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Using PVA with HPL6/25
Ok I would like to figure out a system for using PVA adhesive to adhere our laminates to a MDF substrate. This has to yield flawless results. We have a Joos 4x8 hot press and a Marbel 60" pinch roller for machinery. Can someone take me through the procedure they use. I need details on type of PVA used, heat setting on the press, glue application, suggested glue roller, press pressure, press sequence, and etc. Thank you for your help. We specialize in table tops so this hard glue line you get from PVA is what I'm after.
Most of those questions can and should be answered by your glue supplier. Tell them what you want to do, what equipment you have and they will advise you on which product to use and the details (press pressure, temp, cycle time, etc) necessary to be successful. A good supplier will walk you through the process and be there when you run trials. You need to find out what works on your equipment.
The one thing that you say that gives me pause, is the "This has to yield flawless results" comment. There are many variables to pressing and in my experience, achieving "flawless" is a learning process, not a starting point. Plastic laminate is definitely more forgiving than veneer, but don't expect perfection on the first run. Good luck!
Ideally you will need a panel cleaner and glue spreader. Panel cleaner prevents dimples from dust on panels and glue spreader give consistent glue amount and application pattern (not sure I would want to hand roll on glue).
Then you can go into either the pinch roller or the press depending on type of glue.
I agree with John you need to talk to your glue supplier as they will be able to recommend products and application methods.
I don't hot press in my current shop, I do occasionally press laminate to MDF. I have a 5 x 10 flip top vacuum press.
I don't know how much experience you have with pressing, but how you treat the panels after pressing is important in avoiding warping. I lay my veneered or laminate panels on leveled beams to allow even air exposure. In the winter I will cover the top of the stickered stack with cardboard or a ply sheet with stick between so that the top doesn't dry unevenly.
A good supplier will walk you through the process and be there when you run trials. You need to find out what works on your equipment.
I have been experiencing chronic bonding issues with HPL on green MDF, purchased from two different suppliers. Baltic birch gets a better bond but not great. You can easily pull off the entire piece of HPL and we see thin lines/stripes of glue from the spreader. In some cases a little green MDF transfers to the HPL and the substrate feels fuzzy which indicates that there was some bonding. My question is: Is it a correct testing method to attempt to pull off the entire sheet of HPL by hand starting at the corner? I would expect a tiny chip to come off, no more. What other guage do I have to ensure the bond is good?
The fact that you can easily pull the laminate off the substrate, and you see the glue spreader lines on the core, states very clearly that you are having "pre-cure" issues with the glue. In other words, the glue is starting to set-up (skin over) before the panel gets into the press and under pressure. One thing is clear, you need to get the panel into the press and under pressure much more quickly. The fact that this is happening repeatedly, means you need to "fix" your laminating process, it isn't working for you.
You should not be able to pull the whole sheet of laminate off, period. On a well bonded laminate panel you should break off an over-hanging corner and leave the rest of the panel intact, no question.
The best test is first to pull the corners, those are generally the most likely spots to be loose. After that, do the "tap test" where you go over the whole surface of the laminate and tap on it, listening for a "hollow" sound, or actually any sound that does not sound "solid". If you find an area that sounds different than the rest of the panel, there is likely a loose spot (blow) underneath that spot, even if it isn't apparent from looking at it.
My personal take on such situations is that if there is even one small loose spot in the panel, the whole panel is suspect and can't be trusted, throw it out.
Thanks that was very helpful.