DESC:FIELD
The present disclosure relates to UV curable screen printing ink compositions.
DEFINITIONS
As used in the present disclosure, the following words and phrases are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used to indicate otherwise.
Squeegee: The term “squeegee” refers to a scraping implement with a rubber-edged blade set on a handle.
Radiation-curable material: The term “radiation-curable material” refers to a material that polymerizes or crosslinks when exposed to radiation, commonly ultraviolet light, in the presence of a photoinitiator.
Bio-solvent: The term “bio-solvent” refers to solvents from biological sources having the potential to reduce the amount of environmentally-polluting volatile organic compounds (VOCs) released in to the atmosphere and have the further advantage that they are sustainable.
Actinic radiation: The term “actinic radiation” refers to ionic electromagnetic radiation that can produce photochemical reaction.
Photoinitiator: The term “photoinitiator” refers to a molecule that creates reactive species (for e.g., free radicals, cations or anions) when exposed to radiation (UV or visible).
Pas: The term “”Pas” refers to a pascal-second which is derived metric SI (System International) measurement unit of dynamic viscosity.
High flexibility: The term “High flexibility” refers to a film that does not crack when it is stretched.
Ink set: The term “Ink set” refers to a standard set of colours that can be intermixed to obtain different shades of colour.
Evaporation rate: The term “Evaporation time” refers to a time at which solvent evaporates.
BACKGROUND
In screen printing, an ink which forms an image is supported on a mesh stretched across a frame. The ink is forced through the openings in the mesh and onto the substrate by the action of squeegee which is drawn across the mesh. Once the ink has been transferred to the substrate it must dry within a reasonable amount of time which is dependent on the application.
Generally, the ink used for screen printing can be dried using different drying processes. Two of the most commonly used techniques are i) inks that dry by solvent or mobile liquid vehicle evaporation, and ii) inks that dry by exposure to ultraviolet radiation.
Screen printing inks that dry by solvent or mobile liquid vehicle evaporation are commonly formulated to contain a large proportion of a mobile liquid vehicle or solvent. However, inks that include a large proportion of water or solvent cannot be handled after printing until the inks have dried, either by evaporation of the solvent or its absorption into the substrate. The drying process is often slow and in many cases (for example, when printing on to a heat-sensitive substrate, such as, paper) cannot be accelerated.
Screen printing inks that dry by exposure to ultraviolet radiation contain unsaturated organic compounds, termed monomers or oligomers, which polymerize by radiation, typically UV radiation, in the presence of a photoinitiator. Drying the ink by exposure to UV has the advantage that it is not necessary to evaporate the liquid phase to dry the print; instead the print is exposed to radiation to cure or harden it, a process which is more rapid than evaporation of solvent at moderate temperatures. However, it is difficult to formulate inks which polymerize by radiation and at the same time also provide printed images having both scratch and chemical resistance and high flexibility.
The high ink deposit that is provided by screen printing provides high colour strength, and opacity. However, unless the degree of crosslinking that occurs during the curing process is controlled, films with very low flexibility are produced. As the ink film becomes thicker, the UV light penetrating the film decreases in intensity, resulting in a film which is cured at the surface, but essentially uncured at the substrate/coating interface. The resulting stresses within the coating tend to show as a wrinkling of the surface that is easily removed, leaving still fluid material below.
The attenuation of light energy as it passes into, or through any material, is described by Beer-Lambert's Law:

where Io is the intensity of incident energy, Ia is the intensity of the energy at a given depth, A is the absorbance of a coating at a given wavelength, and d is the depth from the surface.
In order to minimize the stress in curing of thick films, the coating should be formulated to cure throughout the thickness at a relatively uniform rate as opposed to curing from the surface down. The film thickness can be controlled to some extent by mesh selection but even with the finest possible meshes, the film weight deposited is still 5 microns. The high film weight produced makes it difficult to get the required flexibility whilst retaining the chemical and scratch resistance properties.
Therefore, there is felt a need to provide a screen printing ink composition that overcomes the drawbacks mentioned herein above.
OBJECTS
Some of the objects of the present disclosure, of which at least one embodiment is adapted to provide, are described herein below:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Another object of the present disclosure is to provide a screen printing ink composition.
Still another object of the present disclosure is to provide a UV curable screen printing ink composition.
Other objects and advantages of the present disclosure will be more apparent from the following description which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to UV curable screen printing ink compositions. The UV curable screen printing ink composition comprises at least one fluid media in an amount in the range of 20 wt% to 85 wt% of the total weight of the ink composition, at least one UV radiation-curable material in an amount in the range of 2 wt% to 75 wt% of the total weight of the ink composition, and at least one photoinitiator in an amount in the range of 1 wt% to 20 wt% of the total weight of the ink composition.
Typically, the viscosity of UV curable screen printing ink composition is in the range of 0.1 Pas to 10 Pas at a temperature in the range of 20 °C to 30 °C.
DETAILED DESCRIPTION
In screen printing, an ink is forced through the openings in a mesh and onto a substrate by the action of a squeegee which is drawn across the mesh. Once the ink has been transferred to the substrate it must dry within a reasonable amount of time which is dependent on the application. However, inks that include a large proportion of water or solvent cannot be handled after printing until the inks have dried either by solvent evaporation or its absorption into the substrate. The drying process is often slow and in many cases e.g. when printing on to a heat-sensitive substrate, such as, paper, cannot be accelerated. Whereas, drying the ink by exposure to UV has the advantage that it is not necessary to evaporate the liquid phase to dry the print, instead the print is cured by exposing the print to radiation. A process of curing the print by radiation is more rapid than evaporation of solvent at moderate temperatures. However, it is difficult to formulate inks which polymerize by radiation and at the same time also provide printed images having both scratch and chemical resistance with high flexibility.
