CN114829142A

CN114829142A - Coated substrate, heat exchanger, method for producing coated substrate, and liquid composition

Info

Publication number: CN114829142A
Application number: CN202080087335.5A
Authority: CN
Inventors: 寺田达也; 细田朋也
Original assignee: Asahi Glass Co Ltd
Current assignee: AGC Inc
Priority date: 2019-12-18
Filing date: 2020-12-10
Publication date: 2022-07-29
Also published as: JPWO2021125049A1; TW202142406A; WO2021125049A1

Abstract

The invention provides a coated substrate having a layer with excellent thermal conductivity and corrosion resistance and less unevenness of the properties, a method for manufacturing the coated substrate, a heat exchanger having the coated substrate, and a liquid composition suitable for forming the coated substrate. The coated substrate of the present invention comprises a substrate and a heat conductive layer coated on the surface of the substrate, wherein the heat conductive layer contains a material having a melt viscosity of 1X 10 at 380 DEG C ⁶ The ratio of the length of the long axis of the heat conductive filler to the thickness of the heat conductive layer is 0.1 or more. The liquid composition of the present invention comprises a tetrafluoroethylene polymer powder having a cumulative 50% by volume diameter of 0.1 to 6 μm, the thermally conductive filler, and a liquid medium, wherein the content of the thermally conductive filler is 10% by mass or more, and the ratio of the cumulative 10% by volume diameter of the powder to the cumulative 50% by volume diameter of the powder is 0.5 or less.

Description

Coated substrate, heat exchanger, method for producing coated substrate, and liquid composition

Technical Field

The present invention relates to a coated substrate having a predetermined heat conductive layer, a method for producing the same, a heat exchanger provided with the coated substrate, and a liquid composition suitable for producing the coated substrate.

Background

A boiler that generates steam from boiler water using combustion gas employs a heat exchanger including heat transfer tubes.

The combustion gas contains water vapor, sulfur oxides, and the like. Therefore, when the temperature is not higher than the temperature at which sulfuric acid is produced from the combustion gas (sulfuric acid dew point temperature) by heat exchange in the heat exchanger, sulfuric acid is produced in the heat exchanger, and the heat transfer pipe and the like are easily corroded.

As a heat transfer pipe of a heat exchanger in which corrosion by sulfuric acid is suppressed, a heat transfer pipe having a heat conductive layer (corrosion resistant coating layer) formed by electrostatically coating a mixture of dry powders of each of tetrafluoroethylene polymer, carbon fiber, lead-free solder alloy, graphite, and silicon carbide on the outer surface of a pipe main body and subjecting the mixture to a firing treatment has been proposed (see patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-164247

Disclosure of Invention

Technical problem to be solved by the invention

However, in the case of electrostatic coating of the mixture, it is necessary to set the average particle diameter of each dry powder (particularly, the average particle diameter of the dry powder of the tetrafluoroethylene polymer) to several tens of μm. Therefore, the formed heat conductive layer is likely to have unevenness in each component, and the unevenness in heat conductivity is likely to occur.

An object of the present invention is to provide a coated substrate having a layer excellent in thermal conductivity and corrosion resistance with little variation in these properties, a method for producing the coated substrate, a heat exchanger provided with the coated substrate, and a liquid composition that can be suitably used for forming the coated substrate.

Means for solving the problems

The present invention has the following aspects.

<1>A coated substrate comprising a substrate and a heat conductive layer coating the surface of the substrate, wherein the heat conductive layer has a melt viscosity of 1X 10 at 380 ℃ ⁶ A tetrafluoroethylene polymer having Pa · s or less and a thermally conductive filler having an aspect ratio exceeding 1, wherein the ratio of the length of the major axis of the thermally conductive filler to the thickness of the thermally conductive layer is 0.1 or more.

<2> <1> wherein the heat conductive layer has a thermal conductivity of 1.0W/m.K or more.

<3> <1> or <2>, wherein the coefficient of linear expansion of the heat conductive layer is 100 ppm/DEG C or less.

The coated substrate of any one of <4> <1> to <3>, wherein the length of the long axis of the heat conductive filler is more than 0.1 μm and 500 μm or less, and the thickness of the heat conductive layer is 0.1 to 450 μm.

[ claim 5 ] the coated substrate according to any one of the <5> to <1> to <4>, wherein the tetrafluoroethylene polymer is a polymer containing a unit based on tetrafluoroethylene and a unit based on perfluoro (alkyl vinyl ether), or polytetrafluoroethylene having a number average molecular weight of 20 ten thousand or less.

[ claim 1 ] A coated substrate according to any one of <6> to <5>, wherein the thermally conductive filler is fibrous in shape.

The coated substrate according to any one of <7> <1> to <6>, wherein the thermally conductive filler is a carbon-containing filler.

[ claim 8 ] A coated substrate according to any one of <8> to <7>, wherein the content of the thermally conductive filler in the thermally conductive layer is 10 mass% or more, and the sum of the content of the tetrafluoroethylene polymer and the content of the thermally conductive filler is 90 mass% or more.

The coated substrate according to any one of <9> <1> to <8>, wherein the material of the substrate is metal, glass or ceramic.

<10> A heat exchanger comprising the coated substrate according to any one of <1> to <9 >.

<11> the method for producing a coated substrate according to any one of <1> to <9>, which comprises preparing a liquid composition containing a powder of the tetrafluoroethylene polymer, the thermally conductive filler and a liquid medium, applying the liquid composition to the surface of the substrate to form a liquid coating film, and heating the liquid coating film to form the thermally conductive layer, thereby obtaining the coated substrate.

<12>A liquid composition comprises a total 50% by volume of a resin having a diameter of 0.1 to 6 μm and a melt viscosity of 1 x 10 at 380 ℃ ⁶ A tetrafluoroethylene polymer powder having Pa · s or less, a thermally conductive filler having an aspect ratio of more than 1, and a liquid medium, wherein the content of the thermally conductive filler is 10% by mass or more, and the ratio of the volume-based cumulative 10% diameter of the powder to the volume-based cumulative 50% diameter of the powder is 0.5 or less.

<13> <12> wherein the powder is a powder having a viscosity of 50 to 400 mPas in a dispersion prepared by dispersing 100g of the powder in 100g of water.

<14> <12> or <13>, wherein the thermally conductive filler is a coating agent having no coated surface or a thermally conductive filler having no functional group on the surface.

<15> <12> to <14>, wherein the viscosity at 25 ℃ is 50 to 10000 mPas.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention provides a coated substrate and a heat exchanger having a layer excellent in thermal conductivity and corrosion resistance with little variation in these properties, and a liquid composition suitable for formation of the coated substrate and excellent in dispersion stability and workability.

Drawings

Fig. 1 is a sectional view showing an example of a heat transfer pipe composed of the coated base material of the present invention.

