Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D1/00—Coating compositions, e.g. paints, varnishes or lacquers, based on inorganic substances
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D127/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers
  • C09D127/02—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment
  • C09D127/12—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C09D127/18—Homopolymers or copolymers of tetrafluoroethene
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
  • C09D183/04—Polysiloxanes
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/65—Additives macromolecular
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/1204—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material inorganic material, e.g. non-oxide and non-metallic such as sulfides, nitrides based compounds
  • C23C18/122—Inorganic polymers, e.g. silanes, polysilazanes, polysiloxanes
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/125—Process of deposition of the inorganic material
  • C23C18/1254—Sol or sol-gel processing
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/125—Process of deposition of the inorganic material
  • C23C18/1262—Process of deposition of the inorganic material involving particles, e.g. carbon nanotubes [CNT], flakes
  • C23C18/127—Preformed particles
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/36—Silica
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2205/00—Polymer mixtures characterised by other features
  • C08L2205/14—Polymer mixtures characterised by other features containing polymeric additives characterised by shape
  • C08L2205/18—Spheres
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L27/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers
  • C08L27/02—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L27/12—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L27/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers
  • C08L27/02—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L27/12—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C08L27/18—Homopolymers or copolymers or tetrafluoroethene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
  • C08L83/04—Polysiloxanes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
  • C08L83/10—Block- or graft-copolymers containing polysiloxane sequences
  • C08L83/12—Block- or graft-copolymers containing polysiloxane sequences containing polyether sequences
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/13—Hollow or container type article [e.g., tube, vase, etc.]
  • Y10T428/1352—Polymer or resin containing [i.e., natural or synthetic]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/3154—Of fluorinated addition polymer from unsaturated monomers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/3154—Of fluorinated addition polymer from unsaturated monomers
  • Y10T428/31544—Addition polymer is perhalogenated
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31652—Of asbestos
  • Y10T428/31663—As siloxane, silicone or silane
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31678—Of metal

Definitions

• the present invention relates to a sol-gel coating which is based on a sol-gel precursor and which comprises substantially homogeneously distributed fluoropolymer particles.
• Fluoropolymer coatings that provide anti-stick and low-friction properties in medium to high temperature applications such as steam irons or frying pans usually contain a certain amount of heat resistant polymers, such as polyamide imide, which acts as a binder.
• the mechanical properties of these coatings, such as scratch and wear resistance, are inferior to those that contain sol-gel binder materials
• the anti-stick properties of fluoropolymer in sol-gel formulations do not meet the expectations.
• a convenient measure for the anti-stick property is the contact angle with water. The contact angle will depend on the volume fraction of the fluoropolymer particles and their particle distribution in the coating. If the particles are flocculated, there is little chance of finding them at the interface. Consequently the binder will largely determine the contact angle.
• Known sol-gel formulations that are mixed with fluoropolymer tend to comprise a considerable degree of flocculation of the fluoropolymer particles. Consequently, contact angles with a maximum of about 85° can only be achieved.
• the present invention aims to provide a sol-gel coating according to the preamble, which coating provides relatively high anti-stick properties.
• the present invention provides a sol-gel coating, based on a coating composition comprising at least one sol-gel precursor and fluoropolymer particles, which coating has hydrophobic properties such that the contact angle of water at the surface thereof is at least 88°, preferably at least 90°, and more preferably at least 94°.
• a high contact angle results in a high anti-stick property of the coating.
• Said anti-stick property is considerably higher that that of the known coatings of sol-gel binder and fluoropolymer particles in which flocculation of the latter occurs.
• the sol-gel coating composition comprises at least one sol-gel precursor and a stabilized aqueous dispersion of fluoropolymer particles.
• the fluoropolymer particles are stabilized with polysiloxane polyoxyalkylene copolymer.
• the polysiloxane portion of the stabilizer provides the hydrophobic portion of the stabilizer that is attracted to the dispersed fluoropolymer particles, and the oxyalkylene portion of the stabilizer provides the hydrophilic portion of the stabilizer enabling the stabilizer to be dispersed in the aqueous medium, the presence of these two portions enabling the stabilizer to function as such in the dispersion.
