DE1907535A1 - Methods for improving the photographic properties of metal-containing photoconductors - Google Patents

Description

Process for improving the photographic properties of metal-containing photoconductors

Data or image storage media that are sensitive to radiation Substances such as titanium dioxide are contained in the details U.S. Patents 3,152,903, 3,052,541, French Patents 345,206 and 1,245,215 and U.S. Patent Application Serial Ho. 199 211 of May 14, 1962. According to the last-mentioned US patent application, a radiation-insensitive material, such as titanium dioxide, acts as a light-sensitive component of the image carrier, and the exposure of the image carrier to activating radiation, such as radiant energy, Electron beams or the like results in the storage of a reversible latent image on the carrier. The reversible latent image only exists for a finite period of time, during which the image can be converted into an irreversible form and read visually by treating the image with a developer such as a chemical redox mixture. According to the above-mentioned US and French patents, the radiation-sensitive materia ^ before exposure to min-

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tones of a component of a developer combined. For example, U.S. Patent 3,152,904 describes a photosensitive image support containing a photosensitive material such as titanium dioxide in combination with a more reduced metal ion such as silver nitrate. If this image carrier is exposed to activating radiation and then treated with a reducing agent, a visible © image is obtained. On the other hand, US Pat. No. 3,152,9-3 describes a system in which the photosensitive material comes into play in combination with both an oxidizing agent and a reducing agent such as hydroquinone. A visible image is then formed during exposure with an activating spray. The above-mentioned surfactant-or however image storage media have the Kachteil that their sensitivity photographieche not hook 'to that of silver, Uo the application de? In the above-mentioned patent specifications and the photographic f rig © rm described in the above-mentioned patent application, there is therefore a need to increase their p & otograpfrieelie sensitivity bu. Much research has already been expended on experiments. To find ways and means of explaining the sensitivity of such image carriers? up to now, however, these efforts have been accompanied by little success

been.

It has now surprisingly been found that the photographic sensitivity τοη metal-containing semiconductors ei oh Significantly improve if construction the semiconductor, that is Photoconductor, heated to a higher temperature and then it quickly aborts. According to a preferred embodiment, the photoconductor is heated in an atmosphere that causes the disturbance » motrie of the photoconductor changes reversibly, and then rapidly in deterred by the same atmosphere. The atmosphere is preferably a reducing atmosphere containing oxygen, and when heated, the photoconductor is reduced, i.e. the

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SttJehiometry dos Photoloiters is changed. Revenge Quenching formerly absorbs the surface of the photoconductor the action of the atmosphere is oxygen, the mass of the Photoconductor essentially retains the non-stoichiometric composition caused by the heat treatment. At or near room temperature the chemisorption of atmospheric oxygen takes place very quickly, and the equilibrium is quickly established, i.e. there is no further chemisorption τοη oxygen on the surface instead, and the surface of the photoconductor comes into equilibrium with the oxygen.

To create the reducing atmosphere, the oxygen is used in the form of a mixture with other oases, such as carbon dioxide, or is sucked in on the spot, b.B. in mixtures of carbon monoxide and carbon dioxide, preferably with an oxygen fugacity of less than 1. After the treatment, the semiconductors show a multiple increase in photographic sensitivity. Zua example were with samples of titanium dioxide increases the photographic Sensitivity two to four times «that of untreated Sample reached.

According to the invention, the preferred photoconductors or photocatalysts are metal-containing photocatalysts. Sine preferred group of such light-sensitive materials are the inorganic materials, compounds wio of a tie tall β with a non "β tall YIA the group of the Periodic Table (gemäae"Lange'β Handbook of Chemistry ", 9th Ed. _T 1966, 56- 57), such as oxides, e.g. zinc oxide, titanium dioxide, zirconium dioxide, germanium dioxide, indium trioxide, metal sulphides, e.g. cadmium sulphide (CdS), zinc sulphide (ZnS) and tin dieulphide (SnS ₂ ), as well as metal elenides, such as cadmium selenide (OdSe). Metal oxides are particularly preferred as photoconductors. Titanium dioxide is a defective metal oxide because it has unexpectedly good properties. Particularly preferred is titanium dioxide with a medium partial size τοη

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about 250 πμ or less and especially titanium dioxide, which has been produced by high temperature pyrolysis of titanium halide.

