Liquid ejection head and image forming apparatus

Abstract

The liquid ejection head includes: a nozzle plate formed with a nozzle through which a droplet of liquid is ejected; a liquid chamber which contains the liquid and is connected to the nozzle; and a pressure generating device which causes the liquid chamber to contract and expand, wherein: the nozzle has a first portion having a first diameter on a side from which the liquid is ejected, and a second portion having a second diameter on a side from which the liquid is supplied from the liquid chamber, the second diameter being not less than 2.5 times and not more than 5 times the first diameter; a non-wetting surface is formed on the nozzle plate at an inner face of the first portion of the nozzle and a face that contacts an outside air; a wetting surface is formed on an inner face of the nozzle other than the inner face of the first portion; and when starting ejection of the droplet of the liquid from the nozzle, force applied to the liquid inside the liquid chamber by the pressure generating device acts only in a direction which contracts volume inside the liquid chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures and wherein:

FIGS. 1A to 1D are illustrative diagrams of the initial stage of a pull ejection method for ejecting ink;

FIGS. 2A to 2E are illustrative diagrams of the latter stage of the pull ejection method;

FIGS. 3A to 3C are illustrative diagrams of the initial stage of a push ejection method for ejecting ink;

FIGS. 4A to 4E are illustrative diagrams of the latter stage of the push ejection method;

FIG. 5 is a cross-sectional diagram of the structure of a nozzle section of a liquid ejection head according to an embodiment of the present invention;

FIG. 6 is a cross-sectional diagram of the structure of the nozzle section, in order to explain the principles of the present invention;

FIG. 7 is a diagram showing the relationship between a nozzle diameter in a second nozzle plate and a refill time;

FIG. 8 is a cross-sectional diagram of the structure of another nozzle section, in order to explain further principles of the present invention;

FIG. 9 is a diagram showing the relationship between a taper angle of a nozzle region in the second nozzle plate and the refill time;

FIG. 10 is a general schematic drawing of an image forming apparatus according to an embodiment of the present invention;

FIG. 11 is a principal plan diagram of the periphery of a print unit in the image forming apparatus;

FIGS. 12A to 12C are plan view perspective diagrams showing embodiments of the composition of a liquid ejection head in the image forming apparatus;

FIG. 13 is a cross-sectional diagram of the liquid ejection head;

FIG. 14 is a drive waveform diagram for the liquid ejection head;

FIG. 15 is a further drive waveform diagram for the liquid ejection head;

FIG. 16 is a schematic drawing showing an approximate view of an ink supply system for the liquid ejection head;

FIG. 17 is a principal block diagram showing the system configuration of the image forming apparatus;

FIG. 18 is a diagram of the relationship between T2/D2 and the refill time; and

FIG. 19 is a diagram of the relationship between D2/D1 and T2/D2.

Claims

1. A liquid ejection head, comprising: a nozzle plate formed with a nozzle through which a droplet of liquid is ejected;a liquid chamber which contains the liquid and is connected to the nozzle; anda pressure generating device which causes the liquid chamber to contract and expand, wherein:the nozzle has a first portion having a first diameter on a side from which the liquid is ejected, and a second portion having a second diameter on a side from which the liquid is supplied from the liquid chamber, the second diameter being not less than 2.5 times and not more than 5 times the first diameter;a non-wetting surface is formed on the nozzle plate at an inner face of the first portion of the nozzle and a face that contacts an outside air;a wetting surface is formed on an inner face of the nozzle other than the inner face of the first portion; andwhen starting ejection of the droplet of the liquid from the nozzle, force applied to the liquid inside the liquid chamber by the pressure generating device acts only in a direction which contracts volume inside the liquid chamber.

2. A liquid ejection head, comprising: a nozzle plate formed with a nozzle through which a droplet of liquid is ejected;a liquid chamber which contains the liquid and is connected to the nozzle; anda pressure generating device which causes the liquid chamber to contract and expand, wherein:the nozzle has a first portion having a first diameter on a side from which the liquid is ejected, and a second portion having a shape tapered from the liquid chamber to the first portion, an angle formed by an inner surface of the first portion and an inner surface of the second portion being not less than 90° and not more than 120°;a non-wetting surface is formed on the nozzle plate at an inner face of the first portion of the nozzle and a face that contacts an outside air;a wetting surface is formed on an inner face of the nozzle other than the inner face of the first portion; andwhen starting ejection of the droplet of the liquid from the nozzle, force applied to the liquid inside the liquid chamber by the pressure generating device acts only in a direction which contracts volume inside the liquid chamber.

3. An image forming apparatus comprising the liquid ejection head as defined in claim 1.

4. An image forming apparatus comprising the liquid ejection head as defined in claim 2.