Detailed Description

The following terms have the following meanings.

The "volume-based cumulative 50% diameter (D50) of the powder" is a value obtained by a laser diffraction/scattering method. That is, the particle size distribution of the powder was measured by a laser diffraction scattering method, and a cumulative curve was obtained with the total volume of the powder particle group as 100%, and the particle size of a point on the cumulative curve where the cumulative volume reached 50%.

"volume-based cumulative 10% diameter of powder (D10)" is the volume-based cumulative 10% diameter of powder measured in the same manner.

"melt viscosity of polymer" is a value measured by holding a polymer sample (2g) heated to a measurement temperature in advance for 5 minutes at the measurement temperature under a load of 0.7MPa according to ASTM D1238 with a flow tester and a 2. phi. -8L mold.

The "melting temperature of the polymer" is a temperature corresponding to the maximum value of the melting peak of the polymer measured by a Differential Scanning Calorimetry (DSC) method.

"glass transition temperature of polymer" is a value measured by analyzing a polymer by a dynamic viscoelasticity measurement (DMA) method.

The "thermal conductivity of the thermally conductive layer" is a value measured in accordance with ASTM D5470.

The "coefficient of linear expansion of the heat conductive layer" is a displacement amount caused by linear expansion of the heat conductive layer measured by a thermomechanical analyzer (product of SII corporation, "TMA/SS 6100").

The "viscosity of the object" is a value obtained by measuring the object (liquid composition or dispersion) with a B-type viscometer at a temperature of 25 ℃ and a rotation speed of 6 rpm.

The "aspect ratio of the thermally conductive filler" is an average value of values calculated from the length value and the short diameter value of the thermally conductive filler (the value obtained by dividing the length value by the short diameter) obtained by observing 50 or more thermally conductive fillers randomly extracted with an electron microscope.

The "long axis length of the thermally conductive filler" is a value obtained by the following method through image analysis of the thermally conductive filler with a microscope.

A30 mL Erlenmeyer flask was filled with 5mL of mobile paraffin of the primary reagent by a dropper. Samples of the thermally conductive filler were taken with a micro spatula and dispersed in flowing paraffin. A300. mu.L dispersion was measured from the flask with a micropipette, dropped on the 1 st glass slide, and covered with the 2 nd glass slide for pressure bonding. An image of a sample sandwiched between slides is taken with a CCD MICROSCOPE (for example, "SCOPEMAN DIGITAL CCD MICROSCOPE MS-804" manufactured by MORTEX CORPORATION), the long axis length is measured for 1000 to 1300 conductive fillers with image analysis software (for example, "WiROOF 2015" manufactured by Sanko Co., Ltd.), an accumulation curve is obtained with the total number of filler clusters as 100%, and the value of a point at which the accumulated fraction on the accumulation curve reaches 90% is taken as the long axis length.

The coated substrate of the present invention (hereinafter also referred to as "the present substrate") comprises a substrate and a heat conductive layer coated on the surface of the substrate, wherein the heat conductive layer contains a melt viscosity of 1X 10 at 380 ℃ ⁶ A tetrafluoroethylene polymer having Pa.s or less (hereinafter also referred to as "TFE polymer") and a thermally conductive filler having an aspect ratio of more than 1. The thermally conductive filler having an aspect ratio exceeding 1 is hereinafter also referred to as "thermally conductive filler a".

In the present invention, the ratio of the length of the major axis of the thermally conductive filler a to the thickness of the thermally conductive layer is 0.1 or more.

The TFE-based polymer is a polymer containing a Tetrafluoroethylene (TFE) unit (TFE unit).

The reason why the present substrate is excellent in thermal conductivity and corrosion resistance and the variation in these properties is small is not necessarily clear, but is considered to be the following.

The thermally conductive filler a of the present invention is, in other words, an anisotropic filler having a major axis length (length in the longitudinal direction) and a minor axis length (length in the short direction) that are different from each other. The present inventors have studied to orient the long axis direction of the thermally conductive filler a in the thermally conductive layer in a direction perpendicular to the surface of the thermally conductive layer facing the base material (hereinafter also referred to as "facing surface").

As a result, they have found that the orientation is easily exhibited by using a TFE-based polymer having a melt viscosity within a predetermined range, and that a highly adhesive layer is formed by the TFE-based polymer and the thermally conductive filler a. Then, it was found that if the length of the major axis of the thermally conductive filler a is equal to or greater than a certain value with respect to the layer thickness of the thermally conductive layer, an aggregate of fillers having high continuity is generated, and the thermally conductive portion is easily formed.

That is, the heat conductive layer of the present substrate is a dense layer having high adhesion between the TFE-based polymer and the heat conductive filler a, and the heat conductive filler a is a layer oriented in a direction perpendicular to the facing surface with high continuity. Therefore, the present substrate is excellent in thermal conductivity and corrosion resistance and has little variation in these properties.

In the base material, at least a part of the thermally conductive filler a can be in contact with the facing surface or exposed on a surface (hereinafter, also referred to as an "exposed surface") of the thermally conductive layer opposite to the facing surface. Therefore, the present substrate is considered to be excellent in thermal conductivity and corrosion resistance and to have less variation in these properties.

The TFE polymer of the present invention preferably has a melt viscosity at 380 ℃ of 1X 10 ⁶ Pa · s or less, more preferably 5X 10 ⁵ Pa · s or less, more preferably 1X 10 ⁵ Pa · s or less. The melt viscosity is preferably 1X 10 ² Pa · s or more, more preferably 1X 10 ³ Pa · s or more. In this case, the TFE-based polymer is likely to be dense, and a heat conductive layer having high homogeneity and smoothness is likely to be formed. As a result, a heat conductive layer with less variation in heat conductivity can be formed.

The TFE polymer preferably has a melting temperature of 280 to 325 ℃ and more preferably 285 to 320 ℃.

The glass transition temperature of the TFE polymer is preferably 75 to 125 ℃, more preferably 80 to 100 ℃.

The TFE-based polymer is preferably a Polymer (PFA) containing TFE units and units based on perfluoro (alkyl vinyl ether) (PAVE units), and polytetrafluoroethylene PTFE (hereinafter also referred to as "low molecular weight PTFE") having a number average molecular weight of 20 ten thousand or less.

PFA can also contain other units.

As PAVE, CF is preferred ₂ ＝CFOCF ₃ ，CF ₂ ＝CFOCF ₂ CF ₃ And CF ₂ ＝CFOCF ₂ CF ₂ CF ₃ (PPVE), more preferably PPVE.

PFA can also have polar functional groups. The polar functional groups may be included in units within the PFA or may be included in the end groups of the polymer backbone. The latter form may, for example, be: PFA having a polar functional group as an end group derived from a polymerization initiator, a chain transfer agent, or the like has a polar functional group obtained by subjecting PFA to plasma treatment, ionization treatment, or radiation treatment.

