DE102019108984B3 - Use of a coil-coated sheet metal with an organic coating - Google Patents

Abstract

The invention relates to the use of a coil-coated sheet (1) comprising a sheet (2) made of metal and an organic coating (3), the organic coating (3) having a thickness of at least 400 μm and being connected to the sheet (2) . It is proposed to use the coil-coated sheet metal for household appliances as protection against burns and for furniture and / or work surfaces containing metal and, alternatively, as an appliance cover for household appliances and / or refrigerators.

Description

The present invention relates to a use of a coil-coated sheet comprising a sheet made of metal, in particular steel, and an organic coating.

Steel is a material with an extremely wide range of possible uses. In the course of production, steel is usually rolled into a strip and wound into a coil, which is then delivered to the customer. Depending on the desired application, the steel rolled in the form of a strip undergoes a pretreatment before being wound into a coil, e.g. in the form of a coating that makes it particularly suitable for a desired end use. For reasons of corrosion protection, a coating of zinc or a zinc alloy is often applied to the carrier material before the coating.

It is known to provide strip-shaped rolled steel, which has an organic coating, with a thin, temporary protective film, which is intended to offer mechanical protection, in particular scratch protection, before being wound into a coil.

It is also known to use galvanized and organically coated, strip-shaped rolled steel for use in household appliances, e.g. Tumble dryers or washer dryers, to be provided with an approximately 120 µm thick film made of polyethylene, which is intended to serve as protection against burns.

According to the EU regulation IEC 60335-2-11, however, it is required that metallic surfaces of electrical household appliances, which can reach temperatures above 74 ° C, are to be provided with an at least 400 µm thick organic coating as protection against burns, so that the user can stay safe during or cannot burn as a result of the operation of the device.

The currently used approx. 120 µm thick polyethylene films are, however, suitable for temperatures above 74 ° C, as e.g. may appear on the back of some tumble dryers and washer-dryers, not enough because they are too thin. In addition, at the high temperatures prevailing on the backs of these devices during operation, polyethylene becomes so soft that long-term use, e.g. over a period of 20 years seems problematic. For this reason, the application of thicker polyethylene films is not suitable.

It is also known that polyvinyl chloride is applied in a coil coating process to steel rolled in the form of a coil as an organic coating. However, due to the phthalate content, this is also unsuitable for use in household appliances.

It is the object of the present invention to provide an alternative use for a coil-coated sheet. This sheet should preferably overcome the aforementioned disadvantages known from the prior art and should be distinguished in particular by a high level of protection against burns and preferably by adequate UV resistance and temperature resistance to temperatures of up to 100.degree. In addition, the coil-coated material should preferably also be suitable for use in household appliances in accordance with IEC 60335-2-11.

The invention solves this problem with the features of the claims and in particular by means of a coil-coated sheet, comprising a sheet of metal, in particular steel, and an organic coating, the organic coating having a thickness of at least 400 μm and being connected to the sheet.

For the purposes of the invention, a coil-coated sheet metal is understood to be a piece or a cut of a strip of any length produced in a coil-coating process and provided with a coating. A sheet of metal, in particular steel, is accordingly to be understood as a piece or a cut of a strip of metal, in particular steel, of any length. Optionally, the sheet metal, in particular steel, is provided with corrosion protection on one or both sides, in particular galvanized, e.g. Hot-dip galvanized or electrolytically galvanized.

The connection between sheet metal and coating is particularly durable and adheres well when the organic coating is firmly bonded to the sheet metal.

In particular, coil coating adhesives and paints based on polyester, polyurethane and epoxy have proven to be suitable for producing the permanent and cohesive connection. Therefore, according to a preferred embodiment of the coil-coated sheet, the organic coating is connected to the sheet by means of a coil-coating adhesive or lacquer based on polyester, polyurethane or epoxy.

The organic coating is preferably halogen-free and comprises or consists of polypropylene, polyurethane and / or polyester. In this context, halogen-free in the sense of low-halogen is to be understood in accordance with the applicable standards or guidelines.

The thickness of the organic coating on sheet metal is at least 400 μm, for example 400 μm-1 mm, in particular 400-700 μm, preferably 400-500 μm and particularly preferably 430-480 μm, while the thickness of the optionally galvanized sheet without the organic coating is preferred 0.3-3.0 mm and in particular about 0.5-1.5 mm, for example 1 mm. The coil-coated sheet metal particularly preferably comprises the organic coating in the form of a film. This can be either transparent or homogeneously colored, for example in white or gray.

