INK-JET PRINTING HEAD AND METHOD OF MAKING SAID HEAD

Abstract: An ink-jet printing head used on the ink-jet printer, which is characterized in that a water-repellent layer (21) comprising a uniform layer of polymer including fluorine is formed on the surface of a nozzle from which ink is jetted. Said water-repellent layer can be formed to be solid and homogeneous by the use of polymer soluble in solvent and including fluorine, and thus an ink-jet printing head excellent in persistence of water-repellent characteristic and effect and durability is provided by a comparatively simple method.

Description: Technical Field The present invention relates to an ink jet recording head having an excellent water repellency for use in an ink jet recording device and a process for producing the same. Background Art A material such as glass, a metal or a resin is used for an ink jet recording head. In the use of a water-based ink in an ink jet recording head, when the water repellency of the surface of a nozzle is unsatisfactory, droplets of an ink are liable to adhere to the surface of the nozzle, which spoils the rectilinearity of jetted ink droplets, so that it often becomes impossible to conduct recording due to occurrence of troubles such as disturbance of setting. For this reason, the surface of a nozzle which is a portion for jetting an ink has hitherto been subjected to a treatment for rendering the surface of the nozzle water-repellent. For example, a proposal has been made on a method wherein a particle of a water-repellent material is deposited on the surface of a nozzle, for example, by using a dispersion of carbon fluoride particles in an epoxy matrix (see Japanese Patent Application Laid-Open No. 157765/1982) and vacuum baking and plasma polymerization (see Japanese Patent Application Laid-Open Nos. 183161/1985 and 176059/1984) to render the surface of the nozzle water-repellent. In the above-described conventional treatment for rendering the surface of the nozzle water-repellent, it is not always easy to form a smooth repellent surface free from any defect such as a pinhole. This causes properties to be varied from product to product, and the properties to change with the elapse of time. Further, in the electrostatic powder coating, the baking temperature should be 300°C or above. In the case of a metal, the dimensional accuracy is spoiled, and it is impossible to apply this method to a resin. When use is made of vacuum deposition, a large device should be used and it is difficult to conduct the process control. Further, in this method, since the bonding strength is insufficient, only a product having an insufficient bonding strength can be obtained. The present invention can solve the above-described problem, and an object of the present invention is to provide an ink jet recording head which is excellent in the water repellency of the surface of the nozzle, the persistence of the water repellency and the durability and enables a high printing quality to be maintained for a long period of time, and a process for producing the same. Ink jet recording devices in which a water-repellent layer of a fluoropolymer is formed on the surface of a nozzle are disclosed in JP-A 62-202743, in IBM Technical Disclosure Bulletin, Vol. 22, No. 5, October 1979, Pages 1965 and 1966, and in JP-A 58-124661. Disclosure of the Invention The present invention provides an ink jet recording head for use in an ink jet recording device, wherein a water-repellent layer comprising a homogeneous layer comprising an LB film of a fluoropolymer is formed on the surface of a nozzle for jetting an ink. The invention also provides a process for producing an ink jet recording head for use in an ink jet recording device, comprising subjecting the surface of a nozzle for jetting an ink of the ink jet recording head to a treatment for rendering the surface of the nozzle water-repellent, characterised in that the process comprises the steps of: preparing a polymer solution of a fluoropolymer dissolved in a solvent; spreading the polymer solution on the surface of water; evaporating the solvent in the thus spread polymer solution to form a Langmuir film from the resultant spread film; bringing the resultant Langmuir film into contact with the surface of the nozzle to transfer the resultant Langmuir film therein to form an LB film on a predetermined portion of the surface of the nozzle. In the treatment for rendering the surface of the nozzle water-repellent, since the contact angle of water to the surface of the nozzle should be at least 90°, preferably at least 100°, the polarizability is so small that it is useful to introduce fluorine having a remarkably small inter-molecular