CA1053991A - Ink development of electrostatic images - Google Patents
Ink development of electrostatic imagesInfo
- Publication number
- CA1053991A CA1053991A CA207,526A CA207526A CA1053991A CA 1053991 A CA1053991 A CA 1053991A CA 207526 A CA207526 A CA 207526A CA 1053991 A CA1053991 A CA 1053991A
- Authority
- CA
- Canada
- Prior art keywords
- ink
- dielectric liquid
- image
- process according
- charge
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Wet Developing In Electrophotography (AREA)
Abstract
INK DEVELOPMENT OF ELECTROSTATIC IMAGES
Abstract of the Disclosure The process disclosed relates to the ink development of an electrostatic image. It includes the steps of forming an electrostatic image on a charge retaining surface, wetting the charge retaining surface with a thin layer of dielectric liquid which is chemically inert toward the surface, inking the charge retaining surface with an electrically conductive liquid ink formulation which is immiscible with the dielectric liquid, inducing at the interface between the ink and the dielectric liquid a charge differential with respect to the electrostatic image on the charge retaining surface, and, when the induced charge density at the dielectric liquid-oil interface exceeds a threshold value, penetrating the dielectric liquid with the complete ink formulation, and wetting the charge retaining surface with the ink formulation.
Abstract of the Disclosure The process disclosed relates to the ink development of an electrostatic image. It includes the steps of forming an electrostatic image on a charge retaining surface, wetting the charge retaining surface with a thin layer of dielectric liquid which is chemically inert toward the surface, inking the charge retaining surface with an electrically conductive liquid ink formulation which is immiscible with the dielectric liquid, inducing at the interface between the ink and the dielectric liquid a charge differential with respect to the electrostatic image on the charge retaining surface, and, when the induced charge density at the dielectric liquid-oil interface exceeds a threshold value, penetrating the dielectric liquid with the complete ink formulation, and wetting the charge retaining surface with the ink formulation.
Description
Field of the Invention The present invention is concerned with a process for developing electrostatic images by means of irlk development. In the past, development in transfer electrophotography has been carried on chiefly by means of dry toners. The use of dry toners requires fusing the dry toner i~nage. Such fusing re-quires a considerable amount of heat energy. The process of . - . : - . . . : : - . : :
:: -:
~, ~ : . .,: , . - . .
,, ., . : . . ~. - . - . : .
~ii3~
l the present invention overcomes this requirement, since little
:: -:
~, ~ : . .,: , . - . .
,, ., . : . . ~. - . - . : .
~ii3~
l the present invention overcomes this requirement, since little
2 if any heat is required for drying. It also possesses the
3 additional advantage of yielding background free development
4 and is suitable ~or solid area development with good densi~y.
The process of the present invention is a simple one requiring 6 only inexpensive equipment. It is adaptable for use at high 7 speed, and can be applied to ordinary bond paper. It is 8 especially suitable for use with systems employing reusable 9 photoconductors.
Prior ~rt 11 U. S. Patent 3,512,965 discloses the use of a "barrier 12 substance" which in some instances may be a dielectric liquid.
13 In contrast to the process of the present invention, the 14 patent uses a development process which is dependent upon mi-gration of charged particles in a dielectric medium, i.e., the 16 development process of the patent may be characterized as 17 electrophoretic, and it is imaye polarity dependent.
18 The IBM Technical Disclosure Bulletin, Vol. lO, Mo. 6, l9 November 1967, at pa~e 735 discloses an electrostatic copying ~
20 process which employs a dielectric liquid. The process there -21 disclosed, however, is one of powder development, and not ink 22 development as in the present invention.
23 U. S. patents 3,068,115 and 3,363,89~, and Canadian patent 24 729,134 each describe electrophoretic processes in which charged droplets of ink or toner particles held in a solid matrix are 26 selectively electrostatically attracted. The process of the 27 present invention differs from the process of these patents 28 because in the present invention the same ink may be used both 29 when the electrophotographic pla-te has been charged positively and when it has been charged negatively with the same end result, SA971003X -2~
.
3~
1 i.e., positive image. The presen-t invention does not depend, 2 as do these patents, on selective electrostatic attraction of 3 charged droplets or toner particles.
4 Summary_of the Invention According to the process of the present invention, the 6 electrostatic image-bearing surface is wetted with a thin layer 7 of dielectric liquid. It is pre~erred that the liquid have a 8 conductivity of less than about 10 9 ohm 1 cm 1. There are 9 many liquids suitable for this purpose. Particularly ou-tstand-ing results have been obtained with liquid hydrocarbons, such 11 as mineral spirit type liquids. Liquids of this type are 12 available commercially under a variety of names and including 13 such materials as kerosene, paraffin oil, ligroin, Sohio*3440, 1~ and the like. Mineral spirits characteristically have a low surface tension (25-28 dynes per cm), low viscosity and low 16 density. Aliphatic hydrocarbons, such as hexane and heptane, 17 are also suitable, as is cyclohexane. Very good results have 18 also been obtained with silicone oils, for example, Dow-Corning*
19 DC 200. Fluorinated hydrocarbon liquids may also be used, for example, the Freons. Fluorinated ethers such as duPont's*Freon 21 E3, may be used. The dielectric liquid may also be a mixture 22 of above materials.
