JPS60257232A - Manufacture of packaging bag - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 using linear low-density polyethylene with high heat-sealing strength and high body strength.

[Prior art]

Normally, when bags for packaging are manufactured using linear low-density polyethylene by inflation molding and heat sealing, the strength of the body of one bag is high.

There was a practical problem in that the strength of the heat-sealed portion was extremely low.

[Problems that the invention attempts to solve]

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 multi-molecular orientation through melt-stretching, etc., so when heat-sealing is performed, the heat-sealed portion will shrink due to heat. If this happens, the film thickness will decrease and the heat sealing strength will not be as good.

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 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 blending the amount of 4f, molding in 7v-'''a under constant conditions, and heat-sealing strength), and first published a patent application for Sho Jr. -J'3/7r
I proposed the issue. Furthermore, when the mixture of linear low-density polyethylene and branched low-density polyethylene mentioned above was reacted with a radical generator, the heat-sealing strength was significantly improved by inflation molding and heat-sealing under specific conditions. I learned that it was possible to obtain a packaging bag made using the same methods, and applied for a patent application in 1988-370! I proposed this to / issue.

However, although the strength of the heat-sealed portion of the packaging bag is greatly improved with the above proposed method, the strength of the body of the bag tends to decrease, causing the packaging bag to tear vertically or become stuck. It was found that this leads to the problem of vertical splitting and easy filling.

[Failure to solve the problem]

In view of these circumstances, the present inventors have investigated both the heat seal strength and body strength of the packaging bag.

This is the result of extensive research to produce packaging bags that are completely satisfactory using linear low-density polyethylene.

In the above proposed method, the physical properties of the branched low-density polyethylene to be blended with the specific linear low-density polyethylene and its blending amount are further selected;

Finding 1: By using a radical generator, a packaging bag with excellent heat sealing strength and body strength can be obtained.
The invention has been completed.

That is, one gist of the present invention is that the melt index J t
/10 minutes or less, flow ratio 3! Linear low density polyethylene below? ! ~? / parts by weight, melt inch 22252 fufu 0
Less than a minute, flow ratio! Low density polyethylene of θ or less is blended with 9 parts by weight of turf and θ, 000/~o, i parts by weight of a radical generator, and the radical generator is decomposed and reacted with the polyethylene while or after reacting. , blow-up ratio 0.9~. 2. θ, draft rate 10~yo.

A method for manufacturing a packaging bag, which is characterized by performing inflation molding under conditions of a cooling rate index of 3Q 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. Exists.

The present invention will be explained in more detail below.

The linear low-density polyethylene used in the present invention is a copolymer of ethylene and other α-olefins, and is different from the triangular low-density polyethylene resin produced by the conventional high-pressure method. Linear low-density polyethylene contains 1, for example, ethylene, and other α-olefins such as butene, hexene, octene, thecene, 4t methylpentene/etc.
About PIt, preferably t~/! It is a weight-to-degree copolymerized product, and it is produced using a Chive 2-type catalyst or a Phillips-type catalyst, which is used in the production of high-density polyethylene by a medium-low pressure method. By making a short branched structure and using the original short chain branching to appropriately lower the density, θ, ri/~θ, 9J
'2/cI/, and has a higher linearity than conventional branched low-density polyethylene.

It is a polyethylene with 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.

The above linear low density polyethylene has a melt index of 2 f//0 min or less, preferably 0.2 to 8 J-t.
yio range, flow ratio is 3! below.

Preferably/! -30 is used. If the melt index is above the above range.

This is not preferable because the heat sealing strength and body strength are reduced when used as a packaging bag. Moreover, if the flow ratio exceeds the above range, it is not preferable because the body ff1i degree when used as a packaging bag decreases. Furthermore, the above linear low density polyethylene is
It is desirable that the density is in the range of 0.9/j to θ, 9J, tkg/cI11 from the viewpoint of rigidity and impact resistance when used as a packaging bag.

In the method of the present invention, the melt index is JIBK4
The value is measured at 190°C in accordance with 7≦0, and the flow ratio is the shear force /
θ"dyne/(d(load///3t) and 10'dyne/
The extrusion rate (9710 minutes) was Cr1 (load ii/l/?).

It is calculated by Further, the density is a value measured in accordance with J Engineering 5K4740.

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 broad molecular weight distribution.

