The invention relates to crosslinked polymerizates which are capable of absorbing, which are based on partially neutralized, monoethylenically unsaturated monomers that carry acidic groups, which exhibit improved properties, in particular, with regard to their ability to transport liquids when in a swollen state, and which are subsequently crosslinked on the surface thereof at temperatures xe2x89xa7150xc2x0 C. with a combination consisting of polyol used as a subsequent crosslinker compound and of a cation provided in the form of an aqueous solution.

The invention relates to powdered, crosslinked polymers (superabsorbers) which absorb water, aqueous liquids, as well as blood, and have improved properties, particularly improved retention and improved liquid retention capability under pressure and an improved capability of conveying liquids, and to their production and their use as absorbents in hygiene articles and in technical fields.
Superabsorbers are water-insoluble, crosslinked polymers capable of absorbing large amounts of aqueous liquids and body fluids such as urine or blood with swelling and formation of hydrogels, and retaining them under a specific pressure. As a result of these characteristic properties, these polymers are predominantly used for incorporation in sanitary articles, e.g., in diapers for babies, incontinence articles, or in liners.
Essentially, the superabsorbers commercially available at present are crosslinked polyacrylic acids or crosslinked starch/acrylic acid graft polymers wherein the carboxyl groups are partially neutralized with sodium hydroxide or potassium hydroxide solution.
For aesthetic reasons and from environmental aspects, there is an increasing tendency of designing sanitary articles such as diapers for babies, incontinence articles and liners increasingly smaller and thinner. In order to ensure a constant retention capability of the sanitary articles, the above requirement can only be realized by reducing the percentage of large-volume fluff. As a result, the superabsorber also has to assume functions with respect to conveyance and distribution of liquid, which may be summarized as permeability properties.
Permeability in the case of a superabsorber material is understood to be the ability of conveying added liquids and distributing them in a three-dimensional fashion in its swollen state. In a swollen superabsorber gel, this process takes place via capillary conveyance through interstices between the gel particles. The actual conveyance of liquid through swollen superabsorber particles complies with the laws of diffusion and is an exceedingly slow process which, in the service condition of the sanitary article, does not play any role in the distribution of liquid. In superabsorber materials incapable of accomplishing capillary conveyance due to lacking gel stability, separation of the particles from each other has been ensured by embedding these materials in a fiber matrix, thereby avoiding the gel blocking phenomenon. In new generation diaper constructions, the absorber layer has only minor amounts of fiber material to support the conveyance of liquid, or none at all. Accordingly, the superabsorbers used therein must have sufficiently high stability in their swollen state, so that the swollen gel still has a sufficient quantity of capillary space, through which conveyance of liquid is possible.
In one aspect, in order to obtain superabsorber materials having high gel strength, the polymer crosslinking level could be increased, which would inevitably result in a loss of swelling capacity and retention capability. Indeed, an optimized combination of various crosslinkers and comonomers as described in the patent specification DE 196 46 484 is able to improve the permeability properties, but not to such a level that incorporation in a diaper construction of a layer optionally consisting of superabsorbers only would be possible.
Furthermore, methods of surface secondary crosslinking of the polymer particles may be used. During the so-called secondary crosslinking, the carboxyl groups of the polymer molecules at the surface of the superabsorber particles are reacted with various secondary crosslinking agents capable of reacting with at least two of the carboxyl groups near the surface. In addition to increasing the gel strength, the capability of absorbing liquids under pressure is highly improved in particular, because the well-known phenomenon of gel blocking is suppressed, where slightly swollen polymer particles adhere to each other, thereby preventing further absorption of liquid.
The surface treatment of liquid-absorbing resins is already well-known. To improve the dispersibility, ionic complexing of the carboxyl groups near the surface using polyvalent metal cations has been suggested in U.S. Pat. No. 4,043,952. This treatment is effected using salts of multivalent metals dispersed in organic solvents (alcohols and other organic solvents) optionally containing water.
A secondary treatment of superabsorber polymers using reactive, surface-crosslinked compounds (alkylene carbonates) to increase the liquid absorption capability under pressure has been described in DE-A-40 20 780.
The EP 0,233,067 describes water-absorbing resins crosslinked at their surface, obtained by reacting a superabsorbent polymer powder with an aluminum compound. A mixture of water and diols is used as treatment solution, which is intended to render the use of lower alcohols as solvents unnecessary. Preferably, 100 parts of crosslinker solution is applied on 100 to 300 parts of absorber. According to the examples, the reaction with the aluminum component takes place at room temperature. The diols (e.g., polyethylene glycol 400 and 2000, 1,3-butanediol or 1,5-pentanediol) added to the water reaction medium serve to prevent aggregation of the superabsorber during the treatment with such large amounts of aqueous treatment solution used therein. The solvent is removed in a subsequent drying operation at 100xc2x0 C. The polymers thus treated have an insufficient level of properties, with improvement of the absorption capability under pressure not being achieved. Furthermore, a treatment using large amounts of treatment solution is not economically feasible in modern, continuously operating processes.
WO 96/05234 describes a process for the production of superabsorbing polymers, according to which a crosslinked layer is formed at the surface of the absorber particles containing at least 10 wt.-% of water by reacting a reactive, hydrophilic polymer or a reactive organometallic compound with an at least bifunctional crosslinker below 100xc2x0 C. The polymer products are said to have a well-balanced correlation of absorption, gel strength and permeability, the measured values having been determined according to extremely poor criteria of evaluation. Thus, for example, the absorption and permeability have been determined without any pressure load. One drawback in this well-known process is the use of solvents and toxically critical crosslinking reagents such as polyimines, alkoxylated silicone or titanium compounds, and epoxides which are mentioned as being preferred.
An improvement in the properties of permeability and liquid conveyance is achieved in WO 95/22356 and WO 97/12575 by appropriately treating commercially available superabsorber products with aminopolymers in organic solvents. In addition to using toxicologically critical polyamines and polyimines, a serious drawback of the process described therein is the use of large amounts of organic solvents required in the treatment of the polymers. Industrial production is excluded by the safety aspect and cost associated therewith. In addition to the toxicological risk of these treatment agents, their tendency to decompose under the high temperatures of secondary crosslinking must also be taken into account which, among other things, can be seen in a yellow discoloration of the absorber particles.
The state of the art as described above does not provide any indication that a dramatic augmentation in the permeability properties is also possible in this secondary crosslinking stage, while retaining high retention capacity and capability of absorbing liquids under pressure.
It was therefore the object of the present invention to provide superabsorbing polymers which, as a combination of properties, not only have high absorbing capacity under pressure but also the normally contrary properties of high retention capability and good permeability in combination, i.e., a level of combined properties where, in addition to a retention value of at least xe2x89xa725 g/g, an SFC value of at least 30xc3x9710xe2x88x927, preferably at least 50xc3x9710xe2x88x927 cm3xc2x7s/g is present. In particular, it was the object to provide superabsorbing polymers which particularly would be suitable for use in very thin diaper constructions having a very high percentage of superabsorber. In particular, polymers having retention values of xe2x89xa725 g/g and permeability values SFC of  greater than 70xc3x9710xe2x88x927 cm3xc2x7s/g are required in this case.
It was another object of the invention to find production processes for these superabsorbing polymers that would be easy, economically and safely feasible, provide constant product quality and wherein, in particular, low amounts of solvent are used, and organic solvents are avoided as far as possible. In addition, these processes should be feasible without the use of toxicologically critical substances.
The object of the invention is accomplished by providing a powdered polymer product which has been subjected to secondary crosslinking at its surface, and which absorbs water, aqueous or serous fluids, as well as blood, and is constituted of
a) 55-99.9 wt.-%, preferably 70-90 wt.-% of polymerized, ethylenically unsaturated monomers which contain acid groups and are neutralized to at least 25 mole-%,
b) 0-40 wt.-%, preferably 0-20 wt.-% of polymerized, ethylenically unsaturated monomers copolymerizable with a),
c) 0.1-5.0 wt.-%, preferably 0.1-3 wt.-% of one or more polymerized crosslinking agents,
d) 0-30 wt.-%, preferably 0-5 wt.-% of a water-soluble polymer, the sum of the weight amounts a) through d) always being 100 wt.-% , characterized in that the polymer product has been coated with
e) 0.01-5 wt.-%, relative to the polymer product, of at least one polyol as surface secondary crosslinking agent in the form of an aqueous solution, and
f) 0.001-1.0 wt.-%, relative to the polymer product, of a cation in the form of an aqueous solution, and heated to a secondary crosslinking temperature of from 150 to 300xc2x0 C.
Surprisingly, a superabsorber resin with significantly improved permeability properties and high retention capability is obtained by coating a particulate absorber resin with an aqueous solution of a polyol which has reacted with molecular groups near the surface, preferably with carboxyl groups, in the presence of a cation of a salt component with heating at 150 to 300xc2x0 C.
Quite unexpectedly, the aqueous solution of the inventive combination of secondary crosslinker components provides the desired result, namely, superabsorber resins having high retention capability even under pressure and, at the same time, excellent permeability properties. Successive, separate use of an aqueous solution of the organic secondary crosslinking agent and an aqueous solution of the salt with heating in each case does not result in comparably good product characteristics.
The sole use of a polyol as organic secondary crosslinking agent in aqueous solution results in products having high retention capacity, high gel strength and high absorption capability under pressure. However, a significant increase of permeability in the swollen state can only be achieved by a correspondingly higher crosslinking level of the polymers during polymerization, or by more intensive secondary crosslinking (increased amounts of secondary crosslinking agent or more severe conditions) and an associated loss of retention capacity.
