INORGANIC SALT-RESIN CONDUCTIVE COATINGS FOR ELECTROPHOTOGRAPHIC PAPER
United States Patent 3615403
Electrophotographic paper, having thereon conductive coatings applied from an aqueous coating composition containing an N-vinylpyrrolidone polymer, polyvinyl acetate emulsion and an inorganic salt--polyhydric alcohol system.
US Patent References:
Radiation sensitive photoconductive member
Dessaner et al. - August 1959 - 2901348
Electrostatographic recording medium and a method of making the same
Kubata et al. - October 1965 - 3212931
Electrophotographic recording member
Schoenfeld - January 1967 - 3295967
Electrophotographic material
Kosche - July 1967 - 3331687
Vinylidene chloride-ethylenically unsaturated monomer-ethylenically unsaturated acid-gelatin emulsion polymerized coating composition
Ream - September 1968 - 3403116
Radiation sensitive photoconductive member
Dessaner et al. - August 1959 - 2901348
Electrostatographic recording medium and a method of making the same
Kubata et al. - October 1965 - 3212931
Electrophotographic recording member
Schoenfeld - January 1967 - 3295967
Electrophotographic material
Kosche - July 1967 - 3331687
Vinylidene chloride-ethylenically unsaturated monomer-ethylenically unsaturated acid-gelatin emulsion polymerized coating composition
Ream - September 1968 - 3403116
Application Number:
04/715995
Publication Date:
10/26/1971
Filing Date:
03/26/1968
View Patent Images:
Export Citation:
Assignee:
Corporation, Gaf
Primary Class:
Other Classes:
430/87, 162/138
International Classes:
G03G5/10; G03G5/00; G03G7/00
Field of Search:
96/1.5 117/161UN,201,219,218,17.5 162/138
US Patent References:
| 3489597 | POLYESTER - CELLULOSIC POLYMER - VINYLPYRROLIDONE - VINYL ACETATE POLYMER IMAGE-RECEIVING SHEET MATERIALS | January 1970 | Paker |
Primary Examiner:
Lesmes, George F.
Assistant Examiner:
Miller, John R.
Claims:
While exemplary embodiments of the invention have been described, the true scope of the invention is to be determined from the following claims
1. Electrophotographic recording material having a paper base of which both faces have coatings thereon of a conductive layer applied from an aqueous coating composition consisting essentially of 2 to 4 percent by weight of an inorganic salt, 2 to 4 percent by weight of a polyhydric alcohol selected from the group consisting of glycerol, ethylene glycol, propylene glycol, 1,4-butanediol and polyethylene glycol, 0.25 to 5 percent by weight of an N-vinylpyrrolidone polymer selected from the group consisting of poly-N-vinyl pyrrolidone, N-vinylpyrrolidone/vinyl acetate copolymer, N-vinyl pyrrolidone/ethylacrylate copolymer and mixtures thereof, 2.5 to 5 percent by weight of a polyvinyl acetate emulsion, 2 to 6.5 percent by weight of an acetylated starch and 2 to 6.5 percent by weight of a polyvinyl alcohol, said inorganic salts having a nonvolatile, conductive anion, and having a cation selected from the group consisting of the ions of ammonium, lithium, sodium, potassium, rubidium, and cesium, and one face of said base having a coating thereon overcoated with a second coating containing a photoconductive zinc oxide pigment.
2. Electrophotographic recording material as defined in claim 1 wherein the inorganic salt is sodium chloride and the polyhydric alcohol is glycerol.
3. Electrophotographic recording material as defined in claim 1 wherein the inorganic salt is sodium chloride and the polyhydric alcohol is ethylene glycol.
4. Electrophotographic recording material as defined in claim 1 wherein the inorganic salt is ammonium chloride and the polyhydric alcohol is glycerol.
5. Electrophotographic recording material as defined in claim 1 wherein the N-vinylpyrrolidone polymer is a copolymer of N-vinylpyrrolidone and vinyl acetate in which the proportion of N-vinylpyrrolidone in the copolymer is from 10 to 25 percent by weight.
