US20010044019A1

US20010044019A1 - Highly filled undercoat for non-stick finish

Info

Publication number: US20010044019A1
Application number: US09/880,264
Authority: US
Inventors: Peter Huesmann
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-05-14
Filing date: 2001-06-13
Publication date: 2001-11-22
Also published as: ES2274790T3; WO2000069984A1; CN1195812C; EP1187887B1; CN1350568A; JP2002544363A; EP1187887A1; DE60031531T2; US6403213B1; DE60031531D1

Abstract

The invention relates to a composition applicable as a undercoat for a non-stick coating on a substrate, comprising (a) inorganic filler of ceramic particles, the particles having an average particle size of 1 micrometer or less and an aspect ratio of not greater than 2.5, (b) adhesion promoter wherein the weight proportion of inorganic filler to adhesion promoter is in the range of 5:1 to 1.7:1, and (c) from 0 to 25 wt. % of a fluoropolymer based on the weight of the composition of the undercoat layer after baking.

Description

RELATED APPLICATION

This application claims the benefit of Provisional Application No. 60/134,358, filed May 14, 1999.[0001]

FIELD OF THE INVENTION

This invention relates to primers and base coats for use with non-stick fluoropolymer coatings.

BACKGROUND OF THE INVENTION

Fluoropolymer resins, and especially perfluoropolymer resins, are known for their low surface energy and non-stick properties as well as thermal and chemical resistance. It has long been desirable to achieve durable non-stick polymer coatings on a variety of substrates. As discussed in U.S. Pat. No. 5,562,991 to Tannenbaum, a primer was developed for use on a variety of substrates, including smooth substrates, which has adequate adhesion both to the substrate and to a fluoropolymer overcoat. Tannenbaum achieved this objective by applying a primer comprising fluoropolymer and polymer binder in the weight proportion of 0.5 to 2.0:1 and in addition, from 5 to 30 weight % of an inorganic film hardener. There still remains a need for fluoropolymer coatings that have improved adhesion to substrates as well as improved scratch, abrasion, and wear resistance.

However in order to achieve a better level of adherence, it would be desirable to develop a coating system which exhibits reduced shrinkage during the drying and curing processes normally associated with the application of fluoropolymer systems. More specifically, such processes which require the application of heat to remove volatile components of the coating system as well as to melt flow and cure organic polymeric components, create dimensional changes in the coating and adversely affect adherence to substrate materials.

A particular concern in the cookware industry is decorative cookware where ceramic coating covers at least a portion of the interior of the cookware. This can occur when a ceramic “frit” is intentionally applied to the interior of the cookware to harden the surface. This can also occur when a ceramic coating is applied to the exterior of a metal preform that is geometrically complex and the masking of the interior is difficult and expensive. In these cases, ceramic over-spray can partially coat the interior of the preform and interfere with the adhesion of a non-stick coating which is subsequently applied.

SUMMARY OF THE INVENTION

The present invention provides a composition which is applicable as a undercoat for a non-stick coating on a substrate, comprising (a) inorganic filler of ceramic particles, the particles having an average particle size of 1 micrometer or less and an aspect ratio of not greater than 2.5, (b) adhesion promoter wherein the weight proportion of inorganic filler to adhesion promoter is in the range of 5:1 to 1.7:1 and (c) from 0 to 25 wt. % of a fluoropolymer based on the weight of the composition of the undercoat layer after baking.

In another embodiment the present invention includes a coated substrate having a non-stick coating, wherein the coating comprises an undercoat and a fluoropolymer overcoat, the undercoat containing (a) inorganic filler of ceramic particles, the particles having a particle size of 1 micrometer or less and an aspect ratio of not greater than 2.5, (b) at least one adhesion promoter wherein the weight proportion of inorganic filler to adhesion promoter is in the range of 5:1 to 1.7:1 and (c) from 0 to 25 wt. % of a fluoropolymer based on the weight of the composition of the undercoat layer after baking.

