JP2021088180A - Non-contact thermal printing of color thermochromic material - Google Patents

Abstract

To provide non-contact thermal printing of a color thermochromic material.SOLUTION: A system includes an un-patterned heater 110 configured to pre-heat a thermochromic coating 195 disposed on a substrate 190 to a first temperature. The thermochromic coating has a threshold temperature at which a thermochromic material undergoes color change. The system also includes a patterned heater 130 comprising a plurality of heating elements configured to heat selected pixels of the thermochromic coating to a temperature equal to the threshold temperature or more according to a predetermined pattern. An air gap 150 is maintained between the plurality of heating elements and the thermochromic material while the patterned heater is heating the thermochromic material. Air in the air gap is heated to a second temperature.SELECTED DRAWING: Figure 1

Description

(Related patent documents)
This application is a partial continuation of US Patent Application No. 16 / 382,884 filed April 12, 2019, which is incorporated herein by reference in its entirety.

(Field of invention)
The present disclosure relates to systems and methods for processing thermochromic materials.

Thermochromic materials change color in response to exposure to temperature. Thermochromic inks can be applied to relatively large areas on a substrate by a number of printing or coating processes such as lithography, flexographic printing, gravure printing, screen printing, and spreading with a film applicator. After coating or printing a larger area with a thermochromic material, the area is exposed to heat and / or light to cause a color change in a precisely controlled area.

State-of-the-art thermal printing systems for printing thermochromic materials / coatings that can be used for printing on thermal paper, such as point-of-sale (POS) receipt printers, rely on the use of contact-based techniques. In this technique, an array of heater elements in a thermal print head is used to locally heat individual "pixels" on a substrate by contact to create the desired text / pattern.

Contact-based thermal printing may be undesirable in certain mass production applications due to associated maintenance requirements. Wear, periodic cleaning, and the need for overall maintenance of contact thermal printheads that are subject to constant friction with the print medium can result in unacceptable downtime and cost in a high volume environment. In these applications, the printhead heater element array and by maintaining a small gap between the heater element and the substrate and relying on the conduction / convection of thermal energy through the gap to print the desired image. A non-contact approach may be preferred that avoids constant scraping action between the thermochromic material and the coated substrate. For smaller applications, the non-contact approach is also desirable because it extends the life of the printhead and thus improves maintenance costs.

According to some embodiments, the system includes an unpatterned heater configured to preheat a thermochromic coating placed on the substrate to a first temperature. Thermochromic coatings have a threshold temperature at which the thermochromic material undergoes color change. The system also includes a patterned heater with a plurality of heating elements configured to heat selected pixels of the thermochromic coating to a temperature above a threshold temperature according to a predetermined pattern. The air gap is maintained between the plurality of heating elements and the thermochromic material while the patterned heater heats the thermochromic material. The air in the air gap is heated to a second temperature.

Some embodiments relate to a method involving preheating a substrate having a thermochromic coating placed on the substrate to a first temperature. Thermochromic coatings have a threshold temperature at which the thermochromic material undergoes color change. The air gap between the thermochromic coating and the patterned heater is heated to a second temperature. The patterned heater is operated to heat the preheated thermochromic coating above a threshold temperature according to a predetermined pattern.

It is a conceptual block diagram of a thermochromic image formation system according to some embodiments. It is a conceptual block diagram of a thermochromic image forming system including an air gap heater according to some embodiments. FIG. 5 is a diagram of a patterned heater heating element according to some embodiments. It is a flowchart of the thermochromic image formation method by some embodiments. FIG. 5 is a diagram of a laminate used to model the thermal properties of a system according to the embodiments described herein. It is a graph of the optical density of the thermochromic material with respect to the air gap distance obtained by using the non-contact thermal imaging technique described herein. According to the first embodiment, when the stack heater can provide a heating rate (power) of 94.54 W / mm2 and the coated substrate is moving at a rate of 0.05 m / sec. , G = 0.1 μm, 1 μm, 5 μm, 10 μm, and 20 μm air gap distances, showing the temperature (K) of the thermochromic coating. 6 is a graph showing the optical density of a thermochromic material, which is a measure of saturation as a function of the air gap distance g. It is a graph of the optical density of the thermochromic material with respect to the air gap g when the stack heater can provide a heating rate (power) of 94.54 W / mm2 and the air gap air is heated to 77 ° C.

The drawings are not always on scale. Similar numbers used in drawings refer to similar components. However, it will be understood that the use of numbers to refer to components of a given figure is not intended to limit the components in another figure labeled with the same number.

