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(11) | EP 4 245 426 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | OPTIMISED POWDER COATING TECHNIQUE FOR THE COATING OF METAL SURFACES |
| (57) The invention is technically based on the coating process of the new decorative powder
coating on the metal surfaces. The innovation lies in the new type of ion transmission
or electrification from the coating gun through an ion-permeable membrane to the solid
surface. Such ion transfer is precisely controlled and positioned on the solid surface. |
[0001] The present invention relates to an optimised powder coating technique for the coating of metal surfaces.
Background of the Invention
[0002] The powder coating technique was invented in 1945 and was granted a patent in the US (US 2538562A). In the process, a coating is applied electrostatically to a surface and cured by heat or UV light. In comparison to conventional liquid paint, surfaces coated by powder coating are more resistant. The technique is often used on metal type surfaces such as aluminium or steel. UV curable powder coatings furthermore allow the use of other materials such as plastics, composites, carbon fibre or MDF.
[0003] Powder coating allows a thicker coating than conventional liquid coatings and furthermore allows colour blending and colour bleeding special effects, since several layers of different colour can be applied subsequently without the need of cure in between applications. Powder coatings are solvent free, meaning there is no release of volatile organic compounds into the atmosphere, thus providing a greener coating technique than conventional liquid coatings.
[0004] The layer-by-layer technique is a known coating technique, wherein the coating layers are formed by applying alternating layer of oppositely charged coatings with wash steps in between. Within the layer-by-layer technique, various application techniques, including spin, spray, electromagnetism or fluidics can be used.
[0005] Through the alternating application of positively and negatively charged polyelectrolyte solutions, a stable layer system is achieved through Coulomb interactions.
[0006] The state of the art techniques only allow for either a thin coating, if liquid coatings are used or several layers using powder coatings, but a long process including several washing steps in between.
[0007] The present invention solves these issues by implementing an optimised powder coating technique of metal surfaces.
Summary of the Invention
[0008] A first aspect of the invention relates to a method for powder coating of a surface comprising the steps of
- a. provision of a pre-coated metal surface, wherein said pre-coated metal surface comprises a charged polymer surface, particularly a positively charged polymer surface,
- b. application of a membrane and subsequent application of an electrostatic potential to said membrane, wherein said membrane is applied in such way to said charged polymer surface that ion permeation takes place after the application of the electrostatic potential in sections, of the polymer yielding a charged polymer surface with activated polymer surface sections,
- c. removal of said membrane, yielding an activated surface,
- d. application of at least one positively or negatively charged powder coating onto
said activated surface,
yielding a patterned surface.
[0009] A second aspect of the invention relates to an activated surface comprising a pre-coated metal surface, wherein said activated surface comprises activated surface sections and non-activated surface sections, charged contrarily to the activated surface sections.
Terms and definitions
[0010] For purposes of interpreting this specification, the following definitions will apply and whenever appropriate, terms used in the singular will also include the plural and vice versa. In the event that any definition set forth below conflicts with any document incorporated herein by reference, the definition set forth shall control.
[0011] The terms "comprising," "having," "containing," and "including," and other similar forms, and grammatical equivalents thereof, as used herein, are intended to be equivalent in meaning and to be open-ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. For example, an article "comprising" components A, B, and C can consist of (i.e., contain only) components A, B, and C, or can contain not only components A, B, and C but also one or more other components. As such, it is intended and understood that "comprises" and similar forms thereof, and grammatical equivalents thereof, include disclosure of embodiments of "consisting essentially of" or "consisting of."
[0012] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit, unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the disclosure, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure.
[0013] Reference to "about" a value or parameter herein includes (and describes) variations that are directed to that value or parameter per se. For example, description referring to "about X" includes description of "X."
[0014] As used herein, including in the appended claims, the singular forms "a," "or," and "the" include plural referents unless the context clearly dictates otherwise.
[0015] The term pre-coated in the context of the present specification relates to a coating of a surface with a charged primer, wherein the primer provides a stable, charged base for the application of further coatings. The charge can be positive or negative and is generated through friction or ionisation.
