Process for carpet manufacture

An improved process is disclosed for manufacturing carpet. The improved process involves replacing from 4% to 25% of a carboxylated styrene-butadiene rubber carpet backing adhesive in a conventional carpet manufacturing process with a water soluble saponified tall oil pitch tackifier, thereby improving the bond strength between the carpet and backing.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates to an improved process for carpet manufacture. More 
particularly, this invention relates to an improved carpet manufacturing 
process employing a carboxylated styrene-butadiene rubber (SBR) adhesive 
whereby the improvement comprises forming a mixture of from 4% to 25% by 
dry weight saponified tall oil pitch and from 96% to 75% by dry weight 
carboxylated SBR to enhance the tack and final bond strength of the rubber 
adhesive. Fillers can also be included in the mixture as well as other 
ingredients. 
(2) Description of the Prior Art 
For many years the production of backsized tufted carpet has been 
accomplished by an aqueous latex method. This method involves preparing a 
tufted structure by stitching a primary backing material with yarn in such 
a manner as to form on the top surface of the material a pile composed of 
numerous closely spaced erect loops of fiber bundles, i.e., tufts of yarn. 
If desired, the loops can be cut. After forming the tufted structure, the 
bottom surface thereof is coated with a latex containing a polymer binder 
such as a styrene-butadiene copolymer and a secondary backing material is 
applied thereto. The structure is then passed through an oven to dry the 
latex. By such a process, the tufts of yarn and secondary backing material 
are bonded to the primary backing material. Also, the individual fiber 
filaments making up a fiber bundle are bonded together at the primary 
backing material. 
The proccess of this invention may employ a latex foam backing in place of 
a secondary backing wherein the raw tufted carpet is pre-coated so that 
the latex is dried by passing through an oven prior to applying the foam 
to the underside, or latex coated side, of the carpet. After applying the 
foam backing, the carpet is passed again through a high temperature zone 
to cure the foam. 
The foam backing may be applied via either the "gelled" or "no-gelled" 
systems. The gelled system includes in the foam formulation a gelling 
agent, such as ammonium acetate which, upon exposure to infrared heat, 
gels the foam for curing. Whereas, the no-gelled system does not contain a 
gelling agent. That system employs a surfactant which promotes excessive 
colloid stability which, in turn, maintains the foam during curing. 
SBR has a relatively low polarity compared to other synthetic rubbers; and 
unlike natural rubber, SBR does not develop surface peroxidal activity 
upon mastication. Therefore, SBR has relatively poor inherent or processed 
tack. An adhesive is said to possess tack if, under the conditions of 
application, only light pressure is required to produce a bond 
sufficiently strong to require work to restore the interface to its 
original separated state. Poor tack in SBR can be overcome by: (1) 
reducing the molecular weight or changing the molecular weight 
distribution, (2) decreasing the viscosity with plasticizer or surface 
treating with solvent, or (3) adding tackifiers, such as resins or natural 
rubber. 
It has been known for several years that incorporation of a very small 
percent of an unsaturated fatty acid monomer with styrene or styrene and 
butadiene improves the adhesive properties of the resulting polymer (i.e., 
Netherlands Application 6,411,493, Apr. 15, 1965--acrylic acid and fumaric 
acid and German Offenlegungschrift No. 2,437,365, Feb. 13, 
1975--itaconic). Also, methacrylic and crotonic acids are suited to this 
purpose. In addition to improving adhesion, carboxylation provides 
reaction sites for cross-linking with curing agents to improve water 
resistance and improves processing properties. Thus, carboxylated 
polystyrene or styrene-butadiene rubber latex has been the backbone of 
many water-based adhesives for some time. Just as natural rubber is added 
to SBR to improve its tack (German Offenlegungschrift No. 2,005,244, Aug. 
6, 1970), addition of natural rubber latex to the carboxylated latex 
increases the wet grab (green tack) of the adhesive system. 