23 The dielectric liquid should, of course, be chemically 24 inert toward the particular type of electrostatic image bearing surface being employed in the process, i.e., there should be 26 no chemical reaction which will impair the reusability of the 27 surface. The present invention is suitable for use with any 28 o~ the various types of electrophotographic plates curren-tly 29 used. Particularly good results have been obtained using organic photoconductive pla-tes of the type shown in U. S. Patent * Trade Mark ~3~
1 3,484,237 of Shattuck and Vahtra. Binder -type elec-trophoto-2 graphic plates, such as those shown in U. S. Patents 3,121,006 3 and 3,121,007 are also suitable for use in -the present lnvention, 4 and so are plates where the photoconductive material is selenium or an alloy of selenium. This invention is also suitable 6 for use for development of electrostatic patterns on any di-7 electric surface, e.g., dielectric coated paper or metal.
8 It is preferable that the dielectric liquid be spread over 9 the surface of the electrophotographic or electrostatographic plate in a thin layer. It is usually desirable that this layer 11 be less than about 15 microns thick, and prefera~ly less than 12 about 5 microns thick.
13 It should be emphasized that the wetting of the electro-1~ static image-bearing surface with the liquid dielectric can be carried out either before, during, or after charging, and also 16 before, during, or after formation o~ the electrostatic image.
17 In like manner, the wetting may occur either before or during 18 inking.
19 The usual way to form an electrostatic image is hy charging and imagewise exposure to light o~ an electrophotographic plate 21 surface. The charging step may be accomplished in any of the 22 ways known to the art, for examPle, corona charging. The 23 charging may be in either the positive or the negative mode.
2~ (This versatility is an additional advantage of the present invention.) In like manner, the imagewise exposure to light 26 may ba accomplished in any conventional manner. The electro-27 static image may alternatively be formed by means of charging 2~ with a stylus, as is known in the art.
29 Inking may be conveniently carried out by any method of bringing the ink in contact with the wetted electrostat:ic imageO
SA971003X -~-~s~
l Doctor blading, the use of a roller, and the use of an impression development member may all be employecl For this purpose. A substan-tially embossed inked image can be observed on the plate. The plate is background free, and the inked image can easily be transferred, to a plain copy paper by direct contact, by pressure contact with a roller, or by corona transfer to the copy shPet.
The liquid ink development process of the present invention is believed to operate through an alteration of the inter-Facial surface energy between the dielectric liquid and ink layer. This change in interfacial energy is caused by inducing charge at the interface. In the absence of any charge at the interface between the dielectric liquid and ink, the interfacial surface area will be a minimum due to the surface tensions of the two immiscible liquids, or stated in an alternative manner, the interfacial surface energy is positive. Since a pysical system will always seek the lowest energy configuration, the dielectric liquid-ink system will assume a configuration with minimum interfacial area. ~This mechanism is discussed more fully below.) Two characteristics result from the mechanism outlined above which clearly distinguish this process from the conventional electrophoretic development process usually referred to as liquid development. (l) Because the interfacial charge between the ink and dielectric liquid is induced, the process does not depend on the sign of charge on the photoconductor surface. This is not true oF electrophoretic developmen-t where reversal of the developed image occurs when the latent electro-static i~age charge changes in sign. (2) No inking of the photoconduc-tor surface occurs until the induced charge density at the dielectric liquid-ink interface exceeds a threshold value. This results in a very DLM/Fl ~5 3~3~
1 abrupt increase in inked image density as a function of surface poten-tial, as illustrated in Figure 3 (discussed below). This effect is a distinct advantage of this type of development since the sharp threshold value for development insures extremely low bac:kground density. This characteristic is in sharp contrast to that observed for electrophoretic development where a very gradual (or low gamma) variation of developed image density vs. photoconductor surface potent:ial occurs.
Description of the Drawings FIGURE 1 (not to scale) illustrates one type of apparatus suitable for use with the process of the present invention.
FIGURE 2 (not to scale) illustrates the induced charge densities at the ink-dielectric liquid interface for two bias conditions and the resultant penetration of the complete ink formulation through the di-electric liquld.
FIGURE 3 is a plot of inked image density against surface poten-tial.
Referring more particularly to FIG. 1, the electrophotographic plate has been shown in the form of a photoconductive drum 19. The dielectric liquid is supplied from a suitable wetting device 10 which deposits a film of dielectric liquid 11. The corona charging device is shown at 12. 13 represents a system for i~agewise exposure, while ink applying means are shown at 14. 15 represents a transfer station from which the inked copy 16 emerges. A cleaniny station is shown at 17, ~hile l$ represents an erasing station.
The cleaning station 17, and the wetting station 10 may be com-bined~
The drying step, not shown in the drawing, may b~ included when ~;
desired.
SA~-71-003X - 6 -.. : . .
~Lq~5 3~ L
1 Referring more particularly to FIG. 2, the electrophotographic plate has been shown in the form of photoconductor 20 on a conducting substrate 21. A film of dielectric liquid 11 is present on top of the photoconductor and a conducting ink film 22 has been applied over the dielectric liquid. The potential of the conduct-ing ink film is controlled by means of a conducting developmenl; electrode 23 which is in contact with the ink.