1. Electrophotographic recording material having a paper base of which both faces have coatings thereon of a conductive layer applied from an aqueous coating composition consisting essentially of 2 to 4 percent by weight of an inorganic salt, 2 to 4 percent by weight of a polyhydric alcohol selected from the group consisting of glycerol, ethylene glycol, propylene glycol, 1,4-butanediol and polyethylene glycol, 0.25 to 5 percent by weight of an N-vinylpyrrolidone polymer selected from the group consisting of poly-N-vinyl pyrrolidone, N-vinylpyrrolidone/vinyl acetate copolymer, N-vinyl pyrrolidone/ethylacrylate copolymer and mixtures thereof, 2.5 to 5 percent by weight of a polyvinyl acetate emulsion, 2 to 6.5 percent by weight of an acetylated starch and 2 to 6.5 percent by weight of a polyvinyl alcohol, said inorganic salts having a nonvolatile, conductive anion, and having a cation selected from the group consisting of the ions of ammonium, lithium, sodium, potassium, rubidium, and cesium, and one face of said base having a coating thereon overcoated with a second coating containing a photoconductive zinc oxide pigment.
2. Electrophotographic recording material as defined in claim 1 wherein the inorganic salt is sodium chloride and the polyhydric alcohol is glycerol.
3. Electrophotographic recording material as defined in claim 1 wherein the inorganic salt is sodium chloride and the polyhydric alcohol is ethylene glycol.
4. Electrophotographic recording material as defined in claim 1 wherein the inorganic salt is ammonium chloride and the polyhydric alcohol is glycerol.
5. Electrophotographic recording material as defined in claim 1 wherein the N-vinylpyrrolidone polymer is a copolymer of N-vinylpyrrolidone and vinyl acetate in which the proportion of N-vinylpyrrolidone in the copolymer is from 10 to 25 percent by weight.
Description:
This invention relates to novel coatings for solvent-based electrophotographic paper and, in particular, to both the coating solutions therefor and the resulting coated electrophotographic paper containing an inorganic salt-polyhydric alcohol ingredient.
Electrophotographic recording is a process for producing visible images involving the conversion by the imagewise exposure to light of a uniformly electrostatically charged surface into a surface having a patterned configuration of electrostatically charged and discharged areas. Subsequent development of this patterned surface results in reproduction of the original image.
More particularly and as disclosed, for example, in U.S. Pat. No. 3,052,539, the electrophotographic recording material is charged in the dark by exposing its photoconductive zinc oxide pigment-coated surface to a charging device such as an arrangement of fine wires connected to a high-voltage DC source while the paper base is supported on a grounded metal plate. The pigment-coated surface, bearing a uniform electrostatic charge, is then exposed imagewise to light (e.g. by projection) whereby the light-exposed areas are rendered conductive, and their electrostatic charge is withdrawn through the conductive base and the grounded support, to yield a residual electrostatic charge pattern constituting a latent image of the projected subject matter. The image is then developed by application of a colored powder with an opposite charge, which adheres to the charged areas of the latent image. The powder may be dusted on the image-bearing surface or applied in suspension from nonconductive liquid, the excess powder being removed to yield a positive image of the projected subject matter. If a powder is used having the same charge as electrostatic image, it is repelled thereby and adheres instead to the remaining areas to provide a negative image of the projected subject matter. The powder is preferably fusible so that it may be caused to adhere permanently to the recording sheet by temporarily heating (e.g., with infrared radiation).
Coating compositions for the preparation of electrophotographic recording materials may be applied from either organic solvent solutions or from aqueous emulsions. There are, of course, many advantages to the use of aqueous emulsions among which are reduced costs, ease of application and the improved safety factor from the standpoint of both nonflammability and reduced toxicity.
It is in the area of development that complications have arisen, especially where the sheet material base is paper or other semiporous substrate. There are several processes for development as discussed above, but the mode of application of primary concern in the practice of this invention is that using liquid dyes or colored materials dispersed in a liquid vehicle. Since these liquid toner particles must be substantially immiscible with the vehicle or carrier liquid but capable of being dispersed therein in the form of very small droplets, the concentration ratio of vehicle to toner is critical. In addition the vehicle should be a neutral organic liquid, highly insulating in nature--that is having high electrical resistivity and low dielectric constant. This high resistivity is necessary to avoid the discharge of the latent electrostatic image.
