NL2016429B1

NL2016429B1 - Digital Printing Apparatus and Digital Printing Process

Info

Publication number: NL2016429B1
Application number: NL2016429A
Authority: NL
Inventors: Erik Dries Deprez Lode; Jozef Johan Op De Beeck Werner
Original assignee: Xeikon Mfg Nv
Priority date: 2016-03-14
Filing date: 2016-03-14
Publication date: 2017-10-02

Abstract

A liquid toner digital printing process, wherein the liquid toner used in said printing process comprises a carrier liquid, curable marking particles, and a dispersing agent, and wherein said process comprises: (i) forming a latent image as a pattern of electric charge 5 on a surface of an imaging member, (ii) transferring the liquid toner onto a development member, (iii) developing the latent image by transferring liquid toner from the development member onto the imaging member in accordance with the pattern, (iv) transferring the liquid toner from the imaging member, (v) modifying the dispersing agent in the liquid toner transferred in step (iv) to reduce the dispersion capacity of the dispersing agent, (vi) heating the liquid toner modified in step (v) to at least a temperature at which the marking particles form a polymer melt, and (vii) irradiating the liquid toner heated in step (vi) with actinic radiation or particle beams to cure the heated marking particles, wherein the temperature of the heated marking particles is at least the glass transition temperature.

Description

Digital Printing Apparatus and Digital Printing Process Field of the invention

The present invention relates to a digital printing process using liquid toner and a digital printing apparatus.

Background

An apparatus and a process for digital printing using liquid toner are described in the earlier US patent application published under no. 2009/0052948. This US application describes a digital printing apparatus that uses a liquid toner comprising chargeable imaging particles and a carrier liquid.

In US 2009/0052948, the apparatus is said to comprise an imaging member adapted to sustain a pattern of electric charge forming a latent image on its surface, a development member arranged to receive a quantity of liquid toner from a reservoir and to develop the latent image by transferring a portion of the quantity of liquid toner onto the imaging member in accordance with the pattern, and depositing means arranged to deposit the transferred portion (i.e. the developed image) onto a printing substrate.

Liquid toners for use in digital printing processes such as that described in US 2009/0052948 are known in the art and usually comprise at least a carrier liquid and a marking particle.

For example, earlier European patent application publication no. 2713210 describes a liquid toner (also called a liquid developer dispersion) for use in a digital printing apparatus comprising a nonvolatile carrier liquid, a marking particle and a dispersing compound or a combination of dispersing compounds.

In this earlier European patent application, the carrier liquid is said to be any suitable non-volatile liquid such as a silicone fluid, a hydrocarbon liquid, a vegetable oil, or any combinations thereof.

In addition, in EP2713210, the marking particles are said to comprise coloured particles (i.e. a pigment) and a binder resin such as a polyester resin. The marking particles may be formed by extruding the binder resin and the pigment.

It is also stated in EP2713210 that the marking particles are chargeable imaging particles (or have chargeable locations) which allows the marking particles to develop a static electric charge, enabling them to be transported between different components of a printing system by applying a suitable electric field.

In EP2713210 it is explained that, upon heating the liquid toner towards the fusing temperature, the liquid developer should readily collapse into a carrier liquid phase and a marking particles phase so that the marking particles and the carrier liquid are separated from each other. When the liquid developer dispersion collapses, the individual marking particles can then coalesce to form a continuous resin film that can adhere to the surface of the recording medium.

In EP2713210 it is also said to be important for the marking particles to remain homogeneously dispersed throughout the carrier liquid during storage and in the printing process before the stage at which the image is fused onto a recording medium. In order to keep the marking particles homogeneously dispersed in the carrier liquid, the toner of EP2713210 comprises a dispersing agent. A problem with printing systems that use a dispersing agent is that the fusing process may be hindered by the dispersing agent. This is because the dispersing agent may prevent the coalescence of the marking particles, thus preventing the formation of a continuous resin film. This may result in a low quality printed image and/or poor adhesion of the marker particles to the substrate.

Therefore, a dispersing agent is needed to ensure the stability of the imaging particles in the liquid toner dispersion, typically both during and after the preparation of the toner. However, the presence of such a dispersing agent may hinder the fusing process.

Application WO2014/209108 addresses this problem with the dispersing agent. WO2014/209108 discloses a digital printing apparatus with a dispersing capacity modification unit downstream of the imaging member of the printing apparatus, wherein this dispersing capacity modification unit is configured to reduce the dispersing capacity (i.e. the capacity of the dispersing agent to separate the marking particles and prevent settling or clumping of the dispersing agent) in the liquid toner transferred from the imaging member to a substrate.

The present invention is directed towards an improved digital printing process and apparatus.

Summary of the invention

According to a first aspect of the invention there is provided a liquid toner digital printing process, wherein the liquid toner used in said printing process comprises a carrier liquid, curable marking particles, and a dispersing agent, and wherein said process comprises: (i) forming a latent image as a pattern of electric charge on a surface of an imaging member, (ii) transferring the liquid toner onto a development member, (iii) developing the latent image by transferring liquid toner from the development member onto the imaging member in accordance with the pattern, (iv) transferring the liquid toner from the imaging member, (v) modifying the dispersing agent in the liquid toner transferred in step (iv) to reduce the dispersion capacity of the dispersing agent, (vi) heating the liquid toner modified in step (v) to at least a temperature at which the marking particles form a polymer melt, and (vii) irradiating the liquid toner heated in step (vi) with actinic radiation or particle beams to cure the heated marking particles, wherein the temperature of the heated marking particles is at least the glass transition temperature.

In the present invention, the term “actinic radiation” is understood to cover any kind of radiation that can induce a cross-linking reaction in the marking particles after coalescence. In the invention, suitable actinic radiation includes IR-radiation, visible light, UV-light and γ-radiation. Suitable particle beams include electron beams.

Preferably, in step (v), the marking particles are below their glass transition temperature during this modification step because film formation or coalescence should happen before the crosslinking of the complete printed image occurs. For example, in embodiments in which the liquid toner heated in step (vi) is irradiated with actinic radiation in step (vii), the marking particles are preferably below their glass transition temperature during step (v).

At the glass transition temperature Tg, the solid marking particles undergo a glass transition and change from an amorphous rigid structure to a flexible structure in which the internal molecules of the marking particles can move relative to each other. If the solid is continued to be heated above its glass transition temperature Tg, the marking particles will eventually form a disordered polymer melt. As well as having marking particles with an entirely amorphous structure, the marking particles may have a semi-crystalline structure comprising amorphous portions. If the marking particles comprise such a semi-crystalline material, the glass transition temperature Tg will correspond to the point at which these amorphous portions undergo the glass transition.

In step (vii) of the process, the heated marking particles may be at a temperature of just above Tg. Preferably, the heated marking particles are at a temperature of at least Tg + 15°C, more preferably at a temperature of at least Tg + 30°C.

As the marking particles may cool down slightly between steps (vi) and (vii) of the process, the temperature of the marking particle in steps (vi) and (vii) may be different.

In digital printing processes operating with liquid toner, the marking particles are supplied as solid particles suspended in a carrier liquid.

The marking particles used in the present invention may be cured by irradiating the liquid toner with electromagnetic radiation in step (vii) of the process. In such embodiments, the marking particles are preferably below their glass transition temperature during step (v) of the process. If the marking particles are irradiated with electromagnetic radiation in step (vii), preferably, the marking particles are UV-curable marking particles, and the electromagnetic radiation is ultraviolet light (i.e. in step (vii), the liquid toner is irradiated with UV-light).

If the particles are UV-curable, the ultraviolet light source of the melting and curing unit may be a combination of a mercury vapour lamp and a LED-type light source.

In some embodiments of this process, the marking particles of the liquid toner may comprise coloured particles (also called ink particles, dyes or pigment) and a binder resin. In such embodiments, this binder resin may be a polymer, preferably a transparent polymer. The coloured particles and other optional components of the marking particles such as wax, plasticizer or other additives may be embedded in the binder resin. The marking particles may be extrudates of the binder resin and the coloured particles. Also, in some instances, the marking particle may be noncoloured particles, for example, if the printing of gloss effects or certain security features is desired.

