How to Choose a Polyurethane System for Sandwich Panels

1. Your line and the panels you make

Start with the process, because it sets most of what the system has to do. Two plants making the same panel on different lines need different systems.

• Continuous line. The mix is laid down on the moving lower facing, rises to meet the upper facing and cures in a heated double belt press. A saw then cuts the panel to length. The reactivity of the system has to match your line speed and press length, and the foam must be firm enough to cut when it leaves the press.
• Discontinuous press. The facings go into a press and the mix is poured between them or injected into the closed cavity, one panel at a time. The foam has to reach every edge and fill the joint profile before it sets, then cure in time for your press cycle. Press frames and moulds also need a release agent. We make our own, water-based and solvent-based.
• Block pouring. Some truck body builders pour the complete insulated box in one piece. That job needs its own system, and we make separate systems for it.

Next, list the panels you make and their thickness: cold room walls, ceilings and floors, wall and roof panels for buildings, refrigerated truck body panels. Thick freezer panels and thin wall panels ask different things of the foam. In a thick panel the foam has to fill a deeper cavity and cure evenly through the core, where more heat builds up. Our cold room panel systems cover insulation thicknesses from 4 to 20 cm. If one system has to cover your whole range, say so.

2. Facings and adhesion

The foam is also the adhesive. It bonds the two facings into one structural panel, so a weak bond means a weak panel that can delaminate in transport, in service or when it is cut. Common facings are:

• Pre-painted galvanised steel, the usual choice for cold room and building panels
• Stainless steel, for hygiene areas in food plants
• Aluminium, where weight or corrosion matters
• Glass fibre reinforced plastic (GRP), common in refrigerated truck bodies

Adhesion depends on the coating or primer on the facing, on how clean the surface is and on the facing temperature when the foam meets it. Tell us the material and coating type for each side, and use your own production coils or sheets in the trial. If you change your coil supplier later, run an adhesion check, because a new coating can bond differently.

3. Fire requirement, and when PIR makes sense

Before you choose a system, find out which fire class your panel must reach and which standard it will be tested to. The answer comes from the building code, the project specification or the insurer.

Fire classes are usually assessed on the finished panel, so the facings, the joints and the way the panel is built count as well as the foam. JiTPOL's cold room panel system comes in a flame-retardant version, classified B1 in laboratory fire testing. Tell us the class and the standard, and we will work out with you whether that version fits your panel.

PIR (polyisocyanurate) is worth considering when the code or the insurer asks for a fire class that a PUR panel does not reach. PIR behaves better in fire, but it reacts faster, is more demanding on the line, is more brittle and costs more. Where the rules accept a PUR panel, PUR is usually the simpler and cheaper choice. Our guide PIR vs PUR insulation panels explains the difference.

4. The blowing agent your equipment and site can run

The blowing agent is usually blended into the polyol side, or added to it at the foaming machine. It turns to gas as the foam rises and stays in the closed cells, where it does most of the insulating. Our insulation systems use blowing agents from the n-pentane, HFC and HFO families, and none contain HCFC-141b. Which one fits is a plant decision as much as a chemical one.

• n-pentane is low in cost, does not harm the ozone layer and has a very low global warming potential, but it is flammable. It needs equipment built for flammable blowing agents, such as explosion-protected electrics, extraction, gas detection and earthing, plus safety measures and permits on site. Do not switch to pentane on a line that was not built for it.
• HFC blowing agents have a high global warming potential and are being phased down under the Kigali Amendment to the Montreal Protocol, on schedules that differ between groups of countries. Check the rules in your country and in the markets you sell panels into.
• HFO blowing agents have a very low global warming potential. They cost more, and the system has to be formulated for them.

Tell us what your line runs on today. We agree the blowing agent with you so that it suits your equipment and the rules in your market.

5. Storage and climate in hot regions

Both components are sensitive to heat and moisture, and summer in the Gulf or in Iraq is hard on drums left in the yard. Good general practice:

• Store drums and IBCs indoors or under a roof, out of direct sun, in a dry and ventilated area.
• Keep containers closed until use. The isocyanate reacts with moisture in the air, forms solids and gives off carbon dioxide, which can build pressure in a closed drum. Close part-used drums tightly.
• If the blowing agent is blended into the polyol, heat raises the pressure inside the drum. Open it slowly and do not leave it open, because lost blowing agent changes how the foam rises.
• Bring both components to the processing temperature on the data sheet before use, and check that your day tanks can cool as well as heat in summer.
• In cold winters, protect the components from low temperatures too, and keep both within the storage range on the data sheets.
• Use stock in the order it arrived, and check the shelf life on the data sheet.

The ISOPA guidelines for packaged TDI and MDI, listed under the sources below, cover safe storage and handling in more detail.

6. Monthly volume, packaging and your quote request

Your monthly volume shapes how the system is packed and how you plan stock. Our cold room panel systems are supplied in 200 kg drums and 1000 kg IBCs and shipped from Bursa, Türkiye. Drums suit smaller or irregular use. IBCs suit a line with steady consumption and mean fewer containers to handle and dispose of.

To get a quote that fits your line, send us:

• Line type: continuous line, discontinuous press or block pouring
• Panel types (cold room, wall and roof, truck body) and your thickness range
• Facing material and coating type on each side
• The fire class the panel must reach, and the test standard, if any
• The blowing agent you use now, and your foaming machine
• The system you use today, if any, and what you want to improve
• Expected monthly volume and preferred packaging
• Destination country

Ask for the technical data sheet and the safety data sheet in the same request. We send them on request through the quote form, for the system matched to your line. Export orders are normally paid in advance by bank transfer (T/T) in EUR or USD, and terms are agreed with each quote.

7. How a first trial works

Two lines of the same type still differ in line speed, press length and temperature, mixing head, facing temperature and the temperature in the hall. That is why we do not pick a panel system from a catalogue. We adapt one of our own formulations to your process, and a trial on your line confirms the choice. A first trial on a panel line normally goes like this:

• We agree a starting system with you from your checklist and send the data sheets.
• You run the system on your line with your own facings, at normal production settings.
• You check the panels: full fill to the edges and joints, adhesion to both facings, an even core without voids, and flat surfaces after cutting and in the days that follow.
• If the panels need it, we adjust reactivity and flow to suit your line before the next run.

For suitable projects, our technical team can visit your line and run production trials with you.

Selected sources

• PU Europe: the European association of the PUR/PIR insulation industry
• ISOPA: Guidelines for the safe transportation, unloading and storage of packaged TDI and MDI (PDF)
• UNEP Ozone Secretariat: the Kigali Amendment to the Montreal Protocol (HFC phase down)
• Sandwich panel: overview
• Polyisocyanurate (PIR): overview