KR830001538B1 - Microporous film with improved permeability and reduced electrical resistance - Google Patents

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[Name of invention]

Microporous film with improved permeability and reduced electrical resistance

Detailed description of the invention

The present invention relates to a microporous film having improved permeability and reduced electrical resistance. Recent developments of continuous porous microporous polymer films are also described in U.S. Pat.Nos. 3,839,516, 3,801,404, 3,679,538, 3,558,764 and 3,426,754. Research is being promoted to find applications that can be developed. This film is actually a gas-permeable moisture barrier that can be used for exhaust vents, gas-liquid delivery media, storage separators and many other applications. One drawback of these films, which had been restricted in use in the past, is their hydrophobicity. This is particularly true when using polyolepan films, which are one of the polymers often used in the production of microporous films. Since these films are not wettable to moisture and solution, they cannot be used in the field of theoretical application as a filtration medium such as an electrochemical separator component.

In order to solve these problems, various proposals have been made in the past, and examples thereof include U.S. Patent Nos. 3,853,601, 3,231,530, 3,215,486, and Canadian Patent No. 981,991. These patents have various hydrophilic coating agents. V) or impregnant is used. Such coatings or impregnants, although effective for a limited time, tend to be removed in a relatively short time by a solution that comes in contact with the film or fiber in which they are contained.

Various attempts have been made to impart hydrophilicity to hydrophobic microporous films, usually by low energy plasma treatment. This plasma treatment is accomplished by first activating the surface of the microporous film using argon or hydrogen plasma and then grafting a suitable free radical polymerized species such as polyacrylic acid.

Plasma treatment results in a film having only rewetable surfaces. The surface of the film is also closed when wet, so that free movement of moisture through the interior of the film is inhibited or prevented.

Inevitably closing the surface pores renders the film unusable for any filtration use, increases the electrical resistance of the film and reduces the dimensional stability of the film, as manifested in significant dry shrinkage. As mentioned above, a disadvantage of plasma treatment is that it is limited in its ability to wet only the surface of the microporous film. It has been observed that due to the particularly large surface area of the microporous film of the type described above, the film exhibits some functional properties such as low electrical resistance only, low electrical resistance, or the rate of water movement through the film compared to known surfactant systems. There is no guarantee that they will appear. In other words, pore closure and simple surface wettability, which are the main drawbacks of plasma treatment, are thought to be due to the complex combination of factors such as low energy plasma tends to be easily deactivated by the large surface area of the microporous film.

This reduces the likelihood that the internal areas in the microporous film can be activated. Likewise, when the grafted monomer first comes into contact with the surface of the microporous film activated by the plasma, it is competingly accepting the grafting monomer represented by the free radical polymer graft first generated at the film surface.

Therefore, the graft polymer chain existing from the beginning on the surface of the film develops as its speed gradually accelerates as the reaction proceeds. The resulting elongated graft polymer chain appears on the film surface and is closed by disrupting the micropores on the surface in the presence of moisture. Examples for producing hydrophilic films using plasma treatment are described in US Pat. Nos. 3,992,495 and 4,046,843.

Another method for making wettable polyethylene films that can be used for electrical battery separators is described in V.D'Agostion and J. Lee, "Method of Making High Performance Graft Polyethylene Battery Separator" [U.S. Summarized in National Technical Information Service, AD Report No 745,571 (1972), US 78chemical Abstract 5031 f (1973)], "Low Temperature Alkaline Capacitor Separator" by V.D'Agostino and J.Lee [27 Power Sources symp . 87-91 (1976), summarized in 86 chmical Abstract 158277f], in V.D'Agostino, J.Lee and G.Orban's "Zinc-Silver Oxidation Storage Battery" (A.Fleischer and J.Lander ed, 1971). It is included.

The paper here mentions a product known as RERMION ^™ developed by RAI Research corp. In short, the method for preparing this material uses beta-radiation to crosslink 1 mil-thick polyethylene sheets and to graf them with methacrylic acid under Co 60 gamma irradiation in a suitable solution.

The grafted material is rinsed to remove the homopolymer, and then converted to a salt form in high temperature KOH, followed by rinsing to remove the remaining base and to dry. In the initial cross-linking step, microcracks or longitudinal gaps are generated in non-porous polyethylene. The microcracks or longitudinal gaps are too small to be seen as electron microscopes. The diameter of these microcracks is estimated to be about 20 mm (10 ^-8 cm). In the sense of the microporous film used in the present invention, the film prepared by grafting the microcracks with methacrylic acid is not microporous and has an average size of about 100-5,000 mm 3. The extremely small microcracks of PERMION ^™ inhibit the mass transfer of mobile electrons with species, usually caused by oxidation-reduction reactions through any significant rate of film. This occurs at relatively large (30-40 millionhms-in ² ) electrical resistance. Moreover, PERMION ^™ is not dimensionally stable in more than one direction, which is a sign of significant swelling.

Non-porous polymeric materials, such as polyethylene and polypropylene, can be reacted with various monomers such as acrylic acid using various ionizing radiations as detailed in US Pat. Nos. 2,999,056, 3,281,263, 3,372,100 and 3,709,718. It is a known fact.

None of these patents are concerned with microporous films, so they are related to the particular problem associated with them.

Therefore, the research on the hydrophilic microporous film having a relatively low wettability and a permanently wettability with improved partial permeation rate exceeding the microporous film is continued. The present invention has been developed in accordance with this research trend.

An object of the present invention is to develop a method for imparting relatively permanent hydrophilicity and improved permeability to a hydrophobic microporous film and lowering the electrical resistance of the film. In addition, to produce a hydrophilic microporous film with reduced electrical resistance to solve the various problems of the prior art as described above.

According to one aspect of the present invention, as a method of improving the water permeability and lowering the electrical resistance by making the microporous film made of hydrophobic polyolefin-based hydrophilic,

(A) A microporous continuous porous film of hydrophobic polyolefin type having a much smaller bulk density than the bulk density of the precursor film before processing and having an average pore length of about 200-10000 Å and a surface area of at least about 10 / g. The surface of the micropores of is coated with at least one hydrophilic organic hydrocarbon monomer having at least one double bond and at least one polar functional group and having about 2-18 carbon atoms,

(B) about 0.1-10 wt. Chemically fix hydrophilic organic hydrocarbon monomer of sufficient amount to microporous film of microporous film to the weight of uncoated microporous film to be able to maintain adhesion of micropore and maintain continuous bubble characteristics of micropore. In (a), the coated microporous film is irradiated with ionizing radiation of about 1-10 megarad.

