JP2552819B2 - Polyethylene resin film - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyethylene film having high strength, which can be suitably used as various packaging materials, filtration materials, medical materials and the like.

[0002]

2. Description of the Related Art Polyethylene films are often used as films because of their good chemical resistance. If a high strength film is obtained, the demand for the film will be further expanded. In order to produce a high-strength polyethylene film, it is indispensable to perform stretching, but uniaxial stretching has a drawback that it is strong in one direction but weak in a direction perpendicular to it, so biaxial stretching is desirable.

[0003]

It is well known that the strength of a stretched film is increased by increasing the molecular weight of polyethylene to be used. However, if the molecular weight is increased, the moldability such as extrudability may decrease. Obviously, in consideration of industrial production, the molecular weight is currently about 200,000, and therefore, the upper limit of the strength of the film is observed.

[0004]

SUMMARY OF THE INVENTION In view of the above situation, the inventors of the present invention have conducted diligent research for the purpose of providing a film having a high strength which has never been achieved. No high strength polyethylene film has been obtained. The gist of the present invention is to mix polyethylene with a viscosity average molecular weight of 400,000 or more with a swelling / humidifying agent, swell or wet the polyethylene under heating, form this into a film, and then stretch it, before or during the stretching. comprising extracting <br/>膨湿Jun agent non-porous ultrahigh molecular weight polyethylene
It exists in a stretched film.

In order to obtain a film having strength in the present invention, first of all, high molecular weight polyethylene having a viscosity average of 400,000 or more is used. The high-molecular-weight polyethylene may be an ethylene homopolymer, or a copolymer with propylene, butylene, pentene, hexene, 4-methylpentene, octene or the like, and the copolymerization component is preferably 5 mol% or less. However, polyethylene with a high molecular weight of 400,000 or more has a high melt viscosity. Therefore, the molding method is limited, and compression molding, extrusion molding using a special molding machine, and injection molding are carried out, but most of them are used for compression molding. It is limited, and the molding time may take several hours per time. Even if you try to make a raw sheet of stretched film by extrusion molding, high pressure is required to pass through the die at the time of molding, and even if it flows in the die,
So-called melt fracture occurs at the time of outflow, and a uniform sheet cannot be obtained. Further, even if an attempt is made to obtain a film by stretching the raw fabric, the stretchability is worse than that of ordinary polyethylene, and it is impossible to uniformly stretch the film to a desired ratio.

In order to improve the above-mentioned moldability and stretchability, high-molecular-weight polyethylene (PE) {(A) component} is added to the swelling or wetting component (A) as a moldability and stretchability improving agent. A wetting agent, specifically an aliphatic or alicyclic compound {(B) component} is added. As the component (B),
It has good compatibility with high molecular weight PE, especially when it is mixed uniformly in the molten state, and because it improves the stretchability and accelerates the melting of high molecular weight PE, it has a lower melting point than high molecular weight PE and easily swells it. Alternatively, it should be moistened, soluble in water, a lower alcohol, or a mixture thereof, which is a solvent that is easy to handle, and more preferably, it should be solid at room temperature because of its ease of handling after being processed into a sheet, etc. Must meet the requirements of.

The aliphatic or alicyclic compound (B) component generally has a melting point of less than 100 ° C. and easily swells or wets the high molecular weight polyethylene at a temperature above the melting point of the high molecular weight polyethylene, that is, above 150 ° C. As the number of carbon atoms in the aliphatic compound increases, the compatibility with the high molecular weight polyethylene becomes better, so that the aliphatic compound preferably has 15 or more carbon atoms in order to swell or wet the high molecular weight polyethylene sufficiently. Further, when the number of carbon atoms is 15 or less, it is liquid at room temperature, and it is not preferable in that the component (B) easily bleeds when formed into a stretch-molded product.