The exact mechanism by which the photoconductors work »is ss was not yet known; however, it is assumed * that the The action of activating radiation on the photoconductor or photocatalyst causes the transition of one or more electrons from the valence band into the conductivity band of the pnotoconductor or riotocatalyst or in at least one similar excited state in which the electron is loosely bound, so that the photoconductor from an inactive in an active form passes over. When the active form of the photoconductor or photocatalyst is in the presence of an electron-accepting compound, a Transfer of electrons between the photographic compound and the compound acting as an electron acceptor. Therefore, a simple experiment can be used to determine whether A substance is a photoconductor or photocatalyst by atmospheric the substance in question with an aqueous silver nitrate solution aiacht. No action should then take place in the dark » The mixture is then exposed, e.g. with ultraviolet addiction, and at the same time a control sample of pure exposed to aqueous silver nitrate solution. When the mixture darkens faster than the pure silver nitrate solution, the substance in question is a photoconductor or photocatalyst.

If, for example, “B. Titanium dioxide is converted into the non-stuchiometric state, its crystallite mass cannot easily be restored to its atoichiometric composition at room temperature. For example, find below the Tamaaaiiachen! Temperature * t ⁰ K gleioh Half te the melting temperature i (and FTIR Pitandioxid 780 ° C amounts), no oxygen diffusion through the crystal lattice of the titanium dioxide to a "significant outlet instead. At room temperature, however, is in the air the total equilibrium composition very close to IiO ₀

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bo that there is a tendency to go back to the stoichiometric Composition, although the equilibrium composition extends through the total mass of the crystals can not cause. Therefore, the surface of the photoconductor can be on the stoichiometric composition or any close to the same, while the main nose of the photoconductor remains practically unchanged, i.e. the light stoichiometry of the main mass dee generated by the heating Photoconductor "frozen" iat.

Because of this non-atoichiomatry, electrons are in or very close to the conductivity band, so that they are relatively mobile, especially compared to Saueretoffionen. Therefore, the oxygen from the atmosphere can possibly withdraw electrons from the conductivity band and be chemisorbed on the surface, which leads to an equilibrium etching, which almost corresponds to the equivalence, although the oxygen is the inside of the crystals still can't achieve. This process leads to * building up a potential difference between the inside and outside of each particle, and this is · potential difference takes the crystals with the non-stoichiometry of the main nose until no further oxygen can be isorbed near the surface and the difference becomes constant.

Activating radiation, i.e. light coming from the band gap energy, generates Looh slectron pairs, which are due to the potential difference between the main body and the Separate the surface of the crystal, the holes possibly combining with the chemisorbed oxygen, releasing oxygen and leaving behind an electron trapped in the conductivity. Venn that Once switched off, the electron can either slowly reunite with the atmospheric oxygen, or if it is in a reducible metal ion, such as silver ion, containing solution is brought, can be calibrated with this ion

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connect to the elemental metal. Saraus does not result in an imbalance in terms of electrical neutrality »- a negative ion of the solution, eg a kitrate or hydrideyl ion, can be absorbed on the surface so that the electrical neutrality of both the solution and the surface surface is retained.

The effectiveness of the photographic properties, which are increased by increasing potential differences of the main mass and the surface of the crystals, is so great that there is practically no chemisorption, 12 and then 8 minutes begin amass Leitfänigkeitsband * piping schüssigen electrons reduce the effectiveness due äew increased likelihood of association of Εοο & θε- si "the electrons before the holes the eheasieorbiertem SSISA reach © t @ ff and versohwinäen by?" Sa the gen electrons redusieren also silver ions begins. The graphical sensitivity will decrease again at about the point at which the fog begins to form.

