CA2160088A1 - Process for the production of cellulose-containing sheet-like structures which have been given a dry strength and/or wet strength treatment - Google Patents

Abstract

Process for the production of optionally wood-containing cellulose-containing sheet-like structures, such as paper, pasteboard and card, which have been given a dry strength and/or wet strength treatment and have improved whiteness, using water-dispersible isocyanates, wherein the water-dispersible isocyanates:

a) are aliphatic, cycloaliphatic, araliphatic or aromatic isocyanates having an NCO
functionality of 1.8 to 4.2, mixed with polyether-modified aliphatic, cycloaliphatic, araliphatic or aromatic isocyanates having an average NCO
functionality of 0.8 to 3.2, b) the isocyanate mixtures a) contain 1 to 25% by weight of isocyanate groups, c) have a content of ethylene oxide units, arranged in the form of polyether chains of average molecular weight 10 to 3500 (number-average), of 20 to 60% by weight, based on the isocyanate mixture, and if appropriate d) have a content of tertiary amino groups and/or ammonium groups of 1 to 500 milliequivalents per 100 g of isocyanate mixture a).

Description

BAYE~ AK~IE~NGESli~l I ~CHA~T 51368 Leve~en KDIU~ C RP
Paten'le KDnzem Pv/wa/1022-P

Process for the production of cellulose-co~ g sheet-like structures which have been 5 given a dry stren~h and/or wet strength treatment The present invention relates to a process for the production of optionally wood-g cellulose~,~ sheet-like structures, such as, for example, paper, pasteboard and card, which have been given a dry strength and/or wet strength tre~ nt and h~ve improved whiteness, using water-dispersible isocyanates.

10 Isocyanates have been known for a long time as additives in pap~ king A process for wet strength treatment of paper with the aid of water-dispersible polyisocyanate mixtures cont.~inin~ 2 to 20% by weight of ethylene oxide units arranged in the form of polyether chains, the polyether chains cu, ~ g on average 5 to 70 ethylene oxide units, is known specifically from DE-A 4 211 480.

15 This tre~trn~nt does not impair the whiteness of the paper.

EP-A 0 582 166 describes the use of polyisocyanate mixtures which contain tertiary amino groups and/or ammonium groups and 0 to 30% by weight (based on the mixture) of ethylene oxide units in the form of polyether chains for the production of cellulose-colll~ sheet-like structures which have been given a dry streng~ and wet 20 strength treatment and/or sized. Here also, the whiteness of the product produced is not influenced.

The invention is based on the finding that higher contents of ethylene oxide units in the Le A 30 651 - Foreign Countries ~ 2160088 form of polyether chains, based on the polyisocyanate mixture, as envisaged in EP-A
._ 0 582 166 and DE-A 4 211 480, have the effect of an additional increase in wet strength. This is unexpected, because the increase in the polyether content results in a reduction of the isocyanate content, that is to say the groups which react with cellulose.
The increase in whiteness of the papers, pasteboards and cards treated as the polyether content increases is completely surprising. An increase in whiteness during pap~ king is usually possible only by ble~hing the chemical pulp or by co-using optical brighteners.

The invention relates to a process for the production of optionally wood-cont7.ining sheet-like structures, such as paper, pasteboard and card, which have been given a dry strength and/or wet strength tre~tm~nt and have improved whiteness, using water-dispersible isocyanates, which is characterized in that the water-dispersible isocyanates used:

a) are aliphatic, cyclo~ h~tic, araliphatic or aromatic isocyanates having an NCO
functionality of 1.8 to 4.2, mixed with polyether-modified aliphatic, cycloaliphatic, araliphatic or aromatic isocyanates having an NCO functionality of 0.8 to 3.2, b) the isocyanate mixtures a) contain 1 to 25% by weight of isocyanate groups, c) have a content of ethylene oxide units, arranged in the form of polyether chains of average molecular weight 100 to 35000 (number-average), of 20 to 60% by weight (or 30 to 60% by weight if tertiary amino and/or ~mmonium groups are present), based on the isocyanate mixture, and if a~plol,liate d) have a content of tertiary amino groups andlor ammonium groups of 1 to 500 milliequivalents per 100 g of isocyanate mixture a).

25 The isocyanate mixtures a) plc~ bly contain 1 to 23% by weight of isocyanate groups and have a content of ethylene oxide units, arranged in the form of polyether chains of average molecular weight 100 to 1000, preferably 100 to 600 (nurnber-average), of 20 ~eA30651 -2-to 50% by weight (or 30 to 50% by weight if tertiary amino and/or ~mm(mium groups are present), based on the isocyanate mixture.

The water-dispersible polyisocyanates are obtainable by reaction, in any desiredsequenoe, of:

5 I. one or more non-modified polyisocyanates having an average NCO
functionality of 1.8 to 4.2, II. mono- or polyfunctional polyalkylene oxide polyether alcohols C~ ;"g on average 5.0 to 70 ethylene oxide units and optionally cont~ining ester groups, and o~ianaLly, ~
0 III.A) amines which contain a group which is reactive towards isocyanates, of the formula A1) H-Y'-X-N (A1), in which Y' represents 0, NH or NR3, (R3 = methyl or ethyl), R' and R2 a) independently of one another represent C,-C4-alkyl or C3-C6-cycloalkyl or b) represent a radical of the formula ~e A 30 651 - 3 --(CH - CH-O-)a CH--CH-o-R6 R4 Rs R4 Rs wherein R4 and Rs independently of one another denote hydrogen or methyl, but one of the radicals is always hydrogen, R6 denotes methyl or ethyl and a is a number from O to 10, or c) represent a C2-C4-allyl radical s~ t~ by one or more tertiary amino groups and/or ammonium groups, of the formula ~(CH2)q~CH2--N ~ R
-CH2-CH2-(CH2)b-N~
[(CH2)t-CH2--N ~ R6 or -cH2-cH2-(cH2)b-N~N~ (CH2)q~CH2--1 ~ R6 wherein b is a number from O to 2, -~e A 30 651 - 4 -q and t independently of one another denote 1 or 2 and r and s independently of one another denote a number from 0 to 3 and R6 has the abovementioned m~ning, or S d) toge~her with the N atom to which ~ey a~e bonded form a 5- or ~membered ring of the formula CH - CH
N~ ~Z
CH - CH

