NL2018013B1

NL2018013B1 - Digital printing process and printed recording medium

Info

Publication number: NL2018013B1
Application number: NL2018013A
Authority: NL
Inventors: Jeroom Maria Van Gaens Wouter; Jozef Johan Op De Beeck Werner; Erik Dries Deprez Lode; Gustaaf Maria Mampaey Kurt; Praet Tomas; Jan Godelieve Van De Straete Herman
Original assignee: Xeikon Mfg Nv
Priority date: 2016-12-16
Filing date: 2016-12-16
Publication date: 2018-06-26

Abstract

A digital printing process for printing liquid toner on a recording medium, said liquid toner comprising marking particles, a dispersing agent, and a carrier liquid, said recording medium comprising a base layer capable of absorbing the carrier liquid, said process comprising: Providing the recording medium having a barrier layer on a first surface of the base layer, said barrier layer being configured for blocking a movement of the carrier liquid towards the base layer of the recording medium; Producing a latent image as a pattern of electric charge on an imaging member; Transferring a quantity of liquid toner onto a development member; Developing said latent image by transferring a portion of said quantity of liquid toner onto said imaging member in accordance with said pattern; Transferring a developed portion of liquid toner onto the barrier layer; Adhering the marking particles of said transferred portion of liquid toner on the barrier layer; Removing carrier liquid of said transferred developed portion from said recording medium.

Description

Digital printing process and printed recording medium Field of the invention

The present invention relates to a digital printing process using liquid toner and a printed recording medium.

Background

Liquid toners are known in the art and usually comprise at least carrier liquid and marking particles.

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 particles and a dispersing agent or a combination of dispersing agents.

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. It is stated in this earlier application that the marking particles may be formed by extruding the binder resin and the pigment particles, wherein preferably a polyester resin, which is preferably chemically non-compatible with the carrier liquid, is used as binder resin, meaning that the carrier liquid has no tendency of dissolving rapidly into the binder resin of the marking particles.

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

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 liquid toner comprising chargeable marking particles and a carrier liquid.

In US 2009/0052948, the apparatus comprises 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 recording medium.

An electrostatic printing process using liquid toner can be used to print on a variety of different recording mediums. For example, it is known to use such a digital printing process to print on paper and polymeric films. However, if there is some carrier liquid remaining on the recording medium after printing, this may cause problems in finishing processes, like a cutting process or like a coating process or applying a lamination coating. Also, any remaining carrier liquid on the printed image may have impact on image performance and touch related properties, such as wet and fatty feeling of the printed material.

Moreover, if liquid toner is used to print on a recording medium, which has a liquid absorbing base layer, carrier liquid may migrate from the printed surface of the material to the base layer of the recording medium. The carrier liquid, being absorbed by the base layer of the recording medium, may cause problems, such as a shine-through effect of the recording medium. In that case, the opacity of the recording medium is reduced due to the absorbed carrier liquid. An opacity reduction of the recording medium due to absorption of carrier liquid is related to the thickness of the recording medium and becomes even more critical for a recording medium having a relatively low weight, such as 40 gsm - 70 gsm. Even more, the fact that the recording medium contains a part of this carrier liquid may be a problem both for thinner as well for thicker recording media, as the carrier liquid may become mobile later on during use of the printed recording medium and may migrate in an uncontrolled way to food, packaging or other surfaces.

Summary

It is therefore an object of embodiments of the present invention to overcome problems associated with said known liquid toner digital printing processes using a carrier liquid, thereby providing adequate print quality on the recording medium. Particular embodiments are intended to prevent a reduction of opacity of the recording medium.

According to a first aspect of the invention there is provided a digital printing process for printing liquid toner on a recording medium, said liquid toner comprising marking particles, dispersing agent and a carrier liquid, said process comprising: (i) Providing a recording medium comprising a base layer, typically a base layer capable of absorbing the carrier liquid, and a barrier layer on a first surface of the base layer, said barrier layer being configured for blocking a movement of the carrier liquid towards the base layer of the recording medium; (ii) Producing a latent image as a pattern of electric charge on an imaging member; (iii) Transferring a quantity of liquid toner onto a development member; (iv) Developing said latent image by transferring a portion of said quantity of liquid toner onto said imaging member in accordance with said pattern; (v) Transferring a developed image of liquid toner onto the barrier layer; (vi) Adhering the marking particles of said transferred image of liquid toner on the barrier layer; and (vii) Removing carrier liquid of said transferred developed portion from the recording medium.

The barrier layer blocks the movement of the carrier liquid towards the base layer of the recording medium, when the developed image of the liquid toner is transferred in step (v) onto the barrier layer at the first surface of the recording medium. The carrier liquid is removed from the recording medium in step (vii). Hence, the carrier liquid is not absorbed in the base layer of the recording medium and any reduction of the opacity of the recording medium can be prevented.

The marking particles of the transferred portion of liquid toner are adhered onto the barrier layer in step (vi) prior to the carrier liquid removing step (vii). In this way, the print quality of the transferred liquid toner on the printed recording medium is enhanced as the adhered marking particles, which are adhered to the barrier layer, are substantially not removed during the carrier liquid removing step.

In a particular example, the barrier layer can be provided on a recording medium being relatively thin, such as having a weight of 40 gsm - 70 gsm, thereby making the recording medium suitable for printing the liquid toner while preventing a reduction of the opacity of the recording medium.

The liquid toner comprises a dispersing agent. Said dispersing agent is configured for stabilising a dispersion of the marking particles in the carrier liquid, when the liquid toner is used in the process during steps (iii) - (v) to produce the developed image of liquid toner on the recording medium. The dispersing agent may comprise anchor groups to which stabilising groups are coupled. The anchor groups are suitably chosen for connecting or adsorbing the dispersing agent to the marking particles. The stabilising groups are suitably chosen, such as from the groups of fatty acid compounds and polyolefins, to stabilise a dispersion of marking particles in the carrier liquid.

In an embodiment, the transferring step (v) comprises transferring a portion of carrier liquid from the imaging member onto the barrier layer in non-imaging areas, wherein during step (iv) no image is developed in said non-imaging areas. In practice, during step (iv) in the non-imaging areas on the imaging member carrier liquid will be present and will be at least partly transferred onto the barrier layer. The carrier liquid in the non-imaging areas does not contain marking particles. However, in step (vii) the carrier liquid in the non-imaging areas is also removed from the recording medium.

In embodiments, the removing step (vii) may comprise removing carrier liquid mechanically, the removing step (vii) may comprise heating the carrier liquid and /or heating the recording medium, the removing step (vii) may comprise a combination of both mentioned embodiments and the removing step (vii) may be carried out by any other suitable technique for removing the carrier liquid from the recording medium. The mechanical removal may comprise, for instance, removing the carrier liquid by means of rollers, by means of blowing off the carrier liquid and by means of suction. By removing the carrier liquid mechanically, the carrier liquid can be removed from the recording medium within a certain timeframe and using a predetermined temperature below a critical temperature of a high speed digital printing process

The amounts of carrier liquid that needs to be removed during step (vii) will depend on the image content. It will be the sum of the carrier liquid present in non-imaging areas and liquid liberated during the adherence step.

In a preferred embodiment the removing step (vii) comprises a removal using one or more roller pairs operated at a temperature below the glass transition temperature Tg of a binder resin of the marking particles, wherein each roller pair has a discharge means configured to carry away carrier liquid from the roller pair. After each passage through a roller pair, the amount of carrier liquid on the printed substrate may be approximately reduced to halve the amount. The number of roller pairs can vary, e.g. from 2 to 10 and will depend on the amount of carrier liquid that needs to be removed.

In another embodiment, the mechanical removing step (vii) comprises adding an amount of volatile liquid to the carrier liquid on the surface of the recording medium before or during the mechanical removal of the carrier liquid from the surface of the recording medium. Addition of an amount of volatile liquid to the carrier liquid on the surface of the recording medium provides a mixed layer of a mixture of both the carrier liquid and the volatile liquid. The mixed layer enhances a removal by the remaining carrier liquid in a subsequent step of removing the mixed layer (or mixture) of the carrier liquid and the volatile liquid. Any volatile liquid remaining on the recording medium may additionally be removed from the recording medium by evaporation, such as evaporation enhanced by raising the temperature of the recording medium above room temperature.

Alternatively or additionally, an amount of volatile liquid may be added to the carrier liquid on the surface of the recording medium during the mechanical removal process, such as added between roller pairs of the mechanical removal device and / or by applying the volatile liquid on the surface of the contacting roller of the roller pair of the mechanical removal device.

In a preferred example of the volatile liquid, the volatile liquid is selected based on the marking particles such that the volatile liquid is chemically substantially non-compatible with the binder resin of the marking particles. In this way, the volatile liquid will substantially not be absorbed by the marking particles, likewise as described earlier for the carrier liquid of the liquid toner.

In step (vii) substantially all carrier liquid may be removed from the recording medium. In practice, a small part of the carrier liquid may remain on the surface of the recording medium, such as an amount of carrier liquid being absorbed by the marking particles and /or an amount of carrier liquid being adsorbed to the dispersing agent. However, as this small amount of remaining carrier liquid remains caught near the barrier layer, it will not have any significant negative effects on the print quality.

