JP3015114B2 - Manufacturing method of packaging bag - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 seal strength and body strength using a modified linear low-density polyethylene having improved properties.

[0002]

2. Description of the Related Art Usually, when a bag for packaging is manufactured by inflation molding using linear low-density polyethylene and heat-sealing, the strength of the body of the bag is very strong, but the strength of the heat-sealed portion is extremely low, so that it is practical. There was a 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 heat sealing is performed, the heat sealing portion does not undergo heat shrinkage, the film thickness is reduced, and the heat sealing 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. As a result, the specific linear low-density polyethylene was replaced with a specific branched low-density polyethylene. A specific amount,
It has been found that by performing inflation molding and heat sealing under specific conditions, a packaging bag having good heat sealing strength can be obtained.
No. 825. Furthermore, the heat-sealing strength is greatly improved by performing inflation molding and heat-sealing the mixture of the above-described linear low-density polyethylene and the branched low-density polyethylene reacted with a radical generator under specific conditions. It was found that such a packaging bag could be obtained and proposed in Japanese Patent Application Laid-Open No. 60-183132.

[0004]

Although the strength of the heat seal portion of the packaging bag is greatly improved in the above-mentioned proposed method, the strength of the body portion of the bag is not sufficient, and the bag is used at an extremely low temperature. In some cases, it has been found that this leads to the problem that the packaging bag is easily split vertically (easy to split vertically).

[0005]

In view of these circumstances, the present inventors have manufactured a packaging bag using linear low-density polyethylene which is sufficiently satisfactory in both the heat sealing strength and the body strength of the packaging bag. As a result of intensive studies, in the above proposed method, a linear low-density polyethylene having a specific polymerization method, that is, one having specific physical properties obtained by a gas-phase polymerization process was used to generate radicals. Inflation molding and heat sealing of the modified linear low-density polyethylene having specific physical properties obtained by reacting with the agent under specific conditions, a packaging bag having good heat seal strength and body strength can be obtained. This led to the completion of the present invention.

That is, the gist of the present invention is as follows: (1) Ethylene and carbon number 6 by a gas phase polymerization process.
Having a melt index (MI ₁ ) of 0.8 g / 10 min or less, a density of 0.910 to 0.925 g / cm ³ , and a fluidity ratio (MFR ₁ ) of 35 or less produced by copolymerization with α-olefin Linear low-density polyethylene (branched low-density polyethylene
10001 parts by weight of the radical generator is added to 100 parts by weight of the radical generator, and then (2) the radical generator is reacted with the polyethylene to obtain a melt index (MI ₂ ). Is 0. 7 g / 10 min or less, the flow ratio (MFR ₂ ) is 100 or less, the value of (MI ₂ ) / (MI ₁ ) is 0.3 to 0.8,
And the following formula: 67.56−73.6 (ρ ₂ ) −log (MI ₂ ) ≧ 0 (where (ρ ₂ ) is the density (g / cm) of the modified polyethylene.
^The linear low-density polyethylene is modified so as to satisfy the value of ³ ) , and (3) after or while the polyethylene is modified , the blow-up ratio is 0.9 to 2.0, and the draft ratio is 5 to 40. And (4) heat-sealing and cutting the obtained tubular film along a direction intersecting the take-off direction.

Hereinafter, the present invention will be described in more detail. As the linear low-density polyethylene used in the present invention, a production process of a gas phase polymerization method using a fluidized-bed reactor, a stirred-bed reactor, a tubular reactor or the like is applied, and ethylene and an α-olefin having 6 carbon atoms are used. For example, hexene, 4-methylpentene-1 or the like is added in an amount of about 4 to 17% by weight, preferably 5 to 17% by weight.
About 15% by weight copolymerized and produced using a Ziegler-type catalyst or a Phillips-type catalyst used in the production of high-density polyethylene at medium and low pressures. The density is appropriately reduced by utilizing this short-chain branching to about 0.910 to 0.925 g / cm ^3, which is more linear than the conventional branched low-density polyethylene and has a higher density. Polyethylene having a structure with more branches than polyethylene.

The above-mentioned chain low-density polyethylene is described, for example, in JP-A-54-148093 and JP-A-54-15448.
No. 8, etc. (gas phase polymerization using a fluidized bed reactor). As the linear low-density polyethylene used in the present invention, ethylene and a carbon number 6
Has a melt index (MI ₁ ) of 0.8 g / 10 min or less, preferably 0.1 to 0.8 g / 10 min, more preferably 0.3 to 10 g.
0.6 g / 10 min, density (ρ ₁ ) 0.910
0.925 g / cm ³ , preferably 0.915 to 0.92
Those having a range of 2 g / cm ³ and a flow ratio (MFR ₁ ) of 35 or less, preferably 15 to 30 are used.

