WO2022246121A1

WO2022246121A1 - Improved chemochromic indicator element

Info

Publication number: WO2022246121A1
Application number: PCT/US2022/030121
Authority: WO
Inventors: Koichi Nakamura; Nahid Mohajeri; Anna BALENKO; Jen-Chieh Liu
Original assignee: Nitto, Inc.
Priority date: 2021-05-19
Filing date: 2022-05-19
Publication date: 2022-11-24

Abstract

Described herein are chemochromic indicator elements that may include a cover layer, an indication layer, and a color contrast layer to provide improved shelf life and durability for extended monitoring for gases, especially carbon dioxide.

Description

IMPROVED CHEMOCHROMIC INDICATOR ELEMENT

Inventors: Koichi Nakamura, Nahid Mohajeri, Anna Balenko, and Jen-Chieh Liu

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 63/190,412, filed May 19, 2021, which is incorporated by reference in its entirety.

BACKGROUND

In the chemical industry, many hazardous gases are used. Any leakage of these gases may create fatal incidents. Gas leaks are inherently more dangerous than liquid leaks since the majority of gas leaks cannot be observed by the naked eye.

Carbon dioxide (CO2) gas has been used in many industries as a refrigeration coolant, carbonation gas for beverages, modified atmosphere packaging in food industries, and raw material for chemical industries. CO2 is a non-flammable gas and is relatively benign compared with other harmful gases. However, if CO2 concentration reaches a certain level, it may create a dangerous situation. OSHA regulation has established a Permissible Exposure Limit (PEL) of 5,000 ppm, and a NIOSH REL. TWA 5000 ppm for C0₂ gas.

Indicators including CO2 responsive dyes may be decomposed when exposed to air and light (mainly UV), and a short shelf life of indicating dyes is very inconvenient in many applications. Additionally, it may be difficult to recognize if the indicator has lost its ability to detect existence of CO2 gas. A shelf life of a minimum of 1 month, preferably 3 months, and ideally 6 months or more is desirable.

Typically, a gas leak is detected when pressure drops in a pipeline, and/orwhen there is an unusual consumption rate, and/or by using area gas sensors. Furthermore, leak tests need to be performed carefully to ensure tightness of all connections.

Wrapping joint parts on pipes with a tape that changes color when a gas leak occurs may be preferable to other conventional methods of detecting leaks.

Thus, there is a need for an indicator element that provides long term protection and function for the detection of CO2 gas leaks. SUMMARY

The disclosure relates to a chemochromic indicator for carbon dioxide having increased durability and/or activity lifetime. This increased durability and/or activity lifetime may be achieved by exposing the indicator to the desired test location while concurrently isolating the indicator element from the environment.

In some embodiments, a chemochromic indicator, may comprise an organic polymer and pH responsive dyes, wherein the chemochromic indicator changes color when it is exposed to carbon dioxide. In some embodiments, a chemochromic indicator may comprise an indication layer having a first side and second side. In some embodiments, the indication layer may comprise an organic polymer matrix and at least one pH chemochromic dye. The chemochromic dye may be dispersed within the organic polymer matrix, and the indicator may change color when it is exposed to carbon dioxide. In some embodiments, the chemochromic indicator may further comprise a cover layer, wherein said cover layer may be disposed upon the indication layer's first side. In some embodiments, the chemochromic indicator may further comprise a color contrasting layer. In some embodiments, the color contrasting layer may comprise a pressure sensitive adhesive. In some embodiments, the color contrasting layer may be disposed upon the indication layer's second side, e.g., opposite from the cover layer. In some embodiments, the color contrasting layer may be white or opaque. In some embodiments, the color contrasting pressure sensitive adhesive layer may comprise silicone polymer, polyurethane polymer, or synthetic rubber, e.g., a silicone polymer. In some embodiments, the color contrasting layer may comprise T1O₂, BaSC>₄, alumina, and/ or silica. In some embodiments, the adhesive layer may comprise T1O₂. In some embodiments, the cover layer may comprise polyethyleneterephthalate (PET), polyethylene (PE), poly propylene (PP), polyurethane (PU), orfluorinated polymers. In some embodiments, the transparent layer comprises PET. In some embodiments, the transparent protective layer may comprise a pressure sensitive, hot melt, or heat curable adhesive and/ or glue. In some embodiments, the pressure sensitive, hot melt, or heat curable adhesive and/ or glue may be translucent. In some embodiments, the transparent protective layer may comprise pressure sensitive adhesive. In some embodiments, the indication layer may have a first color before exposure to CO₂, a second color after exposure to CO₂, and a third color when the pH dye is decomposed. In some embodiments, the indication layer may comprise a CO₂ communicating conduit disposed lengthwise within the indication layer. In some embodiments, the conduit may comprise a film, paper, cloth, nonwoven material, and / or rubber. In some embodiments, the chemochromic indicator may further comprise a release liner disposed upon the color contrasting layer, e.g., pressure sensitive adhesive layer. In some embodiments, the release liner may comprise plural independently detachable sections. In some embodiments, the release liner may comprise at least three plural independently detachable sections.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of a possible embodiment of a chemochromic indicator element described herein.

FIG. 2 is a depiction of a possible embodiment of a chemochromic indicator element described herein.

FIG. 3 is a depiction of a possible embodiment of a chemochromic indicator element described herein.

FIG. 4A is a depiction of a possible embodiment of a chemochromic indicator element described herein.

FIG. 4B is a depiction of a possible embodiment of a chemochromic indicator element described herein.

FIG. 5 is a depiction of a possible embodiment of a chemochromic indicator element described herein.

FIG. 6 is a depiction of a possible test embodiment of a chemochromic indicator element described herein

FIG. 7 is a depiction of a possible test embodiment of a chemochromic indicator element described herein.