• the polysiloxane polyoxyalkylene copolymers used in the present invention are nonionic, i.e. free of electrical charge, with the stabilization effect being achieved by the presence of the hydrophobic and hydrophilic portions of the stabilizer.
• the sol-gel coating according to the present invention also comprises filler particles, in particular silica particles.
• filler particles in particular silica particles.
• Such particles may originate from aqueous silica sol.
• Sol-gel materials undergo significant shrinkage upon curing, and therefore they are advantageously filled with other particles, often silica particles, in order to achieve a sufficient layer thickness for the application.
• the volume fraction of fluoropolymer particles in the sol-gel coating is lower than 50%.
• the volume fraction of fluoropolymer particles in the sol-gel coating is in the range of 15-30%.
• the fluoropolymer particles in the coating comprise polytetrafluoroethylene (PTFE) particles having a melt viscosity of at least 1 x 10 8 Pa «s at 380°C, which has the highest heat stability among the fluoropolymers.
• PTFE polytetrafluoroethylene
• Such PTFE may also contain a small amount of comonomer modifier which improves film- forming capability during baking (fusing), such as perfluoroolefin, notably hexafluoropropylene (HFP) or perfluoro(alkyl vinyl) ether, notably wherein the alkyl group contains 1 to 5 carbon atoms, with perfluoro(ethyl or propyl vinyl ether) (PEVE or PPVE) being preferred.
• HFP hexafluoropropylene
• PEVE or PPVE perfluoro(ethyl or propyl vinyl ether)
• the amount of such a modifier will be insufficient to confer melt fabricability to the PTFE, generally being no more than 0.5 mole%.
• the PTFE may also be of the micropowder type, wherein a chain transfer agent is present in the aqueous polymerization medium to produce low molecular weight PTFE, characterized by a melt viscosity of 0.1-100 X 10 3 Pa»s at 372°C.
• a chain transfer agent is present in the aqueous polymerization medium to produce low molecular weight PTFE, characterized by a melt viscosity of 0.1-100 X 10 3 Pa»s at 372°C.
• Such PTFE is melt-flowable, but not melt- fabricable, i.e. when fabricated from the melt, the fabricated article of such PTFE lacks integrity and fractures either spontaneously or upon being subjected to slight stress.
• the fluoropolymer component may also be melt-fabricable fluoropolymer.
• melt-fabricable fluoropolymers include copolymers of tetrafluoroethylene (TFE) and at least one fluorinated copolymerizable monomer (comonomer) present in the polymer in a sufficient amount to reduce the melting point of the copolymer to substantially below that of PTFE homopolymer, e.g. to a melting temperature no higher than 315°C.
• Preferred comonomers with TFE include the perfluorinated monomers such as perfluoroolefins having 3-6 carbon atoms and perfluoro(alkyl vinyl ethers) (PAVE) wherein the alkyl group contains 1 -5 carbon atoms, especially 1-3 carbon atoms.
• Especially preferred comonomers include hexafluoropropylene (HFP), perfluoro(ethyl vinyl ether) (PEVE), perfluoro(propyl vinyl ether) (PPVE), and perfluoro(methyl vinyl ether) (PMVE).
• TFE copolymers include FEP (TFE/HFP copolymer), PFA (TFE/PAVE copolymer), TFE/HFP/PAVE wherein PAVE is PEVE and/or PPVE, and MFA (TFE/PMVE/PAVE wherein the alkyl group of PAVE has at least two carbon atoms).
• the molecular weight of the melt-fabricable tetrafluoroethylene copolymers is unimportant except that it be sufficient to be film- forming and be able to sustain a molded shape so as to have integrity, i.e. being melt-fabricable. Typically, the melt viscosity will be
• 2 3 at least 1 x 10 Pa*s and may range up to about 60-100 x 10 Pa*s as determined at 372°C according to ASTM D-1238.
• the fluoropolymer particles containing sol-gel formulations are preferably made from hybrid sol-gel precursors, comprising an organosilane compound.
