Preferred acryl amides are disclosed in Table 1.

TABLE 1

AA-1

[Image Omitted]

AA-2

AA-3

AA-4

AA-5

AA-6

AA-7

AA-8

AA-9

AA-10

A highly preferred acryl amide according to Formula I is acryloyl morpholine (ACMO).

Acid Group Containing (Meth)Acrylates

The radiation curable composition preferably comprises a (meth)acrylate containing a carboxylic acid group, a phosphoric acid group or a phosphonic acid group; or a mixture thereof.

The amount of the (meth)acrylate containing a carboxylic acid group, a phosphoric acid group or a phosphonic acid group is preferably between 1 and 25 wt %, more preferably between 3 and 20 wt %, most preferably between 5 to 15 wt %, with all weight percentages (wt %) based on the total weight of the radiation curable composition.

It has been observed that such (meth)acrylates containing a carboxylic acid group, a phosphoric acid group or a phosphonic acid group may improve the adhesion of the jetted and cured radiation curable compositions on various substrates. These compounds are therefore also referred to as adhesion promoters.

Suitable examples of a carboxylic acid group-containing (meth)acrylate include a compound represented by the Formula (II):

[Image Omitted]

- wherein
- n is 0 or 1,
- R₄is selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group and a substituted or unsubstituted aryl group.
- L₁represents a divalent linking group, comprising 20 carbon atoms or less, with the proviso that L₁is linked to the carboxylic acid via an aliphatic carbon atom,
- X represents O or NR₇,
- R₇is selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted alkaryl group, a substituted or unsubstituted aralkyl group and a substituted or unsubstituted (hetero) aryl group,
- R₇and L₁may represent the necessary atoms to form a 5 to 8 membered ring.

R₅and R₆are independently selected from the group consisting of hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group and a substituted or unsubstituted heteroaryl group.

R₄is preferably a hydrogen atom or a substituted or unsubstituted C₁to C₄alkyl group, more preferably a hydrogen atom or a methyl group, a hydrogen atom being particularly preferred.

X is preferably an oxygen atom or NH, an oxygen atom being particularly preferred.

L₁preferably represents a substituted or unsubstituted alkylene group, an unsubstituted alkylene group being particularly preferred.

The adhesion promoter according to Formula II, or a salt thereof, may copolymerize with other polymerizable compounds of the radiation curable inkjet ink.

Examples of adhesion promoters according to Formula II are given in Table 2.

TABLE 2

ADH-1

ADH-2

ADH-3

ADH-4

ADH-5

ADH-6

ADH-7

ADH-8

ADH-9

ADH-10

ADH-11

ADH-12

ADH-13

ADH-14

ADH-15

ADH-16

ADH-17

Preferred examples of a (meth)acrylate containing a phosphoric acid group or a phosphonic acid group include 2-(methacryloyloxy)ethyl phosphate, hydroxyethyl methacrylate phosphate, bis-(2-methacryloyl oxyethyl) phosphate.

Preferred examples of the (meth)acrylate containing a phosphoric acid group are compounds according to Formula P-1 or P-2:

[Image Omitted]

wherein R represents C_nH_2n+1with n representing an integer between 6 and 18.

Preferred examples of the (meth)acrylate containing a phosphoric acid group are disclosed in Table 3.

TABLE 3

MP-1

[Image Omitted]

MP-2

MP-3

In a particularly preferred embodiment of the UV curable inkjet ink, the (meth)acrylate containing a carboxylic acid group, a phosphoric acid group, or a phosphonic acid group is selected from the group consisting of acrylic acid,

- 2-carboxyethyl acrylate, 2-acryloyl ethyl succinate, and 2-hydroxyethyl methacrylate phosphate, or a mixture thereof.

Polyfunctional Acrylates

The radiation curable composition preferably includes a polyfunctional acrylate.

The amount of the polyfunctional acrylate is preferably between 15 and 65 wt %, preferably between 20 and 55 wt % and most preferably between 30 and 50 wt % of a polyfunctional acrylate, with all weight percentages (wt %) based on the total weight of the radiation curable composition.

