EP1457267A1 - Method for manufacturing of formed metal parts of aluminium sheet with a decorative surface - Google Patents

Abstract

A coil-coating process for the production of weather- and corrosion-resistant, decorative formed parts from aluminum (or aluminum alloy) strip involves the application and hardening of a protective, polysiloxane-based sol-gel varnish before stamping out and forming the parts. A method for the production of weather- and corrosion-resistant formed parts with a decorative surface from aluminum or Al alloy sheet by a coil-coating process involves (1) preparation of a strip of Al or Al alloy (2) optional continuous degreasing (3) optional burnishing by an electrochemical, chemical or mechanical method (4) continuous pretreatment to form a primer layer (5) continuous application of polysiloxane-based sol-gel varnish to form a protective layer (6) continuous drying and hardening in a through-type oven (7) stamping out the parts (8) forming the stamped-out parts .

Description

The invention relates to a method for producing weather and corrosion resistant Formed sheet metal parts made of aluminum or an aluminum alloy with a decorative surface.

In the production of decorative formed parts from aluminum sheet, such as Decorative strips, the parts are first made from a conventional process Band punched out and formed. Pretreatment and application Further surface layers are carried out on the parts that have already been formed. This procedure is very complex and complex Handling connected because the sheet metal parts to be treated in different baths put on holder and often from one holder to another have to be repositioned.

The invention has for its object a method of the aforementioned To create kind that under the continuous production of formed parts Allows application of a coil coating process.

• Bereitstellen eines Bandes aus Aluminium oder aus einer Aluminiumlegierung,
• gegebenenfalls kontinuierliches Entfetten des Bandes,
• gegebenenfalls elektrochemisches, chemisches oder mechanisches Glänzen des gegebenenfalls entfetteten Bandes,
• kontinuierliche Vorbehandlung des gegebenenfalls entfetteten und/oder geglänzten Bandes zur Erzeugung einer als Haftgrund für eine Lackschicht geeigneten Vorbehandlungsschicht,
• kontinuierliches Lackieren des vorbehandelten Bandes mit einem Sol-Gel-Lack aus einem Polysiloxan zur Erzeugung einer Schutzschicht,
• kontinuierliches Trocknen und Härten der Schutzschicht in einem Durchlaufofen,
• Ausstanzen der mit der Schutzschicht versehenen Blechteile aus dem Band,
• Umformen der ausgestanzten Blechteile.

A method which comprises the following steps in succession leads to the achievement of the object according to the invention:

• Providing a strip made of aluminum or an aluminum alloy,
• if necessary, continuous degreasing of the belt,
• optionally electrochemical, chemical or mechanical glossing of the optionally degreased strip,
• continuous pretreatment of the possibly degreased and / or polished tape to produce a pretreatment layer suitable as a primer for a lacquer layer,
• continuous painting of the pre-treated tape with a sol-gel paint made of a polysiloxane to create a protective layer,
• continuous drying and hardening of the protective layer in a continuous furnace,
• Punching the sheet metal parts provided with the protective layer out of the strip,
• Forming the punched sheet metal parts.

The sol-gel varnish is preferably an alcoholic silane solution, preferably an alkoxysilane solution, and an aqueous colloidal silica solution manufactured polysiloxane and consists in particular of cross-linked inorganic polysiloxanes with over carbon bonds with the Silicon-linked organic groups, especially alkyl groups. polysiloxane is the term for polymers made from cross-linked siloxanes.