• Preferred sol- gel precursors comprise methyltri(m)ethoxysilane, phenyltri(m)ethoxysilane, di ⁇ henyldi(m)ethoxysilane, glycidoxypropyl-tri(m)ethoxysilane, or combinations thereof.
• a small amount of a non-hybrid sol-gel precursor material such as tetra(m)ethoxysilane may be added.
• the sol-gel coating according to the present invention is temperature-resistant up to 400°C.
• sol-gel formulations mixed with aqueous dispersions of fluoropolymer particles are obtained, without the occurrence of flocculation of the fluoropolymer particles.
• Coatings made with these formulations have an improved hydrophobicity due to the better distribution of fluoropolymer particles.
• at least 80 % of the fluoropolymer particles are present as substantially free, non-aggregated particles within the coating.
• the sol-gel coating according to the present invention is advantageously deposited on a substrate.
• the substrate may be of any material which can withstand high baking temperature, such as metal and ceramics, examples of which include aluminum, or an aluminum alloy, cold-rolled steel, stainless steel, enamel, glass, and pyroceramic materials
• the aluminum sole plate of a (steam) iron may be mentioned as an example.
• the sol-gel coating according to the present invention is applied in domestic appliances to form coated articles, such as steam irons, toasters, sandwich makers, kettles and coffee makers, vacuum cleaners, fans and domestic air treatment devices, mixers and food processors, ice cream makers, deep fat fryers, grills and electric gourmet sets and woks.
• coated articles such as steam irons, toasters, sandwich makers, kettles and coffee makers, vacuum cleaners, fans and domestic air treatment devices, mixers and food processors, ice cream makers, deep fat fryers, grills and electric gourmet sets and woks.
• sol-gel coatings find further applications in articles such as cookware, frying pans and other cooking pots and utensils, bakeware, oven liners, rice cookers, and inserts therefor.
• sol-gel coatings of this invention have many industrial uses for articles such as cutting blades, valves, wire, shoe molds, snow shovels and plows, ship bottoms, chutes, conveyors, roller surfaces, dies, tools, industrial containers, molds, lined reactor vessels, automotive panels, heat exchangers, tubing, and the like.
• the present invention also relates to a method of obtaining a sol-gel coating in which fluoropolymer particles are not flocculated but are mostly present as single individual particles.
• the present invention provides a method of preparing a sol-gel coating comprising fluoropolymer particles, said method comprising the steps of:
• these fluoropolymer particles containing sol-gel formulations can be made from sol-gel precursors such as methyltri(m)ethoxysilane (MTMS, MTES), which is often used in scratch-resistant and temperature-resistant coatings, for example on the sole plates of laundry irons.
• sol-gel precursors such as methyltri(m)ethoxysilane (MTMS, MTES), which is often used in scratch-resistant and temperature-resistant coatings, for example on the sole plates of laundry irons.
• MTMS, MTES methyltri(m)ethoxysilane
• Sol-gel precursors are not soluble in water, so alcohols are often added to obtain a single-phase system right from the start of the hydrolysis reaction in common practice.
• the fluoropolymer dispersion may be modified to give an improved compatibility with the sol-gel coating liquid, or the sol-gel lacquer formulation may be adjusted to arrive at a better compatibility with the fluorocarbon dispersion. In practice a combination of these two approaches will prove most useful.
• fluoropolymer particles are stabilized with a polysiloxane polyoxyalkylene copolymer.
• the addition of alcohols to these dispersions may easily lead to changes in the layer of adsorbed surfactants with respect to the adsorbed amount and orientation of the surfactant molecules, which may result in the loss of colloidal stability.
• the amount of alcohol used needs to be minimized.
• Alcohol is formed in the hydrolysis and alcohol condensation reactions of the sol-gel precursors. This is inevitable in sol-gel processing.
• the addition of alcohol to ensure a single phase from the beginning of the hydrolysis reaction is not necessary if the precursors are thoroughly mixed with water.
• Aqueous silica sols are often used for this purpose.
• Flocculation of the silica sol can be avoided during the hydrolysis of the sol-gel precursors by the adjustment of its pH value to around 3, preferably by dissolving a solid acid such as maleic acid, followed by the addition of a very small amount of a sol-gel precursor, for instance methyltrimethoxysilane.
