Thermochromic Ink Research Articles

Optical properties of deinked pulp containing thermochromic offset inks

This paper evaluates the efficiency of thermochromic offset prints recycling using deinking flotation method. Since offset thermochromic inks differ in their composition from conventional offset inks, the aim of this research was to determine how effectively they can be recycled. In the experimental part of the work, the laboratory printing of two thermochromic inks was conducted. For both types of inks, white uncoated paper was used as a substrate. After accelerated aging, the prints were mixed in equal proportions and then recycled in laboratory conditions, by means of deinking flotation. During the recycling process, handsheets and filter pads were prepared from the pulp obtained before and after deinking flotation. Handsheets and filter pads were also prepared from unprinted paper that was used as printing substrate, in order to obtain reference samples. The deinking flotation efficiency was evaluated by calculating the flotation loss, ash elimination, pulp’s brightness and whiteness increase and determination of residual ink area. The obtained results indicate that thermochromic prints are poorly deinkable. A small increase in deinked pulp’s brightness and whiteness (approx. 7% and 11%) is noticed. The image analysis shows that flotation deinking managed to eliminate around 40% of the total dirt area of thermochromic ink.

The Effect of Glass Fiber Powder on the Properties of Waterborne Coatings with Thermochromic Ink on a Chinese Fir Surface.

In this study, the effect of glass fiber powder on the properties of waterborne coatings with thermochromic ink was investigated, using Chinese fir board as the base material and temperature-sensitive thermochromic waterborne coatings with thermochromic ink as the paint base. The concentration of glass fiber powder was determined when the microstructure, optical properties, mechanical properties, liquid resistance, and heat preservation effect were the best. The results showed that the paint film with glass fiber powder concentration of 1.0% to 7.0% had better discoloration performance. With an increase of the glass fiber powder concentration, the gloss of the paint film decreased gradually, and when the concentration of glass fiber powder was 0% to 5.0%, the gloss of the paint film was better. The concentration of glass fiber powder had no effect on the adhesion, impact resistance, and liquid resistance. In the first 2.5 min, the temperature value of the waterborne coating with 3.0% glass fiber powder was higher than that without glass fiber powder, which has a certain heat preservation effect. When the glass fiber powder content was 3.0%, the microstructure of paint film was the best. The composition of paint film with different glass fiber powder concentrations was not different and the discoloration performance of paint film with heat preservation effect was not affected by time. The analysis showed that the waterborne coating with 3.0% glass fiber powder had the best comprehensive performance. This work provides a technical reference for the industrialization of heat preservation and thermochromic coating on wood.

CNT/cotton composite yarn for electro-thermochromic textiles

Electro-thermochromic yarn was prepared by wrapping pure cotton yarn on carbon nanotube/cotton composite yarn. The CNT/cotton composite yarn as the core yarn provides good electrical conductivity while the pure cotton yarn as the wrapped yarn plays a protective role and enables the color changing effect after coating with thermochromic inks. The electro-thermochromic yarn showed remarkable resistive heating and color-changing properties under different applied currents. Abundant and reversible color changes are clearly observed by coating the thermochromic inks onto the surface of yarn and fabric. Depends on the methods, a pure color changing fabric can be made from the electro-thermochromic yarns and fabrics with color changing patterns can be achieved by printing the thermochromic inks into the fabrics from the CNT/cotton cored yarn. Moreover, when the current is 5 mA, the surface temperature of the CNT/cotton cored yarn can increase within several seconds to its maximum 60 °C. The average temperature of the electro-thermochromic fabric can reach up to 90 °C under 4 mA. The printed pattern changes color from deep rose to yellow when a current of 4 mA is applied on the electro-thermochromic fabric. The electro-thermochromic yarns and fabrics show repeatable and reversible color changing effects.

