JP4915749B2 - Polyolefin multilayer shrink film - Google Patents

Description

  The present invention relates to shrink wrapping materials, and more specifically, polyolefin having excellent waist strength and low-temperature shrinkability, and maintaining good suitability for high-speed wrapping machines and finish of shrink wrapping in an automatic wrapping machine, and having a good seal line during fusing sealing The present invention relates to a multilayer shrink film.

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, although the polypropylene-based shrink film is excellent in waist strength, heat resistance, etc., it has drawbacks such as poor low temperature shrinkage, impact resistance, and tear resistance. On the other hand, the polyethylene-based shrink film is excellent in low-temperature shrinkage, impact resistance, tear resistance, and the like, but has drawbacks such as poor waist strength and heat resistance. In order to solve such problems, a polyolefin multilayer shrink film using a polypropylene resin as both surface layers and a polyethylene resin as an inner layer is disclosed (Patent Document 1).
Since these polyolefin multilayer shrink films are excellent in low-temperature shrinkage and heat resistance, they have a feature that a beautiful shrink-wrapped finish is obtained and that impact resistance and tear resistance are relatively high. However, there is a problem that it is difficult to achieve both the properties of waist strength and low-temperature shrinkability.

The present applicant has previously proposed a polyolefin-based multilayer shrink film (Patent Document 2) that does not have such disadvantages and has both low waist strength and low-temperature shrinkability. The shrink film is compatible with both high-speed packaging machine suitability and shrink-wrapping finish in an automatic packaging machine, but when an L-shaped half-fold packaging machine is used as the packaging machine, As the resin adheres to the seal bar and the cradle, the molten resin becomes like a thread between the film and the seal bar (hereinafter referred to as “threading”), the seal line becomes dirty, and the appearance of the package deteriorates. There was a problem.
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, etc. JP 2005-144725 A

The present invention has been made in view of the above circumstances, and has excellent waist strength and low-temperature shrinkability, and maintains high-speed packaging machine suitability and shrink-wrapping finish in an automatic packaging machine, and also has a good seal line during fusing sealing. Thus, an object of the present invention is to provide a polyolefin-based multilayer shrink film having a good package appearance.

As a result of intensive studies to solve the above problems, the present inventors have found that propylene / 3 is contained in the inner layer.
The inventors have found that the problem can be solved by adding a methylbutene-1 copolymer copolymer, and have reached the present invention.
That is, the present invention
(1) Melting peak temperature measured by a differential scanning calorimeter (hereinafter referred to as DSC) is 135 to 165 ° C., and melt flow rate (hereinafter referred to as MFR; measuring temperature 230 ° C., load 2.16 kgf) is 1.0 to Both surface layers (X) made of polypropylene resin (A) at 10.0 g / 10 min, a crystalline propylene polymerized by a metallocene catalyst having a melting peak temperature measured by DSC of 110 to 135 ° C. An inner layer (Y) mainly composed of an α-olefin random copolymer (B; hereinafter referred to as metallocene PP), and a polyethylene resin (C) having a density of 0.900 to 0.940 g / cm ³ at 23 ° C. A polyolefin-based multilayer multilayer shrink film comprising at least four layers, which contains an inner layer (Z) mainly composed of bismuth and stretched at least three times in length and width. And 0.5 to 10% by weight of propylene / 3-methylbutene-1 copolymer (D) is added to the inner layer (Y) and / or the inner layer (Z). Polyolefin multilayer shrink film,
(2) The polyolefin-based multilayer shrink film according to (1), wherein the thickness of the inner layer (Y) is 10% or more and 45% or less of the whole, and the thicknesses of both surface layers are each 1 μm or more,
(3) The polyolefin-based multilayer shrink film according to any one of (1) to (2), wherein the polypropylene-based resin (A) is a crystalline propylene-α-olefin random copolymer,
(4) The polyolefin-based multilayer shrink film according to any one of (1) to (3), wherein the polyethylene-based resin (C) is a linear low-density polyethylene,
(5) Melting peak temperature (Tma) of polypropylene resin (A) and metallocene PP (B)
The difference (Tma−Tmb) from the melting peak temperature (Tmb) is 10 ° C. or higher (1)
Thru | or the polyolefin-type multilayer shrink film as described in any one of thru | or (4),
(6) The polyolefin multilayer shrink film according to any one of the above (1) to (5), wherein the polyolefin multilayer shrink film satisfies the following characteristics (1) and (2) simultaneously:
Characteristic (1): MD and TD tensile elastic moduli are each 0.80 GPa or more.
Characteristic (2): MD, TD heat shrinkage average value at 100 ° C. is 25% or more,
(7) In any one of the above (1) to (6), in the stretching, the difference between the longitudinal and lateral stretching ratios is 0.2 or less, and the longitudinal and lateral stretching ratios are each 4.3 times or more. The polyolefin-based multilayer shrink film as described,
Is to provide.

