US1828338A - Fiber bleaching - Google Patents

Description

' Patented Oct. 20, 1931 UNITED STA JOHN Known, or

GHICAGO, ILLINOIS FIBER BLEAGHING .No Drawing.

This invention relates to the bleaching of u paper and other fiber pulps, and among other ob ects aims to reduce the time and cost f bleaching and to minimize loss of fiber and fiber strength.

The invention may best be disclosed b reference to an illustrative method emb ying the invention and described in the following specification. The inventive method may ad- 10 vantageously be described as applled to the. bleaching of kraft or sulphate pulp, slnce it is considered particularly difiicult to bleach.

The kraft pulp is supplied in slush form of a consistency which-may advantageously be 5 about ten per cent. The process may be carried on inany appropriate apparatus provided with agitating means, means for heating the pulp both under and without pressure. It will be obvious, however, that the various steps of the process need not be carried out in a single piece of apparatus. While specially designed apparatus may be advantageous under certain conditions the process may be carried out in existing apparatus commonly employed in pulp treatment.

The unit proportions of treating substances used in the illustrative method will be based as is the usual practice, upon one ton of kraft pulp, air-dry weight. Into the apparatus above referred to isintroduced an oxidizing agent, in this instance bleaching powder, in the amount of from fifty to one hundred (50 to 100) pounds. This ingredient is advantageousl prepared in liquor form consisting of one 1) pound of bleaching powder per gallon of water. The quantity of bleaching powder used (between the limits above specified) depends upon the character of the water (whether it be hardor soft) and upon the character of the pulp, i. e. for example,

whether it is a hard cook or soft cook pulp-the less oxidizing agent being used when the fibers are well opened up. In the apparatus the bleaching liquor is furtherdiluted with a quantity of water which will bring the pulp, when added, to a consistency of from five tosix per cent. (5% to 6%) of pulp.

By adding the pulp to the bleaching liquor (instead of vice versa) the'burning of the Application filed March. 29,

1929. Serial No. 351,127.

pulp, in spots, by the liquor is avoided. If the apparatusadmits of it, the contents are agitated while the pulp is being added or w ile the bleaching liquor is added, if the sequence of the additions be reversed.

The pulp is then agitated for one hour at a temperature of from forty to eighty degrees Fahrenheit (40 to 80 F), depending on thecharacter of the pulp, the igher temperature stimulating action and being advantageous for pulp in which the fibers are not well opened up.

The strength of the bleachin liquor used in the foregoing treatment is re atively weak but it bleaches the pulp to a yellow color. Its 1 action is not apparently primarily a bleaching one. It seems to attack the coloring matter and the fiber encrusting substances (with the possible exception of ltch) and thus prepares the pulp for the e ective dissolving or removal by the next ensuing treatment, of those encrusting substances which have not already been eliminated.

In preparation for such treatment the bleaching liquor is withdrawn and the pulp 7 washed. It does no harm and possibly is advantageous to have a trace of the bleaching liquor remain in the pulp. This simplifies and shortens the washing of the pulp.

Into the same apparatus, assuming it to be adapted for cooking under a low steam pres sume (and from which the pulp may have been removed) an alkaline cookin liquor, in this instance comprising the fol owing ingredients, is added:

10 pounds caustic potash. 100 pounds soda ash.

5 pounds sodium perborate BO3-4 o i i Enough water is added to bring the consistency of the pulp, when added, to five or six per cent. (5% or 6%) of pulp. The above named, ingredients are preferably added in 'the order named, L e., with the perborate last.

The pulp is then added (again while the contents are agitated if that be possible) and the batch cooked andagitated for from thirty (30) minutes to one (1) hour (depending on the character of the pulp) at from two to five (2 to 5) pounds steam pressure.

This treatment apparently dissolves or removes the fiber encrusting substances with out causin substantial lossof fiber or fiber strength. to preserve the fiber strength, resulting in a qualit and character of fiber particularl suitab e for rayon and high grade alpha oe lulosep.

