US3903107A - Direct alpha to X phase conversion of metal containing phthalocyanine - Google Patents

Direct alpha to X phase conversion of metal containing phthalocyanine Download PDF

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Publication number
US3903107A
US3903107A US366395A US36639573A US3903107A US 3903107 A US3903107 A US 3903107A US 366395 A US366395 A US 366395A US 36639573 A US36639573 A US 36639573A US 3903107 A US3903107 A US 3903107A
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Prior art keywords
deposit
alpha
metal containing
phthalocyanine
containing phthalocyanine
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US366395A
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English (en)
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Clifford H Griffiths
Michael S Walker
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Xerox Corp
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Xerox Corp
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Priority to US366395A priority Critical patent/US3903107A/en
Priority to CA194,524A priority patent/CA1032803A/en
Priority to DE2421022A priority patent/DE2421022C3/de
Priority to BE144833A priority patent/BE815632A/xx
Priority to GB2380474A priority patent/GB1474264A/en
Priority to JP6067974A priority patent/JPS5319933B2/ja
Priority to IT23510/74A priority patent/IT1014699B/it
Priority to BR4567/74A priority patent/BR7404567D0/pt
Priority to ZA00743536A priority patent/ZA743536B/xx
Priority to FR7419231A priority patent/FR2231990B1/fr
Priority to NL7407521A priority patent/NL7407521A/xx
Application granted granted Critical
Publication of US3903107A publication Critical patent/US3903107A/en
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/02—Charge-receiving layers
    • G03G5/04—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor
    • G03G5/06—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor characterised by the photoconductive material being organic
    • G03G5/0664—Dyes
    • G03G5/0696—Phthalocyanines

