US3377235A

US3377235A - Process for bleaching multi-colored broke with hypochlorites

Info

Publication number: US3377235A
Authority: US
Inventors: George R Webster; Norman S Lea; Edmund S Oshetsky
Original assignee: Scott Paper Co
Current assignee: Kimberly Clark Tissue Co
Priority date: 1964-12-03
Filing date: 1964-12-03
Publication date: 1968-04-09
Anticipated expiration: 1985-04-09

Description

United States Patent 3,377,235 PROCESS FDR BLEACHING MULTI-COLORED BROKE WITH HYPOCHLQRITES George R. Webster, Snohomish, and Norman S. Lea,

Everett, Wash, and Edmund S. 'Oshetsky, Wallingford, Pa., assignors to Scott Paper Company, Phiiadelphia, Fa, a corporation of Pennsylvania No Drawing. Filed Dec. 3, 1964, Ser. No. 415,803 6 Claims. (Cl. 162-6) This invention pertains to a new and useful process for the bleaching of colored broke. More particularly, the process of this invention involves a combination of bleaching steps utilizing a hypochlorite bleach liquor or powder.

The expression colored broke as used herein and in the claims is a well-known term to those skilled in the paper industry. It includes all types of broke, trim and other scrap found in all present-day paper mills. It includes whole roll broke and log broke. It further includes broke, trim, slabs and other scrap of any color and mixture of colors. The term colored broke includes broke, trim and other scrap which contains unbleached or partially bleached kraft cores, groundwood and pulp.

In all paper mills a certain amount of the product is lost as broke, trim or other scrap and every effort has been made to reconstitute this paper and thereby eliminate Waste. The products of todays paper mills are made in just about every imaginable color and hence a highly elfective bleaching process for the broke, trim and other scrap is necessitated for removing the colors (dyes, pigments, groundwood, kraft, etc.) if the material is to be returned to the normal paper-making channels. Production rates of colored papers have increased significantly over recent years and the trend is continuing, both in total tonnage of paper produced and in varieties and number of color combinations produced. Thus, a bleaching process which is highly effective on all paper mill colors and mixtures thereof and yet is economical has great importance.

Heretofore, utilization of colored broke in the papermaking systems required in most all instances removal of cores and often the baling of separate broke colors to permit reuse at the time the paper machines are operating on a specific color. This involves, obviously, high handling costs, and in some cases fluctuations in the percent of broke in the furnish when the mill attempts to minimize handling costs by increasing or decreasing broke utilization to cope with variations in availability of the supply of a particular color.

By means of the process of this invention it is possible to eliminate high handling costs since it is not necessary to decore or separate the broke into specific colors. Further, quality fluctuations resulting from variations in the percent of broke in furnish is avoided by reason of the effective bleaching attained by the process of this invention on all colored broke.

A principal object, therefore, of this invention is to provide a highly effective and economical bleaching process for colored broke thereby eliminating waste.

Another object of this invention is to provide a bleaching process having the ability to decolorize all paper mill colors and mixed-colored broke.

Another object of this invention is to provide a bleaching process having the ability to bleach whole-roll broke or unbleached kraft contained in cores.

Another object of this invention is to provide a process having the ability to bleach unbleached or partially bleached groundwood and pulp contained in the broke.

Still another object of the invention is to provide a process for the bleaching of colored broke which does not require the removal of cores nor that the broke be 3,377,235 Patented Apr. 9, 1968 separated into specific colors and thereby significantly reduce handling costs.

Still another object of the invention is to accomplish the foregoing objects in a single two-step bleaching process in a short period of time.

Additional objects and advantages will be apparent as the invention is hereinafter described in detail.

In acordance with the invention, hypochlorite bleachant is mixed with aqueous suspensions of colored broke in a multi-stage process under specified conditions of pH. Adva-ntageously, the bleaching may be completed in only two steps, and the resultant bleached material has a superior whiteness and is free of hues and unbleached kraft fibers.

Calcium hypochlorite is the preferred bleaching agent for practicing the invention. However, any alkali or alkaline earth metal hypochlorite may be used.

The amount of bleaching agent necessary will vary to some degree according to the color and type of broke being bleached. However, it has been found that a range of about 15 to about 30 pounds of available chlorine per ton of broke on a dry-weight basis is suitable for the first bleaching step and about 10 to about 20 pounds in the second bleaching step.

The consistency of the broke suspension may be varied widely. Most hypochlorite bleaching processes are carried out at consistencies in the range of about 1 to 20% and the use of the process of the invention at any consistency within known ranges is contemplated. However, a consistency of about 5 to 6% is preferred.

The temperature of the broke suspension is also susceptible to wide variation. The temperature used will depend upon in large part the equipment available in a given mill. The process can be operated at relatively low or high temperatures with suitable compensations in time, the process taking ashorter time at high temperatures and an extended time at low temperatures. The range of temperature can be about to about 195 F. depending on mill equipment. A range of about F. to about F. has been found satisfactory. The heating of the broke suspension may take place during or after its preparation, as by sparging in live steam; or, hot water can be used in forming the suspension.

