JPH0355233A - Preparation of bag for packaging - Google Patents

Abstract

PURPOSE:To attempt to improve heat seal strength and trunk strength by performing inflation molding of a substance obtd. by compounding a linear low density polyethylene with an ethylenic copolymer. CONSTITUTION:An inflation molding with a blow-up ratio of 0.9-2.0, a draft factor of 5-40 and a cooling speed index of 30 sec or smaller is performed by using a compsn. prepd. by compounding 50-90wt.% linear low density polyethylene obtd. by copolymerizing ethylene and a 6c alpha-olefin with a melt index of 2g/10min or smaller, a density of 0.935-0.950g/cm<3> and a flow ratio of 35, and 10-50wt.% ethylenic copolymer with a melt index of 2g/10min, a density of 0.910g/cm<3> or smaller and a flow ratio of 35 or smaller and satisfying an equation I wherein melt indexes of the linear low density polyethylene and the ethylene copolymer are MIa and MIb, densities thereof are rhoa and rhob and loading of compounding thereof are A wt.% and B wt.%.

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 1/N.

[Conventional technology and its problems]

Normally, when packaging bags are manufactured using linear low-density polyethylene by inflation or heat-sealing, the body of the bag is strong, but the strength of the heat-sealed portion is extremely low, which poses a practical problem. Ta.

This is due to the molecular structure of linear low-density polyethylene, which will be explained later.
Even if linear low-density polyethylene is tried to have heat shrinkability by giving it molecular orientation by melt-stretching, etc., it is not possible to make it have strong shrinkability. No shrinkage occurs, 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 seal strength using linear low density polyethylene, the present inventors identified a specific branched low density polyethylene as a specific linear low density polyethylene. It was discovered that a packaging bag with good heat-sealing strength could be obtained by inflating and heat sealing under specific conditions. 1986-2 da 53 da/). Furthermore, heat-sealing strength can be improved by inflation-forming and heat-sealing a mixture of a specific high-density polyethylene and a specific ethylene-α-olefin copolymer in specific amounts to the above-mentioned linear low-density polyethylene under specific conditions. discovered that it was possible to obtain a packaging bag that was further improved, and filed a patent application in 1983-42.
I proposed it in issue 298.

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

[Means to solve the problem]

In view of these circumstances, the inventors of the present invention have made extensive studies to manufacture packaging bags using linear low-density polyethylene that are fully satisfactory in terms of both the heat-sealing strength and the body strength of the packaging bag, and as a result, the above-mentioned results have been developed. In the proposed method, a specific ethylene-based copolymer (ultra-low density polyethylene) is added to a specific linear low-density polyethylene produced by copolymerizing polyethylene and an α-olefin having 6 carbon atoms in a gas phase polymerization process.
A packaging bag having good heat-sealing strength and body strength can be obtained by inflating and heat-sealing a product with specific physical properties obtained by blending a specific amount of They discovered this and completed the present invention.

That is, the gist of the present invention is that the melt index obtained by copolymerizing ethylene and an α-olefin having 6 carbon atoms using a gas phase polymerization process is 2 t//0 minutes or less, and the density is 0.9 J. O~0.9 1 O t/1, and the fluidity ratio is 3S or less % Linear low density polyethylene 10-90 Weight X and melt index are cot//0 min or less, and the density is θ. 9/0?
/1 or less, and the flow ratio is 3! The melt index of the following ethylene copolymer/0 to SO weight ethylene is (
Mla), 'ii is (ρa), the blending amount is eight weight liters, and in the above case, the composition obtained by blending both of them satisfies the following formulas (1) to (III), provided that using a blow-up ratio of 0.9 to 2. Q. Inflation molding is performed under the conditions of a draft rate of 5 to tio and a cooling rate index of 30 seconds or less, and the resulting cylindrical film is heat-sealed and cut along a direction intersecting the drawing direction. It consists 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:
Applying the production process of gas phase polymerization method using fluidized bed reactor, stirred bed reactor, tubular reactor, etc., ethylene and carbon number 6
α-olefin, such as hexene, dermethylbentene, etc., in an amount of about 9 to 7% by weight, preferably 3;-/5
It is produced by copolymerizing approximately % by weight using a Ziegler type catalyst or a Phillips type catalyst used in the production of high density polyethylene using the medium and low pressure process. The density is also appropriately reduced by utilizing this short chain branching to about 0.9 J O to 0.9 1 O f/ad, and it has more linearity than conventional branched low-density polyethylene. , a polyethylene with a more branched structure than high-density polyethylene.

For example, the linear low-density polyethylene mentioned above is
It can be produced based on the method (gas phase polymerization method using a fluidized bed reactor) described in No. 41-/'41093, No. 41-/'41093, No. 41-/'41093 and the like (gas phase polymerization method using a fluidized bed reactor).