Therefore, the present disclosure envisages UV curable screen printing ink compositions that polymerize by radiation and at the same time also provides printed images having both scratch and chemical resistance with high flexibility.
In one aspect of the present disclosure, there is provided a UV curable screen printing ink composition. In accordance with an embodiment of the present disclosure, the UV curable screen printing ink composition comprises at least one fluid media in an amount in the range of 20 wt% to 85 wt% of the total weight of the ink composition, at least one UV radiation-curable material in an amount in the range of 2 wt% to 75 wt% of the total weight of the ink composition, and at least one photoinitiator in an amount in the range of 1 wt% to 20 wt% of the total weight of the ink composition.
The viscosity of the UV curable screen printing ink composition is in the range of 0.1 Pas to 10 Pas at a temperature in the range of 20 °C to 30 °C.
The fluid media is at least one selected from the group consisting of glycol ether, propylene carbonate, alcohol, ketone, ester, bio-solvent, and pyrrolidones.
The bio-solvent is at least one selected from the group consisting of soy methyl ester, lactate esters, polyhydroxyalkanoates, terpenes, and D-limonene.
The inclusion of the fluid media in the composition of the present disclosure, in combination with the UV radiation-curable material and the photoinitiator, allows the final dry film thickness to be controlled and results in improved film flexibility whilst still enabling a high cross link density to be used. Use of the ink composition of the present disclosure, produces films with high flexibility, which still possess high film hardness and chemical resistant properties.
The fluid media can be in the form of a liquid at ambient temperatures and is capable of acting as a carrier for the remaining components of the ink composition. The fluid media can be a single solvent or a mixture of two or more solvents. The fluid media used in the ink composition of the present disclosure can be evaporated from the printed ink by heating, in order to allow the ink to dry.
The resulting volatility of the ink produced when using the fluid media is a key factor to consider when selecting the fluid media for the ink composition. The ‘open’ nature of the screen printing process freely allows evaporation. There is a large amount of wet ink that is being processed on or above the substrate. Inks should not be so volatile that the ink undesirably thickens during the printing process, nor should they clog or block the printing screen (also due to thickening or solidifying in the holes in the mesh), if the print process is to be temporarily stopped. Thus, the inks need to be ‘screen stable’. A good indicator therefore, for making screen stable inks is the selection of fluid media with lower volatilities. Fluid media having an evaporation rate of 100 or less can be used in ink composition of the present disclosure. The selection of the fluid media will be dependent on the printing environment, for example, when printing in a hot country, fluid media that are less volatile (having a lower evaporation rate number), can be selected.
Other important factors in selecting the fluid media include the compatibility of the fluid media with the oligomers used, and health and safety considerations. Typically, the fluid media used in the ink composition of the present disclosure has a low toxicity and/or a low odour. Fluid media that have been given VOC exempt status by the United States Environmental Protection Agency or European Council can also be used as the fluid media in the ink composition of the present disclosure.
The UV radiation-curable material is at least one selected from the group consisting of monomer having a molecular weight of less than 600, and an oligomer having a molecular weight in the range of 600 to 4,000.
The UV radiation-curable material can comprise a cationically curable oligomer in an amount in the range of 0.1 % to 40 % by weight based on the total weight of UV radiation-curable material in the ink composition and a cationically curable monomer in an amount in the range of 60 % to 100 % by weight based on the total weight of UV radiation-curable material in the ink composition. The monomers and/or oligomers can possess different degrees of functionality. Further, a mixture including combinations of mono, di, tri and higher functionality monomers and/or oligomers can also be used. In an exemplary embodiment, the UV radiation-curable material comprises a UV radiation-curable oligomer.
In accordance with the present disclosure, the cationically curable monomer is at least one selected from the group consisting of acrylate, a,ß-unsaturated ether, and vinyl amide.
The acrylate is at least one selected from the group consisting of 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), lauryl acrylate, hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, polyethyleneglycol diacrylate, dipropyleneglycol diacrylate, tri(propylene glycol) triacrylate, neopentylglycol diacrylate, bis(pentaerythritol) hexaacrylate, propoxylated neopentyl glycol diacrylate, ethoxylated trimethylolpropane triacrylate, hexanediol dimethacrylate, trimethylolpropane trimethacrylate, triethyleneglycol dimethacrylate, diethyleneglycol dimethacrylate, ethyleneglycol dimethacrylate, 1,4-butanediol dimethacrylate, aliphatic polyester urethane acrylate, aliphatic urethane acrylate, tripropylene glycol diacrylate, and glycerol propoxylate triacrylate. The a,ß-unsaturated ether is at least one selected from the group consisting of triethylene glycol divinyl ether, diethylene glycol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether and ethylene glycol monovinyl ether. The vinyl amide is at least one selected from the group consisting of N-vinyl caprolactam (NVC), N-vinyl pyrrolidone (NVP), and N-acryloylmorpholine (ACMO).
a,ß-unsaturated ether monomers can polymerize by free radical polymerization and can be used in combination with one or more methacrylate monomers.