cohesive force. Although a fluoropolymer represented by polytetrafluoroethylene has excellent features such as heat resistance, chemical resistance and weather resistance, it is insoluble in a solvent, so that only powder coating can be applied to the fluoropolymer. This makes it possible to attain a good water-repellent property. Brief Description of Drawings Fig. 1 is a schematic cross-sectional view of an ink jet recording head according to an embodiment of the present invention; Fig. 2 is a schematic cross-sectional view of an ink jet recording head according to an embodiment of the present invention; Figs. 3 and 4 are explanatory views showing a process for forming a water-repellent layer according to a water surface spreading method; Fig. 5 is a typical cross-sectional view showing the steps of rendering the surface of a nozzle water-repellent; and Figs. 6 and 7 are explanatory views showing a process for forming a water-repellent layer according to a LB film forming method. Best Mode for Carrying Out the Invention Embodiments of the present invention will now be described. The ink jet recording head according to the present invention is mounted on an ink jet recording device and characterized in that a water-repellent layer comprising a homogeneous layer of a fluoropolymer is formed on the surface of a nozzle for jetting an ink. The above-described water-repellent layer is formed through the use of a solvent-soluble fluoropolymer. The solvent-soluble fluoropolymer is preferably amorphous. Specific preferred examples of the solvent-soluble fluoropolymer include polydiperfluoroalkyl fumarate, Teflon AF (trademark, De Pont (E.I.) de Nemours & Co), solvent-soluble fluoropolymers such as CYTOP (trademark, Asahi Glass Co., ltd.) and alternating copolymers of fluoroethylenes with hydrocarbon ethylenes such as an alternating copolymer of diperfluoroalkyl fumarate with styrene, an alternating copolymer of ethylene trifluoride chloride with a vinyl ether and an alternating copolymer of ethylene tetrafluoride with a vinyl ester, and their analogues and derivatives. Preferred examples of the solvent include fluorinated liquids include Fluorinert (trademark, 3M Co.), Garden (trademark, Montefluos), trifluoromethylbenzene and hydrochlorofluorocarbon. The concentration of the fluoropolymer in the fluoropolymer solution is preferably 0.01 to 7 % by weight, still preferably 0.1 to 5 % by weight. Since the above-described fluoropolymer is solvent-soluble, it is possible to form a water-repellent layer through the use of the fluoropolymer in a solution form according to a coating method or a transfer method. The water-repellent layer thus formed comprises a dense, homogeneous film comprising a homogeneous layer or continuous layer of a fluoropolymer, and it is believed that such a film structure contributes to a remarkable improvement in the water-repellent property and the persistence of the effect of water repellency. In the present invention, it is also possible to form a water-repellent layer through a coupling compound layer for the purpose of further improving the adhesion between the water repellent layer and the surface of the nozzle. A further feature of the present invention is that the water-repellent layer can be formed by simple and rapid methods, for example, a coating method such as dipping and a transfer method which will be described later. In the above-described LB film, at least one layer may be laminated to a desired thickness. A more homogeneous and dense water-repellent layer can be formed by conducting a heat treatment after the transfer of the LB film. Prior to the transfer of the polymer layer, a coupling compound layer can be formed on the surface of the nozzle, and a combination of the transfer method with the formation of the coupling compound layer enables a water-repellent layer having an excellent adhesion and a large thickness to be formed. Methods of rendering the surface of the nozzle water-repellent including a method of forming a coupling compound layer will now be described. At the outset, the nozzle plate is immersed in a coupling solution comprising a coupling compound and a solvent and then in a solvent. The immersion of the nozzle plate in a solvent advantageously has the effect of making the thickness of coating of the coupling compound uniform to further stabilize the adhesion between the water-repellent layer and the surface of the nozzle plate. Water and alcohols, such as methanol and ethanol, can be used as the solvent for the coupling solution. When water is used as the solvent, the handleability becomes better. Further, since the surface tension is so large that it is possible to prevent the coupling compound