JPH09176399A - Oriented film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an oriented film excellent in flexibilityt strength and transparency, capable of optionally providing contractility, comprising a resin composition composed of two kinds of ethylene/α-olefin copolymer resins having prescribed physical properties respectively. SOLUTION: A resin composition for this oriented film comprises (A) 30-90wt.% of an ethylene/a 4-8C α-olefin copolymer resin having 0.915-0.935g/cm<3> density and (B) 70-10wt.% of an ethylene/a 4-8C α-olefin copolymer resin having <0.915g/cm<3> density and <=3 ratio Mw/Mn of a weight-average molecular weight Mw to a number-average molecular weight Mn. The component A is preferably a linear low-density polyethylene copolymer and has 0.3-3g/10 minutes melt flow rate (under 2.16kg load at 190 deg.C). The component B has preferably 1-6g/10 minutes melt flow rate and 0.91-0.89g/cm<3> density. Hexene, octene or 4- methylpentene is preferable as the α-olefin in the component A and the component B.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The film of the present invention is flexible and excellent in strength and transparency and is used for packaging products such as fruits and vegetables, processed foods, clothing, cosmetics, stationery, office supplies and the like. The film of the present invention can be obtained as a shrinkable film that shrinks when heated and a non-shrinkable film that does not easily shrink, depending on the production conditions, and the shrinkable film is used for shrink wrapping.

[0002]

2. Description of the Related Art Conventionally, products that are lined up in stores and purchased by consumers are packaged with polypropylene (hereinafter referred to as "strength" and "transparent luster", which are strong and have excellent transparency and gloss to protect and confirm the contents and to make the products look beautiful. , PP), polyvinyl chloride (hereinafter abbreviated as PVC), polystyrene (hereinafter P
Stretched films such as S) are often used.
Stretched PP film makes use of its strength, rigidity, and transparency to package fruits and vegetables, confectionery, snacks, clothing, stationery,
It is widely used for packaging office supplies and the like, and it is often used for overlap shrink wrapping such as cup ramen, etc., which has been given shrinkage under the conditions of stretch molding. Stretched films of PVC and PS make use of rigidity and transparent luster and are used for packaging various products including shrink wrapping, and are useful for protecting products and improving product value.

While these stretched films have high rigidity,
It is inferior in flexibility, is likely to be damaged when an impact force is applied, has low strength in the heat-sealed portion, and is unsuitable when strength such as packaging of a heavy product is required. For these applications requiring high strength, unstretched films of low density polyethylene are often used.
Although it is flexible and has high impact strength, it is inferior in tensile strength and rigidity and easily stretches, so it is necessary to use a thick film, the weight of the package increases, and the transparency is low, making it easy to confirm the content product and make it look beautiful. It was unsuitable for that. It has been studied for a long time to stretch low-density polyethylene to improve its strength, rigidity, and transparency, as well as to impart heat-shrinkability. Cross-linking low-density polyethylene or designing linear low-density polyethylene as a material. Etc., technology development for improving the drawability of low density polyethylene has been carried out, and some biaxially stretched films of these materials are commercially available. Generally, stretching of low density polyethylene is more difficult than polypropylene and is commercially available. The film is stretch-formed by an advanced processing technique.

Although linear low-density polyethylene is basically a stretchable resin, it still has a narrow temperature range in which it can be stretched. When it is low, it cannot be stretched and bursts, and when it is high, it melts and stretches. The resulting stretched film is stable and cannot be stably formed. Attempts have also been made to improve stretch formability by mixing linear low-density polyethylene with branched low-density polyethylene (hereinafter abbreviated as branched PE) by the high-pressure radical method to widen the stretching temperature range and improve the stretching stability. Although it could be improved a little, the physical properties such as strength of the formed film were poor. These polyethylene-based stretched films require advanced technology for molding,
It was a product with a lot of production loss and poor productivity. Also, from the viewpoint of physical properties, the start temperature of heat shrinkage is close to the melting point, and when it is used for shrink wrapping, it melts into holes in the film in the heat shrinking tunnel, or shrinkage is insufficient and wrinkles may occur. It was not possible to shrink-wrap uniformly.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a stretched film that is flexible, has high strength, is excellent in transparency, and can impart shrinkage as required. It is intended to provide a packaging film having improved stretchability, good productivity, sufficient strength to protect products even if it is thin, and eventually contributing to resource saving.