In the method of the present invention, a radical generator is further added to the above-mentioned linear low-density polyethylene to decompose the radical generator, react with the polyethylene, and then carry out inflation molding. The radical generator to be added to the linear low-density polyethylene preferably has a decomposition temperature in which the half-life is 1 minute and ranges from 130 ° C. to 300 ° C., for example, dicumyl peroxide, 2,5-dimethyl-2,5 Di (t-butylperoxy) hexane, 2,5-dimethyl-2,5 di (t-butylperoxy) hexyne-3,
α, α'-bis (t-butylperoxyisopropyl)
Benzene, dibenzoyl peroxide, di-t-butyl peroxide and the like can be mentioned.

The amount of the radical generator to be added depends on the linear low-density polyethylene (branched low-density polyethylene is blended).
0.0001 for 100 parts by weight
The addition amount is less than 0.0001 part by weight, and the strength of the heat seal portion of the obtained packaging bag is almost the same as that of the non-added one, and If the amount is more than 0.1 part by weight, the melt index becomes too low, so that the film tends to be cut off at the time of film formation, and the surface of the film is rough.

However, the amount of addition is 0.002 to 0.0
When the content is in the range of 2 parts by weight, the film formability and the strength of the heat seal portion are remarkably improved. In the present invention, the method for adding a radical generator to the linear low-density polyethylene and decomposing the radical generator to react with the polyethylene is not particularly limited. For example, the method is performed by the following method. Can be.

(1) At the time of inflation molding, the linear low-density polyethylene and the radical generator are fed simultaneously or sequentially and melt-extruded. (2) The linear low-density polyethylene and the radical generator are kneaded and reacted using a kneader such as an extruder or a Banbury mixer, and then pelletized. The pellets are used for inflation molding. (3) A masterbatch containing a large amount of a radical generator (a polyethylene such as a high-density polyethylene, a branched low-density polyethylene, or a linear low-density polyethylene; A polyethylene master batch containing a high concentration (usually about 200 to 20,000 ppm) of a radical generator melt-kneaded at a temperature at which polyethylene does not react with the radical generator, for example, at a temperature of 130 to 160 ° C., is prepared in advance. The master batch and the linear low density polyethylene are blended and blown.

The radical generator itself is used as it is or after being dissolved in a solvent. By reacting the linear low-density polyethylene with a radical generator,
The polyethylene causes a cross-linking reaction, whereby a high-molecular-weight component is increased, and a modified polyethylene having a reduced melt index is obtained. The modified polyethylene has improved film formability as compared with the unmodified linear low-density polyethylene, and is likely to be oriented in the longitudinal direction during inflation molding, and the film thus obtained is oriented in the direction of heat sealing. And the thickness of the film becomes larger than the original thickness of the film, and the strength of the heat-sealed portion is improved.

In the crosslinking reaction using the above radical generator, the modified polyethylene obtained by the reaction is adjusted so that the melt index (MI ₂ ), density (g / cm ³ ), and flow ratio (MFR ₂ ) fall within the following ranges. I do. (MI
₂ ) is 0.7 g / 10 min or less, preferably 0.05 to
0.5 g / 10 min, more preferably 0.2 to 0.4 g
/ 10 min, (MFR ₂ ) is 100 or less, preferably 15 to 70, and (MI ₂ ) / (MI ₁ )
Is 0.3 to 0.8, and the amount of the radical generator is adjusted so as to satisfy the following expression: 67.56-73.6 (ρ ₂ ) -log (MI ₂ ) ≧ 0. The density (ρ ₁ ) of the linear low density polyethylene is selected.

The melt indexes (MI ₁ ) and (MI ₁ )
_{If 2} ) is more than the above range, the heat seal strength and body strength of a packaging bag are undesirably reduced. If the flow ratios (MFR ₁ ) and (MFR ₂ ) are not less than the above ranges or the value of (MI ₂ ) / (MI ₁ ) is out of the above ranges, the body strength of the packaging bag is reduced, which is preferable. Absent. The linear low-density polyethylene preferably has a density in the range of 0.910 to 0.925 g / cm ³ from the viewpoint of rigidity and impact resistance when used as a packaging bag.

