GB2512430A - Method of printing - Google Patents

Abstract

A method of printing onto a non elongatable substrate comprises: depositing a primer layer onto the substrate, the primer comprising a thermoplastic resin; at least partially drying and/or curing the primer; inkjet printing a hybrid solvent/radiation curable ink onto the primer layer; drying and curing the hybrid ink layer; optionally depositing a protective layer onto the solvent-based ink layer, wherein the protective layer comprises a thermoplastic resin and a crosslinking agent; and drying and/or curing the protective layer; wherein the hybrid solvent/radiation-curable ink comprises at least 50% by weight organic solvent, based on the total weight of the ink, radiation-curable material and a photoinitiator and the primer and protective layer thermoplastic resins are selected from: polyurethane polymethacrylate, polyvinyl, poly(cellulose acetate butyrate), polyester, epoxy resin, hydrocarbon resin, ketone or aldehyde resin, amino resin, and copolymers and blends thereof, and a solvent and/or monofunctional radiation-curable diluent, and, when a monofunctional radiation-curable diluents is present, a photoinitiator, The present invention also relates to a printed substrate obtainable by the method of the invention; the printed substrate is preferably an item of sportswear or sports equipment.

Description

Method of printing The present invention is concerned with a method of printing and more particularly to a method of printing onto difficult substrates. The present invention is further concerned with a printed substrate obtainable by the method of the present invention.

The printing of ink images onto substrates which are non-permeable and non-elongatable, e.g. leather or synthetic leather, is a significant challenge. Such substrates present an impervious (often thermoset) surface that is highly flexible and it is difficult to gain adhesion thereto. It is also essential that the finished printed substrate retains excellent flexibility, has high resistance to abrasion and is resistant to water.

The current process for printing ink onto such substrates, like leather or synthetic leather, is a screen printing process. Screen printing is currently used because such a process allows for the use of an ink having a wide viscosity range, allows for the alteration of film thickness and provides tough films.

However, such a screen printing process is labour intensive. A large number of screens are required as individual screens are required for each colour and for each size of print. This is costly and time consuming.

Therefore an improved process for printing on such difficult substrates is required.

lnkjet printing is desirable and therefore an inkjet ink process has been contemplated in order to produce a printed image onto such difficult substrates because colours can be printed concurrently and any image size can be printed simply by varying the data file used.

However, the use of traditional UV curable inkjet inks in such an inkjet ink process is not a solution to the problem. Traditional UV curable inkjet inks which are inkjet printed onto such substrates provides good abrasion and reasonable adhesion. However, the high film weight which is deposited onto the substrate for such inks limits the formulation latitude available to achieve flexible films. To formulate films with the required high flexibility, the ink system must be largely based on UV curable monofunctional monomers. However, such films are soft and easily abraded. The inclusion of UV curable multifunctional monomers into the inkjet ink can provide the required resistance properties but the films produced are hard and brittle and do not meet the flexibility requirements. It is therefore not possible to provide the required combination of flexibility, resistance and adhesion.

The use of hybrid solvent/radiation-curable inks (e.g. U'!) in such an inkjet ink process, in which a UV reactive binder is diluted in a volatile carrier, such as water or an organic solvent, is also not a solution to the problem. The inclusion of a volatile carrier results in the reduction of the film weight deposited, which lessens the adverse effect of the film on the substrate properties, thus allowing the use of higher functionality UV materials with the necessary resistance properties. In such inkjet systems, the image quality is fixed (or pinned) by applying heat to the substrate to evaporate partially the carrier solvent from the ink droplets to effect an increase in the ink viscosity, hence arresting the flow of the ink droplet and controlling the spread of the deposited ink droplet. However, the typical materials used for industrial printing processes, such as those used for the production of printed containers, sportswear and sports equipment, and the like have relatively high film thickness and hence have a high heat capacity. The high heat capacity means that it is not possible to increase the temperature of the substrate quickly enough to effect the required viscosity increase in the ink droplets. The heat cannot penetrate through the substrate sufficiently, meaning that the pinning process is disabled, leading to excessive ink flow, yielding very poor image quality. In addition the non-permeable nature of the substrate severely limits any penetration of the solvent into the upper layers of the material further reducing the rate of viscosity rise and pinning efficiency. In other words, the time needed to pin the ink droplets is too long owing to the high heat capacity and impervious nature of the substrates, which results in the pooling of ink droplets and a poor quality image.

Hence there exists a requirement in the art for a method of printing onto difficult substrates, which eliminates or reduces the aforementioned problems.

Accordingly, the present invention provides a method of printing onto a non-elongatable substrate having a primer layer obtainable by providing the substrate, depositing a primer onto the substrate to form a primer layer, wherein the primer comprises a thermoplastic resin selected from polyurethane, polymethacrylate, polyvinyl, poly(cellulose acetate butyrate), polyester, epoxy resin, hydrocarbon resin, ketone or aldehyde resin, amino resin, and copolymers and blends thereof, and a solvent and/or monofunctional radiation-curable diluent, and, when a monofunctional radiation-curable diluent is present, a photoinitiator, and at least partially drying and/or at least partially curing the primer, wherein the primer layer has a thickness of 40 microns or less based on the dry film thickness; the method comprising each of the following steps in order: (i) inkjet printing a hybrid solvent/radiation-curable ink onto the primer layer to form a hybrid solvent/radiation-curable ink layer, wherein the hybrid solvent/radiation-curable ink comprises at least 50% by weight organic solvent, based on the total weight of the ink, radiation-curable material and a photoinitiator; (U)(a) optionally depositing a protective layer onto the hybrid solvent/radiation-curable ink layer, wherein the protective layer comprises: a thermoplastic resin selected from polyurethane, polymethacrylate, polyvinyl, poly(cellulose acetate butyrate), polyester, epoxy resin, hydrocarbon resin, ketone or aldehyde resin, amino resin, and copolymers and blends thereof, a solvent and/or radiation-curable diluent, and, when a monofunctional radiation-curable diluent is present, a photoinitiator, and a crosslinking agent; and (b) drying and curing the hybrid solvent/radiation-curable ink layer; wherein when (U)(a) is present, (U)(a) and (ii)(b) can be in either order, with the proviso that when step (U)(b) occurs before step (H)(a), the method further comprises the step of drying and/or curing the protective layer.

The present invention further provides a method of printing onto a non-elongatable substrate comprising each of the following steps in order: (0 providing the substrate; (ii) depositing a primer onto the substrate to form a primer layer, wherein the primer comprises: a thermoplastic resin selected from polyurethane, polymethacrylate, polyvinyl, poly(cellulose acetate butyrate), polyester, epoxy resin, hydrocarbon resin, ketone or aldehyde resin, amino resin, and copolymers and blends thereof, and a solvent and/or monofunctional radiation-curable diluent, and, when a monofunctional radiation-curable diluent is present, a photoinitiator, wherein the primer layer has a thickness of 40 microns or less based on the dry film thickness; (Hi) at least partially drying and/or at least partially curing the primer; (iv) inkjet printing a hybrid solvent/radiation-curable ink onto the primer layer to form a hybrid solvent/radiation-curable ink layer, wherein the hybrid solvent/radiation-curable ink comprises at least 50% by weight organic solvent, based on the total weight of the ink, radiation-curable material and a photoinitiator; and (v)(a) optionally depositing a protective layer onto the hybrid solvent/radiation-curable ink layer, wherein the protective layer comprises: a thermoplastic resin selected from polyurethane, polymethacrylate, polyvinyl, poly(cellulose acetate butyrate), polyester, epoxy resin, hydrocarbon resin, ketone or aldehyde resin, amino resin, and copolymers and blends thereof, a solvent and/or radiation-curable diluent, and, when a monofunctional radiation-curable diluent is present, a photoinitiator, and a crosslinking agent; and (b) drying and curing the hybrid solvent/radiation-curable ink layer; wherein when (v)(a) is present, (v)(a) and (v)(b) can be in either order, with the proviso that when step (v)(b) occurs before step (v)(a), the method further comprises the step of drying and/or curing the protective layer.