Commercial material can be used as the strip material for the production of the formed parts Aluminum with a purity of 98.3% and higher can be used depending on the requirements placed on the surface quality e.g. Aluminum with a purity of 99.0% and higher, sometimes also with a purity of 99.5%. In particularly stored cases, a purity of 99.8% and be displayed higher. In addition to aluminum, the purities mentioned can also Aluminum alloys are used. Preferred alloys are those of the series AA 1000, AA 3000 and AA 5000. Further possible ones Alloys contain, for example, 0.25 to 5% by weight, in particular 0.5 to 4% by weight magnesium or 0.2 to 2% by weight manganese, or 0.5 to 5% by weight Magnesium and 0.2 to 2 wt .-% manganese, in particular 1 wt .-% magnesium and 0.5% by weight of manganese, or 0.1 to 12% by weight, preferably 0.1 to 5 % By weight copper, or 0.5 to 6% by weight zinc and 0.5 to 5% by weight magnesium, or 0.5 to 6% by weight zinc, 0.5 to 5% by weight magnesium and 0.5 to 5% by weight Copper, 0.5 to 2% by weight iron and 0.2 to 2% by weight manganese, in particular 1.5% by weight iron and 0.4% by weight manganese, or AIMgSi or AIFeSi alloys. Other examples are AIMgCu alloys such as AlMg0.8Cu or AIMg alloys such as AIMg1, or AIFeMn alloys such as AlFeMn1.5.

The sheet metal parts can for example be bent, deep drawn or cold extruded or roll forming, but also be formed using other forming processes.

The pretreatment layer can be made, for example, by chromating, Phosphating or layer produced by anodic oxidation. Preferably is the pre-treatment layer made of anodized aluminum.

The pretreatment layer can have a thickness of, for example, at least 10 nm, preferably of at least 20 nm, in particular of at least 50 nm and advantageously have at least 100 nm. The maximum thickness of the pretreatment layer is, for example, 5000 nm, preferably 1500 nm and especially 300 nm.

The pretreatment layer is preferably an anodically produced oxide layer, built up in a non-redissolving or in a redissolving electrolyte has been. The pretreatment layer is preferably a porous, anodic generated oxide layer.

The anodization preferably takes place in an acidic electrolyte from the Series of phosphoric, citric, tartaric, chromic acid electrolytes and especially from the series of sulfuric acid electrolytes. The anodization takes place in the AC or DC method.

The pretreatment layer can also be a yellow chromating layer, a green chromating layer, a phosphate layer or a chrome-free pretreatment layer, those contained in at least one of the elements Ti, Zr, F, Mo or Mn Electrolyte has been formed included.

Furthermore, the aluminum surface can be pretreated in a chemical or electrochemical processes or an alkaline pickling process be subjected. Such glossy or pickling processes are before nodize performed.

Before applying a pre-treatment layer or performing the first pre-treatment steps the belt surface is expediently degreased and cleaned. The pretreatment can only be degreased and cleaned of the belt surface. The belt surface can be cleaned on known way, e.g. chemical and / or electrochemical and acidic or alkaline. Its purpose is to remove foreign substances and, if necessary the naturally created oxide layer on the aluminum surface. Suitable cleaning agents are e.g. acidic, aqueous degreasing agents, alkaline Degreasing agent based on polyphosphate and borate. A cleaning with moderate to heavy material removal forms pickling or etching by means of strongly alkaline or acidic pickling solutions, e.g. Caustic soda or a mixture of nitric acid and hydrofluoric acid. The existing one Removed oxide layer and its impurities. With strongly attacking alkaline Pickling may require acidic after-treatment.

With known electrochemical, chemical or mechanical Shine processes can also be used to clean the belt surface. Due to the glossy process, the visual appearance of the Belt surface on the end product can be influenced.

a) Entfetten bei pH 9 - 9,5 bei ca. 50°C,

b) Spülen mit Leitungswasser (Raumtemperatur),

c) Elektrochemisches Glänzen,

d) Spülen mit Leitungswasser (Raumtemperatur),

e) Anodisieren in 20% H₂SO₄ bei ca. 25°C und 20V Spannung,

f) Spülen in Leitungswasser bei ca. 50°C und

g) Spülen in entionisiertem Wasser bei ca. 85°C.

