KR102430316B1 - Fluororesin tube with high thermal conductivity and low gas permeability - Google Patents

Abstract

The present invention relates to a fluororesin tube used in a heat exchanger requiring corrosion resistance and contamination resistance, and more specifically, to a fluororesin tube having low gas permeability and high thermal conductivity by adding a filler to the fluororesin. it's about

Description

High thermal conductivity and low gas permeability fluororesin tube {Fluororesin tube with high thermal conductivity and low gas permeability}

The present invention relates to a fluororesin tube used in a heat exchanger requiring corrosion resistance and stain resistance, and more specifically, to prevent scale generation and sludge adhesion, corrosion resistance, fouling resistance, ultrapure water resistance, crack resistance It relates to a fluororesin tube with high thermal conductivity and low gas permeability that is further improved on this excellent conventional fluororesin tube.

Heat exchangers are used throughout the industry, and are designed to transfer heat energy between fluids. There are several types of heat exchangers depending on the shape and material. Among them, the fluororesin heat exchanger is difficult to generate scale or adheres to sludge, unlike graphite or metal heat exchangers. It has been used in processes that require ultra-precision and ultra-purity, such as in the semiconductor industry and fine chemical industry.

The fluid used in the semiconductor industry and fine chemical industry contains highly corrosive chemical components, so the tube of the heat exchanger is easily corroded and oxidized, and frequent replacement is inevitable. Such frequent replacement work lowered the operation rate of the equipment and required a lot of maintenance cost.

As a means to solve such problems, fluororesin, a plastic material with excellent chemical resistance, is used as a heat transfer tube of a heat exchanger used to heat or cool a highly corrosive process fluid in conventional semiconductor industrial piping, plating tanks, and various reaction tanks. there was.

However, the fluororesin tube is a pure fluororesin that does not contain a filler, and has a disadvantage in that it has low thermal conductivity like general plastics, and high gas permeability due to the limitation of the material that it has fine pores.

If the gas permeation rate is high, the corrosive component of the process fluid in the fluororesin tube heat exchanger penetrates the tube wall and diffuses into the cooling water to cause corrosion of the cooling pipe, or conversely, trace metal ions in the cooling water component, that is, calcium and magnesium , potassium ions, etc. permeate the tube wall and contaminate the chemical solution.

In addition, even if a thin tube with a small tube diameter is used, the tube wall thickness is thinned to achieve high heat transfer efficiency due to the low thermal conductivity due to the nature of the plastic. Although there have been methods of constructing complex shapes such as a shape in which a sealing structure of a shape is formed, there is a limit in reducing the volume of the heat exchanger even with this method.

In order to improve low thermal conductivity, a technique of partially coating a metal tube with a fluororesin and a technique of including a filler in the tube have been tried. Specifically, in European Patent No. EP0900991, PTFE (Poly Tetra Fluoro Ethylene), a type of fluororesin, was coated on the outer surface of the tube to prevent corrosion and oxidation. If the surface is damaged due to the carelessness of the In addition, the fluororesin tube including the spherical filler (Chinese Patent No. CN106554589A) has a disadvantage in that the thermal conductivity is somewhat improved, but the burst pressure, tensile strength, and elongation strength are rather decreased, and the gas permeation rate is hardly improved.

European Patent Publication No. EP0900991 Chinese Laid-Open Patent Publication No. CN106554589A

The present invention was devised to solve the problems of low thermal conductivity and high gas permeability of conventional fluororesin, and by manufacturing a fluororesin tube with flat and fibrous fillers added to fluororesin, gas permeation of the tube for a heat exchanger is minimized The purpose is to improve the thermal conductivity while doing so.

In order to solve the above problems, the present invention is a fluororesin 60 to 95% by weight, 0.5 to 30% by weight of a thermally conductive flat filler having a maximum particle size of 3 μm or less, and 0.5 to 10% by weight of a filler in the form of a nano-sized thermally conductive fiber It provides a high thermal conductivity and low gas permeability fluororesin tube, characterized in that it comprises.

The flat-shaped filler bypasses the gas diffusion path to reduce the gas permeation rate to reduce the gas permeation amount, and is composed of relatively high thermal conductivity carbon or inorganic material to increase the thermal conductivity. The flat-shaped filler may be at least one selected from the group consisting of graphite, boron nitride, graphene, and molybdenum disulfide, and the content ratio of the flat-shaped filler is 0.5 to 30% by weight, preferably 1.0 to 20 % by weight, more preferably from 1.5 to 15% by weight. If the content of the flat-shaped filler is 0.5 wt% or less, the effect of improving the thermal conductivity is small, and if it is 30 wt% or more, there are disadvantages in that mixing difficulty and gas permeability are rather increased during manufacturing.

