60/245,966 entitled POLYURETHANE COATING PROCESS FOR CARPET filed on November 3,2000, the entire specification of which is incorporated herein by reference.

FIELD OF THE INVENTION [0001] The present invention relates to improved methods for adhering secondary backing to tufted or woven carpeting employing polyurethane adhesive systems.

BACKGROUND OF THE INVENTION [0002] It is customary in the carpet and rug industry to use various forms of filled and unfilled latex or polyurethane to coat the back of carpet. The coating is used to bond the face fibers to the primary backing and also thereby creating good tuft bind or fiber lock, to bond secondary backing material to the greige (fibers/primary backing). For example, carpets having attached polyurethane layers as backing are described in U. S. Pat. Nos. 3,755, 212 ; 3,821, 130 ; 3,862, 879 ; 4,022, 941 ; 4,515, 646 ; 5,604, 267 ; 5,908, 701 ; and 6,299, 715. A key property of the carpet produced by these methods is annealing strength, the force required to separate the secondary backing from the carpet.

In order to achieve optimal annealing strength, the secondary backing must be in direct contact with the greige, and a sufficient amount of adhesive must be between the greige and the secondary backing to thoroughly wet the fibers. Another key property is, the fiber lock, which measures the force necessary to pull face fibers from the carpet.

[0003] The most widely used annealing adhesive is latex. Latex is typically applied by methods involving roll over flatbed or roll over roll processes. Regardless, of the method used, the greige is coated with an adhesive precoat of latex, and the secondary backing, also coated with latex, is married to the greige and cured.

[0004] Although, latex is a popular adhesive, carpet prepared from latex displays numerous shortcomings. For example, the strength and hydrolytic stability of latex is less than desired, and latex is less durable over time than alternative polymer systems such as PVC plastisol or polyurethane. Moreover, latex curing requires the evaporation of large amounts of water during cure, a process that is both expensive and energy intensive. To minimize the cost of latex adhesives, substantial quantities of filler material are added. The use of latex filler hinders the effective recycling of manufacturing remnants and used carpet at the end of its life cycle. Alternatively, polyurethane adhesives have been employed to form carpet with superior annealing strength and other desirable physical properties. However, despite the advantages of polyurethane, technical problems have kept it from widespread use in the industry.

[0005] Attempts to replace latex with polyurethane have resulted in a variety of new problems, requiring modifications to the usual latex annualing process. One striking example is the difficulty associated with placing polyurethane onto a greige material, while maintaining the necessary adhesiveness to attach the second backing. After the pre-polymers have been mixed and polymerization begins polyurethane soon begins to lose its adhesive properties.

[0006] Loss of adhesiveness is generally not a problem with the use of latex. Conventional latex maintains its adhesiveness and viscosity during processing, even into the curing oven. Following application of latex adhesive to both the greige and the secondary backing the two components are married and good temporary adherence of the secondary backing to the greige is observed. In the curing oven, the viscosity of latex does not drop significantly as water is evaporated.

Thus, the secondary backing satisfactorily adheres to the greige, and little dripping of latex from the bottom of the carpet to the oven is observed.

[0007] On the other hand, polyurethane application from bulk troughs, common in latex systems, is made very difficult due to premature polymerization in the delivery line. Typically, polyurethane is applied as"froth,"having been mixed with air and polymerization initiated prior to application onto the primary or secondary backing before the upstream edge of a doctor blade. However, unless the manufacturer guards against premature polymerization the delivery line becomes clogged retarding the flow of polyurethane to the dispensing apparatus. In addition polyurethane begins to lose its adhesiveness soon after polymerization begins unless the manufacturer controls the polymerization rate by using heat sensitive catalysts or other chemical agents designed to maintain the viscosity of the polyurethane. Regardless of the manufacturer's attempts at controlling premature polymerization the manufacturer has only a finite amount of time after the pre-polymers (polyol and isocyanate) have been mixed in which to apply the polyurethane and contact the greige to the backing before the polymer begins to lose its adhesive properties.

