Vesiculated polyester granules

Details Vesiculated polyester granules Vesiculated polyester granules

2002-06-28

2004-08-17

Short, Patricia A. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S063000, C521S069000, C521S088000, C521S114000, C521S138000, C521S149000, C523S502000, C524S043000, C524S044000, C524S045000, C524S048000, C524S049000

Reexamination Certificate

active

06777454

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to vesiculated polyester granules and more particularly to a process of preparing such granules utilising a particular class of non-alkylphenolethoxylate surfactant.
2. Disclosure of the Related Art
Opacifiers are important components of paints, having the primary function of scattering light incident on the paint film. How well a paint is able to visually obliterate a surface over which it is applied is referred to as its opacity. Titanium dioxide pigment is traditionally used as the main opacifier and it, together with the polymeric film former (most usually a latex), are the two main contributors to paint formula cost. In the formulation of lowsheen (eggshell) but more particularly flat paints, mineral extender pigments such as calcite, clay or talc are incorporated to reduce specular reflection down to the desired level.
Since mineral extenders are comparatively cheap they may be added at such a level that there is insufficient film former to bind (space fill) all the pigment present. The paint formulator uses the term critical pigment concentration (CPVC) to describe the point where complete space filling can no longer occur. Addition of further quantities of mineral extender therefore leads to the formation of air voids in the film as drying occurs. These voids scatter light in their own right and contribute to paint film opacity thereby allowing an opportunity to reduce the level of titanium dioxide and still achieve acceptable opacity or coverage. The accompanying formula cost saving, however, is at the expense of other paint film properties such as scrub resistance and stain resistance. In the case of stain resistance, the problem is that of stains penetrating into the voids in the film (film porosity).
In order to improve film integrity (reduce film porosity) vesiculated polyester granules were developed which encapsulated the voids within a polyester granule or bead. Although air is not as good as titanium dioxide in scattering light, these vesiculated beads have been successfully used as opacifiers in paints for many years. In addition to reducing the amount of TiO
2
required in the paint, the use of vesiculated polyester beads reduces the amount of latex solids required to form a well integrated paint film. The spherical shape and smooth surface of the beads (low specific surface area) combined with their particle size distribution means that less latex is required to provide the level of binding required. The light scattering ability of the beads can be increased by incorporating an inorganic pigment, such as TiO
2
, into the beads.
It is well known that vesiculated granules of carboxylated unsaturated polyester crosslinked with ethylenically unsaturated monomer can confer advantageous properties on coating compositions in which they are incorporated, and as a result there has been extensive usage of such granules in a variety of applications. The background to the subject is well covered in the literature, for example, in articles by Kershaw (Australian OCCA Proceedings and News, 8 No. 8, 4 (1971)), Lubbock (Australian OCCA Proceedings and News, 11, No. 5, 12 (1974)), Hislop and McGinley (Journal of Coatings Technology, 50 (642), 69 (1978)), and Bierwagen (Congress Book of the XVth FATIPEC Congress, 3E-Activities, Vol. 111, 110 (1980)). A number of patents relating to these granules and their use in coating compositions have also been issued; these including U.S. Pat. Nos. 3,822,224, 3,879,314, 3,891,577, 3,923,704, 3,933,579, 4,137,380 and 4,321,332.
The preferred process of preparation of such granules is now well established. It is a “double emulsion” process wherein water is first stably dispersed in a solution in polymerisable monomer of a carboxylated unsaturated polyester to give a “first emulsion” and the first emulsion is itself stably dispersed in water to give a “double emulsion”.
Free radical polymerisation is then initiated to give vesiculated granules of crosslinked polyester resin. If pigmented vesiculated granules are required, pigment may be dispersed in either or both of the first emulsion components using conventional pigment dispersants.
Of the patents referred to above, U.S. Pat. No. 3,879,314 (Gunning et al.) describes “dimensionally stable” vesiculated granules, with U.S. Pat. No. 3,923,704 describing an improved process of preparing these dimensionally stable granules and U.S. Pat. No. 4,321,332 (Beresford and Braun) demonstrates the achievement of dimensional stability without the need for the polyamide bases of Gunning et al. In U.S. Pat. No. 4,321,332, the polyamine required for stabilisation of the first emulsion was replaced by an oxide, hydroxide or weak acid salt of a selected metal cation; in this way, the odour and yellowing effects of the polyamine could be considerably reduced (these granules shall hereinafter be referred to as “oxide granules”). Both of these types of granules have been used successfully in coating compositions.
However, it had sometimes been found that when oxide granules were prepared on a large scale that there had been an unacceptably high incidence of “grit” particles, that is, aggregates of two or more granules which are formed during large scale production thereof. One cause of this was the coming together and partial coalescence of individual granules prior to curing; on polymerisation initiation, they fuse to give “grit” particles. These particles are visible to the naked eye and their presence in coating compositions is highly undesirable as they appear as visible imperfections in the film.
WO84/00764 describes a process for preparing granules using an alkyl phenol containing anionic surfactant. The process described in that specification was said to reduce or completely eradicate the incidence of grit in oxide granules and to achieve opacities higher than could be previously achieved. In fact the surfactant described in WO84/00764 has been found to be particularly useful in ensuring that:
(a) the granules have the correct level, size and size distribution of internal microvoids to maximise light scattering thereby optimising the opacity or coverage of any paint which contains these granules;
(b) the spherical particles have few if any surface imperfections (surface holes) as such imperfections compromise the stain resistance of paints containing the granules;
(c) the granules/beads are sufficiently well stabilised to not aggregate (form grit) to any significant degree during polymerisation; and
(d) the process for making the granules is sufficiently robust to accommodate higher temperatures for formation of the granules prior to polymerisation being initiated (up to 50 EC.). Such higher temperatures lead to higher temperatures of exotherm leading to better levels of conversion of monomer to polymer thus reducing residual odour of the granule slurry. This is described in Australian Patent No. 670363 (ICI Plc).
In addition to the above, the surfactant was effective as a dispersant for pigment in water if that was the chosen route toward preparing the first emulsion as past of a process for making pigmented vesiculated granules.
While the alkylphenol ethoxylate surfactant described in WO84/00764 allowed the consistent production of vesiculated polyester granules with the desired properties, the commercial use of such surfactants has fallen out of favour.
In recent years there has been an increased focus on the toxicity profile of all raw materials used in industrial processes. In particular, and especially in Europe, the use of alkyl phenol based surfactants such as the alkylphenolethoxylates (APE) described in WO84/00764 are being phased out of consumer product formulations. Alkyl phenol surfactants, when they enter waterways, degrade to residues which can be toxic to fish (gill function). In fish, these residues also mimic oestrogen and are said to give rise to hormone malfunction with anatomical consequences in some laboratory test situations. Whether or not these findings could relate to real situations with consequences

Affiliated with

Also associated with

Rating

Vesiculated polyester granules does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Vesiculated polyester granules, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Vesiculated polyester granules will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3270527