S.P. Van Remortel, R.E. Ratcliff, D.D. Kragten, Unimin Corporation
Abstract
Nepheline syenite, a durable, commonly
employed hard feldspathic, is a crystalline silica-free functional filler used in all
types of decorative, industrial, and OEM
coating applications. Previous research
and mineral processing advancements
showed that new ultrafine grades have
superior optics at high loadings, contribute to improved mechanical properties,
and assist UV curing in aqueous UV-cure
clear PUD systems. This paper builds on
these previous findings using advanced
FTIR techniques to better quantify the
contributions that affect UV cure rate.
Moreover, this paper demonstrates the
ability of ultrafine nepheline syenite to
reduce formulation costs by replacing
part of the expensive photoinitiators
and resins without compromising coating performance.
Introduction
Nepheline syenite is a silica-deficient
functional filler and additive widely
employed in a variety of polymer-filled
coating, adhesive, ink, and colorant ap-
plications. Micronized sizes are valued
for purity of color, gloss control, ease of
dispersion with minimal viscosity build,
surface property modification, and su-
perior durability. Nepheline syenite is
composed of three minerals: soda and
potash feldspars, and the mineral neph-
eline. Although deficient in crystal-
line silica, nepheline syenite otherwise
provides physical performance proper-
ties which match ground silica fillers.
Since nepheline syenite functional fill-
ers are naturally derived, and deficient
in free silica and heavy or transition
metals, they are typically less burdened
by regulatory requirements such as
REACH, RoHS, and TSCA.
Figure 1 shows the typical particle
size and shapes of ultrafine nepheline sy-
enite. Table 1 lists the typical properties
of nepheline syenite. Nepheline syenite
is considered a moderate gloss reducer
based on its low oil absorption and com-
bination of angular, rectangular, and nod-
ular shapes. Mohs hardness on the 1 to
10 scale is about 6. The particles them-
selves are moderately hard or rigid, and
possess high compressive strength provid-
ing scratch and abrasion resistance in the
polymer matrix. The low oil absorption
and alkali aluminosilicate surface chemis-
try contribute to the ease of wetting and
rapid dispersion with low viscosity build.
The essential physical property of
nepheline syenite that provides high
Advancements for UV/EB Performance, Economics and Cure Rate
Transparent Ultrafine
Mineral Filler Technologies
Figure 1. SEM photomicrograph of ultrafine nepheline syenite at 10,000x.
