TW201617227A - Polyolefin microporous film and manufacturing method thereof - Google Patents

Abstract

A polyolefin microporous film includes a polyolefin precursor film and a coating layer. The polyolefin microporous film has a plurality of through holes. The through holes have inner surface. The coating layer is disposed on one surface of the polyolefin precursor film. Part of coating layer extends to the through holes to cover part of inner surface.

Description

Polyolefin porous membrane and method of producing the same

The present invention relates to a polyolefin porous film and a method for producing the same, and particularly to a polyolefin porous film for use in a lithium battery and a method for producing the same.

The lithium battery generally includes a positive/negative electrode material and an electrolyte. Generally, the positive and negative electrodes of the lithium battery need to pass through a separator to block the positive and negative electrodes of the lithium battery to avoid contact between the two to cause a short circuit. At present, the common lithium battery isolation membrane is mainly a polyolefin porous membrane for ion transfer of electrolyte. The material of the electrolyte is corrosive, so the separator of the lithium battery needs to consider the heat resistance, permeability, mechanical strength and stability of the lithium battery.

In general, in order for the lithium battery to function well, the separator membrane needs to have porosity and low shrinkage to achieve performance requirements such as heat resistance, permeability, mechanical strength and stability.

Embodiments of the present invention provide a polyolefin porous film and a method for producing the same, which have a coating layer capable of reducing a shrinkage ratio of a polyolefin porous film and providing a lithium battery with good operation.

One embodiment of the present invention provides a polyolefin porous film comprising a polyolefin precursor film and a coating. The polyolefin precursor film has a plurality of through holes, each of which has an inner surface. The coating is disposed on one of the surfaces of the polyolefin precursor film, wherein a portion of the coating extends to the through hole to cover a portion of the inner surface of the through hole.

A method of producing a polyolefin porous film according to another embodiment of the present invention, which comprises providing a polyolefin film. The first heat treatment of the polyolefin film is carried out to raise the temperature of the polyolefin film from room temperature to 80 degrees Celsius. After the first heat treatment of the polyolefin film, the first stretching treatment is performed in the mechanical direction of the polyolefin film. After the first stretching treatment of the polyolefin film, the polyolefin film subjected to the first stretching treatment is subjected to a second heat treatment to repeatedly heat the polyolefin film. After the second heat treatment of the polyolefin film, a second stretching treatment is performed along the mechanical direction of the polyolefin film to form a polyolefin precursor film. After forming the polyolefin precursor film, the coating material is applied to one of the surfaces of the polyolefin precursor film. The coating material is hardened by ultraviolet light irradiation to form a coating.

In summary, the present invention provides a polyolefin porous film and a method for manufacturing the same, wherein the shape of the through-hole of the polyolefin porous film penetrates from the upper surface of the polyolefin precursor film to the lower surface and is curved. It is not in an upright position. Thus, the volume of the through-holes in the overall polyolefin precursor film is increased, so that the pore curvature is higher than the conventional pore curvature. Therefore, the pore curvature is high, and the time during which the electrolyte ions of the lithium battery pass through the holes increases, thereby further reducing the self-discharge rate of the lithium battery.

Further, by forming a coating layer on the surface of the polyolefin precursor film, the melting point of the polyolefin porous film is improved by 5 to 10 degrees Celsius, which improves the heat resistance of the polyolefin porous film. Further, the polyolefin precursor film and the coating are added in a thickness of between 20 μm and 40 μm, and the polyolefin porous film has a shrinkage ratio in the mechanical direction of less than 1%.

For a better understanding of the features and technical aspects of the present invention, reference should be made to the accompanying drawings.

100‧‧‧Polyolefin porous membrane

110‧‧‧Polyolefin precursor film

120‧‧‧Coating

H1‧‧‧through holes

S1‧‧‧ inner surface

S101~S107‧‧‧Steps

1A is a schematic view showing the structure of a polyolefin porous film according to an embodiment of the present invention.