Likewise, sole secondary crosslinking using high positive charge density cations will not result in polymer products having the desired combination of properties. In particular, satisfactory values of liquid absorption under pressure and good permeability properties cannot be achieved. As a consequence, treating superabsorber polymers with multivalent cations only can only increase the rate of liquid absorption. An improvement of pressure stability or even liquid conveyance properties in the swollen state is not achieved.
According to the invention, polyols reacting with the surface COOH groups of the polymer product are used as organic secondary crosslinker component e).
Preferably, aliphatic polyhydroxy compounds such as C2-C8 alkylenediols, e.g. ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, dianhydrosorbitol, C2-C8 alkylenetriols such as glycerol, trimethylolpropane, higher-functional hydroxy compounds such as pentaerythritol and sugar alcohols, e.g. sorbitol, as well as di- and polyalkylene glycols such as diethylene glycol, di-propylene glycol, triethylene glycol, tetraethylene glycol, tetrapropylene glycol, polyethylene glycol, polypropylene glycol, polyglycols based on 2 or more different monomer units, e.g. a polyglycol of ethylene oxide and propylene oxide units, are used as polyols. The organic secondary crosslinker component or the mixtures thereof are employed in amounts of from 0.01 to 5 wt.-%, preferably from 0.1 to 2.5 wt.-%, and more preferably from 0.5 to 1.5 wt.-%, relative to the polymer product to be crosslinked.
According to the invention, aqueous solutions of salts are preferably used as component f) to crosslink the carboxylate groups near the surface, the anions of which are chloride, bromide, sulfate, carbonate, nitrate, phosphate, or organic anions such as acetate and lactate. The cations preferably are derived from uni- or multivalent cations, the univalent ones preferably from alkali metals such as potassium, sodium, lithium, with lithium being preferred. Bivalent cations used according to the invention are derived from zinc, beryllium, alkaline earth metals such as magnesium, calcium, strontium, with magnesium being preferred. Other examples of polyvalent cations which may be used according to the invention are cations of aluminum, iron, chromium, manganese, titanium, zirconium, and other transition metals, as well as double salts of these cations, or mixtures of the above-mentioned salts. It is preferred to use aluminum salts and alums and their various hydrates, such as AlCl3xc3x976H2O, NaAl(SO4)2xc3x9712H2O, KAl(SO4)2xc3x9712H2O, or Al2(SO4)3xc3x9714-18H2O. It is particularly preferred to use Al2(SO4)3 and the hydrates thereof. Calculated relative to the cation, the salt component is employed in amounts of from 0.001 to 1.0 wt.-%, preferably 0.005 to 0.5 wt.-%, and more preferably 0.01 to 0.2 wt.-%, relative to the polymer product.
The water-absorbing polymer product to be surface-crosslinked is obtained by polymerizing a) 55-99.9 wt.-% of a monounsaturated monomer having acid groups, where monomers containing carboxyl groups are preferred, e.g., acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, or mixtures of these monomers. Preferably, at least 50% and more preferably at least 75% of the acid groups are carboxyl groups. The acid groups are neutralized to at least 25 mole-%, i.e., they are present as sodium, potassium or ammonium salts. The degree of neutralization preferably is at least 50 mole-%. Particularly preferred is a polymer product obtained by polymerization, in the presence of crosslinkers, of acrylic acid or methacrylic acid, the carboxyl groups of which have been neutralized to 50-80 mole-%.
From 0 to 40 wt.-% of ethylenically unsaturated monomers copolymerizable with a), such as acrylamide, methacrylamide, hydroxyethyl acrylate, dimethylaminoalkyl (meth)acrylate, dimethylaminopropylacrylamide, or acrylamidopropyltrimethylammonium chloride may be used as other monomers b) in the production of the absorbent polymer products. Monomers in excess of 40 wt.-% might deteriorate the swelling capability of the polymer products.
All those compounds bearing at least two ethylenically unsaturated double bonds or one ethylenically unsaturated double bond and one functional group reactive towards the acid groups of the monomers a) or multiple functional groups reactive towards acid groups may be used as crosslinker component c) present during the polymerization of a) and b). As examples may be mentioned: aliphatic amides such as methylenebisacryl- or -methacrylamide, or ethylenebisacrylamide, and also, aliphatic esters of polyols or alkoxylated polyols with ethylenically unsaturated acids, such as di(meth)acrylates or tri(meth)acrylates of butanediol or ethylene glycol, polyglycols, trimethylolpropane, di- and triacrylate esters of trimethylolpropane preferably alkoxylated with from 1 to 30 mol of alkylene oxide, preferably ethoxylated, acrylate and methacrylate esters of glycerol and pentaerythritol and of glycerol and pentaerythritol preferably ethoxylated with from 1 to 30 mol of ethylene oxide, and also, allyl compounds such as allyl (meth)acrylate, alkoxylated allyl (meth)acrylate reacted preferably with from 1 to 30 mol of ethylene oxide, triallyl cyanurate, triallyl isocyanurate, maleic acid diallyl ester, polyallyl esters, tetraallyloxyethane, triallylamine, tetraallylethylenediamine, allyl esters of phosphoric acid or phosphorous acid, and also, crosslinkable monomers such as N-methylol compounds of unsaturated amides like methacrylamide or acrylamide and the ethers derived therefrom. Mixtures of the above-mentioned crosslinkers may also be used. The percentage of crosslinking comonomers is from 0.1 to 5 wt.-%, preferably from 0.01 to 3.0 wt.-%, relative to the total amount of monomers.
From 0 to 30 wt.-% of water-soluble polymer products, such as partially or completely saponified poly(vinyl alcohol), polyvinylpyrrolidone, starch or starch derivatives, polyglycols, or poly(acrylic acids) may be included as watersoluble polymers d) in the absorbent polymer products according to the invention, preferably incorporated by polymerization. The molecular weight of these polymers is not critical as long as they are soluble in water. Preferred water-soluble polymers are starch and poly(vinyl alcohol). The preferred content of these water-soluble polymers in the absorbent polymer product of the invention is around 1-5 wt.-%, preferably 0-5 wt.-%, relative to the total amount of components a) through d). The water-soluble polymers, preferably synthetic ones such as poly(vinyl alcohol), may also serve as grafting basis for the monomers to be polymerized.
Conventional initiators such as azo or peroxo compounds, redox systems or UV initiators (sensitizers) are used to initiate the free-radical polymerization.
Preferably, the polymer products of the invention are produced according to two methods:
According to the first method, the partially neutralized monomer a), preferably acrylic acid, is converted to a gel by means of free-radical polymerization in aqueous solution and in the presence of crosslinkers and optionally other components, which gel is subsequently crushed, dried, milled, and screened to the desired particle size. Such a solution polymerization may be conducted in a continuous or batchwise fashion. The state of the art includes a broad spectrum of possible variants with respect to concentration conditions, temperatures, type and amount of initiators. Typical processes have been described in the publications U.S. Pat. No. 4,286,082, DE 27 06 135, and U.S. Pat. No. 4,076,663, the disclosures of which are hereby incorporated by reference.
Inverse suspension and emulsion polymerization may also be used to produce the products of the invention. According to these processes, an aqueous, partially neutralized solution of the monomers a), preferably acrylic acid, is dispersed in a hydrophobic organic solvent using protective colloids and/or emulsifiers, and the polymerization is initiated using free-radical initiators. The crosslinkers are either dissolved in the monomer solution and metered together with same or added separately and optionally during the polymerization. Optionally, a water-soluble polymer d) as a grafting basis is added via the monomer solution or by directly placing in the oil phase. Subsequently, the water is removed azeotropically from the mixture, and the polymer product is filtrated and optionally dried. Crosslinking may be effected by incorporating a polyfunctional crosslinker via polymerization, which is dissolved in the monomer solution, and/or by reacting suitable crosslinking agents with functional groups of the polymer during the polymerization steps. For example, these processes have been described in U.S. Pat. No. 4,340,706, DE 37 13 601, DE 28 40 010, and WO 96/05234, the disclosures of which are hereby incorporated by reference.
The polymer gel is dried to a water content of 0.5-25 wt.-%, preferably 1-10 wt.-%, and more preferably 1-8 wt.-%, at temperatures normally ranging from 100-200xc2x0 C.
There are no particular limitations regarding the particle shape of the absorbent polymer products according to the invention. The polymer product may be in the form of beads obtained by inverse suspension polymerization, or in the form of irregularly shaped particles derived from drying and powdering the gel mass from solution polymerization. The particle size normally is below 3000 xcexcm, preferably between 20 and 2000 xcexcm, and more preferably between 150 and 850 xcexcm.
The secondary crosslinker components according to the invention are applied in the form of their aqueous solutions. Suitable solvents are water and optionally, polar watermiscible organic solvents such as acetone, methanol, ethanol, or 2-propanol, or mixtures thereof. With respect to the solvent component, the term xe2x80x9caqueous solutionxe2x80x9d in the meaning of the invention indicates that other organic solvents may also be included in addition to water. The concentration of each secondary crosslinker component in the aqueous solvent may vary within wide limits, ranging from 1-80 wt.-%, preferably from 5 to 65 wt.-%, and more preferably from 10 to 40 wt.-%. The preferred solvent for the polyols as secondary crosslinking agents and for the salt component is water which is used in an amount of from 0.5 to 10 wt.-%, preferably from 0.75 to 5 wt.-%, and more preferably from 1.0 to 4 wt.-%, relative to the polymer product.
