Coating bituminous substrates

Details Coating bituminous substrates Coating bituminous substrates

1999-04-16

2003-03-04

Pezzuto, Helen L. (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...

C524S832000, C526S318400, C526S318440, C526S328000, C526S328500, C526S329000, C526S329200

Reexamination Certificate

active

06528581

ABSTRACT:

This invention is concerned with coating bituminous substrates. More particularly, though not exclusively, this invention is concerned with a method for improving the quality of a mastic coating system.
A large proportion of the roofing market utilizes asphalt-based products, for example, modified bituminous rolls, as a base substrate which is then topcoated with conventional roof mastics to improve durability (asphalt degradation), provide energy savings (white coating vs. black asphalt), reduce the fire rating and improve aesthetics. Such coatings are frequently referred to as “roof mastics” although “mastic coatings” as used herein includes any such thick coatings applied to a substantially horizontal surface such as, for example, a roof deck, to a substantially vertical surface such as, for example, a wall, or to other substrate surfaces. Unfortunately, these mastic coatings have deficiencies. A roof deck, or other surfaces, by design or because of imperfections, may retain water. This ponded water results in loss of adhesion and blistering leading to failure of the mastic coating. There is also a tendency for mastic coatings to become discolored by the bleedthrough of black chemicals from the asphaltic substrate on which the mastic is applied.
A mastic coating system which displays good adhesion and superior resistance to blistering especially when exposed to ponded water is disclosed in U.S. Pat. No. 5,059,456. This system relies upon the use of a water-based tiecoat between the substrate and the mastic coating. The tiecoat consists of a water-insoluble latex polymer and multivalent metal ion, wherein the latex polymer comprises units such as would result from preparation from a monomer mixture comprising at least 20 weight %, based on the weight of the monomer mixture, of at least one hydrophobic monomer selected from the group consisting of (C
4
-C
20
)-alkyl methacrylates and (C
8
-C
20
)-alkyl acrylates, and from 3.0 weight % to 7.5 weight % of methacrylic acid, based on the weight of the monomer mixture, and where the latex polymer has a glass transition temperature of from −20° C. to 5° C., and where the molar ratio of the multivalent metal ion to the methacrylic acid in the latex polymer is from about 1:1 to about 0.375:1. The tiecoat is applied to a substrate before subsequent application of a mastic coating. Though this system offers properties of adhesion and resistance to blistering which are superior to conventional mastic systems, there remains a desire to improve upon these properties.
It is an object of the present invention to provide a mastic coating system which offers improved adhesion and resistance to blistering over those described in U.S. Pat. No. 5,059,456. Moreover, it is preferred if the above improvements in the quality of a mastic coating system can be achieved with a system which does not essentially rely upon the use of a tiecoat between the substrate and mastic composition.
In accordance with the present invention, there is provided a method for improving the quality of a mastic coating system comprising:
(A) forming a mastic topcoat composition and optionally a tiecoat composition;
(B) optionally applying said tiecoat composition onto a bituminous substrate;
(C) applying said mastic topcoat composition either onto a bituminous substrate directly or, when present, onto said tiecoat composition which has already been applied onto said bituminous substrate;
wherein at least one of said mastic topcoat composition and said optional tiecoat composition comprises a water-insoluble latex polymer;
wherein said latex polymer has a Tg of from −25° C. to 20° C., preferably from −10° C. to 0° C., and is prepared from a monomer mixture comprising:
(a) at least 20%, preferably from 30 to 70%, by weight, of at least one hydrophobic monomer selected from the group consisting of (C
8
to C
24
) alkyl (meth)acrylates;
(b) 0 or up to 45%, preferably 0 or up to 35%, more preferably 0 or up to 10%, by weight of at least one vinyl aromatic monomer;
(c) 0 or up to 75%, preferably up to 74.5%, more preferably 5 to 70%, even more preferably 5 to 50%, by weight of at least one monomer selected from the group consisting of (C
1
to C
4
) alkyl (meth)acrylates; and
(d) 0 or up to 5%, preferably from 0.5 to 2.5%, by weight of at least one monomer selected from acrylic or methacrylic acid;
provided that when (b) is not present in the mixture the amount of (d) is in the range from 0 or up to less than 3%, preferably 0.05 to less than 3% by weight; and wherein the weight of (a) and (b) together constitute at least 25%, preferably 30% or more, more preferably 35% or more, even more preferably 45% or more, by weight of said monomer mix.
In another aspect, the present invention provides a composition suitable for use as a mastic topcoat composition or a mastic tiecoat composition comprising a water-insoluble latex polymer; wherein said latex polymer has a Tg of from −25° C. to 20° C., preferably from −10° C. to 0° C., and is prepared from a monomer mixture comprising:
(a) at least 20%, preferably from 30 to 70%, by weight, of at least one hydrophobic monomer selected from the group consisting of (C
8
to C
24
) alkyl (meth)acrylates;
(b) 0 or up to 45%, preferably 0 or up to 35%, more preferably 0 or up to 10%, by weight of at least one vinyl aromatic monomer;
(c) 0 or up to 75%, preferably up to 74.5%, more preferably 5 to 70%, even more preferably 5 to 50%, by weight of at least one monomer selected from the group consisting of (C
1
to C
4
) alkyl (meth)acrylates; and
(d) 0 or up to 5%, preferably from 0.5 to 2.5%, by weight of at least one monomer selected from acrylic or methacrylic acid;
provided that when (b) is not present in the mixture the amount of (d) is in the range from 0 or up to less than 3%, preferably 0.05 to less than 3% by weight; and wherein the weight of (a) and (b) together constitute at least 25%, preferably 30% or more, more preferably 35% or more, even more preferably 45% or more, by weight of said monomer mix.
In yet another aspect, the present invention provides the use in a mastic coating system to improve adhesion and resistance to blistering of a mastic topcoat of a water-insoluble latex polymer; wherein said latex polymer has a Tg of from −25° C. to 20° C., preferably from −10° C. to 0° C., and is prepared from a monomer mixture comprising:
(a) at least 20%, preferably from 30 to 70%, by weight, of at least one hydrophobic monomer selected from the group consisting of (C
8
to C
24
) alkyl (meth)acrylates;
(b) 0 or up to 45%, preferably 0 or up to 35%, more preferably 0 or up to 10%, by weight of at least one vinyl aromatic monomer;
(c) 0 or up to 75%, preferably up to 74.5%, more preferably 5 to 70%, even more preferably 5 to 50%, by weight of at least one monomer selected from the group consisting of (C
1
to C
4
) alkyl (meth)acrylates; and
(d) 0 or up to 5%, preferably from 0.5 to 2.5%, by weight of at least one monomer selected from acrylic or methacrylic acid;
provided that when (b) is not present in the mixture the amount of (d) is in the range from 0 or up to less than 3%, preferably 0.05 to less than 3% by weight; and wherein the weight of (a) and (b) together constitute at least 25%, preferably 30% or more, more preferably 35% or more, even more preferably 45% or more, by weight of said monomer mix.
Preferably at least one of (b) and (d) is present in the monomer mixture.
Mastic coating systems employing the topcoat and/or tiecoat of this invention display surprisingly improved adhesion and resistance to blistering, especially when exposed to ponded water. They are also resistant to bleedthrough of dark chemicals from the bituminous substrate.
A common substrate for application of the invention is modified bituminous sheet.
The latex polymer can be prepared by emulsion polymerization techniques well known in the art. For example, U.S. Pat. No. 5,521,266 discloses a very suitable process of aqueous polymerization suitable for forming polymers containing monomers having low water solubility.
T

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