Non-contact printing preferably avoids wear, periodic cleaning, and the need for overall maintenance of the contact thermal print head, which is subject to constant friction with the printing medium. However, the air gap between the heater element and the substrate results in a rapid loss of heating effectiveness. Resolution and printing speed capabilities with air gaps greater than a few micrometers are reduced to below commercially viable levels. At the same time, maintaining an air gap of less than a few micrometers is the roughness of the substrate and any other microscopic dust / debris that may be present in the environment (eg, aerosolized food in a restaurant environment / It is very difficult from a practical point of view, as oil particles) can make it difficult to maintain such an accurate and clean air gap to enable the desired non-contact thermal printing.

The techniques described herein enable reliable non-contact thermal printing with relatively large air gaps of up to 20 micrometers, eg, about 5 μm to about 20 μm. The disclosed approach involves preheating the substrate on which the thermochromic coating is placed and heating the air in the gap between the thermochromic coating and the heating element. In some embodiments, substrate heating and air gap heating are performed so that the thermochromic material is maintained at a temperature just below its threshold temperature.

The thermal substrate on which the print pattern is formed is typically coated with a thermochromic material that changes color (or lightness / darkness) in response to temperature changes. An example of such a coating is a solid mixture of dye and suitable matrix, such as a combination of fluorene leuco dye and octadecylphosphonic acid. When the coating is heated above its melting point, the dye reacts with the acid and shifts to its colored form, and then as the matrix quickly solidifies, the altered form is preserved in a metastable state (thermo). A process known as chromism).

The temperature at which the thermochromic material discolors is called its threshold temperature. The threshold temperature is the temperature at which the color change is first detectable. Color change at full color saturation can be achieved by exposing the thermochromic material to a temperature above its threshold temperature over a predetermined period of time. The saturation level of the thermochromic material can be adjusted by exposing the thermochromic material to a shorter period of time and / or a low temperature above the threshold temperature. For some thermochromic materials, the threshold temperature can be about 80 ° C.

Types of thermoplastic materials useful in the embodiments disclosed herein are, for example, diacetylene ethers and diacetylene ethers thereof, as described in US Pat. No. 5,149,617, which is incorporated herein by reference. Contains homopolymers. Some other types of thermochromic materials are a) a solid yellow-brown gray (white) material at room temperature and a copper (I) iodide; b) a white material that converts to orange at 60-62 ° C. Ammonium metavanadate; and c) a purple material that turns brown at 150 ° C and then black at 170 ° C, a common purple pigment, and manganese violet (Mn (NH4)) that turns white at 400 ° C. ) 2P2O7) may be included. It should be noted that this is not an exhaustive list and other materials may be used in conjunction with the disclosed approach.

The techniques disclosed herein relate to systems and methods for image formation based on thermochromic materials. The thermochromic material is first preheated to a temperature below the threshold temperature. After preheating the thermochromic material to a subthreshold temperature, or simultaneously, the area of the thermochromic material is exposed to a patterned amount of energy dose and a given pattern, eg, text, image, or other two-dimensional. According to the symbol, it results in local heating above the threshold temperature.

FIG. 1 is a conceptual block diagram of the image forming system 100 according to some embodiments. The image forming system 100 includes an unpatterned heater 110 shown as a heated roller configured to preheat the substrate 190, which disperses heat onto the substrate. It is transmitted to the thermochromic coating 195. The unpatterned heater 110 supplies unpatterned thermal energy to the substrate 190, eg, thermal energy that is substantially constant over the surface of the substrate. Although shown as heated rollers in FIG. 1, the unpatterned heater may include any type of contact or non-contact heater, such as a radiant heater, a resistor heater, an infrared lamp, and the like. The temperature of the first heater 110 can be below the threshold temperature of the thermochromic material or, in some embodiments, above the threshold temperature. Overall heat transfer from the unpatterned heater 110 to the thermochromic coating is maintained by the system so that the temperature of the thermochromic coating remains below its threshold temperature. The heating rate, heating time, and / or temperature of the unpatterned heater 110 is such that the temperature below the appropriate threshold of the thermochromic coating 195 is the desired rate of movement of the substrate 190 through the image forming system 100 (“printing rate”. It can be controlled using a closed loop control system (not shown) configured to be achieved in).

