US3419885A - Image depelopment of thermoplastic layers - Google Patents

Description

Dec. 31, 1968 P. P. AUGOSTINI IMAGE DEVELOPMENT OF THERMOPLASTIC LAYERS Filed Oct. 20, 1964 FIG./

Sheet of 2 FIG. 2

POWER SOURCE PowkR SOURCE INVENTOR PETER P. AUGOSTINI A T TORNEY Dec. 31, 968 P. P. AUGOSTINI 3,419,885

IMAGE DEVELOPMENT OF THERMOPLASTIC LAYERS Filed Oct. 20, 1964 Sheet 2 of 2 HEATER I I I v I a a OPTICAL I DENSITY I I a I I c I I I I l I I HEATING TIME PETER P. AUGOSTINI ATTORNEY United States Patent 3,419,885 HVIAGE DEPELOPMENT OF THERMOPLASTIC LAYERS Peter P. Augostini, Webster, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Oct. 20, 1964, Ser. No. 405,174 4 Claims. (Cl. 346-74) ABSTRACT OF THE DISCLOSURE This invention relates to thermoplastic recording and particularly to improved method and apparatus for the development of image forming thermoplastic deformable layers.

There has recently been discovered a novel image forming process capable of continuous-tone reproduction and disclosed in copending application, Ser. No. 193,277 in the name of Gunther et al., now US. Patent No. 3,196,- 011. As disclosed therein, a charged thermoplastic layer overlying a photoconductor can be optically exposed in image configuration to deform imagewise when subsequenty developed by softening. One method of softening the layer is by the application of heat thereto causing the thermoplastic to take on a microscopically uneven surface which can be described as rippled, stippled, reticulated, wrinkled or frosted. This local deformation has a milky appearance in proportion to the amount of illumination received in different areas being generally comprised of alternating ridges and valleys that recur at substantially uniform spacing with recurrently variable width and/or height. A distinctly different type of deformation also may occur depending on operating conditions and caused by fringing fields existing solely at the edge or boundary separating charged and uncharged areas. These latter fields are likewise capable of deforming a thermoplastic layer to form a relief pattern at such boundaries only. Such relief patterns may have utility per se or can generally be eliminated or minimized by softening the deformable material just long enough for the frost pattern to appear.

Whatever deformation type is desired, including other unmentioned variations disclosed in the Gunther et al. application, controlled heat softening of a charged deformable layer, such as Staybelite Ester 10, manufactured by the Hercules Powder Company, supported on a photoconductor, such as vitreous selenium, will produce the desired end result, Once produced, the image thus formed can be utilized in a variety of different ways including removal for remote utilization or be affixed to the photoconductor and used for optical projection or reflection. Subsequently, the image can be erased by the reapplication of heat usually in the presence of light uniformly applied and generally of greater intensity than that employed for developing.

Heating for development has included such well known means as hot plates, infrared sources, long wavelength sources, dielectric heating, conductive sources, convective sources, etc. to produce temperatures in the thermoplastic on the order of 180 F. plus or minus depending on the properties of the particular deformable material and the desired development time. A problem associated with heating by these prior techniques, particularly where the exposed image comprises varying gradients of density such as is associated with continuous tone type reproductions,

has been the difficulty in obtaining optimum heating uniformity in all areas of the thermoplastic for best results. As will be explained below, underheating fails to effect the required degree of deformation while overheating produces erasure. Therefore whatever heating method has been employed heretofore for development it has been found that because of various factors such as surface irregularities in the thermoplastic, imperfect surface conformance of the heating platen or the like has resulted in the inability to effect uniform thermal contact between the thermoplastic and the heating elements to handicap or limit uniformity of the final reproduction. That is, by development in acordance with prior techniques, some areas of the deformable layer have developed to optimum, while other adjacent areas have been underdeveloped and still other areas have been overdeveloped as not to realize maximum uniformity potential available in the system.

Now in accordance with the instant invention, it has been found that developing the deformable layer by means of a hot liquid material provides more uniform thermal contact, reduces dust contamination, and produces excellent and greater uniformity than heretofore, as to enable greater control over optical image density while at the same time generally achieving this result in a shorter time period than was known by prior art techniques.

