JPH0724926A - Manufacture of packing bag - Google Patents

Abstract

PURPOSE:To enable a packing bag which is large in heat sealing strength to be manufactured by a method wherein a resin composition in which linear low density polyethylene and polybutene resin are mixed is inflation molded under a specific condition and heat-sealed. CONSTITUTION:A resin composition composed by mixing 100 pts.wt. of linear low density polyethylene and at most 100 pts.wt. of polybutene resin, is inflation molded under conditions wherein a blow-up ratio is 0.9 to 2.0, a draft ratio is 10 to 40, and a cooling rate index is at most 30sec. The obtained cylindrical film is heat-sealed to be cut by taking a direction intersecting a receiving direction as a longitudinal direction. A melt index of the linear low density polyethylene is made 10g/1min or under and a melt index of polybutene resin is made 20g/10min or under.

Description

Detailed Description of the Invention

The present invention relates to a method for manufacturing a package. More specifically, it relates to a method for producing a packaging bag having a high heat-sealing strength by inflation-molding and heat-sealing a resin composition containing a linear low-density polyethylene and a polybutene resin under specific conditions. Usually, when inflation molding is performed using linear low-density polyethylene and a bag for packaging is manufactured by heat sealing, the strength of the body of the bag is strong, but the strength of the heat sealing part is extremely low, which is a problem in practical use. .

This is because, due to the molecular structure of linear low-density polyethylene, which will be described later, linear low-density polyethylene can be given a strong shrinkage even if it is intended to have a heat-shrinkability by imparting molecular orientation by melt drawing or the like. Since the heat-sealing portion cannot be heat-sealed when heat-sealed, the film thickness of the film is reduced, and the heat-sealing strength cannot be obtained.

The inventors of the present invention have conducted various studies to obtain a packaging bag having good heat-sealing strength by using linear low-density polyethylene, and as a result, a specific linear low-density polyethylene was
It was found that a packaging bag with greatly improved heat-sealing strength can be obtained by performing inflation molding and heat-sealing a product reacted with a radical generator under a specific condition, and previously filed (Japanese Patent Publication No. 4-19931). However, as a result of further studies, the heat-sealing strength was significantly increased by inflation molding and heat-sealing the resin composition obtained by blending the linear low-density polyethylene with a specific polybutene resin under specific conditions. The inventors have found that an improved packaging bag can be obtained, and completed the present invention.

That is, the gist of the present invention is to provide a resin composition obtained by mixing 100 parts by weight of a linear low-density polyethylene and 100 parts by weight or less of a polybutene resin with a blow-up ratio of 0.9 to 2.0 and a draft ratio. Inflation molding under the conditions of 10 to 40 and a cooling rate index of 30 seconds or less, and heat-sealing and cutting the obtained tubular film with the direction crossing the take-up direction as the longitudinal direction. It depends on the manufacturing method.

The present invention will be described in more detail below. The linear low density polyethylene used in the present invention is a copolymer of ethylene and another α-olefin, and is different from the low density polyethylene resin produced by the conventional high pressure method. Linear low density polyethylene includes, for example, ethylene and other α-olefins such as butene, hexene, octene,
It is a copolymer of decene, 4-methylpentene-1 and the like in an amount of about 4 to 17% by weight, preferably about 5 to 15% by weight. Manufactured using. This is a conventional high-density polyethylene having a short branched structure by a copolymerization component, and the density is appropriately reduced by utilizing this short-chain branching to 0.91 to 0.95 g / c.
m ^3, preferably is obtained by a 0.915~0.935g / cm ³ or so, traditional have linear properties than low density polyethylene, polyethylene high density polyethylene than branched many structures.

When heat-sealing such a linear low-density polyethylene, the shrinkage of the heat-sealing portion is small, because the molecular structure of the linear low-density polyethylene is short-chain branched as described above, and therefore, the heat-sealing is difficult. It is considered that thermal relaxation occurs between the molecules. As described above, since the linear low density polyethylene has a low strength in the heat seal portion, in the present invention, the linear low density polyethylene is blended with the specific polybutene resin, and the linear low density polyethylene is blow-molded under specific conditions to obtain the linear low density polyethylene. It is intended to improve the heat seal strength of low density polyethylene.

That is, the linear low density polyethylene used in the present invention has a melt index of 10 g / 10 min or less, preferably 0.2 to 1.5 g / 10 min. When the melt index is larger than 10 g / 10 minutes, the strength of the body is reduced when a resin composition containing a polybutene resin is used to form a packaging bag, and the shrinkage due to heat relaxation during heat sealing is favorable. No heat seal is obtained.

