Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D1/00—Processes for applying liquids or other fluent materials
  • B05D1/02—Processes for applying liquids or other fluent materials performed by spraying
  • B05D1/04—Processes for applying liquids or other fluent materials performed by spraying involving the use of an electrostatic field
  • B05D1/06—Applying particulate materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D1/00—Processes for applying liquids or other fluent materials
  • B05D1/02—Processes for applying liquids or other fluent materials performed by spraying
  • B05D1/12—Applying particulate materials

Definitions

• the invention relates to a method for powder coating of metal surfaces according to the preamble of claim 1. Such methods are used for example for coating metal parts in vehicle construction, in mechanical engineering, in housings for household and other devices, for metal furniture and shelves or for toys.
• the manufacture of these metal parts is usually based on a sheet wound as a "coil", which is oiled, painted or coated in another way to protect against corrosion during transport and storage ("coil coating").
• the sheet is unwound from the coil and processed into the desired product by sawing, punching, drilling, folding and edging.
• the oil or paint coating also serves as a lubricant and release agent between the tool and the workpiece (sheet metal).
• an oiled coil is assumed, it is then painted or coated to protect against corrosion and to give the parts the desired color.
• a solvent-based paint is used for wet painting.
• the evaporation of the solvent is usually associated with a considerable environmental impact. This can be avoided when using an electrostatic powder coating process.
• Electrostatically charged powder is sprayed onto the surface to be coated, where it adheres due to the electrostatic attraction.
• Thermoplastic materials such as polyester or epoxy resins or a mixture thereof are suitable as powders.
• the powder layer is melted to a viscous mass by heating adheres well to the metal and results in a smooth surface.
• the coating hardens on cooling.
• edges of the sawn, punched or drilled metal parts are not coated and are therefore susceptible to rust. There is also a considerable risk of injury when handling these sharp-edged parts.
• Electrostatic powder coating is particularly advantageous because the electric field lines can be directed so that a particularly large amount of powder is deposited on the edges of the workpiece.
• the plastic coating that forms after curing is therefore particularly thick there and leads to rounded corners and edges.
• this process leaves the cost and environmental problems associated with de-oiling.
• the powder coating method according to the invention is based on an oiled metal surface.
• the powder is applied directly to the oil film. There is therefore no need to deoil the metal part to be coated.
• the invention makes it possible to coat iron materials which are provided with an oil film as corrosion protection and as a lubricant in mechanical processing steps. Since it is not necessary to remove the oil film, the process is inexpensive to use and environmentally friendly.
• the method according to the invention is suitable both for coating semi-finished products, for example unprocessed flat material or coils, and for coating parts that have already been completely mechanically processed.
• the latter case is preferable if, for reasons of corrosion protection and to avoid a possible risk of injury, no uncoated edges should remain.
• the method can be applied to all metals and steel types and is also suitable for parts of any shape, for example also for profiles or pipes.
• an oil is used according to claim 3, which is stable during the heating process, as long as it remains on the surface. This includes the possibility that individual components or all of the oil diffuse and evaporate through the powder layer during the heating process or that parts or even the entire amount of oil remain on the workpiece during the heating process and mix with the powder layer. If the oil on the workpiece surface in the kiln were unstable and would burn, for example, the color of the plastic coating would be strongly influenced by the oil and in particular by the oil's conversion processes under the influence of temperature. The slightest local temperature fluctuations in the kiln would lead to an uneven structure and color of the surface. This is reliably avoided with an oil that meets the condition specified in claim 3.
• the embodiment according to claim 5 has the advantage that the electrostatically applied powder adheres as completely as possible to the workpiece surface and little powder falls off in the coating booth, which powder has to be recycled for economical powder utilization.
• a surface coating that is particularly uniform both in terms of color and in terms of thickness and structure is achieved if, according to claim 6, the surface density of the oil film is less than approx. 3 g / m2, preferably approx. 0.3 to 1.5 g / m2, and the plastic coating is at least about 50 microns, preferably about 50 microns up to about 80 microns thick.
• An oil film which remains on the surface of the cured coating according to claim 8 is an excellent lubricating film in further mechanical processing steps. For this purpose enough oil must be applied and the heat supplied by the furnace must be low enough so that there is still oil on the Workpiece surface remains.
• test series with which particularly preferred configurations of the method according to the invention were determined, are summarized in Tables 1 and 2.
• type R steel test panels from Q-Panel were oiled, electrostatically coated with powder and passed through a baking oven.
• the coated sample plates were assessed under a microscope with regard to their optical quality and subjected to a cupping test according to DIN ISO 1520 to determine the paint adhesion.
• Table 1 shows the result of the optical assessment the hardened paint layer. The tests were carried out with different oils, which are given with their trade name, the manufacturer, the specification of the base oil and the respective viscosity at 40 ° C. The five columns on the right of Table 1 relate to different amounts of oil applied, area densities of 0.5 to 2.5 g / m2 being investigated in steps of 0.5 g / m2. The table contains the symbol "x" if the oil in question has led to the formation of visible oil islands or oil inclusions in the paint layer. The paint layer then makes a "scarred” impression. An optically perfect surface is marked with the symbol "o".
• Table 1 shows that there is a high optical quality of the coated plate when the surface density of the oil is at most 2.0 g / m2 and the viscosity of the applied oil at 40 ° C is below 40 mm2 / s, i.e. when the oil is very thin.
• a low viscosity oil has the advantage that it can be applied particularly evenly and also diffuses particularly easily through the powder layer in the stoving oven and volatilizes. This is especially true when the amount applied is very small. With a surface density of 0.5 g / m2, optically perfect surfaces result for almost every oil.
• the optical quality of the surface is independent of whether the oil is based on mineral oil or based on a vegetable oil, such as rapeseed oil.
• Table 2 shows the results of the cupping test according to DIN ISO 1520, with which the adhesion of the paint layer was measured. During the deepening test, the sample plate is deformed by a stamp and the depth of the deformation at which the lacquer layer tears is noted. With good paint adhesion, high values are achieved.
• Table 2 shows various oils and the length of time in the stoving oven.
• the right five columns are arranged as in Table 1 according to the amount of oil applied.
• the table contains the values of the deformation in mm at which one Cracking occurred.
• the oven temperature was always 180 ° C. This temperature was reached by the sample plates after a residence time of 14 minutes. The cupping values were measured after a stay of 14, 16 and 18 min.
• test plates were examined which were completely degreased in a conventional manner before the tests (“unoiled test plates”).
• Table 2 shows that the cupping value is 5.0 mm or more, which corresponds to a particularly good paint adhesion if the amount of oil applied does not exceed a surface density of 1.5 g / m 2 and a sufficient residence time in the oven is set.
• the sufficient residence time was 18 minutes at an oven temperature of 180 ° C.
• the amount of heat supplied to the sample plates under this condition is sufficient to essentially diffuse the oil through the powder layer and allow it to volatilize.
• the depression value is in the order of the value for unoiled or degreased sheets, ie in the order of 10 mm. This value indicates excellent paint adhesion.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Paints Or Removers (AREA)
• Disintegrating Or Milling (AREA)
• Chemically Coating (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)