According to another feature of the present invention, a method for producing a microporous film made of a hydrophilic continuous bubble,

(A) make a hydrophobic microporous film of continuous bubbles with a bulk density much smaller than the bulk density of the precursor film before processing, with an average pore size of about 200-10,000Å and a surface area of at least 10 m ² / g;

(B) Approx. 0.1-10 wt. In applying the microporous surface of the microporous film of at least one hydrophilic organic hydrocarbon monomer having about 2-18 carbon atoms having at least one double bond and at least one polar functional group. Irradiation of about 1-10 megalates is possible in an amount sufficient to the weight of the uncoated microporous film to maintain the continuous bubble properties of the microporous film. To chemically fix the hydrophilic organic hydrocarbon monomer coating film to the surface of the micropores of the microporous film,

The backbone of the present invention is relatively permanent in wetted microporous film made of continuous bubbles by chemically fixing the pores in the amount of graft hydrophilic monomers while irradiating ionizing radiation while maintaining the continuous bubble properties of the microporous film. It is to give hydrophilicity. Moreover, chemical fixation of hydrophilic monomers occurs even up to the pores located inside the microporous film. By controlling the amount of monomer chemically fixed to the surface of the micropores, the grafts of the polymer chains appearing in the irradiation can be arranged along the pore surface, so the pores were confused and closed.

The present invention relates to a hydrophilic microporous film and a method for producing the same. Porous films are divided into two general forms, the first of which is an independent bubble (or closed pores) with no pores interconnected. It is a film of continuous bubbles (or openings) connected to each other to the surface. Porous films according to the invention belong to the latter form.

In addition, the pores of the porous film according to the present invention are microscopically small, and the arrangement or configuration of these pores is distinguished only by microscopic observation. In practice, the continuous bubbles in the film are usually much smaller than can be measured using an optical microscope because the wavelength of visible light is about 5000 kHz, so the longest surface dimension or planar dimension of the continuous bubble is much longer. . However, if the microporous film according to the present invention can be resolved in detail up to a pore structure of 5000 kPa or less, electron microscopy can be used.

A feature of the microporous film according to the present invention is that the bulk density is small (hereinafter referred to as "small" density). That is, these microporous films have a bulk density much smaller than that of films of the same polymer. "Volume density" is the weight per unit of geometric or total volume of a film, the total volume of which is measured by immersing the film having the weight of the base in a vessel partially filled with mercury at 25 ° C. and atmospheric pressure. When the mercury level rises in volume, it represents the total volume. This method is called the mercury volumetric method and is described in detail in the Encyclopedia of Chemical Technology (Vol. 4, p. 892, Interscience, 1949).

It has a microporous continuous bubble structure, and a porous film having a small bulk density is produced. Examples of such a film having a microporous structure are described in US Pat. No. 3,426,754, which is patented to the inventors. According to the manufacturing method described herein, a film having a crystalline elasticity at about 10-300% of its original length at room temperature may be contracted to a limited extent even if the film is not contracted or contracted after cold drawing. When heat setting the stretched film while applying tension

All of the above patents relate to a process for preparing hydrophobic microporous films which become hydrophilic according to the present invention, but suitable hydrophobic microporous films can be prepared according to US Pat. No. 3,839,516. In other words, this patent is a method for producing a microporous film called "dry stretching method". In addition, US Patent No. 3,839,516 can also be prepared according to the microporous film manufacturing method called "solvent stretching method", the above two patents are also presented by reference in the present invention. In each of these patents, the untreated film is

Suitable precursor films that can be used for producing microporous films according to the dry stretching method and the solvent stretching method are detailed in each of the above patents. In other words, in the dry drawing method, when a standard strain of 65% relative humidity and 50% standard stress (height) of 25% at 25 ° C. is given (at least 50% in this case and at least 80% is better) A nonporous, crystalline, elastic polymer film with elastic recovery at recovery time 0 is used.

Elastic recovery refers to a measure of the ability to return to its original size after drawing an object or structure with a certain shape, such as a film, and is calculated according to the following equation.

×100Elastic Recovery (ER)% =

× 100

A standard strain of 50% can be used to confirm the elastic properties of the starting film, but this is just an example. In general, these starting films exhibit greater elastic recovery at less than 50% strain and somewhat smaller at 50% or more, which is comparable to each elastic recovery at 50% strain. The starting material is an elastic film having a% crystallinity of at least 20%, at least 30% range is best, and at least 50% (50-90% or more). The percent crystallinity is determined by the X-ray method by R.G.Quynn et al. (Journal of Applied Polymer Science, Vol. 2, No. 5, pages 166-173, 1959).

The importance of crystallinity and examples of polymers can be found in detail in Golding's book (polyners and Resins, D. van Nostrand, 1959).

Other elastic films that are considered suitable for producing pioneer films used in the dry softening method are described in British Patent No. 1,052,550 (December 21, 1966).

Elastic precursor films used in the manufacture of microporous films by the dry soft method should be distinguished from films made of classical elastomers such as natural and synthetic rubbers. In this classical elastomer, the stress-strain actuation, in particular the relationship with stress-temperature, is governed by the centrophy-strain mechanism (rubber elasticity). The positive temperature coefficient of resilience, i.e. the reduction of stress due to the falling temperature and the complete loss of elastic properties at the glass transition point, is a special result of entropy-elasticity. On the other hand, the elasticity of the elastic precursor film used in the present invention is different

In normal thermodynamic experiments on these elastomeric precursor films, the increase in stress with the falling temperature means that the elasticity of these materials is dependent on the terms of energy without being influenced by the entropy.

In particular, it was confirmed that the elastic precursor film by dry stretching maintains the stretching characteristics at a temperature at which normal entropy-elasticity does not work any more. Therefore, the stretching mechanism of the elastic precursor film by dry stretching is considered to be based on an energy-elastic relationship, and such an elastic film can be regarded as a "nonclassical" elastic body. In addition, the solvent stretching method uses a precursor film containing at least two components, an amorphous component and a crystalline component. Thus, crystalline materials that are crystalline and amorphous are suitable for the process. The degree of crystallinity of the precursor film is at least 30 vol. % Of cotton may be at least 50vol. % Is best.

