US3345253A - Process of forming cellulosic webs containing urea-alkyleneimine condensation products - Google Patents

Description

In the manufacture of 'cellulosic fibrous materials, in particular papers, cardboards and cellulosic pulps, it is usual to employ auxiliary agents besides the fibrous material or paper material. Such auxiliary agents are intended, for example, to shorten the time necessary to dewater the paper pulp or to increase the tensile strength of the finished product in the wet or dry state, or to modify, for example, the water absorbability, the surface smoothness or other properties. Auxiliary agents are also used which are capable of retaining to a large extent or of depositing other products on the fibrous material, for example, pigments. Thus, for example, for increasing the speed of dewatering of a pulp of fibrous material, surface-active substances of the alkylaryl-sulfonate type have been used. The wet tensile strength or the wet scufiing resistance can be increased, for example, by products that are based on melamine-formaldehyde precondensates or similar compounds; these products may be applied alone or, if required, together with other products such as plasticizing, filling or pigmenting additives. For retaining the fibrous material or the filling material during the formation of the paper web, there are used, for example, bone glues or similar substances and water-soluble highly polymeric substances based, for example, on polyacrylamide. I

Now, we have found that in the manufacture of cellulosic fibrous materials, in particular paper, cardboard and cellulosic pulps, some of the afore-mentioned effects can be produced simultaneously by adding to the aqueous suspension of the fibrous material, prior to the formation 'of a paper web, water-soluble or in water self-emulsifying, nitrogen-containing condensation products of 1,2- alkyleneimines in which one of the hydrogen atoms at the nitrogen is substituted, and/ or their oligomers with urea.

For-preparing the water-soluble or in water self-emul- United States Patent-O carried out in the molten mass, i.e. in the absence of solvents or diluents. This method of operation permits, for example, the conversion of the oligomeric ethyleneimines or 1,2-propyleneimines with urea into resinous condensation products. When following this method of operation, there is first obtained a highly viscous, amorphous mass which is still soluble in water. Upon further heating, there are formed cross-linked products which are only swellable in water. Preferably, however, the reaction of the 1,2-alkyleneimines with urea is carried out in a solvent or diluent or in a mixture of such substances, in order to withdraw easier the reaction heat. As solvents or diluents, there are suitable all products which do not react with the alkylene-imines. As such, there may be mentioned alcohols, esters, amides, and even hydrocarbons. The use of water as the diluent is especially favorsifying, nitrogen-containing condensation products of 1,2-

alkyleneimines and urea, there may be used 1,2-a1kyleneimines which are not substituted at the nitrogen atom. Preferably, there are used easily accessible imines having small alkylene radicals, for example, ethyleneimine, 1,2-propyleneimine, 1,2- or 2,3-butyleneimine or 2,2-dimethylethyleneimine. Instead of the monomeric cyclic compounds, there may also be used the dimeric, trimeric and other oligomeric forms, especially, however, the oligomers of ethyleneimine and of 1,2-propyleneimine. The preparation of the oligomeric alkyleneimines is described in the hand book by Houben-Weyl, Methoden der organischen Chemie, 4th edition, volume XI/2,

page 261, 1958.

For preparing the condensation products, it is not necessary to use the pure oligomeric 1,2-alkyleneimines for the reaction with urea. The oligomeric mixture as it is obtained in the preparation of the alkyleneimines may also be reacted with urea, if required or desired, in the presence of the monomeric alkyleneimine. The reaction yielding the condensation products proceeds exothermically with separation of ammonia. The reaction can be able and advantageous from a technical point of View. The quantity of the water used can vary within wide limits. Even when the reaction is carried out in a diluent, for example, water, there are first formed low molecular,

'still soluble products, which can then be converted into insoluble cross-linked products by further heating.

The reaction of the components is carried out at elevated temperature, namely in a temperature range of from about 40 C. to about 200 0., preferably from about 60 C. to about 140 C. If water is used, the reaction is suitably carried out at about C. and the aqueous reaction mixture is then kept boiling weakly. The preparation of the condensation products is usually carried out at normal pressure. For removing the am- I monia which is forming during the reaction, it may be of advantage to apply a reduced pressure. On the other hand, the reaction time is shortened, if, especially in the case of a reaction in aqueous solution, the reaction mixture is allowed to boil at elevated temperature, for example, in a range of from 100 C. to C., by the application of overpressure. The condensation products obtained are highly viscous to solid amorphous masses of high molecular weight.

