JPS61287720A - Cold high-orientation multi-layer film and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture the cold high-orientation multi-layer film capable of causing heat shrinkage at comparatively low temperature, by a method wherein at least one layer of ethylene-based copolymer layer and the layer of saponified nylon or ethylene-vinyl acetate are laminated and high orientation thereof is effected at a low temperature. CONSTITUTION:Vinyl ester-ethylene copolymer A, such as ethylene-vinyl acetate copolymer, a copolymer of ethylene and aliphatic unsaturated carbonic acid or the ester thereof or at least one kind of copolymer selected from ionomer series copolymer C, derived from the copolymer B, other layer consisting of saponified copolymer of nylon or ethylene-vinyl acetate and another different layer, consisting of copolymer of A-C but different from said one layer or crystalline polypropylene, are melted and laminated. This laminate is cooled suddenly by liquid refrigerant and is cold-orientated at a temperature up to 80 deg.C with the draw ratio per unit area of 5-30X by employing a flow-regulating and -contacting guide. The film is useful as a heat-shrinkable packing material.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates primarily to multilayer highly oriented films for use as packaging materials and to their production.

Specifically, it has at least one layer containing a resin whose main component is an ethylene-based copolymer, and also contains nylon, ethylene-based copolymer, etc.
A multilayer highly stretched and highly oriented high strength cold highly oriented multilayer film having at least one layer containing a resin selected from saponified vinyl acetate, and by highly stretching at a specific low temperature. The present invention relates to a method for producing such a multilayer film.

Conventional packaging methods using film include various packaging methods that take advantage of the characteristics of the film, such as sealing into a bag, twisting the film, shrinking by applying heat, and Saran wrap (Asahi Kasei Corporation). A large number of methods are used, such as the tight wrap method, stretch wrap method, and skin pack method represented by Co., Ltd. (product name), and each method requires its own packaging and characteristics. At present, products with suitable composition, shape, properties, etc. are selected and packaged.

Among them, the shrink method utilizes the heat-shrinkability of a film that has been stretched and set in orientation, and after loosely pre-wrapping, for example sealing, the object to be packaged and enclosing the object, the film is exposed to hot air or infrared rays. This method involves heating and shrinking the contents using hot water or other heat medium to tightly adhere the contents. Its features are that the appearance of the package is beautiful and increases the product value, that the quality of the contents can be confirmed visually and tactile while keeping the contents sanitary, and that even irregularly shaped items or multiple items can be tightly fixed in one package. It can be packaged and has excellent protection against vibrations and shocks. Furthermore, compared to the stretch wrapping method currently widely used in supermarkets and the like, the wrapping speed can be increased.

It is also possible to package irregularly shaped items that cannot be wrapped with stretch wrapping, such as trays, etc. without containers. It also has the advantage of being able to be packaged more tightly, but has the disadvantage of having to be heated sufficiently until the film shrinks.

If the above-mentioned drawbacks can be solved, it is possible to create a packaging method that has more advantages than stretch packaging in terms of the area of use of the film, reduced internal thickness of the film, packaging speed, etc.

Problems to be Solved by the Invention Although the present invention does not particularly limit its use, shrink wrapping will be described below as a preferred example of its use.

Plasticized polyvinyl chloride (hereinafter referred to as PVC) is currently used in large quantities as a high-grade shrink wrapping film.
It is a stretched film. This is because it causes a high rate of heat shrinkage at relatively low temperatures and has the great advantage of being able to produce good shrink packaging over a wide heating temperature range.On the other hand, it has poor heat sealability and moisture resistance, and there are hygiene problems caused by plasticizers. The problem of deterioration over time, the generation of toxic gas such as chlorine gas when melted by heat rays, corrosive toxic gas when incinerating used film, and the problem of storing packages at low temperatures in cold regions. When handled in a cold environment, there are problems such as the film becoming hard, brittle, and easily torn due to its poor cold resistance.

Therefore, in recent years, polypropylene-based (hereinafter referred to as PP) films for shrink wrapping have attracted attention, but their drawback is that their shrinkability is inferior to that of PVC films. PP-based stretched films are excellent in terms of mechanical properties, moisture resistance, heat sealability, etc., and are excellent as shrink wrapping films.

Also, compared to PVC, it has advantages in terms of raw material cost and low specific gravity. However, PP is a crystalline polymer with a high softening temperature and a higher heating shrinkage temperature than conventional stretched films, and its shrinkage rate is small at low temperatures of around 100°C. Therefore, it is necessary to heat the product to a high temperature in the shrink packaging process, and the permissible range of heating temperature is narrow, and the shrinkage rate has a steep temperature dependence, so uneven heating in some areas during packaging can cause significant uneven shrinkage. It is easy to cause practical defects such as "wrinkles" and "pockmarks", and in order to prevent this, sufficient heating may cause overheating of the packaged material, devitrification of the film, holes due to melting, performance deterioration, and sealing parts. This has resulted in major drawbacks such as tearing of the air vent hole. Moreover, after packaging, the stress is released and the packaged item tends to loosen, and the film after packaging becomes hard and brittle.

In addition, conventional polyethylene films have not been able to impart sufficient stretching orientation to the molecules, and therefore, the obtained films have a low heat shrinkage rate, particularly a low heat shrinkage stress, and a high shrinkage temperature, making it difficult for the film to Its strength and optical properties are poor, and the cohesiveness of the packaged items after packaging is also low, so it is used in a thicker form for special purposes.

In addition, even in polyethylene films, films that are stretched at high temperatures after using high-energy rays to sufficiently induce a cross-linking reaction in the molecules have a high heat shrinkage rate and heat shrinkage stress, and are less transparent and glossy than regular polyethylene. It has very excellent optical properties, heat resistance, etc. However, it shrinks in high temperature ranges and deteriorates (particularly when its optical properties become large), and it also shrinks rapidly with temperature. It has disadvantages such as poor heat-shrinking properties, high degree of crosslinking that makes it difficult to heat seal, poor tear resistance and easy tearing, and difficulty in cutting with heating wire, resulting in poor packaging speed. As mentioned above, one of the important characteristics of shrink wrapping is that it can be wrapped sufficiently at low temperatures, which is particularly required when packaging fresh foods.

