JP5545627B2 - Polyolefin thin film multilayer shrink film - Google Patents

Description

  The present invention relates to a heat-shrinkable packaging material for overlap. More specifically, although the thickness is as thin as 6 to 11 μm, the high tensile elastic modulus, high heat shrinkage, high tear strength, small shrinkage with time, etc. The present invention relates to a polyolefin-based thin-film multilayer shrink film that has excellent property balance and is suitably used for high-speed automatic packaging and printing.

  Conventionally, polyvinyl chloride films, polypropylene films, polyethylene films, and the like are known as heat-shrinkable packaging materials. However, polypropylene, polyethylene, etc. are low in terms of cost and ease of disposal after use. Polyolefin shrink films are preferred. However, polypropylene-based shrink film is excellent in elastic modulus, heat resistance, etc., but poor in low-temperature shrinkage, while polyethylene-based shrink film is excellent in low-temperature shrinkage, but has disadvantages such as poor elasticity and heat resistance. doing. In order to solve such problems, a polyolefin multilayer shrink film in which a propylene resin and an ethylene resin are laminated has been disclosed (Patent Document 1).

  On the other hand, in the market, in order to reduce the environmental load, it is desired to make the film thinner. However, if the conventional film is simply made thinner, the high-speed automatic packaging suitability and printing suitability are inferior due to the decrease in elastic modulus, and the tearing strength is lowered from the air vent needle hole provided by the automatic packaging machine. There was a problem that it was easy to break. Furthermore, when polyethylene resin is used frequently in order to increase the tear strength, there is a problem that shrinkage with time increases or the elastic modulus decreases.

JP-A-58-166049, JP-A-63-17361, JP-A-63-214446, JP-A-64-56547, JP-A-64-1535, JP-A-4-50444, JP-A-4-21936. Gazettes, 6-50096, 8-99393, 11-254610, and JP-A-2005-144725.

  The present invention has been made in view of the above situation, and has a good balance of properties such as high tensile elastic modulus, high thermal shrinkage, high tear strength, and small shrinkage over time, although the thickness is as thin as 6 to 11 μm. An object of the present invention is to provide a polyolefin-based thin-film multilayer shrink film that is suitably used for high-speed automatic packaging and printing.

As a result of intensive studies, the present inventors have found that both surface layers containing a propylene-based resin and a crystalline propylene resin polymerized by a metallocene catalyst (hereinafter referred to as metallocene PP) or an inner layer containing an ethylene-based resin. The inventors have found that the problem can be solved by stretching a multilayer film having at least three layers at a specific stretching ratio, and have reached the present invention.
That is, the present invention provides the following.
(1) A multi-layer structure having at least three layers having both surface layers containing a propylene-based resin and an inner layer containing a metallocene PP or ethylene-based resin has a lateral magnification larger than a vertical magnification and an area stretch magnification of 20 times or more. And a polyolefin-based multilayer shrink film satisfying all of the following (a) to (d).
(A) The thickness is in the range of 6 to 11 μm.
(B) The tensile elastic modulus is 0.8 GPa or more.
(C) The thermal shrinkage rate at 120 ° C. is 35% or more.
(D) The shrinkage after storage for 7 days in a 40 ° C. atmosphere is 4% or less.
(E) The tear strength is 30 mN or more.
(2) The biaxial stretching process is a tubular stretching method, wherein the longitudinal stretching ratio is 4.0 to 5.5 times and the transverse stretching ratio is 5.5 to 7.0 times. 1. A polyolefin-based multilayer shrink film according to 1.
(3) The polyolefin-based multilayer shrink film as described in (1) to (2), wherein the thickness of (a) is in the range of 7 to 9 μm.
(4) The polyolefin multilayer shrink film according to any one of (1) to (3), wherein both surface layers are made of a propylene resin containing 10 to 30% by weight of metallocene PP.
(5) The melting peak temperature of the metallocene PP measured by a differential scanning calorimeter (hereinafter referred to as DSC) is 110 to 130 ° C., and the melt flow rate (measuring temperature 230 ° C., load 2.16 kgf) is 1. The polyolefin-based multilayer shrink film according to any one of (1) to (4), characterized in that the thickness is from 0.0 to 10.0 g / 10 minutes.
(6) The polyolefin-based multilayer shrink film according to any one of (1) to (5), wherein the thickness of the inner layer is 60 to 80% of the whole and both surface layers are each 1 μm or more.
(7) The polyolefin multilayer shrink film according to any one of (1) to (6), wherein the shrinkage after storage for 7 days in a 40 ° C. atmosphere of (d) is 1.7% or less.