Ink tack stability readings of the offset thermochromic inks

PurposeThis paper aims to analyse the tack stability measurement readings of thermochromic offset inks. For this purpose, three reversible leuco-dye formed thermochromic inks were used to evaluate their tack. The used inks differ in their activation temperature, colour, drying mechanism, viscosity and chemical content. Thermochromic offset inks differ from conventional inks in formulation and size of colourants due to the presence of the microcapsules.Design/methodology/approachPrinting inks in offset lithography must have sufficient tack so they can be transported from a reservoir onto the substrate. The ink transfer takes place through the ink splitting by inking rollers, printing plate and blanket transport. An IGT Tackoscope device was used to produce the dynamic readings of ink tack as a function of distribution and splitting time. The data can be used for prediction of the ink press stability under controlled settings, such as temperature.FindingsThis research explains the temperature and velocity influence on the tack stability measurement readings of thermochromic inks. It also gives an insight of the chemical compounds that dictate the tack measuring reading results.Originality/valueDevelopment of new printing inks, such as thermochromic printing inks, may affect the printing of different products. The research was conducted due to a lack of available data for the tack of thermochromic inks.

Direct screen printing of single-faced conductive cotton fabrics for strain sensing, electrical heating and color changing

A simple but effective method of developing multifunctional wearable cotton fabrics was achieved via screen printing of carbon nanotube (CNT) ink on one side of a weft knitted cotton fabrics. Scanning electron microscopy was employed to investigate the morphology of the CNT/Cotton Composite fabric (CCCF). The deposition of conductive CNT paste has brought electric conductivity (50.75 Ω/sq) to CCCF. The electromechanical performance of the CCCF was evaluated, and the CCCF showed great stability and flexibility in terms of strain sensing. The CCCF was demonstrated to sense different human activities such as speaking, drinking, writing, and bending of finger and wrist. The developed CCCF also exhibited excellent electrothermal performance with the potential to be used as an electric heater. Color changing performance was generated by screen printing thermochromic inks on the back side of CCCF. The flexible strain sensors, electric heaters, and color-changing textiles made from CCCF are promising candidates as smart textiles to be used as wearable electronic devices, cold weather conditioners, and smart displays.

Tissue-mimicking thermochromic phantom for characterization of HIFU devices and applications

Purpose: Tissue-mimicking phantoms (TMPs) are synthetic materials designed to replicate properties of biological tissues. There is a need to quantify temperature changes following ultrasound or magnetic resonance imaging-guided high intensity focused ultrasound (MR-HIFU). This work describes development, characterization and evaluation of tissue-mimicking thermochromic phantom (TMTCP) for direct visualization and quantification of HIFU heating. The objectives were to (1) develop an MR-imageable, HIFU-compatible TMTCP that reports absolute temperatures, (2) characterize TMTCP physical properties and (3) examine TMTCP color change after HIFU.Methods and materials: A TMTCP was prepared to contain thermochromic ink, silicon dioxide and bovine serum albumin (BSA) and its properties were quantified. A clinical MRI-guided and a preclinical US-guided HIFU system were used to perform sonications in TMTCP. MRI thermometry was performed during HIFU, followed by T2-weighted MRI post-HIFU. Locations of color and signal intensity change were compared to the sonication plan and to MRI temperature maps.Results: TMTCP properties were comparable to those in human soft tissues. Upon heating, the TMTCP exhibited an incremental but permanent color change for temperatures between 45 and 70 °C. For HIFU sonications the TMTCP revealed spatially sharp regions of color change at the target locations, correlating with MRI thermometry and hypointense regions on T2-weighted MRI. TMTCP-based assessment of various HIFU applications was also demonstrated.Conclusions: We developed a novel MR-imageable and HIFU-compatible TMTCP to characterize HIFU heating without MRI or thermocouples. The HIFU-optimized TMTCP reports absolute temperatures and ablation zone geometry with high spatial resolution. Consequently, the TMTCP can be used to evaluate HIFU heating and may provide an in vitro tool for peak temperature assessment, and reduce preclinical in vivo requirements for clinical translation.

Development of Augmented Reality Application for Interactive Smart Materials

The paper presents research related to thermochromic inks printed on textile materials. These types of materials are smart materials, they act as packaging indicators, and we use them to develop a software application on mobile devices. That application identifies the most significant changes in parameters of the goods contained in the packaging, such as temperature changes during the storage and transport (goods packaged in packaging that is sensitive to heat), or such as pharmaceuticals and frozen food, etc. This paper aims to demonstrate the possibility of connecting thermochromic materials and Augmented Reality technology through the development of an application for identifying thermochromic materials changes. The tested samples were printed on the textile with a screen printing technique with conventional and thermochromic leuco inks on various textile materials. The Augmented Reality platform Vuforia was used for developing a software application for mobile devices. The application was developed for the iOS mobile platform. The result of the research is the functional application that actively monitors and displays changes in thermochromic materials due to temperature changes, which identifies the effect of heat on the goods in textile packaging.

