JPH0152175B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a packaging bag. Specifically, the present invention relates to a method of manufacturing a packaging bag with high heat-sealing strength using linear low-density polyethylene. Normally, when packaging bags are manufactured using linear low-density polyethylene by inflation molding and heat sealing, the body of the bag is strong, but the strength of the heat sealing part is extremely low, which poses a practical problem. It was hot. This is because, due to the molecular structure of linear low-density polyethylene, which will be described later, linear low-density polyethylene cannot be made to have strong shrinkability even if you try to give it heat-shrinkability by imparting molecular orientation by melt-stretching or the like. When heat-sealing is performed, the heat-sealed portion does not undergo thermal contraction, the film thickness decreases, and heat-sealing strength is not achieved. As a result of various studies in order to obtain a packaging bag with good heat-sealing strength using linear low-density polyethylene, the present inventors blended a specific amount of a specific resin into a specific linear low-density polyethylene, By performing inflation molding under these conditions, the objective was achieved and the present invention was completed. In other words, the gist of the present invention is the melt index
Melt index 0.1 to 2 g/10 to linear low density polyethylene with flow ratio 18 to 35, 0.2 to 2 g/10 min.
minutes, low density polyethylene with a flow ratio of 30 to 70.
The blow-up ratio of the mixture containing % by weight is 0.9~
1.5. Manufacture of a packaging bag characterized by inflation molding under the condition of a draft rate of 10 to 40, heat sealing and cutting the obtained cylindrical film with the longitudinal direction in the direction intersecting the taking direction. It lies in the method. The present invention will be explained in more detail below. The linear low-density polyethylene used in the present invention is a copolymer of ethylene and other α-olefins, and is different from low-density polyethylene resins produced by conventional high-pressure methods. Linear low-density polyethylene contains, for example, ethylene and other α-olefins such as butene, hextine, octene, decene,
It is a copolymer of about 4 to 17% by weight, preferably about 5 to 15% by weight of methylpentene-1, etc., and is produced using a Ziegler type catalyst or Phillips type catalyst used in the production of high density polyethylene by medium and low pressure process. The conventional high-density polyethylene is made into a short branched structure using a copolymer component, and the density is appropriately lowered to 0.91 using this short chain branching.
~0.95 g/cm ³ , and is a polyethylene with a structure that is more linear than conventional low-density polyethylene and more branched than high-density polyethylene. When such linear low-density polyethylene is heat-sealed, the shrinkage of the heat-sealed portion is small because the molecular structure of linear low-density polyethylene is short-chain branched as mentioned above, so heat is generated between the molecules during heat-sealing. This is thought to be due to relaxation. Melt index 0.2-2g/10min, flow ratio
18 to 35 are used. If the melt index and flow ratio are out of this range, the strength of the body when used as a packaging bag decreases, which is not preferable. It includes a low-density ethylene homopolymer blended with linear low-density polyethylene and a copolymer of ethylene and other copolymer components. Examples of copolymerization components include vinyl compounds such as vinyl acetate, ethyl acrylate, and methyl acrylate, and olefins having 3 or more carbon atoms such as hexene, propylene, octene, and 4-methylpentene-1. As for the copolymerization amount of copolymerization components,
The amount is about 0.5 to 18% by weight, preferably about 2 to 10% by weight. These low-density polyethylenes are preferably obtained by radical polymerization using a radical generator such as oxygen or an organic peroxide using a normal high-pressure method (1000 to 3000 Kg/cm ² ), but if the fluidity ratio is 35 ~
70 (excluding 35) linear low-density polyethylene may be substituted. Among these low-density polyethylenes, vinyl acetate content is 0.5 to 18% by weight.
Particularly preferred is 2 to 10% by weight of ethylene-vinyl acetate copolymer. What is melt index in the method of the present invention?
Values measured at 190℃ in accordance with JIS K6760,
The fluidity ratio is calculated using the above melt index measuring device with a shear force of 10 ⁶ dynes/cm ² (load 11131 g).
Extrusion rate (g/10 min) with 10 ⁵ dynes/cm ² (1113g)
Flow ratio = Extrusion amount at load 11131g (10 minutes) / Load 1113
Calculated by the extrusion amount in g (10 minutes). 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. A major feature of the present invention is that low-density polyethylene with a wide molecular weight distribution is blended with linear low-density polyethylene with a narrow molecular weight distribution. As mentioned above, when trying to manufacture a bag with sufficient strength for the body, it is necessary to use linear low-density polyethylene with a flow ratio of 18 to 35. As mentioned above, the strength of the parts is significantly reduced. In the present invention, low density polyethylene having a wide molecular weight distribution is blended in order to improve the heat sealing strength of the linear low density polyethylene. Low-density polyethylene, which has a wide molecular weight distribution, has long chain branches and high melt elasticity, so molecular orientation tends to occur during inflation molding.Films made from such resins undergo molecular orientation during heat sealing. This causes the film to shrink in the direction of the film, making it thicker than its original thickness and improving the strength of the heat-sealed portion. By blending low-density polyethylene with the above-mentioned linear low-density polyethylene, the shrinkage effect of the above-mentioned low-density polyethylene can be imparted to the linear low-density polyethylene, or the shrinkage effect of low-density polyethylene can be imparted to the linear low-density polyethylene. Whether or not the polyethylene is canceled out will need to be investigated after molding, but by inflation molding the mixture of the present invention under specific conditions, it has good heat-sealability, that is, the heat-sealed part shrinks. It was found that the phenomenon of increasing thickness occurs due to the increase in thickness. The molding conditions include a blow-up ratio of 0.9 to 1.5.
Inflation molding is performed with a draft rate of 10 to 40. Here, the draft rate is obtained by the following formula. Draft rate = ∫m/∫f・G/t・1/BUR In the formula, the symbols are as follows. G: Width of the die slit t: Thickness of the obtained film ∫m: Density of the resin extruded from the die slit ∫f: Density of the film BUR: Blow-up ratio When the blow-up ratio is set to 1.5 or more, the longitudinal Shrinkage occurs and distortion occurs in the direction opposite to the orientation of the bag body, which reduces the strength of the heat-sealed end of the resulting bag, causing the bag to break. If the draft rate is less than 10, good shrinkage will not occur during heat sealing, and if it is more than 40, the molecular orientation of the body of the bag will become too large in one direction, causing tearing of the body. 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 Linear low density polyethylene {melt index (Ml): 1 g/10 min, flow ratio: 20, density: 0.920
g/cm ³ , copolymerization component: butene-1, copolymerization amount: 10
Weight%} to high pressure low density polyethylene {Ml: 0.4
g/10 minutes, flow ratio: 45:, density: 0.924 g/cm ³ ,
Contains 30% by weight of Novatek-L F100 (manufactured by Mitsubishi Chemical Industries, Ltd.) (Novatek is a registered trademark of Mitsubishi Chemical Industries, Ltd.), and manufactured by Modern Machinery Co., Ltd., Delsa 65φ
The extruder was equipped with an inflation molding machine with an annular slit diameter of 200φ, an inflation die with a lip clearance of 3 mm, and a cooling air ring, with an extrusion rate of 50 kg/hr and a blow-up ratio (BUR).
An blown film with a film thickness of 150μ was obtained under the conditions of 1.4 and draft ratio of 24. The length of the resulting blown film is 670 mm.
cm, width 440 cm, and heat-sealed using a Newlong HS22B-2 type heat sealer (heating section length: 150 mm, heating section clearance: 0.3 mm, cooling section length: 150 mm, cooling section clearance: 1 mm). (Surface temperature of heating part) 250℃, temperature of cooling part 30℃, film feed speed 15m/sec.
The heat-sealed part that was heat-sealed at the cm position shrinks in the film take-up direction (vertical direction),
It 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 described above to obtain a packaging bag for the drop bag test. In the drop bag test, a bag filled with 20 kg of fertilizer was left for 18 to 24 hours after being heat-sealed, and then the body of the packaging bag was parallel to the floor and the heat-sealed part was approximately perpendicular to the floor. A test was conducted by dropping 20 bags in such a manner (sideways drop), and the bag breakage rate was determined. Drop conditions were room temperature -5℃, fall height 1.5m,
Each bag was dropped 5 times. The bag breakage rate was calculated as the percentage of bags that were broken among the packaging bags used in the test. In addition, the thermal shrinkage rate of the inflation film was measured in order to understand the condition of the heat-sealed portion. To measure the heat shrinkage rate, cut out a circular test piece with a diameter of 6 mm from any position on the film, and then
The film was placed on a hot plate at 200° C. for 5 seconds, and changes in length in the longitudinal direction (direction in which the film was taken) and in the transverse direction (direction of film width) were expressed as a percentage of the original length. It is recognized that if the shrinkage rate in the longitudinal direction is large, the shrinkage rate in the film take-off direction during heat sealing will be large, and the strength of the heat-sealed portion will be improved. The results are shown in Table 1. Comparative example 1 Linear low density polyethylene (Ml: 2g/10min,
Fluidity ratio: 20, density: 0.918 g/cm ³ , copolymerization component: butene-1, copolymerization amount: 10% by weight), that is, without mixing low-density polyethylene, but otherwise in the same manner as in Example 1. A packaging bag was obtained by inflation molding and heat sealing. The obtained packaging bags were subjected to a drop bag test and the heat shrinkage rate was measured. The results are shown in Table 1.

