US2941255A - Process for treating film - Google Patents

Description

June 21, 1960 F. E. HOFFMAN 2,941,255

PRQCESS FOR TREATING FILM Filed Sept. 14, 1955 INVENTOR FRANK E. HOFFMAN BY WW ATTORNEY shaft.

United States Patent() PROCESS FOR TREATING FILM Frank Edward Hoffman, Camanche, Iowa, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Sept. 14, 1955, Ser. No. 534,351

1 Claim. (Cl. 1S--57) The present invention relates to the processing of traveling web material and more particularly to the wet processing of regenerated cellulose film.

In the manufcature of regenerated cellulose film, viscose solution is extruded (cast) through the lips of a hopper into a tank containing a coagulating and regenerating medium. The gel film, as cast, is then led in serpentine fashion over and under rollers through several purification, washing and softening tanks and finally through a dryer. The details of the process are described in US. Patent 1,548,864.

The dried film is wound on a roll and, when examined prior to coating and slitting, may show-raised areas along its length. These raised areas may not he very significant on a a single thickness of film but, when wound on a roll, overlapping raised areas appear as unsightly ribbons throughout the length of the film. These bands, called gauge bands, cause stretching of the film in the immediate ,vicinity of the hands. When the roll is slit into narrower widths, the film strips showing the effects of the gauge hands are discarded. This may amount to discarding as much as 20% of the film.

Attempts to minimize the loss of film due to this cause have ranged from increased cleaning schedules on all equipment that contact the traveling film (squeegees, rollers, etc.) to efforts to remove the bands mechanically or chemically during drying. None has proved successful.

The present invention overcomes the situation in a surprisingly simple manner. It comprises reciprocating the traveling web of gel film at any stage during wet processing, but prior to the application of a softener to the fihn in a direction transverse to the direction of travel. For a web of conventional width, 30-50 inches, the amount of reciprocation need only be A to 1 /2 inches on either side of the center line of the film.

in the accompanying drawings, a preferred apparatus for accomplishing the above result is disclosed.

Figure 1 is a side elevation of the apparatus.

Figure 2 is a sectional view along 2--2 of Figure 1.

Figure 3 is a sectional view along 33 of Figure 2.

The traveling film 17 is led from tank 11, after passing under roller 13, over roller 15 to roller 16 and then under roller 14 in tank 12. The film is reciprocated while it passes over positioning roller 16. To accomplish this, roller 16 is mounted on shaft 18, one end of which is pivotally held by bolt 31 between brackets 19 and 29. The brackets are mounted on a support 25'extending from one wall of tank 12. Slots 21 are provided in the brackets to permit adjustment of the height of the A threaded rod 22 provided with wing nuts 23 and 24, serves to set and maintain the height of the shaft 18. The height is set so that the center line of the film corresponds to the center line of the machine A ice 2 and reciprocation will, occur on either side of this'center lines I i ;A plate 26 is freeto move up and down between guide brackets 20 and 30. These latter brackets are mounted on a support, 27, extending from a wall of tank 12. Two circular openings are out out of the plate; a lower opening 27 to receive one end of shaft 18, and an upper opening to receive an offset shaft 28. An additional support 32 is provided adjacent the tank 12. A variable speed motor 33 is mounted on support 32 and a cam 34 is mounted on the shaft of motor 33. The cam 34 cooperates with the offset shaft or rod 28 to raise and lower the plate 26 periodically as the cam rotates. This movement of the plate also raises and lowers the shaft 18 and accompanying roller 16, thus serving to reciprocate the film 17 as it passes over roller 16. This in turn causes the traveling film to track from side to side as it progresses through the washing operations, the softening treatment and the dryer. As the film moves from side to side, any imperfections in the film sheet tend to shift from side to side. The result is that the film, as wound on the final roll, has the imperfections scattered across its width rather than piled over a narrow area. Thus, the gauge hands are prevented. The speed of the variable speed motor is dictated by the intensity of the gauge band problem. In general, motor speeds of Va to /5 revolution per minute have proven satisfactory.

Although an offset shaft 28, in combination with a moveable plate 26 has been shown in the drawings, it is possible for the cam and motor arrangement to act directly on shaft 18. A smooth rod over which the wet film will slide without scratching may be used in place of roller 16 and shaft 18. For convenience in operation, however, the illustrated design is preferred.

When the device was used in the wet processing of regenerated cellulose film having a width of from 30 to 50 inches with a reciprocation of A to 1 inch, the number of rejected rolls (as slit) was reduced from 20.5% to 3.71% of the total slit rolls. In another case where a different type of regenerated cellulose film was being processed, the rejected rolls were reduced from 4.05% to zero. In still another case, rejects fell from 6.65% when the reciprocating device was not used to 0.64% when it was used.

The commercial advantages are immediately obvious. The amount of film that formerly had to be discarded is reduced at least five-fold. The device for accomplishing this result is simple to install, requires little maintenance and is easily adjustable. It is believed that the device will be useful wherever traveling webs of film such as regenerated cellulose, cellulose acetate, polyethylene, polyesters, etc. must be processed with liquids in a continuous manner.

As many different embodiments may he made without departing form the spirit and scope of this invention,

it is understood that the invention is not limited except (References on following page) l ,9 ,205 References Cited in the file of this patent 2,476,070 UNITED STATES PATENTS $32 32? Marshall June 15, 1909 Hill "Iune 29, 1926" 5 Davis Sept 13, 193s- 385,783 1,062,707

Solliday July 12, 1949 Smith'et a1. Jan. 11, 1955 Russell Mar. 29, 1955 FOREIGN PATENTS Great Britain Jan. 5, 1933 France Apr. 27, 1954

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