The flow ratio of the linear low-density polyethylene is preferably in the range of 15 to 70, particularly 15 to 35, from the viewpoint of the strength of the heat seal portion. In the method of the present invention, the melt index is in accordance with JIS K6760 19
It is a value measured at 0 ° C., and the flow ratio is a shearing force of 10 ⁶ dynes / cm ² using the melt index measuring device.
(Load 11131 g) and 10 ⁵ dynes / cm ² (load 1
113 g) and the extrusion rate (g / 10 minutes).

[0009]

[Equation 1]

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.
The larger the flow ratio value, the wider the molecular weight distribution. Next, as the polybutene resin, 1-butene, 2
-Butene, isobutene, 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 10% by weight or less or propylene contents of 40% by weight or less are preferred. The melt index is 20 g / 10 minutes or less, preferably 0.1 to 10 g / 10 minutes, and particularly preferably 0.2 to 2.0 g / 10 minutes.

If the melt index is larger than 20 g / 10 minutes, the heat-shrinkage does not cause sufficient shrinkage during heat-sealing, and a good heat-sealed portion cannot be obtained. Also,
Polybutene resin has a density of 0.885 to 0.920 g / c
m ³ is preferable, and those having a weight average molecular weight of 200,000 to 5,000,000, preferably 800,000 to 3,000,000 are suitable. The amount of the polybutene resin compounded is 100 parts by weight or less, preferably 5 to 70 parts by weight, and particularly preferably 10 to 5 parts by weight based on 100 parts by weight of the linear low-density polyethylene.
It is in the range of 0 parts by weight. If this mixing amount is more than 100 parts by weight, the molding stability during inflation molding will decrease.

In the present invention, the method of blending the polybutene resin with the linear low density polyethylene is not particularly limited, and for example, the following method can be used. (1) At the time of inflation molding, the linear low-density polyethylene and the polybutene resin are simultaneously supplied and melt-extruded. (2) Using a mixer such as an extruder or a Banbury mixer, the linear low density polyethylene and the polybutene resin are melt-mixed, and then pelletized, and inflation molding is performed using the pellets.

As described above, the polybutene resin has a very large molecular weight of 200,000 to 5,000,000, and when it is mixed with the linear low-density polyethylene, the polymer main component increases, and it is obtained by introducing a radical generator. A resin composition such as a modified linear low density polyethylene is obtained. The resin composition is more likely to be oriented in the longitudinal direction during inflation molding as compared with the case of the linear low-density polyethylene alone, and the film thus obtained shrinks in the direction subjected to the orientation during heat sealing, It is presumed that the thickness of the heat-sealed portion becomes larger than the original thickness and the strength of the heat-sealed portion is improved.

Further, when a general linear low density polyethylene having the same melt index as the resin composition is compared, the resin composition has a higher heat seal strength. This is presumed to be because the resin composition has more high molecular weight components effective for improving the physical properties of the seal. Further, even if the above resin composition is simply inflation-molded, a product having a good heat-sealed portion strength cannot be obtained, and molding requires specific molding conditions.

The specific molding conditions are inflation molding with a blow-up ratio of 0.9 to 2, a draft ratio of 10 to 40, and a cooling rate index of 30 seconds or less. Here, the draft rate is obtained by the following formula.

[0016]

[Equation 2]

In the formula, symbols are as follows. G: width of die slit t: thickness of the obtained film ρ _m : density of resin extruded from the die slit ρ: density of film BUR: blow-up ratio Further, the cooling rate index is the molten resin extruded from the die. It is the time (seconds) to reach the frost line and is obtained by the following formula.

[0018]

[Equation 3]

Τ: Cooling rate index (seconds) FLH: Frost line height (cm) V ₀ : Linear velocity (cm) when the molten resin passes through the lip portion
/ Sec) V ₁ : Take-up speed (cm / sec) When the blow-up ratio is 2.0 or more, shrinkage in the longitudinal direction of the heat seal occurs during heat sealing, and strain occurs in the direction opposite to the orientation of the bag body. The strength of the heat-sealed end of the obtained bag is reduced, which causes bag breakage.

If the draft ratio is 10 or less, good shrinkage does not occur during heat-sealing, and if it is 40 or more, the molecular orientation of the bag body itself becomes too large in one direction, which may cause tearing of the body itself. Become. When the cooling rate index is 30 seconds or more, the molecular orientation generated in the film from the draft during film forming is relaxed by thermal relaxation, and the shrinkage does not occur during heat sealing. Flesh.