The present invention further provides a printed substrate obtainable by the methods of the present invention.

The present invention will now be described with reference to the accompanying drawings, in which: Fig. I shows a schematic of the printed substrate obtainable by the method of the present invention; Fig. 2 shows a photograph of a printed substrate of the present invention; and Fig. 3 shows a photograph of a printed substrate in the absence of a primer layer of the present invention.

It has been found that depositing a primer as defined herein onto the substrate to form a primer layer aids the pinning of the hybrid solvent/radiation-curable ink. In the method of the invention the primer is deposited onto the substrate to form a primer layer. The primer layer is then at least partially dried and/or at least partially cured. The resultant at least partially dry and/or at least partially cured primer layer is then deposited with the desired inkjet image by inkjet printing a hybrid solvent/radiation-curable ink onto the primer layer to form a hybrid solvent/radiation-curable ink layer. Without wishing to be bound by theory, it is believed that the primer layer absorbs some of the solvent from the inkjet droplets resulting in a rise in viscosity of the hybrid solvent/radiation-curable ink, thus pinning the ink droplets without the need forthe application of heat. The solvent is pulled into the primer and results in an increase in viscosity of the hybrid solvent/radiation-curable ink, preventing reticulation (or pooling) of the ink. This results in an ink image of excellent quality. The resulting film also has excellent flexibility and water, chemical and abrasion resistance. Thus, the method of the present invention allows for the production of a printed substrate having an improved image quality, flexibility and abrasion, water and chemical resistance.

The substrate is a non-elongatable substrate. Such substrates typically consist of long linear polymer chains, or contain low levels of plasticiser. This makes the substrates suitable for certain technical applications, like sportswear and sports equipment. But it makes them difficult to print onto because the long linear polymer chains and low levels of plasticiser lead to a structure which is unreceptive to wetting by the solvent/diluent.

By "non-elongatable" is meant that the substrate does not elongate readily at room temperature.

Specifically, the load required to elongate a sample of the substrate having a fixed width of 50.8 mm by 5% at 25°C was 300 N or more (typically measured using an electromechanical pull tester, such as an Instron 5544 tester).

Examples of such substrates are leather or synthetic leather substrates.

Leather or synthetic leather surfaces are non-porous, non-elongatable, but highly flexible which makes them difficult to print onto. The substrate is, however, typically found in the sportswear or sports equipment field. Sportswear and sports equipment require the printed substrate to have excellent flexibility, have high resistance to abrasion and be resistant to water.

Leather is a well-known material, created by the tanning of animal rawhide and skin. The tanning processes available to transform hides and skins into leather are well known and do not require further discussion. The leather may be natural leather, where the surface to be printed is obtained solely by tanning the rawhide and skin. Alternatively, the leather may be coated leather, where the leather is split (to provide two batches from one hide) and coated with polyurethane.

Synthetic leather is produced from a fibrous base layer, typically polyester, coated with polyurethane.

Again, synthetic leathers are well known in the art.

Thus, the substrate will often be natural leather, polyurethane-coated leather, or synthetic leather (a material having a fibrous base layer coated with polyurethane). Thus, the surface which contacts the primer is often either composed of leather or polyurethane.

Other substrates include polyvinyl chloride, polystyrene, polyethylene terephthalate, polycarbonate, polypropylene, polyethylene, acrylonitrile butadiene styrene (ABS), glass and metals. Specific examples include PET bottles and polymer film labels. Grades of plastics that are non-elongatable are generally termed rigid" plastics, e.g. rigid polyvinyl chloride etc. The primer comprises a thermoplastic resin. The thermoplastic resin is selected from polyurethane, polymethacrylate, polyvinyl, poly(cellulose acetate butyrate), polyester, epoxy resin, hydrocarbon resin, ketone or aldehyde resin, amino resin, and copolymers and blends thereof Preferably, the resin is selected from polyurethane, polymethacrylate, polyvinyl, poly(cellulose acetate butyrate), polyester, and copolymers and blends thereof Copolymers may be methacrylate copolymer which includes copolymers with different alkyl substituents like methyl, ethyl, propyl and butyl methacrylates, or polyvinyl copolymer which includes copolymers of vinyl chloride and vinyl acetate. Copolymers are typically chosen for their favourable glass transition temperatures. Blends are mixtures of polymers or copolymers, like methacrylate copolymer and polyvinyl copolymer blend or cellulose acetate butyrate and methacrylate copolymer blend.

The thermoplastic resin preferably has a weight-average molecular weight (Mw) of 1,500 to 200,000.

The Mw may be measured by known techniques in the art, such a gel permeation chromatography (GPC) using polystyrene standards. A suitable GPC apparatus for measuring Mw is an LC instrument having the following parameters -Column set: MiniMix F or MiniMix D (depending on molecular weight), Eluent: THE, Detector: UV/vis and/or ELS, Calibration: conventional vs polystyrene. This approach is applicable to polymers having a Mw of 400-400,000.

The resins are chosen such that the resultant primer layer which has been at least partially dried and/or at least partially cured is resoluble in the solvent of the ink that will be deposited thereon and will soften with heat. It is important that the primer layer is not thermoset. If the primer layer were not resoluble in the solvent of the ink, the hybrid solvent/radiation-curable ink layer would fail to be pinned by the primer layer.

The resoluble nature of the thermoplastic resin can be tested in the primer layer by a solvent rub test.

The resultant primer layer must be soluble in the primary solvent of the ink after ito 50 double rubs and more preferably 1 to 20 double rubs. The primary solvent is the solvent present in the highest weight percent. Where two or more solvents are present in the same amount (this rarely occurs), the primary solvent is taken as a mixture of those solvents. The double rub test is well known in the art.

The primer is applied to the substrate by any suitable means. It is then at least partially dried and/or at least partially cured. One then takes a lint4ree (cotton) cloth saturated in the solvent. One then carries out a double rub, each rub being 10cm. The number of rubs is counted until the substrate is visible under the primer. Optionally a coloured solvent-based ink, preferably having one rub solvent resistance, may be printed under the primer so that the colour is easily visible. The substrate will then become visible when the colour is removed.

When it is stated that the primer is "at least partially dried and/or "at least partially" cured, it means that the drying/curing is performed to a sufficient extent that the primer layer retains its resolubility properties as determined by the above-described double solvent rub test.

The thermoplastic resin may be a passivelinert thermoplastic resin or a radiation-crosslinkable (e.g. U\") thermoplastic resin. A UV crosslinkable thermoplastic resin is preferably acrylate functionalised and is hence crosslinkable when exposed to UV radiation.

Preferably, the primer comprises polyurethane. Preferably, the primer comprises a passive polyurethane resin or UV crosslinkable polyurethane. The UV crosslinkable polyurethane may be an aqueous polyurethane dispersion (PUD) which is acrylate functionalised. The aqueous PUD comprises acrylate functionalised polyurethane that is dispersed in water and is crosslinkable when exposed to UV radiation.

The primer comprises a solvent andlor monofunctional radiation-curable diluent. Preferably, the primer comprises a solvent and is hence a solvent-based primer. Preferably, the primer comprises a monofunctional radiation-curable diluent and is hence a radiation-curable-based primer. Preferably, the primer comprises a solvent and a monofunctional radiation-curable diluent and is hence a hybrid solvent radiation-curable-based primer. Preferably, the primer is a white/clear hybrid solvent radiation-curable-based primer.

A solvent-based primer may comprise a passive (or inert) thermoplastic resin or a UV crosslinkable thermoplastic resin. A radiation-curable-based primer layer comprises a passive/inert thermoplastic resin. A hybrid solvent/radiation-curable-based primer may comprise a passive/inert thermoplastic resin or a UV crosslinkable thermoplastic resin.

The solvent is selected such that it provides solvation to the resin and has good adhesion properties to the particular substrate in question. This is especially important for sportswear and sports equipment applications which utilise difficult substrates. Suitable solvents are discussed hereinbelow with reference to the ink.

