KR20010033429A - Fluororesin Powder Liquid Dispersion Capable of Forming Thick Coatings - Google Patents

Abstract

An anticorrosive thick film coated with a heat-flowable fluororesin powder, a liquid dispersion medium having a surface tension of 45 dyne / cm or less, and a colloidal particle fluororesin powder dispersion having an average particle size of 1 μm or less is provided. Preferred colloidal particles for the dispersion are particles of polyether sulfone (PES) added to an aqueous dispersion comprising an organic solvent and a water miscible organic solvent. An aqueous dispersion of PES colloidal particles having an average particle size of 1 μm or less preferably comprises the steps of (1) dissolving PES in an organic solvent capable of dissolving it, (2) dissolving the dissolved PES with a water miscible solvent soluble in the organic solvent. Combining, and (3) combining water with dissolved surfactant with the dissolved polyether sulfone and water miscible solvent.

Description

Fluororesin Powder Liquid Dispersion Capable of Forming Thick Coatings}

Heat-flowable fluororesins, which have properties such as chemical resistance, non-tackiness, heat resistance, low friction rate and electrical insulation, can also form pinhole free films and are thus useful as coating materials. Heat-flowable fluororesins used in such coating applications include, for example, copolymers of tetrafluoroethylene and perfluoro (alkyl vinyl ether) (hereinafter referred to as PFA), tetrafluoroethylene and hexafluoropropylene (FEP). ) And copolymers of tetrafluoroethylene and ethylene (ETFE). These resins are insoluble in water and organic solvents and therefore cannot be used as solution coatings. Accordingly, these resins are applied to the substrate or used as a dispersion by various other methods, such as electrostatic application of powder coating compositions. The dispersion may be based on water and stabilized with a surfactant or may be applied to the substrate by spray-coating, dipping or curtain-coating, followed by heating and fusing to produce a film coating.

Film coatings obtained from electrostatic application of powder coating compositions generally have a thickness of about 50 μm to 100 μm, while dispersion coating compositions generally provide a coated film having a thickness of 20 μm. However, this level of thickness is not sufficient for applications requiring corrosion protection, and there is a need for development of coating compositions capable of forming thicker coatings.

Japanese Patent Application No. 57-15607 discloses a fluororesin dispersion for thick film coating comprising a thermo-flowable fluororesin powder having an average particle size of 2 μm to 300 μm and a porosity of 0.74 or less in a liquid dispersion medium having a surface tension of 45 dyne / cm or less. It is starting. These dispersions form a thick coating of 500 μm when the surface to be coated is horizontal and flat, but the fluororesin powder is baked and film formed when the surface to be coated is vertical or inclined at an angle. It is peeled off the previously coated surface.

In order to also form thick coatings on vertical surfaces, U. S. Patent No. 5,502, 097 discloses an average particle size of 5 microns to 300 microns and a porosity of 0.74 or less and a total surface area of 10 m ² / in a liquid dispersion medium having a surface tension of 45 dyne / cm or less. Disclosed are fluororesin powder dispersions for thick film coatings comprising thermo-flowable fluororesin powders of cm ³ or less and also containing organic liquids having a boiling point of 150 ° C to 340 ° C. The invention allows the formation of a thick coating even when the surface to be coated is vertical. However, there is a risk of explosion due to the flammability of the organic liquid in the dispersion, which causes the working environment to be limited.

Thus, there is still a need for coating compositions that can form thick coated films on vertical surfaces and that can be safely applied, especially in applications requiring corrosion resistance, for example, in chemical plants where the performance of the coating generally follows the thickness of the film. exist.

<Summary of invention>

The present invention is directed to the discovery that when the colloidal particles having an average particle size of 1 μm or less are included in the heat-flowable fluororesin powder dispersion, a thick powder coating can be formed on the vertical surface where the coating does not peel off from the substrate prior to baking and film formation. It is about. This effect is further enhanced by including fibrous heat resistant fillers in the dispersion.

Accordingly, the present invention provides a fluororesin powder coating composition capable of forming a thick coating having a thickness of 100 μm to 1000 μm with excellent corrosion resistance. This coating allows the film to be formed in a single step using a simple and convenient spray gun or the like without any explosion hazard.

Specifically, the fluororesin powder dispersion has a volume of 5 to 50% by volume based on the dispersion of heat-flowable fluororesin powder having an average particle size of 5 μm to 300 μm, a porosity of 0.74 or less, and a total surface area of 10 m ² / cm ³ or less. The liquid dispersion medium has a surface tension of 45 dyne / cm or less and the colloidal particles have an average particle size of 1 μm or less. Preferably, the colloidal particles are selected from the group consisting of inorganic oxides and organic heat resistant polymers. More preferably, the fluororesin powder dispersion further comprises a fibrous heat resistant filler having a length of at least 20 μm and an aspect ratio of at least two.

Preferably, the colloidal particles in the fluororesin powder dispersion are particles of polyether sulfone added as an aqueous dispersion comprising an organic solvent and a water miscible solvent. An aqueous dispersion of PES colloidal particles having an average particle size of 1 μm or less comprises 1) dissolving PES in an organic solvent capable of dissolving it, (2) combining the dissolved PES with a water miscible solvent soluble in an organic solvent, and (3) preferably prepared by combining water with dissolved surfactant with dissolved PES and a water miscible solvent.

