Recording sheet for OHP

Abstract: A recording sheet for an OHP for use in a wet-type copying machine, the recording sheet for an OHP having: a base made of a transparent plastic film; and a toner fixing layer formed on the base, wherein the toner fixing layer is transparent and is composed mainly of a resin which can be dissolved or bloated in the solvent contained in a liquid developer. A recording sheet for an OHP for use in an electrostatic dry-type copying machine, the recording sheet for an OHP having: a base made of a transparent plastic film; and a toner fixing layer formed on the base, wherein the toner fixing layer is transparent and is composed mainly of a rubber type resin.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a recording sheet for use in an OHP in such a manner that a toner image is transferred/fixed to the surface of a film. Related Art Statement A conventional wet-type copying machine employs a copying method arranged in such a manner that a liquid developer is used to perform developing, a toner image is transferred to the surface of a film and a heat source is brought into direct contact with the surface of the film to which the toner image has been transferred so that the above-described toner image is fixed. Therefore, there arises a problem of an abnormal phenomenon such as undesirable run of the image or the like because the ordinary OHP sheet for use in a conventional dry-type copying machine cannot satisfactorily absorb the solvent contained in the liquid developer. In order to overcome a problem of the type described above, there have been made a variety of disclosures. That is, a technology has been disclosed in Japanese Patent Laid-Open No. 1-302266 which is arranged in such a manner that the surface of the sheet is subjected to a roughening treatment by using a hydrophobic resin and thereby the above-described solvent can be absorbed by the roughened surface layer of the sheet so that the image can be fixed satisfactorily. According to this method, no problem arises in a case where the quantity of the toner to be transferred is a small quantity. However, if a large quantity of the toner must be transferred, the above-described problem of the run of the image cannot be overcome because the roughened surface layer cannot satisfactorily absorb the above-described solvent. Another technology has been disclosed in Japanese Patent Laid-Open No. 2-47667 which is arranged in such a manner that a porous surface layer made of a devitrified resin is formed on the surface of the sheet to cause the toner to be perfectly absorbed by the porous surface layer regardless of the quantity of the toner. Furthermore, the sheet is passed through heating rollers so that the porous surface layer is melted and the devitrified porous surface layer is returned to the transparent state. As a result, the image is fixed as desired. Although the generation of the run of the image can be prevented according to the above-described method, excessively large thermal energy is required to melt the resin such that the temperature of the heating rollers must be raised to a level which is, by 20°C to 30°C, higher than the temperature which is required to fix an image to an ordinary sheet. SUMMARY OF THE INVENTION An object of the present invention is to provide a recording sheet for an OHP for a conventional wet-type copying machine capable of preventing generation of image run on the sheet regardless of the quantity of a solvent to be transferred even if direct heat fixing is performed by using heating rollers and as well as capable of eliminating a necessity of providing considerably high temperature heating rollers. According to one aspect of the present invention, there is provided a recording sheet for an OHP for use in a wet-type copying machine, the recording sheet for an OHP comprising: a base made of a transparent plastic film; and a toner fixing layer formed on the base, which is characterized in that the toner fixing layer is transparent and is composed mainly of a polynorbornene resin which can be dissolved or bloated in the solvent contained in a liquid developer. That is, inventors of the present invention have studied hard in order to overcome the above-described problems. As a result, a knowledge, from which the present invention could be established, was acquainted that it is effective for a toner layer on a transparent plastic film for use in a wet-type copying machine to be transparent and be composed mainly of a resin which can be dissolved or bloated in the solvent contained in a liquid developer. In this case, the above-described solvent can be absorbed into the toner fixing layer after the toner image has been transferred from the photosensitive member to the fixing layer. Therefore, the image run can be prevented even if the above-described surface of the toner image is brought into direct contact with a heating source, causing a clear image to be fixed and formed. Other and further objects, features and advantages of the invention will be appear more fully from the following description. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A recording sheet for an OHP according to the present invention can be manufactured as follows: A transparent plastic film for use as the base of the recording sheet for an OHP is exemplified by a transparent thermal plastic resin film, a polyvinyl alcohol film, a film made of a cellulose derivative and a film formed by orienting any of the above-described materials. The transparent thermal plastic resin film is exemplified by a film made of polyethylene terephthalate, polypropylene, polystyrene, polyvinyl chloride, polymethyl methacrylate, polyethylene or polycarbonate or a film having an undercoat layer for the purpose of improving the adhesive facility between the surface made of any of the above-described materials and the toner fixing layer, and a film subjected to the corona discharge process. Usually, the polyethylene terephthalate film or a polyester film is employed because of its excellent heat resistance. As a resin for constituting a transparent toner fixing layer of the recording sheet for an OHP for use in the wet-type copying machine, polynorbornene resin which is dissolved or bloated out in a solvent for use in the liquid developer and which becomes transparent after it has been dried in the form of film is employed. As the above-described solvent, a petroleum solvent having a high boiling point is employed to serve as the main component, and specifically ISOPER (manufactured by Exxon) is preferably employed. The polynorbornene resin exhibits an excellent solubility and bloating tendency among the above-described rubber type resins. Therefore, the above-described solvent can significantly be absorbed when