Classifications

• • 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
  • G03G5/07—Polymeric photoconductive materials
  • G03G5/071—Polymeric photoconductive materials obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • G03G5/072—Polymeric photoconductive materials obtained by reactions only involving carbon-to-carbon unsaturated bonds comprising pending monoamine groups
  • G03G5/073—Polymeric photoconductive materials obtained by reactions only involving carbon-to-carbon unsaturated bonds comprising pending monoamine groups comprising pending carbazole groups
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S101/00—Printing
  • Y10S101/37—Printing employing electrostatic force

Definitions

• This invention relates to photographic reproduction and more particularly to electrophotographic layers and electro-photographic processes, namely processes in which an electrostatic latent image is produced by utilizing the property of photoconduction (i.e. a variable conductivity dependent on the intensity of illumination).
• the electrostatic latent image may be produced in a conventional exposure operation, for example by means of a lens-projected image or by contact-printing techniques, whereby a non-visible electrostatic charge pattern (the so-called electrostatic latent image) is created on a surface, in which pattern the charge density at any point is related to the intensity of illumination obtaining at that point during the exposure.
• the latent image may be developedi.e. rendered visible-by means of an electroscopic powder, such as a colored. synthetic resin powder, and the resulting visible image may be fixed by rendering the powder permanently adherent to a support on which the image is desired, for example in suitable cases by heating to soften or melt the powder particles and/or the surface of the image support, or by application of an electric field, or with volatile solvents.
• the electrostatic latent image is commonly formed on the surface of a photoconductive insulating layer carried on a support.
• material comprising such support and photoconductive layer may be sensitized by applying a uniform surface charge to the free surface of the photoconductive layer, for example by means of a corona discharge, which charge is retained owing to the substantial insulating character, i.e. the low conductivity, of the layer in the dark.
• the photoconductive property of the layer causes the conductivity to increase in the illuminated areas to an extent dependent on the intensity of illumination, whereby the surface charge in the illuminated areas leaks away, leaving the charge located in the unilluminated areas, thus constituting the aforementioned charge pattern or electrostatic latent image.
• the electrostatic latent image can be developed (i.e. rendered visible) by means of an electroscopic powder which adheres to the charged areas, particularly if the powder carries a charge of opposite polarity to that of the charge on the photoconductive material.
• an electroscopic powder which adheres to the charged areas, particularly if the powder carries a charge of opposite polarity to that of the charge on the photoconductive material.
• Such opposite charge may be obtained by using the powder in admixture with a carrier such that the powder becomes suitably charged triboelectrically.
• a suitable developer may consist of a toner, such as a pigmented resin, and a carrier such as glass beads, and the powder image produced may be rendered permanent (fixed) by for example softening such resin toner by heat so that it a jewet heres to a support carying the powder imagewhich may be the original photoconductive material, or a separate support to which the powder image can have been transferred.
• the present invention contemplates the provision and use of photoconductive insulating substances which may, if desired, be used Without admixture with binding agents to produce photoconductive insulating layers on supports, and may furthermore be used in the form of self-supporting foils as electrophotographic materials.
• the invention provides a method of electrophotographic reproduction, which comprises the formation of an electrostatic latent image on a photoconductive insulating layer carried on a support, or on a self-supporting photoconductive insulating foil, said layer or foil consisting of or comprising a poly-N-carbazole as a photoconductive substance.
• a preferred method of carrying out the invention comprises the steps of applying an electrostatic charge to a surface of a photoconductive insulating layer comprising a poly-N-vinyl-carbazole carried on a support, or of a photoconductive insulating foil comprising a poly- N-vinyl-carbazole, exposing the charged surface so as to produce thereon an electrostatic latent image corresponding to a master, developing the electrostatic latent image by means of an electroscopic powder, and fixing the powder image on the surface of the photoconductive layer or foil or on a separate image-carrier after transference of the powder image thereto.
• the invention further provides a material for use in electrophotographic processes, being capable of being rendered light sensitive by applying an electrostatic charge thereto, and comprising a paper or other support carrying a photoconductive insulating layer comprising a poly-N-vinyl-carbazole.