DETAILED DESCRIPTION

The present invention, in certain of its embodiments, provides a coating system comprising a substrate with a multilayer non-stick coating of a primer, and a top coat with one or more intermediate layers and optionally a base coat applied directly to the substrate beneath the primer. The base coat and primer are referred to as undercoats. The intermediate coating(s) and topcoat are referred to as overcoats. [0008]
Inorganic Filler [0009]
The major component of the undercoat composition of the present invention is an inorganic filler of ceramic particles. The inorganic filler together with a minor amount of adhesion promoter surprisingly produces a smooth, continuous film with superior adhesion to a variety of substrates as well as to fluoropolymer applied as an overcoat to the undercoat. By “undercoat” it is meant either the base coat applied directly to a substrate or a primer applied either to the base coat or to the substrate. By “overcoat” it is meant one or more intermediate coatings or a topcoat which are applied over the primer layer. The high level of inorganic filler present reduces the level of shrinkage that occurs during normal drying and coating operations. By reducing the levels of stress in a coating, adhesion of the coating to a substrate is increased. This reduction results because the levels of stress that contribute to shrinkage are in direct opposition to the force needed to secure the coating layer to the substrate. By increasing the amount of inorganic filler that contributes no or very little shrinkage, the coating comprised of inorganic and organic components undergoes decreased dimensional change upon heat application. The inorganic filler is composed of ceramic particles, the particles having an average particle size of 1 micrometer or less and the weight proportion of inorganic filler to adhesion promoter is in the range of 5:1 to 1.7:1. Thus the inorganic filler is usually present as 45-85 wt. %, preferably 60-85 wt. %, and more preferably 48-72 wt. % of the undercoat composition based on the baked weight, depending on the amount of optional fluoropolymer component. It is to be recognized that the levels of inorganic filler in the present invention are considerably higher than conventionally known compositions such as those disclosed in the prior art represented by U.S. Pat. No. 5,562,991 to Tannenbaum, and U.S. Pat. No. 5,250,356 to Batzar. Additionally, the high level of inorganic filler contributes to increased scratch, wear and abrasion resistance. [0010]
The inorganic filler component is one or more filler type materials that are inert with respect to the other components of the composition and thermally stable at its eventual baking temperature that fuses the undercoat composition and/or subsequent fluoropolymer overcoats. The inorganic filler is water insoluble so that it is typically uniformly dispersible but not dissolved in the aqueous dispersion form of the composition of the invention. Typically, the inorganic filler of this invention preferably comprises ceramic particles having an average particle size of 1 micrometer or less and preferably an average particle size in the range of 0.1 micrometer to 1.0 micrometer. [0011]
It is also preferred that the ceramic particles have an aspect ratio of not greater than 2.5 and preferably not greater than 1.5. By aspect ratio is meant a ratio of the longest diameter of the particle to the greatest distance of a dimension measured perpendicular to the longest diameter (major axis) of the particle. The aspect ratio is a means of quantifying a preferred particle shape. Particles with a high aspect ratio are whisker-like or rod shaped unlike the preferred particles of this invention, which are preferably more spherical and more closely approach an ideal aspect ratio of 1. Also the particle size distribution is preferably narrow with a monodisperse distribution being most preferred. The particle shape and size distribution are important in order to maximize the packing density of the resulting coating. [0012]
The inorganic filler is preferably selected from a group of inorganic nitrides, carbides, borides and oxides. Examples of ceramic particles that may be especially useful include particles of inorganic oxides such as silicon oxide, aluminum oxide, zinc oxide, and tin oxide, and inorganic carbides such as silicon carbide. [0013]
Adhesion Promoter [0014]
The adhesion promoter component of the undercoat composition is preferably composed of organic polymer that is film-forming upon heating to fusion and is also thermally stable. This component is well known in undercoat applications for non-stick finishes, for adhering a fluoropolymer-containing undercoat layer to substrates and for film-forming within and as part of a undercoat layer. The fluoropolymer by itself has little to no adhesion to a smooth substrate. The adhesion promoter is generally non-fluorine containing and yet adheres to the fluoropolymer. In this invention, the adhesion promoter is used as minor component in conjunction with a major amount of inorganic filler. Fluoropolymer as discussed below can also be used as an additional minor component. Preferred adhesion promoters are those that are soluble or dispersible in water or a mixture of water and organic solvent for the adhesion promoter, which solvent is miscible with water. This solubility aids in the blending of the adhesion promoter with the fluoropolymer component (when present) in the aqueous dispersion form. [0015]
An example of the adhesion promoter component is polyamic acid salt which converts to polyamideimide (PAI) upon baking of the composition to form the undercoat layer. This adhesion promoter is preferred because in the fully imidized form obtained by baking the polyamic acid salt, this binder has a continuous service temperature in excess of 250° C. The polyamic acid salt is generally available as polyamic acid having an inherent viscosity of at least 0.1 as measured as a 0.5 wt % solution in N,N-dimethylacetamide at 30° C. It is dissolved in a coalescing agent such as N-methylpyrrolidone, and a viscosity-reducing agent, such a furfuryl alcohol and reacted with tertiary amine, preferably triethylamine, to form the salt, which is soluble in water, as described in greater detail in U.S. Pat. No. 4,014,834 (Concannon). The resultant reaction medium containing the polyamic acid salt can then be blended with a fluoropolymer aqueous dispersion, and because the coalescing agent and viscosity-reducing agent are miscible in water, the blending produces a uniform coating composition. The blending can be achieved by simple mixing of the liquids together without using excess agitation so as to avoid coagulation of the fluoropolymer aqueous dispersion, if present. Other adhesion promoters that can be used include polyether sulfone (PES) and polyphenylene sulfide (PPS). [0016]
