JPH07314618A - Multilayered shrink film and production thereof - Google Patents

Abstract

PURPOSE:To eliminate the imperfection of the packaging aptitude of a film subjected to shrink packaging and reduce the cost by forming a core layer composed of a specific resin and a coating layer composed of a specific resin and setting the heat shrinkage factors within a specific temp. range and heat shrinkage stresses at the time of heat shrinkage of them to definite values or less. CONSTITUTION:A multilayered shrink film is obtained from a core layer composed of a mixture prepared by mixing 0-30 pts.wt. of an ethylene/vinyl acetate copolymer with vinyl acetate content of 5-30wt.% with 100 pts.wt. of an alpha-olefin/ propylene copolymer with alpha-olefin content of 1-7wt.% and propylene content of 99-93 wt.% and a coating layer composed of an ethylene/vinyl acetate copolymer. The heat shrinkage factors at 80 and 110 deg.C of the multilayered shrink film are respectively set to 10-30% and 40-60% and the heat shrinkage stresses at the time of heat shrinkage thereof are respectively set to 20kgf/cm<2> or less. By this constitution, heat-shrinking work can be performed while the effect on an article to be packaged is minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-layer shrink film which is used for various packaging such as pallet packaging and which is used as a packaging film, especially for food packaging. A heat-shrinkability / heat-sealing property, which comprises a core layer made of a mixture of a polymer and an ethylene-vinyl acetate copolymer in a specific ratio and a coating layer made of an ethylene-vinyl acetate copolymer.
The present invention relates to a multilayer shrink film having excellent recyclability and low cost, and a method for producing the same.

[0002]

2. Description of the Related Art As an example of the use of a food packaging film, various packaging films have been used as a prepackaging form for foods which is widely used in supermarkets and the like today. Stretch wrapping and shrink wrapping are mainly used. In both of these wrapping methods, food may be directly wrapped with a film, but so-called tray wrapping using a tray as a container is mainly used. The stretch wrapping is a process of stretching a wrapping film and wrapping the film in a tensioned state, and is widely used as a wrapping with excellent wrinkles and sagging and a good fit. The film used for this stretch packaging is plasticized polyvinyl chloride (hereinafter PVC).
A film whose main component is a so-called wrap film is widely known. This wrap film has excellent packaging suitability and beautiful packaging finish such as easy stretchability, excellent transparency, luster, moderate water vapor permeability, gas permeability, and wide range of heat seal temperature. It is widely used because it has it.

On the other hand, the shrink wrapping is a wrapping that utilizes the heat shrinkage property of the film. The shrink wrapping is performed by loosely wrapping an object to be wrapped in advance and then passing through a heating tunnel at about 100 ° C. to heat shrink the film. The finish is tight. As the film provided for this method,
Shrink films, which are made of PVC as a main component and have heat-shrinkability, are widely used. As a method of imparting heat shrinkability to this film, there is a film which is stretched at least monoaxially. The shrink film containing PVC as a main component is characterized in that it can be packaged under a low temperature condition for an object to be packaged (fresh food etc.) because it can obtain heat shrinkage at a relatively low temperature.

As described above, a film containing PVC as a main component has been widely used as a packaging film used in a prepackage. Further, the fact that the price of the film containing PVC as the main component is low was a major factor in its widespread use. The film containing PVC as a main component is a single-layer film having a single composition, and the fact that scrap can be recycled in the manufacturing process has greatly contributed to the realization of low cost.

However, in recent years, stretch films and shrink films containing PVC as a main component have a sanitary problem due to the inclusion of a plasticizer, and chlorine such as hydrogen chloride is used when the packaging machine is melted by heat rays or when used films are incinerated. Generating system gas is a problem, and in terms of functionality, frozen packaging tends to increase with increasing demand for frozen foods, but due to poor cold resistance, the film becomes brittle and ruptures and cracks occur, especially during transportation. The problem is that it is not possible to impart sufficient resistance to vibration and impact in the stage.

