JPH0353930A - Manufacture of packing bag - Google Patents

Abstract

PURPOSE:To improve heat-sealing strength and belly part strength, by performing inflation molding and heat sealing of a matter obtained by compounding specific high-density polyethylene and an ethylene-olefin copolymer to specific linear low-density polyethylene in a specific quantity under a specific condition. CONSTITUTION:A composition constituted of 70-99 pts.wt. linear low-density polyethylene which is obtained by copolymerizing ethylene and 6C alpha olefin by making use of gas phase polymerization method process and possesses a melt index, density and a flow ratio of respectively 2g/10 minutes or lower, 0.910-0.945g/cm<3> and 50 or lower, 0.5-10 pts.wt. high-density polyethylene whose melt index and flow ratio are respectively 0.1/10 minutes or lower and at least 70 and 0.5-20 pts.wt. ethylene-olefin copolymer whose melt index and density are respectively 20g/10 minutes or lower and 0.910g/cm<3> or lower is used. Then inflation molding is performed under conditions where a blow-up ratio, draft rate and cooling speed index are respectively 0.9-20, 5-40 and 30 seconds or less. An obtained cylindrical film is heat-sealed and cut off along a direction crossing with a receiving direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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.

[Conventional technology and its problems]

Normally, when manufacturing bags for packaging by inflation molding and heat-sealing linear low-density polyethylene, the body of the bag is strong, but the strength of the heat-sealed part is extremely low, which poses a practical problem. there were.

This is due to the molecular structure of linear low-density polyethylene, which will be explained later.
Linear low-density polyethylene cannot be made to have strong shrinkability even if it is given molecular orientation by melt-stretching, etc., so when heat-sealing is performed, the heat-sealed part will shrink due to heat. First, the film thickness is reduced and the heat sealability 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 have found that a specific amount of a specific branched low-density polyethylene is blended into a specific linear low-density polyethylene. They discovered that a packaging bag with good heat-sealing strength could be obtained by performing inflation molding and heat-sealing under specific conditions. 21133ll./ ) l,ta. Furthermore, the above linear low-density polyethylene is blended with a specific amount of a specific high-density polyethylene and a specific ethylene-α-olefin copolymer, and then subjected to inflation or shaping and heat sealing under specific conditions to form a heat seal. It was discovered that a packaging bag with further improved strength could be obtained and was proposed in Japanese Patent Application No. 3-2227G.

However, although the strength of the heat-sealed part of the packaging bag is greatly improved in the above proposed method, the strength of the body of the bag is not sufficient, and if the film thickness is made thin, the packaging bag tends to tear vertically ( It was found that this leads to the problem of vertical tearing.

[Means to solve the problem]

In view of these circumstances, the inventors of the present invention have conducted extensive studies in order to produce packaging bags that are fully satisfactory in terms of both the heat-seal strength and body strength of the packaging bags using linear low-density polyethylene. , by clicking on the above proposed method, a specific linear low density polyethylene produced by copolymerization of ethylene and an alpha olefin having 2 carbon atoms, a specific high density polyethylene and a specific ethylene-α It has been discovered that a packaging bag having good heat seal strength and body strength can be obtained by inflation molding and heat sealing a bag containing a specific amount of an olefin copolymer under specific conditions, and has developed the present invention. Completed.

That is, the gist of the present invention is that the melt index obtained by copolymerizing ethylene and an alpha olefin having a carbon number of O using a gas phase polymerization process is 29//0 minutes or less and has a density of 0.9/0. ~0.9 4'j? / cyn3 and a flow ratio of so or less linear low density polyethylene 7
0-77 parts by weight, melt index o. iy/io
minute or less and has a fluidity ratio of 70 or more. Evening: lO weight part and melt index are 20f
//70 minutes or less and the density is 0,9/10? /
Ethylene-α olefin copolymerization cooling rate index of cm3 or less. Inflation molding is performed under conditions of 30 seconds or less, and the resulting cylindrical film is heat-sealed and cut along the direction crossing the take-up direction. The main feature lies in the manufacturing method of packaging bags.

