US1797789A - Manufacture of paper - Google Patents

Description

' aper web. Such attempts Patented Mar. 24, 1931 UNITED: STATES PATENT OFFICE DON ALD K. PATTILLQ OF FULTON, NEW YORK, ASSIGNOR, BY DIRECT AND MESNE AS- SIGNMENTS, TO THE MATHIESON ALKALI WORKS, IN 0., OF NEW YORK, Y., A COR- PORATION OF VIRGINIA Io Drawing.

This invention relates to improvements in the operation of paper mills. More particularly, it relates to improvements in such operation in which the formation of objection- 5, able pitch, as well as of slime, is 'prevented'or minimized.

One of the worst evils encountered in the pulp and paper mills is the occurrence of slime and pitches at various points in the mill.

Pitches or beater gum form for the most part in the beating engines and subsequent stock chests, and differ radicall from slime in that they are denser and usua ly of a much darker color and for the most part contain.

sulfides. They have the characteristics of a dehydratedslime. Such material is usually hard nd brittle when cold, of a dark brown or lack color, and becomes plastic when warmed. O n ignition, it gives off the characteristic odor of hydrogen sulfide.

It has been generally assumed that such material is attributable to resinous compounds, either in the cellulose or in the rosin sizing frequently used; and many attempts have been made to'eliminate pitch b the addition of clay, coagulants and loa ing materials to the-beaters, onthetheory that such added materials would cover the pitch particles and permit their incor oration in the ave, however,

een unsuccessful in overcoming the pitch problem.-

My investigations have indicated that pitch or heater gum is not caused by res-' inous materials, but rather by bacterial decomposition of cellulose materials underi'favorable conditions, and that it differs from slime, which is also of bacterial origin, in being ofa dehydrated character,

The most serious pitch troubles are encountered wherethe beating operation is of great duration, and, other things being ual, wher'e materials like soluble starch are a ded during the beating. Pitch formation occurs particularly in the manufacture of tissue and other lightweight papers in which the majority of the furnish consists of ground wood pulp. Ground wood pulp, and

to some extent sulfite pulp, as well as mixtures of the two pulps, are beaten for a coniranurncrunn or rarnn Application filed January 1 2, 1928. Serial No. 246,375.

siderable length of time, c. g., four to twent hours, in a tissue mill in the presence of loa ing materials. and at a temperature such that any fun or mold of the wood destroying variety nds favorable conditions for breeding, particularly in the presence of materials like starch. As a result, bacterial decomposition of the cellulose sets in and continues throughout the beating operation, and the resulting pitch sticks to the sides and bottom of the heater and is held there. Accordingly, while the formation of pitch appears to take place mainly on the walls of the heater and to some extent in subsequent chests, it may take place in small particles throughout the stock in the beater,.and the bacterial contamination which forms it and which results from it extends throughout the mill through which the stock subsequently passes, and into the white water which, if brought back to the beater, promotes pitch formation in subsequent operations.

The present invention provides an improved process based upon my investigations and observations, in whichpitch formation is effectively prevented, and sterile conditions, or substantially sterile conditions, maintained not only in the beating operation but throughout the entire paper mill.

According to the present invention, I subject the raw material before or at the beginning of the beating operation to a sterilizing treatment, and, if necessary, I subject the raw water employed to a sterilizing treatment by introducing v chlorine into the water and by treating the raw material or the stock in the beater at the beginning of the beating operation with chlorine in regulated amounts.

Where the raw materials have not been subjected to a sterilizing treatment, I combine such treatment with the beating operation. For example, in using ground woods which have been stored and which are contaminated with cellulose-destroying fungi or mold, I subject the stock in the beater at the beginning or near the beginning of the beating operation to treatment with chlorine suflicient to leave in the mixture a small but definite residuatchlorine content, e. g., of around onehalf part to one part per million,-based on theiwater present. Where the raw water is a source of contamination, I likewise subject it to the action of chlorine to leave in it a similar small'but definite'residual' chlorine content. Such chlorine treatment is efiective to destroy the mold or fun us or other bac-r terial source of contamination, with the 'result that the beating operation can be carried out without further cellulose deterioration by bacterial action and without objectionable pitch or beater gum formation.

Such preliminary treatment of the stock in the beater with chlorine not only pre-. vents pitch or .beater'gum formation, but also prevents liver formation or slime formation; and, by sterlizing the stock in the beater, and also sterilizing the raw water subsequently supplied to the process. it becomes possible to overcome both the pitch and the slime problem and to give a stock or fibrewater mixture for paper making which is free from both slime and pitch contamination, and which may be of a sterile character, if subsequent contamination is prevented.

