JP2625813B2 - Manufacturing method of packaging bag - Google Patents

Description

The present invention relates to a method for manufacturing a packaging bag. More specifically, the present invention relates to a method for producing a packaging bag having high heat sealing strength using linear low-density polyethylene.

[Conventional technology and its problems]

Normally, when inflation molding is performed using linear low-density polyethylene and a packaging bag is manufactured by heat sealing, although the body strength of the bag is strong, the strength of the heat sealing portion is extremely low, and there is a practical problem. .

This is because on the molecular structure of the linear low-density polyethylene described below, since the linear low-density polyethylene can not have strong shrinkage even if it attempts to have heat shrinkage by imparting molecular orientation by melt drawing or the like, When a heat sheet is applied, the heat seal portion does not undergo heat shrinkage, the film thickness is reduced, and the heat seal strength is not obtained.

The present inventors have conducted various studies to obtain a packaging bag having good heat sealing strength using linear low-density polyethylene, and as a result, mixed a specific linear low-density polyethylene with a specific branched low-density polyethylene in a specific amount. However, they have found that a packaging bag having good heat seal strength can be obtained by performing inflation molding and heat sealing under specific conditions, and have previously filed applications (JP-A-59-178221 and JP-A-60-178221).
However, as a result of further study, the above-mentioned linear low-density polyethylene was blended with a specific amount of a specific high-density polyethylene and a specific ethylene-α-olefin copolymer in a specific amount under inflation molding under specific conditions. Further, the present inventors have found that a packaging bag having further improved heat sealing strength can be obtained by performing heat sealing, and thus completed the present invention.

[Means for solving the problem]

The gist of the present invention is that the melt index is 10 g / 10 min or less, the density is 0.910 to 0.945 g / cm ³ , and the flow ratio is 70 to 99 parts by weight of a linear low-density polyethylene having a melt index of 0.1 g or less. / 10 min or less, and, in high-density polyethylene 0.5 to 10 parts by weight and the melt index of the flow ratio of 70 or higher 20 g / 10 min or less, and a density of 0.910 g / cm ³ or less ethylene -α-olefin copolymerization Using a composition consisting of 0.5 to 20 parts by weight, blow-up ratio 0.9 to 2.0, draft rate
10-40, inflation molding under the condition of a cooling rate index of 30 seconds or less, the obtained tubular film is heat sealed and cut in a longitudinal direction in a direction intersecting the take-off direction of the packaging bag. Lies in the manufacturing method.

 Hereinafter, the present invention will be described in more detail.

The linear low-density polyethylene used in the present invention is a copolymer of ethylene and another α-olefin, and is different from a branched low-density polyethylene resin produced by a conventional high-pressure method. Linear low-density polyethylene is, for example, ethylene, butene, hexene, and other α-olefins.
It is obtained by copolymerizing octene, decene, 4-methylpentene-1 or the like in an amount of about 4 to 17% by weight, preferably about 5 to 15% by weight. used has been produced, a conventional high-density polyethylene and short branched structure by the copolymerization component, density obtained by this use of short chain branching suitably reduced by 0.91~0.945g / cm ³ approximately It is a polyethylene having a structure that is more linear than conventional branched low-density polyethylene and has more branches than high-density polyethylene.

When heat-sealing such a linear low-density polyethylene, the heat-shrinkable portion is less shrunk because the molecular structure of the linear low-density polyethylene is short-chain branched as described above, It is considered that thermal relaxation occurs.

In the present invention, a specific low-density polyethylene is mixed with a specific high-density polyethylene and a specific ethylene-α-olefin copolymer in a specific amount to form a linear low-density polyethylene by inflation molding under specific conditions. The purpose is to improve the heat seal strength and further stabilize the film formability.

That is, the linear low density polyethylene used in the present invention has a melt index of 10 g / 10 minutes or less, preferably 0.
It is in the range of 2 to 1.5 g / 10 minutes. If the melt index is greater than 10 g / 10 minutes, the strength of the trunk is undesirably reduced when the bag is used as a packaging bag.

Also, the flow ratio of the linear low-density polyethylene is 70 or less,
It is preferably in the range of 15 to 70, more preferably 15 to 35. If the flow ratio is larger than 70, the heat seal strength is undesirably reduced.

In the method of the present invention, the melt index is JIS K676
It is a value measured at 190 ° C. according to 0, and the flow ratio is a shear force of 10 ⁶ dynes /
the ratio of cm ² (load 11131G) 10 ⁵ extrusion rate of dynes / cm ² (load 1113 g) (g / 10 min), Is calculated.

The flow ratio is a measure of the molecular weight distribution of the resin used,
If the value of the flow ratio is small, the molecular weight distribution is narrow, and if the value of the flow ratio is large, the molecular weight distribution is wide.

