JPH03136831A - Preparation of packing bag - Google Patents

Abstract

PURPOSE:To obtain a packing bag having good heat-sealing strength and body part strength by subjecting modified linear low density polyethylene specified in its physical properties to inflation molding and heat sealing under a specific condition. CONSTITUTION:0.0001 - 0.1pts.wt. of a radical generating agent is compounded with 100pts.wt. of a linear low density polyethylene or polyethylene mixture consisting of 100 - 60pts.wt. of linear low density polyethylene wherein a melt index is 2.0g/10 min or less, density is 0.910 - 0.945g/cm<2> and a flow ratio is 35 or less prepared by the copolymerization of ethylene and 6C alpha-olefin due to a gaseous phase polymerization process and 0 - 40pts.wt. of branched low density polyethylene wherein a melt index is 1.9g/10 min or less, density is 0.915 - 0.930g/cm<2> and a flow ratio is 50 or less to modify said mixture and the modified mixture is subjected to inflation molding under such a condition that a blow-up ratio is 0.9 - 2.0 and a draft ratio is 5 - 40 or said mixture is subjected to inflation molding under the same condition while modified by the above mentioned method. The cylindrical film thus obtained is heat-sealed and cut along the direction crossing a taking-up direction.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method of manufacturing a packaging bag.

Specifically, the present invention relates to a method for manufacturing a packaging bag with high heat seal strength and body strength using modified linear low density polyethylene having improved properties.

[Conventional technology and its problems]

Normally, when packaging bags are manufactured using linear 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.
Linear 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 may undergo heat shrinkage. However, the film thickness decreases and heat sealing strength is not achieved.

Therefore, 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 added a specific amount of a specific branched low-density polyethylene to linear low-density polyethylene of the characteristic. It was discovered that a packaging bag with good heat-sealing strength could be obtained by blending, inflation molding and heat-sealing under specific conditions, and this was previously proposed in JP-A-60-180825. Furthermore, the heat-sealing strength was significantly improved by inflation molding and heat-sealing the mixture of linear low-density polyethylene and branched low-density polyethylene described above with a radical generator under specific conditions. The inventors discovered that a packaging bag with the same characteristics could be obtained, and proposed it in Japanese Patent Application Laid-open No. 183132/1983.

However, although the strength of the heat-sealed part of the packaging bag is greatly improved with the above proposed method, - the strength of the body part of the bag is not sufficient and when the film thickness is reduced,
It has been found that this leads to the problem that the packaging bag tends to tear vertically (easily split vertically).

[Means for solving problems]

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, linear low-density polyethylene with specific physical properties obtained by a specific polymerization method, that is, a gas phase polymerization process, is used and a specific polymer obtained by reacting it with a radical ordering agent is used. They discovered that a packaging bag with good heat-sealing strength and body strength can be obtained by inflation-molding and heat-sealing modified linear low-density polyethylene having the following physical properties under specific conditions, and completed the present invention. reached.

That is, the gist of the present invention is that a melt index of 2.0 g/10 minutes or less and a density of 0.910 to 0.000 g/10 minutes or less are produced by copolymerizing ethylene and an α-olefin having 6 carbon atoms using a gas phase polymerization process. 100 to 60 parts by weight of linear low density polyethylene with a melt index of 1.9 g/10 minutes or less, a density of 0.915 to 0.930 g/cm', and a flow ratio of 945 g/cm' and a flow ratio of 35 or less. Linear low density polyethylene or polyethylene mixture 1 consisting of 50 or less branched low density polyethylene O to 40 parts by weight
1 to 0.1 parts by weight of a radical generator is added to 00 parts by weight, and then the radical generator is reacted with the linear low-density polyethylene or polyethylene mixture to achieve a melt index (Ml loss of 1.0 g/10 minutes or less). , the fluidity ratio is 100 or less, the value of (M 1 2) / (MI1) is 0.1 to 0.9, and the following formula % formula %) (However, (MI1) is a linear low density Apparent melt index of polyethylene or polyethylene blends 93.5-1
00 (ρt) is the melt index of the density (g/am3) of the modified linear low-density polyethylene or polyethylene mixture, and (ρ2) is the melt index of the modified linear low-density polyethylene or polyethylene mixture after or after modification. Blowup ratio 0.9~2.0, draft rate 5~
The method of manufacturing a packaging bag is characterized by carrying out inflation molding under the conditions of 40, heat-sealing and cutting the obtained cylindrical film along a direction intersecting the take-up direction.

