Offset printing ink.

0001The present invention relates to a low-viscosity offset printing ink which essentially consists of a binder, additives and 5-40% by weight of pearlescent pigments.

0002Offset printing inks usually consist of binders, pigments or dyes and additives. In the case of printed products for packaging prints, labels and high-quality magazines, there is an increasing demand for the objects shown to have a high gloss.

0003Pearlescent pigmented offset printing inks all have the disadvantage that they have problems with the printing stability. They tend to build up quickly on the inking unit, printing plate and rubber blanket, so that it is usually not possible to continue printing without problems over 10,000 sheets. Furthermore, the glossiness of such proofs is generally unsatisfactory, which is due to the insufficient amount of pigments transferred to the printed product. The ink becomes poor in pigment on the transport route via the inking unit, plate and rubber blanket. The latter accumulates in exposed areas on the plate and cloth and leads to build-up and fur. As a rule, only pearlescent pigments with a very small average particle size can be used, since the particle size is critical for pigment transfer in offset printing. Such pigments only exist for pearl white and pastel tints, but not for the very interesting gold, silver, bronze and copper tones. So far, such shades with pearlescent pigments could not be produced satisfactorily in the offset process.

0004The use of platelet-shaped bismuth oxychloride pigments to achieve a pearlescent effect likewise does not lead to satisfactory results, since the pigment particles are very sensitive to mechanical shear forces and are ground in the color gap.

0005The use of pearlescent pigments in printing inks for offset printing is known from DE 29 03 212, where the pigmentation is disclosed by a commercially available oil-based printing varnish with a preferably very finely divided pearlescent pigment. The offset printing varnish preparation described there is distinguished by the fact that the proportion of pearlescent pigments is very high, the upper limit of the pigment concentration in the suspension being essentially limited only by the flowability of the mixture which is required. The proportion of pearlescent pigments is in the range up to 65% by weight. Varnishes with such a high pigment content are very viscous and may need to be made more flowable with a thinner in order to be processed in conventional offset printing machines. Experiments have shown that, in contrast to the teaching from DE 29 03 212, the pigment transfer from the inking unit to the substrate is disturbed with such high pigmentations. There are production pressure disorders such as build-up and fur, ie that the achievable pearlescent effect cannot be optimized solely by high pigmentation. Furthermore, the color systems according to DE 29 03 212 generally do not have sufficient point sharpness, so that the color systems described there are essentially restricted to the printing of solid areas.

0006The object was therefore to find an offset printing ink preparation which contains pearlescent pigments and yet does not have any of the disadvantages mentioned above.

0007Surprisingly, it was found that the quality of the pearlescent effect and the amount of pigment particles transferred is optimal for ink viscosities that are <15 Pas. The pigmented printing ink according to the invention has viscosities <12 Pas, preferably <8 Pas. The printing inks show no problems with the spraying off of the inking rollers, not even at printing speeds of 10,000 sheets per hour. The ratio of pearlescent pigment / non-volatile portion of the color is decisive for an optimal pigment transfer from the inking unit to the substrate. The ratio should not be too high, otherwise the pigment cannot be transported satisfactorily. The pigment / non-volatile fraction of the color is preferably <0.40, in particular <0.30.

0008The invention therefore relates to a low-viscosity offset printing ink consisting essentially of binders, pigments and additives, characterized in that it contains 5-40% by weight of pearlescent pigments or pearlescent pigment mixtures based on platelet-shaped substrates coated with one or more metal oxides or metal oxide mixtures contains based on the printing ink and has a viscosity <12 Pas.

0009The invention furthermore relates to the fact that the ratio of pearlescent pigment / non-volatile component of the color is <0.40.

0010The pearlescent pigment or pearlescent pigment mixture is an essential component of the offset printing ink according to the invention. The proportion of pearlescent pigments in the offset printing ink is 5-40% by weight, preferably 10-30% by weight. In contrast to the prior art, even with only low pigment concentrations, printed products with a high pearlescent are obtained. The color / water balance must of course be monitored during pigmentation and corrected if necessary to ensure problem-free printing without building up on the rollers.

