Polyurethane is a plastic material formed by more or less cross-linked polymeric chains, resulting in final pieces that can be either soft or rigid.

This material consists of a family of polymers derived from exothermic reactions between two main components: isocyanate and polyol.

It is a highly versatile product with numerous applications, including but not limited to paint products, automobiles, fibers, adhesives, foams, textiles, among others.


Impact of Mold Release Agents on the Industrial Production of Polyurethane

Mold release agents are among the most crucial products in the overall industry, enabling the rapid, straightforward, and effective manufacturing of parts in molds, employed in a multitude of production processes.

With the increasing use of polymeric materials in the industry, the use of these compounds has become critical for the existence of many sectors. Polyurethanes exhibit strong adhesive properties, and without the application of a mold release agent, molded pieces may adhere to the mold’s surface. The primary objective of mold release agents, therefore, is to establish a barrier between the mold and the surface of the molded piece.

Mold release agents are responsible for the appearance and surface properties of a molded piece, processability in the production line, repairs and rejections, as well as the more or less attractive appearance of final pieces, mold cleanliness, working environment, etc.

In this article, we will explore the usage and characteristics of integral skin polyurethane flexible foam in the footwear sector.


How is Integral Skin Polyurethane Foam Used in the Footwear Sector?

The footwear component manufacturing industry is one of the sectors that extensively utilizes mold release agents. Specifically, these agents are employed in the production of monodensity soles, bidensity soles, including safety footwear, insoles, as well as other direct injection processes.

The molds required for creating these pieces must be made from aluminum, stainless steel, or epoxy resin. In the case of epoxy molds, it is important to consider that the mold’s surface is more porous, requiring a higher amount of mold release agent or a higher concentration to adequately cover the mold and ensure proper demolding and surface finishing. Additionally, in epoxy molds, the temperature is usually lower compared to metallic molds, as heat transfer is inferior. It should also be noted that if water-based or hybrid products come into contact with ferrous surfaces, signs of oxidation may appear in the short or medium term.

The mold temperature will depend on each production line and the components used, but generally falls between 40°C and 60°C.

Mold release agents can have different chemical natures, such as:

  • Solvent-based mold release agents.
  • Concentrates for dilution in solvent base.
  • Hybrids with 30 to 50% solvent and the rest water.
  • Water-based, with or without solvent.

In the case of bidensity, mold release agents must provide an impeccable finish and a good bond of soles.

Regardless of the product used, Concentrol mold release agents offer excellent characteristics and properties for molded pieces. The main strengths of our solutions are:

  • Closed pores with a non-greasy and uniform finish.
  • Glossy or matte, according to requirements.
  • Without any visual defects, such as stains or holes.


Application Systems for Mold Release Agents

Products classified as class 1 and with a flash point below 21°C can be applied seamlessly with airless equipment, as they do not require air assistance for drying the film on the mold.

Class 2 products have a slower drying time, and it is advisable to use airbrush and/or air-mix equipment to ensure the film reaches all corners of the mold, undergoing pre-drying thanks to the air mixed with the product at the filter outlet.

Class 3 products, with a flash point above 55°C, have significantly slower drying. They have a minimum time of 1 to 1.5 minutes, with the mold between 50 and 70°C. The airless applicator only has air pressure to propel the product, and with the help of the shape and dimensions of the gun nozzle, it is necessary to find the optimal fan for each case. It does not aid in drying at all and is not useful in many applications for this reason.

Regarding the use of airbrush or air-mix equipment, it can be highlighted that the former are convenient to use, especially Shütze brand guns, small in size and lightweight. Air-mix is more effective in robotized mold release agent application, where more movement and fan shapes are required to reach the entire mold without complex path programming.

In terms of electrostatic equipment, all solvent-based products can have their electrostatic application version. Water-based products are much less effective due to infinite conductivity and have not allowed good application so far. Water-based products have been studied for application, but no 100% positive results have been achieved. In solvent base, there is no problem in formulating a working product, although it is not used extensively due to the associated cost. What is frequent is the use of robotized application equipment and electrostatic application if the product used is class 3 solvent base without any electrostatic property.

It is essential to remember that a solvent-based product usually has zero conductivity; water-based has infinite conductivity, and a functioning product is around 200 mohms. It seems that, without being a truly electrostatic application like robotized application, it performs better and leads to the belief that electrostatics are what facilitates the application. In general, we can talk about nozzle sizes of 0.3 mm or smaller in Shütze guns. This is because the applied flow rates are very low, between 10 and 30 grams/minute, with high solid contents (from 10 to 60%).

After applying the mold release agent, the next process, which involves deburring and painting the soles with or without prior degreasing, should be considered.


Cleaning of Molds

Another crucial step is the cleaning of molds after using mold release agents. The cleaning process depends heavily on the type of residue left in the mold after work cycles, varying according to the type of polyurethane pieces molded, the PUR system, and the type of mold release agent. It is always important to bear in mind that the interaction of mold residue with components is present, to a greater or lesser degree.

It is necessary to remember that only mold release agents that leave soft residue can be cleaned with liquid-type products. As seen in the following diagram, others allow variations according to each chain and client.