FIG. 8 is a depiction of a possible test embodiment of a chemochromic indicator element described herein.

FIGS. 9A, 9B and 9C are depictions of a possible test embodiment of a chemochromic indicator element described herein. FIG.10A is an elevational depiction of a possible embodiment of a chemochromic indicator element described herein, e.g., with a multi-sectioned liner layer.

FIG.10B is a top depiction of a possible embodiment of a chemochromic indicator element described herein, e.g., with a multi-sectioned liner layer, with later sections being peeled away.

FIG. IOC is an elevational depiction of a possible embodiment of a chemochromic indicator element described herein, e.g., with a multi-sectioned liner layer, with later sections being peeled away.

FIG. 11 is a photograph of a possible pennant shaped embodiment of a chemochromic indicator element described herein.

FIG. 12 is a photograph of a possible flag-shaped embodiment of a chemochromic indicator element described herein.

DETAILED DESCRIPTION

The present embodiments are related to a gas colorimetric indicator elements for indicating the presence of carbon dioxide (CO2).

For the purposes of this application, the following abbreviations may be used:

Silicone = Si

MEK= Methyl ethyl ketone Benzoyl peroxide = BPO Pressure sensitive adhesive = PSA Phr = parts per 100 rubber Room temperature = R.T.

Minute = min

Polyethylene terephthalate = PET Polyethylene =PE Average = av.

CO2 = Carbon dioxide

For the purposes of this application, the terms indicator layer and indication layer are considered to be equivalent. Use of the term "may" or "may be" should be construed as shorthand for "is" or "is not" or, alternatively, "does" or "does not" or "will" or "will not," etc. For example, the statement "the device may comprise a protection layer" should be interpreted as, for example, "In some embodiments, the device comprises a protection layer," or "In some embodiments, the device does not comprise a protection layer."

In some embodiments, a chemochromic indicator element may comprise an indication layer, a cover layer disposed on a first side of the indicator layer, and a color contrasting layer. In some embodiments, the color contrasting layer may be disposed on the second or opposite side of the indication layer. In some embodiments, the color indication layer may be disposed between the cover layer and the color contrasting layer. In some embodiments, the indicator element comprises, from the surface it is being placed upon, the contrasting color layer, the indication layer, and the cover layer. In some embodiments, the color contrasting layer may comprise an adhesive material. In some embodiments, the color contrasting layer may comprise an opaque or white material. In some embodiments, the indicator element may be disposed around or upon a surface to be tested for the presence of carbon dioxide (CO2). In some embodiments, the indicator element may further comprise a gas permeable substrate layer. In some embodiments, the cover layer is distal the surface being tested and/or proximal to the ambient environment. In some embodiments, the color contrasting layer and/or the permeable substrate layer may be proximal to the surface being tested for CO2 and distal the ambient environment. In some embodiments, the color indicator layer may be externally viewed or may be isolated from the ambient environment, and/or in gas communication with the surface being monitored, e.g., a pipe or conduit surface. It is believed that this isolates the indicator layer from the ambient environment while concurrently maintaining gaseous communication with the surface or area being monitored for the presence of CO2 or leakage therethrough. In some embodiments, the cover layer may be retained upon the indication layer during the duration of the monitoring.

In some embodiments, the chemochromic indicator element may comprise a first morphological element, e.g., a rectangular shape for placement at the monitoring location. In some embodiments, the chemochromic indicator element may comprise a tail element, e.g., a second rectangular or pennant shaped element extending from the first morphological element, e.g., downward, or away from the monitored site location which may or may not be attached to the actual desired monitored location. While being described as a rectangular or pennant shape, the first morphological element and/or the tail element may be any geometric or other type of shape. It is believed that the aforementioned tail element may provide additional monitoring activity away from the immediate disposed location, since CO2 is heavier than air and may drift downward away from the specified monitored location.

A chemochromic indicator element, such as element 10, is shown in FIG. 1. The element may comprise a cover layer, such as cover layer 14; an indication layer, such as indication layer 16; a color contrasting layer, such as color contrasting layer 20; and/or a release liner, such as release liner 22.

In some embodiments, as shown in FIG. 2, the cover layer may be attached to the indication layer by an adhesive layer24.

In some examples, as shown in FIG. 3, the color contrasting layer 20 may comprise a double-sided adhesive comprising a first adhesive layer 30, a double-sided adhesive backing layer 32, and a second adhesive layer 34 interposed between the indication layer, such as indication layer 16, and the release liner, such as release liner22.

In some embodiments, as shown in FIG. 4A, the chemochromic indicator element may comprise an indication layer 16, a first adhesive layer 30, a double-sided adhesive backing layer 32, a second adhesive layer 34 and a release liner 22 (FIG. 4A). Optionally, cover layer 14 may be placed on the indicator layer with adhesive layer24, as shown in FIG. 4B. In some embodiments, the cover layer is retained or maintained over the indication layer during the entirety of application of the chemochromic indicator element to the monitored location. It is believed that this construction may enable immediate indication of the presence of the contemplated gas leak despite a time interval from the initial disposition of the indicator element to the time of the perceived indication of gas presence.

In some embodiments, as shown in FIG. 5, the cover layer 14 may be combined with a contrast agent-containing adhesive layer23, so as to make the color contrasting layer20. In some embodiments, the contrast agent used in the contrast agent-containing adhesive layer 23 may be T1O2. This contrast agent-containing adhesive layer 23 may be the adhesive that fixes the indication layer 16 on the targeted area. To make the contrast agent-containing adhesive layer 23 adhere to the target, the indication layer 16 may be narrowerthan the cover layer 14 and the contrast agent-containing adhesive layer 23.