[Table] *: The minus sign indicates that the material has expanded beyond its original length without shrinking.
Example 2 High-pressure low-density polyethylene used in Example 1 was replaced with high-pressure low-density polyethylene {Mitsubishi Chemical Industries, Ltd.
Manufactured by Novatec Co., Ltd. LT0110, Ml: 0.74g/10
A packaging bag was obtained in the same manner as in Example 1, except that 10% by weight of 10% by weight of 10% by weight of 10% by weight, flow ratio: 55, density 0.929} was added. The obtained packaging bag was subjected to a drop bag test and a heat shrinkage rate measurement in the same manner as shown in Example 1. The results are shown in Table 2. Examples 3 and 4 Ethylene-vinyl acetate copolymer was used in place of the high-pressure low-density polyethylene used in Example 1 {Mitsubishi Yuka Co., Ltd.
Manufactured by Yucalon HE60, vinyl acetate content 6% by weight, Ml: 0.4g/10min, fluidity ratio 40, density:
0.927g/cm ³ } (Example row 3), ethylene-vinyl acetate copolymer {Mitsubishi Yuka Co., Ltd.
Co., Ltd., product ^name : Yucalon A packaging bag was obtained in the same manner as in Example 1 except that Example 4) was used. The obtained packaging bag was subjected to a drop bag test and a heat shrinkage rate measurement in the same manner as shown in Example 1. The results are shown in Table 2.

