Method for producing a ceramic anti-adhesive coating and corresponding item with such an anti-adhesive coating

Technical field

p0001The invention relates to a method of manufacturing a ceramic non-stick coating. The invention further relates to an article, insbsondere a household item or a utensil with such Antifhaftbeschichtung.

Background of the Invention and Prior Art

p0002Conventionally, non-stick coatings of polytetrafluoroethylene (PTFE) are prepared containing compositions. Such PTFE coatings are known to have a number of disadvantages. On one hand, the production process requires a sintering process at a temperature 360-420 ° C, at which decompose parts of the coating composition to form toxic compounds (eg Fluorophosgene, tetrafluoroethylene or trifluoroacetic acid) (<nplcit id="ncit0001" npl-type="s"><text>Nature, Vol. 412, 19, July 2001, p. 321-324</text></nplcit>). In addition, during the sintering process, the greenhouse gas fluoroform (HFC-23) is released. The sintering process is a costly and energy-consuming process due to the high temperatures used. On the other hand, containing PTFE non-stick coatings to insufficient hardness. Moreover, the overheating of the cookware to the release of toxic decomposition products - as already mentioned above for manufacturing - lead.

p0003Due to these disadvantages of PTFE containing coatings different PTFE-free ceramic coatings have been developed sol-gel base in recent years.

p0004Thus discloses <patcit id="pcit0001" dnum="EP1835002A2"><text>EP 1835002 A2</text></patcit> a non-stick coating of two layers, wherein the first so-called base layer made of a matrix of a condensation product of the silica sol is made with an organoalkoxysilane and on it a top layer of a matrix of a condensation product of a silica sol is applied with a mixture of organoalkoxysilanes and a fluoroalkoxy silane.

p0005In the <patcit id="pcit0002" dnum="DE19714949A1"><text>DE 197 14 949 A1</text></patcit> is an abrasion-resistant glass-like coating composition is described which is obtained by hydrolysis and condensation of a silane RSi (OR ')₃ with nanoscale SiO₂Particles and hydroxides of the alkali and alkaline earth metals with subsequent conversion at a temperature of more than 400 ° C in a dense film.

p0006From the <patcit id="pcit0003" dnum="EP2177580B1"><text>EP 177 580 B1 2</text></patcit> is a ceramic non-stick coating known which, by hydrolysis and polycondensation of a silane RSi (OR ')₃ with nanoscale SiO₂Particles, a hydroxy-terminated polydimethylsiloxane, a carboxylic acid, water-miscible organic solvent and water is obtained.

p0007These ceramic non-stick coatings on metal substrates have, however, only sufficient adhesion when the surface is roughened beforehand. This roughening is usually completed by sand blasting with corundum. Alternatively, etching processes and a metallic or oxide thermal spray coating can produce the necessary surface roughness.

p0008Ceramic non-stick coatings, which are manufactured by the sol-gel method, moreover have steel insufficient corrosion resistance. This could of course be avoided by the use of high-alloy stainless steels suitable but are more expensive.

p0009Said corrosion resistance is of course a gradual property. If one takes a corresponding lower corrosion resistance in purchasing, one can nevertheless - continue waiving alloyed steel - use korrosionsverbesserte metals.

p0010Usual pre-treatment process to improve the corrosion behavior of metals, such as the application of phosphate coatings or phosphate-free conversion layers as Bonderite NT-1 show as a base for ceramic sol-gel layers insufficient roughness and thus show the ceramic sol-gel layers no sufficient adhesion to the prepared substrate.

p0011<patcit id="pcit0004" dnum="US20070036900A1"><text>US 2007/0036900 A1</text></patcit> describes a method in which a fluoropolymer-free binder with inorganic particles is applied with an average particle size of not more than two microns to a substrate and is dried. On the thus-coated base layer, the non-stick coating is applied. The corrosion resistance is achieved here due to the small particle size of the inorganic filler particles, which form a dense packing in the dried coating. However, the roughness of this base layer is not sufficiently large to allow a sufficient adhesion of ceramic sol-gel coatings of this base layer.

