We have had several questions lately about build and viscosity when converting varnish users from solvent based resins to solventless resin, particularly in polyesters. Most of the questions center around the loss of build in a solventless material that is similar in viscosity to an existing solvent based product.
As an example, our solvent-based material HI-THERM® BC-346A averages 200 cps and 1.5 mil build. DOLPHON® CC-1105 typically is 650 cps and ½ mil build. This is often the problem in making the conversion.
There are several reasons for this difference. Solvent-based material is made of very high viscosity polyester that is thinned with solvent. As the solvent is evaporated during the cure process, the resin rapidly increases in viscosity, which allows it to remain without drip and loss of build. On the solventless side, particularly with DAP monomer, there is no solvent coming off and the viscosity actually drops as it increases in temperature. So in this case, the resins experience run off during cure. Also, the nature of the solventless system uses lower viscosity polyesters to develop the final resin. All of this gives you less build. Hover, this also allows high viscosity solventless polyesters to penetrate better after a preheat process.
If build is an issue getting in the way of the sale, you might look to a higher viscosity solventless product. The relationship is far from linear, but for the most part, the higher viscosity solventless products produce higher builds than low viscosity products.
This is one reason that DOLPHON® CC-1305 and DOLPHON® XL-2103 have become such popular products. Even though the viscosities are approximately 1700 cps, they get good penetration on dip and bake if you preheat to the spec sheet. They also give better film build, DOLPHON® CC-1305 is close to 1 mil and DOLPHON® XL-2103 film build is close to 2 mil. The additional benefit of all solventless products, as compared to solvent based products, is a great decrease in VOC's. To this end nothing is better than the DOLPHON® XL line in polyester. In comparing VOC's, HI-THERM® BC-346 is typically 4 pounds per gallon. DOLPHON® CC-1305 is typically .7 pounds per gallon and the DOLPHON® XL-2103 is near .3 pounds per gallon.
There is one final note to consider in dealing with these issues. It is very important that the customers understand that they will be increasing their bond strength in moving to a solventless product. This might eliminate the need for build and diminish this difference as an issue. In this case, even though DOLPHON® CC-1105 is a lower build product, it has possibly the highest bond strength you will see in solventless polyester.