The present invention will be explained in more detail below.

The linear low density polyethylene used in the present invention includes:
By applying a gas phase polymerization process using a fluidized bed reactor, stirring reactor, tubular reactor, etc., ethylene and α-olefins having 6 carbon atoms, such as hexene and 4-methylpentene-1, etc. About 4-17% by weight, preferably 5-15%
% by weight.

As the catalyst, a Ziegler-type catalyst or a Phillips-type catalyst, which is usually used in the production of medium-low-quality high-density polyethylene, is used.

The linear low-density polyethylene thus obtained forms a short chain branched structure with the above copolymer components, and the density is appropriately reduced by utilizing this short chain branching to 0.910~
The polyethylene has a linearity of about 0.945 g/era" and has 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 No. 5
The method described in No. 4-148093, No. 54-154488, 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 is obtained by copolymerizing ethylene and an α-olefin having 6 carbon atoms using the above-mentioned gas phase polymerization process, and has a melt index (MI1) of 2 g/ 10 minutes or less, preferably 0.1 to 2.0 g/10 minutes, more preferably 0.3
~1.5g/10min range, density (ρI) is 0.910
~0.945 g/cs' preferably 0.915~0.
940 g/cs3 and a fluidity ratio of 35 or less, preferably 15 to 30 is used.

In the method of the present invention, a radical generator is further added to the above-mentioned linear low-density polyethylene, the radical generator is decomposed and reacted with the polyethylene, and then inflation molding is performed.

The radical generator added to the linear low-density polyethylene has a decomposition temperature of 130°C to 300°C with a half-life of 1 minute.
℃ range, such as dicumyl peroxide, 2,5-dimethyl-2,5 di(t-butylperoxy)hexane, 2,5-dimethyl-2,5 di(t-butylperoxy) hexin-3,α,α′-bis(t-
butylperoxyisopropyl)benzene, dibenzoyl peroxide, di-t-butyl peroxide, and the like.

The amount of the radical generator added is selected from the range of o, oooi to 0.1 parts by weight based on the linear low density polyethylene, but if this amount is less than 0.0001 parts by weight, the obtained The strength of the heat-sealed part of the packaging bag is almost the same as that without additives, and if the amount is more than 0.1 part by weight, the melt index will be too low and film breakage will easily occur during film forming. This is not preferable because it causes roughness on the surface of the film.

However, when the amount added is in the range of 0.002 to 0.02 parts by weight, the film formability and the strength of the heat-sealed portion are significantly improved, so it is preferable.

In the present invention, there are no particular 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, it can be carried out by the following method). be able to.

(1) During inflation molding, the linear low density polyethylene and the radical generator are fed simultaneously or sequentially and melt extruded.

(2) Using a kneading machine such as an extruder or a Banbury mixer, the linear low-density polyethylene and the radical generator are kneaded and reacted, and then pelletized, and the pellets are used to make inflation silane. Shape.

(3) A masterbatch containing a large amount of a radical generator (a large amount of a radical generator is added to polyethylene such as high density polyethylene, branched low density polyethylene or linear low density polyethylene at a temperature above the melting point of the polyethylene,
A master bunch of polyethylene containing a high concentration (usually about 200 to 20,000 pp-) of a radical generator, which is melt-kneaded at a temperature at which the polyethylene does not react with the radical generator, for example, at a temperature of 130 to 160°C.
This master bunch is blended with the above linear low-density polyethylene and then inflation molded.

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

By reacting the above-mentioned linear low-density polyethylene with a radical generator, a modified polyethylene in which the polyethylene undergoes a crosslinking reaction, the high molecular weight component is increased, and the melt index is decreased is obtained. The modified polyethylene has improved film formability compared to unmodified linear low-density polyethylene, and is easily oriented in the longitudinal direction during inflation molding, and the film obtained in this way is oriented in the direction in which it is oriented during heat sealing. This is preferable because it shrinks to a thickness greater than the original thickness of the film and improves the strength of the heat-sealed portion.

In the crosslinking reaction using the above radical generator, the melt index (Ml, ), density (ρt), fluidity ratio (MF
Rl) is set within the following range.

