It looks like you are planning to use a (partially?) veneered low-density particleboard.
3m of length of almost any material is going to need support, and that is just as true for this stuff.
Even a wood plank top would need an "apron" or support system of some kind at this size. And the longer the span, the beefier the support has to be. Just look at almost any larger 4-legged table.
Now, the material you link to looks like it is at least partially wrapped veneered material (i.e., the usual sort of LD veneered particle board used for countertops) but even if it was fully wrapped (which is a fair bit stronger than the stuff with only a veneer on the top and sides) there is still only so much the material will span.
Ikea, et al, get away with this by
- Keeping overall lengths down, and using actual wood for spanning/support
- Using steel aprons and supports for larger dimensions
- Letting the smaller, cheaper items just fall apart after a few years, or a few moves
For what sounds like a digital workstation of some sort (which is going to take a lot more abuse than you suggest!) I'd suggest a metal or wood apron and maybe even a dimension piece of some sort along the bottom centre that ties to the side apron pieces. You could use angle-iron, but since we don't know the size of what you want to use you might have to do a little homework.
The idea is that you want some material that is resistant to deflection, and that ends up being either wood support "beams" (i.e., with the force being applied along the thinner side), or some sort of metal beam (a folded box of metal, or an L- or I- beam). The latter is how Ikea designs their largest SOHO task desks.
I actually would not generally recommend low-density particleboard for a top. That being said, the stuff you want to use (if it is fully wrapped by a veneer), will be a little better at spanning, but it will still need support. Ikea, et a, use these sorts of veneers, too, and they are surprisingly light and strong (though, often a honey-comb material inside, not LD board). But they could not span 3m unsupported with it.
So if you do use this stuff, think about how countertops are installed, with plenty of supports taking the forces to the floor. You either have to take those forces directly to the floor, or distribute them along spans that direct the forces to the legs and then to the floor.
I think this is going to be a heavy desk, so make sure you design it to be taken apart!
Based on a late comment by the OP, aluminium scaffolding would be very appropriate as a task table base (it can be hard to level; make sure you get adjustable feet) though I'd make sure I used more support for any composite material unless it was very strong and stiff. Plywood/veneer (e.g., the nice Baltic birch plywood the big box stores use for furniture) would be perfect. In a pinch, thick enough chipboard or OSB would probably be fine for that span as well. But if you want a smooth top, chipboard is not going to work.
Of course, scaffolding is intended to be used with the appropriately thick boards; so that material would work. You wouldn't even have to join the boards to make a complete panel, but this depends on how flat and continuous the top has to be.
As per the comments, counter top LD particle board can't even support its own weight. So whatever you use would have to have support every 4ft or so.
To recap:
- Figure out what sort of material qualities you need. Does it need to be nice and flat? Does it need to take screw without tearing out? How are the sides going to be finished. Unfinished edges get tiresome real quick, BTW.
- Consider how the dynamic forces at the top need to be addressed. The taller the table, the more moving mass at the top will need to be dampened. Two 3D printers going might actually set up some oscillations that will make your prints come out wonky. Make sure this thing is as stiff as you can reasonably make it. I don't know how stiff scaffolding stays, since I've always used it after years in service where it is strong but moves quite a bit. YMMV.
- Select a material that give you the qualities you need at the dimensions you need.
- Design a support that will give the material you choose the stiffness it needs.
The reference desk I have in my mind is a similarly sized desk from Ikea I use as my workstation. It uses a powder coated boxed steel apron with integrated adjustable steel legs and Baltic birch veneer on top. It has been in service for almost two decades and still very stable.
