JPH0621177B2 - Method for producing ultra high molecular weight polyolefin porous permeable film - Google Patents

Description

The present invention relates to an ultrahigh molecular weight polyolefin porous permeable film, and more particularly to a method for producing a highly permeable film.

[Conventional technology]

As a typical method for producing a polyolefin porous film, in JP-A-55-60537, a mixture of a polyolefin and a paraffin wax is extruded to obtain a sheet or film, and a paraffin wax is extruded to obtain a porous film. However, since normal polyolefin is used, the amount of paraffin wax that can be added is limited from the viewpoint of moldability, and as a result, a high permeation amount is obtained. In addition, it has the disadvantage of weak strength.

[Problems to be solved by the invention]

The present invention is to solve the problems of the above-mentioned method, and in particular to provide a polyolefin permeable porous film having a high permeation amount and a high strength at an industrial production rate and economical efficiency. It is about. Further, the gist of the present invention is to use a mixture of an ultrahigh molecular weight polyolefin and a specific hydrocarbon-based plasticizer with an extruder to obtain a film or a hollow sheet-shaped molded product, and then extract the plasticizer and the stretching conditions. And an appropriate combination of and to carry out biaxial stretching to provide an ultrahigh molecular weight porous polyolefin permeable film as described above.

[Means for solving problems]

Porosity of permeable film described in the present invention, various breathable films, although application to the micro filter etc various filter is expected that this case is particularly high permeation amount is a mandatory condition, which of the N ₂ gas The transmittance PN _{2 is} at least The above is necessary.

Further, the film thickness is further specifically required to be 100 μm or less. The melt of the mixture of the ultra-high molecular weight polyolefin and the plasticizer used in the present invention is a film obtained in the case of industrially high-speed molding from the problem of stability of flow etc.
The thickness of the sheet or hollow molded product is limited to several 100 μm, and it is necessary to stretch this molded product to make it thinner.

Further, this stretching has the advantage of increasing the film strength.

Next, a specific method of the present invention will be described.

As the ultrahigh molecular weight polyolefin used as the base material, polyethylene and polypropylene having an intrinsic viscosity [η] in decalin at 135 ° C. of 5 dl / g or more are suitable. Below this, the molecular weight is too low, and the viscosity of the melt mixed with the plasticizer (B) is too low, making it difficult to form a sheet or film hollow body by extrusion.

Next, as the hydrocarbon-based plasticizer (B), if it is liquid at room temperature, especially when the ratio of the plasticizer is increased, it is liquid even if it is simply mechanically blended with the ultrahigh molecular weight polyolefin and supplied to the extruder. In the feeding section, there are drawbacks such as slippage and difficulty in extrusion molding, and further, bleeding of the plasticizer to the surface of the film or the like in the subsequent stretching step or the like to make the composition non-uniform. Paraffin wax, which is solid at room temperature, or higher aliphatic alcohols such as stearyl alcohol and ceryl alcohol are not suitable for general production. In particular, higher aliphatic alcohols such as stearyl alcohol and ceryl alcohol that are solids at room temperature can obtain fine particles, and mechanical dry blending with powder ultra-high molecular weight polyolefin tends to be very uniform. If it is supplied to the supply part, stable extrusion molding is possible, and it is very suitable for industrial production. Furthermore, since aliphatic alcohols have hydroxyl groups, they have a slightly poorer compatibility with polyolefins than paraffin wax, and are prone to phase separation during cooling and solidification, and the ease of phase separation should be controlled. Due to
The porous permeable film has the advantages of increasing the diameter of the holes and increasing the amount of permeation. The mixing ratio of the ultra high molecular weight polyolefin (A) and the plasticizer (B) is appropriately 5 to 60% by weight of (A) and 40 to 95% of (B). When the component (A) is too much, Firstly, it becomes impossible to extrude the melt of the mixture by the extruder. Secondly, even if the component (B) is extruded, the porosity does not increase and the desired film having a high permeation amount can be obtained. Can not.

