Nitrogenous Condensation Products Used as Retention Aids in Papermaking

This invention relates to novel reaction products of polyalkylene polyamines with relatively high molecular weight difunctional crosslinkers, which are of value for the papermaking industry. The invention also relates to the manufacture and use of such products as retention aids and flocculants in the papermaking industry.

It is well known that polyethyleneimine and, to a lesser extent, polypropyleneimine are useful in the papermaking industry as retention aids for fillers and fibers, as drainage aids during sheet formation and as flocculants in pulp recovery. Such products have been known for more than 30 years. New progress was achieved by the use of epichlorohydrin as crosslinker giving crosslinked polyethyleneimines such as are described, for example, in German Pat. No. 1,670,296.

Finally, it is also known that crosslinking, for example with epichlorohydrin, of polyamidoamines, i.e. reaction products of such polyamines with dicarboxylic acids, gives paper auxiliaries which also constitute good retention aids. However, in use, these groups of products suffer from the drawback that each shows its optimum effect only within a limited pH range. For example, crosslinked polyamines obtained according to German pat. No. 1,670,296 show best results only at neutral pH, whilst crosslinked polyamidoamines such as are disclosed in U.S. Pat. No. 3,250,664 exhibit optimum properties only at acid pH.

In papermaking, more or less rapid changes in manufacturing conditions from acid to neutral and vice versa are usually necessary when different types of paper are made, and this gave rise, at an early stage, to the desire to develop an auxiliary which is capable of producing optimum results both at neutral and at acid pH.

The last improvement which took place in this field and which has long given satisfactory results is the teaching of German Published Application 1,802,435, according to which the problem is solved by first grafting ethyleneimine onto a polyamidoamine and then crosslinking with epichlorohydrin.

The increasing demands of paper manufacturers for rationalization in the process, i.e. for maximum retention of fiber and filler, for good clarification of waste water, for acceleration of the process and maximum paper whiteness, have led to the problem on which the present invention is based, i.e. the problem of providing novel auxiliaries by means of which the drainage rate is higher than that achieved with the auxiliaries of the last-mentioned reference, the retention of fiber and filler on the wire screen is increased and also the flocculating action obtained in the recovery of pulp is improved whilst maintaining the good paper whiteness as far as possible and effecting minimum impairment of the effect of optical brighteners without recurrence of the already solved problem of use at both acid and neutral pH.

Thus the present invention aims at improvements leading to more economical operation of the various processes for the manufacture of paper.

The subject matter of German Published Application 1,546,290 is the exclusive use of water-soluble products containing amino groups and ether groups and having a molecular weight of at least 2,000 and which have been obtained by reacting polyfunctional derivatives of polyols with amines which are at least difunctional with reference to the polyfunctional derivatives of the polyols, of which components at least one contains one or more ether groups, or quaternization products thereof as floatation agents for the recovery of fibers and fillers from waste waters coming from papermaking machines.

Such agents are preferably those derived from polyalkylene polyamines having from 2 to 6 alkyleneimine units, for example pentaethylene hexamine, diethylene triamine or propylene diamine.

These agents are particularly suitable for improving floatation in pulp recovery and ensure a success of the process equal to that obtained in German Published Application 1,802,435. However, these agents are not equal to those mentioned in the above reference as regards their properties as retention and drainage aids in paper manufacture.

The invention relates to a process for the manufacture of nitrogenous condensation products by reacting polyalkylene polyamines having at least two alkyleneimine groups with polyalkylene oxide derivatives containing chlorohydrin groups at the ends of the molecule, which process is characterized in that

a. one nitrogen equivalent of a polyalkylene polyamine containing from 15 to 500 alkyleneimine units is reacted with

b. from 0.08 to 0.001 and preferably from 0.06 to 0.002 molar portions of a polyalkylene oxide derivative which contains at least 8 alkylene oxide units and which has been reacted, at the terminal OH grups, with at least the equivalent amount of epichlorohydrin,

at a temperature of from 20.degree. to 100.degree. C and preferably from 40.degree. to 80.degree. C, the reaction being carried to a point at which high molecular weight resins which are still water-soluble are formed, the viscosity thereof being greater than 300 mPa.sec at 25.degree. C, measured on a 20-25 % aqueous solution.

