Method for determining the migration potential of an at least partially cured energy curing ink and/or varnish printed on a substrate, and especially of a printed food packing

Abstract

The present invention relates to a method for determining the migration potential of an at least partially cured energy curing ink and/or varnish printed on a substrate comprising: —providing a substrate, which is printed with the ink and/or varnish, which comprises at least one extractable compound, which absorbs or emits radiation at at least one wavelength between 190 and 3,000 nm, —cutting at least one sample from the printed substrate, placing and incubating the sample in a solvent, in which the extractable compound is soluble, and removing the sample from the solvent to obtain a solvent extract, —quantitatively measuring a spectroscopic characteristic of the solvent extract at at least one wavelength between 190 and 3,000 nm, at which the extractable compound absorbs or emits radiation, so as to obtain a measured numeric value of the spectroscopic characteristic, and —comparing the measured numeric value of the spectroscopic characteristic with a calibration curve.

Claims

1. A method for determining the migration potential of an at least partially cured energy curing ink and/or varnish printed on a substrate and especially of a printed food packing, which comprises the following steps: a) providing a substrate, which is printed with the at least partially cured energy curing ink and/or at least partially cured energy curing varnish, wherein the at least partially cured energy curing ink and/or at least partially cured energy curing varnish comprises at least one extractable compound, which has a molecular weight of at most 5,000 g/mol and which absorbs or emits radiation at at least one wavelength between 190 and 3,000 nm, b) cutting at least one sample from the printed substrate provided in step a), placing the at least one sample in a solvent, in which at least one of the at least one extractable compound is soluble, incubating the solvent with the at least one sample placed therein for at least 10 seconds and removing the at least one sample from the solvent to obtain a solvent extract, c) optionally, recording a spectrum for at least a part of the wavelength range between 190 and 3,000 nm of the solvent extract, d) quantitatively measuring a spectroscopic characteristic of the solvent extract at at least one wavelength between 190 and 3,000 nm, at which at least one of the at least one extractable compound absorbs or emits radiation, so as to obtain a measured numeric value of the spectroscopic characteristic and e) comparing the measured numeric value of the spectroscopic characteristic with a calibration curve, in which for at least one printed substrate, in which the same energy curing ink and/or energy curing varnish is printed on the same substrate as in step a), the correlation between i) the results of a migration test regarding the overall migration and/or of the migration of specific compound(s) of the at least one printed substrate and ii) a numeric value of the spectroscopic characteristic measured at the same wavelength as in step d) of a solvent extract obtained from a sample of the at least one printed substrate by performing step b), is shown in dependency of the curing degree of the energy curing ink and/or energy curing varnish so as to obtain the migration potential, wherein the calibration curve used in step e) has been prepared iii) by determining the overall migration and/or the specific migration of one or more migrating compound(s) for different printed substrates, in which for each of the different printed substrates the same energy curing ink and/or energy curing varnish has been printed on the same substrate as in step a), wherein each of the different printed substrates has been cured to a different curing degree, iv) by obtaining for each of the different printed substrates a solvent extract by performing step b) and by determining for each of these solvent extracts the extinction or transmittance at the same wavelength as in step d) and v) by correlating the respective data obtained in steps iii) and iv) into a graph.

2. The method in accordance with claim 1, wherein the substrate is selected from the group consisting of papers, cardboards, plastic foils, glass, nonwovens, fabrics, tissues, metal foils, metal sheets and arbitrary combinations of two or more of the aforementioned substrates.

3. The method in accordance with claim 1, wherein the solvent is an alcohol or a water-alcohol mixture, wherein the alcohol is a C.sub.1-10-alcohol.

4. The method in accordance with claim 1, wherein the sample is incubated in step b) for 30 seconds to 5 hours.

5. The method in accordance with claim 1, wherein step c) is performed and the spectrum in step c) is recorded for at least a part of the wavelength range between 190 and 1,500 nm.

6. The method in accordance with claim 1, wherein the spectroscopic characteristic of the solvent extract is measured in step d) at a wavelength, at which the numeric value of the spectroscopic characteristic is at least 50% of the peak maximum of the spectroscopic characteristic in the spectrum of the solvent extract, from which the respective spectrum of the solvent has been subtracted.

7. The method in accordance with claim 1, wherein the spectroscopic characteristic, which is quantitatively measured in step d), is selected from the group consisting of extinction, transmittance, absorbance, fluorescence and arbitrary combinations of two or more thereof.

8. The method in accordance with claim 7, wherein the spectroscopic characteristic, which is quantitatively measured in step d), is the extinction or transmittance of the solvent extract.