As the polar functional group, a hydroxyl-containing group and a carbonyl-containing group are preferable, and a carbonyl-containing group is more preferable.

The hydroxyl-containing group is preferably an alcoholic hydroxyl-containing group, more preferably-CF ₂ CH ₂ OH and-C (CF) ₃ ) ₂ OH。

The carbonyl-containing group is preferably a carbonyl group (> C (O)) containing group, and the carbonyl-containing group is preferably a carboxyl group, an alkoxycarbonyl group, an amide group, an isocyanate group, a carbamate group (-OC (O) NH), or the like ₂ ) Anhydride (-) (-CO (O) OC (O) -), imide (-) (-C (O) NHC (O) -, etc.), and carbonate (-OC (O) O-).

The number of carbonyl-containing groups in the TFE polymer is 1X 10 carbon atoms per main chain ⁶ Preferably 10 to 5000, more preferably 100 to 3000, and further preferably 800 to 1500. In this case, the TFE polymer is likely to be dense, and a heat conductive layer having high homogeneity and smoothness is likely to be formed.

The PFA is preferably a PFA having a TFE unit and a PAVE unit and having a melting temperature of 280 to 320 ℃ in an amount of 1.5 to 5 mol% based on the total units, more preferably a PFA (1) having a polar functional group and comprising a TFE unit, a PAVE unit and a unit based on a monomer having a polar functional group, and a PFA (2) having no polar functional group and comprising a TFE unit and a PAVE unit and comprising 2.0 to 5.0 mol% based on the total units.

These PFAs tend to form fine spherulites in the heat conductive layer, and adhesion between the TFE-based polymer and the heat conductive filler a and the base material tends to be improved.

The PFA (1) preferably contains, based on the monomer having a polar functional group, 90 to 99 mol% of a TFE unit, 1.5 to 9.97 mol% of a PAVE unit, and 0.01 to 3 mol% of a unit based on the monomer, relative to the total units.

Further, as the monomer having a polar functional group, itaconic anhydride, citraconic anhydride and 5-norbornene-2, 3-dicarboxylic anhydride (alias: nadic anhydride; hereinafter also referred to as "NAH") are preferable, and NAH is more preferable.

Specific examples of PFA (1) include the polymers described in International publication No. 2018/16644.

The PFA (2) preferably consists of only TFE units and PAVE units, and contains 95.0 to 98.0 mol% of TFE units and 2.0 to 5.0 mol% of PAVE units relative to the total units.

The content of PAVE units in PFA (2) is preferably 2.1 mol% or more, more preferably 2.2 mol% or more, based on the total units.

The fact that PFA (2) has no polar functional group means that the number of carbon atoms constituting the main chain of the polymer is 1X 10 ⁶ And the number of the polar functional groups of the polymer is less than 500. The number of the polar functional groups is preferably 100 or less, and more preferably less than 50. The lower limit of the number of the polar functional groups is usually 0.

The PFA (2) can be produced by using a polymerization initiator or a chain transfer agent that does not generate a polar functional group that becomes an end group of a polymer chain, or by subjecting PFA having a polar functional group (PFA having a polar functional group derived from a polymerization initiator at an end group of a polymer main chain, or the like) to a fluorination treatment. As a method of the fluorination treatment, a method using a fluorine gas can be mentioned (see Japanese patent laid-open publication No. 2019-194314).

The TFE-based polymer may also be a low molecular weight PTFE. The number average molecular weight of the low molecular weight PTFE is a value calculated according to the following formula (1).

Mn＝2.1×10 ¹⁰ ×ΔHc ^-5.16 ···(1)

In the formula (1), Mn represents the number average molecular weight of the low molecular weight PTFE, and Δ Hc represents the heat of crystallization (cal/g) of the low molecular weight PTFE measured by differential scanning calorimetry. When low molecular weight PTFE is used, the heat resistance and chemical resistance are excellent, and a heat conductive layer with less variation in heat conductivity is easily formed.

The number average molecular weight of the low molecular weight PTFE is preferably 20 tens of thousands or less, more preferably less than 10 thousands. The number average molecular weight is preferably 1 ten thousand or more.

Low molecular weight PTFE also includes copolymers of TFE with very small amounts of comonomers (HFP, PAVE, FAE, etc.).

The thermally conductive filler a of the present invention may, for example, be a carbon-containing filler, a metal oxide-containing filler, a nitride-containing filler or a glass-containing filler, and preferably a carbon-containing filler. In addition, these fillers may be composed of a single component or may be composed of a plurality of components. For example, the metal oxide filler may also contain a metal oxide and other filler components (nitrides, etc.).

The carbonaceous filler may, for example, be a carbonaceous filler containing at least one of carbon fiber (carbon fiber), carbon black, graphene oxide, fullerene, graphite and graphite oxide, and preferably a carbon fiber-containing filler. Examples of the carbon fibers include PAN-based carbon fibers (polyacrylonitrile-based carbon fibers), pitch-based carbon fibers, vapor grown carbon fibers, and carbon nanotubes (single-layer, double-layer, multilayer, cup-stacked type, etc.).

As the filler containing a metal oxide, alumina-containing filler may be exemplified.

Examples of the nitride-containing filler include a boron nitride-containing filler and an aluminum nitride-containing filler.

The thermally conductive filler a is preferably a coating agent having no coating surface or a filler having no functional group on the surface. In this case, the contact between the thermally conductive fillers a and the base material, and the exposure of the thermally conductive fillers a on the exposed surface improve the thermal conductivity efficiency, and the thermal conductivity of the thermally conductive layer is more excellent. Further, since a TFE-based polymer having a specific melt viscosity and high adhesion to the thermally conductive filler a is used, the heat conductive layer of the present substrate is not damaged in compactness and is easily provided with corrosion resistance.

The coating agent is a component for improving the affinity between the thermally conductive filler a and the polymer, and specifically may be a sizing agent (サイジング) (epoxy resin, polyamide resin, or the like). Further, as the functional group introduced into the surface, a functional group introduced by oxidation etching or a silane coupling agent may be mentioned.

The thermally conductive filler a can be prepared by removing the coating agent and the functional group on the surface of the filler. The removal method may be a method of washing or thermal decomposition.

The aspect ratio of the thermally conductive filler a is preferably 3 or more, more preferably 5 or more. The upper limit of the aspect ratio is typically 100 ten thousand.

The shape of the thermally conductive filler a may be, for example, a granular shape, a fibrous shape, or a plate shape, and is preferably a fibrous shape. Specific examples of the fibrous form include a leaf form, a column form, a leaf form, a filament form and a capillary form. If the shape of the thermally conductive filler a is fibrous, the thermally conductive filler a in the thermally conductive layer is easily oriented with high continuity in a direction perpendicular to the facing surface. Further, the state in which the heat conductive filler a is in contact with the facing surface and the state in which it is exposed on the exposed surface of the heat conductive layer are easily formed, and the heat conductivity and corrosion resistance of the base material are easily further improved.