[0016] The term primer in the context of the present specification relates to a base coat, which protects the base material and improves the conditions for the application of further coatings. The used primers are such as described in Pietschmann, J. "Industrielle Pulverbeschichtung-Grundlagen." Anwendungen, Verfahren, JOT-Fachbuch.1
[0017] The term polymer surface in the context of the present specification relates to a surface coated with a polymer, wherein the polymer is a substance consisting of large molecules or macromolecules composed of several repeating subunits. The used polymers are such as described in Pietschmann, J. "Industrielle Pulverbeschichtung-Grundlagen." Anwendungen, Verfahren, JOT-Fachbuch.1
[0018] The term electrostatic potential in the context of the present specification relates to the application of a positive or negative potential onto a surface, wherein the potential is generated through friction or ionisation.
[0019] The term membrane in the context of the present specification relates to a permeable and/or impermeable material.
[0020] The term ion permeation in the context of the present specification relates to the ability of ions to permeate through a material, e.g. an ion-permeable material, which is electrically conductive. The ion transport is then governed by the laws of diffusion.
[0021] The term electrostatic film in the context of the present specification relates to a material, usually an organic or inorganic polymer with (ionic) side groups, such as ion-exchange resins, which is electrically conductive and therefore possesses the ability to be charged positively or negatively. Alternatively, textiles, nylon or plastics may be used, where the same effect can be achieved.
[0022] The term powder coating in the context of the present specification relates to a type of coating that is applied as a free-flowing dry powder which is applied electrostatically by using frictional force or ionisation.
[0023] The term activated polymer surface sections in the context of the present specifications relate to the sections of the charged polymer surface whose charge was reversed through the application of an electrostatic potential.
[0024] The term activated surface in the context of the present specification relates to the surface, which is obtained after the ion-permeable membrane is removed after the application of an electrostatic potential, in which case the activated surface comprises activated polymer surface sections, where the membrane was ion-permeable and contacting the charged polymer surface and non-activated polymer surface sections, where the membrane was not contacting the surface or the membrane was not ion-permeable, and where the non-activated polymer surface sections are charged contrary to the activated polymer surface sections.
[0025] The term charged polymer surface in the context of the present specification relates to a polymer surface comprising charged sections and, as presumed by the inventors, neutralised sections.
Detailed Description of the invention
[0026] A first aspect of the invention relates to a method for powder coating of a surface comprising the steps of
- a. provision of a pre-coated metal surface, wherein said pre-coated metal surface comprises a charged polymer surface, particularly a positively charged polymer surface,
- b. application of a membrane and subsequent application of an electrostatic potential to said membrane, wherein said membrane is applied in such way to said charged polymer surface that ion permeation takes place after the application of the electrostatic potential in sections, yielding a charged polymer surface with activated polymer surface sections,
- c. removal of said membrane, yielding an activated surface
- d. application of at least one positively or negatively charged powder coating onto
said activated surface,
yielding a patterned surface.
[0027] In certain embodiments, a pre-coated metal surface is provided, wherein a metal surface is pre-coated with a charged primer and subsequently thermally fixated, yielding a charged polymer surface.
[0029] In certain embodiments, the metal surface is charged negatively prior to the application of a primer.
[0030] In certain embodiments, a pre-coated metal surface is provided, wherein the metal surface is pre-coated with a charged primer and subsequently thermally fixated, yielding a charged polymer surface.
[0031] In certain embodiments, a pre-coated metal surface is provided, wherein the metal surface is pre-coated with a positively charged primer and subsequently thermally fixated, yielding a charged polymer surface.
[0032] The charged polymer surface is obtained through thermally induced polymerisation of the surface coated with the primer.
[0033] In certain embodiments, the charged primer pre-coating the metal surface is selected from epoxide or polyester resins.
[0035] In certain embodiments, the membrane is
- a homogeneous ion permeable membrane applied sectionally, wherein sections of said homogeneous ion permeable membrane are contacting the charged polymer surface and other sections are not contacting the charged polymer surface or,
- a mesh-like ion permeable membrane applied evenly, comprising holes and sections of said mesh-like ion permeable contacting the charged polymer surface, or,
- a partially ion permeable membrane applied evenly, comprising ion-permeable sections and ion-impermeable sections.
