DEINKING OF PRINTED SUBSTRATES

Abstract

The present invention is related to a deinking primer composition for deinking of a substrate, wherein said deinking primer composition comprises a binder component that has a polymeric backbone with pendent hydroxy or carboxy groups that have been esterified or acetalised or ketalised to such an extent that the binder component has an acid value of 0-50 mg KOH/g or a hydroxyl value of 0-600 mg KOH/g, preferably 0-400 mg KOH/g, so that a primer layer prepared from said deinking primer composition is dissolvable in an alkaline aqueous medium.

Claims

1.-15. (canceled)

16. A deinking primer composition for deinking of a substrate, wherein said deinking primer composition comprises a binder component that has a polymeric backbone with pendent hydroxy or carboxy groups that have been esterified or acetalised or ketalised to such an extent that the binder component has an acid value of 0-50 mg KOH/g or a hydroxyl value of 0-600 mg KOH/g, so that a primer layer prepared from said deinking primer composition is dissolvable in an alkaline aqueous medium.

17. The deinking primer composition according to claim 16, wherein said binder component is a polyester or a polyvinyl acetal.

18. The deinking primer composition according to claim 16, wherein said binder component is present in an amount from 5 to 20 wt. %, based on the weight of the entire primer composition.

19. The deinking primer composition according to claim 16, further comprising at least one additional binder component and at least one solvent.

20. A printed product comprising a substrate and a primer layer applied to at least one surface of said substrate, wherein said primer layer is made from a deinking primer composition according to claim 16.

21. The printed product according to claim 20, further comprising a printing ink layer on a side of said primer layer that is not in contact with said substrate.

22. The printed product according to claim 21, wherein said printing ink layer is provided between two additional layers, so that one of said additional layers is arranged between said primer layer and said printing ink layer.

23. A printed article comprising a printed product according to claim 20.

24. The printed article according to claim 23, wherein said printed article is selected from the group consisting of a flexible packing, a label and a shrink sleeve.

25. A method of making the printed article of claim 23, the method comprising applying the deinking primer composition onto a substrate wherein the deinking primer composition comprises a binder component that has a polymeric backbone with pendent hydroxy or carboxy groups that have been esterified or acetalised or ketalised to such an extent that the binder component has an acid value of 0-50 mg KOH/g or a hydroxyl value of 0-600 mg KOH/g, so that a primer layer prepared from said deinking primer composition is dissolvable in an alkaline aqueous medium.

26. A method of deinking a printed article according to claim 23, comprising a step of treating the printed article in an alkaline aqueous medium so as to dissolve the primer layer that is present on the printed article.

27. The method according to claim 26, wherein said alkaline aqueous medium comprises 0.1 to 5 wt. %, based on the entire weight of the aqueous medium, of a base.

28. The method according to claim 26, wherein in said step of treating the printed article said aqueous medium is heated to a temperature in the range from 50 to 90° C.

29. The method according to claim 26, wherein said step of treating the printed article is conducted for a length of time of from 1 to 10 min.

Description

[0078] The present invention will now be described below in more detail by reference to non-limiting figures and examples.

[0079] FIG. 1 shows an illustration of a printed product according to a first embodiment of the present invention.

[0080] FIG. 2 shows an illustration of a printed product according to a second embodiment of the present invention.

[0081] FIGS. 3a-c show an embodiment of the deinking process of the present invention.

[0082] FIG. 4 shows an example of a substrate that has been deinked according to the present invention.

[0083] In FIG. 1 a printed product 1 according to a first embodiment of the present invention is shown. The printed product 1 comprises a substrate 2, e.g. a plastic substrate such as a PE, PP or PET. On one surface of said substrate 2, there is applied a primer layer 3 according to the present invention. On one surface of said primer layer 3 that is remote from the substrate 2, there is provided a printing ink layer 4.

[0084] In FIG. 2, a printed product 1 according to a second embodiment of the present invention is shown. Same reference numbers designate same components as in FIG. 1. The printed product 1 according to the second embodiment differs in the additional presence of an overprint varnish layer 5 on top of the printing ink layer 3, and of an encapsulating layer 6 between the primer layer 3 according to the present invention and the printing ink layer 4. Thus, according to the embodiment of FIG. 2, the printing ink layer 4 is encapsulated between the additional layers 5 and 6.