As a specific example of the component (B) which satisfies the above requirements,
Cetyl alcohol {CH₃(CH ₂)₁₄OH}, hepta
Decyl alcohol {CH₃(CH₂)_FifteenCH₂OH},
Allyl alcohol {CH₃(CH₂)₁₆CH₂OH}, Seri
Alcohol (CH₃(CH₂) _{twenty four}CH₂OH}, behenyl
Alcohol {CH₃(CH₂)₂₀CH₂OH} etc.
Dioctyl ether {(C₈H₁₇)₂O}, Didec
Ruther {(C_TenH _{twenty five})₂O}, didodecyl ether
{(C₁₂H_{twenty five})₂O}, dioctadecyl ether {(C₁₈
H₃₇)₂O} and other ethers; methyl tetradecyl ketone
{CH₃CO (CH₂)₁₃CH₃}, N-propylhexyl
Sadecyl ketone {CH₃(CH₂)₂CO (CH₂)_FifteenC
H₃}, Didotecil ketone {CH₃(CH₂)₁₁CO (CH
₂)₁₁CH₃}, Dioctadecyl ketone {CH₃(CH₂)₁₇
CO (CH₂)₁₇CH₃} And other ketones; lauric acid
Chill {CH₃(CH₂)_TenCOO (CH₂)₇CH₃}, Pal
Ethyl mitinate {CH₃(CH₂)₁₄COOCH₂C
H₃}, Butyl stearate {CH₃(CH₂)₁₆COO
(CH₂)₃CH₃}, Octyl stearate {CH₃(C
H₂)₁₆COO (CH₂)₇CH₃} Fats such as esters
Average based on aliphatic compounds and dicyclopentadiene
Petroleum resin having a molecular weight of 500 to 2000 or water of the petroleum resin
Examples thereof include alicyclic compounds such as additives.

As a method for uniformly mixing both components (A) and (B), a twin-screw extruder Brabender kneader, a Banbury mixer or the like can be used.
After mixing both components (B) with a powder and then leaving them under heating, for example, at 150 to 180 ° C., the component (B) is swollen or moistened with the component (A) and supplied to the above mixer. It is possible to efficiently achieve uniform mixing of the components.
In this uniform mixing, if the weight of the component (A) exceeds 60% by weight, it becomes difficult to perform uniform mixing by the above-mentioned ordinary kneader. If the kneading is continued for a long time in order to make the ultra-high molecular weight polyethylene not sufficiently dissolved and uniform in a short time, the temperature becomes abnormally high due to the heat generation and a high shearing force is applied. Is greatly reduced.

The necessity of uniform mixing is mainly due to the following two points. That is, first, for example, when both components (A) and (B) are simply powder blended and supplied to a single-screw extruder which is usually used for molding, only the component (B) having a low melting point is dissolved first, so that the inside of the extruder is melted. As a result, slippage occurs, and no shearing force is applied to the polymer PE itself, resulting in incomplete melting.
For this reason, when the composition is extruded intermittently or in a worse case, it is blocked and cannot be extruded.

Secondly, if the composition is non-uniform, the flow in the die or the like will not be constant, and for example, a uniform thickness, especially 1
It becomes difficult to obtain a thin sheet having a thickness of mm or less. In order to carry out more uniform molding, it is desirable to supply the homogeneous mixture mixed in the kneading machine to the extruder in a molten state without solidifying. The reason for this is that, once cooled and solidified, some phase separation occurs, so that in the above-mentioned single-screw extruder feed part, both components (A) and (B) are not melted uniformly. To be

As a method for processing the composition obtained as described above into a raw material for stretching, since the component (B) has sufficiently improved fluidity, a molding method similar to ordinary polyethylene is used. Can be adopted. Specific examples include a T-die-roll method and an inflation film molding method. Here, in the conventional method, the low molecular weight material (component (B)) as a flow improver (swelling / wetting agent) bleeds to the surface after molding and causes a decrease in mechanical strength. For this reason, it is necessary to limit the amount of addition, which causes deterioration of moldability. In the present invention, in consideration of the above points, by extracting the component (B) before or during the stretching of the film, it is possible to prevent a decrease in mechanical strength.
(B) component of the extraction handle in step easy, for example, lower alcohols Given in terms of drying of the film, such as methanol, ethanol, butanol, or water or it can be carried out in a mixture of water and alcohol, desirable.

Next, in order to obtain a high-strength film from the original film obtained as described above, it is necessary to biaxially stretch. In this biaxial stretching, the stretching temperature is 50 ° C to 150 ° C.
It is possible to uniformly achieve high-magnification stretching in a wide temperature range of ° C. However, as described later, in the present invention, the film tends to become porous because the component (B) is extracted before or during stretching.

To obtain a high-strength film having no pores, the component (B) is extracted before or during stretching, and the stretching temperature is 130 ° C.
It is necessary to stretch at about 150 ° C so that the holes are closed. Further, in order to achieve a tensile strength of 25 kg / mm ² or more, at a stretching speed of 50% / sec or more, 3 × 3
It is desirable to stretch the film more than twice.

