TWI472584B - Non-stick finish - Google Patents

Description

Non-stick surface coating

This invention relates to non-stick fluoropolymer surface coatings that exhibit improved wear resistance.

The formation of a non-stick fluoropolymer surface coating on a substrate such as aluminum to form a release surface for applications such as cooking utensils generally involves the use of at least two coatings on the substrate, a commonly known The primer is applied to the underlying coating on the substrate, and a coating is provided in addition to the non-stick coating (surface coating). Due to the non-stick properties of the fluoropolymer, the primer is formulated to contain one or more adhesion promoters. Colloidal ceria and a thermally stable polymeric binder (usually fluorine free) are examples of adhesion promoters as disclosed in U.S. Patent No. 5,562,991 to Tannba. The adhesion promoter constitutes a majority of the primer, typically at least 40% by weight based on the combined weight of the fluoropolymer plus adhesion promoter. The surface of the outer coating is rich (even if not at all) of the fluoropolymer. The fluoropolymer present in the primer and overcoat promotes adhesion between the coatings (coating adhesion).

It is known that relatively large particles of inorganic non-metallic particles can be incorporated into the undercoat layer to increase the abrasion resistance of the non-tacky surface coating. EP 0 724 915 to Bignami discloses the use of a SiO ₂ mineral cristobilite having a Moh's hardness of 6.5 (corresponding to a Knoop hardness of 820) in an undercoat layer. U.S. Patent No. 6, 291, 054 to Thomas et al., and U.S. Patent No. 6,761,964 to Tannenbaum discloses the use of hard, large ceramic particles having a Knott hardness of at least 1200 in an undercoat layer. In Example 1 of '054, a single coating system is disclosed in which the single coating is extremely thick (19.5-59.7 microns) and the amount of polymeric binder exceeds the amount of fluoropolymer. In U.S. Patent No. 6,863,974 to Shah et al., there is no fluoropolymer in the undercoat layer, only the heat resistant adhesion promoter (polymer binder) is present together with an average particle size of at least 10 microns and a Mohs hardness of at least 5 Inert inorganic particles (ceramic particles). The adhesion to the coating of the top coat is obtained by including an adhesion promoter in the top coat composition containing the fluoropolymer.

Although the '054 and '964 patents have provided improvements in abrasion resistance on a commercial basis, there is still a need to further improve wear resistance.

The present invention provides a non-stick surface coating on a substrate that exhibits further improved wear resistance. Accordingly, an embodiment of the present invention is a substrate having a non-stick coating thereon, the non-stick coating comprising an overcoat layer and a primer for adhering the overcoat layer to the substrate, The overcoat layer comprises a fluoropolymer and an effective amount of ceramic particles having an average particle size of at least about 10 microns to increase the abrasion resistance of the coating as determined by the dry SBAR process.

Preferably, the effective amount of ceramic particles having an average size of at least about 10 microns is an amount that improves the wear resistance of the coating on the substrate by at least 10% as determined by the dry SBAR method.

The outer coating is not a primer, that is, a non-stick surface coating is formed. The surface coated by the outer coating is not a bare substrate that accommodates the non-stick surface coating. Actually, the substrate has an undercoat layer for adhering to the substrate, and the undercoat layer forms a surface on which a coating layer containing fluoropolymer/ceramic particles is formed. The overcoat layer cannot serve as an undercoat layer because the composition of the overcoat layer does not contain an adhesion promoter, or even if it contains an adhesion promoter, the adhesion promoter is present in such a small amount that it cannot provide a commercial with the substrate. Useful for sticking. Typically, the fluoropolymer is present in the undercoat layer, which is necessary for adhesion to the coating of the non-stick fluoropolymer layer. However, as in U.S. Patent No. 6,863,974, when the primer layer does not contain a fluoropolymer, a small amount of adhesion promoter may be present in the overcoat layer to promote adhesion between the primer layer and the overcoat layer.

Accordingly, the present invention is a combination of the overcoat applied to the undercoat coated substrate as described above. The outer coating can serve as an exposed surface of the non-stick surface coating on the substrate or can serve as an intermediate coating on which the top coating is formed. The topcoat has a fluoropolymer having a concentration greater than the intermediate coating to provide optimum non-stick properties for the entire surface coating. Whether the outer coating is a single layer (on the primed substrate) that forms the exposed surface of the non-stick coating, or an intermediate coating containing a fluoropolymer and ceramic particles having an average size of at least 10 microns, Preferably, the layer contains at least 3% by weight of ceramic particles based on the combined weight of the fluoropolymer and ceramic particles. If an adhesion promoter is present in the layer to promote adhesion between the layer and the undercoat layer, the amount of adhesion promoter should be no greater than 10% by weight of the fluoropolymer in the overcoat layer. As used herein, the expression outer coating refers to the outer coating as a single layer forming the exposed surface of the non-stick surface coating and the intermediate coating in the composite layer of the intermediate coating and the top coating.

