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▶ Index	▒ Textile Application 1. Textile treatment(Sizing) 2. Textile Coating 1)Secection of the textile substrate 2)The polymer structure of the PU-products 3)Coating process 4)Finishing of PU-coatings 3. Nonwoven Bonding 4. Poromeric-imitation leather 1)Polyaddition using dispersions 2)Polyaddition in solution 3)The use for poromeric imitation leather
	▒ Paper Application
	▒ Leather Application

▒ Textile Application

1. Textile treatment (sizing)

In the textile industry treatment indicates mechanical as well as chemical-physical posttreatment to improve (resp. to increase) the wear quality of fabrics, including woven and knitted goods. Specially formulated polyurethanes are suitable for treating or sizing wool and blend wool commodities as well as textiles of synthetics, cellulose based fibers and mixtures thereof.
They reduce the objectionable matting of keratin fivers, especially of wool, without the normally required prechlorination. They also reduce the pilling and snag formation and improve the surface stability and the rubbing resistance.
The so-called "Sirolan BAP-Process" (Bisulfite-Adduct-Polyurethane) was developed for wool sizing. It is suitable for preventing matting during washing because of the use of a combination of blocked PU-prepolymer with a special polymer dispersion.
Equivalent effects are also obtained with textiles from synthetic and cellulose fibers. The application of these products is accomplished by either the padding or spraying process, using aqueous-alcoholic solutions. The final step requires drying for a short time at temperatures between 125 to 140℃. In this process sulfur dioxide is split off and the prepolymer is fixed by crosslinking.

2. Textile coating

Polyurethane products for textile coating were first marketed in the fifties. They were hydroxyl groups containing polyesterurethane polymers (oligourethanes) which were crosslinked with poly-functional isocyanates. These fundamental, under cross-linked oligourethanes were prepared at an NCO/OH ratio of less than 1 and therefore were soluble in relatively nonpolar solvents (so-called soft solvents).
These products in combination with the crosslinking agent and pigment (in ethyl acetate solution) are applied on a substrate with a doctor blade by the direct coating process. At first, chintz articles were predominantly produced, but soon tent-roofs, tent-floors, blinds, ironing board covers, light rain coats and other products were manufactured.
In the fifties and sixties textile coating developments with polyurethanes continued using special direct coating on cotton-velvet roughened fabrics. In the years from 1967 until 1970 they were very successful in the fields of men's, women's and children's clothing, and industrial safety clothing, as well as fancy goods and carrying cases.
In the beginning of the seventies the transfer coating with one component polyurethanes stirred new interest. A top coat is produced on a release paper (siliconized paper), which may be grained or smooth. Then it is transferred with an aid of a lamination adhesive onto the textile. It is estimated that in 1976 300 to 350 million square meters of PU-coatings were produced worldwide. Assuming an average coating weight of 70g/sqm, about 24,000 metric tons of PU-solid were processed.
The combination of PU and textiles is distinguished by being comfortable to wear, rugged, and easy to care for.
Typical properties are:

interesting leather-like surface,
warm comfortable touch (hand),
wash and cleaning stability,
good adhesion between substrate and coating,
high elongation and elasticity,
good abrasion resistance,
high flexibility at low temperature (without plasticizers),
very good resistance to oils and fats,
low specific weight.

The resistance to dry cleaning solvents and water is necessary for outerware such as coats. The materials for shoes have specific requirements with regard to adhesion and flexibility.
The quality of PU-coatings is determined by the selection of the substrate, the chemical structure of the polyurethane product, the coating process and by the king of products used for the finish.

