US1975771A - Process for the recovery of pulp from printed paper - Google Patents

Description

Fatenteci @et. 9,- i934 PROCESS E ght 'EIHIE REQDQVERY F 1? ,FRUM PRINTED PAPER Alex B. Davis and Ears E. Thompson, Cincinnati, Wis,

(Dhio, and Aiired ii. Gardner, Appleton, assigncrs to lL. Alstcd, Appleton,

No Drawing. Application October 24, 1931, Serial No. 570,968

5 @laims.

This invention relates to the preservation or paper for repeated printing in the sense that the paper may be periodically restored to its original color and quality for successive printings. For

5 example, after the paper has been originally= iii;

printed andhas served its purpose as so printed, it may be readily and economically restored to its original quality and color and rendered available for further printing and use.

Paper upon which newspapers, directories, books, catalogues and the like are printed, usually, if not always, contains a substantial quantity of ground wood pulp and the ink utilized for printing of this character comprises a carbon black pigment and a suitable vehicle. Numerous processes have been proposed, and many patented, directed to the recovery of paper pulp from printed paper of this character. Such processes consist of various modes of loosening the carbon black pigment from the paper, usually by breaking down the vehicle or the binder between the pigment and the paper by means of detergents or by other agents suitable for 'the purpose, coupled with various methods of efiecting, as completely as possible, a separation of the loosened pigment from the fibers of the paper, as, for example, by flotation, by mechanical separation or the like. In the prior processes, these steps are followed up or accompanied by a pulping of the paper and a bleaching of the fibers thereof, and are usually completed by washing the paper fibers and remanufacturing the resulting pulp into paper. The bleaching agents have no material efiect on such of the carbon pigment as remains with the pulp. Furthermore, a substantial amount of carbon pigment tenaciously adheres to the fibers of paper containing ground wood pulp with the result that it is impossible to eiiect a complete separation of such pigment from the pulp. It has been a matter of experience in this art that any pulp recovered from newspapers,'

directories, books, catalogues or other printed {paper containing ground wood is slightly colored, usually gray or brown, and is suitable only for use in manufacturing laundry boxes, heavy wrapping paper, cheap grades of cardboard, or the like. It has never been possible to produce from printed paper containing ground wood pulp, a pulp suitable for manufacturing paper of the quality and color of the original and consequent- 1y suitable for general printing purposes.

. It is true that certain inks have been proposed containing mineral pigments as for example, manganese dioxide. Such inks, however, have never found their way into commercial use. and

are unsuited for such use mainly because of their high cost and their poor printing properties. The costs of such inks are so high as to tend to ofiset any advantage resulting from possible recovery of the pulp. It is dimcult to keep such an ink suspended in any suitable ink vehicle and because the pigment is mineral the ink possesses high abrasive qualities and is unfit for use on the modern high speed presses. Its tinctorial value is low and the structure of its particles is such that it does not have the capability of lifting properly from half tone plates. Furthermore, its specific gravity is so high that the ink is too heavy to give good coverage, that is to say, an excessive amount of ink is required to print a given quantity of paper withordinary printed matter. For similar reasons the fugitive inks susceptible of being eradicated by the ordinary ink eradicators or incorporated in bank checks or the like to preclude alteration are unsuitable for generalprinting purposes, as, for example, printing newspapers, directories, books, catalogues, and the like.

One of the principal objects of the present invention is to provide for the printing of paper containing ground wood pulp and for the subsequent recoveryv of paper pulp therefrom of such a character that it may be remamiiactured into paper of the quality and color of the origbnal and capable of reprinting for the same purpose, and all of this in a simple, practical and economical manner and in a manner consistent with the requirements of standard printing and paper manufacturing practices. In other words, the broad object of the invention is to render available the paper of newspaper directories, books, catalogues, and the lik for repeated printing operations and repeated or successive use and to preserve such paper in its original color and condition over an extended range of printings and uses.

In carrying out the present invention the paper is originally printed with an ink of low cost,

of the desirable printing properties and having the capability of being bleached. Such an ink 1 consists of a suitable vehicle and a pigment pre dominately organic in character and'capable of being bleached. The next step in the process consists in bleaching the pigment of the ink after the paper has been used and when it is ready ing into substances which either go into solution or into substances which are white or have color or color characteristics corresponding to or in to be repulped; The pigment itself is converted from.a substance of the desired color for printharmony with the color and character of the original paper. After the conversion of the pigment in this manner the paper is repulped and remanufactured into paper of original quali y. grade and color, and is thus rendered available for reprinting.