The present invention will be explained in more detail below.

The linear low density polyethylene used in the present invention includes:
By applying the production process of gas phase polymerization method using fluidized bed reactor, stirred bed reactor, tubular reactor, etc., ethylene and α-olefin with 6 carbon atoms, flu
, t, hexene, ψ-methylpentene/etc., about 7 to 17 weight percent, preferably! It is a product obtained by copolymerizing the ~ / evening weight coefficient using a Ziegler-type catalyst or a Phillips-type catalyst used in the production of high-density polyethylene using a medium-low pressure process. A short branched structure is formed, and the density is appropriately lowered by utilizing the original short chain branching to reduce θ. 2/O~θ
．． 2ψj f//cm", and is polyethylene with a structure that is more linear than conventional branched low-density polyethylene and more branched than high-density polyethylene.

Examples of the above-mentioned linear low-density polyethylene include JP-A-Sho!
Goo/Gu♂093, same evening Goo! 3. The method described in Google and g, etc. (gas phase polymerization method using a fluidized bed reactor)
can be manufactured based on

The linear low-density polyethylene used in the present invention has a melt index (MI) obtained by copolymerizing ethylene and α-olefin having a carbon number of t using the above-mentioned gas phase polymerization process. 27//0
Preferably less than 0.2 minutes! 2//0 min range, the density (ρ) is 0.7/0 - t), ta ≠ 2/cm3, preferably 0.9/j to 0.9 II O ii'
/cm3 range, flow ratio (MFR) is below SO, preferably 1
Preferably/evening~so, more preferably/! A period of up to 3 evenings is used.

If the above-mentioned melt index is larger than the upper limit, the strength of the body will decrease when used as a packaging bag, which is not desirable. 1.
If the fluidity ratio is larger than the upper limit, the heat sealing strength will decrease, which is not preferable.

Further, if the density is less than the lower limit, the rigidity will be insufficient when used as a packaging bag, and if the density is higher than the upper limit, the impact resistance will be insufficient when used as a packaging bag, which is not preferable.

In the method of the present invention, the melt index and the JIS
The value is measured at 190℃ in accordance with Kt7t011C,
The flow ratio is the extrusion rate (9
//0 minutes) and is calculated as follows.

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.

1. Density is a value measured in accordance with JIS Kt7tO.

If a copolymer of ethylene and an α-olefin having 6 carbon atoms is not used as linear low-density polyethylene by a vapor phase process, the strength of the body of the bag will decrease when the film thickness is reduced. This is not sufficient and the packaging bag tends to tear vertically, which is not desirable.

The high-density polyethylene used as the second component in the present invention is produced as an ethylene homopolymer or a copolymer of ethylene and a small amount of α-olefin by a medium-low pressure process. , usually its density is 0.9! Say more than t.

The high density polyethylene used in the present invention has a melt index of 0. /f///0 minutes or less The flow ratio must be 70 or more. Such high-density polyethylene contains an appropriate amount of a fraction with a considerably high molecular weight (for example, 1,000,000 or more), and this high-molecular-weight component has a molecular structure similar to that of the aforementioned linear low-density polyethylene. Since they are similar, it is highly compatible with linear low-density polyethylene, and as a result, it is presumed that the aforementioned difficulty in molecular orientation, which is a drawback of linear low-density polyethylene, is improved.

Therefore, if the melt index and flow rate ratio of the high-density polyethylene used is other than the above, the improvement effect will be insufficient.

The A-9-ethylene-α-olefin copolymer used as the third component in the present invention includes ethylene and α-olefins having 3 or more carbon atoms, such as putene, hexene,
Octendecene, goomethylpentene/etc. preferably IO weight factor or more! It is copolymerized in the range of ~ SO wt %, and its density is 0.9 / Of / produced using a Ziegler type catalyst or a Phillips type catalyst.
tyn3 or less, preferably θ. ♂ Evening~0. ? 0 9
/ cm” and the melt index is 2097 lO min or less, desired L, < (l-j0.2~/
j in the range of 9//0 minutes is used.