Further, if (MI ₂ ) and (ρ ₂ ) satisfy the above expression, it is not preferable because the strength of the body of the packaging bag decreases. When a copolymer of ethylene and an α-olefin having 6 carbon atoms produced by a gas phase process is not used as the linear low-density polyethylene,
When the thickness of the film is reduced, the body strength of the bag is not sufficient, and the packaging bag tends to tear vertically, which is not preferable.

In the method of the present invention, the melt index is a value measured at 190 ° C. in accordance with JIS K6760, and the flow ratio is a shear force of 10 ⁵ dynes / cm ² (1113 g load) using the above-mentioned melt index measuring device. Is the ratio (g / 10 minutes) of the extruded amount of 10 ⁶ dynes / cm ² (load 11131 g). The extruded amount under the load of 11131 g (10 minutes) 分 間 the extruded amount under the load of 1113 g (10 minutes).
Is calculated. The density is a value measured according to JIS K6760.

The flow ratio is a measure of the molecular weight distribution of the resin used, and the smaller the value of the flow ratio, the narrower the molecular weight distribution.
A higher flow ratio value indicates a broader molecular weight distribution. In the present invention, a small amount of branched low-density polyethylene, for example, 2 parts per 75 parts by weight of linear low-density polyethylene is used to improve the moldability of the linear low-density polyethylene.
By blending at a ratio of 5 parts by weight or less, moldability is further improved.

The branched low-density polyethylene blended with the linear low-density polyethylene includes an ethylene homopolymer and a copolymer of ethylene and another copolymer component. Examples of the copolymerization component 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. The copolymerization amount of the copolymer component is 0.5 to 18% by weight, preferably about 2 to 10% by weight. These low-density polyethylenes are desirably obtained by radical polymerization using a conventional high-pressure method (1000 to 3000 kg / cm ² ) using a radical generator such as oxygen or an organic peroxide.

The branched low-density polyethylene has a melt index of 1.9 g / 10 min or less, preferably 0.1 g / min.
A fluid having a flow rate of 50 to 50 g, preferably 30 to 50 g is used. If the melt index is higher than the above range, the strength of the body and / or the heat seal strength of the bag when packaged is reduced, which is not desirable. On the other hand, if the flow ratio is higher than the above range, the strength of the body of the bag decreases when it is made into a packaging bag, which is not desirable.

The branched low-density polyethylene preferably has a density in the range of 0.915 to 0.925 from the viewpoint of improving the body strength and heat sealing strength of the bag when it is made into a packaging bag. Further, the above-mentioned linear low-density polyethylene or a mixture of the linear low-density polyethylene and the branched low-density polyethylene, which is modified by adding a radical generator to the modified polyethylene, is simply subjected to inflation molding, but the heat-sealing part Good strength and body strength cannot be obtained, and specific molding conditions are required for molding.

The specific molding conditions are that the blow-up ratio is set to 0.9 to 2 and the draft rate is set to 5 to 40 for inflation molding. Here, the draft rate is obtained by the following equation. Draft rate = (ρm / ρf) × (G / t) × (1 / BU)
R) In the formula, the symbols are as follows. G: width of die slit t: thickness of obtained film ρm: density of resin extruded from die slit ρf: density of film BUR: blow-up ratio If the blow-up ratio is 2.0 or more, heat sealing at the time of heat sealing The longitudinal shrinkage occurs, and a distortion occurs in the direction opposite to the orientation of the bag body, so that the strength of the heat-sealed end portion of the obtained bag is reduced and the bag is broken.

If the draft ratio is less than 5, good shrinkage does not occur during heat sealing, and if it is more than 40, the molecular orientation of the body of the bag itself becomes too large in one direction, causing the body itself to tear. Becomes In addition, a heat bar, a heat belt, or the like is used for heat sealing, but 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 is not obtained.
A heat seal method is used in which the heat seal portion is rapidly heated at a temperature of about 280 ° C. without applying a pressing force as much as possible, and then the heat seal portion is caused to shrink by leaving the heat seal portion in a free state. It is desirable.