In the present invention, the polymer i' (that is, the melt index is small) is used in linear low-density polyethylene with a narrow molecular weight distribution.

Another major feature is that a specific amount of branched low-density polyethylene with a narrow molecular weight distribution is blended.

The branched low-density polyethylene blended into the powdery 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 goomethylpentene. The amount of copolymerization of the copolymerization components is θ,! ~/r% by weight, preferably λ~1
It is about 0 weight. These low-density polyethylenes are preferably obtained by radical polymerization using a conventional high-pressure method (9/cd in 7000 to 3θθθ) using a radical generator such as K, oxygen, or an organic peroxide.

The branched low-density polyethylene mentioned above has a melt index! The flow ratio is f//θ minutes or less, preferably 12/10 minutes or less, more preferably in the range of 0.7 to 19770 minutes!
Q or less, preferably 30~! A range of 0 is used. If the melt index exceeds the above range, it is not preferable because the strength of the body of the bag decreases when it is made into a packaging bag. Furthermore, if the flow ratio exceeds the above range, the strength of the body portion of the bag will decrease when it is made into a packaging bag, which is not preferable. Further, the branched low-density polyethylene mentioned above has a density of θ, 3θ or less, especially 0. the law of nature/! ~θ, ri, 2! It is desirable that the range is from the viewpoint of improving the body strength and heat sealing strength of the bag when it is made into a packaging bag.

The blending amount of the above-mentioned linear low-density polyethylene and branched low-density polyethylene is 9! ~ // Parts by weight, preferably ! ~/! One branched low density polyethylene per weight part! ~/parts by weight, preferably! ~/! Used within the range of parts by weight. If the branched low-density polyethylene is less than the above range, the film formability during inflation molding will be reduced, and if it is more than the above range, the body strength of the bag will be reduced when it is made into a packaging bag, which is not preferable.

In the method of the present invention, a radical generator is further added to the above-described mixture of linear low density polyethylene and branched low density polyethylene, the radical generator is decomposed, and the mixture is reacted with the polyethylene, followed by inflation molding.

The radical generator to be added to the mixture of linear low-density polyethylene and branched low-density polyethylene is preferably one having a half-life of 7 minutes and a permeation degree of /30°C to 300°C. Dicumyl peroxide, λ,!
-Dimethylco,! di(1-butylperoxy)hexane, 2. ! -dimethyl-2. ! Examples include di(t-butylperoxy)hexyne-3,α,α'-bis(1-butylperoxyisopropyl)benzene, dibenzoyl peroxide, di-t-butyl peroxide, and the like.

The amount of the radical generator added is 0.0 to the total amount of the linear low density polyethylene and branched low density polyethylene.
00/~θ,/part by weight, but if the amount added is less than 0.0001 part by weight, the strength of the heat-sealed part of the resulting packaging bag will be almost the same as that without additives. No change.

Furthermore, if θ is larger than the heavy background area, the melt index will be too low and film breakage will easily occur during film molding, and the surface of the film will be rough, which is undesirable.

However, this amount added is 0. A range of θ02 to θ,02 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 no particular restrictions on the method of adding a radical generator to the linear low density polyethylene and branched low density polyethylene, causing the radical generator to decompose and react with the polyethylene. For example, it can be implemented by the following method.

(1) During inflation molding, the linear low density polyethylene, branched low density polyethylene and 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, branched low-density plate polyethylene, and 2Gy force generator are kneaded and reacted, and then
Turn into pellets.

The pellets are used for inflation molding.

(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 higher than the melting point of the polyethylene, and Under humidity conditions where polyethylene does not react with radical generators.

For example, master polyethylene of polyethylene containing a radical generator at a high concentration (usually about 200 to 20θ00 ppm) melt-kneaded at a temperature of /3θ to /0°C is blended and then inflation molded.

Also, the radical generator itself remains the same.

Alternatively, it can be used by dissolving it in a solvent.

By reacting the linear low-density polyethylene and 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 can be obtained.

The modified polyethylene has improved film formability compared to a blend of unmodified linear low-density polyethylene and low-density polyethylene, and is easily oriented in the longitudinal direction during inflation molding.

The film 1 thus obtained shrinks in the direction in which it is oriented during heat sealing, making the film thicker than the original thickness and improving the strength of the heat sealed portion, which is preferable.