N-vinyl amides and N-methacryloyl amines may also be used in the ink composition of the present composition. 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 methacrylate monomers. Similarly, N-acryloyl amines having 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 methacrylate monomers.
Multifunctional oligomer comprises two or more radical polymerizable groups. In an exemplary embodiment of the present disclosure, the multifunctional oligomer comprises two to six radical polymerizable groups i.e., Di functional Aliphatic Urethane Oligomer.
The cationically curable oligomers comprise a backbone selected from the group consisting of polyester backbone, urethane backbone, epoxy backbone and polyether backbone. The polyester backbone is urethane methacrylate oligomer, and the epoxy backbone is bisphenol A epoxy acrylate, and epoxy novolac acrylate. Urethane methacrylate oligomers from the group of polyester backbone have excellent adhesion and elongation properties.
The UV radiation-curable material used in the ink composition of the present disclosure cures upon exposure to UV radiation in the presence of a photoinitiator to form a cross-linked, solid film. The resulting film has good adhesion to substrates and good solvent resistance. Any UV radiation-curable oligomer that is compatible with the remaining ink components and that is capable of curing to form a cross-linked, solid film is suitable for use in the ink composition of the present disclosure. Also, the UV radiation-curable material is capable of being polymerized by cationic polymerization.
The photoinitiator is at least one selected from the group consisting of free radical photoinitiator, and cationic photoinitiator.
The free radical photoinitiator is at least one selected from the group consisting of benzophenone, 1-hydroxycyclohexyl phenyl ketone, 2-Methyl-4'-(methylthio)-2-morpholinopropiophenone, 2-Hydroxy-2-methyl-1-phenyl-propan-1-one, 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one, 2-benzyl-2-dimethylamino-(4-morpholinophenyl)butan-1-one, iso propyl thioxanthone, benzil dimethylketal, and bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide.
The cationic photoinitiator is at least one selected from the group consisting of sulphonium based system, iodonium based system, 4-Isopropyl-4'-methyldiphenyliodonium Tetrakis (pentafluorophenyl) borate, photoactive iodonium salt solution, 3,4 - epoxycyclohexyl - methyl - 3,4 - epoxycyclohexane carboxylate, 50% propylene carbonate solution of Arylsulfonium Hexafluorophosphate salts, and MC AA, MC BB, MC CC, MC CC PF, MC SD from Siber Hegner.
The UV curable screen printing ink composition optionally comprises at least one colouring agent in an amount in the range of 0.01 wt% to 20 wt% of the total weight of the ink composition, at least one resin in an amount in the range of 1 wt% to 5 wt% of the total weight of the ink composition, at least one binder in an amount in the range of 1 wt% to 5 wt% of the total weight of the ink composition, and water in an amount in the range of 0.1 wt% to 5wt% of the total weight of the ink composition.
The coloring agent can be either dissolved or dispersed in the fluid media of the ink composition. The coloring agent is at least one selected from the group consisting of Paliotol (available from BASF plc), Cinquasia, Irgalite (both available from Ciba Speciality Chemicals), Hostaperm (available from Sudarshan chemicals), Carbon black HAFN330 CI No 77266, Mogal L, Lemon Yellow 1240 CI No 77603, Simular Fast Yellow, Lemon Chrome CI No 77600, Middle Chrome, Cromopthal Yellow 8GN CI No 20037, Scarlet Chrome 1475 CI No 77605, Cromopthal Reb BRN CI No 20735, Cromopthal Scarlet RN CI No 20730, Sudarshan Pink 2190 CI No 73915, Fast Pink DB – CI 146, Beta Blue 2680 CI No 74160, Sudarshan Green 2724 CI-17 CI No 74260, Prime Rose Chrome 1011 CI No 77603, Hostaperm Orange GR, Printex 45, Sudarshan Yellow 162 CI – 17, Novaperm Yellow HR-1D CI No 21108, Hostaperm Violet RL021N CI No 51319, Sudaperm Orange 2915 CI-36 CI No 11780, Carmine Red BB10, Novaperm Red F5RK – IN, Novaperm Yellow HR70 CI No 211808, Bismuth Vandate 6615B, Cromopthal Yellow 8GN, Cromopthal Red BT CI No 20735, Silberline E2945, Alluminium Paste SS3500, Alluminium Paste TT 77, 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, and Black: carbon black pigments such as Pigment black 7.
The resin is at least one selected from the group consisting of epoxy, polyester, vinyl, and methacrylate resins. Typically, the resin comprises methyl methacrylate/n-butyl methacrylate copolymer, Ethylene-vinyl acetate copolymer resin, hydrocarbon resin such as Picolastic 100 (available from Eastman), polystyrene polymer, methacrylic resin such as Plexigum M890, and Plexigum P28 (available from Evonik). The resin is used as adhesive between ink and substrate. The binder is vinyl chloride copolymer.
Conventional screen printing ink compositions prepared by using known fluid media and dried by evaporating fluid media forms a print with no crosslinking or polymerization. The print produced therefore has limited chemical resistance. Hence, the binder is added to common fluid media, such as, alcohols and petrol in order to improve the chemical resistance of the prints. Binders having a limited solubility in these fluid media are added to the screen ink composition. Typically, the binder is in solid form at 25 °C, so that a solid printed film is produced when fluid media is evaporated from the ink composition.
