JP2836156B2 - Method for producing stretched polyethylene film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a stretched polyethylene film. More particularly, the present invention relates to a reusable biaxially stretched film made of high-density polyethylene and a method for producing the same.

[Prior art and its problems] Conventionally, high-density polyethylene has high rigidity and strength but poor transparency, and it has been difficult to use it in applications where it is used as a package that allows the contents to be seen through.

As a method for improving the transparency and stretchability, a polyethylene film is irradiated with radiation and uniformly crosslinked.
Axial stretching method (Japanese Patent Publication No. 37-18893).

The polyethylene sheet is cross-linked from both sides in the thickness direction so that the degree of cross-linking decreases toward the inside, and then 2
A method of axial stretching (JP-A-59-174322) has been proposed. However, although the stretchability of the film is improved by these methods, when the film is recovered and reused, it is difficult to form again because the film is highly crosslinked. It is also conceivable to use it by mixing it with other new raw materials, but since the crosslinked resin has a significantly different viscosity from the non-crosslinked resin, the dispersion becomes poor and unmelted small lumps generally called gels are generated, It will not be practical.

Therefore, the loss generated during the production cannot be reused, and the production cost becomes very high.

[Means for Solving the Problems] The present inventors have conducted various studies to obtain a stretched polyethylene film that can be reused without impairing transparency and rigidity. It has been found that the object can be achieved by molding below, and the method for producing a film of the present invention has been completed.

That is, the gist of the present invention is that the melt flow index (MI) is 2 g / 10 minutes or less and ρ is 0.940 g / cm ³ or more.
/ 10 min or less linear low density polyethylene (L-LDPE) 1-4
0 parts by weight and 0.0001 to 0.1 parts by weight of a radical generator are added, and while reacting or reacting the radical generator, a raw sheet is formed and then 5 ° C. higher than the melting point (Tm) of the resin composition. The present invention resides in a method for producing a stretched polyethylene film, which comprises biaxially stretching a film at a temperature lower by 30 ° C. than a melting point.

 Next, the production method of the present invention will be described in detail.

The (A) HDPE resin used in the present invention is a polyethylene obtained by polymerizing ethylene by a medium / low pressure method using a Ziegler type catalyst or a Phillips type catalyst and having a density (ρ) of 0.940 to 0.9.
65 g / cm ^3, preferably 0.940～0.960G / what is and density of cm ³ is not rigidity obtained when is this less, transparency If it is more reduced. The melt flow index (MI) is 2 g / 10 min or less, preferably 1 g / 10 min or less.
More than a minute. When the MI is larger than the upper limit, the tensile strength decreases, and when the MI is smaller than 0.01 g, extrusion molding becomes difficult.
The (B) L-LDPE to be blended is a copolymer of ethylene and another α-olefin, and propylene, butene, hexane, octene, decene, 4-
Methylpentene or the like is copolymerized at about 4 to 17% by weight, preferably α-olefin having 6 or more carbon atoms (for example, hexane, 4-methylpentene-1, octene, decene, etc.) is polymerized at about 5 to 15% by weight. Made of polyethylene, α
-The greater the carbon number of the olefin, the better the stretchability. L-LDPE has a MI of 2 g / 10 min or less, preferably 1 to 0.5
g / 10 minutes. If the MI is greater than 2 g / 10 minutes, the tensile strength will decrease. ρ is 0.915 to 0.950 g / cm ³ , especially 0.915
It is preferably 0.935 g / cm ³ . A: B = 9 for the two resins
A ratio of 9: 1 to 60:40, preferably A: B = 90: 10 to 70:30. If the blending amount of the component B is less than the lower limit, the stretchability is insufficiently improved, and if it is more than the upper limit, the physical properties (rigidity) of the film are undesirably reduced.

Further, a radical generator is added to the composition in a range of 0.1 to 0.0001 part by weight. For example, dicumyl peroxide,
2.5-dimethyl-2.5 di (t-butylperoxy) hexane, 2.5-dimethyl-2.5di (t-butylperoxy) hexane-3, dibenzoyl peroxide, di-t-butyl peroxide and the like. If the amount is more than 0.1 part by weight, it is not preferable because the film is liable to break at the time of forming the raw material and the surface of the film is roughened.

If the amount is less than 0.0001 part by weight, the effect of improving the stretchability of the obtained resin composition cannot be obtained.

It is needless to say that an antioxidant, an ultraviolet absorber, a lubricant, an antiblocking agent, an antistatic agent and the like which are usually added to these resins may be added to these resins.

In the present invention, in order to produce a raw material for obtaining a stretched film, the above-mentioned polyethylene resin is supplied to a commonly used extruder, melt-extruded, cooled and solidified to form a film-shaped (sheet-shaped) or tube-shaped raw material. Molding. Melt extrusion molding is a method of extruding from a commonly used T die into a flat raw material, a method of extruding from a circular die into a tubular raw material, or a method of cutting and opening a tubular raw material into a sheet raw material. Alternatively, any method may be used, such as cutting both sides of a tube-shaped raw material into two sheet-shaped raw materials.

The raw film (sheet) is then heated to a predetermined temperature and subjected to a biaxial stretching process to produce a stretched film.

For the biaxial stretching, a tenter sequential biaxial stretching, a tenter simultaneous biaxial stretching, a tubular biaxial stretching method, a rolling method, and the like can be employed.

The stretching temperature is Tm + 5 to Tm-30 ° C, preferably Tm-5 to Tm-15 ° C, where Tm is the melting point of the polyethylene resin. If the temperature is higher than the upper limit temperature, the tensile strength of the film after stretching cannot be improved. If the temperature is lower than the lower limit temperature, the film will be broken during stretching and cannot be stretched. The stretching ratio is at least 2 times, preferably at least 4 times, in the longitudinal and transverse directions. If the stretching ratio is less than 2 times, uniform stretching becomes difficult.