When the undercoat composition is applied as a liquid medium, wherein the liquid is water and/or organic solvent, the adhesion properties described above will manifest themselves upon drying and baking of the undercoat layer together with baking of the next-applied layer of fluoropolymer to form the non-stick coating of the substrate. [0017]
For simplicity, only one adhesion promoter may be used to form the adhesion promoter component of the composition of the present invention. However, multiple adhesion promoters are also contemplated for use in this invention, especially when certain end-use properties are desired, such as flexibility, hardness, or corrosion protection. Common combinations include PAI/PES, PAI/PPS and PES/PPS. [0018]
The weight proportion of inorganic filler to adhesion promoter, is preferably in the weight ratio of 5:1 to 1.7:1. The weight ratios of inorganic filler to adhesion promoter disclosed herein are based on the weight of these components in the applied layer formed by baking the composition after application to its substrate. The baking drives off the volatile materials present in the coating composition, including the salt moiety of the polyamic acid salt as the imide bonds are formed during baking. For convenience, the weight of adhesion promoter, when it is polyamic acid salt which is converted to polyamideimide by the baking step, can be taken as the weight of polyamic acid in the starting composition. [0019]
Fluoropolymer [0020]
In addition to the inorganic filler and the adhesion promoter, the undercoat composition of this invention may contain from 0 to 25 wt. %, preferably from 1 to 15 wt. %, of a fluoropolymer based on the baked weight of the composition, and more preferably from 4 to 8 wt. % of a fluoropolymer. The fluoropolymer component of the composition this invention can be non melt-fabricable fluoropolymer with a melt viscosity of at least 1×10[0021] ⁷Pa.s. One embodiment is polytetrafluoroethylene (PTFE) having a melt viscosity of at least 1×10⁸Pa.s at 380° C. with the highest heat stability among the fluoropolymers. Such PTFE can 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(propyl vinyl ether) (PPVE) being preferred. The amount of such modifier will be insufficient to confer melt-fabricability to the PTFE, generally being no more than 0.5 mole %. The PTFE, also for simplicity, can have a single melt viscosity, usually at least 1×10⁹Pa.s, but a mixture of PTFEs having different melt viscosities can be used to form the fluoropolymer component.
The fluoropolymer component can also be melt-fabricable fluoropolymer, either combined (blended) with the PTFE, or in place thereof. Examples of such melt-fabricable fluoropolymers include copolymers of TFE and at least one fluorinated copolymerizable monomer (comonomer) present in the polymer in sufficient amount to reduce the melting point of the copolymer substantially below that of TFE homopolymer, polytetrafluoroethylene (PTFE), e.g., to a melting temperature no greater 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). Preferred 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 in the undercoat application. Typically, the melt viscosity will be at least 1×10[0022] ²Pa.s and may range up to about 60-100×10³Pa.s as determined at 372° C. according to ASTM D-1238. A preferred composition is a blend of non melt-fabricable fluoropolymer with a melt viscosity in the range from 1×10⁷to 1×10¹¹Pa.s and melt fabricable fluoropolymer with a viscosity in the range from 1×10³to 1×10⁵Pa.s.
The fluoropolymer component is generally commercially available as a dispersion of the polymer in water, which is the preferred form for the composition of the invention for ease of application and environmental acceptability. By “dispersion” is meant that the fluoropolymers particles are stably dispersed in the aqueous medium, so that settling of the particles does not occur within the time when the dispersion will be used; this is achieved by the small size of the fluoropolymer particles, typically on the order of 0.2 micrometers, and the use of surfactant in the aqueous dispersion by the dispersion manufacturer. Such dispersions can be obtained directly by the process known as dispersion polymerization, optionally followed by concentration and/or further addition of surfactant. [0023]
Useful fluoropolymers also include those commonly known as micropowders. These fluoropolymers generally have a melt viscosity 1×10[0024] ²Pa.s to 1×10⁶Pa.s at 372° C. Such polymers include but are not limited to those based on the group of polymers known as tetrafluoroethylene (TFE) polymers. The polymers may be directly polymerized or made by degradation of higher molecular weight PTFE resins. TFE polymers include homopolymers of TFE (PTFE) and copolymers of TFE with such small concentrations of copolymerizable modifying comonomers (<1.0 mole percent) that the resins remain non-melt-processible (modified PTFE). The modifying monomer can be, for example, hexafluoropropylene (HFP), perfluoro(propyl vinyl) ether (PPVE), perfluorobutyl ethylene, chlorotrifluoroethylene, or other monomer that introduces side groups into the molecule.
The invention pertains to coated substrates having an undercoat and a fluropoymer overcoat the undercoat containing (a) inorganic filler of ceramic particles, the particles having a particle size of 1 micrometer or less and an aspect ratio of not greater than 2.5, (b) at least one adhesion promoter wherein the weight proportion of inorganic filler to adhesion promoter is in the range of 5:1 to 1.7:1 and (c) from 0 to 25 wt. % of a fluoropolymer based on the weight of the composition of the undercoat layer after baking. Further the invention pertains to coated substrates wherein the overcoat contains inorganic filler of ceramic particles, the particles having an average particle size of 1 micrometer or less. Further the invention pertains to coated substrates wherein the overcoat contains organic adhesion promoter. [0025]
Coating Application [0026]
The compositions of the present invention can be applied to substrates by conventional means. Spray and roller applications are the most convenient application methods, depending on the substrate being coated. Other well-known coating methods including dipping and coil coating are suitable. [0027]
The substrate can be of any material that can withstand the bake temperature, such as metal and ceramics, examples of which include aluminum, anodized aluminum, cold-rolled steel, stainless steel, enamel, glass, and pyroceram. The substrate can be smooth, i.e. having a surface profile of less than 50 microinches (1.25 micrometers) as measured by a model RT 60 surface tester made by Alpa Co. of Milan, Italy, and needs to be clean. The composition of the present invention is especially useful for adhering non-stick coatings to a metal preform that has a rim of ceramic overspray on its interior. [0028]
Products having non-stick finishes made using compositions of the present invention include cookware, bakeware, rice cookers and inserts therefor, water pots, iron sole plates, conveyors, chutes, roll surfaces, cutting blades, etc. [0029]