Since most printed matter capable of yielding stock which can be recovered are printed preferably in black, it is obvious that the inks desirable for this process would be black or nearly so; While marry mixtures of organic lakes may yield nearly black inks, many such mixtures cannot be bleached but we have found several types of organic coloring matters capable .of yielding lakes and capable of being bleached in a practical manner. Those compounds commonly called tannins and those also called dye wood extracts may be advantageously employed. r-

dinarily tannic and-gallic acids are specific examples of one of this group of substances of vegetable origin and log wood extracts consisting principally of hzmatein and hamatoxylin is an example of a suitable extract from dye wood.

The process of preparing the pigment for the manufacture of the ink is very simple and consists of converting the dyestufl into insoluble or nearly insoluble lakes according to the many processes known for doing this. The dye woods and tannins yield insoluble lakes with iron and manganese salts. These lakes are, after precipitation, filtered, dried, and ground into a suitable vehicle with a bodying agent and the ink is then ready for printing upon the paper. Only that amount of pigment is used which is required to give a sufilcient depth of shade. In preparing the ink, the pigment is ground on proper grinding machinery into a mineral oil vehicle hearing such amount of varnish of one kind or another as may be required to bind the pigment in place and there is also added some form of bodying agent to give the ink a proper printing body. This may be either organic in the form of a small amount of heavy varnish, or it may be a finely divided mineral pigment such, for instance, as alumina hydrate or carbonate of magnesia. The ink when used on some kinds of paper need have no va'rnish' content, the pigment adhering to the paper fiber after absorption of the mineral oil vehicle by cohesion only, but higher grade inks will require a small amount of varnish to bind the pigment in place. If cost of the ink' be not too serious a factor, then a sufficient amount of pigment to give the ink a proper body may be used without the addition of a separate bodying agent, or the pigment in course of manufacture maybe precipitated upon alumina hydrate or any other suitable base in which case the bodying agent becomes a part of the pigment.

With inks made from the usual forms of lakes produced from tannins and dye woods, we find the most suitable bleaching agent to be some form of sulphurous acid and it may be applied to the disintegrated paper either gaseous or as an alkali sulphite. After the bleaching operation has been carried out by means of the sulphite, the mass is often left acid in reaction, and better results may be obtained under some conditions and with some pigments if the acid reaction be destroyed by the addition of a, portion of some neutralizing agent. For this purpose we find ordinary borax to be most satisfactory for more active alkalies, soda for instance, tends to turn the ground wood yellow, while borax does not have this disadvantage. However, where the pigment includes logwood and similar dyestuifs acidification may be desirable and under certain conditions it may be desirable to still further increase the acidity in order to hold in solution the products of the composition of the pigment until they can be washed out.

The importance of using a pigment and bleaching agent which will not discolor the ground wood, either because of by-products left from the ,reduced ink or of the action of the bleach or neutralizing agentupon the ground wood, is not to be overlooked if white pulp is to be recovered.

In carrying out the process of the present invention, the paper is first printed withan ink of the character disclosed hereinabove. After the paper has been used and is ready for recovery it is first shredded or disintegrated. After shredding or disintegrating the paper I add to the mass -suspended in a suitable volume of water some form of sulphurous acid, either gaseous or combined in the form of sulphite and in a quantity sufilcient to bring about the practically complete bleaching of the pulp. The sulphite or sulphurous acid not only bleaches the ink but also bleaches the ground wood portion of the pulp. The quantity required does not exceed 10% of the dry weight of the pulp, and the cost of chemicals, therefore; is very small. The use of the sulphite usually leaves the pulp acid in reaction to some extent, and if this be then neutralized by the addition of a small amount of borax, the pulp will remain white for a longer period of time than if alkali neutralizing agents be used, although it is entirely possible that ordinary soda ash may be used with some kinds of pulp. The bleaching action takes place in a few minutes after the sulphite is added, and at ordinary temperature so that no heating is required.

