Fast film, powerful battery improve Polaroids Increased amounts, size of silver halide grains, new sensitizer, proprietary layers increase film speed; stronger battery powers strobe flash
Two technological advances paved the way for development of the improved instant camera systems introduced last month by Polaroid Corp., Cambridge, Mass. (C&EN, June 1, page 19). One was a fourfold increase in film speedcompared to film used by the company's SX-70 camerato ASA 600. The second was a tripling in power of the film pack battery which charges the strobe flash, in addition to operating the focusing system, sonar distance
finder, and photo ejection motor of the new systems.
The high film speed allows use of narrower lens openings and 0.01-second shutter speeds for sharper pictures. The fast film also allows use of the strobe as an indoor flash with a range from 2 to more than 14 feet, and as a supplemental light source outdoors to fill in shadows and dark areas.
Polaroid research vice president Peter O. Kliem details four changes the company made in SX-70 film to increase the speed for the new system. First, the amount of silver halide in the three layers sensitive to red, blue, and green light was increased 30%. Second, the company developed new techniques for silver halide crystal growth and increased silver halide grain size to a mean diameter of 1.8 .
Third, a new sensitizer dye was in
corporated into the green-light-sensitive emulsion. Sensitizers are merocyanine dyes, which are adsorbed onto silver halide grains, and which absorb red, blue, or green light. Sensitizer molecules absorb light and then emit electrons, which flow into a silver halide grain to expose it.
Finally, Polaroid added two new spacer layers, one between the blue-sensitive emulsion and the yellow-dye-developer layers, and the other between the red-sensitive emulsion and the cyan (blue) dye developer. Kliem says the proprietary layers enhance light utilization.
Use of the strobe flash with every picture taken, whether indoors or out, lets Polaroid cash in on the dynamic range of the new film. Dynamic range is the response of a film to varying brightness levels in a scene, gauged according to the log curve. A log curve is a plot of the picture density
Following exposure of new film . . . No White Blue Green Red
light light light light light
. . . reagent spreading leads to development
Clear plastic protects image
Receiving layer forms image by fixing dyes that migrate to it
Alkali in injected reagent causes dyes to diffuse upwards, while titanium diox ide both forms white background for image and protects unexposed silver halide crystals
Proprietary new spacer layers increase film speed by using light more efficiently
Blue light exposes silver halide crystals that immobilize yellow dye
Green light exposes silver halide crystals that immobilize red dye
Red light exposes silver halide crystals that then immobilize blue dye
Unexposed silver halide
# Exposed silver halide
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52 C&EN June 22, 1981
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Our traditional processes: - Nitration - Catalytic hydrognation and other reactions
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on the vertical axis versus the log of the light exposure on the horizontal axis. Such plots take the form of a letter S.
Films with limited dynamic ranges have steep log curves for each of the three emulsions, resulting in sharp separations of color responses and, so, sharper colors. Extended dynamic ranges respond to greater ranges of brightness differences, but color resolution is poorer and colors are flatter.
In the new Polaroid system, the 0.01-second shutter speed results in a limited dynamic range for good color resolution, but the intense 300-microsecond strobe flash causes what photographic engineers call high-intensity failure of the silver halide reciprocity effect expressed in the log curve. The result is that the dynamic range of the film seems greater and the S-shaped curve more shallow for the light contribution from the strobe than for ambient light from the scene. Thus pictures taken in this way show more of the brightness differences in the scene without sacrificing sharpness of colors.
Tripling of the film pack battery power was needed because charging the strobe takes 10 times as much power as all of the other camera functions combined, says Sheldon A. Buckler, executive vice president for nonphotographic products. Though the length and width of the 0.18-inch-thick battery were unchanged, Polaroid now works closer to the edges in the new battery to increase available surface area. Amounts of electrolyte and electrode materials also were increased. The ammonium chloride/zinc chloride-based electrolyte also was changed slightly and the battery compressed to reduce void volume, both of which improvements reduced internal battery resistance.