wherein Z represents ,o or ~N--(CH2 CH2 N)m R6 or ~N-( ICH--I H~O)a I H- I H-O-R

wherem m is a number from 0 to 2 and ~eA30 651 . - 5 -a, R4 and R6 have the abovementioned m~nin~

X represents C2- to C~O-alkylene, C5- to C~O-cycloalkylene, a radical of the formula ~ (CH--CH ~ )a CH ~ CH-wherein R4, Rs and a have the abovementioned m~nin~;
or a radical of the formula Rl Rs --CH--CH2--(O ~ CH--CH)a CH2--(O - CH ~ CH)8 N--R1 in which a, R4, Rs, Rl ~Id R~ have the abo~ementiolled mt-~nin~ or A2) of the formula / (CH2)p H y2 CH /N-R
(CH2)n ~,vherem y2 represents -~, -NH- or NR3, wherein R3 has the abovementioned m~nin~
n and p indep~n~Pntly of one another assume the values 1 or 2 and R' has the abovementioned mt-~ning~

-Le A 30 651 - 6 -or A3) of the forrnula ~ (CH2)p H-N~ ~N-R' (CH2)n wherein n, p and Rl have the abovementioned m~nin~

S or A4) of the formula ~ (CH2)'E~ / R1 H-N~ CH--N
(CH2)n R

wherein n, p, R' and R2 have the abovementioned me~nin~, or 10B) amines which contain more than one group which is reactive towards isocyanates and optionally contain ether andlor ester andlor amide groups and have a molecular weight of less than 10000 g/mol or C) ~e compounds which are obtained by reaction of A) or B) by protonation 15and/or quaternization, contain ammonium groups and are reactive towards isocyanates, or ~eA30651 -7-~160088 any desired mixtures of A) to C).

The amines III are described in more detail in EP-A 582 166.

In this context, the term~'water-dispersible" means that in a concentration of up to 70%
by weight, preferably up to 50% by weight, in water, the mixtures give finely divided S dispersions with particle sizes (ultracentrifuge) of <500 nm.

Examples of possible starting substances for the water-dispersible isocyanates are:

I. Non-modified, aliphatic, cyclo~lirh~tic, araliphatic or aromatic isocyanates having an NCO functionality of 1.8 to 4.2. Aliphatic and cyclo~liph~tic polyisocyanates which contain uretdione and/or isocyanurate and/or allorh~n~t~
and/or biuret and/or ox~ 7in~ structures and uhich can be ~,el)aled in a manner known per se from aliphatic, cyclo~liph~tic, araliphatic or aromatic diisocyanates are pl~r~l,ed. Examples which are suitable are:
1,4-diisocyanatobutane, 1,6-diisocyanatohexane, 1,5-diisocyanato-2,2-dimethylpentane, 2,2,4- and 2,4,4-l~ lhyl-1,6-diisocyanatohexane, 1,3-and 1,4-diisocyanatocyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocy~n~t--m~thylcyclohexane, 1-isocyanato-1-methyl~isocyanatomethyl-cyclohexane and 4,4-diisocyanatodicyclohexyl-methane, or any desired mixtures of such diisocyanates.

The pl~r~l.ed reaction products of these diisocyanates co~ uretdione, isocyanurate, allupl1all~e or ox~ 7ine groups are P~ss~nti~lly polyisocyanate mixtures having an NCO content of 19 to 24% by weight which comprise trimeric 1,6-diisocyanatohexane or 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane and the corresponding higher homologues and co~ i"i.,g isocyanurate groups and optionally uretdione groups. The corresponding polyisocyanates ofthe NCO content mentioned which are largely free from uretdione groups and contain isocyanurate groups, such as are obtained by catalytic trimeri_ation, which is known per se, of 1,6-diisocyanatohexane or 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-~e A 30 651 - 8 -cyclohexane to form isocyanurate and which plcrel~bly have an (average) NCO
functionality of 3.2 to 4.2 are particularly ~ulcr~l~bly used. ~he trimeric polyisocyanates having an NCO content of 19 to 24% by weight which are obtained by reaction of 1,6-diisocyanatohexane with less than the equimolar amount of water in a known manner and essentially cont~in biuret groups are also ~Icrelled.

Other suitable polyisocyanates are aliphatic or aromatic diisocyanates, such as hexa-m~ylene diisocyanate, tolylene diisocyanate, 1,5-diisocy~n~ton~ th~lene, diphenylmethane diisocyanate and higher homologues thereof with uretdione, isocyanurate, allo~ le and biuret groups.

II. The polyalkylene oxide ether alcohols are monc~ or polyfunctional polyalkylene oxide polyether alcohols which contain a statistical average of 5 to 70, plcrcl~bly 6 to 60, ethylene oxide units per molecule, such as are ~ ihle in a manner known per se by alkoxylation of suitable starter molecules.