Summary of the Invention

p0012The object of the present invention is accordingly to provide a method for applying an anti-adhesive coating, with the means of the coating composition contains both a high corrosion resistance as well as good adhesion of a ceramic sol-gel coating on metallic substrates without sandblasting, etching, or thermal spray coatings is possible.

p0013The object is inventively achieved by a method as claimed in claim 1, if one desires a single ceramic non-stick coating or according to claim 2, if one desires a two-layer non-stick coating.

p0014In a modified form of the method - if less corrosion resistance is taken into account or a high-alloy steel may be used - one can dispense with the conversion layer and the required corrosion resistance by the choice of substrate - ie a high-alloy steel or korrosionsverbesserte metals - reach.

p0015The inorganic filler particles used have an average particle size from 9 to 40 microns. The average particle size is defined as the particle size, in a given volume, at which 50% of the total volume of the particles has a particle size that is less than or equal to the specified particle size (d₅₀). In a particularly preferred embodiment, the average particle size of the inorganic filler used is 9 microns.

p0016The inorganic filler particles prevent shrinkage of the undercoat during drying and create the necessary roughness to ensure adequate adhesion of the following ceramic sol-gel coating of the top layer to achieve. Excessive roughness lead to loss of gloss of the following ceramic sol-gel coating. In a particularly preferred embodiment the roughness is R_A 2-3 microns.

p0017Advantageous embodiments of the inventive method are indicated in the dependent patent claims.

p0018It is advantageous if the lower layer is dried. It is especially advantageous if the drying of the undercoat layer is a baking process. Furthermore, as has been found advantageous if the dry film thickness of the underlayer between 9 and 40 microns. The liquid coating composition of the underlayer advantageously contains organic solvents. The fluoropolymer-free binder may be dispersed by means of a suitable wetting agent in water or in water-soluble form. Advantageously, these binders polyethersulfone (PESU) and / or polyphenylene sulfides (PPS) and / or polyimide (PI) and / or polyamide-imides (PAI). It may also include silicone-modified polyester.

p0019The inorganic filler particles are advantageously selected from the group of inorganic oxides, carbides, borides and nitrides, and mixtures thereof. In addition to reducing the shrinkage of the lower layer, the said fillers usually have high hardness, which contributes to an increased wear resistance of the overall layer construction.

p0020Another object of the invention is achieved by providing an article with a metallic surface as a substrate, a conversion layer, a subbing layer and at least one ceramic of a ceramic non-stick coating, wherein said layers are formed or applied by means of the inventive method. Advantageously, such an article as household or commodity, especially when baking dish.

p0021The solids of the underlayer used is present in a particularly preferred embodiment, 15-55.%.

p0022The aforementioned and the claimed and described in the following exemplary embodiments, in the present invention to be used elements are in their size, shape, material use and its technical conception exceptional conditions, so that the well-known in the respective field of selection criteria can be applied without restriction.

Brief Description of the Figures

p0023Embodiments of the invention are described below with reference to drawings which show this:<dl id="dl0001"><dt>figure 1</dt><dd>a layer configuration diagram according to a first embodiment with a ceramic non-stick coating;</dd><dt>figure 2</dt><dd>a layer configuration diagram according to a further embodiment with two ceramic non-stick coatings.</dd></dl>

WAYS OF CARRYING OUT OF THE INVENTION

p0024The substrate 1 to which the backsheet 3 is applied, consists of a defatted untreated metallic substrate by chemical pre-treatment - is provided with a corrosion-resistant as possible conversion layer 2 - with or without the application of electric current. In a particularly preferred embodiment, a phosphate-containing conversion layer 2 is applied to the untreated metallic substrate. The skilled person such conversion coatings and the procedures for their preparation in the art.

p0025The direct application of sol-gel ceramic coatings 4 to corrosion-resistant phosphate-containing or phosphate-free conversion coatings do not show sufficient adhesion of the ceramic layer on the conversion layer, since the roughness of the conversion layer is too low.

