JPS6377957A - Polyethylene resin composition - Google Patents

Abstract

PURPOSE:To provide the title compsn. having excellent transparency, squeezability, resistance to environmental stress cracking and heat and ultrasonic sealability, consisting of a specified branched low-density, PE, a linear low- density PE and a high-density PE. CONSTITUTION:90-50pts.wt. branched low-density PE having an MI of 0.2-10g/10min and a density of 0.915-0.930g/cm<3> is melt-mixed with 5-25pts.wt. linear low-density PE having an MI of 0.2-5g/10min, a density of 0.915-0.935g/cm<3> and a flow ratio of 15-70, 5-25pts.wt. high-density PE having an MI of 0.2-5g/10min, a density of 0.94-0.96g/cm<3> and a flow ratio of 15-150 and optionally, an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, etc., at 120-280 deg.C. The mixture is pelletized.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to polyethylene resin compositions.

Specifically, the present invention mainly relates to a polyethylene resin composition for blow molding that uses low-density polyethylene and has excellent environmental stress cracking resistance, heat resistance, ultrasonic sealability, etc.

[Conventional technology]

Branched low-density polyethylene has excellent transparency and squishability (a measure of flexibility and stretchability of a container). It is used in applications requiring rounding transparency and squishability, such as blow-molded buttons for frozen dessert containers, tofu containers (egg tofu), dropper containers, and the like.

However, branched low-density polyethylene has low resistance to environmental stress cracking, and when used as the above-mentioned molded product, an undesirable situation often occurs in which small cracks occur due to residual stress in the polyethylene applied during molding. Furthermore, when sterilizing frozen dessert containers and tofu containers, etc. O~
Due to the 30 to 90 minute heat treatment in IIσ'CK, cracks occur and deformation occurs due to insufficient heat resistance. Furthermore, as the method of sealing containers shifts from heat sealing to ultrasonic sealing, the problem of poor sealing, which did not occur with the heat sealing method, has arisen.

In the past, various methods have been proposed to improve the environmental stress cracking resistance, ultrasonic sealing properties, heat resistance, etc. of polyethylene mentioned above, but all of them have advantages and disadvantages, and are insufficient and rarely adopted for industrial use. .

For example, (1) Method of adding rubber-like substances (Journal of Japan Rubber Association, Vol. 3!1, ///~1 pages (6 pages)) (2) Fins with specific physical properties Methods of adding wax (Japanese Patent Application No. 7709) (3) Method of adding polyethylene grease wax having specific physical properties (Japanese Patent Application No. 7709) and the like are known.

[Problem that the invention seeks to solve]

Although method (1) above is expected to improve the environmental stress cracking resistance of polyethylene, it is not preferred because it causes a decrease in strength and is also inferior in heat resistance and light resistance. Also, (2) above
This method reduces the strength of polyethylene and requires a large amount of polyethylene to be added, making it unsuitable for industrial use from a cost perspective.

Furthermore, although the above method (3) is expected to improve the environmental stress cracking resistance of polyethylene, it is unsuitable for industrial use because it results in a decrease in strength.

Measures for Solving Problems c] In view of the prior art, the present inventors have developed a method for improving environmental stress cracking resistance, ultrasonic sealing properties, and the like while maintaining the excellent transparency and squishability of branched low-density polyethylene. As a result of extensive research in order to provide a polyethylene resin composition for blow molding that has improved heat resistance and can be used industrially, we have identified branched low-density polyethylene that has specific physical properties. The present inventors have discovered that the object can be achieved by blending linear low density polyethylene and high density polyethylene having the physical properties in specific proportions, and have completed the present invention.

That is, the gist of the present invention is that the melt index is 0.2.
~1011710 min branched low density polyethylene 20~
Melt index in jθ weight part is O, ko ~ 3: i/
/ Linear low-density polyester 26'' with ethylene j~-exposed weight part and melt index of 0.
- ~ jpyio minute and density is 0.9'l ~ 0.94
A polyethylene resin composition for blow molding is comprised of a high density polyethylene j having a molecular weight of 1//a/l to a single layer.