It is therefore an object of the invention to effect improvements in the art of thermoplastic recording.

It is a further object of the invention to provide novel method and apparatus for developing charge bearing image deformable thermoplastic layers.

It is a further object of the invention to provide novel method of effecting thermal development of an image deformable thermoplastic layer whereby increased uniformity is obtained than heretofore.

It is a still further object of the invention to provide novel method for developing image deformable thermoplastic layers whereby greater development uniformity is achieved in a shorter development period as compared to prior development methods known in the art.

The various features, advantages and limitations of the invention will become apparent from the following description and drawings in which:

FIG. 1 is a sectional view through an embodiment of image deformable material on a support;

FIG. 2 is a sectional view through a second embodiment of image deformable layer on a support;

FIG. 3 sectionally illustrates an apparatus for effecting development in accordance with the invention hereof;

FIG, 4 is a second apparatus embodiment for effecting image development in accordance herewith.

FIG. 5 is yet another apparatus embodiment for effecting image development in accordance herewith; and,

FIG. 6 is a graph illustrating characteristic properties of frost development.

Referring now to FIG. 1, there is illustrated an image forming member designated 10, on which the method and apparatus of the invention is operable. As more fully described in the above cited copending Gunther et al. application, member 10 may comprise a support member 11, on a layer of photoconductive insulating material 12 on which is supported the deformable layer 13. Support member 11 is generally a material which is relatively electrically conductive when compared to photoconductive insulating layer 12 and may comprise, in accordance with conventional xerographic usage, such materials as alumi num, brass or other materials, including paper or glass with a transparent or other conductive coating or the like known layers.

Layer 12 generally may comprise any of the photoconductive insulating materials known to be useful in the art of xerography. Such materials preferably include such layers as vitreous selenium, sulfur or anthracene and other organic photoconductors as well as dispersions of photoconductive pigments such as zinc oxide and various resins or other electrically insulating binder materials. Layer 12 is generally characterized as being a good electrical insulator capable of maintaining a surface charge in the dark and becoming substantially more conductive when illuminated by visible light, X-rays, or other forms of actinic radiation. Thus, it may also comprise insulating layers which become more conductive upon undergoing a photochemical reaction such as described in U.S. Patent No. 3,081,165. Layers 11 and 12 should preferably have smooth surfaces.

Deformable layer 13 comprises a thin layer of material Which is generally normally soft and electrically insulating but which may be temporarily softened by the application of heat. Layer 13 may be opaque when viewed by reflection only; otherwise, it should be and normally is transparent. For illustrative purposes only, layer 13 may be considered a uniformly thick layer of thermoplastic resin typically of approximately 2 to 5 microns in thickness and having a smooth surface. Where a transparent support member is employed, rear exposure may be utilized and for which layer 13 need not be transparent, For relief imaging, material requirements are not as critical as for frost imaging and generally include a wide choice of materials having electrically insulating properties and which can be softened and set. Table I below is a partial list of materials usable for frost and/ or relief image deformation.

TABLE I Trade name Chemical type Manufacturer Piccotex Pennsylvania Industrial Chemicals Co. Piccolyte Terpene resin Do. Staybelite 5 Rosin ester Hercules Powder Co. Staybellte do Do. Piceoumaron Coumarone Pennsylvania Industrial Chemicals Co. Plccolastic D150 Styrene Do. Piceoflex 100A Polyvinyl chloride. Do.

Coumarone indene. Neville Chemical Co. Nevillac softsr Phenol modified Do.

coumarone indene. Piccolastic E125 Styrene Pennsylvania Industrial Chemicals Co. Plccolastie D125. Do. Plcco 75 I Do. Piccopale 70 Hydrocarbon (un- Do.

saturated). Piccolastlc A-50 Styrene Do. Piccolastic A-75 do Do. Velsicol X-37 Aromatic petroleum Velslcol Chemicals Co.

polymer.