The present invention relates to a fluororesin powder dispersion suitable for coating articles, in particular a fluororesin powder dispersion capable of forming a very thick film coating without undergoing irreversible solidification of the dispersion.

Thermo-Flowable Fluororesins

Thermo-flowable fluororesins that may be used in the present invention are copolymers of tetrafluoroethylene and other comonomers that can melt and liquefy and flow at temperatures above their melting point. Examples of such copolymers are copolymers of tetrafluoroethylene and perfluoro (alkyl vinyl ether) (PFA), for example pefluoro (propyl vinyl ether), tetrafluoroethylene and hexafluoropropylene (FEP) Copolymers of tetrafluoroethylene and ethylene (ETFE). "Heat-flowable" as used herein means that the fluororesin can be melt processed, and as such the fluororesin particles will flow and fuse together when heated above their melting point.

The average particle size of the heat-flowable fluororesin powder used in the present invention is preferably in the range of 5 μm to 300 μm. If the average particle size of the thermo-flowable fluororesin powder exceeds 300 μm, the coating formed tends to have pinholes. On the other hand, when the average particle size is less than 5 μm, the surface of the film tends to crack when a thin film is formed. In addition, the heat-flowable fluororesin powder may also include a filler, or may be a heat-flowing powder prepared by surface-modifying the particles.

The heat-flowable fluororesin powder used in the present invention has an average porosity of 0.74 or less, preferably in the range of 0.34 to 0.65. If the porosity exceeds 0.74, the coating formed tends to crack and the smoothness of the coating surface tends to be broken. In the present invention, the term "porosity" means the volume of space in the powder layer represented by the following formula.

Porosity = 1- (apparent specific gravity of powder) / (true specific gravity of material constituting powder)

In addition, the total surface area of the heat-flowing fluororesin powder of the present invention is 10 m ² / cm ³ or less. As used herein, the term "total surface area" means the total surface area of the fluororesin powder per unit volume of resin and is given in units of m ² / cm ³ . This value can be derived using the following formula.

Total surface area = (total surface area per gram of powder) x (specific gravity of resin)

The total surface area per gram of powder is measured using the BET method. The heat-flowable fluororesin powder having a total surface area of 10 m ² / cm ³ or less used in the present invention is not easily decomposed when stirred or sprayed with a spray gun to form a dispersion in the dispersion medium, and the powder is also dissolved in the dispersion medium. If separated and precipitated, it can be easily redispersed by stirring. Therefore a smooth and thick coating can be formed.

Heat flowable fluororesin powders with a total surface area of more than 10 m ² / cm ³ tend to degrade when sprayed with a spray gun, which causes cracks and non-uniform films. In addition, such powders are not easily redispersed, making it difficult to obtain a uniform concentration of fluororesin coating composition and making it impossible to form a coating of uniform thickness.

Such heat-flowable fluororesin powders having an average particle size of 5 μm to 300 μm, porosity of 0.74 or less and total surface area of 10 m ² / cm ³ or less are copolymer powders as described, for example, in JP-B 53-11296. Can be prepared by spraying with a gas stream into a sintering chamber whose environment is maintained at a temperature above the melting point of the copolymer under conditions such that individual particles do not fuse with others. It may also be prepared by solidifying colloidal particles, semi-melting the particles and pulverizing them, as disclosed in JP-A No. 4-202329. Thus, the powder used in the dispersion of the present invention may be an aggregate of smaller particles.

Heat-flowable fluororesin powder is included in amounts of 5% by volume to 50% by volume based on the dispersion. Resin concentrations above 50% by volume lead to poor dispersion fluidity and make it difficult to obtain a uniform coating with coating application methods such as curtain coating and dip coating. In addition, spray coating with spray guns require high spray pressures, which is undesirable. On the other hand, when the resin concentration is less than 5% by volume, the thick film cannot be easily formed, and the amount of the fluororesin paint composition used is so large that the drying time is excessive, which is economically disadvantageous.

Dispersion

The dispersion medium used in the present invention has a surface tension of 45 dyne / cm or less. In the case of using a multicomponent dispersion medium, a dispersion medium which can be used in combination with each other and whose surface tension of the mixed dispersion medium is 45 dyne / cm or less is required. When the surface tension of the dispersion medium exceeds 45 dyne / cm, the powder of the present invention is not sufficiently wetted, resulting in an unstable dispersion. Surface tension is measured at room temperature (20 ° C.).

Dispersions with a surface tension of less than 45 dyne / cm are preferably liquid mixtures of water and water-soluble organic liquids. Examples of such water soluble organic liquids are alcohols such as methanol, ethanol, isopropanol and t-butanol, ketones such as acetone and methyl ethyl ketone (MEK), and mixtures thereof. However, a high proportion of water in the liquid mixture is undesirable because it leads to poor film-forming efficiency. Therefore, the mixing ratio is determined based on the purpose of the coating application and the target film thickness.