The principle of the reaction is known, as mentioned bove, from German Published Application 1,546,290. However, said publication does not disclose that this reaction may be preferably carried out with higher polyalkylene polyamines containing at least 15 alkyleneimine units in the molecule and that products are thereby obtained which show maximum action as retention and drainage aids in addition to their action as floatation auxiliaries.

German Published Application 2,162,567 discloses a sequence of reactions in which, however, a small amount of filamentous polyethers having terminal tertiary amino groups, for example ethers obtained from glycol and epichorohydrin and dimethylamine as crosslinker, is reacted with a (polyamide)-polyalkylenepolyamine and then with from 0.2 to 2 moles of epichlorohydrin per equivalent of secondary amino group.

Thus, the process of the invention, which basically relates to the use of a specific number of alkyleneimine units in the starting product and to specific molar ratios and, above all, to the achievement of specific final viscosities and which therefore produces novel products of optimum efficiency, constitutes an unexpected technical advance in the art.

As mentioned above, the polyalkylene polyamides to be used as starting products in the manufacture of the products of the invention are those having from 15 to 500 alkyleneimine units, preferably ethyleneimine units. They are obtained by conventional polymerization of, say, ethyleneimine in an acid medium. We prefer to use compounds having from 15 to 500 ethyleneimine units.

The other reactant is the polyalkylene oxide derivative which has been reacted with epichlorohydrin at the terminal OH groups. Suitable compounds of this kind are generally those containing, in the unreacted polyalkylene oxide, from 8 to 100 alkylene oxide units per polyalkylene oxide group. This means that when polyfunctional compounds are reacted in alkylene oxide the amount of alkylene oxide units contained per polyalkylene oxide chain must be such that the number 100 is not exceeded in each chain. Preferably however, we use block copolymers of the formula

in which R.sup.1 is an ethylene radical, R.sup.2 is a 1,2 -propylene radical, m and p denote values of from 4 to 50, n is a value of from 0 to 50, x is a value from 2 to 6 and A is the radical of a polyhydric alcohol having from 2 to 6 carbon atoms or a polypropylene oxide radical having from 1 to 50 propylene oxide units, in which case n is equal to 0. Examples of individual representatives are ethoxylated or ethoxylated-oxypropylated polyhydric alcohols such as glycol, propylene glycol, glycerol, trimethylolpropane and pentaerythritol and simple polypropylene glycol which may contain up to 50 propylene oxide units in the molecule. The latter substance produces, on ethoxylation on both sides, mixed blockcopolymers of ethylene oxide and propylene oxide. Basically however, mixed polymerized ethylene oxide and propylene oxide chains may be reacted with the groups of the polyfunctional compounds bearing active hydrogen atoms, but this generally has no added advantage.

The polyethoxylated or polyethoxylated/polyoxypropylated compounds are thus those bearing at least two terminal free hydroxyl groups. The terminal hydroxyl grups are the reactive sites for subsequent reaction with epichlorohydrin. In this reaction at least equivalent amounts of epichlorohydrin are used with reference to the number of OH groups present and it is preferred to use from 1.0 to 1.5 moles of epichlorohydrin per equivalent of OH groups. This finally results in compounds which are converted by elimination of HCl to polyglycidyl ethers, compounds which effect the actual crosslinking action on the beforementioned polyalkylene polyamines and which are hereinafter referred to as crosslinkers. The reaction of the epichlorohydrin with the polyalkylene oxide derivatives takes place according to well-known reaction mechanisms and is initiated by Lewis acids. Examples of suitable Lewis acids are borofluoride etherate, phosphoric acid, sulfuric acid, perchloric acid, chloroacetic acid, aromatic sulfonic acids, zinc chloride and aluminum chloride. It is generally convenient, however, to use borofluoride etherate as Lewis acid for this reaction.

