JPH08276550A - Polyolefinic resin multilayered film for stretch packing - Google Patents

Abstract

PURPOSE: To provide a film used in stretch packing, especially a film generating no wrinkles after packing even in a linear packing machine. CONSTITUTION: A multilayered film consists of both surface layers, a stretched auxiliary layer and a core layer and the stretched auxiliary layer is a layer composed of an ethylene/α-olefin polymer with density of 0.865-0.885g/cm<3> and an m.p. of 50-70 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin resin multi-layer stretch packaging film, and more particularly to a polyolefin resin multi-layer film suitable for a packaging material to be packaged by a linear stretch packaging machine.

[0002]

2. Description of the Related Art Conventionally, both surface layers (Z layers) and a polyolefin-based elastomer having a Vicat softening point of 60 ° C. or less are used.
A stretching auxiliary layer (X layer) made of a mixed resin containing 90 to 90% by weight,
And a core layer (Y layer) of at least 4 layers,
Polyolefin resin multi-layer stretch wrapping films having a shrinkage rate at 20 ° C of 20 to 50% are, for example, Japanese Patent Publication No.
It is disclosed in Japanese Patent No. 52624 and is publicly known. According to the description of this publication, the surface layer (Z layer) has a role of providing the surface layer of the multilayer film with surface characteristics such as heat-sealing property, antifogging property, surface gloss property, and flexibility. Is EVA (ethylene-vinyl acetate copolymer) or EMA
A synthetic resin such as A (ethylene-methacrylic acid copolymer) is used. In particular, for the surface layer, it is recommended to select a resin in which the antifogging agent is easily kneaded and the kneaded antifogging agent easily bleeds out. The core layer (Y layer) mainly has a role of providing heat resistance and mechanical strength to the entire multilayer film. For example, a resin such as crystalline polypropylene (PP) or polybutene-1 (PB-1) is used. Has been done. The stretching assist layer (X layer) has a Vicat softening point of 60.
A mixed composition layer containing 5 to 90% by weight of a polyolefin-based elastomer having a temperature of 30 ° C. or less, and having a role of facilitating the stretching of the Y layer, which is difficult to stretch by a single layer at a low temperature of 30 to 80 ° C. Is. Specifically, a mixed composition of an ethylene-propylene copolymer elastomer having a Vicat softening point of 40 ° C. or lower, EVA, and PP is adopted.
And this X-layer has 5 to 5 polyolefin-based elastomers.
The absolute condition is 90% by weight, and by disposing it in close proximity to the Y layer, the total thickness of the multilayer film is 30 to 30%.
It is possible to stretch at an area ratio of 9 to 30 times at a low temperature of 80 ° C. (referred to as cold stretching), and as a result, the multilayer film has a shrinkability of 20 to 50% at 80 ° C. The quality characteristic as a packaging film is provided, that is, for example, "moderate elongation load at a specific elongation and high elongation at break = stretchability", "excellent deformation recovery and modest elastic modulus = indentation after packaging. It is possible to combine "recoverability of deformation mark (indentation recovery), tension and waist", "sufficient mechanical strength = suitability for operation with a packaging machine", and it can be used in the stretch packaging field. is there.

On the other hand, in the stretch wrapping by a machine, the film is stretched by pushing up the central portion of the cut film with the object to be wrapped, and the stretch type stretch wrapping that wraps the object to be wrapped in that state and the film is stretched. Meanwhile, there is a linear stretch wrapping in which the object to be packaged is wrapped in a tubular shape, the film before and after the object to be packaged is cut in a stretched state, and the film end is folded onto the bottom surface of the object to be packaged. The packaging capacity of both types of packaging machines is about 30 to 50 packs / minute for the thrust type and about 60 to 120 packs / minute for the straight type, and double that of the straight type packaging machine. It is known to be reasonably efficient.

[0004]

However, for example, the conventional polyolefin resin multilayer film disclosed in Japanese Patent Publication No. 2-52624 is extremely unsuitable for use in the above-mentioned linear stretch wrapping machine. It was The reason will be described with reference to FIG. FIG. 3 is a conceptual diagram of a process of continuously packaging an article to be packaged with a linear stretch packaging machine. In the figure, (1) is an object to be packaged, (2) is a film, (3) is a cutter blade, (5) is a post-folding device,
(6) is a front folding device, large arrows are (a), (b),
The order of the packaging process which advances to (c), (d), and (e) is shown.

Step (a) shows a state in which the film is cut while being stretched in the longitudinal direction between the objects to be packaged,
Step (b) shows a state in which the film before and after the object to be packaged has been cut. Further, the steps (c) to (e) show a state in which the free film is folded before and after the packaged object and the film is heat-sealed on the bottom surface of the packaged object.

[0006] The problem with the conventional multilayer film is that the packaging wrinkles (4) remain in the final product in step (e), which reduces the commercial value of the package. The cause is presumed to be the elastic recovery of the film. That is, in the straight type stretch wrapping machine, only the horizontal direction is stretched and the vertical direction is hardly stretched, but in the step (a), the film is stretched in the vertical direction by about 10% (arrow (7)). ), The force that was stretched by being released is released, and the film returns instantly due to elastic recovery like rubber. At this time, the returning speed is too fast and the film returns to the original size or more, causing wrinkles (4). This wrinkle (4) is a post-folding step (step (c)) of the film before and after the object to be packaged.
It is a wrinkle that does not disappear even if it is pulled in the front folding step (step (d)).

