WO2007135394A1 - Inkjet print head - Google Patents

Inkjet print head Download PDF

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Publication number
WO2007135394A1
WO2007135394A1 PCT/GB2007/001851 GB2007001851W WO2007135394A1 WO 2007135394 A1 WO2007135394 A1 WO 2007135394A1 GB 2007001851 W GB2007001851 W GB 2007001851W WO 2007135394 A1 WO2007135394 A1 WO 2007135394A1
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WO
WIPO (PCT)
Prior art keywords
formula
compound
print head
group
plasma
Prior art date
Application number
PCT/GB2007/001851
Other languages
French (fr)
Inventor
Stephen Coulson
Original Assignee
P2I Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by P2I Ltd filed Critical P2I Ltd
Publication of WO2007135394A1 publication Critical patent/WO2007135394A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1606—Coating the nozzle area or the ink chamber
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C59/00—Surface shaping of articles, e.g. embossing; Apparatus therefor
    • B29C59/14—Surface shaping of articles, e.g. embossing; Apparatus therefor by plasma treatment
    • B29C59/142—Surface shaping of articles, e.g. embossing; Apparatus therefor by plasma treatment of profiled articles, e.g. hollow or tubular articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/162—Manufacturing of the nozzle plates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/164—Manufacturing processes thin film formation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F114/00—Homopolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
    • C08F114/18—Monomers containing fluorine
    • C08F114/185—Monomers containing fluorine not covered by the groups C08F114/20 - C08F114/28
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/46—Polymerisation initiated by wave energy or particle radiation
    • C08F2/52—Polymerisation initiated by wave energy or particle radiation by electric discharge, e.g. voltolisation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
    • C08J7/12—Chemical modification
    • C08J7/16—Chemical modification with polymerisable compounds
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M10/00—Physical treatment of fibres, threads, yarns, fabrics, or fibrous goods made from such materials, e.g. ultrasonic, corona discharge, irradiation, electric currents, or magnetic fields; Physical treatment combined with treatment with chemical compounds or elements
    • D06M10/02—Physical treatment of fibres, threads, yarns, fabrics, or fibrous goods made from such materials, e.g. ultrasonic, corona discharge, irradiation, electric currents, or magnetic fields; Physical treatment combined with treatment with chemical compounds or elements ultrasonic or sonic; Corona discharge
    • D06M10/025—Corona discharge or low temperature plasma
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M14/00—Graft polymerisation of monomers containing carbon-to-carbon unsaturated bonds on to fibres, threads, yarns, fabrics, or fibrous goods made from such materials
    • D06M14/18—Graft polymerisation of monomers containing carbon-to-carbon unsaturated bonds on to fibres, threads, yarns, fabrics, or fibrous goods made from such materials using wave energy or particle radiation

Definitions

  • the present invention relates to novel products in the form of ink jet print heads, the surfaces of which are modified to provide enhanced non-wetting properties so as to reduce accumulation of ink on the surface around the nozzles of the print head, as well as to processes for their production.
  • An inkjet print head comprises a nozzle plate in which are formed a multiplicity of nozzles through which the ink is directed at the material on which printing is to be carried out.
  • the nozzle outlets are of relatively small diameter, especially in print heads designed to deliver very high printing resolution. This brings with it the problem that the nozzles are susceptible to blockage or partial blockage which leads to reduced print quality. This is especially likely to be problematic if ink is allowed to build up on the nozzle plate surface around the nozzle outlets.
  • Polymers suitable for coating a nozzle plate should suitably have the property that they repel the liquid ink, so that if ink should stray onto the surface it will form discrete beads rather than spreading across the surface.
  • a surface with this attribute may be described as a non-wetting surface. Wetting of the plate surface can interfere with the free-flowing of ink through the nozzles and accumulation of large amounts of ink in the region around the nozzles can cause blockage of the nozzles.
  • a non-wetting coating which reduces these effects can significantly enhance the print head performance.
  • Examples of polymers which have been deposited on printer heads to provide such a non-wetting surface include block polymers as discussed, for example, in US 6,345,880 which describes a sputtering coating technique. Printer heads have also been coated by cross-linking with fluorinated organic compounds such as fluorinated organosilanes, as described in US 5,910,372.
  • Plasma deposition techniques have been quite widely used for the deposition of polymeric coatings onto a range of surfaces, and in particular onto fabric surfaces. This technique is recognised as being a clean, dry technique that generates little waste compared to conventional wet chemical methods. Using this method, plasmas are generated from organic molecules, which are subjected to an electrical field. When this is done in the presence of a substrate, the radicals of the compound in the plasma react on the substrate to form a polymer film. Conventional polymer synthesis tends to produce structures containing repeat units that bear a strong resemblance to the monomer species, whereas a polymer network generated using a plasma can be extremely complex.
  • the properties of the resultant coating can depend upon the nature of the substrate as well as the nature of the monomer used and conditions under which it is deposited. Formation of an ink-repellent film by continuous wave plasma processing using a compound containing fluorine or a silane compound on a previously roughened surface of an ink jet nozzle plate is described in JP 2000326514. Pulsed plasma deposition of a polymeric coating onto the surface of an ink jet print head has not hitherto been described.
  • an improved ink jet print head may be provided. Pre-roughening of the surface of the nozzle plate is not required. Using such improved ink jet print heads, the quality and reliability of inkjet printing may be improved and the need for print head maintenance may be reduced.
  • modification of the surface of the nozzle plate to impart non-wetting properties may be brought by chemical modification of surface groups.
  • Plasma processing to achieve non-wetting properties may be achieved, for example, by exposing the surface to plasma comprising small molecules such as CF 4 and a variety of saturated and unsaturated hydrocarbon and fluorocarbon compounds (see, for example, "Plasma Polymerisation", Academic Press Inc. (London) Ltd. 1985). Longer chain semi and fully fluorinated compounds may also be used to impart non-wetting properties.
  • the present invention provides an inkjet print head comprising a nozzle plate having a non-wetting polymeric coating formed on the surface thereof by pulsed plasma deposition.
  • a nozzle plate having a non-wetting polymeric coating formed on the surface thereof by pulsed plasma deposition. Any monomeric compound or gas which undergoes plasma polymerisation or modification of the surface to form a non-wetting, water-repellent polymeric coating layer or surface modification on the surface of the nozzle plate may suitably be used.