The high molecular weight polyfunctional crosslinking compounds are then reacted with the polyalkylene polyamines, from 0.08 to 0.001 mole of crosslinker being used per equivalent of nitrogen in the polyalkylene polyamine. Although the amount of said polyfunctional compound required for crosslinking depends, of course, on the constitution of the polyalkylene polyamine used, hydrolysis of this high molcular weight crosslinkers is always possible and it is therefore necessary, for a given starting polyalkylene polyamine, to use more crosslinker the higher the reaction temperature and the higher the water content of the resin solution if a solution of a specific viscosity is to be obtained. Use is made of the aforementioned amounts of crosslinker, preferably from 0.06 to 0.002 molar portions per equivalent of nitrogen in the polyalkylene polyamine. The crosslinking reaction is conveniently carried out in 5 to 50 % and preferably in 10 to 30 % aqueous solution, based on the total weight of the reactants. The amount of crosslinker necessary to achieve the desired degree of crosslinking may be added to the reaction solution either all at once or in portions. The course of the reaction is followed by observing the increase in viscosity of the aqueous solution. The portion-wise procedure is always preferable, since the reaction can be better controlled in this manner and the risk of the reaction mixture gelling is much less. Furthermore, the portion-wise addition of the higher molecular weight crosslinker obviates the addition of an excessive quantity and makes it easy to obtain a specific viscosity. The reaction is carried to the point where the high-molecular weight resins formed are still just water-soluble and have a viscosity of more than or equal to 300 mPa.sec when measured at 20.degree. C on a 20-25 % aqueous solution. It is preferred to aim at resins having viscosities of from 400 to 1500 mPa.sec. The reaction is generally carried out at temperatures of from 20.degree. to 100.degree. C and preferably from 40.degree. to 80.degree. C over from 1 to 10 hours.

On account of the amino groups contained therein, the condensation products of the invention are alkaline. However, the action of the products (resins) of the invention, particularly their action as drainage and retention aids, is not affected by neutralization of the resin solutions with acids. In the majority of cases, they have the same advantages as the products of German Publication Application 1,802,435, i.e. they can be used under both acid and alkaline conditions. Compared with products obtained from basically crosslinked polyamido amines or 1,2 -polyalkylene polyamines crosslinked with epichlorohydrin alone, they again shown an improved action as regards the retention of fillers and the drainage rate. Compared with the products of German Published Application 1,802,435 there is generally also an unexpected increase in the effects achieved, particular mention being made of the greatly improved whiteness of the papers, which show much less tendency to yellow even when stored for relatively long periods. These products make it possible to operate in all pH ranges occurring in papermaking. As compared with the products of German Published Application 1,546,290, in which low molecular weight polyalkylene polyamines are used, the products of the invention show improved action as retention aids for fillers and fibers.

The products of the invention may be successfully used in the manufacture of papers of all kinds, of sized and unsized cardboard, in the presence or absence of aluminum sulfate. The amount of agent used is from 0.01 to 0.3 % by weight, based on the dry weight of the cellulose fibers in the pulp.

In the following Examples the parts and percentages are by weight.

A solution of E g of ethyleneimine in F g of water is added dropwise to a solution of A g of ethylene diamine monosulfate in B g of water at C .degree. C over D hours. The mixture is then maintained at H .degree. C for G hours until no ethyleneimine ring can be detected with p-nitrobenzyl pyridine. The resulting polyethylene polyamine solutions show the following properties:

I: molecular weight: Ultra centrifuge (via the sedimentation equilibrium).sup.+1 measured by vapor pressure osmometry .sup.+2

K: viscosity (45 % solution, 20.degree. C, falling ball method by Hoeppler): centipoise

L: density (45 % solution, 20.degree. C) g/ml

M: refractory index (45 % solution, 20.degree. C)

To I g of a polyethylene glycol ether having an average molecular weight of II EO units (hydroxyl number III, water content according to K. Fischer IV), there are added V g of epichlorohydrin, VI g of borofluoride etherate are added and the mixture is held at from 60.degree. to 75.degree. C whilst a further VII g of epichlorohydrin are added over from about 0.5 to 1.5 hours. Condensation is continued at from 60.degree. to 70.degree. C until the epoxide titer of the solution has fallen to 0 (VIII hours). The resulting product has a chlorohydrin content of IX milliequivalents/g (determined by boiling for 30 minutes with 0.1 N NaOH followed by back-titration) and an acid content of X milliequivalents/g.