The UV curable screen printing ink composition of the present disclosure includes UV radiation-curable material. The UV radiation-curable material cures the printed images with the help of photoinitiator and hence it is not necessary to include a binder in the UV curable screen printing ink composition of the present disclosure in order to provide a printed film having improved solvent resistance. Therefore, the fluid media can be suitably selected with more freedom to prepare UV curable screen printing ink composition as the fluid media selected need not required solubilizing the binder
The ink composition of the present disclosure is free of water, although some water will typically be absorbed by the ink composition from the air or will be present as impurities in the components of the inks, and such levels are acceptable.
The UV curable screen printing ink composition can further comprise at least one surfactant, at least one defoamer, at least one dispersant, at least one synergist for photoinitiator, at least one stabilizer, and at least one inorganic extender powder.
The surfactant is at least one selected from the group consisting of silicon acrylate, Tego disperse 2500 (available from Evonik), multi-acrylic functional modified polydimethylsiloxane, and Tego Disperse 685 (available from Evonik). The surface tension of the ink composition can be controlled by the addition of one or more surfactants. Adjustment of the surface tension of the ink composition allows control of the surface wetting of the ink on various substrates, for example, plastic substrates.
The defoamer is EFKA 2720 (available from BASF). Further, the defoamer can be selected from any defoamer which is compatible with UV resin system.
The dispersant is at least one selected from the group consisting of Solsperse 22000, and Solsperse 32000.
The synergist is at least one selected from the group consisting of 4-N,N-dimethylaminobenzoate, 2-ethylhexyl 4-N,N- dimethyl aminobenzoate, N-methyldiethanolamine, N,N-dimethylethanolamine, and triethanolamine. The amine synergist scavenges the oxygen present in the formulation and hence allows polymerization process to proceed.
The stabilizer is at least one selected from the group consisting of benzophenones.
The inorganic extender powder is at least one selected from the group consisting of talc, clay, silica, and fumed silica.
In another embodiment of the present disclosure, the UV curable screen printing ink composition, comprises the fluid media selected from lactone, and glycol ether; the UV radiation-curable material selected from cationically curable monomer and cationically curable oligomer; and the photoinitiator which is selected from free radical photoinitiator.
In still another embodiment of the present disclosure, the UV curable screen printing ink composition, comprises the fluid media selected from gamma butryl lactone and ethylene glycol n-butyl ether acetate; the UV radiation-curable material selected from aliphatic polyester urethane acrylate, tripropylene glycol diacrylate, difunctional aliphatic urethane oligomer, and glycerol propoxylate triacrylate; and the photoinitiator selected from 2-Methyl-4'-(methylthio)-2-morpholinopropiophenone, 1-hydroxycyclohexyl phenyl ketone, and 2-Hydroxy-2-methyl-1-phenyl-propan-1-one.
In a present disclosure, a method for preparing said UV curable ink composition is also provided. The method comprises charging of a mixer with a UV radiation-curable material, a photoinitiator, and a fluid media to obtain a mixture. The so obtained mixture is stirred at a temperature below 25 °C to obtain a first mixture. To this so obtained first mixture a colouring agent is added and stirred at a temperature below 25 °C to obtain a second mixture. Then, defoamers are added to the so obtain second mixture and stirred at a temperature below 25 °C to obtain a homogeneous mixture of the UV curable ink composition. The viscosity of the UV curable ink composition is determined by Rotothinner.
The ink set of the present disclosure can optionally include one or more of green ink, an orange ink and a violet ink.
The ink set of the present disclosure can optionally include a white ink. White ink can be used in two ways. When printing onto a transparent substrate, white ink can be printed over the image such that the image can be viewed from the reverse. Alternatively, the white ink can be used to print a base coat onto a coloured substrate before the image is printed.
In an exemplary embodiment of the present disclosure, there is provided an ink set containing a plurality of colours that can be intermixed to achieve a wide range of tones and shades, such an ink set comprising one or more of the following components (base colours): Yellow (green shade), Yellow (red shade), Orange, Red (blue shade), Red (yellow shade), Magenta, Blue, Violet, Green, White and Black. The ink compositions of the present disclosure can be intermixed to produce the exact colour to match to a standard.
An additional protection is provided to the printed images, obtained by using the UV curable screen printing ink composition of the present disclosure, using overcoat i.e., a clear ink of the present disclosure that can be applied over the printed images.
Optionally, the ink set of the present disclosure, can include one or more metallic effect inks. The use of metallic colours as such increases the aesthetic effect of the end product.
Conventional solvent-based metallic inks can produce very bright metallic effects. The metallic pigments are used to prepare metallic inks. The metallic pigments are in the form of flakes or platelets and are randomly orientated in the undried liquid ink. The films produced can often have very poor rub properties, resulting in the easy removal of the metallic pigment from the print surface. UV cured solvent-based metallic inks have better rub properties, but are often dull in appearance because the metallic pigment flakes do not have time to align during the rapid UV curing process.
Metallic inks of the present disclosure overcome these problems as the drying of the ink can take place in in two stages. During the fluid media evaporation step, the metallic flakes have time to align, allowing a bright metallic effect to be produced in the final image. However, the UV curing stage yields a rub-resistant film.
Colourless inks according to the present disclosure may be used as a varnish. In one embodiment of the present disclosure, the colourless ink may be used as a varnish for a conventional solvent-based metallic effect ink. Metallic effect prints can be protected with known UV curable varnishes but the films with high thickness are produced when these materials are jetted that dulls the metallic luster of the prints and is deleterious to their appearance. The presence of a relatively large proportion of volatile fluid media in the colourless inks of the present disclosure produces films with low thickness. Typically, a UV varnish would produce a 12 µm film over the surface of the print. By using a colourless ink according to the present disclosure, the film thickness can be reduced to 2 µm to 3 µm. The low film thickness of the hybrid varnish has a far less deleterious effect on the appearance of the metallic print.
