JPH026621B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention mainly relates to shrink wrapping films with excellent transparency for use as packaging materials, etc. Specifically, the present invention relates to shrink wrapping films with a vinyl acetate group content of 3 to 3.
30% by weight of ethylene-vinyl acetate copolymer (a) with a melt index of 0.2-10 and 95-10% by weight of ethylene-α- with a melt index of 0.1-10.
Olefin copolymer elastomer (b) 5-90% by weight
A low-temperature shrinkable, high-strength flexible packaging film with a 20% shrinkage temperature of 85°C or less and a tensile strength at break of 5 Kg/mm ² or more, especially a shrink-wrapping film and a specific low-temperature film. The present invention relates to a method for manufacturing the same using a biaxial stretching method. There are various packaging methods using film that take advantage of the characteristics of the film, such as sealing into a bag, twisting the film, shrink wrapping by applying heat, and Saran Wrap (Asahi Dow product name). Many methods are used, such as the tight wrap method and stretch wrap method, each of which requires unique packaging characteristics.
At present, films are packaged by selecting films that match the base material, composition, shape, properties, etc. of each method. Among them, the shrinking method utilizes the heat-shrinkability of a stretched and oriented film to loosely pre-pack the packaged item, for example, to enclose the packaged item with a seal, and then the film is heated using hot air, infrared rays, etc. ,hot water,
Another method is to shrink the contents tightly using a heating medium. Its features include the ability to visually and tactilely check the quality of the package while increasing its beauty and product value while keeping the contents sanitary; and the ability to securely secure even irregularly shaped items or multiple items in one package. Excellent packaging and protection against vibrations and shocks. Furthermore, compared to the stretch packaging method currently widely used in supermarkets, it is possible to increase the packaging speed. It is also possible to package irregularly shaped items that cannot be wrapped with stretch packaging, such as trays, etc. without containers. or,
Although it has the advantage of being able to be packaged more tightly, its disadvantage is that it must be heated sufficiently until the film shrinks. Currently, the most commonly used film for shrink wrapping is plastic polyvinyl chloride (hereinafter referred to as PVC).
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. Generates toxic gases such as chlorine gas when melting with hot rays, corrosive toxic gases when incinerating used films, and has poor cold resistance when storing packages at low temperatures or handling them in cold regions. Therefore, there are problems in that the film becomes hard, brittle, and easily torn. Therefore, in recent years polypropylene (hereinafter referred to as PP)
Shrink wrapping film has been attracting attention, but its drawback is that its shrinkability is inferior to that of PVC. PP-based stretched film has excellent mechanical properties, moisture resistance, and heat sealability, making it an excellent shrink wrapping film. It also has the advantage of lower raw material cost compared to PVC. However, PP is a crystalline polymer with a high softening temperature, and has a higher heating shrinkage temperature than conventional stretched films, and has a low shrinkage rate at low temperatures of around 100°C.
Therefore, heating must be carried out to a high temperature in the shrink packaging process, and since the tolerance range for heating temperature is narrow and the shrinkage rate has a steep temperature dependence, uneven heating in some areas during packaging can cause significant uneven shrinkage. Practically undesirable defects such as wrinkles and pockmarks tend to occur, and in order to prevent this, sufficient heating may cause overheating of the packaged material, devitrification of the film, and tearing of seals and air vent holes. This has become a major drawback. In addition, in conventional polyethylene films, it is not possible to impart sufficient stretching orientation to the molecules, and therefore, the obtained film has a low heat shrinkage rate, especially a low heat shrinkage stress, and a high shrinkage temperature, which makes the film difficult to use. It has poor strength and optical properties, and has low cohesiveness for packaged items after packaging, so it is used thicker for special purposes. In addition, even in the case of polyethylene films, films that are stretched using high-energy rays to sufficiently cause a cross-linking reaction in the molecules have a high heat shrinkage rate and heat shrinkage stress, and have optical properties such as transparency and gloss compared to ordinary polyethylene. Although it has very excellent properties such as heat resistance, it has poor heat shrinkage properties at high temperatures, is difficult to heat seal, has poor tear resistance, and is difficult to cut with a heating wire, so the packaging speed is limited. It has disadvantages such as inferior quality. One of the important characteristics of the above-mentioned shrink wrapping is that it can be wrapped sufficiently at low temperatures, and is especially required when packaging fresh foods. On the other hand, in the case of polypropylene, the method of manufacturing stretched film involves heating it to a high temperature of 150 to 160°C, and once using an extruder.