[0008] In an attempt to combat the rapid loss of adhesiveness manufacturers have applied one coating of polyurethane to the greige as fiber lock and a second coating of polyurethane just prior to contacting the secondary backing to insure sufficient adhesion between the backings. Even with the additional polyurethane, the slow advancement of most commercial carpet lines, and the inherent lack of adhesiveness associated with polyurethane, does not allow for the desired adherence between the greige and the secondary backing.

[0009] Curing the backing to the greige is also complicated because of the considerable decrease in viscosity of the polyurethane prior to cure. The viscosity of the polyurethane, and likewise its adhesiveness, may decrease to only 10% of its initial value prior to application as the catalyzed polyurethane-forming reaction begins to exert its effect. The greatest decrease in viscosity is often exhibited over the temperature range of ambient to 70°C., where the polyurethane catalysts are not optimally active. As a result, if the initial adherence of the secondary backing to the greige is insufficient the secondary backing may separate during this period of low viscosity.

[0010] In an attempt to address the problems associated with the use of polyurethane several changes to the underlying process have been disclosed. For example, U. S.

Pat. No. 6,264, 775 offers the addition of various chemical thickening agents to the polyurethane to maintain viscosity and adhesiveness. Another process provides for the use of multiple applications of polyurethane to the primary backing prior to joining the secondary backing. See e. g. , U. S. Pat.

No. 6,299, 715. Still another technique disclosed in U. S. Pat.

No. 6,299, 715, is the application of both polyurethane to the primary backing and another tacky composition to the secondary backing prior to joining the two backings. None of these techniques have been favored over standard latex based carpet laminates, primarily due to the increased cost and complexity associated with building and using separate manufacturing lines to implement the new technologies.

[0011] It would therefore be desirable to provide a polyurethane carpet annealing process requiring only a single application of the polyurethane, while providing acceptable fiber lock and annealing strength. It would also be desirable to provide a polyurethane annealing system which does not require excessive quantities of polyurethane to provide sufficient annealing strength. It would be beneficial to provide a polyurethane annealing system which does not require an oven for curing.

SUMMARY OF INVENTION [0012] The present invention pertains to a polyurethane carpet annealing system which discloses two unique advantages over the prior art. First it requires only a single application of polyurethane. The lower amount of polyurethane employed in a single application significantly decreases the weight of the carpet and decreases raw material costs. At low weights of polyurethane, costs remain comparable to the cost of latex adhesives. Second, the polyurethane is blown and cured at ambient temperature. The absence of an oven-curing step markedly decreases the time from application of the polyurethane to product roll-up. The carpet produced by the process exhibits acceptable fiber lock and initial secondary backing adhesion without the use of large quantities of polyurethane and without the expensive heat curing step common in other annealing systems. In combination, the two advantages significantly increase the commercial utility of the product.

BRIEF DESCRIPTION OF DRAWINGS [0013] Figure 1 illustrates a typical prior art latex- based carpet annealing process.

[0014] Figure 2 illustrates a prior art single application polyurethane-based carpet annealing process.

[0015] Figure 3 illustrates a prior art dual application polyurethane-based carpet annealing process.

[0016] Figure 4 illustrates a prior art polyurethane- based process that coats primary backing with polyurethane and the secondary backing with a skip-coat adhesive.

[0017] Figure 5 illustrates one embodiment of the present invention.

[0018] Figure 6 illustrates a second embodiment of the present invention.

[0019] Figure 7 illustrates a third embodiment of the present invention.

[0020] Figure 8 illustrates a fourth embodiment of the present invention.

[0021] Figure 9 illustrates a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION [0022] The present invention is designed to improve the annealing of secondary backing to tufted or woven carpeting utilizing a polyurethane adhesive system. Referring now to the drawings in more detail, Figure 1 illustrates a typical prior art commercial latex-based carpet annealing process. The greige 5, with top carpet face 10 and bottom primary backing side 15 to which fiber lock adhesive is applied, is directed by rollers 20 to place the primary backing side 15 of the greige under trough 25, which is supplied with latex through line 30. The downstream edge of trough 25 serves as a doctor blade 35, in conjunction with plate 40. Adjusting the amount of latex applied also serves to force the latex through the primary backing 15 into the fibers. Further penetration is provided by pressure roller 45.