(MtZ) is 1.0g/10min or less, preferably 0.0
5 to 1.0 g/10 minutes, more preferably 0.2 to 0.
7g/10 minutes, (MFRl) is 1°O or less, preferably in the range of 15 to 70, and (Mlz)/(
At the same time, the density (ρ1) of the linear low density polyethylene is adjusted so that the value of Ml, ) is 0.1 to 0.9 and the following formula (% formula %) is satisfied. Select.

If the melt index (Ml, ) and (Ml, ) exceed the above ranges, the heat sealing strength and body strength when used as a packaging bag will decrease, which is not preferable. In addition, the flow ratio (M
If FR, ) and (MFRz) are more than the above range, (M
I! )/(M!+) exceeding the above range is not preferable because the strength of the body portion when used as a packaging bag decreases. Furthermore, it is preferable that the density of the above-mentioned linear low-density polyethylene is in the range of 0.910 to 0.945 g/cs'' from the viewpoint of rigidity and impact resistance when used as a packaging bag.

Furthermore, if (Ml, ) and (ρ2) do not have a relationship that satisfies the above equation, the strength of the body portion when used as a packaging bag will decrease, which is not preferable.

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

In the method of the present invention, the melt index is JIs
It is a value measured at 190°C in accordance with K6760, and the flow ratio is a shear force of 10S dynes/c11! using the above-mentioned melt index measuring device. (load 11132) and 106
Ratio of extrusion amount of dyne/cIat (load 111312) (
g/10 minutes) and is calculated as Also, density JIS
This is a value measured in accordance with K6760.

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.

In the present invention, in order to improve the moldability of the linear low-density polyethylene, a small amount of branched low-density polyethylene is added, for example, 0 to 40 parts by weight, preferably 5 to 30 parts by weight, per 100 parts by weight of the linear low-density polyethylene. More preferably 1
It is considered to be blended in a proportion of 0 to 30 parts by weight.

The branched low-density polyethylene blended into 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 xeno, propylene, octene, and 4-methylpentene-1. The copolymerization amount of the copolymerization component is 0.5 to 18% by weight, preferably 2 to 18% by weight.
It is about 10% by weight. These low-density polyethylenes are preferably obtained by radical polymerization using a radical generator such as oxygen or an organic peroxide using a conventional high-pressure method (1,000 to 3,000 kg/am'').

The branched low density polyethylene has a melt index of 1.9 g/10 minutes or less, preferably 0.1 to 0.5 g/10 min.
In the range of 10 minutes, the flow ratio is 50 or less, preferably 30-5
A value in the range 0 is used. If the melt index exceeds the above range, the body strength and/or
Otherwise, it is undesirable because the heat seal strength decreases.

Furthermore, if the flow ratio exceeds the above range, it is not desirable because the strength of the body of the bag decreases when it is made into a packaging bag.

Furthermore, the above-mentioned branched low-density polyethylene has a density of 0.9
A range of 15 to 0.930, particularly 0.915 to 0.925, is desirable from the viewpoint of improving the body strength and heat sealing strength of the bag when used as a packaging bag.

A radical generator was added to 100 parts by weight of linear low-density polyethylene or a mixture of linear low-density polyethylene and branched low-density polyethylene.

1 to 0.1 part by weight is added, and then a radical generator is reacted with the polyethylene mixture to modify the mixture.

Modified polyethylene mixture (the modified mixture has a melt index (Ml-t) of 0 minutes or less, a flow ratio of 100 or less, and a value of <MIz)/(MID) of 0.1 to 069. , and the following formula % formula %) (However, (MID) is the apparent melt index of the polyethylene mixture 93.5-100 (p,) satisfies the value of the density (g/am3) of the modified polyethylene mixture It is necessary to.

Even if the above-mentioned modified polyethylene, which is obtained by adding a radical-generating agent and a green agent to the above-mentioned linear low-density polyethylene or a blend of linear low-density polyethylene and branched low-density polyethylene, is simply inflation-molded, it cannot be heat-sealed. Good part strength and body strength cannot be obtained, and specific molding conditions are required during molding.

The specific molding conditions include a blow-up ratio of 0°9 to 2.
The method is to carry out inflation molding at a draft rate of 5 to 40.

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

In the formula, the symbols are as follows.

