Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2000-11-08
2003-04-29
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S206000, C428S323000, C428S327000, C428S331000, C428S339000, C428S404000, C428S407000, C428S304400
Reexamination Certificate
active
06555206
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns receiver sheets, particularly transparent receiver sheets adapted to receive a colour toner image by an electrophotographic or electrostatic process and suitable for use in an overhead projector (OHP).
BACKGROUND TO THE INVENTION
Overhead projectors project an image by passage of light through a transparent film, known as a receiver sheet, bearing the image to be projected. The image is formed or the film by electrophotography or electrostatic printing. The receiver sheet is placed into an electrophotographic or electrostatic printer or copier and toner (black for a black and white image, or a series of colour toners (CMYK (cyan, magenta, yellow, black)) for a full colour image) is deposited imagewise and fused into the receiver surface to form an image on the receiver sheet.
For black and white OHP purposes, OHP receiver sheets are usually in the form of polyester such as biaxially oriented poly(ethylene terephthalate) (PET) base film typically about 100 &mgr;m thick (eg Melinex (Melinex is a Trade Mark) from ICI/Dupont) with a coating on the surface to promote adhesion of the toner to the base film. The coating is typically of an acrilic polymer and is either applied during the manufacture of the PET film or is coated off-line, i.e. as a separate step. The coating usually also contains filler to improve the handling properties and some Aintistatic agent (sometimes applied as an extra coating known as a supercoat). Such materials work well in black and white OHPs, where the aim of the toner is simply to block out projected light and hence project a dark area. Different considerations apply, however, in projecting colour images on an OPP. In this case light must be transmitted through a coloured block and accurately transmit the correct spectrum of light onto a screen. This must be achieved with minimum loss due to light scatter. It is therefore necessary for the coloured block on the film to be as transparent as possible. If the toner particles stick to the OHP surface and remain proud of the surface, there will be a haze in the film and scattering of the light at the surface of the film. This will cause the projected image on the screen to look dull and rather grey.
If conventional black and white OHP receiver sheets are used for colour OHPs, poor results are obtained. The present invention aims to provide a novel receiver sheet better suited to use with colour OHPs.
SUMMARY OF THE INVENTION
According to the present invention there is provided a transparent receiver sheet adapted to receive a colour toner image by an electrophotographic or electrostatic process and suitable for use in an overhead projector, comprising a toner acceptance layer that comprises a resin condensation product of toluene sulphonamide.
The resin is conveniently a condensation product of toluene sulphonamide and formaldehyde.
The resin suitably has a melting point of at least 60° C.
Suitable resins may be made by known techniques, or are available commercially. One preferred commercially available resin is Ketjenflex MH (Ketjenflex MH is a Trade Mark) from Akzo, which has as its main functional component a resin condensation product of toluene sulphonamide and formaldehyde present in the form of a mixture of mainly dimer, trimer and tetramers. Ketjenflex MH has the desirable properties of being compatible with a wide range of polymer classes (which is of importance for reasons to be discussed below), having a low melting point (about 62° C.) which is very sharp, and having a low melt viscosity. Ketjenflex MH has a glass transition temperature (Tg) of 40° C.
The resin preferably constitutes an amount in the range 40 to 100% by weight of the weight of the toner acceptance layer.
The toner acceptance layer optionally includes one or more secondary polymers, typically in an amount in the range of 0 to 60% by weight of the weight of the toner acceptance layer. The secondary polymer preferably has a molecular weight as low as possible compatible with good film-forming properties, with the molecular weight typically being in the range 1000 to 20000. Low molecular weight is also important in reducing the melt viscosity to a value that allows easy penetration of toner, in use. The lower the molecular weight of the secondary polymer, the better the fusion performance as discussed below. However, low molecular weight polymers may present manufacturing difficulties, so a compromise balance should be reached. The secondary polymer is preferably selected for compatibility with the resin and with the toner with which the sheet is intended for use. Thus, the secondary polymer desirably has a melting point that is similar to or slightly higher than that of the resin. The secondary polymer advantageously has a chemical structure and/or chemical properties and/or solubility parameters similar to those of the toner to ensure compatibility on blending. Compatibility between secondary polymer, resin and toner is also important to reduce light scattering as far as possible. Further, the melting point of the secondary polymer is desirably sufficiently low to ensure efficient fusing of toner particles into the surface of the toner acceptance layer in use.
The secondary polymer desirably has a Tg below 60° C.
For good performance in use, a number of factors need to be controlled, as follows:
a/ Compatibility
The polymers/resins in the acceptance layer must be compatible with polymer in the toner particles. This can be controlled by using materials with similar chemical properties and/or similar solubility parameters. Compatibility can be improved with the use of low molecular weight resins/polymers.
b/ Melting Point
For the fusing of the compatible materials, the melting point of the toner acceptance layer must be similar to or slightly lower than that of the toner. The temperature that the toner is exposed to during production of an image is above its melting point, which allows it to adhere to the receiver sheet. If both the toner acceptance layer and the toner melt at the same time, they have the possibility of mixing and forming a coherent fused layer.
c/ Melt Viscosity
For the toner acceptance layer and toner particles to become fused into one layer, the two must be able to mix rapidly. To ensure this occurs, the melt viscosity of the acceptance layer must below. However, if the melt viscosity is too low or if the melting range of the acceptance layer is smooth, rather than sharp, then there is a possibility that the toner particles can spread too far and produce a blurred image. The acceptance layer should therefore have a low melt viscosity but with a sharp melting point.
While a toner acceptance layer comprising resin alone functions well in use providing the electrical characteristics are sufficient to accept charged toner, secondary polymer is preferably included to facilitate manufacture and improve the handling properties of the layer.
Good results have been obtained using secondary polymer selected from the following.
(a) Vinyl chloride/vinyl acetate (VC/VA) copolymer, eg Vinylite VYES-4 (Vinylite VYES-4 is a Trade Mark) from Union Carbide.
(b) Polyesters, eg Vylon 200 (Vylon 200 is a Trade Mark) from Toyobo, and the amorphous polyesters Dynapol 850, Dynapol 411 and Dynapol 206 (Dynapol is a Trade Mark) from Allchem/Huls.
(c) Fumarate polymers, eg Atlac 363E (Atlac 363E is a Trade Mark) from DSM Resins, which is a propoxylated bisphenol A fumarate polymer, with unsaturation on the fumarate ester group still present.
(d) Epoxy resin, eg Epikote (Epikote is a Trade Mark) from Shell, which is a bisphenol A epoxide.
(e) Acrylates, eg quarternised acrylates such as Surcol 860 and Surcol SP6 (Surcol ia a Trade Mark) from Ciba Speciality Chemicals.
It is expected that similar results would be obtained with a wide range of other secondary polymers including polymers including polyurethanes and polystyrenes.
Mixtures of secondary polymers may be used.
The toner acceptance layer desirably also includes a minor amount of particulate filler material, typically constituting an am
Edwards Paul Andrew
Hann Richard Anthony
Moore Godfrey William
Morrison Gary Wayne
Pett Mark
Imperial Chemical Industries PLC
Jones Deborah
Pillsbury & Winthrop LLP
Xu Ling
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