CA1197334A - Polyvinylalcohol/melamine-formaldehyde interaction products - Google Patents

Abstract

Stable aqueous polyvinyl alcohol/melamineformaldehyde resin interaction products are provided comprising polyvinyl alcohol polymer and cationic melamineformaldehyde resin acid colloid in a polyvinyl alcohol/melamine-formaldehyde resin acid colloid weight ratio, on a dry basis, of from about 1/1 to about 5/1, and sufficient water to give a solids content of from about 0.7% by weight up to a level that will not cause gelation to a stage of no flow under the force of gravity in 48 hours but not in excess of 6% by weight. These aqueous polyvinyl alcohol/melamineformaldehyde interaction products have good stability, and high absorption capacity onto cellulose pulp. The use of these interaction products in paper making results in increased processing capability and improved wet and dry strength of the paper.

Description

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Polyvinylalcohol/Melamine-Formaldehyde Interaction Products BACKGROUND OF T~E INVENTION
Field of the Invention This invention relates to polyvmyl alcohol and more s~ec;fi~Ally it relates ~ stable aqueous p~lyvinyl alcohoV
mPlAm;nP-f~n~l~Phyde nesin interaction ~ u~.
Description Of The Prior Art There are numerous commercial wet and additives being used in paper making at the present~ These have many limitations. Some examples of the additives used most commonly, are as follows.
Cationic starches are often used for improving re-tention of cellulosic fines, filler and pigment, and also for increasing the dry strength of the resulting paper. However, such improve~ents are generally modest, and at the same time cationic starch use can lead to irregularities in performance (irreproducibility of batches, low solution stability, low wet strength), incompatibility with other components in the furnish (alum, size, other salts~, and high biological oxygen demand (BOD) for additive not on the pulp or recycled, and which is lost in the waste water.
Other wet-end additives are often used to confer permanent wet strength to the resulting paper, such as cationicurea-formaldehyde UF resins, amine-containing polyamides treated with epoxides (e.g., Hercules' KYMENE*
557) or melamine-formaldehyde (MF) resins (e.g., PAREZ*607 of ~mPri~n Cyanamid). Hcwever, UF resins are slcw curing on the m~hinP, while the polyamides are relatively expensive, slow to adsorb on the cellulose pulp, and make repulping of the paper rela-tively dificulto The MF resins show poor pigment and filler retention and also exhibit low water absorbency, whereas absorbency is often desired along with wet strength.
All of these types of additives give only modest ennancement of dry strength. Also, none of the above *denotes trade mark ,,`~1 7~

types are now rPcognized as improvers of wet web strength tat their usual ccncentration of application) which would permit greater production control and in some cases, increased productivity.
C~lv~LItional soluble polyvinyl alcohol in the form oE
pc~der, gr~m~ or rhr~l?~fl fiber has been used in Japan as an additive in the wet-end of a paper~making mArh;n~ Increased paper sLr~lyul and oil resistance was disclosed~ H~-ever, careful control of polyvinyl alcohol particle size, pr~limin~ry heat treat-ment, and degree of hydrolysis of the polyvinyl alcohol is required.
Similarly, careful control of the temperature, and level of water pickup by the particles and the forming paper is required before passing through the drier rolls (see "Polyvinyl Alcohol"~ edited by C. A. Finch, Wiley, N.Y. (1973) pp 301-305). As these particles are n-~nir)ni~!, low retention of fines would be expected and as they are non-curing have no wet strength ci~hility.
I~e use of m~l~min~f~rm~l~phyde resins as wet-end additives to give high wet ~ yUI papers is well known (see C. S. Ma~well's 20 review in TAPPI ~/lnn~r~h No. 29, "Wet SLL~[-gUI in Paper and Paper-board,' Editor J. P. Weidner (1965), pages 20-32.
The interaction of starch and the cationic precondensate of melamine-formaldehyde to make a cationic starch (promoting adsorption of the binder) is 25 disclosed in U.S. 2,993,344 (cf. column 3). No concentra-tion effects were indicated as important. Also the product was unsatisfactory per se as a binder for ellulosic pulp (cf. column 6).
U.S. 3,594,271 disclosed aqueous acidic 30 colloidal solutions of a cationic reaction product oE a cationic thermosetting melamine-formaldehyde acid colloid with 5 to 50 times its weight of a water soluble starch and the process of treating paper therewith. Such products are disclosed to give good 35 adsorption on the fibers and enhanced dry strength ~:19'73;~

coupled with low wet strength. Total solids content of the mixture is 2-10%, but it is indicated that "this is not critical," (column 2). It was also disclosed that the low wet strength is a result of the low concentration _ 5 of the melamine-formaldehyde resin relative to the starch.
UoS~ 3,424,650 ~ losed that starch reacted with f~ Phyde~guamdir~mPl~m-n~ resins was r~ndered n~ch more ads~
- - tive to cellulose f~s. Inclusion of all three materials as reactants in 9-14/0.4-1.6/o.4-1.6 ratios, respectively, was critical in order to produce a relatively stable resin and for sufficient activity for increasing dry strength of paper articles by prior reaction with starch. Also con~.~d~on of reactants can be 1-40% by weight.
A combination of a guanidine-formaldehyde resin and a hydrocolloid ~such as starch or polyvinyl alcohol), in about 2/1 ratio by weight, is disclosed in U.S. 3,002,881 as a good wet-end additive, increasing the wet strength of the resulting paper. Presumably, com-ponents are added independently to the dilute pulp slurry. There is no indication of prereaction of resin and polyvinyl alcohol, because of lack of stability of premixes (cf. column 5).
The advantage of using a cationic material (cationic starch) at the wet-end of a papermaking machine are disclosed in U.S. 4,029,885.
Other methods to prepare cationic highly adsorbant polyvinyl alcohols have also been described.
However ! these would be at higher costs and/or would offer problems with a toxic reactant. These are as follows:
U.S. 3,597,313 and 3,772,407 disclose copoly-mers of vinyl alcohol modified with cationic monomers.
U.S. 3,051,691 discloses that polyvinyl alcohol and calcium cyanamide form cationic polymeric polyols that are substantive to cellulose.

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The use of polyv-inyl alcohol plus methylol melamines (the monomeric-melamine-formaldehyde in paper coatings is described in Brit. Pat. 551,950 of ICI, granted 1943 rlarch 17. Applica-tion as a textile finish is disclosed in U.S. 2,876,135. In the latter, reaction between the two components probably didn't take place until after application to the substrate (the catalyst was added at this point). The polyvinyl alcohol/methylol compound ratio disclosed was from lû 1/1 to 1/125.
IJ.S. 3,067,160 disclosed that the addition of even small amounts of polyvinyl alcohol to cationic melamine-Eormaldehyde resin acid colloids (methyl ether form) was unsuccessful. Such systems were very unstable and gelled thus indicating that one would not expect stable melamine-formaldehyde acid colloid solutions containing polyvinyl alcohol.
It has been known for a long time that addition of a crosslinking agent to polyvinyl alcohol in aqueous solution at moderate-to-elevated concentra-tions, will lead to gel formation, but if the solution is dilute enough intramolecular interaction will occur almost exclusively, so that no gel would form (cf. W.
Kuhn and G. Balmer, Journal of Polymer Science ~lol. 57 page 311-319 (1962). Further the work of these authors indicates that in reaction of a polyvinyl alcohol having a degree of poly-m~r;~t;r~n on the order of 1000-2000, with a highly functional cross-linking agent such as the m~l~m;nP-form~ Phyde resin acid colloid (and with -the latter at a concentration of as high as 20 to 100% by weight of the PVA), a very low c~n~ cLion of the PVA
must be present (est. 0.3-0.5%) to ~)L~Vt:~llt ~Pl~t;f~n. mus it is surE~r;q;ng that ;ntPr~ction of PVA and the ME' resin acid colloid can occur in solution (~ nl.,,tions as high as 3.75% to give stable yet active systems even with P~Pn~ive heating of the solution.
These authors indicate that complete separation of the polymer chains is nPcP~ry for this dilution effect to occur. Gther ~rkers also indicated that co~lete separations of molecules of ~'7;33~