In the present base material, the ratio of the length of the major axis of the thermally conductive filler a to the thickness of the thermally conductive layer is 0.1 or more, preferably 0.5 or more, and more preferably more than 1. The above ratio is preferably 2 or less. Thus, the thermally conductive filler can be more effectively brought into contact with the facing surface and exposed to the exposed surface of the thermally conductive layer, and the thermally conductive filler a in the thermally conductive layer can be more easily prevented from peeling off.

The length of the major axis of the thermally conductive filler A is preferably more than 0.1. mu.m, more preferably 5 μm or more, and still more preferably 10 μm or more. The length of the major axis of the thermally conductive filler A is preferably 500 μm or less, more preferably 300 μm or less, and still more preferably 200 μm or less.

The length of the minor axis of the thermally conductive filler A is preferably 0.01 μm or more, more preferably 0.05 μm or more. The length of the minor axis of the thermally conductive filler A is preferably 1 μm or less, more preferably 0.1 μm or less.

When the thermally conductive filler is fibrous, the major axis length of the thermally conductive filler is a value at which the cumulative fraction of the fiber lengths of the thermally conductive filler is 90%, and the minor axis length of the thermally conductive filler is a value at which the cumulative fraction of the fiber diameters of the thermally conductive filler is 90%.

The thickness of the heat conductive layer is preferably 0.1 μm or more, more preferably 5 μm or more, and still more preferably 10 μm or more. The thickness of the heat conductive layer is preferably 450 μm or less, more preferably 250 μm or less, and still more preferably 150 μm or less.

The content of the TFE-based polymer in the heat conductive layer is preferably 30 mass% or more, and more preferably 40 mass% or more. The content of the TFT-based polymer is preferably 90% by mass or less, and more preferably 65% by mass or less.

The content of the thermally conductive filler a in the thermally conductive layer is preferably 10 mass% or more, and more preferably 35 mass% or more. The thermally conductive filler a is preferably 70 mass% or less, more preferably 60 mass% or less.

When the content of the TFE-based polymer and the content of the thermally conductive filler are within the above ranges, the corrosion resistance and the thermal conductivity of the thermally conductive layer are excellent, and the peeling of the thermally conductive filler a is easily suppressed.

The sum of the content of the TFE-based polymer and the content of the thermally conductive filler a in the thermally conductive layer is preferably 90 mass% or more, and more preferably 95 mass% or more. The sum is preferably 100% by mass or less.

The mass ratio of the content of the TFE polymer in the heat conductive layer to the content of the heat conductive filler A is preferably 0.1 to 9, and more preferably 0.25 to 4. In this case, not only the physical properties of the TFE-based polymer (physical properties of the polymer represented by corrosion resistance) and the properties of the thermally conductive filler a (physical properties of the thermally conductive filler a represented by thermal conductivity) in the thermally conductive layer are well balanced, but also the coefficient of linear expansion thereof is reduced, so that the thermally conductive layer is less likely to warp, and the thermally conductive layer having high adhesion strength to the base material is likely to be formed.

The thermally conductive layer may further contain components other than the TFE-based polymer and the thermally conductive filler a. Examples of the other component include polymers other than TFE-based polymers, thixotropy imparting agents, antifoaming agents, fillers other than thermally conductive filler a, silane coupling agents, dehydrating agents, plasticizers, weather-resistant agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, colorants, conductive agents, mold release agents, surface treatment agents, viscosity modifiers, and flame retardants.

The heat conductivity of the heat conductive layer is preferably 1.0W/mK or more, more preferably 2.0W/mK or more, and still more preferably 3.0W/mK or more. The upper limit of the thermal conductivity of the heat conductive layer is 100W/m.K. The heat conductive layer in the present base material exerts the above thermal conductivity by the above action mechanism.

The coefficient of linear expansion of the heat conductive layer is preferably 100 ppm/DEG C or less, more preferably 70 ppm/DEG C or less, and still more preferably 50 ppm/DEG C or less. The lower limit of the coefficient of linear expansion of the heat conductive layer is 1 ppm/DEG C. In this case, the adhesion strength of the heat conductive layer to the base material can be maintained sufficiently high even in a high-temperature environment. The coefficient of linear expansion of the heat conductive layer is also preferably about the same as that of the base material.

Alternatively, the base material may be removed from the base material to obtain a single-layer heat conductive layer in the form of a film. Examples of the method for removing the base material include a method of peeling the base material from the base material and a method of dissolving the base material of the base material. For example, when the base material is a copper foil, a single-layer heat conductive layer can be obtained as a film by removing the base material by contacting the base material surface with an etching solution such as hydrochloric acid.

The material of the substrate is preferably metal, glass, or ceramic, and more preferably metal.

Examples of the metal include copper, aluminum, iron, zinc, nickel, and alloys of these metals.

Examples of the glass include soda lime glass, soda potassium glass, soda aluminate glass, aluminum borate glass, aluminum borosilicate glass, low expansion glass, quartz glass, and porous glass.

The ceramic may, for example, be a sintered body of alumina, zirconia, magnesium titanate, calcium titanate, strontium titanate, aluminum nitride, silicon carbide, silicon nitride or the like (mullite, cordierite, talc or the like).

Examples of the shape of the substrate include a flat plate, a tube, a sphere, a curved surface, a wedge, and a wave.

A preferred embodiment of the substrate may be a main body of a heat transfer pipe described later. When a heat conductive layer is formed on the outer surface of a tubular base material such as a tube or a finned tube, a heat conductive tube that can be used for a heat exchanger or the like can be obtained.

The method for producing the substrate may, for example, be as follows: a liquid composition containing a powder of a TFE polymer, a thermally conductive filler A, and a liquid medium is prepared, the liquid composition is applied to the surface of the base material to form a liquid coating film, and the liquid coating film is heated to form a thermally conductive layer. As the liquid composition, the liquid composition of the present invention described later can be used.

Examples of the method of applying the liquid composition include coating and spraying (spray).

When the liquid composition is applied by spraying, the liquid composition is sprayed as droplets, and the droplets adhere to the surface of the substrate to form a liquid coating film. At this time, the liquid composition passes through the small-diameter flow path of the nozzle and is then discharged as droplets from the tip opening. Therefore, the thermally conductive filler a in each droplet is easily oriented with its long axis direction as the ejection direction of the droplet (i.e., the thickness direction of the base material). Before adhering to the substrate, the liquid medium is scattered and volatilized from the droplets. In this state, since the liquid droplets adhere to the surface of the base material, it is considered that the thermally conductive filler a is easily oriented in the thickness direction of the liquid coating film. That is, more of the thermally conductive filler is easily brought into contact with the facing surface and exposed on the exposed surface.

