost layer is 1 μm or more after the stretching process in the subsequent step. The extruded film that has been extruded and quenched and solidified once is set to a temperature of several
The present invention provides a method for producing a multilayer polyethylene-based stretch shrink film that is stretched under the condition that the tensile strength represented by the formula: 40 ≦ S ≦ 130 Kg / cm ² .

(A) a density of 0.915 to 0.935 g /
cm ³ , MI is 0.1 to 1.5 g / 10 min.
In the melting point measurement by DSC, 30 ° C. at 190 ° C.
The main peak temperature (melting point) of the melting curve obtained when the temperature is lowered to 20 ° C. at a temperature lowering rate of 10 ° C./min after holding the temperature for 10 minutes and then at a rate of 10 ° C./min. A linear low-density polyethylene having a calorific value in the range of 120 to 150 mJ / mg. (B) a density of 0.917 to 0.935 g / cm ³ , MI
Is a high pressure method polyethylene of 0.3 to 7.0 g / 10 min. (C) Density of 0.870 to 0.900 g / cm ³ , MI
Is 0.1 to 20 g / 10 minutes, and in the melting point measurement by DSC, the temperature was lowered at a rate of 10 after holding at 190 ° C. for 30 minutes.
An ethylene-α-olefin copolymer having a main peak temperature (melting point) of 50 to 100 ° C. in a melting curve obtained by lowering the temperature to 20 ° C. at a rate of 10 ° C./min and then increasing the temperature at a rate of 10 ° C./min. (D) a density of 0.890 to 0.920 g / cm ³ , MI
Is 0.3 to 7.0 g / 10 min. In the melting point measurement by DSC, the temperature is lowered to 20 ° C. at a rate of 10 ° C./min after holding at 190 ° C. for 30 min.
A linear low-density polyethylene having a main peak temperature (melting point) of a melting curve obtained at a temperature rise of 0 ° C./min of 112 ° C. or more and a heat of fusion in the range of 75 to 130 mJ / mg. The above-mentioned DSC measurement method is 8 to 10 mg.
Is sealed in an aluminum pan and performed in a nitrogen stream.

[0010]

(Equation 2) (However, p indicates the bubble internal pressure (Kg / cm ² ), d indicates the bubble diameter (cm), and t indicates the thickness (cm) of the film.)

Examples of the linear low-density polyethylene (A) used in the intermediate layer of the present invention include ethylene and propylene, butene-1, hexene-1, 4-methyl-pentene-1, octene-1, and decene-1. , Dodecene-1
And a copolymer of 1 to 2 or more α-olefins having 3 to 20 carbon atoms, preferably 4 to 8 carbon atoms, preferably ethylene and 4-methyl-pentene-1 Copolymer of ethylene, butene-1, ethylene and 4-methylpentene-1, terpolymer of butene-1, ethylene and octene-1, butene-1
Are preferable.

The resin (A) has a density of 0.915 g / c.
If it is less than m ^3, the stiffness (especially in the vertical direction) of the film is too small, and the running property of the automatic wrapping machine is not stable, resulting in poor folding. If the density exceeds 0.935 g / cm ³ , The stretchability decreases. MI is 0.1g
If it is less than / 10 minutes, the workability is undesirably reduced, and if it exceeds 1.5 g / 10 minutes, the tube stretching stability during stretching is undesirably reduced. Also, DSC
When the main peak temperature (melting point) in the measurement is less than 121 ° C. or the heat of fusion is less than 120 mJ / mg, the heat resistance of the film is reduced, and the upper limits of the heat seal suitability temperature and the heat shrink suitability temperature range are lowered. If it exceeds 150 mJ / mg, it is not preferable because the tear strength and the uniform stretchability during stretching are reduced.