Color change Indication layer

In some embodiments, the chemochromic indicator element may comprise an indication layer. In some embodiments, the indication layer may comprise a pH responsive chemochromic dye. In some embodiments, the indication layer may comprise a structural matrix. In some embodiments, the pH responsive chemochromic dye may be dispersed within or upon the structural matrix. The pH responsive chemochromic dye may change its chemical structure and thus its perceived color by the change in acidity caused by the presence of CO2. Any suitable (but non-limiting) example of a pH responsive dyes may be m- cresolsulfonphthalein (metacresol purple or m-cresol purple), o-cresolsulfonephthalein (cresol red), phenolsulfonphthalein (phenol red or PSP) and the like. In some embodiments, the indication layer may have a first color before exposure to CO2, e.g., purple, a second color after exposure to CO2, e.g., yellow, and/or a third color when the pH dye is decomposed, e.g., transparent or the color of the color contrasting layer, e.g., white, or opaque. The indicator colors may vary according to the particular pH responsive dye selected, e.g., m-cresol purple. In some embodiments, the pH responsive indicator dye may change from a first color to a second color in response to the change in pH of the monitored location, e.g., the presence of CO2 resulting in a change in the pH. In some embodiments, the pH responsive dye may provide a visually perceptive color change from a first pH in the monitored location. It is believed that CO2 at a leakage site converts to carbonic acid, which, based on its concentration, may alter the color of the pH responsive indicator layer. Depending on the particular indicator dye selected, the pH effecting color change may be altered.

In some embodiments, the indicator layer may comprise a structural matrix. In some embodiments, the structural matrix may comprise an organic polymer. In some embodiments, the structural matrix may comprise a thermoplastic resin and/or rubber. In some embodiments, the thermoplastic resin may be polyethylene, polypropylene, polyethyleneterephthalate, polyvinyl chloride, polyurethane, or any combination thereof. It is believed that if the polymer has some measure of acidity, it may cause a color change of pH dye in the indicating layer. In some embodiments, the rubber may be styrene-isoprene- styrene (SIS) rubber, styrene-butadiene (SBR) rubber, styrene-butadiene-styrene (SBS) rubber, latex of Hevea brasiliensis, mainly poly-cis-isoprene (natural or NR) rubber, nitrile (NR) rubber (made from cyanobutadiene or 2-propenenitril and butadiene), or any combination thereof.

In some embodiments, the indication layer may comprise a communicating conduit disposed lengthwise within the indication layer. In some embodiments, the communicating conduit may comprise a conduit, passageway and/or channel defined within the indication layer. In some embodiments, the communicating conduit may extend lengthwise along a first dimension. In some embodiments, the conduit may be medially disposed within the width dimension. In some embodiments, the conduit may comprise a gas permeable material. In some embodiments, plural apertures may be defined within the communicating conduit, said apertures connecting the interior of the conduit with the indication layer containing pH responsive dye. In some embodiments, the communicating conduit may comprise film, paper, cloth, nonwoven material, or rubber. In some embodiments, the communicating conduit may extent within the tail element of the indicator element.

In some embodiments, the pH responsive dyes may be mixed with thermoplastic resin or rubber in extruder or open mixing rollers. In some embodiments, the pH responsive dye may be dispersed throughout the thermoplastic resin or rubber. In some embodiments, the pH responsive dye may have a concentration gradient within the thermoplastic resin or dye. In some embodiments, the higher concentration of the pH responsive dye may be disposed in the region proximal to the surface being monitored. After it is mixed well, the mixture may be extruded from die or rolled out to be thin film form.

Cover layer

In some embodiments, the chemochromic indicator element may comprise a cover layer. It is believed that pH responsive dyes may be decomposed by exposure to light and/or air. It is also believed that pH responsive dyes tend to decompose faster when they dyes are exposed both to light and air together. A cover layer may be disposed over the indication layer to isolate the indication layer from the environment. In some embodiments, the cover layer may be disposed upon the indication layer to continually isolate the indication layer from the environment during the application of the indicator element at the desired monitored location. In some embodiments, the cover layer may have a CO2 gas permeability of less than 200,000 ml/m²*day*MPa, less than 100,000 ml/m²*day*MPa, less than 50,000 ml/m²*day*MPa, less than 40,000 ml/m²*day*MPa, less than 30,000 ml/m²*day*MPa, or less than 20,000 ml/m²*day*MPa. In some embodiments, the cover layer may have a CO2 gas permeability of at least 100 ml/m²*day*MPa, at least 500 ml/m²*day*MPa, at least 1,000 ml/m²*day*MPa, or at least 5,000 ml/m²*day*MPa. In some embodiments, the cover layer may be a transparent layer. In some embodiments, the cover layer may be a translucent layer. This cover layer may not only minimize exposing the indicating layer that has pH responsive dyes to air but also may reflect back or absorb some parts of light's energy. To assess the color change of pH responsive dyes by CChto the naked eye, the cover layer may be a translucent color. In some embodiments, white color may be added to the cover layer to provide a color contrast difference in order to detect exposure to CO2.

In some embodiments, the cover layer may comprise an ultraviolet radiation absorber and/or hindered amine light stabilizers. In some embodiments, the UV absorber may comprise Tinuvin 326 of BASF. In some embodiments, the hindered amine light stabilizers (HALS) may be Chimassorb 944 from BASF. However, without adding those aforementioned additives, it is believed that the transparent or translucent (clear color) film may provide significant improvement to the chemochromic indicator element. In some embodiments, the cover layer may be co-extruded resin layer with the indicating layer. In some embodiments, the protective layer may comprise the same resin is used for as the indicator layer, only without pH responsive dyes, or with less than 1.0 wt%, less than 0.5 wt%, less than 0.25 wt% less than 0.1 wt%, less than 0.05 wt%, less than 0.01 wt%, or less than 0.001 wt% pH responsive dye in the cover layer. In some embodiments, the cover layer may have no pH responsive dye in the cover layer. In some embodiments, the cover layer may be laminated upon the indicator layer with single coated adhesive tape.