The polyolefin-based multilayer shrink film of the present invention is mainly composed of a layer made of a specific polypropylene resin excellent in waist strength and heat resistance on both surface layers, and a specific metallocene PP excellent in waist strength and low-temperature shrinkability as an inner layer. And a layer mainly composed of a specific polyethylene-based resin excellent in low-temperature shrinkage and tear resistance, and propylene / 3-methylbutene-1
By adding a copolymer, both waist strength and low-temperature shrinkability are excellent, and both high-speed packaging machine suitability and shrink-wrapping finish in an automatic packaging machine are compatible, and packaging is performed using an L-shaped seal-type half-fold packaging machine. However, the sealing line at the time of fusing sealing is also good, and there is an effect that the appearance of the package that does not generate a cloud after shrink wrapping is good.

Hereinafter, the present invention will be described in detail.
In the present invention, the polypropylene resin (A) used for both surface layers (X) is DSC.
The melting peak temperature measured by is 135 to 165 ° C., and the MFR is 1.0 to 10.0 g /
In the range of 10 minutes, polypropylene homopolymers, copolymers of propylene and α-olefins such as propylene-ethylene, propylene-butene copolymers, and propylene-
It consists of at least one selected from ethylene-butene terpolymers, and mainly serves to impart heat resistance and waist strength. Among these, a crystalline propylene-α-olefin random copolymer is preferably used in consideration of the balance of heat resistance, waist strength and heat shrinkage characteristics.
When the melting peak temperature of the polypropylene resin (A) is less than 135 ° C., the heat resistance is low, which is not preferable. When the melting temperature exceeds 165 ° C., the low temperature shrinkability is decreased, which is not preferable. Also, MFR
Is less than 1.0 g / 10 min, there are problems such as high motor load during melt extrusion,
Exceeding 10.0 g / 10 minutes is not preferable because the fusing and sealing properties are reduced.

The thicknesses of both surface layers (X) are each preferably 1 μm or more, and if it is less than 1 μm, the fusing sealing properties, heat resistance, and waist strength may be reduced.

In the surface layer (X), additives such as a lubricant, an antiblocking agent, an antistatic agent, an antifogging agent, and an antioxidant can be appropriately used for the purpose of providing each effective action as desired.

