Thermal Printhead Research Articles

Numerical study of the heat transfer characteristics of wide-format thermal print head

Thermal printing technology has achieved remarkable success in the realm of portable printing due to its advantages such as high printing speed, easy maintenance, and energy efficiency. Nevertheless, there have been no reports on the application of thermal print technology in the booming field of wide-format printing. This article presents the design and construction of a primordial wide-format thermal printer. The corresponding heat transfer model used to design it is proposed subsequently, and the accuracy of the model is validated through experimental methods. The heat transfer characteristics of the wide-format thermal printer during operation are investigated using the model, providing essential technical support for the advancement and proliferation of thermal printing technology in the wide-format printing domain. The findings demonstrate that, during stable operation of the wide-format thermal printer, 84.7% of the heat generated by the heat generator is effectively transferred to the protective film for dye melting, while 13.3% of the heat is dissipated as waste heat to the glass substrate. The temperature distribution in the splicing area is greatly affected due to the non-working heat generation dots. Furthermore, the heat flux between adjacent heat generation dots is nonnegligible and exerts a mutual effect on the respective temperatures.

Numerical study of drop dynamics for inkjet based 3D printing of pharmaceutical tablets

Interest in 3D printing has been growing rapidly especially in pharmaceutical industry due to its multiple advantages such as manufacturing versatility, personalization of medicine, scalability, and cost effectiveness. Inkjet based 3D printing gained special attention after FDA’s approval of Spritam® manufactured by Aprecia pharmaceuticals in 2015. The precision and printing efficiency of 3D printing is strongly influenced by the dynamics of ink/binder jetting, which further depends on the ink’s fluid properties. In this study, Computational Fluid Dynamics (CFD) has been utilized to study the drop formation process during inkjet-based 3D printing for piezoelectric and thermal printhead geometries using Volume of Fluid (VOF) method. To develop the CFD model commercial software ANSYS-Fluent was used. The developed CFD model was experimentally validated using drop watcher setup to record drop progression and drop velocity. During the study, water, Fujifilm model fluid, and Amitriptyline drug solutions were evaluated as the ink solutions. The drop properties such as drop volume, drop diameter, and drop velocity were examined in detail in response to change ink solution properties such as surface tension, viscosity, and density. A good agreement was observed between the experimental and simulation data for drop properties such as drop volume and drop velocity.

Simulation of a Hemispherical Chamber for Thermal Inkjet Printing.

It is crucial to improve printing frequency and ink droplet quality in thermal inkjet printing. This paper proposed a hemispherical chamber, and we used the CFD (computational fluid dynamics model) to simulate the inkjet process. During the whole simulation process, we first researched the hemispherical chamber's inkjet state equipped with straight, conical shrinkage, and conical diffusion nozzles. Based on the broken time and volume of the liquid column, the nozzle geometry of the hemispherical chamber was determined to be a conical shrinkage nozzle with a specific size of 15 µm in height and 15 µm in diameter at the top, and 20 µm in diameter at the bottom. Next, we researched the inkjet performance of the square chamber, the round chamber, and the trapezoidal chamber. The round chamber showed the best inkjet performance using 1.8 µs as the driving time and 10 MPa as the maximum bubble pressure. After that, we compared the existing thermal inkjet printing heads. The results showed that the hemispherical chamber inkjet head had the best performance, achieving 30 KHz high-frequency printing and having the most significant volume ratio of droplet to the chamber, reaching 14.9%. As opposed to the current 15 KHz printing frequency of the thermal inkjet heads, the hemispherical chamber inkjet head has higher inkjet performance, and the volume ratio between the droplet and the chamber meets the range standard of 10-15%. The hemispherical chamber structure can be applied to thermal inkjet printing, office printing, 3D printing, and bio-printing.

A Simple Method for Fabricating Ink Chamber of Inkjet Printheads.

The process of fabricating chambers is becoming more important for inkjet printheads. However, there are some problems with the majority of present fabrication methods, such as nozzle structural deformation, blocked chambers, and collapsed chambers. In this paper, we propose a new process for preparing printhead chips by bonding tantalum nitride thin-film heaters and SU-8 chamber film using UV curing optical adhesive. This process simplifies the preparation process of printhead chips and overcomes the limitations of the traditional adhesive bonding process. Firstly, a chamber film was prepared by the molding lithography process based on a PDMS mold. The chamber film was then bonded with the membrane heater by the adhesive bonding process based on film transfer to form a thermal bubble printhead chip. Finally, the chip was integrated with other components to form a thermal inkjet printhead. The results show that the overflow width of bonding interface of 3.10 μm and bonding strength of 3.3 MPa were achieved. In addition, the printhead could stably eject polyvinyl pyrrolidone binder droplets, which are expected to be used for binder-jetting printing of powder such as ceramics, metals, and sand molds. These results might provide new clues to better understand the adhesive bonding process based on film transfer and the new applications of inkjet printheads.