Synthetic resin materials, i.e., polymers, of the precursor film used in the process according to the present invention include olefin polymers (e.g. polyethylene, polypropylene, poly-3-methylbutene-1, poly-4-methyl pentene-1) and propylene. , 3-methyl butene-1,4-methyl fenton-1 or copolymers of ethylene and their mutual or minor amounts of other olefins (e.g. copolymers of propylene and ethylene, large amounts of 3-methylbutene-1 and n Copolymers of small chains of straight chain n-alkenes or other relatively long chains, such as octene-1, n-hexadecene-1, n-octadecene-1, 3-methylpentene-1 and 3-methylbutene-1 and

For example, in general, when a propylene homopolymer is to be used in the dry drawing method, it has a% crystallinity as described above, has a weight average molecular weight of about 100,000-75,000 (e.g., about 200,000-500,000), and a melt index (ASTM-D -1236-57T, Part 9, p. 38) use isostatic polypropylene, approximately 0.1-75, to produce a final film product with the required properties. It should be noted that "olefin polymer" and "olefin polymer" are used interchangeably and refer to polymers prepared by polymerizing olefin monomers using an unsaturation degree.

w/

n)가 약 3.8정도(약 3.8-13정도가 좋음)인 폴리에틸렌 단독중합체를 사용하여 용매연신법으로 미소다공성필름을 제조하면된다. 더욱이 핵생성제(nucleating agent)를 중합체에 가하여 용융지수가 0.3정도로 낮은 중합체를 사용한 soehugen 특허출원에 상술된 선구 필름을 제조할 수 있다.Suitable polymers for the solvent stretching method are those polymers used in the invention described in the US patent application No. 44,805 (June 1, 79) by the inventor and Johnw soehngen, which have been described in the patent. The low solvent stretching method for producing microporous film "] is cited in the present invention. Therefore, the density is about 0.960-0.965g / cc, the highest melt index is about 3 (about 3-20 is good), and the molecular weight distribution ratio (

w /

The microporous film may be prepared by solvent stretching using a polyethylene homopolymer having n) of about 3.8 (about 3.8-13). Furthermore, a nucleating agent can be added to the polymer to produce the precursor film described in the soehugen patent application using a polymer having a low melt index of about 0.3.

The precursor film forming apparatus may be a known one. For example, a conventional film extruder equipped with a shallow channel measuring screw and a coat hanger die may be used. In general, the resin is supplied to the heated jacket and the hopper of the screw extruder.

The resin is melted and moved to the die with a screw to extrude the resin into a film through a slit of the die and then stretched using a take-up roll or casting roll. Use one or more takels in various combinations. The die holes or die slits are in the range of about 10-200 mils. Using a device of this type, the film is extruded at a drawdown ratio of about 5: 1-200: 1, preferably 10: 1-50: 1. "Draw down ratio" or simply "draw ratio" means the ratio of the film take-up speed or film take-up speed to the film speed exiting the extrusion die. In general, the melt temperature for film extrusion should not be higher than about 100 ° C. above the melting point of the polymer and should not be about 10 ° C. below the melting point of the polymer. For example, polypropylene is extruded at a melt temperature of about 180-270 ° C, preferably 200-240 ° C. The polyethylene is extruded at a melt temperature on the order of 175-225 ° C.

When using the precursor film in the dry drawing method, it is better to perform the extrusion operation under the conditions of quick cooling and quick draw down to obtain maximum elasticity. This would allow the rake up roll to be relatively adjacent to the extrusion slot, i.e. within 2 inches and within 1 inch. The “air knife” operated at a temperature between 0 ° -40 ° is used in a 1 inch slot to quickly cool and solidify the film. Take-up rolls rotate at a speed of 10-1000 ft / min, preferably 50-500 ft / min.

When the precursor film is used in the solvent stretching method, the extrusion process is performed under slow cooling conditions so that large condensation generated can be avoided, but it may be caused by rapid cooling to obtain the maximum crystallinity. It is desirable to minimize any orientation structure and stress. This can be done by adjusting the distance between the cooling take-up roll and the extrusion slit.

While the content so far relates to the slit die extrusion method, another method for forming the precursor film considered in the present invention is the blown film extrusion method, which uses the same hopper and extruder as in the above-mentioned slit extruder. to be. The melt is fed into the die from the extruder and from the die the melt is extruded through a circular slot to form a tubular film having an initial diameter of D ₁ . As the air enters the tubular film through the inlet, it is attached so that the diameter of the tubular film becomes D ₂ . Different cooling rates can be achieved by blowing air around the inside of the extruded tubular film using a device such as an air ring.

A device such as a cooling mandrel may be used to cool the inside of the tubular film. After a while, the film is wound in a take-up roll while the film is cold cured.

When using the blown film method, the drawdown ratio is 5: 1-100: 1, the slot diameter is 10-200ml (40-100mil is preferred), and the D ₂ / D ₁ ratio is 1.0-4.0 (about 1.0 -2.5 is recommended) Take-up speed should be 30-700ft / min. The melt temperature range is the same as for the slit die extrusion method as previously described.

The extruded film is first heat treated or slow cooled to improve the crystal structure, which can be achieved by increasing the crystal size and removing defects. In general, this slow cooling operation is carried out for several seconds to several hours, that is, 5 to 24 hours (preferably about 30 seconds to 2 hours) at a temperature about 5-100 ° C. below the melting point of the polymer.

For polypropylene, the suitable slow cooling temperature is about 100-155 ° C. An exemplary method for carrying out the slow cooling operation is to heat the extruded film under tension or tensionless state while remaining in the oven at the required temperature for about 30 seconds to 1 hour. As a suitable example, the crystalline western film produced is treated by one of the two alternative methods described above to obtain a hydrophobic microporous film that can be used in the present invention.

The first suitable method is described in U.S. Patent No. 3,801,404, known as the dry stretching method, which (1) increases the elastic film by extending the cooling film so that the porous surface portion or area is perpendicular or parallel to the stretching direction. , (2) hot stretching the stretched film to increase the fibrous or pores or continuous bubbles parallel to the stretching direction, and (3) stabilizing the film by heat-setting the prepared porous film with a constant length. To grant.

"Cooling stretching" refers to stretching the film longer than the original length at a constant temperature, in which case the stretching temperature of the film is when the film is uniformly heated at a rate of 20 ° C per minute starting at 25 ° C. The temperature is below the temperature at which melting starts. "Hot stretching" refers to stretching the film above the temperature at which melting occurs when the film is uniformly heated at a rate of 20 ° C. starting at 25 ° C. for 1 minute, in which case the temperature below the temperature at which melting occurs, ie the polymer Which means stretching at temperatures below the normal melting temperature of

The temperature at which melting begins depends on the type of polymer, the molecular weight distribution of the polymer, and the crystal form of the film. For example, it is convenient to draw a polypropylene elastic film at room temperature (25 ° C.) while cold drawing it at about 120 ° C. or less, if possible, at about 10-70 ° C. It is preferred to draw the cold drawn polypropylene film between about 130 ° C. and 150 ° C. for hot drawing above 120 ° C. and below the melting temperature. The stretched temperature is regarded as the stretching temperature of the film itself. Drawing operations in these two stages must be continuous in the order of hot drawing after cold drawing in the same direction, but the continuous method, unless the cold drawn film contracts to a significant extent less than 5% of the cold drawn length before hot drawing, It can also be done as semi-continuous or discontinuous.

