Diisocyanate monomers for light stable PU resins
Raw materials for water-based polyurethane dispersions (PUD), radiation curable urethane acrylates, prepolymers for moisture curable one pack coatings and solvent borne polyurethanes
Evonik offers a wide range of products used in the production of light stable and weather resistant PUR resins. Our products are essential for manufacturing water-based polyurethane dispersions (PUD),conventional and water-based radiation curable urethane acrylates, prepolymers for moisture curable one pack PUR coatings and solvent borne polyurethanes. Another application is the urethanization of alkyd resins to significantly improve yellowing resistance, drying and hardness of coatings.
Radiation Curable Resins
Radiation curable resins are a solution for low-VOC coatings. Since the resins usually are liquid, viscosity can be adjusted by the use of a reactive diluent. Instead of physical drying, the solidification on the film is caused by a curing reaction induced by UV or electron beam radiation. This reaction usually takes place in seconds. As there is no need to eliminate solvents, there is no need for large drying ovens and the process is very fast, economic and environmental friendly. Most UV curable coatings are based on acrylate functional resins. Diisocyanates like VESTANAT® IPDI, H12MDI and TMDI are widely used to produce numerous oligomers to take advantage of urethane groups in the coating for high flexibility, the right softness/hardness and light-stability. Casting resins, i.e. for dental fillings, are another application for UV-curable resins. VESTANAT® TMDI based resins have very low viscosities and are thus the preferred solution in this application. Even with high loads of fillers, the resins can be used without solvents/VOC/reactive diluents.
- Curing within seconds by radiation, very fast process
- Low / no emission (VOC)
- Low/no solvents and also no water no drying necessary
- Low curing temperature, so suitable for heat sensitive substrates like wood, plastics
- Low coating thickness, low material consumption
- High crosslinking, high weatherability
- High toughness, high transparency and high gloss
- Excellent scratch resistance and chemical resistance
UV-resin production process
Recommended products for radiation curable urethane acrylates (UV resins)
VESTANAT® IPDI (isophorone diisocyanate) is a cycloaliphatic diisocyanate and characterized by its two reactive isocyanate groups comprising differences in reactivity (primary and secondary NCO groups). This leads to a high selectivity in the reaction with hydroxyl groups bearing compounds. This unique property is advantageous for the processing of low viscosity prepolymers leading to a comparably low content of residual, monomeric diisocyanate at the same time. By choice of an appropriate catalyst (i.e. dibutyl tin dilaurate, DBTDL), the rate of conversion is increased, but also the degree of selectivity is further enhanced. The low viscosity of IPDI-based prepolymers allows for the reduction of solvents (VOC). The methyl groups attached to the cyclohexane ring make VESTANAT® IPDI and the corresponding derivatives widely compatible with resins and solvents.
The cycloaliphatic ring itself gives products based on VESTANAT® IPDI more rigidity and a high glass transition temperature. VESTANAT® IPDI is a colorless, low viscosity liquid with a solidification point of – 60°C. Semi-finished products, e.g. NCO terminated prepolymers have low tendencies to crystallize but rather stay liquid and are easy processable. As a cycloaliphatic diisocyanate, VESTANAT® IPDI meets all requirements for the manufacture of light stable and weatherable polyurethanes also comprising excellent mechanical properties and chemical resistance.
- Differently reactive isocyanate groups
- High selectivity
- Low viscosity of prepolymers
- Low residual monomer content in prepolymers
- High glass-transition temperature
- Low tendency for crystallization
- High NCO content
- Highest toughness and flexibility at low temperature
VESTANAT® H12MDI (main component: dicyclyhexylmethane-4,4’-diisocyanate) is a cycloaliphatic diisocyanate with two cyclohexane rings. It resembles the hydrogenated analogue to MDI (methylendiphenylisocyanate). Nevertheless, properties of VESTANAT® H12MDI differ a lot from the aromatic MDI.