Colloidal particles

The colloidal particles used in the present invention have an average particle size of 1 μm or less, preferably 0.5 μm or less. The colloidal particles may be spherical or fibrous in shape. Preferably they are fibrous in order to increase the film forming ability.

The term "colloid" exists in a split state that prevents the passage of a semipermeable membrane and consists of particles that are too small to be analyzed by ordinary light microscopy, and does not settle in a suspension or solution, which may have the appearance of a solution, causing diffraction of light. Mean material. Colloidal particles suitable for the present invention have a small particle size and thereby form colloids in water or organic solvents which act as dispersion medium. This promotes the evaporation, drying and curing of the dispersion medium at a temperature below the melting point of the heat-flowing fluororesin powder. When the colloidal particles are thermally stable (heat resistant), ie they form bubbles in the coating, they do not cause vaporization or dehydration reactions above the melting point of the heat-flowable fluororesin. In addition, high temperature is undesirable in that it can promote decomposition of the thermo-flowable fluororesin powder.

Examples of colloidal particles that can be used include colloidal particles of inorganic oxides such as silicon oxide, aluminum oxide, zinc oxide, tin oxide and aromatic polyimides (including polyamidoimide), aromatic polyamides, aromatic polyesters, polyethylene terephthalates, poly Colloidal particles of organic heat resistant resins such as phenylene sulfide, polyether ether ketones, polysulfones, polyetherimides, polyether sulfones. The type of colloidal particles is preferably selected according to the requirements of the coating application in consideration of waterproofness and chemical resistance.

Organic heat resistant resins include polymers that are heated to fuse to form a film, are thermally stable and have a sustained use temperature of at least about 140 ° C. Heat resistant resins are well known as non-stick finishes for attaching fluoropolymers to substrates and for imparting film formation and wear resistance. The resin is generally fluorine free but adheres to the fluoropolymer. Examples of such polymers include polysulfone, an amorphous thermoplastic polymer having one or more (1) glass transition temperatures of about 185 ° C. and a continuous use temperature of about 140 ° C. to 160 ° C., and (2) a glass transition temperature of about 230 ° C. and continuous use. Polyethersulfone, an amorphous thermoplastic polymer having a temperature of about 170 ° C to 190 ° C, (3) Polyphenylene sulfide, which is a partially crystalline polymer having a melting point of about 280 ° C and a continuous service temperature of about 200 ° C to 240 ° C, (4) (5) polyimide and / or polyamideide precursors or polyamide acid precursors thereof (e.g., polyamic acid salts), which have a sustained use temperature of at least 250 ° C and which crosslink upon heating of the coating for fusion The amorphous ketone polymer should have a glass transition temperature of at least about 145 ° C., and the crystalline ketone polymer should have a melting point of at least about 290 ° C., and a polyether having a sustained use temperature of at least about 250 ° C. It comprises a polyarylene ether ketone, such as Le ketone and polyether ketone ketone. All of these polymers are thermally stable, dimensionally stable at temperatures below their sustained use temperature range, and are wear resistant. These polymers also adhere well to clean metal surfaces. Polyimides and / or polyamideimides have been found to be particularly useful because of their ability to impart excellent wear and heat resistance to the composition.

The colloidal particles dispersed in the fluororesin powder act as both a crosslinking agent and an adhesion promoter to the substrate before the baking of the dispersion and until the thermally-flowable fluororesin powder particles fuse to form a film, thereby coating the coated substrate. To prevent heat-flowing fluororesin powder from being peeled off. This makes it possible to form thick coatings.

The colloidal particle content is preferably 6.0% by weight or less based on the heat-flowable fluororesin powder. Preference is given to colloidal particles which can inhibit peeling from the coating applied at the lowest possible content. Colloidal particle contents of greater than 6.0 wt% tend to cause discoloration and bubbles in the applied coating. If this content is excessively high, the coating formation ability decreases, defects such as pinholes in the coating are formed, and the coating has poor strength.

Preferably, the colloidal particles are organic heat resistant resins having self-coating forming ability. In particular, colloidal particles made of polyether sulfone (hereinafter referred to as PES) having high heat resistance and high chemical resistance are preferable.

PES colloidal particles

In the preferred conditions of the present invention using PES colloidal particles, PES colloidal particles having an average particle size of 1 m or less, preferably 0.5 m or less, are used in the present invention. The colloidal particles are preferably added in the form of PES colloidal particles, preferably in the form of an aqueous dispersion comprising an organic solvent and a water miscible solvent capable of dissolving PES at room temperature, ie from 20 ° C. to 25 ° C.

Commercially available PES with an average particle size of more than 1 μm is undesirable. Since the PES colloidal particles used according to the invention have a small particle size, the colloidal solution can be formed using water or an organic solvent as a dispersion medium. This is preferred because it promotes evaporation, drying and curing of the dispersion medium at a temperature below the melting point of the heat-flowing fluororesin powder.

PES is a polymer compound having a repeating unit represented by the following formula. PES polymers or copolymers may be used.

