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ULTRAVIOLET CURABLE ENAMEL COMPOSITIONS

20240417313 ยท 2024-12-19

    Inventors

    Cpc classification

    International classification

    Abstract

    An enamel composition having a glass frit; a pigment; and an organic carrier medium, wherein the organic carrier medium has a UV-curable composition, and wherein the UV-curable composition comprises at least one mono-functional acrylate monomer. The at least one mono-functional acrylate monomer comprises a compound according to Formula (I) or Formula (II):

    ##STR00001##

    where n is 0 or 1.

    Claims

    1. An enamel composition comprising: glass frit; a pigment; and an organic carrier medium, wherein the organic carrier medium comprises a UV-curable composition, wherein the UV-curable composition comprises at least one mono-functional acrylate monomer, and wherein the at least one mono-functional acrylate monomer comprises a compound according to Formula (I) or Formula (II): ##STR00005## where n is 0 or 1.

    2. The composition according to claim 1, wherein the at least one mono-functional acrylate monomer comprises tricyclodecane methanol mono-acrylate or hexahydro-4,7-methano-1H-indenyl acrylate.

    3. The composition according to claim 1, wherein the enamel composition exhibits a change in viscosity after 2 hours which is less than 25%.

    4. The composition according to claim 3, wherein the change in viscosity is less than 2%.

    5. The enamel composition according to claim 1, wherein a change in the viscosity of the enamel composition after being applied by screen printing is less than about 25%.

    6. The composition according to claim 5, wherein the change in viscosity after 2 hours is less than 2%.

    7. The composition according to claim 5, wherein the at least one mono-functional acrylate monomer comprises tricyclodecane methanol mono-acrylate or hexahydro-4,7-methano-1H-indenyl acrylate.

    8. The composition according to claim 1, wherein the UV-curable composition comprises one or more polymeric binders.

    9. The composition according to claim 1, wherein the UV-curable composition comprises one or more curable polymers.

    10. The composition according to claim 9, wherein the curable polymer(s) comprises an acrylated polymer or oligomer.

    11. The composition according to claim 1, wherein the UV-curable composition further comprises one or more difunctional acrylic monomers.

    12. The composition according to claim 11, wherein the one or more difunctional acrylic monomers comprises tripropylene glycol diacrylate (TPGDA).

    13. The composition according to claim 11, wherein the UV-curable composition comprises the one or more difunctional acrylic monomers in amount of 10 to 20 wt %.

    14. The composition according to claim 1, wherein the UV-curable composition comprises the at least one monofunctional acrylic monomer in amount of 20 to 40 wt %.

    15. The composition according to claim 1, wherein the UV-curable composition further comprises one or more surfactants or dispersants.

    16. The composition according to claim 1, wherein the UV-curable composition further comprises one or more photo-initiators and/or photosensitisers.

    17. The composition according to claim 1, wherein the UV-curable composition further comprises one or more additives selected from the list consisting of UV stabilizers, adhesion promoters, thickeners, and anti-foaming agents.

    18. The composition according to claim 1, wherein the organic carrier medium further comprises one or more diluents or solvents.

    19. The composition according to claim 1, wherein the viscosity of the composition before curing is in the range of 10 to 20 Pa.Math.s.

    20. A method of forming an enamel coating comprising: depositing an enamel composition according to claim 1 on a substrate; curing the enamel composition; and firing the cured enamel composition.

    21. The method according to claim 20, comprising depositing the enamel composition by screen printing.

    22. The method according to claim 20, wherein the curing step comprises curing the UV-curable composition of the enamel composition by exposing the composition to a source of UV radiation.

    23. The method according to claim 20, comprising, subsequent to the curing step, printing at least a portion of the enamel composition with an outer metallic layer.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0034] For a better understanding of the present invention and to show how the same may be carried into effect, certain embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

    [0035] FIGS. 1 shows a graph illustrating the change in viscosity of a composition as described herein;

    [0036] FIGS. 2 and 3 show graphs illustrating the change in viscosity of alternative compositions; and

    [0037] FIG. 4 shows a graph plotting the viscosity increase for the composition of FIGS. 1 to 3.