  The polyolefin-based multilayer shrink film of the present invention has an excellent balance of properties such as high tensile elastic modulus, high thermal shrinkage, high tear strength, and small shrinkage over time despite its thin thickness of 6 to 11 μm, and high-speed automatic packaging And it can be suitably used for printing.

Hereinafter, the present invention will be described in detail.
In the present invention, the propylene-based resin has a melting peak temperature measured by a differential scanning calorimeter (hereinafter referred to as “DSC”) of 130 to 165 ° C., a melt flow rate (hereinafter referred to as “MFR”) (measurement temperature 230 ° C.). , Load 2.16 kgf) is in the range of 1.0 to 10.0 g / 10 min, propylene homopolymer, copolymer of propylene and α-olefin, such as propylene-ethylene, propylene-butene copolymer, etc. And at least one selected from the group consisting of propylene-ethylene-butene terpolymers, and mainly serves to impart heat resistance and high elastic modulus. Among these, a crystalline propylene-α-olefin random copolymer is preferably used in consideration of the balance between heat resistance, high elastic modulus, heat shrinkage characteristics and transparency.
When the melting peak temperature of the propylene-based resin is less than 130 ° C., the heat resistance is low, which is not preferable. When the melting peak temperature exceeds 165 ° C., the low-temperature shrinkability is decreased, which is not preferable. Further, if the MFR is less than 1.0 g / 10 minutes, there is a problem that the motor load at the time of melt extrusion becomes high, and if it exceeds 10.0 g / 10 minutes, the fusing sealability when using an automatic packaging machine is lowered. Therefore, it is not preferable.

In the present application, the metallocene PP has a melting peak temperature in the range of 110 to 130 ° C., and if it is less than 110 ° C., the heat resistance of the multilayer film as a whole is lowered, which is not preferable. Therefore, it is not preferable. A MFR (measurement temperature 230 ° C., load 2.16 kgf) of 0.5 to 10.0 g / 10 min is preferably used. If it is less than 0.5 g / 10 minutes, there is a problem that the motor load at the time of melt extrusion becomes high, and if it exceeds 10.0 g / 10 minutes, the fusing and sealing properties are lowered, which is not preferable.
The metallocene PP used in the present invention has a low temperature shrinkage characteristic, and can exhibit a heat shrinkage characteristic similar to that of polyethylene without laminating a polyethylene resin.

For the surface layer, a propylene resin or a mixed resin of a propylene resin and a metallocene PP can be used. When a propylene resin is used alone for the surface layer, the fusing seal and heat resistance are improved. Further, by mixing the propylene resin and the metallocene PP, it is possible to further impart low temperature shrinkage. The mixing ratio when using a mixture of propylene resin and metallocene PP is preferably in the range of propylene resin: metallocene PP = 70: 30 to 90:10. If the propylene resin is less than 70%, the fusing sealability and heat resistance are lowered, and if the metallocene PP is less than 10%, it is not possible to obtain a low-temperature shrinkage more than that when the propylene resin is used alone.

