JPH0788447B2 - Polyethylene film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyethylene film, and more particularly to a polyethylene film having excellent performance as an agricultural coating film.

[Conventional technology]

Conventionally, mulch cultivation has been widely performed to promote the growth of plants, and low-density polyethylene has been widely used for this purpose. However, when using a low-density polyethylene film, the damage caused by heat melting of the film during use is large, the strength and elongation of the film itself is directional, easy to tear during construction, and the film strength is insufficient. There are many problems such as the necessity of using a thick film.

On the other hand, it has been proposed to use high-density polyethylene and linear low-density polyethylene as a base material to overcome these problems (Japanese Patent Laid-Open Nos. 56-116735 and 57-28).
114 publication). However, these films are not sufficiently satisfactory, and it is desired to provide a more useful agricultural coated polyethylene film with a new technique.

[Problems to be solved by the invention]

The inventors of the present invention have diligently studied to solve the above problems found in conventionally used low-density polyethylene coated films and to develop a polyethylene-based film having well-balanced heat retention, strength, and flexibility. It has been found that a polyethylene film using a composition obtained by blending a specific ethylene-vinyl acetate copolymer with high density polyethylene is extremely suitable as a coated polyethylene film for agriculture.

[Means for solving problems]

That is, the present invention comprises a high-medium density polyethylene (A) of high molecular weight and a high-medium density polyethylene (B) of low molecular weight with a density of 0.94 to 0.97 g / cm ³ and a melt index of 0.01 to 0.5 g / 10 minutes (190 ° C.). It is a homogeneous melt mixture, (A) has an average molecular weight of 100,000 to 1,500,000, (B) has an average molecular weight of 01,000 to 100,000, and (A) to (B) has a molecular weight ratio of 5 to 200, the mixing ratio of (A) and (B) is 30:70 to 80
70 to 95 parts by weight of high-density polyethylene of 20 to 20 and 5 to 30 parts by weight of ethylene-vinyl acetate copolymer having a melt index of 0.05 to 10 g / 10 minutes (190 ° C.) and a vinyl acetate content of 2 to 20% by weight. The present invention relates to a polyethylene film comprising 100 parts by weight of the polymer composition.

The high-density polyethylene used in the present invention has a density of 0.94 to
It is a 0.97 g / cm ³ ethylene homopolymer or a copolymer of ethylene with other olefins and dienes.

Other olefins and dienes used in the copolymerization include α-olefins such as propylene, butene-1, pentene, 4-methylpentene-1, hexene, octene and decene, diolefins such as butadiene and isoprene, cyclopentene. , Cyclohexene, cyclopentadiene, norbornene and the like.

As the polymerization method, usual suspension polymerization, gas phase polymerization, or solution polymerization can be used. As the catalyst used for the polymerization,
A catalyst system obtained from a transition metal compound (eg, titanium-containing compound) or a transition metal compound supported on a carrier (eg, magnesium-containing compound) and an organometallic compound (eg, organoaluminum compound), or a carrier (eg, silica, silica) -A catalyst system obtained by using at least a chromium-containing compound supported on alumina) can be used.

The high-density polyethylene of the present invention is a mixture of the high-molecular weight component (A) and the low-molecular weight component (B) of the high-medium density polyethylene described below. This mixture can be produced by multistage polymerization of two or more stages, or by separately producing the polyethylenes (A) and (B), then uniformly mixing and melt-kneading.

The mixing ratio of component (A) and component (B) is 30: weight ratio.
Must be 70 to 80 to 20. The amount of ingredient (A) is 30
When the ratio is less than (A) / (B) ratio of 70, the excellent physical properties of the present invention are difficult to obtain because the amount of the high molecular weight component in the resin is small, and conversely the amount of the component (A) is 80. / 20 (A) /
If the ratio is higher than the ratio (B), the amount of high molecular weight components in the resin is large and the moldability is lowered, which is not preferable.

The high molecular weight component (A) of the high-density polyethylene has an average molecular weight of 100,000 to 1,500,000, preferably 300,000 to 1,000,000, and the low molecular weight component (B) has an average molecular weight of 01,000 to less than 100,000.
It is preferably 5,000 to 50,000. The ratio of the molecular weights of (A) and (B) is 5 to 200, preferably 10 to 100. When the molecular weight ratio is less than 5, it is difficult to obtain the excellent physical properties of the present invention, and the moldability deteriorates. On the other hand, when the molecular weight ratio exceeds 200, there is no advantage in improving the physical properties and moldability,
Moreover, it is disadvantageous in manufacturing.

