Inkjet recording apparatus and inkjet recording method

Abstract

An object of the present invention is to provide a stainless steel nozzle plate for an inkjet head which has little deformation on the inner wall of the nozzle or at the nozzle tip, a method for manufacturing the same, and an inkjet head and an inkjet recording apparatus which use the nozzle plate for an inkjet head. [Solution] The nozzle plate for an inkjet head of the present invention is a nozzle plate for an inkjet head made of at least stainless steel, characterized in that the stainless steel is an austenitic stainless steel with a martensite phase content of 5.4% or less.

Description

Technical Field

[0001] The present invention relates to a nozzle plate for an inkjet head, a method for manufacturing the same, an inkjet head, and an inkjet recording apparatus. More specifically, the present invention relates to a stainless steel nozzle plate for an inkjet head with less deformation on the inner wall of the nozzle and the tip of the nozzle.

Background Art

[0002] An inkjet head discharges ink from a nozzle plate in which an actuator is arranged in each ink channel and an ink discharge port, that is, a nozzle communicating with each ink channel is formed.

[0003] Conventionally, as a base material for a nozzle plate for an inkjet head (hereinafter, also simply referred to as "nozzle plate"), stainless steel having excellent chemical stability against ink and durability against mechanical friction has been used. In particular, steel grades such as SUS304 and SUS316, which are austenitic stainless steels, are often used. These steel grades are produced generally and are more cost-effective than other steel grades. In addition, since the Cr content is relatively high and the corrosion resistance is excellent, it has excellent chemical stability as a base material for the nozzle plate in contact with ink.

[0004] As a method for forming a nozzle on a base material made of the above-described austenitic stainless steel, a method by laser processing (Non-Patent Document 1) and a method of forming a concave portion by punching and then polishing and removing the convex portion on the back surface (Patent Document 1) are known.

[0005] However, a nozzle plate in which nozzles are formed by laser processing using a conventional austenitic stainless steel as a base material has a problem that minute recesses (needle holes) are likely to occur on the inner wall of the nozzle.

[0006] Furthermore, even with the method of forming a recess by punching and then polishing off the protrusion on the back side, when conventional austenitic stainless steel is used as the base material, when forming the recess, plastic deformation causes streaky irregularities to form on the inner wall of the nozzle from the flow path side toward the nozzle tip (discharge direction tip), and when the protrusion on the back side is polished off, these streaky irregularities remain as burrs (protrusions) at the nozzle tip, which is a problem.

[0007] If the nozzle's inner wall has irregularities such as the aforementioned minute recesses or streaky uneven surfaces, air bubbles generated in the ink can get stuck, making nozzle breakage more likely. This increases the frequency of maintenance and reduces the operating rate of the inkjet recording device. Furthermore, if irregularities such as the aforementioned minute recesses, streaky uneven surfaces, and burrs exist near the nozzle tip, the ink ejection angle from that nozzle will bend, leading to variations in the landing position, uneven drawing, streaks, and pattern breaks, resulting in a decrease in drawing quality.

[0008] Therefore, there is a need for stainless steel nozzle plates for inkjet heads that have fewer irregularities such as minute recesses, streaky unevenness, and burrs on the inner wall and tip of the nozzle. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Patent No. 3755332 [Non-patent literature]

[0010] [Non-Patent Document 1] Xinbing Liu "Industrial applications of ultrahigh precision short-pulse laser processing (Invited Paper)", Proc. SPIE 5713, Photon Processing in Microelectronics and Photonics IV, (12 April 2005) [Overview of the project] [Problems that the invention aims to solve]

[0011] This invention has been made in view of the above-mentioned problems and circumstances, and its objective is to provide a stainless steel nozzle plate for an inkjet head that has fewer irregularities in the inner wall of the nozzle and the nozzle tip, a method for manufacturing the same, an inkjet head using the inkjet head nozzle plate, and an inkjet recording device. [Means for solving the problem]

[0012] In order to solve the above problems, the inventors investigated the causes of the above problems and found that by using stainless steel having a specific crystal structure ratio, it is possible to provide a stainless steel nozzle plate for an inkjet head with fewer irregularities in the inner wall of the nozzle and the nozzle tip, thus leading to the present invention. In other words, the above-mentioned problems according to the present invention are solved by the following means.

[0013] 1. An inkjet head nozzle plate made of at least stainless steel, The nozzle plate for an inkjet head is characterized in that the stainless steel is an austenitic stainless steel having a martensitic phase content of 5.4% or less.

[0014] 2. An inkjet head nozzle plate made of at least stainless steel, The nozzle plate for an inkjet head is characterized in that the stainless steel has an area ratio of 92.0% or more of face-centered cubic crystals and an area ratio of 5.4% or less of body-centered cubic crystals, as measured by electron beam backscattering analysis.

[0015] 3. The nozzle plate for an inkjet head according to paragraph 1 or 2, characterized in that the stainless steel is stainless steel having a frequency-average grain size of 0.9 μm or less as measured by electron beam backscattering analysis.

