Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1998-12-09
2002-03-19
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S401000, C524S451000, C525S330500
Reexamination Certificate
active
06359076
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a carpet back coating composition which is an aqueous emulsion polymerization product of ethylene, vinyl acetate, and a ethylenically unsaturated hydroxy-functional monomer to form an emulsion copolymer which is combined with a crosslinking agent selected from the group consisting of multifunctional aziridine, multifunctional isocyanate, and multifunctional epoxide. Carpets prepared with the carpet back coating compositions exhibit improved wet strength. The improvement in wet strength is achieved by means of crosslinking reactions which do not generate volatile organic compounds as by-products.
BACKGROUND OF THE INVENTION
An important characteristic of carpet, especially carpet tiles, is the wet strength. Currently, carpets may be routinely exposed to water from steam cleaning processes. In such situations wet strength of the carpet is important since inadequate wet strength can cause fraying of the carpet edges, and shrinking or curling of carpet tiles. Such surface changes in carpet are undesirable and can result in personal injuries.
Carpets generally comprise a tufting substrate with yarn tufts in the form of cut or uncut loops extending upwardly from the tufting substrate to form a pile surface. In the case of tufted carpets, the yarn is inserted into the tufting substrate by tufting needles and a pre-coat or binder is applied thereto. In the case of non-tufted or bonded pile carpets, the fibers are embedded and held in place by the binder composition.
With both types of carpets, the carpet also usually includes a secondary backing bonded to the primary backing. The secondary backing provides extra padding to the carpet, absorbs noise, adds dimensional stability, and functions as a heat insulator. The secondary backings commonly used are fabrics, PVC plastisol, polyurethane, foam sheet such as PVC or urethane, and bitumen.
The physical properties of a carpet pre-coat or carpet binder, hereinafter referred to as a “carpet back coating”, are important. Such properties include the following: (1) it must be capable of being applied to a carpet and dried using conventional processes and equipment; (2) it must provide excellent adhesion to the pile fibers to secure them firmly to the backing both in the tufted and non-tufted constructions; (3) it must have low smoke density values and high flame retardant properties; and (4) it must maintain sufficient softness and flexibility, even with a high filler loading or at low temperature, to enable the carpet, if prepared in continuous form, to be easily rolled and unrolled during installation and, in the case of carpet tiles that the tile have sufficient rigidity so as to be easily set in place.
Typical carpet tile backings have either been prepared from an all polyvinyl chloride (PVC) plastisol matrix or a combination of ethylene-vinyl acetate precoat with a PVC plastisol secondary coating. While PVC plastisols exhibit good water resistance, the disadvantage with PVC plastisol is a high degree of smoke generation which can present a serious safety issue. Carpet prepared with an ethylene-vinyl acetate precoat with a PVC secondary backing exhibits low smoke density values and high flame retardant properties, but tends to have lower wet strength than all PVC plastisol-based carpets as evidenced by low wet tuft bind values.
Japan Patent No. 56-140152 describes a fiber bonding agent which is composed of (A) an aqueous dispersion of a copolymer composed of 0.1-3.0 parts by weight ethylenically unsaturated monocarboxylic acids or ethylenically unsaturated polyhydric carboxylic acids per 100 parts by weight ethylene vinyl acetate copolymer, and (B) an aqueous dispersion of a compound containing two or more multifunctional aziridine groups. However, the disadvantage of the compositions described in Japan Patent No. 56-140152 is poor compound stability due to the presence of the carboxyl groups on the copolymer.
U.S. Pat. No. 3,458,485 describes a resin solution prepared from styrene, vinylidene or vinyl chloride, and 13 to 45 weight percent of hydroxyethyl acrylate, based on the weight of the copolymer, which is combined with 6 to 20 weight percent, based on the weight of the copolymer, of a crosslinking agent to form a thermosettable resin mixture. However, the disadvantage of the resin solution described in U.S. Pat. No. 3,458,485 is the amount of hydroxyethyl acrylate and crosslinking agent which render the resins prohibitively expensive for use as carpet coatings.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a crosslinkable carpet back coating composition which is applied to a carpet and dried/cured without emitting volatile organic compounds (VOC's) as a by-product of the crosslinking reaction.
It is another object of the invention to provide a carpet back coating which has low smoke density values and high flame retardant properties.
It is also an object of the invention to provide carpet with improved wet strength resisting the tendency of edge fraying and shrinking/curling when exposed to moisture or water.
It is a further object of the invention to provide a carpet back coating which maintains sufficient softness and flexibility, even with a high filler loading and at a low temperature, to enable the carpet, if prepared in continuous form, to be easily rolled and unrolled during installation and, in the case of carpet tiles that the tile have sufficient rigidity so as to be easily set in place.
With regard to the foregoing and other objects, the present invention provides a crosslinkable carpet back coating composition comprising:
(i) an aqueous emulsion polymerization product of
(a) from about 4 to about 25 weight percent of ethylene;
(b) from about 67 to about 95 weight percent of vinyl acetate; and
(c) from about 0.1 to about 8 weight percent of at least one ethylenically unsaturated hydroxy functional monomer, wherein the weight percents of monomers used to prepare the copolymer are based on the weight of (a)+(b)+(c); and
(ii) from about 0.5 to about 9 weight percent, based on the weight of the copolymer, of a crosslinking agent selected from the group consisting of multifunctional aziridine, multifunctional isocyanate, and multifunctional epoxide, wherein the crosslinking reaction does not generate volatile organic compounds as by-products. Preferably the ethylenically unsaturated hydroxy-functional monomer has the formula
wherein R
1
is hydrogen or methyl and R
2
is a hydroxy alkyl group having from 2 to 6 carbon atoms.
According to another aspect the invention provides a method for treating carpet to improve the wet strength of the carpet, said method comprising:
(I) applying a carpet back coating composition to carpet or tufts of yarn, said carpet back coating composition comprising:
(i) an aqueous emulsion polymerization product of
(a) from about 4 to about 25 weight percent of ethylene;
(b) from about 67 to about 95 weight percent of vinyl acetate; and
(c) from about 0.1 to about 8 weight percent of a ethylenically unsaturated hydroxy-functional monomer, wherein the weight percents of monomers used to prepare the copolymer are based on the weight of (a)+(b)+(c); and
ii) from about 0.5 to about 9 weight percent, based on the weight of the copolymer, of a crosslinking agent selected from the group consisting of multifunctional aziridine, multifunctional isocyanate, and multifunctional epoxide to form a crosslinkable carpet back coating composition; and
(II) drying the crosslinkable carpet back coating composition at a temperature sufficient to react the aziridine, isocyanate, or epoxide functional groups on the crosslinking agent with the hydroxy functional groups on the copolymer, wherein the crosslinking reaction does not generate volatile organic compounds as by-products.
The carpet back coatings of the present invention display significant improvements in wet strength as compared to commercially available carpet back coatings. Additionally, carpets prepared with the carpet back coatings of the inven
Leighton John C.
Lunsford David J.
Egwim Kelechi
National Starch and Chemical Investment Holding Corporation
Roland, Esq. Thomas F.
Wu David W.
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