The metallocene PP (B) that is the main component of the inner layer (Y) of the present invention is a crystalline propylene-α-olefin random copolymer polymerized by a metallocene catalyst, and a comonomer is introduced into the main chain. . The polymer polymerized with this catalyst has a narrow molecular weight distribution, a narrow crystallinity distribution, and a uniform comonomer composition distribution. Such a metallocene PP can be produced by a method described in, for example, JP-A Nos. 2001-240711 and 2002-60566. Examples of the α-olefin copolymerized with propylene include ethylene, an α-olefin having 4 to 20 carbon atoms, or a mixture thereof. Preferably, a copolymer with ethylene is used.
Metallocene PP (B) has a melting peak temperature in the range of 110 to 135 ° C.
Less than 10 ° C is not preferable because the heat resistance of the entire multilayer film is lowered, and 135 ° C is not preferable.
Exceeding this is not preferable because the low-temperature shrinkage is reduced. MFR (measurement temperature 230 ° C, load 2
. As for 16 kgf), 0.5 to 10.0 g / 10 min is preferably used. 0.5g /
If it is less than 10 minutes, there is a problem that the motor load at the time of melt extrusion becomes high, and 10.0 g / 1
If it exceeds 0 minutes, the heat resistance of the multilayer film as a whole is lowered, which is not preferable.
The metallocene PP (B) used in the present invention has characteristics such as high waist strength and low temperature shrinkage, and is a polyolefin-based multilayer shrink using a polypropylene resin as both surface layers and a polyethylene resin as an inner layer. By using it as the inner layer of the film, it is possible to achieve the effect of improving the suitability of the high-speed packaging machine and the finish of shrink packaging.

In the inner layer (Y) of the present invention, the metallocene PP is used within the range not hindering the object of the present invention.
In addition to (B), a polypropylene resin or a polyethylene resin can be mixed. Polypropylene resin and polyethylene resin that can be mixed are both surface layers (X)
Polypropylene resin (A) used for coating, polyethylene resin (C) used for inner layer (Z)
It can be used for scrap reuse. When these resins are mixed, the mixing ratio of the metallocene PP (B) is 40% by weight with respect to the total weight of the inner layer (Y).
It is preferable to become above. If it is less than 40% by weight, the improvement level of waist strength and low-temperature shrinkage is lowered, which is not preferable.

The thickness of the inner layer (Y) is preferably 10% or more and 45% or less of the whole, and if it is less than 10%, it is not possible to achieve both waist strength and low temperature shrinkage, and if it exceeds 45%, the tear resistance may be inferior. is there.

In the inner layer (Y), additives such as a lubricant, an anti-blocking agent, an antistatic agent, an antifogging agent, and an antioxidant can be appropriately used for the purpose of providing each effective action as desired.

The polyethylene resin (C) which is the main component of the inner layer (Z) has a density at 0.9C of 0.9.
Low density polyethylene having a long chain branch, carbon containing ethylene and butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1 in a range of 00 to 0.940 g / cm ³ Linear low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylic acid which is a copolymer with several to 20 α-olefins It consists of at least one selected from an acid ester copolymer and an ionomer resin, and has the effect of imparting low-temperature shrinkage, tear resistance, and impact resistance. Of these, linear low-density polyethylene is preferably used because it can impart excellent low-temperature shrinkage.
When the density of the polyethylene resin (C) is less than 0.900 g / cm ³ , the tensile strength at break is unfavorable, and when it exceeds 0.940 g / cm ³ , the low-temperature shrinkage property is undesirably lowered. Moreover, MFR (measurement temperature 190 degreeC, load 2.16kgf) is 0.3-5.0.
Those having g / 10 minutes are 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.

In the inner layer (Z) of the present invention, a polypropylene resin and a metallocene PP can be mixed in addition to the polyethylene resin as long as the object of the present invention is not hindered. The polypropylene resin and metallocene PP to be mixed are the same as the polypropylene resin (A) used for both surface layers (X) and the metallocene PP (B) used for the inner layer (Y), respectively, and should be used for scrap recycling. You can also. When these resins are mixed, the mixing ratio of the polyethylene resin (C) is preferably 40% by weight or more based on the total weight of the inner layer (Z). If it is less than 40% by weight, the low-temperature shrinkage, tear resistance and impact resistance are lowered, which is not preferable.

The thickness of the inner layer (Z) is preferably 10% or more of the whole, and less than 10% is not preferable because the low-temperature shrinkage and tear resistance deteriorate.

In the inner layer (Z), additives such as a lubricant, an antiblocking agent, an antistatic agent, an antifogging agent, and an antioxidant can be appropriately used for the purpose of providing each effective action as desired.