A heat bar, a heat belt or the like is used for heat sealing. However, since the heating machine causes thermal relaxation by pressing the heat sealing portion for a long time, the strength of the heat sealing portion cannot be obtained. , 230 to 280 ° C, the heat seal part is heated rapidly without applying pressure to the heat seal part as much as possible, and then the heat seal part is set in a free state to cause shrinkage in the heat seal part. It is preferable to use the method.

[0022]

EXAMPLES 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 (M
I): 0.5 g / 10 minutes, flow ratio 20, density: 0.92
1 g / cm ³ , copolymerization component: butene-1, copolymerization amount: 1
0 parts by weight} 100 parts by weight and polybutene-1 {melt index (MI): 1.0 g / 10 minutes, density: 0.91
20 parts by weight of 0 g / cm ³ and a molecular weight of about 1.3 million} were mixed and then melt-kneaded at 170 ° C. in an extruder and extruded into pellets. This is a modern machinery Delsa 65φ
Using an inflation molding machine in which an inflation die having an annular slit diameter of 250 mmφ and an air ring for cooling were attached to the die extruder, the extrusion rate was 100 kg / hr, the blow-up ratio (BUR) was 1.1, and the draft rate was 14. The amount of air blown out from the air ring was changed under the conditions to obtain an inflation film having a cooling rate index of 28 and 150μ.

The resulting blown film was cut into a tubular film having a length of 670 cm and a width of 440 cm, and a HS22B-2 type heat sealer manufactured by New Long Co. (heating section length 150 mm, heating section clearance 0.3 mm,
Cooling unit length: 150 mm, cooling unit clearance 1 mm)
Heat seal temperature (heating part surface temperature) 250
C., cooling part temperature 30.degree. C., film feed speed 15 m / sec.
The heat-sealed portion, which was heat-sealed at the position of cm, contracted in the film take-up direction (longitudinal direction) and was thicker than the original film thickness.

20 kg of the obtained bag was filled with fertilizer, and the opening was heat-sealed under the same conditions as above to obtain a packaging bag for the drop-bag test. In the drop bag test, the bag filled with 20 kg of the fertilizer is heat-sealed, accumulated for 18 to 24 hours and left to stand, and then the body of the packaging bag is parallel to the floor surface and the heat-sealed portion is substantially perpendicular to the floor surface. In this way, 20 bags were dropped (lateral drop) to carry out the test, and the bag breakage rate was obtained.

The dropping condition is that the room temperature is −5 ° C. and the dropping height is 1.
5 m, the number of drops per bag was 5 times. The bag breakage rate was obtained as a percentage of the broken bags of the packaging bags used in the test. As for the uneven thickness state, the obtained tubular film was measured at 36 points at equal intervals in the circumferential direction, and the thickness thereof was measured with a dial gauge.
○, ± 10 when within ± 10% of the average value of the measured values
%, Within ± 15% of the average value △, ±
The case where it was larger than 15% was marked with x. The results are shown in Table 1.

Example 2 15 was carried out in the same manner as in Example 1 except that the blow-up ratio was 1.4 and the cooling rate index was 16.
A blown film of 0μ was obtained. Then, in the same manner as in Example 1, the bag breakage rate and the uneven thickness state were measured. The results are shown in Table 1.

Comparative Examples 1 to 2 Using the linear low-density polyethylene used in Example 1, the blow-up ratio, draft ratio and cooling rate index were changed as shown in Table 1 to obtain a 150 μm film. Then, in the same manner as in Example 1, the bag breakage rate and the uneven thickness state were measured. The results are shown in Table 1.

[0028]

[Table 1]

[0029]

According to the method of the present invention, a packaging bag having significantly improved heat seal strength can be obtained.

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Claims (4)

[Claims] 1. A resin composition prepared by mixing 100 parts by weight of linear low-density polyethylene and 100 parts by weight or less of a polybutene resin with a blow-up ratio of 0.9 to 2.0, a draft rate of 10 to 40, and a cooling rate. A method for producing a packaging bag, which comprises performing inflation molding under conditions of an index of 30 seconds or less, and heat-sealing and cutting the obtained tubular film with a direction intersecting the take-up direction as a longitudinal direction. 2. The linear low density polyethylene has a melt index of 10 g / 10 minutes or less, and the polybutene resin has a melt index of 20 g / 10 minutes or less.
The manufacturing method according to claim 1. 3. A polybutene resin having a density of 0.885-0.
The production method according to claim 1 or 2, wherein the production method is 920 g / cm ³ . 4. The heat seal comprises a heat seal part 23
4. The manufacturing method according to claim 1, wherein the film is heated at a temperature of 0 to 280 [deg.] C. until the films are fused, and then the heat-sealed portion is brought into a free state to cause shrinkage in the heat-sealed portion. .