The carpet is then redirected by roller 50. Secondary backing 55 is supplied from roll 60 and directed by rollers 65 across wheel-roll 70, which rotates in trough 75 filled with additional latex which coats the secondary backing 55. The coated secondary backing 77 is pressed onto the latex-coated greige 80 by their travel through ligation rolls 85. The carpet then passes through oven 90 where water is removed from the latex, and the latex cures, adhering fibers and secondary backing to form a lamellar carpet.

[0023] Figure 2 illustrates a single application polyurethane-based carpet annealing process. The greige 5 with carpet face 10 downward is fed onto a metering plate 95.

Here polyurethane"froth"100 is placed on the backing side 15 using a mixing head 105. The polyurethane froth contains isocyanate, polyol, and usually one or more catalysts, fillers, or even chemical retardants to slow polymerization, but no water. After the polyurethane 100 is applied, its thickness may be adjusted by doctor blade 35, or alternatively a roller or air knife, and metering plate 95. A secondary backing 55 is then applied to the surface of the uncured polyurethane 100 using a ligation roller 85. The coated and backed greige 78 is then passed through oven 90 to cure the polyurethane layer 100. After the carpet has been cured, it may then be advanced through a trimmer 115 and finally to an accumulator or roll-up area 128. The polyurethane backing of Figure 2 is not blown, and therefore the only volumization of the polyurethane layer is due to the air introduced in frothing one or more ingredients.

[0024] Figure 3 illustrates a dual application polyurethane-based carpet annealing process. To the primary backing side 15 of the greige 5, frothed polyurethane 100 is applied from first line 30. Doctor blade 35, in cooperation with plate 40, limits the applied weight of polyurethane 100 and forces it into the greige 5. Following the first line 30 is second line 32, which supplies additional frothed polyurethane 100. Doctor blade 36, in conjunction with plate 41, adjusts the thickness of the deposited polyurethane 100.

While the first doctor blade 35 substantially contacts the primary backing 15, the second doctor blade 36 is spaced a distance away to allow enough polyurethane 100 to be deposited to temporarily bind the secondary backing 55 before curing.

The secondary backing 55, supplied from roll 60, contacts the coated greige 80 below ligation roller 85. Prior to entry into the oven 90 for curing, press rollers 125 assist in maintaining stable contact between the secondary backing 55 and the greige 5. Again, the polyurethane backing of Figure 3 is not blown, as no water or other blowing agents are included in the frothed polyurethane.

[0025] Figure 4 illustrates a polyurethane-based process that coats the primary backing with polyurethane and the secondary backing with a polyurethane adhesive. Following application of the frothed polyurethane 100 from line 30 and its impregnation onto and into the primary backing side 15 of the greige 5 between doctor blade 35 and plate 40, the carpet is contacted with a wheel-coated secondary backing 55. The secondary backing 55, supplied from roll 60, has been directed by rollers 65 past wheel roll 130 which rotates in trough 135 filled with wheel coating agent. Rotation of wheel roll 130 in the trough 135 coats the roll with wheel coating agent which is then transferred to the secondary backing 55 to form a wheel-coated secondary backing 140. Wheel roll 130, supplies a tacky polyurethane based coating agent which is not "self-curing"and therefore does not substantially increase in viscosity over the life of the composition in the trough 135.

Wheel-coated secondary backing 140 mates with the polyurethane adhesive coated greige below roller 85, which may be supplemented with a roller directly below, or a plate, to form a pair of ligation rollers or equivalent devices. The carpet then passes between press rollers 125 into oven 90 for curing.

[0026] It will be understood that in Figure 4 and most prior art polyurethane backings, water is not added to the froth and the resulting polyurethane backing is not"blown," the only volume in the backing layer having been injected in the form of air in the froth. The reaction of water with the isocyanate prepolymer releases carbon dioxide gas which "blows"the polyurethane, resulting in a polyurethane foam material.

[0027] Figure 5 illustrates the carpet manufacturing process according to the present invention. The greige 5 with carpet face 10 downward is fed onto a tenter roll 12 that directs the greige 5 to metering plate 95, the carpet face 10 is advanced over the metering plate 95 using pulling rollers 21.