• the amount of sol-gel precursor will be about 0.01-1% of the total amount of sol-gel precursor that is ultimately added. This small amount is hydrolyzed in the sol and will adsorb onto the surface of the silica particles.
• Such a treatment makes the colloidal stability of the silica less dependent on the amount of alcohol produced in the hydrolysis of the bulk of the silanes, which can cause flocculation. It has been documented frequently that, upon addition of sol-gel precursors, silica sols first show an increase in turbidity, indicating flocculation, later followed by a decrease in turbidity, indicating restabilization. This is not desirable as the restabilization may not be complete and additional filtering steps may be required. The stepwise addition of the sol-gel precursor can prevent this.
• the above method differs from the one described in Handbook of Advanced Electronic and Photonic Materials 5, pp.219-262, 2000, Academic Press, where the sol-gel precursor is prehydrolyzed and leads to a more dilute formulation.
• the prehydro lysis step also leads to the formation of partially condensed products, which have a much lower affinity for the silica surface, and may lead to insufficient stabilization of the silica particles to withstand the second addition of MTMS without the occurrence of flocculation.
• the fluoropolymer dispersion can be added and no flocculation will occur.
• the resulting formulation can then be applied by spray coating. After curing, a coating of 10 ⁇ m thickness can be obtained in which the fluoropolymer particles are homogeneously distributed, leading to a high contact angle with water.
• Fig. 1 schematically represents the definition of contact angle
• Fig. 2 is a Scanning Electron Microscopy image showing a cross-section of a sol-gel basecoat layer provided with a sol-gel/PTFE topcoat layer prepared according to Example 1;
• Fig. 3 is a Scanning Electron Microscopy image showing a cross-section of a sol-gel basecoat layer provided with a sol-gel/PTFE topcoat layer prepared according to Comparative Example 1;
• Fig. 4 schematically shows an iron, the sole plate of which is provided with a sol-gel coating comprising homogeneously distributed fluoropolymer particles.
• Figure 1 schematically represents the definition of contact angle.
• Reference numeral 1 indicates a coating surface.
• a water droplet on said coating surface 1 is indicated by reference numeral 3.
• Line 4 is tangent to the outer surface of the droplet 3 at the intersection with the surface 1.
• the contact angle is defined as the angle between line 4 and the surface 1.
• the contact angle was measured using a Surface Contact Angle Goniometer manufactured by Rame-Hart Inc, USA.
• the following examples illustrate the fluoropolymer- containing sol-gel coating according to the present invention and the method of preparation thereof, compared with sol-gel coatings and methods of preparation thereof according to the prior art.
• Example 1 In a reaction vessel 5.5g of maleic acid was dissolved in 380g of Ludox AS40. The measured pH value of the acidified silica sol was between 2.5 and 2.9. 0.95g of MTMS was then added and the mixture was stirred for 45 minutes. Subsequently 391g of MTMS was stirred into the acidified and surface-modified silica sol. 60 minutes later the mixture was diluted with 196g of water before the gradual addition of 315g of a 30% polytetrafluorethylene (PTFE) dispersion in water stabilized with a polysiloxane polyoxyalkylene copolymer (SILWET L77 ®) together with a suitable defoaming agent. After the addition of the PTFE had been completed, 30g of a mica-based pigment was added.
• PTFE polytetrafluorethylene
• Coatings were sprayed on previously dried sol-gel layers applied on anodized aluminum plates and cured at 300°C.
• the amount of PTFE particles in the cured coating was approximately 18% by volume.
• the water contact angle of the cured coating was determined at 94 ⁇ 2°.
• the PTFE particles were homogeneously distributed through the coating and no sign of flocculation could be observed from the cross-sectional images obtained by Scanning Electron Microscopy.
• a typical cross-sectional picture is given in Figure 2.
• the sprayed coating properties in terms of gloss, scratch resistance, and water contact angle were the same for coatings sprayed immediately after preparation and for coatings sprayed 8 hours after completion of the coating liquid formulation.
• the viscosity of the coating lacquer remained constant over this period of time.