Due to the good thermal insulation properties of the organic coating, it protects from a thickness of at least 400 µm against the heat generated by some electrical devices during operation. A coil-coated sheet metal, which comprises an organic coating with a thickness of at least 400 μm, is therefore particularly well suited as the rear wall of tumble dryers and washer dryers, on which temperatures above 74 ° C. can prevail during operation. Due to the organic coating with a minimum thickness of 400 µm, the heat generated is sufficiently shielded so that no additional heat protection or subsequently attached to the rear wall of the electrical device is necessary to protect against burns in the event of contact. In particular, when the coil-coated sheet metal is used as the rear wall of tumble dryers and washer-dryers, no manual attachment of protective mats and no complex piece coatings are required.

Furthermore, a coil-coated sheet metal is particularly suitable when using polypropylene as an organic coating due to the hard-wearing and chemically very resistant surface as a device cover for electrical devices, in particular household devices, such as washing machines, dryers, dishwashers and refrigerators.

Up until now, device covers have been made from chipboard with a melamine coating. Since this is a piece coating and the edges of the device cover also have to be sealed to protect the wood, it is a very complex production that is associated with high costs for the device manufacturer. The construction makes a plastic border necessary and overall the component is very thick in order to achieve the required rigidity.

In contrast to this, a coil-coated sheet metal used as a device cover does not have to be sealed like wood, but a subsequent coating of the edges is sufficient to ensure corrosion protection, which could even be dispensed with with a suitable construction if the good formability of the product were used. When using the coil-coated sheet metal according to the invention, the total thickness of the device cover can be significantly reduced in comparison to the melamine-coated chipboard, or alternatively device covers with the same thickness, e.g. as a sandwich element, offer increased rigidity.

In addition to its suitability as a device cover and as protection against burns for household appliances, the coil-coated sheet metal, especially when using polypropylene as an organic coating, is also suitable according to the invention as a decorative and hard-wearing metal-containing furniture and / or work surface, e.g. Kitchen countertops, because in addition to the heat-insulating properties already mentioned, it is also chemically and scratch-resistant and sufficiently UV-resistant. In addition, the coil-coated sheet also offers electrical breakdown security, which is why it is particularly suitable for switch cabinets, for example. For this application a thickness of the organic coating of at least 400 µm is not necessarily required, but a thickness of approx. 200-250 µm is also sufficient.

The invention thus relates to the use of a coil-coated sheet metal for household appliances as protection against burns and for furniture and / or work surfaces containing metal, and also the use of a coil-coated sheet metal as a device cover for household appliances and / or refrigerators.

In a method for producing a coil-coated sheet metal, a strip made of metal, in particular steel, with a zinc-based coating optionally applied to the steel strip on one or both sides is permanently provided with an organic coating in a strip coating process, the organic coating having a thickness of at least 400 μm having.

In the process, the organic coating is preferably permanently connected to the strip made of metal, in particular steel, by means of adhesive and / or paint. According to a particularly preferred embodiment, the adhesive used is a coil coating adhesive or lacquer based on polyester, polyurethane or epoxy, the adhesive or lacquer being in particular in a thickness of 5-15 μm and particularly preferably in a thickness of about 7 - 10 µm is applied between the band made of metal, in particular steel, and the organic coating.

It is also as described above with reference to the coil-coated sheet metal in the method it is preferred that the thickness of the organic coating is 400 µm - 1 mm, in particular 400 - 700 µm, preferably 400 - 500 µm and particularly preferably 430 - 480 µm, while the thickness of the uncoated sheet is preferably 0.3 - 3, 0 mm, in particular about 0.5-1.5 mm, for example 1 mm.

The organic coating used in the method is preferably a halogen-free coating which in particular comprises polypropylene, polyurethane and / or polyester or consists of one or more of these compounds. The organic coating is preferably applied in the form of a film to the strip made of metal, in particular steel, it being possible for the film to be either transparent or homogeneously colored, for example in white or gray.

The invention is illustrated below by means of examples and with reference to 1 described.

The 1 shows schematically a sectional view of a coil-coated sheet 1 . This includes a sheet 2 of metal, in particular steel. The sheet 2 Made of metal, in particular steel, optionally has corrosion protection on its upper side, for example hot-dip coating or electrolytic galvanizing (dotted layer). Also optionally, a conversion layer (dashed layer) is applied to the corrosion protection layer, which improves the adhesion of the adhesive or paint. The layer of glue and / or varnish 4th has a thickness of 5 to 15 μm, in particular a thickness of approximately 7 to 10 μm. On the layer of glue and / or varnish 4th Another layer is applied which is the organic coating 3 includes in particular in the form of a film.

