JPS60180825A - Manufacture of packaging bag - Google Patents

Abstract

PURPOSE:To obtain a packaging bag having a high heat-seal strength by a method in which a linear low-density polyethylene is treated with a radical agent and molded by inflation and heat-sealed under specific conditions. CONSTITUTION:A hundred (100)pts.wt. a linear low-density polyethylene (A) having a melt index of 10g/10min or less is mixed with 0.0001-0.1pts.wt. a radical generator (B) (e.g., dicumyl peroxide preferably). While reacting the components (A) and (B) or after the reaction of the components (A) and (B), the material is molded by inflation under the conditions of 0.9-20 blow-up ratios, 10-40 draft ratios, and 30sec or less cooling rate index. The cylindrical film so formed is heat-sealed and cut in such a way that the direction of crossing the withdrawing direction of the film becomes longitudinal direction to obtain a packaging 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 for producing packaging bags with high heat-sealing strength by inflation-molding and heat-sealing linear low-density polyethylene treated with a radical generator.

Usually, linear low-density polyethylene is inflation-molded and heat-sealed. D. When manufacturing bags for packaging, the chest strength of one bag is strong, but the strength of the heat-sealed part is extremely low, which is a practical problem.

Due to the molecular structure of linear low-density polyethylene, which will be described later,
Reticulated low-density polyethylene cannot be made to have strong shrinkability even if it is made to have heat shrinkability by imparting molecular orientation through melt-stretching, etc., so when heat-sealing is performed, the heat-sealed portion does not shrink due to heat shrinkage. As a result, the film thickness decreases and heat seal 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 present inventors have found that specific linear low-density polyethylene is subjected to inflation molding and heat-sealing under specific conditions. However, as a result of further investigation, it was discovered that the above-mentioned linear low-density positive ethylene was reacted with a radical generator and then subjected to inflation molding and computational sealing under specific conditions. The present invention was completed based on the discovery that a packaging bag with significantly improved heat-cool strength can be obtained.

That is, the gist of the present invention is that the melt index is /θr
0.000/~θ, 1 part by weight of a radical generator is added to 100 parts by weight of linear low-density polyethylene of / /θ min or less, and while the radical generator is decomposed and reacted with the polyethylene, a Hiro reaction is carried out. After that, the blow-up ratio O6
Riko, O, draft rate lθ~aO, cooling rate index 3θ
The method of manufacturing a packaging bag is characterized by carrying out inflation molding under conditions of seconds or less, and heat-sealing and cutting the obtained cylindrical film with the longitudinal direction being in a direction that intersects with the take-up direction.

The present invention will be explained in more detail below.

The door-shaped low-density polyethylene used in the present invention is a copolymer of ethylene and other α-olefins, and is different from the low-density polyethylene resin produced by the conventional 6C1 high-pressure method. Linear low density polyethylene is, for example, ethylene and
Other α-olefins include butene, hexene, octene, decene, damethylpentene, etc.
It is copolymerized to a degree of 3 to 13% by weight, preferably 3 to 13% by weight, and it is produced using a Ziegler type catalyst or Phillips dredging catalyst used in medium and low pressure process high density polyethylene production, and it is not a conventional high density polyethylene. is made into a short branched structure using a copolymer component, and the density is appropriately lowered using the original short chain branching to 0.9/~o, vzt7al
Polyethylene has a more linear structure than conventional low-density polyethylene, and has a more branched structure than high-density polyethylene.

When such linear low-density polyethylene is heat-sealed, the shrinkage of the heat-sealed part is small because the molecular structure of linear low-density polyethylene is short-chain branched as described above, so there is no shrinkage between the molecules during heat-sealing. This is thought to be due to thermal relaxation.

As mentioned above, linear low-density polyethylene has low strength in the heat-sealed portion, and in the present invention, a radical generator is added to a specific linear low-density counterfeit polyethylene, and the radical generator is decomposed to form the linear low-density polyethylene. The heat-sealing strength of the linear low-density polyethylene is improved by inflation molding it under specific conditions while or after reacting with the high-density polyethylene.

That is, the linear low density polyethylene used in the present invention has a melt index of /Ot/ / 0 minutes or less,
Preferably O9-~/,! r f / / in the range of 0 minutes.

If the melt index is larger than /θf / /θ, when a packaging bag is made of a product treated (reacted) with a radical generator, the strength of the body will decrease, and the bag will suffer from thermal relaxation during heat sealing. Shrinkage does not occur and a good heat-sealed part cannot be obtained.

