Flame-retardant carpet and composition for preparing the same

Combinations of certain hydroxycarboxylic acids with certain metal oxides and hydroxides provide unexpectedly enhanced flame retardancy to carpets, said flame retardancy being durable to usual carpet cleaning procedures.

BACKGROUND OF THE INVENTION 
This invention relates to flame-retardant carpets and compositions which 
impart improved flame retardancy thereto. In one of its more specific 
embodiments, this invention relates to flame-retardant polyester and 
polyamide carpets and process for the preparation thereof. 
A number of metal compounds have been reported in the literature as flame 
retardants for various substrates. By far the most notable prior art 
compounds are antimony oxide and antimony chloride. Other metal compounds 
described as fire retardants include phosphates and borates of alkali 
metals and alkaline earth metals, aluminum hydrate, titanium salts, tin 
salts, and double salts such as potassium hexafluorozirconate and 
potassium hexafluorotitanate. 
When applied to carpets, most of the prior art flame-retardant materials 
provide flame retardancy which is not durable to usual cleaning procedures 
unless the compounds are incorporated in the polymeric materials, e.g., by 
incorporating the flame retardant in the polymer melt during production of 
polyester or polyamide fibers. Unfortunately, incorporation of the flame 
retardant in the polymer melt may cause serious problems such as change of 
melt viscosity of change of physical properties of the fibers produced. 
In recent years, much research has been carried out directed to production 
of flame-retardant carpeting. The following patents indicate the state of 
this art. U.S. Pat. No. 3,418,267, to W. F. Busse, relates to 
flame-resistant polyamides and process thereof. The patent discloses that 
polyamide resin is made flame retardant by incorporating therein from 5 to 
20 percent by weight of an organic halide, e.g., chlorinated biphenyl, 
which is reactive with the resin only at its pyrolysis temperature, and 
from 3 to 15 percent by weight of an oxide of tin, lead, copper, iron, 
zinc, or antimony. 
U.S. Pat. No. 3,663,345, to G. G. Jaisinghani, discloses a flame-retardant 
carpet in which the pile fibers are fixed to the primary backing by a 
compound comprising a latex binding material combined with an aluminum 
hydrate. 
U.S. Pat. No. 3,719,547, to D. H. Martin et al., describes a 
flame-retardant pile fabric. A fibrous layer composed of combustible 
filaments or fibers extends from the top surface of a fibrous backing to 
present a pile surface. A coating of a film-forming halogen-containing 
polymer and a water-insoluble organophosphorus compound is applied to and 
confined essentially to the top surface of the backing. Where the backing 
is made of a thermoplastic material, a coating of the halogen-containing 
polymer may be used without the organo-phosphorus compound. 
It has been suggested in U.S. Pat. No. 3,956,236, to F. E. Evans, et al., 
that flame resistance of carpets, such as polyamide and polyester carpets, 
can be increased by adding a synergistic composition comprising a metal 
salt of certain organic acids, particularly metal salts of 
hydroxycarboxylic acids, with certain organic acids or their ammonium 
salts, particularly hydroxycarboxylic acids or their ammonium salts. Also, 
U.S. Pat. No. 3,943,100, to M. B. Berenbaum et al., described flame 
retardants based on certain organic acids, e.g., gallic acid, citric acid, 
or tartaric acid, or the ammonium, lithium or magnesium salts thereof. 
Although these patents constitute a major contribution to this art, 
investigations have been continued to develop an improved flame-retardant 
carpet wherein the flame retardancy is particularly durable to usual 
carpet cleaning procedures. 
SUMMARY OF THE INVENTION 
In accordance with this invention, it has been discovered that polyester 
and polyamide carpets can be treated with certain synergistic additive 
compositions to give a flame-retardant carpet wherein the flame retardancy 
is particularly durable to usual carpet cleaning procedures. 
