Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS1951017 A
Publication typeGrant
Publication dateMar 13, 1934
Filing dateJul 20, 1933
Priority dateJul 20, 1933
Publication numberUS 1951017 A, US 1951017A, US-A-1951017, US1951017 A, US1951017A
InventorsRaymond S Hatch
Original AssigneeWeyerhaeuser Timber Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method of treating chemical pulf
US 1951017 A
Abstract  available in
Images(1)
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

March 13, 1934.

R. s. HATCH 1,951,017

METHOD OF TREATING CHEMICAL PULP Filed July 20, 1933 VENTOR' ATTORN EYS Patented Mar. 13, 1934 UNITED STATES PATENT OFFICE METHOD OF TREATING CHEMICAL PULP Application July 20, 1933, Serial No. 681,251

9 Claims.

This invention relates to the preparation of chemical paper pulp and particularly to an improved method of treating pulp to facilitate bleaching thereof and a product of enhanced whiteness and better physical properties.

Chemical paper pulp is produced by cooking Wood chips in various chemical solutions. The present invention can be applied to pulps produced by any of the well known processes. It is particularly applicable to pulps produced from coniferous woods, but it may be utilized in treating pulp from any source.

The fibres or cells which make up the original wood structure may be divided roughly'into two classes, longitudinal fibres and medullary ray fibres. The longitudinal fibres are those which are arranged substantially parallel to the vertical axis of the tree and which make up the main cellulosic component of the wood. The medullary ray fibres are short fibres which in the original wood are substantially perpendicular to the axis of the tree. They serve as binders for the longitudinal fibres and .as conductors of sap from the inner bark to the longitudinal fibres.

When the wood substance is resolved by chemical agents, the bulk of the non-cellulosic wood substance, generally referred to as lignin is dissolved out and the remaining chemical wood pulp is made up of a more or less pure fibre mixture consisting of longitudinal fibres and medullary ray fibres. The proportion of these two constituents is roughly 90-92% by weight of longitudinal or long fibres, and 840% by weight of medullary ray fibres. the longitudinal fibres vary in length, depending upon the wood species, from about 2.8 millimeters to about 4.5 millimeters. The medullary ray fibres are readily distinguishable because they are much shorter than the longitudinal fibres, being about 1/25 to 1/30 of the length thereof, and having about the diameter of the longitudinal fibres. v

The medullary ray fibres are much morere-r sistant to the action of the cooking liquor than,

are the longitudinal fibres. It is much more difficult to remove the non-cellulosic material from the medullary ray fibres. Whether thisis due to the manner in which the lignin or non-cellulosic constituents are combined withthe Il'lfid', ullary ray fibre substance is not known. I have discovered, howeven-that after cooking the med- "ullary ray fibres contain a larger proportion of non-cellulosic constituentsand particularly coloring elements than the longitudinal fibres. In

In coniferous woods,-

order to bleach the medullary ray fibres it is necessary to subject them to a much more dras tic bleaching treatment than is required to whiten the longitudinal fibres. If, therefore, the pulp is bleached to a suitable whiteness, the lonat; gitudinal fibres are considerably weakened and the physical properties of the pulp are deterio-= rated.

It is the object of the present invention to provide a method of treating chemical paper as pulp so as to facilitate the bleaching operation and to produce a brighter pulp having improved physical properties.

Another object of the invention is to provide a method of removing the medullary ray fibres from the longitudinal fibres before the pulp is bleached, whereby coloring elements are separated from the pulp and bleaching is accomplished'more readily and with a lower consumption of bleaching agents.

Other objects and advantages of the invention will be apparent as it is better understood by reference to the following specification and accompanying drawing, in which the figure represents diagrammatically an apparatus adapted for 30 use in separating the medullary ray fibres from the unbleached chemical paper pulp.

In carrying out the invention, pulp may be produced by any of the well known chemical processes. After the completion of the cooking, the pulp is washed to removethe chemical cooking agent and is screened to remove knots and shieves or unresolved wood particles in the usual manner. The pulp as thus prepared consists of longitudinal fibres and the short medullary ray fibres, and is then subjected to the procedure hereinafter described to separate the medullary ray fibres from the longitudinal fibres.

In carrying out the invention, the pulp is first diluted to a consistency of approximately .2% to 3% by weight with water, and it is then caused toflow over a suitable separating medium, for example, a screen of wire cloth having about 25 meshes to an inch. In thus flowing over the screen, the large excess of ater carries the short 10o medullary ray fibres thrcugh'the screen and effectively separates them. From 90 to 95% of the short medullary ray fibres may be removed thus from the pulp, leaving the longitudinal fibres which may be delivered to, a suitable conveyor the short medullary ray fibres from the pulp.

