GB2068034A - Polyurethane Polymer Amine Salt as a Paper Additive - Google Patents

Abstract

Improved paper and paper products exhibiting increased wet and dry tensile strength and increased stiffness are achieved by the use of the polyurethane amine salt of specification 2,048,289A as an additive to the pulp or by spraying a web with an aqueous solution or dispersion of the polyurethane amine salt. Various types of latex polymers may also be used along with the polyurethane amine salt as paper making additives.

Description

SPECIFICATION Polyurethane Polymer Amine Salt as a Paper Additive This invention relates to a process for improving the properties of products obtained from aqueous suspensions of cellulose fibres, wood pulp, or synthetic fibres and mixtures thereof. In particular, the invention is concerned with a process for increasing the wet strength of paper, carton, cardboard and other products prepared from aqueous suspensions of the aforementined raw materials by processes involving shaping. In order to simplify the description of the invention, the end products of these processes are generally referred to below as paper.

It is already known that paper has a characteristic property which makes it unsuitable for many applications, namely the limited resistance of its fibrous structure to the action of water and other liquids. The bonds existing between the paperforming fibres are loosened or eliminated through swelling so that the mechanical strength of the paper when it is wet is reduced very considerably and the paper itself is converted back into the originaily shapeless fibrous pulp.

The large consumption and wide variety of paper products has created a great need for continuing efforts in the field of chemical additives which will impart various physical properties to the paper products. Among the more important of the strength improving chemical additives are the synthetic or starch-derived cm tonic polymers, oxidatively cross-linked starch xanthates (low. Patent No. 3,160,552), and starch polyethyleneiminothiourethane (U.S. Patent No. 3,436,305) which is made by reacting starch xanthate with polyethleneimine. There are several strength factors, which must be considered when producing paper products.These include wet and dry-tensile, dry-burst strength, crush resistance, tear factor, fold endurance, and pick resistance. Most of the prior art additives will improve either the wet strength or certain of these dry properties, sometimes at the expense of other properties. One problem that often occurs is low retention of the additive, which then ends up in the white water creating an environmental problem.

Many substances are placed into aqueous suspension of paper pulp fibres in an attempt to produce improved paper and paper products. Chemicals are frequently added to various types of paper pulps to produce finished paper having improved properties, such as wet and dry strength, increased tear resistance, better suiface charac'enstics, and the like. Also, chemicals are added to paper pulps to improve the manufacturing characteristics o-i the pulp as k is processed from an aqueous slurry into a finished sheet.For example, chemicals are added to improve fine and filler retention and to improve the receptivity of the paper for various additives, all of which processes have as their main objective producing better paper with less wastage or better utilization of raw material.

It would be a valuable contribution to the art if a paper-making process and additive or additives could be provided which could produce finished paper products having improved chemical and mechanical characteristics, could be used either alone or in combinations with other known additives for paper at low economical doses, and which would incorporate itself into the paper and be intimately combined therewith to provide a finished paper having improved characteristics.

Also of importance would be a chemical additive for paper pulp which could be used in the various types of papermaking processes such as, for example, mechanical pulping, soda processing, sulphite processing, sulphate processing and semichemical processing. Of further utility would be an additive which would work over a wide variety of pH ranges, would be relatively compatible with other known papermaking additives, and would uniformly distribute itself throughout the pulp so that the finished paper contained the additive as an integral part thereof.

This invention is based upon the concept that improved paper and paper products are afforded either by (1) adding to an aqueous pulp slurry a novel heat curable polyurethane polymer amine salt, forming the web and curing the web or by (2) spraying on or impregnating a web prior to the drying stage in the paper making operation with a heat curable polyurethane polymer amine salt in an aqueous system.

The novel polyurethane polymer amine salt is the subject of our Application No. 8,014,327 to which reference is made for a detailed description.

The polyurethane polymer amine salt consists essentially of the reaction product of an NCOterminated prepolymer blocked with an oxime, reacted with an amine and then further reacted with an acid whereby inifinitely water dilutabie waterborne polyurethane polymer amine salts are obtained.

As used throughout this application the term "waterborne" will indicate the state or condition of the amine salts of the amine reaction product with the oxime blocked isocyanate prepolymers in an aqueous medium. It is not always apparent whether the polyurethane polymers in water are a microscopically heterogeneous mixture of two or more finely divided phases, i.e., liquid in liquid, and thus a dispersion, or whether the polyurethane polymers are partially or wholly dissolved in the aqueous base and thus a solution.

