JPH0624789B2 - Double packaging bag manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a double packaging bag. More specifically, the present invention relates to a method for producing a double packaging bag suitable for packaging relatively heavy items such as rice grains and fertilizers.

[Prior art]

Recently developed linear low density polyethylene (hereinafter LLD
Is superior in mechanical strength such as tensile strength, impact strength and rigidity to the conventional (manufactured) branched (high pressure method) low density polyethylene (hereinafter referred to as HPLD), and is easily heat-sealed. From what can be done, packaging materials, for example,
It has come to be used in fertilizers such as ammonium sulfate and urea, industrial chemicals such as caprolactam and a surfactant, and heavy packaging bags such as rice grains.

The packaging bag made using the above LLD is a conventional HPLD
Although it is thinner than the bag and has high strength,
Due to the thin film thickness of the bag, the breaking strength at the body of the bag is reduced, and the bag may be torn by protrusions or the like during transportation, or when the contents are put in the bag and carried by hand, the fingertips holding the bag are bags. There was a problem in practical use that a phenomenon of sticking to the skin, a so-called "finger omission", occurred.

[Means for solving problems]

In view of such a situation, the present inventor, in the body portion of the packaging bag using the linear low-density polyethylene, in order to improve the breaking tensile strength, as a result of diligent study, using a specific linear low-density polyethylene, specific The above-mentioned object is achieved by molding an unstretched film under the conditions of, and then subjecting this to a stretching treatment under specific conditions to make the resulting stretched film double and produce a packaging bag. That is, the present invention has been completed.

That is, the gist of the present invention is that the melt index is 2 g /
75 to 100 parts by weight of linear low-density polyethylene having a flow ratio of 35 or less and 10 minutes or less, and 0 to 25 parts by weight of branched low-density polyethylene having a melt index of 2 g / 10 minutes or less and a flow ratio of 50 or less. The polyethylene composition consisting of and is subjected to inflation molding or T-die molding under the condition of a draft rate of 2 to 50, and the obtained film or sheet is stretched in at least one direction to have an area ratio of 1.2 to 9 times, and then stretched. A method for producing a double bag is characterized in that the stretched film is doubled to produce a bag.

To explain the present invention in detail, the linear low-density polyethylene used in the present invention is a copolymer of ethylene and other α-olefin, and is a low-density polyethylene resin produced by a conventional high-pressure method. Is different. The linear low-density polyethylene includes, for example, ethylene and other α-olefins such as butene, hexene, octene, decene, and 4-methylpentene-1 at about 4 to 17% by weight, preferably 5 to 15%.
It is a copolymer of about% by weight and is produced by using a Ziegler type catalyst or a Phillips type catalyst used in the production of medium- and low-pressure method high-density polyethylene.The conventional high-density polyethylene is made into a short branched structure by a copolymerization component. , The density is also appropriately reduced by utilizing this short chain branching
It is about 0.91 to 0.95 g / cm ^3, which is a polyethylene having a structure more linear than conventional low density polyethylene and more branched than high density polyethylene.

The linear low density polyethylene used has a melt index of 2 g / 10 minutes or less, preferably 0.2 to 1.5 g / 10 minutes, and a flow ratio of 35 or less, preferably 15 to 30. When the melt index is more than the above range, the heat-sealing strength and the body strength of the packaging bag are reduced, which is not preferable. Further, if the flow ratio is more than the above range, the strength of the body portion of the packaging bag is reduced, which is not preferable. Further, the linear low-density polyethylene described above preferably has a density in the range of 0.915 to 0.935 Kg / cm ³ from the viewpoint of rigidity and impact resistance when used as a packaging bag.

In the method of the present invention, the melt index is JIS K 6760.
Is a value measured at 190 ° C. in accordance with the above, and the flow ratio is a shear force of 10 ⁶ dyne / cm ² (load 11131 g) and 10 ³ dyne / cm ² (load 11
13 g) 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.

In the present invention, although only the linear low-density polyethylene described above may be used, the linear low-density polyethylene is the main component, and by blending a specific amount of the branched low-density polyethylene, film formability and stretching It is desirable because it improves the property.

The branched low-density polyethylene to be blended with the linear 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, 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 10%.
It is about% 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 having a melt index of 2 g / 10 min or less, preferably 0.1 to 1 g / 10 min, and a flow ratio of 50 or less, preferably 30 to 50 is used. When the melt index is more than the above range, the strength of the body of the bag is reduced when it is formed into a packaging bag, which is not preferable. Further, if the flow ratio is more than the above range, the strength of the body of the bag is reduced when the bag is formed into a packaging bag, which is not preferable.
Furthermore, the above branched low-density polyethylene has a density of 0.930.
In the following, the range of 0.915 to 0.925 is particularly preferable from the viewpoint of improving the strength of the body of the bag and the heat sealing strength of the bag.

