JP2798236B2 - Multi-layer shrink film and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art An example of the use of a food packaging film is as follows. As a food prepackage widely used today in supermarkets and the like, various packaging films are used. Stretch wrapping and shrink wrapping are mainly used. In both of these packaging methods, food may be directly wrapped with a film, but so-called tray wrapping using a tray as a container is mainly used. Stretch wrapping is a method of stretching a wrapping film and wrapping the film in a tensioned state, and is widely used as a wrapping with excellent fit without wrinkles or sagging. The film used for this stretch packaging is plasticized polyvinyl chloride (hereinafter referred to as PVC).
) As a main component, so-called wrap films are widely known. This wrap film has excellent packaging aptitude such as easy stretch of the film, excellent transparency, gloss, appropriate water vapor permeability, gas permeability, wide range of heat seal temperature, and beautiful packaging finish. Widely used because it has.

[0003] On the other hand, shrink wrapping is a wrapping utilizing the heat shrinkage of a film. After loosely wrapping an object to be wrapped in advance, the film is passed through a heating tunnel at about 100 ° C to shrink the film by heat. The finishing is done tightly. Films used in this method include:
Also, a shrink film having a heat-shrink property made of a film mainly composed of PVC is widely used. As a method for imparting heat shrinkability to the film, there is a method in which the film is stretched at least uniaxially. This shrink film containing PVC as a main component is characterized in that heat shrinkage can be obtained at a relatively low temperature, so that it can be packaged under low-temperature conditions for an article to be packaged (such as fresh food).

[0004] As described above, a film mainly composed of PVC has been widely used as a packaging film to be provided in a prepackage. In addition, the inexpensiveness of films containing PVC as a main component was a major factor in widespread use. The fact that the film mainly composed of PVC is a single-layer film having a single composition, and the recycling of scrap in the manufacturing process has greatly contributed to the realization of low cost.

However, in recent years, these stretch films and shrink films containing PVC as a main component have problems in hygiene due to the inclusion of a plasticizer, chlorine or hydrogen chloride or the like at the time of fusing by a hot wire of a packaging machine or incineration of a used film. The generation of system gases is a problem, and in terms of function, frozen packaging tends to increase as demand for frozen foods increases.However, due to poor cold resistance, the film becomes brittle, breaks, cracks, and is particularly damaged in transportation. The problem is that it is not possible to provide sufficient resistance to vibration and impact at the stage.

In order to solve these problems, in recent years,
For the purpose of replacing a stretch film and a shrink film containing PVC as a main component, a film containing a so-called polyolefin-based 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 is an increasing demand for solving problems as waste and recycling. As the material used for this tray, expanded polystyrene (expanded polystyrene, high-impact polystyrene, biaxially oriented polystyrene), polypropylene, a mixture of polypropylene with a filler such as calcium carbonate, and this foam are used. However, in order to solve the above-mentioned problems and to reduce the packaging cost, a thin tray is used. A thin tray naturally has a lower strength than a normal thick tray, and therefore, depending on the characteristics of the film used in stretch packaging and shrink packaging, the tray may be broken at the time of packaging or the heat shrinkage stress of the film may be reduced. 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-based film having packaging suitability for such a thin tray.

Further, since the cost of the various polyolefin-based films proposed so far is as high as two to three times that of the PVC film, the cases used as packaging materials are small. The reason why this film is expensive is that various materials are combined in a specific amount in order to exhibit the characteristics of the film, and the product is produced by a complicated manufacturing method, so that it is impossible to recycle in the manufacturing process. And so on. Therefore, cost reduction is required together with the above functions.

Hereinafter, several examples proposed for the purpose of replacing a film containing PVC as a main component will be described.
Of these, for the purpose of replacing the stretch film, for example, JP-A-53-6194 discloses an ethylene-vinyl acetate copolymer as both outer layers and a polyolefin resin having a higher melting point than the inner layer, such as polypropylene or polyethylene. Are disclosed. However, although this has an effect of improving the heat sealability, it is only a laminated film, so that the stretch required for the stretch film or the tension (tensity) and elastic recovery of the film after packaging are small. In addition, the packaging finish is insufficient and cannot be replaced with a conventional stretch film mainly composed of PVC.