p0026A first ceramic layer is obtained in the present embodiment, by hydrolysis and polycondensation of an aqueous mixture wherein the mixture contains - 10 - 70 wt .-% of a silane of the general formula (I)          (I) RSiX₃ in the groups X are hydrolyzable groups or hydroxyl groups and the residues R stand for alkyl or aryl groups having 1 to 6 carbon atoms,<ul><li>8 to 21 wt .-% of nanoscale SiO₂particles</li><li>0 to 2 wt .-% of a polydimethylsiloxane of the general formula (II)</li></ul>          (II) HO- [Si (CH₃)₂-O]_n-H in which n is a number 2-170 represents<ul><li>0.1 to 2 wt .-% of a carboxylic acid having 1 to 4 carbon atoms,</li><li>7 to 50 wt .-% water</li><li>10 to 60 wt .-% water-miscible organic solvent, where the aforementioned weight of up to 100 wt .-% yield.</li></ul>

p0027A two-layer ceramic coating is - in an alternative embodiment - obtained by hydrolysis and polycondensation of an aqueous mixture obtained, the mixture contains<ul><li>10-70 wt .-% of a silane of the general formula (I)</li></ul>          RSiX₃     (I) in the groups X are hydrolyzable groups or hydroxyl groups and the residues R stand for alkyl or aryl groups,<ul><li>8 to 21 wt .-% of nanoscale SiO₂particles</li><li>0.1 to 2 wt .-% of a carboxylic acid having 1 to 4 carbon atoms,</li><li>7 to 50 wt .-% water</li><li>10 to 60 wt .-% water-miscible organic solvent, and then by hydrolysis and polycondensation of an aqueous mixture, which mixture contains</li><li>10-70 wt .-% of a silane of the general formula (I)          RSiX₃     (I) in the groups X are hydrolyzable groups or hydroxyl groups and the residues R stand for alkyl or aryl groups having 1 to 6 carbon atoms,</li><li>8 to 21 wt .-% of nanoscale SiO₂particles</li><li>0 to 2 wt .-% of a polydimethylsiloxane of the general formula (II)          HO- [Si (CH₃)₂-O]_n-H (II) in which n is a number 2-170 represents</li><li>0.1 to 2 wt .-% of a carboxylic acid having 1 to 4 carbon atoms,</li><li>7 to 50 wt .-% water</li><li>10 to 60 wt .-% water-miscible organic solvent, where the aforementioned weight of up to 100 wt .-% yield.</li></ul>

test Methods

Investigation of adhesion and corrosion resistance

p0028The provided with a corrosion resistant conversion coating metal sheets are coated with the inventive undercoat layer in a spraying process and, as indicated in the embodiments dried. Onto the dried cooled underlayer the ceramic non-stick coating is sprayed and as indicated in the examples, dried.

p0029The test panels thus obtained are provided with a 2 mm cross-cut in accordance with DIN EN ISO 2409 and 3 times covered with 3M 8402 tape on the cutting grid and jerky demolished. The test panels are then the steam boiling 2.5% aqueous acetic acid and subjected to cool down for 10 minutes. The average grid is again 3 times covered with 3M 8402 adhesive tape, bobbing demolished and evaluated the results. Subsequently, the test panels are an additional 20 minutes the steam boiling 2.5% exposed to aqueous acetic acid (total 30 minutes) and cooled. The average grid is again 3 times covered with 3M 8402 adhesive tape, bobbing demolished and evaluated the results.

p0030Subsequently, the test panels are an additional 30 minutes the steam boiling 2.5% exposed to aqueous acetic acid (60 minutes) and cooled. The average grid is again 3 times covered with 3M 8402 adhesive tape, bobbing demolished and evaluated the results.

Examples

example 1

p0031On a Zn, Mn phosphated test steel GARDOBOND^® 26S 6800 0C the Fa. Chemetall GmbH, Frankfurt, Germany, is by spraying an inventive underlayer <b>Table 1</b> and dried at 150 ° C for 5 minutes and then crosslinked at 280 ° C for 20 minutes. After cooling, a two-layer ceramic coating is applied to this sub-layer.<tables id="tabl0001" num="0001"><table frame="topbot"><title><b>Table 1</b></title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="86mm" /><colspec colnum="2" colname="col2" colwidth="15mm" /><colspec colnum="3" colname="col3" colwidth="33mm" colsep="0" /><thead><row><entry valign="top"><b>raw material</b></entry><entry valign="top"><b>. Wt%</b></entry><entry valign="top"><b>Solids wt.%</b></entry></row></thead><tbody><row><entry>Silicone Modified Polyester 60% solid, 10% silicon content</entry><entry>33.33</entry><entry>20</entry></row><row><entry>xylene</entry><entry>8.63</entry></row><row><entry>butylglycol</entry><entry>5.73</entry></row><row><entry>cyclohexanone</entry><entry>2.87</entry></row><row><entry>Dowanol^® PMA</entry><entry>14:37</entry></row><row><entry>Estasol^®</entry><entry>1.73</entry></row><row><entry>silicon carbide</entry><entry>33.33</entry><entry>33.33</entry></row><row><entry><b>SUM</b></entry><entry><b>100</b></entry><entry><b>53.33</b></entry></row></tbody></tgroup></table></tables>