The fibrous fillers serve to connect the flat-shaped fillers to each other to increase heat transfer in the tube wall. Since fibrous particles have a weaker bypass function for permeation than flat-shaped particles, in order not to increase the amount of gas permeation, nanoparticles having a narrow diameter and short length of less than 1 μm are preferable. The fibrous filler may be at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, and graphite nanofibers (GNF), and the content ratio of the fibrous filler is 0.5 to 10% by weight, preferably 1.0 to 7% by weight, more preferably 1.5 to 4% by weight. The fibrous filler has a disadvantage in that the effect of thermal conductivity is small at 0.5 wt% or less, and air permeability increases by forming pores at 10 wt% or more.

In one embodiment of the present invention, the fluororesin may be at least one selected from the group consisting of modified PTFE, PFA, FEP, PTFE, and PVDF, and the fluororesin PTFE is a general PTFE composed only of tetrafluoroethylene monomers. (hereinafter referred to as PTFE) may include a modified PTFE copolymerized with a monomer for modification.

In the present invention, modified PTFE refers to a copolymer obtained by copolymerizing a small amount of the following modified monomers during polymerization of tetrafluoroethylene, but is not limited thereto.

In one embodiment of the present invention, the fluororesin may be modified PTFE for paste extrusion or PTFE for paste extrusion, and may be one or more heat melt processable fluororesins selected from the group consisting of PFA, FEP, and PVDF.

In one embodiment of the present invention, as a monomer for modification of the modified PTFE, X(CF ₂ )nOCF=CF ₂ (X may be hydrogen, fluorine, or chlorine, and n represents an integer of 1 to 6). ) or C ₃ F ₇ (OCF ₂ CF ₂ CF ₂ )m(OCF(CF ₃ )CF ₂ )lOCF=CF ₂ (m and l represent integers from 0 to 4. However, the sum of m+l is 1 or more.) fluoro vinyl ether, CF ₃ -CF=CF ₂ , CF ₂ =CFH, CF ₂ =CFCl, CF ₂ =CH ₂ , RfCY=CH ₂ (Rf is straight-chain or molecular carbon number 3 ~21 is a polyfluoroalkyl group, and Y is a hydrogen atom or a fluorine atom.) and the like) may be a fluorine-containing unsaturated monomer other than tetrafluoroethylene, but is not limited thereto.

In one embodiment of the present invention, the monomer for modification may be added in an amount of 0.01 to 1.0 wt% based on tetrafluoroethylene. When the amount of the monomer for modification is 0.01 wt% or less, when the fluororesin tube is fused to the tube sheet, the effect of improving the adhesion does not appear, and when it is 1.0 wt% or more, there is a disadvantage in that the heat resistance of the tube is reduced.

In one embodiment of the present invention, the structure of the tube may be a single-layer structure or a multi-layer structure, and the multi-layer structure includes a pure fluororesin layer and a filler-containing fluororesin layer. If the process fluid requires cleanliness, a multi-layer tube may be used, and the layer in contact with the process fluid may be a pure fluororesin layer, and the layer in contact with the heating medium may be a fluororesin layer containing a filler.

More specifically, an example of a fluororesin tube containing a filler is shown in FIG. 2 . As shown in FIG. 2, the wall of the fluororesin tube may be a single layer (104, 105) or multiple layers (106, 107, 108) depending on the modified PTFE composition, and the single layer structure is a pure modified PTFE layer 110 or Including a filler-containing modified PTFE layer (111), the multilayer structure includes a pure modified PTFE layer (112) and a filler-containing modified PTFE layer (113), and is a heat exchanger when the process fluid fluid allows contamination by the filler. A tube 105 with a single layer of modified PTFE containing filler may be used, and if the process fluid does not tolerate contamination by the filler, place a layer of pure modified PTFE on the side in contact with the process fluid 111 so that the filler A multi-layer tube (106, 107, 108) that prevents leakage into the fluid may be used.

In one embodiment of the present invention, the thickness of the tube is 50 ~ 400㎛ thickness of the pure fluororesin layer in the multilayer tube, preferably 100 ~ 300㎛, more preferably 150 ~ 250㎛. If the thickness of the pure fluororesin layer is less than 50㎛, the fluororesin layer containing filler may be exposed due to abrasion by the process fluid, etc., and when the thickness of the pure fluororesin layer is 400㎛ or more, the thermal conductivity of the tube wall decreases Therefore, the effectiveness of the thermally conductive tube is reduced.

