JPH03189124A - Manufacture of film - Google Patents

Abstract

PURPOSE:To obtain a multi-layer film which is superior in strength properties and has favorable sliding properties, by a method wherein co-extrusion molding and stretch treatment of linear low-density polyethylene and specific high-density polyethylene are performed at a specific layer ratio. CONSTITUTION:Resin A comprised of a composition obtained by compounding a radical generating agent with 100 pts. wt. resin containing at least 50 wt. % linear low-density polyethylene, whose melt index is not exceeding 2g/10 minutes and density is 0.910-0.945g/cm<3>, within a range of 0.001-0.01 pts. wt. and resin B comprised of high-density polyethylene whose melt index is 0.5-10g/10 minutes and density is higher than 0.945g/cm<3> are co-extruded under their thickness ratio where the thickness of the resin B of at least one side surface is made into a ratio of 5-30 in the case where the thickness of the resin A is regarded as 100. Then inflation molding is performed by making a blow-up ratio at 2-8 and a height of a frost line into 2-50 times as long as the diameter of an annular slit and an obtained film is stretched biaxially in a receiving direction of the film by making a stretching temperature at the melting point of the resin A-704 deg.C to the melting point of the resin A-20 deg.C and a draw ratio into 1.5-8 times.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for producing a film that is excellent in longitudinal direction (stretching direction) tear/tear strength, impact strength, rigidity, tensile strength, and slip property. It is. Specifically, it relates to a method for producing a film for packaging bags, which is mainly made of linear polyethylene, can be made thinner than conventional films, and is suitable for packaging relatively heavy items such as rice grains and fertilizers. .

[Conventional technology]

Linear low-density polyethylene with less branching, produced by copolymerization of ethylene and α-olefin, has higher tensile strength, impact strength, rigidity, and other strengths than high-pressure low-density polyethylene produced by radical polymerization at high temperature and high pressure. It has excellent properties such as environmental stress cracking resistance (ESCR), heat resistance, and heat sealability, and has been used in various fields in recent years. Particularly in the film field, high-pressure low-density polyethylene is rapidly being replaced by linear low-density polyethylene due to its superior physical properties.

[Problem to be solved by the invention]

Due to molding constraints, unstretched films or sheets (hereinafter referred to as "original film") made from such linear low-density polyethylene resin by the T-die method or the inflation method,
It is difficult to obtain a material with extremely thin thickness. Furthermore, the strength of the raw fabric obtained in this way is low. Therefore, it has been conventionally proposed to perform a stretching process.

Therefore, biaxial stretching of the original fabric has been considered, but the equipment cost is high, and the range of stretching conditions is narrow, so operation management is difficult, and this method is only used in a few fields.

In addition, although the longitudinal-axial stretching method that has been known up to now has low equipment costs and easy operation management, it has problems with the anisotropy of film physical properties, especially the tear resistance and surface strength in the longitudinal direction (stretching direction). However, a film that could be put to practical use could not be obtained.

Therefore, in order to obtain a film with good impact strength, rigidity, and tear resistance suitable for heavy-color applications using linear low-density polyethylene, the present inventors have developed a specific linear polyethylene. A film with significantly improved tear resistance and impact strength can be obtained by blending a specific amount of a specific branched low-density polyethylene into the film and reacting it with a radical generator, and then inflation-molding and stretching the product under specific conditions. I learned this and proposed it in Japanese Patent Application No. 174527-1982.

Furthermore, patent application No. 62-316443.63-19054.
In No. 63-151980, it was proposed to improve the impact strength and tear resistance of a film by using a specific resin composition and molding conditions.

However, in the above-mentioned proposed method, although the strength characteristics of the film were significantly improved, it was found that there was a problem in that the bag manufacturing speed was not fast due to insufficient slipperiness of the film.

[Means to solve the problem]

Therefore, the present inventors conducted intensive studies to improve the slipperiness of the film without reducing the strength characteristics of the film using linear low-density polyethylene, and found that linear low-density polyethylene and a specific We have discovered that a multilayer film with excellent strength properties and greatly improved slipperiness can be obtained by coextruding and blow-molding and stretching high-density polyethylene at a specific layer ratio, leading to the completion of the present invention. Ta.

