Manufacturing method of porous multilayered polyolefin

1. A manufacturing method of a polyolefin-based multilayer composite porous film as a battery separator, comprising:

a) forming a composition including a polyolefin resin and diluent into a sheet;

b) stretching the sheet and extracting the diluent to manufacture a film;

c) performing heat-treatment on the manufactured film; and

d) coating one surface or both surfaces of the heat-treated film with a coating solution containing a heat resistant resin, inorganic particles, and latex particles in an emulsion form that includes an acrylate group in which a glass transition temperature Tg is −60° C. to 0° C.,

wherein step c) and step d) are continuously performed.

2. The manufacturing method of claim 1 , wherein the heat-treatment in step c) includes heat-setting process, and includes a heat-stretching process or a heat-relaxing process of the film in at least one direction.

3. The manufacturing method of claim 2 , wherein in the heat-relaxing process, a width of the film after the heat-relaxing process is reduced by a ratio of 50 to 99% as compared to a width of the film before the heat-relaxing process.

4. The manufacturing method of claim 2 , wherein in step b), a stretching ratio is four times or more in a machine direction and a transverse direction, respectively, and a total stretching ratio is 20 to 80 times, and

in step c), a heat stretching ratio is 1.01 to 2.0 times in a machine direction or a transverse direction.

5. The manufacturing method of claim 1 , wherein the composition of step a) includes 15 to 50 wt % of the polyolefin resin and 85 to 50 wt % of the diluent.

6. The manufacturing method of claim 1 , wherein the polyolefin resin of step a) has a weight average molecular weight of 1×10 5 ˜2×10 6 g/mol.

7. The manufacturing method of claim 1 , further comprising:

e) drying the film coated in step d),

wherein the drying is performed by using air or an infrared drying device.

8. The manufacturing method of claim 1 , wherein the stretching process of step b) is performed within a range between a temperature lower than a melting point of the polyolefin resin by 40° C. and the melting temperature of the polyolefin resin, and

the heat-treatment process of step c) is performed within a range between a temperature lower than the melting point of the polyolefin resin by 30° C. and a temperature higher than the melting point of the polyolefin resin by 10° C.

9. The manufacturing method of claim 1 , wherein the heat resistant resin in step d) includes a water-soluble polymer or a water-insoluble polymer in which a melting temperature or a glass transition temperature is 150° C. or more.

10. The manufacturing method of claim 9 , wherein the water-soluble polymer is at least any one selected from the group consisting of polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone, carboxyl methyl cellulose, hydroxyethyl cellulose, maleic anhydride-based resin, dextrin and mixtures thereof, and

the water-insoluble polymer is a mixture including any one or two or more selected from polypolyphenylene sulfone, polysulfone, polyimide, polyamideimide, polyarylamide, polyarylate, polycarbonate, polyvinylidene fluoride, and copolymers thereof, or includes an acrylate group in which a glass transition temperature is −60° C. to 0° C.