EXPANCEL microspheres consist of a polymeric shell encapsulating a blowing agent. The polymeric shell is a copolymer of a vinylidene chloride and acrylonitrile. The blowing agent is isobutene.

EXPANCEL microspheres can be delivered unexpanded or expanded. Unexpanded microspheres are white, spherically formed particles with a means particle size of 10-16 pm. When heated, the polymeric shell gradually softens and the liquid isobutene starts to evaporate thus expanding the microspheres.

With EXPANCEL in a paint the following advantages can be obtained:

-          Reduced density

-          Better applicability

-          Higher water vapour permeability

-          Lower water absorption

-          Better filling capacity

-          Lower cost of material

As additive to waterborne paints we recommend one of our EXPANCEL WE grades. These are all expanded to a very low density, the true density being 36 kg/m³. They are available in three sizes, with a mean particle diameter of appr 70, 40 and 20 pm respectively. The low density microspheres are moistened which facilitates handling.

Table 1 on page 5 gives the specifications of the EXPANCEL grades used in the paint industry.

PROPERTIES OF PAINT WITH EXPANCEL

Reduced Weight

By using 0.5 per cent EXPANCEL, the weight of a 12 litre paint pot will be reduced from about 18 kg to 14 kg. Such a paint can save a lot of work, energy and transportation costs.

The density of the paint has decreased to 1.20 kg/cm³, and thus the volume per kg paint increased by 30 per cent.

Application

The paint can easily be applied by roller or brush because of the spherical form of the particles. Even spraying is possible. i.e. in airless spray guns. Compared to a conventional paint a light weight paint with EXPANCEL with equal viscosity does not splash to the same extend by using a roller because of lower centrifugal forces working on the light weight microsphere particles. The expanded microspheres are highly elastic and withstand hard mechanical treatment.

In textured coatings EXPANCEL makes it easier to get the structural filler more evenly distributed.

The drying time of a paint with EXPANCEL will be shorter due to higher solid content by volume.

Water Vapour Permeability

Paints with EXPANCEL WE are more permeable than corresponding standard paints. EXPANCEL WE could be utilized as an additive to regulate the water vapour permeability in tight exterior paint fillings and primer coatings.

Water Absorption

Paints with EXPANCEL WE are more hydrophobic than corresponding standard paints. One of the reasons for the degradation and destruction of a paint filling is the water absorption. The addition EXPANCEL WE will decrease the water absorption causing a delay in the destruction and reduce the rate of destruction in paint.

Hiding Power Opacity

One of the objects when making a light weight formulation with EXPANCEL is to replace part of the heavy fillers by EXPANCEL microspheres. It is then very important to achieve a very high packing degree in order to improve the hiding power. Unfilled spaces between the particles are not to be recommended in this case as the microspheres themselves contribute with a lot of unfilled spaces in the film.

Surface Finish

EXPANCEL microspheres can be used as a matting agent in paints with low gloss.The microspheres are providing a matt fine structured finish of the surface.

Filling Capacity

As the solid content by volume is increased when EXPANCEL is incorporated, the paint gets a better filling capacity and thus a higher capacity of covering cracks in the substrate. The high solid content by volume will also shorten the drying time.

Viscosity

A suitable level of viscosity of a light weight paint with EXPANCEL can easily be obtained by using more or less thickener. A decrease of viscosity by adding water can not be recommended, Since the opacity will be negatively effected in this case.

If EXPANCEL microspheres are added to a conventional formulation, or to a formulation not intended to contain any light weight filler the viscosity will increase considerably.

Cost of Material

EXPANCEL has a lower binder demand because the oil absorption on a volume basis is very low. This makes it possible to increase the PVC (Pigment Volume Concentration) without sacrificing quality. The costs of raw material per litre paint will be lower with EXPANCEL microspheres. A standard formulation of an interior flat wall paint will show a cost saving of 3 5% per litre by using EXPANCEL while an exterior paint  will show a cost saving of approx 7%.

Storage Stability

When using EXPANCEL microspheres as a light weight filler the storage stability of the paint will not be effected. There is no risk of EXPANCEL microspheres flotating at a viscosity suitable for painting. pH should be kept below 8.3 in order to avoid discoloration.

Health Aspects

EXPANCEL microspheres in light weight paints will not give any health or safety problems to the users.

PREPERATION OF A LIGHT WEIGHT PAINT WITH EXPANCEL WE

Two things of utmost importance concerning the preparation. The addition of EXPANCEL ought to take place just after dispersing the heavy fillers, and the peripherical speed should be high enough to disperse EXPANCEL WE microspheres completely. The following dispersing program, which has been developed at our laboratory, is suitable to obtain completely dispersed particles at the manufacturing of a light weight paint with EXPANCEL WE.

-          Water

-          Dispersing agents

-          Preservative

-          Antifoamer

-          Wetting agent

-          Pigment

-          Opacifying extender

-          Fillers

The mixtures is dispersed for 10 minutes at a peripherical speed of at least

10 m/s.

-          EXPANCEL WE

-          Thickener

-          pH-buffer

-          Coalescent

Disperse for 5 minutes at a peripherical speed of at least 10 m/s.

-          Binder

Disperse for 5 minutes at a lower peripherical speed, e.g. 5 m/s.