One drawback to the use of these liquid toners is the absorption of the toner or its vehicle into the porous base which disturbs the liquid toner-vehicle balance and results in loss of contrast and sharpness in the developed image. This is true to a degree in the case of any paper support and especially true where the sensitizing solution and other coating solutions are applied from aqueous emulsions.
These drawbacks have been overcome in the case of aqueous-based paper by the use of certain vinylpyrrolidone-styrene/butadiene polymers for the application of nonconductive barrier layers and, alternatively for the application of conductive layers, by the addition of quaternary ammonium salts thereto. In the case of solvent-based paper, the drawbacks were overcome by the quaternization of copolymers of vinylpyridine/vinylpyrrolidone with certain quaternizing agents.
However, even with the significant improvements afforded by the carrier and conductive coatings described above, there still remained several problems with solvent-based papers attributable chiefly to the specialized uses to which the papers are put. In general the conductive-coated solvent-based papers have undesirable glossy backs and excessive sensitivity to humidity. In copying machines utilizing liquid toner solutions such as the Bruning Copytron 2000, on the one hand, problems are odor, back curl and a 3-inch problem while in copying machines utilizing dry toner such as the Apeco Dial-A-Copy, on the other hand, odor, back-blistering and roll feed trouble have been the problems. Heretofore these problems were minimized by preparing specially coated papers for each type of copying machine.
It has been found, however, that by the process of this invention such problems can not only be overcome thereby providing one paper suitable for use in both wet and dry process machines, but providing also a resulting conductive film-coated paper having properties superior to any solvent-based paper heretofore available on a commercial basis.
Therefore this invention is based on the discovery that the replacement of the conductive resin in the aforesaid conductive-treating solutions by an inorganic salt-polyhydric alcohol system results in coated papers having greatly improved properties. Among these improvements are:
a. excellent solvent and dispersant hold-out,
b. good conductivity,
c. acceptable moisture retention and
d. minimal sensitivity to humidity changes over a relative humidity range of 16-80percent.
These results are all the more surprising since previous evaluations using inorganic salts alone had not only been unsuccessful but were, in fact, shown to have a deleterious effect on the coated paper due to the resulting sensitivity to humidity. Thus, totally unexpected results arise from the unique combination of a polyhydric alcohol having moisture-regulating properties with an inorganic salt.
A typical conductive barrier film-forming solution is composed of the following ingredients in the range and preferred quantities as listed:
Range, Preferred, Ingredient parts parts ____________________________________________________________ ______________ 1. Inorganic salt 2-4 2.25-3 2. Polyhydric alcohol 2-4 2-4 3. A polyvinylpyrrolidone polymer or a poly(vinylpyrrolidone-vinyl acetate)copolymer 0.25-5 3.3-4.3 4. Polyvinyl acetate emulsion 2.5-5 3.5-4.5 5. Acetylated starch 2-6.5 2.2-3 6. Polyvinyl alcohol 2-6.5 3-5 7. Water to make 100 100
While this invention is not limited to any specific inorganic salts, it is delimited to those containing monovalent cations because of the known hygroscopic or deliquescent properties of inorganic salts containing polyvalent cations and, in particular, of those containing divalent cations. To eliminate or at least minimize these aforesaid deleterious effects, a high purity criterion for the inorganic salt was established. One example of such compound is sodium chloride of 99.95 percent purity sold by Morton Salt Co. under the trade name Culinox 999. Other acceptable salts include compounds containing the ammonium ion or cations of the elements of Group I of the Periodic Table, i.e. lithium, sodium, potassium, rubidium and caesium with such anionic moieties as chloride, bromide, nitrate, sulfate, phosphate and other nonvolatile, conductive ions.
Suitable polyhydric alcohols include glycerol, glycols such as ethylene or propylene glycol, 1,4-butanediol and polyethylene glycols, sold, for example, under the trademarks Gafanol E 200 AND Gafanol E 300.