The additive flame-retardant composition with which the carpet is treated 
comprises: 
a. About 10 to about 90 weight percent of a polyvalent metal compound 
selected from the group consisting of oxides and hydroxides of tin, 
antimony, aluminum, and zinc; and 
b. About 10 to about 90 weight percent of a hydroxycarboxylic acid selected 
from the group consisting of malic acid, citric acid, tartaric acid, 
gallic acid, and 2,4-dihydroxybenzoic acid. 
The combination of the polyvalent metal oxide or hydroxide and the 
hydroxycarboxylic acid as defined above provides synergistic improvement 
in flame retardance of the carpet. Moreover, surprisingly, this flame 
retardance is durable to usual carpet cleaning procedures. 
The process of the present invention for increasing the flame retardance of 
the polyester or polyamide carpet wherein said flame retardancy has 
improved durability to carpet cleaning procedures, comprises treating the 
carpet with from 1 to 15 weight percent of the foregoing composition and 
curing said composition on the carpet at a temperature of 100.degree. to 
200.degree. C., preferably at a temperature of 100.degree. to 150.degree. 
C. 
The present invention provides a flame-retardant carpet which retains its 
aesthetic properties and is more flame retardant than prior art carpets, 
particularly after cleaning said carpet. We postulate that this 
improvement involves a synergistic interaction between the several 
elements of the present invention. In one embodiment, the present 
invention provides a flame-retardant carpet having a relatively pliable 
primary backing and a tufted surface, said surface being comprised of 
fibers selected from the group consisting of polyester and polyamide 
fibers, said carpet having incorporated therein from 1 to 15 percent by 
weight of the foregoing composition. 
The term "flame-retardant carpet" is used herein to mean that the carpet 
burns very slowly when exposed in air to a direct flame or its equivalent. 
The preferred method of testing for flame-retardant properties is a 
modified United States Department of Commerce test, DOC FF 1-70, wherein a 
250 watt heat lamp is positioned 5 inches from the carpet surface and is 
controlled by a variac. The lamp is turned on for 5 minutes at a preset 
voltage on the variac in order to provide a more vigorous test. The higher 
the voltage applied to the heat lamp, the greater the heat applied to the 
carpet prior to burning the carpet. The temperature of the carpet is 
measured with a thermocouple. The carpet is then burned by placing a 150 
milligram methenamine pill in the center of the carpet. The pill is then 
ignited. The higher the temperature, which can be applied to the carpet 
before the carpet fails to extinguish within 90 seconds after the pill has 
finished burning, the better the flame-retardant properties of the carpet. 
The durability of the flame-retardant treatment is preferably determined by 
retesting the carpet in accordance with the above-described 
flame-retardancy test, after laundering the treated carpet by a procedure 
described in Technical Manual of the American Association of Textile 
Chemists and Colorists, AATCC 124-1973. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred process of this invention is an improvement over known 
processes for preparing carpeting. When carpeting is conventionally 
manufactured, the fibers are tufted on a relatively pliable primary 
backing which may be manufactured from any suitable materials such as jute 
or a man-made fiber such as polypropylene. The non-wear side of the 
backing is then coated with a bonding material of any suitable type such 
as latex. The latex serves to hold the fibers in place so that they cannot 
be pulled free from the primary backing, and also to bond the primary 
backing to the secondary backing. In the past, clay has been added to the 
latex as a filler to reduce the cost of the bonding compound. The 
secondary backing, which may also be jute or artificial fiber, strengthens 
the carpet and ensures that the bonding material does not come into 
contact with the floor upon which the carpet is laid. 
Accordingly, the preferred process of the present invention may be briefly 
stated as follows: In a process for producing a carpet having a relatively 
pliable primary backing through which polyamide or polyester fibers are 
tufted, the improvement which comprises adding to said carpet from about 1 
to 15 weight percent of a composition comprising 
a. about 10 to about 90 weight percent of a polyvalent metal compound 
selected from the group consisting of oxides and hydroxides of tin and 
antimony, and 
b. about 10 to about 90 weight percent of a hydroxycarboxylic acid selected 
from the group consisting of citric acid, tartaric acid, and gallic acid; 
and curing said composition on the carpet at a temperature of about 
100.degree. to 150.degree. C., whereby said carpet has improved flame 
retardancy and said flame retardancy has improved durability to carpet 
cleaning procedures. 