In order to solve these problems, in recent years,
For the purpose of substituting a stretch film and a shrink film containing PVC as a main component, a film containing a so-called polyolefin resin as a main component has been developed and proposed. On the other hand, with regard to containers used for pre-packages, so-called trays, there are increasing demands for solving problems as waste and recycling. Materials used for this tray include expanded polystyrene (expanded polystyrene, high-impact polystyrene, biaxially oriented polystyrene), polypropylene, and a mixture of polypropylene and a filler such as calcium carbonate, and this foam. However, in order to solve the above-mentioned problems and to reduce the packaging cost, a tray having a small wall thickness is used. The thin tray naturally has a lower strength than the normal thick tray, and therefore, depending on the characteristics of the film used in stretch packaging and shrink packaging, the tray may be broken during the packaging or the heat shrinkage stress of the film. If it is inappropriate, the tray may be twisted or warped after packaging, and a satisfactory packaging finish may not be obtained. Therefore, there is an increasing demand for the development of a polyolefin film having suitability for packaging such a thin tray.

Further, the price of various polyolefin films proposed so far is as high as 2 to 3 times that of PVC film, so that the case used as a packaging material is small. The reason why this film is expensive is that it is impossible to recycle within the manufacturing process because various materials are combined in specific amounts in order to realize the characteristics of the film and are made into a multilayer and manufactured by a complicated manufacturing method. Etc. Therefore, cost reduction is required in addition to the above functions.

Hereinafter, several examples proposed for the purpose of substituting a film containing PVC as a main component will be described.
Among them, for the purpose of substituting a stretch film, for example, in JP-A-53-6194, an ethylene-vinyl acetate copolymer is used as both outer layers and an inner layer is a polyolefin resin having a higher melting point than that, such as polypropylene or polyethylene. A film using is disclosed. However, this product has the effect of improving the heat-sealing property, but since it is simply a laminated film, the stretch required for the stretch film or the tension (tension) and elastic recovery of the film after packaging are small. However, the packaging finish was insufficient and could not replace the conventional stretch film containing PVC as the main component.

Further, Japanese Patent Publication No. 5-88663 discloses a film containing an ethylene resin as a main component and having a specific degree of cross-linking with a gel fraction, and a method for producing the film.
This aims to propose a polyolefin film having excellent stretchability by imparting stress-strain characteristics similar to those of a stretch film containing PVC as a main component. However, this requires practical control of the degree of cross-linking and the manufacturing method thereof, and it is difficult to realize the target stress-strain curve, which is a practical problem. Furthermore, a specific gel fraction is required in order to achieve the desired stress-strain characteristics. That is, when the scrap generated at the manufacturing stage is recycled to the manufacturing process because it contains a non-melting component as a component, perforation and tearing of the film at the time of stretching due to the inclusion of unmelted substances and its influence occur, and the original fabric When it is manufactured in a tube shape, it cannot be recycled because it is so punctured that it cannot be molded, and its manufacturing cost is more than twice as high as that of a stretch film containing PVC as a main component. It is said to be difficult to put into practical use as a material. in this way,
When a polyolefin film is used for stretch wrapping, due to the characteristics of polyolefin resin, PVC
It is extremely difficult to exert the stress and strain characteristics of a film containing as a main component, and it is necessary to provide a shrink characteristic to substitute for stretch packaging.

On the other hand, regarding a polyolefin-based shrink film intended to replace a shrink film containing PVC as a main component, for example, Japanese Patent Publication No. 1-47311 discloses that a layer containing a specific mixed resin component is provided under specific conditions. Disclosed is a cold-oriented film, which is cold-stretched under the following conditions, and whose heat shrinkage stress value and tensile strength are specified. However, this is highly oriented and highly stretched like the one proposed in the above-mentioned Japanese Patent Publication No. 5-88663, which is a conventional example, in order to obtain desired heat shrinkage stress and tensile strength. Is one that requires a specific gel composition by subjecting a specific mixed composition and components to energy ray treatment. That is, when scrap generated in the production stage containing non-melting components is recycled, perforation and tearing of the film during stretching due to the inclusion and influence of unmelted matter occur, and when the original fabric is produced in a tube shape, It is said that it is impossible to recycle because it is so-called punctured and cannot be molded, and its manufacturing cost is about twice or more that of shrink film containing PVC as a main component, and it is said that it is difficult to use as a packaging material. ing. Furthermore, since this is highly oriented and highly stretched, it has a problem that it is not suitable for a packaging method using a thin tray having a high heat shrinkage stress. Further, this manufacturing method is a method of rapidly cooling and solidifying a resin extruded from a multi-layer die with a liquid refrigerant, but in this cooling method, the refrigerant adheres to the film surface of the film formed, and the film is not sufficiently dried and removed. However, it is difficult to raise the line speed and the productivity is low in order to perform sufficient drying as a countermeasure against it.

