JPH0548737B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a heat-shrinkable film with excellent transparency and a method for producing the same. The present invention relates to a heat-shrinkable film consisting essentially of an ethylene-based copolymer and a method for easily producing the heat-shrinkable film continuously using a small-sized device. [Prior art] Conventionally, it has been used for food packaging such as soft drinks and confectionery, for integrated packaging of photosensitive paper, small home appliances, medicines, etc., for bundling long objects such as building materials, and for roll-shaped lengths of textiles, paper, etc. 2. Description of the Related Art Heat-shrinkable films are used for packaging objects, etc., in order to simplify packaging and save labor. The above-mentioned shrink wrapping methods include the overlap method, which completely wraps the packaged item, and the sleeve wrap method, which wraps the packaged item in a cylindrical film with both ends open.However, the sleeve wrap method is widely used because it is simpler and more labor-saving. There is. In this sleeve wrap method, a uniaxially stretched oriented film having a relatively high heat shrinkage rate and binding strength in the longitudinal direction is preferably used. These shrinkable films are made of polyethylene, ethylene-
Unstretched films and stretched films made of ethylene polymers such as vinyl acetate copolymers, polypropylene, polyvinyl chloride, and mixtures thereof, and films crosslinked by irradiation with electron beams and the like are known. However, high-pressure polyethylene (hereinafter simply referred to as
Heat-shrinkable films made of unstretched films of LDPE (hereinafter abbreviated as LDPE) or a mixture of LDPE and ethylene-vinyl acetate copolymer (hereinafter simply abbreviated as EVA) have the drawbacks of low tensile strength and poor transparency.
In addition, the stretched film has a low stretching ratio, so it cannot be stretched uniformly, leaving uneven stretching,
It has drawbacks such as uneven thickness. On the other hand, cross-linked uniaxially stretched shrink film of LDPE is
Since crosslinking is carried out by irradiating electron beams, it is difficult to control the crosslinking, which not only poses problems in production, but also has poor heat sealing properties and is expensive due to the crosslinking process required (for example, JP-A-145771 (Japanese Patent Application Laid-open No. 55-71529, Japanese Patent Application Laid-Open No. 50-72942, Japanese Patent Application Laid-open No. 51-101079, etc.). There is also a method of producing a low-density ethylene-α-olefin copolymer, that is, a linear low-density polyethylene with short chain branches (abbreviated simply as LLDPE), by stretching such as roll stretching or close roll stretching. It has been proposed (for example, Japanese Patent Application Laid-Open No. 1986-
119827, 59-229317, etc.)
In these stretching processes, there is a large amount of net-in during stretching, and the ends of the film are cut off to produce a product, resulting in a large amount of loss. Further, there are problems such as uneven thickness, narrow stretching area for imparting low-temperature shrinkability, and extremely limited manufacturing conditions. Furthermore, in Japanese Patent Application Laid-Open No. 54-72191,
Made from 95-50% by weight of polyethylene with a density of 0.930 g/ ^cm3 or less and 5-50% by weight of polyolefin resin containing 20% by weight or more of ethylene-propylene rubber with an elongation (E150) at 150°C of 500% or more. Disclosed is a film which is uniaxially stretched by making a film of a composition pass between pressure rolls,
Similarly, as a device using a pressure roll, JP-A-52
-117378, JP-A-53-98375, etc. have been proposed. However, when these usual pressure roll stretching methods are used for ethylene-α-olefin copolymers, unlike the above-mentioned close roll stretching methods, they have the advantage of no neck-in and no thickness unevenness; In order to improve the properties, the diameter of the rolling roll must be made very large, or in order to prevent uneven thickness, the production speed must be significantly reduced. [Problems to be Solved by the Invention] The present invention has been made to solve the above problems, and provides a heat-shrinkable film that has excellent low-temperature heat-shrinkability, transparency, and shrinkage stress, and a heat-shrinkable film that has excellent low-temperature heat-shrinkability, transparency, and shrinkage stress. The purpose is to provide a method for continuous and easy production using small-sized equipment. [Means for Solving the Problems] The present invention provides: a) a density of 0.86 to 0.95 g/cm ³ , a boiling n-hexane insoluble content of 10% by weight or more, and a maximum peak measured by differential scanning calorimetry (DSC); 70 to 95% by weight of ethylene-α-olefin copolymer having a temperature (Tm) of 100°C or higher b) Ethylene-α-olefin copolymer rubber and/or ethylene-vinyl acetate copolymer 5 to 30%
The present invention provides a heat-shrinkable film which is a non-uniaxially rolled uniaxially oriented film consisting essentially of % by weight and has excellent transparency that satisfies the following () to (), and a method for producing the same. () Tensile strength is 500 Kg/cm ² or more () Shrinkage stress is 50 Kg/cm ² or more () 50% shrinkage temperature is 110°C or less () Haze is 5% or less Ethylene-α-olefin which is component a) of the present invention The copolymer is a copolymer of ethylene with an α-olefin having 3 to 12 carbon atoms,
As α-olefins, propylene, butene-
1, hexene-1,4-methyl-pentene-1,
Examples include octene-1, and propylene, butene-1, and hexene-1 are particularly preferred. The copolymer has a density of 0.86 to 0.95 g/cm ³ , preferably 0.88 to 0.93 g/cm ³ , more preferably 0.90
~0.92g/ ^cm3 , boiling n-hexane insoluble content of 10% by weight or more, and differential scanning calorimetry (DSC)
It is important that the ethylene-α-olefin copolymer has a maximum peak temperature (Tm) of 100°C or higher. If the density is less than 0.86 g/cm ³ , it is difficult to satisfy the tensile strength, heat shrinkage stress and heat shrinkage rate, and if the density exceeds 0.95 g/cm ³ , the degree of haze becomes poor. In addition, if the boiling n-hexane insoluble content is less than 10% by weight, the oil resistance and stiffness will be poor, and if the (Tm) of DSC is less than 100℃, the heat resistance will be poor, and both are the most commonly used packaging materials. It is not satisfactory as a heat-shrinkable film. The melt index (hereinafter simply abbreviated as MI) of the above ethylene-α-olefin copolymer is 0.05~