Surprisingly, the presence of ceramic particles in the overcoat layer provides a further improvement in the ability to provide abrasion resistance, as will be demonstrated in the examples. Thus, the non-stick surface coating (coating) of the present invention provides surprisingly improved abrasion resistance. For example, a small amount of ceramic particles in the outer coating exhibits greater wear resistance than: (a) the primer contains a relatively large amount of the same ceramic particles, and (b) the outer coating does not contain Any ceramic particles. Surprisingly, placing ceramic particles in the outer coating improves wear resistance compared to the use of ceramic particles only in the undercoat.

In one aspect of the invention, the outer coating has a thickness of from about 0.5 mils to 1 mil (12.7 microns to 25.4 microns). In another aspect, the overcoat layer has a thickness greater than a minor dimension of the ceramic particles. In still another aspect, the thickness of the outer coating is less than the major dimension of the ceramic particles. From the foregoing, it can be seen that the shape of the ceramic particles is generally irregular, and the appearance is similar to gravel or ingot (viewed at magnification), with major dimensions (length or long axis) and minor dimensions (height or short axis). After the overcoat composition is applied from the liquid medium to the primed substrate, followed by drying, the particles tend to stand within the thickness of the resulting overcoat, whereby only the minor dimensions of the particles tend to Spread vertically from the coated substrate. This tends to result in a good non-stick exposed surface that contributes to the non-stick properties of the coating. This intermediate coating can be further coated with a topcoat having substantially all of the fluoropolymer to provide further improvements in release characteristics.

Another embodiment of the invention is the above outer coating (intermediate coating) composition. The composition may be adapted to provide a non-tacky abrasion resistant coating on a surface, particularly on an undercoat layer, the composition comprising a fluoropolymer and an effective amount of ceramic particles having at least about 10 microns The average size is preferably at least 10% improvement of the abrasion resistance of the coating on the surface as determined by the dry SBAR method, and the composition optionally contains up to about 10 parts by weight of the fluoropolymer. % adhesion promoter. Preferably, the amount of the fluoropolymer in the overcoat layer is an effective amount to provide a continuous film in which the ceramic particles are dispersed after application of the composition to a surface to form a coating, the ceramic present in the composition The particles comprise at least about 3% by weight of the combined weight of the fluoropolymer and the ceramic particles. The outer coating composition of the present invention also preferably contains, as other components, inorganic film hardener particles having an average particle size of less than about 5 microns.

The main components of the overcoat layer used in the present invention are a fluoropolymer as a non-tacky component and ceramic particles having an average size of at least 10 μm as a wear-resistant component. These components may also be present in the primer layer along with a sufficient adhesion promoter to achieve adhesion to the substrate containing the non-stick coating.

With regard to the fluoropolymer, the following description applies to the fluoropolymer present in the primer and in the topcoat and topcoat. The fluoropolymer is a fluorocarbon resin. The fluoropolymer may have at least 1×10 ⁷ Pa. A non-meltable fluoropolymer of s melt creep viscosity. One embodiment has the highest thermal stability in the fluoropolymer and has at least 1 x 10 ⁷ Pa at 380 ° C. The s melt creep viscosity of polytetrafluoroethylene (PTFE). The non-meltable PTFE may also contain a small amount of a comonomer modifier which improves the film forming ability during baking (fusion), such as a perfluoroolefin which is especially hexafluoropropylene (HFP), or especially wherein the alkyl group contains 1 Perfluoro(alkyl vinyl) ethers having up to 5 carbon atoms are preferably perfluoro(propyl vinyl ether) (PPVE). The amount of the modifier will not be sufficient to impart meltable manufacturability to PTFE which is typically no greater than 0.5 mole percent. Also for the sake of simplicity, PTFE may have a typical of at least 1 x 10 ⁸ Pa. A single melt creep viscosity, but a mixture of PTFE having different melt viscosities can be used to form a non-stick component.

The fluoropolymer may also be a melt-fabricated fluoropolymer that is combined (blended) with PTFE or substituted for PTFE. Examples of such melt-fabricable fluoropolymers include copolymers of TFE with at least one fluorinated copolymerizable monomer (comonomer) present in the polymer in an amount sufficient to render the copolymer The melting point is substantially reduced below the melting point of the TFE homopolymer polytetrafluoroethylene (PTFE), for example to a melting temperature of no more than 315 °C. Preferred comonomers copolymerized with TFE include perfluoromonomers such as perfluoroolefins having from 3 to 6 carbon atoms, and wherein the alkyl group contains from 1 to 5 carbon atoms, especially from 1 to 3 carbon atoms. (alkyl vinyl ether) (PAVE). Particularly 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, of which PAVE The alkyl group has at least two carbon atoms). The molecular weight of the melt-fabricable tetrafluoroethylene copolymer is not critical as long as it is sufficiently film-forming and can maintain a molded shape for integrity in the undercoat coating. Typically, the melt viscosity will be at least 1 x 10 ² Pa as measured according to ASTM D-1238 at 372 ° C. s, and the upper limit of the range can be as high as about 60-100×10 ³ Pa. s.