If the polyol and the salt component are present in an aqueous solution, the soluble quantities of both components may be limited by salting-out effects and have to be adapted in accordance with the composition. Because the amount of organic solvents must be held as low as possible for safety reasons in order to avoid explosions, a stable mixed phase of water/organic solvent/organic secondary crosslinker compound/salt component cannot be achieved at any concentration of compound. For example, a preferred solution consists of 1.5-3 parts by weight of water, 0.5-1 parts by weight of polyol component, and 0.4-0.6 parts by weight of an inorganic salt. Conventionally, the total amount of solvent employed ranges from 0.5-12 wt.-%, preferably from 1 to 7 wt.-%, and more preferably from 1 to 5 wt.-%, relative to the polymer product.
In addition to water and the above-mentioned organic solvents, other solubilizers such as inorganic or organic acids or complexing agents may also be used in order to reduce the amounts of liquid applied on the polymer product.
Depending on the solubility of both components e) and f), the solution is heated to 20-100xc2x0 C., preferably 20-60xc2x0 C. prior to application on the polymer product. Separate, yet simultaneous metering of a solution of the polyol and a solution of the salt component is also possible if homogeneous distribution of both components on the polymer product is ensured and the material is subjected to a thermal subsequent treatment. Preferably, one single solution is applied on the polymer product, wherein both components are dissolved.
The secondary crosslinker solution should be mixed thoroughly with the polymer particles. Suitable mixing units for applying the secondary crosslinker solution are, e.g., Patterson-Kelley mixers, DRAIS turbulence mixers, Lxc3x6dige mixers, Ruberg mixers, screw mixers, pan mixers, and fluid-bed mixers, as well as continuously operated vertical mixers wherein the polymer powder is mixed at a rapid frequency using rotating knives (Schugi mixer). It is also possible to coat the polymer product in the course of a particular processing step during the production of the polymer product. To this end, the process of inverse suspension polymerization is particularly suited.
Once the secondary crosslinker solution has been mixed with the polymer particles, the secondary crosslinking reaction preferably is performed at temperatures ranging from 150xc2x0 C. to 300xc2x0 C., preferably from  greater than 150xc2x0 C. to 250xc2x0 C., and more preferably from 160xc2x0 C. to 210xc2x0 C. The optimum time period for additional heating can easily be determined for each single type of crosslinker in just a few tests and is limited by that point where the desired pattern of properties of the superabsorber is destroyed as a result of heat damage. The thermal treatment may be carried out in usual dryers or ovens; as examples may be mentioned: rotary-tube dryers, fluid-bed dryers, disc dryers, blade dryers, or infrared dryers.
The polymers of the invention can be produced on an industrial scale according to well-known processes in a continuous or batchwise fashion.
The polymer products according to the invention may be used in a wide field of applications. If used in liners, diapers or in wound dressings, for example, they have the property of rapidly absorbing large amounts of menstruation blood, urine, or other body fluids. Because the agents according to the invention retain absorbed liquids even under pressure and, in addition, are capable of distributing additional liquid within the construction in their swollen state, it is particularly preferred to use them at higher concentrations, relative to the hydrophilic fibrous material such as fluff, than has been possible so far. They are suitable for use as homogeneous superabsorber layers, with zero amounts of fluff within the diaper construction, thereby enabling particularly thin diapers. Furthermore, the polymers are suitable for use in hygiene articles (incontinence articles) for adults.
The polymers according to the invention are also used in absorber articles suitable for most various purposes, e.g. by mixing with paper, fluff or synthetic fibers, or by dispersing the superabsorber between substrates made of paper, fluff or nonwoven textiles, or by processing into support materials to form a web. In addition, the polymers of the invention are used in all those cases where aqueous liquids have to be absorbed, e.g., in cable sheathings, in food packagings, in the agricultural field in plant breeding, as water reservoir, and as a vehicle for active substances involving the function of delayed release into the environment.
Surprisingly, the superabsorbers according to the invention exhibit a significant improvement in permeability, i.e., an improvement in liquid conveyance in the swollen state. Polymer products are obtained having permeability values (SFC) of up to 70xc3x9710xe2x88x927 cm3xc2x7s/g at a retention (TB) of at least 27 g/g, and preferably such polymers having SFC values of from  greater than 70xc3x9710xe2x88x927 to xe2x89xa7150xc3x9710xe2x88x927 cm3xc2x7s/g at a retention (TB) of at least 25 g/g. In addition to these excellent SFC and retention values, the polymers of the invention exhibit measured values of liquid absorption under pressure (AAP0.7) of at least 18 g/g.
The products of the invention having this outstanding combination of properties comprising very high SFC values, high retention and high absorption under pressure can be produced without using toxicologically critical substances.
As can be seen from the following Examples, the secondary crosslinking according to the invention is applicable to a variety of polymer products having various chemical structures. Thus, it is no longer necessary to fall back on special crosslinker combinations, comonomers or expensive secondary treatment procedures at such an early stage as during the production of the polymer products in order to achieve an at least slightly increased permeability.
In order to characterize the absorbent polymer products of the invention, the retention (TB), absorption under pressure (AAP) and permeability for a 0.9% saline solution in the swollen state (SFC) are determined.
a) The retention is determined according to the tea bag method and is given as mean value of three measurements. About 200 mg of polymer product is welded in a tea bag and immersed in a 0.9% NaCl solution for 30 minutes. The tea bag is subsequently centrifuged in, a centrifuge (23 cm in diameter, 1,400 rpm) for 3 minutes and weighed. A tea bag having no water-absorbing polymer is run as a blank.   Retention  =                              Final                                xe2x80x83                              weight                -        Blank                    Initial                          xe2x80x83                        weight                        xe2x80x83                  [g/g]
b) Liquid absorption under pressure (AAP test according to EP 0,339,461)
The absorption under pressure (pressure load 50 g/cm2) is determined according to the method described in EP 0,339,461, page 7. About 0.9 g of superabsorber is weighed in a cylinder having a screen bottom. The uniformly spread superabsorber layer is loaded with a piston exerting a pressure of 50 g/cm2. The previously weighed cylinder then is placed on a glass filter plate situated in a tray containing a 0.9% NaCl solution, the liquid level of which precisely corresponds to the height of the filter plate. After allowing the cylinder unit to absorb 0.9% NaCl solution for 1 hour, it is reweighed, and the AAP is calculated as follows:
AAP=Final weight (cylinder unit+superabsorber)xe2x88x92Initial weight (cylinder unit+soaked superabsorber)/Initial weight of superabsorber
c) Permeability in the swollen state (SFC Test according to WO 95/22356)
0.9 g of superabsorber material is weighed in a cylinder having a screen bottom and spread carefully over the screen surface. The superabsorber material is allowed to swell in JAYCO synthetic urine [composition: 2.0 g of potassium chloride, 2.0 g sodium sulfate, 0.85 g of ammonium dihydrogen phosphate, 0.15 g of ammonium hydrogen phosphate, 0.19 g of calcium chloride, 0.23 g of magnesium chloride as anhydrous salts dissolved in 1 l of distilled water] for 1 hour against a pressure of 20 g/cm2. After detecting the swelling height of the superabsorber, a 0.118 M NaCl solution is allowed to flow from a levelled reservoir vessel through the swollen gel layer at a constant hydrostatic pressure. During measurement, the swollen gel layer is covered with a special screen cylinder which ensures uniform distribution of the 0.118 M NaCl solution above the gel and constant conditions (measuring temperature 20-25xc2x0 C.) during measurement with respect to the gel bed structure. The pressure acting on the swollen superabsorber still is 20 g/cm2. Using a computer and a scale, the amount of liquid passing through the gel layer as a function of time is detected at intervals of 20 seconds within a time period of 10 minutes. The flow rate g/s through the swollen gel layer is determined using regression analysis with slope extrapolation and determination of the center to time t=0 of the flow rate over the minutes 2-10. The SFC value (K) is calculated as follows:   K  =                                          F            s                                          (                          t              =              0                        )                          xc3x97                  L          0                            r        xc3x97        A        xc3x97        Δ                          xe2x80x83                        P              =                                        F            s                                          (                          t              =              0                        )                          xc3x97                  L          0                    139506
wherein
Formal addition of the figures from tea bag retention and the SFC value illustrates the abrupt increase of this combination of properties in the polymer products of the invention as compared to non-treated superabsorber powder or to products subjected to surface secondary crosslinking according to well-known methods. In the products according to the invention, said figure is not achieved by a high contribution of one of these two values (e.g., a high TB retention value and a low SFC value or vice versa).

Powdery, cross-linked polymers which absorb aqueous liquids and blood, method for the production thereof and their use


Compounds of the formula I

It is known that the bleaching power of peroxide bleaches, such as hydrogen peroxide, perborates, percarbonates, persilicates and perphosphates, in detergents and cleaners, and hence their efficiency in removing tea, coffee, fruit or red wine stains, is only fully attained at temperatures of significantly greater than 60xc2x0 C. To improve the bleaching effect, which is greatly reduced at, especially, temperatures below 60xc2x0 C., it is possible to use compounds to activate the peroxide bleaches. A number of transition metal salts or corresponding complexes with mostly chelating compounds have been proposed for this purpose, although the effectiveness of a metal or of a specific combination of transition metal and complex ligand cannot be predicted.