[0016] 4. The nozzle plate for an inkjet head according to any one of claims 1 to 3, wherein the stainless steel has an area ratio weighted average crystal grain size of 2.3 μm or less measured by an electron backscatter diffraction analysis method.

[0017] 5. The nozzle plate for an inkjet head according to any one of claims 1 to 4, wherein the stainless steel has a ratio of the number average crystal grain size measured by an electron backscatter diffraction analysis method to the opening diameter of the nozzle tip of 4.7% or less.

[0018] 6. The nozzle plate for an inkjet head according to any one of claims 1 to 5, wherein the stainless steel has a ratio of the area ratio weighted average crystal grain size measured by an electron backscatter diffraction analysis method to the opening diameter of the nozzle tip of 12.0% or less.

[0019] 7. A method for manufacturing a nozzle plate for an inkjet head, which manufactures the nozzle plate for an inkjet head according to any one of claims 1 to 6, characterized by having a step of forming a nozzle by laser processing. A method for manufacturing a nozzle plate for an inkjet head, characterized by having a step of forming a concave portion by punching and then forming a nozzle by polishing and removing a convex portion on the back surface.

[0020] 8. A method for manufacturing a nozzle plate for an inkjet head, which manufactures the nozzle plate for an inkjet head according to any one of claims 1 to 6, characterized by having a step of forming a concave portion by punching and then forming a nozzle by polishing and removing a convex portion on the back surface. A method for manufacturing a nozzle plate for an inkjet head, characterized by having a step of forming a concave portion by punching and then forming a nozzle by polishing and removing a convex portion on the back surface.

[0021] 9. An inkjet head characterized by using the nozzle plate for an inkjet head according to any one of claims 1 to 6.

[0022] 10. An inkjet recording apparatus comprising the inkjet head according to claim 9.

Advantages of the Invention

[0023] By the above means of the present invention, it is possible to provide a nozzle plate for an inkjet head made of stainless steel with less irregularities on the inner wall of the nozzle and at the tip of the nozzle, a method for manufacturing the same, an inkjet head using the nozzle plate for the inkjet head, and an inkjet recording apparatus.

[0024] Although the mechanism of manifestation or the mechanism of action of the effects of the present invention is not clear, it is presumed as follows.

[0025] The present inventor has found that the cause of irregularities such as minute concave stripe-shaped irregularities and burrs generated when forming a nozzle in the conventionally used austenitic stainless steel lies in the martensite phase contained in minute amounts. Specifically, it has been found that when using an austenitic stainless steel in which the content ratio of the martensite phase is larger than 5.4%, the area ratio of the face-centered cubic crystal is smaller than 92.0%, and the area ratio of the body-centered cubic crystal is larger than 5.4%, irregularities can be remarkably generated in the formation of the nozzle.

[0026] The austenite phase and the martensite phase have different crystal structures. The austenite phase has a face-centered cubic structure, and the martensite phase has a body-centered cubic structure. Since the space filling rate of the unit lattice is different between the body-centered cubic structure and the face-centered cubic structure, the material physical properties are also different, which may affect the generation of irregularities on the inner wall of the nozzle and at the tip of the nozzle.

[0027] As an example, it is known that general martensitic stainless steel has a lower melting point and a higher thermal conductivity than austenitic stainless steel. From this, it is considered that the martensite phase has a higher thermal conductivity than the austenite phase and a higher laser ablation rate during laser processing. Therefore, in laser processing, if austenitic stainless steel contains a martensite phase as a separate phase, the minutely present martensite phase will be preferentially laser ablated, resulting in the formation of minute recesses (needle holes) on the inner wall of the nozzle.

[0028] Furthermore, as another example, common martensitic stainless steel tends to have a lower density and less elongation than austenitic stainless steel, making it less susceptible to plastic deformation under tensile load. From this, it can be considered that the martensitic phase is less susceptible to plastic deformation than the austenitic phase. Therefore, when austenitic stainless steel contains a martensite phase as a separate phase, a discrepancy occurs in the plastic deformation response between the austenite phase and the martensite phase when the stainless steel substrate undergoes plastic deformation during punching with a punch tool. As a result, it is thought that streaky irregularities may form on the inner wall of the nozzle, moving from the flow path side towards the nozzle tip side.

[0029] Furthermore, if such streaky irregularities are formed on the inner wall of the nozzle, it can cause burrs to form on the edge of the nozzle tip when the subsequent polishing and removal of the protrusions on the back surface is performed.

[0030] Therefore, as in the present invention, by using an austenitic stainless steel having a martensite phase content of 5.4% or less, or by using stainless steel in which the area ratio of face-centered cubic crystals measured by electron beam backscattering analysis is 92.0% or more and the area ratio of body-centered cubic crystals is 5.4% or less, the occurrence of deformities during nozzle formation can be suppressed.