  • Suitable monomers which may be used include those known in the art to be capable of producing water-repellent polymeric coatings on substrates by plasma polymerisation including, for example, carbonaceous compounds having reactive functional groups, particularly substantially -CF3 dominated perfluoro compounds (see WO 97/38801) , perfluorinated alkenes (Wang et al., Chem Mater 1996, 2212-2214) , hydrogen containing unsaturated compounds optionally containing halogen atoms or perhalogenated organic compounds of at least 10 carbon atoms ( see WO 98/58117), organic compounds comprising two double bonds (WO 99/64662), saturated organic compounds having an optionally substituted alky chain of at least 5 carbon atoms optionally interposed with a heteroatom (WO 00/05000), optionally substituted alkynes (WO 00/20130), polyether substituted alkenes (US 6,482,531B) and macrocycles containing at least one heteroatom (US 6,329,024B), the contents of
  • the invention provides an ink jet print head comprising a nozzle plate having a polymeric coating, formed by exposing at least the nozzle plate of the print head to pulsed plasma comprising a compound of formula (I)
  • R 1 , R 2 and R 3 are independently selected from hydrogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R 4 is a group X-R 5 where R 5 is an alkyl or haloalkyl group and X is a bond; a group of formula -C(O)O(CH 2 ) n Y- where n is an integer of from 1 to 10 and Y is a bond or a sulphonamide group; or a group -(O)pR 6 (O) q (CH 2 ) t - where R 6 is aryl optionally substituted by halo, p is 0 or 1, q is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where q is 1, t is other than 0, for a sufficient period of time to allow a non-wetting polymeric layer to form on the surface of the nozzle plate.
  • the expression "non-wetting polymeric layer” refers to poly
  • halo or “halogen” refers to fluorine, chlorine, bromine and iodine. Particularly preferred halo groups are fluoro.
  • aryl refers to aromatic cyclic groups such as phenyl or napthyl, in particular phenyl.
  • alkyl refers to straight or branched chains of carbon atoms, suitably of up to 20 carbon atoms in length.
  • alkenyl refers to straight or branched unsaturated chains suitably having from 2 to 20 carbon atoms.
  • Haloalkyl refers to alkyl chains as defined above which include at least one halo substiruent.
  • Suitable haloalkyl groups for R 1 , R 2 , R 3 and R 5 are fluoroalkyl groups.
  • the alkyl chains may be straight or branched and may include cyclic moieties.
  • the alkyl chains suitably comprise 2 or more carbon atoms, suitably from 2-20 carbon atoms and preferably from 6 to 12 carbon atoms.
  • alkyl chains are generally preferred to have from 1 to 6 carbon atoms.
  • R 5 is a haloalkyl, and more preferably a perhaloalkyl group, particularly a perfluoroalkyl group of formula C m F 2m+ i where m is an integer of 1 or more, suitably from 1- 20, and preferably from 4-12 such as 4, 6 or 8.
  • Suitable alkyl groups for R 1 , R 2 and R 3 have from 1 to 6 carbon atoms.
  • R 1 , R 2 and R 3 are hydrogen.
  • R 1 , R 2 , R 3 are all hydrogen, hi yet a further embodiment however R 3 is an alkyl group such as methyl or propyl.
  • n is an integer which provides a suitable spacer group.
  • n is from 1 to 5, preferably about 2.
  • Suitable sulphonamide groups for Y include those of formula -N(R 7 )SO 2 " where R 7 is hydrogen or alkyl such as C ⁇ alkyl, in particular methyl or ethyl.
  • the compound of formula (I) is a compound of formula (II)
  • R 5 is as defined above in relation to formula (I).
  • the compound of formula (I) is an aery late of formula m
  • n and R 5 as defined above in relation to formula (I) and R 7 is hydrogen, C 1-I o alkyl, or C 1-1( )haloalkyl.
  • R 7 is hydrogen or such as methyl.
  • a particular example of a compound of formula (III) is a compound of formula (IV)
  • R 7 is as defined above, and in particular is hydrogen and x is an integer of from 1 to 9, for instance from 4 to 9, and preferably 7.
  • the compound of formula (TV) is lH ⁇ H ⁇ H ⁇ H-heptadecafluorodecylacylate.
  • the polymeric coating is formed by exposing at least the nozzle plate of the print head to pulsed plasma comprising one or more organic monomeric compounds, at least one of which comprises two carbon-carbon double bonds for a sufficient period of time to allow a polymeric layer to form on the surface of the nozzle plate.
  • the compound with more than one double bond comprises a compound of formula (V)
  • R 8 , R 9 , R 10 , R 11 , R 12 , and R 13 are all independently selected from hydrogen, halo, alkyl, haloalkyl or aryl optionally substituted by halo; and Z is a bridging group.
  • Suitable bridging groups Z for use in the compound of formula (V) are those known in the polymer art. In particular they include optionally substituted alkyl groups which may be interposed with oxygen atoms. Suitable optional substituents for bridging groups Z include perhaloalkyl groups, in particular perfluoroalkyl groups.
  • the bridging group Z includes one or more acyloxy or ester groups.
  • the bridging group of formula Z is a group of sub-formula (VI)
  • n is an integer of from 1 to 10, suitably from 1 to 3
  • each R 14 and R 15 is independently selected from hydrogen, alkyl or haloalkyl.
  • R 8 , R 9 , R 10 , R 11 , R 12 , and R 13 are haloalkyl such as fluoroalkyl, or hydrogen. In particular they are all hydrogen.
  • the compound of formula (V) contains at least one haloalkyl group, preferably a perhaloalkyl group.
  • the polymeric coating is formed by exposing at least the nozzle plate of the print head to pulsed plasma comprising a compound of comprising a monomeric saturated organic compound, said compound comprising an optionally substituted alkyl chain of at least 5 carbon atoms optionally interposed with a heteroatom for a sufficient period of time to allow a polymeric layer to form on the surface of the nozzle plate.
  • saturated means that the monomer does not contain multiple bonds (i.e. double or triple bonds) between two carbon atoms which are not part of an aromatic ring.
  • heteroatom includes oxygen, sulphur, silicon or nitrogen atoms. Where the alkyl chain is interposed by a nitrogen atom, it will be substituted so as to form a secondary or tertiary amine. Similarly, silicons will be substituted appropriately, for example with two alkoxy groups.
  • Particularly suitable monomeric organic compounds are those of formula (VET)
  • R 16 , R 17 , R 18 ' R 19 and R 20 are independently selected from hydrogen, halogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R 21 is a group X-R 22 where R 22 is an alkyl or haloalkyl group and X is a bond; a group of formula -C(O)O(CH 2 ) X Y- where x is an integer of from 1 to 10 and Y is a bond or a sulphonamide group; or a group - (O)pR 23 (O) s (CH 2 )r where R 23 is aryl optionally substituted by halo, p is 0 or 1, s is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where s is 1, t is other than 0.
  • Suitable haloalkyl groups for R 16 , R 17 , R 18 , R 19 , and R 20 are fluoroalkyl groups.
  • the alkyl chains may be straight or branched and may include cyclic moieties and have, for example from 1 to 6 carbon atoms.
  • the alkyl chains suitably comprise 1 or more carbon atoms, suitably from 1-20 carbon atoms and preferably from 6 to 12 carbon atoms.
  • R 22 is a haloalkyl, and more preferably a perhaloalkyl group, particularly a perfluoroalkyl group of formula C z F 2z+ i where z is an integer of 1 or more, suitably from 1-20, and preferably from 6-12 such as 8 or 10.
  • y is an integer which provides a suitable spacer group.
  • y is from 1 to 5, preferably about 2.
  • Suitable sulphonamide groups for Y include those of formula -N(R 23 )SO 2 " where R 23 is hydrogen, alkyl or haloalkyl such as Ci ⁇ alkyl, in particular methyl or ethyl.
