Adhesive for bonding Polypropylene sheets

[behboodi]

For a project (an evaporative humidifier), I want to stack some polypropylene sheets to create a unit of multiple airflow channels. So between each two sheets there should be some spacers to form those airflow channels.
in my designs these spacers are made using hot melt adhesive strips.

The process of making this unit should be done in two steps.
1. gluing sheets and forming spacer strips.
2. Reactivating glue strips and stacking sheets.

To elaborate my idea I created a graphical presentation and attached it to this message.

I think I need some kind of Reactivating Hot-Melt Adhesive, but I don't know anything about adhesives and can't figure out what adhesive I should use exactly. someone please help me and refer me to something which fits my needs.

Thanks

 

[MintJulep]

Your design is not feasible.

 

[behboodi]

I've made a sample already using general purpose glue and thin woods as spacers. I want replace those thin woods with adhesive.
I got the idea from a video. as you can see those strips are hot melt adhesive. in that video those adhesive strips are reactivated by hot water steam or something like that and sheets are bond to each other.
below image is from that video. Using this technique, They make kind of HMX which is more more complex than the moisturizer unit I'm trying to build.

thanks

 

[btrueblood]

Why not make your evaporator from sheets of corrugated poly, like these:

http://www.preservationequipment.com/UserData/root/Products/Images/000311_0.jpg

Just one of about a million variations.

 

[behboodi]

Can't use anything but Spunbond polypropylene. I've tested it before and results were great. I just need an adhesive.

 

[btrueblood]

The problem is, polypropylene is one of the most difficult materials to bond to. What about ultrasonic welding strips of polypropylene to the sheet?

 

[behboodi]

I can customize glue strips specification like their shapes, thickness or space between them in order to have different airflow channels, simply by changing glue applicator nuzzles. Ultrasonic welding or any other technique cant bring this much flexibility to my design.

 

[btrueblood]

"I can customize glue strips specification like their shapes, thickness or space between them in order to have different airflow channels, simply by changing glue applicator nuzzles."

Wow. I've only ever extruded blobs from hot glue guns. Good for you.

 

[MintJulep]

It is not reasonable to expect to be able to control the thickness and uniformity of a bead of hot-melt.

It is not reasonable to expect that you can selectively reactivate only the "bottom" of a previously applied bead.

It is not likely that you can uniformly heat many beads of previously applied hot melt deep within a stack of insulating material.

Consider a PSA on a strip of something so that you can control the thickness.

As noted by btrueblood, polypropylene is very difficult to bond.

 

[behboodi]

When I said I can simply control shape and formation of my hot-melt glue, I used the word simply to compare my method with other methods for example ultrasonic welding.
You know I can control the shape and formation with acceptable margin of error
the nozzle changing thing is a example of what can I control, sure I should control many parameters like nozzle types, PSA, cooling process and some other thing.

 

[behboodi]

"It is not reasonable to expect that you can selectively reactivate only the "bottom" of a previously applied bead."
"It is not likely that you can uniformly heat many beads of previously applied hot melt deep within a stack of insulating material."
this is my exact problem. I've seen something like that in a video.

 

[TomQuinn]

A lot is going to depend on what kind of tolerance you can accept with the spacing after reactivation. Much will also depend on the bond requirements. Do you have peel strength requirements? Heat resistance? Solvent/water resistance? How much flexibility do you need? How many layers? Color? Cost?

Have you considered using a 3 mm plastic rod with a thin layer of heat activated adhesive coextruded around it to assure a consistent spacer?

Tom Quinn
Adherent Laboratories

http://www.adherentlabs.com

 

[behboodi]

Hi Tom

I cant use plastic rods. Each unit has 80 layers and I would need about 1600 rods between those layers, so using rods could be very time consuming. Beside that, because of layer structure of units I cant heat both side of the rods to activate them. Finally my PP sheets cant tolerate direct heat.

peel strength: Not required
Heat resistance: No
Water resistance: Yes
flexibility: Not needed
color: not important
layers: between 80
space between layers: 3mm (± 0.5mm)