20 g/10 minutes, preferably in the range of 0.1 to 10 g/10 minutes. The method for measuring the boiling n-hexane insoluble matter and DSC in the present invention is as follows. Measuring method for boiling n-hexane insolubles: Use a heat press to form a sheet with a thickness of 200 μm, cut out three sheets of 20 mm x 30 mm lengthwise and widthwise, and cut them using a double-tube Soxhlet extractor. Then extract with boiling n-hexane for 5 hours. After taking out the n-hexane insoluble matter and vacuum drying (7 hours under vacuum, 50° C.), the boiling n-hexane insoluble matter is calculated using the following formula. Boiling n-hexane insoluble content (weight %) = (extracted sheet weight / unextracted sheet weight) x 100 (weight %) DSC measurement method: Weigh out approximately 5 mg of a sample from a 100 μm thick hot press-molded film. , set it in the DSC device, raise the temperature to 170℃ and hold it at that temperature for 15 minutes,
Cool to 0°C at a cooling rate of 2.5°C/min. next,
From this state, the temperature is raised to 170°C at a heating rate of 10°C/min and measurements are taken. The temperature at the position of the maximum peak that appears during the temperature increase from 0°C to 170°C is defined as Tm. The ethylene-.alpha.-olefin copolymer used in the present invention described above is clearly distinguished from the ethylene-.alpha.-olefin copolymer obtained by using vanadium as a solid catalyst component. That is, conventional ethylene-propylene copolymers and the like have almost no crystallinity, and even if crystal parts exist, they are in extremely small amounts, and the maximum peak temperature (Tm) measured by DSC is less than 100°C. This indicates that it cannot be used in applications that require heat resistance, mechanical strength, etc. The ethylene-α-olefin copolymer rubber that is component b) of the present invention is generally one containing vanadium as a solid catalyst component, which is excluded from the above-mentioned ethylene-α-olefin copolymer. It is an ethylene-α-olefin copolymer obtained by Substantially no crystallinity. In addition, the b) component of the present invention has a vinyl acetate content of 5 to 30% by weight.
EVA can also be used. The blending ratio of component a) and component b) above is 70 to 95/
30-5% by weight, preferably 80-90/20-10% by weight
It is blended within the range of. The blending method is carried out by methods such as dry blending and melt mixing using a conventional kneading machine such as a Henschel mixer, extruder, or tumbler. If the amount of component b) exceeds 30% by weight, the blocking properties of the film will increase, causing trouble during sleeve packaging. Moreover, if it is less than 5% by weight, transparency and heat shrinkability will deteriorate. The heat-shrinkable film of the present invention is produced by forming the film using the above-mentioned compound as a main component by a conventional film forming method, such as an inflation method or a T-die method, in a solid phase state at a temperature below the melting point of the film, at a rolling ratio of 2 to 8. The following ()~()
It is important to satisfy the following. () Tensile strength is 500 Kg/cm ² or more () Shrinkage stress is 50 Kg/cm ² or more () 50% shrinkage temperature is 110°C or less () Haze is 5% or less The method for producing the heat-shrinkable film of the present invention is detailed below. Describe. A film obtained by a conventional manufacturing method is rolled at a rolling ratio of 2 to 100°C in a solid state below its melting point, preferably in a temperature range of 40 to 110°C, more preferably 70 to 100°C.
This is achieved by uniaxial rolling at a rolling speed of 8 times, preferably 3 to 6 times, and at a circumferential speed ratio of 1:1.1 to 1:4. When the above-mentioned rolling ratio is less than 2 times, it is difficult to obtain required physical properties such as predetermined haze and heat shrinkage rate, and when the rolling ratio exceeds 8 times, the rolling force becomes extremely large, making it difficult to achieve industrial It is difficult to apply to production. Further, the above rolling method is different from conventional constant speed rolling and requires non-uniform speed rolling. In other words, non-uniform speed rolling refers to at least one pair of rolls in which the peripheral speeds (peripheral speed ratio) of the rolls are different, and the rolling force is much lower than that of conventional uniform speed rolling, there is no neck-in, Does not cause thickness unevenness, does not increase the rolling roll diameter, and
This is an effective rolling method that allows the above-mentioned heat-shrinkable film to be manufactured easily and continuously without reducing production speed. The above peripheral speed ratio is preferably in the range of 1:1.1 to 1:4.0, preferably 1:1.5 to 2.5. When the circumferential speed ratio is less than 1:1.1, the rolling effect is poor and the required physical properties of the heat-shrinkable film, which is the object of the present invention, cannot be satisfied. Also, if the ratio exceeds 1:4.0, that is, if the peripheral speed ratio is increased,
The rolling force decreases, but the cloudiness becomes worse. The heat-shrinkable film of the present invention obtained in this manner not only has superior mechanical strength such as transparency, tensile strength, and shrinkage stress, but also has more appropriate shrinkage in a shrinking furnace than conventional polyethylene heat-shrinkable films. It has a wide temperature range, and even when packaging in tight shrink sleeves, the film does not melt or break, allowing for packaging with a good finish. In addition, in the present invention, other synthetic resins, rubbers, organic and inorganic fillers, antioxidants, ultraviolet inhibitors,
Additives such as pigments, nucleating agents, crosslinking agents, and antistatic agents may be added. [Example] The present invention will be explained in more detail with reference to Examples below.
The present invention is not limited to this example. Examples 1 to 3 and Comparative Example 1 a) Component density: 0.92 g/cm ³ , MI: 0.88 g/10
Ethylene-butene-1 copolymer (hereinafter abbreviated as LLDPE) with a DSC maximum peak temperature of 125°C and a boiling n-hexane insoluble area of 97% (Product name: Nisseki Linirex AF1210, manufactured by Nippon Oil Engineering Co., Ltd.) ) and b) ethylene with a density of 0.88 g/cm ³ and an MI of 1.2 g/10 min.
Propylene copolymer rubber (product name: Tafmer
P040 (manufactured by Mitsui Petrochemicals Co., Ltd.) was blended in a predetermined ratio, and a film with a thickness of 0.2 mm was formed using an inflation molding method. Using the above film, roll diameter 220m/mφ
Roll length 500m/m, rolling magnification 5
A heat-shrinkable film with a thickness of 0.04 m/m was produced by rolling at a circumferential speed ratio of 1:2 and a rolling temperature of 90°C.
The physical properties of the film were measured. Furthermore, in Comparative Example 1, the blending amount of b) was 40% by weight, which is out of the range of the present invention, and only a film with inferior shrinkage stress was obtained. The results are shown in Table 1.