0011Suitable base substrates for the coating are transparent platelet-shaped substrates. Preferred substrates are layered silicates and platelet-shaped materials coated with metal oxides. Particularly suitable are mica, talc, kaolin, bismuth oxychloride, glass, SiO₂ or synthetic ceramic flakes, synthetic carrier-free platelets or other comparable materials. In addition, there are also metal platelets such as aluminum platelets or platelet-shaped metal oxides such as Aluminum platelets or platelet-shaped metal oxides, such as platelet-shaped iron oxide and mica coatings with colored or colorless metal oxides such as TiO₂, Fe₂O₃, SnO₂, Cr₂O₃, ZnO and other metal oxides, alone or in a mixture in a uniform layer or in successive layers. These pigments known as pearlescent pigments are, for example from German patents and patent applications 14 67 468, 19 59 998, 20 09 566, 22 14 545, 22 15 191, 22 44 298, 23 13 331, 25 22 572, 31 37 808, 31 37 809, 31 51 343, 31 51 354, 31 51 355, 32 11 602 and 32 35 017 are known. Pearlescent pigments are preferably used for the printing ink. In particular, mica pigments coated with TiO₂ and / or Fe₂O₃, SiO₂ or glass flakes are used.

0012In addition to the finely divided pearlescent pigments, coarse-grained particles can also be printed due to the optimal transfer properties of the binder. Particles with an average particle size of D₅₀ = 4-100 μm, in particular D₅₀ = 5-20 μm, are preferably used in the printing ink according to the invention. Pearlescent pigments with an average particle size of DX = 10 µm show interesting gold, silver, bronze and copper tones in the offset process.

0013In addition to the pearlescent pigments, the offset printing ink can be pigmented by carbon black, metallic effect, fluorescent and / or organic colored pigments. The pigmentation then preferably consists of 50-100% by weight of pearlescent pigment and 0-50% by weight of carbon black, metallic effect, fluorescent and / or colored pigment. However, the content of all pigments in the printing ink should not exceed 40% by weight.

0014The binder or the non-volatile portion of the pearlescent offset printing ink according to the invention consists of known synthetic or natural resins, drying oils, mineral oils and additives, as described, for example, in Karsten, Lackrohstoffabellen, 9th edition 1992. The resins used preferably have a relatively low melt or solvent viscosity. Highly polymerized and highly viscous components can also be included. Combinations of hard resins and alkyd resins have proven to be particularly suitable, since these wet the pearlescent pigments better and produce glossy and rub-resistant prints. In particular, binders are used which are composed of 50-90% by weight of hard resin and 5-50% by weight of alkyl resin. The hard resins used are preferably hydrocarbon resins. The hydrocarbon resins used can have an acid number close to 0 mg KOH / g substance, but they can also be modified and have acid numbers up to 30 mg KOH / g substance. Furthermore, the binder can contain 1-50% by weight of a mineral oil. The color components are matched to one another in such a way that a stable color / water balance suitable for the low color viscosity is achieved.

0015The offset printing ink is dried by oxidative polymerization of the resins and by oils, such as. B. linseed, wood or castor oil, which knock away when printing in the paper. The drying process can be further accelerated by adding drying catalysts (siccatives), mostly fatty acid salts of cobalt, lead, manganese, etc. The proportion of drying oils in the offset printing inks according to the invention is in the range of 0-50% by weight, preferably 0-30% by weight. Additional additives can be added to the printing ink to change the color properties for special applications. These additives can be wax compounds, drying agents, dispersants, solvents, thickeners, lubricants, pigment fillers and / or antioxidants. Further details on the basic properties of offset printing inks can be found in A. Rosenberg, Der Polygraph (11), 1153 (<u>1987</u>) or B. Grande, Coating (4), 138 (<u>1987</u>).