In order to be suitable for use in the present invention, the marking particle may comprise an actinic radiation curable composition. Preferably, the actinic radiation curable composition forms at least part of the binder resin.

Alternatively, the marking particle may comprise a composition that can be cured using a particle beam, for example, an electron beam. In such embodiments, the curable composition may form at least part of the binder resin.

In embodiments of the invention, the marking particle may comprise a polymeric compound having at least two active groups, wherein these active groups are activated by the actinic radiation or particle beam. The active groups may be located at the end of the polymeric chain or within the polymeric chain.

In embodiments where the actinic radiation applied during step (vii) is ultraviolet light, the marking particle may comprise a UV-curable epoxy resin, and/or a polymeric compound with at least two alkene groups (i.e. at least two ethylenically unsaturated groups). For example, in one embodiment, the marking particle may comprise a polymer comprising a polyester resin and at least two alkene groups.

In an embodiment of the invention, the UV-curable marking particle may comprise a (meth)acrylate containing polyester. Examples of suitable polymers include unsaturated polyesters based on terephthalic and/or isophthalic acid as the carboxylic acid-containing components, and on neopentylglycol and/or trimethylolpropane as the polyol component and whereon afterwards an epoxy-acrylate such as glycidyl (meth)acrylate may be attached. Such polymers are available from Allnex under the trade name Uvecoat®. In another embodiment, the curable marking particle may be composed of a mixture of an unsaturated polyester resin in which maleic acid or fumaric acid is incorporated and a polyurethane containing a vinylether available from DSM Resins under the tradename Uracross®.

In addition to the radiation curable composition, the marking particle may also comprise other components. For example, in some embodiments, the binder resin may comprise a radiation curable composition mixed with condensation polymers such as polyesters, polyamides, co-(polyester/polyamides), epoxy resins, addition polymers or mixtures thereof.

Another UV-curable resin is a polyester-urethaneacrylate polymer which may be obtained by the reaction of an hydroxyl-containing polyester, a polyisocyanate and a hydroxyacrylate.

In some embodiments, the marking particles in the liquid toner may comprise an initiator which is able to initiate cross-linking and, thus, curing of the marking particles. The initiator can be selected such that the toner particles can be cured by electromagnetic radiation. Preferably, the initiator is selected so that the toner particles can be cured using UV-light. If the initiator is activated by electromagnetic radiation, it can be called a “photoinitiator”. Suitable photo-initiators include benzophenone and substituted benzophenones, 1-hydroxycyclohexyl phenyl ketone, thioxanthones such as isopropylthioxanthone, 2-hydroxy-2-methyl-l-phenylpropan-l-one, 2-benzyl-2-dimethylamino- (4-morpholinophenyl) butan-l-one, benzil dimethylketal, bis (2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,4,6-trimethoxybenzoyldiphenylphosphine oxide, 2-methyl-l-[4-(methylthio)phenyl]-2-morpholinopropan-l-one, 2,2-dimethoxy-l,2-diphenylethan-l-one or 5,7-diiodo-3-butoxy-6-fluorone, Irgacure™ 184, Irgacure™ 500, Irgacure™ 369, Irgacure™ 1700, Irgacure™ 651, Irgacure™ 819, Irgacure™ 1000, Irgacure™ 1300, Irgacure™ 1870, Irgacure™ 2959, Darocur™ 1173, Darocur™ 2959, Darocur™ 4265 and Darocur™ ITX and Lucerin™ TPO available from BASF, Esacure™ KT046, Esacure™ KIP150, Esacure™ KT37 andEsacure™ EDB available from Lamberti, H-Nu™ 470 and Η-Nu™ 470X available from Spectra Group.

In embodiments in which step (vii) of the process comprises irradiating the liquid toner heated in step (vi) with electron beams to cure the heated marking particles, the marking particles preferably do not comprise an initiator.

The carrier liquid may comprise any suitable liquids as is known in the art, and may include silicone fluids, mineral oils, low viscosity or high viscosity liquid paraffin, isoparaffinic hydrocarbons, fatty acid glycerides, fatty acid esters, vegetable oils, chemically modified vegetable oils, or any combinations thereof. The carrier liquid may further contain variable amounts of charge control agent (CCA), wax, plasticizers, and other additives, although they also can be incorporated into the toner particle itself.

The carrier liquid may be volatile or substantially non-volatile. For volatile carrier liquids, embodiments of the invention will allow obtaining an improved phase separation by the evaporation of the carrier liquid. The use of volatile carrier liquids has, however, also some drawbacks such as occurrence of corona wire contamination and scraper failure inducing image defects. In the present invention the use of non-volatile carrier liquids is preferred. This is due to the improved ease of recyclability making the use of non-volatile carrier liquids more eco-friendly, for example.

In some embodiments, the process of the present invention may utilise toner with solids concentrations between 5% and 60 wt%, preferably between 15% and 45 wt%. In embodiments of the invention, the high-shear viscosity of the liquid toner, as measured at a shear rate of 3000 s'1 at 25°C with a cone plate geometry of C60/10 and a gap of 52 pm, is may be in the range of 5 to 500 mPa-s.

Liquid toner used in digital printing processes is a dispersion of marking particles in a carrier liquid. A dispersing agent or dispersant is added to a liquid toner to avoid clustering of the toner particles. As the name suggests, a dispersing agent aids the dispersing of the marking particles in the carrier liquid, i.e. dispersants deflocculate the imaging particles and thus can reduce the viscosity of the liquid toner dispersion by reducing the particle-particle interaction. A dispersing agent is added to produce stable formulations and ensure stability during storage and during developing/imaging.

In the context of the invention, the term “dispersing capacity” refers to the capacity of the dispersing agent to separate the marking particles, i.e. the ability of the dispersing agent to prevent settling or clumping of the marking particles in the carrier liquid.

After modifying the dispersing agent in step (v) of the process, the liquid toner destabilises, or tends to destabilise due to the reduction of the dispersing capacity of the dispersing agent. Once destabilised, the liquid toner forms or tends to form two different layers, namely a layer of carrier liquid and a layer of the marking particles. Upon heating the marking particles to a temperature at which they form a liquid or melt polymer, the destabilised liquid toner can be considered to form two different phases: the carrier liquid phase and the marking particle phase, the so called coalescence.

In the process of this invention, the transferred portion of the liquid toner is deposited by the imaging member, either directly or via one or more intermediate members such as intermediate rollers and/or belts, on a printing substrate.

In some embodiments, the process may involve: (iv) transferring the liquid toner from the imaging member, (v) modifying the dispersing agent in the portion of the liquid toner transferred in step (iv), and (vi) heating the liquid toner modified in step (v).

Such embodiments may involve the direct transfer of the liquid toner from the imaging member to the printing substrate.

In embodiments in which the liquid toner is transferred directly from the imaging member to a printing substrate in step (iv), the dispersion capacity of the dispersion agent is modified after the image has been transferred to the substrate. In addition, the transferred portion of the liquid toner is heated once the image has been transferred to the substrate.

In alternative embodiments, the transferred quantity of liquid toner may be transferred to an intermediate member such as intermediate roller or belt in step (iv) of the process. In these embodiments, the dispersing agent may be modified before the image is transferred to the substrate. In such embodiments, the transferred portion of the liquid toner may also be heated before the image is transferred to the substrate.

However, in other embodiments, the liquid toner may transferred to an intermediate member in step (iv), but the dispersing agent may only be modified after the toner has transferred to the substrate.

The dispersing agent is modified in step (v) of the above process so that dispersion capacity of the dispersing agent is reduced. Preferably, the dispersing capacity of the dispersing agent is greatly reduced or removed.

The dispersion capacity of the dispersing agent may be reduced by chemically modifying the dispersing agent. For example, the modification of the dispersing agent in step (v) may involve a conformational change in the structure of the dispersing agent, or a decomposition of the dispersing agent.