In one embodiment of the present invention, a heat exchanger using a fluororesin tube with high thermal conductivity and low gas permeability according to the present invention is provided, and will be described in detail with reference to the drawings for the heat exchanger (FIG. 1) as follows.

As shown in FIG. 1, the fluororesin tube heat exchanger 2 of the present invention is a heat exchanger having a plurality of tubes 10 for exchanging heat between two fluids moving in and out of a plurality of fluororesin tube walls as a boundary. In this case, a tube sheet (3) having a tube support hole is connected to a plurality of tubes and installed on both sides of the heat exchanger, respectively, and a plurality of tube end portions (5) are provided in the tube sheets (3, 4) on both sides of the tube sheet (4) It is a device that is fused with

According to the present invention, heat exchange is performed between the process fluid (12) flowing inside the plurality of fluororesin tubes and the heat transfer medium (13) flowing outside the plurality of fluororesin tubes. Depending on the type of fluid, a process fluid may flow from the outside of the plurality of fluororesin tubes, and a heat transfer medium may flow therein. Fluids (process fluids) circulating inside the fluororesin tube include, for example, fluids such as gas or liquid chemical liquids, and fluids circulating outside the fluororesin tube include heat transfer media such as refrigerants and heat mediums. .

As described above, the heat exchanger using a fluororesin tube according to the present invention uses a tube extruded of a fluororesin containing nano-flat particles and nanofiber particles to the fluororesin, thereby reducing the gas permeability of the tube and improving the thermal conductivity. can do it

In the present invention, since the fluororesin tube using the flat filler and graphite nanofibers has a low gas permeation amount, the amount of corrosive components or metal ions of the process fluid in the tube of the heat exchanger is reduced, so that the cooling pipe is reduced. It is possible to prevent the problem of corrosion or contamination of the chemical solution.

The heat exchanger using the fluororesin tube according to the present invention improves the overall heat transfer coefficient by two times compared to the conventional one due to the improvement of the thermal conductivity of the tube, and it can be miniaturized by reducing the volume of the heat exchanger.

1 is a schematic diagram of a heat exchanger made of a fluororesin tube of the present invention.
2 is a cross-sectional view of the fluororesin tube of the present invention.
3 is a schematic diagram of a method for measuring a gas permeation amount of a tube according to the present invention.
4 is a graph showing the overall heat transfer coefficient of the heat exchanger with respect to the temperature of the process fluid of the present invention.

The terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical idea of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Example 1]

The composition of the modified PTFE tube containing filler is modified PTFE (TFM2001, 3M) powder, 5.0 wt% of graphite powder (Graphite) having an average particle diameter of 2㎛, and 2.0 wt% of GNF (Graphite nano fiber), the above three By mixing the powder, ethyl alcohol is used as a binder to form a powder with a particle diameter of 0.3 to 2 mm, and drying it at 120° C. to prepare a modified PTFE powder containing a filler. The molding method of the modified PTFE tube is PTFE paste extrusion (paste extrusion) which is a well-known method. A single-layer preform in the form of a pipe was compressed by filling the preformer cylinder with the filler-containing modified PTFE powder in which 20 wt% of the weight of the modified PTFE was mixed with the filler-containing modified PTFE powder in a single layer. After molding and extruding the tube in an extruder, the solvent is heat-dried, sintered at 350-400°C, and air-cooled to obtain a single-layer modified PTFE tube. The outer diameter of the modified PTFE tube is 6.4mm, and the inner diameter is 4.8mm.

[Examples 2 to 5]

A tube was prepared according to the composition of Table 1 below in the same process as in Example 1. However, in the method of manufacturing the PFA tube, which is a melt-extrudable fluororesin, the PFA resin and the filler are mixed by a known method to produce a filler-containing fluororesin pellet, and then the tube is extruded at about 365° C. in a conventional extruder, and the modified filler The outer diameter of the containing modified PFA tube is 6.4 mm and the inner diameter is 4.8 mm.

