US1979864A - Art of paper and board manufacture - Google Patents

Description

Patented Nov. 6, 1934 I UNITED STATES PATENT OFFICE ART OF PAPER AND BOARD MANUFACTUBE No Drawing. Application January I, 1931, Serial No. 507,296

3 Claims. (CI. 92-39) v The present invention relates to improvements in the art of paper and board manufacture. The invention has particular reference to improve- 1 ments in the manipulation of the fibre stock 5 prior to or during the period of sheet or board formation.

It is well known to those skilled in the art that in manufacturing paper or board from vegetable fibres it is necessary to subject the fibres to certain preliminary treatments, such as boiling in water under pressure or hot digestion with sodium sulphite, also under pressure, in order that the fibres may be obtained in a condition such that they will not form "clots, balls or knots in the liquid in which they are conveyed from one operation to the next, as from the beater to the Jordan engine, and furthermore, that they will readily mat to form .a sheet when it is desired to do so. In any event, it is common practice to subject the fibre stock to some sort of prelim inary treatment, one of whose principal objects is in reality to obtain the fibres in a condition such that they will readily be suspendable in water or other conveying medium which is waterthin.

Fibre thus treated is usually in the form of a pulp, and it is then subjected to further treatment in mechanical beaters, Jordan machines or the like, the purpose being to obtain the fibres in the necessary state of refinement, shortness, separation and softness, so as to permit the free suspending of the same within the conveying liquids now commonly used;-

Fibre treated as above and suspended in a Water solution of approximately two hundred times the weight of the fibre conveyed, allows a proper freedom of fibre within the solution and the formation of a proper felt or mat, by the same, upon the filtering screen, for the formation of sheets or boards.

It is a common practice in the art at present to introduce sizing or other chemicals into the conveying solution in the beater engines for various purposes, thereby of course contaminating the conveying liquid with chemicals which prohibit the re-use of such solution.

The disposal of such solutions, as above described is one of the great ills of the art as now conducted.

One object of my invention is to prapare a conveying liquid of such character that it will hold the untreated or raw fibres or. fibrous material in suspension so as to permit of proper matting on the screen or filter plate. That is to say, I eliminate the necessity of the ordinary pressure digestion or cooking of the fibre stock mentioned in the preceding paragraphs.

Another object of my invention is to eliminate the necessity of subjecting the fibre stockto the usual operations carried out in the heater and Jordan engine and in fact, (mechanical) treatment of the fibres in any manner, except mechanical mixing of fibre stock and suspending medium, which requires a much shorter time than heretofore employed for accomplishing the same purpose.

Another object of my invention is to prepare media adapted to convey a mixture of raw vegetable fibre and processed pulp.

Another object of my invention is to prepare media for conveying reclaimed cellulose.

Another object of my invention is to prepare media for conveying untreated animal fibres or mineral fibres such as asbestos or mineral wool.

Another object of my invention is to provide a viscous solution which will greatly reduce the amount of water necessary in the process of manufacturing paper or board, whether made from the usual treated fibre or pulp or from raw untreated fibres or fibrous materials of vegetable, animal or mineral origin.

Finally, a very important object of my invention is to re-use the conveying medium after removal of the raw fibre from a given quantity, for conveying succeeding quantities of fibre.

With these and other objects in view, the following description of my novel process will be observed to involve the method of suspending raw fibre in a viscous conveying mediumcontaining starch or its equivalent.

To illustrate the above term "viscous medium, I may cite by way of example a starch solution containing from one-half of one per cent by weight to five percent by weight of vegetable starch. To prevent the formation of lumps in the preparation of this solution, oneskilled in the art will realize that it is first necessary to form a thick paste by adding cold water to the starch and mixing the same until a homogeneous mass is obtained which is free from lumps. This paste may then be diluted with additional water and this mixture boiled to give the starch solution. As equivalent of starch solution I may use a 40 .B. sodium silicate solution. Other equivalents would be the gels of glue, gelatine, pectin, gum mastic, gum tragacanth, gum arabic and molasses.

