JPH062841B2 - Porous permeable polyethylene film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a porous permeable polyethylene film having both high strength and high permeability, and various packing materials that require air permeability, and battery separators. The present invention relates to a porous permeable film suitable for use as a filter material and various filter materials.

[Prior art]

Polyethylene films are often used as films because of their good chemical resistance. A porous permeable polyethylene film is used for various separators such as battery separators and pharmaceutical packaging materials. If a high strength film or a porous film can be obtained, the demand for it will further increase. 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.

It is well known that the strength of a stretched film is increased by increasing the molecular weight of polyethylene used.
It is also clear that when the molecular weight is increased, the moldability such as extrudability decreases, and at present the molecular weight is only about 200,000 considering the industrial production. Also has an upper limit.

Regarding the porous permeable film, the following are typical methods for producing the permeable membrane.

(A) Sintering resin fine powder (b) Heat treatment after melt-drawing polyolefin resin
Re-stretch. (For example, Japanese Examined Patent Publication No. 46-40119) (C) An extraction method in which a liquid or solid is mixed with a resin, and after mixing and molding, the mixed liquid or solid is extracted. (For example, JP-A-54-52167, JP-A-55-131028, and JP-A-55-746) However, it is difficult to say that the film obtained by the above-mentioned conventional method is sufficient.

That is, in the porous membrane obtained by the method (a), the pore diameter formed is as large as several tens of μm, it is difficult to control the pore diameter, and the application is limited. In the method (b), the thermoplastic resin is melt-stretched, and the obtained film is further stretched to form a porous film. However, the anisotropy of the porous film becomes large due to the limitation of the production method, and the film is unidirectional. Easy to avoid Next (C)
In the above extraction method, the higher the porosity of the obtained film, the more brittle it becomes, and the film tends to be broken, and cannot be used in applications requiring some strength in view of the balance between film strength and permeability.

[Object of the Invention]

In view of the above situation, the present inventors have conducted various investigations for the purpose of providing an unprecedented strength and a porous permeable film having an excellent balance of permeability. The purpose was achieved and the present invention was completed by using.

[Structure of Invention]

The gist of the present invention is to uniformly mix a high-molecular-weight polyethylene having a viscosity-average molecular weight of 400,000 or more with a non-polymerizable aliphatic or alicyclic compound to be extracted for porosity in a subsequent step, to obtain a composition The sheet has a strength of 5 after being formed into a sheet and stretched.
Tensile strength of kg / mm ² or more and nitrogen gas permeability coefficient of 1.0
A porous permeable polyethylene film characterized by having a density of × 10 ⁻⁶ (ml · cm / sec · cm ² · cmHg) or more.

In order to obtain a porous film having a balance between strength and permeability in the present invention, it is first to use a high molecular weight polyethylene having a viscosity average of 400,000 or more. 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, 40
Polyethylene with a high molecular weight of 10,000 or more has a high melt viscosity.Therefore, the molding method is limited, and compression molding or extrusion molding or injection molding using a special molding machine is performed, but most are limited to compression molding. Therefore, the molding time may require several hours per time. Even if an original sheet of a stretched film is to be formed by extrusion, a high pressure is required to pass through the forming die, and even if it is made to flow in the die, a so-called melt fracture occurs and a uniform sheet is formed. Can't get 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.

Aliphatic or alicyclic compound {(B) component} that swells or wets the high molecular weight polyethylene {(A) component} to improve the moldability and stretchability as described above.
Add. The component (B) has good compatibility with high-molecular-weight polyethylene (PE), and particularly has a high melting point because it is uniformly mixed in a molten state, improves stretchability, and accelerates melting of the high-molecular PE. It has a molecular weight lower than PE and is capable of easily swelling or wetting the PE, soluble in a solvent that is easy to handle, soluble in a lower alcohol or a mixture thereof, and capable of being extracted after being formed into a sheet or a film. Preferably, it is necessary to satisfy the requirements such as being solid at room temperature for easy handling after processing into a sheet.

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 equal to or higher than the melting point of the high molecular weight polyethylene, that is, 150 ° C. or higher. 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.