Water may be sprayed uponthe pulp as it passes over the separating screen, although dilution of the pulp as indicated is usually sufiicient to ac- 5 complish the desired purpose.

The separation of the medullary ray fibres from the pulp removes a considerable proportion of coloring elements from the original pulp. This is shown readily by the improved whiteness of the pulp from which the medullary ray fibres have been removed, and also by the color of the medullary ray fibres which have been separated. The medullary ray fibres may be collected from the water in which they are suspended and formed into sheets. Such sheets show a distinctly darker tone than the original pulp, whereas sheets formed from the longitudinal fibres display a distinctly lighter tone than the original pulp.

The improvement can be demonstrated, moreover, by definite tests indicating bleachability and lignin content. As an example, a pulp subjected to the test for bleachability with chlorine gave the following results: 26 Per cent (0) Original pulp -1 5.54 (b) Longitudinal fibres 5.12 (c) Medullary ray fibres 7.8

o This pulp, when tested for lignin content, gave the following results:

' Per cent (41) Original pulp 2.54 (b) Medullary ray fibres 5.10

Uniractlonated Fractionated 0 Mullen. 108 113 Teen-.. 2. 2. Fold 1 72 Alpha per cent 88. 36 89. 41 Copper No 2. 20 2. 08 0 It will be observed that in the fractionated pulp every characteristic of the product has been improved as the result of,the separation of the short medullary ray fibres.

The fractionated pulp may be subjected to any .of the .usual bleaching operations. The details of such operations are well known and form no part of the present invention. The bleached pulp .can. be brought to a high degree of "whiteness closely approximating a complete absence of color, without reducing the strength and other desirable qualities of the product.

It is evident from the foregoing tests that the longitudinal fibres from.',which the medullary ray .5 fibres have been separated may be bleached with a smaller proportion of bleaching agent, and particularly need not be subjected to'the more drastic treatment necessary to removecoloring elements from the medullary ray fibres. The deterioration of the longitudinal fibres through excessive bleaching necessary to secure'a white product is thus avoided by the expedient of removing medullary ray fibres before the bleaching operation. The reduced 'cost of bleaching and I6 the resulting improvement in the product compensate for a loss of upward to 10% of the original pulp, even where the short medullary ray fibres are discarded.

The short medullary ray fibres may be bleached after separation by any of the well known bleaching processes. It is possible to utilize the short medullary ray fibres after separation for the production of paper stock, or for mixing with various pulps to secure the desired results, such as a quick-beating pulp, since the fine material hydrates much more readily than the longer fibres. The short medullary ray fibres may be used also as a raw material for"the preparation of alpha cellulose and in the viscose and cellophane industries.

As anexample of a suitable apparatus for the practice of the invention, 5 indicates a trough from which the pulp, previously diluted to approximately .2% to .3%, is permitted to overflow onto. screens 6 which are disposed at a suitable angle, for example about 45. The angle of inclination'is not important except that it must be sufiicient to permit the pulpto fiow freely but not too rapidly. The screens may consist of wire mesh cloth having about 25 meshes per inch. In the practical apparatus, the screens may be about 8 feet from the trough 5 to trough 7 in which the pulp is collected and from which it may be withdrawn by screw conveyors 8. Pipes 9 may be provided to spray water onto the screens 6, particularly near the lower ends thereof; The water which dilutes the pulp and any additional spray water passes through the screens 6 carrying with it the short medullary ray fibres, so that the pulp which accumulates in the trough '7 consists substantially of longitudinal fibres only. The water with the short medullary ray fibres is collected in a receptacle 10 beneath the screens and may be withdrawn through a pipe 11 and delivered to suitable settling or separating tanks 12. If desired, pipes 13 may be provided to spray water 1 into the trough 7 which may be perforated to Iii) permit the escape of the water with any residual pass therethrough, while the longer longitudinal fibers pass thereover.

2. The method of treating cellulosic pulp to separate the medullary ray or other fibers of similar length, from the longer longitudinal fibers, which" consistinfiowing the pulp, having a consistency of approximately 0.2 to 0.3 percent, downwardly over an inclined screen, the inclination of the screen and the mesh thereof being so correlated that the medullary ray, and other short fibers, will pass therethrough, whilethe longer longitudinal fibers will pass thereover..

3. The method of treating unbleached cellulosic pulp, which comprises separating the medullary ray, or other fibres of similar length from the longer longitudinal fibres of the pulp by the method which consists in flowing the pulp downwardly-over an inclined screen, the inclination of the screen and the mesh thereof being so correlated that the medullary ray, and other fibers of similar length, will pass therethrough, while the longer longitudinal fibers will pass 15c thereover, and thereafter bleaching the pulp consisting of substantially only the longer longitudinal fibers.