• the layers are, in themselves, non-light-s ensitive, by applying a positive or negative electrostatic charge thereto, by means for example, of a corona discharge the layers are rendered light sensitive and can be used with long-wave UV. light of 3.600 to 4.200 A.U. in producing electrostatic latent images as described above. Very good images may be obtained by a short exposure under a master to a high-pressure mercury vapour lamp.
• the layers when charged are but slightly sensitive to light in the visible spectrum, it has further been found that their spectral sensitivity can be extended into the visible part of the spectrum by the addition to the layers of sensitizers, preferably in the proportion 0.1 to 5 percent weight for weight of photoconductive substance.
• the most suitable sensitizers are dyestufi com- Reference (Schultz' Dyestufl Group Dyestufi Compound Farbstoiftabellen,
• Mineral acids such as hydrogen halides, sulphuric acid and phosphoric acid;
• Organic carboxylic acids such as acetic acid and the substitution products thereof, monochloro-acetic acid, di-
• chloroacetic acid trichloroacetic acid, phenylacetic acid, and 6-methyl-coumarinylacetic acid (4); maleic acid; cinnamic acid, benzoic acid, l-(4-diethylamino-benzoyl)-benzene-2-carboxy1ic acid, phthalic acid, and
• tetrachlorophthalic acid ,5-dibromo- 8-formyl-acrylic acid (muco-bromic acid), dibromo-maleic acid, 2- brorno-benzoic acid, gallic acid, 3-nitro-2-hydroxy-1- benzoic acid, Z-nitro-phenbxyacetic acid, 2-nitro-benzoic acid, 3-nitrobenzoic acid, 4-nitro benzoic acid, 3-
• nitro-4-ethoxy-benzoic acid 2-chl0ro-4-nitro-1-benzoic acid, 3-nitro-4-methoxy-benzoic acid, 4-nitro-l-methylbenzoic acid, Z-chloro-S-nitro-l-benzoic acid, 3-chlo-ro 6-nit-ro-1-benzoic acid, 4-chloro-3-nitro-l-benzoic acid, 5-chloro 3-nitro-2-hydroxy-benzoic acid, 4-chloro-2-hydroxy-benzoic acid, 2,4-dinitro-1-benzoic acid, Z-bromo- S-nitro-benzoic acid, 4-chlorophenyl-acetic acid, 2-chloro-cinnamic acid, 2-cyano-ci1mamic acid, 2,4-dich1orobenzoic acid, 3,5-dinitro-benzoic acid, 3,5-dinitr0-salicylic acid, malonic acid, mucic acid, acetosalicylic acid,
• Organic phosphonic acids such as 4-chloro-3-nitro-benzene-phosphonic acid
• Nitrophenols such as 4-nitrophenol, and picric acid
• Acid anhydrides for example:
• Metal halides of the metals and metalloids of the groups IB, II through to group VIII of the periodical system for example:
• Aluminium chloride zinc chloride, ferric chloride, tin tetrachloride (stannic chloride), arsenic trichloride, stannous chloride, antimony pentachloride, magnesium chloride, magnesium bromide,calcium bromide, calcium to dide, strontium bromide, chromic bromide, manganous chloride, ferrous chloride, cobaltous chloride, cobaltic chloride, cupric bromide, cuprous chloride, ceric chloride, cerous chloride, cerous bromide, mercuric chloride (corrosive sublimate), thorium chloride, arsenic triiodide;
• Quinones such as p-benzoquinone, 2,5-dichlorobenzoquinone, 2,6-dichloro benzoquinone, chloroanil, naphthoquinone-( 1,4) 2,3-dichloro-naphthoquinone-( 1,4), anthraquinone, Z-methyIanthraquinone, 1,4-dimet-hylanthraquinone, l-chloroanthraquinoue, anthraquinone- Z-carboxylic acid, 1,5-dichloroanthraquinone, 1-chloro- 4-nitroauthraquinone, phenanthrene-quinone, acenap-hthenequinone, pyranthrenequinone, chrysene-quinone, thio-naphthene-quinone, anthraquinone-l,8-disulfonic acid
• Aldehydes such as bromal, 4-nitrobenzaldehyde, 2,'6-dichlorobenzaldehyde, 2-ethoxy-l-naphthaldehyde, anthIacene-9-aldehyde, pyrene3'-aldehyde, oxind0le-3- aldehyde, pyridine-2,6 -dialdehyde, biphenyl-4-aldehyde, furfural;
• aldehydes such as bromal, 4-nitrobenzaldehyde, 2,'6-dichlorobenzaldehyde, 2-ethoxy-l-naphthaldehyde, anthIacene-9-aldehyde, pyrene3'-aldehyde, oxind0le-3- aldehyde, pyridine-2,6 -dialdehyde, biphenyl-4-aldehyde, furfural;
• Ketones such as acetophenone, benzophenone, 2-acetylnaphthalene, benzil, benzoin, S-benzoyl-acenaphthene, biacene-dione, Q-acetylanthracene, 9-benzoyl-anthracene, 4-(4'-dimethylamino-cinnamoyl)-1-acetylbenzene, acetoacetic acid-anilide, indandione-(LB), (1,3-diketohydrindene), acenaphthenequinone-dichloride, an-isil, 2,2-pyridil, fun'l.