Mapping technological trajectories as the main paths of knowledge flow: Evidence from printers

AbstractIn this paper, we recognize that technological trajectories can be modeled as a series of problem-solving activities, manifesting the cyclical pattern of divergence–convergence knowledge flow. This recognition is applied to study the technological development of the thermal inkjet print head, using main path analysis and an assignee cross-citation network. Our analysis shows that the thermal inkjet print head experienced three cycles of divergence–convergence knowledge flow. Each of the cycles was evidently characterized by a problem of most concern and a referred solution. Our research contributes to explaining why, when, and how trajectories diverge and converge cyclically.

Research on Intelligent Control System of Thermal Print Head Based on FPGA

Thermal print head heating realtime temperature fluctuations are too large, often causing damage to the print head heating point, resulting in poor print quality and unsatisfactory print results. Therefore, in order to improve the stability of the thermal print head during printing, and at the same time solve the inefficiency of the traditional single chip microcomputer control of the thermal print head heating method, a field programmable gate array (FPGA) based thermal print head heating control method is proposed. In order to control the core, the intelligent fuzzy PID control algorithm is used to ensure that the temperature of the print head can be stabilized quickly. Through simulation and experimental verification, it is shown that the intelligent fuzzy PID control algorithm greatly improves the temperature stabilization effect, and the time required to reach stability short, not only improve the printing accuracy, but also extend the life of the print head.

Patterns of Knowledge Flow: Cycles of Divergence and Convergence in Printers

This paper considers technological trajectories as a series of problem-solving activities, manifesting the pattern of divergence-convergence knowledge flow. We propose that technological trajectories diverge when new knowledge is able to solve the problem of most concern. Relatedly, technological trajectories converge when existing knowledge becomes obsolescent in the face of new problems. To illustrate our ideas, we choose to study the technological evolution of the thermal inkjet print head, using key-route search and the patent assignee cross-citation network. The thermal inkjet print head experienced three cycles of divergence-convergence knowledge flow, each of which is characterized by the problem of most concern and referred solution. To enhance the rigor of our analysis, we also draw on archival data to examine in more detail the identified main paths as well as the assignee cross-citation network.

Thin-Film MEMS Resistors with Enhanced Lifetime for Thermal Inkjet.

In this paper, the failure mechanisms of the thermal inkjet thin-film resistors are recognized. Additionally, designs of resistors to overcome these mechanisms are suggested and tested by simulation and experiment. The resulting resistors are shown to have improved lifetimes, spanning an order of magnitude up to 2 × 109 pulses. The thermal failure mechanisms were defined according to the electric field magnitude in three critical points—the resistor center, the resistor–conductor edge, and the resistor thermal “hot spots”. Lowering the thermal gradients between these points will lead to the improved lifetime of the resistors. Using MATLAB PDE simulations, various resistors shapes, with different electric field ratios in the hot spots, were designed and manufactured on an 8″ silicon wafer. A series of lifetime experiments were conducted on the resistors, and a strong relation between the shape and the lifetime of the resistor was found. These results have immediate ramifications regarding the different printing apparatuses which function with thermal inkjet technology, allowing the commercial production of larger thermal printheads with high MTBF rate. Such heads may fit fast and large 3D printers.

Simulation of Contact Heat Transfer between Thermal Print Head and Belt in Printer

Simulation of Contact Heat Transfer between Thermal Print Head and Belt in Printer

中間熱転写印刷のヘッド-ベルト間の接触伝熱状態の解明

An indirect thermal transfer printing is capable of printing on both flat and uneven surfaces and is generally used for IC card printer. At present, a transfer unit of the indirect thermal transfer printer has a problem with large power consumption. To overcome this problem a technique of a thermal print head in place of a heating roller currently used has been proposed as power saving technology of the transfer unit of the indirect thermal transfer printer. However, it is difficult to design it because contact heat transfer characteristics between the thermal print head and an indirect transfer belt are not clear. In this study, we simulated the transfer process, and revealed the contact heat transfer characteristics of the thermal print head through evaluation of the temperature distribution and the pressure distribution. First, contact heat transfer coefficients which are dominant parameters in the contact heat transfer characteristics were determined by inverse analysis method. Next, to find out the suitable shape of the thermal print head, three different types of thermal print heads were prepared. The flat thermal print head has shown the most sufficient heat transference to the indirect transfer belt and the heat transfer coefficient decreased in the order of the convex and the concave. However, the manufacturing cost of the concave thermal print head is about one half of those of the other two types. Then, the possibility of improving the heat transference of the concave thermal print head was considered. The heat transference of the concave thermal print head was able to be improved by spreading the concave width.