  • the monomeric compounds used in the method of the invention preferably comprises an C ⁇ . 25 alkane optionally substituted by halogen, in particular a perhaloalkane, and especially a perfluoroalkane.
  • the polymeric coating is formed by exposing at least the nozzle plate of the print head to pulsed plasma comprising an optionally substituted alkyne for a sufficient period of time to allow a polymeric layer to form on the surface of the nozzle plate.
  • the alkyne compounds used in the method of the invention comprise chains of carbon atoms, including one or more carbon-carbon triple bonds.
  • the chains may be optionally interposed with a heteroatom and may carry substituents including rings and other functional groups.
  • Suitable chains which may be straight or branched, have from 2 to 50 carbon atoms, more suitably from 6 to 18 carbon atoms. They may be present either in the monomer used as a starting material, or may be created in the monomer on application of the plasma, for example by the ring opening
  • Particularly suitable monomeric organic compounds are those of formula (VEI) R ⁇ -C ⁇ C-X ⁇ R 25 (v ⁇ i)
  • R 24 is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl optionally substituted by halo;
  • X 1 is a bond or a bridging group
  • R >25 is an alkyl, cycloalkyl or aryl group optionally substituted by halogen.
  • Suitable bridging groups X 1 include groups of formulae
  • Particular alkyl groups for R 26 include C 1-O alkyl, in particular, methyl or ethyl.
  • R 24 is alkyl or haloalkyl, it is generally preferred to have from 1 to 6 carbon atoms.
  • Suitable haloalkyl groups for R 24 include fluoroalkyl groups.
  • the alkyl chains may be straight or branched and may include cyclic moieties.Preferably however R 24 is hydrogen.
  • R 25 is a haloalkyl, and more preferably a perhaloalkyl group, particularly a perfluoroalkyl group of formula C 1 F 21+I where r is an integer of 1 or more, suitably from 1-20, and preferably from 6-12 such as 8 or 10.
  • the compound of formula (VTS) is a compound of formula (IX)
  • R 27 is haloalkyl, in particular a perhaloalkyl such as a C ⁇ -u perfluoro group like CeFi 3 .
  • the compound of formula (VIII) is a compound of formula (X)
  • p is an integer of from 1 to 20, and R 27 is as defined above in relation to formula (IX) above, in particular, a group CgF] 7 .
  • p is an integer of from 1 to 6, most preferably about 2.
  • R 26 is as defined above an in particular is ethyl
  • R 27 is as defined in relation to formula (IX), in particular a group C 8 F 17 .
  • the alkyne monomer used in the process of the invention is a compound of formula (XTV)
  • R 28 C ⁇ C(CH 2 ) n SiR 29 R 30 R 31 (XTV) where R 28 is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl optionally substituted by halo, R 29 , R 30 and R 31 are independently selected from alkyl or alkoxy, in particular Q -6 alkyl or alkoxy.
  • Preferred groups R 28 are hydrogen or alkyl, in particular C 1-6 alkyl.
  • R 29 , R 30 and R 31 are C 1-6 alkoxy in particular ethoxy.
  • the expression "in a gaseous state” refers to gases or vapours, either alone or in mixture, as well as aerosols.
  • the invention is applicable to any ink jet print head conventional in the art, including thermal ink jet print heads and piezoelectric ink jet heads.
  • the formation of the polymeric layer on the surface of the nozzle plate may occur before or after the nozzle plate is formed from a blank.
  • the nozzle plate which may be integral with the print head or which may be separately attached to the print head, may be formed from any suitable material conventional in the art such as polymers, metals or glass.
  • Print heads treated in this way exhibit enhanced non-wetting properties and may advantageously be used in ink jet printing processes to minimise problems associated with clogging of the nozzles which are commonly experienced with known ink jet print heads.
  • Precise conditions under which the plasma polymerization takes place in an effective manner will vary depending upon factors such as the nature of the polymer, the print head device etc. and will be determined using routine methods and/or the techniques.
  • Suitable plasmas for use in the method of the invention include non-equilibrium plasmas such as those generated by radiofrequencies (Rf), microwaves or direct current (DC). They may operate at atmospheric or sub-atmospheric pressures as are known in the art. In particular however, they are generated by radiofrequencies (Rf).
  • Rf radiofrequencies
  • DC direct current
  • Various forms of equipment may be used to generate gaseous plasmas. Generally these comprise containers or plasma chambers in which plasmas may be generated. Particular examples of such equipment are described for instance in WO2005/089961 and WO02/28548, but many other conventional plasma generating apparatus are available.
  • the item to be treated is placed within a plasma chamber together with the material to be deposited in gaseous state, a glow discharge is ignited within the chamber and a suitable voltage is applied, which may be pulsed.
  • the gas used within the plasma may comprise a vapour of the monomeric compound alone, but it may be combined with a carrier gas, in particular, an inert gas such as helium or argon.
  • helium is a preferred carrier gas as this can minimise fragmentation of the monomer.
  • the relative amounts of the monomer vapour to carrier gas is suitably determined in accordance with procedures which are conventional in the art.
  • the amount of monomer added will depend to some extent on the nature of the particular monomer being used, the nature of the substrate being treated, the size of the plasma chamber etc.
  • monomer is delivered in an amount of from 50- 250mg/min, for example at a rate of from 100-150mg/min.
  • Carrier gas such as helium is suitably administered at a constant rate for example at a rate of from 5-90, for example from 15-30sccm.
  • the ratio of monomer to carrier gas will be in the range of from 100:0 to 1:100, for instance in the range of from 10:0 to 1:100, and in particular about 1:0 to 1:10. The precise ratio selected will be so as to ensure that the flow rate required by the process is achieved.
  • a preliminary continuous power plasma may be struck for example for from 2- 10 minutes within the chamber. This may act as a surface pre-treatment step, ensuring that the monomer attaches itself readily to the surface, so that as polymerisation occurs, the coating "grows" on the surface.
  • the pre-treatment step may be conducted before monomer is introduced into the chamber, in the presence of only an inert gas.
  • the plasma is then suitably switched to a pulsed plasma to allow polymerisation to proceed, at least when the monomer is present.
  • a glow discharge is suitably ignited by applying a high frequency voltage, for example at 13.56MHz. This is applied using electrodes, which may be internal or external to the chamber, but in the case of larger chambers are internal.
  • the gas, vapour or gas mixture is supplied at a rate of at least 1 standard cubic centimetre per minute (seem) and preferably in the range of from 1 to lOOsccm.
  • this is suitably supplied at a rate of from 80- 300mg/minute, for example at about 120mg per minute depending upon the nature of the monomer, whilst the pulsed voltage is applied.
  • Gases or vapours may be drawn or pumped into the plasma region.
  • gases or vapours may be drawn into the chamber as a result of a reduction in the pressure within the chamber, caused by use of an evacuating pump, or they may be pumped or injected into the chamber as is common in liquid handling.
  • Polymerisation is suitably effected using vapours of compounds of formula (I), which are maintained at pressures of from 0.1 to 200mtorr, suitably at about 80-100mtorr.