In some embodiments, step (v) comprises modifying the dispersing agent by irradiating the liquid toner transferred in step (iv) with light. For example, the transferred liquid toner may be irradiated with visible, ultraviolet (UV), infrared and/or microwave radiation.

Therefore, the dispersing agent may be modified through exposure to a stimulus, where suitable stimuli may include visible, ultraviolet (UV), infrared or microwave radiation, a change in pH, contact with a compound, or any combination of these.

In step (v), the dispersion capability of the dispersion agent is preferably modified using UV-light. In such embodiments, preferably a non-heating UV source such as an LED-type light source is used to irradiate the liquid toner in step (v) of the process.

The temperature used in step (v) is preferably lower than the glass transition temperature of the marking particles, for example, in embodiments where the marking particles are curable by electromagnetic radiation such as UV light. In such embodiments, the application of the stimulus in step (v) does not cause any noticeable curing of the marking particles. It is thought that this may be because, at temperatures below the glass transition temperature, the molecules forming the marking particles remain in fixed positions. Therefore, even if the stimulus was to have an effect on an active group of the marking particle, it is highly likely that this active group will not react further due to the low degree of mobility of the active groups in the core of the particle and so there would be no noticeable curing or crosslinking of the marking particles in step (v).

In embodiments in which the dispersing agent is modified through contact with a compound, the substrate on which the image is printed may contain a compound that alters the dispersing properties of the dispersing agent. For example, this compound may be provided in or on the substrate. In such embodiments, the image must be transferred to the printing substrate before step (v) of the process.

In such embodiments, the compound may be such that the dispersing agent is chemically modified, for example, by catalytic reactions by metal salts, photoacids, acid base interactions, catalytic ring opening or retro pericyclic reactions. In some embodiments, the dispersing agent may be modified through a combination of a compound in/on the substrate and the application of a further stimulus, e.g. UV light.

In some embodiments, the dispersing agent may comprise an anchoring part, a stabilising part and a stimulus responsive part. The anchoring part is configured to interact with the marking particle and is thus chemically compatible with the marking particle. The stabilising part stabilises the marking particle in the carrier liquid. In such embodiments, after exposure to a stimulus in step (v) of the process, the stimulus responsive part changes and the liquid toner collapses or tends to collapse into separate carrier liquid and a marking particle layers (for example, the liquid toner may collapse into a carrier liquid phase and a marking particle phase).

In embodiments of the process, the dispersing agent (or a part of it) may form part of the carrier liquid layer/phase or the marking particle layer/phase. In embodiments in which the dispersing agent forms part of the carrier liquid layer/phase, the dispersing agent is preferably chosen so that it only has a minor or no influence on the conductivity of the carrier liquid layer/phase (especially in cases where the carrier liquid is collected and reused after the collapse).

In some embodiments, the stimulus responsive part is a conformational changeable stimulus responsive part which undergoes a conformational change upon exposure to a stimulus. Due to the conformational change of the stimulus responsive part, the stimulus responsive dispersing agent undergoes a conformational change reducing the dispersing capacity of the liquid toner. Preferably, the conformational change of the stimulus responsive part is irreversible during a period that is sufficiently long for performing a digital printing process.

In an embodiment, the stimulus responsive part of the dispersing agent may be decomposable into two or more parts. For example, this could occur through breaking a covalent bond or a salt bridge. Alternatively, if the stimulus responsive part is formed from two individual units with opposite charges, i.e. a positively charged unit and a negatively charged unit, the stimulus may cause the stimulus responsive part to break apart by changing one or more of these charges.

The decomposition of the stimulus responsive part is preferably irreversible for at least a period of time that is sufficiently long to perform the digital printing process.

In embodiments in which the stimulus applied in step (v) of the process is a change in pH, this can decompose a salt bridge, for example.

In some embodiments, the anchoring part and/or the stabilising part of the dispersing agent may comprise the stimulus responsive part. For example, in some embodiments, the stabilising part or the anchoring part can also be the stimulus responsive part. Alternatively, the stimulus responsive part may connect the stabilising part to the anchoring part.

In embodiments of the dispersing agent, the dispersing agent may comprise 1 to 10 or more stimulus responsive parts. The number of stimulus responsive parts depends on the size and molecular weight of the dispersing agent. Furthermore, the number of the stimulus responsive parts in the stimulus responsive dispersing agent may depend on the response efficiency and kinetics of the part towards the stimulus in the printing process.

As mentioned above, in embodiments of the dispersing agent comprising an anchoring part, this anchoring part interacts with the marking particle. In some embodiments, the anchoring part may interact with the binder resin, the plasticiser and/or the pigment of the marking particle.

The anchoring part may be selected from the group consisting of: aromate, polyaromate, heteroaromate, polyamide, such as carboxylated polyethylenimine, polyester, polyurethane, polyketon, poly(acrylo)nitrile, polyacrylate, vinylether polymer arylvinyl polymer, and a copolymer of vinylether and arylvinylether, or a derivative thereof, or any combination thereof. Preferably, the anchoring part is a caboxylated polyethylenimine (PEI). PEI interacts well with a marking particle that comprises polyester.

As also explained above, the stabilising part of the dispersing agent stabilises the marking particle in the carrier liquid. The stabilising part may be selected from the group consisting of: polysiloxane, polyhydroxystearic acid, polyricinoleic acid, polyacrylate, polyacrylate with long aliphatic chains such as poly-stearic acrylate, polystyrene, polyarylether and polyethylene, or a derivative thereof, or any combination thereof. Preferably, the stabilising part is polyhydroxystearic acid.

In other embodiments, the dispersing agent may be selected from the group consisting of: • an ortho-nitrobenzyl derivative comprising the anchoring part and the stabilising part, where, after exposure to a stimulus, it decomposes to a 2-nitrosobenzaldehyde derivative, the anchoring part and the stabilising part, and where the nitrobenzyl derivative comprises or is part of the stabilising part or the anchoring part; • a derivative of bis(2-nitrophenyl)methylformate, comprising the anchoring part and the stabilising part, that decomposes, after exposure to a stimulus, into (2-nitrophenyl)(2-nitrosophenyl)methanone derivative and the stabilising part, wherein the (2-nitrophenyl)(2-nitrosophenyl)methanone derivative comprises or forms part of the anchoring part; • a derivative of (E)-di(propan-2-yl)diazene comprising the anchoring part and the stabilising part, wherein, after exposure to a stimulus, this derivative is decomposed into nitrogen, the anchoring part and the stabilising part; • a benzoine derivative with the structural formula (I), wherein Rl, R2, R3 and/or R4 form part of the anchoring part, and X comprises the stabilising part, wherein, after exposure to a stimulus, the derivative is decomposed into derivatives of a compound with the structural formulas (II) and (III):

• a benzoine derivative comprising the structural formula (IV), wherein Rl, R2, R3 and/or R4 form part of, or comprise the anchoring part, and X comprises the stabilising part, wherein, after exposure to a stimulus, the derivative is decomposed to derivatives having the structural formulas (V) and (VI);

• a derivative of hydroxyacetophenone (HAP) comprising the anchoring part and the stabilising part, that decomposes, after exposure, in a phenylacetone derivative and the stabilising part, wherein the phenyl acetone derivative comprises or forms part of the anchoring part; • a derivative of alkoxy acetophenone comprising the structural formula (VII), wherein X forms part of, or comprises the stabilising part, and Rl, R2 and/or R3 form part of the anchoring part, wherein the derivative, after exposure to a stimulus, decomposes to derivatives with the structural formula (VIII) and (IX);

• an alkylaminoacetophenone derivative (AAAP) comprising the anchoring part and the stabilising part that decomposes, after exposure to a stimulus, in a phenylacetone derivative and an amino derivative, and wherein the phenylacetone derivative comprises or forms part of the anchoring part and the amino derivative comprises or forms part of the stabilising part; • a derivative comprising the structural formula (XI), wherein X forms part of, or comprises the anchoring part, and Rl, R2, R3 and/or R4 form part of, or comprise the stabilising part, wherein the derivative, after exposure to a stimulus, decomposes in derivatives with the structural formulas (XII) and (XIII), or in derivatives with the structural formulas (XIV) and (XV):