The high-density polyethylene used in the present invention has a density of 0.94 to
0.97g / cm ³ and melt index (MI) 0.01-0.5g / 10
Minutes (190 ° C.), preferably 0.01 to 0.2 g / 10 minutes (190 ° C.). When the MI is less than 0.01, the extrudability during film forming is poor, while when it exceeds 0.5, the film strength is insufficient. Further, in the present invention, by using a composition comprising the above high molecular weight component (A) and low molecular weight component (B) as the high density polyethylene, a film having an excellent balance between moldability and strength can be obtained.

The ethylene-vinyl acetate copolymer used in the present invention is
It is produced by a so-called high pressure method such as an autoclave method or a tubular method. Its MI is 0.05-10 g / 10 min and the vinyl acetate content is 2-20% by weight. If MI is less than 0.05g / 10 minutes,
It is difficult to manufacture by the high pressure method. On the other hand, when it exceeds 10 g / 10 minutes, the physical properties of the film deteriorate. A more preferable MI is 0.1 to 1 g / 10 minutes from the viewpoint of moldability and physical properties. When the vinyl acetate content is less than 2% by weight, not only the effect of improving the directionality of the film strength is scarce but also the heat retaining property is not sufficiently improved. If the vinyl acetate content exceeds 20% by weight, the formability of the film is deteriorated, blocking is likely to occur during construction, and workability is impaired. The vinyl acetate content is more preferably 3 to 15% by weight in view of moldability and physical properties.

Ethylene to high density polyethylene in the present invention
As the blending ratio of the vinyl acetate copolymer, high density polyethylene 70 to 95 parts by weight, preferably 75 to 90 parts by weight of ethylene-vinyl acetate copolymer 5 to 30 parts by weight, preferably 10 to 25 parts by weight. This is the case where the total amount is 100 parts by weight within the range of parts. If the ethylene-vinyl acetate copolymer is less than 5 parts by weight, the intended effect of the present invention cannot be obtained, while if it exceeds 30 parts by weight, not only the mechanical strength is impaired,
Moldability and workability are also inferior, which is not preferable. For blending, a dry blending method using a Henschel mixer, a tumbler or the like can be used, and a blending method using a Banbury mixer, an extruder or the like can also be used.

In producing the polymer composition of the present invention, a usual stabilizer,
It is possible to mix lubricants, antistatic agents, pigments, inorganic or organic fillers. Examples of these added substances are:
2,6-ditert-butyl-4-methylphenol (BHT), Irganox 1010 and 1076 (Ciba Geigy Co., Ltd. trademark), Tinuvin 327 (Ciba Geigy Co., Ltd. trademark), Sanol LS770 (Sankyo Co., Ltd. trademark), Examples thereof include dilauryl thiodipropionate (DLTP), dimyristyl thiodipropionate (DMTP), calcium stearate, zinc stearate, titanium white, calcium carbonate, carbon black and the like.

The inflation film method can be used as a method for producing a film in the present invention. The thickness of the film can be arbitrarily changed depending on the intended use, but 5 to 25 µ is suitable particularly when used as an agricultural coating film.

The preferable film forming conditions in that case are as follows.

Expansion ratio: 4 to 8 Frost line height: 3 to 10 times the die diameter. If the expansion ratio is less than 4, the vertical and horizontal balance of film strength is not sufficient, and if it exceeds 8, the bubbles roll and stabilize. Film formation becomes difficult.

In order to obtain a high-strength polyethylene film using high-density polyethylene, it is known to form an inflation film with a resin having a high molecular weight at a high expansion ratio (ratio of bubble diameter to die diameter). However, even if a high expansion ratio is set, a film in which the orientation in the longitudinal direction and the orientation in the lateral direction are well balanced is obtained when the melted polymer does not sufficiently relax the stress when passing through the die even after exiting the die exit. I can't get it.

If the height of the frost line is less than 3 times the die diameter, the strength balance of the film is not sufficiently improved, and if it exceeds 10 times, the strength balance of the film is improved, but the bubbles are not stabilized, and On the contrary, the quality will be deteriorated due to uneven thickness.

The polyethylene-based film obtained by the present invention has a longitudinal and lateral orientation degree ratio measured by the polarization fluorescence method in the range of 0.7 to 3.0. The polarization fluorescence method used here is the alignment behavior of the molecular axis of the fluorescent molecule previously dispersed in the film, excited by polarized excitation light, and the angular distribution of the polarization component intensity of the emitted fluorescence is measured. To know.

Use 365nm as the wavelength of the excitation light, and use W as the fluorescent dye.
It was measured using hite Fluor PSN (Sumitomo Chemical Co., Ltd.).

When the ratio of the degree of orientation in the machine direction and the degree of orientation in the direction obtained by the above method exceeds this range, the tear propagation property increases and it is not suitable as a polyethylene film for agricultural coating.

