Tufted floor covering having binder with less than 0.5% water soluble compounds

Aqueous latex base binder of a synthetic polymer for manufacturing tufted floor covering having improved wear-resistance. The content of hydrosoluble compounds dissolved in the aqueous phase in the latex is less than 0.5% by weight in relation to the polymer.

The present invention relates to an aqueous latex base binder of a 
synthetic polymer used in manufacturing tufted floor covering. It also 
relates to the tufted floor coverings produced by means of the 
aforementioned binder. 
Due to the increase in use of flooring intended for domestic use, such as 
indoor floor and wall coverings, outdoor flooring and automobile floor 
coverings, just to name a few, consumption has increased of synthetic 
polymer aqueous latexes as textile fiber binders used in manufacturing 
tufted floor covering. 
Due to the various types of tufted floor covering (flat, looped vertical, 
cut vertical), the numerous binding processes (full bath impregnation, 
back-controlled impregnation, pulverization, etc.) and the variety of 
fibers used (wool, polypropylene, polyamides, polyesters, acrylic 
polymers), the manufacturers of synthetic latex binders have had to 
provide a more extensive selection of latexes. 
The quality of latexes used as binders is steadily improving because it is 
necessary that tufted floor coverings which, for economic reasons are 
composed of less and less fibers, be maintained wear-resistant. 
The binders in the invention have an aqueous latex base of a synthetic 
polymer, in which the hydrosoluble compounds dissolved in the aqueous 
phase is less than 0.5% by weight in relation to the polymer. 
Hydrosoluble compounds primarily include salts formed, for example, by 
catalytic residues, surface-active agents and macromolecular compounds 
such as carboxyl compounds. 
It has been found that, all things being equal in other respects, latexes 
with a sufficiently low content of hydrosoluble compounds dissolved in the 
aqueous phase lead to tufted floor coverings with improved 
wear-resistance. 
The following can be cited as synthetic polymers usable as latexes 
according to the invention: styrene-butadiene copolymers, 
carboxylated-styrene-butadiene copolymers, alkyl acrylate-styrene 
copolymers, carboxyl alkyl acrylate-styrene copolymers, alkyl 
acrylate-alkyl acetate copolymers, carboxyl alkyl acrylate-alkyl acetate 
copolymers, alkyl acrylate-vinyl chloride copolymers, carboxyl alkyl 
acrylate-vinyl chloride copolymers, vinylidene chloride-vinyl chloride 
copolymers, carboxyl vinylidene chloride-vinyl chloride copolymers. 
The content in the latex of hydrosoluble compounds dissolved in the aqueous 
phase can be estimated by using the method hereinafter described in which 
semi-permeable membranes with high cutoff are used to let 
low-molecular-weight compounds flow therethrough and, if need be, carboxyl 
macromolecular compounds, while preventing passage of polymer particles. 
The latex to be tested, having a ponderal dry material content t.sub.l, 
expressed in percent by weight, undergoes ultrafiltration by passing 
through a laboratory ultrafiltration module equipped with a semi-permeable 
membrane marketed by Rhone-Poulenc Industries of France under the 
tradename: "Iris 3538". The ponderal dry material content is determined 
from the first drop of permeate collected t.sub.p, expressed in percent by 
weight, which equals that of the aqueous phase of the latex. 
The content in the latex of hydrosoluble compounds dissolved in aqueous 
phase t.sub.s, expressed in percent by weight in relation to the polymer 
is obtained by the formula: 
##EQU1## 
A latex usable as a binder according to the invention is usually obtained 
from a latex of a synthetic polymer which is known to be usable for 
binding tufted floor coverings and which is prepared by any known aqueous 
emulsion polymerization process, and by eliminating from the latter a 
sufficient quantity of the aforementioned hydrosoluble compounds. For 
example, these can be eliminated by ultrafiltration through a 
semi-permeable membrane. As ultrafiltration progresses, the compounds 
dissolved in the aqueous phase flow through the membrane in the permeate 
while the hydrosoluble compounds adsorbed at the surface of the latex 
particles are progressively desorbed and eliminated. The ultrafiltration 
operation can be carried out in a conventional unit of a type commonly 
employed in industry.