In the context of the method according to the invention, in a preferred embodiment, the pretreatment layer can be applied to the aluminum strip, for example, in compliance with the following process conditions:

a) degreasing at pH 9 - 9.5 at approx. 50 ° C,

b) rinsing with tap water (room temperature),

c) electrochemical shine,

d) rinsing with tap water (room temperature),

e) anodizing in 20% H ₂ SO ₄ at approx. 25 ° C and 20V voltage,

f) rinsing in tap water at approx. 50 ° C and

g) Rinse in deionized water at approx. 85 ° C.

The aluminum strip runs through the various treatment baths continuously at a speed of, for example, 40 m / min.

The protective layer and if necessary, additional layers are applied.

The sol-gel lacquer applied to the pretreatment layer is preferably a from an alcoholic silane solution, in particular an alkoxysilane solution, and a colonial silica solution polysiloxane. The polysiloxane is particularly hydrolyzed by a condensation reaction between and crosslinkable silanes, especially alkoxysilanes, and colloidal Silica produces.

The condensation reaction between hydrolyzed silanes, especially alkoxysilanes, with each other as well as hydrolyzed silanes, especially alkoxysilanes, and colloidal silica leads to the formation of an inorganic Network of polysiloxanes. At the same time, organic groups, in particular Alkyl groups or simple alkyl groups via carbon bonds built into the inorganic network. The organic groups or the alkyl groups, however, do not take part directly in the polymerization or the Cross-linking of the siloxanes, i.e. they are not used to form an organic Polymer system but only for functionalization. The function is that the organic groups, especially the alkyl groups, attached to the outside of the polysiloxanes during the sol-gel process and thereby form a layer that is water-repellent to the outside, which gives the sol-gel varnish a pronounced hydrophobic property gives.

The sol-gel process described leads, as mentioned, by targeted hydrolysis and condensation of alkoxides of silicon and silica to form a sol-gel lacquer from an inorganic network with built-in alkyl groups. The polysiloxanes thus obtained are therefore rather inorganic Classify polymers.

In the production of a preferred embodiment of a sol-gel lacquer as Protective layer is expediently based on two basic solutions A and B.

Solution A is an alcoholic solution of one or more different ones Alkoxysilanes, the alkoxysilanes not in an anhydrous medium hydrolyzed form. An alcohol is expediently used as solvent, such as, for example, methyl, ethyl, propyl or butyl alcohol and preferably isopropyl alcohol, used.

The alkoxysilanes are described by the general formula X _n Si (OR) _4-n , in which "R" is simple alkyl, preferably from the group comprising methyl, ethyl, propyl and butyl. "X" is also expediently an alkyl, preferably from the group comprising methyl, ethyl, propyl and butyl. Suitable alkoxysilanes are, for example, tetramethoxysilanes (TMOS) and preferably tetraethoxysilane (TEOS) and methyltrimethoxysilane (MTMOS) and other alkoxysilanes.

In a particularly preferred embodiment, solution A is made from tetraethoxysilane (TEOS) and / or methyltrimethoxysilane (MTMOS) with a methyl, Ethyl or propyl alcohol and especially with an isopropyl alcohol as Prepared solvent. Solution A can e.g. 25-35% by weight, in particular 30% by weight, TEOS and 15-25% by weight, in particular 20% by weight, Contain MTMOS, both dissolved in 40-60% by weight, in particular 50% by weight, Isopropyl alcohol.

Solution B contains colloidal silica dissolved in water. In an expedient embodiment, solution B is adjusted to a pH between 2.0-4, preferably between 2.5-3.0 and in particular 2.7, using acid, preferably nitric acid (HNO ₃ ).

The silica used is expediently a silica stabilized in an acidic environment, the pH of the silica advantageously being 2-4. The silica is advantageously low in alkali. The alkali content (eg Na ₂ O) of the silica is preferably below 0.04% by weight.

Solution B contains, for example, 70-80% by weight, in particular 75% by weight, water as solvent and 20-30% by weight, in particular 25% by weight, of colloidal silica. Solution B is expediently adjusted to a pH between 2.0-3.5, preferably between 2.5-3.0, and in particular 2.7, using nitric acid (HNO ₃ ). A preferred silica solution is, for example, by the company Nissan Chemical Industries Ltd. with the product name "SNOWTEX® O".