• a benzyl ketal derivative comprising the structural formula (XVI) comprising an anchoring and a stabilising part, wherein Rl, R2 and/or R3 form part of, or comprise the stabilising part, and X comprises or form part of the anchoring part, wherein the derivative decomposes, after exposure to a stimulus, in derivatives with the structural formula (XVII) en (XVIII);

• a TPO derivative (i.e. a derivative of (diphenylphosphoryl)(2,4,6-trimethylphenyl)methanone) comprising the anchoring part and the stabilising part and/or wherein the TPO group forms part or comprises the anchoring part; • a TPO-L derivative (i.e. a derivative of phenyl-(2,4,6-trimethyl-benzoyl)-phosphinic acid ethyl ester) comprising the anchoring part and the stabilising part and/or of which the TPO-L group forms part of the anchoring part; • a BAPO derivative ((i.e. a derivative of [phenyl-(2,4,6-trimethyl-benzoyl)-phosphinoyl]-(2,4,6-trimethyl-phenyl)-methanon) comprising the anchoring part and the stabilising part, and/or wherein the BAPO group forms part of the anchoring part; or a combination thereof.

In other embodiments, the dispersing agent may comprise a photoisomerisable group that is selected from the group consisting of: • a derivative of trans-stilbene (i.e. a derivative of l,T-(E)-ethene-l,2-diyldibenzene) comprising the structural formula (XIX) which after stimulation changes in a cis-stilbene derivative (l,l'-(Z)-ethene-l,2-diyldibenzene) comprising the structural formula (XX) where R forms part of, or comprises the anchoring part and X forms part of or comprises the stabilising part;

• a derivative of trans-azobenzene (i.e. (E)-diphenyldiazene) comprising the structural formula (XXI) that after stimulation changes to a cis-azobenzene derivative (i.e. (Z)-diphenyldiazene) comprising the structural formula (XXII) where R forms part of or comprises the anchoring part, and X forms part or comprises the stabilising part;

• a derivative of a spiropyrane comprising the structural formula (XXIV), which changes in the corresponding meroderivative comprising the structural formula (XXV) where Rl, R2, R3 and/or R4 form part of or comprises the anchoring part or the stabilising part and X comprises or forms part of the stabilising part or the anchoring part respectively;

• a derivative of a spirooxazine comprising the structural formula (XXVI), which decomposes to a corresponding meroderivative comprising the structural formula (XXVII), where Rl, R2, R3 and/or R4 form part of or comprises the anchoring part or the stabilising part and X comprises or forms part of the stabilising part or the anchoring part respectively; or a combination thereof.

In some embodiments, the stimulus responsive part of the dispersing agent may be a derivative of a photodecomposer. A photodecomposer is a compound which decomposes after exposure to UV light, visible light or infrared light through the breaking of a covalent bond.

In such embodiments, the photodecomposer may be selected from the group consisting of: • ortho-nitrobenzyl moiety; • bis(2-nitrophenyl)methylformate moiety; • (E)-di(propane-2-yl)diazene moiety; • 2-fenyl-2-hydroxy-1 -phenylethanone moiety; • 2-oxo-1,2-diphenylethyl formate moiety; • hydroxyacetophenone derivative; • alkylaminoacetophenone derivative; • benzyl ketal derivative comprising the compound with structural formula (XVI);

• a TPO derivative (i.e. a derivative of (diphenylphosphoryl)(2,4,6-trimethylphenyl)methanone); • a TPO-L derivative (i.e. a derivative of phenyl-(2,4,6-trimethyl-benzoyl)-phosphinic acid ethyl ester); • a BAPO derivative ((i.e. a derivative of [phenyl-(2,4,6-trimethyl-benzoyl)-phosphinoyl]-(2,4,6-trimethyl-phenyl)-methanone); or a combination thereof.

Preferably, the stimulus responsive part is a conformational changeable part which is a photoisomeriser, or a derivative thereof. A “photoisomeriser” is a compound that undergoes a conformational change after exposure to UV-light, visible light or infrared radiation. An example of a photoisomeriser is a photochrome. The photoisomerisor may be selected from the group consisting of: • a derivative of trans-stilbene (i.e. l,l'-(E)-ethene-l,2-diyldibenzene); • a derivative of trans-azobenzene {i.e. (E)-diphenyldiazene); • a derivative of a spiropyrane; • a derivative of a spirooxazin; or a combination thereof.

In the context of the application “derivative” is to be understood as the basis skeleton of the compound as is shown via the compound name or the structural formula. The derivative may comprise a compound with other moieties, comprising but not limited to the anchoring part or the stabilising part. A “derivative” may also refer to a radical form of the basis skeleton of the compound as is shown via the compound name or the structural formula.

In embodiments of the process, the printing process may further comprise removing carrier liquid from liquid toner after step (v) of the process. After the dispersion capacity of the dispersion agent has been modified, the liquid toner will more readily collapse into separate marking particle and carrier liquid layers. For example, the liquid toner may collapse more readily into a marking particle phase and a carrier liquid phase upon heating. Once a liquid toner has collapsed, it may be easier to remove carrier liquid from the liquid toner.

In a preferred embodiment, the carrier liquid is removed between steps (vi) and (vii) of the process, i.e. excess carrier liquid is removed from the liquid toner after heating the marking particles in step (vi) but before curing the toner particles in step (vii).

Most preferably, the process may comprise: (vi) heating the liquid toner modified in step (v) to at least a temperature at which the marking particles form a polymer melt, and then removing carrier liquid toner from the transferred portion of the liquid toner in a carrier liquid removal step; and (vii) irradiating the liquid toner heated in step (vi) with actinic radiation or particle beams to cure the heated marking particles, wherein the temperature of the heated marking particles is at least the glass transition temperature.

As described above, the present invention uses curable toners in the process. In such liquid toners, it is the marking particles that must be curable. Nevertheless it can be beneficial that also the carrier liquid and/or the dispersing agent (or its decomposition products) are curable. For example, if the dispersing agent (or its decomposition products) are cured together with the marking particles, they will no longer be able to migrate towards packaged goods, e.g. food products.

According to a second aspect of the invention there is provided a digital printing apparatus for use with a liquid toner, wherein the liquid toner used in said printing apparatus comprises a carrier liquid, curable marking particles, and a dispersing agent, and wherein said apparatus comprises: (a) an imaging member adapted to sustain a pattern of electric charge forming a latent image on its surface, (b) a development member arranged to receive liquid toner, and to develop said latent image by transferring said liquid toner onto said imaging member in accordance with said pattern, (c) a dispersing capacity modification unit, wherein said dispersing capacity modification unit is located downstream of the imaging member, and wherein the dispersing capacity modification unit is configured to modify the dispersing agent in the liquid toner transferred from the imaging member to reduce the dispersion capacity of the dispersing agent, and (d) a melting unit located downstream of the imaging member, wherein the melting unit comprises a heat source, and wherein the melting unit is configured to heat liquid toner to at least a temperature at which the marking particles form a polymer melt, and (e) a curing unit located downstream of the melting unit, wherein the curing unit comprises a source of actinic radiation or particle beams.

According to the second aspect of the invention, there is a digital printing apparatus that can be used to perform the digital printing process described above. The advantages, embodiments and preferred forms of the digital printing process described above correspond mutatis mutandis to this second aspect of the invention.

In some embodiments, the marking particles are UV-curable marking particles, and the curing unit comprises an ultraviolet light source. In these embodiments, the heated marking particles are irradiated with ultraviolet light by the curing unit to cure the marking particles.

If the particles are UV-curable, the ultraviolet light source of the curing unit may be a combination of a mercury vapour lamp and a LED-type light source.

