What is the cause of 'orange peel' in stone effect colours.

1. Rotomould Workshop
Problem 4
What is the cause of ‘Orange peel’ in stone effect colours
Materials, by Ian Hansen, Rotoconsult

2. “Orange Peel” [OP] defined
Ian Hansen Consult
1: STUDY OF ORANGE PEEL PHENOMENA IN ROTATIONAL MOLDING, E. Soos Takacs, M. Emami, D. D’Agostin and J. Vlachopoulos,
Department of Chemical Engineering, McMaster University, Canada
The term “orange peel” describes an inside surface
defect that is characterized by irregular grooves and
pitting—much like the topography of the outer skin of
an orange.1

3. “Orange Peel” [OP] effect
Ian Hansen Consult
 Rough internal surface.
 Seen in varying levels from mild to severe
 Found thru whole batch of parts of a batch of powder
Source : Orange Peel in Rotomoulded Parts; Bloys Rijkmans – ICO Polymers – ARMA Rotomould Conference 2009 Sydney
 Intermittent
 Difficult to predict
 Occurs Natural &
Colour
 Not well understood

4. “Orange Peel” [OP] effect in Colours
Ian Hansen Consult
 Example of same base polymer, “same” green colour, same Particle Size –
but different pigment formulation, in 50/50 blend of 2 batches.
 Pigment can act as a nucleating agent and affect the crystallization process.1
 Density has stronger effect on OP than MI - Differential shrinkage
Particles
RAISED
Particles
SUNKEN
1.Theeffectofcolourcompoundingoncrystalgrowthduringrotomoulding
M.P.McCourt,MarkP.Kearns,G.M.McNally,PolymerProcessingResearchCentre,Queen'sUniversityBelfast,
andR.J.Crawford,UniversityofWaikato
Source : Test This : Materials Guide – Ian Hansen – ARMA Rotomould, Penang 2011ianhansenconsult.com

5. Crystal Structure affected by pigment
Homogeneous
crystal structure. Some
air bubbles are observed.
Dissimilar crystal structure. Indicating two
different materials. This was a mixture of
Batch 1 and Batch 2
Homogeneous crystal
structure. Change in
crystal size. Some air bubbles
are observed.
Batch 1 Batch 2
Batch 1 +2
50/50
Source : Test This : Materials Guide – Ian Hansen – ARMA Rotomould, Penang 2011

6. Cause of “Orange Peel” effect in Stone Effect
Ian Hansen Consult
1. Small DENSITY differences of coloured
polymer particles shrink differently.
Different colours, are different pigments,
are different densities
Independent of degree of cure or additive
depletion.

7. Cause of “Orange Peel” effect in Stone Effect
Ian Hansen Consult
2. Effect of Pigment
Different colours create different crystal structure.
Dry blending of colours results in more severe OP
3. Effect of Particle Size
Higher % coarse particles increases ease at which you
can observe OP – but PS is not the cause.

8. Ian Hansen Consult