As mentioned above, the shrinkage temperature of the film (practically 20%
If the shrinkage is high, or if the shrinkage rate is large and rapid depending on the temperature, it is necessary to use a temperature that far exceeds the melting point of the polymer, especially in order to improve the finish of the packaged product. The film had to be packaged under very narrow conditions, and the film properties were severely degraded, causing problems.

On the other hand, in the case of polypropylene, the stretched film is produced by melt-extruding and quenching the tube-shaped raw material using an extruder, then reheating it to a high temperature of 150° to 160°C and introducing air inside. In the case of low-density polyethylene, the conventional method of biaxial stretching to set a high degree of stretching orientation is considered to be technically extremely difficult as it tends to tear during processing. There is.

For this purpose, for example, 180 ~
A common method is to extrude at a temperature of 220° C., then immediately expand it while cooling with air to form a film of a predetermined size.

Although this method has the feature of being able to easily produce a film at a very low cost, intermolecular flow tends to occur and it is not possible to set a satisfactory molecular orientation by stretching. or,
The optical properties are also inferior to those of large cloth. Therefore, the heat shrinkage rate and heat shrinkage stress are low and on the high temperature side, and it can only be used for special purposes by increasing the film thickness. For this purpose, after molding low-density polyethylene, it is irradiated with high-energy radiation under appropriate conditions to cause a partial crosslinking reaction, and then reheated to a high temperature exceeding its melting point (for example, 140°C) and stretched. Although there are methods of preventing intermolecular flow and setting sufficient molecular orientation, the degree of low-temperature shrinkability is low and the film tends to tear easily.

Also, recently, several attempts have been made to improve the shortcomings of these films. For example, the special public official court Sho 45-269
No. 9 discloses a method of obtaining a stretched film by using a mixed composition of an ethylene-vinyl acetate copolymer and an ionomer resin and stretching the film at, for example, 100° C. to improve the flow characteristics upon heating. With this method, the strength was also lower than that of the film of the present invention (tensile strength 4.2 kg/mm
2), the optical properties are inferior. Furthermore, the optical properties after shrinkage tend to deteriorate significantly. Also special public service 1977-407
No. 5 discloses a method of stretching using a specific ethylene-propylene copolymer, but the optical properties, heat shrinkage properties, strength, etc., and processability are still insufficient compared to PvC films.

Furthermore, various types of composite multilayer films are known as new packaging films.

Recently, due to the increasing sophistication of required characteristics, there is a trend towards more and more complexities. For example, there are films that are almost unstretched or films that are stretched and melt-laminated with other resins.

For example, polypropylene (C
, PP) or stretched polypropylene (
Films with improved heat-sealability made by laminating other resins on 0, PP) or films coated with vinylidene chloride latex to provide barrier properties (referred to as K-coated films) are available depending on the application. A wide variety of films and combinations are selected.

On the other hand, coextrusion films are generally known in which multiple types of resins are melted in separate extruders, merged and fused inside a multilayer die, extruded and cooled to form a film or sheet. .

However, in order to obtain a highly stretched film for each of the layers that make up the multilayer, the optimal extrusion conditions, stretching conditions, etc. are different for each resin. Defect phenomena such as peeling of the film and whitening due to interface roughness occur, and the film also differs from the desired characteristics, and it has been extremely difficult to solve these defects until now.

Means for Solving the Problems The inventors conducted research to further improve the shortcomings of these films and manufacturing methods, and found that the heat shrinkage properties, particularly the heat shrinkage rate at low temperatures, heat shrinkage stress, and heat shrinkage We have discovered an excellent film that simultaneously greatly improves the temperature dependence of properties, optical properties, film sealability, strength, etc., as well as a specific method for producing the same at low cost and with excellent processability.

That is, the present invention provides a multilayer highly stretched film comprising three or more types of polymer layers, in which one layer is made of the following copolymers (A) to (
At least one copolymer selected from C); (A) a copolymer of a vinyl ester monomer and ethylene; (B) an aliphatic unsaturated carboxylic acid and an aliphatic unsaturated carboxylic acid alkyl ester a copolymer of ethylene and a monomer derived from the copolymer (B); (C) mainly contains an ionomer copolymer derived from the copolymer (B), and other layers include nylon and a saponified ethylene-vinyl acetate copolymer; The other layer contains at least one copolymer selected from the above polymers (A) to (C), and the other layer contains at least one copolymer selected from the above polymers (A) to (C). A cold-stretched multilayer comprising at least one copolymer selected from polymers and crystalline polypropylene, having a tensile strength of 5 kg/mm2 or more and a shrinkage gradient of 2.0 or less. Provide film.

It also relates to its manufacturing method.

By providing the above-mentioned layers and cold-stretching them under specific conditions, the composite film of the present invention can achieve unprecedentedly high degree of stretching orientation and excellent properties between the above-mentioned resin combination layers or between the layers of other resins. It is characterized by the fact that it can be exerted by the synergistic effect of the two.

By combining the copolymers with different types of copolymers or with other types of resins, stretching conditions exceeding those of the single resins, that is, conditions that cannot be achieved alone, can be achieved, e.g. Under low-temperature conditions, a particularly high degree of stretch orientation is imparted to each layer in a very stable manner, resulting in a film that is particularly excellent in strength, transparency, and other properties.

The film of the present invention has good properties as a shrinkable film, although it is not particularly limited, as a variety of packaging films. In particular, it has excellent optical properties, strength, heat seal strength, and gas barrier properties, and is shrinkable at low temperatures. A film with excellent characteristics, shrinkage response (speed), etc. can be obtained.

The highly stretched film of the present invention is extruded, for example, into a tube shape using a multilayer goo containing at least one layer of each of the above-mentioned polymers, and the extruded product is rapidly cooled and solidified using, for example, a liquid refrigerant, and then heated if necessary. It can be produced by cold stretching at a stretching temperature of 80° C. or lower and an area stretching ratio of 3 to 30 times.