Physical properties according to the composition of the fluororesin tube (Unit: wt%) Suzy filling thermal conductivity
(W/m °K) air permeability
(ml/m hr) denaturalization
PTFE PFA Graphene flat
Graphite GNF Comparative Example 1 100 0.22 1.15 Comparative Example 2 100 0.21 0.74 Example 1 92 5 3 0.61 0.27 Example 2 88 10 2 0.68 0.25 Example 3 88 10 2 0.70 0.20 Example 4 92 8 0.54 0.25 Example 5 90 10 0.60 0.28

[Example 6]

The same process as in Example 1 was used, and the powder of Example 2 was used as the filler-containing modified PTFE powder. The steps after the preparation of the filler-containing modified PTFE powder are as follows. Modified PTFE powder containing filler mixed with 20% by weight of the weight of modified PTFE with a solvent (Isopar G, Exxonmobil) mixed with the above-mentioned modified PTFE powder containing filler, and modified PTFE powder containing 18% by weight of solvent (Isopar G, Exxonmobil) mixed with pure modified PTFE powder PTFE powder is obtained, and the two solvent mixture powders are filled in the cylinder of the preformer in two layers, the inner and outer layers, respectively, to form a compressed multi-layer preform in the shape of a pipe, extruding the tube in the extruder, and heating the solvent Dry, sinter, and air-cool to obtain a multi-layer modified PTFE tube. The outer diameter of the modified PTFE tube is 6.4mm, the inner diameter is 4.8mm, and the pure PTFE layer thickness of the inner diameter is 0.2mm.

[Comparative Examples 1 and 2]

Comparative Example 1 was prepared by the same process as in Example 1, and Comparative Example 2 was prepared in the same manner as in Example 3, except that the tube material was changed to a single-layer tube made of pure modified PTFE or pure PFA layer, The outer diameter and inner diameter of the tube are the same as the tube dimensions of Example 1.

[Experimental Example 1: Measurement of gas permeation amount of fluororesin tube]

3 is a gas permeation meter 190 for measuring the air permeability of a test tube, and is approximately composed of a water tank 191 and an assembly stand 193 . The assembly stand is a device that allows the air transmitted from the test tube 195 to be collected in the collection test tube 196, and the test tube 195, the funnel 197, and the collection test tube 196 are connected with three clamps 198. each was fixed. The filled test tube 195 was kept in equilibrium in the water bath for at least 72 hours while continuously supplied with compressed air at a constant pressure (9 kg/cm ² ), and then the gas permeation amount was measured, and the results are shown in Table 1 above. indicated.

[Experimental Example 2: Measurement of thermal conductivity]

A small, thin cylindrical specimen is irradiated with high-intensity heat incident energy radiated for a short period of time. Energy in the form of a pulse is incident on the front surface of the specimen, and as a result, the temperature of the rear surface of the specimen rises due to thermal diffusion, and a thermal rise curve (thermogram) with time is recorded. The thermal diffusivity value is calculated by the value of the time to reach a certain ratio of the thickness of the specimen and the maximum rising temperature on the back side of the specimen, and the ASTM E1461 laser flash method to obtain the thermal conductivity value from the thermal diffusivity value was used. The thermal conductivity specimen was measured to have a diameter of 25.4 mm and a thickness of 0.5 mm, and the results are shown in Table 1 above.

As can be seen from Table 1 above,

In fluororesins containing flat fillers (Graphene, graphite with an average particle diameter of 2.0㎛) and fibrous fillers (GNF), thermal conductivity is increased by 2.5 times or more compared to pure fluororesins (modified PTFE or PFA), and gas permeability is It can be seen that there is a decrease of more than 75%.

Depending on the type of filler, when the total filler content is the same, when the flat shape and the fiber shape are mixed rather than when the flat shape is used alone, the gas permeability is slightly increased, but the thermal conductivity is greatly increased. In the case where the flat-shaped filler content is the same, it can be seen that the thermal conductivity is improved and the gas permeation amount is also reduced when using the mixed fiber shape rather than using the flat shape alone.

[Experimental Example 3: Measurement of overall heat transfer coefficient]

Examples 2, 6 and Comparative Example 1 set the external dimensions of each heat exchanger, the size of the tube, and other conditions to be the same for the purpose of comparing the performance of heat exchangers using different tubes, and the unit area of the tube surface, 4 and Table 2 show the results of heat transfer per unit time and unit temperature as the overall heat transfer coefficient under the same conditions.

4 is a comparison of the overall heat transfer coefficients of Examples 2 and 6 and Comparative Example 1 (conventionally commercially available products) with the horizontal axis as the process fluid temperature. As shown in the measurement result of FIG. 4, the filler-containing modified PTFE tube heat exchangers of Examples 1 and 2 obtained more than twice the overall heat transfer coefficient compared to the conventional pure modified PTFE tube heat exchanger, so the required heat transfer area is also reduced by 1/2 to reduce heat exchange It may contribute to the miniaturization of the machine.