Any desired mono- or polyhydric alcohols of molecular weight range 32 to 150 ~/mol can be employed as starter molecules for the ~ lion of these polyalkylene oxide polyether alcohols. Monofunctional aliphatic alcohols having 1 to 4 carbon atoms are plcrellcd. Methanol or ethylene glycol monomethyl ether is particularly plcr~llcd. Alkylene oxides which are suitable for the alkoxylation reaction are, in particular, ethylene oxide and propylene oxide, which can be employed in the alkoxylation reaction in any desired sequence or also as a mixture.

The polyalkylene oxide polyether alcohols II are either pure polyethylene oxide polyethers or mixed polyalkylene oxide polyethers which contain at least one polyether sequence, have at least 5, in general 5 to 70, plcrel~bly 6 to 60 and particularly preferably 7 to 20, ethylene oxide units, and the alkylene oxide units of which consist of ethylene oxide units to the extent of at least 60 mol/O, preferably to the extent of at least 70 mol%. Preferred such polyalkylene oxide polyether alcohols are monofunctional polyalkylene oxide polyethers which -Le A 30 651 - 9 -have been started on an aliphatic alcohol co~ ;";"g 1 to 4 carbon atoms and ,._ contain a statistical average of 6 to 60 ethylene oxide units. Particularly plerell~d polyalkylene oxide polyether alcohols are pure polyethylene glycol monomethyl ether alcohols which contain a statistical average of 7 to 20 ethylene oxi~e units. Suitable polyalkylene oxide polyethers co"l~ ;,-g ester groups are OH-tr~ polyester ethers which are obtainable by reaction of aliphatic C2- to Cg-dicarboxylic acids or esters or acid chlorides thereof with polyethers from the group con~i~ting of polyethylene oxides, polypropylene oxid~s or n~u~es or copolyethers thereof, 0.8 to 0.99 eq~livalents Or carboxyl groups or derivatives thereof being employed per OH equivalent of the polyether, and which have an average molecular weight of less than 10000 g/mol, pl~r~l~bly less than 3000 g/mol, and contain hydroxyl end groups.

III. ~he following amines III.A) may be mentioned as examples:
N,~-dimethylethyl~nYli~mine, N,N'-dimethylpropylene(li~min.- dimethyl-aminohydroxyethane, dimethylaminohydroxypropane, diethylamino-hydroxyethane, dibutyl~tninohydroxyethane, diethylaminoethoxyhydroxyethane, (2-diethylaminoethoxy}ethoxyhydroxyethane, N,NI-triethyl-N'-[cl)-hydroxy-tetra-ethoxyethyl]propylene(1i~rnin~ N-hydroxyethyl-morpholine, N-hydroxy-ethylmethylpiperazine, N-hydroxyethylpiperidine, N-hydroxyethylpyrrolidine, ~
hydroxy-N-methylpiperidine, ~hydroxy-1-dimethylaminocyclohexane, 1,3-bis(dimethylarnino-ethoxy~2-hydroxypropane,1 ,3 -bis(dimethylamino-propoxy~
2-hydroxypropane and the amines of the following forrnulae:

Cl H3 (C2H5)2-B~CH2)2-NH2, (CH3)2N - CH2- Cl - CH2-NH2, A A
~,~N-(CH2)3-OH.CH3-N~N-(CH2)2-H~ N-(CH2)2-OH, (C2H5)2N-(CH2)3-CH-NH2, O~ ~N-(CH2)3-NH2, LeA30651 - 10-O~N CH2 CH-NH2 (C2HS)NCH2 CH-NH2 (CH3)2N-CH2 CH-NH2 N-(CH2)2-OH

CH3 A , CH3 N--(CH2)2--N N-(CH2)2-OH. HO-(CH2)6 N

CN(CH2)3 NH2 CN CH2--CH NH (CH ) N-CH I NH

HO-(CH2)2-N ~ , HO-(CH2)2-N, s ~ ~
HO-(CH2)2-N~O, HO-(CH2)2-N~N-CH3~
(+)/ 2 S
H0-(CH2)2-N\ C2Hs where An(~) = CH30S03(~ ), Br(~), (_) C2Hs (+)/ 3 -(CH2)3-N CH3COO

/~ /CH3 HO~ N CH3 HN N--CH3 HO-(CH2)2--N

/C2Hs H (O - CH - CH2)2--N \
CH3 (CH2-CH2-0)2-CH3 HO (CH2 CH--)n CH2--CH N

where n = 1 to 10, -Le A 30 651 - 1 1 -/C2Hs HO-(CH2--CH2--)n CH2--CH2 N\
C2Hs where n = 1 to 10, CH3 ,CH3 ~(CH2)2--N--(CH2)2--N~
HO--(CH2)2- N
A ,CH3 (CH2)2--N N ---(Cl~Z)2--N

CH\3 OH /CH3 C2\Hs OH /c2Hs C2Hs C2Hs CH\3 CH3 fH fH3 /CH3 N--CH2--CH2--CH2--N--CH2- CH--CH2--Nl--CH2 CH2 CH2 N \
CH3 3 An( ) An( ) CH3 where An(~) = Cl(-), Br(-), CH30S03(-) CH\3 fH ,CH3 / N--CH2--CH2--O--CH2--CH--CH2--O ~ CH2--CH2- N

