Of the presently known various printing systems, the ink jet printing system has been evaluated as a very effective non-impact printing system in that printing can be conducted at a high speed while substantially not causing noise.
A typical ink jet printing head used in the ink jet printing system is of the configuration shown in FIG. 2.
In FIG. 2, reference numeral 1 indicates a substrate for an ink jet printing head. The substrate is constituted by a glass, aluminum or silicon material. Reference numeral 4 indicates liquid pathways formed by joining the substrate 1 to a top plate 2 provided with a plurality of grooves which define liquid pathways. In each of the liquid pathways 4, there is installed an energy generating element 3 for generating energy for discharging ink. Reference numeral 7 indicates a nozzle plate provided with a plurality of discharging outlets 7a each being communicated with the corresponding liquid pathway 4. The nozzle plate 7 is joined to the assembly comprising the substrate 1 and the top plate 2 to establish an ink jet printing head.
In the ink jet printing head thus configured, when printing is conducted by discharging ink droplets through the discharging outlets of the ink jet printing head, part of those ink droplets are sometimes dropped to deposit on the discharging outlet face at which the discharging outlets are arranged. There is a tendency that such an ink deposit on the discharging outlet face comes to contact with ink droplets successively discharged from the discharging outlets, causing the flying direction of the ink droplets discharged to be deviated, and or the ink deposit causes a load to the ink droplets discharged and so reduces their discharge speed. These phenomena are apparently found in the case where the ink discharging is conducted at high frequency. And, in the case of the high speed printing system in which ink discharging is conducted at a frequency of 10,000 or more times per second, the occurrence of these phenomena causes serious problems such that not only the ink discharging direction but also the ink discharging speed are varied and in addition to this, in the worst case, the foregoing ink deposits on the discharging outlet face sometimes plug up the discharging outlets to prevent ink droplets from being discharged from the discharging outlets.
In order to prevent these problems from occurring, there is a proposal of applying a water repellent treatment at peripheral portions of the arrangement of the discharging outlets of the ink jet printing head. In the case of subjecting the peripheral portions of the arrangement of the discharging outlets to water repellent treatment in accordance with this proposal, it is possible to prevent ink deposition from occurring at the peripheral portions of the arrangement of the discharging outlets so that the foregoing problems can be solved, to some extent. It is known that the water repellent treatment herein is desired to be conducted for the discharging outlet face only. The reason for this is due to the fact that in the case where the water repellent treatment is applied on portions other than the discharging outlet face, particularly, the liquid pathways, a reduction is caused in the capillary action effected for the ink supply in the liquid pathways to diminish the ink supply efficiency.
The above water repellent treatment to the discharging outlet face is usually conducted so that a distinct contrast is established between the discharging outlet face and the liquid pathway inner walls, in order to enable stable discharging for the discharging outlets.
Now, the discharging outlet face thus applied with the water repellent treatment desirably exhibits its water-repellent property in the earlier printing operations of the ink jet printing head, but as the ink jet printing head is repeatedly used, the water repellent material applied on the discharging outlet face is gradually oxidized by air or ink or is sometimes partially peeled off by the action of ink effused whereby the discharging outlet face is deteriorated in terms of the water-repellent property. In view of this, in the water repellent treatment of the discharging outlet face, it is necessary to have due care for the chemical stability and adhesion properties of the water repellent material applied.
Incidentally, even in the case where the discharging outlet face applied with the foregoing water repellent treatment is satisfactory in terms of the ink-repellent property, ink droplets are sometimes deposited thereon. These ink droplets deposited on the discharging outlet face are only slightly removed unless they are removed by way of an external force, specifically, by applying an external vibration so as to remove them or by wiping them off using a mechanical means. In the case where such ink droplets remain on the discharging outlet face without being removed, they collect and grow in size, forming large-sized ink droplets, wherein problems arise in that the discharging outlets are hindered by those large-sized ink droplets in terms of the ink discharging performance, the direction of ink discharged from the discharging outlets is deflected due to those large-sized ink droplets, or some of the discharging outlets are liable to be defective in terms of the ink discharging performance due to those large-sized ink droplets. In order to prevent these problems from occurring, the ink jet printing apparatus is usually provided with a wiping mechanism comprising a cleaning blade which serves to wipe the discharging outlet face in terms of conducting the recovery treatment for the ink jet printing head.