• the quantity of the substances required for obtaining the best possible improvement varies with the nature of such substance, but generally is from 0.01 to 5 percent, preferably from. 1 to 2 percent weight for Weight of the
• the addition of even a much smaller quantity causes a considerable increase of the sensitivity of the poly-vinyl-carbazole layer.
• Larger quantities of the additive substances even up to 20 percent weight for weight of the poly-vinyl carbazole, may be used if desired.
• "Non-volatile solid compounds amongst the class referred to are preferably used as the additive sub stances. Liquid or gaseous additive substances of the class referred to may also be used.
• the invention further includes a material for use in electrophotographic processes comprising a self-supporting foil of poly-N-vinyl-carbazole which may contain a sensitizer being a dyestufi or other substance capable of modifying the spectral sensitivity of the foil when electrostatically charged, and/ or an additive of the class set forth above elfective to increase the photo-semiconductive capacity of the polyvinyl-carbazole and comprising acids, acid anhydrides, metal halides, boron halides, and organic carbonyl compounds.
• a sensitizer being a dyestufi or other substance capable of modifying the spectral sensitivity of the foil when electrostatically charged
• an additive of the class set forth above elfective to increase the photo-semiconductive capacity of the polyvinyl-carbazole and comprising acids, acid anhydrides, metal halides, boron halides, and organic carbonyl compounds.
• Material embodying the invention both in the form of a self-supporting foil and of a layer carried .on a support, may also be employed as record paper for charting purposes, for example for photographic recorders and like apparatus.
• Polyvinyl-carbazoles i.e. polymerisation products of N-vinyl-carbazole, are known in various stages of polymerisation. They have resin-like character, rendering superfluous the use of binding agents for the purpose of increasing the homogeneity of a photo-conductive insulating layer.
• High-molecular poly-N-vinyl carbazoles are available as commercial products, for example, the products marketed by the firm of Badische Anilinund Sodafabrik A.G., Ludwigshafen/Rhein, under the registered trademark Luvican, such as Luvican K 323, Luvican M 170 and Luvican K 260. They dissolve with strong fluorescence in many organic solvents.
• the polyvinyl carbazoles are preferably coated in organic solvents onto the support which may be of the kind commonly used in electro-photography, for example metal, paper or a plastic foil, in known manner for example by hopper coating or by direct coating.
• the polyvinyl carbazoles may be used for coating supports, also for aqueous dispersions or dispersions in organic solvents, with equally good results.
• Photoconductive insulating layers of exceptional uniformity are obtained by this means with which excellent copies can be prepared by electrophotographic means. Hitherto it has been recognised as advisable, when paper was used as support ,tfor the photoconductive layer, for special pretreated paper incapable of being penetrated by organic solvents to be used.
• the polymers of N-vinyl carbazoles can be applied in the form of solutions in organic solvents even to untreated base papers without excessive penetration of the coating solution taking place.
