JPH0826185B2 - Polyethylene composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel polyethylene composition, more specifically, a novel polyethylene composition having high rigidity and capable of giving a film excellent in transparency and appearance. It relates to a composition.

Conventional technology Conventionally, so-called high-density polyethylene film with a density of 0.940 g / cm ³ or more has excellent mechanical properties, cold resistance, slipperiness, etc., and is widely used in industry, business, daily life, etc. ing.

However, this high-density polyethylene film
Compared to films such as low density polyethylene obtained by high pressure polymerization method, it is inferior in transparency and gloss.
It is unsuitable for packaging that requires good appearance and perspective, and is subject to limited applications.

Therefore, various methods have been tried so far for the purpose of improving the transparency of the high-density polyethylene film, and for example, a two-stage air ring method, a water cooling method, a T die cast molding method, etc. have been proposed. However, in the two-stage air ring method, the width of the film is limited and the degree of freedom is low, which causes a decrease in workability and an increase in loss, and in the water cooling method, the melt tube extruded from the annular die is used. Since it is difficult to make uniform contact with cooling water in the same direction, there is a drawback that uneven cooling occurs and the transparency becomes non-uniform. Further, the T-die cast molding method has a drawback in that the film tends to be uniaxially oriented in the take-up direction during molding, so that the tendency of vertical tearing increases.

On the other hand, attempts have been made to improve the transparency by sharpening the molecular weight distribution of high-density polyethylene (JP-A-54-87778). However, in this method, in order to obtain good transparency, it is necessary to bring the molten tube extruded from the annular die into contact with a cooling liquid having a temperature not higher than the melting point of the polyethylene. When the device is used, the desired transparency cannot be obtained because this becomes insufficient.In addition, when the molecular weight distribution of high-density polyethylene is made sharp, the melt extruded from the annular die during inflation molding This causes an unfavorable situation such as roughening of the tube, that is, melt fracture, which significantly deteriorates the appearance. In order to solve such problems, it is necessary to take measures such as using a rough skin preventive agent, for example, an expensive additive such as a fluorine-based elastomer, or suppressing the extrusion amount to be low, resulting in a decrease in productivity. There are economic disadvantages such as cost and cost increase.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention overcomes the above-mentioned drawbacks of the prior art, uses an ordinary air-cooled inflation molding device, has high rigidity, is excellent in transparency, and is good in terms of melt fracture and the like. The purpose of the present invention is to provide a polyethylene composition capable of giving a film having excellent appearance.

Means for Solving the Problems The inventors of the present invention have conducted diligent research to develop a polyethylene composition capable of giving a film having the above-mentioned excellent properties, and as a result, a specific high density polyethylene has been identified. It was found that the object can be achieved by blending low density polyethylene in a predetermined ratio, and the present invention has been completed based on this finding.

That is, the present invention has (A) a density of 0.94 to 0.96 g / c
m ^3, a melt index measured under a load of 2.16kg is 0.04
The ratio of the melt index measured at a load of 1.50g / 10 minutes and a load of 21.6kg to the melt index measured at a load of 2.16kg.
(B) Density of 0.93 kg / cm ³ or less with respect to 100 parts by weight of polyethylene consisting of an ethylene homopolymer or a copolymer of ethylene and another olefin or diene having MI _21.6 / MI _2.16 of 20 to 45 , The melt index measured with a load of 2.16 kg is 0.1 to 15.0 g / 10 minutes, the ratio Mw / Mn of the weight average molecular weight to the number average molecular weight is 2.5 to 7.0, and the low molecular weight portion of the molecular weight 10,000 or less in the molecular weight distribution The present invention provides a polyethylene composition characterized by being mixed with 15 to 45 parts by weight of polyethylene by a high-pressure polymerization method in the presence of a radical generator, which accounts for 4.0% or more of the whole.

 Hereinafter, the present invention will be described in detail.

The polyethylene used as the component (A) in the composition of the present invention is a so-called high-density polyethylene having a density in the range of 0.94 to 0.96 g / cm ³ , and not only ethylene homopolymer but also ethylene is the main constituent. And a copolymer of ethylene with another olefin or diene.