An advantage of carrier liquid removal is that this carrier liquid may be recycled and reused within the machine, e.g. to dilute a concentrated liquid toner by adding the carrier liquid to the concentrated liquid toner supplied from a toner concentrate tank to obtain a liquid toner having appropriate concentration of marking particles for developing a liquid toner image.

In an embodiment, the barrier layer comprises an adhesion component configured for preferentially attracting the marking particles relative to the carrier liquid during step (vi). The adhesion component provides adequate adhesion of the marking particles to the barrier layer. The adhesion component in the barrier layer may attract the marking particles towards the surface of the barrier layer and / or repel the carrier liquid. As such, the adhesion component prevents the carrier liquid from forming a film on the barrier layer, which may disturb the adhesion of the marking particles to the barrier layer.

In a preferred embodiment, the adhesion component may be the same component as a barrier component of the barrier layer for blocking a transport of the carrier liquid towards the base layer of the recording medium. In a preferred embodiment, the barrier layer consists essentially of the adhesion component, which adhesion component is also the barrier component of the barrier layer for blocking a movement of the carrier liquid towards the base layer of the recording medium.

In this way, the barrier layer may consist essentially of the adhesion component, thereby providing both the blocking functionality towards the carrier liquid as well as the adhesion functionality to the marking particles.

In a preferred embodiment, the polarity of a material component of the barrier layer is higher than the polarity of the carrier liquid.

As defined herein, the polarity P of a certain material may be calculated based on yjSp2 + Sh2, wherein δρ and δρ are Hansen solubility parameters (HSP) as is described in the book “Hansen solubility parameters User’s Handbook” second edition. Hansen describe three major types of interactions (see page 5), namely the nonpolar interactions or dispersive interactions öd, the polar cohesive energy δρ and the hydrogen bonding energy δΐι. The principle is that when a material A is within the Hansen solubility space of a material B, material A is compatible or soluble with material B.

The HSP values are determined by checking the solubility of the materials in solvents with known HSP values over the total HSP range.

In a preferred embodiment, the difference in polarity P of the carrier liquid and the material component of the barrier layer is at least 5, more preferably the difference in polarity P of the carrier liquid and the material component of the barrier layer is at least 8.

As such, a material component may suitably be selected by a person skilled in the art for the barrier layer.

Although the polarity parameter will be a good measure for selecting materials for the barrier layer in respect of the carrier liquid used, a skilled person understands that other parameters, such as film formation behaviour of the material component of the barrier layer and coating process conditions and drying / curing process conditions, may also affect the barrier properties of the barrier layer.

In other embodiments, the adhesion component may be present throughout the barrier layer in combination with a separate barrier component for blocking the movement of the carrier liquid towards the base layer of the recording medium, such as in a blend of the adhesion component with a barrier component for blocking the movement of the carrier liquid towards the base layer of the recording medium.

Alternatively or additionally, the adhesion component may be predominantly present at the outer surface of the barrier layer, such as in an adhesion layer being arranged at the outer surface of the barrier layer.

In an embodiment, the barrier layer comprises a polymer comprising a vinyl alcohol segment or unit.

It has been found that a barrier layer comprising a polymer comprising a vinyl alcohol segment, such as a polyvinylalcohol or a poly(ethylene-vinylalcohol) (EVOH), provides improved adhesion to marking particles, such as marking particles having a binder resin based on a polyester resin, and provides adequate blocking of the carrier liquid, such as a carrier liquid having a relatively low polarity, i.e. P is below 5.

The barrier layer may comprise additional components to reduce the moisture sensitivity of the barrier layer based on a polymer consisting essentially of a vinyl alcohol segment.

In an embodiment, the barrier layer has a layer with a coating weight of at least 0.75 gsm, preferably at least 2 gsm. It has been found, that said coating weight of the barrier layer provides a sufficiently closed barrier layer on top of the recording medium, which blocks the movement of the carrier liquid towards the base layer of the recording medium. In case a coating weight is used lower than 0.75 gsm, the barrier layer may contain pin holes, leading to a local absorption of the carrier liquid into the base layer of the recording medium. Thus, the opacity of the recording medium is maintained over the whole surface of the recording medium by applying a coating weight of at least 0.75 gsm, preferably at least 2gsm.

In an embodiment, the barrier layer comprises a polymer comprising an acrylate monomer. It has been found, that a polymer or copolymer comprising an acrylate monomer may provide improved adhesion of the marking particles, such as marking particles having a binder resin based on a polyester, to the barrier layer of the recording medium.

In examples, the polymer may be a curable acrylate polymer, such as an acrylate polymer being curable by UV light, and may be a non-curable acrylate polymer.

Furthermore, in an embodiment, the polymer comprising an acrylate monomer may be present in the barrier layer in a blend with a polymer comprising a vinyl alcohol monomer, such as a polyvinylalcohol. The polymer comprising the acrylate monomer may additionally reduce the moisture attraction of the barrier layer. A coating based on polyvinylalcohol alone absorbs water or vapour easily, thereby providing a tacky surface which makes the recording medium not suited for further use of the printed article, especially when high humidity environmental conditions are present.

As such, the adhesion of the marking particles to a barrier layer comprising the polymer comprising a vinyl alcohol monomer can be improved by the polymer comprising an acrylate monomer.

It is to be noted that while UV-curable coatings based on an acrylate monomer may be difficult to remove during a paper recycling process, there are solutions for this problem known in the art. For instance, one could use hydrolysable monomers, such as hydrolysable acrylate monomers, to prepare the UV curable coating. During the paper recycling process the cured coating could then be partially hydrolysed, resulting in detachment of the coating layer from the paper substrate.

Additionally or alternatively, the barrier layer may comprise a copolymer comprising a vinyl alcohol segment and another monomer segment. In an example, the copolymer comprises a vinyl alcohol segment and an ethylene segment, such as a polyethylene-vinylalcohol copolymer.

In an embodiment, the adhering step comprises reducing the dispersing capacity of the dispersing agent, such that the carrier liquid in between the marking particles is removed.

In this way, the reduction of the dispersion capacity enhances the separation of the marking particles from the carrier liquid. By separation of the marking particles from the carrier liquid, the marking particles may interact more closely with the barrier layer.

In the context of the present application the term “dispersing capacity” refers to the capacity of the dispersing agent to separate the marking particles, i.e. to prevent settling or clumping, in the carrier liquid, and in particular to prevent having a high viscosity in high dispersion concentration systems, especially at room temperature during the development and transfer of the liquid toner and supporting the stability of the liquid toner at room temperature during storage and transport of the liquid toner system to customers.

In typical toner liquids the viscosity will be a measure for the dispersing capacity of the dispersing agent.

Preferably, during the adhering step, the dispersing capacity is reduced to enable the free movement of the marking particles towards the barrier layer and to support the movement of the carrier liquid away from the barrier layer.

In an embodiment, the marking particles comprise a binder resin, and wherein the adhering step (vi) comprises dissolving an amount of the dispersing agent into the binder resin, such that the carrier liquid is removed from the marking particles, preferably the binder resin comprising a polyester.

Dissolving the dispersing agent into the binder resin reduces the dispersing capacity of the agent. The dispersing agent may be partly or completely dissolved into the binder resin. In an example, the dispersing capacity of the dispersing agent may be reduced by raising the temperature to a temperature above room temperature to dissolve the dispersing agent into the marking particle.

In a preferred example, the dispersing agent comprises an anchoring part for anchoring the dispersant to the marking particle, such as an amine, an imide group and / or an imine group providing an anchoring part to a polyester binder, and the dissolving step comprises dissolving the anchoring part into the binder resin of the toner resin.

In another embodiment an amount of the dispersing agent is a part of the time freely soluble in the carrier liquid. This amount of dispersing agent is not permanently anchored onto the marking particle. This amount of the dispersing agent may also be absorbed / dissolved into the binder resin of the binder resin and/or may be removed from in between the marking particles together with the carrier liquid during the adherence step vi.

In an embodiment, the adhering step comprises raising the temperature of the developed image of the liquid toner to reduce the dispersing capacity. In this way, the dispersing agent may easily be partly or completely dissolved in the binder resin of the marking particles. This is a fast and direct mechanism to enhance the adhesion of the marking particles to the barrier layer.

This reduction in dispersing capacity depending on temperature can be measured by performing a so called “hotplate test” on the toner liquid. A hotplate test is a test where the liquid toner is put on a hot plate of e.g. 150°C. The toner liquid can collapse in two phases, a marking particle phase and a carrier liquid phase. When after 60 seconds the liquid toner does not collapse, and there is no phase separation of the toner liquid, this indicates that the liquid toner is stable. On the other hand, when the liquid toner collapses within 60 seconds, and there is a phase separation, this indicates that the liquid toner is unstable at said temperatures.

In a preferred embodiment, the temperature of the developed and transferred image of the liquid toner is raised above a glass transition temperature Tg of the binder resin of the marking particles. Preferred temperatures are at least 30 to 50 degrees above Tg.

In a preferred embodiment, the adhering step comprises fusing said developed portion of liquid toner on the barrier layer, preferably the fusing step comprising film formation of the marking particles on the barrier layer.

This fusing is to result in coalescence of the marking particles on the recording medium. The term ‘coalescence’ refers herein to the process wherein marking particles melt together and form a film or continuous phase that adheres well to the barrier layer of the recording medium and that is separable from the carrier liquid. The fusing has to avoid formation of an emulsion, since an emulsion does not give a good printing image.

