JPH07100348B2 - Film production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a method for producing a film which is excellent in tear strength, impact strength, rigidity and tensile strength in the machine direction (stretching direction) of the film. More particularly, it relates to a method for producing a packaging film, which is mainly composed of linear polyethylene, which can be made thinner than conventional films, and which is suitable for packaging relatively heavy articles such as rice grains and fertilizers.

[Prior art]

Linear low-density polyethylene with less branching produced by copolymerization of ethylene and α-olefins has higher tensile strength, impact strength, rigidity, etc. than high-pressure low-density polyethylene produced by radical polymerization under high temperature and high pressure. It has excellent properties, such as environmental stress crack resistance (ESCR), heat resistance, and heat sealability, and has been used in various fields in recent years. Particularly in the field of film, the substitution of high-pressure low-density polyethylene for linear low-density polyethylene is rapidly progressing because of its superior physical properties.

It is difficult to obtain an unstretched film or sheet (hereinafter referred to as “raw material”) obtained by molding such a linear low-density polyethylene resin by the T-die method or the inflation method, because of its molding restrictions. Is. Further, the original fabric thus obtained has low strength. Therefore, it has been conventionally proposed to perform a stretching process.

Therefore, it is conceivable that the raw fabric is biaxially stretched, but the equipment cost is high, and the range of stretching conditions is narrow, so the operation management is strict and it is used only in a limited part of the field.

Further, the longitudinal uniaxial stretching that has been known so far has low equipment cost and easy operation management, but has problems in the anisotropy of the physical properties of the film, particularly the tear resistance and surface strength in the longitudinal direction (stretching direction). The remaining film for practical use was not obtained.

[Means for solving problems]

Therefore, as a result of solving the drawbacks of the prior art and earnestly studying to produce a thin (stretched) film having excellent strength characteristics from linear polyethylene, the present inventor has found that a specific linear polyethylene resin can be used under specific conditions. 40-70 by uniaxially stretching the original fabric inflation-molded under
% It has been found that a film excellent in tear resistance, impact strength, rigidity and tensile strength can be obtained even when the thickness is reduced, and the present invention has been completed.

That is, the gist of the present invention has a density of 0.91 to 0.965 g / cm ₃ , a melt index of 20 g / 10 min or less, a flow ratio of 70 or less linear polyethylene 100 to 50 parts by weight, MI 20 g / 10 min or less, and a flow ratio of 0.0001-0.1 part by weight of a radical generator is added to 0-50 parts by weight of branched low-density polyethylene of 70 or less, and the radical generator is decomposed and reacted with the polyethylene, or after the reaction, a blow-up ratio of 2- 8. Inflation molding under the conditions of frost line height (hereinafter referred to as FLH) 2D to 50D (D is the diameter of the die), and the obtained film is stretched in the film-drawing direction at a melting point of the above resin composition. A film manufacturing method is characterized in that the film is uniaxially stretched under the conditions of −70 to melting point −20 ° C. and a stretching ratio of 1.5 to 8.

The present invention will be described in more detail below.

The linear polyethylene used in the present invention is 0.91 to 0.
95 g / cm ₃ linear low density polyethylene and 0.965 g / cm ₃ or less high density polyethylene are used.

The linear low density polyethylene means ethylene and other α-
It is a copolymer with an olefin and is different from the branched low-density polyethylene resin produced by the conventional high-pressure method. Linear low density polyethylene includes, for example, ethylene and other α-
As the olefin, butene, hexene, octene, decene, 4 methylpentene-1 etc. are copolymerized at about 4 to 17% by weight, preferably at about 5 to 15% by weight, and are used in the medium and low pressure method high density polyethylene production. It is manufactured using a catalyst or Phillips type catalyst, and has a conventional branched structure with a high density polyethylene having a short branching structure, and the density is appropriately reduced by utilizing this short chain branching 0.91 to 0.95 g / cm 3. _The polyethylene has a structure of about ₃ which is more linear than conventional branched low-density polyethylene and more branched than high-density polyethylene.

Further, as the high-density polyethylene, an ethylene homopolymer obtained by polymerization using a Ziegler-type catalyst alone or a Phillips-type catalyst and having a density of 0.965 g / cm ₃ or less is used.

The above linear polyethylene has a melt index of 20 g / 10
Min or less, preferably 10 g / 10 min or less, more preferably 0.001
It is suitably used in the range of -5 g / 10 min and the flow ratio of 70 or less, preferably 10-50. If the melt index is higher than the upper limit, the surface strength decreases, which is not preferable. If the fluidity ratio is higher than the upper limit, the surface strength decreases, which is not preferable. Further, it is desirable that the linear polyethylene has a density of 0.910 to 0.965 g / cm ₃ , preferably 0.915 to 0.940 g / cm ₃ . If the density is higher than the upper limit, the impact resistance is remarkably lowered, and if it is lower than the lower limit, the rigidity and the tensile strength are lowered, which is not preferable.