An Electrothermochromic Fabric Prepared by Electrodeposition of Polypyrrole on Single Side

An electrothermochromic fabric triggered by electric voltages was prepared by combining the electric heating feature of conductive polypyrrole (PPy) and the temperature-response color-changing feature of thermochromic inks. PPy was deposited selectively on the carbon-coated side of the sailcloth fabric via electrochemical polymerization. Thermochromic inks were painted on the reverse side with white color. The obtained fabric could be heated to about 48 °C and change its color significantly under an applied voltage of 3 V.

Using thermochromism to simulate blood oxygenation in extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO) training programs employ real ECMO components, causing them to be extremely expensive while offering little realism in terms of blood oxygenation and pressure. To overcome those limitations, we are developing a standalone modular ECMO simulator that reproduces ECMO's visual, audio and haptic cues using affordable mechanisms. We present a central component of this simulator, capable of visually reproducing blood oxygenation color change using thermochromism. Our simulated ECMO circuit consists of two physically distant modules, responsible for adding and withdrawing heat from a thermochromic fluid. This manipulation of heat creates a temperature difference between the fluid in the drainage line and the fluid in the return line of the circuit and, hence, a color difference. Thermochromic ink mixed with concentrated dyes was used to create a recipe for a realistic and affordable blood-colored fluid. The implemented "ECMO circuit" reproduced blood's oxygenation and deoxygenation color difference or lack thereof. The heat control circuit costs 300 USD to build and the thermochromic fluid costs 40 USD/L. During a ten-hour in situ demonstration, nineteen ECMO specialists rated the fidelity of the oxygenated and deoxygenated "blood" and the color contrast between them as highly realistic. Using low-cost yet high-fidelity simulation mechanisms, we implemented the central subsystem of our modular ECMO simulator, which creates the look and feel of an ECMO circuit without using an actual one.

Thermochromic ink–paper interactions and their role in biodegradation of UV curable prints

In this study, biodegradability aspects of UV thermochromic leuco dye print on three different paper materials (synthetic, recycled, and bulky) were studied using the soil burial test under anaerobic conditions. Biodegradation of UV curable thermochromic prints were evaluated for changes by visual examination, microbial growth assay, weight loss measurements, Fourier transform infrared spectroscopy, scanning electron microscopy and colorimetric measurements. Results showed a better absorption of ink into the bulky paper structure, followed by recycled paper. Synthetic paper is not absorbent. The ink binder altogether with classic pigment and microcapsules penetrates into the structure of bulky paper. Recycled paper absorbs ink binder mostly with classic pigment. Better adsorption of binder into the bulky paper structure results in thinner layer of ink binder on the paper surface. On non-absorbent synthetic paper, microcapsules are covered with thicker layer of ink binder. In the case of bulky paper, the highest rate of biodegradation was observed, resulting in a higher number of bacteria, higher weight loss, higher changes in colour (destruction of almost all microcapsules) and almost complete reduction in thermochromic effect of the prints. Results show that microcapsules, which penetrate into the structure of bulky paper, are promoting the rate of bulky paper biodegradation. The opposite behaviour was noticed for the penetration of classic pigment into the structure of recycled paper, which resulted in remarkable reduction of recycled paper biodegradation rate. The thicker layer of ink binder (containing classic pigment) on the surface of microcapsules on recycled paper resulted in slower rate of microcapsules degradation and smaller colour change of the print. The thickest layer of ink binder and classic pigment on synthetic paper surface causes the slowest rate of biodegradation of print.