Examples of other olefins and dienes used in the copolymer include propylene, butene-1, pentene,
Examples thereof include α-olefins such as 4-methylpentene-1, hexene, octene and decene, diolefins such as butadiene and isoprene, cycloolefins such as cyclopentene, cyclohexene, cyclopentadiene and norbornel.

The (A) is the density of the polyethylene used as the component 0.94~0.96g / cm ^3, preferably required to be in the range of 0.94~0.95g / cm ^3, the density is less than 0.94 g / cm ^3,
The obtained film has insufficient waist strength, and also 0.96 g / cm ³
If it exceeds, sufficient transparency cannot be obtained.

The polyethylene has a melt index of 0.04 to 1.50 g / min, preferably 0.1 to 1.0 g / 10, measured under a load of 2.16 kg.
Min, more preferably 0.4 to 0.8 g / 10 min. If the melt index is less than 0.04 g / 10 minutes, melt fracture occurs and a film having good appearance cannot be obtained, and if it exceeds 1.50 g / 10 minutes, the strength of the film decreases. Further, the polyethylene has a ratio MI _21.6 / MI _2.16 (hereinafter referred to as MIR) of the melt index measured under a load of _21.6 kg and the melt index measured under a load of 2.16 kg in the range of 20 to 45, preferably in the range of 30 to 35. Need to be in. When the MIR is less than 20, melt fracture occurs on the surface of the film and a film having a good appearance cannot be obtained, and when it exceeds 45, the transparency of the film is insufficient.

The polyethylene used as the component (B) in the composition of the present invention is required to have a density of 0.93 g / cm ³ or less, and when the density exceeds 0.93 g / cm ³ , the film having sufficient transparency. Can't get This polyethylene is obtained by a high-pressure polymerization method in the presence of a radical generator, that is, a method of polymerizing ethylene at a high pressure in the presence of a radical generator. In the presence, polymerization pressure 400-400
A product obtained by polymerizing at a high pressure of 0 kg / cm ² can be used.

The polyethylene used as the component (B) has a melt index of 0.1 to 15.0 g / 1 measured with a load of 2.16 kg.
It should be in the range of 0 minutes, preferably 0.2 to 10.0 g / 10 minutes. If the melt index is less than 0.1 g / 10 minutes, the transparency of the obtained film is insufficient,
On the other hand, if it exceeds 15.0 g / 10 minutes, the bubble stability during molding becomes poor. Further, this polyethylene needs to have a ratio Mw / Mn of weight average molecular weight to number average molecular weight in the range of 2.5 to 7.0. When the value is less than 2.5, the moldability is poor, while when it exceeds 7.0, the transparency of the obtained film is deteriorated. Further, the polyethylene, in the molecular weight distribution, the proportion of the low molecular weight portion having a molecular weight of 10,000 or less in the whole is 4.0% or more, preferably 4.0 to 15.0%, and more preferably 4.0 to 10.0%. To be
If this ratio is less than 4.0%, melt fracture occurs, and a film with good appearance cannot be obtained.
If it exceeds the range, the waist strength of the film decreases, which is not preferable.

In the composition of the present invention, the polyethylene as the component (A)
15 to 45 parts by weight of polyethylene (B) per 100 parts by weight
Parts by weight, preferably 15 to 30 parts by weight, more preferably 20 to
It is mixed in a ratio of 25 parts by weight. If the content of polyethylene as the component (B) is less than 15 parts by weight, the transparency of the obtained film is insufficient, while if it exceeds 45 parts by weight, the stiffness of the film is lowered.

To the polyethylene composition of the present invention, if desired, various additives usually used in polyethylene compositions, such as stabilizers, lubricants and antistatic agents, may be added within a range that does not impair the effects of the present invention. You can

The composition of the present invention comprises polyethylene (A) and (B) when a film is formed by an inflation device.
It is also possible to supply polyethylene as a component directly to a molding machine for preparation, but in order to prevent the risk of insufficient uniform dispersion of both, preliminarily kneading both,
It is preferable to feed to an inflation molding machine. Examples of means for pre-kneading include a kneader, a Banbury mixer, an open roll, a single-screw or twin-screw extruder, and the like.
A batch type or a continuous type kneading method can be used using a commonly used kneader.