the same is used to form the surface layer of the OHP sheet. The polynorbornene can be obtained by a method comprising the steps of synthesizing norbornane from ethylene and cyclopentadiene by the Diels-Alder reaction and ring-opening-polymerizing the norbornane monomer. In general, the above-described image run at the time of the image fixing process can be substantially prevented and thereby an image exhibiting excellent quality can be formed when 40% or more, preferably 45% or more of the solvent in the liquid developer is absorbed into the toner fixing layer. Therefore, it is preferable that the thickness of the toner layer containing the polynorbornene resin be 0.1 µm or more. In order to prevent undesirable blocking which can be taken place at the time of stacking the sheets, it is preferable that an inorganic or organic filler be mixed in the above-described toner fixing layer by a quantity with which the transparency can be maintained. The inorganic filler is exemplified by calcium carbonate, magnesium carbonate, zinc oxide, titanium oxide, mica, clay, silica powder, colloidal silica and diatomaceous. The organic filler is exemplified by polyethylene and an acrylic resin. Small uneven portions can be formed on the surface layer of the toner fixing layer depending upon the particle size of the filler. Furthermore, ethylene bisamide and stearic acid amide are respectively effective to prevent blocking. Then, a method of forming the toner fixing layer on a substrate will now be described. A transparent plastic film serving as the base is coated with any one of the above-described resins of an emulsion, latex, water solution or solvent dissoluble type by any one of a known wire bar method, a doctor blade method or an air knife method to form a layer having a predetermined thickness. Then, the coated resin is dried so that the desired recording sheet for an OHP for the wet-type copying machine is obtained. During the above-described process, a charge prevention treatment may, of course, be performed in order to prevent the undesirable charge. As described above, the recording sheet for an OHP according to the present invention for use in the wet-type copying machine is obtained in such a manner that the transparent plastic film serving as the base is coated with the resin for forming the toner fixing layer by the known means. The resin becomes transparent after it has been dried. Therefore, excellent transparency can be realized as the overall body of the sheet. Furthermore, since the resin for forming the toner fixing layer is the resin which can be dissolved or bloated in the solvent of the liquid developer for use in the wet-type copying machine, a solvent absorbing mechanism can be formed even if the toner fixing layer is a transparent and non-porous layer. Therefore, excellent solvent aborptivity can be realized. As a result, the undesired image run can be prevented even if the image surface is brought into direct contact with the surface of the heating source after the toner image has been transferred from the photosensitive member to the surface of the sheet fixing layer. Consequently, a very clear image can be fixed and formed. On the other hand, the recording sheet for an OHP for use in the electrostatic copying machine exhibits a satisfactory printing performance such as the dot reproducibility of the toner particles and the fixing facility. Furthermore, the same has satisfactory abrasion resistance. Examples Then, an example according to the present invention and a comparative example will now be described. Comparative Example A styrene-acryl copolymer resin (emulsion type Movinyl 8000 manufactured by Hext having a solid portion of 40%) was, by using an applicator, applied to a transparent polyester film the thickness of which was 100 µm before it was dried for 3 minutes by a constant-temperature drier set to 100°C so that a recording sheet for an OHP for use in the wet-type copying machine according to the present invention was manufactured. The surface layer of the recording sheet for an OHP thus-formed, that is, the toner fixing layer was completely transparent and the thickness of the layer was 30 µm. The sheet thus-obtained was subjected to a continuous copying operation by using a wet-type copying machine CT-5085 manufactured by RICOH at a line speed of 266 mm/sec. As a result, the run of the image, the contamination of the surface of the roller and that of the image offset and the like were completely prevented and a clear image was obtained. In this state, the fixing temperature was set to 145°C. Example Liquid to be applied was prepared by mixing 100 parts by weight of polynorbornene resin solution (Norsolex NSX-L manufactured by Zeon) with 400 parts by weight of toluene before they are stirred sufficiently. It was then, by using an applicator, applied to a transparent polyester film the thickness of which was 100 µm before it was dried for 3 minutes by a constant-temperature drier set to 100°C so that a recording sheet for an OHP was manufactured. The surface layer of the recording sheet for an OHP thus-formed, that is, the toner fixing layer was completely transparent and the thickness of the layer was 0.3 µm. The sheet thus-obtained was subjected to a continuous copying operation by using the same copying machine under the same conditions as those according to Comparative Example. As a result, an image which was clearer than that obtained according to Comparative Example was formed.

Claims: A recording sheet for an overhead projection OHP for use in a wet-type copying machine, said recording sheet for an OHP comprising: a base made of a transparent plastic film; and a toner fixing layer formed on said base, characterized in that said toner fixing layer is transparent and is composed mainly of a polynorbornene resin. A recording sheet according to Claim 1, characterized in that the thickness of said toner fixing layer is 0.1 µm or more. A recording sheet according to Claim 1 or 2, characterized in that said toner fixing layer further comprises an inorganic filler selected from the group comprising calcium carbonate, magnesium carbonate, zinc oxide, titanium oxide, mica, clay, silica powder, colloidal silica and diatomaceous. The recording sheet according to one of Claims 1 to 3, characterized in that said toner fixing layer further comprises an organic filler selected from the group comprising polyethylene and an acrylic resin. The recording sheet according to one of Claims 1 to 4, characterized in that said toner fixing layer further comprises ethylene bisamide and stearic acid.

Inventors: KAZUO SATO, Kazuo Sato, c/o Nisshinbo Ind.Inc.
Applicants: NISSHIN SPINNING, NISSHINBO INDUSTRIES, INC.
Application year: 1991
Main classification: G03G7
IPC codes: G03G7