JP2000178383A - Polyethylene resin composition for inflation molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin composition which can give an ultrathin balance film having excellent mechanical strengths and reduced unevenness of thickness, has excellent bubble stability, and can be molded into a film at a high speed. SOLUTION: A composition is used which is prepared by adding 0.008-1.5 pts.wt. polyglycerol fatty acid ester to 100 pts.wt. polyethylene resin comprising 35-60 wt.% (A) low-molecular-weight ethylene homopolymer or ethylene/3-20C α-olefin copolymer having a limiting viscosity number of 0.3-1.5 dl/g and a density of 0.94-0.98 g/cm3 and 65-40 wt.% high-molecular-weight ethylene/3-20C α-olefin copolymer having a limiting viscosity number of 2-15 dl/g and a density of 0.89-0.95 g/cm3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polyethylene resin composition for inflation molding, and more particularly, to a polyethylene resin composition for inflation molding.
The present invention relates to a polyethylene resin composition capable of obtaining an ultra-thin balance film having excellent mechanical strength, stable and capable of inflation molding at high speed.

[0002]

2. Description of the Related Art Ultra-thin balance films used in supermarket shopping bags, garbage bags and various industrial packaging films are:
It is produced by inflation molding a high-density polyethylene resin having at least two types of molecular weight components, a high molecular weight component and a low molecular weight component, and having an expanded molecular weight distribution.

[0003] A high-density polyethylene resin having improved molding fluidity by having a bimodal molecular weight distribution is usually used.
A Ziegler catalyst is obtained by using at least two-stage polymerization mainly of ethylene using a catalyst comprising a solid catalyst component essentially containing titanium, magnesium and halogen and an organoaluminum compound. For the purpose of improving the thermal stability during inflation molding, a phenolic antioxidant and a phosphorus antioxidant, and a lubricant and / or a neutralizing agent are added to the high-density polyethylene resin.

However, even when a high-density polyethylene resin having a molecular weight distribution expanded as described above and a lubricant such as calcium stearate is used, the bubble shape does not become a perfect circle during inflation molding, Causes fluctuations in pitch and roll, and a die mark is generated, resulting in a decrease in bubble stability. As a result, this phenomenon becomes remarkable at the time of high-speed molding in which the inflation molding speed is 70 m / min or more, the uniformity of the film thickness is reduced, and the product value of the film is reduced.

As an improved method, the design of a spiral die, which is frequently used as a die of an inflation molding machine, is changed to suppress local heat generation and stagnation in the die, or to increase a contact area of a molten material between spirals. Although a method for improving the molding stability of a film has been adopted, there is a limit in remodeling a molding machine.

Further, a method of using calcium stearate in combination with zinc stearate (JP-A-4-10638) has been proposed for the purpose of improving fluidity. However, although a slight improvement in fluidity is observed, The development of polyethylene resin for inflation molding has not yet been achieved.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a polyethylene resin composition in which the obtained ultra-thin balance film has excellent thickness uniformity and mechanical strength, and is excellent in film formation stability and high-speed molding during inflation molding. To provide.

[0008]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the above problem can be solved by adding the compound to a polyethylene resin having a specific compound, and reached the present invention.

Namely, a low molecular weight ethylene homopolymer or ethylene satisfying the following (a) and (b) and ethylene having 3 to 3 carbon atoms:
20 α-olefin copolymer (A) 35 to 60% by weight of high molecular weight ethylene satisfying the following (c) and (d) and α-olefin having 3 to 20 carbon atoms (B)
Polyethylene resin (I) 10 consisting of 65 to 40% by weight
0 parts by weight of polyglycerin fatty acid ester (I
I) A polyethylene resin composition for inflation molding characterized by adding 0.008 to 1.5 parts by weight.

