Process control sensing of toner coverage

Abstract

A toner coverage sensing system is provided for sensing toner particles printed onto a surface of a process element using an electrophotographic printing system. The printed toner particles include porous color toner particles. An infrared radiation source directs infrared radiation onto the printed toner particles on the surface of the process element A diffused radiation detector senses infrared radiation scattered from the printed toner particles, wherein the diffused radiation detector is oriented such that that the sensed infrared radiation does not include specular reflections from the surface of the process element. A data processing system determines a sensed toner coverage for the porous color toner particles on the surface of the process element responsive to the sensed scattered infrared radiation.

Claims

1. A toner coverage sensing system for sensing toner particles printed onto a surface of a process element using an electrophotographic printing system, the printed toner particles including printed porous color toner particles, comprising: an optical sensing system including: an infrared radiation source that directs infrared radiation in an infrared wavelength band onto the printed toner particles on the surface of the process element; and a diffused radiation detector for sensing infrared radiation scattered from the printed porous color toner particles on the surface of the process element, wherein the diffused radiation detector is oriented such that the sensed infrared radiation does not include specular reflections from the surface of the process element; and a data processing system that determines a sensed toner coverage for the porous color toner particles on the surface of the process element responsive to the sensed scattered infrared radiation; wherein the porous color toner particles absorb less than 5% of the radiation in the infrared wavelength band.

2. The toner coverage sensing system of claim 1, wherein the infrared wavelength band has a peak wavelength in the range of 850-1050 nm.

3. The toner coverage sensing system of claim 1, wherein the process element is a photoconductor element, an intermediate transfer element or a receiver medium.

4. The toner coverage sensing system of claim 1, wherein the diffused radiation detector is positioned on a same side of the process element as the infrared radiation source to sense reflected infrared radiation.

5. The toner coverage sensing system of claim 1, wherein the diffused radiation detector is positioned on an opposite side of the process element as the infrared radiation source to sense transmitted infrared radiation.

6. The toner coverage sensing system of claim 5, wherein the sensed transmitted infrared radiation is sensed using an integrating sphere.

7. The toner coverage sensing system of claim 5, wherein the sensed transmitted infrared radiation does not include specularly transmitted infrared radiation.

8. The toner coverage sensing system of claim 1, wherein the porous color toner particles have a porosity of at least 10%.

9. The toner coverage sensing system of claim 1, wherein the color toner particles have an aspect ratio in the range of 0.6 to 1.0.

10. The toner coverage sensing system of claim 1, wherein the sensed scattered infrared radiation from the printed porous color toner particles is at least 20% higher than would be sensed for printed non-porous color toner particles having a same pigment and resin and a substantially equivalent particle geometry and toner coverage as the printed porous color toner particles.

11. The toner coverage sensing system of claim 1, wherein the printed toner particles on the surface of the process element also include non-porous black toner particles, the non-porous black toner particles absorbing at least 20% of the radiation in the infrared wavelength band; wherein the optical sensing system further includes a specular radiation detector oriented to sense infrared radiation specularly reflected from the surface of the process element; and wherein the data processing system determines a sensed toner coverage for the non-porous black toner particles on the surface of the process element responsive to the sensed specularly reflected infrared radiation.

12. The toner coverage sensing system of claim 1, wherein the printed toner particles are dry toner particles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a cross-sectional view of an infrared process control toner coverage sensor with separate photoelectric detectors for specularly reflected and diffusely reflected light;

(2) FIG. 2 shows graphs illustrating the response of the diffused light sensor to color toner coverage and the specular light sensor to black toner coverage;

(3) FIG. 3 is a graph illustrating absorbance spectra for an exemplary set of cyan, magenta, yellow and black toners;

(4) FIG. 4 is a graph showing diffused light detector signal as a function of toner coverage for porous and solid color toners;

(5) FIG. 5 is a graph showing specular light detector signal as a function of toner coverage for porous and solid color toners;

(6) FIG. 6 is a graph showing diffused light detector signal at a specified toner coverage for porous and solid color toners as a function of toner aspect ratio;

(7) FIG. 7 is a graph showing diffused light detector signal as a function of toner coverage for porous and solid black toners;

(8) FIG. 8 is a graph showing specular light detector signal as a function of toner coverage for porous and solid black toners; and

(9) FIG. 9 is a graph of absorbance measured in transmission as a function of toner coverage for porous and solid color toners.

