US1994750A - Typewriter paper of deferred indelibility and method of preparing the same - Google Patents

Description

March 19, 1935. g 1,994,750

TYPEWRITER PAPER 0F DEFERRED INDELIBILITY' AND METHOD PREPARING THE SAME Filed Sept. 23, 1935 Patented Mar 1 earns or nnrnnnnn mnnarnrrr awn rm'rnon or rare "t 'l in THE S .lio G. Calian, @ambridge, Mass.

This invention relates to writing paper of the several classes that are intended principally as typewriter papers for receiving typewriting by the impressions of the raised type either from the inked ribbon or from carbon paper. The

paper of this invention is as well suited as are most writing papers for receiving markings from pen and ink or from lead pencil, but the advantages that it possesses relate more particularly to its use as a typewriter paper.

The objects of the invention are as follows: To produce a paper from which recent typing can be erased easily, quickly and practically completely by means of a pencil eraser of soft rubber or the composition known as art gum without resort to a sand rubber containing abrasive such as is commonly used for erasing typewriting:

Tomake it possible to erase several times in the same place in the manner described:

To provide that although the recent inked im- I pression can be wiped oif easily with soft rub-. her or art gum and without noticeable defacement of the surface, it shall nevertheless be ad herent enough so that it cannot be wiped 013 nor easily smeared by casual friction from other substances:

To avoid any requirement for" special typewriter ribbon or special carbon paper not already in prevalent use, and to assure the stated erasing properties for red impressions as well as black:

To insure that with passage of time a typed record on the said paper shall become progressiveiy harder to erase so that it shall eventually acquire enough resistance to erasure to constitute the said record a safe one that cannot be altered or removed without the vigorous use of such customary erasers as the sand rubber,'which so disturb and deface the surface of the paper that it is possible to ascertain that a change has been made.

It is well known that writing papers made of difierent substances and made and finished in different ways show widely different degrees of resistance to erasure, but so far as this applicant. knows, all of them require the'use of an abrasive rubber or equivalent to eradicate the typed impression. it may therefore be emphasized that the firsto'bject of this invention contemplates an erasure wherein the fresh impression can be wiped cleanly from the surface in a manner difiering in more than degree from that characterizing even the more easily erasable papers of the prior art.

In accordance with the present invention, those constituents of the paper sheet capable of receiving a relatively permanent mark from the" of top sizing.

s, 1933, Serial No.69llfld2 ink are protected from immediate contact therewith, afterthe ink has been applied, by other constituents. In order to confer ultimate indelibility these other constituents are of such character as to be progressively and ultimately so com- 5 pletely penetrated by the ink, or by certain of its constituents capable of producing a relatively permanent mark, as to render the mark effectively indelible.

I have found that all of the objects that have 10" been specified are accomplished very satisfactorily by process and means that will next be disclosed. Wherever possible the requirements will be defined along with preferred means for meeting them.

For a more complete understanding of this in;- vention reference may be had to the accompanying drawing in which is represented in perspective, and much magnified, a fragment of a sheet of paper treated in accordance with this inven- 2 tlon. All the objects are met if the surface of the paper on which the writing is to appear is evenly covered by a scum or film of a material'of properties that will be defined, laid on much thinner than the coating of ordinary coated papers, following the minute surface irregularities, hills I and hollows, and coating them without obliterating them to any such degree as is usual with coated papers, and penetrating the porous suro face of the paper to a controlled and limited degree, much less than that sought in the operation As a practical matter, however, both faces of the paper will ordinarily be so treated, partly because either side can then be equally well printed upon, and also because if the paper be treated on one side only it may Show some tendency to curl, while with both sides alike this tendency is not found. Such a film is indicated at 1 on the drawing, on opposite faces of the paper 2. v

The properties of the materials suitable for forming this film intermediate between a coating and a top-sizing, should be as follows;

The material should be one that can be applied from solution or dispersion, preferably water dispersion, and dried on the surfaces ofthe paper; that will form on the paper surface a thin protective film or scum that shall have such' inherent properties,.and that shall be so related to the m superficial layers of the paper, as to kiep the ink of the typed impression from coming at once into direct contact with the cellulosic paper substance itself; and that shall be only slowly permeable to miss ordinarily used on typewriter ribbons and carbon papers, but shall eventually allow such inks or constituents thereof to penetrate it by diffucion, or otherwise, and reach the paper and permeate, stain or mark the paper itself.