After or at the same time as preheating the thermochromic coating 195, the unpatterned heater 110, the patterned heater 130, eg, a one-dimensional or two-dimensional spatially patterned heat source, may be selected pixels or The area of the preheated thermochromic coating is configured to be exposed to an energy dose amount according to a predetermined pattern. The thermochromic coating 195 may include multiple pixels, and a predetermined pattern defines the amount of energy dose to which each pixel is exposed. The amount of energy dose involves heating the selected pixels according to a predetermined pattern to a predetermined temperature above the threshold temperature of the thermochromic material for a predetermined time causing a change in the color of the pixels. For example, a non-selected pair of pixels with a thermochromic coating may not be exposed to an energy dose above the threshold dose. A first set of selected pixels of a thermochromic coating may be exposed to a first amount of energy dose, including a first temperature above a threshold temperature, for a first time. A second set of selected pixels may be exposed to a second amount of energy dose, including a second temperature above the threshold temperature, for a second time. According to some embodiments, one or both of the first temperature and the second temperature is within about 25% of the threshold temperature.

Non-selected pixels that are not exposed to the amount of energy dose from the patterned heat source do not rise above the threshold temperature, thereby remaining colorless. The first energy dose amount causes the first set of pixels to change color to achieve the first saturation level. The second energy dose amount causes the second set of pixels to change color to achieve a second saturation level. Although the present embodiment refers to reference to a first and second set of selected pixels exposed to a first and second dose amount, a given pattern is for three or more sets of pixels. It is understood that they may each be exposed to different energy dose amounts, thereby achieving three or more different temperatures above the threshold temperature and resulting in three or more resulting saturation levels. Let's go.

In many embodiments, the patterned heater can be a resistance heater, and the individual heating elements corresponding to the pixels are heated by the current flowing through the resistance heating elements.

The heating element of the patterned heater 130 does not contact the surface of the thermochromic coating 195. While the patterned heater 130 heats the thermochromic material 195 to a second temperature above the threshold temperature, the air gap 150 is between the plurality of heating elements 130a, 130b and the thermochromic material 195. Be maintained. The air gap 150 can be, for example, up to 20 μm, for example from about 5 μm to about 20 μm.

As shown in FIG. 1, in some embodiments, the substrate 190 comprises an elongated web or film on which a thermochromic coating 195 is placed. The moving mechanism 140, illustrated in FIG. 1 as a motor-driven pinch roller, moves an elongated substrate 190 through the system. For example, the moving mechanism 140 can move the elongated base material 190 at a printing speed of up to about 4 m / s. At these speeds, significant energy is required for the patterned heater 130 to meet the fast patterned heating requirements. By using the unpatterned heater 110 to preheat the thermochromic material and heat the air gap 150, the energy requirement of the patterned heater 130 is reduced.

As mentioned above, the unpatterned heater 110 may include at least one rotating heated roller or drum, wherein the moving mechanism 140 takes an elongated film 190 along the direction indicated by the arrow 199. When moved, it comes into contact with or is in close proximity to the elongated film 190. The roller 110 can be heated to any temperature as long as the effect of heating results in achieving the temperature of the thermochromic coating 195, which is close to the threshold temperature but below the threshold temperature. For example, the roller 110 achieves a thermochromic coating temperature at which the movement of the thermochromic material in conjunction with heating of the substrate is below the threshold temperature, eg, 10 ° C., 5 ° C., or even less than 5 ° C. below the threshold temperature. Can be heated as such. For example, in some configurations, the heated roller 110 may be heated to a temperature above the threshold temperature of the thermochromic coating 195. However, the residence time of the thermochromic coating 195 on the heated roller 110 is short, so the movement of the film 190 is controlled so that the thermochromic coating 195 is not heated above the threshold temperature.

FIG. 2 illustrates another embodiment of the image forming system 200 according to some embodiments. In addition to the unpatterned heater 110, the patterned heater 130, and the other components described above, the image forming system 200 is configured to preheat the air in the air gap 150, the gap heater 120. including. The air gap heater 120 may include any suitable type of heater, such as a forced air heater, a radiant heater, and the like.

According to some practices, the operation of the unpatterned heater 110 in conjunction with the air gap heater 120 preheats the thermochromic coating 195 to a temperature below the threshold temperature of the coating 195. In this practice, the thermochromic coating 195 does not show a color change depending on the subthreshold temperature resulting from the heating effect supplied by the unpatterned heater 110 and the air gap heater 120.