G: Width of the die slit t: Thickness of the obtained film ρIII: Density of the resin extruded from the die slit ρf: Density of the film BIIR Niblow-up ratio during heat sealing with a blow and up ratio of 2.0 or more This causes shrinkage in the longitudinal direction and 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, leading to bag breakage.

If the draft rate is less than 5, good shrinkage will not occur during heat sealing, and if it is greater than 40, the molecular orientation of the body of the bag will become too large in one direction, causing tearing of the body.

In addition, heat bars, heat belts, etc. are used for heat sealing, but if the heat seal part is pressed for a long time with these heating devices, thermal relaxation will occur and the strength of the heat seal part will not be obtained, so A heat-sealing method is used in which the heat-sealed part is heated quickly at a temperature of about 280°C with as little pressure applied to it as possible, and then the heat-sealed part is left in a free state to cause the heat-sealed part to contract. is desirable.

〔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) Manufacturing melt index (MID) of packaging bag is 0.8 g/10
75 parts by weight of linear low-density polyethylene manufactured by a vapor phase process with a fluidity ratio of 20 and a density of 0.929 g/cm2 and a copolymer component of hexene-1, melt index as high-pressure branched low-density polyethylene. is 0.4 g
/ 10 minutes, animal ratio 45, density 0.924 g
/am3, 25 parts by weight, 2.5-dimethyl-2,
30.02 parts by weight of 5-di(t-butylperoxy)hexyne were mixed, and then melt-kneaded using an extruder at 250°C for 3 minutes, extruded, and pelletized. The obtained modified polyethylene had a dynamic property of MI: 0.3 g/10 min and flow ratio: 50. This was made using an inflation molding machine manufactured by Modern Machinery, which was equipped with a delta-shaped 65φ extruder, an inflation die with an annular slit diameter of 200nφ, and a cooling air ring, and an extrusion rate of 50 kg/hr and a blow amplifier ratio (Bull?) of 1.4. , draft rate 6.5
A blown film with a film thickness of 110 μm was obtained under these conditions.

The obtained blown film was cut into a cylindrical film with a length of 670 ms and a width of 440 ms.
mm, heating part clearance 0.3 m, cooling part length 71
50mm, cooling part clearance 1mm), heat sealing temperature (heating part surface temperature) 200℃, cooling part temperature 3
One side of the opening of the cylindrical film was heat-sealed at a position 1.5 cm from the end under conditions of 0° C. and a film feed rate of 15 m/sec.

The resulting bags were filled with 20 kg of fertilizer, and the openings were left open for 18 to 24 hours under the same conditions as the heat seal bags to obtain packaging bags for the 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 dropping conditions were that the room temperature was -5°C, the drop height was 1.5 m, and the number of drops per bag was 5 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 1.

(al) 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 approximately perpendicular to the floor to determine the bag breakage rate. 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.

(c) Film forming stability In the inflation molding described in (a) above, when the extrusion amount was increased, the stable forming limit extrusion amount at which the tubular film in the molten state could be formed into a stable bubble state was measured. The results are shown in Table 1. The larger the stable forming limit extrusion amount is, the better the film forming stability is.

Example 2 The same procedure as in Example I was carried out except that in Example 1 (a), branched low-density polyethylene was not blended and the radical generator was blended at 0.01 part by weight. The results are shown in Table 1.

Example 3 In Example 2, the melt-in-deluxe produced by the vapor phase process as linear low-density polyethylene was 1.0
g/10 min, flow ratio 18, density 0.923 g/c
The same procedure as in Example 2 was carried out, except that a material having physical properties of "m" was used and the radical generator was mixed in an amount of 0.04 parts by weight. The results are shown in Table 1.

Example 4 Melt index of linear low density polyethylene manufactured by vapor phase process in Example 2 is 1.0 g
/10 minutes, flow ratio 18, density 0, 931 g/c
The same procedure as in Example 2 was carried out except that a material having physical properties of "ra" was used and the radical generator was mixed in parts by weight of o and o o s.

The results are shown in Table 1.

Comparative Example 1 In Example 1, linear low-density polyethylene was produced using butene as a copolymerization component in a vapor phase process, with a melt index of 0.5 g/10 min, a fluidity ratio of 24, and a density of 0. The same procedure as in Example 1 was carried out, except that a material having a physical property of 922 g/3 was used, and the radical generator was changed to 0.005 parts by weight, and the branched low-density polyethylene was changed to 15 parts by weight. Ta. Table 1 shows the results.
Shown below.