Example 1: Production of a coil-coated sheet metal

To produce a coil-coated sheet metal, in particular a galvanized steel strip can be used, which undergoes the following process steps as part of the coil coating.

First, the steel strip is unwound from the coil and optionally attached to a previous strip, before it is also optionally cleaned and pretreated. Further optionally, a primer, for example a lacquer, can now be applied to the upper side of the belt and a coating can be applied to the lower side of the belt. This primer and underside coating is now baked in an oven before it is then cooled with water.

A layer of adhesive and / or lacquer is applied to the top of the tape, with a second layer of lacquer optionally also being able to be applied to the underside. The applied adhesive and / or lacquer layer (s) is or are then baked in the oven. The belt temperature is 100-300 ° C, preferably 160-250 ° C, depending on the adhesive used. The organic coating is then laminated, preferably in the form of a film at least 400 μm thick, onto the still hot strip. The coated strip is then cooled in a water cooler, at the end of which the water lying on it is blown off.

After an optional quality control and the likewise optional application of a self-adhesive, temporary protective film for mechanical protection of the sheet metal, the now coated strip is wound up again into a coil. The tape must no longer be too hot, as otherwise undesirable surface changes can occur. The temperature of the tape during winding should therefore be below 50 ° C.

Depending on the desired application, the steel used as the starting material can in particular be a soft steel for cold forming or a structural steel. In principle, however, any steel grade can be used. The choice of organic coating is based on the application. Foils made of polyurethane are particularly suitable for washer-dryer and tumble dryer back walls, and foils made of polypropylene or polyester are suitable for washer-dryer and tumble-dryer back walls as well as for device covers and metal furniture and / or work surfaces.

Example 2: Bending tests with coil-coated sheets

• -5 streifenförmige Proben eines mit einer 430 µm dicken Polyurethan-Folie beschichteten Stahlbandes mit einer Ausgangsdicke von 1 mm;
• -5 streifenförmige Proben eines mit einer 430 µm dicken Polypropylen-Folie beschichteten Stahlbandes mit einer Ausgangsdicke von 1 mm;
• -5 streifenförmige Proben eines mit einer 430 µm dicken Polyester-Folie beschichteten Stahlbandes mit einer Ausgangsdicke von 1 mm.

In order to assess how stable the adhesion of the organic coating to the strip made of metal, in particular steel, is, the strip-coated sheets mentioned below are subjected to a T-bend test (bending test) DIN EN 13523-07 subjected:

• -5 strip-shaped samples of a steel strip coated with a 430 μm thick polyurethane film with an initial thickness of 1 mm;
• -5 strip-shaped samples of a steel strip coated with a 430 μm thick polypropylene film with an initial thickness of 1 mm;
• -5 strip-shaped samples of a steel strip coated with a 430 μm thick polyester film with an initial thickness of 1 mm.

In the bending test, the strip-shaped samples were each folded by 180 ° at room temperature and the resulting bending shoulders were examined with a magnifying glass (10x magnification) for possible crack formation. All samples showed excellent flexibility, since no crack formation could be found on any of the samples. This corresponds to the best possible achievable result ("0T") according to DIN EN 13523-07. If cracks had been detectable on the bending shoulders, the strip-shaped samples to be tested would have been wrapped again with renewed folding. Since the wrapping with this renewed folding would no longer take place around one but around two sheet metal layers, the radius of the sheet metal at the bending shoulder would be correspondingly larger and the stress on the material correspondingly lower. This double wrapping, during which the bending shoulder is examined again for the presence of cracks, would correspond to a result of "1 / 2T". Another triple wrap corresponds to a result of “1T”.

In the present case, however, no further wrapping of the samples was necessary because the shoulders of all examined samples were free of cracks during the "0T" folding.

An adhesive strip was then attached to the flexural shoulders of the samples, pressed on and then removed again. The adhesive strips were then examined with regard to possible adhesions of the organic coating. These could not be found on any of the adhesive strips. In all of the samples examined, the organic coating therefore exhibits excellent adhesion to the steel strip.

Example 3: Erichsen cupping tests

Another possibility for assessing the quality of the adhesion of the organic coating on the strip made of metal, in particular steel, is to test the coated samples in accordance with an Erichsen cupping test DIN EN 13523-06 (without cross-cut). In the cupping test, a hemispherical punch is pressed from below against the sheet to be tested until a dome with a height of 8 mm has formed. Then an adhesive strip is applied to the Erichsen indentation, pressed on and removed again, and examined for possible buildup.

• -4 Proben eines mit einer 430 µm dicken Polyurethan-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -4 Proben eines mit einer 430 µm dicken Polypropylen-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -4 Proben eines mit einer 430 µm dicken Polyester-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm.