• polymers of the N-vinylcarbazoles make the addition of other substances unnecessary, plasticizers and other resins, e.g. ketone resins, may if desired be added to photoconductive layers prepared in accordance with the invention, which in some circumstances could result in improvements, for example, in light sensitivity.
• Resins which are suitable to be added to the polymerized N-vinyl-carbazoles include also synthetic polymers or other organic colloids. As examples of such resins the following substances are stated:
• Natural and synthetic resins e.g. balsam resins, phenol resins and other resins modified with colophony, coumarone resins and indene resins and the substances covered by the collective term synthetic lacquer resins, which includes processed natural substances such as cellulose ether, see the Kunststofftaschenbuch (Plastics Pocket Book) published by Saechtling-Zebrowski (11th edition, 1955, page 212 onwards);
• Polymers such as the polyvinyl chlorides, polyvinyl acetate, polyvinyl acetals, polyvinyl alcohols, polyvinyl ethers, polyacrylic and polymethacrylic esters, and polystyrene and isobutylene polymers;
• Polycondensates e.g. polyesters, such as phthalate resins, alkyd resins, maleic acid resins, colophony esters of mixed higher alcohols, phenol-formaldehyde resins,
• additives which may if desired be used, include pigments such as zinc oxide or titanium dioxide and also other photoconductive organic substances.
• the polyvinyl carbazole foil, or support carrying a layer comprising polyvinyl carbazole may be utilized for the production of images by electrophotographic means, for example, as follows:
• the thus sensitized layer is exposed to light under a master or by episcopic or diascopic projection and is then dusted over in known manner with a suitable developing agent such as a resin powder colored with carbon black.
• a suitable developing agent such as a resin powder colored with carbon black.
• the image that now becomes visible can easily be wiped oif, and therefore needs to be fixed; it can for example, be heated briefly to approximately C. by means of an infrared radiator. The temperature need not be as high as this if the heat treatment is carried out in the presence of vapours of solvents such as trichloroethylene, carbon tetrachloride or ethyl alcohol.
• the powdered image can also be fixed by means of steam. From positive masters, positive images of good contrast are produced.
• the support e.g. the paper or plastic foil
• a solvent for the photoconductive layer e.g. alcohol, or acetic acid
• positive printing plates are obtained which can be set up in an oflset machine and used for printing. They give very long runs.
• the electrophotographic images can also be used as masters for the production of further copies on any sort of light sensitive sheets.
• the photoconductive compounds to be used as provided by the invention are superior to substances such as selenium or zinc oxide, inasmuch as the latter give cloudy layers.
• polyvinyl carbazoles disclosed in the examples are polymerization products of N-vinyl-carbazole.
• Examples l A solution of 10 gms. of polyvinyl carbazole in 150 ml. of benzene is applied to paper by means of a coating hopper and the coated paper is dried. The solution is applied onto the paper until the thickness of the dried layer amounts to 5 1.. A larger quantity of the solution can be applied in order to obtain a dried layer of an essentially uniform thickness of up to 20a.
• the coated paper is negatively charged to about 300 volts by means of a corona discharge, exposed for a few seconds under a positive transparent master to the light of a high-pressure mercury vapour lamp watts, 30 cm. distance) and dusted over with a developer comprising a mixture of 100 gms. of glass balls (approx. a) and 2.5 gms. of a toner the particle size of which is 20-50;!
• Said toner can be prepared by fusion of:
• the images produced are suitable as copying masters (intermediate originals) for the production of duplicates by 'any convenient photo reproduction method, a 1
• the coated paper can be positively charged by means of a corona discharge, the thus sensitized paper exposed under a positive transparent master to the light of a highpressure mercury vapour lamp for M second and dusted over with a developer consisting of methyl cellulose as carrier and the toner described in Example 1. A positive image of the master becomes visible which can be fixed by heating.
• the foil produced can be charged by means of a corona 8 Paper is coated with this solution by means of a hopper device, and the coating dried;
• the coating in the paper can be negatively charged by means of acorona discharge and then an image of one side of a sheet printed on both sides can be projected episcopically on the charged paper to produce an electrostatic latent image of the said side.