The liquor employed is then drained off and may be reclaimed and used again if restored to strength by addition of the chemicals exhausted. The pulp is then washed.

The ulp is now in condition where it will respond effectively to bleaching treatment.

I have found that satisfactory results may also be obtained if in the foregoing cooking treatment five (5) pounds of caustic potash and from forty to one hundred pounds of sodium silicate (depending, as before, on character of fiber) be used in place of the caustic potash, soda ash and perborate,other proportions and details of treatment remainin the same. Where appropriate, as with jack and southern pine and other highly resinous woods, such modified treatment commends itself because of the cheapness of the chemicals. If traces of silica remain in the pulp, the latter treatment would probably not be satisfactory if the pulp were to be used for rayon.

In the final bleaching treatment, a bleaching agent, in this case consisting of fifty pounds of bleaching powder in liquor form (a concentration of one (1) pound of bleaching powder to a gallon of water), is introduced into an agitating vessel and water added to bring the conslstency of the pulp, when added, to from five to six per cent. (5% to 6%). The washed pulp is then introduced and the contents agitated at a temperature of from forty to sixty degrees Fahrenheit (40 to F.) A solution containing a reducing bleaching agent, in this instance three (3) pounds of oxalic acid and one (1) pound of common salt (NaCl), is also added but such addition can advantageously be deferred until the ulp and chlorine liquor have been agitat a short while. The total agitation and treatment should consume one (1) hour.

The interaction between the three chemicals in this treatment is not definitely understood but the eifect of the treatment is to produce a deadwhite pulp. Treated with the chlorine liquor alone, the pulp, while bleached so that it can be termed bleached pulp and used commercially for many purposes as bleached pulp, is not dead white.

Apparently the oxalic acid acts only as a reducing or bleaching agent, but reacts with the chlorine (or perhaps there is a catalytic action) to stimulate the bleaching action and to carry it beyond the point which could be reached by successive treatments of the chlorine liquor and the oxalic acid and salt, of the strengths referred to. Apparently the he perborate seems to cooperate oxalic acid finally neutralizes the chlorine because the pulp requires little washing to bring 1t to a condition where there is no objectionable after effect, such as chlorine discoloratlon. The action of the salt is not fully understood,-apparently it reacts to temper the harsh characteristics of the oxalic acid, making it practically available in a bleaching I process of this character.

After treatment for one hour and subsequent washin the pulp is a dead white color and has su stantially' its original fiber strength. Although the entire process consumes a relatively short time bleaching has been accomplished without harsh treatment 'of the pulp and the loss of fiber and fiber strength has therefore been minimized.

Obviously the invention is not limited to the precise chemical agents and other details of the illustrative method. With pulps which respond more readily to removal of encrusting substances or to bleaching, the length of treatment or strength of chemicals ma be substantially varied or even some of the chemicals omitted,

or changed, depending upon the character and structure of the fiber, which characteristics are well known as regards -most fiber yielding materials.

. I claim:

1. The method of bleachin kraft pul to a dead white color which is c aracterize by cooking the pulp to free the fibers from the encrustin substances and then treating the pulp wit a bleaching agent containing oxalic acid and sodium chloride.

2. The method of bleaching kraft pulp which is characterized by treating the pulp to w free the fiber from encru-sting matter and then bleaching the pulp by treatment with chlorine liquor, oxalic acid, and sodium chloride.

3. The method of bleaching kraft pulp which is characterized by treating the pulp with chlorine liquor and then cooking it in an alkaline solution to remove the fiber encrusting substances, and then bleaching the pulp with chlorine liquor and oxalic acid in the presence of sodium chloride.

In testimony whereof, I have signed my name to this specification.

JOHN NEUMANN.

CERTIFICATE or connection Patent No. 1,828, 333.- Granted October 20, 1931, w

JOHN NEUMANN.

It is hereby certified thaterror appears m the printed specification of the above numbered patent requiring correction as follows; Page 2, line 58; after the vvord "acts" insert the word not; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of December, A. D. 1931.

. I M. J. Moore, (Seal) Acting Commissioner of Patents.