The high-density polyethylene used as the second component in the present invention is manufactured as a homopolymer of ethylene or a copolymer of ethylene and a small amount of α-olefin by a medium-low pressure process in the same manner as the linear low-density polyethylene described above. Usually having a density of 0.945 or more.

The high-density polyethylene used in the present invention must have a melt index of 0.1 g / 10 min or less and a flow ratio of 70 or more. Such high-density polyethylenes have a fairly high molecular weight in their components (for example, contain an appropriate amount of more than one million fractions, and this high-molecular-weight component is similar in molecular structure to the linear low-density polyethylene described above. From these facts, it is presumed that the compatibility with the linear low-density polyethylene is good, and as a result, the difficulty in molecular orientation, which is a disadvantage of the linear low-density polyethylene described above, is improved.

Therefore, if the high-density polyethylene used has a melt index and a flow rate ratio other than those described above, the improvement effect is insufficient.

Ethylene used as the third component in the present invention
The α-olefin copolymer is a copolymer similar to the linear low-density polyethylene described above, but as the third component used in the present invention, the α-olefin content in the copolymer is 10% or more, It should preferably be between 15% by weight and 50% by weight and have a density of 0.910 g / 10 minutes or less.

The incorporation of such an ethylene-α-olefin copolymer is effective in appropriately reducing the anisotropy of the molecular orientation caused by the incorporation of the high-density polyethylene described above. The resulting packaging bag has improved vertical tear resistance and impact resistance.

The melt index of the ethylene-α-olefin copolymer needs to be 20 or less, and if it is 20 or more, the blocking properties of the film are undesirably deteriorated.

The mixing ratio of the linear low-density polyethylene, high-density polyethylene and ethylene-α-olefin copolymer is 70 to 99 parts by weight of linear low-density polyethylene, preferably 85 to 97 parts by weight, and 0.5 to 10 parts by weight of high-density polyethylene. Parts by weight, preferably 1 to 5 parts by weight, the ethylene-α-olefin copolymer is 0.1 part by weight.
It is used in the range of 5 to 20 parts by weight, preferably 2 to 10 parts by weight.

Outside of this range, the balance of the film formability, heat seal strength, film impact resistance, film stiffness, etc. is unfavorably deteriorated.

By adjusting to such a composition, a high molecular weight component and an elastomeric component are introduced into the composition, and compared to a conventional linear low density polyethylene and a branched low density polyethylene blend, the longitudinal direction during inflation molding is longer. It is presumed that the film thus obtained tends to be oriented, and the film obtained in this way shrinks in the direction of the orientation during heat sealing, the heat-sealed portion becomes thicker than the original thickness of the film, and the strength of the heat-sealed portion is improved. .

In addition, a film molded using such a composition is compared with a film molded using a composition in which, for example, a linear low-density polyethylene is modified with an organic peroxide to produce a high molecular weight component. Thus, problems such as off-flavors and gels derived from organic peroxides are eliminated, and the surface gloss of the film is suppressed, resulting in a film having excellent commercial properties.

Further, even if the above-mentioned polyethylene composition is simply blown-molded, a product having good heat-sealed portion strength cannot be obtained, and specific molding conditions are required for molding.

The specific molding conditions include a blow-up ratio of 0.9 to 2
The draft rate is set to 10 to 40, and the cooling rate index is set to 30 seconds or less to perform inflation molding.

 Here, the draft rate is obtained by the following equation.

In the formula, the symbols are as follows.

Further, the cooling rate index is a time (second) until the molten resin is extruded from the die and reaches the frost line, and is obtained by the following equation.

τ: Cooling rate index (second) FLH: Frost line height (cm) V ₀ : Linear velocity when the molten resin passes through the lip (cm / se)
c) V ₁ : Take-off speed (cm / sec) When the blow-up ratio was 2.0 or more, shrinkage occurred in the longitudinal direction of the heat seal during heat sealing, and distortion was generated in the direction opposite to the orientation of the bag body. The strength of the heat-sealed end of the bag is reduced, causing the bag to break.

If the draft rate is 10 or less, good shrinkage does not occur during heat sealing, and if it is 40 or more, the molecular orientation of the body of the bag itself becomes too large in one direction, which causes the body itself to tear.

When the cooling rate index is 30 seconds or more, the molecular orientation generated in the film by drafting during film forming is relaxed by thermal relaxation, so that shrinkage does not occur at the time of heat sealing, and the strength of the heat seal portion is not high.