The linear low-density polyethylene used in the present invention has a melt index (Ml) obtained by copolymerizing ethylene and an α-olefin having 6 carbon atoms using the above-mentioned gas phase polymerization process. J t / / less than 0 minutes,
Preferably 0.2 ~/. jf // Range of 0 minutes, density (ρ) is 0.9,? 0~o. qsor/=, preferably 0.9, l O ~ 0.9 II! r? /(
d range, flow ratio (MFR) is 3S or less, preferably /
Those in the range of j to 3S are 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 preferable. Moreover, if the flow ratio is larger than the upper limit, the heat sealing strength will decrease, so it is preferable.

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

In addition, if a copolymer of ethylene and an α-olefin having 6 carbon atoms produced as linear low-density polyethylene by a gas phase process is not used, the strength of the body of the bag will not be sufficient when the film thickness is reduced. This is not preferable because the packaging bag tends to tear vertically.

In the method of the present invention, melt index is JIS
It is a value measured at /9θ℃ in accordance with K bqbo,
The flow ratio is defined as the shear force/06 dynes/ffl (load lll3/f) and /
05 die: //cd (load itt.yt) extrusion amount (f
l//0 min) and is calculated as:

The fluidity ratio is a measure of the molecular weight distribution of the resin used; a smaller fluidity ratio means a narrower molecular weight distribution, and a larger fluidity ratio means a broader molecular weight distribution.

Moreover, the density is a value measured based on JIS K bqbθ.

The ultra-low density ethylene copolymer used in the present invention is usually a copolymer of ethylene and an α-olefin having 3 or more carbon atoms (hereinafter simply referred to as ultra-low density polyethylene), Ethylene and α-olefins having 3 or more carbon atoms, such as butene, hexene, octene, decene,
It is a product copolymerized with dermethylbentene-l, etc. in an amount of lθ weight % or more, preferably in the range of /j-10 weight κ, and is produced using a Ziegler type catalyst or a Phillips type catalyst, and its density is 0.9 IOf. / /θ minutes or less.

The ultra-low density polyethylene has a high melt index! ? // 0 minutes or less, preferably O. Two exports eight! ?
// Density in the range of 0 minutes is 0.9 7 0t/cr
Y? Below, preferably o. pr. t~o. qo
y/crd, and the fluidity ratio is 3S or less, preferably /3 to 3! Those within the range of are used. If the melt index and density are larger than the upper limit, the strength of the body will be reduced when used as a packaging bag, and if the flow ratio is larger than the upper limit, the heat sealing strength will be reduced, which is preferable.

Incidentally, the above-mentioned ultra-low density polyethylene also includes a terpolymer copolymerized with ethylene, an α-olefin having 3 or more carbon atoms, and a non-conjugated diene. Examples of such non-conjugated dienes include /,←-hexadiene, cyclobentadiene, ethylidenenorbornene, and the like.

The melt index of the above linear low density polyethylene is (Mla), the density is (ρa), the blending ratio is A7% weight l, and the mel I index of the ultra low density polyethylene is (Mlb), the density is (ρb) , when the blending % ratio is B weight l, the following formula /00? ．． 3. ! ;--1β≧o (1
) However, it is necessary to adjust the mel index, density, and blending ratio of the linear polyethylene and ultra-low density polyethylene to satisfy the above formula, and if the above formula is not satisfied, the body strength will decrease when used as a packaging bag. Therefore, it is not desirable.

The blending ratio of the linear low-density polyethylene and the very low-density polyethylene is Qκ of the linear low-density polyethylene, and is used within a range that satisfies the above (1) to (III).

If the amount of the ultra-low density polyethylene is less than the lower limit, the body strength will be insufficient when used as a packaging bag, and if it is more than the upper limit, the rigidity will be insufficient when used as a packaging bag, which is not preferable.

A film formed using such a composition is compared with a film formed using a composition in which a high molecular weight component is produced by modifying linear low-density polyethylene with an organic peroxide, for example. As a result, problems such as off-odor and gel originating from organic peroxides are eliminated, and the surface gloss of the film is suppressed, resulting in a film with excellent marketability.

Merely inflation molding the above-mentioned polyethylene composition does not provide a good heat-sealed part strength, and specific shaping conditions are required for shaping.

The specific molding conditions include a blow-up ratio of 0.9 to λ
, the draft rate is 3~←O, and the cooling rate index is 3θ
Inflation is to be treated as less than a second.

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

During the ceremony, The symbols are as follows.

In addition, the cooling rate index is the time (seconds) it takes for the molten resin to reach the 7 lost line after it is extruded from the die, and is obtained by the following formula.

FLH: v0: Cooling rate index (seconds) Frost line height (α) Linear velocity when molten resin passes through the lip (crrL/see) v1: Take-up speed (bi/sec) Blow-up ratio to 2.0 If this is the case, shrinkage in the longitudinal direction of the heat seal will occur during heat sealing, and distortion will occur in the direction opposite to the orientation of the bag body, resulting in a decrease in the strength of the heat-sealed end of the resulting bag, leading to breakage. Cause.