For the initial length of the elastic pitch drawn in the above two steps, the total amount should be in the range of about 10-300 %% and about 50-150%. Furthermore, the ratio between the hot draw amount and the total draw amount is in the range of about 0.10-1 or more and -0.99: 1 or less, preferably about 0.50: 1-0.97: 1 and about 0.50: 1-0.95: 1 is best. The relationship between cold drawing and hot drawing is called "drawing ratio" (hot drawing%: total drawing%).

In the stretching operation that requires the application of heat, the film is heated by a moving roller through a heated liquid, heated gas, etc., and then heated by an electric resistance method.

Heat-fix the stretched film after the two-step stretching method above. The heat treatment is carried out in the temperature range of about 125 ° C-melting temperature or less, preferably in the range of about 130-160 ° C for polypropylene and about 75 ° C-melting temperature or less for polyethylene. The range of 130 ° C. is suitable and for the other polymers listed above is carried out at similar temperatures.

This heat treatment should be performed under tension conditions where the shrinkage does not occur or shrinks at all, only to a controlled degree of no more than about 15% of the stretched length of the film. However, additional tension should not be given to stretch the film by more than 15%. In addition, the degree of tension should be such that the stretched length does not shrink below 5% or there is no shrinkage at all.

The heat treatment time performed together with the stretching work and sequentially after the stretching work should not be more than 0.1 second at higher annealing temperature, and generally within the range of about 5 seconds to 1 hour. Do. The heat setting step described above may be carried out in the atmosphere or in a nitrogen, helium or argon atmosphere. A second suitable method for producing a microporous film is the solvent stretching method described in US Pat. No. 3,839,516, which (1) differs in the volume of one of at least two components (amorphous and crystalline).

In general, solvents with values of or near the Hildebrand solubility parameter of the polymer should have a solubility suitable for the stretching process. Hildebrand solubility parameter is a measure of the cohesive energy density. The basic principle is thus based on the fact that solvents having a cohesive energy density similar to that of the polymer should have a great affinity for the polymer and be suitable for the process of the invention.

Common categories of swelling agents that can be selected for special polymer films include lower aliphatic ketones (e.g. acetone, methyl ethyl ketone, cyclohexane), lower aliphatic acid esters (e.g. ethyl formate, butyl acetate, etc.), halogenated hydrocarbons (E.g. carbon tetrachloride, trichloroethylene, perchloroethylene, chlorobenzene, etc.), hydrocarbons (e.g. heptane, cyclohexane, benzene, xylene, tetralin, decalin, etc.), nitrogen-containing organic compounds (e.g. pyridine, formamide) , Dimethylformamide, etc.), ethers (eg methyl ether ethylether, dioxane, etc.).

Mixtures of two or more of these organic solvents are also used. The swelling agent is a compound consisting of carbon, nitrogen, hydrogen, oxygen, halogen, and sulfur. It is preferable to use a carbon atom having a carbon atom number of about 20 or more (about 10 is preferable).

Solvent stretching is carried out in the range from the freezing point of the swelling or swelling agent to a temperature below the temperature at which the polymer is solubilized (ie room temperature to about 50 ° C.).

The thickness of the precursor film used in the solvent stretching method is about 0.1 to about 20 mils or two or more. As a suitable example, the precursor film is biaxially stretched according to the method described in US Patent Application No. 44,801 (June 1, 79). This method is suitable for the stretching conditions in the uniaxial direction and improves the water permeability of the microporous film uniaxially stretched. The uniaxially stretched microporous film can be stretched laterally to further improve the water permeability. Therefore, it is good to solvent-stretch the precursor film in the short axis direction which does not exceed about 350% of the initial length (30% is the best).

Typically, after removing the solvent, do not stretch in the same direction. The stabilization phase can be either heat setting or crosslinking. In this heat treatment, the temperature range is about 125 ° C-below the melting temperature, about 130-150 ° C for polypropylene, and about 115 °-below the melting temperature for polyethylene. 130 ° C is good and similar temperatures can be applied to the other polymers listed above. This heat treatment does not shrink or pre-shrink only to a controlled degree not exceeding about 15% of the length drawn on the film.

The heat treatment time carried out together with the solvent stretching operation and the net after the solvent stretching operation should not be more than 0.1 seconds at the higher annealing temperature, and generally within the range of about 5 seconds to 1 hour is good. Is suitable.

The above heat fixation step may be carried out in the atmosphere or in a nitrogen, helium or argon atmosphere.

When the precursor film is biaxially stretched, the stabilization process should be carried out after transverse stretching.

The content and examples of the present invention relate mainly to the olefin polymers described above, but the present invention is also contemplated for high molecular weight acetals such as oxymethylene polymers. Both acetal homopolymers and copolymers are also considered, but suitable acetal polymers in terms of polymer stability include irregular oxymethylene copolymers in which the -OR-group is mixed with -CH ₂ -O-, a cyclic oxymethylene unit in the polymer main chain. In the above-OR-group, R is directly bonded to each other and at least two of the two valences are located on the hex

Other relatively crystalline polymers to which the present invention is applicable include polyalkylene sulfides (e.g. polymethylene sulfide, polyethylene sulfide), polyarylene oxides (e.g. polyphenylene oxide), polyamides (e.g. polyhexamethylene Adiphamide (nylon 66), polycaprolactam (nylon 6), and the like, all of which are known, and need not be described further here.

The hydrophobic microporous film used in the present invention in the tensionless state has a much smaller bulk density compared to that of a polymer having no continuous bubble structure. Therefore, the bulk density of these films is about 95%, preferably 20-40% for the precursor film. In other words, the bulk density is reduced by at least 5%, so 60-80% is good. In the case of polyethylene, it is reduced by 30-80%. The bulk density is about 20-40% of the starting material and the processing rate increases by 60-80% due to the porosity.

When the microporous film is produced by dry stretching or solvent stretching, the final crystallinity of the microporous film is at least 30%, preferably at least 65%, and more preferably about 70-85%. These crystallinities are R.G. It was measured according to the X-ray method of Quynn et al. (Journal of applied poymer science, Vol. 2, No. 5, pages 166-173). The importance of crystallinity and its importance to polymers can be found in detail in Golding's book (polymers and Resins, S. Van Nostrand, 1959).