Specific examples of the component (B) satisfying the above requirements include cetyl alcohol {CH ₃ (CH ₂ ) ₁₄ CH ₂ OH}, heptadecyl alcohol {CH ₃ (CH ₂ ) ₁₅ CH ₂ OH}, and stearyl alcohol {CH ₃ Alcohols such as (CH ₂ ) ₁₆ CH ₂ OH}, ceryl alcohol {CH ₃ (CH ₂ ) ₂₄ CH ₂ OH}, behenyl alcohol {CH ₃ (CH ₂ ) ₂₀ CH ₂ OH}; dioctyl ether {(C ₈ H ₁₇ ) ₂ O}, didecyl ether {(C ₁₀ H ₂₁ ) ₂ O}, didodecyl ether {(C ₁₂ H ₂₅ ) ₂
O}, dioctadecyl ether {(C ₁₈ H ₃₇ ) ₂ O}, and other ethers; methyl tetradecyl ketone {CH ₃ CO
_{(CH 2) 13 CH 3}} , n- propyl-hexadecyl ketone _{{CH 3 (CH 2) 2} CO (CH 2) 15 CH 3}, didodecyl ketone _{{CH 3 (CH 2) 11} CO (CH 2) 11 CH _3}, dioctadecyl ketone _{{CH 3 (CH 2) 17} CO (CH 2) 17 CH
₃ } and other ketones; octyl laurate {CH ₃ (C
_{H 2) 10 COO (CH 2} ) 7 CH 3}, ethyl palmitate _{{CH 3 (CH 2) 14} COOCH 2 CH 3}, butyl stearate _{{CH 3 (CH 2) 16} COO (CH 2) 3 CH 3 }, Octyl stearate {CH ₃ (CH ₂ ) ₁₆ COO (CH ₂ ) ₇ C
H ₃ }, aliphatic compounds such as esters, etc., and average molecular weight 500 to 2000 containing dicyclopentadiene as a main component
Aliphatic compounds such as petroleum resin to a degree or hydrogenated products of the petroleum resin and the like can be mentioned.

As a method for uniformly mixing both components (A) and (B), a twin-screw extruder, Brabender kneader, Banbury mixer, or the like can be used. However, both components (A) and (B) are mixed with powder in advance. After that, leave it at 150 to 180 ° C (B)
When the component (A) is swollen and supplied to the above mixer, uniform mixing of both components can be efficiently achieved. In this uniform mixing, the weight of the component (A) was 6
If it exceeds 0% by weight, uniform mixing by the above-mentioned ordinary kneader becomes difficult. The ultra-high molecular weight PE is not sufficiently dissolved in a short time, and when kneading is added for a long time to make it uniform, the temperature becomes abnormally high due to heat generation and a high shearing force is applied. The molecular weight is drastically reduced.

The necessity of uniform mixing is mainly due to the following two points.
That is, firstly, for example, when the components (A) and (B) are simply powder blended and supplied to a single-screw extruder that is usually used for molding, only the component (B) having a low melting point melts first. Slip occurs in the extruder, and shearing force is not 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 it will be difficult to obtain, for example, a uniform thin sheet having a thickness of 1 mm or less.

In order to perform more uniform molding here, the homogeneous mixture mixed by the kneader is in a molten state without solidifying,
It is desirable to supply to the extruder. The reason for this is that once it is cooled and solidified, some phase separation occurs, and for this reason, in the above-mentioned single-screw extruder feed section, both components (A) and (B) are not melted uniformly. Conceivable.

As a method for processing the composition obtained as described above into a raw fabric for stretching, a molding method similar to that for ordinary polyethylene is adopted because the component (B) has sufficiently improved fluidity. I can do things. Specific examples include a T-die-roll method and an inflation film molding method.

Next, it is necessary to biaxially stretch in order to obtain the porous permeable film obtained as described above from the original fabric which has an excellent balance of strength and permeability as in the present invention. In this biaxial stretching, the stretching temperature can uniformly achieve high-stretching in a wide temperature range of 50 to 150 ° C. However, if it is stretched at a high temperature, it does not become porous, so that stretching in the range of 50 to 130 ° C. is desirable in order to obtain high permeability. Further, in order to achieve the high strength of the present invention, it is desirable to carry out stretching of 3 × 3 times or more at a drawing speed of 50% / sec or more.

Further, in order to apply the porous and permeable film to battery separators, medical applications, etc., it may be effective to have water absorption, but this can be achieved by including a surfactant. .

The porosity of the permeable film varies depending on the use and cannot be determined unconditionally, but is usually 10 to 90%, preferably 30 to 80%.
%.

The inclusion of the surfactant in the porous film or sheet is performed by mixing or dissolving the surfactant in a liquid that is substantially uniformly mixed with the surfactant, and immersing the porous film or sheet in the solution. You can As the liquid which is substantially uniformly mixed with the surfactant, pure water and alcohols such as methyl alcohol, ethyl alcohol and isopropyl alcohol are used. Also, a mixture of these can be used. Furthermore, aliphatic hydrocarbons, aromatic hydrocarbons, chloroform, acetone,
It is also possible to use carbon tetrachloride and the like, or also mixtures thereof.

The concentration of the surfactant is 0.1% by weight or more, and further 1
It is preferable that the content is at least wt%. The concentration of the surfactant
When it is less than 0.1% by weight, the immersion time becomes long even if the hydrophilic treatment is possible, which is not preferable.

