US2668111A - Paper making processes - Google Patents

Description

Patented Feb. 2, 1954 UNITED STAT ES FFAT ENT OFFICE PAPER MAKING PROCESSES John R. Lindquis't, Chicago, Ill., ass'i'gnor to Certain-Tee'd Products Corporation, Ardmorc, Pa., a corporation-"of Maryland No Drawing. Application March 5,, 1952, Serial N0. 275,023

8 Claims.

This invention relates to the art of paper making and more particularly to those paper processes wherein a rubber-like ingredient in the form of a latex or resin emulsion is added to the aqueous beaten-fiber suspension, or so-called furnish, prior to the sheeting of the latter on the paper machine.

From the standpoint of fold endurance, resistance to oils, elimination of scufiing tendencies, high Wet strength, and other like properties, it is desirable in certain paper manufactures to coat the pulp fibers with a latex or resin compound prior to sheeting procedures. This specialized treatment of the beaten pulp fibers has been referred to as beater addition, being descriptive of treatment at the beater or at any other point prior to the sheeting operation. Since the latex or resin used is characteristically in the form of an emulsion, it is necessary to coagulate the particles comprising such emulsion in order that they Will precipitate on the pulp fibers. Particles of latex or resin precipitated in this manner are tenaciously adherent on the pulp fibers, and when the latter are intimately associated in the sheeting operation as by a cylinder in a cylinder-type paper machine, the bond between them is somewhat modified according to some of the characteristics of the rubber-like emulsion. Such emulsions exhibit the usual properties of colloidal dispersions of this class and hence coagulation is conveniently effected by adding an electrolyte to the furnish following the emulsion addition.

The general manner of processing pulp to which a resin or latex has been added for the purpose of coating the beaten fibers as outlined above is in no wise different from ordinary procedures. Moreover, since the precipitation of the particular emulsion employed, depending upon the corresponding particular property desired of the finished sheets, is an electro-physical disturbing of charged particle repulsion rather than a chemical reaction, the nature of the stock material used, as well as that of the usual additive and filler, is immaterial. rag fibers comprising the stock material, after being reduced to approximate size in the beater or other pulping machine, are treated with dyes, and fillers as desired. The pulp suspension, usually referred to as the furnish, is charged into a head box where further mixing occurs, after which the more coarse fibers and incompatible agglomerates: arescreened out on sifting? screens t produce a furnish of the proper particle. and fiber size suitable for sheeting. Subsequent Thus, the cellulose and processing may vary insofar as the paper machine is concerned, but one widely used procedure is to make use of the so-called cylinder machine in which a rotating cylindrical screen is partially submerged in a vat which is continuously charged with the furnish. Due to a difference in pressure between the vat and the interior of the rotating screen, a large percentage of the water in the furnish is extracted and drawn into the interior of the screen as a stream of so-called white water while the pulp fibers adhere in sheet form to the outer periphery of the screen. The pulp sheet formed in this manner is the-n transferred on to an endless felt band, and any excess water present in the pulp sheet is either pressed out or drawn through the interstices of the felt band to constitute an additional source of white water. It will be appreciated that the white water will have unused chemicals entrained therein, and the usual procedure is to recycle this stream back to the beater as make-up water and to the head box for purposes of dilution.

Insofar as the use of emulsions is concerned in paper manufacture of the above type, little, if any, chemical change accompanies the addition of emulsion to the aqueous pulp suspension. That is to say, the only consideration, broadly speaking, accompanying emulsion addition to furnishes is the property or properties that the emulsion may be capable of imparting to the finished product, and therefore the emulsion may be one of many known types. In this respect, Buna S, Buna N, neoprene, isoprene, melamine resins, urea formaldehyde resins and other latexes, resins, and elastomers are conventionally employed for imparting desirable properties such as high wet strength, grease-resistance, nonscufiing tendencies, body reinforcement and like to the finished paper product.