The process through which the latent electrostatic image is developed by the ink is illustrated in Figure 2. We consider first Figure 2a and 2b where it has been assumed that a grounded conducting electrode resides on top of the ink. This electrode can be, for ex-ample, the roller with which the ink is applied. A latent electro-static image has been formed on the photoconductor surface such that the surface potential is - V in the unexposed areas and substantially zero in the exposed areas. Due to the conductivity of the ink and the bias condition of the development electrode in areas where the sur-face of the photoconductor is charged, a charge is induced at the in-terface between the ink and the dielectric liquid as illustrated in Figure 2a. The charges along the ink-dielectric liquid interface re-pell each other, but are unable to move laterally because they areattracted by the stationary charges sn the photoconductor surface. The interfacial charges can become ~urther separated from each other if ripples are created in the ink-dielectric liquid interface~ but the tendency of the system to maintain minimum interfacial energy prevents ripples ~rom occurring until the interfacial charge reaches a threshold densit~ Once this threshold charge density is exceeded~ the minimum energ~ configuration of the s~stem becomes one with maximum interfacial ar~a so th~t the charges can be separated as much as possible. As il-lustrated ~3S 3~ L
1 in Figure 2b, rippling of the interface occurs and the amplitude of the ripples increases rapidly so that the ink comes into contact with the photoconductor surface and wets it.
A variation of this process occurs i-f the conducting development electrode is biased to a potential of - ~ as illustrated in Figures 2c and 2d. For this bias condition no charges are induced at the ink-dielectric liquid interface where the photoconductor is charged, but as illustrated in Figure 2c, an induced charge appears at the ink-dielectric liquid inter~ace in areas where no charge resides on the photoconductor. These induced charges are also mutually repulsive, but are unable to move along the ink-dielectric liquid interface because they are repelled by the stationary charges on the photoconductor sur-face. The same argument given above now applies, and ~he ink pene trates the dielectric liquid and wets the photoconductor surface once a threshold induced charge density has been exceeded. In this case the image obtained is the reverse of the image obtained when the develop-ment electrode is grounded.
Similar considerations to those discussed For the two cases above can be used to explain the effects of arbitrary bias conditions on the development electrode and diFferent char~e densities on the photocon-ductor surface. In particular, i~ the charge on the photoconductor in the exposed areas is non-zero, causing a potential V at ~he photocon-ductor surface, it may be desirable to set -the bias on the development electrode to a potential V to reduce the background density developed in these areas.
Referring more particularly to FIG. 3, the surface potential in volts (negative charge) is plotted on the ordinate. On the abscissa there is plotted the inked image density. The experiment was conducted using a p~otoconductor prepared as described SA9-71-Q~3X - 8 -DLM/~4 s~
1 in U.S. Patent 3,48~,237. The dielectric liquid was mineral spirits and the ink was glycol based speciFically Formulabs Black 587.*
As may be seen from inspection of the figure the process of the present invention is characterized by a sharp threshold effect. There is a very abrupt change in the developed image density as a -function of photoconductor surface potential. In FIG. 3, the threshold is at approximately 140 volts. It is obvious that the ink and the dielectric liquid may each be chosen for their surface energy property to shift this threshold charge density for development to any desired level.
The voltage of 1~0 volts shown in FIG. 3 is a relatively low potential for producing development compared to some commercial processes such as magnetic brush or cascade development. This ability to use low voltages represents a still additional advantage of the present process.
It should be emphasized that the process of the present invention can use inks which are true solutions. This is in contrast to many liquid development processes employed in the past, where emulsions or dispersions were involved. Because inks of the present process can ~e true solutions, problems of emulsion stability are ~hereby avoided. It is believed that in the process of the present invention, the ink acts to displace the dielectric liquid film on the charge retaining surface.
The inks of the present invention are preferably made from a polar liquîd with a dissolved dye. For improved cleaning of residual ink carbon black, pigments or both may be used in place of dye or in con-junction ~ith it. Water, formamide, glycols such as ethylene glycol, and propylene glycol and the like are ~Trade Mark SA9-71-aO3X - 9 -DLM/F~
: . - ' .' ' 1 suitable liquids. It is essential that the ink be immiscible with the dielectric liquid.
In one particularly preferred variation of the present invention, the viscosity of the ink is increased by adding a small amount of water soluble thickening agent, such as hydroxy propyl methyl cellulose or the like. The best results are obtained where the ink has moderate to high surface tension for liquids and relatively high viscosity. It is also preferred that the ink have a dielectric constant greater than that of the dielectric liquid. It is believed that best results are obtained when the dielectric constant of the charge bearing surface in the dark is greater than that of the dielectric liquid.
In general, the ink roller or the inking member may be biased with a low DC field to minimize background devèlopment.
The general nature oF the invention having been set forth, the following examples are now presented as to the speciFic preparation of preferred embodiments of the invention. The specific details presented are for purposes of illustration and not limitation.
A standard IBM organic photoconductor plate (see U.S. Patent 3,484,~37) is uniformly wetted with a thin layer of mineral spirits (Sohio *34~0) charged in the dark with a corona emitting device to a surface potential of approximately -700 volts. The plate then is exposed to produce a latent electrostatic image having a contrast po-tential of approximately 400 volts (-50Q volts in the image region, -100 volts in the background region~. A layer of suitable ink, for example3 Formulabs Black 587*, is brought in contact with the image bearing, oil ~etted surface, *Trade Mark SA~-71-Q03X - 10 -~LM/F7 .. .
