Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-07-14
2001-10-09
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S331400, C156S331700, C428S097000
Reexamination Certificate
active
06299715
ABSTRACT:
TECHNOLOGICAL FIELD
The present invention pertains to carpet manufacture. More particularly, the present invention pertains to improved methods for adhering secondary backing to tufted carpeting employing polyurethane adhesive systems.
DESCRIPTION OF THE RELATED ART
Laminated carpets are produced by tufting carpet yarns into a primary backing, which is then coated with adhesive and secured to a secondary backing, generally of polypropylene or jute. A key property of the laminate produced by this process is delamination strength, the force required to separate the secondary backing from the carpet. In order to achieve suitable delamination strength, the secondary backing must be in intimate contact with the tufted yarn/primary backing (“greige good”) during the curing process, and a sufficient amount of adhesive which ensures complete wet out of the tufted fibers and secondary backing must be used. In addition to delamination strength, the tuft bind, which measures the force necessary to pull the tufted yarn from the carpet, is also important.
In the past, SBR latex has been almost exclusively used as the laminating adhesive. The latex may be applied by numerous methods, such as the indirect applicator (pan application) which is now used infrequently, and “direct” methods, these involving roll over flatbed or roll over roll processes, either as a single unitary process, or in series as a tandem process. Regardless of the actual method used, the reverse of the greige good is coated with a precoat of adhesive, and the secondary backing, also coated with adhesive, is married to the greige good, and cured.
While SBR latex has been the adhesive of choice, carpet prepared from SBR latex also exhibits numerous deficiencies. For example, the tensile strength and hydrolytic stability of SBR latexes is less than desired, and SBR polymers are less durable than desired. Greige goods in which SBR latexes are used as tuft bind adhesives also are subject to “rewicking”. Moreover, use of SBR latexes requires the evaporation of large quantities of water during cure, a process which is energy intensive. Polyurethane adhesives are capable of forming a laminate with superior delamination strength as well as other desirable physical properties. However, technical problems have prevented widespread use of polyurethanes despite the increased performance potential.
Substitution of reactive polyurethane systems for latex laminating adhesives has not been straight forward, and has required numerous process modifications. For example, conventional latex maintains its tackiness and viscosity during processing, even in the curing oven. Following application of latex adhesive, the back-side of the greige goods is faced downward. A coat of additional latex is applied to the secondary backing by a skip roll. As a result of the latex properties, good temporary adherence of the secondary backing to the greige goods is obtained. In the curing oven, the latex viscosity does not drop significantly as water evaporates. Thus, the secondary backing satisfactorily adheres to the greige goods, and little dripping of latex from the bottom of the laminate into the oven is observed.
With polyurethanes, however, the single adhesive application common with latex has not been found operable. Due to its limited pot life, polyurethane adhesive cannot be applied from troughs which are common with latex systems, but rather must be applied from a “puddle” which accumulates before the upstream edge of the doctor blade. Polyurethane froth adhesives are also not as inherently tacky as SBR latex. Following application of polyurethane adhesive to the greige good and the working of the adhesive into the tufts by means of a closely spaced doctor bar or similar device, a considerable additional amount of polyurethane must be applied from a second puddle in order to provide enough adhesive to temporarily adhere the secondary backing. Even with this additional adhesive, the slow advancement of the adhesive and its low level of tack does not allow for the desired adherence between the greige goods and secondary backing.
In the curing oven, polyurethanes generally exhibit a considerable initial decrease in viscosity prior to cure. As a result, unless the carpet laminating line is run with the greige goods reverse side uppermost, considerable loss of polyurethane into the curing oven would occur. Moreover, if sufficient initial adherence of secondary backing to the greige good has not been obtained, separation of the secondary backing may occur during this period of low viscosity.
Increasing the viscosity of the polyurethane adhesive would assist in ameliorating some of the foregoing problems. However, the increased viscosity will detract from the ability of the adhesive to be forced into the tufts and to wet out the fibers. Tuft bind will thereby be compromised. Catalyzing the cure of the adhesive would enable viscosity to increase. However, some portion of the now-curing polyurethane will begin to gel and cure on the doctor blade and in portions of the puddle. These cured and partially cured portions of polyurethane will have to be removed, generally while the line is operating, a procedure which is not desirable from a safety standpoint. In current polyurethane carpet laminating adhesive processes, therefore, heat activated (latent) catalysts are used. Even with these catalysts, some system advancement which requires removal of cured polyurethane from the puddle occurs. Due to the inability to increase viscosity, delayed cure systems again lack sufficient tack to firmly adhere the secondary backing, requiring a second adhesive puddle.
For the same reasons that actively catalyzed polyurethanes cannot be used in the polyurethane adhesive puddles, skip coats of catalyzed polyurethane have not been practiced as well. Advancement of the reacting polyurethane in a skip coat trough would not only alter the applied skip coat weight over time, but moreover, the polyurethane in the trough would eventually set up, halting the process.
Commercial polyurethane laminating systems have thus far employed two puddle systems. In some such systems, two puddles are employed prior to cure. In one commercial system, two puddles are used with the first puddle used exclusively as a tuft bind adhesive which is oven cured, the second puddle then supplying a secondary backing adhesive which is also cured. None of these systems have met with overwhelming commercial success, and the majority of carpet laminates continue to be latex based.
It would be desirable to provide a polyurethane carpet laminating process which requires but a single puddle, yet which allows for acceptable tuft bind as well as satisfactory delamination strength. It would be further desirable to provide a polyurethane laminating system which does not require excessive amounts of polyurethane to provide sufficient delamination strength. It would be yet further desirable to provide a polyurethane laminating system which does not require a second oven for curing.
SUMMARY OF THE INVENTION
The present invention pertains to a polyurethane carpet laminating system which requires the use of but a single polyurethane adhesive puddle. The carpet laminates produced by the subject process exhibit acceptable tuft bind and initial secondary backing adhesion without the use of large amounts of applied polyurethane supplied by a second puddle. The lower amount of polyurethane employed markedly decreases the weight of the carpet and decreases raw material cost at the same time.
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ASTM D-2849-69, Standard Methods of Testing o
Allen Gary L.
Duffy Robert D.
Evangelist Barry V.
Holeschovsky Ulrich B.
Langsdorf Leah J.
Bayer Antwerp N.V.
Brooks & Kushman P.C.
Yao Sam Chuan
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