[Table] △: Some rolling unevenness occurs.
×: Rolling unevenness occurs.
Examples 4 to 6 and Comparative Examples 2 to 3 Same composition and same method as Example 1, thickness 0.06 m/m, 0.12 m/m, 0.24 m/m, 0.28
We produced five types of films of m/m, 0.34m/m,
A heat-shrinkable film having a thickness of 0.04 m/m was obtained by rolling at a rolling ratio of 3 times, 6 times, and 7 times under conditions of a circumferential speed ratio of 1:2 and a roll rolling temperature of 90° C. The physical properties of the obtained film were measured. In Comparative Example 2, the rolling ratio is as low as 2 or less, the rolling force is small, and a film with poor shrinkage stress is obtained. In Comparative Example 3, the rolling ratio was 8.5.
This is a case where the rolling force is too high and is outside the scope of the present invention, and the rolling force becomes extremely large, causing rolling unevenness and making stable continuous operation impossible. The results are shown in Table 2.

[Table] △: Some rolling unevenness occurs.
×: Rolling unevenness occurs.
Examples 7 to 9 and Comparative Examples 4 to 5 Films with a thickness of 0.2 m/m were manufactured using the same composition and method as in Example 1, and the rolling ratio was 5 times and the rolling temperature was 90.
The film was rolled at a temperature of 1:1 to 1:4.5 at a circumferential speed ratio of 1:1 to 1:4.5 to obtain a heat-shrinkable film having a thickness of 0.04 m/m. Comparative Example 4 is a case of uniform speed rolling, and in order to obtain the heat-shrinkable film of the present invention, the rolling force must be extremely large, resulting in uneven rolling, making stable continuous operation impossible. Comparative Example 5 is a case where the peripheral speed ratio exceeds 1:4 and is 1:4.5, and only a film with poor haze can be obtained. The results are shown in Table 3.