We have observed the polyurethane polymers in water where the resulting product appears to be optically clear indicating a homogeneous solution. In this situation we believe that the individual molecules of polyurethane polymers are not bound together. On the other hand we have also observed polyurethane polymers in water where the resulting product is cloudy indicating a dispersion. Thus when used in this application the term "waterborne" will mean the novel amine salts in an aqueous system and may be either a homogeneous solution, a dispersion or any combination thereof.

In order to provide a satisfactory end product having adequate film forming characteristics it has been recognized that branched reactants must be included in the preparation of the waterborne polyurethane in order to get the necessary cross-linking to produce a three dimensional polymeric structure upon curing. Therefore it is understood throughout the following description that either the polyol, the polyfunctional amine, the prepolymer, a portion of each or any combination thereof shall have a reactive functionality greater than two.

The novel polyurethane polymer amine salt is made in four basic steps. First, a polyol is reacted with a polyisocyanate to prepare an NCO-terminated prepolymen The prepolymer is blocked with an oxime in the second step. Third, the oxime blocked NCO-terminated prepolymer is reacted with one or more selected polyfunctional amines as hereinafter described. The amine reaction product is reacted with an acid. We have found that in order to obtain a product with useful properties that a reactant having functionality greater than 2 should be used in the first and/or third steps. Thus functionality of the NCO-prepolymer plus functionality of the polyfunctional amine will be greater than four.

It has been found that the reaction product of the polyfunctional amines with the oxime blocked NCO-terminated prepolymertends to increase in viscosity with time until a complete gelation/setting up of the product occurs. Thus in another aspect it has unexpectedly been discovered that the gelation time and viscosity of the waterborne polyurethane polymer dispersion can be controlled and/or adjusted by the addition of a secondary amine to the reaction product.

The isocyanate capped polyoxyalkylene polyol, NCO-terminated prepolymer or urethane prepolymer useful in the invention are prepared by reacting polyoxyalkylene polyol with an excess of polyisocyanate, e.g., toluene diisocyanate. The polyol should have a molecular weight of from about 200 to about 200 to about 20,000, and preferably from about 600 to 6,000. The hydroxyl functionality of the polyol and the corresponding isocyanate functionality following reaction is from 2 to about 8.

When the isocyanate functionality of the prepolymer is two the functionality of the step 3 amine reactant must be greater than two. When the isocyanate functionaiity of the prepolymer is greater than two the functionaiity of the amine reactant in step 3 may be as little as two.

The preferred isocyanate capped or NCO-terminated prepolymer consists of a mixture of (1) an isocyanate capped hydrophil,c polyoxyethylene diol, said diol having an ethylene oxide content of at least 40 mole percent: and (2) an isocyanate capped polyol having a hydroxy functionality in the range 3 to 8 prior to capping; said isocyanate capped polyol being present in an amount in the range 2.9 to 50% by weight of(1) and (2).

The polyoxyethylene diol is the reaction product of alkylene oxides of which at least 40 mole percent is ethylene oxide with an initiator such as ethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol or mixtures thereof. Preferably the molecular weight of the diol is between about 400 to about 6,000.

Examples of suitable polyols (to be capped with polyisocyanates) include: (A) essentially linear polyols formed, for example, by reaction of ethylene oxide with ethylene glycol as an initiator Mixtures of ethylene oxide with other alkylene oxides can be employed so long as the mole percent of ethylene oxide is at least 40 percent. Where the linear polyethers are mixtures of ethylene oxide with e.g., propylene oxide, the polymer can be either random or a block copolymer. A second class of polyol (B) includes those with a hydroxy functionality of 3 or more. Such polyols are commonly formed by reacting alkylene oxides with a polyfunctional initiator such as trimethylolpropane, pentaerythritol, etc.

In forming the polyol B, the alkylene oxide used can be ethylene oxide or mixtures of ethylene oxide with other alkylene oxides as described above. Useful polyols can be further exemplified by (C) linear branched polyfunctional polyols as exemplified in A and B above together with an initiator or crosslinker. A specific example of C is a mixture of polyethylene glycol (m.w. about 1,000) with trimethylolpropane, trimethylolethane or glycerine. This mixture can be subsequently reacted with excess polyisocyanate to provide a prepolymer useful in the invention. Alternatively, tile linear or branched polyols, (e.g. polyethylene glycol) can be reacted separately with excess polyisocyanate. The initiator, e.g. trimethylolpropane, can also be separately reacted with polyisocyanate.Subsequently the two capped materials can be combined to form the prepolymer.