The heating temperature of the liquid coating is preferably a temperature at which the TFE polymer is melt-fired.

The heating temperature may be constant or may be different. Specifically, it is preferable to heat the coating to a temperature (100 to 200 ℃) at which the liquid medium (liquid component) of the liquid coating volatilizes and then to a temperature (340 to 400 ℃) at which the TFE polymer is melt-fired.

Examples of the heating means include an oven, a forced air drying oven, and irradiation with heat rays such as infrared rays

The substrate may be a heat transfer tube or a heat transfer plate.

The heat pipe has a tubular substrate and a heat conductive layer on an outer surface of the tubular substrate.

Fig. 1 is a cross-sectional view showing an example of the heat transfer pipe. The size ratio in fig. 1 is different from the actual size ratio for the convenience of explanation.

The heat transfer pipe 10 includes: the heat conductive layer 16 includes a tubular base material including tubes 12 and fins 14 provided on the outer periphery of the tubes 12, and a heat conductive layer covering the outer surfaces of the tubes 12 and the surfaces of the fins 14.

The material of the tube 12 may be the above-mentioned metal, and from the viewpoint of improving the thermal conductivity, copper, a copper alloy, aluminum, and an aluminum alloy are preferable.

The outer diameter and the inner diameter of the pipe 12 can be set as appropriate depending on the material of the pipe, the use of the heat transfer pipe, and the like.

The material of the fin 14 may be the above-mentioned metal, and from the viewpoint of improving the thermal conductivity, copper, a copper alloy, aluminum, and an aluminum alloy are preferable. The fins are generally of the same material as the tubes.

The number, shape, thickness, area, and arrangement pitch of the fins 14 can be appropriately set according to the material of the fins 14, the use of the heat transfer pipe 10, and the like.

In the heat transfer pipe 10, the thickness of the heat conductive layer 16 is preferably 2 to 400 μm, and more preferably 10 to 200 μm. In this case, the heat conductive layer 16 has excellent heat conductivity.

The shape of the heat exchanger tube 10 may be a plate-fin heat exchanger tube, a solder plate (welding plate) heat exchanger tube, a plate-fin heat exchanger tube, a spiral-fin heat exchanger tube, a double-tube heat exchanger tube, a cross-fin heat exchanger tube, a corrugated fin heat exchanger tube, a slit-fin heat exchanger tube, a net-fin heat exchanger tube, a tube-fin heat exchanger tube, an air-fin heat exchanger tube, or the like, and specific examples thereof may be the shapes described in the drawings of japanese patent publication No. 59-38517, japanese patent application laid-open No. 60-141437, and japanese patent application laid-open No. 63-54984.

The heat exchanger of the present invention preferably includes the heat transfer pipe 10 made of the base material.

In the heat exchanger of the present invention, the heat transfer pipe 10 is preferably provided at a portion where the combustion gas containing moisture and sulfur compounds is cooled to a temperature equal to or lower than the dew point temperature of sulfuric acid to generate sulfuric acid.

The heat exchanger of the present invention can be used, for example, as a economizer in a boiler.

The liquid composition of the present invention (hereinafter also referred to as "the present composition") comprises a melt viscosity of 1X 10 at 380 ℃ ⁶ Powder of a TFE polymer of Pa · s, a thermally conductive filler having an aspect ratio exceeding 1, and a liquid medium.

The D50 of the powder is 0.1 to 6 μm, and the ratio of the D10 of the powder to the D50 of the powder is 0.5 or less.

The content of the thermally conductive filler a in the present composition is 10 mass% or more.

When the present composition is used, the content of the thermally conductive filler a is high, and a coating layer excellent in thermal conductivity and corrosion resistance can be easily formed on the surface of the base material. The reason is not necessarily clear, but is considered to be as follows.

The ratio of D10 to D50 in the powder in the present composition is within a predetermined range, in other words, the powder contains fine particles at a certain ratio. The fine particles have a large specific surface area, and when the fine particles are contained in a liquid composition, the affinity (wettability) between the powder and the thermally conductive filler a is generally improved, and the dispersion state thereof is considered to be improved. Therefore, the present composition is excellent in dispersibility and workability even if the content of the thermally conductive filler a is high.

Further, it is considered that when the heat conductive layer is formed, the fine particles promote dense deposition of other particles, and the vertical orientation of the heat conductive filler a is improved. Specifically, it is considered that the fine particles are densely packed between the stacked particles and support the vertically oriented thermally conductive filler a. In other words, it is considered that the thermally conductive filler a is formed in a fixed state in the thermally conductive layer. As a result, it is considered that when the present composition is used, a dense coating layer in which the heat conductive filler a is highly vertically oriented with respect to the facing surface can be formed.

Therefore, it is considered that when the present composition having excellent dispersibility and workability is used, a heat conductive layer having excellent heat conductivity and corrosion resistance can be formed on the surface of the base material even if the content of the heat conductive filler a is high.

The content of the TFE-based polymer in the powder of the present composition is preferably 80 mass% or more, and more preferably 100 mass%.

The powder in the present composition may contain at least one of a polymer other than the TFE-based polymer and an inorganic substance.

Examples of the different polymer include aromatic polyester, polyamideimide, polyimide, polyphenylene ether and maleimide.

Examples of the inorganic substance include silicon dioxide (silica), metal oxides (beryllium oxide, cerium oxide, aluminum oxide, basic aluminum oxide, magnesium oxide, zinc oxide, titanium oxide, and the like), boron nitride, and magnesium metasilicate (talc).

The powder containing the above components preferably has a core-shell structure in which the TFE-based polymer is used as a core and the above components are used as shells, or a core-shell structure in which the TFE-based polymer is used as a shell and the above components are used as cores. The powder can be obtained, for example, by bonding (collision, aggregation, or the like) a powder of a TFE-based polymer to a powder of the above components.

The powder D50 is 0.01 to 6 μm, preferably 0.1 to 4 μm, and more preferably 0.5 to 3 μm. The powder D10 is preferably 0.001 to 1.8. mu.m, more preferably 0.005 to 1.5. mu.m, and still more preferably 0.1 to 1 μm.

The powder has a ratio of D10 to D50 of 0.5 or less, preferably 0.3 or less, more preferably 0.2 or less. Thereby, the above-described effect is easily exhibited while suppressing the aggregation of the powder.

The above ratio is preferably 0.1 or more. Thus, the above-described mechanism of action is easily exhibited.

When 100g of the powder is dispersed in 100g of water to prepare a dispersion, the viscosity of the powder is preferably 50 to 400 mPas, more preferably 100 to 200 mPas.

When the dispersion is passed through a 200-mesh sieve according to JIS Z8801-1:2006, the amount of residue on the sieve is preferably 3g or less, more preferably 1.5g or less.