In the digital printing apparatus of the second aspect of the invention, the liquid toner is preferably below the glass transition temperature of the marking particles whilst the dispersion capacity of the dispersing agent is being modified. In addition, the heated marking particles are at a temperature of at least the glass transition temperature when in the curing unit.

The melting unit may configured to emit radiation having a wavelength between 1 pm and 5 pm onto the substrate. The conditioning also comprises at least one infrared radiator which is configured to operate at a surface temperature of the heater between 500°C and 2500°C.

In some embodiments, the dispersing capacity modification unit may be configured to reduce the dispersing capacity of the dispersing agent by subjecting the dispersing agent to a chemical modification of the dispersing agent. This chemical modification may be a conformational change in the dispersing agent or a decomposition of the dispersing agent, for example. In such embodiments, the dispersing capacity modification unit may be configured to chemically modify the dispersing agent by adding a compound capable of altering the dispersing properties of the dispersing agent to the transferred portion of the liquid toner.

In some embodiments, the dispersing capacity modification unit may be configured to remove the dispersing capacity of the dispersing agent.

In embodiments of the apparatus, the dispersing capacity modification unit may comprise a source of UV, infrared, or microwave radiation. Alternatively (or additionally), the dispersing capacity modification unit may comprise a device for generating ultrasonic waves, or a device capable of changing the pH of the liquid toner. In such embodiments, the dispersing capacity modification unit is configured to subject the transferred part of liquid toner to one or more of the following stimuli: UV light, ultrasonic waves, infrared radiation, microwave radiation, or a change in pH value.

In a preferred embodiment, the dispersing capacity modification unit comprises an ultraviolet light source, and the dispersing capacity modification unit is configured to use this ultraviolet light source to modify the dispersing agent in the transferred portion of the liquid toner to reduce the dispersion capacity of the dispersing agent.

In such embodiments, the UV-light source is preferably a non-heating UV source such as an LED-type light source.

In embodiments of the apparatus, the melting unit, the curing unit and the dispersing agent modification unit may be separate units. However, these units may also be grouped into a single component causing the sequential dispersing capacity modification of the dispersing agent, heating of the liquid toner, and curing of the imaging particles.

Also, in some embodiments of the apparatus, the melting unit and the curing unit could be grouped together into a single component. However, it is preferred to provide the heat source and the actinic radiation or particle beam source in separate components, i.e. as separate heating and curing units.

In one embodiment, the apparatus may comprise a substrate support member for supporting a substrate downstream of the imaging member. In such embodiments, the dispersing capacity modification unit, the melting unit and/or the curing unit may be arranged for operating on liquid toner present on a substrate on the substrate support member. Therefore, in such embodiments, the dispersion capacity modification is done after the liquid toner is transferred to the substrate.

In another embodiment, the apparatus may comprise an intermediate member for transferring the transferred portion of the liquid toner via the imaging member onto a substrate. In such embodiments, the liquid toner is transferred from the imaging member to an intermediate member such as an intermediate roller or belt.

In embodiments of the apparatus comprising an intermediate member, the dispersing capacity modification unit may be arranged for operating on liquid toner present on the intermediate member. In other words, according to this embodiment the dispersion capacity modification may be done on an intermediate member, downstream of the imaging member, before transferring the liquid toner onto the substrate.

However, in other embodiments of the apparatus comprising an intermediate member, the reduction of the dispersing capacity may be performed on the substrate. In these embodiments, the dispersing capacity modification unit is arranged for operating on liquid toner present on the substrate.

In embodiments without an intermediate roller, the liquid toner will be transferred from the imaging member directly to the printing substrate.

In some embodiments, the apparatus may further comprise a carrier liquid removal means downstream of the dispersing capacity modification unit.

In one embodiment, the carrier liquid removal means may be provided downstream of the curing unit. This has the advantage that the occurrence of image defects during the carrier liquid removal step can be reduced.

In a preferred embodiment of the apparatus, the carrier liquid removal means is provided downstream of the melting unit and upstream of the curing unit. In such embodiments, it may be necessary to provide a heating unit downstream of the carrier liquid removal means and upstream of the curing unit to heat the marking particles to at least the glass transition temperature once the carrier liquid has been removed. In an alternative embodiment, the curing unit may be configured to heat the marking particles to at least the glass transition temperature once the excess carrier liquid has been removed (if required).

The carrier liquid removal means of the digital printing apparatus may comprise a mechanical means such as a roller or suction means for removing the carrier liquid. Alternatively, the carrier liquid removal means may comprises a drying means to assist with the evaporation of the carrier liquid.

Brief description of figures

These and other technical effects and advantages of embodiments of the invention will be described in more detail in connection with the accompanying figures, in which:

Figure 1 presents a schematic diagram of an apparatus according to a first embodiment of the present invention;

Figure 2 presents a schematic diagram of an apparatus according to a second embodiment of the present invention;

Figure 3 presents a schematic diagram of an apparatus according to a third embodiment of the present invention;

Figure 4 presents a schematic diagram of an apparatus according to a fourth embodiment of the present invention;

Figure 5 presents a schematic diagram of an apparatus according to a fifth embodiment of the present invention;

Figure 6 illustrates schematically the decomposing of the dispersing agent in a dispersing capacity modification unit according to an embodiment of the invention;

Figure 7 illustrates schematically the effects of melting on imaging particles in a portion of liquid toner; and

Figure 8 illustrates schematically the effects of melting and curing on imaging particles in a portion of liquid toner.

Description of exemplary embodiments

Figure 1 schematically illustrates a first embodiment of a printing apparatus comprising a development member 110, an imaging member 120, an optional intermediate member 130, a transfer member 140, a dispersing capacity modification unit 150, a melting unit 160, and a curing unit 180. Without loss of generality, the aforementioned members are all illustrated and described as rollers.

In the embodiment of Figure 1, the development member 110, imaging member 120, and intermediate member 130 all transfer part of the liquid toner adhering to their surface to then-successor; if there is any liquid toner remaining on the member’s surface, this may be removed after the transfer stage by appropriate removal means (not illustrated).

In the embodiment of Figure 1, a latent image is developed by transferring a quantity of liquid toner from the development member 110 onto the imaging member 120 in accordance with the pattern. Subsequently, liquid toner will be transferred from the imaging member 120 onto the intermediate member 130. Liquid toner can then be transferred from the intermediate member 130 to the substrate 170. The printed substrate will then pass through the dispersing capacity modification unit 150, then the melting unit 160, before finally passing through the curing unit 180

The embodiment of Figure 2 is substantially the same as the embodiment of Figure 1. However, in Figure 2, the apparatus additionally comprises a separate carrier liquid removal means 190 downstream of the dispersing capacity modification unit 150. In the embodiment of Figure 2, the carrier liquid removal means 190 is located downstream of the melting unit 160, and upstream of the curing unit 180.

In an alternative embodiment not shown in the figures, the carrier liquid removal means 190 may be located downstream of the dispersing capacity modification unit 150 and upstream of the melting unit 160 as long as it can perform its task of removing carrier liquid without disturbing the image.

In a further alternative embodiment also not shown in the figures, carrier liquid removal means 190 may be located downstream of the curing unit 180.

The embodiment of Figure 3 is substantially the same as the embodiment illustrated in Figure 2. However, in the apparatus shown in Figure 3, the apparatus further comprises a heating unit 191.

In the embodiment of Figure 3, the liquid toner is heated to a temperature at which the marking particles are heated and melted in the melting unit 160. When the liquid toner comprising the melted marking particles passes though the carrier liquid removal means 190, the temperature of the liquid toner may drop. After the excess carrier liquid has been removed by the carrier liquid removal means 190, it may then be necessary to re-heat the marking particles to at least the glass transition temperature before they pass into the curing unit 180. In the apparatus shown in Figure 3, the heating unit 191 will heat the marking particles to the required temperature.

In an alternative embodiment, the curing unit 180 of the apparatus may additionally comprise a means for heating the marking particles to the glass transition temperature.