By the way, as a method of preventing the wrinkle (4), a film having no elastic recovery from rubber, in other words,
It is possible to use a film with a small recovery property,
The final product wrapped with a small recoverable film is
There is a problem in that the film on the surface of the package is touched with a finger or the like in the distribution process or at the store and is pushed into the film surface to leave a trace of the dent deformation.

In view of the above, the present invention solves such a problem at 80 ° C.
In the state where the excellent properties of the conventional multilayer film having a shrinkage ratio of 20 to 50%, that is, antifogging property, optical property, strength, etc. are maintained, "wrinkles remain when wrapped in a linear stretch wrapping machine. Non-recoverability (wrinkle recovery) "and" Recovery against dent deformation when a finger or the like is pressed in (indentation recovery) "
It is an object of the present invention to provide a film for a stretch wrapping machine that satisfies the two required characteristics, particularly a film suitable for a linear stretch wrapping machine for the first time.

[0009]

That is, the present invention relates to a stretching auxiliary layer comprising a mixed resin containing both surface layers (Z layer) and a polyolefin-based elastomer having a Vicat softening point of 60 ° C. or lower in an amount of 5 to 90% by weight. (X layer) and core layer (Y layer) at least 4 layers, and the shrinkage rate at 80 ° C. is 20 to 5.
In the 0% polyolefin resin multilayer stretch packaging film, the polyolefin elastomer contained in the X layer has a density of 0.865 to 0.885 g / cm 3.
³ is a polyolefin resin multilayer stretch packaging film characterized in that and melting point of the ethylene-.alpha. · olefin copolymer is 50-70 ° C. at.

The details of the present invention will be described below. The present invention is different from the prior art in that the polyolefin-based elastomer used in the stretching auxiliary layer (X layer) of the multilayer film is
This is because "ethylene-α-olefin copolymer having a density of 0.865 to 0.885 g / cm ³ and a melting point of 50 to 70 ° C" was used.

FIG. 1 is an experimental diagram showing the characteristics of the film of the present invention. The vertical axis represents the recovery rate (100% indicates that the size has completely returned to the original size), and the horizontal axis represents the time from the time when the extended force is released. In the experiment, assuming the cutting process (process (a) in FIG. 1), the film is set to 1 in the longitudinal direction.
The recovery rate of the film when released immediately after 0% elongation was measured over time. Four types of film samples were used. In FIG. 1, the film 1 of the present invention (Experiment No. 1 of Example 1) is marked with a star, and the conventional multilayer film 2 (corresponding to Experiment No. 2 of Comparative Example 1) is used. ) Is a circle, and Experiment N of Comparative Example 1
o. The film 3 of No. 3 is shown by Δ, and the film 4 having a small recoverability (Experiment No. 4 of Comparative Example 1) is shown by □.

In FIG. 1, a conventional multilayer film 2 (○
The mark () indicates that the recovery rate (L2) up to 2 seconds is as high as 99%, and 100% is recovered after 3 seconds. Assuming that the difference between the saturation recovery rate and L2 is the delay recovery rate ΔL, ΔL remains 1%. On the other hand, the film 1 of the present invention (marked with *) has a slower recovery speed up to 2 seconds than the conventional multilayer film 2, so L2 is as low as 93% and 100% is recovered. Is a large value of 7%.

On the other hand, in Experiment No. 1 of Comparative Example 1. In Film 3 (marked with Δ) of No. 3, L2 has a low value of 94%, and ΔL also remains at 2%. Film 4 with less recovery
In the case of (□), the recovery speed is slower than that of the film 1 of the present invention, L2 is as low as 86%, and ΔL is as large as 8%, but the saturation recovery rate is 94%. There is.

First, the film satisfying both the prevention of wrinkling during packaging and the indentation recovery property was only the film 1 (*) of the present invention using a specific ethylene-α / olefin copolymer. That is, the conventional multilayer film 2 (marked with ◯) satisfies the indentation recovery property, but wrinkles are significantly generated during packaging.
In addition, the experiment No. The film 3 (marked with Δ) of No. 3 has poor wrinkle remaining and poor recovery from indentation.
o. Film 4 (marked with □) was able to prevent wrinkles during packaging, but was observed to have a phenomenon that the indentation recovery property was significantly deteriorated.

The inventors of the present invention have further clarified the above phenomenon from the relationship with the characteristics of each film shown in FIG. 1, and as a result, a film having suitability for packaging in a linear packaging machine has L2 of 95%.
It has been found that the film has the following properties and ΔL is greater than 3%. That is, when L2 is 95% or less, there is no packaging wrinkle (slack wrinkle) that occurs when the film stretched at the time of cutting returns to the original size or more, and ΔL
If it is more than 3%, even if small wrinkles occur, the film retains the components that recover after the folding step and has a wrinkle removing effect, so that the final product can be a beautiful package without wrinkles. .