That is, the gist of the present invention is that the melt index is 2g.
/10 minutes or less, and the density is 0.910-0.945g
0 radical generator per 100 parts by weight of resin containing at least 50% by weight of linear low density polyethylene of /cd.
．． Resin A consisting of a composition blended in the range of 0.001 to 0.1 part by weight and a melt index of 0.5 to 10 g/10
When the thickness ratio of resin B made of high-density polyethylene with a density of 0°945g/a+t and greater than 0°945g/a+t is 100, the thickness of resin B on at least one side is 100.
Co-extrusion is performed with a thickness of 5 to 30, and inflation molding is performed with a blow-up ratio of 2 to 8 and a frost line height of 2 to 50 times the diameter of the annular slit. In the direction, the stretching temperature is changed from the melting point of the resin A -70 to the melting point -
A method for producing a film characterized by uniaxial stretching at 20 DEG C. and a stretching ratio of 1 DEG 5 to 8 times.

The present invention will be explained in more detail below.

The raw material for resin A used in the present invention has a density of 0.9.
Linear low density polyethylene of 1 to 0.945 g/cd is used.

The linear low density polyethylene mentioned above refers to ethylene and other α-
It is a copolymer with olefin and is different from branched low-density polyethylene resin produced by conventional high-pressure methods. Linear low density polyethylene, for example, contains ethylene and other α-
Ziegler is a product obtained by copolymerizing olefins such as butene, hexene, octene, decene, 4-methylpentene-1, etc. in an amount of about 4 to 17% by weight, preferably about 5 to 15% by weight, and is used in the production of high-density polyethylene using medium and low construction methods. It is produced using a type catalyst or a Phillips type catalyst, and the conventional high density polyethylene is made into a short branched structure by copolymerization components, and the density is appropriately reduced by using this short chain branching to 0.91 to 0. It is about .95 g/cj, and is polyethylene with a structure that is more linear than conventional branched low-density polyethylene and more branched than high-density polyethylene.

The above linear low density polyethylene has a density of 0.91 to 0.9.
45g/c+J, preferably 0.915-0.940g
/a+1 range, and melt index is 2g
/10 minutes or less, preferably 0.1 to Ig/10 minutes or less,
More preferably, the range is from 0.1 to 0.5 g/10 min, and the flow ratio is preferably 70 or less, preferably from 10 to 50.

If the density is less than the lower limit, the rigidity and tensile strength will be lowered, and if it is higher than the upper limit, the impact resistance will be significantly lowered, which is not preferable. Moreover, if the melt index is higher than the upper limit, the surface strength will decrease, which is not preferable. Furthermore, if the flow ratio is higher than 70, the surface strength will decrease, which is not desirable.

In the method of the present invention, the melt index is JIS
JIS K7210, which is a reference standard for K 6760
The flow ratio is a value measured in accordance with Condition 4 of Table 1, and the flow ratio is measured using the above-mentioned melt index measuring device, with a shear force of 1
0b dyne/Cl11 (load 11131 g) and 10
'Dyne/cd (load 1113g) extrusion amount (g/1
0 minutes) and is calculated as In addition, the density is JIS K 6760
This is a value measured in accordance with .

The fluidity ratio is a measure of the molecular weight distribution of the resin used; a small fluidity ratio value indicates a narrow molecular weight distribution, and a large fluidity ratio value indicates a wide molecular weight distribution.

In the present invention, only the linear polyethylene described above may be used, but by using linear polyethylene as the main component and adding a specific amount of branched low-density polyethylene to this, film formability and stretchability are improved. Therefore, it is desirable.

The branched low-density polyethylene blended into the linear polyethylene includes an ethylene homopolymer and a copolymer of ethylene and other copolymer components.

Copolymerization components include vinyl acetate, ethyl acrylate,
Examples include vinyl compounds such as methyl acrylate, and olefins having 3 or more carbon atoms such as hexene, propylene, octene, and 4-methylpentene-1. The copolymerization amount of the copolymerization component is 0.5 to 18% by weight, preferably 2 to 1% by weight.
It is about 0% by weight. These low-density polyethylenes are processed using the normal high pressure method (1000 to 3000 kg/cd).
It is preferable that the material be obtained by radical polymerization using a radical generator such as oxygen or an organic peroxide.