In the present invention, propylene / 3-methylbutene-1 copolymer (D) is added to the inner layer (Y) and / or the inner layer (Z).
The addition amount of the copolymer (D) is 0.5 to 10% by weight with respect to the layer to be added. If the added amount is less than 0.5% by weight, stringing may occur, the seal line becomes dirty, and the appearance of the package may be deteriorated. On the other hand, if it exceeds 10% by weight, the heat shrinkability is inferior, and good packaging finish cannot be obtained, and the appearance of the package may be deteriorated.
By adding the copolymer (D) to the inner layer, the crystallization temperature of the metallocene PP or linear low-density polyethylene is increased, and the fusion between the film and the seal bar during fusing sealing is suppressed, An effect is obtained in that a good seal wire at the time of fusing sealing is obtained.
Specific examples of such a copolymer (D) include Prime Polymer F132.

In the present invention, the difference (Tma−Tmb) between the melting peak temperature (Tma) of the polypropylene resin (A) and the melting peak temperature (Tmb) of the metallocene PP (B) is preferably 10 ° C. or more. If it is less than 10 ° C., the heat shrinkage characteristics are deteriorated, so that the tunnel temperature range in which good shrinkage packaging finish can be obtained becomes narrow, which is not preferable.

The polyolefin multilayer shrink film of the present invention preferably satisfies the following characteristics (1) and (2) at the same time.
Characteristic (1): MD and TD tensile elastic moduli are each 0.80 GPa or more.
Characteristic (2): The average value of MD and TD thermal shrinkage at 100 ° C. is 25% or more.
What does not satisfy the characteristics (1) and (2) at the same time is not preferable because the compatibility level of high-speed packaging machine suitability and shrink packaging finish is low.

In the present invention, the inner layer does not necessarily have to be two layers, and can be formed into two or more layers as necessary, and a layer configuration of four or more layers as a whole can be adopted. For example, X / Y / Z
/ X 4 layer configuration, X / Y / Z / Y / X, X / Z / Y / Z / X 5 layer configuration, X / Y / Z / Y
Although a layer structure such as a / Z / X six-layer structure is mentioned, a symmetrical structure is preferable from the viewpoint of preventing the curling phenomenon of the film.

Next, the manufacturing method of the film of this invention is shown. The method for producing the stretched film of the present invention using the above-mentioned resin can be performed by a known method, and will be specifically described below by taking the case of 5-layer laminated annular film-forming stretch as an example.
First, a polypropylene resin (A) is used for both surface layers, a resin composition mainly composed of metallocene PP (B) is an intermediate layer, and a resin composition mainly composed of polyethylene resin (C) is a core layer (intermediate layer and / or Alternatively, the core layer is added with a copolymer (D), and melted and kneaded by five extruders, co-extruded in a ring shape from a five-layer annular die, and then rapidly cooled and solidified without stretching. An unstretched film is produced.
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. Simultaneous biaxial orientation is caused by expansion and stretching by applying gas pressure inside the tube at temperature. In order to obtain excellent physical properties such as strength and shrinkage, the stretching ratio is preferably stretched by 3 times or more in both the longitudinal and lateral directions. Furthermore, if the vertical and horizontal stretch ratios are 4.3 or more and the difference between the vertical and horizontal stretch ratios is 0.2 or less, the cloud after shrink wrapping can be suppressed.
In particular, it can be suitably used for applications that require a beautiful appearance or for applications in which a cloud for packaging a dark packaged item is easily noticeable.
The film taken out from the stretching apparatus can be annealed as desired, and the natural shrinkage during storage can be suppressed by this annealing.

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. Thickness ratio: Measured by observing the cross section of the film with a microscope.
3. Tensile modulus: measured according to JIS-Z7127.
4. 100 ° C. heat shrinkage: 100 mm of a film cut into a 100 mm square each in length and width
After being immersed in a glycerin bath at 10 ° C. for 10 seconds, it was rapidly cooled in water, the lengths in the vertical and horizontal directions were measured, and the thermal shrinkage ratios of MD and TD were calculated by Equation 1.

