ORGANIC COATED MATERIALS FOR REFLECTORS AND DECORATIVE PURPOSES

Abstract: Coated flat rolled material for vacuum metallised materials having a metal substrate, where the substrate is covered by an organic coating consisting of at least two different layers. The first layer closest to the base material has a flexibility of at least 0T according to ECCA T7-1996, has good adhesion to the substrate and is vacuum resistant. The top layer has a micro hardness of at least 40 Kp/mm<2> measured as Vickers Hardness, is vacuum resistant and has good adhesive properties to the metallised layer.

Description: Organic coated materials for reflectors and decorative purposes. The invention concerns organic coated materials for reflectors and decorative purposes. A material suitable for use as a reflecting material for lighting purposes has to fulfil certain demands. The material should have the highest possible reflectivity. Dependent on the application, the material should in addition have certain light scattering properties. It should withstand mechanical stress, e.g. in forming operations and it should withstand cleaning operations without the formation of scratches. Protective layers on the surface of the material must adhere properly to the substrate. Finally, the material should have the lowest weight possible. The most commonly used reflecting material is aluminium. However, aluminium is a soft material, and in physical contact with other materials the surface is easily damaged. In addition, an unprotected surface of aluminium is disposed to corrosion. In most applications of aluminium, lighting appliances included, it is therefore necessary to protect the surface. The most common protection methods include anodising or organic coating. Traditionally batch processes were used for surface treatment of aluminium for lighting appliances. The aluminium substrate was first formed to the desired shape and thereafter surface treated. In order to reduce the production cost, continuous processes were developed. The forming of the products could then be carried out with already processed material. The reflectivity of pure aluminium is approximately 92 % for light with a wavelength of 550 nanometers for which the human eye is most sensitive. Commercial aluminium alloys have a slightly lower reflectivity, depending on amount and type of the alloying elements. The protective transparent layer which is usually applied to the alloy surface by either anodising or organic coating reduces the reflectivity due to multiple reflections. Precipitation of impurities in the anodic layer yields an extra reduction of reflectivity, when anodising commercial purity alloys. Anodised reflector materials are therefore usually made out of very high purity alloys (typically > 99.7 Al%). This way it is possible to obtain a reflectivity of up to 88 %. Different solutions have been proposed, and are applied in order to reduce material cost. The most common solution is to apply a thin layer of high purity metal on a lower purity substrate. This is either possible by lamination of a thin, high purity rolled sheet onto a sheet of lower purity metal, or by vacuum-deposition of a thin film of high purity aluminium onto a sheet of lower purity metal. Due to its favourable forming properties and low weight, aluminium alloys are preferred as the base material for these products as well. The invention is an improvement of the products based on vacuum deposition. A vacuum-deposited layer of aluminium is very sensitive to mechanical or chemical damage. The surface can be protected by organic coating, with a reduction of the reflectivity as a result (reflectivity approximately 88 %). It is well-known that the reflectivity of a material can be increased by deposition of thin layers with alternating refractive indices, and carefully controlled thicknesses. The reflectivity of the substrate, the applied refractive indices and the precision of the layer thicknesses, decide how many layers which are necessary to obtain a certain reflectivity. Usually, the layers are applied by a vacuum process. A layer system consisting of high purity aluminium (>99.99 Al%), with a SiO 2 layer, and a TiO 2 layer on top with the right thicknesses, result in a reflectivity of 95 %. Deposition of the reflectivity enhancing layers with sufficient thickness accuracy on extremely curved surfaces is difficult. The technology is therefore seldomly applied in large-scale batch processes, where the reflector elements are formed prior to surface treatment. The method is however successfully used in continuous vacuum treatment of flat, rolled materials. A thin aluminium layer and the reflectivity enhancing layers are deposited sequentially on the surface of the substrate. The reflector products are then formed after the surface treatment of the material has been concluded. The following technical requirements are set to the substrate material when applied in the continuous process described above (substrate material is the material prior to vacuum treatment): The substrate material must have a surface topography that gives the finished processed material the desired light scattering properties The substrate material must have a surface giving sufficient adhesion to the vacuum deposited coating system. The substrate must have a surface adapted to treatment in a vacuum chamber. The substrate material must , together with a vacuum deposited coating system, give sufficient protection against chemically degrading of the surface for example by corrosion. The