US1939378A - Process of making safety paper by one continuous operation - Google Patents

Description

:50 too much andbecome wet.

Patented Dec. 12, 1933 PROCESS OF MAKING SAFETY PAPER "BY ONE CONTINUOUS .OPERATION Frank S. Wood, Quincy, Mass, assignor to Inkset Safety Paper Co., a corporation of Massachusetts No Drawing. Application November 8, 1930 Serial No. 494,443

1 Claim.

My invention belongsto that class of safety papers in which the safety feature is imparted by treating ordinarywriting paper with a chemical compound and more especially with the I chemical compound for which an application for a patent was filed by me, on October 13, 1930, Serial Number 488,545,.

This compound may be made in any quantity by dissolving one grain of tannic acid in each gallon of water and adding 2 to 5 cubic centimeters of glacial acetic acid; to'this add onetenth of a gallon of decolorized iodine; Ordinary paper treated by my process is transmuted into safety paper which discolors and sets ink written on its surfaces when eradicators are usedto remove the ink. If only 2 cubic centimeters of acetic acid are used the inkset will be thrown out and will not appear; the same thing will happen if 6 cubic centimeters or more of acetic :0 acid are used. Between'2 and 5 the different colors require different amounts to get the best results. Different gradesof paper require special formulas to be worked out between the two extremes specified; but anyone skilled in the art may quickly determine the best formula.

Heretofore, safety paper has required two or more operations or mechanical handlings. The first operation is the manufacture'of the paper, to formula, in the usual way, leaving 'aproxia0 mately 8% of moisture (water) in thepaper. The second operation consists in some form of subsequent re-handling involving chemical treatment of the paper or printing or both which second operation costs, at least, as much ,as the 85 first; and this cost is considerably augmented if it be necessary to dry out any part of the water content left in the paper by the first operation.

The object of my invention is to eliminate the entire cost of the second operation and only 4'0 slightly increase the cost-of the first by adapting it to better achieve the combined purposes of both in one continuous operation. a

-Paper has, in itself, anaflinity for moisture called absorption that varies-with its temperatuxe, with the amount of moistureapplied to it, and withthe chemical character of the liquid supplying the moisture. When chemicals, for which paper has a strong'aflinity, are brought in contact with it, the natural tendency is to absorb In saturated paper, there is a moisture'content of over .After it has gone through three roll-pressings in the paper machine, it contains 40% of moisture. For the'purposes of my invention, ,allp'aper is '65 wet which contains 9% or more of moisture,

(Cl. ill-67.95)

and any'degree of this range of wetness destroys the purpose of my process. It is, therefore, absolutely necessary to control the amount of moisture whichthe paper shall absorb "to a very delicate degree. This is done by having the paper in the right condition at a certain time, by having the right positive chemical for absorption by thenegative papen'and by having the chemical applied to'the'paper under perfect mechanical and chemical controland regulation. All the essentials of perfect regulation, repressed affinity and mechanical and chemical supply, control and application are comprehended in the phrase, mechanico-chemical absorption. Inher'ently, in 7 order for the purpose of'my process to beaccom-' plished, the paper must. be commercially dry after'the chemicals have been absorbed. No subsequent drying is essential; therefore there can be no previous wetness and especialy no saturation; otherwise the" paper would be. spoiled. 76 It is a fact that my process is diametrically opposite to saturating, wringing, scraping, and then drying; Such methods all apply a surplus of moisture to the paper, too much moisture for my purpose, and then remove the surplus by various methods of elimination subsequent to the application of moisture. .With my process there is no wetting of the paper and no saturation. The paper is prevented from absorbing more than the amount of moisture to make it commercially dry byfseveral mechanical and chemical balanced adjustments. A description of one of my experiments may illustrate and clear up any thing lacking. I have taken a web of paper dried out to a 3% moisture content as it came from the paper machine and have run that web, while still warm, through a machine comprised of a battery of spray-guns. These guns use compressed air at any desired pressure which spray a very fine. fog of chemical upon the surfaces of 95 the paper, the liquid being sucked into the airblast before spraying. After being sprayed the paper was wound on a reel, still warm, and felt dry to the touch. It was found to contain 8% of moisture. This showed that it. had absorbed 5% 1 of chemical compound. It was neither saturated nor wet; it was dry and yet it had gone through no drying subsequent to the. application of chemicals. The reason was that the moisture, being controlled and properly applied 105 to the warm and super-dry paper, is absorbed by thepaper without any'perceptible moistening of its surface. By no possibility can any coating, saturating or oiling machine function in this way when using other liquids than oil. 011 and 110 water work entirely different on paper. In my process, it is a combination of delicate means, conditions and balances, at just the right time and place that constitutes the novelty of my invention.

In brief, my invention consists of a process involving dehydration and subsequent mechanicochemical absorption.

To this end, my invention eliminates the necessity of drying out the paper in a second handling, by dehydrating it as it is being made. This may be accomplished in two ways: Either by slowing down the speed of the paper-making machine and thus increase the time that the paper is on the drying-rolls, or by adding two steam drying-rolls to the paper-making machine which gives the same result. This turns outa paper which is known to the art as bone-dry.