[0024]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which, however, are not intended to limit the scope of the present invention. Example 1 (a) Production of packaging bag Gas phase method using a melt index (MI ₁ ) of 0.8 g / 10 min, a flow ratio of 20, a density of 0.920 g / cm ³ , and a copolymer component of hexene-1. 75 parts by weight of linear low-density polyethylene produced by the process and a high-pressure branched low-density polyethylene having a melt index of 0.4 g / 10
And 25 parts by weight of a substance having a flow ratio of 45 and a density of 0.924 g / cm ³ , and 0.02 parts by weight of 2,5-dimethyl-2,5 di (t-butylperoxy) hexyne-3. Then, the mixture was melt-kneaded at 250 ° C. for 3 minutes in an extruder, extruded, and pelletized. The resulting modified polyethylene had MI: 0.
It had physical properties of 3 g / 10 minutes and a flow ratio of 50. Using an inflation molding machine equipped with an inflation die with a circular slit diameter of 200 mmφ and a cooling air ring mounted on a Delsa 65φ extruder manufactured by Modern Machinery Co., Ltd., an extrusion rate of 50 kg / hr and a blow-up ratio (BU)
R) A film thickness of 1 under conditions of 1.4 and a draft rate of 6.5.
A 50μ blown film was obtained.

The obtained 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 Neurong Co. (heating section length 150 mm, heating section clearance 0.3 mm, cooling section length) : 150 mm, cooling unit clearance 1 mm), heat sealing temperature (heating unit surface temperature) 220 ° C., cooling unit temperature 30 ° C., film feeding speed 15 m / sec. Was heat-sealed at a position of 1.5 cm from the bottom.

The obtained bag was filled with 20 kg of fertilizer, and the opening was heat-sealed under the same conditions as described above, and left to stand for 18 to 24 hours after the heat sealing to obtain a packaging bag for a bag drop test. (B) Performance test of packaging bag The packaging bag obtained in the above (a) was subjected to a horizontal bag test and a vertical bag test by the following methods. (A) Side drop bag test A test is performed by dropping 20 bags (side drop) so that the body of the packaging bag is parallel to the floor and the heat-sealed portion is substantially perpendicular to the floor, and the bag breaking rate is determined. Was. The side drop bag test was performed to measure the strength of the heat seal portion of the bag.

The drop condition was set at room temperature of -5 ° C. and the drop height was 1.
The number of drops was 5 times per bag of 5 m. The bag breaking ratio was determined as the percentage of the bags that were broken in the packaging bags used in the test. Table 1 shows the results. It is unusable if there is a bag break from the practical point of view. (B) Vertical bag drop test 20 bags are dropped (longitudinal drop) so that the heat seal part of the packaging bag is parallel to the floor surface and the trunk is substantially perpendicular to the floor surface, and the test is performed to reduce the bag breakage rate. I asked. The vertical bag test was performed to measure the strength of the body of the bag.

The drop conditions were a room temperature of -20 ° C., a drop height of 2.5 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. Table 1 shows the results. From the viewpoint of practicality, the bag breaking rate is acceptable up to 10%. (C) Film forming stability In the inflation forming of the above (a), when the extruding amount was increased, a stable forming limit extruding amount at which a tubular film in a molten state could be formed in a stable bubble state was measured. Table 1 shows the results. The larger the extrusion limit of the stable molding, the better the film forming stability.

Example 2 Example 2 was repeated except that the low-density polyethylene was not changed to 100 parts by weight of the linear low-density polyethylene and the mixing of the radical generator was changed to 0.01 part by weight. Was performed in the same manner as in Example 1. Table 1 shows the results.

COMPARATIVE EXAMPLE 1 In Example 1, a linear low-density polyethylene was produced in a gas phase process using butene as a copolymerization component. The melt index was 0.5 g / 10 min, the flow ratio was 24, and the density was 24. Has a physical property of 0.922 g / cm ³
Using 85 parts by weight , the content of the radical generator was 0.005.
Parts, the blending of branched low density polyethylene, except that went changed to 15 parts by weight was carried out as in Example 1.
Table 1 shows the results.

Comparative Example 2 In Example 2, as a linear low-density polyethylene, 4-methylpentene-1 was used as a copolymer component in a solution process.
Is 1.2 g / 1 using a melt index manufactured using
0 minutes, a flow ratio of 22 and a density of 0.935 g / cm ³ were used.
The procedure was performed in the same manner as in Example 2, except that the amount was changed to parts by weight. Table 1 shows the results.

Comparative Example 3 In Example 2, a linear low density polyethylene was produced by a high pressure process using butene as a copolymerization component, and had a melt index of 0.8 g / 10 min, a flow ratio of 27, and a density of 27. Example 2 was carried out in the same manner as in Example 2 except that a substance having physical properties of 0.925 g / cm ³ was used, and the mixing ratio of the radical generator was changed to 0.02 parts by weight. Table 1 shows the results.

COMPARATIVE EXAMPLE 4 In Example 1, a linear low-density polyethylene was produced by a gas phase process using hexene as a copolymer component. The melt index was 0.8 g / 10 min, the flow ratio was 20, and the density was 20%. Was carried out in the same manner as in Example 1 except that a material having physical properties of 0.929 g / cm ³ was used and the ratio of the radical generator was changed to 0.02 parts by weight. Table 1 shows the results.

