US2107343A - Process of treating paper - Google Patents

Description

n... as im 2,101,343 I PROCESS OF TREATING PAPER Chester D. Rockwood and Kenneth L. am on.

Cincinnati, Ohio, assignors to The Union Sellingogq mpany, Gincin'natl, Ohio. a corporation 0 o No Drawing. Application April 14, 1936, Serial No. 74,341

- s cum. (0]. 8-20) Our invention is concerned with a process of the like, with the exception of concentrated sultreating paper in order to produce certain dephuric acid and sodium hydroxide. sirable results, and is a continuation in part of These and other objects of our invention which our copendlng application Serial No. 31,362, filed will be pointed out hereinafter or which will be July 15, 1935. In that application we disclosed apparent to one skilled in the art upon reading 5 a process of treating paper and the like, in order these specifications, vwe accomplish by that procto obtain certain advantageous qualities, and also ess which we shall now describe in an exemplary a packing material made from such treated mamanner. terial. In this application we have carried the Briefly, in the practice of our invention, we 1 process farther, and have produced a material treat paper, cotton or cellulose fibres with a so- 10 which has other very advantageous qualities, lution comprising equal parts by weight of zinc which will be described hereinafter, chloride- (commercial or technical grade), and

Generally speaking, the treatment of paper with formaldehyde (commercial forty per cent grade) zinc chloride (ZnCh) is well known in the art. water may be adde if i is sired to il te he The product of such treatment isa permanently mixture, but the resultant sheet will be less sat- 15 brittle sheet, and this process is therefore used isfa to 'y, p $0 a Point beyond which the addiwhere it is desired to manufacture stiif board, tion of water will prevent the production of our for articles which do not require bending or foldsheet entirely. These materials are mixed until ing. the solids are completely dissolved. Since the Genuine vegetable parchment is produced by solution is an exothermic reaction, the mix must go treating stock with sulphuric acid (H1504, spebe cooled, and since dirt particles are usually presciflc gravity about 1.69). The sulphuric acid reent in the zinc chloride, it must be strained.

acts with the starch in-paper to .form a surface The fibre to be treated is conducted through coating of amyloid (CBHiOOS) which is watera bath of this solution in such a way as to comproof. A type of parchment is also said to have pletely saturateit. Excess moisture is evaporated 25 I been produced by the use of weak acids, organic ff by y heat at a temperature of C- a I i and inorganic, and acid salts, with or without to be understood that variation in heat, time of formaldehyde (HCHO) Such a teaching is made immersion, strength of the solution and the like, ina pa. ant to Fues, No. 1,082,757, dated July 23, will produce variations in the qualities of the 1912. It has been shown, however, ("Separation finished stock, although in any event the above 30 of cellulose particles in membranes of cotton outlined qualities will be exhibited in varying deflbres by treatment with HCl by Wanda K. Farr grees. Furthermore, the formula recommended and Sophia H. Eckenson-reprint from "Contrlby us may be unsuitable for certain types of butions from Boyce Thompson Institute", vol. 6, fibres, and necessary changes must be made ac- Pp. 3093l3, 1934) that weak acids will comcordingly. 35

pletely dissolve the cementing materials between The dried sheet, which at t Stage of the pro the cellulose particles, making the sheet necesess should contain at least ten percent moisture, sarily brittle due to the crystalline structure of is then conducted through hot calender rolls, the remaining cellulose. whereby the fibre, while it is in a soft gelatinous 40 Thus it has been shown that weak acids with condition, is ironed or mashed together into a 40 or without formaldehyde, and zinc chloride alone, more or less homogeneous film. This condition do not produce a satisfactory sheet. With the is readily apparent from the condition of the above facts in mind, it is an object of our invensheet. tion to produce a sheet which will have improved The sheet will now be quite hard, and tending 5 qualities as to stretchability, tensile strength toward brittleness, but on standing, it will take (Elmendorf test), surface tension (Mullen test), up moisture and become soft and pliable, astearing strength (Schopper test), waterproofness, suming-the characteristics of cloth, leather and toughness, pliability, softness, feel, leatheriparchment. The tensile strength at this point ness, and packing qualities. These qualities genis markedly increased, an effect which we aterally are included in the term parchment-like tribute to the action of the zinc chloride which effect" as used. in the claims. 4 sets up a hydrolysis within the fibres and expands Further objects lncludethe provision of a sheet them to several diameters, thereby increasing which will not disintegrate upon prolonged satuthe matting effect .within the sheet and the fricration in water, and which will be impervious tion'of onefibre over another. The heavy calto strong acids, alkalies, salts, soap solution and endering whi h it has undergwe 8.15.0 has m 7 sheet in air, we term air conditioning" the sheet.

and-to a certain extent, greaseproofness.

