JPH0724912A - Oriented film and packing bag employing it - Google Patents

Abstract

PURPOSE:To obtain a thin film with an excellent impact strength, rigidity, anti-tensile strength, and tearing strength by blending polybutene resin in linear and branch low-density polyethylene resin, and subjecting the film obtained by inflation to uniaxial orientation under the specified conditions. CONSTITUTION:Polybutene resin being equal to or lower than 100 pts.wt. is blended to 100-50 pts.wt. polyethylene resin, 0-50 pts.wt. polyethylene resin and a total of 100 pts.wt. of linear polyethylene resin and branch low density polyethylene resin. The blended resin composite is inflation-molded under the condition of 2-8 blow up ratio, and the film obtained is uniaxially oriented in the film undertaking direction under the conditions of an orientation temperature of the resin composite melting point from -70 to -20 deg.C and an orientation magnification of 1.5-8. There is obtained a packing bag for heavy contents with an inside bag consisting of obtained film and an outside bag of paper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film having excellent tear resistance, impact strength, rigidity and tensile strength in the machine direction (stretching direction) of the film, and a packaging bag using the film. More specifically, it 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, and a heavy-weight film using the same. Regarding packaging bags.

[0002]

2. Description of the Related Art Linear low-density polyethylene with few branches produced by copolymerization of ethylene and α-olefins has higher tensile strength and impact strength than high-pressure low-density polyethylene produced by radical polymerization under high temperature and high pressure. , Strength characteristics such as rigidity, environmental stress crack resistance (ESCR), heat resistance,
It has excellent properties such as 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.

Such a linear low density polyethylene resin is
It is difficult to obtain an unstretched film or sheet (hereinafter referred to as "raw material") formed by a die method or an inflation method, which has an extremely thin thickness, due to restrictions in molding. Further, the original fabric thus obtained has low strength. for that reason,
Conventionally, it has been 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.

The longitudinal uniaxial stretching, which has been publicly known so far, has a low equipment cost and is easy to manage in operation, but the anisotropy of the physical properties of the film, particularly the tear resistance and surface strength in the longitudinal direction (stretching direction). However, the film could not be obtained for practical use. Then, by inflation-molding and uniaxially stretching a specific linear polyethylene reacted with a radical generator under specific conditions, it was found that a thin film having a significantly improved tear strength and surface strength can be obtained, I filed an application earlier (Japanese Patent Laid-Open No. 1-186
No. 25), it remained difficult to control the reaction of radicals.

On the other hand, a multilayer kraft bag is mainly used as a bag for packaging heavy goods, particularly a packaging bag of polyethylene resin raw material (polyethylene chip), nylon resin raw material (nylon chip) or the like. This multi-layer kraft has a multi-layer structure in order to impart strength and water resistance, but the contents may get wet due to water wetting, or the strength may drop and bag breakage may occur. Therefore, a bag made of kraft paper and a woven fabric made of a stretched string of synthetic resin to give water resistance and strength (hereinafter referred to as "craft cloth lami bag").
Is also used, but the manufacturing process increases and the cost also increases. A packaging bag made of only a synthetic resin film has also been put into practical use, and although it has excellent water resistance, its surface tends to slip and the load tends to slip. Also, by reducing the film thickness of the bag, the tensile strength at break in the body of the bag decreases,
There is a practical problem that when a bag is torn by a projection or the like, or the contents are put in a bag and carried by hand during transportation, a phenomenon in which a fingertip holding the bag sticks into the bag, so-called “finger dropout” occurs.

Therefore, in view of such a situation, water resistance,
In order to obtain a packaging bag having mechanical strength and anti-slip properties and improved manufacturing efficiency, a two-layer packaging bag using a polyethylene resin as an inner bag and a paper layer as an outer bag has been developed. Proposed. However, the tear strength and surface strength of the polyethylene used for the inner bag were insufficient.

That is, the gist of the present invention is 100 to 50 parts by weight of a linear polyethylene resin, 0 to 50 parts by weight of a branched low-density polyethylene resin, and 100 parts by weight in total of the linear polyethylene resin and the branched low-density polyethylene resin. On the other hand, a resin composition obtained by blending 100 parts by weight or less of a polybutene resin was inflation-molded under the conditions of a blow-up ratio of 2 to 8, and the obtained film was stretched in the film-drawing direction at the above-mentioned resin composition. Melting point of substance-70 ° C ~
The present invention resides in a film uniaxially stretched under the conditions of a melting point of −20 ° C. and a stretch ratio of 1.5 to 8, and a packaging bag composed of an inner bag made of the film and an outer bag made of paper.