A single polyfunctional acrylate or a mixture of polyfunctional acrylates may be used.

In a preferred embodiment, the polyfunctional acrylate is selected from the group consisting of dipropylene glycol diacrylate, neopentylglycol diacrylate, neopentylglycol (2× propoxylated) diacrylate, penta erythritol tetraacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, tripropylene glycol diacrylate, ditrimethyloylpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, and polyethyleneglycol diacrylate.

In the most preferred embodiment of the UV curable inkjet ink, the polyfunctional acrylate includes a neopentylglycol hydroxy pivalate diacrylate.

Liquid Penetrating Controlling Monomer

The radiation curable composition preferably comprises at least 0.1 wt % of a liquid penetrating controlling monomer selected from the group consisting of a long chain alkyl (meth)acrylate, a fluorinated (meth)acrylate and a silicone (meth)acrylate, or a mixture thereof, the wt % relative to the total weight of the radiation curable composition.

The amount of the liquid penetrating controlling monomer is preferably at least 0.1 wt %, more preferably at least 0.5 wt %, most preferably at least 1 wt %, particularly preferred at least 1.5 wt %, with all weight percentages (wt %) based on the total weight of the radiation curable composition.

The amount of the liquid penetrating controlling monomer is preferably between 0.1 and 10 wt %, more preferably between 0.5 and 7.5 wt %, most preferably between 1.5 and 5 wt %, with all weight percentages (wt %) based on the total weight of the radiation curable composition.

Long Chain Alkyl (Meth)Acrylate

The long chain alkyl (meth)acrylate is a C₆-C₂₂alkyl (meth)acrylate, more preferably a C₈-C₂₀alkyl (meth)acrylate, most preferably a C₁₂-C₁₈alkyl (meth)acrylate.

As used herein, C₆-C₂₂, C₈-20, C₁₂-C₁₈alkyl (meth)acrylate means an alkyl ester of (meth)acrylic ester having alkyl group of respectively 6 to 22, 8 to 20 and 12 to 18 carbon atoms.

An alkyl chain referred to herein may include a linear, branched or cyclic alkyl group.

Examples of such alkyl (meth)acrylates include lauryl (meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, stearyl (meth)acrylate, docosyl (meth)acrylate or icosyl (meth)acrylate.

A particularly preferred long chain acrylate is lauryl acrylate.

A mixture of different long chain alkyl (meth)acrylate may be used.

Fluorinated (Meth)Acrylate

A fluorinated (meth)acrylate as used herein means a (meth)acrylate comprising an alkyl chain functionalized with a fluorine atom, preferably functionalized with at least 2 fluorine atoms, more preferably functionalized with at least 3 fluorine atoms.

An alkyl chain referred to herein may include a linear, branched or cyclic alkyl group.

Examples of fluorinated polymerizable compounds include 2,2,2-trifluoroethyl-α-fluoroacrylate (TFEFA), 2,2,2-trifluoroethyl-methacrylate (TFEMA), 2,2,3,3-tetrafluoropropyl-α-fluoroacrylate (TFPFA), 2,2,3,3-tetrafluoropropyl-methacrylate (TFPMA), 2,2,3,3,3 pentafluoropropyl-α-fluoroacrylate (PFPFA), 2,2,3,3,3 pentafluoropropyl-methacrylate (PFPMA), 1H, 1H-perfluoro-n-octyl acrylate, 1H, 1H-perfluoro-n-decyl acrylate, 1H, 1H-perfluoro-n-octyl methacrylate, 1H, 1H-perfluoro-n-decyl methacrylate, 1H, 1H,6H,6H-perfluoro-1,6-hexanediol diacrylate, 1H, 1H,6H,6H-perfluoro-1,6-hexanediol dimethacrylate, 2-(N-butylperfluorooctanesulfonamido)ethyl acrylate, 2 (N ethyl perfluorooctanesulfonamido)ethyl acrylate, 2 (N ethyl perfluorooctanesulfonamido) ethyl methacrylate, C₈F₁₇CH₂CH₂OCH₂CH₂—OOC—CH═CH₂and C₈F₁₇CH₂CH₂OCH₂CH₂—OOC—C(CH₃)═CH₂.