[0036] A homogenous ion permeable membrane is applied sectionally, which results in a creased covering of the charged polymer surface by the membrane. Charged polymer surface sections with direct contact with the ion-permeable membrane will allow ion permeation, while charged polymer surface sections with a crease do not have direct contact with the ion-permeable membrane and will not allow ion permeation.
[0037] After applying a negative electrostatic potential to the ion-permeable membrane, the activated surface contains negatively charged sections where the membrane is contacting the charged polymer surface, and sections where the membrane was creased and is not contacting the charged polymer surface will remain positively charged.
[0038] To achieve the same permeation effect, the ion permeable membrane may also be evenly applied onto the charged polymer surface but contain a mesh-like structure with holes, so that charged polymer surface sections with direct contact with the ion-permeable membrane allow ion permeation, and sections with a hole in the ion-permeable membrane do not allow ion permeation.
[0039] After applying a negative electrostatic potential to the ion-permeable membrane, the activated surface contains negatively charged sections where the ion-permeable membrane is contacting the charged polymer surface, and sections where the ion-permeable membrane contains holes and is not contacting the charged polymer surface will remain positively charged.
[0040] For the use of a partially ion permeable membrane, the membrane is applied evenly across the whole charged polymer surface but contains ion-permeable sections and ion-impermeable sections, for example through thicker sections in the film.
[0041] After applying a negative electrostatic potential to the membrane, the activated surface contains negatively charged sections where the membrane contained ion-permeable sections, and sections where the membrane was ion-impermeable, the charged polymer surface will remain positively charged.
[0042] Excess counterions from the charged polymer surface attract the negatively charged ions from the powder gun. This enables the charge reverse of the charged polymer surface at contacting sections. The activated surface will remain stable for up to 1 h after removal of the membrane.
[0043] In certain embodiments, the membrane is a homogeneous ion permeable membrane applied sectionally, wherein sections of said homogeneous ion permeable membrane are contacting the charged polymer surface and other sections are not contacting the charged polymer surface.
[0044] Homogenous ion-permeable membranes are easier and more cost effective in their production in comparison to the mesh-like and partially ion permeable membrane. They are furthermore easier in use and the desired pattern can be achieved as preferred since the application of the homogenous ion permeable membrane can be performed individually each time.
[0045] The use of such an ion-permeable membrane and said way of application enables a sectional charge reverse of the charged polymer surface, so that further application of coatings with the same charge as previous powder coatings applied, can be applied completely evenly or partially in a targeted manner.
[0048] The possible use of any kind of material makes the production step particularly sustainable, since all materials present in the work environment may be re-used, e.g. tarpaulins, foils, films, bags etc.
[0049] In certain embodiments, the electrostatic film is characterised in that the film thickness is 0.3 mm to 0.01 mm, particularly 0.15 mm to 0.01 mm, more particularly 0.05 mm to 0.01 mm.
[0050] The ion-permeability decreases with increasing film thickness, regardless of the type of material the film is made of, due to the laws of diffusion, so that a thinner film yields higher surface charges.
[0051] In certain embodiments, a first charged powder coating, charged contrarily to the activated surface, is applied to the activated surface, yielding a primarily coated surface, wherein the first powder coating is attached preferably to the activated surface sections.
[0052] In certain embodiments, a first charged powder coating, charged positively, is applied to the activated surface, yielding a primarily coated surface, wherein the first powder coating is attached to the activated surface sections, charged negatively.
[0053] The first powder coating is charged positively through triboelectric friction. Through the positive charge, the powder coating will preferably stick to the activated surface sections, charged negatively, but not to remaining sections of the activated surface, containing a positive charge. The powder coating may be of any colour. The surface is primarily coated at all sections of the activated surface, with a stronger coating at the activated surface sections, which results in a patterned surface, wherein the surface pattern is determined through the application pattern of the membrane.