TEST METHODS

Post Boiling Water Fingernail Adhesion (PWA) [0030]
Coated test substrates are submerged in boiling water for 15 minutes. The water is allowed to come to a full boil after inserting the coated substrate, before timing is begun. After the boiling water treatment, the substrate is cooled to room temperature and dried thoroughly. The fingernail scratch test involves the use of the fingernail, to chip or peel away the coating from the edge of a deliberate knife scratch in the film, to test the degree of adhesion of the film. Improved adhesion is judged by the distinctively increased difficulty in peeling the film from the panel. In some cases the film cannot be peeled from the panel. Cookware passes this test if no coating is removed, even with extended pulling. [0031]
Cross-Hatch Adhesion [0032]
Coated test substrates are submerged in boiling water for 15 minutes. The water is allowed to come to a full boil after inserting the coated substrate, before timing is begun. After the boiling water treatment, the substrate is cooled to room temperature and dried thoroughly. Eleven parallel lines are cut in the coated substrate surface using a template and a razor blade. The template is then rotated 90 degrees and eleven more cuts are made, forming 100 squares on the surface. Reinforced adhesive tape is applied across the squares and pressure is firmly applied to secure the tape to the squares. The tape is then quickly pulled from the squares and the number of squares for which coating has been removed (if any) is recorded. The pan is then rotated and reinforced tape is again applied, pressed and pulled, recording the number of squares for which the coating has been removed. Cookware passes this test if either one or no squares come off on the tape, depending on the type of coating. [0033]