[0031] These mechanisms of expression or action make it possible to provide stainless steel nozzle plates for inkjet heads with minimal deformation of the nozzle inner wall and nozzle tip. [Brief explanation of the drawing]

[0032] [Figure 1A]Optical microscope image of stainless steel A [Figure 1B] Optical microscope image of stainless steel B [Figure 1C] Optical microscope image of stainless steel C [Figure 2A] Grain map of stainless steel A obtained by EBSD measurement [Figure 2B] Crystal grain map of stainless steel B obtained by EBSD measurement [Figure 2C] Crystal grain map of stainless steel C obtained by EBSD measurement [Figure 3A] SEM image of the entire nozzle of a nozzle plate made of stainless steel A. [Figure 3B] SEM image of the entire nozzle of a nozzle plate made of stainless steel B. [Figure 3C] SEM image of the entire nozzle of a nozzle plate made of stainless steel C. [Figure 4A] SEM image of the inner wall of a nozzle plate made of stainless steel A. [Figure 4B] SEM image of the inner wall of a nozzle plate made of stainless steel B. [Figure 4C] SEM image of the inner wall of a nozzle plate made of stainless steel C. [Figure 5] SEM image of an irregularly shaped micro-indentation (needle hole) [Figure 6] Cross-sectional SEM image of a nozzle with irregularly shaped ridged and uneven surfaces and burrs. [Figure 7] Cross-sectional SEM image of a nozzle without irregularities [Modes for carrying out the invention]

[0033] In one embodiment, the inkjet head nozzle plate of the present invention is an inkjet head nozzle plate made of at least stainless steel, characterized in that the stainless steel is an austenitic stainless steel having a martensite phase content of 5.4% or less.

[0034] Furthermore, in one embodiment, the inkjet head nozzle plate of the present invention is an inkjet head nozzle plate made of at least stainless steel, characterized in that the stainless steel has an area ratio of face-centered cubic crystals of 92.0% or more and an area ratio of body-centered cubic crystals of 5.4% or less, as measured by electron beam backscattering analysis.

[0035] In the present invention, it is preferable that the stainless steel used in the inkjet head nozzle plate is stainless steel having a frequency-average grain size of 0.9 μm or less, as measured by electron beam backscattering analysis, in order to suppress the occurrence of deformities.

[0036] In the present invention, it is preferable that the stainless steel used for the inkjet head nozzle plate is stainless steel having an area-weighted average grain size of 2.3 μm or less, as measured by electron beam backscattering analysis, in order to suppress the occurrence of deformities.

[0037] In the present invention, it is preferable that the stainless steel used in the inkjet head nozzle plate is stainless steel in which the ratio of frequency-average grain size measured by electron beam backscattering analysis to the aperture diameter of the nozzle tip is 4.7% or less, as this can suppress the occurrence of deformities.

[0038] In the present invention, it is preferable that the stainless steel used for the inkjet head nozzle plate is stainless steel in which the ratio of area-weighted average grain size, measured by electron beam backscattering analysis, to the aperture diameter at the nozzle tip is 12.0% or less, as this can suppress the occurrence of deformities.

[0039] One embodiment of the present invention is a method for manufacturing an inkjet head nozzle plate, characterized by comprising a step of forming a nozzle by laser processing, for manufacturing an inkjet head nozzle plate of the present invention.

[0040] Furthermore, as one embodiment of the present invention, the method for manufacturing an inkjet head nozzle plate is a method for manufacturing an inkjet head nozzle plate of the present invention, characterized by comprising the step of forming a recess by punching, and then forming a nozzle by polishing off the protrusion on the back surface.

[0041] The nozzle plate for an inkjet head or an inkjet head using the same according to the present invention can be suitably used in an inkjet recording device.

[0042] The present invention, its components, and embodiments and models for carrying out the present invention will be described in detail below. In this application, "~" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0043] (1) Overview of the nozzle plate for inkjet heads of the present invention In one embodiment, the inkjet head nozzle plate of the present invention is an inkjet head nozzle plate made of at least stainless steel, characterized in that the stainless steel is an austenitic stainless steel having a martensite phase content of 5.4% or less.

[0044] Furthermore, in one embodiment, the inkjet head nozzle plate of the present invention is an inkjet head nozzle plate made of at least stainless steel, characterized in that the stainless steel has an area ratio of face-centered cubic crystals of 92.0% or more and an area ratio of body-centered cubic crystals of 5.4% or less, as measured by electron beam backscattering analysis.

[0045] In this application, "ink" is not limited to liquids containing dyes or pigments, but also includes liquids used for printing, recording, dyeing, etc., such as polymer materials like varnish, or liquids containing metal fine particles. Therefore, the ink ejected by the inkjet head nozzle plate of the present invention is not limited to liquids containing dyes or pigments.

[0046] (2) Crystal structure of stainless steel In this application, "austenitic stainless steel" refers to stainless steel whose main structure is austenite at room temperature. Examples include austenitic steels specified in JIS G 4304, such as SUS301, SUS304, and SUS316. In this invention, SUS304 is preferred in terms of chemical stability with respect to ink.