Preferred fluorinated (meth)acrylates are the MEGAFACE™ RS series available from DIC Corporation such MEGAFACE™ RS-75, MEGAFACET RS-72-K, MEGAFACE™ RS-76-E, MEFAFACE™ 76-NS, MEGAFACE™ 78, MEGAFACE™ RS-90, MEFAFACE™ RS-55, MEFAFACE™ RS-56.

A particularly preferred fluorinated (meth)acrylate is 2,2,2-trifluoroethyl-methacrylate.

A mixture of different fluorinated (meth)acrylates may be used.

Silicone (Meth)Acrylate

A silicone (meth)acrylate as used herein means a (meth)arylate comprising at least one group comprising a Si atom.

A preferred silicone (meth)acrylate has a chemical structure according to Formula S-1,

[Image Omitted]

- wherein
- R₈and R₉independently from each other represent an optionally substituted alkyl group or optionally substituted aryl group;
- n represents an integer between 1 and 50.

Preferably R8 and R9 represent an alkyl group, more preferably a methyl group.

Preferably n represents an integer between 1 and 25, more preferably between 2 and 15.

A preferred silicone acrylate is a polyether modified (meth)acrylated polydimethylsiloxane or a polyester modified (meth)acrylated polydimethylsiloxane.

Preferred commercially available silicone (meth)acrylates include: Ebecryl™ 350, a silicone diacrylate from Cytec; the polyether modified acrylated polydimethylsiloxane BYK™ UV3500 and BYK™ UV3530, the polyester modified acrylated polydimethylsiloxane BYK™ UV3570, all manufactured by BYK Chemie; Tego™ Rad 2100, Tego™ Rad 2200N, Tego™ Rad 2250N, Tego™ Rad 2300, Tego™ Rad 2500, Tego™ Rad 2600, and Tego™ Rad 2700, Tego™ RC711 from EVONIK; Silaplane™ FM7711, Silaplane™ FM7721, Silaplane™ FM7731, Silaplane™ FM0711, Silaplane™ FM0721, Silaplane™ FM0725, Silaplane™ TM0701, Silaplane™ TM0701T all manufactured by Chisso Corporation; DMS-R05, DMS-R11, DMS-R18, DMS-R22, DMS-R31, DMS-U21, DBE-U22, SIB1400, RMS-044, RMS-033, RMS-083, UMS-182, UMS-992, UCS-052, RTT-1011 and UTT-1012 all manufactured by Gelest, Inc, and SILMER™ ACR D208, SILMER™ Di-50, SILMER™ Di1508, SILMERT Di-2510, SILMER™ Di-4515-O, SILMER™ ACR Di-10, all manufactured by Siltech.

A mixture of different silicone (meth)acrylates may be used.

Other Monomers

The radiation curable composition may in addition to the monomers described above comprise other monomers, oligomers and/or prepolymers.

In a preferred embodiment, such monomers, oligomers or prepolymers include an acrylate group as polymerizable group.

Preferred monomers and oligomers are those listed in paragraphs to in EP-A 1911814.

The other monomers are preferably monofunctional monomers, more preferably monofunctional acrylates or methacrylates.

Photoinitiators

The radiation curable composition preferably contains a photoinitiator.

A free radical photoinitiator is a chemical compound that initiates polymerization of monomers and oligomers when exposed to actinic radiation by the formation of a free radical. A Norrish Type I initiator is an initiator which cleaves after excitation, yielding the initiating radical immediately. A Norrish type II-initiator is a photoinitiator which is activated by actinic radiation and forms free radicals by hydrogen abstraction from a second compound that becomes the actual initiating free radical. This second compound is called a polymerization synergist or co-initiator. Both type I and type II photoinitiators can be used in the present invention, alone or in combination.