(A) ortho-dichlorobenzene (ODC)
B) The intrinsic viscosity (η1) at 140 ° C. is 0.3 to 1.5 d.
l / g (b) Density (JIS K6760-1981) is 0.9
4 to 0.98 g / cm ³ (c) ODCB, intrinsic viscosity (η2) at 140 ° C. of 2-1
5 dl / g (d) Density (JIS K6760-1981) is 0.8
The polyethylene resin composition for inflation molding of the present invention will be described in more detail below 9 to 0.95 g / cm ³ .

The polyethylene resin (I) for inflation molding according to the present invention is an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms, which satisfies the following (a) and (b) as low molecular weight components: Coalescing (A) 35 ~
It is composed of 60 to 40% by weight of a copolymer (B) of ethylene and an α-olefin having 3 to 20 carbon atoms which satisfies the following (c) and (d) as the high molecular weight component.

(A) ODCB, intrinsic viscosity at 140 ° C. (η
1) 0.3 to 1.5 dl / g (b) Density (JIS K6760-1981) 0.9
4 to 0.98 g / cm ³ (c) ODCB, intrinsic viscosity (η2) at 140 ° C. of 2-1
5 dl / g (d) Density (JIS K6760-1981) is 0.8
9 to 0.95 g / cm ³ The polyethylene resin (I) for inflation molding of the present invention is obtained by separately polymerizing the above low molecular weight component (A) and high molecular weight component (B) using a highly active catalyst. The obtained components may be mixed. In addition, low molecular weight component (A)
Alternatively, either the high molecular weight component (B) is polymerized first and then transferred to the same polymerization reactor or another connected polymerization reactor in the presence of the polymer, and the remaining molecular weight components are batch-wise or continuous. May be adopted.

3 carbon atoms used for copolymerization with ethylene
Propylene, 1-butene, 4-methyl-1-pentene, 1-pentene, 1-
Hexene, 1-octene, 1-nonene, 1-decene, 1
-Hexadecene, 1-octadecene and the like.

As the highly active catalyst, Ziegler catalysts,
Or what is called a metallocene catalyst is suitable. Among them, 10 g of ethylene (co) polymer per g of catalyst
A polymerizable polymer having a weight of at least Kg is preferable. Specific examples of such a highly active catalyst include, for example, a Ziegler-based catalyst comprising a solid catalyst component essentially containing titanium, magnesium and halogen and an organic aluminum compound. More specifically, JP-A-48-66178, JP-A-50-51587, JP-A-55-78005,
JP-A-56-61406, JP-A-56-155205
JP-A-57-212210, JP-A-59-580
No. 05, JP-A-60-262802, JP-A-4-35
No. 1616, JP-A-5-287020, JP-A-7-4
Catalysts proposed in, for example, US Pat.

Ethylene alone or ethylene and carbon number 3
The polymerization of α-olefins of from 20 to 20 is carried out batchwise or continuously at a polymerization temperature of 50 to 200 ° C. At a polymerization temperature lower than this temperature range, the catalytic activity cannot be sufficiently exhibited. Further, at a polymerization temperature higher than this temperature range, the catalyst is deactivated by heat, so that it is difficult to sufficiently exert the catalytic activity. Further, examples of the polymerization method include a gas phase polymerization method, a slurry polymerization method, and a solution polymerization method.