To explain the present invention in detail, the branched low-density polyethylene used in the present invention is high-pressure polyethylene, that is, processed using a radical generator such as organic peroxide or oxygen at a pressure of 1000 to 3000 kIl/yf, II degree/ It is obtained by homopolymerizing ethylene or copolymerizing ethylene and other copolymer components under conditions of 00°C to 00°C. Examples of copolymerization components include α-olefins such as propylene and butene-1, and vinyl compounds such as vinyl acetate, methyl acrylate, and methyl methacrylate. % by weight, preferably 2
It is about 70% by weight.

The branched low density polyethylene has a melt index of 0,1 to 1011710 minutes, preferably 0,'1-Al
In the range of 1/10 minute, and the density is o, qij ~ o,
A range of y3o1/dt is used. If the melt index is less than the above range, there is a problem that parison breakage occurs during blow molding. In addition, if it exceeds the above range, the melt tension of the polyethylene may be too small;
There is a problem that a drawdown phenomenon and a sagging phenomenon of the parison occur during blow molding, and the environmental stress cracking resistance and strength of the molded product are reduced.

In the method of the present invention, the melt index is J-8KA.
The density is a value measured at 7-0° C. in accordance with J.S. K. 60, and the density is a value measured in accordance with J.

What is the linear low-density polyethylene that is blended into the branched low-density polyethylene to improve the environmental stress cracking resistance and ultrasonic sealing properties of the above-mentioned branched low-density polyethylene? A copolymer of ethylene and other α-olefins. This is different from low-density polyethylene resin produced by conventional high-pressure methods. Linear low density polyethylene, for example, contains ethylene and other α-olefins such as butene, hexene, octene,
It is a product obtained by copolymerizing decene, methylpentene-1, etc. to an extent of about 20% by weight, preferably about 100% by weight, preferably about 100% by weight. υ, conventional high-density polyethylene is made into a short branched structure using a copolymer component, and the density is appropriately reduced by utilizing this short chain branching, θ, ? /˜o, q jI /d It is a polyethylene with a structure that is more linear than conventional low-density polyethylene and more branched than high-density polyethylene.

The linear low density polyethylene used in the present invention is:
The melt index is in the range of 0.2 to 11//Q minutes, preferably o, q-cog7io minutes, and the flow ratio is in the range of /J to 70, preferably /j-QO. , its density is o, q /j−o, q s j11/di
Those within the range of are preferably used. If the melt index is less than the above range, there is a problem that fringing occurs during blow molding. In addition, if the above range is exceeded, the melt tension of the polyethylene becomes too small, resulting in drawdown phenomenon and parison sagging phenomenon during blow molding, which reduces the environmental stress cracking resistance and strength of the molded product. There is a problem with doing so.

Furthermore, if the flow ratio is less than the above range, a rough surface problem will occur during blow molding, and if it exceeds the above range, the effect of improving the environmental stress cracking resistance of the button will be reduced, which is not preferable.

The invention is to improve the heat resistance of the polyethylene composition by blending high-density polyethylene with the branched low-density polyethylene and linear low-density polyethylene.

As the above-mentioned high-density polyethylene, those generally commercially available as high-density polyethylene can be used, and ethylene homopolymers or copolymers of ethylene and other mono-F olefins such as butene-7 and propylene can be used. It includes.

The above-mentioned high-density polyethylene is obtained by homopolymerizing ethylene or copolymerizing ethylene with an α-olefin such as propylene, butene-1, etc. using a catalyst comprising a transition metal compound and an organometallic compound.

Examples of the transition metal compound include one or more transition metal-based compounds such as titanium, vanadium, and chromium, or compounds supported or reacted with silica, alumina, magnesium compounds, and the like. In particular, a solid catalyst component in which a titanium compound such as a titanium chloride, haloalcolade, or alcolade is supported on or reacted with a magnesium compound such as magnesium dialkholate or magnesium chloride is preferably used.

Examples of organometallic compounds include organoaluminum compounds represented by the general formula AJRnXa-n (wherein R is a hydrocarbon group having 7 to 1 carbon atoms, X is a halogen atom, and n is 1 to 3). It will be done.

