Electrostatic Printing Composition Comprising Didodecyl Sebacate

Abstract

Printing is effected with a hot melt type ink comprised of coloring material and a vehicle therefor and having a resistivity within the range of about 10.sup.6 to about 10.sup.11 ohm-centimeters and a viscosity in a range with an upper limit of about 50 centipoises when in a liquid phase. To that end, a stream of ink drops are drawn across and deflected in a span between an ink supply and a carrier for impingement thereon. The vehicle of the ink is comprised of at least one compound which is solid at room temperature, and has the general formula: in which each R and R' is an alkyl group containing from one to 12 carbon atoms.

Description

BACKGROUND OF THE INVENTION

This invention relates to electrostatic printing. Particularly it relates to the art of printing with an ink which electrostatically is moved across and deflected in a span between an ink supply and a record carrier for forming intelligence patterns thereon.

This art has been the subject of considerable investigation and is exemplified by U.S. Pat. No. 3,060,429 issued to C. R. Winston, Oct. 23, 1962. However, a dearth of literature available relative inks which can be effectively transferred thereby tends to limit practice of the processes because many, if not most, compositions which might be considered suitable in the art will not produce commercially satisfactory graphic products when used in heretofore known apparatuses. The inadequacy of such compositions results from absence therein of physical and electrical properties compatible with known processes.

In a copending application of R. J. Dunlavey and C. R. Winston, Ser. No. 853,825 filed Aug. 28, 1969, which is a continuation in part of Ser. No. 513,196, filed Dec. 13, 1965 and assigned to the assignee of the present application, parameters of viscosity and resistivity of inks suitable in the referenced art are set forth. But all however, additionally, should be of the hot melt type with a melting point at a sufficiently low level to enable manipulation without special clothing or equipment.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a process wherein a stream of a hot melt type ink comprised of coloring material and a vehicle therefor electrostatically is drawn across and deflected in a span between a supply nozzle and a carrier on which the ink impinges for forming record patterns is characterized by the vehicle. The latter is a material selected from class of compounds having the general formula

in which each R and R' is an alkyl group containing from one to 12 carbon atoms. In another aspect of the invention, the vehicle is proportioned such that the ink has a resistivity in the range of about 10.sup.6 to about 10.sup.11 ohm centimeters and a viscosity in a range with an upper limit of about 50 centipoises.

DESCRIPTION OF THE DRAWING

The ensuing detailed description of the invention refers to the accompanying drawing which is a perspective of a scheme of apparatus for effecting a process embodying the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawing, apparatus generally designated 10 comprises ink supply means or source shown as a reservoir 12 fluidally coupled to a nozzle 14. Heating means here shown as a heating element 16 is mounted relative the reservoir to maintain ink used in the process in a fluid phase to the end that continuous flow may be maintained to the nozzle tip and thereafter for printing on a carrier 18.

As used herein the term "printing" is not limited to intelligence formation by alphanumeric symbols but includes any graphic representation in the form of, for example, script and other pattern and symbol formation. The term "ink" means any material with which printing can be effected. The term "hot melt" defines ink and means in a solid phase at room temperature and in a liquid phase at some higher temperature, generally, to enable flow during transfer to a carrier.

In the illustrated apparatus, the nozzle is electrically conductive and has an inside diameter at its tip of about 0.0065 inch. Hydrostatic pressure of the ink for the process is sufficient to cause formation of a convex meniscus at the nozzle tip to the end that the ink will intrude into the electrostatic field generated according to ensuing description. Neither the nozzle diameter nor the level of hydrostatic pressure exerted in the direction of the carrier 18 is critical in the invention, as an ink stream suitable for printing can be drawn electrostatically from a puddle.

In accordance with the present invention ink is drawn in a single file stream 26 of drops electrostatically in a span 21 between the tip of nozzle 14 and carrier 18 through means including a valving or metering electrode 22. Said electrode is shown as a plate with a central aperture 23 aligned horizontally with the nozzle tip such that the path of flow of the ink will be normal to the plane of the plate and through said aperture. Herein the electrode is spaced from the nozzle tip about 0.045 inch.