[Table] ○: No rolling unevenness.
Δ: Some rolling unevenness occurs.
×: Rolling unevenness occurs. Comparative Example 6 [When using only high-pressure low-density polyethylene (LDPE)] LDPE with a density of 0.924 g/cm ³ and an MI of 0.3 g/10 minutes (product name: Nisseki Lexron F105, manufactured by Nippon Petrochemical Co., Ltd.) was used to form a film with a thickness of 0.14 m/m by inflation molding, and the film was rolled to a thickness of 0.04 m under the rolling conditions of a rolling ratio of 3.5 times, a rolling temperature of 95°C, and a circumferential speed ratio of 1:2. /m of heat-shrinkable film was produced and various physical properties of the film were measured, and the results are shown in Table 4. Comparative Example 7 (When using a composition containing LDPE and EVA)
0.938g/cm ³ , MI1.5/10min, vinyl acetate content 15
A resin composition consisting of 20% by weight of EVA and 20% by weight of EVA was molded into a film with a thickness of 0.14 m/m by the inflation molding method, and the resulting film was subjected to non-uniform speed rolling in the same manner as in Comparative Example 6. The results were evaluated in the same manner as in Example 6 and are shown in Table 4. Comparative Example 8 (When only LLDPE is used) A heat-shrinkable film was produced in the same manner as in Comparative Example 6 using the LLDPE used in Example 1, and the results of evaluating its physical properties are shown in Table 4.

