US1873924A

US1873924A - Paper pulp bleaching process

Info

Publication number: US1873924A
Application number: US323575A
Authority: US
Inventors: Hirschkind Wilhelm
Original assignee: Great Western Electro Chemical Co
Current assignee: Great Western Electro Chemical Co; GREAT WESTERN ELECTRO-CHEMICAL Co
Priority date: 1928-12-03
Filing date: 1928-12-03
Publication date: 1932-08-23
Anticipated expiration: 1949-08-23

Description

Patented Aug. 23, 1932 UNITED srarss PATEINTQQOFFICFE WILHELM msonxmn. or ANTiOGH, cann'onum, Assmn'on 'rounnarwns'rnnn ELECTED-CHEMICAL G0,, on sen nnanorsco onmronmafa' oonronarrou or CALIFORNIA No Drawing.

This invention relates to the bleaching of wood pulp, either ground wood or mechanical pulp, or chemical wood pulp as derived from the soda, sulphate or sulphite'processes and the object of the process is to lighten thecolor of such pulps while preserving the strength and paper yield to the maximum. The purpose of my process is not to produce highly bleached or white pulp but rather to cause a lightening of the original dark color.

For instance, ground wood pulp can not be converted into a white pulp because all of the lignin and incrusting matters are still presant, and which preclude the use of oxidizing agents as for instance chlorine so necessary for producing white pulp. The dark color of such pulp can be lightened somewhat by treatment with reducing agents, and some of these have been so used for some time.

It is also common knowledge that sulphur dioxide gas or bisulphite liquor will brighten 'or lighten dark pulps to some extent. The action however is slow and the quantity or sulphite necessary to use is considerable.

I have discovered that the compound, sodium hydrosulphite f the chemical composition NmS O, has a lightening action on the colorof wood pulp infinitely greater and far more rapid than sulphur dioxide or bisul- 'phit-es. I found that sodium hydrosulphite when added to very darkly colored mechanical Wood pulp in a quantity of one quarter of one per cent by weight and thoroughly mixed therewith in the presence of water, produced a lightening of the color far beyond any 'efiect obtainable with the bisulphites, and

that the whole process was completed in very before going to the paper-machlnes.

Ground wood which has been in storage 40 for some time gradually darkens and profew minutes.

duces a paper, after treatment in the ordinary way, which is considerably oil color, whereas a hydrosulphite added to the pulp in quantities of as little as one quarter of one per cent of the weight of the dry ground wood pulp will bring back the color of. fresh ground wood, and a very small additional quantity will lighten the color beyond the original color. I

Kraft pulp as produced by the sulphate rarnnrunr BLEAGHRQ'G rnoonss 1 5 Application filed December 3, 192a. -Se'rla1 No. 323,575.

bleached sulphite" solved in water and run as an aqueous soluprocess is naturally very dark'in color and. can be considerably improved by the use of one to two per cent of a hydrosulphite.

Even, the color of-sulphite pulp can be considerably lightened and improved by small quantities of a; hydrosulphitc, without. of course reaching the color of the so called pulp produced with hyp0chlorites.-:

I have already mentionedthe rapidity of the action of the hydrosulphite in treatment of paper pulp and it is quite remarkable that this action is hardly infiuencedby-fltemperature ranges between 50 F. and 120 F. so that at the rather low temperatures of approximately 50? F. the effect isjust the same. 7 Sodium hydrosulphite has beenmentioned above because it is theycheapest and best known representative of ,these compounds. But other hydrosuiphites, such as vpotassium or ammonium hydrosulphite, calcium, or. those of the alkaline earth group have been used by me withsatisfactory results, and zinc. hydrosulphite (2116 0;) which is -particularly easy to manufacture has also been found suitable for this purpose.

A further advantage of the use of a hydro-l sulphite for the bleachingof paper pulp .is

the ease of its application. It can be dis- 80 tion into a mixergorbeater-whcre the pulp is being mixed or it can be added as a solid direct to the wet pulpfl'and thoroughly incorporated therewith. 'Since the reaction is completed within very few minutes it is only necessary to add the hydrosulphite to the beater or mixer in which the pulp is agitated As an example of its application to news print paper 2,300 pounds, of ground wood pulp were mixed with 400 pounds of sulphite pulp to a stock density of approximately five per cent. Five and three-quarters pounds of anhydrous sodium hydrosulphite were added to this mixture. Ten minutes later the necessary sizing and bluing ingredients were added to 'thejbatch and the material was run directly on the paper ma chine. 7

News print paper resulting from a mixture A aspen Re ssue of about 83% ground wood to about 17% bleached sulphite pulp may be closely approximated in grade by using unbleached sulphite pulp with the ground wood if a small quantity of a hydrosulphite is incorporated in the proportions indicated. ,The

advantages are in substituting the cheaper unbleached sulphite pulp for the bleached pulp ordinarily required.

Since various quantities of the chemical from .25 to 10% of the weight of the pulp produce corresponding degrees of action on the color of the pulp and the amount to be used will be governed entirely by the effects desired, I do not confine myself to any particular quantity or percentage of cal to the pulp treated.

I claim: 7

l. The process of lightening the color of mechanical wood pulp which comprises agitating the same substantially at room temperature for about ten minutes with an aqueous solution of a hydrosulphiteas substantially the only active agent therein and in amount ranging from 25% to 10% of the weight of the pulp without subsequent washing. i

2.-Tl1e process of li htening thecolor of mechanical wood pulp which comprises agitating the same substantially at room temperature for about ten minutes-with an aqueous solution of sodium hydrosulphite substantially as the onlyactiveagent therein and in amount ranging from 25% to 10% of the weight of the pulp Without subsequent washing.

3. The process of making paper from mechanical :wood pulpywhich comprises agitating the pulp at substantially room temperature for a short time with an aqueous solution of a hydrosul hite as substantially the only active'bleachmg agent therein and in amount ranging from 25% to 10% of the weight of the pulp, and without subsequent washing converting the pulp into paper before reversion of color can take place in the pulp. V

' WILHELMLIHRSGHKIND.

the chemi;