Examples of PES include the following, i.e., a polymer having the above repeating units alone ("VICTREX PES" of ICI, "ULTRASON E" of BASF) and the following repeating units Polymers (Amoco's "UDEL", BASF's "ULTRASON S").

An aqueous dispersion of PES colloidal particles having an average particle size of 1 μm or less comprises (1) dissolving PES in an organic solvent that can dissolve it preferably at room temperature, ie, from 20 ° C. to 25 ° C., (2) organically dissolving the dissolved PES Combining with a water miscible solvent soluble in the solvent, and (3) combining water with dissolved surfactant with dissolved polyether sulfones and water miscible solvents to produce dispersed colloidal particles. The present invention relates to a process for the preparation of an aqueous dispersion of polyethersulfone colloidal particles with good dispersibility and microparticle size.

Preferred organic solvents for dissolving PES are N-methyl-2-pyrrolidone (hereinafter referred to as NMP) or dimethylacetamide (hereinafter referred to as DMA) or a mixture of NMP and DMA. If the solvent is used to disperse the PES rather than dissolve it, a large particle size PES with poor dispersibility is obtained.

The content of PES in an organic solvent (preferably NMP or DMA or mixture) in which PES is dissolved is preferably 20% by weight or less. When the content of PES exceeds 20% by weight, when a water miscible solvent dissolved in NMP or DMA is added and mixed, the NMP solution or DMA solution in which PES is dissolved in or in a mixture thereof is coagulated or purified water and If mixed, coagulation occurs. Such coagulation is undesirable. In addition, the greater the weight of the water miscible solvent dissolved in NMP or dimethylacetamide, the smaller the average particle size of the PES colloidal particles in the PES aqueous dispersion.

Any water miscible solvent that is a solvent for the PES solution, that is, a water miscible solvent (preferably NMP or DMA, or a mixture thereof) that can be dissolved in an organic solvent, can be used as the solvent for adding to the PES-containing organic solution. The water miscible solvent is preferably at least one organic solvent selected from the group consisting of alcohols, glycols, ketones or esters. Specific examples include ethanol, isopropyl alcohol, tetrahydrofurfuryl alcohol, ethylene glycol, propylene glycol, acetone, methyl acetate and the like. But these are not exclusive.

When the weight of the water-miscible solvent dissolved in the organic solvent increases, the average particle size of the PES colloidal particles in the PES aqueous dispersion tends to decrease.

If an excessively large amount of water miscible solvent is added, PES dissolved in the solution will coagulate and precipitate. If an excessively small amount of water miscible solvent is added, the PES will solidify and precipitate in the next step of adding the water miscible solvent containing solution to distilled water with stirring. The amount of water miscible solvent added depends on the type of water miscible solvent. However, an amount which does not cause the above problem at all is preferable.

When a solution containing PES dissolved in the solution prepared as described above is added to purified water in which the surfactant is dissolved and mixed by stirring, a colloidal solution made of colloidal particles of PES can be obtained. Preferred surfactants dissolved in purified water are anionic and nonionic surfactants that can ensure stable emulsification of PES aqueous dispersions made from PES colloidal particles. Octyl phenoxypolyethoxyethanol is particularly preferred.

The average particle size of the PES contained in the aqueous PES dispersion appears to be 1 μm on average as measured by a grain-size analyzer. The aqueous PES dispersion prepared with the present invention comprises PES colloidal particles of small particle size. The aqueous PES dispersion may be used alone or in combination with other resins such as fluorine resins to obtain a mixed aqueous dispersion, and may be used as a heat resistant coating material or polymer for coating materials.

Fibrous fillers

The fluororesin powder dispersion of the present invention preferably comprises a fibrous heat-resistant filler having a length of 20 µm or more and an aspect ratio of 2 or more. Fibrous heat resistant fillers help prevent the heat-flowable fluororesin powder from peeling off from the coated surface during drying of the coating. Fibrous fillers of at least 20 μm in length and of at least aspect ratio are warped by entanglement with large particle size heat-flowable fluororesin powders and also due to thermal expansion and heat shrinkage differences between the substrate and heat-flowable fluororesin powders occurring during film formation. It is believed to reduce film drop-off by mitigating. Fibrous fillers less than 20 μm in length and less than aspect ratio 2 are less effective in preventing film drop-off.

Examples of suitable fibrous fillers of at least 20 μm in length and at least two aspect ratios are glass fibers, carbon fibers, rock wool, ceramic fibers and inorganic fibers such as potassium titanate whisker, organic fibers such as aramid fibers and mixtures thereof.

The content of the fibrous filler is up to 65% by volume based on the total solids comprising the thermo-flowable fluororesin powder and the fibrous filler. Contents above 65% by volume cause too many voids, making it difficult to obtain a uniform film.

