US 3630835 A
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Description (OCR text may contain errors)
United States Patent  Inventor Thomas W. Busch Appleton, Wis.
 Appl. No. 705,076
 Filed Feb. 13, 1968  Patented Dec. 28, 1971  Assignee Appleton Coated Paper Company Appleton, Wis.
[54} METHOD FOR COATING PAPER WITH PRESSURE RUPTURABLE FLUID CONTAINING CAPSULES 8 Claims, 6 Drawing Figs.  US. Cl 162/184, 117/156, 118/212, 162/158, 162/162, 162/174  Int. Cl D21d 3/00  Field of Search 162/1 19,
3,384,536 5/1968 Sandberg et a1.
Primary Examiner-S. Leon Bashore Assistant Examiner-Frederick Frei Attorney-McDougall, Hersh, Scott and Ladd ABSTRACT: The invention in a machine and method for onthe-machine coating of a paper web to coat one surface of the paper web with a uniform distribution of pressure rupturable liquid containing capsules wherein the papermaking machine is provided with a printing couple while the paper is in a substantially uncured state with one roll of the couple comprising an impression roller having a resilient surface and the other roll comprising a printing roll having a multiplicity of cells uniformly distributed in closely spaced-apart relation in the peripheral surface of the roll with means for application of the fluid composition containing the rupturable capsules in suspension onto the peripheral surface of the roll in an amount at least sufficient to fill the cells and means for doctoring the peripheral surface of the roll to remove coating composition from the area between the cells whereby, when the paper web is advanced in pressure contact between the roll pair, substantially pressureless transfer occurs of the coating composition in the cells to the adjacent side of the paper web to coat the paper web with the pressure rupturable capsules as a continuous operation with papermaking.
METHOD FOR COATING PAPER wmi PRESSURE RUI'IURABLE FLUID CONTAINING CAPSULES This invention relates to paper base material having rupturable, liquid containing, microcapsules on one surface thereof and to a new and improved method for the preparation of same.
Paper of the type described finds many uses, as will hereinafter be described. Most representative for the present is usage as one of the components of a carbonless copy paper system in which use is made of one sheet having the layer of microcapsules containing undeveloped oil soluble dyes dissolved in droplets of a water insoluble organic fluid. The droplets are encased in a thin wall of tanned gelatin in the form of microcapsule aggregates having an average diameter within the range of 8 to 12 microns. The other component employed in combination with the described capsule containing sheet is a sheet of paper having a special mineral or clay coating adapted to be positioned in intimate contact with the capsular coating in the assembly for transfer of underdeveloped dye liquid from the ruptured capsules to the adjacent mineral coating for development of the dye color.
In a conventional commercial assembly, the carbonless copy paper system consists of a first or top sheet coated on its back side with the microcapsules and a second sheet coated on its front side with the special mineral coating. In a typical multiple sheet assembly, such as a five-part sales form, the three intermediate sheets will be coated on their front sides with the special mineral coating and on their back sides with the described microcapsular system while the top sheet is coated on its .back side only with the microcapsular system and the bottom sheet coated only on its top side with the special mineral coating.
The front or special mineral coating more closely resembles an ordinary paper coating. Since it does not contain any rupturable or other pressure sensitive materials, it can be produced economically and successfully as a coating applied as a part of the continuous paperrnaking process since it can be calendered or finished, as the case may be.
Because the microcapsules are pressure sensitive and are capable of being ruptured in response to pressure of the magnitude encountered in mechanical nips of a paper machine, it has been the practice to make application of the microcapsular system as a separate operation applied onto the previously fabricated paper base sheet. For this purpose, use has been made of a composition in which the microcapsules are admixed with adhesive, lubricating pigment such as talc, and cellulosic fibers which operate to protect the capsules from premature rupture in the coating.
The described ofi'-the-machine coating of the microcapsular system poses a number of requirements including I additional machinery for such separate off-the-machine coating; (2) additional floor space for such separate operation and equipment; (3) movement of paper from the paperrnaking machine to the described separate coating operation in which packaging, shipping and labor represent additional costs; (4) additional waste resulting from a two-stage process, and (5) procurement of paper as a separate commodity with its attendant costs, etc.
Thus it is an object of this invention to provide a new and improved method and means for the production of a paper base material having rupturable microcapsular material on at least one surface thereof and it is a related object to provide a method of the type described which can be carried out on the paperrnaking machine materially to reduce the cost thereof; which provides for economical and efficient utilization of the encapsulated material; which provides for uniform coating of the encapsulated material in a layer well bonded or integrated with the paper base sheet; and which can be applied as a continuous operation without an excessive rupture of the capsules and which produces a product of good appearance and capable of use in the development of copy of good quality.