Further, the film satisfying the indentation recovery property is a film having a saturation recovery rate of 100%, and the film is deformed in order to completely eliminate the marks of depression deformation formed by pressing a finger or the like into the film. Must be fully recovered against. Therefore, a film satisfying both wrinkle recovery property and indentation recovery property is possible only when it has recovery properties like the film of the present invention.

Next, the ethylene-α-olefin copolymer used in the present invention has a "density of 0.865 to 0.885 g /
cm ³ and melting point of 50 to 70 ° C. ”will be described. FIG. 2 is an analysis diagram of the experimental results of the present invention.
The melting point is plotted on the vertical axis and the density is plotted on the horizontal axis, and the evaluation of the experimental results (packing property, indentation recovery property) shown in Table 1 is plotted in relation to the physical properties of the resin used. The symbol "◎" satisfies both wrapping property (wrinkle recovery) and indentation recovery. The symbol "xB" indicates excellent wrapping property but poor indentation recovery, and symbol "xA". The mark indicates that the indentation recovery is excellent, but the wrapping property is inferior.

As is apparent from FIG. 2, it can be seen that the region satisfying both the packaging property and the indentation recovery property can be separated by a line.
That is, the density is 0.865 g / cm ³ or more and 0.88
Region of 5 g / cm ³ or less and melting point of 50 ° C. or more and 70
This is the region below ℃. When the melting point was less than 50 ° C, L2 exceeded 95% and the recovery speed was fast, and slack wrinkles occurred in actual packaging.

When the density is less than 0.865 g / cm ³ , L2 is 95% or less like the film of the present invention, but ΔL is as small as less than 3%, and small wrinkles may remain and disappear in actual packaging. There wasn't. Density is 0.885g / c
When it exceeds m ³ , or when the melting point exceeds 70 ° C.,
The saturation recovery rate of the film did not reach 100%, and the indentation recovery property was poor.

Therefore, the ethylene-α-olefin copolymer used in the present invention has a density of 0.865 to 0.885 g /
It can be seen that the melting point must be cm ³ and the melting point must be 50 to 70 ° C. Here, ethylene-α · that satisfies the above conditions
Specific examples of the olefin copolymer include a random copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms. Specific examples of the α-olefin include propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, decene-1, dodecene-1, tetradecene-1, hexadecene-1, Octadecene-1, eicosene-1, etc. may be mentioned, and a cyclopentadiene-based monomer, a norbornene-based monomer (eg ethylidene norbornene), etc. may be copolymerized with this.
The structural unit derived from ethylene is preferably 50 to 95.
% By weight, more preferably 60 to 90% by weight and having 3 carbon atoms
The constituent unit derived from .alpha..olefin of .about.20 is preferably 5 to 50% by weight, more preferably 10 to 40% by weight.
Is. Among the above copolymers, those polymerized with a single site catalyst such as a metallocene catalyst rather than a multi site catalyst and having a narrow molecular weight distribution (Mw / Mn of 3 or less) are particularly preferable. Also preferably, long chain branching is controlled and relatively long short chain branching (eg hexene-1.
And octene-1) are considered to be due to the relationship between the bulkiness of the molecule and the crystal structure thereof, but they are preferable for satisfying the MIR shown below.

Next, the ethylene-α-olefin copolymer used in the X layer has an Mw (weight average molecular weight) / Mn (number average molecular weight) of 3 or less and an MIR represented by the following formula of 25 to 40.
The reason why is preferable is explained. MIR = HMI / MI (1) (where MI is 19 in accordance with JIS K7210)
Melt flow rate measured under conditions of 0 ° C. and a load of 2.16 kg. The HMI is a value measured under a load of 21.6 kg among the measurement conditions of the MI. ) The reason why the ethylene-α-olefin copolymer used in the X layer is limited as described above is that the optical properties of the final film, particularly the glossiness, are improved.

First, a resin having a narrow molecular weight distribution has a uniform structure of oriented crystals when formed into a film and has a uniform dispersion in the film, and has excellent gloss. From this viewpoint, Mw (weight average molecular weight) / Mn (number average molecular weight) showing the molecular weight distribution of the copolymer is preferably 3 or less. In addition, usually, Mw / Mn> 1. In addition, when the resins are blended or multilayered and extruded from the die, if the viscosity characteristics of the resins differ, the blending may cause poor dispersion, and in the case of multiple layers, the layers may become opaque or roughen due to interlayer disturbance, resulting in optical Poor characteristics. From this point of view, it is desirable that the MIR, which is an index of extrusion processability, is 25 to 40, which is the same as other resins used in the multilayer film of the present invention.

The MI of the above copolymer is preferably 0.2 to 3 g / 10 minutes from the viewpoint of preventing puncture of bubbles during cold stretching and the strength of the resulting film. Next, another resin that constitutes the stretching auxiliary layer (X layer) will be described. The X layer is an essential layer when cold drawing is performed, and mainly contains the above ethylene-α-olefin copolymer (A) in an amount of 5 to 9
0% by weight, and the following polymers (B) and (C)
Is a layer composed of a blend composition of the three polymers described above.