Other fillers

The fluororesin powder dispersion coating composition of the present invention may include fillers other than the above-mentioned fibrous fillers. Examples of such fillers include inorganic materials such as metal powders, metal oxides, glass beads, ceramics, silicon carbide, calcium fluoride, carbon black, graphite, glass flakes and mica and other inorganic substrates, PPS (polyphenylene sulfides), PEEK ( Polyether ether ketones), aramids, "Econol (registered trademark of aromatic polyester)" and other heat resistant plastics. Such fillers may be added together with the fibrous heat resistant fillers described above. However, they must have a heat resistance of at least 200 ° C., or preferably at least 300 ° C. and not promote thermal decomposition of the heat-flowable fluororesin. The incorporation of PPS in the range of 0.05% to 5% by weight, based on heat-flowable fluororesin powder with an average particle size of 20 μm or less, is effective to suppress bubbles or bubbles in the coated film in the event of decomposition of the fluororesin powder. .

When the fluororesin powder dispersion is applied by spraying, the dispersion preferably has a viscosity of 8 seconds as measured by Zahn Cup No. 4 Viscometer (manufactured by Toyo Seiki Company). Since it is from 14 seconds, the liquid is prevented from becoming too thin when sprayed, resulting in liquid immersion, or from being too concentrated, resulting in an uneven coating.

The fluororesin powder dispersion of the present invention may be coated directly on the substrate, or the dispersion of the present invention may be applied after first priming the substrate with a primer made of a colloidal solution of PTFE or PFA.

The fluororesin powder dispersions obtained by the present invention are suitable for use for the purpose of corrosion resistance, non-tackiness, abrasion resistance, or for electrical or conductive use by selecting filler types and amounts thereof or overcoating with filler loaded coating materials. Examples of anticorrosive applications include coating of reactors, stirrer blades, exhaust and heat-exchange pipes. Examples of wear protection applications include coating of hoppers, waterways, compressor rotors, paper rolls, split molds and sliding members. Examples of electrical insulation applications are coatings of electrodes.

The invention is illustrated by the following examples. The following describes starting materials such as resins, dispersion media, and other raw materials, as well as methods for testing coated film formation, physical properties of coated films, and the like.

(1) starting material

(a) Heat-flowable fluororesin powder

PFA Powder Products of Mitsui Du Pont Polyfluorochemical Co., Ltd. (average particle size 28 μm, porosity 0.64 and total surface area 0.6 m ² / cm ³ ) FEP Powder Mitsui DuPont Polyfluoro Chemicals Co., Ltd. (average particle size 45 µm, porosity 0.47 and total surface area 0.4 m ² / cm ³ ) ETFE Powder Mitsui DuPont Polyfluoro Chemicals Co., Ltd. (average particle size 22 μm, porosity 0.46 and total surface area 0.7 m ² / cm ³ )

The properties of the fluororesin powder were measured using the following method.

(i) Average particle size:

Micro-Track Method: Measurements were made using a Micro-Track particle size analyzer model 7991-01, a product of Leeds & Northrup Co. (Leeds & Northrup Co.).

(ii) porosity:

Porosity = 1- (apparent specific gravity of powder) / (true specific gravity of material constituting powder)

(iii) total surface area:

Total surface area = (total surface area per gram of powder) x (specific gravity of resin)

The total surface area per gram of powder was measured using the BET method.

(b) colloidal particles

(b-i) colloidal particles of PES

A solution of NMP comprising 5.0% by weight of PES was prepared by dissolving PES (“polyether sulfone 5003P”, product of Sumitomo Chemical Co., Ltd.) while stirring in NMP.

10 g of ethanol were added to 40 g of the solution with stirring to form a clear solution. This solution was then added to 37.5 g of purified water in which 2.5 g of 10.0 wt.% Octylphenoxy polyethoxyethanol was dissolved and stirred to form 2 wt.% Milky colloidal solution prepared from PES colloidal particles. The PES colloidal particles of the colloidal solution were measured using a particle size analyzer (particle size analyzer "Microtrack" UPA 150, manufactured by Nikkiso K. K.), and found to be 0.16 μm.

As described above, the water miscible solvent used in this example was ethanol. Colloidal particles, which are particles suitable for the present invention, are alternatively PES using 10 g of isopropanol, terhydrohydrofurfuryl alcohol, acetone or methyl acetate with particle sizes of 0.16 μm, 0.16 μm, 0.20 μm, 0.18 μm and 0.18 μm, respectively. Prepared by obtaining Similarly, 6.0 wt% and 20 wt% PES solutions in NMP and NMP / DMA were prepared by varying the amount of water-miscible solvent ethanol added and the amount of surfactant to obtain particles ranging from 0.17 μm to 0.20 μm.

It was also observed that when water-miscible solvents were not added to the PES solution prior to the addition of water or surfactant-containing water, a solution with coagulated and milky precipitate was obtained instead of the colloidal particles of the present invention.

(b-ii) other colloidal particles

SiO ₂ Snowtex UP (near diameter of 5 μm to 30 μm and major diameter of 40 μm to 300 μm), a product of Nissan Chemical Industry Co., Ltd. Al ₂ O ₃ Alumina Sol-100 (10 µm in diameter and 100 µm in diameter) from Nissan Chemical Industries, Ltd. SiO ₂ / LiO ₂ Lithium silicate 75 (SiO ₂ / LiO ₂ molar ratio 7.5) from Nissan Chemical Industries, Ltd.