When the dispersibility of the powder is low when the powder is prepared as a dispersion, the dispersion may be prepared by using a surfactant. The surfactant may, for example, be the same as the surfactant which may be contained in the present composition described later.

The powder having the dispersion viscosity and the amount of residue in the above ranges can be said to have a sufficiently high circularity. That is, the higher the circularity of the powder, the higher the fluidity of the powder in the dispersion, and therefore the viscosity thereof is liable to decrease. In addition, aggregation between powders is suppressed, and therefore the amount of residue on the sieve is easily reduced.

When such a powder having a high circularity is used, the dispersibility of the present composition is improved, and the physical properties of a layer (heat conductive layer) formed therefrom are easily further improved.

The ranges of TFE-based polymers in the present compositions, including their preferred ranges, are the same as those in the present substrates. Particularly, as the TFE-based polymer, the polymer (1) and the polymer (2) are preferable. When such a polymer is used, the dispersibility of the present composition can be easily improved.

The range of the thermally conductive filler a in the present composition includes the same preferable ranges as those in the present base material.

The content of the powder in the present composition is preferably 10% by mass or more, more preferably 15% by mass or more, and still more preferably 20% by mass or more. The content of thermally conductive filler a in the present composition is preferably 50% or less, and more preferably 40% or less by mass. In this case, the present composition is easy to disperse and has excellent stability.

The content of the thermally conductive filler a in the present composition is 10 mass% or more, preferably 15 mass% or more, and more preferably 20 mass% or more. The content of the thermally conductive filler a in the present composition is preferably 50% or less, and more preferably 40% or less by mass. In this case, the dispersion liquid is easy to be excellent in dispersion stability. By the above action mechanism, even if the present composition contains a large amount of the thermally conductive filler a, the dispersibility is excellent.

The liquid medium in the present composition is a liquid compound which functions as a dispersion medium for the powder and the thermally conductive filler a and is inert at 25 ℃. The liquid medium may be water or a nonaqueous dispersion medium. The liquid medium may be two or more. In this case, the different liquid media are preferably miscible.

The boiling point of the liquid medium is preferably 125-250 ℃. In this case, the physical properties of the heat conductive layer formed from the present composition are easily improved.

As the liquid medium, a liquid compound selected from the group consisting of amides, ketones and esters is particularly preferable, and as the liquid dispersion medium, N-methyl-2-pyrrolidone, γ -butyrolactone, cyclohexanone and cyclopentanone are more preferable.

The content of the liquid medium in the present composition is preferably 50% by mass or more, more preferably 60% by mass or more. The content of the liquid medium is preferably 90% by mass or less, more preferably 80% by mass or less.

The composition may also contain a resin other than a TFE-based polymer. The other resin may be a thermosetting resin or a thermoplastic resin.

Examples of the other resin include epoxy resins, maleimide resins, polyurethane resins, elastomers, polyimides, polyamic acids, polyamideimides, polyphenylene ethers, liquid crystal polyesters, and fluoropolymers other than TFE-based polymers.

The present composition in the case of containing another resin may be produced by mixing the present composition with powder of another resin, or may be produced by mixing the present composition with a varnish containing another resin.

The composition may contain, in addition to the above components, additives such as a thixotropy-imparting agent, an antifoaming agent, a silane coupling agent, a dehydrating agent, a plasticizer, a weather-resistant agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, a whitening agent, a colorant, an electrically conductive agent, a mold release agent, a surface treatment agent, a viscosity modifier, a flame retardant, and a filler other than the thermally conductive filler a.

The component forming the heat conductive layer in the present composition preferably contains a TFE-based polymer and a heat conductive filler a as main components. The total content of the TFE polymer and the thermally conductive filler A in the components forming the thermally conductive layer in the composition is preferably 80 to 100% by mass.

The viscosity of the composition is preferably 50 to 10000 mPas. The viscosity of the present composition is preferably 100 mPas or more. The viscosity of the present composition is preferably 1000 mPas or less, more preferably 800 mPas or less.

The thixotropic ratio of the present composition is preferably 1.0 or more. The thixotropic ratio of the present composition is preferably 3.0 or less, more preferably 2.0 or less.

The present composition can be easily adjusted to the viscosity and thixotropy within the above ranges by the above mechanism of action, and is excellent in handling properties.

The present composition preferably contains a surfactant from the viewpoint of promoting dispersion of the thermally conductive filler a and the powder and further improving the physical properties of the thermally conductive layer.

As the surfactant, nonionic surfactants are preferable.

When the present composition contains a surfactant, the proportion thereof is preferably 1 to 20% by mass.

As the hydrophilic site of the surfactant, alcoholic hydroxyl group and polyoxyalkylene group are preferable.

The polyoxyalkylene group may be composed of two or more types of oxyalkylene groups. In the latter case, the different types of oxyalkylene groups may be arranged randomly or in blocks.

As the oxyalkylene group, an oxyethylene group is preferable.

The hydrophobic portion of the surfactant preferably has an ethynyl group, a polysiloxane group, a perfluoroalkyl group, or a perfluoroalkenyl group, with a polysiloxane group being preferred. In other words, the surfactant is preferably an acetylene surfactant, a silicone surfactant, or a fluorine surfactant, and more preferably a silicone surfactant.

When the surfactant is used, the surface tension of the liquid medium can be reduced, the wettability of the liquid medium on the powder surface can be improved, and the dispersibility of the powder can be improved. In addition, the hydrophobic part of the surfactant is adsorbed on the surface of the powder, the hydrophilic group extends into the liquid medium, and the aggregation of the powder is prevented by the steric hindrance of the hydrophilic group, thereby further improving the dispersion stability. In addition, the dispersion stability of the thermally conductive filler a is also improved.

Specific examples of the surfactant include: "Ftergent" series (available from Nippon Kabushiki Kaisha (ネオス)), "Surflon" series (available from AGC Qing beautification chemical Co., Ltd. (AGC セイミケミカル)), "MEGA FACE" series (available from DIC corporation)), "Unidyne" series (available from Dajin Industrial Co., Ltd. (ダイキン, )), "BYK-347", "BYK-349", "BYK-378", "BYK-3450", "BYK-3451", "BYK-3455", "BYK-3456" (available from Bikk chemical Japan (ビックケミー. ジャパン)), "KF-6011", "KF-6043" (available from shin-Etsu chemical Co., Ltd.).

The composition is useful as a heat-dissipating and heat-conducting resin material and a heat-conducting film-forming material in various fields such as the electric and electronic industry field and the automobile field, and is particularly useful as the latter material.

The heat transfer tube 10 composed of the coated substrate of the present invention can be used in applications where corrosion resistance is required for the heat exchanger, or the fins or tubes constituting the heat exchanger.