The intermediate layer may contain 15% by weight or less of another ethylene copolymer in addition to the linear low density polyethylenes (A) and (D). Examples of such an ethylene-based copolymer include, for example, a low-melting-point ethylene-α described below.
-Olefin copolymers, high-pressure polyethylene, copolymers of ethylene and propylene, and copolymers of ethylene and (meth) acrylic acid. If the amount of the other ethylene-based copolymer exceeds 15% by weight, the stretching stability at the time of stretching at low tensile strength becomes insufficient.

In the present invention, the high pressure process polyethylene (B) used for the innermost layer and the outermost layer is ethylene-α-
The copolymer (C) is used as a low-temperature heat-sealability-imparting first component, and is used together with the copolymer (C) as a low-temperature heat-sealability-imparting second component having a blocking suppressing effect. When the density of the resin (B) is less than 0.917 g / cm ³ , the blocking suppressing effect is reduced, the slipperiness and the roll releasability are deteriorated, and the suitability for the automatic packaging machine is hindered.
If it exceeds 5 g / cm ³ , the adhesiveness will be low, and this will cause poor folding. MI is 0.3 g / 1
If the time is less than 0 minutes, the moldability, transparency and gloss are reduced, and if it is more than 7.0 g / 10 minutes, the transparency and gloss after heat shrink packaging tend to decrease, which is not preferable.

In the present invention, the ethylene-α-olefin copolymer (C) used as the first component for imparting the low-temperature heat-sealing property is, for example, ethylene and propylene, butene-1, pentene-1, hexene-1,4-methyl. Examples include pentene-1, octene-1, decene-1, and a copolymer of these with a mixture thereof, and a copolymer of ethylene and butene-1 is particularly preferably used. When the density of the resin (C) is less than 0.870 g / cm ³ , the low-temperature heat sealability is good, but even when a surfactant composition is added, blocking of the film easily occurs, and the density is 0.90 g / cm ^3.
When the amount exceeds g / cm ³ , the low-temperature heat sealability is undesirably reduced. Further, those having an MI of less than 0.1 g / 10 minutes are not preferred in terms of the reduction in workability and the stretchability as in the case of the linear low-density polyethylene. 20
If it exceeds g / 10 minutes, there is a problem that the stability of the stretched tube is deteriorated.

In the present invention, the linear low-density polyethylene (D) is added to each layer for the purpose of imparting a transverse stretch property. When added to the innermost and outermost layers, some of them exhibit an effect as a low-temperature heat seal imparting second component, but must be used in combination with the above-mentioned resin (B) because blocking easily occurs. Examples of the linear low density polyethylene (D) used include ethylene and propylene,
Butene-1, hexene-1,4-methyl-pentene-
Copolymers with one or two or more α-olefins having 3 to 20 carbon atoms, preferably 4 to 8 carbon atoms, including 1, octene-1, decene-1, and dodecene-1 can be mentioned. .

The density of the resin (D) is 0.890 to 0.8.
920 g / cm ³ , but preferably 0.89 g / cm ^3.
The range is ^{5 to} 0.915 g / cm ³ . 0.8 density
When the density is less than 90 g / cm ^3, the stiffness of the film becomes small, and when the density exceeds 0.920, there is no effect of improving the transverse stretching property. MI is 0.3 to 7.0 g /
It is in the range of 10 minutes, but is preferably 1.0 to 5.0 g /
The range is 10 minutes. When the MI is less than 0.3 g / 10 minutes, the effect of improving the stretchability in the lateral direction is small, and the MI is 7.0.
If it exceeds g / 10 minutes, the effect of improving the stretchability does not change, but the stretching stability of the tube tends to decrease, which is not preferable. Main peak temperature of 1 in DSC measurement
If the melting temperature is less than 12 ° C. or the heat of fusion is less than 75 mJ / mg, the heat resistance of the film, particularly when added to the intermediate layer, is reduced.