VESTANAT® H12MDI comprises two reactive isocyanate groups, both of secondary nature, showing nearly no differences in reactivity or pronounced selectivity. Due to this, semi-finished products, e.g. NCO terminated prepolymers show a broader molecular weight distribution resulting in an increased content of residual monomeric diisocyanate compared to VESTANAT® IPDI. Also, the viscosity of above mentioned products is significantly higher compared to similar products based on VESTANAT® IPDI.
VESTANAT® H12MDI leads to superior properties of finished products, i.e. outstanding resistance against aqueous media. Also the mechanical properties are on a high level, as well as abrasion resistance and solvent or chemical resistance. Due to the aliphatic nature of the diisocyanate, the produced elastomers or coatings benefit from an excellent light stability and weathering resistance. To combine the advantages of high selectivity and low viscosity of IPDIbased prepolymers with high resistance of H12MDI-based prepolymers, VESTANAT® IPDI and VESTANAT® H12MDI can also be employed as a blend. The main applications of H12MDI are PUDs as well as TPUs, where high softening temperatures can be achieved.
VESTANAT® H12MDI is a colorless, low viscosity liquid but tends to crystallize at temperatures below 25°C. Therefore the recommended storage temperature is about 30°C. Colder storage conditions do not harm the product, but make heating respectively a liquefying and homogenization step necessary.
- Crystallinity/hard segment orientation
- Good chemical resistance
- Good mechanical properties
- High glass-transition temperature
VESTANAT® TMDI (trimethyl-hexamethylene diisocyanate) is a linear, aliphatic diisocyanate, also derived from the isophorone chemistry. Structural similarities to the hexamethylene diisocyanate (HDI) are obvious but due to the three methyl groups along the chain, the products, as well as the properties of (semi-) finished products, differ signifcantly compared to HDI.
Semi-finished products, e.g. NCO terminated prepolymers based on HDI, tend to crystalize due to the pure linear structure of the diisocyanate. Using VESTANAT® TMDI instead prevents the prepolymer from crystallization. VESTANAT® TMDI also shows a good compatibility with solvents and other raw materials used in polyurethane chemistry.
VESTANAT® TMDI comprises two primary reactive isocyanate groups offering a higher reactivity compared to VESTANAT® IPDI or VESTANAT® H12MDI. The similar structural surrounding is for both NCO functions leads to a low selectivity towards hydroxyl groups, but by choice of the right catalyst, the selectivity may be increased.
The linear structure, and thus the lack of cyclic structures, of the VESTANAT® TMDI leads to comparably low viscosities of semi-finished products and a pronounced flexibility to the resulting polyurethanes. These properties are especially favorable for the production of UV curing resins.
With the features of low viscosity and high flexibility make the VESTANAT® TMDI also an ideal combination partner for VESTANAT® IPDI or VESTANAT® H12MDI.
Similar to other (cyclo-) aliphatic diisocyanates VESTANAT® TMDI offers high light stability and excellent weatherability.
- Linear structure
- High flexibility
- Low tendency to crystallization
- Good compatibility
- Low glass-transition temperature
VESTANAT® EP-DC 1241 is a heterofunctional monomer, comprising both, an isocyanate group and an acrylic function. It is based on isophorone diisocyanate (IPDI) and a hydroxyfunctional acrylate. VESTANAT® EP-DC 1241 is characterized by a very low content of di-adduct and monomeric IPDI. This allows for a very selective synthesis of the resin with low viscosities and low risk of gelation in case of highly branched polyols used as starting component. VESTANAT® EP-DC 1241 is used to incorporate acrylic functions into PUR resins or NCO functions into acrylates to form lightfast and weatherable UV cure coatings or adhesives. Another option is to attach acrylate functionality to components/additives/activators to fix them to a cured coating/adhesive to avoid migration.
- Very selective UV-resin manufacture
- Low content of diadduct
- Low content of residual diisocyanates
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