[0047] The "austenite phase" in stainless steel refers to the phase with a face-centered cubic (FCC) crystal structure. The "martensite phase" refers to the phase with a body-centered cubic (BCC) crystal structure.

[0048] The composition ratio of stainless steel is not perfectly uniform at a microscopic level, and even austenitic stainless steel contains a region that is thermodynamically metastable at a microscopic level. In such a region, at room temperature, the free energy of the martensite phase is lower than that of the austenite phase. When subjected to plastic deformation such as cold rolling, a work-induced martensitic transformation occurs, and the austenite phase may contain a small amount of martensite phase.

[0049] Whether the crystal structure of stainless steel is face-centered cubic or body-centered cubic can be determined by electron backscatter diffraction (EBSD).

[0050] "Electron backscattering analysis" is a method for obtaining crystal information by analyzing electron scattering patterns (Kikuchi lines) obtained by irradiating a tilted sample with an electron beam inside a scanning electron microscope (SEM), according to the crystal orientation. It can identify areas with a certain or greater orientation difference between adjacent measurement points as boundaries of individual crystal grains, and create a crystal grain map. Furthermore, it can measure the crystal structure and grain size of each crystal grain.

[0051] In addition, while there are crystal grains whose crystal structure cannot be determined by electron beam backscattering analysis (hereinafter also referred to as "EBSD measurement"), the area percentage of face-centered cubic crystals [%] and body-centered cubic crystals [%] in this invention are the percentages relative to the area excluding crystal grains whose crystal structure cannot be determined.

[0052] A stainless steel according to one embodiment of the present invention is characterized in that the area ratio of face-centered cubic crystals measured by the above method is 92.0% or more, and the area ratio of body-centered cubic crystals is 5.4% or less. This makes it possible to suppress the occurrence of deformities during nozzle formation. In this invention, the area percentages [%] for face-centered cubic crystals and body-centered cubic crystals are rounded to two decimal places.

[0053] Furthermore, the area percentages of face-centered cubic crystals [%] and body-centered cubic crystals [%] measured by electron beam backscattering analysis can be considered as the austenite phase content [%] and the martensite phase content [%], respectively. Note that the austenite phase content [%] and martensite phase content [%] in this invention are values ​​rounded to two decimal places.

[0054] In other words, the stainless steel according to one embodiment of the present invention is an austenitic stainless steel having a martensite phase content of 5.4% or less, in which the crystal structure is body-centered cubic. This makes it possible to suppress the occurrence of deformities during nozzle formation.

[0055] Furthermore, the stainless steel according to the present invention can also be made from stainless steel with a low carbon concentration. In punching, work-induced martensitic transformation occurs, the grain size becomes finer, the stainless steel hardens, and deformities are more likely to occur. In stainless steel with a low carbon concentration, work-induced martensitic transformation is less likely to occur, so the occurrence of deformities can be suppressed. Examples of stainless steel with a low carbon concentration include SUS304L and SUS316L.

[0056] (3) Grain size of stainless steel The stainless steel according to the present invention is preferable in that it has a small average grain size as measured by electron beam backscattering analysis, which can suppress the occurrence of deformities. Specifically, it is preferable that the frequency-average grain size is 0.9 μm or less, or the area-weighted average grain size is 2.3 μm or less. In this invention, the frequency-average grain size [μm] and area-weighted average grain size [μm] are values ​​rounded to two decimal places.

[0057] Furthermore, it is preferable that the stainless steel according to the present invention has a frequency-average grain size ratio measured by electron backscatter analysis to the aperture diameter of the nozzle tip (discharge direction tip) of 4.7% or less, or an area-weighted average grain size ratio measured by electron backscatter analysis to the aperture diameter of the nozzle tip (discharge direction tip) of 12.0% or less. This makes it possible to suppress the occurrence of deformities during nozzle formation. Note that the ratio of frequency-average grain size to nozzle tip diameter [%] and the ratio of area-weighted average grain size to nozzle tip diameter [%] are rounded to two decimal places.

[0058] "Frequency-averaged grain size" is the value obtained by dividing the total grain size within the measurement area by the frequency (number of particles).

[0059] "Area-weighted average grain size" is calculated by weighting the data according to the proportion of the area it occupies within the measurement region. It is obtained by dividing the sum of the product of grain size and grain area by the total grain area.

[0060] Here, "opening diameter of the nozzle tip" refers to the diameter of the nozzle tip opening if it is circular, or, if it is not circular, the diameter of the circle that would replace it with a circle of the same area as the opening.

[0061] (4) Nozzle formation One embodiment of the present invention is a method for manufacturing an inkjet head nozzle plate, characterized by comprising a step of forming a nozzle by laser processing.

[0062] Furthermore, as one embodiment of the present invention, the method for manufacturing an inkjet head nozzle plate is a method for manufacturing an inkjet head nozzle plate of the present invention, characterized by comprising the step of forming a recess by punching, and then forming a nozzle by polishing off the protrusion on the back surface.