Formation of an image on member 10 in accordance with the prior art may be achieved by first applying a uniform potential onto the surface of layer 13 of about 800' volts positive in a manner to produce a like opposite charge at the interface of layers 11 and 12. After charging, the image member is exposed to a pattern of light and shadow and where subjected to light the photoconductive insulating layer 12 becomes electrically conductive permitting charges bound at the interface between layer 12 and support member 11 to migrate to the interface of layer 12 and layer 13. Following exposure, surface 13 is again charged to a uniform potential which may be the same as that initially applied. In areas of previous exposure, and thus of internal charge migration, the surface of layer 13 accepts additional charge such that the electrical field is increased in regions of layer 13 corresponding to illuminated areas. Electrostatic energy in these areas is likewise increased while unexposed areas retain only the original charge. This produces a somewhat higher field in layer 13 in exposed areas such that on subsequent softening of the deformable layer, it becomes physically altered by the mechanical forces associated with the electrostatic pattern thereon. As the material of layer 13 is softened, it is enabled to fiow in response to electrostatic forces in the areas of high field which develop as a microscopically uneven surface described above as frosting and/ or relief. This localized deformation occurs, it is believed, because the electrically charged surface of layer 13 is inherently unstable, i.e. the layer is in a lower energy condition when in the deformed or rough condition than when smooth. Likewise, by effecting a high field in the non-illuminated areas as opposed to the illuminated areas, deformation can be effected in the former.

It is usual practice following development to freeze the deformation surface pattern in place as by removing the source of heat used to soften the deformable layer. Erasure of the deformed image for reuse can be achieved by employing the same procedure of applying heat of usually greater intensity than used to soften layer 13 preferably in the presence of light. Light causes dissipation of charges in photoconductive insulating layer 12 while extensive softening of layer 13 permits diffusion and neutralization of charges thereof and permits surface tensions to restore the surface of layer 13 to a smooth condition.

In FIG. 2, the deformable imaging member is designated 15 and comprises a thermoplastic layer 13 optionally supported by a conductive layer 16 in turn supported on a durable form of support layer 17 such as Mylar or the like. Imaging member 15 is processed, as is known in the art, in combination with a photoconductive insulating layer for imparting the imagewise charge densities thereon similarly as described above for subsequent deformation. For development, the imaging member is separated from the photoconductive support.

Whether the imaging member is constructed in accordance with the embodiments of FIGS. 1 and/ or 2, or otherwise as described in the Gunther et al. copending application supra, after application of the appropriate image charge on the thermoplastic surface, the member is subsequently processed for effecting development to produce the deformed image reproduction described above. In accordance with the invention hereof development is effected by means of a hot liquid presented in thermal contact against the surface of the deformable layer. The liquid employed as will be described more fully below, comprises a liquid material which at high temperatures will not chemically attack the particular choice of deformable layer and preferably will also not attack the underlying support layers thereof.

As shown in FIG. 3 a quantity of liquid material 20 is contained in an open tank 21 in which the liquid is maintained at a temperature of approximately 65-75 0., usually about 70 C., by means of an immersion heater 22 thermostatically controlled and connected to a power source 23. Supported for rotation at least partially submerged within the hot liquid is a cylindrical dispensing roll 24 rotated continuously by means of a motor 25. The surface of the roll is slightly roughened or the like in order to better retain a thin film of the liquid on the peripheral portion emerging from the tank. An electrical heating element 29 is supported distributed about the internal periphery of the roll and is effective to maintain the exterior periphery at a temperature of about 5 to 10 above the tank temperature of liquid 20. This serves to overcome the cooling effect of the liquid film being conveyed by the roll and exposed to ambient temperatures.

In order to place the thermoplastic layer of the imaging member into thermal contact with the liquid, there is provided an idler roll 30 supported spaced closely to the dispenser roll and defining a bite dimension therewith approximately corresponding to the sectional dimension of the imaging member. Development, therefore is effected by passing an imaging member between the rolls in a manner whereby the deformable layer 13 contacts the heated liquid on the periphery of roll 24. The rate of passage between the rolls is a function of the liquid temperature as well as a particular choice of deformable imaging layer 13. With a Staybelite type layer, it has been found that with this arrangement, a travel speed of approximately 10 inches per second effects high quality development in accordance with the invention hereof. With the apparatus of FIG. 3 it is apparent that imaging member need not be flexible in nature and that the liquid material contacts only the deformable layer and not the backing layer thereof. Where the latter is deleteriously effected by the liquid material, this arrangement has been found most suitable.