OH ~_~
O~N--CH2--CH-CH2--N O

OH (-NH2. -NHCH3) / \
CH3-N~N--CH2--CH - CH2--N~N-CH3 -~eA30651 -12-2 s~N_CH--CH OH CH2--CH2--N--C H

~ N--CH2--CH2 2 \ CH--CH--N ~ C2H 5 CH3-N N--(CH2)2 OH / CH3 \ --N--CH2--CH--CH2 N~CH

Examples which may be mentioned of amines III.B) which contain more than one group which is reactive towards isocyanates and if ap~l~liate contain ether and!or ester and/or amide groups and have a molecular weight of less than 10000 g/mol are:
methyl-bis(2-hydroxyethyl)-amine, methyl-bis(2-hydroxypropyl)-amine, N,N'-bis(2-hydroxyethyl}N,N'-dimethylethylene(li:~mine, N,~'-bis(2-hydroxyethoxy-ethyl)~N,NI,N"-tlin~ yl-diethylenetriamine,N,N-dimethylamino-propyl-bis-[~-hydroxy-tetraethoxyethyl]amine, triethanolamine, reaction products of triethanolamine with 3 to 20 mol of ethylene oxide and/or propylene oxide per mole of amine, reaction products of poly~min~s, such as aminoethylpiperazine, triethylenetetramine or bis~2-aminoethyl)piperazine, with ethylene oxide and/or propylene oxide, diethylenetri~min~bispropionamide, N,N'-bis-propionylarninoethyl-~'{2-hydroxy~thyl~
amine and reaction products of tetramethylethylene li~mine-dichloroethane condensates with ethylene oxide and/or propylene oxide. Suitable amines III.B) are, for example, also the following polycondensates:

a) hydroxy-tç~min~t~l polyesters prepared by con~11 n~tion of C2- to C8-dicarboxylic acids, polyethylene oxide and/or polypropylene oxide, or copolyethers of ethylene oxide and propylene oxide, and dihydroxyalkylamines, preferably N-methyl-diisopropanolamine, having an OH functionality of 2, b) hydroxy-termin~ted polyesters prepared by cond~n~tion of C2- to C8-dicarboxylic acids and the dihydroxyalkylamines listed under a) having an OH functionality of 2, -LeA30651 - 13-c) hydroxy-termin~tPrl or amino-functional polyester-amides of C2- to C8-dicarboxylic acids, C2- to C6~ mino~lk~nes, preferably ethyleneAi~mine and the dihydroxyalkylamines listed under a), having an OH functionality of 2, d) hydroxy-terrnin~t~ polyesters of C2- to C8-dicarboxylic acids, trishydroxy~lk~n~, preferably trimethylolpropane, and reaction products thereof with 1 to 10 mol of ethylene oxide or propylene oxide, and the dihydroxyalkylamines listed under a), having a functionality of more than 2, e) hydroxy-functional polyamines which are obtainable by reaction of ammonia or linear or branched (poly)alkylenepoly~mines, such as, for exarnple, ethylene~ min~, diethylenetriarnine, triethylen~ nille, bis(3-aminopropyl}
methylamine, a~-polyether~ min~ with primary or secondary amino groups or con~l~n~t~s thereof with less than the equimolar arnount of dihalo~eno~lk~n~, such as dichloroethane, with alkylene oxides, plefelal~ly triethanolamine, tris(2-hydroxypropyl)amine or tetrakis(2-hydroxypropyl}
ethylene~ mine, f) hydroxy-functional polyamiclo~min~s which are obtainable by reaction of linear or branched polycon-i~n~atç~ of C2- to C8-dicarboxylic acids, diamines and polyamines c~.lll~illill~ at least three acylatable amino groups, such as diethyl~n~mine or triethylenet~ll~oine, and/or polyamines having at least two acylatable amino groups and further tertiary amino groups, such as bis-(3-aminopropyl}methylamine, and if ~l~liate caprolactam or if a~plo~liate polyetherdiols or polyether li~min~, with alkylene oxides, 1-3 mol of alkylene oxide being employed per primary and secondary amino group in the polycondensate, 25 g) hydroxy-functional polyami~lo~min~ according to fl which, instead of reaction with alkylene oxides, contain hydroxyethyl end groups and are obtainable by cocontl~n~tion with ethanolamine, h) amino alcohols of the formula ~eA30651 - 14--` 2160088 R R R R
H-(O-lH--CH)k NR8[(CH2)d-CH2-CH2-NR ]e (CH-CH-O)cH

wherem R4 and Rs represent hydrogen or methyl, with the condition that one radical always represents hydrogen, Rx arld R7 ~dep~clently of one another represent methyl~ ethyl or a radical of the formula ~CHR5-CHR4-o)t-H or -[CH2~CH2)g-NR')hR2, wherein R' and R2 have the abovementioned m~ning and g assumes values from 1 to 6, h represents 0 to 4, R4 and R5 have the abovementioned m~nin~

k, c and f assume values from 0 to 20, e assumes values from 0 to 3 and d assumes values of 0 or 1.

Ihe amines III.B) in general preferably have an average molecular weight of less than 10000 g/mol. Ihose having an average molecular weight of less than 5000 g/mol, in particular less than 3000 g/mol, are particularly pl~relled.

LeA30651 - 15-- 216008~
Exarnples which may be mentioned of the compounds mentioned under III.C) which are obtained by protonation and/or qll~t~i7~tion~ contain ammonium groups and are reactive towards isocyanates are:
the compounds obtainable by reaction of acids or alkylating agents with the 5 components III.A) or III.B), all or ~ome of the tertiary amino groups of which have been converted into ~mmnnium groups.