I have discovered that a viscous liquid medium having a selected or predetermined fluidity can be used as a vehicle for conveying. fibrous material onto a screen or into forms and molds and thus easily fabricate sheets of paper thinness, or blocks of any desired thickness, or forms of any desired shape.

I have discovered that mechanically produced raw vegetable fibre may be introduced into and conveyed by a viscous solution without the occurrence of lump formation, improper felting or uneven felting, so prevalent where the same fibre is introduced into a solution having the viscosity of tap water.

I have discovered that by the use of a viscous solution as a suspending or conveying medium for the various fibrous materials, I secure a stable suspension of the fibre stock in the liquid and a uniform felting at the proper subsequent stage.

I have also discovered that I need not confine myself to the aforementioned water solutions or suspensions, but that I can successfully use viscous solutions of the natural resins, the synthetic resins and residual resins of commerce when such resins, are dissolved in suitable solvents, such as gasoline, kerosene, heavy distillates, benzol and alcohol, and that I can successfully use solutions of nitrocellulose of viscosities such as are used for lacquers.

I have discovered that I need not confine myself to any particular range of specific gravity in'selecting my viscous medium, as variations in the specific gravity or density of the medium have no effect on the results obtained by the process and I can therefore use as my vehicle, a relatively light viscous medium, as for instance in the case where alcohol, benzol orgasoline have been used as the solvent, or I can use as my vehicle a relatively heavy viscous medium, as for instance where sodium silicate isdissolved in water. The viscosity of the conveying media is the important consideration.

I have discovered that by the use of my viscous medium, the length of the fibres or pieces in the fibrous material is not an important factor, and that I may use fibrous aggregates as short as onethousandth of an inch, or as long as three inches or more, or mixtures of various proportions of these lengths.

I have also discovered that the fibres or fibre pieces need-not be treated to render them uniform in size or form or softened but that I can use crude mixtures of individual fibres, strings or groups of fibres, chips, etc. While I may use sawdust or chips alone or mixed with fibres more or less in individual form, it will be readily seen that the amount of each used in a mixture will depend entirely upon the nature of the product I desire to produce.

I have discovered that the nature of the fibre or fibrous material that I use plays an important part in the ratio of the. amount of viscous medium to the amount and character of fibre stock.

.Where I use short fibrous aggregates as forinstance those averaging one half of an inch long, or when I use sawdust or chips, I convey the material with twenty parts of viscous medium to one of fibre, by weight. When I use long fibrous aggregates which are mostly three and one-half inches long, I have discovered that I have to increase the volume of my viscous medium in ratio to the weight of fibre and in case of the fibrous aggregates as long as three and one-half inches I have found that I have to use as high a ratio as one hundred parts by weight of viscous solution to one part by weight of fibre.

I have discovered that raw shredded redwood bark may be suspended and conveyed in my vis- 'cous media, illlustrative methods of preparing which, will be given hereinafter. At this point,

however, it is deemed desirable to describe briefly the method of shredding the redwood bark and also the physical appearance of the shredded material. There are of course, numerous devices for sub-dividing fibrous material. I prefer however, to use the Williams swing-hammer mill. The bark which has been removed from the redwood tree in a previous operation is cut into convenient lengths, preferably about four feet and continuously fed, in this form, to the above mentioned mill. The material discharged from themill is not homogeneous as regards size but varies from a virtually impalpable powder to fibrous aggregates three inches long. This non-homogeneous material may be sized or graded by screening operations, air-flotation or water-flotation.

In dealing with other fibrous material, which may be delivered to the board manufacturing plant in a disaggregated form, it is merely necessary to grade or size the material. The methods of disaggregating fibrous material have been worked out previously and form no part of the .present invention.

