Coatings and articles with light-blocking properties

Abstract

The present invention is related to a composition for manufacturing a layer (4a, 4b, 4c) that is capable of at least partially blocking light in the UV/VIS region and is deinkable, said composition comprising a blend of a pigment and a filler. The present invention is also related to a printed article, comprising a transparent substrate (3) and on said transparent substrate (3) at least one ink layer (4a, 4b, 4c) being made from said composition. The present invention is furthermore related to a container for storing a product, preferably a food product, wherein said container comprises a transparent substrate (2) containing on its outer surface said printed article, and to a method for deinking said container.

Claims

1. A composition for manufacturing a layer that is capable of at least partially blocking light in the UV/VIS region and is deinkable, said composition comprising: 10-50 wt.-% of a blend of a pigment and a filler; 10-40 wt.-% of a first binder component, selected from the group consisting of nitrocellulose, polyurethane, and combinations thereof 5-30 wt.-% of a second binder component selected from the group consisting of maleic resin, a polyvinyl ester, and combinations thereof wherein all wt.-% are based on the entire weight of the composition.

2. The composition according to claim 1, wherein said pigment is selected from the group consisting of a white pigment, preferably TiO2, and a silver pigment.

3. The composition according to claim 1, wherein said filler is selected from the group consisting of clay, barium sulfate, mica and calcium carbonate.

4. The composition according to claim 1, wherein the blend contains said at least one white pigment and said filler in a range from 99:1 to 80:20, or said at least one silver pigment and said filler in a range from 5:95 to 90:10.

5. The composition according to claim 1, wherein said white pigment has an average particle size (crystal size) in the range from 0.12 to 0.3 m.

6. A printed article, comprising a transparent substrate and on said transparent substrate at least one ink layer that is capable of at least partially blocking light in the UV/VIS region and is deinkable, said layer being made from a composition according to claim 1.

7. The printed article according to claim 6, wherein the transparent substrate is composed of polyethylene terephthalate.

8. The printed article according to claim 6, wherein on said transparent substrate there is provided a sequence of 2-5 of said ink layers.

9. The printed article according to claim 8, wherein at least one of said layers contains a silver pigment, and at least another one of said layers contains a white pigment.

10. The printed article according to claim 6, further comprising an overprint varnish applied on said sequence of ink layers.

11. The printed article according to claim 6, wherein said printed article exhibits a light-blocking performance in the range from 95-100%.

12. The printed article according to claim 6, wherein said printed article exhibits an L* value in the range from 85-95.

13. A container for storing a light-sensitive product, preferably a food product, wherein said container comprises a transparent substrate containing on its outer surface a printed article according to claim 6.

14. The container according to claim 13, wherein the substrate of said container is composed of polyethylene terephthalate.

15. A method for recycling the container according to claim 13, comprising a step of deinking the container in an alkaline aqueous medium at a temperature in the range from 50-90 C. for 1 to 15 min.

16. The composition of claim 1 comprising an organic solvent and additives.

17. The composition of claim 5 wherein the average particle size is from 0.22 to 0.25 m.

18. The printed article according to claim 8 wherein on said transparent substrate there is provided a sequence of 3 of said ink layers.

19. The method of claim 15 wherein the alkaline aqueous medium contains 1 wt % NaOH based on the entire weight of the alkaline medium.

20. The method of claim 15 wherein the step of deinking the container is at a temperature in the range of from 60 to 85 C.

Description

(1) The present invention will now be described below in more detail by reference to non-limiting figures and examples.

(2) FIG. 1 shows an illustration of a container according to an embodiment of the present invention.

(3) FIG. 2a shows a schematic illustration of the deinking process of the present invention.

(4) FIG. 2B shows another schematic illustration of the deinking process of the present invention.

(5) FIG. 3 shows a graphical illustration of the light blocking properties of different printed products with a different upper ink layer.

(6) FIG. 4 shows a graphical illustration of the light blocking properties of different printed products with different white pigments.

(7) FIG. 5 shows a graphical illustration of the light blocking properties of different silver products.

(8) FIG. 6A shows a photograph of printed samples of the present invention before the deinking process.

(9) FIG. 6B shows a photograph of printed samples of the present invention after the deinking process.

