Metal offset printing ink with specular gloss, and printing method

Abstract

The invention relates to an offset printing ink containing platelet-shaped aluminum pigments with an average thickness h.sub.50 ranging from 15 to 80 nm, binders, and solvents. The invention is characterized in that the platelet-shaped aluminum pigments are produced using a PVD method and are at least partly coated with a leafing additive, and the offset printing ink has a viscosity of 4 to 15 Pa s, measured on a sample which is temperature-controlled at 25 C. by means of a rotation viscometer with a cone/plate geometry under a shear stress of 185.9 Pa. The invention further relates to a method for producing a high-gloss printed metal image on a substrate, having the following steps: a) optionally applying a primer onto the substrate; b) applying an offset printing ink according to the invention onto the primer layer or onto the substrate, thereby forming a high-gloss printed layer B, and c) optionally applying additional color layers C onto the layer B.

Claims

1. An offset printing ink comprising platelet-shaped aluminum pigments having an average thickness h.sub.50 from a range from 15 to 80 nm, and also binders and solvents, wherein the platelet-shaped aluminum pigments are produced by PVD methods and are coated at least partly with a leafing additive, and in that the offset printing ink has a viscosity of 4 to 15 Pa s, measured on a sample conditioned at 25 C., using a rotational viscometer having a cone/plate geometry at a shear stress of 185.9 Pa; wherein the solvent is selected from the group consisting of mineral oils, vegetable oils, and fatty acid esters, or mixtures thereof, the vegetable oils not being used without at least one of the other two solvents and wherein the solvent content is in a range of 40-72 wt%, based on the overall offset printing ink.

2. The offset printing ink as claimed claim 1, wherein the viscosity is in a range from 4.1 to 12 Pa s.

3. The offset printing ink as claimed in claim 1, wherein the viscosity is in a range from 4.0 to 9.2 Pa s.

4. The offset printing ink as claimed in claim 1, wherein the leafing additive is a phosphorus-containing organic compound which is a) phosphoric acids or phosphoric esters having the general formula (I)
(O)P(OR.sup.1)(OR.sup.2)(OR.sup.3)(I) and/or b) phosphonic acids or phosphonic esters of the general formula (II)
(O)PR.sup.4(OR.sup.1)(OR.sup.2)(II) and/or c) phosphinic acid or phosphinic esters of the general formula (III)
(O)PR.sup.4R.sup.5(OR.sup.1)(III) wherein R.sup.1, R.sup.2 and R.sup.3 independently of one another is H or a branched or unbranched alkyl, aryl, alkylaryl or arylalkyl group having 1 to 30 carbon atoms and optionally containing heteroatoms such as O, S, and/or N, with the proviso that in the case of a compound of the formula (I), at least one of these radicals is a branched or unbranched alkyl, aryl, alkylaryl or arylalkyl group having 8 to 30 carbon atoms, R.sup.4 and R.sup.5 independently of one another is a branched or unbranched alkyl, aryl, alkylaryl or arylalkyl group having 8 to 30 carbon atoms and optionally containing heteroatoms such as O, S, and/or N, or is a compound of the general formula (IV)
R.sup.6X(IV) wherein R.sup.6 is an aliphatic alkyl radical having 12 to 30 carbon atoms and wherein X is a carboxyl group or a carboxylate group, an amino group or a trialkoxysilane.

5. The offset printed ink as claimed in claim 4, wherein R.sup.6 is unbranched.

6. The offset printing ink as claimed in claim 4, wherein for the leafing additive R.sup.4, R.sup.5 and R.sup.6 independently of one another is a branched or unbranched alkyl, aryl, alkylaryl or arylalkyl group having 14 to 20 carbon atoms.

7. The offset printing ink as claimed in claim 4, wherein the leafing additive i) is a phosphonic acid, where R.sup.1R.sup.2H and R.sup.4 is a branched or unbranched alkyl, aryl, alkylaryl, or arylalkyl group having 8 to 18 carbon atoms or ii) is a phosphoric ester, wherein at least one of the radicals R.sup.1, R.sup.2 and R.sup.3 is a branched or unbranched alkyl group having 8 to 18 carbon atoms; or iii) is selected from the group consisting of stearic acid, ammonium stearate, alkali metal stearate, alkaline earth metal stearate or mixtures thereof.