This method involves reheating a tube-shaped raw material that has been melt-extruded from a die and rapidly cooling it, and drawing it by introducing air inside.Also, in the case of low-density polyethylene, it is biaxially stretched in two stages as in the conventional method, resulting in a high degree of stretching orientation. Attempting to set it is technically extremely difficult as it tends to tear during processing. For this purpose, by using the inflation method, for example,
A common method is to extrude the film at a temperature of 180 to 220°C and immediately expand it while cooling it with air to form a film of a predetermined size. This method has the advantage of being able to easily produce a film at a very low cost, but it tends to cause intermolecular flow and makes it impossible to set a satisfactory molecular orientation by stretching. Therefore, the heat shrinkage rate and heat shrinkage stress are small, both of which are on the high temperature side, and it can only be used for special purposes by increasing the film thickness. For this purpose, after forming low-density polyethylene, it is irradiated with high-energy radiation under appropriate conditions to cause a partial crosslinking reaction, and then reheated and stretched to prevent intermolecular flow and achieve sufficient molecular orientation. Although there are methods for setting this, the disadvantage is that the manufacturing equipment is expensive and complicated. Recently, several attempts have been made to improve these drawbacks. For example, Japanese Patent Publication No. 45-2699 discloses a method for obtaining a stretched film by improving heat flow characteristics by using a mixed composition of ethylene-vinyl acetate copolymer and ionomer resin, and in this method, the strength is also higher than that of the film of the present invention. In addition, Japanese Patent Publication No. 46-4075 discloses a method of stretching using a specific ethylene-propylene copolymer, but it has poor optical properties and heat shrinkage properties compared to PVC films. , strength, etc., and workability are still insufficient. Therefore, the present inventors conducted research to further improve the shortcomings of these films and manufacturing methods, and at the same time improved the temperature dependence of the heat shrinkage characteristics, the sealing performance of the optical characteristics film, the strength, etc. We have discovered an excellent soft film that is comparable to plasticized PVC films, which also has improved flexibility in the plasticized PVC stretch film area, and a specific method for producing them that is inexpensive and has excellent processability. That is, in the present invention, the vinyl acetate group content is 3
~30% by weight of ethylene-vinyl acetate copolymer (a) with a melt index of 0.2-10 95-10% by weight
and 5 to 90% by weight of a thermoplastic elastomer (b) made of an ethylene-α-olefin copolymer with a melt index of 0.1 to 10, and the 20% shrinkage temperature of the film is
This cold highly oriented stretched film has excellent low-temperature shrinkability at 85° C. or lower and has a tensile strength at break of 5 Kg/mm ² or higher, and is suitable for packaging over a wide temperature range. In addition, the manufacturing method consists of ethylene-vinyl acetate copolymer (a) having a vinyl acetate group content of 3 to 30% by weight and a melt index of 0.2 to 10 (95 to 10% by weight) and a melt index of 0.1 to 0.1 to 10% by weight. 10 ethylene-
A thermoplastic elastomer (b) consisting of an α-olefin copolymer with a mixed composition of 5 to 90% by weight is mixed and melted, extruded through an annular die, rapidly solidified with a liquid refrigerant, and heated to 100°C or below. It is characterized by being cold-stretched by the inflation method at a stretching temperature of room temperature (20°C) to 100°C, with an area stretching ratio of 5 times or more and 30 times or less, and a transverse direction stretching ratio of 2 to 7 times. Low-temperature shrinkability with excellent optical properties,
This is a method for producing a high-strength stretched film. Ethylene-vinyl acetate copolymer used in the present invention
When the vinyl acetate group content in (a) is less than 3% by weight,
Poor cold stretchability, film strength, heat shrinkage, and 30
If it exceeds % by weight, the rubber-like elasticity will be too high and the stretchability will become unfavorable. Preferably it is 5 to 25% by weight, and if the melt index is less than 0.2, there will be problems with mixability.
If the above is the case, the strength as a base material will be insufficient and it will be easy to tear during stretching, which is undesirable. Preferably
It is 0.3-5. Furthermore, the thermoplastic elastomer (b) made of an ethylene-α-olefin copolymer is ethylene, and any one of butene-1, isobutylene, 1-pentene, 4-methyl-1-pentene, and propylene, or a mixture thereof. (the content of ethylene is in the range of 60 to 95 mol%, preferably 65 to 90 mol%), and the melt index is 0.1.
to 10, preferably 0.2 to 6, preferably amorphous, but also includes low partially crystalline ones with a crystallinity of about 30% or less. ) etc. It is preferable that these materials can be processed singly into a sheet or film, and have a density of
Vicat softening point ( ^ASTM-
D1525 with a load of 1 kg) is below 80℃, preferably
A soft copolymer having a temperature of 70° C. or lower is preferable, and other so-called brittle uncrosslinked rubber-like cold flow-inducing copolymers, such as ethylene-propylene rubber, are not preferable because they weaken the properties of the base material. A preferred copolymer elastomer is one or two selected from ethylene, butene-1, and propylene.