In addition, the flow ratio of #linear low density polyethylene is 73 to 70
．． In particular, a range of K13 to 3S is desirable from the viewpoint of the strength of the heat seal portion.

In the method of the present invention, the melt index is JIS K
The flow ratio is a value measured at 790C in accordance with A-60.The flow ratio is calculated using the shear force lO1'dyne/m (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.

Next, as a radical generator to be added to linear low density polyethylene, the decomposition temperature with a half-life of 7 minutes is /30C ~, y
oor;, for example, dicumyl peroxide, co, j-dimethyl-, di(t-butylperoxy)hexane, co,! -pdimethyl-,2,!
rdi(t-butylperoxy)hexyne-J1α, α′
-bis(t-butylperoxyisopropyl)benzene, dibenzoyl peroxide, di-t-butyl peroxide, and the like.

The amount of the radical generator added is selected from within the range of θ,00θ/~θ,/parts by weight based on the linear low density polyethylene/θθ parts by weight, but this amount is less than 0.0007 parts by weight. In some cases, the strength of the heat-sealed part of the resulting packaging bag is almost the same as that without additives, and in cases where the amount is more than 0.7 parts by weight, the melt index is too low and the film is not formed during film forming. This is undesirable because it tends to break easily and causes roughness on the surface of the core film.

However, this addition amount is o, o o o, t~o, o
A range of r parts by weight is preferable because the film formability and the strength of the heat-sealed portion are significantly improved.

In the present invention, there are many restrictions on the method of adding a radical generator to the linear low-density polyethylene, decomposing the radical generator, and reacting with the polyethylene. For example, the following method may be used. can.

(1) At the time of In7 Rayon molding, the linear low density polyethylene and the radical generator are simultaneously fed and melt extruded.

(The linear low-density polyethylene is reacted with a radical generator using a mixer such as a two-inch extruder or a Banbury mixer, and then formed into pellets, and the pellets are used for inflation molding.

(3) A masterbatch containing a large amount of a radical generator is prepared in advance, and the masterbatch and the above-mentioned linear low-density polyethylene are blended and subjected to inflation molding.

Further, the radical generator itself is used either in its own form or dissolved in a solvent.

By reacting the linear low-density polyethylene with a radical generator, the linear low-density polyethylene undergoes a crosslinking reaction, resulting in modified linear low-density polyethylene in which the high molecular weight component increases and the melt index decreases. can get. The modified linear low-density polyethylene is more easily oriented in the longitudinal direction during inflation molding than unmodified linear low-density polyethylene, and the film thus obtained shrinks in the oriented direction during heat sealing. However, it is presumed that the strength of the heat-sealed portion, which is thicker than the original thickness of the film, is improved.

Furthermore, when comparing modified linear low-density polyethylene with unmodified linear low-density polyethylene having the same melt index, modified linear low-density polyethylene has greater heat seal strength. It is presumed that this is because low-density polyethylene has more high molecular weight components that are effective in improving cool physical properties.

The above linear low density polyethylene is crosslinked so that the melt index of the modified linear low density polyethylene obtained by crosslinking reaction is in the range of o, i to /f/10 minutes, particularly in the range of 0.3 to 0.7 f/10 minutes. It is desirable to react.

Furthermore, simply inflation molding the above-mentioned modified linear low density polyethylene does not provide good heat seal strength, and the molding requires specific molding conditions.

The specific molding conditions and ° have a blowup ratio of 0.9~
-, the draft rate is lθ~daθ, and the cooling rate index is 3
Inflation molding is performed in 0 seconds or less.

Here, it is obtained by the draft rate and the Moriji equation.

In the formula, the symbols are as shown below.

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.

τ: Cooling rate index (seconds) FLH=70 line height (CIL) vo: Linear velocity when molten resin passes through the lip (cIL/sec) V,: ° Take-up speed (cIIL/5eC) Blow-up ratio If it is 2.0 or more, shrinkage in the longitudinal direction of the heat seal occurs during heat sealing, causing distortion 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. It causes bags.

If the ratio is less than IO, good shrinkage will not occur during heat sealing, and if it is over 4IO, the molecular orientation of the body of the bag will be too large in one direction, causing tearing of the body itself. 0 If the cooling rate index exceeds 30 seconds, the molecular orientation that occurs in the film due to draft during film molding will be relaxed due to thermal relaxation, and no shrinkage will occur during heat sealing, increasing the strength of the heat sealed part. This will result in uneven thickness of the film.・Although a heat belt or the like is used for heat sealing, do not press the heat sealed part with these heating machines for a long time. Since thermal relaxation will occur and the strength of the heat-sealed part will not be achieved, heat the heat-sealed part quickly at a temperature of about 130 to -5 OC while minimizing pressure on the heat-sealed part. 1. Leave the heat-sealed part in a free state. It is desirable to use a heat-sealing method that causes the heat-sealed portion to shrink.