In second aspect of the present disclosure, there is provided a screen printing method using the UV curable ink composition. The screen printing method comprises delivering the UV curable-screen printing ink composition on a substrate to obtain a wet film. The wet film is subjected to evaporation to evaporate at least a portion of the fluid media from the printed ink, followed by exposing the printed ink to actinic radiation to cure the UV radiation-curable material.
The substrate can be selected from polyesters, fabric meshes, vinyl substrates, paper, glass, metals, plastics, styrene, polyester, polycarbonate), PVC, and polyethylene terephthalate glycol modified.
The ink composition of the present disclosure comprises a UV radiation-curable component and therefore requires curing of the UV radiation-curable material upon exposure to actinic radiation. The source of actinic radiation can be any source of actinic radiation that is suitable for curing UV 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.
Overall, the printed images obtained by using the UV curable screen printing ink composition of the present disclosure have scratch, abrasion, and chemical resistance with high flexibility.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.

EXPERIMENTAL DETAILS
The general procedure to prepare UV curable ink composition in accordance of the present disclosure:
A mixer having stirrer is charged with weighed quantities of UV radiation-curable material, photoinitiator, and fluid media to obtain a mixture. The so obtained mixture is stirred at 25 °C to obtain a first mixture. To this so obtained first mixture, a colouring agent is added and stirred at 25 °C to obtain a second mixture. Then, defoamers are added to the so obtain second mixture and stirred at 25 °C to obtain a homogeneous mixture of UV curable ink composition. The viscosity of the UV curable ink composition is determined by Rotothinner.
Experiment 1: Process for preparing UV curable ink composition using ingredients as given in Table 1 [Colour: Metallic Silver]
Table 1: Ingredients for preparing the UV curable ink composition
S.No Description Quantity
(in gms)
1 Genomer 4215 - Aliphatic Polyester Urethane Acrylate (UV radiation-curable material) 44.1
2 Gamma Butryl Lactone (fluid media) 12.4
3 Ethylene Glycol n-butyl Ether Acetate (fluid media) 9.1
4 Tripropylene glycol diacrylate (UV radiation-curable material) 7.8
5 CN 9007 - Di functional Aliphatic Urethane Oligomer (UV radiation-curable material) 7.00
6 Glycerol propoxylate triacrylate (UV radiation-curable material) 0.6
7 2-Methyl-4'-(methylthio)-2-morpholinopropiophenone (photoinitiator) 1.8
8 1-hydroxycyclohexyl phenyl ketone (photoinitiator) 1.8
9 2-Hydroxy-2-methyl-1-phenyl-propan-1-one (photoinitiator) 2.6
10 Silberline E2945 (Colouring agent) 12.00
11 Silicone polyether acrylate (surfactant) 0.5
12 Silicone acrylate (surfactant) 0.5
Total 100

The ingredients in Table 1 were used to prepare UV curable ink composition of the present disclosure. The UV curable ink composition was prepared in accordance with the general procedure mentioned above. The viscosity of the UV curable ink composition of Experiment 1 was found to be 2 Pas.
Experiment 2: Process for preparing UV curable ink composition using ingredients as given in Table 2 [Colour: Blue]
Table 2: Ingredients for preparing the UV curable ink composition
S.No Description Quantity
1 Di functional Urethane Acrylate Oligomer (UV radiation-curable material) 10.00
2 CN 964 E75 - Aliphatic Urethane Acrylate (UV radiation-curable material) 25.00
3 CN9007 - Difunctional Alipahtic Urethane Acrylate (UV radiation-curable material) 10.6
4 Tripropylene Glycol Diacrylate (fluid media) 10.00
5 Glycerol propoxylate triacrylate (UV radiation-curable material) 0.4
6 Gamma Butryl Lactone (fluid media) 14.00
7 Ethylene Glycol n-butyl Ether Acetate (fluid media) 10.00
8 Beta Blue 2680 (colouring agent) 10.0
9 1-hydroxycyclohexyl phenyl ketone (photoinitiator) 3.0
10 2-Hydroxy-2-methyl-1-phenyl-propan-1-one (photoinitiator) 4.0
11 2-Methyl-4'-(methylthio)-2-morpholinopropiophenone (photoinitiator) 3.0
12 Silicone polyether acrylate (surfactant) 0.5
13 Silicone acrylate (surfactant) 0.5
Total 100

The ingredients in Table 2 were used to prepare UV curable ink composition of the present disclosure. The UV curable ink composition was prepared in accordance with the general procedure mentioned above, except the mixture was stirred at 20 °C in Experiment 2. The viscosity of the UV curable ink composition of Experiment 2 was found to be 2.5 Pas.

