GB2239872A

GB2239872A - Dyestuff pastilles

Info

Publication number: GB2239872A
Application number: GB9100272A
Authority: GB
Inventors: Brian John Williams; Reinhard Weigmann
Original assignee: Ciba Geigy AG
Current assignee: Novartis AG
Priority date: 1990-01-10
Filing date: 1991-01-07
Publication date: 1991-07-17
Also published as: GB9000543D0; GB9100272D0

Abstract

Dyestuffs (including colour-formers) are obtained in the form of solid pastilles (Fig. 1), typically of 1-3mm diameter, by solidifying droplets of the molten dyestuff while depositing them on, e.g., a moving endless conveyor belt whose inner surface is sprayed with cold water. Preferably the molten droplets are extruded from two coaxial apertured cylindrical vessels, the outer of which rotates about the inner. The process is particularly applicable to colour-formers e.g. of the phthalide, fluoran or carbazolylmethane series, the pastilles of which dissolve rapidly in organic solvents thereby facilitating the mfr. of heat. and pressure-sensitive papers. <IMAGE>

Description

Dvestuff vastilles This invention relates to dyestuffs in the form of pastilles, including latent dyestuffs such as colour formers used in pressure-sensitive carbonless copying paper or in thermographic systems.

Dyestuffs are usually produced in finely divided form by manufacturers for delivery to users. Production in powder form from dyestuffs prepared as melts is conventionally carried out by pouring a molten dyestuff onto the surface of a conveyor such as an endless belt, allowing the molten dyestuff to cool to form a solid layer on the conveyor and then breaking up the solid layer, e.g. using a flaker, to produce a powder.

Dust arising from powdered dyestuffs during operations such as packing, unpacking, weighing and blending can often constitute a potential fire hazard and a potential health hazard to operators. Agglomeration of powdered dyestuffs tends to occur during storage or processing, leading to inconvenient non-uniform behaviour, for example different rates of dissolution in organic solvents.

It has now been found that by cooling droplets of molten dyestuff to solidify them, a solid dyestuff can be produced in the form of non-agglomerating, free-flowing pastilles which are free from dusting problems and therefore present a reduced health and fire hazard during operations such as those hereinbefore described. The pastilles can be produced with a high degree of uniformity of size so that they exhibit corresponding uniformity of behaviour in processes such as dissolution in organic solvents.

Accordingly, the present invention provides a dyestuff in the form of a solid pastille produced by solidifying a droplet of the dyestuff in molten form. The invention also provides a process for the production of a dyestuff of the invention which comprises forming a droplet of molten dyestuff, depositing the droplet on a conveyor and cooling the droplet to a temperature below the melting point of the dyestuff.

The conveyor on which the droplet of molten dyestuff is deposited generally has a substantially flat surface, so that the pastille formed on solidification of the droplet has a corresponding substantially flat bottom surface with a curved periphery. The upper surface of the solidifled droplet is generally convex and may have different radii of curvature in the horizontal and vertical planes. Such a pastille of the invention is illustrated in the accompanying drawings in which Figure 1 is a perspective view of a pastille and Figure 2 is a vertical cross-sectional view along a vertical plane passing through the highest point of the pastille. As illustrated, the pastille has a flat surface 1 and a convex surface 2.

The size of the pastille can vary according to the chemical nature of the dyestuff and the intended use of the dyestuff. The size may be determined, for example, by a required rate of dissolution in an organic solvent. By means of the present invention, a dyestuff can be provided in the form of plurality of pastilles which are sufficiently uniform in size that they all dissolve in a solvent within a very short time of each other. If desired, the maximum diameter (of the flat surface) of the pastille may be up to 15 mm. More usually, this diameter is 3 mm or less, for example 1 to 1.5 mm. The height of the pastille is usually about half the diameter.

The conveyor on which the droplet of molten dyestuff is deposited may conveniently be a moving endless belt, for example a steel conveyor belt, which can be cooled, if desired, by spraying the inner surface of the belt with cold water.

The droplet of molten dyestuff may be formed by passing the molten dyestuff through an aperture in a vessel, which is usually heated, for example by an internal heating element, to maintain the dyestuff in molten form while it is in the vessel. In a preferred embodiment of the invention, the aperture is in the cylindrical wall of a rotating cylindrical vessel mounted above the conveyor, the droplet is formed by passing the molten dyestuff from the inside of the vessel through the aperture to the outside of the vessel and the resulting droplet is deposited on the conveyor. In commercial practice, of course, a plurality of droplets of molten dyestuff would be produced simultaneously using a rotating cylindrical vessel having a plurality of apertures in the circumferential wall thereof.