  • the applied fields are suitably of power of from 40 to 500W, suitably at about IOOW peak power, applied as a pulsed field.
  • the pulses are applied in a sequence which yields very low average powers, for example in a sequence in which the ratio of the time on : time off is in the range of from 1:500 to 1:1500.
  • Particular examples of such sequence are sequences where power is on for 20-50 ⁇ s, for example about 30 ⁇ s, and off for from lOOO ⁇ s to 30000 ⁇ s, in particular about 20000 ⁇ s.
  • Typical average powers obtained in this way are 0.01 W.
  • the fields are suitably applied from 30 seconds to 90 minutes, preferably from 5 to 60 minutes, depending upon the nature of the compound of formula (I) and the nozzle plate.
  • a plasma chamber used is of sufficient volume to accommodate multiple print heads .
  • the plasma is created with a voltage as a pulsed field, at an average power of from 0.001 to 500w/m 3 , for example at from 0.001 to 100w/m 3 and suitably at from 0.005 to 0.5w/m 3 .
  • These conditions are particularly suitable for depositing good quality uniform coatings, in large chambers, for example in chambers where the plasma zone has a volume of greater than 500cm 3 , for instance 0.5m 3 or more, such as from 0.5m 3 -10m 3 and suitably at about Im 3 .
  • the layers formed in this way have good mechanical strength.
  • the dimensions of the chamber will be selected so as to accommodate the particular print head being treated.
  • generally cuboid chambers may be suitable for a wide range of applications, but if necessary, elongate or rectangular chambers may be constructed or indeed cylindrical, or of any other suitable shape.
  • the chamber may be a sealable container, to allow for batch processes, or it may comprise inlets and outlets for the print head device, to allow it to be utilised in a continuous process.
  • the pressure conditions necessary for creating a plasma discharge within the chamber are maintained using high volume pumps, as is conventional for example in a device with a "whistling leak".
  • high volume pumps as is conventional for example in a device with a "whistling leak”.
  • the invention provides a method for enhancing the free-flowing properties of ink through a printer head during printing , said method comprising using a printer head wherein at least the nozzle plate thereof has a non-wetting polymeric coating or surface modification formed by plasma processing.
  • the nozzle plate material or sub-assembly is placed in a plasma deposition chamber, a glow discharge is ignited within said chamber, and a voltage applied as a pulsed field.
  • a print head was placed into a plasma chamber with a processing volume of ⁇ 300 litres.
  • the chamber was connected to supplies of the required gases or vapours, via a mass flow controller and/or liquid mass flow meter and a mixing injector as appropriate.
  • the chamber was evacuated to between 3 - 10 mtorr base pressure before allowing helium into the chamber at 20 seem until a pressure of 80 mtorr was reached.
  • a continuous power plasma was then struck for 4 minutes using RF at 13.56 MHz at 300 W. After this period, lH,lH,2H,2H-heptadecafluorodecylacylate (CAS # 27905-45-9) of formula
  • the plasma was brought into the chamber at a rate of 120 milli grams per minute and the plasma switched to a pulsed plasma at 30 micro seconds on-time and 20 milli seconds off-time at a peak power of 100 W for 40 minutes.
  • the plasma power was turned off along with the processing gases and vapours and the chamber evacuated back down to base pressure. The chamber was then vented to atmospheric pressure and the print head removed.
  • the print head was covered with a non-wetting polymer layer which protected it from accumulation of ink on the surface around the nozzles of the print head during use, thereby enhancing the free-flowing properties of the ink through the printer head.

Abstract

An ink jet print head comprising a nozzle plate having a non-wetting polymeric coating or surface modification formed on the surface thereof by pulsed plasma deposition, for example by exposing at least the nozzle plate of the print head to pulsed plasma comprising a gas which causes modification of the surface to impart non-wetting properties thereto or to pulsed plasma comprising a monomeric compound which undergoes plasma polymerisation to form a non-wetting polymer, devices of this type are protected from accumulation of ink on the surface around the nozzles of the print head, thereby enhancing the free-flowing properties of the ink through the print head during use.

Description

Novel Products
The present invention relates to novel products in the form of ink jet print heads, the surfaces of which are modified to provide enhanced non-wetting properties so as to reduce accumulation of ink on the surface around the nozzles of the print head, as well as to processes for their production.
An inkjet print head comprises a nozzle plate in which are formed a multiplicity of nozzles through which the ink is directed at the material on which printing is to be carried out. The nozzle outlets are of relatively small diameter, especially in print heads designed to deliver very high printing resolution. This brings with it the problem that the nozzles are susceptible to blockage or partial blockage which leads to reduced print quality. This is especially likely to be problematic if ink is allowed to build up on the nozzle plate surface around the nozzle outlets.
A number of approaches have been proposed to reduce the risk of such ink accumulation on the nozzle plate. These include mechanical wiping devices for wiping the print head between print runs and the development of new ink compositions for reducing clogging of the nozzle outlet. Other approaches have involved coating the nozzle plates of the print head, particularly the region around the nozzle orifice, with a layer of a polymer.
Polymers suitable for coating a nozzle plate should suitably have the property that they repel the liquid ink, so that if ink should stray onto the surface it will form discrete beads rather than spreading across the surface. A surface with this attribute may be described as a non-wetting surface. Wetting of the plate surface can interfere with the free-flowing of ink through the nozzles and accumulation of large amounts of ink in the region around the nozzles can cause blockage of the nozzles. A non-wetting coating which reduces these effects can significantly enhance the print head performance. Examples of polymers which have been deposited on printer heads to provide such a non-wetting surface include block polymers as discussed, for example, in US 6,345,880 which describes a sputtering coating technique. Printer heads have also been coated by cross-linking with fluorinated organic compounds such as fluorinated organosilanes, as described in US 5,910,372.
Plasma deposition techniques have been quite widely used for the deposition of polymeric coatings onto a range of surfaces, and in particular onto fabric surfaces. This technique is recognised as being a clean, dry technique that generates little waste compared to conventional wet chemical methods. Using this method, plasmas are generated from organic molecules, which are subjected to an electrical field. When this is done in the presence of a substrate, the radicals of the compound in the plasma react on the substrate to form a polymer film. Conventional polymer synthesis tends to produce structures containing repeat units that bear a strong resemblance to the monomer species, whereas a polymer network generated using a plasma can be extremely complex. The properties of the resultant coating can depend upon the nature of the substrate as well as the nature of the monomer used and conditions under which it is deposited. Formation of an ink-repellent film by continuous wave plasma processing using a compound containing fluorine or a silane compound on a previously roughened surface of an ink jet nozzle plate is described in JP 2000326514. Pulsed plasma deposition of a polymeric coating onto the surface of an ink jet print head has not hitherto been described.
The present inventors have found that by exposing at least the nozzle plate of an ink jet print head to a pulsed plasma which causes modification of the surface of the nozzle plate to impart non-wetting properties, an improved ink jet print head may be provided. Pre-roughening of the surface of the nozzle plate is not required. Using such improved ink jet print heads, the quality and reliability of inkjet printing may be improved and the need for print head maintenance may be reduced.