Acids which are suitable for this reaction are pl~r~l~ly acetic acid, formic acid and HCl, and possible allylating ~gents ar~, ~or e-~ample, C~-C4-alkylclllorides andbromides, as well as dialkyl s llph~t~s, such as dimethyl s llph~te or diethyl slllph~te 10 Ihe water-dispersible polyisocyanates can be prepared by reaction of the following residual monomers in any desired sequence:

I. non-modified polyisocyanates II. mono- or polyfunctional polyalkylene oxide polyether alcohols III. ~min~

15 If the amines III.A) to III.C) contain polyether chains, reaction of III.A) and/or III.B) and/or C) with the polyisocyanates I. can also lead directly to water-dispersible polyisocyanates, so that the content of component II. can be reduced if a~ le. Ihe non-modified polyisocyanates I. to be employed according to the invention can also be employed in con~il~lion with external ionic or nonionic Pmlll~ifiers. Such emulsifiers 20 are described, for example, in Methoden der organischen Chemie [Methods of organic chemistry], Houben-Weyl, vol. XlV/1, part 1, pages 190-208, Ihieme-Verlag, Stuttgart (1961), in US-PS 3 428 592 and in EP-A 0 013 112. me .omlll~ifiers are employed in an amount which ensures dispersibility. If polyisocyanates I. are initially reacted with polyalkylene oxide polyether alcohols II., this reaction can be carried out in a manner 25 known per se, ~n~ an NCO/OH equivalent ratio of at least 2: 1, in general 4: 1 to about 1000: 1, polyether-modified polyisocyanates having an average NCO
functionality of 1.8 to 4.2, preferably 2.0 to 4.0, a content of aliphatically or LeA30651 - 16-cycloaliphatically bonded isocyanate groups of 12.0 to 21.5% by weight and a content of ethylene oxide units located within polyether chains (calculated as C2H4O, molecular weight = 44 g/mol) of 2 to 20% by weight, the polyether chains containing a statistical average of 5 to 70 ethylene oxide units, being obtained.

5 The corresponding water-dispersible polyisocyanate mixtures which are obtainable by protonation and/or qll~t~n~tion of the non-modified polyisocyanate mixtures I. to be - employed according to the invention and which contain ammonium groups are also suitable for carrying out the process. Al~yla~ing ag~ts, such as, i~or ~xample, dimethyl sulphate, diethyl s~ h~te or C,-C4-alkyl halides and C,-C4-alkylsulphonates, can be 10 used for the q~ ."i~lion.

The starting components can be reaeted in any desired sequence, with exelusion of moisture and ~ler~l~bly without a solvent. As the amount of alcohol component increases, a higher viscosity of the end product is achieved, so that in eertain eases (if the viscosity rises above 100 Pas, for example) a solvent whieh is pler~ ly water-15 miscible but is inert towards the polyisoeyanate ean be added. Suitable solvents are:

Alkyl ether ~cet~t~ glycol diesters, toluene, carboxylic acid esters, aeetone, methylethyl ketone, tetrahydrofuran and dimethylforrnamide.

The reaction can be accelerated by eo-using catalysts which are known per se, such as dibutyltin dilaurate, tin(II) octoate or 1,4-diazabicyclo[2.2.2]octane, in amounts of 10 20 to 1000 ppm, based on the reaction eomponents. The reaetion is carried out in the temperature range up to 130C, pl~relably in the range between 10C and 100C, particularly preferably between 20C and 80C. The reaetion is monitored by titration of the NCO eontent or by measurement of the IR speetra and evaluation of the NCOband at 2260-2275 cm~', and has ended when the isocyanate content is not more than 25 0.1% by weight above the value which is aehieved with complete conversion at the given stoichiometry. Reaction times of less than 24 hours are as a rule sufficient.
Solvent-free synthesis of the polyisocyanates to be employed according to the invention is ~l~r~ d.

Le A 30 651 . - 17 -In another embodiment, it is also possible to prepare the polyisocyanate mixtures to be employed according to the invention by mixing 1) non-modified polyisocyanates I), 2) polyisocyanates which are obtained by reaction of polyisocyanates I) with the amines mentioned under III), the equivalent ratio of groups of III) which are reactive towards isocyanates to the NCO groups employed in component II) being 1:1 to 1:1000, and 3) polyisocyanates which are obtained by reaction of polyisocyanates I. with polyalkylene oxide polyether alcohols II., the equivalent ratio of groups of component II. which are reactive towards isocyanates to the NCO groups employed in component I) being 1:1 to 1:1000. The number of amine equivalents, the polyether content, the NCO content and the NCO functionality here are to be adjusted by ap~loyliate weights by the expert such that the resulting mixture has the composition required for water-dispersibility, the pler~llcd ranges already mentioned applying.

The water-dispersible polyisocyanate mixtures are easy to handle industrially and are storage-stable for many months with exclusion of moisture.

The water-dispersible polyisocyanate mixtures are plc;rel~dbly employed according to the invention without organic solvents. They are very easy to emulsify in water - if20 ~r~liate with addition of acids - and/or at temperatures up to 100C. The active compound content of the emulsion can be up to 70% by weight. However, it is moreadvantageous to prepare emulsions having an active compound content of 1 to 50% by weight, which can then be diluted further, if necessary, before the metering point. The mixing units customary in the art (stirrers, mixers with the rotor-stator principle and, 25 for example, high-pressure emulsifying machines) are suitable for the emulsification.

The plef~ d polyisocyanates are self-emulsifying, i.e. they can easily be emulsified after addition to the aqueous phase even without the action of high shearing forces. A
LeA30651 - 18-static mixer is as a rule sufficient. The resulting emulsions have a processing time of up to 24 hours, which depends on the structure of the polyisocyanates to be employed according to the invention, in particular on their content of basic N atoms.

The processing time is the period within which the optimum dry and wet strength 5 action is achieved.

To facilitate incorporation into the aqueous phase, it may be expedient to employ the watel dispersible polyisocyanate mixture as a solution in a solvent which is inert towards isocyanate groups. Suitable solvents are, for example, ethyl acetate, ethylene glycol ~ et~tç, propylene glycol tli~cet~t~, 2-b~lt~non~, 1-methoxyprop-2-yl acetate, 10 toluene or rnixtures thereof. The content of the solvent in the solution of the polyisocyanate should be not more than 80% by weight, pl~f~.~ly not more than 50%
by weight. The use of solvent-free, water-dispersible polyisocyanates is particularly preferred.