Since the paper surface in liquid toner systems must be completely immersed in the developer solutions, a barrier layer coating must be applied thereon. It has been found that an essential constituent in the coating compositions is a polyvinylpyrrolidone polymer. Examples of some vinylpyrrolidone polymers which are acceptable include:
a. Poly-N-vinylpyrrolidone,
b. N-vinylpyrrolidone-vinyl acetate copolymer (10:90),
c. N-vinylpyrrolidone-vinyl acetate copolymer (25:75),
d. N-vinylpyrrolidone-vinyl acetate copolymer (30:70),
e. N-vinylpyrrolidone-ethylacrylate copolymer (30:70), and
f. N-vinylpyrrolidone-ethylacrylate copolymer (30:70) mixed with poly-N-vinylpyrrolidone-vinyl acetate copolymer (25:75).
The ratios given in the parentheses indicate the proportions by weight of the component monomers.
Additional ingredients, polyvinyl acetate, acetylated starch and polyvinyl alcohol add body and gloss properties to the paper substitute or import the required viscosity to the coating compositions.
Several examples are set forth below to illustrate the nature of the invention and the method of carrying it out.
I. Preparation of Coating Solutions
The coating compositions listed below were used in the examples that follow. These compositions were formulated by standard chemical procedures, i.e., the salt was dissolved in water and added to a starch-polyvinyl alcohol slurry. This mixture was then heated to and maintained at 195° F. for 15 minutes. The resulting solution was cooled to 120° F. and the other ingredients were added followed by dilution of the mixture to the desired percent solids (15-35 percent). The formulations are identified by letter for purposes of convenience of reference to indicate these compositions in the examples below. The higher quantities for the ingredients in formulation E were necessary to achieve the required percent solids solution for size press purposes. ##SPC1##
II. Solvent and Toner Holdout Test
An empirical test was developed to measure the efficiency of the various coatings in resisting both solvent and liquid dye penetrations.
A frame assembly, having an 81/2×11-inch sheet of coated paper tightly clamped thereon, is positioned on a support with the surface of the paper at a 45°-degree angle to the horizon.
A funnel connected through a valve to a hypodermic syringe whose tip delivers a 2 mm. diameter drop is positioned above the paper with the tip 12 mm. from the paper's surface and perpendicular to the horizon.
In operation, a drop from the pipette strikes the paper surface and travels until completely absorbed or dried. The length of this free travel path is directly relatable to the efficiency of the various coatings. Measurements are made on both the wire and felt sides of the paper.
III. Resistivity Test
Data were also obtained on both surface and bulk resistivity.
Surface resistivity was calculated from measurements made of the voltage developed between a pair of 1-inch brass electrodes spaced 1 inch apart when placed on a paper sample mounted on an insulated surface. Bulk resistivity, i.e. the resistivity through the thickness of the paper, was calculated in an analogous manner with the paper placed on a conductive surface. In this procedure, however, the recorded voltage was that developed between the same pair of electrodes so positioned that one was on the paper and the other was on the conductive surface. These voltage measurements which were, in turn, converted into resistivity, were determined over a range of humidities. Since they are indicative of the static susceptibility of the paper surface, they are, of course, indicative of moisture content and, hence, humidity sensitivity.
Examples 1-4
These examples illustrate the beneficial effects to be obtained in using coating compositions containing various inorganic salts in combination with a polyhydric alcohol--in this case, glycerol.
Coating compositions prepared as described above were applied to various paper surfaces using the air knife techniques, at such a rate as to yield a coating, when dry, of 4.5 pounds for 3,000 square feet.
Solvent and toner holdout were determined by the procedure described above. The coatings offered excellent resistance to both solvent and toner absorption or penetration. Surface and bulk resistivities, determined at several humidities using the procedure described earlier, indicated that the coated papers were acceptable for electrophotographic use in either wet (liquid) or dry development processes.
Details as to the compositions of the coatings, the surface coated and the test data obtained are tabulated below. ##SPC2##
Examples 5-9
These examples show that various polyhydric alcohols can be used in the coating formulations.
Coatings were applied using the air knife procedure.
Solvent and toner holdout and resistivities were determined by the procedures described above. The coating offered excellent resistance to both solvent and toner absorption. Surface and bulk resistivities, determined at several humidities, indicated that the coated papers were acceptable for electrophotographic use in either wet or dry developed processes.
Details as to the compositions of the coatings, the surfaces coated and the test data obtained are tabulated below. No holdout data is available for examples 7 and 8. However, the resistivities indicate that such coatings would be acceptable for use in both wet and dry electrophotographic processes. ##SPC3##
Examples 10-15
These examples illustrate the suitability of the inorganic salt-polyhydric alcohol-based coatings when applied by size press with subsequent calendering.