from penetrating into the hole in the nozzle. The transferred polymer layer is then baked. It is preferred to conduct the baking at a temperature not below the glass transition point of the polymer. The baking enables the volatile solvent contained in the polymer layer to be completely removed. Further, the present inventors have found that the heating of the transferred polymer layer to a temperature not below the glass transition point of the polymer leads to an increase in the fluidity of the polymer layer which improves the coating property and further contributes to an improvement in the adhesion. Further, in the above-described method, the following procedure may be used. After exposure of the surface of the nozzle plate to an ozone atmosphere, a coupling layer is formed, and a water-repellent layer is then formed. Alternatively, after the formation of the coupling layer, the surface of the coupling layer may be exposed to an ozone atmosphere followed by the formation of a water-repellent layer. The surface cleaning treatment wherein use is made of ozone removes stains on the surface, which contributes to a further improvement in the adhesion of the formed layer. The ozone atmosphere can be formed by irradiation with oxygen plasma or ultraviolet rays. The present invention will now be described in more detail with reference to the following embodiments. Embodiment G In the process according to this embodiment, an ink jet recording head comprising a fluoropolymer layer formed on the surface of a nozzle for jetting an ink is produced by spreading a solution of a fluoropolymer dissolved in a solvent on the surface of water, evaporating the solvent and bringing the spread film into contact with the surface of a nozzle. In the treatment for rendering the surface of the nozzle water-repellent, since the contact angle of water to the surface of the nozzle should be at least 90°, preferably at least 100°, the polarizability is so small that it is indispensable to introduce fluorine having a remarkably small inter-molecular cohesive force. Further, in the treatment for rendering the surface of the nozzle water-repellent, a high adhesion is separately required from the viewpoint of use. The fluoropolymer represented by polyethylene tetrafluoride has excellent features such as heat resistance, chemical resistance and weather resistance. It, however, is insoluble in a solvent, so that, as described above, only powder coating can be applied thereto. Therefore, not only the film strength is low, but also the adhesion at the interface is remarkably low. In recent years, a copolymer of a solvent-soluble polymer with a fluoropolymer and a synthetic polymer having a special fluorine-containing side chain have become prepared. Since these polymers can maintain properties of the conventional fluoropolymers and are soluble in a solvent, a smooth surface free from a pinhole can be easily prepared by coating. In order to attain a film strength and a bonding strength between the film and the substrate derived from the film strength, it is indispensable for the molecular weight to be increased prior to the formation of the film. When a solution of a fluoropolymer dissolved in a solvent is spread on the surface of water and the solvent is then evaporated, a water surface spread film of a fluoropolymer is formed. The film thickness can be regulated by preparing a calibration curve and regulating the amount of dropping of the solution, the concentration of the solution, etc. When the surface of a nozzle is brought into contact with the surface of water, the water surface spread film of a fluoropolymer is transferred to only a portion which has been brought into contact with the spread film but not transferred within the nozzle. Even in a failure in operation, the inner diameter of the nozzle is merely reduced by the film thickness of the water surface spread film, so that the water surface spread film enters the inside of the nozzle by the same distance as the inner diameter of the nozzle at the maximum. Ink repellency can be attained even when the thickness of the fluoropolymer film is as small as about 10 nm (100 Å). Since the nozzle diameter is 100 µm or less, there occurs no problem in the practical use. The water surface spread film of a fluoropolymer has a sufficient film strength. A sufficient film strength can be obtained by transferring a water surface spread film of a fluoropolymer on the surface of a nozzle and heat-treating the transferred film. If necessary, the transfer of the water surface spread film of a fluoropolymer on the surface of the nozzle can be repeated a plurality of times for the purpose of enhancing the ink repellency. Example G1 Fig. 2 