WO2021077296A1

WO2021077296A1 - Non-stick cookware coating

Info

Publication number: WO2021077296A1
Application number: PCT/CN2019/112567
Authority: WO
Inventors: Ngai Kin LAM
Original assignee: Foshan Shi Shunde Jetwell Stainless Steel Products Limited
Priority date: 2019-10-22
Filing date: 2019-10-22
Publication date: 2021-04-29
Also published as: CN114008144A

Abstract

A method of manufacture of a coated substrate comprises the steps of applying to the substrate a first coating layer of a primary particulate composition comprising, by weight: SiO₂ 40-50 parts AI₂O₃ 8-15 parts Fe₂O₃ 1-2 parts ZrO₂ 5-8 partsTiO₂ 6-12 parts and a volatile liquid; allowing the liquid to vaporise to form a primary coated substrate; applying to the primary coated substrate a second coating of a secondary particulate composition comprising, by weight: SiO₂ 30-45 parts 8-10 parts AI₂O₃ Fe₂O₃ 1-2 parts ZrO₂ 3-5 partsTiO₂ 8-15 parts and a volatile liquid: heating the substrate to cause volatilisation of the volatile liquid; and further heating to form a coated substrate having a non-stick coating.

Description

NON-STICK COOKWARE COATING

This invention relates to a non-stick coating particularly, but not exclusively, for application to cookware. The invention also relates to coatings for other products such as domestic cooking or storage vessels, utensils or other equipment, for example for use in restaurants or food manufacturing facilities. The invention further relates to a method of application of the coating to cookware or other products or equipment.

Commercially available non-stick coatings for cookware, for example composed of polytetrafluoroethylene (PTFE) can not reach a hardness value of 9H or withstand a heating test at 400℃.

According to a first aspect of the present invention, a method of manufacture of a coated substrate comprises the steps of:

applying to the substrate a first coating layer of a particulate composition comprising, by weight:

and a volatile liquid;

allowing the liquid to vaporise from the substrate to form a primary coated substrate;

applying to the primary coated substrate a second coating of a secondary particulate composition comprising by weight:

and a volatile liquid,

heating the substrate to cause volatilisation of the volatile liquid; and further heating to form a non-stick coating on the substrate.

Parts, percentages or other amounts referred to in this specification are by weight unless indicated otherwise. Percentages, but not parts, may be selected from any ranges given to total 100%.

The substrate and first coating composition may be heated to volatilise the liquid.

The substrate may be an enamel coated surface, for example of a cooking vessel, utensil or other product or equipment. The amounts of the oxides referred to above, may each independently have a tolerance of ± 5%w/w of the stated range of parts by weight.

One or both of the first and second coating compositions are preferably applied by spraying.

The liquid may be a volatile organic liquid. Preferably the same liquid is used for the first and second coating compositions. Mixtures of liquids may be employed.

In a preferred embodiment, the liquid may be an alcohol or mixture of alcohols, more preferably ethanol. Ethanol has been found to be advantageous to allow formation of a homogeneous suspension of the oxide mixture with wetting of the substrate surface.

In a preferred embodiment the first coating layer is applied to an enamel coated surface of a substrate.

Alternatively, the coating may be applied directly to an uncoated metallic surface of a substrate.

The primary and secondary coatings may consist, or consist essentially, of the recited ingredients. In this specification, the term “consist essentially of” refers to a composition comprising the recited ingredients in the sense that no further compounds or ingredients are present in functional amount sufficient to affect the essential properties of the composition, excluding possible traces of impurities.

An enamelled substrate surface or uncoated metal surface may be prepared by sandblasting or other abrasion to remove any superficial oxide layer, imperfections or impurities and to provide a roughened surface adapted to form a strong bond to the coating layer.

The surface may be roughened by sandblasting using 80 to 100 mesh particles, preferably alumina particles. The particles may be applied to the surface using an air gun with a pressure of 0.5 to 0.8 MPa.

The roughened surface may have a texture with cavities to a depth of 30 to 60 μm.

The primary and secondary coating layers may be heated to a temperature greater than 200℃, preferably in the range 200-350℃, more preferably in the range 250-300℃, more preferably in the range 275-300℃, particularly in the range 285-295℃.

The duration of the heating may be in the range 5-20 minutes, preferably 5-15 minutes, more preferably 8-10 minutes.

The thickness of the primary coating after evaporation of the liquid may be in the range 2-20μm, preferably 3-15μm, more preferably 5-10μm.

According to a second aspect of the present invention an article comprises a substrate having a surface coated with a composition applied by the method of the first aspect of the present invention.