〔Example〕

Examples will be shown below. Prior to that, the production conditions of the high-density polyethylene used in the examples, the measuring method of each characteristic value, the film forming conditions and the like will be shown.

(1) Solid catalyst A for producing high-density polyethylene A A solution of 1 mol of trichlorosilane (HSiCl ₃ ) in 1 hexane, 2 l, was placed in an 8 l autoclave, and the temperature was 50 ° C.
Kept at. Al Mg _6.0 (C ₂ H ₅ ) _2.0 (nC ₄ H ₉ ) _9.5 (OC
₄ H ₉ ) _3.5 Organoaluminum-magnesium complex (1 mol) dissolved in 1 hexane solution
The mixture was added dropwise over a period of time, and further reacted at this temperature for 2 hours.
The solid component formed was washed twice with 2 l of hexane by the precipitation method. Titanium tetrachloride is added to the slurry containing this solid component.
After charging 2 l and reacting at 130 ° C. for 2 hours, the solid catalyst was isolated and washed with hexane until no free halogen was detected. The solid catalyst contained 2.1% titanium.

(2) Production of high-pressure polyethylene Polyethylene was produced by continuous polymerization using a 200-liter reaction volume stainless steel polymerization vessel. Polymerization temperature is 86 ℃, polymerization pressure is 12Kg / cm ²
Polymerization was controlled so that the amount of G produced was 8 Kg / hr. The catalyst was triethylaluminum at a concentration of 0.5 mmol / l, and the solid catalyst A produced in (1) above had a polymerization production amount.
It was introduced together with 30 l / hr of hexane so as to be 8 Kg / hr.

Hydrogen was used as a molecular weight regulator. High molecular weight component (A)
Adjusted the gas phase composition so that the molecular weight was 600,000. The low molecular weight component (B) was polymerized to have a molecular weight of 24,000.

Polymerization of the high molecular weight component (A) and the low molecular weight component (B) at a polymerization production ratio of 50:50 results in 1000 ppm of Irganox 1010, 1000 ppm of calcium stearate and 1500 of Sanol LS770.
Kneaded and extruded pellets were obtained together with ppm in a twin-screw extruder at 200 ° C. The MI was 0.06 g / 10 minutes and the density was 0.953 g / cm ³ .

(3) Measuring method of each characteristic value Density: It measured according to ASTM D-1505.

Melt index (MI): Measured according to ASTM D-1238 under the conditions of a temperature of 190 ° C. and a load of 2.16 Kg.

 Film Tensile Properties: Measured according to ASTM D-882.

Film impact strength: measured according to ASTM D-1709.

 Total light transmittance: Measured according to JIS K-6714.

 Haze: Measured according to JIS K-6714.

Melting start temperature: measured according to ASTM D-3417, and the melting point was defined as the intersection of the baseline and the tangent line from the melting peak.

Hand tearability: A test piece of 50 × 200 mm was prepared in each of the vertical and horizontal directions, and a cut having a depth of 20 mm was provided at the center of the short side. The results of tearing 10 pieces of each test piece by hand were ranked and evaluated.

○ More than 80% of the tears did not propagate to the end and could not be easily torn.

△ The tear propagates in the tearing direction to the end
20 to 40% × All the samples could be easily torn in either the vertical or horizontal direction (4) Film film forming conditions Molding machine: Modern Machinery Co., Ltd. air-cooled inflation film device Extruder : Modern Machinery Co., Ltd. 50mmφ Delcer Molding condition: Extrusion temperature 200 ℃ Die 150mmφ Spiral die Die cap 2.0mm Blow ratio 5.0 Discharge rate 30Kg / hr Film thickness 10μ Front line height 900mm (5) Heat insulation evaluation The ridges made experimentally with the film produced in the example were coated on both sides with a stone-fixing method. The measurement was carried out in the middle of February, and the temperature difference between the outside temperature twice at 11:00 am and 4:00 pm and the ground temperature 5 cm below the ground was recorded.

Example 1 High-density polyethylene (MI0.06g / 10
Min, density 0.953 g / cm ³ ) 80 parts by weight and ethylene-vinyl acetate copolymer (MI 0.3 g / 10 min, vinyl acetate content 6% by weight) 2
By mixing 0 parts by weight, a film having a thickness of 10 μm was obtained under the condition (4). Table 1 shows the results of evaluating the physical properties and heat retention of the obtained film.

Example 2 In Example 1, the high-density polyethylene was changed to 70 parts by weight and the ethylene-vinyl acetate copolymer was changed to 30 parts by weight, and a film having a thickness of 10 μm was obtained by the same method. The physical properties and heat retaining properties of the obtained film are shown in Table 1.