Bei keiner der getesteten Proben konnte nach Entfernung des Klebestreifens ein Ablösen der Beschichtung beobachtet werden, weshalb die Haftung der Beschichtung auf den jeweiligen Stahlbändern als sehr gut zu beurteilen ist.The cupping tests were carried out with the following coil-coated sheets:

• -4 samples of a steel sheet coated with a 430 μm thick polyurethane film with an initial thickness of 1 mm;
• -4 samples of a steel sheet coated with a 430 μm thick polypropylene film with an initial thickness of 1 mm;
• -4 samples of a steel sheet coated with a 430 μm thick polyester film with an initial thickness of 1 mm.

No peeling of the coating could be observed in any of the samples tested after removal of the adhesive strip, which is why the adhesion of the coating to the respective steel strips can be assessed as very good.

Example 4: Temperature Storage Tests

• -5 flache Proben eines mit einer 430 µm dicken Polyurethan-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -5 verformte Proben (7 mm Erichsen Tiefung und T-Bend 1T, d.h. dreifach gefaltet) eines mit einer 430 µm dicken Polyurethan-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -5 flache Proben eines mit einer 430 µm dicken Polypropylen-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -5 verformte Proben (7 mm Erichsen Tiefung und T-Bend 1T, d.h. dreifach gefaltet) eines mit einer 430 µm dicken Polypropylen-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -5 flache Proben eines mit einer 430 µm dicken Polyester-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -5 verformte Proben (7 mm Erichsen Tiefung und T-Bend 1T, d.h. dreifach gefaltet) eines mit einer 430 µm dicken Polyester-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm.

To assess the temperature resistance of the coil-coated sheets, the following samples were each stored in an oven for 24 hours at 100 ° C:

• -5 flat samples of a steel sheet coated with a 430 μm thick polyurethane film with an initial thickness of 1 mm;
• -5 deformed samples (7 mm Erichsen cupping and T-bend 1T , ie folded three times) of a steel sheet coated with a 430 μm thick polyurethane film with an initial thickness of 1 mm;
• -5 flat samples of a steel sheet coated with a 430 μm thick polypropylene film with an initial thickness of 1 mm;
• -5 deformed samples (7 mm Erichsen cupping and T-bend 1T , ie folded three times) a steel sheet coated with a 430 μm thick polypropylene film with an initial thickness of 1 mm;
• -5 flat samples of a steel sheet coated with a 430 μm thick polyester film with an initial thickness of 1 mm;
• -5 deformed samples (7 mm Erichsen cupping and T-bend 1T , ie folded three times) of a steel sheet coated with a 430 μm thick polyester film with an initial thickness of 1 mm.

In the case of the flat samples, the foiled side was facing the grating in order to check whether the grating left marks on the specimen. This was not the case with any of the sheets. Other changes in the flat samples as a result of temperature storage could not be determined either.

In the case of the deformed specimens, in particular the areas that had previously been subjected to a deformation, examined precisely optically. However, no cracks or delamination of the coating could be found in any of the samples. Blisters, marks, discoloration or other visual changes were also not visible.

The temperature resistance of both the flat and the reshaped samples can therefore be rated as very good.

Example 5: Temperature cycling tests

• -5 verformte Proben (7 mm Erichsen Tiefung und T-Bend 1T, d.h. dreifach gefaltet) eines mit einer 430 µm dicken Polyurethan-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -5 verformte Proben (7 mm Erichsen Tiefung und T-Bend 1T, d.h. dreifach gefaltet) eines mit einer 430 µm dicken Polypropylen-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -5 verformte Proben (7 mm Erichsen Tiefung und T-Bend 1T, d.h. dreifach gefaltet) eines mit einer 430 µm dicken Polyester-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm.

To test the material behavior against a temperature-related shock load, the coated metal sheets were each stored for one hour at -20 ° C and immediately afterwards for one hour at 90 ° C. This cycle was repeated two more times in immediate succession. The temperature change test was carried out on the following panels:

• -5 deformed samples (7 mm Erichsen cupping and T-bend 1T , ie folded three times) of a steel sheet coated with a 430 μm thick polyurethane film with an initial thickness of 1 mm;
• -5 deformed samples (7 mm Erichsen cupping and T-bend 1T , ie folded three times) a steel sheet coated with a 430 μm thick polypropylene film with an initial thickness of 1 mm;
• -5 deformed samples (7 mm Erichsen cupping and T-bend 1T , ie folded three times) of a steel sheet coated with a 430 μm thick polyester film with an initial thickness of 1 mm.