(10) It is to be understood that the attached drawings are for purposes of illustrating the concepts of the invention and may not be to scale. Identical reference numerals have been used, where possible, to designate identical features that are common to the figures.

DETAILED DESCRIPTION OF THE INVENTION

(11) The invention is inclusive of combinations of the embodiments described herein. References to a particular embodiment and the like refer to features that are present in at least one embodiment of the invention. Separate references to an embodiment or particular embodiments or the like do not necessarily refer to the same embodiment or embodiments; however, such embodiments are not mutually exclusive, unless so indicated or as are readily apparent to one of skill in the art. The use of singular or plural in referring to the method or methods and the like is not limiting. It should be noted that, unless otherwise explicitly noted or required by context, the word or is used in this disclosure in a non-exclusive sense.

(12) Prior art toner coverage sensing systems using infrared radiation, such as that described with respect to FIG. 1, rely on optical scattering characteristics of the toner to sense a toner coverage of color toners which do not absorb significantly in the infrared wavelength range. With conventional solid toners, the measurement sensitivity using such toner coverage sensing systems is limited by the amount of light scattering provided by the toner particles.

(13) Inventors have discovered that use of porous toner particles in an electrophotographic printing system will produce improved measurement sensitivity, and therefore higher signal-to-noise ratios, in a toner coverage sensing system than are achievable with solid toner particles due to an increased level of light scattering (i.e., light diffusing) by the presence of cavities containing air when compared to the scattering properties of solid toner. In a preferred configuration, the porous toner particles have a porosity of at least 10%, wherein the porosity is measured by the method described in the aforementioned U.S. Pat. No. 7,887,984. Therefore, the present invention provides an improvement to the sensing of the cyan, magenta and yellow toner deposits by providing porous toner particles which scatter infrared light and thus increase the sensitivity and robustness of the toner coverage sensing process.

(14) None of the prior art references discussed earlier describe or suggest a toner coverage sensing system in which toner coverage levels of porous toner particles are sensed using a detector oriented to collect scattered or diffused infrared radiation. Nor is there any recognition that enhanced scattering characteristics that can be achieved using porous toner particles can be used to provide improved sensitivity characteristics in a toner coverage sensing system.

(15) The porous toner particles of this invention can be prepared using any method known in the art including the porous particle fabrication processes described earlier in the background section. Examples of such porous particle fabrication processes would include methods that employ multiple emulsions with either solvent evaporation or polymerization as the hardening mechanisms, methods that employ extraction of removeable components, variants of aggregation methods such as emulsion aggregation, and expansion methods such as foaming with a gas.

(16) The inventive examples described in the present disclosure are all based on porous toner samples prepared by the evaporative limited coalescence technique using the double emulsion method with a hydrocolloid additive to create porosity, as described in the aforementioned, commonly-assigned U.S. Pat. Nos. 7,887,984 and 9,029,431. The preparative formulations were adjusted such that a porosity of about 40% was obtained with pores averaging about 0.7 microns in size with the toner particles themselves at about 6 microns in volume median diameter. Comparative examples utilize commercially available color toners as well as solid toners prepared in the present laboratory by the evaporative limited coalescence method as described in the aforementioned, commonly-assigned U.S. Pat. Nos. 4,833,060, 6,207,338, 6,380,297 and 6,482,562.

(17) Table 1 describes the toner samples prepared in the inventors' laboratory by the evaporative limited coalescence process, which are either porous or solid. The pigments used are given by the abbreviated color index identification. Table 2 describes a set of commercially obtained toner samples which are used for comparative examples.