Applications Claiming Priority (2)

Publications (3)

Family

ID=6414726

Family Applications (1)

Country Status (16)

Families Citing this family (6)

Family Cites Families (12)

• 1990
  • 1990-09-21 DE DE19904029985 patent/DE4029985A1/de not_active Withdrawn
• 1991
  • 1991-09-13 DK DK91115563T patent/DK0476539T3/da active
  • 1991-09-13 ES ES91115563T patent/ES2093665T3/es not_active Expired - Lifetime
  • 1991-09-13 EP EP19910115563 patent/EP0476539B1/fr not_active Expired - Lifetime
  • 1991-09-13 AT AT91115563T patent/ATE143837T1/de not_active IP Right Cessation
  • 1991-09-13 DE DE59108255T patent/DE59108255D1/de not_active Expired - Lifetime
  • 1991-09-17 AU AU84552/91A patent/AU639138B2/en not_active Ceased
  • 1991-09-18 ZA ZA917425A patent/ZA917425B/xx unknown
  • 1991-09-19 JP JP23997391A patent/JP2851728B2/ja not_active Expired - Lifetime
  • 1991-09-19 CA CA 2051879 patent/CA2051879C/fr not_active Expired - Fee Related
  • 1991-09-20 KR KR1019910016555A patent/KR100221771B1/ko not_active Expired - Fee Related
  • 1991-09-20 SK SK2870-91A patent/SK279241B6/sk unknown
  • 1991-09-20 RU SU915001640A patent/RU2004385C1/ru not_active IP Right Cessation
  • 1991-09-20 BR BR9104047A patent/BR9104047A/pt not_active IP Right Cessation
  • 1991-09-20 CZ CS912870A patent/CZ283154B6/cs not_active IP Right Cessation
  • 1991-09-23 US US07/763,467 patent/US5264254A/en not_active Expired - Fee Related
• 1996
  • 1996-12-04 GR GR960403281T patent/GR3021870T3/el unknown

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