The polymer (B) has, for example, a density of 0.890 in order to impart easy stretchability, transparency and antifogging property.
To 0.920 g / cm ³ of ethylene-α / olefin copolymer, ethylene-vinyl acetate, ethylene-ethyl acrylate and other ethylene and ester monomers, aliphatic unsaturated monocarboxylic acid, and alkyl ester of monocarboxylic acid At least a part of the copolymer obtained by saponifying at least a part of the copolymer of the selected monomer or the copolymer of the above-mentioned monomer and ethylene, for example, a metal ion such as Na, Zn, or Mg. It is a polymer or the like that is ionically bonded by.

The polymer (C) is, for example, isotactic polypropylene or syndiotactic polypropylene, and ethylene or butene-1 in order to impart strength (elasticity), low temperature shrinkability, heat resistance, etc. of the film. It is a copolymerized propylene polymer or polybutene-1 polymer. The composition may be blended with 1,2-polybutadiene, petroleum resin such as hydrogenated dicyclopentadiene and hydrogenated terpene, hydrogenated styrene-butadiene copolymer (block, random) and the like.

Next, the surface layer and core layer constituting the multilayer film will be described. First, the surface layer (Z layer) is provided with surface characteristics such as heat-sealing property, antifogging property, surface glossiness and flexibility, and is selected from the above-mentioned polymers (B).
Further, the core layer (Y layer) is mainly provided with heat resistance, mechanical strength and the like, especially delayed recovery property in the whole multilayer film. For example, isotactic polypropylene, syndiotactic polypropylene and ethylene and Butene-1 etc. Copolymerized crystalline polypropylene resin, polybutene-
1 and a polybutene-1 type polymer in which ethylene, propylene, etc. are copolymerized, or a layer of a mixed composition thereof. In addition to these resins, petroleum resins such as hydrogenated polydicyclopentadiene and hydrogenated polyterpenes may be mentioned as resins to be mixed in a small amount (5% by weight or less). In addition to these resins, examples of the resin to be mixed include petroleum resins such as 1,2-polybutadiene, hydrogenated polydicyclopentadiene and hydrogenated polyterpene, and hydrogenated styrene-butadiene copolymer (block, random).

As a combination of each of these layers, Z / Y / X / Z for 4 layers, Z / X / Y / X / Z for 5 layers, and Z / Y
/ X / Y / Z, Z / X / Y / X / Y / X / Z for 7 layers,
Z / Y / X / Y / X / Y / Z, Z / Y / X /.../ Z, Z
Examples include /X/Y/.../Y/Z. Preferably Y
This is a combination having two or more layers. The above film is
It is possible to collect, repelletize and blend into the X layer.

The thickness ratio of each layer is usually 10 for the X layer because of the strength, optical characteristics and heat sealability of the multilayer film.
-40%, the Y layer is 5-40%, and the Z layer is 5-20%. The total thickness of the multilayer film is preferably 5 to 25 in view of wrapping property, stretch property and handleability.
μm. Further, an antifogging agent, an antibacterial agent, a defrosting agent, an ultraviolet absorber, an antioxidant and the like may be added to the above X layer and Z layer, and further, silicone oil or its emulsion, It may be coated with a surfactant, powder, polymer or the like.

Next, as an example of a preferable method for obtaining the film of the present invention, the cold stretching method is shown below. First, the resin composition of each layer is melt-extruded by a separate extruder, and combined and laminated by a multi-layer die (preferably a circular die). This laminated body is rapidly cooled and solidified with a refrigerant to form a tube-shaped raw material. As a result, the crystallinity of each resin layer is suppressed to a low level, and cold drawing becomes easy. At this time, the surface of the tube is filled with a surfactant, silicone oil or the like for the purpose of improving properties such as antifogging property and slipperiness. Next, 30-80 ° C (usually 35-65
C.) and stretched to have an area ratio of 9 to 30 times.
After stretching, the film is taken out and heat-treated if necessary.
The temperature in this case is lower than the Vicat softening point of the polymer of the surface layer (Z layer) (usually 40 to 70 ° C.), and at the time of heat treatment, it is 5% or more in both length and width as compared to when the film is in a tension state. It is preferable to perform the relaxation. Further, corona discharge treatment or the like may be performed after the heat treatment.

Here, the evaluation method of the present application will be described below. (1) Shrinkage rate (%) A film sample was cut into 50 mm x 50 mm so as to be orthogonal to the longitudinal and lateral directions of the film, and the temperature was 80 ° C.
The dimensional shrinkage ratio was determined by putting the hot air circulating constant temperature bath of No. 1 in a state in which it could freely shrink, leaving it for 30 minutes, and then taking it out. Numerical values are represented by average values in the vertical and horizontal directions.

(2) Density (g / cm ³ ) Using a density gradient tube method specific gravity measuring device manufactured by Shibayama Scientific Instruments Co., Ltd., in accordance with JIS K-7112 D method, 23 ° C.
The measurement was performed under the conditions of. The specific gravity liquid used was an isopropyl alcohol / water system. (3) Melting point (° C) According to JIS-K7121, the measuring device used was Perkin Elmer DSC-7. The melting point is indicated by the highest peak temperature among the melting peaks.