Further, Japanese Patent Publication No. 5-88663 discloses a film having a specific gel fraction and a degree of crosslinking containing an ethylene resin as a main component, and a method for producing the film.
This intends to propose a polyolefin-based film having excellent stretchability by imparting similar stress-strain characteristics to a stretch film containing PVC as a main component. However, this requires a high degree of control of the degree of cross-linking and the method of producing the same, and it is difficult to achieve the desired stress-strain curve, which poses a practical problem. Furthermore, a specific gel fraction is required in order to achieve the desired stress-strain characteristics. In other words, if the scrap generated during the manufacturing stage is recycled to the manufacturing process because it contains a non-melting component as a component, the perforation and tearing of the film at the time of stretching due to the incorporation of the unmelted material and its influence will occur, When manufactured in the form of a tube, it cannot be recycled because it is so-called punctured and cannot be molded, and its manufacturing cost is about twice as high as that of a stretch film containing PVC as a main component. It is said that practical use is difficult as a material. in this way,
When a polyolefin-based film is used for stretch packaging, PVC can be used due to the properties of the polyolefin-based resin.
It is extremely difficult to exhibit 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, with respect to a polyolefin-based shrink film intended to substitute for a shrink film containing PVC as a main component, for example, Japanese Patent Publication No. 1-47311 discloses a layer containing a specific mixed resin component and a specific condition. A highly oriented cold-cold film and a method for producing the same are disclosed, which specify a heat-shrinkage stress value and a tensile strength of a film that is to be cold-stretched below. However, this is highly oriented and highly stretched like the one proposed in the above-mentioned Japanese Patent Publication No. Hei 5-88663, in order to obtain the desired heat shrinkage stress and tensile strength. Is a method in which a specific mixed composition and components are subjected to energy ray treatment and a specific gel fraction is required. That is, if the scrap generated in the manufacturing stage containing the non-molten component is recycled, the unmelted material is mixed or the film is perforated or torn at the time of stretching due to the influence thereof, and when the raw material is manufactured in a tube shape, It is said that it is impossible to recycle because it cannot be molded because it is so-called punctured, and its manufacturing cost is about twice as high as shrink film containing PVC as a main component, and it is said that it is difficult to use it as a packaging material. ing. Furthermore, since it is highly oriented and highly stretched, it has a problem that its heat shrinkage stress is high and it is not suitable for a packaging method using a thin tray. In addition, this manufacturing method is a method in which the resin extruded from the multilayer die is rapidly cooled and solidified with a liquid refrigerant, but in this cooling method, the refrigerant adheres to the surface of the formed film, and if the drying is insufficient, the film is insufficient. However, there is a problem that the surface condition is deteriorated, and as a countermeasure against this, it is difficult to increase the line speed in order to perform sufficient drying, resulting in low productivity.

Japanese Patent Publication No. 5-64589 discloses ethylene-
A three-layer crosslinked film comprising a vinyl acetate copolymer and polyethylene and a method for producing the same have been proposed. However, this requires an electron beam cross-linking treatment in order to obtain the characteristic value of the target film, so that it cannot be recycled in the production process, and the production cost and the product price are increased, so that practical use is not possible. This is a problem. In addition, since the manufacturing method is performed in a continuous process of co-extrusion → cooling and solidification → electron beam irradiation → heating → stretching, control in each process is extremely important, but variations in each condition affect film quality. There is a problem that it is easy to do.

Further, Japanese Patent Application Laid-Open No. Hei 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 are made of linear low-density polyethylene. Films have been proposed. This is characterized by a high recovery elasticity and no odor of acetic acid. However, since linear low-density polyethylene is used for both outer layers, heat sealability is reduced. However, in order to achieve the desired recovery elasticity, a high heat shrinkage stress is required, and packaging suitability for a thin tray cannot be obtained. Further, when the thickness of the linear low-density polyethylene as the outer layer is increased, the strength of the film is reduced, which is disadvantageous in that the film is suitable for an automatic wrapping machine, in particular, the film is easily broken during high-speed wrapping.

[0013]

SUMMARY OF THE INVENTION As described above, the present invention solves the problems of the conventional polyolefin-based film, especially the film used for shrink wrapping having heat shrinkage properties, which is inadequate in packaging suitability and high cost. The purpose is to do. That is, the present invention provides an α-olefin content of 1 to 7% by weight excluding propylene and a propylene content of 99 to 9
A core layer comprising a mixture of 5 to 25 parts by weight of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 5 to 30% by weight with respect to 100 parts by weight of an α-olefin-propylene copolymer of 3% by weight; A heat-shrinkage ratio of 10 to 30%, 40 to 60% at 80 ° C. and 110 ° C., respectively.
A shrink film characterized in that a heat shrinkage stress during heat shrinkage is 20 kgf / cm ² or less, an α-olefin content excluding propylene of 1 to 7% by weight,
To propylene copolymer 100 parts by weight, vinyl acetate content of 5 to 30% by weight of ethylene - - propylene content of 99 to 93 wt% of α-olefin vinyl acetate copolymer 5
２５25 parts by weight of a mixture of the core layer and the coating layer comprising 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. With the internal cooling air from the internal cooling cylinder provided at the tip and the external cooling air from the external cooling cylinder attached to the periphery of the internal cooling cylinder in front of the out-die portion of the annular die, the co-extruded molten resin is moved inside and outside. After rapidly cooling to 60 to 120 ° C from both sides and starting up with the diameter of the annular die, continuously blowing to a blow ratio of 2.0 to 15.0.
2. The method for producing a multilayer shrink film according to claim 1, wherein the film thickness is increased.

