US1976873A - Removing solvents from plastic colloids - Google Patents

Description

l atented Got. 16, 1 934 llNl'lEfi STATES REMOVING SOLVENTS FRGM PLASTIC CQLLOIDS Harry P. Bassett, Cynthiana,'ly.

No Drawing. Application .lune 26, 1931, Serial No. 547,191

7 Ulaims. (Cl. 18-51 This invention relates to a process of removing solvents from semi-solid or plastic colloids and in its specific embodiment relates particularly to the removal oi solvents from cellulose nitrate plastic compositions such as celluloid.

The principal object of this invention is to provide a simole and eiilcient process of removing solvents from plastic colloids whereby a product or superior quality is obtained and the r 10 moval of solvents is accomplished in a relatively short period as compared with the time required in similar processes heretofore generally employed.

An important object of this invention is to provide a simple, rapid and efficient process of removing solvents from nitro-cotton or similar plastic compositions which is substantially free from the disadvantages commonly encountered in the proce heretofore generally employed for similar purposes.

A further object of this invention is to provide improved process of preparing celluloid or other plastic sheets which are particularly adapted for use in rnaiiin shatter-proof glass.

Other objects and advantages of the invention will become apparent during the course or" the following description. 7

I have discovered a simple process for removsolvents from freshly formed or partially finished plastic colloids such as vulcanized fiber,

celluloid, and the like, which process not only is particularly effective in removing the solvents but produces finished products of superior qualities and appearance. While, as suggested, the

process is applicable for use for removing solvents such as zinc chloride from plastic compositions such as vulcanized fiber, the invention is particularly adapted for application in the removal of solvents from cellulose nitrate plastic.

compositions, particularly celluloid. The process is based on my discovery that solvents may be removed from plastic colloids Without harm to the quality or color of the final product by exposing such colloids to an atmosphere of the vapor of a nonsolvent of the colloid which is miscible with the solvent in the colloid and thereafter heating the colloid in a dryer at gradually increasing temperatures between the approximate limits of 100 F. and 160 F. In the preferred practice of the process the vapor bath or atmosphere to which the colloid is initially exposed contains a major proportion of the solvent-miscible nonsolvent of the colloid, the concentration of which in the atmosphere is reduced during the process, the heating of the eierrcd to being of e concen- "old and becolloid in started a; tration as the nonsolve is mi cible with the solven cordingly, in preferred p iy formed or partially le plastic colloid to be treated to the action or an tinosphere of water vapor. While the per entage of the water vapor present in the vapor bath atmosphere may be varied to a considerable extent, i found that ii proved results are obtained if the water vapor is in such an: cunt that the relat midity oi the atmosphere 1 the v no bath is about and preferably in the neighborhood of "26%. While various vapors or gases may be employed the di ing factor in the vapor bath, air is the obvious a fluid to be employed for this purpose and c.nce fully satisfactory results are obtaine when air is employed, I recommend its use. Thus, in preferred practice the plastic colloid im ally subjected to a vapor bath of air and water vapor, relative humidity in which atmosphere is above 75% and preferably about 75% After subjecting the colic 1 cc, 1 subject a fresh- 5 1 b0 such an atmosphere for from several hours to se eral days, depending upon the nature, size, thickness, etc. of the colloid under treatment, the concentration of the water vapor in the bath is preferably reduced so that the relative humidity of the resulting a mosphere is materially lowered, say to 40%. Thereafter, the content water vapor is lowered ag in, preferably to such an extent that the resuiting atmosphere will have relative humidity of about 15%. Of course, the lowering of humidity may be more gradual than just indicated, if

desired, but I have found that a more gradual reduction in the concentration of water vapor in the atmosphere is not necessary general practice. Either after the original humidity of the vapor bath has been lowered, to say. about 46%, 1 or after the reduction or" the to the lowest point to which it is to be lowered (or at any intermediate point, for that matter), the colloid is heated to a temperature of say 160 F. and the temperature is gradually raised, over a period of from several hours to several days, to a more elevated temperature which ordinarily should not exceed 160 F. As stated above, the temperature is gradually increased as the humidity of the vapor bath is gradually decreased. After the atmosphere for about five days.

completion of this treatment it will be found that the solvents present in the colloids are substan tially removed and the products are in condition for general use.