The microporous film that can be used in the present invention also has an average pore size of about 200-10,000 mm 3, representatively about 400-5000 ° A, and more preferably about 500-5000 m 3. These values are R.G. Mercury porosity measurements detailed in Quynn et al. (Textile Research Journal, pp. 21-34, Jan. 1963) or electron microscopy as detailed in Geil's book (Polymer Single Crystals, p. 69, Interscience Press, 1963). Can be determined by. Electron tissue photographs can be used to directly measure the length and width of pores. The pore width in an electron tissue photograph is generally 5000-10,000 times larger and enlarged. In general, the length of the pores from the electron microscope is about the same as the pore size obtained from the mercury porosimetry.

The microporous film used in the present invention exhibits a surface area within certain predictable limits when produced by the solvent stretching method or the dry stretching method. Typically, the surface area of such a microporous film is inde at least 10m ² / g is suitable to be about 15-25m ² / g.

The surface area is obtained from nitrogen or krypton gas adsorption isotherms using the methods and apparatus described in US Pat. No. 3,262,319. The surface area obtained in this way is usually expressed in m ² / g.

For easy comparison of different materials, multiply this value by the bulk density (g / cc) of the material to obtain the surface area (m ² / cc). Usually the hydrophobic microporous polymer film according to the present invention is suitable and can be hydrophilic in thickness of about 1 mil to about 9 mils.

The hydrophobic microporous film prepared by the above method is wettable and hydrophilic when the surface of the micropores of the film is coated with a hydrophilic monomer or a mixture thereof and exposed to ionizing radiation. Ionizing radiation chemically bonds the hydrophilic monomer to the surface of the micropores, making the hydrophilic relatively permanent. The amount of chemically fixed hydrophilic monomers to be fixed within a certain limit that can control the total porosity of the hydrophilic film while not closing the pores. In addition, by controlling the porosity, it is possible to control the permeability and electrical resistance of the film.

The term "hydrophobic" means a surface through which water passes 0.010 ml or less in 1 minute per 1 cm2 of a flat film surface under water pressure of 100 psi. Likewise, the term "hydrophilic" refers to a surface that will pass more than 0.01ml of water for 1 minute per cm2 under the same pressure.

The hydrophilic monomer used to apply the pore surface of the microporous film according to the present invention comprises at least one double bond which allows the monomer to polymerize or copolymerize at a temperature that does not adversely affect the microporous film under the nutrition of ionizing radiation. Organic hydrocarbon compounds with 2-18 carbon atoms with at least one polar functional group (e.g., carboxy, sulfo, sulfino hydroxyl, ammonio, amino, phosphono, etc.).

Accordingly, the hydrophilic monomers according to the present invention are hydrocarbon compounds such as substituted and unsubstituted carboxylic acids or dicarboxylic acids and ethers thereof having 2 to 18 carbon atoms and having at least one polymerizable and copolymerizable double bond. In the case of vinyl and allyl monomers, in particular itaconic acid, malonic acid, fumaric acid and crotonic acid and their esters or anhydrides, unsubstituted or alkyl-substituted acrylic acids (e.g. acrylic acid, methacrylic acid, acrolein or acrylonitrile): unsubstituted or alkyl Substituted alkyl, cycloalkyl, aryl, hydroxyalkyl or hydroxyaryl acrylates, alkyl substituted dialkylaminoalkylacrylates, epoxyoxy acrylates, vinylsulfonic acid and styrene sulfonic acids: vinyl esters (e.g. vinyl acetate, higher carboxy) Liver vinyl esters, alkyl-substituted vinyls of carboxylic acids with sulfo groups E) vinyl ethers (e.g. unsubstituted or substituted alkyl, cycloalkyl or aryl vinyl ethers): vinyl substituted silicones: vinyl substituted aromatic or heterologic hydrocarbons: diallyl fumarate: diallyl maleic acid: alkyl substituted Phosphate, Phosphate or Carbonate: Vinylsulfo, Ethoxylated Monylphenol and Arc

Since hydrophilic monomers tend to penetrate into the microporous film, it is preferable to use a hydrophilic monomer having 2-14 carbon atoms (preferably about 2-4).

Suitable hydrophilic monomers used in the present invention are acrylic acid, methacrylic acid and vinyl acetate. The amount of hydrophilic monomer that plots the pore inner surface of the microporous film is adjusted to give an appropriate amount of adhesion to impart the required permeability or electrical resistance. As described above, this control is made to preserve the continuous bubble properties of the micropores and to prevent the pores from being closed, and the characteristics of the preceding requirements when treating the microporous film impregnated with the monomers according to the radiation treatment method detailed in the present invention. It can be maintained for a longer time than can be obtained using conventional representative surfactant application. The specific amount of hydrophilic monomer that is chemically fixed to the pore surface is expressed in terms of adhesion (%), i.e. in weight percent of the untreated microporous film, which represents the weight of the hydrophilic monomer coating in the cured microporous film. Therefore, in order to avoid pore closure of the microporous film, the adhesion amount (%) of the hydrophilic monomer chemically fixed to the microporous surface is about 10 wt.% Based on the weight of the uncoated microporous film. About 0.1- about 10 wt. % Is usually about 0.5-2.5wt. % Is good and about 1-2.0wt. The best is% (e.g. 1.5 wt.%).

Depending on the end use of the produced hydrophilic microporous film, a specific amount of adhesion is determined and this amount varies within the range of the amount of adhesion (5) above. For example, when the grafted hydrophilic microporous film is to be used as an electrical storage battery separator, the adhesion amount (%) is selected based on the electrical resistance (milliohm / in ² ) of the final hydrophilic microporous film. It is a function of the adhesion amount (5) of the monomers.

Electrical resistance is a measure of the ability of a microporous film to conduct electrons. Therefore, in general, the greater the electrical resistance of the microporous film, the smaller the efficiency of the microporous film as a battery separator. Therefore, the electrical resistance of the microporous film is determined according to the various adhesion amounts 5 of the hydrophilic monomers, and the electrical resistance is expressed as a function of the adhesion amount 5, and then the adhesion amount 5 is determined for the required electrical resistance. When the electrical resistance of the microporous film a hydrophilic according to the present invention inde it is usual to adjust to about ^{30millihm / in 2 (milliohm-in} 2) good not more than about 10milliohm-in ² to about 5milliohm-in ² below most good.

When the grafted hydrophilic microporous film is to be used as the filter medium, the adhesion amount 5 of the microporous film is determined with respect to the permeation rate of the microporous film. Therefore, the permeation rate is expressed as a function of the amount of adhesion of the hydrophilic monomer (5) and the appropriate amount of attachment (5) is determined for the permeation rate.

If the microporous film is to be used for filtration purposes, the pore size of the film is selected to act as a barrier to the material to be separated and the permeation rate is adjusted to the extent necessary within the limits of the selected pore size.