    DETAILED DESCRIPTION

    [0038] As described in the summary section, the present specification provides a enamel composition which comprises glass frit, a pigment, and an organic carrier, and which advantageously displays good viscosity stability after being applied by screen printing, and which also exhibit good adhesion on glass and high hardness, structural integrity and/or chemical resistance, compared to existing enamel compositions.

    [0039] Typically, the organic carrier medium comprises a UV-curable composition which includes a mono-functional acrylate monomer, wherein the mono-functional acrylate monomer comprises a compound according to Formula (I) or Formula (II), such as tricyclodecane methanol mono-acrylate or hexahydro-4, 7-methano-1H-indenyl acrylate.

    [0040] Without wishing to be bound by theory, it is believed that the provision of tricyclodecane methanol mono-acrylate as a mono-functional acrylate monomer in the UV-curable composition, may stabilise the viscosity of the UV-curable composition by exhibiting a low evaporation rate. For example, tricyclodecane methanol mono-acrylate may exhibit a lower evaporation rate than, for example, isobornyl acrylate. Additionally, it is thought that provision of tricyclodecane methanol mono-acrylate as a mono-functional acrylate monomer in the UV-curable composition, may provide the resulting coating with superior hardness, structural integrity, and/or chemical resistance.

    [0041] The organic carrier medium may consist of the UV-curable composition. The organic carrier medium, e.g. UV-curable composition, may comprise one or more binders. Typically, the binder(s) may comprise or may be a polymer. The binder(s) may comprise an acrylic resin, a cellulosic resin, or the like. The binder(s) may comprise one or more resins selected from the list consisting of cellulose acetate butyrate resin, acrylic resin, or the like. The binder or combination of binders may be selected to provide the composition with a desired viscosity or rheology and/or with a desired level of harness. The organic carrier medium, e.g. UV-curable composition, may comprise the binder(s) in amount of about 0.1-20 wt %, e.g. about 1-10 wt %, e.g. about 2-6 wt %.

    [0042] The organic carrier medium, e.g. UV-curable composition, may comprise one or more curable polymers. The curable polymer(s) may comprise an unsaturated polymer or oligomer, for example an acrylated polymer or oligomer. The curable polymer(s) may include an aliphatic polyurethane acrylate. The organic carrier medium, e.g. UV-curable composition, may comprise the one or more curable polymers in amount of about 5-60 wt %, e.g. about 10-50 wt %, e.g. about 20-40 wt %.

    [0043] The organic carrier medium, e.g. UV-curable composition, may comprise one or more acrylic monomers. The one or more acrylic monomers may comprise at least one mono-functional acrylate monomer. The organic carrier medium, e.g. UV-curable composition, may comprise the one or more acrylic monomers in amount of about 20-70 wt %, e.g. about 30-60 wt %, e.g. about 40-50 wt %.

    [0044] The organic carrier medium, e.g. UV-curable composition, may comprise one or more difunctional acrylic monomers, e.g. tripropylene glycol diacrylate (TPGDA). The organic carrier medium, e.g. UV-curable composition, may comprise the one or more difunctional acrylic monomers in amount of about 5-30 wt %, e. g. about 10-20 wt %.

    [0045] As mentioned above, preferably, the UV-curable composition may comprise a compound according to Formula (I) or Formula (II), e.g. tricyclodecane methanol mono-acrylate (TCDA) or hexahydro-4, 7-methano-1H-indenyl acrylate. The organic carrier medium, e.g. UV-curable composition, may comprise the one or more monofunctional acrylic monomers, e.g. TCDA, in amount of about 10-50 wt %, e.g. about 20-40 wt %.