It is a random copolymer consisting of at least one polyene, and these may also be copolymerized with a small amount of polyenes, such as hexadiene or ethylidene norbornene derivatives. These can be polymerized using, for example, a vanadium-based compound and an organoaluminum compound-based catalyst. The present invention comprises a mixture having the above composition, and the ethylene-α-
The amount of thermoplastic elastomer (b) made of olefin copolymer mixed is 5 to 90% by weight based on the total amount of both.
Preferably 7 to 70% by weight, more preferably 10 to 50%
If it is less than 5% by weight, the mixture will not exhibit a synergistic effect, the processability will deteriorate, the strength of the film will decrease, and the low-temperature shrinkability will tend to deteriorate, and if it is less than 5% by weight, When this happens, the film forming properties and stretching processability of the tube-shaped original fabric deteriorate, resulting in disadvantages such as poor sealing properties. As described above, in the present invention, the synergistic effect is achieved only under specific stretching conditions, that is, by using a tube-shaped quenched original fabric using a specific mixing amount of the two specific base materials mentioned above, that is, low-temperature stretching 20 It can be formed at a temperature of ~100°C, and as a result, a film with excellent properties can be obtained. In the present invention, there is no problem in mixing and using other compositions, resins such as polyethylene, etc., as long as the stretchability and various properties are not impaired. The film of the present invention is characterized in that its optical properties [haze value (ASTM D1003-52)] are 3% or less, preferably 2%, and it is further characterized in that it hardly deteriorates even after heat shrinkage. For example, Example 2 RUN No. 2 has an extremely excellent value of [0.5%]. This is a value characterized by its composition and manufacturing method, and it can be processed without impairing the quenched properties of the composition of the present invention, and can be stably stretched in a bubble shape at low temperatures even below the melting point of the composition, and even below the softening point. Due to the synergistic effect of the composition, the composition does not cause structural defects such as voids, and the thinly dispersed mixed components are stretched to form a flat shape with less light scattering, making it particularly transparent. It seems to be. In addition, low-temperature shrinkability is one of the properties that is especially necessary when used as a shrink wrapping film, and it shrinks by 20% or 40% of the value expressed by the heat shrinkage rate when the film is processed at various temperature conditions. (represented by the average shrinkage rate in the vertical and horizontal directions), and the lower this value is, the better the low-temperature shrinkage characteristics are. Further, the shrinkage rate required for a shrink film is usually 20% or more, preferably 40% or more, although it varies depending on the packaging method. Specifically, a test piece cut from a film is marked with vertical and horizontal markings of specified dimensions, coated with powder such as talc to prevent it from sticking to itself or other objects during shrinkage, and then heated with hot air at a specified temperature for 5 minutes. The heat shrinkage rate is expressed as the vertical and horizontal average value of the value expressed as the change rate of dimensions in each direction after heat shrinkage.This value is measured at each temperature and graphed. 20% or 40%
The temperature expressed by the heating shrinkage rate is called the 20% and 40% shrinkage temperature. The film according to the present invention is characterized in that this value is low and has a gentle temperature dependence. For example, as shown in 3 in Figure 1 below, a commercially available shrinkable polypropylene film is heated at 120°C at 20% and 40%
Compared to the high temperature of 134℃, which changes rapidly,
For example, as shown in Figure 1, at 20%, 55℃, 40℃
It has the characteristics of a low value of 73℃ and a gentle shape. This degree is expressed as a 20% value and is 85°C or lower, preferably 75°C or lower, and more preferably 70°C or lower. This value is secondarily influenced by the temperature, degree, composition, etc. of stretching, but one of the major features of the cold stretching of the present invention is that it is at a low level and has a gentle shrinkage curve. If this value is high, heat shrinkage will not occur unless exposed to a fairly high temperature for a long time in practical use, so the amount of heat from the heater must be increased, the speed of packaging work will be slow, and the product to be packaged will be damaged. It is unsuitable for items that are dangerous due to heat transmission, items that are susceptible to deformation, especially textiles, and fresh foods.Also, films whose shrinkage curve tends to rise suddenly at high temperatures are subject to shrinkage during packaging. Because the shrinkage rate changes greatly in response to very small changes in temperature, if the film is loosely wrapped in advance and passed through a shrink tunnel, if the overall temperature of the hot air hitting the film is a little too low, it will not shrink tightly and will not fit tightly. Moreover, if the temperature is slightly high, not only the optical properties after shrinkage but also the mechanical properties such as strength will be significantly reduced. Further, there may be defects such as the seal portion or the air vent hole being torn. On the other hand, if this value is too extremely low, the dimensions of the film wound into a roll may change at room temperature, which is undesirable. Commercially available PVC film for plastic shrink packaging has this value at 58℃ and 40℃ at 20% shrinkage, as shown in 2 in Figure 1.