8. The offset printing ink as claimed in claim 1, wherein the level of pigmentation of the aluminum pigment is 2 to 8 wt % based on the overall weight of the offset printing ink.

9. The offset printing ink as claimed in claim 8, wherein the level of pigmentation of the aluminum pigment is 2.5 to 6 wt % based on the overall weight of the offset printing ink.

10. The offset printing ink as claimed in claim 1, wherein the binder is selected from the group consisting of alkyd resins, modified rosins, maleate resins, aromatic hydrocarbon resins, modified hydrocarbon resins, allyl esters of polybasic organic acids, polyallyl ethers and mixtures thereof.

11. The offset printing ink as claimed in claim 1, wherein the offset printing ink comprises further additives selected from the group consisting of dryers, waxes, film-forming assistants, dispersing assistants, antioxidants and mixtures thereof.

12. The offset printing ink as claimed in claim 1, wherein the average sizes d.sub.50 of the PVD aluminum effect pigments are in a range from 4 to 15 m.

13. A method for producing an offset printing ink as claimed in claim 1, wherein the method comprises the following steps: a) providing an offset varnish by mixing and heating binders and solvents, b) providing a paste with PVD aluminum effect pigments which have an average thickness h.sub.50 of 15 to 80 nm and are coated with a leafing additive, c) adding at least one further solvent and optionally further additives to the varnish a) and carrying out mixing with the PVD aluminum pigment paste b) d) setting the viscosity in a range from 4 to 15 Pa s and wherein the viscosity is measured on the sample conditioned at 25 C. using a rotational viscometer having a cone/plate geometry at a shear stress of 185.9 Pa, d) optionally ageing the offset printing ink until it has attained a viscosity in a range from 4.0 to 12 Pa s; wherein the at least one solvent is selected from the group consisting of mineral oils, vegetable oils, and fatty acid esters, or mixtures thereof, the vegetable oils not being used without at least one of the other two solvents.

14. A method according to claim 13, wherein the viscosity is set by addition of solvent.

15. A printed substrate with metallic specular gloss, comprising a) optionally a primer layer A, b) a layer B applied by offset printing using an offset printing ink as claimed in claim 1, applied where appropriate on the primer layer A, c) optionally the further color layers C.

16. The printed substrate with metallic specular gloss as claimed in claim 15, wherein a primer layer is applied on the substrate.

17. The printed substrate with metallic specular gloss as claimed in claim 15, wherein the primer is a translucent layer.

18. The printed substrate with metallic specular gloss as claimed in claim 15, wherein a further color layer C is applied which is transparent or comprises chromatic pigments.

19. A method for producing a printed substrate with metallic specular gloss, comprising the following steps: a) optionally applying a primer to a substrate, b) applying an offset printing ink to the primer layer or to the substrate, to form a high-gloss print layer B, c) optionally applying further color layers C to the layer B, the offset printing ink comprising: an offset printing ink comprising platelet-shaped aluminum pigments having an average thickness h.sub.50 from a range from 15 to 80 nm, and also binders and solvents, wherein the platelet-shaped aluminum pigments are produced by PVD methods and are coated at least partly with a leafing additive, and in that the offset printing ink has a viscosity of 4 to 15 Pa s, measured on a sample conditioned at 25 C., using a rotational viscometer having a cone/plate geometry at a shear stress of 185.9 Pa; wherein the solvent is selected from the group consisting of mineral oils, vegetable oils, and fatty acid esters, or mixtures thereof, the vegetable oils not being used without at least one of the other two solvents and wherein the solvent content is in a range of 40-72 wt%, based on the overall offset printing ink.

20. The method for producing a printed substrate with metallic specular gloss as claimed in claim 19, comprising applying a primer to the substrate.

