UP resin for knifing fillers

UP resin for knifing fillers

We want to formulate a knifing filler which can be easily sanded down by hand and which should be based on an unsaturated polyester resin. Could you tell us how high the resin content should be, and what should be the ratio of hard to soft resin ? Would it be possible, as an alternative to use nitrocellulose ?



For knifing fillers one normally uses a filler (pigment) : UP resin ration of 3:1 to 7:1, depending on the desired consistency but, above all, on the resin absorption capacity of the filler. This, too, is normally used in compound form. Whiting, for example, binds large amounts of resin, but produces a relatively soft knifing filler. Powdered slate binds resin just as readily but produces harder knifing filler. The solution could be to use a combination of both, especially where ease of sanding is important.  Talc, kaolin and zinc oxide may also be used.

As far as the ratio  of hard to soft resin is concerned, flexibility can be readily controlled by using a universally acceptable formulation, i.e. about one mole each of maleic and o-phthalic anhydride esterified with two moles of propylene glycol. Long chain dioles such as hexane diole, increase flexibility and this also applies to dioles containing esther groups, e.g. diethylene and dipropylene glycol.

The opposite effect is observed in the case of short-chain dioles, as well as if the advantages offered by these UP knifing fillers, nitricellulose based fillers are likely to be used only where extremely fast drying times are required and the solvent problem can somehow be managed. These low-viscosity substances moreover neccessitate the use of fillers in stable dispersion in order to prevent settling out after prolonged storage.




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