% of 88°C, and has favorable low-temperature shrinkage characteristics that are gentle with respect to temperature. FIG. 3 shows an example of the range in which good products can be obtained as a result of the packaging test described later, and it has the characteristic that it can be packaged at lower temperatures and for a shorter time than PVC films. This is probably due to the fact that it has a faster response than PVC films. Until now, no film other than plasticized PVC with such shrinkage rate characteristics and strength has ever been commercially available. The film of the present invention achieves this and is an unprecedented film. In addition, heat shrinkage stress during shrinkage is one of the important characteristics when used as a shrink wrapping film.
For example, as described below, even if the heat shrinkage rate is high, if the stress during shrinkage is extremely low, it will not fit the packaged object during or after packaging, and will not have binding strength, making it completely useless as a shrink wrapping film. Don't do it. Furthermore, if the binding force is insufficient even to a small extent, it is necessary to use a thick film to cover it, which is uneconomical and inconvenient. Normally, this value is at least 50 g/mm ² or more, preferably 80 g/mm ² or more. As shown in Figure 2, commercially available polyethylene shrink film (4 in the figure) has a value of 10 g/mm 2 or more. mm ² or less, about 5 g/mm ² , and its uses are limited. The film of the present invention is, for example, as shown in 1 in the same figure.
180g/ ^mm2 is also available. Usually, the film of the present invention has this value of 100 to 400 g/
It has a sufficiently high level of about mm ² .
In addition, for low-temperature shrinkable films, this shrinkage stress is meaningless unless it is exerted at a low level of temperature corresponding to the shrinkage rate, and the temperature dependence curve is (vertical,
The shrinkage rate (expressed as a horizontal average value) must be well balanced with the temperature curve. In the present invention, the stiffness of the film can be freely adjusted by changing the composition within a certain range within a specific mixture composition, up to a flexible region such as a stretch film made of plasticized PVC (plasticizer 33% by weight). obtain. Furthermore, the present invention is characterized by its high tensile strength, and has a breaking strength of at least 5 Kg/mm ² (value measured by the method of JIS Z1702) and preferably 7 Kg/mm ²
Above, more preferably, it has a value of 10Kg/mm ² or more, and the elongation at that time is also 50% or more, preferably
It is 100% or more, more preferably 150% or more. Such high tensile strength and elongation mean that the film is tough and difficult to tear, which is very advantageous as a protective film for packages, and the thickness of the film can be saved. The film of the present invention can be used, for example, in RUN as described below.
Like No. 4, it has a breaking strength of 15 kg/mm ² and an elongation of 185%. In contrast, when the strength is increased through orientation, the elongation tends to be extremely low.
For example, a commercially available fully crosslinked (gel 67% by weight) and fully oriented film has a strength of 8 kg/mm ² and an elongation of 45%.
It is easy to tear. Further, the application is not limited to shrinkage films, but can generally be used as industrial films that utilize toughness. Next, the method for manufacturing the packaging film of the present invention will be explained in detail. The method of the present invention comprises a thermoplastic elastomer (b) consisting of 95 to 10% by weight of an ethylene-vinyl acetate copolymer (a) and 5 to 90% by weight of an ethylene-α-olefin copolymer.