Coating compositions prepared as described above were applied to various paper surfaces through a size press and machine-calendering operation. Solutions of higher solids content (35-40 percent solids) were needed to reach the desired solids pickup. For comparison purposes, a commercial paper containing an organic conductive agent in the barrier film and paper coated by air knife techniques with a composition of this invention were also evaluated.
Solvent and toner holdout were determined by the procedures described earlier. The size-press-applied coatings offered excellent resistance to both solvent and toner absorption. Surface and bulk resistivities, determined at several humidities using the procedure described earlier, show that the inorganic salt-polyhydric alcohol-coated papers were acceptable for electrophotographic use in either wet or dry development processes.
Details as to the compositions of the coatings, the surfaces coated, the application techniques and the data obtained are tabulated below. ##SPC4##
Electrophotographic recording is a process for producing visible images involving the conversion by the imagewise exposure to light of a uniformly electrostatically charged surface into a surface having a patterned configuration of electrostatically charged and discharged areas. Subsequent development of this patterned surface results in reproduction of the original image.
More particularly and as disclosed, for example, in U.S. Pat. No. 3,052,539, the electrophotographic recording material is charged in the dark by exposing its photoconductive zinc oxide pigment-coated surface to a charging device such as an arrangement of fine wires connected to a high-voltage DC source while the paper base is supported on a grounded metal plate. The pigment-coated surface, bearing a uniform electrostatic charge, is then exposed imagewise to light (e.g. by projection) whereby the light-exposed areas are rendered conductive, and their electrostatic charge is withdrawn through the conductive base and the grounded support, to yield a residual electrostatic charge pattern constituting a latent image of the projected subject matter. The image is then developed by application of a colored powder with an opposite charge, which adheres to the charged areas of the latent image. The powder may be dusted on the image-bearing surface or applied in suspension from nonconductive liquid, the excess powder being removed to yield a positive image of the projected subject matter. If a powder is used having the same charge as electrostatic image, it is repelled thereby and adheres instead to the remaining areas to provide a negative image of the projected subject matter. The powder is preferably fusible so that it may be caused to adhere permanently to the recording sheet by temporarily heating (e.g., with infrared radiation).
Coating compositions for the preparation of electrophotographic recording materials may be applied from either organic solvent solutions or from aqueous emulsions. There are, of course, many advantages to the use of aqueous emulsions among which are reduced costs, ease of application and the improved safety factor from the standpoint of both nonflammability and reduced toxicity.
It is in the area of development that complications have arisen, especially where the sheet material base is paper or other semiporous substrate. There are several processes for development as discussed above, but the mode of application of primary concern in the practice of this invention is that using liquid dyes or colored materials dispersed in a liquid vehicle. Since these liquid toner particles must be substantially immiscible with the vehicle or carrier liquid but capable of being dispersed therein in the form of very small droplets, the concentration ratio of vehicle to toner is critical. In addition the vehicle should be a neutral organic liquid, highly insulating in nature--that is having high electrical resistivity and low dielectric constant. This high resistivity is necessary to avoid the discharge of the latent electrostatic image.
One drawback to the use of these liquid toners is the absorption of the toner or its vehicle into the porous base which disturbs the liquid toner-vehicle balance and results in loss of contrast and sharpness in the developed image. This is true to a degree in the case of any paper support and especially true where the sensitizing solution and other coating solutions are applied from aqueous emulsions.
These drawbacks have been overcome in the case of aqueous-based paper by the use of certain vinylpyrrolidone-styrene/butadiene polymers for the application of nonconductive barrier layers and, alternatively for the application of conductive layers, by the addition of quaternary ammonium salts thereto. In the case of solvent-based paper, the drawbacks were overcome by the quaternization of copolymers of vinylpyridine/vinylpyrrolidone with certain quaternizing agents.