5. Thread pull evaluation: Kyowa Denki Co., Ltd. L type seal type half folding automatic packaging machine (model: AT-500
), 30 commercially available video tapes were continuously packaged under the conditions of fusing seal temperature: 200 ° C. and fusing seal time: 2 seconds. Then, the fusing seal part of the packaging sample was observed, and the stringiness was evaluated according to the following criteria.
<Criteria>
○: No threading occurs in 30 pieces.
(Triangle | delta): An average of stringing is 5 or less in 1 packaging.
X: The average number of stringing is 6 or more in one package.
6). High-speed packaging machine suitability: Automatic packaging machine manufactured by Tokiwa Industry Co., Ltd. (model: NEO type, pillow packaging machine)
Then, commercially available cup ramen was packaged at a speed of 150 pieces / min, and the running state of the film was observed.
7). Shrink wrapping finish: Film burned 2 by packaging commercially available cup ramen at a speed of 150 pieces / min with an automatic wrapping machine (model: NEO type, pillow wrapping machine) manufactured by Tokiwa Industry Co., Ltd.
The inside of the shrink tunnel set at a temperature of ˜20 ° C. was allowed to stay for 3 seconds, and 5 samples were randomly selected from the packaging samples after passing through the tunnel, and the shrink packaging finish was evaluated according to the following criteria.
<Evaluation criteria>
○: The tunnel temperature range in which the average angular height of the packaging sample is 10 mm or less exceeds 10 ° C.
(Triangle | delta): The tunnel temperature range from which the average angle height of a packaging sample will be 7 mm or less is 4-10 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.)
8). Cloud evaluation: Kyowa Denki Co., Ltd., which uses a L-type seal-type half-fold automatic packaging machine (model: AT-500) manufactured by Kyowa Denki Co., Ltd. The shrink tunnel (L-1500FC) made from manufacture was made to stay for 5 seconds, the film surface of the packaging sample after tunnel passage was observed, and cloud evaluation was carried out with the following criteria.
<Criteria>
A: Cloud is not seen at all.
○: Cloud is slightly seen.
Δ: Cloud is slightly noticeable.
×: The cloud is quite conspicuous.

Example 1
As shown in Table 1, a propylene-ethylene random copolymer having a melting peak temperature of 145 ° C. and an MFR of 2.3 g / 10 min is used as both surface layers (X), and the melting peak temperature is 1
The copolymer (D) is added to a metallocene PP having the characteristics of 25 ° C. and MFR of 4.0 g / 10 min.
The inner layer (Y) is added by weight%, the density is 0.920 g / cm ³ , and MI is 1.0 g.
/ 10 min. Linear low density polyethylene having the characteristics of 10 minutes as the inner layer (Z), melt-kneaded at 130-240 ° C. with 5 extruders, respectively, and the thickness ratio is X / Y / Z / Y / X = 1/1/4
The extrusion amount of each extruder was set so as to be 1/1/1, and coextrusion was performed downward using a 5-layer annular die maintained at 240 ° C. The formed five-layer tube is cooled by passing through the water tank while sliding the outer surface of the cylindrical cooling mandrel in which the cooling water circulates on the inner side, and has a diameter of 75 mm and a thickness of 210 μm. An unstretched film was obtained.
This tubular unstretched film was guided to a tubular biaxial stretching apparatus, and stretched at 90 to 110 ° C. four times in length and breadth to obtain a laminated biaxially stretched film.
Next, this stretched film was heated in a tube annealing apparatus with hot air at 75 ° C. for 10% each in length and width.
After relaxing, the film was cooled to room temperature, and both ends of the film were trimmed and wound up separately.
The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and non-uniform stretching conditions such as necking were not observed.
As shown in Table 1, the obtained stretched film was excellent in both tensile modulus and 100 ° C. heat shrinkage. Stringing did not occur at the time of fusing and sealing in a half-fold packaging machine, and the seal line was good.
In the packaging evaluation with a pillow packaging machine, the film is easy to run due to its firmness, and the shrinkable packaging finish also has a wide tunnel temperature range where a beautiful finish can be obtained due to its excellent heat shrinkage characteristics. It was good. A slight cloud was observed after shrink wrapping.