[0063] The shape of the nozzle to be formed is preferably funnel-shaped from the viewpoint of ink ejection stability. For example, it can be the shape described in paragraph

[0037] of Japanese Patent Application Publication No. 2017-19174. By making the nozzle shape funnel-shaped, it is possible to suppress the entrapment of air bubbles into the nozzle when the meniscus surface is retracted during ink ejection.

[0064] <Nozzle formation by laser processing> For the method of forming a nozzle by laser processing, for example, the methods described in paragraphs

[0014] to

[0035] of Japanese Patent Publication No. 4455884, paragraphs

[0016] to

[0036] of Japanese Patent Application Publication No. 2017-19174, etc., can be used.

[0065] Specifically, a nozzle is formed by laser ablation processing on a stainless steel substrate while focusing and scanning the laser beam using a laser light source that emits laser light with a pulse width of 30 picoseconds or less, a piezo-controlled mirror for scanning the laser light, and a focusing lens for focusing the laser beam. The three-dimensional shape of the nozzle can be controlled by the scanning pattern of the laser beam.

[0066] The shorter the laser pulse width, the less thermal impact on stainless steel. It is preferable to use femtosecond pulses rather than picosecond pulses. Furthermore, since laser ablation generates stainless steel dust, it is preferable to perform laser processing while blowing a gas such as air to remove the dust from the nozzle processing position. Additionally, by splitting the laser beam using a diffractive optical element (DOE), multiple nozzles can be processed simultaneously, thereby improving the productivity of the nozzle processing process.

[0067] As the ablation process of the stainless steel substrate progresses, it is preferable to change the height of the stainless steel substrate or the lens so that the focal point of the lens contacts the substrate surface. By synchronizing the nozzle processing height and the lens focal height, processing in a defocused state can be prevented, and the influence of lens aberrations can be reduced, thereby reducing abnormalities in the nozzle processing shape.

[0068] <Nozzle formation by punching and grinding> The formation of the nozzle by punching and grinding can be carried out, for example, by the method described in paragraphs

[0008] to

[0014] of Japanese Patent Publication No. 3755332.

[0069] A punch tool is used to form recesses by punching. The punch tool is shaped to match the nozzle shape. By pressing the punch tool into the flow channel side of the stainless steel substrate, the stainless steel substrate is plastically deformed, and a recessed shape with the nozzle shape transferred onto it can be formed. In addition, a die with a punching mold is used to receive and grip the stainless steel substrate that deforms and protrudes when the punch tool is pressed in.

[0070] Next, the protrusions formed on the discharge surface are removed by polishing to form the nozzle. Specifically, the protrusions can be removed by polishing in two stages: rough polishing and finish polishing. For rough polishing, tape polishing is preferable. Tape polishing is a method of polishing by pressing a film to which fine abrasive particles are fixed is applied. By feeding out the film before the abrasive particles wear down or become clogged, the finish is stable and the process can be automated. For finish polishing, chemical mechanical polishing (CMP) is preferable. By simultaneously supplying a polishing solution containing abrasives, pressing a polishing pad, and moving the workpiece relative to it, the combined action of chemical and mechanical polishing removes any remaining irregularities from the rough polishing, resulting in a very flat surface.

[0071] (5) Use of nozzle plates for inkjet heads The nozzle plate for inkjet heads of the present invention can be used in inkjet heads, inkjet recording devices, and inkjet recording methods, etc.

[0072] The nozzle plate for inkjet heads of the present invention has fewer irregularities in the inner wall and tip of the nozzle. Therefore, inkjet heads using this nozzle plate are less prone to nozzle failure, and the maintenance frequency of inkjet recording devices using this inkjet head can be reduced. In addition, variations in impact position, uneven drawing, streaks, and pattern breaks are less likely to occur, resulting in good drawing quality.

[0073] Furthermore, the inkjet head of the present invention is not particularly limited in its configuration other than using the nozzle plate for the inkjet head of the present invention, and can be configured in the same way as a general inkjet head, including a pressure chamber, piezoelectric actuator, diaphragm, wiring board, common ink chamber, and drive unit.

[0074] Furthermore, the inkjet recording apparatus of the present invention is not particularly limited in its configuration other than being equipped with the inkjet head of the present invention, and can be configured in the same way as a general inkjet recording apparatus, by including a conveyor belt and conveyor rollers in addition to the head unit composed of the inkjet head.

