DE2020196C3 - Production of coatings using the electrostatic powder coating process - Google Patents

Description

It is known for the production of surface coatings various powdery masses using the electrostatic powder coating process based on polyethylene, polypropylene, epoxy resins, polyamides, polystyrene, chlorinated Polyethylene, cellulose acetobutyrate, polyurethane is and plasticized polyvinyl chloride. (»Kunststoffberater« volume 3, 1967: »Electrostatic Powder coating «; Information brochure of Electrostatic Equipment Corp./Fairfield/USA: "Sales Manual-History of Powder Coating" 1969; "Industrie-Lackier-Betrieb" magazine, June 1969: "The electrostatic plastic powder spraying"; Modem Plastics, July 1969 Electrostatics spark powder growth "; “Kunststoffe”, volume 10, 1969: “Vortex sintering and electrostatic powder spraying «).

Unplasticized polyvinyl chloride or vinyl chloride copolymers weichniacherfreie are so far not become known coating method ^r as materials for the electrostatic Pulve.

It has now been found that special vinyl chloride-ethylene copolymers in powder form are suitable for this purpose, provided that they have a particle size between 20 and 100 μ, preferred have between 40 and 80 μ.

The invention therefore relates to the use of copolymers of 90 to 99.5 percent by weight Vinyl chloride and 0.5 to 10 percent by weight ethylene for the production of homogeneous, pore-free coatings according to the electrostatic powder coating process. The K value can be 45 to 65.

The surface coatings obtained lie without a subsequent thermal aftertreatment is required, homogeneous and pore-free.

The addition of pigments and dyes is possible.

The copolymers mentioned can, for. B. in accordance with French patents 1 48! 932 and 1,481,319.

A distinction is made between electrostatic powder coating essentially three processes:

1. Powder application with hand gun (e.g. Ransburg system),

2. Powder application with one or more automatically working application guns (e.g. Ransburg),

3. Powder application in an electrostatic fluidized bed (e.g. system of electrostatic equipment Corp., Fairfield / USA).

All three procedures are based on the same principle, namely the charging of the material particles by passing one or more high-voltage electrodes ΐη a stream of air, moving the particles in an electrostatic field between High voltage electrode and object and finally precipitation on the object surface. The one with it The voltages used are approximately between 30 and 100 kV, in a subsequent operation

55 exposed the powder-coated workpieces in a heating furnace to the melting temperature of the plastic powder used, the powder particles melting and forming a uniform, pore-free, firmly adhering layer on the surface to be coated, layer thicknesses of at least 30 to 50 μ according to this Method achievable. A layer thickness of 50 to 150 μm is generally preferred.

Numerous materials can be coated using this process, as far as the subsequent melting process there are no limits, B. except metals: glass, ceramics, textiles, wood, leather, Paper, rubber, plastics and others

The layer thickness achieved is essentially dependent on the dwell time of the object in the particle flow, the distance between the object surface and the gun and the voltage output.

Due to the electrostatic fundamentals of this process, the operational capability the vinyl chloride-ethylene copolymers for the production of homogeneous, pore-free coatings the full width electrostatic powder coating process for coating the above Materials given both with the application gun and by means of the electrostatic fluidized bed process.

The plasticizer-free coatings obtainable according to the invention are very advantageous over this the previous plasticizer-containing loads, especially with regard to the lifespan of the layer, as defects such as embrittlement and migration of plasticizers are not required.

Electrostatic coating also occurs in the case of electrostatic coating that is not carried out in closed apparatus now no longer acidic and sometimes poisonous decomposition products of the plasticizers, so that a special one Securing the job becomes avoidable.

example 1

A powdery, plasticizer-free mass based on a vinyl chloride-ethylene copolymer with a K value of 64 and an ethylene content of 5 percent by weight, which by mixing 100 parts of the polymer with 3.0 parts of a liquid organotin stabilizer, 2.5 parts of a epoxidized fatty acid esters with an epoxy oxygen content of 6 to 6.5% and 1 part of eir ^ s montanic acid esters with a carbon atom chain length of C ₁₈ to C ₃₆ (focus on C ₇₈ ) in a high-speed mixer was prepared by further Grinding to a particle size of 20 to 100 μ - with a maximum between 40 and 80 μ - and with a Ransburg hand gun at a voltage of 80 to 90 kV and an object distance of 8 to 10 cm from the (one-sided) electrostatic coating a 0.8 mm thick, 80 × 150 mm large iron sheet degreased with methylene chloride was used. The adherence of the particles to the metal sheet after a spraying time of tO seconds was good, and there was no detachment even with rocking movements and light bumps. At a material-specific favorable temperature of 260 ^° C. determined by preliminary tests, the melting process then took place, which after 3 minutes led to a homogeneous, pore-free, firmly adhering coating with a layer thickness of about 100 to 150 μm.

The investigation of the mechanical properties

2

value? the coating composition described, measured on 4 mm thick press plates according to DIN standards 53 455, 53 453 or VDE 0302 showed that the data are comparable with those of the corresponding rigid PVC types, but the Vicat value is somewhat lower is:

Yield strength (Kp / cm ^a ) 540

Elongation (%) 25

Notched impact strength (cmKp / cm ² )

bri + 20 ° C 4.4

at TO ⁰ C 3.8

at-2O ⁰ C 3 8

Vicat (5Kp, glycol) ° C 58

Example 2

A powdery, plasticizer-free mass made of a vinyl chloride-ethylene copolymer with a 196

K value of 55 and an ethylene content of 1 percent by weight, consisting of 100 parts of the copolymer, 3.0 parts of a solid Bartum cadmium stabilizer and 2.5 parts of the montan ester mentioned in Example 1 was described in Example 1 Way and applied to an aluminum sheet under the conditions given there. Here, too, the subsequent smear process resulted in a homogeneous, pore-free, fire-adhering one Coating in a layer thickness of about 100 to 15μ.

The mechanical property values were also determined on 4 mm press dies:

Yield strength (Kp / cm ² ) 550

Elongation (%) 35

Notched impact strength (cmKp / cm ^a , 20 ° C) 2.8

Vicat (5Kp, GlykoI) ° C 60

Claims (1)

Claim: Use of copolymers from 90 to 99.5 percent by weight vinyl chloride with 0.5 to 10 percent by weight ethylene for the production of homo-S generous, pore-free coating using the electrostatic powder coating process.