Experiment 3: Process for preparing Overcoat 1 using ingredients as given in Table 3
Table 3: Ingredients for preparing the overcoat 1
S.No Description Quantity
1 Aliphatic Polyester Urethane Acrylate (UV radiation-curable material) 43.2
2 Gamma Butryl Lactone (fluid media) 14.00
3 Ethylene Glycol n-butyl Ether Acetate (fluid media) 10.00
4 Tripropylene glycol diacrylate (UV radiation-curable material) 11.00
5 Di functional Aliphatic Urethane Oligomer (UV radiation-curable material) 14.00
6 Glycerol propoxylate triacrylate (UV radiation-curable material) 0.6
7 2-Methyl-4'-(methylthio)-2-morpholinopropiophenone (photoinitiator) 1.8
8 1-hydroxycyclohexyl phenyl ketone (photoinitiator) 1.8
9 2-Hydroxy-2-methyl-1-phenyl-propan-1-one (photoinitiator) 2.6
10 Silicone polyether acrylate (surfactant) 0.5
11 Silicone acrylate (surfactant) 0.5
Total 100

The ingredients in Table 3 were used to prepare overcoat 1 of the present disclosure. The overcoat 1 was prepared in accordance with the general procedure mentioned above, except the mixture was stirred at 20 °C in Experiment 3. The viscosity of the overcoat 1 of Experiment 3 was found to be 1 Pas.
Experiment 4: Process for preparing Overcoat 2 using ingredients as given in Table 4
Table 4: Ingredients for preparing the overcoat 2
S.No Description Quantity
1 Difunctional Alipahtic Urethane Acrylate (UV radiation-curable material) 15.00
2 Aliphatic Urethane Acrylate (UV radiation-curable material) 28.00
3 Di functional Urethane Acrylate Oligomer (UV UV radiation-curable material) 10.00
4 Tripropylene Glycol Diacrylate (fluid media) 13.6
5 Glycerol propoxylate triacrylate (UV radiation-curable material) 0.4
6 Gamma Butryl Lactone (fluid media) 12.00
7 Ethylene Glycol n-butyl Ether Acetate (fluid media) 10.00
8 1-hydroxycyclohexyl phenyl ketone (photoinitiator) 2.7
9 2-Hydroxy-2-methyl-1-phenyl-propan-1-one (photoinitiator) 3.6
10 2-Methyl-4'-(methylthio)-2-morpholinopropiophenone (photoinitiator) 2.7
11 Silicone polyether acrylate (surfactant) 1.00
12 Silicone acrylate (surfactant) 1.00
Total 100

The ingredients in Table 4 were used to prepare overcoat 2 of the present disclosure. The overcoat 2 was prepared in accordance with the general procedure mentioned above. The viscosity of the overcoat 2 of Experiment 4 was found to be 1 Pas.
Experiment 5: Process for preparing UV curable ink composition using ingredients as given in Table 5 [Colour: Metallic Silver]
Table 5: Ingredients for preparing the UV curable ink composition
S.No Description Quantity
1 Aliphatic Polyester Urethane Acrylate (UV radiation-curable material) 23.9
2 20% Elvacite 2028 in DPGDA (resin) 20
3 Gamma Butryl Lactone (fluid media) 12.4
4 Ethylene Glycol n-butyl Ether Acetate (fluid media) 9.1
5 Tripropylene glycol diacrylate (UV radiation-curable material) 7.8
6 Di functional Aliphatic Urethane Oligomer (UV radiation-curable material) 7.00
7 Glycerol propoxylate triacrylate (UV radiation-curable material) 0.6
8 2-Methyl-4'-(methylthio)-2-morpholinopropiophenone (photoinitiator) 1.8
9 1-hydroxycyclohexyl phenyl ketone (photoinitiator) 1.8
10 2-Hydroxy-2-methyl-1-phenyl-propan-1-one (photoinitiator) 2.6
11 Silberline E2945 (colouring agent) 12.00
12 Silicone polyether acrylate (surfactant) 0.5
13 Silicone acrylate (surfactant) 0.5
Total 100

The ingredients in Table 5 were used to prepare UV curable ink composition of the present disclosure. The UV curable ink composition was prepared in accordance with the general procedure mentioned above, except the mixture was stirred at 20 °C in Experiment 5. The viscosity of the UV curable ink composition of Experiment 5 was found to be 2 Pas.
Experiment 6: Screen printing of the UV curable ink composition prepared using experiment 1 of the present disclosure
The ink composition prepared using Experiment 1 [Colour: Metallic Silver] of the present disclosure was screen printed on a self-adhesive vinyl substrate using a 140 PW screen to obtain a wet film. The so obtained wet film was further coated using overcoat 1 of experiment 3 of the present disclosure to obtain coated film. The so obtained coated film film was oven dried for 3 minutes at 60 ºC before being UV cured by passing the print through a conveyorised drier running at 10 meter/min. The drier was fitted with an 80 W/cm2 medium pressure mercury lamp.

Solvent resistance test:
The UV cured print was tested for solvent resistance by rubbing the UV cured print with a soft cloth soaked in isopropyl alcohol (IPA). The number of double rubs required to break through to the substrate are provided in table 6.
Table 6: IPA resistance of ink compositions
Ink IPA resistance (double rubs)
UV curable ink composition as given in Table 1 of the present disclosure 100+
Comparative Example
UZ 121 (Conventional screen ink available from Fujifilm SIS) 100+

It is evident from table 6 that the UV curable ink composition prepared using ingredients as given in Table 1 of the present disclosure forms the crosslinks in the cured ink film that leads to improved adhesion to a range of substrates, and improved chemical and scratch resistance.
Flexibility and Extensibility
The flexibility and extensibility of the print was assessed using the test detailed herein below.
Equipments used:
1 large aluminium panel (30 x 30 cm); 2 small aluminium panels (5 x 10 cm); Infrared thermometer gun; Hot air gun; and Felt-edged squeegee.