0016The very low-viscosity offset printing inks containing pearlescent pigment according to the invention often do not have sufficient dot sharpness. However, this is necessary especially in fine grids to avoid clogging of the print. It is therefore advisable to structure the printing varnishes. The addition of a structuring agent can sufficiently improve the point sharpness. The offset printing ink according to the invention then preferably contains 0.1-3% by weight of a structure former. In addition to the improved dot sharpness, such a modified printing varnish shows a significantly better pigment transfer and better production properties.

0017The invention therefore also relates to the fact that the offset printing ink contains &lt;10% by weight of additives. The invention furthermore relates to the fact that the offset printing ink contains 0.1-3% by weight of a structure former.

0018The preparation of the offset printing ink preparation is carried out by dispersing the pearlescent pigment in the ink with the aid of a ball mill, sand mill or a roller mill (three rollers), if appropriate at different dispersion temperatures. The pigment particles are enveloped by the binder. The grinding pastes running out of the devices are then mixed with the additives to the finished product.

0019By choosing the resins in the binders and the proportion of pearlescent pigments in the offset printing ink, the parameters that are decisive for the printing process, such as dispersibility, viscosity and viscosity, can be set individually. The viscosity and the speed are interdependent for the same color structure, but can also be individually changed by using a special color structure. It should be noted here that inks with too high a degree of elasticity can cause parts of the paper to tear (picking). Inadequate colors are not adequately transferred during the printing process. If the penetration of the color is too great, the color on the opposite side of the paper becomes visible or causes the image to become blotchy or unclear. Poorly controlled intrusion can cause smearing and discarding. In contrast, too viscous inks will not flow appropriately from the fill sources to the rollers. The offset printing inks on the market are adjusted to viscosities in the range of 12-30 Pas. In contrast, the printing inks according to the invention can be adjusted to viscosities &lt;12 Pas, preferably &lt;10 Pas, in particular &lt;8 Pas.

0020The offset printing ink can be used for both web offset and sheetfed offset printing in dry and wet processes; however, it is particularly suitable for wet offset sheetfed printing. With the offset printing ink according to the invention, very high printing speeds are achieved due to the very good rheological properties. It is easy to print 10,000 sheets per hour, with no problems with production printing or with halftone dot sharpness.

0021The use of the offset printing ink according to the invention is particularly important with regard to graphic products from the advertising industry and for high-quality printed products, since the finished prints meet the highest aesthetic standards due to their pearlescent sheen.

0022The following examples are intended to explain the invention in more detail without, however, limiting it.