By heating the marking particles of the transferred liquid toner, the marking particles can form films on the recording medium whilst additional carrier liquid (which was present between the marking particles) is liberated during heating.

The step of heating the liquid toner to at least a temperature at which the marking particles start to coalesce and to form a polymer melt, is a so-called fusing step which is such that the marking particles of the liquid toner form films on the recording medium. At the glass transition temperature Tg, the solid marking particles undergo a glass transition and change from an amorphous hard and rigid structure to a flexible structure in which the polymer chains 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 a preferred embodiment the fusing step is taking place during a non-contact fusing step. Examples of non-contact fusing methods are fusing methods based on Infrared radiation. The wavelength of the IR emitters is preferably chosen in such a way that the temperature difference between colours during fusing is not greater than 15°C in order to avoid image defects.

In a preferred embodiment, the temperature raising step comprises providing infrared light to the developed image of liquid toner to raise the temperature of the developed image of the liquid toner. In an example, an infrared emitting device can be used as a non-contact type device for raising the temperature of the developed image of the liquid toner without contacting the image of liquid toner.

Such non-contact type fusing has the advantage of minimizing the risk of distorting the image onto the recording medium since the adhering step(s), e.g. a first step of the adhering due to reducing the dispersing capacity of the dispersing agent, and a next step of fusing or film formation, takes place without the toner image being contacted.

In a preferred embodiment, the non-contact type fusing step precedes the liquid removal step. This order has the advantage that the liquid removal may be highly efficient. The infrared irradiation may induce film formation. Furthermore, it has been observed that the film formation upon IR irradiation results in liberation of any carrier liquid absorbed or dispersed around the marking particles. Carrying out any liquid removal step subsequent to the IR irradiation thus enables removal of this liberated carrier liquid.

In exemplary embodiments where the adhering step comprises a reducing step for reducing the dispersion capacity of the dispersion agent, the reducing step comprises chemically modifying the dispersing agent. In exemplary embodiments, the barrier layer of the recording medium may contain a compound that alters the dispersing properties of the dispersing agent. The compound may be such that the dispersing agent is chemically modified, e.g. by catalytic reactions by metal salts, photoacids, acid base interactions, catalytic ring opening or retro pericyclic reactions. In these embodiments, the compound provides a stimulus to the dispersing agent for chemically modifying the dispersing agent.

In an embodiment, the chemically modifying step comprises subjecting the transferred portion of liquid toner on the recording medium to a stimulus in order to chemically modify the dispersing agent; wherein preferably the stimulus is visible light, UV-light, infrared light, microwave radiation , a change in temperature, a change in pH value, a contact with a compound, or a combination thereof.

In the chemically modifying step the dispersing agent of the portion of liquid toner transferred onto the barrier layer is decomposed or is conformationally changed. In a preferred embodiment, the stimulus is UV-light and the dispersing agent is decomposable in response to said UV-light and / or is conformationally changeable in response to said UV-light. The stimulus responsive part of the dispersing agent is further described in WO2014209108 in the name of the applicant, which is hereby incorporated by reference.

In an embodiment, the adhering step comprises the step of layer splitting of the liquid toner dispersion between a first layer rich in marking particles adjacent to the barrier layer and an outer layer primarily consisting of carrier liquid.

This layer splitting step can be advantageous for the adherence step of the marking particles to the barrier layer as the first layer rich in marking particles is already present adjacent to the barrier layer and the carrier liquid is at least partly separated from this first layer.

It will be understood that the first layer and the outer layer may gradually change over, or that an intermediate layer would be formed in between of the outer layer and the first layer.

The step of layer splitting may be carried out by applying an electric field so as to push charged marking particles in the liquid toner away from the outer surface of the transferred liquid toner towards the barrier layer of the recording medium.

Preferably, the carrier liquid according to the invention has a very low conductivity. This allows the dispersed and charged marking particles to be susceptible to acceleration under the effect of an electric field (electrophoresis), and that the marking particles are capable of retaining an electrical charge for some time. This charge may be attained by the particles as a result of charge exchange between the particles and salts on the surface of the marking particle, or it may be induced by an externally applied electric field. The carrier liquid can be any suitable liquid as is known in the art, and may be silicone fluids, natural or synthetic hydrocarbon liquids, hydrocarbon ethers, hydrocarbon carbonates and vegetable oils, fatty acid esters, UV or EB curable liquids or any combinations thereof.

The marking particles may further contain charge regulating agents to provide a charge to the marking particles, when they are dispersed in the carrier liquid.

The digital printing process may further comprise a second fusing step being carried out after the adhering/coalescence and/or fusing step, preferably being carried out after the liquid removal step, which second fusing step may additionally comprise providing a pressure to the printed marking particles on the recording medium to further enhance the adherence of the marking particles on the barrier layer. The pressure may be provided in a pressure nip comprising a pair of rotating members, such as a pair of rollers. Also the gloss can be adjusted by suitably choosing the temperature and pressure in the pressure nip.

This pressure fusing may only be applied after a basic degree of adhesion to the barrier layer has been established in a previous adhering step.

In an embodiment, the base layer of the recording medium comprises paper or cardboard, such as paperboard or corrugated fibre board. The base layer provides a simple and cheap base for a recording medium having adequate opacity, while the barrier layer provides a solution for preventing a shine-through problem or loss of opacity of the recording medium due to absorption of the carrier liquid and the prevention of absorbing the carrier liquid into the base layer.

In an embodiment, in step (i) the recording medium additionally comprises a barrier layer on a second surface of the base layer opposite to the first surface of the base layer. In this way, the recording medium may be used for printing with liquid toner on both sides of the recording medium in a duplex printing process.

In an embodiment, the providing step (i) comprises forming a coating on the first surface of the base layer by applying a coating composition comprising a carrier liquid barrier material to form the barrier layer on the first surface of the base layer, for blocking a movement of the carrier liquid towards the base layer of the recording medium.

The coating step provides a simple way of providing a recording medium having a barrier layer at the first surface of the base layer. In the coating step properties of the coating can be controlled, such as the coating weight, and the composition of the barrier layer.

In an embodiment, the providing step (i) comprises forming a coating on the first surface and on a second surface, opposite to the first surface, of the base layer by applying a coating composition comprising a carrier liquid barrier material to form the barrier layer on the first surface and the second surface of the base layer, for blocking a movement of the carrier liquid towards the base layer of the recording medium.

In a preferred embodiment, the carrier liquid barrier material is a polymer comprising a vinyl alcohol monomer. This provides a simple barrier layer for blocking the movement of the carrier liquid towards the base layer of the recording medium.

In an embodiment, the coating composition of step (i) comprises a polymer comprising an acrylate monomer. In this way, the adhesion of the marking particles is improved, such as marking particles comprising a binder resin containing a polyester.

In an alternative embodiment, the step (i) comprises forming an adhesion coating on the barrier layer by applying a coating composition comprising an adhesion component to form an adhesion coating on top of the barrier layer. This adhesion coating can be applied having different properties than the barrier layer, such as a thinner coating layer with respect to the barrier layer.

In an example, the barrier layer may comprise organic or inorganic components for controlling the gloss of the recording medium.

In another example, the barrier layer may comprise a component for controlling the whiteness of the barrier layer. The whiteness of the barrier layer may be adjusted by incorporating whiteness control components into the barrier layer, such as by adding optical brighteners or Ti02 particles or any other suitable components for improving the whiteness of the barrier layer, such as specific colour components.

In an embodiment, the step of forming a coating at the first surface of the base layer occurs in-line with the step of (v) transferring the liquid toner. In this way, a variety of recording mediums can be processed, independent of the type of recording medium, and the barrier layer properties can be controlled depending on the printing process needs, such as controlling the coating weight and / or layer position depending on the printing process.

In an alternative embodiment, the barrier layer may be formed at the first surface on a first layer, which is arranged on top of the base layer of the recording medium. Said first layer may be configured to adhere the barrier layer to the base layer and may be any other suitable layer.

In an embodiment, the step of forming a coating at the first surface of the base layer occurs in a coating system off-line with the step of (v) transferring the liquid toner in a printing system.

This provides a simple way of providing the recording medium including the barrier layer in large quantity, which can be stored before performing steps (ii) - (vii) of the printing process to print the liquid toner image onto the recording medium having the barrier layer.

According to a second aspect of the invention there is provided a printed recording medium, the printed recording medium being obtainable by a digital printing process for printing liquid toner on the recording medium according to the present invention, said liquid toner comprising marking particles, dispersing agent and a carrier liquid, the recording medium having a barrier layer on a first surface of the base layer, said barrier layer being configured for blocking a movement of the carrier liquid towards the base layer of the recording medium.

The printed recording medium is obtainable by a digital printing process for printing liquid toner on the recording medium according to the present invention. The printed recording medium has an adequate print quality, an adequate adhesion of marking particles on the recording medium for use and has an adequate opacity. Substantially no carrier liquid is absorbed in the base layer of the recording medium. Some residues of the carrier liquid are likely to remain in the film of marking particles adhering on the barrier layer, as an amount of carrier liquid may be dissolved in the binder resin and / or adhered to the dispersing agent of the liquid toner.

In an embodiment, the recording medium without the barrier layer has a weight of 40 gsm - 70 gsm. The barrier layer makes such a recording medium capable of for receiving an image of liquid toner while maintaining the opacity of the recording medium substantially constant.