Several of the lakes which work satisfactorily with reducing agents are also bleached by oxidizing agents andwhere a pulp is encountered which bears no ground wood, then active chlorine in some form might be applicable as a bleaching agent, but ingeneral since ground wood is so many times encountered in book papers, the process requiring reducing agents for the bleach appears preferable. Destroying the color by bleaching with oxidizing agents may also be carried out when certain pigments are used by treatting the pulp at ordinary temperatures with one percent nitric acid for a short time.

It is to be understood that the bleaching step in the present invention results in an actual destruction of the color since the bleaching agent acts directly on the ink and on its pigment and chemically changes the pigment into substances which usually go into solution and which are either white or have a. color corresponding to that of the original paper. Their presence in the pulp may enhance the quality of the paper.

The best form of ink for working with the sulphite bleaching agents above described, as previously stated, are of vegetable origin and primarily of course are the lakes of vegetable extracts capable of yielding successful pigments, primarily black, and as is well known, this group of vegetable extracts falls within two classes of products, the tannins and dyewoods extracts. I have found the iron lakes made from certain tannin extracts and consisting primarily of the iron lakes of various-tannic and gallic acids, and the iron lakes of certain dyewoods, logwood for instance, to be most satisfactory. Logwood alone may be too high in cost or unnecessarily strong stance, the manganese lakes. We find that a' maximum of 20% of logwood lakes, or probably not more than 20% of mixtures of logwood with tannin lakes, or about 20% or a little more of tannin lakes alone, when ground into a suitable mineral oil, or mineral oil and varnish vehicle and with a suitable bodying agent such as, for instance, alumina hydrate, yield inks of sufficient strength to be applicable to this process and they are capable of being bleached with great ease. If pure logwood lakes alone be used then as little as 10% of the weight of the ink of a pigment consisting of the iron lake of logwood may in certain instances, or on proper kinds of paper, yield inks of sufficient depth of color for satisfactory printing operations, and this limited amount of coloris easily bleached from the paper by the bleaching agents above described to yield a pulp of practically the original color, or so nearly so that by the addition of sizes, china clay, or a small amount of new pulp, in no case to exceed about 30%, the pulp is then capable of yielding paper of practically original whiteness and equal to, if not superior, in printing properties to the original paper.

It will be understood that the present invention contemplates such variations in the process above described, in the steps thereof and in the substances used as will be understood by those skilled in the art and be within the spirit of the invention and the scope of the subjoined claims.

The invention claimed is: A

1. In the art of rendering paper containing ground wood and previously printed upon with an ink capable of being bleached, available for repeated printing and use, the step which consists in subjecting the ink of such paper to the action of a bleaching agent for destroying the color of the ink while maintaining the fibers of the paper substantially white.

2. In the art of rendering paper containing ground wood and previously printed upon with an ink capable of being bleached and predominantly organic in character, available for repeated printing and use, the steps which consistin disintegrating the paper so printed upon into pulp, subjecting the ink contained in the pulp to a bleaching action to destroy its color while maintaining the fibers substantially white and manufacturing paper from the resulting pulp.

3. The hereindescribed' process of rendering paper containing ground Wood available for repeated useas a support for printed matter comprising printing upon the paper with a bleachable ink having the requisite printing properties, repulping the printed paper, subjecting the ink carried by the pulp to the action of a bleaching agent capable of destroying the color characteristics of the ink and of maintaining the original color and other original characteristics of the pulp, and subsequently making the pulp into fresh paper.

4. The hereindescribed process of rendering paper containing ground wood available for repeated use as a support for printed matter, comprising printing upon the paper with ink made from a bleachable log-wood pigment, repulping the printed paper, subjecting the ink carried by the pulp to the action of a bleaching agent capable of destroying the color characteristics of the ink to free the pulp from discoloration due to the printing step anti also capable of maintaining the original color and other original characteristics of the pulp, and subsequently making the pulp into fresh paper. 1

5. In the art of rendering paper containing ground wood and previously printed upon with a bleachable ink predominantly organic in char- 1 5 acter and having the requisite printing properties, available for repeated printing and use, the step which consists in subjecting the ink of such paper to the action of sulphur dioxide in some active form for bleaching the ink and destroying the color thereof while maintaining the fibers of the paper substantially white.

ALEX B. DAVIS. JAMES F. THOMPSON. ALFRED .T. GARDNER.