The polymerization order of the component (A) and the component (B) and the method of obtaining a mixture are not limited, but ethylene homopolymer, which is the low molecular weight component, or ethylene and C 3 -C 2
0 α-olefin copolymer (A) is ODCB, 1
An intrinsic viscosity (η1) at 40 ° C. of 0.3 to 1.5 dl / g,
More preferably, those having 0.4 to 1.3 dl / g are used. If η1 is less than 0.3 dl / g, smoke is generated during molding, and if η1 exceeds 1.5 dl / g, the fluidity of the resulting mixture decreases. The component (A) having a density of 0.94 to 0.98 g / cm ³ is used. When the density is less than 0.94 g / cm ³ , the rigidity of the mixture is insufficient, and when the density exceeds 0.98 g / cm ³ , the impact strength of the film is reduced. The copolymer (B) of ethylene and the α-olefin having 3 to 20 carbon atoms as the high molecular weight component has an ODCB and an intrinsic viscosity (η2) at 140 ° C. of 2 to 15 dl / g, more preferably 2.5 dl / g. -10 dl /
g. When η2 is less than 2 dl / g, the melt tension of the obtained mixture is reduced and the mechanical strength of the film is reduced. When η2 exceeds 15 dl / g, a gel is formed on the film. The density of the component (B) is 0.1.
89 to 0.95 g / cm ³ , more preferably 0.90 to 0.95 g / cm ³
0.94 g / cm ³ is used. 0.8 density
If it is less than 9 g / cm ³ , the rigidity of the film is insufficient, and
When the density exceeds 0.95 g / cm ³ , the impact strength of the film decreases. The blending ratio of the low molecular weight component (A) and the high molecular weight component (B) is 35-60% by weight for component (A).
The component (B) is 65 to 40% by weight. Component (A)
If the compounding ratio of the component (A) is less than 35% by weight, the fluidity of the obtained mixture is reduced. If the compounding ratio of the component (A) exceeds 60% by weight, gel is formed on the film.

Further, in order to reduce the shaking of the molten bag (bubble) during inflation molding and to obtain a stable molded product, the above-mentioned components (I) are required for producing the inflation molding polyethylene resin (I) of the present invention. The mixture of the polymer of A) and the component (B) is preferably subjected to a crosslinking treatment. Cross-linking treatment is a method of melt-kneading the mixture in the presence of oxygen, a method of heat-treating or melt-kneading the mixture at or above the decomposition temperature of the organic peroxide by adding an organic peroxide, and irradiating the mixture with radiation. And the like. Among these methods, particularly, a method of melt-kneading the mixture in the presence of oxygen and a method of adding an organic peroxide to the mixture and melt-kneading the mixture at a temperature equal to or higher than the decomposition temperature of the organic peroxide are economical and operationally efficient. It is more preferable than the nature.

When oxygen is used, the gas atmosphere in the granulator has an oxygen concentration of 100 ppm to 10%, preferably 0.1%, depending on the granulation speed and the supply speed of the oxygen-containing gas sent to the granulator. 1 to 5%.

When an organic peroxide is used, not only the organic peroxide but also a crosslinking aid may be added.
Examples of the organic peroxide include di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-bis (t
-Butylperoxy) hexane, 2,5-dimethyl-
2,5-bis (t-butylperoxy) hexyne-3,
dialkyl peroxides such as α, α′-bis (t-butylperoxy) diisopropylbenzene;
-Dimethyl-2,5-bis (benzoylperoxy) hexane, t-hexylperoxybenzoate, t-butylperoxy-m-toluylbenzoate, t-butylperoxybenzoate, bis (t-butylperoxy) isophthalate Peroxyesters such as 1,
1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-hexylperoxy) cyclohexane, 1,1-bis (t-hexylperoxy) 3,3,5 -Trimethylcyclohexane,
Peroxy such as 1,1-bis (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) cyclododecane, n-butyl-4,4-bis (t-butylperoxy) valerate Ketals. Among them, dialkyl peroxides, especially α, α′-bis (t-butylperoxy) diisopropylbenzene, 2,5-dimethyl-2,5-bis (t
It is preferred to use -butylperoxy) hexyne-3. When an organic peroxide is used, 0.0005 to 0.02 per 100 parts by weight of the polyethylene resin (I)
It is preferable that 5 parts by weight of the above-mentioned organic peroxide is added and crosslinked. The amount of the organic peroxide added is 0.
If it is at least 0005 parts by weight, the melt elasticity will be high, the stability of the bubbles will be improved, and the amount of the organic peroxide added will be 0.02.
The amount of 5 parts by weight or less is preferable in that the generation of gel due to local crosslinking can be reduced.