WO 96 06154 and EP 458 397 claim metal complexes with a high activation potential. A disadvantage of the types of complex described therein is that they considerably damage the fibers and colors of textiles. J. Am. Chem. Soc., 1989, 111, 5102-5114 describes the crystalline structure of a bicyclic manganese complex containing a bridging 2,6-bis(1,4,7-triazacyclononan-1-ylmethyl)4-methylphenoxide ligand, two bridging acetate groups and two perchlorate anions, where the oxidation states of the two metal centers are mixed, and one manganese atom is ascribed the oxidation number II and the second manganese atom the oxidation number III. The applications-related relevance of this compound has hitherto not been reported.
The present invention therefore provides unknown compounds of the formula I which intensify the bleaching power of peroxo compounds, even at low temperatures, without attacking the textile fibers or textile dyes
[LnMmXp]ZYq xe2x80x83xe2x80x83formula I
where
M is manganese in oxidation state II, III, IV and/or V, iron in oxidation state II and/or III or cobalt in oxidation state II and/or III,
X is a coordination group or bridging group,
Y is a counterion in the corresponding stoichiometric amount to balance an existing charge z, where
z as the charge of the metal complex can be positive, zero or negative, n and m, independently of one another, are integers from 1 to 4,
p is an integer from 0 to 15,
q is z/charge of Y,
L is an organic ligand of the general formula II
where
R1 and R2, independently of one another, are hydrogen, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, an alkenyl or alkinyl group having 2 to 8 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms or a phenyl group which may also be substituted,
each D, independently of one another, is NR3, O, PR3 or S, where R3 is an alkyl group having 1 to 6 carbon atoms, an alkenyl or alkinyl group having 2 to 8 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms or a phenyl group which may also be substituted,
each E, independently of one another, is N, P or C(R1) with the meanings given above for R1,
t is a number from 0 to 6, s is a number from 1 to 5 and u is a number from 1 to4,
A is a C3- to Cg-cycloalkyl, phenyl, 1,1xe2x80x2-biphenyl, naphthyl, anthracenyl or pyridinyl radical,
each R4, independently of one another, is hydrogen, a C1- to C6-alkyl group, a C1- to C3-alkoxy group, a C3- to C10-cycloalkyl group or a phenyl group which may also be substituted,
v is a number from 0 to 15,
K is a group coordinating to at least one of the metal centers M and is of the type xe2x80x94O, xe2x80x94OR, xe2x80x94S, xe2x80x94SR, xe2x80x94NR2, xe2x80x94NR, xe2x80x94PR2 or xe2x80x94PR, where R is hydrogen, an alkyl group having 1 to 6 carbon atoms, an alkenyl or alkinyl group having 2 to 8 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms or a phenyl group which may also be substituted, X is an anion of the following formulae:
Fxe2x88x92, Clxe2x88x92, Brxe2x88x92, SCNxe2x88x92, OHxe2x88x92, O22xe2x88x92, O2xe2x88x92, O2xe2x88x92, R10OO31 , H2O, HS31 , CNxe2x88x92, OCNxe2x88x92, S2xe2x88x92,N3xe2x88x92, NH3, NR103, NR102, R10Oxe2x88x92, R10COOxe2x88x92, R10SO3xe2x88x92 and R10SO431 , where R10 is in each case hydrogen, C1- to C8-alkyl, C3- to C8-cycloalkyl or C6- to C18-aryl, and
Y
if z is positive, is an anion of the following formulae: Fxe2x88x92, Clxe2x88x92, Brxe2x88x92, NO3xe2x88x92, ClO4xe2x88x92, SCNxe2x88x92, PF6xe2x88x92, R10SO4xe2x88x92, R10COOxe2x88x92, R10SO3xe2x88x92, BF4xe2x88x92, BPh4xe2x88x92 and SO42xe2x88x92 and
if z is negative, is a cation of the following formulae: Li+, Na+, K+, Mg2+, Ca2+, Al3+, NH4+, R10NH330 , R102NH2+, R103NH+ and R104N+, where R10 has the meaning given above.
Preference is given to compounds in which D is NR3, E is nitrogen, R1 and R2 are hydrogen, s is a number from 1 to 3, t is a number from 1 to 4 and K is a group of the type xe2x80x94O, xe2x80x94OR, xe2x80x94S or xe2x80x94NR2, and the other symbols have the meanings given above.
Particular preference is given to compounds in which A is a phenyl or C3- C9-cycloalkyl group, m is a number from 1 to 3 and n is a number from 1 to 2. If individual symbols in the formula II are a substituted phenyl group, such phenyl groups can be substituted by one to three groups of the following type: C1- C4-alkyl, C1-C4-alkoxy, halogen atoms, substituted or unsubstituted amino or ammonium groups, sulfo groups, carboxyl groups or groups of the formula xe2x80x94(CH2)r-COOH, xe2x80x94(CH2)r-SO3H, xe2x80x94(CH2)r-PO3H2, xe2x80x94(CH2)1xe2x80x94OH, where r is an integer from 0 to 4 and I is an integer from 1 to 4, and said acid groups can also be in salt form.
The novel transition metal complexes according to formula I are synthesized from a heterocyclic bridging ligand L according to formula II, e.g. 2,6-bis(4,7-dimethyl-1,4,7-triazacyclonon-1-ylmethyl)-4-methylphenol, dissolved in a polar solvent, for example an alcohol, to which, in the molar ratio 1:2, a transition metal compound, e.g. manganese(ll) acetate tetrahydrate, and the required amount of a compound comprising the counterion Y, e.g. KPF6, is added at a pH between 7 and 11 in a temperature range between 0 to 100xc2x0 C., preferably 25 to 50xc2x0 C. The bridging ligands of the formula II present in the complexes according to the invention can, for example, be synthesized analogously to the synthesis described in J. Am. Chem. Soc. 1994, 116, 22, 10334-10335, by reacting a heterocyclic compound of the type of the formula Ill
having the abovementioned definitions for D, E, R1, R2, t and s, for example 1,4-dimethyl-1,4,7-triazacyclononane, dissolved in a polar solvent, preferably an alcohol, in the presence of equimolar amounts of a base, preferably triethylamine, with a compound of the type Z-(CR1CR2)u-A(K)(R4)v-(CR1CR2)U-Z with the abovementioned definitions for R1, R2, R4, A, K, u and v, where Z is chlorine, bromine, iodine or another leaving group, in the molar ratio 2 to 1 in the temperature range from xe2x88x9230 to 80xc2x0 C., preferably xe2x88x9210 to 50xc2x0 C., in the course of 10 to 120 hours.
The novel polycyclic complexes of the formula I are highly suitable as bleaching and oxidation catalysts, in particular in detergents and cleaners, and in the bleaching of textiles and paper. Particular emphasis should be placed here on textile detergents in the form of pulverulent detergents or as liquid formulations, and dishwashing detergents. An advantage of the bleaching catalysts according to the invention is their stability to hydrolysis and oxidation and also their catalytic effect even at low temperatures. In such formulations, they not only improve the bleaching action of hydrogen peroxide, but also of organic and inorganic peroxy compounds.
The present invention accordingly also provides a method of bleaching soiled substrates in which the soiled substrate is brought into contact in an aqueous bleaching liquor with a peroxy compound and an effective amount of one or more of the novel metal complexes according to formula I, where R3 can also be hydrogen and A can also be carbon, as bleaching catalysts.
The detergent and cleaner formulations according to the invention comprise metal complexes of this type in amounts by weight of from 0.0001 to 0.5% by weight of metal, in particular 0.00025 to 0.25% by weight of metal, especially 0.0005 to 0.1% by weight of metal, based on the weight of the formulations.
These detergents and cleaners, which can be in the form of pulverulent or tablet-shaped solids, homogeneous solutions or suspensions, can, in principle, apart from the bleaching catalyst used according to the invention, comprise all known ingredients customary in such compositions, such as peroxygen compounds, bleach activators, further conventional bleaching catalysts, surfactants, builders, water-miscible organic solvents, enzymes, sequestering agents, electrolytes, pH regulators and further auxiliaries, such as silver corrosion inhibitors, foam regulators, thickeners, preservatives, pearlizing agents and emulsifiers, and dyes and fragrances.
Suitable peroxygen compounds are, in particular, organic peracids or salts of organic peracids. Examples thereof are peroxynaphthoic acid, peroxylauric acid, peroxystearic acid, N,N-phthaloylamidoperoxycaproic acid, perbenzoic acid, 1,1 2-diperoxydodecanedioic acid, 1 ,9-diperoxyazelaic acid, diperoxysebacic acid, diperoxyisophthalic acid, 2-decyldiperoxybutane-1,4-dioic acid, 4,4xe2x80x2-sulfonylbisperoxybenzoic acid and alkanoylamidoperoxycarboxylic acids. Also suitable are hydrogen peroxide and compounds which release hydrogen peroxide and at the washing and cleaning conditions, such as alkali metal peroxides, organic peroxides, such as urea/hydrogen peroxide adducts and inorganic persalts, such as the alkali metal perborates, percarbonates, perphosphates, persilicates, persulfates, peroxynitrites and hydrogen peroxocarbonate peroxohydrates. Particular preference is given to sodium perborate tetrahydrate and, in particular, sodium perborate monohydrate. Sodium perborate monohydrate is preferred because of its good storage stability and its good solubility in water. Sodium percarbonate may be preferred for environmental protection reasons. Alkyl hydroperoxides are a further suitable group of peroxide compounds. Examples of these substance are cumine hydroperoxide and butyl hydroperoxide. Also suitable as peroxy compounds are inorganic peroxi acid salts, e.g. potassium monopersulfate. Mixtures of two or more of these compounds are likewise suitable.