Suitable photoinitiators are disclosed in CRIVELLO, J. V., et al. Photoinitiators for Free Radical, Cationic and Anionic Photopolymerization. 2nd edition. Edited by BRADLEY, G. London, UK: John Wiley and Sons Ltd, 1998. p. 276-293.

Specific examples of free radical photoinitiators may include, but are not limited to, the following compounds or combinations thereof: benzophenone and substituted benzophenones; 1-hydroxycyclohexyl phenyl ketone; thioxanthones such as isopropylthioxanthone; 2-hydroxy-2-methyl-1-phenylpropan-1-one; 2-benzyl-2-dimethylamino-(4-morpholinophenyl) butan-1-one; benzyl dimethylketal; bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide; 2,4,6 trimethylbenzoyl-diphenylphosphine oxide; 2,4,6-trimethoxybenzoyldiphenylphosphine oxide; and 2,4,6-trimethylbenzoyldi-phenylphosphinate.

2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one; 2,2-dimethoxy-1, 2-diphenylethan-1-one or 5,7-diiodo-3-butoxy-6-fluorone.

Suitable commercial free radical photoinitiators include for example the Omnirad™, Omnipol™ and Esacure™ type photoinitiators from IGM. Examples of such photoinitiators are Omnirad 379, Omnirad 369, Omnirad 819, Omnirad 184, Omnirad 2959, Omnipol ASA and Esacure KIP 150.

A preferred amount of photoinitiator is 0.1-20 wt %, more preferably 2-15 wt %, and most preferably 3-10 wt % of the total weight of the radiation curable inkjet ink.

In order to increase the photosensitivity further, the radiation curable composition may additionally contain co-initiators. Suitable examples of co-initiators can be categorized in three groups: 1) tertiary aliphatic amines such as methyldiethanolamine, dimethylethanolamine, triethanolamine, triethylamine and N-methylmorpholine; (2) aromatic amines such as amylparadimethyl-aminobenzoate, 2-n-butoxyethyl-4-(dimethylamino) benzoate, 2-(dimethylamino)-ethylbenzoate, ethyl-4-(dimethylamino)benzoate, and 2-ethylhexyl-4-(dimethylamino)benzoate; and (3) (meth)acrylated amines such as dialkylamino alkyl (meth)acrylates (e.g., diethylaminoethylacrylate) or N-morpholinoalkyl-(meth)acrylates (e.g., N-morpholinoethyl-acrylate). The preferred co-initiators are aminobenzoates.

Colorants

The radiation curable composition may be a substantially colourless composition, but preferably the radiation curable composition includes at least one colorant. The colorant makes the temporary mask clearly visible to the manufacturer of conductive patters, allowing a visual inspection of quality.

The colorant may be a pigment or a dye, but is preferably a dye that is not bleached by the UV curing step during the inkjet printing process of the UV curable inkjet ink.

The pigments may be black, white, cyan, magenta, yellow, red, orange, violet, blue, green, brown, mixtures thereof, and the like. A colour pigment may be chosen from those disclosed by HERBST, Willy, et al. Industrial Organic Pigments, Production, Properties, Applications. 3rd edition. Wiley-VCH, 2004. ISBN 3527305769.

Suitable pigments are disclosed in paragraphs to of WO 2008/074548.

Pigment particles in inkjet inks should be sufficiently small to permit free flow of the ink through the inkjet-printing device, especially at the ejecting nozzles. It is also desirable to use small particles for maximum colour strength and to slow down sedimentation. Most preferably, the average pigment particle size is no larger than 150 nm. The average particle size of pigment particles is preferably determined with a Brookhaven Instruments Particle Sizer BI90plus based upon the principle of dynamic light scattering.

Generally, dyes exhibit a higher light fading than pigments, but cause no problems on jettability. It was found that anthraquinone dyes exhibit only minor light fading under the normal UV curing conditions used in UV curable inkjet printing.

In a preferred embodiment, the colorant in the radiation curable composition is an anthraquinone dye, such as Macrolex™ Blue 3R (CASRN 325781-98-4) from LANXESS.

Other preferred dyes include crystal violet and a copper phthalocyanine dye.

