JPH07102612B2 - Film manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a film which is excellent in tear strength in the longitudinal direction (stretching direction), impact strength, rigidity and tensile strength. Specifically, it relates to a method for producing a film for a packaging bag, 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. is there.

[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 to biaxially stretch the raw fabric, but since the equipment cost is high and the range of stretching conditions is narrow, the operation management is severe and it is used only in a very limited field.

In addition, longitudinal uniaxial stretching has low equipment costs and is easy to operate and manage, but the anisotropy of the physical properties of the film, especially the problem of tear strength and surface strength in the longitudinal direction (stretching direction) remains, and a film that can be put to practical use I couldn't get it.

[Means for solving problems]

Therefore, the present inventor has made intensive studies to eliminate the drawbacks of the prior art and produce a thin (stretched) film having excellent strength properties from linear polyethylene, and as a result, a specific linear polyethylene resin, a thermoplastic elastomer, and radicals have been obtained. A film excellent in tear resistance, impact strength, rigidity and tensile strength even if it is made thin by stretching a composition inflation-molded under specific conditions from a composition consisting of a generator by longitudinally uniaxially stretching it under specific conditions. The present invention has been completed 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 minutes or less, and a flow ratio of 70 or less linear polyethylene or a mixture of the linear polyethylene and branched low density polyethylene 99 to 50 parts by weight, Mooney viscosity measured at 100 ° C {ML _{1 + 4} (100 ° C)} is 5 to 100, and the main chain is basically composed of saturated hydrocarbon bonds and carbonized with double bonds in the pendant side chains. Hydrogen-based thermoplastic elastomer 1
50 parts by weight, a composition consisting of 0.0001 to 0.1 parts by weight of a radical generator, while decomposing the radical generator and reacting with polyethylene or an elastomer, or after reacting,
Blow-up ratio 2-8, frost line height (hereinafter FL
H) 2D to 50D (D is the diameter of the die) is subjected to inflation molding, and the obtained 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 at a stretch ratio of 1.5 to 8 times.

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.

The high-density polyethylene is an ethylene homopolymer obtained by polymerizing ethylene alone using a Ziegler type catalyst or a Phillips type catalyst, and its density is 0.965 g / cm ^3.
Below, preferably 0.95 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. Furthermore, the linear polyethylene has a density of 0.910 to 0.965 g / cm ³ , preferably 0.910 to 0.950 g / cm ³ ,
More preferably, the range is 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 6
760 is a value measured in accordance with Condition 4 of Table 1 of JIS K 7210 which is a reference standard of 760, and the flow ratio is a shear force of 10 ⁶ dyne / cm ² (load 1
1131g) and 10 ⁵ dynes / cm ² (load 1113g) extrusion rate (g / 10
Minutes) 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.

The thermoplastic elastomer blended with the above-mentioned linear polyethylene refers to one in which the main chain is basically composed of saturated hydrocarbon bonds and double bonds are contained in pendant side chains.

An example of such an elastomer is a copolymer of ethylene and / or α-olefin and a diene monomer, and an ethylene-propylene-diene terpolymer (EPDM) is generally known. Of these, the diene component is not particularly limited, but generally ethylidene norbornene, dicyclopentadiene and the like are used. Other examples of elastomers include 1,2 addition polymerization products of polymerizable diene compounds, and specific examples include 1,2 polybutadiene, 1,2 polyisoprene, and 3,4 polyisoprene. These are ethylene and α- as long as the diene component is 1,2 addition.
It may be a copolymer with olefin.

On the other hand, thermoplastic elastomers containing unsaturated bonds in the main chain, such as styrene-butadiene rubber and isoprene rubber, are not preferable because they have insufficient reactivity with the radical generator described later.

The above-mentioned thermoplastic elastomer must have a Mooney viscosity {ML _{1 + 4} (100 ° C)} measured at 100 ° C in the range of 5 to 100. When the Mooney viscosity is above the above range, the compatibility with linear polyethylene is poor, and below the above range, the effect of blending the elastomer is small and the blocking property of the film is deteriorated, which is not preferable.

The blending amount of the linear polyethylene and the thermoplastic elastomer is 99 to 50 parts by weight of linear polyethylene, preferably 90 to 70.
The thermoplastic elastomer is used in an amount of 1 to 50 parts by weight, preferably 10 to 30 parts by weight, based on parts by weight.

If the blending amount of the thermoplastic elastomer is less than the above range, the film moldability and stretchability are insufficiently improved, and if it is more than the above range, the film strength decreases, which is not preferable.

Further, in the above composition, a part of the linear polyethylene is replaced with a branched low-density polyethylene, for example, 50% by weight or less, preferably about 10 to 30% by weight, so that the characteristics of the linear polyethylene are not lost. be able to. The use of branched low-density polyethylene is desirable because it further improves film moldability and stretchability. The branched low density 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. It is desirable that these low-density polyethylenes are obtained by radical polymerization by a normal 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 density of 0.930 g / c
m ³ or less, preferably 0.910 to 0.925 g / cm ³ range, melt index 20 g / 10 minutes or less, desirably 1 to 10 g / 10 minutes range, flow ratio 70 or less, desirably 30 to 70 range Those are preferably used.