Polyoxyalkylene polyol is terminated or capped by reaction with a polyisocyanate. The reaction may be carried out in an inert moisture-free atmosphere, such as under a nitrogen blanket, at atmospheric pressure with a temperature in the range of from about OOC to about 200C for a period of time of about 20 hours depending upon the temperatur and degree of agitation. This reaction may be effected also under atmospheric conditions provided the product is not exposed to excess moisture.

Capping of the polyoxyalkylene polyol ma+, ba effected using stoichiometric amounts of reactants.

Desirably, however, an excess of isocyanate is used to insure complete capping of the polyol. Thus, the ratio of isocyanate groups to the hydroxyl groups used is between about 2 to about 4 isocyanate to hydroxyl, and preferably about 2 to about 2.5 isocyanate to hydroxyl molar ratio.

To obtain the maximum strength, solvent resistance, heat resistance and the like, the isocyanate capped polyoxyalkylene polyol reaction products are formulated in such a manner as to give crosslinked polymer network.

Any ketoxime is effective. Among these are acetone oxime, butanone oxime, cyclohexanone oxime, and the like. An oxime based on a relatively volatile ketone is believed to be preferred. The most preferred oxime is butanone oxime, also commonly known as methyl ethyl ketoxime. Mixtures of oximes may be used. The proportions of oxime utilized may range from about 0.7 to about 1.2 equivalents of the isocyanate groups present. A more preferred range is 1.05 to 1.15 equivalents.

To prepare the blocked prepolymer, the oxime and prepolymer are simply admixed at temperatures of from 50 to 700C for from about 1/2 to 1-1/2 hours. A solvent is not generally necessary although materials such as butyl cellosolve acetate can be employed. Other appropriate solvents include materials which are not reactive with either the oxime or urethane groups. Based on the moles of reactive oxime and NCO groups involved, the NOHINCO molar ratio should be from about 0.7 to about 1.2 and preferably from about 1.05 to about 1.1 5. Generally it is most effective to use sufficient oxime to completely react with the NCO groups.

In preparing the blocked prepolymer the oxime is selected to provide a product that will undergo curing reactions in a reasonable time at a reasonable temperature. Numerous oximes and catalysts which can be employed are described in: Petersen, Liebigs Ann. Chem., 562 (1949), p. 215; Wicks, Progress in Organic Coatings, 3 (1975), pp. 73-99; and Hill et al, Journal of Pain Tech., 43 (1971) p.

55. Oximes having the above unblocking temperatures are liquid materials at temperatures of about 800 C, and the condensation products with urethane prepolymers are miscible with water or can be dispersed in water with the aid of surfactants. Generally the oximes are aliphatic, cyclic, straight-chain or branched materials containing 2-8 (preferably 3-6) carbon atoms.

The oxime blocked, NCO-terminated prepolymer is reacted with an amine that is capable of causing the polymer to cure at a low temperature. Many of the amines usable are well known in the art and are referred to as polyfunctional amines. Specific examples of amines include, but are not limited to, ethylenediamine, 1 ,3-propane-diam ine, diethylenetriamine, triethylenetetramine, iminobispropylamine, tetraethylenepentamine, methyliminobispropylamine, 2(2aminoethylamine)ethanol and the polyoxypropyleneamines manufactured by Jefferson Chemical Company, Inc. and sold under the trade names JEFFAMINE D-400, D-2000 and T-403. The polyoxpropyleneamines are aliphatic polyether primary di and tri-furictional amines derived from propylene oxide adduct of diols and triols.

As can be observed from the amines listed, some of the manes can be represented by the general formulae, NH2-R'-NH2, and HO-R'-NH2, where R' is a C2-C6 group.

We have found in our experimental work that polyfunctional amines with a functionality of at least 2 primary amine end groups are the preferred amines for getting adequate curing of the polymer subsequently produced.

Some of the polyfunctional amines may be represented by the formula

where z is an integer from 1 to 4; n is an integer larger than 1; and R is hydrogen, an alkyl group of 1 to 4 carbon atoms, or a hydroxyalkyl group of 1 to 4 carbon atoms.

