NL2020460B1 - Method for the preparation of a printed article by dye-sublimation - Google Patents

Abstract

Described is a method for the preparation of a printed article by dye-sublimation, comprising the steps of providing a substrate material comprising a coated surface to be printed, subjecting the coated surface to dye sublimation wherein dye is penetrated into the said coating at elevated temperature and pressure wherein the dye is in a gaseous state, lowering the temperature of the coated surface allowing the dye to become embedded in the coating material, wherein the surface to be printed comprises a first transparent coating layer, comprising a transparent fluoropolymer. Further, a substrate comprising a coated surface to be printed, the use of such a substrate for dye-sublimation, a method for the preparation of a coated substrate material, the use of a fluoropolyol in the preparation of a coated substrate material for dye-sublimation and an article, comprising a substrate, printed according to the described method are presented.

Description

Patent center

Θ 2020460

(2?) Application number: 2020460 (22) Application submitted: 19 February 2018

Int. Cl .:

B41M 5/035 (2018.01) B41M 5/52 (2019.01) B41M

5/44 (2019.01)

0 Application registered: 0 Patent holder (s): August 27, 2019 Lamoral Holding B.V. te Weert. 0 Request published: August 28, 2019 0 Inventor (s): Theodorus Matheus Maria Verweerden 0 Patent granted: te Weert. September 4, 2019 Thom Martinus Johannes Mario Martens in Loosbroek. 0 Patent issued: Gernot Klaus Brueck in Hoensbroek. September 5, 2019 0 Authorized representative: Dr. T. Wittop King PhD in Delft.

54) Method for the preparation of a printed article by dye-sublimation

57) Described is a method for the preparation of a printed article by dye-sublimation, including the steps of providing a substrate material including a coated surface to be printed, subjecting the coated surface to dye, sublimation being dye is penetrated into the said coating at elevated temperature and pressure the dye is in a gaseous state, lowering the temperature of the coated surface allowing the dye to become embedded in the coating material, the surface to be printed comprises a first transparent coating layer, including a transparent fluoropolymer. Further, a substrate containing a coated surface to be printed, the use of such a substrate for dye sublimation, a method for the preparation of a coated substrate material, the use of a fluoropolyol in the preparation of a coated substrate material for dye- sublimation and an article, including a substrate, printed according to the described method are presented.

NL B1 2020460

This patent has been granted regardless of the attached result of the research into the state of the art and written opinion. The patent differs from the documents originally submitted. All submitted documents can be viewed at the Netherlands Patent Office.

Method for the preparation of a printed article by dye-sublimation

The invention relates to a method for the preparation of a printed article by dyesublimation, to the use of a substrate comprising a coated surface to be printed, in dye-sublimation, to a coated substrate material for dye-sublimation, to a method for the preparation of a coated substrate material and to an article, including a substrate, printed by dye-sublimation.

Dye sublimation, also referred to as digital sublimation, is a printing technique in which heat and pressure are applied to a solid dye material, turning it into a gas through an endothermal reaction without passing through the liquid phase. This technique is e.g. described in US3,363,557. In sublimation printing, unique sublimable dyes, e.g. as described in US3,829,286 are transferred to a temporary support, such as described in US3,860,388, US3,829,286, US4,576,610 and US4,619,665. For examples, sublimable ink Is transferred to sheets or transfer paper via liquid gel ink through a piezoelectric print head. The ink is deposited on these high-release inkjet papers, which are used for the next step of the sublimation printing process. After the digital design is printed on sublimation transfer sheets, it is placed on a heat press along with the substrate to be printed. In order to transfer the image from the paper to the substrate, it requires a heat press process that is a combination of time, temperature and pressure. The heat press applies this special combination, which can change depending on the substrate, to transfer the dyes after sublimation, i.e. in the gaseous phase onto or into the substrate. The most common dyes used for sublimation activate at about 175 ° C. However, a range of 195 ° C to 215 ° C is normally recommended for optimum color. The end result of the sublimation process is a nearly permanent, high resolution, full color print. Because the dyes are infused into the substrate at the molecular level, rather than applied at a topical level such as with screen printing and direct to garment printing, the prints are less susceptible to cracking, fading or peeling from the substrate. Substrates for dye sublimation must therefore be resistant to the applied pressures and temperatures, and capable of absorbing the dyes. Suitable substrate materials for dye-sublimation are eg metal, wood, wooden board materials, plastic sheet material, eg sheet materials including melamine-based or phenol-based resins, composite materials (such as made by Trespa BV The Netherlands), ceramics, glass, metal, such as aluminum (Dibond,

Alupanel, Vibond, Prepanel), temperature resistant polymer sheets such as acrylate (Perspex, Plexiglass), high pressure wood laminates etc.

