Use of Color-changing Pigment to Detect Wire and Cable Hazards
This technology represents an opportunity for forward-looking wire and cable manufacturers to provide and market new cables
that meet the increasing demand for safer products.
By Walt Ogrodnik
This paper presents the latest technology types of thermochromic material most used pensive and substantially easier to process process and material of the shell and the re-
of color-changing thermochromic sub- for commercial purposes today are Liquid and apply. However, LDs are not nearly as sultant quality and thickness are primarily
stances for wire and cable professionals, fo- Crystals (LC) and Leuco Dyes (LD). accurate at changing color at a precise tem- responsible for dictating the temperature re-
cusing on thermochromic applications to perature when compared to LCs. Typically, sponses, including the previously explained
the insulation/jacketing of electrical con- color will begin to change over a 2-5°C hysteresis phenomenon. Some microencap-
ductors (including plugs) to detect thermal range although certain LDs have been sulators claim to have nearly eliminated
hazards. Thermochromics are poised to processed to have more or less of a range. hysteresis in their LD material.
transcend their prior novelty and food tem- Further, LDs exhibit a unique and desirable The process of microencapsulation is com-
perature applications by providing an effi- property for the wire and cable industry plex and critical to the quality of the ther-
cacious, high-value, low-cost substance for called “Hysteresis.” This property, which is mochromic material and end application.
innovative color-changing wire and cable defined as a lag or delay in response to the Better microencapsulating labs incorporate
safety uses. change of stimuli (in this case it is the re- many important factors and additives in their
The paper begins with a brief scientific turning temperature decrease), causes the end product such as, particle size, shell thick-
description of various classifications of return color change to maintain its colorless ness, thermal stability, impermeability, shear
“Chromism,” including the two most com- state until it cools 2-5°C below the temper- strength, and compatibility with the surround-
mon types of chemical colorants used in Fig. 1. Principle of Thermochromism. ature at which it originally “cleared” during ing material to be used. UV additives can also
thermochromic color applications today. the warming process. The desired range of be processed into one of the shell layers. It is
One colorant, in particular, is the focus of Liquid Crystals (LC). These crystals (of hysteresis is another variable that can be therefore critical to identify a LD supplier that
this paper, i.e. color-changing Leuco Dyes the thermochromic cholesteric type) pos- customized by the encapsulation processor. will listen and compound to the functional
(LD). The paper also addresses some of the sess both liquid (flow) and optically solid See Fig. 2. needs of wire and cable manufacturing.
principles and more common conditions (anisotropic) properties. They are very sen-
leading to hazardous conductor over-heat- sitive to temperature in that, thermal ex-
ing; some statistics about damage caused by pansion (within a narrow range) results in
undetected wire and cable faults; best prac- a change in spacing, pitch and layering,
tices for the extrusion/injection process; and hence, discernable reflection of changing
non-extruded/injected LD applications. Fi- wavelengths of light from their structures.
nally, for an industry constantly competing LC can be modified in their composition to
with price-sensitive generic wire and cable respond to very specific temperature ranges
commodities, there is a detailed model of although color density and color choice is
the typical financial costs and expected re- very limited.
turns, along with a market survey summary Because of the inherent sensitivity of
LCs, they are used in many applications Fig. 3. Microencapsulation photo.
on consumer pricing and preference.
where very precise readings of temperature Fig. 2. Hysteresis of Leuco Dyes.
The science of chromism are required, such as children’s forehead
thermometers, vaccine vials and even mood Most LDs used today are reversible.
A world of color and patterns
Chromism is a process that induces a LDs come in virtually every color in
ring jewelry. The most common method of However, LDs can be fabricated to change
change (typically reversible, yet, it can be both cold and hot form. LDs lose their color
applying LCs is by inking them on to a sub- colors only once when a certain pre-selected
irreversible) in the colors of certain com- when they reach their “clearing tempera-
strate. While LCs are very temperature sen- temperature is reached. This one-time
pounds. In most situations the change is ture.” When properly mixed with a clear
sitive, they are neither inexpensive nor easy change involves using stronger acids within
based on external stimuli which, in effect, polymer, the plastic should be opaque when
to process or apply. Hence, LCs are typi- the microencapsulation shell that effectively
transfers energy and alters the density of the cold and nearly clear when hot. See Fig. 4.
cally used in limited applications of higher arrest any further electron exchange.