Examples of the above-mentioned use include: a facility that burns sulfur-containing fuel and generates exhaust gas that may be exposed to sulfuric acid (for example, a thermal power plant that is a combustion facility for sulfur-containing fuel such as coal or heavy oil), and a stack and an exhaust pipe for discharging exhaust gas generated during combustion.

The composition can also be used as a material for forming a heat conductive film on a heat dissipating member or the like for dissipating heat from each heat generating member.

The heat dissipation components include power devices, transistors, thyristors, rectifiers, transformers, power MOS FETs, and CPUs.

As the heat radiating member, a heat radiating fin and a metal heat radiating plate may be mentioned, and more specifically: computer or display casing, electronic device material, automobile interior and exterior, sealing material for processing machines or vacuum furnaces which perform heat treatment under low oxygen, plasma processing apparatus, and the like, and heat dissipation member in processing units of sputtering or various dry etching apparatuses, and the like.

The present composition can also be used as a material for impregnating and drying an insulating layer of a printed wiring board, a thermal interface material, a substrate for a power module, a coil used in a power device such as a motor, and the like to form a heat-conductive and heat-resistant coating layer.

The composition is also useful for applications in which a resin layer is formed by coating on sliding members such as bearings, pistons, bearings, slide switches, gears, bushings, seals, thrust washers, wear rings, cams, conveyor belts, food conveyor belts, etc.), wear pads, wear strips, tube lamps, test sleeves, wafer guides, wear members for centrifugal pumps, hydrocarbon/chemical and water supply pumps, and separators for fuel cells, and for applications in which a coating layer is formed on glass substrates and metal appliances. Useful as coating materials for the interior and exterior of glass containers. The glass containers include vials, syringes (syringes), syringes with needles, syringe type syringes, and ampoules.

The present compositions are also suitable for use in applications requiring electrical conductivity. The molded article obtained from the present composition is excellent in thermal conductivity and also easily excellent in electrical conductivity. In particular, the present composition can be easily adjusted to an appropriate viscosity and does not require high temperature for curing, and therefore, the present composition can be suitably used in the field of printed electronics. In particular, it is useful for manufacturing conductive elements of printed circuit boards, sensor electrodes, displays, chassis, RFID (radio frequency identification), solar power generation, lighting, disposable electronic devices, automobile heaters, electromagnetic wave (EMI) shields, membrane switches, and the like.

The composition can also be used as an adhesive. The adhesive is used for bonding an IC chip mounted on a substrate, an electronic component such as a resistor or a capacitor, a circuit board to a heat sink, an LED chip to a substrate, and the like in a semiconductor element, a high-density substrate, a module component, and the like.

The composition can also be used as a conductive bonding material between a circuit wiring and an electronic component in a mounting process of the electronic component (as an application of replacing soldering).

In addition, the composition can be used for bonding ceramic parts or metal parts in an in-vehicle engine.

Further, in the printed wiring board, in order to prevent the temperature rise of the printed board on which electronic parts are mounted at high density, the present composition can also be used as a novel printed wiring board material in place of the conventional glass epoxy board.

The composition can also be used for the application described in paragraph [0149] of International publication No. 2016/017801.

Examples

The present invention will be described in detail with reference to examples, but the present invention is not limited thereto. Example 2 is a comparative example.

The following materials were used in examples and comparative examples.

< TFE polymer powder >

Powder 1: comprising a main chain having 1X 10 carbon atoms and, in order, 97.9 mol%, 0.1 mol%, 2.0 mol% of TFE units, NAH units and PPVE units ⁶ Polymer 1 having 1000 carbonyl groups (melt viscosity at 300 ℃ C. and 380 ℃ C. of 1X 10) ⁶ Pa · s or less) (D10: 1.0 μm, D50: 2.1 μm, D10/D50 about 0.48)

Powder 2: from PTFE (non-fusible, melt viscosity at 380 ℃ C. of more than 1X 10) containing 99.5 mol% TFE units ⁶ Pa · s) (D50: 7 μm, "L173J" from AGC)

Powder 3: comprising a main chain having 1X 10 carbon atoms and containing, in order, 98.7 mol% and 1.3 mol% of TFE units and PPVE units ⁶ Polymer 2 having 40 carbonyl groups (melt temperature: 305 ℃ C., melt viscosity at 380 ℃ C. of 1X 10) ⁶ Pa · s or less) (D10: 0.8 μm, D50: 1.8 μm, D10/D50 ═ 0.44)

Powder 4: powder composed of Polymer 2 (D10: 1.1 μm, D50: 2.0 μm, D10/D50 ═ 0.55)

The viscosity of a dispersion obtained by dispersing 100g of each of the powders 1 to 4 in 100g of water was 100 mPas, 300 mPas, 200 mPas and 250 mPas in this order of the powders 1 to 4.

< liquid Medium >

NMP: n-methyl-2-pyrrolidone.

< surfactant >

Surfactant 1: (meth) acrylate Polymer having perfluoroalkenyl, hydroxyl group and polyoxyethylene group in side chain (available from Nippon corporation, "Ftergent 710 FL")

< carbon fiber >

Carbon fiber 1: carbon fiber having a fiber diameter of 6 μm and a fiber length of 80 μm without a coating agent and a functional group on the surface (manufactured by AIRTEX corporation, エアテクス, "ATU-75")

The linear expansion coefficient and the thermal conductivity of the obtained coating material were measured by the following methods.

< coefficient of linear expansion >

A long (4 mm wide, 55mm long) sample was cut out of the coated substrate. The sample was then dried in an oven at 250 ℃ for 1 hour. Thereafter, the Coefficient of Thermal Expansion (CTE) of the sample was measured by a thermomechanical analyzer (manufactured by SII, "TMA/SS 6100"). Specifically, the temperature of the sample was raised from 25 ℃ to 260 ℃ at a rate of 2 ℃ per minute while applying a load of 20mN with a chuck pitch of 20mm in an air atmosphere. At this time, the amount of displacement accompanying the linear expansion of the sample was measured. Then, the displacement is used as the linear expansion coefficient (ppm/DEG C) of the heat conductive layer at 25-260 ℃.

< thermal conductivity >

The base material is peeled off from the coated base material to obtain the heat conductive layer as a single-layer film. A test piece of 10 mm. times.10 mm square was cut out from the center of the film, and the thermal conductivity (W/m.K) in the in-plane direction was measured.

1. Preparation example of liquid composition

(liquid composition 1)

100 parts of powder 1, 10 parts of dispersant 1, 40 parts of carbon fiber 1 and 90 parts of NMP were charged into a horizontal ball mill, and stirred at 500rpm for 30 minutes using zirconia balls having a diameter of 15mm to obtain liquid composition 1 (viscosity: 100 mPas).

