GB2458198A

GB2458198A - Inkjet printer with solvent-based ink

Info

Publication number: GB2458198A
Application number: GB0900199A
Authority: GB
Inventors: David S Seuferling
Original assignee: Sericol Ltd
Current assignee: Sericol Ltd
Priority date: 2008-03-10
Filing date: 2009-01-07
Publication date: 2009-09-16
Also published as: GB0900199D0

Abstract

An inkjet printer comprises a bulk ink delivery system having a reservoir and an inkjet ink in fluid communication with a print-head, and an inline degassing system between the delivery system and the print-head. The inkjet ink comprises a thermoplastic carrier resin, a colouring agent, a di(C1-C4 alkyl) ester of a saturated dicarboxylic acid having 3-8 carbon atoms as a first solvent, and a second solvent in which the carrier resin is soluble. The dialkyl ester may be the dimethyl esters of butanedioic (succinic) acid, pentanedioic (glutaric) acid and/or hexanedioic (adipic) acid. The second solvent may be selected from ketones, esters, glycol ethers, alcohols or isoparaffins and is preferably propylene glycol monomethyl ether acetate. The carrier resin may be a vinyl chloride-vinyl acetate copolymer. A method of printing by applying the ink to a substrate using the printer is also disclosed.

Description

Ink-jet printer This invention relates to an ink-jet printer for a solvent-based ink.

In ink-jet printing processes minute droplets of black, white or coloured ink are ejected in a controlled manner from one or more reservoirs or printing heads through narrow nozzles on to a substrate which is moving relative to the reservoirs. The ejected ink forms an image on the substrate. For high-speed printing, the inks must flow rapidly from the printing heads, and, to ensure that this happens, they must have in use a low viscosity, typically below 100 mPas at 25°C although in most applications the viscosity should be below 50 mPas, and often below 25 mPas.

Typically, when ejected through the nozzles, the ink has a viscosity of less than 25 mPas, preferably 5-15 mPas and ideally 10.5 mPas at the jetting temperature which is often elevated to about 40°C (the ink might have a much higher viscosity at ambient temperature). The inks must also be resistant to drying or crusting in the reservoirs or nozzles. For these reasons, ink-jet inks for application at or near ambient temperatures are commonly formulated to contain a large proportion of a mobile liquid vehicle or solvent. In one common type of ink-jet ink this liquid is water -see for example the paper by Henry R. Kang in the Journal of Imaging Science, 3 5(3), pp. 179-1 88 (1991). In those systems, great effort must be made to ensure the inks do not dry in the head due to water evaporation. In another common type the liquid is a low-boiling solvent or mixture of solvents -see, for example, EP 0 314 403 and EP 0 424 714.

Commercially available solvent-based ink-jet inks such as Triangle VUV Solvent Ink for Vutek Ultravu Machines, Mimaki HS series for the JV-5 Printer, and Fujifilm Sericol Colors-Series ink produce a wide colour gamut, perform reliably with ink-jet printers and are capable of drying within a reasonable time at a suitable substrate temperature, for example 35 to 50°C. However, films produced by printing known solvent-based inks may demonstrate poor film toughness and/or poor adhesion to the printed substrate. This can be a particular problem where the printed substrate is a vinyl film, such as plasticised polyvinyl chloride (PVC).

Ink-jet printers include an ink path from an ink supply to a nozzle in the printhead from which ink drops are ejected. Ink drop ejection is controlled by pressurising ink in the ink path with an actuator, which may be for example a piezoelectric deflector, a thermal bubble jet generator or an electrostatically deflected element. In high performance printheads, the nozzle openings are very narrow and typically have a diameter of 50 microns or less. The ink is generally provided in a compressible bag housed inside a rigid cartridge. The cartridges have a limited capacity and it is therefore necessary to replace the cartridges frequently, which can lead to significant expense. Furthermore, cartridge replacement results in printer downtime. There is therefore a demand for cheaper and more efficient methods of providing ink to ink-jet printers.

There is therefore a requirement for an ink-jet printing system that overcomes the above disadvantages.

Accordingly, the present invention provides an ink-jet printer comprising: (i) a printhead, (ii) a bulk ink delivery system that comprises a reservoir and an ink-jet ink in fluid communication with the printhead, and (iii) an in-line degassing unit located between the bulk ink delivery system and the printhead; wherein the ink-jet ink comprises a first solvent that is at least one di(C1-C4 alkyl) ester of a saturated aliphatic dicarboxylic acid having 3 to 8 carbon atoms, at least one thermoplastic carrier resin, a second solvent in which the thermoplastic carrier resin is soluble, and at least one colouring agent.