There are several materials that meet the requirements andare not prohibitively expensive; casein,preferably with additions its ink-permeability is one suitable one, and the preferred proportions of the mixture will be described hereinafter.

The physical relation of the protective dilm to the paper-substance is important, and a preliminary statement of the two extremes to avoid will help define the limits between which .good results are found. Ordinary coatings are commonly applied for the purpose of giving a smoother and more glossy and specular surface for receiving halftone printing or for other uses by filling in the minute superficial depressions in the felted mass of paper fibres. This will not serve the purpose of this invention, because the desired film should cover each paper fibre to about the same thickness so that the eventual penetration of the ink to these fibres (insuring eventual permanence of record) will proceed evenly and not be spotty. Early experiments with thick coatings showed this point to be an important one. Furthermore, such filler coatings contain sucha large proportion'of mineral matter such as clay or the like, that surface finish of the paper is destroyed by even light rubbing with a soft rubber. On the other hand, where sizing material, even in excess of the usual amount, is applied hot,'and the excess immediately removed by squeeze-rolls, as it is in the top-sizing or tub-sizing operation as commonly practiced in paper-sizing, the hot sizing liquid sinks into the paper structure like butter on very hot toast, and leaves the protuber-' ant tops of the fibres so thinly covered that the typewriter ink finds access to them at once and the operation does not confer the necessary sort of complete initial erasability that'is desired; it makes erasing with a sand-rubber easier, as is well known, but so far as this applicant's experiments have developed the facts, and so far' as can be judged from many examples of heavily top-sized paper's, it never makes a surface from which a'new typed impression can be cleanly wiped by the use of asoft rubber. The two extremes or boundaries in procedure that are to be avoided, having thus been pointed out, the desired effect or result, and the preferred means of obtaining it, may the better be defined. The surfacing material should be applied as a cold solution or dispersion well evened over the surface, leaving enough so that the is distinctly wetncl; merely very damp. There is some latitude as to the thickness of the solution or dispersion to be used, but its character should be such that either initially or with progressive .-drying it becomes gelatinous rather than merely viscous, so that once it coats the tops of the very minute protuberant fibres characterizing the surthan the hollows between them. Examination under a strong magnifying glass of colored films in process of drying shows that with a suitable residuum of a proper surface-filmingsolution this evenness can be well accomplished if thejfilm is dried, as it should be, free from substantial surface pressure and without application of such heat as would confer flowing or leveling properties on the wet surfacing material before it has a chance to "scum over" and establish sumcient form-stability so that subsequent drying will not materially disturb the evenness of the application. This last named condition is well fulfilled by the well known air blast drying used on paper-coating machines which apply coating on both sides simultaneously and "fioat the wet coated paper on a seriesof upwardly directed streamsof air emerging from a blower-trimk of rectangular section above which the paper fioats untilit is dry enough to be hung in festoons without adhering to the wooden sticks.

4 If the paper is not well-sized prior to this scumming or filming operation, it is absorbent, and a part of the solution or dispersion of filming material soaks in with the undesirable results of increasing expense, and, mor important, of tending to give irregularity of e finally remaining protective surface. Experience has shown thata suitable degree of initial sizing will result from the use of the usual amount of rosin size in the beater, varying with different grades of paper and following good current practice, and a final "top-sizing" with the material known in the trade as Hercules gum" of 5 concentration 'rather than the 2 concentration that is in more, common use. There is some latitude in these proportions, and glue-size of equivalent concentration may be substituted for the ercules gum". The resulting protective scum, f a thickness that appears from weight of added terial to be of the general order of one to two tenths of a mil (0.000Ito 0.0002 inch), must be practically continuous so that it shall not leave exposed pin-holes that give access forthe ink to the paper-substance beneath. If the film is well formed, a very slightly moist piece of the paper, on being held above a flaming match, will form a blister or balloon in which the steam, unable to escape, splits the paper into two layers; when this testis made it ing paper, and has been well calende'red on the paper machine.