The present invention will be described in more detail below. The linear polyethylene resin used in the present invention is 0.9
1～0.95G / linear low density polyethylene and 0.95 g / cm ³ or less such as high-density polyethylene in cm ³ is used. The linear low-density polyethylene is a copolymer of ethylene and another α-olefin, and is different from the branched low-density polyethylene resin produced by the conventional high pressure method. The linear low-density polyethylene is, for example, 4 to 17% by weight of ethylene and other α-olefins such as butene, hexene, octene, decene, and 4methylpentene-1.
The copolymer is a copolymer of about 5 to 15% by weight, and is produced by using a Ziegler type catalyst or Phillips type catalyst used for producing high density polyethylene by the medium and low pressure method. A conventional high-density polyethylene is made into a short branched structure by a copolymerization component, and the density is appropriately reduced by utilizing this short chain branching to about 0.91 to 0.95 g / cm ³ . That is, it is a polyethylene having a structure that 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 polymerizing ethylene alone using a Ziegler type catalyst or a Phillips type catalyst and having a density of 0.95 g / cm ³ or less is used.
The linear polyethylene resin has a melt index of 20 g / 10 minutes or less, preferably 10 g / 10 minutes or less, more preferably 0.001 to 5 g / 10 minutes,
A fluidity ratio of 70 or less, preferably 10 to 50, is preferably used. If the melt index is too high, the surface strength will decrease, which is not preferable. If the flow ratio is too high, the surface strength will decrease, which is not preferable. Furthermore, the density of the linear polyethylene resin is preferably in the range of 0.915 to 0.940 g / cm ³ . If the density is too high, the impact resistance will be remarkably lowered, and if it is too low, the rigidity and the tensile strength will be lowered, which is not preferable.

In the method of the present invention, the melt index is JIS K which is a reference standard of JIS K 6760.
It is a value measured according to the condition 4 of Table 1 of 7210,
The flow ratio is a shear force of 10 ⁶ dynes / cm ² (load 11131 g) and 1 using the above melt index measuring device.
Extrusion rate of 0 ⁵ dynes / cm ² (load 1113 g) (g /
10 minutes)

[0011]

[Equation 1]

It is calculated by Also, the density is JIS K
It is a value measured according to 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 resin may be used, the linear polyethylene resin is contained as a main component, and a specific amount of the branched low-density polyethylene resin is blended with the linear polyethylene resin to obtain a film formability. And the stretchability is improved, which is desirable. The branched low-density polyethylene resin blended with the linear polyethylene resin includes an ethylene homopolymer and a copolymer of ethylene and another copolymerization component.

As a copolymerization component, vinyl compounds such as vinyl acetate, ethyl acrylate and methyl acrylate, hexene, propylene, octene and 4-methylpentene-
Examples thereof include olefins having 3 or more carbon atoms such as 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 produced by the usual high-pressure method (1000-3000 kg / c
m ² ) is preferably obtained by radical polymerization using a radical generator such as oxygen or organic peroxide.

The branched low-density polyethylene resin has a melt index of 20 g / 10 minutes or less, preferably 10
A material having a flow ratio of 70 to 1 g / 10 minutes and a flow ratio of 70 or less, preferably 30 to 70 is used. If the melt index is too high, the surface strength of the film will decrease, which is not preferable. On the other hand, if the flow ratio is too large, the surface strength of the film decreases, which is not preferable. Further, the above branched low-density polyethylene resin has a density of 0.930 g /
cm ³ or less, it is desirable from the viewpoint of improving the surface strength in particular in the range of 0.915~0.925g / cm ^3.