[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, the core layer and the coating layer having the specific compositions as described above 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 formed. An internal cooling air 5 ′ from the internal cooling cylinder 3 provided at the tip and an external cooling air 6 ′ from an external cooling cylinder attached around the internal cooling cylinder 3 in front of the out-die portion 2 ″ of the annular die 2. Quenching the co-extruded molten resin to 60 to 120 ° C. from both the inside and outside, starting up with the diameter of the annular die, and continuously blowing up to a blow ratio of 2.0 to 15.0 It is.
This will be described in more detail with reference to FIGS.

The apparatus of the manufacturing method of the present invention includes
And three extruders 1, 1 ′ (1 ″ is not shown), one of which has an α-olefin content of 1 to 7% by weight excluding propylene as a resin for the core layer, and a propylene content of 100 parts by weight of an α-olefin-propylene copolymer of 99 to 93% by weight, and a vinyl acetate content of 5 to 3
A mixture comprising 5 to 25 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. Extrusion supply.

In the extruder for supplying the core layer, the scrap of the film generated by the production method of the present invention is
When the content of the ethylene-vinyl acetate copolymer in the mixed resin is 5
It is also possible to extrude and supply the mixed resin that is weighed so as to be 25 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 in a tube shape. This device includes 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 installed around the internal cooling cylinder 3 in front of the out-die portion 2 ″ of the annular die 2. Cooling cylinder 4
It has. The inner cooling cylinder 3 and the outer cooling cylinder 4 transfer the molten resin A co-extruded from the annular die 2 to the annular die 2.
The position and dimensions are such that the tube can be raised in the shape of a tube with the same diameter. The molten resin A co-extruded in a tube shape from the annular die 2 is passed between the internal cooling cylinder 3 and the external cooling cylinder 4. The internal cooling cylinder 3 has a plurality of outlets 5 for 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.
A plurality of partitions 7 are provided at positions opposed to the outlets 5 of the internal cooling air 5 ′ of the internal cooling cylinder 3. Further, the position of the internal cooling cylinder 3 is higher than that of the external cooling cylinder 4.

Therefore, the molten resin A co-extruded from the annular die 2 is passed through the gap between the internal cooling cylinder 3 and the external cooling cylinder 4 while keeping the diameter of the annular die 2 substantially the same. 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. , Resulting in a tube-shaped material T. The molten resin is co-extruded in a 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 ′, 6 ′ by each cooling cylinder, and stands almost in an annular die diameter. can give. At this time, the inner and outer cooling air 5 'and 6' are blown from both the inner and outer surfaces of the tube-shaped material T made of molten resin, so that the diameter of the tube-shaped material T is kept constant and stably. Is a major feature of the manufacturing method of the present invention. here,
When the temperature of the molten resin at the time of co-extrusion is lower than 170 ° C., the melting of the resin becomes incomplete, the resulting film has reduced transparency, and thickness unevenness occurs. In addition, burns and the like are generated due to the addition, and the production becomes unstable. The resulting film does not have the desired strength, and pinholes and the like are easily generated. This cooling effect and dimensional stability make it possible to effectively and stably exert the stretching effect in the subsequent stretching step.
In order to exhibit this effect, it is necessary to cool the resin to below the melting point or the Vicat softening point of the resin.
Is 60 ° C to 120 ° C before reaching the upper end of the external cooling cylinder 4.
It is preferable to cool to 70 ° C or more.
80 ° C. Here, the temperature of the tubular raw material T is 12
If the temperature is higher than 0 ° C, the melting point of the molten resin will be exceeded, and the stretching effect in the subsequent stretching step will not be obtained. It becomes difficult, and furthermore, by cooling with the diameter of the annular die, the coating layer and the core layer can be taken off at an even drop-off rate. The tube-shaped raw material T cooled to the temperature condition is supplied to a partition 7 at the upper end of the external cooling cylinder 4.
Is reached, the tube-shaped raw material T is formed by the air pressure in the raw material 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. The stretching effect is 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, and more preferably 6.0.
What is necessary is just what is above and 15.0 or less. If the blow ratio is less than 2.0, no stretching effect can be obtained. Inconsistencies such as puncture occur easily due to unevenness in puncture. The tube-shaped raw material T thus stretched is folded by the pinch roll 9 to obtain a flat raw material T '. The web T ′ passes through a take-up machine 10 and is taken up and down by a take-up machine 11 and wound up as three-layer films P and P ′. It is preferable that the internal cooling air 5 'and the external cooling air 6' are appropriately temperature-controlled in order to exhibit the cooling effect.