The present invention will now be described with reference to the drawings, in which: Figure 1 shows a simple design of a membrane contactor that is suitable for use according to the present invention; Figure 2 shows a degassing unit according to the present invention; Figure 3 shows a bulk ink delivery system according to the present invention; and Figure 4 shows a flow diagram including the bulk ink delivery system and a membrane contactor according to the present invention.

When compared to known solvent based ink-jet inks, the inks used in the present invention are capable of providing superior film toughness and adhesion when applied to vinyl substrates. However, the inventors of the present application have discovered that these inks surprisingly provide a printed film of poor quality when used in a bulk ink delivery system. This problem has been overcome by providing an in-line degassing unit between the ink reservoir in the bulk ink delivery unit and the printhead. Thus, the printing machine of the present invention provides printed films having excellent colour gamut and reliability, and superior film toughness and adhesion when applied to vinyl substrates. Furthermore, the printing machine of the present invention is more economical to run than ink-jet printers that require the end user to purchase ink in pre-packaged cartridges.

The ink-jet printer of the present invention includes a bulk ink delivery system. By "bulk ink delivery system" is meant a system (i.e. device) that is adapted to hold large quantities of ink (> 2 1) that is refillable by the user. It provides a steady supply of ink to the printer through the use of mechanical pumps.

This is in contrast to ink supply systems that make use of replaceable ink cartridges.

A preferred bulk ink delivery system comprises, for each ink colour, a first reservoir and a second reservoir. A pumping system delivers ink from the first reservoir to the second reservoir and the second reservoir takes the place of the traditional ink cartridge in the printing machine. The second reservoir typically includes a level sensor mechanism that allows control of the ink height in the second reservoir, which controls the pressure of the ink at the print head. The first reservoir generally has a greater volume than the second reservoir, and can be refilled as necessary. The first reservoir will typically have a capacity in the range of 3-5 1 and the second reservoir will typically have a capacity of about 400 ml. Purchasing ink in a relatively large volume in order to replenish the first reservoir is generally more economical than replacing traditional ink cartridges, which have a limited capacity. A suitable bulk ink delivery system is disclosed in WO 2006/014280, for example. Bulk ink delivery systems are also commercially available, such as the Bulk Ink System (BIS) available from Mutob.

The degassing Unit used according to the present invention can be any degassing unit that is suitable for use with solvent based ink. The degassing unit removes bubbles and dissolved gases from the ink before the ink reaches the print head.

Membrane degassers are preferred for use in the invention because membrane separation of gases from the ink is carried out under mild conditions and the composition of the ink is therefore relatively unchanged. The degasser of the invention is most preferably a membrane contactor. Membrane contactors comprise a membrane that forms a barrier between a vacuum phase and the liquid to be treated, in this case ink-jet ink. Gases can pass through the membrane but liquids are retained by the membrane. When a vacuum is applied to one side of the membrane, gases in the ink will pass through the membrane and be carried away in the vacuum, reducing the dissolved gas content in the ink. The vacuum may be applied by a commonly available diaphragm pump, located inside or nearby the printing machine. The vacuum can be regulated by a needle valve to 700mbar � 5Ombar.

Suitable membrane contactors are commercially available under the name of Liqui-Cel�, Celgard�, SuperPhobic� and MiniModule� from Membrana-Charlotte, a division of Celgard, LLC, N.C., USA. SuperPhobic� 1x4 and 1x6 contactors are particularly preferred.

Accordingly, in a preferred embodiment the de-gassing unit comprises a membrane defining a first region and a second region, wherein the membrane forms a gas-permeable liquid-impermeable barrier between the first region and the second region, and the first region is under reduced pressure and the second region is in fluid communication with the bulk ink delivery system and the printhead.

Fig. 1 shows a simple design of a membrane contactor 16 that is suitable for use according to the present invention. The contactor 16, comprises a perforated core 17 having a first end 18 in fluid communication with an ink supply and a second end 19 in fluid communication with an ink delivery port 2. The ink delivery port 2, when in use in an ink-jet printer, allows the connection to the receiver of the ink-jet printer and subsequently the supply of the ink to the nozzles of the printhead. The ink delivery port 2 is a conventional design.