<b>Examples</b>

0023<ul id="ul0001" list-style="none"><li><b>I. <u>Example 1 - Comparative Example</u></b>A "Fine Ink" sheetfed offset ink from Nippon Ink Company is printed with the "Aquastabil" fountain solution additive from Hartmann Druckfarben. The dampening solution (5% dissolved in water) is modified with 5% of a 2% phosphoric acid. Printing plate: Kalle p5S, Kalle, Wiesbaden Printing blanket: Perfect Dot mx, Streb After 2000 sheets, there is a clear pigment build-up on the printing plate and the blanket. The pearlescent effect is judged to be insufficient. The viscosity is 25 Pas with a proportion of 30 wt.% TiO₂ mica pearlescent pigments with an average particle size D₅₀ = 6 µm.</li><li><u><b>Example 2</b></u>A commercially available oil printing varnish 11A0524 from Gebrüder Schmidt, Frankfurt is made with Iriodin 123 bright gloss satin (with TiO₂ coated mica pigment with an average particle size D₅₀ = 10 µm), or Iriodin 323 Royal Goldsatin (with Fe₂O₃ / TiO₂ coated mica pigment with average particle size D₅₀ = 10 µm from E. Merck, Darmstadt, FRG) pigmented in increasing proportions. The printing tests are carried out in accordance with Example 1. The corresponding viscosities and pigment and binder ratios are shown in Table 1.</li><li><u><b>Example 3</b></u>85 g of the commercially available printing varnish 11A0524 from Gebrüder Schmidt, Frankfurt are mixed with a mixture of 0.5 g Aliso B (structuring agent from Manchem) and 0.5 g mineral oil PKWF 28/31 (from Haltermann) and incorporated homogeneously . It is pigmented with 15 g of Iriodin 123 light-gloss satin (pearlescent pigment coated with TiO₂ and having an average particle size of D₅₀ = 10 µm), and a printing ink with a viscosity of η = 5.2 Pas is obtained. The ink is printed on a Heidelberg MO at 6000 sheets / hour under the printing conditions from experiment 1. The color shows no tendency to build up over the entire printing period. The production run is stable and you get prints with an optimal gloss. Furthermore, the color is characterized by its excellent point sharpness. The results are summarized in Table 1.</li><li><u><b>Example 4</b></u>15 g of Bentone 38 (from NL Chemicals) are placed in 230 g of oil-based varnish 11A0524 from Gebr. Schmidt / Frankfurt and homogenized with a high-speed stirrer. The suspension is made into a paste with 5 g of isopropanol.</li><li><u><b>Example 5</b></u>650 g of the commercially available printing varnish 11A0524 from Gebrüder Schmidt, Frankfurt are mixed with 200 g of the stock paste (Example 4) and stirred homogeneously. It is pigmented with 150 g of Iriodin 123 bright gloss satin and a printing ink with a viscosity of 6.2 Pas is obtained. The color is printed as in Example 3. The results are shown in Table 1.</li><li><u><b>Example 6</b></u>64.7 g of a Hercules A 101 hydrocarbon resin (Hercules BV) are mixed with 16.0 g of PKWF 28/31 mineral oil from Haltermann (aniline point = 82) and 19.3 g of a refined linseed oil with a viscosity> 90 Pas Nitrogen atmosphere boiled to a varnish at 200 ° C. 15.0 g of Alftalat 810 (from Hoechst) are mixed with 20 g of Iriodin 111 fine satin (mica pigment coated with TiO₂ with an average particle size D₅₀ = 6 µm from E. Merck, Darmstadt, FRG) and 3 g of oleic acid (from E. Merck) into a paste and then with 59 g of the hydrocarbon pollutant, 1.5 g of mineral oil PKWF 28/31 (from Haltermann) and 1.5 g of 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (from Eastman ) processed into a homogeneous color. To complete, 0.83 g of dry substance (chromium and manganese salts) from Hartmann are added. The viscosity of the finished printing ink is 5.5 Pas. The results are summarized in Table 1.</li><li><b>II. <u>Results</u></b>The viscosity is measured according to DIN 53222 (1990) at 25 ° C. It is evaluated according to Casson and the plastic viscosity according to the formula<maths id="math0001" num=""><math display="inline"><mrow><msub><mrow><mtext>η</mtext></mrow><mrow><mtext>∞</mtext></mrow></msub><mtext> = 0.1 · g / S · C · a² [Pas]</mtext></mrow></math><img file="EP0633299A2_D0001.tif" /></maths> determined where<dl id="dl0001"><dt>g =</dt><dd>Gravitational acceleration,</dd><dt>S =</dt><dd>Friction surface of the drop rod,</dd><dt>C =</dt><dd>Device constant, determined by calibrating the measuring apparatus with a calibration oil 20000A from PTB, Braunschweig and Berlin,</dd><dt>a =</dt><dd>Slope of the regression line y = ax + b with y = √m₁ + m₀, x = √1 / t with m_i = Support weight and m₀ = mass of the drop rod.</dd></dl> All units are CGS units (centimeters, grams, seconds). The ratio of pearlescent pigment / non-volatile content of the printing ink is determined based on the standard DIN 53219. The samples are dried to constant weight at 110 ° C. and a vacuum of 5 torr. The pearlescent effect achieved is assessed visually. Furthermore, microscopic images are taken and the number of pearlescent pigment platelets per unit area is determined.</li></ul>