Example 2
In Example 1, a 5-layer biaxially stretched film was obtained in the same manner as in Example 1 except that 6% by weight of the copolymer (D) was added to the internal layer (Z) instead of the internal layer (Y). . Next, the stretched film was relaxed by 10% in the longitudinal and lateral directions with hot air at 75 ° C. in a tube annealing apparatus, cooled to room temperature, trimmed at both ends of the film, and wound up two separately. The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and non-uniform stretching conditions such as necking were not observed.
As shown in Table 1, the obtained stretched film was excellent in both tensile modulus and 100 ° C. heat shrinkage. Stringing did not occur at the time of fusing and sealing in a half-fold packaging machine, and the seal line was good.
In the packaging evaluation with a pillow packaging machine, the film is easy to run due to its firmness, and the shrinkable packaging finish also has a wide tunnel temperature range where a beautiful finish can be obtained due to its excellent heat shrinkage characteristics. It was good. A slight cloud was observed after shrink wrapping.

Example 3
In Example 1, a 5-layer biaxially stretched film was obtained in the same manner as in Example 1 except that 2% by weight of the copolymer (D) was also added to the inner layer (Z). Next, the stretched film was relaxed by 10% in the longitudinal and lateral directions with hot air at 75 ° C. in a tube annealing apparatus, cooled to room temperature, trimmed at both ends of the film, and wound up two separately. The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and non-uniform stretching conditions such as necking were not observed.
As shown in Table 1, the obtained stretched film was excellent in both tensile modulus and 100 ° C. heat shrinkage. Stringing did not occur at the time of fusing and sealing in a half-fold packaging machine, and the seal line was good.
In the packaging evaluation with a pillow packaging machine, the film is easy to run due to its firmness, and the shrinkable packaging finish also has a wide tunnel temperature range where a beautiful finish can be obtained due to its excellent heat shrinkage characteristics. It was good. A slight cloud was observed after shrink wrapping.

Example 4
In Example 1, a 5-layer biaxially stretched film was obtained in the same manner as in Example 1 except that the film was stretched 4.5 times in length and width. Next, the stretched film was relaxed by 10% in the longitudinal and lateral directions with hot air at 75 ° C. in a tube annealing apparatus, cooled to room temperature, trimmed at both ends of the film, and wound up two separately. The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and non-uniform stretching conditions such as necking were not observed.
As shown in Table 1, the obtained stretched film was excellent in both tensile modulus and 100 ° C. heat shrinkage. Stringing did not occur at the time of fusing and sealing in a half-fold packaging machine, and the seal line was good. In the packaging evaluation with a pillow packaging machine, the film is easy to run due to its firmness, and the shrinkable packaging finish also has a wide tunnel temperature range where a beautiful finish can be obtained due to its excellent heat shrinkage characteristics. It was good. The cloud after shrink wrapping was not observed and was good.

Example 5
In Example 1, a 5-layer biaxially stretched film was obtained in the same manner as in Example 1 except that the film was stretched 5.0 times in the longitudinal and lateral directions. Next, the stretched film was relaxed by 10% in the longitudinal and lateral directions with hot air at 75 ° C. in a tube annealing apparatus, cooled to room temperature, trimmed at both ends of the film, and wound up two separately. The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and non-uniform stretching conditions such as necking were not observed.
As shown in Table 1, the obtained stretched film was excellent in both tensile modulus and 100 ° C. heat shrinkage. Stringing did not occur at the time of fusing and sealing in a half-fold packaging machine, and the seal line was good. In the packaging evaluation with a pillow packaging machine, the film is easy to run due to its firmness, and the shrinkable packaging finish also has a wide tunnel temperature range where a beautiful finish can be obtained due to its excellent heat shrinkage characteristics. It was good. The cloud after shrink wrapping was not observed and was good.