According to one aspect, modification of the surface of the nozzle plate to impart non-wetting properties may be brought by chemical modification of surface groups.
Plasma processing to achieve non-wetting properties may be achieved, for example, by exposing the surface to plasma comprising small molecules such as CF4 and a variety of saturated and unsaturated hydrocarbon and fluorocarbon compounds (see, for example, "Plasma Polymerisation", Academic Press Inc. (London) Ltd. 1985). Longer chain semi and fully fluorinated compounds may also be used to impart non-wetting properties.
According to another aspect, the present invention provides an inkjet print head comprising a nozzle plate having a non-wetting polymeric coating formed on the surface thereof by pulsed plasma deposition. Any monomeric compound or gas which undergoes plasma polymerisation or modification of the surface to form a non-wetting, water-repellent polymeric coating layer or surface modification on the surface of the nozzle plate may suitably be used. Suitable monomers which may be used include those known in the art to be capable of producing water-repellent polymeric coatings on substrates by plasma polymerisation including, for example, carbonaceous compounds having reactive functional groups, particularly substantially -CF3 dominated perfluoro compounds (see WO 97/38801) , perfluorinated alkenes (Wang et al., Chem Mater 1996, 2212-2214) , hydrogen containing unsaturated compounds optionally containing halogen atoms or perhalogenated organic compounds of at least 10 carbon atoms ( see WO 98/58117), organic compounds comprising two double bonds (WO 99/64662), saturated organic compounds having an optionally substituted alky chain of at least 5 carbon atoms optionally interposed with a heteroatom (WO 00/05000), optionally substituted alkynes (WO 00/20130), polyether substituted alkenes (US 6,482,531B) and macrocycles containing at least one heteroatom (US 6,329,024B), the contents of all of which are herein incorporated by reference.
According to one embodiment, the invention provides an ink jet print head comprising a nozzle plate having a polymeric coating, formed by exposing at least the nozzle plate of the print head to pulsed plasma comprising a compound of formula (I)
Figure imgf000004_0001
where R1, R2 and R3 are independently selected from hydrogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R4 is a group X-R5 where R5 is an alkyl or haloalkyl group and X is a bond; a group of formula -C(O)O(CH2)nY- where n is an integer of from 1 to 10 and Y is a bond or a sulphonamide group; or a group -(O)pR6(O)q(CH2)t- where R6 is aryl optionally substituted by halo, p is 0 or 1, q is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where q is 1, t is other than 0, for a sufficient period of time to allow a non-wetting polymeric layer to form on the surface of the nozzle plate. The expression "non-wetting polymeric layer" refers to polymeric layers which are liquid repellent, in particular ink repellent, such that any liquid on the surface does not spread across the surface but rather forms discrete beads.
As used therein the term "halo" or "halogen" refers to fluorine, chlorine, bromine and iodine. Particularly preferred halo groups are fluoro. The term "aryl" refers to aromatic cyclic groups such as phenyl or napthyl, in particular phenyl. The term "alkyl" refers to straight or branched chains of carbon atoms, suitably of up to 20 carbon atoms in length. The term "alkenyl" refers to straight or branched unsaturated chains suitably having from 2 to 20 carbon atoms. "Haloalkyl" refers to alkyl chains as defined above which include at least one halo substiruent.
Suitable haloalkyl groups for R1, R2, R3 and R5 are fluoroalkyl groups. The alkyl chains may be straight or branched and may include cyclic moieties.
For R5, the alkyl chains suitably comprise 2 or more carbon atoms, suitably from 2-20 carbon atoms and preferably from 6 to 12 carbon atoms.
For R1, R2 and R3, alkyl chains are generally preferred to have from 1 to 6 carbon atoms.
Preferably R5 is a haloalkyl, and more preferably a perhaloalkyl group, particularly a perfluoroalkyl group of formula CmF2m+i where m is an integer of 1 or more, suitably from 1- 20, and preferably from 4-12 such as 4, 6 or 8.
Suitable alkyl groups for R1, R2 and R3 have from 1 to 6 carbon atoms.
In one embodiment, at least one of R1, R2 and R3 is hydrogen. In a particular embodiment R1, R2, R3 are all hydrogen, hi yet a further embodiment however R3 is an alkyl group such as methyl or propyl.
Where X is a group -C(O)O(CEt)nY-, n is an integer which provides a suitable spacer group. In particular, n is from 1 to 5, preferably about 2.
Suitable sulphonamide groups for Y include those of formula -N(R7)SO2 " where R7 is hydrogen or alkyl such as C^alkyl, in particular methyl or ethyl. In one embodiment, the compound of formula (I) is a compound of formula (II)
CH2=CH-R5 (H)
where R5 is as defined above in relation to formula (I).
In compounds of formula (H), X in formula (I) is a bond.
However in a preferred embodiment, the compound of formula (I) is an aery late of formula m
CH2=CR7C(O)O(CH2)nR5 (m)
where n and R5 as defined above in relation to formula (I) and R7 is hydrogen, C1-Io alkyl, or C1-1()haloalkyl. In particular R7 is hydrogen or
Figure imgf000006_0001
such as methyl. A particular example of a compound of formula (III) is a compound of formula (IV)
Figure imgf000006_0002
where R7 is as defined above, and in particular is hydrogen and x is an integer of from 1 to 9, for instance from 4 to 9, and preferably 7. In that case, the compound of formula (TV) is lH^H^H^H-heptadecafluorodecylacylate.
According to another aspect, the polymeric coating is formed by exposing at least the nozzle plate of the print head to pulsed plasma comprising one or more organic monomeric compounds, at least one of which comprises two carbon-carbon double bonds for a sufficient period of time to allow a polymeric layer to form on the surface of the nozzle plate.
Suitably the compound with more than one double bond comprises a compound of formula (V)
Figure imgf000007_0001
where R8, R9, R10, R11, R12, and R13 are all independently selected from hydrogen, halo, alkyl, haloalkyl or aryl optionally substituted by halo; and Z is a bridging group.
Examples of suitable bridging groups Z for use in the compound of formula (V) are those known in the polymer art. In particular they include optionally substituted alkyl groups which may be interposed with oxygen atoms. Suitable optional substituents for bridging groups Z include perhaloalkyl groups, in particular perfluoroalkyl groups.
In a particularly preferred embodiment, the bridging group Z includes one or more acyloxy or ester groups. In particular, the bridging group of formula Z is a group of sub-formula (VI)
Figure imgf000007_0002
where n is an integer of from 1 to 10, suitably from 1 to 3, each R14 and R15 is independently selected from hydrogen, alkyl or haloalkyl.
Suitably R8, R9, R10, R11, R12, and R13 are haloalkyl such as fluoroalkyl, or hydrogen. In particular they are all hydrogen.
Suitably the compound of formula (V) contains at least one haloalkyl group, preferably a perhaloalkyl group.