Circuit means 24 are arranged between electrode 22 and nozzle 14 in a manner which may be conventional for producing an electrostatic field therebetween. A field of about 2,450 volts is employed in the illustrated embodiment to initiate formation of stream 26 and draw it in a line through aperture 23 from the nozzle. To produce the effect a DC potential of about -1,900 volts is applied to the nozzle while a DC potential of about 550 volts is applied to electrode 22. When the potential difference across the field is reduced to about 1,900 volts any flow from the nozzle will shut off.

Stream 26 may be electrostatically deflected vertically and horizontally in span 21 to form a pattern 29 on the carrier. Vertical deflection is achieved with a pair of vertical deflection electrodes 30 and 31 which are spaced downstream of valving electrode 22. Horizontal deflection is achieved with a pair of horizontal deflection electrodes 32 and 33 spaced downstream of the vertical deflection electrodes. The electrodes of each vertical and horizontal deflection pair are arranged to define the path of fluid flow toward said carrier.

In the illustrated embodiment, the vertical deflection electrodes are vertically spaced apart each from the other about 0.02 inch and spaced from valving electrode 22 about 0.035 inch. A non-deflecting DC potential averaging about 1,350 volts can be applied on them by circuit means 34. The horizontal deflection electrodes are spaced horizontally apart each from the other about 0.025 inch and from electrode 22 about 0.07 inch. A non-deflecting DC potential of about 2,100 volts can be applied on them by circuit means 36. Deflecting signals may be superimposed on the non-deflecting DC components of the deflecting electrodes by a conventional signal generator 38 from coded means (not shown) for producing a magnitude of stream deflection required for forming recognizable variation in pattern 29 while printing at the rate of 60 alphanumeric characters per second, horizontally spaced 10 per inch with the horizontal lines being spaced six per inch and on the carrier supported about 0.43 inch from the nozzle. Variation of about 560 volts between the electrodes of each pair of deflection electrodes is sufficient for any character.

A conductive platen 40 to which a DC potential of about 10,000 volts is applied by circuit means 42 during the illustrated printing process provides a backing for carrier 18 which herein is paper of sheeting thickness and is arranged to be driven transversely of stream 26 at any selected rate by means (not shown) which may be conventional. This last voltage is sufficient to insure movement of the stream in a straight line from the nozzle to the carrier when deflecting voltages are not applied and will draw the stream as deflected against the carrier to produce any selected pattern.

We have found that di-esters of sebacic acid which have been esterified with alcohols of paraffins having 12 or less carbon atoms in their chains provide excellent vehicles for pigments and dyes for producing high quality electrostatic printing. They have the desired characteristics of viscosity and resistivity at the operating temperature of the reservoir. That is to say, at such temperature an ink will have a viscosity within a range having an upper limit of 50 centipoises and a resistivity within the range of 10.sup.6 to 10.sup.11 ohm-centimeters. These compounds have the general formula:

in which each R and R' is an alkyl group containing from one to 12 carbon atoms.

However, the esters of the shorter chains, though producing good inks for electrostatic printing, do not provide solid inks at room temperature alone or in combination with other shorter chain esters. Specific compositions of high quality, with compounds of said general formula as vehicles, but not solid at room temperature are set forth in the following:

EXAMPLE I Ingredient % by Weight dibutyl sebacate 21.2 dioctyl sebacate 63.8 methyl violet toner 15.0

EXAMPLE II dibutyl sebacate 92 methyl violet toner 8

In practice and according to the invention, a hot melt type ink, which will not flow after striking the carrier, is employed.

Each of the inks according to the invention preferably has a melting point which does not exceed about 51.degree. C. and a freezing point which is not below 30.degree. C. This insures that the ink will be in a liquid phase at the operating temperature of the exemplary reservoir, namely, about 56.degree..+-.3.degree. C. and will be solid at generally encountered room temperatures to minimize its flow from the carrier.