[0054] In certain embodiments, a first charged powder coating, charged equally to the activated surface sections, is applied to the activated surface, yielding a primarily coated surface, wherein the first powder coating is attached preferably to the non-activated polymer surface sections charged contrarily to the activated polymer surface sections.
[0055] In certain embodiments, a first charged powder coating, charged positively, is applied to the activated surface, yielding a primarily coated surface, wherein the first powder coating is attached preferably to the non-activated polymer surface sections, charged positively.
[0056] The first powder coating is charged positively through high voltage ionisation of the surrounding air and is applied to the activated surface. In this case, the first powder coating preferably sticks to the non-activated polymer surface sections of the activated surface, i.e. sections that were not in direct contact with ion-permeable sections of the ion-permeable membrane and remain positively charged. The powder coating may be of any colour. The surface is coated at all sections of the activated surface, with a stronger coating at the positively charged surface sections, yielding the reversed effect of the previous embodiment.
[0057] In certain embodiments, the first charged powder coating is charged positively or negatively, particularly positively.
[0058] In certain embodiments, a second charged powder coating, charged contrarily to the first charged powder coating, is applied onto the primarily coated surface, yielding a secondarily coated surface.
[0059] In certain embodiments, a second charged powder coating, charged negatively, is applied onto the primarily coated surface, yielding a secondarily coated surface.
[0060] The second powder coating is charged negatively through high voltage ionisation of the surrounding air and is applied to the partially covered surface, so that the powder coating only sticks to the sections of the activated surface, which have not been fully covered by the first powder coating. The colour of the second powder coating may be any colour that is different from the first powder coating.
[0062] The first powder coating is charged the same way at each application and may be of the same or different colour each time. The colour effect may be enhanced using the same colour for each application or the surface pattern may be further individualised by using a different colour.
[0064] The second powder coating is charged the same way at each application and may be of the same or different colour each time. The colour effect may be enhanced using the same colour for each application or the surface pattern may be further individualised by using a different colour.
[0065] In certain embodiments, a positively charged polymer surface is covered sectionally with an ion-permeable membrane, to which then a negative electrostatic potential is applied resulting in negatively charged activated surface sections. The ion-permeable membrane is removed and a positively charged first powder coating is applied once or multiple times, yielding a primarily coated surface. A negatively charged second powder coating is applied to the primarily coated surface once or multiple times, yielding a secondarily coated surface.
[0066] In certain embodiments, the steps applying an ion-permeable membrane, applying a negative electrostatic potential, removal of the ion-permeable membrane, applying a first charged powder coating one or multiple times and applying a second charged powder coating one or multiple times may be repeated.
[0067] The repetition of these steps may be applied to the primarily coated surface or secondarily coated surface. The repetition allows the generation of an additional pattern on the surface.
[0070] In certain embodiments, the top coat is applied after the application of the first charged powder coating.
[0072] In an optional application of a colourless top coat, the powder coating is charged negatively through high voltage ionisation of the surrounding air and is applied to the patterned surface.
[0073] A second aspect of the invention relates to an activated surface comprising a pre-coated metal surface, wherein said activated surface comprises activated surface sections and non-activated surface sections, charged contrarily to the activated surface sections.
Method of Manufacture and Method of Treatment according to the invention
[0074] The invention is further illustrated by the following examples and figures, from which further embodiments and advantages can be drawn. These examples are meant to illustrate the invention but not to limit its scope.
Description of the Figures
[0075]
- Fig. 1
- shows an polyester powder coating on a metal surface.
- Fig. 2
- shows the application pattern of the ion-permeable membrane on top of the polymer surface.
- Fig. 3
- shows the application of the electrostatic potential onto the ion-permeable membrane.
- Fig. 4
- shows A) the application of the first powder coating; B) the resulting primarily coated surface after applying the first powder coating; C) the application of the second powder coating in a different colour from the first powder coating
- Fig. 5
- shows the final surface after application of the first and second powder coating.
Examples
Example 1: Coating of the metal surface
[0076] The negatively charged metal surface was coated with the positively charged DB703 FSM Primer coating and polymerised for 10 min at 195 °C. Through the thermally induced polymerisation, the primer coating structure is crosslinked and softened resulting in a charged polymer surface. It is presumed by the inventors that the polymer surface is partly neutralised through the action of heat.