The blending amount of the linear low-density polyethylene and the branched low-density polyethylene is 100 to 75 for the linear low-density polyethylene.
0 to 25 parts by weight of branched low-density polyethylene, preferably 5 to 15 parts by weight with respect to parts by weight, preferably 95 to 85 parts by weight.
Used within the range of parts by weight.

The linear low-density polyethylene or the blend of the linear low-density polyethylene and the branched low-density polyethylene may be used in ordinary polyethylene such as an antioxidant, an ultraviolet absorber, an antistatic agent, and a lubricant, if necessary. Known additives may be added.

In the present invention, the linear low-density polyethylene or a blend of linear low-density polyethylene and branched low-density polyethylene is used to form an unstretched film or sheet, and then the unstretched film or sheet is molded. A stretched film is manufactured by stretching the film at an area ratio of 1.2 to 9 in at least one direction.

The unstretched film or sheet is molded by using an ordinary film or sheet molding apparatus and molding method, for example, an isoflasion molding method using a circular die, a T die molding method using a T die, and the like.
Molding is carried out under molding conditions of ˜250 ° C. and draft ratio of 2-50.

When molding by inflation, set the blow up ratio to
It is desirable to carry out under conditions of 0.9 to 2 and draft ratio of 2 to 50.

In the present invention, the draft rate is obtained according to the table below.

In the formula, the symbols are as follows.

In the case of T-die molding, it is represented as BUR = 1.

If the draft rate is less than 2, the film formability becomes poor,
On the other hand, if it is greater than 50, longitudinal tearing tends to occur during stretching, which is not preferable.

The unstretched film obtained as described above is then stretched. Stretching in the present invention is to reduce the film thickness before and after stretching and its surface area is 1.2 ~
It means extending in at least one direction so that it becomes 9 times. The stretching is uniaxially stretched in the machine direction of the film (the film take-up direction of the film forming machine) or in the transverse direction (direction orthogonal to the film take-up direction), or biaxially stretched in the machine direction and the transverse direction. It is done by

In the case of uniaxial stretching, the unstretched film obtained by the T-die method or the inflation method is heated as it is or after being slit into a predetermined width, for example, by changing the peripheral speed of the stretching roll. It is carried out by a method of stretching in the take-up direction, that is, a longitudinal direction, or a method of heating an unstretched film with its end portions fixed and stretching it in the transverse direction by widening this interval.

In the case of biaxial stretching, an unstretched film obtained by the T-die method or the inflation method as it is or slit into a predetermined width is successively biaxially stretched or simultaneously stretched.
It is carried out by axial stretching. Sequential biaxial stretching is performed either in the longitudinal direction and then in the transverse direction, or vice versa. In the simultaneous biaxial stretching, the time distribution of the stretching in the machine direction and the stretching in the transverse direction is arbitrary. For example, the stretching is gradually continued in the machine direction until the stretching in the machine direction is completed, or the stretching is started in the machine direction. You can make the horizontal direction at the same time,
It is done by a method such as completing the vertical direction first.

When biaxial stretching is carried out, a tenter method sequential biaxial stretching method and a Cheebler method simultaneous biaxial stretching method are suitably adopted. The stretching temperature is the melting point of the linear low-density polyethylene or a blend of the linear low-density polyethylene and the branched low-density polyethylene-20 ° C.
To melting point -5 ° C, especially melting point -20 ° C to melting point -15 ° C
It is desirable that the range is. At a temperature below the melting point of −20 ° C., the mobility of the molecular chain is poor, so that it is easy to cut during stretching, and even if it can be stretched, the stretching ratio does not increase, and it is difficult to obtain a stretched film with excellent physical properties. At a high temperature, the resin partly melts and cannot be stretched and oriented, which makes it difficult to obtain a stretched film having excellent physical properties, which is not desirable.

The stretching speed is in the range of 2 to 40% / sec, preferably 10 to 2
It is in the range of 0% / sec. If the stretching speed is slower than 2% / sec, the stretchability is likely to be hindered by oriented crystallization during stretching,
On the other hand, if it is higher than 40% / sec, the deformation of the polymer cannot keep up with the stretching speed and the stretch breakage occurs.