The contactor comprises a gas outlet port 4 which, when in use, is in fluid communication with a vacuum supply within the printing machine. The gas outlet port 4 is a conventional design.

A plurality of hollow fibres 9 formed form a membrane 5 surround the perforated core 17. The hollow fibres 9 have two ends 10, 11 and a lumen. The lumen of the hollow fibres is in fluid communication with the gas outlet port 4. The ink therefore is able to flow over the outer surface of the hollow fibres 9, therefore providing a large surface area over which gasses may diffuse through the membrane 5, and the removed gasses are drawn through the lumen by the applied vacuum and removed at the gas outlet port 4. Preferably, the perforated core 17 is tubular. Perforations 21 allow the ink to flow out of the perforated core 17.

The membrane 5 is preferably composed of a synthetic polymer, cellulose or synthetically modified cellulose. More preferably, the membrane is composed of a synthetic polymer selected from polyolefin, fluorinated polyolefin, polysulfone, polyethersulfone, polyester, polyetherimide, polyacrylonitrile, polyamide and polymethylmethacrylate (PMMA), together with copolymers and/or blends thereof.

Suitable example of a polyolefin are selected from polyethylene, polypropylene, polybutylene, poly(isobutylene) and poly(methylpentene), together with copolymers and/or blends thereof.

The membrane 5 preferably has a wall thickness of 5 to 1000 l.tm; a Gurley number of 6 to 13000 seconds per meter column of air; and an average pore size of 10 to 2000 nm. A Gurley number is the volume flow rate of air at a fixed pressure difference through a fixed area of sample, and thus indicates the resistance to gas flow.

The contactor also comprises fibre supports 22 which secure the ends of the hollow fibres and a shell 23 which encloses the fibres and fibre supports 22. The contactor may further comprise a baffle 20 located between fibre supports 22. The baffle 20 is preferably located equidistant from the first end 18 and the second end 19. In use, the baffle acts as a flow directing device to direct the ink radially outwards as shown by arrows 24 to maximise contact of the ink with the membrane thereby maximising gas removal. Preferably, core 17 is coaxial with shell 23, baffle 20 is equidistant from fibre supports 22 and in contact with core 17 and the density of hollow fibres 9 on either side of baffle are identical.

The first and second ends 10,11 of the hollow fibres are preferably secured at the fibre supports 22 in a resinous potting material using either thermosetting or thermoplastic materials, arid is preferably polyethylene. The fibre supports 22 may be cylindrical in cross section with sufficient thickness to provide support for the hollow fibres 9 and to withstand the pressure exerted on them during use.

The fibres may be open at the baffle and the lumen 12 of each hollow fibre may be open and exposed to the gas outlet port 4, so that there is fluid communication through the hollow fibre lumen from the first end 10 to the second end 11 of the hollow fibre. Alternatively, the fibres 9 may be closed at the baffle 20 and the end of the fibres distal to the baffle are open and in fluid communication with a gas outlet port 4 and a vacuum may be applied at each open end of the fibres.

The contactor 16 is housed within shell 23 which may be made of any resilient material such as polyethylene, polypropylene, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene copolymer tetrafluoroethylene (ECTFE), fluorinated ethylene polymer (FEP), polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS), fibre-reinforced plastic (FRP), a metal or a composite material. Shell 23 may have any length or any diameter.

In use, an ink containing dissolved gasses passes from the ink supply and into the contactor 16 via the first end 18, then into the core 17 and flows outside of core through perforations 21. The ink flows over the hollow fibres 9 and the baffle 20, if present, directs the ink radially across the hollow fibres. A vacuum is applied to the lumen of the hollow fibres 9 and dissolved gas diffuses from the ink into the lumen of the hollow fibres. Degassed ink passes out of the contactor via the second end 19 and to the ink delivery port 2 for use in an ink-jet printer.

The ink-jet printer of the present invention comprises an in-line degassing unit between the bulk ink delivery system and the printhead. This means that the degassing unit is in fluid communication with the bulk ink delivery system and the printheads and, in use, ink passes through the degassing unit as it is transferred from the bulk ink delivery system to the printhead. The degasser can be connected to the ink supply and the printhead using any suitable tubing and fittings, which would be known to the person skilled in the art.