The cured prints (prints prepared by using the UV curable ink composition as given in Table 1 of the present disclosure) were cut into 15 cm x 6 cm lengths. The backing was removed from the prepared print sample and 1 cm strip was adhered to the large aluminium panel at line 1 as shown in Figure 1. 1 cm strip at the opposite end was adhered to one of the small aluminium panels at line 2 as shown in print A of Figure 1 and the second small aluminium panel was held on top to grasp the print firmly as shown in Figure 2. The print sample was heated to 60 ºC with the hot air gun, and elongated to reach line 3 from line 2 as shown in print B of Figure 1. The squeegee was used to smooth the stretched print onto the surface of the panel. The appearances of the elongated film are provided in table 7.
Table 7: Appearances of the elongated film
Ink Appearance of elongated film
UV curable ink composition as given in Table 1 of the present disclosure No loss of gloss or colour
No cracking
Comparative Example
UZ 121 (Conventional screen ink available from Fujifilm SIS) Significant loss of colour strength
Extensive fine cracking of film

It is evident from table 7 that the presence of at least 25 % by weight of fluid media in the ink composition of the present disclosure results in the control of the final dry film thickness and hence the film flexibility is improved, while maintaining an improved chemical, scratch resistance, and abrasion resistance.
Further, the solvent resistance test and the flexibility and extensibility test was performed on the prints obtained by using UV curable ink composition of the experiment 2 and experiment 5 of the present disclosure and the results were found to be similar as given for print obtained using UV curable ink composition of the experiment 1 of the present disclosure.
It is evident from experiment 6 of the present disclosure that the UV curable ink composition provides printed images that have scratch, abrasion, and chemical resistance with high flexibility.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a UV curable screen printing ink composition that:
- polymerize by irradiation; and
- provides printed images that have scratch, abrasion, and chemical resistance with high flexibility.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:WE CLAIM:
1. A UV curable screen printing ink composition comprising:
i. at least one fluid media in an amount in the range of 20 wt% to 85 wt% of the total weight of said ink composition;
ii. at least one UV radiation-curable material in an amount in the range of 2 wt% to 75 wt% of the total weight of said ink composition; and
iii. at least one photoinitiator in an amount in the range of 1 wt% to 20 wt% of the total weight of said ink composition,
wherein the viscosity of said ink composition is in the range of 0.1 Pas to 10 Pas at a temperature in the range of 20 °C to 30 °C.
2. The composition as claimed in claim 1, wherein said fluid media is at least one selected from the group consisting of glycol ether, propylene carbonate, alcohol, ketone, ester, bio-solvent, and pyrrolidones.
3. The composition as claimed in claim 2, wherein said bio-solvent is at least one selected from the group consisting of soy methyl esters, lactate esters, polyhydroxyalkanoates, terpenes, and D-limonene.
4. The composition as claimed in claim 1, wherein said UV radiation-curable material is at least one selected from the group consisting of a monomer having a molecular weight of less than 600, and an oligomer having a molecular weight in the range of 600 to 4,000.
5. The composition as claimed in claim 1, wherein said UV radiation-curable material comprises a cationically curable oligomer in an amount in the range of 0.1 % to 40 % by weight based on the total weight of UV radiation-curable material in said ink composition and a cationically curable monomer in an amount in the range of 60 % to 100 % by weight based on the total weight of said UV radiation-curable material in said ink composition.
6. The composition as claimed in 5, wherein said cationically curable monomer is at least one selected from the group consisting of acrylate, a,ß-unsaturated ether, and vinyl amide.
7. The composition as claimed in 6, wherein said acrylate is at least one selected from the group consisting of phenoxyethyl acrylate, cyclic trimethylolpropane formal acrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, octadecyl acrylate, tridecyl acrylate, isodecyl acrylate, lauryl acrylate, hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, polyethyleneglycol diacrylate, dipropyleneglycol diacrylate, tri(propylene glycol) triacrylate, neopentylglycol diacrylate, bis(pentaerythritol) hexaacrylate, propoxylated neopentyl glycol diacrylate, ethoxylated trimethylolpropane triacrylate, hexanediol dimethacrylate, trimethylolpropane trimethacrylate, triethyleneglycol dimethacrylate, diethyleneglycol dimethacrylate, ethyleneglycol dimethacrylate, 1,4-butanediol dimethacrylate, aliphatic polyester urethane acrylate, tripropylene glycol diacrylate, and glycerol propoxylate triacrylate; said a,ß-unsaturated ether is at least one selected from the group consisting of triethylene glycol divinyl ether, diethylene glycol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether and ethylene glycol monovinyl ether; and said vinyl amide is at least one selected from the group consisting of N-vinyl caprolactam, N-vinyl pyrrolidone, and N-acryloylmorpholine.
8. The composition as claimed in claim 5, wherein said cationically curable oligomer comprises a backbone selected from the group consisting of polyester backbone, urethane backbone, epoxy backbone and polyether backbone.
9. The composition as claimed in claim 8, wherein said polyester backbone is urethane methacrylate oligomer; and said epoxy backbone is selected from bisphenol A epoxy acrylate, and epoxy novolac acrylate.
10. The composition as claimed in claim 1, wherein said photoinitiator is at least one selected from the group consisting of free radical photoinitiator, and cationic photoinitiator.