One of the copolymers (A) that can be used in the present invention is
It is a copolymer of vinyl ester monomer and ethylene. The content of the monomer is preferably 3 to 13 mol%. A typical example of this copolymer is an ethylene-vinyl acetate copolymer, and particularly preferred is one having a vinyl acetate content of 3.5 to 12 mol % and a melt index of 0.2 to 6. More preferably, the vinyl acetate content is 4.0 to 11 mol% and the melt index is 0.2 to 4.

Other copolymers (B) include aliphatic unsaturated carboxylic acids and/or
Or it is a copolymer of a monomer such as the carboxylic acid alkyl ester and ethylene. The content of the monomer is similarly 3
It is 13 mol% to 13 mol%, preferably 3 to 12 mol%, and more preferably 4.0 to 11 mol%. These include copolymers of ethylene and at least one monomer selected from the group consisting of acrylic acid, acrylic esters, methacrylic acid, methacrylic esters, and the like.

The copolymer (C) refers to the above-mentioned ethylene-methacrylic acid copolymer, ethylene-acrylic acid copolymer, ethylene-
At least a part of the copolymer selected from partially or more saponified polymers such as methacrylic ester copolymer and ethylene-acrylic ester copolymer is
+, Zn++, Mg'', and other metal ions.Among these, preferable ones depending on the application are ethylene-methacrylate ester and partially saponified polymer of ethylene-acrylate ester. The copolymer is an ionomer in which at least a portion of the copolymer is ionically bonded.In the present invention, any mixture selected from the copolymers (A) to (C) can also be used.

A copolymer containing 3 mol% or less of a monomer other than ethylene does not have good cold stretchability, makes it difficult to achieve a synergistic effect, and tends to be punctured during stretching. or,
For the surface layer, sealability, optical properties, for the inner layer, strength,
Problems arise in interlayer adhesion and the like. On the contrary, 13
If the amount exceeds mol%, the elastic modulus of the film tends to decrease, particularly in the case of copolymers (A) and (B), and the heat resistance tends to decrease.

In addition, in the case of the surface layer, the surfaces of the film tend to block each other. Furthermore, the rubbery properties become stronger, making it difficult to set during cold stretching, and the orientation and dimensions change easily at room temperature, resulting in a tendency to deteriorate in strength, and the synergistic effect in multilayers also decreases. .

In the case of the copolymer (C), although the rubber properties are not limited to those mentioned above, the stretchability is still reduced. Among copolymers (C), ionomer resins having partial ester bonds have good stretchability and have flexibility even when used as a surface layer, and may be preferable depending on the intended use.

Further, in the present invention, other suitable polymers may be mixed with the above-mentioned polymer composition. The copolymer then preferably has a
The copolymer (C
) may be mixed with a nylon resin or the like, such as a nylon 6-66 copolymer. Also, other suitable resins may be used as long as they do not inhibit cold stretchability.
) can be done. When used as a mixture, cold stretching is characterized by the fact that not only those with good compatibility but also those with slightly poor compatibility are stretched synergistically during stretching, resulting in a decrease in optical properties (in particular, a decrease in optical properties). Furthermore, it is surprising that not only is there often little decrease in optical properties (after shrinkage), but on the contrary, good properties are often exhibited synergistically. This relationship disappears more rapidly as the stretching temperature increases, and on the contrary, bad points begin to appear. That is, a film with excellent properties can be obtained by low-temperature stretching under the specific stretching conditions of the present invention, that is, at a temperature of 80° C. or lower (for example, 35° C. below the softening point).

In the present invention, the above copolymer or a multilayer original fabric having a layer mainly composed of the copolymer is irradiated with high energy rays, and the copolymer is boiled as a xylene-insoluble gel of 0 to 70% by weight, with a melt index of 2 or less. After the treatment, cold stretching may be performed. In this case, the cold stretchability may be improved, and the web properties, particularly heat resistance, etc. may be improved, making it more desirable depending on the application.

The preferred range is 0.5 to 50% by weight of the insoluble gel and a melt index of 0.5 or less. More preferably,
Insoluble gel 3-30% by weight, melt index 0.07
It is as follows. If the amount of insoluble gel is more than the above amount, the molded product will elongate, lose strength, and deteriorate, resulting in deterioration of heat-sealing properties especially when made into a film, such as not being able to be sealed, being unable to be cut by heat rays, and becoming easily torn. In some cases, the above-mentioned degree is preferable.

In the multilayer film of the present invention, when forming a multilayer between different resins of the above-mentioned copolymers, the layer structure may be determined depending on the necessary requirements, but among them, each copolymer (A)
, when group C) is combined with group C) as a multilayer, it is often preferable to use copolymer (C) as the surface layer. The copolymer (C) generally forms a hard surface layer due to ionic bonds. This is also because it is more suitable in terms of sealability and optical properties. Next, examples of other resin layers to be combined with a layer made of a resin other than the copolymer-containing layer include nylon (abbreviated as Ny), ethylene-vinyl acetate copolymer saponified polymer (
It is made of a composition containing a resin selected from SEVA (abbreviated as SEVA), and more preferably, crystalline polypropylene (abbreviated as PP) may be disposed as another layer. or other mixed polymers. In particular, it has been found that when the above-mentioned barrier resin is used as an intermediate layer, the barrier properties and pinhole resistance can be improved compared to those obtained by stretching at a high temperature according to the present invention. The ratio of the copolymer layer as the thickness structure of each layer is not particularly limited, and the lower limit is, for example, when the copolymer (C) is used as the surface layer, when other layers (A), (B), etc. are arranged, or If other resins with good cold stretchability are used, generally 1
It is 0% or more. The ratio of the copolymer layer to the total layer thickness is preferably at least 30% or more, more preferably at least 50% or more. The combination of layers may be a two-layer structure, a three-layer structure or more, but preferably three layers or more. For example, (the copolymers (A), (B), and (C) are simply abbreviated as ASBSC), C/Ny/C, Ny /B/C, C/5EVA/
There are C, etc.