It will be understood that the above-described flame-retardant carpet is 
normally given a secondary backing, e.g., it may be given a secondary 
backing of jute using a latex binder. A conventional latex may be used, 
e.g., a styrene-butadiene latex, which is commercially available. A latex 
binder containing no flame retardant is normally adequate. However, if 
desired, a flame retardant may be incorporated in the latex material, 
e.g., the bonding substance may comprise a latex material and a hydrate 
material selected from the group consisting of aluminum hydroxide, 
hydrated aluminum oxide and hydrated aluminum silicates, such as 
kaolinite, dickite, nacrite and endellite, the ratio by weight of said 
latex material to said hydrate material being from 1:2 to 1:4.5. 
The primary carpet backing is made from any suitable material. It may be a 
conventional woven jute construction. Also, the backing may be made of a 
nonwoven fibrous mass made of cellulosic or noncellulosic material, 
including nylon, polyester, and polyolefin. Other fabric backing 
structures likewise can be used. 
The preferred polyamides which are useful in the improved flame-retardant 
carpets of the present invention include polycaprolactam, the polyamides 
which are derived from the condensation of a dicarboxylic acid with a 
diamine, such as polyhexamethylene adipamide and polyhexamethylene 
sebacamide, and copolymers thereof. The preferred polyesters are the 
linear terephthalate polyesters, i.e., polyesters of a glycol containing 
from 2 to 20 carbon atoms and a dicarboxylic acid component containing at 
least about 75% terephthalic acid. The remainder, if any, of the 
dicarboxylic acid component may be any suitable dicarboxylic acid such as 
sebacic acid, adipic acid, or isophthalic acid. The glycols may contain 
more than two carbon atoms in the chain, e.g., diethylene glycol, butylene 
glycol, or decamethylene glycol. Examples of linear terephthalate 
polyesters which may be employed include poly(ethylene terephthalate) and 
poly(butylene terephthalate). 
In treating the carpet in accordance with the process of this invention, 
from about 1 to 15 weight percent of the treating composition is applied 
to the carpet, as previously described. In practicing the invention, the 
composition is dissolved in a solvent, preferably water, to make a 
solution of about 0.5 to about 12 weight percent and more. The carpet is 
then soaked by the solution, which may contain other additives commonly 
used in finishing baths to improve properties such as penetration. The 
carpet is then squeezed with any suitable apparatus such as pad rollers to 
remove excess solution. The squeezing apparatus, such as the rollers, is 
adjusted to give from about 25 to about 300 weight percent wet pick-up. 
The carpet is then dried and cured in a dryer or oven, preferably at 
temperatures of 100.degree. to 150.degree. C. The solution may be applied 
to the carpet in numerous ways. For example, the carpet may be immersed in 
the solution or the solution may be sprayed upon the carpet or applied to 
the carpet by means of pad rollers. 
In accordance with another preferred procedure, after padding, the wet 
carpet is exposed to steam at atmospheric pressure for several minutes, 
rinsed with water and dried at 100.degree. to 150.degree. C. The steamed 
carpet is superior to unsteamed carpet in appearance and softness of hand.

The following examples serve to illustrate the present invention. Unless 
otherwise indicated, all parts and percentages are by weight. 
EXAMPLE 1 
About 132 grams of gallic acid monohydrate is dissolved in 1,000 grams of 
hot distilled water. The solution is allowed to cool to about 40.degree. 
C., and 87.6 grams of an aqueous dispersion of colloidal antimony oxide is 
added and uniformly distributed in the solution, the weight ratio of 
gallic acid monohydrate to antimony oxide solids being about 5.5:1.0. The 
resulting composition is made up to 3,500 grams with distilled water and 
used to produce a flame-retardant carpet as described in the following 
example. For convenience, this composition may be called Composition A. 