209 接触熱伝達を考慮した中間熱転写印刷における熱転写ヘッドの最適設計(OS13-2 機械要素とトライボロジー)

209 接触熱伝達を考慮した中間熱転写印刷における熱転写ヘッドの最適設計(OS13-2 機械要素とトライボロジー)

Electrically Programmable All-Fiber Structured Second Order Optical Temporal Differentiator

We propose and experimentally demonstrate an electrically programmable second order optical temporal differentiator (OTD) based on linearly chirped fiber Bragg grating (LCFBG) and digital thermal print head (TPH). For the high-speed optical signal with 25-GHz repetition rate, an efficient second-order OTD has been achieved for arbitrary wavelength and bandwidth with the software-defined TPH configurations. By optimizing the thermooptic effect induced optical phase change in the LCFBG, the central wavelength of the differentiator can be reconfigured flexibly from 1543.5 to 1561.7 nm, with a step size of 0.114 nm. By dynamically controlling the heating elements bonded with the LCFBG, optical pulses with 0.55- and 0.8-nm 3-dB bandwidths have been successfully processed with acceptable deviation compared with the theoretical calculations.

Measurement of real contact area on thermal print head using a laser microscope with a wide field of view

In a dye-sublimation printer, a thermal print head presses and heats a dye-based ribbon to diffuse ink dyes to the desired positions into the receiving layer of paper. The print quality will deteriorate if the contact condition between the thermal print head and the paper is insufficient. Thus, it is necessary to analyze the contact condition for finer printing. Direct observation of the contact area with an optical microscope is effective to clarify the contact conditions of the thermal print head. However, conventional optical microscopes take too much time to observe the whole apparent contact area, because their fields of view are not sufficiently wide. Previously, we developed a laser microscope with a wide field of view and applied this laser microscope to observe the whole apparent contact area of rubber elements. In this study, we examined the contact conditions between the thermal print head and the paper. In general, when we observe the contact area of two solid surfaces, one is restricted to a transparent material such as a glass plate. Instead of the thermal print head, a glass head of the same shape as an existing thermal print head was pressed on the paper and observed through the glass head. This allowed us to clearly determine the contact situations of the interface and measure the contact widths and distributions of real contact area. In this method, it was confirmed that the contact width and the real contact area changed in accordance with the type of paper used, steps of the printing process, and density of color printing.

In situ microanalysis of organic colorants by inkjet colloid deposition surface‐enhanced Raman scattering

We present a new method for the minimally invasive in situ identification of inks and colorants on documents and other objects on the basis of the deposition of silver colloid nanodroplets on a region of interest in the objects to be tested using inkjet technology. By adapting commercially available thermal and piezoelectric inkjet heads, volumes of silver colloid in the 60–220 picoliters range (corresponding to impact diameters in the range of 50–150 µm) can be delivered onto substrates with great accuracy and precision. We demonstrate that the instantaneous superheating of the colloid in the thermal print head does not adversely affect the surface‐enhanced Raman spectroscopy efficiency of the Ag nanoparticles. Furthermore, by mounting a compact piezoelectric inkjet head within a large‐stage Raman microscope, we developed an instrument where all phases of surface‐enhanced Raman spectroscopy microanalysis are integrated, with great advantages in sample handling, spatial accuracy, and colloid delivery reproducibility. The approach can be considered functionally nondestructive as the amount of silver delivered, and the area affected are too small to be detected by visual observation, and in most conditions, even by optical microscopy. The method was successfully applied to the analysis of textile fibers, gel pen ink writing on paper, and a Japanese woodblock print dating to the end of the 19th century. Copyright © 2013 John Wiley & Sons, Ltd.

Improvements for electrostatic discharge immunity in thermal printing head

Electrostatic discharge (ESD) is one of the important sources of electromagnetic interference which would cause a reversible or permanent damage in modem electronic equipment. ESD may be introduced by the human body operating the electronic equipment or accumulated by friction, heating or other reasons when the electronic equipment is working. In this paper we use the print head of the thermal printer (TPH) suffered from electrostatic hazard as an example to analyze the reasons of the ESD happening, and some necessary improvements measures for protection of the TPH are also suggested.