The branched low-density polyethylene used has a melt index of 2 g/10 minutes or less, preferably in the range of 0.1-1 g/10 minutes, and a fluidity ratio of 70 or less, preferably in the range of 30-70. If the melt index exceeds the above range, it is undesirable because the surface strength of the film decreases, and if the flow ratio exceeds the above range, it is undesirable because the surface strength of the film decreases. Furthermore, the above branched low density polyethylene has a density of 0.91 to 0.94 g/aJ,
The range is preferably from 0.91 to 0.930 g/cd, particularly preferably from 0.915 to 0.925 g/aJ, from the viewpoint of improving surface strength.

The blending amount of the linear low density polyethylene and branched low density polyethylene is 100 to 50 parts by weight, preferably 90 to 70 parts by weight of the linear low density polyethylene, and 0 to 50 parts by weight, preferably 0 to 50 parts by weight of the branched low density polyethylene. It is used in a range of 10 to 30 parts by weight.

Next, the radical generator to be added to the linear low density polyethylene and the branched low density polyethylene is preferably one having a decomposition temperature in the range of 130°C to 300°C with a half-life of 1 minute, such as dicumyl peroxide, 2 .5-dimethyl-2,5 di(t-butylperoxy)hexane, 2.
5-dimethyl 2.5 di(t-butylperoxy)hexyne-3,α,α'-bis(t-butylperoxyisopropyl)benzene, dibenzoyl peroxide, di-
Examples include t-butyl peroxide.

The amount of the radical generator is o, o relative to the total amount of the linear low density polyethylene and branched low density polyethylene.
ooi to 0.1 parts by weight, but if this amount is less than 0.0001 parts by weight, the surface strength of the resulting film is almost the same as that without additives, and If the amount is more than 1 part by weight, the melt index will be too low and film breakage will easily occur during film forming.
Moreover, it is not preferable because it causes roughness on the surface of the film.

In the present invention, there are no particular limitations on the method of blending a radical generator into the linear low-density polyethylene and branched low-density polyethylene, decomposing the radical generator, and reacting with the polyethylene, for example, the following method. It can be carried out in

(1) During inflation molding, the linear low density polyethylene, branched low density polyethylene and radical generator are fed simultaneously or sequentially and melt extruded.

(2) Using a kneading machine such as an extruder or a Banbury mixer, the above-mentioned linear low density polyethylene, branched low density polyethylene and radical generator are kneaded and reacted, and then pelletized, and the pellets are used. Inflation molding.

(3) A master bunch containing a large amount of a radical generator, that is, polyethylene such as linear low density polyethylene, branched low density polyethylene, high density polyethylene, etc., containing a large amount of radical generator (usually 5000 to 110000 pp)
A masterbatch is made in advance by blending the above-mentioned linear low-density polyethylene and melt-kneading it into a pellet shape at a temperature above the melting point of polyethylene at which the radical generator hardly reacts with the polyethylene. and branched low-density polyethylene are blended and inflation molded.

Further, the radical generator itself may be used as it is or dissolved in a solvent.

By reacting the linear low-density polyethylene and the branched low-density polyethylene with a radical generator, a modified polyethylene in which the polyethylene undergoes molecular coupling, the high molecular weight component is increased, and the melt index is decreased is obtained.

The modified polyethylene is more easily oriented in the lateral direction during inflation molding than a blend of unmodified linear low density polyethylene and branched low density polyethylene, and when the film thus obtained is stretched, it is easily oriented in the lateral direction. The cracks have significantly improved strength and impact strength.

On the other hand, the high-density polyethylene used as resin B can be obtained by homopolymerizing ethylene using a Ziegler type catalyst or Phillips type catalyst or by copolymerizing ethylene with other α-olefins such as propylene and butene-1. with a density of 0.945g/cd
larger, preferably in the range of 0.95 to 0.965 g/aJ, and with a melt index of 0.5 to 10 g/1
0 minutes, preferably in the range of 0.5 to 5 g/10 minutes. If the density is less than the lower limit, the slipperiness of the film is insufficient, and if the melt index is less than the lower limit, the film thickness during coextrusion will not have a uniform layer ratio,
Moreover, if it is higher than the upper limit, the physical properties of the film deteriorate, which is not preferable.