Whereas, in accordance with the preferred embodiment of the invention, solvent is to be removed from cellulose ester colloids, the freshly formed articles which may be obtained either by slicing a block of the partially finished plastic colloid or by extruding a plastic colloid mix, are suspended in a chamber which may conveniently be a drying chamber of conventional type for ageing or seasoning plastic colloid articles. In the initial stage of the process the vapor treating bath is introduced into the drier preferably by causing water vapor to enter from the bottom of the drier together with air. The drier should be provided with an outlet at the top so that there will be a current of the treating vapor through the drier. I have found it convenient to employ a cold water spray at the inlet of the drier which may be controlled to regulate the humidity in the drier. As stated above, I prefer that the atmosphere to which the freshly formed plastic colloids are initially exposed shall have a relative humidity preferably in excess of and, for best commercial practice under ordinary conditions, about 76%. The temperature of the atmosphere in the initial treatment of the articles may advantageously be normal atmospheric temperature. Such an atmosphere may be used for all thicknesses of articles in the initial treatment but the time of treatment with this atmosphere will be varied according to the particular thickness of article. For example, in the case of a plastic colloid article having a gauge of 215, I prefer to leave the article in this On the sixth day the humidity in the drier is preferably reduced to about 40% and heated air is introduced into the drier so that the temperature therein will be approximately from to 104 F. On the seventh day, the humidity is dropped to about 15% and the temperature in the drier is raised to about F. Thereafter, the temperature is raised gradually to F. for the eighth day, to F. for the ninth day, and to F. for the tenth and eleventh days. At the end of this time, the stock is fully aged and ready to be used.

As is apparent from the foregoing, a treatment for eleven days is suflicient for relatively thick celluloid articles. As articles of lesser thickness are treated, the time of treatment may be correspondingly decreased. For example, with a 60 gauge plastic colloid article, I have found that complete ageing is obtained by treatment for approximately one day in a vapor bath of the characteristics set forth above at ordinary temperature, followed by a treatment for about twelve hours at reduced humidity and a temperature of 100 F., subsequent treatment for twelve hours at 130 F., with treatment for one day at 160 F. as a final step. Of course, the increase in temperature is preferably gradual and the decrease in humidity of the vapor bath is likewise gradual. However, some satisfactory measure of success may be obtained by initially reducing the humidity to the minimum degree of humidity employed followed by the gradually increasing heat treatment.

- While I have described in detail the preferred practice of my process it is to be understood that ,the details of procedure, such as the time of treatment, the vapor bath employed, and the concentration of treating agent in the vapor bath, may be variously modified without departing from the spirit of the invention or the scope of the subjoined claims.

I claim:

l. The process of removing solvent from a cellulose ester plastic composi same and containing pla comprises treating such cello of water vapor, thereafter heating the colloid at gradually increasing temp tween the approximate lim F., and gradually reducing the water vapor in the atmosphere surroun ing said colloid during said heating.

2. The process of removing solvent from a cellulose ester plastic compotion containing the same and containing a plasticising agent which comprises exposing such colloid to atmosphere of water vapor, the relative humidity of which is above '70, thereafter heating the thus treated colloid at gradually increasing temperatures be tween the approximate limits of 100 F. and 160 F., and gradually reducing the concentration of water vapor in the atmosphere surrounding said colloid during said heating.

3. The process of removing solvent from a cellulose ester plastic composition containing the same and containing a plasticizing agent which comprises exposing such colloid to an atmosph of water vapor, the relative humidity of w o. is above 70, gradually reducing the humidity of atmosphere and, while the humidity is being reduced, heating the colloid at gradualiy increasing temperatures'between the approximate limits of 100 F. and 160 F.

4. The process of removing solvent from a cellulose ester plastic composition containing the same and containing a plasticising agent which comprises exposing such colloid to an atmosphere of water vapor, t -e relative humidity of which is approximately 76, gradually reducing the humidity and simultaneously heating the colloid at gradually increasing temperatures between the approximate limits of 100 F. and 160 F. k

5. The process of removing freshly formed cellulose nitrate plastic composition which comprises treating such composition with a bath of water vapor, thereafter heating t e composition at gradually increasing temperatures between the approximate limits of 100 F. and 160 F., and gradually reducing the concentration of Water vapor in the atmosphere surrounding said composition during said heating.

6. The process of removing solvent from a freshly formed cellulose nitrate plastic composition which comprises exposing such composition to an atmosphere of water vapor, the relative humidity of which is above '70, and reducing the humidity of said atmosphere and heating the coinposition at gradually increasing temperatures between the approximate limits of 100 F. and 160 F.

'7. The process of seasoning .eshly formed cellulose ester plastic composition sheets contr 'ng a solvent and plasticizing agent which corn woes solvent from a exposing such sheets for a period of from several hours to several days to an atmosphere of w te vapor, the relative humidity of wla proximately 76%, gradually reducing the hum said atmosphere, and heating the sheets over a period of several days at gradually increasing temperatures between the approximate limit 100 F. and 160 F.

HARRY P. BASSETT.