The article may comprise cookware having a non-stick surface, made by a method in accordance with the first aspect of the present invention.

A preferred primary coating composition consists of:

Base Coat

Component	CAS Registry No.	wt. %
SiO ₂	7631-86-9	40-50%
Al ₂O ₃	1344-28-1	8-15%
Fe ₂O ₃	1309-37-1	1-2%
ZrO ₂	1314-23-4	5-8%
TiO ₂	13463-67-7	6-12%
Ethanol		5-8%

The mixture had a particle size of 30nm ±5nm.

A preferred secondary coating composition consists of the following composition:

Top Coat

Component	CAS Registry No.	Wt. %
SiO ₂	7631-86-9	30-45%
Al ₂O ₃	1344-28-1	8-10%
Fe ₂O ₃	1309-37-1	1-2%
ZrO ₂	1314-23-4	3-5%
TiO ₂	13463-67-7	8-15%
Ethanol		5-10%

A coating in accordance with the present invention confers many advantages in relation to conventional non-stick coatings composed for example of PTFE. A hardness value, for example on a pencil hardness scale of 9H, using a Japanese Mitsubishi pencil, may be achieved in comparison with a hardness of 1H for a PTFE non-stick coating.

A working temperature of 400℃ may be achieved in comparison with a maximum working temperature of 260℃ for a PTFE non-stick coating.

The coating may be washed and cleansed using a scouring pad. This is not possible with a PTFE coating.

Cookware or other products coated in accordance with this invention emit a higher release of far infra-red radiation (FIR) in comparison to conventional PTFE-coated non-stick cookware.

Metal utensils may be used without damaging the surface. In contrast, PTFE non-stick surfaces may be scratched or damaged, particularly on prolonged use of metal utensils. Utensils made of wood, bamboo, nylon or silicone are recommended for use with PTFE-coated cookware.

Release of FIR has the advantage of improving the taste of food, particularly in frying steak or other meats. In addition to improving the taste of foods cooked using utensils for this invention, fast transmission of heat and retention of heat by carbon steel substrate utensils can save energy heating during cooking. A carbon steel frying pan or other cookware is less heavy than a corresponding cast iron pan. The performance of the coated layer is superior to a cast iron frying pan. Furthermore, less cooking oil may be used due to the excellent non-stick performance of the coating.

The invention is further described by means of example, but not in any limitative sense.

Example 1:

A coated frying pan or other cooking utensil was made using the following procedure.

An enamel-coated substrate was prepared as follows.

A carbon steel body was cleaned until free from grease and rust. A first enamel layer was applied with kilning up to a temperature of 830 to 860℃. The enamelled metal body was allowed to cool to room temperature. A second enamel layer was applied with kilning to 830 to 860℃.

After two enamel coating processes the thickness of the enamel layer was in the range of 150 to 180μm. The enamel surface was sandblasted using 80-100 mesh alumina grains and an air gun with a pressure of 0.5 –0.8 MPa resulting in an irregular texture with a depth of 30-60μm.

The cookware was heated to 36-42℃.

The coating of the present invention was applied as follows.

A first base coat composition comprising the following ingredients was applied by spraying to a thickness of 5-10μm.

Base Coat

The coated substrate was left to stand for three hours to complete penetration of the composition into the substrate.

The cookware was heated to 45-50℃ and a second topcoat composition consisting of the following ingredients was applied by spraying.

Top Coat

The thickness of the second coating was 5-10 μm.

The coated product was heated from 8-10 minutes in a kiln at 285-295℃ to produce a non-stick coating on the surface of the product.

Comparative Example 1

A ceramic coated frying pan was prepared by sandblasting the oven steel metal body with 60-80 mesh alumina grains. A coating composition comprising elements A and B in a 3: 1 ratio was mixed together for 35-40 minutes.

The substrate was heated to 45-55℃ and the coating composition was applied followed by drying for 10 to 15 minutes in an oven at 275-285℃.

The thickness of the coating layer was 20-25μm.

The standard hardness of the coating was measured at 7H using a graphite pencil hardness test. The maximum working temperature for the coating was measured to be 300℃.

A polytetrafluoroethylene (PTFE) non-stick coating was applied to a carbon steel pan as follows by the following process.

The surface of the pan was blasted with 40-60 mesh alumina grains. A first coating layer was sprayed onto the body and the coated body was dried in an oven at 100-160℃ and allowed to cool to 30-35℃.

A second layer of PTFE coating was applied, and the process repeated. A third layer of PTFE was applied followed by heating in a kiln at 380-430℃.

The coating thickness was measured at 35-40μm and the standard hardness of the coating was 1H. The maximum temperature of the coated pan was determined to be 260℃.