polyvinyl Al~nhnl req~lire con~ LaLions below 0.25%, and that if ,~n~,;raLion is increased to about 0.9% the ~ n polymer coils must int~L~w~LlaLe, and ~ntAnglPmPnts become quite important [cf.
"Polyvinyl Alcohol"/ by J.G. Pritchard, Gorden and Breach, NYD, (1979), page 15].
SUM~I~RY OF THE INVFNTION
~c~r~;ng to the present invention, there is pr~vided a stable aq~leous pol~vinyl Al ~nh~l /mPlAmin~-fnrmAl~Phyde resin inter-action ~s~L c~m~ri~;n~ polyvinyl alcohol polymLPr and cationic mPl~m;nP-form~ hyde resin acid colloid in a polyviny~ hol/
mPlAm;n~-f~rn~ hyde resin acid collo;~ weigh~ ratio, on a dry basis, of frcm about Vl to about 5/1 and s~ff;~;Pnt water to give a solids ~"l~L of from about 0.7% by weight up to a level that will not cause gelation to a stage of no flcw under the force of gravity but not in excess of 6% by weight.
Further provided according to the present invention are procP~s~ for pr~p~r; n~ the stable aq~leous polyvinylAl r~h~l ~mPl Am; nP-f~rm~ hyde resin ;nt~rA~tion ~ U~L of ~he present invention.
Still further provided A~c~r~;n~ to the present irlvention are prw ~P~ to increase the wet ~LL~1YUIr dry ~LL~1YU1 and other ylu~elLies of a ~uo~CL derived from fibrous cellulosic materials and of payer by treating ~he fibrous c~ l1O~-c materials or the paper pulp with the ~ U~LS of the present invention, and the resulting paper having improved ~1~ ~es.
As used herein the word "stable" in the cont~xt of st~ble aqueous polyvinyl Alcnh~l/m~lAm;n~-fo ~ 1~Phyde resin in~eraction ~lu~L means ~at ~ ti~n to a stage of no glcw under the force of gravity does not occur within 48 hours.
DET~TT.~n DESCRIPTION OF THE INVENTION
Contrary to the indications of the above referred to prior art and very surprisingly it was discovered that blends of polyvinyl alcohol and cationic melamine-formaldehyde resin acid colloid can interact in solutions at concentrations as high as about 3~ or even higher at l~ tul~s of up to 85-90C, for 1-2 hours, if desired, without leading to appreciable levels '733'~

of gel or loss of adsorption activity of the interaction product to cellulose. This discovery renders the polyvinyl alcohol~mel~m-n~-formaldehyde interaction ~ ially fe~;hl~ as these concentrations and reaction rate permit equipment already employed for solutions of cationic starch added to the paper machine in order to obtain improved prope~ies.
r~he limitations of the prior art wet-end additives discussed above are alleviated by the use of the polyvinyl alcohol/
mel~m;n~-f~ hyde resin interaction products of the present invention. Improvement over the cationic starches is shown in r-eproducibility of batches, high solution stability, high wet web strength, better compatibility with other components in the furnish tsalts, size, fillers), lower BOD (biological oxygen demand), hi-gher retention of fines and higher dry strength, dry toughness and wet strength and toughness in the rasulting paper. With regard to the wet strength agents, improvement OVeE urea/formalde-hyde resins is indicated by the high curing rate on the machine. Advantage over the melamine-formaldehyde resins is indicated by higher water absorbency rate (in nonsized compositions), higher retention of fines, and higher wet toughness of the resulting paper. Advantages over nonionic polyvinyl alcohols as a wet-additive are easier process control, better retention of fines, and better sheet properties, including paper wet strength capability. The improvement over the use of other cationic polyvinyl alco-hol is demonstrated by wet strength capability, and the process advantages mentioned above.
Thus, the preparation of certain interaction products of polyvinyl alcohol and cationic melamine-formaldehyde resin acid colloid are provided which are highly adsorbant to cellulose pulp and as such, are eminently suitable for application in the '~

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paper industry. mese products are c~pAh1e of forming water resistant products on drymy, yet also exhibit good solution stability at solution concentrakions of up to about 3.75 weight ~L~lL or éven higher. These interaction products can be prepared more readily and at lower cost to the custo~er th~n previously ~P~r;hP~ highly adsorbant polyvinyl alcohols. ~ley do re~lire, however, rather specific conditio~s for their preparation to obtain products with enhanced prope~ies over other wet-end additives to the paper making process. The enhanced properties of good solution stability, high adsorption capacity on the cellulose pulp, increased processing capability and con-trol and improved paper properties rende:r the interaction properties of the present invention particularly suitable for use in the wet end of the paper making machine permit~
ting also lower overall costs to the paper mill.
The polyvinyl alcohol polymer component of the product of the present invention can be a "com-pletely" hydrolyzed grade (mole percent hydrolysis of acetate groups 99.0 to about 100%), a partially hydrolyzed grade (percent hydrolysis 80-90%~, a polymer o~ intermediate level of hydrolysis, or blends thereof. The completely hydrolyzed grades and also the higher molecular weight commercial grades are preferred when papers are desired with the highest wet strength properties. The polyvinyl alcohol should have a degree of polymerization of from about 600 to about 3000, as reflected in the inherent viscosity values t~inh) of from about 0.3 to about 1.4 dl/g. The inherent viscosity is measured in water at 30C at a concentration of 0.5 g/dl.
This approximately corresponds for many commercial grades of polyvinyl alcohol to a solution viscosity (4~ aqueous at 20C, Hoeppler Ealling ball method), o~ from about 4 to about 160 cps, with about 10-70 centipoises being preferred.

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The polyvinyl ~l~rhol ~--mr~n~nt of the present invention can also be a copolymer of vinyl alcohol, such as one obtained by hydrolyzing a copolymer of vinyl acetate with small amounts (up to about 15 mole percent) of other monomers~
Suitable comonomers are e.g. esters of acrylic acid, methacrylic acid, maleic or fumaric acids, itaconic acid, etc. Also, copolymerization of vinyl acetate with hydrwarbons, e.g. ~ f;ns such as ethylene, propylene or oc~ nn~, etc., with higher vinyl esters such as vinyl butyrate, 2-ethyl hexoate, stearate, trimethyl acetate, or homologues thereof (W -10*
type of vinyl esters sold by Shell Chem. Co.), etc~ gives copolymexs that can be hydrolyzed to suitable polyvinyl alcohol copolymers. Other suitable comonomers are N-substituted acrylamides, vinyl fluoride, allyl acetate, allyl alcohol, etc. Also the free unsaturated acids such as acrylic acid, methacrylic acid, monomethyl maleate, etc. can act as comonomers, although final product stability (that is, after reaction with melamine-formaldehyde resins) is reduced.
The other major component, the cationic melamine-formaldehyde resin acid colloid, is a colloi-dal solution of low molecular weight polymer (MW of about 1700) which result when trimethylol melamine (TMM) (or the slightly polymerized TMM furnished by certain suppliers for ease of solution in water, such as the American Cyanamid Corporation product PAREZ 607) is dissolved in water con-taini~ hydrochloric acid (about 0.8 mole HCl per mole of TMM) and aged at room temperature for at least one hour. These colloidal particles are positively charged (cationic), and are known to adsorb irreversibly, even at very low concentrations, onto negatively charged cellulose fibers. These are called the "regular"
colloids.

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A detailed discussion of the melamine-formal-dehyde resin acid colloids is given in TAPPI Monograph Series No. 29, "Wet Strength in Paper and Paperboard", (John Weidner, editor, Tech. Assoc. of the Pulp and Paper Industry, NYC, (1965), pages 20-32). Included in this discussion and suitable or use in the products of the present invention are so-called "high efficiency"
melamine colloids, in which 1 to 7 moles of extra formal-dehyde per mole of TMM are added to the TMM, and the optimum HCl/TMM mole ratio is reduced from about 0.8 to about 0.6. For m~ximllm effectiveness, the "high effi-ciency" col~oids are preferred. We have also found some advanta~e in ultimate paper properties when the "high efficiency" melamine-formaldehyde colloid is prepared by dissolving the T~ in cold waterr followed by the addition of the acid. The preparation of the melamine-formaldehyde component by this "cold" pro-cedure is described below.
In order to avoid poor solution and h;n~;ng ~L~er Lies the polyvinyl alcohol should not be present in solution during the preparation of the m~ ;nP-f~ hyde resin acid colloid.
In the preparation of the "high efficiency"
type of cationic melamine formaldehyde resin acid colloid one can add aldehydes other than formaldehyde during the ripening process for the colloid. These aldehydes can have up to about ten carbon atoms.
Concentrations can be 8-100% by weight based on the weight of trimethylolmelamine. The types of aldehydes which can be used include simple homologues of formaldehyde, including branched-chain types. Examples are acetaldehyde, propionaldehyde, butyraldehyde, or 2-ethyl hexyl aldehyde. Acetaldehyde is parti-cularly e~fective, especially at lower concentrations (see Example 14). Also useful are substituted alclehydes such as phenyl acetaldehyde, chloroacetal-dehyde, 3~methoxypropionaldehyde, aldol and crotonaldehyde. Polyaldehydes which can be used include glutaraldehyde, glyoxal, adipaldehyde and terephthalaldehyde. ~lutaraldehyde is particularly useful (see Example 15) in gi.ving unusually high filler retention, Scott internal bond strength and wet tensile energy adsorptio:n values.
The optimum HCl/TMM mole ratio with the addition of the higher aldehydes is closer to 0.8 than to 0.6.
Other components can also be present during the reaction of polyvinyl alcohol and melamine-formal-dehyde resin acid colloid which components can act as extenders to reduce cost, while n.ot lowering certain propert.ies such as pigment retention. These include unmodified starches, degraded (acid modified, enæyme conve.rted) starches, modified starches such as hypo-chlori.te~oxidized starch, or starch derivatives such as hydroxyethyl starch or cationic starches. The amount of starch that can be added can be as high as about 5 parts by weight of the above-mentioned starch to 1 part by weight of the polyvinyl alcohol to form for example a 6/1/l starch/polyvinyl alcohol/melamine formaldeh~de interaction product and still get some improvement over the use of starch/melamine-formalde-hyde interaction products. For example see Tables XIand XII in Example 13 in which the advantage of 3/1/1 starch/polyvinylalcohol/melamine-formaldehyde is shown over a 3/1 starch/melamine-formaldehyde.
The polyvinyl ~l~ohnl/m~l~; n~-fo~l ~Phyde resin ratio, on a dry basis can be from about l/l to about 5/1 by weight. Higher ratios lead to a low adsorption level on the pulp. Cn the other hand, too low a ratio leads to brittle product, which is reflected in reduced physical ~L~eL~ies oE ~he resulting paper.
The polyvinyl alcohol and the melamine-formaldehyde resin acid colloid can be interactedby mixing a~ueous solutions o:E each Eor several ,' .,, ~ ~ ~'7~ 3f~