Therefore, the permeation rate can be adjusted to be about 0.01cc / min / cm2 or more at a pressure difference of about 1 atmosphere, preferably about 0.05cc / min / cm2 or more, and more preferably about 0.5cc / min / cm2.

Therefore, the present invention has several advantages over the hydrophilic films produced in the past.

Since the continuous bubble characteristics of the hydrophilic microporous film prepared in the present invention can be maintained, the film can be transported mass through the film with respect to the movement of water passing through the film by diffusion, which is a much slower process. will be. Mass transport also results in a decrease in electrical resistance.

Another advantage of the microporous film according to the present invention is that the hydrophilic monomer is chemically immobilized on the microporous film, so that the hydrophilic monomer can remain on the microporous surface for a longer time than a typical surfactant, especially after repeated washing. . Moreover, the dimensional stability of the film by this invention is also improving.

Expressed appropriately, the curable functional groups in the hydrophilic monomer can be converted into the most polar form.

This is possible, for example, by reacting an acidic functional group with a base such as KOH to produce the corresponding salt. The salt can thus be obtained by immersing the chemically fixed film in a 2% KOH solution for about 5-30 minutes. This enhances the wettability and flexibility of the film.

Any known coating method can be used to apply the microporous film, but this method can precisely control the amount of adhesion of the hydrophilic monomer. A suitable method for accurately and effectively applying the pore inner surface of the microporous film is to contact the microporous film with various monomers that condense on the microporous surface.

The equilibrium vapor pressure of the hydrophilic monomer (i.e., the vapor pressure at which the condensation rate of the monomer vapor becomes equal to the vaporization rate at a given temperature and the adhesion time (%) is controlled by controlling the contact time with the hydrophilic monomer with the microporous film).

The equilibrium vapor pressure required to apply the hydrophilic monomer at a constant temperature is determined by plotting the amount of attachment (%) and the equilibrium vapor pressures under a constant temperature. As mentioned above, the amount of adhesion depends on the characteristics imparted to the microporous film. The equilibrium vapor pressure to obtain the proper% of attachment is easily determined from the chart above. The contact time of the monomer vapor and the microporous film is also determined in the same manner.

Therefore, in the continuous method, the microporous film is continuously passed through an appropriate equilibrium vapor pressure and temperature into a chamber containing a hydrophilic monomer. The contact time between the microporous film and the hydrophilic monomer vapor is controlled by adjusting the passage length and linear velocity of the microporous film in the vapor.

Obviously, steam coating can be used if the critical temperature of the hydrophilic monomer (ie, the temperature at which the liquid monomer cannot exist regardless of pressure) is above the temperature at which the properties of the microporous film will be adversely affected at specific contact times. to be. It is advisable to carry out the vapor coating method at atmospheric pressure and at temperatures that indicate a suitable vapor pressure.

Typically, the temperature of the steam 4 coating method, which is applied when atmospheric pressure is applied, varies in the range of 60-170 ° C, even when methacrylic acid, acrylic acid or acetic acid are used as the hydrophilic monomer.

Auxiliary and superatmospheric pressures can also be applied with proper control of temperature and contact time. It should be noted that since the amount of adhesion (%) is determined after curing, the amount of hydrophilic monomer in the excess amount of adhesion (%) is initially applied to the microporous film to compensate for the loss of monomer that may occur during curing. to be.

Another suitable method of applying the microporous film with the hydrophilic monomer is to dissolve the hydrophilic monomer in a vaporizable solvent such as methylene chloride to form a pad bath.

This pad bed is used for reverse roll application. In this method, a doctor roll is partially installed in the pad bed of the monomer coating solution. The second drive roll leads to the uncoated hydrophobic microporous film through the doctor roll and its own nip. The two rolls are driven separately and are rotated in the same direction, causing the applied film web to be directed in the direction in which the uncoated film starts.

The amount of monomer applied on the film is a function of the speed difference between the doctor roll and the secondary film drive roll, and also a function of the nip size formed by the two rolls. You can also use the squeeze roll method. In this method a film is drawn into the pad bed of the monomer coating liquid and squeezed between the two squeeze rolls beneath it. The application amount is a function of the size of the gap between the two squeeze rolls and the pressure applied between them.

拳取計量捧法)이다. 이 방법은 스퀴즈 로울법과 같으나 단지 도포가 된 미소다공성 필름이 단량체 도포액중으로 유도되어 들어간후 한쌍의 철사를 감은 계량봉 사이에서 스퀴징되는 것인데, 이 계량봉은 주위에 감긴 철사의 구조에 의해위에 부착되는 도포량을 조절하게 되어 있는 것이다.Another method of applying a hydrophobic microporous film is the wire winding metering rod method.

拳 取 計量 捧 法). This method is the same as the squeeze roll method, but the applied microporous film is guided into the monomer coating liquid and then squeezed between a pair of wire wound dipsticks, which are attached to the top by the structure of the wire wound around it. It is to adjust the application amount.

The amount of hydrophilic monomer initially applied to the microporous film in the inverse roll method, the squeeze roll method and the wire winding metering rod method is a function of one or two variables described in each method. Furthermore, in all three methods, the amount of monomer applied is also a function of the monomer concentration of the pad. Dissolving the monomer in a common organic solvent (methylene chloride, acetone, methanol, ethanol, isopropanol, etc.) having a boiling point lower than that of the hydrophilic monomer results in a hydrophilic monomer pad.

The concentration of hydrophilic monomer in the feedbed is adjusted to ensure that the appropriate amount of monomer is formed as soon as the solvent is volatilized. Generally, the monomer concentration in the pad bed is about 1-30 wt. About 5-15 wt.% Change. It is appropriate to vary by%.

When the hydrophilic monomer is applied onto the microporous film using the pad bed, the solvent used in the present invention is removed by passing the coated film in a solid state apparatus. The temperature of the drying apparatus should be high enough so that only the solvent is evaporated and the monomers adhere to the microporous surface of the film.

After the pores of the microporous film are applied with the hydrophilic monomer and the solvent is removed, the applied microporous film is treated with ionizing radiation to chemically fix the hydrophilic monomer to the hydrophobic microporous surface to make it hydrophilic.

Various possible mechanisms work in ionizing radiation to produce the desired effect. Thus, hydrophilic monomers are chemically attached to the microfabricated surface to form a polymer or a sleeve by polymerization or copolymerization, and the layer or the sleeve is indiscriminately chemically attached or physically attached to the microporous surface. The chemical bonds to the surface of the microporous surface are attached to each other, resulting in a bond to the polymer sleeve around the surface of the microporous surface.

"Chemical fixation" refers to all of the above mechanisms. The nature of the hydrophobic microporous film can be changed in one or more ways depending on the amount of hydrophilic monomer (%) attached, without being limited to a special mechanism that can improve the requirements.