It is also expected that the eyes will turn from oxygen to the surface after a change triggered by exposure in substances that produce more oxygen the surface, the gate is slower than with fabrics with a smaller rope of the surface covered, That is, the image capture time increases with increasing stoichiometry of the main crystal structure MaximuD strides through and then falls again with increasing non-etiooetry. Furthermore, the image disintegration time increases with increasing vichtochioaetry.

The above theoretical explanation of the invention The appearance of the procedure should only be better otändnie serve the invention.

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According to the invention, the photoconductor is heated in any way according to US patent application Serial No. 463 037 of June 10, 1965. In its broadest scope, the invention includes heating the photoconductor to the respective elevated temperature for a certain period of time and that Rapid quenching of the heated photoconductor _t ζ · Β · cooling to a temperature below about 50 ° G and preferably to or about below EauE temperature. For best results, the heated sample is quenched as quickly as possible. This can usually be done within 2 to 3 minutes, and this period of time provides satisfactory results. After quenching, the photoconductor of EinwirfeSBg is exposed to atmosphere, to bring the surface with oxygen into balance "what _s as mentioned above, very quickly going look. Equilibrium of the surface with atmospheric oxygen is preferred because this procedure is easy to perform and does not require special equipment. However, the calibration weight adjustment can also be carried out in any oxygen-containing atmosphere from which the surface of the photoconductor can absorb oxygen. Such an atmosphere can a.Bo in the quench exerts Torrichtung described below are implemented, or ± ä m sample can vferd introduced into a suitable device. · :. - in which the desired oxygen atmosphere is located.

After that? preferred embodiment of the invention, the method is carried out in a device in which the Maintain required atmosphere during heating leaves. For example, one can use the device shown in FIG use »The device consists of the oven zone 22, the Absehreekzone 23, the gas inlet 24- and the outlet 25. The container 26 for the photoconductor sample, e.g. a platinum boat, is heated in the furnace zone 22 and after heating in the Absehreekzone 25 by actuating the gate direction 27, with-

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means of which the container 26 can be moved, withdrawn, To equilibrate the surface of the heated photoconductor, the container 26 is removed and exposed exposed to nasty atmospheric oxygen, oöer der whole stove is opened to the outside air,

for the preferred photoconductor ₅ namely titanium dioxide, is the oxygen eugacity of the Atisoophärö in the sample chamber? Controlled by using known gas mixtures that achieve the desired partial pressure. Particularly suitable mixtures are those of oxygen and carbon dioxide and of carbon monoxide and carbon dioxide, which can be achieved within a wide range. Both the gas inlet and the The gas outlet is located in the hot zone of the furnace, which is preferably kept at a constant temperature (fluctuation 2 ° 0) over the entire sample. The constant temperature also prevents thermal separation of the gases, which could occur if there were a temperature gradient between the inlet and the outlet.

When you use carbon dioxide, it becomes oxygen first before it is mixed with other gases, e.g. by getting the carbon dioxide at higher temperatures over copper shavings directs »Pure carbon dioxide delivers a at 750 ° C Oxygen fugacity of 1.8 χ 10 "* ^ at. If you consider the carbon dioxide mixed with carbon monoxide, the oxygen fuga

—20

Reduce the rate to 1.7 x 10. By mixing carbon dioxide with oxygen, the oxygen pugacity can be varied from 1 χ 10 " ² at.

The powdery photoconductor is placed in the container and heated in the desired atmosphere until the desired change in the stoicfaiometry has taken place, whereupon the sample is quenched as described above.

& To get the best results, the samples are 24 hours heated, although there is an aaxial atebiometry change in the

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BAD ORiGSNAL

generally achieved in a shorter time. For example , heating titanium dioxide to 750 ° C usually requires a period of about 16 hours; however, prolonged heating has no adverse effect on the samples. Of course, heating in the reducing atmosphere has a beneficial effect on the photoconductor, regardless of whether or not the maximum change in stoichiometry is achieved, since one will strive to achieve the most favorable results. you almost ioraer strive for the greatest possible change.

