|Title of Invention||
PROCESS FOR COATING ON METALLIC SURFACES
|Abstract||The invention relates to a method for coating metal surfaces, whereby at least one layer of a composition is applied to the surface, said composition comprising hydrolyzates/condensates of at least one silane or a silicone resin binder and optionally a suitable solvent, and additionally containing at least one metal filler. The coating is subsequently dried and/or cured.|
Process for coating on metallic surfaces
The following invention relates to a process for coating of metallic surfaces, in which minimum one layer of a composition on the surface is brought on consisting of hydrolysate/condensate of at least one silan or a silicon binding material as well as, where applicable, a suitable solvent.
In consideration of today's high security requirements in the manufacture of vehicles, selected types of steel with very high strength are being applied for load carrying chassis components and safety-relevant components such as, for instance, side impact rail and reinforcements.
In the design of automobiles, these days for certain vehicles some of the components are for instance fabricated out of mangnaese-bor-steel (22 MnB5). Using these steel types, strengths of up to 1650 MPa could be achieved through warm forging, as against the values of up to 1100 MPa obtained through the customary cold forging. In the warm forging, the steel would be brought to the austenitic range through heating up to 950° under protective gas atmosphere (nitrogen), subsequently brought to the forging tool and shaped. In this process, lasting for a few seconds between the withdrawal from the furnace and the subsequent forging operation, the steel component experiences a cooling to temperatures between 100-200 °C. As a result, a martenssitic structure with a very high strength is obtained.
A problem with this process is oxidation of the component, which occurs immediately, as soon as the component heated to 950°C is taken out from the furnace containing protective gas and is put in contact with atmospheric oxygen. The resultant scale layer is not homogenous, brittle and breaks into pieces and does not offer a strong basis for consequent processing such as welding, KTL painting etc., and therefore these scales are removed before the further processing of the component through blasting/radiation. This blasting operation, which is partially carried out manually, is a time consuming and expensive process and is connected with generation of heavy dirt and fine particles. In addition, particles of the scale layer remain in the forging tool and therefore must be regularly removed with a considerable degree of effort and time, which does not serve the purpose of obtaining the desired number of pieces in series production. Therefore, there exists a very strong demand for a process which prevents the oxidation in the warm forging process right before its inception.
State-of-the-art of Technology is the so called allitization. Under this surface protection process, aluminium is brought on the surface of the steel. Aluminium-Iron compound crystals are created which bring about a very good oxidation protection upto 950°C. The liquid aluminium brought on through spraying or dipping penetrates in the surface during the subsequent diffusion annealing. The spray-allitization is adopted in all places where objects made of steel are subjected to a thermal oxidation through high operating temperature, and a production using heat resistant special material is not economically justified. The oxidation protection through spray-allitization is based on the principle that aluminum at temperatures of above 800°C gets diffused under creation of a iron-aluminium alloy into the steel. That is, it builds a layer decreasing in aluminium between the aluminium on the surface and the basic iron material. The resultant iron-aluminium alloy by itself is more oxidation resistant than steel itself, and moreover in actual practice we get a high heat resistance Al203-skin on the surface quickly, which prevents a rapid penetration of the oxygen on the
fron/steel. Components correspondingly treated find application in heat forging at automobile manufacturers, where through the aluminization, an effective oxidation protection is achieved. In several application cases, however, a number of components are used with very high degree of shaping/forming, which forming exercise is done in two steps. In the first step, a rough cold forging is done and in the subsequent warm forging, the component is brought to its end-geometry and simultaneously hardened. The aluminized components referred to cannot be applied here because already at the cold forging damage to the surface of for instance above 25-28 μm thickness occurs, which would lead during the subsequent warm forging to oxidation on the damaged parts and/or breakages.
In the patent document EP 30 895 B1, a lubricant is described for the warm forging, which relates to a compound made of alkali silicates, an additional alkali compound, for instance, an alkali hydroxide, water and a share of upto 20 weight percentage of sillane-adhesive material. This compound is used as lubricant in the manufacture of seamless steel tubes, in accordance with the Mannesmann process. In the manufacture of hollow bodies, because of high friction, temperatures in the magnitude of about 1000°C all above prevail. As a result of the lubricant compound referred to above, an iron oxide foil/film is supposed to be generated, with the use of which the protection of the surfaces against the friction forces arising during the forging process could be achieved.