A preferred composition is, for example, at 1 x 10 ⁷ Pa. s to 1×10 ¹¹ Pa. A non-meltable fluoropolymer having a melt creep viscosity in the range of s and having, for example, at 1 × 10 ³ Pa. s to 1×10 ⁵ Pa. A blend of melt-fabricated fluoropolymers having a viscosity in the range of s.

When the fluoropolymer is present in an adjacent layer, the fluoropolymer is selected in the undercoat and overcoat and in the intermediate and topcoat layers to be sufficiently compatible with each other to achieve a coating after baking. Adhesion.

The fluoropolymer component is generally commercially available as a dispersion of the polymer in water, which is the primer, overcoat, intermediate coating and top used in the present invention for ease of application and environmentally acceptable purposes. A preferred form of the coating composition. By "dispersion" is meant that the fluoropolymer resin particles are colloidal in size and are stably dispersed in an aqueous medium so that the particles do not settle during the time the dispersion is used. This object is achieved by using small sized fluoropolymer particles typically less than about 0.5 microns and the dispersion manufacturer using a surfactant in the aqueous dispersion. These dispersions can be obtained directly by known methods such as polymerization of an aqueous dispersion, followed by concentration and/or further addition of a surfactant.

Another liquid form of the fluoropolymer to be used to form any of the above layers is a dispersion of the fluoropolymer in an organic liquid. This form is especially useful when the fluoropolymer is a PTFE micropowder of low molecular weight PTFE having melt flowability. The PTFE micropowder can also be used in the form of an aqueous dispersion. The aqueous dispersion of the above fluoropolymer may include a miscible organic liquid.

With regard to the ceramic particle component, the ceramic from which the particles are made is one or more inorganic non-metallic filler materials which are inert with respect to the other components of the composition and at their final baking temperature (fusion of the fluoropolymer) ) The heat is stable. The ceramic particles are insoluble in water and/or solvent so that they are generally uniformly dispersed but are not soluble in the aqueous or organic medium in which the fluoropolymer is dispersed. The ceramic particles preferably have an average particle size of no greater than about 50 microns. The ceramic particles preferably have an average particle size of from about 14 microns to about 36 microns and most preferably from about 20 microns to about 30 microns. Ceramic particles having an average particle size of at least about 10 microns as disclosed herein can be described as large ceramic particles.

The ceramic particles preferably have a Knott hardness of at least 1200 and more preferably at least 1500. Knoop hardness is a measure of the indentation or scratch resistance of a material. The large ceramic particles impart abrasion resistance and durability to the non-stick coating used in the present invention by biasing the abrasion force applied to the surface of the coating.

The large ceramic particles typically have an aspect ratio greater than 1.5, indicating a slightly irregular shape, but preferably no greater than about 5:1 so as not to be disc shaped. As shown in Figure 1 of U.S. Patent No. 6,291,054, the aspect ratio means the ratio of the longest diameter or dimension (long axis or length) of the particle to the maximum distance of the minor dimension (height) measured perpendicular to the longest diameter of the particle. The aspect ratio is a means of quantifying the shape and orientation of the preferred particles.

Examples of the inorganic filler film hardener include inorganic oxides, carbides, borides, and nitrides having a Knott hardness of at least 1200. Preferred are inorganic oxides, nitrides, borides and carbides of zirconium, hafnium, titanium, tungsten, boron, aluminum and cerium. Particularly preferred are niobium carbide and aluminum oxide. Typical Kelvin hardness values of preferred inorganic compositions are: zirconium (1200); aluminum nitride (1225); lanthanum (1300); zirconium nitride (1510); zirconium boride (1560); titanium nitride (1770) Tantalum carbide (1800); tungsten carbide (1880); alumina (2025); zirconium carbide (2150); titanium carbide (2470); niobium carbide (2500); aluminum bromide (2500); titanium boride (2850) . Therefore, it can be seen from the foregoing examples of the ceramic from which the large ceramic particles used in the present invention are prepared that the ceramic is an inorganic compound rather than a single element. Ceramics can also be considered as oxides, nitrides, borides or carbides of metal elements. The large ceramic particle component of the composition used in the present invention may be a single ceramic or a mixture of different ceramic particles. The preferred large ceramic particles are SiC. Another preferred large ceramic particle is Al ₂ O ₃ .

According to the invention, large ceramic particles are present in the outer coating and are also preferably present in the undercoat layer.

