US1767662A - Process of treating cellulose to produce vulcanized fiber and the like - Google Patents

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Patented June 24, 1930 UNITED STATES ROBERT R. FULTON, OF 'WILKINSBURG, PENNSYLVANIA, ASSIGNORITO T COMPANY, A CORPORATION OF DELAWARE PATENT OFFICE PROCESS OF TREATING CELLULOSE TO PRODUCE VULCANIZED FIBER AND THE LIKE able features of the prior art may beavoided. Y

My invention has for further objects such other operative advantages or results as may hereinafter be found to obtain.

At the present time, the manufacture of vulcanized fiber is generally conducted according to the well-known zinc chloride method. According to this'procesager- Application filed March 16, 1927. Serial No. 175,932.

properties of such solutions with respect to cellulose could be utilized to gelatinize cellulose. According to the patented process, cellulosic material, such as cotton rag paper, is treated with calcium thiocyanate solutions of such concentration as to boil at 157 C., and preferably having an acid reaction. The paper is treated with such solution at a temperature of 130 C. for about 30 seconds and is thereafter washed and dried in the usual manner.

The' solutions proposed in the above recited patents are very concentrated, being, in fact, so concentrated that they are very viscous, even at 130 C.,-and solidify at atmospheric temperatures, especially in acid condition.

According to my invention, I treat cotton rag pulp paper, paper made from chemical wood pulp, or the like, with a neutral or alkaline solution of calcium thiocyanate or IIE KOPPERS other thiocyanates of such concentration as to have a boiling point of from about 130 tain grade of cotton rag paper is subjected toabout llOig and preferably containing for a few seconds to the action of a 70 Baum solution of zinc chloride at a temperature of about 50 C. After this treatment and while the paper retains some of the solutions, the paper is rolled upon a large heated drum and is subjected to a slight perature of the bath and the time of the treatment must be carefully controlled to prevent the formation of a dark, brittle fiber.

The use of concentrated calcium thiocyanate solutions has been proposed in U. S. Patents Nos. 1,301,652 and 1,333,465, to Clayton et al.,-who discovered that the solvent from about 15% to about 30% of formaldehyde. The treatment is carried out at substantially atmospheric temperatures, for example, from about 20 to 40 C. Preferably I do not allow the fiber to remain in the treating bath until gelatinization is complete, but I remove the fiber from the bath after a short time and allow the treated fiber to lie flat for a sufficient interval to insure that gelatinization is carried to a satisfactory degree.

By formaldehyde is meant the usual aqueous solution thereof containing approximately 40% by volume of CH O and some times known as formalin.

It will be obvious to those skilled in the art that the actual treatment of the fiber will be subject to' many modifications, such as time of treatment, concentration of solution, nature and state of cellulosic materials used, pressure and the like, according to the nature of the materials treated or the character of the results desired. However, in order that my invention may be clearly set comparatively largewmounts fp gample, li

solution of 0a(0NS).3H O and one part of formaldehyde. The reaction of the solution is preferably-neutral or slightly alkaline and the temperature of the solution is maintained at any convenient point within the approximate range of from 20 to 40 0..

Higher temperatures are to be avoided. The paper is runthrough" the bath at any speed that permits'thorough wetting without retaining the paper in the-bath for extended intervals. It is then wound, as in prior practice, upon a large drum, except that the drum is not heated. After a sufficient number of layers of the paper have been wound upon the drum to produce a sheet of desired thickness, it is removed, out to desired size and allowed to lie fiat for from 30' minutes to several hours in order to permit gelatinization to take place. It is then pressed, either with or without heat, washed, preferably by the counter-current system, dried and again pressed to form a flat sheet of hard fiber which may be drilled, machined and polished, as desired.

Although a certain amount of adhesion of the built-up layers or laminations of fiber may take place prior to the initial pressing operation, such pressing is desirable to insure that the layers adhere thoroughly to each other.

The length of time required for the gelatinization period will vary considerably with the nature of the raw material treated and the quality of the result desired and is best determined by previous experiment for every condition.