EXAMPLE 2 
In accordance with this invention, Composition A of Example 1 is used to 
produce a flame-retardant carpet having excellent durability to carpet 
cleaning procedures. A typical polyamide carpet may be produced as 
follows: A reactor equipped with a heater and stirrer is charged with a 
mixture of 1,520 parts of e-caprolactam and 80 parts of aminocaproic acid. 
The mixture is then flushed with nitrogen and stirred and heated to 
255.degree. C. over a one-hour period at atmospheric pressure to produce a 
polymerization reaction. The heating and stirring is continued at 
atmospheric pressure under a nitrogen sweep for an additional four hours 
in order to complete the polymerization. Nitrogen is then admitted to the 
reactor and a small pressure is maintained while the polymer is extruded 
from the reactor in the form of a polymer ribbon. The polymer ribbon is 
subsequently cooled, pelletized, washed and then dried. The polymer is a 
white solid having a relative viscosity of about 50 to 60 as determined at 
a concentration of 11 grams of polymer in 100 ml. of 90 percent formic 
acid at 25.degree. C. (ASTM D-789-62T). 
The polymer is melt extruded under pressure of 1,500 psig to a 70-orifice 
spinnerette to produce a fiber having about 3,600 denier. The fiber is 
collected, drawn at about 3.2 times the extruded length and textured with 
a steam jet to produce yarn suitable for use in carpet. The yarn is 
two-plied by twisting two ends together with a 1.5 S twist. The yarn is 
tufted into a level loop 22 ounce/yard.sup.2 carpet is about 8 stitch 
rate. A relatively pliable nonwoven polypropylene fabric is used as the 
primary backing. Tufting is carried out on a conventional tufting machine 
operated to give a pile having a height of 5/32 to 7/32 inch. An untreated 
portion of this carpet is used as a control and a second portion is padded 
with Composition A of Example 1 to give a wet pickup sufficient to deposit 
6.6 percent of the gallic acid monohydrate and 1.2 percent antimony oxide 
solids on the fibers. The treated carpet is dried at 125.degree. C. in an 
air circulating oven until dry, then cured at 125.degree. C. for about 10 
minutes. The treated and untreated carpets are then given a jute secondary 
backing using a conventional latex binder containing no flame retardant. 
For convenience, the treated carpet is called Carpet A and the untreated 
carpet is called Carpet B. The following table compares the carpets with 
respect to flame retardancy (before and after laundering) as measured by 
the above-described flame retardancy test (DOCFF 1-70), together with the 
above-described laundering procedure (AATCC 124-1973). The above shows the 
highest temperature applied to the carpet before the carpet fails to 
extinguish within 90 seconds after the pill has finished burning. 
Measurements were made on the carpet initially and after 1-5 launderings. 
______________________________________ 
Highest Temperature Before Failure, 
.degree.C. 
After After 
Carpet System 
Initial 1 Laundering 
5 Launderings 
______________________________________ 
Carpet A 205 203 206 
Carpet B 141 130 115 
______________________________________ 
These results indicate that the fire retardancy of Carpet A is 
significantly greater than that of Carpet B and that said fire retardancy 
of Carpet A is surprisingly durable to the cleaning procedure. 
EXAMPLE 3 
The procedure of Example 2 is followed except that in place of Composition 
A of Example 1, the carpet is padded with an aqueous solution of gallic 
acid monohydrate in amount sufficient to deposit 6.0 percent of the gallic 
acid monohydrate on the fibers. For convenience, this treated carpet is 
called Carpet C. 
In a similar manner, the procedure of Example 2 is followed except that in 
place of Composition A, the carpet is padded with aqueous colloidal 
antimony oxide in amount sufficient to deposit 1.5 percent antimony oxide 
solids on the fibers. For convenience, this treated carpet is called 
Carpet D. The following table compares Carpets C and D with Carpet A of 
Example 2, using the above-described flame retardancy test, before and 
after laundering. 