In some embodiments, the cover layer may be attached to the first side of the indication layer by an adhesive element. In some embodiments, the adhesive element may be transparent. In some embodiments, the adhesive element may allow about 50-60%, about 60-70%, about 70-75%, about 75-80%, about 80-85%, about 85-90%, about 90-95%, or about 95-99% total light transmission therethrough. In some embodiments, the adhesive may comprise a silicone polymer, polyurethane polymer, acrylic polymer and/or resins. In some embodiments, the polymer and/or resin may have a pH that is numerically greater than the pH threshold for effecting a perceptible color change. In some embodiments, the polymer and/or resin may have a pKa greater than H2CO3. It is believed that if the adhesive has acidity, it may effect color change of pH responsive dye in the indicating layer. It is also believed that if the adhesive has acidity, it may facilitate the reversibility of the pH responsive dye to CO2 coloration. In some embodiments, the adhesive element may comprise a backing layer. In some embodiments, the backing layer may be transparent. In some embodiments, the backing layer may comprise polyethylene, polypropylene, polyethylene terephthalate, polyurethane, or any combination thereof.

In some embodiments, the color change retention time may be extended to about 15 minutes, about 15-30 minutes, about 30-45 minutes, about 45-60 minutes, about 60-75 minutes, about 75-90 minutes, about 90-105 minutes, or about 105-120 minutes. It is believed that the cover layer may make color change retention time longer by isolating the indication layer from the deteriorating sources, e.g., environmental CO2 and/or light. It is believed that the cover layer may make the color change retention time longer by increasing the CO2 residential time and contact with the pH responsive dye.

In some applications, when a gas leak is recognized by a drop in pressure or unusual consumption, the gas flow in a pipeline may be stopped to secure safety, then detection of the leak point is carried out. During this search period, if the color of a chemochromic indicator element film is reversed to its initial (e.g., non-exposed to CO2) color immediately, the exact leak point may not be able to be recognized, particularly if the pipeline is long and/or the piping system is complicated. It is believed that it is desirable for the color change of a chemochromic indicator element film to continue after the color changing gas supply is stopped. In some embodiments of pH responsive dyes, the color change may be reversible. If both sides of the indication layer are covered with cover layers, CO2 gas penetration to the indication layer may take time or may not occur although a longer color change retention time may be expected. However, if just one side of the indication layer is not adjacent or contacting the targeted monitored location, like as applied to pipes or flanges, the gas permeation to indication layer may not be affected. Once the gas permeates into the indication layer, the cover layer may prevent releasing of CO2 gas from the surface of the indication layer, yet also allow the CO2 gas to pass to the indication layer from the pipe or location to which the chemochromic indicator element is applied. In addition, continued leakage of CO2 may minimize or reduce the reverse coloration. In some embodiments, one side (e.g., the second side) of the indication layer is in contact or communication with a surface to be monitored for CO2 leaks, such as a pipe, flange, or other vessel that may potentially contain CO2, while the first side of the indication layer is in contact or communication with the cover layer.

Color contrasting layer

In some embodiments, the chemochromic indicator element may comprise a color contrasting element to facilitate perception of the chemochromic color change. In some embodiments, the color contrasting element may comprise a white or opaque background. When the chemochromic indicator element with clear pressure sensitive adhesive is wrapped on pipes or flanges, the color change may not be obvious if the pipe color is black, silver, etc. because the indicating layer may be translucent. The chemochromic indicator element layer may have adhesion to apply on the monitored target, e.g., pipe, flange, and the like. It is believed that adhering the chemochromic indicator element to the target location creates or defines a confined space that leaked gas may stay within and maintain or attain a concentration of gas sufficient to result in a perceptible color change. This may allow the chemochromic indicator element tape or element to change color before gas dissipates or becomes diluted.

In some embodiments, the color contrasting layer may comprise an adhesive polymer. In some embodiments, the adhesive polymer may be a pressure sensitive adhesive. In some embodiments, the adhesive layer may have a pKa greater than that of H2CO3. It is believed that if the adhesive has acidity, it may cause a color change of the pH responsive dye in the indicating layer without the presence of leaked CO2. For example, silicone polymer base adhesive may have a pH that may not be low and /or below that of H2CO3. In some embodiments, another consideration may be whether the adhesive selected is easy to remove from the target (e.g., pipe, flange, etc.) in case adhesive residue remains when tape is peeled off. Silicone may also provide better gas permeability.

In some embodiments, the adhesive polymer may have a CO2 permeability (cubic centimeters of gas passage at standard temperature and pressure [STP]/ cm²*mm*S*cmHg*10¹⁰) of greater than about 500, greater than about 750, greater than about 1,000 or greater than about 5,000. For example, silicon rubber may have a CO2 permeability of about 6,000 to 30,000; SBR may have a CO2 permeability of about 1,240; NR may have a CO2 permeability of about 1,330.

In some embodiments, the adhesive may comprise acrylic base adhesive, polyurethane, synthetic rubber base adhesive, or a combination thereof. In general, adhesive residue of acrylic adhesive, polyurethane adhesive, or synthetic rubber base adhesive may be more difficult to remove than silicone adhesive if it occurs on target.

In some embodiments, the adhesive may be noble metal-cured. In some embodiments, the noble metal may be platinum.

In some embodiments, the adhesive may be curable. After the adhesive is dried and optionally cured, it may be laminated with the indicating layer (also known as transfer coat). To apply silicone base adhesive as a transfer coat, a platinum cure system silicone adhesive may be more efficient than a BPO (benzoyl peroxide) curing system. A BPO curing system tends to react with the fluoro-silicone release agent on the release liner, which may make the liner release from adhesive heavier and difficult to remove.