On the other hand, if the amount of the component (A) is too small, the melt viscosity of the mixture becomes too low, making it difficult to form a film or a hollow sheet body. Sheet, film and hollow molded body (C) are (A)
After mixing (B) with a Henshur mixer, V-blender, etc., this mixture is fed to an extruder and molded by a T die or a cylindrical die. The molded body (C) thus obtained is combined with biaxial stretching and extraction and removal of the plasticizer (B) to obtain a porous permeable film. In order to obtain, it is necessary to combine the following conditions appropriately.

At what stage the plasticizer (B) is extracted and removed Stretching method: uniaxial stretching, biaxial stretching (same or successive) Stretching rate Stretching temperature Stretching ratio The lower the stretching rate, the higher the permeation amount. ,
Assuming industrial production, it is inappropriate to reduce the size.

The combinations of conditions for obtaining the desired high-permeability film are shown below.

Generally speaking, uniaxial stretching is unsuitable because the amount of permeation is extremely reduced under any condition and the film is easily torn. Also, in the biaxial stretching, it is necessary to select a condition in which stress is not applied to the ultra-high molecular weight polyolefin as much as possible.

Extraction and removal of the plasticizer (B) can be carried out with the solvent (D) in which the component (B) is soluble.For example, in the case of paraffin wax, in the case of higher aliphatic alcohol such as hexane etc. stearyl alcohol etc. , Methanol, ethanol, butanol etc. can be easily implemented. This extraction and removal may be carried out before or after biaxial stretching, further by stretching in the machine direction in the first stage, then extracting and removing, and further stretching in the transverse direction in the second stage.

Hereinafter, these are respectively referred to as extraction stretching, post-extraction stretching, and intermediate extraction stretching. The pre-extraction drawing is more susceptible to the draw ratio and temperature than the other two, and it is necessary to pay attention to the selection of conditions. When the longitudinal stretching ratio is λ ₁ and the lateral stretching ratio is λ ₂ , λ ₁ > 1.
5, λ ₂ > 1.5 and λ ₁ × λ ₂ <9 must be satisfied. This is because when λ ₁ × λ ₂ exceeds 9, the amount of transmission is significantly reduced. Furthermore, the reason that λ ₁ and λ ₂ are 1.5 times or more is that when the above-mentioned molded body (C) is obtained by a T die or a cylindrical die, when a high speed molding is performed, shear force is exerted on the melt in the die. This is because the ultra-high molecular weight polyolefin molecules are oriented, so that it is necessary to give a stretch of 1.5 times or more in both directions from the viewpoint of increasing the film strength transmission amount.

Stretching temperature is below the melting point of ultra high molecular weight polyolefin Tm T
Temperatures above m-10 ° C are suitable. Above Tm, it is difficult to achieve industrially stable stretching.
When the temperature is lower than 0 ° C, the amount of permeation decreases sharply. Further, the successive stretching is more preferable than the simultaneous stretching because the reduction in the amount of permeation due to the stretching is low. It is also a method that is industrially suitable.

Next, in the post-extraction stretching method and the intermediate extraction stretching method, the selection of conditions becomes looser than in the above-described pre-extraction stretching method. That is, the stretching ratio should satisfy λ ₁ > 1.5, λ ₂ > 1.5, and λ ₁ × λ ₂ <20, and the stretching temperature should be below the melting point Tm of the ultrahigh molecular weight polyolefin (A).

By the method of the present invention described above, it becomes possible to obtain an ultrahigh molecular weight porous polyolefin permeable film having high permeability and excellent strength. This film is applied to moisture permeable film, and 0.01 ~ 0.5μ
It can be applied to various types of microfilters because it has good fine particle removability.

〔Example〕

Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist. Various physical properties shown in the specification and examples of the present invention were measured according to the following methods.

N ₂ gas permeability coefficient Using Amicon UF stirring cell 12 type cell, differential pressure 1kg
/ Cm ² , measured at a temperature of 25 ° C Porosity (%): (pore volume / porous film volume) x 1
00 Examples-1 to 2 Comparative Examples 1 to 4 Intrinsic viscosity [η] = 13.5 20% by weight of ultra-high molecular weight polyethylene powder having a melting point of 135 ° C and 80% by weight of stearyl alcohol fine particles were dry blended, and then the supply part was water-cooled. It was supplied to a 40 mm extruder cooled in step 3. A 30 mm extruder was further attached to this tip, and the above blend was made into a uniform melt and extruded from a T-die having a width of 20 cm to obtain a 0.5 mm sheet.