In the process described above, the tufted carpet industry depends on 
highly filled carboxylated styrene-butadiene rubber latex to 
simultaneously bond the carpet tufts to the primary backing through which 
they are punched and adhere a secondary backing or a foam backing to the 
bottom of the carpet. Due to the high cost of natural rubber latex, the 
natural latex gradually has been removed from this adhesive system. A 
typical composition is as follows: 
______________________________________ 
Parts Dry Weight 
______________________________________ 
Carboxylated SBR (45% to 60% styrene) 
100 
Filler 400 
Antioxidant 1-2 
Thickener 0.5 
Water to adjust final solids 
______________________________________ 
Adhesive solids are normally in the range of 70% to 85%. The filler portion 
of the formulation may contain more than one type. Whiting (calcium 
carbonate) is the most common filler. Certain systems contain alumina 
trihydrate (ATH) to meet the fire retardant standard. 
With the carboxylated SBR latex alone, unaided by the natural latex, wet 
grab to the secondary backing is borderline. If the secondary backing 
separates from the carpet at any stage of drying, the final bond will 
never be as strong as if a coherent system were retained throughout the 
drying cycle. For this reason, the carpet industry, in particular, is 
interested in more economic methods of increasing the green tack of the 
carboxylated SBR adhesive, thereby enhancing the final bond of carpet to 
backing. 
Therefore, it is an object of this invention to provide an improved carpet 
manufacturing process employing a carboxylated styrene-butadiene rubber 
adhesive wherein the improvement comprises replacing 4% to 25% of the 
rubber with saponified tall oil pitch to improve the bond of the carpet 
and primary and secondary backing materials. Another object of this 
invention is to provide an improved carpet manufacturing process wherein 
the green tack of the carboxylated styrene-butadiene rubber adhesive is 
improved. Still another object of this invention is to provide an improved 
process for carpet manufacture wherein the improvement comprises replacing 
4% to 25% of carboxylated SBR with saponified tall oil pitch to increase 
the volume of the adhesive over the volume produced with carboxylated SBR 
alone, due to enhanced ability of the adhesive to incorporate air. The 
advantages obtained are good coverage at lower application weights and 
lower application cost per square yard (as air is used to extend the 
adhesive material). 
SUMMARY OF THE INVENTION 
It has been found that by replacing from 4% to 25% (6% to 9% preferred) of 
carboxylated SBR latex adhesive with a saponified tall oil pitch in a 
carpet manufacturing process, the green tack of the adhesive is improved, 
the bond of the carpet to primary backing material to secondary backing 
material is improved, and the total volume of adhesive is increased, due 
to frothing induced by the saponified pitch. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
The practice of the invention comprises first forming a carpet backing 
adhesive of from 96% to 75% by dry weight of a carboxylated 
styrene-butadiene rubber latex, preferably from 94% to 91%, and from 4% to 
25% by dry weight of a saponified tall oil pitch, preferably from 6% to 
9%. Carboxylated SBR is SBR which contains carboxyl functions introduced 
by incorporation of a suitable monomer, such as acrylic acid, fumaric 
acid, itaconic acid, etc. The carboxylated latex should contain 40% to 60% 
solids, preferably 50% to 55%, and from 45% to 60% styrene, preferably 
50%. Saponified tall oil pitch is the distillation residue from the 
distillation of crude tall oil to extract fatty acids and rosin which 
residue (pitch) has been subjected to saponification. One such 
saponification of tall oil pitch process is described in U.S. Pat. No. 
3,943,117. If necessary, a sufficient amount of water is added to make the 
solids content of the mixture from 70% to 85%, preferably 82%. To this 
mixture may be added up to 600 parts of filler material, per 100 parts dry 
weight of carboxylated SBR plus saponified tall oil pitch. Typical of such 
filler material are calcium carbonate (CaCO.sub.3) and alumina trihydrate 
(ATH) or a combination of the two, wherein the ratio of ATH to CaCO.sub.3 
is from 3:1 to 1:2. The mixture is complete upon adding an amount of a 
polymeric thickener, such as a polyacrylate, sufficient to increase the 
viscosity of the mixture to from 15,000 to 20,000 centipoise. 