Comparative Example 2 In Example 2, linear low-density polyethylene was produced using butene as a copolymerization component in a vapor phase process, with a melt index of 1.0 g/10 min, a fluidity ratio of 18, and a density of 0. The same procedure as in Example 2 was conducted except that a material having physical properties of 922 g/cm3 was used and the radical generator was mixed in an amount of 0.0125 parts by weight. The results are shown in Table 1.

Comparative Example 3 In Example 2, 4-methylpentene-1 was used as a copolymerization component in a solution process as linear low-density polyethylene.
The melt index produced using
0 minutes, flow ratio 22, density 0, 935 g/cs'
Using a material with the physical properties of
．． The same procedure as in Example 2 was carried out except that the amount was changed to 0.02 parts by weight. The results are shown in Table 1.

Comparative Example 4 In Example 2, linear low-density polyethylene was produced using butene as a copolymerization component in a high-pressure process, with a melt index of 0.8 g/10 minutes and a flow ratio of 2.
7. The same procedure as in Example 2 was carried out except that a material having a physical property of a density of 0.925 g/cm3 was used and the radical generator was mixed in an amount of 0.02 parts by weight.

The results are shown in Table 1.

Comparative Example 5 In Example 2, linear low-density polyethylene was produced using hexene as a copolymerization component in a gas phase process, with a melt index of 1.1 g/10 minutes, a flow ratio of 30, and a density of 0. The same procedure as in Example 2 was carried out except that a material having a physical property of .942 g/as' was used and the radical generator was mixed in an amount of 0.02 parts by weight.

The results are shown in Table 1.

Comparative Example 6 In Example 2, linear low-density polyethylene was produced using hexene as a copolymerization component in a vapor phase process, with a melt index of 1.1 g/10 min, a flow ratio of 30, and a density of 0. The same procedure as in Example 2 was carried out except that a material having physical properties of 930 g/3'' was used and the radical generator was mixed in an amount of 0.05 parts by weight.

The results are shown in Table 1.

Comparative Example 7 In Example 2, linear low-density polyethylene was produced using hexene as a copolymerization component in a vapor phase process, with a melt index of 0.8 g/10 minutes, a flow ratio of 20, and a density of 0. The same procedure as in Example 2 was conducted except that a material having physical properties of 929 g/C11' was used and no radical generator was blended.

The results are shown in Table 1.

〔Effect of the invention〕

According to the method of the present invention, by inflation molding under specific conditions using modified linear low density polyethylene having specific physical properties obtained by reacting specific linear low density polyethylene with a radical generator, A packaging bag having good heat seal strength and body strength can be obtained.

Further, in the present invention, even if a specific amount of a specific branched low-density polyethylene is blended, it is possible to obtain a film having similarly good heat seal strength and body strength.

Claims (1)

[Scope of Claims] (1) Manufactured by copolymerization of ethylene and α-olefin having 6 carbon atoms using a gas phase polymerization process, the melt index is 2.0 g/10 min or less, and the density is 0.910 to 0.910.
100 to 60 parts by weight of linear low density polyethylene with a flow ratio of 0.945 g/cm^3 and 35 or less, a melt index of 1.9 g/10 minutes or less, and a density of 0.915 to 0.
Add 0.0001 to 0.1 parts by weight of a radical generator to 100 parts by weight of linear low density polyethylene or polyethylene mixture consisting of 930 g/cm^3 and 0 to 40 parts by weight of branched low density polyethylene with a fluidity ratio of 50 or less. The melt index (
MI_2) is 1.0 g/10 minutes or less, the flow ratio is 100 or less, and the value of (MI_2)/(MI_1) is 0.1 to
0.9, and the following formula 93.5-100(ρ_2)-log(MI_2)≧0
(However, (MI_1) is the apparent melt index of linear low density polyethylene or polyethylene mixture, (
ρ_2) is the value of the density (g/cm^3) of the modified linear low-density polyethylene or polyethylene mixture) after or during blow-up of the linear low-density polyethylene or polyethylene mixture. Ratio 0
．． 9 to 2.0 and a draft rate of 5 to 40, and the resulting cylindrical film is heat-sealed and cut along the direction intersecting the take-up direction. Production method.