Another convenient test for the minute uncovered or insufiicintly covered spots called pinholes consists in flowing gasoline over the surface of the sample and noting any progressive formation of translucent grease-spots" resulting from penetration of the gasoline through such pin-holes into the untreated interior of the sheet. The size and rate of growth of such greasespots when the surface is covered'with a film of gasoline gives'a quick and very searching 'means of estimating the continuity of thesurface film. Their number'and size should be relatively small after 20 seconds, but if there are none, it usually indicates that the scum is so thick that while the initial erasing properties will be excellent, the penetration of the typewriter ink with passage of time .will be slow. The operator soon learns to correlate test performance on the typewriter with this indication,

It will be understoodthat this protective film closely follows the minute hills and hollows of the interlaced fibres of the paper, and maintains as nearly as possible aneven thickness over'the whole contour, as shown by the drawing. The protective material seems to penetrate and fill such very small or narrow .fissures between fibres as are somewhat parallel-sided and-of capillary dimensions, as indicated at 3 in the drawing, but-so far as microscopic examination is able to show, it follows vwell the other irregular contours if the precautions indicated have been observed, and if the preferred solution and method or their equivalents are used,' as specified hereinafter. There is some shallow penetration of the surface, largely in the nature 'of such filling of microscopically narrow interstices and crevices as described, but with a properly sized sheet, well machine-calendered, this capillary absorption is small and the addition of weight due to the protective scum on writing paper of 20 pounds ream weight should be between 5% and with about 7 as the normal value to be taken as standard for two-side coating.

The scum or film may consist of any material that has the properties that have been defined. Excellent results have been obtained with filmforming colloids as, for example, casein, hardened and prevented from becoming sticky with moisture by addition of formaldehyde, and preferably made somewhat more quickly penetrable to oilbase typewriter inks by addition to the solution of some material such as sulphonated castor oil or soap, that oil will wet more readily, and diffuse through more rapidly, than is the case with a film of casein alone. Experience has shown, however, that a film of casein hardened with formaldehyde and with no other additions gives excellent initial erasure, and gives enough time-penetration to insure the appearance within two or three days of an impression of the typed letters in the papersubstance, rather faint, but not erasable with anything less drastic than a sandrubber-. Special copying ribbons with glycerin or other watersoluble or alcohol-soluble involatile material as the agent for maintaining printing qualities, penetrate fairly rapidly through casein films without admixtures, but the admixtures do not prevent this penetration of impressions from such unusual inks. Of promoters of penetration of the nearly universal Vaseline-base inks, either sulphonated castor oil (Turkey-red oil), or a pure soap, in quantities that will be specified, cause the impression that eventually appears in the paper substance to be heavier, and somewhat accelerate the appearance of that impression. Of the two, the soap is rather the more effective in promoting both these purposes, and it is not objectionable in any respect known to this applicant unless it should tend to cause yell-owing in the paper after the passage of much more tirne than has been so far occupied by the experiments.

Among alternative materials gelatin, and its equivalent, glue, hardened by any of the wellknown tanning agents used in hardening gluesize, have been tried with good results. The glue film is rather less penetrable to Vaseline inks than a casein film, and the glue solution is much more intractable to handle in the machine. while there are no marked advantages. over casein for the purposes of this invention- Starch cooked in the ordinary manner forms an excellent film, somewhat softer and less resistant to repeated erasures than hardened casein or tannedgelatin or glue, but presenting a material 'quite satisfactory and but little inferior to the other two.