is a schematic view of an ink jet recording head. Numeral 101 designates a pressure chamber which is a portion for obtaining a pressure used in the ejection of an ink by means of a PZT element or a heating element. Numeral 102 designates an ink passage, and numeral 103 designates an ink jet nozzle. Fig. 3 is a typical cross-sectional view showing the step of treatment for rendering the surface of a nozzle water-repellent. Fig. 3 (a) shows a state obtained when "Teflon AF" (manufactured by De Pont (E.I.) de Nemours & Co) is dissolved in a fluorocarbon solvent and the solution is spread on the surface of water. Although the concentration of the solution and the amount of dropping of the solution can be suitably selected, in this example, a solution having a concentration of 0.05 % by weight was prepared, the amount of solution capable of forming a 0.1 µm-thick polymer layer of "Teflon AF" was calculated, and the solution in the determined amount was dropped on the surface of water. Fig. 3 (b) shows a state obtained when the surface of a nozzle comprising an acrylic resin is brought into contact with the water surface spread film of a fluoropolymer formed by evaporating the fluorocarbon solvent. It is not always necessary that the surface of the nozzle be brought into contact with the surface of water in a parallel manner, and the surface of the nozzle may be brought into contact with the surface of water in a slightly inclined state. Further, the nozzle may be submerged into the water to some extent. Fig. 3 (c) shows a state obtained when a nozzle is pulled up from the surface of water to transfer a water surface spread film of a fluoropolymer to the surface of the nozzle. Fig. 4 is an enlarged view of the nozzle portion for jetting an ink shown in Fig. 3 (c). When the surface of the nozzle was brought into contact with the surface of water, the water surface spread film of a fluoropolymer was transferred to the surface of the nozzle only at a portion which had been brought into contact with the water surface spread film and the water surface spread film positioned at the hole of the nozzle was left as it was on the surface of water. The transferred film was heat-treated at 150°C for one hour, and then observed under a microscope. As a result, it was confirmed that the formed thin film was very dense and homogeneous. The film had a contact angle of 100° to water, that is, a high water repellency. Further, it was confirmed that the inside of the nozzle was subjected to no treatment for rendering it water-repellent. The ink jet recording head thus produced was mounted on a recording device, and a setting test was conducted. As a result, neither omission of dot nor disturbance of setting occurred. That is, it was confirmed that the nozzle was successfully rendered water-repellent. Then, the ink jet recording head was immersed in a dye ink at 70°C for 5 days, and a setting test was conducted in the same manner as that described above. The setting quality was the same as the initial property. That is, the recording head maintained a sufficient ink repellency. A rubbing test was conducted through the use of a silicone rubber while injecting a dye ink. As a result, the contact angle of the recording head to water was 100° or more after rubbing the recording head 5000 times. Thus, an ink jet recording head which gives rise to substantially no deterioration of the water repellency and can provide a high setting quality for a long period of time could be realized. Example G2 Fig. 1 is a typical cross-sectional view of an embodiment of an ink jet recording head. Numeral 1 designates a pressure chamber which is a portion for obtaining a pressure used in the ejection of an ink by means of a PZT element or a heating element. Numeral 3 designates an ink jet nozzle. Numeral 31 designates a first substrate provided with a pattern groove for an ink passage. Numeral 32 designates a second substrate. An ink passage is formed by laminating both members on top of the other. Numeral 33 designates a nozzle plate. Fig. 5 is a typical cross-sectional views showing the steps of rendering the surface of a nozzle water-repellent. Fig. 5 (a) is an enlarged view of the vicinity of a nozzle in a nozzle plate 43 comprising nickel prior to the treatment. Fig. 5 (b) shows a state obtained when "CYTOP" (manufactured by Asahi Glass Co., Ltd.) is dissolved in a fluorocarbon solvent, the solution is spread on the surface of water, a 0.05 µm-thick water surface spread film 31 of a fluoropolymer formed on the surface of water is transferred on the surface of a nozzle plate and the transferred film is heat-treated at 180°C for one hour. The observation of the thin film under a microscope