[0006]

In order to solve the above-mentioned problems, the present invention has a density of 0.915 to 0.935 g.
/ Cm ³ ethylene / α-olefin copolymer resin (provided that the α-olefin has 4 to 8 carbon atoms) 30 to
90% by weight, a density of less than 0.915 g / cm ³ , and a ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of 3 or less ethylene / α-olefin copolymer resin (provided that α- The olefin has a carbon number of 4 to 8) and a stretched film comprising a resin composition of 70 to 10% by weight. Since the stretched film of the present invention is produced from the resin composition as described above, stretch moldability is improved, flexibility and strength are high, transparency is excellent, and shrinkability can be imparted to packaging of products. It is provided as an excellent film.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The polyethylene-based stretched film of the present invention will be described in detail below. One of the components of the resin composition used for producing the stretched film of the present invention is ethylene.α- with a density of 0.915 to 0.935 g / cm ^3.
It is an olefin copolymer resin (however, the carbon number of α-olefin is 4 to 8) (hereinafter, abbreviated as resin A). Resin A is a copolymer of ethylene with an α-olefin having 4 to 8 carbon atoms, and is preferably a linear low density polyethylene copolymer. The content of α-olefin is 2
It is 15% by weight, preferably 4 to 12% by weight, more preferably 5 to 10% by weight. Examples of the α-olefin include butene, hexene, octene, 4-methylpentene and the like, and among them, α-olefin having 6 to 8 carbon atoms, particularly hexene, octene and 4-methylpentene-1 are preferable. Resin A melt flow rate (2.16 kg load,
190 [deg.] C., the same below) is preferably 0.1 to 10 g / 10 minutes, and more preferably 0.3 to 3 g / 10 minutes.
The density of the resin A is 0.915 to 0.935 g / cm ³ from the viewpoint of flexibility, strength, transparency and heat resistance. If the density is less than 0.915 g / cm ³ , the heat resistance of the film will be poor, and if it exceeds 0.935 g / cm ³ , the flexibility, strength and transparency will be poor.

Another one of the components of the resin composition used for producing the stretched film of the present invention has a density of 0.915 g /
ethylene · α- having a ratio Mw / Mn of less than ³ cm ^{3 and} a weight average molecular weight Mw to the number average molecular weight Mn of 3 or less.
It is an olefin copolymer resin (however, the carbon number of α-olefin is 4 to 8) (hereinafter, abbreviated as resin B). Resin B is a copolymer of ethylene with an α-olefin having 4 to 8 carbon atoms, and the content of α-olefin is 5
The amount is at least wt%, preferably 8 to 25 wt%, more preferably 10 to 20 wt%. As an α-olefin,
There are butene, hexene, octene, 4-methylpentene, and the like. Among them, α-olefins having 6 to 8 carbon atoms, particularly hexene, octene, and 4-methylpentene-1 are preferable. Resin B has a melt flow rate of 0.1 to 10 g / 1
It is preferably 0 minutes, more preferably 1 to 6 g / 10 minutes. The density of the resin B is 0.915 from the viewpoint of stretch moldability.
less than g / cm ³ , preferably 0.910 to 0.890 g /
cm ³ . When the density is higher than this range, the stretch molding temperature range when combined with the resin A is narrowed, and the stretch moldability is not improved. Also, the shrinkability is poor. The Mw / Mn ratio of Resin B is 3 or less, preferably 2.7 to 1.7, more preferably 2.5 to 1.9. When it exceeds 3, the low molecular weight component in the resin increases, the strength cannot be improved, and blocking is more likely to occur.

The method for producing the resin A and the resin B used in the present invention is not particularly limited, but known high pressure ionic polymerization method, gas phase polymerization method, solution polymerization method, slurry polymerization method,
Bulk polymerization methods can be used. As the catalyst, known transition metal complex catalysts such as Ziegler catalyst and metallocene catalyst are used. In the case of resin B, it is preferable to use a metallocene catalyst.

Resin A is a material that has a property of increasing strength as it is stretched (strain hardening property) in a high temperature region close to the melting point and has stretch moldability. When stretched by the inflation re-blow molding method, the position where the tube swells changes vertically and horizontally when stretching by the inflation re-blow molding method, stable stretching cannot be performed, and stretching is performed even when stretched by the tenter method. At times, film cracking occurred and stretching was not stable.

Although the resin B has a large elongation near the melting temperature, the strength is not significantly improved even when it is stretched, and the tension is drastically lowered during stretching, which makes it difficult to stretch-mold. By combining these resins A and B, it was found that stretch molding is remarkably stable, the stretched film is flexible and strong, has excellent transparency, and has excellent shrinkability depending on the stretching conditions. . The content of the resin B is 10 to 70% by weight, preferably 20 to 60% by weight.
It is. If the blending amount is less than 10% by weight, stable stretch moldability cannot be obtained, and if it exceeds 70% by weight, the strength is not sufficiently improved and the stretch molding becomes unstable. In the present invention,
Other resins, preferably branched PE and the like can be blended within a range that does not impair the effects of the present invention. Above all, resin B
On the other hand, it is preferable to add branched PE. Branched P
When E is blended, the viscosity at the time of extrusion is lowered and the extrudability is improved. In addition, the temperature range in which the resin B can be stretched can be expanded. The blending amount of the other resin is 0 to 60% by weight, preferably 0 to 40% by weight as a ratio in the composition. When blended with the resin B, the resin B is at least 10% by weight.
Since it is necessary to mix the resin B with other resins, the amount of the other resin compounded together with the resin B is 70% by weight or less.