Effect of Nicotinic Acid as a Toner on Photothermographic Materials Based on Silver Benzotriazole

The photothermographic(PTG) imaging materials are the kind of digital hardcopy imaging medium usually used in diagnostic medical field. The hardcopy image was obtained by thermal printing process using driving laser or thermal print head on PTG materials based on electronic data. Toner, as the most important of components to provide better image quality, is a compound could modify the shape and size of Ag0 particles to correct the image color from yellow-brown to black in thermal imaging process. In the paper, the effect of nicotinic acid as a new toner on PTG based on silver benzotriazole as silver sources had been studied. The results indicated that development of silver benzotriazole PTG materials was promoted by the introduction of nicotinic acid and the function of nicotinic acid was influenced by the pH of the silver benzotriazole emulsion and the amounts of nicotinic acid. The promotion of nicotinic acid was strengthened with the pH in system increased in the condition of the same amounts of nicotinic acid added in PTG emulsion. The best promotion could be obtained in the case of the mol ratio of nicotinic acid to silver benzotriazole 0.1 and value of pH in emulsion about eight. The IR spectrum data implied that the silver complex, which was supposed to be easy to transmit silver ions from silver salt to development center, was produced by nicotinic acid and silver benzotriazole.

New Development of Multi-Purpose Heating Head

The majority of existing thermal printers are made so that the print media is sandwiched between the drive roller and heating element of the thermal head. Our new heating head is an extension of the thermal printhead concept with the exception of heating a whole section of the head rather than a portion of it. The heating head utilizes the thick-film heating element on the ceramic substrate. The new design prevents energy diffusion by heat accumulation and retention. Also, the new structure makes it possible for the device to be miniaturized and the heat transfers to the media easily. Another distinction of the new heating head is that the heating/contacting surface is on the opposite side of the heat generating side of the ceramic substrate. This improves the heat dispersion throughout the heating head. The best benefit of this structure, however, is there will be no life problems on the heating surface such as abrasion, scratch and chemical corrosion which is a serious concern for any contact heating device. The temperature sensor is located very close to the heating element on the same side of substrate and temperature monitoring can be done very fast, easily and accurately. The unique heating element construction makes it possible to join multiple ceramic substrates making the head heating as long as required.

サーマルプリントヘッドに関する著名な特許―USP3，161，457 NCR社―

サーマルプリントヘッドに関する著名な特許―USP3，161，457 NCR社―

Novel Approach to Plastic Card Overcoating Process

Plastic cards are widely used in various industries all over the world. Many on-demand non-embossed pictured cards require overcoating (also referred to as laminating) processes for surface protection from fading, abrasion, alteration and counterfeiting. There are several lamination types, such as wet lamination, dry lamination, hot-melt lamination and extrusion lamination. The focus on this paper is the hot-melt lamination type which utilizes heat and pressure to adhere the film on the card. The laminating / overcoating layer material can be clear material with antiabrasion capability or hologram material for authentication. Typical overcoating process in the thermal transfer card printer is done by thermal printhead or heat roller. This paper suggests the heating head for this process. The heating head works on a very similar principle as the thermal printhead. The heating resistive element and temperature sensing element are placed on the alumina head substrate. When power is applied, the resistive element generates heat for the overcoating material to thermally adhere to the plastic card surface. Unlike the thermal printhead, however, which has hundreds of tiny heating elements, the heating head has one contiguous heating element. The construction of the heating head gives more robust thermal performance and even heating capability across the overcoating material on the card surface. In comparison to a heat roller, the heating head can be used on-demand and does not require the constant pre-heating while the unit is on stand-by (more “eco-friendly” efficiency and safety).

Development of the High Durability Overcoat for Thermal Printhead

The market for the thermal-type printer is expanding. The thermal printers are used in various environments, where the thermal printhead is exposed to year round temperature and humidity fluctuations. In these harsh environments, stronger corrosion resistance is required.In this paper, we describe the new overcoat for the thermal printhead to achieve higher corrosion resistance. It is six times stronger than Kyocera's conventional ones. The overcoat for the thermal printhead has an important function as the prevention of corrosions. Generally, the thicker overcoat is used in order to enhance the corrosion resistance. However, this new overcoat enables to make it 15 percent thinner, despite the enhancement of durability to corrosion. Moreover, this new overcoat increases the energy efficiency and the printing quality.