In an embodiment, the printed recording medium has a shine-through below 120% according to the shine-through test. The shine-through is expressed as a relative transmission increase: ST = transmission of coated substrate with oil / transmission of substrate without oil * 100%

The shine-through is tested as defined in the experimental section of this application.

In an embodiment, the barrier layer of the printed recording medium is configured to provide an adhesion to the marking particles above 70% according to the tape test. According to the tape test, before and after taping the optical density is measured and the adhesion is expressed as a relative optical density decrease: Adhesion = optical density after taping / optical density without taping * 100%

The adhesion is tested as defined in the experimental section of this application.

According to a third aspect of the invention there is provided a digital printing device for printing liquid toner on a recording medium, said liquid toner comprising marking particles, a dispersing agent and a carrier liquid, said device comprising: (i) a feeding unit configured for feeding a recording medium comprising a base layer and a barrier layer on a first surface of the base layer, which feeding unit is arranged upstream of an image forming unit; (ii) the image forming unit comprising an imaging member adapted to sustain a pattern of electric charge forming a latent image on its surface, 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, wherein the image forming unit is further configured to transfer the liquid toner from the imaging member onto the barrier layer; (iii) an adhesion forming unit configured for treating the transferred image of liquid toner on the barrier layer to adhere the marking particles of said transferred image of liquid toner on the barrier layer; and (iv) a carrier liquid removal device configured for removing carrier liquid of said transferred developed portion from the recording medium.

In an embodiment, the feeding unit comprises a base layer feeding unit configured for feeding a base layer to a barrier forming unit, the barrier forming unit being configured for forming a barrier layer on the first surface of the base layer.

The barrier layer forming unit may be configured for forming the barrier layer by applying a coating on the first surface using a solution of at least one barrier component, optionally the barrier component being an adhesion component according to the present invention.

In an embodiment, the barrier forming unit comprises: a barrier coating unit configured for applying a barrier coating on the first surface of the recording medium; a barrier drying device configured for drying the barrier coating, which is applied on the first surface of the recording medium; a moisture measuring unit configured for measuring moisture of the recording medium, when dried by the barrier drying device; and a control unit configured for controlling the barrier drying unit based on a measuring signal of the moisture measuring unit, which indicates a moisture level of the recording medium.

In an embodiment, the barrier forming unit comprises a barrier drying device configured for drying the barrier coating to form the barrier layer. The barrier drying device may be configured to dry the barrier coating by removing a coat liquid such as by evaporating the coat liquid. In another example, the barrier drying device may be configured to cure the barrier coating, such as by providing a curing stimulus, such as heat, UV light or EB radiation, to cure the barrier coating to form the barrier layer.

In an embodiment, the barrier forming unit comprises a moisture measuring unit configured for measuring moisture of the recording medium. The moisture measuring unit may comprise a moisture sensor, such as an electrometer, which determines the moisture content of the recording media e.g. by an electrical conditioning of the recording media, as described in detail in referenced patent EP0955572.

In a fourth aspect of the invention there is provided a digital printing system for printing liquid toner on a recording medium, said liquid toner comprising marking particles, a dispersing agent and a carrier liquid, said system comprising: (i) an image forming unit comprising an imaging member adapted to sustain a pattern of electric charge forming a latent image on its surface, 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, wherein the image forming unit is further configured to transfer the liquid toner from the imaging member onto a first surface of the recording medium; and (ii) a mechanical carrier liquid removal device configured for removing carrier liquid of said transferred developed portion from the recording medium, the mechanical carrier liquid removal device comprising a liquid application unit adapted for adding an amount of volatile liquid to the carrier liquid on the surface of the recording medium before or during the mechanical removal of the carrier liquid from the surface of the recording medium.

The volatile liquid is a liquid which is more volatile than the carrier liquid. Said carrier liquid preferably has a boiling point of at least 250°C and the volatile liquid has a boiling point lower than 250°C , preferably lower than 225 °C. Herein, the boiling point of the volatile liquid and the carrier liquid is a measure of the volatility of the volatile liquid and the carrier liquid, respectively.

In case a layer of (non-volatile) carrier liquid is present on the surface of the recording medium before or after at least one step of mechanical removal of the carrier liquid, addition of an amount of volatile liquid to the carrier liquid on the surface of the recording medium provides a mixed layer of a mixture of both the carrier liquid and the volatile liquid. The mixed layer may enhance a removal of the remaining carrier liquid in a subsequent step of mechanical removing the mixed layer (or mixture) of the carrier liquid and the volatile liquid. Any remaining mixture on the recording medium may evaporate more easily, e.g. during storage. However, it is also possible to additionally remove mixture remaining on the recording medium by an evaporation device, such as an evaporation device configured to heat the recording medium.

In a fifth aspect of the invention there is provided a digital printing system for printing liquid toner on a recording medium, said liquid toner comprising marking particles, a dispersing agent and a carrier liquid, said system comprising: (i) an image forming unit comprising an imaging member adapted to sustain a pattern of electric charge forming a latent image on its surface, 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, wherein the image forming unit is further configured to transfer the liquid toner from the imaging member onto a first surface of the recording medium; and (ii) a mechanical carrier liquid removal device, the mechanical carrier liquid removal device comprising: a pair of rotating members for removing carrier liquid of said transferred developed portion from the recording medium to a surface of a rotating member of the pair of rotating members; and a liquid application unit adapted for adding an amount of volatile liquid onto the surface of said rotating member of the pair of rotating members.

The volatile liquid will mix with the layer of carrier liquid, which is present on the surface of the rotating member or roller. By adding the volatile liquid to the rotating member, dilution of the removed carrier liquid on the rotating member occurs so that a more efficient removal of the non volatile carrier liquid from the rotating member can take place.

In a particular embodiment, a mechanical removal element, such as a scraper, may be arranged contacting the rotating member for removing the liquid from the rotating member so that the surface of the rotating member is substantially free from carrier liquid.

In an example, the pair of rotating members may be a pair of rollers.

In an example of a digital printing system having a mechanical carrier liquid removal device according to exemplary embodiments described above, the recording medium has a barrier layer according to exemplary embodiments of this application and the mechanical carrier liquid removal device is used to remove carrier liquid from the barrier layer of the recording medium.

In a particular example, combinations of features of a mechanical carrier liquid removal device having a first plurality of rotating member pairs arranged along a transport path of the recording medium for removing carrier liquid from the recording medium and of the mechanical carrier liquid removal device of the fifth aspect of the present invention (with a pair of rotating members) may be envisaged, wherein the mechanical carrier liquid removal device of the fifth aspect is arranged downstream of the first plurality of rotating member pairs. In this way, the first plurality of rotating member pairs may remove the carrier liquid easily from the recording medium by layer splitting when the layer of carrier liquid is still substantial while the step of adding the volatile liquid is merely applied in a second stage, when the remaining layer of carrier liquid is considerably thin.

In another example, in a combination, a first liquid application unit is provided for adding an amount of volatile liquid to the carrier liquid on the surface of the recording medium, and a second liquid application unit is provided for adding an amount of volatile liquid onto the surface of said rotating member of the pair of rotating members of the mechanical carrier liquid removal device.

In another aspect of the invention there is provided a digital printing process for printing liquid toner on a recording medium, said liquid toner comprising marking particles and a curable carrier liquid, said process comprising: (i) Providing a recording medium comprising a base layer and a barrier layer on a first surface of the base layer, said barrier layer being configured for blocking a movement of the curable carrier liquid towards the base layer of the recording medium; (ii) Producing a latent image as a pattern of electric charge on an imaging member; (iii) Transferring a quantity of liquid toner onto a development member; (iv) Developing said latent image by transferring a portion of said quantity of liquid toner onto said imaging member in accordance with said pattern; (v) Transferring a developed image of liquid toner onto the barrier layer; and (vi) Adhering the marking particles of said transferred image of liquid toner on the barrier layer, wherein said adhering comprises curing the curable carrier on the recording medium.

The barrier layer blocks the movement of the curable carrier liquid towards the base layer of the recording medium, when the developed image of the liquid toner is transferred in step (v) onto the barrier layer. Hence, the carrier liquid cannot be absorbed in the base layer of the recording medium and any reduction of the opacity of the recording medium is prevented. The base layer may be a layer capable of absorbing the carrier liquid.

The marking particles of the transferred portion of liquid toner are adhered onto the barrier layer in step (vi) by curing the curable carrier liquid. In this way, the print quality of the transferred liquid toner on the printed recording medium is enhanced as the adhered marking particles are adhered to the barrier layer.

In an embodiment, the carrier liquid is an EB curable carrier liquid which is curable by EB radiation or particle beam radiation. In this embodiment, the adhering step may comprise providing a curing stimulus, such as heat, UV light or EB radiation, to cure the carrier liquid of the developed image of liquid toner, which is present on top of the barrier layer resulting in a varnish or lacquer effect or when a counterfoil laminate is used a fully ready one step lamination is done

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.

Brief description of figures

The accompanying drawings are used to illustrate presently preferred non-limiting exemplary embodiments of the present invention. The above and other advantages of the features and objects of the invention will become more apparent and the invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

Fig. 1 is a schematic view illustrating a first embodiment of digital printing process and apparatus of the invention;

Fig. 2 is a schematic view illustrating a cross section of a recording medium according to the first embodiment of the invention;

Fig. 3 is a schematic view illustrating a second embodiment of digital printing process and apparatus of the invention.