In this condition, the bone-dry, hot paper is threaded through the calender-stack for the purpose of giving it the desired finish which, in a writing paper, would'probably be either a bond or a ledger finish. Having received its finish, the hot paper then is permitted to absorb approximately 8%, by weight, of a chemical com-' pound adapted to transform the paper into safety paper. The chemical compound which supplies the moisture for absorption by the paper, may or may not be the chemical compound which has hereinbefore been mentioned as the subject of separate patent proceedings, as my invention comprehends the use of any chemical compound which produces safety paper in one continuous operation through the two steps of dehydration and subsequent mechanico-chemical absorption.

The amount of moisture which any paper may absorb without damage is approximately 8% of its bone-dry weight; and this is also the approximate amount of chemical compound necessary to produce a commercial, clear-stock safety paper by my process. While it is possible to strengthen and adapt a chemical formula to 1% or possibly 2% of water content left in the paper before being chemically treated, it is not safe to go beyond that, for the reason that any moisture ed or put through my process.

moisture, whether it be water, chemical comleft in the paper will, by so much, prevent the absorption of chemical compound, and insufiicient chemical compound may have the same effect upon the paper as if it had never been treat- Again, too much pound or both will cause the paper to wind-up in a perfect honeycomb of wrinkles; an uneven application of moisture will make the paper,

draw, fold and even break, wasting both paper and compound. Hence, the necessity for a very fine adjustment of moisture in the form of chemical compound to be delivered to the paper for absorption. Having absorbed its predetermined,

' regulable and controlled quota of chemical compound, the paper then-goes to the winder where it is made into a roll, thus completing the process of producing a safety paper at one continuous operation.

to the fraction of 1%. However, any moisturecontrol device with a fine degree of adjustment will meet the demands of my process. Any attempt to apply the liquid to an upward traveling roll, such as a calender roll, and thence to the paper, results in failure, for two reasons. First, from lack of moisture control; and second, from insufficient treatment. Such application floods the roll with liquid; the speed of the roll carries the compound upward until it contacts with the paper; but the speed of the paper together with the nipbetween the calender-rolls necessary to give the paper the desired finish, blocks absorption by the paper and results in partial treatment, only. Then again, this method of applying moisture is known in the art as a water-finish. Its eifect is to give the paper a gloss. Since a gloss makes a bond finish impossible, only ledger paper may be turned out by such a method.

'Another objection to this method is that the calender-rolls wear unevenly. Where the surface is not true, the'worn part or parts act as a trough through which too much moisture will flow, caus ing the paper to pucker, fold and wind up in a damaged condition; while a little more wet will cause the paper to break, wasting both paper and chemicals. It is to overcome such difiiculties that my process is designed.

Another serious obstacle that has many times defeated the objects and purposes of their inventors was in having the chemical solution too powerful or off balance; that is to say, they were too strong, too alkaline or too acid, any one of which will surely cause the paper to discolor after being chemically treated. This spoilage and damage ends in complete fiasco. Besides that, heavy damage was caused by ruining the brass'rolls of the paper-making machine.

With my process, such outcomes are guarded against by using a chemical compound so delicately balanced'with effectual acids and bases as to be neutral in all of its contacts. It neither injurespaper machines, equipment, paper nor color. On the contrary, color is preserved by the chemical compound and the fiber of the paper L is improved and strengthened.

In many paper-mills, it is customary to set the calender-stack close to the drying-rolls. This makes it impracticable to set up an absorption unit between the steam-rolls and the calender. If, however, there were sufiicient space between the last drying-roll and the calender to install an absorption unit, there is no reason why the chemical compound could not be absorbed directly by the bone-dry paper which would, then, be threaded through the calender where it would receive its finish and then go direct to the winder. Such a set-up would be consistent with the purposes of my invention and yet it 'might be impracticable to apply in most existing papermills, on account of lack of space to install the The result would be the'same in either I have found that the treatment of paper by my process strengthens the fiber so that paper of the same weight will register a higher bursting strength after going through my process than it did before. It is a fact that a pure sulphite paper made from wood pulp and put through my process has a higher bursting strength than an ordinary 60% rag paper.

It is a fact that paper of the most delicate and attractive tints may be made into a safety paper by my inventions without changing the shade of the tint, thus lending itself to the highest demands of the lithographers art in colorful blends, contrasts and pictorial illustrations. This has heretofore been impossible with safety papers.

It is a fact that by giving a sulphite writing paper my process, its value, as represented by the wholesale selling price of inferior safety papers, will be increased 3 /2 times; while the cost of production will be increased less than 10%.

What I claim as my invention and desire Letters Patent for is:

Steps in a process of making safety paper by one continuous operation comprising complete or approximate dehydration and subsequent controlled application and absorption of approximately 8% of water, decolorized iodine, tannic acid and acetic acid or their impregnating equivalents, adapted to transmute ordinary paper into a safety paper having the power of setting ink and causing discoloration when ink eradicators are applied to ink written on its surfaces, whereby said safety paper is produced commercially dry without requiring any further drying.

FRANK S. WOOD.