EXAMPLES

Examples 1 and 2 [0034]
Examples 1 and 2 are examples of a four layer coating system using two undercoats which are a base coat made according to the present invention and a primer and two overcoats, an intermediate coating and a topcoat. An aluminum oxide dispersion to be used in formulating base coats for Examples 1 and 2 is prepared in accordance with the ingredients listed in Table 1. An aluminum oxide dispersion to be used in formulating a primer coat and an intermediate coating for Examples 1 and 2 is prepared in accordance with the ingredients listed in Tables 2. A base coat for Example 1 as represented in Table 3 and a base coat as represented in Table 4 are respectively sprayed on two separate smooth aluminum 3004 substrates which have been thoroughly cleaned but not grit blasted or subjected to other chemical treatment. The coatings are dried at 150° F. (66° C.). The coatings are then baked at 300° F. (149° C.) for 5 minutes and then 800° F. (427° C.) for 5 minutes. The resulting brown coating is measured to be 0.26 mil (6.6 micrometers) and 0.16 mil (4.1 micrometers) respectively. An initial nail adhesion test is performed and the coating adhesion is found to be very good. The initial nail adhesion test is performed by scratching with a knife but without the boiling water immersion as described in the PWA test above. A scratch is only made after a good degree of difficulty and the coating can not be peeled back after much effort. [0035]
Both the substrates with base coats are subsequently sprayed with the primer formulation as listed in Table 6 and dried at 150° F. (66° C.). The substrates are then coated with the intermediate coating formulation as listed in Table 7 followed by the topcoat formulation as listed in Table 8. The primer is applied to a thickness of 0.32 and 0.37 mil (8.1 and 9.4 micrometers) respectively; the intermediate coating is applied to a thickness of 0.62 and 0.77 mil (15.8 and 19.6 micrometers) respectively; and the top coat is applied to a thickness of 0.30 and 0.31 mil (7.6 and 7.9 micrometers) respectively. The coated substrates are baked at 300° F. (149° C.) for 5 minutes and then 800° F. (427° C.) for 5 minutes. [0036]
For the base coat compositions of Example 1 and Example 2, the ratio of inorganic filler to adhesion promoter is 4.5:1 and 1.79:1, respectively. [0037]
The coated substrates are subjected to initial adhesion, post boiling water adhesion and cross hatch adhesion tests as described above. No removal of the coating is observed. [0038]
Comparative Example 1 [0039]
For comparison to the present invention, an aluminum substrate having a four coating system (base coat, primer, intermediate coating and topcoat) is prepared with the base coat having inorganic filler particles of substantially larger size than the invention. A base coat for Comparative Example 1 as represented in Table 5 is sprayed on a smooth aluminum 3004 substrate which has been thoroughly cleaned but not grit blasted or subjected to other chemical treatment. The base coat uses a dispersion of aluminum oxide particles wherein the particles have an average particles size of 2.7-3.7 micrometers. The base coat is dried at 150° F. (66° C.). The coating is then baked at 300° F. (149° C.) for 5 minutes and then 800° F. (427° C.) for 5 minutes. The resulting coating is measured to be about 0.3 mil (8 micrometers). [0040]
The substrate with base coat is subsequently sprayed with the primer formulation as listed in Table 6 and dried at 150° F. (66° C.). The substrate is then coated with the intermediate coating formulation as listed in Table 7 followed by the topcoat formulation as listed in Table 8. The primer is applied to a thickness of about 0.3 mil (8 micrometers); the intermediate coating is applied to a thickness of about 0.7 mil (18 micrometers) respectively; and the top coat is applied to a thickness of about 0.3 mil (8 micrometers). The coated substrate is baked at 300° F. (149° C.) for 5 minutes and then 800° F. (427° C.) for 5 minutes. [0041]
For the base coat composition of Comparative Example 1, the ratio of inorganic filler to adhesion promoter is 2.3:1. [0042]

The coated substrate is subjected to post boiling water adhesion as described above. Failure was observed by easy removal of the coating at the substrate interface.

TABLE 1


Aluminum oxide dispersion for base coat of Examples 1 and 2

	Ingredient	Weight %

	deionized water	59.80
	Triton ® X100 surfactant	0.20
	alpha aluminum oxide	40.00
	(AKP-30, made by Sumitomo Chemical Co.
	D50 reported as 0.39 micrometers
	with 96% <1 micrometer; aspect ratio <2.5)
	Total	100.00

Pre-mixed and dispersed with a Mini Motor Mill, Model 250 manufactured by Eiger Machinery Inc.

TABLE 2


Aluminum oxide dispersion for primer and intermediate coating
of Examples 1 and 2, and Comparative Example 1

	Ingredient	Weight %

	deionized water	59.80
	Triton ® X100 surfactant	0.20
	alpha aluminum oxide	40.00
	(AKP-20, made by Sumitomo Chemical Co.
	D50 reported as 0.54 micrometers
	with 95% <1 micrometer; aspect ratio <2.5)
	Total	100.00

Pre-mixed and dispersed with a Mini Motor Mill

TABLE 3


Base coat formulation for Example 1

	Ingredient	Weight %

	Polyamic acid	4.564
	Deionized water	66.479
	Triton ® X100 surfactant	0.101
	Diethyl alcohol amine	0.637
	Triethyl amine	1.274
	Furfuryl Alcohol	3.516
	N-methylpyrrolidone	2.959
	Alpha aluminum oxide AKP-30	20.470
	(% solids in dispersion, Table 1)
	Total	100

TABLE 4


Base coat formulation for Example 2

	Ingredient	Weight %

	Polyamic acid	5.727
	Deionized water	73.427
	Triton ® X100 surfactant	0.051
	Diethyl alcohol amine	0.799
	Triethyl amine	1.598
	Furfuryl Alcohol	4.411
	N-methylpyrrolidone	3.713
	Alpha aluminum oxide AKP-30	10.274
	(% solids in dispersion, Table 1)
	Total	100