In the present invention, when the compounding ratio of the linear low-density polyethylene (D) added to each layer is less than 10% by weight with respect to all the layers, the effect of imparting the transverse stretching property is small, which is not preferable. If it exceeds, the heat resistance of the film and the stiffness of the film in the longitudinal direction decrease, which is not preferable. The compounding ratio of the high pressure method polyethylene (B) added to the innermost and outermost layers is
When the amount is less than 15% by weight, the low-temperature heat-sealing property and the effect of suppressing blocking are lost. On the other hand, when the amount is more than 50% by weight, the tackiness is undesirably reduced. In the present invention, when the blending ratio of the ethylene-α-olefin copolymer (C) added to the innermost layer and the outermost layer is less than 20% by weight, the low-temperature heat sealing property is poor and the heat of the tray bottom surface in an automatic packaging machine is poor. Plate heat sealability is poor. Further, the adhesiveness becomes small, and it is not preferable because bag making using the adhesiveness in an automatic packaging machine cannot be performed well. Conversely, when the amount exceeds 60% by weight, the low-temperature heat sealing property and the stretch property are good, but even when the surfactant composition is added, the roll peeling property at the time of being unwound from the film roll and the slip property with an automatic packaging machine. However, it is not possible to obtain the performance satisfying the adhesiveness between the films at the same time. In addition to the above components, each layer has an appropriate amount of surface activity for the purpose of imparting anti-fogging property, peeling property from the film roll together with the resin composition, slipping property in an automatic packaging machine, and adhesion between the films. Commonly used additives such as an agent and a lubricant, an anti-blocking agent, and an antistatic agent can be appropriately added for the purpose of providing their respective effective effects.

In the present invention, if the thickness of the intermediate layer with respect to all layers is less than 60%, the stability of the bubble during stretching is deteriorated, and the thickness of the innermost layer and the outermost layer after stretching is less than 1 μm. In the case of, the low-temperature heat sealing property cannot be exhibited,
Neither of them can achieve the object of the present invention. In the present invention, the thickness of each of the above-mentioned layers is limited, that is, the thickness of the intermediate layer is 60% or more of the total, and the thickness of the innermost and outermost layers after stretching is 1 μm.
One or more polyethylene resin layers may be included between the intermediate layer and the innermost layer or the outermost layer as long as the condition that m or more is satisfied. Examples of polyethylene resins that can constitute such a layer include general-purpose linear low-density polyethylene resins, ethylene-α-olefin copolymers, high-pressure polyethylene, copolymers of ethylene and propylene, ionomers, and ethylene. -Vinyl acetate copolymers, copolymers with ethylene (meth) acrylic acid, and the like.

The method of producing an unstretched film used for producing the stretched film of the present invention and the method of stretching this unstretched film to produce a stretched film can be carried out by known means. S ≦ 130Kg /
It is necessary to stretch under the condition of cm ² ,
Specific conditions will be described by taking as an example the case of forming a tubular film comprising three layers of an innermost layer, an intermediate layer and an outermost layer, and stretching.

First, the resin composition in the above-mentioned specific range is heated, melted and kneaded with three extruders for each layer, co-extruded from a three-layer annular die into a tube, and rapidly cooled and solidified without stretching. The obtained unstretched film is produced. The obtained tubular unstretched film is supplied to, for example, a tubular stretching apparatus as shown in FIG.
For example, a gas pressure is applied to the inside of the tube at a temperature lower than the melting point of the intermediate layer resin at 10 ° C., preferably at a temperature lower than 15 ° C. to cause simultaneous biaxial stretching by expansion and stretching. It is necessary to adjust so as to be ≦ 130 kg / cm ² . Tensile strength S is 40 kg / c
When it is less than m ^{2, the} stretchability in the horizontal direction is good, but the stiffness of the film in the longitudinal direction is reduced, the folding property is deteriorated, and the stability of the stretched bubble tends to be reduced. Has an elastic recovery of less than 90%, which is one of the characteristics of the present invention, and is poor in returnability after shrink wrapping. When the tensile strength S exceeds 130 kg / cm ² , the resulting film has excellent heat shrinkage, but the tensile strength in the transverse direction when stretched by 50% increases, and the elongation decreases.
Improvement in lateral stretchability cannot be achieved.