Example 6
In Example 1, a 5-layer biaxially stretched film was obtained in the same manner as in Example 1 except that the film was stretched 5.0 times in length and 4.3 times in width. Next, the stretched film was relaxed by 10% in the longitudinal and lateral directions with hot air at 75 ° C. in a tube annealing apparatus, cooled to room temperature, trimmed at both ends of the film, and wound up two separately. The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and non-uniform stretching conditions such as necking were not observed.
As shown in Table 1, the obtained stretched film was excellent in both tensile modulus and 100 ° C. heat shrinkage. Stringing did not occur at the time of fusing and sealing in a half-fold packaging machine, and the seal line was good. In the packaging evaluation with a pillow packaging machine, the film is easy to run due to its firmness, and the shrinkable packaging finish also has a wide tunnel temperature range where a beautiful finish can be obtained due to its excellent heat shrinkage characteristics. It was good. A slight cloud was observed after shrink wrapping.

Comparative Example 1
In Example 1, a 5-layer biaxially stretched film was obtained in the same manner as in Example 1 except that the copolymer (D) was not added to the inner layer (Y). Next, the stretched film was relaxed by 10% in the longitudinal and lateral directions with hot air at 75 ° C. in a tube annealing apparatus, cooled to room temperature, trimmed at both ends of the film, and wound up two separately. The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and non-uniform stretching conditions such as necking were not observed.
As shown in Table 2, the obtained stretched film has sufficient tensile elastic modulus and 100 ° C. heat shrinkage, and even in packaging evaluation with a pillow wrapping machine, the stretchability of the film is strong, and the running property of the film is good. As for the shrink-wrapping finish, the tunnel temperature range in which a beautiful finish can be obtained is excellent due to the excellent heat-shrinkage characteristics, and it was good. However, in the half-fold packaging machine, stringing occurs at the time of fusing sealing, and the sealing wire becomes dirty. A slight cloud was observed after shrink wrapping.

Comparative Example 2
In Example 1, a five-layer biaxially stretched film was obtained in the same manner as in Example 1 except that the copolymer (D) added to the inner layer (Y) was changed from 6% by weight to 0.1% by weight. It was. Next, the stretched film was relaxed by 10% in the longitudinal and lateral directions with hot air at 75 ° C. in a tube annealing apparatus, cooled to room temperature, trimmed at both ends of the film, and wound up two separately. The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and non-uniform stretching conditions such as necking were not observed.
As shown in Table 2, the obtained stretched film has sufficient tensile elastic modulus and 100 ° C. heat shrinkage, and even in packaging evaluation with a pillow wrapping machine, the stretchability of the film is strong, and the running property of the film is good. As for the shrink-wrapping finish, the tunnel temperature range in which a beautiful finish can be obtained is excellent due to the excellent heat-shrinkage characteristics, and it was good. However, in the half-fold packaging machine, stringing occurs at the time of fusing sealing, and the sealing wire becomes dirty. A slight cloud was observed after shrink wrapping.

Comparative Example 3
In Example 1, the copolymer (D) added to the inner layer (Y) was added in an amount of 6% by weight to 20% by weight.
A 5-layer biaxially stretched film was obtained in the same manner as in Example 1 except that the change was made. Next, the stretched film was relaxed by 10% in the longitudinal and lateral directions with hot air at 75 ° C. in a tube annealing apparatus, cooled to room temperature, trimmed at both ends of the film, and wound up two separately. The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and non-uniform stretching conditions such as necking were not observed.
As shown in Table 2, the obtained stretched film has a sufficient tensile elastic modulus, and even in packaging evaluation with a pillow wrapping machine, the stretchability of the film is strong and the film travels well. There was no stringing at the time of sealing, and the sealing wire was good. However, the shrinkage rate is 25% or less,
The shrink-wrapping finish in the pillow wrapping machine was also very sharp, and good finish was not obtained. A slight cloud was observed after shrink wrapping.