Infra-red radiation test

The emission of infra-red radiation of a frying pan coated with a coating in accordance with Example 1 was measured by the China National Accreditation Service for Conformity Assessment of the National Institute of Measurement and Testing Technology.

Measurements were carried out at an ambient temperature of 22.7℃ and relative humidity of 55%. A black body radiation source with a measuring range of 0-415℃ and an infrared thermal image apparatus with a measuring range of 30-1000℃were used.

A first test carried out at a test temperature of 150℃ gave a normal total emissivity of 0.89. The infrared spectrum as shown in Figure 1 exhibited a maximum of 0.016 Wcm ^-2 at a wavelength of 6-8μm and greater than 0.01 Wcm ^-2 between 4-12μm.

A second test carried out at a test temperature of 250℃ gave a normal total emissivity of 0.90. The infra-red spectrum as shown in Figure 2 exhibited a maximum of 0.05 Wcm ^-2 at 6μm and greater than 0.025 Wcm ^-2 between 4-9μm.

Claims

A method of manufacture of a coated substrate comprising the steps of applying to the substrate a first coating layer of a primary particulate composition comprising, by weight:

and a volatile liquid;

allowing the liquid to vaporise from the substrate to form a primary coated substrate;

applying to the primary coated substrate a secondary coating of a secondary particulate composition comprising, by weight:

and a volatile liquid:

heating the substrate to cause volatilisation of the volatile liquid; and further heating to form a coated substrate having a non-stick coating.
A method of manufacture of a coated substrate as claimed in claim 1; wherein the primary coating composition is applied to an enamel coated surface of a substrate.
A method of manufacture of a coated substrate as claimed in claim 2, wherein the enamelled surface is roughened before application of the primary coating liquid.
A method of manufacture of a coated substrate as claimed in claim 3, wherein the surface is roughened by sandblasting with 80-100 mesh particles.
A method of manufacture of a coated substrate as claimed in claim 4, wherein the particles are alumina particles.
A method of manufacture of a coated substrate as claimed in claim 4 or 5, wherein the sandblasting is carried out using an air gun with a pressure of 0.5 to 0.8 MPa.
A method as claimed in any of claims 3 to 6, wherein the roughened surface has cavities with a depth of 30 to 60 μm.
A method of manufacture of a coated substrate as claimed in any preceding claim, wherein the primary and secondary compositions are applied by spraying.
A method of manufacture of a coated substrate as claimed in any preceding claim, wherein the liquid is a volatile organic liquid.
A method of manufacture of a coated substrate as claimed in any preceding claim, wherein the liquid is an alcohol or mixture of alcohols.
A method of manufacture of a coated substrate as claimed in claim 6, wherein the liquid is ethanol.
A method of manufacture of a coated substrate as claimed in any preceding claim, wherein the amount of liquid in the primary composition is 5-8%w/w.
A method of manufacture of a coated substrate as claimed in any preceding claim, wherein the amount of liquid in the secondary coating is 5-10%w/w.
A method of manufacture of a coated substrate as claimed in any preceding claim, wherein the primary and secondary coating compositions consist essentially of the recited ingredients.
A method of manufacture of a coated substrate in accordance with any preceding claim wherein the primary and secondary coatings consist of the recited ingredients.
A method of manufacture of a coated substrate as claimed in any preceding claim, wherein the primary and secondary coating layers are cured by heating to a temperature greater than 200℃.
A method of manufacture of a coated substrate as claimed in claim 16, wherein the primary and secondary coating layers are cured by heating to a temperature in the range of 200-350℃.
A method of manufacture of a coated substrate as claimed in claim 17, wherein the primary and secondary coating layers are cured by heating to a temperature in the range of 250 to 300℃.
A method of manufacture of a coated substrate as claimed in claim 18, wherein the primary and secondary coating layers are cured by heating to a temperature in the range of 275 to 300℃.
A method of manufacture of a coated substrate as claimed in claim 19, wherein the primary and secondary coating layers are cured by heating to a temperature in the range of 285 to 295℃.
A method of manufacture of a coated substrate as claimed in any of claims 16-20-19, wherein the duration of heating is in the range of 5-20 minutes, preferably 5-15 minutes, more preferably 8-10 minutes.
A method of manufacture of a coated substrate as claimed in any preceding claim, wherein the thickness of the primary coating, after evaporation of the liquid, is in the range of 2-20μm, preferably 3-15 μm, more preferably 5-10μm.
A method of manufacture of cookware, as claimed in any preceding claim.
An article of cookware comprising a substrate, having a surface coated with a non-stick coating applied by the method of any preceding claim.