electron state of the molecules. It is the ab- LDs can be combined with other pig-
value and in smaller quantities. While polymerized LDs are used for in-
sorption of this energy and subsequent re- ments to affect both the cold color and the
Leuco Dyes (LD). These dyes are the jection and extruding, they can also be used
flection of light in different wavelengths resulting hot color. For example a “blue to
other and most common of all ther- on as a topical color-changing ink on wire
that causes a color change. clear” LD combined with a generic 1-3%
mochromic material in commercial use and cable that can be contact printed in
There are many artificially synthesized, yellow colorant will take on a green cold
today. Three major components makeup wheel-printing, embossing, and hot foil ap-
as well as natural, compounds that exhibit look (blue + yellow = green). When the LD
most LDs including; the leuco dye, a weak plications; used for pattern printing (e.g.,
chromism. Specific classes of chromism are heats up and “clears,” the visible hot color
acid and a solvent. LDs work because of a banding, hash marks, spiral or longitudinal
generally divided by the external stimuli re- becomes the yellow underlying color. In all
temperature induced change in the solid striping); or for verbiage or numerals.
quired to induce or create the change. The combinations, the cold color needs to be a
form of the material. As the material gently LDs can be used effectively on adhesive
most common chromism classes today are: darker color than the lighter hot color.
melts, the pH inside the LDs shell lowers and wrap-around labels for retro-fitting existing
Thermochromism, which is induced by
the LD becomes protonated, consequently conductors. This type of LD application
temperature (the focus of this paper); Pho-
shifting its color absorption dramatically. (which can be made UV/weather tolerant)
tochromism, is induced by light irradiation;
LDs are unique in that they are normally is often irreversible or historical. Irre-
Electrochromism, which is induced by the
colored in their cool state and, when tem- versible color-change labels are often ap-
gain or loss of electrons; Solvatochromism,
perature activated, they transform to a col- plied to wire and cable since the label can
which is induced by the polarity of sol-
orless (actually translucent) state. This have multiple temperature settings (includ-
vents; Ionochromism, which is induced by
property allows for many color combina- ing high temperature settings exceeding
an exchange of ions; Piezochromism,
tions (cold and hot) when the “clearing tem- 150°C+) and can be replaced if required.
which is induced by mechanical pressure;
perature” (i.e., the temperature when the Hidden wiring and/or “warranty voiding” is
Tribochromism, which is induced by me-
material becomes colorless) of the LD is also a practical application for such labels.
chanical friction; and Hydrochromism,
reached. Since the opaque/cold LD be-
which is induced by a change in moisture.
Examples of chromism include liquid
comes colorless when heated, the LD Microencapsulation Fig. 4. Color-changing cable
allows the underlying or “hot” color to be of Leuco Dyes prototypes.
crystal and LED display screens, films,
visible. LDs are able to be creatively com-
Transition® eyeglasses, Hot Wheels® toy Leuco Dyes (and liquid crystals) must be
bined with other LDs of different clearing Even more interesting and complex than
cars, thermal print paper, carbonless paper, microencapsulated before use. See Fig. 3.
temperatures (and color opacities) to create the above is the ability of LDs to be com-
aquarium thermometers, Energizer® and Microencapsulation of the organic dyes
sequential and near animated changes at in- bined with two or more LDs with different
Duracell® battery testers, etc. adds stability, color, temperature control
creasing clearing temperatures and with dif- clearing temperatures in the same plastic.
and protection of the coloring agents from
ferent colors. The current range of clearing One example would be to start with the
Principles of Thermochromism temperatures can be as low as -10°C to as
the environment. In this process, the small
particles of color-changing pigment (called above [green (cold)] to have a color change
Materials that undergo temperature- much as 70°C+ and can be fabricated in al-
the “core material”) are carefully coated at 105°F (to warm yellow) while a second
induced color changes are said to be ther- most any color.
with a shell. An interfacial polymerization color change (using the same or different
mochromic. See Fig. 1. The two major Unlike the LCs, the LDs have very robust
process is used to form the shell around the coloration) could take place at 115°F (say
color possibilities. They are relatively inex- continued on p. 14
dye and solvent. The microencapsulation
12 | WIRE BULLETIN
to hot clear). (If no hot color is used, then hot appliance, or even if it has been placed ceptable long term outdoor grade. One nies and organizations who generously re-
by default the hot color becomes the color near or on a very hot surface, such as an au- commercial LD encapsulator incorporated viewed this paper, supplied information
of the polymer used.) In effect, one can pro- tomotive engine. UV protection in its outdoor LD products and/or were referenced in this paper.