a g of a b % solution of the polyethylene imine c (ditri denotes diethylene triamine, tritetra denotes triethylene tetramine) are heated to d .degree. C and are crosslinked over e hours by the addition of f g of a g % solution of crosslinker h (epi denotes epichlorohydrin). During crosslinking, the pH of the solution is maintained at 9.5 by the addition of caustic soda (50 % solution) added is i g. The final viscosity of the approximately k % resin is l centipoise (measured at 20.degree. C) and its pH is m. It is neutralized with n g of formic acid (75 % solution) to a pH of o and diluted with p g of water to give an active content (WS) (caustic soda and formic acid not being regarded as WS) of q %. The final viscosity is r centipoise, measured at 20.degree. C by the falling ball method. Comparative Examples (action inferior) Examples (action good) Designatio n V16V17 V18 V19 V20 V21 V22 V23 V24 V25 V26 V27 V28 V29 V30 V31 V32 PEI 50 ditri tritetra 20 20 100 tritetra 35 tritetra 20 35 50 75 50 50 100 100 PDCH epi 4 4 4 4 4 9 9 18 34 90 18 18 90 34 34 90 molar ratio of PDCH:epi = 1: 3.0 2.2 2.2 2.2 2.2 3.0 3.0 2.2 2.2 3.0 2.2 2.2 3.0 2.6 3.0 2.2 a 1600 250 400 500 1200 1400 300 800 250 2000 500 3400 1000 400 800 1000 800 b 22 20 20 25 20 20 20 20 20 20 25 20 20 25 20 20 20 c V 3 ditritritetra V 1 V 1 V 5 tritetra V 2 tritetra V 1 V 2 V 3 V 4 V 3 V 3 V 5 V 5 d 70-76 68-71 66-70 68-75 70 69-71 68-71 69-71 68- 70 68-73 77-80 65-70 69-71 75-80 69-70 68-70 68-72 e 5.3 5.06.2 5.3 6.5 5.5 3.5 5.5 9.5 5.7 10 7.5 6.0 6.3 5.2 5.5 14 f 57.8.sup.1 1350 1068 250 582 319 1505 413.5 1754 3038 1015 1971 40.4 610 653 479 1218 g 100.sup.1 20.sup.2 20.sup.2 25.sup.2 20.sup.2 20.sup.2 20 20.sup.3 20 20 25 20 20 25 20 20 20 h epi V 7 V 8 V 8 V 8 V 8 V 9 V 9 V 10 V 11 V 15 V 10 V 10 V 15 V 12 V 13 V 14 i -- 90.0 80.5 24 61.5 3072 19 43.5 34 18 47 11 10 8 7 19 k 22 20 20 15.sup.4 20 20 20 20 20 20 25 20 20 25 20 20 20 l 844 1100 926 1560 1940 2300 809 1360 2360 1560 2490 836 1460 4945 1340 659 1650 m 10.3 10.3 10.1 9.5 10.5 10.4 10.4 9.8 10.3 9.9 10.1 10.3 10.0 10 10.4 10.6 10.5 n 105 30 33 not 126 123 31 60 20 170.5 -- 292 78.5 not 74.5 92.5 70.5 o 8.5 8.0 8.0 neu- 8.0 8.0 8.0 8.0 8.0 8.0 10.1 8.0 8.0 neu- 8.0 8.0 8.0 p 81 57 57 tra- 10 67 95 75 121 367 362 250 69 tra- 78 64 134 q 20 18 18 lized 18 18 18 18 18 18 20 18 18 lized 18 18 18 r 720 920 740 760 1535 514 857 1080 980 614 470 869 968 492 572 .sup.1 a further 250 g of water are added (22% crosslinker) .sup.2 in a 1:2 w/w mixture of alcohol and water .sup.3 in a 1:3 w/w mixture of alcohol and water .sup.4 diluted to 15% WS during resin formation

The following Tables present a comparison of the papermaking properties of our products compared with those of a modified polyethylene (PEI) prepared according to Examples of German Published Application 1,802,435.

Acceleration of drainage

This is characterized by the reduction in the degree of freeness in .degree.SR. The degree of freeness in .degree.SR is determined according to Leaflet 107 of the Verein der Zellstoff- und Papierchemiker und Ingenieure.

Filler retention

This is characterized by the ash content of sheets of paper produced on a Koethen apparatus according to Leaflet 108 of the Verein der Zellstoff- und Papierchemiker und Ingenieure.

Composition of pulp for paper to be tested:

80 % of bleached sulfite cellulose 35.degree. SR

2 % of China clay

Pulp density: 0.24 g/l.