However, even with the significant improvements afforded by the carrier and conductive coatings described above, there still remained several problems with solvent-based papers attributable chiefly to the specialized uses to which the papers are put. In general the conductive-coated solvent-based papers have undesirable glossy backs and excessive sensitivity to humidity. In copying machines utilizing liquid toner solutions such as the Bruning Copytron 2000, on the one hand, problems are odor, back curl and a 3-inch problem while in copying machines utilizing dry toner such as the Apeco Dial-A-Copy, on the other hand, odor, back-blistering and roll feed trouble have been the problems. Heretofore these problems were minimized by preparing specially coated papers for each type of copying machine.
It has been found, however, that by the process of this invention such problems can not only be overcome thereby providing one paper suitable for use in both wet and dry process machines, but providing also a resulting conductive film-coated paper having properties superior to any solvent-based paper heretofore available on a commercial basis.
Therefore this invention is based on the discovery that the replacement of the conductive resin in the aforesaid conductive-treating solutions by an inorganic salt-polyhydric alcohol system results in coated papers having greatly improved properties. Among these improvements are:
a. excellent solvent and dispersant hold-out,
b. good conductivity,
c. acceptable moisture retention and
d. minimal sensitivity to humidity changes over a relative humidity range of 16-80percent.
These results are all the more surprising since previous evaluations using inorganic salts alone had not only been unsuccessful but were, in fact, shown to have a deleterious effect on the coated paper due to the resulting sensitivity to humidity. Thus, totally unexpected results arise from the unique combination of a polyhydric alcohol having moisture-regulating properties with an inorganic salt.
A typical conductive barrier film-forming solution is composed of the following ingredients in the range and preferred quantities as listed:
Range, Preferred, Ingredient parts parts ____________________________________________________________ ______________ 1. Inorganic salt 2-4 2.25-3 2. Polyhydric alcohol 2-4 2-4 3. A polyvinylpyrrolidone polymer or a poly(vinylpyrrolidone-vinyl acetate)copolymer 0.25-5 3.3-4.3 4. Polyvinyl acetate emulsion 2.5-5 3.5-4.5 5. Acetylated starch 2-6.5 2.2-3 6. Polyvinyl alcohol 2-6.5 3-5 7. Water to make 100 100
While this invention is not limited to any specific inorganic salts, it is delimited to those containing monovalent cations because of the known hygroscopic or deliquescent properties of inorganic salts containing polyvalent cations and, in particular, of those containing divalent cations. To eliminate or at least minimize these aforesaid deleterious effects, a high purity criterion for the inorganic salt was established. One example of such compound is sodium chloride of 99.95 percent purity sold by Morton Salt Co. under the trade name Culinox 999. Other acceptable salts include compounds containing the ammonium ion or cations of the elements of Group I of the Periodic Table, i.e. lithium, sodium, potassium, rubidium and caesium with such anionic moieties as chloride, bromide, nitrate, sulfate, phosphate and other nonvolatile, conductive ions.
Suitable polyhydric alcohols include glycerol, glycols such as ethylene or propylene glycol, 1,4-butanediol and polyethylene glycols, sold, for example, under the trademarks Gafanol E 200 AND Gafanol E 300.
Since the paper surface in liquid toner systems must be completely immersed in the developer solutions, a barrier layer coating must be applied thereon. It has been found that an essential constituent in the coating compositions is a polyvinylpyrrolidone polymer. Examples of some vinylpyrrolidone polymers which are acceptable include:
a. Poly-N-vinylpyrrolidone,
b. N-vinylpyrrolidone-vinyl acetate copolymer (10:90),
c. N-vinylpyrrolidone-vinyl acetate copolymer (25:75),
d. N-vinylpyrrolidone-vinyl acetate copolymer (30:70),
e. N-vinylpyrrolidone-ethylacrylate copolymer (30:70), and
f. N-vinylpyrrolidone-ethylacrylate copolymer (30:70) mixed with poly-N-vinylpyrrolidone-vinyl acetate copolymer (25:75).
The ratios given in the parentheses indicate the proportions by weight of the component monomers.
Additional ingredients, polyvinyl acetate, acetylated starch and polyvinyl alcohol add body and gloss properties to the paper substitute or import the required viscosity to the coating compositions.
Several examples are set forth below to illustrate the nature of the invention and the method of carrying it out.
