For nose cone manufacturer(s): why polypropylene?

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prfesser

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I don't know who actually manufactures the nose cones for most mid- and high-power rockets. Surely someone on here knows.

Many threads in the past and one that's currently active have commented on the difficulty of painting and gluing polypropylene (PP). It seems an odd choice for nose cone material. I would have thought that polystyrene or maybe PET/PETE would provide better glue- and paint-ability. Is there a manufacturing issue? Or is it simply cost? Can the same molds used for PP be used with PS or PETE?

Best -- Terry
 

justforfun

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That's been my experience.

~99.9% of all items that are blow molded are polypropylene.

~99.9% of injection molded hobby parts are polystyrene.

~99.9% of vacuum formed parts are PETG ie Polyethylene terephthalate glycol or polystyrene.

Roy
 

GlueckAuf

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I've had pretty good luck getting paint to stay on my own polypropylene nose cones by...

1) Washing the mold-release residue from the cone using acetone. Don't touch the to-be-painted surface with anything thereafter, especially bare hands. (So as not to pass oils or other contaminates to the clean nose cone.)

2) Roughening up the nose cone with fairly course sandpaper, making cross-hatches in the plastic. (Good opportunity, too, to sand off any flashing at the mold line.) Wipe off the dust with a damp paper towel.

3) Using a primer specifically recommended for polypropylene to lay down 6 or more layers of it, wet sanding between coats to eventually cover the scratches. I use Valspar plastic primer (but Rustoleum for the color coats). Don't worry, they're compatible. Specifically I use "Valspar Brand 410-68109 SP 12 Oz Clear Plastic Primer."

4) Allowing the nose cone to dry for several days before applying the color coat.

This technique has worked well for me. The nose cones hold their paint just as well as the air frame. In the pic below, the multiple iterations of priming and wet-sanding are nearly complete. The nose cone shows the Valspar plastic primer's off-white color, while the air frame components are primed with Rustoleum's white primer.

Now, as far as gluing something to polypropylene? Fuhgettaboutit.

Good skies,
GlueckAuf

1618707227834.png
 
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Initiator001

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When I was working at AeroTech we confronted the issue of nose cone material.

Polystyrene does not blow mold in large sizes. One can make an injection mold for polystyrene nose cones but that would be
really big money.

Polyethylene has worse properties when it come to paint adhesion.

Polypropylene was the best option.
 

BEC

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Polystyrene does not blow mold in large sizes. One can make an injection mold for polystyrene nose cones but that would be
really big money.
This explains why THIS was posted:
That's been my experience.

~99.9% of all items that are blow molded are polypropylene.
and my experience was completely different. Almost all the blow molded nose cones on my models are polystyrene, except for those from LOC. But they're not all that big, as they are LPR, not HPR.
 

Ez2cDave

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Of course, another alternative to painting would be for the manufacturers to produce the nose cones in different colors . . .

Dave F.
 

cwbullet

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I think it comes down to cost and ease of manufacturing. It has to be cost-effective.
 

John Kemker

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I had the owner of a paint/body shop recommend a product called "Self Etching Primer" by a company called SEM. Amazon sells rattle-cans of it for about $20/can. If you're using an HVLP or other type of spray gun, you can get quarts at http://dadscustoms.com/sem_self-etching_primer_gray_quart.html for $31.

EDIT: After doing just a little bit of googling, I found this: https://www.finishing.com/61/59.shtml#:~:text=To get better paint adhesion,called 10-pp wipe primer.

Might be worth looking into.
 

SkyFire

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I had the owner of a paint/body shop recommend a product called "Self Etching Primer" by a company called SEM. Amazon sells rattle-cans of it for about $20/can. If you're using an HVLP or other type of spray gun, you can get quarts at http://dadscustoms.com/sem_self-etching_primer_gray_quart.html for $31.

EDIT: After doing just a little bit of googling, I found this: https://www.finishing.com/61/59.shtml#:~:text=To get better paint adhesion,called 10-pp wipe primer.

Might be worth looking into.
Self etching primer works well with bare metal. It can be used with other materials as well. Several companies sell it. I have used Duplicolor self etching primer in a rattle can with very good results. For polypropylene nosecones I think an adhesion promotor and regular primer would work better.
As many have found, paint and glue don't adhere well to polypropylene. Adhesion promoter slightly dissolves the surface creating a bond. Primer adheres well to the adhesion promoter.
 
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John Kemker

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Self etching primer works well with bare metal. It can be used with other materials as well. Several companies sell it. I have used Duplicolor self etching primer in a rattle can with very good results. For polypropylene nosecones I think an adhesion promotor and regular primer would work better.
As many have found, paint and glue don't adhere well to polypropylene. Adhesion promoter slightly dissolves the surface creating a bond. Primer adheres well to the adhesion promoter.
Yeah, as I was reading the description of the Self-Etching Primer, I realized that it's not what it needs. However, I did find SEM makes this:
 

Stable1

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How about flame treating the nosecone -- https://faqs.cs.uu.nl/na-dir/model-rockets/construction.html
The article reference epoxy adhesion but the same goes for paint.