Fig. 4 is a schematic view illustrating a third embodiment of digital printing process and apparatus of the invention;

Figs. 5A-5E are diagrammatical illustrations of the stages of the adhesion process in accordance with an exemplary embodiment of the invention;

Figs. 6A-6E are alternative diagrammatical illustrations of the stages of the adhesion process in accordance with an exemplary embodiment of the invention

Fig. 7 is a schematic view illustrating an exemplary embodiment of a carrier liquid removal device. Fig. 8 is a schematic view illustrating another exemplary embodiment of a carrier liquid removal device.

Detailed discussion of illustrated embodiments

The figures are not drawn to scale and purely diagrammatical in nature. Equal reference numerals in different figures refer to equal or corresponding features.

Fig. 1 illustrates diagrammatically a first embodiment of a digital printing apparatus of the invention. The apparatus shown in Fig. 1 comprises a printing station with a reservoir 100, a feed member 120, a development member 130, an imaging member 140, an intermediate member 150, a transfer member 160, and a adhesion forming unit 170 and a liquid removal unit 700. A recording medium 199 is transported between intermediate member 150 and transfer member 160.

Now referring to Fig. 2, the recording medium 199 used in the digital printing process comprises a base layer 202 capable of absorbing the carrier liquid. Furthermore, the recording medium 199 comprises a barrier layer 204 arranged at the first surface 206 of the base layer 202, as shown in Fig. 2. The base layer 202 may be a paper containing layer or any other absorbing material suitable for layer for absorbing the carrier liquid of the liquid toner. The barrier layer 204 is a substantially closed layer, which is configured for blocking a movement of the carrier liquid towards the base layer 202 of the recording medium. In a particular example, the barrier layer 204 comprises poly vinyl alcohol, which acts to block the movement of the carrier liquid towards the base layer of the recording medium.

The barrier layer 204 of the recording medium 199 comprises an adhesion component 206, which is configured for preferentially attracting the marking particles relative to the carrier liquid during step (vi). Preferably the polarity of the marking particles is higher than the polarity of the carrier liquid.

The adhesion component provides adequate adhesion of the marking particles to the barrier layer. Additionally or alternatively, the adhesion component in the barrier layer attracts the marking particles towards the surface of the barrier layer and repels the carrier liquid. As such, the adhesion component prevents the carrier liquid from forming a film on the barrier layer, which may disturb the adhesion of the marking particles to the barrier layer.

The polarity of the marking particles is higher than the polarity of the carrier liquid. As such the adhesion component may suitably be selected for preferentially attracting the marking particles relative to the carrier liquid based on the difference of the polarity of the marking particles with respect to the polarity of the carrier liquid.

The development member 130, the imaging member 140 and the intermediate member 150 are each shown to be provided with a removal device 133, 146, 153, for example, a scraper. This removal device could, for example, also be a scraper in combination with a loosening roller. Without loss of generality, the aforementioned members are illustrated and described as rollers, but the skilled person understands that they can be implemented differently, e.g. as belts.

In operation, an amount of liquid toner, initially stored in a liquid toner reservoir 100, is applied via a feed member 120, to a development member 130, an imaging member 140, and an optional intermediate member 150, and finally to a recording medium 199. The development member 130, imaging member 140, and intermediate member 150 all transfer part of the liquid toner adhering to their surface to their successor; the part of the liquid toner that remains present on the member’s surface, i.e. the excess liquid toner which remains after selective, imagewise transfer, is removed after the transfer stage by the appropriate removal device 133, 146, 153.

The charging of the toner on the development member 130 is done by charging device 131. This charging device 131 can be a corona or a biased roll, for example. Charging the toner causes the liquid toner dispersion to split into an inner layer at the surface adjacent of the development member 130 and an outer layer. The inner layer is richer in marking particles and the outer layer is richer in carrier liquid. The transition between these two layers may be gradual. Fig. 1 further shows a discharging corona 132 that is provided downstream of the area of the rotational contact between the toner roller 130 and the imaging roller 140. The discharging corona 132 is suitable for modifying or removing the charge in the dispersion. The removed material is preferably recycled (with or without adjustment of the composition) by adding it back into liquid toner reservoir 100.

Adhering and fusing is carried out by means of a adhesion forming unit 170, which is a non-contact fusing unit such as an IR fusing unit. The non-contact adhesion forming unit 170 raises the temperature of the developed image of liquid toner to a temperature, which causes reduction of dispersing capacity of the dispersing agent, thereby inducing coalescence of the marking particles, resulting in the formation of a film that adheres to the recording medium 199 and (further) liberation of carrier liquid. The term ‘coalescence’ refers herein to the process wherein marking particles melt together and form a film or continuous phase that adheres well to the recording medium and that is separated from any carrier liquid, see Figs. 6A-6E.

It will be understood that for duplex and/or multi colour printing several such non-contact fusing units may be available. During the fusing step induced by the adhesion forming unit 170, no contact is made by the fusing unit to the developed image of liquid toner on the recording medium, as the marking particles do not yet adhere to the barrier layer 204 of the recording medium 199.

In a further embodiment (not shown), the liquid toner present on the recording medium 199 is subjected to a further charging treatment after its transfer to the recording medium 199 and before fusing the toner in adhesion forming unit 170. The charging treatment is part of the adherence step of the marking particles onto the barrier layer. The charging treatment is for instance applied by means of a charging unit (not shown), which is arranged upstream of the adhesion forming unit 170, and is for instance a corona treatment. Such a treatment ensures that the charged marking particles are pushed or drawn to the recording medium 199 and the carrier liquid is removed from the marking particles. In this way, the adhering step comprises the step of layer splitting of the liquid toner dispersion between a first layer rich in marking particles adjacent to the barrier layer and an outer layer primarily consisting of carrier liquid. In an example of the layer splitting step, a charging unit, such as a corona treatment unit, may be arranged close to the outer surface of the transferred liquid toner to provide an electric field acting on the transferred liquid toner on the barrier layer. It is deemed beneficial, in one implementation, that the charging unit comprises an electrically conductive material to which a voltage may be applied. The electrically conductive material is suitably a metal. It will therefore be understood that the charging unit is suitably based on metal, but that it also may contain non-metal parts and/or layers and coatings like a conductive rubber roller. The applied voltage will be such that the charged elements in the liquid toner, such as the marking particles, are moved towards the recording medium surface and hence away from the charging unit. Thereto, it is suitable that a support member is present at the opposed side of the recording material, which support member is held at another potential, for instance ground. The applied voltage is particularly chosen such that layer splitting occurs. As such, the splitting will occur between a first layer rich in marking particles adjacent to the recording medium coated barrier surface and an outer layer primarily consisting of carrier liquid. The applied voltage will depend on the exact composition of the liquid toner, and the amount of charging applied thereto. Typically, the charge is fixed within the liquid toner dispersion on the dispersing agent, the resin and optional other agents. The carrier liquid is not easily charged.

The carrier liquid that is liberated during the fusing/adhesion step is removed from the recording medium 199 downstream of the non-contact adhesion forming (fusing) unit 170 by a mechanical removal means 700, for instance by means of rollers, by means of blowing off the carrier liquid, by means of suction.

The liquid removal unit 700 is suitably embodied as a member that is in rotational contact with the recording medium, or at least with an outer layer of the liquid toner present on the recording medium. It is deemed suitable to provide a counter-member at the opposed side of the recording medium 199 to form a nip providing adequate pressure.

In a preferred embodiment liquid removal unit 700 comprises multiple roller pairs arranged along the transport path of the recording medium. The number of pairs will be determined by the residual amount of carrier liquid that can be tolerated. Typically less than 0.5 g/m2 of carrier liquid is preferred during duplex printing which can be achieved by 3 to 8 roller pairs.

Suitably, this process occurs at “high speed”, for instance 50 cm/s or up to 3 m/s or more, so as to enable high-speed printing. In this way, substantial all carrier liquid is removed from the recording medium 199 and substantially no carrier liquid is absorbed into the recording medium 199 due to the barrier layer 202. The removed carrier liquid may be recycled and reused within the machine.

Fig. 3 illustrates schematically another embodiment of a digital printing apparatus. The apparatus shown in Fig. 3 comprises a first image forming unit 1100a for applying liquid toner Ta having a first colour, e.g. black, onto a recording medium (also known as a “substrate) SI, a second image forming unit 1100b for applying liquid toner Tb having a second colour, e.g. cyan, onto the recording medium SI, a third image forming unit 1100c for applying liquid toner Tc having a third colour, e.g. magenta, onto the recording medium SI, and a fourth image forming unit 1 lOOd for applying liquid toner Td having a fourth colour, e.g. yellow, onto the recording medium SI.

The first image forming unit 1100a comprises a toner reservoir 1110a, a feed member 1120a, a first development member 1130a, a first imaging member 1140a, and an optional intermediate member 1150a. The first imaging member 1140a is adapted to sustain a first pattern of electric charge forming a first latent image on its surface. The first development member 1130a is arranged to receive first liquid toner Ta from the feed member 1120a, and to develop said first latent image by transferring a portion of said first liquid toner Ta onto first imaging member 1140a in accordance with said first pattern. Similarly, the second image forming unit 1100b comprises a toner reservoir 1110b, a feed member 1120b, a second development member 1130b, a second imaging member 1140b, and an optional intermediate member 1150b. The second imaging member 1140b is adapted to sustain a second pattern of electric charge forming a second latent image on its surface.