______________________________________ 
Highest Temperature Before 
Failure, .degree. C. 
Carpet System 
Initial After 1 Laundering 
______________________________________ 
Carpet A 205 203 
Carpet C 201 153 
Carpet D 155 Not Required 
______________________________________ 
These results indicate that Carpet A of Example 2 is significantly better 
than Carpet C or Carpet D, i.e., colloidal antimony oxide alone provides 
little flame retardancy, whereas gallic acid alone provides good initial 
flame retardancy but this good flame retardancy is not durable to 
laundering. 
EXAMPLE 4 
The procedure of Example 2 is followed except that after padding the carpet 
with Composition A of Example 1, the wet carpet is exposed to steam for 
about 10 minutes, then rinsed with cold water prior to drying. The steamed 
carpet is much superior to unsteamed carpet of Example 2 in appearance and 
softness of hand. The resulting dried carpet is given a secondary backing 
as described in Example 2, then tested using the above-described flame 
retardancy test, before and after laundering. The test shows excellent 
initial flame retardancy which is durable to 10 launderings or more. 
EXAMPLE 5 
The procedure of Example 2 is followed except that the weight of antimony 
oxide deposited on the carpet fibers is changed relative to the weight of 
gallic acid deposited on the fiber. Flame retardancy tests indicate that 
good results are obtained over a broad range of gallic acid to antimony 
oxide ratios; however, optimum results appear evident using about 2-3 
percent gallic acid and about 2.1-3.2 percent antimony oxide on the carpet 
fiber. We particularly prefer to use gallic acid and antimony oxide in 
proportions which are in the weight ratio to form antimony subgallate, 
although we have no evidence that this compound is actually formed in the 
carpet. 
EXAMPLE 6 
The procedure of Example 2 is followed except that instead of using 
Composition A of Example 1, the individual components of Composition A are 
applied sequentially, i.e., one at a time. Flame retardancy is effectively 
imparted to the samples, but durability of said flame retardancy to 
laundering is not as good as Carpet A of Example 2. 
EXAMPLE 7 
The procedure of Example 2 is followed except that in place of Composition 
A of Example 1, the carpet is padded with an aqueous solution of gallic 
acid fully neutralized with stannic hydroxide in amount to deposit the 
equivalent of 6.4 percent gallic acid and 1.6 percent stannic hydroxide on 
the fibers. For convenience, this treated carpet is called Carpet E. The 
following table compares Carpet E with Carpet A of Example 2, using the 
flame retardancy test, before and after laundering. 
______________________________________ 
Highest Temperature Before 
Failure, .degree. C. 
Carpet System 
Initial After 1 Laundering 
______________________________________ 
Carpet A 205 203 
Carpet E 203 193 
______________________________________ 
EXAMPLE 8 
The procedure of Example 2 is followed except that in place of Composition 
A of Example 1, the carpet is padded with an aqueous solution of tartaric 
acid and colloidal antimony oxide in amount sufficient to deposit the 
equivalent of 5 percent tartaric acid and 2 percent antimony oxide on the 
fibers. For convenience, this treated carpet is called Carpet F. The 
following table compares Carpet F with Carpet A of Example 2, using the 
flame retardancy test, before and after laundering. 
______________________________________ 
Highest Temperature Before 
Failure, .degree. C. 
Carpet System 
Initial After 3 Launderings 
______________________________________ 
Carpet A 205 207 
Carpet F 205 182 
______________________________________ 
EXAMPLE 9 
The procedure of Example 2 is followed except that in place of Composition 
A of Example 1, the carpet is padded with an aqueous solution of citric 
acid and colloidal antimony oxide in amount sufficient to deposit the 
equivalent of 5.1 percent citric acid and 2.0 percent antimony oxide on 
the fibers. For convenience, this treated carpet is called Carpet G. The 
following table compares Carpet G with Carpet A of Example 2, using the 
flame retardancy test, before and after laundering. 