Particular examples of compounds of formula (VI) include the following:
A
Figure imgf000007_0003
Figure imgf000008_0001
In a further aspect, the polymeric coating is formed by exposing at least the nozzle plate of the print head to pulsed plasma comprising a compound of comprising a monomeric saturated organic compound, said compound comprising an optionally substituted alkyl chain of at least 5 carbon atoms optionally interposed with a heteroatom for a sufficient period of time to allow a polymeric layer to form on the surface of the nozzle plate.
The term "saturated" as used herein means that the monomer does not contain multiple bonds (i.e. double or triple bonds) between two carbon atoms which are not part of an aromatic ring. The term "heteroatom" includes oxygen, sulphur, silicon or nitrogen atoms. Where the alkyl chain is interposed by a nitrogen atom, it will be substituted so as to form a secondary or tertiary amine. Similarly, silicons will be substituted appropriately, for example with two alkoxy groups.
Particularly suitable monomeric organic compounds are those of formula (VET)
R16 RJ 17
-C-R 19 vπ
R20 R21
where R16, R17, R18' R19 and R20 are independently selected from hydrogen, halogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R21 is a group X-R22 where R22 is an alkyl or haloalkyl group and X is a bond; a group of formula -C(O)O(CH2)XY- where x is an integer of from 1 to 10 and Y is a bond or a sulphonamide group; or a group - (O)pR23(O)s(CH2)r where R23 is aryl optionally substituted by halo, p is 0 or 1, s is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where s is 1, t is other than 0. Suitable haloalkyl groups for R16, R17, R18, R19, and R20 are fluoroalkyl groups. The alkyl chains may be straight or branched and may include cyclic moieties and have, for example from 1 to 6 carbon atoms.
For R22, the alkyl chains suitably comprise 1 or more carbon atoms, suitably from 1-20 carbon atoms and preferably from 6 to 12 carbon atoms.
Preferably R22 is a haloalkyl, and more preferably a perhaloalkyl group, particularly a perfluoroalkyl group of formula CzF2z+i where z is an integer of 1 or more, suitably from 1-20, and preferably from 6-12 such as 8 or 10.
Where X is a group -C(O)O(CH2)yY-, y is an integer which provides a suitable spacer group. In particular, y is from 1 to 5, preferably about 2.
Suitable sulphonamide groups for Y include those of formula -N(R23)SO2 " where R23 is hydrogen, alkyl or haloalkyl such as Ci^alkyl, in particular methyl or ethyl.
The monomeric compounds used in the method of the invention preferably comprises an Cδ.25 alkane optionally substituted by halogen, in particular a perhaloalkane, and especially a perfluoroalkane.
According to another aspect, the polymeric coating is formed by exposing at least the nozzle plate of the print head to pulsed plasma comprising an optionally substituted alkyne for a sufficient period of time to allow a polymeric layer to form on the surface of the nozzle plate.
Suitably the alkyne compounds used in the method of the invention comprise chains of carbon atoms, including one or more carbon-carbon triple bonds. The chains may be optionally interposed with a heteroatom and may carry substituents including rings and other functional groups. Suitable chains, which may be straight or branched, have from 2 to 50 carbon atoms, more suitably from 6 to 18 carbon atoms. They may be present either in the monomer used as a starting material, or may be created in the monomer on application of the plasma, for example by the ring opening
Particularly suitable monomeric organic compounds are those of formula (VEI) R^-C≡C-X^R25 (vπi)
where R24 is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl optionally substituted by halo;
X1 is a bond or a bridging group; and
R >25 is an alkyl, cycloalkyl or aryl group optionally substituted by halogen.
Suitable bridging groups X1 include groups of formulae
-(CH2V, -CO2(CH2)P-, -(CH2)pO(CH2)q-, -(CH2)pN(R26)CH2)q-,
-(CH2)pN(R26)SO2-, where s is 0 or an integer of from 1 to 20, p and q are independently selected from integers of from 1 to 20; and R26 is hydrogen, alkyl, cycloalkyl or aryl.
Particular alkyl groups for R26 include C1-O alkyl, in particular, methyl or ethyl.
Where R24 is alkyl or haloalkyl, it is generally preferred to have from 1 to 6 carbon atoms.
Suitable haloalkyl groups for R24 include fluoroalkyl groups. The alkyl chains may be straight or branched and may include cyclic moieties.Preferably however R24 is hydrogen.
Preferably R25 is a haloalkyl, and more preferably a perhaloalkyl group, particularly a perfluoroalkyl group of formula C1F21+I where r is an integer of 1 or more, suitably from 1-20, and preferably from 6-12 such as 8 or 10.
In a preferred embodiment, the compound of formula (VTS) is a compound of formula (IX)
CH≡C(CH2)S-R27 (EX)
where s is as defined above and R27 is haloalkyl, in particular a perhaloalkyl such as a Cβ-u perfluoro group like CeFi3.
In an alternative preferred embodiment, the compound of formula (VIII) is a compound of formula (X)
CH≡C(O)O(CH2)pR27 (X) where p is an integer of from 1 to 20, and R27 is as defined above in relation to formula (IX) above, in particular, a group CgF]7. Preferably in this case, p is an integer of from 1 to 6, most preferably about 2.
Other examples of compounds of formula (T) are compounds of formula (XI)
CIfeC(CH2)pO(CH2)qR27, (XI) where p is as defined above, but in particular is 1, q is as defined above but in particular is 1, and R27 is as defined in relation to formula (IX), in particular a group COFI3;
or compounds of formula (XIT)
CH=C(CH2)pN(R26)(CH2)qR27 (XII) where p is as defined above, but in particular is 1, q is as defined above but in particular is 1, R26 is as defined above an in particular is hydrogen, and R27 is as defined in relation to formula (IX), in particular a group C7F15;
or compounds of formula (XHT)
CHsC(CH2)pN(R26)SO2R27 (XUT)
where p is as defined above, but in particular is 1,R26 is as defined above an in particular is ethyl, and R27 is as defined in relation to formula (IX), in particular a group C8F17.
In an alternative embodiment, the alkyne monomer used in the process of the invention is a compound of formula (XTV)
R28C≡C(CH2)n SiR29R30R31 (XTV) where R28 is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl optionally substituted by halo, R29, R30 and R31 are independently selected from alkyl or alkoxy, in particular Q-6 alkyl or alkoxy.
Preferred groups R28 are hydrogen or alkyl, in particular C1-6 alkyl.
Preferred groups R29, R30 and R31 are C1-6 alkoxy in particular ethoxy. As used herein, the expression "in a gaseous state" refers to gases or vapours, either alone or in mixture, as well as aerosols.
The invention is applicable to any ink jet print head conventional in the art, including thermal ink jet print heads and piezoelectric ink jet heads.
It will be appreciated that the formation of the polymeric layer on the surface of the nozzle plate may occur before or after the nozzle plate is formed from a blank. The nozzle plate, which may be integral with the print head or which may be separately attached to the print head, may be formed from any suitable material conventional in the art such as polymers, metals or glass.
Print heads treated in this way exhibit enhanced non-wetting properties and may advantageously be used in ink jet printing processes to minimise problems associated with clogging of the nozzles which are commonly experienced with known ink jet print heads.
