DK2130951T3

DK2130951T3 - A process for preparing a metal plate and a metal plate.

Info

Publication number: DK2130951T3
Application number: DK07823003.4T
Authority: DK
Inventors: De La Fuente Carlos Tapia
Original assignee: Recubrimientos Plasticos S A
Priority date: 2007-02-27
Filing date: 2007-10-23
Publication date: 2015-10-05
Also published as: PL2130951T3; EP2130951A1; EP2130951A4; ES2310112A1; ES2547277T3; EP2130951B1; ES2310112B1; PT2130951E; WO2008104611A1

Description

DESCRIPTION Current situation

The sharp increase in the consumption of stainless steel in recent years in diverse industries such as electrical appliances (refrigerators, dishwashers, ovens, washing machines, microwave ovens, etc.), the elevator, cold storages in catering, and all types of decorative metal furniture has, in turn, produced a sharp increase in its price. This tension in the market, jointly with the search for new coatings that make it possible to protect against stains and sources of corrosion to stainless steel while maintaining its aesthetic appearance, has brought about continuous development of new products that can be grouped in two blocks: 1) The development of new transparent organic coatings applied on real stainless Steel, that make it possible to maintain its aesthetic characteristics, but at the same time, protect the material against corrosion and allow the use of lower alloy steels with lower cost. 2) The development of organic coatings on film base that imitate the design of stainless steel but applied on cold-rolled steel of low carbon content, zinc-plated or galvanized, which makes it possible to obtain similar aesthetic appearance and provides adequate corrosion-resistance for the aforementioned sectors.

Issue to be resolved

The problem of the first type of solution is that its price continues to be high, as the substrate is stainless steel, and the corrosion resistance necessary for many applications is not as high as this product has. On the other hand, its great advantage is the metal aesthetic appearance and the possibility of different designs.

The problem of the second type of solution is that its aesthetic appearance is not as good as that of real stainless steel; it is not metallic, it is plastic. On the other hand, its corrosion resistance is sufficient for many applications and its price is much more competitive.

In conclusion, the line of action of the large steel companies in the market has been to try to improve the aesthetic appearance of a substrate of steel with low carbon content using mechanical means to simulate the appearance obtained in stainless steel, and applying a series of organic layers to enhance corrosion resistance.

But the known products (metal panels) are not satisfactory, as they do not even meet the specifications of the industrial sectors mentioned because: - The drawing of the material according to ECCA T6 test is less than 8mm (value required in the electrical appliance, elevator sectors, etc.) (The adhesion of the organic coating is lower than that required) - The folding strength according to ECCA T7 test is 0.5-1 T (value required 0-0.5T) (The metal coating cracks and in turn, the organic coating cracks) - Corrosion resistance in salt spray chamber according to ECCA T8 test is lower than 150 hours (requirement 300 to 500 hours) (The material corrodes and cannot be used (ECCA is the European Coil Coating Association, and its testing codes are standardized for the sector and the customers of other sectors, as well as being correlated with ISO, EN and ASTM standards).

The applicant has studied the problem and in accordance with the tests at its facilities, considers that the main cause of the problem resides in that: If mechanical action is performed on a metal substrate of steel with low carbon content coated with a sacrificial anode (for example, zinc, chrome, tin....) that improves its corrosion resistance (zinc in galvanized steel, tin in tinplate, or chrome in chrome plate), the sacrificial anode is damaged, and even though an organic coating is applied the behaviour of the material is not valid. A metal panel of a ferrous metal substrate with a corroded metal coating that has the outer appearance of stainless steel is known by the Patent US 2006/198988A1. A metal panel of a steel substrate with corroded sides and a coating of Zn electroplating is known by the Patent JP S63 140098.

The solution proposed by the applicant consists of reversing in time the phases of coating and satin finish, arranging in the new process to first satin-finish and then coat.

Other problems and solutions will be explained later.

Specifically, the process of manufacturing of a metal panel, of this invention, is characterized in that a sheet of steel with low carbon content of between 0.10% and 0.20% and thickness of between 0.10mm and 2.00mm is subjected: a) in a first phase, to a mechanical satin finish by sanding with aluminium oxide sandpaper, with a sanding speed of between 4 and 20 metres/minute, and then b) to a second phase in which the satin-finished sheet is coated by electroplating with a coat of a sacrificial anode chosen from chrome, tin and zinc with a quantity of between 40 mg/m2 and 500 mg/m2.

