clear coat question for the engineers out there...
30 replies to this topic
Posted 29 July 2008 - 10:48 AM
Definitely do not want to start epoxy world war III.
But I'm trying to lock into various combinations/alternatives in clearcoats.
What I need is some help on the technical data.
Hardness I understand, whether Barcol, Durometer, or Rockwell. For my purposes it's scratch resistance.
Where I lose it is the various tests of flexural modulus, flexural strength, compression yield, Izod impact, compressive strength. Many things list only a few of these tests, and so I feel I'm often comparing apples to oranges. Which of above tests indicates the ability to take a deforming impacting force, not yield, and return to normal??? How are these tests related?
Yes, I realize there's a lot more to choosing a clearcoat, like cost, clarity, UV, ease of use, adhesion, compatibilty, gloss, etc. etc., but What I really need is the above!
Posted 29 July 2008 - 06:56 PM
Below are a few links for your questions, but IMHO, you're barking up the wrong tree. Those specs are mainly for plastics, and epoxies in a "glue" situation. The two properties you should pay attention to are tensile strength and elongation%. A nice balance of the two is the key, especially when you're coating balsa. You're going to kill your brain trying to sort through data sheets trying to find a coating. Nothing beats real life trial and error. I formulate coatings for a living and I couldn't find an off the shelf clear that worked on all lures. I ended up finding a flexible epoxy and modifying it a little harder, adding U.V. inhibitors, and slip/mar additives to get the results I wanted. The biggest misconception is that harder is better. Impact and chip resistance are properties of a more flexible coating. I would say, for the glue epoxy guys, to give epoxy glue for plastics a try. Much more flexible than the 2ton all purpose types and should yeild much better results on balsa lures.
Flexural Strength Testing of Plastics
Izod Impact Strength Testing of Plastics
Posted 29 July 2008 - 09:13 PM
A good way to test your clear is to cycle fully cured lures 10 times as follows. You'll need a sacrificial lure. Freeze the lure for at least 5 hours, take it out and immediately immerse it in boiling water for 10 seconds. Throw it right back in the freezer for 5 hours and repeat. Sounds like alot of work, but that cycle testing should tell you if your clear can withstand the repeated expansion and contraction related to balsa lures. If they crack, you need to increase flexibility(elongation% & tensile strength). Even if they don't crack, check adhesion afterwards.
Edited by Downriver Tackle, 29 July 2008 - 09:22 PM.
Posted 30 July 2008 - 09:20 AM
This is great, this is the kind of information I need. Thank you!
I know that hardness isn't the end all, as I said, it is important for chipping and abrasion.
And yes, I understand that flexibilty is highly important on wood, that's why I was looking for more info on flexural strength/modulus and yield. (kind of like jumping on a trampoline versus a sheet of glass. Glass is harder, but you would break right through as it wouldn't flex.
But you've confused me a little on a few of your points. On an online material science textbook, I found that tensile strength is strongly positively correlated with hardness, so that seems to make it less about flex, more on hardness.
Also with your second post, I'm not sure that your test is testing what you think. First case, the temps may well be beyond the operating temperature of the epxoy. For example the max temp for 2-ton is 200 degrees, and even using distilled water you'd exceed that. Secondly, wouldn't this test be only comparing the coefficient of thermal expansion of the balsa and the epoxy? Yes, this could be an important measure relating to delamination of a topcoat under extreme temperature changes, but not, I think, a major concern. Sacraficing the bait wouldn't be the problem, as you could use identical scraps of balsa finished different ways. But perhaps a better test might be dropping a dumbell on a coated piece of balsa from a set height. You could also do the same with taking the scrap out a fridge to see real world brittleness effects in cold temps.
As for experimenting, I'm past the point of trying the readily available (i've tried most, with modifications), and there are those that are fine, just always looking for improvements if possible if I were ever to get a good enough product to make comercialization possible (definitely not there yet!). The problem is beyond the readily available retail products, you get into larger minimum quantities, and more combinations. Each company has say 6 formula combinations, that are like $60-$100 a piece, and there are lots of companies....
Thanks for your help!, and please don't take any of this the wrong way! I'm just trying to inform what I do understand (or quite possibly misunderstand!) so far, and what I'm trying to learn!
Posted 30 July 2008 - 12:40 PM
I've found the hard way that, for wooden lures, especially jointed baits, tough is more important than hard. That's why I went back to Etex Lite after a short romance with D2T. Hard doesn't forgive encounters with rocks. In fact, it chips or peels off in big sections. Tough might dent, but it doesn't peel off.
Of course, more accurate casting might help, but the nature of throwing swimbaits parallel and in windy conditions kind of makes rocky encounters inevitable.
Is it possible, or practical, to add UV inhibiters to Envirotex?
Posted 30 July 2008 - 05:07 PM
Pour some one inch pools of D2T, Etex, Dick Nites onto some 2" Duct tape, and let it set for a month or two (or more) - then start bending/scuffing the resulting flat discs of coatings, you will quickly find which is the hardest/most brittle, and which is the toughest. Some break like glass.pete
Edited by hazmail, 30 July 2008 - 05:09 PM.