The photoconductor is heated to temperatures τοή at least 500 ° 0, preferably to temperatures in the range of around 700 to 800 ° C. Temperatures above 800 ° C are common avoided, v'eil at extremely high temperatures of the photoconductors can sinter and no additional benefits can be achieved.

After heating, the one containing the treated sample becomes Container transferred to the quenching zone and at room temperature or at almost room temperature, preferably a little below äaumteroperabur, cooled down. The quenching zone can, for example, be »water-cooled and in terms of size the sample will be within 2 to 3 Minutes quenched. By quickly quenching the sample the return of the mass to the original stoichiometry, That is, the re-oxidation of the bulk of the OJitandiOxids is suppressed or prevented.

Any type of photoconductor which is suitable for image formation can be used as the starting material »as described in the USA Paäentaniaeldimgen above. For example, samples of titanium dioxide 3 hours euf erhltat 650 ° G vo ^ to chlorides and andera flUchtigo _Ye-au iiinre.tr.inunsen remove.

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190753 p

After the photoconductor sample is heated and quenched, it is used to photosensitive body h @ r _r 2USteilen where the photographic evaluation is vorgenoÄraen, as leaves from the sample material by coating Pilnien or sheets of paper with a dispersion of Photolei · "tera. The dispersions are preferably produced using an overhead probe as a table-top device. NatriuaihexsjBetaphoaphati phosphate or other well-known dispersants can be used as a grease agent

performed, with the upper pull not through of the staff, but through forward ssish & a d © s paper - on ge « is brought.

As the inert carrier on which the photolites * are deposited xriissi , loan can use any suitable underlay of sufficient and durability. As used sheets or plates each, any Fora may comprise, for example, sheets, ribbons "Hollen etc. piping leaves bew. Plates can be made of any suitable material _r such as wood, rag paper, pulp paper, Innate toffee, such as polyethylene terephthalate or Celliiloaesoetat , fttoa sheet metal, like Aluainiuableoh, or Glae,! »eBtshea» The eyed carrier is tin düimaa, biegeaaoa ano rtau * rige leaf. - t '■''■■ - ■

uses aän äuü * ordaa a 3iM «ai- | tel _r whether the photoconductor binds the carrier eu. In general, these binders are translucent or transparent, so that they do not interfere with the passage through the door yarn. Prevented © Biadaiaittöl are organic substances, v / io Hare ©. butadiene copolymers are suitable for resin ©. Styrene, Polyacrjlßliur © alkyl # si; 0r, wi © Polyjaathae ^ lsäuna metkyleDtaf, Polyamide,
Polyvinylpyrrole - -

^ D ORIGINAL

The photoconductor can also be fine 2eilcheii in Force slides are distributed in a carrier such as paper. Can also the Faoto leader in the form of a susaraiaenängönden 3? ϊ1ιοθ for see alone or in combination with a separate carrier O

the exposure is the photolei tar iia generally 1 to Conditioned in the dark for 24 hours. Haoh the conditioning The photoconductor must gate the exposure to the activating radiation awecka image generation not the effect of idche get abandoned" ,

The exposure time depends on the intensity of the light source, the respective developer, their respective photoconductors and similar factors known to those skilled in the art. In general The exposure time can range from about 10 seconds to several Minutes vary.

Developers which are "suitable for your process according to the invention are described in US Pat. No. 3,152,903 and in US Pat. Application Serial Ho, 199 211". These developers preferably consist of an oxidizing and reducing agent Developers are often referred to as physical developers. * The oxidant is generally the image absorbent component of the developer _o However, this is not always the case. Organic or inorganic oxidizing agents can be used as the oxidizing component of the developer. Preferred oxidizing agents are the reducible metal ions which have at least the oxidizing power of the copper (II) ion. These include hotallions * such as Ag ⁺ ^ Hg ⁺² , Pb ⁺⁴ , Au ⁺⁵ , Pt ⁺⁴ , Hi ⁺² , Sn ⁺² , Pb * ² , Cu ⁺¹ and Cu ⁺² . Other suitable oxidizing agents, which ale ^ ingredients may be of the developer used in the inventive process are, permanganate (MNG / "), various Xeukofarbstoff e as eie in US Patent Application Serial No" 623534 described Bind _t and the like. For the organizational

see oxidants, include fe-fcrazoliurasalsse, wi © tetrazolium blue and -red, Diphenylceebason and Genacryirot 61 (Methine dye).