In the Japanese Patent Document Abstract, JP 3291325, a process is described using which metallic surfaces can be protected against oxidation during hot rolling. In this context, on the metallic surface, a friction material is brought on which contains a glass component. This coating material includes aluminium oxide, silicium oxide and zircon oxide, and has a melting point in the range of 900 to 1300° and is said to produce on the metallic surface a film with anti-oxidizing characteristics; this foil is to be removed after the rolling, for instance through sand blasting.
The Patent Document DE 100 63 519 A1 describes a process for manufacture of low solvent solgel systems through hydrolyse or condensation of a sillane with alkoxyl under addition of water and separation of the condensate phase. The condensate phase is assembled with nano particles and the dispersion so obtained can be reduced to an optional substrate through a wet chemical process such as for instance, spraying, dipping or rolling. Glass, ceramic, wood, stone, plastic, textiles, paper, are specially mentioned as substrates, whereby even metal is mentioned. After bringing the dispersion to substrate, a drying in temperature range of 20 to above 500° C can take place.
Proceeding from the above mentioned state-of-the-art of technology, the objective of the following invention lies therein to make available a process for coating of metallic surfaces, which enables the production of a more effective protective layer against oxidation.
This solution to this task is given by an invention based process for coating of metallic surfaces with the exemplary characteristics of the main claim.
The following process is suitable especially for surface coating of a substrate, whose surface at least partially is made of steel. The invention based process is especially visualized for surface coating of substrates made of high strength steel and suitable ideally for surface coating of substrate made of high tensile steels which would be subjected to a warm forging process after the surface coating, especially a warm forging at temperatures between approximately 800°C and approximately 1000°C, ideally between about 880°C and about 970°C.
Object of the following invention is the creation of a special protective layer which is brought on the steel and subsequently dried at ambient temperature or thermally hardened and the painted components are effectively protected before oxidation during the hot forging process under, for instance, a temperature of 950° C.
The application of the invention-based coating can be purposeful even then if no hot gorging of the substrate is planned, especially for obtaining a corrosion protection layer.
Surprisingly, it has been shown that through a combination of a binding material and at least one metallic filling material, a coating composition is obtained is obtained, which allows itself to be applied on a metallic surface, especially as a wet-chemical and by means of this the metallic surface, especially a surface made of steel, at such temperature levels as are customary in warm / hot forging, can be protected effectively against oxidation while coming in contact with atmospheric oxygen. The advantage of the invention therefore lies therein that an oxidation protection can be easily guaranteed through wet-chemical application and drying and/or thermal hardening of a paint-like coating composition.
Therefore, this process can be very flexibly applied, that means, the paint can be applied at the paint-shop or directly at the automobile manufacture through spraying, rolling flow-coating, print / impregnation or dipping on almost all components. Further advantage lies therein that the paint, by virtue of its excellent adhesibility, flexibility and ideally at a lesser coat thickness in lower jam-range of a cold and warm forging demonstrates a with standability and thus is pre-destined for a direct coating of the steel coil in the coating plant.
tn keeping with the invention-based process, a paint layer with a coating thickness of, for instance, less than about 30 μm, ideally less than about 10 μm can be brought on. After the invention-based surface coating, for instance, a KTL-painting and/or phosphating can follow. For producing the invention-based paint layer, at least one of the alkyl-silane is used as the basis for obtaining the paint layer. As per the invention, a compound comprising minimum one Alkyl-alkoxy-silane and minimum one Akoxy-silane are hydrolyzed and /or condensed. The minimum one silane and/or a compound of silanes is hydrolyzed and/or condensed, for instance, in the manner mentioned before, preferably in a weak / light acidic solution. For this purpose, one could for instance, use a weak organic acid, such as formic acid or something similar. In this context, for obtaining at least one paint-layer, one should add at least one metallic filler-material to the silane to be condensed and /or to the silanes to be hydrolyzed and condensed. Especially a metal-pigment of one of the metals, Al, Zn, Mg, Fe, Sn or an alloy of these metals can be used as filler-material.