The second development member 1130b is arranged to receive second liquid toner Tb from the feed member 1120b, and to develop said second latent image by transferring a portion of said second liquid toner Tb onto second imaging member 1140b in accordance with said second pattern. The third and fourth imaging member 1100c, 1 lOOd may be implemented in a similar manner.

The recording medium SI is supported on a substrate support assembly which comprises in the illustrated embodiment first, second, third and fourth support members 1200a, 1200b, 1200c, 1200d for supporting the recording medium SI during the subsequent transfer of first, second, third and fourth liquid toner Ta, Tb, Tc, Td from the first, second, third and fourth image forming unit 1100a, 1100b, 1100c, llOOd, respectively, whilst the recording medium SI moves in a movement direction M from the first image forming unit 1100a to the fourth image forming unit llOOd.

In the development stage, marking particles travel from a development member 1130a supplied with a thin, film-like layer of liquid toner Ta, onto the imaging member 1140a that carries the first latent image. In a subsequent step, the developed first latent image is transferred from the imaging member 1140a onto the intermediate member 1150a. In the final transfer step, the developed image is transferred from the intermediate roller 1150a onto the recording medium SI, which is supported by the support roller 1200a that may be kept at a suitable potential. Similar development stages apply for the second, third and fourth image forming units 1100b, 1100c, 1 lOOd.

Throughout the application, the various stages of the image forming units 1100a, 1100b, 1100c, llOOd and of the support assembly 1200a, 1200b, 1200c, 1200d have been described as members. These members may be rotating rollers, but the skilled person will appreciate that the same principles may be applied with other members, e.g. comprising a suitably designed rotating belt with a roll and/or a belt tracking shoe.

The embodiment of the invention illustrated by Fig. 3 further comprises a non-contact adhesion forming unit 1400 downstream of the image forming units 1100a, 1100b, 1100c, 1 lOOd. The non-contact adhesion forming unit 1400 may have the same attributes as the non-contact adhesion forming unit 170 shown in Fig. 1. The non-contact adhesion forming unit 1400 raises the temperature of the developed image of liquid toner to a temperature, which causes reduction of dispersing capacity of the dispersing agent, thereby inducing coalescence of the marking particles, resulting in the formation of a film that adheres to the recording medium 199 and (further) liberation of carrier liquid. The term ‘coalescence’ refers herein to the process wherein marking particles melt together and form a film or continuous phase that adheres well to the recording medium and that is separated from any carrier liquid, see Figs. 6A-6E. It will be understood that in modified embodiments of the embodiment of Fig. 3, e.g. for multicolour printing, several such non-contact fusing 1400 units may be available between the 1100a, 1100b, 1100c, 1 lOOd additional to the non-contact fusing 1400 unit downstream of the image forming units 1100a, 1100b, 1100c, 1 lOOd. In this way, each of the colour images is adhered to the barrier layer of the recording medium prior to developing another colour image of liquid toner.

During the fusing step induced by the fusing unit 170, no contact is made between a fusing portion of the fusing unit and the developed image of liquid toner, as the marking particles do not yet adhere to the barrier layer 204 of the recording medium 199.

The carrier liquid is removed from the recording medium 199 downstream of the non-contact adhesion forming unit 1400 by a mechanical removal means 1700, for instance by means of rollers, by means of blowing off the carrier liquid, by means of suction.

In a preferred embodiment liquid removal step 1700 are multiple roller pairs. The number of pairs will be determined by the residual amount of carrier liquid that can be tolerated. Typically less than 0.5 g/m2 of carrier liquid is preferred during duplex printing which can be achieved by 3 to 8 roller pairs.

This process results in a thin layer of liquid toner being applied to the recording medium S1.

When four colours are printed the thickness of the liquid toner layer on the recording medium before fusing is typically between 1 and 15 micron. For example, in areas where an image with four colours is printed the thickness may be approximately 8to 12 micron, in areas where no image is present the thickness may be approximately 0.5 to 2 micron, and in areas with an image with one colour the thickness may be approximately 2 to 4 micron. After fusing and carrier liquid removal the thickness of the image will become 4 to 7micron where 4 colours are printed and 0-0.6 micron where no image is present.

Particular embodiments of the invention relate to the field of digital printing apparatus and processes for so-called “continuous” webs, i.e. printing systems where a continuous roll of recording medium is run through the printer, in particular to print large numbers of copies of the same image(s), or alternatively, series of images, or even large sets of individually varying images.

The digital printing apparatus comprises to that end a substrate feeding means 1500 configured to feed the recording medium SI as a continuous web during printing. The resulting substrate S’ with the printed image may then be rolled on a roll 1600.

Now reference is made to Fig. 4 which shows a third embodiment of digital printing process and apparatus of the invention. In the third embodiment, the embodiment of Fig. 1 is modified by adding a barrier layer application unit 300. The application of the coating for forming the barrier layer 204 onto the recording medium 199 can be carried out in-line by the barrier layer application unit 300 prior to the transfer of the developed liquid toner onto the barrier layer 204. In Fig. 4 is shown, that upstream of the transfer process at the intermediate member 150 relative to the transport direction indicated by arrow T, the coating is applied onto the first surface of the base layer 202.

In a preferred embodiment an application roller (not shown) is used. In such an embodiment a nip may be formed between the application roller and a support roller, further using a doctoring blade arranged adjacent the application roller for controlling the coating layer applied by the application roller onto the recording medium 199 on the support roller.

In some embodiments, the barrier layer may be formed on the first surface of the base layer 202 by applying an aqueous solution of one or more components to the surface(s) of the recording medium 199. For example, Topsol 20 obtained from Topchim dissolved in water provides an aqueous solution of a poly vinyl alcohol component that can be coated directly onto a recording medium. This coating may be applied by any means known in the industry such as by using a rod, a knife, an anilox roller device or using any other suitable coating technique followed by a drying means for drying the applied wet coating.

In this way, a variety of recording mediums can be processed, independent of the type of recording medium, and the barrier layer properties can be controlled depending on the printing process needs, such as controlling the coating weight and / or layer position depending on the printing process.

Alternatively, such a barrier layer application unit 300 can also be added to the embodiment shown in Fig. 2.

Figs. 5A-5E shows diagrammatically four stages in the adhesion process occurring at the barrier layer 204 of the recording medium and a step of removing the carrier liquid. Figs. 5A-5E show effectively two ellipsoid marking particles with dispersing agent D having stabilizing parts in the forms of tails or hairs. A layer of carrier liquid 210 is present on the barrier layer 204 and an amount of carrier liquid is shown around the marking particles 212. At least a portion of this amount of carrier liquid is believed to remain there because of the presence of the dispersing agents molecules D adsorbed on the surface. This amount may not be negligible.

In Fig.5A, the initial situation after transfer is shown. Separate marking particles are each encapsulated in a layer of carrier liquid. A layer of carrier liquid may be present covering the whole barrier layer 204 of the recording medium 199, even in non-imaged positions.

In Fig. 5B, the situation is shown upon infrared irradiation, wherein carrier liquid from the surface of the marking particles is started to be released due to the dispersing agents D that are dissolving into the marking particle. Such dissolution is understood to occur, because the marking particle is heated to above the glass transition temperature of the toner resin.

In Fig. 5C, a next stage is shown with coalescence of the marking particles of the liquid toner forming a marking particle layer, see also FIG. 5D. Herein, the dispersion stability of the dispersing agent for dispersing the marking particles in the carrier liquid (i.e. for keeping the marking particles separate from each other) has been removed, and the carrier liquid is removed in between the marking particles.

In Fig. 5D a next stage is shown wherein now preferentially the adhesion component in the barrier layer 204 attracts the marking particle layer 214 which is attracted by the barrier layer 204. The marking particle layer 214 forms a layer rich in marking particles. The barrier layer 204 repels the carrier liquid 210 which forms an outer layer away from the barrier layer 204. The marking particle layer 214 adheres to the barrier layer 204.

In Fig. 5E a next stage is shown wherein carrier liquid layer 210 has been removed from the recording medium. No marking particles 214 are removed from the recording medium as the marking particles 214 are adequately adhered to the barrier layer 204 of the recording medium.

In Figs. 6A-E a similar adhesion process is shown as shown in Figs. 5A - E. In this exemplary embodiment the dispersing agent has an amount that is anchored to the marking particles I ) and an amount that is present as free dispersing agent between the marking particles D2.

In Fig. 6B, the situation is shown upon infrared irradiation, wherein carrier liquid 210 from the surface of the marking particles is started to be released due to the dispersing agents I ) , including optionally D2, that are dissolving into the marking particle. Such dissolution is understood to occur, because the marking particle is heated to above the glass transition temperature of the toner resin.

In Fig. 6C shown a coalescence of the marking particles 212 of the liquid toner occurs and the part of the dispersing agent D2 that is not anchored onto the marking particles is removed from between the marking particles together with the carrier liquid 210.

Now referring to Fig. 7, wherein a mechanical removing device is shown according to an embodiment of the present invention for removing the carrier liquid from the recording medium. The recording medium 199 is transported along a transport path in the transport direction T along the mechanical removing unit 700.