The amount of large ceramic particles present in the outer coating is an effective amount that increases the wear resistance of the layer by at least 20% compared to the wear resistance of the layer in the absence of large ceramic particles. More preferably, the large ceramic particles are present in an amount effective to increase the abrasion resistance by at least 50%, and even more preferably by at least 100%, compared to the layer without the large ceramic particles. The amount of fluoropolymer present in the outer coating is at least a sufficient (effective) amount to provide a continuous film after baking the layer, wherein the fluoropolymer forms a matrix in which the large ceramic particles are dispersed. When the content of the large ceramic particles is at least about 3% by weight based on the combined weight of the two components in the coating layer containing the large ceramic particles and the fluoropolymer, preferably the large ceramic particles in the layer and The combined weight of the fluoropolymer is from about 3% by weight to 40% by weight, whereby the fluoropolymer content is from 96% by weight to 60% by weight, and the abrasion resistance is remarkably improved. The amount of fluoropolymer is sufficient to provide the desired film after baking the coating obtained from the composition. More preferably, the large ceramic particles constitute from about 5 to 40% by weight, most preferably from about 5% to 20% by weight, both based on the combined weight of the two components of the layer comprising the particles and the fluoropolymer. Thus, the fluoropolymer content is from 95% by weight to 60% by weight. Such ratios of large ceramic particles to fluoropolymers are suitable for each particle size of the large ceramic particles disclosed above.

Other components may be present in the outer coating of the non-stick coating used in the present invention. For example, the overcoat layer may comprise a small particle size inorganic film hardener, i.e., an inorganic film hardener having an average particle size of less than 5 microns, preferably less than about 3 microns, and more preferably less than about 1 micron. The consistency of the small particle size inorganic film hardener may be the same as that of the large ceramic particles, except that the large particles and the small particles do not have to have the same particle consistency. The presence of the small inorganic film hardener particles does not tend to increase the abrasion resistance of the non-stick coating obtained from the composition used in the present invention, but increases the hardness of the coating and thereby increases its scratch-resistant durability. . Therefore, the outer coating layer used in the present invention may contain from 0 to about 30% by weight of the small inorganic film hardener particles. Preferably, there are about 5% by weight to 30% by weight, more preferably about 8% by weight to 20% by weight, of such small particles, based on the combined weight of the large ceramic particles, the fluoropolymer and the small inorganic film hardener particles in a single layer. .

The outer coating used in the present invention preferably does not contain (i.e., does not have) an adhesion promoter. The adhesion promoter is a material that is typically present in the undercoat layer to adhere the undercoat layer to an uncoated substrate, such as a metallic material, a glass material, or a ceramic material. The fluoropolymer does not adhere to the uncoated substrate due to its non-stick properties and thus does not perform the adhesion promoter function. The fluoropolymer present in the overcoat layer is also not an adhesion promoter, although the fluoropolymer will adhere to the adjacent layer containing the fluoropolymer during the baking process, i.e., to provide a coating Adhesion between layers. However, a small amount of the adhesion promoter may be present in the outer coating composition used in the present invention to obtain adhesion between the coating layers when the layer on which the overcoat composition is applied does not contain the fluoropolymer. Since adhesion promoters present in the layer formed from the composition tend to (a) detract from the non-stick properties of the exposed surface of the layer, and (b) increase the difficulty of spraying the composition in the form of an aqueous dispersion, adhesion promotion The amount of the agent should be as small as possible. The amount of adhesion promoter present in the composition, if present, is preferably no greater than about 8% by weight, more preferably no greater than about 5% by weight, based on the weight of the fluoropolymer in the coating. The composition may also be substantially free of adhesion promoters, i.e., containing less than 2% by weight, preferably less than 1.5% by weight, and more preferably less than 1% by weight of the adhesion promoter, such weight being in the composition. The weight of the polymer.

Adhesion promoters generally do not contain fluorine. Typical adhesion promoters are those used in the undercoat layer, such as colloidal cerium oxide and/or thermally stable polymers, commonly referred to as polymeric binders. Although the polymeric binder is generally free of fluorine, it adheres to the substrate to which the fluoropolymer and the primer are applied. In this case, especially when the primer contains a polymer binder but does not contain a fluoropolymer, the adhesion promoter promotes adhesion between the coating layers. Preferred polymeric binders are polymeric binders which are soluble in water or a mixture of water and an organic solvent used in the binder which is miscible with water. This solubility facilitates blending of the binder with the fluoropolymer component in the form of an aqueous dispersion.

An example of a binder component is a polyamidomate that is converted to polyamidoximine (PAI) after baking the composition. This binder is preferred because it is in the form of a fully yttrium imidized form obtained by baking a polyamidate having a continuous use temperature in excess of 250 °C. The polyamidate can generally be obtained in the form of poly-proline, as measured in a 0.5% by weight solution in N,N-dimethylacetamide at 30 ° C, the polyamine having at least 0.1 Intrinsic viscosity. Dissolving it in a coalescent such as N-methylpyrrolidone, and a viscosity reducing agent such as decyl alcohol, and reacting it with a third amine, preferably triethylamine, to form a salt soluble in water. , as described in more detail in U.S. Patent 4,014,834 (Concannon). The resulting polyammonium containing reaction medium can then be blended with the aqueous fluoropolymer dispersion, and since the coalescent and viscosity reducing agent are miscible in water, the blending procedure produces a uniform coating composition. Blending can be achieved by simply mixing the liquids together without excessive agitation to avoid coagulation of the aqueous fluoropolymer dispersion. Examples of other binders suitable for use with the present invention include polyamidimide (PAI), polyimine (PI), polyphenylene sulfide (PPS), polyether oxime (PES), polyarylene - ether ketone, polyether oximine and poly(1,4(2,6-dimethylphenyl) oxide) (commonly known as polyphenylene ether (PPO)). All such resins are thermally stable at temperatures of at least 140 °C. The polyether oxime is an amorphous polymer having a continuous use temperature (thermal stability) of up to 190 ° C and a glass transition temperature of 220 ° C. The polyamidoximine is thermally stable at a temperature of at least 250 ° C and melts at a temperature of at least 290 ° C. The polyphenylene sulfide was melted at 285 °C. The poly(aryl ether ketone) is thermally stable at a temperature of at least 250 ° C and melts at a temperature of at least 300 ° C.

