When we speak of molded polyurethane, we always think, in the first instance and as essential, of isocyanates and their pre-polymers, ether or ester polyols, molds, high or low pressure injectors, polyol formulations, amines, metal salts, blowing agents, etc. Little is said about the use of mold release agents, until the start-up trials of the molding projects begin.
A release agent is not necessary, it is essential, since polyurethane cannot be molded without it. Not only does it release from the mold, as its name suggests, but it also interacts with polyurethane to a greater or lesser degree, for better or for worse.
We must take into account the high adhesion power that polyurethane implies. In other words, without a release agent, the part adhered to both sides of the mold, bottom and lid, either splits or the mold cannot be opened.
Actually, this lack of prominence of the release agents is due to the unknowledge of the advantages or problems that can occur, depending on the release agent that is chosen for a new project.
Basically, the way the formulation of a release agent is stated is something like: “wax dissolved in solvent” or “wax in water”, with mention of silicone in some cases; and little else. It is something like considering that polyurethane is always the same “isocyanate and polyol”. It is not that they are misguided, but in both cases it is more complex than that.
We can consider that the release agent is fed back from the increasingly sensitive polyurethane formulations, its work is being each time more complex as well as the molded parts.
In fact, when the pre-series start, all those involved in the release, operators and technicians, begin to see the influence, and importance, of the release agent on the appearance of the part produced, on the rejection and repair of parts, and in general on everything that depends on the demolded surface.
The surface finish is strongly influenced, in terms of formation and characteristics, also from the formulation, but we can consider that the surface properties depend on it and on what we could define as “interaction with the release agent”.
Sometimes for better and sometimes for worse, the release agent is largely responsible for the appearance and properties of the parts, in all types of PUR foams or in compact polyurethane without internal cell.
Among the properties that we can mention which the release agent is involved in, we can list the following as an example (although many others are possible):
- Seats and backrests, head rests: it must give the surface a softening – sliding effect to facilitate covering and subsequent assembly. Open pore to be able to break the cell.
- Soundproofing for cars: open pore to absorb noise inside the foam.
- Flexible HR foam in general: to avoid the appearance of bubbles due to under-drying or excess temperature, both possibly due to the release agent, although the formulation of the components may also cause this.
- In flexible foam with integral skin: finish of the part in sight, without material flows or dragging, more or less glossy finish depending on the requirements of the parts. Without any appreciable surface defects, total surface equality.
- Other properties where the release agent and the components may influence: touch (soft – rough), noise (of the mounted seat), imitation leather plastic bag finish (rigid foam, continuous or discontinuous process, for the production of sandwich panels intended for thermal insulation), slippery, non-slip, waterproof (densified flexible parts), adhesiveable (applied to heating pads, motion sensors; the residue of the release agent on the part must allow to stick a self-adhesive), etc.
Without forgetting the physicochemical characteristics that differentiate them, among others.
- Flammable or combustible solvent based, but always ATEX
- Combinations of water and solvent as vehicle in hybrid formulations 50:50 to 70:30 (water: solvent), co-solvents with <10% solvent participation and 100% water-based ones.
Diferent application systems
- Air-mix, air-less, aerographic and electrostatic spraying equipment, which may or may not be robotized.
If to all this we add the possible risks of flammability, toxicity, VOC (emission of volatile organic compounds), transport, storage, stability and sturdiness of the product; and we take into account additional parameters such as the degree of mold build-up when working, the adequate cleaning for each type of residue that remains in the mold, possible allergies depending on the raw materials used and the sensitivity of the operators, and applications in which food contact is required. We can affirm that release agents are complex products due to the multitude of possibilities that are available when formulating them, and the multitude of properties expected of them.
Taking into account all these parameters, and the working system of each client, CONCENTROL adapts the optimal release agent for each line, by designing formulations that will cover all their needs.
Our team made up of Commercial and Technical Managers, as well as Application Technicians with a lot of experience accumulated at production lines, are the best guarantee of success in the implementation and optimization of custom release agents for polyurethane foam, for any client that needs it.
Author: Joaquim Serra, Technical Director.