A cross-section of this type of unit is shown in the attached FIGURE. 
Basically, it consists of tank 1 containing the latex to be processed, 
tank 2 containing deionized water, ultrafilter 3 and pump 4. Tank 1 is fed 
by tank 2 which supplies deionized water through pump 5; and automatic 
valve 6, actuated by float 7, maintains constant the level of the bath 
contained in tank 1. Pump 4 ensures latex flow through pipe 8 toward 
ultrafilter 3. Through pipe 9, on which flowmeter 10 is fitted, the 
concentrate delivered by ultrafilter 3 is recycled into tank 1. Heat 
exchange fluid, circulated through coil 11 immersed in the latex contained 
in tank 1, maintains it at a constant temperature. Pipe 12 is used to 
maintain the unit in stable working conditions. 
The unit is also equipped with shut-off valves 13, 14, 15, 16 and 17 and 
manometers 18 and 19. 
The maintenance of stable working conditions and the operation proceed as 
follows: With valve 14 closed and valve 13 open, pump 4 is turned on; then 
valves 14 and 15 are opened and valve 13 closed. By successive 
approximations, the opening of valves 14 and 15 is regulated so as to 
obtain the desired flow of latex at the desired pressure, the pressure 
differences indicated by manometers 18 and 19, representing the pressure 
drop in ultrafilter 3. 
To ensure good operation of the ultrafiltration technique, it is 
advantageous in accordance with the practice of the invention to respect 
the following conditions: 
The semi-permeable membrane must have a high cutoff, generally between 5000 
and 10000, expressed as the molecular-weight-value of standard proteins in 
a neutral, buffered medium. 
The flow rate of the latex on the membrane must be higher than 0.5 m/s 
(meters per second), and preferably between 1 and 2 m/s, to prevent the 
membrane from clogging, at the same time, it limits the pressure drop in 
the ultrafilter and also the shearing which the latex undergoes. 
The pressure differences on each side of the membrane must be between 0.1 
and 6 bars, and preferably between 1.5 and 3 bars. 
The temperature of the latex must be between 0.degree. and 100.degree. C., 
and preferably between 0.degree. and 50.degree. C. 
Since the flow rate of the permeate decreases as the ponderal dry material 
content of the latex increases, it is preferable to accomplish 
ultrafiltration with a perceptibly constant ponderal content, generally 
between 5 and 70%, and preferably between 45 and 55%, possibly after 
dilution especially if the latex viscosity is very high. 
Unit shutdown must be followed by an adequate cleaning cycle with pure 
water to prevent irreversible clogging, hence destroying the membrane. 
If the mechanical stability of the latex is insufficient to permit 
ultrafiltration without forming agglomerates, one can proceed by first of 
all bringing the latex to an alkaline pH value of usually between 7.5 and 
9.5. After ultrafiltration is completed, the latex can be concentrated, if 
need be, until its dry material content is suitable for the intended 
usage. 
The following examples are provided to illustrate the invention. 
EXAMPLES 1 and 2 
Example 1 is given for comparative purposes. Example 2 illustrates the 
invention. 
Complete impregnation of a tufted sheet, consisting of a surface coat of 
polypropylene and an undercoat of knitted-goods waste, is carried out with 
a binder. The sheet is then sized at a pressure of 5 kg/cm2 and then dried 
in a tunnel furnace at 130.degree. C. for 10 minutes. 
The treated sheet is tested for wear-resistance by the following three 
tests: 
Writing Test: A streak is made on the top side of a sample of the sheet 
with a metallic object which leaves a whitish trace. The degree of this 
trace is determined visually and compared with a standard range of 
samples. The results are given in grades ranging from 1 to 10; the higher 
the grade, the fainter the streak on the sample. 
Whiteness Test: The wear layer of a sample of the sheet undergoes repeated, 
standardized hammering which leaves it more or less shiny and whitened. 
The hammering is done with a device commercially known as the "British 
Tetrapod Walker" (BTW). This device primarily consists of a hollow, 
rotating cylinder, on the inner surface of which a test sample is applied, 
and also inside of which is a hammer, in a free state, with four 
ball-shaped striking masses fitted at the top of a regular tetrahedron. 
After the cylinder has completed several cycles, in this case 10.sup.5 
cycles, the effect on the sample is determined visually by comparison with 
a standard range of samples. The results are given in grades ranging from 
1 to 10; the higher the grade, the less the hammering has effected the 
sample. 
Lisson Test: The wear layer of a sample of the sheet undergoes abrasion 
caused by a mechanical walker known in industry under the tradename 
"Lisson pedal wheel". This device primarily consists of a wheel equipped 
at its periphery with 4 shoes (sabots in French), covered with a 
rubber-shoe-sole with a Wellen standardized profile; in this case, the 
shoes weigh a total of 13 kg, and their action causes the surface fibers 
to become more or less tousled. As it rotates, the wheel moves back and 
forth from one end of the sample to the other, accomplishing one cycle per 
round trip. The degree of tousling is determined visually after a given 
number of cycles, in this case 200 cycles, by comparison with a standard 
range of sample. The results are given in grades ranging from 1 to 10; the 
higher the grade, the lower the degree of tousling. 
In Examples 1 and 2, the binders used are aqueous latexes A and B, 
respectively, of carboxylated styrenebutadiene copolymer, composed of 43% 
butadiene, 53% styrene and 4% ethylene carboxylic acids by weight. 
The content in the latex of hydrosoluble compounds dissolved in the aqueous 
phase, by weight with respect to the polymer, is 4.7% for latex A and 0.3% 
for latex B. 
Latex B was obtained from latex A, with 50% dry material by weight, by 
subjecting the latter to the ultrafiltration process as hereinafter 
described. 
Ultrafiltration takes place in a unit with an ultrafiltration surface area 
of 0.7 m.sup.2. The unit is equipped with a membrane with a cutoff of 
20000, which is marketed by Rhone-Poulenc Industries in France under the 
tradename "Iris 3538", and is fed by a pump capable of supplying 6 m.sup.3 
/h at a pressure of 3 bars. During ultrafiltration, the dry material 
content in the latex is maintained constant with deionized water. After 
drainage, the unit is flushed clean with water. No clogging of the 
membrane is noticed. 
Latexes A and B are brought to a pH of 9 by adding ammonia, are diluted 
with 0.4% by weight, with respect to the polymer, of sodium 
alkylarylsulfonate, an emulsifying agent, the function of which is to 
improve the wettability of the sheet fibers, and are diluted with 
deionized water to a ponderal dry material content of 20% by weight. 
The following table shows the results obtained for each example. It also 
shows the weight of the binder deposited. 
______________________________________ 
EXAMPLE 1 EXAMPLE 2 
______________________________________ 
Weight of binder deposited 
in g/m2 130 .+-. 9 120 .+-. 12 
in % with respect to 
the sample 20 .+-. 1 19 .+-. 2 
Writing Text 6 7.5 
Whiteness Test 4.5 7.5 
"Lisson" Test 7.5 8.5 
______________________________________ 
It can be seen that latex B, used as a binder according to the invention, 
leads to a tufted sheet with better properties than the one impregnated 
with latex A.