Printable objects are e.g. apparel, signs and banners, textile, as well as novelty items such as cell phone covers, plaques, coffee mugs and the like.

Before being printed, the multiple of the substrate material materials is coated with a polymer layer or e.g. polyester or polyurethane. During the sublimation printing, the dyes penetrate this layer and become embedded therein, resulting in the substrate being printed. Some materials, such as polyester fabric, can be penetrated by the dyes during printing and an additional coating is not necessary. However, most of the substrates, such as metal and most plastic sheets are impermeable for the dyes, i.e. do not allow the dyes to penetrate therein. Such a coating material also needs adhering properties for the envisaged substrate material. The thickness of the coating may vary, although it is important during the printing, the dyes are embedded in the coating, without passing therethrough to reach the impermeable substrate material; when this happens, the printing is negatively affected, resulting in e.g. blurry images. The layer should be permeable for the gaseous dyes, without being deteriorated by the heat and pressure conditions during printing. At such conditions, the ink components will turn into the gas phase and will diffuse and migrate into the coating. Polymer materials that are molten at the conditions of dye-sublimation are not suitable as coating material.

A problem with the presently used polymer materials for coating substrates for dye sublimation is the limited resistance to UV radiation, in particular UV-A, i.e. having a wavelength or 315-400 nm. As a result, the color of articles printed by the dyesublimation technique become faint in time, and the printed surface may lose its original color. Such articles can be used for outdoor application for a maximum of about two years. So in the art, there is a need for improved methods for the preparation of printed articles by dye-sublimation that have an improved resistance against UV radiation (ie less UV-transparent) as compared to those known in the art and have a longer keepability when kept outdoors.

JP2005001392, JP2003231346, EP1504918 and US5364412 describe methods for the preparation of a printed article by dye-sublimation, a substrate material with a coated surface is printed, the coated surface including a fluoropolymer.

To this end, a method for the preparation of a printed article by dye-sublimation is provided, including the steps of:

a) providing a substrate material including a coated surface to be printed,

b) subjecting the coated surface to dye sublimation where dye is penetrated into said coating at elevated temperature and pressure the dye is in a gaseous state,

c) lowering the temperature of the coated surface allowing the dye to become embedded in the coating material, including the coated surface to be printed comprises a first transparent coating layer, the first coating layer including

- a fluoropolymer, including a polytetrafluoroethylene terpolymer comprising fluoropolyol monomers, being soluble in methyl ethyl ketone, ethylbenzene, xylene, acetone or a mixture of two or more.

- isocyanate, the weight ratio between the fluoropolymer and the isocyanate, based on dry weight, being 5 - 25: 1.

The term 'transparent' means that the coating is colorless and transmits visible light for at least 95%, preferably at least 96%, 97%, 98%, in particular 99% or even more particular 100%, and preferably the same is true for light in the IR range.

Steps a) to c) are common steps in the dye-sublimation technique and are known to the skilled person. It was surprisingly found that transparent coatings including a fluoropolymer are very suitable as coating for substrate material for dye-sublimation. It was surprisingly found that such fluoropolymers allow sublimable dyes to penetrate such coating at dye sublimation conditions and to become embedded therein.

It is believed that the transparent fluoropolymer matrix somehow relaxes during the printing conditions, allowing the sublimation dyes to penetrate the polymeric coating. Upon cooling, the matrix would become denser, therewith embedding the dyes in the matrix, providing a coating that is tight for water, vapor and UV.