The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless the gist of the invention is exceeded.

Example 1 Linear low density polyethylene f melt index (MI)
: OJ 1710 minutes, fluidity ratio J (7, density: O0?cottt7d, copolymerization component nibten-/, copolymerization component 0% by weight) 100 parts by weight, 3-dimethyl-co, 3-di(1
-butylperoxy)hexyne-30,0013 parts by weight were mixed and then co-produced using an extruder. The mixture was melt mixed in OC for 3 minutes and extruded into pellets. What was obtained is MI = O, da f / / 0 minutes, flow ratio = core. This was put into a Delsa 63φ type extruder manufactured by Modern Beak Scenery with an annular slit diameter. Using an inflation molding machine equipped with an rOvmφ inflation die and a cooling air ring,
Extrusion amount/00 kf//hr, blow-up ratio (
B, U, R,) /, /, draft rate/4! By changing the amount of air blown out from the air ring under the following conditions, a blown film of 130μ was obtained with a cooling rate index of 2g.

The obtained blown film was cut into a cylindrical film with a length of 6 mm and a width of 0 cIIL, and was used with New Sun Co., Ltd. 11HEl Coco B--Fine Heat Sealer (heating part length 150cm, heating part clearance 0, J Heat sealing temperature (heating part surface temperature) is calculated using wI, cooling part length Htrθ, cooling part clearance l■). 0C1 cooling section temperature, yor:, film feeding speed/! Under conditions of FIL/sec, one of the openings of the cylindrical film was opened 83 cI from the end.
The heat-sealed portion, which was heat-sealed at the rL position, shrank in the film take-up direction (vertical direction) and became thicker than the original film thickness.

The obtained bag was filled with 10 # of fertilizer, and the opening was heat-sealed under the same conditions as above to obtain a packaging bag for the drop bag test.

In the drop bag test, the bags filled with J0 # fertilizer were left to accumulate for 1-10 hours after being heat-sealed, and then the body of the packaging bag was parallel to the floor and the heat-sealed part was approximately perpendicular to the floor. A test was conducted by dropping 10 bags (sideways drop) in such a manner as to determine the bag breakage rate.

The falling conditions were a room temperature of -5C, a fall height of 8 m, and the number of falls per bag! It was times. The bag breakage rate is the percentage of bags that are broken among the 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 with a dial gauge, and when the obtained measured value is within ±10% of the average value of the measured values. If it is greater than O1±10174 and within ±13% of the average value, Δ, ±l! The case where it is very large is set as X.

The results are shown in Table 1.

Example a In Example 1, the blow-up ratio was set to waste and the cooling rate index was set to 76.
Obtain the 7th inset film of μ. Next, the bag breakage rate and uneven thickness were measured in the same manner as in Example 1.

Using the linear low-density polyethylene used in Example 1, the blow-up ratio, draft rate, and cooling rate index were varied as shown in Table 1, and iz.

A film of μ was obtained.

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

The results are shown in Table 1.

Procedural amendment (own ship) 2 Title of the invention Method for manufacturing packaging bags 5 Target of correction “Detailed description of the invention” column in the statement of claim

Claims (3)

[Claims] (1) 0 parts by weight of linear low-density polyethylene ioθ with a melt index of 1ot7tθ or less
,000/-0.1 part by weight is added, the radical generator is decomposed and reacted with the polyethylene, or after the reaction, the blow-up ratio is 0.9 to 0.01, the draft ratio is 10 to aO1, and the cooling rate is 1. A method for producing a packaging bag, which comprises performing inflation molding under conditions of an index of 30 seconds or less, and heat-sealing and cutting the obtained cylindrical film with the longitudinal direction in a direction that intersects with the take-up direction. (2) Linear low density polyethylene has a density of 0.9/, t
~o, q,? 8. The method according to claim 7, wherein the method is of k Jrg/at. (3) Heat seal the heat seal part.
Claim 1 or 1, characterized in that the heat-sealed portion is caused to shrink by heating at a temperature of oC until the films are fused together, and then leaving the heat-sealed portion in a free state. The method described in section.