The polyoxypropyleneamines may be represented by the formula NH2CH(CH3)CH2$OCH2CH(CH3)xNH2 where x is greater than 2, and by the formula

where x+y+z is about 5.3. The molecular weights of these polyoxypropylene amines range from about 200 to 2000 or larger with the preferred polyoxypropyleneamines having molecular weights of about 400 and 2000.

The amount of polyfuncitonal amine added to the oxime blocked NCO-terminated prepolymer should be in the range of 0.6 to 1.5 equivalents with the preferable range between 0.9 to 1.1 equivalents based on the total equivalents of all the isocyanate groups present in the NCO-terminated prepolymer.

Where the isocyanate functionality of the NCO-terminated prepolymer is two, a polyfunctional amine having a functionality of greater than two is required in order to provide a satisfactory crosslinked product. When the isocyanate functionality of the NCO-terminated prepolymer is greater than two, the polyfunctional amine functionality may be as little as two. It is to be understood from this that in the same reactive system that the functionality of the NCO-terminated prepolymer and the amine or polyoxypropyleneamines will have a total functionality of greater than four.

The The reaction between the oxime blocked prepolymer and the polyfunctional amine is controlled adding an adding an acid or a mixture of acid and water prior to the completion of the reaction. Failure to control the amine-oxime blocked prepolymer reaction at the proper time may result in an arnine reaction product that is too viscous. Thus the proper portions of the blocked prepolymer and polyfunctional amine are placed in a reaction vessel and reacted under controlled conditions of heating and stirring. With experience we have been able to determine the state of the reaction by observing the increase in viscosity. With proper equipment, the reaction can be carried out more rapidly at elevated temperatures.For example, reaction times can be as short as about 3 minutes at about 950C, 4 minutes at about 800 C, etc. Preferred reaction times are from about one-half hour to about one hour with temperatures between about 40 and 600C. Sufficient acid or water-acid mixture is stirred into the amine reaction product to lower the pH value to about 5 or below.

The cationically stabilized waterborne polyurethane polymers are prepared by dispersing the amine reaction product in water in the presence of sufficient acid to provide a pH of from about 6 or less. In preparing the waterborne polymers, a concentrated acid solution can be added directly to the amine reaction product, admixed therewith and followed by dilution with water. This is the preferred method. However, it is also possible to first add the acid to the water followed by dispersion of the amine reaction product in the water. Other additives such as surfactants, ultraviolet absorbers, stabilizers, pigments, etc., may be formulated into the waterborne polyurethane polymers as required.

It has been found that if the pH is not controlled within the broad range set forth above, settling problems are encountered and/or portions of the amine reaction product react with the water to form a crust. While the pH value range is to be considered, we have found that from about 1 to 10 parts or more of acid may be used for each 100 parts of amine reaction product. A more preferred range is from about 4 to 8 parts acid per 100 parts amine reaction product. These waterborne polymers have been found to be stable for periods of several months at ambient temperatllr6s, e.g., 20 C, and also exhibit excellent resistance to freeze-thaw cycles.

While any organic or inorganic acid will fom- the aniline salt and perform the function of controlling the pH value, the acids which we have used include g!acial acetic acid, acrylic acid, citric acid, ethylene diaminetetreacetic (EDTA) acid, formic acid, glycine (aminoacetic acid), hydrochloric acid, lactic acid (alpha-h-ydroxypropionic acid), orthophosphoric acid (H3P0,), phosphorous acid (H3P03), sulphamic acid, sulphuric acid, tartaric acid (dihydroxysuccinic acid), paratol uenesulphonic acid and mixtures thereof.

Some of these acids, for example, sulphuric, hydrochloric and acetic acids tend to discolour.

However, where other additives such as pigments and ultraviolet absorbers are added to the waterborne polyurethane, the tendency for discoloration by the acids may be masked by the additives.

Through expenmentation we have found that a blend of acetic and phosphoric acids seems to discolour less than other acids or combination of acids. Phosphoric acid alone provides good colour stability.

It has been found that as little as 0.1% by weight of the polyurethane prepolymeramine salt based on weight of fibre improves the physical characteristics of the paper product. The preferred range is from about 0.1% to about 2% by weight of the amine salt based on fibre content of the paper but as much as 10% may be used. Expressed another way, the quantity of polyurethane prepolymer amine salt is from about 0.02 to about 0.2% by weight based upon the quantity of water in the aqueous slurry to be used in the paper making operation.