1) Selection of the textile substrate

Today, fabrics chosen for coating with polyurethane products are prddominately woven and knitted goods as well as nonwovens. Textile and woven goods are mostly used in the napped state, and the PU is coated on the nap-side. In carlier times, when the articles were only produced by direct coating process ("Vistram") fabrics with an expensive brushed nap determined the quality of the coated goods. In the late sixties coating transfer became possible with the introduction of the thermoplastic one component polyurethanes.
With these products simpler, lighter and cheaper fabrics could be coated. Certainly, the quality of the substrate for shoe upper material remains important today because of the high demands made on the mechanical properties of the substitute the pile of cotton fabric by foamed intermediate layers blown by using polyurethane systems splitting off nitrogen, a method used for a long time already in the areas of PVC, latex and aeroplasts.
A polyurethane top coat is coated on a release paper in the transfer process. Next, a mixture of polyol, isocyanate prepolymer, chemical propellant, e.g. azodicarbonamide, auxiliary and filling material is coated with a doctor blade, foamed and cross-linked at 150 to 170℃. This layer is pressed into the textile by a pressure roll. After heating, the foamed imitation leather is pulled from the release paper.
Inequalities of a substrate, especially nonwovens, can be equalized by using nearly solvent free coatings of reactive foam. Shoe upper material with a foam layer of 0.3 to 0.35mm and with a scratch-resistant PU-top coat of 0.04mm thickness can be produced by this process.
PU-coated, non-roughened cotton fabrics are used for fashionable and light weight overcoats for women and men. Light to heavy polyamide fabrics are used for special work clothes, back packs and camping articles. Polyester and polyamide fabrics are suitable for canvas hood and technical articles, acrylic, or vinyl fabrics for tent roofs and walls.

2) The polymer structure of the PU-products

The polyurethanes used for coatings are primarily linear thermoplastic materials. Cross-linking by triols, amines or isocyanates causes undesirable hardening of the coating film and reduces the essential bending resistance and the softness of the coated substrate. Moreover cross-linked products are not soluble.
The linear polyurethanes are built-up by using polyols as soft segments, which are combined with hard segments (urethane-, urea-, hydrazodicarbonamide groups) (Fig. 10.7).

The above-mentioned hydroxy groups containing oligourethanes with few hard segments are soft and soluble in many organic solvents. They form insoluble, elastic films by cross-linking with polyisocyanates on the textile substrate (two component systems). One component polyurethanes, which require polar solvents like dimethylformamide/methyl ethyl ketone can contain 3 times the quantity of urethane nitrogen compared to oligourethanes containing hydroxyl groups.
They are relatively hard, highly elastic polymers which do not require chemical cross-linking because of strong hydrogen bonding effects. Therefore they are typical PU elastomers.
In the seventies cycloaliphatic isocyanates such as isophorone diisocyanate became available and one component light stable polyurethane urease were developed. These polyurethane-ureas are soluble in soft solvents such as blends of alcohol and aromatic solvents. In addition to being light stablel they offer simple and safe processing, and the products exhibit high elasticity.
Linear, segmented polyurethane ionomers form storage stable aqueous dispersions. These dispersions are suitable for textile top coats and adhesive coats or for foamed intermediate layers prepared by the whipped foam process.
The so-called high solid systems are another important group of polyurethanes for coatings, in which NCO-prepolymers and diamines must be processed by the aid of a mixing head.
Complementary to this are the blocked isocyanate-prepolymers, which when mixed with diamines at room temperature have a longer pot life and react rapidly only after being heated.
Fig. 10.8 gives a view of the explained processes and product group for textile coating in a restricted sense. Other processes like foil lamination e.g. with the "thermo-transfer-process", calendaring with thermoplastic granulated polyurethane for technical articles, and coagulation with 1-component-solution in dimethylformamide and precipitation in aqueous phase are only mentioned for reasons of completeness.

In recent years aqueous PU-dispersions and high-solid-systems have been used more and more because of reduced solvent requirements and ecological considerations.

3) Coating processes

The methods of coating also influence the quality of an article.
The hardness or elasticity of the base (air knife, knife over roll, knife over blanket), on which the PU-solutions are directly coated in the nap of the textile, influence the feel of the end-product.
The direct coating process is based on comparatively high viscosity solutions of about 40,000 mPa . s, because solutions with lower viscosity soak deeper into the textile and cause a hardening during heating. The transfer process is composed of the top coat, adhesive coat, textile and separation from transfer paper and is especially suitable for soft coating. The lowviscosity solutions (5,000 to 15,000 mPa . s) are applied to a release paper, heated, and then bonded to the textile via a thin adhesive coat. For the transfer coating, high-solid-systems are also suitable. Aqueous PU-dispersions can be used in the same process.
They are made by the addition of a few percent of thickener to increase the coating viscosity to about 5,000 mPa . s.
The mechanical foaming of these thickened PU-dispersions gives a product for clothing articles which have a very soft hand.

