Лако-красочные материалы — производство

Benzimidazolone pigments cover a broad spectral range from very greenish yellow through orange, red and violet to brown. The tinctorial strength of the pigments pre­pared varies considerably because oftheir different physical characteristics. This fact does not surprise us, as the median of the particle size distribution ranges from 50 nm to 1000 nm (compare Table 10.1). Typical pigment loadings for printing inks range from 7.5 to 25% to obtain 1/3 standard depth, depending on intrinsic color strength and particle size distribution. Generally, the tinctorial strengths of yellow and the orange benzimidazolone colorants are similar to those found for classical yellow monoazo pigments. The same analogy in terms of color strength can be observed for the red series of Naphtolon™ and Naphtol AS™ derived pigments.

The performance of the pigments considerably depend on the system in which they are processed and applied.

1) Hue angle at 1/3 standard depth SD (German standard: DIN 6174).

2) Parts ТЮ2 required to reduce 1 part of pigment to 1/3 SD (l:x Ti02). These data represent guide values that can be influenced by the binder used and the dispersion status.

3) Light fastness was tested in air drying paint at 1/3 SD. Assessment was made against the 8-step Blue Scale (DIN 54003) in which rating 8 denotes excellent and rating 1 very poor light fastness.

4) Evaluation was made by comparison with the 5-step ‘change of shade’ Grey Scale (DIN 54001) after 12 month outdoors weathering of an air drying paint. Rating 5 is the best, rating 1 the poorest.

5) Assessment of bleeding into a white nitrocellulose combination laquer against the 5-step ‘bleeding’ Grey Scale (DIN 54002) in which rating 5 is the best and rating 1 the poorest.

6) Assessment against the 5-step ‘change of shade’ Grey Scale.

7) Assessment against the 5-step ‘bleeding’ Grey Scale (DIN 54002).

8) Methyl ethyl ketone.

1) Hue angle at 1/3 standard depth SD (German standard: DIN 6174), determined in HDPE.

2) Indicated is the amount of pigment needed to reach 1 /3 SD in 5% rutile titanium dioxide white reductions in PVC unless indicated.

3) Against the 8-step Blue Scale (DIN 54003). The evaluation was done according to DIN 53388. Pigment concentration: 0.1%.

4) 1/3 SD was tested to determine the heat resistance in PE injection moulding (DIN 53772).

5) The fastness to bleeding was determined at 100 °С/15 h against the 5-step, bleeding’ Grey Scale (DIN 54002).

6) Assessment against the 5-step ,change of shade’ Grey Scale (DIN 54001).

7) Assessment against the 5-step ,bleeding’ Grey Scale.

8) Indicated is the pigmentation level of a printing ink (in percent) applied at 1.0 g/m2 to reach 1/3 SD.

9) 60 vol% ethanol, 30 vol% ethyl acetate, 10 vol% 1-methoxy-2-propanol.

10) Against the 8-step Blue Scale.

11) Methyl ethyl ketone.

12) Print on a metal sheet; start at 140 °С, steps of 20 °C/10 min.

All benzimidazolone pigments exhibit outstanding light fastness and weather resistance combined with excellent solvent, overpainting and bleeding fastness. In this respect benzimidazolone pigments are markedly superior to their coloristic counterparts in the monoazo yellow or red Naphtol AS™ series. In fact, the class of benzimidazolone pigments contains colorants matching high-performance polycyclic pigments in terms of light fastness and weatherability.

Figure 10.4 compares important application properties of the benzimidazolone P. Br. 25 (data from Hostaperm™ Brown HFR01 and PV Fast Brown HFR 01) with the Naphtol AS™ pigment P. R. 2 (Permanent™ Red FRR). From a chemical point of view P. Br. 25 can be considered as a Naphtol AS™ pigment wherein the anilide function derives from 5-amino-benzimidazolone instead of aniline. The effect of this difference is tremendous. With respect to the fastness properties, the better fastness to light and solvents of the benzimidazolone pigment compared to the Naphtol AS™ species is striking. Thus, the fastness to light, measured using the 8-step wool scale according to German standards, equals step 7 for the benz­imidazolone and only step 5 for the Naphtol AS™ pigment. This result is remark­able since a difference of two steps on the wool-scale corresponds approximately to a four-fold exposure time. Furthermore, Figure 10.4 contains data reflecting the solvent fastness as well as fastness to alkali and acids. The evaluation has been done according to a five-step scale, in which rating 5 is the best and rating 1 the poorest. P. Br. 25 is thus completely resistant to solvents such as ethyl acetate, methyl ethyl ketone (MEK) or toluene, as well as to acids and alkali (all step 5), while P. R. 2 tolerates acids and bases (both step 5) but is sensitive to the above solvents (steps 3, 3-4). In addition, P. Br. 25 has a 39% higher color strength than P. R. 2. Owing to these properties, P. R. 2 is primarily used in water based printing inks, because it does not show sufficient performance in other fields. In contrast, the application properties of P. Br. 25 qualify this benzimidazolone pigment for use in printing inks and plastics, as well as in paints.

Chemical similarities between classical monoazo and benzimidazolone pig­ments are of academic interest only. The positioning of a pigment is determined by its coloristics and fastness properties as well as the price/performance ratio, as when we compare Naphtol AS™ Pigment Red 146 with the somewhat more yel­lowish benzimidazolone Pigment Red 185 (see Figure 10.4). As expected, the benzimidazolone type pigments Novoperm™ Carmine HF4C and Graphtol™ Carmine HF4C, respectively, show better fastness properties than the Naphtol AS™ derived Permanent™ Carmine FBB 02 (e. g. bleed fastness 5 versus 2).

It is well known that classical azo as well as benzimidazolone pigments are sta­bilized by intramolecular hydrogen bonds. These bonds are stronger than the ubiquitous van der Waals forces that hold together molecules within a crystal. As revealed by X-ray studies, the exceptional properties of benzimidazolone pigments can be explained by the supportive function of their intermolecular hydrogen bonds. These bonds remarkably stabilize the pigment crystals, thereby improving the fastness properties [9]. Like other azo pigments (e. g. monoazo yellow, b-naphthol and Naphtol AS™-types), benzimidazolone pigments are almost pla­nar molecules that exist as oxohydrazone tautomers in the solid state. Figure 10.5

Figure 10.4a Comparison of the fast­ness properties of benzimidazolone and Naphthol AS™ pigments; P. R. 2 and P. Br. 25.

OMe P. R. 185

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shows a two-dimensional scheme as well as crystal structures [9b, 9d, 10] from both a yellow and a red benzimidazolone pigment. The molecules form “flat bands” by hydrogen bonds. These bands in turn are held together by van der Waals forces only. Polycyclic pigments, e. g. quinacridones and diketopyrrolopyr — roles, are also known to form intermolecular hydrogen bonds in their crystals.

10.5