Mats for asphalt underlay

A woven or non-woven mat comprising natural or synthetic fibers bonded together with the residue formed by removing water from an aqueous composition comprising a thermoplastic emulsion and a melamine formaldehyde resin forms an underlay for asphalt paving for road surfaces.

BACKGROUND OF THE INVENTION 
This invention relates to mats for asphalt underlay as a base for asphaltic 
road surfaces. 
In one of its more specific aspects, this invention pertains to a 
composition mat and binder suitable for use as an underlay for asphalt 
paving for road surfaces. 
The use of non-woven mats as an underlay for asphalt paving is well known. 
Generally, such mats are employed by first applying to the highway to be 
repaired an asphalt composition over which the mat is laid and to which 
the mat adheres. A tack coat may, or may not, be applied over the mat. In 
either instance, an asphalt mix is then deposited over the mat and the 
surface is leveled and rolled. One of the mats presently so employed is 
comprised of non-woven, needle-punched polypropylene. 
The most important property such mats must possess is tensile strength. In 
addition, such mats should possess low porosity to prevent excess asphalt 
for strike-through, should exhibit high flexibility and elongation and 
should not cause skin irritation to those handling the mats. 
STATEMENT OF THE INVENTION 
There has now been developed a mat which possesses such properties. This 
mat comprises a woven or non-woven composite having on its surface a 
residue formed by removing water from an aqueous composition comprising a 
thermoplastic emulsion and a melamine formaldehyde resin. 
In a preferred embodiment, the thermoplastic emulsion will be selected from 
the group consisting of carboxylated styrene-butadiene latexes, vinyl 
chloride-ethylene acrylamide terpolymers, styrene acrylics and vinyl 
acrylics, or mixtures thereof, a carboxylated styrene-butadiene polymer in 
combination with an ethylene-vinyl chloride-acrylamide being the most 
preferred combination of thermoplastics. 
The mat of this invention has been found to be highly satisfactory in the 
laying of composition road surfaces in which the road paving composition 
is superimposed on the mat. 
DESCRIPTION OF THE INVENTION 
If an acrylic polymer is employed, it will preferably be in the form of an 
aqueous acrylic emulsion such as E-1653, available from Rohm and Haas, 
Philadelphia, PA. This material is about 47.5 weight percent solids, is 
contained in an anionic surfactant system and has a 13.degree. C. film 
forming temperature. 
If a carboxylated styrene-butadiene latex is employed, it will preferably 
be in the form of an aqueous emulsion such as Dow Latex 485, available 
from Dow Chemical Co., Midland, MI. This material is 46 weight percent 
solids and has a film forming temperature of about 25.degree. C. 
If an ethylene vinyl chloride is used, it will preferably be in the form of 
an aqueous emulsion of vinyl chloride-ethylene-acrylamide terpolymer such 
as Airflex 4514, available from Air Products and Chemicals, Inc., 
Philadelphia, PA. This material is 48 weight percent solids. 
Any suitable melamine-formaldehyde resin can be employed. One particularly 
suitable malamine-formaldehyde resin is Diaron 27-611, available from 
Reichhold Chemicals Inc., White Plains, NY. This material is a methylated 
malamine formaldehyde provided as a water soluble composite containing 60 
weight percent solids. 
Another suitable melamine-formaldehyde resin is Cymel 303, available from 
American Cyanamid, Bound Brook, NJ. This material is 
hexamethoxymethylmelamine having a specific gravity (25.degree. C.) of 
1.2, a refractive index of 1.515-1.520 and a viscosity (Gardner-Holdt, 
25.degree. C.) of X-Z.sub.2. 
The binder formulation will comprise, on a parts by weight-solids basis, 
from about 91 to about 97 weight percent aqueous thermoplastic emulsion, 
from about 3 to about 7 weight percent of the melamine formaldehyde resin 
and up to about 2 weight percent of a water-soluble ammonium salt 
catalyst, such as ammonium sulfate. It can also contain minor amounts of 
ammonium hydroxide as a pH modifier, and defoamers commonly used in the 
art. 
In the preferred embodiment of the invention, the binder will be comprised 
of about 94 weight percent of the thermoplastic emulsion, about 5 weight 
percent of the melamine formaldehyde resin and about 1 weight percent of 
the catalyst. 
In the preferred embodiment of the invention in terms of commercially 
available materials, the binder will be comprised of carboxylated 
styrene-butadiene latex (Dow's Latex 485) in an amount of from about 36.4 
to about 58.2 weight percent, an ethylene-vinyl chloride-acrylamide (Air 
Products Airflex 4514) in an amount of from about 36.4 to about 58.2 
weight percent, a methylated melamine formaldehyde (Reichhold's Diaron 
27-611) in an amount of from about 3 to about 7 weight percent and up to 
about 2 weight percent ammonium sulfate as catalyst. 
The binder of this invention can be applied to any mat of any material, 
however formed. For example, it can be applied to sized glass fibers, 
mineral fibers, synthetic fibers or natural fibers, or mixtures thereof. 
For the perferred underlay mat of this invention, it will be applied to a 
mixture of glass fibers and synthetic polymeric fibers, such as polyester 
fibers. 
Any suitable size and quantity of glass fibers will be employed. 
Preferably, the sized glass fibers will be 6.4 to 15.7 microns in diameter, 
6.35-50.8 mm in length and will comprise about 60 to about 100 weight 
percent of the fibers of the mat. 
The polyester fibers will be 6 to 15 denier, about 25 mm to about 40 mm in 
length and will comprise up to about 40 weight percent of the fibers of 
the mat. 
In the preferred embodiment, the glass fibers will be 19.05 mm long by 
about 10.9 microns and will comprise about 60 to about 80 weight percent 
of the mat. The polyester fibers will be 11/2 inches long, 15 denier and 
will comprise about 20 to about 40 weight percent of the fibers of the 
mat. 
The mats of this invention can be made in any manner. However, they are 
preferably made by dispersing a well-mixed quantity of the selected fibers 
in an aqueous medium containing a dispersant such as a polyalkoxylated 
alkylamine wetting agent and withdrawing the fibers as a wet-laid mat from 
the aqueous medium. The entire process is well known in the art. 
The binder of this invention can be applied to the dry mat in any suitable 
manner, all of which methods are known in the art. For example, the binder 
can be sprayed on or, preferably, the binder can be poured over the mat 
and the excess binder removed under vacuum. In the final cured mat, the 
binder will comprise about 20 to about 35 weight percent of the mat, 
preferably about 30 weight percent. 
The binder on the mat can be cured in any suitable manner. Preferably, it 
will be passed through an oven at a temperature of about 500.degree. to 
about 650.degree. F. for a time sufficient to cross-link the components of 
the binder and to produce a non-tacky mat.