It is also characterized in that the steel sheet already coated with the sacrificial anode is subjected to cleaning baths, the last of them with water of a conductivity of less than 50pS/cm.

The following is achieved with the solution of the invention: 1) The base substrate is a steel with low carbon content (0.10% to 0.20%), cold-rolled or galvanized or tinplate of thicknesses (0.10 mm to 2.00 mm), which reduces the cost of the product. 2) This substrate is satin-finished mechanically in a process similar to that of the stainless steel, obtaining a design and aesthetic appearance very similar to that of this steel 3) Subsequent to the satin finish, it is coated with a fine layer of chrome, tin or zinc (40mg/m2 to500mg/m2) which fulfils two functions. On the one hand, it acts as a sacrificial anode to improve the corrosion-resistance of the base metal, and on the other hand, it homogenizes the surface and gives it a brighter and more metallic appearance, similar to that of stainless steel. On electroplating this fine layer of chrome after the mechanical satin finish, the satin finish is prevented from damaging the sacrificial material and it remains intact to be able to achieve good adhesion in the organic coating

With this new process, the values required by the customers in the aforementioned tests are achieved, and the applicability to said sectors of a product with aesthetic appearance similar to that of stainless, with mechanical and anti-corrosion properties that are more than acceptable for the product, and at a much lower cost.

Description of the process

The process consists of the following phases: 1) The base substrate of the product is a steel with low carbon content (0.10% to 0.20%) (its mechanical characteristics, yield strength, ultimate tensile strength and elongation cover all the values of the standard), with a thickness of 0.10mm to 2.00mm and that is mechanically satin finished with aluminium oxide sanding rollers or belts in any internationally approved standard finish (Grades between 60-320 or “Scotch Brite” finish) in a process whose range of speeds is 4 to 20 metres/min.) 2) The satin finished substrate is coated by electroplating with a sacrificial anode (chrome, tin or zinc) (it could be a mixture of them) in a quantity of between 40 mg/m2 and 500 mg/m2, obtaining a surface that is homogeneous, bright, and maintaining the satin-finish design applied on the substrate base.

Sacrificial anode is the name given to the metal that will be corroded by the environmental conditions, instead of the iron (Fe) component of the steel. 3) The material obtained is treated chemically by a series of cleaning baths, chemical degreasing and washes; the last bath is with demineralized water with a conductivity of less than 50pS/cm. 4) The product is prepared to apply an adhesive on the outer face or exposed part; its resin base can be polyester, polyurethane or acrylic, in a layer of 10 to 50 wet microns (before the curing process) and a polyester primer, poly vinyl butyral, epoxy or polyurethane on the inner face or unexposed part. The material is put into an oven that can reach a metal temperature of 150 to 210°C to cure the liquid organic coating, and when it comes out a PET film is applied which seals the product. 5) (Optional phase) After the cleaning baths, and optionally, to increase even more the corrosion resistance in especially demanding products, a transparent primer in water base can be applied, to deposit a fine layer of a noble material (for example, zirconium, titanium) (not greater than 10mg/m2). This primer is cured in an oven that makes it possible to reach a metal temperature of 100°C to evaporate the water from the primer. 6) (2nd Optional phase) Optionally, a protective film can be placed after the application of the PET film to allow the customer to handle and shape the steel without damaging the coatings.

The product resulting from this process shows substantial improvements as compared to a conventional product, as is indicated in the following tests.

Tests Conventional product Product of invention ECCA T6 (Erichsen drawing) less than 6mm more than 8mm ECCA T7

Folding strength 0.5-1 T (substrate cracking) 0T without cracking ECCA T8

Corrosion resistance in

Salt spray chamber Less than 150h 300-500h ECCA T9

Resistance to immersion in water Less than 10Oh 500h ECCAT13

Resistance to aging

by heat 200h to 120°C 500h to 120°C

Examples:

Example 1

Substrate: Cold-rolled steel with low carbon content (0.12%) and thickness of 0.50mm.