It is also possible to add a surfactant after subjecting the porous film or sheet to a known surface treatment such as corona treatment or frame treatment.

The surfactant may be impregnated either before or after stretching, but more preferably after stretching. Further, when the component (B) is extracted with alcohol or the like, if a surfactant is dissolved in the alcohol in advance, the impregnation can be carried out simultaneously with the extraction.

Although various kinds of surfactants can be used, examples of the nonionic surfactant include polyol, fatty acid monoglyceride, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkyl ether, and polyoxyethylene. Alkyl allyl ether, polyoxyethylene alkyl ether phosphoric acid, etc., quaternary ammonium salts as cationic surfactants, polyoxyethylene alkyl amines, alkyl amine oxides, etc., alkyl sulfonates, alkyl benzenes as anionic surfactants Sulfonate, alkyl naphthalene sulfonate, alkyl sulfosuccinate, alkyl sulfonate ester salt,
Polyoxyethylene alkyl sulfonate ester salt,
It is used from polyoxyethylene alkylallyl sulfonic acid ester salt, alkyl phosphate, polyoxyethylene alkyl phosphate and the like.

〔Example〕

Examples are shown to clarify the effects of the present invention. However, the invention is not limited by these examples. Various physical properties shown in the specification and examples of the present invention were measured according to the following methods.

-Tensile strength (kg / mm < ² >): Measured at a tensile speed of 50 mm / min according to ASTM D-882.

・ N ₂ gas permeation coefficient (ml ・ cm / sec ・ cm ²・ cmHg): Acicon UF stirring cell 12 type is used, differential pressure 1 kg /
Measured at cm ² and temperature of 25 ° C.

-Porosity (%): (pore volume / porous membrane volume) x 100-Viscosity average molecular weight (Mv): Solvent tetralin, [η] was measured at a measurement temperature of 135 ° C, and calculated by the following formula.

[Η] = 4.60 × 10 ⁻⁴ <M> ^0.725 (Tung's formula) Example 1 After powder blending 80% by weight of stearyl alcohol with 20% by weight of polyethylene having a viscosity average molecular weight of 1.5 million, The polyethylene was wetted with alcohol by leaving it in the oven for 30 minutes. At this time, 0.5 part by weight of a phenolic stabilizer was added to 100 parts by weight of the mixture. The mixture is heated to a jacket temperature of 170
The mixture was kneaded for 10 minutes at a temperature of 100 ° C. and a rotation speed of 100 rpm. The resin temperature was constant at 185 ° C., the torque was also constant, and the mixture was transparent and uniform in the molten state.

Before the homogeneous 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 extraction was stretched 4 × 4 times at the same time at a temperature of 120 ° C. at a rate of 200% / sec using a biaxial stretching machine.

Properties of the film at this time are shown in Table 1.

Examples 2 to 5 Stretched films were prepared in the same manner as in Example 1 except that the biaxial stretching temperature and the stretching ratio were as shown in Table 1. The properties of each film are shown in Table 1.

Comparative Examples 1 and 2 Example-1 except that biaxial stretching was conducted under the conditions shown in Table-1.
A stretched film was prepared in the same manner as in. The properties of each film are shown in Table 2.

Example 6 After immersing the porous permeable film obtained in Example-1 in a 1% ethyl alcohol solution of nonionic surfactant polyoxyethylene sorbitan monolaurate [Tween 20, Tokyo Kasei Co., Ltd.] for 1 minute Air dried. The water vapor transmission rate and moisture absorption rate of this treated film are shown in Table 2. It can be seen that both the water vapor transmission rate and the moisture absorption amount are improved as compared with the case where no hydrophilic treatment is performed. The measuring directions are as follows.

(A) Water vapor transmission rate (g / m ² 24 hours): JIS Z0208
According to -1976, the temperature was 30 ° C and the relative humidity was 90%.

(B) Moisture absorption rate (% by weight): The film was dried at 40 ° C. for 3 hours, then at 20 ° C., and the relative humidity was 100%, and the increase in weight after 24 hours was measured and shown as a weight percentage.

[Effects of the Invention] The film of the present invention has high strength and good permeability, and is very suitable for use as various packaging materials that require air permeability, battery separators, various filtration materials, medical materials, etc. Is.

Claims (2)

[Claims] 1. A composition obtained by uniformly mixing high molecular weight polyethylene having a viscosity average molecular weight of 400,000 or more with a non-polymerizable aliphatic or alicyclic compound which is extracted for porosity in a subsequent step. Strength of 5kg /
With a tensile strength of mm ² or more and a nitrogen gas permeability coefficient of 1.0 × 1
0 ^-6, characterized in that it (ml · cm / sec · cm 2 · cmHg) or more, porosification permeable polyethylene film. 2. The porous permeable polyethylene film according to claim 1, which is obtained by hydrophilizing the porous permeable film.