Instead of hydrolyzing or condensing silane, one could also use as binding-agent or silicone resin pre-dissolved in a solvent, where the solid material content should ideally be between about 10% and about 90% . Ideally the commercially available Alcohol, Ester, Ether or hydro-carbon, for instance Zenzine is suitable for use as solvent, where preferably solvents with a flash point of > 23° C should be used. For example, Butyl-glycol, 1-Butanol, 1-Methoxy-2-Propanal or similar solvent are suitable for use as solvents. The coating obtained, especially after a hot-forging, has an adequate corrosion-resistance for further processing of the metallic substrate, especially steels. A subsequent phosphating and/or KTL-painting can follow using a process generally in vogue in the automobile industry.
Where applicable, it is also possible to work in a solvent-free manner, if for instance, a silicon-resin is used as binding additive or material. In this case, the silicone resin can be processed similar to powder-coating.
The hardening of the coating material can be done through ventilation at ambient temperature or under enhanced temperature if the hardening needs to be accelerated, where temperatures of ideally, up to 400° C can be applied for drying and hardening of the coating. An accelerated hardening can also be meaningful for instance, through IR-Radiation, Circulatory-Air Drying, UV-Radiation or Electron-Radiation-Hardening. The coating can be applied both on flat substrate, or, also on coils, which pass through a step of the cold- and/or warm-forging; however, the coating can also be applied on already cold-forged sheet substrate.
The network of the coating composition can be further strengthened in keeping with a further development of the invention through nano-particles, where these are especially chosen from metal-oxidic and non-metal-oxidic particles with a size range of ideally between 2 nm and about 50 nm. In this context, for instance, substances such as AIOOH, corund, zirconium-oxide, Si02, Ti02 or similar substances can be considered.
As per a further development of the invention, an additional modification of a coating composition can be purposeful, where one would add for the hot-forging and/or cold-forging of this coating mass, a solid lubricant, for instance a wax, stearate, graphite, MoS2 Bornitride, aluminium oxide, titanium oxide, a classifier pigment for instance mica or similar item. Moreover, where applicable, commercially available rheology-additive can be added, for example, thixotroping agent, flow-control agent or similar substances.
After drying and hardening especially through heating at for example, up to about 400°C, a firmly-sticking film/foil on the substrate (for example steel strip) is obtained, which is flexible as a result of the organic components used. The ideally micro-scale filler material improves the lubrication effect already in a cold forging of a metallic substrate so coated. During a further heating at such temperatures, as customarily applied for hot-forging of steel strip, the organic
components burn out (that means the organic residues substituted in the Silanes), such that a glass-like Matrix remains on the coated surface. This gets baked jointly with the filler-material to form a solidly sticking dense layer. A metallic substrate with such a coated surface can be subjected thereafter to a hot-forging. The glass-like matrix, through the lesser layer thickness and the intimate connection with the component and the temperature-resistant filler-material remains such that it can be shaped or forged, where the lubrication effect is retained. In a possibly subsequent secondary treatment of a substrate so coated, for example during a cathodic dip-painting (CDP), the metallic filler material on the layer carries the electrical conductivity required for the CDP.
Objects of the following invention is further an automobile component, particularly the body shell which has at least partially a surface coating obtained as per one of the processes in keeping with the following invention. The invention-based process makes itself suitable particularly for coating of load carrying body-shell components or safety- relevant components such as for instance, side impact load carriers or reinforcements for which generally chosen steel types with high hardness/strength are used.
The following invention is explained here-below on the basis of the design examples:
Basically, three basic recipes are for example described for the production of the paint with the corresponding results/characteristics:
100 g of 5% formic acid is added to 100 g methyl-tri-ethoxysilane (MTEOS) 40 g glycidyloxy-propyl-triethoxy-silane (GLYEO, Degussa) and 40 g tetra-ethoxy-silane (TEOS, Degussa) and at ambient temperature stirred through the night. Thereafter, 50 g of aluminium pigment paste, Decomet extra shine Al 1002/10 of
M/s. Schlenk is stirred in with the use of a blade agitator and after complete distribution of the pigment under stirring, 100 g ethanol is added. Before carrying out further processing, 5 g of a wetting material of type Byk Dynwet 800, (M/s. Byk Chemie) is added.