In the case of 5 layers, PP/EPE/A/EPE/PP, C
/B/5EVA/B/CSC/A/5EVA/A/C,
etc.

These are effective for improving surface hardness, sealing properties, optical properties, etc., or for improving film stiffness, mechanical suitability for packaging, mechanical strength, etc., and are highly functional and expensive. For the seed resin, it is convenient if measures such as making this layer particularly thin and improving stretching processability are taken.

The film of the present invention can be cold-stretched, that is, in addition to biaxial stretching, it can be uniaxially stretched vertically or horizontally, but it is preferable to biaxially stretch in a bubble shape to obtain better stretch properties.

The film of the present invention has optical properties [haze value (AST
M-D1003-52)] is generally 3.0% or less, preferably 2.0%. For example, this is a value that is characterized by its manufacturing method, and can be processed or processed at temperatures below the melting point of the main composition, more preferably below the softening point, without impairing the quenched properties of the composition of the present invention. It is particularly transparent because it can be stably stretched in a bubble form at low temperatures. In addition, when used as a shrink film, the haze after shrinkage hardly deteriorates even if it is shrunk by 20 to 40%, but in many other films, the haze deteriorates significantly (for example, PP has a haze of 2.8%). 6.5%, and 2.5% for cross-IPE film to 4.8%). This value is preferably 4.0% or less after 20% shrinkage, more preferably 3.0%
It is as follows.

In addition, low-temperature shrinkability is one of the properties necessary when used as a shrink packaging film, and it shrinks by 20% or 40% of the value expressed by the heat shrinkage rate when the film is treated at various temperature conditions. (hereinafter expressed as the average vertical and horizontal shrinkage rate), and the lower this value is, the better the low-temperature shrinkage characteristics are. The shrinkage rate required for a shrink film usually varies depending on the packaging method, but is usually 20% or more, preferably 40% or more. Specifically, a square test piece cut from a film is marked with vertical and horizontal markings of specified dimensions, and the test piece is coated with powder such as talc to prevent it from sticking to itself or other objects during shrinkage. The heat shrinkage rate is the average value of the vertical and horizontal values expressed as the change rate of dimensions in each direction after heat shrinkage after being treated with hot air for 5 minutes, and this value is measured at each temperature. However, when graphed, the temperatures expressed by a heat shrinkage rate of 20% or 40% are referred to as 20% and 40% shrinkage temperatures, respectively.

When the film according to the present invention is used for shrink wrapping, this value is low; for example, the commercially available shrinkable polypropylene film mentioned below has a temperature of 120°C at 20% value and 134°C at 40% value.
For example, as in Experimental Example INα1, 20%
It has characteristics with low values of 49°C at 40% and 72°C at 40%. This level is expressed as a 20% value and is below 85°C, preferably 75°C.
The temperature is preferably 70°C or lower, more preferably 70°C or lower. This value is secondarily influenced by the stretching temperature, composition, layer combination, etc., but it is at a low level as one of the major features of the cold stretching of the present invention. If this value is high, thermal shrinkage will not occur unless exposed to considerably high temperatures for a long period of time in practical use, requiring a large amount of heat from the heater and slowing down the packaging process. In addition, heat is transmitted to the packaged items, especially items that are dangerous due to heat, items that may deteriorate or deform, etc.
It is particularly unfavorable for fibers and fresh foods. In addition, for films whose shrinkage curve tends to rise suddenly at high temperatures, the shrinkage rate changes greatly in response to very small changes around the shrinkage temperature during packaging, so if the film is loosely wrapped in advance and passed through a shrink tunnel, If the overall temperature of the hot air that hits the film is too low, the package will not shrink properly due to insufficient shrinkage, and if the temperature is too high, it will melt and cause holes or devitrification in the film, resulting in optical unevenness. It is common knowledge that the temperature of the film differs between areas that are in contact with the packaged item and those that are not, which causes unsightly pock-like shrinkage unevenness and significantly reduces the product value. It will be a loss.

Furthermore, if this temperature is high, not only the optical properties after shrinkage but also the mechanical properties such as strength will be significantly reduced.

Further, there may be problems such as the seal portion or the air vent hole being torn.

Moreover, if this value is too extremely low, the dimensions of the film wound into a roll may change at room temperature, which is not preferable. A commercially available PVC film for plasticized shrink packaging has this value of 58° C. at 20% shrinkage and 83° C. at 40% shrinkage, and has favorable shrinkage properties at low temperatures and gentle changes in temperature.

Shrinkage rates of 20% and 60% are values that represent the smoothness of the shrinkage curve, which is one of the other characteristics of sufficiently cold and highly oriented.
If we express the slope of the curve at the corresponding temperature between, that is, the shrinkage slope = (60-20)/Δt (%/l'), the film of the present invention has a slope of 2°0 or less, preferably 1.5 or less, and Preferably it is 1.3 or less. In addition, the shrinkage rate is small6
If it is saturated near 0% or below, 20~
The shrinkage gradient is between 40%. In the case of biaxial stretching, this value is expressed as the average value of the vertical and horizontal directions, and the same applies to other properties hereinafter. However, in the case of -axis stretching, this is not the case, and the value is mainly in the direction of stretching.

Another characteristic is that the shrinkage rate at the Vicat softening point (hereinafter referred to as Vicat shrinkage rate) of the main association forming the film is at least 15% or more, preferably 20% or more, and more preferably 25% or more.

ν1cat softening point is ΔSTM-D1525 (load 1kg
) is the value measured at If this value is low, low-temperature shrinkability is insufficient for practical shrinkage, and the packaging temperature must be significantly increased. As a result, the film becomes greatly softened, its shrinkage stress is greatly reduced, and it is exposed to temperatures above its melting point for a long period of time, making it impossible to package uniformly without wrinkles, and deteriorating the string properties. result.