The detergent and cleaner formulations according to the invention usually comprise 1 to 30% by weight, in particular 2 to 25% by weight, of peroxy compounds.
The addition of small amounts of known bleach stabilizers, such as, for example, phosphonates, borates, metaborates and metasilicates and magnesium salts, such as magnesium sulfate, may be expedient.
In addition to the peroxy compounds, the detergents and cleaners can additionally also comprise bleach activators in customary amounts of from about 1 to 10% by weight.
Bleach activators which may be used are compounds which, under perhydrolysis conditions, produce aliphatic percarboxylic acids having, preferably, 1 to 10 carbon atoms, in particular 2 to 4 carbon atoms and/or optionally substituted perbenzoic acid. Suitable substances are those which carry O- and/or N-acyl groups of said number of carbon atoms and/or optionally substituted benzoyl groups. Preference is given to polyacylated alkylenediamine, in particular tetraacetylethylenediamine (TAED), acylated triazine derivates, in particular 1,5-diacetyl-2,4-dioxohexahydro-1,3,5-triazine (DADHT), acylated glycoluriles, in particular tetraacetylglycoluril (TAGU), N-acylimides, in particular N-nonanoylsuccinimide (NOSI), acylated phenolsulfonates, in particular n-nonanoyl- or isononanoyloxybenzenesulfonate (n- or iso-NOBS), alkanoylamidocarboxylic esters, in particular alkanoylamidocaproic phenolsulfonates, carboxylic anhydrides, in particular phthalic anhydride, acylated polyhydric alcohols, in particular triacetin, ethylene glycol diacetate, 2,5-diacetoxy-2,5-dihydrofuran, sodium nonanoyloxybenzenesulfonate, sodium isononanoyloxybenzenesulfonate, sodium 4-benzoyloxybenzenesulfonate, sodium trimethylhexanoyloxybenzenesulfonate, lactones, acylals, carboxamides, acyllactams, acylated ureas and oxamides, N-acylated hydantoins, for example 1-phenyl-3-acetylhydantoin, hydrazides, triazoles, hydrotriazines, urazoles, diketopiperazides, sulfurylamides and/or N-acylated lactams, for example N-benzoylcaprolactam, but also quaternary nitrile compounds, for example quaternary trialkylammonium nitrile salts, in particular the cyanomethyl-trimethylammonium salt, but also heterocyclically substituted quaternary nitrile compounds and the enol esters known from German Patent Applications DE 196 16 693 and DE 196 16 767, and acylated sorbitol and mannitol or the mixtures thereof described in EP 0 525 239 (SORMAN), acylated sugar derivatives, in particular pentaacetylglucose (PAG), pentaacetylfructose, tetraacetylxylose and octaacetyllactose, and acetylated, optionally N-alkylated glucamine and gluconolactone.
Such bleach activators are present in the customary quantitative range, for example in amounts of from 1 to 10% by weight, in particular 2 to 8% by weight, based on the total composition.
In addition to the conventional bleach activators listed above, or instead of them, it is also possible for sulfonimines and/or further bleach-enhancing transition metal salts or transition metal complexes to be present. Suitable transition metal compounds include, in particular, the manganese, iron, cobalt, ruthenium or molybdenum complexes known from DE 195 29 905 and DE 196 05 688.
As surface-active agents, the detergents and cleaners according to the invention can comprise anionic surfactants in amounts of from approximately 1 to 50% by weight, based on the total amount of all surfactants. Preferred anionic surfactants are C8-C20-fatty acid alpha-methyl ester sulfonates, alkyl ether sulfates and secondary alkanesulfonates. The alkyl ether sulfates used in the compositions according to the invention are water-soluble salts or acids of the formula RO(A)mSO3M, in which R is an unsubstituted C10-C24-alkyl or C10-C24-hydroxyalkyl radical,.preferably a C12-C20-alkyl or C12-C20-hydroxyalkyl radical, particularly preferably C12-C18-alkyl or C12-C18-hydroxyalkyl radical. xe2x80x9cAxe2x80x9d is an ethoxy or propoxy unit, m is a number greater than 0, preferably between 0.5 and about 6, particularly preferably between about 0.5 and about 3, and M is a hydrogen atom or a cation, such as, for example, a metal cation (e.g. sodium, potassium, lithium, calcium, magnesium, etc.), ammonium or a substituted ammonium cation. Specific examples of substituted ammonium cations are methyl, dimethyl, trimethylammonium and quaternary ammonium cations, such as tetramethylammonium and dimethylpiperidinium cations, and those derived from alkylamines, such as ethylamine, diethylamine, triethylamine. Examples of these alkyl ether sulfates which may be mentioned are C12-C18-alkyl polyethoxylate(1.0) sulfate, (C12-C18E(1.0)M), C12-C18-alkyl polyethoxylate(2.25) sulfate (C12-C18E(2.25)M), C12-C18-alkyl polyethoxylate(3.0) sulfate (C12-C18E(3.0)M), C12-C18-alkyl polyethoxylate(4.0) sulfate (C12-C18E(4.0)M).
ln the case of the secondary alkanesulfonates, the alkyl group can either be saturated or unsaturated, branched or linear and optionally substituted by a hydroxyl group. The sulfo group is randomly distributed over the entire carbon chain, where the primary methyl groups on the start of the chain and on the end of the chain do not have sulfonate groups. Preferred secondary alkanesulfonates contain linear alkyl chains having 9 to 25 carbon atoms, preferably from 10 to 20 carbon atoms and particularly preferably 13 to 17 carbon atoms. The cation is sodium, potassium, ammonium, mono- , di- or triethanolammonium, calcium or magnesium and mixtures thereof. For the sake of simplicity, sodium is preferred as cation.
In addition to or instead of these preferred anionic surfactants, the formulations according to the invention can also comprise other types of anionic surfactants within the limits given above, such as, for example, alkylsulfates, alkylsulfonates, alkylcarboxylates, alkylphosphates and mixtures of said compounds. Suitable cations are, for example, sodium, potassium, calcium or magnesium, and ammonium, substituted ammonium compounds, including mono- , di- or triethanolammonium cations, and mixtures of these cations. The anionic surfactants which are suitable for the present invention have surfactant properties and are water-soluble or water-dispersible.
Here, alkylsulfates are water-soluble salts or acids of the formula ROSO3M, in which R is preferably a C10-C24-hydrocarbon radical, preferably an alkyl or hydroxyalkyl radical having C10-C20-alkyl components, particularly preferably a C12-C18-alkyl or hydroxyalkyl radical. M is hydrogen or a cation, e.g. sodium, potassium, lithium or ammonium or substituted ammonium, e.g. methyl-, dimethyl- and trimethylammonium cations and quaternary ammonium cations, such as tetramethylammonium and dimethylpiperidinium cations and quaternary ammonium cations derived from alkylamines, such as ethylamine, diethylamine, triethylamine and mixtures thereof.
A further suitable anionic surfactant is alkylbenzenesulfonate. The alkyl group can either be saturated or unsaturated, branched or linear and optionally substituted by a hydroxyl group. The preferred alkylbenzenesulfonates contain linear alkyl chains having 9 to 25 carbon atoms, preferably 10 to 13 carbon atoms, and the cation is sodium, potassium, ammonium, mono-, di- or triethylammonium, calcium or magnesium and mixtures thereof.
Further suitable anionic surfactants are carboxylates, e.g. fatty acid soaps and comparable surfactants. The soaps can be saturated or unsaturated and can contain various substituents, such as hydroxyl groups or alpha-sulfonate groups. Preference is given to linear saturated or unsaturated hydrocarbon radicals as hydrophobic component in the soaps. The hydrophobic components usually contain 6 to 30 carbon atoms, preferably 10 to 18 carbon atoms. Further anionic surfactants are salts of acylaminocarboxylic acids, which are formed by reacting fatty acid chlorides with sodium sarcosinate in alkaline medium (acyl sarcosinates), and also fatty acid protein condensation products which are obtained by reacting fatty acid chlorides with oligopeptides. The salts of alkylsulfamidocarboxylic acids and the salts of alkyl and alkylaryl ether carboxylic acids also have surfactant character.
