Method for coating light alloy rims

Abstract

The present invention relates to a method for coating light alloy rims, to coating materials for use in this method, and to the coated light alloy rims obtained in this way. A primer layer, a base coat layer, and a clear coat layer are applied to a machined light alloy rim blank. The primer layer includes a radiation-curable coating material having an acid number of 10 to 120 mg KOH/g. The clear coat layer has a double-bond density of free-radically polymerizable reactive groups per unit mass of coating material of at least 1 mol/kg. The coating materials can be cured by radiation.

Claims

1. A method for coating light alloy rims, the method comprising: applying a primer (A) layer directly on a machined light alloy rim blank comprising a cast aluminum alloy, the primer (A) layer comprising at least one radiation-curable coating material having an acid number in accordance with DIN EN ISO 3682 (by potentiometry) of 10 to 120 mg KOH/g; after applying the primer (A) layer, applying a base coat (B) layer; after applying the base coat (B) layer, applying a radiation-curable clear coat (C) layer on an outside surface of the light alloy rim, the clear coat (C) layer having a double-bond density of free-radically polymerizable reactive groups per unit mass of coating material of at least 1 mol/kg; and curing the primer (A) layer, the clear coat (C) layer, and optionally the base coat (B) layer by high-energy radiation selected from the group consisting of light in the wavelength range of 200 nm to 700 nm, an electron beam in the range of 150 keV to 300 keV, and combinations thereof; wherein: the primer (A) layer is fully cured with the high-energy radiation and without being further heated after being applied; and the primer (A) layer, the base coat (B) layer, and the clear coat (C) layer are different from each other.

2. The method of claim 1, wherein the primer (A) layer comprises at least one radiation-curable coating material comprising (A2a) at least one binder selected from the group consisting of aliphatic urethane (meth)acrylates, aromatic urethane (meth)acrylates, and epoxy (meth)acrylates, (A2b) at least one reactive diluent, and (A2c) optionally at least one anticorrosion pigment and/or corrosion inhibitor.

3. The method of claim 1, wherein the base coat (B) layer comprises at least one water-based, two-component coating material comprising at least one pigment and/or metallic flakes.

4. The method of claim 3, wherein the base coat (B) layer coating material has a solids content of between 20% and 80% by weight.

5. The method of claim 1, wherein the base coat (B) layer comprises at least one water-based, radiation-curable coating material comprising at least one pigment and/or metallic flakes.

6. The method of claim 5, wherein the base coat (B) layer coating material has a solids content of between 20% and 80% by weight.

7. The method of claim 1, comprising performing curing by high-energy radiation under inert gas.

8. The method of claim 1, further comprising, after applying the base coat (B) layer and before applying the clear coat (C) layer: curing the base coat (B) layer, removing the base coat (B) layer on an outer facing side of the light alloy rim down to bare metal of the light alloy rim, such that during application of the clear coat (C) layer, the clear coat (C) layer is applied to the bare metal.

9. The method of claim 1, wherein the clear coat (C) layer is fully cured with the high-energy radiation and without being further heated after being applied.

10. The method of claim 1, further comprising: after applying the primer (A) layer and before applying the base coat (B) layer, partially curing the primer (A) layer with the high-energy radiation, but not fully curing the primer (A) layer; and after applying the clear coat (C) layer, fully curing the primer (A) layer with the high-energy radiation.

11. The method of claim 1, further comprising: after applying the clear coat (C) layer, fully curing the primer (A) layer with the high-energy radiation, wherein the primer (A) layer is not cured with the high-energy radiation after applying the primer (A) layer and before applying the base coat (B) layer.

Description

EXAMPLES

Example 1: Adhesion Primer A1 (1st Layer Directly on Substrate)

(1) TABLE-US-00001 Proportion in the Trade formulation Function in the name Chemical description [%] Component formulation Difunctional aliphatic urethane 28.0 A1a Binder for film acrylate, having a molecular weight forming of about 1500 g/mol, diluted in trimethylolpropane formal monoacrylate 4-tert-Butylcyclohexyl acrylate 39.0 A1b Low-shrink reactive diluent Preparation based on: 10.0 A1b Acidic 2-(phosphonooxy)ethyl adhesion methacrylate, promoter bis(methacryloyloxyethyl)hydrogenphosphate Lugalvan 1-Benzyl-3-carboxylatopyridinium 1.0 A1c Corrosion BPC 48 inhibitor Shieldex Synthetic, amorphous silicon 14.0 A1c Anticorrosion C303 dioxide - exchanged with calcium pigment ions Kronos Titanium dioxide 3.5 White pigment 2310 for coloring Flammru Carbon black 0.1 Black pigment 101 for coloring Talkum IT Magnesium silicate hydrate 2.0 Filler extra Irgacure -Hydroxy ketone 2.0 Photoinitiator 184 Irgacure Acylphosphine oxide 0.4 Photoinitiator 819

(2) The formulation has an acid number of about 30 mg KOH/g.