【table】

[Table] △: Some rolling unevenness occurs.
×: Rolling unevenness occurs.
Comparative Example 6 is a case where only LDPE is used,
Only films with inferior tensile strength and shrinkage stress can be obtained. Comparative Example 7 uses a composition in which LDPE is blended with EVA, and a film with poor tensile strength and shrinkage stress is obtained. Comparative Example 8 is a case where only LLDPE is used, and in order to obtain the heat-shrinkable film of the present invention, the rolling force must be extremely large, resulting in uneven rolling, making stable continuous operation impossible. Furthermore, in Comparative Examples 6 and 7, the range of rolling conditions was very narrow, and slight changes in conditions caused frequent stretching breaks, making continuous production difficult. Comparative Example 9 (In the case of close roll stretching) The resin composition of Example 1 was formed into a film with a thickness of 0.20 m/m by inflation molding, and the film was stretched between two rolls with a diameter of 200 m/mφ. The air gap was 2 m/m, and the stretching ratio was 5.
Stretched by close rolls at a stretching temperature of 90℃, the thickness
A film of 0.40 m/m was produced and the physical properties of the film were evaluated. The results are shown in Table 5. Comparative Example 10 (Proximity Roll Stretching) Proximity roll stretching was performed in the same manner as Comparative Example 9 using only the LLDPE used in Example 1, and the physical properties of the obtained film were evaluated. Table 5 shows the results.

[Function and effect of the invention]

The heat-shrinkable film of the present invention has transparency, tensile strength,
It has excellent mechanical strength such as shrinkage stress, has a wide range of appropriate shrinkage temperatures in a shrinkage furnace, and does not cause the film to melt or break even when wrapped in tight shrink sleeves, allowing for good finished packaging. Therefore, the product value can be improved. In addition, the method of the present invention has many advantages such as the reduction force required during rolling is small, effective rolling is possible, and production can be carried out continuously on an industrial scale using small equipment. There is.

Claims (1)

[Claims] 1 a) A density of 0.86 to 0.95 g/cm ³ , a content insoluble in boiling n-hexane of 10% by weight or more, and a maximum peak temperature (Tm) measured by differential scanning calorimetry (DSC).
70 to 95% by weight of ethylene-α-olefin copolymer having a temperature of 100°C or higher b) Ethylene-α-olefin copolymer rubber and/or ethylene-vinyl acetate copolymer 5
A non-uniaxially rolled uniaxially oriented film consisting essentially of ~30% by weight, as shown below () ~ () () Tensile strength of 500 Kg/cm ² or more () Shrinkage stress of 50 Kg/cm ² or more () 50% shrinkage A heat-shrinkable film with excellent transparency that satisfies a temperature of 110℃ or less () and a haze level of 5% or less. 2. A heat-shrinkable film with excellent transparency according to claim 1, wherein the ethylene-α-olefin copolymer of component a) is an ethylene-butene-1 copolymer. 3 a) Density is 0.86 to 0.95 g/cm ³ , boiling n-hexane insoluble content is 10% by weight or more, and maximum peak temperature (Tm) by differential scanning calorimetry (DSC)
70 to 95% by weight of ethylene-α-olefin copolymer having a temperature of 100°C or higher b) Ethylene-α-olefin copolymer rubber and/or ethylene-vinyl acetate copolymer 5
~30% by weight in a solid state below the melting point of the film at a rolling ratio of 2 to 8 times,
The following () to () () Tensile strength is 500 Kg/cm ² or more () Shrinkage stress is 50 Kg/cm ² () 50% shrinkage temperature is 110°C or less () A method for producing a heat-shrinkable film with excellent transparency that satisfies a haze level of 5% or less. 4. A heat-shrinkable film with excellent transparency according to claim 3, wherein the ethylene-α-olefin copolymer of component a) is an ethylene-butene-1 copolymer. Production method.