    [0046] The organic carrier medium, e.g. UV-curable composition, may further comprise one or more surfactants or dispersants (e.g. Soja Lecithin).

    [0047] The organic carrier medium, e.g. UV-curable composition, may further comprise one or more photo-initiators and/or photosensitisers.

    [0048] The organic carrier medium, e.g. UV-curable composition, may further comprise one or more additives selected from the list consisting of UV stabilizers (e.g. 4-Tert-Butylcatechol), adhesion promoters, thickeners, anti-foaming agents, or the like.

    [0049] The enamel composition, e.g. organic carrier medium thereof, may further comprise one or more diluents, e.g. a solvent. Alternatively, the enamel composition, e.g. organic carrier medium thereof, may not comprise a diluent, e.g. solvent. A solvent may not be required, for example when one of the components of the composition, e.g. one or more acrylic monomers, acts as a reactive diluent for the composition.

    [0050] The viscosity of the enamel composition, e.g. before curing, may be in the range of about 5-25 Pa.Math.s, e.g. about 10-20 Pa.Math.s, e.g. about 15-18 Pa.Math.s, e.g about 16-17 Pa.Math.s. Typically, viscosity may be measured in a continuous shear rate measurement program (0.10-50 s.sup.1) using cone plate geometry (CP 40 mm 1) at 21 C., recording the viscosity as paste viscosity at shear rate 10 s.sup.1.

    [0051] An enamel composition according to the present invention can be deposited, preferably using a screen printing on a substrate. The composition is then cured, for example by irradiating the composition with UV light.

    [0052] If required, a portion of the enamel composition may be coated, e.g. printed, with an outer coating, such as a conductive metallic (e.g. silver) layer that may, for example, form bus bars and/or wiring connections of a backlight defrosting system. Advantageously, the present enamel composition may have a superior hardness and/or chemical resistance making it particularly suitable to undergo such overprinting process.

    [0053] A number of more detailed examples are set out below to illustrate different embodiments of the present invention.

    EXAMPLES

    Example 1Preparation of a Composition According to a First Embodiment

    Formulation

    [0054] An embodiment of a formulation for the enamel ink composition is given in Table 1:

    TABLE-US-00001 TABLE 1 # Component Description Wt % 1 SR306 Tripropylene glycol diacrylate 2.812 (TPGDA), Sartomer 2 SR789 Tricyclodecane methanol Acrylate 6.152 (TCDA), Sartomer 3 Genomerr 1122 Mono functional urethane 5.100 acrylate, Rahn 4 Disperbyk 145 Dispersant BYK-Altana 0.800 5 Soja Lecithin Wetting/Dispersing agent 0.100 6 Miramer SC 1400 Adhesion promotor, Miwon 0.500 7 Omnirad 379 Photo-initiator, IGM Resins 0.848 8 Speedcure 2-ITX Sensitizer, Lambson 0.848 9 Speedcure EDB Co-initiator, Lambson 0.424 10 4-Tert- UV stabilizer 0.021 Butylcatechol 11 Florstab UV UV stabilizer 0.105 12 Genomer 4269/M22 Aliphatic urethane acrylate in 1.050 Genomer 1122, Rahn 13 CAB 551-0.2 Cellulose acetate butyrate 0.500 resin, Eastman 14 Neocryl B-731 Acrylic resin, DSM 0.400 15 1T1768 Pb-free automotive black enamel 80.00 for toughening application, JM AGT 16 Thixatrol Max Organic Thickener 0.250

    Preparation of Composition

    [0055] Table 2 shows a formulation recipe to prepare the composition of Table 1:

    TABLE-US-00002 TABLE 2 # Component Description Wt % 1 A 40 wt % wetting/dispersant solution 2.00 SR306 2 SR306 Tripropylene glycol diacrylate 1.70 (TPGDA), Sartomer 3 B Photo-initiator/Urethane oligomer 9.45 diacrylate solution in SR789 4 C Cellulose acetate butyrate solution 3.33 in Genomer 1122 5 D Acrylic resin solution in Genomer 2.67 1122 6 Soja Lecithin Wetting/Dispersing agent 0.10 7 Miramer SC 1400 Adhesion promotor, Miwon 0.50 8 1T1768 Pb-free automotive black enamel for 80.00 toughening application, JM AGT 9 Thixatrol Max Organic Thickener 0.25