The MI of the biaxially stretched film obtained by the above method is preferably 2 to 0.01 g / 10 minutes. The MI of the film
If the length is longer than 2 g / 10 minutes, stable stretching is difficult, and practically no production is possible. If the MI is less than 0.01 g / 10 minutes, the resin will have poor fluidity when it is reused, and it will not be possible to use it. The film gel fraction is preferably less than 1%. When the content is 1% or more, when the film is reused, the film becomes a film having irregularities in which gel portions are scattered, and cannot be used as a product.

The ρ of the film, preferably 0.935 g / cm ³ or more, and particularly preferably 0.940 g / cm ³ or more, and most preferably 0.950 g / cm ³
That is all. If ρ is less than 0.935 g / cm ³ , rigidity and tensile strength are reduced, and the original strength of HDPE does not appear.

Haze value is preferably 30% or less, particularly preferably 20%
It is as follows. If it is larger than 30%, the transparency is poor for use in packaging.

 Next, the present invention will be described in more detail with reference to examples.

Example 1 High density polyethylene (ρ: 0.965 g / cm ³ , MI: 1.0 g / 10
Min) to 80 parts by weight of linear low-density polyethylene (ethylene-
Hexane copolymer) (ρ: 0.921 g / cm ³ , MI: 1.0 g / 10
Min) in a dry blend of 20 parts by weight and 2.5-cimethyl-2,5-di (t-butylperoxy) hexyne-3.
Using a mixture of 0.03 parts by weight as a raw material, a 200 μm raw material is formed using a T-die sheet forming machine, and a drawing temperature of 120 μm in the machine direction (MD).
Stretching 3 times at 130 ° C and 3 times at 130 ° C in the transverse direction (TD).
It was stretched twice. Table 1 shows the physical properties of the stretched film.

 The evaluation method in the present invention is as follows.

(1) Tensile strength and elongation: Based on JIS Z-1702 (2) MI: JIS K-6760 (3) Gel fraction: ASTM D 2765 (4) Density: JIS K-6760 (5) HAZE: JIS K-6714 (6) Modulus of elasticity: ASTM D-882 (7) Melting point: DSC method (8) Stretching stability: The number of breaks in 2 hours when stretched at a speed of 20 m / min was examined.

(8) Recyclability: The film is separated and extruded (40φ
Extruder) and extrude with a die having 6 nozzles of 3φ in diameter,
The pelletability was tested. Possible items are indicated by 、, and impossible items are indicated by ×.

Example 2 High-density polyethylene (MI: 0.03 g / 10 min, ρ: 0.940 g / c
m ³ ) 80 parts by weight, L-LDPE (ethylene-hexane copolymer) (MI: 1.0 g / 10 min, ρ: 0.921 g / cm ³ ) 20 parts by weight, 2.5-
A raw material consisting of 0.015 parts by weight of dimethyl-2.5-di (t-butylperoxy) hexyne-3 was mixed with a T-die molding machine at 140 μm.
And stretched at a longitudinal stretching temperature of 110 ° C and a transverse stretching temperature of 120 ° C. Table 1 shows the physical properties of the obtained film.

Examples 3 and 4 The stretching ratio of Example 2 was changed as shown in Table 1. Table 1 shows the physical properties of the obtained film.

Example 4 A film was obtained in the same manner as in Example 2 except that the raw materials and the stretching conditions were changed as shown in Table 1.

 Table 1 shows the physical properties of the obtained film.

Comparative Example 1 High density polyethylene (MI: 1.0 g / 10 min, ρ: 0.965 g / c
m ³ ) A 200 μm raw material was molded simply, but could not be biaxially stretched.

Comparative Example 2 High-density polyethylene (MI: 1.0 g / 10 min, ρ: 0.965 g / c
900 parts of (2.5-dimethyl-2,5-di (t-butylperoxy) hexyne-3) was added to 100 parts of m ³ ), and the film was stretched at a longitudinal stretching temperature of 120 ° C. and a transverse stretching temperature of 130 ° C. Table 1 shows the physical properties of the obtained film.

[Effects of the Invention] According to the production method of the present invention, a film that is excellent in rigidity and strength, has excellent transparency, and is preferably used as a packaging material through which contents can be seen through can be stably and efficiently produced.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-122735 (JP, A) JP-A-1-196326 (JP, A) JP-A-60-161131 (JP, A) JP-A-1 168426 (JP, A) JP-A-63-20347 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B29C 55/02-55/28 C08J 5/18

Claims (2)

(57) [Claims] 1. A linear low-density resin having a melt flow index of 2 g / 10 minutes or less and 99 to 60 parts by weight of a high-density polyethylene resin having a density of 0.940 g / cm ³ or more and a melt flow index of 2 g / 10 minutes or less. Polyethylene 1 to 40 parts by weight and a radical generator 0.0001 to 0.1 parts by weight are added, and while reacting or reacting the radical generator, a raw sheet is formed, and then 5 ° C. from the melting point of the resin composition. A method for producing a stretched polyethylene film, comprising: biaxially stretching a film at a temperature from a high temperature to a temperature 30 ° C. lower than a melting point. 2. The stretched polyethylene film has a melt flow index of 2 to 0.01 g / 10 minutes, a density of 0.935 g / cm ³ or more, a gel fraction of less than 1%, and a transparency of 30% in haze value. % Or less, the method for producing a stretched polyethylene film according to claim 1.