These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawings in which FIG. I is a detailed elevational view of the roll applicator embodying the features of this invention;
FIG. 2 is a partial plan view of the roll surface formed with pyramid cells;
FIG. 3 is a view similar to that of FIG. 2 with the surface formed with trihelical cells;
FIG. 4 is a view similar to that of FIGS. 2 and 3 with the surface formed with quadrangular cells;
FIG. 5 is a view similar to that of FIG. 2 with the surface formed of hexagonal cells; and
FIG. 6 is a schematic view of a paperrnaking machine embodying the features of this invention.
In accordance with the practice of this invention, application of the microcapsules is made at a point in the operation of the paperrnaking machine which occurs after the web has been formed as an uncured web or partially cured web so that the applied coating will enable the capsules to become partially embedded with the fibrous structure on the surface of the paper while, at the same time, eliminating the uneconomical features of excessive capsule loading of the paper web or loss of capsules with the water drained from the sheet during the web forming process.
In the preferred practice of this invention, modification is made of a paperrnaking machine at a point after the web has been formed but before the internal water resistance of the paper web has been developed, to insert a processing step for application of the microcapsule containing coating composition. For this purpose, use is made of a roll pair between which the formed web 10 is passed for engagement between the peripheral surface of the rolls. One roll 12 of the roll pair is formed preferably, but not necessarily, with a surface 14 of resilient material while the other roll 16 of the roll pair is in the form of a cylindrical roll having its peripheral surface etched or otherwise formed to define a multiplicity of closely spaced cells and which has a doctor blade or wiper 18 in engagement with the peripheral surface of the etched roll 16 in advance of engagement with the web 10 to remove coating composition from the surface other than that filling the cells thereby to provide a direct gravure type printing station for the pressureless application of the capsular coating in uniform distribution onto the surface of the paper web 10 as the peripheral surface of the cylinder 16' comes into contact with the one side of the paper web.
The applicator cylinder 16 is etched, engraved or otherwise formed with thousands of minute recessed cells which are capable of being filled with the emulsion of rupturable microcapsules with the lands between the cells forming the relatively true cylindrical surface. The cells can be formed with various configurations such as of the type referred to in the rotogravure art as pyramid cells, trihelical cells, quadrangular cells, hexagonal cells and the like cells of various cross sections or configurations uniformly distributed over the entire peripheral surface of the cylinder. The depth of the cells will be efiective to determine the amount of fluid retained in the cells after the peripheral surface of the cylinder has been cleaned by the wiper blade 18.
As the etched cylinder revolves, the lower portion, immersed in a bath 20 of capsular coating composition, picks up an excess of liquid on its surface. Surplus liquid is removed by the doctor or wiping blade 18 to leave the surface clean while capsule containing liquid remains substantially to fill the cells. A system of the type described is self-flushing whereby any foreign fibers or material picked off the web will be removed so that little will remain on the roll surface to introduce defects in the applied coating.
As the cylinder continues to revolve, the capsule containing fluid composition remaining in the cells transfers from the cylinder to the adjacent surface of the web in response to pressure exerted by the resilient surface 14 of the impression roll 12 of the roll pair. The impression roll presents the web 10 against the surface of the etched or engraved roll 16 whereby the capsule containing liquid becomes displaced from the cells to the web primarily by capillary action and the affinity of the uncured paper for the capsule containing fluid.
Because the resilient surface of the impression roller 12 makes uniform contact across the face of the engraved or etched cylinder 16 and because pressure is hydraulically applied, variation in paper thickness has little influence on the uniform distribution of the capsule containing liquid thereby to provide for uniformity in deposition from run to run and over large runs. By proper selection of cell dimension, such as width, depth and shape, it becomes possible to effect uniform control of coating weight.
Since the capsules are applied during a stage of web formation which enables the capsules partially to become embedded in the fibers at the surface of the web, it becomes possible to make use of a coating composition of emulsified capsules without the need of floc and/or cellulosic fibers for protection of the capsules, as in compositions heretofore employed in offthe-machine coating although such materials may be employed in coating compositions applied in accordance with the practice of this invention if necessary.
It will also be apparent that the capsule containing liquid retained in the cells is not subjected to excessive pressures for transfer such that the capsular coating can be transferred in any desired concentration without the danger of capsule rupture, as in other coating processes.
It will be apparent further that the overall pattern of cells in the surface of the applicator cylinder will provide for the printing of a relatively uniform and substantially continuous coating over the entire surface of the paper web with application thereof being made to the surface so that the capsules will be deposited at the point for most efficient utilization thereby to make maximum use of the capsules making up the coating composition.