The stretching ratio is preferably about the same in the vertical and horizontal directions in order to obtain a good balance of physical properties such as strength, but the resulting stretched film more effectively expresses the waist in the vertical direction and the stretchability in the horizontal direction. In order to achieve this, it is better to slightly increase the stretching ratio in the longitudinal direction. Stretching ratio is 8 in area ratio
~ 25 times is preferred.

The film obtained by the method of the present invention is 50%
The tensile strength in the transverse direction at the time of extension is 400 kg / cm ² or less, and the area shrinkage at 90 ° C. is 20% or more. Further, the elastic recovery rate of one minute after 30% elongation of the film thermally shrunk to an area shrinkage of 15% at 90 ° C. is 90% or more. The film stretched as described above and taken out of the stretching device can be annealed as needed.

[0024]

FIG.

[0025]

The present invention will be described more specifically with reference to the following examples. In addition, each physical property measurement shown in this example was based on the following methods. (1) 90 ° C. heat shrinkage rate After talc powder is applied to a film cut into a square of 10.0 cm in length and width, left in an oven at 90 ° C. for 15 minutes, taken out, quenched, and measured in length and width. Then, it was calculated by Equation 3.

[0026]

[Equation 3] 90 ° C. heat shrinkage = 100−A × B (%) where A and B are the lengths in the vertical and horizontal directions after quenching (unit: c
m).

(2) Elastic recovery rate after 15% shrinkage The film was uniformly sagged so as to have an area shrinkage rate of 15%, set in a wooden frame, and heat-treated in an oven at 90 ° C. Remove when the slack has disappeared. Next, the film was cut in a width of 15 mm and a length of 200 mm in parallel with the MD and TD of the film, and marked with 100 mm intervals.
Attach so that the marked line comes between the chucks of m). After pulling 30% at a pulling speed of 200 mm / min, the film was returned to the original chuck position at the same speed, the film was removed, and left for 1 minute, the dimension between the marked lines was measured.

[0028]

(Equation 4) Here, C indicates a dimension (unit: mm) between marked lines in the MD or TD direction after one minute.

(3) Suitability for automatic packaging machine (foldability) An apple having a height of about 10 cm is placed on a foamed polystyrene tray having a width of 105 mm, a length of 195 mm and a depth of 20 mm.
The packaging test was performed using a commercially available automatic packaging machine equipped with a hot plate seal and a shrink tunnel. Evaluation of suitability for the packaging machine was based on the following criteria. ：: The running of the film is stable, and a clean fold is made. Δ: Although the fold was made, the overlapping portion of the film was uneven and the appearance was not very good. X: The unwinding of the roll and the running of the film were not stable, the folding was turned up, and no bag making was possible.

(4) Suitability of automatic packaging machine (heat sealing property) The hot plate sealing temperature was the same as that of (3) except that the packaged material was changed into two oranges with a diameter of about 5 cm, and the folding was performed neatly. The temperature of the hot plate seal (heat sealing start temperature) at which the welding starts sufficiently to break when the tray bottom surface is forcibly peeled off, and the temperature at which holes are formed in the film on the tray bottom surface (heat-resistant temperature) were examined. (5) Suitability for automatic packaging machine (stretchability) 2 croquettes of 25 mm height were placed on a tray made of expanded polystyrene having a width of 125 mm, a length of 180 mm and a depth of 33 mm.
The packaging test was performed using a commercially available push-up type automatic packaging machine equipped with a hot plate seal and a shrink tunnel. The evaluation of the tray deformation during packaging was based on the following criteria. ：: A beautiful finish can be obtained without any trouble such as cracking or deformation of the tray when pushed up (when the wrapped object is wrapped while stretching the film). ×: The tray is deformed or cracked when pushed up.