______________________________________ 
Highest Temperature Before 
Failure, .degree. C. 
Carpet System 
Initial After 3 Launderings 
______________________________________ 
Carpet A 205 207 
Carpet G 208 184 
______________________________________ 
EXAMPLE 10 
The procedure of Example 2 is followed except that in place of Composition 
A of Example 1, the carpet is padded with an aqueous solution of malic 
acid and colloidal antimony oxide in amount sufficient to deposit the 
equivalent of 5 percent malic acid and 2 percent antimony oxide on the 
fibers. For convenience, this treated carpet is called Carpet H. The 
following table compares Carpet H with Carpet A of Example 2, using the 
flame retardancy test, before and after laundering. 
______________________________________ 
Highest Temperature Before 
Failure, .degree. C. 
Carpet System 
Initial After 1 Laundering 
______________________________________ 
Carpet A 205 203 
Carpet H 202 167 
______________________________________ 
EXAMPLE 11 
The procedure of Example 2 is followed except that in place of Composition 
A of Example 1, the carpet is padded with an aqueous solution of 
2,4-dihydroxybenzoic acid and colloidal antimony oxide in amount 
sufficient to deposit the equivalent of 5 percent 2,4-dihydroxybenzoic 
acid and 2 percent antimony oxide on the fibers. For convenience, this 
treated carpet is called Carpet I. The following table compares Carpet I 
with Carpet A of Example 2, using the flame retardancy test, before and 
after laundering. 
______________________________________ 
Highest Temperature Before 
Failure, .degree. C. 
Carpet System 
Initial After 1 Laundering 
______________________________________ 
Carpet A 205 203 
Carpet I 195 140 
______________________________________ 
EXAMPLE 12 
The procedure of Example 2 is followed except that in place of Composition 
A of Example 1, the carpet is padded with an aqueous solution of gallic 
acid and aluminum hydroxide in amount sufficient to deposit the equivalent 
of 5.3 percent gallic acid and 1.5 percent aluminum hydroxide on the 
fibers. For convenience, this treated carpet is called Carpet J. The 
following table compares Carpet J with Carpet A of Example 2, using the 
flame retardancy test, before and after laundering. 
______________________________________ 
Highest Temperature Before 
Failure, .degree. C. 
Carpet System 
Initial After 5 Launderings 
______________________________________ 
Carpet A 205 206 
Carpet J 204 180 
______________________________________ 
EXAMPLE 13 
The procedure of Example 2 is followed except that in place of Composition 
A of Example 1, the carpet is padded with an aqueous solution of gallic 
acid and zinc oxide in amount sufficient to deposit the equivalent of 5 
percent tartaric acid and 2.5 percent zinc oxide on the fibers. For 
convenience, this treated carpet is called Carpet K. The following table 
compares Carpet K with Carpet A of Example 2, using the flame retardancy 
test, before and after laundering. 
______________________________________ 
Highest Temperature Before 
Failure, .degree. C. 
Carpet System 
Initial After 1 Laundering 
______________________________________ 
Carpet A 205 207 
Carpet K 206 131 
______________________________________ 
The particular polyvalent metal compound and hydroxycarboxylic acid 
selected are very critical, particularly with respect to durability of the 
improved flame retardancy to carpet cleaning procedures. Excellent results 
are obtained with use of antimony oxide, stannic hydroxide, or aluminum 
hydroxide with gallic acid, citric acid or tartaric acid; however, optimum 
results are obtained with use of antimony oxide with gallic acid. 
Additional tests involving use of aqueous solutions of monovalent salts of 
various hydroxycarboxylic acids, e.g., lithium tartrate, ammonium malate 
and lithium citrate, in production of flame retardant carpet, show 
significantly poorer flame retardancy results as compared with results 
obtained using the process of the present invention. Specifically, using 
the monovalent salts, the highest temperature before failure in the 
above-described flame retardancy test is generally no higher than about 
160.degree. C. and this flame retardancy is not durable to the 
above-described laundering procedure.