A process for producing successive droplets of ink of different sizes

Claim 2

A process for producing successive droplets of ink of different sizes, comprising the steps of supplying a thermal ink jet drop ejector including a container (24) holding a volume of ink, an orifice (26) in one wall (22) of the container, and a heat source (30) for heating the ink, characterized by ejecting a first droplet of ink by heating the ink with the heat source (30) operated under two different conditions of heat production, a first condition of heat production wherein the heat output of the heat source is less than that required to vaporize any ink, and thereafter a second condition of heat production wherein the heat output of the heat source is greater than that required to vaporize a volume of the ink, thereby ejecting a first droplet of ink through the orifice; and ejecting a second droplet of ink by heating the ink with the heat source operated under two different conditions of heat production, a first condition of heat production wherein the heat output of the heat source is less than that required to vaporize any ink, and the heating of the ink is different from the heating of the ink during the first condition of heat pro­duction in the step of ejecting a first droplet of ink, and thereafter a second condition of heat production wherein the heat output of the heat source is greater than that required to vaporize a volume of the ink, thereby ejecting a second droplet of ink through the orifice (26).

Claim 3

The process of claim 1, characterized in that the time duration of heating ink during the first condition of heat production in the step of ejecting a second droplet is greater than the time duration of heating ink during the first condition of heat production in the step of ejecting a first droplet.

Claim 4

3 The process of claim 1 or 2, characte­rized in that the rate of introducing heat into the ink during the first condition of heat production portion of the step of ejecting a second droplet is greater than the rate of intro­ducing heat into the ink during the first condition of heat production portion of the step of ejecting a first droplet.

Claim 5

The process of one of claims 1 to 3, cha­racterized in that the total heat introduced into the ink under the first condition of heat production portion of the step of ejecting a second droplet is greater than the total heat introduced into the ink under the first condition of heat production portion of the step of ejecting a first droplet.

Claim 6

The process of one of claims 1 to 4, cha­racterized in that the first condition of heat production portion of the step of ejecting a first droplet involves a single pulse of heat.

Claim 7

The process of claim 5, characterized in that the single pulse is continuous with a pulse of heating in the second condition of heat production of the step of ejecting a first droplet.

Claim 8

The process of one of claims 1 to 6, cha­racterized in that the second condition of heat production in the step of ejecting a first droplet is the same as the second condition of heat production in the step of ejecting a second droplet.

Claim 9

A process according to the precharacterizing part of claim 1, characterized in that for ejecting a first droplet of ink the ink is heated to a first temperature insufficient to nucleate a vapor bubble in the ink; and thereafter the ink is heated to a second temperature sufficient to nucleate a vapor bubble in the ink and drive a droplet of ink through the orifice, the heating to the second temperature to occur at a time sufficiently shortly after the heating to the first temperature that the ink has not cooled to its initial temperature; and for ejecting a second droplet of ink the ink is heated to a first temperature insufficient to nucleate a vapor bubble in the ink, the first temperature in the step of ejecting a second droplet being different from the first temperature in the step of ejecting a first droplet; and thereafter the ink is heated to a second temperature suffi­cient to nucleate a vapor bubble in the ink and drive a droplet of ink through the orifice, the heating to the second temperature to occur at a time sufficiently shortly after the heating to the first temperature that the ink has not cooled to its initial temperature.

Claim 10

A process according to the precharacterizing part of claim 1, characterized by ejecting a first droplet of ink by heating the ink with the heat source operating at a heat output greater than that required to vaporize a volume of the ink; and ejecting a second droplet of ink by heating the ink with the heat source operated under two different conditions of heat production, a first condition of heat production wherein the heat output of the heat source is less than that required to vaporize any ink; and thereafter a second condition of heat production wherein the heat output of the heat source is greater than that required to vaporize a volume of the ink, thereby ejecting a second droplet of ink through the orifice.

Claim 11

The process of claim 9, including the additional step, after the step of supplying and before the step of ejecting a first droplet, of heating the ink with the heat source operated so that the heat output is less than that required to vaporize any ink.

Claim 12

The process of one of claims 1 to 10, cha­racterzed in that the heat source is an electrical resistance heater (30) located in the wall (38) of the container (24).

Claim 13

A process according to one of claims 1 to 10, characterized in that the heat source is an electrical resistance heater (28) located in the wall of the container in proximity to the orifice (26), that a power supply (50) is connected to the electrical resistance heater (30), that a first electrical precursor signal (62) is applied to the resistance heater (30) from the power supply (50) to preheat the ink adjacent the resistance heater, the precursor signal having insufficient energy to cause vaporization of the ink in the container, applying a first electrical ejector signal (60) to the resistance heater (30) from the power supply (50) to eject a droplet of ink, the ejector signal having sufficient energy to vaporize ink adjacent the resistance heater, the ejector signal being applied while the ink adjacent the resistance heater is still heated from applica­tion of the precursor signal; applying a second electrical precursor signal (62′) to the resistance heater from the power supply to preheat the ink adjacent the resistance heater, the precursor signal having insufficient energy to cause vaporization of the ink in the container, the second electrical precursor signal being different from the first electrical precursor signal, and applying a second electrical ejector signal (60′) to the resistance heater from the power supply to eject a droplet of ink, the ejector signal having sufficient energy to vaporize ink adjacent the resistance heater, the ejector signal being applied while the ink adjacent the resistance heater is still heated from applica­tion of the precursor signal.

Claim 14

The process of claim 12, characterized in that each precursor signal (62,62′) is applied as a single pulse, and each ejector signal (60,60′) is applied immediately upon completion of the precursor signal (Fig. 3).

Claim 15

The process of claim 12, characterized in that each precursor signal (62,62′) is applied as a succession of pulses (64) (Fig. 4).

Claim 16

The process of claim 12 or 14, characte­rized in that each ejector signal (60,60′) is applied as a single pulse having a square leading edge (Fig. 4,5):