Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C71/00—After-treatment of articles without altering their shape; Apparatus therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C59/00—Surface shaping of articles, e.g. embossing; Apparatus therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
  • B29D7/00—Producing flat articles, e.g. films or sheets

Definitions

• This invention relates to the manufacture of regenerated cellulose film. More particularly, this invention relates to a method for improving the dimensional stability and appearance of regenerated cellulose films.
• a puckered film will eventually flatten out as moisture equilibrium is reached in all parts of the film; rippling, however, persists as long as the film is exposed to the high humidity. Rippling has been a particularly serious problem on those films which have been promoted as a premium quality film giving improved appearance on the package.
• Rippling of cellophane at high humidity is caused by simultaneous machine direction shrinkage and transverse direction expansion of the film on an overwrap package when the moisture in the film is increased.
• an object of this invention to improve the dimensional stability of regenerated cellulose films.
• a further object of this invention is to provide a method for producing substantially rippledree regenerated cellulose films.
• a still further object is to provide a method for producing such films while maintaining good film flatness and good appearance.
• the present invention comprises, in a process for improving the dimensional stability of regenerated cellulose film, the improvement which consists in: (1) drying softened gel regenerated cellulose film to about to moisture while applying 2 to 4% draw, (2) further drying the said film to about 25 to 60% moisture while permitting about 1.5 to 2.5% relaxation, and (3) completing said drying to about 3.0 to 7.5% moisture while applying from about 0.5 to 1.0% draw.
• the drying in step (2) will be conducted to about 25 to 35% moisture.
• percent moisture refers to the percentage of Water present based on the dry weight of cellulose over and above the dry weight of the cellulose itself (e.g., 50% moisture means for every grams of wet cellulose, 50 grams of water and 100 grams of dry cellulose are present).
• percent draw means the percentage extension of length of the film caused by stretching in the machine direction.
• applying draw means the step of extending the length of the film in the machine direction by a given percentage of its original length.
• percent relaxation is the opposite of the term percent draw and refers to the percentage decrease in length of the film caused by shrinking in the machine direction.
• permitting relaxation refers to the step of decreasing the length of the film in the machine direction by a given percentage of its length by taking advantage of the tendency of the moist film to shrink. Specific means for accomplishing draw and relaxation of the film will appear hereinafter.
• soften gel regenerated cellulose refers to regenerated cellulose in a gel condition containing about 3.0 to about 3.5 times the weight of dry cellulose as water. Further clarification of this term will appear hereinafter.
• the process of the present invention is generally applicable to the drying of continuous Webs of any wet cast cellulosic film.
• such film constitutes the preferred material for treatment in accordance with theprinciples of the present invention.
• the pr'esefit invention is concerned with the drying stage of the above-described process of manufacture.
• the web is passed over a second series of conventional dryer rolls driven at a peripheral speed 1.5 to 2.5% lower than that of the preceding rolls to effect a decrease in, or a relaxation of, the tension of web.
• the moisture content of the film is reduced to to 60% after which the film is passed through an additional series of conventional dryerrolls drawn at a peripheral speed of from 0.5 to 1.0% greater than that of the rolls in the previous stage to exert 0.5 to 1.0% draw on the film.
• the moisture content of the film is reduced to about 3.0 to 7.5% moisture based on the weight of dry cellulose.
• the table below indicates the various tension patterns used in eight different examples with the resulting distortions having been produced by subjecting the finally dried regenerated cellulose films to the distortion test which will be described below.
• MD indicates the distortion in millimeters in the machine direction
• TD indicates the distortion in millimeters in the transverse direction after the samples have been subjected to the distortion test.
• Each of the film samples was supported against a frame having the approximate dimensions of each film sample, and the film sample was fixed at the top of the frame so that its long dimension was running vertically when the frame was hung in a conditioning chamber. A 20 gram weight was clamped at the bottom of each film. The frames to which each film sample was afiixed at one end thereof were hung in a room maintained at 81% relative humidity and 85 F. The change in dimensions under the conditions of 81% relative humidity was recorded as change in length (in millimeters) after 72 hours. The corresponding values are recorded in the following table under MD and TD.
• the percent distortion in the machine direction (MD) and transverse direction (TD) is calculated by the follow-
• the differential distortion (expressed as percent) is calculated by the following:
• the transverse direction distortion was greater than and excessive edge droop.
• the transverse direction distortion was greater than and excessive edge droop.
• Flatness of a film is a characteristic of continuous films which is an important determining factor in their running abilities on converter and processing equipment.
• An absolutely fiat sheet, having no droop, is the goal of all continuous film manufacturers. Flatness is determined by stretching a film longitudinally across two carefully aligned, horizontal parallel supporting rolls or bars 15 feet apart. The film ends are rigidly held and tension is applied longitudinally to the film over the unsupported span of 15 feet. The contour of a transverse section of the film at approximately the center of an unsupported span is observed and the major departures from the straight, horizontal line are measured in inches.
• This invention provides for the production of a trade acceptable film from the standpoint of rippling, while maintaining good appearance and the desired film flatness.
• the improvement which consists in: (1) drying softened gel regenerated cellulose film to about to moisture while applying 2 to 4% draw, (2) further drying the said film to about 25 to 60% moisture While permitting about 1.5 to 2.5% relaxation and (3) completing said drying to about 3.0 to 7.5% moisture While applying about 0.5 to 1.0% draw.
• step (2) Process according to claim 1 wherein the moisture in step (2) is from about 25 to 35% moisture.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)
• Shaping By String And By Release Of Stress In Plastics And The Like (AREA)
• Moulding By Coating Moulds (AREA)

Priority Applications (6)

Applications Claiming Priority (1)

Publications (1)

Family

ID=22008701

Family Applications (1)

Country Status (5)

Cited By (2)

Citations (3)

• 0
  • NL NL269406D patent/NL269406A/xx unknown
• 1960
  • 1960-09-20 US US57133A patent/US3068529A/en not_active Expired - Lifetime
• 1961
  • 1961-09-15 GB GB33255/61A patent/GB925635A/en not_active Expired
  • 1961-09-19 BE BE608329A patent/BE608329A/fr unknown
  • 1961-09-19 DE DE19611504651 patent/DE1504651B2/de not_active Withdrawn

Patent Citations (3)

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