In Figures 1 to 3, the development member 110 may be supplied with liquid toner from a reservoir via a toner supply roller and a metering roller (not illustrated), with a pick-up roller and/or a feeder roller optionally arranged between them (not illustrated). Preferably, a carrier liquid displacement device (not illustrated) is provided, which may take various forms, including the form of a corona generating device or the like, or it may take the form of a roller type mechanism. The carrier liquid displacement device is placed upstream of the interface with the imaging member 120, in a position adjacent to the development member 110, and is configured to create a spatial separation of the toner particles and the carrier liquid within the toner deposit, whereby the carrier liquid is displaced to the surface of the toner layer, to supply or adjust the charge on the individual toner particles and to provide additional particle compaction for enhanced density uniformity of the developed image.

Electrostatographic printing processes involve the creation of a visible image by the attraction of charged imaging particles or marking particles to charged sites present on a substrate. Such charged sites, forming a latent image, can be transiently supported on the imaging member 120 which may consist of photoconductors or pure dielectrics and may be rendered visible in situ or be transferred to another substrate to be developed in that location. The imaging member 120 is preferably a photoconductor roll or belt, upon which the latent image is produced by selectively illuminating the roll with a sufficiently focused light source, such as a laser or LED array. In particular, the image forming stage may consist of providing a uniform electrostatic charge to the surface by means of a charging device, and selectively discharging the uniform electrostatic charge by illumination, to form the electrostatic latent image.

In the development stage, toner particles travel from a development member 110 supplied with a thin, film-like layer of liquid toner, onto the imaging member 120 that carries the latent image. In a subsequent step, the developed image is transferred from the imaging member 120 onto the intermediate member 130. An intermediate roller 130 with a sufficiently elastic surface, e.g. a surface made of hardened rubber or a suitable elastomer, may be used when the surface of the printing substrate is not perfectly smooth. This is the case when the printing substrate is uncoated paper or a textured substrate. The elasticity of the surface of the intermediate roller will allow the deposition of an image with appropriate quality, thanks to the roller’s ability to adapt to the unevenness of the substrate. In the final transfer step, the developed image is transferred from the intermediate roller 130 onto the substrate 170, which is supported by the transfer roller 140 that is kept at a suitable potential.

In the embodiment of Figures 1 to 3, the dispersing capacity modification unit 150, the melting unit 160 and the curing unit 180 are all arranged downstream of a contact surface between the intermediate roller 130 and the transfer roller 140.

In the embodiments of Figures 1 to 3, the melting unit 160 is configured to melt the imaging particles of a transferred part of liquid toner. After they have been melted, the marking particles pass through the curing unit 180. In the embodiments of Figures 1 to 3, the curing unit 180 may comprise a source of UV light (not shown) to cure these imaging particles using UV light. Alternatively, the curing unit 180 may comprise a source of electron beams (not shown) to cure these imaging particles using the electron beams.

In the embodiments shown in Figures 1 to 3, the melting unit 160 comprises a heat source configured to melt the marking particles. As the melting unit 160 is melting the marking particles, it will heat the marking particles above their melting temperature. In some embodiments, the melting unit 160 may use heat and compression between rollers to melt the curable imaging particles. Alternatively, the melting unit 160 may use a non-contact method such as infrared radiation to heat and melt the imaging particles.

In the apparatus of Figures 1 to 3, there is also provided a dispersing capacity modification unit 150 upstream of the melting unit 160 and downstream of the intermediate member 130. The dispersing capacity modification unit 150 is configured to reduce the dispersing capacity of the dispersing agent in the liquid toner dispersion present on the substrate 170. Preferably, the dispersing agent is chemically modified, e.g. at least partially decomposed, or conformationally changed by the dispersing capacity modification unit 150 so that the dispersing agent will not hinder the melting the melting unit 160. The decomposing or conformational change will typically be the result of a reaction changing the dispersing capacity of the dispersing agent.

The dispersing capacity modification unit 150 is configured to subject the liquid toner to a stimulus in order to cause a chemical reaction reducing the dispersing capacity of the dispersing agent. The stimulus may be UV-light, infrared radiation, microwave radiation, a change in pH value, or an interaction with an added compound. If a compound is used, it is noted that this compound could be present beforehand on the printing substrate 170, so that the dispersion capacity modification unit 150 may be omitted.

In the embodiment of Figures 1 to 3, the dispersing agent modification unit 150, the melting unit 160 and the curing unit 180 are illustrated as three separate units. However, according to alternative embodiments, the dispersing capacity modifying unit 150 and the melting unit 160 (and, optionally, the curing unit 180) may be grouped in a single component. In such an embodiment, the reduction of the dispersing capacity, the melting of the marking particles, and the curing of these particles must be performed sequentially. In this way, the reduction of the dispersion capacity can take place at a temperature below Tg, and the curing of the toner can occur at a temperature above T 1g· A fourth embodiment of a digital printing process according to the present invention will now be described in connection with Figure 4. The printing apparatus comprises a development member 210, an imaging member 220, an intermediate member 230, a melting unit 260, a curing unit 280 a pressure member 240, and a dispersing capacity modification unit 250. The members 210 and 220 may be similar to the corresponding elements of the first three embodiments and reference is made to the description of those elements given above.

In Figure 4, downstream of the imaging roller 220, there is provided an intermediate member in the form of a belt 230. The melting unit takes the form of a fuse roller 260 arranged along the intermediate belt 230, upstream of the pressure roller 240 and downstream of the imaging roller 220. The fuse roller 260 is configured to fuse imaging particles of a transferred part of liquid toner using heat. The fuse roller 260 is brought at a temperature T1 suitable for melting the liquid toner.

The roller 260 can also be at the outside of the member 230 or opposite to member 240 to form a nip and assist the transfer to the paper.

The dispersing capacity modifying unit 250 is also provided between the imaging roller 220 and pressure roller 240 in order to change the dispersing capacity of the dispersing agent in the liquid toner that is going to be fused. The dispersing agent modifying unit 250 is located upstream of the melting unit 260.

The embodiment of Figure 4 may also comprise a carrier liquid removal means (not shown).

These means for removing the carrier liquid would be preferably located downstream of the dispersing agent modifying unit 250 and upstream of the melting unit 260. Alternatively, the carrier liquid removal means could be located downstream of the melting unit 260 and upstream of the pressure roller 240. As with the embodiment of Figure 3, the apparatus illustrated by Figure 4 may further comprise an additional heating means (not shown) downstream of the carrier liquid removal means and upstream of the curing unit 280. A fifth embodiment of a digital printing process according to the present invention will now be described in connection with Figure 5. The printing apparatus comprises a development member 310, an imaging member 320, an intermediate member 330, a transfer member 340, a dispersing capacity modification unit 350, a melting unit 360 and a curing unit 380. The members 310, 320, 330, and 340 may be similar to the corresponding elements of the first three embodiments described above and reference is made to the description of those elements given above.

In this fifth embodiment, the dispersing capacity modification unit 350 is arranged upstream of an area of contact between the intermediate roller 330 and the transfer roller 340, and reduces the dispersing capacity of the liquid toner before being transferred to the substrate 370. The melting unit 360 and curing unit 380 are arranged downstream of said area, and operate directly on the substrate 370. The heating and curing units 360, 380 are configured to melt and cure the transferred image particles.

It will be understood that all features described in more detail in connection with the apparatus of Figures 1 to 5, apply also to the process according to the invention, with the same technical effects and advantages. Hence, these features and their operation will not be repeated.

Additionally, while the invention has been described hereinabove in connection with a single imaging stage (single-colour printing), it will be appreciated by a person skilled in the art that the relevant parts of the invention can be replicated several times to allow for multi- colour printing.

In such a case one could transfer all images onto the substrate and then use only one dispersing stability modification unit and one melting unit. According to an exemplary embodiment, when printing different colours, e.g. in the embodiment of Figure 4, there could be provided four imaging rollers around the belt 230. According to another variant, the embodiment of Figure 5 could be implemented with a large intermediate member 330 surrounded by four imaging members.