[0085] In FIGS. 3a to 3c, the deinking process of the present invention is schematically illustrated. In FIGS. 3a to 3c, as an example a printed product 1 according to the second embodiment of FIG. 2 is shown. However, it is understood that the deking process can be equally applied to a printed product 1 according to FIG. 1, for example.

[0086] In FIG. 3a, the printed product 1 before deinking is shown. In FIG. 3b, it is shown that during the deinking step the primer layer 2 becomes dissolved (as illustrated by the dotted boundaries). In FIG. 3c, it is shown that after the deinking step the substrate 1 and the stack of printing ink layer 4 and additional encapsulating layers 5 and 6 are separated from each other, and can be separately recycled.

EXAMPLE 1: PREPARATION OF A FIRST DEINKING PRIMER COMPOSITION

[0087] The following components were added together under stirring, so as to result in a deinking primer composition according to the present invention:

TABLE-US-00001 Component Weight-% Nitro varnish 46.1 PVA varnish 18.1 Polyurethane resin 1.8 Epoxidized soybean oil 0.5 Wax 2.2 Isopropyl acetate 31.3

[0088] The nitro varnish was a 50:50% mixture of nitrocellulose and isopropyl acetate. The PVA (polyvinyl acetate) varnish was a 50:50% mixture of polyvinyl acetate and neopentyl acetate.

EXAMPLE 2: PREPARATION OF A SECOND DEINKING PRIMER COMPOSITION

[0089] The following components were added together under stirring, so as to result in a deinking primer composition according to the present invention:

TABLE-US-00002 Component Weight-% 2,6-Di-t-butyl-p-cresol (BHT) 0.088 Polyvinyl butyral 14.529 Ethanol 83.683 Polyvinyl ether resin 1.705

EXAMPLE 3: PREPARATION OF A THIRD DEINKING PRIMER COMPOSITION

[0090] The following components were added together under stirring, so as to result in a deinking primer composition according to the present invention:

TABLE-US-00003 Component Weight-% Acrylic polymer emulsion (acid value 40 mg 85.6 KOH/g) Glycol ether 5.4 Plasticizer 2.0 Ammonium hydroxide 0.2 Water 1.8 n-propanol 5.0

EXAMPLE 4A-C: PREPARATION OF PRINTED PRODUCT

[0091] The deinking primer composition of example 1 was diluted with ethanol to a suitable printing viscosity (26-32 seconds in 3 mm DIN cup). The diluted primer composition was applied onto an untreated PE or PP substrate, using an Erichsen-printing proofer, to obtain a coating weight of 0.2-1.5 g/m.sup.2.

[0092] On top of the thus applied primer layer, a conventional (one or two-component) flexo or gravure printing ink was applied and allowed to cure in case of the two-component ink, so as to give a product according to example 4a.

[0093] The same procedure was repeated with the deinking primer compositions of examples 2 (ex. 4b) and 3 (ex. 4c), respectively.

EXAMPLE 5: DEINKING

[0094] Following the APR Critical Issues Guidance Document for Sleeve Label Inks and PET Substrate Bottles test method, an alkaline aqueous medium was prepared by combining 98.7 wt.-% water, 1 wt.-% NaOH and 0.3 wt.-% of a surfactant (Triton X-100).

[0095] 200 ml of said alkaline aqueous medium were heated to 65° C. or 80° C., 0.8 g of the printed products of examples 4a-c were cut into pieces, put into the caustic solution and stirred. After 15 minutes, the solution was filtered, and the treated cut pieces were washed with water. The test was repeated, but the pieces were filtered off after shorter treatment times.

[0096] The results are shown in the following table:

TABLE-US-00004 Complete deinking duration (min.) Substrate/ Deinking Example Example Example printing ink temperature 4a 4b 4c PE/1K 65° C. 2 1 2 PP/1K 65° C. 3 2 2 PE/1K 80° C. <1 1 <1 PP/1K 80° C. <1 <1 <1 PE/2K 65° C. 7 PP/2K 65° C. 7 PE/2K 80° C. 7 PP/2K 80° C. 3 1K: 1-component solvent based cyan ink 2K: 2-component solvent based cyan ink (with 5% additional aliphatic hardener)

[0097] In addition, it was found that when UV-cured printing inks were present on a primer layer made according to the present invention, deinking could be achieved at 65° C. in 2-3 min.