▶ Direct coating

a. Fabric	b. Coating head	c. Drying oven
d. Cooling roll	e. Winder

▶ Dry Lamination Method

a. Release paper	b. Coating head	c. Drying oven	d. Cooling roll
e. Coating head	f. Drying oven	g. Press roll	h. Backing roll
i. Winder

▶ Dry Coating Process

a. R/P	b. Top skin	c. 1'st Chamber	d. Skin
e. 2'nd Chamber	f. ADH	g. 3'rd Chamber	h. Press
i. Winder	j. B/C

▶ Wet Lamination Method

a. Release paper	b. Coating head	c. Drying oven	d. Cooling roll
e. Coating head	f. Press roll	g. Backing cloth	h. Drying oven
i. Colling roll	j. Winder

▶ Wet Coating Process

a. B/C	b. Ante-process	c. PU Solution	d. Coater
e. Dipping bath	f. Manglc	g. Nip roll	h. Winder

▶ Lamination Method

a. Release paper	b. Coating head	c. Drying oven	d. Cooling roll
e. Coating head	f. Press roll	g. Backing cloth	h. Drying oven
i. Colling roll	j. Separater	k. Leather	l. Release paper

4) Finishing of PU-coatings

Often the coatings require a thin finish coat. In addition to polyamides and polymino acids the finishing products are primarily polyurethanes. These medium soft to hard finishes are applied by spraying, printing, or knife-coating. The 5 to 8 ㎕ thick finishes modify the coated products with regard to hand and fashion-related aspects.

3. Nonwoven bonding

Generally, nonwoven can only be coated to imitation leather when it is bonded beforehand with a polymer, This causes a compression and an improvement of the tensile strength.
Predominantly rubber dispersions are applied for nonwoven bonding. They are made "thermosensitive" by the addition of coagulation aids which causes precipitation of the polymers when increasing the temperature. Also, polyurethane dispersions can be applied alone or in combination with rubber dispersions for nonwoven bonding.
Nonwovens can be produced by the so-called "wet process" similar to paper. Most of the time the pulp contains the binders.
In this type of nonwovens bonding, polyurethanes are applied only in small amounts, however they are especially suited as binders for nonwovens in the production of microporous imitation leather.

4. Promeric-imitation leather

Imitation leather is defined in DIN 16922 as a "textile or other substrates with or without a top coat, having properties and/or surface designing corresponding to the use " The products described in subsection "Textile Coating" fall under this definition. The poromerics are also classifiable in the generic notation of "imitation leather" The most important property of the poromerics is the microporosity. The name poromeric comes from the words porous and polymeric.
Microporosity is, in addition to water vapor adsorption and desorption, one of the most important characteristics of leather. Before the development of "Corfam" there were no synthetical materials which looked like leather and had these properties. The imitation leather has been made microporous by coagulation or other processes, which will be described later.
Shoes made from these microporous materials are able to breathe similar to leather. Extensive investigations of wear hygiene have been reported. Not all of the comfort properties of leather have been achieved by the use of synthetic materals.
Until the ban of the Supreme Court of Hamburg (W. Germany) such products were designated as "Syntheseleder". Polyurethanes are the most important polymers for manufacture of poromeric imitaion leather. The structure of a classical poromeric is shown if Figs. 10.10 and 10.11. There is a microporous top coat of polyurethane on a fleece bonded by a polyurethane adhesive, which is also microporous.