It is essential, of course, that the solids content of such emulsions be efliciently and properly coagulated on the individual beaten fibers comprising the furnish, and to this end the prior art has generally followed a three-step procedure. First, and after the furnish has been reduced to a suitable consistency inthe heaters, a basic material such as soda ash or the like is usually added to the beaten pulp suspension in order that a pH at or above seven may be had. Second, the emulsion is added in the desired quantity; and finally, an agent such as aluminum sulfate, which has an acid reaction or effect, is added to thus treated furnish until the pH has been lowered to a value conducive tocoagulation of the emulsion, usually between pH 4-5 depending to a large part upon the emulsion employed. The prior art as outlined above conceives of the use of soda ash or equivalent caustic as being essential to proper processing, and in the usual case of continuous runs wherein white water is recycled back to the heaters as make up water the use of caustic as above described is continuous. This continuous addition of basic material is due to the fact that the white water is acidified at about pH 4-5 or slightly higher, being representative of the hydrogen ion condition of the water medium after coagulating the emulsion. It will thus be seen that a definitely acid condition prevails in the prior art method. Not only does such condition necessarily result in the consumption of large quantities of caustic at the beater in order to permit a proper addition of emulsion at this stage, but corrosion occurs in those sections exposed to the acidified furnish, thus requiring the. use of expensive and specialized piping and pump installation. In addition, the continuous use of caustic is accompanied by a build up of insoluble foreign matter in the system reducing the effective withdrawal of white water from the sheeted furnish and resulting in weak sheets and clogged felts.

In view of the foregoing, it is the primary object of this invention to substantially reduce corrosive tendencies in those paper manufactures which depend upon the addition of emulsions to the furnish, and a related object is to greatly simplify prior procedures to the extent that certain steps heretofore deemed necessary, as well as the need for a carefull controlled pH in this particular type of paper manufacture, are eliminated.

Further objects of the present invention are to improv upon the quality of the finshed product, and to neutralize or avoid altogether the tendency for the machine felt or band to become clogged with foreign matter.

Other and still important objects of the present invention will be apparent from the disclosure to follow, particularly in regard to the coagulating agent which I am using and the attendant method of the present invention.

As will be apparent from the foregoing, the prior methods to which the present invention relates depend first upon the use of caustics and second upon the subsequent use of an agent such as alum for lowering the pH to between 4 and 5, and continuous runs require continuous addition of the basic or caustic material. In contrast to this, the present invention dispenses altogether with the use of caustics or the like for counteracting the acidified condition of the recycled white water, and in addition makes possible a system in which the pH need not be maintained on the acid side during any stage or at any time. These novel results are presently attained through the use of a new coagulating agent and in accordance with the practice of the present invention, this agent is in the form of guanidine formaldehyde. The exact chemical formula of guanidine formaldehyde is not definitely known, but it is formed by the action of formaldehyde, or a formaldehyde-producing reactant, on guanidine carbonate, the following reaction having been postulated:

ll HOCHz-NHCCH:OH 1120 00, The present invention makes possible complete coagulation of the emulsion at the beater and the procedure is as follows: The desired quantity and kind of resin Or latex emulsion is added to the beaten fiber suspension th latter being preferably maintained neutral or slightly basic in order to assure against any pre-coagulation of the emulsion. After the furnish thus treated has been sufiiciently agitatedto produce a homogeneous dispersion of emulsion throughout, the guanidine formaldehyde in an amount sufiicient to produce a coagulation of the emulsion can be added directly to the beater. It will be appreciated that no exact amount of guanidine formaldehyde can be specified for all conditions since this amount depends upon extrinsic factors such as purity, acid condition of th furnish prior to addition, the quantity of emulsion employed, etc. In general, however /2 by weight of guanidine formaldehyde based on the dry weight of the pulp will produce satisfactory coagulation of the latex on the furnish or beaten fiber suspension. For example, using a furnish of 0.75% consistency at pH '7, to which had been added 10% by weight of neoprene latex in emulsion form based on the dry weight of the pulp, 0.5% guanidin formaldehyde also based on the dry Weight of the pulp produced complete precipitation of the latex.

For somewhat better results, the guanidine formaldehyde can be added after the pulp has been further refined in the jordans. Thus, since the contact time necessary to cause complete 00-- agulation is less than one minute, the guanidine formaldehyde may be introduced at almost any stage of furnish flow prior to sheeting operations and after the pulp has been prepared at the beaters.