The blending amount of the linear polyethylene resin and the branched low-density polyethylene resin is linear polyethylene resin 1
The branched low density polyethylene resin is used in an amount of 0 to 50 parts by weight, preferably 10 to 30 parts by weight, based on 0 to 50 parts by weight, preferably 90 to 70 parts by weight. Next, as the polybutene resin to be blended with the linear polyethylene resin and the branched low-density polyethylene resin, 1-butene, 2
-Butene, inbutene, butane and the like are polymerized with a Ziegler-Natta catalyst or the like. Homopolymers of 1-butene or copolymers with an ethylene content of up to 10% by weight or copolymers with a propylene content of up to 40% by weight are preferred. Usually has a density of 0.885 to 0.920 g / cm
³ , preferably 0.890 to 0.915 g / cm ³ ,
Melt index is 20 g / 10 min or less, preferably 0.1 to 2.0 g / 10 min, and weight average molecular weight is 200,000 to
It is in the range of 5,000,000, preferably 800,000 to 3,000,000.

In particular, it is preferable to use a melt index of 20 g / 10 minutes or less. If the melt index is too large, longitudinal tear strength and impact strength will be lowered, which is not preferable. The blending amount of the polybutene resin is 100 parts by weight or less, preferably 5 to 70 parts by weight, based on 100 parts by weight of the total of the linear polyethylene resin and the branched low-density polyethylene resin.
Parts by weight, particularly preferably 10 to 50 parts by weight. If this blending amount is too large, the molding stability during inflation molding decreases.

In the present invention, the method of blending the linear polyethylene resin, the branched low-density polyethylene resin and the polybutene resin is not particularly limited, and for example, the following method can be used. (1) At the time of inflation molding, the linear polyethylene resin, the branched low-density polyethylene resin, and the polybutene resin are simultaneously supplied and melt-extruded.

(2) The linear polyethylene resin, the branched low-density polyethylene resin and the polybutene resin are melt-mixed using a mixer such as an extruder or a Banbury mixer, and then pelletized, and inflation molding is performed using the pellets. . The polybutene resin has a molecular weight of 2 as described above.
It is very large, from 0 to 5,000,000, and the high molecular weight component is increased by further mixing it with the mixture of the linear polyethylene resin and the branched low-density polyethylene resin, and it is as if the modified polyethylene obtained by introducing a radical generator is obtained. Such a resin composition can be obtained. Compared with the case where only the mixture of the linear polyethylene resin and the branched low-density polyethylene resin is used, the resin composition tends to be oriented in the lateral direction when inflation-molded under specific conditions, and thus the film thus obtained is stretched. When it does, the vertical tear strength and impact strength are significantly improved.

The above resin composition, that is, the resin composition obtained by blending the linear polyethylene resin or a mixture of the linear polyethylene resin and the branched low-density polyethylene resin with a polybutene resin, is further required. Depending on the case, known additives generally used for polyethylene, such as antioxidants, ultraviolet absorbers, antistatic agents and lubricants, may be added.

In the present invention, an unstretched film is formed by the inflation method using the above resin composition, and then the unstretched film is stretched in the machine direction (the film take-up direction) to produce a stretched film. The unstretched film is produced by an inflation molding method under a blow-up ratio of 2 to 8, preferably 3 to 8. At that time, the height of the frost line is 2 to 50 times the diameter of the die,
It is preferably carried out under the condition of 5 to 50 times. 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 too low, the tear resistance of the film in the machine direction is lowered, and if it is too high, the molding stability of bubbles 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 the melting point of the resin composition of −70 ° C. to a 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, more preferably −30 ° C. to −60 ° C. At temperatures below the range, stretch unevenness occurs in the film, and at temperatures above the range, the impact strength of the film is greatly 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.

Next, the paper constituting the outer bag of the packaging bag of the present invention is not particularly limited, and any paper for general industrial packaging materials can be used in the present invention. Of these, kraft paper and stretch paper (Kurpack paper) are suitable. The weight of these papers (weight per unit area, index of thickness) is 73 to 88 g / m ² . The inside may be laminated with polyethylene.

In the present invention, a two-layer packaging bag is manufactured from the above-mentioned stretched film and paper. As a method of manufacturing the two-layer packaging bag, a well-known method known in the related art can be adopted. The outer bag and the inner bag of the packaging bag may be simply laminated or may be integrally bonded with an adhesive.