The reducing components of the developer include organic compounds, such as oxalates, ormates, substituted ones and unsubstituted hydroxylamine and substituted and unsubstituted hydrazine, ascorbic acid, aminophenols and the like dihydric phenols. Also polyvinylpyrrolidone »alkali and Alkaline earth oxalates and mononates can be used as reducing agents will «Suitable reducing compounds are Z.Bo Hydroquinone or derivatives thereof, o- and p-aminophenol, p-Methylaminophenolsulfat, p-Hydroxyphenylglycine »o ~ and £ p-Phenylenediaoin and 1-Ehenyl-3-pyrasolidone.

Auseerdera can use the physical developer organic Acids contain »which react with metal ions to form complex metal anions. Furthermore, the developers can contain other complexing agents and the like to imaging and other desirable properties too to enhance. -,

Furthermore, electrical tinting agents can also be used in the context of Invention can be used as a developer.

The erfihdungsgemässe method can also be supplemented by additional stabilizing and Pixierstufen, ^ the Iierbens- W duration and to increase durability of the finished impression "

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Determining the most favorable conditions to achieve the the most favorable results are achieved through routine tests ^ ending in Pig. 1 illustrated door direction. A Biötoiei- · The test is being carried out at various Saueretoff-Jugazi tatett in dfem Container 26 heated, then quenched to skin temperature and balanced with atmospheric oxygen *

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/ 5

on the light sensitivity of the photoconductor is determined. A diagram showing the dependence of the photographic Indicating sensitivity of the pugacity of oxygen, then shows the most favorable fugacity for the optimal photographic one Sensitivity on.

For example, titanium dioxide samples are kept at 650 ° C for 3 hours preheated and then 24 hours "with different oxygen pugaeitätan, which are achieved by gas mixtures with different compositions, heated to 750 ° C. Samples that last longer when heated for 16 hours show no change the photographic sensitivity more. The gas inlet and the Gaeauslass are both located within the hot zone of the furnace, which extends over the entire sample chamber within is kept at a constant temperature within a margin of -2 ° C. After heating, the platinum boat will be in the bit Water-cooled quenching zone transferred and within 2 to 3 Move to room temperature or a slightly lower temperature The samples were then placed for 5 to 10 minutes of exposure exposed to atmospheric oxygen.

Then sheets are made from the samples, and the photographic one Evaluation is carried out with a sensor at a Exposure time of 10 "* 'seconds using a neutral density filter with a value of 1.54 in the range of Titanium Dioxide Sensitivity. Vm to ensure that the results are not from a spectral sensitivity shift be influenced, v.drd along one edge of the used Step wedges placed a Wratten 2A limiting filter. (This filter darkens at 405 to 420 ιημ). By no sensitivity can be detected through this filter. To rule out developmental errors, the samples are stored in freshly prepared solutions developed.

The results can be found in Table I and Fig. 2. The samples are developed simultaneously in the same solution. Again-

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kolungspro'osn who in des? gl-aieYes. Weis © fceIiaMelt e3? Gel3 ©: a in general, a heproäiisisibarkeit τγοώ. -ö-ö? loga ^ ithaisolieii Siialieitsii »How it after dei? above tliso ^ efeisolier explanation srwartsa au which ^1., is to the Fig. 2 that the photogrspliisciäa SrnpfisidlicBkeit sm © i * st © in masif & ii läuf'b and then drops nad * that it matches jum & luae e tv / a of, with AES ® der SeiiXeier is the developed ^ feofes su ~ zimeiusen "bg

