JPH0358288B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing an ultra-high molecular weight α-olefin polymer film. Conventional technology Ultra-high molecular weight α-olefin polymers, such as ultra-high molecular weight polypropylene, have superior tensile modulus, tensile strength, abrasion resistance, chemical resistance, impact resistance, etc. compared to normal molecular weight polypropylene. ,
Its use as an engineering plastic is expanding. However, this ultra-high molecular weight polypropylene has extremely entangled molecular chains compared to normal molecular weight polypropylene, has an extremely high melt viscosity, and has poor fluidity, making it extremely difficult to mold into thin films using conventional extrusion molding. However, there were problems with workability. As a method for producing an ultra-high molecular weight α-olefin polymer molded article, for example, an ultra-high molecular weight thermoplastic crystalline polymer that is essentially polyethylene or polypropylene is dissolved in a non-volatile solvent, and a gel is formed from this solution. Then, a method for producing a thermoplastic shaped article that is substantially a fiber (Japanese Unexamined Patent Application Publication No. 1983-1999 5228
No. 2) has been proposed. However, with this method, it was difficult to obtain a uniform stretched film with a high magnification, and the film was not sufficiently thin. Problems to be Solved by the Invention The present invention obtains a thin ultra-high molecular weight α-olefin polymer film with high elasticity, high strength, and transparency by stretching an ultra-high molecular weight α-olefin polymer at a high magnification. The purpose is to Means for Solving the Problems The present inventors conducted various studies on the method for producing a stretched film of an ultra-high molecular weight α-olefin polymer, and as a result, the inventors found that a stretched film formed from a solution of an ultra-high molecular weight α-olefin polymer was formed from a solution of an ultra-high molecular weight α-olefin polymer. The present invention was completed based on the discovery that uniform stretching at a high magnification is possible within a specific range of solvent contained in a gel-like molded product. That is, in the present invention, the weight average molecular weight is 5×
A gel-like product is formed from a solution in which an α-olefin polymer of 10 ⁵ or more is heated and dissolved in a solvent, and at least 10% by weight of the solvent contained in the gel-like product is removed to form the gel-like product. After adjusting the α-olefin polymer content to be 10 to 90% by weight, the α-olefin polymer is
- Stretching at a temperature below the melting point of the olefin polymer + 10°C, removing residual solvent contained in the resulting stretched product, and then applying pressure treatment at a temperature below the melting point of the α-olefin polymer. This is a characteristic method for producing an ultra-high molecular weight α-olefin polymer film. The ultra-high molecular weight α-olefin polymer used in the present invention has a weight average molecular weight of 5×10 ⁵ or more, preferably in the range of 1×10 ⁶ to 15×10 ⁶ .
If the weight average molecular weight is less than 5×10 ⁵ , a film with high elastic modulus and high strength, which are characteristics of ultra-high molecular weight α-olefin polymers, cannot be obtained. On the other hand, although the upper limit is not particularly limited, if it exceeds 15×10 ⁶ , the molding processability is poor even in gel molding. Such ultra-high molecular weight α-olefin polymers include propylene, 1-butene, 4-methyl-1-pentene,
Examples include crystalline homopolymers obtained by polymerizing 1-hexene and the like, and copolymers of these α-olefins and 10 mol% or less of ethylene or other α-olefins. Among these, ultra-high molecular weight polypropylene mainly composed of propylene is preferred. In addition, the above ultra-high molecular weight α-olefin polymer may contain antioxidants, ultraviolet absorbers, lubricants,
Various additives such as antiblocking agents, pigments, dyes, and inorganic fillers can be added within the range that does not impair the purpose of the present invention. The solution of the ultra-high molecular weight α-olefin polymer used as a raw material in the present invention has a weight average molecular weight of 5.
