Method for preparing microporous polyolefin film with improved productivity and easy control of physical properties

A microporous polyolefin film manufactured by a method by using a roll type stretching machine, the method at least including:

• (a) melting/mixing/extruding a sheet composition containing a polyolefin composition having a weight-average molecular weight of not less than 1×105 to less than 1×106 (component I) and a diluent (component II) in a ratio by weight of 15˜50:85˜50 and shaping these compositions into a sheet form through a T-die;
• (b) using the stretching machine of roll type consisting of at least three rolls to stretch the sheet to the machine direction, and then, stretch the film stretched uni-axially to the machine direction into the transverse direction by a stretching machine of tenter type, in order to form a film by sequential biaxial stretching;
• and
• (c) extracting the diluent from the film stretched to the machine and transverse direction and drying the film,
• wherein the stretching machine to the machine direction includes at least one preheating roll, at least one stretching roll and at least one cooling roll or air-cooled device, a total roll contact time at the preheating rolls ranges from 1 to 500 seconds, the stretching is executed in at least one section between rolls, a stretching ratio in one section between two rolls ranges from 1.05 to 6 times, a roll contact coefficient of the sheet on the stretching roll ranges from 1.5 to 54 degree (of angle)×m, and a coefficient of non-contact section between rolls ranges from 0.1×10−3 to 200×10−3 min.

A microporous polyolefin film manufactured by a method by using a roll type stretching machine, the method at least including:

• (a) melting/mixing/extruding a sheet composition containing a polyolefin composition having a weight-average molecular weight of not less than 1×105 to less than 1×106 (component I) and a diluent (component IS) in a ratio by weight of 15˜50:85˜50 and shaping these compositions into a sheet form through a T-die;
• (b) using the stretching machine of roll type consisting of at least three rolls to stretch the sheet to the machine direction, and then, stretch the film stretched uni-axially to the machine direction into the transverse direction by a stretching machine of tenter type, in order to form a film by sequential biaxial stretching;
• and
• (c) extracting the diluent from the film stretched to the machine and transverse direction and drying the film,
• wherein the stretching machine to the machine direction includes at least one preheating roll, at least one stretching roll and at least one cooling roll or air-cooled device, a total roll contact time at the preheating rolls ranges from 1 to 500 seconds, the stretching is executed in at least one section between rolls, a stretching ratio in one section between two rolls ranges from 1.05 to 8 times, a roll contact coefficient of the sheet on the stretching roll ranges from 1.5 to 54 degree (of angle)×m, and a coefficient of non-contact section between rolls ranges from 0.1×10−3 to 200×10−3 min, and
• wherein the polyolefin composition in (a) includes at least one polyolefin resin component, or 80 to 99.9 wt % of at least one polyolefin resin and 0.1 to 20 wt % of a component selected from an inorganic material or other resins except for the polyolefin resin.

A microporous polyolefin film manufactured by a method by using a roll type stretching machine, the method at least including:

• (a) melting/mixing/extruding a sheet composition containing a polyolefin composition having a weight-average molecular weight of not less than 1×105 to less than 1×106 (component I) and a diluent (component II) in a ratio by weight of 15˜50:85˜50 and shaping these compositions into a sheet form through a T-die;
• (b) using the stretching machine of roll type consisting of at least three rolls to stretch the sheet to the machine direction, and then, stretch the film stretched uni-axially to the machine direction into the transverse direction by a stretching machine of tenter type, in order to form a film by sequential biaxial stretching;
• and
• (c) extracting the diluent from the film stretched to the machine and transverse direction and drying the film,
• wherein the stretching machine to the machine direction includes at least one preheating roll, at least one stretching roll and at least one cooling roll or air-cooled device, a total roll contact time at the preheating rolls ranges from 1 to 500 seconds, the stretching is executed in at least one section between rolls, a stretching ratio in one section between two rolls ranges from 1.05 to 6 times, a roll contact coefficient of the sheet on the stretching roll ranges from 1.5 to 54 degree (of angle)×m, and a coefficient of non-contact section between rolls ranges from 0.1×10−3 to 200×10−3 min,
• wherein the stretching to the machine direction is performed by stretching the sheet introduced info the stretching machine while applying a tensile strength of 550N/cm2 in the machine direction for 4˜12 times, and the stretching to the transverse direction is performed by stretching the film introduced into the stretching machine while applying a tensile strength of 100˜700N/cm2 in the machine direction for 4˜9 times,
• wherein the method further includes a heat setting process that uses heat setting equipment of tenter type, after the extracting in (c), to stretch the film for 20˜100% to the transverse direction, and then, shrink the film to have a width of 5˜50%, compared to the film after stretching, with conducting thermal relaxation in a range of temperatures in which crystals of 5˜50% in the film are molten,
• wherein the stretching includes:
• stretching to the machine direction wherein the temperature of the preheating roll ranges from a melting temperature of the resin in the sheet −50° C. to a temperature at which 70% of crystals contained in the resin of the sheet are molten, the temperature of the stretching roll ranges from the melting temperature of the resin in the sheet −50° C. to a temperature at which 90% of crystals contained in the resin of the sheet are molten, the temperature of the cooling roll is a temperature of the stretching roll −5° C., or less, or air-cooling is conducted, so that a sheet width holding ratio between rolls in the stretching roll after stretching ranges from 70 to 99% and an overall sheet width holding ratio after stretching to the machine direction ranges from 50 to 95%;
• and stretching to the transverse direction wherein the stretching machine to the machine direction includes a preheating part, a stretching part, and a heat setting part, and the temperature of the preheating part is a melting temperature of the resin in the sheet +20° C., or less, the temperature of the stretching part ranges from a melting temperature of the resin in the sheet −20° C. to the melting temperature of the resin in the sheet +10° C., and the temperature of the heat setting part is the melting temperature of the resin in the sheet, or less.