(4) Molecular weight distribution (Mw / Mn) The weight average molecular weight (Mw) and the number average molecular weight (Mn) were determined by the following method and their ratios were taken. Mw and Mn are Wa
ters Associates 150 type high temperature G
Connect a PC device and FTIR made by PERKIN ELMER, and use GMH-H6 made by Tosoh Corporation as a column.
This was measured using one piece, Showa Denko's AT-807S. Trichlorobenzene (TCB) is used as the solvent.
The measurement was performed at 40 ° C.

(5) MIR Using a melt indexer conforming to JIS K7210, first, the melt flow rate (MI) was measured under the conditions of a temperature of 190 ° C. and a load of 2.16 kg. Next, under the same temperature conditions, the value measured with a load of 21.6 kg is the HMI.
And The ratio of the values of MI and HMI obtained in this way (H
MI / MI) was defined as MIR.

(6) Recovery rate [L2, ΔL] A film sample was cut into a size of 1200 mm in the lengthwise direction and 350 mm in the widthwise direction at a temperature of 23 ° C. and an atmosphere of 50% RH.
A sample of 1000 mm × 350 mm was prepared by providing an end portion of m. One end of this sample was fixed, and a weight of 175 g (0.5 g / cm width) was attached and hung on the other end. This weight is for preventing the film having a fast recovery speed from jumping when the film is released after stretching. In this state, pull 100 mm in the longitudinal direction (10% elongation) to immediately open, and then obtain the recovery rate (L2) after 2 seconds and the contraction rate (L120) after 120 seconds when the contraction is completely saturated. It was Further, the difference between L120 and L2 is ΔL (delay recovery rate).

(7) Indentation recoverability-Method: 125 mm in a state where a film sample is stretched by 0% in the longitudinal direction and 5% in the lateral direction in an atmosphere of 50% RH at 23 ° C.
The film is pulled in a vertical direction by a pushing rod having a diameter of 15 mm and a radius R of 7.5 mm at a tip of 25 mm at a speed of 1000 mm / min, and is pulled out at the same speed. When the time of withdrawal is set to 0 seconds, the indentation recovery time t
(Sec) was measured. -Evaluation criteria Scale symbol Remark t ≤ 20 ◎ Immediate indentation marks disappear 20 <t ≤ 60 ○ It takes time but the marks disappear completely. Up to this level, the value as a product is recognized.

60 <t ≦ 100 △ Traces do not disappear easily, and you can see the traces when you look closely 100 <t × The traces remain completely (8) Packability / method Omori Machinery Co., Ltd. linear stretch ST is a packaging machine
With -7000 (normal specifications), the following three types of foam trays made by Chuo Kagaku Co., which are loaded with 200 g of clay, are packed at a packing speed of 50 packs / minute, and the finished state is observed 10 seconds after the completion of packing. did.

C-27: 330 × 98 × 12 (mm) ... Packaging is the most difficult. C-12: 281 x 131 x 22 (mm) ... Packaging property is between the upper and lower sides SK-20F: 194 x 155 x 30 (mm) ... Packaging is the easiest.・ Evaluation criteria Scale symbol Remarks 3 types of trays can be packaged without wrinkles ◎ Trays with difficult shapes can be used 2 types of trays can be packaged without wrinkles ○ Normal use level 1 type of tray Can be packaged without wrinkles. Can be used only for easy packaging. Has all wrinkles remaining. × Not suitable for practical use. (9) Gloss (5) ・ Method 60 degree mirror surface according to JIS K7105. Gloss (G)
Was measured.・ Evaluation Criteria Scale Symbol Remark G ≧ 150% ◎ High gloss 140% ≦ G <150% ○ Practically no problem level 130% ≦ G <140% △ Inferior light level 130% ≦ G × Poor gloss and no commercial value (10) Anti-fog property ・ Method Put 200 g of pork loin slice on PSP tray FS-B5 made by Chuo Kagaku Co., wrap with film and open showcase at around 5 ℃ It was displayed for one day and then observed.・ Evaluation criteria Scale symbol Remarks Water film is uniform and contents look neat ◎ Suitable for practical use Large water drops are visible when viewed carefully ○ Above practical level Contents appear distorted by water drops △ Not suitable for practical use Is white and the inside cannot be seen. (11) Dirt impact strength-Method Measured in accordance with ASTM D-1709. The measurement is 2
It is performed at 3 ° C. in an environment of 50% RH, and when a dart of a certain weight is dropped 20 times and ruptured 10 (50%) times, it is represented by the product of the weight and the height at that time.