In the method of the present invention, the melt index is JIS K 6760.
Is a value measured in accordance with Condition 4 of Table 1 of JIS K 7210 which is a reference standard of the flow ratio, and the flow ratio is a shear force of 10 ⁶ dyne / cm ² (load 11131
g) and 10 ⁵ dynes / cm ² (load 1113 g) extrusion rate (g / 10 minutes)
And It is calculated by. The density is a value measured according to JIS K 6760.

The flow ratio is a measure of the molecular weight distribution of the resin used, and the smaller the flow ratio value, the narrower the molecular weight distribution, and the larger the flow ratio value, the wider the molecular weight distribution.

In the present invention, although only the above-mentioned linear polyethylene may be used, the film formability and the stretchability are improved by using the linear polyethylene as a main component and adding a specific amount of the branched low-density polyethylene thereto. So desirable.

The branched low-density polyethylene to be blended with the linear polyethylene includes an ethylene homopolymer and a copolymer of ethylene and another copolymerization component.

As a copolymerization component, vinyl acetate, ethyl acrylate,
Examples thereof include vinyl compounds such as methyl acrylate, 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 about 2 to 10% by weight. These low-density polyethylenes are preferably obtained by radical polymerization by a conventional high-pressure method (1000 to 3000 kg / cm ² ) using a radical generator such as oxygen or organic peroxide.

The branched low density polyethylene has a melt index
Those having a flow ratio of 20 g / 10 minutes or less, preferably 10 to 1 g / 10 minutes and a flow ratio of 70 or less, preferably 30 to 70 are used. When the melt index is more than the above range, the surface strength of the film decreases, which is not preferable. Further, if the flow ratio is in the above range or more, the surface strength of the film decreases, which is not preferable. Further, the above branched low-density polyethylene preferably has a density of 0.930 or less, particularly in the range of 0.915 to 0.925, from the viewpoint of improving the surface strength.

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

Next, the radical generator to be added to the linear polyethylene and the branched low-density polyethylene is preferably one having a decomposition temperature of 130 ° C. to 300 ° C., which has a half-life of 1 minute, for example, dicumyl peroxide, 2,5 -Dimethyl-2,5 di (t-
Butylperoxy) hexane, 2,5-dimethyl-2,5di (t-butylperoxy) hexyne-3, α, α'-bis (t-butylperoxyisopropyl) benzene, dibenzoylperoxide, di- Examples thereof include t-butyl peroxide.

The content of the radical generator is 0.0001 to 0.1 with respect to the total amount of the linear polyethylene and the branched low density polyethylene.
It is selected from the range of parts by weight, but the surface strength of the film obtained when this blending amount is less than 0.0001 parts by weight is almost the same as that of no addition, and when it is more than 0.1 parts by weight, It is not preferable because the melt index becomes too low and film breakage easily occurs during film formation, and the surface of the film becomes rough.

In the present invention, a method of blending a radical generator with the linear polyethylene and the branched low-density polyethylene, and decomposing the radical generator and reacting with the polyethylene is not particularly limited, and for example, the following method is used. can do.

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

(2) Using a kneader such as an extruder or a Banbury mixer, the linear polyethylene, the branched low-density polyethylene and the radical generator are kneaded to react with each other, pelletize, and inflation molding is performed using the pellets. .

(3) A masterbatch containing a large amount of radical generator, that is, polyethylene such as linear low-density polyethylene, branched low-density polyethylene, and high-density polyethylene, is mixed with a large amount of radical generator (usually about 5000 to 10,000 ppm),
A master batch was prepared in advance by melting and kneading it at a temperature above the melting point of polyethylene, at which the radical generator hardly reacts with polyethylene, and the master batch and the above linear polyethylene and branched low density polyethylene were blended. Inflation molding.

The radical generator itself is used as it is or after being dissolved in a solvent.

By reacting the above-mentioned linear polyethylene and branched low-density polyethylene with a radical generator, the above polyethylene causes molecular coupling to increase the high molecular weight component and to obtain a modified polyethylene having a reduced melt index. The modified polyethylene is more likely to be oriented in the lateral direction during inflation molding as compared with a blend of unmodified linear polyethylene and branched low-density polyethylene, and the film thus obtained has a longitudinal tear strength when stretched. And the impact strength is significantly improved.

In the present invention, the modified polyethylene is used to form an unstretched film by an inflation method, and the unstretched film is then stretched in the machine direction (the film take-up direction).
To obtain a stretched film.

The unstretched film is produced by the inflation molding method,
Blow-up ratio is 2-8, preferably 3-8, frost line height is 2-50 times of die diameter, preferably 5-50
Double the conditions. If the blow-up ratio is less than the lower limit, the tear resistance and impact strength of the film in the machine direction are reduced, and if it is higher than the upper limit, the bubble molding stability is reduced, which is not preferable. If the height of the frost line is less than the lower limit, the tear strength of the film in the machine direction is lowered, and if it is higher than the upper limit, the bubble molding stability is lowered, which is not preferable.