Other anionic surfactants which are useful for use in cleaners are C8- C24 olefinsulfonates, sulfonated polycarboxylic acids prepared by sulfonating the pyrolysis products of alkaline earth metal citrates, as described, for example, in GB 1 082 179, alkyl glycerol sulfates, fatty acyl glycerol sulfates, oleyl glycerol sulfates, alkyl phenol ether sulfates, primary paraffinsulfonates, alkylphosphates, alkyl ether phosphates, isethionates, such as acyl isethionates, N-acyltaurides, alkylsuccinamates, sulfosuccinates, monoesters of sulfosuccinates (particularly saturated and unsaturated C12-C18-monoesters) and diesters of sulfosuccinates (particularly saturated and unsaturated C12-C18-diesters), acylsarcosinates, sulfates of alkylpolysaccharides, such as sulfates of alkylglycosides, branched primary alkylsulfates and alkylpolyethoxycarboxylates, such as those of the formula RO(CH2CH2)kCH2COOM, in which R is a C8-C22-alkyl, k is a number from 0 to 10 and M is a cation which forms a soluble salt. Resin acids or hydrogenated resin acids, such as rosin or hydrogenated rosin or tall oil resins and tall oil resin acids can likewise be used. Further examples are described in xe2x80x9cSurface Active Agents and Detergentsxe2x80x9d (Vol. I and II, Schwartz, Perry and Berch). A large number of such surfactants are also described in U.S. Pat. No. 3 929 678. Typical examples of anionic surfactants are also alkyl ether sulfonates, glycerol ether sulfonates, sulfo fatty acids, fatty alcohol ether sulfates, glycerol ether sulfates, hydroxy mixed ether sulfates, fatty acid amide (ether) sulfates, mono- and dialkylsulfosuccinates, mono- and dialkylsulfosuccinamates, sulfotriglycerides, amide soaps, alkyloligoglucosidesulfates, alkylamino sugar sulfates and alkyl (ether) phosphates. If the anionic surfactants contain polyglycol ether chains, they can have a conventional or a narrowed homolog distribution. In the compositions according to the invention it is possible to use nonionic surfactants, such as fatty acid alkyl ester alkoxylates, alkyl and/or alkenyl oligoglycosides, fatty alcohol polyglycol ethers, alkylphenol polyglycol ethers, fatty acid polyglycol esters, fatty acid amide polyglycol ethers, fatty amine polyglycol ethers, alkoxylated triglycerides, fatty acid glucamides, polyoil fatty acid esters, sugar esters, sorbitan esters and polysorbates and/or alkoxylated fatty alcohols. The proportion of nonionic surfactants overall relative to the total amount of all surfactants in the cleaners according to the invention is generally 1 to 50% by weight.
Furthermore, in the compositions according to the invention it is possible to use foam-enhancing cosurfactants from the group consisting of alkylbetaines, alkylamidobetaines, aminopropionates, aminoglycinates, imidazoliniumbetaines and sulfobetaines, amine oxides and fatty acid alkanolamides, particularly the monoethanolamides of palm kernal oil and coconut oil fatty acids or polyhydroxyamides in the amounts from 1 to 50% by weight.
The total amount of surface-active compounds can be up to 50% by weight, preferably 1 to 40% by weight, in particular 4 to 25% by weight, of the overall detergent or cleaner.
Suitable organic and inorganic builders are neutral or, in particular, alkaline salts which can precipitate out calcium ions or form complexes with them. Suitable and particularly ecologically acceptable builder substances are crystalline, layered silicates of the formula NaMSi(X)O(2xc3x97+1), where M is sodium or hydrogen, x is a number from 1.9 to 22, preferably from 1.9 to 4 and y is a number from 0 to 33, for example Na SKS-5 (xcex1-Na2Si2O5), Na SKS-7 (xcex2-Na2Si2O5, natrosilite), Na SKS- 9 (NaHSi2O5*H2O), Na SKS-10 (NaHSi2O3*3H2O, canemite), Na SKS-11 (t-Na2Si2O5) and Na SKS-1 3 (NaHSi2O5), but in particular Na SKS- 6 (xcex4-Na2Si2O5), and finally crystalline synthetic hydrous zeolites, in particular of the type NaA, which have a calcium-binding capacity in the range from 100 to 200 mg of CaO/g. Zeolites and phyllosilicates can be present in the composition in an amount of up to 20% by weight. Also suitable are non-neutralized or partially neutralized (co)polymeric polycarboxylic acids. These include the homopolymers of acrylic acid or of methacrylic acid or copolymers thereof with further ethylenically unsaturated monomers, such as, for example, acrolein, dimethylacrylic acid, ethylacrylic acid, vinyl acetic acid, allyl acetic acid, maleic acid, fumaric acid, itaconic acid, (meth)allylsulfonic acid, vinylsulfonic acid, styrenesulfonic acid, acrylamidomethylpropanesulfonic acid, and monomers containing phosphorus groups, such as, for example, vinylphosphoric acid, allylphosphoric acid and acrylamidomethylpropanephosphoric acid and salts thereof, and hydroxyethyl(meth)acrylate sulfate, allyl alcohol sulfate and allyl alcohol phosphates.
Preferred (co)polymers have a mean molar mass from 1000 to 100,000 g/mol, preferably from 2000 to 75,000 g/mol and in particular from 2000 to 35,000 g/mol. The degree of neutralization of the acid groups is advantageously 0 to 90%, preferably 10 to 80% and in particular 30 to 70%.
Suitable polymers include, in particular, homopolymers of acrylic acid and copolymers of (meth)acrylic acid with maleic acid or maleic anhydride.
Further suitable copolymers are derived from terpolymers which can be obtained by polymerizing from 10 to 70% by weight of monoethylenically unsaturated dicarboxylic acids having 4 to 8 carbon atoms, salts thereof, 20 to 85% by weight of monoethylenically unsaturated monocarboxylic acids having 3 to 10 carbon atoms or salts thereof, 1 to 50% by weight of monounsaturated monomers which, following hydrolysis, release hydroxyl groups at the polymer chain, and 0 to 10% by weight of further, free-radically copolymerizable monomers.
Likewise suitable are graft polymers of monosaccharides, oligosaccharides, polysaccharides and modified polysaccharides, and animal or vegetable proteins. Preference is given to copolymers of sugar and other polyhydroxy compounds and a monomer mixture of 45 to 96% by weight of monoethylenically unsaturated C3- to C10-monocarboxylic acids or mixtures of C3- to C10-monocarboxylic acids and/or salts thereof containing monovalent cations, 4 to 55% by weight of monomers containing monoethylenically unsaturated monosulfonic acid groups, monoethylenically unsaturated sulfuric esters, vinylphosphoric esters and/or the salts of these acids containing monovalent cations, and 0 to 30% by weight of water-soluble unsaturated compounds which have been modified with 2 to 50 mol of alkylene oxide per mol of monoethylenically unsaturated compounds.
Further suitable polymers are polyaspartic acid or derivatives thereof in non-neutralized or only partially neutralized form. Particularly suitable are also graft polymers of acrylic acid, methacrylic acid, maleic acid and further ethylenically unsaturated monomers to salts of polyaspartic acid, as are customarily produced during the above-described hydrolysis of polysuccinimide. In this connection, it is possible to dispense with the otherwise necessary addition of acid for the preparation of the only partially neutralized form of polyaspartic acid. The amount of polyaspartate is usually chosen such that the degree of neutralization of all of the carboxyl groups incorporated in the polymer does not exceed 80%, preferably 60%.
Further builders which can be used are, for example, the percarboxylic acids, preferably used in the form of their sodium salts, such as citric acid, in particular trisodium citrate and trisodium citrate dihydrate, nitrilotriacetic acid and its water-soluble salts; alkali metal salts of carboxymethyloxysuccinic acid, ethylenediaminetetraacetic acid, mono-, dihydroxysuccinic acid, xcex1-hydroxypropionic acid, gluconic acid, mellitic acid, benzopolycarboxylic acids and [lacuna] as disclosed in U.S. Pat. No. 4,144,226 and 4,146,495. Phosphate-containing builders, for example alkali metal phosphates, which can be in the form of their alkaline, neutral or acidic sodium or potassium salts, are also suitable. Examples thereof are trisodium phosphate, tetrasodium diphosphate, disodium dihydrogenphosphate, pentasodium triphosphate, so-called sodium hexametaphosphate, oligomeric trisodium phosphate with amounts of oligomerization in the range from 5 to 1000, in particular 5 to 50, and mixtures of sodium and potassium salts. The builder substances can be present in amounts of from 5% by weight to 80% by weight, preference being given to a proportion of from 10% by weight to 60% by weight.
The desired viscosity of the compositions can be adjusted by adding water and/or organic solvents or by adding a combination of organic solvents and thickeners.
In principle, suitable organic solvents are all mono- or polyhydric alcohols. Preference is given to using alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, propanol, isopropanol, straight-chain and branched butanol, glycerol and mixtures of said alcohols. Further preferred alcohols are polyethylene glycols having a relative molecular mass below 2000. In particular, the use of polyethylene glycol having a relative molecular mass between 200 and 600 and in amounts of up to 45% by weight, and of polyethylene glycol having a relative molecular mass between 400 and 600 in amounts of from 5 to 25% by weight is preferred. An advantageous mixture of solvents consists of monomeric alcohol, for example ethanol and polyethylene glycol in the ratio 0.5:1 to 1.2:1.
Further suitable solvents are, for example, triacetin (glycerol triacetate) and 1-methoxy-2-propanol.
The thickeners used are preferably hydrogenated castor oil, salts of long-chain fatty acids, which [lacuna] preferably in amounts of from 0 to 5% by weight and in particular in amounts of from 0.5 to 2% by weight, for example sodium, potassium, aluminum, magnesium and titanium stearates or the sodium and/or potassium salts of behenic acid, and polysaccharides, in particular xanthan gum, guar guar, agar agar, alginates and Tyloses, carboxymethylcellulose and hydroxyethylcellulose, and also higher molecular weight polyethylene glycol mono- and diesters of fatty acids, polyacrylates, polyvinyl alcohol and polyvinylpyrrolidone, and electrolytes such as sodium chloride and ammonium chloride. Suitable thickeners are water-soluble polyacrylates which have, for example, been crosslinked with approximately 1 % of a polyallyl ether of sucrose, and which have a relative molecular mass above one million. Examples thereof are the polymers obtainable under the name Carbopol(copyright) 940 and 941. The crosslinked polyacrylates are used in amounts not exceeding 1% by weight, preferably in amounts of from 0.2 to 0.7% by weight.