Posted 30 July 2008 - 05:11 PM
No offense taken. Why I refered to tensile strength, is that in thin films like we use on lures, it is just more applicable and the results are more "real world". Tensile strength does somewhat relate to hardness, but I think Mike hit the key word. "Toughness"! You can take one polymer that is very flexible and soft by pencil harness standards, like HB or so, and it may have a higher tensile strength than a very hard polymer with a 6-7H harness. It would probably be more abrasion resistant also at light loads.
The reason I suggested the test is because it closely resembles the true cycle test used in the coatings industry. I've used it to screen my coatings in the past and it revealed problems that the customer would not have seen for months. Even if it exceeds the working temp of the epoxy, it should still work fine. It's the initial thermal shock that does the damage milliseconds before the entire coating heats up. And you're exactly right that you're pitting the coefficient of expansion of the different materials against eachother. It's kinda like the mother-scratcher of all adhesion tests. Besides cracking, delamination is a major concern. I didn't want to get too cumbersome with the test, but normally a cross-hatch adhesion test is done at each stage. I say delamination is important because it is generally the difference between a rock or tooth taking a chip out of the clear, or a CHUNK. If the bond between layers is broken, there's nothing to stop a tooth or abrasive from tearing a chunk off. If the adhesive strength remains stronger than the tensile strength of the coating, the coating will just chip off mostly in the area that was compromised, not continue to tear. It's all a balancing act with the properties. I wish I had specs on my coating to forward, but the new lab I work in doesn't have that type of equipment available. When I used to do auto interior coatings over elasomers, I had all kinds of test toys to play with.
And yes Mark, you could add UV inhibitor to your coating, IF you could find them, AND the right kind. Different types for different paint systems. They can be added either with a little solvent, or like I do and heat the part A to 85C until it's water thin, then mix them in with the other additives. You might want to check with and auto paint dealer for an inhibitor additive for automotive paints. Should be compatible if the have it.
That's an excellent idea haz!
Edited by Downriver Tackle, 30 July 2008 - 05:24 PM.
Posted 30 July 2008 - 05:54 PM
You got to keep an eye on hazmail - he's sneaky smart like a fox; right Pete?
Just had to jump in to say Hi Pete. Those of us that had a chance to meet Pete last spring at the 2008 TU Meet in Clinton, MO, made a friend who willingly shares what he knows and is great at providing solutions that the common man can use to make better tackle and an enjoyable conversationalist. Without getting to far off the subject at hand, how's work on the new boat is coming along - maybe you need to start a thread in the Boat building forum on "Boat Building Downunder"
Posted 30 July 2008 - 08:18 PM
hi Bruce, I think you are 'gilding the lilly' a bit there, the older I get, the stupider I get- the boat is pretty slow at the moment, I tore it apart, and have been working ever since, but should be able to give it a few days this weekend. I will post some pics in the boating section. Pete
Posted 30 July 2008 - 10:12 PM
Not to confuse the issue.....but.......
harder can also mean more brittle and more likely to come off of the lure upon impact. Sometimes gummy is better ...it will absorb shock. Take for instance what they do for cameras. When they want impact resistance they dont coat it in Devcon...they coat it with rubber. However, when you add sharp hooks and teeth to the equation, gummy means tears and hook rash. I would assume there is no one type that is best for all. Maybe that is why tackle companies list specific species and duties for thier products.
Just my two cents.....
Posted 31 July 2008 - 05:16 AM
I remember that Mark Poulson said once that he wants to use what is the best in Devcon 2 ton and Etex, so the first layer of epoxy in his baits would be Devcon, and the second layer would be Etex, or something like that. Others use Devcon + Dick nite. I have used thinned epoxy + propionate solution (bonds very well to epoxy, or so it seems). The ideea is that when you have a first layer of hard epoxy which might chip off, it is better to cover it with a better impact absorbing clearcoat than to add a second layer of epoxy. I have had no chance to test such a double coating in the mouth of a pike (couldn't find a volunteer yet), and I definately do not like rock-testing.
Also, I usually thin the epoxy, which, I guess, makes it less brittle (this is not a proven fact, but maybe 2 coats of thinned epoxy are better than a single unthinned one).
Thanks, Clemmy, for starting this thread. I was searching the internet for more than a year, trying to figure out what those tests meant, when I was trying to find out a plastic material to be dissolved then applied as clearcoat. What I know better now is that I will never be able to understand those tests.
Posted 31 July 2008 - 08:31 AM
I think you got it right. I use Etex, which is softer but tougher. I avoid hook rash by Ting my trebles.
I bend the two hooks that would normally rub the lure out until they're flat, parallel to each other. That way, there's not hook points rubbing the lure.
Someone on this site who trolls a lot taught me that trick, but I can't remember his name. Sorry.