The following example sets forth the procedure for producing a preferred 
binder composition of this invention. 
EXAMPLE I 
One thousand pounds of water were added to a mix tank and with slow 
agitation, 2983 pounds of carboxylated styrene-butadiene rubber latex and 
2567 pounds of ethylene-vinyl chloride-acrylamide were sequentially 
introduced hereinto. 
One hundred pounds of a water diluted anti-foam agent were introduced into 
the tank and the composite was stirred for 16 hours. Thereafter, 230 
pounds of methylated melamine formaldehyde were introduced into the main 
mix tank, followed by 1000 pounds of water. 
While continuing to stir, sufficient ammonium hydroxide was added to adjust 
the pH to 6.5.+-.0.2. and 267.4 pounds of 10 weight percent ammonium 
sulfate were sequentially added to the mix tank. 99.1 pounds of the 
antifoam agent were then added to the mix tank and sufficient water was 
added to the main mix tank to bring the total weight of the aqueous binder 
to 9000 pounds. Mixing was continued for a time sufficient to attain 
uniformity. 
The aqueous binder had a pH of 6.6, a solids content of 32 weight percent 
and a viscosity of 8.5 cps 96.degree. F. 
It will be evident from the foregoing that various modifications can be 
made to this invention. Such, however, are within the scope of the 
invention.