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BATH ORIGINAL

be 1 1 θ 1

ι sample 750 Sour,
Hours. gas ° 2 «Λ ·
vn
i I. 750 24 ⁰⁰ p II 750 24 Og / OOg? 1/10 to III 750 24 Og / OOg? 1/50 O
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OO IT 750 24 00 / 0O ₂ ? 1/10 09 V 750
750 00 / 0O ₂ S 10/1. / 127 YI
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opportunity * 0.04 1.84 69 0.04 2.06 115 0.04 1.90 79 0.03 2.11, 130, _ 0 08 % 45 527 Ο, ΊΟ 1.40 25th 0.31 1.39 25th

Photographic Sensitivity ™ 100 / Bq ^; the reproducibility τοη recreation samples is -0.07 logarithial units. The EapfindlicMreit of
untreated titanium dioxide is 30-35 *

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You Zerfalleaeit the latent Bilüea äse, verifiable naah exposure to the sample has formed> is for sample I, XII and YII determined ₅ by these samples au beetiminten Eeitpunkten be developed after exposure. The results can be found in Table II and fig.

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BATH ORIGINAL

! 907535

Similar to © BrgetoissQ sshMlt m & n with Zialcoxid «ad .ladluaoxid.

One works according to example 1, jadoeii with eineai aadarea. titanium

diozid ale dom in B@iap.lsl 1 Te

io ■ Bauaratoff-Fugasität voa 1 euf 1Ό ^"20 abniäatj, -ergibt ßich Gio most favorably © Fugaisltäfc 9ia value toh 1 χ (Γ * ¹ Empfindliohkait äes litsadiosids niiEs ^ nit t! 'Bi @ Gographiaohö.'? nga3itlVb su mia the Masiauia is 1 χ ΙΟ "- Ό

-Jx-, iL-lg- J ^ .- t- ^

Sin Geiaisch aus 4 ßawieiifestalXsn das fite äis fmbt IT I # g opiols 1 YQTWQU &B'b& ii ! Eltaaflloisidf! ®S 1 flswi «ätst®H © ia-S T? 8jiilsion aißSB Polyaurylstliars® © ^ flls 30 Clsmi © litspiros @ st s to rf © in Waasar an thält» is used from l3 © oiiiö & t @ a tern. ·

The leaves are suitable for eich sur ¥ © rw © aftimg ia öete photographiBGiian luarüetufif aux? Htr reproductions γοη paotographia © h © a

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Man arbaitot according to BaispiaX 3 »

des .Beiopiela 2, the bsi eiats?

1 s 1O ~ ^1>? InB balance

tefcvj Fapi © ^ signet ei oh ffte 'photographi @ oh @

B; .. e..i B ₁₁ Bj ₁₁ I ₁₁ (B ₁₁ I ₁ 5

T-as used in example 3 © Tit ^ Edio] versed and di @ Diapersioa in one acetate applied a. This pils eigaot sica '

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Ebenao obtained photographisehes suitable material when Kan Polyäthylontsrephthalatfilme coated with the same gelatin dispersion. .

The gelatine flisperaion is made by first slurried the photoconductor in water and then an aqueous one Gelatin solution added. The plastic lilac is then aitteli a wire-wrapped rod with the gelatin dispenser coated. -

It is known that the photographic properties of photoconductors can be improved by heating them in a vacuum or in air. This method is described in the ÜSA patent application Serial Ho. 463 037 of June 10, 1965. A comparison of the photographic speed, for example, titanium dioxide, viölchee according to the latter method, by heating to 650 ° C bsvr, 730 ° G has been activated, with those of the sample II of the present example 1, however, shows that the sensitivity is the latter sample iet much higher . The “LoE ₀ S.” Value (sensitivity to exposure) both at a density of 0.1 and at a density of 0.2 is twice as high as that of the sample heated to 730 ° C. and three times as high as that of d © r sample heated to 650 ^{° C.}