(c) fibrous heat resistant filler

Carbon fiber Carbon fiber M2007S (Normal diameter 14.5 μm and Major diameter 100 μm) from Kureha Chemical Co., Ltd. glass fiber Glass fiber EPG140M (9.0 μm in diameter and 140 μm in major diameter) from Nippon Denki Glass K.K.

(d) foam inhibitors

PPS Toso KK steel can (Susteel Toso KK) riton product ^{(R) (Ryton) V-} 1 pulverized product (average particle size 14 ㎛) of

(e) organic liquid components in the dispersion medium

ethyl alcohol Boiling point 78.3 ℃, surface tension 24.0 dyne / cm t-butyl alcohol Boiling point 82.5 ℃, surface tension 22.2 dyne / cm

(f) other fillers

Polytetrafluoroethylene Molding Powder Mitsui DuPont Polyfluoro Chemicals Co., Ltd. 70-J (average particle size 35 ㎛) Polyether ether ketone 150PF / PB134 (average particle size 35 ㎛) from Mitsui Chemicals

(2) coating formation test method

(a) primer coating

A dispersion prepared by mixing PTFE emulsified polymerized dispersion and PFA emulsified polymerized liquid in a resin ratio of PTFE: PFA = 3: 1 on a SUS plate measured 1 mm thick, 50 mm wide and 100 mm long. The coating was 3 μm to 5 μm thick. The fluororesin powder dispersion was then sprayed to form a layer of a certain thickness. With the coated surface disposed at an angle of 45 DEG, the coated plate was placed in a forced hot air circulation oven, dried using the temperature cycles described in Table I or Table II, and sintered to form a film.

(d) direct coating

A fluororesin powder dispersion was sprayed onto a SUS plate measured 1 mm thick, 50 mm wide and 100 mm long to form a layer of specific thickness. With the coated surface disposed at an angle of 45 DEG, the coated plate was placed in a forced hot air circulation oven, dried using the temperature cycles described in Table I or Table II, and sintered to form a film.

Temperature cycle

Table I-Temperature Cycles for Examples 1-7

PFA (film thickness about 600 μm to about 1200 μm) Heated at 80 ° C. to 110 ° C. over 60 minutes Heated at 110 ° C. to 180 ° C. over 30 minutes Heated at 180 ° C. to 210 ° C. over 60 minutes Heated at 210 ° C. to 310 ° C. over 60 minutes Heated at 310 ° C. to 350 ° C. over 80 Sintered at 350 ° C for 30 minutes

ETFE (film thickness about 600 μm to about 1200 μm) Heated at 80 ° C. to 110 ° C. over 60 minutes Heated at 110 ° C. to 180 ° C. over 30 minutes Heated at 180 ° C. to 210 ° C. over 60 minutes Heated at 210 ° C. to 300 ° C. over 90 Sintered at 300 ° C for 30 minutes

Table II-Temperature Cycles for Examples 8-16

PFA and FEP (film thickness about 300 μm to about 500) Dried at 110 ° C. for 40 minutes and then heated at 210 ° C. over 20 minutes. Dried at 210 ° C. for 40 minutes and then heated at 310 ° C. over 20 minutes Dry at 310 ° C. for 40 minutes, then heat at 340 ° C. over 20 minutes Sintered at 340 ° C. for 20 minutes

ETFE (film thickness about 300 μm to about 500) Dried at 110 ° C. for 40 minutes and then heated at 200 ° C. over 20 minutes Dried at 200 ° C. for 40 minutes and then heated at 280 ° C. over 20 minutes Dry at 280 ° C. for 40 minutes and heat at 310 ° C. over 20 minutes Sintered at 310 ° C for 20 minutes

(3) Characteristic evaluation method

(a) Film formation and peeled state

O: A coating of the desired thickness was formed.

X: The resin powder was peeled off during drying so that no coating was formed.

(b) film thickness:

Measured using a micrometer

<Examples 1 and 2>

Heat-flowable fluororesin powder PFA, liquid mixture of ethanol, t-butanol and ethylene glycol as liquid dispersion medium with a surface tension of 45 dyne / cm or less, carbon fiber as a fiber filler and 2% by weight PPS as a foam inhibitor, are indicated in Table III. A fluororesin powder dispersion was prepared by mixing in the corrected amounts.

Water and 2 wt% PES colloidal solution were then added to the resulting mixture to form a fluororesin powder dispersion.

The fluororesin powder dispersion was coated on a SUS plate by the coating method (2-a) and sintered at the temperature cycle shown in Table IA. The properties of the coatings were evaluated and the results are shown in Table III.

<Example 3>

A fluororesin powder dispersion was prepared in the same manner as in Example 2 except that glass fiber was used instead of carbon fiber as the fibrous filler in Example 2, and the amount of PFA powder was changed to 19.4 g. The composition is shown in Table III.

In the same manner as in Example 2, the fluororesin powder dispersion was coated on a SUS plate and sintered to form a film. The properties of the coatings were evaluated and the results are shown in Table III.