The stretching ratio is 1.2 to 9 times, preferably 1.2 to 5 times, more preferably 1.5 to 5 times in terms of area ratio in at least one direction from the viewpoints of stretching operability (stretchability) and physical properties of the obtained stretched film. It is a range. When biaxially stretching,
The length of the film is 1.2 to 3 times, preferably 1.2 to 2 times, and the width is 3 to 9 times, preferably 4 to
The range is 7 times. If the draw ratio is less than 1.2 times, the effect of improving the strength property and breaking strength of the film is small, which is not preferable. On the other hand, if it is more than 9 times, the stretching operability is deteriorated and a satisfactory stretched film cannot be obtained.

In the present invention, a double bag is produced from the stretched film obtained above. As a method of manufacturing the double bag, a well-known method which has been conventionally known can be adopted.

For example, (1) two stretched film sheets are superposed on each other, then the left and right end portions of the sheets are superposed, and the side faces of both end portions are heat-sealed (heat-sealed) or adhesive seal by applying an adhesive (hereinafter referred to as an adhesive seal) ), A tubular double film is formed, and then a double bag is produced by heat-sealing or adhesively sealing the upper portion or the lower portion of the tubular double film, respectively, (2) the upper and lower portions of the tubular stretched film. A method in which both ends are overlapped and both ends are heat-sealed or adhesive-sealed, then either the left or right side is heat-sealed or adhesive-sealed to form a double bag. (3) Others in a single tubular stretched film And a method of producing a double bag in which the upper portion or the lower portion of the double tubular film is heat-sealed or adhesive-sealed.

The heat-sealing direction during the production of the double bag is preferably such that the direction in which the heat shrinkage rate of the stretched film is small 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, so 230 to 280 ° C. It is recommended to use a heat-sealing method in which the heat-sealing portion is heated rapidly at a temperature as low as possible without applying a pressing force, and then the heat-sealing portion is allowed to contract by causing the heat-sealing portion to be in a free state. desirable.

〔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) Production of stretched film 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%} 90 parts by weight of high-pressure branched low-density polyethylene (melt index: 0.4 g / 10 minutes, flow ratio: 20, density: 0.922 g
/ Cm ³ ) 10 parts by weight dry blended (melting point 1
(18 ° C.) as a raw material, and extruded from a modern machinery, Delsa 65φ type extruder using an inflation molding machine equipped with an inflation die having an annular slit diameter of 250 mmφ and a slit width of 4 mm and a cooling air ring. Quantity 50Kg / hr, blow up ratio (BUR) 2, draft rate
The amount of air blown from the air ring was changed under the conditions of 6.7 to obtain an inflation film having a cooling rate index of 28 and 300μ. A film obtained by slitting this film original in the film take-up direction was drawn at a drawing temperature of 105 ° C., a drawing speed of 10% / sec, and a draw ratio (longitudinal direction 1.2 times and transverse direction 5 times) using a tenter sequential biaxial drawing device. 50 under conditions
A biaxially oriented film having a thickness of μ was manufactured. In producing a double bag from the obtained biaxially stretched film, the heat shrinkage rate of the film was measured by the following method in order to determine the heat sealing direction of the bag.

(2) Measurement of heat shrinkage The heat shrinkage was measured by cutting a circular test piece with a diameter of 6 mm from an arbitrary position on the film, placing it on a hot plate with a surface temperature of 200 ° C for 20 seconds, and setting it in the longitudinal direction (film take-up direction). ), And the change in length in the lateral direction (film width direction) are expressed as a percentage of the original length. The results are shown in Table 1.

From the results of the heat shrinkage obtained, the direction with the smaller heat shrinkage was taken as the heat-sealing direction (upper and lower openings when made into a bag), and the direction with the larger heat shrinkage was given with the adhesive backing direction (made into the bag). The double bag was manufactured so that it would be the case body direction).

(3) Manufacture of double bag The biaxially stretched film obtained in (1) above is used in a direction with a small heat shrinkage ratio, that is, in the longitudinal direction (film take-up direction).
0 mm, cut in a direction with a large heat shrinkage, that is, 670 mm in the lateral direction (width direction of the film), stack two films and round the upper and lower parts so that the overlapping part is 100 mm, and the hot melt to the overlapping part. An adhesive (Grade HX-960 manufactured by Nitta Gelatin Co., Ltd.) is applied, and the overlapped portion is heated and bonded with a hot gun to form a tubular body, and either of the left and right side surfaces of the tubular body is manufactured by Nyurong HS22B- Type 2 heat sealer (Heating section length 150mm, Heating section clearance 0.3m
m, cooling section length: 150 mm, cooling section clearance 1 mm)
Heat seal temperature (heating part surface temperature) 250
℃, the temperature of the cooling part 30 ℃, the film feed rate of 15m / s, 1.5cm from one end of the opening of the tubular film
The heat-sealed portion, which was heat-sealed at the position, contracted in the film take-up direction (longitudinal direction) and was thicker than the original film thickness.