"LES" (abbreviation for Bapfinälifehkäit g®Q® & S «l ± ohtunf) refers to the Espfindllehkeitebeifert ^ p ^ eepgtes, the tob of the Wright Air Development DiTieioa des Air Β © β · & 3? Ο! Ι and Development Goimsand der iet been US Armed & räft® develops and ale d © r reciprocal of the exposure in meter candle seconds is defined, the required iet to produce us a double · diffuse Reflezionsdichte that vm 0 _t 2 Dlohteelnheiten than the sum of the Grunddiohte.und the veil seal · lies. As with your conventional ASA system, the evaluation of silver halide files, the higher the photographic sensitivity of the film, the higher the "LES ^!" Value.

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'-. 7:. · _ .. ■■■ "■ '-; ■ :.; · ■ 7; 7 ^Γ '" -. In the above examples the latent image is treated with a saturated silver nitrate solution in methanol and then with a solution of 5 g of pkenidium and 40% of citric acid. hjäT & t converted into a visible image in 1 l of methanol. The imprint bearing the visible © image is treated with an intermittent bath made of methanolic potassium cyanate, then fixed in aqueous sodium thiosulphate solution and washed with water. "

You spectral ©. Sensitivity of the product © of the invention » mass can be done by doping with. Freradmetallionen, such as chromium or ax can be changed with the help of dyes, for which we especially use those dyes that the spectral sensitivity down to the visible Φβ13. of Expanding spectrum into; Examples of such dyes can be found in the US patent applications Serial ϊίο. 633 689 April 26th, 1967 and Serial NoY 623 534 of 19 * Mrs

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Claims (1)

Claims Methods of improving photographic bigenochromes of metal-containing photoconductors, thus rewarded, that the photoconductor is heated to a higher temperature and then quickly deterred. 2. The method according to claim 1, characterized in that the Photoconductor is heated to a temperature at which eioh reversibly changes the stoichiometry of the photoconductor. 3. The method according to claim 1 or 2, characterized in that that a photoconductor with a mean wire size of about 250 κμ or less is used 4. The method according to claim 1 to 3, characterized in that that < will. that the photoconductor heats to at least about 500 ° G 5 ♦ Method according to claim 4 »characterized in that the Photoconductor is heated to about 700 to 800 ° C. 6. The method according to claim 1 to 5, daduroh gekennseiohnet, that as a photoconductor an inorganic compound of a net with a non-metal of group VIA of the periodic Systems is used. - 21 -909838/1275 7. Ancestors according to claims 1 to 5, thereby ö.aes a metal oxide or a photoconductor is used. 8. The method according to claim 2 to 7, characterized in that the heating is carried out in a reducing atmosphere dtarofr, the oxygen from a pugasy gate contains less than 1. 9. The method according to claim 8, characterized in that "heating is carried out in a reducing atmosphere" which contains oxygen of a ffugaity in the range of wa 1 i10 " ^{1 to} 1 χ 10 ~ ²⁰ . 10. The method according to claim 1 to 9 »characterized» that the heating is carried out at least about 16 hours will. - 11. The method according to claim 1 to 10, characterized in that cla.es titanium dioxide is used as the photoconductor. 12. The method according to claims 1 to 10, characterized in that » that used as a photoconductor zinc oxide or indiuaoxid will. 13. The method according to claim 11 or 12, characterized that the quenched oxide is in equilibrium with oxygen is brought. 14. The method according to claim 1 to 13, characterized in gekezrastlcb & et, that the heating is carried out in an atmosphere containing carbon dioxide. 15. The method according to claim 1 to 13, characterized gekeozuseloirarty that the heating in a mixture of carbon ion oxide and the like Carbon dioxide is carried out. - 22 ~ . 909 83 8 / 127S 16. Partly reduced, aetalHialfeiger photoconductor, thereby marked that its surface ait oxygen ins Balance "has been brought up to practically none Chemisorption can take place more. 17ο photoloiter according to claim 16 _f, characterized in that Qr consists of titanium dioxide. 209838/1275 Blank page