~63~3~
1 using an ink roller device. The plate may now be examined in the room light to observe an excellent black and white inked image which can be transferred with ease to a copy paper. The transfer can be accomplished either by direct contact to the receiving medium, by the aid of a flexible roller, or any other means. The plate now is ready to be cleaned and used for the next imaging cycle. The copy may either be heat dried or air dried.
The plate may be charged first, then wetted with dielectric -liquid. The rest of the process is similar to Example 1, with good results obtained.
The wetting may be accomplished after imagewise exposure, instead of before, as in the previous examples. Good results are obtained.
EXAMPLE ~ ;
The process of Example 1 was repeated except corona charginy is positive. A positive inked image is observed.
The image potential of Example 1 can vary, from 150 volts on up, with background potential being lower than 150 volts. A positive image with good density and no background development is obtained.
When the di~lectric li~uid of Example 1 is replaced with the following liquids, inking of the image results in positive develop-ment: Isopar G *(Humble Oil's insoparaffinic hydrocarbon, with a boiling range of 320-350F~, kerosene, ligroin, cyclohexane, hexane, heptane, fluorochemical FC-77* (a perfluorinated *Trade Mark SA~-71-OQ3X - 11 -DLMiF8 .... ... .
;~
1 fluid from 3M Company), paraffin oil, silicon oil (DC200)*.
(a) The ink of Example 1 can be replaced with 0.2% solution of malachite green oxalate in water. A recognizable but poor inked image, composed o~ ink droplets, instead of a continuous solid llne, is ob-served. Transfer oF this liquid image to paper causes further image deterioration due to spreading of the low viscosity ink.
~b~ The dye concentration of paragraph (a) above is increased to
The process of the present invention is a simple one requiring 6 only inexpensive equipment. It is adaptable for use at high 7 speed, and can be applied to ordinary bond paper. It is 8 especially suitable for use with systems employing reusable 9 photoconductors.
Prior ~rt 11 U. S. Patent 3,512,965 discloses the use of a "barrier 12 substance" which in some instances may be a dielectric liquid.
13 In contrast to the process of the present invention, the 14 patent uses a development process which is dependent upon mi-gration of charged particles in a dielectric medium, i.e., the 16 development process of the patent may be characterized as 17 electrophoretic, and it is imaye polarity dependent.
18 The IBM Technical Disclosure Bulletin, Vol. lO, Mo. 6, l9 November 1967, at pa~e 735 discloses an electrostatic copying ~
20 process which employs a dielectric liquid. The process there -21 disclosed, however, is one of powder development, and not ink 22 development as in the present invention.
23 U. S. patents 3,068,115 and 3,363,89~, and Canadian patent 24 729,134 each describe electrophoretic processes in which charged droplets of ink or toner particles held in a solid matrix are 26 selectively electrostatically attracted. The process of the 27 present invention differs from the process of these patents 28 because in the present invention the same ink may be used both 29 when the electrophotographic pla-te has been charged positively and when it has been charged negatively with the same end result, SA971003X -2~
.
3~
1 i.e., positive image. The presen-t invention does not depend, 2 as do these patents, on selective electrostatic attraction of 3 charged droplets or toner particles.
4 Summary_of the Invention According to the process of the present invention, the 6 electrostatic image-bearing surface is wetted with a thin layer 7 of dielectric liquid. It is pre~erred that the liquid have a 8 conductivity of less than about 10 9 ohm 1 cm 1. There are 9 many liquids suitable for this purpose. Particularly ou-tstand-ing results have been obtained with liquid hydrocarbons, such 11 as mineral spirit type liquids. Liquids of this type are 12 available commercially under a variety of names and including 13 such materials as kerosene, paraffin oil, ligroin, Sohio*3440, 1~ and the like. Mineral spirits characteristically have a low surface tension (25-28 dynes per cm), low viscosity and low 16 density. Aliphatic hydrocarbons, such as hexane and heptane, 17 are also suitable, as is cyclohexane. Very good results have 18 also been obtained with silicone oils, for example, Dow-Corning*
19 DC 200. Fluorinated hydrocarbon liquids may also be used, for example, the Freons. Fluorinated ethers such as duPont's*Freon 21 E3, may be used. The dielectric liquid may also be a mixture 22 of above materials.
23 The dielectric liquid should, of course, be chemically 24 inert toward the particular type of electrostatic image bearing surface being employed in the process, i.e., there should be 26 no chemical reaction which will impair the reusability of the 27 surface. The present invention is suitable for use with any 28 o~ the various types of electrophotographic plates curren-tly 29 used. Particularly good results have been obtained using organic photoconductive pla-tes of the type shown in U. S. Patent * Trade Mark ~3~
1 3,484,237 of Shattuck and Vahtra. Binder -type elec-trophoto-2 graphic plates, such as those shown in U. S. Patents 3,121,006 3 and 3,121,007 are also suitable for use in -the present lnvention, 4 and so are plates where the photoconductive material is selenium or an alloy of selenium. This invention is also suitable 6 for use for development of electrostatic patterns on any di-7 electric surface, e.g., dielectric coated paper or metal.
8 It is preferable that the dielectric liquid be spread over 9 the surface of the electrophotographic or electrostatographic plate in a thin layer. It is usually desirable that this layer 11 be less than about 15 microns thick, and prefera~ly less than 12 about 5 microns thick.
13 It should be emphasized that the wetting of the electro-1~ static image-bearing surface with the liquid dielectric can be carried out either before, during, or after charging, and also 16 before, during, or after formation o~ the electrostatic image.