Throughout the application, the various stages off the printing system have been described as members. In specific cases, these members have been described and/or illustrated as rollers. The skilled person will appreciate that the same principles may be applied with suitably designed belts.

Figure 6 illustrates schematically the effect of a modifying the dispersing capacity of the dispersing agent. Before entering the dispersing capacity modification unit, the imaging particles 401 are stabilised in the liquid developer dispersion by the dispersing agent 402. The dispersing capacity modification unit subjects the dispersing agent to a reaction, e.g. a photochemical reaction, deactivating or reducing its dispersing capacity, resulting in a modified dispersing agent 402’. The reduced dispersing capabilities of the modified dispersing agent 402’ lead to an improved fusing of the imaging particles due to better coalescence and/or a better adherence to the substrate.

Figure 7 illustrates schematically a dispersing agent (DA) modification step followed by a melting step. Before performing the DA modification step the imaging particles 501 are well dispersed in the liquid toner. By subjecting the dispersing agent to a suitable reaction the dispersing capacity of the agent is reduced or eliminated so that imaging particles 501’ can approach each other. Next, heating at a suitable temperature causes the melting of the particles 501” and film formation.

As with Figure 7, Figure 8 illustrates schematically a dispersing agent (DA) modification step followed by a melting step. In Figure 8, the melting step is additionally followed by a UV-curing step. Therefore, in the drawing of Figure 8, the effect of the different stages of the process on the internal structure of the UV-curable toner particles is schematically illustrated.

As in Figure 7, the imaging particles 501 are well dispersed in the liquid toner before the DA modification step. When the dispersing capacity of the agent is reduced or eliminated, the imaging particles 501’ will coalesce. As can be seen from figure 8, the effect of reducing the dispersion capacity whilst the temperature is below the glass transition temperature (Tg) of the imaging particles has no effect on the internal structure of these imaging particles.

In the next step of the process shown in Figure 8, the imaging particles are heated to a temperature T1 which is at least the temperature at which the imaging particles form a polymer melt. This causes the particles 501” to melt, coalescence and form a film. Then, whilst the temperature of the imagining particles is still at least the glass transition temperature, UV light is to cure the imaging particles by initiating a cross-linking reaction.

The examples below provide synthesis examples of dispersing agents that can be used in liquid toner according to the invention.

Example 1: the decomposable part is located between the anchoring part and the stabilising part

Polyhydroxystearic acid chains (PHSA) have optimal stabilising effect in nonpolar media such as mineral oils and vegetable oils.

Reaction Scheme:

1.1 Synthesis of Polyhydroxystearic acid

In a 250 ml flask equipped with a Dean-Stark apparatus and a reflux condenser, there are added 100 g of 12-hydroxy-octadecanoic acid (12-hydroxystearic acid) and 50 ml of mixed xylene. The reaction mixture is heated under nitrogen in an oil bath at 195 - 200 ° C, and refluxed for 36 h. The progress of the reaction can be monitored by the amount of separated water. The degree of condensation was determined by means of IR and titration. In the IR spectroscopy is the carbonyl stretch ratio of the carboxylic acid and the ester a measure of the degree of condensation. By means of titration, the acid value can be determined. In this example, it amounted to 35 mg KOH / g, which is a value of n = 4 yields, or 6 HSA units.

In the following synthetic sequence, the photolabile group is synthesized and also the coupling of the anchoring and the stabilising part.

Reaction Scheme:

1.2 Synthesis of 2 - [4 - (2-methylpropanoyl) phenoxy] ethyl acetate

To a stirred solution of 29.4 g anhydrous aluminum trichloride at -5 to - 0 ° C in 20 ml of dichloromethane, 11.2 g of butaric acid is added dropwise during 30 min. After this, 18.0 g of 2-phenoxyethyl acetate is added dropwise at the same temperature for 1 h. The reaction mixture is stirred for 2 h at this temperature and then poured into a mixture of 60 ml concentrated HC1-solution and 80 ml of water. The organic phase is separated and the aqueous phase is extracted with 60 ml of dichloromethane. The organic phases are combined and washed with water, dried and evaporated in vacuo. 24.7 g (98.7%) of 2 - [4 - (2-methylpropanoyl) phenoxy] ethyl acetate was obtained. 1.3 Synthesis of 2-[4-(2-bromo-2-methylpropanoyl) phenoxy]ethyl acetate 25 g of 2-[4-(2-methylpropanoyl)phenoxy]ethyl acetate from example 1.2 is dissolved in 20 ml of glacial acetic acid. To this, 19.2 g of bromine is added dropwise with stirring at room temperature over 2 h. After 10 h stirring, the reaction mixture was poured into 300 ml of glacial acetic acid and extracted with 3 x 150 ml of ethyl acetate. The combined extracts are dried with magnesium sulfate, filtered and evaporated to a viscous oil.

In the next step, the photo-labile component is coupled with a polyethylenimine (PEI). This can be a linear or a branched PEI (such as the Lupasol ® polyethylenimines from BASF orthe EPOMIN ® products of Nippon Shokubai). In the synthesis described below, is worked with the linear pentaethylenehexamine (PEI-6). 1.4 Synthesis of 2-[4-(2-bromo-2-methylpropanoyl)phenoxy] ethyl acetate adduct to PEI-6 25 g of 2-[4-(2-bromo-2-methylpropanoyl)phenoxy]ethyl acetate from 1.3 is dissolved in 100 ml of ethanol. With stirring, 7.7 g of pentaethylenehexamine and then 15 g of N, N-diisopropylethylamine were added. After 2 h stirring, if necessary, the remaining free amino groups are acetylated with acetic anhydride and then 38 g of a 32% sodium hydroxide solution was added at room temperature. Ethanol is evaporated off and 300 ml of water is added. This mixture is extracted with 3 x 50 ml each of ethyl acetate. The organic phase is dried with sodium sulphate, filtered and evaporated. 1.5 Coupling of the product of 1.4 and the PHSA from Example 1.1. 12.5 g of CDI (carbonyldiimidazole) is mixed in 25 ml of ethyl acetate with 125 g PHSA from Example 1.1. After 30 min of stirring, 25 g of the product from example 1.4, dissolved in 25 ml of ethyl acetate, are added. This mixture is stirred for 6 to 60 ° C. After evaporation in vacuo an oil is obtained, and mixed with 50 ml of water and then extracted with 3 x 50 ml of butyl acetate. After evaporation of the organic phase an oil is obtained which as such can be used as a dispersing agent “example 1”.

Example 2: central decomposable photolabile group comprising the anchoring part and the stabilising part

Reaction Scheme:

2.1 MeO-PPG-PEG-O-benzaldehyde

To a solution of 12.2 g of 3-hydroxybenzaldehyde and 0.2 g of methanesulfonic acid in 25 ml of tetrahydrofuran (THF) at -20 ° C, a cooled mixture (-20 ° C) of 22.1 g of ethylene oxide and 29.1 g of propylene oxide in 167 ml of THF was added for 90 min. The reaction mixture is stirred for 1 h and brought to room temperature. Then, 16.7 g of DBU was added, and to this 15 g of methyl iodide was added dropwise. After stirring for 1 hour, 100 ml of water was added at room temperature, and the mixture is extracted with 3 x 100 ml dichloromethane. The combined organic phase is dried, filtered and evaporated under vacuum. 2.2 2-phenyl-l,3-dithiane adduct to PPG-MeO-PEG-O-benzaldehyde of 2.1 A solution of 10.5 g of 2-phenyl-l, 3-dithiane in 50 ml of THF is cooled to 0 ° C and to this 3.3 g of butyl lithium was added. After 30 min of stirring, 32.3 g of MeO-PEG-PPG-O-benzaldehyde from example 2.1 was dissolved in 50 mL of THF and added. After 1 h stirring at room temperature, the reaction mixture was quenched by adding 200 ml of ammonium chloride solution. THF was largely removed by vacuum distillation and the remaining phase was extracted with 3 x 100 ml of dichloromethane. The combined organic phase is dried, filtered and evaporated under vacuum 2.3 Coupling of the adduct from 2.2 to polyhydroxystearic acid and deprotection of the dithiane protective carbonyl group

The procedure for coupling with the polyhydroxystearic acid is analogous as in example 1.5.