The products may also be obtained in non cross-linked form and are in this state water-soluble. When the reaction is continued until cross-linking of the reaction product is achieved, glass-like or gelatin-like solidified masses are obtained which are only swellable in water.

As the condensation products which may be used according to the present invention, those products are especially considered in which the ratio of urea to alkyleneimine is in the range of 0.25 to 1.5 mol of urea, preferably 0.5 to 1.3 mol of urea, per 1 mol of alkyleneimine. Molecular proportions of somewhat more than 1 mol of urea per 1 mol of alkyleneirnine are of special interest. Instead of alkyleneimines, there may also be used in the same quantitative proportions their oligomers. If the alkyleneimines are mixed with oligomer s, they may be mixed in any desired quantitative proportion.

The nitrogen-containing condensation product of 1,2- 'alkyleneimines and urea-to be added according to the present invention to the aqueous suspension of the fibrous material-are usually added in quantities of about 0.1 to about 4%, preferably 0.2-l%, referred to the dry fibrous material. The condensation products may be added either during the beating of the fiber material or shortly before it is transferred on the wire. Other products, for example, plasticizing, glueing or antistatic agents may then also be added to the usual extent. It is also possible to apply with the products to be used according to the present inventionabout 1.5-8%, preferably 24%, referred to the dry fiber material, of condensation products of urea and formaldehyde and/ or triazines and formaldehyde. In the case of mixtures of urea/formaldehyde condensation products with such of triazines and formaldehyde, the molecular proportion may have any desired ratio. In certain cases, a further increase of the wet strength and wet scufiing resistance can thereby be achieved. The fibrous material is then further treated and finished in known manner; it does not'turn yellow atthe drying temperatures usually applied.

The application of the condensation products of 1,2-alkyleneimines and urea distinctly shortens the time necessary for dewatering the paper web. In addition thereto, the wet tensile strength is considerably increased, a special advantage being that the absorbency of a fibrous material thus prepared is practically not reduced. This advantage renders the process especially suitable for the manufacture of filter papers.

The use of the condensation products according to the present invention also brings about an increased retention of the fiber and filling materials. As compared with the polyethyleneimines proposed for a similar use, the compounds to be used according to the present invention are distinguished by an essentially lower tendency to yellowing of the papers prepared therewith, in particular at elevated temperatures.

The following examples illustrate the invention, but they are not intended to limit it thereto:

Example 1 A condensation product of 1 mol of ethyleneimine and 1.1 mol of urea was added during beating in concentrations of 0.5%, 1%, 2%, and 3%, referred to absolutely dry substances, to different cellulosic pulp suspensions, and a paper sheet was formed from each of these suspensions on a sheet form. For comparison, a paper sheet having the same weight was prepared from the same cellulosic pulp suspensions, but without addition of auxiliary agents. The physical determination of the wet tensile strength and of the water absorption by measurement of the suction height gave the following results:

The above table shows that the wet tensile strength was distinctly increased, while the water absorption was not reduced.

Example 2 A condensation product of 1.5 mol of urea and 1 mol of ethyleneimine was added in a quantity of 0.4 and 1%, referred to absolutely dry material, to a cellulosic pulp suspension having a beating degree of 75 S-R and a pH-value of 4.7 in a paper mill beater. In another experiment, the pH-value of the suspension was adjusted to 7.5. The effect of the reduction of swelling and of the increase of the speed of dewatering could be determined in known manner by measuring the reduction of the beating degree according to SR and the time required for dewatering The following values were determined:

The above Values show that the speed of dewatering was distinctly increased in the neutral as well as in the alkaline pH-range.

Example 3 To a cellulosic pulp suspension having a beating degree of 45 5-H. and containing as a filler 40% of kaolin, referred to absolutely dry material, there were added 2%, referred to absolutely dry material, of a condensation product of 1 mol of urea and 2 mols of ethyleneimine. For determining the filler retention effect, the weights per square meter and the ash content of the papers finished with or without addition of the condensation product as well as the content of solids and floating particles in the waste water was measured after adjustment of the equilibrium in the wire water circulation.

The following values were obtained:

Without 2% addition addition G/m. 68 70. 2 Ash content, percent 16. 7 18. 1 Content in waste water, mg 340 174 Example 4 Paper sheets were formed from the following mixtures with bleached sulfite pulp having a beating degree of 40 S-R:

Sheet No.

