1.1Cataphoresis-Anaphoresis

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GENERAL DESCRIPTION OF THE PROCESS OF ELECTRODEPOSITION OF PRIMER

History:

  • 1963 – the first industrial application (anaphoretic primer – small parts)
  • 1967 – the first electrophoresis line for coloring bodies (anaphoretic primer)
  • 1975 – industrial application of cataphoretic soil in the USA
  • 1978 – the first body painted with cataphoretic ground in Europe – CHRYSLER France

 

  • 1st GENERATION – 1967 Anaphoretic soil for carbody
  • 2nd GENERATION – 1976 the first cataphoretic primer in the automotive industry
  • 3rd GENERATION – 1981 medium and high coating thickness
  • 4th GENERATION – 1988 improved surface leveling
  • 5th GENERATION – 1991 ability to reduce pigment content
  • 6th GENERATION – 1994 environmentally friendly cataphoresis primer
  • 8th GENERATION – 2013 economy, high degree of edge concealment

 

Components of the developmental and evolutionary progress force of the CTF (KTL / ED):

  1. Quality: prolongation of the anticorrosion guarantee and operation of the coating.
  2. Environment: reduction in emissions in the coloring shops weight reduction, processing and disposal.
  3. Costs: finding the most effective ways to achieve goals.

Costs and efficiency:

  • Finding the cheapest ways to achieve the expected performance.
  • Reducing the cost of material applied to body: low film thickness, low density of dry film and low losses in the production process (furnace), i.e. evaporation of soil at high temperature, soils of the 8th generation have a high dry residue with a lower consumption on the body.
  • Appearance: ability to cover uneven metal.
  • Increased warranty period from through corrosion from 6 to 12 years.
  • Protection against stone shocks (up to pure metal).
  • Hiding power of the edges of a thin metal.
  • Penetration of soil into hard-to-reach parts of the body (parts).
  • Ability of various substrates (Al, Mg steel).
  • Wide drying window with the same quality

1.Electrophoresis.

The transfer of a substance by an electric current is called electrodeposition or electrophoresis.

Compared with other methods of applying paint, electroplating has the following advantages:

  • Automation of the process: the process of applying the paint is completely done without the participation of a person whose role is limited to observation and control;
  • Fast application of paint: 150-250 seconds is enough;
  • Efficiency of the process: all parts of the body are covered (both external and internal) with uniform thickness and, possible defects (such as debris) are reduced to almost zero;
  • Productivity: can exceed 99% due to repeated use of paint, which does not lie on the surface to be painted under the influence of electric current;
  • Environmental and technical safety: water-soluble paint (less than 2% organic solvent);
  • Anticorrosion resistance: the properties of the polymers used and the method of applying the cataphoresis primer have excellent characteristics that are responsible for the corrosion resistance.


2.Methods of painting.

 

  • CATAPHOROSIS – the paint is charged positively (+) and is considered as “cationic”; the part intended for painting should be connected with the minus (-) of the electrical circuit and acts as a “cathode”.
  • ANAPHOROSIS – the paint is charged negatively (-) and is considered as “anionic”; the part intended for painting should be connected with the plus (+) of the electric circuit and serves as an “anode”.

3.Stages of application and components of cataphoretic color.

The 1st stage is dipping: it is necessary to have a painting bath with sufficient volume for complete immersion of the painted part; The immersion always occurs automatically with the help of a suspended conveyor vertically;

2nd stage – electric current supply: it is necessary to have a direct current source where the negative terminal is connected to the painted part – the cathode (-), and the positive terminal with the counter electrode is the anode (+) and with immersion of both in the bath.

The cataphoretic method of applying paint requires:

  • Electrical conductivity of the paint;
  • Low viscosity of the paint to ensure its full penetration into hard-to-reach places;
  • The part must be metal; the counterelectrode (+) must also be immersed in the bath;
  • The painted part and the counter-electrode must be connected to the same DC source.

The technology of cataphoretic coloring provides for the presence in the bath of three main components:

  • Emulsion – consists of several cationic (+) polymers that make the film elastic and increase its resistance, and the blocked isocyanate provides polymerization while passing through the drying oven;
  • Pigment paste – a concentrate of pigments and mineral fillers, spread with another binder;
  • DI – water.

Equipment of the application of the cataphoretic coating on the part.


