Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-04-03
2003-10-28
Shosho, Callie (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S560000, C523S160000, C430S007000
Reexamination Certificate
active
06639006
ABSTRACT:
This invention relates to inks comprising acrylic polymers; to their use in ink jet printing to prepare patterned substrates (e.g. colour filters); and patterned substrates prepared by this method.
Ink jet printing (IJP) methods involve a non-impact printing technique for printing an image onto a substrate using ink droplets ejected through a fine nozzle onto a substrate without bringing the nozzle into contact with the substrate.
The ability to produce a patterned polymeric coating on a substrate, where the coating has high resistance (fastness) to solvents, water and heat is important in many areas of for instance the electronics and printing industries. IJP is a convenient method of producing such patterns in a precise and rapid manner. In this process, inks containing precursors for cross-linked acrylic polymer(s) are applied to the substrate to produce a continuous film, and the substrate is subsequently treated in order to produce a cross-linking reaction within the film to give a coating with the requisite fastness properties. The use of IJP, particularly thermal IJP, does however impose significant demands on the precursors used to produce such patterns, as they must be chosen such that they are able to produce inks of low viscosity and high stability, and yet are sufficiently reactive to produce the high fastness properties needed once they are applied to the substrate.
There are many demanding performance requirements for colorants and inks used in IJP. For example, they desirably provide sharp images having good water-fastness, light-fastness and optical density. The inks are often required to dry quickly when applied to a substrate, but they should not form a crust over the tip of an ink jet nozzle because this will stop the printer from working. The inks should also be stable to storage over time without decomposing or forming a precipitate which could block the fine nozzle. The most popular ink jet printers are the thermal and piezoelectric ink jet printers. There is a need for inks which are suitable for both thermal and piezo ink jet printers, have high colour strength and produce images having a high light-fastness and water-fastness when printed on a substrate.
Colour filters, alternatively known as optical filters, are a component of coloured liquid crystal displays (LCDs) used as flat screen displays as, for example, in small television receivers or portable computers. Typically, a white back-light is shone through a liquid crystal layer and then a colour filter to produce an image of the desired colour by the transmitted light. The LCD layer comprises an addressable array of pixels. The light at any pixel can be switched on and off by applying a voltage to the liquid crystal film which changes the orientation of the polarising liquid crystals to block the back-light. The pixels are in register with a trichromatic array of colour filter elements to produce a full colour screen capable of displaying images. Some LCD displays are constructed to be viewed by reflected light, but still require a colour filter to produce a full colour image. Colour filters are equally useful for other display technologies such as plasma display panels, cathode ray tubes and electroluminescent displays and as a component of solid state imaging devices. It is advantageous that the coloured elements of a colour filter are formed by a printing process such as IJP. Compared to other methods (e.g. etching or photolithography) the wastage of colorant is much less and the manufacturing steps are reduced, leading to a simpler and cheaper process.
For the IJP of colour filters it is important to maximise the solids content of the ink formulation to enhance film quality and minimise the number of processing steps. This must be achieved whilst maintaining low ink viscosity. It is particularly preferable to be able to achieve sufficiently high solids loadings in the ink to allow the deposition of enough material on to the substrate to produce the desired properties in a single pass of the ink-jet head. It is also important that the colour filter is resistant to solvents, water, heat and light. Such resistance can be achieved by cross-linking polymeric components using a thermal cross-linking reaction. It is vital that cross-linking reactions employed do not take place in the print head if a thermal IJP method is to be used.
Certain photosensitive acrylic resins have previously been used to produce colour filters by photolithography, which, as mentioned above, is a wasteful and complicated process. Much of the colorant that is applied to the substrate is removed in later process steps. These photosensitive acrylic resins are not applied by IJP, and are unsuitable for such a process, particularly in the demanding conditions experienced in a thermal ink-jet print head.
WO 95-034024 (Zeneca) (=EP 0764290) discloses a method for producing a colour filter by IJP a precursor for a polymer and a resin reactive dye so that the dye is covalently attached to the cross-linked polymer matrix on the substrate surface. The polymeric inks disclosed in this reference are not especially optimised for being fired in a thermal ink-jet print head, whereas the acrylic polymers used in the present invention are optimised to be thermally ink-jettable. Thus for example certain inks disclosed in WO 95-034024 may comprise too much melamine-formaldehyde resin cross-linker to be fired from a thermal IJ print head (see Comparative Example A, herein). The present invention does not require use of a resin-reactive colorant, where the colorant is chemically bound to the cross-linked polymer. Thus the present invention may use colorants incompatible with those described in WO 95-034024 which thus teaches away from the present invention. The ability to use dyes which are not covalently bound to the polymer greatly increases the flexibility in the choice of colorant used.
JP-A-08-311383 (Canon) describes the use of an alkali soluble styrene-acrylic acid co-polymer as a pigment dispersant for a thermal ink-jet ink. Although this ink uses ethanolamine as a base, this would not be a particularly effective cross-linker. This document does not suggest to cross-link the resin or to try to form a continuous film, both of which are important when making a colour filter.
JP-A-09-157563 (Kao Corp.) describes an ink which has good operability in a thermal ink-jet head and contains a carboxylic acid containing polymer such as poly(ethylene-co-acrylic acid). It is believed that the polymer is present to improve the water resistance of the dye. As with the previous Canon reference, this document does not teach to cross-link the acrylic polymer or form a continuous film.
EP-A-0703471 (Canon) describes a method for producing colour filters by IJP an acrylic polymer as an ink-receiving layer. This requires applying the polymer and colorant in two separate stages, whereas in the present invention only one processing step is required to apply both colorant and polymer.
JP-A-09-090115 (Toray Ind.) discloses an ink containing a pigment, styrene-acrylic acid polymer and melamine-formaldehyde resin to form a colour filter using an IJP process. The applicant has found that melamine-formaldehyde resins give poor operability in a thermal ink-jet head. The inks described in the present invention also allow the use of dyes as colorants to give filters with particularly good spectral properties.
JP-A-09-132740 (Asahi Glass) describes the use of a resin and pigment ink for making colour filters by ink-jet, but the inks contain mixtures of colloidal silica and water dispersible resins which will not fire efficiently through a thermal print head at the high loadings required to produce a durable colour filter in a single pass.
JP-A-09-165541 (Kao Corp.) is similar to the previous Kao patent, but uses polymers which are cross-linked by UV and solubilised with styrene sulphonic acid comonomer. These inks are not used to form continuous films and are not thermally cured. Thermal curing is advantageous compared to the alternatives such as UV-curing, as t
Cottrell David
Padget John Christopher
Pears David Alan
Tallant Neil Anthony
Yeates Stephen George
Avecia Limited
Pillsbury & Winthrop LLP
Shosho Callie
LandOfFree
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