In the art, many fluoropolymers are known, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene tetrafluoroethylene (EFTE), copolymers such as tetrafluoroethylene perfluoromethylvinyl ester (MFA) and terpolymers such as tetrafluoroethylene-hexafluoropropylene-fluorofluoropropylene-fluorofluoropropylene fluoride . Because of the strong C-F bond, fluoropolymers have a high chemical inertness and are inherently UV stable. However, most of the fluoropolymers have a limited transparency and are not suitable for being used in a transparent coating. For a transparent coating, it is necessary for the fluoropolymer to be transparent as well. Further, the various or fluoropolymers is hardly soluble in organic solvents. However, the feature of being soluble makes the polymers particularly suitable to be coated on surfaces, e.g., by spraying or any other suitable technique, known to the skilled person. Perfluoroalkoxy (PFA) may have a high degree of transparency but has a low solubility and poor substrate adhesion and may therefore be a less suitable fluoropolymer for the method of the present invention. Therefore, the transparent fluoropolymer used in the method of the present invention is preferably solvent-based. The term "solvent-based" means that the polymer is soluble in a solvent to be used for coating the fluoropolymer onto the substrate surface to be printed.

The polymer comprises a fluoropolyol. Fluoropolyols have hydroxyl groups that makes them more readily soluble in organic solvents such as xylene, ethylbenzene and methyl ethyl ketone (MEK). The more hydroxyl groups, the more soluble the polymer is. Also, the adhesion to substrates improves when more hydroxyl groups are present. In particular polytetrafluoroethylene terpolymers including fluoropolyol monomers are very suitable in view of solubility, transparency and UV resistance. Suitable fluoropolymers are e.g. Lamoral 100 series.

The first transparent coating layer further comprises isocyanate. It was found that the presence of isocyanate improves the UV resistance even further. The weight ratio between the fluoropolymer and the isocyanate, based on dry weight, is 5-25: 1, preferably 10-20: 1. In the mixture with the fluoropolyol based polymer, the isocyanate reacts with the hydroxyl groups to produce polyurea.

The fluoropolymer has an intrinsic UV resistance to UV, and the UV resistance is increased even more by the presence of isocyanate. In an attractive embodiment, however, the coating, the coating further comprises at least a UV stabilizer, or UV absorber, to increase the UV resistance even further. Suitable UV stabilizers / absorbers are e.g. hindered amine light stabilizers (HALS) and azo compounds, known to the skilled person.

In an attractive embodiment, the first coating layer has a thickness of 4 - 50 pm. Such a thickness provides for improved UV resistance, i.e. capacity or blocking UV transmission. It is believed that the UV penetrates the coating and is converted therein to infrared light. However, the coating is transparent for infrared, and for that reason, the coating is not affected by any heat formation and remains stable upon UV.

The thickness is preferably 10-40 pm. A thickness of 15 pm already provides forums UV block or 99.5%.

For optimal UV resistance, the thickness of the first coating layer is at least or about 30 pm. It was found that at a thickness of 30 pm, 99.998% of the UV radiation is blocked. A higher thickness may be used but is not necessary. If the dye-sublimation printing conditions are chosen such, the dyes would penetrate further than 30 pm, a corresponding thicker coating layer can be used.

When a thicker coating is required because of the envisaged penetration depth of the dyes, it is also possible that the coating comprises a second transparent coating layer, positioned between the substrate surface and the first coating layer, said second coating layer comprising coating material known in the art for penetration and embedding of dyes in the sublimation printing technique, such as a polyester or polyurethane coating. In this embodiment, a known substrate material being coated with known transparent coating materials can be used to be further coated with the fist transparent coating layer, which first coating layer provides for the UV resistance, and the second coating, together with the first coating, allow the dyes to become embedded therein. However, it is also possible to allow the dye to penetrate the coating until it reaches the surface of the substrate, where the dye will be deposited.

The invention further described a substrate including a coated surface to be printed by dye-sublimation, the coating layer being as defined above. The substrate can be any printable material as described above, that remains inert at the conditions of dye-sublimation. The substrate material for dye sublimation is preferably form stable at ambient conditions, i.e. at ambient temperature, pressure and humidity, in particular in view of the coating thickness of 20 - 50 pm. Metal, polymer-based and wooden sheets are examples of such form stable materials. Textiles, not being form stable, are less suitable, as the coating will result in the textile to become too stiff for envisaged purposes.

