KR102190864B1 - Preparation method of porous fluorine resin sheet - Google Patents

Abstract

The present invention relates to a method for producing a fluorine-based resin porous membrane. In the present invention, there is provided a method for producing a fluorine-based resin porous membrane having improved pore characteristics while minimizing changes in processing conditions such as extrusion and stretching.

Description

Manufacturing method of fluorine-based resin porous membrane {PREPARATION METHOD OF POROUS FLUORINE RESIN SHEET}

The present invention relates to a method for producing a porous membrane using a fluorine-based resin as a raw material.

The fluororesin-based porous membrane may have properties such as high heat resistance, chemical stability, weatherability, non-flammability, strength, non-adhesiveness, low friction coefficient, and low dielectric constant resulting from the fluorine-based resin itself. It may have properties such as flexibility, liquid permeability, and particle collection efficiency.

Among these fluorine-based resins, porous membranes made using polytetrafluoroethylene (PTFE), in particular, have high stability against various compounds, so they are in gas and liquid form in semiconductor-related fields, liquid crystal-related fields, and food and medical-related fields. It is widely used as a microfiltration filter (membrane filter) for a mixture of.

In order to manufacture a high-performance fluorine-based porous membrane, it is necessary to maximize a high filtration efficiency and a flow rate that can be processed under a constant pressure while maintaining a small pore size. To this end, according to the previously known method for producing a fluorine-based porous membrane, a raw material having a high molecular weight is used, a high extrusion pressure is applied during extrusion, or a method of compressing the film after stretching is used.

However, it is not easy to control the properties of the porous membrane by controlling the molecular weight of the raw material. In addition, a method of implementing specific extrusion conditions by changing the structure of the extrusion die or adjusting the content of the lubricant causes a decrease in processability.

Accordingly, there is a need to develop a method of manufacturing a fluorine-based resin porous membrane having improved pore characteristics while minimizing changes in processing conditions such as extrusion and stretching.

The present invention is to provide a method for producing a fluorine-based resin porous membrane having improved pore characteristics while minimizing changes in processing conditions such as extrusion and stretching.

According to the present invention,

Heat-treating the fluorine-based resin powder by heating at 280 to 320° C. for 30 to 60 minutes;

Compressing a paste containing the heat-treated fluorine-based resin powder to form a preform;

Extruding the preform to form a sheet; And

Stretching the sheet

There is provided a method for producing a fluorine-based resin porous membrane comprising a.

Hereinafter, a method of manufacturing a fluorine-based resin porous membrane according to embodiments of the present invention will be described.

Unless expressly stated in the specification, terminology is only intended to refer to specific embodiments and is not intended to limit the invention.

The singular forms used in the present specification also include plural forms unless the phrases clearly indicate the opposite.

The meaning of'comprising' as used herein specifies a specific characteristic, region, integer, step, action, element or component, and excludes the addition of another specific characteristic, region, integer, step, action, element, or component. It is not.

On the other hand, a method of preparing a preform using a resin composition containing a fluorine-based resin and a lubricant, and stretching the preform to form a film having specific pore characteristics has been known previously. However, with the previous method, there is a limitation in forming finer and more uniform pores, and there is a problem that the uniformity of the formed pores is not good.

As a result of continuous research by the present inventors, when raw materials (fluorine-based resin powder) for manufacturing a fluorine-based resin porous membrane are heat-treated under specific conditions, the provision of a fluorine-based resin porous membrane having a narrow pore distribution while minimizing changes in processing conditions such as extrusion and stretching It was confirmed that it enables.

In particular, as the raw material used in the manufacturing method of the present invention is heat-treated under specific conditions, the degree of connection between the raw material particles is improved compared to the raw material that is not heat-treated, so that during the extrusion and stretching process using the same, Stretching occurs. When uniform force is applied under processing conditions, formation of large pores caused by particles with poor connection conditions can be suppressed. And, due to this change, it was confirmed that the fluorine-based resin porous membrane prepared using the heat-treated raw material can exhibit improved pore characteristics (especially narrow pore distribution).

According to one embodiment of this invention,

Heat-treating the fluorine-based resin powder by heating at 280 to 320° C. for 30 to 60 minutes;

Compressing a paste containing the heat-treated fluorine-based resin powder to form a preform;

Extruding the preform to form a sheet; And

Stretching the sheet

There is provided a method for producing a fluorine-based resin porous membrane comprising a.

As a step of preparing a raw material for manufacturing the fluorine-based resin porous membrane, a step of heat treatment of the fluorine-based resin powder is performed.