  1. Characteristics of watet solutions for cataphoresis.One of the characteristic properties of water solutions for cataphoresis paints is their limited stability in time. With the aging of working solutions during the working operation of the electrodeposition bath, the property of the paint material changes due to the following processes:
    • Oxidation of film-forming air in the presence of oxygen, leading to an increase in the molecular weight of the resin and a decrease in the molecular weight of the binder; the process is enhanced by constant mixing of the working solution and the release of oxygen during the electrolysis of water;
    • saponification of ester groups in the alkaline medium of the working solution, which leads to the elimination of fatty acids, an increase in the acid number and a decrease in the molecular weight of the binder, the process proceeds at a high rate at elevated temperatures and the pH of the working solution;
    • hydrolysis of salt groups, leading to a decrease in the solubility of the resin in water during coagulation of the binder due to a change in the hydrophilic-hydrophobic balance;
    • imbalance in the pigment / binder ratio, leading to a deterioration in the quality of the coating and its protective properties;
    • evaporation of organic solvents resulting in increased craters and a decrease in coating thickness, as well as a decrease in the stability of an water solution of the paint and water material;
    • accumulation of foreign electrolytes in the working solution, due to anodic dissolution of the substrate metal and in case of unsatisfactory washing of the products after surface preparation operations leading to an increase in the electrical conductivity of the working solution, accumulation of sludge and coagulation of the binder;
    • accumulation of a neutralizer, which leads to a reduction in the stability time of the working solution and changes in process parameters and coating properties due to a change in the degree of neutralization of the binder.

    Stability of the properties of the paint and varnish solution in the process of bath production is maintained by maintaining the parameters of the working solution within the limits of the standard values and their periodic adjustments.


General description of ED-coat primer.

The process is a lead-free cataphoretic soil of the 6th or 8th generation. The main corrosion resistance of the coating, obtained by the technology providing pigment yttrium oxide.

Cataphoresis of the 6th or 8th generation is a lead-free soil.

Compared to previous generations of cataphoretic soils, the product has the following significant advantages:

  • ecological safety (absence of lead and chromium, low content of volatile components – organic solvents);
  • high penetrating power;
  • low sedimentation rate;
  • low drying temperature;
  • Improved anticorrosion properties at lower coating thicknesses; resistance to oils;
  •  low consumption(flow rate).

Generation 6 (the edge is not covered) / Generation 8 (the edge is covered evenly)

 

Cataphoresis primer provides the best distribution of coating thickness; meets the technical requirements of European automobile manufacturers, providing thickness in the hidden cavities up to 12 microns.

Advantages of cataphoretic primer:

  • Appearance: the ability to cover the unevenness of the substrate (metal)
  • Extending the warranty from 6 to 12 years
  • Protection against stone impacts: mainly to the destruction of raw tin
  • Hiding power: door edges
  • Penetrating power: details of a more complex shape
  • The ability to protect various substrates (steel, Al, Mg)
  • Wide drying window with the same quality

Cataphoretic primer consist of the following components:

  • binder (resin) – epoxy resin in the form of milk emulsion (delivery in containers, 1 m³);
  • paste (pigment paste) – a mixture of pigments and fillers of gray color (delivery in containers, 1 m³).


6.Requirements to the surface.

Coated substrates (substrates): cold-rolled steel, all types of galvanized steel, aluminum, pre-phosphated steel. Preliminary surface is processed and phosphated (preferably with passivation). To obtain a substrate surface with high corrosion resistance, the phosphate must be homogeneous with an acceptable crystal structure, clean, completely wet or dry, free of oil, dirt, sludge. Weight of phosphate should be 2 – 4 g / m². The last wash before the electrodeposition bath must have an electrical conductivity below 30 μS / cm.


7.Black cataphoresis.

Black cataphoresis, i.e. cataphoresis for parts without subsequent painting, is an autonomous coating.

It is used (used) on chassis parts, engine compartment, frame, interior (brackets, brackets, holders, seat frame, etc.).

This primer is also used in the production of furniture, railway, urban transport (buses, trams, metro, etc.)

For black cataphoresis, the application process is completely identical to the bodywork, the only difference in costliness is the purchase of raw materials (initial).

The rise in price for this type of cataphoresis includes:

  1. Consumption per m2 – the thickness of the coating is higher than on the gray cataphoresis;
  2. Components of the paste and emulsion, which help protect the coating from UV rays.

Black cataphoresis or cataphoresis for parts provides minimal protection in the salt spray chamber for 800 hours, with the possibility of increasing to 1500 hours by surface preparation (phosphate) by increasing the thickness of the coating.

Coating thickness in the range 25-35 microns.

The difference of the “black” primer from the body is the increased hardness and high density of the film (wear resistance) allowing to ensure the minimum penetrating ability of harmful factors (salts, acids, moisture, etc.) on the metal.

In the case of comparing the black cataphoretic soil with the bodywork on the m2 (requiring the coloring of the subsequent protective layers), it has a lower economic component for production, because it does not require costs in subsequent operations, such as energy carriers (for example gas), paint consumption and human labor, in percentage terms, the savings go in favor of black cataphoresis of about 30%, which allows faster return on investment.