21. The method as claimed in claim 19, wherein the layer B is applied only once in one printing procedure.

22. The method for producing a high-gloss metallic printed image as claimed in claim 19, wherein the color layer C is applied in a first printing by printing in line in one pass using an offset printing inking unit or a subsequent flexographic inking unit, or in that the color layer C is alternatively applied by any other printing method in offline mode in a second pass after drying of the first printing.

Description

EXPERIMENTAL SECTION

I Production of Offset Printing Inks

Example 1

(1) 1a. Production of Varnish 1:

(2) In accordance with the formula shown in table 1, the solvents of item 4 and item 5 were introduced and heated to 135 C. At this temperature, the resins of items 6, 7 and 8 were added to the mixture and heating was continued to 170 C. At this temperature, after a dissolution time of 15 minutes, items 9, 10, 11 and 12 were added. Following complete homogenization, the varnish was cooled to room temperature.

(3) 1b. Production of the Pigment Paste:

(4) Item 2 was dissolved in item 3 and additionally 3% of ethyl acetate. Then item 1 (commercially available pigment dispersion Metalure A-41510 (15 wt % dispersion of a PVD aluminum pigment in ethanol, d.sub.50=10 m, h.sub.50=25 nm; from Eckart America; the amount of Metalure reported in table 1 refers to the pure aluminum content of the dispersion) was added and homogenization took place with stirring. As a final step, the ethyl acetate and ethanol solvents were evaporated off under reduced pressure.

(5) 1c. Offset Printing Ink:

(6) Items 13 and 14 were added to and dispersed in the varnish 1 produced in the first step.

(7) Following addition of the pigment paste produced in step 2, homogenization was repeated with stirring.

(8) 1d. Adjustment to Print Viscosity:

(9) The print viscosity was adjusted, lastly, using the vegetable oil Estisol 312. The viscosity was measured using a rotational viscometer (model: Bohlin CVO 100, from Malvern Instruments) with a cone/plate geometry (cone inclination angle: 4, cone diameter: 40 mm).

(10) In this case the sample for measurement was conditioned at 25 C. and the measurement program was set so that the shear stress was varied in a range from 11.6 to 744.1 Pa. The viscosity value used here was the value at a shear stress of 185.9 Pa.

(11) TABLE-US-00001 TABLE 1 Formula constituents, example 1: Constituent Amount of introduced Ingredient Formula formula Item [Wt %] trade name Manufacturer constituent Ingredient description Metallic 1 5.4405 Metalure Eckart America PVD Aluminum pigment A-41510 aluminum paste pigment dispersion 2 1.0881 stearic acid HEMA GmbH & Leafing Stearic acid Co. KG additive 3 5.1714 PKWF 28/31 Haltermann Solvent Mineral oil, aromatic-free, AF new boiling range 280-310 C. Varnish 1 4 9.23 PKWF 28/31 Haltermann Solvent Mineral oil, boiling range 280-310 C. 5 5.68 Tung oil HEMA GmbH & Solvent Tung oil Co. KG 6 9.94 Setaprint Lawter Resin Phenol-modified rosin 1856 E 7 7.1 Worle Worle Resin Aromatic hydrocarbon Petroleum resin; petroleum resin; resin SK- modified HC resin 150 8 15.62 Novarez TA Rtgers Resin Phenol-modified HC 120 resin 9 8.52 SYNTHALA Synthopol Resin Alkyd resin T D 272 10 11.005 PKWF 28/31 Haltermann Solvent Mineral oil, boiling range 280-310 C. 11 2.13 OPTIFILM Eastman Film-forming ENHANCER assistant 300 12 0.71 PKWF 28/31 Haltermann Solvent Mineral oil, boiling range 280-310 C. Offset 13 0.65 Borchers OMG Group Dryer Manganese carboxylate printing Dry 0411HS in solution in fatty acid ink ester 14 17.715 Estisol 312 Easti Chem A/S Solvent Fatty acid ester Total: 100

Example 2

(12) 2a. Production of Varnish 2:

(13) In accordance with the formula shown in table 2, items 4 to 8 were mixed and heated to 170 C. After a boiling time of 15 minutes, the mixture was cooled to 150 C. and then items 9 to 10 were added and the mixture was homogenized. The varnish could then be cooled to room temperature.