The heat treatment may be performed by placing the fluorine-based resin powder in a conventional convection oven and heating it at 280 to 320°C for 30 to 60 minutes.

As a non-limiting example, the fluorine-based resin is polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene- At least one fluorine-based selected from the group consisting of tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-chlorotrifluoroethylene copolymer (TFE/CTFE), and ethylene-chlorotrifluoroethylene copolymer (ECTFE) It can be a compound.

And, in order to secure the basic physical properties of the porous membrane, the fluorine-based resin may preferably have a number average molecular weight of 5,000,000 to 15,000,000 g/mol. And, in order to control the microporous properties of the porous membrane, one or more fluorine-based resins having different number average molecular weights may be mixed and used.

The particle size of the fluorine-based resin powder is not particularly limited. However, for extrusion and sheet molding using this, a fluorine-based resin powder having an average particle diameter (ASTM D 4895) of 20 to 1000 µm, or 100 to 900 µm, or 200 to 800 µm, or 400 to 700 µm is preferably used. I can.

Preferably, the heat treatment is at least 280°C, or at least 285°C, or at least 290°C, or at least 295°C, or at least 300°C; And it may be carried out at a temperature of 320 ℃ or less, or 315 ℃ or less, or 310 ℃ or less, or 305 ℃ or less.

When the heat treatment temperature is too low, the heat treatment is not sufficiently performed on the fluorine-based resin powder, and it is difficult to expect an improvement in the pore characteristics of the fluorine-based resin porous membrane manufactured using the same. On the other hand, when the heat treatment temperature is too high and a long time is processed, there may be a problem that pores disappear and micropores cannot be formed due to stretching.

And, the time of the heat treatment may be adjusted in the range of 30 to 60 minutes depending on the temperature of the heat source.

Subsequently, a step of forming a preform by compressing the paste containing the heat-treated fluorine-based resin powder is performed.

The paste for forming the preform may include a lubricant together with the heat-treated fluorine-based resin powder.

The lubricant is added to wet the surface of the heat-treated fluorine-based resin powder, and to smoothly perform compression, extrusion, and sheet processing.

The type of the lubricant is not particularly limited as long as it is a material that can be removed by means such as evaporation extraction by heat after sheet processing. For example, as the lubricant, liquid compounds such as liquid paraffin, naphtha, white oil, hydrocarbon oils such as toluene and xylene may be preferably used. In addition, as the lubricant, compounds well known as lubricants in the art, such as various alcohol compounds, ketone compounds, and ester compounds, may be used.

The content of the lubricant included in the paste is not particularly limited, and may vary depending on the type of lubricant and molding conditions. For example, the lubricant may be used in an amount of 5 to 50 parts by weight, 10 to 50 parts by weight, or 10 to 40 parts by weight based on 100 parts by weight of the heat-treated fluorine-based resin powder.

The preform is an intermediate for manufacturing the fluorine-based resin porous membrane of the embodiment, and the shape is not particularly limited. For example, the preform may be prepared by compressing a paste containing the heat-treated fluorine-based resin powder by a conventional method such as a rolling method.

Subsequently, the step of extruding the preform to form a sheet is performed.

The extrusion is a process for processing the preform into a sheet form having a predetermined thickness, and a conventional device such as a roller may be used.

In order to allow this extrusion process to proceed smoothly, the extrusion may be performed under a temperature of 30 to 100 °C.

In addition, a drying process for removing the lubricant contained in the sheet may be performed on the sheet obtained by extrusion. This drying process may be performed under a temperature of 100 to 300 °C.

Then, the step of stretching the sheet is performed.

The stretching may be performed by supplying the sheet to rollers rotating at different speeds. Further, the stretching may be performed in an oven using a tenter.

The stretching may be performed by biaxial stretching, and the stretching ratio at this time may be determined according to the use of the porous membrane. For example, the stretching may be performed by biaxial stretching of 2 to 10 times of longitudinal stretching and 2 to 50 times of transverse stretching of the sheet.

Here, it may be preferable to perform the stretching near or below the melting point of the sheet in order to secure workability. For example, the stretching may be performed under a temperature of 100 to 400 °C.

If necessary, prior to the stretching process, a step of sintering the sheet obtained by extrusion of the preform may be additionally performed. This sintering process may be performed under a temperature of, for example, 200 to 400°C.