has revealed that the formed thin film was very dense and homogeneous. The film had a contact angle of 108°C to water, that is, a high water repellency. Further, it was confirmed that the inside of the nozzle was subjected to no treatment for rendering it water-repellent. Fig. 5 (c) shows a state obtained when the nozzle plate subjected to the above-described surface treatment for rendering the surface of the nozzle water-repellent and a first substrate 52 comprising a polycarbonate resin are washed and dried and then bonded to each other with an adhesive 51. The ink jet recording head thus produced was mounted on a recording device, and a setting test was conducted. As a result, neither omission of dot nor disturbance of setting occurred. That is, it was confirmed that the nozzle was successfully rendered water-repellent. Then, the ink jet recording head was immersed in a dye ink at 70°C for 5 days, and a setting test was conducted in the same manner as that described above. The setting quality was the same as the initial property. That is, the recording head maintained a sufficient ink repellency. A rubbing test was conducted through the use of a silicone rubber while injecting a dye ink. As a result, the contact angle of the recording head to water was 100° or more after rubbing the recording head 5000 times. Thus, an ink jet recording head which gives rise to substantially no deterioration of the water repellency and can provide a high setting quality for a long period of time could be realized. Example G3 A high polymer of a diperfluoroalkyl fumarate/dialkyl fumarate copolymer was dissolved in a fluorocarbon solvent, and the solution was spread on the surface of water. The resultant water spread film of a fluoropolymer having a thickness of 0.01 µm was transferred on the surface of a nozzle in the same manner as that of Example 1. The above step of transfer was additionally repeated twice, and the resultant film was heat-treated at 120°C for one hour. The observation of the thin film under a microscope has revealed that the formed thin film was very dense and homogeneous. The film had a contact angle of 105° to water, that is, a high water repellency. Further, it was confirmed that the inside of the nozzle was subjected to substantially no treatment for rendering it water-repellent. The ink jet recording head thus produced was mounted on a recording device, and a setting test was conducted. As a result, neither omission of dot nor disturbance of setting occurred. That is, it was confirmed that the nozzle was successfully rendered water-repellent. Then, the ink jet recording head was immersed in a pigment ink at 70°C for 5 days, and a setting test was conducted in the same manner as that described above. The setting quality was the same as the initial property. That is, the recording head maintained a sufficient ink repellency. A rubbing test was conducted through the use of a silicone rubber while injecting a pigment ink. As a result, the contact angle of the recording head to water was 95° or more after rubbing the recording head 5000 times. Thus, an ink jet recording head which gives rise to substantially no deterioration of the water repellency and can provide a high setting quality for a long period of time could be realized. The present invention was described above with reference to examples. Materials used in the ink jet recording head and structures of the ink jet recording head and the kind of the fluoropolymer layer formed on the surface of the nozzle may be varied and are not particularly limited. Embodiment H In the present embodiment, a LB film of a fluoropolymer is formed on the surface of a nozzle for jetting an ink. The LB film is formed through the use of a polydiperfluoroalkyl fumarate or its copolymer as a fluoropolymer. In the process according to the present embodiment, a LB film is formed by spreading a solution of a fluoropolymer dissolved in a solvent on the surface of water, evaporating the solvent, moving a barrier to form a Langmuir film from the resultant spread film and forming a LB film of a fluoropolymer on the surface of a nozzle by a horizontal deposition method. In the treatment for rendering the surface of the nozzle water-repellent, since the contact angle of water to the surface of the nozzle should be at least 90°, preferably at least 100°, the polarizability is so small that it is indispensable to introduce fluorine having a remarkably small inter-molecular cohesive force. Further, in the treatment for rendering the surface of the nozzle water-repellent, a high adhesion is separately required from the viewpoint of use. The fluoropolymer represented by polyethylene tetrafluoride has excellent features