For the sake of simplicity, only one polymeric binder may be used to form the adhesion promoter component of the topcoat, if present. However, a variety of polymeric binders are also contemplated for use in the present invention. This is especially true for the use of polymeric binders in the basecoat. Preferred polymeric binders are at least one polymer selected from the group consisting of PAI, PES and PPS. This preference applies to the polymeric binder used in the primer and overcoat (if the adhesion promoter is present in the overcoat).

The non-stick coating of the present invention may comprise other filler materials having a Knoop hardness value of less than 1200 in one or more of the non-stick coatings. Suitable other fillers include glass flakes, glass beads, glass fibers, aluminum niobate or zirconium silicate, mica, metal flakes, metal fibers, ceramic fine powder, ceria, barium sulfate, talc, etc., which can be used for the bottom. In the paint, top coat and / or top coat. Non-stick coatings may also contain pigments, depending on the desired color and the particular pigment used. The pigment may be present in any of the primer, top coat and top coat (composition) used in the present invention.

Each layer of the non-stick coating of the present invention can be applied to the substrate in a conventional manner, preferably in the form of a liquid medium, and more preferably wherein the liquid of the medium contains water and the composition applied to the substrate is Aqueous dispersion. The primer may be any of the primers disclosed in the prior art, and usually contains an adhesion promoter such as those described above and a fluoropolymer as an essential component. A variety of polymeric binders can be used in the primer, especially when certain end use properties such as flexibility, hardness or corrosion protection are desired. Common combinations include PAI/PES, PAI/PPS, and PES/PPS. The adhesion promoter in the primer may also include a combination of different adhesion promoters such as colloidal cerium oxide and polymeric binders.

The primer contains an adhesion promoter and the adhesion promoter which may be used in the overcoat layer as described above can be used in the primer. Preferred adhesion promoters for use in the primer include at least one of PAI, PES, and PPS. However, the primer may or may not contain large ceramic particles and may not include fluoropolymers. When large ceramic particles (average size of at least 10 microns) are used in the undercoat layer, they increase the effective amount of wear resistance (dry SBAR) of the non-stick coating in which the outer coating also contains large ceramic particles. presence. Typically, this would require the presence of at least 3% by weight of large ceramic particles in the basecoat based on the total weight of the primer layer (as dry solids). The undercoat layer may also contain up to 60% by weight of large ceramic particles based on the weight of the primer layer (as dry solids). The undercoat layer may also contain an inorganic film hardener having an average particle size of less than 5 μm as described above. The use of a fluoropolymer in the undercoat layer is preferred, but is not required to practice the invention. Thus, the primer may be substantially free of fluoropolymer, i.e., will contain less than 10% by weight, based on the weight of the solids in the basecoat composition, of a fluoropolymer, preferably less than 5% by weight of the fluoropolymer. The solid weight referred to herein refers to the weight after baking.

In general, when the fluoropolymer is present in the primer layer, it will constitute from 10 to 45% by weight of the primer layer, at least 70% by weight of the intermediate coating layer and at least 90% by weight of the overcoat layer. All such weight percentages are based on solids.

Depending on the substrate to which the primer is applied, the coating and roll coating of each layer is the most convenient coating method. Other well known coating methods including dip coating and coil coating are suitable. The overcoat layer can be applied to the undercoat layer by a conventional method before it is dried. However, when the primer and topcoat composition are aqueous dispersions, the overcoat composition may preferably be applied to the primer after drying. The same applies to the application of the top coat to the top coat, which then becomes the intermediate coat of the non-stick surface coating. The topcoat composition can be any of the disclosed topcoat fluoropolymer compositions. When the undercoat layer is prepared by coating the primer composition from an organic solvent, and the overcoat layer is coated with an aqueous medium, the undercoat layer should be dried to coat all of the coat prior to application of the overcoat layer. Solvent incompatible with water. Adhesion properties between the primer and the substrate and coating will be in the dry and baked overcoat as well as the dry and baked primer (mandatory) and topcoat (as appropriate) to form a non-sticky layer on the substrate. After the surface coating, it appears on its own.