The first bleaching step is conducted at a pH of about 5.0 to about 6.8 and the second bleaching step is conducted at a pH of about 8.0 to about 11.0. Most advantageously, the first bleaching step is conducted at a pH of about 6.0 to 6.5 and the second bleaching step at a pH of about 9.0 to 9.5. While the pH of the aqueous broke suspension should be maintained close to the stated ranges throughout the bleaching steps, adjustment thereof for each step may be accomplished before, after, or concurrently with the addition of the hypochlorite bleaching agent. Adjustment of the pH may be accomplished by the addition of mineral acid(s), such as sulfuric acid, or by addition of alkali, such as caustic soda, as appropriate.

Despite the above-described degree of freedom in the matters of the timing and manner of adjustment of the pH, it has nevertheless been found somewhat advantageous to preliminarily adjust the pH of the suspension to certain specified values prior to addition of the bleaching agent in either step or both. The purpose of such preliminary adjustment of the pH is to insure that as much as possible of the bleaching agent is consumed within the above-mentioned ranges and, conversely, to insure that as little as possible of the bleaching agent is flashed off and wasted, e.g. as during the passage of the pH value from the lower pH of the first bleaching step to the higher pH of the second bleaching step. Thus, the pH is preferably adjusted to about 4 prior to the addition of the first step bleaching agent to the broke suspension. Similarly, the pH of the suspension is adjusted to at least about 8 prior to addition of the second step bleaching agent. Subsequent to the preliminary pH adjustment and following the addition of the bleaching agent for either bleaching step, some further adjustment may be required to bring the suspension pH within the specified range for the particular step. The preliminary adjustment of the suspension pH to at least about 4 prior to adding the first step bleaching agent is especially advantageous when operating upon a suspension containing a substantial proportion of wet-strength colored broke.

In the case of a mixed-colored broke, it has been found to be advantageous to allow the first bleaching step to proceed until all color is removed since some dyes will not be decolorized by the second bleaching step, which is conducted at a higher pH. The first bleaching step is usually complete after about 15 minutes or when visual inspection indicates that all or substantially all color has been removed. After the first bleaching step is completed, there may or may not be excess chlorine: left.

Despite the fact that at the end of the first bleaching step the suspension contains large amounts of color bodies, and the adoption of such a course of action might therefore appear inadvisable, it has been found that the pulp need not be drained and washed prior to the second bleaching step, This makes it possible to conduct the second bleaching step in the presence of the first step bleaching liquor, so that any excess chlorine remaining after completion of the first step may be taken advantage of in the second step. Of course, the pulp could be drained and washed between the bleaching steps, but a distinct advantage would thereby be lost.

In the second bleaching step, the bleaching is allowed to continue until all the chlorine is used up, which generally takes about ten minutes. At the end of the second step, a sample of stock is taken for visual examination to see that complete bleaching of kraft fibers and groundwood has taken place.

Upon completion of the bleaching process, the bleached broke, 'with or without any washing step, is fed into the papermill system with the normal furnish going to the paper machine. Due to the effectiveness of the bleaching process of this invention, the bleached broke can be utilized with all furnish of any color. Heretofore, it was necessary to be selective in the particular bleached broke that could be fed to furnish of a particular color. This, obviously, is of significant importance in regard to handling costs and quality control.

The following examples serve to illustrate the invention and should not be regarded as unduly limiting the invention. Unless otherwise indicated, all parts are expressed in parts by weight.

EXAMPLE 1 An aqueous suspension of about 5 percent consistency was prepared from a mixture of colored tissue broke (green, blue, pink, yellow, lilac and turquoise) plus tubeboard by beating in a large earthen crock, The suspension was then heated to about 170 F. 'with live steam. Sufficient sulfuric acid was then added to lower the pH of the suspension to about 4. After this pH adjustment, calcium hypochlorite bleach liquor in an amount of about 25 pounds chlorine per ton of colored broke on a dry-weight basis was added to the suspension and the suspension adjusted to a pH of about 6.5 by the addition of sulfuric acid. The bleaching action of this step was allowed to continue for approximately 15 minutes. A slight brownish tinge remained from the groundwood and kraft fiber. The pH of the suspension was then adjusted to about 8 by the addition of caustic soda. Then, calcium hypochlorite liquor in an amount of about 10 pounds available chlorine per ton of broke on a dry basis was added. The pH of the suspension was adjusted to about 9.0. The bleaching action of this step was allowed to continue about 10 minutes. All the chlorine was used up. Visual examination showed that the colorremoval had been good and that the groundwood and kraft fiber had bleached well.

4 EXAMPLE 2 In this example, the same materials, quantities, procedure and conditions were employed as set forth in Example 1 with the exception that the hypochlorite bleacl1 ing steps were reversed. In other Words, the first bleaching step was made at a pH of about 9.0 and the second bleaching step was made at a pH of about 6.5. Inspection showed this method to be greatly inferior to that of Example 1 in that a yellow tinge remained and unbleached kraft fibers were apparent in the bleached product.

