EP0633327A1 - Process for coating household and kitchen utensils - Google Patents

Abstract

A method of coating household and kitchen utensils, especially the bases of frying pans, comprises the steps of: - making dome-shaped depressions (30) in the surface of a preferably metallic substrate (15), the depressions having a diameter (D) of between 1.0 and 3.0 mm and a depth (t) of between 0.2 and 0.5 mm; - applying at least one thermally sprayed, especially plasma-sprayed, layer (16, 17) to the surface provided with depressions (30), the thickness (d1, d2) of the layer (16, 17) being less than half as great as the depth (t); and - applying a non-stick coating (18) to the thermally sprayed layer (16, 17), the thickness (d3) of the non-stick coating (18) being less than the thickness (d1, d2) of the thermally sprayed layer (16, 17). <IMAGE>

Description

The invention relates to a method for coating household and kitchen appliances. The invention further relates to a household and kitchen appliance with a metallic base body, the surface of which is structured, a hard layer of less than 100 μm thick being applied to the surface and an anti-adhesive layer being applied to the hard layer.

A method and a device of the type mentioned above are known from EP-A-0 510 546.

It is known to provide household and kitchen appliances, for example irons, frying pans, pots, baking tins, warming plates, browning plates and the like, with an anti-adhesive layer. According to the method mentioned at the beginning, at least one ceramic hard material layer, preferably first an adhesive base layer and then the hard material layer is applied to a surface of a metallic base body by flame spraying, plasma spraying or the like. The surface is preferably first cleaned and / or sandblasted. The non-stick layer in the form of a non-stick varnish, preferably a PTFE varnish, is then sprayed onto the hard material layer lying on top, in such an amount that the pores of the porous hard material layer are just filled and the surface of the hard material layer is covered by a thin film of the non-stick layer after it has been burned in by heat treatment.

As a result of the known methods, equipment is obtained in which a hardened PTFE film covers the porous hard material layer, which is provided with valleys and peaks due to its structure on the surface.

Although a coating is achieved in this known manner, the non-stick properties of which are determined by the non-stick layer and whose mechanical stability is determined by the tips of the hard material layer acting as support points, under certain conditions there may be a reduction in the non-stick properties if the material of the non-stick layer has a high Exposed to stress. The reason for this is as follows:
As is well known, polytetrafluoroethylene (PTFE) consists of elongated linear chains of strung-together CF₂ units. The FCF angle, ie the angle between the fluorine and carbon atoms, is in the range of the tetrahedron angle, ie approximately 109 °. The three molecules that make up a CF₂ unit are at the corners of a triangle. Seen in the direction of the longitudinal central axis of the PTFE chain, which is formed by the lined-up carbon atoms, successive CF₂ units are each rotated in the same direction by about 27 °. This forms a helix structure of the strung CF₂ units, a complete helix of the helix structure being formed from about 13 CF₂ units. This twisting of the polymer chain leads to the stretched chain structure. The extraordinary chemical resistance of PTFE is based on the dense and "protective" skin of the fluorine atoms around the chain of carbon atoms. The thermal stability is primarily a result of the high binding energy of the CF bond. The low interaction forces between the molecules explain properties such as a low coefficient of friction and minimal adhesion to other materials. The elongated, twisted PTFE chains can lie very close to one another and thus form a dense, compact bond on individual macromolecule chains. This results in excellent mechanical properties against pressure forces and the like.

Viewed macroscopically, the tendency to form linear chains also leads to a certain elasticity, ie a restoring moment is generated if a chain is bent out of its linear orientation.

Microscopically, however, there are no electrostatic interactions in the sense of attractive forces between the individual elongated PTFE chains, since the “outer skin” of the twisted chains is consistently formed from fluorine atoms, all of which are locations of a relatively high negative charge component.

If a "short-range order" between adjacent PTFE chains is now disturbed, for example by external mechanical influences, there is no restoring force due to electrostatic intermolecular interactions that could cause the chains to either return to their original short-range order or in the now disturbed short-range order being held. This would in itself be possible through the formation of new electrostatic intramolecular interactions after changing the original short-range order due to the action of the external force.