In the present invention, the ethylene-based resin has a density in the range of 0.900 to 0.940 g / cm ³ at 23 ° C., low-density polyethylene having long chain branching, ethylene and butene-1, pentene-1, hexene -Linear low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-fat, which is a copolymer with α-olefin having 4 to 20 carbon atoms, including 1,4-methylpentene-1, octene-1 Consisting of at least one selected from aliphatic unsaturated carboxylic acid copolymers, ethylene-aliphatic unsaturated carboxylic acid ester copolymers, and ionomer resins, and has the effect of imparting low-temperature shrinkage, tear resistance, and impact resistance Eggplant. Of these, linear low-density polyethylene is preferably used because it can impart excellent low-temperature shrinkage.
If the density of the polyethylene-based resin is less than 0.900 g / cm ³ , the tensile modulus and heat resistance are undesirably lowered, and if it exceeds 0.940 g / cm ³ , the low-temperature shrinkability is undesirably lowered. A melt index (hereinafter referred to as MI, measuring temperature 190 ° C., load 2.16 kgf) of 0.3 to 5.0 g / 10 min is preferably used. If it is less than 0.3 g / 10 minutes, there is a problem that the motor load at the time of extrusion becomes high, and if it exceeds 5.0 g / 10 minutes, the stretching stability is lowered, which is not preferable.

There is no problem as long as the layer structure of the present invention is a layer structure of at least three layers, and a propylene resin, metallocene PP, or ethylene resin can be used for the inner layer. In addition, a propylene-based resin, a metallocene PP, and an ethylene-based resin can be mixed and used as long as the object of the present invention is not hindered. Usable resins are the same as the propylene-based resin, metallocene PP, and ethylene-based resin used in the present invention described above. In addition, a scrap of a mixture of propylene resin, metallocene PP, and ethylene resin can be reused.

In the present invention, the thickness of the surface layer is preferably 1 μm or more, and less than 1 μm is not preferable because the heat resistance is insufficient.

The thickness of the inner layer is preferably 60% or more and 80% or less of the whole, and if it is less than 60%, the low-temperature shrinkage and tear resistance are inferior, and if it exceeds 80%, the heat resistance is inferior.

In the surface layer and / or the inner layer, additives such as a lubricant, an antiblocking agent, an antistatic agent, an antifogging agent, an antioxidant, and a nucleating agent may be appropriately used for the purpose of providing each effective action. it can.

One of the features of the present invention is good flatness, but it is also an important property that there is no loss of flatness due to natural shrinkage during long-term storage of the film product roll. The shrinkage rate after storage for 1 week in a 40 ° C. atmosphere, which is a measure of natural shrinkage by the present inventors, is preferably 4% or less in both length and width, and 1.7% or less considering long-term storage such as in summer. Is preferred. If the flatness failure due to natural shrinkage during storage becomes large, the high-speed packaging suitability and printability intended by the present invention cannot be sufficiently obtained.
Despite having a high heat shrinkage rate, which is a feature of the present invention, a film having a low natural shrinkage rate can be obtained by setting the area draw ratio multiplied by the vertical and horizontal draw ratios to 20 times or more. It is achieved by things.

In the present invention, the thickness of the polyolefin-based multilayer shrink film is preferably 11 to 6 μm, more preferably 9 to 7 μm, in order to reduce environmental burden and achieve high-speed finish. For the film in the present invention, a polypropylene resin, a metallocene PP, or an ethylene resin is suitably used even if the film thickness is 11 μm or less, while the film thickness of a commercially available product exceeds 11 μm in consideration of strength characteristics. The stretching ratio is set to a stretching condition in which the transverse ratio is larger than the longitudinal ratio and the area stretching ratio is 20 times or more. Preferably, the longitudinal stretching ratio is 4.0 to 5.5 times, and the transverse stretching ratio is 5.5. By setting up to 7.0 times, it is possible to suppress the film elongation due to the temperature and tension applied during printing, and to suppress the tearing of the vertical needle holes that are likely to occur during packaging, and to obtain sufficient tear resistance. Can do.