Following this temperature cycle test, which lasted a total of 6 hours, all the samples were precisely examined optically, with none of the samples being able to detect any visible changes. The sheets are therefore also stable against a temperature-related shock load.

Example 6: Climate change test

• -3 verformte Proben (7 mm Erichsen Tiefung und T-Bend 1T, d.h. dreifach gefaltet) eines mit einer 430 µm dicken Polyurethan-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -3 verformte Proben (7 mm Erichsen Tiefung und T-Bend 1T, d.h. dreifach gefaltet) eines mit einer 430 µm dicken Polypropylen-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -3 verformte Proben (7 mm Erichsen Tiefung und T-Bend 1T, d.h. dreifach gefaltet) eines mit einer 430 µm dicken Polyester-Folie beschichteten Stahlbleches mit einer Ausgangsdicke von 1 mm.

To test the corrosion resistance of coil-coated sheets, the following samples were subjected to a 20-cycle AHT test (alternating humidity and temperature test) according to DIN EN ISO 6270-2:

• -3 deformed samples (7 mm Erichsen cupping and T-bend 1T , ie folded three times) of a steel sheet coated with a 430 μm thick polyurethane film with an initial thickness of 1 mm;
• -3 deformed samples (7 mm Erichsen cupping and T-bend 1T , ie folded three times) a steel sheet coated with a 430 μm thick polypropylene film with an initial thickness of 1 mm;
• -3 deformed samples (7 mm Erichsen cupping and T-bend 1T , ie folded three times) of a steel sheet coated with a 430 μm thick polyester film with an initial thickness of 1 mm.

The AHT test is a climate change test in which both the temperature and the moisture content of the air are changed several times during the test period. Each cycle consists of 24 hours. First up were the samples 8th Stored for hours at 40 ° C and 100% relative humidity, and then for 16 hours at room temperature and lower relative humidity. After a total of 20 cycles had elapsed, the test was terminated and the specimens were carefully examined visually. It was found that no changes were visible on any of the tested panels. The sheets are therefore to be regarded as insensitive to this type of corrosion.

Example 7: boiling test

• -4 flache Proben eines mit einer 430 µm dicken Polyurethan-Folie beschichteten verzinkten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -4 flache Proben eines mit einer 430 µm dicken Polypropylen-Folie beschichteten verzinkten Stahlbleches mit einer Ausgangsdicke von 1 mm;
• -4 flache Proben eines mit einer 430 µm dicken Polyester-Folie beschichteten verzinkten Stahlbleches mit einer Ausgangsdicke von 1 mm.

The following coil-coated sheets were prepared for a boiling test:

• -4 flat samples of a galvanized steel sheet coated with a 430 μm thick polyurethane film with an initial thickness of 1 mm;
• -4 flat samples of a galvanized steel sheet coated with a 430 μm thick polypropylene film with an initial thickness of 1 mm;
• -4 flat samples of a galvanized steel sheet coated with a 430 μm thick polyester film with an initial thickness of 1 mm.

For this purpose, a cross cut was made on each of the aforementioned samples with the aid of a cutting device, which reached as far as the galvanization. A 6 mm recess was then made on the cross cut and the samples were stored in boiling water for one hour. After the samples had been removed from the water, a test was carried out to determine how far the respective film, which represents the organic coating, could be peeled off. In all of the samples tested, the films could not be peeled off more than 2 mm.

In summary, the examples described above show that the coil-coated sheets are characterized by high flexibility and formability, good temperature and corrosion resistance and excellent adhesion of the organic coating to the steel sheet.

The features of the invention disclosed in the above description, in the figure and in the claims can be essential both individually and in any combination for the implementation of the invention in its various embodiments.

List of reference symbols

1

coil-coated sheet metal

2

sheet

3

organic coating

4th

Glue and / or varnish

Claims (5)

Use of a coil-coated sheet (1) comprising a sheet (2) made of metal and an organic coating (3), the organic coating (3) having a thickness of at least 400 μm and being connected to the sheet (2) for Household appliances as protection against burns and for furniture and / or work surfaces containing metal and, alternatively, as appliance covers for household appliances and / or cooling appliances. Use after Claim 1 , characterized in that the organic coating (3) is firmly bonded to the sheet metal (2). Use after Claim 1 or 2 , characterized in that the sheet is made of steel. Use after Claim 1 , characterized in that the organic coating (3) is connected to the existing sheet metal (2) by means of a coil coating adhesive or lacquer based on polyester, polyurethane or epoxy. Use according to one of the preceding claims, characterized in that the organic coating (3) is halogen-free and comprises or consists of polypropylene, polyurethane and / or polyester.

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