Glue, When Too Much of a Good Thing is Too Much
With cyanoacrylate glue (Super Glue) sometimes too much of a good thing is too much.
One way to make a rotary die fail is to not glue the rubber down properly and have it fly off. We’ve all had this happen at one time. The corrective action often taken to keep it from happening again is to use more glue next time. As a glue salesman, I applaud that… but as a rubber salesman I have my concerns as well with that tactic.
There are different causes that can keep the rubber from bonding properly to the board. Such as the glue may have cured before it touches the wood. Perhaps there was dust or dirt on the board. Maybe not enough, or even too much accelerator was used.
If you find that a piece is missing from a die, a quick inspection of what is actually left on the board will help identify what went wrong. For example if just half the original footprint has some rubber still stuck the board and where the other half of the piece was, there is nothing left, that would typically mean that either the adhesive started to cure before it touched the board or the adhesive wasn’t properly spread across the face of the piece prior to pressing against the board.
If you find that the entire footprint has rubber still stuck the board and it appears the block has been ripped off this can mean there was a problem in the nip…… or too much glue was used. (More on that later)
Other than PSA, there basically two types of cyanoacrylate glue used on a rotary die; low viscosity and high viscosity. The One Step Perma-Bond glue from Essential Products is an example of the low viscosity glue that has a consistency much like water. This adhesive is perfect for applying blocks in that with one motion the block can be dipped, slipped across the edge of the pan and applied to the board. As soon as it touches the board it bonds, almost always without an accelerator. Because of the thin viscosity very little glue is actually used to bond the piece to the board.
What many die makers use however is a high viscosity glue that is thicker. The nice thing with this glue is it gives a couple seconds to move the piece into place before the glue bonds. With this glue an accelerator of some type is needed whether it be acetone based or just water.
In situations where the block of rubber has been ripped off the board and the entire footprint has rubber left on the board, take note of where the edge of the block was and notice if there is a sharp edge of glue remaining on the board.
Here is where I say too much glue is a problem, if when using the thicker glue, the excess is not removed prior to bonding the piece to the board, that extra glue squishes out around the block and often times works its way up the side of the block like in the picture below.
That glue on the sides of the block solidifies the surface of the block where it is, not allowing it compress all the way which does two things that are a problem. One, it can cause an over-compression of the block by reducing the range of motion of the piece which can cause the block to fail; two, the glue can dry with a sharp edge that when the rubber is compressed, the sharp edge can cut into the block starting a tear that will then allow piece to be completely torn off.
What’s the solution? Take note of the bond surface between the block and board with the low viscosity One Step Perma-Bond. There is no glue ooze present at all. This glue eliminates that problem however, if the higher (thicker) viscosity is preferred, then, be sure to scrape off the excess glue on the piece prior to pressing against the board so there is no chance of excess creeping up the sides of the blocks which not only looks bad, but performs poorly as well.Back To Blog