The tensile elastic modulus of the polyolefin-based multilayer shrink film in the present application is 0.8 GPa or more and the thermal shrinkage at 120 ° C. is 35% or more. Other than this, the characteristic balance of the present application is excellent even when the film is thinned, and a film suitable for high-speed automatic packaging and printing cannot be obtained. The physical properties can be measured by the methods of the examples.

The tear strength of the polyolefin multilayer shrink film in the present application is 30 mN or more. If it is 30 mN or less, needle hole breakage is likely to occur during high-speed automatic packaging, and sufficient tear resistance cannot be obtained. The tear strength can be measured by the method of the example.
The polyolefin multilayer shrink film of the present application is suitable for high-speed automatic packaging and printing even if it is thinned. Tensile modulus, thermal shrinkage at 120 ° C, tear strength, and storage at 40 ° C for 1 week All subsequent shrinkage needs to be met.

Next, the manufacturing method of the film of this invention is shown. The method for producing the film of the present invention using the above resin can be carried out by a known longitudinal and transverse biaxial stretching method.
Hereinafter, the case of three-layer laminated annular film-forming stretching will be described as an example.
First, both surface layers mixed with a propylene-based resin and a metallocene PP, and a metallocene PP are melt-kneaded by three extruders so as to be an inner layer, and are co-extruded in a ring form from a three-layer annular die, and without stretching. A tube-shaped unstretched film is prepared by rapid solidification.
The obtained tubular unstretched film is supplied to a tubular stretching apparatus, and is in a highly orientable temperature range, for example, at a temperature lower than 10 ° C below the melting point of the core layer resin, preferably lower than 15 ° C below the melting point. By applying gas pressure to the inside of the tube at a temperature and expanding and stretching, the longitudinal and transverse draw ratios are 4.0 to 5.5 times in the longitudinal draw ratio and 5.5 to 7.0 times in the transverse draw ratio. Cause orientation. The film taken out from the stretching apparatus can be heat-treated or annealed as desired, thereby suppressing natural shrinkage during storage.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.
In addition, each physical property measurement shown in a present Example was based on the following method.
1. Film thickness: measured according to JIS-Z1709.
2. Flatness: The flatness of the film was evaluated according to the following criteria.
<Evaluation criteria>
○: The film has no tarmi or is hardly noticeable.
Δ: Tarmi is seen in the film, but it becomes inconspicuous if it is stretched lightly.
X: Talmi is seen in the film, and it remains even if lightly stretched.
3. Thickness ratio: Measured by observing the cross section of the film with a microscope.
4). Haze: Measured according to JIS-K7105.
5. Gloss (60 °): Measured according to JIS-Z7105.
6). Tensile modulus: measured according to JIS-Z7127.
7). Tear strength: Measured with a light load tear tester manufactured by Toyo Seiki in accordance with JIS-P8116.
8. Shrinkage after 7 days at 40 ° C .: Films cut into 200 mm squares in length and breadth are stored in an oven at 40 ° C. for 7 days, then the lengths in both length and breadth are measured. Calculated.

9. 120 ° C. heat shrinkage ratio: Films cut into 100 mm squares in the vertical and horizontal directions were immersed in a glycerin bath at 100 ° C. for 10 seconds, then rapidly cooled in water, and the lengths in both the vertical and horizontal directions were measured. The thermal contraction rate of TD was calculated.