    [0056] This recipe is based on the preparation of 100 g of an enamel ink composition. The composition is prepared using the intermediate components labelled as #1-7. Some of these components, namely #1, 3, 4, and 5, are provided as intermediate components identified respectively as A, B, C and D. The formulation of each of intermediate components A, B, C and D is provided below in Table 2a, 2b, 2c and 2d.

    TABLE-US-00003 TABLE 2a Composition Intermediate A: Component Description Wt % Disperbyk 145 Dispersant BYK-Altana 40.00 SR306 Tripropylene glycol 60.00 diacrylate, Sartomer

    TABLE-US-00004 TABLE 2b Composition Intermediate B: # Component Description Wt % 1 4-Tert-Butylcatechol UV stabilizer 0.22 2 Omnirad 379 Photo-initiator, IGM Resins 8.98 3 Speedcure 2-ITX Sensitizer, Lambson 8.98 4 Speedcure EDB Co-initiator, Lambson 4.49 5 SR789 Tricyclodecane methanol 65.11 Acrylate (TCDA), Sartomer 6 Genomer 4269/M22 Aliphatic urethane acrylate 11.11 in Genomer 1122, Rahn 7 Florstab UV UV stabilizer 1.11

    TABLE-US-00005 TABLE 2c Composition Intermediate C: Component Description Wt % CAB 551-0.2 Cellulose acetate butyrate resin, Eastman 15.00 Genomerr 1122 Mono functional urethane acrylate, Rahn 85.00

    TABLE-US-00006 TABLE 2d Composition Intermediate D: Component Description Wt % Neocryl B-731 Acrylic resin, DSM 15.00 Genomer 1122 Mono functional urethane acrylate, Rahn 85.00

    [0057] Components #1-7 were weighed into a plastic container and speed-mixed to yield a homogeneous solution. . . . An enamel powder (component #8) and Thixatrol Max (Component #9) were added, and the mixture was speed-mixed for 20 seconds at 3000 rpm. The paste mixture was homogenized by triple roll milling twice. The paste was diluted with a medium based on mixture #1-7 to a viscosity of around 15 Pa.Math.s.

    Analysis of Viscosity

    [0058] The change in viscosity of an enamel paste over time was assessed using the following test method.

    [0059] The visco-stability of paste was assessed by applying a thin paste film (200 m) on glass plate and measuring viscosity and weight loss of thin film after exposure to 30 C. and 65% RH in a climate chamber at interval times of 0.5, 1.0, 1.5 and 2.0 hrs.

    [0060] Measurement of viscosity was made in a continuous shear rate measurement program (0.10-50 s.sup.1) using cone plate geometry (CP 40 mm) 1 at 21 C., recording the viscosity as paste viscosity at shear rate 10s.sup.1.

    [0061] Details of the formulations of three different compositions are shown is Table 3 below. Composition 1 corresponds to the composition of Table 1. Compositions 2 to 4 are similar UV-curable compositions but based on different acrylate monomers.

