Difference between Pigment Red 170 F3RK and F5RK

Difference between Pigment Red 170 F3RK and F5RK

The difference between Pigment Red 170 F3RK and F5RK


By Simon Chiang

Hangzhou Origo Chemical CO.,Ltd.


Brief:  Introduce the different between Red 170 F3RK and F5RK.

Key Words: Pigment Red 170 Crystal Modification Origo Chemical


Several days ago, I saw a question on internet that he is asking “ what’s difference between Red 170 F3RK and F5RK”.


Well, I think the grades name F3RK and F5RK is the most popular and well-known within all organic pigments. As nowadays, almost each producers suppliers or dealers have their own symbol to each grades pigments, and they are quite different between different companies.


But one thing in common is that, they normally keep Red 170 as 3RK or 5RK. Even include Ourselves, for naming the Pigment Red 170, we firstly separated it into 3RK and 5RK, or even 2RK.

And then we will modify the name of 3RK and 5RK with some postfix according the shade or some specific properties.  For example, for a waterbased application Red 170, we might named it as Origo Red 170 F3RK-WB, I guess most suppliers doing this quite similar.


Here I’m introducing the difference between 3RK and 5RK.


Pigment Red 170 is a Naphthol AS pigment, and the commercial available types which are made from two kinds of crystal modifications, differ primarily in terms of opacity.


Actually Red 170 is known in 3 types crystal modifications, α, β, γ.

a type is dull and not commercial valuable;

B type has attractive gloss and transparent, use for inks and coatings;

r type also has good gloss, and opaque than b type, widely use for Coatings and Plastics.


In the production of Organic Pigments, normally a step naming Coupling Reaction.

The the basic different came since the sightly different of Coupling Reaction.


Once the coupling reaction is in the environment of water, the products being a type crystal modification.

Once the coupling reaction is in fatty alcohols, that achieved β form.

Simply introduce as below


The opacity kinds we common class into 3RK, and some yellowish than transparent version,

The transparent version we class into 5RK, it’s sightly bluer.


The very opaque modification is much more stable to a variety of agents than the more transparent type. The opaque type is, for instance, slightly more resistant to organic solvents than the transparent one. It should be noted, however, that even transparent varieties are very resistant to solvents, compared to other members of this class of pigments.


I hope the above introduction would help involved concern better understanding the 3RK or 5RK.


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