(18) TABLE-US-00001 TABLE 1 Example toners fabricated in inventors' laboratory Aspect D.sub.vol Example Toner Colorant(s) Ratio (microns) Porous ELC Toner 1 P.R. 122/P.R. 185 0.67 6.2 Porous ELC Toner 2 P.R. 122/P.R. 185 0.69 6.2 Porous ELC Toner 3 P.B. 15:3 0.82 6.1 Porous ELC Toner 4 P.B. 15:3 0.82 6.1 Porous ELC Toner 5 P.Y. 155 0.85 6.2 Porous ELC Toner 6 P.Y. 155 0.87 5.9 Porous ELC Toner 7 P.B. 15:3 0.89 5.8 Porous ELC Toner 8 P.B. 15:3 0.90 6.0 Porous ELC Toner 9 P.B. 15:3 0.96 6.6 Porous ELC Toner 10 carbon/P.B. 15:3 0.81 6.5 Porous ELC Toner 11 carbon/P.B. 15:3 0.96 6.2 Solid ELC Toner 1 P.B. 15:3 0.77 5.9 Solid ELC Toner 2 P.B. 15:3 0.81 5.9 Solid ELC Toner 3 P.B. 15:3 0.82 6.2 Solid ELC Toner 4 P.B. 15:3 0.82 6.1 Solid ELC Toner 5 P.B. 15:3 0.83 5.8 Solid ELC Toner 6 P.B. 15:3 0.84 5.9 Solid ELC Toner 7 P.Y. 155 0.87 5.5 Solid ELC Toner 8 P.B. 15:3 0.87 5.9 Solid ELC Toner 9 P.B. 15:3 0.89 5.9 Solid ELC Toner 10 P.B. 15:3 0.90 5.9 Solid ELC Toner 11 P.B. 15:3 0.90 6.7 Solid ELC Toner 12 P.R. 122/P.R. 185 0.91 6.6 Solid ELC Toner 13 P.Y. 155 0.91 6.1 Solid ELC Toner 14 P.R. 122/P.R. 185 0.96 6.3 Solid ELC Toner 15 P.B. 15:3 0.97 5.8 Solid ELC Toner 16 P.Y. 155 0.97 6.2 Solid ELC Toner 17 carbon/P.B. 15:3 0.84 6.0

(19) TABLE-US-00002 TABLE 2 Commercially-available toner examples Example Toner Source Product Color Solid Toner A Samsung C5045 C (cyan) Solid Toner B Samsung M5045 M (magenta) Solid Toner C Samsung Y5045 Y (yellow) Solid Toner D Samsung K5045 K (black) Solid Toner E Konica Minolta TN616C C Solid Toner F Konica Minolta TN616M M Solid Toner G Konica Minolta TN616Y Y

(20) The porous toner particles of this invention can be spherical or non-spherical depending upon the desired use. The shape of porous particles can be characterized by an aspect ratio that is defined as the ratio of the largest length of the particle which is perpendicular to the longest overall length of the particle (the caliper diameter) to the longest overall length of the particle. These lengths can be determined for example by optical measurements using a commercial particle shape analyzer such as the Sysmex FP1A-3000 (Malvern Instruments). For example, porous particles that are considered spherical for this invention can have an aspect ratio of at least 0.95 and up to and including 1.0. For the non-spherical porous particles of this invention the aspect ratio can be at least 0.4 and up to and including 0.95. Table 1 includes aspect ratio measurement results for the toners prepared by the evaporative limited coalescence process in the present laboratory.