    TABLE-US-00007 TABLE 3 Composition #4 #3 #2 #1 # Component Description wt % 1 SR306 Tripropylene 3.9174 3.5270 7.1517 2.9018 glycol diacrylate (TPGDA), Sartomer 2 SR789 Tricyclodecanem 6.1518 ethanol Acrylate (TCDA), Sartomer 3 Genomer Isobornyl 7.6996 7.6996 1121 acrylate (IBOA) 4 Genomer Mono functional 2.8333 2.8331 7.4750 5.1000 1122 urethane acrylate, Rahn 5 Disperbyk Dispersant, 0.8000 0.8000 0.8000 0.8000 145 BYK-Altana 6 Soja Wetting/ 0.1000 0.1000 0.1000 0.1000 Lecithin Dispersing agent 7 Miramer Adhesion 0.2870 0.2870 0.2870 0.5000 SC 1400 promotor, Miwon 8 Omnirad Photo- 0.7813 907 initiator, IGM Resins 9 Omnirad Photo- 0.7813 0.7813 0.8482 379 initiator, IGM Resins 10 Speedcure Sensitizer, 0.7813 0.7813 0.7813 0.8482 2-ITX Lambson 11 Speedcure Co-initiator, 0.3907 0.3907 0.4241 EDB Lambson 12 4-Tert- UV stabilizer 0.0193 0.0193 0.0193 0.0210 Butylcate chol 13 Florstab UV stabilizer 0.0967 0.0967 0.0967 0.1050 UV 14 Genomer Aliphatic 1.9340 1.9340 0.9670 1.0498 4269/M22 urethane acrylate in Genomer 1122, Rahn 15 CAB 551- Cellulose 0.5000 0.5000 0.5000 0.5000 0.2 acetate butyrate resin, Eastman 16 Neocryl BMA polymer, 0.4000 0.4000 B-731 DSM 17 1T1768 Pb-free 80.0000 80.0000 80.0000 80.0000 automotive black enamel for toughening application, JM AGT 18 Thixatrol Organic 0.2500 0.2500 0.2500 0.2500 Max Thickener Total: 100.0000 100.0000 100.0000 100.0000

    [0062] In Composition 1, the organic carrier medium includes three acrylic monomeric components, namely a difunctional acrylic monomer in the form of tripropylene glycol diacrylate (TPGDA) and two monofunctional acrylic monomers in the form of tricyclodecane methanol mono-acrylate (TCDA) and a monofunctional urethane acrylate.

    [0063] In contrast, Composition 2 contains TPGDA and a monofunctional urethane acrylate as the acrylic monomeric components. That is, composition 2 does not include tricyclodecane methanol mono-acrylate (TCDA).

    [0064] In Composition 3, the organic carrier medium includes a mixture of TPGDA, isobornyl acrylate (IBOA) and a monofunctional urethane acrylate. That is, it is similar to Composition 1 but uses IBOA instead of TCDA.

    [0065] Composition 4 is similar to Composition 3 (both using isobornyl acrylate as a monofunctional acrylic monomer), and only differs in the photo-initiator used, which does not affect qualitatively either viscosity behaviour or hardness.

    [0066] The viscosities measured over time for the Compositions 1, 2 and 3 of Table 3 are shown in FIGS. 1 to 3.

    [0067] As can be seen from FIG. 1, the viscosity of the UV-curable Composition 1, which uses tricyclodecane methanol mono-acrylate (TCDA) as monofunctional acrylic monomer, remained substantially stable over 2 hours.

    [0068] Referring to FIG. 2, the viscosity of the UV-curable Composition 2, was also relatively constant over time. However, as composition 2 contains TPGDA and a monofunctional urethane acrylate as the acrylic monomeric components, the solvent resistance of the resulting coating was found to be of lesser quality (see Table 5 later), and was therefore not optimum for subsequent overprinting with, for example, a metallic bus bar.

    [0069] In contrast, the viscosity of the UV-curable Composition 3, which uses only tripropylene glycol diacrylate (TPGDA) as the acrylic monomer component, exhibited a significant increase in viscosity over the same period of time. Without wishing to be bound by theory, this is believed to be due at least in part to the relatively high evaporation rate of isobornyl acrylate in comparison with tricyclodecane methanol mono-acrylate.

    [0070] FIG. 4 shows a graph plotting the viscosity increase for each of Compositions 1, 2 and 3, further illustrating the above observations in respect of FIGS. 1, 2 and 3.