Blending such an ethylene-α-olefin copolymer is effective in moderately relaxing the anisotropy of molecular orientation caused by the above-mentioned blending of high-density polyethylene, and as a result, for example, the final The resulting packaging bag is improved in tearability in the vertical direction and impact resistance.

The melt index of the ethylene-α-olefin copolymer must be 20 or less. If it is 20 or more, the prosodic properties of the film will deteriorate by -10, which is not desirable.

The blending ratio of the linear low-density polyethylene, high-density polyethylene, and hyethylene-α-olefin copolymer is such that the linear low-density polyethylene is 70 to 72 parts by weight, preferably gj to
7 parts by weight, high density polyethylene 0. Evening~lO parts by weight, preferably /~! parts by weight, the ethylene-α olefin copolymer is o3~. It is used in a range of 20 parts by weight, preferably 2 to 0 parts by weight.

If it is out of this range, the balance of the film's moldability, heat-sealing strength, impact resistance of the film, stiffness of FINOREM, etc. will be poor, which is not preferable.

By adjusting the composition in this way, a high molecular weight component and an elastomeric component are introduced into the composite. The film thus obtained shrinks in the direction of orientation during heat rolling, and the heat-sealed portion becomes thicker than the original thickness of the film. Compared to films formed using compositions in which high molecular weight components are produced by denaturing with peroxides, problems such as off-odors and gels originating from organic peroxides are eliminated, and trenches are formed. The surface gloss of the film is suppressed, resulting in a film with excellent marketability.

Furthermore, simply inflation molding the above-mentioned polyethylene composition does not provide a good heat seal strength, and molding requires specific conditions.

The specific molding conditions include a blow-up ratio of 0.7 to 2.
And the draft rate! ~UO, cooling rate index 30
Inflation is to take shape as less than a second.

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

During the ceremony, The symbols are as follows.

The cooling rate index is the time (seconds) it takes for the molten resin to reach the frost line after being extruded from the goo, and is obtained by the following formula.

r: Cooling rate index (seconds) FLH: Frost line height (cm) Vo:
Linear velocity when the molten resin passes through the lip part (cm/
s ec ) ■,: Pick-up speed (cm/s ec )-1
3- If the blow-up ratio is set to 2.0 or more, the heat seal shrinks in the longitudinal force direction during heat sealing, causing distortion in the direction opposite to the orientation of the bag body, which reduces the strength of the heat sealed end of the resulting bag. This will cause the bag to break.

What is the draft rate? Below, good shrinkage does not occur during heat sealing, and if the temperature exceeds po, the molecular orientation of the body of the bag becomes too large in one direction, causing tearing of the body.

If the cooling rate index is 30 seconds or more, the molecular orientation generated in the film due to draft during film molding is relaxed due to thermal relaxation, and shrinkage does not occur during heat sealing, resulting in a loss of strength in the heat sealed portion.

For heat sealing, heat bars, heat belts, etc. are used, but if you press the heat seal part for a long time with these heating devices, thermal relaxation will occur and the strength of the heat seal part will not be achieved. /3θ to 210°C, with as little pressure applied to the heat-sealed part as possible -14- After heating quickly, the heat-sealed part is left in a free state so that the heat-sealed part shrinks. It is desirable to use a suitable heat sealing method.

〔Example〕

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/ (a) Production of packaging bag Melt index is O. 2//0 minutes, flow ratio is 20
, 73 parts by weight of linear low-density polyethylene produced by a vapor phase process with a density of 0.9 2 / f /an3 copolymer and a hexene content in the weight ratio, melt index o, o y7io. 2 parts by weight of high-density polyethylene with a flow ratio of /2Q1 density of 0.933 f/cm" and ethylene with a melt index of 177//0 min and a density of 0.1'.1'7/cm3.
3 parts by weight of butene/copolymer was dry branded and used as a raw material. This is Modern Machinery's Telsa Z! Using a φ-type extruder equipped with an inflation die with an annular slit diameter of 2θθ and a cooling air ring, the extrusion amount/0θ#/Iirs blow-up ratio (B.U.R.)/. draft rate l. The cooling rate index was determined by changing the amount of air blown out from the air ring under evening conditions. A blown film of //0μ was obtained as 2g.i.