In some embodiments, the adhesive may comprise T1O2, BaSC>4, alumina, or silica to provide the white color or opacity. In some embodiments, the above described constituents may be added in a range between 1 to 10 parts per 100 rubber/resin (phr). In some embodiments, T1O2, BaSC>4, alumina, or silica constituents in a range between about 1-2, about 2-3, about 3-4, about 4-5, about 5-6, about 6-7, or about 7-10 phr may be added.

In some embodiments, the adhesive and/or color contrasting layer may be gas permeable. In some embodiments, the adhesive and/or color contrasting layer may have a CO2 gas permeability (cubic centimeters of gas passage at standard temperature and pressure ([STP]/ cm²*mm*S*cmHg*10¹⁰) of greater than about 500, greater than about 750, greater than about 1,000, or greater than about 5,000. For example, silicon rubber may have a CO2 permeability of about 6,000 to about 30,000; SBR may have a CO2 permeability of about 1,240; NR may have a CO2 permeability of 1,330. It is believed the permeability allows the CO2 gas to pass through the color contrasting layer to the indicator pH responsive dye, enabling the presence of CO2 to result in a color change upon interaction with the pH responsive dye. In some embodiments, the cover layer may be color contrasting layer, wherein the level of translucent and opacity to get color contrast may be balanced. When opacity is too high, the color change by a leak gas may not be observed.

Release liner

In some embodiments, the chemochromic indicator element may comprise a release liner. In some embodiments, the release liner may be disposed upon the color contrasting layer, e.g., applied on a white or opaque adhesive layer attaching the chemochromic element to the desired location to be monitored.

In some embodiments, the release liner may comprise a carbamate compound release agent or silicone release agent. In some embodiments, if the indicating layer comprises a silicone adhesive, a release agent may comprise a fluoro-silicone release agent, e.g., Loparex, S2 CL PET 5100/000. In some embodiments, the release liner may comprise polypropylene, polyethylene terephthalate, polyethylene, or paper. In some embodiments, the release liner may comprise plural independently detachable sections such that it may have splits and it may be released partially or sequentially. In some embodiments, the release liner may comprise at least 3 plural independently detachable sections, such that the release liner may have 2 splits and it may be released partially or sequentially.

Using double coated tape for white or opaque adhesive layer and release liner

In some embodiments, the color contrasting layer (e.g., the white or opaque adhesive layer) may comprise a double coated adhesive tape and/or may be laminated onto the indication layer. In some embodiments, either the adhesive and/or backing layer may be a white or opaque color to better contrast the colored indication layer as it changes color from one color to another with changing pH conditions (CO2 concentrations).

In some embodiments, the backing layer may comprise a gas permeable material. In some embodiments, the gas permeable material may comprise nonwoven material, paper, or cloth, so that CO2 gas may penetrate through. If paper, or non-woven material is used, the natural color of those are considered sufficiently opaque. In this case, the adhesive does not have to be white or opaque. In some embodiments, the gas permeable material may have a CO2 permeability (cubic centimeters of gas passage at standard temperature and pressure [STP]/ cm²*mm*S*cmHg*10¹⁰) of greater than about 500, greater than about 750, greater than about 1000 or greater than about 5000.

The embodiments of the chemochromic CO2 indicatorelements described herein have improved durability as compared to other CO2 indicator elements. These benefits are further demonstrated by the following examples, which are intended to be illustrative of the disclosure only, but are not intended to limit the scope or underlying principles in any way.

Example 1: Preparing the Membrane elements

Methods Used in the Examples

Method 1 - Making white or opaque adhesive layer.

A coating machine with a glass plate was prepared. A 12" width x 14" length film release liner was placed on the clean glass plate wherein the plate was larger than the film backing. One end of the film backing is fixed on the glass temporarily with double coated adhesive tape. A draw down bar (effective width 9", Tester Sangyo Co. LTD, Tokyo Japan) was placed on the film backing. An appropriate amount, e.g., 5-10 g, of adhesive solution, e.g., polyurethane, was placed in front of the draw down bar, and then the dial of the coating machine was adjusted to control the gap between the film and the bar in order to get a target thickness, e.g., 5 to 150 microns. The bar was drawn down so as to coat the adhesive onto the release liner. The coated release liner was placed on the support plate. The release liner may be fixed onto the plate with clips. The coated release liner was air dried at room temperature for about 3 to 5 minutes, and then dried and cured at high temperature, e.g., 130 °C for Pt cured silicon, for 3 minutes.

Method 2 - Exposing sample to CO2 gas inside vial

A carbon dioxide source 100 was connected by a silicone tube 104 to the flowmeter 106 with the carbon dioxide gas (arrow 110) flowing out at a sufficient rate, e.g., 15 ml/min, from the other end through a needle 108. This needle pierced a rubber top 112 covering a 24 mL glass vial 114. A second needle 116 was in the rubber top as an exhaust to enable gas to outflow (arrow 117). The specimen 118 was placed inside the glass vial. (Figure 6) Method 3 - Exposing sample to CO2 gas when placed on top of vial

Chemochromic indicator tape 118 was placed on top of an LDPE plastic vial 114 (30 mL) with 100% CO2 gas (15 mL/min) flowing (arrow 110) inside the vial through a needle 108. A second needle 116 pierced the other side of the plastic vial as an exhaust (exhausted gas indicated by arrow 117). All samples were purple before insertion on top of the test chamber. All samples changed colorfrom purple to yellow within 10 minutes. (Fig. 7) Results are shown in Table 5.