    [0071] A comparison of the viscosity change over time between compositions 1 and 4, is shown in Table 4.

    TABLE-US-00008 TABLE 4 Sample Code Composition 4 Composition 1 Start viscosity (Pa .Math. s) 16.7 16.4 (@ 10 s.sup.1) 30 C./60% RH After 1.0 hr 33.3 16.5 After 2.0 hr 33.3 16.6 (%) after 2.0 hrs 99 1

    [0072] As can be observed from Table 4, the viscosity of the UV-curable Composition 1, which uses tricyclodecane methanol mono-acrylate (TCDA) as monofunctional acrylic monomer, remained substantially stable over 2 hours. In contrast, the viscosity of the UV-curable Composition 4, which uses only tripropylene glycol diacrylate (TPGDA) as the acrylic monomer component, exhibited a significant increase in viscosity over the same period of time.

    [0073] This is consistent with the observations made in relation to Composition 3, as Composition 4 is similar to Composition 3(both using isobornyl acrylate as the monofunctional acrylic monomer), and only differs in the photo-initiator used, which was not expected to affect either viscosity behaviour or hardness.

    Assessment of Solvent Resistance

    [0074] Compositions #1 (including TCDA as a monofunctional monomer) and #2 (no TCDA) as described above, were used to prepare a film which was cured and then exposed to solvent attack using butyl diglycol acrylate (BDGA). A qualitative assessment of solvent resistance was performed, and is shown in Table 5.

    TABLE-US-00009 TABLE 5 Composition # #1 #2 UV medium composition (wt %) RM.7136 (SR789, TCDA) 30.8 RM.476 (Genomer 1121, IBOA) RM.407 (SR306, TPGDA) 14.5 35.8 RM.558 (Genomer 1122, UA) 25.5 37.4 Paste stability (30 C./60% RH) Start viscosity (@ 10 s.sup.1) (Pa .Math. s) 15.4 14.7 Viscosity after 2 hrs (Pa .Math. s) 14.7 14.1 (%) after 2 hrs 4.5 4.1 Smell Typical TCDA Neutral odour (fruity) Cured film properties - Solvent attack resistance Curing setting (6 m/min, 220 mJ/cm2) No attack Light attack Preheating to 35 C. Exposure (4 hrs) to RM.867 (BDGA) + Firing Curing setting (8 m/min, 150 mJ/cm2) Light attack Moderate- Preheating to 35 C. attack Exposure (4 hrs) to RM.867 (BDGA) + Firing

    [0075] As shown in Table 5, it can be seen that UV-curable Composition 1, which uses tricyclodecane methanol mono-acrylate (TCDA) as monofunctional acrylic monomer, exhibited improved solvent resistance to BDGA, compared to Composition 2 which was free of TCDA.

    Application of Enamel Layer

    [0076] To mimic the visco-stability of paste in the screen printing process, a thin film (wet film thickness: 50 micron) of paste was cast on a glass substrate and was exposed to 30 C. and 60% RH in a climate chamber with controlled air circulation. According to the results shown in Table 4, the viscosity change of the paste made according to Composition 1 was almost negligible, whereas the isobornyl acrylate-based UV paste (Composition 4) showed a significantly higher increase in viscosity.

    [0077] The UV-curable paste (Composition 1) was screen printed on a glass sheet using screen mesh size (77T, 90T). It will be understood that in practice the glass substrate may be any glass suitable for use in the automotive industry, such as clear, green or dark coloured (i.e. privacy glass) float glass. The screen-printed film (wet film thickness about 20-22 micron) was exposed to UV curing using an industrial UV curer.

    [0078] The cured film was over printed with silver paste (AG330L-80) in the form of a bus bar (wet film thickness: 25-30 micron) and was dried in an industrial IR belt drier. The cured black enamel with silver overprint was in a roller kiln according to a firing cycle suitable for toughening enamel for backlight.

    [0079] While this invention has been described with reference to certain examples and embodiments, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.