METHOD FOR THE APPLICATION OF A PROTECTIVE LIGHT-TRANSMITTING COATING ON A TONER IMAGE FORMED ON A SUBSTRATE

Abstract: Method for forming a protective transparent coating on a toner image formed electrophotographically by depositing a transparant protective toner electrophotographically and in registration on said toner image, using the same original.

Description: Method for the application of a protective light-transmitting coating on a toner image formed on a substrate. The invention relates to a method for the application of a protective light-transmitting coating on a toner image formed on a substrate which is obtained by charging up a photoconductive substrate, image-wise discharging this by exposure and its development by means of pigmented toner and the subsequent transfer of the toner image obtained to a receptor substrate. The formation of images by means of electro-photographic techniques, utilizing one or more pigmented toners adhering to a substrate, e.g. a sheet of paper, forms part of stote of the art. As compared with known printing techniques, where use is made of a black or coloured ink, this electrophotographic technique possesses many advantages, but also the disadvantage that different types of toner which have nevertheless to be employed for certain reasons adhere more poorly to the recipient surface than the conventional ink. For this reason a known method is that after the formation of an image with such toners, the entire substrate is covered with a thin layer consisting of a suitable protective substance which is for example polymerisable or dissolved in a volatile solvent. This method, where the entire surface of the substrate, i.e. also the sections not carrying any toner, is covered suffers however from the disadvantage that the substrate obtains a surface structure other than that normally obtained during printing. The surface appears unnatural to the observer. Especially if electrophotographic techniques are employed for the formation of a proof print, this is a major disadvantage. The present invention provides a solution for this problem. In accordance with the invention, from the same orgininal, on the photoconductive substrate a second toner image is formed with a protective light-transmitting toner, this second toner image being registered with the first image on the receptor substrate, and subsequently fixed. Thus with the method in accordance with the invention protective toner is applied exclusively to the substrate where pigmented toner is present so that the surface portions of the substrate not provided with an image retain their original surface structure. The image ultimately obtained, protected by a layer of protective toner, as a result appears to be much more "natural". The invention can be used especially where, using known electrophotographic techniques a proof print is formed from a colour print, using a number of colour separations obtained from an original. Here the operation of applying the protective toner can be undertaken precisely as many times as there are colour separations, using on each occasion another colour separation, but it is also possible to form the protective toner image starting with an exposure of the photoconductive coating via all the colour separations employed during image formation and brought into registration therewith. The invention will now be explained with the aid of the drawing which illustrates the various stages which lead to the procurement of the ultimate protective coating. Fig. la illustrates schematically a substrate 1 which is image-wise covered with toner of different colour; toner of the first colour is indicated by the toner sections 2 shown as solidly filled, and toner of the second colour is indicated by toner sections 3 which are shown thatched. The toner images are obtained in the conventional manner starting from respectively the light-transmitting colour separations 4 and 5; toner image 2 is obtained'after exposure via colour separation 4 and subsequent development with toner 2, and toner image 3 after exposure via colour separation 5 and development with toner 3. Naturally there are also loca tions where toner images of the two different colours are there placed one on top of the other, and locations where/is no toner present at all. In accordance with the present invention the image obtained in this manner is covered with a transparent, non-pigmented protective toner only where pigmented toner is present. To achieve this two different methods can be employed: Fig. 1b illustrates how, on a suitable photoconductive coating 6, a toner image is formed from the desired protective toner 7, utilising the first colour separation 4 and this toner image is registered precisely on the image to be protected. Fig. 1c shows the result obtained. At that point where solely toner 3 of the second colour is present no protective toner is applied. These locations are covered in the next stage: once again an image is formed from protective toner 8, on this occasion utilising the second colour separation 5 (see fig. ld) and the image obtained in this way is once again registered precisely on the substrate already partially covered with protective toner. The situation which then prevails is shown schematically in fig. le. All pigmented toner is now covered by protective toner, the latter fusing as a result of heating on the surface of the substrate. Fig. 1f indicates that it is also possible to apply the pro tective toner in a single operation. Then a toner image 9 is formed using all the colour separations 4, 5 employed during the formation of the respective partial images, these being registered one above the other, and via which the photoconductive covering 10 to be employed is exposed. The toner image obtained after exposure and development with protective toner as shown in fig. 1f is then registered on the image 2, 3 which is to be protected. Fig. lg shows the result finally obtained. It is observed that the reference numerals in the claims are not intended to restrict the scope thereof, but are only denoted for clarification.

Claims: Claims: 1. Method for application of a protective light-trans mitting coating on a toner image formed on a substrate which is obtained by charging up a photoconductive substrate, discharging this image-wise by exposure, and developing it with the aid of pigmented toner and the subsequent transfer of the toner image obtained to a receptor substrate, characterised in that a second toner image is formed from the same original on the photoconductive substrate with a protective light-transmitting toner, this second toner image being brought into registration with the first image on the receptor substrate and subsequently fixed. 2. Method as in claim 1, as used in the case in which the image transferred to the substrate is obtained using a number of colour separations, by means of which a number of toner images of different colour and in precise registrations are formed consecutively, characterised in that the cycle of applying a protective light-transmitting coating is repeated as many times as there are colour separations, on each occasion with a different colour separation. 3. Method as in claim 1, as used in the case in which the image transferred to the substrate is obtained using a number of colour separations, by means of which a number of registered toner images of different colour are formed consecutively, characterised in that the second protective toner image is formed starting with an exposure of the photoconductive coating via all the colour separations employed in the preceding stages and being into registration with each other. 4. Method as in claims 1 - 3, characterised in that the protective toner layer is colourless.

Inventors: PERCIC, MILAN, REITSMA, EDO
Applicants: COULTER STORK PATENTS B.V.
Application year: 1982
Main classification: G03G8
IPC codes: G03G13, G03G15, G03G11, G03G8