17 In like manner, the wetting may occur either before or during 18 inking.
19 The usual way to form an electrostatic image is hy charging and imagewise exposure to light o~ an electrophotographic plate 21 surface. The charging step may be accomplished in any of the 22 ways known to the art, for examPle, corona charging. The 23 charging may be in either the positive or the negative mode.
2~ (This versatility is an additional advantage of the present invention.) In like manner, the imagewise exposure to light 26 may ba accomplished in any conventional manner. The electro-27 static image may alternatively be formed by means of charging 2~ with a stylus, as is known in the art.
29 Inking may be conveniently carried out by any method of bringing the ink in contact with the wetted electrostat:ic imageO
SA971003X -~-~s~
l Doctor blading, the use of a roller, and the use of an impression development member may all be employecl For this purpose. A substan-tially embossed inked image can be observed on the plate. The plate is background free, and the inked image can easily be transferred, to a plain copy paper by direct contact, by pressure contact with a roller, or by corona transfer to the copy shPet.
The liquid ink development process of the present invention is believed to operate through an alteration of the inter-Facial surface energy between the dielectric liquid and ink layer. This change in interfacial energy is caused by inducing charge at the interface. In the absence of any charge at the interface between the dielectric liquid and ink, the interfacial surface area will be a minimum due to the surface tensions of the two immiscible liquids, or stated in an alternative manner, the interfacial surface energy is positive. Since a pysical system will always seek the lowest energy configuration, the dielectric liquid-ink system will assume a configuration with minimum interfacial area. ~This mechanism is discussed more fully below.) Two characteristics result from the mechanism outlined above which clearly distinguish this process from the conventional electrophoretic development process usually referred to as liquid development. (l) Because the interfacial charge between the ink and dielectric liquid is induced, the process does not depend on the sign of charge on the photoconductor surface. This is not true oF electrophoretic developmen-t where reversal of the developed image occurs when the latent electro-static i~age charge changes in sign. (2) No inking of the photoconduc-tor surface occurs until the induced charge density at the dielectric liquid-ink interface exceeds a threshold value. This results in a very DLM/Fl ~5 3~3~
1 abrupt increase in inked image density as a function of surface poten-tial, as illustrated in Figure 3 (discussed below). This effect is a distinct advantage of this type of development since the sharp threshold value for development insures extremely low bac:kground density. This characteristic is in sharp contrast to that observed for electrophoretic development where a very gradual (or low gamma) variation of developed image density vs. photoconductor surface potent:ial occurs.
Description of the Drawings FIGURE 1 (not to scale) illustrates one type of apparatus suitable for use with the process of the present invention.
FIGURE 2 (not to scale) illustrates the induced charge densities at the ink-dielectric liquid interface for two bias conditions and the resultant penetration of the complete ink formulation through the di-electric liquld.
FIGURE 3 is a plot of inked image density against surface poten-tial.
Referring more particularly to FIG. 1, the electrophotographic plate has been shown in the form of a photoconductive drum 19. The dielectric liquid is supplied from a suitable wetting device 10 which deposits a film of dielectric liquid 11. The corona charging device is shown at 12. 13 represents a system for i~agewise exposure, while ink applying means are shown at 14. 15 represents a transfer station from which the inked copy 16 emerges. A cleaniny station is shown at 17, ~hile l$ represents an erasing station.
The cleaning station 17, and the wetting station 10 may be com-bined~
The drying step, not shown in the drawing, may b~ included when ~;
desired.
SA~-71-003X - 6 -.. : . .
~Lq~5 3~ L
1 Referring more particularly to FIG. 2, the electrophotographic plate has been shown in the form of photoconductor 20 on a conducting substrate 21. A film of dielectric liquid 11 is present on top of the photoconductor and a conducting ink film 22 has been applied over the dielectric liquid. The potential of the conduct-ing ink film is controlled by means of a conducting developmenl; electrode 23 which is in contact with the ink.
The process through which the latent electrostatic image is developed by the ink is illustrated in Figure 2. We consider first Figure 2a and 2b where it has been assumed that a grounded conducting electrode resides on top of the ink. This electrode can be, for ex-ample, the roller with which the ink is applied. A latent electro-static image has been formed on the photoconductor surface such that the surface potential is - V in the unexposed areas and substantially zero in the exposed areas. Due to the conductivity of the ink and the bias condition of the development electrode in areas where the sur-face of the photoconductor is charged, a charge is induced at the in-terface between the ink and the dielectric liquid as illustrated in Figure 2a. The charges along the ink-dielectric liquid interface re-pell each other, but are unable to move laterally because they areattracted by the stationary charges sn the photoconductor surface. The interfacial charges can become ~urther separated from each other if ripples are created in the ink-dielectric liquid interface~ but the tendency of the system to maintain minimum interfacial energy prevents ripples ~rom occurring until the interfacial charge reaches a threshold densit~ Once this threshold charge density is exceeded~ the minimum energ~ configuration of the s~stem becomes one with maximum interfacial ar~a so th~t the charges can be separated as much as possible. As il-lustrated ~3S 3~ L
1 in Figure 2b, rippling of the interface occurs and the amplitude of the ripples increases rapidly so that the ink comes into contact with the photoconductor surface and wets it.