This sheet was stretched under various conditions using a biaxial stretching machine, and then stearyl alcohol was extracted and removed with ethanol at 50 ° C. to obtain various porous permeable films. The results are shown in Table-1.

Examples 3 to 7 Comparative Examples 5 to 7 Stearyl alcohol was extracted and removed from a 0.5 mm sheet obtained in the same manner as in Example 1 with ethanol at 50 ° C., and then stretched with a biaxial stretching machine under various stretching conditions. To obtain various porous permeable films. The results are shown in Table-2.

Example-8 A 0.5 mm sheet obtained in the same manner as in Example-1
After stretching 4 times in the machine direction at 4 ℃, extract stearyl alcohol with ethanol at 50 ℃, and then in the transverse direction at 120 ℃.
It was stretched twice. The thickness of the obtained porous permeable film is 1
Porosity at 9μ The value of was shown.

Examples 9 to 11 Ultra high molecular weight polyolefin (A), type of plasticizer (B) (A),
Table 3 shows the results of obtaining a porous permeable film by performing extraction and subsequent stretching in the same manner as in Example 3 while changing the mixing ratio of (B) variously.

Example-12 With respect to the permeable film obtained in Example-3, styrene latex having a particle diameter of 0.038 µ was dispersed in water,
When the removal rate was measured, it showed a value of 99% or more.

Claims (4)

[Claims] 1. A hydrocarbon-based plasticizer (B) 40 having an intrinsic viscosity [η] of 5.0 dl / g or more and an ultrahigh molecular weight polyolefin (A) of 5 to 60% by weight and a boiling point of at least the melting point of (A). ~ 95% by weight
The mixture consisting of is extruded through a die into a film, a sheet, or a hollow molding (C), and the stretching ratio in the longitudinal direction is λ.
₁ , λ ₁ > 1.5, where λ ₂ is the draw ratio in the transverse direction,
A film obtained by biaxially stretching the above molded product (C) below the melting point of (A) so as to satisfy λ ₂ > 1.5 and λ ₁ × λ ₂ <9.
A method for producing an ultrahigh molecular weight polyolefin porous permeable film, which comprises extracting and removing component (B) with a solvent (D) in which component (B) is soluble. 2. Polyolefin (A) having an ultrahigh molecular weight at a stretching temperature.
A melting point (Tm) of Tm and Tm-10 ° C.
The method for producing a transparent film according to item (1). 3. An ultrahigh molecular weight polyolefin (A) of 5 to 60% by weight having an intrinsic viscosity [η] of 5.0 dl / g or more and a hydrocarbon plasticizer (B) 40 having a boiling point of not less than the melting point of (A). ~ 95% by weight
The mixture consisting of a film, a sheet or a hollow molded article (C) is extruded through a die, and a plasticizer (B) is added from the (C) (B).
After extraction and removal with the component-soluble solvent (D), when the longitudinal magnification is λ ₁ and the lateral magnification is λ ₂ , λ ₁ > 1.5, λ ₂ > 1.5 and λ ₁ × λ ₂ <20 are satisfied. So that the molded product (C) is (A)
A method for producing an ultrahigh molecular weight polyolefin porous permeated film, which comprises biaxially stretching at a temperature equal to or lower than the melting point. 4. A hydrocarbon plasticizer (B) 40 having an intrinsic viscosity [η] of 5.0 dl / g or more and an ultrahigh molecular weight polyolefin (A) of 5 to 60% by weight and a boiling point of at least the melting point of (A). ~ 95% by weight
The mixture consisting of is extruded through a die into a film, sheet, or hollow molding (C), and the molding (C) is first stretched in the machine direction at a temperature not higher than the melting point of (A) at a stretching ratio λ _1. , The plasticizer (B) is extracted and removed with the solvent (D) in which the component (B) is soluble,
Then, in the transverse direction, at a temperature below the melting point of (A), the draw ratio λ
_When stretched to ₂ , λ ₁ > 1.5, λ ₂ > 1.5 and λ ₁
A method for producing an ultra-high molecular weight polyolefin porous permeable film, which comprises biaxially stretching a molded product (C) so as to satisfy xλ ₂ <20.