The area of the disturbed short-range order of the individual PTFE chains can be seen as a tangle of individual threads that no longer return to a state of ordered alignment of linear chains arranged side by side. The disturbed short-range order of the tangled chains can now increase due to permanent mechanical loads and lead to a complete breakup of the bond.

If one considers the example of a frying pan that is provided with a non-stick layer made of PTFE, mechanical loads, for example caused by a knife edge, can initially cause microscopic disturbances in the close-up range of the adjoining PTFE chains. By further mechanical loads, or also by the other intended Use, ie temperature changes, contact with hot fats or the like, can further widen the change in the disturbed short-range order state. For example, an initially invisible microscopic "cut" can gradually develop into a macroscopically recognizable cut or tear.

When using PTFE filler mixtures (so-called "compounds"), in which fillers are added to the PTFE chains, these fillers are protected from external influences by the linear PTFE chains with a high short-range order. If this nano arrangement is disturbed, the fillers between the PTFE chains are exposed to the external influences more unprotected, so that these fillers can be removed. This then changes the mechanical properties of the PTFE compounds, namely precisely those to which these fillers have been added. The areas depleted of fillers with disturbed near-order area on PTFE chains form places where external influences can become more effective, which is manifested in the detachment or fanning out of PTFE layers on metal surfaces.

It follows from the above consideration that an anti-adhesive layer of the type of interest here, as used in a household and kitchen appliance, cannot only be destroyed by direct mechanical influence (for example by cutting), but the pressure acting also has direct effects on the molecular Structure due to the special macromolecular structure of non-stick materials.

If one remembers once again that hard layers of material are used in the known methods and equipment, in which the height difference between valleys and peaks of the surface is only a few 10 µm, it is easy to see that a mechanical load is practically the whole Material volume spreads, even if due to the geometry of the surface, the direct mechanical action can only occur in the area of the tips of the hard material layer. However, a pressure cone also forms in the vicinity of the tip, which, due to the very small dimensions, covers the entire area of the non-stick material.

From the above-mentioned EP-A-0 510 546 it is known to design the structuring of the surface in a method of the type mentioned at the outset by introducing grooves into the surface, the grooves having a width and a depth of between 100 μm and 400µm.

This structuring of the surface with grooves, the dimensions of which are substantially greater than the layer thickness, ensures that the negative effects described above cannot occur in the lower-lying zones of the grooves. The dimensions of the grooves are so small on the one hand that conventional hard instruments from home and kitchen with their cutting edges or tips cannot get in, but on the other hand the grooves are so large that mechanical loads are exerted on the top tips , cannot spread into the deeper zones of the grooves. In this way, wide areas of non-stick material remain in the deeper zones of the grooves, which are spared from all such influences, so that their full non-stick properties are retained.

It is also known, e.g. to provide the frying surfaces of frying pans with a honeycomb structure in which a large number of depressions are made in the surface. However, these known structures have considerably larger dimensions. In these known honeycomb structures, the depressions are approximately 10 mm wide or have a corresponding diameter and they are also over 1 mm deep, so that their interior can be accessed with the usual hard instruments such as those used in the home and kitchen is.

The invention is based on the object of developing a method and a device of the type mentioned in such a way that on the one hand the non-stick properties and on the other hand the mechanical resistance to damage to the coating are further improved.

• Einbringen von kappenförmigen Einsenkungen in eine Oberfläche eines vorzugsweise metallischen Grundkörpers, wobei die Einsenkungen einen Durchmesser zwischen 1,0 und 3,0 mm und eine Tiefe zwischen 0,2 und 0,5 mm aufweisen;
• Aufbringen von mindestens einer thermisch gespritzten, insbesondere plasmagesprühten Schicht auf die mit Einsenkungen versehene Oberfläche, wobei die Dicke der Schicht weniger als halb so groß wie die Tiefe ist; und
• Aufbringen einer Antihaftschicht auf die thermisch gespritzte Schicht, wobei die Dicke der Antihaftschicht kleiner als die Dicke der thermisch gespritzten Schicht ist.