The cellulose-cont~ining materials which are suitable for the process according to the 15 invention are, for example, paper or paper-like materials, such as pasteboard or card.
The polyisocyanate mixtures l)lef~lled for the wet strength and dry strength tre~tnn~nt have an NCO functionality of greater than 2.

According to the invention, the water-dispersible polyisocyanates can be employed in the pulp, and they are then added directly to the cellulose-cont~ining dispersion of the 20 fibrous raw materials. For this, the polyisocyanate mixture is emulsified in water at a temperature of 20C to 80C and the resulting emulsion is added to a suspension of the fibrous raw material or dispersed directly in the suspension of the fibrous materials and the paper is formed by dewatering from the suspension formed and then dried. Foremulsification of the polyisocyanate rnixture, it is expedient to initially introduce 1 to 25 4 times the amount of water into the container. Hi her amounts of water are also possible. For use in the surface, a finished basepaper is treated with an emulsion of the polyisocyanate mixture in water and then dried. Use in the sizing press is possible. In this case, the polyisocyanate mixture, emulsified in water, is ~ r~lled to the finished paper web. The dry and wet strength effect is achieved immetli~1ely after drying. The ~eA30651 - 19-wet strength effect which can be achieved by surface treatment considerably exceeds that which can be achieved with the wet streng~ agents known to date using the same dosage of active substance.

It is particularly preferable to meter the aqueous emulsion of the polyisocyanates into S the fibrous material in the course of 60 mimlt~, ~ r~l~bly in the course of 15 mimlt~.
To achieve the optimum wet strength effect under conditions in practice, it is particularly advisable to meter in the polyisocyanate, for example, shortly before the headbox of tne pap~m~king rl~r~in~. For testing, sh~;e-ts of paper hav~ng a weight per unit area of S0 to 100 glm2 are in general formed in the laboratory.

10 In water, the NCO groups of the polyisocyanate rnixtures to be employed according to the invention hydrolyse slowly with evolution of CO2 to give the collesponding ~min~, which partly react with NCO groups still present to give urea groups. Advantageously, however, no precipitates occur. In the process according to the invention, the products can be metered into the solid in the pulp in the pH range b~lw~ll 4 and 10, pr~rel~bly between 5.5 and 9. Use in the neutral pH range (pH 6 to 7.5) is particularly pl~;r~llcd.
In this pH range, some of the tertiary amino groups are present in protonated form.

It is also possible to carry out the dispersing operation with the addition of acid. A
cationic charge independent of the pH is obtained if polyisocyanates obtained byq"~t~ni7~tion of the tertiary amino groups are employed. However, qll~l~ni7~tion is 20 not necessary for most uses.

The amounts of water-dispersible polyisocyanate depend on the effect required. As a rule, amounts of 0.001 to 50% by weight, pl~r~l~bly 0.1 to 10% by weight, particularly pl~r~l~bly 0.1 to 2.0% by weight of active compound, based on the dry fibrous raw material, are sufficient. The dosage of the active substance, based on the fibrous raw 25 material, corresponds to that of known wet strength agents of the polyamiclo~min~
epichlorohydrin type. The polyisocyanates give ready-to-use papers of good wet strength imm~ tely from the m~rhine. An intrn~ification of the wet strength action can be achieved by storage of the fini~h~l paper and/or after-condensation. Generally, however, a higher level of wet strength can already be achieved from the machine than Le A 30 651 - 20 -with conventional wet strength agents. The dry strength is also improved compared with conventional wet strength agents.

Ihe process according to the invention is carried out at c~loll~y telll~l~lures.Ihe processing time depends on the temperature. At len~l~l lres of 20 to 25C, the 5 processing time is relatively long. After storage of the aqueous emulsion for 6 hours, the wet strength action still reaches about 70% of the value on imm~Ai~te use of the emulsion. At a higher temperature, for example at 50C, processing within 6 hours is to be recomm( nfleA On the other ha~ he ~n~ximul-n we~ s~eng~ action surprisingly depends hardly at all on the contact time with the cellulose. Papers which have been 10 formed immeAi~tely and after a contact time of 2 hours after addition of the water-dispersible polyisocyanate to the paper fibrous material each show the same level of wet strength. Ihe strength of the paper can be adjusted in the desired manner bysuitable choice of the starting components. Ihe process according to the invention is suitable not only for production of papers with dry strength and wet strength, but also 15 for production of papers which are resistant to oil and petrol.

The water-dispersible polyisocyanates can be employed in con~bil~ion with other cationic auxiliaries. such as retention agents, fixing auxiliaries, drying auxiliaries and wet strength agents. In particular, the fixing of fillers can be intensified further by addition of commercially available retention agents of the type of cationic 20 polycondensates and polymers, for exarnple polyamides, polyethyleneirnines, polyamidoamines and polyacrylamides, as well as of dual systems comprising cationic or cationic and anionic and if ~pl~l;ate particular components, such as silica sols and the like. This is of particular interest if use in the l~min~te(l paper sector is intended.
Preferred retention agents are cationic polycon~ t~ of poly~minP~, pl~rel~ably N-25 methyl-bis(3-amino-propyl}amine, and alkylene dihalides, preferably dichloroethane.
However, it should be el~ asized that the desired wet strength effect can also be achieved without addition of particular fixing agents. The strength of the paper can be increased, in particular, by combination with polysaccharides, such as hydroxyethylcellulose, carboxymethylcellulose, starch, galactol-w-~w-~ or cationic 30 derivatives thereof.