Specific inks according to the invention are set forth in the following:

EXAMPLE III Ingredient % by Weight didodecyl sebacate 48.2 dibutyl sebacate 12.1 methyl violet toner 13.2 C.I. solvent yellow 29 13.3

EXAMPLE IV didodecyl sebacate 61.2 dibutyl sebacate 18.8 methyl violet toner 13.3 C.I. solvent yellow 29 6.7

EXAMPLE V didodecyl sebacate 72.0 dibutyl sebacate 18.0 C.I. solvent black 12 4.0 C.I. solvent yellow 29 6.0

EXAMPLE VI didodecyl sebacate 66.0 dimethyl sebacate 24.0 C.I solvent black 12 4.0 C.I. solvent yellow 29 6.0

EXAMPLE VII didodecyl sebacate 57.2 dibutyl sebacate 13.1 methyl violet toner 17.9 C.I. solvent black 12 2.8 C.I. yellow 29 9.0

EXAMPLE VIII didodecyl sebacate 53.8 dimethyl sebacate 13.4 methyl violet toner 19.2 C.I. solvent black 12 4.0 C.I. solvent yellow 29 9.6

EXAMPLE IX didodecyl sebacate 64.1 dimethyl sebacate 19.4 methyl violet toner 10.7 C.I. solvent black 12 1.9 C.I. solvent yellow 29 3.9

EXAMPLE X Ingredient % by Weight didodecyl sebacate 66.9 dimethyl sebacate 21.1 methyl violet toner 9.0 C.I. solvent yellow 29 3.0

EXAMPLE XI didodecyl sebacate 88.6 methyl violet toner 11.4 EXAMPLE XII didodecyl sebacate 93.0 C.I. solvent black 12 4.2 C.I. solvent yellow 29 2.8

EXAMPLE XIII didodecyl sebacate 85.2 methyl violet toner 11.0 C.I. solvent yellow 29 3.8

The inks according to the invention comprise a carrier and a dye or pigment with proportions which may vary over a wide range. Specific effective ink compositions illustrative of the range of ingredients follow:

EXAMPLE XIV Ingredient % by Weight didodecyl sebacate 46.1 dibutyl sebacate 11.5 methyl violet toner 25.6 C.I. solvent black 12 4.0 C.I. solvent yellow 29 12.8

EXAMPLE XV didodecyl sebacate 97.5 C.I. solvent black 12 1.5 C.I. solvent yellow 29 1.0

The methyl violet toner of the examples comprises about 40 percent methyl violet tannate in a transparent yellow mineral oil carrier. It is a product of Ad-Co Color Company, now merged with Magruder Color Company of Newark, N. J., and identified as RM-457-50.

Claims

We claim:

1. An ink composition of the hot melt type consisting essentially of a coloring material including a dye, and 85-97.5 percent by weight of a vehicle consisting essentially of a mixture of a major proportion of didodecyl sebacate with a minor proportion of a second dialkyl sebacate selected from the class consisting of dimethyl sebacate and dibutyl sebacate, the ink composition being further characterized in that the vehicle is solid at room temperature and is proportioned with the coloring material such that the ink composition, when a liquid phase, has a resistivity within the range of about 10.sup.6 to 10.sup.1 ohm-centimeters and a viscosity in a range with an upper limit of about 50 centipoises.

2. A composition according to claim 1 in which the amount of coloring material is in the range of about 2.5 to 28 percent by weight and the amount of the vehicle is in the range 97.5 to 72 percent by weight.

3. A composition according to claim 1 in which the coloring material is selected from the group consisting of C. I. solvent yellow 29, methyl violet tannate, C. I. solvent black 12, and mixtures of the foregoing.

4. A composition according to claim 1 in which the vehicle consists of a mixture of didodecyl sebacate in an amount in the range of about 46 to 72 percent by weight and said second sebacate in an amount in the range of about 24 to 12 percent by weight.

5. A composition according to claim 1 in which the melting point of the ink does not exceed about 54.4.degree. C. and the freezing point is not below about 30.degree. C.

6. As a hot-melt ink composition for electrostatic ink-jet printing in which the ink composition in a fluid phase at a printing temperature of approximately 53.degree. to 59.degree. C. is electrostatically formed into a stream of droplets which are deposited on a paper sheet to form characters, the composition consisting essentially of approximately 12 percent by weight of coloring material including a dye, and approximately 88 percent by weight of a vehicle consisting of approximately 67 percent by weight of didodecyl sebacate and approximately 21 percent by weight of dimethyl sebacate.

7. A composition according to claim 6, wherein the coloring material consists of approximately 9 percent by weight of methyl violet toner and approximately 3 percent by weight of C. I. solvent yellow 29.