TABLE 5


Base coat formulation for Comparative Example 1

	Ingredient	Weight %

	Polyamic acid	7.204
	Deionized water	62.593
	Diethyl alcohol amine	1.005
	Triethyl amine	2.01
	Furfuryl alcohol	5.554
	N-Methylpyrrolidone	4.671
	Sodium Napthalene Sulfate	0.311
	Hydroxypropyl Cellulose	0.072
	Aluminum Oxide 2430-137*	16.58
	Total	100

TABLE 6


Primer formulation for Examples 1 and 2
and Comparative Example 1

	Ingredient	Weight %

	Black pigment	1.366
	Ultramarine blue pigment	3.074
	Ludox ® colloidal silica	0.309
	Zinc Oxide	0.004
	PTFE (solids in aqueous disp)	4.237
	FEP (solids in aqueous disp)	2.799
	Polyamic acid	4.779
	Deionized water	70.675
	Triethanolamine	0.055
	Triton ® X100 surfactant	0.633
	Sodium Polynapthalene Sulfonate	0.102
	Diethyl alcohol amine	0.667
	Triethyl amine	1.334
	Furfuryl Alcohol	3.684
	N-methylpyrrolidone	3.098
	alpha aluminum oxide AKP-20	3.184
	(% solids in dispersion, Table 2)
	Total	100

TABLE 7


Intermediate coating formulation for Examples 1 and 2
and Comparative Example 1

	Ingredient	Weight %

	Black pigment	1.059
	Ultramarine blue pigment	0.307
	Titania coated mica, EM Ind	0.743
	Cerium octoate	0.497
	PTFE (solids in aqueous disp)	28.736
	PFA (solids in aqueous disp)	5.074
	Triton ® X100 surfactant	2.721
	Sodium Polynapthalene Sulfonate	0.079
	Oleic Acid	1.043
	Deionized water	40.238
	Diethylene glycol monobutyl ether	2.062
	Triethanolamine	3.955
	Hydrocarbon Solvent	2.526
	Acrylic (solids in aqueous disp)	4.106
	(terpolymer parts by weight
	39 methyl acrylate/57 ethyl acrylate/
	4 methacrylic acid)
	alpha aluminum oxide AKP-20	6.854
	(% solids in dispersion, Table 2)
	Total	100

TABLE 8


Clear Topcoat formulation for all Examples

	Ingredient	Weight %

	Titania coated mica, EM Ind	0.371
	Cerium octoate	0.583
	PTFE (solids in aqueous disp)	39.677
	PFA (solids in aqueous disp	2.089
	Triton ® X100 surfactant	3.110
	Oleic Acid	1.224
	Deionized water	37.804
	Diethylene glycol monobutyl ether	2.419
	Triethanolamine	4.591
	Hydrocarbon Solvent	2.962
	Acrylic (solids in aqueous disp)	4.106
	(terpolymer parts by weight
	39 methyl acrylate/57 ethyl acrylate/	5.170
	4 methacrylic acid)
	Total	100

Examples 3, 4, 5 [0051]
Examples 3, 4, and 5 are examples of a three layer coating system using one undercoat which is a primer made according to the present invention and two overcoats, an intermediate coating and topcoat. Three separate smooth aluminum 3004 substrates which have been thoroughly cleaned but not grit blasted or subjected to other chemical treatment are partially coated with a black ceramic-based enamel coating to a surface area coverage between 40-50% to be representative of enamel over-spray encountered in the manufacture of decorative cookware. Primer layers for Example 3, 4, and 5 having the formulas as listed in Table 9 are respectively sprayed on the three substrates. The primers are applied at film builds in the range 0.25-0.4 mil (6.4-10 micrometers) and dried at 150° F. (66° C.) for 5 minutes. [0052]
Subsequently intermediate coatings having the formulas as listed in Table 10 are applied for each substrate of Examples 3, 4, and 5. A top coat having the formula listed in Table 8 is applied to all three substrates. The intermediate coating and topcoat are applied at film builds in the range 0.5-0.8 mil (13-20 micrometers) and 0.3-0.5 mil (8-13 micrometers) respectively followed by drying at 300° F. (149° C.) for 5 minutes and then baking at 800° F. (427° C.) for 4-5 minutes. [0053]
The coated substrates are subjected to the cross hatch adhesion test as described above with the exception that boiling water submersion is 20 minutes. Results are listed in Table 11. Adhesion is excellent with none or one square of coating being removed by the tape. [0054]
Comparison Examples 2, 3 [0055]
For comparison to the present invention, two aluminum substrates having a three coating system (primer, intermediate coating and topcoat) are prepared with the primer layers have substantially less inorganic filler than the invention and a greater fluoropolymer content. The substrates are prepared as described in Examples 3, 4, and 5 including having the 40-50% enamel overspray. The compositions of the primer layers are listed in Table 9. The compositions of the intermediate coatings are listed in Table 10. The top coat composition as listed in Table 8 is the same for both substrates. The application of the coatings and processing conditions are the same as described in Examples 3, 4, and 5. [0056]

The coated substrates are subjected to the cross hatch adhesion test as described above with the exception that boiling water submersion is 20 minutes. Results are listed in Table 11 and it is evident that the coatings applied in the Comparison Examples 2 and 3 perform poorly as evidenced by the number of squares of coating removed by the tape.

