Eliminating the Char Enemy Best Practices and Procedures for Char-Proof Hot Melt Systems

You are the hot melt superhero Coating and laminating is your mission. That means char is one of your biggest enemies. Char is the cause of costly downtime and damage.

Understanding Your Enemy What is char? – Adhesive that has been blackened or burned – A particular challenge to hot melt operations because of heat involved – The result of too much heat or too much time being heated

Understanding Your Enemy What is char? – Adhesive that has been blackened or burned – A particular challenge to hot melt operations because of heat involved – An expensive problem to fix

Understanding Your Enemy What creates char? – Heating hot melt adhesive at a temperature that is too high – Exposing hot melt adhesive to heat for too long – Exposing hot melt to heat and oxygen

Understanding Your Enemy How char forms – Heat, time and oxidation begin to attack the hot melt. – The adhesive begins to break down, forming polymer chains, which become active sites and combine to form gels. – Gels form anchor sites on the walls of hoses and crevices in melt tanks.

Understanding Your Enemy How char forms – Anchored pieces of hot melt cannot move – Unmoving adhesive becomes exposed to too much heat

Understanding Your Enemy Char is born.

Understanding Your Enemy In almost all cases, char turns black, and char wreaks havoc on your coating and laminating process. Also in almost all cases, char is the result of poor housekeeping.

Understanding Your Enemy If the lid of the melter or adhesive container is left open, exposing the contents to particulates, then you are inviting char into your operation.

What are the effects of char? Once formed, char will bake onto the heated grids. Once this happens it will break off in pieces and …

The disastrous effects of char Clogs filters Stops up spray nozzles Clogs bead nozzles Works its way onto the substrate leaving marks, streaks, and uneven surfaces

The disastrous effects of char In worst cases, char works its way into pumps breaking seals, scoring and damaging the pump walls

The biggest problem with char Once char gets into your system, it cannot be simply flushed out. It will cause ongoing product quality problems, extensive maintenance issues and work stoppages. You will be fighting a never-ending char battle until you take extreme measures.

You CAN defeat char Once char sets up, your only have two options: – Take apart the entire system and burn out all components in a burn out oven – OR replace the system

You CAN defeat char Now the good news. With proper procedures, you can prevent char entirely.

Char-proof hot melt systems Many systems can be char-proof The keys are – Adhering to the correct procedures required by these systems – Developing a thorough understanding of the adhesive – Maintaining effective and consistent communication between the production and maintenance departments

Know your adhesive Understand the softening point of the adhesive and know the temperature versus viscosity curve Know the adhesive’s maximum temperature, but avoid heating to that temperature Maintain the lowest temperature possible for effective application

Know your adhesive Know how susceptible your adhesive is to breakdown Sometimes called “pot life,” this is the amount of time that a particular adhesive can be under heat in a static state before it starts to break down

Know your adhesive Consult the adhesive manufacturer for all of this information Communicate it to everyone who works with the adhesive Consult your adhesive manufacturers to see if there are less-char- susceptible adhesives you could use

Wide applicators and narrow coating PROBLEM: Narrow coating with a wide applicator creates adhesive dead zones This can be a problem with fiberized spray and slot systems, but there are solutions!

Wide applicators and narrow coating Fiberized spray systems – A company might purchase a 72-inch-wide applicator, but also run products that are as narrow as 48 inches. – The tendency is to turn off the nozzles not being used when running a narrow product. – That creates blocked adhesive, which becomes char.

Wide applicators and narrow coating Fiberized spray systems – SOLUTION: Design the applicator head in section sizes that can be separated and completely turned off – Smaller sections should be turned off and also slid out of the way to prevent heat transfer

Applicator width

Wide applicators and narrow coating Slot dies – Tendency is to buy a die for the widest part and shim it down for narrower widths. – Adhesive sits behind the shim, cooks, breaks down and becomes char. – Anytime a wider shim is inserted, the char either creates streaks in the coating or puts char onto the substrate.

Wide applicators and narrow coating Slot dies – SOLUTION(S) – Simple slot dies: For narrow widths in simple slot dies, you can have close down some of the modules to the die OR Insert pieces of O-ring cord to block off the dead areas inside the die.

Simple Slot Die

Wide applicators and narrow coating Slot dies – SOLUTION(S) – Precision contoured manifold type dies: Have the die manufacturer make sets of filler blocks that match the contour of the internal manifold.

Precision Contoured Manifold Type Dies

Adhesive level in the tank Neglecting adhesive level is a user error that is one of the greatest causes of char.

Adhesive level in the tank When adhesive level gets too low, the heater grids become exposed, creating a hot spot that can be oxidized and that means … CHAR.

Adhesive level in the tank Error typically occurs when you manually load pellets of adhesive into the melter. People get busy and forget to keep the tank full.

Adhesive level in the tank SOLUTIONS: 1.Automated filling system Suction wand communicates with a level control device on the melt tank Pellets fed automatically into the melt tank on demand

Automated filling system A suction wand communicates with the level control device.

Adhesive level in the tank SOLUTIONS: 2.Level control system Monitors the adhesive level, ensuring that the level will never get low enough to expose grids. This is the single most important thing a company can do to help prevent char.

Adhesive level in the tank SOLUTIONS: 2.Level control system One of the best types is a three-point level control system with adjustable set points

Level Control System Three-point level control system with adjustable set points – Full – Low – Critical

Adhesive melt tanks It is critical to size the melt tanks properly. In a too-large melt tank, adhesive will not turn over frequently enough. Adhesive that is retained in the tank for long periods of time will begin to break down and eventually char.

Adhesive temperature set points Set the temperature as low as possible while still accomplishing optimum coating or laminating. Look for a system with a temperature adjustment screen that allows you to adjust temperatures by zone.

Adhesive temperature set points

You should also be able to set an acceptability range or band on either side of the set point. Should the temperature drift outside the band of acceptability, the system will set off a temperature alarm and shut down the system.

Adhesive temperature set points Your melt system should also have a set-back temperature to drop temperature significantly when system is idle.

Nitrogen blankets A good solution for charring-prone adhesives Place a nitrogen port on the side of the melt tank. Connect a nitrogen bottle to this port and slowly feed nitrogen, under very low pressure, into the melt tank. The nitrogen forms a blanket to protect adhesive from oxygen.

Adhesive hoses When adhesive sits in heated hoses for long periods of time… you guessed it: Char SOLUTION:

Poorly designed melt tank systems Melt-on-demand systems are ideal. No heat is applied to adhesive until there is a demand for it.

Poorly designed melt tank systems This style melter uses surface area and wattage to generate the heat rather than bands, which demand higher temperatures.

Char: Enemy Number One Your weapons against this preventable scourge: – The right melt equipment – The right set up – The right maintenance – A thorough knowledge of the adhesive.

Char: Enemy Number One Questions?