4. The method of treating unbleached cellulosic pulp, to separate the medullary ray, or other fibers of similar length, from the longer longitudinal fibers of the unbleached pulp, which consists in flowing the pulp downwardly over an inclined screen, the inclination of the screen and the mesh thereof being so correlated that the medullary ray, and other short fibers, will pass therethrough, while the longer longitudinal fibers will pass thereover.

5. The method of treating unbleached cellulosic pulp to separate the medullary ray, or other fibers of similar length, from the longer longitudinal fibers of the unbleached pulp, which consists in flowing the pulp, having ,a consistency of approximately 0.2 to 0.3 percent, downwardly over an inclined screen, the inclination of the screen and the mesh thereof being so correlated that the medullary ray, and other short fibers, will pass therethrough, while the longer longitudinal fibers will pass thereover.

6. The method of improving cellulosic pulp for bleaching, which comprises removing the medullary ray, or other fibers of similar length, and colloidal matter from the longer longitudinal fibers by the method which consists in flowing pulp downwardly over an inclined screen, the inclination of the-screen and the mesh thereof being so correlated that the medullary ray, and other short fibers, and the colloidal matter will pass therethrough, while the longer longitudinal fibers will pass thereover.

7. The method of improving cellulosic pulp for bleaching, which comprises removing the medullary ray, or other fibers of similar length, and

the mesh thereof being so correlated that the medullary ray, and other short fibers, and the colloidal matter will pass therethrough, while the longer longitudinal fibers will pass thereover.

8. The method of treating cellulosic pulp, which comprises separating the medullary ray, or other fibres of similar length from the longer longitudinal fibres of the pulp by the method which consists in flowing unbleached pulp downwardly over an inclined screen, the inclination of the screen and the mesh thereof being so correlated that the medullary ray, and other fibers of similar length, and colloidal matter will pass therethrough, while the longer longitudinal fibers will pass thereover, and thereafter bleaching the pulp consisting of substantially only the longer longitudinal fibers.

9. The method of treating cellulosic pulp, which comprises separating the medullary ray, or other fibres of similar length from the longer longitudinal fibres of the ..pulp by the method which consists in flowing unbleached pulp, having a consistency of approximately 0.2 to 0.3 percent, downwardly over an inclined screen, the inclination of the screen and the mesh thereof being so correlated that the medullary ray, and other fibers of similar length, and colloidal matter will pass therethrough, while the longer 1ongitudinal fibers will pass thereover, and thereafter bleaching the pulp consisting of substantially only the longer longitudinal fibers.

RAYMOND S. HATCH.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2730932 *Oct 4, 1954Jan 17, 1956Sandy Hill Iron & Brass WorksApparatus for interval feed and jet screening of stock
US2924548 *Jul 16, 1956Feb 9, 1960Masonite CorpProcess for making laminated hardboard product
US3085927 *Nov 16, 1960Apr 16, 1963Int Paper CoProcess for preparation of fibers having differing characteristics
US3441130 *Nov 30, 1967Apr 29, 1969Procter & GambleProcess for the removal of fines from wood pulp fibers
US3477571 *Nov 14, 1966Nov 11, 1969Procter & GambleApparatus and method for screening fibrous slurries
US5228954 *May 28, 1991Jul 20, 1993The Procter & Gamble Cellulose CompanyCellulose pulps of selected morphology for improved paper strength potential
US5405499 *Jun 24, 1993Apr 11, 1995The Procter & Gamble CompanyCellulose pulps having improved softness potential
US5582685 *Aug 9, 1994Dec 10, 1996The Procter & Gamble CompanyMethod for producing a cellulose pulp of selected fiber length and coarseness by a two-stage fractionation
US5679218 *Mar 13, 1996Oct 21, 1997The Procter & Gamble CompanyTissue paper containing chemically softened coarse cellulose fibers
DE969601C *Nov 18, 1942Jun 19, 1958Phrix Werke AgVerfahren zur Herstellung eines aschearmen, fuer die chemische Weiterverarbeitung geeigneten Zellstoffes aus Einjahrespflanzen
DE1119106B *Mar 25, 1959Dec 7, 1961Phrix Werke AgVerfahren zum Herstellen eines Kunstfaserzellstoffes aus Holz u. dgl.
EP0500109A1 *Feb 20, 1992Aug 26, 1992BHS-Bayerische Berg-, Hütten- und Salzwerke AktiengesellschaftProcess for operating a filtration plant and filtration plant for carrying out this process
Classifications
U.S. Classification162/55, 209/17, 162/87
International ClassificationB01D29/01, D21D5/04
Cooperative ClassificationD21D5/04, B01D29/01
European ClassificationD21D5/04, B01D29/01