The liquid removing unit 700 comprises a liquid application unit 710, which is configured for applying a volatile liquid onto the barrier layer of the recording medium 199, as shown by arrow 715. The volatile liquid will mix with the outer layer of carrier liquid of the developed and adhered image of the marking particles on the recording medium 199. The liquid removing unit 700 is arranged downstream of the fuser unit 170, 1400, as shown in the embodiments shown in Fig. 1, 3 and 4.

The mixed layer of carrier liquid and volatile liquid is mechanically removed by the roller pairs 720a, 720b, 702c by direct contact to one of the rollers of each roller pair 720a, 720b, 702c. The direct contact to the rollers in the nip of the roller pairs 720 enhances the mixing of the carrier liquid and the volatile liquid.

Due to the contact to each roller pair in the roller nip, the mixed layer is reduced in thickness by a splitting process of the layer due to transfer of a part of the layer to the surface of the contacting roller. In the embodiment shown, three roller pairs 720a, 720b, 702c are used. Any other number of roller pairs 720 may be arranged along the transport path depending on the need to further reduce the layer thickness of the mixed layer of carrier liquid and volatile liquid. In a next evaporating step, the remaining layer, which is relatively thin, having about 50% in volume of volatile liquid, is further reduced by evaporating the volatile liquid as shown by arrow 730. The evaporating step may be enhanced by actively heating the recording medium, such as by using an Infrared light heater or using a contact heater.

The mechanical removing device of this embodiment, including the liquid application unit 710, may be used in any application or printing device, wherein the carrier liquid needs to be removed from a recording medium. The mechanical removing device of this embodiment may also be used for removing carrier liquid from a recording medium without a barrier layer, such as a recording medium having a base layer, which is not able to absorb the carrier liquid.

Another embodiment of a mechanical removal device is shown in Fig. 8. The recording medium 199 is transported along a transport path in the transport direction T along the mechanical removing unit 800. The liquid removing unit 800 is arranged downstream of the fuser unit 170, 1400, as shown in the embodiments shown in Fig. 1, 3 and 4. The mechanical removing unit 800 comprises a roller pair 820, 822, which is engaged into contact with the recording medium 199 for taking up carrier liquid from the recording medium 199 onto the surface of the roller 820. The liquid removing unit 800 further comprises a liquid application unit 810, which is configured for applying a volatile liquid onto a surface of one of the rollers 820 of the roller pair 820, 822, as shown by arrow 815. In this example a low viscous and volatile liquid, such as isopar L, isopar M, isopar N from Exxon Mobil, or heptyl acetate, hexyl propionate, dipentyl ether or dihexyl ether from Sigma Aldrich, is applied by liquid application unit 810. The volatile liquid will mix with the layer of carrier liquid, which is present on the surface of the roller 820.

Downstream of means 810 a mean 840, such as a scraper, is arranged for removing the liquid from the roller 820 so that the surface of the roller 820 after the removal means 840 is substantially free from carrier liquid and that a very efficient carrier liquid removal in a next roller pair (not shown) can take place. By adding the volatile liquid to the roller, dilution of the removed carrier liquid on the roller occurs so that a more efficient removal of the non volatile carrier liquid can take place. The removed liquid 830 can be recycled and used again in liquid application unit 810. This setup is preferred to remove small amounts of carrier liquid form the substrate.

In a preferred embodiment, a combination of two types of carrier liquid removal are used: in a first stage roller pairs are used to remove carrier liquid from the recording medium 199 and in a second stage , when the amount of residual carrier liquid on the recording medium 199 is low, typical below 1.5g/m2, a removal device 800 as shown in Fig. 8 is used.

Examples

As shown in Table I, the following coatings were applied to the substrate Sappi gallery fine 90gsm by a bar coater and dried in an oven afterwards to obtain a coating weight of approximately 5gsm. Coating B and E were dried by UV curing with an iron doped bulb of 180W/cm.

As defined herein, the polarity P of a certain material may be calculated based on

wherein p and p are Hansen solubility parameters (HSP) as is described in the book “Hansen solubility parameters User’s Handbook” second edition. Hansen describe three major types of interactions (see page 5), namely the nonpolar interactions or dispersive interactions d, the polar cohesive energy p and the hydrogen bonding energy h. The principle is that when a material A is within the Hansen solubility space of a material B, material A is compatible/soluble with material B. The polarity is expressed in Mpal/2. The HSP values are determined by checking the solubilty of the materials in solvents with known HSP values over the total HSP range.

Table I - Examples of tested barrier coatings

For coating sample H and I the polarity is calculated based on the polarity of the individual coating material components and their respective weight ratio in the coating.

Barrier

In a first step the barrier properties were evaluated. The barrier properties were evaluated by measuring the shine-through (ST). Shine-through was determined using a fiber optic spectrometer of the 'Black-Comet CXR’ type supplied by Stellarnet Inc. which can detect wavelengths between 190-850 nm at a resolution of 1.5 nm. This fiber optic spectrometer was used in combination with a SL1 tungsten halogen light source. This SL1 tungsten halogen light source was also supplied by Stellarnet Inc. and emits light in the 350-2300 nm wavelength range.

For each wavelength from 190 nm to 850 nm (e.g. for 190, 191, 192, 193, 194.. .etc. all the way up to 850 nm) the transmission of the produced by the SFI tungsten halogen light source through the recording medium sample was recorded over an integration time of 1000 ms. The transmission values for each wavelength measured were then summed and divided by the number of different wavelengths tested to yield an average transmission value across the 190 nm to 850 nm range.

Transmission values were also measured for each wavelength detected by the fiber optic spectrometer at eight different locations on a single recording medium to account for any inhomogeneities in the recording medium. A single transmission value for the recording medium was then obtained by averaging the average transmission values recorded for the different locations.

Thereafter, approximately 4-5 gsm of a preferred carrier liquid was applied on the coated side of coated substrate, using a wire coating bar depositing a wet layer of 4-6μιη thickness. Then the samples (with coated side on the top) were placed on a hotplate of 120°C for 20 sec, using a petri dish in order to ensure good contact between the hotplate and the sample.

Two types of carrier liquids were selected: a. Radia 7131 fatty acid ester, Oleon; having polarity P = 2.2 b. C18IO alkene, Ineos; having polarity P = 1.5

After 5 minutes the excess oil on the coated sample was removed.

The shine-through is expressed as a relative transmission increase: ST = transmission of coated substrate with oil / transmission of substrate without oil * 100%

The shine through was categorized in three groups ST < 110%: most preferred 110% < ST < 120%: preferred ST > 120%: not acceptable

As can be seen from Table II, coatings based on materials having a polarity difference of 5 or more relative to the carrier liquid have a good barrier effect. Only sample C shows a moderate barrier effect. This indicate that other parameters like coating quality (see the different coating amount for coating A) and or wetting or film forming properties can be of importance.

From coating sample H it is also clear that by adding some coating component A to coating C the desired barrier properties can be achieved. The tackiness of coating H was also better than for coating A.

Also from table II it is shown, that coating F with a polarity difference lower than 5 shows no barrier properties.

Table II: barrier effects of coating samples Adhesion

The check the adhesion the different coatings were applied on a UPM digi finesse 170gsm with a coating weight of 5gsm. After drying of the barrier layer, a liquid toner with a solid content of 25% was applied with a ΙΟμπι rod so that a toner layer was applied of approx. 7-9 pm.

After 30 seconds these samples were placed on a hotplate of 120°C for 30 sec, using a petri dish in order to ensure good contact between the hotplate and the sample.

The adhesion of this toner layer on the coated recording medium is a measure for the fusing degree and is measured by a tape test. Excess oil is first removed by a KIMTECH paper wipe, then a strip of Scotch® MagicTM tape (25 mm wide) is put on the fused image and removed slowly under an angle of 90 to 150°. The use of the paper cleaning wipe ensures that excess oil is not affecting the peel force.

Before and after taping the optical density is measured and the adhesion is expressed as a relative optical density decrease:

Adhesion = optical density after taping / optical density without taping * 100%

Adhesion > 90%: most preferred 70% < Adhesion < 90%: preferred Adhesion < 70%: not acceptable

Table III: adhesion effects of coating samples

From this table it is clear that coatings sample are found with both barrier properties and proper adhesion properties (Coatings A, B, D, G, H and I). Coating sample E however has barrier properties, but provides no proper adhesion to the marking particles.

It is to be noted that while UV-curable coatings may be difficult to remove during a paper recycling process, there are solutions for this problem known in the art. For instance, one could use hydrolysable monomers to prepare the UV curable coating. During the paper recycling process the cured coating could then be partially hydrolysed, resulting in detachment of the coating layer from the paper substrate.

Materials of liquid toner

The carrier liquid of this application is particularly a substantially non-polar carrier liquid. The term ‘substantially non-polar’ refers in the context of the present invention to a chemical entity that is overall non-polar even though it may contain some polarisable groups such as ester, hydroxyl group, and/or carboxyl group. The substantially non-polar carrier liquid is suitably selected from the group consisting of a mineral oil, a low or high viscosity liquid. Specific examples include silicone fluids, mineral oils, low viscosity or high viscosity liquid paraffin, isoparaffinic hydrocarbons, fatty acid triglycerides, fatty acid esters, vegetable oils or any combinations thereof. The carrier liquid may further contain variable amounts of additives, such as charge control agent (CCA), wax and plasticizers. Typical commercially available carrier liquids white mineral oils from Sonneborn Inc., Paraffin oils of Petro Canada and vegetable oils from Cargill or oils derived from vegetable sources by chemical means, fatty acid esters under the tradename Radia from Oleon Chemicals.

