Titanium Dioxide in Coatings, Gloss

The gloss potential of a titanium dioxide pigment is mainly controlled by its primary particle size and the number of particles with a diameter greater than 500 nanometers (0.5 microns). A high percentage of oversize particles will reduce the gloss potential. Uniform particle size also gives better pigment packing within the film, which again increases gloss potential.

Millennium Inorganic Chemicals manufacturing processes ensure that the primary particle size of the pigment is optimized and oversize particles minimized by a combination of high-energy milling and classification. This ensures high specular gloss and improved distinctness of image with superior haze, when used in high quality gloss finishes, (Figure 1). 

Specular gloss is the gloss measured at fixed and identical angles of incidence and reflection. The normal angles of gloss measurement are 20^o, 45^o, 60^o and 85^o.

Haze is a measure of the clarity of gloss of a film and is normally measured using a slightly offset gloss meter. The reflected light is not measured at precisely the same angle as the incident light. This gives a very accurate measure of the degree of light scattering at the surface. This light scattering reduces the sharpness of the gloss and detracts from the appearance of the final article.

Distinctness of Image (DOI) is a measure of the surface smoothness of the film evaluated by examining a standard image and its reflection in the film. The test is set up so that image distinctness can be visually determined.

The same influences affect the haze and DOI of a film as affect the gloss, but haze and DOI are more sensitive to the changes.

The gloss developed by a coating on application is influenced by a number of factors, some of which are given below.

It well known that the pigment selected for a coating can influence the gloss potential of the coating. The following suggestions will assist in the choice of a pigment, although individual pigments may not always comply with the suggestions.

1. In general, multipurpose pigments, particularly modern multipurpose pigments, will have the best gloss potential in most coatings systems.
2. Until recently superdurable pigments, particularly the silica encapsulated types have previously been known for their lower gloss potential.
3. The introduction of the zirconia treated pigments overcame this except where maximum chalk resistance was required.
4. Some amongst the newest of the silica encapsulated pigments now offer an optimized balance between gloss potential and durability that allows you to use them for high gloss and high chalk resistance options.
5. "Flat" paint grades of titanium dioxide generate the lowest gloss potential as would be anticipated.

Pigment Factors Influencing Gloss in Coatings Top

The degree of dispersion of the pigment is probably the largest contributor to the coating's gloss. Highest gloss levels are achieved when the particle size distribution of the pigment is narrow and the proportion of oversize material is minimized. The excellent final gloss obtainable from Tiona^® pigments is the result of careful particle size control combined with high energy milling during manufacture. Excellent dispersion performance and flocculation resistance ensures that Tiona pigments demonstrate a high gloss potential in a wide range of coating systems. This level of gloss potential is only reached when the pigment is dispersed to its fullest degree.

Pigment Factors Influencing Gloss in Coatings

Whether you brush, roll or spray, the technique you choose to apply the coating will influence its final gloss. Brush or roller marks will reduce the gloss of the film, as will overspray micro wrinkling and sags caused by lack of control of film thickness. It is also the case that the actual spray method used can also impact on final film gloss. The gloss of films applied by the electrostatic minibell can be quite different to that achieved by normal spray techniques. In general terms the minibell appears to give lower gloss and especially higher haze than other electrostatic spray methods. Thus the pigment must be optimized for its final end use. Individual pigments of similar tytpe can give very different results.

Pigment Factors Influencing Gloss in Coatings