Meanwhile, the fluorine-based resin porous membrane obtained through the process of the embodiment may have a thickness of 5 to 200 μm and a density of 0.10 to 1.00 g/cm 3. The thickness and density of the fluorine-based resin porous membrane may be adjusted within a suitable range according to the use of the porous membrane.

In particular, the fluorine-based resin porous membrane obtained through the process of the above embodiment may have a narrow pore distribution as it is manufactured using the heat-treated fluorine-based resin powder.

Specifically, the fluorine-based resin porous membrane may have a pore distribution satisfying the following Equation 1:

[Equation 1]

(P _M /P _m ) <1.3

In Equation 1 above,

P _M is the maximum pore size (nm) of the fluorine-based resin porous membrane measured using a capillary flow porometer (fluid: Galwick),

P _m is the mean pore size (nm) of the fluorinated resin porous membrane measured using a capillary flow porometer (fluid: Galwick).

*

In addition, the fluorine-based resin such as polytetrafluoroethylene (PTFE) has excellent heat resistance and chemical resistance, and the porous membrane manufactured using it is used as a filter medium for corrosive gases and liquids, a permeable membrane for electrolysis, and a battery separator. It can be widely used, and can also be used to finely filter various gases and liquids used in the semiconductor industry.

In particular, the fluorine-based resin porous membrane manufactured according to the method of the embodiment has a narrow diameter distribution of pores distributed therein, and the amount of fluid passing through the porous membrane per unit time under a predetermined pressure is relatively high.

In general, a porous membrane having a fine thickness may change its shape or diameter characteristics of pores distributed therein due to the applied pressure during filtration, and the filtration characteristics may be greatly degraded due to rupture of the membrane itself. On the other hand, the fluorine-based resin porous membrane manufactured according to the method of the above embodiment has excellent mechanical properties such as strength, and thus its shape or internal pore characteristics do not change significantly during the manufacturing process and the use process (filtration operation).

The method of manufacturing a fluorine-based resin porous membrane according to the present invention makes it possible to provide a fluorine-based resin porous membrane having improved pore characteristics (especially a narrow pore distribution) while minimizing changes in processing conditions such as extrusion and stretching.

1 is a field emission scanning electron microscopy (FESEM) image observing the surface of a porous membrane according to Example 1. FIG.
2 is a FESEM image observing the surface of a porous membrane according to Comparative Example 1.

Hereinafter, preferred embodiments are presented to aid the understanding of the present invention. However, the following examples are only for illustrating the present invention, and the present invention is not limited thereto.

Example 1

Polytetrafluoroethylene powder (POLYFLON PTFE F-106C; number average molecular weight about 15,000,000 g/mol; average particle diameter 400-700 µm; manufactured by Daikin) was placed in a convection oven and heated at 300° C. for 30 minutes. Heat treated.

A paste was prepared by mixing 18 parts by weight of a liquid lubricant (product name: (ISOPAR ^TM H FLUID; Hydrocarbons, C11-C12, isoalkanes, <2% aromatics; ExxonMobil Chemical Company) based on 100 parts by weight of the heat-treated PTFE powder. The paste was compressed to prepare a preformed block.

The preformed block was extruded at a rate of 50 mm/min under a temperature of 50° C. to form a sheet having a thickness of about 400 μm. The prepared sheet was heated and dried under a temperature of about 200° C. to completely remove the liquid lubricant.

Then, the sheet was stretched 6 times in the longitudinal direction (MD) under a temperature of about 300°C, and the sheet was stretched 25 times in the transverse direction (TD) under a temperature of about 100°C. The biaxially stretched sheet was heat-set at a temperature of about 300° C. to obtain a porous membrane having a thickness of about 20.1 μm.

Example 2

Polytetrafluoroethylene powder (POLYFLON PTFE F-106C; number average molecular weight about 15,000,000 g/mol; average particle diameter 400-700 μm; manufactured by Daikin) was placed in a convection oven and heated at 300° C. for 60 minutes. Heat treated.

A paste was prepared by mixing 18 parts by weight of a liquid lubricant (product name: (ISOPAR ^TM H FLUID; Hydrocarbons, C11-C12, isoalkanes, <2% aromatics; ExxonMobil Chemical Company) based on 100 parts by weight of the heat-treated PTFE powder. The paste was compressed to prepare a preformed block.

The preformed block was extruded at a rate of 50 mm/min under a temperature of 50° C. to form a sheet having a thickness of about 400 μm. The prepared sheet was heated and dried under a temperature of about 200° C. to completely remove the liquid lubricant.