In the crosslinking reaction using the above radical generator, the melt index of the modified polyethylene obtained by the crosslinking reaction is 0.7 to 19710 minutes, especially Ol, 2 to 0.7 minutes.
It is desirable to adjust the blending amount of the radical generator so that the range of 9//θ minutes is exactly correct.

In addition, even if the above-mentioned modified polyethylene, which is obtained by adding a radical generator to the above-mentioned blend of the proboscis-like low density polyethylene and the branched low-density polyethylene, is simply inflation-molded, the heat-sealed part strength and the body part strength are good. However, specific molding conditions are required for molding.

The specific molding conditions include a blow-up ratio of 0.9 to -
2, and the draft rate is set to 7θ to 7θ.

Inflation molding is performed with a cooling rate of 45 j of 0 seconds or less.

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 ρm = Density of the resin extruded from the die slit ρf
: Density of film BUR Nib blow ratio Also, the cooling rate index is the time (seconds) it takes for the bath molten resin to reach the frost line after it is extruded from the die, and is obtained by the following formula.

τ: Cooling rate index 1 second) FLH nifrost line height cm) ■o: Linear velocity when the molten resin passes through the lip section]1i4- (tyn/
θθC) ■1: Take-up speed (α/BθC) If the blow-up ratio is set to 2.0 or more, shrinkage occurs in the longitudinal direction of the heat seal during heat sealing, causing distortion in the direction opposite to the orientation of the bag body. The strength of the heat-sealed edges of the bag is reduced.

This may cause the bag to break.

If the draft ratio is less than 10, good shrinkage will not occur during heat sealing, and if it is more than 70, the molecular orientation of the bag body itself will be too large in one direction, causing tearing of the bag body itself.

If the cooling rate index is 3θ seconds or more, the molecular orientation that occurs in the film due to drum 7) K during film molding will be thermally relaxed and will be more relaxed, and no contraction will occur during heat sealing, resulting in a loss of strength in the heat sealed part. .

Note that heat seals, heat belts, etc. are used for heat sealing, but if these heating machines press the heat seal part for a long time, thermal relaxation will occur and the strength of the heat seal part will decrease. Since there is no, 230-. A heat-sealing method in which the heat-sealed part is heated quickly at a temperature of about 2Fθ°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. It is preferable to use

[For production]

In the method of the present invention, a specific amount of branched low-density polyethylene having a specific melt index and a narrow molecular weight distribution is blended with linear low-density polyethylene having a specific melt index and a narrow molecular weight distribution, Furthermore, by using a radical generator, the strength of the heat-sealed portion can be significantly improved without reducing the strength of the body when used as a packaging bag.

Example/ Linear low density polyethylene (melt index (M process)
:0. ．． 3-9710 minutes, flow ratio: 20. Density: o,
9. xoy/crd, copolymerization component nibten-/.

Copolymerization amount: 70% by weight) 20 double twill parts and high pressure branched low density polyethylene (melt index: 0.41f/
10 minutes, flow ratio: 411. Density: Q, Takoda f/7)/
ON Okibe 2. Odimethyl-,2,J-di(1-butylperoxy)hexyne-30, O0! Mix the parts by weight and then use an extruder for 2 steps! The mixture was melt-kneaded at θ° C. for 3 minutes and extruded into pellets.

The obtained modified polyethylene had physical properties of M process: 0.39710 minutes and fluidity ratio: 27.

This was extruded using a Modern Machinery Delsatteg extruder equipped with an inflation die with an annular slit diameter of 2Ω and a cooling air ring. R, ) /, / , t 7 rate/4t
The amount of air blown out from the air ring is changed under the following conditions.
Cooling rate index, 2 times/! Obtained θμ no inflation film.

The length of the obtained blown film is d 70ey
Cut into a cylindrical film with a width of 0.

Newlong fJJHF322B-2 type heat sealer (heating part length 100mm, heating part clearance 0.3
Heat sealing temperature (heating part surface temperature) 2! One of the openings of the cylindrical film is moved from the end under the conditions of 0°C, cooling part temperature 30°C, and film feeding speed /jfn/sec! It was heat sealed in the position of Yu. The heat-sealed portion contracted in the direction in which the film was taken (vertical direction) and became thicker than the original film thickness.

The obtained bag was filled with 1 θ of fertilizer, and the opening was heat-sealed under the same conditions as above, and then 24 hours of fertilizer was deposited and released again to obtain a packaging bag for the drop bag test. .