TABLE 9


Primer formulations for Examples 3-5 and Comp. Examples 2, 3

	Comp.	Comp.
Primers	Ex. 2	Exp. 3	Ex. 3	Ex. 4	Ex. 5

Ingredient	Weight %

Black pigment	1.423	0.305
Ultramarine blue pigment	3.204	1.770
Zinc oxide	0.004	0.002
Zinc Phosphate		0.108
Polyamic acid	4.99	4.719	5.502	5.382	5.323
PTFE (solids in aq. disp.)	4.417	4.211		1.315	1.301
FEP (solids in aq. disp.)	2.916	2.863
Ludox ® colloidal silca	0.314	0.951
Deionized water	69.337	66.368	62.431	61.86	67.532
Triethanolamine	0.14	0.214
Triton ® X100	0.659	0.578	0.187	0.262	0.552
surfactant
Surfynol ® 440		0.244			0.185
Sodium Polynapthalene	0.106	0.023
Sulfonate
Diethyl alcohol amine	0.696	0.659	0.768	0.751	0.743
Triethyl amine	1.393	1.317	1.536	1.502	1.485
2-amino-2-methyl-1-		0.947
propanol
Furfuryl Alcohol	3.842	3.595	4.240	4.147	3.634
N-methylpyrrolidone	3.235	3.060	3.567	3.489	3.451
Calcined aluminum oxide			21.769	21.292	15.794
Alcoa Grade A16 SG,
made by Alcoa Industrial
Chemical Division,
Median Particle size 0.48
microns; aspect ratio
<2.5
Ceralox HPA-0.5	3.324	8.066
aluminum oxide, alpha,
99.98% calcined
aluminum oxide, made
by Condea Vista CO.,
Median Particle size 0.5
microns; aspect ratio
<2.5
Al₂O₃/PAI ratio	0.67	1.71	3.96	3.96	2.97
% Fluoropolymer of	35.61	30.76	0.00	4.70	5.80
Solids

TABLE 10


Intermediate coating formulations for Examples 3-5 and
Comparative Examples 2, 3

	Comp.	Comp.
Intermediate Coatings	Ex. 2	Exp. 3	Ex. 3	Ex. 4	Ex. 5

Ingredient	Weight %

Black pigment	1.032	1.172	0.833	0.797	0.764
Ultramarine blue pigment	0.275	0.255	0.222	0.212	0.203
Titania coated mica,	0.724	0.217	0.584	0.559	0.537
EM Ind
PTFE (solids in aqueous	28.003	39.75	22.594	21.628	20.743
dis)
PFA (solids in aqueous	4.945		3.989	3.819	3.662
disp)
Polyamic acid			1.360	1.739	1.667
Cerium octoate	0.484	0.591	0.391	0.374	0.359
Triton ® X100	2.651	3.124	2.159	2.067	1.982
surfactant
Sodium Polynapthalene	0.077	0.05	0.062	0.059	0.057
Sulfonate
Oleic Acid	1.017	1.241	0.820	0.785	0.753
Deionized water	41.62	38.593	49.160	50.231	52.281
Diethylene glycol	2.01	2.453	1.621	1.552	1.488
monobutyl
Triethanolamine	4.021	4.681	3.110	2.977	2.855
Triethyl amine			0.380	0.485	0.465
Diethyl alcohol amine			0.190	0.243	0.233
2-amino-2-methyl-1-	2.46	3.003	1.986	1.9	1.821
propanol Hydrocarbon
Solvent
Furfuryl Alcohol			1.048	1.187	1.138
N-methylpyrrolidone			0.882	1.127	1.081
Acrylic (solids in	4.002	4.87	3.228	3.100	2.964
aqueous dispersion),
terpolymer of 39 parts by
weight methyl acrylate/
57 parts ethyl acrylate/
4 parts methacrylic acid.
Calcined aluminum oxide			5.381	5.159	4.947
Alcoa Grade A16 SG,
made by Alcoa Industrial
Chemical Division,
Median Particle size 0.48
microns; aspect ratio
<2.5
Ceralox HPA-0.5	6.679
aluminum oxide, alpha,
99.98% calcined
aluminum oxide, made
by Condea Vista CO.,
Median Particle size 0.5
microns; aspect ratio
<2.5