Method 4 - Ab difference

A colorimeter device (Color-Tec PCM+, Color-Tec, NJ, USA) was used to measure Ab, which represents the blueness-yellowness difference between sample and standard colors of the lightness index L* a* b* color system in CIELAB1976. The Ab of the specimen was measured against the standard white panel (i.e., the blank) that was equipped with this device. This is the Ab i_nitial value. After the specimen was exposed to carbon dioxide gas, the Ab of the specimen was measured against the standard white panel. This is the Ab after value. The Ab difference is calculated by subtracting Ab initial from Ab after to obtain the Ab difference. The absolute value of the Ab difference is recorded. The higher value of Ab difference corresponds to a more intense color-change.

Ab difference ⁼ | Ab after ^— Ab before |

When the specimen was measured, the adhesive side was covered with a clear fluoro- silicone PET release liner. Then, the specimen was placed on white copy paper. The Ab value was measured from the backing film side.

If the Ab difference is > 5, it is easy to recognize the difference in color by the naked eye.

Method 5 - Contrast check on silver and black back grounds

In actual industry application, the chemochromic gas indicator may be applied on pipes, flanges, connections that are silver metallic color or in some cases, they have darker color paint. To check if indicator's color change is easy to recognize on these background color or not, Carbon oxide gas exposed samples were placed on silver and black color background. Example 2 - Using Pt cure Silicone adhesive as white or opaque pressure sensitive adhesive

A platinum (Pt) catalyst (CAT-Pt-50T, Shin-Etsu silicone, Akron OH, USA, 0.09g) along with toluene (T324-4 Fisher chemical, Fair lawn, NJ, USA, 6.81g) was added to the adhesive (KR-3700 Shin-Etsu silicone, Akron OH, USA, 30. Og) and mixed. In a 30 mL glass vial, T1O2

(224227-500G Sigma Aldrich St. Louis MO, USA, 0.9g) and MEK (31069 Alfa Aesar Ward Hill, MA USA, 6.0g) were sonicated for 5 min. using Branson 200, Ultra sonic cleaner and the resulting slurry solution was poured into the adhesive and mixed. Formulations are shown in Table 1. This adhesive solution was coated on fluoro-Silicone release liner (Loparex, S2 CL PET

5100/000) using Method 1. Oven condition of 130 degree C for 3 min. was applied to cure and dry it up. Thickness of dried adhesive was adjusted to 70 micrometer (pm).

This completed white adhesive layer was laminated on pH dye containing polyethylene (PE) film (NOVAS CR, Insignia Technologies LTD, BioCity Scotland, United Kingdom) with a roller. On the opposite side of the pH responsive dye containing PE film, Cover layer (P904 Clear PET Silicone single side tape. Nitto Inc. Teaneck, NJ USA) was laminated.

Table 1- Formulation of example 1

Example 3

White translucent silicone adhesive described below in Table 2 was coated on 1 mil thickness PET film. Thickness of adhesive coating was 45 miti. Coating was carried out using the method described in Examplel. Then, fluoro-Silicone release liner (Loparex, S2 CL PET 5100/000) was laminated on the adhesive. This adhesive sheet was cut into 2 inches width. pH dye containing polyethylene (PE) film (NOVAS CR, Insignia Technologies LTD, BioCity Scotland, United Kingdom disclosed in United States Patent No. 8,790,930, issued July 29th, 2014) was cut into 1 inch width.

This 1-inch width pH dye containing PE was laminated on the middle of a 2-inch white translucent adhesive sheet after the release liner was removed. Lamination was done with roller that surface was covered by fluoro-silicone release liner film.

After both were laminated, another fluoro-silicone release liner was placed on adhesive and pH dye containing PE as shown Fig.5.

Table 2- Formulation of example 2

Comparison 1

BPO (Sigma Aldrich Luperox A98, 0.41g) was dissolved in toluene (4.5g) and added into a SilGrip™ 518 adhesive (Momentive Westchester County, NY USA, 30. Og). T1O2 (224227- 500G Sigma Aldrich St. Louis MO, USA, 0.83g) and MEK (31069 Alfa Aesar Ward Hill, MA USA, 6.0g) were added into a 30 ml glass vial. Then, the vial was sonicated for 5 min. with sonicator

(Branson 200, Ultra sonic cleaner), and the resulting slurry was poured into the SilGrip™ 518 adhesive. The vial was rinsed with MEK (l.Og) and poured into the adhesive. The vial was rinsed one more time with extra MEK (1.0 g) and poured into the adhesive. A draw down sample was made on fluoro-silicone release liner (Loparex, S2 CL PET 5100/000) using Method 1. The sample was cured and dried by heated the sample in an oven at 177 °C for 3 min.

Formulations are shown in Table 3.

Completed white adhesive layer was laminated on pH responsive dye containing PE film (NOVAS CR, Insignia Technologies LTD, BioCity Scotland, United Kingdom disclosed in United States Patent No. 8,790,930) with roller. A cover layer (P904 Clear Silicone single side tape, Nitto, Inc., Teaneck, NJ USA) was lamined on the opposite side of the PE film containing the pH responsive dye.

Table 3- Formulation of comparison 1

Comparison 2 - No T1O2 in pressure sensitive adhesive layer (not white or opaque adhesive) The formulation for Comparison 2 was prepared by the method described in example 1, except that T1O2 slurry was not made and not added in the adhesive layer. This sample does not have opacity. Formulation is shown in Table 4.

Table 4- Formulation for Comparison 2

Comparison 3,4 - No cover layer and utilizing double coated tape as white or opaque pressure sensitive adhesive layer Comparison 3

Acrylic adhesive, double coated pressure sensitive adhesive tape No. 5000NS (Nitto, Osaka, Japan) was laminated on pH dye containing PE film (NOVAS CR, Insignia Technologies LTD, BioCity Scotland disclosed in US PAT08790930) with roller. Cover layer was not applied.