hours at ambient temperatures or by heating ~30-90C
from about 3 to about 15 minutes), or by slurrying polyvinyl alcohol powder or granules in the melamine-formaldehyde acid colloid, followed by heating and stirring at about 80-95C until the polyvinyl alcohol is dissolved. It is important, however, in all variations that the overall solids concentration after mixing be from about 0.7 to about 3.75% by weight or even higher up to a level that will not cause gelation to a stage of no flow under the force of gravity but not in excess of 6% by weight. At higher concentrations, the viscosity of the mixture increases more rapidly than is probably useful, and leads to gel fo~lation. At 8% solids s~n~ntratio~ gelation could result in a few m;mltP~, and at 5% conc~l~d~on, depending on how fav~urable other conditions are, gelation might or might not occur in about 48 hours. Preferably, the overall sollds concentration should be between about

2%-3% by weight.
One of the most economical ways to prepare the product is as follows. The trimethylol melamine is dissolved and ripened to the oligomer in water and hydrochloric acid at room temperature in an acid resistant tank. It is then pumped into another tank (interaction tank) where it is diluted with water to about a 0.6% by weight concentration. In a third tank polyvinyl alcohol is dissolved with heat and stirring, to give a 10% by weight solution. The latter is then pumped hot into the interaction tank (containing the melamine-formaldehyde resin acid colloid) and the mixture is stirred slightly to form the final product.
Preferably about 2/1 to 3/1 polyvinyl alcohol/
melamine-formaldehyde ratio and about 2% by weight overall solids concentration is employed~ The tempera-ture of the reaction mixture is then about 33C, which is high enough to insure product formation within ;1 ~'?i (

3~3 about 15 minu~es mixing timeO The mixing temperature can be arnbien~ ~abou~ 20~ abou~ 24 hours mixing time is allowed.
1~ alt~x~ative route to the interaction pro-5 duct f as men~ioned above is to add the powdered polyvin~l alcohol direc~ly ~:o ~he dilu~ed mel ~ni ne~
formaldehYde resin acid coll.oid in the interaction tar~k to form a slurry, and ~hen kLeat to abou~ 85-90C or O ~ 25 hour to 2 hours, or un~:il the poly~inyl alcohol 10 dissolv~s~ Ad~ran~ages o~ this rou~e are tha~ solution o the polyvinyl alcohol is rapid in such a medium tabout 15 minutes~ and the third tanX is no~ reguired~
The disadvantaye of the latter method is ~hat more energy is re~uired to heat up a larger ~oluxne of solu~
The products rom bot~ proe~dures axe shelf s~able ~with regard to viscosity, ac~ivity) fo~ at leas~
thr~e weeks. We have observed no change in 5~ o~
viscosities in several cases for o~er three mon~
Blends of certain grades of solid pol~rinyl ~0 alcohol in powder or gr~ r fo~, with solid~ w~ter or aqueous acid solu~:3le conA~ns~ti4n products o~
mf~ m;n~ with 3 moles of fo~naldehyde carl al5Q be used, e.g~, by ar~ adaptation of ~he slurxy procedure. The ~ry blend can be added to water or a~ueous acid plus 25 additional ~orm~ hyde if des ired, pref erably cald to dissol~ he me~ formaldehyde con~ns~tion p~
and cor~ver~ them ~o the cationic resin acid colloid, while the polyvinyl alcohol remaills in substantially undissolved for:21 as a slurr~. Then wi~h an 30 appropriate amount of water added ~o give ultimat21y about 0 ~ 7~ to abou~ 6% solids solution, ~he slurry is heated as before ko dissolve and reac~ the polyvinyl alcohol. Th.e ra~io of polyvinyl alcohol/melamine-formaldehyde resin acid colloid can be fxom about S/l 35 to abou~ 1~1 by weight. The polyvinyl al~hol us~l should 3 ~

have a cold water solubles content as low as possible;
a grade with about 8% by weight m~; mllm cold wa-ter solubles content might be acceptable while a grade with about ~.5% by weight maximum would be preferable.
Maximum cold water solubles content of about 2% by weigh-t is most desirable. The melamine-formaldehyde resin acid colloid should be pxepared under milder conditions than the previous procedures, such as using higher dilution to prevent gelation: 9% by weight rather than the usual 14-18~ by weight solids concentra-tion gave good results.
The structure of the polyvinyl alcohol/
melamine-formaldehyde interaction products of this invention have not been precisely determined. However, the infrared spectra of cast films indicated chemical interaction of the polyvinyl alcohol and the melamine-formaldehyde resin through the -O~ groups to form graft copolymersO
The polyvinyl alcohol/melamine-formaldehyde product is preferably employed using the conventional methods of preparing paper sheets and other cellulosic products. Preferably, interaction with cellulose pulp material is carried out by internal addition to the cellulose pulp prior to formation of the paper sheet.
Thus the aqueous solution of the interaction product may be added to the aqueous suspension of the paper stock while the latter is in the head box of the Fourdrinier, at the fan pump, in the stock chest, the hydropulper or any other poin-t in the process prior to the point of sheet formation. The high adsorption rate of the polyvinyl alcohol/melamine~formaldehyde interaction product with the pulp permits many options in this regard. Among the variety of pulps which may be effectively treated are bleached and unbleached sulfate (kraft), bleaGhed and unbleached sulfite, soda, ~,7 ~733~

neutral sulfite, semichemical, groundwood or blends of these fibers. In addition, fibers of viscose rayon, glass, re~enerated cellulose, polyamide, polyester or polyvinyl alcohol can also be used in conjunction with the cellulose pulp. The preferred pH range of the pulp stock containing the polyvinyl alcohol/melamine-formaldehyde intera~tion product is from about 5 to about 8; with good adsorption and filler retention demonstrated over this range. The best wet strength properties of the resulting paper occur in the pH range of from about 4 to about 6.5.
Materials which could be added to the pulp slurry along with the polyvinyl alcohol/melamine-formaldehyde interaction product include cationic surfactants, cationic urea-formaldehyde resins, or cationic polyacrylamides. Also, polymers derived from polyamides containing amino groups along the polymer backbone, and reacted with epichlorohydrin (such as KYMENE 557 from Hercules) can be added.
Anionic polyacrylamide polymers, fortified rosin size, fillers, pigments, alum, etc. also can be present.
The sheet is then formed, pressed and dried by conventional means. The latter step serves to cure the polyvinyl alcohol/melamine-formaldehyde interaction product to its water insensitive state.
Good runnability and good paper formation has been exhibited.
The amount of polyvinyl alcohol/melamine-formaldehyde interaction product added to the pulp slurry ranges from about 0.02 to about 10%, based on the dry weight of the pulp. The preferred range is from about 0.05% to about 3%, and will depend on the characteristics desired in the finished paper product, the type of pulp, and the specific operating conditions.
Thus too little polyvinyl alcohol/melamine-formaldehyde 733~

in the slurry will give -too low a property enhance-ment to be of interest. Too high a polyvinyl alcohol/-melamine-formaldehyde could be uneconomic.
The following examples serve to illustrate the present invention~ All par-ts and percentages and proportions are by weight unless otherwise indicated.
Preparation of melamine-formaldehyde resin acid colloids Example A
"High efficiency" melamine-formaldehyde resin acid colloid was prepared by adding 13.2 g of reagent grade concentrated hydrochloric acid to 365 g of distilled water. Then with stirring, 50 g of tri-methylol melamine powder was added, followed with 95 g of 37% aqueous formaldehyde solution. After slow stirring overnight at room temperature, the expected blue haze was evident. The acid colloid was dilu~ed with 365 g of distilled water, to give 7.4% solids (determined ~y drying in a circulating air oven at 110C/
1 hour~. Thissis about 74% of theory if no formaldehyde i5 lost during the drying process. The above initial xatios give 0.6 moles of HCl/mole of trimethylolmel-amine, and 5 moles of formaldehyde/mo]e of trimethylol-melamine. Addition of a drop of concentrated HCl to a few milliters of the acid colloid led to immediate coagulation, as expected if the melamine-formaldehyde acid colloid was adequately aged. The pH of the colloid was 1~8. The stability of the acid colloid was excellent for at least one month.
Example B
An alternative method for preparing the melamine-formaldehyde resin acid colloids is as follows~
Reagent grade concentrated HCl (11.6 c~) was added to 346 g of distilled water. Then, with stirring, 43.2 g of commercial spray dried trimethylolmelamine (PAREZ
607, from American Cyanamid Corpoxation) were added.