The resulting composite layer structure can be baked to simultaneously fuse all of the coating to form a non-stick surface coating on the substrate. When the fluoropolymer is PTFE, a fast high baking temperature is preferred, for example starting at a temperature of 800 °F (427 °C) and rising to 815 °F (435 °C) for 5 minutes. When the fluoropolymer in the primer or overcoat is a blend of PTFE and FEP (for example, 50-70% by weight PTFE and 50-30% by weight FEP), the baking temperature can be 3 minutes (total baking) Within time), it is reduced to 780 °F (415 °C) and rises to 800 °F (427 °C).

The resulting coated substrate preferably has an undercoat layer having a thickness of no greater than 0.6 mils (16 microns), more preferably from 0.3 mils to 0.5 mils (8-13 microns). Preferably, the intermediate coating is thicker than the base coat and more preferably at least 50% thicker. The intermediate coating thickness after baking can range from 0.5 mils to 1.0 mils (12.5 microns to 15 microns). After baking, the intermediate coating (layer) preferably has a thickness greater than the minor dimension of the ceramic particles present in the intermediate coating and less than the major dimension of the particles. Preferably, the intermediate coating is from 0.6 mils to 0.9 mils (15-23 microns) thick and the topcoat layer is from 0.2 mils to 0.5 mils (5-12 microns) thick. The thickness of the layer containing large ceramic particles after baking is measured by the eddy current principle (ASTM B244). The eddy current value reflects the average of the values on the substrate, including the height of the large particles and the depth of the recess between the particles. This method is further described under test methods as being applied to the construction of layers of the coating on the substrate in the formation of a non-stick coating. The thickness of the undercoat layer can also be measured on the baked non-stick coating by splitting the coated substrate (eg, a frying pan) and measuring the thickness from a photomicrograph obtained by scanning electron microscopy (SEM). Measure. By using SEM, the height of the large particles can be distinguished from the depth of the recess between the particles. The SEM value of the thickness of the inner coating of the recess between the particles is reported to be about 50% of the reported eddy current value.

The substrate used in the present invention may be metal or ceramic, and examples thereof include aluminum, anodized aluminum, cold rolled steel, stainless steel, enamel, glass, and high temperature ceramic. These materials may form the entire substrate or, in the case of a composite, only the surface of the substrate. The substrate can be smooth, i.e., has a surface profile of less than 50 micro 吋 (1.25 microns) as measured by a model RT 60 surface tester manufactured by Alpa Co. (Milan, Italy) and needs to be clean. For high temperature ceramics and some glasses, the improved results are obtained by activating the surface of the substrate, such as by slight chemical etching, which is not visible to the naked eye, ie the surface is still smooth. The substrate can also be chemically treated with an adhesive such as a mist-like coating of a polyamidamine, such as disclosed in U.S. Patent No. 5,079,073 to Tannba.

Products having the non-stick surface coating of the present invention include cooking utensils, baking utensils, rice cookers and their inserts, kettles, iron legs, conveyors, chutes, reel surfaces, cutting blades, and the like.

testing method

Dry SBAR test: The non-stick coated substrate was evaluated for the abrasion resistance of the non-stick coating using the SBAR test. This test is based on British Standard Specification BS 7069:1988 for Cooking Appliances, in which the coating system is subjected to a polishing pad attached to a vertical arm that is relatively horizontally moved. The device moves relative to the arm at 100 mm ± 5 mm (4 in. +/- 0.25 in.) from the center of the cylinder at an average speed of ±10 m/min. The polishing pad (3M Scotch-Brite 7447) is a random nylon fabric impregnated with a phenolic resin, and the alumina is fastened to the cylinder and loaded to apply a total force of ±15 N to the coating (arm mass + static) Weight = 4.5 kg or 10 lbs). Test samples were prepared by coating the substrate as illustrated in the examples while drying and baking as specified.

The prepared unwashed coated substrate was tested. The coated substrate is affixed to a fixed support and the loaded polishing pad is applied to a non-stick surface. The sample was held stationary and the pad arm was moved forward and backward at a distance of 50 mm ± 2.5 mm (2 in +/- 0.1 in) on both sides of the center point of the cylinder.

After 250 cycles, the polishing pad was turned over and restarted after another 250 cycles. This procedure is continued until the metal is visible and the number of cycles through which the coating penetrates is then recorded. The coating penetration was the end of the test.

The release test heats the non-stick coated pan to a range of 374 °F (190 °C) to 392 °F (200 °C) and remains within this temperature range throughout the test, such as by contact high temperature on the surface of the substrate. Measured by the meter. Omelette on a pan without seasoning. For this test, the eggs were broken on a pan and cooked for 3 minutes. Lift the egg with a spatula and tilt the pan to allow the egg to slide. Evaluate the ease of egg slip. Reposition the pan on the burner and turn the egg over. Use a spatula to break the egg yolk and cook the egg for another 2 minutes. The ease with which the egg is lifted by the spatula and the spatula removes the egg from the non-stick coating is the release rate of the coating. This release test was repeated after each of the 7500 SBAR test cycles for the non-stick coating. For all non-stick coatings (including comparative coatings) of the following examples, the egg is easily self-adhesive by the spatula during the time when the coating is used in the SBAR test until the metal of the substrate becomes visible for the first time. Sexual surface removal. The exception to this observation was the non-stick coating of Example 12 in Table 8, where the release began to weaken at 45,000 cycles.