Although any known paper making materials may be used within the scope of this invention, the preferred paper making fibres include used newspaper stock, corrugated carton stock, bleached and unbleached pulps such as, Southern Western Kraft, High Alpha, Southern Sulphite, and Hardwood Kraft. It may also be advantageous to incorporate glass fibres in the paper making stock to provide desired characteristics in the finished product The following examples illustrate but are not limitative of our invention, it being understood that similar improved results are obtainable with other combinatioris of different components specified above.All such variations which do not depart from the basic concept of the invention and compositions disclosed above are intended to come within the scope of the appended claims.

Preparation of Polyurethane Prepolymer Amine Sa't A preferred isocyanate terminated polyol prepolymmar la prepared by mixing a hydrophilic polyoxyethylene diol having an ethylene oxide content oat least 40 mole percent with a polyol having a hydroxyl functionality in the range of 3 to C, said polyol being present in the admixture in an amount in the range 1.0 to 20% by weight, reacting ';-Jit: : he mixture at a temperature in the range 0 to 1 200C an amount of a diisocyanate equal to 1.8-1.9 NCO to OH equivalents for a time sufficient to cap substantially all the hydroxyl groups of che admixture, adding additional diisocyanate to provide 0.1 0.3 equivalents of NCO per initial equivalent of OH In excess of the theoretical amount necessary to react with the hydroxyl groups To 100 grams of the NCO terminated polyol prepolymer at 240C in a stainless steel vessel is added 22 grams of butanone oxime with stirring. The reaction of the oxime with the isocyanate is exothermic and the temperature goes to 600C. A hot water bath is used to control the temperature between 80-900C for twenty minutes.

After twenty minutes and the temperature at 900 C, 1 2 grams of diethylenetriamine is added with stirring. The reaction with the amine is also exothermic, which accelerates chain extension.

The viscosity continues to increase and after ten minutes at 90-950C, 7.1 grams of glacial acetic acid and 7.1 grams of O-phosphoric acid dissolved in 100 grams of deionized water is slowly added to control the viscosity. After all the acid/water mixture is in, the material is cooled and packaged. Water may be added to achieve the desired % non volatiles (%N.V) and viscosity.

Typical physical properties of the additive prepared as described are: % N.V. 52.0 pH 4.5-6.9 Viscosity (Brookfield LVF) 600 1000 cps Appearance clear, straw coloured solution Example #1 A blend of newspaper and corrugated carton stock was slurred in a Waring blender to a 550 Canadian Standard Freenes. The polyurethane prepolymer amine salt was added to the pulp and the slurry was stirred for five minutes. Sheets (25 grams, dry) were formed in a 1 2"x 12" Williams sheet mould, pressed one minute at 1500 psig and dried in a William sheet drier at 2000 F. After a one-hour cure at 21 50 F and 1 6 hours conditioning at 730 F and 50% RH, the sheets were tested.For wet tensiles, the samples were soaked six hours in a one percent solution of AEROSOL OT wetting agent.

The test data are presented in the table below for a series of sheets with increasing amounts of polyurethane prepolymer amine salt added to the pulp.

% Polyurethane prepolymer Dry Wet Gurley amine salt Tensile Tensile Elemendorf Stiffnes Sample on plup #/1" #/1" Grams milligrams NH 473-1/2 0 15.7 G.6 140 3800 3/4 0.1 19.1 4.3 173 3850 5/6 0.2 21.9 5.9 192 4100 7/8 0.5 22.1 5.9 203 4450 9/10 1.0 33.5 10.9 233 4700 11/12 2.0 27.9 10.2 228 5950 13/14 5.0 33.7 14.4 221 5550 Example #2 Sheets were made as in Example #1 except that 50 grams sheets were made and a varity of different pulps was used. The data are presented below.

% Polyurethane prepolymer Dry Wet Gurley Sheet Pulp amine salt Tensile Tensile Stiffness No. Used on pulp #1" #/ 1" milligrams NH432-1 Unvleached 0 38.5 1.5 29,400 -2 Western Kraft 2.0 93.9 30.4 42,800 -7 Bieached 0 40.2 2.4 19,800 -8 Western Kraft 2.0 60.3 24.6 25,000 -10 High Alpha 0 19.8 1.0 17,200 -11 Southern Sulphite 2.0 25.2 10.4 21,200 -13 Bleached Southern 0 38.3 1.1 26,700 --14 Hardwood Kraft 2.0 41.9 13.2 27,600 Example #3 Fifty gram sheets were prepared as in Example #;1 using a blend of newspaper and corrugated carton stock except that after adding the polyurethane prepolymer amine salt and before forming the sheet in the Williams sheet mould, a 90/10 styrene/butadiene latex was added to the slurry. The amount of polyurethane prepolymer amine salt added and the amount of latex added were varied.