[0028] In Figure 5, a layer 100 of polyurethane polymer is deposited onto the primary backing side 15 as it passes over metering plate 95 using a mixing head 105.

Preferably, the polyurethane is applied to the primary backing 15 at an area concentration of about 1.0 oz/yd2 (33.9 g/m2) to about 30 oz/yd2 (1017.2 g/m2) or in a more preferred concentration of about 5.0 oz/yd (168. 5 g/m2) to about 12 oz/yd2 (406. 9 g/m2). In an even more preferred embodiment of the present invention, the polyol and isocyanate pre-polymer components are mechanically blown through a mixing head 105 and sprayed on the primary backing 15 to form the polyurethane layer 100.

[0029] This prevents the pre-polymers from contact until just prior to application to the primary backing 15.

Some water and catalysts are also added which facilitates the polymerization reaction and the water serves as a blowing agent to create a polyurethane foam. According to this method, the polymerization process does not begin to occur until just prior to the exit of the polyurethane components from the mixing head 105. This process allows the relatively low viscosity polyurethane to deeply penetrate the fibers in the primary backing, resulting in excellent fiber lock characteristics. A preferred method of blowing the polyurethane layer is by feeding separate lines of polyol and isocyanate components and a stream of air into a Gusmer Corporation spray attachment (model GX7-400). If the need arises a third line is available for the introduction of catalyst, or catalyst and water mix. The spray attachment combined with the air stream provides sufficient turbulence to provide a homogenous solution of the urethane-forming components. The concentration of water will vary depending upon the use of a steam box, but generally will be added in the range of 0.5 to 5 parts per 100 parts of polyol. Water concentrations may be reduced to even about 0.1 parts per 100 parts of polyol in some cases.

[0030] After the polyurethane components are applied polymerization accelerates and foaming begins. The thickness of the polyurethane foam may be adjusted by various means known in the art such as a doctor blade 35 or air knife. The polyurethane coated greige is then optionally passed across a vacuum (not shown) and a steam box 150. If necessary, the vacuum helps ensure adequate penetration of the polyurethane into the primary backing. Steam box 150 adds more water to the reaction, to aid in accelerating the polymerization rate.

In addition the steam serves to enhance blooming of the yarns passing through the primary backing for deeper penetration and assures a more level coverage of polyurethane. A fume hood 155 is placed above the steam box 150 to capture escaping volatiles released with the steam. Conspicuously absent at this stage of the process is an oven curing step. An oven is not necessary in the process because the polyurethane components are essentially kept separate until they are applied to the primary backing 15, therefore there is no need to dope the polyurethane components in order to control the rate of polymerization. In a preferred embodiment of the present process temperatures are generally maintained within 30°F of ambient temperature except directly adjacent to the steam box. In contrast, prior art polyurethane curing processes are required to utilize heat sensitive catalysts and other chemical additives to maintain sufficient viscosities to apply the polyurethane, from various holding lines and troughs, to the backing surface. These additives, and the absence of water, necessitate a heat curing stage.

[0031] After applying the polyurethane coating, and steaming the coated greige, the coated greige is rapidly pulled to merge roll 160 where the secondary backing 55, supplied from roll 60, contacts the coated greige 79 downstream from roller 87. Due to the short time that elapses between the initial application of polyurethane and the merger of the secondary backing 55 with the coated greige, the polyurethane possesses sufficient tackiness to anneal the secondary backing in place.

[0032] The independence gained by controlling the mixing of polyol and isocyanate has lead to the removal of a curing station. The excision of this step has dramatically improved the processing speed of laminated carpets, cutting manufacturing time by as much as 50-60% without sacrificing the annealing strength or fiber lock properties of the carpet.

The annealed carpet can then be cooled briefly 190 and rolled for storage and transport.

[0033] Figure 6 illustrates an alternative carpet manufacturing process according to the present invention. The greige 5 with carpet face 10 downward is fed to metering plate 95. Polyurethane (with polyol, isocyanate, catalysts and water) is dispersed from mixing head 106 onto the primary backing side 15. The mixing head may be either a spray attachment as in Figure 5 or a regular polyurethane froth line as in Figures 2-4. A doctor blade 35 or air knife insures that the sprayed polyurethane or polyurethane froth is not excessively puddled and the resulting primary backing has a relatively even layer of polyurethane 100. The carpet may at this point be fed over a vacuum 52 in order to pull the viscous polyurethane deeper into the primary carpet backing.

