Rotomould WorkshopProblem 4 What is the cause of ‘Orange peel’ in stone effect colours

Materials, by Ian Hansen, Rotoconsult

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“Orange Peel” [OP] defined

Ian Hansen Consult1: 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

“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

“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. The effect of colour compounding on crystal grow

th during rotomoulding

M.P.M

cCourt, M

ark P.Kearns, G

.M.M

cNally, Polym

er Processing Research C

entre, Queen's U

niversity Belfast,

and R.J.C

rawford, U

niversity of Waikato

Source : Test This : Materials Guide – Ian Hansen – ARMA Rotomould, Penang 2011

ianhansenconsult.com

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

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.

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.

Ian Hansen Consult

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