In the present invention, an unstretched film is formed by a coextrusion inflation method using the modified polyethylene (resin A) and high-density polyethylene (resin B), and then the unstretched film is molded in the longitudinal direction (the direction in which the film is taken off).
A stretched film is produced by stretching the film.

The coextrusion inflation molding uses a cylindrical round multilayer die used for inflation molding to form 2 types of 2 layers (resin B/resin A) or 2 types of 3 layers (resin B/resin) using a cylindrical round multilayer die used for inflation molding. A-phase resin) is coextruded into a tube shape, and at the same time, air is blown into the tube to form a multilayer unstretched film using a normal inflation molding method.

The thickness layer ratio of the multilayer unstretched film is that the thickness of resin A is 10
When set to 0, the thickness of resin B is 5 on at least one side.
-30, preferably 10-30. The resin B
If the layer ratio is less than the lower limit, the layer ratio of the resin B in the inner and outer layers will not be uniform, resulting in insufficient slipperiness of the film, and if it exceeds the upper limit, the film will be This is undesirable because it reduces the impact strength and tear strength of the material.

As for the structure of the multilayer film, a structure of (resin B/resin A phase resin), ie, a structure in which the inner and outer layers are made of resin B, is desirable from the viewpoint of improving the slipperiness of the inner and outer layers of the film.

The multilayer unstretched (hereinafter referred to as unstretched) film is produced using an inflation molding method, with a blow-up ratio of 2 to 8.
Preferably 3 to 8, frost line height to die diameter (
2 to 50 times the diameter of the annular slit, preferably 5 to 5
The test is carried out under conditions in the 0x range. If the above blow-up ratio is less than the lower limit, the film's longitudinal tear resistance and impact strength will decrease, and if it is higher than the upper limit, the bubble forming stability will decrease, which is undesirable. Also, if the frost line height is less than the lower limit, the film will The tear resistance in the longitudinal direction decreases, and if it is higher than the upper limit, the molding stability of the bubble decreases, which is not preferable.

The unstretched film is then uniaxially stretched in the longitudinal direction at a stretching temperature of -70 to -20°C, the melting point of the resin composition (modified polyethylene), and a stretching ratio of 1.5 to 8 times.

The stretching temperature is desirably below the melting point of -20°C, and above the melting point of -70°C, preferably between -30°C and -60°C. Below this range, stretched rings will occur in the film, and above this range, the impact strength of the film will increase. descend.

The stretching ratio is 1.5 times or more and 8 times or less, preferably 2 times or more and 5 times or less. The stretching ratio is 1.
If it is less than 5 times, the effect of stretching is insufficient, and the film will not have sufficient rigidity and tensile strength. If it is more than 8 times, the stretched film will have excessive molecular orientation in the longitudinal direction, and the film will not have sufficient rigidity and tensile strength. Vertical cracks are undesirable because they reduce strength.

〔Example〕

EXAMPLES The present invention will be explained in more detail by way of examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 (11 Linear low density polyethylene (melt index (
MI): 0.5g/10min, flow ratio: 20゜Density: 0
．． 921 g/d, 80 parts by weight of the copolymer component nibutene-1° copolymerized amount: 10% by weight, melting point 118°C) and high-pressure branched low-density polyethylene (MI: 0.4 g/10 min, fluidity ratio = 45 .density: 0.922g/aJ) with 20 parts by weight (melting point of the mixture: 118°C
) and 0.03 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3.
From a 5φ type extruder, high density polyethylene (Ml: 1
．． Og/10 min, density: 0.960 g/aJ) to 4
The molding temperature was determined from the coextrusion die of an inflation coextrusion molding machine (a molding machine equipped with an inflation coextrusion die with an annular slit diameter of 250 mm and a slit width of 4 fl, and a cooling air ring) from each of the 5 Tsuru φ type extruders. 2
Co-extrusion at 20℃, extrusion amount (total) 80 ktr/
hr, blow amplifier ratio 3, and F L H/D = 8 to form a 200μ laminated film (
An inner layer (high density polyethylene) of 20μ and an outer layer (modified polyethylene) of 180μ) were obtained. This original film was slit in the film take-up direction, and a longitudinally-axially stretched film with a thickness of 80 μm was produced using a roll stretching device at a stretching temperature of 80°C and a stretching ratio (3 times in the longitudinal direction). did.