In Japanese Patent Publication No. 5-64589, ethylene-
A three-layer crosslinked film composed of a vinyl acetate copolymer and polyethylene and a method for producing the same have been proposed. However, this requires electron beam cross-linking treatment in order to obtain the target film characteristic values, and therefore it is also impossible to recycle in the manufacturing process, resulting in high manufacturing cost and product price and practical use. It is a problem above. In addition, since the manufacturing method is performed in a continuous process of coextrusion → cooling and solidification → electron beam irradiation → heating → stretching, control in each step is extremely important, but variations in each condition affect film quality. There is a problem that it is easy to do.

Further, JP-A-5-318682 discloses a stretch-shrink packaging in which an ethylene-propylene copolymer or an ethylene-butene-propylene copolymer is used as a core layer and both outer layers thereof are linear low density polyethylene. A film has been proposed. This is characterized by a high recovery elastic modulus and no odor of acetic acid. However, since the linear low density polyethylene is used for both outer layers, the heat sealing property is lowered. However, in order to achieve the desired recovery elastic modulus, high heat shrinkage stress is required, and packaging suitability for a thin tray cannot be obtained. Further, if the thickness of the linear low-density polyethylene, which is the outer layer, is increased, the strength of the film is reduced, which is disadvantageous in that it is suitable for an automatic wrapping machine, and in particular, rupture of the film is likely to occur during high-speed packaging.

[0013]

SUMMARY OF THE INVENTION As described above, the present invention solves the problems of the conventional polyolefin film, particularly the film used for shrink packaging having heat shrinkage property, which is the problem of packaging suitability and high cost. The purpose is to do. That is, in the present invention, the α-olefin content excluding propylene is 1 to 7% by weight, and the propylene content is 99 to 9
A core layer comprising a mixture of 0 to 30 parts by weight of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 5 to 30% by weight, and 100 parts by weight of an α-olefin-propylene copolymer of 3% by weight, and the ethylene. A coating layer made of a vinyl acetate copolymer, having a heat shrinkage ratio at a temperature of 80 ° C. and 110 ° C. of 10 to 30% and 40 to 60%,
A shrink film having a heat shrinkage stress of 20 kgf / cm ² or less during heat shrinkage, and having an α-olefin content of 1 to 7% by weight except propylene,
The ethylene-vinyl acetate copolymer having a vinyl acetate content of 5 to 30% by weight is added to 100 parts by weight of the α-olefin-propylene copolymer having a propylene content of 99 to 93% by weight.
˜30 parts by weight of a mixture of a core layer and a coating layer of the ethylene-vinyl acetate copolymer are coextruded from an annular die at a resin temperature of 170 to 240 ° C. to form an inner mandrel portion of the annular die. The molten resin coextruded inside and outside by the internal cooling air from the internal cooling cylinder provided at the tip and the external cooling air from the external cooling cylinder mounted around the internal cooling cylinder in front of the out die portion of the annular die. After being rapidly cooled to 60 to 120 ° C from both sides and started up with the annular die diameter kept, the blow ratio was continuously increased to 2.0 to 15.0.
The method for producing a multilayer shrink film according to claim 1, wherein the method is up.

[0014]

First, the manufacturing method of the present invention will be described with reference to FIGS. FIG. 1 is an example of a manufacturing apparatus used in the manufacturing method of the present invention, and FIG. 2 is a partially enlarged view of FIG. In the production method of the present invention, as described above, the core layer and the coating layer having a specific composition are co-extruded from the annular die 2 at a resin temperature of 170 to 240 ° C., and the inner mandrel portion 2 ′ of the annular die 2 is extruded. Internal cooling air 5'from the internal cooling tube 3 provided at the tip and external cooling air 6'from the external cooling tube mounted around the internal cooling tube 3 in front of the out die portion 2 "of the annular die 2. According to the method, the coextruded molten resin is rapidly cooled to 60 to 120 ° C. from both inside and outside, and is started up with the annular die diameter, and then continuously blown up to a blow ratio of 2.0 to 15.0. Is.
This will be described in more detail with reference to FIGS.