• This example is comparable to example 1, except that the ratio of silica particles to polytetrafluorethylene (PTFE) particles was adjusted to increase the volume fraction of PTFE in the final coating.
• PTFE polytetrafluorethylene
• Coatings were sprayed on previously dried sol-gel layers applied on anodized aluminum plates and cured at 300°C.
• the amount of PTFE particles in the cured coating was approximately 30% by volume.
• the water contact angle of the cured coating was determined at 98 ⁇ 2°.
• This example is comparable to example 1, except that the ratio of silica particles to polytetrafluorethylene (PTFE) particles was adjusted to reduce the volume fraction of PTFE in the final coating.
• PTFE polytetrafluorethylene
• the measured pH value of the acidified silica sol was between 2.5 and 2.9. l.lg of MTMS was then added and the mixture was stirred for 45 minutes. Subsequently 385g of MTMS was stirred into the acidified and surface-modified silica sol. 60 minutes later the mixture was diluted with 193g of water before the gradual addition of 194g of a 30% PTFE dispersion in water stabilized with a polysiloxane polyoxyalkylene copolymer (SILWET L77 ®) together with a suitable defoaming agent. After the addition of the PTFE had been completed, 37g of a mica-based pigment were added.
• SILWET L77 ® polysiloxane polyoxyalkylene copolymer
• Coatings were sprayed on previously dried sol-gel layers applied on anodized aluminum plates and cured at 300°C.
• the amount of PTFE particles in the cured coating was approximately 10% by volume.
• the water contact angle of the cured coating was determined at 89 ⁇ 3°.
• a polytetrafluorethylene (PTFE) dispersion stabilized with an alkyl phenol ethoxylate surfactant 348 g of MTMS was mixed with 18 g of mica- based pigment, 5 g of maleic acid, and 174 g of ethanol. The hydrolysis was started by addition of 345 g Ludox AS40. After one hour of continuous stirring a suitable defoamer was added, followed by the addition of 107 g of a commercially available PTFE dispersion consisting of 62 weight% PTFE particles stabilized by an alkyl phenol ethoxylate surfactant and 3.5 g of a perfluoroalkylsulfonamido oxyethylene surfactant.
• PTFE polytetrafluorethylene
• the PTFE primary particle size was around 250 nm. After mixing for at least 15 minutes, this coating liquid was sprayed on previously dried sol-gel layers applied on an anodized aluminum ironing plate of a steam iron and was cured at 300°C.
• a Scanning Electron Microscope picture of the cross-section of the coating is given in Figure 3. The picture shows inhomogeneities in the coating, caused by flocculation of the PTFE particles. Energy Dispersive Analysis of X-rays reveals that the inhomogeneity is rich in fluorine, indicative of flocculated PTFE particles. The flocculation of the PTFE particles reduces the PTFE amount at the surface and results in water contact angles of only 84+2°.
• PTFE polysiloxane polyoxyalkylene copolymer
• Coatings were sprayed on previously dried sol-gel layers applied on anodized aluminum plates and cured at 300°C.
• the gloss of the first coating sprayed was much higher than that of a coating sprayed 2 hours after completion of preparation of the coating liquid.
• the viscosity had increased to unacceptably high values after no more than 2 hours.
• the amount of PTFE particles in the cured coating was approximately 18% by volume, however, the water contact angle of the cured coating was determined at only 82 ⁇ 3°.
• FIG 4 is a schematic side view of an iron according to the present invention.
• Said iron comprises a housing 5, which may be made of a synthetic resin material.
• the bottom side of the housing is provided with a metal sole plate 6.
• the sole plate is made of a block 7 of diecast aluminum to which a thin plate 8 of aluminum is secured. This thin plate 8 is also referred to as the ironing plate.
• the aluminum plate may comprise aluminum as well as an aluminum alloy.
• a sol-gel coating 10 comprising homogeneously distributed fluoropolymer particles, according to the present invention, is applied on top of the thin plate 8. Said sol-gel coating provides a very good wear and scratch resistance, as well as high anti-stick properties, which is very advantageous for the gliding properties of the sole plate.

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