1B is a partial schematic view of a polyolefin porous film according to an embodiment of the present invention.

2 is a schematic flow chart showing a method of producing a polyolefin porous film according to an embodiment of the present invention.

The exemplary embodiments are described with reference to the accompanying drawings, in which FIG. It should be noted that the inventive concept may be embodied in many different forms and should not be construed as being limited to the illustrative embodiments set forth herein. Rather, these exemplary embodiments are provided so that this invention will be in the In each of the figures, the relative proportions of the various layers and regions may be exaggerated, and like numerals indicate the like elements.

Fig. 1A is a schematic view showing the structure of a polyolefin porous film according to an embodiment of the present invention. Referring to FIG. 1A, the polyolefin porous film 100 includes a polyolefin precursor film 110 and a coating layer 120. The polyolefin precursor film 110 has a plurality of through holes H1, and the coating layer 120 is disposed on one surface of the polyolefin precursor film 110, and a portion of the coating layer 120 extends into the through holes H1. In practice, the polyolefin porous film 100 is mainly applied to a separator film for a lithium battery, and is used to block the positive and negative electrodes of the lithium battery to avoid contact between the two to cause a short circuit.

The polyolefin precursor film 110 is used as a substrate of the polyolefin porous film 100, which may be a single layer structure of polyethylene or polypropylene. Alternatively, the polyolefin precursor film 110 may also be a multilayer structure composed of a mixture of polyolefins, for example, a two-layer structure in which two polypropylene layers sandwich a polyethylene layer. The present invention does not limit the material of the polyolefin precursor film 110. The polyolefin precursor film 110 has a plurality of through holes H1 having an inner surface S1 and a through hole having a diameter of between 0.01 μm and 0.1 μm. It is worth noting that the through hole H1 is for passing ions of the electrolyte. It is to be noted that the shape of the through hole H1 is curved and penetrates from the upper surface of the polyolefin precursor film 110 to the lower surface, and is not in an upright shape.

The coating layer 120 is disposed on one surface of the polyolefin precursor film 110. The material of the coating may be a photocurable material composed of a monomer including at least two reactive functional groups, and the reactive functional group includes a trifunctional glycol diacrylate (TPGDA). 1,6-Hexanediol diacrylate (HDDA), trifunctional methyltripropane Trimethylolpropane triacrylate (TMPTA). The thickness of the coating 120 is between 0.5 microns and 1 micron. Since the thickness of the coating layer 120 is thin, in the process of preparing the coating layer 120 on the polyolefin precursor film 110, the coating layer 120 is partially distributed in the through hole H1. Specifically, please refer to FIG. 1B, which is a partial schematic view of a polyolefin porous film according to an embodiment of the present invention. A portion of the coating 120 extends through the through hole H1 to cover a portion of the inner surface S1 of the through hole H1.

2 is a schematic flow chart showing a method of producing a polyolefin porous film according to an embodiment of the present invention. As shown in FIG. 2, the method for producing a polyolefin porous film according to an embodiment of the present invention mainly forms a coating layer 120 on the surface of the polyolefin precursor film 110.

First, in step S101, a polyolefin film is provided. The material of the polyolefin film may be a single layer structure of polyethylene or polypropylene. Alternatively, the polyolefin precursor film 110 may also be a multilayer structure composed of a mixture of polyolefins, for example, a two-layer structure in which two polypropylene layers sandwich a polyethylene layer.

In step S102, the polyolefin film is subjected to a first heat treatment to increase the temperature of the polyolefin film from room temperature to 80 to 90 degrees Celsius, and the heating time is maintained for 1 to 2 minutes, so that the temperature of the polyolefin film can be maintained. The average temperature is 80 to 90 degrees Celsius.

In step S103, after the first heat treatment of the polyolefin film, the first stretching treatment is performed along the mechanical direction (MD) of the polyolefin film, so that the stretching ratio of the polyolefin film is 20 to 30. %.

