US1667691A - Proofed paper - Google Patents

Description

April 24, 1928. 1 1,667,691.

J. REID PROOFED PAPER Filed Nov. 1926 INFUSED NON Hwy/5E0 LA YER LA rips INVENTOR/ CHQJEI% MM.

ATTORNEYS Phtented Apr. 24, 1928.

UNITED STATES 1,661,691 PATENT m cs;

JAMES REID, OF MOUNT VERNON, NEW YORK, ASSIGNOR TO THE SCU'IAN COMPANY, A CORPORATION OF DELAWARE.

PROOFED PAPER.

Application filed November 28, 1926. Serial No. 150,868.

The resent invention relates to a proofed cellulosic product, particularly to a waterproof aper made from a paper having a base of wood or cotton fibre. My inventlon is primarily directed to the treatment of close grained materials such as paper as d1stinguished from loose formed bodies suchas building felt. Accordingly, I broadly term the basic material close grained cellulosie fibrous material. Y

My invention is based upon the d scovery that if proper precautions and conditions are had, it is possible to infuse the surface layers of a sheet of close grained cellulo'sic fibrous material with a viscous compound at a temperature which normally would substantially destroy such material. By us ng such a'high temperature, a type of impregnation or infusion can be obtained which has never before been possible, with the result that I can produce a product having markedly different characteristics from those which have heretofore been made.

Ordinarily, if cellulosic fibrous material such as paper, the fibres of which are unprotected, is exposed to a temperature substantially above 250 F. it will be so carbonized that it will lose all its strength. According to my process such a material is plunged into a bath of viscous proofing compound which has a temperature substantially above 250 and preferably is above 400, under such conditions that the surface layers will be infused with the proofing agent, but the middle of the sheet will have lts fibres 'uncoated. In applying such a temperature to the paper or similar material, great care must be taken to reduce the access of air. Also the time of treatment must be short 40 and after the treatment, provisionmust be made for rapid cooling so that air does not contact with uncoated fibres at carbonizing temperature. This can be taken care of by havlng a. web of paper or other fibrous ma- 1 terial which moves quite rapidly and plunges into a bath of molten but viscous proofing compound. The web should be submerged in the viscous compound only a short time and when it emerges the web should be stripped almost immediately, so that the mass of viscous compound in the web is small and the temperature may .drop promptly.

The proofing compound may be of various rubber or bituminous material which I have used has a melting point above 250, for example, I may use a material having a melting point of from 290 to 310 F., ring and ball method. The scale wax, which is a paraflin product, has a melting point of about 122. The Montan wax is a natural wax in'iported from Germany, and the type which I have used is a crude Wax, black 1n color, with a melting point of about 168. The mixed bath has a melting point of above 250 F. and when cool has very little tackiness due to the presence of-tfic waxes. I heat this bath to a temperature above 350 F.-say 450---at which temperature it isliquid but still extremely viscous.

I believe that the phenomena which take place in my process are somewhat as follows, but I do not wish to limit myself to the theory herein set forth.

The web of fibrous material always contains a certain amount of moisture. As soon as the web enters the hot bath, -steam is evolved; The-steam escaping from the web forms a stiff but cellular coating over the bath which I term a brat because of its resemblance-to the coating which forms when cheese is made. In operation, the brat should be allowed to develop until it is several inches thick when the surface will be found to be quite cool. The brat serves to keep the heat in the bath and also serves as a protective coating through which the web passes as it is being heated, so that the hot fibres are not exposed to the air.

The team and entrained air will leave the web until the pressure in the web equalizes the pressure in the bath which is a little above atmospheric, but a certain amount of air and superheated steam will remain in the web. The bath, although melted, is viscous and so the web will absorb some of the'proofing agent but not as much as would be the case ifa non-viscous liquid were being used. Apparently there is a substantial infusion of the liquid between the fibres onthe surfaces of the web but only a negligible amount of permeation toward the center of thickness.

- m In treating ordinary paper, I find that the.

web should be in the bath for only about five seconds where the bath is heated to a temperature of about 450 F. Under these conditions, infusion does not reach a maximum, with a rmult that in the finished prodnot the fibres of the center layers are substantially unaffected by the proofing material. This gives to the finished product a high degree of flexibility, for the unproofed fibres of the center layers can move relativelyto each other, permitting the surface layers to act more or less independently. For example, using kraft paper as a base, the finished product can be creased and folded without cracking in the same way as can be done with the unproofed paper. At the same time the bursting strength of the paper is somewhat increased. I

As the paper leaves the bath it is stripped of all surplus proofing material. I prefer to do this stripping by the use of scrapers which will leave the paper at about its original thickness but the surface will be smoothed and polished and the thickness of the paper appears to be more uniform. The relatively small amount of bituminous material infused through the surface portions will carry only a small amount of heat and will permit the web to cool very rapidly. If a heavy paper is being treated, it may be advisable to cool the paper artificially as by passing it over a chilled roll, for it must be remembered that the middle fibres will be almost dry and are not individually protected by coating material, so that they will filickly carbonize ifopportunity is iven. s cooling takes place, there must e a shrinkage in the gas content at the center of thickness (which will be accentuated by condensation of any residual moisture) will create a strong suction on the infused surfaces, drawing the proofing material closely around the fibres and probably drawing a certain amount into the actual cells or tubes of the fibres. It is my belief that this suction action is strong enough to cause minute perforations to be formed in the surface, for when the coated web is first formed and stripped, its strength will be markedly less than will be the case after twenty-four hours when the web has had an opportunity to reabsorb its normal complement of water. It may bethat as soon as the moisture content of the fibres reaches equilibrium, the colloidal surface infusion will flow together closing the minute pores, for the final prodnot isfound to be extremely impervious to Water and to have excellent dielectric quali ties.