Precise conditions under which the plasma polymerization takes place in an effective manner will vary depending upon factors such as the nature of the polymer, the print head device etc. and will be determined using routine methods and/or the techniques.
Suitable plasmas for use in the method of the invention include non-equilibrium plasmas such as those generated by radiofrequencies (Rf), microwaves or direct current (DC). They may operate at atmospheric or sub-atmospheric pressures as are known in the art. In particular however, they are generated by radiofrequencies (Rf).
Various forms of equipment may be used to generate gaseous plasmas. Generally these comprise containers or plasma chambers in which plasmas may be generated. Particular examples of such equipment are described for instance in WO2005/089961 and WO02/28548, but many other conventional plasma generating apparatus are available.
In general, the item to be treated is placed within a plasma chamber together with the material to be deposited in gaseous state, a glow discharge is ignited within the chamber and a suitable voltage is applied, which may be pulsed. The gas used within the plasma may comprise a vapour of the monomeric compound alone, but it may be combined with a carrier gas, in particular, an inert gas such as helium or argon. In particular helium is a preferred carrier gas as this can minimise fragmentation of the monomer.
When used as a mixture, the relative amounts of the monomer vapour to carrier gas is suitably determined in accordance with procedures which are conventional in the art. The amount of monomer added will depend to some extent on the nature of the particular monomer being used, the nature of the substrate being treated, the size of the plasma chamber etc. Generally, in the case of conventional chambers, monomer is delivered in an amount of from 50- 250mg/min, for example at a rate of from 100-150mg/min. Carrier gas such as helium is suitably administered at a constant rate for example at a rate of from 5-90, for example from 15-30sccm. In some instances, the ratio of monomer to carrier gas will be in the range of from 100:0 to 1:100, for instance in the range of from 10:0 to 1:100, and in particular about 1:0 to 1:10. The precise ratio selected will be so as to ensure that the flow rate required by the process is achieved.
In some cases, a preliminary continuous power plasma may be struck for example for from 2- 10 minutes within the chamber. This may act as a surface pre-treatment step, ensuring that the monomer attaches itself readily to the surface, so that as polymerisation occurs, the coating "grows" on the surface. The pre-treatment step may be conducted before monomer is introduced into the chamber, in the presence of only an inert gas.
The plasma is then suitably switched to a pulsed plasma to allow polymerisation to proceed, at least when the monomer is present.
In all cases, a glow discharge is suitably ignited by applying a high frequency voltage, for example at 13.56MHz. This is applied using electrodes, which may be internal or external to the chamber, but in the case of larger chambers are internal.
Suitably the gas, vapour or gas mixture is supplied at a rate of at least 1 standard cubic centimetre per minute (seem) and preferably in the range of from 1 to lOOsccm. In the case of the monomer vapour, this is suitably supplied at a rate of from 80- 300mg/minute, for example at about 120mg per minute depending upon the nature of the monomer, whilst the pulsed voltage is applied.
Gases or vapours may be drawn or pumped into the plasma region. In particular, where a plasma chamber is used, gases or vapours may be drawn into the chamber as a result of a reduction in the pressure within the chamber, caused by use of an evacuating pump, or they may be pumped or injected into the chamber as is common in liquid handling.
Polymerisation is suitably effected using vapours of compounds of formula (I), which are maintained at pressures of from 0.1 to 200mtorr, suitably at about 80-100mtorr.
The applied fields are suitably of power of from 40 to 500W, suitably at about IOOW peak power, applied as a pulsed field. The pulses are applied in a sequence which yields very low average powers, for example in a sequence in which the ratio of the time on : time off is in the range of from 1:500 to 1:1500. Particular examples of such sequence are sequences where power is on for 20-50μs, for example about 30μs, and off for from lOOOμs to 30000μs, in particular about 20000μs. Typical average powers obtained in this way are 0.01 W.
The fields are suitably applied from 30 seconds to 90 minutes, preferably from 5 to 60 minutes, depending upon the nature of the compound of formula (I) and the nozzle plate.
Suitably a plasma chamber used is of sufficient volume to accommodate multiple print heads .
A particularly suitable apparatus and method for producing print heads in accordance with the invention is described in WO2005/089961, the content of which is hereby incorporated by reference.
In particular, when using high volume chambers of this type, the plasma is created with a voltage as a pulsed field, at an average power of from 0.001 to 500w/m3, for example at from 0.001 to 100w/m3 and suitably at from 0.005 to 0.5w/m3.
These conditions are particularly suitable for depositing good quality uniform coatings, in large chambers, for example in chambers where the plasma zone has a volume of greater than 500cm3, for instance 0.5m3 or more, such as from 0.5m3-10m3 and suitably at about Im3. The layers formed in this way have good mechanical strength.
The dimensions of the chamber will be selected so as to accommodate the particular print head being treated. For instance, generally cuboid chambers may be suitable for a wide range of applications, but if necessary, elongate or rectangular chambers may be constructed or indeed cylindrical, or of any other suitable shape.
The chamber may be a sealable container, to allow for batch processes, or it may comprise inlets and outlets for the print head device, to allow it to be utilised in a continuous process. In particular in the latter case, the pressure conditions necessary for creating a plasma discharge within the chamber are maintained using high volume pumps, as is conventional for example in a device with a "whistling leak". However it will also be possible to process print heads at atmospheric pressure, or close to, negating the need for "whistling leaks"
In a further aspect, the invention provides a method for enhancing the free-flowing properties of ink through a printer head during printing , said method comprising using a printer head wherein at least the nozzle plate thereof has a non-wetting polymeric coating or surface modification formed by plasma processing.
Suitably, the nozzle plate material or sub-assembly is placed in a plasma deposition chamber, a glow discharge is ignited within said chamber, and a voltage applied as a pulsed field.
Suitable monomers and reaction conditions for use in this method are as described above.
The invention will now be particularly described by way of example.
Example 1
A print head was placed into a plasma chamber with a processing volume of ~ 300 litres. The chamber was connected to supplies of the required gases or vapours, via a mass flow controller and/or liquid mass flow meter and a mixing injector as appropriate.
The chamber was evacuated to between 3 - 10 mtorr base pressure before allowing helium into the chamber at 20 seem until a pressure of 80 mtorr was reached. A continuous power plasma was then struck for 4 minutes using RF at 13.56 MHz at 300 W. After this period, lH,lH,2H,2H-heptadecafluorodecylacylate (CAS # 27905-45-9) of formula
Figure imgf000016_0001
was brought into the chamber at a rate of 120 milli grams per minute and the plasma switched to a pulsed plasma at 30 micro seconds on-time and 20 milli seconds off-time at a peak power of 100 W for 40 minutes. On completion of the 40 minutes the plasma power was turned off along with the processing gases and vapours and the chamber evacuated back down to base pressure. The chamber was then vented to atmospheric pressure and the print head removed.
It was found that the print head was covered with a non-wetting polymer layer which protected it from accumulation of ink on the surface around the nozzles of the print head during use, thereby enhancing the free-flowing properties of the ink through the printer head.

Claims

Claims
1. An ink jet print head comprising a nozzle plate having a non-wetting polymeric coating or surface modification formed on the surface thereof by pulsed plasma deposition.
