US1599831A - Process of preparing paper half stock - Google Patents

Description

Patented Sept. 14, 1926.

UNITED STATES ALFRED MA KAY, or PHILADELPHIA, PENNSYLVANIA.

' PROCESS OF PREPARING PAPER HALF STOCK.

No Drawing.

Some of the objects of the present l11-' vention are to provide an improved process of making paper half stock; to provide a paper making process wherein a more uniform paper half stock is produced; to provide a paper making process wherein the final beating time is materially reduced while a better grade of paper stock is produced; to provide a process wherein predeter- .mined results can be accurately produced by controlling the treatment of the raw paper stock; to provide a process for treating paper stock whereby cotton linters, or any other long fibre stock tending to curl, will pass through the paper machine screens as readily as any other grade of stock; 'to provide an improved process of hydrating raw material for paper making; to provide a process for chemically hydrating cellulose fibre and mechanically subjecting it to a beating action during hydration; and to provide other improvements as will hereinafter appear.

In the manufacture of paper stock it is well known that any grade of fibre placed in a beater will be hydrated by the action of the'roll and bed plate, the degree of hydration being influenced by the grade of the fibre used, as well as by the length of time it is subjected to the beater. Such hydration, by the aid of mechanical means, has proven ununiform, uneconomical and inefficient, and has in consequence led to much study and experiment, particularly in the last year or two, to devise a process whereby hydration may be hastened, the

final beater time reduced, better control over the finished product obtained, and an improved paper produced. The result of such experiment has been to produce a process, including as a step the chemical hydration of the paper stock prior to final beating which gives a commercial product equal to'and generally better than that of the old process, but making the same in muchless time than heretofore. 'It has been found, however, in such chemical hydration, that certain long fibre stock having a tendency to curl, such as cotton linters, did not and could, not be made to pass through the ma chine screens unless there was -a longer period offinal beating than usual, or a quick beating which was found to so cut the fibre-as to weaken the sheet. V

Broadly rconsidered, the processof the present invention consists in the chemical Application filed January 10, 1922. Serial No. 528,293,

hydration of paper making stock while undergomg a preliminary mechanical beating,

the hydrating chemical, the stock, and the beating time being sci-proportioned as to produce a predetermined result with respect tothe grade and strength of paper.

This process insures the permanent straightening of long fibres, such as cotton linters, and enables them to pass readily through the screens after final heating, thereby eliminating the excessive loss of fibre due to rejection by the screens. 0

The chemical hydrating step consists in treating the paper making material, such as cotton or other cellulose fibre, with a relativelyweak solution of an acid or an acid salt, preferably a mineral acid, such as sulphuric acid, or a mineral salt acid. The perccntage of such acid or acid salt, and the temperature, may vary considerably accordingto requirements but preferably an acid strength of approximately from .05 per cent to 1 per cent at a temperature ranging from 20 (1. to not materially in excess of 100 C. has been found effective for the purpose of hydrolyzing the fibre and forming more or less cementing material at the same time.

A selected amount of the cellulose fibre to' be treated is placed in a beater with the predetermined percentage of hydrating chemical and subjected to a mechanical beating for a given time at the appropriate temperature. This mechanical beating during chemical hydrolyzation has been found to result in a more complete and uniform hydration of the stock than has heretofore been attained by prior or known process,

.and in addition results in the long fibres of the stock being drawn out and permanently straightened so that they pass freely through the screens in the subsequent treatment of the stock. Where chemical hydration has been attempted in accordance with the more recent advancement in the art, the

drate the stock as effectively as possible, to follow this by a washing step, and thento subject thewashed stock to the" usual digesting, bleaching and mechanical beating. It has, been found by such a method that, when the beating time is prolonged, almost as long as under mechanical hydrating methods, there is excessive cementing vmate; rial produced, a weak non-uniform'stoc-k formed, and a high p'ercen'tageof'los'sdue to chemical fibre destruction and fibres curl 100 only known way has been to chemically hybeating.