The prepared paint is applied using a painting pistol (for instance, Sata Jet, nozzle 1,4 mm) on a grease-free drawn part., so that the entire surface is covered by a thin wet film. The paint layer is allowed to be aired at an ambient temperature of 5 minutes and thereafter depending upon the required abrasion resistance, it is either dried for an additional 30 minutes under ambient temperature or hardened for 5-15 minutes under a temperature of 80 to 200°C.
After the hardening and recooling at ambient temperatures, the drawn part is covered by about 2 - 6 μm thick silvery layer, which sticks firmly to the substrate (very good results have been achieved in cross-cut adhesion test / tape test) as well as not susceptible to scratches with finger nails. The coated components are corrosion resistant when stored under dry atmosphere. The coated components can be applied directly after the coating, but also after storage in hot forging processes, and show even after contact with atmospheric oxygen under 950°C, no trace of oxidation. Under 950°C, a firmly sticking mixed oxide layer is created made of iron, aluminium, silicium, oxygen, which is suitable as the adhesive base for a subsequent cold dip painting.
108 gram of 5% formic acid is added to a compound of 120 g methyl-tri-ethoxy-sliane (MTEOS) and 60 g tetra-ethoxy-silane (TEOS), drawn from Degussa-Huels, and stirred at ambient temperature through the night. Thereafter 50 g aluminium pigment paste Decomet high shine Al 1002 of M/s. Schlenk is stirred
in with a blade agitator, and after complete distribution of the pigment under stirring, 150 g of N-Methyl 2-pyrrolidinon is added. Before further processing, 5 g of a wetting material of type Byk 306 (BYK Chemie) is added to the preparation. 5 grams of molybdenum disulphide powder with a particle size of less than 5 urn is added as solid lubricant and is dispersed for 20 minutes with a dissolver under an'RPM 1000 in a homogenous manner.
The prepared paint is rolled in a coil/strip coating plant under a speed of 60 meter/minute on a grease-free cleaned steel strip, and hardened under a temperature of 200 to 250°C.
After the hardening, the coil is covered with a homogenously silvery layer with a thickness in the range of above 2 - 6 μm (adjustable), which is mechanically so capable of resistance that the steel strip can be rolled without damaging the layer and can be further processed with the usual procedures. Cut platinum components can be cold-forged without damaging the coating on fold spots and subsequently processed without oxidation in the hot forging process. Firmly sticking mixure of oxide layer made of iron, aluminium, silicium and oxygen is created under 950°C and this layer is suitable as the adhesive base for a subsequent cold dip painting.
100 g 1% tri-fluoro-acetic acid is added to a mixture of 120 g methyl-tri-ethoxy-silane (for instance, Dynasylan MTES, M/s. Degussa) and 40 g of tetra-ethoxy-silane (Dynail A, M/s. Degussa) and stirred under ambient temperature over the night. Thereafter 150 g of high boiling solvent butyl glycol, 0,2 g dispersion materials Disperbyk 180 (M/s. Byk Chemie as well as 35 g aluminium pigment paste Decomet 1006/30 (M/s. Schlenk) is added and stirred with a blade agitator.
Five grams of ground natural graphite with a particle size of The finished paint is applied with the use of a coil coating machine under a speed of 60 meter/minute on a grease-free pre-cleaned steel strip and hardened at a temperature of 200-250 °C.
After the hardening, the coil is covered with a homogenously silvery layer with a thickness in the range of above 2-6 μm (adjustable) which is mechanically so highly resistant that the steel strip can be rolled without damaging the layer and further processed using the usual methods. Cut platinum components could be cold forged without damaging the layer at folding spots, and subsequently processed without oxidation using hot forging process. Under 950°C, a firmly sticking mixed oxide layer made of iron, aluminium, silicium oxygen is created which is suitable as the adhesive base for the subsequent cold dip painting procedure.