Another feature is that the film must already shrink sufficiently up to the crystal melting point of the main polymer constituting the film, and the film of the present invention fully satisfies this requirement. If this value is low, the product cannot be packaged unless it is sufficiently exposed to temperatures above that temperature during packaging. This value (referred to as mp shrinkage rate) is preferably 25% or more, more preferably 30%
or more, more preferably 35% or more, most preferably 40% or more
% or more.

A film other than plasticized PVC with such shrinkage rate characteristics and strength has never been commercially available.

The film of the present invention has achieved a level of properties higher than this and is a film that is unprecedented.

In addition, the heat shrinkage stress during shrinkage is one of the important heat shrinkage characteristics, along with the heat shrinkage rate, when used as a shrink packaging film. However, if the stress during shrinkage is extremely low, it will not fit the packaged items during or after packaging, and the binding strength will be poor, making it completely useless as a shrink wrapping film.

Furthermore, if the binding force is insufficient even to a small extent, a thick film must be used to tie the cover, which is uneconomical and inconvenient. As a feature of the film of the present invention, the peak value is usually at least 50 g/n+m'', more preferably 100 g/mm'' or more, and more preferably 150 g/mm2 or more. For commercially available polyethylene shrink films, this value is less than 10g/mm2 and 5g/+n.
It is about +n2, and its uses are limited. The film of the present invention has a weight of 210g/++un2, such as RunNαl.
There is also. Usually, the film of the present invention has this value of 100 to 4.
It has a sufficiently high level of about 00g/m1112.

In addition, for low-temperature shrinkable films, this shrinkage stress has no meaning unless it is exerted from a temperature close to the level corresponding to the change in shrinkage rate, and the temperature dependence curve (expressed as the average value of vertical and horizontal values) is meaningless. It must be well balanced with the temperature curve.

In some cases, it may be preferable for the temperature to extend to a high temperature range. The temperature at the peak value of this stress is 90°C or less, preferably 80°C or less.
below ℃.

Furthermore, the present invention is characterized by its particularly high tensile strength and high elongation at break due to its manufacturing method, with a minimum of 5 kg/
It has the breaking strength of Carp 2 (value measured by the method of JIS-21702), preferably a value of 7 kg/mm2 or more, and the elongation at that time is also 100% or more, preferably 150% or more, and Preferably it is 200% or more. Furthermore, y is the breaking strength (kg/mJ2),
x is elongation at break (%).

Such high tensile strength and elongation mean that the film is tough and resistant to tearing, making it very advantageous as a protective film for packages and saving on film thickness.

The film of the present invention is, for example, Run No. 1, which will be described later.
2, breaking strength 12.8kg/mm2, elongation 230%
level. Normally, when the strength is increased by orientation, the elongation tends to decrease extremely. For example, a commercially available film that is fully crosslinked (67% boiling xylene insoluble gel) and stretched at high temperature has a strength of 8 kg/mm2 and an elongation of 45%, making it easy to tear. . In addition, falling cone impact strength (referred to as dart strength) AS
It is measured according to TM-Di 709-67, and because it is difficult to measure without tearing with normal methods, it is expressed as a value using a sharp special head that has a groove edge on the missile head to make it easier to tear the film. is characterized in that this value is particularly strong. For example, shrinkable PVC,
Although the PP film is 16 kg-cm and 8 kg-cm, Run No. 12 is actually 33 kg-cm (both converted to 17μ), which is 100 ~
This value is equivalent to that of a material with a thickness of 150 μm.

This value is generally greater than 15kg-0m, preferably 20k
g-cm (hereinafter converted to 17μ).

High tensile strength and elongation mean that the film is tough and difficult to tear, making it very advantageous as a protective film for packages, a film for skin packs, etc., and it can save on film thickness. . Film thickness is not limited, but usually 5 to 200μ, preferably 8 to 100μ
It is. The application is not limited to shrinkage films, but can be generally used as industrial films using Kufunesu.

Next, a preferred example of the method for producing a highly stretched film of the present invention will be described in detail.

The method of the present invention involves heating, mixing, and melting the above-mentioned copolymers, extruding them through a multilayer annular gouer, and rapidly cooling and solidifying them with a liquid refrigerant to obtain a tube-shaped material with sufficiently small thickness deviation, which can be used immediately as it is, or if necessary, can be After treatment with energy rays, it is left as it is at room temperature or heated slightly, and then cold stretched at a stretching temperature of 80°C or less and an area stretching ratio of 5 to 30 times (the stretching temperature here refers to the temperature at the starting point of stretching). ). Here, the stretching is carried out using a rectifying contact guide designed to substantially isolate the stretching start part and the heating part, while at least discontinuously contacting and removing the fluid accompanying the film surface and its film in the circumferential direction. .

Examples Preferred embodiments will be described below, but the invention is not limited thereto.

Extrusion is carried out by using a multilayer annular goo, which does not give sufficient unevenness in thickness, heat, or time history, at an extrusion temperature of 150 to 280°C, and uniformly quenching and solidifying the surrounding area with a liquid refrigerant. (also) into a tube-shaped raw material. This raw fabric may be pretreated with high-energy radiation, for example, with electron beams, gamma rays, ultraviolet rays, etc., for example, at a dose of 1 to 10 megarads. Excessive treatment may actually have negative effects on the properties of the fibers.

Next, the stretching is carried out at room temperature as it is, or by heating if necessary, at a temperature at which the main crystals of the main polymer, and preferably the main crystals of the polymers forming each layer, melt (the peak value determined by the DSC method). (measured at a scanning speed of 20°C/min).The reason for this is that once a crystal is melted, when the temperature rises and falls at a fast rate, the hysteresis effect causes the crystal to reach a temperature considerably lower than its melting point. This is because the crystallization occurs at the crystallization temperature, making it difficult to provide sufficient cold orientation. For example, this tendency is particularly strong in ionomer resins, and Na crosslinked type methacrylic acid content 1 made of ethylene-methacrylic acid: 5.4 mol%, melt index = 1.3, density: 0.942 g/cm3
At a scanning speed of 20°C/min (actual film formation speed is much faster), the melting point may peak at 100°C, and the crystallization temperature may peak at 50°C.
However, this is not the case when the degree of crystallinity is low.

