looking for a light-fast dye or pigment with peak absorption centered between about 570-590 nm

Dear Paula,

I came across your website on dyes, it’s great! Currently, I’m experimenting with an idea to understand how insects see color in plants and how it may relate to a decreased use of pesticides. Something that we all may benefit from. In this, I’m looking at a light-fast dye or pigment with peak absorption centered between about 570-590 nm. The narrower the absorption band the better, and the lower the fluorescence quantum yield the better (for a controlled experiment on absorption).

The material substrate is polyurethane or other plastics. Would you know some dyes that would fit the mold?

Thank you!

Keenan

Hi Keenan,

You want a dye that absorbs in the orange range, which means you want a dye that looks blue. To help with visualizing this, let’s look at a graph I happen to have handy, which shows the absorption spectra of a number of dichlorotriazine dyes that are popularly used for hand dyeing:

absorption spectra of a number of dichlorotriazine dyes that are popularly used for hand dyeing CLICK TO SEE FULL SIZE

(Image provided by Olli Niemitalo.)

The closest of this range (which is not suitable for your substrate; I’m using it only because it is handy) is Procion Blue MX-7RX, which is Colour Index Reactive Blue 161. Its peak is not as sharp as you’d like, anyway, as it absorbs pretty significantly from 530 to 640 nm. Procion Blue MX-7RX is notable for a deep violet-blue color. It is also noted for being quite poorly lightfast when used on cotton, though its lightfastness is significantly greater when it is used with an acid dye recipe on silk.

Dyes that have narrow absorption ranges are unusually clear and bright in color. Wider absorption ranges result in duller colors. A dye that has a very narrow absorption range cannot be used to produce a dark color, no matter how high a concentration of it is used, because it allows most colors of wavelengths to be passed freely. Your desired dye will be a very bright, clear blue, on the violet side of blue, since it will not absorb any wavelengths in either end of the spectrum. You do not want a dye whose color is described as a navy blue, because navy blue dyes always absorb over a wide range of the visible spectrum. You may want to look for a blue dye whose name includes the words “brilliant” or “bright”. There are many dyes that are of a medium royal blue color or of a cyan color, or of a reddish violet, but violet-blue dyes are far rarer. Of course, it is no use to look at dyes that are composed of mixtures of other dyes, as these will always tend to absorb a winder spectrum.

The one person I know who has made a great study of blue dyes is Dr. Steve Mihok, who looked at dyes that attract tsetse flies when used in fly traps. You can see his descriptions of many blue dyes using the Internet Archive (his original site appears to have been taken over by spam and no longer contains useful information). See his page “Blue Dyes” at the Internet Archive, captured in January of 2012.

Mihok concentrated on metal phthalocyanine dyes, which tend to absorb in a turquoise-blue range, I’d say around 600 to 700 nm. My one example dye which absorbs near your target, Colour Index Reactive Blue 161, has as a chromophore a triphenodioxazine structure, I believe. It would make sense to look for a dye with this same chromophore. Following is an image of Direct Blue 106, as an example of the triphenodioxazine structure:

an image of Direct Blue 106, as an example of the triphenodioxazine structure


Unfortunately, the large size of this chromophore may make it unsuitable for use in plastics. Disperse dyes are typically relatively small molecules. The 2003 book “Industrial Dyes: Chemistry, Properties, Applications”, edited by Klaus Hunger, says, “Like phthalocyanine dyes, triphenodioxazine dyes are large molecules, and therefore their use is restricted to coloring the more open-structured substrates such as paper and cotton.” (page 112) I suspect that this leaves you having to find an antraquinone dye. Anthraquinone dyes include many popular blue dyes, such as Procion Blue MX-R (reactive blue 4) and Remazol Brilliant Blue R (reactive blue 19), and many violet dyes, as well. This is disperse blue 3, an example of an anthraquinone dye:

disperse blue 3, an example of an anthraquinone dye

It is important to consider what class of dye you need. Different materials require different dyes; for example, a dye that works on wool is unlikely to work on cotton, and dyes that work on either cotton or wool will not work on polyester, but wool dyes will work on nylon. You say that you want to color polyurethane or other plastics. Polyurethane is quite different from PET plastic, in its dyeing properties, which in turn is quite different from nylon plastic. Although no acid dyes work on polyester (which includes PET), acid dyes can be used to dye polyurethane, though with varying degrees of washfastness. The most washfast acid dyes to use on polyurethane would be metal complex acid dyes. Disperse dye, which is used on most synthetic fibers and is the only option for dyeing polyester, can be used to dye polyurethane, but the washfastness is poor, and the heat required may damage the polyurethane.

It is probably best to dye polyurethane in liquid form before fabricating it into objects. Solution-dyed plastics tend to be more resistant to both light-faging and wash-fading than fabrics dyed after manufacture. This is the explanation of why, for example, Sunbrella brand acrylic fabric is so resistant to fading that it can be used in outdoor furniture that retains its color even after extensive exposure to run and rain. I imagine that you would use a solvent dye for coloring the liquid plastic before using it in manufacturing. Solvent dyes are not soluble in water, but are soluble in organic solvents. Many disperse dyes, which are used with special carrier chemicals to dye polyester fiber after manufacture, are actually identical to solvent dyes.

To color the widest range of already-manufactured plastics, I’d suggest you concentrate on disperse dyes, especially since washfastness is not as much of an issue for you. They will work on nylon, polyester, and polyurethane. When dyeing polyester it is generally necessary to use boiling temperatures and an additional carrier chemical; when dyeing other plastics, the carrier chemical should be omitted, and lower temperatures may be adequate, though the water must still be very hot, at least abot 60 degrees C. Nylon can be dyed at lower temperatures than polyester, and I think the same is probably true of polyurethane as well.

Sourcing your blue dye is an issue. You will note that many textile dyes are sold in the form of in-house mixtures, whose constituents are not made public. Dyes obtained from chemical suppliers tend to be much more expensive per gram, perhaps with greater purity, prohibitive for dyeing large quantities. Textile dye suppliers such as PRO Chemical & Dye and Aljo Manufacturing sell dyes in useful quantities for hand dyers, often at much better prices, but in some cases the generic identity of dyes is not made clear, and many dyes are sold as mixtures in order to produce specific colors. I have listed a number of disperse dyes that are used for hand dyeing in a large chart on my page, “About Disperse Dyes”, at
http://www.pburch.net/dyeing/disperse_dyes.shtml , including disperse blue 3, which is described a sky blue and is sold by Aljo, and disperse blue 56, sold by ProChem, which is described as royal blue; disperse blue 60 is described as turquoise, so its absorbance is probably at a greater wavelength than you want, and disperse blue 281 is described as navy blue, which would have far too wide an absorption band to suit you.
Sigma Aldritch sells Disperse blues 1, 3, 14, 27, 35, 56, 60, and 124. All of the ones whose structures are indicated on their web site are anthraquinone type dyes. I suggest that you contact Sigma Aldritch and ask about the absorption spectra of all of these dyes.

I’ve been discussing only dyes, but you did mention pigments as an alternative. Pigments differ in that they do not bond directly to a substance, but instead are glued to it by some sort of binder, or they can be incorporated directly into some materials. Pigment dyes are pigments whose binder systems allow them to be applied in much the same way as dyes. Unless a pigment is sold with a Colour Index number, it probably consists of a mixture of more than one colored substance. The only pigments I would recommend you look at would be those sold by a chemical supplier such as Sigma Aldrich.

I am very interested in your project and would appreciate it if you would let me know more about it in the future.

For more information, see the following pages:

About Disperse Dyes

Dyeing Polyester with Disperse Dyes

What to Use to Dye White Polyurethane Foam, December 19, 2007

Steve Mihok’s Blue Dyes, captured by the Internet Archive on January 24, 2012

Sigma Aldrich

Lightfastness of Different Types of Dyes

(Please help support this web site. Thank you.)

Paula

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