[Table] Examples 5 and 6 Ethylene-vinyl acetate copolymer used in place of high-pressure low-density polyethylene used in Example 1 {manufactured by Mitsui Polychemical Co., Ltd., trade name: Mirason Ace30N, vinyl acetate content 6% by weight, Ml=0.5g/10min, fluidity ratio
40, density: 0.928 g/cm ³ } (Example 5), ethylene-vinyl acetate copolymer {manufactured by Mitsui Polychemical Co., Ltd., product name: Mirason H625
-4, vinyl acetate content 5.9% by weight, Ml=0.24
g/10 min, flow ratio 45, density: 0.933 g/cm ³ } to 60
A packaging bag was obtained in the same manner as in Example 1, except that the weight percent blend (Example 6) was used and the extrusion rate was 35 Kg/hr. The room temperature of the drop condition for the obtained packaging bag is -10℃.
A drop bag test and a heat shrinkage rate measurement were carried out in the same manner as in Example 1, except that The results are shown in Table 3.

【table】

Claims (1)

[Scope of Claims] 1. Linear low density polyethylene with a melt index of 0.2 to 2 g/10 minutes and a flow ratio of 18 to 35 and 5 pieces of low density polyethylene with a melt index of 0.1 to 2 g/10 minutes and a flow ratio of 30 to 70. A mixture containing ~70% by weight was inflation-molded under conditions of a blow-up ratio of 0.9-1.5 and a draft rate of 10-40, and the resulting cylindrical film was heat-sealed with the longitudinal direction intersecting the drawing direction. and a method for producing a packaging bag, which comprises cutting the bag. 2 Linear low density polyethylene has a density of 0.915 to 0.935
2. A method according to claim 1, characterized in that it is of g/cm ³ . 3 Low density polyethylene has a density of 0.915 to 0.940g/
3. The method according to claim 1 or 2, characterized in that it is of cm ³ . 4 Low density polyethylene has a vinyl acetate content of 0.5
4. A method according to any one of claims 1 to 3, characterized in that the amount of ethylene-vinyl acetate copolymer is ~18% by weight. 5 Heat-seal the heat-sealed part at 230-280℃
Any one of claims 1 to 4, characterized in that the heat-sealed portion is heated until the films are fused to each other at a temperature of Method described in Crab.