0024<tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="8" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="19.68mm" /><colspec colnum="2" colname="col2" colwidth="19.68mm" /><colspec colnum="3" colname="col3" colwidth="19.68mm" /><colspec colnum="4" colname="col4" colwidth="19.68mm" /><colspec colnum="5" colname="col5" colwidth="19.68mm" /><colspec colnum="6" colname="col6" colwidth="19.68mm" /><colspec colnum="7" colname="col7" colwidth="19.68mm" /><colspec colnum="8" colname="col8" colwidth="19.68mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="center">Ink components [% by weight]</entry><entry namest="col2" nameend="col8" align="center">example</entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center">2</entry><entry namest="col3" nameend="col3" align="center">2</entry><entry namest="col4" nameend="col4" align="center">2</entry><entry namest="col5" nameend="col5" align="center">2</entry><entry namest="col6" nameend="col6" align="center">3</entry><entry namest="col7" nameend="col7" align="center">5</entry><entry namest="col8" nameend="col8" align="center">6</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Binder 11A0524 (Gebr. Schmidt, Frankfurt)</entry><entry namest="col2" nameend="col2" align="right">83</entry><entry namest="col3" nameend="col3" align="right">78</entry><entry namest="col4" nameend="col4" align="right">78</entry><entry namest="col5" nameend="col5" align="right">77</entry><entry namest="col6" nameend="col6" align="right">83</entry><entry namest="col7" nameend="col7" align="right">83</entry><entry namest="col8" nameend="col8" align="right">-</entry></row><row><entry namest="col1" nameend="col1" align="left">Binder from Example 6</entry><entry namest="col2" nameend="col2" align="right">-</entry><entry namest="col3" nameend="col3" align="right">-</entry><entry namest="col4" nameend="col4" align="right">-</entry><entry namest="col5" nameend="col5" align="right">-</entry><entry namest="col6" nameend="col6" align="right">-</entry><entry namest="col7" nameend="col7" align="right">-</entry><entry namest="col8" nameend="col8" align="right">80</entry></row><row><entry namest="col1" nameend="col1" align="left">Iriodin 111 fine satin</entry><entry namest="col2" nameend="col2" align="right">-</entry><entry namest="col3" nameend="col3" align="right">-</entry><entry namest="col4" nameend="col4" align="right">-</entry><entry namest="col5" nameend="col5" align="right">-</entry><entry namest="col6" nameend="col6" align="right">-</entry><entry namest="col7" nameend="col7" align="right">-</entry><entry namest="col8" nameend="col8" align="right">20</entry></row><row><entry namest="col1" nameend="col1" align="left">Iriodin 123 light gloss satin</entry><entry namest="col2" nameend="col2" align="right">15</entry><entry namest="col3" nameend="col3" align="right">20</entry><entry namest="col4" nameend="col4" align="right">30</entry><entry namest="col5" nameend="col5" align="right">-</entry><entry namest="col6" nameend="col6" align="right">15</entry><entry namest="col7" nameend="col7" align="right">15</entry><entry namest="col8" nameend="col8" align="right">-</entry></row><row><entry namest="col1" nameend="col1" align="left">Iriodin 323 Royal Gold Satin</entry><entry namest="col2" nameend="col2" align="right">-</entry><entry namest="col3" nameend="col3" align="right">-</entry><entry namest="col4" nameend="col4" align="right">-</entry><entry namest="col5" nameend="col5" align="right">20</entry><entry namest="col6" nameend="col6" align="right">-</entry><entry namest="col7" nameend="col7" align="right">-</entry><entry namest="col8" nameend="col8" align="right">-</entry></row><row><entry namest="col1" nameend="col1" align="left">Colorant RED (from Kast + Ehinger)</entry><entry namest="col2" nameend="col2" align="right">2</entry><entry