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The solution was slowly stirred overnight at room temperature. The acid colloid was diluted with 346 g of distilled water, to give 5.70% solids colloidal dispersion. The mole ratio of ~ICl/TMM was 0.6/1Ø
Example C
Another alternative preparation of melamine-formaldehyde resin acid colloid is illustrated below.
Reagent grade concentrated ~[Cl (15.8g) was added to 390 g of distilled H2O. Then, with stirring 43.2 g of PAREZ 607 was added slowly. The solution was then stirred overnight at room temperature. The acid colloid was diluted with 340 g oE distilled water to yive a 6.6% solids colloidal dispersion. The mole ratio of HCl/T~M was 0.8/1Ø
Example D
The "cold" procedure for preparing melamine-formaldehyde resin acid colloid is illustrated below.
The component ratios are the same as in Example A.
To 150 g of distilled water cooled to 14C in an ice bath, was added 25 g of trimethylolmelamine with stirring. Then 47.5 g of 37% formaldehyde was added, and to the suspension was added 6.6 g of concentrated HCl in 32.5 g of distilled water. After several hours of stirring the suspension became a milky solution.
The temperature was allowed to rise to ambient over-night, with slow stirring, then diluted with 182 g of distilled water. Percent solids was 6.9%.
Preparation of polyvinyl alcohol/melamine-formaldehyde interaction products Example 1 The "slurry technique" is illustrated in thls example. To 10.~ g of "high efEiciency" type melamine formaldehyde resin acid colloid (7.2% solids, prepared according to the method of Example A) was added 96 g of distilled water, with slow stirring, at room tempera-ture. To the above was added with stirring 1.5 g of ,,,~,?~

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a medium molecular weight, fully hydrolyzed grade of a commercial polyvinyl alcohol powder having a ~% aqueous solution viscosity at 20C of 30 mPa.s (30 cps), about 1% acetate groups, over 99.0% passing through a #10 sieve.) The slurry was then heated with stirring to 85-95C for 15 minutes, in which time the polyvinyl alcohol appeared to be completely dissolved. The clear solution of product was cooled to room tempera-ture. The pH was about 2.8, solids content 2.0%, and solution viscosity low (Brookfield less than 1 cps).
The polyvinyl alcohol/melamine-formaldehyde resin ratio was 2/1. Tnteraction products of this type attempted at 12% total solids failed (gelled in a few minutes) also failed at 4% solids (gelled in less than 16 hours)l but was stable at 2.9% solids.
Example 2 This example is similar to Example 1 except for using melamine-formaldehyde resin acid colloid prepared according to the method of Example B.
The run was essentially successful in this case even with 5% total solids present (although the viscosity did rise to about 3.2 cps after 48 hours, and traces of gel were evident). The adsorption efficiency on bleached cellulose pulp at a pH of 4.0 was greater than 73% (as compared to about 18% for straight polyvinyl alcohol)O
Example 3 This example is similar to Example 1, except for using melamine-formaldehyde resin acid colloid prepared according to the method of Example D.
Successful products resulted at 2~ level, and at 2.7% solids but failed at 6% solids (gelled within 16 hours), but was stable at 2.9% solids.
Example ~
To a 250 ml Erlenmeyer flask containing a magnetic s-tirring bar was added 55.6 g of a 4.05%
aqueous soLution of the polyvinyl alcohol employed in ,~

Example 1. To this solution, at room temperature, was added, wi-th stirring, 10.5 g of a melamine-formaldehyde resin acid colloid, 7.15% solids, pre-pared according to the method of Example D. This was followed with 84 g of dis-tilled water, and the tempera-ture was then raised to 65C for 15 minutes. An active, stable product resulted, the polyvinyl alcohol/melamine-formaldehyde weight ratio was 3/1, and solids in solution were 1.9%.
.~;m;l~r successful examples were run with other grades of polyvinyl alcohol, with various m~l~m;n~-form~ hyde resin acid colloids, with polyvinyl alcohol copolymers at dif-ferent ~olyvinyl alcohol/m~l~m;n~f~ hyde ratios, and in the presence of corn starch or potato starch. Also successful was the addition of a hot ~ul~c~ltL~d (10%) solution of polyvinyl alcohol to the ~ t~d (0.6%)T~l~m;n~.-fo~1~hyde resin acid colloid. In fact -this is one of the preferred procedures of preparing the polyvinyl alcohol/~ m;n~-f~1d~hyde resin interaction products of the present invention.
Comparative Example 1 A 10.1% solution of the polyvinyl alcohol employed in Example 1 (66.6 g) was mixed with a 7.2%
melamine-formaldehyde resin acid colloid ("high efficiency" type) (31.2 g) plus 2.2 g of distilled water at room temperature to give a 3/1 polyvinyl alcohol/melamine-formaldehyde blend at 8.7% overall solids. The viscosity of the "solution" rose rapidly;
from 6.3 poises (as measured with Gardner Holdt cali-brated viscosity tubes) after about one minute after mixing, to greater than 148 poises after 30 minutes, to form a flrm gel.
Comparative Example 2 To 37.2 g of a 7.2% melamine-formaldehyde resi.n acid colloid ("high efEiciency" type) was added 158 g o:E water and then, with stirring 5.36 g of the polyvinyl alcohol powder ~mployed in Example 1. The '733~

polyvinyl alcohol/melamine-formaldehyde ratio was 2/1, and the solids of the product in solution were

4%. The slurry was then heated to 85CI with stirr-ing. A gel resulted in less -than 16 hours~
Comparative Example 3 To a solution of 4.4 g o~ medium molecular weight fully hydrolyzed grade of a commercial polyvinyl alcohol [having a 4% aqueous solution viscosity at 20C of 14 mPaOs (cps) and about 1% acetate groups]
in 100 mils of water was added 1 g of PAREZ 607, TMM
with stirring. The T~M slowly dissolved. The pH was then lowered by addition of 2.9 g of concentrated HCl.
After stirring 16 hours at room kemperature, a colloi-dal solution resulted~ The product activity was very low (adsorption efficiency on cellulose pulp only 8 at pH 4.5).
Example 5 As suggested above, interaction between pol~vinyl alcohol and the melamine-formaldehyde resin acid colloid to form a new product is indicated by:
(1) the marked increase in viscosity which occurs when the components are mixed at somewhat higher concentrations than within the scope of the present invention, but otherwise under the same or even milder reaction conditions;
(2) the marked increase in adsorption efficiency on cellulose pulp compared to that obtained when straight polyvinyl alcohol is used which indicates a polyvinyl alcohol with cationic groups.
This is shown in Table I.

.., ..~, 73~
.. , t TABI,E I
Composition of Percent Adsorption Additive to Pulp(a) of Additive on Pulp (b)

5 3/1 PVA/MF (HE) 69 2/1 PVA/MF (HE) 94 MF (HE) 89 Cationic Starch 32 (a) All applied at 1. 6% concentration based on dry pulp. The polyvinyl alcohol was that employed in Example 1. MF (HE) was the melamine-formaldehyde resin acid colloid, "High Efficiency" type. The cationic starch was CATO* 15 (National Starch).
(b) The pulp used was unbleached western kraft, Canadian standard freeness (CSF) value of 600.
The consistency of the beaten stock in the slwrry was 2 . 5%. The initial concentration of the additive in the aqueous phase was 0.041%.
A gravimetric procedure was used for determining the concentration of the additive in the filtrate after exposure to the pulp. The pH of the stock was 4.5 except in the case of straight polyvinyl alcohol, where the pH was 6 . 5.

* denotes trade mark '~;1 ~3~

It is evident from Table I that adsorption level of the polyvinyl alcohol/melamine-formaldehyde "high ef~iciency" interaction products on the pulp are much higher than straight polyvinyl alcohol or even than a commercial cationlc starch.
(3) Spectral data also indicate interaction between the polyvinyl alcohc>l and the melamine-formal-dehyde resin acid colloid~ (a) The solutions gave colored reaction products with boric acid-iodine, as does straight polyvinyl alcohol. However, the inten-sity of the complex was less than expected from straight polyvinyl alcohol~ (b) In the infrared spectra of cast films air-dried at room temperature, the 1000 cm 1 peak for the melamine-formaldehyde resin acid colloid has disappeared, suggesting that most of the methylol groups have reacted. Also, the polyvinyl alcohol absorption at about 830 cm 1 ascribed to the -O~ bond has decreased, suggesting some reaction with these groups.
Example 6 Increased adsorption efficiency over straight polyvinyl/alcohol and increased adsorption rate over commercial cationic wet-end additives (such as KYMENE 557 presumably a cationic polyamide containing amino groups post-reacted with epichlorohydrin, obtained from Hercules) were shown using a mixture of bleached pulps (50/50 bleached northern softwood sulfite/bleached northern hardwood kraft) with other conditions being the same as in Example 5. Results are summarized in Table II. Thus, the 3/1 polyvinyl alcohol/melamine-formaldehyde interaction product has an adsorption efficiency after 15 minutes exposure to the wet pulp of about 80%, while straight polyvinyl alcohol has only 18~.
Also, the polyvinyl alcohol/melamine-formaldehyde , t' ~