% Poly- urethane prepolymer latex Dry Wet Gurley Sheet amine salt on Tensile Tensile Stiffness No. on pulp pulp #1" #/1" milligrams NH417-1 0 0 36.8 1.2 21,500 NH415-1 0.4 0.8 51.2 6.5 27,300 -2 1.0 2.6 43.4 11.9 29,200 -3 1.5 5.0 58.0 16.3 35,200 -6 4.0 18.0 65.3 30.7 52,200 -7 6.0 31.0 90.3 37.8 56,900 -8 10.0 60.0 199.3 82.0 82,900 Example #4 Fifty gram sheets were made as in Example #3 using unbleached western graft pulp and adding polyvinylacetate latexes.

% Poly urethane prepolymer Latex Dry Wet Sheet amine salt on PVAc Tensile Tensile No. on pulp pulp Latex #/1" NH432-1 0 0 None 38.5 1.5 NH439-1 0.5 5.0 B 67.6 21.1 -6 2.0 15.0 B 82.2 35.5 -2 0.5 5.0 61 67.7 20.7 -7 2.0 15.0 61 156.5 56.0 B=DARATAK B, a polyvinylacetate copolymer ernulsion 61=DARATAK 61L, a high molecular weight polyvinylacetate homopolymeremulsion DARATAK is a registered trademark of W. R. Grace and Co.

Example #5 Fifty gram sheets were made as in Example #3 using unbleached kraft pulp and acrylic latexes.

% Poly urethane prepolymer Latex Dry Wet Sheet amine salt on Acrylic Tensile Tensile No. on plup pulp Latex #/1" NH432-1 0 0 None 38.5 1.5 NH440-1 0.5 5.0 410 36.9 15.5 -4 2.0 15.0 410 64.0 28.1 NH440-2 0.5 5.0 400 52.8 18.9 -5 2.0 15.0 400 99.7 53.8 NH440-3 0.5 5.0 442 48.3 16.7 -6 2.0 15.0 442 114.7 54.5 410=DAREX X41 0, a vinyl modified acrylic latex 400=DAREX X400, a self-curing polyacrylic latex 442=DAREX X442, a styrene-acrylate copolymer latex DAREX is a registered trademark of W. R. Grace and Co.

Example #6 Fifty gram sheets were made as in Example Ht3 using a blend of newspaper and corrugated box stock to which were added glass fibres. Varying amounts of polyurethane prepolymer amine salt and 90/10 SBR latex were added.

% Poly % urethane Glass prepolymer % Sheet on Type amine salt Latex Dry Wet Gurley No. Pulp Glass on pulp on Type Tensile Tensile Stiffness pulp Latex #/1" #/1" milligrams NH476-12 0 - 0 0 -- 48.9 1.3 29,700 -2 15 DE636-1/4 0 0 -- 21.0 0.5 34,100 -1 15 " 4 0 -- 38.7 16.0 41,400 -4 15 " 1 10 SBR 35.2 5.9 46,400 -11 15 M670-1/2 4 4 SBR 75.5 20.0 54,300 -7 15 DE610-1/2 4 4 SBR 44.3 13.4 48,800 The terms and expressions which have been employed are used as terms of description and not of limitation. There is no intention in the use of such terms and expressions as excluding any equivalents of the features shown and described. It is recognized that various modifications are possible within the scope of the invention claimed.

Claims (20)

Claims

1. A method of making a paper product which comprises incorporating into a paper stock before or after formation of a web therefrom from 0.1 to 10% based on the dry fibre weight of the said web, ol a polyurethane polymer amine salt prepared by reacting (a) a first component comprising an isocyanate-capped hydrophilic polyol having a functionality of at least two with (b) a second component comprising a ketoxime to form an oxime-blocked prepolymer, reacting the said oximeblocked prepolymer with (c) a third component comprising a polyfunctional amine to form an amine reaction product, and reacting said amine reaction product with (d) a fourth component comprising an aqueous acid to form the said polyurethane polymer amine salt

2.The method according to Claim 1 which comprises adding to a paper pulp from 0.1% to 10% by weight, based on the weight of oven dried pulp fibres, of the polyurethane polymer amine salt comprising a waterborne composition consisting essentially of the product of reacting together sequentially (a) a first component comprising an isocyanate-capped polyether polyol prepolymer having a reactive functionality of at least two with (b) a second component comprising a ketoxime to form an oxime-blocked prepolymer, reacting with said oxime-blocked prepolymer with (c) a third component comprising a polyfunctional amine to form an amine reaction product, and reacting said amine reaction product with (d) a fourth component comprising an aqueous acid to form a heat-curable waterborne polyurethane polymer composition, and making paper from the result 9 pulp.