Example 3 MI 0.6 as ethylene-vinyl acetate copolymer, density 0.92
7. A film having a thickness of 10 .mu.m was obtained in the same manner as in Example 1 except that a vinyl acetate content of 6% by weight was used.
The physical properties and heat retaining properties of the obtained film are shown in Table 1.

Comparative Example 1 Commercially available low density polyethylene (MI2.0, density 0.920
g / cm ³⁾ Extrusion Temperature 0.99 ° C. The die diameter 300 mm in diameter, to obtain a film having a thickness of 20μ under conditions of expansion ratio of 2.0. The physical properties and heat retaining properties of the obtained film are shown in Table 1.

Comparative Example 2 In Example 1, the ethylene-vinyl acetate copolymer was replaced with an ethylene-α-olefin random copolymer rubber (MI0.2,
A film was obtained in the same manner as in Example 1 except that the density was changed to 0.89). The physical properties and heat retaining properties of the obtained film are shown in Table 1.

Comparative Example 3 A film was obtained in the same manner as in Example 1, except that the ethylene-vinyl acetate copolymer in Example 1 was changed to high-pressure low-density polyethylene (MI0.4, density 0.920). The physical properties and heat retaining properties of the obtained film are shown in Table 1.

Comparative Example 4 A film was obtained in the same manner as in Example 1 except that the ethylene-vinyl acetate copolymer in Example 1 was changed to the ethylene-octene-1 copolymer (MI0.8, density 0.924). The physical properties and heat retaining properties of the obtained film are shown in Table 1.

Comparative Example 5 Commercially available linear low density polyethylene (MI0.8, density
0.924), extrusion temperature 180 ℃, die diameter 300mmφ,
A film having a thickness of 10 μm was obtained under the condition that the expansion ratio was 2.5. The physical properties and heat retaining properties of the obtained film are shown in Table 1.

Comparative Example 6 A film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that 100 parts by weight of the same high-density polyethylene as used in Example 1 was used. The physical properties and heat retaining properties of the obtained film are shown in Table 1.

[Effects of the Invention] The agricultural coated polyethylene film of the present invention has the following features.

With a thickness less than 1/2 of low density polyethylene film,
The strength is equal to or higher than that, and the strength balance in each direction is good. Therefore, the planting holes formed in the original film for transplanting seedlings and the like do not gradually expand and are not broken in the recovery work after the installation, and thus the workability is extremely excellent.

The film is mainly made of high-density polyethylene, but has excellent transparency. Therefore, the light transmittance is improved to the same level as the low density polyethylene film, and 9
Infrared transmittance in the radiation range of ~ 11μ was lower than that of low-density polyethylene and high-density polyethylene by blending ethylene-vinyl acetate copolymer, and these two effects significantly improved heat retention (ground temperature raising effect) The film is obtained.

Even if it is used in a high temperature period (June to September), it does not tear or break due to heat fusion.

Compared to low density polyethylene film, it is possible to reduce the thickness and reduce the weight per film roll,
Good workability. It also saves raw material resources. Furthermore, the amount of disposal and incineration after construction is small, and it is easy to greatly increase the amount.

Rigidity is higher than low-density polyethylene film and it is difficult to block, so construction work and recovery work are easy.

The film of the present invention is suitable for agricultural coating, but can also be widely used for applications other than agricultural coating, for example, packaging materials, interleaving paper, civil engineering, construction sheets, and the like.

Claims (3)

[Claims] 1. A uniform composition comprising a high-medium density polyethylene (A) having a high molecular weight and a high-medium density polyethylene (B) having a low molecular weight at a density of 0.94 to 0.97 g / cm ³ and a melt index of 0.01 to 0.5 g / 10 minutes (190 ° C.). It is a melt-mixed product, (A) has an average molecular weight of 100,000 to 1,500,000, (B) has an average molecular weight of 01,000 to less than 100,000, and the ratio of (A) to (B) is 5 70 to 95 parts by weight of high density polyethylene having a mixing ratio of (A) and (B) of 30:70 to 80:20 by weight and a melt index of 0.05 to 10 g / 10 minutes (190 ° C) and acetic acid. A polyethylene film comprising a total of 100 parts by weight of a polymer composition with 5 to 30 parts by weight of an ethylene-vinyl acetate copolymer having a vinyl content of 2 to 20% by weight. 2. A polyethylene film according to claim 1, wherein the film is a film suitable for an agricultural coating film having a thickness of 5 to 25 μm. 3. The invention according to claim 1, wherein the ratio of the degree of orientation in the vertical direction and the degree of orientation in the horizontal direction measured by the polarization fluorescence method of the film is in the range of 0.7 to 3.0.
The polyethylene film according to the item.