As the apparatus of the manufacturing method of the present invention, first,
Or 3 extruders 1 and 1 '(1 "is not shown) are installed, one of which has an α-olefin content of 1 to 7 wt% excluding propylene as a resin for the core layer, and a propylene content of 100 parts by weight of α-olefin-propylene copolymer, which is 99 to 93% by weight, and a vinyl acetate content of 5 to 3
A mixture comprising 0 to 30 parts by weight of an ethylene-vinyl acetate copolymer of 0% by weight was supplied, and another extruder used an ethylene vinyl acetate copolymer having a vinyl acetate content of 5 to 30% by weight as a resin for the surface layer. It is supplied by extrusion.

In the extruder for supplying the core layer, the film scrap generated by the manufacturing method of the present invention is
Content of ethylene-vinyl acetate copolymer of mixed resin is 0
It is also possible to extrude and feed the mixed mixed resin, which is weighed to be about 30 parts by weight. The resin supplied by extrusion is superposed on the coating layer / core layer / coating layer in the annular die 2 and coextruded into a tube shape. This device comprises an internal cooling cylinder 3 provided at the tip of an inner mandrel portion 2'of the annular die 2 and an external cooling device provided around the internal cooling cylinder 3 in front of the outer die portion 2 "of the annular die 2. Cooling tube 4
Is equipped with. The internal cooling cylinder 3 and the external cooling cylinder 4 are provided with the molten resin A coextruded from the annular die 2 and the annular die 2.
It is provided at the position and size where it can be raised in a tube shape with the diameter of. The molten resin A co-extruded in a tube shape from the annular die 2 is passed between the inner cooling cylinder 3 and the outer cooling cylinder 4. The internal cooling cylinder 3 is provided with a plurality of stages 5 for blowing internal cooling air 5'for cooling the molten resin A. On the other hand, the external cooling cylinder 4 has an external cooling air 6'at the bottom.
Of the internal cooling air 5'of the internal cooling cylinder 3 and a plurality of partitions 7 at positions facing the outlet 5 of the internal cooling air 5 '. Further, the position of the internal cooling cylinder 3 is higher than that of the external cooling cylinder 4.

Therefore, the molten resin A coextruded from the annular die 2 is passed through the gap between the inner cooling cylinder 3 and the outer cooling cylinder 4 with the diameter of the die being substantially the same as that of the annular die 2. At this time, the molten resin A is rapidly cooled by the internal cooling air 5 ′ and the external cooling air 6 ′ blown out from the internal cooling air outlet 5 of the internal cooling cylinder 3 and the external cooling air outlet 6 of the external cooling cylinder 4, respectively. , Tube-shaped original fabric T. The molten resin is co-extruded in the temperature range of 170 ° C to 240 ° C, and is cooled to 60 ° C to 120 ° C by the internal and external cooling air 5'and 6'by each cooling cylinder, while standing in an almost annular die diameter. can give. At this time, the inner and outer cooling airs 5'and 6'are blown onto the tube-shaped raw fabric T made of molten resin from both inside and outside, so that the diameter of the tube-shaped raw fabric T can be kept constant and stable. This is a major feature of the manufacturing method of the present invention. here,
If the temperature of the molten resin at the time of co-extrusion is less than 170 ° C., the melting of the resin will be incomplete, the transparency of the resulting film will decrease, and thickness unevenness will occur. The resulting film becomes unstable due to the occurrence of burns and the like, the finished film does not have the desired strength, and pinholes are likely to occur. This cooling effect and dimensional stability enable the stretching effect in the subsequent stretching step to be effectively and stably exhibited.
In order to exert this effect, it is necessary to cool the resin below the melting point or the Vicat softening point, so that the tube-shaped original fabric T
Is 60 ° C to 120 ° C until reaching the upper end of the external cooling cylinder 4.
It is preferable to cool to 70 ° C.
It is 80 ° C. Here, the temperature of the tube-shaped original fabric T is 12
If it is higher than 0 ° C, the melting point of the molten resin will be exceeded, and the stretching effect in the subsequent stretching step cannot be obtained. If it is lower than 60 ° C, the melt tension that can be stretched in the stretching step will be exceeded, and the stretching It becomes difficult, and further, by cooling with the annular die diameter, it becomes possible to take out the coating layer and the core layer at a uniform withdrawal rate. The tube-shaped original fabric T cooled to the above temperature condition has a partition 7 at the upper end of the external cooling cylinder 4.
When the tube-shaped original fabric T reaches the position of, the original fabric T is formed by the air pressure in the original fabric and the air flow generated when the air blown out from the external cooling cylinder 4 diffuses into the atmosphere. It expands rapidly and is blown up with a blow ratio in the range of 2.0 to 15.0. A stretching effect can be obtained by the change in the tube diameter. The blow ratio is in the range of 2.0 to 15.0, preferably 4.0 or more, more preferably 6.0.
It is sufficient that the above is 15.0 or less. If the blow ratio is less than 2.0, the stretching effect cannot be obtained, and conversely, if the blow ratio exceeds 15.0, the stretching becomes high, which exceeds the target range of the heat shrinkage stress, and the thickness at the time of molding is further increased. Variation easily occurs, causing inconvenience such as flat tire. The tube-shaped original fabric T thus stretched is folded by the pinch roll 9 to obtain a flat original fabric T ′. The original fabric T ′ is passed through a take-up machine 10 and divided into upper and lower parts by a take-up machine 11 to be wound up as three-layer films P and P ′. Further, the internal cooling air 5 ′ and the external cooling air 6 ′ are preferably temperature-controlled as appropriate in order to exert their cooling effect.