The bottom, nonpile surface of a raw tufted carpet, i.e., the underside of 
the primary backing material, is then coated evenly with from 6 to 35 
ounces per square yard, preferably 32 ounces per square yard, of the thus 
formed carpet backing latex adhesive. The primary backing material can be 
either jute or a woven polypropylene material. Next, a secondary backing 
material is applied to the coated backside of the carpet by pressing with 
a roller. The secondary backing material can be either jute or a woven 
polypropylene material. 
Finally, the carpet is passed into a heating section, or oven, at from 
125.degree. C. to 160.degree. C., preferably 135.degree. C., for up to 20 
minutes whereby the primary backing and secondary backing materials are 
firmly bonded to each other and the base of each loop in the pile is 
firmly bonded to the primary backing. 
The practice of the invention is clearly illustrated in the following 
examples.

EXAMPLE 1 
Latex carpet backing adhesives were prepared containing 0, 6, 7, 8, 9, 10, 
12 and 15 percent by dry weight, of saponified tall oil pitch (Westvaco 
CUSTOFAC.RTM. CS) and 100, 94, 93, 92, 91, 90, 88 and 85 percent, 
respectively, by dry weight of a carboxylated SBR latex (Firestone FR-S 
256). The latex and saponified pitch were blended by heating to less than 
50.degree. C. with agitation. Water was added to make up for water loss 
during heating and to adjust the solids content of the final product to 
82%. While stirring, CaCO.sub.3 was gradually added in the amount of 400 
parts dry weight per 100 parts dry weight of the rubber plus saponified 
pitch. The viscosity of the mixture was increased to from greater than 
16,000 to less than 20,000 centipoise in each sample by the dropwise 
addition of a polyacrylate thickener (Rockmart RH 46). Viscosity 
measurements were obtained using a Brookfield RVH Viscometer, spindle #5, 
at 10 RPM. 
Rectangles, fourteen-inches by eight-inches, of both raw tufted carpet (in 
a woven polypropylene primary backing material) and jute were cut for each 
formulation prepared. Approximately 72 grams of the latex adhesive were 
spread on the 14-inch by 6-inch portion of the underside of the carpet (32 
ozs./yd..sup.2). Next, the secondary jute backing was applied against the 
latex adhesive and the sample was rolled with an iron shaft (221/2 inches 
long, 7/8 inch in diameter, and weighing 1,739.4 grams) once across the 
width and once from the center to each side across the length of each 
sample. The sample was then placed in a 135.degree. C. oven to cure. 
Two-inch by eight-inch strips were cut after 3, 5, 7, 9, 11 and 15 minutes 
heating. After removal from the oven and cutting, each strip was tested 
immediately in a Scott Tester, Model No. L5, to measure the strength of 
the bond. The remaining 2-inch by 8-inch strip was removed from the oven 
after 15 minutes, cooled slightly, and saturated with water. The bond of 
the wet sample was also measured with the Scott Tester. The results are 
reported in Table I. 