[0038]

EXAMPLES First, the polymers used in this example are shown below. EVA: ethylene-vinyl acetate copolymer [vinyl acetate group content = 14% by weight, MI = 1.0 g / 10 minutes, melting point =
90 ° C.) IPP: isotactic polypropylene [Density = 0.
900 g / cm ³ , MI = 2 g / 10 min, melting point = 163
° C] -PB-1: butene-1-propylene copolymer [density =
0.900 g / cm ³ , MI = 1.0 g / 10 min, melting point = 71 ° C.)-VL1: ethylene-octene-1 copolymer [octene-1 content: 25% by weight, density = 0.868 g / cm ³ ,
MI = 0.5 g / 10 minutes, melting point = 56 ° C., Vicat softening point ≦ 40 ° C., Mw / Mn = 2.7, MIR = 38 (Equivalent to ENGAGE.EG8150 manufactured by Dow Chemical Co.)]-VL2: ethylene-propylene Copolymer [propylene: 15 mol%, ethylidene norbornene: 3% by weight,
Density = 0.880 g / cm ³ , MI = 0.4 g / 10
Min, melting point = 40 ° C., Vicat softening point ≦ 40 ° C., Mw / M
n = 2.5, MIR = 21] VL3: ethylene-butene-1 copolymer [butene-
1:12 mol%, density = 0.890 g / cm ³ , MI =
3.6 g / 10 minutes, melting point = 40 ° C., Vicat softening point = 5
0 ° C., Mw / Mn = 3.7, MIR = 35] VL4: ethylene-propylene-butene-1 copolymer [propylene: 17 mol%, butene-1: 9 mol%, density = 0.860 g / cm ³ , MI = 1.7 g / 10 minutes,
Melting point = 67 ° C., Vicat softening point ≦ 40 ° C., Mw / Mn =
2.5, MIR = 25] VL5: ethylene-octene-1 copolymer [octene-1: 8 mol%, density = 0.863 g / cm ³ , MI =
1.5 g / 10 minutes, melting point = 51 ° C., Vicat softening point ≦ 4
0 ° C., Mw / Mn = 2.7, MIR = 33] VL6: ethylene-octene-1 copolymer [octene-1: 8 mol%, density = 0.865 g / cm ³ , MI =
2.5 g / 10 min, melting point = 53 ° C., Vicat softening point ≦ 4
0 ° C, Mw / Mn = 2.5, MIR = 33] VL7: ethylene-butene-1 copolymer [butene-
1:16 mol%, density = 0.867 g / cm ³ , MI =
3.0 g / 10 minutes, melting point = 48 ° C., Vicat softening point ≦ 4
0 ° C., Mw / Mn = 2.5, MIR = 20] VL8: ethylene-octene-1 copolymer [octene-1 content: 22% by weight, density = 0.875 g / cm ³ ,
MI = 3.0 g / 10 minutes, melting point = 67 ° C., Vicat softening point ≦ 40 ° C., Mw / Mn = 2.7, MIR = 35 (Equivalent to ENGAGE KC8852 manufactured by Dow Chemical Co.)] VL9: ethylene-octene -1 copolymer [octene-1: 6 mol%, density = 0.880 g / cm ³ , MI =
1.0 g / 10 minutes, melting point = 72 ° C., Vicat softening point ≦ 4
0 ° C., Mw / Mn = 2.7, MIR = 30] VL10: ethylene-butene-1 copolymer [butene-
1:10 mol%, density = 0.882 g / cm ³ , MI =
3.0 g / 10 minutes, melting point = 68 ° C., Vicat softening point ≦ 4
0 ° C., Mw / Mn = 2.5, MIR = 17] VL11: ethylene-butene-1 copolymer [butene-
1 content: 9 mol%, density = 0.85 g / cm ³ , MI
= 2.2 g / 10 minutes, melting point = 66 ° C., Vicat softening point ≦
40 ° C., Mw / Mn = 2.5, MIR = 16 (EXACT4021 equivalent product manufactured by Exxon)] VL12: ethylene-propylene copolymer [propylene: 10 mol%, density = 0.886 g / cm ³ , MI =
3.6 g / 10 minutes, melting point = 60 ° C., Vicat softening point ≦ 4
0 ° C., Mw / Mn = 3.2, MIR = 17]

[0039]

Example 1 The X layer was composed of an ethylene-α.olefin copolymer containing 20% by weight of VL1 and 65% by weight of EVA and I.
A layer in which 2% by weight of diglycerin oleate (Rikemar O-71D manufactured by Riken Vitamin Co.) was added to a composition obtained by blending 10% by weight of PP and 5% by weight of PB-1, and the Y layer was 80% by weight of IPP. % And 20% by weight of PB-1 in the composition layer, the Z layer is EVA with 1% by weight of diglycerin laurate (L-71D manufactured by Riken Vitamin Co.).
Each layer was added as Z / X / Y / X / Z (= 10).
% / 35% / 10% / 35% / 10%) was extruded from a circular multi-layer die into a 5-layer structure, and the extruded laminate was
It was rapidly cooled with cold water of ℃ and folded to obtain a raw fabric having a thickness of 50 μm. Here, sodium oleate was applied to the inner surface of the raw fabric tube (dry weight: about 2 mg / m ² ). Air is injected into the folded original fabric to form a tube, which is heated to 50 ° C and cooled in the longitudinal direction (TU by cooling with 15 ° C air).
(R) 2.5 times and transverse direction (BUR) 4.5 times, and stretched by a roll type deflator with an opening of 60 °, and the speed ratio of the deflator to the main pinch roll is 0.90. I took it with a roll. Next, the film was heat-treated at a temperature of 60 ° C. and a relaxation rate of 10% in length and 20% in width, and both ends of the film were cut and wound into two films. The final magnification of the film was about 2.0 times the length and about 2.1 times the width, and the thickness of the final film was adjusted to 11 μm (Experiment No. 1). The obtained film was evaluated for shrinkage rate, recovery rate (L2, ΔL), indentation recovery property, wrapping property, and glossiness by the methods described in the text.