The combination and mixing of the two basic solutions A and B in the presence of the nitric acid leads to a hydrolysis reaction between the water contained in solution B and the alkoxysilanes contained in solution A. Hydrolysis reaction: Si (OR) _n + nH ₂ O → Si (OH) _n + nR (OH) At the same time, a condensation reaction occurs in which a siloxane bond (Si-O-Si) is built up from two Si-OH groups each with elimination of water. As the polymerization progresses, a network of polysiloxanes to which alkyl groups are attached is formed. The new mixed solution is in a gel state. The two solutions A and B are preferably mixed in a weight ratio of 7: 3 parts.

The sol-gel lacquer is expediently applied in gel form to the surface of the Aluminum tape applied and then dried or hardened.

The continuous coating is done in the coil painting process, too Coil coating process called. A typical coil coating process is a Roller application process with two or three rollers. The layer thickness of the cured Sol-gel lacquer is preferably at least 1 μm and is preferably between 1 and 4.5 µm, in particular between 1 and 3 µm. contains If the sol-gel lacquer also contains color pigments, the layer thickness can be up to 10 µm.

The drying process consists of the water remaining in the sol-gel varnish and drive out alcohols, whereby the sol-gel varnish hardens and a weather-resistant and corrosion-resistant protective layer on the belt surface arises.

The tape coated with the sol-gel varnish is expediently used Radiation, such as UV radiation, electron radiation, laser radiation, or by means of Heat radiation, such as IR radiation, or by means of convection heating or a combination of the aforementioned drying or curing processes, dried respectively. hardened.

The temperature measured on the belt surface for drying or hardening the sol-gel lacquer is expediently greater than 60 ° C., preferably greater than 150 ° C and especially greater than 200 ° C. The elevated temperature is furthermore expediently less than 400 ° C., preferably less than 350 ° C. and in particular less than 300 °. The temperature is particularly preferred between 250 ° C and 300 ° C. The temperature specification is a so-called "Peak Metal Temperature" (PMT).

The elevated temperature can, for example, last for 5 seconds to 2 minutes act on the tape. The sol-gel varnish is preferred for a period of time less than 90 seconds, especially less than 60 seconds, and preferably more than 10 seconds, especially more than Dried or hardened for 30 seconds. When using IR radiation, the Drying times tend to be in the lower range of the specified stay times.

Convection heating can be carried out expediently by applying heated gases such as air, nitrogen, noble gases or mixtures thereof. The sol-gel lacquer layer is dried in a continuous oven.

The formed parts are after the application and drying of the protective layer punched out of the band and formed. The forming hardly leads to crack formation in the protective layer.

The formed parts produced by the process according to the invention have thanks to the hard protective layer with excellent adhesion good protection against weather, corrosion and mechanical Abrasion and are characterized by good UV resistance out.

The molded parts produced according to the invention have a sol-gel protective layer made of polysiloxanes with a high surface hardness. The sol-gel protective layer expediently has a pencil method according to Wolf Wilburn "according to DIN 55350 part 18 hardness of greater than "f ', preferably greater than" h ", in particular greater than" 2h "and advantageous from larger "3h", whereby larger in the sense of harder to understand is.

The sol-gel layer is also characterized by excellent adhesion on the formed sheet metal parts.

The preparation and manufacture of a described particularly preferred embodiment of a sol-gel lacquer. To a solution A and a solution B are prepared.

50 Gew.-% Isopropylalkohol

30 Gew.-% Tetraethoxysilan (TEOS)

20 Gew.-% Methyltrimethoxysilan (MTMOS)

Solution A contains:

50% by weight isopropyl alcohol

30% by weight tetraethoxysilane (TEOS)

20% by weight methyltrimethoxysilane (MTMOS)

75 Gew.-% Wasser

25 Gew.-% Kolloidale Kieselsäure

Solution B contains:

75% by weight of water

25% by weight colloidal silica

The pH of solution B is adjusted to approximately 2.7 with the addition of an acid, in particular nitric acid (HNO ₃ ).