1. Process for coating of metallic surfaces in which one would bring at least one layer of a composition on the surface comprising hydrolysate/condensate of minimum one silane or a silicon resin binding material as well as, where applicable a suitable solvent is thereby characterized that the composition contains furthermore minimum one metallic filler material and the coating is subsequently dried and/or hardened.
2. Process according to Claim 1 is thereby characterized that the coating composition contains minimum one metallic salt
3. Process according to Claim 1 or 2, is thereby characterized that the coating composition includes as metallic filler material at least one metal pigment in such a quantity that a proportion of between 10% and 90% of filler material is obtained after the hardening.
4. Process according to one of the claims 1-3 is thereby characterized that the coating composition is applied on wet chemistry basis on the surface of the substrate and thereafter hardened.
5. Process according to one of the claims 1 -4 is thereby characterized that a surface coating on a substrate happens, whose surface is made at least partially of steel.
6. Process according to claim 5 is thereby characterized that the surface coating is done a substrate made of a high tensile/steel.
7. Process according to one of the claims 1-6 is thereby characterized that the substrate is subjected to a hot forging process after the surface coating.
8. Process according to claim 7 is thereby characterized that the hot forging process is carried out under a temperature ranging between about 800°C and about 1000°C ideally under between about 880 and 970°C.
9. Process according to one of the claims 1-8 is thereby characterized that the coating composition contains further a solid lubricant for the hot forging and/or cold forging, ideally a wax, stearate, graphite, MoS2, bornitride, aluminium oxide, titanium dioxide or a classifier pigment.
10. Process according to one of the claims 1-9 is thereby characterized that the coating composition furthermore contains nano particles, especially selected from metal- and non-metal oxidic particles, ideally with a particle size in range between 2 nm and about 15 nm.
11. Process according to one of the claims 1-10 is thereby characterized that the direct coating of steel coils is done preferably in a coil coating plant.
12. Process according to one of the claims 1-11 is thereby characterized that the paint layer with a coating thickness of less than about 30 μm, ideally less than about 10 μm is applied.
13. Process according to one of the claims 1 -12 is thereby characterized that the coating composition is hardened through ventilation at ambient temperature or under enhanced temperature of up to 400 °C.
14. Process according to one of the claims 1-13 is thereby characterized that the coating composition is harnened in an accelerated manner with the use especially of IR-Radiation, circulatory air drying, UV radiations or electron radiation.
15. Process according to one of the claims 1-14 is thereby characterized that a cold dip painting and/or phosphating takes place after the surface coating.
16. Process according to one of the claims 1-15 is thereby characterized that a substrate provided with a painted layer is subsequently subjected to at least one work-step of cold forging.
17. Process according to claim 16, is thereby characterized that the minimum one cold forging step is visualized before carrying out the hot forging process.
18. Process according to one of the claims 1-17 is thereby characterized that for creation of the coating, at least one of the alkoxy-silane, aryl-silane and/or alkyl-silane, is kept as the bases, and which is hydrolyzed and/or condensed.
19. Process according to one of the claims 1-18 is thereby characterized that the silane hydrolisat-/condensate or silicon resin used as binding material is applied after dissolving it in a solvent, whereby the solid material content should be ideally between about 10% and about 90%.
20. Process according to claim 19 is thereby characterized that a alcohol, esther, ether or a hydrocarbon material is used as solvent, ideally with a flash point of > 23°C.
21. Process according to one of the claims 1-20 is thereby characterized that a metal pigment of one of the metals Al, Zn, Mg, Fe, Sn or an alloy of one of these metals is used as filler materials.
22.Automobile component, especially body shell component is thereby characterized that it has at least partially a surface coating obtained in accordance with one of the processes under one of the claims 1-21 above.
MODIFIED CLAIMS: [Received at the international office on 20th February 2006]
1. Material for production of a protective layer against oxidation metal surfaces is thereby characterized that the material contains as binding material hydrolysate/condensate of minimum one silan or a silicon resin binding material as well as minimum one metallic filler material.