[0075] When using the inkjet head nozzle plate of the present invention in an inkjet recording method, it is preferable to use ink with a surface tension in the range of 20 to 40 mN / m together with the nozzle plate. Furthermore, it is preferable to reduce the amount of dissolved oxygen in the ink to 20% or less compared to atmospheric pressure by providing an ink degassing mechanism in the recording device or by using degassed ink before use. More preferably, the amount of dissolved oxygen should be 3.0 g / mL or less. This makes it less likely for air bubbles, which cause nozzle failure, to form in the ink, thus further reducing the occurrence of nozzle failure. [Examples]

[0076] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0077] (1) Example 1: Nozzle plate with nozzle formed by laser processing (1.1) Stainless steel For the stainless steel used, we employed the following stainless steels A to C, manufactured by Nippon Steel Chemical & Material, with a thickness of 50 μm and being austenitic. Stainless steel A: SUS304-CSP-H-TA material Stainless steel B: SUS304-CSP-H material, Lot 1 Stainless steel C: SUS304-CSP-H material, Lot 2

[0078] The "H" in the above stainless steel designation indicates that it is a hard material. Furthermore, "TA" indicates that the material has undergone tension annealing, a process that removes stress and warping from the stainless steel through rolling. In other words, stainless steel A is a tension-annealed hard material, while stainless steel B and stainless steel C are hard materials that have not undergone tension annealing. "CSP" stands for cold-rolled steel strip for springs.

[0079] Figures 1A-C are optical microscope images of stainless steels A-C, respectively, taken at 100x magnification. No differences were observed in the surface morphology of stainless steels A-C.

[0080] Next, we will explain the EBSD measurement results. The EBSD measurements were performed using a JEOL SEM JSM-7001F and TSL OIM software Ver. 7.3, with a SEM acceleration voltage of 15kV, a sample tilt angle of 70°, a measurement area of ​​100μm × 40μm, a measurement step (measurement point interval) of 0.2μm, and a threshold value of 5° for grain boundary orientation difference.

[0081] Figures 2A to 2C are grain maps obtained by EBSD measurements for stainless steels A to C, respectively. In each of Figures 2A to 2C, differences in crystal structure are mapped into regions that are face-centered cubic, regions that are body-centered cubic, and regions where the crystal structure cannot be determined.

[0082] Furthermore, the area percentages [%] of face-centered cubic crystals and body-centered cubic crystals in this invention are percentages of the area excluding crystal grains whose crystal structure cannot be determined. Therefore, these percentages are not relative to the entire area including regions where the crystal structure cannot be determined (the values ​​of Iron bcc and Iron fcc shown in the figure), but rather must be calculated using the following formulas.

[0083] Area ratio of face-centered cubic crystal [%]=Iron fcc / (Iron bcc+Iron fcc)×100 Area ratio of body-centered cubic crystal [%]=Iron bcc / (Iron bcc+Iron fcc)×100

[0084] The area percentages [%] of face-centered cubic crystals and body-centered cubic crystals obtained by the above calculations are shown in Table I below.

[0085] The area percentages of face-centered cubic crystals [%] and body-centered cubic crystals [%] in stainless steel can be considered as the austenite phase content [%] and martensite phase content [%] in stainless steel, respectively.

[0086] In all of stainless steels A through C, the area proportion of face-centered cubic crystals exceeds 90%, indicating that the austenite phase is the dominant phase. Furthermore, in all of stainless steels A through C, the area proportion of body-centered cubic crystals is considerably smaller than that of face-centered cubic crystals, suggesting that the martensite phase is an alien phase.

[0087] The frequency-average grain size [μm] and area-weighted average grain size [μm] obtained by EBSD measurement are shown in Table I below.

[0088] (1.2) Fabrication of a nozzle plate formed by laser processing Nozzle plates No. 1 to 3 were fabricated by forming nozzles on the stainless steels A to C using laser processing.

[0089] Laser processing was performed using picosecond laser processing. Specifically, a laser beam with a wavelength of 1053 nm, pulse width of 25 ps, output power of 1 W, and repetition frequency of 1 kHz, emitted from a YLF (yttrium lithium fluoride) laser, was split into 208 beams by a diffractive optical element (DOE), focused onto the channel-side surface of the stainless steel substrate using a 100 mm focal length f-sinθ lens, and ablation processing was performed while scanning the beam with a piezo-controlled mirror, thereby forming 208 nozzles. As the ablation process of the stainless steel substrate progressed, the height of the stainless steel substrate was changed so that the focal point of the lens was in contact with the substrate surface.

[0090] The nozzle shape for nozzle plates No. 1 to 3 is a funnel shape in which the taper angle of the inner wall of the nozzle changes in two stages. The opening diameter on the flow path side is 90 μm, the taper angle of the first stage is approximately 45°, the depth of the first stage taper is 30 μm, the taper angle of the second stage that connects to it is approximately 9°, the depth of the second stage taper is approximately 20 μm, and the opening diameter at the nozzle tip is 19.1 μm.

[0091] The frequency-average grain size / nozzle opening diameter [%] and area-weighted average grain size / nozzle opening diameter [%] calculated based on the nozzle tip opening diameter of 19.1 μm are as shown in Table I below.

[0092] (1.3) Evaluation of nozzle plates formed by laser processing To evaluate the occurrence of deformities in nozzle plates No. 1 to 3, SEM observation was performed using a Hitachi High-Technologies Corporation scanning electron microscope (SEM) S4800.