As with SX-70 batteries, Polaroid starts with polyvinyl chloride film, solvent-coated with carbon black to make it conductive. "Spots" of zinc powder or manganese dioxide are printed on films by a gravure process. Anode and cathode films are separated by nonwoven fabric battery separators, gravure-impregnated with electrolyte. Four such cells are laminated together in series, bonded with polyamide adhesive at the edges, and encased in aluminum foil, which serves both as vapor barrier and current collector.
The basic chemistry of the highspeed film also remains the same as in earlier Polaroid instant films. After red, blue, and green light from the
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CIRCLE 43 ON READER SERVICE CARD June 22, 1981 C&EN 53
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Learn from the Leaders-In Person! An ACS Lecture-Laboratory Demonstration Course
Priority Pollutant Analysis Wastewater Co-sponsored by Battelles Columbus Laboratories
August 19-21,1981- Columbus, Ohio The course is a comprehensive introduction to the analysis of 129 priority pollutants in wastewater. It is a lecture intensive program with some procedures demonstrated in the laboratory. Important topics include theory of instrumentation, protocol methodology ( the "600" methods), sample handling, quality control, quality assurance and laboratory demonstrations showing basic GC, HPLC and AA methods along with GC/MS and ICAP procedures.
The course will benefit industrial and academic chemists, techni-cians, and students who have little experience in priority pollutant analysis. Specialists with backgrounds in relatively narrow areas of the field will also find the course useful as a means of broadening their skills.
Faculty Dr. Marcus Cooke, Projects Manager, Battelle-Columbus. Dr. Harold M. McNair, Professor of Chemistry, Virginia Polytechnic Institute and State University. Dr. Walter M. Shackelford, Research Chemist, U.S. EPA. Dr. Ralph Riggin, Associate Section Manager, Battelle-Columbus. Guest lecturers from Battelle will also participate.
Comments from Previous Attendees 'Very informative course. Well-organized and well-prepared course. All the instructors were very knowledgeable and helpful. They also did a good job of pointing out actual problems which may occur during testing. "
'The variety of people that attended and the chance to ask questions of those who were already doing this type of analysis was a real plus. "
'The course was timely and well-organized with excellent speakers. "
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For More Information To obtain a detailed brochure on the course, write to the Department of Educational Activities, American Chemical Society, 1155 16th Street, N.W., Washington, DC 20036 or Call Collect: 202-872-4508.
scene exposes appropriate emulsion layers, ejection of the film from the camera between rollers expresses re-agent from a three-compartment pod at the edge of the film between two interlayers near the top surface.
Titanium dioxide in the reagent both protects underlying emulsions from further exposure outside the camera and serves as a white back-ground for the image formed on top of it by the colored dyes. Strong alkali in the reagent converts developer groups bonded to dye molecules to their conjugate bases, solubilizing and mobilizing them for upward migra-tion.
As dye-developer molecules diffuse upward through emulsion layers, any exposed silver halide grains they meet oxidize developer groups, rendering the dyes insoluble and immobilizing them within the emulsion. Molecules that do not meet exposed silver halide grains continue migrating upward through the reagent layer to a mord-ant layer just below the clear plastic protective top film, where they are fixed to form the image.
Steve Stinson, New York
USDA process converts xylose to ethanol Scientists at the Department of Ag-riculture's Northern Regional Re-search Center (NRRC) in Peoria, 111., are developing a new and promising process for making ethanol from crop residues and other plant wastes. What's new about the process is that it depends upon a particular strain of yeast, Pachysolen tannophilus, that ferments D-xylose directly to eth-anol.
Microbiologist Rodney J. Bothast, the NRRC research team leader, notes that the 500 million tons of crop residues produced annually in the U.S. contain 10 to 25% xylose, de-pending on the crop. Even if the lower 10% figure is assumed, 50 million tons of xylose would yield 4 billion to 5 billion gal of ethanol. (This is more than 10 times combined U.S. pro-duction of synthetic and fuel-grade fermentation ethanol.)
Paper mill wastes could prove an even better source of xylose for fer-mentation. These wastes naturally accumulate at the mills, Bothast points out, and thus would cost less than crop residues to collect and ship. Also, recovering xylose from the al-ready processed wastes might prove more economical than separating it from raw crop residues.
54 C&EN June 22, 1981
TechnologyFast film, powerful battery improve Polaroids