Preferably, the monofunctional radiation-curable diluent comprises monofunctional (meth)acrylate alone or in combination with an N-vinyl amide and/or, N-acryloyl amine monomer. Multifunctional monomers are avoided because they form crosslinked three-dimensional networks which are not resoluble by the ink. For this reason, the primer, when it contains a reactive diluent, is preferably free of multifunctional monomers.

By "radiation-curable" is meant a material that polymerises or crosslinks when exposed to actinic radiation, commonly ultraviolet light, in the presence of a photoinitiator. Thus, when a monofunctional radiation-curable diluent is present, a photoinitiator is required. Suitable photoinitiators are the same as those described with reference to the ink.

Monofunctional (meth)acrylate monomers are esters of (meth)acrylic acid and are well known in the art. Examples include a monomer selected from phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA), isobornyl acrylate (IBOA), tetrahydrofurfuryl acrylate (THFA), dicyclopentenyl oxyethyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, octadecyl acrylate, tridecyl acrylate, isodecyl acrylate (iso-decyl A), lauryl acrylate or combinations thereof.

(Meth)acrylate is intended herein to have its standard meaning, i.e. acrylate and/or methacrylate.

Mono and multifunctional are also intended to have their standard meanings, i.e. one and two or more groups, respectively, which take part in the polymerisation reaction on curing.

N-Vinyl amides and N-(meth)acryloyl amines may also be used in the primer. N-vinyl amides are well-known monomers in the art and a detailed description is therefore not required. N-vinyl amides have a vinyl group attached to the nitrogen atom of an amide which may be further substituted in an analogous manner to the (meth)acrylate monomers. Preferred examples are N-vinyl caprolactam (NVC) and N-vinyl pyrrolidone (NVP). Similarly, N-acryloyl amines are also well-known in the art. N-acryloyl amines also have a vinyl group attached to an amide but via the carbonyl carbon atom and again may be further substituted in an analogous manner to the (meth)acrylate monomers. A preferred example is N-acryloylmorpholine (ACMO).

In an alternative embodiment, the radiation-curable material is capable of polymerising by cationic polymerisation. Suitable materials include oxetanes and epoxides. The radiation-curable material can also comprise a combination of free-radical polymerisable and cationically polymerisable materials.

The primer includes one or more photoinitiators.

The free-radical photoinitiator can be selected from any of those known in the art. For example, benzophenone, 1 -hydroxycyclohexyl phenyl ketone, 1 -[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-i -propane-i -one, 2-benzyl-2-dimethylamino-(4-morpholinophenybutan-i -one, isopropyl thioxanthone, benzil dimethylketal, bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide or mixtures thereof Such photoinitiators are known and commercially available such as, for example, under the trade names Irgacure and Darocur (from Ciba) and Lucerin (from BASF).

In the case of a cationically curable system, any suitable cationic initiator can be used, for example sulfonium or iodonium based systems. Non limiting examples include: Rhodorsil P1 2074 from Rhodia; MC AA, MC BB, MC CC, MC CC PF, MC SD from Siber 1-legner; UV9380c from Alfa Chemicals; Uvacure i590 from UCB Chemicals; and Esacure i064 from Lamberti spa.

The primer optionally comprises a flow aid. Preferable flow aids include silicone fluids, and non-silicone defoamers and levelling agents. The primer layer can optionally contain inorganic materials such as extender powders and the like waxes, matting agents and in the case of UV curable systems photo in itiato is.

The primer is deposited onto the substrate to form a primer layer. The primer layer may be deposited onto the substrate by any means known in the art. Preferably, the primer layer is deposited onto the substrate by screen printing, flexographic printing, inkjet printing, bar coating spraying, curtain coating, slit coating or wipe on by hand.

A solvent-based primer is preferably deposited onto the substrate by screen printing both flatbed and rotary, flexographic printing, inkjet printing, bar coating spraying, curtain coating, slit coating or wipe on by hand. A radiation-curable-based primer is preferably deposited onto the substrate by screen printing, flexographic printing, inkjet printing or bar coating. A hybrid solvent radiation-curable-based primer is preferably deposited onto the substrate by screen printing flatbed or rotary, fiexographic printing, inkjet printing, bar coating, spraying, curtain coating or slit coating. A water-based UV crosslinkable polyurethane dispersion is preferably deposited onto the substrate by screen printing flatbed or rotary, flexographic printing, bar coating, spraying, curtain coating or slit coating.

The primer is then at least partially dried and/or at least partially cured to form a primer layer.

It should be noted that the terms "dry" and "cure" are often used interchangeably in the art when referring to radiation-curable inkjet inks to mean the conversion of the inkjet ink from a liquid to solid by polymerisation and/or crosslinking of the radiation-curable material. Herein, however, by "drying" is meant the removal of the solvent by evaporation and by "curing" is meant the polymerisation and/or crosslinking of the radiation-curable material.

A solvent-based primer layer is at least partially thermally dried and is preferably fully dried to evaporate the solvent before the hybrid solvent/radiation-curable ink is deposited on the surface of the primer layer. A radiation-curable-based primer layer is at least partially cured, preferably fully cured, to produce an at least partially cured, preferably fully cured, primer layer before the deposition of the hybrid solvent/radiation-curable ink onto the primer layer. A hybrid solvent radiation-curable-based primer is at least partially dried and/or at least partially cured to produce an at least partially dry and/or at least partially cured primer layer before the deposition of the hybrid solvent/radiation-curable ink onto the primer layer. A white/clear hybrid based primer is preferably at least partially dried and at least partially cured. For the hybrid solvent radiation-curable primer, when the primer is jetted onto the substrate a small amount of UV pinning is required to pin the droplets to prevent reticulation on the non-receptive substrate. However, for higher viscosity hybrid solvent radiation-curable systems, such as screen orfiexographic printing, the ink would not suffer from pooling and could simply be thermally dried. In all cases, the hybrid solvent radiation-curable primers should not be fully cured before jetting the image layer onto the primer as crosslinking the hybrid solvent radiation-curable primers would prevent solvent absorption and hence the pinning effect. In other words, the primer layer would lose its resolubility properties as determined by the above-described double solvent rub test and become non-receptive to the hybrid solvent radiation-curable ink which is inkjet printed onto the primer layer.

A water-based UV crosslinkable thermoplastic resin dispersion primer, preferably a polyurethane dispersion, is at least partially dried to form an at least partially dry film before depositing the inkjet ink.

A key factor for the pinning efficiency of the primer layer is the resolubility of the primer layer in the solvent used in the hybrid solvent/radiation-curable ink which is to be deposited onto the primer layer.

In the case of the solvent based primers, the at least partially dried, preferably fully dried, films are readily resoluble by the solvent of the ink. The at least partially dried, preferably fully dried, films will still be receptive to solvent from the overlaying ink because it leaves behind a thermoplastic resin that is resoluble.

The radiation-curable-based primers can be fully cured because they contain monofunctional radiation-curable diluents and thermoplastic resins. A lack of crosslinking in the cured radiation-curable-based primer layer means that the fully cured radiation-curable-based primers are readily resoluble by the solvent of the ink after curing of the primer with radiation. Excessive crosslinking would render the cured primer layer insoluble in the solvent and hinder the pinning process.

The thermally dried water-based UV crosslinkable thermoplastic resin dispersion primer is not UV crosslinked before the ink is deposited as this would render the primer layer insoluble and non-receptive in the solvent and hence it could not perform its pinning role.

For the hybrid solvent radiation-curable-based primers, such as the hybrid solvent radiation-curable white/clear primers, some degree of radiation and thermal drying is preferably used. This is in order to control primer wetting and flow on the substrate. A low UV dose is used to pin the droplets to prevent excessive flow and heat is also preferably applied to evaporate some of the solvent before the hybrid inks are deposited. This combination of low UV dose and heat is to increase the viscosity of the ink droplets and arrest flow. It is essential that the primer layer retains its resolubility in the solvent system of the hybrid ink. Therefore, such primers must not be fully cured, so that the monofunctional radiation-curable diluent remains not fully cross-linked and so still retains some useful affinity for the solvent. If a too high a UV dose is used and the film is crosslinked, the primer layerwill not function.