Ink-jet printers generally comprise a mobile carriage for moving the printheads over the substrate to be printed. Although the degassing unit may be located on the mobile carriage, the degasser is preferably arranged such that the degassing unit is stationary during use. This means that the plumbing that connects the degasser to the ink delivery mechanism is simpler.

When the ink-jet printer of the invention comprises more than one ink reservoir, the inks having different colours, a degassing unit is preferably provided for each ink colour.

The ink-jet printer of the present invention comprises an ink-jet ink comprising a first solvent that is at least one di(C1-C4 alkyl) ester of a saturated aliphatic dicarboxylic acid having 3 to 8 carbon atoms; at least one thermoplastic carrier resin; a second solvent in which the thermoplastic carrier resin is soluble; and at least one colouring agent.

The di(C1-C4 alkyl) ester of a saturated aliphatic dicarboxylic acid having 3 to 8 carbon atoms is a compound of the following formula: R"O R'OR" in which R' represents (CH2)1 and R" may be the same or different and represents C1-C4 alkyl. The first solvent of is a compound of the above formula or a mixture of two or more compounds of the above formula. C1-C4 alkyl is a linear or branched alkyl radical having 1 to 4 carbon atoms. Preferably the ester is a dimethyl or diethyl ester. Particularly preferably the ester is a dimethyl ester.

The ink preferably comprises 15 to 30% by weight of at least one di(C1-C4 alkyl) ester of a saturated aliphatic dicarboxylic acid having 3 to 8 carbon atoms, more preferably to 25% by weight based on the total weight of the ink.

The ink-jet ink preferably comprises at least one di(C,-C4 alkyl) ester of a saturated aliphatic dicarboxylic acid having 4 to 6 carbon atoms. In other words, the ink preferably comprises a di(C1-C4 alkyl) ester of butanedioic acid (succinic acid), a di(C1-C4 alkyl) ester of pentanedioic acid (glutaric acid) a di(Ci-C4 alkyl) ester of hexanedioic acid (adipic acid), or a mixture thereof. More preferably the ink comprises the dimethyl ester of butanedioic acid (dimethyl succinate), the dimethyl ester of pentanedioic acid (dimethyl glutarate) or the dimethyl ester of hexanedioic acid (dimethyl adipate), or a mixture thereof. Most preferably the ink of the invention comprises a mixture of the dimethyl esters of butanedioic acid, pentanedioic acid and hexanedioic acid. Mixtures of the dimethyl esters of butanedioic acid, pentanedioic acid and hexanedioic acid are generally known as "dibasic esters" or "DBE" and are commercially available from Invista Speciality Intermediates, for example.

A typical DBE product comprises 55-65% by weight of the dimethyl ester of pentanedioic acid, 10-25% by weight of the dimethyl ester of hexanedioic acid and 15-25% by weight of the dimethyl ester of butanedloic acid, for example 59 wt% of the dimethyl ester of pentanedioic acid, 21 wt% of the dimethyl ester of hexanedioic acid and 20 wt% of the dimethyl ester of butanedioic acid together with trace amounts of methanol and water.

The ink comprises a second solvent in which the thermoplastic resin is soluble. The second solvent can be any solvent that is different from the first solvent and which is suitable for use in solvent based ink-jet inks. Suitable solvents are known to the person skilled in the art of ink-jet ink formulation and include ketones, esters, glycol ethers, alcohols, isoparaffins and mixtures thereof. Examples include ketones having a molecular weight of 75 to 150 and having a straight chain, branched, or cyclic structure such as cyclohexanone and diacetone alcohol; lactones such as gamma-butyrolactone; propylene glycol ethers and propylene glycol acetate esters; ethylene glycol ethers and ethylene glycol acetate esters; and acetate esters of alcohols having 3 to 8 carbon atoms such as tertiary butyl acetate. Such solvents are commercially available.

The ink preferably comprises 60 to 80% by weight of the second solvent, more preferably 65 to 75% by weight based on the total weight of the ink In a particularly preferred embodiment the second solvent is selected from mono-, di-or tripropylene glycol ethers, mono-, di-or tripropylene glycol acetates, mono-, di-or triethylene glycol ethers, mono-, di-or triethylene glycol acetates and mixtures thereof. By mono-, di-or tripropylene glycol ether is meant a compound that can be obtained by reacting one, two or three moles, respectively, of propylene oxide with one mole of alcohol. The alcohol preferably has 1 to 4 carbon atoms and is most preferably methanol. Similarly, mono-, di-or triethylene glycol ethers are compounds that can be obtained by reacting one, two or three moles, respectively, of ethylene oxide with one mole of an alcohol as described above. Mono-, di-or tripropylene glycol acetates and mono-, di-or triethylene glycol acetates are compounds that can be obtained by reacting a mono-, di-or tripropylene glycol ether or a mono-, di-or triethylene glycol ether as described above with acetic acid or acetic anhydride.