Definitions

  • the X form of metal containing phthalocyanines are known to possess good electrophotographic speed, and, thus, can be used either alone or in combination with other photoconductive PATENTEU 2 975 FIG.
  • This invention relates to a process for preparation of electrophotographic pigments and the use of such pigments in electrophotographic imaging elements and methods. More specifically, this invention provides a novel route for the preparation of the X polymorph of metal containing phthalocyanines from the alpha form of these pigments.
  • the developed image can then be read or permanently affixed to the photoconductor in the event that the imaging layer is not to be reused. This latter practice is usually followed with respect to the binder-type photoconductive films where the photoconductive layer is an integral part of the finished copy.
  • the latent image can be developed on the imaging surface of a reusable photoconductor or transferred to another surface, such as a sheet of paper, and thereafter devel oped.
  • the latent image is developed on the imaging surface of a reusable photoconductor, it is subsequently transferred to another substrate and then permanently affixed thereto.
  • Any one of a variety of wellknown techniques can be used to permanently affix the toner image to the copy sheet, including overcoating with transparent films, and solvent or thermal fusion of the toner particles to the supportive substrate.
  • the materi als used in the photoconductive layer should preferably be capable of rapid switching from insulative to conductive to insulative state in order to permit cyclic use of the imaging layer.
  • the failure of the photoconductive material to return to its relative insulative state prior to the succeeding charging sequence will result in an increase in the rate of dark decay of the photoconductor.
  • This phenomenon commonly referred to in the art as fatigue, has in the past been avoided by the selection of photoconductive materials possessing rapid switching capacity.
  • Typical of the materials suitable for use in such a rapidly cycling imaging system include anthracene, sulfur, selenium and mixtures thereof (US. Pat. No. 2,297,691 selenium being preferred because of its superior photosensitivity.
  • phthalocyanine pigments are also reportedly useful in electrophotography, see for example US. Pat. No. 3,594,163. These pigments can generally be classified into two major subgroups; the metal-free phthalocyanines and the metal-containing phthalocyanines. X-ray diffraction studies and/or infrared spectral analysis of these pigments indicate that phthalocyanines also exist in at least two different polymorphic forms; they being designated alpha and beta (listed in order of increasing stability). In addition to these well-known forms of the metal-free and metal-containing phthalocyanines, additional polymorphs of the metalcontaining phthalocyanines have also been recently reported, US. Pat. Nos. 3,051,721 (R form); 3,160,635 (delta form); and 3,150,150 (delta form).
  • phthalocyanines have been prepared almost exclusively for use as a pigment, where color, tinctorial strength, light fastness, dispersability, etc. are prime considerations and the purity of the pigment being of only incidential importance.
  • the reported methods for synthesis of these compounds very often introduce metals and/or other complex organic materials into the pigment which are very difficult to remove; see Moser and Thomas, Phthalocyanine Compounds. Reinhold Publishing Co., pp. 104 189.
  • Two of the more common methods used in the manufacture of phthalocyanine pigments generally involve 1 indirect formation of the pigment from an acid and a metal phthalocyanine containing a replaceable metal and (2 direct synthesis from phthalonitrile.
  • the object of this invention to pro vide a process for preparation of the X form of metal containing phthalocyanines substantially free of the contaminants and/or impurities associated with its preparation by more conventional prior art techniques.
  • the above and related objects are achieved by providing a process for the direct synthesis of the X form of metal containing phthalocyanines from their corresponding alpha polymorph.
  • This process comprises providing a substrate having deposited thereon at least one alpha metal containing phthalocyanine pigment; said deposit having a thickness of up to about 1400 A.
  • This deposit is at least partially converted directly to the X form by heating at a rate in excess of from about C per minute to a temperature in the range of from about 220 to about 450C.
  • the alpha metal containing phthalocyanine deposit forms a thin compact film overlying at least one surface of the substrate.
  • the average thickness of the alpha metal containing phthalocyanine deposit used in this process should preferably be less than about 1300 A and thermal conversion to the X polymorph carried out by heating at about 60C per minute to a temperature in the range of from about 330 to about 390C.
  • FIG. 1 is a graphical illustration of the absorption spectrum of a vacuum deposited film of the alpha polymorph of zinc phthalocyanine and the absorption spectrum of this same film after in situ thermal conversion to its corresponding X polymorph.
  • FIG. 2 is a graphical illustration of the absorption spectrum of a vacuum deposited film of the alpha polymorph of cobalt phthalocyanine and the absorption spectrum of this same film after in situ thermal conversion to its corresponding X polymorph.
  • an alpha metal containing phthalocyanine is deposited on a substrate material and thereafter thermally converted by controlled heating to its corresponding X polymorph.
  • metal containing phthalocyanines which can be used in the process of this invention are readily commercially available or where not so available can be prepared by any of the conventional techniques described in the technical literature; see for example Chapter 4 of the previously reference Moser and Thomas publication.
  • metals forming known phthalocyanine derivatives which can be used in this process include Group I metals such as lithium, sodium, potassium, copper and silver; Group II metals such as beryllium, magnesium, calcium, zinc, cadmium, barium and mercury; Group III metals such as aluminum, gallium, indium, lanthanum, neodymium, samarium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium and lutecium; Group IV metals such as titanium, tin, hafnium, lead and thorium; Group V metals such as vanadium and antimony; Group VI metals such as chromium, molybdenum and uranium; Group Vll metals such as manganese; and Group VIII metals such as iron, cobalt, nickel, rhodium, palladium, osmium, platinum.