733;~

achieved its maximum adsorption level wlthin 1 minu-te, while K~MEME 557, did not achieve high levels of adsorption for over 5-10 minutes. Thus polyvinyl alcohol/melamine-formaldehyde offers more flexibility in points of addition (fan pump, machine chest, head box, etc.) to the Fourdrinier paper machine than other cationic wet-end additives.
TABLE II
Percent Adsorption of Additive on Pulp after indicated minutes of exposure Composition of Additive to Pulp 1 5 10 15 3/1 P~A/MF (~E) 84 79 - 80 Example 7 As mentioned above, the solutions of the polyvinyl alcohol/melamine-formaldehyde interaction products of the present invention possess excellent shelf stability. Thus no buildup of viscosity or gel occurs over a period of weeks-to-months, and activity remains high for at least two months for the polyvinyl alcohol/melamine-formaldehyde products of -the above examples. Also, unlike the sitll~t;~n in cationic starch solutions, no tendency for mold buildup is seen.
These products also are heat curable on the paper machine. That is, significant levels of permanent wet strength are rapidly attained, apparently faster than with urea-formaldehyde resins, and probably as fast as with straight melamine-formaldehyde resins.
On the other hand, recovery of waste paper or broke is ~aster than with melamine-formaldehyde resins by heating under very mild acid conditions (see Example 12).
This example quantitatively indicates the advantages in wet web strength for the polyvinyl alcohol/melamine formaldehyde interaction products .~1 3~

of the present lnvention. Paper was made on a 36 inch wide Fourdrinier, operated at lO0 feet/min. Pulp was a mixture of 70/30 hardwood bleached kraft/softwood bleached kraft, refined to 500 CSF. The additives were introduced to the furnish at the fan pump. For wet web studies, 2" wide strips were cut off the edge of the web at the couch roll, and the breaking force at two differ-ent water loadings was measured on an Instron. The breaking length (strength) was calculated, and inter-polated values of the breaking length were compared atequivalent water loadings (35% solids), and at concen-trations of the additives at which they are usually used for dry and/or wet paper strength applications.
These are given in Table III.
TABLE III
Breaking Length Additive Conc., % Meters Primary Use KY~ENE 557H 0.6 57 for wet strength CATO 9 cat- ~ 0.6 63 for dry strength ionic starch~ 2.0 est. 60-65 " "
MF Resin 2.0 58 for wet strength None - 7l 3/l P~A/MF 1 .6 9l of Example 4~ 2.0 96 It can be seen that most of these additlves actually decrease the strength of the wet web (presumably by interfering with cellulose pulp-pulp interactions).
The polyvinyl alcohol/melamine-formaldehyde interaction product, however, truly enhances the wet web strength.
Example 8 This example demonstrates the higher retention of cellulosic fines possible with the use of polyvinyl alcohol/melamine-formaldehyde as an additive. The pro-cessing advantages that result with high first pass retention are recognized in the literature (K.W. Britt, ~!

r` ~ 3 2~
Paper Trade Jour~al, April 15, 1977, p. 36). ~lso, it is well kn~ hat retention of cellulosic fines (.and also pigment and/or iller) can be mar}cedly lowPr at the high shear rates experienced in the co~aercial paper 5 mill than at th~ low shear rates in con~en~ional lab tests. R. Britt has de~eloped a single screen device for de~exmination o~ cellulosic fines, :filler and pigment he laboratory, under condition~ which approximate the ~urbul~nce experienced by the pulp s~ock as i-~ drains 9 iR ~he initial sections of a paper ~ h;ne wire. This is called ~he l'dyn~[~ic draina~e ~ar", or thP "Britt Jar".
This is described iIl TAPPI Repoxt Wo. 57, "Retention of ~ine So~ids During Paper Manufacture" (9jl~75).
App~n~; ~ in t:~lapter 8 by K. W. Britt.
. Following Britt ' s procedures f t}le following results su~arized i~ Table IV were ob~; n~ for the ~/1 PtJA/MF
teractio~ product compared with two co~mnexclal cationic starch~s f at ~arious addil:ive concentra~ions and at variou~ pE~'s of the puLp s~ock.

~t~33'~

rAsLE IV
CON~;.t;~ xAT::ON ~a) ~-JO NL1~ Çb~
A~DITIV~ r ~ ) DEI ( 96 ) Wo~e - 4S 39.5 5.5 34.3

6~,5 45O~
Cationic Starch ~) 0 .1 4 . 5 37 O 9 5.5 50.~
6.5 54.3 .7 ~O5 53~8 5~5 510 ~
6~5 54O9 2~0 4.~ 3~.9 5.5 4~.5 6.5 49.. 8 3/1 PtJ1~/L~?( 0 . 1 4 . 5 62 . d, _ 5.5 50.8 6 . 5 0 7 ~05 61~3 5.,5 53.
6.5 45.2 2.0 4.5 8400 5.5 71.g 6.5 62.7 Ca~ionic Starch~e~ 2.0 6.5 31.4 (a) Based orl dry pulp (b) Ba~ed on dry pulp, as detPrrn; ne~ in Britt J~r, at 10~0 ~pm~ Western u~ble-tche~ kraf~ pulE~, CS~
620, tap water used. Le~el o~ cellulosic fines in this pulp 9 . 3 ~ ~
(c) C~O 15, National Starch.
~d) P~:epared by method o~ Exa~;lple 4.
~e) CU~TO~ 9, Na~,io~ Starch.

7~3~

It is evident that pEI 4 . 5 ~s op timum ~ x ~etention purpases ~o~ t}~e polyvinyl a~coh~l/m~l ~m; n,o~
~ormaldehyde, while p~I 6 . 5 is perhaps best for th~
cationic st rches.. It is also e~id~n~ ~ha~ ~or eac~
5 additi~e at its opt~um p~, the ~olvvinyl alcohol/
nel ~m; n~-form~l ~ehyd.~. is su~?erior ~o ~he cationic starch~s a~ a 1 addi~ive concentration~.
simi ~r a~a~tagss were ~hs:wn in retention o~ elay or of pigment (TiO2) on the unbleached 10 k~aft ~ul~ us~d abo~e, and a;Lso on b1~che~ Dulps, as shot~m iIl Tables V a~d VI.
~AB~ V ' AdAitiv~ t~ Conc. ~ % Cla~ Retention(a) ~one ~2 Cationic Starch lS
~? (~E) ~esi~ 12 3~1 PV~/MP 28 ~a) 50/50 Bleached ~o~wood sulphit~bleached harawood k~a~ pulps~ SF ~50û. ~ri~t ;~a~ a~
1000 rp~a. Cationic s~arch was GhTO ~.
~he poly~rinyl ~lcoh~ m;r~form~l ~ehyde was prepared by me~hod of Exa~aple 4.
Z5 T~BLE VI
~dditive Conc.~ TiO~ Retention ~a) Cati~ c Starch ~ . 7 22 2.û 37 ~ Resin 2 . û ~ 16 3~'1 PVa~F a.~ 45 2~0 58 ta) 50/5a bl.~ached softwo~d sulphi~/bleached har~wood kraft pulps, CS:F 500~ Britt J~r at 1000 rprn.
3 S Concentrati~n o additi~re based on pulp ., The cation:ic starch was CA~O ~. ThQ P~A/MP was prepared by method o ~ Example 4 0 2~

73~

To show that these high le!vels o ines retent:ion were not ac:comparlied by over10 ::culation, which c:ouJ.d hurt the p~per properties or processin5 character.istics, ~ L op~ical properties of ~}le resulti2lg S paper were ~x~m~ r~ed, and fot~ to be excell~t. This.
is discus~ed below in Exam~?le 9.
T~e iEollQwing examples show the e~ha~ced paper and paper-rela~ed prcdu :: ~s that can be ob~ai~ed th:rough ~he use of th~ poly~inyl al~:ohol~mel ~ ; n~
10- for~ yae i~texa::tion prorluc~s as additi~res ~o ~e paper m~hin~, Ex mple 9 ~ 5ir~y paps~x manufac~ured on the Fourdrinier ~-~hi n~ as des ::r bed n Exa~nple 7 ~ the scattering coe ficien~ w;~a5 de~rm;tt~ s per T~PPI method T21~-05-63 for de~erm; ~i ng r~lQrtanc~, th~n using data i~ TAPPI
425~05 75 for SW ~aluPs, di~iai.ng }:y the basis wei~ht . . and ~nultiplyi~g by ~o,ooa ~c ge~ ~ralues in cm~/g. The da~a ar~ gi~ren in Table ~7II ,, :Eor paper eont~; ~;ng lQ96 2U elay.
T~BI,E VII
Sca~tering Addit ve Conc., ~ Coe~ ie~t (cm2/g~
~one ~AT0 9 0, 6 2 u 0 420 ChT0 15 0 . 6 416 2.0 3a2 0 o 6 ~ 0 8 ~.0 ~ 420 3~1 P~M~? 0.6 ~7Z
~ . ~ 45a ta) 70/30 Hardwood bl~ached kraft~so~twood bleached 5 kra~t:, CSF 500, cancentration is ~ased on dry pulp.. The p~rA/MF was made by me~hod of Example 4.