In a preferred embodiment, the colorant is present in an amount of 0.5 to 6.0 wt %, more preferably 1.0 to 2.5 wt %, based on the total weight of the radiation curable composition.

Polymeric Dispersants

If the colorant in the radiation curable composition is a pigment, then the radiation curable composition preferably contains a dispersant, more preferably a polymeric dispersant, for dispersing the pigment.

Suitable polymeric dispersants are copolymers of two monomers but they may contain three, four, five or even more monomers. The properties of polymeric dispersants depend on both the nature of the monomers and their distribution in the polymer. Copolymeric dispersants preferably have the following polymer compositions:

- statistically polymerized monomers (e.g. monomers A and B polymerized into ABBAABAB);
- alternating polymerized monomers (e.g. monomers A and B polymerized into ABABABAB);
- gradient (tapered) polymerized monomers (e.g. monomers A and B polymerized into AAABAABBABBB);
- block copolymers (e.g. monomers A and B polymerized into AAAAABBBBBB) wherein the block length of each of the blocks (2, 3, 4, 5 or even more) is important for the dispersion capability of the polymeric dispersant;
- graft copolymers (graft copolymers consist of a polymeric backbone with polymeric side chains attached to the backbone); and
- mixed forms of these polymers, e.g. blocky gradient copolymers.

Suitable polymeric dispersants are listed in the section on “Dispersants”, more specifically to and to [0077], in EP-A 1911814.

Commercial examples of polymeric dispersants are the following:

- DISPERBYK™ dispersants available from BYK CHEMIE GMBH;
- SOLSPERSE™ dispersants available from NOVEON;
- TEGO™ DISPERS™ dispersants from EVONIK;
- EDAPLANT dispersants from MÜNZING CHEMIE;
- ETHACRYL™ dispersants from LYONDELL;
- GANEXT dispersants from ISP;
- DISPEX™ and EFKA™ dispersants from CIBA SPECIALTY CHEMICALS INC;
- DISPONER™ dispersants from DEUCHEM; and
- JONCRYL™ dispersants from JOHNSON POLYMER.

Polymerization Inhibitors

The radiation curable composition may contain at least one inhibitor for improving the thermal stability of the ink.

Suitable polymerization inhibitors include phenol type antioxidants, hindered amine light stabilizers, phosphor type antioxidants, hydroquinone monomethyl ether commonly used in (meth)acrylate monomers, and hydroquinone. t-butylcatechol, pyrogallol, 2,6-di-tert.butyl-4-methylphenol (=BHT) and phenothiazine may also be used.

Suitable commercial inhibitors are, for example, Sumilizer™ GA-80, Sumilizer™ GM and Sumilizer™ GS produced by Sumitomo Chemical Co. Ltd.; Genorad™ 16, Genorad™ 18 and Genorad™ 22 from Rahn AG; Irgastab™ UV10 and Irgastab™ UV22, Tinuvin™ 460 and CGS20 from Ciba Specialty Chemicals; Florstab™ UV range (UV-1, UV-2, UV-5 and UV-8) from Kromachem Ltd, Additol™ S range (S100, S110, S120 and S130) and PTZ from Cytec Solvay Group.

The inhibitor is preferably a polymerizable inhibitor.

Since excessive addition of these polymerization inhibitors may lower the curing speed, it is preferred that the amount capable of preventing polymerization is determined prior to blending. The amount of a polymerization inhibitor is preferably lower than 5 wt %, more preferably lower than 3 wt % of the total radiation curable composition.

Surfactants

The radiation curable composition may contain at least one surfactant, but preferably no surfactant is present.

The surfactant can be anionic, cationic, non-ionic, or zwitter-ionic and is usually added in a total quantity less than 1 wt % based on the total weight of the radiation curable inkjet ink.