According to the method mentioned at the outset, this object is achieved according to the invention by the following method steps:

• Introducing cap-shaped depressions into a surface of a preferably metallic base body, the depressions having a diameter between 1.0 and 3.0 mm and a depth between 0.2 and 0.5 mm;
• Applying at least one thermally sprayed, in particular plasma-sprayed, layer to the recessed surface, the thickness of the layer being less than half the depth; and
• Applying a non-stick layer to the thermally sprayed layer, the thickness of the non-stick layer being smaller than the thickness of the thermally sprayed layer.

Furthermore, the above object is achieved in a device of the type mentioned at the outset in that the structure of the surface consists of depressions whose diameters are between 1.0 and 3.0 mm and their depths are between 0.2 and 0.5 mm.

The object underlying the invention is completely achieved in this way.

It has been shown that a surface structure with many cap-shaped depressions is even better than the known groove-shaped structures both in terms of the non-stick properties and in terms of mechanical resistance. The improvement in the non-stick properties results from the fact that the cap-shaped depressions each represent small volumes which, in contrast to relatively long grooves, in particular crossed grooves, are each individually insulated. When using the method according to the invention for coating frying pan bases, air bubbles are formed in the small volumes of the depressions, because even hot fat does not immediately fill these small volumes due to its cohesion or its still present viscosity, and above all does not completely fill it. In this way, a microscopic air cushion is created between the pan base and the food to be fried, which is formed from a large number of such air bubbles in the depressions. The same applies to the steam generated during the boiling of the frying fat, the bubbles of which can also remain in the small volumes of the depressions, so that, to this extent, a direct contact of the fried food with the pan base is reduced, macroscopically.

As far as the mechanical resistance is concerned, it has been shown that, in contrast to a grooved surface with elongated webs between the grooves, a structure with cap-shaped depressions is advantageous because the support portion is now distributed over a very irregular structure of "webs" between the depressions is. It can therefore not happen, for example, that when the surface is loaded with a long cutting edge, the cutting direction happens to be parallel to the groove direction, with corresponding punctual overloading of a web between the grooves. Rather, even with elongated cutting edges, the supporting parts of the structure according to the present invention are designed in such a way that the mechanical load is introduced into a large number of small sections of the webs.

It is important that the depressions are formed with the stated dimensions of between 1.0 and 3.0 mm in diameter and 0.2 to 0.5 mm in depth, work being preferably carried out at the lower end of these size ranges, i.e. with diameters around 1.0 mm and depths around 0.2 mm. Surprisingly, it has been shown that in the two directions mentioned, namely improvement of the non-stick property and improvement of the mechanical resistance, with such a dimensioning of the depressions, clear advantages are achieved compared to both the known grooved surface structure and the known honeycomb structure, the The dimples are almost an order of magnitude larger.

In a preferred embodiment of the method according to the invention, the depressions have the shape of a spherical cap.

This measure is preferred because a particularly regular structuring can be achieved in this way. However, it is not ruled out to use ellipsoids, paraboloids or the like instead of using spherical caps.

It is further preferred if the depressions are arranged on a hexagonal grid.

This measure has the advantage of being able to arrange the depressions as close as possible to one another, the load-bearing portion of the webs between them being able to be set very low.

It is therefore particularly preferred if the non-recessed webs of the surface remaining between the depressions between adjacent depressions have a width which is less than 20%, preferably less than 10% of the diameter of the depressions.

This measure has the advantage that the load-bearing component of the surface can be set as low as possible.

In further exemplary embodiments of the invention, it is preferred that the step of introducing the depressions is carried out after the metallic base body has been heated.

This measure has the advantage that lower pressing forces can be used to apply the depressions because the strength of the respective metallic material decreases with temperature.