(21) The porous color toner particles of the present invention can contain either dyes or pigments. Full color images are normally printed with four toners comprising cyan (C), magenta (M), yellow (Y) and black (K). Cyan toners utilize colorants that absorb largely red wavelengths, but not infrared wavelengths; magenta toners utilize colorants that absorb largely green wavelengths, but not infrared wavelengths; yellow toners utilize colorants that absorb largely blue wavelengths, but not infrared wavelengths; black toners based on carbon black as a colorant absorb all wavelengths of the visible spectrum, and also significantly absorb infrared wavelengths. (Within the context of the present disclosure, significantly absorb will be taken to mean absorbs at least 20% of radiation in the infrared wavelength band sensed by the toner coverage sensor 31 as measured in transmission at 0.4 mg/cm.sup.2 toner coverage for a well fused sample on a clear support material as previously discussed.) For the purposes of discussion, we will refer to cyan, magenta and yellow toners as color toners, while black will not be considered to be a color toner. Color toners can also include colorants that are chosen to be used for spot or accent color reproduction, or color gamut enhancement. Examples include toners that would be considered to be red, blue, green, orange or violet, etc. Commercially available toner materials largely utilize pigments as colorants, however dyes are also represented. Useful cyan colorants include those with the Color Index designations of Pigment Blue 15, Pigment Blue 15:1, Pigment Blue 15:2. Pigment Blue 15:3, Pigment Blue 16 and Pigment Blue 79. Useful magenta colorants include those with the Color Index designations of Pigment Red 57:1, Pigment Red 81, Pigment Red 81:1, Pigment Red 122, Pigment Red 169, Pigment Red 185, and Pigment Violet 19. Useful yellow colorants include those with the Color Index designations of Pigment Yellow 12, Pigment Yellow 13, Pigment Yellow 17, Pigment Yellow 74, Pigment Yellow 155, Pigment Yellow 180, Pigment Yellow 185, Pigment Yellow 194 and Solvent Yellow 162. Useful colorants for accent, spot and gamut enhancement purposes include those with the Color index designations of Pigment Blue 61, Pigment Violet 1, Pigment Violet 3, Pigment Violet 23, Pigment Red 53:1, Pigment Red 53:3, Pigment Red 112, Pigment Red 146, Pigment Green 7, Pigment Orange 5, and Pigment Orange 34. This list should not be considered to be limiting as to which colorants are suitable to use in porous toner used in an electrophotographic printing process using a toner coverage sensor (i.e., a DMA sensor) operating at infrared wavelengths that detects scattered light. Color toners can utilize mixtures of colorants. Carbon black has the Color Index designation Pigment Black 7; toners based on carbon black absorb too much light at infrared wavelengths to be useful for measuring the infrared scattering in accordance present invention, and will be seen to be instructive as comparative examples to understand the nature of the invention.

(22) The porous color toner particles of the present invention can be based on a variety of resin materials that are useful in dry toner based electrophotographic printing. Included are polyester resins, styrene-acrylic copolymer resins, epoxy resins, acrylic resins, hydrocarbon resins, bio-derived resins, and many other suitable materials. The porous toner particles can contain additives that are useful for other aspects of toner performance such as waxes including polyethylene waxes, ester waxes, paraffin waxes, and other suitable materials, charge control agents, adhesion promoting additives, anti-blocking additives, anti-microbial additives, magnetic additives, conductive additives, and others.

(23) A desktop device that can directly measure the Image Density Control (IDC) or Developed Mass per unit Area (DMA) response of a color printer to toner deposits was fabricated by using the IDC sensor of a Samsung Xpress C1810W printer. FIG. 1 describes the underlying geometry of this sensor. The Samsung Xpress C1810W IDC sensor contains an infrared LED emitter element 32 as the toner patch illuminant and two photoelectric sensors with the geometry defined so that one sensor (specular radiation detector 34) detects specularly reflected light and the second sensor (diffused radiation detector 36) detects diffused or scattered reflected light. The LED emission was measured to be centered at 930 nm. In an electrophotographic process the toner images used as test patches, transferred or developed onto process element 1, are transported past the toner coverage sensor 31 by the process element 1.

(24) After measuring the IDC sensor bracket to intermediate transfer belt spacing in the Samsung Xpress C1810W printer, the IDC sensor was removed from the printer and mounted so that the IDC sensor bracket to toner deposit distance of 0.075 and the general sensor to toner patch geometry was duplicated. +5.2V DC was supplied to connector pin #2. Power supply ground was supplied to connector pin #3. A potentiometer was wired in series with the LED emitter ground return (connector pin #5) to control the output of the IDC sensor's LED emitter. The voltage drop across the potentiometer under the measurement conditions was 2.3 V. The output signals of the two photoelectric sensors were monitored by measuring the voltage on connector pins #1 and #4 relative to power supply ground.

(25) The apparatus just described was used to study the sensor response to patches of toner prepared on a reflective black substrate such as the intermediate transfer belt taken from a Samsung Xpress C1810W printer. Patches of unfused toner were electrostatically coated on strips cut from the transfer belt, and measured for toner coverage (i.e., DMA) in units of milligrams per square centimeter (mg/cm.sup.2). The electrostatic coating device comprised a small magnetic brush developer station with a 1 cm wide development zone that utilizes two-component development with strontium ferrite carrier. Direct toning of a strip of substrate that is transported at constant speed past the developing station was accomplished with application of a DC bias voltage applied to the toning roller. The weight and area of the toner patches were measured, and the coated strip was placed under the Samsung Xpress C1810W IDC sensor to record the output of both the scattered and reflected light photoelectric sensors. The patches were seen to be free of any magnetic carrier particles.