• the electrostatic latent image is treated with a developer consisting of finely divided glass balls and a resin and carbon-black mixture, and fixed for example by heating.
• the foil can be subjected to a corona discharge, exposed under a positive master for 4 second to the light of a high-pressure mercury vapour lamp and dusted over with a developer containing coloured resin particles, such as the developer described in Example 1.
• a positive image is obtained which can be fixed by heating.
• Example 6 Theprocedure described in Example 1 is followed except that the coating solution used contains 10 gms. of ketone resin (for example the resin known as Kunststoffharz AP produced by the Chemische Werke Hills A.G., Marl/Kr. Recklinghausen) as well as 10 gms. of polyvinyl carbazole, in 150 ml. of benzene.
• the coated paper is dried, then negatively charged by means of a corona discharge and exposed undera positive transparent master for three seconds to the light of a 125-watt high-pressure mercury vapour lamp at a distance of cm. An electrostatic positive image is obtained which is developed and fixed by steam treatment.
• ketone resin for example the resin known as Kunststoffharz AP produced by the Chemische Werke Hills A.G., Marl/Kr. Recklinghausen
• 10 gms. of polyvinyl carbazole in 150 ml. of benzene.
• the coated paper is dried, then negatively charged by means of a cor
• electrostatically charged paper is exposed under a trans parent positive master to light for 1 second using a Watt high-pressure mercury yapour lamp at a distance of 30 cm. Subsequently the paper is dusted over with a resin powder, coloured with carbon black. The finely divided resin remains at those parts of the polyvinylcarbazole layer which have not been struck by light during exposure and thus a positive image of the original becomes visible, which is'then. made stable (fixed) by image shows a very good contrast.
• the electrostatically charged paper is placed with its coated side contacting a book-page printed on both sides as original, and is exposed to light for 3 seconds by means of a 100-watt incandescent lamp. Exposure is thus effected through the copying paper. After exposure, the electrostatic latent image is dusted with a resin powder colored with carbon black, in known manner. A positive reversed image is obtained, which shows good contrast. By firmly pressing paper or a plastic foil onto the powder image obtained, the image can be transferred onto the paper or foil, and a non-reversed image of the book-page is thus obtained. During the transfer operation on the powder image, an electric field may, as is well-known in the art, be applied to the paper or foil, to which the reversed powder image is intended to be transferred. If the paper or foil (known as transfer material) is transparent, the copies produced thereon are suitable as intermediate originals for further copying such as printing onto diazotype paper or blue-print paper.
• the mixture is applied onto paper which is then dried.
• the paper may be provided with a positive charge by means of a corona-discharge apparatus rendering it sensitive to light-rays, exposed for 1 second under a positive transparent original to light from a 40 watt incandescent lamp at a distance of 30 cm. and then dusted over with a resin powder coloured with carbon black. A positive image of the original is thus made visible and is fixed by heating.
• the layer side of the exposed paper is treated with a developer consisting of a mixture of small glass beads and very finely divided particles of a resin-carbon-black mixture.
• the black colored resin which becomes positively charged triboelectrically sticks to those parts of the polyvinyl canbazole layer which have not been struck by light during exposure, and a positive image is thus obtained, which is fixed by slightly heating it.
• the image shows good contrast.
• Example 17 The procedure described in Example 10 is followed except that for coating the paper, a solution is used, prepared by mixing gms. of benzene containing 9.6 gms. of polyvinyl carbazole dissolved therein, 07 cc. of a l-molar solution of dichloroacetic acid in benzene and 2 mgms. of the dyestutf Victoria blue B (see the foregoing table of dyestuffs) in 1 cc. of methanol. When using a 40 watt incandescent lamp at a distance of 30 cc. the exposure time needed is 1 second. An image may be pro quiz from a book-page, both sides of which have been printed, by episcopic projection. The images show the half-tones and the full-tones with good contrast.
• a direct image can be electrophotographioally produced by providing the layer with a negative electric charge by means of a corona discharge apparatus, exposing the charged layer of one second under a positive transparent original to light from a high-pressure mercury vapor lamp of 125 watts at a distance of 25 cms., and subsequently dusting (developing) the exposed layer with a resin powder colored with carbon black in a manner known per se.