3. A method according to claim 1 for making a paper product which comprises: A. preparing a polyurethane poiymer amine salt by (1) preparing an isocyanate-capped prepolymer wherein the isocyanate capped prepolymer consists of a mixture of (a) from 2.9 to 50% by weight of said mixture of an isocyanate capped polyol having a hydroxyl functionality in the range of 3 to 8 prior to capping; and (b) from 97.1 to 50% by weight of said mixture of an isocyanate-capped hydrophilic polyoxyethylene diol, said diol having an ethylene oxide content of at least 40 mole percent.

(2) reacting said prepolymer with from 0.8 to 1.2 equivalent of acetone oxime, butanone oxime, cyclohexanone oxime or a mixture thereof to block the NCO groups of said prepolymer to form an oxime-blocked prepolymer, (3) reacting said oxime-blocked prepolymer with a polyfunctional amine containing at least 2 functional groups and capable of causing polyurethane polymers to cure at low temperatures, to form an amine reaction product and, (4) reacting said amine product with an organic or inorqanic acid to form an infinitely water dilutable, low temperature-curable polyurethane polymer amine salt; B. forming a web from a paper stock system; and C. intimately dispersing said salt within the paper stock either before or after formation of the said web but prior to passing said web through a drying stage of a paper-making operation in an amount sufficient to provide a concentration of said salt of from 0.1 to 10% based on a dry fibre weight of the said web.

4. A method according to claim 3, wherein the said salt is in an aqueous system when dispersed.

5. A method according to claim 3 wherein the said salt is waterborne and is sprayed onto the web prior to the drying operation.

6. A method according to claim 1 for the manufacture of paper products from cellulose papermaking fibres, which comprises incorporating in said fibres from; 0.1 to 10% by weight, based on weight of said fibres, of a composition consisting essentially of a waterborne polyurethane polymer wherein said polymer is formed by reacting from 0.7 to 1.2 equivalents of, based on prepolymer NCO groups, a ketoxime with a polyurethane prepolymer having free NCO groups to form an oxime-blocked prepolymer, reacting said blocked prepolymer with from about 0.6 to about 1N.5 equivalents of, based on prepolymer NCO groups, a polyfunctional amine to ft'rm an amine reaction product, reacting said amine reaction product with from 1 to 10 parts of an acid per 100 parts of said amine reaction product to form an amine salt and diluting said arninu salt with water to less than 60% total non-volatiles content, and subsequently curing said composiFion to a water-insoluble form.

7. A method according to claim 6 whe. R said composition is cured by heating to a temperature between about 220 and 3000F (104--t 500C).

8. A method according to claim 1 of making a paper product of increased wet strength which comprises the steps of (1) admixing with paper pulp a wet strength increasing amount of an aqueous solution or suspension of a crosslinkable polyurethane polymer amine salt product, said product consisting essentially of the sequential reaction product of (a) a first component comprising isocyanate-capped hydrophilic polyether polyol prepolymer having a reactive functionality of at least two with (b) a second component comprising a ketoxime to form an oxime blocked prepolymer, reacting said oxime blocked prepolymer with (c) a third component comprising a polyfunctional amine to form an amine reaction product, and reacting said amine reaction product with (d) a fourth component comprising an aqueous acid to form a heat curable waterborne polyurethane polymer amine salt product, (2) forming paper from said pulp admixed with said product, and (3) drying said paper at elevated temperature thereby effecting crosslinking of said product.

9. A method according to any of claims 1 to 8 wherein the paper stock system includes a paper additive selected from styrene-butadiene latexes, polyvinyl acetate latexes, acrylic latexes, and mixtures thereof.

10. A method according to claim 9 wherein the paper stock system includes glass fibres.

11. A method according to any of claims 1 to 10 wherein the paper stock system is a blend of newspapers and corrugated carton stock.