(26) The toner coverage of the patches was controlled by the bias voltage level or the toner concentration of the developer loaded into the station. It was learned that reflective black coated paper from the Leneta Company as Opacity Charts Form 2A, could be used instead of strips cut from an intermediate transfer belt with no change in the resulting sensor output vs. toner coverage relationship. All of the data reported in this disclosure were prepared on this black reflective paper substrate.

(27) Table 3 describes both inventive examples and comparative examples of toner coverage sensing (i.e., DMA sensing) of toner deposits in reflection with the materials listed in Table 1 and Table 2. Table 4 describes inventive and comparative examples of toner coverage sensing of toner deposits in transmission with materials listed in Table 1 and Table 2.

(28) TABLE-US-00003 TABLE 3 Toner coverage sensing examples (in reflection) Sensor Signal at 0.4 Example Geometry Toner Example(s) Color mg/cm.sup.2 Inventive Ex. 1 diffuse Porous ELC Toner 4 C 2.55 Inventive Ex. 2 diffuse Porous ELC Toner 1 M 2.56 Inventive Ex. 3 diffuse Porous ELC Toner 5 Y 2.47 Inventive Ex. 4 specular Porous ELC Toner 4 C 1.02 Inventive Ex. 5 specular Porous ELC Toner 1 M 1.03 Inventive Ex. 6 specular Porous ELC Toner 5 Y 0.99 Inventive Ex. 7 diffuse Porous ELC Toners 1-9 C, M, Y Comp. Ex. 1 diffuse Solid Toner A C 1.59 Comp. Ex. 2 diffuse Solid Toner B M 1.59 Comp. Ex. 3 diffuse Solid Toner C Y 1.58 Comp. Ex. 4 specular Solid Toner A C 0.57 Comp. Ex. 5 specular Solid Toner B M 0.55 Comp. Ex. 6 diffuse Solid Toner C Y 0.56 Comp. Ex. 7 diffuse Solid Toner E C 1.34 Comp. Ex. 8 diffuse Solid Toner F M 1.40 Comp. Ex. 9 diffuse Solid Toner G Y 1.26 Comp. Ex. 10 diffuse Solid ELC Toners 1-16 C, M, Y Comp. Ex. 11 diffuse Solid Toner D K 0.138 Comp. Ex. 12 diffuse Solid ELC Toner 17 K 0.126 Comp. Ex. 13 diffuse Porous ELC Toner 10 K 0.186 Comp. Ex. 14 diffuse Porous ELC Toner 11 K 0.205 Comp. Ex. 15 specular Solid Toner D K 0.079 Comp. Ex. 16 specular Solid ELC Toner 17 K 0.069 Comp. Ex. 17 specular Porous ELC Toner 10 K 0.079 Comp. Ex. 18 specular Porous ELC Toner 11 K 0.090

(29) TABLE-US-00004 TABLE 4 Toner coverage sensing examples (in transmission) Sensor Signal at 0.4 Example Geometry Toner Example(s) Color mg/cm.sup.2 Inventive Ex. 8 Transmission Porous ELC Toner 4 C 0.286 Comp. Ex. 19 Transmission Solid Toner A C 0.107

(30) FIG. 4 shows a graph 60 of the output of the diffused light sensor 36 (FIG. 1) as a function of toner coverage (developed mass per area) in units of mg/cm.sup.2 for inventive examples with porous toner particles, and comparative examples with solid toner particles. Inventive Examples 1, 2 and 3 used cyan, magenta and yellow porous toners, respectively. Comparative Examples 1, 2 and 3 illustrate the sensing of the solid cyan, magenta and yellow toners sold with the Samsung Xpress C1810W printer from which the sensor itself was removed. It is seen that as toner coverage is increased, the sensor signal increases for all the inventive and comparative examples, but that the signals are approximately 50% to 60% larger for the inventive porous toner sensing examples. In preferred embodiments, the porous nature of the porous toner particles causes the sensed scattered infrared radiation from the printed porous color toner particles to be at least 20% higher than would be sensed for printed non-porous color toner particles having the same pigment and resin and a substantially equivalent particle geometry and toner coverage. Within the context of the present disclosure, a substantially equivalent particle geometry is one having the same size and aspect ratio distributions to within 10%, and a substantially equivalent toner coverage is one having the same mass per unit area to within 5%. It is seen that for both types of toner there is no significant difference in signal levels among the cyan, magenta and yellow samples.