Specific examples include triethylaluminum, tri-n-propylaluminum, triisobutylaluminum, dimethylaluminum monochloride, ethylaluminum sesquichloride, and the like.

The above-mentioned high-density polyethylene used in the present invention is:
The melt index is in the range of 0,0 to 1/10 min, preferably in the range of 0 to 1/l θ, and the density is θ,
? lI~o, q b 11/crl, preferably O,
The range is from des to o, qt, i/air, and the fluidity ratio is from lj to iso, preferably from 20 to JO. If the melt index is less than the above range, rough skin will occur during blow molding, and if it exceeds the above range, a drawdown phenomenon will occur during blow molding, resulting in uneven wall thickness of the molded product. There is a problem of reduced environmental stress cracking resistance. Further, if the density exceeds the above range, the environmental stress cracking resistance of the molded article will decrease and the transparency will become poor, and if the density is below the above range, the effect of improving heat resistance will be reduced, which is not preferable. Furthermore, if the fluidity ratio is less than the above range, a rough surface problem will occur during blow molding, and if it exceeds the above range, the transparency of the molded product will be poor, which is not preferable.

In the present invention, the fluidity ratio refers to the shear force io@dyne/d (load///J
/, p) and 10” dyne/cd (load///31
It is calculated by the ratio of the extrusion amount (j//10 minutes) of 1).

The blending amount of the branched low density polyethylene, linear low density polyethylene and high density polyethylene is 90 to 50 parts by weight, preferably 90-40 parts by weight, of the linear low density polyethylene J-coated polyethylene. j parts by weight
Preferably j-20 parts by weight and high density polyethylene j~
-5 parts by weight, preferably in the range of -20 parts by weight (total ioo parts by weight of the three).

If the blending amount of linear low-density polyethylene is less than the above range, the effect of improving the environmental stress cracking resistance and ultrasonic sealability of the molded product will be small, and if it exceeds the above range, the transparency of the molded product will decrease. However, this is not preferable because it also gives a poor appearance. Furthermore, if the amount of high-density polyethylene is less than the above range, the effect of improving the heat resistance of the molded product will be small, and if it exceeds the above range, the transparency of the molded product will decrease and the environmental stress cracking resistance will also decrease. So I don't like it.

The polyethylene resin composition of the present invention can be prepared by tri-blending the branched low-density polyethylene, linear low-density polyethylene and high-density polyethylene in a blender or the like, or by tri-blending and then applying a conventional melt mixing method, for example, By Banbury mixer, unitary mixer, mixing roll, extruder, etc./+20A-+2g
It is obtained by melt-mixing at a temperature of θ°C and pelletizing.

The polyethylene resin composition thus obtained may contain various known additives normally used in polyethylene, such as antioxidants, ultraviolet absorbers, antistatic agents, and lubricants, as required.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

In addition, the melt index and density in the examples.

Flow ratio, stiffness, environmental stress cracking resistance (
Hereinafter, it will be abbreviated as E8OR. ), squeezability, and transparency were measured as follows.

■Measurement of Melt Index Measurement was performed at 190°C in accordance with J Engineering 8KA 60, and expressed in units of gyio minutes.

■Measurement of density The density was measured in accordance with J Engineering S K 1,71.0 and expressed in units of i/crl.

■ Measurement of fluidity ratio Using the melt index measuring device described in ■ above, the shear force l
O@dyne/Cr1 (load ///31g) and 701dyne/cIl (load/1i31 extrusion amount (iyio min)
Calculated using the ratio of

■ Stiffness (Measurement of stiffness) Measured in accordance with ASTM D 7Q7 and expressed in units of 1 Kg/ffl.

■ Measurement of B5OR according to A8TM D/A 3-66,
Ten samples of alkylarylpolyethylene glycol were immersed in an SO heavy weight ice water solution, and the time until cracks appeared in three of them was observed with the naked eye.F.・hr
O expressed in units of s Squeezability (11 Forming containers of the same thickness under certain conditions.

The body of this container is deformed to a certain amount of strain beyond its yield point,
When you open it, measure the number of seconds it takes for it to return to its original container.

In this study, the number of seconds required for the container to return to its original shape after deformation with an outer diameter of 500 was measured (the wall thickness of the container was approximately WOOμ).