Dry film thickness (DFT) baked coating thickness is measured using a film thickness instrument (eg, Fisherscope) based on the eddy current principle (ASTM B244). Thickness measurements were made on test pieces placed in a pan due to the presence of large particles in the coating. To prepare the test piece, a test piece was attached to a metal pan and taped to two adjacent points before any coating was applied. The primer was applied as specified in the examples and a tape was removed to expose the bare metal, and a second test piece was placed thereon. The intermediate coating is then applied and the second tape is removed for exposure, and a third test piece is applied thereon. The measurement of the first test piece provides a total thickness of a total of three coats - primer, intermediate coat and top coat. The measurement of the second test piece provides the thickness of the intermediate coating and the top coating. The measurement of the third test piece provides the thickness of the top coat. The individual values of the primer thickness and the thickness of the intermediate coating are calculated by subtraction. The thickness of the primer is determined by subtracting the thickness value of the second test piece from the thickness value of the first test piece. The thickness of the intermediate coating is determined by subtracting the thickness of the third test piece from the thickness of the second test piece.

Fluoropolymer PTFE dispersion: DuPont TFE fluorine dispersion having a solids content of 59-61% by weight and an RDPS of 170-210 nm. The PTFE fluoropolymer dispersion grade 30 is available from DuPont Company, Wilmington, DE.

FEP dispersion: a TFE/HFP fluoropolymer dispersion having a solids content of 54.5 to 56.5 wt% and an RDPS of 150 to 210 nm, having a HFP content of 9.3-12.4% by weight and a melt flow rate as in, for example, U.S. Patent 4,380,618 The modified ASTM D-1238 method measures 11.8-21.3 g/10 min of resin at 372 °C.

PFA dispersion: DuPont PFA fluoropolymer dispersion having a solids content of 58-62% by weight and an RDPS of 185-245 nm, a PPVE content of 2.9-3.6 wt% and a melt flow rate as taught in, for example, U.S. Patent 4,380,618. The modified ASTM D-1238 method measures 1.3 to 2.7 g/10 min of resin at 372 °C. PFA fluoropolymer dispersion grade 335 is available from DuPont Company, Wilmington, DE.

Polymer binder PAI is Torlon AI-10 poly(Solvay Advanced polymers), a solid resin containing 6-8% of residual NMP (which can be reduced to polyamidomate).

The polyamidate can generally be obtained as a polyglycine having a viscosity of at least 0.1 as measured in a 0.5% by weight solution in N,N-dimethylacetamide at 30 °C. Dissolving it in a coalescent such as N-methylpyrrolidone, and a viscosity reducing agent such as decyl alcohol, and reacting it with a third amine, preferably triethylamine, to form a salt soluble in water. It is described in more detail in U.S. Patent 4,014,834 (Concannon).

Tantalum carbide The tantalum carbide supplied by Elektroschmelzwerk Kempten GmbH (ESK), Munich Germany.

P 1200 = 15.3 ± 1 micron average particle size P 600 = 25.8 ± 1 micron average particle size P 400 = 35.0 ± 1.5 micron average particle size P 320 = 46.2 ± 1.5 micron average particle size F 1000-D = 5-7 micron average particle size average particle size system The FEPA-Standard-43-GB 1984R 1993 resp. ISO 8486 is used by the deposition method to measure according to the information provided by the supplier.

Alumina Alumina (small particles) was supplied by Aluminum Corporation (America) - grade SG A-16, 0.35-0.50 micron average particle size.

Instance

A representative 3-coat non-stick system of the present invention was sprayed onto a test smooth aluminum pan which had been treated by a wash only to remove grease but not mechanically roughened. The aqueous dispersion compositions of the primer, intermediate coating and topcoat are listed in Tables 1, 2, 3 and 4, respectively.

Primer A has a fluoropolymer and SiC. Primer B has a fluoropolymer but does not have SiC. Primer C has SiC but no fluoropolymer.

The intermediate coating A does not contain SiC, and the intermediate coating B contains SiC.

The intermediate coatings C, D, E, F, and J contain about equal amounts of SiC, but have different average particle sizes. The intermediate coatings G, H and I contain the same average particle size SiC but differ in amount.

The primer was sprayed onto an aluminum substrate and dried at 150 °F (66 °C) for 10 minutes. The intermediate coating is then sprayed onto the dry primer. The top coat is wet-to-wet coated (sprayed) onto the intermediate coat. The coating was forced to dry at 300 °F (149 °C) for 10 minutes and then cured at 800 °F (427 °C) for 5 minutes. The dry coating film thickness (DFT) of the primer/intermediate coating/topcoat layer was determined by eddy current analysis as described above by means of a test piece. In general, the thickness is: primer 0.11-0.55 mil (7.8-13.8 micron) / intermediate coating 0.62-0.82 mil (15.5-20.5 micron) / top coat 0.2-0.48 mil (5-12 micron) ).