Comparison 4

Synthetic rubber base adhesive, double coated pressure sensitive adhesive tape No. 513 (Nitto, Osaka, Japan) was laminated on pH dye containing PE film (NOVAS CR, Insignia Technologies LTD, BioCity Scotland disclosed in US PAT08790930) with roller. Cover layer was not applied.

5.2 Test Results

5.2.1 Color change by 100% CO2 gas

Samples from example 1 and comparison 2-4 were exposed to 100% CO2 gas using Method 3. Color change were measured using Test Method 4. Table 5 - Test result of comparison 2-4 conditions with 100% CO2 using test Method

3 and Method 5

5.2.2 Color change vs. temperature, Example 1 Color change of carbon dioxide indicator was tested in various temperatures using the device depicted in Fig. 8. Silicone oil 120 in bath 122 was placed on a hot plate (not shown) and heated up to 60°, 70°, or 80 °C. A 40 ml glass vial 114 with rubber top 112 that has specimen of example 1 (sample 118) was partially immersed in silicone oil for 30 min. to condition. In parallel, specimen (tape sample of example 1) was conditioned in heated oven at test temperature for 30 min. Then, specimen was placed in glass vial. Two needles (108 and 116 respectively) were inserted into the vial 114 from rubber top 112. One is for feeding (arrow 110) and other one is for exhaust (arrow 117) of 100% CO2. CO2 gas (15 ml/min) was fed into the glass vial. Color change of specimen 118 was observed. At temperatures up to 70 °C, a color change by CO2 was observed. However, at 80 °C, color change was not observed. (Table 6)

Table 6- Color change of carbon dioxide indicator in various temp.

5.2.3 Testing color change at -18.5 °C

A 24 ml of glass vial 114 with screw top 120 that has rubber film was purged and filled with 100% CO2. To purge and fill, 2 needles (108 and 116 respectively) are pierced to rubber at top as shown in Fig. 9A. One is for feeding 100% CO2 (indicated by arrow 110); the other one is for exhaust (indicated by arrow 117) (FIG. 9A). 15ml/min of 100% CO2 was added for 30 min at in room temperature. Then, needles were taken away and vials were sealed by screw top 120 (FIG. 9B). This CO2 filled glass vial and specimen (118) (indicator, example 1) were conditioned at -18.5 °C for 30 min. The screw top of the glass vial was removed, and specimen 118 was adhered on top of glass vial 114 to see if a color change occurred. (Fig. 9C) Table 7 shows that the sample changed color to yellow within 2 minutes after exposure to CO2 gas.

Table 7 Color change by 100% CO2 in low temp.

Using Method 2, Insignia film (NOVAS-CR) (Insignia Technologies, Lanark, South Lanarkshire, United Kingdom) was exposed to 0.1% CO2 (15 mL/min) inside a glass vial (24 mL). Results are shown in Table 8. Color change was measured using Method 4.

Table 8- Color change measurement of Insignia film when exposed to 0.1% CO2

Table 8 Color change by 0.1% CO2

Using Method 2, Insignia film (NOVAS-CR) was exposed to 1% CO2 (15 mL/min) inside a glass vial (24 mL). Results are shown in Table 9. Color change was measured using Method

4. Table 9- Color change measurement of Insignia film when exposed to 1% CO2

.2.5 Color change vs. CO concentration for Insignia tape using NOVAS-CR

Using Method 3, Insignia tape (NOVAS-CR film with P904 cover tape and ShinEtsu silicone KR3700/TiO₂ layer) was exposed to 1% CO2 (15 mL/min). The tape was placed on top of an LDPE plastic vial (30 mL) with gas flowing inside. Color change was measured using Method 4. The test results are shown in Table 10.

Table 10- Color change measurement of Insignia tape when exposed to 1% CO2

5.2.6 Photodegradation by room light

Sample A: 2 inches x 2 inches size of NOVAS-MCP (Insignia Industries) film without white or opaque adhesive

Sample B: 2inches x 2 inches size of NOVAS-MCP (Insignia industries) covered with P904 (Nitto, Inc., Teaneck, NJ, USA), without white or opaque adhesive. Both samples were placed on laboratory bench and exposed to room light for 4 months. Table 11 shows the test result for before and after room light exposure. Color change was measured using Method 4.

Table 11- Before and after room light exposure

This experiment showed applying cover tape on just one side of indication layer may significantly increase color change retention time.

5.2.7 Release liner

Release liner of sample were peeled off from adhesive layer and observed for ease of removability. Results are shown in Table 12.

Pt. catalyst curing system is better than BPO curing system in the sense of easy liner releasing.

Table 12- Ease of removing release liner

Release liner may split into 2 or 3 in length direction. A split liner makes it easy to find entry to peel off liner. A 3-way split is for, e.g., cold temperature application. In cold temp application, after the leak indicator was applied on joint part of pipe, flanges, entire pipe, the leak indicator tended to be covered by ice. This could cause a color change caused by a CO2 to not be observable. To avoid such situation, a long tail (baggage-claim tag-like) way may be a better way to apply and indicate the presence of CO2 gas by extending downward and away from the target site to provide a better viewing of the color change. This tail may extend from the lower side of the gas pipe since CO2 gas is heavier than air.

When long tail embodiment is applied, if the chemochromic indicator adhesive tape has communicating conduit to lead leaked gas to travel in length direction of the tail, color change may be observed out of ice encrusting on the pipes. Shown in FIG. 10A is a side (elevational) view of a chemochromic element 10, having a cover layer 14, an indicator layer 16, a color contrasting layer 20 and adhesive 24 and one section 22A of the release liner. FIG. 10B is a top (plan) view of the chemochromic element of FIG. 10A, with two sides of a 3-way split being partially pulled away. In this case, the release liner may have a 3-way split, wherein both sides of the split liner (e.g., liner sections 22A and 22C) may be removed, and the middle (liner section 22B) may stay on adhesive, as shown in FIG. IOC. The middle section, such as section 22B, may become a conduit. Figs.11 and 12 show the tape construction with middle liner for long tail application after exposure to CO2 gas.