3~3~3~

The above shows the enhanced scattering with the PVA/MF
interaction product, which suggests better paper forma-tion and/or filler distribution in the paper.
Example 10 Handsheets were prepared in a Noble and Wood sheet mold (8" x 8"), pressed between rolls, and dried in a Noble and Wood Model E-8 drier. The pulp was unbleached western kraft refined to CSF 600. Tensile properties were determined as per TAPPI 494-05-70.
Results are indicated in Table VIII.
TABLE VIII
Dry Tensile Dry Breaking Energy 2 AdditiveConc., %Len~th (m) Absorption (J~n ) None - 4570 82 15 MF (HE) 0.7 5830 128 2.0 6070 131 Cationic Starch) 0.75480 123 (CATO 9) ) 2.0 6420 152 ~m; nnrol yamide-~r~X~ ed 20 (K~E 557) 0.7 5820 126 3/1 PVA~ E) ) O.7 6770 166 of Ex. 3 ~ 2.0 7740 174 3/1 PVA/MF(HE) ) 0.77300 161 of Ex. 1 ~ 2.0 7430 176 It can be seen from these data that the PVA/
MF interaction products exhibit superior dry strength and dry toughness over commercial additives, and, in fact, the PVA/MF's are better at 0.7% concentration than are the controls at 2%. Such advantage is also maintained in the presence of filler.
Example 11 The PV~/MF interaction products are also quite effective wek strength agents for paper. This is shown in Table IX.

"~

73~

2~
~E :[X
Wet Breaking Len~() Wet Tensile Ener~
~m)Absorption(a)(J/m ) A~ditive No Clay ~ith Clay No Clay Wi~h Clay None 260 350 4 5 Cationic Starch(b) ~00 300 7 5 ~minopoly~.d~
e~X;~ze~(c) 2300 1500 76 45 MF (HE~ 1700 1200 55 36 2/1 PU~/MF (HE) of ~lmple 4 18Q0 1200 76 44 (a) determined on unbleached western kraft pulp, refined to-~SF 600. Data on handsheets; additive level 2% based on dry pulp, filler leval 10% clay based on dry pulp.
(b~ CATO 9.
(c) KYMENE 557.
The PVA/MF interaction product demonstrates better wet toughness, wet tensile energy absorption (TEA), than the commercial straight MF resin or, of course, the cationic starch, which is known to have no wet strength properties. The aminopolyamide-epoxidized appears to be somewhat better than the PVA/MF product of the present invention in wet strength (wet breaking length). However, the aminopolyamide-epoxidized is much more expensive, and also is much inferior to the polyvinyl alcohol/
melamineformaldehyde product in ease of broke or waste paper recovery.
~.x~mp1e 12 The present example il].ustrates that epoxidized aminopolyamide (KYMENE 557) is much inferior compared to the polyvinyl alcohol/melamine-formaldehyde interaction product of this invention in ease of :bxoke or waste paper recovery. This is demonstrated in Table X, where data on paper made from i `~'' f~

3~

bleached kraft pulps on a Fourdrinler show the loss in wet strength of the paper on heating the paper in very dilute acid solution. Such loss is s-tength in of course necessary for ready paper recovery. Apparently 5 paper containing polyvinyl alcohol/melamine-formaldehyde additive is more readily broken down by dilute acid than is straight melamine-formaldehyde resin, and quite evidently much more readily broken down than is the epoxidized aminopolyamide.
TABLE X
Wet Tensile Energy ~et E~reaking Length (a)(m) ~bsorption(a)(J/m2) Yi2~/25~ 0.~2-5N-~ICL/H2O/25C/0.025N HCl/
Additive 0.5 hrs90C/0.5 hrs 0.5 hrs90C/0.5 hrs 15 None 78 78 1.2 1.2 Cationic Starch(b) 197 130 1.6 1.6 3/1 PVA/~V 1012 213 28.4 2.1 (HE~ o~
MF (HE) 1497 409 2~.4 2.6 20 ~m; n~-~lyamide~
Pr)~ ~ (e) ~1500 ~1490 ~28.0 ~27.0 (a) Machine sheets ex Fourdrinier, 70/30 bleached hardwood/sc~ftwood kraft blend, refined to CSF
500. All additives at 2% concentration based on dry pulp~
(b) CATO 9.
(e) KYMENE 557. The change in wet property values on acid treatment using this additive were esti-mated from data in paper by M.E. Carr et al, TAPPI _, No. 10, Oct. (1977) pp. 66-69.
Example 13 A 3/1 by weight raw potato starch/MF (HE) aqueous solution at 2~6 concenkration was made in 35 analogous fashion to the 3/1 PVA/ME` (HE) interaction product. Also, a 3/1/1 starch/PVA/MF

~1 ~ 3 3~
(HE) in~eraction product was made in similar fashion.
In ~hese ~ases, ~h~ MF (~E) resi~ acid colloid was made as in Example A, and the latter was then reacted with the potato starch and/or the polyvinyl alcohol as in Example 4. The starch~melamine formaldehyde and the starch/poly~inyl alcohol/m~ ;ne formaldehyde solutions were s~able for less than.three (3) weeks, while ~he pol~vinyl alcohol/melamine-formaldehyde was stable for over three ~3) months. ~a~dsheets were prepared using bleached sulfite pulp. A list of pr~per~ies of ~he h~n~shee~s, along wi~ a control con~;ni~g no wet-end addi~ive is gi~en in Table XI.
Thus the superiority of the 3/1 polyvinyl alcohol/
m~l ~m; ne-fo~maldehyde o~er the 3/1 ~tarch~ ~elamine formaldehyde i~ shown in solution stability and in paper properties. In fact, in ~everal properties, the 3/1 p~ly~inyl alcohol/melamine-formaldehyde at O.7% is e~al or s~perior ~o the 3/1 s~arch/melamine-formaldehyae at 2~ concentration. Also kh~ 3~1/1 starch/polyvinyl a~cohol/mel ~m~ ~e-formaldehyde is superior to 3/1 starch/m~l ~m; ne-ormaldehyde~

~5 3~:

TABI~ XI
- Additi~7e 3/1 3/1 ~/1/1 P~ Star~? S~ar~JP~
~ qh~ p,~ a) N~ne 0.7~ ~.~ 2.0%2~09 ~,t F~tor (Mullen) 19 30 3S 25 31 Tear Factor (~ ldr~r rr~ 88 114 118 69 lO~
Fold ~ ~ (TL-~V~.La~ 12 23 33 :23 38 ~ 17~b~
l~y ~eaki~g I~ h ~ 2950 4~ao 4sao 3760 gS70 Dry TerLsile ~ergy 35 83 80 77 84 on (1~) ~J/m2) I:~y Initial ~dulus (~SI~150 220 290 250 240 reakir~ Ien~h ~m~230 360 630 270 290 ~e~ Tensil~ Energy 5 9 21 9 8 ~soL~)LiarL (T~) ~J/m~
h~t IDi~ 8 8 l~i 9 10 (a)~Bl~ached Mor~he~n Sul~i~e Pulp, CSF 5000 Shee~s aged.
one (1) monthO
tb1Value in parenthesis for sheet aged two (2) months~

3~

, 33~

3~
With clay at 10~ concentxation in the papert -similar advan~ages of 3/1 PV~ over 3/1 s~arch/MF
were ~hown in burs~, rolding endurance and dry and wet breaking length and tensile energy a}~sorption.
5 Again ~he 3~1/1 starch/P~A/L~F showed some a~va~a~ages over 3fl starch/MF. The results are summarized in Table XII.

T~LE XIT

~ddi~ive FrAT~ f~t PVA jMF5 ~arch/~lFS tarch~PVA/
Properties (a) ~ 0 . 7~ 2 . 0% 2 . 0 ~ 2 . û %
~urs~ Factor ~11~3 15 22 28 16 22 T~ar Pa~or (Fl.. - .~r~ r) 100 111 111 103 105 E~old ~ r ~J ~
~v~a~, ~T) 7 lt) 26 12 15 ~ ~g 2 oL~gth (m)26QU33704û90 2690 3440 ~:y ~ (J/m2) 2~ 52 75 49 57 R~ Initi~
~lt~ (~?SI~180230250. 250 220 ~t Brea~n~
~h (m)160180 540 160 230 25 ~t ~ (~2)3.5 5 18 5 6 ~ibt Irli~ial (~eSI) 9 9 12 6 11 -(a) ~ hf~d Nor~ Sulfite Pulp, C5F 500. Sheets c~nt~;nin.
1096 clay~`a.~ed one (1) ~nth.
~b) Valu~ L~I~t~ted f~am h~tl-t~it~ ; cont~inin~ U~ 96 O:f clay.

3'7~33~
3~
E ~LE 14 This exampl~ illus~ra~es the use o highex aldehydes ~o modi~y ~he PVA~F interaction productsO
In run (C) "high efficiencyl' mel~;n~-formaldehyae resin acid co~lold was prepared as in Example ~. In runs ~D~ a.nd ~E) in place of the ad~itional ~ormaldehyde ace~ Phyde was added during ~he l!ripening'3 of ~he ~F resin acid colloid. These were ~hen aaded to t~e pulp and handshee~s were made. ~n Table XIII are shown ~he adsorp~ion of the a~di~ives to ~he pulp and ~he resul~ing ~aper handsheet properties. It is.
clear ~hat results with addi~ional ace~aldehyae were as good, at least in dxy proper~ies, as with ~h~
additional ~oxmaldehyde.