10. Elongation behavior: Using a heat / stress / strain measuring device (hereinafter referred to as TMA, model: EXSTAR6000) manufactured by Seiko Instruments Inc., the film was cut into length × width = 20 mm × 3 mm and 345 mN corresponding to the tension applied during printing. Was applied in the longitudinal direction, the elongation behavior of the film in the longitudinal direction when heated to 50 ° C. was measured, and evaluated according to the following criteria.
<Evaluation criteria>
A: The elongation of the film is less than 10%.
A: The elongation of the film is 10 to 20%.
Δ: The elongation of the film exceeds 20%.
11. High-speed automatic packaging aptitude: Tokiwa Kogyo Co., Ltd. automatic packaging machine (model: NEO type, pillow packaging machine) was used to package commercially available cup noodles at a speed of 175 pieces / min, and the following items were evaluated according to the following criteria. .
<Running>
○: The running is stable and the cup noodles can be packaged stably.
X: Running is not stable and cup noodles cannot be packaged stably.
<Finish>
Film burned 2 to 10 ° C, the shrinking tunnel set at a temperature just before 10 ° C was retained for 3 seconds, and randomly selected 5 from the packaging samples after passing through the tunnel,
○: The tunnel temperature range in which the average angular height of the packaging sample is 7 mm or less exceeds 6 ° C.
(Triangle | delta): The tunnel temperature range from which the average angle height of a packaging sample will be 7 mm or less is 4-6 degreeC.
X: The tunnel temperature range in which the average angular height of the packaging sample is 7 mm or less is less than 4 ° C.
(Note: Angular height means the height of the projections on the side of the package after heat shrinking the packaging preparatory body with a moderate margin with a shrinking tunnel.)
<Needle hole resistance>
Film shrinkage The shrinking tunnel set at a temperature of 2 ° C. was retained for 3 seconds. About 50 packages after passing through the tunnel,
◯: There is no breakage from the needle hole out of 50.
Δ: 5 out of 50 breaks from the needle hole.
X: Generation of breakage from the needle hole exceeds 5 out of 50.

Example 1
As shown in Table 1, a propylene-based resin having a melting peak temperature of 140 ° C. and MFR of 2.3 g / 10 min and a metallocene having a melting peak temperature of 115 ° C. and MFR of 2.0 g / 10 min. PP blended at a blending ratio of 80:20 is used as both surface layers, melting peak temperature is 115 ° C, MFR is 2.0 g / 10 min. After kneading, the extrusion amount of each extruder was set so that the thickness ratio would be 1/5/1, and coextrusion was performed downward with a three-layer annular die. The formed three-layered tube was cooled by passing through a water tank while the outer surface of a cylindrical cooling mandrel in which cooling water circulated was slid, and was taken out to obtain an unstretched film.
This tubular unstretched film was guided to a tubular biaxial stretching apparatus, and stretched 5.0 times and 6.0 times in length and breadth to obtain a laminated biaxially stretched film having a film thickness of 10.5 μm.
As shown in Table 1, the stretchability was good, there was no vertical movement of the stretching point or swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 2
As shown in Table 1, a laminated biaxially stretched film was obtained in the same manner as in Example 1 except that the film thickness was 8 μm.
As shown in Table 1, the stretchability was good, there was no vertical movement of the stretching point or swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 3
As shown in Table 1, a laminated biaxially stretched film was obtained in the same manner as in Example 2 except that the film was stretched 5.5 × 6.0 times in the vertical and horizontal directions.
As shown in Table 1, the stretchability was good, there was no vertical movement of the stretching point or swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 4
As shown in Table 1, a linear low density polyethylene having a density of 0.900 g / cm ³ and MI of 1.0 g / 10 min is used as an inner layer, and the thickness ratio is 1/4/1. In the same manner as in Example 1, a laminated biaxially stretched film having a film thickness of 10.5 μm was obtained.
As shown in Table 1, the stretchability was good, there was no vertical movement of the stretching point or swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 5
As shown in Table 1, a laminated biaxially stretched film was obtained in the same manner as in Example 4 except that the film thickness was 8 μm.
As shown in Table 1, the stretchability was good, there was no vertical movement of the stretching point or swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 6
As shown in Table 1, a laminated biaxially stretched film was obtained in the same manner as in Example 5 except that the film was stretched 5.5 × 6.0 times in the vertical and horizontal directions.
As shown in Table 1, the stretchability was good, there was no vertical movement of the stretching point or swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 7
As shown in Table 1, the same method as in Example 1 except that a propylene-based resin having a melting peak temperature of 138 ° C. and an MFR of 2.5 g / 10 min was used as both surface layers and the film thickness was 8 μm. A laminated biaxially stretched film was obtained.
As shown in Table 1, the stretchability was good, there was no vertical movement of the stretching point or swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 8
As shown in Table 1, an inner layer is a layer obtained by blending a metallocene PP having a melting peak temperature of 115 ° C. and an MFR of 2.0 g / 10 min with the scrap obtained in Example 1 at a blending ratio of 50:50. A laminated biaxially stretched film having a film thickness of 8 μm was obtained in the same manner as in Example 1 except that.
As shown in Table 1, the stretchability was good, there was no vertical movement of the stretching point or swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 9
A layer obtained by blending a linear low density polyethylene having a density of 0.900 g / cm ³ and MI of 1.0 g / 10 min and the scrap obtained in Example 4 at a blending ratio of 50:50 was used as an inner layer. A laminated biaxially stretched film having a film thickness of 8 μm was obtained in the same manner as in Example 1 except for the above.
The drawability was good, there was no up-and-down movement of the drawing point and the swinging of the drawing tube, non-uniform drawing conditions such as necking were not observed, and the flatness was good. The evaluation result of the obtained film was good.