• a positive image of the transparent original becomes visible, which is made stable (fixed) by slightly heating it. The image shows good contrast.
• 2-methylanthraquinone other quinones can be added in equivalent quantity to the polyvinyl carbazole solution, for example, another substitution product of anthraquinone, anthraquinone itself, benzoquinone, naphthoquinone, or a substitution product of the two last mentioned quinones.
• a transparent support such as a sheet of cellulose acetate instead of paper, the positive copy produced electrophotographically can be used as a master for printing on to other light sensitive layers.
• foil images can be produced from patterns by the electrophotographic process in a manner known.per se, from which images copies with good contrast can be obtained 7 on paper by transference.
• non-transparent opaque paper which is permeable to light (translucent) and dried.
• the polyvinyl carbazole layer thus provided on the paper is negatively charged by means of a corona discharge apparatus and is put with its layer-side upon a doublesided printed book-page which serves as an original lying on a backing of black paper. It is then exposed to light under a 100 watt incandescent bulb for 2 seconds. The exposure takes place reflex-wise from the back side of the coated paper through the paper sheet.
• the paper After exposure the electrostatic latent image'on the paper is powdered with resin-soot-powder and a positive reversed image, rich in contrast, is obtained which image is transferred to a transfer sheet of paper or plastic foil, which is firmly pressed on the powder image A nonreversed copy of the book-page used as pattern is obtained.
• the transference may also becarried out in the manner known per se wherein an electric field is applied to'the transfer material.
• the transferred image is then fixed. If the paper or the plastic foil (transfer sheet) are transparent the non-reversed image obtained can be used as an intermediate original for making further copies for example on diazotype or blueprint paper.
• Example 18 The procedure described in Example 18 is followed, except that for coating the paper a solution of 44 gms. of polyvinyl carbazole and 0.42 gm. of indandione- 1,3 (l,3diketohydrindene) in 820 cc. of benzene, is used. With the material produced positive images also rich in contrast are obtained. The exposure of the charged material s elfected under a 125'watt high-pressure mercury vapor lamp at a distance of about 25 cms., with an exposure time of 2 seconds.
• Example 18 The procedure described in Example 18 is followed, except that for coating the paper a solution is used of 50 cc. of benzene containing 4 gms. of polyvinyl carbazole and 0.065 g. of phthalic anhydride. The time of exposure necessary for producing positive latent elect-rostatic images amounts to 1 second. t Y
• Example 9 The'procedure described in Example 9 is followed except that for coating the paper a mixture issued prepared by mixing a solution of 10 gms. of polyvinyl car- 'oazole and 0.126 gm. of l-chloro-anthraquinone in 200 cc. of benzene, a solution of 0.06 g. of .maleic acid in 30 cc. of tetrahydrofurane, and a solution of 0.05 g. of the dyestuff Rhodamine B extra (see the foregoing table of dyestuffs) in 5 cc. of methanol.
• the paper is exposed for 5 seconds under a 40 watt incandescent lamp at a distance of 25 cms. After developing and fixing the images produced show good contrast.
• a photographic reproduction process which comprises exposing an electrostatically charged photoconductive insulating layer comprising solid polyvinylcarbazole to a light image, whereby the light-struck area is discharged, and developing the resulting image with an electroscopic material.
• the photoconductive layer also contains a dyestufl? and a compound selected from the group consisting of mineral acids, metal halides, boron halides, and compounds containing a carbonyl group.

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• 0
  • DE DENDAT1068115D patent/DE1068115B/de active Pending
  • NL NL99153D patent/NL99153C/xx active
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• 1958
  • 1958-07-25 DE DEK35382A patent/DE1111935B/de active Pending
  • 1958-09-03 CH CH6355158A patent/CH379276A/de unknown
  • 1958-09-04 FR FR1210153D patent/FR1210153A/fr not_active Expired
  • 1958-09-04 GB GB28401/58A patent/GB856770A/en not_active Expired
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