The primer layer preferably has a thickness of 40 microns or less, more preferably 20 microns or less and most preferably 10 microns or less, based on the dry film thickness. The dry film thickness means the thickness of the film after it is at least partially dried and/or at least partially cured, i.e. when the primer layer receives the ink. It is surprising that such a small amount of primer provides the required image quality combined with the necessary robustness and flexibility. The thickness is preferably 1 micron or above, more preferably 5 microns or above. Film thicknesses can be measured using a confocal laser scanning microscope.

The inkjet ink is a hybrid solvent/radiation-curable ink jet ink which comprises at least 50% by weight organic solvent, based on the total weight of the ink, radiation-curable material and a photoinitiator.

The ink comprises a modified ink binder system. The presence of a radiation-curable material and a photoinitiator in the ink means that crosslinked polymers can be formed in the dried ink film, leading to improved adhesion to a range of substrates and improved resistance to solvents. The presence of organic solvent means that the advantageous properties of solvent-based inkjet inks are maintained.

By "radiation-curable" is meant a material that polymerises or crosslinks when exposed to actinic radiation, commonly ultraviolet light, in the presence of a photoinitiator.

The radiation-curable material may optionally comprise a radiation-curable oligomer. The oligomers may possess different degrees of functionality, and a mixture including combinations of mono, di, tn and higher functionality monomers/oligomers may be used.

Radiation-curable oligomers suitable for use in the present invention comprise a backbone, for example a polyester, urethane, epoxy or polyether backbone, and one or more radiation polymerisable groups. The oligomer preferably comprises a urethane backbone. The polymerisable group can be any group that is capable of polymerising upon exposure to radiation. Preferably the oligomers are (meth)acrylate oligomers. Preferably they are multifunctional and most preferably have a functionality of 2-6.

Particularly preferred radiation-curable materials are urethane acrylate oligomers as these have excellent adhesion and elongation properties. Most preferred are tn-, tetra-, penta-, hexa-or higher functional urethane acrylates, particularly hexafunctional urethane acrylates as these yield films with good solvent resistance.

Other suitable examples of radiation-curable oligomers include epoxy based materials such as bisphenol A epoxy acrylates and epoxy novolac acrylates, which have fast cure speeds and provide cured films with good solvent resistance.

Preferred oligomers have a molecular weight of 450 to 4,000, more preferably 600 to 4,000.

Molecular weights (number average) can be calculated if the structure of the oligomer is known or molecular weights can be measured using gel permeation chromatography using polystyrene standards.

In one embodiment the radiation-curable oligomer polymerises by free-radical polymerisation. The radiation-curable oligomer cures upon exposure to radiation in the presence of a photoinitiatorto form a crosslinked, solid film. The resulting film has good adhesion to substrates and good solvent resistance. Any radiation-curable oligomer that is compatible with the other ink components and that is capable of curing to form a crosslinked, solid film is suitable for use in the ink. Thus, the ink formulator is able to select from a wide range of suitable oligomers.

Preferred oligomers for use in the invention have a viscosity of 0.5 to 20 Pa.s at 60°C, more preferably 5 to 15 Pa.s at 60°C and most preferably 5 to 10 Pa.s at 60°C. Oligomer viscosities can be measured using an ARG2 rheometer manufactured by T.A. Instruments, which uses a 40 mm oblique /2° steel cone at 60°C with a shear rate of 25 seconds1.

The ink optionally contains radiation-curable monomers as the radiation-curable material. Suitable free-radical polymerisable monomers are well known in the art and include (meth)acrylates, a,-unsaturated ethers, vinyl amides and mixtures thereof.

The monomers may possess different degrees of functionality, and a mixture including combinations of mono, di, tn and higher functionality monomers/oligomers may be used.

Monofunctional (meth)acrylate monomers are well known in the art and are preferably the esters of acrylic acid. Preferred examples include phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA), isobornyl acrylate (IBOA), tetrahydrofurfuryl acrylate (THFA), 2-(2-ethoxyethoxy)ethyl acrylate, octadecyl acrylate (ODA), tridecyl acrylate (TDA), isodecyl acrylate (IDA) and lauryl acrylate.

Suitable multifunctional (meth)acrylate monomers include di-, tn-and tetra-functional monomers.

Examples of the multifunctional acrylate monomers that may be included in the ink-jet inks include hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, polyethylene glycol diacrylate (for example tetraethylene glycol diacrylate), dipropylene glycol diacrylate, tri(propylene glycol) triacrylate, neopentyl glycol diacrylate, bis(pentaerythritol) hexaacrylate, and the acrylate esters of ethoxylated or propoxylated glycols and polyols, for example, propoxylated neopentyl glycol diacrylate, ethoxylated trimethylolpropane triacrylate, and mixtures thereof Suitable multifunctional (meth)acrylate monomers also include esters of methacrylic acid (i.e. methacrylates), such as hexanediol dimethacrylate, trimethylolpropane trimethacrylate, triethyleneglycol dimethacrylate, diethyleneglycol dimethacrylate, ethyleneglycol dimethacrylate, 1,4-butanediol dimethacrylate. Mixtures of (meth)acrylates may also be used.

(Meth)acrylate is intended herein to have its standard meaning, i.e. acrylate and/or methacrylate.

Mono and multifunctional are also intended to have their standard meanings, i.e. one and two or more groups, respectively, which take part in the polymerisation reaction on curing.

In an alternative embodiment of the invention, the radiation-curable material is capable of polymerising by cationic polymerisation. Suitable materials include, oxetanes and epoxides (e.g. cycloaliphatic epoxides, bisphenol A epoxides and epoxy novolacs). The radiation-curable material according to this embodiment may comprise a mixture of cationically curable monomer and oligomer.

For example, the radiation-curable material may comprise a mixture of an epoxide oligomer and an oxetane monomer.

The radiation-curable material can also comprise a combination of free-radical polymerisable and cationically polymerisable materials.

cl,13-Unsaturated ether monomers can polymerise by free-radical polymerisation and may be useful for reducing the viscosity of the ink when used in combination with one or more (meth)acrylate monomers. Examples are well known in the art and include vinyl ethers such as triethylene glycol divinyl ether, diethylene glycol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether and ethylene glycol monovinyl ether. Mixtures of op-unsaturated ether monomers may be used.

N-Vinyl amides and N-(meth)acryloyl amines may also be used in the ink. N-vinyl amides are well-known monomers in the art and a detailed description is therefore not required. N-vinyl amides have a vinyl group attached to the nitrogen atom of an amide which may be further substituted in an analogous manner to the (meth)acrylate monomers. Preferred examples are N-vinyl caprolactam (NVC) and N-vinyl pyrrolidone (NVP). Similarly, N-acryloyl amines are also well-known in the art. N-acryloyl amines also have a vinyl group attached to an amide but via the carbonyl carbon atom and again may be further substituted in an analogous manner to the (meth)acrylate monomers. A preferred example is N-acryloylmorpholine (ACMO).

Preferably the ink comprises 10 to 30% by weight of radiation-curable material based on the total weight of the ink, preferably at least 12% by weight, more preferably 10 to 20% by weight, based on the total weight of the ink.

The ink includes one or more photoinitiators. The ink includes a free-radical polymerisable material and hence the photoinitiator system includes a free-radical photoinitiator.

The free-radical photoinitiator can be selected from any of those known in the art. For example, benzophenone, 1 -hydroxycyclohexyl phenyl ketone, 1 -[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-i -propane-i -one, 2-benzyl-2-dimethylamino-(4-morpholinophenyl)butan-1 -one, isopropyl thioxanthone, benzil dimethylketal, bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide or mixtures thereof Such photoinitiators are known and commercially available such as, for example, under the trade names Irgacure and Darocur (from Ciba) and Lucerin (from BASF).