duce a double (or triple) animated sequence By having a pre-alerting system, a user which are currently being used on bridge Leuco Dye Suppliers: Chuck Boyce,
of color change over predetermined tem- can see when conductor conditions pro- surfaces to alert drivers to freezing temper- Managing Director, Matsui Int’l Co.,
perature ranges. gressively deteriorate. With such visual atures. Until more UV protection is per- www.matsui-color.com; Tim Homola, Presi-
Finally, it should be noted that while alerts, the user may be able to circumvent fected, wire and cable produced with LDs dent, Color Change Corp., www.color-
color to color (-less) change is the heart of costly circuit shut-downs, prevent more ex- should be used away from strong UV light. change.com; Scott Szafraniec, Sales
LDs, the creative use of patterns that appear tensive damage to load devices, lower Manager, Liquid Crystal Resources, LLC,
or disappear can become a powerful alert- maintenance and repair cost, and perhaps Summary and future www.lcr.usa.com; Doug Koerner, Business
ing mechanism in itself or for those who are most importantly, mitigate the extensive The first-generation of color-changing Manager, Keystone Aniline Corporation,
colorblind or visually challenged. One ex- risk to human lives. wire and cable and plugs has already been www.dyes.com; and Yves Ortais, President,
ample is the use of striping. The striping ef- prototyped and initially tested. Preliminary Gem’innov Societe, www.geminnov.fr.
fect can also be applied as an “inked” spiral LD suppliers analysis indicates the samples fall within Prototyping Manufacturers: Grant
stripe, albeit the stripe would be more prone Few U.S. based companies supply mi- regulatory compliance tests for the wire and Campbell, vice president, Multi/Cable
to abrasive and strong solvent effects. As in croencapsulated LD material for plastics cable industry. All compounded LD mate- Corporation, www. multicable.com.
the examples above, consider a spiral (see references). The original processing rial being used is believed to meet RoHS R&D and Test Equipment: Jonathan
blended (not visibly noticeable) onto the was developed and patented by the Matsui standards, as well. Currently, several “pre- Meckley, Assistant Professor, Penn State
surface of the wire and cable, as the under- Shikiso Chemical, Co., Ltd., of Japan in the ferred compounders” are devoting addi- University, Plastics Engineering Technol-
lying color disappears the ink spiral now (as late 1980s. When the original patent expired tional R&D effort to “best formulating” the ogy, The Behrend College; and Alan J.
a “candy-cane” pattern) is contrastingly in early 2000, several companies began plastics to ensure the masterbatch pelletized Cortazzo, Custom Test Equipment; cortaz-
very noticeable. R&D to microencapsulate LDs using pro- concentrate and/or “ready to use” forms are email@example.com.
prietary processing methods and materials. commercially feasible for specific targeted Other: Consumer Product Safety Commis-
Principles of wire and cable Most but not all U.S. suppliers obtain markets. These same compounders may sion, www.cpsc.gov, and National Fire Pro-
overheating their encapsulated LD material already pre- soon be approaching wire and cable manu- tection Association, www.nfpa.org.|WB
The carrying capacity of a conductor is pared from sources in Japan, Taiwan, England, facturers to ensure such “best formulas” and
commonly defined as the amperage it may and France. specific cold/hot colors and “clearing tem- Biographical Information
safely handle. See Table 1. Theoretically, peratures” have been standardized for or-
the amount of current that can pass through Best production practices derly market introduction and acceptance.
a single bare copper conductor is limited by and lessons Despite the remaining fine tuning of LD
the melting point of the bare copper (i.e., compounding before eventual commercial-
Based on numerous wire and cable pro-
1980°F). However, the polyolefin or PVC ization and licensing to the wire and cable
totyping experiences of the author’s com-
insulation/jacketing on most wires and ca- market, the biggest hurdle to wide-spread
pany (see Fig. 4), the following production
bles will begin to melt at about one-tenth introduction is expected to be the industry
methods have been established. It is noted
of that temperature. itself. The wire and cable industry is, in
that variations among LD material/suppli-
Electric current passing through a con- general, a mature commodity producer
ers, polymer types, processing methods,
ductor always incurs some resistance result- under intense pressure to reduce costs and Ogrodnik
equipment and even colors will have an ef-
ing in heat. Under normal conditions where to compete with off-shore producers. LDs
fect on individual end results. Walt Ogrodnik is the CEO of HazardGuard
the conductor is sufficiently sized and prop- will add incrementally to the unit cost of
Some whiteners such as TiO2 will visu- Safety Wire, Inc., Pittsburgh, Pennsylvania,
erly wired, the heat produced by resistance production and like any new innovation
ally block the LD color intensity and should USA. He worked for 17 years as the Sr.