Since the composition of the capsule containing coating does not constitute a part of this invention, detailed description thereof will not be made. Suffice it to say that such coating composition may be formulated in an aqueous system containing capsules having an average size of from 7 to 9 microns, with or without starch, talc or floc, and in a solids concentration within the range of 18-24 percent in which the amount of emulsified capsules may be within the range of l3-22 percent. The composition can be applied in appropriate coating weights of 2% to 3% pounds per 3,300 square feet of surface area.
By way of example, use can be made of a cylinder having a 50 trihelical etch pattern corresponding to 30-40 micron bridges and 48-50Xl0 cubic micron cell volume.
Having described the basic concepts of this invention, illustration will now be made with respect to the utilization thereof as a part of a conventional papermaking machine.
Referring now to FIG. 6 of the drawing, illustration is made schematically of a typical papermaking machine which operates continuously to produce an endless web of paper but which has been modified to embody the printing couple of this invention. The machine includes a head box 30 at the head end of the machine which contains the pulp slurry that is spread uniformly over the width of the continuously moving endless screen 32 which filters the cellulose fibers in interfelted relationship on the surface thereof to produce the wet web 34 as water drains through the screen 32. By the time the web reaches the delivery end of the screen, it has adequate self-sufficiency to permit removal from the screen for passage first through a series of felted press rolls to compact the web of interfelted fibers and then through a drying section 38 which reduces the amount of water in the paper web. Before the paper web is completely dried and before it is calendered and preferably while it is still in the uncured stage, the paper web is advanced in continuous fashion and at forming speed through the printing couple including the impression roller 12 and the engraved printing roller 16 whereby the coating of emulsified capsular material is transferred by substantially pressureless transfer onto the ad'acent side of the paper web. Thereafter the coated paper we can be further processed as by advancement through driers 40 and finishing rolls 42, with and preferably without light calendering before the coated paper web is collected on the reel 44 and subsequently sheeted. As in the case with conventional on-the-paper-machine coating, supplementary drying or Teflon covered drier drums may be required following the coating application to prevent transfer of the wet coating to the drier drum surface. This may be required to make the process practical at high speeds, but it is not foreign to the papermaking art.
The impression roll 12 may be formed of a rubber roll having a metallic core or it can be formed of a metal roll having a surface coating or blanket of resilient, rubberlike material. The rolls are adapted to be driven by conventional means at a peripheral speed corresponding to the linear speed of the paper in the paper-forming operation.
Aside from the described use as a colorless carbon system, the sheet with the capsular coating finds many other uses, such for example as a wiping cloth when the capsules are filled with a suitable lubricant liquid or dusting liquid, as a pressure sensitive label or wall paper when the capsules are filled with a liquid adhesive, as a cologne when the capsules are filled with suitable perfume oils, and numerous other applications which will become obvious.
It will be understood that changes may be made in the details of construction, arrangement and operation without departing from the spirit of the invention, especially as defined in the following claims.
1. An on-the-machine" coating method for producing a sheet of paper having a surface coated with pressure rupturable fluid containing capsules comprising the steps of passing a paper web continuously before it has been completely cured through a roll couple, one of which is an impression roll and the other of which is a printing roll having an overall pattern of uniform closely spaced cells in the peripheral surface, wetting the peripheral surface of the latter roll with a fluid composition containing the rupturable capsules in unifonn suspension therein and in amounts to at least fill the cells, removing excess coating composition from the peripheral portion of the roll between the cells before the peripheral surface of the roll comes into contact with the paper web and then bringing the peripheral surface of the printing roll into contact with one side of the paper web while the opposite side is engaged by the impression roll whereby fluid coating composition transfers without excessive pressure from the cells to the adjacent surface of the paper web to coat the surface of the paper web with the pressure rupturable capsules.
2. The method as claimed in claim I in which the roll couple makes pressure engagement with the opposite surfaces of the paper web as it is advanced therebetween.
3. The method as claimed in claim 1 in which the paper web is in the form of an uncured paper at the time that it is advanced between the roll couple.
4. The method as claimed in claim 1 in which the impression roll comprises a roll formed of a resilient material.
5. The method as claimed in claim 1 in which the impression roll is a metal roll having a blanket formed of a resilient material.
6. The method as claimed in claim 1 in which the cells in the printing roll are etched into the surface of the roll.
7. The method as claimed in claim I in which the cells in the printing roll are engraved in the surface of the roll.
8. The method as claimed in claim 1 which includes the step of drying the applied coating.