substrate material must, together with a deposited coating system stand forming to a desired geometry without giving defects to the coating system that will result in reduced optical or corrosion protective properties. The substrate material must, together with a deposited coating system have a sufficient scratch resistance to facilitate for example cleaning. Until now, anodised aluminium has been regarded to be the only substrate material which is acceptable in view of the requirements described above. The topography of an anodised surface is strongly affected by the topography of the aluminium sheet before anodising. In order to be able to use anodised aluminium, it is therefore necessary to create the desired topography prior to anodising. Often very specular surfaces are desired, which means that the aluminium base material needs to be brightened. This is usually achieved through a combination of bright rolling and chemical or electrochemical surface treatment prior to anodising, which increase substrate cost significantly. There is also a considerable market for highly reflective materials with non-specular, isotropic surfaces. The desired topography is then usually achieved by the combination of bright rolling, texture rolling and chemical or electrochemical surface treatment prior to anodising, which also makes a very costly process. Another problem with an anodised substrate is that requirements are set to the purity of the aluminium alloy which is applied. Precipitation of impurities in the anodic layer affects the surface topography of the anodic layer. After deposition of the high-purity aluminium and reflectivity enhancing films, these topography features cause light scattering yielding a reduction of gloss and a hazy surface appearance. For most reflection applications this is mostly undesirable. In order to produce the required light scattering properties, the industry is therefore forced to apply high purity alloys (> 99.7 Al%), which increases the cost of the substrate material even more. The anodic layer is very hard and brittle. In forming the material to the desired geometry of the end-product the layer often cracks in bends and in other areas with relatively strong deformation. This results in reduced optical and protective properties. The disadvantages of using an anodised substrate for vacuum deposition of a reflection enhancing coating system in a continuous process can be summarised as follows: Generation of the desired surface topography involves very expensive processes (bright rolling, texture rolling, chemical or electrochemical surface treatment) Generation of the desired surface topography is only possible with expensive high purity aluminium. The anodising process has very limited possibilities for variations of the topography, and thereby a limited choice of light scattering properties. Cracking of the anodised layer in the forming processes reduces the optical quality and corrosion protection. Anodising is energy consuming and a relatively slow process. The object of this invention is to produce a coated substrate material for vacuum deposition of a reflection enhancing layer system which fulfils the requirements mentioned earlier, and which, compared to an anodised substrate, has better forming properties, and is considerably cheaper to produce. It is well known that it is possible to use an organic coated material as a substrate for vacuum deposition of reflection enhancing systems. The use of a proper organic coating relaxes the requirements on the topography of the metal base material. The surface topography of the coating can be varied independently of the surface topography of the aluminium base material. Relatively rough (and therefore cheaper) base materials can be used in order to produce very specular surfaces, provided that the coating has a levelling effect to the underlying topography. Moreover, the topography of the organic coated surface can be modified creating the possibility of producing a very large variety of surface lusters. The use of an organic coating does not impose any requirement on to the composition of the base material that is applied, other than that the coating evidently should adhere to the base material. When applying coatings with a large degree of flexibility, only micro cracks occurs in the forming processes. However, base materials, coated with conventional organic coatings have proven to be less suitable for vacuum deposition of a limited amount of reflection enhancing layers. Flexible coatings have very good forming properties, but are too soft in order to avoid damage in forming and cleaning operations. Very hard coatings can yield an acceptable resistance against mechanical damage, but they crack and do not stick to the surface in forming operations. The invention concerns a solution to the mentioned problem by applying a coated substrate material as described below. The invention is further described and characterised by the patent claims. The base material can be any metal, but due to its good mechanical properties and low weight, aluminium or an aluminium alloy is often preferred. There are no requirements to the topography of the base material, except for the production of specular materials. The requirements for the latter are strongly relaxed in comparison to base material for anodising and will be further specified in example 1. There are no requirements to the alloy purity which allows the use of recycled material. The choice of alloy may depend on other factors, like mechanical properties. The