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					                                          TECHNICAL ARTICLE
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
                                           TECHNICAL ARTICLE
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     zoa@bellsouth.net.
                                                  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
                                                                                                  human life.
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%
                                                                                                  Acknowledgments
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
                                                                                                                                                                      (Irradiated) Nylon
sonnel understand the associated costs with       tion/ jacket and the diluting polymer’s in-            Size            (Semi-Rigid)               (High Density)
                                                                                                                                                                           At 105°C
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.


14 | WIRE BULLETIN

				
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