Next, the film of the present invention will be described.
In the film of the present invention, the core layer thereof has an α-olefin content other than propylene of 1 to 7% by weight, and a propylene content of 99 to 93% by weight.
A mixture of a propylene copolymer and an ethylene-vinyl acetate copolymer is preferably used, among which α-olefin-
The α-olefin used in the propylene copolymer includes ethylene, butene-1, hexene-1, pentene-1, 4-methyl-pentene-1, isopentene-1,
Heptene-1, octene-1, isooctene-1, nonene-1, decene-1, undecene-1, dodecene-1 and the like are mentioned, and among these, alone or at least 2
Although it is used as a mixture of seeds, ethylene or butene-1 is preferably used alone or as a mixture thereof, for example, 1 to 2% of ethylene and 5 to 1 of butene-1.
Those containing 6% are preferably used, and ethylene alone is most preferable. The film of the present invention preferably has a flexural modulus of 5,000 to 17,000 kgf / cm ² , more preferably 7,000 to 12,000.
Those of 0 kgf / cm ² are suitable for obtaining the characteristics of the film, particularly the desired heat shrinkage characteristics. The MFR of the resin used in the film of the present invention is 0.4 to 10.0 g /
min, preferably 0.5 to 2.0 g / min. If the MFR is less than 0.4 g / min, the film is too soft, and it is difficult to obtain the desired heat shrinkage, and if it exceeds 10.0 g / min, the film becomes hard and the film may be stretched. It is easy to become difficult.

Further, α-olefin-propylene copolymers include so-called random copolymers and block copolymers, but random copolymers are preferred because the transparency of the film becomes high. The ethylene-vinyl acetate copolymer is of the same quality as the ethylene-vinyl acetate copolymer constituting the coating layer of the film of the present invention, and specifically, one having a vinyl acetate content of 5 to 30% by weight is preferable. , And more preferably 7 to 15% by weight. This MFR is 0.
4 to 10.0 g / min, preferably 0.5 to 2.
It is 0 g / min. Further, the mixing ratio of the α-olefin-propylene copolymer and the ethylene-vinyl acetate copolymer is preferably 0 to 30 parts by weight of the ethylene-vinyl acetate copolymer with respect to 100 parts by weight of the α-olefin-propylene copolymer, It is more preferably 5 to 25 parts by weight. If the mixing amount of the ethylene-vinyl acetate copolymer is more than 30 parts by weight, the film formed will have a high tackiness, and the film will become sticky to reduce the packaging suitability, and the ethylene-vinyl acetate copolymer will not be contained. Then, recycling becomes impossible. Further, a nonionic surfactant may be used as an additive in the coating layer for the purpose of imparting slipperiness or antifogging property to the film surface. At least one selected from polyglycerin fatty acid ester, sorbitan fatty acid ester, and polyoxyethylene alkylphenyl ether is used for this, and the addition amount is 100 parts by weight of the above ethylene-vinyl acetate copolymer. 0.5
~ 15 parts by weight.