The polyethylene resin (I) for inflation molding of the present invention comprises a component (A) satisfying the above (a) and (b) and a component (B) satisfying the above (c) to (d). ), But the density of the mixture (JIS K6760-1981) is preferably 0.9.
35 to 0.960 g / cm ³ . When the density of the mixture is 0.935 g / cm ³ or more, the rigidity of the film is satisfied, and when the density is 0.960 g / cm ³ or less, the impact strength of the film is preferably prevented from lowering. Further, the melt flow rate of the mixture at 190 ° C. under a load of 21.6 kg (JIS K7210-1976, condition 7, HLMFR
Is preferably 3 to 15 g / 10 min.
An HLMFR of 3 g / 10 min or more satisfies the fluidity, and an HLMFR of 15 g / 10 min or less is preferable in preventing a decrease in the impact strength of the film. Weight average molecular weight (Mw) of the polyethylene resin (I) determined by gel permeation chromatography (GPC)
And the ratio Mw / Mn of the number average molecular weight (Mn) is preferably 10 to 30. When the Mw / Mn ratio is 10 or more, the fluidity is satisfied, and when the Mw / Mn is 30 or less, it is preferable in that the impact strength of the film is prevented from lowering.

The polyglycerin fatty acid ester used in the present invention is obtained by esterifying a fatty acid to polyglycerin obtained by polymerizing glycerin. Glycerin has a polymerization degree of 2 to 12, and the fatty acid is a saturated or unsaturated fatty acid having 8 to 22 carbon atoms.

Among them, a polyglycerin condensed ricinoleate obtained by esterifying polyglycerin with ricinoleic acid, which is an unsaturated fatty acid having one carbon atom and having 18 carbon atoms, is preferable.

The amount of the polyglycerin fatty acid ester to be added is 0.008 to 1.0 per 100 parts by weight of the polyethylene resin.
5 parts by weight. If it is less than this, the film thickness uniformity is poor, and if it is more than this, the impact strength of the film is reduced.

Further, the polyethylene resin used in the present invention may contain additives such as known antioxidants, light stabilizers and neutralizers. Here, the neutralizing agent is a fatty acid metal salt represented by calcium stearate, magnesium stearate and zinc stearate, and hydrotalcites. Further, an organic pigment or an inorganic pigment may be added to the polyethylene resin of the present invention.

The polyethylene resin used in the present invention may be obtained by mixing high-pressure LDPE (low-density polyethylene) with the above-mentioned polyethylene resin composition for inflation molding. Particularly, it is preferable to add 5 parts by weight or more of LDPE to 100 parts by weight of the polyethylene resin composition for inflation in that the melt elasticity and the skin of the molded article are improved, and if the addition of LDPE is 40 parts by weight or less, the mechanical strength decreases. It is preferable in that it prevents High pressure LDPE
Is produced under a polymerization pressure of 800 atm or more in the presence of air or an organic peroxide as a radical source. The LDPE has a density of 0.91 to 0.94
g / cm ^3, preferably 0.915~0.935g / c
In the range of m ³ , MFR (JIS K7210-1976,
Condition 4, 190 ° C., 2.16 kg load) is 0.1 to 10
g / 10 minutes, preferably 0.1 to 4 g / 10 minutes.

The polyethylene resin composition for inflation molding of the present invention is effective for forming a thin balance film having a thickness of 20 μ or less, particularly for forming a film having a thickness of 10 μ or less. Similar effects can be obtained even when a pigment, an inorganic filler, or a recycled product is added.

[0027]

EXAMPLES The present invention will be described below with reference to examples, but is not limited to these examples.

The test method followed the following method.

Density: According to JIS K6760-1981, the test piece was immersed in hot water at 100 ° C. for 1 hour and then cooled slowly to room temperature, and measured with a density gradient tube kept at 23 ° C. Mw / Mn: Waters 150C ALC / G
PC (column; GMHHR-H (S) manufactured by Tosoh, solvent;
GPC using 1,2,4-trichlorobenzene)
Mw and Mw / Mn were calculated by the method. In addition,
The column elution volume was calibrated by the universal calibration method using Tosoh standard polystyrene. Intrinsic viscosity: Using an Ubbelohde viscometer, at 140 ° C. ODCB (ortho-dichlorobenzene), polymer concentration 0.1% (supplier A) and polymer concentration 0.02%
(Supplier B).