Physical properties according to tube wall structure Example 6 Example 2 Comparative Example 1 tube material Pure Modified PTFE +
Modified PTFE with filler (composition of Example 2) Modified PTFE with filler Pure Modified PTFE gas permeation
(ml/m hr) 0.33 0.25 1.15 total heat transfer coefficient
(kcal/hr·℃·m ² ) 320~410 390-480 180-240

As shown in Table 2,

In comparison with the single-layer and multi-layered fluororesin tube, it can be seen that the gas permeability of the single-layer structure (Example 2) is lower than that of the multi-layer structure (Example 6), and the overall heat transfer coefficient is higher. This indicates that the gas permeation amount of the fluororesin tube containing the filler is reduced and the thermal conductivity is excellent. However, the tube of the multi-layer structure (Example 6) is a configuration that can be adopted depending on the contamination sensitivity of the process fluid, and both Examples 2 and 6 have a significant reduction in gas permeability and It shows the effect of increasing the overall heat transfer coefficient.

In the above, a preferred embodiment of a method for manufacturing a fluororesin tube including a filler according to the present invention has been described, but the present invention is not limited thereto, and within the scope of the claims and the detailed description of the invention and the accompanying drawings. It will be apparent to those skilled in the art that various modifications are possible, and this also falls within the scope of the present invention.

2: heat exchanger 3, 4: tube sheet 5: tube end
10: tube 11: shell 12: process fluid
13: heat transfer medium 14: process fluid inlet 15: process fluid outlet
16: heat transfer medium inlet 17: heat transfer medium outlet 18: partition
19: end plate 20: connector
104: pure modified PTFE single-layer tube
105: filler-containing modified PTFE single-layer tube 106: double-layer tube whose inner diameter layer is pure modified PTFE
107: double-layer tube in which the outer diameter layer is pure modified PTFE 108: double-layer tube in which the inner and outer diameter layers are pure modified PTFE
110, 112: pure modified PTFE layer of tube 111, 113: modified PTFE layer containing filler material of tube
190: gas permeation meter 191: water tank
193: assembly stand 195: sample tube 196: collection test tube
197 funnel 198 clamp

Claims (12)

High thermal conductivity and low thermal conductivity, characterized in that it contains 60 to 95% by weight of a fluororesin, 1.5 to 15% by weight of a thermally conductive flat filler having a maximum particle diameter of 3 μm or less, and 1.5 to 4% by weight of a filler in the form of a nano-sized thermally conductive fiber A gas-permeable fluororesin tube comprising:
The fluororesin is modified PTFE,
Modification monomer included in the modified PTFE is X(CF ₂ )nOCF=CF ₂ (X may be hydrogen, fluorine, or chlorine, n represents an integer of 1 to 6) or C ₃ F ₇ (OCF Fluoro represented by ₂ CF ₂ CF ₂ )m(OCF(CF ₃ )CF ₂ )1OCF=CF ₂ (m and l represent integers from 0 to 4, provided that the sum of m+l is 1 or more) raw vinyl ether, CF ₂ =CFH, CF ₂ =CFCl and RfCY=CH ₂ (Rf is a linear or molecular polyfluoroalkyl group having 3 to 21 carbon atoms, Y is H or F) Any one or more fluorine-containing unsaturated monomers,
The monomer for modification is high thermal conductivity and low gas permeability fluororesin tube, characterized in that it is added in an amount of 0.01 to 1.0% by weight based on tetrafluoroethylene. The high thermal conductivity and low gas permeability fluororesin tube according to claim 1, wherein the flat filler is at least one selected from the group consisting of graphite, boron nitride, graphene, and molybdenum disulfide. The high thermal conductivity and low gas permeability fluororesin tube according to claim 1, wherein the fibrous filler is at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, and graphite nanofibers. delete The high thermal conductivity and low gas permeability fluororesin tube according to claim 1, wherein the fluororesin is modified PTFE for paste extrusion or PTFE for paste extrusion. The high thermal conductivity and low gas permeability fluororesin tube according to claim 1, wherein the fluororesin is at least one heat-melt processable fluororesin selected from the group consisting of PFA, FEP, and PVDF. delete delete The high thermal conductivity and low gas permeability fluororesin tube according to claim 1, wherein the wall of the fluororesin tube has at least one single layer structure or a multilayer structure selected from pure fluororesin or fluororesin containing fillers. The high thermal conductivity and low gas permeability fluororesin tube according to claim 9, wherein in the multilayer structure, the outer or inner layer of the tube to which the process fluid can be contacted is a pure fluororesin layer. The high thermal conductivity and low gas permeability fluororesin tube according to claim 10, wherein the pure fluororesin layer has a thickness of 50 to 400 μm. A heat exchanger comprising the high thermal conductivity and low gas permeability fluororesin tube of any one of claims 1 to 3, 5, 6, and 9 to 11.

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