Suitable enzymes are those from the class of proteases, such as BLAP, Optimase, Opticlean, Maxacal, Maxapem, Esperase, Savinase, Purifect OxP and/or Durazym, lipases, such as Lipolase, Lipomax, Lumafast and/or Lipozym, amylases, such as Termamyl, Ainylase-LT, Maxamyl, Duramyl and/or Purafect OxAm, and cutinases, pullulanases and mixtures thereof. Their proportion can be from 0.2 to 1% by weight. The enzymes can be adsorbed to carrier substances and/or embedded in coating substances.
Possible silver corrosion inhibitors are the compounds given in DE 196 49 375.
As foam regulators, it is possible to add, preferably, up to 6% by weight, in particular about 0.5% by weight to 4% by weight, of foam-suppressing compounds, preferably from the group of silicone oils, mixtures of silicone oil and hydrophobicized silica, paraffins, paraffin/alcohol combinations, hydrophobicized silica, bis-fatty acid amides and other known commercially available antifoams.
To set a desired pH which does not result by mixing the other components by itself, the compositions according to the invention can comprise system- and environmentally-compatible acids, in particular citric acid, acetic acid, tartaric acid, malic acid, lactic acid, glycolic acid, succinic acid, glutaric acid and/or adipic acid, or else mineral acids, in particular sulfuric acid or alkali metal hydrogensulfates or bases, in particular ammonium or alkali metal hydroxides. Such pH regulators are present in the compositions according to the invention in amounts which, preferably, do not exceed 10% by weight, in particular in amounts of from 0.5% by weight to 6% by weight.
Examples of suitable preservatives are phenoxyethanol, formaldehyde solution, pentanediol or sorbic acid. Suitable pearlizing agents are, for example, glycol distearic esters, such as ethylene glycol distearate, but also fatty acid monoglycol esters. Suitable salts or extenders are, for example, sodium sulfate, sodium carbonate or sodium silicate (water glass).
Typical individual examples of further additives which can be mentioned are sodium borate, starch, sucrose, polydextrose, RAED, stilbene compounds, methylcellulose, toluene sulfonate, cumene sulfonate, soaps and silicones.
The bleaching catalysts of this invention can be used in a large number of products. These include textile detergents, textile bleaches, surface cleaners, toilet cleaners, dishwasher detergents and also denture cleaners. The detergents can be in solid or liquid form.
For reasons of stability and handlability, it is advantageous to use the bleach activators in the form of granules which, in addition to the bleaching catalyst, comprise a binder. Various methods of preparing such granules are described in the patent literature, for example in Canadian Patent No. 1102966, GB 1561333, U.S. Pat. No.4087369, EP 240057, EP 241962, EP 101634 and EP 62523. The granules which comprise the bleaching catalyst according to the invention are generally added to the detergent composition together with the other dry constituents, such as, for example, enzymes, inorganic peroxide bleaches. The detergent composition to which the catalyst granules are added can be obtained in a variety of ways, such as, for example, mixing the dry components, extruding or spray-drying.
In a further embodiment, the bleaching catalysts according to the invention are particularly suitable for non-aqueous liquid detergents, together with a bleaching peroxide compound as described in EP-0 869 171. These are compositions in the form of a non-aqueous liquid medium in which a solid phase can be dispersed. The non-aqueous liquid medium can be a liquid, surface-active substance, preferably a nonionic surface-active substance, a nonpolar liquid medium, such as, for example, liquid paraffin, a polar solvent, such as, for example, polyols, for example glycerol, sorbitol, ethylene glycol, possibly in conjunction with low molecular weight monohydric alcohols, such as ethanol or isopropanol or mixtures thereof.
The solid phase can consist of builder substances, alkalis, abrasive substances, polymers and solid ionic surface-active compounds, bleaches, fluorescent substances and other customary solid ingredients.
The examples below serve to illustrate the invention in more detail without limiting it thereto.

Abstract: Compounds of the formula I

Abstract: are claimed, where L is a ligand of the formula II

Abstract: and the individual symbols have the meanings defined in the description. The metal complexes are suitable as bleaching catalysts in detergents, cleaners and disinfectants which comprise peroxy compounds.


Spray on polyurethaneurea coatings provide corrosion resistance over long periods of time to marine fixtures, particularly of active metals such as aluminum and steel. Radar arches, fishing platforms, railing systems, etc. can maintain their aesthetics over extended periods of time, even in salt water environments, when the coating has been penetrated to the metal surface.

1. Field of the Invention
The present invention is directed to a process for preparing corrosion-resistant articles for marine use, and the products prepared by the process.
2. Background Art
Metal articles and structures are widely used in the marine field, particularly in pleasure craft, fishing boats, and the like. Unless stainless steel or certain marine bronzes are used to manufacture such articles, corrosion, with its associated aesthetic problems and failure modes can be expected to severely limit product lifetime. Even when these two relatively corrosion-resistant classes of materials are used, corrosion may still take place, particularly in salt water or brackish environments. It is partially for this reason that pleasure boats operated in salt water have considerably lower resale value than similar vessels operated in fresh water.
Corrosion problems are most severe when more active metals such as magnesium, aluminum, and carbon steel are used. Such items may become severely corroded over relatively short periods of time in salt water environments.
To lessen the corrosive effects on metals, it has been common to provide surface treatments. Chrome and nickel plating have been used, for example. However, plating is relatively expensive, particularly when large fabricated structures constructed by welding are to be plated. In addition, such plating procedures do not work well on many active metals such as aluminum.
Anodizing has also been used to increase corrosion resistance, and is effectively used on small parts. However, large tubular structures such as radar arches are typically welded together. The anodized coating is destroyed locally during the welding process. Anodizing very large, prefabricated structures is not cost-effective.
Painting has long been used to provide corrosion resistance, and literally hundreds, if not thousands, of coating systems have been proposed. Powder coating systems, for example using epoxy-type powdered resins which are subsequently heat cured can produce excellent finishes. However, powder coating of large articles becomes expensive due to the size of the cure oven necessary. Moreover, powder coating systems exhibit the same corrosion deficiencies associated with other coatings.
Use of conventional, solvent-borne coatings is becoming increasingly difficult due to environmental legislation limiting emissions of volatile organic compounds (VOCs). Moreover, most such coatings do not provide the necessary levels of corrosion protection, and application to substrates involves a time and labor-extensive combination of primer application, smoothing filler, and topcoat application, with numerous sanding and smoothing steps in-between.
A problem with coatings subject to corrosion occurs when a prefabricated structure is altered to mount to non-standard surfaces or to mount additional components thereon. For example, flybridges and radar arches are often used to mount flag holders, GPS and RF antennae, hand holds, cleats, xe2x80x9crocket launcherxe2x80x9d fishing pole receptacles, and the like. Drilling the necessary mounting holes into the coated structure penetrates the coating, exposing untreated metal to the environment. Corrosion rapidly occurs at such areas, frequently spreading between the coating and its metal substrate causing ultimate separation of the coating.
It would be desirable to provide a process by which metal (and non-metal) articles slated for marine use could be coated with a corrosion-resistant coating employing a minimum of finishing steps. It would further be desirable to provide a coating which offers extended corrosion resistance even after having had bare metal exposed.
It has now been surprisingly discovered that a two-part polyurethaneurea coating derived from a low viscosity isocyanate-terminated prepolymer and a mixture of diamine and hydroxyl-functional curing agents can be applied to marine products by conventional spraying techniques to produce a smooth, corrosion-resistant coating which maintains its corrosion resistance even after exposure of bare metal to the environment by penetration of the coating, and even under salt spray conditions.
The process of the present invention involves coating marine articles with a two-part coating polyurethaneurea composition at elevated temperature, and allowing the coating to cure to a corrosion-resistant film.
The articles to be coated include both metal and non-metal articles to be used in marine environments. Preferably, the articles are metal items used as fittings and structures on watercraft. Non-limiting examples include cleats, plates antennas, antenna mounts, radar arches, bow rails, rub rails, fishing pole holders, downrigger mounts, rails, stanchions, swim platform supports, exhaust ports, mast bases, back stays, chain plates, transom, swim, and boarding ladders, tuna towers, fishing platforms, flybridges, anchors, anchor rollers, and the like. The metal substrate may be any metal, for example brass, bronze, bright metal, zinc, magnesium, aluminum, steel, stainless steel, and the like. Preferred are steel (non-stainless), stainless steel, chrome-plated metals, aluminum, and magnesium. Terms such as aluminum, magnesium, bronze, etc. include the various alloys of these metals. Preferred non-metal substrates are thermoplastic sheet material and fiber-reinforced thermoset and fiber-reinforced thermoplastics. Fiber reinforcement of the latter includes fiberglass, thermoplastic fiber, carbon fiber, ceramic fiber, etc., whether in the form of strands, tow, yarn, woven or non-woven products, felted products, and whether the fiber reinforcement is short fiber, long fiber, continuous fiber, etc.
The two-part polyurethaneurea coating is supplied in at least two components to a spray gun. Although it is possible to supply three or more components, it is simple and most economical to supply the components in what are conventionally termed xe2x80x9cA-sidexe2x80x9d and xe2x80x9cB-sidexe2x80x9d components, the A-side containing the isocyanate-functional components and the B-side containing the isocyanate-reactive components.
Both the A-side and B-side desirably have viscosities which are below 500 cp at the spray temperature in order for sufficient mixing and atomization to take place However, higher viscosities are possible provided suitable mixing and atomization can be achieved.