Comparative Example 1
As shown in Table 2, a laminated biaxially stretched film was obtained in the same manner as in Example 1 except that the film was stretched 5.0 × 5.0 times in the vertical and horizontal directions.
As shown in Table 2, the stretchability was good, there was no vertical movement of the stretching point and the swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. As shown in Table 2, the evaluation result of the obtained film was that the draw ratio was equal to the vertical and horizontal ratios, so that the tear strength in the vertical direction was inferior, and the resistance to tearing of needle holes during high-speed packaging was inferior.

Comparative Example 2
As shown in Table 2, a laminated biaxially stretched film was obtained in the same manner as in Example 1 except that the film was stretched 6.0 × 6.0 times in the vertical and horizontal directions.
As shown in Table 2, the stretchability was good, there was no vertical movement of the stretching point and the swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. As shown in Table 2, the evaluation result of the obtained film was that the draw ratio was equal to the vertical and horizontal ratios, so that the tear strength in the vertical direction was inferior, and the resistance to tearing of needle holes during high-speed packaging was inferior.

Comparative Example 3
As shown in Table 2, a laminated biaxially stretched film was obtained in the same manner as in Example 4 except that the film was stretched 6.0 × 6.0 times in the vertical and horizontal directions.
As shown in Table 2, the stretchability was good, there was no vertical movement of the stretching point and the swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. As shown in Table 2, the evaluation result of the obtained film was that the draw ratio was equal to the vertical and horizontal ratios, so that the tear strength in the vertical direction was inferior, and the resistance to tearing of needle holes during high-speed packaging was inferior.

Comparative Example 4
As shown in Table 2, a laminated biaxially stretched film was obtained in the same manner as in Example 1 except that the thickness ratio was 1/10/1 and the film was stretched 5.0 × 5.0 times in the vertical and horizontal directions.
As shown in Table 2, the stretchability was good, there was no vertical movement of the stretching point and the swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. As shown in Table 2, the evaluation result of the obtained film is that the thickness of the metallocene PP of the inner layer exceeds 80% and the thickness of the surface layer is 1 μm or less, so that the heat resistance is poor and a beautiful finish is obtained. The tunnel range was narrow. Moreover, since the draw ratio was equal to the vertical and horizontal ratios, the tear strength in the vertical direction was inferior, and the resistance to needle hole tearing during high-speed packaging was inferior.