surface of the base metal should be pre-treated in order to assure good adhesion between base metal and the first coating. Flash-anodising is recommended for this purpose. An advantage of this pre-treatment with respect to many other methods is its environmental friendliness. Other methods are also possible as for example chromate pre-treatment. The invention concerns an organic coated flat rolled material for vacuum metallised materials having a metal substrate where the substrate is covered by an organic coating consisting of at least two different layers. The first layer closest to the substrate has a flexibility of at least OT according to ECCA T7-1996, has good adhesion to the substrate and is vacuum resistant. The top layer has a micro hardness of at least 40 Kp/mm 2 at a load of 8.2 g during 30s, 25°C measured as Vickers Hardness, is vacuum resistant and has good adhesive properties to the metallised layer. It is preferred that the coating system has levelling properties that provide for a gloss of at least 1900 GU at 20 °C according to DIN 67530 or ISO 7668 after vacuum treatment (100nm Al, 99.9 %, 90nm SiO 2 , 50 nm TiO 2 ). At least one layer can have particles embedded therein, which provide for a surface topography giving the required optical and aesthetic properties after vacuum treatment. It is preferred that the layer closest to the metal substrate has an adhesion to the pre-treated metal substrate of at least: GtO according to DIN 53151. The coating should be vacuum resistant, meaning that the amount of gases evaporating from the coating after curing should be limited, in order to allow exposure to low pressures in the vacuum treatment. The upper layer should have an adhesion to the first coating of at least GtO according to DIN 53151, adhesion to vacuum deposited aluminium giving no delamination(class 5) according to a modified version of the standard adhesion test ASTM D 3359-92a, where the metallised surface is not cross hatched prior to the tape test, and should also be vacuum resistant. The coating layer closest to the metal substrate comprises a blend of two polymers where the first polymer is formed by condensation polymerisation of the monomers epichlorohydrin and bisphenol A and a second polymer comprising anhydride. The upper coating layer comprises a blend of two polymers where the first polymer is formed by condensation polymerisation of phenol and formaldehyde and a second polymer which is a heat curing aminopolymer. It is preferred to use a substrate of aluminium or an aluminium alloy. The substrate material could be coated in a continuous coating process. Preferably a substrate of aluminium or an aluminium alloy coated with a two layer coating system is used. According to the present invention the described problem has been solved by applying two or more layers of coating with different chemical and mechanical properties, which make it possible to combine an adequate resistance against mechanical damage and good forming properties. The invention is preferably implemented in a continuous coil coating process. The invention will be further described and exemplified on the basis of implementation of a two layer coating system, but a system consisting of more than two coating layers is also possible. The first coating should fulfil the following general requirements: Minimum thickness: 2.5 μm Adhesion to pre-treated base metal: > GtO, according to DIN 53151 Flexibility: OT , according to ECCA T7 1996 Flow: Depending on application Vacuum resistance: After curing, evaporation of gasses should be limited, in order not to increase the pressure in the vacuum chamber unacceptably. The limit is dependent on the design of the vacuum equipment. The proposed lacquer system in examples 1 and 2 have proven to have an adequate vacuum resistance in typical production equipment. Maximum viscosity: 60 seconds Din 4 cup according to DIN 53211 (20°C) The second coating should fulfil the following general requirements: Thickness. > 3 μm Adhesion to first coating: > GtO, according to DIN 53151 Adhesion to vacuum deposited aluminium: Conventional adhesion tests are too harsh in order to test adhesion between the aluminium layer and the second coating. A modified version of the standard adhesion test ASTM D 3359-92a is used. The metallised surface is not cross hatched prior to the tape test. Minimum requirement : No delamination (class 5) Micro hardness: > 40 Kp/mm 2 at a load of 8.2 g during 30 s, 25°C ( Vickers Hardness) according to NS 1861 , 1969 Flow: Depending on application Vacuum resistance: As for the first coating Maximum viscosity: , 70 seconds Din 4 cup according to DIN 53211 (20°C) The desired flow and viscosity of the coatings entirely depends on the desired surface topography of the completed product. The topography of the second coating surface might be varied by adjusting the flow properties of either coating, or by introducing particles in one of the coatings. In principle any particles can be applied that yield the required optical and aesthetic properties after vacuum treatment as for example silica or polymer particles as polyamide, polyethylene and polypropylene. Example 1 and 2 describe coating combinations which yield two different surface topographies. The relative and total thickness of the coatings need to be optimised in order to obtain the required mechanical and optical properties. Examples 1 and 2 describe coating systems where the thicknesses have been optimised. The completed reflector material, including a reflector enhancing