JPS60183132A - Preparation of packing bag - Google Patents

Abstract

PURPOSE:To enhance a heat sealing property to a large extent, by applying decomposition reaction to a composition consisting of branched low density polyethylene having specific characteric values and a radical generating agent before applying inflation molding thereto under a specific condition. CONSTITUTION:A composition, which consists of 95-30pts.wt. of linear low density polyethylene with a melt index of 10g/10min or less, 5-70pts.wt. of branched low density polyethylene with a melt index of 0.1-2g/10min and a flow ratio of 30-70 and 0.0001-0.1pts.wt. of a radical generating agent, is prepared and inflation molding is applied to said composition under such a condition that a blow-up ratio is 0.9-2.0, a draft ratio is 10-40 and a cooling speed index is 30sec or less while the radical generating agent in the composition is decomposed to be reacted polyethylene and the obtained cylindrical film is heat sealed and cut so that the direction crossing the take-up direction of said film is set as a longitudinal direction to obtain a packing bag.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a packaging bag. Specifically, the present invention relates to a method of manufacturing a packaging bag with high heat-sealing strength using door-shaped low-density polyethylene.

Normally, when packaging bags are manufactured using axial low-density polyethylene by inflation molding and heat sealing, the body of the bag is strong, but the strength of the heat sealing part is extremely low, which poses a practical problem. .

This is due to the molecular structure of linear low-density polyethylene, which will be explained later.
Even if you try to make linear low-density polyethylene e have heat shrinkability by imparting molecular orientation to it by melt-stretching, etc., you cannot 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-sealing strength using linear low-density polyethylene, the inventors of the present invention discovered that a specific forest-like low-density polyethylene with a specific branched low-density polyethylene It was discovered that a packaging bag with good heat-sealing strength could be obtained by blending the bag and carrying out inflation molding and heat-sealing under specific conditions. As a result of further studies, we found that by reacting the above-mentioned blend of linear low-density polyethylene and branched low-density polyethylene with a radical generator, and performing inflation molding and heat sealing under specific conditions, we were able to improve the heat seal strength. It was discovered that a packaging bag with significantly improved properties could be obtained, and the present invention was completed.

That is, the gist of the present invention is the melt index 7017
10 minutes or less linear low density polyethylene 9S to 30 parts by weight, melt 1712220.7 to 22710 minutes, fluidity ratio 3
0 to 70 branched low-density polyethylene 5 to 0 heavy leaves and radical generator 0. Using a composition consisting of a heavy portion of θooi-o, the radical generator in the composition is decomposed and reacted with the polyethylene, or after the blow-up ratio is 0.9 to 0. Inflation molding is carried out under the conditions of , draft rate / θ ~ da θ, cooling rate index 3θ seconds or less, and the obtained cylindrical film is heated and cut with the longitudinal direction intersecting the drawing direction. ? The manufacturing method of the packaging bag is based on the percentage characteristics.

The present invention will be explained in more detail #1 below.

The linear low-density polyethylene pipe used in the present invention is a copolymer of ethylene and other α-olefins, and the branched low-density polyethylene pipe is manufactured by a conventional high-pressure method.
The fat melts differently. Linear low density polyethylene contains, for example, ethylene and other α-olefins such as butene, hexene,
Octene, decene, dameterpentene-/etc. f4'~/
7″4 ('J8%, preferably !r-/j3i amount) is a mixture of 8 melons and is produced using a Cheedler type catalyst or Phillips δ type catalyst used in the production of medium and low pressure high density polyethylene. A short branched structure is created using a conventional high-density polyethylene pipe copolymer component, and the density is appropriately lowered using the original short chain branching to reduce O0?
/~0.93 f 74, and has more straight button properties than conventional branched low-density polyethylene, and has a structure with more branches than high-density polyethylene.

When such powdered low-density polyethylene is heat-sealed, the shrinkage of the heat-sealed portion is small because the molecular structure of linear low-density polyethylene is short-chain branched, as described above, and during heat-sealing, there is a This is thought to be due to thermal relaxation.

As mentioned above, KN-like low-density polyethylene has low strength in the heat-sealed portion, and in the present invention, a composition consisting of a specific linear low-density polyethylene, a specific branched low-density polyethylene, and a radical generator is used. The heat-sealing strength of linear low-density polyethylene is improved by completely decomposing the radical generator in the material and reacting it with the polyethylene, or after the reaction, by inflation molding under specific conditions, and film forming. This further stabilizes the properties.

That is, the linear low density polyethylene used in the present invention has a melt index of 10 f/10 minutes or less, preferably in the range of 0.2 to t, sy/lo minutes. If the melt index is thicker than 101710 minutes, the strength of the body will decrease when used as a packaging bag, which is not preferable.