Instead of 3 ways slit liner, narrow film, or paper may be applied in middle of indicator tape instead. Flowever, this may be more labor intensive.

5.2.9 Color change retention time of pH dyes containing PE film with Cover tape

NOVAS-MCP and NOVAS-CP (Insignia technologies, Scotland) with cover tape P904, without cover tape were exposed to 100% CO2 gas 15ml/ min for 5 min. in 30 ml glass vial.

Specimens exhibited full color change caused by CO2 gas. Then, those samples were left upon the laboratory bench to exposed air. Gradually, CO2 gas was dissipated from the indication film. At same time, color of indication film resumed back to original color. Ab Yellow-blue color was measured by time to see how long color change was retained. Table 13 shows the color change test result for with and without cover tape.

In case where the cover tape was not applied, at 15 min., the color returned back to almost original color. In case where the cover tape was applied, it took about 2 hrs. to return back to almost the original color. At the 1 hr time point, there was a clear difference from original color. Even at 1.5 hrs., the difference was still recognizable. Thus, it appears providing a cover layer on top of indication layer was very effective in slowing down the color reversibility by allowing the detection layer to be in contact with CO2 gas for a longer time. These results revealed applying cover tape on just one side of indication layer may significantly increase color change retention time.

Table 13- Color change of with and without cover tape using Method 4. Exposing to 100% CO2

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and etc. used in herein are to be understood as being modified in all instances by the term "about." Each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Accordingly, unless indicated to the contrary, the numerical parameters may be modified according to the desired properties sought to be achieved, and should, therefore, be considered as part of the disclosure. At the very least, the examples shown herein are for illustration only, not as an attempt to limit the scope of the disclosure. The terms "a," "an/' "the" and similar referents used in the context of describing embodiments of the present disclosure (especially in the context of the following embodiments) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. All methods described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein is intended merely to better illustrate embodiments of the present disclosure and does not pose a limitation on the scope of any embodiment. No language in the specification should be construed as indicating any non-embodied element essential to the practice of the embodiments of the present disclosure.

Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and embodied individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability.

Certain embodiments are described herein, including the best mode known to the inventors for carrying out the embodiments. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the embodiments of the present disclosure to be practiced otherwise than specifically described herein. Accordingly, the embodiments include all modifications and equivalents of the subject matter recited in the embodiments as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context.

In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the embodiments. Other modifications that may be employed are within the scope of the embodiments. Thus, by way of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Accordingly, the embodiments are not limited to embodiments precisely as shown and described.

Claims

CLAIMS What is claimed is:

1. A chemochromic indicator element comprising: an indication layer having a first side and a second side, wherein the indication layer comprises an organic polymer matrix and at least one pH chemochromic dye, wherein the dye is dispersed within the organic polymer matrix, and wherein the indicator changes color when it is exposed to carbon dioxide.

2. The chemochromic indicator element of claim 1 further comprising a cover layer, wherein the cover layer is disposed upon the chemochromic indicator element layer's first side, wherein the cover layer comprises less than 1.0 wt% of the pH chemochromic dye.

3. The chemochromic indicator element of claim 2, further comprising a color contrasting layer disposed upon the second side of the indicator layer, or wherein the cover layer is a color contrasting layer.

4. The chemochromic indicator element of claim 3, wherein the color contrasting layer is white or opaque.

5. The chemochromic indicator element of claim 4, wherein the color contrasting comprises silicone polymer, polyurethane polymer, or synthetic rubber.

6. The chemochromic indicator element of claim 5, wherein the color contrasting layer comprises a silicone polymer.

7. The chemochromic indicator element of claim 4, wherein the color contrasting layer comprises a noble metal catalyst.

8. The chemochromic indicator element of claim 4, wherein the color contrasting layer comprises T1O2, BaSC , alumina, or silica.

9. The chemochromic indicator element of claim 8, wherein the color contrasting layer comprises T1O2.

10. The chemochromic indicator element of claim 2, wherein the cover layer comprises polyethyleneterephthalate, polyethylene, poly propylene, urethane, orfluorinated polymers.

11. The chemochromic indicator element of claim 2, 3, 4, 5, 6, 7 , 8, 9, or 10, wherein the cover layer comprises less than 1% of the pH chemochromic dye.

12. The chemochromic indicator element of claim 11, wherein the cover layer comprises polyethyleneterephthalate.

13. The chemochromic indicator element of claim 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, wherein cover layer comprises pressure sensitive, hot melt, or heat curable adhesive or glue.

14. The chemochromic indicator element according to claim 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, wherein the cover layer comprises pressure sensitive adhesive.

15. The chemochromic indicator element according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, wherein indication layer has a first color before exposure to CO2, a second color after exposure to CO2, and a third color when the pH chemochromic dye is decomposed.

16. The chemochromic indicator element according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, wherein the indication layer comprises a communicating conduit disposed lengthwise within the indication layer.

17. The chemochromic indicator element of claim 16, wherein the conduit comprises a film, paper, cloth, nonwoven material, or rubber.

18. The chemochromic indicator element according to claim 1, further including a release liner disposed upon the color contrasting layer.

19. The chemochromic indicator element according to claim 18, wherein the release liner comprises plural independently detachable sections.

20. The chemochromic indicator element according to claim 18, wherein the release liner comprises at least 3 plural independently detachable sections.