Le A 30 651 - 21 -The polyisocyanate mixtures can of course also be employed, if ~lu~l;ate, together with the abovementioned cationic auxiliaries, i.e. simultaneously or successively.
However, since many of the auxiliaries contain organically bonded halogen, combil~Lion with AOX-free and/or AOX-low auxiliaries is particularly pl~r~ d, since 5 chlorine-free pap~ kin~ is the chief aim.

The polyisocyanates not only are readily compatible with the usual optical brighteners, but also cause an additional increase in whiteness together with these.

Fur~h~nore, a soft handle of the paper can be produced for use in the hygiene paper sector.

10 In the following examples, the percentage data are perc~nt~ by weight, unless stated otherwise.

E~es 1. Pl~a,~lion of the water-dispersible isocyanates Water-dispersible isocyanate 1 15 80 g of a polyisocyanate which is prepared by trimerization of some of the isocyanate groups of 1,6-diisocyanatohexane, containin~ isocyanate gr~ups, essentially calprises tris-(6-isocyanato-hexyl) isocyanurate and higher homologues thereof and has an NCO
content of 20.5%, a content of monomeric 1,6-diisocyanatohexane of less than 0.3%
and a viscosity of 1000 mPas (25C) are reacted, by stirring at 60C, with 20 g of a 20 polyether which is based on ethylene oxide, has been started from 2-(2-methoxyethoxy~ethanol and has a number-average molecular weight of 350 g/mol and a hydroxyl number of 160 mg of KOH/g.

NCO content: 15.6%
~lSCOSity (25C): 1470 mPas -Le A 30 651 - 22 -Water-dispersible isocyanate 2 As described above (water-dispersible isocyanate 1), the following are reacted using the same starting compounds:
78 g of isocyanate 5 22 g of polyether NCO content: 15%
`Viscosity (25C): 850 rnPas Water-dispersible isocyanate 3 As described above, the following are reacted using the same starting compounds:10 76 g of isocyanate 24 g of polyether NCO content: 14.7%
Viscisoty (25C): 835 rnPas Water-dispersible isocyanate 4 15 As described above, the following are reacted using the same starting compounds:
73 g of isocyanate 27 g of polyether NCO content: 12.9%
Viscosity (25C): 1490 mPas 20 Water-dispersible isocyanate 5 As described above, the following are reacted using the same starting compounds:70 g of isocyanate 30 g of polyether LeA30651 -23 -NCO content: 12.2%
Viscosity (25C): 1470 mPas Water-dispersible isocyanate 6 As described above, the following are reacted using the sarne starting cornpounds:
5 67 g of isocyanate 33 g of polyether NCO c~ r~ 11.2%
Viscosity (25C): 1470 rnPas Water-dispersible i~ocyanate 7 10 As described above, the following are reacted using the sarne starting compounds:
64 g of isocyanate 36 g of polyether NCO content: 10.3%
Viscosity (25C): 1490 mPas 15 Water-dispersible isocyanate 8 As described above, the following are reacted using the same starting compounds:61 g of isocyanate 39 g of polyether NCO content: 9.4%
Viscosity (25C): 1420 mPas Water-dispersible isocyanate 9 (comparison) As described above, the following are reacted using ~e same starting com~ounds:
Le A 30 651 - 24 -85 g of isocyanate 15 g of polyether NCO content: 17.3%
Viscosity (25C): 1425 mPas 5 Water-dispersible isocyanate 10 (comparison) As described above, the following are reacted using ~dle same starting compounds:
82 g of isocyanate 18 g of polyether NCO content: 16.5%
Viscosity (25C): 1000 mPas All the reaction products are water-clear liquids with an oily appearance which can easily be dispersed in water (in a glass beaker by stirring by means of a spatula).

Use examples (mechanical wood pulp) 1 to 10 Mechanical wood pulp is beaten at a consistency of 2.5% to a degree of freeness of 38 SR in a beater. 100 g portions of the resulting mechanical wood pulp suspension are then diluted to a volume of 1000 ml with water in glass beakers. 0.5% by weight and 1.0% by weight of the water-dispersible isocyanates prepared, based on the solid, are added to the mech~nical wood pulp dispersions, after prior dispersion in water (dispersion cn"~ g 20% by weight of polyisocyanate), and after the addition, these 20 dispersions are stirred for a further 3 minutes.
Thereafter, sheets of paper having a weight per unit area of about 80 g/m2 are formed on a sheet former (Rapid-Kothen apparatus) with the contents of the glass beakers. Ihe sheets of paper are dried at 85C for 8 mimlte~ in vacuo under 20 mm Hg and after-heated in a drying cabinet at 110C for a further 10 min~lt~.
25 After climatic conditioning, 5 test strips of 1.5 cm width are cut out of each sheet of paper and immersed in distilled water for S minutes. The wet strips are then LeA30651 -25-imrnediately tested for their wet breaking load on a tensile tester.
Ihe test results are sumrnarized in the following summary table.

-Le A 30 651 - 26 -Wet brealcing loads when used in the pulp, after condensation at 110C

Use Water- NCO % Polyether Wet breaking load Notes exarnple d;~ !e content % when no. isocyanate no. 0.5 / 1.0%
Is used 1 9 17.3 15 4.7 5.7 Colll~;sol~ exarnple 2 10 16.5 18 6.3 7.2 "
3 1 15.6 20 4.3 7 Exzunple aco~,J;.,g to the invention 4 2 15.0 22 6.6 7.9 "
3 14.3 24 6.9 8.7 "
6 4 12.9 27 7.2 8 "
7 5 12.2 30 7.5 9 "
8 6 1 1.2 33 7.3 7.9 "
9 7 10.3 36 6.3 7.3 "
8 9.4 39 5.9 7.4 "

15 Use exarnples for surface treatment of wood-free paper 11-21 Paper comprising eucalyptus and pine sulphate chemical pulp having a weight per unit area of 70 g/m2 is treated with a sizing liquor of water-dispersible isocyanates in a laboratory sizing press from Mathis, Zurich, Switzerland, type HF.