But Ting the hooks lets me use a softer, but tougher, coating on my wood lures.
I use D2T on plastic crank bait repaints, but the second coat is Etex, since it smooths out better on the wheel.
I'm playing around with glow in the dark eyes on a deep diving Norman DD22 crank right now. I hope the epoxy topcoat won't cut down on the effect.
Posted 31 July 2008 - 03:10 PM
Try Triple Grip hooks. Already bent inwards and it's one mean hook. I can't think of one body type that they've left a rash on.
Posted 31 July 2008 - 04:16 PM
The triple grips are cool hooks, but I've had problems with them bending outward on bass 3# and larger.
Posted 31 July 2008 - 06:47 PM
I use Owner stinger hooks on my swimbaits. The smallest is a 1, and most are 1/0 to 3/0.
I like the round bend, because the second hook can swing around and get the fish, too, while it's thrashing around. Sometimes they get them both in their mouths, and that kind of paralyzes them. The more hooks I get in them, and the bigger, the better, because they can sure throw those heavy lures.
I had one fish swallow down my 6" trout lure, with 1/0 trebles front and back, and then she semi-jumped and spit it right back at me. I don't think she even felt the hooks, she grabbed that lure so hard. Even though I thought I put a good swing on her, I never got a hook in her. Frustrating. Might have been double digits. All I saw was a huge swirl, and then this enormous head shaking and throwing the lure. She never got up enough for me to see all of her, just enough to make me mad!
Funny, when I lose a fish on a worm or a crank bait, I always say, "It was a small fish anyway", but when I lose a swimbait fish, I sound like Roland Martin. "It's a giant!":lol:
Posted 31 July 2008 - 06:52 PM
I use triple grips on the back of my cranks, and round bends on the belly. I think they can't throw the triple grips as easily when they only nip at the back hook and get one in the lip.
I still T any hook that's going to rub the belly of a lure. But cheap hooks can break when you try to bend them.
Maybe that's a good test.
Posted 31 July 2008 - 07:01 PM
I actually only used Etex over D2T when I was trying to prevent the D2T from chipping, and it didn't work. I had use the D2T on the whole wooden lure for the first time, instead of just in the joints. Mistake.
I just finished stripping and repainting/re coating three of the swimbaits whose top coats failed, even though I tried to save them with an Etex overcoat. I stripped them down to wood, and started over completely, from the sealer on up.
I put two coats of Etex as the top coat this time.
Etex has enough give to adjust to wood's "moods", and my inaccurate casting.
I'll save the D2T for coating plastic cranks and lures, and coating the insides of my swimbait joints.
Posted 31 July 2008 - 08:59 PM
That's the one thing that's hard for most to deal with on Triple Grips. They're light wire and do bend. Honestly though, it's an asset IMHO. 90% of the time they bend so that the fish is locked up even harder. I use #6 on Shad Raps and a few other lures to SLAM 10-12# walleye in the fall. I just but them by the 100's and keep 20 or so on the boat ready to swap them out. Well worth the money to me. BTW, I just ripped in a 40" muskie on a Reef Runner swapped out with #6 grips and they held strong. No bend. And one little 1mm tooth chip on the custom lure.
Posted 31 July 2008 - 10:11 PM
I also use the triple grips, but usually only the black nickle ultra point. Stronger, just a little more brittle than regular. I just wish Mustad would make them in the xx-short triple grips. Hey, as long as I'm wishing to mustad, how about a triple grip double hook?
Posted 03 August 2008 - 10:14 PM
getting back to the original ?, the material property that you are looking for is basically toughness. But toughness depends on many things like loading conditions(how quickly specimen is loaded, etc). The types of tougness data you would find would not be a good representaion of a crank banging off a rock. Typically toughness is measured by taking the area underneath the curve of a "stress vs strain" plot prior to catastrophic failure when a specimen (of one of various types of standard "dog bone" dimensions) is pulled on a tensile tester (like an Instron).
Any #'/data s you will be able to find regarding tougness (probably very little, unless you really bug the manufacturers) will basically be meaningless since they aren't simulating the sudden impact of a crank hitting a rock. Even if you could find toughness data from different manufacturers that were tested under the same condtions, the fact that the coatings are different thickness, essentially voids out any comparisons you may make(etex goes on thinner than D2T,etc). Your best bet is actually a simple old "trial and error" of difn't epoxies/clear coats.
Not sure about Izod, just remember it is an impact test. But even data on this is basically meaningless for the same reasons given above (it isn't a good simulation of a crank hitting a rock, and different coatings are different thicknesses and data is dependent on thicknesses, etc)
Not a fan of the #6 triple grips(too small a distance bw the points and the main shaft of the treble, not good in intitial hook up %). I hear the long shank triple grip hooks work better in the #6 size. Haven't used the standard #4 triple grips but here they are better than the standard #6 triple grips. I actually just started a thread on riversmallies about #6 triple grips (lost one too many pig smallies a few days ago on a bandit footloose with #6 triple grips) and this is what people said.