[0040]

[Comparative Example 1] The ethylene-α / olefin copolymer used in the X layer was prepared using VL2 (Experiment No. 2) and VL3 (Experiment N).
o. 3) and VL4 (Experiment No. 4) were changed, and the same experiment as in Example 1 was repeated. In addition, the experiment No. 2 and Experiment No. The ethylene-α-olefin copolymer used in 3 corresponds to the copolymer described in JP-B-2-52624.

The above experiment No. 1-Experiment No. The evaluation results of the film No. 4 are shown in Table 1. In addition, Table 1 also shows the physical properties of the ethylene-α.olefin copolymer used for the X layer (described as physical properties of the copolymer in the table). Further, FIG. 1 is an experimental diagram in which the recovery rates of the above four kinds of films were measured and plotted over time in accordance with the recovery rate measurement method described in the text.

The experiment is performed in the cutting step (step (a) in FIG. 1).
Assuming that, the recovery rate of the film when the film was opened immediately after being stretched by 10% in the machine direction was measured over time. In FIG. 1, the film 1 of the present invention (Experiment No. 1 of Example 1) is marked with a star, and the conventional multilayer film 2 (Comparative Example 1) is shown.
Experiment No. (Corresponding to 2) is indicated by a circle, and Experiment N of Comparative Example 1 is performed.
o. The film 3 of No. 3 is shown by Δ, and the film 4 having a small recoverability (Experiment No. 4 of Comparative Example 1) is shown by □.

The film 1 of the present invention (Experiment No. 1) was L
2 is as small as 93%, ΔL (saturation recovery rate-L2) is as large as 7%, and 100% recovery is achieved, so that both wrinkle recovery and indentation recovery are excellent. On the other hand, in the conventional multilayer film 2 (Experiment No. 2), L2 was as large as 99%, and large slack wrinkles occurred in all trays in actual packaging.

Experiment No. The film 3 of No. 3 has a small ΔL of 2%, and has an experiment number. No slack wrinkles as in Film 2 of 2 were generated, but small wrinkles remained in all the trays. Furthermore, film 4 with a low recovery rate (Experiment No. 4)
The saturation recovery rate was 94%, and the indentation recovery property was poor. Therefore, it is understood that the film having the recovery characteristics like the film of the present invention can satisfy both the wrinkle recovery property and the indentation recovery property for the first time.

The above experiment No. 1 to No. Dart impact strength of films 1 to 4 is 14.0 kg in order
・ Cm, 12.0 kg ・ cm, 11.0 kg ・ cm, 1
It is 3.5 kg · cm, and the antifogging property is “◎” in order.
“O”, “⊚”, “O”, strength and antifogging property maintained the characteristics of the conventional multilayer film 2 (Experiment No. 2).

[0046]

[Example 2] As an ethylene-α / olefin copolymer for the X layer, in place of VL1 used in Example 1, the experiment No.
5 is VL6, and the experiment No. No. 6 is VL8, and Experiment No. 7
To VL10, the experiment No. The same experiment as in Example 1 was repeated except that VL11 was replaced with VL11 to obtain a film having a thickness of 11 μm.

[0047]

Comparative Example 2 Instead of VL1 used in Example 1 as the ethylene-α / olefin copolymer for the X layer, Experiment N was used.
o. No. 9 is VL4, and experiment No. 10 for VL7, experiment N
o. No. 11 is VL9, and experiment No. No. 12 was replaced with VL12, and the same experiment as in Example 1 was repeated to obtain a thickness of 11 μm.
Was obtained.

The above experiment No. 5 to Experiment No. Table 1 shows the evaluation results of 12 films. Further, FIG. 2 shows an analysis diagram of the experimental results of the present invention. The melting point is plotted on the vertical axis and the density is plotted on the horizontal axis, which is plotted in relation to the physical properties of the resin used in the evaluation of the experimental results (packing property, indentation recovery property) shown in Table 1. The symbol "◎" satisfies both wrapping property (wrinkle recovery) and indentation recovery. The symbol "xB" indicates excellent wrapping property but poor indentation recovery, and symbol "xA". The mark indicates that the indentation recovery is excellent, but the wrapping property is poor.

The ethylene-α / olefin copolymer used in the present invention has a "density of 0.865 to 0.885 g /
cm ³ and melting point of 50 to 70 ° C. ”will be described. As is clear from FIG. 2, it can be seen that the region satisfying both the packaging property and the indentation recovery property can be separated by a line. That is, the density is 0.865 g / cm ³ or more and 0.885 g / cm ³ or more.
Area below g / cm ³ and melting point above 50 ° C and 70 ° C
The areas are as follows:

First, when the melting point is less than 50 ° C., the experiment No.
No. 2 had L2 of 99%, and the experiment No. 10 is 98% and L2 is 9
Greater than 5%, resulting in slack wrinkles on all trays. Then if the density is less than 0.865 g / cm ³ ,
Experiment No. 3 has ΔL of 2%, and the experiment No. 9 has ΔL of 1%
And remained at less than 3%, and as a result, small wrinkles remained on all trays.