p0032The dry film thickness of the applied ceramic coating in this case was 47 microns. The average roughness R_A the GARDOBOND^® 26S 6800 0C surface was R_A= 1.56 microns.

p0033The results of the adhesion and corrosion tests are in <b>Table 3</b> combined.

example 2

p0034On a Zn, Mn phosphated test steel GARDOBOND^® 26S 6800 0C the Fa. Chemetall GmbH, Frankfurt, Germany, is by spraying an inventive underlayer <b>Table 2</b> and dried at 140 ° C for 5 minutes and then crosslinked at 280 ° C for 20 minutes. After cooling, a two-layer ceramic coating is applied to this sub-layer.<tables id="tabl0002" num="0002"><table frame="topbot"><title><b>Table 2</b></title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="32mm" /><colspec colnum="2" colname="col2" colwidth="15mm" /><colspec colnum="3" colname="col3" colwidth="33mm" colsep="0" /><thead><row><entry valign="top"><b>raw material</b></entry><entry valign="top"><b>. Wt%</b></entry><entry valign="top"><b>Solids wt.%</b></entry></row></thead><tbody><row><entry><i>N</i>-Methylporrolidon</entry><entry>60</entry></row><row><entry>polyether</entry><entry>10</entry><entry>10</entry></row><row><entry>silicon carbide</entry><entry>30</entry><entry>30</entry></row><row><entry><b>SUM</b></entry><entry><b>100</b></entry><entry><b>40</b></entry></row></tbody></tgroup></table></tables>

p0035The dry film thickness of the applied ceramic coating in this case was 22 microns. The average roughness R_A the GARDOBOND^® 26S 6800 0C surface was R_A= 1.56 microns.

p0036The results of the adhesion and corrosion tests are in <b>Table 3</b> combined.

example 3

p0037On a sheet steel (1.0394), which with BONDERITE^® CC40 Fa. Henkel AG &amp; Co KGaA, Dusseldorf, Germany, has been pretreated, is by spraying an inventive underlayer <b>Table 1</b> and dried at 150 ° C for 5 minutes and then crosslinked at 280 ° C for 20 minutes. After cooling, a two-layer ceramic coating is applied to this sub-layer.

p0038The dry film thickness of the applied ceramic coating in this case was 64 microns. The average roughness R_A the BONDERITE CC40^® Surface was R_A= 1.15 microns.

p0039The results of the adhesion and corrosion tests are in <b>Table 3</b> combined.

example 4

p0040In a Fe-phosphated test steel GARDOBOND^® WH 60 0C the Fa. Chemetall GmbH, Frankfurt, Germany, by spraying an inventive underlayer according <b>Table 1</b> and dried at 150 ° C for 5 minutes and then crosslinked at 280 ° C for 20 minutes. After cooling, it is a two-layer ceramic coating plotted in this sublayer.

p0041The dry film thickness of the applied ceramic coating at this time was 26.5 microns. The average roughness R_A the GARDOBOND^® WH 60 0C surface was R_A= 2.66 microns.

p0042The results of the adhesion and corrosion tests are in <b>Table 3</b> combined.

example 5

p0043On a Zn -phosphatiertes testing steel GARDOBOND^® 26S 60 OC the Fa. Chemetall GmbH, Frankfurt, Germany, is by spraying an inventive underlayer according <b>Table 1</b> and dried at 150 ° C for 5 minutes and then crosslinked at 280 ° C for 20 minutes. After cooling, a two-layer ceramic coating is applied to this sub-layer. The dry film thickness of the applied ceramic coating in this case was 31 microns. The average roughness R_A the GARDOBOND^® 26S 60 OC surface was R_A= 2.72 microns.

p0044The results of the adhesion and corrosion tests are in <b>Table 3</b> combined.