In the case of a cationically curable system, any suitable cationic initiator can be used, for example sulfonium or iodonium based systems. Non limiting examples include: Rhodorsil P1 2074 from Rhodia; MC AA, MC BB, MC CC, MC CC PF, MC SD from Siber Hegner; UV9380c from Alfa Chemicals; Uvacure 1590 from UCS Chemicals; and Esacure 1064 from Lamberti spa.

Preferably the photoinitiator is present in an amount of ito 20% by weight, preferably 4 to iO% by weight, based on the total weight of the ink.

The ink contains an organic solvent. The organic solvent is in the form of a liquid at ambient temperatures and is capable of acting as a carrier for the remaining components of the ink. The organic solvent component of the ink may be a single solvent or a mixture of two or more solvents.

As with known solvent-based inkjet inks, the organic solvent used in the ink is required to evaporate from the printed ink, typically on heating, in order to allow the ink to dry. The solvent can be selected from any solvent commonly used in the printing industry, such as glycol ethers, glycol ether esters, alcohols, ketones, esters, organic carbonates, lactones and pyrrolidones.

The organic solvent is present in an amount of at least 50% by weight, preferably at least 60% by weight, based on the total weight of the ink.

Known solvent-based inkjet inks dry solely by solvent evaporation with no crosslinking or polymerisation occurring. The film produced therefore has limited chemical resistance properties. In order to improve resistance of prints to common solvents such as alcohols and petrol, binder materials that have limited solubility in these solvents are added to the ink. The binder is typically in solid form at 25°C so that a solid printed film is produced when solvent is evaporated from the ink.

Suitable binders such as vinyl chloride copolymer resins generally have poor solubility in all but the strongest of solvents such as glycol ether acetates and cyclohexanone, both of which are classified as "harmful" and have strong odours. In order to solubilise the binder, these solvents are generally added to the ink.

The ink includes radiation-curable material that cures as the ink dries and it is not therefore necessary to include a binder in the ink in order to provide a printed film having improved solvent resistance. In one embodiment of the invention the organic solvent is not therefore required to solubilise a binder such as a vinyl chloride copolymer resin, which means that the ink formulator has more freedom when selecting a suitable solvent or solvent mixture.

In a preferred embodiment the organic solvent is a low toxicity and/or a low odour solvent. Solvents that have been given VOC exempt status by the United States Environmental Protection Agency or European Council are also preferred.

The most preferred solvents are selected from glycol ethers and organic carbonates and mixtures thereof. Cyclic carbonates such as propylene carbonate and mixtures of propylene carbonate and one or more glycol ethers are particularly preferred.

Alternative preferred solvents include lactones, which have been found to improve adhesion of the ink to PVC substrates. Mixtures of lactones and one or more glycol ethers, and mixtures of lactones, one or more glycol ethers and one or more organic carbonates are particularly preferred. Mixtures of gamma butyrolactone and one or more glycol ethers, and mixtures of gamma butyrolactone, one or more glycol ethers and propylene carbonate are particularly preferred.

In another embodiment of the invention, dibasic esters and/or bio-solvents may be used.

Dibasic esters are known solvents in the art. They can be described as di(C1-C4 alkyl) esters of a saturated aliphatic dicarboxylic acid having 3 to 8 carbon atoms having following general formula: R1 OAOR2 in which A represents (CH2)15, and R1 and R2 may be the same or different and represent C1-C4 alkyl which may be a linear or branched alkyl radical having 1 to 4 carbon atoms, preferably methyl or ethyl, and most preferably methyl. Mixtures of dibasic esters can be used.

Bio-solvents, or solvent replacements from biological sources, have the potential to reduce dramatically the amount of environmentally-polluting VOCs released in to the atmosphere and have the further advantage that they are sustainable. Moreover, new methods of production of bio-solvents derived from biological feedstocks are being discovered, which allow bio-solvent production at lower cost and higher purity.

Examples of bio-solvents include soy methyl ester, lactate esters, polyhydroxyalkanoates, terpenes and non-linear alcohols, and D-limonene. Soy methyl ester is prepared from soy. The fatty acid ester is produced by esterification of soy oil with methanol. Lactate esters preferably use fermentation-derived lactic acid which is reacted with methanol and/or ethanol to produce the ester. An example is ethyl lactate which is derived from corn (a renewable source) and is approved by the FDA for use as a food additive. Polyhydroxyalkanoates are linear polyesters which are derived from fermentation of sugars or lipids. Terpenes and non-linear alcohols may be derived from corn cobs/rice hulls. An example is D-limonene which may be extracted from citrus rinds.

Other solvents may be included in the organic solvent component. A particularly common source of other solvents is derived from the way in which the colouring agent is introduced into the inkjet ink formulation. The colouring agent is usually prepared in the form of a pigment dispersion in a solvent, e.g. 2-ethylhexyl acetate. The solvent tends to be around 40 to 50% by weight of the pigment dispersion based on the total weight of the pigment dispersion and the pigment dispersion typically makes up around 5 to 15% by weight of the ink and sometimes more.

Although in some embodiments, a waterbased PUD may be used, preferably, the ink is substantially free of water, although some water will typically be absorbed by the ink from the air or be present as impurities in the components of the inks, and such levels are tolerated. For example, the ink may comprise 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 may also contain a passive (or "men') thermoplastic resin. Passive resins are resins which do not enter into the curing process, i.e. the resin is free of functional groups which polymerise under the curing conditions to which the ink is exposed. In other words, resin is not a radiation-curable material.

The resin may be selected from epoxy, polyester, vinyl, ketone, nitrocellulose, phenoxy or acrylate resins, or a mixture thereof and is preferably a poly(methyl (meth)acrylate) resin. The resin has a weight-average molecular weight of 1,500-200,000, as determined by GPC with polystyrene standards as previously described hereinabove.

The ink may be a coloured or a colourless ink. By "colourless" is meant that the ink is free of colorant such that no colour can be detected by the naked eye. Minor amounts of colorant that do not produce colour that can be detected by the eye can be tolerated, however. Typically the amount of colorant present will be less than 0.3% by weight based on the total weight of the ink, preferably less than 0.1%, more preferably less than 0.03%. Colourless inks may also be described as "clear" or "water white". Colourless inks may also be used as a varnish, where it is applied over a coloured ink. For the avoidance of doubt, coloured inks include white inks.

The coloured inks comprise at least one colouring agent. The colouring agent 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 under the trade-names Paliotol (available from BASF plc), Cinquasia, Irgalite (both available from Ciba Speciality Chemicals) and Hostaperm (available from Clariant UK). 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. Mixtures of pigments may be used.

In one aspect the following pigments are preferred. Cyan: phthalocyanine pigments such as Phthalocyanine blue 15.4. Yellow: azo pigments such as Pigment yellow 120, Pigment yellow 151 and Pigment yellow 155. Magenta: quinacridone pigments, such as Pigment violet 19 or mixed crystal quinacridones such as Cromophtal Jet magenta 2BC and Cinquasia RT-355D. Black: carbon black pigments such as Pigment black 7.

Pigment particles dispersed in the ink should be sufficiently small to allow the ink to pass through an inkjet nozzle, typically having a particle size less than 8 pm, preferably less than 5 pm, more preferably less than 1 pm and particularly preferably less than 0.5 pm.

The colorant is preferably present in an amount of 20 weight% or less, preferably 10 weight% or less, more preferably 8 weight% or less and most preferably 2 to 5% by weight, based on the total weight of the ink. A higher concentration of pigment may be required for white inks, however, for example up to and including 30 weight%, or25 weight% based on the total weight of the ink.

The inkjet ink exhibits a desirable low viscosity (200 mPa.s or less, preferably 100 mPa.s or less, more preferably 25 mPa.s or less and most preferably 10 mPa.s or less, at 25°C).

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, surfactants, defoamers, dispersants, synergists for the photoinitiator, stabilisers against deterioration by heat or light, reodorants, flow or slip aids, biocides and identifying tracers.

The inkjet ink preferably comprises a radiation-curable material, a photoinitiator, a colorant and a solvent.