These solvents are commercially available from The Dow Chemical Company.

Preferred solvents include ethylene glycol monobutyl ether acetate (EB acetate), diethylene glycol mono ethyl ether acetate (DE acetate), propylene glycol monomethyl ether (PM), propylene glycol monomethyl ether acetate (PM acetate) and dipropylene glycol methyl ether (DPM). Most preferred are glycol ethers or glycol acetate esters based on propylene glycol. Such solvents are preferred because they are not classed as hazardous or pollutants.

The second solvent preferably has an evaporation rate of 0.1 to 0.5 relative to n-butyl acetate. The evaporation rate relative to n-butyl acetate for any particular solvent is readily available from commercial suppliers.

Preferably, the second solvent is PM acetate. Most preferably, the ink comprises a mixture of the dimethyl esters of butanedioic acid, pentanedioic acid and hexanedioic acid, and PM acetate.

The ink preferably comprises less than 5% by weight of water, more preferably less than 2% by weight of water and most preferably less than 1% by weight of water, based on the total weight of the ink.

The ink preferably comprises a first solvent and a second solvent as described above in a total amount of greater than 90% by weight, more preferably greater than 95% by weight and most preferably greater than 99% by weight, based on the total weight of solvent present in the ink.

Preferably the ink comprises a mixture of the dimethyl esters of butanedioic acid, pentanedioic acid and hexanedioic acid; and PM acetate in a total amount of greater than 90% by weight, more preferably greater than 95% by weight and most preferably greater than 99% by weight based on the total weight of solvent present in the ink.

The ink also includes a thermoplastic carrier resin. Carrier resins suitable for use in solvent-based ink-jet inks are known in the art. Examples of suitable resins include acrylic resins, epoxy resins, ketone resins, nitrocellulose resins, phenoxy resins, polyester resins, PVC resins, polyvinyl acetate resins or mixtures or copolymers thereof. A preferred resin comprises a copolymer of vinyl chloride and vinyl acetate.

Such copolymers a commercially available and include Vinnol� H 14/36, available from Wacker Polymer Systems GmbH & Co. KG, Burghausen, for example.

The ink preferably comprises I to 5% by weight of carrier resin, more preferably 1 to 3% by weight based on the total weight of the ink.

The ink also includes a colouring agent, which may be either dissolved or dispersed in the liquid medium of the ink. Preferably the colouring agent is a dispersible pigment, of the types known in the art and commercially available such as such as, for example under the trade-names Microlith, Cinquasia, and Irgalite (all from Ciba Speciality Chemicals), Paliotol (available from BASF plc), Hostaperm (available from Clariant UK) and Sun Yellow 271-9151 and Yellow 4G0 (available from Sun Chemical Performance Pigments). The pigment may be of any desired colour such as, for example, Pigment Yellow 13, Pigment Yellow 83, Pigment Red 9, Pigment Red 184, Pigment Blue 15:3, Pigment Green 7, Pigment Violet 19, Pigment Black 7.

Especially useful are black and the colours required for trichromatic process printing (i.e. CMYK), although other colour sets may be used, such as Hexachrome (CMYKOG). Mixtures of pigments may be used in the same ink if required.

The colorant is preferably present in the ink of the invention in an amount of from I to 10% by weight, preferably 3 to 8% by weight based on the total weight of the ink.

Other components of types known in the art may be present in the ink to improve the properties or performance. These components may be, for example, dispersants, surface tension modifiers, defoamers, stabilisers against deterioration by heat or light, reodorants, flow or slip aids, biocides and identifying tracers. Inks of the present invention may, for example, comprise 0.50 to 3% by weight of a dispersant and/or 0.02 to 0.10% by weight of a surface tension modifier. Suitable dispersants include Solsperse� 32000 (available from Lubrizol) and BYK-l 68 (available from BTK Chemie), for example. Suitable surface tension modifiers include polydimethyl siloxane polymers such as TegoGlide 410 (available from Tego Chemie, a subsidiary of Degussa).