Further, articles including a substrate, printed according to the method as described above are disclosed.

The invention will now be further explained by way of the following non-limiting examples.

Preparation of samples

Fluoropolymers or Lamoral series 100 (Lamoral, Netherlands), a methyl ethyl ketone solution, having a solids content of 40% and a density of 0.9-1.0 kg / l (at 20 ° C), optionally mixed with isocyanate Lamoral C20 (Lamoral, The Netherlands) a solution in methyl ethyl ketone, having a solids content of 20% and a density of 0.8-0.9 kg / l (at 20 ° C), in a weight ratio of 10: 1 were used to coat different substrates, varying from High Pressure Laminate (HPL), Aluminum, Trespa composite materials and transparent polyester films.

The surface to be coated was rinsed with acetone and allowed to dry. Lamoral 100, or a 10: 1 mixture of Lamoral 100 and Lamoral C20, diluted with acetone to 1520% solids, were applied to the substrate surface by spraying the fluoropolymer solution thereon and allowing the substrate to dry. The coating thickness was measured using an Elcometer 456-layer meter (Elcometer, UK) with a ferro probe.

UV transmittance

UV transmittance was measured by coating a polyester film as described above and measuring the UV transmittance with UV-VIS spectrophotometer LISR-3100 (Shimadzu, Japan) with the settings shown in table 1.

Table 1 settings UV spectophotometer

Measurement Properties] Wavelength Range (nm.): 200.00 to 1200.00 Scan Speed: Fast Sampling Interval: 2 Auto Sampling Interval: Disabled Scan Mode: Single [Instrument Properties] Instrument Type: UV-3600 Series Measuring Mode: Slit Width: Time Constant: Source Lamp: Light Source Change Wavelength: Detector Unit: Detector Change Wavelength: Transmittance 2.0 nm 0.1 sec. Auto 295.00 nm External (2D detectors) 850.00 nm Grating Change Wavelength: 850.00 nm S / R Exchange: Normal Detector Lock: Car Slit Program: Normal Beam Mode: Double Stair correction: Disable [Attachment Properties] Attachment: None [Operation] Threshold: 0.001 Points: 4 Interpolate: Disabled Average: Disabled [Sample Preparation Properties] Weight: Volume: 1ml Dilution: Path Length: 1 cm Additional Information:

UV transmission data are shown in figure 1 for a coating with Lamoral 100, and in figure 2 for a coating with Lamoral 100: Lamoral C20 10: 1.

The coating without isocyanate blocks 99.998% UV radiation (wavelengths 320380 nm) from a thickness of 30 µm (figure 1). When isocyanate is present in the coating, 99.5% UV blocking from a coating thickness or 20 pm is observed, see figure

2. It is observed that when PE is coated, transmittance or visible and infrared radiation is not effected.

Dye-sublimation printing and UV weathering

High Pressure Laminate Trespa meteon pure white tiles with a thickness of 6 mm (Trespa, Netherlands) provided with a white polyurethane layer (Interpon D1010 Series, AkzoNobel, Netherlands) varying from 20 to 50 microns was spay-coated with a layer of Lamoral 100 - Lamoral C20 as described above, with a thickness varying from 30 to 80 pm. The coating was cured for one hour at 80 ° C, and the coating was cured for 7 days at ambient conditions.

After curing, the substrates were subjected to dye-sublimation coating, where an array of 12 x 6 squares or 12 x 12 mm each, or different colors with different intensity were printed using a sublimation printer or the WSE series (Wischt, Serbia) according to to the instructions of the manufacturer. As a control a brushed aluminum plate having a thickness of 3 mm (Alupanel), coated with a polyester layer or 40 µm (Interpon HST Series, AkzoNobel, Netherlands) was subject to the same printing.