(6) Returnability after packaging Using the same packaging machine as in (3) above, a tray having a height of 12 mm is packed without any contents, and packaging is performed under the same conditions as in (3). The film at the center of the tray was pressed with a finger until it hit the tray, released, and the time required for the film to return to its original state was measured. The evaluation was performed according to the following criteria. ：: Within 10 seconds △: Within 1 minute ×: 1 minute or more with traces of the finger and those that cannot be restored

(7) Antifogging property After adding 50 ml of water at 60 ° C. to a 100 ml beaker,
Cover the top of the beaker with a film without wrinkles and fix it. Next, the film was left in a refrigerator at 5 ° C. for 1 hour, the degree of cloudiness of the film was observed, and the film was evaluated according to the following criteria. ：: No fogging Δ: Some water droplets adhere, but the inside of the beaker is visible. ×: The entire surface is cloudy, and the inside of the beaker cannot be seen.

(8) Thickness of each layer The thickness of each layer of the laminate is determined by observing the cross section of the film with a microscope.
I read. (9) Haze after packaging The haze value of the packaged product of the above (3) was measured. (10) Gloss after packaging The packaged product of (3) was measured for gloss value.

Example 1 Linear low density polyethylene (A) 7 having the properties shown in Table 1
A high-pressure polyethylene having a composition shown in Table 1 having a composition of 0% by weight, a linear low-density polyethylene (D) 25% by weight, and an ethylene-α-olefin copolymer (C) 5% by weight as an intermediate layer. B) A composition of 25% by weight, 50% by weight of ethylene-α-olefin copolymer (C) and 25% by weight of linear low-density polyethylene (D) was used as the innermost and outermost layers. An intermediate layer composition containing a total of 1.0 part by weight of a surfactant composition comprising 0.25 parts by weight of polyethylene glycol oleate, 0.40 part by weight of oleyldiethanolamine, and 0.35 part by weight of sorbitan trioleate; The innermost and outermost layer compositions are each extruded by 170 to 2 extruders (for the inner layer, the middle layer, and the outer layer).
The mixture was melt-kneaded at 40 ° C., and extruded downward from a slit of a three-layer annular die maintained at 240 ° C. by adjusting the amount of extrusion from each extruder assuming the thickness ratio shown in Table 1. The diameter of the slit of the annular die was 75 mm, and the gap of the slit was 0.8 mm. The extruded three-layered molten tubular film is attached directly under the die. The outer surface of a cylindrical mandrel having an outer diameter of 76 mm and circulating cooling water at 20 ° C inside is slid while passing the outer surface through a water tank. Water cooled, cooled at room temperature and taken off, about 75 mm in diameter,
A tubular unstretched film having a thickness of 240 μm was obtained. This tubular unstretched film was guided to a tubular biaxial stretching apparatus as shown in FIG. 1 and expanded and stretched. At this time, the voltage and current of the annular infrared heater of the preheater 4 were adjusted, and the film temperature at the outlet of the preheater was adjusted. The eight annular infrared heaters of the main heater 5 are divided into four sections, the voltage and current are adjusted to heat the film, and the low-speed nip roll 2, while supplying air flowing along the tube from below the main heater, Pressurized air is fed into the tubular film between the high-speed nip rolls 3, and depending on the air pressure and the peripheral speed ratio of the low-speed and high-speed nip rolls, the length is 5.0 times and the width is 4.0 times (area stretching ratio is 20 times).
Times). The air pressure (tube internal pressure) at the time of stretching was adjusted according to the voltage and current of the pre-heater and the annular infrared heater of the main heater, the air volume of the cooling air ring 6, and the air temperature so that the tensile strength became 70 kg / cm ² . .
The stability during stretching was good, there was no vertical movement of the stretching point or sliding of the stretching tube, and no uneven stretching state such as necking was observed. As shown in Table 2, the obtained film was excellent in transparency, glossiness, longitudinal film stiffness, lateral stretchability, heat shrinkage, elastic recovery, and anti-fog properties. Using this film, a tray packing test of two bulky apples was performed by a pillow-type automatic packing machine, and a clean folding was possible. In addition, two trays of tangerines, which are relatively easy to fold, were packaged in trays, and the heat sealing start temperature and the upper limit of heat sealing temperature (heat resistant temperature) were examined. A sealable temperature range was obtained. In addition, this packaged product has good shrinkage in the tunnel portion, no wrinkles or sagging of the film, and a beautiful finish of the package. I returned to the state. Further, a packaging test of a slightly deep tray was carried out by an automatic push-up type packaging machine. As a result, the wrapping with a film at the time of pushing up was smoothly performed without deformation or breakage of the tray, and a beautiful packaging finish was obtained.
Tables 1 and 2 show the raw material formulation, stretching conditions, properties of the film after stretching, and the results of each test.