[0077] The metal surface may also be charged positively onto which then a negatively charged primer coating is applied and polymerised for 10 min at 195 °C.
Example 2: Application of the electrostatic film and electrostatic potential
[0078] The charged polymer surface was covered with the electrostatic film in a creased way, so that sections of the film are in direct contact with the charged polymer surface and other sections of the film are not in direct contact with the charged polymer surface. A negative electrostatic potential (spraygun make: Nordson Company) was applied onto the covered surface resulting in a charge reversal at the sections with direct contact between electrostatic film and charged polymer surface. The section without direct contact remain positively charged.
[0080] In case of the application of a negatively charged primer, a positive electrostatic potential needs to be applied accordingly.
Example 3: Application of the charged powder coatings
[0081] The first powder coating (green colour) was charged positively through tribolelectric friction using a Tribo spraygun (make: Gema Company). The whole surface is coated with the powder coating, but the coating sticks mainly to the negatively charged sections of the surface.
[0082] The second charged powder coating (RAL 3009) was charged negatively through high voltage using a Corona spraygun (make: Gema Company). The second powder coating sticks to the remaining positively charged sections of the surface.
[0083] In case of the application of a negatively charged primer, the first charged powder coating is charged negatively and the second charged powder coating is charged positively.
Thermal fixation of the coatings
Example 4: Application of a top coat
[0086] The colourless powder coating was charged negatively through high voltage using a Corona spraygun (make: Gema Company).
Thermal fixation of the final product
List of references
1. A method for powder coating of a surface comprising the steps of
a. provision of a pre-coated metal surface, wherein said pre-coated metal surface comprises a charged polymer surface, particularly a positively charged polymer surface,
b. application of a membrane and subsequent application of an electrostatic potential to said membrane, wherein said membrane is applied in such way to said charged polymer surface that ion permeation takes place after the application of the electrostatic potential in sections, of the polymer yielding a charged polymer surface with activated polymer surface sections,
c. removal of said membrane, yielding an activated surface,
d. application of at least one charged powder coating onto said activated surface,
yielding a patterned surface.
2. The method according to claim 1, wherein the activated polymer surface sections are
charged negatively.
3. The method according to any of the preceding claims, wherein the membrane is
a. a homogeneous ion permeable membrane applied sectionally, wherein sections of said homogeneous ion permeable membrane are contacting the charged polymer surface and other sections are not contacting the charged polymer surface or,
b. a mesh-like ion permeable membrane applied evenly, comprising holes and sections of said mesh-like ion permeable contacting the charged polymer surface, or,
c. a partially ion permeable membrane applied evenly, comprising ion-permeable sections and ion-impermeable sections.
4. The method according to any of the preceding claims, wherein the membrane is a homogeneous
ion permeable membrane applied sectionally, wherein sections of said homogeneous ion
permeable membrane are contacting the charged polymer surface and other sections are
not contacting the charged polymer surface.
5. The method according to any of the preceding claims, wherein the ion permeable membrane
is an electrostatic film.
6. The method according to claim 4, wherein the electrostatic film is characterised in that the film thickness is 0.3 mm to 0.01 mm, particularly 0.15 mm to 0.01 mm, more particularly
0.05 mm to 0.01 mm.
7. The method according to any of the preceding claims, wherein a first charged powder
coating, charged contrarily to the activated polymer surface sections, is applied
onto the activated surface, yielding a primarily coated surface, wherein the first
powder coating is attached preferably to the activated polymer surface sections.
8. The method according to any of the preceding claims, wherein a first charged powder
coating, charged equally to the activated polymer surface sections, is applied to
the activated surface, yielding a primarily coated surface, wherein the first powder
coating is attached preferably to the non-activated surface sections.
9. The method according to any of the preceding claims, wherein a second charged powder
coating, charged contrarily to the first charged powder coating, is applied onto the
primarily covered surface, yielding a secondarily coated surface.
10. The method according to claim 8, wherein the first charged powder coating is applied
multiple times.