There are many formula: for the ink for type- .writer ribbons and carbon papers, andalconsiderable number of dyes and mixtures of dyes is found even in black ribbon. Thus far allthe ribbons and carbon papers tried have shown the desired results, although with some black mixtures, especially when sulphonatedjcastor oil is used in the film as the medium for promoting ink diifusiom,

a purple component shows preferential diffusion and the deferred relatively indelible impression on the paper substance, after erasing what a soft rubber will still remove after passage of time, is found to be purple instead of black. In so far as inks which do not contain dyes are concerned, and when the protecting coating on the paper contains no penetrant, the indelible mark from the ink appears initially as small black dots which gradually increase in size and number and on magnification give somewhat the appearance of the spots of the gray part of a half-tone print. At least in those instances where no penetrant is employed in the coating, an important factor in the development of indelibility appears to be the capability of the film through its inherent fragility to have its continuity locally,impaired as through incipient cracking or shattering under the blows of the type, developing numerous slight localized discontinuities through which the ink may gradually pass to the paper beneath. While the heaviness of the touch of the operator on the typ writer keys is of some eifect in determining the time of ultimate indelibility of any particular paper treated in accordance with this invention, the nature of the impact of the type against the paper is found to be of much more importance, it being possible to use a thinner protective coating satisfactorily ith the so-called noiseless machines where the impact of the type is in the nature of a pressure than with other machines where the type strikes a sharp blow.

One coatingsolution that has given excellent results is as follows: A casein solution is made by adding casein to cold water in the proportion of 1% pounds of casein to each gallon of water. The casein is allowed to soak in the cold water for one to two hours and the mixture is then cooked as in preparation of caseinjor coating; at some time during the cobking either borax or ammonia are added in proportions well known, to cut the casein. This cooked solution is allowed to stand at robm temperature for about 12 hours, whereby its physical character becomes more gelatinous and less viscous. The working solution,-or dispersion,is made by diluting this with water, and here there is some latitude; excellent results have been attained with a concentration reached by adding 20 gallons of water to 15 gallons of the strong casein solution, and adding thereto 2 quarts of commercial (50%) formaldehyde. To this is added the amounts of color and china-clay that will give the film the desired appearance and tint, and the whole is very thoroughly mixed. If it is desired to accentuate the strength of the indelible impression that will eventually be'developed, as it commonly will be, there is then added either of the following: cubic centimeters of sulphonated castor oil for each litre of solution or 25 grams of a pure soap, free from uncombined alkali. The soap is less expensive, and. gives results as good in all respects aside from'some apprehension of possible The treating material can be applied in any way There are also vathat will insure the formation of a continuous and very thin sufliciently cohesive film following the minute contours of. the irregular paper surface. The preferred method is by the use of a coating machine, the aqueous dispersion being spread while at about room temperature. The initial drying or setting is effected cold, at or below room temperature, though the final drying after the film has been formed may be 'by heat, if desired, as in the usual paper coating operation. The coating machine may well be one having a roller feed and a pair of oscillatory brushes for evening the coating. It is preferable to cover both sides at one time on a two-side coating machine of wellknown type where the paper is floated on up wardly directed successive jets of air during the initial period of the drying up to the time when it is no longer sticky. However, excellent paper has been made on a machine covering one side at a time; with this form, curling in process of manufacture makes handling difiicult.

I claim:

1. 'A sheet of typewriter paper including sizing material constituting a thin coating of even thickness following surface irregularities of the paper and capable of receiving ink from a typewriter type impressibn and from which said ink is initially easily erasable without noticeable defacement of the sheet, but which coating permits slow penetration therethrough of constituents of said ink capable of indelibly marking constituents of said paper, whereby said typewritten impression becomes progressively indelible.

2. A sheet of typewriter paper having a surface sizing coating of substantially even thickness following the surface irregularities of the paper and of such thickness as to initially prevent a typewritten ink impression on said paper from reaching constituents of the paper capable of receiving an indelible impression therefrom but sufficiently"thin to permit constituents of such ink to gradually penetrate such coating and progressively render said impression indelible.