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

The hybrid solvent/radiation-curable ink is deposited onto the at least partially dried and/or at least partially cured primer layer to form a hybrid solvent/radiation-curable ink layer or deposited inkjet image by inkjet printing. lnkjet printing is well known in the art. The image may be deposited using a roll-to-roll solvent UV hybrid printer. Alternatively, the inks may be deposited using a flatbed printer where the print head scans across a stationary substrate before it is advanced ready for the next print swathe to deposited. In this case there is an optional top down heater or air knife to assist the efficiency of the pinning process by removal of the solvent carrier form the solvent UV hybrid ink.

Following the pinning process, in one embodiment the print is removed manually from the printer to a separate thermal drier where the remainder of the solvent carrier is removed from the ink before finally curing the image by exposure to a source of actinic radiation. This final curing stage can either be completed in-line by using a combination drier fitted with both a source of heat and a UV curing system or using separate thermal drying and UV curing systems.

In a further embodiment the printing pinning, thermal drying and final UV curing can be completed in-line. After deposition of the image with the solvent UV hybrid ink and pinning on the primed material, the print is transferred to a thermal drying apparatus before finally passing under a source of actinic radiation to effect the final cure process. The transfer of the print through the combination printer can either be accomplished using sheets of the substrate held in grippers that move it through each stage of the process or alternatively via a roll-to-roll process where the primed substrate is moved as a web through each stage by the use of rollers. In a further embodiment the roll4o-roll web production process above can be modified to apply the primer layer in-line using a suitable method, for example rotary screen printing, flexographic printing, roller coating, bar coating or slit coating The hybrid solvent/radiation-curable ink layer may then be dried and cured.

The printing is preferably all performed by inkjet printing, e.g. on a roll-to-roll printer or flat-bed printer.

Evaporation of the solvent can occur simply by exposure of the inks to the atmosphere, but the inks may also be heated to accelerate evaporation. In addition, the inks are exposed to actinic radiation to cure the ink.

The ink can be printed using inkjet printers that are suitable for use with solvent-based inkjet inks, in combination with a source of actinic radiation. The features of printers that are suitable for printing solvent-based inkjet inks are well known to the person skilled in the art and include the features described below.

The printing apparatus may comprise a means for evaporating solvent from the ink at the appropriate time after the ink has been applied to the substrate. Any means that is suitable for evaporating solvent from known solvent-based inkjet inks can be used in the apparatus. Examples are well known to the person skilled in the art and include dryers, heaters, air knives and combinations thereof.

In one embodiment, the solvent is removed by heating. Heat may be applied through the substrate and/or from above the substrate, for example by the use of heated plates (resistive heaters, inductive heaters) provided under the substrate or radiant heaters (heater bars, IR lamps, solid state IR) provided above the substrate. In a preferred embodiment, the ink can be jetted onto a preheated substrate that then moves over a heated platen. The apparatus may comprise one or more heaters.

As previously stated however, typical materials used for the production of the sportswear and sports equipment have relatively high film thickness and hence have a high heat capacity. The high heat capacity means that it is not possible to increase the temperature of the substrate quickly enough to effect the required viscosity increase in the ink droplets. The heat cannot penetrate through the substrate sufficiently, meaning that the pinning process is disabled, leading to excessive ink flow, yielding very poor image quality. In other words, the time needed to pin the ink droplets is too long owing to the high heat capacity of the substrates, which results in the pooling of ink droplets and a poor quality image.

Accordingly, the primer layer absorbs some of the solvent from the inkjet droplets resulting in a rise in viscosity of the hybrid solvent/radiation-curable ink, thus pinning the ink droplets without the need for the application of heat. The solvent is pulled into the primer and results in an increase in viscosity of the hybrid solvent1radiation-curable ink, preventing reticulation (or pooling) of the ink.

When printing the ink, a significant portion of the solvent is preferably allowed to evaporate before the ink is cured. Preferably substantially all of the solvent is evaporated before the ink is finally cured.

This is achieved by subjecting the printed ink to conditions that would typically dry conventional solvent-based inkjet inks. In the case of the ink, such conditions will remove most of the solvent but it is expected that trace amounts of solvent will remain in the film given the presence of the radiation-curable component in the ink.

Unlike standard solvent-based inks, once the solvent has evaporated, the ink is not expected to be completely solid. Rather, what remains on the surface is a high viscosity version of a radiation-curable ink. The viscosity is sufficiently high to inhibit or significantly hinder ink flow and prevent image degradation in the timescale that is needed to post-cure the ink. Upon exposure to a radiation source, the ink cures to form a relatively thin polymerised film. The ink of the present invention typically produces a printed film having a thickness of ito 20 pm, preferably ito 10 pm, for example 2 to 5 pm. Film thicknesses can be measured using a confocal laser scanning microscope.

The source of actinic radiation can be any source of actinic radiation that is suitable for curing radiation-curable inks but is preferably a UV source. Suitable UV sources include mercury discharge lamps, fluorescent tubes, light emitting diodes (LEDS), flash lamps and combinations thereof. One or more mercury discharge lamps, fluorescent tubes, or flash lamps may be used as the radiation source. When LEDs are used, these are preferably provided as an array of multiple LEDs.

Preferably the source of actinic radiation is a source that does not generate ozone when in use.

The source of UV radiation could be situated off-line in a dedicated conveyor UV curing unit, such as the SUVD Svecia UV Dryer. Preferably, however, the source of radiation is situated in-line, which means that the substrate does not have to be removed from the printing apparatus between the heating and curing steps.

The radiation source can be mobile, which means that the source is capable of moving back and forth across the print width, parallel with the movement of the printhead.

In one embodiment, one or more sources of actinic radiation are placed on a carriage that allows the source of actinic radiation to traverse the print width. The carriage may be placed up and downstream of the printer carriage in allow irradiation before and after evaporation of the solvent. In this embodiment the source of actinic radiation moves independently of the printer carriage and movement of the printhead does not therefore have to be slowed in order to provide adequate time for solvent evaporation. Thus, overall productivity can be improved.

When the source of radiation is provided on separate carriage, it is necessary to provide an additional carriage rail, motor and control systems. This adaptation can lead to large increases in equipment costs.

Preferably the source of radiation is static. This means that the source does not move backwards and forwards across the print width of the substrate when in use. Instead the source of actinic radiation is fixed and the substrate moves relative to the source in the print direction.

When the source of actinic radiation is provided in the print zone of the printer, light contamination at the printhead, which could lead to premature curing in the nozzle, must be avoided. Adaptations to prevent light contamination, such as lamp shutters, give rise to additional costs. The source of radiation is therefore preferably located outside the print zone of the printing apparatus. By print zone is meant the region of the printing apparatus in which the printhead can move and therefore the region in which ink is applied to the substrate.

Static curing units preferably span the full print width, which is typically at least 1.6 m for the smaller wide format graphics printers. Fluorescent tubes, mercury discharge lamps, and light emitting diodes can be used as static curing units.

Any of the sources of actinic radiation discussed herein may be used for the irradiation of the inkjet ink. A suitable dose would be greater than 200 mJ/cm2, more preferably at least 300 mJ/cm2 and most preferably at least 500 mJ/cm2. The upper limit is less relevant and will be limited only by the commercial factor that more powerful radiation sources increase cost. A typical upper limit would be J/cm2.

The wavelength of the pinning source is typically 200-700 nm, preferably 300-500 nm and most preferably 350-450 nm.

The delay between evaporating the solvent and providing a final cure of the ink is typically at least 1 minute after jetting.

High and medium pressure mercury discharge lamps may be used.

In another embodiment of the invention the source of radiation comprises one or more flash lamps.

Flash lamps operate by discharge breakdown of an inert gas, such as xenon or krypton, between two tungsten electrodes. Unlike mercury discharge lamps, flash lamps do not need to operate at high temperature. Flash lamps also have the advantage of switching on instantaneously, with no thermal stabilisation time. The envelope material can also be doped, to prevent the transmission of wavelengths that would generate harmful ozone. Flash lamps are therefore economical to operate and therefore suitable for use.