  • Group III metals such as aluminum, gallium, indium
  • Especially preferred metal containing phthalocyanines useful in this process are the alpha and beta froms of copper, cobalt, zinc and nickel phthalocyanines.
  • the phthalocyanine Prior to deposition of the phthalocyanine on the substrate it should be substantially free of impurities. For example, where the phthalocyanine is prepared directly from phthalonitrile, residual phthalonitrile can be readily removed by washing the phthalocyanine with acetone.
  • the metal containing phthalocyanine can then be de posited on an appropriate substrate by standard vapor deposition techniques. For example, in such procedures a measured quantity of alpha or beta metal containing phthalocyanine is placed in an open container or boat, the boat placed in a vacuum deposition chamber, a substrate positioned above the boat, the chamber sealed and evacuated to a pressure of less than 10" Torr. The temperature on the boat is then increased to about 400C whereupon the phthalocyanine sublimes and deposits on the substrate. The quantity of the deposition is monitored and upon obtaining the desired amount of alpha metal containing phthalocyanine on said substrate, deposition is terminated by interposition of a shutter between the substrate and the boat.
  • the substrate upon which the alpha metal containing phthalocyanine is deposited is maintained at ambient temperatures (approximately 20C) during such deposition.
  • the form of the deposit on the substrate will vary with the extent of such deposition. Ordinarily, where the deposition is terminated within a few seconds after the alphs metal containing phthalocyanine begins to collect upon the substrate, the deposit may appear as a discontinuous coating. On the other hand, where the deposition is allowed to proceed for about a minute the deposit will appear as a thin compact film.
  • the thickness of such deposition is critical to the process of this invention and must be maintained within previously prescribed limits in order to insure the direct alpha to X phase conversion of the phthalocyanine deposit.
  • the precise chemical composition and geometry of the substrate used in the condensation of the alpha metal-free phthalocyanine does not appear to be critical, provided, that it is inert toward the alpha metal containing phthalocyanine and its corresponding X polymorph and thermally stable during the heating phase of this process.
  • the substrate be nonhygroscopic and relatively transparent.
  • any one of a variety of materials possessing the above characteristics are suitable for use as substrates in this process; typical of such materials include quartz, tin oxide coated glass (NESA glass) and select plastic films (e.g., poly( N-vinylcarbazole).
  • SOSA glass quartz, tin oxide coated glass
  • select plastic films e.g., poly( N-vinylcarbazole
  • This confinement of the deposit can be achieved by simply placing a plate in contact with the deposit and maintaining this sandwich-like structure during the thermal treatment phase of this process.
  • the composition of this plate is not believed to be critical, and good results have been obtained using materials similar to those employed as substrates.
  • the physical geometry of the plate should be such as to afford maximum confinement of the deposit on the substrate.
  • Both the rate of heating and the temperature to which the deposit is heated are critical in determining the direction and extent of conversion of the alpha metal containing phthalocyanine.
  • alpha metal containing phthalocyanine deposits are heated at a rate in excess of from about to about 60C per minute to a temperature in the range of from about 220 to about 450C direct conversion of the deposit to the X polymorph is observed. This conversion is manifest by a change in color and a transformation in the apparently structureless character of the deposit to one having a fine uniform grain.
  • the rate of heating is below about 10C per minute, substantial quantities of the alpha metal containing phthalocyanine are converted to the corresponding beta polymorph and the deposit takes on a nonuniform appearance.
  • the formation of the beta polymorph within the alpha metal containing phthalocyanine deposit also ap pears to occur at temperatures in the range of from about 420- 450C. At such elevated temperatures, there is a competitive formation of both the X and beta polymorphs and thus, the temperature of such thermal conversion chamber should be maintained below this upper level and perferably in the range of from about 330-390C.
  • thermal treatment step of this process is carried out in a combined differential thermal analysis-spectrophotometric cell, it is possible to monitor the absorption spectra of the phthalocyanine deposit before and immediately after thermal treatment without removal of the sample from the cell; cell design shown in REVIEW OF SCIENTIFIC INSTRUMENTS, Vol. 41, 1313 I315 (I970).
  • FIGS. 1 & 2 provide graphic illustration of such a shift in absorption spectra resulting from controlled thermal treatment of the alpha polymorphs of zinc and cobalt phthalocyanines films; each having a film thickness of about 800 A.
  • the X form of metal containing phthalocyanines prepared as described above have rapid photoresponse in the red and near infrared regions of the spectrum and thus, can be used as the photoresponsive medium of an clectrophotographic imaging member.
  • the X form of the pigment can be prepared directly on a conductive substrate, such as tin oxide coated glass, or subsequent to its preparation removed therefrom and dispersed in a film forming insulating resin and sprayed, draw or dip coated on a conductive substrate.
  • the photoresponsive layer containing the X form of the phthalocyanine pigment can be overcoated with an insulating film in order to improve its charge storage characteristics.
  • the rate of dark decay of such members may also be reduced by the interposition of a barrier layer between the photoconductive insulating layer and the conductive substrate.
  • This barrier layer provides a blocking contact thus preventing premature injection of charge carriers from the conductive substrate into the photoconductive insulating medium.