FAMILY Mold Release Agent Wax Fusion Cold Mold + Peeling Cryogenic Cleaners Abrasives
Integral Skin Polyurethane Flexible Foam for Footwear Solvent-Based (-) (-) (-) (x) (-)
Water-Based (-) (-) (o) (x) (-)

(x): Recommended (o): Possible use (-): Not recommended

  • Wax Fusion: Wax is melted onto the mold based on temperature, and infrared light is applied for reinforcement. When melted, it is removed with a clean cloth several times if necessary.
  • Cold Mold + Peeling: The mold is allowed to cool to room temperature. Upon hardening, the wax tends to break, and with the help of a spatula, the entire layer is removed.
  • Cryogenic: Applied to the mold with dry ice as an abrasive, resulting in a mold that looks like new. To start working, it is necessary to apply several layers of mold release agent or reinforcement paste before foaming. This system is very necessary, especially with water-based mold release agents.
  • Cleaners:  Only for soft residues such as waxes, resins, oils, silicones, etc. These cleaners are usually liquid or gel products based on N-Methyl-2-pyrrolidone, but due to their toxicity and restrictions within the European Union, there are already equally effective and less toxic alternatives.
  • Abrasives: Similar to the cryogenic system, although less aggressive. Instead of dry ice, sand, walnut shell, baking soda, etc., are used.

Products for integral skin footwear generally leave soft residues and can, therefore, be perfectly removed with liquid products. It is important to note that cleaners dissolve mold release agent and epoxy resin residues, so it is necessary to leave the product in contact with the resin part of the mold for a maximum of 5 minutes. Then, the remaining mold residues should be removed with clean cloths, and a rinse should be done by passing a low boiling point aliphatic solvent over the entire mold to ensure it is clean of any cleaner residue.


Concentrol references for cleaners are included in the LP range, and they are as follows:

CLEANER LML-950 Low toxicity mold cleaner Does not contain NMP
CLEANER LML-1200 Mold cleaner Contains NMP
CLEANER LML-1300 Biodegradable, low toxicity Does not contain NMP
CLEANER LML-1300 W Mold cleaner gel For vertical surfaces
CLEANER LML-539 Mold cleaner Contains NMP. Broad spectrum of action


CLEANER LX LM-01 NP Water soluble Contains NMP
CLEANER LX LM-02 TDE Blend of organic solvents Without NEP or NMP
CLEANER LX LM-03 AM Contains 2-Pyrrolidone
CLEANER LX LM-04 GS Blend of aliphatic and oxidized organic solvents Rapid evaporation
CLEANER LX LM-05 FM Contains amine derivatives
CLEANER LX LM-07 GL Contains 2-Pyrrolidone In gel form

In addition to those mentioned above, for the footwear sector, Concentrol also offers the reference CLEANER LML-08 HT for the injection heads of polyurethane lines. In this case, its effect is enhanced when hot, being a very safe product due to its low toxicity and flammability.


Concentrol Mold Release Agent References for the Footwear Sector

Within the Performance Materials line, Concentrol has an extensive catalog of solutions depending on the type of product manufacturers want to create and the desired characteristics. The main references are:


Monodensity Polyether Soles:


REFERENCE Type of Mold Release Agent Finish Class Main Application Notes
CONCENTROL LP ZMC-17 AP Solvent r.t.u Satin II Monodensity soles DBTDL free
CONCENTROL LP ZMC-17 TBM Solvent r.t.u Matte II Monodensity soles Tin Free
CONCENTROL LP ZMDC-17 AP Concentrated solvent for dilution Satin II Monodensity soles DBTDL free
CONCENTROL LP IA-118 CX Concentrated water-based dilution Satin Water Monodensity soles
CONCENTROL LP IA-118 TF Concentrated water-based dilution Satin Water Monodensity soles Tin Free


Suelas Poliéster monodensidad:

REFERENCE Type of Mold Release Agent Finish Class Main Application Notes
CONCENTROL LP IDC-121 PC Concentrated solvent for dilution Glossy 100% Monodensity soles DBTDL free
CONCENTROL LP IC-121-12 ANB Solvent r.t.u Satin II Monodensity soles


Bidensity Footwear:

REFERENCE Type of Mold Release Agent Finish Class Main Application Notes
CONCENTROL LX ZBAC-01 Water-based concentrated for dilution Satin Water Bidensity footwear Use as is or dilute 1:2 in water
CONCENTROL LP ZBDC-49 GVE Concentrated solvent for dilution Satin II Bidensity footwear Soluble
CONCENTROL LP ZBDC-49 J Concentrated solvent for dilution Satin II Bidensity footwear Soluble 1:15-1:30
CONCENTROL LP ZBC-49-2 GVZ Concentrated electrostatic solvent Satin II Bidensity footwear Ideal for application with electrostatic robot
CONCENTROL LP ZBC-49 GVE Concentrated solvent Satin II Bidensity footwear Very suitable for entire PU boots
CONCENTROL LP ZBD-49 GVE Solvent r.t.u Satin I Bidensity footwear


New Developments

Concentrol también ha trabajado en el desarrollo de nuevas formulaciones diferenciadas del resto, tales como:

  • Tin Free Hybrid for Polyether Monodensity: CONCENTROL LP ZBC-17 TFAN

With a solvent content of approximately 30%, there is a drastic reduction in Volatile Organic Compounds (VOC) applied. This improves the environment and occupational safety by reducing hazard indicators, and it also benefits transportation and storage by no longer having ADR classification. Additionally, this reference provides a very convenient matte finish for markets that value the quality and finish of the demolded sole.

  • Solvent-Based Matte Bidensity: CONCENTROL LP ZBC-49 LXP

In the specific sector of safety footwear, mold release agents that provide a satin finish are generally used. In this case, a completely matte finish is provided without interfering with demolding or sole adhesion.

  • Water-Soluble Bases for Post-Painting Without Degreasing:

This is a line of products in the development phase that would allow painting soles without any subsequent degreasing process, achieving a clear advantage in time and cost compared to usual market products.

At Concentrol, we innovate with chemistry to have a positive impact on society and the planet. We are a company committed to our customers, and therefore, we work day by day to improve our solutions and provide effective solutions for the industry.