Comparative Example 5
As shown in Table 2, a laminated biaxially stretched film was obtained in the same manner as in Comparative Example 5 except that the film thickness was 13.5 μm.
As shown in Table 2, the stretchability was good, there was no vertical movement of the stretching point and the swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. As shown in Table 2, the evaluation results of the obtained film are as follows. The thickness of the metallocene PP in the inner layer exceeds 80%, the heat resistance is inferior, and the film thickness exceeds 11 μm. It was narrow. Moreover, since the thickness exceeded 11 μm, the needle hole was not particularly broken during high-speed packaging.

Comparative Example 6
As shown in Table 2, a propylene-based resin having a melting peak temperature of 140 ° C. and an MFR of 2.3 g / 10 min and a metallocene having a melting peak temperature of 115 ° C. and an MFR of 2.0 g / 10 min. the PP compounding ratio 65: a layer blended with 35 and both surface layers, melting peak temperature of 115 ° C., a metallocene PP which MFR has a property of 2.0 g / 10 min as the internal layer, the thickness ratio of 1/8 / The extrusion amount of each extruder was set so as to be 1, and the laminated biaxially stretched film was formed in the same manner as in Example 1 except that the film thickness was 8 μm and the film was stretched 4.5 × 4.5 times in length and width respectively. Obtained.
As shown in Table 2, the stretchability was good, there was no vertical movement of the stretching point and the swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. As shown in Table 2, the evaluation result of the obtained film is that the blending amount of the metallocene PP in the surface layer exceeds 30% and the thickness of the metallocene PP in the inner layer exceeds 80%. The tunnel range that can be obtained was narrow. In addition, since the draw ratio was equal in length and width, the tear strength was inferior, and the resistance to tearing of needle holes during high-speed packaging was inferior.

The heat-shrinkable packaging material of the present invention has an excellent balance of properties such as high tensile elastic modulus, high heat shrinkage, high tear strength, and small shrinkage over time despite its thin thickness of 6 to 11 μm, and high-speed automatic packaging. It can be suitably used as a polyolefin-based thin film multilayer shrink film suitably used for printing.

Claims (7)

Stretching a multilayer structure of at least three layers having both surface layers containing a propylene resin and a crystalline propylene resin polymerized by a metallocene catalyst (hereinafter referred to as “metallocene PP”) or an inner layer containing an ethylene resin A polyolefin-based multilayer shrink film that is biaxially stretched under stretching conditions in which the lateral magnification is larger than the vertical magnification and the area stretching magnification is 20 times or more, and satisfies all of the following (a) to ( e ).
(A) The thickness is in the range of 6 to 11 μm.
(B) The tensile elastic modulus is 0.8 GPa or more.
(C) The thermal shrinkage rate at 120 ° C. is 35% or more.
(D) The shrinkage after storage for 7 days in a 40 ° C. atmosphere is 4% or less.
(E) The tear strength is 30 mN or more. The biaxial stretching process is a tubular stretching method, wherein the longitudinal stretching ratio is 4.0 to 5.5 times, and the transverse stretching ratio is 5.5 to 7.0 times. Polyolefin-based multilayer shrink film. The polyolefin multilayer shrink film according to claim 1 or 2, wherein the thickness of (a) is in the range of 7 to 9 µm. Both the surface layers consist of a propylene-type resin which contains 10-30 weight% of metallocene PP, The polyolefin-type multilayer shrink film as described in any one of Claims 1-3 characterized by the above-mentioned. Metallocene PP has a melting peak temperature measured by a differential scanning calorimeter of 110 to 130 ° C. and a melt flow rate (measuring temperature 230 ° C., load 2.16 kgf) of 1.0 to 10.0 g / 10 min. The polyolefin multilayer shrink film according to any one of claims 1 to 4 , wherein The polyolefin multilayer shrink film according to any one of claims 1 to 5 , wherein the thickness of the inner layer is 60 to 80% of the whole, and both surface layers are each 1 µm or more. The shrinkage ratio after being stored for 7 days in a 40 ° C atmosphere of (d) is 1.7% or less, and the polyolefin-based multilayer shrink film according to any one of claims 1 to 6.