In step S104, the polyolefin film subjected to the first stretching treatment is subjected to a second heat treatment. Specifically, the polyolefin film is first heated to raise its temperature from room temperature to 80 degrees Celsius for 2 minutes and then back to room temperature. Next, the polyolefin film was heated again, and the temperature was raised from room temperature to 90 degrees Celsius for 2 minutes and then returned to room temperature. Thereafter, the polyolefin film was reheated to raise the temperature from room temperature to 100 degrees Celsius for 2 minutes. Through the second heat treatment, the polyolefin film is subjected to a plurality of repeated heating processes to stabilize the polyolefin film and achieve uniformity. The second heat treatment may be passed through a hot furnace or a preheating roll set, which is not limited in the present invention.

In step S105, after the second heat treatment of the polyolefin film, the temperature of the polyolefin film is maintained between 80 degrees Celsius and 90 degrees Celsius, and a second stretching treatment is performed along the mechanical direction of the polyolefin film to make the polyolefin. The film has a stretch ratio of 70 to 100% to form a polyolefin precursor film. Specifically, after the above-described process, the polyolefin precursor film 100 has a plurality of through holes H1. The through hole H1 has an inner surface S1, and the through hole H1 has a diameter of between 0.01 μm and 0.1 μm. The pore curvature (Tortuosity) ranges from 36 to 41. In detail, since the shape of the through hole H1 of the polyolefin porous film is curved and penetrates from the upper surface of the polyolefin precursor film to the lower surface, it does not appear to be in an upright shape. Therefore, the volume occupied by the through-hole H1 in the overall polyolefin precursor film is increased, so that the pore curvature is higher than the conventional pore curvature. With the curved shape of the through hole H1, the time required for the lithium battery electrolyte ions to pass through the hole H1 increases, and the self-discharge rate of the lithium battery is lowered.

In step S106, after forming the polyolefin precursor film, a coating material is applied on one surface of the polyolefin precursor film 100. The coating material may be a photocurable material composed of a monomer including at least two reactive functional groups, and the reactive functional group includes a trifunctional glycol diacrylate (TPGDA), 1,6-Hexanediol diacrylate (HDDA), trimethylolpropane triacrylate (TMPTA). In practice, tripropylene glycol diacrylate, fatty acid modified Hexa-function polyester acrylate and 1-hydroxycyclohexyl phenyl ketone (1-hydroxy-) Cyclohexylpheneyl ketone) was mixed as a solute in a ratio of 16:4:1, and toluene was used as a solvent to form a coating material having a solid content of 2.5%. Next, the coating material is coated on the surface of the polyolefin precursor film 110, waiting for the solvent to evaporate. It should be noted that when the coating material is applied to the surface of the polyolefin precursor film 110, a part of the coating material may penetrate into the through hole H1, and a portion of the inner surface S1 covering the through hole H1 may have a thickness of the coating 120. Between 0.5 microns and 1 micron.

In step S107, the coating material is hardened to form a coating layer 120 on one surface of the polyolefin precursor film 110. Specifically, ultraviolet light may be irradiated on the surface of the coating material to form the coating layer 120. By forming the coating layer 120 on the surface of the polyolefin precursor film 110, the melting point of the polyolefin porous film 100 is increased by 5 to 10 degrees Celsius as compared with the conventional one, and the heat resistance of the polyolefin porous film 100 is improved. Further, the thickness of the polyolefin precursor film 110 and the coating layer 120 is between 20 μm and 40 μm, and the shrinkage ratio of the polyolefin porous film 100 in the mechanical direction is less than 1%.

By applying the above process, the present invention can provide an embodiment of a method for producing a polyolefin porous film. It should be emphasized that the order of most process steps can be adjusted according to different preparation conditions or according to different preparation machines.