The sealing method is, for example, a method in which the inner bag is heat-sealed or adhesively sealed by applying an adhesive, and the outer bag is sewn with a sewing machine, or both the inner bag and the outer bag are sewn with a sewing machine. Can be mentioned. The heat-sealing direction during the production of the packaging bag is preferably such that the direction in which the stretched film has a smaller heat shrinkage ratio is the heat-sealing direction. A heat bar, a heat belt, or the like is used for heat sealing, but if the heat sealing portion is pressed for a long time by these heaters, heat relaxation occurs and the strength of the heat sealing portion does not appear.
A heat-sealing method in which the heat-sealing portion is heated at a temperature of about 280 ° C. as quickly as possible without applying a pressing force, and then the heat-sealing portion is made to contract to cause the heat-sealing portion to contract. It is desirable to use.

[0027]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Example 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.} and 80 parts by weight of high pressure branched low density polyethylene (MI: 0.4 g / 10 min, flow ratio: 4
5, a density of 0.922 g / cm ³ ) and 20 parts by weight of dry blend were added (melting point of mixture: 118 ° C.) to polybutene-1 {melt index (MI): 1.0 g.
/ 10 minutes, density: 0.910 g / cm ³ , molecular weight of about 13
A raw material was obtained by further dry blending 20 parts by weight of 0,000} and using this as a circular slit diameter of 250φ and a slit width of 4 m / m in a Delsar 65φ type extruder manufactured by Modern Machinery.
Using an inflation film molding machine equipped with an inflation die and a cooling air ring,
An inflation film of 200μ was obtained under the conditions of 0 kg / hr, blow-up ratio 3, FLH / D = 8. A film obtained by slitting the raw film of the film in the film-drawing direction was manufactured using a roll drawing device under the conditions of a drawing temperature of 80 ° C. and a draw ratio (longitudinal direction 3 times) of 80 μ in thickness. .

<Evaluation Method> (a) The strength of the obtained film was tested according to JISP8116 for Elmendorf tear strength and ASTM D1709 for dirt drop impact (DDI). (B) A finger pull-out strength test was conducted to examine the tensile strength of the film.

The test method is as follows: The longitudinally stretched film obtained in (1) above is cut to 760 mm in the stretching direction and 1000 m / m in the transverse direction (the width direction of the film), and the rounded and overlapped portion is cut in the transverse direction. The hot melt adhesive (Grade HX-9 manufactured by Nitta Gelatin Co., Ltd.)
60) is applied and the overlapped portion is heat-bonded with a hot gun to form a tubular body, and either the upper or lower portion of the tubular body is heat-sealed using a HS22B-Z type heat sealer manufactured by Neurong Co., Ltd., and then obtained. The 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, and the 20 kg fertilizer bag was lifted by hand so that the heat-sealed portion was parallel to the floor surface. The state where the finger bites into the film surface was observed. Evaluation A: The finger did not bite at all, and there was no problem at all. B: The finger bites slightly, but there is no particular problem. C: The finger bites deeply and there is a problem. The results are shown in Table 1.

Example 2 Linear low density polyethylene 100 used in Example 1
In the parts by weight, the polybutene used in Example 1 was used.
20 parts by weight of 1 was blended and dry-blended (melting point: 118 ° C.) was used as a raw material, and molding and stretching were performed in the same manner as in Example 1 except that FLH / D (D is a die diameter) was 15. The results are shown in Table 1.

Comparative Examples 1 to 6 The same procedure as in Example 1 was repeated except that the amounts of polyethylene, polybutene-1 blended, molding conditions and stretching conditions were changed as shown in Table 1. The results are shown in Table 1.
Shown in. (Note that the melting point of each mixture is 118 ° C.)

[0032]

[Table 1]

Example 3 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.} and 80 parts by weight of high pressure branched low density polyethylene (MI: 0.4 g / 10 min, flow ratio: 4
5, a density of 0.922 g / cm ³ ) and 20 parts by weight of dry blend were added (melting point of mixture: 118 ° C.) to polybutene-1 {melt index (MI): 1.0 g.
/ 10 minutes, density: 0.910 g / cm ³ , molecular weight of about 13
A raw material was obtained by further dry blending 20 parts by weight of 0,000} and using this as a circular slit diameter of 250φ and a slit width of 4 m / m in a Delsar 65φ type extruder manufactured by Modern Machinery.
Using an inflation film molding machine equipped with an inflation die and a cooling air ring,
An inflation film of 130 μm was obtained under the conditions of 0 kg / hr, blow-up ratio of 3 and FLH / D = 8. A film obtained by slitting the raw material film in the film-drawing direction was used to produce a longitudinally uniaxially stretched film having a thickness of 50 μm 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. .

