Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Coated or impregnated synthetic organic fiber fabric
Reexamination Certificate
2001-03-26
2003-01-14
Barr, Michael (Department: 1762)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
Coated or impregnated synthetic organic fiber fabric
C442S063000, C442S071000, C442S396000, C427S385500, C427S389900, C427S393500, C428S297700
Reexamination Certificate
active
06506696
ABSTRACT:
BACKGROUND OF THE INVENTION
Crosslinking systems for effecting cure of emulsion polymers are used to provide nonwoven articles with a desired property such as water or solvent resistance.
Most crosslinking systems for emulsion polymers which are employed today require temperatures in excess of 100° C. to ensure the development of a decently cured system. While high temperature cures may be acceptable for many applications, such temperatures may be unacceptable in other applications because of an unsuitability of certain types of substrates, operational difficulties, and lastly, they may represent economic hardship due to the high cost of energy.
One type of crosslinking system employed for polymeric binders includes a crosslinking mechanism based upon the use of pendent acetoacetate functionality such as that derived by the polymerization of acetoacetoxyethyl methacrylate (AAEM) into the polymer and a polyfunctional reactant therewith. The acetoacetate containing polymer then can be reacted with a multi-primary amine functional moiety, for example, to effect crosslinking. This combination has a very short pot-life and often requires the addition of a blocking agent which tend to severely retard cure.
Another type of crosslinking functionality for polymeric binders is based upon the reaction of carboxyl functionality and a polyaziridine.
Still another type of crosslinking system is based on dual functionality in the polymeric binder. For example, U.S. Pat. No. 6,117,492 (Goldstein et al., 2000) discloses emulsion polymers utilizing a dual crosslinking package which contains an acetoacetate moiety that reacts with a polyaldehyde, and a carboxylic acid moiety that reacts with a polyaziridine.
BRIEF SUMMARY OF THE INVENTION
The invention is directed to the use of aqueous polymeric binders having dual crosslinkable functionalities to produce high performance nonwoven webs by bonding synthetic fiber based webs or webs comprising a blend of synthetic fibers and cellulosic fibers with the aqueous polymeric binders. The high performance synthetic fiber based webs exhibit unexpected properties. For example, when used as a topsheet, the high performance webs allow water to transport through the web to an absorbent web below and the topsheet remains dry to the touch.
The aqueous polymeric binders used to form the high performance webs of this invention have two functionalities copolymerized into the polymeric backbone—a acetoacetate moiety and a carboxylic acid moiety. Dual crosslinkability is effected by adding a polyfunctional compound capable of reacting with the acetoacetate moiety and adding another polyfunctional compound capable of reacting with the carboxylic acid functionality. A polyfunctional compound capable of reacting with the acetoacetate moiety is a polyaldehyde, preferably a dialdehyde such as glyoxal or glutaraldehyde. A polyfunctional compound capable of reacting with the carboxyl functionality is a polyaziridine functional compound.
The process of forming the high performance nonwoven webs comprises:
applying an aqueous polymeric emulsion containing a polymer having dual crosslinkable functionality to a synthetic based nonwoven web, wherein the dual crosslinkable polymer incorporates acetoacetate functionality and carboxylic acid functionality;
removing water; and
crosslinking the crosslinkable polymer with an effective amount of a polyaldehyde and an effective amount of a polyaziridine compound.
There are significant advantages to using a dual crosslinkable polymeric emulsions described herein as a binder for synthetic fiber based nonwoven webs:
an ability to effect a low temperature cure sufficient to approach target performance requirements as currently achieved by thermally activated systems; and
an ability to form synthetic based nonwoven fabrics with unexpected excellent topsheet acquisition properties; i.e., properties that render the fabrics dry to touch when exposed to liquids.
DETAILED DESCRIPTION OF THE INVENTION
The aqueous emulsion polymers are produced by emulsion polymerization methods and are described in detail in U.S. Pat. No. 6,117,492 which is hereby incorporated by reference.
Two types of techniques generally have been utilized in preparing polymeric components having activated acetoacetate functionality. One technique involves the addition polymerization of an ethylenically unsaturated monomer having at least one acetoacetate group via solution, emulsion or suspension polymerization. Examples of preferred ethylenically unsaturated monomers capable of providing acetoacetate functionality include acetoacetoxyethyl acrylate (AAEA), allyl acetoacetate, vinyl acetoacetate, acetoacetoxyethyl methacrylate (AAEM) and N-acetoacetylacrylamide. A second technique for preparing the polymeric component having acetoacetate functionality involves the solution or emulsion polymerization of monomers capable of forming polymers having pendant functional groups convertible to acetoacetate units. The use of hydroxyl functional monomers, e.g., hydroxy acrylates, is one way of forming these polymers. Pendent hydroxyl groups then can be converted to acetoacetate units by reaction with an alkyl acetoacetate, e.g., tert-butyl acetoacetate or by reaction with diketene.
Carboxylic acid functionality can be incorporated into the polymer in a variety of ways well known in polymerization technology. A conventional mechanism is in the polymerization of a carboxyl functional monomer with other monomers in polymer formation. Representative carboxyl functional monomers include acrylic and methacrylic acid, crotonic acid, carboxyl ethyl acrylate, maleic anhydride, itaconic acid, and so forth.
The acetoacetate and carboxyl functional monomers can be polymerized with a variety of ethylenically unsaturated monomers having reactive functionality to form the base polymers. Examples of these monomers include C
1-13
alkyl esters of acrylic and methacrylic acid, preferably C
1-8
alkyl esters of (meth)acrylic acid, which include methyl methacrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, isodecyl acrylate and the like; vinyl esters such as vinyl acetate and vinyl propionate; vinyl chloride, acrylonitrile; hydrocarbons such as ethylene, butadiene, styrene, etc.; mono and diesters of maleic acid or fumaric acid, the mono and diesters being formed by the reaction of maleic acid or fumaric acid with a C
1-13
alkanol, preferably a C
1-3
alkanol such as, n-octyl alcohol, i-octyl alcohol, butyl alcohol, isobutyl alcohol, methyl alcohol, amyl alcohol (dibutyl maleate is preferred); C
1-8
alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, isopropyl vinyl ether, n-propyl vinyl ether, tert-butyl vinyl ether and n-butyl and isobutyl vinyl ether and alpha, beta-ethylenically unsaturated C
3-6
carboxylic acids and vinyl esters can also be employed. Also vinyl esters of C
8-13
neo-acids which are comprised of a single vinyl ester or mixture of tri- and tetramers which have been converted to the corresponding single or mixture of C
8-13
neo-acids may be polymerized.
In producing the relatively ambient temperature dual crosslinkable polymer, the polymer should incorporate from about 1 to 10% preferably 2 to 5% by weight of the acetoacetate functionality as measured relative to the molecular weight of acetoacetoxyethyl methacrylate and based upon the total weight of the polymer. (For monomers other than acetoacetoxyethyl methacrylate, acetoacetate functionality should be relative to the molecular weight of acetoacetoxyethyl methacrylate.) Increasing the level of acetoacetoxyethyl methacrylate or molar equivalent in the polymer beyond about 10% and generally even above about 8% by weight of the polymer may lead to an unstable emulsion or require additional stabilizing surfactant. The latter reduces water resistance. In addition thereto, the system may require an increased level of external crosslinker to effect crosslinking. That increased level too may result in an unstable formulation. Given that the preferred monomer employed in form
Goldstein Joel Erwin
Pangrazi Ronald Joseph
Air Products Polymers, L.P.
Barr Michael
Blanton Rebecca A.
Bongiorno Mary E.
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