Examples 2 to 6 As shown in Tables 1 and 2, except that the constituent resins of the intermediate layer and the innermost and outermost layers, the mixing ratio, the thickness ratio of each layer, and the tensile strength at the time of stretching were changed. Similarly, a laminated stretch shrink film was manufactured. When the obtained films were evaluated in the same manner as in Example 1, they were all transparent, glossy, longitudinal film waist, transverse stretchability, heat shrinkage, elastic recovery, antifogging, heat sealability. Excellent packaging suitability for each automatic packaging machine and packaging conditions, resulting in a beautiful packaging finish. Table 2 shows the test and evaluation results.

[0036]

[Table 1]

[0037]

[Table 2]

Comparative Example 1 As shown in Tables 3 and 4, a multilayer stretch shrink film was produced in the same manner as in Example 1 except that the resin (D) having a density and heat of fusion outside the scope of the claims was used. Then, physical properties and suitability of the packaging machine were evaluated. The resulting film is
Insufficient lateral stretch resulted in tray deformation and breakage in tests on the push-up automatic packaging machine.

Comparative Examples 2 and 3 As shown in Tables 3 and 4, the compounding ratio of the resin (D) was 5% by weight in each layer in Comparative Example 2, and in the intermediate layer 4 in Comparative Example 3.
A multilayer stretch shrink film was produced in the same manner as in Example 1 except that the weight was 0% by weight and the innermost and outermost layers were 30% by weight, and physical properties and suitability for a packaging machine were evaluated. The film obtained in Comparative Example 2 had insufficient lateral stretchability, and the tray was deformed and damaged in a test using an automatic push-up packaging machine. The film obtained in Comparative Example 3 was inferior in tensile modulus in the longitudinal direction, and in a wrapping-type automatic wrapping machine, the folded portion was almost turned up and the bag could not be formed. Further, even when the folding was performed neatly, the heat resistance of the film was inferior, and the suitable temperature range for heat sealing on the high temperature side was narrow.

Comparative Example 4 As shown in Tables 3 and 4, a multilayer stretch shrink film was produced in the same manner as in Example 1 except that the mixing ratio of the resin (B) used in the innermost and outermost layers was 10% by weight. Then, physical properties and suitability of the packaging machine were evaluated. In the packaging test of the obtained film with a pillow-type automatic packaging machine, the running performance was slightly unstable, the folded part was not clean, and the film overlap was uneven, so the subsequent heating with a hot plate The seal was not enough. In addition, even in the case where the fold was finely formed, the heat-sealing starting temperature was slightly higher, and the heat-sealing suitable temperature range on the low-temperature side was narrow.

[0041]

[Table 3]

[0042]

[Table 4]

Comparative Example 5 As shown in Tables 5 and 6, the tensile strength S during stretching was 150 kg.
A multilayer stretch shrink film was produced and evaluated for physical properties and suitability for a packaging machine in the same manner as in Example 1 except that the film thickness was changed to / cm ² . The obtained film lacked the stretchability in the horizontal direction, and was tested in a push-up automatic packaging machine.
Tray deformation and breakage occurred.