In the case of forming a film, an anti-blocking agent, a lubricant and the like are usually used in order to prevent sticking between the films and improve slipperiness. The material of the present invention can also be blended with additives, fillers, pigments, etc., which have been conventionally used in films, to impart performance depending on the application. The blended material can be molded by a conventional inflation re-blow stretch molding method or a tenter stretch molding method.
In the case of the inflation re-blow stretch molding method, the molten resin extruded into a tube shape from the extruder is rapidly cooled with water, etc., and the solidified tube is flattened with a nip roll and taken out, and reheated and re-blown to form a horizontal and vertical biaxial direction. Is stretched to a predetermined ratio.

In L-LDPE, the temperature range during stretching is just before the melting point, and stretch molding becomes unstable due to a temperature change of 1 to 2 ° C., whereas the material of the present invention has a temperature range during stretching. It has a wide range, and can be stably stretched even in a temperature range lower than the melting point by about 20 ° C. If the stretching ratio is about 3 times or more in each of the length and width, a film having high strength and excellent transparency can be obtained as a stretched film. If it is 2 times or less, the strength and rigidity are poor, and if it is 10 times or more, the film breaks during stretching. When the stretched tube is wound up as it is, a shrinkable film is obtained. The heat shrinkage that can be applied exceeds 40% at 110 ° C., and a practically sufficient shrinkage can be obtained. In addition, a non-shrinkable film having good dimensional stability can be obtained because it is difficult to shrink by being blown again or kept at a high temperature with a clip of a tenter and kept at a high temperature to be heat-fixed.

In the case of the tenter stretch molding method, the resin extruded in a sheet form from the extruder is cooled and solidified by a cooling roll, reheated by a heated roll, and then by a roll having a different rotational speed. It is stretched in the machine direction, then both ends are gripped by clips that move along the rails, heated in a tenter and stretched in the cross direction. After stretching, the film is heat-fixed by holding it at a temperature close to the stretching temperature while being gripped by a clip, and becomes a non-shrinkable film. If the film is rapidly cooled after stretching, a shrinkable film can be obtained. In addition, stretch molding can also be carried out by a simultaneous biaxial molding method in which biaxial stretching is carried out simultaneously in the longitudinal and lateral directions as the clip moves in the tenter. The stretching ratio is in the range of 2 to 10 times as in the inflation reblowing method.

The stretch-formed film can be subjected to corona discharge treatment, flame treatment, or other surface modification conventionally used for films, to activate the surface of the film and improve the adhesion of printing ink. Alternatively, the adhesiveness can be improved when it is attached to another film. The obtained film is flexible, has excellent strength, good transparency,
It can be used for packaging fruits and vegetables, processed foods, medical supplies, office supplies and stationery, and various other products. Since the stretched film according to the present invention has excellent strength, even a thin film can sufficiently protect a product and help to reduce the weight of packaging. Further, since it is highly transparent, it is not only easy to check the contents, but also the product can be appealed beautifully. The film that has been made more shrinkable is a conventional PV film that can be used as a shrink wrapping film.
It can be used in applications where C and PS shrink films are used, and because of its excellent strength and heat sealability, it offers high product protection. The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples.

[0016]

【Example】

Embodiment 1 FIG. 80% by weight of a commercially available linear low-density polyethylene resin A (ethylene / hexene copolymer, hexene content: 8% by weight) having a melt flow rate of 1 g / 10 minutes and a density of 0.920 g / cm ³ and a melt A commercially available resin B (ethylene / hexene copolymer, having a flow rate of 3.5 g / 10 minutes, a density of 0.895 and an Mw / Mn of 2.1,
20% by weight of hexene content: 18.5% by weight), 0.2 parts by weight of fine particle silica having a particle size of 2 μm as an anti-blocking agent per 100 parts by weight of resin, and “Nutron S” (Japan) as a lubricant. Seikasha brand name) 0.0
The material blended so as to be 5 parts by weight was biaxially stretched by an inflation re-blow stretch molding machine to form a film. Molding is performed by cooling the molten resin extruded into a tube shape from a single-screw extruder with a diameter of 70 mm with water and draining the water with a take-up roll.
While reblowing in a cylindrical heating furnace, the film was heated to 120 ° C. and stretched 5 times lengthwise and 5 times widthwise to obtain a flexible and highly transparent film having a thickness of 20 μm.