9. The method in accordance with claim 8, wherein the extinction or transmittance of the solvent extract is measured in step d) at a wavelength, at which the numeric value of the extinction or of the transmittance is at least 50% of the peak maximum of the extinction or transmittance spectrum, from which the respective spectrum of the solvent has been subtracted.

10. The method in accordance with claim 9, wherein the extinction or transmittance of the solvent extract is measured in step d) at the wavelength of the peak maximum of the extinction or transmittance spectrum, from which the respective spectrum of the solvent has been subtracted.

11. The method in accordance with claim 1, wherein the curing of each of the different printed substrates to a different curing degree is achieved by printing the energy curing ink and/or energy curing varnish for each of the different printed substrates with a different printed weight and/or with a different printing speed, with a different wet film thickness and/or with a different curing energy dose onto the substrate and then by drying the different printed substrates under the same conditions.

12. The method in accordance with claim 1, wherein the curing of each of the different printed substrates to a different curing degree is achieved by printing the energy curing ink and/or energy curing varnish for each of the different printed substrates with the same printed weight, with the same printing speed and with the same wet film thickness onto the substrate and then by drying the different printed substrates under different conditions, namely for different drying times, with different curing speeds, with different UV lamp powers and/or at different drying temperatures.

13. The method in accordance with claim 1, wherein the calibration curve used in step e) has been prepared i) by determining the overall migration and/or the specific migration of one or more migrating compound(s) for different printed substrates, in which for each of the different printed substrates the same energy curing ink and/or energy curing varnish has been printed on the same substrate as in step a) for each of the different printed substrates with a different printed weight and/or with a different printing speed and/or with a different wet film thickness onto the substrate, wherein each of the different printed substrates has been cured under the same conditions, ii) by obtaining for each of the different printed substrates a solvent extract by performing step b) and by determining for each of these solvent extracts the extinction or transmittance at the same wavelength as in step d) and iii) by correlating the respective data obtained in steps i) and ii) into a graph.

14. The method in accordance with claim 1, wherein the overall and specific migration is measured in accordance with norms EN 1186:13:2002 and EN14338:2003.

Description

EXAMPLE

(1) UV offset printing inks with following components were prepared:

(2) TABLE-US-00001 Pigment Black 7 Pigment Black 7 19.0% Pigment Blue 15:3 Pigment Blue 15:3 2.0% Ebecryl LEO 10801 reactive Epoxyacrylate 16.0% Ebecryl LEO 10601 reactive Polyester Acrylate polymer 30.0% Ebecryl Leo 10501 diluting reactive acrylate 10.0% Pentaerythritol functional reactive polyol 6.0% triacrylate acrylate oligomer Photoinitiator Photoinitiator 8.0% mixture* mixture* EHA** aminobenzoate co-initiator 3.0% Ceridust 3620 wax 1.3% BHT*** stabilizer 0.2% Genorad 19 stabilizer 0.1% ASP 600 filler 4.4% *Photoinitiator-Mixture: Irgacure 369 (3%), Speedcure 7005 (2.5%), Omnipol TX (2.0%), Irgacure 819 (0.5%) **2-Ethylhexyl-4-dimethylaminobenzoate ***Butylhydroxytoluene (2,6-Di-tert-butyl-4-methylphenol)
Preparation of Laboratory Print Proofs:

(3) Inks were printed on coated paper (220 g/m.sup.2, format 4.6×23 cm) using a Prüfbau test printer with a printing speed of 0.5 m/s and cured with an integrated UV lamp (curing speed: 0.1 m/s). The ink quantity on the substrate (printing weight in g/m.sup.2) was determined by weighing the inked print form before and after printing. Samples with printing weight 1 g/m.sup.2; 1.5 g/m.sup.2 and 2 g/m.sup.2 were prepared.

(4) Extraction of Print Proofs and UV/VIS-Measurements.

(5) Directly after printing a sample of 1 cm×1 cm was cut out of the print proof and set into a solution of 10 mL EtOH at a temperature of 21° C. To obtain the solvent extract, the cut out sample was removed after 5 minutes.

(6) A solvent extract from unprinted substrate was used as a reference sample applying identical conditions for the extraction as for the printed samples.

(7) To find the optimal wavelength for the UV/VIS measurements an UV/VIS-spectra of the solvent extract of the printed sample and the reference sample were determined with a dual beam UV/VIS-spectrometer (Perkin Elmer Lambda 2) in a range of 250 to 500 nm at room temperature. The resulting spectrum is shown in FIG. 1.

(8) The difference of the sample E(λ).sub.sample and reference spectrum E(λ).sub.reference, results in the corrected spectrum of the printed sample E(λ).sub.corrected.
E(λ).sub.corrected=E(λ).sub.sample−E(λ).sub.reference  (1)

(9) At a wavelength of 310 nm the maximal absorption was observed in the corrected spectrum. This wavelength was defined as the measurement wavelength for the determination of the absorption of the solvent extracts. Results are given as the corrected absorption at 310 nm: E(310 nm).