When the primer contains a monofunctional radiation-curable diluent or a crosslinkable resin, either of these materials may remain uncured after the at least partial drying/curing step. In this case, after deposition and thermal drying of the hybrid solvent/radiation-curable ink jet ink, both the primer layer and the hybrid solvent/radiation-curable ink layer are cured concurrently.

A protective layer may optionally be deposited onto the hybrid solvent/radiation-curable ink layer. The protective layer may be deposited before or after the step of drying and curing the hybrid solvent/radiation-curable ink layer.

The protective layer comprises a resin selected from polyurethane, polymethacrylate, polyvinyl, poly(cellulose acetate butyrate), polyester, epoxy resin, hydrocarbon resin, ketone or aldehyde resin, amino resin, and copolymers and blends thereof. Preferably, the protective layer comprises polyurethane.

The protective layer further comprises a solvent and/or radiation-curable diluent. The solvent is the same as those discussed hereinabove with reference to the ink, with the proviso that the solvent should not be selected such that they will react with the crosslinker. For example, in the case where an isocyanate crosslinker is used, hydroxyl solvents that will react with this should be avoided, e.g. water, alcohols and glycol mono ethers. The radiation-curable diluent is not so limited, although when a radiation-curable diluent is present, a photoinitiator is required. The monofunctional monomers described with reference to the primer layer may be used. Alternatively, or in addition, other radiation-curable materials may be used, including multifunctional monomers.

Suitable multifunctional (meth)acrylate monomers include di-, hi-and tetra-functional monomers.

Examples of the multifunctional acrylate monomers that may be included in this layer include hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, polyethylene glycol diacrylate (for example tetraethylene glycol diacrylate), dipropylene glycol diacrylate, tri(propylene glycol) triacrylate, neopentyl glycol diacrylate, bis(pentaerythritol) hexaacrylate, and the acrylate esters of ethoxylated or propoxylated glycols and polyols, for example, propoxylated neopentyl glycol diacrylate, ethoxylated trimethylolpropane triacrylate, and mixtures thereof.

Suitable multifunctional (meth)acrylate monomers also include esters of methacrylic acid (i.e. methacrylates), such as hexanediol dimethacrylate, trimethylolpropane trimethacrylate, triethyleneglycol dimethacrylate, diethyleneglycol dimethacrylate, ethyleneglycol dimethacrylate, 1,4-butanediol dimethacrylate. Mixtures of (meth)acrylates may also be used.

Suitable photoinitiators are the same as those described with reference to the ink.

The protective layer further comprises a crosslinking agent. The crosslinking agent should be capable of reacting with the resin system used in the protective top coat. Depending on the resin selected suitable crosslinkers include amines, acids, aziridines, carbodimides and isocyanates. Preferably, the crosslinking agent is isocyanate as these have the widest range of reactivity.

The protective layer may comprise formulations used for the primer, together with a crosslinking agent. The crosslinker may optionally also crosslink with the primer to provide additional toughness to the film.

The protective layer is applied by any means known in the art but is preferably applied by traditional printing process such screen printing, flexographic printing or roller coating.

In the event that the step of drying and curing the hybrid solvent/radiation-curable ink layer occurred before the deposition of the protective layer, the protective layer is then thermally dried and/or cured.

In the event that the step of drying and curing the hybrid solvent/radiation-curable ink layer did not occur before the deposition of the protective layer, the protective layer is then thermally dried and radiation cured. The hybrid solvent/radiation-curable ink layer is cured through the protective layer.

When the primer contains a monofunctional radiation-curable diluent or a crosslinkable resin, either of these materials may remain uncured after the at least partial drying/curing step. In this case, after deposition and thermal drying of the hybrid solvent/radiation-curable ink jet ink, and optional deposition of the protective layer, both the primer layer and the hybrid solvent/radiation-curable ink layer are cured concurrently through the protective layer.

The present invention also provides a printed substrate obtainable by the method of the present invention. Preferably, the substrate is sportswear or sports equipment.

The invention will now be described with reference to the following examples, which are not intended to be limiting.

Examples

Example 1

A primer, as detailed in Table 1, was prepared by mixing the components in the given amounts.

Amounts are given as weight percentages based on the total weight of the primer.

Table 1

Primer Amount Polyurethane (Estane 5715 P) 31.78 Solvent naptha 160/1 85 0.7 Isopropyl oxitol acetate 58.15 Cyclohexanone 9.07 Silicone fluid Fl 11/300 0.30 The primer was applied to a synthetic leather with a polyurethane top coat substrate by screen printing through a 90.48 PW screen to form a primer layer. The primer layer was then thermally dried for 3 minutes at 70°C to form a dry film.

Hybrid solvent/radiation-curable ink formulations shown in Table 2 were prepared by mixing the components in the given amounts. Amounts are given as weight percentages based on the total weight of the ink.

Table 2

Cyan ink Magenta ink Yellow ink Black ink Component _________________________ (ink 1) (ink 2) (ink 3) (ink 4) Gamma butyrolactone 16.3 15.5 15.6 16.5 Diethylene glycol diethyl ether 53.1 51.7 52.4 51.4 Nippon Goshei UV7630B 18 15 12 19.5 Cyan pigment dispersion 6 --- Magenta pigment dispersion -11.2 -- Yellow pigment dispersion --13.4 -Black pigment dispersion ---6 Irgacure 819 4 4 4 4 Irgacure 2959 2 2 2 2 UV 12 stabiliser 0.5 0.5 0.5 0.5 Byk331 0.1 0.1 0.1 0.1 The hybrid solvent/radiation-curable inks were then ink-jetted onto the resultant primer layers (dry films) to form hybrid solvent/radiation-curable ink layers and desired inkjet images. The resulting hybrid solvent/radiation-curable ink layers were then dried for 3 minutes at 60°C before UV curing the hybrid UV ink layers to produce the finished prints.

The higher functionality (meth)acrylate oligomer used in the hybrid ink gives a far higher resistance film than that of a standard UV inkjet ink.

Example 2

A protective layer, as detailed in Table 3, can optionally be applied to the hybrid solvent/radiation-curable ink layers of Example 1. The protective layer was prepared by mixing the components of Table 3 in the given amounts. Amounts are provided as weight percentages based on the total weight of the ink.

Table 3

Protective layer Amount Primer of Table 1 95.0 Desmodur N75 (isocyanate functional crosslinker) 5.0 If it is desirable to apply the protective layer, there are two processes that can be used -process A or process B. The protective layer is optional depending on the level of resistance required.

Process A The protective layer is applied over the hybrid solvent/radiation-curable ink layer (printed image) without thermally drying or UV curing the hybrid solvent/radiation-curable ink layer. The protective layer is applied to the hybrid solvent/radiation-curable ink layer by screen printing through a 90.48 PW screen.

The protective layer is then thermally dried for 3 minutes at 60°C before being exposed to UV radiation. The UV radiation readily passes through the protective layer to cure the ink layer beneath.

The UV cure process is highly efficient as the top coat excludes air from the UV components thus avoiding inhibition by atmospheric oxygen.

Process B The hybrid solvent1radiation-curable ink layer is thermally dried for 3 minutes at 60°C before being UV cured. The protective layer is then applied over the image by screen printing through a 90.48 PW screen and dried at 70°C for 3 minutes to produce the composite.

Example 3

Further primers were provided in order to investigate the pinning effects of the primer layer. Primers were provided comprising a thermoplastic resin as detailed in Table 4.

Table4

Thermoplastic resin Solvent Aqueous methacrylate copolymer emulsion Water and methoxy propanol Methacrylate copolymer / polyvinyl copolymer Isopropyl oxitol / cyclohexanone blend blend Polyvinyl copolymer Isopropyl oxitol / cyclohexanone blend Cellulose acetate butyrate / methacrylate Isopropyl oxitol I cyclohexanone blend copolymer blend Saturated polyester Solvesso 150 (naptha9o/200) / butoxyethanol Polyurethane ShelIsol A (naptha 160/1 85)! isopropyl oxitol / cyclohexanone The primers were applied to the substrate in solution form. The solvent used in each primer varied depending on the solubility characteristics of the thermoplastic resins being used.