2~

3s TABLE X I I I
EIandsheet Propertïes ~c) Dry Adsorption Mullen Bre~king OI1 pulpBurst Leslgth Additi~e (b) (96 ) (a)Factor (~) ~A3 None - 39 5800 (B) PVP~ 4 . 9 (C) 2/1 PV~/~ 96 . 8 ~8 6~00 (~ldP~yde) (66~) (d3 (D) 2/1 PVA/UF 94 . 9 4g 7200 (acetalde~yde) (66%) (d) (E) ~/1 PVA/MF - 4~ 7~00 (239~) ~d) ' ~0 ~5 TA:E~LE XIII (cont7d.) ~andsheet Proper-ties ~C) Dry Tens ile ~
Energy Scot~ (f) ~reak AbsorptionInternal Length Additive (b) (J/M~) Bonding (~1) (e) (A) Nc~e 100 76 220 ~B) PVA - ~ .
(C:) 2~1 Pt?A/~qF 105 97 1800 (~ A~hyd~) (66%~ (d~
(D) 2/1 PVA/~F 124 105 1380 ~ac:etaldehyde) (66~6) (d~
(E~ 2/1/ ~ F 142 lOS 1520 ~a~etalde~de~
( 23% ) (d) ta~ Determined as described in footTlote ~ o Table I.
(h) ~ 2% loading of additive based on dry pulp.
LC) Made with unbleached kraft pulpt CSF ~600, no i~iller or size presen~. Measuremen~s usi~g TAPPI procedures as in Table XI.
td~ The percent indicated is the concentration of the aldehyde on a weigh~ asis, xelative ~o ~he trim@thylol m~ e used in making the P~F resin ac:id colloid.
(e) l~easured after exposure to H~O/25t::~0 . 5 hr ~
~f) In ft-lb x Lo3. TAPPI method Tr403 was fo}lowed.

. . .

y ~ V3 ~dy EX~MPL~ 15 :: This example illustrates ~e utili~y of PVA/l~E in~erac~ion products, in which a dialdehyde t glutaraldehyde was added during ~he MF xesin acid oolloid ripening process. Runs (~), (C~ and (D~ were carried ou~ following ~he general procedure of Example 14, Data are s~marized in Table XIV, compar-ing the addition of slutaraldehyde wi~h ormaldehyde.
The solution s~ability of t:he glu~araldehyde-modified produc~ was consideralb~7 lower than ~h~ formaldehyde~
modified products. Ne~ertheless, when used shortly af~er prepara~ion~ the filler ~eten~ion in the pulp is surprisingly high using the glutaraldehyde~ ~lso, goQd paper propertie~ resulted even though the conce~tra~ion of the products added to the pulp was lower than in Example 14. Impro~ed solu~ion stabili~y ~a~ least five days) was ob~a;ne~ with a lower level o~ ad~ed glutaraldehyde ~13~ ~y weight b~sed o~ th~
MP resin).

33~

TAE~LE XIV

( 3 Filler Scot~
Solution e Retention Internal Additive~ ~ Stabilitv ~g~) (c) Bondin~(d~
(A) ~one - 1. 3 4 2 ~B) 2/1 PV2~ >3 mo. So2 49 ~f~ hyde) t66~d) (h) ~::) 2~1 P~ >3 mo. 7.6 63 (fi~ P~de) ~239e;) tb) (D) 2~ 4 8 hr . 11. û 75 ~23~3 (b) ~0 33~

TABLE XIV (cont'd) Wet Wet Tensile Breaking Energy Length Absorption Additive(a) (M) (d) (J/M2) (d) (A) None 220 4 (B) 2/1 PVA/MF 840 17 (formaldehyde) (66%) (b) (C) 2/1 PVA/MF 900 18 (formaldehyde) (23%) (b) (D) 2/1 PVA/ML~1000 26 (glutaraldehyde) (23%) (b) 15 (a) At 0.7% concentration of additive based on pulp. ~o size or alum present. Pulp is unbleached kraft as used in Example 10.
(b) Concentration of aldehyde by weight, based on trimethylolmelamine.
(c) Clay filler data at low shear rate. Clay was added at 20% based on weight of dry pulp.
(d) At æero filler level. Data for Scott Internal Bonding in ft-lb X 1000.
(e) Refers to stability of additive solutions com-pared at 2% solids concentration.

Claims (61)

1. A stable aqueous polyvinyl alcohol/
melamine-formaldehyde resin interaction product com-prising polyvinyl alcohol polymer and cationic melamine-formaldehyde resin acid colloid in a polyvinyl alcohol/
melamine-formaldehyde resin acid colloid weight ratio, on a dry basis, of from about 1/1 to about 5/1 and sufficient water to give a solids con-tent of from about 0.7% by weight up to a level that will not cause gela-tion to a stage of no flow under the force of gravity in 48 hours, but not in excess of 6% by weight.

2. The product of Claim 1 wherein the solids content of said polyvinyl alcohol/melamine-formaldehyde resin acid colloid interaction product is from about 0.7 to about 3.75% by weight.

3. The product of Claim 2 wherein the poly-vinyl alcohol polymer is at least about 99 mole %
hydrolyzed.

4. The product of Claim 3 wherein the poly-vinyl alcohol polymer has an inherent viscosity of from about 0.3 to about 1.4 dl/g measured in water at 30°C
at a concentration of 0.5 g/dl.

5. The product of Claim 4 wherein the poly-vinyl alcohol polymer has an inherent viscosity of from about 0.5 to about 1.1 dl/g.

6. The product of Claim 2 wherein the poly-vinyl alcohol polymer is a copolymer of vinyl alcohol and up to about 10 mole % of a comonomer selected from the group consisting of a-olefins having 2 to 18 carbon atoms, vinyl esters of saturated carboxylic acids wherein the acid moiety has up to 18 carbon atoms, unsaturated mono- or dicarboxylic acids of 3 to 5 car-bon atoms, and esters of said unsaturated mono- or dicarboxylic acids wherein the alcohol moiety has 1 to 8 carbon atoms, N-substituted amides of unsaturated monocarboxylic acids, allyl alcohol, allyl esters of saturated carboxylic acids wherein the acid moiety has up to 18 carbon atoms and vinyl halides.

7. The product of Claim 6 wherein the melamine-formaldehyde resin acid colloid is prepared by adding from about 8 to about 100 percent by weight, based on the weight of trimethylolmelamine, of aldehyde having up to about 10 carbon atoms to tri-methylolmelamine dissolved in water and aging said solution in the presence of about 0.6 to 0.8 mole of hydrochloric acid per mole of trimethylolmelamine.

8. The product of Claim 7 wherein said aldehyde is selected from the group consisting of formaldehyde and its homologues, substituted aldehydes and polyaldehydes.

9. The product of Claim 8 wherein said aldehyde is selected from the group consisting of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, 2-ethyl hexyl aldehyde, phenylacetalde-chloroacetaldehyde, 3-methoxy propionaldehyde, aldol, crotonaldehyde, glutaraldehyde, glyoxal, adipaldehyde and terephthalaldehyde.

10. The product of Claim 8 wherein said aldehyde is formaldehyde.

11. The product of Claim 8 wherein said aldehyde is acetaldehyde.

12. The product of Claim 8 wherein said aldehyde is glutaraldehyde.

13. The product of Claim 2 having a solids content of from about 2 to about 3% by weight.

14. The product of Claim 13 wherein the polyvinyl alcohol/melamine-formaldehyde resin acid colloid weight ratio, on a dry basis, is from about 2/1 to about 3/1.

15. The product of Claim 2 containing up to about 6 parts by weight, per 1 part by weight of poly-vinyl alcohol, of starch selected from the group con-sitting of unmodified, modified and degraded starches and starch derivatives.

16. The product of Claim 15 containing up to about 3 parts by weight, per 1 part by weight of polyvinyl alcohol, of starch.

17. A process for preparing stable aqueous polyvinyl alcohol/melamine-formaldehyde resin inter-action product comprising (a) preparing cationic melamine-formaldehyde resin acid colloid, (b) mixing said melamine-formaldehyde resin acid colloid with polyvinyl alcohol for a sufficient time to yield said polyvinyl alcohol/melamine-formaldehyde resin inter-action product at the given mixing temperature, in the presence of sufficient water to give a solids content of from about 0.7% by weight up to a level that will not cause gelation to a stage of no flow under the force of gravity in 48 hours, but not in excess of 6% by weight, the polyvinyl alcohol/melamine-formaldehyde resin acid colloid weight ratio, on a dry basis, being from about 1/1 to about 5/1.

18. The process of Claim 17 wherein the solids content of said polyvinyl alcohol/melamine-formaldehyde resin acid colloid interaction product is from about 0.7 to about 3.75% by weight.

19. The process of Claim 18 wherein said melamine-formaldehyde resin acid colloid and poly-vinyl alcohol are mixed at about ambient temperature for about 24 hours.

20. The process of Claim 18 wherein said melamine-formaldehyde resin acid colloid and polyvinyl alcohol are mixed at a temperature of from about 30 to about 90°C for a period of from about 3 to about 15 minutes.

21. The process of Claim 18 wherein poly-vinyl alcohol powder or granules are slurried in said melamine-formaldehyde resin acid colloid and the slurry is heated and stirred at a temperature of from about 80 to about 95°C for a period of from about 0.25 to about 2 hours or until the polyvinyl alcohol dissolves.

