Patent GB-1099983-A (GB)
Title: Improvements in and relating to printing processes using magnetisable substances
IPC: C09D5/23
Filed: 1965-02-02
Abstract: 1,099,983. Printing through the utilization of magnetic forces. AGFA A.G. Feb. 2, 1965 [Feb. 6, 1964], No. 4553/65. Heading B6C. In a method for the production of a magnetic image utilizable in a printing process for the production of a corresponding printed image, a layer of a magnetizable substance of which the permeability is dependent upon temperature is exposed to a thermal image having a temperature range corresponding to a temperature range of permeability variation of the substance and the resulting image-wise magnetic permeability changes in the substance are employed to produce a magnetic image in the layer. In the printing process the image-wise magnetic permeability changes are used to cause imagewise attraction of a layer of magnetizable ink toward a support for the printed image. The magnetic ink used may be a powder, the grains of which are enveloped in a material which is fusible at a temperature above the temperature range referred to above and wherein the powder deposited on a print support is brought to the fusion temperature of the fusible material. The transfer of the ink to the support may be effected by means of a magnetic field in a substantially non-contact operation. The temperature range employed may be near or including the Curie point of the magnetizable substance of temperature-dependent permeability, in which range a steep fall in permeability takes place. One form of apparatus for effecting the printing process comprises a cylinder 20, Fig. 11, to which magnetizable ink powder is supplied from a box 22. An original 23 to be copied is passed over the powder layer on the cylinder and is irradiated from a heat source 18 such that a thermal image is produced in the powder. A permanent magnet 24 holds the resulting magnetic powder image on the cylinder in a descending arc of movement thereof during which any non-magnetic powder drops off into a receptacle 22a. Material to be printed 27 receives the powder image at that area of the cylinder where the effect of the magnet 24 ceases. The resulting print is heat fused at 28. Another form of apparatus, Fig. 12, comprises an endless radiation transmitting flexible belt 34 suitable for receiving the magnetic ink and mounted for movement over rollers 30, 31 and 32. Magnetic ink is supplied from a trough 35, whilst the original to be copied is moved with the belt past a heat source 18 where an image corresponding to the original is produced on the belt. Copy material 40 is fed over a roller 39 and image transfer is effected by a permanent magnet 42. In yet a third form of apparatus, Fig. 13, a highly permeable printing cylinder 44 bears a permanently magnetizable double layer and is kept at a temperature slightly below the working temperature of the double layer by a controlled heating device 45. A displaceable " original " bearing carriage 46 is coupled, during the application of the thermal image, to the cylinder by a rack below the carriage and a gear-wheel train 47, 48, 49, 65, one wheel of which can be disengaged from the train. Thus, the image of an original placed on a glass plate 46a of the carriage, e.g. a page of a book 50, while the carriage moves from left to right, may be transferred to the cylinder surface by an optical system 51. Irradiation is effected by radiators 52 whilst magnetization or demagnetization of the thermal image emanates from a pole assembly 53. The latent magnetic image is inked by a rotating magnet 54. Paper sheets from a stack 59 are printed whilst passing between the cylinder 44 and pressure cylinder 61. When the desired run of copies has been completed, the cylinder 44 is cleaned by an assembly comprising a magnetized roller 63 and blade 66. In order to erase the magnetic record, a mirror 68 is inserted into the ray path of the heat source 52. The invention is also used for the production of relief printing plates, the magnetic powder being attracted image-wise to a plate support.