2. Material according to claim 1 is thereby characterized that the material contains furthermore one metallic salt
3. Material according to one of the claims 1 or 2 above is thereby characterized that the hydrolisate/condensate of at least one silane is made of minimum one alkoxy-silane, aryl-silane, and/or alkyl silane
4. Material according to one of the claims 1 to 3 is thereby characterized that the binding material is dissolved previously in a solvent where the solid material content ideally is between about 10% and about 90%
5. Material according to claim 4 is thereby characterized that the solvent is an alcohol, ester, ether or a hydro carbon material, preferably with a flash point > 23°C
6. Material according to one of the claims 1 to 5 is thereby characterized that the metallic filler material is a metal pigment of one of the metals Al, Zn, Mg, Fe, Sn or an alloy of one of these metals.
7. Material according to one of the claims 1 to 6 is thereby characterized that the material used as metallic filler material contains metal pigments at least in such a quantity that a proportion of between 10% and 90% of solid material is obtained after hardening the coating
8. Material according to one of the claims 1 to 7 is thereby characterized that the material contains nano particles, especially metal- and non-metal oxidic particles, ideally with a particle size in the range of about 2 nm and about 50 nm
9. Material according to one of the claims 1 to 8 above is thereby characterized that the material contains at least one solid lubricant, ideally a wax, stearate, graphite, MoS2 bore-nitride, aluminium-oxide, titanium-dioxide or a classifier pigment, especially mica.
10. Material according to claim 1 to 9 is thereby characterized that the material contains rheology additive, preferably thixo-tropier material and/or flow control material
11. Process for coating of metallic surfaces characterized through the following steps:
- Application of a material as per one of the claims 1 to 10 above on the surface
- Drying and/or hardening of the coating
12. Processing according to claim 11 is thereby characterized that the coating
composition is applied on wet chemistry basis on the surface of substrate
and hardened thereafter.
13. Processing according to one of the claims 11 or 12, is thereby characterized that the surface coating is done on a substrate whose surface at least partially is made of steel
14. Processing according to claim 13 is thereby characterized that a substrate made of a high tensile steel is surface coated.
15. Processing according to one of the claims 11 to 14 is thereby characterized that the substrate is subjected to hot forging process after the surface coating.
16. Processing according to claim 15 is thereby characterized that a hot forging process is carried out at a temperature between about 800°C and about 1000°C ideally under between about 880 and 970°C
17. Processing according to one of the claims 11 to 16 is thereby characterized that a direct coating of steel coil takes place, especially in a coil coating machine
18. Processing according to one of the claims 11 to 17 is thereby characterized that a paint coating with a layer thickness of less than about 30 jam, ideally less than about 10 μm is brought on.
19. Processing according to one of the claims 11 to 18 is thereby characterized that the coating composition is hardened through ventilation at ambient temperature or at an enhanced temperature of up to 400°C
20. Processing according to one of the claims 11 to 19 is thereby characterized that the coating composition is hardened in an accelerated manner especially using IR-Radiation, circulatory air drying, UV radiation or electron radiation.
21. Processing according to one of the claims 11 to 20 is thereby
characterized that after the surface coating, a cold dip painting and/or
phosphating takes place.
22. Processing according to one of the claims 11 to 21 is thereby
characterized that the substrate with a painted layer is subjected
subsequently to a cold forging in at least one work-step.
23. Processing according to claim 22 is thereby characterized that the
minimum cold forging step is visualized before a hot forging process
24. Automobile component especially body shell is thereby characterized that
it has at least partially a surface coating, which has been obtained using
one of the processes as per claims 11 to 23
|Indian Patent Application Number||1431/CHENP/2007|
|PG Journal Number||10/2012|
|Date of Filing||09-Apr-2007|
|Name of Patentee||VOLKSWAGEN AKTIENGESELLSCHAFT|
|Applicant Address||38436 WOLFSBURG, GERMANY|
|PCT International Classification Number||C09D 183/04|
|PCT International Application Number||PCT/EP05/10622|
|PCT International Filing date||2005-10-01|