The obtained oil is dissolved in 100 ml of acetonitrile and to this 2 equivalents of [bis (trifluoroacetoxy) iodo] benzene were added. After 20 min of stirring, 50 ml of water was added at room temperature, and after an additional 1 h of stirring, the acetonitrile is evaporated. Then 100 ml of water was added and the remaining phase is extracted with 3 x 100 ml of dichloromethane. The combined organic phases are dried, filtered and evaporated under vacuum. The thus obtained dispersing agent can be used as such as dispersing agent “example 2”.

Example 3: The anchoring part is connected with the stabilising part comprising decomposable groups.

Reaction Scheme:

3.1 Coupling of polyethylenimine with 12-hydroxysteraric acid 23.2 g of pentaethylenehexamine is mixed together with 90.1 g of 12-hydroxy stearic acid under a nitrogen flow for 6 h and heated at 150 0 C. After cooling, a waxy solid is obtained. 3.2 Coupling HSA-PEI polymer with a photoinitiator and a polyhydroxystearic acid 9.4 g PEI-HSA from 3.1 is coupled by means of CDI with 8.4 g of photoinitiator 4,4 (E)-diazene-1 ,2-diylbis (4-cyanopentanoic acid), and then with 48,9 g polyhydroxystearic acid (Mw 1630, example 1.1) using the procedure described in example 1.5, with the difference that toluene was used in place of ethyl acetate yielding dispersing agent “example 3”.

Example 4: The anchoring part is connected with the stabilising part that comprises the decomposable group

Reaction scheme:

4.1 Coupling of polyacrylic acid with a photoinitiator and polyhydroxystearic acid

The molecular weight (Mw) of the polyacrylic acid and the poly-hydroxystearic acid is first determined by means of titration, so that the stoichiometry of the reaction is ensured. 1.8 g of polyacrylic acid (Mw 1800), 5.0 g photoinitiator. 2,2'- (E)-diazene-l, 2-diylbis (2-methylpropanimidamide) and 40.8 g polyhydroxystearic acid (Mw 1630 Example 1.1) are dissolved in 100 ml toluene at room temperature and stirred for 1 h. Subsequently, the toluene is evaporated under vacuum resulting in a dispersing agent “example 4”.

Example 5 : stimulus collapsible group

Pentaethylenehexamine is converted with acetic anhydride to a partially acetylated poly-amine. This product is further functionalized with chloroacetyl chloride.

The stilbene-aldehyde-derivative is synthesized with a polyester of hydroxystearic acid and conventional synthetic protocols like the Michaelis-Arbuzov and the Wittig-Horner-type reactions. The coupling between the partially acetylated poly-amine derivative and the stilbene-aldehyde-derivative is again accomplished via a Michaelis-Arbuzov and a Horner-Wadsworth-Emmons reaction yielding a conformationally changeable dispersing agent “example 5”.

While the invention has been described hereinabove with reference to specific embodiments and examples, this is done to illustrate and not to limit the invention. The skilled person will appreciate that other ways of implementing the inventive concept described herein are within the scope of the invention, as defined by the accompanying claims.

Claims

A process for digital printing with liquid toner, wherein the liquid toner used in the printing process comprises a carrier liquid, curable toner particles, and a dispersing agent, and wherein the process comprises, (i) forming a latent image as a pattern of electrical charge on a surface of an imaging member, (ii) transferring the liquid toner to a developing member, (iii) developing the latent member by transferring liquid toner from the developing member to the imaging member in accordance with a pattern , (iv) transferring liquid toner from the imaging member, (v) changing the dispersant to the liquid toner transferred in step (iv) to reduce the dispersion capacity of the dispersant, (vi) heating the liquid toner which was changed in step (v) to at least a temperature at which the toner particles form a polymer melt, and (vii) irradiating the toner liquid toner with actinic radiation or particle bundles heated in step (vi) for curing the heated toner particles, wherein the temperature of the heated toner particles is at least the glass transition temperature.

The process of claim 1, further comprising further removing carrier fluid from the liquid toner after step (v).

The process of claim 2, wherein the carrier fluid is removed between steps (vi) and (vii) of the process.

The process of claim 3, wherein the process further comprises a heating step after removing the carrier liquid from the liquid toner, wherein the toner particles are heated to at least the glass transition temperature during the heating step.

The process according to any of the preceding claims, wherein the toner particles are UV-curable toner particles and the liquid toner heated in step (vi) is irradiated with UV light.

The process of any one of claims 1-4, wherein the toner particles are curable toner particles by an electron beam, and the liquid toner heated in step (vi) is irradiated with an electron beam.

The process of any one of the preceding claims, wherein the portion of the liquid toner is transferred from the imaging member to a print substrate in step (iii) of the process.

The process of any one of claims 1-6, wherein the portion of the liquid toner is transferred from the imaging portion to an intermediate portion in step (iii) of the process.

The process of any one of the preceding claims, wherein the dispersion capacity of the dispersant is reduced by chemically modifying the dispersant.

The process of claim 9, wherein the chemical change of the dispersant in step (v) involves a conformational change in the structure of the dispersant, or a dissolution of the dispersant.

The process according to any of the preceding claims, wherein the dispersing capacity of the dispersing agent is removed.

The process according to any of the preceding claims, wherein the liquid toner transferred in step (iv) is irradiated with UV light in step (v) for reducing the dispersing capacity of the dispersant.

A digital printing device for use with a liquid toner wherein the liquid toner used in the printing device comprises a carrier liquid, curable toner particles and a dispersing agent, and wherein the device comprises: (a) an imaging part adapted to form a pattern of electrical to retain charge due to a latent image on its surface, (b) a developing member adapted to receive liquid toner, and to develop the latent image for transferring the liquid toner to the imaging member in accordance with the cartridge, (c) a dispersing capacity modification unit, wherein the dispersing capacity modification unit is located downstream of the imaging part and wherein the dispersing capacity modification unit is adapted to change the dispersing agent of the liquid toner transferred from the imaging section to the dispersing capacity of the dispersing agent to leave and, (d) a melting unit located downstream of the imaging member, the melting unit comprising a heating source, and wherein the melting unit is adapted to heat the liquid toner to at least a temperature at which the toner particles form a polymer melt, and (e a curing unit located downstream of the melting unit, the curing unit comprising a source of actinic radiation or particle beams.

The apparatus of claim 13, further comprising a carrier fluid removal means located downstream of the dispersing capacity modification unit.

The apparatus of claim 14, wherein the carrier fluid removal means is located downstream of the melting unit and upstream of the curing unit.

The apparatus of claim 15, wherein the apparatus further comprises a heating unit downstream of the carrier fluid removal means, the heating unit being adapted to heat the toner particles to at least the glass transition temperature after the carrier fluid has been removed.

The apparatus of any one of claims 13-16, wherein the toner particles are UV-curable toner particles, and wherein the curing unit comprises a UV light source.

The apparatus of any one of claims 13-16, wherein the toner particles are electron beam curable toner particles, and wherein the curing unit comprises an electron beam source.

The device of any one of claims 13-18, wherein the dispersing capacity modification unit is adapted to chemically change the dispersing agent.

The apparatus of claim 19, wherein the dispersing capacity modification unit is arranged to cause a conformational change in the structure of the dispersing agent, or wherein the dispersing capacity modification unit is arranged to decompose the dispersing agent.

The apparatus of any one of claims 13-20, wherein the dispersing capacity modification unit is adapted to remove the dispersing capacity of the dispersing agent.

The apparatus of any one of claims 13-21, wherein the dispersing capacity modification unit comprises a UV light source, and wherein the dispersing capacity modification unit is adapted to use the UV light source to dispense the dispersant in the liquid toner transferred from the liquid toner. to modify the imaging portion to decrease the dispersing capacity of the dispersant.