To mimic UV weathering, the printed tiles were subjected to UV radiation for 168 hours with a UV middle pressure HG lamp, iron doped, having an electrical performance of 500W and the following UV outputs: UCV (200-280nm) 7% = 35W UVB (280-315nm) 5% = 25W UVA (315,380nm) 17% = 85W or in total 145W UV radiation, producing an irradiation area or 1,257 cm ² , and an irradiance or 0.115W / cm ² . The total dose of irradiation was 19.4Wh / cm ² , corresponding to the UV radiation during 10 years in Florida, or 20 years in the Netherlands. The Aluminum plates were subjected to 84 hours of the irradiation described above, ie mimicking the UV radiation during 5 years in Florida, or 10 years in the Netherlands.

Before and after the weathering, Delta E values were tasks for each color square, using a MA98 Portable Multi-Angle Spectrophotometer (X-Rite, US), see figures 3 and 4, in figure 3 the uncoated aluminum plate is shown before (left panel) and after weathering (right panel). The delta E value is over 20, i.e. very well visible. All colors were faint after the weathering. Figure 4 shows the Trespa tiles before (upper) and after (lower) weathering, where the thickness of the coating increases from 30 pm in panel A, stepwise by 10 pm to a thickness or 80 pm in panel F. The Delta E value for all colors was below 3, meaning that no visible color change occurred.

Similar results were obtained when using Lamoral 100 coating without isocyanate, also resulting in Delta values or below 3 (data not shown).

Claims (17)

CONCLUSIONS A method of manufacturing a printed article by ink sublimation, the method comprising the steps of: a) providing a substrate material comprising a coated surface to be printed, b) subjecting the coated surface to ink sublimation whereby the ink is penetrated into the coating at elevated temperature and pressure, the ink being in a gaseous state, c) lowering the temperature of the coated surface to embed the ink in the coating material, the coated surface to be printed comprising at least a first transparent coating layer, which first coating layer comprises: a fluoropolymer, which comprises a polyterfluoroethylene terpolymer comprising fluoropolyol monomers, which is soluble in methyl ethyl ketone, ethylbenzene, xylene, acetone or a mixture of two or more thereof, and isocyanate, the weight ratio between the fluoropolymer and the isocyanate based on dry weight Is 5-25: 1. The method of claim 1, wherein the coating further comprises a UV stabilizer. Method according to claim 1 or 2, wherein the first coating layer has a thickness of 20 - 50 µm. Method according to any of the preceding claims, wherein the coating comprises a second transparent coating layer, which is located between the surface of the substrate and the first coating layer. The method of claim 4, wherein the second coating layer comprises a transparent polyester or a transparent polyurethane. A substrate comprising a coated surface to be printed by ink sublimation, the coating comprising a first coating layer, which first coating layer comprises: a fluoropolymer, which comprises a polyterfluoroethylene terpolymer comprising fluoropolyol monomers, which is soluble in methyl ethyl ketone, ethylbenzene, xylene, acetone or a mixture of two or more thereof, and isocyanate, the weight ratio between the fluoropolymer and the isocyanate based on dry weight Is 5-25: 1. The substrate of claim 6, wherein the coating further comprises a UV stabilizer. A substrate according to claim 6 or 7, wherein the first coating layer has a thickness of 20 - 50 µm. The substrate of any one of claims 6-8, wherein the coating comprises a second transparent coating layer that is located between the surface of the substrate and the first coating layer. The substrate of claim 9, wherein the second coating layer comprises a transparent polyester or a transparent polyurethane. 11. Use of a substrate according to any of claims 6 in ink sublimation. A method of producing a coated substrate material according to any of claims 6 to 11, wherein a solution of the fluoropolymer is applied to the surface. The method of claim 12, wherein the fluoropolymer is dissolved in methyl ethyl ketone, ethylbenzene, xylene, acetone or a mixture of two or more thereof. A method according to claim 12 or 13, wherein the solution comprises 10-40% by weight of solids. The method of claim 14, wherein the fluoropolymer is at least 90% by weight of the solids. A method according to any of claims 12 to 15, wherein the coating is applied in a layer thickness of 20 - 50 µm. A product comprising a substrate printed in accordance with the method of any one of claims 1 to 5. Figure 1 Coating thickness ----- OsdoXx ibi-SiX .; ----------- <; 10: xk; O: S 15: i ^; ;: C: s <«« ««: χθ.ι ·· χι Wssveissngirt (w $ n) Figure 2 Figure 3 Figure 4