Comparative Example 4
In Example 1, the polymer added to the inner layer (Y) is a polypropylene homopolymer (E).
Instead of adding 6% by weight, a 5-layer biaxially stretched film was obtained in the same manner as in Example 1.
Next, the stretched film was relaxed by 10% in the longitudinal and lateral directions with hot air at 75 ° C. in a tube annealing apparatus, cooled to room temperature, trimmed at both ends of the film, and wound up two separately. The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and non-uniform stretching conditions such as necking were not observed.
As shown in Table 2, the obtained stretched film has sufficient tensile elastic modulus and 100 ° C. heat shrinkage, and even in packaging evaluation with a pillow wrapping machine, the stretchability of the film is strong, and the running property of the film is good. As for the shrink-wrapping finish, the tunnel temperature range in which a beautiful finish can be obtained is excellent due to the excellent heat-shrinkage characteristics, and it was good. However, in the half-fold packaging machine, stringing occurs at the time of fusing sealing, and the sealing wire becomes dirty. A slight cloud was observed after shrink wrapping.

The polyolefin-based multilayer shrink film of the present invention is excellent in both waist strength and low-temperature shrinkage, and in packaging using an L-type seal-type half-fold packaging machine while maintaining high-speed packaging machine suitability and shrink packaging finish in an automatic packaging machine. Since the seal line at the time of fusing sealing is good and the generation of cloud after shrink packaging is suppressed, it can be suitably used for various shrink packaging.

Claims (7)

The melting peak temperature measured by a differential scanning calorimeter (hereinafter referred to as DSC) is 135 to 165 ° C., and the melt flow rate (hereinafter referred to as MFR. Measurement temperature 230 ° C., load 2.16 kgf) is 1.0 to 10.0 g. / 10 minutes of both surface layers (X) composed of a polypropylene resin (A) and a crystalline propylene-α-olefin polymerized by a metallocene catalyst having a melting peak temperature measured by DSC of 110 to 135 ° C. Mainly an inner layer (Y) mainly composed of a random copolymer (B; hereinafter referred to as metallocene PP), and a polyethylene resin (C) having a density at 23 ° C. of 0.900 to 0.940 g / cm ^3. A polyolefin-based multilayer shrink film comprising at least four layers, each of which contains an inner layer (Z) and is stretched at least three times in length and width. A polyolefin-based multilayer, wherein 0.5 to 10 wt% of propylene / 3-methylbutene-1 copolymer (D) is added to the inner layer (Y) and / or the inner layer (Z). Shrink film.   2. The polyolefin-based multilayer shrink film according to claim 1, wherein the thickness of the inner layer (Y) is 10% or more and 45% or less of the whole, and the thicknesses of both surface layers are each 1 μm or more.   The polyolefin multilayer shrink film according to any one of claims 1 to 2, wherein the polypropylene resin (A) is a crystalline propylene-α-olefin random copolymer.   The polyolefin multilayer shrink film according to any one of claims 1 to 3, wherein the polyethylene resin (C) is a linear low density polyethylene.   5. The difference (Tma−Tmb) between the melting peak temperature (Tma) of the polypropylene resin (A) and the melting peak temperature (Tmb) of the metallocene PP (B) is 10 ° C. or more. The polyolefin-based multilayer shrink film according to Item. The polyolefin multilayer shrink film according to any one of claims 1 to 5, wherein the polyolefin multilayer shrink film satisfies the following characteristics (1) and (2) simultaneously.
Characteristic (1): MD and TD tensile elastic moduli are each 0.80 GPa or more.
Characteristic (2): The average value of MD and TD thermal shrinkage at 100 ° C. is 25% or more.   The polyolefin-based multilayer shrink according to any one of claims 1 to 6, wherein, in the stretching, the difference between the longitudinal and lateral stretching ratios is 0.2 or less, and the longitudinal and lateral stretching ratios are each 4.3 times or more. the film.