If the draft rate is lower than 1000, good shrinkage will not occur during heat sealing, and if it is higher than qo, the molecular orientation of the body of the bag will become 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 by draft during film molding will be relaxed due to thermal relaxation, and no contraction will occur during heat sealing, resulting in a loss of strength in the heat sealed portion.

Note that heat bars, heat bells, etc. are used for heat sealing, but if the heat sealed part is extruded for a long time with these heating machines, thermal relaxation will occur and the strength of the heat sealed part will not be achieved, so please use l30. A heat-sealing method in which the heat-sealed part is heated quickly by applying as much pressure as possible to the heat-sealed part at a temperature of about 210°C, and then the heat-sealed part is left in a free state to cause the heat-sealed part to contract. It is preferable to use

〔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 1 (a) Production melt index of packaging bag is 0. G? //0 minutes, flow ratio is 20
, the density is 0.9. A raw material was prepared by dry blending linear low-density polyethylene with a melt index of 60% by weight and 80% by weight, which was produced by a gas phase process with a hexene/content of t% by weight in a 7t y lcd copolymer. This was transferred to a Modern Machinery Delsa & 5O type extruder with an annular slit diameter of 2. 0 0 t
Using a tvnn inflation molding machine equipped with an inflation die and cooling air ring, the extrusion amount/
0 0 Kg/h. r, blow-up ratio (B.U.
．． R. )/． q. Under the condition of draft rate 6.5, change the amount of air blowing from the air ring and increase the cooling rate number to 2g.
I got a 110μ blown film.

4 Rah. Lengthen the tine inflation film A7
Cut it into a cylindrical film of 07y1ms @lIda0, and use New Long's HS 2u3-type heat sealer (heating part length!!rOrran, heating part clearance 0.3mm, cooling part length: /!; Ortan, Heat 1 seal temperature (heated part surface temperature) is 220°C, cooling part temperature is 30°C,
One of the openings of the cylindrical film was heat-sealed at a position 8 mm from the end under the condition of a film feed speed of tsm/sec. The film was thicker than the original.

The obtained bag was filled with 20 kg of fertilizer, and the opening was heat-sealed under the same conditions as described above, and the bags were left to accumulate for ~1 hour to obtain a packaging bag for a drop bag test.

(b) Performance test of packaging bag The packaging bag obtained in (a) above was subjected to a horizontal drop bag test and a vertical drop bag test using the following method.

The drop conditions are room temperature, -0°C for the horizontal drop bag test, -s°C for the vertical drop bag test, and the drop height/. ! fm,/number of drops per bag S 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 IIC.

(a) Side drop bag test A test was conducted by dropping 20 bags (sideways drop) with the body of the packaging bag parallel to the floor and the heat-sealed part hanging approximately perpendicular to the floor to determine the bag breakage rate. I asked for it. Note that the side-drop bag test was conducted to measure the strength of the heat-sealed portion of the bag.

(b) Vertical drop bag test A test was conducted by dropping 20 bags (vertical drop) with the heat-sealed part of the packaging bag parallel to the floor and the body almost perpendicular to the floor to determine the bag breakage rate. I asked for it. The vertical drop bag test was conducted to measure the strength of the body of the bag.

Examples 2 to 3 Examples 2 and 3 were carried out in the same manner as in Example /j/(except that the physical properties and formulation conditions of the raw resin were changed as shown in Table 1.The results are shown in Table 1).

Comparative Examples 1 to S Linear low-density polyethylene produced by copolymerization with the α-olefin shown in Table 1 by the process shown in Table 1 was used, except that the blend of raw materials and molding conditions were changed as shown in Table 1. , in the same manner as in Example-7.

The results are shown in Table 7.

〔Effect of the invention〕

According to the method of the present invention, a bag can be obtained which has excellent body strength and excellent heat-sealed strength, and is suitable for use as a bag for packaging heavy items such as fertilizers and synthetic resin pellets.

Claims (1)

[Scope of Claims] (1) Ethylene and carbon number 6 using a gas phase polymerization process
The melt index obtained by copolymerization with α-olefin is 2 g/10 minutes or less, and the density is 0.930 to 0.
Linear low-density polyethylene 50-90% by weight with a flow rate of 950 g/cm^3 and a flow ratio of 35 or less, a melt index of 2 g/10 minutes or less, and a density of 0.910 g/c
m^3 or less and 10 to 50% by weight of an ethylene copolymer having a fluidity ratio of 35 or less, and the melt index of the linear low density polyethylene is (MIa
), the density is (ρa), the blending amount is A weight %, and the melt index of the above ethylene copolymer is (MIb
), the density is (ρb), and the blending amount is B weight %, the composition obtained by blending both is expressed by the following formula (I) to (III) 93.5-100/α-β≧0 (I) However, α=A/(A+B)・1/(ρa)+B/(A+B)・
1/(ρb)(II)β=2/1log{((MIa)・
(MIb)} Using a composition that satisfies (III), inflation molding was performed under the conditions of 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 or less. A method for manufacturing a packaging bag, which comprises heat sealing and cutting a cylindrical film along a direction intersecting a take-up direction.