JPH0380092B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a porous film of ultra-high molecular weight polyethylene.

Ultra-high molecular weight polyethylene has superior impact resistance, abrasion resistance, chemical resistance, tensile strength, etc. compared to general-purpose polyethylene, and its use as an engineering plastic is expanding. However, compared to general-purpose polyethylene, it has an extremely high melt viscosity and poor fluidity, so it is very difficult to mold it using conventional extrusion molding or injection molding, and most of it is molded by compression molding. Currently, some rods and the like are extruded at extremely low speeds.

Under such circumstances, the present inventors conducted various studies in order to develop a method for producing ultra-high molecular weight polyethylene film, and as a result, they unexpectedly found that when rolling a sheet of ultra-high molecular weight polyethylene, the rolling temperature exceeded the melting point. They have discovered that a uniformly whitened film with a uniform thickness can be obtained by pulling it under tension at a specific temperature range, and that such a whitened film is also porous, such as ultra-high molecular weight polyethylene powder. It was found that this porous film is more flexible and has superior mechanical strength compared to conventional porous films produced by compression processing and partially heating and sintering, leading to the completion of the present invention.

That is, the present invention provides at least the intrinsic viscosity [η]
Porous ultra-high molecular weight polyethylene, which is produced by rolling a sheet of ultra-high molecular weight polyethylene with a temperature of 5.0 dl/g or more with rolls at a temperature of from melting point +15°C to +25°C while applying tension and taking it off. A method for manufacturing a film is provided.

The ultra-high molecular weight polyethylene used in the method of the present invention has an intrinsic viscosity [η] of decalin solvent at 135°C.
is 5.0dl/g or more, preferably 15 to 30dl/g
It is within the range of . If [η] is less than 5.0 dl/g, the melt tension is low, and the film breaks when tension is applied and taken off while rolling at a temperature above the melting point, resulting in poor moldability. On the other hand, the upper limit of [η] is not particularly limited, but if it exceeds 30 dl/g, the melt viscosity is high, and even when rolled, a thin film (e.g.
50μ or less) may not be obtained. Such ultra-high molecular weight polyethylenes contain ethylene or ethylene and small amounts of other α-olefins such as propylene, 1-butene, 4-methyl-1-pentene, 1
Among the polyethylenes obtained by polymerizing -hexene and the like by so-called Ziegler polymerization, it has a much higher molecular weight.

The melting point of the ultra-high molecular weight polyethylene in the present invention is a value measured using a differential scanning calorimeter (DSC) according to ASTM D 3417.

There are various known methods for manufacturing sheets using the ultra-high molecular weight polyethylene, such as the method proposed by the applicant of the present invention in Japanese Patent Publication No. 11576/1983, in which ultra-high molecular weight polyethylene powder is formed into a porous plate. A method of producing a sheet by sandwiching the product between two belts, heating, pressing, and cooling after forming a shape, or simply hardening with heat to make a porous plate-like sheet, or compression molding. Among them, the method disclosed in Japanese Patent Publication No. 48-11576 is preferable because it allows continuous and uniform sheets to be obtained.

The method of the present invention produces a porous film of ultra-high molecular weight polyethylene by rolling the ultra-high molecular weight polyethylene sheet with a roll at a temperature of melting point +15°C or more to melting point +25°C or less while applying tension and taking it off. This is the way to do it.

Before the sheet is rolled, it is preheated to a melting point of 60 to +
It is preferable to heat the sheet to a temperature in the range of 30°C, since this makes rolling with rolls easier. Preheating of the sheet can be performed using an oven, a heating roll, a far-infrared heater, or the like.

A porous film cannot be obtained if the rolling temperature is lower than the melting point +15°C;
If the temperature exceeds ℃, the film will break and cannot be formed.

As mentioned above, the rolling temperature should be within the range of from +15°C to melting point +25°C, but the rolling temperature can be controlled by setting the roll temperature within the above range.

In the method of the present invention, it is essential to apply additional tension during roll rolling, but in order to apply tension, specifically, for example, a take-up roll is installed after the rolling roll, and the rolling roll and the take-up roll are Since the melted film contracts due to melt elasticity, the peripheral speed ratio is usually 1:0.5 or more, preferably 1:0.8.
This can be done by doing the above.

Also, the circumferential speed ratio when taking it off with the take-up roll is 0.5
If it is above, there is no particular limitation, but if it becomes too large, there is a risk that the film in a molten state may stretch and break, so it is preferably in the range of approximately 0.8 to 1.5. Further, since the take-up roll also has the purpose of cooling the film melted by the rolling roll, it is usually cooled to room temperature to 120°C.

Moreover, when two or more pairs of rolling rolls are used for rolling, the formability becomes more stable and a good porous film can be produced.

The ultra-high molecular weight polyethylene used in the method of the present invention includes heat-resistant stabilizers, weather-resistant stabilizers, lubricants, anti-blocking agents, slip agents, pigments, dyes, inorganic fillers, etc., which are usually added to polyolefins. Various additives may be blended within the range that does not impair the purpose of the present invention.

The thickness of the ultra-high molecular weight polyethylene porous film obtained by the method of the present invention can be appropriately selected depending on the application, but is usually in the range of 50 to 500μ, preferably 100 to 250μ. Further, the film may be used alone or may be laminated with other resins, paper, cellophane, or aluminum foil.

The porous film of ultra-high molecular weight polyethylene obtained by the method of the present invention is thinner, more flexible, and has better mechanical strength than the porous film obtained by the conventional method, and the size of the micropores is relatively uniform. Because of this, it is suitable for applications such as battery separators, paper, and sliding tapes.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Ultra-high molecular weight polyethylene with an intrinsic viscosity [η] of 17 dl/g and a melting point of 137°C (trade name Hi-Zex Million 240M, Mitsui Petrochemical Industries, Ltd.)
A block was formed by compression molding using a commercially available product (manufactured by J.D. Co., Ltd.), and the block was sliced to obtain a sheet with a width of 50 mm and a thickness of 0.5 mm. Next, the sheet is heated with a far infrared heater.
After preheating to 80℃, it was rolled at a speed of 37cm/min with the first rolling roll preheated to 145℃, and then
Rolling at a speed of 37 cm/min with a second rolling roll heated to 155°C, taking off at a speed of 40 cm/min with a take-up roll heated to 80°C, width 45 mm x thickness 210 μ
porous film (pore size, 3~5μ x 20
~30μ) was obtained. The degree of haze of the porous film was measured according to ASTM D 1003 and was found to be 68%.

Comparative Example 1 The molding method of Example 1 was carried out in the same manner as in Example 1 except that the temperature of the second rolling roll was 145°C. As a result, the resulting film has a haze of 15
% and transparency was good and did not become porous.

Comparative Example 2 In the molding method of Example 1, when the temperature of the second rolling roll was set to 165° C., the film was torn when taken off and molding could not be performed.

Claims (1)

[Claims] 1. A sheet of ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of at least 5.0 d/g or more, with a melting point +15
1. A method for producing an ultra-high molecular weight polyethylene porous film, which comprises rolling it with rolls at a temperature of from 0.degree. C. to melting point + 25.degree.