[0098] For comparison, the deinking process was repeated with a printed product where a conventional two-component-flexo or gravure printing ink was applied onto a PET substrate with no primer layer included in said printed product. Also, pure substrate (PET flakes) was treated under the same deinking conditions.

[0099] The comparative printed product without primer layer was not deinked within 15 minutes at 80° C. Thus, the printed products according to the present invention could be deinked not only more quickly even at a relatively low temperature of 65° C., but could be deinked under conditions where the comparative printed product was not deinked at all. This is a significant economic and environmental advantage allowing to reuse the material multiple times.

[0100] In FIG. 4, the printed product of example 4a before and after the deinking process is shown. It can be seen that the substrate (PET flakes) were completely deinked, resulting in uncolored clear flakes.

[0101] The colour of the treated pieces was evaluated with a Gretag Spectroeye and compared with the pure PET flakes (which are absolutely clear without any shade). From the obtained L*-, a*- and b*-values, the ΔE value was calculated by the following known formula (wherein the values with the index 1 are the values of the pure PET flakes and the values with the index 1 are the values of the printed product sample):

ΔE−√{square root over ((L.sub.2*−L.sub.1*).sup.2+(a.sub.2*−a.sub.1*).sup.2+(b.sub.2*−b.sub.1*).sup.2)}

[0102] Sufficient deinking is indicated by a ΔE value below 2, more preferably below 1.5. Otherwise, in a subsequent recycling process only shaded PET flakes can be obtained.

[0103] For printed products according to example 4a, the following results were obtained:

TABLE-US-00005 L* a* b* ΔE Pure PET flakes 91.4 −0.1 1.36 Printed product of example 4a Cyan 89.72 −0.29 1.13 1.73 Yellow 90.31 −0.38 1.87 1.24 Magenta 90.36 −0.09 1.2 1.04

[0104] Thus, the deinking process of the present invention applied on the printed product according to example 4a yielded well deinked pieces in a very short time.

[0105] On the other hand, the comparative printed product without primer layer needed much more time for deinking, and even then yielded insufficiently deinked pieces (ΔE higher than 2).

EXAMPLE 6: OVERPRINTABILITY

[0106] The printed products according to examples 4a-c were compared with comparative examples 4d-f. In comparative examples 4d-f, instead of a deinking primer composition according to the present invention a primer layer was made from a primer composition comprising a binder component with a high acid value of more than 100 mg KOH/g.

[0107] In each case, a conventional (two-component) flexo or gravure printing ink was applied on the respective primer layer and allowed to dry and cure. Overprintability was assessed visually. The results are shown below:

TABLE-US-00006 Primer Overprintability Example 4a 5 Example 4b 4 Example 4c 4 Example 4d 1 Example 4e 1 Example 4f 1
Example 4d: primer with Indurez SR 30 (acid value <250 mg KOH/g)
Example 4e: primer with Joncryl 586 (acid value 110 mg KOH/g)
Example 4f: primer with Joncryl 682 (acid value 238 mg KOH/g)

[0108] Assessment of overprintability was made according to the following classification:

1: many printing defects in full tone
2: few printing defects in full tone
3: many printing defects in half tone
4: few printing defects in half tone
5: no printing defects

EXAMPLE 7: WATER (WIPING) RESISTANCE

[0109] For the assessment of water (wiping) resistance, examples 4a to 4f were subjected to soaking in water for 2 h and subsequent wiping. Water resistance was assessed visually (by adding some colorant to the primer layer). The results are shown below:

TABLE-US-00007 Primer Wiping resistance Example 4a 5 Example 4b 5 Example 4c 3 Example 4d 2 Example 4e 1 Example 4f 1
Example 4d: primer with Indurez SR 30 (acid value <250 mg KOH/g)
Example 4e: primer with Joncryl 586 (acid value 110 mg KOH/g)
Example 4f: primer with Joncryl 682 (acid value 238 mg KOH/g)

[0110] Assessment of water (wiping) resistance was made according to the following classification:

1: complete primer detachment
2: strong primer detachment
3: clearly visible primer detachment
4: slight primer detachment
5: No primer detachment