% by weight, mixed and melted, extruded through an annular die, quenched and solidified using a liquid refrigerant to obtain a tube-shaped original fabric with sufficiently low thickness deviation, heated at a temperature not exceeding 100℃, and heated to a temperature of 20℃ (room temperature) to 20℃ (room temperature). Optical properties characterized by an area stretching ratio of 5 times or more and 30 times or less, and a lateral direction stretching ratio of 2 to 7 times, by introducing air into the film under a stretching temperature condition of 100°C. The present invention also provides a method for producing a high-strength stretched film that has excellent low-temperature shrinkage characteristics and is suitable for packaging over a wide temperature range. Here, the ethylene-vinyl acetate copolymer (a) has a vinyl acetate group content of 5 to 30% by weight and a melt index of 0.2 to 10, and the reason for this is as described above. The thermoplastic elastomer formed by coalescence preferably has an ethylene content of 60 to 95 mol%, more preferably 65 to 90 mol%.
Mol% of ethylene and butene-1,4-methyl-
It refers to a copolymer with a compound mainly composed of 1-pentene, isobutylene, propylene, or a mixture thereof, and has a melt index of 0.1 to 10.
Preferably, 0.2 to 6 amorphous or partially crystalline ones are also included. It is preferable that these materials be within the range that can be processed into a film even when used alone. If a large amount of so-called brittle rubber-like materials other than those listed above are used, they will weaken the properties of the base material, make it sticky, and cause punctures during stretching. I don't like it because it looks like this. In the present invention, after the above-mentioned mixed composition is heated and melted and sufficiently kneaded, it is extruded at an extrusion temperature of 180 to 280°C through an annular die that does not give sufficient uneven thickness and heat and time history, and is surrounded by a liquid refrigerant. The material is uniformly rapidly cooled and solidified to form a tube-shaped material that is sufficiently uniform (both externally and internally). This original fabric is heated to 100℃ or below, preferably 90℃ or below.
More preferably, the mixture is heated to 80°C or lower and at a temperature of 20°C (normal temperature) to 90°C, preferably 25°C to 80°C, and even more preferably 30°C to 70°C, to absorb most of the heat of fusion in the mixed components. It can only be obtained by expanding biaxially in a bubble shape at a temperature lower than the melting point of the components determined by the DSC method and preferably below the Vikatto softening point of the mixture under sufficient internal pressure, e.g. 100 to 1000 mm of water column pressure. The optimal area stretching ratio varies depending on the temperature at that time, but is preferably 7 to 30 times,
More preferably, the stretching ratio is 10 to 20 times, and the stretching ratio in the transverse direction is preferably 3 to 6 times. At this time, it is particularly important that the composition be within the range described above to prevent punctures and allow for sufficiently cold stretching, and at the same time, as mentioned above, it is necessary to make a sufficiently uniform raw fabric. If the thickness deviation is about ±10% or more with respect to the thickness of the original fabric, it may become punctured during stretching and may not be stretched properly. The thickness deviation of the original fabric is preferably ±5% or less, more preferably ±3% or less. The degree of stretching is determined by the speed ratio of the sending nip roll and the take-up nip roll, and then the stretching ratio in the vertical direction is determined, and then the next step is to fill the bubble with air and stretch the bubble until it reaches the end of stretching (just before whitening), and then expands in the lateral direction. The best way to carry out the stretching most stably is to keep it at a certain level. Further, in view of the internal pressure and the diameter of the original fabric bubble, it is convenient to have a large size of about 50 mm or more in diameter, preferably 100 mm or more as long as the device allows. In addition, due to the physical properties of the obtained film, it is preferable to keep the film as cold as possible as long as the stability of the bubbles is allowed, but in reality, the degree of stretching is determined by the composition at that time, with a balance with stability (avoiding punctures). do it. The film obtained by the composition method of the present invention has the above-mentioned excellent properties, 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 due to the fact that the unstretched portions of the film are stretched due to the high internal pressure of the bubbles, which applies a strong stretching force to the film during stretching, and also because the thermal history of heating and cooling unlike in conventional methods is particularly small and the film is uniform and stable. It will be done. The optical properties (both haze and gloss) are characterized by being much better after cold stretching by the method of the present invention compared to the original fabric stage. This seems to be due to a change in the shape of the resin dispersed in the form of islands. In other words, in this method, the dispersed particles are also stretched and oriented and flattened, making them less likely to be optically scattered.Although it is a blend system that does not mix to the point of molecular dispersion, it can be stretched well at low temperatures, and at the same time it has strength. It becomes a film, and during this processing, the surface becomes molecules,
This is thought to be because it is not roughened by the flow of crystal grains. In the present invention, each of the mixed compositions exhibits a synergistic effect, and when high strength is desired, any of the components does not become a defect that tends to be seen and cause a decrease in strength. This does not happen at all with the normal stretching method in which the film is heated above its melting point, and in order to improve the optical properties, it is necessary to raise the stretching temperature (for example, to 160°C) to improve the optical properties.