<Example 4>

Fluororesin powder dispersion in the same manner as in Example 2, except that not only the glass fibers used in Example 2 but also 10% by weight of PEEK in the amounts shown in Table III were added and the amount of PFA powder was changed to 16.4 g. Was prepared.

In the same manner as in Example 2, the fluororesin powder dispersion was coated on a SUS plate and sintered to form a film. The properties of the coatings were evaluated and the results are shown in Table III.

<Example 5>

A fluororesin powder dispersion was prepared in the same manner as in Example 2 except that the polytetrafluoroethylene molding powder in the amount shown in Table III was used instead of the PEEK used as another filler in Example 4. The composition is shown in Table III.

In the same manner as in Example 4, the fluororesin powder dispersion was coated on a SUS plate and sintered to form a film. The properties of the coatings were evaluated and the results are shown in Table III.

<Example 6>

Fluororesin was prepared in the same manner as in Example 4, except that 18.0 g of ETFE powder was used instead of PFA used as the heat-flowing fluororesin powder in Example 2, and the amount of carbon fibers was changed to 2.0 g. Powder dispersions were prepared.

In the same manner as in Example 2, the fluororesin powder dispersion was coated on a SUS plate and sintered at the temperature cycles described in Table IB to form a film. The properties of the coatings were evaluated and the results are shown in Table III.

<Example 7>

A fluororesin powder dispersion was prepared in the same manner as in Example 6, except that the amount of the 2 wt% PES colloidal solution used in Example 6 was changed to 20.0 g.

In the same manner as in Example 6, the fluororesin powder dispersion was coated on a SUS plate and sintered to form a film. The properties of the coatings were evaluated and the results are shown in Table III.

<Comparative Example 1>

A fluororesin powder dispersion was prepared in the same manner as in Example 1 except that the PES colloidal solution used in Example 1 was not added.

In the same manner as in Example 1, the fluororesin powder dispersion was coated on a SUS plate and sintered to form a film. The properties of the coatings were evaluated and the results are shown in Table III.

<Examples 8 to 11>

Heat-flowable fluororesin powder PFA, liquid mixture of ethanol, t-butanol and ethylene glycol as liquid dispersion medium with a surface tension of 45 dyne / cm or less, SiO ₂ as colloidal particles, carbon fiber as a fibrous filler and PPS as a foam inhibitor A fluororesin powder dispersion was prepared by mixing in the amounts indicated in IV.

The fluororesin powder dispersion was coated on a SUS plate by the coating method (2-a) and sintered at the temperature cycles described in Table IIA. The properties of the coatings were evaluated and the results are shown in Table IV.

<Examples 12 to 14>

PFA powder as heat-flowable fluororesin powder, liquid mixture of ethanol, t-butanol and water as liquid dispersion medium, Al ₂ O ₃ as colloidal particles, carbon fiber as fibrous filler and PPS as foam inhibitor in the amounts indicated in Table IV A fluororesin powder dispersion was prepared by mixing. The same coating formation and testing methods were used and employed in Examples 8-11, and the coatings were then formed, their properties evaluated and the results are shown in Table IV.

<Example 15>

Examples 8 to 10-11 - a fluid-fluoro use FEP powder in place of the PFA powder used as the resin powders, and the embodiment for using SiO ₂ / LiO _2, instead of the SiO ₂ used in Examples 8 to 11 except for Example 8 A fluororesin powder dispersion was prepared in the same manner as in the above. The same coating formation and testing methods were used and employed in Examples 8-11, and the coatings were then formed, their properties evaluated and the results are shown in Table V.

<Example 16>

Fluororesins were used in the same manner as in Examples 8-11, except that ETFE powder was used instead of the PFA powder used as the heat-flowable fluororesin powder in Examples 8 to 11, and the same components in the amounts shown in Table V were used. Powder dispersions were prepared. The same coating formation and test methods as employed and employed in Examples 8-11 were used, followed by coating and sintering at the temperature cycles described in Table IIB to form primer-free coatings. These properties were evaluated and the results are shown in Table V.

<Comparative Example 2>

A fluororesin powder dispersion was prepared in the same manner as in Example 8 except that the SiO ₂ colloidal particles used in the amounts shown in Table V were not added. Coating and sintering were carried out using the same coating formation and testing methodology employed and employed in Example 8. These properties were evaluated and the results are shown in Table V.

<Comparative Example 3>

A fluororesin powder dispersion was prepared in the same manner as in Example 8 except that SiO ₂ colloid particles and carbon fibers were not added. Coating and sintering were carried out using the same coating formation and testing methodology employed and employed in Example 8. These properties were evaluated and the results are shown in Table V.

In Examples 1-7, a PES colloidal solution was added and in Examples 8-16 an inorganic colloidal solution was added to form a high quality coating. The coating was formed without delamination and separation as shown in the results of Tables III-V. In comparison, when no colloidal particles were added as shown in Comparative Examples 1-2, the coating did not peel off, but separation occurred in about 50% of the coated sample. In Comparative Example 3, in which no colloidal particles or fibrous fillers were added, the coating was peeled off leaving no coating on the substrate.