A variation of this process occurs i-f the conducting development electrode is biased to a potential of - ~ as illustrated in Figures 2c and 2d. For this bias condition no charges are induced at the ink-dielectric liquid interface where the photoconductor is charged, but as illustrated in Figure 2c, an induced charge appears at the ink-dielectric liquid inter~ace in areas where no charge resides on the photoconductor. These induced charges are also mutually repulsive, but are unable to move along the ink-dielectric liquid interface because they are repelled by the stationary charges on the photoconductor sur-face. The same argument given above now applies, and ~he ink pene trates the dielectric liquid and wets the photoconductor surface once a threshold induced charge density has been exceeded. In this case the image obtained is the reverse of the image obtained when the develop-ment electrode is grounded.
Similar considerations to those discussed For the two cases above can be used to explain the effects of arbitrary bias conditions on the development electrode and diFferent char~e densities on the photocon-ductor surface. In particular, i~ the charge on the photoconductor in the exposed areas is non-zero, causing a potential V at ~he photocon-ductor surface, it may be desirable to set -the bias on the development electrode to a potential V to reduce the background density developed in these areas.
Referring more particularly to FIG. 3, the surface potential in volts (negative charge) is plotted on the ordinate. On the abscissa there is plotted the inked image density. The experiment was conducted using a p~otoconductor prepared as described SA9-71-Q~3X - 8 -DLM/~4 s~
1 in U.S. Patent 3,48~,237. The dielectric liquid was mineral spirits and the ink was glycol based speciFically Formulabs Black 587.*
As may be seen from inspection of the figure the process of the present invention is characterized by a sharp threshold effect. There is a very abrupt change in the developed image density as a -function of photoconductor surface potential. In FIG. 3, the threshold is at approximately 140 volts. It is obvious that the ink and the dielectric liquid may each be chosen for their surface energy property to shift this threshold charge density for development to any desired level.
The voltage of 1~0 volts shown in FIG. 3 is a relatively low potential for producing development compared to some commercial processes such as magnetic brush or cascade development. This ability to use low voltages represents a still additional advantage of the present process.
It should be emphasized that the process of the present invention can use inks which are true solutions. This is in contrast to many liquid development processes employed in the past, where emulsions or dispersions were involved. Because inks of the present process can ~e true solutions, problems of emulsion stability are ~hereby avoided. It is believed that in the process of the present invention, the ink acts to displace the dielectric liquid film on the charge retaining surface.
The inks of the present invention are preferably made from a polar liquîd with a dissolved dye. For improved cleaning of residual ink carbon black, pigments or both may be used in place of dye or in con-junction ~ith it. Water, formamide, glycols such as ethylene glycol, and propylene glycol and the like are ~Trade Mark SA9-71-aO3X - 9 -DLM/F~
: . - ' .' ' 1 suitable liquids. It is essential that the ink be immiscible with the dielectric liquid.
In one particularly preferred variation of the present invention, the viscosity of the ink is increased by adding a small amount of water soluble thickening agent, such as hydroxy propyl methyl cellulose or the like. The best results are obtained where the ink has moderate to high surface tension for liquids and relatively high viscosity. It is also preferred that the ink have a dielectric constant greater than that of the dielectric liquid. It is believed that best results are obtained when the dielectric constant of the charge bearing surface in the dark is greater than that of the dielectric liquid.
In general, the ink roller or the inking member may be biased with a low DC field to minimize background devèlopment.
The general nature oF the invention having been set forth, the following examples are now presented as to the speciFic preparation of preferred embodiments of the invention. The specific details presented are for purposes of illustration and not limitation.
A standard IBM organic photoconductor plate (see U.S. Patent 3,484,~37) is uniformly wetted with a thin layer of mineral spirits (Sohio *34~0) charged in the dark with a corona emitting device to a surface potential of approximately -700 volts. The plate then is exposed to produce a latent electrostatic image having a contrast po-tential of approximately 400 volts (-50Q volts in the image region, -100 volts in the background region~. A layer of suitable ink, for example3 Formulabs Black 587*, is brought in contact with the image bearing, oil ~etted surface, *Trade Mark SA~-71-Q03X - 10 -~LM/F7 .. .
~63~3~
1 using an ink roller device. The plate may now be examined in the room light to observe an excellent black and white inked image which can be transferred with ease to a copy paper. The transfer can be accomplished either by direct contact to the receiving medium, by the aid of a flexible roller, or any other means. The plate now is ready to be cleaned and used for the next imaging cycle. The copy may either be heat dried or air dried.
The plate may be charged first, then wetted with dielectric -liquid. The rest of the process is similar to Example 1, with good results obtained.
The wetting may be accomplished after imagewise exposure, instead of before, as in the previous examples. Good results are obtained.
EXAMPLE ~ ;
The process of Example 1 was repeated except corona charginy is positive. A positive inked image is observed.
The image potential of Example 1 can vary, from 150 volts on up, with background potential being lower than 150 volts. A positive image with good density and no background development is obtained.
When the di~lectric li~uid of Example 1 is replaced with the following liquids, inking of the image results in positive develop-ment: Isopar G *(Humble Oil's insoparaffinic hydrocarbon, with a boiling range of 320-350F~, kerosene, ligroin, cyclohexane, hexane, heptane, fluorochemical FC-77* (a perfluorinated *Trade Mark SA~-71-OQ3X - 11 -DLMiF8 .... ... .
;~
1 fluid from 3M Company), paraffin oil, silicon oil (DC200)*.