The obtained bag was filled with 20 kg of fertilizer, and the opening was heat-sealed under the same conditions as above to obtain a packaging bag for drop bag test.

(4) Performance test of packaging bag (A) Drop test The packaging bag obtained in (3) above was subjected to a lateral drop bag test and a vertical drop bag test by the following methods.

The dropping conditions were room temperature, −10 ° C. for the horizontal falling bag test, −5 ° C. for the vertical falling bag test, a drop height of 1.5 m, and 5 drops per bag. The bag breakage rate was obtained as a percentage of the broken bags of the packaging bags used in the test. The results are shown in Table 1.

(B) Side-dropping bag test A test is conducted by dropping 20 bags (side-down) so that the body of the packaging bag is parallel to the floor surface and the heat-sealed portion is substantially vertical to the floor surface, and the bag-breaking rate is determined. I asked. The falling bag test was conducted to measure the strength of the heat-sealed portion of the bag.

(B) Vertical drop bag test Dropping 20 bags (vertical drop) so that the heat-sealed part of the packaging bag is parallel to the floor surface and the body part is substantially perpendicular to the floor surface, and the test is performed to determine the bag breakage rate. I asked. The vertical drop bag test was performed to measure the strength of the body of the bag.

(B) Finger pull-out strength test The heat-sealed part of the packaging bag filled with 20 kg of the fertilizer was lifted by hand so that the heat-sealed part 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, problem (C) Film puncture 82.6 mm φ cylindrical shape Fix the film used in the above packaging bag to the test tool, and project a plunger with a hemispherical tip and a diameter of 19.05 mmφ (3/4 inch) at the center of the film at a speed of 500 mm / mm. The tensile strength at break (Kg) applied to the plunger and its elongation (mm) were expressed.

(D) Logistics test Prepare 500 bags of the above 20Kg fertilizer, load them on a pallet, then transport them by 400km by freight car, and then investigate the occurrence of pinholes in the bags after arrival, and break the bags. I asked for the number. In this distribution test, the pinhole generated by rubbing the surface of the bag during transportation was confirmed by placing it in water.

Example 2 In Example 1, a blow-up ratio was set to 4 and a draft ratio was changed to 3 to mold an inflation film of 100 μ, and after slitting this film, the film was slit and then 2.0 in the longitudinal direction.
The same procedure as in Example 1 was carried out except that a uniaxially stretched film was produced by double stretching. The results are shown in Table 1.

Comparative Example 1 In Example 1, a 50 μm inflation film was formed by changing the die slit width of the inflation molding machine to 1.5 mm and cut into a tubular film having a length of 670 mm and a width of 440 mm. Prepare a sheet of tubular film, 1
The same procedure as in Example 1 was carried out except that another tubular film was placed in one tubular film, and one of the openings of the tubular film was heat-sealed to form a double packaging bag. The results are shown in Table 1.

Comparative Example 2 In Example 1, the inflation slitting machine of the inflation molding machine was changed to 3 mm to mold an inflation film of 100 μ, and the obtained film had a length of 670 mm.
The procedure of Example 1 was repeated, except that a tubular film having a width of 440 mm was cut and heat-sealed as it was to form a single packaging bag. The results are shown in Table 1.

Comparative Examples 3 to 7 Same as Example 1 except that the compounding amounts of the linear low-density polyethylene and the branched low-density polyethylene, the respective physical properties, or the molding conditions were changed as shown in Table 1. I went to The results are shown in Table 1.

[Effect of the invention] The double packaging bag of the present invention has a high breaking strength in the body,
Therefore, when the contents are accommodated in the bag and the bag is manually carried, a finger does not hit the bag, so-called "finger dropout" or the like does not occur. Therefore, the work efficiency is good and it is very effective in practice.

Claims (1)

[Claims] 1. A linear low density polyethylene 7 having a melt index of 2 g / 10 minutes or less and a flow ratio of 35 or less.
5 to 100 parts by weight and melt index of 2 g / 10
Obtained by subjecting a polyethylene composition consisting of 0 to 25 parts by weight of branched low-density polyethylene having a flow ratio of 50 or less to inflation molding or T-die molding under a draft ratio of 2 to 50. A method for producing a double bag, comprising: stretching a film or a sheet in at least one direction at an area ratio of 1.2 to 9 times, and then making the stretched film double to produce a bag.