Colorimetric analysis of thermochromic samples in different forms employing a digital camera

The calibrated and characterised digital camera was used for the recording of a dynamic colour change of thermally treated three-component leuco dye based thermochromic samples in various forms – bulk system, dry pigment, water- and solvent-based ink formulations, and their dry layers coated on different paper substrates. The study has proved that the proposed approach enables to examine the thermochromic behaviour through the individual stages of the thermochromic coating preparation process. The measured path in CIELAB colour space and derived characteristics of the dynamic colour change were obtained with higher time-temperature resolution than with previously employed methods, enabling to observe even the less distinct features. The most significant differences were related to the length and complexity of the colour path. Dry layers of the water-based thermochromic ink coated on papers had higher values of the total length of the path and the total colour contrast than the layers of the solvent-based ink. The colour of water-based coatings had higher chroma and also it was less influenced by paper substrate. When compared to the bulk thermochromic system, the dry pigment and dry ink layers on paper substrates exhibited a larger width of a hysteresis loop at the decolouration limit, mainly due to the decrease of the temperature at which the colouration starts on cooling.

Visual and flexible temperature sensor based on a pectin-xanthan gum blend film

With the rapid progress in electronics technology, there has been an increasing trend towards making electronic devices light, flexible, and wearable. This study investigates an artificial skin-like temperature sensor based on pectin and xanthan gum. The highly flexible and transparent temperature sensor that was fabricated was simple in structure and the sensitivity was 53–130%°C−1 in the temperature range of 26 °C–50 °C. The temperature-sensitive thermochromic ink that was added to the sensing film enables the visualization of the temperature-sensing process. This smart thermal sensor can be widely applied in industries as electronic skin, human body temperature measurements, and environmental monitoring, etc.

Thermochromic offset ink – paper interactions and print biodegradation

This study examines the adhesion and interactions between thermochromic offset ink and different papers as well their role in papers and prints biodegradation. Obtained results show that biodegradation of prints depends upon the adhesion, i.e. lower adhesion will result in reduction of biodegradation rate, while the strong adhesion will result in better paper degradation. Reactions between paper and thermochromic ink will form different prints properties due to different affinity of paper for ink while interactions between them will affect the prints biodegradation. When the ink is applied on paper, the polar interactions of paper will react with polar interactions of ink. Smaller amount of polar components of paper will give a print with polar character.

Dichroism Infrared-reflective Thermochromic Ink of Mobile Terminals’ Recognition

The decoration of thermochromic ink has applications ranging from engineering devices to liquid sensors. However, when it comes to accurate computer identification the characteristic as dichroism is not fully used. Thus, we have recently proposed a manufacture method of dichroism infrared-reflective thermochromic ink. (DITI). By rubbing to heat DITI coated layer, this method enables us to finely and separately create dichroism manuscript after the handwriting is complete. Moreover, the microcapsules have cheerful compatibility. We have decorated conventional microcapsules with bola-type copolymer which allow us to fill them with Infrared (IR) reflective perssad. We consider this method promising to distinguish dichroism printing or writing on a tanglesome surface much quicker, for the IR reflective low-colour-density layer will be easily locked by an IR camera or a mobile phone camera to adjust specific characters of interest. We anticipate that this DITI ink will find use in markable temperature measurement, fluid machinery, anti-counterfeiting techniques and daily printing or writing.

Safety Evaluation of Deinked Pulp Containing Offset Thermochromic Inks

Evaluating the safety of thermochromic inks for offset lithography in deinked pulp samples is a major area of investigation. In this study, three offset inks were analyzed – one that dries by absorption and two that dry by oxypolymerization of vegetable oils. Inks were printed separately on strips of white uncoated paper, and the prints were recycled by chemical deinking flotation. Thermochromic inks, handsheets, filter pads, and process waters obtained from deinking were tested for the presence of heavy metals, while concentrations of bisphenol A (BPA), total organic compounds, and antimicrobial agents were examined in handsheets and filter pads. The concentration of heavy metals cations was determined from ashes of undeinked and deinked pulp handsheets as well as from ashes of blank paper, flotation froth, and process water filtrates. BPA originates from thermochromic inks, and a 50% reduction of BPA was noticed in the samples after flotation. Considering the results, deinked pulp is undesirable due to the presence of BPA. Despite the presence of BPA, there was no release of toxic components from deinked pulp.