In FIG. 4 there is shown an apparatus embodiment in which the materials comprising the imaging member are both flexible and completely unaffected by the liquid employed for heating. As there shown, liquid 20 is likewise contained in a tank 21 and is similarly heated by means of an immersion heater 22. A drive roll 31, driven by means of a motor 32 is partially submerged below the liquid level. A plurality of guide idler rolls 33 are spaced immersed about the lower periphery of the drive roll for guiding the imaging member into and out of the heated liquid solution. Again, as before, time of immersion with this arrangement is a function of the properties of the particular material to be deformed as well as the temperature of the liquid in which it is submerged. In order to effect optimum development with this arrangement, it is preferred that each incremental area of imaging member be immersed for a period not longer than the optimum time for the particular material choice.

In FIG. 5, there is shown an apparatus embodiment in which heating is effected uniformly by applying the hot liquid against the underside support layer 17 of the imaging member without contacting the thermoplastic deformation layer per se. This arrangement is most suitable wherein the thermoplastic layer would be subject to chemical attack or chemical reaction by the heating solution in contrast to the supporting layer which is not. This approach is similarly advantageous where the liquid is characterized by excessive electrical conductivity. Also, this embodiment can be utilized as a heating method by which to maintain the thermoplastic layer dry during the development step. The apparatus thereof includes an open tank 35 having peripheral ledges 36 to which is secured a sealing gasket or the like 37 to support the imaging member in reasonably liquid-tight relation to the tank opening. Liquid 38 is circulated through the tank into contact with the underside of the imaging member by means of a circulating pump 40, the eye of which is connected to a drain port 41 in the lower portion of the tank. The pump circulates the liquid through a conduit arrangement that connects to tank lower openings 44 and 45 and which includes a liquid tank heater 46. A thermostatic element 47 supported in the conduit system controls operation of the heater for maintaining liquid temperature in contact with the imaging member. Baffies 48 and 49 are effective in producing slight turbulence and in ensuring a continuous fiow of uniformly heated liquid in contact with the imaging member 15. After operating the pump 40 for a controlled time period in order to effect development, the pump is de-energized to stop circulation after which the developed image member can be removed.

Heat development for thermoplastic recording can be understood by referring to the characteristic curves contained in FIG. 6, which graphically illustrates optical density of frost build up and decay (or erase) during the development step. Three curves representing the kinetics of development at one specific temperature are plotted corresponding to three possible electrical charge density levels Where level w is greater than level 11 and 1 is greater than 0 Different temperatures would result in similar curves excepting for the time intervals which change inversely because of a corresponding change in the thermoplastic response time to achieve the same development state. In other words, the effect of a lower development temperature is equivalent to a decrease in heating time and the effect of a higher development temperature is equivalent to an increase in development time. The usual electrostatic image might be comprised of many different areas, each with a different electrostatic charge density level corresponding, as in the case of a photographic application, to the various brightness levels of the objects in the scene being photographed. However, the three electrostatic charge density levels shown in FIG. 6 can be regarded as three typical levels covering the range from high to low charge.

Three heating times are denoted by means of dashed lines and designated in order of increasing time as t t and t Intersection of the time lines with the density curves gives the optical density resulting for each electrical charge density when heated for the designated time. It is seen that time t results in the highest optical densities and gives increasing optical density with increase in electrical charge density. At development time t optical densities are less than at t and at development time t the erasure phenomenon has caused a relersal in characteristics so that the highest electrical charge density no longer results in the highest optical density. This results in a photographic characteristic analogous to solarization in silver halide photography and is generally undesirable.