22. The process of Claim 18 wherein sur-ficient water is employed to give a solids content of from about 2 to about 3% by weight.

23. The process of Claim 22 wherein the polyvinyl alcohol/melamine-formaldehyde resin acid colloid weight ratio, on a dry basis, is from about 2/1 to about 3/1.

24. The process of Claim 22 wherein poly-vinyl alcohol is dissolved in water with mixing and heating to give about 10% by weight solution, said hot polyvinyl alcohol solution is added to about 0.6% by weight of the melamine-formaldehyde resin acid colloid, said melamine-formaldehyde resin acid colloid being at about ambient temperature, and the resulting mixture is mildly stirred for about 15 minutes.

25. The process of Claim 18 wherein said melamine-formaldehyde resin acid colloid and said polyvinyl alcohol are mixed in the presence of up to about 6 parts by weight, per 1 part by weight of polyvinyl alcohol, of starch selected from the group consisting of unmodified, modified and degraded starches and starch derivatives.

26. The process of Claim 25 wherein said starch is present in an amount of about 3 parts by weight per 1 part by weight of polyvinyl alcohol.

27. The process of Claims 18, 22, 23 and 26 wherein the polyvinyl alcohol polymer is at least about 99 mole % hydrolyzed and has an inherent vis-cosity of from about 0.5 to about 1.1 dl/g measured in water at 30°C at a concentration of 0.5 g/dl.

28. In a process for increasing the wet strength, dry strength and other properties of a product derived from fibrous cellulosic material, the improvement which comprises treating said fibrous cellulosic material with the polyvinyl alcohol/
melamine-formaldehyde resin interaction product of Claim 1 in an amount of from about 0.02 to about 10%, based on the dry weight of said fibrous cellulosic material.

29. The process of Claim 28 wherein the solids content of said polyvinyl alcohol/melamine-formaldehyde resin acid colloid interaction product is from about 0.7 to about 3.75% by weight.

30. The process of Claim 29 wherein the polyvinyl alcohol polymer is at least about 99 mole % hydrolyzed.

31. The process of Claim 29 wherein the polyvinyl alcohol polymer has an inherent viscosity of from about 0.5 to about 1.1 dl/g measured in water at 30°C at a concentration of 0.5 g/dl.

32. The process of Claim 29 wherein the polyvinyl alcohol/melamine-formaldehyde resin inter-action product has a solids content of from about 2 to about 3% by weight.

33. The process of Claim 32 wherein the polyvinyl alcohol/melamine-formaldehyde resin acid colloid weight ratio, on a dry basis, is from about 2/1 to about 3/1.

34. The process of Claim 29 wherein the polyvinyl alcohol/melamine-formaldehyde resin acid colloid interaction product is present in an amount of from about 0.05 to about 3%, based on the dry weight of the fibrous cellulosic material.

35. The process of Claim 29 wherein said fibrous cellulosic material is treated with said polyvinyl alcohol/melamine-formaldehyde resin acid colloid interaction product at a pH of from about 4 to about 8.

36. The process of Claim 35 wherein the pH
is from about 4 to about 6.5.

37. In a process for increasing the dry strength and other properties of a product derived from fibrous cellulosic material, the improvement which comprises treating said fibrous cellulosic material with the polyvinyl alcohol/melamine-formal dehyde resin interaction product of Claim 15 in an amount of from about 0.02 to about 10% based on the dry weight of said fibrous cellulosic material.

38. In a process for increasing the dry strength and other properties of a product derived from fibrous cellulosic material, the improvement which comprises treating said fibrous cellulosic material with the polyvinyl alcohol/melamine-formaldehyde resin interaction product of Claim 16 in an amount of from about 0.02 to about 10%, based on the dry weight of said fibrous cellulosic material.

39. In a process for the production of paper having improved strength and other improved properties which process comprises (a) forming an aqueous cellu-losic fiber suspension, (b) adding to said suspension prior to its formation into a sheet an additive, and (c) forming said aqueous cellulosic fiber suspension containing said additive into a sheet, the improvement comprising the use of the polyvinyl alcohol/melamine-formaldehyde resin interaction product of Claim 1 as said additive in an amount of from about 0.05 to about 10%, based on the dry weight of the cellulosic fiber, while maintaining the pH of said aqueous cellulosic fiber suspension within the range of from about 4 to about 8.

40. The process of Claim 39 wherein. the solids content of said polyvinyl alcohol/melamine-formaldehyde resin acid colloid interaction product is from about 0.7 to about 3.75% by weight.

41. The process of Claim 40 wherein the polyvinyl alcohol polymer is at least about 99 mole % hydrolyzed and has an inherent viscosity of from about 0.5 to about 1.1 dl/g measured in water at 30°C at a concentration of 0.5 g/dl.

42. The process of Claim 40 wherein the polyvinyl alcohol/melamine-formaldehyde resin inter-action product has a solids content of from about 2 to about 3% by weight.

43. The process of Claim 42 wherein the polyvinyl alcohol/melamine-formaldehyde resin acid colloid weight ratio, on a dry basis, is from about 2/1 to about 3/1.

44. The process of Claim 40 wherein the PH is from about 4 to about 6.5 and the additive is used in the amount of from about 0.05 to about 3%, based on the dry weight of the cellulosic fiber.

45. In a process for the production of paper having improved strength and other improved properties which process comprises (a) forming an aqueous cellu-losic fiber suspension, (b) adding to said suspension prior to its formation into a sheet an additive, and (c) -forming said aqueous cellulosic fiber suspension containing said additive into a sheet, the improve-ment comprising the use of the polyvinyl alcohol/
melamine-formaldehyde resin interaction product of Claim 15 as said additive in an amount of from about 0.05 to about 10%, based on the dry weight of the cellulosic fiber, while maintaining the PH of said aqueous cellulosic fiber suspension within the range of from about 4 to about 8.

46. In a process for the production of paper having improved strength and other improved properties which process comprises (a) forming an aqueous cellulosic fiber suspension, (b) adding to said suspension prior to its formation into a sheet an additive, and (c) forming said aqueous cellulosic fiber suspension containing said additive into a sheet, the improvement comprising the use of the poly-vinyl alcohol/melamine-formaldehyde resin interaction product of Claim 16 as said additive in an amount of from about 0.05 to about 10%, based on the dry weight of the cellulosic fiber, while maintaining the PH of said aqueous cellulosic fiber suspension within the range of from about 4 to about 8.

47. Paper of improved wet strength and dry strength composed of cellulose fiber treated with the polyvinyl alcohol/melamine-formaldehyde resin inter-action product of Claim 1 in an amount of from about 0.02 to about 10%, based on the dry weight of said cellulose fibers n

48. The paper of Claim 47 wherein the solids content of said polyvinyl alcohol/melamine-formaldehyde resin acid colloid interaction product is from about 0.7 to about 3.75% by weight.

49. The paper of Claim 48 wherein the poly-vinyl alcohol polymer is at least about 99 mole %
hydrolyzed and has an inherent viscosity of from about 0.5 to about 1.1 dl/g. measured in water at 30°C at a concentration of 0.5 g/dl.

50. The paper of Claim 49 wherein the poly-vinyl alcohol/melamine-formaldehyde resin interaction product has a solids content of from about 2 to about 3% by weight.

51. The paper of Claim 50 wherein the poly-vinyl alcohol/melamine-formaldehyde resin acid colloid weight ratio, on a dry basis, is from about 2/1 to about 3/1.

52. The paper of Claim 51 wherein the cellulose fibers are treated with the polyvinyl alcohol/melamine-formaldehyde resin acid colloid inter-action product in an amount of from about 0.05 to about 3%, based on the dry weight of said cellulose fibers.

53. The paper of Claim 48 wherein the cellulose fibers are treated with said polyvinyl alcohol/melamine-formaldehyde interaction product containing up to about 6 parts by weight, per 1 part by weight of polyvinyl alcohol, of starch selected from the group consisting of unmodified, modified and degraded starches and starch derivatives.

54. The paper of Claim 53 wherein said poly-vinyl alcohol/melamine-formaldehyde interaction product contains up to about 3 parts by weight, per 1 part by weight of polyvinyl alcohol, of starch.

55. A composition comprising solid poly-vinyl alcohol having a maximum cold water soluble content of about 8% by weight and solid water soluble condensation products of melamine with 3 moles of formaldehyde in a polyvinyl alcohol/melamine-formalde-hyde condensation product weight ratio of from about 1/1 to about 5/1.

56. The composition of Claim 55 wherein said polyvinyl alcohol has a maximum cold water soluble content of about 4.5% by weight.

57. The composition of Claim 56 wherein the polyvinyl alcohol/melamine-formaldehyde condensation product weight ratio is from about 2/1 to about 3/1.

58. The composition of Claim 56 wherein said polyvinyl alcohol has a maximum cold water soluble content of about 2% by weight.

59. The composition of Claim 58 wherein the polyvinyl alcohol/melamine-formaldehyde condensation product weight ratio is from about 2/1 to about 3/1.

60. The composition of Claim 56 containing up to 6 parts by weight, per 1 part by weight of poly-vinyl alcohol, of cold water resistant starch.

61. The composition of Claim 60 containing up to about 3 parts by weight, per 1 part by weight of polyvinyl alcohol, of cold water resistant starch.