Then, the sheet was stretched 6 times in the longitudinal direction (MD) under a temperature of about 300°C, and the sheet was stretched 25 times in the transverse direction (TD) under a temperature of about 100°C. The biaxially stretched sheet was heat-fixed at a temperature of about 300° C. to obtain a porous membrane having a thickness of about 19.1 μm.

Comparative Example 1

Polytetrafluoroethylene powder (POLYFLON PTFE F-106C; number average molecular weight of about 15,000,000 g/mol; average particle diameter of 400 to 700 µm; manufactured by Daikin) 18 parts by weight of a liquid lubricant (product name: (ISOPAR ^TM H FLUID; Hydrocarbons, C11-C12, isoalkanes, <2% aromatics; ExxonMobil Chemical Company) were mixed to prepare a paste, and the paste was compressed to prepare a preformed block.

The preformed block was extruded at a rate of 50 mm/min under a temperature of 50° C. to form a sheet having a thickness of about 400 μm. The prepared sheet was heated and dried under a temperature of about 200° C. to completely remove the liquid lubricant.

Then, the sheet was stretched 6 times in the longitudinal direction (MD) under a temperature of about 300°C, and the sheet was stretched 25 times in the transverse direction (TD) under a temperature of about 100°C. The biaxially stretched sheet was heat-fixed at a temperature of about 300° C. to obtain a porous membrane having a thickness of about 18.4 μm.

Test Example 1

The surfaces of the porous membranes according to Example 1 and Comparative Example 1 were observed using a field emission scanning electronen microscope (FESEM), and images thereof are shown in FIGS. 1 (Example 1) and 2 (Comparative Example 1).

Referring to FIGS. 1 and 2, it is confirmed that the porous membrane according to Example 1 has a more dense and uniform pore distribution than the porous membrane according to Comparative Example 1.

Test Example 2

The pore distribution of the porous membranes according to the Examples and Comparative Examples was measured using a Capillary flow porometer (CFP 1500AE; manufactured by PMI; fluid: Galwick). Among the measurement results, the maximum pore size (P _M , nm) and the average pore size (P _m , nm) of the porous membrane are shown in Table 1 below.

P _M (nm) P _m (nm) P _M /P _m Example 1 100.0 83.1 1.203 Example 2 116.0 89.4 1.298 Comparative Example 1 223.0 89.0 2.506

Referring to Table 1, it is confirmed that the porous membranes of the examples have a narrow pore distribution having a P _M /P _m value of less than 1.3 as they are manufactured using heat-treated PTFE powder.

On the other hand, the porous membrane of Comparative Example prepared using PTFE powder that was not heat treated has a similar average pore size compared to the porous membrane of Examples, but showed a difference of about 2 times or more in the maximum pore size, resulting in a wide pore distribution. It is confirmed to have.

Claims (6)

Heat-treating the fluorine-based resin powder by heating at 280 to 320° C. for 30 to 60 minutes;
Compressing a paste containing the heat-treated fluorine-based resin powder to form a preform;
Extruding the preform to form a sheet; And
Stretching the sheet
Method for producing a fluorine-based resin porous membrane comprising a.
The method of claim 1,
The fluorine-based resin is polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer Containing one or more fluorine-based compounds selected from the group consisting of coalescence (ETFE), tetrafluoroethylene-chlorotrifluoroethylene copolymer (TFE/CTFE), and ethylene-chlorotrifluoroethylene copolymer (ECTFE), Method for producing a fluorine-based resin porous membrane.
The method of claim 1,
The extrusion is performed under a temperature of 30 to 100 °C, a method for producing a fluorine-based resin porous membrane.
The method of claim 1,
The stretching is carried out by biaxial stretching of 2 to 10 times of longitudinal stretching and 2 to 50 times of transverse stretching of the sheet under a temperature of 100 to 400° C., a method for producing a fluorine-based resin porous membrane.
The method of claim 1,
The fluorine-based resin porous membrane has a thickness of 5 to 200 ㎛, the method of manufacturing a fluorine-based resin porous membrane.
The method of claim 1,
A method for producing a fluorine-based resin porous membrane having a pore distribution that satisfies the following formula 1:
[Equation 1]
(P _M /P _m ) <1.3
In Equation 1 above,
P _M is the maximum pore size (nm) of the fluorine-based resin porous membrane measured using a capillary flow porometer (fluid: Galwick),
P _m is the mean pore size (nm) of the fluorinated resin porous membrane measured using a capillary flow porometer (fluid: Galwick).

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