It is prepared by heating and dissolving an α-olefin polymer of ×10 ⁵ or more in a solvent. As this solvent, the α-
It is not particularly limited as long as it can sufficiently dissolve the olefin polymer. For example, nonane, decane,
Examples include aliphatic or cyclic hydrocarbons such as undecane, dodecane, decalin, and paraffin oil, and mineral oil fractions whose boiling points correspond to these. Non-volatile solvents such as oils are preferred. The heating and dissolving is performed while stirring at a temperature at which the α-olefin polymer is completely dissolved in the solvent.
The temperature varies depending on the polymer and solvent used, but for example, in the case of polypropylene, 160 -
It is in the range of 250℃. Further, the concentration of the α-olefin polymer solution is preferably 1 to 10% by weight. If the concentration is too high, it will be difficult to prepare a uniform solution. In addition, during heating and dissolution, it is preferable to add an antioxidant to prevent oxidative deterioration of the α-olefin polymer. Next, this α-olefin polymer heated solution is extruded into a sheet or tube shape from an appropriately selected die, or cast onto a support, and is heated preferably below the gelling temperature in a water bath, air bath, solvent, etc. Cool to a temperature of 15-25°C at a rate of at least 50°C/min to form a gel. The thickness of the gel-like molding is usually
It is molded to about 0.1 to 5 mm. This gel-like sheet is swollen with the solvent used to dissolve the α-olefin polymer, and requires solvent removal treatment. Solvent removal treatment includes methods such as immersing the gel-like molded product in an easily volatile solvent, extracting it, and drying it, compressing it, heating it, or a combination of these methods. Extractive removal using a readily volatile solvent is preferred since the solvent can be removed without significant changes. Examples of easily volatile solvents include hydrocarbons such as pentane, hexane, and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, fluorinated hydrocarbons such as trifluoroethane, and ethers such as diethyl ether and dioxane. and other alcohols such as methanol, ethanol, and propanol. These solvents are appropriately selected depending on the solvent used to dissolve the α-olefin polymer, and are used alone or in combination. In addition, the amount of solvent removed from the gel-like molded product is at least 10% by weight based on the solvent contained, and the amount of the ultra-high molecular weight α-olefin polymer contained in the gel-like molded product is 10 to 90% by weight. , preferably 20 to 60% by weight. If the amount of solvent removed from the gel-like molded product is less than 10% by weight based on the solvent contained, and the α-olefin polymer contained in the gel-like molded product is less than 10% by weight, the gel-like molded product will be highly affected by the solvent. Because the gel is swollen, the gel tends to dissolve during heating and stretching. In addition, uneven stretching tends to occur locally, making it difficult to obtain a stretched product with a uniform thickness, which is also unfavorable from the viewpoint of handling, such as oozing of solvent during stretching. On the other hand, when removing the solvent in which the α-olefin polymer contained in the gel-like molded product exceeds 90% by weight, the network structure of the gel-like molded product becomes too dense and cannot be stretched at a high magnification, making it extremely thin. Therefore, a film with high elastic modulus and high strength cannot be obtained. The amount of solvent contained in the gel-like molded product removed can be adjusted by adjusting the amount of contact of the easily volatile solvent with the gel-like molded product, the time, or the compression pressure of the gel-like molded product. In addition, when desolventizing a gel-like molded product using a readily volatile solvent, the gel-like molded product shrinks or bends in three axes as the easily volatile solvent substituted in the gel-like molded product evaporates. To prevent this,
In order to obtain a smooth raw fabric that can be stretched uniformly and at high magnification, with minimal shrinkage in the biaxial (longitudinal and horizontal) directions,
It is preferable to selectively shrink the gel-like molded product in the thickness direction. Its shrinkage rate is 50% or more in the thickness direction, preferably 70% or more, and 20% or more in the biaxial direction.
% or less. Selective shrinkage of the gel-like molded product in the thickness direction can be achieved by applying a readily volatile solvent, for example, when the gel-formed product is tightly attached to a smooth support, gripped from two axes, or sandwiched between porous plates. One method is to evaporate it. For stretching, the original fabric of the gel-like molded product that has been subjected to solvent removal treatment is heated and biaxially stretched at a predetermined magnification by the usual tenter method, roll method, inflation method, rolling, or a combination of these methods. . Biaxial stretching may be done simultaneously or sequentially. The stretching temperature is below the melting point of the ultra-high molecular weight α-olefin polymer +10° C., preferably in the range from the crystal dispersion temperature to below the melting point. For example, in the case of polypropylene, the temperature is 90-180℃, more preferably 130-170℃.