Comparative Examples 6 and 7 As shown in Tables 5 and 6, the resin constituting the intermediate layer, the compounding ratio,
A multilayer stretch shrink film was produced in the same manner as in Example 1 except that the resin (B) of the innermost and outermost layers, the blending ratio, and the thickness ratio were changed, and physical properties and suitability for a packaging machine were evaluated. In the film obtained in Comparative Example 6, in a packaging test of the high contents using a pillow-type automatic packaging machine, the runnability was somewhat unstable, the folding was not so beautiful, and the subsequent heat sealing was not sufficient. . In addition, even when the fold was clean, the heat-sealing start temperature was high and the heat-sealing suitability temperature range on the low-temperature side was narrow. The film obtained in Comparative Example 7 has a low longitudinal tensile modulus,
The folded part was almost turned up and the bag could not be made. In addition, even when the folding was successfully performed, the heat-sealing starting temperature was high, the heat-resistant temperature was low, and the heat-sealing suitability temperature range was narrow.

[0045]

[Table 5]

[0046]

[Table 6]

[0047]

According to the present invention, an intermediate layer mainly composed of a mixture of two specific low-density linear polyethylenes, a specific high-pressure polyethylene,
An unstretched film having an innermost layer and an outermost layer mainly composed of a mixed composition of an ethylene-α-olefin copolymer and a linear low-density polyethylene has a tensile strength S of 40 ≦ S ≦ 130K.
The film of the present invention obtained by stretching and orienting under the condition of g / cm ² has excellent transparency, heat shrinkage, elastic recovery, longitudinal tensile elasticity, transverse stretchability, and heat sealability. Yes, it is a polyethylene-based stretch shrink film with good suitability for automatic packaging machines for folding, stretching, and hot-plate heat sealing.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION 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 front page (56) References JP-A-3-215034 (JP, A) JP-A-4-18347 (JP, A) JP-A-2-172737 (JP, A) JP-A-59-1984 179643 (JP, A) JP-A-57-174329 (JP, A) JP-A-58-93741 (JP, A) JP-A-6-87193 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) B32B 1/00-35/00 EPAT (QUESTEL) WPI / L (QUESTEL)

Claims (6)