(b) Performance test of packaging bag The packaging bag obtained in 0) above was subjected to a horizontal drop bag test and a vertical drop bag test using the following method.

The drop conditions were room temperature, -IO℃ for the horizontal drop bag test, and 1! for the vertical drop bag test. ℃ and to the falling height! m, / Number of times the bag tote falls! It was times.

The bag tear rate was calculated as the percentage of bags that were torn among the packaging bags used in the test. The results are shown in Table/.

(a) Side drop bag test A test was conducted by dropping 20 bags (side drop) with the body of the packaging bag parallel to the floor and the heat-sealed part approximately perpendicular to the floor. Improved bag breakage rate. In addition.

The side drop bag test was conducted to measure the strength of the heat-sealed part of the bag.

(b) Vertical drop bag test A bag breakage test was performed by dropping 20 bags under pressure (vertical drop) so that the heat-sealed part of the packaging bag was parallel to the floor and the body was approximately perpendicular to the floor. I got the rate.

In addition.

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 of H) above, when the extrusion rate was increased, the stable forming limit extrusion rate at which the tubular film in the molten state could be formed into a stable bubble state was measured.

The larger the stable forming limit extrusion amount is, the better the film forming stability is.

Example 3 The same procedure as Example 1 was carried out except that the blending amounts of linear low density polyethylene and branched low density polyethylene were changed as shown in Table 1. The results are shown in Table 1. Example 3.41 The same procedure as in Example 1 was carried out except that monobranched polyethylene having the physical properties shown in Table JK was used in Example 3.41. The results are shown in Table/.

In the Bikyo example/example/, &! The same procedure as in Example 1 was conducted except that the blending amounts of the branched low-density polyethylene and the branched low-density polyethylene were changed as shown in Table 2. The results are shown in Table 7.

Comparative Example No. 3 The same procedure as in Example 1 was carried out except that in Example 2, branched low-density polyethylene or linear low-density polyethylene having the physical properties shown in Table 7 was used. The results are shown in Table/.

Comparative Example In Example 2, the same procedure as Example 2 was carried out except that the linear low density polyethylene used in Example 2 was used alone and no radical generator was added. The results are shown in Table/.

C Effects of the Invention'] According to the method of the present invention, by using a mixture of specific proboscis-shaped low density polyethylene and a specific amount of specific branched low density polyethylene reacted with a radical generator, It is possible to obtain a packaging bag with extremely excellent heat seal strength and chest strength. Furthermore, the modified polyethylene compound used in the method of the present invention has superior molding stability during inflation molding than when linear low-density polyethylene is used alone.

The rough quality of inflation molding can be improved.

Applicant: Mitsubishi Chemical Industries, Ltd. Agent: Patent attorney: Mr. Hase - (7 people who don't like it) Continued from page 1 Qlnt, C1,' Identification code Internal office reference number 3-chowa ■
Neyama Jcho 8shi (spontaneous) 2 Title of the invention Method for manufacturing packaging bags (596) Tamake Kasei T @ Haka Co., Ltd. (1 person) 5 Detailed description of the invention in the specification to be amended column

Claims (4)

[Claims] (1) Linear low-density polyethylene 9j~? with a melt index of 2t//, 0 minutes or less, and a flow ratio of 3j or less? / parts by weight, melt index 69 // θ min or less, fluidity ratio! θ
Branched low density polyethylene below! -~/? parts by weight and 0.0007 to 0.7 parts by weight of a radical generator,
After decomposing the radical generator and reacting it with the polyethylene, or after reacting it, inflation molding is performed under the conditions of a blow-up ratio of 0 to 0, θ, a draft ratio of 1 to 4, and a cooling rate index of 30 seconds or less. A method for producing a packaging bag, which comprises heat sealing and cutting the obtained cylindrical film with the longitudinal direction being in a direction that intersects with the take-up direction. (2) Linear low density polyethylene has a density of O0/! ~O
，Wow! 2. A method according to claim 1, characterized in that the method is of jt/crd. (3) Branched low density polyethylene has a density θ, 9/! ~θ
, 3θt/cd. (4) Heat seal the heat seal part to λ30~2r
Claims 1 to 3 are characterized in that the heat-sealed portion is caused to shrink by heating at a temperature of 0° C. until the films are fused together, and then the heat-sealed portion is left in a free state. The method according to any of paragraph 3.