There are many advantages toibegained' b1122%@tiQgcellulcseaccfiding to my inven-.

tion. It requires no high temperatures, the use of which is always attended with considerable cost. Hot solutions of calcium thiocyanate are much more corrosive, especially in acid condition, than the cold, less concentrated'an'd neutral or alkaline solutions which I prefer. Cold solutions of calcium thiocyanate give rise to less occupational hazards than hot solutions. Moreover, the presence of formaldehyde in my preferred solution reduces its corrosive action.

A solution of calcium thiocyanate having a boiling point of 157 0., is ery viscous, and, although applied to the paper at 130 0., cools quickly on the surface of the paper, becoming more viscous, or even crystalline, and rendering its removal from the forming rolls difficult. Much excess material is thus carried to the washing vats.

In my work, I have found that neutral or alkaline solutions of calcium thiocyanate crystallize much less readily than acid solu- I cium thiocyaia'te which I prefer to use, with a boiling point of about 134 0., although viscous, showno tendency to crystallize at .ordinary temperatures, and the addition of formaldehyde reduces the viscosity of such solution and actually increases the gelatinizing action.

In the process of the aforesaid patents and the present zincchloride process, gelatinization of the cellulose takes place in the treat ing bath. Consequently, the fiber leaving the bath is very tender and requires extreme care in handling to avoid damage.

In my process, gelatinization does not take place to any substantial extent in the treating bath and the issuing fiber contains much of its original mechanical strength. The sheets can be removed from the forming roll without diificulty. Furthermore, hard fiber produced by my process. isv not subject to that tendency to blister which at present is the cause of a great deal of annoyance and loss to the manufacturers of vulcanized fiber. Blistering is caused by the presence in the paper of spots which have not been gelatinized to the same degree as surrounding areas and, therefore, do not adhere to the adjacent laminations in the fiber sheet. Especially in the zinc chloride process, the extremely brief period of time which is al-.

lowed for subjecting the paper to the action of the bath makes uniformity of degree of gelatinization very uncertain. A dense area in the paper being treated, being relatively less absorbent than the surrounding paper, will be insufficiently gelatinized.

My process has a further advantage with' respect to the present zincchtoride method in that the fungus growth which occurs in fiber treated according to the prior method,

especially during Warm months, and resulting in the formation of white and friable spots, is not incident to the treatment of fiber according to my invention. Obviously, fiber made from solutions containin ap-' .material which comprises treating it with a solution of formaldehyde and calcium thiocyanate, the latter not being present in sufficient amount to cause crystallization at 'atmo%heric temperatures.

3. he process of gelatinizing cellulosic material which comprises treating it with a solution of calcium thiocyanate and formaldehyde at substantially atmospheric temperatures, and allowing the treated material to gelatinize.

4. The recess of producing vulcanized 1 fiber whic comprises treating paper with a solution of calcium thiocyanate and formaldehyde, allowing the treated paper to stand until gelatinized, and converting the thereby gelatinized paper into vulcanized 5. The process of producing vulcanized fiber which comprises treating paper with a solution of calcium thiocyanate of such concentration as to have a boiling point of 20 from 130 to 140 0., and containing formaldehyde, allowing the treated paper to gelatinize, and sub ecting it to finishing operations to convert it to vulcanized fiber.

6. The process of producing vulcanized 28 fiber which comprises treating paper with a solution composed of substantially 3 parts of an 80% solution of calcium thiocyanate and one art of formaldehyde and converting the t ereby treated paper into vulcana0 ized fiber.

7. The process of producing vulcanized fiber whic comprises treating paper with a solution composed of substantially 3 parts of an 80% solution of calcium tlnocyanate 85 and one part of formaldehyde, and of neutral or slightly alkalinereaction, and converting the thereby treated paper into vulcanized fiber.

In testimony whereof, I have hereunto 4 subscribed my name thisfifteenth (15) day of March 1927.

RGBERT R. FULTON.