New Alkoxylated Monomer Offers New Benefits Compared to Commodity Monomers
In Study 1, the three alkoxylated CHDMDA monomers were evaluated in an aliphatic polyester urethane acrylate oligomer (CN-963J85) at 10, 20 and 30 weight percent.
In Study 2, researchers tested these monomers in a resilient urethane acrylate oligomer (CN-964) at 70 weight percent and compared them to tripropylene glycol diacrylate (TPGDA) and hexanediol diacrylate (HDDA), the standard monomers used in the UV-cure industry.
Study 1 - Alkoxylated CHDMDA Physical Properties
As indicated, the solid CD-406 offers desirable abrasion resistance, hardness, weatherability and chemical resistance. The three alkoxylated CHDMDA monomers (CD-580, CD-581 and CD-582) proved to offer the same performance as CD-406, as well as improved hardness, scratch resistance, impact strength, and abrasion resistance in this study. Table 1 compares the four monomers.Performance Properties
The alkoxylated monomers in this study were evaluated in aliphatic CN-963J85 blended with 15% SR-506, isobornyl acrylate. It is a hard oligomer offering good weatherability. CHDMDA is a low-odor substitute for SR-506, isobornyl acrylate. Glass transition temperature (Tg), tensile strength and elongation properties were evaluated in CN-963J85.
Glass Transition Temperature
Figures 1-3 show the effects of alkoxylation on the Tg of the formulation tested in Study 1. In this case, increasing the alkoxylation level lowers the Tg at 10%, 20% and 30% monomer addition levels.Formulation
CN-963J85, containing 10%, 20% and 30% levels of CD-406, CD-580, CD-581, and CD-582, respectively, were prepared. The films were cured with 5% Esacure KIP100F, an alpha hydroxy ketone type of photoinitiator using a 300-watt-per-inch, medium-pressure Hg vapor bulb to yield a dose of 2 joules/cm2.Physical Properties
Tensile strength and elongation measurements of the formulations were obtained in Study 1 (see Figures 4-6). The figures show that high tensile strength and elongation can be obtained with CHDMDA monomers, particularly CD-582. This is significant, because the alkoxylated CHDMDA monomers can compete with isobornyl acrylates in performance, but CHDMDA-based monomers are significantly lower in odor.Study 2 - Physical Properties
All three alkoxylated CHDMDA monomers showed low viscosities, excellent color and relatively high refractive indices (see Table 2). Table 3 shows that they are significantly lower in skin irritation than the commodity monomers that were tested and analyzed in this study.
Formulation
The three monomers evaluated in the aliphatic polyester urethane acrylate oligomer (CN-964) at 70 weight percent were compared to TPGDA and HDDA. The five formulations analyzed are shown in Table 4.CN-964 is an aliphatic polyester urethane acrylate oligomer known for its resilience. It is often used in wood, metal and floor coatings where toughness, stain resistance, and impact strength are key performance properties.
SR-306 tripropylene glycol diacrylate, is a low-volatility, low-viscosity monomer. It is a frequently used monomer in free radical polymerization.
SR-238 1,6-hexanediol diacrylate is a low-viscosity, fast-curing monomer with low volatility, a hydrophobic backbone and good solvency.
Esacure KIP100F is a liquid mixture of an oligomeric alpha hydroxy ketone and 2-hydroxy-2-methyl-1-phenyl-1-propanone. It is a highly reactive, nonyellowing initiator for the photopolymerization of UV-curable systems based on an acrylic unsaturated oligomers and monomers. It is insoluble in most common organic solvents and monomers.
Esacure TZT is a eutectic mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone. It is practically insoluble in water, but completely soluble in most organic solvents, monomers, oligomers and resins.
Cure Methods
The test films were cured with 3% Esacure KIP100F and 2% Esacure TZT. The films were cured at 150 feet per minute using a 300-watt per-inch, medium pressure Hg vapor bulb.Performance Properties
Pencil hardness, Hoffman scratch resistance, impact strength, Taber abrasion resistance, chemical resistance, glass transition temperatures, and refractive indices of the formulations were tested in Study 2. Graphical presentations of the results allow easy comparison.Pencil Hardness
Pencil hardness testing was performed on the five formulations. Figure 7 shows that the alkoxylated CHDMDA monomers significantly outperform both the TPGDA and HDDA monomers.Hoffman Scratch Resistance
Hoffman scratch resistance is a measure of a formulation’s resistance to scratching and scuffing. Results indicate that again all three alkoxylated CHDMDA monomers outperform the commodity monomers. Results from the Hoffman scratch resistance test are shown in Figure 8.Impact Strength
Impact strength, a performance property crucial for applications such as wood coatings and flooring, was analyzed. Direct impact strength testing was performed on all five formulations. Impact strength results are shown in Figure 9. Results reveal that all three of the alkoxylated CHDMDA products exhibit superior direct and indirect impact strength when compared to HDDA. CD-581 and CD-582 also outperform TPGDA. Films with resistance to impact are typically very tough, resilient films.
Taber Abrasion Resistance
Taber abrasion resistance testing was performed using CS-10 abrasion wheels and two 500-gram weights. Percent weight loss was recorded at 500, 1,000, 1,500 and 2,000 cycles. Results are shown in Figure 10. The abrasion resistance of CD-580, CD-581 and CD-582 exceeds or equals that of the TPGDA and HDDA at all cycle levels. CD-581 is a particularly abrasion-resistant monomer.
Chemical Resistance
The chemical resistance of the formulations was tested using methylethyl ketone (MEK) solvent. The test was performed by rubbing a cloth containing MEK in a back-and-forth motion and observing deterioration in the coating. The number of rubs to observed coating deterioration was recorded. Results of the chemical resistance testing indicate that all of the monomers yield equivalent chemical resistance. Testing was performed to a maximum of 200 double rubs with MEK.
Glass-Transition Temperature
The glass-transition temperature of a formulation is important because it determines the softening point of the coating. The Tg data for the monomers is presented for informational purposes only (see Figure 12). The Tg of the CN-964 oligomer is -24°C.Refractive Index
The refractive indices of the formulations were tested (see Figure 13). The ring structure in the CHDMDA monomers provides a high RI that is reflected in the formulation RI.Conclusion
The results from Study 1 reveal that alkoxylated CHDMDA improves the solubility and usability of the CD-580, CD-581 and CD-582 monomers for UV/EB curing applications. The alkoxylated CHDMDA also provides improved performance properties in terms of tensile strength and elongation. Often an increase in tensile strength corresponds with a decrease in elongation. This simultaneous increase in tensile and elongation properties achieved with the alkoxylated CHDMDA products is unique, with exception of SR-506, isobornyl acrylate. The simultaneous increase tends to correspond to a tougher coating. The alkoxylated CHDMDA monomers are possible substitutes for the more odiferous monomer isobornyl acrylate. The optimal concentration is between 10 and 30 percent by weight. This simultaneous increase tends to correspond to a tougher coating. The alkoxylated cyclohexane dimethanol diacrylate monomers offer improved utility, excellent physical properties, and lower skin and eye irritation.Study 2 confirmed that these monomers with a cyclohexane dimethanol diacrylate backbone offer improved performance properties such as pencil hardness, scratch resistance, and abrasion resistance when compared to TPDGA and HDDA. These properties are crucial in flooring, wood, and metal coating applications. In addition to the performance property improvements, these monomers again offered significantly low skin irritancy.
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