As a result of the colloidal particle-containing fluororesin powder dispersion of the present invention, it is possible to prevent the coating from peeling off from the substrate during the drying and sintering operation, thereby forming a thicker coated film. The above mentioned effect is even more evident when the fluororesin powder dispersion comprises a fibrous filler of at least 20 μm in diameter and at least two aspect ratios. When such dispersions are applied to a substrate, it is possible to form base materials of good properties such as corrosion resistance, non-tackiness, chemical resistance, abrasion resistance, electrical insulation properties and the like which are useful in the chemical factory and the mechanical industry.

Claims (28)

A heat-flowable fluororesin powder having an average particle size of 5 μm to 300 μm, a porosity of 0.74 or less, and a total surface area of 10 m ² / cm ³ or less, based on the dispersion, from 5% by volume to 50% by volume, the liquid dispersion medium having a surface tension A fluororesin powder dispersion having 45 dyne / cm or less and colloidal particles having an average particle size of 1 μm or less. The fluororesin powder dispersion according to claim 1, wherein the colloidal particles have an average particle size of 0.5 µm or less. The fluororesin powder dispersion according to claim 1, wherein the amount of colloidal particles in the dispersion is 6.0 wt% or less based on the heat-flowable fluororesin powder. The fluororesin powder dispersion according to claim 1, wherein the colloidal particles are selected from the group consisting of colloidal particles of an inorganic oxide and an organic heat resistant resin. The method of claim 4 wherein the colloidal particles are aromatic polyimide, polyaromatic polyamidoimide, aromatic polyamide, aromatic polyester, polyethylene terephthalate, polyphenylene sulfide, polyester ether ketone, polysulfone, polyetherimide and polyether A fluororesin powder dispersion selected from the group of organic heat resistant resins consisting of sulfones. 6. The fluororesin powder dispersion of claim 5 wherein the colloidal particles are polyether sulfones. 5. The fluororesin powder dispersion of claim 4 wherein the colloidal particles are selected from the group of inorganic oxides consisting of silicon oxides, aluminum oxides, zinc oxides and tin oxides. The fluororesin powder dispersion according to claim 1, wherein the porosity of the thermo-flowable fluororesin powder is in the range of 0.34 to 0.65. The fluororesin powder dispersion according to claim 1, further comprising up to 65% by volume or less of fibrous heat-resistant filler having a length of 20 µm and a aspect ratio of 2 or more based on the total solids. The fluororesin powder dispersion according to claim 1, wherein the liquid dispersion medium is a mixture of water and a water-soluble organic liquid. The fluororesin powder dispersion of claim 1, further comprising 0.05 to 5 wt% of polyphenylene sulfide having an average particle size of 20 μm or less based on the heat-flowable fluororesin powder. The fluororesin powder dispersion of claim 1 used to form a coating of 100 μm to 1000 μm in a single film forming step. The fluororesin powder dispersion of claim 1, wherein the fluororesin is a copolymer of tetrafluoroethylene. 14. The fluororesin powder dispersion of claim 13 wherein said tetrafluoroethylene is copolymerized with perfluoro (alkyl vinyl ether). The fluororesin powder dispersion according to claim 13, wherein said tetrafluoroethylene is copolymerized with hexafluoropropylene. 14. The fluororesin powder dispersion of claim 13 wherein said tetrafluoroethylene is copolymerized with ethylene. (1) dissolving polyether sulfone in an organic solvent capable of dissolving it, (2) combining the dissolved polyether sulfone with a water miscible solvent soluble in the organic solvent, and (3) combining water with dissolved surfactant with the dissolved polyether sulfone and water miscible solvent to produce dispersed colloidal particles Method for producing an aqueous dispersion of PES colloidal particles comprising a. The method of claim 17, wherein the average particle size of the colloidal particles is 1 μm or less. The method of claim 17, wherein the average particle size of the colloidal particles is 0.5 μm or less. 18. The method of claim 17, wherein the organic solvent is selected from the group consisting of N-methyl-2-pyrrolidone or dimethylacetamide or a mixture of N-methyl-2-pyrrolidone and dimethylacetamide. 18. The method of claim 17, wherein the water miscible solvent is selected from the group consisting of one or more alcohols, glycols, ketones, and esters. 18. The method of claim 17, wherein the surfactant is nonionic or anionic. 18. The method of claim 17, wherein the solution formed by dissolving the polyether sulfone in step (1) comprises up to 20 weight percent polyether sulfone. An aqueous dispersion comprising polyether sulfone colloidal particles, an organic solvent capable of dissolving polyether sulfone, and a water miscible solvent. The aqueous dispersion of claim 24 wherein the average particle size of the colloidal particles is 1 μm or less. The aqueous dispersion of claim 24 wherein the average particle size of the colloidal particles is 0.5 μm or less. The aqueous dispersion of claim 24 wherein the organic solvent is selected from the group consisting of N-methyl-2-pyrrolidone or dimethylacetamide or a mixture of N-methyl-2-pyrrolidone and dimethylacetamide. The aqueous dispersion of claim 24 wherein the water miscible solvent is selected from the group consisting of one or more alcohols, glycols, ketones and esters.