(14) 2b. Production of Pigment Paste:

(15) The procedure of example 1 was repeated, but with the quantities of the ingredient shown in table 2.

(16) 2c. Offset Printing Ink:

(17) Items 11, 12, 13 and 14 were added to and dispersed in the varnish 1 produced in the first step. Following addition of the pigment paste produced in step 2, homogenization was repeated, with stirring.

(18) 2d. Adjustment to Print Viscosity:

(19) The print viscosity, lastly, was adjusted using the mineral oil. The measurement was made as described in example 1.

(20) TABLE-US-00002 TABLE 2 Formula constituents, example 2: Constituent Amount of introduced Ingredient Formula formula Item [Wt %] trade name Manufacturer constituent Ingredient description Metallic 1 8.132 PKWF 28/31 Haltermann Solvent Mineral oil Aromatic- pigment AF free Boiling range 280-310 C. paste 2 5.6544 Metalure Eckart Pigment Aluminum pigment A41506 America dispersion 3 1.4136 RHODAFAC Rhodia Leafing Laurylphosphonic acid Lauryl- additive phosphonic acid Varnish 2 4 7 PKWF 28/31 Haltermann Solvent Mineral oil, boiling range 280-310 C. 5 24.99 Petroleum resin Worle Resin Aromatic modified SK-150 hydrocarbon resin 6 4.2 ALPHA-REZ Hexion Resin Phenol-modified 4700 E KS04 rosin/HC hybrid resin 7 7 Novarez TA Rtgers Resin Phenol-modified HC 120 resin 8 7 Tung oil HEMA Solvent Tung oil GmbH & Co. KG 9 7 SYNTHALAT D Synthopol Resin Alkyd resin 272 10 12.25 PKWF 28/31 Haltermann Solvent Mineral oil, boiling range 280-310 C. Offset 11 5 Worlekyd S23 Worle Resin Alkyd resin printing ink 12 0.5 Borchers Dry OMG Group Dryer Manganese 0411HS carboxylated solution in fatty acid ester 13 2.5 Minerpol 221 BYK Wax 14 7.36 PKWF 28/31 Haltermann Solvent Mineral oil Aromatic- AF new free Boiling range 280-310 C. Total: 100

(21) Further inventive examples and also comparative examples were produced in accordance with the procedure of example 1 or 2, with variation of certain ingredients. Details of this can be found in tables 4 and 5. Also listed therein are the viscosities measured immediately after the preparation of the offset printing ink and also after a storage time of four weeks at room temperature (RT). The offset printing inks of the invention typically exhibit a drop in viscosity after a certain storage time.

(22) As a further varnish 3, a low-migration and low-odor varnish was used, its composition being set out in table 4.

(23) TABLE-US-00003 TABLE 3 Formula, varnish 3 Constituent Amount of introduced Ingredient Formula Ingredient formula Item [Wt %] trade name Manufacturer constituent description Varnish 3 1 53.02 Texaprint Cognis Solvent Fatty acid ester, SPOC pentaerythritol tetraoctanoate 2 25.12 Setaprint Lawter Resin Phenol-modified rosin 3450E 3 10.22 Jonrez IM 816 WestRock Resin Malein-modified rosin 4 6.98 Kristalex F100 Eastman Resin Hydrocarbon resin 5 4.66 Texaprint Cognis Solvent Fatty acid ester, SPOC pentaerythritol tetraoctanoate Total: 100

(24) Inventive examples are set out in table 4. In the case of example 8, the PVD aluminum effect pigment, instead of step 1.b from example 1, was dispersed in ethanol and, following addition of tetraethoxysilane, water, and ammonia as catalyst, was coated with SiO.sub.2 in a conventional way by means of a sol-gel process. This was followed by addition of Dynasilan 9116 (C16 alkyl silane) as leafing additive (3 wt % based on aluminum pigment). The SiO.sub.2 content of the coated pigment was 10 wt %.