In addition, the flow ratio of the linear low density polyethylene is /S~riθ
Especially /S~3! A range of r is desirable from the viewpoint of the strength of the heat-sealed portion.

The branched low-density polyethylene used together with the linear low-density polyethylene includes an ethylene homopolymer and a copolymer of ethylene and other copolymer components.

Copolymerization components include vinyl acetate, ethyl acrylate,
Examples include vinyl compounds such as methyl acrylate, and olefins having 3 or more carbon atoms such as hexene, propylene, octene, and goomethylbentene-1. The copolymerization amount of the copolymerization component is O, S~/gg%, preferably 1~1
It is about 0MM9b. These branched low-density polyethylenes are obtained by radical polymerization at a high pressure of f10θO to 5θ00Jry/cr/ using a radical generator such as oxygen or an organic peroxide as a catalyst. Among these branched low-density polyethylenes, the vinyl acetate content is preferably λ~/(771ti%)
Particularly preferred are ethylene-vinyl acetate copolymers.

The branched low density polyethylene used has a melt index of 0.1 to 22,770 minutes and a fluidity ratio of 30 to 70.

In the method of the present invention, the melt index is JIS K
The flow ratio is a value measured at /9 DC based on A7tθ, and the flow ratio is determined by the shear force to' dyne/Cd (, and the load) using the above-mentioned melt index measuring device.

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.

Is the blending amount of the upper 8-pin linear low-density polyethylene and branched low-density polyethylene linear low-density polyethylene? S~30.
4 parts by weight, preferably tL<' is 90 to 40 parts by weight, and 5 to 0 parts by weight of branched low-density polyethylene, preferably 10-t
Used within the scope of Part 1 of IO Multiple Marriage.

Next, as a radical generator to be added to linear low density polyethylene and branched low density polyethylene, it is preferable to use a radical generating agent having a decomposition temperature in the range of 13oC to JOOT:: with a half-life of 1 minute, such as dicumyl peroxide, , S-dimethylco, S di(1-butylperoxy)hexane 1
．． l, t-dimethyl-, 3-di(t-butylperoxy)hexyne-3, α, α'-bis(1-butylbaroxyisoglobil)benzene, dibenzoyl peroxide, di-t-butyl peroxide, etc. can be mentioned.

The amount of the radical generator is O0θ with respect to the total amount of the linear low density polyethylene and branched low density polyethylene.
It is selected from within the range of 00/~0.1M image area, but when this blending amount is larger than the image area of o, ootz amount, the strength of the heat-sealed part of the packaging bag obtained is almost the same as that of the non-added one. In addition, if it is more than 0.7 parts by weight, the melt index becomes too low and film breakage is likely to occur during film forming, and roughness occurs on the entrance surface of the film, which is not preferable. .

However, this addition amount is 0.00--0. , 01 parts by weight is preferable because the film formability and the strength of the heat-sealed portion are significantly improved.

In addition, there are no particular restrictions on the method of decomposing the radical generator and reacting it with the polyethylene.
The example can be implemented in the following way.

(υ During inflation molding, the above-mentioned glandular low-density polyethylene, branched low-density polyethylene, and radical generator are fed simultaneously or one after another and melt-extruded.

(2) Using a mixer such as an extruder or a Banbury mixer, the linear low density polyethylene, branched image density polyethylene and radical generator are kneaded and reacted, and then formed into pellets, and the pellets'f are used. and then perform inflation molding.

(3) A masterbatch containing a large amount of a radical generator, that is, a large amount of a radical generator (usually about 3,000 to 110,000 pp) is blended with polyethylene such as powdered low-density polyethylene, branched low-density polyethylene, and high-density polyethylene, A masterbatch in the form of a pellet is prepared in advance by bath melt-kneading at a temperature above the melting point of polyethylene at which the radical generator hardly reacts with polyethylene, and this masterbatch is mixed with the linear low-density polyethylene and branched low-density polyethylene. Blend density polyethylene and perform inflation molding.

Further, the radical generator itself may be used as it is or dissolved in a solvent.

By reacting the linear low-density polyethylene and the branched low-density polyethylene with a radical generator, the polyethylene undergoes a crosslinking reaction and the high molecular weight component increases,
In addition, modified polyethylene with a reduced melt index is obtained.

The modified polyethylene is more easily oriented in the longitudinal direction during inflation molding than a blend of unmodified annular low-density polyethylene and branched low-density polyethylene, and the film thus obtained is oriented during heat sealing. It is assumed that the film shrinks in the direction of the film, making the heat-sealed part thicker than the original thickness of the film, improving the strength of the heat-sealed part.