The film of the present invention has at least a three-layer structure, and a three-layer structure having a core layer and a coating layer on both surfaces of the core layer is preferably used, and the total thickness thereof is 5 to 20 μm, more preferably. It is 9 to 12 μm. The thickness of each layer is such that the thickness ratio between the core layer and the coating layer (core layer thickness: coating layer thickness) is 1:
It is 0.2 to 1: 4 and preferably 1: 0.4 to 1: 1. Further, another layer such as printing may be provided on the surface of the coating layer. Although the present invention uses the mixture of the α-olefin-propylene copolymer and the ethylene-vinyl acetate copolymer as the core layer as described above, the major feature of the present invention is slitting and generated in the manufacturing process. It is possible to collect and reuse scraps such as ears. That is, since the same quality as the ethylene-vinyl acetate copolymer used in the coating layer is mixed in the core layer, the resin composition constituting these core layers is used in the above range, and the layer composition of the above range. If the structure, the film formed by the manufacturing method of the present invention satisfies the target characteristic value and the adhesion between the coating layer and the core layer is improved, and the ears slit for trimming in the manufacturing process. It is possible to collect and reuse scraps that are generated in the production process in the manufacturing process.

Next, the characteristics of the film of the present invention will be described. The films obtained by the above resin composition and the production method of the present invention have heat shrinkage rates at temperatures of 80 ° C. and 110 ° C. of 10 to 30% and 40 to 60%, respectively,
The heat shrinkage stress during heat shrinkage is 20 kgf / cm ² or less. The heat shrinkage here is a value represented by the average value of the longitudinal rate and the lateral rate of the film, and the heat shrinkage stress at the time of thermal shrinkage causes the film of the present invention to undergo thermal shrinkage under the above temperature conditions. This is also the stress value, and this value is also expressed as the average value of the heat shrinkage stress in the machine direction and the transverse direction of the film. When these values are in the above range, the thickness is 0.1 to
When using a 0.6 mm thin tray, the desired packaging suitability is obtained. The heat shrinkage ratio is a heat shrinkage ratio that is practically necessary for tightly performing the packaging finish. Since this heat shrinkage ratio can be obtained at 80 ° C. and 110 ° C., the influence on the object to be packaged can be minimized. It is possible to perform heat shrinking work. Furthermore with the heat shrinkage stress maintains the tension of the film after packaging, which does not affect on the packaging container, its value is at 20 kgf / cm ² or less, particularly is 18 kgf / cm ² or less It is more preferably 15 kgf / cm ² or less. Especially when using a thin tray, 15 kgf /
The heat shrinkage ratio is preferably not more than cm ^2, and when the heat shrinkage ratio is in the above range, the effects thereof are combined to obtain good packaging suitability and finish.

[0022]

EXAMPLES The present invention will be described with reference to Examples and Comparative Examples.
The method for measuring the characteristic value of the film of the present invention will be described. Heat shrinkage rate: The average value of the shrinkage rates in the machine direction (MD direction) and the transverse direction (TD direction) of each test piece was defined as heat shrinkage rate [%] according to ASTM D-2732. Thermal contraction stress: A load sensor is equipped with a chuck, a test piece is mounted, and one of them is mounted on a fixed chuck, then immersed in an oil bath set to a predetermined temperature to measure the thermal contraction stress, and longitudinal stress and lateral stress are measured. The average value of (Example 1) Five kinds of 100 parts by weight of α-olefin-propylene copolymer having different α-olefin contents and 20 parts by weight of ethylene-vinyl acetate copolymer having a vinyl acetate content of 11% by weight were mixed. The mixture was used as a core layer raw material, and an ethylene-vinyl acetate copolymer having a vinyl acetate content of 11% by weight was used as a coating layer raw material. A film having an overall thickness of 10 μm and a core layer thickness of 5 μm was prepared. Film No. was formed according to the production method of the present invention. 1 to N
o. It was set to 5. Further, the films having the α-olefin content shown in Table 1 were designated as Comparative Example 1 and Comparative Example 2, respectively. In Comparative Example 1, the desired heat shrinkage was not obtained, and in Comparative Example 2, both the heat shrinkage and the heat shrinkage stress were too high.