(25) Table 6 contains comparative examples. In the case of comparative examples 1 and 2, a very thin aluminum pigment produced by wet milling was employed instead of a PVD aluminum effect pigment. In the case of comparative example 3, a PVD aluminum pigment dispersion (W-520121L), was used which still contains significant residues of a release coat. This pigment was not treated with a leafing additive. The residues of the release coat produce a nonleafing effect. Comparative examples 4, 5 and 6 and also inventive examples 12 to 14 formed an experimental series, with the same fundamental composition, where the viscosity was varied only via the concentration of solvent.

(26) Additionally, the printing inks of inventive example 6 were printed on a wide variety of different substrates. The results are set out in table 7.

II Production of the Proof Prints and Optical Characterization Thereof

II.1 Preparation of Proof Prints Using Prfbau MZ II Multipurpose Sample Printing Machine

(27) (Prfbau, model: MZ II)

(28) A Proof printing of the metallic printing ink without primer

(29) Preparation:

(30) The substrate was adhered to the printing sample carrier and the pressure applied by the printing units was adjusted to 600 N. The drive rolls were set to a temperature of 23 C.

(31) Procedure:

(32) 300 mg of the ink were applied to the first field of the inking roll. The ink was distributed over the two rotating drive rolls by placement onto these rolls. After 30 seconds, the rubber blanket printing form was placed onto the inking roll and was then inked over the course of 60 seconds.

(33) For the printing operation, the rubber blanket printing form was subsequently fitted onto its dedicated mount on the printing mechanism 1, and the print sample carrier with the substrate was placed into its dedicated track. The printing experiment took place with a printing speed of 0.5 m/s.

(34) For all the experiments of inventive examples 1 to 13 and of comparative examples 1 to 9 (see tables 4 and 5), the substrates used were label paper (Profigloss illustration printing 100 g/m.sup.2).

B Proof Printing of the Primer and of the Metallic Ink

(35) Preparation took place as under A.

(36) Procedure:

(37) 200 mg of the primer were applied to the first field of the inking roll, and 300 mg of the ink were applied to the second field of the inking roll.

(38) The inking roll was then placed onto the two drive rolls, and these rolls were set in rotation by actuation of the starting lever. The primer and the ink were then distributed over the three rolls. After a rub-in time of 30 seconds, the rubber blanket printing forms were placed onto the inking roll and inked over the course of 60 seconds.

(39) For the printing operation, the two rubber blanket printing forms were then fitted onto their dedicated mount on the two printing mechanismsthe printing form with primer to the printing mechanism 1, and the printing form with ink to the printing mechanism 2and the print sample carrier with the substrate was placed into its dedicated track, and the specimen print was produced (printing speed: 0.5 m/s).

(40) Two different primers were used for the various experiments:

(41) Primer 1: Huber group Lack TD Spez. 877894 (water-based primer)

(42) Primer 2: Huber group lnkredible CRS MAX transparent white 40N0550

II.2 Gloss Measurements

(43) The gloss measurements of the proof prints were carried out using a micro-TRI-gloss (from Byk-Gardner). The measurements took place at a gloss angle of 60. Measurement was carried out at five different locations on the proof print. The values recorded in table 4 are the average values formed from these measurements.

II. 3 Determination of the Color Density of the Proof Print Using the SpectroDens Instrument (from TECHKON)

(44) The spectro-densitometer possesses four CMYK color filters. The color density values were measured for all four color filters in one measurement. Metallic inks in the silver shade were measured using the value for the color filter C. The measurement was repeated on at least three locations on the sample, and the average value was used in each case. Calibration to paper white took place on the unprinted substrate used.

II.4 Determination of the Luster Value Using the X-Rite SP64 Colorimeter

(45) The proportional difference between scattered light and total reflection is a measure of the visual assessment of brightness, distinctness of image, and milkiness of the mirror effect.

(46) The colorimeter has a sphere geometry and a gloss trap, allowing measurement of the variables SPEX and SPIN.

(47) The SPIN value here indicates the total amount of reflecting light in all spatial directions in accordance with the sphere geometry, whereas for the SPEX measurement the gloss trap is engaged and only the remaining scattered light is measured. The difference between the two values produces the value known as luster. This is a measure of the proportion of irradiated light which is reflected in the total reflection and therefore represents the effect of a mirror. The higher, therefore, the luster (and therefore: the lower the SPEX value and the higher the SPIN value), the more clear the mirror effect is and hence the more clear the distinctness of image is.