Furthermore, when a blend of unmodified linear low density polyethylene and branched low density polyethylene having the same melt index as the modified polyethylene is compared, the modified polyethylene has higher heat seal strength. This is presumed to be because the modified polyethylene contains more high molecular weight components that are effective in improving seal properties.

Furthermore, when linear low-density polyethylene is reacted alone with a radical generator, the crosslinking reaction proceeds rapidly, making it difficult to control the crosslinking reaction, but in the method of the present invention, linear low-density polyethylene and branched Since the radical generator is reacted in the presence of the density polyethylene, the crosslinking reaction can be easily controlled, and the heat seal strength does not deteriorate. Furthermore, by blending branched low-density polyethylene, the melt tension of the modified polyethylene increases, and extrusion-tv
Even when it is increased, the film formability is further stabilized, such as improving bubble stability and uneven thickness, so it is preferable.

In the crosslinking reaction using the radical generator of H[:, the melt index of the modified polyethylene obtained by the crosslinking reaction should be in the range of θ, / ~ 1v7io min, especially in the range of θ,co ~ O1ri f/ / 0 min. It is desirable to adjust the blending amount of the radical generator.

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

The specific molding conditions include molding with a blow-up ratio.

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

In the formula, the symbols are as follows.

In addition, the cooling rate index refers to the rate at which the molten resin is extruded through the die.
This is the time (seconds) until the 0-strike is reached, and is obtained by the following formula.

τ: Cooling rate index (seconds) Fld (: frost line height crn) Vo: Linear velocity when molten resin passes through lip part 'f (G1n/s)
ec) ■1: Take-up speed (cm/5ec) If the blow-up ratio is set to 2.0 or more, shrinkage in the longitudinal direction of the heat seal will occur during heat sealing, causing distortion in the direction opposite to the orientation of the bag body. This reduces the strength of the heat-sealed edges of the bag and causes the bag to break.

If the draft rate is less than 10, good shrinkage will not occur during heat sealing, and if it is greater than lIo, the molecular orientation of the body of the bag will be too large in one direction, which will cause 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 belts, etc. are used for heat cooling, but if the heat-sealed part is pressed for a long time using these heating methods, thermal relaxation will occur and the strength of the heat-sealed part will not be achieved. Heat-sealing that causes contraction in the heat-sealed part by heating the heat-sealed part quickly at a temperature of about 230 to 2 gO'Q while minimizing pressure on the heat-sealed part, and then leaves the heat-sealed part in a free state. It is preferable to use a method.

The F3A of the present invention will be explained in more detail by showing examples below, but the present invention is not limited to the following examples unless the gist thereof is exceeded.

Example 1 Linear low density polyethylene (melt index (MI)
: o, sr/10 minutes, flow ratio knee〇, density: 0.9 pieces/
f/cm, copolymerization component: Pute/-l.

Copolymerization amount: 70% by weight) go weight part and high pressure branched low density polyethylene (melt index: 0.'I
f / / 0 minutes, flow ratio: 4 / evening, density: o, q body f / 7): 10 parts by weight of λ, 5-dimethyl-,2,j
cy(t-butylperoxy)hexyne-30,0/,
The Ik@ portion was mixed and then melt-kneaded in an extruder at 210C for 3 minutes to form extrusion pellets.

The obtained modified polyethylene was Mx:o, 3-710 minutes,
It had all the physical properties of flow ratio: J.

This was carried out using a Delsa 6sφ extruder manufactured by Modern Machinery Co., Ltd. ((
Extrusion 1) yo using an inflation molding machine equipped with an inflation die with an annular slit diameter of 2 kOyHφ and a cooling air ring.

Jcf/hr, blow-up ratio (B, U, R,
) Under the conditions of l, t and draft rate l da, change the amount of air blown out from the air ring, and calculate the inflation dilum of lSθμ as the cooling rate index cog? ＋”J.

Obtained blown film length &70cnt
, Cut it into a cylindrical film with a width lItiocm, and cut it into a cylindrical film with a width lItiocm. /W
l) % - Under the conditions of heat sealing temperature (heating part surface temperature) of 2soC, cooling part temperature of 30C, and film feed speed t sm/sec, one of the openings of the cylindrical film is ljσ from the end. The heat-sealed part shrinks in the direction of film take-up (vertical direction).
It was thicker than the original film thickness.

The resulting bag was filled with cocoon fertilizer, and the opening was heat-sealed under the same conditions as described above to obtain a packaging bag for the drop bag test.

In the drop bag test, a bag filled with 2Q# fertilizer was heat-sealed and left to stand for an is-long time. A test was conducted by dropping 20 bags (sideways drop) in such a manner as to determine the bag breakage rate.