The length of the blown film is A70mm.
It was cut into a cylindrical film with a width of 41 μm, and then cut into a cylindrical film with a width of 41 μm. 2.2B-. Type 2 human sea 2- (heating part length/rOrrrm, heating part clearance 0.3wn
, Cooling section length: /jOrtan, Cooling section clearance/
heat seal temperature (heated part surface temperature) 2.2 using
0°C, cooling part temperature 30°C, film feed speed 13m/sec, one of the openings of the cylindrical film was opened from the end.
I heat-sealed it at the Yusen position. The human seal part had shrunk in the direction in which the film was taken (vertical direction) and had become thicker than the original thickness of the film.

After filling the obtained bag with 2θn fertilizer and heat sealing the opening under the same conditions as above, /I-. The bag was allowed to stand for an estimated 2/+ hours to obtain a packaging bag for the drop bag test.

(b) Performance test of packaging bags The packaging bags obtained in (a) above were subjected to a horizontal drop bag test and a vertical drop bag test using the following methods. ″!.f
c Vertical drop bag test! ℃ and fall height l. Evening m,/Number of falls per bag! It was times. The bag breakage rate was calculated as the percentage of bags that were broken among the packaging bags used in the test. The results are shown in Table/.

(a) Side drop bag test The body of the packaging bag was parallel to the floor and the heat-sealed part was approximately perpendicular to the floor. Drop 20 bags (sideways drop)
In particular, a test was conducted to determine the bag breakage rate. The side-drop bag-1'7- test was conducted to measure the strength of the heat-sealed portion of the bag.

(b) Vertical drop bag test The heat-sealed part of the packaging bag was parallel to the floor tube, and the body was approximately perpendicular to the floor. Drop 20 bags (vertical drop)
A test was conducted to determine the bag breakage rate. The vertical drop bag test was conducted to measure the strength of the body of the bag.

Example 2 In Example/, the blow-up ratio/. mlcI,C/ is the same as Example / except that the cooling rate index is 76.
/0μ blown film was obtained. Next, the bag breakage rate was measured in the same manner as in Example.

The results are shown in Table I.

Example 3 The same procedure as in Example 1 was carried out except that the physical properties of the raw resin and the cutting conditions were changed as shown in Table 1. The results are shown in Table 1.

-18 Comparative Example/~ Linear low-density polyethylene produced by copolymerization with α-olefin shown in Table 1 by the process shown in Table 1 was used, and the blending of raw materials and certain shaping conditions were as shown in Table 1. The same procedure as in Example 11 was carried out except for the following changes.

The results are shown in Table 1.

-19- [Effects of the Invention] According to the method of the present invention, a bag with excellent body strength and excellent heat-sealed strength can be obtained, and can be used as a bag for packaging heavy items such as fertilizers and synthetic resin pellets. It is suitable for use.

Claims (1)

[Claims] (1) Ethylene and carbon number 6 using gas phase polymerization process
The melt index obtained by copolymerization with α-olefin is 2 g/10 minutes or less, and the density is 0.910 to 0.
70 to 99 parts by weight of linear low-density polyethylene with a flow ratio of 945 g/cm^3 and 50 or less, high-density polyethylene 0 with a melt index of 0.1 g/10 minutes or less and a flow ratio of 70 or higher .5 to 10 parts by weight, a melt index of 20 g/10 minutes or less, and a density of 0.
．． Using a composition consisting of 0.5 to 20 parts by weight of an ethylene-α olefin copolymer of 910 g/cm^3 or less, a blow-up ratio of 0.9 to 2.0, a draft rate of 5 to 40, and a cooling rate index of 30 seconds. A method for producing a packaging bag, which comprises performing inflation molding under the following conditions, and heat-sealing and cutting the obtained cylindrical film along a direction intersecting the take-up direction.