Satin finish: Satin finish process applied on the substrate mechanically with aluminium oxide sandpaper in a standardized grade and with the market name of “Scotch Brite”, and which simulates the same finish of stainless steel.

Chrome plating: Chrome electroplating on the satin finished substrate with a layer equivalent to 140mg/m2.

Chemical treatment: chemical cleaning with a series of degreasings and washes, the last one with demineralized water with conductivity lower than 50pS/cm.

Application of liquid organic coating: application of an adhesive polyester (15 microns) on the exposed face and of an epoxy primer (10 microns) on the unexposed face. Curing of the product in oven at metal temperature of over 150°C.

Application of PET film: Application of a bright PET film.

Application protective film: Application of a protective film (50 microns thick).

Example 2

Substrate: Cold-rolled steel with low carbon content (0.12%) and thickness 0.40mm.

Satin finish: Process of satin finish applied on the substrate mechanically with aluminium oxide sandpaper in a standardized grade and with the market name of “Grade 220”, and which simulates the same finish of stainless steel.

Zinc plating: Electroplating of zinc on the satin finished substrate with a layer equivalent to 50mg/m2.

Chemical treatment: chemical cleaning with a series of degreasings and washes, the last one with demineralized water with conductivity lower than 50pS/cm. Application of a primer in water base to lay Titanium in quantity lower than 10mg/m2.

Application of liquid organic coating: application of an acrylic adhesive (25 microns) on the exposed face and of an epoxy-polyester primer (10 microns) on the unexposed face. Curing of the product in oven at a metal temperature higher than 150°C.

Application PET film: application of a tinted matte PET film

Example 3

Substrate: Galvanized steel with low carbon content (0.12%) and a thickness of 0.60mm.

Satin finish: Satin finish process applied on the substrate mechanically by aluminium oxide sandpaper in a standard grade and with the market name of “Scotch Brite”, and which simulates the same finish of stainless steel.

Chrome plating: Chrome electroplating on the satin finished substrate with a layer equivalent to 100mg/m2.

Chemical treatment: chemical cleaning with a series of degreasings and washes, the last one with demineralized water with conductivity lower than 50pS/cm. Application of a primer in water base to lay Zirconium in quantity lower than 10mg/m2.

Application of liquid organic coating: application of a polyester adhesive (15 microns) on the exposed face and of an epoxy primer (10 microns) on the unexposed face. Curing of the product in oven at a metal temperature higher than 150°C.

Application PET film: application of a transparent matte PET film.

Claims

1. A method of fabricating a metal sheet, characterized in that a sheet of steel which is cold-rolled, galvanized or of low carbon content of iron sheet is between 0.10% and 0.20% and has a thickness of between 0.10 mm and 2.00 mm, are subjected to: (a) in a first phase, mechanical smoothing by alumina browning at a speed of 4 to 20 meters / minute, and then b) in a second phase in which the smoothed plate is covered by electrolysis, a cover with a protective metal selected from chromium, tin and zinc, where the amount is between 40 mg / m2 and 500 mg / m2.

Process for producing a metal sheet according to the preceding claim, characterized in that the steel sheet covered with the layer of protective metal is exposed to baths for cleaning, the latter being realized with water having a conductivity of less than 50 pS / cm.

Process for the manufacture of a metal sheet according to the preceding claims, characterized in that after the baths for cleaning, it is applied to a transparent, water-based primer with a noble material to deposit a thin layer in an amount of less than 10 mg / m2 of zirconium. or titanium; Subsequently, the water is evaporated by the primer.

Method of making a metal sheet according to the preceding claims, characterized in that it is subsequently applied to the outer side or the visible part of an adhesive, the base resin of which may be of polyester, polyurethane or acrylic, in a layer of 10 to 50 wet micrometers (before the curing process), then a priming of polyester, polybutyral, epoxy or polyurethane on the inside or invisible side; after which the plate is introduced into an oven where the metal is subjected to a temperature of 150 to 210 ° C to cure the organic liquid coating; when leaving the oven, it is applied to a PET film that seals the product.

Metal plate characterized in that it is provided by the method of claim 1.