Next, the film of the present invention will be described.
In the film of the present invention, the core layer 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.
As the α-olefin used in the propylene copolymer, 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.
Although it is used as a mixture of species, it is preferable to use ethylene or butene-1 alone or as a mixture thereof, for example, 1 to 2% of ethylene and 5 to 5 of butene-1.
Those containing 6% are preferably used, and ethylene alone is most preferred. The film of the present invention preferably has a flexural modulus of 5,000 to 17,000 kgf / cm ² , and more preferably 7,000 to 12,000.
A film having a weight of 0 kgf / cm ² is 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. When the MFR is less than 0.4 g / min, the obtained film is too soft, and it is difficult to obtain a desired heat shrinkage, and when the MFR exceeds 10.0 g / min, the film becomes hard and the film may be stretched. Easy to be difficult.

Further, the α-olefin-propylene copolymer includes a so-called random copolymer and a block copolymer, and a random copolymer is preferable because the transparency of the film is increased. 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, preferably has a vinyl acetate content of 5 to 30% by weight. , More preferably 7 to 15% by weight. The MFR is 0.
4 to 10.0 g / min, preferably 0.5 to 2.
0 g / min. Further, the mixing ratio of the α-olefin-propylene copolymer and the ethylene-vinyl acetate copolymer is preferably 5 to 25 parts by weight of the ethylene-vinyl acetate copolymer with respect to 100 parts by weight of the α-olefin-propylene copolymer. When the mixed amount of the ethylene-vinyl acetate copolymer is 3
0 wrapping suitability cause stickiness sticky increases film parts larger than film formation the film is lowered, et
If the tylene-vinyl acetate copolymer is not contained , 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 of polyglycerin fatty acid ester, sorbitan fatty acid ester, and polyoxyethylene alkylphenyl ether is used as the material, and the addition amount is based on 100 parts by weight of the ethylene-vinyl acetate copolymer. It is 0.5 to 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 sides of the core layer is preferably used, and the total thickness is 5 to 20 μm, more preferably 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:
The ratio is 0.2 to 1: 4, 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 a mixture of an α-olefin-propylene copolymer and an ethylene-vinyl acetate copolymer as its core layer as described above, a major feature of the present invention is that slits were generated during the production process and generated. It is possible to collect and reuse scraps such as ears. That is, since the same thing as the ethylene-vinyl acetate copolymer used for 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 in the above range With this configuration, the film formed by the manufacturing method of the present invention satisfies the desired characteristic values, improves the adhesion between the coating layer and the core layer, and has an edge slit for trimming in the manufacturing process. Scraps generated in parts and the like can be collected and reused in the manufacturing process.