(a) The ink of Example 1 can be replaced with 0.2% solution of malachite green oxalate in water. A recognizable but poor inked image, composed o~ ink droplets, instead of a continuous solid llne, is ob-served. Transfer oF this liquid image to paper causes further image deterioration due to spreading of the low viscosity ink.
~b~ The dye concentration of paragraph (a) above is increased to
5% - 10%. A good inked image is obtained on the liquid dielectric wet-ted surface of the plate in Example 1. However, due to its low vis-cosity, smearing is observed in the transfer process.
(c~ To the solution of paragraph (b) above, a thickening agent is added. For example, methocel (hydroxy propyl methyl cellulose~ to increase the ink viscosity in the range o~ 5,000 to 10,000 cps. Very definite improvement in image smearing is observed.
The ink of Example 1 can be replaced with the Following inks and good inked image can be observed. These inks are all commercially available ball point pen inks from Formulabs:* (Green) M-51, (Red) M-52, Gold 572, Green 295, Turquoise 646, Blue 353, Brown 218, Blue 160.
The dye of ink solution of Exampl-e 7(c) can be replaced with other water soluble dyes. The following are examples: Cyper Black LA*, Methylene Blue*, Naphthylene Black lOBR*, Alizarine Blue Black,* Crystal Violet,* Nyliton Black,* Palanthrene Blue BA*, Mordant Blue B*.
*Trade Mark SA~-71-OQ3X - 12 -DLM~F9 - . , . .: :
. ........ .
, . . . . . ~
~353~
1 Solutions of 5% of each of the above dyes in water were pre-pared and the ink roller of Example 1 was replaced with a doctor blade for inking of the image. Good inked images were obtained on the photoconductor.
The ink of Example 1 was replaced with two well-known low vis-cosity inks, each of which resulted in inked image development; in this example, the doctor blade of Example 9 was used. The two inks are:
(1~ A. B. Dick*video jet (2) Schaeffer Skrip #62*ink The ink roller of Example 1 was biased with 400 volts DC field.
Reversal image development was obtained.
*Trade Mark
(c~ To the solution of paragraph (b) above, a thickening agent is added. For example, methocel (hydroxy propyl methyl cellulose~ to increase the ink viscosity in the range o~ 5,000 to 10,000 cps. Very definite improvement in image smearing is observed.
The ink of Example 1 can be replaced with the Following inks and good inked image can be observed. These inks are all commercially available ball point pen inks from Formulabs:* (Green) M-51, (Red) M-52, Gold 572, Green 295, Turquoise 646, Blue 353, Brown 218, Blue 160.
The dye of ink solution of Exampl-e 7(c) can be replaced with other water soluble dyes. The following are examples: Cyper Black LA*, Methylene Blue*, Naphthylene Black lOBR*, Alizarine Blue Black,* Crystal Violet,* Nyliton Black,* Palanthrene Blue BA*, Mordant Blue B*.
*Trade Mark SA~-71-OQ3X - 12 -DLM~F9 - . , . .: :
. ........ .
, . . . . . ~
~353~
1 Solutions of 5% of each of the above dyes in water were pre-pared and the ink roller of Example 1 was replaced with a doctor blade for inking of the image. Good inked images were obtained on the photoconductor.
The ink of Example 1 was replaced with two well-known low vis-cosity inks, each of which resulted in inked image development; in this example, the doctor blade of Example 9 was used. The two inks are:
(1~ A. B. Dick*video jet (2) Schaeffer Skrip #62*ink The ink roller of Example 1 was biased with 400 volts DC field.
Reversal image development was obtained.
*Trade Mark
Claims (14)
1. A process for the ink development of an electrostatic image com-prising the steps of:
(a) wetting a charge retaining surface with a continuous film of dielectric liquid that is less than about 15 microns thick and is chemi-cally inert toward said surface, (b) applying to said surface an electrical potential of predeter-mined magnitude, (c) forming an electrostatic latent image on said surface, (d) creating an induced charge differential which exceeds a pre-selected threshold value at the interface between the ink and dielectric, selectively at the charged or uncharged image areas on said surface according to whether a bias potential is not or is, respectively, applied to the ink, by inking said surface with an electrically conductive liquid ink that is immiscible with the dielectric liquid, which charge differen-tial causes the electrically conductive ink to displace the dielectric liquid and thus cause all constituents of which the ink consists to selectively wet the image areas subjected to said charge differential.
(a) wetting a charge retaining surface with a continuous film of dielectric liquid that is less than about 15 microns thick and is chemi-cally inert toward said surface, (b) applying to said surface an electrical potential of predeter-mined magnitude, (c) forming an electrostatic latent image on said surface, (d) creating an induced charge differential which exceeds a pre-selected threshold value at the interface between the ink and dielectric, selectively at the charged or uncharged image areas on said surface according to whether a bias potential is not or is, respectively, applied to the ink, by inking said surface with an electrically conductive liquid ink that is immiscible with the dielectric liquid, which charge differen-tial causes the electrically conductive ink to displace the dielectric liquid and thus cause all constituents of which the ink consists to selectively wet the image areas subjected to said charge differential.
2. The process according to claim 1, wherein said ink has the same formulation for positive or negative imaging.
3. The process according to claim 1, wherein the steps (a) and (b) are reversed in time sequence.
4. The process according to claim 1 or 2, wherein the step (a) follows step (c).
5. The process according to claim 1, 2 or 3, wherein the continuous layer of dielectric liquid is applied by a roller in step (a).