(ill) Capacity Test (Evaluation of Container Flexibility and Stretchability) After squeezing and pressing the body of the container with one's hand, the state of recovery of the container was observed when the hand was released.

○: Smoothly restores the original container shape when the hand is released.

×When the second hand is released, the original container shape will not be restored.

■Transparency Based on AsTM Dto03, cloudiness is measured.

The sample is a cut out of the body of the container mentioned above. - There is a correlation between cloudiness (haze value) and transparency; as cloudiness increases, transparency decreases.

Judgment: ○: Good transparency (haze value 30 or less) ×: Poor transparency (haze value QO or more) ■ Ultrasonic sealability The container was sealed using an ultrasonic sealer (manufactured by Seidensha).

The sealed surface was cut out with a strip, and the condition of the sealed surface was manually observed using a peel test.

Judgment criteria O: No peeling (completely sealed).

Δ: Sealed, but easily peeled off by hand.

X: Not sealed.

■After filling a heat-resistant container full of water and applying ultrasonic sealing, the container was placed on a wire mesh, and with a load l'kII placed on the container, it was placed in an air open and left at 110°C for 60 minutes. Thereafter, it was visually determined whether or not the body of the container had a wire mesh pattern.

Q: There is no wire mesh pattern.

×: A wire mesh pattern is attached.

Example 1 Branched low-density polyethylene (high-pressure polyethylene, melt index (hereinafter abbreviated as M): ,z
, o gyi o min, density: 0. Deco 7yd) 70ti
70 parts by weight of linear low density polyethylene (M Koji/, 09770 minutes, fluidity ratio: t1 density: 0.9 copolymer A, butene/copolymerization amount = y@tql,) and high density polyethylene (M Work: 0.91710 minutes, Density: o, q
jy 11/al! , flow ratio: J)-0 parts by weight were triblended, and then melt-kneaded at a temperature of iqo° C. in a single-screw extruder with a cylinder diameter of 10 mm to form extrusion pellets. The physical properties of the obtained polyethylene resin composition were measured according to the above test method. The results are shown in Table/.

Examples 3 and 3 In Example 1, the same procedure as in Example 1 was carried out except that the blending amounts of branched low density polyethylene, tufted low density polyethylene and high density polyethylene were changed as shown in Table 7. The results are shown in Table/.

Comparative Examples/~J The same procedure as in Example 1 was carried out except that branched low-density polyethylene, linear low-density polyethylene, or high-density polyethylene was used alone as shown in Table 1. The results are shown in Table/.

Comparative Example Example 1 was carried out in the same manner as in Example 1, except that the blending amounts of branched low-density polyethylene and linear low-density polyethylene were varied as shown in Table 1. The results are shown in Table/.

Comparative Example j The same procedure as in Example 1 was conducted except that the physical properties and blending amounts of branched low-density polyethylene and high-density polyethylene were changed as shown in Table 1. The results are shown in Table 1.

〔Effect of the invention〕

According to the present invention, by blending specific amounts of linear low density polyethylene and high density polyethylene with branched low density polyethylene having specific physical properties, the squishability and transparency of the branched low density polyethylene can be maintained. Tama,
Polyethylene resin compositions with significantly improved environmental stress cracking resistance, ultrasonic sealability and heat resistance can be obtained. Therefore, the polyethylene resin composition of the present invention is suitably used for blow molding applications such as the above-mentioned frozen dessert containers and tofu containers that require environmental stress cracking resistance, squishability, transparency, ultrasonic sealability, and heat resistance. be able to.

Sender: Mitsubishi Chemical Industries, Ltd. Representative Patent Attorney Hase - (7 others)

Claims (1)

[Claims] (1) 90 to 50 parts by weight of branched low density polyethylene having a melt index of 0.2 to 10 g/10 minutes, and 5 to 25 parts by weight of linear low density polyethylene having a melt index of 0.2 to 5 g/10 minutes. and melt index of 0.2 to 5 g/1
A polyethylene resin composition for blow molding, which contains 5 to 25 parts by weight of high-density polyethylene having a density of 0.94 to 0.96 g/cm^2.