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...
Reexamination Certificate
2002-02-06
2004-05-25
Wu, David W. (Department: 1713)
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...
C524S502000, C524S558000, C524S849000, C525S131000, C526S318500, C526S318600
Reexamination Certificate
active
06740703
ABSTRACT:
This invention relates to a thickened aqueous coating composition containing film-forming polymeric binder and a macromolecular thickener. It also relates to a macromolecular thickener for use in the composition and to a polymerisable compound for use in making the thickener.
Thickened aqueous coating compositions are commonly used in coating surfaces found in buildings where the surfaces are usually coated at ambient temperatures of say 5 to 40° C. using for example brushes, rollers, pads or sprays as the application tools. Such compositions are often called “architectural” coating compositions and they include paints, lacquers, varnishes, woodstains and adhesives. Thickening a coating composition facilitates its loading onto application tools and its subsequent application onto architectural surfaces.
A thickened aqueous coating composition usually contains not only macromolecular thickener, water and a polymeric binder, but also particulate non-binder solids such as inorganic and/or organic pigments or opacifiers (for example rutile titanium dioxide or polymeric organic particles containing voids) or extenders (for example chalk, dolomite, clays or talc) as well as other optional ingredients such as matting agents (for example silica), structuring agents (for example titanium or zirconium chelates or laponite or bentonite clays), coalescing solvents (for example moderately volatile alcohols such as benzyl alcohol or hydrocarbons such as white spirit), antifoaming agents and biocides. After a thickened aqueous coating composition has been applied to a surface, it will dry and lose water whereupon the binder forms a film which binds together the remaining ingredients of the composition and the film bonds to the surface to form a dried coat on the surface.
A problem with dried coats obtained from thickened compositions is that residual thickener in the coat introduces a degree of water-sensitivity which manifests as a reduced so-called “wet wipe-resistance” together with a tendency for the dried coat to soften when wet which problem will be called “wet-softening”. For this reason, thickener concentrations are usually kept below 2 wt % of non vol thickener per 100 g paint composition. The problem is especially troublesome if the dried coat has been obtained from a fluid coating composition in which the volume of particulate solid material is below 30 vol % (based on the total volume of the fluid coating composition) and especially when the volume of the binder in the composition is below 20 vol %. This is because amounts of thickener well above 3 wt % are needed to give the coating compositions viscosities which are high enough for practical use. The problem is further aggravated if the dried coat contains a high volume percentage of particulate non-binder solids for such dried coats are less strongly bound and so are more sensitive to water. The volume percentage of non-binder particulate solids in a dried coat is conventionally called “Pigment Volume Content” or “PVC” even though solids other than pigments may be involved. Serious water-sensitivity arises in conventional dried coats if the PVC is above 70%.
Thickeners inevitably introduce further water-sensitivity into a dried coat because they are necessarily hydrophilic materials as will be explained towards the end of the following brief review of their usefulness in architectural coating compositions. A good account of thickeners and the closely related materials often known as “rheology modifiers” is given by G D Shay in Chapter 30 (headed “Thickeners and Rheology Modifiers”) of the book “Paint and Coating Manual: 14
th
Edition of the Gardner-Sword Handbook” edited by J V Koleske and published in 1995 by ASTM of Philadelphia. The contents of this Chapter 30 are herein incorporated by reference. The distinction between “thickeners” and “rheology modifiers” is somewhat arbitrary and so for the purposes of this Specification, the term “thickener” will be used to include “rheology modifier” too. Shay describes “rheology modifiers” as “inefficient thickeners” which have to be used in concentrations of over 18 g/liter (i.e. over 1.8 wt %) if a useful thickening effect is needed.
Shay explains that architectural coating compositions need to have viscosities which are high enough under all rates of shear, namely under high shear rates of over 1000/sec, moderate shear rates of from 10 to 1000/sec and low shear rates of below 10/sec. In the field of architectural coatings, viscosity is conveniently measured at 18° C. using a concentration of 2 wt % thickener based on the combined weight of water and thickener. A suitable high shear rate viscosity enables the coating compositions to be applied by brush, roller or pad in thicknesses which allow the resulting dried coat to hide blemishes on a surface and so minimise the need for further coatings to be applied. Preferably the high shear rate viscosity should be from 0.05 to 0.25 Pa.sec when measured by an ICI Cone and Plate viscometer as described in ASTM Test D 4287-88, the contents of which are herein incorporated by reference.
A suitable moderate shear rate viscosity facilitates mixing and pumping operations during the manufacture of the coating composition and also gives them a so-called “consistency” which appeals subjectively to many users. Preferably the moderate shear rate viscosity should be from 0.1 to 2.0 Pa.sec when measured by a Sheen Rotothinner viscometer as described in the Sheen Data Sheet called “Sheen/ICI Rotothinners” available from Sheen Instruments Ltd of Kingston on Thames, England. The contents of this Data Sheet are herein incorporated by reference.
A suitable low shear rate viscosity inhibits settling of solid ingredients when the coating compositions are being stored. Secondly, such a low shear rate viscosity reduces the risk of liquid coating compositions flowing down vertical surfaces to which they have just been applied. Such flow creates a disfiguration known as “sagging”. Thirdly, it enables large amounts of coating composition to be loaded onto a tool such as a brush or roller. Preferably the low shear rate viscosity should be from 20 to 150 Pa.sec when measured by a Brookfield viscometer as described in ASTM Test D2196 using Spindle No. 3 at a rotation speed of 12 rpm. The contents of ASTM Test D2196 are herein incorporated by reference.
Most formulations of film-forming polymeric binders and particulate solids in water do not have a sufficiently high viscosity under one or more of the shear rate conditions discussed above. This is particularly true if the fluid coating composition contains less than 30% by volume of solid materials and especially if it contains less than 20% of binder. Therefore, as reported by Shay, the viscosities of the formulations are conventionally increased by the addition of from 3 to 18 g of a thickener per liter of coating composition, ie concentrations of 0.3 to 1.8 wt %. According to Shay, the increase in viscosity is caused by broadly one of three mechanisms operating either alone or in combination. The three mechanisms are known as “hydrodynamic”, “flocculative” and “associative”. All three comprise interactions which involve macromolecules containing polymeric backbones having high weight average molecular weights of over 30,000 and preferably over 50,000.
Viscosities at all three shear rates can be conveniently measured together using a “Carri-Med” CSL 100 rheometer as supplied by TA Instruments Limited of Leatherhead, England.
The hydrodynamic mechanism is the primary mechanism employed by traditional macromolecular thickeners such as the gums, cellulose derivatives, polyethoxylates, polyacrylamides, polyvinyl alcohols and others listed by Shay in his Table 2. The mechanism requires a water-sensitive macromolecular thickener comprising a high molecular weight hydrophilic backbone devoid of any significant hydrophobic character. On adding the thickener to water, its hydrophilic backbones uncoil and occupy a large hydrodynamic volume in the solution so immobilising large volumes of water and thereby creating a substa
Belmudes Stephane Patrick
Sarkar Manish
Hu Henry S.
Imperial Chemical Industries PLC
Stachel Kenneth J.
Wu David W.
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