(10) The absorption at 310 nm E(310 nm) was measured for different printing weights. With an increasing printing weight the degree of curing is decreased which leads to higher absorption values E (310 nm), as shown in the subsequent table 1.

(11) TABLE-US-00002 TABLE 1 Absorption at 310 nm E(310 nm) of the solvent extracts from samples with different printing weights. E(310 nm) Printing weight [g/m2] E(310 nm) 1 0.014 1.5 0.033 2 0.055

(12) These values are also shown in FIG. 2.

(13) Migration Testing

(14) The level of migrating substances was determined by a set-off migration using modified polyphenylene oxide (brand name Tenax®) as a food simulant test according to DIN EN 14338:2003. Therefore, for each ink 5 sheets of laboratory print proofs were stacked and stored under pressure (2 kg/dm.sup.2) for 6 days at room temperature. The three inner sheets of the stack were used for the migration test. The samples were cut (1 dm.sup.2) and put into a petri dish (Ø14 cm) with the printed surface downwards. A glass ring was put onto the sample (outer diameter of the glass ring Ø13 cm, wall thickness 0.5 cm, height 1 cm). 3 g of Tenax® powder (60/80 Mesh) were distributed evenly on the sample (non-printed side) inside the glass ring. The petri dish was closed with a lid, wrapped in aluminum foil and stored in an oven for 10 days at 60° C.

(15) The Tenax® was extracted with acetone for 40 min in a Soxhlet extractor. The acetone is distilled off, the dried residue is solved in 1 mL ethanol containing C13/C24-alkane standard (50 μg/mL) and analysed by GC-MS and LC-MS. For known and migration-relevant components (acrylates, photoinitiators, photoinitiator cleavage products) the analysis is carried out with reference standard solutions of these components. The results are presented as the amount of migratable substances present in 1 kg of food [mg/kg food] according to the EU cube model (assumption: 1 kg food is packed into 6 dm.sup.2).

(16) The migration results for the aminobenzoate co-initiator and a polyol acrylate are shown in Table 2 and in FIGS. 3 and 4. An increasing printing weight leads to a lower degree of curing, resulting in larger amounts of migrants.

(17) TABLE-US-00003 TABLE 2 Migration of aminobenzoate co-initiator at migration test conditions: 60° C., 10 days, Tenax in mg/kg food (assumption: 1 kg food is packed into 6 dm.sup.2) Printing weight Aminobenzoate co-inititiator Polyol Acrylate [g/m2] [mg/kg food] [mg/kg food] 1 0.46 0.11 1.5 1.01 0.47 2 2.20 1.05
Calibration Curve—Correlation of Migration and Absorption Results

(18) For the determination of the calibration curve the results of the migration test were plotted against the absorption E(310 nm) from the solvent extracts for aminobenzoate co-iniator and for the polyol acrylate. The result is shown in FIG. 5.

(19) As can be seen from FIG. 5, for both substances there is a linear correlation of migration and absorption E(310 nm) with a coefficient of determination (R.sup.2) of 97% (Amino benzoate co-initiator) and 99% (Polyol Acrylate).

(20) Calculation of Migration

(21) The estimated migration can be calculated from the absorption E(310 nm) using the determined linear regression equation for aminobenzoate co-initiator (equation 2) and for polyol Acrylate (equation 3):
Migration[mg/kg food]=42,55*E(310 nm)−0.2134  equation (2)
Migration[mg/kg food]=22,908*E(310 nm)−0.2302  equation (3)

(22) In the Figures:

(23) FIG. 1 shows the UV/VIS-spectra of the solvent extracts of (i) the printed sample, (ii) the reference sample (unprinted substrate) and (iii) the difference spectrum of (i) and (ii) of the example.

(24) FIG. 2 shows the corrected absorption at 310 nm from solvent extracts of printed samples at different printing weights of the example.

(25) FIG. 3 shows the migration of aminobenzoate co-initiator at migration test conditions: 60° C., 10 days, Tenax in mg/kg food (assumption: 1 kg food is packed into 6 dm.sup.2), for different printing weight.

(26) FIG. 4 shows the migration of poylol acrylate at migration test conditions: 60° C., 10 days, Tenax in mg/kg food (assumption: 1 kg food is packed into 6 dm.sup.2), for different printing weight.

(27) FIG. 5 shows the calibration curve of the migration of aminobenzoate co-initiator and polyol acrylate against the corrected absorption at 310 nm of the solvent extracts obtained in the example