The production of the sol-gel varnish and the coating of the aluminum strip is carried out in a preferred embodiment as follows:

A base solution A, as described above, in a proportion of 70% by weight of the Mixed solution becomes a solution B in a proportion of 30% by weight with stirring added to the mixed solution. The solutions A and B are under continuous Stirring transferred into a mixed solution, heat due to reaction is released.

The mixed solution is over a certain time, for example for 1 h to 10 h, preferably during 4 to 8 h, in particular stirred for around 6 h. The mixture is then filtered. The filter serves to hold back larger Particles such as Particles of colonial silica. The pore diameter or the mesh size of the filter depends on the desired layer thickness, because particles with a larger diameter than the desired layer thickness affect the surface quality of the protective layer. Filtration can for example using a polypropylene filter with a porosity of 1 µm.

The mixed solution is expediently at a pH of 2-4, preferably from 2 to 3.5, in particular from 2.5 to 3, and particularly preferably from 2.7, held. The pH is adjusted using acid, preferably using Nitric acid.

After completion of the stirring process, the sol-gel varnish can be removed using one of the the aforementioned method is applied to the belt surface and subsequently, can be dried or hardened as described above.

In an advantageous embodiment of the manufacturing process, the sol-gel varnish after its manufacture and before application to the belt surface during a few minutes to several hours, preferably between 1 and 24 hours, especially between 12 and 22 h and particularly preferably for around 17 h immobilized.

The element analysis of the hardened sol-gel varnish using XPS (X-Ray Photoelectron Spectroscopy) has e.g. the elements oxygen, silicon and around 5 - 20 at.% (atomic percent) carbon after.

Claims (11)

Process for producing weatherproof and corrosion-resistant formed sheet metal parts made of aluminum or of an aluminum alloy with a decorative surface using a coil coating process, comprising the steps in succession: Providing a strip made of aluminum or an aluminum alloy, if necessary, continuous degreasing of the belt, optionally electrochemical, chemical or mechanical glossing of the optionally degreased strip, continuous pretreatment of the possibly degreased and / or polished tape to produce a pretreatment layer suitable as a primer for a lacquer layer, continuous painting of the pre-treated tape with a sol-gel paint made of a polysiloxane to create a protective layer, continuous drying and hardening of the protective layer in a continuous furnace, Punching the sheet metal parts provided with the protective layer out of the strip, Forming the punched sheet metal parts. A method according to claim 1, characterized in that the sol-gel lacquer is a polysiloxane made from an alcoholic silane solution, preferably an alkoxysilane solution, and an aqueous colloidal silica solution. Method according to Claim 1 or 2, characterized in that the sol-gel lacquer consists of crosslinked inorganic polysiloxanes with organic groups, in particular alkyl groups, which are bonded to the silicon via carbon bonds. Method according to one of claims 1 to 3, characterized in that a glossy material or a material with a matt decorative surface is used as the band. Method according to one of claims 1 to 4, characterized in that an anodic oxide layer is produced as a pretreatment layer on the strip surface. A method according to claim 5, characterized in that the anodic oxide layer is colored. Method according to one of claims 1 to 4, characterized in that a chromate layer is produced as a pretreatment layer on the strip surface. Method according to one of claims 1 to 4, characterized in that a chromium-free layer is produced as a pretreatment layer on the belt surface. Method according to one of claims 1 to 8, characterized in that the thickness of the protective layer is at least 1 µm and preferably between 1 and 10 µm, in particular between 1 and 4.5 µm and particularly preferably between 1 and 3 µm. Method according to one of claims 1 to 10, characterized in that the sol-gel lacquer contains color pigments. Method according to one of claims 1 to 11, characterized in that the punched and formed sheet metal parts are used as decorative parts, in particular as decorative parts such as trim strips in automobile construction.