Examples 1 to 3 (1) Preparation of solid catalyst component A solid catalyst component (A) was prepared according to JP-A-7-41513. That is, 40 g of metallic magnesium powder was placed in a 3 liter glass flask sufficiently purged with nitrogen.
(1.65 mol) and titanium tetrabutoxide 225
g (0.66 mol), 256 g (3.5 mol) of n-butanol in which 2.0 g of iodine was dissolved was added at 90 ° C. over 2 hours, and under a nitrogen blanket while further removing generated hydrogen gas. Stirred at 140 ° C. for 2 hours. This is 11
After the temperature was reduced to 0 ° C., 37 g of tetraethoxysilane (0.1 g) was added.
8 mol) and 25 g (0.17 mol) of tetramethoxysilane, and the mixture was further stirred at 140 ° C. for 2 hours. Next, 2.1 liters of hexane was added to obtain a homogeneous solution.
This homogeneous solution was placed in a 10-liter stainless steel autoclave equipped with a stirrer, and while maintaining the internal temperature at 45 ° C, 0.74 kg of a hexane solution containing 1.4 mol of diethyl aluminum chloride and 0.56 mol of i-butyl aluminum dichloride was added. Add over 1 hour and add 1 hour at 60 ° C
Stirred for hours. Next, 3.2 kg of a hexane solution containing 10.4 mol of i-butylaluminum dichloride was added, and the mixture was stirred at 60 ° C. for 1 hour to obtain a solid catalyst component. The obtained solid catalyst component (A) was used as a hexane slurry after removing remaining unreacted substances and by-products using hexane.

(2) Production of polyethylene resin (I) Dehydrated and purified 110 l / h of hexane in a continuous polymerization vessel having an internal volume of 370 l, and 164 mmol / l of triisobutylaluminum as an organoaluminum compound.
While supplying the solid catalyst component at a rate of 0.95 g / hour, ethylene at 20.0 kg / hour and hydrogen at an ethylene concentration ratio of 0.6 mol / mol, 85
The first-stage polymerization was carried out continuously at a temperature of 30 ° C., a total pressure of 30 kg / cm ² and an average residence time of 1.6 hours. The first-stage ethylene homopolymer (A) has an intrinsic viscosity of 0.6 dl /
g in density of 0.974 g / cm ³ .

After removing unreacted hydrogen and ethylene in a flash tank, the hexane slurry containing the first-stage polymer was introduced into another continuous polymerization vessel having an internal volume of 545 liters. While feeding additional 121 liters / hour of hexane to the polymerization vessel, ethylene 20.0 kg / hour, 1-butene 0.7 kg / hour, hydrogen to ethylene concentration ratio 0.04 mol / mol, 80 ° C. Pressure 20kg / c
The second stage polymerization was carried out under the conditions of m ² and an average residence time of 1.3 hours. After discharging unreacted hydrogen, ethylene, and 1-butene in a flash tank, the effluent from the second-stage polymerization vessel is subjected to a drying step, followed by a drying process to obtain an ethylene copolymer (a mixture of component (A) and component (B)). Powder). When the polymerization of only the second stage is separately carried out, ethylene / 1
- butene copolymer, a density 0.932 g / cm ³ in intrinsic viscosity 4.6dl / g. The polymerization rate of the component (A) was 45% by weight, and the polymerization rate of the component (B) was 55% by weight.

The polyethylene resin has a density of 0.948.
g / cm ³ , the melt flow rate at 190 ° C. under a load of 21.6 kg was 10 g / 10 min, and the Mw / Mn was 20.