In the accompanying drawing, I show a copy of a microphotograph of a section of kraft paper infused with bituminous mate-,

rial in accordance with the process that I of the web, This shrinkage have described. This drawing emphasizes the manner in which the surface fibres of the paper are thoroughly coated with the infused proofing agent, while the center is left substantially free.

The amount of proofing material that is infused into the surface portions of the paper may be varied with the temperature, time of treatment. etc. but for general results I have found it .advisable to incorporate from 15% to 35% of proofing material (based on the weight of the finished prod net). This will give a product with about one-third to one-quarter of its thickness noninfused. The amount of infused material may be determined by treating the paper with appropriate solvents which will leave ing waterproof bags or containers or as a strong waterproofwrapping where a fixed moisture content is to be maintained, or where dryness is essential as with explosives and some chemicals; it has sufficient strength and a proper surface sov it can be embossed to make a waterproof imitation leather, and its flexibility permits it to be used for making cheap umbrellas. These examples are given only as illustrations of the many and widely varied uses to which the product may be put.

Thus far I have described my product and process as one in which both surface layers of the paper are infused with the proofing agent. This is the preferred embodiment of my invention, but in some instancesvaluable results can be obtained if only one surface is proofed. This can be done by passing the paper over a proofing roll a part of wvhich extends down into a bath of the hot proofing agent. In this case no brat is formed but burning .is prevented by reducing the time of application. A portion of the hot proofing agent will pass into the paper and volatilize the moisture from the fibres at the high temperature used. Infusion will be somewhat more rapid than wherethe paper is passed into a bath, as the steam will not be entrapped. The surplus is stripped off and the paper, as before, allowed to cool quickly causing the proofing agent to be drawn intothe pores of the fibres to replace the volatilized moisture. The amount of proofing agent used should be about the same as in the other case, from one-quarter to one-third of the paper being left non-infused.

1 What I claim is:

1. A process of proofing close-grained paper of substantial strength .and flexibility without destroying such flexibility and strength, which comprises" the steps of assing a sheet of such paper through a ath of relatively high melting point proofing material of a bituminous nature heated to a temperature substantially above 250 F., and until the bath is liquid but still viscous, and removing the sheet from ,the bathbefore it is saturated with the proofing material. I

2. A process as defined in claim 1, in which the proofing material comprises a major proportion of bituminous. material having a melting point above 290 F. and the bath is heated above 400 F.

3. A process as defined in claim 1, in which the bath comprise s'a mixture of-bituminous material and wax.

4. The process of producing a proofed flexible sheet of paper substantially unaffected by atmospheric temperatures which comprises the steps ofpassing a substantially homogeneous flexible and relatively thin sheet of close-grained fibrous cellulosic material through a bath of relatively high melt; ing point proofing material of a bituminous nature heated to a temperature substantially above 250 F. and until the bath is liquid, removing the sheet from the bath before it is entirely saturated with the proofing material, stripping off surplus proofing material and causing the sheet to cool rapidly whereby the cellulosic material is proofed and given a firm surface without having its strength or flexibility substantially injured.

5. A process of producing highly flexible proofed paper with a non-tacky surface which comprises the steps of infusing into the surface of a sheet of close grained fibrous cellulosic material less than enough relatively high melting point bituminous proofing agent to permeate the entire thickness of the sheet by contacting the paper with the proofing agent in an extremely viscous statebut at a temperature substantially above 250 F., withdrawing the paper from the mass of proofing agent before it is fully infused, stripping off surplus proofing material and causing the sheet to cool rapidly.

6. A process of producin proofed paper which comprises the steps 0 heat-ing a muture of bituminous material and wax to a.

temperature above 350 F., causing a rela-.

terial a surface layer of which is infusedwith a bituminous proofing material which has a melting point above 250 F. and which has a layer which is non-infused, the infused layer being substantially non-tacky at atmospheric temperatures.

8. A product as defined in claim 7, in which'both surface layers are infused and the center portion is non-infused.

9. A product as defined in claim 7 in which the fibrous cellulosic material is paper and the proofing material comprises a major portion of bituminous material having a melting point above 290 F.

10. A new product of considerable strength and with flexibility corresponding to t at of paper, comprising paper the surface layers of which are infused with a bituminous proofing agent which is substantially nontacky at atmospheric temperatures and comprises a major portionof bituminous material having a melting point above 290'F., while the center layers are substantially non-infused.

11. A product as defined in claim 10, in which the paper containing the infused proofing agent is substantially the same thickness as the paper without such agent.

'12. A product as defined ,in claim 10, in which from one-quarter to one-third of the paper is non-infused.

13. A product as defined in claim '10, in whichthe proofing agent constitutes from 15 to 35% by weight of the product.

JAMES REID.

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