A particular advantage is achieved in that the metallic base body is converted into a softened state when heated.

This measure has the advantage that it is possible to work with particularly low pressing forces, for example when an aluminum base of a frying pan or an iron soleplate is softened accordingly.

A particularly good effect is achieved in these exemplary embodiments if the metallic base body is heated by means of inductive heating.

This measure has the advantage that a clean heating of the metallic base body can be carried out without the use of organic heating materials in the course of a flow production.

In preferred embodiments of the method according to the invention, the thickness of the thermally sprayed layer in a manner known per se is between 10 .mu.m and 70 .mu.m, again in a known manner preferably two thermally sprayed layers, namely first an adhesive base layer with a thickness between 10 .mu.m and 20 .mu.m and then thereon a hard material layer with a thickness between 30 µm and 70 µm is sprayed.

It is further preferred if the non-stick layer is applied with a thickness between 5 μm and 50 μm.

Further advantages result from the description and the attached drawing.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the combination indicated in each case, but also in other combinations or on their own without departing from the scope of the present invention.

Fig. 1

eine Pfanne, teilweise geschnitten und im Ausschnitt stark vergrößert;

Fig. 2

eine Darstellung, ähnlich Fig. 1, jedoch für ein Bügeleisen;

Fig. 3

eine nochmals stark vergrößerte Darstellung eines Schnitts durch die Beschichtung der Bratpfanne gemäß Fig. 1, und zwar entlang der Linie III-III von Fig. 4;

Fig. 4

eine Draufsicht auf die Beschichtung gemäß Fig. 3;

Fig. 5

in nochmals stark vergrößertem Maßstab einen Ausschnitt aus der Schnittdarstellung gemäß Fig. 3.

Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description. Show it:

Fig. 1

a pan, partially cut and greatly enlarged in the neckline;

Fig. 2

a representation, similar to Figure 1, but for an iron.

Fig. 3

another greatly enlarged illustration of a section through the coating of the frying pan according to FIG 1, namely along the line III-III of Fig. 4.

Fig. 4

a plan view of the coating of FIG. 3;

Fig. 5

on a greatly enlarged scale, a section of the sectional view of FIG. 3.

In Fig. 1, 10 designates a frying pan, which essentially consists of a metallic base 11 with an edge and a handle 12. The bottom 11 in turn consists of a metallic base body 15 with a coating applied thereon. The metallic base body 15 can be made of steel, stainless steel, cast aluminum, cast iron, copper or the like. However, ceramic pans can also be used in the context of the present invention.

The base body 15 has an inner surface which is preferably roughened by mechanical methods, in particular by sandblasting, and / or cleaned by appropriate cleaning methods.

The inner surface is initially provided with an adhesive base layer 16 in the plasma spraying process. The adhesive base layer 16 preferably consists of a metallic alloy, in particular nickel-aluminum or chromium-nickel. However, other adhesive base layers 16 can also be used, as are known per se from the technique of plasma spraying. In this context it goes without saying that the term "plasma spraying" is also to be understood only as an example, because instead of plasma spraying, flame spraying, high-speed plasma spraying (so-called detonation spraying or jet-kote method) or the like can also be used. Overall, a method is to be used in which powdered metallic, ceramic or metal-ceramic materials are applied to a substrate by thermal spraying.

A hard material layer 17 is applied to the adhesive base layer 16, likewise in the plasma spraying process. The hard material layer 17 can consist of a ceramic or a metal, for example of aluminum oxide or a mixture of aluminum oxide / titanium oxide. However, other hard material layers can also be used here, as are known per se from the technique of plasma spraying.

The hard material layer 17 is provided on its surface with a non-stick layer 18. The non-stick layer 18 preferably consists of a plastic based on fluoroethylene polymer, in particular polytetrafluoroethylene (PTFE). The non-stick layer 18 is preferably sprayed onto the hard material layer 17 in the form of a non-stick lacquer. After the anti-adhesive layer 18 has been sprayed on, it is baked. This is preferably done in a temperature range between 200 ° and 500 ° C., preferably 250 ° and 350 ° C., in particular 300 ° C.