The unpatterned heater 110 and the air gap heater 120 can be set to different temperatures or the same temperature. For example, in some embodiments, the unpatterned heater 110 can be controlled by a thermostat to be heated to a first temperature. The air gap heater 120 is thermostat controlled so that the temperature of the air in the air gap 150 is controlled to a second temperature that is different from the temperature of the unpatterned heater 110, eg, higher or lower. obtain. In some embodiments, the unpatterned heater 110 may be set to the same temperature as the air gap heater 120. In various embodiments, one or both of the temperature of the heating element of the first heater 110 and the temperature of the air produced by the second heater 120 are 25%, 20% of the threshold temperature of the thermochromic coating 195. , 15%, 10%, 5%, or even less than 1%.

Optionally, any of the image forming systems 100, 200 may include a housing 122 in which an elongated base material 190 having a thermochromic coating 195 disposed on the substrate enters the housing 122 and the casing. Includes one or more openings that allow exit from body 122. The housing may be used to help maintain a more uniform temperature of the air in the air gap, which keeps the temperature of the thermochromic coating 195 more uniform. The inlet and outlet openings have air control functions as discussed in US Patent Application S / N 16 / 382,884 of the same owner, which is incorporated herein by reference. obtain.

According to some embodiments, the systems 100, 200 control and coordinate the operation of the unpatterned heater 110, any air gap heater 120, the patterned heater 130, and / or the moving mechanism 140. It may include a vessel 160.

In some configurations, the patterned heater 300 may include a plurality of heating elements 310, each heating element having a heating head 301 suspended on a deflection arm 302, as shown in FIG. Be prepared. In the embodiment shown in FIG. 3, the heating head 301 includes a resistance heating element 303. Each of the heating elements 310 may be floating in a manner similar to a floating disk drive read / write head. Each floating heating head floats on a substrate at a floating height that defines an air gap distance g. In some embodiments, the floating height may be equal to the air gap distance g, which is the distance between the heating head 301 and the substrate 392 having the thermochromic coating disposed on the substrate. The heating element may include a linear arrangement of deflections and heating heads that can be made using microfabrication. An air gap between the heater and the substrate is used, either forced air heated just below the threshold temperature of the thermochromic material or air from a mobile substrate heated just below the threshold temperature. Can be maintained.

FIG. 4 is a flowchart showing the operation of the system of FIGS. 1 to 3. The process involves operating an unpatterned heater to preheat a substrate with a thermochromic coating placed on the substrate to a first temperature, where the thermochromic coating is thermochromic. With manipulation (410), the material has a threshold temperature at which it causes a color change. The air gap between the thermochromic coating and the patterned heater is heated to a second temperature (420). The patterned heater is operated to heat the preheated thermochromic coating above a threshold temperature according to a predetermined pattern (430). According to some embodiments, the unpatterned heater can be in contact with the substrate and the patterned heater can be a non-contact heater, such as a resistance heater.

Using the disclosed method, thermal simulation experiments were performed to determine the feasibility of non-contact thermal printing over air gaps of up to 20 micrometers. The laminate used in the model setting is shown in FIG. The thermal model used was a two-dimensional model that included a lateral heat flow to the gold leads in the heater layer. In this experiment, multiple pixels were heated during the cycle time. During each cycle time, the voltage to the heater was pulsed to allow the heater to cool before the next cycle. By this process, the temperature of the heater can be lower than the onset of color development for the next cycle (pixels). The heater temperature and heat flow to the substrate depend on the configuration (material layer, dimensions) during the cycle and the details of the heater pulse width. In addition, history control is frequently used, which allows heating during the cycle, which is adjusted based on past cycles, and maintains the heater temperature on a cycle-by-cycle basis. Thermal cycle T _cycle = pixel_size / U, pixel_size is a pixel size of μm ² , and U is the substrate speed. Pulse time to drive the heater, pulse_time = 0.5 x T _cycle . The heaters are designed to provide a total heating power of approximately 95 W / mm ² when on, and each heating element is 80 micron x 40 micron in size and 0.304 W when on. The heating power per pixel can be obtained.