(liquid composition 2)

In the same manner as the liquid composition 1 except that the powder 2 was used in place of the powder 1, a liquid composition 2 (viscosity: 150 mPas) was obtained.

(liquid composition 3)

In the same manner as the liquid composition 1 except that the powder 3 was used in place of the powder 1, the liquid composition 3 (viscosity: 200 mPas) was obtained.

(liquid composition 4)

In the same manner as the liquid composition 1 except that the powder 4 was used in place of the powder 1, the liquid composition 4 (viscosity: 300 mPas) was obtained.

After the liquid compositions 1 to 4 were stored at 25 ℃ in containers, the dispersibility thereof was visually observed, and the dispersion stability was evaluated according to the following criteria. As a result, the liquid compositions 1 to 4 were "O", "X", "Delta" and "X" in this order.

Good: no aggregates were found.

And (delta): it is seen that fine aggregates are attached to the side wall of the container.

X: it was seen that the bottom of the vessel had also precipitated aggregates.

2. Production example of coated base Material

(example 1)

The liquid composition 1 was sprayed onto the surface of a stainless steel substrate by a spray method to form a liquid coating film on the surface of the substrate. Then, the liquid coating was heated at 100 ℃ for 10 minutes to obtain a dried coating having a thickness of 90 μm. Subsequently, the substrate on which the dry film was formed was heated at 340 ℃ for 15 minutes in a nitrogen atmosphere. The powder was melted to form a heat conductive layer having a thickness of 78 μm, thereby obtaining a coated substrate. The base material of the coated base material is firmly bonded to the heat conductive layer, and the carbon fibers are exposed from the surface of the heat conductive layer. The coefficient of linear expansion of the heat conductive layer is below 20 ppm/DEG C, and the coefficient of heat conductivity of the heat conductive layer is above 1.5W/m.K.

(example 2)

A coated substrate was obtained by forming a thermally conductive layer having a thickness of 78 μm in the same manner as in example 1, except that the liquid composition 2 was used instead of the liquid composition 1, but the substrate and the thermally conductive layer were easily peeled off.

(example 3)

A heat conductive layer having a thickness of 78 μm was formed to obtain a coated substrate in the same manner as in example 1, except that the liquid composition 3 was used instead of the liquid composition 1. The base material of the coated base material is firmly bonded to the heat conductive layer, and the carbon fibers are exposed from the surface of the heat conductive layer. The coefficient of linear expansion of the heat conducting layer is 20 to 30 ppm/DEG C, and the coefficient of heat conductivity of the heat conducting layer is 1.2 to 1.5W/m.K.

(example 4)

A heat conductive layer having a thickness of 78 μm was formed to obtain a coated substrate in the same manner as in example 1, except that the liquid composition 4 was used instead of the liquid composition 1. The base material of the coated base material is firmly bonded to the heat conductive layer, and the carbon fibers are exposed from the surface of the heat conductive layer. The coefficient of linear expansion of the heat conducting layer is 30 to 50 ppm/DEG C, and the coefficient of heat conductivity of the heat conducting layer is 1.0 to 1.2W/m.K.

Industrial applicability of the invention

The coated substrate of the present invention can be used as a heat conductive layer in a heat transfer pipe of a heat exchanger. The liquid composition of the present invention is useful as a coating material for forming a heat conductive layer or the like in a heat conductive pipe of a heat exchanger.

In addition, the entire contents of the specification, claims, abstract and drawings of japanese patent application No. 2019-228258 filed on 12/18/2019 are cited as the disclosure of the present specification.

Description of the symbols

Heat conducting pipe 10 …, tube 12 …, fin 14 … and heat conducting layer 16 …

Claims

1. A coated substrate comprising a substrate and a heat conductive layer covering the surface of the substrate, wherein the heat conductive layer has a melt viscosity of 1 x 10 at 380 ℃ ⁶ A tetrafluoroethylene polymer having Pa · s or less and a thermally conductive filler having an aspect ratio exceeding 1, wherein the ratio of the length of the major axis of the thermally conductive filler to the thickness of the thermally conductive layer is 0.1 or more.

2. The coated substrate according to claim 1, wherein the heat conductive layer has a thermal conductivity of 1.0W/m-K or more.

3. The coated substrate according to claim 1 or 2, wherein the coefficient of linear expansion of the heat conductive layer is 100ppm/° c or lower.

4. The coated substrate according to any one of claims 1 to 3, wherein the length of the long axis of the thermally conductive filler is more than 0.1 μm and 500 μm or less, and the thickness of the thermally conductive layer is 0.1 to 450 μm.

5. The coated substrate according to any one of claims 1 to 4, wherein the tetrafluoroethylene polymer is a polymer containing a tetrafluoroethylene-based unit and a perfluoro (alkyl vinyl ether) -based unit, or polytetrafluoroethylene having a number average molecular weight of 20 ten thousand or less.

6. The coated substrate according to any one of claims 1 to 5, wherein the thermally conductive filler is fibrous in shape.

7. The coated substrate according to any one of claims 1 to 6, wherein the thermally conductive filler is a carbon-containing filler.

8. The coated substrate according to any one of claims 1 to 7, wherein the content of the thermally conductive filler in the thermally conductive layer is 10% by mass or more, and the sum of the content of the tetrafluoroethylene polymer and the content of the thermally conductive filler is 90% by mass or more.

9. The coated substrate according to any one of claims 1 to 8, wherein the substrate is made of metal, glass or ceramic.

10. A heat exchanger comprising the coated substrate according to any one of claims 1 to 9.

11. A method for producing a coated substrate according to any one of claims 1 to 9, wherein a liquid composition containing a powder of the tetrafluoroethylene polymer, the thermally conductive filler, and a liquid medium is prepared, the liquid composition is applied to the surface of the substrate to form a liquid coating film, and the liquid coating film is heated to form the thermally conductive layer, thereby obtaining the coated substrate.

12. A liquid composition comprising a resin having a cumulative 50% diameter by volume of 0.1 to 6 μm and a melt viscosity at 380 ℃ of 1X 10 ⁶ A tetrafluoroethylene polymer powder having Pa s or less, a thermally conductive filler having an aspect ratio of more than 1, and a liquid medium, wherein the content of the thermally conductive filler is 10% by mass or more, and the ratio of the cumulative 10% by volume diameter of the powder to the cumulative 50% by volume diameter of the powder is 0.5 or less。

13. The liquid composition according to claim 12, wherein the powder has a viscosity of 50 to 400 mPa-s when 100g of the powder is dispersed in 100g of water to prepare a dispersion.

14. The liquid composition according to claim 12 or 13, wherein the thermally conductive filler is a coating agent having no coated surface or a thermally conductive filler having no functional group on the surface.

15. A liquid composition according to any one of claims 12 to 14, wherein the viscosity at 25 ℃ is from 50 to 10000 mPa-s.