Evaluation method (a) Strength test for finger removal In order to examine the tensile strength of the film, a strength test was conducted for finger removal.

The test method was to cut the longitudinally stretched film obtained above into 760 m lengths in the stretching direction, and cut them into 10 m lengths in the transverse direction (width direction of the film).
Cut to 00m II width, roll horizontally, overlapped part is 6
Apply hot melt adhesive (
Nitta Gelatin Co., Ltd. grade HX-960) was applied and the overlapped parts were heated and bonded using a hot gun to form a cylindrical body.
One of the upper and lower parts of the cylindrical body is H322 manufactured by Newlong Co., Ltd.
After heat-sealing using a B-Z type heat sealer, the resulting bag was filled with 20 kg of fertilizer and the opening was heat-sealed in the same manner as above to obtain a test packaging bag. I lifted the bag with my hand so that it was parallel to the surface, and observed how my fingers dug into the film surface of the bag.

Rating A: No finger digging in at all, no problem at all B: Finger biting in a little, but no particular problem C: Finger digging in a lot, problem (B) Drop bag test Obtained in (B) above. Lift the packaging bag (20 kg fertilizer bag) by hand so that the body is parallel to the floor, and let it cool to room temperature (25 kg).
℃) from a height of 1.5 m, and the number of times the bag broke was expressed as the average value of 20 bags.

(c) Slip property Using a friction angle tester manufactured by Toyo Seiki Co., Ltd.,
．． Attach it to a thread with a bottom surface of 3cm
ent) is expressed as the value of θ.

(d) Bag-making speed Using the bag-making device shown in Figure 1, paper with a width of 1160 m (semi-cleback paper with a weight of 84 g/rd) and the above film were introduced into the bag-making machine, and the bag-making speed ( m/m1n) was investigated. In addition, the high-density polyethylene layer of the above film was in contact with the surface of the bag-making board.

Example 2 The same procedure as in Example 1 was carried out except that one 45φ type extruder for the outer layer was added and the layer structure was changed to (high-density polyethylene/modified polyethylene/high-density polyethylene).

Examples 3 to 4 The same procedure as in Example 1 was carried out except that the conditions were changed as shown in Table 1.

Comparative Example 1 The same procedure as in Example 1 was carried out except that modified polyethylene was used alone.

Comparative Examples 2-3 The same procedures as in Example 2 were carried out except that the conditions were changed as shown in Table 1.

The evaluation results of Examples and Comparative Examples are shown in Table 1.

〔Effect of the invention〕

According to the method of the present invention, a film with improved slipperiness and excellent strength can be obtained, and a film suitable for constructing bags for packaging heavy objects, etc. can be obtained.

Claims (1)

[Claims] (1) Resin 1 containing at least 50% by weight of linear low density polyethylene with a melt index of 2 g/10 minutes or less and a density of 0.910 to 0.945 g/cm^2
0.001 to 0.1 of radical generator per 00 parts by weight
Resin A made of a composition blended in a range of parts by weight and resin B made of high density polyethylene with a melt index of 0.5 to 10 g/10 minutes and a density of more than 0.945 g/cm^2. When the thickness ratio is 100 for the thickness of resin A, the thickness of resin B on at least one side is 5 to 3.
Coextrusion and inflation molding were performed with a ratio of 0 and a blow-up ratio of 2 to 8, and a frost line height of 2 to 50 times the diameter of the annular slit. A method for producing a film, characterized in that uniaxial stretching is carried out at a temperature of -70° C. to -20° C., the melting point of the resin A, and a stretching ratio of 1.5 to 8 times.