The thermal model assumes a laminate 500 with a substrate 501 separated from the heating assembly 550 by an air gap 502 of 0-20 μm. The heating assembly 550 includes a SiO2 layer 503, a resistance heating layer 504 having a thickness of about 1.5 μm, a glass layer 505 having a thickness of about 45 μm, and a heat conductive heat sink layer 506. Example 1 modeled an unpatterned heating layer without an air gap heater. FIG. 6 shows the temperature of the thermochromic coating with air gap distances of g = 0.1 μm, 1 μm, 5 μm, 10 μm, and 20 μm when the stack heater is on and moving at a speed of 0.05 m / sec. It is a graph which shows (K). FIG. 6 shows that the temperature achieved for thermochromic coatings with air gap distances of 5 μm, 10 μm, and 20 μm is below the 80 ° C. thermochromic threshold temperature of typical thermochromic materials. FIG. 7 shows the optical density of a thermochromic material, which is a measure of saturation, as a function of the air gap distance g. FIG. 7 also shows that in this experiment the optical density was substantially reduced for g> 1 μm. In this example, it was demonstrated that any air gap greater than 1 μm at room temperature air in the air gap results in a rapid loss of temperature on the substrate surface, thus making printing / imaging using a thermochromic coating impossible. ..

The same model as described above heats the ambient air in the gap to 77 ° C (= 350K), just below the threshold temperature of 80 ° C, against a substrate coated with a typical thermochromic material. It was used in the modified example. In this scenario, an air gap of up to 20 micrometers was possible, and it was shown that the loss of print darkness (optical density) of the resulting print was relatively small. FIG. 8 is a graph of the optical density with respect to the air gap g. FIG. 8 superimposes the data from FIG. 7 and the data obtained from the experiment in which the air gap air was heated to 77 ° C.

It will be appreciated that the various modifications and modifications of the embodiments described above will be apparent to those skilled in the art and that the present disclosure is not limited to the exemplary embodiments described herein. The reader should assume that the features of one disclosed embodiment can also be applied to all other disclosed embodiments, unless otherwise stated. It should also be appreciated that all US patents, patent applications, patent application publications, and other patent and non-patent documents referred to herein are incorporated by reference to the extent that they are consistent with the disclosures described above.

Claims (20)

An unpatterned heater configured to preheat a thermochromic coating placed on a substrate to a first temperature, said thermochromic coating is a threshold at which the thermochromic material undergoes color change. With unpatterned heaters that have temperature,
A patterned heater comprising a plurality of heating elements configured to heat selected pixels of the thermochromic coating to a temperature above the threshold temperature according to a predetermined pattern.
The patterned heater comprises an air gap maintained between the plurality of heating elements and the thermochromic material while the thermochromic material is being heated, and the air in the air gap is provided. , A system that is heated to a second temperature. The system according to claim 1, further comprising a moving mechanism configured to move the base material having the thermochromic material arranged on the base material with respect to the plurality of heating elements. The system according to claim 2, wherein each heating element is suspended on a deflection arm that floats on the thermochromic material. The system of claim 1, wherein the gap is from about 5 μm to 20 μm. The system of claim 1, wherein the air is heated by the unpatterned heater. The system of claim 1, wherein the unpatterned heater comprises one or more of a rotating heated drum, an infrared heater, and a resistance heater. The system of claim 1, further comprising an air gap heater configured to heat the air in the air gap to a second temperature. The system according to claim 7, wherein the air gap heater includes one or more of an infrared heater and a forced air heater. The system according to claim 7, wherein one or both of the first temperature and the second temperature is within 25% of the threshold temperature. The substrate comprises an elongated film
The system of claim 1, wherein the unpatterned heater comprises a rotating drum that contacts the elongated film. The system of claim 1, wherein the thermochromic material comprises a fluorene leuco dye. The system according to claim 1, wherein the plurality of heating elements of the patterned heater are resistance heating elements. Preheating the substrate having the thermochromic coating arranged on the substrate to a first temperature, wherein the thermochromic coating has a threshold temperature at which the thermochromic material causes a color change. To do and
Heating the air gap between the thermochromic coating and the patterned heater to a second temperature and
A method comprising operating the patterned heater to heat the preheated thermochromic coating above a threshold temperature according to a predetermined pattern. 13. The method of claim 13, wherein preheating the substrate comprises bringing the substrate closer to a heated rotating drum or in contact with a heated rotating drum. 13. The method of claim 13, wherein the air gap is heated by heat transfer from the preheated substrate. 13. The method of claim 13, wherein the air gap is heated by at least one of a forced air heater and an infrared heater. 13. The method of claim 13, wherein the air gap is 5 μm to 20 μm. 13. The method of claim 13, wherein one or both of the first temperature and the second temperature is below the threshold temperature. 13. The method of claim 13, wherein the patterned heater comprises a plurality of resistance heating elements. 13. The method of claim 13, wherein one or both of the first temperature and the second temperature is within 25% of the threshold temperature.

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