(10) In FIG. 1 a container 1 according to an embodiment of the present invention is shown. The container 1 comprises a transparent substrate 2, e.g. a plastic substrate such as PET. On one surface of said substrate 2, there is applied a printed article according to the present invention. Said printed article comprises a transparent substrate 3, preferably from PET, and a sequence of ink layers 4a, 4b, 4c applied on one surface of the transparent substrate 3. An overprint varnish layer 5 is applied on top of said sequence of ink layers 4a, 4b, 4c.

(11) In said preferred embodiment of the present invention, the ink layers 4a, 4b comprise a white pigment, such as TiO.sub.2, whereas the ink layer 4c comprises a silver pigment.

(12) In FIGS. 2a to 2b, the deinking process of the present invention is schematically illustrated.

(13) In FIG. 2a, the container 1 during deinking is shown. It is shown that during the deinking step the ink layers 4a, 4b, 4c become dissolved (as illustrated by the broken boundaries).

(14) In FIG. 2b, it is shown that after the deinking step the transparent substrate 1 and the transparent substrate 2 are separated and can be separately recycled.

(15) In another preferred embodiment, also the overprint varnish layer 5 can be made such that it becomes dissolved during deinking, by making the overprint varnish layer 5 from a similar composition as the ink layers 4a, 4b, 4c (except for the pigment).

EXAMPLES 1 TO 9: PREPARATION OF AN INK COMPOSITION

(16) The following components were added together under stirring, so as to result in a composition according to the present invention:

(17) TABLE-US-00001 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Component (wt.-%) (wt.-%) (wt.-%) (wt.-%) (wt.-%) (wt.-%) Nitrocellulose 10 15 30 5 20 20 Polyurethane 5 1.5 2 7 resin Maleic resin 7 10 Acrylic resin 20 14 PVA resin 11 19 Pigment/Filler 42 12* 10* 35 30 23* Silicone 1 1 1 PE wax 2.5 1 1 2 3 Plasticizer 1 1.5 0.5 1 1 Solvent 31.5 49.5 45 43 25 40 Total amount 100 100 100 100 100 100 *silver pigment

(18) The white pigment/filler component consisted of 80-99 wt.-% TiO.sub.2 having a particle size (crystal size) in the range from 0.22 to 0.25 m and 1-20 wt.-% filler (selected from the group consisting of Al.sub.2O.sub.3, SIO.sub.2 and ZrO.sub.2), based on the entire amount of the component.

(19) In the same manner, the following UV-curable ink compositions were prepared.

(20) TABLE-US-00002 Ex. 7 Ex. 8 Ex. 9 Component (wt.-%) (wt.-%) (wt.-%) Acrylate Di-functional Monomer 38% 38% 38% Acrylate Monofunctional Monomer 3% 3% 3% Acrylate Di-functional Monomer 21% 25% 25% Aluminum Pigment 13% 13% 13% Polyester Acrylate 19% Epoxy Acrylate 15% Urethane Acrylate 15% Acrylate Stabilizer Blend 3% 3% 3% Photocatalyst 8% 8% 8% Total amount 100 100 100

EXAMPLE 10: PREPARATION OF PRINTED ARTICLE

(21) A printed article according to FIG. 1 was prepared by subsequently applying onto a biaxially oriented transparent PET substrate 3 ink layers 4a, 4b, 4c and an overprint varnish 5, by a flexographic printing process with a fineness of 150-200 lpi (lines per square inch) and a volume transfer of 5-10 bcm (billion cubic microns).

(22) For the ink layers 4a, 4b, 4c, a composition according to example 1 was used, wherein the compositions for the ink layers 4a, 4b contained TiO.sub.2 or a blend of TiO.sub.2 and clay, and the composition for the ink layer 4c contained a silver pigment or a blend of a silver pigment and clay. The ink layers 4a, 4b, and 4c were applied in a coating weight of 8-12 g/m.sup.2, for the sum of all ink layers applied onto the transparent substrate.

(23) The thus obtained printed article was applied by standard methods onto a transparent PET substrate 1 serving as a flexible packaging, so as to obtain a container 1.

(24) The container 1 was measured for its light blocking properties using a UV instrument (such as a spectrophotometer or similar optical instrument) coupled with integrating sphere. Samples that are hazy or turbid tend to scatter light away from the straight-line path from the sample to the detector. Such scattered light can be detected using a integrating sphere, which is a hollow ball of highly reflective material. With an integrating sphere, scattered light is collected by the sphere and led to one or more detectors positioned inside the sphere, yielding a measurement of the transmitted and forward scattered light (Taylor, Integrating sphere functionality: the scatter transmission measurement, Perkin Elmer 2013).