Extracted from an article at: https://www.ineos.com/globalassets/...ents/ineos_polypropylene_processing_guide.pdf

Surface treatment
Polypropylene molded parts, sheet, or film are normally impervious to solvent attack and require surface preparation prior to decorating. Several methods of surface treatment are available for improving the adhesion of printing inks, silk screening inks, and paint to the parts.

Gas flame
This is the most popular method and provides a chemical bond on the polypropylene surface for the adhesion of inks and paint. Parts are rapidly passed through an oxidizing gas/air flame at the corona or at the point where the dark blue and light blue of the flame meet. This forms carbonyl groups on the surface for adhesion and reduces surface tension to allow wetting. The exposed carbonyl functionality begins to oxidize within a short period of time; therefore, printing or painting cannot be postponed. Flame contact time is of extreme importance. If contact time is too short, the chemical reaction does not take place. If too long, surface melting of the polypropylene occurs, making the part useless.
 
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Blast it Tom!

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How about flame treating the nosecone -- https://faqs.cs.uu.nl/na-dir/model-rockets/construction.html
The article reference epoxy adhesion but the same goes for paint.

Extracted from an article at: https://www.ineos.com/globalassets/...ents/ineos_polypropylene_processing_guide.pdf

Surface treatment
Polypropylene molded parts, sheet, or film are normally impervious to solvent attack and require surface preparation prior to decorating. Several methods of surface treatment are available for improving the adhesion of printing inks, silk screening inks, and paint to the parts.

Gas flame
This is the most popular method and provides a chemical bond on the polypropylene surface for the adhesion of inks and paint. Parts are rapidly passed through an oxidizing gas/air flame at the corona or at the point where the dark blue and light blue of the flame meet. This forms carbonyl groups on the surface for adhesion and reduces surface tension to allow wetting. The exposed carbonyl functionality begins to oxidize within a short period of time; therefore, printing or painting cannot be postponed. Flame contact time is of extreme importance. If contact time is too short, the chemical reaction does not take place. If too long, surface melting of the polypropylene occurs, making the part useless.
Holy light touch, Batman! The more I read this thread the more I thought about how wonderful balsa is....
 

prfesser

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When I was working at AeroTech we confronted the issue of nose cone material.

Polystyrene does not blow mold in large sizes. One can make an injection mold for polystyrene nose cones but that would be
really big money.
Thank you! That's the kind of answer I was looking for.

I just looked through a list of synthetic polymers and it doesn't look like there's anything else that might fill the bill at reasonable cost. Too many are chemically inert to a degree, which means paint/glue is unlikely to bond well.

Best -- Terry
 

Bruiser

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Money gif.gif


That brought a smile. Reminds me of my stripper days :) :) :)

Oh, about painting nose cones. I guess I should be happy to write that I have never really had any problems painting them even when I used Rustoleum 2X. All kinds of weird stuff happened on the main body though...

I use most Estes Pro Series parts for most of my builds. I think the only other brand I've built was a Rocketarium kit. I have used DupliColor Primer filler on them followed by DupliColor Perfect Match paints. I've also used Rustoleum 2 in 1 primer filler followed by Rustoleum 2x paint and Krylon Acyri-Quik Laquer paint.

I basically scrape the molding seam down. Sometimes I have to fill low spots with Bondo spot putty (the reddish stuff). I sand it with 220 then prime it. I wet sand it then spray another coat of primer. One more wet sanding and it's usually ready for paint.

Guess I've just been lucky :)
-Bob
 

Back_at_it

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Been using Duplicolor adhesion promoter on pretty much anything plastic for many years without a failure. Of course you still need to prep the nose cone before hand.

- Use Scotch Bright cleaning prep pad and wash in hot water with dish soap.
- Let air dry.
- Final wipe with Alcohol.
- Two coats of Duplicolor Adhesion Promotor then paint within 30 mins.

I once forgot about the promotor on a LOC nosecone. The paint lasted a while until the rocket nose cone was dropped then it flaked off in a couple of places. Have not had that issue with any nose cones that got the promotor treatment and yes I'm clumsy so I do tend to drop things :)



 

rharshberger

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That brought a smile. Reminds me of my stripper days :) :) :)

Oh, about painting nose cones. I guess I should be happy to write that I have never really had any problems painting them even when I used Rustoleum 2X. All kinds of weird stuff happened on the main body though...

I use most Estes Pro Series parts for most of my builds. I think the only other brand I've built was a Rocketarium kit. I have used DupliColor Primer filler on them followed by DupliColor Perfect Match paints. I've also used Rustoleum 2 in 1 primer filler followed by Rustoleum 2x paint and Krylon Acyri-Quik Laquer paint.

I basically scrape the molding seam down. Sometimes I have to fill low spots with Bondo spot putty (the reddish stuff). I sand it with 220 then prime it. I wet sand it then spray another coat of primer. One more wet sanding and it's usually ready for paint.

Guess I've just been lucky :)
-Bob
Estes Pro Series parts are Polystyrene iirc, easy to glue and paint.
 
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