11. The method according to claim 9, wherein the first second charged powder coating is
applied multiple times.
12. The method according to claims any of the preceding claims, wherein the described
steps are repeated.
13. The method according to any of the preceding claims, wherein the primarily and/or
secondarily coated surfaces are thermally fixated prior to applying a top coat.
14. The method according to any of the preceding claims, wherein the top coat is a colourless
powder coating.
15. An activated surface comprising a pre-coated metal surface, and wherein said activated
surface comprises activated surface sections and non-activated surface sections, charged
contrarily to the activated surface sections
Amended claims in accordance with Rule 137(2) EPC.
1. A method for powder coating of a surface comprising the steps of
a. provision of a pre-coated metal surface, wherein said pre-coated metal surface comprises a charged polymer surface, particularly a positively charged polymer surface,
b. application of a membrane to said charged polymer surface and subsequent application of an electrostatic potential to said membrane, wherein said membrane is applied in such way to said charged polymer surface that ion permeation takes place after the application of the electrostatic potential in sections, of the polymer yielding a charged polymer surface with activated polymer surface sections,
c. removal of said membrane, yielding an activated surface,
d. application of at least one charged powder coating onto said activated surface,
yielding a patterned surface.2. The method according to claim 1, wherein the activated polymer surface sections are
charged negatively.
3. The method according to any of the preceding claims, wherein the membrane is
a. a homogeneous ion permeable membrane applied sectionally, wherein sections of said homogeneous ion permeable membrane are contacting the charged polymer surface and other sections are not contacting the charged polymer surface or,
b. a mesh-like ion permeable membrane applied evenly, comprising holes and sections of said mesh-like ion permeable contacting the charged polymer surface, or,
c. a partially ion permeable membrane applied evenly, comprising ion-permeable sections and ion-impermeable sections.
4. The method according to any of the preceding claims, wherein the membrane is a homogeneous
ion permeable membrane applied sectionally, wherein sections of said homogeneous ion
permeable membrane are contacting the charged polymer surface and other sections are
not contacting the charged polymer surface.
5. The method according to any of the preceding claims, wherein the ion permeable membrane
is an electrostatic film.
6. The method according to claim 4, wherein the electrostatic film is characterised in that the film thickness is 0.3 mm to 0.01 mm, particularly 0.15 mm to 0.01 mm, more particularly
0.05 mm to 0.01 mm.
7. The method according to any of the preceding claims, wherein a first charged powder
coating, charged contrarily to the activated polymer surface sections, is applied
onto the activated surface, yielding a primarily coated surface, wherein the first
powder coating is attached preferably to the activated polymer surface sections.
8. The method according to any of the preceding claims, wherein a first charged powder
coating, charged equally to the activated polymer surface sections, is applied to
the activated surface, yielding a primarily coated surface, wherein the first powder
coating is attached preferably to the non-activated surface sections.
9. The method according to any of the preceding claims, wherein a second charged powder
coating, charged contrarily to the first charged powder coating, is applied onto the
primarily covered surface , yielding a secondarily coated surface.
10. The method according to claim 8, wherein the first charged powder coating is applied
multiple times.
11. The method according to claim 9, wherein the second charged powder coating is applied
multiple times.
12. The method according to claims any of the preceding claims, wherein the described
steps are repeated.
13. The method according to any of the preceding claims, wherein the primarily and/or
secondarily coated surfaces are thermally fixated prior to applying a top coat.
14. The method according to any of the preceding claims, wherein the top coat is a colourless
powder coating.
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.
Patent documents cited in the description
Non-patent literature cited in the description
- PIETSCHMANN, JIndustrielle Pulverbeschichtung-Grundlagen.Anwendungen, Verfahren, JOT-Fachbuch, [0016]
- PIETSCHMANN, J.Industrielle Pulverbeschichtung-Grundlagen.Anwendungen, Verfahren, JOT-Fachbuch., [0017]
- Industrielle Pulverbeschichtung-Grundlagen.PIETSCHMANN, J.Anwendungen, Verfahren, JOT-Fachbuch, BraunschweigVieweg Verlag20020000 [0088]