Therefore, the microporous film prepared by radiation treatment has a long hydrophilicity longer than that shown in conventional surfactant application, and the continuous bubble characteristics of the film can also be used in applications requiring mass transfer and low electrical resistance. It can be maintained.

As mentioned above, chemically fixing a hydrophilic monomer to a hydrophobic microporous film requires exposing the microporous film impregnated with the hydrophilic monomer to ionizing radiation.

Ionizing radiation generates photo ions and destroys chemical bonds, causing photoradicals or emitting particles with sufficient intrinsic energy to cause free radical reactions between the hydrophilic monomers used and free radical reactions between the monomers and the microporous surface. It must be capable of generating.

Ionizing radiation is conveniently utilized in the form of ionizing particle radiation, ionizing electromagnetic radiation, and actinic rays. "Ionized particle radiation" is used to indicate that electrons or highly accelerated nuclear particles (protons, neutrons, alpha particles, neutrons, beta particles, or the like) are emitted in a manner that springs out into the object to be irradiated. Charged particles can be applied to such devices as accelerators with ELECTOCURTAINTM (manufactured by Energy Sciences Corroration) resonance chambers, van der Graaf generators, beta-grones, syncrotrons, cyclotrons, etc.

"Ionizing electromagnetic radiation" is produced when bombarding electrons with energy suitable for metal targets such as tungsten.

This energy is given to electrons by accelerators of 0.1 million electron volts (mev.) Or more. In addition to this type of X-ray irradiation, ionizing electromagnetic radiation suitable for the present invention can be obtained by using a natural or artificial radioactive material such as a nuclear reactor or cobalt 60.

Hydrophilic monomers also cause chemical fixation when exposed to actinic rays. In general, the unit of use of the wavelength that causes reactivity to actinic light is about 1800-4000 Å.

Various suitable actinic light sources can be used, including quartz water temperature lamps, ultraviolet arc generating carbon arcs and high intensity flash lamps. If you use actinic rays, use an initiator.

Suitable ionizing radioactive sources are electron beam generators such as those described in US Pat. Nos. 3,702,412, 3,745,396, and 3,769,600.

Accurate process control techniques have been developed to allow one type of radiation to be sufficiently converted to another, and the proper adjustment of this technique is used to produce the required product. For chemical fixation, radiation doses of about 1.0-10 megarad (mrad) are used, preferably about 2-5 mrad (eg 3 mrad). One megarad is one million rads.

One rad is a high ionizing energy dose that produces 100 erg of energy absorbed per gram of absorbent material. This difficulty is widely used as a convenient means of measuring the degree of radiation absorption of materials.

Minimal ionizing radiation is also used for chemical fixation for economic reasons. Excess radiation dose (more than about 20 mrad in a single exposure) should be avoided in order to avoid excessive heating and shrinkage of the film and to prevent degradation of hydrophilic monomers and microporous films. If the radiation dose is too small, no chemical fixation occurs and the hydrophilic monomer is quickly lost.

The minimum radiation dose required to chemically fix the hydrophilic monomers depends on the polymer used to make the microporous film. Therefore, when the polymer is polyethylene, the radiation dose is about 1 mrad or more and polypropylene is about 2 mrad or more, about 3 mrad.

It may be at elevated temperatures but can satisfy the irradiation at room temperature. Oxygen tends to prevent the hydrophilic monomers from being grafted into the microporous film and thus irradiates the microporous film under an inert atmosphere such as nitrogen or other inert gas.

As mentioned above, the adhesion amount (%) should be selected for the electrical resistance of the microporous film. The electrical resistance (direct current method) of the microporous film is 40 wt.% For a sample of microporous film having a surface area (eg 0.2 in ² ). It is installed between the cadmium electrode (anode and cathode) placed in an electrolyte of% KOH aqueous solution, and a direct current of a certain ampere (eg 40 milliamps) is passed through the cells between the electrodes. The voltage drop (E) of the film is measured with an electrometer. The voltage drop E ¹ of the battery without the microporous film is also measured using the same current. beauty

ER =

Where A is the surface area of the exposed film (in ² ), I is the cell current (milliampere), ER is the electrical resistance of the microporous film (milliohm-in ² ), and E ¹ and E are as previously described.

The water permeation rate of the hydrophilic microporous film according to the present invention is obtained by measuring the water permeation rate passing through a specific surface area of the film while maintaining water under a micropressure of 1 atmosphere. Therefore, the permeation rate is expressed in volume (cm 3) of water passing in 1 minute per cm 2 of film surface area (cc / min / cm 2). The air permeability of the microporous film according to the present invention is measured by the Gurley tsst method, i.e., a film having a surface area of 1 in ² , as specified in ASTMD 726, is installed in a standard Gaulay density meter. The film is treated under conditions of standard microhydraulic pressure (pressure drop of the film) of 12.2 in.

The time (in seconds) for 10 cm 3 of air to pass through the film indicates the permeability. When the value of the Guarray reaches about 1.5 minutes or more, it indicates that the pores are closed.

The use of the hydrophilic microporous film according to the present invention is various. This is especially useful when you need to control the moisture passing through a film or surface. Furthermore, the film produced according to the present invention may be used as a filtration membrane support or a filter agent for separating ultrafine materials from various liquids, or as a battery separator.

The present invention will be described in detail according to the embodiment. Unless otherwise specified, the amounts added in the examples are parts by weight and parts by weight (wt.%).

Example 1- (A)

In this embodiment, a hydrophobic polyolefin-based microporous film is prepared by the dry stretching method described in US Patent No. 3,801,404.

Crystalline polypropylene with a melt index of 0.7 and a density of 0.92 was melt-extruded at 230 ° C. through a 8-inch slit die with a coat hanger using a 1 inch extruder with a shallow metering screw. The ratio of length to diameter of the extruder barrel is 24/1.

The extrudate is quickly drawn off with a draw ratio of 150 and contacted with a rotating casting roll maintained at 50 ° C. The distance from the dielip is 0.75 inches. The characteristics of the film thus prepared are as follows.

Thickness: 0.002 inches, Recovery rate at 50% elongation at 250 ° C: 50.3%, Crystallinity: 50.6%.

A sample of this film was unwound in an air oven with a slight tension at 140 ° C. for about 30 minutes, and then taken out and cooled. The annealed elastic film was cold and hot stretched at a draw ratio of 0.50: 1 and then heat-fixed at a constant length in air at 145 ° C. for 10 minutes. Cold stretching was carried out at 25 ° C., hot drawing at 145 ° C., and total drawing was 100% of the initial length of the elastic film. The average pore size length of the treated film was about 3000 mm 3, the crystallinity was about 59.6%, the surface area was about 8.54 m 2 / gm and the thickness of the microporous film was 1 mil.