In the context of the present invention, the liquid toner is a dispersion of marking particles in a carrier liquid. The marking particles, according to this invention, comprise coloured particles (also called ink particles or pigment) and a binder resin although non pigmented resin systems also can be used containing a phosphor or taggant or UV active material. Typically, the diameter of the marking particles is about 0.5 to 4.0 pm. More preferably, the average diameter of the marking particles is smaller than 2 pm, for instance in the range of 1.5 to 2.0 pm. The marking particles suitably have a concentration of about 40-95 % of binder resin. The binder resin is a polymer, preferably transparent, that embeds the ink particles. Preferably, a polyester resin is used as binder resin. Also other types of resin having a very low or no compatibility with the carrier liquid and dispersing agent can be used. Preferably, the resin has a high transparency, provides good colour developing properties and has a high fixing property on the recording medium. Most preferably, the shape of the marking particles is ellipsoid, which is beneficial for the fusing process.. A typical solid content of liquid toner dispersion during printing is a solid content of between 10 to 30 wt%, such as a solid content of 25 wt%. The solid content of the concentrated toner before dilution can go up to 50 or 60 % According to this invention, “solid content” means the amount of marking particles in wt% with regard to the total liquid toner dispersion.

The term ‘dispersing agent of the hyper-dispersant type’ may refer to a dispersing agent provided with anchor groups to which stabilising groups are coupled. Suitably examples of anchor groups of the dispersing agent are amine-functionalized polymers, such as polyalkyleneimines, for instance polyethyleneimine (PEI) and polyallylamines. The stabilizing groups of the dispersing agent are suitably chosen from the groups of fatty acid compounds and polyolefins, but similar groups are not excluded. The fatty acid compounds are for instance hydroxylated, and may be polymerized. A suitable degree of polymerization is for instance 1 (monomer) to 7, preferably 2 to 4. The amine functionality of this backbone can be partly or completely converted to amides or quatemized.

Preferred examples of the stabilizing groups and the dispersing agent in its entirety have been described in Applicants’ patent applications NL2011955 and NL2012086, which are herein included by reference. Alternatively, use may be made of commercially available dispersing agent, such as SolsperseTM 13940, SolsperseTM 11000, which again combine a polyamine anchor group with polymeric stabilizing groups.

In a further embodiment, use can be made of a decomposable dispersing agent, such as described in the patent application NL2011064 in the name of Applicant, which is herein included by reference.

In a further embodiment, the dispersing agent may be composed without anchor groups, wherein an amount of the dispersing agent is freely present in the carrier liquid in between the marking particles, without being adsorbed to the marking particles.

Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. In particular, features presented and described in separate dependent claims may be applied in combination, and any advantageous combination of such claims are herewith disclosed.

Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. The terms "a" or "an", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

A digital printing process for printing a liquid toner on a receiving medium, which comprises liquid toner marking particles, a dispersant and a carrier liquid, which process comprises: (i) providing a receiving medium comprising a base layer suitable for absorbing the carrier fluid, and a barrier layer on a first surface of the base layer, which barrier layer is configured to stop movement of the carrier fluid toward the base layer of the receiving medium; (ii) producing a latent image as an electric charge pattern on an imaging member; (iii) transferring an amount of the liquid toner to a developing member; (iv) developing the latent image by transferring a portion of the amount of the liquid toner to the imaging member in accordance with the pattern; (v) transferring a developed image of the liquid toner to the barrier layer; (vi) adhering the marker particles of the transferred liquid toner image to the barrier layer; (vii) removing carrier fluid from the transferred developed portion of the receiving medium.

The digital printing process according to claim 1, wherein the barrier layer comprises an adhesion component configured to preferentially attract marker particles relative to the carrier fluid during step (vi), wherein preferably the polarity of the material component of the barrier layer is higher then the polarity of the carrier liquid.

The digital printing process according to any of the preceding claims, wherein the barrier layer has a coat weight of at least 0.75 gsm, preferably at least 2 gsm.

The digital printing process according to any of the preceding claims, wherein the barrier layer comprises a polymer which comprises a vinyl alcohol monomer, preferably the polymer comprising a vinyl alcohol monomer, which is the adhesion component.

The digital printing process according to any of the preceding claims, wherein the barrier layer comprises a polymer which comprises an acrylate monomer.

The digital printing process according to any of the preceding claims, wherein the bonding step comprises reducing the dispersing capacity of the dispersant such that the carrier fluid between the marker particles is removed.

The digital printing process according to claim 6, wherein the marker particles comprise a binder resin, and wherein the reducing step (vi) comprises dissolving the dispersant in the binder resin.

The digital printing process according to claim 6 or claim 7, wherein the dissolving step comprises raising the temperature of the developed image of the liquid toner to reduce the dispersing capacity, preferably further comprising providing infrared light on the developed image of the liquid toner to increase the temperature of the developed image of the liquid toner.

The digital printing process of claim 6 or claim 7, wherein the reducing step comprises chemically modifying the dispersant, which comprises subjecting the transferred portion of the liquid toner on the receiving medium to a stimulus for the purpose of chemically converting the dispersant. modify; wherein the stimulus is preferably visible light, UV light, infrared light, microwave radiation, a change in temperature, a change in pH value, a contact with a substance, or a combination thereof, the stimulus being more preferably UV light.

The digital printing process according to any of claims 6 to 9, wherein the bonding step further comprises fusing the developed portion of the liquid toner onto the barrier layer, wherein preferably the fusing step comprises film forming the marker particles on the barrier layer.

The digital printing process according to any of the preceding claims, wherein the bonding step further comprises the step of layer cleavage of the liquid toner dispersion between a first layer rich in marker particles located adjacent to the barrier layer and an outer layer containing mainly the carrier fluid.

The digital printing process according to any of the preceding claims, wherein the base layer of the receiving medium comprises paper or cardboard, such as board paper or wrinkled fiber board or paper labels.

The digital printing process according to any of the preceding claims, wherein the step (i) comprises forming a coating on the first surface of the base layer by applying a bubble coating composition which comprises a carrier liquid barrier material to form a barrier layer on the first surface of the base layer, capable of restraining movement of the carrier fluid to the base layer of the receiving medium, preferably the carrier fluid barrier material being a polymer comprising a vinyl alcohol monomer.

The digital printing process of claim 13, wherein the coating composition of step (i) comprises a polymer, which comprises an acrylate monomer.

The digital printing process according to claim 13 or claim 14, wherein the step of forming a coating on the first surface of the base layer takes place in-line with the step of (v) transferring the liquid toner.

The digital printing process according to claim 13 or claim 14, wherein the step of forming a coating on the first surface of the base layer takes place offline with the step of (v) transferring the liquid toner.

A printed receiving medium, the printed receiving medium obtainable by means of a digital printing process for printing a liquid toner on a receiving medium according to any one of the preceding claims, which liquid toner comprises marker particles, a dispersant and a carrier liquid, which receiving medium comprises a barrier layer comprises on a first surface of the base layer, which barrier layer is configured to restrain movement of the carrier fluid to the base layer of the receiving medium.

The printed receiving medium according to claim 17, wherein the printed receiving medium has a screened level of 120% according to the screened test.

The printed receiving medium according to claim 17 or 18, wherein the barrier layer of the printing receiving medium is configured to provide adhesion to the marker particles of more than 70% according to the adhesive tape test.

A digital printing device for printing a liquid toner on a receiving medium, which comprises liquid toner marking particles, a dispersant and a carrier liquid, which device comprises: - a feed unit configured to feed a receiving medium, which comprises a base layer and a comprises a barrier layer on a first surface of the base layer, which feed unit is located upstream of an imaging unit; - the imaging unit comprises an imaging component adapted to hold an electric charge pattern and thereby form a latent image on a surface, a development component adapted to receive liquid toner, and to develop the latent image through the transferring the liquid toner to the imaging member according to the pattern; wherein the imaging unit is further configured to transfer the liquid toner from the imaging component to the barrier layer; - an adhesion forming unit configured to treat the transferred liquid toner image on the barrier layer to attach the marker particles of the transferred liquid toner image to the barrier layer; and a carrier fluid removal device configured to remove the carrier fluid from the transferred developed portion of the receiving medium.

The digital printing apparatus of claim 20, wherein the feed unit comprises a base layer feed unit and a barrier layer forming unit, the base layer feed unit being configured to feed a base layer to the barrier layer forming unit, which is configured to form a barrier layer on a first surface of the base layer.

The digital printing device of claim 21, wherein the barrier layer forming unit comprises; - a barrier coating unit configured to apply a barrier coating to the first surface of the receiving medium; - a barrier drying unit configured to dry the barrier coating, which is applied to the first surface of the receiving medium; - a moisture measuring unit configured to measure the humidity of the receiving medium when it is dried by the barrier drying unit; and - a control unit configured to control the barrier drying unit based on a measurement signal from the moisture measurement unit, which indicates a humidity level of the receiving medium.