layer system of approximately 100 nm Al (99.99 %), approximately 90 nm SiO 2 and approximately 50 nm TiO 2 is tested with regard to adhesion, formability and scratch resistance. In addition the optical properties are examined. The following tests and standards are used: Adhesion: ASTM D3359-92a (without cross hatching ) Flexibility: ECCA T7 1996 Scratch resistance: No standardised tests available for these materials. The applicant applies a modified version of test DIN 58196-5: Abrasive medium: Felt washer, diameter 10 mm, thickness 3 mm, fibre composition wool/ viscose LE II 0.36 g/ccm ( e.g. V45285 supplied by VFG AG). Normal force 4.5 N. Oscillation amplitude: 7.5 cm. Number of oscillations: 10. Instead of visual inspection, the abraded surfaces are digitally processed in order to calculate the relative amount of scratched area (Scratch Area %). Optical properties: Total reflectivity tested according to DIN 5036-part 3. Gloss tested according to DIN 67530/ ISO 7668. The invention will in the following be further described by two examples. Example 1 relates to the production of a highly specular reflector material. Example 2 relates to the production of a less specular, but isotropic material with a surface lustre known by the name "reflectormat". Example 1 - High specular reflector material Substrate: AA3105, recycled Semi-bright rolled: gloss (20°): 700 GU according to DIN67530 or ISO 7668 Pre-treatment: Flash anodising Coating: Double reverse coil coating Coating 1 : A blend of two polymers where the first polymer is produced by condensation polymerisation of the monomers epichlorohydrin and bisphenol-A and a second polymer being an anhydride. Any strong organic acid can be used as catalyst. Thermal curing was carried out at PMT (Peak Metal Temperature) 270°C for 30 s . Thickness: 3 micrometer Coating 2: A blend of two polymers where the first polymer is produced by condensation polymerisation of phenol and formaldehyde and a heat curing aminopolymer. Any organic acid can by used as catalyst. Thermal curing is carried out at PMT (Peak Metal Temperature) 270°C for 30 s. Thickness:6 micrometer Properties of the completed reflector material, after vacuum treatment ( 100 nm Al (99.99 %), 90 nm Si0 2 , 50 nm Ti0 2 ): Adhesion: No delamination (class 5), according to modified adhesion test ASTM D3359-92a (without cross hatching). Flexibility: OT, micro cracks , according to ECCA T7 1996 Scratch resistance: Scratch Area < 50 % Total reflection: 95 % according to DIN 5036-part 3 Gloss (20°): 1900 GU according to DIN 67530 or ISO 7668 Comparative example Similar tests as in example 1 were carried out on an existing material with similar optical properties based on an anodised substrate. Producer: Alanod, Ennepetal, Germany Material designation: Miro 1 ™ Adhesion: No delamination (class 5), according to modified adhesion test ASTM D3359-92a (without cross hatching). Flexibility: > 35 T, according to ECCA T7 1996 Scratch resistance: Scratch area < 1 % Total reflection: 95 % according to DIN 5036-part 3 Gloss (20°): 1900 GU according to DIN 67530/ ISO 7668 Example 2 - Reflectormat material Substrate: AA3105, recycled Standard mill finish, having a Total reflection 81.5 % according to DIN 5036 part 3 and Gloss: R20 225-230 GU in the rolling direction and 125 GU across rolling direction according to DIN 67530/ ISO 7668 Pre-treatment: Flash anodising Coating: Double reverse coil coating Coating 1: Same as in example 1 Thickness: 3 micrometer Coating 2: Same as in example 1 Particles: Polyamide, commercial quality, VESTASINT 2157 (Hϋls, Germany), nominal size 20 - 60 micrometers, amount 2 % (weight) on solid binder Viscosity: 60 seconds (DIN 4 cup, 21°C) Average thickness: 6 micrometer Properties of the completed reflector material, after vacuum treatment ( 100 nm Al (99.99 %) 90 nm SiO 2 , 50 nm TiO 2 ) : Adhesion: No delamination (class 5), according to modified adhesion test ASTM D3359-92a (without cross hatching) Formability: 1/2 T according to ECCA T7 1996 Scratch resistance: Scratch Area < 50 % Total reflection: 94 % according to DIN 5036-part 3 Gloss (20°): 725 GU according to DIN 67530 or ISO 7668. Comparative example Similar tests as in example 2 were canied out on an existing material with similar optical properties based on an anodised substrate. Producer: Alanod, Ennepetal, Germany Material designation: Miro 7 ™ Adhesion: No delamination (class 5), according to modified adhesion test ASTM D3359-92a (without cross hatching). Flexibility: > 35 T, according to ECCA T7 1996 Scratch resistance: Scratch area < 1 % Total reflection: 94 % according to DIN 5036-part 3 Gloss (20°): 700 GU according to DIN 67530/ ISO 7668 In conclusion, the proposed coated substrate material has the following advantages with respect to an anodised substrate material: No requirements on the composition of the base metal. Possibility of using recycled aluminium. Strongly reduced requirements on the surface topography of the base metal. No expensive surface treatment processes required. Many possibilities of adjusting the upper organic coating surface topography, in order to produce a great variety of surface lustres. Better forming properties. Less enegy consuming and less expensive The advantages are achieved at the cost of a reduced scratch resistance. However, the demand on scratch resistance is highly dependent on the application, and for most reflector applications, lighting applications included, the scratch resistance obtained with an anodised material is many times higher than required.