Then the carpet continues across steam box 150 and fume hood 155 which adds water to the reaction and aids in accelerating the polymerization rate. The heat from the steam box also accelerates polymerization and provides the additional benefit of enhancing blooming of the face yarns on the carpet. Again, oven curing is not necessary. Then a backing roll 60 feeds secondary backing 55 downward to merge roller 160 where the secondary backing is applied to the still curing and tacky polyurethane film layer 100. In the event the polyurethane film has cured sufficiently to lose much of its tackiness, the secondary backing 55 may require coating to enhance its adherence to the product. As in Figure 5, the polyurethane polymer layer 100 is preferably applied to the primary backing 15 at an area concentration of about 1.0 oz/yd2 (33.9 g/m2) to about 30 oz/yd2 (1017.2 g/m2) or in a more preferred concentration of about 5.0 oz/yd2 (168. 5 g/m2) to about 12 oz/yd2 (406. 9 g/m2). In an even more preferred embodiment of the invention, the polyol and the isocyanate prepolymer components are mechanically blown through the mixing head 106 with water and other additives in a fashion that prevents the prepolymers from contact until immediately prior to application of the primary backing. The mixing head may have up to about five separate inputs, so that polyol, isocyanate, catalysts, water and air may be separated metered. Often water and the catalysts are combined, and either or both of water and catalysts are sometimes combined with polyol. In addition, in order to further retard the polymerization process until the polyurethane components reach the primary backing, refrigeration of the prepolymers may be employed in the process of Figure 6 or subsequent Figures 7-9.

[0034] The action of the merge roller 160 after the secondary backing is applied tends to crush the now blown polyurethane layer 100. Crushing, by rupturing many of the still closed cells created by carbon dioxide within the film effectively stops the expansion of the polyurethane backing and permits curing to continue without substantially increasing the volume of the polyurethane layer 100. The polyurethane backed carpet is then fed through accumulator rolls 120 as curing is completed and is finally wound on a take-up roll 61 in a finished state.

[0035] Figure 7 is an illustration substantially of the polyurethane film backing line of Figure 6, however in this configuration, the secondary backing 55 is applied at a much earlier stage in the process. In fact, immediately after the polyurethane layer 100 is deposited on the backing side 15 of the greige as it passes over metering blade 95, the secondary backing 55 is applied, preferably by transition around a doctor bar 35 which causes the secondary backing 55 to come into contact with the polyurethane layer 100 as the reaction of the prepolymers and water is just beginning.

Advancing the secondary backing 55 around the doctor bar 35 provides the additional benefit of keeping the doctor bar 35 clear from any accumulations of polyurethane. The polyurethane polymer layer 100 begins its reaction between the primary backing side 15 and the secondary backing 55 and the use of steam box 150 and fume hood 155 accelerates this process and provides additional water to the reaction. Again passing under merge roller 160 crushes the backing and effectively halts the foaming process so that the polyurethane layer does not gain additional height. The curing process is completed as the carpet passes through accumulator 120 and is finally wound on a master carpet roll 61.

[0036] Figure 8 illustrates another variation of the present invention in which the polyol, catalyst, and water is mixed and applied in a puddle or froth by line 102 onto the primary backing side 15 of the greige 5 over metering plate 95. Doctor bar 35 or air knife or other suitable means are utilized to insure even and controlled amounts of polyol, water and catalyst. As the greige proceeds through the line, one or more spray heads 105, or lines, dispense the isocyanate prepolymer component onto the prepolymer layer of polyol and catalyst. This combination permits the initiation of the polymerization process and the use of steam box 150 and fume hood 155 provides additional water to optimize blowing and foaming and accelerates the polymerization process. Secondary backing 55 is then applied and merging roll 160 crushes the polyurethane layer, both ensuring a complete adherence of the secondary backing to the polyurethane layer and stopping increased volumization of the polyurethane layer. The backed carpet then passes through accumulator 120 to complete its curing and is then wound on to a master roll 61. It will be understood that a vacuum may be added to the configuration of Figure 8 either after the metering plate 95 or after the spray head 105 when needed to help insure that the polyurethane polymer is drawn sufficiently into the primary backing.