The process of the present invention in its broad generic sense is a paper stock treatment preliminary to paper making, though in its application it may form a portion of the general stock treatment for paper making, in that the stock, either before or after treatment by the present invention, is cooked or digested, washed, bleached, washed again, after which it goes to the ,machine beater as usual. It will therefore be understood that the steps of the present invention are not to be limited, when applied to the usual paper stock treatment, to any particular place in the preliminary stock treatment. The digesting step referred to in the foregoing is the usual one employed for removing lignon, gums, and other impurities, and consists in placing the material in a stationary or a rotary boiler where it is treated with a solution of calcium hydroxide, caustic soda, or other alkaline salts, and raising the temperature and pressure by the addition of steam. The digesting operation takes from four to eight hours and a pressure from forty to one hundred ponndsf Another form of the present invention consists in dividing a batch of cellulose fibre into a major portion an a minor portion, the former being then either feebly chemically hydrolyzed or not hydrolyzed at all, and the latter excessively chemically hydrolzed. The hydration of the cellulose fibre may take place by treating it as above described with a dilute acid, or an acid salt, or any other suitable acid for the purpose, at a'selected temperature in'accordance with the conditions. The two portions of the batch are then cooked and bleached sepa-. rately or together ready for the paper ma:

chine beater, the mixingproportions ofthe two portions being such as to produce the desired strength and grade of paper. This step insures the pulp having the proper amount of cementing material added to it to give strength without weakening the fibre, which occurs when an excessive hydration of the whole mass takes place.

The beating ste a) which the individual portions are sub ected before mixing and during chemical hydrations, takes place, according to the present invention, in a manner quite different from that heretofore employed in that the beater roll and bed plate are arranged (preferably by-lowering the roll) to draw out the fibre without excessive shortening of the stock. The effect produced is in the form of beating, and re sults in permanently straightening all long fibres, such as cotton linters, which then pass readily through the fine mesh of the screens after a reasonable time required in the machine beatereaccording to the grade of paper required. When sufiicient hydrolyzation has taken place, the hydrolyzing solution is drawn off and replaced by water to Wash the chemical agent free from the pulp. During this washing operation the relation of the beater roll and plate remains as before and functionsein the same manner as heretofore described to draw out the fibres of the stock lengthwise to leave them straight and free from curl.

Following the washing step the material is subjected to the usual cooking, bleaching and beating steps as desired, and givesa stock which readily passes the machine screens without loss of fibre after a reasonable time required in the machine beater according to the grade of paper required.

While in the foregoing form of the invention a batch of raw fibre is so treated, it will be understood that the process may be applied directly to amass of fibre after it comes from the digester following the removal of the lignon, gums, wax and other impurities.

In either form of the invention, the degree of hydrolyzation may be determined for example by obtaining a solution of cellulose and determining its viscosity, or by determining the degree of alkalinity produced by the property which pulp has of splitting a salt due to the presence of mucilage as a re sult of the hydrolyzation.

While but two forms of the present invention have been described, it is to be understood that the details of procedure, and proportions of ingredients, may be widely varied, and that known chemical equivalents may be employed in place of the materials mentioned without departing from the spirit of the invention or the scope of the appended claims.

Having thus described my invention, I claim: s

1. The process of preparing paper half stock which consists in separately chemically hydrating two batches of cellulose fibres one vof said batches being subjected to a stronger hydration, mixing parts of each hydrated batch in a predetermined proportion, and beating the mixed parts. i

3. The process of preparing paper half 5 stock which consists in chemically hydrating a batch of paper making material, simultaneously drawing out and straightening the fibres of said material, mixing the chemically hydrated material with another batch unhydrated in a predetermined proportion, and 1 subjecting the mixed batches to a mechanical beating.

Signed at Philadelphia, county of Philadelphia, and State of Pennsylvania, this6th day of January, 1922,

ALFRED MAoKAY.