Claims: Patent claims 1. Coated flat rolled material for vacuum metallised materials having a metal substrate, characterised in that the substrate is covered by a coating consisting of at least two different layers where the first layer closest to the substrate has a flexibility of at least OT according to ECCA T7-1996, has good adhesion to the substrate and is vacuum resistant and where the top layer has a micro hardness of at least 40 Kp/mm 2 at a load of 8,2 g during 30s, 25°C measured as Vickers Hardness, is vacuum resistant and has good adhesive properties to the metallised layer. 2. Material according to claim 1, characterised in that the coating system has levelling properties that provide for a gloss of at least 1900 GU measured at 20 °C according to DIN 67530 or ISO 7668 after vacuum treatment (100nm Al, 99.9 %, 90nm SiO 2 , 50 nm TiO 2 ). 3. Material according to claim 1, characterised in that at least one layer has particles embedded therein, which provide for a surface topography giving the required optical and aesthetic properties after vacuum treatment. 4. Material according to claim 1,characterised in that the layer closest to the metal substrate has an adhesion to the pre-treated metal substrate of at least: GtO according to DIN 53151 and is vacuum resistant, meaning that the amount of gases evaporating from the coating after curing should be limited, in order to allow exposure to low pressures in the vacuum treatment. 5. Material according to claim 1, characterised in that the upper layer has an adhesion to the first coating of at least GtO according to DIN 53151, adhesion to vacuum deposited aluminium giving no delamination (class 5) according to a modified version of the standard adhesion test ASTM D 3359-92a, where the metallised surface is not cross hatched prior to the tape test, and is vacuum resistant, meaning that the amount of gases evaporating from the coating after curing should be limited, in order to allow exposure to low pressures in the vacuum treatment. 6. Material according to claim 1 and 4, characterised in that the coating layer closest to the metal substrate comprises a blend of two polymers where the first polymer is formed by condensation polymerisation of the monomers epichlorohydrin and bisphenol A and a second polymer which comprising anhydride. 7. Material according to claim 1 and 5, characterised in that the upper coating layer comprises a blend of two polymers where the first polymer is formed by condensation polymerisation of phenol and formaldehyde and a second polymer which is a heat curing aminopolymer. 8. Material according to claim ^ characterised in that the substrate is aluminium or an aluminium alloy. 9. Material according to claim 1.characterised in that the substrate material is coated in a continuous coating process. 10. Material according to claim 1, characterised i n that the substrate is aluminium or an aluminium alloy coated with a two layer organic coating system.

Inventors: HALLENSTVET MERETE, STORBAKKEN ALBIN SOLEM, HALLENSTVET, MERETE, STORBAKKEN, ALBIN, SOLEM
Applicants: HALLENSTVET MERETE, NORSK HYDRO AS, STORBAKKEN ALBIN SOLEM, VALSPAR NORWAY CORP AS, HALLENSTVET, MERETE, NORSK HYDRO ASA, STORBAKKEN, ALBIN, SOLEM, THE VALSPAR (NORWAY) CORPORATION AS
Application year: 1998
Main classification: C23C14
IPC codes: B05D5, C23C14, F21V7