In summary, the present invention provides a polyolefin porous film and a method for manufacturing the same, wherein the pore curvature is proportional to the impedance increase rate (MacMullin No.) and porosity (porosity), and in the case of a fixed porosity, the present invention The impedance increase rate of the invention is higher than that of the prior art, so that the pore curvature of the present invention is high, and thus the shape of the through-hole of the polyolefin porous film is penetrated from the upper surface of the polyolefin precursor film to the lower surface and is presented. Curved. Since the shape of the through-hole is curved and does not appear to be upright, the volume of the through-hole in the overall polyolefin precursor film is increased, so that the curvature of the pore is higher than the conventional curvature of the pore. Therefore, the pore curvature is high, and the time during which the electrolyte ions of the lithium battery pass through the holes increases, thereby further reducing the self-discharge rate of the lithium battery.

Further, by forming a coating layer on the surface of the polyolefin precursor film, the melting point of the polyolefin porous film is improved by 5 to 10 degrees Celsius, which improves the heat resistance of the polyolefin porous film. Further, the polyolefin precursor film and the coating are added in a thickness of between 20 μm and 40 μm, and the polyolefin porous film has a shrinkage ratio in the mechanical direction of less than 1%.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Therefore, equivalent technical changes made by using the present specification and the contents of the drawings are included in the protection scope of the present invention. .

100‧‧‧Polyolefin porous membrane

110‧‧‧Polyolefin precursor film

120‧‧‧Coating

H1‧‧‧through holes

S1‧‧‧ inner surface

Claims (10)

A polyolefin porous film comprising: a polyolefin precursor film having a plurality of through holes, each of the through holes having an inner surface; and a coating layer disposed on the substrate One of the surfaces of the polyolefin precursor film, wherein a portion of the coating extends to the through hole to cover a portion of the inner surface of the through hole. The polyolefin porous film according to claim 1, wherein the material of the coating layer is selected from the group consisting of tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, and a trifunctional methyltrimethylpropane. One of a group consisting of triacrylates and mixtures thereof. The polyolefin porous film according to claim 1, wherein the coating has a thickness of between 0.5 μm and 1 μm. The polyolefin porous film according to claim 1, wherein the polyolefin precursor film and the coating are added in a thickness of between 20 μm and 40 μm. The polyolefin porous film according to claim 1, wherein the polyolefin porous film has a shrinkage ratio in the machine direction of less than 1%. A method for producing a polyolefin porous film, comprising: providing a polyolefin film; performing a first heat treatment on the polyolefin film to raise the temperature of the polyolefin film from room temperature to 80 degrees Celsius; After the first heat treatment of the polyolefin film, the first stretching treatment is performed along the mechanical direction of the polyolefin film; after the first stretching treatment of the polyolefin film, the first pulling is performed Stretching the polyolefin film for a second heat treatment to repeatedly heat the polyolefin film; after the second heat treatment of the polyolefin film, along the polyolefin film The mechanical direction is subjected to a second stretching treatment to form a polyolefin precursor film; after forming the polyolefin precursor film, coating a coating material on one surface of the polyolefin precursor film; The coating material is hardened by light irradiation to form a coating. The method for producing a polyolefin porous film according to claim 6, wherein the stretching ratio of the polyolefin film is 30% when the first stretching treatment is performed. The method for producing a polyolefin porous film according to claim 6, wherein the stretching ratio of the polyolefin film is 100% when the second stretching treatment is performed. The method for producing a polyolefin porous film according to claim 6, wherein the material of the coating layer is selected from the group consisting of tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, and a trifunctional hydroxyl group. One of a group consisting of methyl propane triacrylate and a mixture thereof. The method for producing a polyolefin porous film according to claim 6, wherein, in the second heat treatment, the temperature of the polyolefin film is raised from room temperature to 80 degrees Celsius and maintained for 2 minutes and then returned to the chamber. Warming, the temperature of the polyolefin film is raised from room temperature to 90 degrees Celsius and maintained for 2 minutes and then returned to room temperature, so that the temperature of the polyolefin film is raised from room temperature to 100 degrees Celsius and maintained. 2 minutes.