In the present invention, the stretching is generally 80°C or less, preferably 20 to 7
It is preferred to stretch at a very low temperature of 0°C, more preferably 20-60°C, and at the same time, more preferably below the Vicat softening point of the polymer. That is, the temperature is preferably 10° C. or lower, more preferably 15° C. or lower than the Vicat softening point. It is preferable to stretch the film properties at a low temperature as long as processing stability allows. If the film is stretched at a temperature higher than the above-mentioned upper limit temperature, the film properties will deteriorate rapidly and at the same time, the stretching stability will also deteriorate, resulting in non-uniformity such as uneven thickness and bubble wobbling. The phenomenon begins to occur. In terms of properties, the low-temperature shrinkability, shrinkage gradient, etc. referred to in the present invention deteriorate, and the optical properties, strength, elongation, and other properties such as pinhole resistance in the case of barrier films also deteriorate significantly. Bubbling during heating and stretching is preferably performed uniformly while blowing temperature-controlled air using an air ring or the like, and while controlling the air flow in the surface layer as uniformly as possible. The heating temperature of the original fabric is 20° below the temperature at the start of stretching.
Preferably, the temperature does not exceed °C. Further, it is often preferable to conduct the stretching with a temperature difference of at least 5° C., preferably 10° C., between the stretching start point and the stretching end point.

One way to control the air flow in the surface layer is to use a rectifying contact guide, which is designed to substantially isolate the heating area and the stretching start area, to control the fluid (gas) entrained on the surface of the film and its surrounding film. There is a method of discontinuous contact removal in the direction to remove non-uniformity due to interaction between the heating section, the stretching start section, and the cooling section. This method can also be used in the stretching start section, stretching section, and stretching end region. It can be done. The internal pressure inside the bubble is high;
For example, 100-5000 mm water column pressure (H2O) (20
It is preferable to stretch the film to a sufficiently high degree under high pressure (based on an original fabric of 0μ and 100mmφ), more preferably 200 to 200
0 mm (H2O).

Further, the stretching ratio is 5 to 30 times in area stretching ratio, preferably 5 to 30 times in area stretching ratio, and 2 times in transverse direction.
~7 times. More preferably, the former is 7 to 20 times, and the latter is 2 to 5 times.

At this time, as mentioned above, it is important to make a sufficiently uniform raw fabric. For example, the uneven thickness of the raw fabric is ±10% of the thickness of the raw fabric.
If the thickness is above or below this level, punctures may occur during stretching, resulting in poor stretching. Uneven thickness of raw fabric is preferably ±5%
It is more preferably ±2% or less. The degree of stretching is determined by the speed ratio of the feed nip roll and the take-up rup roll, which determines the stretching ratio in the vertical direction.Then, air is sealed in the bubble and the bubble is stretched until it reaches the end of stretching (just before whitening), and the expansion in the lateral direction stops. The most stable method is to stretch at a certain level. In addition, the original fabric bubble has a diameter of about 50n+m or more, preferably 10nm or more in relation to the internal pressure and diameter.
It is convenient to use a carp diameter of 0 or more as large as the equipment allows.

In addition, in view of the physical properties of the obtained film, it is preferable to keep the film sufficiently cold as long as the stability of the bubbles allows, but in reality,
The stretching temperature may be determined by making some adjustments depending on the composition at the time, in balance with stability (avoiding punctures).

The film obtained by the method of the present invention has excellent physical properties as described above, and at the same time, the thickness deviation of the film after stretching is very small, often about ±5% or less. This is thought to be because a strong tensile force is imparted to the film due to the high internal pressure of the bubbles, and also because the thermal history of heating and cooling as usual is particularly small, resulting in uniformity and good stability. Even if the optical properties (both haze and gloss) appear somewhat poor at the raw stage, they become much better after cold stretching by the method of the present invention. Furthermore, by using multiple layers as described above, processing stability is greatly improved compared to when using a single layer, and more uniform and sophisticated products can be produced.

In comparison to the above, in the stretching method in which heating is performed above the normal melting point,
This does not happen, and in order to improve the optical properties, it is necessary to increase the stretching temperature.
In many cases, orientation becomes increasingly difficult and strength tends to decrease.

Moreover, the same thing can be said at temperatures of ±5 to 10°C around the melting point, and not only will the optical properties not produce even more favorable results, but in addition, in the case of mixed compositions, the temperature conditions will make the original fabric particularly brittle, causing punctures and imparting high properties. It's difficult to do.

As shown in the later-described embodiments of the present invention, the stretching described in the present invention can be successfully achieved at extremely low temperatures, for example, 31° C., and is not limited to the use of, for example, a multilayer tube containing a specific copolymer. This was achieved for the first time through the synergistic effect of using a uniformly quenched original fabric and satisfying conditions such as a specific stretching method.

For example, in the case of single PP shoes, continuous stretching can only be achieved under very narrow conditions of 140 to 160°C, which is difficult, and can only be achieved under delicate conditions. Moreover, if the temperature is higher than that, a whitened, weak and inferior film cannot be obtained, and if the temperature is lower than that, around 80°C, let alone, as in the case of the above example, 32°C, it is difficult to achieve stretching at all, which is surprising. That's a thing.

In addition, the properties obtained are superior to those of a single layer in terms of strength, optical properties, low-temperature shrinkability, sealing properties, tear strength, impact strength, etc., and the level of stretching is higher than that of normal stretching. .

In addition, after the film of the present invention has been stretched, it can be freely heat-treated, for example, on-line, after winding, etc., and when stored near room temperature, for example, to prevent dimensional changes and collapse of the roll when it is wound into a roll. can be treated to make it safer, and components that shrink at room temperature can be removed. Furthermore, depending on the degree of treatment, components that shrink at low temperatures can be freely controlled without degrading other physical properties. Furthermore,
It is also possible to freely move the orientation vertically or horizontally using a biaxially stretched film.