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

The stretching temperature is preferably −20 ° C. or lower, −70 ° C. or higher, preferably −30 ° C. to −60 ° C. If it is less than the range, stretch unevenness occurs in the film, and if it is more than the range, the impact strength of the film is significantly reduced. The stretching ratio is 1.5 times or more and 8 times or less, preferably 2 times or more and 5 times or less. If the stretching ratio is less than 1.5 times, the effect of stretching is insufficient, and the rigidity and tensile strength of the film are not sufficient. On the other hand, if it is 8 times or more, the stretched film has an excessive molecular orientation in the machine direction, and the longitudinal tear strength of the film decreases, which is not preferable.

〔Example〕

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Example 1 (1) Linear low-density polyethylene (melt index (MI) 0.5 g / 10 minutes, flow ratio 20, density: 0.921 g / cm ² , copolymerization component: butene-1, copolymerization amount: 10 wt% , Melting point 118 ° C} 80
Parts by weight and high pressure branched low density polyethylene (MI: 0.48g / 1
0 minutes, flow ratio: 45, density: 0.922 g / cm ² ) and 20 parts by weight of dry blend (melting point of mixture: 118 ° C.) and 2,5-dimethyl-2,5 di (t-butylperoxy) ) Hexin-3
A mixture of 0.03 parts by weight was used as the raw material, and this was applied to a modern machine Delsar 65φ type extruder with an annular slit diameter of 250.
Using an inflation film molding machine equipped with a φ, slit width 4 m / m inflation die and cooling air ring, extrusion rate 80 Kg / hr, blow-up ratio 3, FLH / D = 8
An inflation film of 200μ was obtained under the conditions of.
A film obtained by slitting this film original in the film take-up direction was used to produce a longitudinally uniaxially stretched film having a thickness of 80μ under the conditions of a stretching temperature of 80 ° C and a stretching ratio (3 times in the longitudinal direction) using a roll stretching device. .

Evaluation method (a) The strength of the obtained film was tested according to Elmendorf tear strength-JIS P8116 Dirt drop impact (DDI) -ASTM D1709.

(B) Finger pull-out strength test A finger pull-out strength test was conducted to examine the tensile strength of the film.

The test method is to cut the longitudinally stretched film obtained in the above (1) to 760 mm in the stretching direction, and to measure 1 in the transverse direction (width direction of the film).
Cut it to 000m / m, round it in the lateral direction so that the overlapping part becomes 60mm, apply hot melt adhesive (Grade HX-960 manufactured by Nitta Gelatin Co., Ltd.) to the overlapping part, and heat the overlapping part with a hot gun. After adhering to form a tubular body, one of the upper and lower sides of the tubular body was heat-sealed using a HS22B-Z type heat sealer manufactured by Neurong Co., and the obtained bag was filled with 20 Kg of fertilizer to form an opening. A heat-sealed test packaging bag was obtained in the same manner as in the previous period, and it was lifted by hand so that the heat-sealed portion of the 20 kg fertilizer bag was parallel to the floor surface, and the state where the fingers bite into the film surface of the bag was observed.

Evaluation A: No finger biting, no problem at all B: Some finger biting, no particular problem C: Large finger biting, problematic Results are shown in Table 1.

Example 2 The linear low density polyethylene used in Example 1 was 100
Except that FLH / D (D is the die diameter) is 15 is used as the raw material, which is obtained by mixing 0.03 part by weight of 2,5-dimethyl-2,5di (t-butylperoxy) hexyne-3 with 0.03 part by weight. Is Example 1
Molded and stretched in the same manner as. The results are shown in Table 1.

Comparative Example 1 In Example 1, BUR was changed to 1.5, and molding and stretching were performed in the same manner.

Comparative Examples 2 to 6 The procedure of Example 1 was repeated, except that the linear polyethylene, the amount of radical generator, the molding conditions and the stretching conditions were changed as shown in Table 1. The results are shown in Table 1.

[Effects of the Invention] According to the present invention, it is possible to produce a film which has not been heretofore considered to be thin, and which has improved impact strength, rigidity, tensile strength and tear strength, at a lower cost than biaxial stretching or transverse uniaxial stretching.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to reduce the thickness of a film for a packaging bag suitable for packaging a relatively heavy article such as a heavy and medium weight packaging bag.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-59-198121 (JP, A) JP-A-60-257232 (JP, A) JP-A-63-173622 (JP, A)

Claims (1)

[Claims] 1. A linear polyethylene having a density of 0.91 to 0.965 g / cm ₃ , a melt index of 20 g / 10 minutes or less, and a flow ratio of 70 or less, 100 to 50 parts by weight, MI 20 g / 10 minutes or less, and a flow ratio of 70 or less. 0.0001 to 0.1 part by weight of a radical generator is added to 0 to 50 parts by weight of branched low-density polyethylene, and the radical generator is decomposed and reacted with the polyethylene, or after the reaction, a blow-up ratio of 2 to 8; Frostline height 2D
-50D (D is the diameter of the die) is inflation-molded, and the resulting film is stretched in the film-drawing direction at a melting point of the resin composition of −70 to a melting point of −20 ° C.
A method for producing a film, which comprises uniaxially stretching a film at a draw ratio of 1.5 to 8.