In each case the primer was applied to the substrate by drawing down a film onto the substrate using a No. 2 K bar coater. The substrate used in this case was 220 micron gloss white genotherm (PVC).

The films were dried at 60°C for 3 minutes.

The dried primer layers were then printed with the hybrid solvent'radiation-curable inks of Table 2 using a JV200 inkjet printer. The substrate was positioned such that part of the image was deposited on the primed area and part on non-primed PVC.

In all cases the image quality was far higher in the primed area of the substrate. Without wishing to be bound by theory, it is believed that the primer absorbs the solvent in the hybrid solvent/radiation-curable ink causing a rapid rise in viscosity of the ink and thus arresting the spread of the droplet. In non-primed areas, excessive ink pooling was seen leading to a grainy image with poor resolution.

It has hence been shown that a wide range of thermoplastic resins can be used to formulate the primer. The choice of the thermoplastic resin and solvent combination is partly determined by the substrate to be used; the primer must have good adhesion to the material being used. In addition, the at least partially dried primer layer must have good resolubility in the carrier solvent used in the hybrid solvent/radiation-curable ink. The solvent used in the hybrid solvent/radiation-curable ink in this case was diethylene glycol diethyl ether (DEGDEE).

It has hence been shown that the pinning effect can also be achieved using various thermoplastic resins.

Example 4

In order to check the resolubility of the various primer layers in DEGDEE, dried films were assessed for the number of double rubs required to break through to the substrate using cloth soaked in DEGDEE. The dried films were produced similarly to before, however in this case, in order to facilitate determination of the end point, the primer layers were applied over a dried film of a magenta solvent based inkjet with poor solvent resistance. The results are shown in Table 5 hereinbelow.

Table 5

Thermoplastic resin DEGDEE Double rubs to remove under colour layer Aqueous methacrylate copolymer emulsion 1 Methacrylate copolymer / Polyvinyl copolymer blend 10 Polyvinyl copolymer 4 Cellulose acetate Butyrate / methacrylate copolymer 10 blend Saturated polyester 1 Cellulose acetate Butyrate / methacrylate copolymer 8 blend Thermoplastic polyurethane 3 Uncoated magenta ink (control) 1 The maximum solvent resistance of the primers tested was 10 double rubs with DEGDEE.

Example 5

Differentiation of substrates based on rigidity and permeability Polymers, such as PVC, are naturally hard and brittle. Modification of these materials with plasticiser softens them and the greater the plasticiser content, the softer polymer film becomes. Addition of plasticiser also increases the receptivity of the substrate to solvent absorption. The higher solvent absorption improves pinning efficiency when printed with inks of the present invention. Both self-adhesive PVC and PVC banner materials have quite high plasticiser content and are readily elongated at room temperature and both exhibit excellent pinning efficiency with the present inks.

Non-elongatable PVC films are less plasticised and are stiffer in nature. These materials are also far less receptive to solvent absorption and hence have poor pinning efficiency with the present inks.

However, the goal of the present invention it to print onto such substrates.

The difference in elongation between these types of PVC was assessed by use of an Instron 5544 tester. A fixed width (50.8 mm) of each test material was held in the two jaws of the tester and the load required to elongate each sample by 5% was measured. In the case of the self-adhesive vinyl the backing sheet was removed before testing. The results are shown in Table 6.

Table 6

Material Type Load to produce Ink pinning 5% elongation (N) 1JC608 (supplied by Banner PVC 205 Good Oce) MPI 3500 (supplied by Self-adhesive PVC 115 Good Avery) 220 micron gloss white Semi-rigid PVC 490 Poor PVC (supplied by Genothem) The deposition of a suitable pinning primer layer on materials such as the 220 micron gloss white PVC restores the efficiency of the pinning process and hence produces a good quality image.

Claims (8)

1. Claims 1. A method of printing onto a non-elongatable substrate having a primer layer obtainable by providing the substrate, depositing a primer onto the substrate to form a primer layer, wherein the primer comprises a thermoplastic resin selected from polyurethane, polymethacrylate, polyvinyl, poly(cellulose acetate butyrate), polyester, epoxy resin, hydrocarbon resin, ketone or aldehyde resin, amino resin, and copolymers and blends thereof, and a solvent and/or monofunctional radiation-curable diluent, and, when a monofunctional radiation-curable diluent is present, a photoinitiator, and at least partially drying and/or at least partially curing the primer, wherein the primer layer has a thickness of 40 microns or less based on the dry film thickness; the method comprising each of the following steps in order: (i) inkjet printing a hybrid solvent/radiation-curable ink onto the primer layer to form a hybrid solvent/radiation-curable ink layer, wherein the hybrid solvent/radiation-curable ink comprises at least 50% by weight organic solvent, based on the total weight of the ink, radiation-curable material and a photoinitiator; (U)(a) optionally depositing a protective layer onto the hybrid solvent/radiation-curable ink layer, wherein the protective layer comprises: a thermoplastic resin selected from polyurethane, polymethacrylate, polyvinyl, poly(cellulose acetate butyrate), polyester, epoxy resin, hydrocarbon resin, ketone or aldehyde resin, amino resin, and copolymers and blends thereof, a solvent and/or radiation-curable diluent, and, when a monofunctional radiation-curable diluent is present, a photoinitiator, and a crosslinking agent; and (b) drying and curing the hybrid solvent/radiation-curable ink layer; wherein when (ii)(a) is present, (ii)(a) and (ii)(b) can be in either order, with the proviso that when step (U)(b) occurs before step (H)(a), the method further comprises the step of drying and/or curing the protective layer.
2. 2. A method of printing onto a non-elongatable substrate comprising each of the following steps in order: (i) providing the substrate; (ii) depositing a primer onto the substrate to form a primer layer, wherein the primer comprises: a thermoplastic resin selected from polyurethane, polymethacrylate, polyvinyl, poly(cellulose acetate butyrate), polyester, epoxy resin, hydrocarbon resin, ketone or aldehyde resin, amino resin, and copolymers and blends thereof, and a solvent and/or monofunctional radiation-curable diluent, and, when a monofunctional radiation-curable diluent is present, a photoinitiator, wherein the primer layer has a thickness of 40 microns or less based on the dry film thickness; (iii) at least partially drying and/or at least partially curing the primer; (iv) inkjet printing a hybrid solvent/radiation-curable ink onto the primer layer to form a hybrid solvent/radiation-curable ink layer, wherein the hybrid solvent/radiation-curable ink comprises at least 50% by weight organic solvent, based on the total weight of the ink, radiation-curable material and a photoinitiator; and (v)(a) optionally depositing a protective layer onto the hybrid solvent/radiation-curable ink layer, wherein the protective layer comprises: a thermoplastic resin selected from polyurethane, polymethacrylate, polyvinyl, poly(cellulose acetate butyrate), polyester, epoxy resin, hydrocarbon resin, ketone or aldehyde resin, amino resin, and copolymers and blends thereof, a solvent and/or radiation-curable diluent, and, when a monofunctional radiation-curable diluent is present, a photoinitiator, and a crosslinking agent; and (b) drying and curing the hybrid solvent/radiation-curable ink layer; wherein when (v)(a) is present, (v)(a) and (v)(b) can be in either order, with the proviso that when step (v)(b) occurs before step (v)(a), the method further comprises the step of drying and/or curing the protective layer.
3. 3. A method according to claims I or 2, wherein the primer comprises polyurethane.
4. 4. A method according to any preceding claim, wherein the hybrid solvent/radiation-curable ink further comprises a colorant.
5. 5. A method according to any preceding claim, wherein the protective layer comprises polyurethane.
6. 6. A method according to any preceding claim, wherein the primer layer is deposited onto the substrate by screen printing, flexographic printing, inkjet printing, bar coating or wipe on by hand.
7. 7. A method according to any preceding claim, wherein the substrate is sportswear or sports equipment.
8. 8. A printed substrate obtainable by the method of claims ito 7.