Pulp (bleached sulfite 40 g T102, g- BaSO g Kaolin, g Product A, percent abs. dry

subst., g A. Product B, perze it abs. dry

subst., g

obtained showed a distinct increase of the retention by the addition of the condensation product of alkyleneimine and urea according to the invention, in comparison with that of the paper prepared without this addition as shown by comparison of test 4 with 3 and test 6 with 5.

Sheet No. Mean ash value, g. Residue in g./l. of wire waste water We claim:

1. The process for preparing cellulosic fibrous materials having increased wet tensile strength, wherein to the fibrous material in aqueous suspension is added 0.1 to 4% on basis of the dry fibrous material a nitrogen-containing condensation product of 0.25 to 1.5 mole to 1 mole, respectively, of urea and a member selected from the group consisting of 1,2-alkyleneimines, oligomers of 1,2-alkyleneimines, and mixtures of 1,2-alkyleneimines and their oligomers, and thereafter dewatering said suspension, sheeting the fibrous material and drying the sheeted material.

2. The process for preparing cellulosic fibrous mate rials having increased wet tensile strength, wherein to the fibrous material slurry is added on basis of the dry fibrous material 0.1 to 4% a Water-soluble, nitrogen-containing condensation product of 0.25 to 1.5 mole to 1 mole, respectively, of urea and a member selected from the group consisting of 1,2-alkyleneimines, oligomers of 1,2-alkyleneimines, and mixtures of 1,2-alkyleneimines and their oligomers wherein said nitrogen-containing material is on basis of an absolutely dry material, and dewatering said fibrous material slurry, sheeting the fibrous material and drying the sheeted material. 3. The process for preparing cellulosic fibrous materials having increased wet tensile strength, wherein to the fibrous material slurry is added 0.1 to 4% on basis of the dry fibrous material a nitrogen-containing condensation product of 0.25 to 1.5 moles to 1 mole, respectively, of urea and a member selected from the group consisting of 1,2-alkyleneimines, oligomers of 1,2-alky1eneimines, and mixtures of 1,2-alkyleneirnines and their oligomers, and, additionally adding to said slurry 1.5 to 8%, on basis of the dry fibrous material, condensation product selected from the group consisting of urea with formaldehyde, triazines with formaldehydes, and mixtures thereof, and thereafter dewatering said fibrous material slurry, sheeting the fibrous material and drying the sheeted material.

4. The process for preparing cellulosic fibrous materials having increased wet tensile strength, wherein to an aqueous suspension of the fibrous material is added on basis of dry fibrous material 0.1 to 4%, of water-soluble, nitrogen-containing condensation products of 0.25 to 1.5 moles to 1 mole, respectively, of urea and a member selected from the group consisting of 1,2-alkyleneimines, oligomers of 1,2-alkyleneimines, and mixtures of 1,2- alkyleneimines and their oligomers wherein said nitrogencontaining material is on the basis of an absolutely dry material, and, additionally adding to the aqueous suspension of fibrous material, 1.5 to 8% a condensation product selected from the group consisting of urea with formaldehyde, triazines with formaldehyde, and mixtures of condensation products of urea/formaldehyde and triazine/formaldehyde wherein said formaldehyde condensation product is on basis of absolute dry material, and thereafter dewatering said aqueous suspension of fibrous material, sheeting the fibrous material and drying the sheeted material.

References Cited UNITED STATES PATENTS 467,655 12/1951 Italy.

S. LEON BASHORE, Primary Examiner.

Claims (1)

1. THE PROCESS FOR PREPARING CELLULOSIC FIBROUS MATERIALS HAVING INCREASED WET TENSILE STRENGTH, WHEREIN TO THE FIBROUS MATERIAL IN AQUEOUS SUSPENSION IS ADDED 0.1 TO 4% ON BASIS OF THE DRY FIBROUS MATERIAL A NITROGEN-CONTAINING CONDENSATION PRODUCT OF 0.25 TO 1.5 MOLE TO 1 MOLE, RESPECTIVELY, OF UREA AND A MEMBER SELECTED FROM THE GROUP CONSISTING OF 1,2-ALKYLENEIMINES, OLIGOMERS OF 1,2-ALKYLENEIMINES, AND MIXTURES OF 1,2-ALKYLENEIMINES AND THEIR OLIGOMERS, AND THEREAFTER DEWATERING SAID SUSPENSION, SHEETING THE FIBROUS MATERIAL AND DRYING THE SHEETED MATERIAL.