For heat sealing, a heat bar or a heat belt is used.However, when the heat seal portion is pressed for a long time by these heaters, thermal relaxation occurs and the strength of the heat seal portion does not appear, so that the heat seal portion is not heated. Use a heat-sealing method that quickly heats the heat-sealed part at a temperature of about 280 ° C without applying a pressing force as much as possible, and then causes the heat-sealed part to contract by causing the heat-sealed part to be in a free state. It is desirable.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples,
The present invention is not limited to the following examples unless it exceeds the gist.

Example 1 9.3 parts by weight of a linear low-density polyethylene having a melt index of 0.5 g / 10 minutes, a flow ratio of 20, and a density of 0.921 g / cm ³ butene-1 content of 8% by weight in a copolymer was melt-indexed. Is 0.06 g / 10 min, the flow ratio is 120, the density is 0.953 g / cm ³ , 2 parts by weight of high-density polyethylene, and the melt index is
5 parts by weight of an ethylene-butene- / copolymer having a density of 0.88 g / cm ³ at 4 g / 10 minutes was dry-blended as a raw material. Using an inflation molding machine equipped with a modern machine Delsa 65φ type extruder equipped with an inflation die with an annular slit diameter of 250mmφ and a cooling air ring, extrusion rate 100kg / hr, blow-up ratio (BUR) 1.1, drafts
The amount of air blown from the air ring was changed under the conditions of 14, and a cooling rate index of 28 was used to obtain a 150 μm blown film.

The obtained blown film is 670 cm long and 4 width wide.
Cut into a 40 cm cylindrical film, HS 22B manufactured by Neuron
-2 type heat sealer (heating section length 150mm, heating section clearance 0.3mm, cooling section length: 150mm, cooling section clearance
Heat sealing temperature (heating part surface temperature) 250
One of the openings of the tubular film was heat-sealed at a position 1.5 cm from the end under the conditions of ℃, cooling unit temperature of 30 ℃, and film feeding speed of 15 m / sec. ) Caused shrinkage, and the film 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 a bag drop test.

The bag drop test is that the bag filled with the above 20 kg of fertilizer is deposited for 18 to 24 hours after heat sealing and left to stand, and then the body of the packaging bag is parallel to the floor surface and the heat sealing portion is substantially perpendicular to the floor surface As described above, a test was performed by dropping 20 bags (lateral drop), and the bag breaking ratio was obtained.

The drop conditions were a room temperature of -10 ° C., a drop height of 1.5 m, and five drops per bag. The bag breaking ratio was determined as the percentage of the bags that were broken in the packaging bags used in the test.

The uneven thickness state is obtained by measuring the thickness of the obtained cylindrical film at 36 points at equal intervals in the circumferential direction with a dial gauge, and the obtained measured value is within ± 10% of the average of the measured values. Was evaluated as ○, Δ when the value was greater than ± 10% and within ± 15% of the average value, and X when the value was greater than ± 15%.

 The results are shown in Table 1.

Example 2 An inflation film of 150 μm was obtained in the same manner as in Example 1 except that the blow-up ratio was 1.4 and the cooling rate index was 16. Next, the bag breaking ratio and the uneven thickness state were measured in the same manner as in Example 1.

 The results are shown in Table 1.

Example 3 Example 3 was carried out in the same manner as in Example 1 except that the amount of the raw material resin and the molding conditions were changed as shown in Table 1. The results are shown in Table 1.

Comparative Examples 1-4 Except for changing the blending of the raw materials and the molding conditions as shown in Table 1,
It carried out like Example-1.

 The results are shown in Table 1.

[Effects of the Invention] According to the method of the present invention, a bag excellent in the strength of the trunk portion and in the strength of the heat seal portion is obtained, and is suitable for use as a bag for packing heavy materials such as fertilizers and synthetic resin pellets. It is.

Continuation of front page (56) References JP-A-60-183132 (JP, A) JP-A-62-39226 (JP, A) JP-A-63-77957 (JP, A) JP-A-60-257232 (JP) , A)

Claims (1)

(57) [Claims] A linear low-density polyethylene having a melt index of 10 g / 10 min or less, a density of 0.910 to 0.945 g / cm ³ and a flow ratio of 70 or less, 70 to 99 parts by weight, and a melt index of 0.1 g / min. 10 minutes or less, and the flow ratio is 70 or less high-density polyethylene 0.5 to 10 parts by weight and the melt index is 20 g
/ 10 minutes or less, and using a composition consisting of 0.5 to 20 parts by weight of ethylene-α olefin copolymer having a density of 0.910 g / cm ³ or less, a blow-up ratio of 0.9 to 2.0, a draft rate of 10 to 40,
A method for producing a packaging bag, comprising inflation molding under a condition of a cooling rate index of 30 seconds or less, and heat-sealing and cutting the obtained tubular film with a direction intersecting a take-off direction as a longitudinal direction.