The ink preferably has a viscosity below 100 mPas at 25°C, more preferably below 50 mPas, and most preferably below 25 mPas. Viscosity may be measured using a digital Brookfield viscometer fitted with a thermostatically controlled cup and spindle arrangement, such as model LDVI+ with the ULA spindle and cup arrangement.

The inks may be prepared by known methods such as, for example, stirring with a high-speed water-cooled stirrer, or milling on a horizontal bead-mill.

The ink-jet printer of the invention may comprise a single reservoir of an ink-jet ink as defined above. Alternatively, the ink-jet printer of the invention may comprise more than one reservoir of ink-jet ink, the inks having different colours. The ink-jet printer of the invention preferably comprises reservoirs of inks having the colours required for trichromatic process printing (i.e. CMYK).

As discussed above, ink-jet printers include an ink path from an ink supply to a nozzle in the printhead from which ink drops are ejected. Ink drop ejection is controlled by

II

pressurising ink in the ink path with an actuator, which may be for example a piezoelectric deflector, a thermal bubble jet generator or an electrostatically deflected element. The ink-jet printer of the invention can comprise any arrangement of printhead, nozzle, means for supplying ink from the ink supply to the nozzle, and means for ejecting the ink from the nozzle that is suitable for ink-jet printing a solvent-based ink-jet ink. Such arrangements are well-known to the person skilled in the art.

The invention also provides a method of ink-jet printing comprising providing the ink-jet printer as described hereinabove and applying the ink-jet ink to a substrate.

Preferably, the substrate is a vinyl substrate, and particularly preferably the substrate comprises polyvinyl chloride. In one embodiment the polyvinyl chloride is plasticised. The invention also provides a printed substrate obtainable by the method according to the invention.

One of the advantages of the present invention is that existing ink-jet printers that use replaceable ink cartridges can be readily adapted to provide an ink-jet printer according to the present invention. In particular, the ink cartridge traditionally used in ink jet printers can be replaced with a bulk ink delivery system, and a degassing unit can be provided in-line between the ink supply and the printhead. Once adapted in this way the printer is able to provide a printed a film of the above-defined ink having excellent print quality. Examples of commercially available printers that can be adapted to provide an ink-jet printer according to the present invention include printers available from Mutoh such as the "Blizzard", "Spitfire", "Valuejet", "Toucan" and "Falcon".