As a result, orientation tends to become more difficult and strength tends to decrease.
Moreover, the same thing can be said at temperatures near the melting point, and not only will the optical properties not produce favorable results, but also the mixed composition will create temperature conditions that make the raw fabric particularly brittle, and furthermore, uneven thickness will be greatly expanded and punctures will occur. , high characteristics cannot be imparted. For example, at a cryogenic temperature of 45
The stretching described in the present invention can be successfully achieved at ℃.
This is something that has never been achieved before, and can only be achieved by using a uniform quenched fabric with a specific composition, and by satisfying conditions such as a specific stretching method. For example, as in the comparative example described below, ethylene-vinyl acetate copolymer, low-density polyethylene, ethylene-α
- When using a single composition such as an olefin copolymer or a composition in which an ethylene-propylene rubber-like copolymer is mixed therewith, the film ruptures and no bubbles grow, that is, stretching is not achieved. A single composition such as EVA has a rubber-like shape with 1
Although it expands to some extent by ~1.5 times, it is difficult to achieve this because it quickly punctures and returns to its original size due to its rubber-like elasticity. Furthermore, if the quenched original fabric is non-uniform, it goes without saying that it will be punctured as described above, making it difficult to stretch it uniformly.
Further, the product of the present invention cannot be obtained at any temperature other than the above-mentioned stretching conditions. Moreover, if the film is stretched only uniaxially, it will tear immediately, and an excellent film having the characteristics of the present invention cannot be obtained, so it must be stretched biaxially under the above-mentioned conditions. Each composition of the present invention is in a state of appropriate compatibility balance, and at the same time, components that act individually with their individual properties, and components that have an appropriate compatibility balance and act synergistically work together to improve processability and film properties. It is thought that it has the characteristics of The film and method of the present invention will be specifically explained in Examples below, but the invention is not limited thereto. Example 1 Ethylene-vinyl acetate copolymer (a) 88 with vinyl acetate group content: 10% by weight, melt index: 1.0
Weight% and melt index 0.45, density 0.88g/
cm ³ , Vicat Ethylene-α-olefin copolymer elastomer with a softening point of 40°C or lower (containing α-olefin equivalent to 20 mol% of butene-1 (b ₁ ): 12
% by weight of the composition was mixed and plasticized and kneaded at a maximum temperature of 250°C in the cylinder part using a mixing head type screw with a diameter of 65mm and L/D37 and an annular die with a slit of 150mm and 1.5mm provided at the tip. was extruded and quenched using a water-cooling ring that uniformly discharged water at a distance of 10 cm from the tip of the die to obtain a raw fabric with a diameter of 100 mm and a thickness of 170 μm and a thickness deviation of ±1.8%. The Vicat softening point of this mixture was 68°C. This raw fabric is passed between two pairs of feeding nip rolls and take-up nip rolls, heated to 45℃ with hot air between them, and by introducing air inside, it is expanded continuously under an internal pressure of 430 mm water column, 3.2 times in length and 3.7 times in width. After stretching, the film is cooled with an air ring blowing cold air at 15°C, folded with a stabilizer plate, taken up with a nip roll, and the edges are slit vertically to separate it into two films, each of which is held at a constant tension. A film having a thickness of 14 μm was obtained by winding it up. The obtained stretched film has excellent optical properties with a haze of 0.6% and a gloss of 150, and is also extremely strong with a tensile strength of 14 Kg/mm ² and elongation.
250%, and the low temperature shrinkage is as shown in Table 1, and as shown in Figure 1, 56% shrinkage at 20% shrinkage.
Commercial Shrink at 75°C and 40% shrinkage
With a gentle pattern similar to PVC film,
Furthermore, the shrinkage rate characteristics shifted toward the low temperature side. Further, the shrinkage stress was at a high level of 173 g/mm ² at the highest value. As a practical packaging test, four cucumbers were passed through a commercially available shrink tunnel that emitted hot air at 80°C for 3 seconds, resulting in a tight, wrinkle-free fit with a good packaging finish and no deterioration in optical properties after shrinkage.