[0015]

EXAMPLES Examples are shown to clarify the effects of the present invention. However, the invention is not limited by these examples. The physical properties shown in the description of the present invention and the examples were according to the following methods. ○ Tensile strength (Kg / mm ² ): According to ASTM D-882 Tensile speed 50 mm / min ○ Viscosity average molecular weight (Mv): Solvent tetralin, [η] was measured at a measurement temperature of 135 ° C [η] = 4.60 Value obtained from × 10 ^-4 (M) ^0.725 (Tung's formula)

EXAMPLE 1 20% by weight of polyethylene having a viscosity average molecular weight of 1.5 million was powder blended with 80% by weight of stearyl alcohol and then left in an oven at 170 ° C. for 30 minutes,
Polyethylene was wet with alcohol. At this time, 0.5 part by weight of the phenolic stabilizer was added to 100 parts by weight of the mixture. This mixture is heated to a jacket temperature of 170 ° C,
Kneading was performed for 10 minutes under the condition of a rotation speed of 100 rpm. The resin temperature was 185 ° C., the constant torque was constant, and the mixture was transparent and uniform in the molten state. Before the uniform mixture was cooled and solidified, it was press-molded at a temperature of 170 ° C. to obtain a 0.5 mm pressed sheet. The sheet was immersed in ethanol at 50 to 60 ° C. for 5 minutes to extract stearyl alcohol. This sheet was white due to porosity. The sheet after this extraction is heated at a temperature rate of 20 ° C. of 135 ° C. using a biaxial stretching machine.
At 0% / sec, stretching was carried out 5 times (5 × 5) simultaneously in the length and width directions. This stretched film was transparent and exhibited the following properties.

[0017]

[Table 1] Thickness 4μ Tensile strength 36kg / mm ² Tensile elongation 60%

Example 2 A 0.7 mm pressed sheet was prepared in the same manner as in Example 1. The sheet was immersed in ethanol at 50 to 60 ° C for 5 minutes to extract stearyl alcohol. This sheet also became white because of its porosity. The sheet after this extraction treatment is 200% / speed at a temperature of 120 ° C. using a biaxial stretching machine.
It was stretched 3 × 3 times in the longitudinal and lateral directions simultaneously in sec. This film was white and was porous. This thickness was about 40μ. Next, the stretched film was further stretched at a temperature of 135 ° C. at a speed of 200% / sec lengthwise and crosswise 3 × 3 times simultaneously. The obtained film was transparent and exhibited the following properties.

[0019]

[Table 2] Thickness 4μ Tensile strength 45kg / mm ² Tensile elongation 43%

Example 3 Polyethylene 40% by weight, stearyl alcohol 60
A 0.5 mm pressed sheet was obtained in the same manner as in Example 1 except that the weight percentage was changed. The resin temperature during kneading was constant at 195 ° C. Subsequently, in the same manner as in Example 1, after extraction with ethanol, biaxial stretching was carried out at 135 ° C. at a magnification of 4 × 4. This film was also transparent and showed the following properties.

[0021]

[Table 3] Thickness 8μ Tensile strength 31kg / mm ² Tensile elongation 80%

Comparative Example 1 Polyethylene (Novatec R40000F Mitsubishi Kasei Kogyo Co., Ltd. Mv = 200,000) (Nova Neck is a trademark of Mitsubishi Kasei Kogyo Co., Ltd.) was press-molded to obtain a 0.5 mm press sheet. The sheet was stretched by a biaxial stretching machine at a temperature of 125 ° C. and a speed of 200% / sec at a speed of 6 × 6 times. The properties of this film were as follows.

[0023]

[Table 4] Thickness 13μ Tensile strength 12kg / mm ² Tensile elongation 41%

Example 4 A uniform melt was obtained in the same manner as in Example 1 except that a Banbury mixer was used at a temperature of 160 ° C. for uniform kneading. 30φ without cooling and solidifying this melt
The sheet was extruded from a T-die with a clearance of 1 mm at a rotation speed of 40 rpm and molded using a cooling roll. The temperature setting of the extruder at this time was 200 ° C for each part.
Is constant. At this time, the extruded amount of the composition was stable, and the state of the sheet was smooth, and a uniform thickness of 0.6 mm could be obtained. The sheet was extracted with ethanol under the same conditions as in Example 1, and then biaxially stretched 4 × 4 times at 135 ° C. The film was transparent and exhibited the following properties.

[0025]

[Table 5]

[0026]

The film of the present invention has excellent strength, and by extracting an aliphatic or alicyclic compound with a solvent, a film having high strength and excellent permeability can be obtained. It can be suitably used as various packaging materials, filtration materials, medical materials and the like.

Claims (1)

(57) [Claims] 1. A mixture of膨湿Jun agent on the viscosity-average molecular weight 400,000 or more polyethylene, polyethylene was swollen or wet under heating, after a film by molding this
Stretched, and the swelling agent is extracted before or during the stretching
Non-porous ultra high molecular weight polyethylene stretched film.