℃ range. If the stretching temperature exceeds the melting point +10°C, the resin will melt excessively, making orientation by stretching impossible. Furthermore, if the stretching temperature is lower than the crystal dispersion temperature, the resin will not be sufficiently softened and the membrane will easily break during stretching, making it impossible to stretch at a high magnification. In addition, the stretching ratio varies depending on the thickness of the original fabric, but is at least 2 times or more in the uniaxial direction, preferably 5 times or more.
~20x, surface magnification 10x or more, preferably 25-400
It's double. If the areal magnification is less than 10 times, stretching is insufficient and a film with high elasticity and high strength cannot be obtained, which is not preferable. On the other hand, if the areal magnification exceeds 400 times, it is not preferable because restrictions will arise in terms of stretching equipment, stretching operations, etc. The stretched product is immersed in the above-mentioned easily volatile solvent to extract and remove the remaining solvent, and then the solvent is evaporated and dried. Extraction of the solvent is carried out by extracting the solvent in the stretched product by 1
It is necessary to remove it to less than % by weight. Furthermore, since the stretched product from which the residual solvent has been removed has pores and is opaque, it is necessary to perform the pressure treatment at a temperature below the melting point of the α-olefin polymer constituting the stretched product. For example, the specific pressure treatment for polypropylene is at a temperature of 80°C.
Examples include a method of pressing or rolling at a temperature of ~160°C. Pressure treatment causes heat shrinkage in the stretched product when the temperature exceeds the melting point, whereas at low temperatures below 80°C, it is impossible to eliminate pores in the stretched product, making it transparent, highly elastic, and strong. An ultra-thin film cannot be obtained. The thickness of the ultrahigh molecular weight α-olefin polymer stretched film of the present invention can be appropriately selected depending on the application, but is usually in the range of 0.05 to 10 μm, preferably 0.1 to 4 μm. As described above, according to the method of the present invention, the tensile modulus is
It is possible to obtain an ultra-high molecular weight α-olefin polymer stretched film having substantially no pores, having a breaking strength of 1000 Kg/cm ² or more, a breaking strength of 200 Kg/cm ² or more, and a haze of 10% or less, preferably 5% or less. . Effects of the Invention According to the method of the present invention, it is possible to form an ultra-thin film from an ultra-high molecular weight α-olefin polymer by stretching at a high magnification. Furthermore, the ultra-high molecular weight α-olefin polymer film obtained is extremely thin, has high elastic modulus, and high strength, which cannot be obtained with conventional stretched α-olefin polymer films of normal molecular weight. Due to the above-mentioned excellent properties, the ultra-high molecular weight α-olefin polymer stretched film produced by the method of the present invention can be used in the field of high elasticity and high strength films in addition to various packaging materials, or can be laminated by combining with various materials. The materials and even ultra-stretched ultrathin films are useful as electrically insulating materials, especially capacitor films. Examples Examples of the present invention are shown below. In addition, the test method in Examples is as follows. (1) Film thickness: Measure the cross section of the film using a scanning electron microscope. (2) Tensile modulus: ASTM D882 compliant. (3) Breaking strength: ASTM D882 compliant. (4) Breaking elongation: ASTM D882 compliant. (5) Haze: JIS K6714 compliant. Example 1 Liquid paraffin ( ⁶⁴ cst/40
℃) 100 parts by weight of the mixed solution, 0.125 parts by weight of 2,6-di-t-butyl-P-cresol and tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate] 〕methane
Add 0.25 parts by weight of antioxidant and mix. Fill this mixture into an autoclave equipped with a stirrer,
A homogeneous solution was obtained by heating to 200°C and stirring for 90 minutes. This solution was filled into a heated mold and rapidly cooled to 15°C to form a gel-like sheet with a thickness of 2 mm. After immersing this gel-like sheet in methylene chloride for 60 minutes, the methylene chloride was evaporated and dried while it was attached to a smooth plate, resulting in an original sheet with a polypropylene content of 19.4% by weight and a shrinkage rate of 79.4% in the thickness direction. Got a sheet. The obtained raw sheet was set in a biaxial stretching machine and subjected to simultaneous biaxial stretching at a temperature of 150° C., a speed of 30 cm/min, and a magnification of 8×8. The obtained stretched film was washed with methylene chloride to extract and remove the remaining liquid paraffin, and then dried to obtain a stretched molded product. The obtained stretched product was heated at 120°C, 200Kg/cm ² G, 10
Pressed for 1 minute. The properties of the obtained ultra-thin polypropylene film are shown in Table 1. Examples 2 to 6 The gel-like sheets molded in Example 1 are shown in the table below.
