Rubber Compound Color Uniformity

Buying quality additives and raw materials is important as is controlled processes in your shop.

http://www.rheinchemie.com/rubber/applications/other-elastomer-products.html

http://www.excel-polymers.com/bizunit/elastomer/stantone_color/stan_tone_color.asp

milo

How reproducable is your process, as far as weighing amounts accurately, and thorough mixing? What is the +/- accuracy of your weighing and process? Is your sulfur dispersion uniform and well-blended? Can you monitor your temperature profile down the line for reproducability? Could you make a bigger master batch, or blend batches to smooth out variability? If all else fails, you could introduce multi-color swirls insoles as a new "fashion" accessory.

Your problem seems to be of the following possible reasons.

1]Possible temperature shooting ups in your process.

2] Heat stability problems of the pigments being used.

3]Higher particle size of pigment powder used in the melt

Best thing is to call your pigment suppler for the trouble and get it set right.

Check the dyes for sulphur compatibility since many Pigment Dyes are susceptible for reduction reactions.

Hi Cash,

When you have colour differences between batches, check your pigments, each of them separately at the temperature of your vulcanization. Pigment blends are difficult to reproduce. Certain pigment, mainly all organics are sensitive to temperature variations or decompose at certain temperature. Check them separately and let us know, Gil.

Hiya!

Thnks for the replies. You guys have ascertained the reason pretty much. Even I feel temperature as the main reason for the dis-coloration but I have checked with my pigment manufacturer and he assured that the temperature resistance of pigments are 320 C..I have even used other pigments but the results are the same. I face the color variation at the following points

1. Batch mixing in two-roll mill (Temp 70-80C)

2. Press temperature during vulcanization (130-150C)

3. After ageing of compound as well as finished product

I was wondering if

A) There is any product like say, a process aid, which will prevent the above from happening or provide color stability. We use Titanium Dioxide (1-2%) as stabiliser.

B) Will masterbatches (SBR-blend) help in reducing this problem

c) Can I use plastic or elastomer masterbatches like TPR/PU/LDPE masterbatches etc in rubber compound??

D) We use Natural Rubber/SBR 568 combination or SBR1502/SBR 568 combination. WIll using PBR or Nitrile-PVC compound help in reducing the above problems?If so, any formulations will be much appreciated.

Thanks again!!

Cash

Hi Cash,

Caution! Never disperse or grind pigment blends. Single pigment dispersion is the best way to obtain repeatedly the same final colours. You blend pigment dispersions, not pigments to disperse. If you blend to pigments, one is softer than the other and you disperse easiest way one and not the other. Constant tinting strength is obtained with one single pigment. Verify your blended pigment dispersions with white. There are variations, guaranteed.

Sulfur at hiegher temperatures must or probably act on many pigments, check it, Gil.

Are you using vulcanization accelerators, catalysts or inhibitors? If color is changing after the process, something is still reacting, possibly oxidizing or reducing the colorant. Often, all the sulfur in the vulcanizer is not fully used up. You may get an idea of what's going on if you leave out the latex, and mix the colorants with the sulfur dispersion and store at elevated temperatures, and add additives one at a time, finally adding some latex, to see what affects color.

We use accelerators in the following proportion

1. Sulfur- 2.5 PHR

2. Pilcure F- 1.5 PHR

3. TMT- 0.5 PHR (:Ultra Thiuram Accelerator)

We also use Antioxidant, TDQ in our compound

AS per post no 3, suspection is laid on reduction compatibility of your pigments used.

*Your recipe used is involved of Sulphur and antioxidants in the formulation,which are basically strong reducing agents.

*what could be done is to choose basic primary yellow, turquoise blue, pink colours so that all hues can be formed of these reduction resistant pigments.

*Your pigment supplier thro'' his shade card should be able to suggest you the reduction resistant pigments of his manufacture.

*Let me give you the simplest hint, so that you can yourself confirm it practically.

*ie, Take a Turquoise pigment, prepare your mould / charge as per your routine recipe and check the uniform build up, since most of the turquoise pigment colours are reduction resistant. Similarly you can fix the other two reduction resistant pigments[yellow and pink] so that you can solve your build up problem.

*the second option is to consider reduction of antioxidant dosage, which could be critical as well as the amount of Sulphur.