Where ground wood is employed in admix ture with other fibres for paper manufacture,

- it can advantageously be subjected to treatment by itself before the ground wood is added to the other fibres. For example, the

.ground wood pulp can be subjected to a separate beating treatment with the addition of chlorine and with sterilization of the ground wood and the resulting mixture of ground wood and water can then be admixed with the other fibres, either by adding the other fibres to the I same beater containing the ground wood pulp, or by conveying the ground wood pulp to another beater in which the other fibres are contained, or to which they are added. The separate treatment of the ground'wood in this way may be sufficient to overcome the danger of pitch formation without treatment of the other fibres with chlorine, in which case the subsequent stock may not be completely sterilized, but may nevertheless be free from objectionable slime and pitch contamination. Where ground wood isiemployed in admixture with sulfite pulp, the sulfite pulp can be subjected to a beating operation by itself for the necessary time, and the ground wood pulp can be subjected to achlorine treatment to sterlize it, and the two pulps can then be admixed in proper proportions for the paper making operation, and the mixture subjected to further beating to produce an intimate mixture and a half stock of the proper characteristics. In such case, the sulfite pulp may'itself be free from objectionable pitch forming constituents, and the sterilization of the ground wood may be sufiicient to overcome danger of pitch formation. In some cases, however, the sulfite pulp or other fibres added to the ground Wood may be subjected toa similar treatment to sterilize them before they are admixed with the ground-wood; or the admixture of ground wood fibres and added fibres may be subjected to a second chlorine treatment by the regulated addition of a further limited amount of chlorine thereto after the mixture takes place and before the beating operation is continued.

The chlorine treatment can be carried out with gaseous chlorine, introducing the ch10 rine in gaseous form into the mixture of pulp and water, or the gaseous chlorine can first be dissolved in water and the chlorine water then added to the stock; or the chlorine can be added in the form of a solution of hypochlorous acid or of a hypochlorite. An advantageous method of adding it is to com-,"

bine it with water in a continuous manner to form chlorine water having a defim'te chlorine content, and then adding such chlorine water in regulated proportions to the beater. I

The amount of chlorine required ma differ considerably with different stocks. In general, the amount of chlorine should be such as will give a residual chlorine content in the stock or fibre-"water mixture from around one-half part to onepart per million of water-as determined by the standard ortho-tolidine test of the American Public Health Association. Where raw water isadded to the beater it may be subjected to a preliminary chlorine treatment before addition, or it may be added and subjected to chlorine treatment in the stock in the beater. When raw water is added subsequently to the stock to dilute it or in the paper making operation, it is advantageously subjected to a chlorine treatment tosterilize it, if it contains objectionable slime forming organisms. The

water, when .itis to be treated, should be such as to give a similar but definite residual chlorine content therein.

In a mill in which pitch or heater gum has been formed, the entire mill maybe con taminated with the organisms which cause such formation. In such case, an excess of amount of chlorine required for treating the,

chlorine may be required until such time as the mill has been sterilized and the objectionable pitch forming organismshave been removed. Thereafter,

only the normal amount of chlorine will be required to maintain the mill in a uniform condition of sterilization or freedom from objectionable contamination.

In general, the effective sterilization of the stock in the beater at the beginning of the beating operation will be sufiicient to maintain the stock in a sterile condition, or free from objectionable contamination, throughout the,flow of the stock through the paper mill and the manufacture of paper therefrom, particularly where any raw water subsequently added to the stock is itself subjected to a chlorine sterilizing treatment.

Where a sterile'half-stock or fibre-water mixor to dilute the stock in further operations without introducing objectionable contaminating organisms therein.

The sterilization of the stock at the begining of a small but definite residual chlorine content therein, benefits the entire paper mill operation, keeping the felts cleaner, giving a,

freer flowing pulp and one free from both pitch and slime contamination, keeping the wires of the paper machine cleaner, and giving both a white water and a paper product free from objectionable cellulose-destroying organisms which might cause deterioration of the paper after its production.

.In some cases, the raw material canbe subjected to a sterilizingtreatment with chlorine before it is added to the beater. Ground wood pulp, for example, when stored, develops a fungus ormold growth which decomposes the cellulose to a considerable ex tent, e. g., up to 6 or 7% or more of its weight. I A similar decomposition may take place to a less marked degree with sulfite pulp. The resulting disintegrated cellulose gives an inferior paper due apparently to the breaking down of a large part of the wood structure by the bacterial action; while the presence of the objectionable decomposing organisms in the contaminated ground wood supplied to the beater results in further decomposition during the beating operation, unless this is prevented. It can be prevented by adding chlorine to the beater charge at the beginning of the beating operation. In some cases, however, the'ground wood pulp can be treated to sterilize it before it is added to the beater; or even before or during the time it is placed in storage, so as to prevent objectionable decomposition during storage, as well as during the subsequent beating operation. Such pulp can be sterilized as a part of its process for manufacture, or subsequent to manufacture, by subjecting it to the action of a limited amount of chlorine or chlorine water suflicient to bring about the sterilization without, however, having any obj ectionable'eflect upon the wood fibres.

' In general, however, the ground wood pulp or other contaminated raw material will be' mechanically reduced to a fibrous state at the beginning of the beating operation and treated with suitable amounts of'chlorine to destroy any existing bacterial growth and at the same time leave a residual chlorine content therein of around one-half part to one part per million of the Water present.