EXAMPLE 3 This example was the same as Example 1 with the following exceptions: (a) the first bleaching step was made at a pH of about 6.0 and the amount of calcium hypo chlorite liquor added was about 15 pounds available chlorine per ton of broke on a dry-weight basis; (b) the second bleaching step was made at a pH of about 9.0 and the amount of calcium hypochlorite liquor added was about 20 pounds available chlorine per ton of broke on a dry-weight basis; and (c) the colored broke used was a lilac whole-roll tissue broke. Excellent color removal and kraft fiber bleaching was obtained.

EXAMPLE 4 This example was the same as Example 3 except: (a) the first bleaching step was made at a pH of about 9.0 and the amount of calcium hypochlorite liquor added at this step was about 10 pounds available chlorine and (b) the second bleaching step was made at a pH of about 6.0 and the amount of calcium hypochlorite liquor added was about 15 pounds available chlorine. Poor kraft fiber bleaching and only fair color removal was obtained.

EXAMPLE 5 The process of Example 3 is repeated, using sodium hypochlorite. Similar results are obtained.

What is claimed is:

1. A process for bleaching multi-colored broke which comprises the steps of: bleaching an aqueous suspension of substantially unbleached multi-colored broke by a first hypochlorite bleach with a hypochlorite bleach liquor at a pH in the range between about 6.0 and 6.5, adjusting the first bleach step liquor to a pH in the range between about 9.0 and 9.5, retaining said liquor in combination with said pulp throughout the process so as not to substantially separate color bodies from said liquor, and effecting a second hypochlorite bleach of said broke at a pH in the latter range.

2. A process for bleaching multi-colored broke comprising the steps of:

(a) adding a bleaching agent selected from the group consisting of alkali metal and alkaline earth metal hypochlorites to an aqueous suspension of substantially unbleached multi-colored broke to provide a bleach liquor intimately contacting said broke;

(b) adjusting said suspension to a pH in the range between about 6.0 and 6.5;

(c) bleaching said broke to remove substantially all color therefrom;

(d) retaining said liquor in combination with said pulp throughout the process so as not to substantially separate color bodies "from said liquor;

(e) adding to said suspension a bleaching agent selected from the group consisting of alkali metal and alkaline earth metal hypochlorites;

(f) adjusting said suspension to a pH in the range of between about 9.0 and 9.5; and

(g) continuing bleaching until substantially all residual chlorine is depleted.

3. The process of claim 2 wherein the amount of bleaching agent added in step (a) is such as to provide a quantity of available chlorine in the range between about 15 and 30 pounds per ton of said broke on a dry-weight basis, and the amount of bleaching agent added in step (d) is such as to provide a quantity of available chlorine in the range between about and pounds per ton of broke on a dry-weight basis.

4. The process of claim 2, including the step of adjusting the broke suspension to a pH of about 4 prior to the introduction of a bleaching agent for the first bleaching step, and adjusting the pH of said suspension to about 8 immediately prior to the introduction of bleaching agent for said second bleaching step.

5. The process of claim 2, including the initial step of heating an aqueous suspension of the multi-colored broke to a temperature in the range between about F. and 195 F.

6. A process for bleaching multi-colored broke comprising the steps of:

(a) heating an aqueous suspension of substantially unbleached multi-colored broke to a temperature in the range between about F. and F.;

(b) adjusting the pH of said suspension to about 4;

(0) adding to said suspension a compound selected from the group consisting of calcium hypochlorite and sodium hypochlorite in an amount which will provide between about 15 and 30 pounds of available chlorine per ton of broke on a dry-weight basis to provide a bleach liquor intimately contacting said broke;

(d) adjusting said suspension to a tween about 6.0 and 6.5;

(e) bleaching said broke until substantially all color is removed therefrom;

pH in the range be- (f) retaining said liquor in combination with said pulp throughout the process so as not to substantially separate color bodies from said liquor;

(g) adjusting the pH of said suspension to about 8;

(h) adding to said suspension an additional amount of a compound selected from the group consisting of calcium hypochlorite and sodium hypochlorite in an amount which will provide between about 10 and 20 pounds of available chlorine per ton of broke on a dry-weight basis;

(i) adjusting said suspension to a pH in the range between about 9.0 and 9.5; and

(j) continuing bleaching until substantially all residual chlorine is depleted.

References Cited UNITED STATES PATENTS 1,768,823 7/1930 Bradley 162-88 X 1,883,193 10/1932 Wells 162-88 1,970,065 8/1934 Tomlinson 16288 1,992,977 4/1935 Wells 162-6 2,203,205 6/1940 Rawling 162-88 2,226,356 12/1940 McCarthy et al. 162-89 X FOREIGN PATENTS 601,643 5/1948 Great Britain.

S. LEON BASHORE, Primary Examiner.