[0093] Figures 3A-C and 4A-C are SEM images of nozzles No. 1-3 taken from the flow path side. Figures 3A-C are SEM images of the entire nozzle, taken at a magnification of 800x for nozzle plates No. 1-3. Figures 4A-C are SEM images of the inner walls of the nozzles, taken at a magnification of 8000x for nozzle plates No. 1-3.

[0094] Nozzle plates No. 1 to 3 all yielded similar nozzle shapes, and it was confirmed that their overall machinability was equivalent.

[0095] However, nozzle plate No. 1, made of stainless steel A, had irregularly shaped micro-recesses (needle holes) on the inner wall of the nozzle. Figure 5 is an SEM image of these micro-recesses. The size of the micro-recesses was approximately 1 μm, and the frequency of irregularity occurrence was 16 / 208 (16 irregularities were found out of 208 nozzles observed).

[0096] On the other hand, for nozzle plate No. 2 made of stainless steel B and nozzle plate No. 3 made of stainless steel C, the frequency of deformation was 0 / 208 (zero deformations were observed in 208 nozzles).

[0097] [Table 1]

[0098] The deformity observed on nozzle plate No. 1, made of stainless steel A, is due to the influence of the body-centered cubic phase, or martensite phase, present as an extraphase in stainless steel. Because the martensite phase has a lower melting point than the austenite phase, it is more easily ablated during laser processing, which contributes to the formation of deformities.

[0099] The results from Example 1 show that when the martensite phase content exceeds 5.4%, as in stainless steel A, the martensite phase manifests as irregular shapes such as minute depressions (needle holes).

[0100] On the other hand, as seen in stainless steels B and C, if the martensite phase content is 5.4% or less, the martensite phase does not manifest as an abnormal shape.

[0101] The reason why stainless steel A has a higher martensite phase content compared to stainless steel B and stainless steel C is likely due to factors such as whether or not tension annealing treatment was performed and the amount of impurities contained in the raw materials.

[0102] Furthermore, in nozzle plate No. 2, which is made of stainless steel B, and nozzle plate No. 3, which is made of stainless steel C, the frequency-average grain size of the stainless steel is 0.9 μm or less, and the area-weighted average grain size is 2.1 μm or less, which is considered to have made the formation of minute recesses less likely.

[0103] (2) Example 2: Nozzle plate with nozzle formed by punching and grinding (2.1) Stainless steel Stainless steel A and stainless steel C used in Example 1 were used.

[0104] (2.2) Fabrication of a nozzle plate formed by punching and grinding. Nozzle plates No. 4 and No. 5 were manufactured by forming recesses in stainless steel A and C using punching, and then grinding away the protrusions on the back surface to form nozzles.

[0105] The nozzle shape was the same as in Example 1.

[0106] The punching process was performed using a punch tool with a shape corresponding to the nozzle shape. By pressing the punch tool into the flow channel side of the stainless steel substrate, the stainless steel substrate was plastically deformed, creating a recessed shape that transferred the nozzle shape. In addition, a die with a punching mold was used to receive and grip the stainless steel substrate that deformed and protruded during the pressing of the punch tool.

[0107] Next, the nozzle was formed by grinding away the protrusions that had formed on the discharge surface. Specifically, the protrusions were removed by grinding in two stages: rough grinding and finish grinding.

[0108] Rough polishing was performed using tape polishing. The polishing film used was a 75 μm thick polyester film with abrasive grains bonded to one side. Finish polishing was performed using chemical mechanical polishing (CMP). By simultaneously supplying polishing fluid containing abrasives, pressing the polishing pad, and moving the workpiece, the combined chemical and mechanical action removed the irregularities remaining from the rough polishing, resulting in a very flat surface.

[0109] (2.3) Evaluation of nozzle plates formed by punching and grinding. Nozzle plates No. 4 and No. 5 were observed using SEM in the same manner as in Example 1. Both nozzle plates No. 4 and No. 5 yielded similar nozzle shapes, confirming that their overall machinability was equivalent.

[0110] However, nozzle plate No. 4, made of stainless steel A, had streaky irregularities on the inner wall of the nozzle, and burrs on the edge of the nozzle tip. Figure 6 is an SEM image of the nozzle showing the streaky irregularities on the inner wall of the nozzle and the burrs on the nozzle tip. It was taken by cutting one of the nozzles on nozzle plate No. 4 and photographing the area near the nozzle tip of the cross-section. The lower part of the figure is the nozzle tip.

[0111] On the other hand, no streaky irregularities or burrs were observed on nozzle plate No. 5, which is made of stainless steel C. Figure 7 is an SEM image of a good nozzle that is free of streaky irregularities and burrs. It was taken by cutting one of the nozzles on nozzle plate No. 5 and photographing the area near the nozzle tip of the cross-section. The lower part of the figure is the nozzle tip.