The obtained mixture powder was mixed with 500 PPM of tetrakis- [methylene-3- (3 ′, 5′-di-tert-butyl-4′-hydroxyphenyl) propionate] methane as an antioxidant and tris (2 , 4-di-t
-Butylphenyl) phosphite 300 PPM, calcium stearate 500 PPM as a neutralizing agent, α, α'-bis (t-butylperoxy) diisopropylbenzene 50 PPM as an organic peroxide, and glycerin as a polyglycerin fatty acid ester are polymerized. A predetermined amount of polyglycerin condensed ricinoleate obtained by esterifying the polyglycerin thus obtained with ricinoleic acid, which is an unsaturated fatty acid having one hydroxyl group and having 18 carbon atoms, was added in a prescribed amount shown in Table 1. Pellets were obtained to obtain a polyethylene resin composition.

(3) Inflation film molding and evaluation Inflation film molding of each of the polyethylene resins thus prepared was performed under the following conditions.

Extruder: manufactured by Placo Co., Ltd. Screw diameter 50mmφ ・ Die: 75mmφ spiral die ・ Die gap: 1.2mm ・ Molding temperature: 210 ° C ・ Blow-up ratio: 5 ・ Molding speed: 70m / min ・ Thickness: 10μm Evaluation of blown film ・ Film thickness uniformity Film The thickness of the film circumference was measured with a thickness measuring instrument, and the thickness unevenness was determined based on the following criteria.

：: 10 μm ± 1.0 μm Δ: 10 μm ± 1.5 μm ×: 10 μm ± 2.0 μm or more Mechanical strength The obtained film was measured by a dirt impact measuring instrument.

Stability The state of the melt (bubble) at the time of forming the blown film is judged according to the following criteria.

：: A state in which there is almost no swaying of the bubble.

Δ: A state in which the bubble sways slightly.

×: A state in which shaking of the bubble was large and molding was impossible.

High-speed performance The state of bubbles during inflation molding is determined based on the following criteria.

：: The bubble is not broken in the circumferential direction.

X: A state where the bubble is cut in the circumferential direction.

The stability and high speed of the bubble during film formation and the physical properties of the obtained film were measured. The results are shown in Table 1.

Examples 4-7, Comparative Examples 1-7 Except that the polymerization ratio of component (A) and component (B), the amount of polyglycerin fatty acid ester and the amount of organic peroxide were changed to the values shown in Table 1, Each polyethylene resin was prepared in the same manner as in Examples 1 to 3, and their inflation film molding and inflation film evaluation were performed.
It was shown to.

[0047]

[Table 1]

[0048]

According to the present invention, an ultra-thin balance film having excellent mechanical strength and thickness uniformity, excellent bubble stability during film formation, and high speed can be obtained by using the polyethylene resin composition adjusted within the scope of the present invention. Show that you get.

Claims (3)

[Claims] 1. A low molecular weight ethylene homopolymer or ethylene having 3 to 20 carbon atoms, satisfying the following (a) and (b):
Α-olefin copolymer (A) of 35 to 60% by weight, a high molecular weight ethylene satisfying the following (c) and (d) and an α-olefin having 3 to 20 carbon atoms (B) 65
Polyglycerol fatty acid ester (II) per 100 parts by weight of polyethylene resin (I) consisting of
A polyethylene resin composition for inflation molding, which is added in an amount of 0.008 to 1.5 parts by weight. (A) orthodichlorobenzene (ODCB), 140 ° C.
Has an intrinsic viscosity (η1) of 0.3 to 1.5 dl / g and (b) a density (JIS K6760-1981) of 0.9.
4 to 0.98 g / cm ³ (c) ODCB, intrinsic viscosity (η2) at 140 ° C. of 2-1
5 dl / g (d) Density (JIS K6760-1981) is 0.8
9 to 0.95 g / cm ³ 2. Polyethylene resin (I) is a resin 100
The polyethylene resin composition for inflation molding according to claim 1, wherein the polyethylene resin composition is crosslinked with 0.0005 to 0.025 parts by weight of an organic peroxide per part by weight. 3. Polyglycerin fatty acid ester (II)
Is a polyglycerol condensed ricinoleate, The polyethylene resin composition for inflation molding according to claim 1 or 2, wherein