(31) FIG. 3 discussed previously demonstrates that the solid toners of Comparative Examples 1, 2 and 3 do not absorb light at the 930 nm wavelength of the sensor; this is also the case for the colorants used in the inventive samples. The sensor response with comparative solid toners is due to light scattered from the surfaces of the unfused toner particles. The signal is enhanced for the inventive porous toners by scattering of light from the internal pores of the toner particles.

(32) The data of FIG. 4 were fit with a second order polynomial in order to interpolate the sensor response at 0.4 mg/cm.sup.2, which approximates the toner coverage of monochrome process color maximum density areas of modern electrophotographic printers using toner of about 6 microns in diameter. These values are listed in Table 3, along with a description of Inventive Examples 1, 2 and 3, and Comparative Examples 1, 2 and 3.

(33) FIG. 5 shows a graph 70 of the response of the specular light sensor 34 (FIG. 1) oriented to collect specularly reflected light to the same toner patches on black reflective paper that were tested for the response of the diffused light sensor 36 as shown in FIG. 4. It is seen that the sensor reading in FIG. 5 for both solid and porous toners are much lower than those in FIG. 4. However, the signal output values with porous cyan, magenta and yellow toner particles (i.e., Inventive Examples 4, 5 and 6) are much higher than those with solid cyan, magenta and yellow toner particles (i.e., Comparative Examples 4, 5 and 6). The values of a second order polynomial fit to these data evaluated at 0.4 mg/cm.sup.2 are included in Table 3. It is seen that the use of porosity in color toner particles allows for the use of the specular radiation detector 34 oriented to collect specularly reflected light to measure toner coverage as there is a substantial slope to the signal vs. toner coverage relationship over the useful range of toner coverage of approximately 0.25 to 0.45 mg/cm.sup.2 for modern 6 micron diameter toners, while the signal for solid toner particles over this range is essentially flat and would not be useful in controlling the amount of toner on a printed page.

(34) FIGS. 4 and 5 illustrate the much improved signal level and robustness of sensing toner coverage in an electrophotographic printing system using the combination of porous toner particles and a toner coverage sensor operating at infrared wavelengths, especially one oriented to collect diffused light. Further, the use of porous toner particles offers the possibility of using a simpler and less expensive sensor that only collects specular light at the equivalent angle to the emitter as demonstrated by FIG. 5.

(35) It is shown in FIG. 2 that for black toner using a geometry selected for specularly reflected light, the signal decreases as the toner coverage of the toner is increased. This is expected since black absorbs infrared light, thus the higher the coverage of black toner, the less light will be reflected and collected by the photoelectric sensor. In the case of Inventive Examples 4, 5 and 6 of FIG. 5 the presence of highly scattering porous toner will block light from being reflected into the specular radiation detector 34, however it will also scatter light at all angles including into the specular radiation detector oriented at the equivalent angle to the emitter. The latter is clearly the dominant phenomena which results in a higher signal with increasing toner coverage. With the solid color toners in Comparative Examples 4, 5 and 6, the blockage of reflected light which would lower the signal is compensated for by a degree of scattering, resulting in an essentially flat signal with toner coverage over the useful range and is thus useless as a printing process control sensor. Toner porosity is seen to enable a useful sensing of color toners for the geometry where the emitter and collector are oriented at equivalent angles.