In Fig. 2, 20 denotes an iron, which has a sliding sole 21 and a handle 22. The sliding sole 22 is again shown greatly enlarged in sections. Their structure corresponds essentially to that of FIG. 1. It can be seen that an adhesive base layer 26, a hard material layer 27 and in turn an anti-adhesive layer 28 have been applied to an underside of a metallic base body 25 of the sliding sole 21. In this case, the non-stick layer 28 forms the underside of the sliding sole 21.

The materials of the layers 26 to 28 and their dimensions correspond analogously to those of FIG. 1.

It goes without saying that the two examples of a frying pan 10 and an iron 20 explained above are only to be understood as preferred applications. Of course, the same applies to other household and kitchen appliances, for example pots, baking tins, warming plates, browning plates and the like. More.

3 and 4, the surface structure of the frying pan 10 is shown on a further enlarged scale in section or in plan view.

It can clearly be seen that the surface is provided with depressions 30, between which non-recessed webs 31 have remained. The depressions 30 are in the example shown formed as spherical caps, which are located on a hexagonal grid 35.

The depressions 30 have a diameter D that is between 1.0 and 3.0 mm. However, the diameter D is preferably set small, i.e. rather in the lower range between 1.0 and 2.0 mm. The depth t of the depressions 30 is between 0.2 and 0.5 mm, with the lower region between 0.2 and 0.3 mm being preferred here as well.

By arranging the depressions 30 on the hexagonal grid 35, the total surface of the webs 31 can be kept as small as possible. This is completely sufficient for the required proportion of the surface. It is preferred if the width a between two adjacent depressions 30 is less than 20%, preferably less than 10% of the diameter D of the depressions 30.

In the illustrated embodiment, the depressions 30 are designed as spherical caps. The radius of curvature R is therefore in the range between 1 and 3 mm for the dimensions of the depressions mentioned (diameter D and depth t).

In order to produce the structure shown on the surface of the preferably metallic base body 15, there are different ways of proceeding.

In the case of the usual metallic materials (steel and aluminum), the structure can be introduced into the already finished pan base 11 (or sliding sole 21) by pressing with a suitably structured pressing tool. However, it is also conceivable to include the structure during the shaping of the socket body (or the sliding sole) bring in. This also applies in particular to non-metallic materials, for example a ceramic.

If the structure is subsequently introduced by pressing, which is a preferred embodiment of the invention, the required pressing force can be reduced by first heating the metallic base body 15 or 25. This can e.g. happen with the help of an inductive heating device of known type. If the metal material is heated to such an extent that the softening limit of the material is reached, the desired structure can be achieved with relatively small pressing forces.

FIG. 5 shows a section from FIG. 3 on a greatly enlarged scale, namely an exemplary embodiment of a coating in the region of a web 31 between two depressions 30.

It can clearly be seen that on the surface of the metallic base body 15, formed by the depressions 30 and the webs 31, first the adhesive base layer 16 with a thickness d 1, then the hard material layer 17 with a thickness d 2 and finally the non-stick layer 18 with a thickness d 3 were applied .

The thickness d₁ of the adhesive base layer 16 is preferably between 10 microns and 20 microns. The thickness d₂ of the hard material layer 17 is preferably between 30 microns and 70 microns. The hard material layer 17 is porous in reality and has a highly irregular structure on its surface.

The anti-adhesive layer 18 is applied to the hard material layer 17 in such a way that the tips 40 of the hard material layer 17 are only thinly coated and valleys 41 of the hard material layer 17 are essentially filled. 5 is extremely schematic, because the material of the non-stick layer 18 penetrates far into the hard material layer 17 due to the porosity of the hard material layer 17. A sharp separation between hard material layer 17 and non-stick layer 18, as shown in FIG. 5, is therefore not present in practice. Nevertheless, it also applies in practice that the hard material layer 17 is only thinly coated at its tips 40, while its valleys 41 are almost completely filled with non-stick material.