(48) For calibration, a black-and-white adjustment was carried out. The SPIN and the SPEX values were measured at five locations each on the proof print, and the average value was formed therefrom. The proof prints B with primer were subjected to measurement.

II.5 Visual Assessment

(49) It was found that the various numerical parameters from the measurements were not always able to reproduce the overall impression to the human eye. Additionally, therefore, for the variables measured, the overall visual impression conveyed by the proof prints in terms of the mirror effect was assessed on the basis of a rating system (rating 1: very good, rating 2: good, rating 3: satisfactory, rating 4: no longer sufficient, rating 5: deficient).

(50) TABLE-US-00004 TABLE 4 Formula constituents, viscosities and optical data for inventive examples Examples Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Metallic Pigment A- A- A- A- A- A- pigment base 41510EN 41510EN 41510EN 41510EN 41510EN 41510EN paste Pigment 5.4% 5.1% 5.4% 5.4% 3.0% 5.4 content Leafing 20% 25% 25% 25% 25% 20% additive Stearic MDST MDST MDST MDST MDST (Amount acid based on metallic pigment) Offset Solvent Mineral Mineral Mineral Mineral Mineral Mineral printing ink oil/ oil/Tung oil/ oil/IPL/ oil/ oil/ constituents Estisol oil Estisol Tung oil Tung oil Estisol 312/ 312/ 312/ Tung oil Tung oil Tung oil Solvent 47% 56% 50% 51% 48% 48% content Varnish Varnish 1 Varnish 2 Varnish 1 Varnish 1 Varnish 2 Varnish 1 used Total 42% 36% 39% 42% 41% 40% resin content Viscosities Viscosity: 10.4 Pa s 5.2 Pa s 9.2 Pa s 9.1 Pa s 5.3 Pa s 13.7 Pas Viscosity 7.8 Pa s 4.4 Pa s 6.3 Pa s 5.9 Pa s 4.3 Pa s 8.5 Pa s after 4 weeks RT Examples Example Example Example 7 Example 8 Example 9 10 11 Metallic Pigment A- A- A- A- A- pigment base 41510EN 41510EN 41510EN 41510EN 41510EN paste Pigment 5.4% 5.4% 5.4% 5.4% 5.4% content Leafing 20% 10% 20% 25% 25% additive Hostaphat SiO.sub.2; Hostaphat Stearic MDST (Amount CC100 9116; CC100 acid based on metallic pigment) Offset Solvent PTO PTO Mineral Mineral Mineral printing ink oil/PTO oil/ oil/Tung constituents Estisol oil 312/ Tung oil Solvent 70% 67% 68% 47% 58% content Varnish Varnish 3 Varnish 3 Varnish 3 Varnish 1 Varnish 1 used Total 24 26 26 42% 34% resin content Viscosities Viscosity: 9.9 Pa s 10.0 Pa s 10.0 Pa s 10.7 Pa s 10.0 Pa s Viscosity 7.6 Pa s 7.4 Pa s 7.8 Pa s 8.1 Pa s 9.0 Pa s after 4 weeks RT

(51) TABLE-US-00005 TABLE 5 Optical assessment and measurements of proof prints of the inventive examples Example Exam- Exam- Exam- Exam- Exam- Exam- Example Example ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 Example 7 Example 8 Example 9 10 11 Proof Gloss 60 226 226 257 269 271 208 244 208 240 194 120 prints + Proof print A optical Optical 1.7 1.35 1.35 1.36 0.95 1.5 1.4 1.2 1.4 1.6 0.8 characterization density A Primer used Primer Primer Primer Primer Primer Primer Primer 2 Primer 2 Primer 2 Primer 2 Primer 2 2 1 2 2 1 2 Gloss 60 213 315 332 318 307 274 264 230 281 194 328 Proof print B Optical 1.6 1.5 1.5 1.5 1.1 1.7 1.5 1.4 1.5 1.6 1.6 density Proof print B Proof print 60.3 64.5 62.5 65.2 64.9 61.6 65.0 63.2 65.3 57.2 62.7 B: SPIN [%] Proof print 39.7 35.5 37.5 34.8 35.1 38.4 35.0 36.8 34.7 42.8 37.3 B: SPEX [%] Proof print 20.6 29.0 24.6 30.3 29.7 23.2 29.9 26.4 30.7 14.4 25.4 B: Luster [%] Distinctness 2 3 1 1 3 1 3 3 2 2 1 of image, visual