A film was obtained in the same manner as in Example 1 except that it was molded under the conditions shown in Example 1. These characteristics are also listed in Table-1. Example 7 A film was obtained in the same manner as in Example 1, except that the gel-like sheet was stretched one after another under the conditions shown in Table 1. These characteristics are also listed in Table-1. Example 8 A 6.0% by weight liquid paraffin solution was prepared using polypropylene with w = 2.5 x 10 ⁶ instead of the polypropylene with w = 4.7 x 10 ⁶ used in Example 1, and each condition shown in Table 1. A film was obtained in the same manner as in Example 1, except that it was molded.
These conditions are also listed in Table-1.

[Table] Comparative Example 1 A film was formed in the same manner as in Example 1 except that the gel-like sheet formed in Example 1 was set in a biaxial stretching machine without removing the solvent and stretched at a temperature of 130°C. However, the film obtained was non-uniform. In addition, the stretched membrane was covered with exuded excess solvent, causing pooling and dripping, making it difficult to handle. Comparative Example 2 A gel-like sheet formed in Example 1 was immersed in a large amount of methylene chloride for 60 minutes, and then attached to a smooth plate and the methylene chloride was evaporated to dry. Set the gel-like sheet without any heat in the biaxial stretching machine and set the stretching temperature to 110.
Attempts were made to stretch the film at a temperature of -170 DEG C. at a speed of 30 cm/min, but due to uneven stretching and breakage, it was not possible to stretch to a ratio of 3.times.3 or more, and an extremely thin film could not be obtained. Comparative Example 3 Instead of the ultra-high molecular weight polypropylene used in Example 1, a gel-like sheet was formed in the same manner as in Example 1 using a 14.0% by weight liquid paraffin solution of polypropylene with a normal molecular weight (w = 19.5 × 10 ⁴ ). Except for the above, stretching was attempted in the same manner as in Example 1, but due to uneven stretching and breakage, stretching was not possible at a magnification of 3×3 or more, and an extremely thin film could not be obtained. Comparative Example 4 Determination of liquid paraffin in a gel-like sheet formed from the polypropylene solution prepared in Example 8
A film was obtained in the same manner as in Example 1, except that 9.0% by weight of polypropylene was removed to make the amount of polypropylene contained in the gel sheet 7.0% by weight, and the stretching temperature was 130°C. The resulting film was non-uniform.

Claims (1)

[Claims] 1. Molding a gel from a solution of an α-olefin polymer having a weight average molecular weight of 5×10 ⁵ or more, and removing at least 10% by weight of the solvent contained in the gel-like molded product. The α-olefin polymer contained in the gel-like molded product is adjusted to 10 to 90% by weight, and then stretched at a temperature equal to or lower than the melting point of the α-olefin polymer by 10°C. A method for producing an ultra-high molecular weight α-olefin polymer film, which comprises removing residual solvent contained in a molded product and then subjecting the molded product to pressure treatment at a temperature below the melting point of the α-olefin polymer. 2. The manufacturing method according to claim 1, wherein the α-olefin polymer is polypropylene.