Experimental Example 1 Vinyl acetate group content: 5.5 mol%, melt index 2 0.6, crystal melting point (hereinafter abbreviated as mp) = 88°C,
Vicat ethylene-vinyl acetate copolymer (al) with a softening point of 72°C and ethylene-methacrylic acid copolymer N
A-type iomer resin: methacrylic acid content 6.6 mol%, melt index 1.0, neutralization degree 25%, mp
83°C and Vicat 64°C (C,) using two extruders, the former having a screw diameter of 35 mm and L/D = 30, and the latter having a screw diameter of 40 mm and L/D = 30. In an extruder with a cylinder part maximum temperature 24
They were each plasticized and melted at 0°C, extruded through a 100 mm diameter two-type, three-layer annular goo having a slit of 1.5 + n + n, and quenched with a water cooling ring that uniformly discharged water at a distance of 10 cm from the tip of the die. Raw fabrics having the respective thicknesses shown in Table 1 were obtained with each layer (outer layer), second layer (intermediate layer), and third layer (inner layer). In all cases, the thickness deviation (circumferential direction) was ±2% or less. These raw fabrics are passed between two pairs of feed nip rolls and take-up nip rolls, and are heated by hot air between them.
℃, then let air into the interior, and expand it continuously using the rectifying contact guide mentioned above, until the height of the balloon is 3.5 cm.
Stretched by 3.5 times and 3.5 times horizontally, cooled the stretched area with an air ring blowing cold air at 15℃, folded with a deflator, taken with a nip roll, and slit the edges lengthwise to form two films. The film was divided into 2 parts and each film was wound up with a constant tension to obtain a film of each thickness.

Table 2 describes the characteristic values of the obtained film in comparison with three commercially available films serving as comparative examples.

*However, both the mp and Vicat shrinkage rates are expressed using the resin with a higher layer ratio as the main layer.

Comparative sample 0 is a commercially available PVC shrink film,
■ indicates the same PP shrink film, ○ indicates the same cross-linked polyethylene shrink film.

All of the obtained films showed excellent properties and are comparative examples■
, (■), had properties superior to that of the O film. In addition, the resulting various films were used as shrinkage films for cucumbers, and the packages were wrapped using a commercially available L-shaped sealer and passed through a commercially available tunnel that emitted hot air at 90°C for 1 second.
It was a tight, wrinkle-free fit, had a good packaging finish, and had no deterioration in optical properties after shrinkage, allowing for beautiful shrink wrapping. Furthermore, as a result of testing by varying the residence time in the hot air temperature tunnel during shrink wrapping, results were obtained that allowed for good packaging over a wide temperature and speed range starting from the low temperature side.

Compared to the above, commercially available polypropylene shrink film has 12
Even at 0℃, there is almost no shrinkage and wrinkles remain on the sample, and under the same conditions, the hot air temperature must be raised and the hot air passed at 180℃ for 5 seconds to achieve sufficient shrinkage. Even if the film was lengthened, the film would be punctured and torn, or the film would become devitrified, and the appropriate temperature range was very narrow. There is almost no change, for example, Ru
nNo.2 was 0.7% after 40% contraction. Furthermore, the commercially available PVC shrink film still did not shrink sufficiently under the same conditions, leaving wrinkles, and it was necessary to set the temperature condition to 160° C. for 4 seconds. It was also found that the shrinkage curve showed faster response than PVC even at the same level. The strength, elongation, and heat shrinkage properties of the film are well-balanced in both the longitudinal and transverse directions when biaxially stretched, so they will be expressed as average values for the paper and transverse directions.

Also, as a comparative example, when trying to stretch the raw fabric with Run No. 2 at a stretching temperature of 92°C, the neck part was bent during stretching, and it was very unstable and easily punctured, so that it could not be stretched successfully. (Comparative example Run No. 1
). When I measured the haze of a small piece of this film, it was 6.
．． It was a film with poor transparency having a high value of 8%. The shrinkage stress value was also as low as 40 g/mm2.

Bubbles were continuously formed only when the stretching temperature was set to 135°C. This film has a haze value of 5.9%, no low temperature shrinkage, a shrinkage slope of 4.8, a 20% shrinkage rate of 89°C, a Vicat shrinkage rate of 14%, and a shrinkage stress of 12 g/
Tensile strength in mm2 is 3.5 kg / mm2 elongation 4
It was 90% and could not be called a highly oriented film. An attempt was made to stretch the original fabric of Run Nα3 at a stretching temperature of 85° C., but the bubbles during stretching were unstable and easily punctured. Also, the optical properties are poor, with a haze value of 8.5%.
The tensile strength was also low at 4.3 kg/mlT12 (the film had low low-temperature shrinkability).

Example 1 In the same manner as in Experimental Example 1, original fabrics were obtained using the combinations of layers having the respective compositions shown in Table 3 using three extruders, three types of three-layer die, and three types of five-layer die. Run No.

After irradiating the original fabric No. 12 with an electron beam as an energy beam,
The other original fabrics were subjected to cold stretching as they were at the stretching temperature described below to obtain films. The properties of these films are shown in Table 4.

Table 3 b2 shows partially saponified ethylene-methyl methacrylate copolymer (methyl methacrylate group content near, 0 mol%, melt index = 5mp: 84°C
, Vicat: 64°C); C2 is partially saponified ester-methyl methacrylate copolymer (40°C);
% Iomer resin (Na type) consisting of polymer (methacrylic acid and ester group content near, 0 mol%, melt index: 1.
0, mp: 9Q℃, Vicat 66℃); NY+ is a nylon 6.66 copolymer; 5EVA is a copolymer (EVA) of 55 mol% ethylene and vinyl acetate with a degree of saponification of 98% * 2) C2, b2 by 8 Mrad electron beam irradiation treatment
The layers each contained 45% by weight and 25% by weight of Gel.
The temperature was 1.42°C, the horizontal stretch ratio was approximately 3 to 4 times, and the vertical stretch ratio was 2.8 to 4 times, and stable stretching was possible in both cases. All of the obtained films had excellent properties, particularly excellent optical properties and strength properties. Also, the aforementioned commercially available ■PVC4@PP.