is not problematic. However, when multiple there may still be a perceived risk/cost
be avoided. CaCO3 and other fillers may VP/COO of a professional systems integra-
wires are bundched in a confined conduit, which only a few selective wire and cable
also affect the final LD color intensity, but tion company in Pittsburgh. His prior work
for example, the cumulative heat can lead to manufacturers (more visionary and early
not the the dominating affect of whiteners. experience included eight years in interna-
hazardous over-heating conditions. adopters) will be able to justify. Optimisti-
LD material is slightly ‘hygroscopic’ and tional development with the U.S. Foreign
cally, LD costs are minimal compared to the
is best kept in dry storage and pre-dried be- Service. He holds a master’s degree in eco-
The case for a color-change alert potential profit margin and market share
fore actual use. nomics from Texas A&M University and an
gains for both the wire and cable manufac-
While advances in circuit interrupters LD material can withstand processing undergraduate degree from Pennsylvania
turer and the compounder. Perhaps most
(including GFCI, AFCI, wire and cartridge- temperatures of approximately 450°F+. State University. This paper, which was
importantly and more difficult to quantify,
type fuses, etc.) working on combinations Processors can exceed this temperature presented at WAI’s 77th Annual Conven-
the color-changing wire and cable user
of heat and electrical current have had a slightly and momentarily if done when shear tion, Cleveland, Ohio, USA, June 2007,
should experience a reduction in property
mitigating effect on faulty electric circuits, force or stress on the LD is light. Excessive won the Urbain J.H. Malo Memorial Medal
damage and maintenance costs, with a
such devices have their limitations and heat, shear, or mixing should be avoided Award for best electrical paper.
priceless improvement in the safety to
drawbacks. The biggest problem is the ex- with certain solvents as they may harm the
pense to purchase and install such devices. LD encapsulation.
Further, there is the issue of whether the de- Most LD provided in concentrated mas-
vice is properly sized and working for the terbatch form will only contain from 10-20%
potentially changing conditions. Many such actual pigment. Powdered concentrate LD is and references
devices have failed over time. Also most also available and contains nearly 100% pig- The author wishes to acknowledge and
devices are either “On or Off” basis and ment. Certain LD suppliers provide their LD thank the following professionals, compa-
lack a way to show an escalating condition. masterbatch in end-use polymer matches
In large commercial/industrial wiring (i.e., PE, PVC, PP, etc.), while others use
systems, where wire and cable are visible, EVA as a ‘Universal’ base polymer resin. Electrical Carrying Capacity of Single Copper Conductors
infrared cameras are now being used to Dilutions of the concentrated master- (Using Various AWG and Insulation Types in 30C Ambient Temp.)
monitor overheating conductors. Mainte- batch are typically around 1:10 but depend Polyethylene Neoprene Polypropylene
nance, Repair and Operation (MRO) per- on the thickness (~30-40 mil) of the insula- Polyvinychloride PVC
Conductor Polyurethane Polyvinychloride Polyethylene
sonnel understand the associated costs with tion/ jacket and the diluting polymer’s in- Size (Semi-Rigid) (High Density)
circuit shut-downs and that many such mal- gredients. It has been shown that the clearer At 80°C At 90°C
functions are due to slowly aggravated the diluting material the better the opacity 30 AWG 2 3 3
chronic conditions. Households with nu- of the LD and the less LD material is 28 AWG 3 4 4
merous extensions cords also understand needed. Thicker extrusions require less ma- 26 AWG 4 5 5
the safety and fire prevention benefits of an terial than thinner extrusions (i.e., most 24 AWG 6 7 7
alerting color-changing cord. Several influ- plugs would be very opaque using a 1:20
22 AWG 8 9 10
ential regulatory agencies have expressed dilution or less if using a clear polymer
20 AWG 10 12 13
interest in further development of the color- base). Using concentrated LD powder
18 AWG 15 17 18
changing wire and cable. translates to
Another consideration and potential ad- approximately the same total percent of 16 AWG 19 22 24
vantage/disadvantage in the use of LD on pigment use as other colorants, i.e., ap- 14 AWG 27 30 33
wire and cable (since it can inadvertently proximately 1-3% loadings. 12 AWG 36 40 45
give a false electrical alert), is that all LDs All LDs are sensitive to UV radiation. 10 AWG 47 55 58
will change colors regardless of the source However, irreversible LD can be made UV 8 AWG 65 70 75
of heat. This means that wire and cable will tolerant. Certain colors fade more easily 6 AWG 95 100 105
change colors when it is exposed to the con- with UV. While certain UV inhibitors, sta- 4 AWG 95 135 145
vection heat of a hot space heater or other bilizers and other additives can be added, 2 AWG 125 180 200
more R&D is required to produce an ac-
Table 1. Carrying capacity of copper wire, in amps.
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