Next, the characteristics of the film of the present invention will be described. The film obtained by the resin composition and the production method of the present invention has a heat shrinkage of 10 to 30% and 40 to 60% at temperatures of 80 ° C and 110 ° C, respectively.
The heat shrinkage stress during heat shrinkage is 20 kgf / cm ² or less. Here, the heat shrinkage ratio is a value represented by an average value of a ratio in a longitudinal direction and a ratio in a horizontal direction of the film, and the heat shrinkage stress at the time of heat shrinkage is such that the film of the present invention thermally shrinks under the above temperature conditions. The stress value at that time, and this value is also expressed as the average value of the heat shrinkage stress in the longitudinal and transverse directions of the film. If these values are in the above range, the thickness is 0.1 to
When a 0.6 mm thin tray is used, desired packaging suitability can be obtained. The above heat shrinkage is a heat shrinkage that is practically necessary for performing tight packaging, and since the heat shrinkage can be obtained at 80 ° C. and 110 ° C., the influence on the packaged object is minimized. It is possible to perform the heat shrinking operation. 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 a thin tray is used, 15 kgf /
cm ² or less. When the heat shrinkage ratio is in the above range, the effects 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 values of the film of the present invention will be described. Heat shrinkage: The average value of the shrinkage in the longitudinal direction (MD direction) and the transverse direction (TD direction) of each test piece was defined as the heat shrinkage [%] according to ASTM D-2732. Thermal shrinkage stress: A load sensor is equipped with a chuck, a test piece is mounted, and one of the test pieces is mounted on a fixed chuck, and then immersed in an oil bath set at a predetermined temperature to measure the heat shrinkage stress, and the longitudinal stress and the transverse stress Was taken as the average value. (Example 1) Five types of α-olefin-propylene copolymer in which 20 parts by weight of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 11% by weight were mixed with 100 parts by weight of each having different α-olefin contents. 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 a total thickness of 10 μm and a core layer thickness of 5 μm was prepared. Formed according to the production method of the present invention, 1 to N
o. It was set to 5. Films having an α-olefin content in Table 1 were used as Comparative Examples 1 and 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 in which the vinyl acetate content in the ethylene-vinyl acetate copolymer was variously changed are shown. No. 6-No. 9 is a film of the present invention. Films having an α-olefin content shown in Table 2 were Comparative Examples 3, 4, and 5, respectively. Comparative Example 3 had a low heat shrinkage, and both Comparative Examples 4 and 5 had a high heat shrinkage and a high heat shrinkage stress. (Example 3) The case where the addition amount (parts by weight) of the ethylene-vinyl acetate copolymer in the core layer was changed is shown. No.
10-No. 12 is a film of the present invention. Table 3
The film having an α-olefin content of Comparative Example 6 was used as Comparative Example 6. In Comparative Example 6, both the heat shrinkage and the heat shrinkage stress were high.

(Example 4) The results of a packaging test performed using the films of Example and Comparative Example are shown. The evaluation criteria are as follows: in the packaging state after heat shrinkage of the film, 1) those with no deformation or cracking of the tray, 2) those with no wrinkles or sagging of the film in the packaging finish, those that satisfy two items: . 1) Those with deformation or cracking of the tray, 2) Insufficient heat shrinkage, 3) Wrinkles or sagging of the film in the packaging finish It was X. Table 4 shows the results. It can be seen that the film of the example is superior to the film of the comparative example. Packaging machine used: STC = II manufactured by Ibaraki Seiki. Tray material used: OPS (oriented, p
polystyrenesheet), PSP (poly
(styrene paper), PP [The numerical values in the table represent the thickness (mm) of the tray]. Packaged goods: Kiyuri (packed in a heap on the tray). Tunnel temperature: 100 ° C. Tables 1 to 4 show the above test results. When two types of α-olefins are mixed in the column of α-olefins in the table, the number in parentheses indicates the mixing ratio of the α-olefins.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

[Table 4]

[Brief description of the drawings]

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

FIG. 2 is a partially enlarged longitudinal sectional view 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,
8 Pinch roll, 2 "out die
9 take-up machine, 3 internal cooling cylinder, 10 take-up machine, 4
External cooling cylinder, A molten resin, 5
Internal cooling air outlet, P, P 'trilayer film, 5' Internal cooling air, T
Tube-shaped material, 6 External cooling air outlet, T 'flat material.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification code FI B29L 9:00 (58) Field surveyed (Int.Cl. ⁶ , DB name) B32B 1/00-35/00 B29C 55/00 -55/30 B29C 61/00-61/10 B65D 30/00-30/28 B65D 65/00-65/46

Claims (2)

(57) [Claims] An α-olefin content of 1 to 1 other than propylene.
5 to 25 parts by weight of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 5 to 30% by weight is mixed with 100 parts by weight of an α-olefin-propylene copolymer having a propylene content of 99 to 93% by weight. A heat-shrinkage rate of 10 to 30% and 40 to 60% at 80 ° C. and 110 ° C., respectively. A multilayer shrink film having a stress of 20 kgf / cm ² or less. 2. An α-olefin content of 1 to 2 excluding propylene.
5 to 25 parts by weight of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 5 to 30% by weight is mixed with 100 parts by weight of an α-olefin-propylene copolymer having a 7% by weight and a propylene content of 99 to 93% by weight. The core layer made of the mixture and the coating layer made of the ethylene-vinyl acetate copolymer are co-extruded from an annular die at a resin temperature of 170 to 240 ° C.,
The internal cooling air from the internal cooling cylinder provided at the tip of the inner mandrel portion of the annular die and the external cooling air from the external cooling cylinder attached around the internal cooling cylinder in front of the outer die portion of the annular die. The co-extruded molten resin is rapidly cooled to 60 to 120 ° C. from both the inner and outer sides, and is started up with the diameter of the annular die.
The method for producing a multilayer shrink film according to claim 1, wherein the blow-up is performed to zero.