2. An ink jet print head according to claim 1 formed by exposing at least the nozzle plate of the print head to a pulsed plasma which causes modification of the surface of the nozzle plate to impart non-wetting properties to the surface.
3. An ink jet print head according to claim 2 wherein the modification is brought about by exposing at least the nozzle plate of the print head to pulsed plasma comprising a monmeric compound which undergoes plasma polymerisation to form a non-wetting polymer for a sufficient period of time to allow a polymeric layer to form on the surface of the nozzle plate..
4. An ink jet print head according to any preceding claim wherein the print head is exposed to the pulsed plasma within a plasma deposition chamber.
5. An ink jet print head according to claim 3 or claim 4 wherein the monomeric compound is a compound of formula (I)
Figure imgf000017_0001
where R1, R2 and R3 are independently selected from hydrogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R4 is a group X-R5 where R5 is an alkyl or haloalkyl group and X is a bond; a group of formula -C(O)O(CH2)nY- where n is an integer of from 1 to 10 and Y is a bond or a sulphonamide group; or a group -(O)pR6(O)q(CH2)t where R6 is aryl optionally substituted by halo, p is 0 or 1, q is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where q is 1, t is other than 0.
6. An ink jet print head according to claim 5 wherein the compound of formula (I) is a compound of formula (II) CH2=CH-R5 (II)
where R5 is as defined in claim 5, or a compound of formula (HI)
CH2=CR7C(O)O(CH2)nR5 (DI)
where n and R5 as defined in claim 5 and R7 is hydrogen, Ci-I0 alkyl, or C1-10haloalkyl.
7. An ink jet print head according to claim 5 wherein the compound of formula (I) is a compound of formula (HI).
8. An ink jet print head according to claim 7 wherein the compound of formula (III) is a compound of formula (IV)
Figure imgf000018_0001
where R7 is as defined in claim 6, and x is an integer of from 1 to 9.
9. An ink jet print head according to claim 8 wherein the compound of formula (IV) is lHJH^H^H-heptadecafluorodecylacylate.
10. An ink jet print head according to claim 3 or claim 4 wherein the monomeric compound is a compound of formula (V)
Figure imgf000018_0002
where R8, R9, R10, R11, R12, and R13 are all independently selected from hydrogen, halo, alkyl, haloalkyl or aryl optionally substituted by halo; and Z is a bridging group.
11. An ink jet print head according to claim 3 or claim 4 wherein the monomeric compound is a compound of formula (VII)
R16 R 17
R18— C C-R19 vπ
R 2/0υ T R, 21
where R16, R17, R18' R19 and R20 are independently selected from hydrogen, halogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R21 is a group X-R22 where R22 is an alkyl or haloalkyl group and X is a bond; a group of formula -C(O)O(CH2)XY- where x is an integer of from 1 to 10 and Y is a bond or a sulphonamide group; or a group - (O)pR23(O)s(CH2)t- where R23 is aryl optionally substituted by halo, p is 0 or 1, s is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where s is 1, t is other than 0.
12. An ink jet print head according to claim 3 or claim 4 wherein the monomeric compound is a compound of formula (VIII)
R^-C≡C-X^R25 (Vm)
where R24 is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl optionally substituted by halo;
X1 is a bond or a bridging group; and
R25 is an alkyl, cycloalkyl or aryl group optionally substituted by halogen.
13. A method for enhancing the free-flowing properties of ink through a printer head during printing , said method comprising using a printer head wherein at least the nozzle plate thereof has deposited thereon a polymeric coating formed by exposing said print head, or at least the nozzle plate thereof, to a pulsed plasma comprising a compound of formula (I)
Figure imgf000019_0001
where R1, R2 and R3 are independently selected from hydrogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R is a group X-R5 where R5 is an alkyl or haloalkyl group and X is a bond; a group of formula -C(O)O(CHa)nY- where n is an integer of from 1 to 10 and Y is a bond or a sulphonamide group; or a group -(O)PR6(O)q(CH2)t- where R6 is aryl optionally substituted by halo, p is 0 or 1, q is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where q is 1, t is other than 0, in a gaseous state for a sufficient period of time to allow a polymeric layer to form on the surface of the nozzle plate.
14. A method according to claim 13 wherein the print head, or at least the nozzle plate thereof, is placed in a plasma deposition chamber, a glow discharge is ignited within said chamber, and a voltage applied as a pulsed field.
15. A method according to claim 13 or claim 14 wherein applied voltage is at a power of from 5 to 500W.
16. A method according to any one of claims 13 to 15 wherein the voltage is pulsed in a sequence in which the ratio of the time on : time off is in the range of from 1:500 to 1:1500.
17. A method according to claim 16 wherein the voltage is pulsed in a sequence where power is on for 20-50μs, and off for from lOOOμs to 30000μs.
18. A method according to any one of claims 13 to 17 wherein the voltage is applied as a pulsed field at for a period of from 30 seconds to 90 minutes.
19. A method according to claim 18 wherein the voltage is applied as a pulsed field for from 5 to 60 minutes.
20. A method according to any one of claims 13 to 19, wherein in a preliminary step, a continuous power plasma is applied to the print head.
21. A method according to claim 20 wherein the preliminary step is conducted in the presence of an inert gas.
22. A method according to any one of claims 13 to 21 wherein the compound of formula (I) in gaseous form is fed into the plasma at a rate of from 80-300 mg/minute, whilst the pulsed voltage is applied.
23. A method according to any one of claims 13 to 22 wherein the plasma is created with a voltage at an average power of from 0.001 to 500w/m3.
24. A method according to claim 23 wherein the plasma is created with a voltage at an average power of from 0.001 to 100w/m3.
25. A method according to claim 24 wherein the plasma is created with a voltage at an average power of from 0.005 to 0.5w/m3.
26. A method according to any one of claims 13 to 25 wherein the compound of formula (T) is a compound of formula (II)
CH2=CH-R5 (H)
where R5 is as defined in claim 5, or a compound of formula (EDT)
CH2=CR7C(O)O(CH2)nR5 (HI)
where n and R5 as defined in claim 5 and R7 is hydrogen, C1-10 alkyl, or
Figure imgf000021_0001
27. A method according to claim 26 wherein the compound of formula (I) is a compound of formula (HI).
28. A method according to claim 27 wherein the compound of formula (HI) is a compound of formula (IV)
Figure imgf000021_0002
where R7 is as defined in claim 9, and x is an integer of from 1 to 9.
29. A method according to claim 28 wherein the compound of formula (IV) is lHjlH^H^H-heptadecafluorodecyl acrylate.
30. An ink jet print head substantially as hereinbefore described with reference to the examples.
31. A method for enhancing the free-flowing properties of ink through a printer head during printing substantially as hereinbefore described with reference to the Examples.
PCT/GB2007/001851 2006-05-20 2007-05-18 Inkjet print head WO2007135394A1 (en)

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GB0610132A GB2438195A (en) 2006-05-20 2006-05-20 Coated ink jet nozzle plate
GB0610132.3 2006-05-20

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