I have discovered that by using viscous media of correct qualities and filtering the surplus liquid from the mat of fibre on the screen of a paper or board making machine, I can save for re-use all of said viscous solution other than that left in the saturated mat upon the screen, thereby curing to a great degree the present ill of waste liquor in the art.

The method of preparing my'novel conveying medium is set forth in the following specific examples. It is to be distinctly understood that the methods described in the specific examples are purely illustrative and that the invention is in nowise limited to the specific details given therein. The parts are by weight.

Example I A colloidal solution is prepared by dissolving 2.75 pounds of starch in 97.25 pounds of water by the method mentioned previously. This viscous solution is used for conveying 5 pounds of raw shreddedredwood bark fibres of a length of approximately three inches and a minimum length such that all of it is retained by a #10 mesh screen.

Erample II 18 pounds of gilsonite are dissolved in 100 10 pounds of sodium resinate are dissolved in 90 pounds of water. This viscous solution is used as a conveying and binding medium for 18 pounds of raw vegetable'fibrous pieces having a degree of subdivision such that passed through a one and a half inch screen, they will remain on a 30 mesh screen. This solution is conveyed to a screen and a board is formed. This board is subsequently waterproofed.

Example IV In 100 pounds of the conveying medium of Example I, I introduce 2.5 pounds of partially digested bagasse. The bagasse is homogeneously dispersed throughout the media and may be conveyed to the board forming screen without danger 'of ball formation or clotting.

Example V Wherein I select a fibre such as mineral asbestos shredded into fine hair-like particles, I use a viscous solution consisting of 4% starch and 10 lbs. of the fine shredded asbestos hair to 100 lbs. of solution. The solution in this case acts as an ideal conveying medium precipitating asbestos in the form of a board or sheet upon the filter screen.

Example VI Where I use materials such as that known as mineral wool (slag residual) the proportions are as above and the product fairly light.

Example VII Where I use vegetable fibres such as that known commercially as balsam wool, I use a 3% starch solution and a ratio of 4.0 parts or solution to 1 part of the finely shredded balsam Wood.

The above media pieces which have been previously shredded but which have undergone no chemical treatment. In other words, the fibre stock. may be added to the above media and when the mixture is stirred until uniformity is attained, this mixture may be conveyed directly to the paper or board making machine.

When the mixture of viscous medium and fibre is conveyed to the screen of the paper or board forming machine, the excess viscous medium which is filtered off through the screen, is recovered for reuse.

From the foregoing description, one skilled in the art will be able to follow and adapt many fibrous materials and many mixtures, solutions the are used to convey fibrous.

and emulsions to the purpose of acting as stable, re-usable conveying solutions for many kinds and types of fibre.

As usedv in the appended claims raw fibre signifies fibre which has not been cooked or otherwise treated with sodium sulphite solution or other chemicals or hot water. Of course, such a fibre will not be pure cellulose or pure protein but will contain the natural impurities and therefore will be water repellent, and not susceptible to hydration. In other words, it means fibre produced by merely shredding, abrading or otherwise mechanically disaggregating the fibrous substance.

My process is applicable to the conveyance of mechanical pulp, digested pulp, or cellulose products of any description. It is also applicable to the conveyance of hair, wool or other animal fibres and of mineral fibres.

I claim:--

1. The process of manufacturing a fibrous sheet comprising introducing raw redwood bark fibres into a viscous medium adapted to maintain the said fibres in suspension, forming a sheet of any desired thickness from the said suspension while removing viscous medium by filtration, drying the said sheet and returning the said viscous medium to the process for the purpose of suspending additional redwood bark fibres.

2. In the process of manufacturing paper or board from raw shredded redwood bark, the step of conveying the shredded hard; in a viscous medium comprising a 2.75% starch solution containing 5 pounds of shreddedredwood bark per one hundred pounds of starch solution.

'3. in the process of manufacturing paper or board from raw shredded redwood bark, the step of conveying to the filter screen or plate the shredded bark while suspended in a viscous liquid