such as heat resistance, chemical resistance and weather resistance. It, however, is insoluble in a solvent, so that, as described above, only powder coating can be applied thereto. Therefore, not only the film strength is low, but also the adhesion at the interface is remarkably low. In recent years, a copolymer of a solvent-soluble polymer with a fluoropolymer and a synthetic polymer having a special fluorine-containing side chain have become prepared. Since these polymers can maintain properties of the conventional fluoropolymers and are soluble in a solvent, a smooth surface free from a pinhole can be easily prepared by coating. In order to attain a film strength and a bonding strength between the film and the substrate derived from the film strength, it is indispensable for the molecular weight to be increased prior to the formation of the film. Since the LB film of a fluoropolymer is a dense film on a molecular level, a very homogeneous water repellent effect can be attained even when the film thickness is small. The surface energy of the LB film of a fluoropolymer having a laminate structure of at least one layer is equal to that of a solid film, so that a more complete ink repellency can be obtained. However, in a usual polymer, since the molecular skeleton has a high degree of freedom, the molecule is in a random coil form. In this case, no LB film is formed, and even when coating was conducted thick, the strength of the resultant film is smaller than that of the LB film and the homogeneity is poor due to the occurrence of interstice. By contrast, when the fluoropolymer is a polydiperfluoroalkyl fumarate or its copolymer, the molecule takes a rigid rod form due to a great bulk of the side chain, which enables the LB film to be easily formed. When a LB film is formed by spreading a solution of a fluoropolymer dissolved in a solvent on the surface of water, evaporating the solvent, moving a barrier to form a Langmuir film from the resultant spread film and forming a LB film of a fluoropolymer on the surface of a nozzle by a horizontal deposition method, only a portion which has been brought into contact with the Langmuir film is rendered ink-repellent and the inside of the nozzle is subjected to no treatment. Even in a failure in operation, the inner diameter of the nozzle is merely reduced by the film thickness of the LB film, so that the LB film enters the inside of the nozzle by the same distance as the inner diameter of the nozzle at the maximum. The LB film of a fluoropolymer has a thickness of about 1 nm (10 Å) per layer, while the diameter of the nozzle is about several tens of µm, so that there occurs no problem in the practical use. The LB film of a fluoropolymer has a sufficient film strength. Since the LB film is formed by a horizontal deposition method, no layer of water or the like is present between the surface of the nozzle and the LB film of a fluoropolymer, so that a satisfactory bonding strength can be obtained. If possible, it is preferred for the film to be heated to a temperature not below the glass transition temperature of the fluoropolymer. Example H1 Fig. 2 is a schematic view of an ink jet recording head. Numeral 101 designates a pressure chamber which is a portion for obtaining a pressure used in the ejection of an ink by means of a PZT element or a heating element. Numeral 102 designates an ink passage, and numeral 103 designates an ink jet nozzle. Fig. 6 is a typical cross-sectional view showing the step of treatment for rendering the surface of a nozzle water-repellent. Fig. 6 (a) shows a state (224) obtained when a polydiperfluoroalkyl fumarate is dissolved in a fluorocarbon solvent and the solution is spread on the surface of water. With respect to the concentration of the solution and the amount of dropping of solution, a preliminary experiment was conducted to prepare a π-A curve, the amount of the solution necessary for forming on the surface of water a monomolecular layer having an area of half of the area of the surface of water was calculated, and the solution in the calculated amount was dropped on the surface of water. Fig. 6 (b) shows a state obtained when after evaporation of the fluorocarbon solvent, a barrier 223 is moved to form a Langmuir film 225 and the surface of a nozzle comprising an acrylic resin in an ink jet recording head 226 is brought into contact with the Langmuir film. It is not always necessary that the surface of the nozzle be brought into contact with the surface of water in a parallel manner, and the surface of the nozzle may be brought into contact with the surface of water in a slightly inclined state. Further, the nozzle may be submerged into the water to some extent. Fig. 