6. The process according to claim 1, 2 or 3, wherein said process is accomplished without a special drying step.
7. The process according to claim 1, 2 or 3, wherein the ink is applied as a continuous thin film.
8. The process according to claim 1, 2 or 3, wherein the copy medium is untreated ordinary bond paper.
9. The process according to claim 1, 2 or 3, wherein said dielectric liquid has a conductivity of less than about 10-9/ohm cm.
10. The process according to claim 1, 2 or 3, wherein said preselected threshold value need only exceed about 150 volts, positive or negative.
11. The process according to claim 1, 2 or 3, wherein the ink is formu-lated from a polar liquid with a dissolved dye, and has a viscosity of the order of about 5,000 to 10,000 cps to minimize smearing, and a dielectric constant greater than that of the dielectric liquid.
12. A process for the ink development of an electrostatic image comprising the steps of:
(a) wetting a charge retaining surface with a continuous film of dielectric liquid that is less than about 15 microns thick and is chemi-cally inert toward said surface, (b) applying to said surface an electrical potential of predeter-mined magnitude to cause a charge to be retained thereon, (c) forming an electrostatic latent image on said surface, (d) inking said surface with an electrically conductive liquid ink that is immiscible with the dielectric liquid, so as to create an induced charge differential which exceeds a preselected threshold value at the interface between the ink and dielectric at the charged image areas, which charge differential causes the electrically conductive ink to displace the dielectric liquid and thus cause all constituents of which the ink consists to selectively wet only the charged image areas on said surface, and (e) transferring the inked image to a copy medium to provide a posi-tive image thereon, said positive image being provided irrespective of whether said charge retaining surface is charged positively or negatively.
(a) wetting a charge retaining surface with a continuous film of dielectric liquid that is less than about 15 microns thick and is chemi-cally inert toward said surface, (b) applying to said surface an electrical potential of predeter-mined magnitude to cause a charge to be retained thereon, (c) forming an electrostatic latent image on said surface, (d) inking said surface with an electrically conductive liquid ink that is immiscible with the dielectric liquid, so as to create an induced charge differential which exceeds a preselected threshold value at the interface between the ink and dielectric at the charged image areas, which charge differential causes the electrically conductive ink to displace the dielectric liquid and thus cause all constituents of which the ink consists to selectively wet only the charged image areas on said surface, and (e) transferring the inked image to a copy medium to provide a posi-tive image thereon, said positive image being provided irrespective of whether said charge retaining surface is charged positively or negatively.
13. The process according to claim 12, including the further step of:
(f) applying a bias potential to said ink to prevent an induced charge differential from being created at the ink-dielectric liquid inter-face at said charged image areas, but cause a charge differential to be induced at said interface at the uncharged areas, thereby to provide a negative image, the formulation of said ink being identical for positive or negative imaging.
(f) applying a bias potential to said ink to prevent an induced charge differential from being created at the ink-dielectric liquid inter-face at said charged image areas, but cause a charge differential to be induced at said interface at the uncharged areas, thereby to provide a negative image, the formulation of said ink being identical for positive or negative imaging.
14. The process according to claim 13, wherein steps (d) and (f) are performed concurrently.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US38992773A | 1973-08-20 | 1973-08-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1053991A true CA1053991A (en) | 1979-05-08 |
Family
ID=23540346
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA207,526A Expired CA1053991A (en) | 1973-08-20 | 1974-08-16 | Ink development of electrostatic images |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1053991A (en) |
-
1974
- 1974-08-16 CA CA207,526A patent/CA1053991A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US3801315A (en) | Gravure imaging system | |
| US5021318A (en) | Process for forming secure images | |
| JP3865815B2 (en) | Image formation process with liquid toner | |
| US4272599A (en) | Ink development of electrostatic images | |
| US3627557A (en) | Liquid development by reducing the viscosity of the developer on a roller applicator prior to development | |
| US4761357A (en) | Electrophoretic development of electrostatic charge images | |
| US3894512A (en) | Electrostatic developing apparatus | |
| US3795011A (en) | Electrostatic printing device | |
| US3806354A (en) | Method of cyclically developing electrostatic latent images | |
| US4804601A (en) | Electrophotographic and electrographic imaging processes | |
| US3244633A (en) | Liquid developers for developing electrostatic images | |
| US6122471A (en) | Method and apparatus for delivery of high solids content toner cake in a contact electrostatic printing system | |
| US6219501B1 (en) | Method and apparatus for toner cake delivery | |
| US3907695A (en) | Liquid developer | |
| US3884684A (en) | Electrostatic developing process employing a porous photoconductive member | |
| US3281241A (en) | Method of forming a visual record of a latent image on an image receiving web | |
| CA1053991A (en) | Ink development of electrostatic images | |
| US3973955A (en) | Electrostatic developing method | |
| US4023898A (en) | Electrostatic developing apparatus | |
| US3729334A (en) | Imaging process | |
| US3251688A (en) | Liquid transfer development | |
| US3256197A (en) | Liquid developer for electrostatic charge images | |
| US3296140A (en) | Liquid developer for electrographic printing | |
| JP3650431B2 (en) | Liquid developing method and liquid developing apparatus for electrostatic latent image | |
| US3946671A (en) | Electrostatic offset printing |