  • the electronic properties of this electrophotographic member require that the image bearing layer thereof have a resistivity in excess of about l0'" ohm centimeters. This insulating quality of the image bearing layer must be maintained even in the presence of an applied electric field.
  • the X polymorph of metaLfree phthalocyanine can be operatively disposed with respect to any one of a number of conductive substrates such as aluminum, brass, chromium or metalized plastic films.
  • the electophotographic imaging members prepared from these photoconductive materials and conductive substrates can be used in electrostatographic imaging systems.
  • the imaging member comprises an imaging layer (generally containing the photoconductive material) operatively disposed in relation to the conductive substrate.
  • This imaging layer is sensitized in the dark by the application thereto of a uniform electrostatic charge.
  • the methods commonly employed for sensitization of this imaging layer include frictional charging or a discharge from a corona electrode. After the imaging layer is sensitized, it is selectively exposed to activating electromagnetic radiation thereby dissipating the charge on the light struck areas of said layer.
  • the remaining charge pattern or latent electrostatic image is rendered visible by development with finely divided colored electroscopic particles, generally referred to in that as toner.
  • This visible toner image can then be fused to the surface of the imaging layer or transferred to a receiving sheet. Fixation of the toner image is generally accomplished by solvent or thermal fusion techniques. Prior to a recycling of the electrostatographic imaging member residual toner particles remaining on the imaging layer are removed by a combination of neutralizing charging and mechanical means.
  • EXAMPLE I A measured quantity of the alpha polymorph of copper phthalocyanine is placed in a molybdenum boat, the boat inserted into a vacuum, deposition chamber, and a quartz substrate two inches square by 0.125 inches thick suspended about 16 inches above the boat so that the face of the substrate is perpendicular to the base of the boat. The pressure within the chamber is then reduced to about 10 Torr and the temperature of the boat thereafter increased to about 400C. thus, resulting in the vaporization of the alpha copper phthalocyanine. These vapors rise within the chamer, condense on the substrate and thus form a thin compact, apparently structureless deposit of alpha copper phthalocyanine.
  • Spectral analysis prior and subsequent to such heat treatment evidences a shift in spectral sensitivity from the alpha to the X polymorph of copper phthalocyanine.
  • the sample can be removed from the cell shortly after heating to the desired temperature or the sample and the cell allowed to cool prior to such removal.
  • the two plates eneasing the sample are separated and the deposit examined under a light microscope at a magnification of 2OOX.
  • the apparently structureless compact film of alpha copper phthalocyanine now possesses a fine grain structure indicating thermal crystallization v during the phase transformation of the copper phthalocyanine from the alpha to the X polymorph.
  • EXAMPLE II EXAMPLE III The procedure of Example I is repeated, except for the heating of the sample at a rate of 5C per minute to a temperature of 330C. The size and randomness of distribution of crystals within the film is seen to increase dramatically and significant quantities of beta copper phthalocyanine are found to be present within the film.
  • Example IV The procedure of Example I is repeated, except for the heating of the sample to about 420C.
  • Example Ill the size and randomness of crystals within the film is seen to increase dramatically and significant quantities of beta copper phthalocyanine are found to be present in the film.
  • the period of exposure of the film to such higher temperatures is a factor in determining the relative concentration of the X and beta polymorphs in the film; the more abbreviated the period of heating at such elevated temperatures, the less beta polymorph present in the film.
  • Example IX The procedure of Example I is repeated, except for the separation of the quartz cover plate from the sample by a 0.01 inch spacer and the maintenance of such separation during thermal treatment. Spectrophotometric evaluation of the sample indicates conversion of the sample directly from the alpha to the beta polymorph.
  • Example X The procedure of Example I is repeated, except for the substitution of a tin oxide coated glass plate (NESA glass) for the quartz substrate.
  • the phthalocyanine product obtained is equivalent to that obtained in Example I.
  • Example XI The procedure of Example I is repeated, except for the substitution of a 50 micron thick film of poly( N- vinylcarbazole) for the quartz substrate.
  • the phthalocyanine product obtained is equivalent to that obtained in Example I.
  • EXAMPLE XII The X copper phthalocyanine plate of Example X is evaluated for use as an electrostatographic imaging member on a Xerox Model D type copier adapted for acceptance of an imaging member of reduced dimensions. Charging, exposure and development sequences utilized in the copying cycle are standard. The electrostatographic reproductions made with this plate are of acceptable quality.
  • EXAMPLE XIII The plate prepared as described in Example XI is placed in a vacuum deposition chamber and a 10 micron thick aluminum film vacuum deposited over the layer of X copper phthalocyanine. The resultant plate is removed from the chamber and evaluated for use as an electrostatographic imaging member on a Xerox Model D type copier in the manner described in Example XII. The electrostatographic reproductions made with this plate are superior to those obtained in Example XII.
  • Example XIV The procedures of Example I are repeated except that the vacuum deposition of the alpha copper phthalocyanine is carried out at a pressure of about 30 Torr. As the alpha copper phthalocyanine sublimes it is converted directly to the X form; nucleation and particle growth occurring in the vapor phase. These X copper phthalocyanine particles are collected on an appropriate substrate and subjected to spectrophotometric and light microscopic examination. Such tests confirm that the product is the X polymorph of copper phthalocyanine and that the deposit has a light fluffy microcrystalline structure characteristic of a particulate deposit.
  • a process for the direct thermal conversion of the alpha polymorph of at least one metal containing phthalocyanine to the corresponding X polymorph comprising:

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US366395A 1973-06-04 1973-06-04 Direct alpha to X phase conversion of metal containing phthalocyanine Expired - Lifetime US3903107A (en)

Priority Applications (11)

Application Number Priority Date Filing Date Title
US366395A US3903107A (en) 1973-06-04 1973-06-04 Direct alpha to X phase conversion of metal containing phthalocyanine
CA194,524A CA1032803A (en) 1973-06-04 1974-03-08 Direct alpha to x phase conversion of metal containing phthalocyanine
DE2421022A DE2421022C3 (de) 1973-06-04 1974-04-30 Verfahren zur Herstellung eines elektrofotografischen Aufzeichnungsmaterials
BE144833A BE815632A (fr) 1973-06-04 1974-05-28 Procede de transformation directe de phase alpha en phase x de phtalocyanines contenant un metal et nouveaux produits ainsi obtenus
JP6067974A JPS5319933B2 (cs) 1973-06-04 1974-05-29
GB2380474A GB1474264A (en) 1973-06-04 1974-05-29 Direct alpha to x phase conversion of metal containing phthalocyanine
IT23510/74A IT1014699B (it) 1973-06-04 1974-06-03 Procedimento per la trasformazione termica diretta della polimorea alfa di una ftalocianina contenente metallo ed elemento elettrofotogra fico impressionabile rivestito con la ftalocianina da detto procedi mento
BR4567/74A BR7404567D0 (pt) 1973-06-04 1974-06-03 Processo para conversao termica direta da forma polimorfica alfa de pelo menos uma ftalocianina contendo metal a forma polimorfica x correspondente revestimento de deposito compacto cristalino sem aglutinante da forma polimorfica x de ftalocianina e peca formadora de imagem eletrofotografica
ZA00743536A ZA743536B (en) 1973-06-04 1974-06-04 Direct alpha to x phase conversion of metal containing phthalocyanine
FR7419231A FR2231990B1 (cs) 1973-06-04 1974-06-04
NL7407521A NL7407521A (en) 1973-06-04 1974-06-04 X-form phthalocyanine electrophotographic pigments prepn. - by thermal conversion of thin alpha-form layer in situ on image-forming element

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US366395A US3903107A (en) 1973-06-04 1973-06-04 Direct alpha to X phase conversion of metal containing phthalocyanine