TABLE 11


Cross Hatch Test Results for Examples 3-5
and Comparative Examples 2, 3

Comp.	Comp
Ex. 2	Ex. 3	Ex. 3	Ex. 4	Ex. 5

Total film build	1.40	1.45	1.44	1.49	1.42
(micrometers)
Test 1	2/100	98/100	0/100	0/100	0/100
Test 2	18/100	2/100	0/100	0/100	0/100
Test 3	5/100	27/100	0/100	0/100	0/100
Test 4			1/100

The non-stick coating system of the present invention characterized by having an undercoat containing high levels of inorganic filler of ceramic particles, adhesion promoter and from 0 to 25 wt. % fluoropolymer exhibits reduced shrinkage during the drying and curing processes normally associated with the application of fluoropolymer systems. The coating system has superior adhesion and wear, scratch and abrasion resistance and is especially useful in application to decorative cookware where a ceramic coating covers at least a portion of the interior of the cookware. [0060]

Claims

What is claimed is:

1. Composition applicable as a undercoat for a non-stick coating on a substrate, comprising (a) inorganic filler of ceramic particles, the particles having an average particle size of 1 micrometer or less and an aspect ratio of not greater than 2.5, (b) adhesion promoter wherein the weight proportion of inorganic filler to adhesion promoter is in the range of 5:1 to 1.7:1, and (c) from 0 to 25 wt. % of a fluoropolymer based on the weight of the composition of the undercoat layer after baking.

2. The composition of

claim 1

wherein the amount of fluoropolymer based on the weight of the composition of the undercoat after baking is from 1 to 15 wt. %.

3. The composition of

claim 1

wherein the particle size of the ceramic particles is in the range of 0.1 micrometer to 1.0 micrometer.

4. The composition of

claim 1

wherein the fluoropolymer is non-melt-fabricable.

5. The composition of

claim 1

wherein the fluoropolymer is a blend of non melt-fabricable fluoropolymer with a melt viscosity in the range from 1×10⁷to 1×10¹¹Pa.s and melt fabricable fluoropolymer with a viscosity in the range from 1×10³to 1×10⁵Pa.s.

6. The composition of

claim 1

wherein said adhesion promoter is at least one of polyamide imide, polyimide, polyarylene sulfide and polyethersulfone resins.

7. The composition of

claim 1

wherein the inorganic filler is selected from a group of inorganic nitrides, carbides, borides and oxides.

8. The composition of

claim 7

wherein the inorganic filler is aluminum oxide.

9. The composition of

claim 1

in the form of a baked layer on a substrate.

10. The composition of

claim 9

wherein the substrate prior to coating is smooth.

11. A substrate coated with a non-stick coating, said coating comprising an undercoat and a fluoropolymer overcoat, said undercoat containing (a) inorganic filler of ceramic particles, the particles having a particle size of 1 micrometer or less and an aspect ratio of not greater than 2.5, (b) at least one adhesion promoter wherein the weight proportion of inorganic filler to adhesion promoter is in the range of 5:1 to 1.7:1, and (c) from 0 to 25 wt. % of a fluoropolymer based on the weight of the composition of the undercoat layer after baking.

12. The coated substrate of

claim 11

wherein said undercoat contains from 1 to 15 wt. % of a fluoropolymer based on the weight of the composition of the undercoat after baking.

13. The coated substrate of

claim 11

wherein the undercoat is a base coat on said substrate.

14. The coated substrate of

claim 11

wherein the undercoat is a primer on said substrate.

15. The coated substrate of

claim 11

wherein the undercoat is a primer applied to a base coat.

16. The coated substrate of

claim 11

wherein said substrate prior to coating is smooth.

17. The coated substrate of

claim 11

which is a metal substrate.

18. The coated substrate of

claim 17

wherein at least a portion of the metal substrate is coated with a ceramic coating.

19. The coated substrate of

claim 11

wherein said overcoat comprises an intermediate coating and a topcoat.

20. The coated substrate of

claim 11

wherein said overcoat comprises a fluoropolymer which is a non-melt fabricable fluoropolymer with a melt viscosity in the range from 1×10⁷to 1×10¹¹Pa.s.

21. The coated substrate of

claim 11

wherein said overcoat comprises a fluoropolymer which is a blend of a non-melt fabricable fluoropolymer with a melt viscosity in the range from 1×10⁷to 1×10¹¹Pa.s and melt-fabricable fluoropolymer with a melt viscosity in the range from 1×10³to 1×10⁵Pa.s.

22. The coated substrate of

claim 11

wherein said overcoat contains in addition inorganic filler of ceramic particles, the particles having an average particle size of 1 micrometer or less.

23. The coated substrate of

claim 22

wherein said overcoat contains in addition organic adhesion promoter.

24. The coated substrate of

claim 23