[0037] Yet another variation of the present invention involves passing the primary backing side 15 of the greige 5 over a froth pan 111 containing polyol, water and catalysts, the mixture being denominated 112 in Figure 9. Wetting roller 113 carries a film of polyol, water and catalysts mixture 112 to the primary backing side 15 of greige 5 and doctor bar 35 facilitates even application. Once the primary backing side 15 is again upward facing, spray head 105, or a line dispenser, dispenses isocyanate so that polymerization may begin. Passing the layer of polyurethane polymer over steam box 150 and fume head 155 provides more water for the reaction and heat to acceleration the polymerization. Again the secondary backing 55 is applied and merge roller 160 crushes the foam back ensuring contact between the secondary backing and the polyurethane layer and halting the increased volumization of the polyurethane layer. The carpet completes its curing as it passes through accumulator 120 and wound onto the master roll 61. A vacuum may be added between froth pan 111 and steam box 150 if needed.

[0038] In all of the foregoing embodiments, the Figures have been simplified for clarity and to ease viewing and understanding. In commercial embodiments, additional devices, e. g. drive motors, tension devices, etc. will be required.

[0039] Polyurethane prepolymers useful in the practice of the present invention are prepared by the reaction of active hydrogen compounds with any amount of isocyanate in a stoichiometric excess relative to active hydrogen material.

[0040] The prepolymer formulations of the present invention include a polyol component. Active hydrogen containing compounds most commonly used in polyurethane production are those compounds having at least two hydroxyl groups or amine groups. However, any active hydrogen containing compound can be used with the present invention, and indeed some soy based oils can be used.

[0041] In the practice of the present invention, preferably at least 50 weight percent of the active hydrogen compounds used to prepare the polyurethane is a polyol having molecular weight of from about 100-400.

[0042] The polyisocyanate component of the formulations of the present invention can be prepared using any organic polyisocyanates, modified polyisocyanates, isocyanate based prepolymers and mixtures thereof. These can include aliphatic or aromatic isocyanates. Preferably the isocyanate used to prepare the prepolymer formulation of the present invention is methyl diisocyanates such as Bayer's 142L or Dow p901 or blends of equal type.

[0043] Catalysts suitable for use in preparing the polyurethane of the present invention include tertiary amines, and organometallic compounds and mixtures thereof. For example, suitable catalysts include stannous octoate, triethylenediamine, N-methyl morpholine, like compounds and mixtures thereof. The catalysts do not necessarily need elevated activation temperatures or other promoters to initiate polymerization.

[0044] Surfactants can be useful for preparing a stable dispersion of the present invention, and especially to ensure even distribution of catalysts and filler materials.

Surfactants useful for preparing a stable dispersion can be cationic, anionic, or non-ionic surfactants. Preferably the surfactants used to prepare the prepolymer formulation of the present invention are silicone surfactants such as Dow Corning DC-194 or Union Carbide's L-540. A surfactant can be included in a formulation of the present invention in an amount ranging from about 0.01 to about 7 parts per 100 parts by weight of polyurethane component.

[0045] A compound of the present invention optionally includes a filler material. The filler material can include conventional fillers such as milled glass, calcium carbonate, aluminum trihydrate, barium sulfate, dyes and pigments or fire retardants (aluminum trihydrate and Tris polyolefin glycol).

Preferably the filler can be present in an amount ranging from 0 to 300 parts per 100 parts of the polyurethane component.

[0046] Generally, any method known to one skilled in the art of preparing polyurethane froths can be used in the practice of the present invention to prepare a polyurethane froth suitable for preparing a carpet of the present invention, however, typically only one of the prepolymer mixtures is frothed, since the use of water as a blowing agent adds ample volume to the polyurethane.

[0047] Although preferred embodiments of the present invention have been disclosed herein, it will be understood that various substitutions and modifications may be made to the disclosed embodiment described herein without departing from the scope and spirit of the present invention as recited in the appended claims.