In a particularly preferred embodiment of the invention, droplets of the molten dyestuff are formed by extrusion from 2 coaxial cylindrical vessels, each having apertures in the circumferential wall thereof, the outer vessel rotating about the inner vessel whereby the apertures in the inner vessel coincide intermittently with the apertures in the outer vessel during relative rotation between the vessels, the molten dyestuff being fed axially into the inner vessel and radially out through the apertures in the inner vessel and, intermittently, through the apertures in the outer vessel to form droplets.

The apertures through which the molten dyestuff is passed to form droplets are preferably circular. The size of the apertures is generally chosen according to the required pastille size. The size of the pastilles is also determined by pressure applied to the molten dyestuff. A suitable combination of aperture size and pressure to achieve a desired pastille size can be readily determined by simple experiment. In general, the diameter of the apertures is between one third and a half of the required pastille diameter.

Apparatus suitable for use in forming and depositing droplets of the molten dyestuff on a conveyor is described in United States Patent No. 4623307 and W. German Patenschrift No. 3813756. The pastilles formed by cooling and solidifying the droplets on the conveyor may be carried by the conveyor to a bagging station.

The present invention can be applied to any dyestuff which melts at a feasible elevated temperature, generally up to 3000C, and which is stable in molten form. It is particularly suitable for use with dyestuffs which are obtained in molten form at the end of the process used for their manufacture. Such materials can be pumped from reaction vessels in which they are prepared to droplet-forming apparatus such as that hereinbefore described.

Dyestuffs of various chemical types can be processed in accordance with the present invention, including azo, anthraquinone, triarylmethane, thiazine, thiazole, oxazine, acridine, quinoline, phthalocyanine and stilbene dyestuffs.

The present invention is particularly useful where the dyestuff is a colour former (chromogenic material) such as is used in the production of pressure-sensitive carbonless copying paper or heat-sensitive thermographic paper. In the manufacture of such paper there are used microcapsules of a solution of a colour former dissolved in an organic solvent. The production of solutions of colour formers on a commercial scale is greatly facilitated by use of pastilles of colour formers in accordance with the present invention, since the high degree of uniformity of size of the pastilles permits the choice of a short processing time for their stirring in solvent, within which time all the pastilles are dissolved.

Colour formers to which the present invention can be applied include triarylmethane compounds such as phthalides substituted by aryl or heterocyclic groups, xanthenes such as substituted fluorans, which may contain heterocyclic groups, thiazines such as benzoylleucomethylene blue, phenoxazines and spiropyrans such as benzo and naphtho spiropyrans. The invention is especially useful in its application to the carbazolylmethane colour formers described in US Patent No. 4154463, particularly that of formula (20) of the US Patent.

Further important classes of colour formers which are used according to the invention are for example 3,3-bis(aminophenyl)phthalides such as CVL, 3-indolyl-3-aminophenylaza- or -diazaphthalides, 3,3-bis(indolyl)phthalides, 2-alkyl-6-diaLkyl-aminofluorans, 6dialkylamino-2-dibenzyiaminofluorans, 6-dia1kylamino-methyl-2-arylaminofluorans, 3,6-bisalkoxyfluorans, 3,6-bis(diarylamino)fluorans, leukoauramines, spiropyrans, spirodipyrans, benzoxazines, chromenopyrazoles, chromenoindoles, phenoxazines, phenothiazines, quinazolines, bisquinazolines, rhodamine lactams, carbazolylmethanes or triarylmethane leuko dyes.

When the dyestuff from which pastilles are to be formed is sensitive to air, the formation and solidification of droplets may be carried out in an inert atmosphere, for example in an atmosphere of nitrogen.

Example: A substituted diphenyl carbazolyl methane colour former of formula

where each Arl denotes phenyl and each Ar2 denotes p-phenylene, is prepared according to the process described in US Patent No. 4154463 by reacting N-n-butylcarbazole aldehyde with N-methyldiphenylamine for 9 hours at 80 C in methanol in the presence of sulphuric acid. The mixture obtained has a methanolic top layer and an oily bottom layer.

The bottom layer is separated, washed with methanol and again separated from the methanolic layer. The residual product is melted and heated at 1300C to dry it. The molten product is then pumped into the inner cylindrical vessel of a Sandvik Rotoformer Type 1200 HV, available from Sandvik Process Systems, which is maintained in an atmosphere of nitrogen at a temperature of 1300C and is mounted above a steel conveyor belt moving at right angles to the cylindrical axis of the Rotoformer. The molten dyestuff passes radially through apertures in the inner vessel into the rotating outer vessel and then, intermittently, through circular apertures of 0.5 mm diameter in the outer vessel to form droplets which are deposited on the conveyor belt.The droplets cool and solidify on the conveyor belt, which is cooled by cold water sprayed onto the underneath of the belt, to form pastilles having a flat circular bottom of diameter 1.3 mm and convex upper surface, the maximum height being 0.7 mm.