0.5 and 1% strength aqueous dispersions of the water-dispersible isocyanates 1 to 10 20 were employed as the sizing liquors. In a further operation, 0.75% of an optical bri~ht~n~ was also added to the sizing liquor in addition to the 1% of water-dispersible isocyanate.

The wet pick-up of the paper was 80%. Ihe papers were dried at 85C for 8 mimlt~c and after-heated at 110C for 10 minlltçs. The wet breaking load was measured as in ~e A 30 651 - 27 -Examples 1 to 10.

The CIE whit~nP~ was additionally clet~mined. The results can be seen from the following s~ lg table.

Wet breakin3~ loads and whiteness when used on the surface Use Water- Wet-breaking load at apolyisocyanate Whiteness inexamI~le dispersible content in the sizing liquor of the presence no. isocyanate ~ of 0.75% of 0.5% of 1% of 1% of polyiso-no. optlcal poly- polyiso- cyanate + 0-75% brightener isocyanate cyanate of optical 11** 9 8.5 11.1 13.3 137.7 12** 10 8.9 10.4 10.8 138.8 13 1 9.9 10.9 8.9 138.6 14 2 11.1 12.5 12.8 138.9 3 10.0 12.8 12.3 138.0 16 4 10.3 12.7 11.5 139.2 17 5 10.7 11.5 11.8 139.5 18 6 9.8 10.8 9.8 139.7 19 7 8.8 10.8 10.6 139.8 8 8.2 10.5 10.3 138.7 * optical brightener: Blankophor P liquid 01, commercial product from Bayer AG
** comparison example -Le A 30 651 - 28 -

Claims (3)

1. Process for the production of optionally wood-containing cellulose-containing sheet-like structures, such as paper, pasteboard and card, which have been given a dry strength and/or wet strength treatment and have improved whiteness, using water-dispersible isocyanates, characterized in that the water-dispersible isocyanates used:

a) are aliphatic, cycloaliphatic, araliphatic or aromatic isocyanates having an NCO functionality of 1.8 to 4.2, mixed with polyether-modified aliphatic, cycloaliphatic, araliphatic or aromatic isocyanates having an average NCO
functionality of 0.8 to 3.2, b) the isocyanate mixtures a) contain 1 to 25% by weight of isocyanate groups, c) have a content of ethylene oxide units, arranged in the form of polyether chains of average molecular weight 10 to 3500 (number-average), of 20 to 60% by weight (or 30 to 60% by weight if tertiary amino and/or ammonium groups are present), based on the isocyanate mixture, and if appropriate d) have a content of tertiary amino groups and/or ammonium groups of 1 to 500 milliequivalents per 100 g of isocyanate mixture a).

2. Process according to Claim 1, characterized in that the isocyanate mixtures a) contain 1 to 23% by weight of isocyanate groups and c) have a content of ethylene oxide units, arranged in the form of polyether chains of average molecular weight 100 to 1000 (number-average), of 20 to 50% by weight, based on the isocyanate mixture.

3. Process according to Claims 1 and 2, characterized in that water-dispersible polyisocyanates are used which have been prepared by reaction, in any desired sequence, of:

I. one or more non-modified polyisocyanates having an average NCO
functionality of 1.8 to 4.2, II. mono- or polyfunctional polyalkylene oxide polyether alcohols containing on average 5.0 to 70 ethylene oxide units and optionally containing ester groups, and optionally III.A) amines which contain a group which is reactive towards isocyanates, of the formula A1) (A1), in which Y' represents O, NH or NR3, (R3 - methyl or ethyl), R1 and R2 a) independently of one another represent C1-C4-alkyl or C3-C6-cycloalkyl or b) represent a radical of the formula wherein R4 and R5 independently of one another denote hydrogen or methyl, but one of the radicals is always hydrogen, R6 denotes methyl or ethyl and a is a number from 0 to 10, or c) represents a C2-C4-alkyl radical substituted by one or more tertiary amino groups and/or ammonium groups, of the formula or wherein b is a number from 0 to 2, q and t independently of one another denote 1 or 2 and r and s independently of one another denote a number from 0 to 3 and R6 has the abovementioned meaning, or d) together with the N atom to which they are bonded form a 5- or 6-membered ring of the formula wherein Z represents or or wherein m is a number from 0 to 2 and a, R4 and R6 have the abovementioned meaning, X represents C2- to C10-alkylene, C5- to C10-cycloalkylene, a radical of the formula wherein R4, R5 and a have the abovementioned meaning, or a radical of the formula in which a, R4, R5, R1 and R2 have the abovementioned meaning, or A2) of the formula wherein y2 represents -O- NH- or NR3, wherein R3 has the abovementioned meaning, n and p independently of one another may assume the values 1 or 2 and R1 has the abovementioned meaning, or A3) of the formula wherein n, p and R1 have the abovementioned meaning, or A4) of the formula wherein n, p, R1 and R2 have the abovementioned meaning, or B) amines which contain more than one group which is reactive towards isocyanates and optionally contain ether and/or ester and/or amide groups and have a molecular weight of less than 10000 g/mol or C) the compounds which are obtained by reaction of A) or B) by protonation and/or quaternization, contain ammonium groups and are reactive towards isocyanates, or any desired mixtures of A) to C).