Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments

Definitions

• the paper with" the wet coating material on its surface is pressed against, a solid casting surface and dried with the coating in intimate contact therewith until the coating material has set or hardened sumciently to no longer adhere to the casting surface.
• the finish on the coated surface of the paper is an accurate replica of the casting surface. Because of the impervious nature of the casting surface, it is a characteristic of this process that at, least enough drying to bring about the necessary setting 'of the coating must be accomplishedby transmission of'moisture from the coating through the fibrous web to the point where evaporation can take place.
• the primary object ofthe present invention process, considerably decreases the length of time which is necessary to dry the paper in contact with the casting surface.
• time required for evaporatlon'can be materially decreased if a large increase is made in the amount of water which must be evaporated, or, a substantial increase in' operating speed is made possible by a large increase in the amount of evaporation which must take place.
• this same wetting of the back of the web serves to largely neutralize the usual tendency of finished paper to curl towards the side which has been wetted by the coating composition.
• This wetting. is preferably done while the web is in contact with the casting surface, but may sometimes be accomplished with advantage before the freshly-applied coating is pressed into contact with the finished casting surface and either before or after the coating operation. It is most advantageously accomplished as soon as possible after the coated'web has been pressed into contact with the castin surface and before the heated metal has had time to materially heat the coating material. The longer the interval is to increase the rate. of drying whereby the between the pressing of the web onto the casting surface and the wetting of the back, the less effective is the wetting in reducing the drying time, until, if the wetting is not accomplished until the coated web is substantially dried, it serves only to correct the tendency to curl and does not make possible any increase in the speed of operation.
• the exact amount of water used does not appear to be critical. with types of paper such as are generallyused as bases for coating, I find that the purposes of the present invention are accomplished by wetting with the amount of water which the surface of the paper will freely take up without prolonged soaking. Any convenient method of wetting may be used. For example, the back of the web may be flooded with water and the excess then removed from the surface. If the wetting is done while the paper is on the casting surface, the excess water may.
• a yielding wiper of felt, rubber, or the like or it may advantageously be removed by a flat, uniform jet of air which is directed backward against the oncoming web of freshly wetted paper. If the wetting is done when the paper is out of contact with the casting surface, the excess may be-removed by one of the aforementioned methods or by wiping over the rounded edge of afixed blade. Alternatively a properly regulated and controlled amount of water may be applied according to known methods by sprays, rolls, etc. so that there is no excess to be removed, but it is usually more satisfactory to apply an abundance of water and remove the excess by simple means such as above described.
• the procedure now practiced is to press the paper with the wet coating into contact with the casting surface and as soon as possible thereafter to flood the back of the web with water by means of a shower or the like, and then almost immediately to remove the unabsorbed surplus by a high velocity air jet blowing backwards against the oncoming freshly wetted paper surface.
• wetting the back is found to make possible a considerable increase in the operating temperature of the casting surface without. causing the defects which usually accompany such increases. This may be due'tolocal cooling of the casting surface which prevents excessive temperaturesdrying on the locally cooled area appears to materially shorten the total drying time required without deleteriously affecting the quality of the final product.
• This invention when applied in the preferred form as described, has been found to make possible increases of from twenty-five to fifty per cent or more, in the speed of operation of the process of the aforementioned patent as heretofore practiced. It therefore makes possible increases up to fifty per cent or more in the plant capacity and in the production obtainable from the same equipment without any sacrifice in quality of the finished product.
• the invention may also advantageously be applied to the manufacture of cast surfaced coated paper according to the modified process as disclosed in Patent No. 2,029,273, preferably by wetting the back of the web just after it is pressed into contact with the coating on the drum. Any of the above described procedures may, however, be used'if desired.
• the paper to which the fresh coating is ap plied may be of any desired weight, and if desired, may previously have been coated with a I claim: l.
• the step which comprises applying .water to the exposed back side of the paper web while said coated side is in contact with said casting surface.
• the process of making cast-surfaced-coated paper which comprises: the application of aqueous coating to one side of a pa or web; the pressing of the paper and coating on a finished casting surface; followed, before any substantial evaporation of water from the coating material, by the application of water to the other side of the web; and the evaporation of said applied water and of aqueous vehicle from the coating composition, from the exposed side of the web, while the coating is in intimate contact with the castin surface.
• The-process of making cast-surfaced-coated pape which comprises: the application of aqueous coating to one side of a paper web; the pressing of the paper and coating onto a finished casting surface followed substantially immediately by a flooding of the back of the web with water andthe substantially immediate blowing on of the unabsorbed surplus water therefrom;
• the step which comprises plied to a web of paper and, the coating dried in contact with a finished casting surface, .with evaporation of moisture from the coating through the paper web and from the exposed side thereof, the improvement which comprises applying water-to the webother than by absorption from the coating, and in amount sufficient to wet the applying water to the back of the paper web substantially immediately after the coated side has been brought into contact with the casting surface.
• the step which comprises promptly applying water to the exposed uncoated side of the paper web after the coated side has been brought into contact with the finishing surface.

Landscapes

• Paper (AREA)

Priority Applications (4)

Applications Claiming Priority (1)

Publications (1)

Family

ID=23348365

Family Applications (1)

Country Status (4)

Cited By (9)

• 1940
  • 1940-07-05 US US343950A patent/US2360919A/en not_active Expired - Lifetime
• 1941
  • 1941-07-23 GB GB9354/41A patent/GB546801A/en not_active Expired
• 1945
  • 1945-11-22 FR FR917902D patent/FR917902A/fr not_active Expired
• 1946
  • 1946-05-07 BE BE465058D patent/BE465058A/xx unknown

Also Published As

Similar Documents