(57) [Claims] An intermediate layer comprising a linear low-density polyethylene of the following (A) and a linear low-density polyethylene of the following (D) as main components, and an innermost layer and an outermost layer comprising a high-pressure polyethylene of the following (B): 50% by weight, 60 to 20% by weight of an ethylene-α-olefin copolymer of the following (C), and a linear low-density polyethylene of the following (D) as main components. The maximum addition amount to the composition is 30% by weight, and the composition is a composition in which 10 to 30% by weight is added to the whole layer, and the thickness of the intermediate layer is 60% or more of the whole layer,
A multilayer polyethylene-based stretch shrink film, wherein each of the innermost layer and the outermost layer has a thickness of 1 µm or more. (A) a density of 0.915 to 0.935 g / cm ³ and a melt index (hereinafter abbreviated as MI) of 0.1 to
1.5 g / 10 minutes, and a differential scanning calorimeter (hereinafter, referred to as
Abbreviated as DSC. In the melting point measurement according to (1), after holding at 190 ° C. for 30 minutes, the temperature is lowered to 20 ° C. at a rate of 10 ° C./min, and then the main peak temperature (melting point) of the melting curve obtained when the temperature is raised at a rate of 10 ° C./min. Is a linear low-density polyethylene having a melting point of at least 121 ° C and a heat of fusion in the range of 120 to 150 mJ / mg. (B) a density of 0.917 to 0.935 g / cm ³ , MI
Is a high pressure method polyethylene of 0.3 to 7.0 g / 10 min. (C) Density of 0.870 to 0.900 g / cm ³ , MI
Is 0.1 to 20 g / 10 minutes, and in the melting point measurement by DSC, the temperature was lowered at a rate of 10 after holding at 190 ° C. for 30 minutes.
An ethylene-α-olefin copolymer having a main peak temperature (melting point) of 50 to 100 ° C. in a melting curve obtained by lowering the temperature to 20 ° C. at a rate of 10 ° C./min and then increasing the temperature at a rate of 10 ° C./min. (D) a density of 0.890 to 0.920 g / cm ³ , MI
Is 0.3 to 7.0 g / 10 min. In the melting point measurement by DSC, the temperature is lowered to 20 ° C. at a rate of 10 ° C./min after holding at 190 ° C. for 30 min.
A linear low-density polyethylene having a main peak temperature (melting point) of a melting curve obtained at a temperature rise of 0 ° C./min of 112 ° C. or more and a heat of fusion in the range of 75 to 130 mJ / mg. 2. The linear low-density polyethylene of (A) is selected from the group of α-olefins consisting of ethylene and butene-1, pentene-1, hexene-1, octene-1, 4-methyl-pentene-1. The multilayer polyethylene-based stretch shrink film according to claim 1, which is at least one kind. 3. The transverse tensile resistance at 50% elongation is 400.
3. The multilayer polyethylene-based stretch shrink film according to claim 1, which has a Kg / cm ² or less. 4. The multilayer polyethylene stretch shrink film according to claim 1, wherein the area shrinkage at 90 ° C. is 20% or more. 5. A film which has been thermally shrunk to an area shrinkage of 15% at 90 ° C. and stretched by 30% in each of longitudinal and transverse directions.
2. The elastic recovery rate after each minute is 90% or more.
5. The multilayer polyethylene stretch shrink film according to any one of items 4 to 4. 6. An intermediate layer comprising a linear low-density polyethylene of the following (A) and a linear low-density polyethylene of the following (D) as main components, and an innermost layer and an outermost layer comprising a high-pressure polyethylene 15 to 15 of the following (B). 50% by weight, 60 to 20% by weight of an ethylene-α-olefin copolymer of the following (C), and a linear low-density polyethylene of the following (D) as main components. The maximum addition amount to the composition is 30% by weight, and the composition is a composition in which 10 to 30% by weight is added to the whole layer, and the thickness of the intermediate layer is 60% or more of the whole layer;
The unstretched film that has been melt-coextruded so that the thickness of the innermost layer and the outermost layer becomes 1 μm or more after the stretching treatment in the subsequent step, and the quenched and solidified unstretched film has a tensile strength represented by Formula 1 in a temperature range where stretching orientation can be performed is 40. A method for producing a multilayer polyethylene-based stretch shrink film, wherein the film is stretched under a condition of ≦ S ≦ 130 kg / cm ² . (A) Density of 0.915 to 0.935 g / cm ³ , MI
Is 0.1 to 1.5 g / 10 min. In the melting point measurement by DSC, the temperature is lowered to 20 ° C. at a rate of 10 ° C./min after holding at 190 ° C. for 30 minutes.
A linear low-density polyethylene having a main peak temperature (melting point) of a melting curve obtained at a temperature rise of 0 ° C./min of 121 ° C. or more and a heat of fusion in the range of 120 to 150 mJ / mg. (B) a density of 0.917 to 0.935 g / cm ³ , MI
Is a high pressure method polyethylene of 0.3 to 7.0 g / 10 min. (C) Density of 0.870 to 0.900 g / cm ³ , MI
Is 0.1 to 20 g / 10 minutes, and in the melting point measurement by DSC, the temperature was lowered at a rate of 10 after holding at 190 ° C. for 30 minutes.
An ethylene-α-olefin copolymer having a main peak temperature (melting point) of 50 to 100 ° C. in a melting curve obtained by lowering the temperature to 20 ° C. at a rate of 10 ° C./min and then increasing the temperature at a rate of 10 ° C./min. (D) a density of 0.890 to 0.920 g / cm ³ , MI
Is 0.3 to 7.0 g / 10 min. In the melting point measurement by DSC, the temperature is lowered to 20 ° C. at a rate of 10 ° C./min after holding at 190 ° C. for 30 min.
A linear low-density polyethylene having a main peak temperature (melting point) of a melting curve obtained at a temperature rise of 0 ° C./min of 112 ° C. or more and a heat of fusion in the range of 75 to 130 mJ / mg. (Equation 1)