This air conditioning is for .the purpose of softening the sheet. It is accomplished by the hygroscopic action of the zinc chloride in the sheet. If this air conditioning step is eliminated, substantially the same result is achieved when the sheet is washed.

The air conditioned sheet is now conducted through a tank of water and scrubbed. By this treatment the zinc chloride and formaldehyde are entirely removed, and the sheet is then normally dried and caiendered to the desired finish. The finished sheet we have found to be tough, strong, flexible, leathery, and inert to disintegration in water. is not brittle and maybe folded indefinitely without fracture. When immersed in water, the sheet retains its toughness and tensile strength, but loses its stiffness and becomes more flexible and pliable.

Cur sheet must not be compared with any form of parchmentized sheet now known. In

parchment paper only the surface is changed, due to the speed at which the operation occurs. This speed is necessary to prevent complete destruction of the sheet. In regard to true vegetable parchment, it must be realized that these papers are seldom made in more than 40# basis weights. The caliper is proportionately less, due to its treatment and calendering. Because of this, it seems as though the sheet were parchmentized throughout, which however is not the case; a microscopic test will show otherwise. A sheet treated in accordance with our process, on the other hand, being of a heavier caliper, readily shows on tearing, that the treatment is complete.

pur treatment completely saturates all fibres and the reaction is carried to the endpoint, and of course the treatment is complete. Parchment izing produces qualities such as water, moisture, We do not claim these qualities with the exception of waterproofness, and perhaps greaseproofness, but we do claim qualities which parchment does not have; viz, leatheriness, toughness, non-disinjtegration in water, tensile strength and an appearanceand feel" hitherto unknown in the,

paper converting industry. It is an accepted fact that some parchment is dlmcult to disintegrate in water, but it more or less retains its stiff, al-

most brittle characteristic, even when wet, and is notcomparable to our sheet in softness. By-our treatment, the paper is given a soft, chamoislike quality when wet, but retains its original strength and toughness for many months in this condition.

While we realize that we are not required by the patent laws to state the theory behind our invention, we'feel it maybe helpful to set forth what we believe to be the reasons for our novel results. The cementing material in the fibres is composed largely of a mixture of pectic materials. Undoubtedly there are also traces of many other substances within the living cytoplasm of the cells which compose the fibres; among thesemay be hemicellulose, lignin, galactose, albumin, haemoglobin, chlorophyll and the like. This cementing material, instead of beingdissolved undergoes It is inclined to stiffness, but it a complete chemical substitution. Phi-maidehyde has an acid reaction, and although it does not combine entirely withthe alkaline zinc chloride, it does render the mixture active. The peetin, which is a constituent of the cell wall, and closely related to the vegetable gums, is thereby converted to pectic acid by hydrolysis due to the presence of pectase (a ,diastase) in the cell wallwhich is energized by the formaldehyde.

Pectic acid is a tough horny mass when dry, but readily becomes soft and gelatinous,.although retaining its strength, when wet. Therefore it is our theory that this tough mass combines the cellulose particles into a. to her. tighter, less .destructible sheet when dry and simultaneously a soft, pliable sheet when wet, which, however,

retains its strength. The untreated sheet, containing pectin, is obviously much weaker.

Therefore,'we believe that the peculiar and "unique condition of the finished sheet which 'we desire, is the direct result of the action of the formaldehyde-zinc chloride solution on the pectin present in the cell, changing it to pectic acid and producing the sheet which we have described.

The term commercial formaldehyde as used by us in the specification and claims, refers to the formaldehyde available on the market today, which usually comprises in the vicinity of forty per cent byweight of formaldehyde dissolved in water.

Having now described our invention, whatwe claim as new and desire to secure by Letters Patent, 'is:

1. A method of treating paper stock to produce a parchment-like effect which comprises conducting said stock through a bath of a solution of commercial grade zinc chloride in commercial forty per cent grade formaldehyde, said solution being prepared by dissolving the zinc chloride in the-formaldehyde solution.

2. A methodof treating paper stock to produce a parchment-like efiect which comprises conducting said stock through a bath of a solution of commercial grade zinc chloride in commercial forty per cent grade formaldehyde, said solution being prepared by dissolving the zinc chloride in the formaldehyde solution, and washing it to remove all traces of said zinc chloride and formal- I dehyde.

3. A method of treating paper stock to produce a parchment-like effect which comprises conducting said stock through a bath of a solution of one part by weight of zinc chloride in one part by weight of a so'lution of commercial formalde-