11. The composition as claimed in claim 10, wherein said free radical photoinitiator is at least one selected from the group consisting of benzophenone, 1-hydroxycyclohexyl phenyl ketone, 2-Methyl-4'-(methylthio)-2-morpholinopropiophenone, 2-Hydroxy-2-methyl-1-phenyl-propan-1-one 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one, 2-benzyl-2-dimethylamino-(4-morpholinophenyl)butan-1-one, iso propyl thioxanthone, benzil dimethylketal, and bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide; and said cationic photoinitiator is at least one selected from the group consisting of sulphonium based system, and iodonium based system.
12. The composition as claimed in claim 1, wherein:
i. said fluid media is selected from lactone, and glycol ether;
ii. said UV radiation-curable material is selected from cationically curable monomer and cationically curable oligomer; and
iii. said photoinitiator is a free radical photoinitiator.
13. The composition as claimed in claim 1, wherein:
i. said fluid media is selected from gamma butryl lactone and ethylene glycol n-butyl ether acetate;
ii. said UV radiation-curable material is selected from aliphatic polyester urethane acrylate, tripropylene glycol diacrylate, difunctional aliphatic urethane oligomer, and glycerol propoxylate triacrylate; and
iii. said photoinitiator is selected from 2-Methyl-4'-(methylthio)-2-morpholinopropiophenone, 1-hydroxycyclohexyl phenyl ketone, and 2-Hydroxy-2-methyl-1-phenyl-propan-1-one.
14. The composition as claimed in claim 1, claim 12, or claim 13 further comprises at least one colouring agent in an amount in the range of 0.01 wt% to 20 wt% of the total weight of said ink composition; at least one resin in an amount in the range of 1 wt% to 5 wt% of the total weight of said ink composition; at least one binder in an amount in the range of 1 wt% to 5 wt% of the total weight of said ink composition; and water in an amount in the range of 0.1 wt% to 5wt% of the total weight of said ink composition.
15. The composition as claimed in claim 14, wherein said colouring agent is at least one selected from the group consisting of Paliotol, Cinquasia, Irgalite, Hostaperm, phthalocyanine pigments, azo pigments, quinacridone pigments, crystal quinacridones, carbon black pigments, Carbon black HAFN330 CI No 77266, Mogal L, Lemon Yellow 1240 CI No 77603, Simular Fast Yellow, Lemon Chrome CI No 77600, Middle Chrome, Cromopthal Yellow 8GN CI No 20037, Scarlet Chrome 1475 CI No 77605, Cromopthal Reb BRN CI No 20735, Cromopthal Scarlet RN CI No 20730, Sudarshan Pink 2190 CI No 73915, Fast Pink DB – CI 146, Beta Blue 2680 CI No 74160, Sudarshan Green 2724 CI-17 CI No 74260, Prime Rose Chrome 1011 CI No 77603, Hostaperm Orange GR, Printex 45, Sudarshan Yellow 162 CI – 17, Novaperm Yellow HR-1D CI No 21108, Hostaperm Violet RL021N CI No 51319, Sudaperm Orange 2915 CI-36 CI No 11780, Carmine Red BB10, Novaperm Red F5RK – IN, Novaperm Yellow HR70 CI No 211808, Bismuth Vandate 6615B, Cromopthal Yellow 8GN, Cromopthal Red BT CI No 20735, Silberline E2945, Alluminium Paste SS3500, Alluminium Paste TT 77, Phthalocyanine blue 15.4, Pigment yellow 120, Pigment yellow 151, Pigment yellow 155, Pigment violet 19, Cromophtal Jet magenta 2BC, Cinquasia RT-355D, and Pigment black 7.
16. The composition as claimed in claim 14, wherein said resin is at least one selected from the group consisting of epoxy, polyester, vinyl, and methacrylate resins.
17. The composition as claimed in claim 14, wherein said binder is vinyl chloride copolymer.
18. The composition as claimed in claim 1, claim 12, or claim 13 further comprises at least one surfactant, at least one defoamer, at least one dispersant, at least one synergist for photoinitiator, at least one stabiliser, and at least one inorganic extender powder.
19. The composition as claimed in claim 18, wherein said surfactant is at least one selected from the group consisting of silicon acrylate, Tego disperse 2500, multi-acrylic functional modified polydimethylsiloxane, Tego Disperse 685; said defoamer is EFKA 2720; said dispersant is at least one selected from the group consisting of Solsperse 22000, Solsperse 32000; said synergist is at least one selected from the group consisting of 4-N,N-dimethylaminobenzoate, 2-ethylhexyl 4-N,N- dimethyl aminobenzoate, N-methyldiethanolamine, N,N-dimethylethanolamine, and triethanolamine; said stabiliser is at least one selected from the group consisting of benzophenones; and said inorganic extender powder is at least one selected from the group consisting of talc, clay, silica, and fumed silica
20. A method for printing said UV curable screen printing ink composition as claimed in claim 1, claim 12, or claim 13 on a substrate, said method comprising the following steps:
i. delivering said UV curable-screen printing ink composition, on a substrate to obtain a wet film;
ii. evaporating at least a portion of said fluid media from said wet film to obtain a dried ink; and
iii. exposing said dried ink to actinic radiation to cure said UV radiation-curable material to obtain a printed ink.
21. The method as claimed in claim 20, wherein said substrate is at least one selected from the group consisting of polyesters, fabric meshes, vinyl substrates, paper, glass, metals, plastics, styrene, polyester, polycarbonate, PVC, and polyethylene terephthalate glycol modified.