In general, such a recovery treatment mechanism in the ink jet printing apparatus comprises, in addition to the above wiping mechanism, a suction recovery mechanism including a pump or the like for removing an ink residue having an increased viscosity in the nozzle portions.
However, in order to comply with a demand for miniaturization of the ink jet printing head in recent years, the suction recovery mechanism is occasionally omitted. In the case of an ink jet printing apparatus with no suction recovery mechanism, an ink residue having an increased viscosity is often left in the vicinity of the arrangement of the discharging outlets without being removed. In order to remove such highly viscous ink residue, the wiping operation by means of the foregoing wiping mechanism has to be conducted while press-contacting the cleaning blade against the peripheral portions of the discharging outlets at a higher cleaning blade contact pressure than that employed in the case of the ordinary ink jet printing apparatus. In this case where the cleaning blade contact pressure is raised, there now may arise a problem such that the discharging outlet face applied with the water repellent treatment, i.e., the water repellent discharging outlet face, is gradually worn due to the press contact of the cleaning blade at an increased contact pressure upon conducting the wiping operation to deteriorate in terms of the water-repellent effect, making the ink discharging performance unstable. In this case, in addition to this problem, a further problem arises. That is, when either the water repellent discharging outlet face of the ink jet printing head or the cleaning blade accumulates foreign matter, there is a tendency for the water repellent discharging outlet face to be readily damaged due to the foreign matter upon conducting the wiping operation while press-contacting the cleaning blade against the discharging outlet face. Other than these problems, there is also a problem in that when trouble occurs in the transportation of a printing member such as a paper, the water repellent discharging outlet face is liable to be worn with such printing member, making the water repellent discharging outlet defective in terms of the water-repellent effect. In order for the water repellent discharging outlet face to be free of the above problems, it is required to be more sufficient in terms of the abrasion resistance than that required in the case of the ordinary ink jet printing apparatus.
Now, as above described, in the case of the high speed printing system in which ink discharging is conducted at a frequency of 10,000 or more times per second, the amount of ink discharged per unit period of time is relatively great and because of this, the opportunity for ink to be deposited on the peripheries of the discharging outlets of the ink jet printing head used is increased accordingly. In order to prevent the occurrence of problems caused by such ink deposits, it is necessary to conduct frequently the wiping operation using the cleaning blade for the ink jet printing head at a relatively shortened interval. In this respect, even in the case of the high speed printing system, it is required for the discharging outlet face of the ink jet printing head used to be sufficient enough in terms of the abrasion resistance.
Incidentally, Japanese Patent Laid-open application No. 211956/1992 discloses a technique of treating a discharging outlet face of an ink jet recording head so as to have a water-repellent property using a water repellent material comprising a polymer having a fluorine heterocyclic structure in the principal chain, in order to improve the discharging outlet face in terms of the abrasion resistance. However, the water repellent material used in this technique is not sufficient enough in terms of providing a satisfactory abrasion resistance to the discharging outlet face although it is sufficient in terms of providing a desirable water-repellent property thereto. Particularly, in the case of the foregoing ink jet printing apparatus in which the suction recovery mechanism is omitted and which requires the wiping operation to be conducted by press-contacting the cleaning blade against the discharging outlet face at an increased contact pressure, even if the discharging outlet face should be treated using the water repellent material, the discharging outlet face applied with the water repellent treatment is still insufficient in terms of the abrasion resistance, wherein the foregoing problems cannot be eliminated as desired.