It is thus clear that for a given temperature there exists an optimum heat development time at which the highest optical densities are achieved and the desired photographic characteristics (generally without solarization) are obtained. This is particularly so when deforming in response to continuous tone reproductions characterized by wide variations in density levels. Hence to obtain optimum development heat development temperature must be controlled and equal for all image areas since slight changes in temperature are equivalent to rather large changes in development time. It was found, for example, that with Staybelite ester 10 films increasing the heat development temperature from 60 C. to 70 C. decreased the optimum heat development time by a factor of over 6.

The particular liquid employed for producing the results in accordance with the invention depends upon whether heating is accomplished with the liquid in contact with the frostable layer or in contact with the underside support material. When the deformable layer is contacted, the liquid must have a high enough resistivity to avoid loss of the electrostatic image. In addition, the deformable material must not be dissolved or otherwise harmed due to chemical reaction with the liquid. For Staybelite Ester 10, one of the most readily attacked frostable materials, fluorocarbon liquids such as FC-43 manufactured by Minnesota Mining and Manufacturing have been found to combine the necessary resistivity and chemical inertness. For more chemically resistive materials, more common organic liquids are suitable. Velsicol X-37 layers, for example, were satisfactorily frosted in isooctane at about 91 C.

Other satisfactory liquids for heating by contact with the deformable layer include silicone liquids such as dimethylpolysiloxane (preferably the higher viscosity grades), and fluorocarbon liquids such as trifiuoroethanol.

For heating from the support side, resistivity is not critical and chemical inertness is with respect to the support material. With relatively inert supports such as polyester films, a wide range of liquids are satisfactory.

In addition to the above requirements for the liquid layer, the liquid chosen must for obvious reasons be stable at the deformation temperature, its boiling point must be Well above the deformation temperature and it must be safe as regards flammability, toxicity, etc. The volatility of the liquid can vary depending upon whether it is to be removed after development is completed, and how. When heating from the support side of the film, excess liquid can be removed by Wiping. Evaporation and washing techniques have been found to be the most convenient means of liquid removal from the deformable layer. It has been found that FC-43, for example, does not evaporate readily from a beaker used for liquid development of Staybelite at about C., but that it forms such a thin film on the deformable layer that it evaporates completely in a few seconds upon removal.

By the above description, there is disclosed novel method and apparatus for effecting development of an image deformable material. The results obtained thereby have been found superior to that obtained by techniques of the prior art in that optimum development is effected uniformly throughout the imaging layer without the attending areas of underdevelopment and overdevelopment as has been associated with techniques of the prior art. At the same time, development speed is enhanced thereby producing optimum development of high uniformity in approximately 3 seconds of contact with the heated liquid solution. The technique is simple, yet capable of producing image uniformities higher than was possible by the prior art techniques.

Since many changes could be made in the above, and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the drawings and specification shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An apparatus for developing by deformation an image charge pattern bearing thermoplastic layer comprising a tank for the storage of a quantity of insulating liquid, means partially submerged within the insulating liquid stored within said tank and adapted for rotation whereby a thin film of insulating liquid will be carried by the surface of said partially submerged means as said surface is removed from the insulating liquid during rotation, means to heat the insulating liquid to at least the softening temperature of the thermoplastic layer, and means to move an image charge pattern bearing surface of the thermoplastic layer into peripheral contact with that portion of the surface of said partially submerged means which has the thin film of insulating liquid thereon.

2. The apparatus of claim 1 wherein said partially submerged means is a cylinder.

References Cited UNITED STATES PATENTS 2,433,094 12/1947 Crowley 165--120 X 2,591,179 4/1952 McBean 165--120 X 2,844,359 7/1958 Annerhed 165120 X 2,904,321 9/1959 Bostroem 263-3 3,258,336 6/1966 Ewing 340173 3,308,234 3/1967 Bean 340-173 3,147,062 9/ 1964 Glenn 346-74 FOREIGN PATENTS 1,354,851 2/1964 France.

OTHER REFERENCES A. Morris Thomas, Heat Developed and Powder Lichtenberg Figures and the Ionization of Dielectric Surfaces Produced by Electrical Impulses; British Journal of Applied Physics, pp. 100, 101 and 106, April 1951.

BERNARD KONICK, Primary Examiner.

L. I. SCHROEDER, Assistant Examiner.

US. Cl. X.R.

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