Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-06-18
2003-01-28
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S296000, C525S056000, C525S061000
Reexamination Certificate
active
06511561
ABSTRACT:
TECHNICAL FIELD
This invention relates to fiber binding powder compositions for consolidating fiber materials and to consolidating processes utilizing said fiber binding powder compositions.
BACKGROUND OF THE INVENTION
Textile sheet materials produced by the usual methods for producing nonwovens as, for example, the air laid, wet laid or spun laid processes require a binding agent to durably fix the fibers and to increase the resistance to mechanical stress. These binding agents are usually based on synthetic, macromolecular compounds and, according to the prior art, they can be applied in the form of solids, for example as powders, granules or fibers, or in the form of liquids such as, for example, aqueous polymer dispersions or solutions. The increased strength of the nonwovens is the result of the fibers becoming bound by the polymers, which adhere to the fiber and thus strengthen the fibrous structure.
When the fibers are laid down by means of a wet laid process, it is frequently desirable to incorporate the binding agent together with the fibers into the aqueous slurry. In this case, the binder system has to meet special requirements. First, the binding agent should be very finely dispersible in the water together with the fibers, in which case the dispersing or the suspending of the generally particulate binder in the water is of particular concern. Secondly, the binder should possess very good fiber adhesion, even in the aqueous liquor, in order that it may not be washed out along with the aqueous liquor in the course of laying down the fibers. Since at elevated temperatures, the glass transition temperature or the melt temperature of the binding agents are often exceeded, there is a need for durable chemical crosslinking of the binding agents in order that the fibrous structures may be provided with dimensional stability even at relatively high temperatures. For this reason, the binding agent should, via a chemical crosslinking reaction, ensure durable fixing of the fibers within the textile sheet material. Such properties are especially of advantage with regard to the prebinding of wet laid glass fibers.
WO-A 90/14457 discloses a method of processing wherein glass fibers, following a carding step, are mixed with thermoplastic powder, for example powders of polypropylene, polyester or polyamide, and the fibrous structure is then consolidated at elevated temperature and under pressure. The wet laid process is said to be inadvisable because of the risk of the binding agent being washed off. AU-B 36659/89 likewise describes consolidating glass fiber materials by means of thermoplastic powders. The use of polyesters or polystyrene is recommended. However, this binder system is not applicable to a wet laid process. In particular, for instance, the low strength of thus-bound fibrous structures on contact with water or solvents is extremely disadvantageous.
Self crosslinking redispersible dispersion powders based on vinyl ester copolymers or (meth)acrylic ester copolymers useful as fiber binding agents are described in EP-B 687317 (U.S. Pat. No. 5,668,216). The disadvantage with this binder system is its relatively high redispersibility in aqueous systems. Consequently, during fiber lay down, the binder is washed out of the aqueous liquor and is thus no longer available for fiber binding.
EP-A 721004 discloses crosslinkable, water-dispersible powders for use in polymer films and coatings, these powders comprising both film forming polymers having at least one functional group and reactive compounds that form a nonionic chemical bond with one another after dispersion in water. More particularly, this polymer mixture is useful for coating applications after dispersion of the binding agent in water. There is no mention in this patent application of any utility with regard to fiber binding in nonwovens. The disadvantage with these binding systems is their high redispersibility in water, as a consequence of which the binder is washed out in the course of the wet laid process before it has a chance to bond to the fibers.
Water redispersible polymer powders for use in adhesives and chemical products for construction are known from DE-A 19545608. The powders are stabilized with polyvinyl alcohol and comprise water soluble, bifunctional, masked aldehydes as a crosslinker component. The unmasking of the aldehyde function may optionally be promoted by the addition of Brönstedt and Lewis acids.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide binding agents for the consolidation of wet laid fiber materials, especially glass fibers, which binding agents can be introduced together with the fibers into the aqueous liquor and, after lay down of the fibers, will ensure durable consolidation of the fibrous sheet material. It is a further object of the present invention to develop a binding agent in powder form which can be mixed and laid down with fibers in a dry process (air laid, carded) and then be activated by a moistening step (dipping, padding, steaming) as a binder to ensure durable consolidation of the textile sheet material.
This object is achieved by the development of a binding agent which is suspendible in aqueous slurry and is based on a dry, pulverulent, thermoplastic polymer preparation which in turn is based on the one hand on a polyvinyl alcohol stabilized polymer and on the other on a reactive component capable of entering a permanent chemical bond with polyvinyl alcohol.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention accordingly provides a fiber binding powder composition for consolidating fiber materials, comprising a) a polymer powder based on a polyvinyl alcohol stabilized polymer of one or more monomers selected from the group consisting of the vinyl esters of branched or unbranched carboxylic acids having 1 to 12 carbon atoms, the esters of acrylic acid and methacrylic acid with branched or unbranched alcohols having 1 to 12 carbon atoms, aromatic vinyl compounds, vinyl halides, olefins and dienes, and b) an inorganic compound which is solid at room temperature (23° C.) and which enters into a chemical bond with the OH groups of the polyvinyl alcohol on introduction of said powder into water.
Preferred vinyl esters are vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate and vinyl esters of alpha branched monocarboxylic acids having 9 to 11 carbon atoms, for example with VeoVa9
R
and VeoVa10
R
(tradenames of Shell). Vinyl acetate is particularly preferred.
Preferred methacrylic esters or acrylic esters are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate. Particular preference is given to methyl acrylate, methyl methacrylate, n-butyl acrylate and 2-ethylhexyl acrylate.
Preferred aromatic vinyl compounds are styrene, methylstyrene and vinyltoluene. A preferred vinyl halide is vinyl chloride. The preferred olefins are ethylene and propylene, and the preferred dienes are 1,3-butadiene and isoprene.
Optionally, the polymer may further contain 0.05 to 10.0% by weight, based on the total weight of the monomers, of comonomers selected from the group consisting of ethylenically unsaturated mono- and dicarboxylic acids and their amides, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, acrylamide, methacrylamide; ethylenically unsaturated sulfonic acids and their salts, preferably vinylsulfonic acid, 2-acrylamidopropanesulfonate and N-vinylpyrrolidone. Further examples of comonomers in the stated amounts are alkoxysilane functional monomers such as acryloyloxypropyltri(alkoxy)- and methacryloyloxypropyltri(alkoxy)-silanes, vinyltrialkoxysilanes and vinylmethyldialkoxysilanes, preferably vinyltriethoxysilane and gamma-meth-acryloyloxypropyltriethoxysilane. Also suitable are co-crosslinkers such as acrylamidoglycolic acid (AGA), methyl methacrylamidoglycolate (MAGME), -methylolacrylamide (NMA), N-methylolmeth
Gruber Sabine
Koegler Gerhard
Kohlhammer Klaus
Proebstl Herbert
Seidl Susanne
Aftergut Jeff H.
Brooks & Kushman P.C.
Wacker-Chemie GmbH
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