The thickness d₃ of the anti-adhesive layer 18 is preferably between 5 microns and 30 microns, the lower limit in the area of the peaks 40 and the higher value in the area of the valleys 41 to be found.

5 clearly shows that the supporting portion of the coating is formed by support points 42 which are located above the webs 31 of the metallic base body 15. The geometric structure of the supporting part is formed by the arrangement of the depressions 30 or webs 31, as can be clearly seen in FIG. 4.

Because of the very small dimensions of the depressions 30, air bubbles can therefore form in the depressions 30 or remain there, as indicated by 43 in FIG. 5.

In practical use, for example in the case of a frying pan 10, this means that the food to be fried rests only on the support points 42, ie the supporting portion of the structure, while the air bubbles 43 form a kind of air cushion or air cushion becomes. The air bubbles 43 can also be vapor bubbles of the boiling fat. They result from the fact that even hot fat is still so viscous that not all of the small depressions 30 are filled out and air bubbles thus remain there. On the other hand, the air bubbles 43 or the steam bubbles remain due to their adhesion in the depressions 30, so that the direct contact of the food to be fried with the pan base 11 is kept as low as possible.

Claims (13)

Process for coating household and kitchen appliances with the process steps: - Introducing cap-shaped depressions (30) into a surface of a preferably metallic base body (15; 25), the depressions having a diameter (D) between 1.0 and 3.0 mm and a depth (t) between 0.2 and 0 .5 mm; - Applying at least one thermally sprayed, in particular plasma-sprayed layer (16, 17) on the surface provided with depressions (30), the thickness (d 1, d 2) of the layer (16, 17) being less than half the depth ( t) is; and - Applying a non-stick layer (18) to the thermally sprayed layer (16, 17), the thickness (d₃) of the non-stick layer (18) being less than the thickness (d₁, d₂) of the thermally sprayed layer (16, 17). Method according to claim 1, characterized in that the depressions (30) have the shape of a spherical cap. Method according to claim 1 or 2, characterized in that the depressions (30) are arranged on a hexagonal grid (35). Method according to one or more of Claims 1 to 3, characterized in that the undumped webs (31) of the surface remaining between the depressions (30) between adjacent depressions (30) have a width (a) which is less than 20%, is preferably less than 10% of the diameter (D) of the depressions (30). Method according to one or more of claims 1 to 4, characterized in that the step of introducing the depressions (30) is carried out after the metallic base body (15; 25) has been heated. Method according to claim 5, characterized in that the metallic base body (15; 25) is converted into a softened state when heated. Method according to claim 5 or 6, characterized in that the metallic base body (15; 25) is heated by means of inductive heating. Method according to one or more of claims 1 to 7, characterized in that the thickness (d₁, d₂) of the thermally sprayed layer (16, 17; 26, 27) is between 10 µm and 70 µm. Method according to one or more of claims 1 to 8, characterized in that first an adhesive base layer (16; 26) with a thickness (d₁) of between 10 µm and 20 µm and then a hard material layer (17; 27) with a thickness ( d₂) is injected between 30 µm and 70 µm. Method according to one or more of claims 1 to 9, characterized in that the non-stick layer (18; 28) is applied with a thickness (d₃) between 5 µm and 50 µm. Method according to one or more of claims 1 to 10, characterized in that the surface is the surface of a bottom (11) of a frying pan (10). Household and kitchen utensils with a metallic base body (15; 25), the surface of which is structured, a hard layer (17; 27) of less than 100 µm thickness on the surface and an anti-adhesive layer on the hard layer (17; 27) 18; 28) are applied, characterized in that the structure of the surface consists of depressions (30), the diameter (D) of between 1.0 and 3.0 mm and the depth (t) of between 0.2 and 0.5 mm. Equipment according to claim 12, characterized in that the depressions (30) are arranged on a hexagonal grid (35).

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