■The average vertical and horizontal dimensions of each sample film of cross-linked PE at the appropriate shrinkage temperature are 20.40.
The Heiss value after 60% contraction was found to be oPVc 1.9.
2.0.2.3%, ○PP 2.8.6.5.11.0
%, () crosslinking resulted in P E of 2.5.4% and 8.6.5%, both of which significantly deteriorated in many cases.

Example 2 Original fabrics were obtained using the combinations shown in Table 5 in the same manner as in Example 1, and films were stably obtained at a stretching temperature of 57° C. with Run No. 20. The properties of this product are shown in Table 6. Table 5 Here, al: Contains vinyl acetate group: 5.5 mol%, Melt index: 0.6, Crystal melting point (hereinafter abbreviated as mp)
: Ethylene-vinyl acetate copolymer 2C2 with Vicat softening point of 72°C at 88°C: 5EVA mentioned above: Chiba ++ Table 6 *) Comparison ■ is a commercially available barrier shrink back for inner packaging, and the barrier layer is vinyldene chloride-based. The film is about 10μ multi-layered with 16μ EVA, and the inner layer is irradiated EVA based film with 36μ.

The RunNa2O sample had better optical properties, low-temperature shrinkability, shrinkage stress properties, tensile strength, and impact strength than the comparative sample, and also had better barrier properties. As a practical test, 3 kg of processed meat was vacuum packed at 80℃.
By placing the package in a hot water shower for 3 seconds, a tightly shrinkable package with good shelf life was obtained.

As a comparative example, al /PVDCI /a+(120/
80/200: each μ), C2/at/PVD
C2/a 1/C2(20/120/60
/ 160 / 40: Stretching was attempted at 100°C using the original fabric of each μ).

Here a, c2. PVDC: Vinylidene chloride copolymer: 10% by weight vinyl chloride copolymer; PVDC2: Vinylidene chloride copolymer and nialic acid copolymer. Moreover, unstretched streaks and the like occurred in the vertical direction, which did not work well. Moreover, the film was whitish, had poor optical properties, had a haze of 13%, and had a low tensile strength of 4.5 kg/+n+n2. In addition, although stretching was attempted at 85° C., the bubbles began to bend and were immediately punctured, making it impossible to continue stretching.

At temperatures from 80 to 66°C, stretching was possible although there were occasional punctures, and below that temperature, from 30 to 50°C, the stretching was most stable as described above, and the physical properties were good.

Also, commercially available film with ratio d, film at 100°C, R
After repeatedly bending the film in Run No. 12 by hand and measuring its barrier properties, the film in Run No. 12 showed almost no deterioration, while the film at R.O. and 100°C. It was 2.3 times worse. This shows that the highly cold stretched film of this example has particularly excellent pinhole resistance in the barrier layer. This seems to be because the barrier layer is also stretched at a sufficiently low temperature.

[Brief explanation of drawings]

FIG. 1 shows the relationship between film shrinkage rate and heat treatment temperature, and FIG. 2 shows the relationship between film shrinkage stress and heat treatment temperature. (In the figure, 1 is a Run Nα3 film; 3 is a commercially available plasticized PVC shrink film; 4 is a commercially available PVC shrink film;
P shrink film; 5 is a commercially available cross-linked polyethylene shrink film; 6 is the aforementioned commercially available barrier shrink film) Masao Miyake

Claims (8)

[Claims] (1) In a multilayer highly stretched film consisting of three or more types of polymer layers, one layer is at least one type of copolymer selected from the following copolymers (A) to (C): (A) Vinyl ester monomer (B) A copolymer of ethylene and a monomer selected from aliphatic unsaturated carboxylic acids and aliphatic unsaturated carboxylic acid alkyl esters; (C) The above copolymer (B) ), another layer contains at least one polymer selected from nylon and saponified ethylene-vinyl acetate copolymer, and another layer contains the above polymer. At least one copolymer selected from (A) to (C), which is different from the above single layer, and at least one copolymer selected from crystalline polypropylene, and whose tensile strength A cold highly stretched multilayer film having a strength of 5 kg/mm^2 or more and a shrinkage gradient of 2.0 or less. (2) At least one copolymer selected from the following copolymers (A) to (C): (A) Copolymer of vinyl ester monomer and ethylene; (B) Aliphatic unsaturated carboxyl A copolymer of ethylene and a monomer selected from acids, aliphatic unsaturated carboxylic acids and alkyl esters; (C) Mainly containing an ionomer copolymer derived from the copolymer (B), and others. The layer contains at least one polymer selected from nylon and saponified ethylene-vinyl acetate copolymer, and the other layer contains at least one copolymer selected from the above polymers (A) to (C). A multilayer molten raw fabric containing at least one polymer selected from a copolymer and crystalline polypropylene other than the above-mentioned single layer is extruded, and then rapidly cooled and solidified with a liquid refrigerant to obtain a multilayered raw fabric. The obtained original film is stretched as it is or at a stretching temperature of 80° C. or less using a rectifying contact guide designed to substantially isolate the stretching start part and the heating part. A method for producing a multilayer highly stretched film, which comprises cold stretching to an areal stretching ratio of 3 to 30 times while contacting and removing the film at least discontinuously in the circumferential direction. (3) The method according to claim (2), in which the multilayer original fabric is heated to a temperature below the crystalline melting point of the main polymer. (4) The method according to claim (2), wherein the multilayer original fabric is stretched at a stretching temperature of 20 to 70°C. (5) The method according to claim (2), wherein the multilayer original fabric is stretched at a temperature below the Vicat softening point of the main polymer. (6) The method according to claim (2), wherein the multilayer original fabric is a tubular original fabric and is stretched at a transverse stretching ratio of 2 to 7 times. (7) The method according to claim (2), wherein the stretching is carried out at an area stretch ratio of 7 to 20 times and a transverse direction stretch ratio of 2 to 5 times. (8) Stretch at least 5 times more at the end of stretching than at the beginning of stretching.
Claim No. (2) which is performed by creating a temperature difference that is as low as ℃
The method described in section.