Suitable surfactants include fluorinated surfactants, fatty acid salts, ester salts of a higher alcohol, alkylbenzene sulfonate salts, sulfosuccinate ester salts and phosphate ester salts of a higher alcohol (for example, sodium dodecylbenzenesulfonate and sodium dioctylsulfosuccinate), ethylene oxide adducts of a higher alcohol, ethylene oxide adducts of an alkylphenol, ethylene oxide adducts of a polyhydric alcohol fatty acid ester, and acetylene glycol and ethylene oxide adducts thereof (for example, polyoxyethylene nonylphenyl ether, and SURFYNOLT 104, 104H, 440, 465 and TG available from AIR PRODUCTS & CHEMICALS INC.).

Preferred surfactants are selected from fluorosurfactants (such as fluorinated hydrocarbons) and silicone surfactants. The silicone surfactants are preferably siloxanes and can be alkoxylated, polyether modified, polyether modified hydroxy functional, amine modified, epoxy modified and other modifications or combinations thereof. Preferred siloxanes are polymeric, for example polydimethylsiloxanes.

Preferred commercial silicone surfactants include BYK™ 333 and BYK™ UV3510 from BYK Chemie and Tego Rad 2100 from Evonik Industries.

Preferably the surfactant is present in the radiation curable inkjet ink in an amount of 0 to 0.1 wt % based on the total weight of the radiation curable inkjet ink.

Flame Retardant

The radiation curable composition may contain at least one flame retardant, but preferably no flame retardant is present.

Preferred flame retardants are inorganic flame retardants, such as Alumina Trihydrate and Boehmite, and organo-phosphor compounds, such as organo-phosphates (e.g. triphenyl phosphate (TPP), resorcinol bis (diphenylphosphate) (RDP), bisphenol A diphenyl phosphate (BADP), and tricresyl phosphate (TCP)); organo-phosphonates (e.g. dimethyl methylphosphonate (DMMP)); and organophosphinates (e.g. aluminium dimethylphosphinate).

Other preferred organo-phosphor compounds are disclosed in U.S. Pat. No. 8,273,805.

Inkjet Printing Devices

The radiation curable inkjet ink may be jetted by one or more print heads ejecting small droplets in a controlled manner through nozzles onto a substrate, which is moving relative to the print head(s).

A preferred print head for the inkjet printing system is a piezoelectric head. Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied thereto. The application of a voltage changes the shape of the piezoelectric ceramic transducer in the print head creating a void, which is then filled with ink. When the voltage is again removed, the ceramic expands to its original shape, ejecting a drop of ink from the print head.

However, the inkjet printing method according to the present invention is not restricted to piezoelectric inkjet printing. Other inkjet print heads can be used and include various types, such as a continuous type.

The inkjet print head normally scans back and forth in a transversal direction across the moving ink-receiver surface. Often the inkjet print head does not print on the way back. Bi-directional printing is preferred for obtaining a higher throughput. Another preferred printing method is by a “single pass printing process”, which can be performed by using page wide inkjet print heads or multiple staggered inkjet print heads which cover the entire width of the ink-receiver surface. In a single pass printing process the inkjet print heads usually remain stationary and the ink-receiver surface is transported under the inkjet print heads.

Curing Devices

The radiation curable inkjet ink can be cured by exposing them to actinic radiation, such as electron beam or ultraviolet radiation. Preferably the radiation curable inkjet ink is cured by ultraviolet radiation, more preferably using UV LED curing.

In inkjet printing, the curing means may be arranged in combination with the print head of the inkjet printer, travelling therewith so that the curable liquid is exposed to curing radiation very shortly after been jetted.

In such an arrangement, with the exception of UV LEDs, it can be difficult to provide a small enough radiation source connected to and travelling with the print head. Therefore, a static fixed radiation source may be employed, e.g. a source of curing UV-light, connected to the radiation source by means of flexible radiation conductive means such as a fiber optic bundle or an internally reflective flexible tube.

Alternatively, the actinic radiation may be supplied from a fixed source to the radiation head by an arrangement of mirrors including a mirror upon the radiation head.

The source of radiation may also be an elongated radiation source extending transversely across the substrate to be cured. It may be adjacent the transverse path of the print head so that the subsequent rows of images formed by the print head are passed, stepwise or continually, beneath that radiation source.