6 (c) shows a state obtained when a nozzle is pulled up from the surface of water to transfer the LB film of a fluoropolymer to the surface of the nozzle. Fig. 7 is an enlarged view of the nozzle portion for jetting an ink shown in Fig. 6 (c). When the surface of the nozzle was brought into contact with the surface of water, the LB film of a fluoropolymer 231 was transferred to the surface of the nozzle only at a portion which had been brought into contact with the LB film and the Langmuir film 225 positioned at the hole of the nozzle was left as it was on the surface of water. The transferred film was heat-treated at 150°C for one hour, and then observed under a microscope. As a result, it was confirmed that the formed thin film was very dense and homogeneous. The film had a contact angle of 110°C to water, that is, a high water repellency. Further, it was confirmed that the inside of the nozzle was subjected to no treatment for rendering it water-repellent. The ink jet recording head thus produced was mounted on a recording device, and a setting test was conducted. As a result, neither omission of dot nor disturbance of setting occurred. That is, it was confirmed that the nozzle was successfully rendered water-repellent. Then, the ink jet recording head was immersed in a dye ink at 70°C for 5 days, and a setting test was conducted in the same manner as that described above. The setting quality was the same as the initial property. That is, the recording head maintained a sufficient ink repellency. A rubbing test was conducted through the use of a silicone rubber while injecting a dye ink. As a result, the contact angle of the recording head to water was 100° or more after rubbing the recording head 5000 times. Thus, an ink jet recording head which gives rise to substantially no deterioration of the water repellency and can provide a high setting quality for a long period of time could be realized. Example H2 Fig. 1 is a typical cross-sectional view of an embodiment of an ink jet recording head. Numeral 1 designates a pressure chamber which is a portion for obtaining a pressure used in the ejection of an ink by means of a PZT element or a heating element. Numeral 2 designates an ink jet nozzle. Numeral 31 designates a first substrate provided with a pattern groove for an ink passage. Numeral 32 designates a second substrate. An ink passage is formed by laminating both members on top of the other. Numeral 33 designates a nozzle plate. Fig. 5 is a typical cross-sectional view showing the step of a treatment for rendering the surface of a nozzle water-repellent. Fig. 5 (a) is an enlarged view of the vicinity of a nozzle in a nozzle plate comprising nickel not subjected to the treatment. Fig. 5 (b) shows a state obtained when a high polymer of a polydiperfluoroalkyl fumarate/polydiisopropyl fumarate (4 : 1) is dissolved in a fluorocarbon solvent, the solution is spread on the surface of water, the spread film is compressed to form a Langmuir film and a LB film having a three-layer structure is formed on the surface of a nozzle plate and the LB film is heat-treated at 180°C for one hour. The observation under a microscope has revealed that the formed thin film was very dense and homogeneous. The film had a contact angle of 108° to water, that is, a high water repellency. Further, it was confirmed that the inside of the nozzle was subjected to no treatment for rendering it water-repellent. Fig. 5 (c) shows a state obtained when the nozzle plate subjected to the above-described treatment for rendering the surface of the nozzle water-repellent and a first substrate comprising a polysulfone resin are washed and dried and then bonded to each other with an adhesive. The ink jet recording head thus produced was mounted on a recording device, and a setting test was conducted. As a result, neither omission of dot nor disturbance of setting occurred. That is, it was confirmed that the nozzle was successfully rendered water-repellent. Then, the ink jet recording head was immersed in a dye ink at 70°C for 5 days, and a setting test was conducted in the same manner as that described above. The setting quality was the same as the initial property. That is, the recording head maintained a sufficient ink repellency. A rubbing test was conducted through the use of a silicone rubber while injecting a dye ink. As a result, the contact angle of the recording head to water was 100° or more after rubbing the recording head 5000 times. Thus, an ink jet recording head which gives rise to substantially no deterioration of the water repellency and can provide a high setting quality for a long period of time could be realized. Example H3 A high polymer of a polydiperfluoroalkyl