Regarding the cooling air ring used in the inflation molding of the composition of the present invention, the intended film can be sufficiently obtained with a normal single annular cooling air ring, but the air ring has a double annular cooling air ring. By using, it is possible to obtain a film having more excellent transparency.

EFFECT OF THE INVENTION The polyethylene composition of the present invention has excellent yield strength of 140 kg / cm ² or more, which is a feature of high-density polyethylene film, and has excellent transparency with a haze of 10% or less, and rough film surface. In addition to providing a film with good appearance such as no so-called melt fracture at all, using a conventional existing inflation device for high-density polyethylene or low-density polyethylene without any modification, The film can be provided with high productivity and at low cost.

This means that special equipment such as the prior art, such as the previously described loss of productivity in the two-step cooling method, or the case of further embedding a localized heater in the annular die to prevent surface roughening of the film. Considering the problems such as the use of, the industrial value of the present invention is extremely high.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples.
The present invention is not limited in any way by these examples.

The properties of polyethylene and the physical properties of the film were measured according to the following methods.

(1) Density Measured according to ASTM D-1505.

(2) Melt index According to ASTM D-1238, load is 2.16k at 190 ℃.
The melt index was measured under the conditions of g or 21.6 kg to obtain the melt index MI _2.16 or MI _21.6 , respectively.

(3) MIR MI _21.6 / MI _2.16 was _defined as the melt index ratio MIR.

(4) Mw / Mn Weight average molecular weight Mw and number average molecular weight Mn were measured with a high temperature high speed type GPC-150C type manufactured by Waters Co.
I asked for / Mn.

(5) Ratio of molecular weight less than 10 ⁵ Perform the same procedure as the above Mw / Mn measurement to create a pattern of molecular weight distribution, find the area occupied by the molecular weight less than 10 ⁵ and divide by the area of the entire molecular weight distribution to obtain the ratio. I asked.

(6) Yield strength Measured according to ASTM D-822.

(7) Measurement of Melt Fracture The film obtained as a tube was opened, and the presence or absence of rough skin in the circumferential direction having a width of 600 mm was observed and evaluated according to the following criteria.

Judgment Criteria ○: No rough skin is observed on the entire surface in the circumferential direction. △: The total rough skin width in the circumferential direction is less than 10% of the total width. ×: Total rough skin width in the circumferential direction. Is observed in the total width of 10% or more. Examples 1 to 11 and Comparative Examples 1 to 10 The polyethylene (B) shown in the table is added to 100 parts by weight of the polyethylene (A) shown in the following table. Blended in the blending amount shown in, then dry blended using a dry blender, extruded at a resin temperature of 200 ° C using an extruder having a screw with a diameter of 50 mm and L / D = 25, and cold cut to produce pellets. did.

Then, the pellets were blown into an inflation molding machine [manufactured by Placo Co., Ltd., 50 mm ^φ extruder, die 75 mm ^φ ].
Thus, a film was produced under the conditions of a die temperature of 200 ° C., a discharge rate of 20 kg / Hγ, a film thickness of 0.025 mm, and a film folding diameter of 30 mm. The physical properties of this film are shown in the following table.

Claims (1)

[Claims] 1. A) Density of 0.94 to 0.96 g / cm ³ , load of 2.16 k
Melt index measured in g is 0.04 to 1.50 g / 10 minutes,
And melt index and load measured at a load of 21.6 kg 2.
Ratio to melt index measured at 16 kg MI _21.6 / MI
_2.16 is 20 to 45, and (B) the density is 0.93 g / c with respect to 100 parts by weight of polyethylene consisting of a homopolymer of ethylene or a copolymer of ethylene and another olefin or diene.
Melt index is 0, measured at m ³ .
1 to 15.0 g / 10 min, ratio of weight average molecular weight to number average molecular weight M
w / Mn is 2.5 to 7.0, and in the molecular weight distribution, the proportion of low molecular weight parts with a molecular weight of 10,000 or less in the whole is
A polyethylene composition, which is blended with 15 to 45 parts by weight of polyethylene by a high pressure polymerization method in the presence of a radical generator, which is 4.0% or more.