(36) Comparative Examples 7, 8 and 9 listed in Table 3 include the interpolated signal data from patches of Solid Toner Examples E, F and G, comprising cyan, magenta and yellow solid toners from a Konica Minolta C6000 printer. These toners are known to be manufactured by an emulsion aggregation chemical process as are the cyan, magenta and yellow toners from the Samsung Xpress C1810W. The diffused radiation detector signals are seen to be higher for the Samsung than the Konica Minolta materials. Cyan, magenta and yellow toners gave 1.59, 1.59, 1.58 volts, respectively, for Solid Toner Examples A, B, C (i.e., the Samsung toners) used in Comparative Examples 4, 5 and 6 compared to 1.34, 1.40, 1.26 volts for Solid Toner Examples E, F, G (i.e., the Konica Minolta toners) used in Comparative Examples 7, 8 and 9. When examined with a scanning electron microscope, the Konica Minolta toners appear smoother and rounder than the Samsung toners, which appear relatively more folded and oblong. Toner particle shape is thus seen to be a strong factor in the degree of scattering of infrared light; shape can be affected by toner manufacturing process variability and thus there is a need for a sensing process that is more robust to toner shape variation in order to be effective with a range of toner geometries.

(37) FIG. 6 shows a graph 80 of the diffused radiation detector signal at a toner coverage of 0.4 mg/cm.sup.2 as a function of toner aspect ratio for the porous and solid toners made by the evaporative limited coalescence process as described in Table 1. Diffused radiation detector data for Inventive Example 7 (corresponding to Porous ELC Toner Examples 1-9), and Comparative Example 10 (corresponding to Solid ELC Toner Examples 1-16), are plotted in the order presented in Table 1. Color toners including cyan, magenta and yellow are included for each curve. Recall that the aspect ratio used here is defined as the ratio of the largest perpendicular length to the longest length of a toner particle; perfect spheres would have an aspect ratio of 1.0. It is seen that the more the shape difference from perfect spheres (i.e., the lower the aspect ratio), the higher is the sensor signal. However, the slope of the solid toner data (i.e. Comparative Example 10), is much higher (by about a factor of 4), than that for the porous toner samples (i.e., Inventive Example 7). Therefore, the use of porous color toner particles is seen to result in toner coverage sensing which is much more robust to toner shape variation than with the use of solid color toner particles.

(38) The sensing behavior of black toner including carbon black as a colorant is much different that the sensing behavior of color toners. Comparative Examples 11 to 14 of Table 3 describe the sensing of both porous black and solid black toner examples using the diffused radiation detector 36 oriented to collect diffused light, and Comparative Examples 15 to 18 of Table 3 describe the sensing both porous black and solid black toners using the specular radiation detector 34 oriented to collect specularly reflected light.

(39) FIG. 7 shows a graph 90 of diffused radiation detector signal as a function of toner coverage for Comparative Examples 11 to 14. It is seen for both the solid black toners (i.e., Comparative Examples 11 and 12) and porous black toners (i.e., Comparative Examples 13 and 14) that there is essentially no slope to the signal as a function of toner coverage, thus these sensing embodiments are not useful for process control of toner coverage in a printer. Therefore, it can be concluded that carbon-black-based black toners absorb the infrared emitter light too strongly to use the diffused radiation detector 36. For this reason, the specular radiation detector 34 is normally used to measure such black toners in a printer as was discussed earlier with respect to FIG. 2.

(40) FIG. 8 shows a graph 100 of specular radiation detector signal as a function of toner coverage for Comparative Examples 15 to 18. Comparative Examples 11 and 15 use the Samsung K504S toner that is sold for with the Samsung Xpress C1810W printer from which the toner coverage sensor 31 was taken. It is seen from Comparative Example 15 in FIG. 8, that when this toner is sensed using the specular radiation detector 34, a slope in the signal as a function of toner coverage exists that can be used for electrophotographic process control. This is clearly how the Samsung Xpress C1810W functions. However, when compared to the behavior of the diffused light sensor with color toners, both solid and porous, in FIG. 4, it is seen that black toner is detected with much less sensitivity than the color toners.

(41) It is seen in FIG. 8 that when sensing with the specular radiation detector 34, the addition of porosity to black toners comprising carbon black as a pigment (as in Comparative Examples 17 and 18) decreases the signal sensitivity to toner coverage, in contrast to the increase in sensitivity for Inventive Examples 4-6 with color toners as seen in FIG. 5. It should be noted that the solid and porous toner samples prepared by the evaporative limited coalescence process in the above discussion contain a major amount of carbon black plus a minor amount of Pigment Blue 15:3 as colorants; the latter is added to provide a hue that is a bluer, colder neutral rather than the browner, warmer hue that results from the use of carbon black alone.