It could be shrink-wrapped beautifully. In addition, as shown in Figure 3, we conducted tests by varying the residence time in the hot air temperature tunnel during shrink wrapping, and the results showed that good packaging was possible over a wide temperature and speed range starting from the low temperature side. Ta. Compared to the above, commercially available polypropylene shrink film hardly shrinks at 90℃, leaving wrinkles on the sample, and under the same conditions, increasing the hot air temperature
Sufficient shrinkage is not possible unless the temperature is 170℃, and even if the temperature is raised higher than this or the residence time is prolonged, the film may become punctured and torn, or the film may become devitrified, and the appropriate temperature range may be exceeded. It was very narrow.
Furthermore, the commercially available PVC shrink film did not shrink enough under the same conditions, leaving wrinkles, and it was necessary to set the temperature condition to 150°C. The strength, elongation, and heat shrinkage properties of the film are well-balanced in both length and width, so they will be expressed as average values in length and width.

[Table] Example 2 Ethylene-vinyl acetate copolymer as shown in Table-2
(a) and ethylene-α-olefin copolymer elastomer (b) in the same manner as in Example 1, stretching temperature
RUN No. 2-8, 61, 48, 54, 43, 38, respectively
Stretching was carried out at 50 and 45°C to obtain a 14μ film with good stability. Both films have minimal thickness deviation of ±5
It was about 8%, and the stretching processability was good. Table 3 shows the physical properties of the film.

[Table] Table 3 is shown on the next page.

【table】

[Table] The film obtained as described above had particularly excellent optical properties and sufficient low-temperature shrinkability, and also had high shrinkage stress and strong strength. When a practical packaging test was conducted in the same manner as in Example 1, the packaging temperature was
The speed range was wide and the results were good. Packaging is judged by defects such as wrinkles in the packaged sample due to unshrinked parts, loose binding, avatars due to unevenness on the film surface, tears at seals, conveyor roll contact parts, tears from air vent holes, melting tears, etc. The judgment was based on good products with no appearance and excellent cohesive strength, and the range in which this could be obtained was determined. Commercially available uncrosslinked polyethylene film that is simply blown through a die has a breaking strength of about 2.5 kg/mm ² , a high 20% shrinkage temperature of 117°C, and a low shrinkage stress of 5 g/mm ² at maximum, making it suitable for packaging. At the time of the test, the temperature was shifted to the high temperature side, and it did not shrink unless it was heated to 180℃, and the film, which was torn, had no cohesion, was loose, and had poor optical properties from the beginning, further devitrified, and was completely compared to the film of the present invention. It was not a problem. In addition, commercially available sufficiently crosslinked polyethylene, Shrink Film (xylene insoluble gel content: 67% by weight), does not shrink well unless it is at a high temperature (170°C), and a good product could not be obtained. This is because the seal part is easy to tear, the film is torn larger than the air vent hole during packaging, and the packaged item is completely thrown out, and the film is devitrified after packaging, which greatly reduces the optical properties and strength of the film. There were many products, and the range of suitability for packaging was narrow. In the film of the present invention, almost no deterioration in optical properties or deterioration in various properties was observed after packaging. Example 3 Using the composition of RUN No. 1 of Example 1, it was processed in the same manner as in the same example, and the diameter was 150 mm, the thickness was 500 μm, and the thickness unevenness in the circumferential direction was ±
Obtain a uniform original fabric of 1.2%, heat it to 42℃, and reduce the length by 3.3
A uniform film with a thickness of 41μ was obtained by stretching 3.7 times. Stretching can be performed stably, and the properties of the obtained film are haze 0.8%, gloss 146, and tensile strength at break.
A film with excellent optical properties and strength of 12.8 Kg/mm ² and elongation of 210% was obtained. Until now, some of the thicker shrink films on the market are made of low-density polyethylene as mentioned above, but since these cannot have sufficient orientation, they have a low heat shrinkage rate as shown in Figure 1. It is misaligned and has low shrinkage stress, which limits its uses. Since thicker films require longer heating times, higher temperatures, and shrinkage stress, the film of the present invention is further advantageous in that it can be packaged quickly at low temperatures. Plastic molded product (30 x 40 made of polystyrene)
As a result of a practical packaging test for a 15cm x 15cm case, it was possible to shrink-wrap the product neatly and quickly without wrinkles. Commercially available polyethylene-based products were unsatisfactory because they were heated to a high temperature (180°C) and took a long time to heat, causing wrinkles and devitrified areas, transmitting heat to the packaged items, and damaging the corner edges. .