Comparative Example 5 In Example 2, a linear low-density polyethylene was produced by a gas phase process using hexene as a copolymerization component, and had a melt index of 0.8 g / 10 min, a flow ratio of 20, and a density of 20. Was carried out in the same manner as in Example 2 except that a sample having physical properties of 0.929 g / cm ³ was used. Table 1 shows the results. Comparative Example 6 In Example 2, a linear low-density polyethylene produced by a gas phase process using hexene as a copolymer component had a melt index of 1.0 g / 10 min, a flow ratio of 18, and a density of 0.1. Example 2 was carried out in the same manner as in Example 2 except that a substance having physical properties of 923 g / cm ³ was used and the amount of the radical generator was changed to 0.04 part by weight. Table 1 shows the results.

Comparative Example 7 The procedure of Example 2 was repeated except that no radical generator was used. Table 1 shows the results.

[0036]

[Table 1]

[0037]

According to the method of the present invention, a modified linear low-density polyethylene having specific properties obtained by reacting a specific linear low-density polyethylene with a radical generator is used to inflation under specific conditions. By molding, a packaging bag having good heat seal strength and body strength can be obtained even when used at extremely low temperatures. Further, in the present invention, a packaging bag having good heat seal strength and body strength can be obtained similarly by using a modified product obtained by blending a specific branched low-density polyethylene in a specific amount.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FIB29L 22:00 (56) References JP-A-1-18825 (JP, A) JP-A-3-136831 (JP, A) Kaihei 3-53930 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 55/22-55/28 B29D 22/00 B31B 1/64 321 C08J 5/18 CES

Claims (2)

(57) [Claims] (1) A melt index (MI ₁ ) produced by copolymerization of ethylene and an α-olefin having 6 carbon atoms by a gas phase polymerization process is 0.8 g / 10 min or less, and the density is 0. A radical generator is mixed with 0.0001 to 0.1 parts by weight to 100 parts by weight of a linear low-density polyethylene having a flow rate (MFR ₁ ) of 910 to 0.925 g / cm ³ and 35 or less, and then (2) radical generation By reacting the agent with the polyethylene, the melt index (MI ₂ ) is 0.7 g / 10 min or less, the flow ratio (MFR ₂ ) is 100 or less, and the value of (MI ₂ ) / (MI ₁ ) is 0.1. 3 to 0.8,
In addition, the following equation 67.56−73.6 (ρ ₂ ) −log (MI ₂ ) ≧ 0 (where (ρ ₂ ) is the density (g / cm ³ ) of the modified linear low-density polyethylene) modified linear low density polyethylene to further (3) after modifying the polyethylene, or denatured blow-up ratio 0.9-2.0 while, and inflation molding under the conditions of the draft ratio 5-40 (4) A method for manufacturing a packaging bag, wherein the obtained tubular film is heat-sealed and cut along a direction intersecting with a take-off direction. (1) Ethylene is produced by a gas phase polymerization process.
Produced by copolymerization of olefins and α-olefins having 6 carbon atoms.
Was Melt index (MI ₁  ) Is 0.8g / 10min or less
under, Density is 0.910 to 0.925 g / cm ^Three  , Flow ratio (MFR ₁  ) Is 35 or less linear low-density polyethylene
75 parts by weight Melt index is 1.9g / 10min or less, Flow ratio of 50 or less Compounded in a proportion of 25 parts by weight or less of branched low density polyethylene
Radical generator to 100 parts by weight of polyethylene
0.0001-0.1 parts by weight, then (2) reacting a radical generator with the polyethylene;
hand, Melt index (MI _Two  ) Is 0.7g / 10 minutes or more
under, Flow ratio (MFR _Two  ) Is less than or equal to 100; (MI _Two  ) / (MI ₁  ) Is from 0.3 to 0.8,
And the following equation 67.56-73.6 (ρ _Two  ) -Log (MI _Two  ) ≧ 0 (However, (ρ _Two  ) Is the density (g / cm) of the modified polyethylene.
^Three  The linear low-density polyethylene is used to satisfy the value
Denatured and further (3) After or while modifying the polyethylene Blow-up ratio 0.9-2.0, Draft rate 5-40 Inflation molding under the conditions of (4) Cross the obtained tubular film in the take-off direction
Heat-sealing and cutting along the direction of
Manufacturing method for packaging bags.