Embodiment 2 FIG. The resin A of Example 1 was 50% by weight, the resin B was 50% by weight, the antiblocking agent and the lubricant were blended in the same manner as in Example 1, and biaxially stretched by a tenter stretching machine to form a film. . Molded diameter is 10
Molten resin extruded into a sheet from a 0 mm single-screw extruder is cooled and solidified by a cooling roll,
It is heated to 0 ° C., stretched 5 times in the machine direction with rolls having different rotation speeds, then both ends are gripped with clips, heated to 110 ° C. in a tenter and stretched 5 times in the transverse direction. The film was heat-solidified at 105 ° C. while narrowing the distance between both ends of the film held by the clip by 5% in the width direction to obtain a flexible and highly transparent film having a thickness of 20 μm.

Embodiment 3 FIG. The resin A of Example 1 was 40% by weight, the resin B was 30% by weight, and the melt flow rate was 0.
30 g by weight of a commercially available high-pressure low-density polyethylene (branched PE) having a density of 7 g / 10 minutes and a density of 0.924 g / cm ³ was mixed, and an anti-blocking agent and a lubricant were blended in the same manner as in Example 1. The obtained material was molded in the same manner as in Example 1,
A flexible and highly transparent film having a thickness of 20 μm was obtained.

Embodiment 4 FIG. The material of Example 2 was uniaxially stretched by a tenter stretch molding machine to form a film. The molding was performed by using a single screw extruder with a diameter of 100 mm to cool and solidify the molten resin extruded into a sheet with a cooling roll, and without stretching in the longitudinal direction, grasp both ends with clips and
The film was heated to 0 ° C. and stretched 5 times in the transverse direction to obtain a flexible and highly transparent film having a thickness of 20 μm.

Comparative Example 1 Similar to Example 1, the anti-blocking agent and the lubricant were added to the resin A of Example 1 alone and molded by the method of Example 1, but the tube ruptured during stretching and stretch molding could not be performed.

Comparative Example 2 92% by weight of Resin A of Example 1, 5% by weight of Resin B, and an antiblocking agent and a lubricant were blended in the same manner as in Example 1 and molded by the method of Example 1, but the tube was It shook vertically and horizontally, and stretch molding could not be performed.

Comparative Example 3. 20% by weight of Resin A of Example 1, 80% by weight of Resin B, and an antiblocking agent and a lubricant were blended in the same manner as in Example 1 and molded by the method of Example 1, but the tube was partially It melted into a hole and opened, and stretch molding could not be performed.

Comparative Example 4. 70% by weight of Resin A of Example 3, 30% by weight of the same branched PE used in Example 3, and the same anti-blocking agent and lubricant as in Example 1 were used. The film was molded by the method 1 to obtain a flexible and highly transparent film having a thickness of 20 μm.

Comparative Example 5. An anti-blocking agent and a lubricant were mixed in the same manner as in Resin A of Example 3, and a flexible film having a thickness of 20 μm was obtained without stretching by the usual inflation molding method.

Comparative Example 6. The material of Comparative Example 1 was uniaxially stretched by a tenter stretch molding machine to form a film. The molding was performed by using a single screw extruder with a diameter of 100 mm to cool and solidify the molten resin extruded into a sheet with a cooling roll, and without stretching in the longitudinal direction, grasp both ends with clips and
When heated to 0 ° C. and stretched 5 times in the transverse direction, the sheet broke and a stretched film could not be obtained. Table 1 shows the physical property data of the films of Examples 1 to 4 and Comparative Examples 4 and 5.

[0026]

[Table 1]

The films of Examples 1 to 4 have high tensile strength and heat seal strength, and have a low degree of haze, and thus have good transparency. The films of Examples 1, 3, and 4 which are not heat-set have heat shrinkability. Express. Comparative examples 1, 2, 3,
In the case of 6, the film could not be stably stretch-molded, and the film of Comparative Example 4 could be stretch-molded, but the strength was poor. In addition, the superiority of the performance of the film of the example is apparent as compared with the unstretched film of the comparative example 5. further,
The films of the examples had a high-strength yet soft feel. As described above, the film of the present invention has excellent moldability,
Since it is flexible and has excellent strength and transparency, it exhibits excellent performance when used for packaging products.

Claims (1)

[Claims] 1. A density of 0.915 to 0.935 g / cm ³
Ethylene / α-olefin copolymer resin (provided that α
-The carbon number of the olefin is 4 to 8) 30 to 90% by weight, the density is less than 0.915 g / cm ³ , and the ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn.
Of 3 or less ethylene / α-olefin copolymer resin (provided that the α-olefin has 4 to 8 carbon atoms) 70 to
A stretched film comprising a resin composition with 10% by weight.