namest="col3" nameend="col3" align="right">2</entry><entry namest="col4" nameend="col4" align="right">2</entry><entry namest="col5" nameend="col5" align="right">-</entry><entry namest="col6" nameend="col6" align="right">2</entry><entry namest="col7" nameend="col7" align="right">2</entry><entry namest="col8" nameend="col8" align="right">-</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Colorant YELLOW (from Kast + Ehinger)</entry><entry namest="col2" nameend="col2" align="right">-</entry><entry namest="col3" nameend="col3" align="right">-</entry><entry namest="col4" nameend="col4" align="right">-</entry><entry namest="col5" nameend="col5" align="right">3</entry><entry namest="col6" nameend="col6" align="right">-</entry><entry namest="col7" nameend="col7" align="right">-</entry><entry namest="col8" nameend="col8" align="right">-</entry></row><row><entry namest="col1" nameend="col1" align="left">P / NF¹</entry><entry namest="col2" nameend="col2" align="right">0,229</entry><entry namest="col3" nameend="col3" align="right">0,296</entry><entry namest="col4" nameend="col4" align="right">0,417</entry><entry namest="col5" nameend="col5" align="right">0,296</entry><entry namest="col6" nameend="col6" align="right">0,227</entry><entry namest="col7" nameend="col7" align="right">0,228</entry><entry namest="col8" nameend="col8" align="right">0,206</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">η_∞ [Pas]</entry><entry namest="col2" nameend="col2" align="right">4,8</entry><entry namest="col3" nameend="col3" align="right">4,5</entry><entry namest="col4" nameend="col4" align="right">5,7</entry><entry namest="col5" nameend="col5" align="right">4,5</entry><entry namest="col6" nameend="col6" align="right">5,2</entry><entry namest="col7" nameend="col7" align="right">6,2</entry><entry namest="col8" nameend="col8" align="right">5,5</entry></row><row><entry namest="col1" nameend="col1" align="left">Printing test (print run in thousands)</entry><entry namest="col2" nameend="col2" align="right">> 10</entry><entry namest="col3" nameend="col3" align="right">-</entry><entry namest="col4" nameend="col4" align="right">0,4</entry><entry namest="col5" nameend="col5" align="right">-</entry><entry namest="col6" nameend="col6" align="right">> 5</entry><entry namest="col7" nameend="col7" align="right">3,5</entry><entry namest="col8" nameend="col8" align="right">-</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Effect²</entry><entry namest="col2" nameend="col2" align="right">4</entry><entry namest="col3" nameend="col3" align="right">-</entry><entry namest="col4" nameend="col4" align="right">3</entry><entry namest="col5" nameend="col5" align="right">-</entry><entry namest="col6" nameend="col6" align="right">5</entry><entry namest="col7" nameend="col7" align="right">5</entry><entry namest="col8" nameend="col8" align="right">-</entry></row></tbody></tgroup><tgroup cols="8" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="19.68mm" /><colspec colnum="2" colname="col2" colwidth="19.68mm" /><colspec colnum="3" colname="col3" colwidth="19.68mm" /><colspec colnum="4" colname="col4" colwidth="19.68mm" /><colspec colnum="5" colname="col5" colwidth="19.68mm" /><colspec colnum="6" colname="col6" colwidth="19.68mm" /><colspec colnum="7" colname="col7" colwidth="19.68mm" /><colspec colnum="8" colname="col8" colwidth="19.68mm" /><tbody valign="top"><row><entry namest="col1" nameend="col8" align="justify">1: Ratio of pearlescent pigment mass / mass of non-volatile portion of the printing ink = P / NF</entry></row><row><entry namest="col1" nameend="col8" align="justify">2: gradation (microscopic evaluation of the print samples) 1 = very little; 2 = little; 3 = medium; 4 = a lot; 5 = a lot</entry></row></tbody></tgroup></table></tables>