III Interpretation

III.1 Inventive Examples (Tables 4 and 5)

(52) The best inventive examples prove to be examples 3, 4, 11 and 6. For all of the examples, decidedly high optical densities and high gloss values were observed in the proof print B. The luster value did not always correlate with the visual assessments of the specular gloss effect. The experiments rated the lowest visually were examples 2 and 5. With these experiments, the primer used was a water-based primer, which was evidently less compatible with the offset printing ink of the invention than the conventional primer 1. Examples 7 and 8, likewise evaluated visually with a rating of 3, were formulated with varnish 3, which had a very high solvent content and a very low binder content. This nonideally balanced binder/solvent ratio may adversely influence the orientation of the aluminum pigments and therefore the development of gloss already. In the case of example 5, the relatively low visual assessment is probably attributable in particular to the low optical density. This in turn may be attributable primarily to the relatively low aluminum pigment concentration. High gloss and luster values were measured for this sample, admittedly, but the poorer optical density is manifested in the overall optical impression.

(53) The specular gloss of all inventive examples, however, was at a high level hitherto unachieved in conventional offset printing inks with metallic pigmentation.

III. 2 Comparative Examples (Table 6)

(54) The two first comparative examples used a wet-milled aluminum pigment rather than a PVD pigment (PLATIN-VARIO AE-82001 from Eckart GmbH). The gloss and luster values and also the visual assessment turned out drastically poorer than for all of the inventive examples with PVD pigments. Similarly poor results were obtained for comparative example 3 with a nonleafing PVD pigment.

(55) When the viscosity was varied, a drop in the mirror effect (gloss and luster values and also the visual assessment) became apparent as the viscosity went up. The highest values were received by comparative example 4. In the case of this low-viscosity printing ink (viscosity: 2.2 Pa s), however, there is already unwanted misting apparent. The smear resistance and dot definition in the case of fine detail elements was also apparent.

(56) In the case of comparative examples 5 and 6, in spite of gloss and luster values that were still relatively good in the measurements, it was clearly apparent that the distinctness of image was no longer sufficient as a result of a significantly increasing milkiness of the mirror, and hence that the mirror effect was no longer sufficient for the status of inventive examples. The high viscosities appear here to prevent optimum orientation of the platelet-shaped aluminum pigments in the proof print.

III.3 Variation of the Substrates

(57) Testing took place on various paper and cardboard substrates.

(58) The paper substrates were relatively comparable grades, produced from virgin fiber, bleached and coated.

(59) In the case of the cardboard substrates, the grades used range from recycled to bleached virgin fiber cardboard. The experiments with bleached, coated virgin fiber cardboard are of higher optical grade from left to right, since in terms of their surface structure they become smoother and on the other hand the solvent can be absorbed, and oxidated drying takes place in a well-balanced proportion. This leads to good orientation of the aluminum pigments. The printing experiment on the highest-quality substrate (Chromalux) resulted in an extremely good specular gloss, which was hitherto unachieved in this pronounced form in offset printing.

(60) The substrates that were the least suitable on account of their very rough surface structures (virgin fiber: Sappi GZ; Recycled: Mayr-Melnhof Mirabell) produced an unexpectedly surprising metallic effect. While the distinctness of image is attenuated by the surface structure on increasing distance from the printed object, there is nevertheless a diffuse, nonmilky mirror produced. Accordingly, a hitherto unachieved, surprising metallic effect can be obtained which was not achievable on these substrates before. In this case, the rough structure of the substrate was still visible, but receives a hitherto unknown printed optical effect by virtue of the metallic pigment printing with the printing ink of the invention.