The examples presented in the table below show the wear resistance of 3-coat systems with different amounts and sizes of SiC particles in the intermediate coating of the coating system. The non-stick coated test pan was subjected to a dry SBAR test to evaluate wear resistance.

SiC Particles in the Intermediate Coating - % Loading Table 5 shows the wear test results for the 3-coating system with SiC particles in the intermediate coating. The SiC particle size system was maintained at 25.8 microns and varied in weight percent. Even for a small amount of SiC, the dry SBAR results are greatly improved and it increases as the SiC particles are loaded higher. There is no SiC particles present in the primer (primer B) used.

SiC Particles in the Intermediate Coating - Particle Size Effect The wear test results for the 3-coating system with SiC particles in the intermediate coating are shown in Tables 6 and 7. The SiC particle size in the intermediate coating was in the range of 5-7 microns to 46 microns and the loading in the dried film was about 12% by weight. In Table 6, the sample also had SiC particles in the primer, and the particles had a particle size of 25.8 microns. In Table 7, the sample did not have SiC particles in the primer. The results show that the dry SBAR results for all samples having particles larger than 14 microns in the intermediate coating are increased, and samples containing SiC particles in the range of 20-30 microns in the intermediate coating have very good results. Comparative Example 2 in which the primer contained 19.30% by weight of SiC and Example 1 in Table 5 in which the SiC particles were absent and only 3.98% by weight of SiC was present in the intermediate coating were compared to reveal the presence of the intermediate coating. Large SiC particles are much more effective than the presence of large SiC particles in the primer. The coating of Example 1 exhibited an improvement in SBAR abrasion resistance over Comparative Example 2 greater than 40%, wherein the amount of SiC used in the primer was 25% less than Comparative Example 2.

Improved calculation %: ((29.0-18.4)÷18.4)×100

Comparison of a system with a fluoropolymer in a primer and a system without a fluoropolymer in a primer. Table 8 shows primer A (fluoropolymer) and C (no fluoropolymer). Abrasion test results were applied to a 3-coat system with an intermediate coating B (13.2% by weight of SiC based on the combined weight of SiC and fluoropolymer). The average SiC particle size in the intermediate coating was 25.8 microns.

In another embodiment of the present invention, a primer having no fluoropolymer is used in combination with an intermediate coating having no adhesion promoter. The primer was similar to the primer C except that the SiC was all P600, that is, 25.2% by weight of the dry weight of the primer composition. The intermediate coating was similar to the intermediate coating D except that the amount of SiC was 11.7% by weight based on the dry weight of the composition. The intermediate coating composition used in this example did not have a PAI adhesion promoter as in the case of the intermediate coating D. The top coat was the same composition as in Table 4. The primer, intermediate coating and topcoat composition were applied sequentially to a substrate (aluminum frying pan) in the same manner as described above to form a non-stick coating on the substrate. The coating thickness (dry) was 0.45 mil (11.3 microns) for the base coat, 0.76 mils (19 microns) for the intermediate coat, and 0.37 mils (9.3 microns) for the top coat. The SBAR test results for this coating were 39,000 cycles.

Claims (9)

a substrate having a non-stick coating thereon, the non-stick coating comprising an outer coating layer and a primer for adhering the outer coating layer to the substrate, the outer coating layer comprising a fluoropolymer and At least 3% by weight of ceramic particles having an average particle size of at least 10 microns, based on the combined weight of the ceramic particles and the fluoropolymer in the overcoat layer, wherein the non-stick coating The layer comprises a top coat comprising a fluoropolymer, and wherein the primer is free of such ceramic particles having an average particle size of at least 10 microns. The substrate of claim 1, wherein the primer comprises an adhesion promoter and, optionally, a fluoropolymer. The substrate of claim 1, wherein an additional inorganic film hardener is present in at least one of the primer and the overcoat, the inorganic film hardener having an average particle size of less than 5 microns. The substrate of claim 1, wherein the thickness of the overcoat layer is at least 50% greater than the thickness of the primer. The substrate of claim 1, wherein the overcoat layer contains an adhesion promoter in an amount of up to 10% by weight based on the weight of the fluoropolymer. The substrate of claim 5, wherein the adhesion promoter is selected from the group consisting of polyamidoximine, polyether oxime, and polyphenylene sulfide. The substrate of claim 1, wherein the overcoat layer is substantially free of an adhesion promoter. The substrate of claim 1, wherein the ceramic particles have a Knoop hardness of at least 1200. The substrate of claim 1, wherein the substrate is a cooking utensil, a baking vessel, a rice cooker and an insert thereof, a kettle, an iron foot plate, a conveyor, a chute, a roll surface, and a cutting blade.