TABLE I 
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COMISONS OF VARIOUS AMOUNTS OF SAPONIFIED 
TALL OIL PITCH IN LATEX CARPET BACKING 
Average 
Saponified 
Weight Mean Bond Strength 
Tall Oil 
Spread 
Viscosity 
Minutes in Oven 
Pitch (%) 
(g) (cps) 
3 5 7 9 11 15 Wet 
Total 
__________________________________________________________________________ 
0 71.2 18400 
9.3 
11.5 
14.8 
18.4 
11.75 
13.1 
24.1 
14.7 
6 75.4 19720 
9.75 
20.25 
39.2 
20.5 
18.4 
17.9 
43.9 
24.3 
7 73.8 18800 
12.3 
16.25 
22.5 
17.2 
18.5 
14.9 
56.7 
22.6 
8 72.7 17080 
14.3 
14.6 
15.9 
18.1 
15.8 
13.9 
49.0 
20.2 
9 72.7 18880 
12.25 
19.6 
16.9 
19.0 
18.4 
18.7 
57.2 
23.1 
10 69.2 19800 
10.6 
12.7 
11.0 
20.25 
18.2 
11.2 
35.3 
17.0 
12 75.6 18800 
4.6 
8.3 
15.1 
17.6 
11.6 
15.75 
44.3 
16.75 
15 77.1 16160 
1.0 
8.3 
14.0 
12.8 
15.25 
17.75 
55.1 
17.75 
__________________________________________________________________________ 
Addition of saponified tall oil pitch improved both the initial tack and 
final adhesion of the carboxylated SBR latex carpet backing. Table I shows 
mean values obtained for the bond strength between the carpet and the jute 
backing. Every level of replacement by saponified pitch gave bond 
strengths which were higher than with carboxylated SBR alone. Replacement 
of 15% rubber with saponified tall oil pitch continues to give improved 
final bond strength. Replacement of 6% to 10% carboxylated SBR with 
saponified tall oil pitch gives green tack and adhesion values generally 
higher than carboxylated SBR alone. The optimum range is 6% to 9% 
saponified pitch as more of these values are significantly higher. 
Improved adhesion was achieved in every case in the wet sample. 
EXAMPLE 2 
During evaluation of the tackifying properties of saponified tall oil 
pitch, it was noted that upon preparing identical dry weight amounts of 
the control formulation (carboxylated SBR alone) and experimental 
formulations (carboxylated SBR plus amounts of saponified tall oil pitch) 
greater volumes of the experimental formulations were produced upon 
agitation to mix the constituents. To measure this increase in volume, 
apparently due to frothing from enhanced air entrainment, and to evaluate 
the formulation's ability to retain the increase in volume over weight, 
the following samples were prepared: 
______________________________________ 
Control Experimental 
Dry Wt Wet Wt. Dry Wt. Wet Wt. 
(g) (g) (g) (g) 
______________________________________ 
Carboxylated SBR 
100 193.4 92 177.9 
Latex 
Saponified Tall Oil 
-- -- 8 12.7 
Pitch 
CaCO.sub.3 400 400.0 400 400.0 
Distilled Water 
-- 16.4 -- 19.2 
Total Weight 500 609.8 500 609.8 
______________________________________ 
Each sample was blended for 10 minutes and polyacrylate thickener was added 
to each to increase their viscosities to the 15,000 to 20,000 centipoise 
range. The volume to weight ratios were calculated after adjusting the 
viscosities, after standing overnight, after being continuously shaken 
over a second night, and after being continuously shaken over three more 
days. The results are presented in Table II. 
TABLE II 
______________________________________ 
COMISONS OF VOLUME 
TO WEIGHT RATIOS IN LATEX CARPET 
BACKING WITH 0% AND 8% SAPONIFIED 
TALL OIL PITCH 
Control Experimental 
Treatment (ml/g) (ml/g) 
______________________________________ 
Initial Formulation 0.5896 0.6234 
Overnight on Shelf 0.5897 0.6095 
Shaken over 2nd Night 
0.6668 0.7383 
Shaken over 3rd, 4th & 5th Nights 
0.6207 0.8015 
______________________________________ 
From this example, it can be seen that due to the increase in volume for 
the same weight of materials, the addition of saponified tall oil pitch 
not only provides improved green tack and final bond strength, it would 
allow good coverage at lower application weights. With little or no 
filler, as low as 6 ounces per square yard rather than the normal 16 to 24 
ounces per square yard can be effectively employed. With substantial 
filler the adhesive material requirements can be reduced from 25 to 35 
ounces per square yard to about 15 ounces per square yard. 
While the invention has been described and illustrated herein by references 
to various specific materials, procedures and examples, it is understood 
that the invention is not restricted to the particular materials, 
combinations of materials, and procedures selected for that purpose. 
Numerous variations of such details can be employed, as will be 
appreciated by those skilled in the art.