Next, the radical generator to be blended with the above-mentioned linear polyethylene and thermoplastic elastomer preferably has a decomposition temperature in the range of 130 ° C to 300 ° C, which has a half-life of 1 minute, such as 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 selected from the range of 0.0001 to 0.1 parts by weight with respect to the total amount of the linear polyethylene and the thermoplastic elastomer, but when the content is less than 0.0001 parts by weight of the film obtained. The surface strength is almost the same as that of the additive-free one, and when it is more than 0.1 part by weight, the melt index becomes too low and film breakage easily occurs during film molding, and the surface of the film is rough. It is not preferable because it occurs.

In the present invention, a radical generator is added to the linear polyethylene and the thermoplastic elastomer, and the method for decomposing the radical generator and reacting with the polyethylene and the thermoplastic elastomer is not particularly limited,
For example, it can be implemented by the following method.

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

(2) Using a kneader such as an extruder or a Banbury mixer, the above-mentioned linear polyethylene, thermoplastic elastomer and radical generator are kneaded to react with each other, then pelletized, 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 is prepared in advance by melting and kneading it at a temperature above the melting point of polyethylene, where the radical generator hardly reacts with the polyethylene, and this master batch is blended with the above linear polyethylene and thermoplastic elastomer for inflation. Mold.

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

By reacting the linear polyethylene with a radical generator, the polyethylene undergoes molecular coupling to increase the high molecular weight component, and a modified polyethylene having a decreased melt index is obtained. The thermoplastic elastomer is blended. This makes the molecular coupling more effective. The modified polyethylene is more likely to be oriented in the transverse direction during inflation molding as compared with a mere blend of unmodified linear polyethylene and a thermoplastic elastomer, and thus the film thus obtained has a longitudinal tear strength and a longitudinal tear strength when stretched. 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,
The blow-up ratio is 2-8, preferably 3-8, and the frost line height is 2-50 times the die diameter (D) (2D-50
D), preferably in the range of 5 to 50 times (5D to 50D). 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 lowered, and if it is higher than the upper limit, the bubble molding stability is lowered, 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 blending in the machine direction, and the longitudinal tear strength of the film is lowered, 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 ³ , copolymerization component: butene-1, copolymerization amount: 10 wt% , Melting point 118 ° C.}
80 parts by weight of ethylene-propylene-ethylidene norbornene-terpolymer (EPDM, EP57P.ML manufactured by Nippon Synthetic Rubber Co., Ltd.
_{1 + 4} (100 ° C.) = 88) and 20 parts by weight of dry blend (melting point of mixture: 118 ° C.) and 2,5-dimethyl-2,5di (t-butylperoxy) hexyne-3 of 0.03 Using a mixture of parts by weight as a raw material, this is extruded using an inflation film molding machine equipped with a modern machine Delsar 65φ type extruder with an annular slit diameter of 250φ and an inflation die with a slit width of 4 m / m and a cooling air ring. 2 under the condition of quantity 80kg / hr, blow-up ratio 3, FLH / D = 8
A blown film of 00μ was obtained. 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 in order to examine the tensile strength of the film.

The test method is to cut the longitudinally stretched film obtained in (1) above to 760 mm in the stretching direction and 1000 m / m in the transverse direction (width direction of the film) so that the overlapped portion is 60 mm in the transverse direction. A hot melt adhesive (Grade HX-960 manufactured by Nitta Gelatin Co., Ltd.) is applied to the overlapped portion, and the overlapped portion is heated and adhered with a hot gun to form a tubular body, and one of the upper and lower sides of the tubular body is sealed with a new adhesive. After heat-sealing with a HS22B-Z type heat sealer manufactured by Long Co., 20 kg of fertilizer was filled in the obtained bag and the opening was heat-sealed to obtain a test packaging bag. It was lifted by hand so that the seal portion was parallel to the floor surface, and the state where the finger bites 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 In Example 1, as the thermoplastic elastomer, poly 1,
2-Butadiene (RB830, ML _{1 + 4} (100
(° C.) = 15) was used and molded and stretched in the same manner as in Example 1.

Comparative Examples 1 to 7 The same procedure as in Example 1 was repeated except that the mixing ratio of the linear polyethylene and the thermoplastic elastomer, the type of the thermoplastic elastomer, 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 (72) Inventor Akihiko Sakai 3-10 Shiodori, Kurashiki City, Okayama Prefecture Mizushima Plant, Mitsubishi Kasei Kogyo Co., Ltd. (56) References JP-A 64-18625 (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, or a mixture of the linear polyethylene and a branched low density polyethylene 99 to 50% by weight. , A hydrocarbon system with a Mooney viscosity {ML _{1 + 4} (100 ° C)} of 5 to 100 measured at 100 ° C and a main chain consisting essentially of saturated hydrocarbon bonds with double bonds in the pendant side chains A composition comprising 1 to 50 parts by weight of a thermoplastic elastomer and 0.0001 to 0.1 parts by weight of a radical generator,
After decomposing the radical generator and reacting it with polyethylene or elastomer, or after reacting, blow molding is performed under inflation conditions of 2 to 8 and frost line height of 2D to 50D (D is the diameter of the die). The obtained film is stretched in the film-drawing direction at a melting temperature of the resin composition of −70 to a melting point of −20 ° C., and a stretching ratio of 1.5.
A method for producing a film, which comprises uniaxially stretching at a stretch ratio of 8 times.