One stretched film thus obtained was left and right rounded so that the overlap portion was 100 mm, and a hot melt adhesive (made by Nitta Gelatin Co., grade HI-
960) and heat-bond the overlapped portion with a hot gun to form a tubular body (making an inner bag with an internal volume of 25 kg), and on the outside thereof, attach an outer bag consisting of Kurupack paper and a weighing amount of 83 g / m ² to a two-layer The lower part of the two-layer cylindrical body was sewn with the inner bag and the lower part of the outer bag together at a pitch of 7 m / m using DS-5 manufactured by Neurong. This two-layer bag was filled with 25 kg of polyethylene chips, and the upper part of the bag was sewn on in the same manner as above.

<Performance test of packaging bag> Drop test Five times each on the front and back of the two-layer bag, 10 times in total, and dropped horizontally onto the concrete surface from a height of 1.5 m. A 20-bag drop test was performed, and the average value was calculated for how many times the bag was torn. Logistics test 1) Prepare 500 bags filled with the above-mentioned chips of 25 kg, find them on a pallet, and then 400 by freight car.
After transporting kg, the number of bags torn after arrival was determined. 2) We asked how many bags the packaging bags stacked in 1) had collapsed after they arrived. The results are shown in Table 2.

Example 4 Linear low density polyethylene 100 used in Example 3
In parts by weight, the polybutene used in Example 3 was used.
20 parts by weight of 1 was blended and dry-blended (melting point: 118 ° C.) was used as a raw material, and FLH / D (D is a die diameter) was changed to 15, and molded and stretched in the same manner as in Example 1 to form a packaging bag. Created. The results are shown in Table 2.

Comparative Example 7 The same procedure as in Example 3 was carried out, except that polyethylene resin was not used and only paper (Kurupack, weighing 83 g / m ² ) was used, and a two-layer kraft packaging bag was used. The results are shown in Table 2. Comparative Example 8 The same procedure as in Example 3 was carried out, except that paper was not used, the molding conditions were changed as shown in Table 2, and a single-layer polyethylene film bag was used. The results are shown in Table 2.

Comparative Examples 9 to 11 The procedure of Example 1 was repeated, except that the amounts of polyethylene and polybutene-1 or the molding conditions were changed as shown in Table 2. The results are shown in Table 2.
(Note that the melting point of each mixture is 118 ° C.)

[0039]

[Table 2]

[0040]

According to the present invention, it is possible to produce a film which has not been considered in the past and has improved impact strength, rigidity, tensile strength and tear strength at a lower cost than biaxially stretched or transverse uniaxially stretched. 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.

The packaging bag of the present invention, which is a combination of a stretched film and a paper bag, is excellent in strength and sliding resistance and is suitably used as a so-called heavy bag for packaging and carrying heavy objects.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location // C08J 5/18 CES 9267-4F B29K 23:00 B29L 7:00 (72) Inventor Koji Akagi Kurashiki, Okayama Prefecture 3-chome, Shiodotsu, Ichi, Mizushima Plant, Mitsubishi Kasei Co., Ltd.

Claims (3)

[Claims] 1. 100 parts by weight per 100 to 50 parts by weight of a linear polyethylene resin and 0 to 50 parts by weight of a branched low-density polyethylene resin, and 100 parts by weight of the total of the linear polyethylene resin and the branched low-density polyethylene resin. Part of the resin composition obtained by blending the following polybutene resin is subjected to inflation molding under the conditions of a blow-up ratio of 2 to 8, and the obtained film is taken in the film take-up direction. The stretching temperature is the melting point of the resin composition- A stretched film uniaxially stretched under the conditions of 70 ° C. to melting point −20 ° C. and a stretching ratio of 1.5 to 8. 2. The density of the polybutene resin is 0.885-
Melt index (MI) at 0.920 g / cm ^3.
Is 20 g / 10 minutes or less, The stretched film of Claim 1. 3. A packaging bag comprising an inner bag made of the stretched film according to claim 1 and an outer bag made of a paper layer.