3. A sheet of typewriter paper having a sizing coating applied thereto under such controlled conditions as to produce a coating of even thickness following surface irregularities of the paper and sufiiciently thin so that a typewriter ink impression made on said coated paper is initially easily erasable but progressively'becomes indelible.

4. A sheet oftypewriter paper having a sizing coating applied thereto under such controlled conditions as to produce a coating of even thickness following surface irregularities of the paper and sufliciently thin so that a typewriter ink impression made on said coated paper is initially easily erasable but progressively becomes indelible, said coating being of a character which initially receives the ink with sufficient adherence to resist smearing.

5. A sheet of typewriter paper having a sizing coating applied thereto under such conditions of temperature and viscosity as to produce a thin superficial coating of even thickness following surface irregularities of the paper and resistant to penetration of typewriter ink therethrough, so that a typewriter ink impression made on .said paper is initially' easily erasable but progressively becomes indelible.

6. A sheet of typewriter paper having a sizing coating applied thereto under such controlled conditions includingthe viscosity of such sizing as to produce a thin superficial coating of even thickness of the order of .1 to .2 of a mil sufiiciently-resistant to penetration of typewriter ink therethrough so that a typewritten impression on said coated paper is initially easily erasable but becomes progressively indelible as the ink penetra-tes said coating and stains the paper substance beneath said coating.

7. A sheet of typewriter paper having a sizing coating applied thereto under such conditions of temperature and viscosity as to produce a thin' superficial coating of substantially even thickness of the order of .1 to. .2 of 9. mil substantially following surface irregularities of the paper, said coating having suflicient cohesion and being suflicient ly resistant to the penetration of typewriter ink therethrough so that a typewritten impression on said coated paper is initially easily erasable without noticeable defacement of said coating but becomes progressively indelible as the ink penetrates said coating and stains the paper substance beneath said coating.

8. A sheet of typewriter paper having a superficial substantia y continuous protecting coating of substantia ly even thickness following surface irregularities of the paper and capable of initially receiving a typewritten ink impression and of suflicient fragility to be locally impaired under impact ofa typewriter type to an extent.

sufiicient to permit said ink gradually to pass writer ink and fragile enough to develop numer- 'ous slight localized discontinuities under impact of a typewriter type. v

10. A sheet of typewriter paper having a casein coating applied thereto under such controlled conditions as to produce a coating of even thickness following surface irregularities of the paper and sufiiciently thin so that a typewriter ink impression made on said coated paper is initially easily erasable but progressively becomes indefible. P

. 11. A sheet of typewriter paper having a starch coating applied thereto under such controlled con'ditions'as to produce a coating of even thickness following surface irregularities of the paper and sufliciently thin so that a typewriter ink impression made on said coated paper is initially easily erasable but progressively becomes indelible. a a

12. A sheet of typewriter paper having a tanned glue coating applied thereto under such controlled conditions as to produce a coating of even thickness following surface irregularities of the paper and sufficiently thin so that a typewriter ink impression made on said coated paper is initially easily erasable but progressively becomes indelible.

13. A sheet of typewriter paper having a sizing 14. The method of treating paper, which comprises applying a liquid coating size thereto and drying the same under such controlled conditions as to produce a coating of even thickness following surface irregularities of the paper and smilciently thin so that typewriter ink applied thereto is initially easily erasable butprogressively becomes indelible. 15. The method of treating paper, which comprises applying a liquid coating size thereto while in a somewhat gelatinous condition and drying the same free from substantial surface pressure delible.

and during initial setting at sufficiently low temperature so as to produce a coating of even thickness and sufilciently thin so that a typewritten ink impression on the-coated paper is initially easily erasable but progressively becomes 'in-' 16. The method of treating paper which coinprises applying, while in 'a somewhat gelatinous condition, a liquid coating size selected from a group consisting of starch casein and glue, and drying said coating free from substantial suris initially easily erasable but progressively be- 10 comes indelible. v

JOHN G. CALLAIL-

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