(61) TABLE-US-00006 TABLE 6 Formula constituents, viscosities and optical data for comparative examples and viscosity variation Wet-milled Non- Al pigments leafing Viscosity variation experimental series Example/comparative example Comparative Comparative Comparative Comparative Example Example Example Comparative Comparative example 1 example 2 example 3 example 4 12 13 14 example 5 example 6 Pigment base PLATIN- PLATIN- W- A-41510EN A- A- A- A-41510EN A- VARIO AE- VARIO AE- 52012IL* 41510EN 41510EN 41510EN 41510EN 82001 82001 (Eckart GmbH) Pigment content [%] 5.4 5.4 5.2 5.7 6.1 6.4 6.5 6.9 7.1 Leafing additive 25% MDST 20% MDST 25% 25% 25% 25% 25% MDST 25% MDST MDST MDST MDST MDST Solvent Mineral oil/ Mineral oil/ PTO/ Mineral oil Mineral Mineral Mineral Mineral oil/ Mineral oil/ Estisol 312 Estisol 312/ Tung oil Tung oil oil/Tung oil/ oil/Tung Tung oil Tung oil Tung oil Tung oil oil Tung oil oil Solvent content 44 44 65 52 48 45 44 41 39 Resin composition Varnish 1 Varnish 1 Varnish 3 Varnish 2 Varnish 2 Varnish 2 Varnish 2 Varnish 2 Varnish 2 Total resin content 42 42 29 32 34 35 36 38 48 Viscosity: 11.7 Pa s 11.7 Pa s 11 Pa s 2.2 Pa s 5.5 Pa s 8.1 Pa s 11.4 Pa s 21.4 Pa s 34.5 Pa s Gloss 60 101 112 53 179 157 171 163 154 141 Optical density 1.1 1.1 0.9 1.6 1.2 1.2 1.3 1.3 1.3 Primer Primer 2 Primer 2 Primer 2 Primer 2 Primer 2 Primer 2 Primer 2 Primer 2 Primer 2 Gloss 60 on Primer 121 121 81 311 309 296 277 221 190 Optical density on 1.25 1.2 0.8 1.9 1.9 1.9 1.8 1.65 1.6 Primer SPIN with Primer [%] 55.8 55.88 57.3 66.5 66.2 65.6 65.5 61.5 60.7 SPEX with Primer 44.2 44.12 42.7 33.5 33.8 34.4 34.6 38.5 39.3 [%] Luster with Primer 11.6 11.76 14.6 33.0 32.4 31.2 30.9 23.0 21.3 [%] Distinctness of 5 5 5 1 1 2 3 4 4 image, visual

(62) TABLE-US-00007 TABLE 7 Printing ink as per example 6 printed onto a variety of substrates Bleached virgin Recycled cardboard, fiber, coated double coating Profigloss Perfect B Mayr-Melnhof Virgin fiber cardboard, bleached, coated Optical Bilderdruck Super Mirabell Sappi GZ Invercote T Truecard Ice assessment/substrate 100 g/m.sup.2 75 g/m.sup.2 WSHG 5 GD2 300 g/m.sup.2 280 g/m.sup.2 240 g/m.sup.2 300 g/m.sup.2 Chromalux Gloss 60 208 186 183 175 191 259 171 228 Proof print A Optical density Proof 1.5 1.2 1.1 1.5 1.6 1.6 1.1 1.1 print A Gloss 60 274 233 263 200 186 232 247 238 Proof print B Optical density Proof 1.7 1.6 1.7 1.6 1.7 1.7 1.7 1.5 print AB Proof print B: 61.59 61.76 62.2 60.47 61.43 62.11 63.39 62.93 SPIN (%) Proof print B: 38.41 38.24 37.8 39.53 38.57 37.89 36.61 37.07 SPEX (%) Proof print B: 23.18 23.52 24.4 20.94 22.86 24.22 26.78 25.86 Luster with Primer (%) Proof print B: 1 2 1 3 3 2 1 1+ Mirror effect, visual