I. Preparation of Coating Solutions
The coating compositions listed below were used in the examples that follow. These compositions were formulated by standard chemical procedures, i.e., the salt was dissolved in water and added to a starch-polyvinyl alcohol slurry. This mixture was then heated to and maintained at 195° F. for 15 minutes. The resulting solution was cooled to 120° F. and the other ingredients were added followed by dilution of the mixture to the desired percent solids (15-35 percent). The formulations are identified by letter for purposes of convenience of reference to indicate these compositions in the examples below. The higher quantities for the ingredients in formulation E were necessary to achieve the required percent solids solution for size press purposes. ##SPC1##
II. Solvent and Toner Holdout Test
An empirical test was developed to measure the efficiency of the various coatings in resisting both solvent and liquid dye penetrations.
A frame assembly, having an 81/2×11-inch sheet of coated paper tightly clamped thereon, is positioned on a support with the surface of the paper at a 45°-degree angle to the horizon.
A funnel connected through a valve to a hypodermic syringe whose tip delivers a 2 mm. diameter drop is positioned above the paper with the tip 12 mm. from the paper's surface and perpendicular to the horizon.
In operation, a drop from the pipette strikes the paper surface and travels until completely absorbed or dried. The length of this free travel path is directly relatable to the efficiency of the various coatings. Measurements are made on both the wire and felt sides of the paper.
III. Resistivity Test
Data were also obtained on both surface and bulk resistivity.
Surface resistivity was calculated from measurements made of the voltage developed between a pair of 1-inch brass electrodes spaced 1 inch apart when placed on a paper sample mounted on an insulated surface. Bulk resistivity, i.e. the resistivity through the thickness of the paper, was calculated in an analogous manner with the paper placed on a conductive surface. In this procedure, however, the recorded voltage was that developed between the same pair of electrodes so positioned that one was on the paper and the other was on the conductive surface. These voltage measurements which were, in turn, converted into resistivity, were determined over a range of humidities. Since they are indicative of the static susceptibility of the paper surface, they are, of course, indicative of moisture content and, hence, humidity sensitivity.
Examples 1-4
These examples illustrate the beneficial effects to be obtained in using coating compositions containing various inorganic salts in combination with a polyhydric alcohol--in this case, glycerol.
Coating compositions prepared as described above were applied to various paper surfaces using the air knife techniques, at such a rate as to yield a coating, when dry, of 4.5 pounds for 3,000 square feet.
Solvent and toner holdout were determined by the procedure described above. The coatings offered excellent resistance to both solvent and toner absorption or penetration. Surface and bulk resistivities, determined at several humidities using the procedure described earlier, indicated that the coated papers were acceptable for electrophotographic use in either wet (liquid) or dry development processes.
Details as to the compositions of the coatings, the surface coated and the test data obtained are tabulated below. ##SPC2##
Examples 5-9
These examples show that various polyhydric alcohols can be used in the coating formulations.
Coatings were applied using the air knife procedure.
Solvent and toner holdout and resistivities were determined by the procedures described above. The coating offered excellent resistance to both solvent and toner absorption. Surface and bulk resistivities, determined at several humidities, indicated that the coated papers were acceptable for electrophotographic use in either wet or dry developed processes.
Details as to the compositions of the coatings, the surfaces coated and the test data obtained are tabulated below. No holdout data is available for examples 7 and 8. However, the resistivities indicate that such coatings would be acceptable for use in both wet and dry electrophotographic processes. ##SPC3##
Examples 10-15
These examples illustrate the suitability of the inorganic salt-polyhydric alcohol-based coatings when applied by size press with subsequent calendering.
Coating compositions prepared as described above were applied to various paper surfaces through a size press and machine-calendering operation. Solutions of higher solids content (35-40 percent solids) were needed to reach the desired solids pickup. For comparison purposes, a commercial paper containing an organic conductive agent in the barrier film and paper coated by air knife techniques with a composition of this invention were also evaluated.
Solvent and toner holdout were determined by the procedures described earlier. The size-press-applied coatings offered excellent resistance to both solvent and toner absorption. Surface and bulk resistivities, determined at several humidities using the procedure described earlier, show that the inorganic salt-polyhydric alcohol-coated papers were acceptable for electrophotographic use in either wet or dry development processes.
Details as to the compositions of the coatings, the surfaces coated, the application techniques and the data obtained are tabulated below. ##SPC4##