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US (1) US3903107A (cs)
JP (1) JPS5319933B2 (cs)
BE (1) BE815632A (cs)
BR (1) BR7404567D0 (cs)
CA (1) CA1032803A (cs)
DE (1) DE2421022C3 (cs)
FR (1) FR2231990B1 (cs)
GB (1) GB1474264A (cs)
IT (1) IT1014699B (cs)
ZA (1) ZA743536B (cs)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4298975A (en) * 1979-01-15 1981-11-03 U.S. Philips Corporation Optical recording medium and method of optically recording information thereon
US4471039A (en) * 1982-11-22 1984-09-11 Eastman Kodak Company Photoconductive elements sensitive to radiation in the infrared region of the spectrum
US4719286A (en) * 1985-03-14 1988-01-12 Northrop Corporation Class of conductive polymers
US4950579A (en) * 1988-07-08 1990-08-21 Minnesota Mining And Manufacturing Company Optical disc recording medium having a microstructure-derived inhomogeneity or anisotropy
US5225551A (en) * 1990-06-04 1993-07-06 Xerox Corporation Imaging member containing titanium phthalocyanines
US5322754A (en) * 1990-06-04 1994-06-21 Xerox Corporation Imaging members containing titanium phthalocyanines
US6506244B1 (en) 1999-08-03 2003-01-14 Ciba Specialty Chemicals Corporation Stable polymorphic copper-free phthalocyanine pigment
WO2003038003A1 (en) * 2001-10-31 2003-05-08 Avecia Limited Phthalocyanine based inks with absorption maxima in the near infra red and visible spectrum

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5389433A (en) * 1977-01-17 1978-08-07 Mita Industrial Co Ltd Photosensitive body for electrophotography
JPS5642236A (en) * 1979-09-14 1981-04-20 Hitachi Ltd Composite type electrophotographic plate
DE3525994A1 (de) * 1985-07-20 1987-01-29 Philips Patentverwaltung Elektronenstrahl-aufzeichnungstraeger

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3293075A (en) * 1962-12-31 1966-12-20 Monsanto Co Thin films of metal polyphthalocyanines on substrates and coating process
FR1530080A (fr) * 1966-07-01 1968-06-21 Rank Xerox Ltd Procédé pour préparer un cliché original en relief pour l'impression des images
FR2016639A1 (cs) * 1968-08-30 1970-05-08 Xerox Corp
BR6909984D0 (pt) * 1968-08-30 1973-04-12 Xerox Corp Processo aperfeicoado para a preparacao de valociamina da forma x metalica ou isenta de metal placa e processo eletrofotografica de formacao de imagens baseados na mesma
US3717462A (en) * 1969-07-28 1973-02-20 Canon Kk Heat treatment of an electrophotographic photosensitive member

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4298975A (en) * 1979-01-15 1981-11-03 U.S. Philips Corporation Optical recording medium and method of optically recording information thereon
US4471039A (en) * 1982-11-22 1984-09-11 Eastman Kodak Company Photoconductive elements sensitive to radiation in the infrared region of the spectrum
US4719286A (en) * 1985-03-14 1988-01-12 Northrop Corporation Class of conductive polymers
US4950579A (en) * 1988-07-08 1990-08-21 Minnesota Mining And Manufacturing Company Optical disc recording medium having a microstructure-derived inhomogeneity or anisotropy
US5225551A (en) * 1990-06-04 1993-07-06 Xerox Corporation Imaging member containing titanium phthalocyanines
US5322754A (en) * 1990-06-04 1994-06-21 Xerox Corporation Imaging members containing titanium phthalocyanines
US6506244B1 (en) 1999-08-03 2003-01-14 Ciba Specialty Chemicals Corporation Stable polymorphic copper-free phthalocyanine pigment
WO2003038003A1 (en) * 2001-10-31 2003-05-08 Avecia Limited Phthalocyanine based inks with absorption maxima in the near infra red and visible spectrum
US20040248027A1 (en) * 2001-10-31 2004-12-09 Campbell James Stanley Phthalocyanine based inks with absorption maxima in the near infra red and visible spectrum
US7070646B2 (en) 2001-10-31 2006-07-04 Avecia Limited Phthalocyanine based inks with absorption maxima in the near infra-red and visible spectrum

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IT1014699B (it) 1977-04-30
BE815632A (fr) 1974-09-16
GB1474264A (en) 1977-05-18
JPS5319933B2 (cs) 1978-06-23
DE2421022B2 (de) 1978-02-09
JPS5022824A (cs) 1975-03-11
FR2231990B1 (cs) 1977-10-07
ZA743536B (en) 1975-06-25
DE2421022C3 (de) 1978-10-12
FR2231990A1 (cs) 1974-12-27
CA1032803A (en) 1978-06-13
DE2421022A1 (de) 1974-12-19
BR7404567D0 (pt) 1975-01-21

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