Example 2: Adhesion Primer A1 (1st Layer Directly on Substrate)

(3) TABLE-US-00002 Proportion in Trade the formulation Function in the name Chemical description [%] Component formulation Bisphenol A diglycidyl ether 28.0 A1a Binder for film diacrylate (55%), diluted with forming a) Versatic acid glycidyl ester acrylate (15%) b) dipropylene glycol diacrylate (30%) Trimethylolpropane formal 39.0 A1b Low-shrink monoacrylate reactive diluent Preparation based on: 10.0 A1b Acidic adhesion 2-(phosphonooxy)ethyl promoter methacrylate, bis(methacryloyloxyethyl)hydrogenphosphate Halox 1.0 A1c Corrosion 650 inhibitor Shieldex Synthetic, amorphous silicon dioxide - 14.0 A1c Anticorrosion C303 exchanged with calcium ions pigment Kronos Titanium dioxide 3.5 White pigment 2310 for coloring Flammru Carbon black 0.1 Black pigment 101 for coloring Talkum IT Magnesium silicate hydrate 2.0 Filler extra Irgacure -Hydroxy ketone 2.0 Photoinitiator 184 Irgacure Acylphosphine oxide 0.4 Photoinitiator 819

(4) The formulation has an acid number of about 30 mg KOH/g.

Example 3: Primer A2 (2nd Layer)

(5) TABLE-US-00003 Proportion in Trade the formulation Function in the name Chemical description [%] Component formulation Difunctional, elastic, 19.0 A2a Binder for film forming aliphatic urethane acrylate, having a molecular weight of about 1500 g/mol, diluted in trimethylolpropane formal monoacrylate Trifunctional aliphatic 38.0 A2a Binder for film forming urethane acrylate having a molecular weight of about 800 g/mol, diluted in HDDA Laromer Radiation-curing, 10.0 A2a Dual-cure resin for LR 9000 polymeric, acrylate- improving interlayer modified isocyanate adhesion Laromer Hexanediol diacrylate 11.0 A2b Difunctional reactive HDDA diluent Laromer Trimethylolpropane 10.0 A2b Trifunctional reactive TMPTA triacrylate diluent Byk 361 Acrylate copolymer 0.2 Flow control additive Byk 020 Polysiloxane solution 0.2 Defoamer Kronos Titanium dioxide 2.1 White pigment for 2310 coloring Flammru Carbon black 0.1 Black pigment for 101 coloring Talkum IT Magnesium silicate 6.0 Filler extra hydrate Tinuvin N-Alkyl-HALS 1.0 Light stabilizer 292 Irgacure -Hydroxy ketone 1.0 Photoinitiator 184 Irgacure Acylphosphine oxide 1.4 Photoinitiator 819

Example 4: Clear Coat C: (4th Layer)

(6) TABLE-US-00004 Proportion in the formulation Function in the Trade name Chemical description [%] Component formulation Difunctional elastic, 28.7 C1 Binder for film aliphatic urethane forming acrylate having a molecular weight of about 1500, diluted in trimethylolpropane formal monoacrylate Trifunctional aliphatic 44.4 C1 Binder for film urethane acrylate forming having a molecular weight of about 800 g/mol, diluted in HDDA Hexanediol diacrylate 21.3 C2 Difunctional reactive diluent Byk 361 Acrylate copolymer 0.2 C3 Flow control additive Tinuvin 400 Hydroxyphenyltriazine 1.5 C3 Light stabilizer Tinuvin 292 N-Alkyl-HALS 0.9 C3 Light stabilizer Irgacure 184 -Hydroxy ketone 2.5 Photoinitiator Lucirin TPO Acylphosphine oxide 0.5 Photoinitiator

(7) Formulations (A1) and (A2) were applied to cast aluminum test castings measuring about 812 cm by pneumatic spraying using a hot spray gun at about 70 C. in a wet film thickness of about 50-70 m.

(8) After about 1 minute, formulation (A1) was irradiated and cured at a belt speed of 10 m/min and at a distance of about 10 cm with a medium-pressure mercury lamp (160 W/cm) and also with a Ga-doped medium-pressure mercury lamp (160 W/cm) under a nitrogen atmosphere (residual oxygen content <5000 ppm). Formulation (A2) was then also irradiated and cured in the same way.

(9) Formulation (B) was applied by pneumatic spraying at room temperature and dried physically at 60 C. for 10 minutes.

(10) Like formulations (A1) and (A2), formulation (C) was applied pneumatically using a hot spray gun and, after about 1 minute, was irradiated and cured at a belt speed of 5 m/min and at a distance of about 10 cm with a medium-pressure mercury lamp (160 W/cm) and also with a Ga-doped medium-pressure mercury lamp (160 W/cm) under a nitrogen atmosphere (residual oxygen content <5000 ppm).

(11) After storage for about 7 days at 21 C. and 50% relative humidity, the coatings tests were conducted, and gave the following results:

(12) CASS test:

(13) DIN EN 4628-8 subfilm corrosion0.9 mm

(14) DIN EN 4628-3 surface rustRi0

(15) DIN EN 4628-2 blistering/degree of blisters0 S0

(16) Cross-cut DIN EN ISO 2409Gt1

(17) Multistone impact DIN EN ISO 12567-1, method Bcharacteristic value 1.0