(42) The toner property that distinguishes the inventive sensing examples with color toners from the comparative sensing examples with black toners is the absorbance of infrared light by the black toners due to the use of carbon black as a colorant. A black toner can be prepared using an appropriate combination of color pigments such as cyan, magenta and yellow or a mixture of cyan, orange and violet, to yield a black hue. Based on the knowledge gained through the present investigation, it is expected that such a toner would be sensed properly by the diffused radiation detector 36 using infrared radiation, and would exhibit improved sensitivity and robustness with the addition of porosity. It is also expect that such a toner could be sensed in a useful manner by the specularly reflected light detector by the addition of porosity.

(43) It is seen in FIG. 3 that the cyan, magenta and yellow colorants of a commercially available color toner set do not absorb significant levels of radiation in the range of 850 to 1050 nm wavelengths. The wavelength range of infrared light is commonly quoted as 700 nm to 1000 nm or higher. The portion of that range that could thus find utility in toner coverage sensing is at least 850 nm to 1050 nm. The toner coverage sensor 31 used in this study operates at 930 nm; sensors discussed previously in the prior art also operate in the mid 900s of nm. For the purposes of the present disclosure, the most useful color toners are those which do not absorb significant amounts (e.g., less than 5%) of infrared light above 850 nm.

(44) The inventive and comparative sensing examples just described were all based on reflective sensing of toner patches on black reflective support with a commercially available toner coverage sensor 31 from a Samsung electrophotographic printer where the toner images to be sensed are located on an opaque black reflective intermediate transfer element. In other configurations, the toner coverage is measured on a transparent or semi-transparent process element. For example, in the Kodak NexPress SX3900 printer is performed on the intermediate transfer element, which is a belt that is transparent to both visible and infrared wavelengths of light. The Kodak NexPress SX3900 printer uses visible light sensing where red, green and blue wavelength emitters are located on one side of the intermediate transfer belt, with the corresponding photoelectric detectors being located on the opposite side of the intermediate transfer belt. Thus, this sensor utilizes transmitted light rather than reflected light as described in the previous examples.

(45) To illustrate toner coverage sensing at IR wavelengths in transmission geometry, a Perkin-Elmer UV-VIS model Lambda 35 spectrophotometer was used to simulate the operation of a transmission sensor designed to fit in an electrophotographic printer. Toner patches were electrostatically coated onto a clear support at a series of toner coverage levels. The total absorbance was measured for patches of a solid toner and a porous toner as described in Table 4. The Perkin-Elmer spectrophotometer was equipped with an integrating sphere detector that collects the forward scattered light that can be captured by the available geometry of the detector. The system can be configured to optionally include or exclude the specularly transmitted (i.e., directly transmitted) light from the measurements. In a preferred configuration, the specularly transmitted light is excluded. The total absorbance at 930 nm is plotted vs. toner coverage in the graph 110 of FIG. 9. It is seen that the signal is about a factor of 2.5 higher for Inventive Example 8 with a porous toner relative to Comparative Example 19 with a solid toner. A toner coverage sensing process using porous toners in transmission is thus seen to be advantaged similar to the toner coverage sensing process using porous toners in reflection. It should be noted that in alternate embodiments it is not necessary to use an integrating sphere to collect the scatter radiation. Rather, a diffused radiation detector 36 can be positioned to collect transmitted scattered radiation within a particular range of scattering angles.

(46) In the described examples, the process element 1 used for the toner coverage measurements has been an intermediate transfer element. In other embodiments, the process element 1 can be other types of media including photoconductor elements (e.g., photoconductor drums or belts), or the final receiver medium.

(47) The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.

PARTS LIST

(48) 1 process element 31 toner coverage sensor 32 emitter element 34 specular radiation detector 36 diffused radiation detector 44 sensor output 46 sensor output 50 graph 60 graph 70 graph 80 graph 90 graph 100 graph 110 graph