From the foregoing, it will be seen that the present invention dispenses with the use of alum, acids or the lik previously used to coagulate emulsions on the individual beaten fibers comprising the furnish, and accordingly any tendency for such materials to corrode the system is eliminated. Moreover, and perhaps more important is the fact that guanidine formaldehyde coagulate latexes and resins at approximately 7 pH and, therefore, eliminates the need for continual use of caustics heretofor used to raise the pH after the alum or acid in previous methods had lowered the pH to 4.5 or 5. Thus, the use of guanidine formaldehyde as specified, eliminates build up alumina, aluminum hydroxide and other insolubles which hinder removal of white water and thus insures proper sheet formation and sheet strength at the sheeting stage of the process.

The guanidine formaldehyde will precipitate emulsions over a wide pH range, and in fact at almost any pH whereat the emulsion is in solution. However, I have found that more of the guanidine formaldehyde is required at a high pH than at a neutral or low pH. In attempting to determine the range of equivalents I have found that other aldehydes or ketones such as benzaldehyde and methyl ethyl ketone when reacted with guanidine carbonat and the like do not produce a reaction product capable of producing a satisfactory coagulation of the emulsion. On the other hand, the use of other sources of guanidine ion such as guanidine nitrate produce satisfactory reaction products when reacted with formaldehyde. Thus, the guanidine formaldehyde used as the coagulant in accordance with the present invention may be the reaction product of formaldehyde on the one hand and a compound which produces guanidine ions in solution on the other.

I claim:

1. In a paper making process wherein an emulsion is added to the furnish and subsequently coagulated on the individual fibers comprising the furnish, the improved method comprising, coagulating the emulsion with guanidine formaldehyde.

2. A method of paper manufacture comprising the steps of, first adding an emulsion to the fibrous beaten pulp suspension and then incorporating in the thus-treated suspension guanidine formaldehyde in an amount sufiicient to coagulate the emulsion on the beaten fibers of the pulp.

3. A method of paper manufacture comprising, at the beater, beating the fibrous pulp suspension to a workable consistency, adding an emulsion to the beaten pulp suspension, agitating the mixture to produce a homogeneous mixture, and coagulating the emulsion on the fibers with guanidine formaldehyde.

4. The method of producing emulsion-treated paper products comprising, beating the fibrous pulp suspension to a workable consistency, adding emulsion to the beaten pulp suspension, adding guanidine formaldehyde to the mixture in an amount sufficient to coagulate the emulsion, and sheeting the emulsion-treated pulp on a paper machine.

5. The method of producing emulsion-treated paper products comprising the steps of beating the fibrous pulp suspension to a workable consisteney, maintaining the pH of the pulp sus pension at or slightly above seven, subsequently adding an emulsion to the beaten pulp suspen- 6 sion, adding guanidine formaldehyde to the mixture in an amount suflicient to precipitate the emulsion on the beaten fibers, and then sheeting the pulp on a paper machine.

6. A paper making process comprising the steps of producing a pulp suspension of the desired consistency, incorporating in the pulp suspension an emulsion to be coagulated on the pulp fibers, and incorporating guanidine formaldehyde in the pulp suspension to coagulate the emulsion on the pulp fibers.

7. A paper making process comprising the steps of producing a pulp suspension of the desired consistency, incorporating in the pulp suspension an emulsion to be coagulated on the pulp fibers, and incorporating in the pulp suspension the reaction product of formaldehyde and a compound of the group consisting of guanidine carbonate and guanidine nitrate to coagulate the emulsion on the pulp fibers.

8. A paper making process comprising the steps of producing a pulp suspension of the desired consistency, incorporating in the pulp suspension an emulsion to be coagulated on the pulp fibers, and incorporating in the pulp suspension the reaction product of formaldehyde and a compound producing guanidine ions in solution to coagulate the emulsion on the pulp fibers.

JOHN R. LINDQUIST.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,621,399 De Cew Mar. 15, 1927 2,607,750 Wilson Aug. 19, 1952

Claims (1)

1. IN A PAPER MAKING PROCESS WHEREIN AN EMULSION IS ADDED TO THE FURNISH AND SUBSEQUENTLY COAGULATED ON THE INDIVIDUAL FIBERS COMPRISING THE FURNISH, THE IMPROVED METHOD COMPRISING, COAGULATING THE EMULSION WITH GUANIDINE FORMALDEHYDE.