Example 1- (b)

A continuous roll of a microporous film of 100 feet in length and 6 inches in width made in Example 1- (a) was passed through an acrylic acid (100%) bath and passed through a squeeze roll to cure the film by weight. Adhesion amount 1.5wt. % To I.R. Confirm the impregnation result by analysis.

The impregnated film is passed under a window of an electron beam generator (24 inches long) at a linear speed of 20 ft / min. The electron beam generator generates three doses of radiation at the linear speed used.

The oxygen content in the atmosphere in contact with the microporous film under the curtain window is kept below 500 ppm by enclosing the window in the chamber cleaned with nitrogen.

The cured dry microporous film sample is tested for wettability by a dropping test. The dropping test was performed with 0.6 ml droplets of a 2% aqueous KOH solution on the film surface to visually observe the film. The film is determined to be wet when the opposite side of the film from which the droplets have come off is wet (indicated by "0" in Table 1). The dropping test is carried out on the film immediately after irradiation and on samples stored for 1 week at room temperature.

Several samples were taken from the cured microporous film rolls and held at 60 ° C. After soaking for 1 hour, 24 hours, 4 days and 8 days in% aqueous solution, the electrical resistance test is performed and the results are averaged.

If the film is immersed for a long time gradually in hot KOH, it will age over time. Electrical Resistance Test Each sample has a surface area of 0.2 in ² and a current of 40 milliamps.

Three samples are taken from the cured microporous film roll and tested for air permeability according to the Gaulay test method ASTM-D-726B. The results are shown in Table 1.

Samples taken from the cured microporous film rolls are also tested for permeability after immersion in a 31% KOH aqueous solution for 60 ° C. for 24 hours. Each sample with a surface area of 11.3 cm 2 is tested in a micropore millipore-filter housing. Fill the microfilter with water and pressurize to create micro atmospheric pressure between both sides of the film sample. Collect water as it passes through the microporous film for at least 5 minutes. The results are converted to the amount of water collected (CC) in 1 minute per 1 cm 2 of film surface. The results are summarized in Table 1.

Comparative Example

Repeating Example 1 differs only in reducing the radiation dose used for curing to 1 megarad. The results are summarized in Table 1.

The uncoated microporous film made according to Example 1 is also exposed to ionizing radiation and tested in the same manner as in Example 1 to be used as a basic test. The results are shown in Table 1.

As can be seen from Table 1, the single-guard radiation dose is considered to be too small for the effective curing of the polypropylene microporous film, as shown in the infinite electrical resistance of the microporous film of the comparative example. It is believed that the positive wettability test of the comparative example for the nonlinear connection of the sample is due to residual acrylic acid not chemically fixed by irradiation. One week later, the wettability of the film of the comparative example is considered to be due to the loss of acrylic acid during long term storage.

In addition, it can be seen that the electrical resistance of the film of Example 1 is increased after 4 days of exposure to hot KOH and slightly falls after 8 days of exposure. The drop in electrical resistance after aging for 8 days is due to the complete conversion of acrylic acid graft to salt form, whereas the aging after 4 days is due to the partial conversion of salts. Therefore, when the acrylic acid graft is completely converted into the salt form, the electrical resistance is lowered.

TABLE 1

Example 2- (A)

In this embodiment, a polyethylene microporous film is produced by the solvent stretching method.

Crystalline polyethylene having a melt index of 5.0, a weight average molecular weight of about 80.000, a density of 0.960 g / cc, and a molecular weight distribution ratio of about 9.0 was prepared by a blown film extrusion method, and formed into a precursor film (thickness: 3 mil), and then 25 in the air. Quench at 캜. The prepared precursor film was immersed in trichloroethylene for 1 minute at 70 ° C. and immersed in trichloroethylene maintained at 70 ° C. and stretched at 4 times the original length (300% total stretching) at a strain of 150% / min. . The sample removed by evaporation of trirolethylene is stretched to about 50% in a high vehicle direction and then air dried in the stretched state. The drying temperature is 25 ° C. Crystallinity of the draft microporous film: about 60%, average processing length: about 5000Å, expressive about 10-25㎡ / g.

Example 2- (b)

When several microporous film samples having a thickness of 1 mil prepared according to Example 2- (A) are immersed in acrylic acid (100%), the film becomes translucent. This sample is dried to give the film a milky white appearance, which represents a titration of the amount of monomeric blanket that can cause the amount of adhesion to be about 1.5%. The treated sample is passed under the electron beam curtain (length 24) and irradiated with different doses of radiation, in which the atmosphere under the window is in contact with the microporous film under 500 ppm of oxygen in the same manner as used in Example 1 Keep it to be. The treated cured film was subjected to the Giray air permeability, electrical resistance (after immersion in a 40% KOH solution at 60 ° C. for 24 hours) and wettability by dropping test as in Example 1. The results are shown in Table 2. Amount of adhesion of the cured film is also measured by infrared analysis, and the results are shown in Table 2.

As can be seen from the results of Test 4 and Test 7 of Table 2, the electrical resistance is infinite and the sample is not wettable. This result may be because radiation dose is too small to cause chemical fixation.

Therefore, it can be said that the hydrophilic monomer evaporates to such an extent that the amount of adhesion that can be measured is small and its properties are lost.

The film samples used for Tests 1, 2, 5, 6 and 8 exhibited small electrical resistance and wettability. The large electrical resistance of the film sample of Test 3 is considered to be because the film has a nonuniformity observed with the naked eye. Moreover, these film samples resulted in chemical fixation with an adhesion amount of 1.5% and only slightly decreased air permeability. This indicates that the pores remain unclosed after chemical fixation.

TABLE 2

It is considered that the electrical resistance is large due to the nonuniformity of the film.

Claims (1)

(A) Microparticles of continuous bubbles of hydrophobic polyolefins, which have a much smaller bulk density than the bulk density of the precursor film before treatment, and have an average pore size of about 200-10,000 mm 3 and a surface area of at least about 10 m 2 / g. The surface of the micropores of the porous film is coated with at least one hydrophilic organic hydrocarbon monomer having at least one double bond and at least one polar functional group and having about 2-18 carbon atoms, and (b) about 0.1-10 wt. Chemically fixed hydrophobic organic hydrocarbon monomer of microporous film on microporous surface of microporous film can be attached to the microporous film, and can be attached to about% and maintains continuous bubble properties of microporous. When (a) the coated microporous film of (a) is irradiated with about 1-10 rads of ionizing radiation to make the hydrophobic polyolefin-based microporous film usually hydrophilic, thereby improving water permeability and lowering electrical resistance.