12. A method according to claim 1, substantially as described in any one of the foregoing Examples.

13. A paper product made by the process of any of claims 1 to 12.

14. A paper product of improved wet strength comprising cellulosic papermaking fibres containing from 0.1 to 10% by weight, based on the weight of said fibres, of a coriiposition obtained by (1) admixing a hydrophilic polyoxyethylene diol having an ethylene oxide content of at least 40 mole percent with a polyol having a hydroxyl functionality in the range 3 to 8, said polyol being present in the admixture in an amount in the range 1.0 to 20% by weight, reacting with the admixture at 3 temperature in the range O to 1 200C an amount of diisocyanate equal to 1 .8-1.9 NCO equivalents for a time sufficient to cap substantially all the hydroxyl groups of the admixture and thereafter adding additional diisocyanate to provide 0.1-0.3 equivalents of NCO per initial equivalents of OH in excess of the theoretical amount necessary to react with the hydroxyl groups to form an NCO-terminated prepolymer; (2) reacting said NCO-terminated prepolymer with from 1.05 to 1.15 equivalents of butanone oxime to form a butanone oxime block prepolymer;; (3) reacting said butanone oxime block prepolymer with from about 0.9 to about 1.1 equivalents of diethylenetnamine to form an amine reaction product; and (4) reacting said amine reaction produce with water containing from about 4 to about 8 parts of a mixture ol acetic and phosphoric acids per 100 parts of said amine reaction product such that the resulting film forming waterborne composition contains from about 2Q to about 50% by weight nonvolatiles, and subsequently curing said composition to a water-insoluble form.

15. Paper impregnated with a polyurethane polymer amine salt in amounts such that the impregnated paper consists essentially of, based on 100 parts by weight of paper, from 0.1 parts to 10 parts of a polyurethane polymer amine salt prepared by the steps of (1) preparing an isocyanate-cappsd prepolymer wherein the isocyanate-capped prepolymer consists of a mixture of (a) -From 2.9 to 50% by weight of said mixture of an isocyanate-capped polyol having a hydroxyl functionality in the range of 3 to 8 prior to capping; and (b) frorn 97.1 to 50% by weight of said mixture of an isocyanate capped hydrophilic polyoxyathylene diol, said diol having an ethylene oxide content of at least 40 mole percent, (2) reacting said prepolymer with from 0.7 to 1.2 equivalents of a ketoCime selected from the group consisting of acetone oxime, butanone oxime, cyclohe;;'anone oxime, and mixtures thereof to block the isocyanate groups of said prepolymer to form an oxime blocked prepolymer, (3) reacting said oxime blocked prepolymer with a polyfunctional amine containing at least 2 functional groups and capable of causing polyurethane polymers to cure at low temperatures to form an amine reaction product and (4) reacting said amine reaction product with an organic or inorganic acid to fonn an infinitely water dilutable, low temperature curable polyurethane polymer amine salt.

1 6. Paper having incorporated therein a wet strength increasing amount of a crosslinked polyurethane polymer amine salt product said product, prior to crosslinking, consisting essentially of a waterborne polyurethane polymer amine salt product wherein said product is formed by reacting from 0.7 to 1.2 equivalents, based on prepolymer NCO groups, of a ketoxime with a polyurethane prepolymer having iree NCO groups to form an oxime blocked prepolymer, reacting said blocked prepolymer with from 0.6 to 1.5 equivalents, based on prepolymer NCO groups, of a polyfunctional amine to form an amine reaction product, r.eacting said amine reaction product with from 1 to 10 parts of an acid per 100 parts of said amine reaction product to form amine salt and diluting said amine salt with water to less than 60% total nonvolatives content.

17. Paper product as claimed in any one of claims 14 to 16 when produced by a process as claimed in any one of claims 1 to 12.

18. Aqueous additive composition for use in paper-making which comprises a waterborne polyurethane polymer prepared by reacting a first component comprising an isocyanate-capped hydrophilic polyol having a reaction functionality of two or greater with a second component comprising a ketoxime to form an oxime-blocked prepolymer, reacting a third component comprising a polyfunctional amine having a functionality of two or greater with said oxime-blocked prepolymer to form an amine reaction product, reacting a fourth component comprising an acid with said amine reaction product to form an infinitely water-dilutable polyurethane polymer amine salt, and diluting said polyurethane polymer amine salt with water.

19. A composition according to claim 18, including an additional additive selected from styrenebutadiene latexes, polyvinyi acetate latexes, acrylic latexes, and mixtures thereof.

20. A composition according to claim 18, substantially as hereinbefore described.