The components are preferably VOC-free. By VOC-free is meant that no added solvent is employed. The coating components are substantially 100% solids. However, it is possible to add minor amounts of solvent, particularly when component viscosity is higher than desired. In such cases, addition of up to 20 weight percent solvent, more preferably 10 weight percent or less, and most preferably 5 weight percent or less of solvent may be practiced. When solvent is added, it is preferably that the solvent be a xe2x80x9czero-VOCxe2x80x9d solvent, i.e., a solvent which is not viewed as contributing to environmental problems. Such solvents are known, for example, in U.S. Pat. No. 6,048,471. An example of such a solvent is t-butylacetate. Mixtures of such solvents may also be used.
The A-side of the polyurethaneurea coating is an isocyanate-terminated prepolymer prepared by reacting an excess of a diisocyanate with a difunctional polyoxyalkylene polyol. The isocyanate is in excess such that an NCO-group content of preferably from about 2 weight percent to about 12 weight percent, more preferably 4 weight percent to 8 weight percent is obtained. The diisocyanates employed are preferably mononuclear cyclic diisocyanates such as isophorone diisocyanate or the toluene diisocyanates, preferably a commercial mixture of 2,4- and 2,6-toluene diisocyanates. While straight chain aliphatic isocyanates such as 1,6-hexane diisocyanate may also be used, their use is less preferred. Also less preferred are the polynuclear diisocyanates such as 2,4xe2x80x2-, 2,2xe2x80x2 and 4,4xe2x80x2-methylene diphenylene diisocyanates. The preferred diisocyanates are an 80:20 blend of 2,4- and 2,6-toluene diisocyanate.
The polyol component employed to react with the isocyanate to form the A-side prepolymer is a 300 to 4000 Da average molecular weight hydrophobic polyoxyalkylene diol. The term xe2x80x9caverage molecular weightxe2x80x9d as used herein is the molecular weight calculated from the polyol hydroxyl number assuming the theoretical functionality of the polyol, not its actual, measured functionality. By xe2x80x9chydrophobicxe2x80x9d is meant that the polyol contains insufficient polyoxyethylene groups to provide substantially hydrophilic segments. Such an amount is 20 weight percent or less, preferably randomly distributed, with no more than 10 weight percent as an internal or external block. Preferably, the hydrophobic polyol contains no oxyethylene moieties.
Preferably, the hydrophobic polyol is a mixture of one or more polytetramethylene ether glycols (PTMEG) and/or low unsaturation polyoxypropylene diols with an unsaturation less than 0.010 meq/g polyol. The polyol component preferably has an average molecular weight between about 500 Da and 2000 Da, more preferably between 600 Da and 1000 Da. Most preferably, mixtures of two different hydrophobic polyols, generating a polyol blend having a bimodal molecular weight distribution is employed. Most preferably, a blend of 1000 Da and 650 Da PTMEG is used. The prepolymer is prepared by conventional prepolymer techniques, i.e., by admixing the isocyanate and polyol components and heating, with or without catalyst, until the isocyanate group content stabilizes. Reference may be had to Saunders and Frisch, Polyurethanes, CHEMISTRY AND TECHNOLOGY, Wiley Interscience, New York.
Although the A-side is most preferably entirely difunctional, it would not depart from the spirit of the invention to include a small percentage, i.e., 10 equivalent percent or less, based on the diol component, of a triol, tetrol or higher functional polyether, preferably 5 equivalent percent or less. Likewise, a tri- or higher functional isocyanate could be used in similar proportions. The presence of other than difunctional components generally increases coating hardness and solvent resistance, but at the expense of increased A-side viscosity and decreased elongation and flexibility. Thus, a two-functional A-side prepolyrmer is desired.
The B-side comprises a diamine and a polyol. The diamine is preferably a sterically hindered diamine such as diethyltoluene diamine, although other diamines such as 2,4-, 2,6-, and 3,5-toluene diamine, ethylene diamine, 1,6-diaminohexane, isophorone diamine, and the like may also be used. Bi- or polynuclear diamines such as 2,2xe2x80x2-, 2,4xe2x80x2-, and 4,4xe2x80x2-methylenedianiline may also be used.
The polyol components of the B-side may be the same polyols as used in the A-side prepolymer, although a mixture of polyols is not preferred. The polyol may preferably be a 200 Da to 4000 Da PTMEG or low unsaturation polyoxypropylene diol, more preferably 400 Da to 2000 Da. Most preferably, a polyoxypropylene diol is employed with diethyltoluene diamine (DETA) in a DETA/polyol weight ratio of about 2:1. The polyoxypropylene diol may be a low unsaturation diol.
The coating is preferably clear, although pigments may be added if desired. Suitable pigments include those commonly known, for example titanium dioxide, iron oxides, metal chromates, metal sulfides, and the like, as well as organic pigments of a wide range of chemical constitution and color. Preferably, no pigments are added. The coating may also contain conventional additives such as flow control agents, rheology modifiers, etc. However, it has been found that such are generally unnecessary.
It is also possible to employ the present coating composition as a base coat, and to spray a top coat, preferably a pigmented top coat, over the polyurethaneurea base coat. Primer coats are generally used, but are not always necessary. A preferred primer is NR-9500 primer, a two-part primer available from Normac Adhesive Products, Inc., Burlington, Ontario, Canada. Primer thickness is generally rather thin, for example between 12.5 xcexcm and 25 xcexcm. The primer is generally applied to surfaces which have been cleaned and degreased by conventional methods.
It has been found that the coatings employed in the inventive process provide a pleasing, aesthetic appearance without the expenditure of numerous man hours or priming, sanding, filling, and other steps. Unlike the majority of other coatings, it is also possible to provide a clear coat of the polyurethaneurea, optionally with underlying primer, whereas many competing products rely on heavy loadings of pigments and finely divided metals to provide corrosion resistance.
Upon drilling through a coating structure, it is still advisable to employ a gel-like or grease-like protectant, i.e., a teflon-containing protectant such as Tefgel(trademark), available from Ultra Safety Systems, to cover exposed bare metal. This is especially so when fasteners of a different material are used, allowing the possibility of galvanic corrosion to occur between dissimilar metals. Teflon coated stainless steel fasteners are recommended for the same reason. However, unlike other coatings which blister, crack, peel, or separate despite such precautions, the present coatings perform exceedingly well over long periods of time despite penetration of the polyurethaneurea coating down to the bare metal.
Particularly preferred A-side and B-side are those previously described, and also those described in U.S. Pat. No. 4,267,299, incorporated herein by reference. A particularly preferred system is NR-95LVHS plural component sprayable urethane, available from Normac Adhesive Products, Inc., Burlington, Ontario, Canada. This product is a TDI prepolymer of a mixture of 650 Da and 1000 Da PTMEG glycols (A-side) and a 2:1 by weight blend of DETA and polyoxypropylene diol as the B-side.
The viscosity of the A and B components, particularly the A component, is generally rather high at room temperature, and thus it is preferred to heat the components prior to mixing and spraying to reduce their viscosity when necessary. The component(s) are preferably heated to a temperature where the most viscous of the two components has a viscosity of 500 cp or less. It is generally impractical to apply the coating at component temperatures in excess of 200xc2x0 F. and temperatures below 180xc2x0 F. are preferred. With the preferred system, spraying temperatures of 150-160xc2x0 F. have proven practical.
Conventional spray equipment suitable for handling heated components may be used for application. The A and B sides are supplied from separate pails, drums, or tanks, and are heated in line prior to being mixed when the component(s) viscosity warrants. Mixing may take place prior to the spray head by mechanical or static mixing, i.e., by an in line static mixer, or may take place in the spray head itself. The A and B ratios can be adjusted to provide the desired NCO/OH ratio. An NCO/OH ratio of 0.85 to 1.15 is preferably used, more preferably 0.90 to 1.10, and most preferably 0.95 to 1.05. The latter ratio has proven to be very satisfactory. With the most preferred system, the A-side is supplied in a 2:1 volume ratio with the B-side.
A preferred spray application system is the TBM spray system available from Normac Adhesive Products, Inc. This system employs a heated A-side with both static mixing as well as impingement mixing, along with individual piston-type pumps for the respective sides to eliminate ratio variances due to viscosity changes. The spray gun is the Probler gun manufactured by Glass Craft, with an adapter to fit Graco RAC IV spray tips.
When a primer coat is utilized, the polyurethaneurea coating is preferably applied within a time frame of 1 to 24 hours. The polyurethaneurea coating is generally applied in a thickness of minimally 10 mil, and as high as 500 mil or higher. It is noted that the polyurethaneurea has substantial strength and modulus, and therefore decreased part weight can be employed, compensating by employing a thicker polyurethaneurea coating. The coating is typically applied at a thickness of 10 to 60 mil, preferably 20 to 40 mil per coat, with additional coats used to supply the total coating thickness desired. Additional coats are preferably applied prior to complete cure of the previous coating, in particular within two hours from application of the first coat. If this preferred application window is missed, further treatment of the prior coating surface, i.e., sanding, steel wooling, grit blasting, solvent-treating, etc., may be necessary for full adhesion.
The present invention also pertains to marine structures having a metal frame, a thin surface of plastic or fiber-reinforced polymer over the frame, and a substantial layer, i.e., preferably from 100 to 200 mil or higher of a polyurethaneurea coating which provides form-holding capability to the structure, i.e., supplies a considerable portion of the overall rigidity of the structure. Substructures of aluminum and thin plastic film of a thickness similar to that of shrink wrap may be coated to form a substantial structure by this process, for example.

Corrosion-resistant metal articles for marine applications