[0112] The irregular shape observed on nozzle plate No. 4, made of stainless steel A, is due to the influence of the body-centered cubic phase, or martensite phase, contained as a separate phase in the stainless steel. When stainless steel undergoes plastic deformation during punching, the plastic deformation responses of the surrounding austenite phase and martensite phase are misaligned, causing streaky irregularities to form on the inner wall of the nozzle, extending from the flow path side towards the nozzle tip.

[0113] From Example 2, it can be seen that when the martensite phase content is greater than 5.4%, as in stainless steel A, streaky irregularities are likely to occur.

[0114] Furthermore, in nozzle plate No. 4, which is made of stainless steel A, streaky irregularities were formed on the inner wall of the nozzle. As a result, when the protrusions on the back surface were subsequently polished away, burrs were formed on the edge of the nozzle tip.

[0115] On the other hand, it can be seen that if the martensite phase content is 5.4% or less, as in stainless steel C, streaky irregularities do not occur.

[0116] Furthermore, in nozzle plate No. 5, which is made of stainless steel C, the frequency-average grain size of the stainless steel is 0.9 μm or less, and the area-weighted average grain size is 2.1 μm or less, which is thought to have made the formation of streaky irregularities less likely. [Industrial applicability]

[0117] This invention can be used in an inkjet head nozzle plate made of stainless steel with minimal irregularities in the inner wall and tip of the nozzle, a method for manufacturing the same, an inkjet head using the inkjet head nozzle plate, and an inkjet recording device.

Claims

1. An inkjet recording apparatus that includes an inkjet head nozzle plate made of at least stainless steel and ejects ink, The stainless steel is an austenitic stainless steel having a martensite phase content of 5.4% or less, and The ink jet recording apparatus is characterized in that the surface tension of the ink is within a range of 20 to 40 mN / m.

2. An inkjet recording apparatus that includes an inkjet head nozzle plate made of at least stainless steel and ejects ink, The stainless steel has an area ratio of face-centered cubic crystals of 92.0% or more and an area ratio of body-centered cubic crystals of 5.4% or less, as measured by electron backscattering analysis, and The ink jet recording apparatus is characterized in that the surface tension of the ink is within a range of 20 to 40 mN / m.

3. 3. The ink jet recording apparatus according to claim 1, wherein the stainless steel has a frequency average crystal grain size of 0.9 [mu]m or less as measured by electron backscattering analysis.

4. 4. The inkjet recording apparatus according to claim 1, wherein the stainless steel has an area-weighted average crystal grain size of 2.3 μm or less as measured by electron backscattering analysis.

5. 5. The inkjet recording apparatus according to claim 1, wherein the stainless steel has a ratio of the number-average crystal grain size to the nozzle tip opening diameter, as measured by electron backscattering analysis, of 4.7% or less.

6. 6. The inkjet recording apparatus according to claim 1, wherein the stainless steel has an area-weighted average crystal grain size ratio of 12.0% or less to the nozzle tip opening diameter as measured by electron backscattering analysis.

7. An inkjet recording device described in any one of claims 1 to 6, characterized in that the stainless steel is SUS304L or SUS316L.

8. An inkjet recording device as described in any one of claims 1 to 7, characterized in that an ink degassing mechanism is provided, and the ink is degassed ink.

9. An inkjet recording method for ejecting ink using a nozzle plate for an inkjet head made of at least stainless steel, comprising: The stainless steel is an austenitic stainless steel having a martensite phase content of 5.4% or less, and The ink jet recording method according to claim 1, wherein the surface tension of the ink is within a range of 20 to 40 mN / m.

10. An inkjet recording method for ejecting ink using a nozzle plate for an inkjet head made of at least stainless steel, comprising: The stainless steel has an area ratio of face-centered cubic crystals of 92.0% or more and an area ratio of body-centered cubic crystals of 5.4% or less, as measured by electron backscattering analysis, and The ink jet recording method according to claim 1, wherein the surface tension of the ink is within a range of 20 to 40 mN / m.

11. The inkjet recording method according to claim 9 or claim 10, characterized in that the stainless steel is a stainless steel having a frequency average crystal grain size of 0.9 μm or less as measured by electron backscattering analysis.

12. An inkjet recording method described in any one of claims 9 to 11, characterized in that the stainless steel is a stainless steel having an area-weighted average crystal grain size of 2.3 μm or less as measured by electron backscattering analysis.

13. An inkjet recording method described in any one of claims 9 to 12, characterized in that the stainless steel is a stainless steel in which the ratio of the frequency average crystal grain size measured by electron backscattering analysis to the opening diameter of the nozzle tip is 4.7% or less.

14. An inkjet recording method described in any one of claims 9 to 13, characterized in that the stainless steel is a stainless steel in which the ratio of area-weighted average crystal grain size measured by electron backscattering analysis to the opening diameter of the nozzle tip is 12.0% or less.

15. The inkjet recording method according to claim 9, wherein the stainless steel is SUS304L or SUS316L.

16. The inkjet recording method according to claim 9, further comprising a mechanism for degassing the ink, the ink being a degassed ink.

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