When the density is higher than 0.885 g / cm ³ or the melting point is higher than 70 ° C., the recovery rate of saturation is the same as that of Experiment No. No. 4 is 94%, and the experiment No. No. 11 is 96%, Experiment No. No. 12 was 98%, which did not reach 100%, and as a result, indentation recovery was poor. Therefore, the ethylene-α-olefin copolymer used in the present invention has a density of 0.865-
It can be seen that the melting point needs to be 0.885 g / cm ³ and the melting point is 50 to 70 ° C.

Next, it will be described that the copolymer preferably has Mw / Mn of 3 or less and MIR of 25 to 40. Experiment No. In 1, the copolymer has Mw / Mn of 2.7.
The MIR is 38, and the glossiness of the film is “◎” (1
55%), while the experimental No. 3 is the polymer M
When w / Mn was as large as 3.7, the glossiness of the film was inferior to "x" (125%), and the test No. 6 has a small MIR of 17, and the glossiness of the film is "△" (13
5%).

Therefore, it is understood that the Mw / Mn of the copolymer is 3 or less and the MIR is 25 to 40 for the gloss of the film. In addition, the above experiment No.
5-No. The dart impact strength of the film No. 12 was about 13.5 kg · cm, and the antifogging property was “⊚”, and the strength and the antifogging property maintained the characteristics of the conventional multilayer film (Experiment No. 2).

[0054]

[Comparative Example 3] The blend ratio of the resin in the X layer was set to VL1 /
The same experiment as in Example 1 was repeated except that the EVA / PP / PB-1 was changed to 0/85/10/5 (wt%), but the bubble was torn during stretching and a film could not be obtained ( Experiment No. 13). Also, as the X layer, diglycerin rate was added to VL1 (Rikemal O- manufactured by Riken Vitamin Co., Ltd.
The same experiment as in Example 1 was repeated except that the layer containing 71%) was added in an amount of 2% by weight, but the bubbles were not stable and only a sample of about several meters was obtained.

Therefore, in order to obtain the film of the present invention, specifically, the film having a shrinkage ratio of 20 to 50% at 80 ° C., ethylene-α.multidot.e as a polyolefin elastomer having a Vicat softening point of 60 ° C. or less. The olefin copolymer must be contained in the X layer in an amount of 5% by weight or more and 90% by weight or less.

[0056]

[Table 1]

[0057]

According to the present invention, the conventional multi-layer film having a shrinkage rate of 20 to 50% at 80 ° C., which has excellent properties such as anti-fogging property, optical property, and strength, is maintained,
Satisfies the two required characteristics: "Recovery that does not leave wrinkles when wrapped in a straight stretch wrapping machine (wrinkle recovery)" and "Recovery against dent deformation when a finger or the like is pushed in (indentation recovery)" This makes it possible to obtain a film suitable for stretch wrapping machines, especially for straight stretch wrapping machines.

[Brief description of drawings]

FIG. 1 is an experimental view showing the characteristics of the film of the present invention.

FIG. 2 is an analysis diagram for determining the scope of the present invention.

FIG. 3 is a process conceptual diagram of continuously packaging an object to be packaged with a linear stretch wrapping machine.

[Explanation of symbols]

 Experiment No. 1 Film No. 1 Experiment No. 2 Film No. 2 Experiment No. 3 Film No. 3 4 Experiment No. Film No. 4 5 Experiment No. Film No. 5 6 Experiment No. Film No. 6 Experiment No. 7 Film No. 7 Experiment No. 8 Film No. 8 Experiment No. 9 Film No. 9 Experiment No. 10 Film No. 10 Experiment No. 11 Film No. 11 Experiment No. 12 12 films (1) Items to be packaged (2) Film (3) Cutter blade (4) Wrinkles (5) Rear folding device (6) Front folding device (7) Arrow

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Claims (2)

[Claims] 1. The surface layer (Z layer) and a polyolefin-based elastomer having a Vicat softening point of 60 ° C. or lower are 5 to 90.
A polyolefin resin multi-layer stretch packaging film having at least 4 layers of a stretching assist layer (X layer) and a core layer (Y layer) made of a mixed resin containing 20% by weight, and having a shrinkage rate of 20 to 50% at 80 ° C. The density of the polyolefin-based elastomer contained in the X layer is 0.865.
A film for polyolefin resin multilayer stretch packaging, which is an ethylene-α-olefin copolymer having a melting point of 50 to 70 ° C and a melting point of 0.885 g / cm ³ . 2. The ethylene-α.olefin copolymer used in the X layer has an Mw (weight average molecular weight) / Mn (number average molecular weight) of 3 or less and an MIR represented by the following formula of 25 to 40. The polyolefin resin multilayer stretch packaging film according to 1. MIR = HMI / MI (1) (where MI is 19 in accordance with JIS K7210)
Melt flow rate measured under conditions of 0 ° C. and a load of 2.16 kg. The HMI is a value measured under a load of 21.6 kg among the measurement conditions of the MI. )