Some of the resulting pastilles (1 g) are added to 100 g of a 3:1 (by weight) mixture of KMC 113, a diisopropylnaphthalene solvent available from Rutgerswerke, and Exxsol D 100, an aliphatic solvent available from Exxon, at 900C. After stirring for 2 minutes, all of the pastilles are completely dissolved.

Utilizing the same process given in the Example the following colour formers were also obtained in pastille form: No. colour former colour on CF-paper 1. 2-tertbutyl-6-diethylaminofluoran orange 2. 2-n-octylamino-6-diethylaminofluoran olive 3. 2-anilino-3-methyl-6-diethylaminofluoran black 4. 2-dibenzylamino-6-diethylaminofluoran green 5. 3 ,3-(bis- 1 -n-octyl-2-methyl-indol-3-yl)- red phthalide 6. 3-(2-ethoxy-4-diethylaminophenyl)-3- blue (1 -n-octyl-2-methylindol-3-yl) -phthalide 7. 3-(2-ethoxy-4-diethylaminophenyl)-3- blue (l-n-octyl-2-methylindol-3-yl)-4-aza phthalide 8. 3,3-(bis-4-dimethylaminophenyl)-6-di- blue methylaminophthalide (CVL) 9. The bisquinazoline according to yellow US Patent 4625 027, Example 1 10. mixture of the colour formers No. 1., 2., black 5., 6., 8. and the colour former of the Example 11. mixture of the colour formers No. 1., 4., black 5., 6., 8. and the colour former of the Example

Claims

What is claimed is: 1. A dyestuff in the form of a solid pastille produced by solidifying a droplet of the dyestuff in molten form.
2. A dyestuff according to claim 1, in which the pastille has on one side a substantially flat surface with a curved periphery and on the other side a convex rounded surface.
3. A dyestuff according to claim 2, in which the substantially flat surface has a maximum diameter of up to 3 mm.
4. A dyestuff according to claim 3, in which the substantially flat surface has a maximum diameter of 1 to 1.5 mm.
5. A process for the production of a dyestuff according to claim 1 which comprises forming a droplet of molten dyestuff, depositing the droplet on a conveyor and cooling the droplet to a temperature below the melting point of the dyestuff.
6. A process according to claim 5, in which the conveyor has a substantially flat surface.
7. A process according to claim 5 or 6, in which the conveyor is an endless belt.
8. A process according to claim 7, in which the belt is cooled by spraying the inner surface thereof with cold water.
9. A process according to any of claims 5 to 8, in which the droplet is formed by passing the molten dyestuff through an aperture in a vessel.
10. A process according to claim 9, in which the aperture is in the circumferential wall of a rotating cylindrical vessel mounted above the conveyor, the droplet is formed by passing the molten dyestuff from the inside of the vessel through the aperture to the outside of the vessel and the resulting droplet is deposited on the conveyor.
11. A process according to claim 10, in which droplets of the molten dyestuff are formed by extrusion from two coaxial cylindrical vessels, each having apertures in the circumferential wall thereof, the outer vessel rotating about the inner vessel whereby the apertures in the inner vessel coincide intermittently with the apertures in the outer vessel during relative rotation between the vessels, the molten dyestuff being fed axially into the inner vessel and radially out through the apertures in the inner vessel and, intermittently, through the apertures in the outer vessel to form droplets.
12. A process according to any of claims 9 to 11, in which the apertures are circular.
13. A process according to claim 12, in which the diameter of the apertures is between one third and a half of the diameter of the required pastille diameter.
14. A process according to any of claims 5 to 13, in which the dyestuff is air-sensitive and the process is effected in an atmosphere of nitrogen.
15. A dyestuff according to any of claims 1 to 4 which is a colour former.
16. A colour former according to claim 15 which is selected from the classes consisting of 3,3-bis(aminophenyl)phthalides, 3-indolyl-3-aminophenylaza- or -diazaphthalides, 3,3-bis (indolyl)phthalides, 2-alkyl-6-dialkylaminofluorans, 6-dialkylamino-2-dibenzylaminofluorans, 6-diallylamino-3-methyl-2-arylaminofluorans, 3 ,6-bisalkoxy- fluorans, 3,6-bis(diarylamino)fluorans, leukoauramines, spiropyrans, spirodipyrans, benzoxazines, chromenopyrazoles, chromenoindoles, phenoxazines, phenothiazines, quinazolines, bisquinazolines, rhodamine lactams, carbazolylmethanes and triarylmethane leuko dyes.
17. A dyestuff in pastille form, substantially as described in the Example.
18. A process for the production of a dyestuff in pastille form, substantially as described in the Example.