Claims

Claims 1. An ink-jet printer comprising: (1) a printhead, (ii) a bulk ink delivery system that comprises a reservoir and an ink-jet ink in fluid communication with the printhead, and (iii) an in-line degassing unit located between the bulk ink delivery system and the printhead; wherein the ink-jet ink comprises a first solvent that is at least one di(C1-C4 alkyl) ester of a saturated aliphatic dicarboxylic acid having 3 to 8 carbon atoms, at least one thermoplastic carrier resin, a second solvent in which the thermoplastic carrier resin is soluble, and at least one colouring agent.
2. An ink-jet printer according to claim 1, wherein the dc-gassing unit comprises a membrane defining a first region and a second region, wherein the membrane forms a gas-permeable liquid-impermeable barrier between the first region and the second region, and the first region is under reduced pressure and the second region is in fluid communication with the bulk ink delivery system and the printhead.
3. An ink-jet printer according to claim 2, wherein the membrane is composed of a synthetic polymer, cellulose or synthetically modified cellulose.
4. An ink-jet printer according to claim 2 or 3, wherein the membrane is composed of a synthetic polymer selected from polyolefin, fluorinated polyolefin, polysulfone, polyethersulfone, polyester, polyetherimide, polyacrylnitrile, polyamide and polymethylmethacrylate (PMMA), together with copolymers and/or blends thereof.
5. An ink-jet printer according to claim 4, wherein the polymer is a polyolefin selected from polyethylene, polypropylene, polybutylene, poly(isobutylene) and poly(methylpentene), together with copolymers and/or blends thereof.
6. An ink-jet printer according to any of claims 2 to 5, wherein the membrane has a wall thickness of 5 to 1000 tm.
7. An ink-jet printer according to any of claims 2 to 6, wherein the membrane has a Gurley number of 6 to 13000 seconds per meter column of air.
8. An ink-jet printer according to any of claims 2 to 7, wherein the membrane has an average pore size of 10 to 2000 nm.
9. An ink-jet printer according to any preceding claim, wherein the ink-jet ink comprises 15 to 30% by weight of said at least one di(C1-C4 alkyl) ester of a saturated aliphatic dicarboxylic acid having 3 to 8 carbon atoms, based on the total weight of the ink.
10. An ink-jet printer according to any preceding claim, wherein the ink-jet ink comprises 20 to 25% by weight of said at least one or more di(C1-C4 alkyl) ester of a saturated aliphatic dicarboxylic acid having 3 to 8 carbon atoms, based on the total weight of the ink.
11. An ink-jet printer according to any preceding claim, wherein the dicarboxylic acid has 4 to 6 carbon atoms.
12. An ink-jet printer according to any preceding claim, wherein the Ci-C4 alkyl is methyl or ethyl, preferably methyl.
13. An ink-jet printer according to any preceding claim, wherein said at least one di(C1-C4 alkyl) ester of a saturated aliphatic dicarboxylic acid having 3 to 8 carbon atoms comprises the dimethyl ester of butanedioic acid, the dimethyl ester of pentanedioic acid, the dimethyl ester of hexanedioic acid, or a mixture thereof.
14. An ink-jet printer according to any preceding claim, wherein said at least one di(C1-C4 alkyl) ester of a saturated aliphatic dicarboxylic acid having 3 to 8 carbon atoms comprises a mixture of the dimethyl esters of butanedioic acid, pentanedioic acid and hexanedioic acid.
15. An ink-jet printer according to any preceding claim, wherein said second solvent is selected from ketones, esters, glycol ethers, alcohols, isoparaffins and mixtures thereof.
16. An ink-jet printer according to any preceding claim, wherein the ink comprises 60 to 80% by weight of said second solvent based on the total weight of the ink, preferably 65 to 75% by weight.
17. An ink-jet printer according to any preceding claim, wherein said second solvent is selected from mono-, di-or tripropylene glyco ethers; mono-, di-or tripropylene glycol acetates; mono-, di-or triethylene glycol ethers; mono-, di-or triethylene glycol acetates and mixtures thereof.
18. An ink-jet printer according to any preceding claim, wherein said second solvent is selected from ethylene glycol monobutyl ether acetate (EB acetate), diethylene glycol mono ethyl ether acetate (DE acetate), propylene glycol monomethyl ether (PM), propylene glycol monomethy! ether acetate (PM acetate), dipropylene glycol methyl ether (DPM) and mixtures thereof.
19. An ink-jet printer according to any preceding claim, wherein said second solvent is PM acetate.
20. An ink-jet printer according to any preceding claim, wherein the ink comprises 15 to 30% by weight of a mixture of the dimethyl esters of butanedioic acid, pentanedioic acid and hexanedioic acid and 60 to 80% by weight of PM acetate.
21. An ink-jet printer according to any preceding claim, wherein the ink comprises less than 5% by weight of water based on the total weight of the ink, preferably less than 2%, more preferably less than 1%.
22. An ink-jet printer according to any preceding claim, wherein the ink comprises said first solvent and said second solvent in a total amount of greater than 90% by weight based on the total weight of solvent present in the ink, preferably greater than 95% by weight and most preferably greater than 99% by weight.
23. An ink-jet printer according to any preceding claim, wherein the carrier resin comprises an acrylic resin, an epoxy resin, a ketone resin, a nitrocellulose resin, a phenoxy resin, a polyester resin, a PVC resin, a polyvinyl acetate resin or a mixture or copolymer thereof.
24. An ink-jet printer according to any preceding claim, wherein the carrier resin comprises a copolymer of vinyl chloride and vinyl acetate.
25. An ink-jet printer according to any preceding claim, wherein the ink comprises I to 5% by weight of carrier resin, more preferably I to 3% by weight, based on the total weight of the ink.
26. An ink-jet printer according to any preceding claim, wherein the ink comprises 1 to 10% by weight of a colouring agent, preferably 3 to 8% by weight, based on the total weight of the ink.
27. A method of ink-jet printing comprising providing the ink-jet printer as claimed in any preceding claim and applying the ink-jet ink to a substrate.
28. The method according to claim 27, wherein the substrate is a vinyl substrate.
29. The method according to claim 28, wherein the substrate comprises polyvinyl chloride.
30. The method according to claim 29, wherein the polyvinyl chloride is plasticised.
31. A printed substrate obtainable by the method of any one of claims 27 to 30.