Лако-красочные материалы — производство

IAN J. FLETCHER and RUDOLF ZINK

4.1. INTRODUCTION

Considering the fact that 3,3-bis(4-dimethylaminophenyl)phthalide (1), commonly known as Malachite Green lactone, was reported1 well over 100 years ago, it is somewhat surprising to realize that the analogous 6- dimethylaminophthalide [Crystal Violet lactone (CVL)] (2) was not de­scribed until 1945,2 and that the vast majority of references cited herein are considerably more recent.

IAN J. FLETCHER and RUDOLF ZINK • Research and Development Department, Chemi­cals Division, Ciba-Geigy AG, CH-4002 Basel, Switzerland; present address: Consumer Care Division, Ciba Speciality Chemicals, D79639 Grenzach-Wyhlen, Germany.

Chemistry and Applications ofLeuco Dyes, edited by Muthyala. Plenum Press, New York, 1997.

The driving force for this development followed the introduction of carbonless copying paper into the marketplace by the National Cash Register Company (NCR) in 1954. The principles of this system have long been described,3’4 and it suffices to demonstrate the color-forming reaction of CVL in Scheme 1.

On reaction of the electron-donating colorless phthalide (color former or dye precurser) with an electron-accepting color developer, reversible opening of the lactone ring occurs, yielding the resonance-stabilized cationic dye. Hence, it is obvious that the properties of the color former also are dependent on those of the developer, but this is a complex problem and hardly the subject of this article. However, where important differences arise these will be referred to, and thus, it is necessary to briefly mention the various types of developers utilized in present-day carbonless copying papers. Originally NCR employed Attapulgus clay as developer but this has been superseded by phenol-formaldehyde resins in the United States. In Europe, however, inorganic developers, particularly bentonite, are of prime importance, whereas in Japan, substituted zinc salicylates prevail.

In the years following the introduction of carbonless papers there has been a requirement for shades differing from the original royal blue, in particular a black script. This has resulted in the development of color formers possessing shades covering the entire visible spectral range. Phthal — ides are particularly versatile in this respect and in the following we shall attempt to describe their varying syntheses and the effects of substitution on their properties.