Comparative Examples

Comparative example

1

p0045A two-layer ceramic coating is applied directly to a Zn, Mn phosphated test steel GARDOBOND^® dried 26S 6800 0C the Fa. Chemetall GmbH, Frankfurt, Germany, applied by spraying, followed by 5 minutes at 150 ° C and baked at 200 ° C for 20 minutes.

p0046The dry film thickness of the applied ceramic coating in this case was 13 microns. The average roughness R_A the GARDOBOND^® 26S 6800 0C surface was R_A= 1.56 microns.

p0047The ceramic coating dissolves the tape stripping off completely to have been exposed without the acetic acid.

Comparative Example 2

p0048A two-layer ceramic coating is applied directly to one with BONDERITE^® CC40 Fa. Henkel AG &amp; Co KGaA, Dusseldorf, Germany, provided the surface of a steel sheet (1.0394) applied by spraying and then dried for 5 minutes at 150 ° C and baked at 200 ° C for 20 minutes.

p0049The dry film thickness of the applied ceramic coating at this time was 14.5 microns. The average roughness R_A the with BONDERITE^® CC40 treated surface was R_A= 1,15μm.

p0050The results of the adhesion and corrosion tests are in <b>Table 3</b> combined. <tables id="tabl0003" num="0003"><table frame="topbot"><title><b>Table 3</b></title><tgroup cols="6"><colspec colnum="1" colname="col1" colwidth="34mm" /><colspec colnum="2" colname="col2" colwidth="17mm" /><colspec colnum="3" colname="col3" colwidth="23mm" /><colspec colnum="4" colname="col4" colwidth="31mm" /><colspec colnum="5" colname="col5" colwidth="31mm" /><colspec colnum="6" colname="col6" colwidth="31mm" colsep="0" /><thead><row><entry valign="top"><b>Example / Comparative Example</b></entry><entry valign="top"><b>DFT of the sol-gel layer [microns]</b></entry><entry valign="top"><b>Adhesion before starting the test</b></entry><entry valign="top"><b>Adhesion after 10 minutes 2.5% acetic acid vapor</b></entry><entry valign="top"><b>Adhesion after 30 minutes 2.5% acetic acid vapor</b></entry><entry valign="top"><b>Adhesion after 60 minutes 2.5% acetic acid vapor</b></entry></row></thead><tbody><row><entry><b>example 1</b></entry><entry align="center">47</entry><entry align="center">Gt0</entry><entry align="center">Gt0</entry><entry align="center">Gt0</entry><entry align="center">Gt0</entry></row><row><entry><b>example 2</b></entry><entry align="center">22</entry><entry align="center">Gt0</entry><entry align="center">Gt0</entry><entry align="center">Gt0</entry><entry align="center">Gt0</entry></row><row><entry><b>example 3</b></entry><entry align="center">64</entry><entry align="center">Gt0</entry><entry align="center">Gt0</entry><entry align="center">Gt0</entry><entry align="center">Gt0</entry></row><row><entry><b>example 4</b></entry><entry align="center">26.5</entry><entry align="center">Gt0-1</entry><entry align="center">Gt0-1</entry><entry align="center">Gt0-1</entry><entry align="center">Gt0-1</entry></row><row><entry><b>example 5</b></entry><entry align="center">31</entry><entry align="center">Gt0-1</entry><entry align="center">Gt0-1</entry><entry align="center">Gt0-1</entry><entry align="center">Gt0-1</entry></row><row><entry><b>Comparative Example 1</b></entry><entry align="center">13</entry><entry align="center">> Gt 5, complete detachment of the layer</entry><entry align="center">Not done</entry><entry align="center">Not done</entry><entry align="center">Not done</entry></row><row><entry><b>Comparative Example 2</b></entry><entry align="center">14.5</entry><entry align="center">gt1</entry><entry align="center">gt1</entry><entry align="center">Gt2</entry><entry align="center">> GT5, complete detachment</entry></row></tbody></tgroup></table></tables>