fumarate/polyvinyl ester copolymer (9 : 1) was dissolved in a fluorocarbon solvent, the solution was spread on the surface of water, and the resultant film was compressed to form a Langmuir film which was then transferred to the surface of a nozzle in the same manner as that of Example H1. The above step of transfer was repeated four times, and the transferred LB film was heat-treated at 120°C for one hour. The observation under a microscope has revealed that the formed thin film was very dense and homogeneous. The film had a contact angle of 105° to water, that is, a high water repellency. Further, it was confirmed that the inside of the nozzle was subjected to no treatment for rendering it water-repellent. The ink jet recording head thus produced was mounted on a recording device, and a setting test was conducted. As a result, neither omission of dot nor disturbance of setting occurred. That is, it was confirmed that the nozzle was successfully rendered water-repellent. Then, the ink jet recording head was immersed in a pigment ink at 70°C for 5 days, and a setting test was conducted in the same manner as that described above. The setting quality was the same as the initial property. That is, the recording head maintained a sufficient ink repellency. A rubbing test was conducted through the use of a silicone rubber while injecting a pigment ink. As a result, the contact angle of the recording head to water was 95° or more after rubbing the recording head 5000 times. Thus, an ink jet recording head which gives rise to substantially no deterioration of the water repellency and can provide a high setting quality for a long period of time could be realized. Industrial Applicability The ink jet recording head of the present invention can be widely applied as a recording head to be mounted on an ink jet recording device such as an ink jet printer.

Claims: An ink jet recording head for use in an ink jet recording device, wherein a water-repellent layer comprising a homogeneous layer comprising an LB film of a fluoropolymer is formed on the surface of a nozzle for jetting an ink. An ink jet recording head according to claim 1, wherein the water-repellent layer comprises a solvent-soluble fluoropolymer. An ink jet recording head according to claim 2, wherein the solvent-soluble fluoropolymer has a fluorine atom in substantially all its molecular ends. An ink jet recording head according to claim 1, wherein the water-repellent layer is formed through a coupling compound layer. An ink jet recording head according to claim 1, wherein the water-repellent layer comprises an alternating copolymer of a fluoroethylene with a hydrocarbon ethylene or its analogue or derivative. An ink jet recording head according to claim 1, wherein the water-repellent layer comprises a fluorocyclic polymer. A process for producing an ink jet recording head for use in an ink jet recording device, comprising subjecting the surface of a nozzle for jetting an ink of the ink jet recording head to a treatment for rendering the surface of the nozzle water-repellent, characterised in that the process comprises the steps of: preparing a polymer solution of a fluoropolymer dissolved in a solvent; spreading the polymer solution on the surface of water; evaporating the solvent in the thus spread polymer solution to form a Langmuir film from the resultant spread film; bringing the resultant Langmuir film into contact with the surface of the nozzle to transfer the resultant Langmuir film therein to form an LB film on a predetermined portion of the surface of the nozzle. A process according to claim 7, wherein, after the transfer of the polymer layer, the transferred polymer layer is heat-treated. A process according to claim 7, wherein, prior to the transfer of the polymer layer, a coupling layer is formed on the surface of the nozzle. A process according to claim 7, wherein the surface of the transfer medium is smooth. A process according to claim 7, wherein the coupling compound layer is formed by immersing a nozzle in a coupling solution comprising a coupling compound and a solvent. A process according to claim 7, wherein, after exposure of the nozzle to an ozone atmosphere, the coupling layer is formed and the water-repellent layer is then formed. A process according to claim 7, wherein, after exposure of the nozzle to an ozone atmosphere, the water-repellent layer is formed through transfer.

Inventors: ATOBE MITSURO, KARASAWA YASUSHI, MIYASHITA SATORU, OUKI YASUHIRO, TAKEMOTO KIYOHIKO, ATOBE, MITSURO, KARASAWA, YASUSHI, MIYASHITA, SATORU, OUKI, YASUHIRO, TAKEMOTO, KIYOHIKO
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1992
Main classification: B41J2
IPC codes: B41J2