The coagulation is the most important manufacturing process for microporous imitation leather (Figs. 10.12 and 10.13).
Example: A 20 percent polyurethane solution in dimethylformamide is mixed together with an aqueous pigment, and ionic polyurethane dispersion as a coagulation accelerator, and a plyelectrolyte (phenolformaldehyde - dihydroxydiphenylsulfone-condensate). The mixture is de-acrated by applying a vacuum. This solution itself can be used for manufacture of top coats or in a thinned form for bonding nonwovens or fabrics. The solution can be brushed directly on the substrate in the manufacture of top coats. Working with a transfer coating process, the solution is first brushed on a temporary carrier (steel belt).
It is exposed to humid air for improvement of coagulation and finally is coagulated by dipping in the dimethylformami-de/water-baths with decreasing dimethylformamide concentrations. Finally it is washed with water.
In addition a microporous foil can be produced which is laminated on a textile substrate by the transfer-process.

To retain the microporosity, the adhesive layer is not applied as a continuous film Fig. 10.14 is a cross-sectional photo of the poromeric imitation leather produced for the first time on a large scale.
For the manufacture of velour imitations, filament or polyurethane adhesives are widely used which have a soluble component. The soluble components (polystyrene, polyvinyl alcohol) are dissolved out after manufacture.
Microstructured fiers in bunches are obtained by these techniques and are not bonded together with the polyurethane binder. In this way the imitation velours (suede imitation) become exceptionally soft.
Along with coagulation, other processes for forming microporosity were also developed.
Examples are the washing out of salt from films which han been produced from solution and the spraying of polyurethane solution in highly volatile solvents, with which the polymers were precipitated as fine filaments. Also, the selective evaporation of solvents results in microporous films.
Non-solvents (e.g. dry-cleaning solvents) are incorporated into solutions of polyurethanes in relatively volatile solvents (e.g. in tetrahydrofuran). Upon evaporation of the more volatile solvent, the polyurethane slowly coagulates with the increasing concentration of non-solvent and finaly it precipitates to form a microporous product. After evaporation of ther residual amount of solvent and non-solvent amicroporous structure is left. Of course, the amount of non-solvent, which can be added, is limited. because high amounts will result in precipitation of the polyurethane. The quantity of added non-solvent induces the microporosity (Fig. 10.15)
The processes described above for producing poromerics are based on the use of completely reacted polyurethanes. It is even possible to use polyurethane prepolymers to prepare microporous structures through polyaddition reactions. For this process, the polyaddition can be performed with either dispersions or solutions.

1) Polyaddition using dispersions

It is preferable to dissolve isocyanate-prepolymers in e.g. aromatic hydrocarbons which have a high interfacial surface tension relative to a non-solvent (e.g. water). The quantity of water dispersed in this solution is limited owing to the fact that a water-in-oil emulsion is supposed to result. The emulsion is usable after addition of chain-extender and mixing. Within 10 to 20 sec, the emulsion has to be cast onto a foil or impregnated into a fabric. The reaction is carried out at normal temperature with the solvents and water evaporating. The resulting poromerics are characterized by spherical pores. Their microporosity depends on the quantity of non-solvent.

2) Polyaddition in solution

This technique differs from polyaddition using dispersions due to the fact that the polyurethane prepolymers are dissolved in solvent or solvent mixtures which cannot dissolve the end product.
The polyurethane becomes less soluble with time until it slowly precipitates and occludes the solvent. A poromeric is obtained after the reaction and evaporation of the solvent.
The structure of the pores does not differ from those obtained from coagulation. Nonwoven bonding is also possible with this technique.

3) The use for poromeric imitation leather

With the exception of polyurethanes there is no other synthetic material at present which is good enough in flexibility, tensile strength and stitch tear resistance having the required microporosity. Most of the poromeric imitation leather based on polyurethane is produced in Japan.
A total of 17 million linear meters of imitation leather are produced there by coagulation. Out of this, 14 million are poromeric imitation velours (suede). In addition, 24 million linear meters are produced by the classical solution technique.
Poromeric imitation leathers are also produced in considerable quantities in the Soviet Union, German Democratic Republic, Poland and Rumania. The only poromeric without textile substrate is made in Great Britain.
In Italy a composite material was developed which is made of a nonwoven treated by coagulation and topcoated using the transfer-technique. The microporosity of the coagulated substrate is largely lost in this process, but the smooth surface and the soft and compact hand are maintained.