If you try to finish the product quickly and raise the temperature further, more parts will reach the melting point and melt by the time it is heated uniformly, and the heat will be transferred to the contents, further deforming the edges of the molded product, resulting in a completely bad result. Summer. Furthermore, if the above-described film of the present invention is stabilized by heat treatment and annealing during and/or after production, a film that does not change in dimensions even at temperatures around 50 to 60°C can be obtained, and its uses are not limited, but it can be used generally. It can be widely used for packaging, agriculture, and industry. Comparative Example 1 The following composition was tried to be stretched in the same manner as in Example 1. Specific RUN No. 1 Ethylene-vinyl acetate copolymer (a ₁ ) alone could not be stretched continuously at temperatures of 40 to 90°C, as it would immediately puncture, burst, and almost return to its original state, and could not be stretched until it was heated to 140°C. A bubble was created. This film has a haze of 3.7%, no low-temperature shrinkage characteristics, a 20% shrinkage temperature of 99°C, a low maximum shrinkage stress of 2 to 3 g/mm ² , and a breaking strength of 2.9 Kg/mm ²
The growth rate was 530%. Specific RUN No. 2 Ethylene-α-olefin copolymer (b ₂ ) alone has elasticity like vulcanized rubber,
At low temperatures below 90 degrees Celsius, the film would swell slightly and become punctured, but the desired film could not be obtained. In the high temperature range of around 140°C, the original fabric blocked and could not be stretched. I tried using RUN No. 3 low-density polyethylene (melt index 1.5, density: 0.918 g/cm ³ ) alone, but it punctured at 40 to 110°C and was completely impossible.
A continuous film was obtained for the first time after heating to 150℃, but the haze was 5.9%, the 20% shrinkage temperature was 107℃, there was no low-temperature shrinkage property, the shrinkage stress was 5g/mm ² , and the breaking strength was
It was low at 2.7Kg/mm ² and was not a problem. Specification RUN No. 4 Low density polyethylene (melt index 1.0, density 0.919g/cm ³ ) 80% by weight and ethylene-α olefin copolymer (b ₁ ): 20% by weight, the composition is similar at 40 to 110℃. I got a puncture and couldn't make it into film. Also, 140
A film was obtained only after heating to ℃, but there was no haze.
At 6.3%, the film had low temperature shrinkage characteristics, no stress, and low strength. RUN No. 5 EPR (ethylene-propylene copolymer rubber: ethylene content 50% by weight) was cut from a rubber block and kneaded with a kneader to 80% by weight of ethylene-vinyl acetate copolymer (a ₁ ) to a total concentration of 20% by weight. 30 when using pelletized compositions
When stretched at ~110°C, it became brittle and broke easily, so it could not be stretched. At higher temperatures, the original fabric was severely blocked and sticky and could not be stretched.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between film shrinkage rate and heat treatment temperature, Figure 2 is a graph showing the relationship between shrinkage stress and heat treatment temperature, and Figure 3 is a graph showing the relationship between shrinkage stress and heat treatment temperature. These are test results and illustrate the range in which good products can be obtained by shrink-wrapping cucumbers. In the figure, 1 is the film of Example 1 of the present invention, 2 is a commercially available plasticized PVC shrink film (thickness 15μ),
3 is a commercially available PP shrink film (thickness 15μ),
4 is an ordinary uncrosslinked low-density polyethylene shrink film (thickness: 50 μm); 5 is a commercially available shrink film made of sufficiently cross-linked low-density polyethylene (thickness: 15 μm).

Claims (1)

[Scope of Claims] 1. Ethylene-vinyl acetate copolymer (a) having a vinyl acetate group content of 3 to 30% by weight and a melt index of 0.2 to 10 (95 to 10% by weight) and a melt index of 0.1 to 10. Thermoplastic elastomer (b) consisting of 10 ethylene-α-olefin copolymers 5 to 90% by weight
A cold highly oriented film having a mixed composition of 20% shrinkage temperature of 85° C. or less and a tensile strength at break of 5 Kg/mm ^{2 or} more. 2. Ethylene-vinyl acetate copolymer (a) having a vinyl acetate group content of 3 to 30% by weight and a melt index of 0.2 to 10 (95 to 10% by weight) and ethylene-α- having a melt index of 0.1 to 10 Thermoplastic elastomer (b) consisting of olefin copolymer (5 to 90% by weight)
A tube-shaped original fabric is made by mixing and melting a mixed composition of
By heating to 100℃ or less and pressurizing air between two pairs of Nippro rolls at a heating temperature of 20 to 100℃, the area stretching ratio is 5 times or more and 30 times or less, and the transverse direction stretching ratio is 2 to 7 times. 1. A method for producing a cold highly oriented film, which is characterized by stretching the film.