(Example 2) Four examples are shown in which the vinyl acetate content in the ethylene-vinyl acetate copolymer was variously changed. No. 6-No. 9 is the film of the present invention. Further, the films having the α-olefin content shown in Table 2 were designated as Comparative Example 3, Comparative Example 4, and Comparative Example 5, respectively. Comparative Example 3 had a low heat shrinkage, and Comparative Examples 4 and 5 both had a high heat shrinkage and a high heat shrinkage stress. (Example 3) A case is shown in which the amount of ethylene-vinyl acetate copolymer added to the core layer (parts by weight) is changed. No.
10-No. 12 is the film of the present invention. Table 3
The film having the α-olefin content of 1 was designated as Comparative Example 6. In Comparative Example 6, both the heat shrinkage rate and the heat shrinkage stress were high.

(Example 4) The results of a packaging test using the films of Examples and Comparative Examples are shown below. The evaluation criteria are: 1) in which the tray is not deformed or cracked in the packaged state after heat shrinking of the film, 2) in which the film has no wrinkles or sagging in the packaging finish, and which satisfies 2 items. . 1) Any of the following items: 1) Tray deformation or cracking, 2) Insufficient heat shrinkage, 3) Wrinkles or slack in the film during packaging. Bad x. The results are shown in Table 4. It can be seen that the film of the example is superior to the film of the comparative example. Packaging machine used: Ibaraki Seiki STC = II. Material used: OPS (oriented, p
Polystyrene, PSP (poly)
styrene paper), PP, [numerical values in the table represent wall thickness (mm) of tray]. Items to be packaged: Kiyuri (packed in a pile on a tray). Tunnel temperature: 100 ° C. The above test results are shown in Tables 1 to 4. In the column of α-olefins in the table, when two kinds of α-olefins are mixed, the number in parentheses indicates the mixing ratio of α-olefins.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

[Table 4]

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of an example of an apparatus for producing a multilayer shrink film of the present invention.

FIG. 2 is a partially enlarged vertical cross-sectional sketch diagram of an example of a multilayer shrink film manufacturing apparatus of the present invention.

[Explanation of symbols]

1, 1'Extruder, 6'External cooling air, 2 Annular die, 7
Partition, 2'inner mandrel part,
8 pinch roll, 2 '' out die
9 take-up machine, 3 internal cooling tube, 10 winder, 4
External cooling tube, A molten resin, 5
Internal cooling air outlet, P, P'three-layer film, 5'Internal cooling air, T
Tube-shaped material, 6 External cooling air outlet, T'flat material.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B32B 27/08 8413-4F 27/32 103 8115-4F // C08L 23/08 LDJ B29K 23:00 B29L 9:00

Claims (2)

[Claims] 1. An α-olefin content excluding propylene 1 to
Mixing 0 to 30 parts by weight of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 5 to 30% by weight with respect to 7 parts by weight of an α-olefin-propylene copolymer having a propylene content of 99 to 93% by weight. And a coating layer composed of the ethylene-vinyl acetate copolymer, the heat shrinkages at temperatures of 80 ° C. and 110 ° C. are 10 to 30%, 40 to 60%, and the heat shrinkage at the time of heat shrinkage, respectively. A multilayer shrink film having a stress of 20 kgf / cm ² or less, respectively. 2. An α-olefin content excluding propylene 1 to
Mixing 0 to 30 parts by weight of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 5 to 30% by weight with respect to 7 parts by weight of an α-olefin-propylene copolymer having a propylene content of 99 to 93% by weight. The core layer made of the above mixture and the coating layer made of the ethylene-vinyl acetate copolymer are coextruded from the annular die at a resin temperature of 170 to 240 ° C.,
By internal cooling air from an internal cooling cylinder provided at the tip of the inner mandrel portion of the annular die and external cooling air from an external cooling cylinder mounted around the internal cooling cylinder in front of the out die portion of the annular die. , The co-extruded molten resin was rapidly cooled to 60 to 120 ° C. from both inside and outside, and was started up with the ring die diameter kept, and then continuously blow ratios of 2.0 to 15.
The method for producing a multilayer shrink film according to claim 1, wherein the blow-up is 0.