The falling conditions were Anonkai-IOC, a falling height of 74 m, and the number of falls j times per 7 bags. The sand bag rate was calculated as the percentage of bags that were torn out of the nine packaging bags used in the test.

Thickness unevenness is determined by measuring the thickness of the obtained cylindrical film at 36 points equally spaced in the circumferential direction using a dial gauge, and when the obtained measured value is within ±io% of the average value of the measured values. ?
○, if it is greater than ±io% and within ±is% of the average value; △, if it is greater than ±/j%? It was set as ×.

The results are shown in Table 1.

Example λ In Example/, lSOμ was the same as Example 1 except that the blow-up ratio was /J and the cooling rate index was 76.
A blown film was obtained. Next, Example 1
The bag breakage rate and uneven thickness were measured in the same manner as above.

The results are shown in Table 1.

Example 3 Linear low-density polyethylene (MI: /, 02770 minutes, flow ratio knee 〇, density: 0.9 of/crl, copolymerization component nibten-11 copolymerization amount: 10% by weight) tro weight part and high pressure Branched low density polyethylene (MI: 0
, 4If//θ min, flow ratio: da j1 density: 04xps'
/d)-0 parts by weight contain co, S-dimethylco, s-di(t-
Butylperoxy)hexyne-30 (7.7 parts by weight) was mixed and then melt-kneaded in an extruder at λSOC for 3 minutes to form extrusion pellets.

The resulting nine-modified polyethylene had an MI of 0.31710 minutes,
It had a physical property of fluidity ratio: 2g.

Blowup ratio of the modified polyethylene pipe: 1. Inflation molding was carried out under the conditions of /, draft rate: Koda, and cooling rate index of 16 to obtain an isoμ in7 region film. Next, the bag breakage rate and uneven thickness were measured in the same manner as Example M/.

The results are shown in Table 7.

Comparative Example 1 - The fc linear low density polyethylene tube used in Example 1 was used and molded under the same conditions as Example 1 (Comparative Example 1) or the same conditions as Example (Comparative Example 2), and a film of lSOμ was produced, respectively. I got it. Then, the bag breakage rate and uneven thickness were measured in the same manner as in Example.

The results are shown in Table 1.

Comparative Example 3 Using a blended resin tube made by mixing the linear low density polyethylene used in Example 1 and the high-pressure branched low density polyethylene, molding was performed according to the same instructions as in Example / to obtain a film of /kOμ. .

Next, the bag breakage rate and uneven thickness were measured in the same manner as in Example 1.

The results are shown in the first column.

Comparative Example A blend resin obtained by mixing the linear low density polyethylene used in Example 3 and the branched low density polyethylene produced by the single-pressure process was molded under the same conditions as in Example J to obtain a film of /3θμ.

Next, the bag breakage rate and uneven thickness were measured in the same manner as in Example 1.

The results are shown on the first page.

Continuing from page 1 ■Int, C1,' Identification code Internal reference number - Ding υa
(Voluntary) (! 1961 Mitsubishi Kasei Professional Co., Ltd. Specification-1-1 Detailed Description of the Invention Column 1

Claims (1)

[Claims] (1) Linear low-density polyethylene with a melt index of 1oy7iθ or less? 3 to 30 parts by weight. Melt index 0.7-29710 minutes, flow ratio 30
~70 parts by weight of branched low density polyethylene and a radical generator O0θθθ/~0. Using a composition consisting of 2 parts / 2 parts, the radical generating agent in the composition is decomposed and reacted with the polyethylene, or after reacting, the blow amplifier ratio is 0.9 to 0.9 to 71.・Rate 10~
production of a packaging bag, which is characterized by inflation molding under the conditions of d θ and a cooling rate index of 30 seconds or less, and the resulting cylindrical film is heat-sealed and cut with the longitudinal direction transverse to the take-up direction. Method. (21m-shaped low-density polyethylene has a density of 0.9 / g ~
The method according to claim 1, characterized in that θ, p3st/cm. (3) Branched low density polyethylene has a density of 0.9/
, t~0. 3. A method according to claim 1 or claim 2, characterized in that the method is of a telOf/cd. (4) Branched low density polyethylene contains vinyl acetate
, Z ~ 7g weight! - The method according to any one of claims 1 to 3, characterized in that the ethylene-vinyl acetate copolymer is an ethylene-vinyl acetate copolymer. (5) Heat sealing The heat sealing part is 23θ ~ 5
Claims 1 to q are characterized in that the films are heated at a temperature of 0C until the films are fused together, and then the heat-sealed part is left in a free state to cause contraction in the heat-cooled part. Any method described.