Development and validation of an HPLC method for the determination of endocrine disruptors bisphenol A and benzophenone in thermochromic printing inks

ABSTRACTThe endocrine disruptors bisphenol A (BPA) and benzophenone (BFN) could be important ingredients in thermochromic printing inks in significant amounts. Due to patent protection and use of the inks, manufacturers are not obliged to state their precise chemical composition. These substances in increasingly used thermochromic printing inks present a hazard for human health and environment in the case of inappropriate application and waste disposal. In this work we enabled identification of the inks that contain these hazardous substances by developing a new method for the analysis of BPA and BFN in thermochromic printing inks. The method is based on the reversed-phase liquid chromatography (LC) with UV detection at 226 and 254 nm. Ultrasound-assisted sample extraction in methanol was proven to be the most suitable and effective among several other solvents. The method was completely validated with satisfactory results. The specificity of the method was proven by the additional LC–tandem mass spectrometry analysis. A representative group of 15 ink samples from various manufacturers, curing and printing modes was analyzed. BPA was found in three samples with mass fractions of about 2% while BFN was found in two samples with mass fractions of 0.34 and 0.66%.

AgNW/Chinese Xuan paper film heaters for electro-thermochromic paper display

Electro-thermochromic paper display is the convenient and low-cost device for information presentation. As an integral part of this device, film heaters (FHs) with conductive layer have attracted much attention. In this paper, the AgNW based film heaters on Chinese Xuan paper (CXP) substrates were fabricated by a drop-coating method. The fabricated AgNW/CXP film heaters exhibited high heating temperature (78.1 °C) at low input voltage (3 V) and short response time less than 15 s. We theoretically analyzed the principles of heating and put forward the non-linear relationship between the input power and steady-state temperature, which is agreeing with our experimental data. The film heaters showed excellent mechanical properties with the change of the resistance as low as 2.7% after 2000 times outer bending tests. Finally, the electro-thermochromic paper display was fabricated using the AgNW/CXP film heaters, with the thermochromic inks on the other side of the paper substrate. Such results showed a useful approach for manufacturing of colorful display and color-changing painting.

Molecular‐Printed Thermochromic with Fast Color Switching

AbstractColor generation by thermochromic materials offers several advantages over the light‐based technology: a passive circuit element‐driven simplified device layout, cost‐effectiveness, and clear visibility. However, thermochromic materials need to be effectively coupled with an external heat source to induce coloration, which generally involves slow heat transfer processes that are not suitable for potential display applications. Here, a method for molecular printing of a thermochromic ink with a low heat capacity, enabling an unprecedented, fast color switching without any optoelectronic elements, is demonstrated. Molecularly printed ink is patterned on fabricated microheaters that induce transient local heat generation, facilitating local heating and cooling processes. Depending on the density of the thermochromic ink, that is, the number of microcapsuled dyes in the form of a monolayer resulting in a low heat capacity, the chroma of the patterned ink could be increased. Using this technique, the thermochromic ink could be printed over centimeter scales, with cyan‐magenta‐yellow‐black colors at a color‐switching rate of 20–500 ms, to be integrated into the thermochromic device prototype for potential display applications.

Electrothermochromic paper fabricated by depositing polypyrrole on one side

Paper with color changes caused by applied electric voltages was fabricated by combining the electric heating feature of conductive polypyrrole (PPy) and the temperature response color-changing feature of thermochromic ink. Highly conductive PPy was deposited selectively on the graphite-coated side of the paper via electrochemical polymerization. Thermochromic ink was coated on the reverse side with white color. The conductive coatings were tightly covered on the paper due to the hydrogen bonding between the pyrrole rings and the hydroxyl groups of cellulose. The obtained paper could be heated to about 45 °C and change its color significantly under an applied voltage of 4 V.

Colorimetric description of thermochromic printing inks

The dynamic colour of three commercial reversible thermochromic inks were studied. Thermochromic printing inks change their colour according to a change in temperature. The two types of thermochromic inks are based on leuco dyes and liquid crystals. The thermochromic effect achieved by liquid crystals is quite different from the effect achieved with leuco dyes. Leuco dyes change from a coloured to a colourless state, or from one colour shade to another due to structural changes inside leuco dye molecules under assistance of developer. Liquid crystal inks change colour continuously throughout the spectrum, producing iridescent colours starting from red and shifting to blue part of the spectrum with temperature. The colour change results from the way light interacts with special arrangement of liquid crystal molecules to produce coloured reflection by interference, and with the variation of this structure with temperature. In this paper we will present differences between two types of thermochromic printing inks giving careful colorimetric characterization.