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Solventborne polyurethane coating systems


Solventborne standard polyurethane coating systems

Two-component polyurethane systems are still the state of the art technology for automotive refinishing. Aliphatic polyisocyanates are the choice for high performance two-component clear coat, primer and filler systems. Bayer MaterialScience is the world leader in polyurethane technology and has a tremendous expertise in this field. More about this technology here. Usually, hydroxy acrylates are used as polyols.

Aliphatic polyisocyanates for solventborne standard two-component polyurethane clear coats, top coats, primers and fillers
    (Examples)

    Solids
    in %
    % NCO
    on solids
    NCO-
    functionality
    Viscosity
    mPas at 23°C
    		Characteristics
    HDI biuret polyisocyanate hardeners
    Desmodur®
    N 100
    100
    22.0
    F = 3.8
    10000
    		For weather-stable, non-yellowing top coats
    Desmodur®
    N 75
    75
    16.5
    F = 3.8
    225
    		Very good weather stability and gloss retention, good chemical resistance, for unforced and forced drying
    Desmodur®
    N 3200
    100
    23.0
    F = 3.5
    2500
    		Similar to N 100, however with lower viscosity
    HDI isocyanurate hardeners
    Desmodur®
    N 3790
    90
    18.0
    F = 4.1
    2000
    		Highly functional crosslinker for fast drying, weather-stable and non-yellowing top coats
    Desmodur®
    N 3300
    100
    21.8
    F = 3.5
    3000
    		Very good weather stability and gloss retention, no yellowing
    Desmodur®
    N 3390
    90
    19.6
    F = 3.5
    550
    		Same as N 3300, however at 90% solids
    Desmodur®
    N 3600
    100
    23.0
    F = 3.2
    1200
    		Low viscosity crosslinker for weatherstable and non-yellowing top coats, for one-component moisture-curing systems also
    Desmodur®
    XP 2679
    80
    15.4
    F = 4.5
    500
    		Highly functional, consequently very resistance against scratches and chemicals, for coatings with very good reflow properties
    IPDI-based polyisocyanate hardeners
    Desmodur®
    Z 4470
    70
    11.9
    F = 3.3
    1500
    		Fast drying, good light stability, good chemical and weather resistance, is mostly used in combination with Desmodur® N products because of its hardness
    Desmodur®
    XP 2565
    80
    12.0
    F = 2.5
    2800
    		For weather resistant and fast drying coatings
    Desmodur®
    NZ 1
    100
    20.0
    F = 2.8
    3000
    		Solvent-free crosslinker with good light stability

    Starting formulations with these products are available, too. Please contact our experts.


    Solvent-reduced polyurethane coatings systems (high solid systems)

    With the general trend to the reduction of VOC-emissions more environmentally friendly coatings systems are gaining market share. Low viscosity polyisocyanates can reduce the solvent requirements significantly. Still, these systems have the same high quality standard of traditional solventborne coatings and in some properties they show an even better performance. Usually, hydroxy acrylates are used as polyols.
      Raw materials for two-component polyurethene high solid systems

      Solids in
      %
      % NCO
      on Solids
      NCO-
      Functionality
      Viscosity
      mPas at 23°C
      		Characteristics
      Low viscosity HDI-based polyisocyanate hardeners
      Desmodur®
      N 3600
      100
      23.0
      F = 3,2
      1200
      		Low viscosity crosslinker for weatherstable and non-yellowing top coats, for one-component moisture-curing systems also
      Desmodur®
      N 3900
      100
      23,5
      F = 3,1
      730
      		Low viscosity crosslinker for lightfast, solventborne or water-based coatings
      Desmodur®
      N 3400
      100
      21.8
      F = 2,5
      170
      		Low viscosity crosslinker for water and solvent-based coatings, for one-component moisture-curing systems also

      Even though the isocyanate component is mostly the smaler part in a coating system, their influence on the properties of the finished coating is quite significant. In automotive refinishes the functionality and viscosity of the polyisocyanate are major parameters. Some polyisocyanates with their functionality in relation with their viscosity are shown here.


      Select starting formulations for high solid polyurethane systems
          RR 4501Two-component polyurethane top coat
          (Desmodur® N 3900 / Desmophen® A HS 1272)

          RR 4445Two-component polyurethane top coat
          (Desmodur® N 3900 / Desmophen® A HS 1272)


      Solvent-reduced very high solid polyurethane coatings systems - Polyaspartics

      The lowest possible solvent content, or rather a maximum solid content can be achieved with a combination of reactive thinners and low-viscosity polyisocyanates (polyaspartates) plus a polyol. These "Very high solid" systems contain less than 250g/l of solvent. More in depth information in this documentation:

      Produktbroschüre - Isocyanate und Prepolymere
      		Polyisocyanates and Prepolymers: Products and Applications
      Produktbroschüre Polyole und Aspartics
      		Resins - Polyols and Aspartics for reaction with Polyisocyanates
      		Polyaspartics - Change the Coatings Game

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