The effective sterilization of the stock at the beginning of the beating operation prevents pitch or beater-gumv formation durin the beating operation and prevents losso cellulose through decomposition thereby, thus giving an increased amount of stock for the paper making operation.

The subsequent steps of the paper making operation, .after the beating of the stock, will be. benefitted by the sterilization treatment. The half stock can be further refined inthe J ordans or other refining engines, then passed ning of the beating operation, with the leavythrough the usual screen and diluted to proper consistency for forming the paper'- web therefrom. If the diluting water, as well as the stock before dilution, 'is' sterilized with chlorine, thediluted stock going to the paper machine will be a sterilized stock fr e from pitch and slime contamination. Such a stock will be free flowing and has many advantages as compared with a slime-containing and pitch-containing stock. The paper produced will be free from wastage or dark spots due to the presence of pitch. It will also be free from the presence of pitch-forming organisms which might cause deterioration of cellulose in the paper. The white water produced from such an operation will also be sterile and can be returned for diluting the stock in further operations, or returned to the heaters for use in forming. additional stocks, thus obtaining the advantages of a closed system in which a considerable part of the raw water supply is replaced by white water, thus cutting down the amount of raw water requiring sterilization and the amount of raw water required.

The improved process of the present invention can advantageously be. combined with a coagulation treatment of the half stock before the making of papertherefrom, as set forth in the joint application of James H. MacMahon and myself, Serial No. 242,159

which has become Patent No. 1,733,070, dated Oct. 22, 1929. It can also be advantageously combined with the subsequent coagulation of the white water for the recovery of coagulable materials therefrom, as set' forth in the joint application of James H. MacMahon and myself, Serial No. 242.283, which has become Patent No.'1 737, 330, dated Nov. 26, 1929.

The present invention, however, is of broader application and can be employed without such subsequent coagulation treatment.

The-present invention presentsmany advantages. It eliminates the loss and decomposition due to bacterial action during the beating operation, and eliminates the forma tion of: pitch therein}, It gives a sterilized stock for use in the subsequent paper making operation. It enables both pitch formation and slime formation to be prevented. It gives a longer life for the felts of the paper mill and also a longer life for the wires of the paper machine. Less time is lost for shutdown and cleaning. An increased yield of paper of high grade is produced, without losses due to bacterial decomposition and mixing the sterilized-pulp with water and pitch formation, and the paper moreover, s ibjecting the mixture to a beating operamay be of a sterilized character which is not tlon, either ,without or w1th the p'esence of subject to further decomposition after its other fibres, and subse uently m ng paper production. I from the resulting stoc J I claim 2-- 9. The improvement. in the operation of 1. The improvement in the operation of p per mills which comprisessubjecting the A paper mills, which comprises adding chlorine stock in the heater to treatment with chlorine to the stock in the beater near the beginning adapted to destroy micro-organisms therein 10 of the beating operation to sterilize th stock, lch wo d attack e organ c tter of the subjecting the resulting stock to a beating opt nd t r after preventlng contamlnaeration and subsequently forming paper tion of the stock with such orgamsms during thereform. subsequent operations.

2. The improvement in .the operation of I11 testlmony whereof I afiix y slgnamle- 15 paper mills, which comprises treating the DONALD PATTILLO. E

' stock in the beater near the beginning of the beating operation with chlorine suflicient to leave in the water of the treated stock a residual chlorine content of around onezhalf part to one part per million, subjecting such 5 stock to a beating operation and forming paper subsequently therefrom. 3. The improvement in the operation of paper mills, which comprises subjecting a 5 stock containing ground wood pulp to treat- 9 ment with chlorine near the beginning of the beating operation to effect sterilization of the same, subjecting the sterilized stock to a beating operation, and subsequently form- 3o ing paper therefrom. v 4. The improvement in the operation of paper mills, which comprises subjecting ground wood pulp in admixture with water to a preliminary beating operation and treat- 85 ing the same with chlorine sufiicient to steri- 1 lize the stock, subsequently admixing the treated ground woodstock with 'other fibres and subjecting the mixture to a beating operation', and subsequently forming' paper 49 fromfthe composite stock.

i 5. .The improvement in the treatment of ground wood pulp which comprises subjecting it in admixture with water to the action of chlorine sufficient to sterilize the mixture and leave in the water a residual chlorine 1 content of about one-half part to one part" per million. K

6. The improvement -in the treatment of ground wood pulp, which comprisessubjectc ing the same in admixture with water to the 1 action of chlorine suflicient to sterilize the stock-without any objectionable action upon the fibres.

7. The improvement in the treatment of 535 ground wood pulp, which comprises subject- I 11 ing the same during its process of manufac- 'ture to the action of chlorine suificient to sterilize-the same without any objectionable actron upon the ground wood fibres, andsub- .sequentlyfstoring the resulting sterilized I i 8 ..The improvement in the production of paper from ground wood pulp, which comprlses sub ecting the pulp to treatment with V chlorine to sterilize the same, subsequently -1