Aqueous paint composition

Details Aqueous paint composition Aqueous paint composition

2000-04-18

2001-11-13

Yoon, Tae H. (Department: 1714)

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

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S431000, C524S535000, C524S523000, C524S812000, C524S522000

Reexamination Certificate

active

06316544

ABSTRACT:

This invention relates to an aqueous paint composition, particularly one useful for painting the interior and exterior walls and the ceilings of buildings, a process for preparing the composition and a process for using it.
Paints for the walls and ceilings of buildings generally comprise a polymeric binder and particulate non-film-forming solid. These paints are generally one of two types. The first type are solventbome paints in which a polymeric binder is dissolved or dispersed in an organic solvent. The second type are waterbome paints in which the polymeric binder is a dispersion of insoluble polymer in water. Waterborne paints of this second type are often referred to as ‘emulsion paints’ and these represent the most common type of wall and ceiling paints now in use. Emulsion paints were developed in the 1950's and have continued largely unchanged to this day.
Emulsion paints comprise a film-forming polymer which is insoluble in water and which is in the form of a colloidal dispersion (sometimes called an “emulsion” or a “latex”). They also comprise one or more particulate non-film forming solids which can be pigments, such as titanium dioxide, or extenders such as powdered chalk. The paints usually also comprise a thickener.
The dispersed insoluble film-forming polymer is usually a vinyl or acrylic addition polymer, although alkyd, epoxy, polyurethane, or polyester polymers are also known. The dispersed insoluble polymer is inherently film-forming so that as the paint film dries, the polymer coalesces to form a continuous film. The coalesced film of insoluble polymer gives the final dried coating cohesion by binding together the pigment and extender and also provides the dried coating with adhesion to the underlying substrate. Both cohesion and adhesion are important in forming paints with good abrasion resistance and water resistance. These two qualities are particularly important in making practical robust paints that can withstand cleaning, for example by rubbing with a wet cloth to remove marks. an operation that is particularly common on walls in homes where there are children. This property is generally referred to as scrub resistance.
In view of their value in providing paints with good end properties such as scrub resistance, acrylic or vinyl polymer dispersions have been considered a central component of waterborne ‘emulsion’ paints for walls and ceilings for decades.
Pigments are particulate non-film-forming solids, which give the final paint film opacity, that is, the ability to hide the underlying substrate. Finely divided titanium dioxide is particularly good at this, and is widely used as a white pigment. The pigments also give the paint film its colour. Many coloured pigments can be used, usually in combination with titanium dioxide, to achieve the desired final paint colour.
Extenders are particulate non-film-forming solids which are often added to paints to lower the cost, to modify the rheology, or to improve pigment utilisation by inhibiting pigment particle agglomeration. They differ from true pigments in having little or no opacifying effect.
Thickeners are generally polymeric materials that, as their name suggests, increase the viscosity of the paint. Emulsion paints, being made from aqueous polymer dispersions, would have a viscosity very similar to that of water if it were not for the addition of thickeners. Such a low viscosity would cause application problems with the paint running down walls and dripping off rollers. Hence, thickeners are added. Thickeners vary widely in their chemical form, but can generally be described as water-soluble or water swellable polymers having hydrophilic groups. The most commonly used thickeners for emulsion paints are based on modified cellulose. Generally, thickeners are added to emulsion paints in amounts of up to 10% by weight of the total binder, most often around 3 to 6%.
With emulsion paints, certain of the important properties of the final paint film depend to a large extent on the amount of particulate non-film-forming solid (i.e. pigment and extender) present. The amount of such particulate solid is usually expressed as the volume of such material as a percentage of the theoretical total volume of dried paint. The theoretical volume is calculated on the basis of the non-volatile components of the paint composition and excludes any air which may in fact become trapped in the dried film and increase its actual volume. This percentage is usually called the “pigment volume content” or “pvc”. When the term “pvc” is used in connection with a liquid paint it means that the liquid paint is such that a coating of the paint when fully dry will have that pvc. Unless otherwise specified, “pvc” is used to mean the total amount of particulate non-film-forming solid, both pigment and extender.
In particular, the opacity of an emulsion paint can be improved by using a relatively high pvc. A pvc above 65% and preferably above 70% or 75% would be desirable to give a high opacity. This is probably because, when the pvc is high, air voids are created in the dried coating which introduce light-scattering and increase its opacity. However, the problem with using a high pvc in a conventional emulsion paint is that the cohesion and adhesion suffer and so scrub resistance tends to be poor. This is probably because the air voids that serve to improve the opacity also introduce weaknesses in the final film.
One way to improve opacity at lower pvc would be to use a higher proportion of opacifying pigment, such as titanium dioxide, relative to the amount of extender. However, the pacifying pigments are much more expensive than extenders and this solution is uneconomic.
The problem which this invention addresses is how to achieve paint compositions which can be used in the same way as conventional emulsion paints but which have a high pvc and so a high opacity while as the same time maintaining, or improving upon, the scrub resistance expected of an emulsion paint.
Certain paint compositions have been suggested to replace conventional emulsion paints, which contain a silanol functionalised resin in solution instead of a dispersed polymer and have a high pvc. The crosslinking of the silanol groups when the water evaporates gives these compositions good scrub resistance. The disadvantages of using silanol groups are that they require expensive silane functional raw materials and also that the compositions can be unstable when stored in very warm conditions for long periods due to premature crosslinking of the silanol groups. An alternative is clearly called for.
We have now discovered that surprisingly one can successfully formulate waterborne paints for walls and ceilings at high pvc with the use of certain film-forming polymers which also act as thickeners for the paint. These thickeners can be used as the sole, or major proportion of the paint binder or even as a relatively minor component in conjunction with other conventional film forming polymer. We have found that at least 20% by weight of the paint binder must be made up of these thickeners if the benefits of good scrub resistance at high pvc are to be achieved.
According to the present invention there is provided an aqueous paint composition comprising a polymeric binder and a particulate non-film-forming solid in which;
(i) at least 20% by weight of the polymeric binder is a thickener which is an, amine or acid functional, acrylic addition polymer which is at least partially neutralised, the thickener being such that a 1% by weight solution of the thickener in water when fully neutralised has a viscosity of at least 10 centipoise (measured using a Brookfield Spindle number 3 at 60 rpm and at 25° C.),
ii) the pvc of the composition is 65 to 95%,
iii) the non-volatile volume solids of the composition is 8 to 30%.
Surprisingly, these compositions have a much better scrub resistance than conventional emulsion paint in this relatively high pvc range in which the compositions have good opacity. This means that they can be applied at lower dry film weight while still giving o

Affiliated with

Also associated with

Rating

Aqueous paint composition does not yet have a rating. At this time, there are no reviews or comments for this patent.

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

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2595665