(25) A light blocking performance of more than 95% was achieved.

(26) The container 1 was measured for its color characteristics with a Gretag SPM50 spectrophotometer. An L value of 95 was obtained.

(27) For comparison purposes, the above experiment was repeated with the exception that the composition for the ink layer 4c contained a white pigment instead of a silver pigment.

(28) The results are shown in FIG. 3. In example 10a, the composition for the ink layer 4c contained a silver pigment. In example 10b, the composition for the ink layer 4c contained a blend of a silver pigment and clay. In example 10c, the composition for the ink layer 4c contained a white pigment. It can be seen that in the visual range of the electromagnetic spectrum (about 400 to 700 nm), example 10c with only white pigments and fillers in the product allowed more light transmittance (i.e. provided less light blocking) than the examples 10a and 10b containing a silver pigment in the upper layer 4c. A blend of silver pigment and filler in layer 4c showed less light transmittance than a silver pigment in layer 4c alone.

(29) In FIG. 4, comparative results are shown for experiments where in the layers 4a and 4b the following white pigments were used: Example 10d: white pigment with a particle size (crystal size) of 0.22 m and an oil absorption value of 19 Example 10e: white pigment with a particle size (crystal size) of 0.24 m and an oil absorption value of 36 Example 10f: white pigment with a particle size (crystal size) of 0.23 m and an oil absorption value of 17.

(30) It can be seen from the results in FIG. 4 that optimum light blocking (least light transmittance was achieved with example 10 f. All examples achieved a light blocking of more than 95% in the visual range of the electromagnetic spectrum (about 400 to 700 nm).

(31) In FIG. 5, comparative results are shown for experiments where in addition to using the same white pigment in the layers 4a and 4b, in layer 4c the following silver pigments were used: Example 10g: silver (aluminium) leafing cornflake pigment with a D.sub.50 particle size of 11 m (65 wt.-%:35 wt.-% blend with clay filler) Example 10h: silver (aluminium) VMP non-leafing pigment with a D.sub.50 particle size of 10 m (8 wt.-%:92 wt.-% blend with clay filler) Example 10i: silver (aluminium) non-leafing cornflake pigment with a D.sub.50 particle size of 11 m (80 wt.-%:20 wt.-% blend with clay filler) Example 10i: silver (aluminium) non-leafing cornflake pigment with a D.sub.50 particle size of 13 m (65 wt.-%:35 wt.-% blend with clay filler).

(32) It can be seen from the results in FIG. 5 that optimum light blocking (least light transmittance was achieved with example 10 h, i.e. a vacuum metalized pigment (VMP) in a non-leafing grade. All examples achieved a light blocking of more than 94% in the visual range of the electromagnetic spectrum (about 400 to 700 nm).

EXAMPLE 11: DEINKING PROCESS

(33) The printed article according to example 4 was cut into pieces of approximately a size of 0.25 to 0.5 inches (0.63 to 1.27 cm).

(34) Into a stainless steel vessel, tap water was added in such an amount that it corresponded to four times the amount of PET to be deinked. The water was heated, and NAOH granules were added in such an amount that an alkaline aqueous medium was prepared that contained 1 wt.-% NaOH. 0.3 wt.-% of a surfactant (for example Triton X-100) was added.

(35) When the temperature of the deinking solution reached 85 C., the calculated amount of flakes of the container 1 were added, and the alkaline solution was stirred (impeller, speed of 240 m/min). After 15 minutes, the solution was allowed to cool and filtered, and the treated cut pieces were washed with water.

(36) In addition, it was found that complete deinking was achieved at 85 C. in 15 min.

(37) The result of this deinking process is shown in FIGS. 3A and 3B. As shown in FIG. 3A, the printed samples before deinking were highly opaque, whereas as shown in FIG. 3B the samples after deinking were transparent, due to removal of the ink layer.

(38) In the table below, values for a pure PET sample (uncoated PET) as compared to a PET sample obtained by the above deinking process are provided.

(39) TABLE-US-00003 Pure PET Deinked PET L* a* b* L* a* b* 89.31 0.02 2.32 88.98 0.18 2.44