Latin American Conference on Rubber Technology
From November 11 to 15, the 15th Latin American Rubber Technology Conference was held in Querétaro, Mexico. It is a key meeting point of the technological, scientific and academic world around the rubber industry. The event is organized by the Latin American Society of Rubber Technology that currently has 4800 associates from 38 different countries.
Concentrol was present at the conference and gave its presentation on the choice of a mold release agent for footwear. During the explanation, the way to choose the most suitable release agent for polyurethane footwear was outlined according to the different parameters and factors that must be taken into account. The current trends in the mold release market were also presented and the company was presented along with its product lines for Phylon footwear (modified EVA rubber).
Importance of the mold release agent
Release agents are one of Concentrol’s strategic divisions and those for shoe soles are one of the company’s star products. The importance of this product in the sector is key, since it has a decisive influence on the appearance of unmolded soles, on operations such as painting or gluing and on profitability measured in waste rates.
The goal of this product is threefold:
> Achieve high mold release power
> Provide a good finish to the sole in terms of gloss or matte
> Provide uniformity on the sole surface
Moreover, a good release agent must achieve minimum mold fouling and great adaptability to the pieces defined in the design of the shoe.
Determining factors to assess when choosing a mold release agent
The most important factors to assess during the process of choosing a release agent for shoe soles are:
- Polyol system: polyether / polyester
Polyesters are usually cheaper and have lower viscosity, while polyether polyols provide better abrasion resistance properties, but have higher viscosity and are more expensive.
Release agents are specifically designed for each type of polyol.
- Concentration and active material
Release agents are water-based or solvent chemicals according to their formulation. All its active material and additives are dispersed in solvents or emulsified in water.
The amount of active material may differ since we can have ready-to-use release agents, having low solids content, generally formulated with a fast evaporating solvent, such as heptane, or ready-to-use concentrated release agents with higher solids content so that we can apply less flow rate with the spraying equipment, and generally formulated with a less volatile solvent, for example C9-C10 naphtha, which will also take longer to dry.
- Mold temperature
The correct mold temperatures are essential to catalyze the reaction between the polyol and the isocyanate at the correct level as the system is formulated, and to obtain properly cured PU soles in a defined cycle time so as not to disturb the productivity goals.
- Finishing the piece and subsequent processes (paint or adhesion)
Depending on whether a matt or glossy surface finish is desired, we will choose one or the other release agent. As a general rule, release agents formulated with a high concentration of waxes give a more satin / matte finish than those containing only a mixture of silicones and resins.
Depending on the post-application process and whether we require cleaning and degreasing before painting, there are some optimal product lines to facilitate and speed up the process.
- Bidensity soles
In the specific case of bidensity soles, used in the safety footwear industry, the release agent must be designed accordingly so as not to interfere with the bonding of the PU sole and the intermediate sole.
Other factors to consider
> Safety and environment
VOC (volatile organic compound) emission level. These emissions are considered one of the most spread pollutants in the atmosphere. There are some release agents that significantly reduce emissions that are harmful to the environment. At Concentrol we are very aware of the disadvantages of the most harmful products for the ozone layer and we are working to optimize the results of water-based solvents (less polluting) to reduce the use of solvent-based solvents (more polluting).
> ATEX regulation (explosive atmosphere)
During the use of release agents, mainly solvent based, the ATEX (Explosive Atmosphere) regulation must also be considered. To avoid having to install ATEX facilities, using water-based release agents can be a solution, although in terms of different degrees of flammability (known in the sector jargon as Class I, Class II and Class III), other solutions can be implemented such as concentrated class III release agent, electrostatic release agent, wax pastes…
> Using application robots
The use of automatic applicators saves costs while ensuring the correct application.
> Protection in the workplace
Tin compounds are a hazard to people’s health. To avoid the use of these restricted substances, a new kind of release agents, tin-free ones, has already been extended worldwide. Its control must be carried out in accordance with the TLV and DNEL indicators.
The duration of work shifts and the exposure to chemical products are regulated by the Time Weighted Average, which is the environmental limit value published by the ACGIH (American Conference of Governmental Industrial Hygienists). They are defined as the “time-weighted average concentration for a normal 8-hour work day and a 40-hour work week, to which almost all workers may be exposed repeatedly day after day, without adverse effects.”
DNEL: Derived No Effect Level is the level of exposure to a substance above which humans should not be exposed. In accordance with EU REACH legislation, manufacturers and importers of chemical substances must calculate DNELs as part of their chemical safety assessment (CSA) for any chemical used in quantities of 10 tons or more per year.
Mold release agent market trends
> To decrease the amount of VOC’s and FOG. The tendency is to reduce the use of solvent release agents and expand the use of water-based release agents. There are also other solutions such as concentrated and electrostatic release agents that also lessen the environmental impact.
The use of concentrated release agents is also crucial to a lower environmental toxicity and greater safety in the work environment.
> To reduce the flammability risk, with all the regulation that this entails regarding the facilities where it is used (ATEX), danger according to the flash point (Class) and aspects related to transport and storage.
> To reduce the toxicity of the products involved in their formulation and their implications in the work environment, with particular reference to tin compounds and solvents.
> To minimize the final impact on the environment (TLV’s and DNEL).
Types of mold release agents
Electrostatic release agents
For some of its advantages, electrostatic application, which works together with electrostatic release agents, must be considered. Any solvent-based release agent can become electrostatic and in those cases the application involves the mold attracting the release agent avoiding product losses. Electrostatic release agents significantly reduce consumption and reduce emitted VOCs, improving the work environment. Another advantage of electrostatic release agents is that their application is controlled more easily.
Hybrid release agents
Co-solvent release agents are made with half water and half solvent. They are a good intermediate solution for footwear manufacturers who currently produce their soles with a solvent-based release agent and do not want to take the step to switch to water due to the inconvenience and changes in the way of working it entails. The change from solvent base to hybrid means an improvement of certain aspects, such as the reduction of prices, the reduction of VOCs emitted into the atmosphere and a better work environment in the production line.
Water based release agents
This kind of solvents have been around for many years but so far it has not been possible to optimize their results and many manufacturers did not choose them because of their disadvantages, such as leaving a greasy finish on the piece of unmolded polyurethane. Improving their results is the main challenge of the sector, and at Concentrol we are achieving very significant improvements in the water-based mold release sector that make us think that in the next few years we will see a clear trend to change without manufacturers’ reluctance.
Release agents for phylon
The trend of soles made with EVA foams. The hot compression process of EVA foam results in phylon, a material that is currently in expansion. This material is less dense and lighter. Phylon is the most common process to create soles for sports shoes.
The extraction of the phylon piece is carried out thanks to the presence of a mold release agent. This agent is applied by airbrush or brush, providing the necessary lubrication to remove the piece without causing superficial damage. In addition, these products are responsible for the appearance and surface feel of the demolded piece.
Work is done at very high temperatures, and then a water-based release agent enables the mold to cool down for the subsequent release of the piece.
At Concentrol we offer a wide variety of release agents and we manufacture them according to the needs of our customers. Depending on the needs of each production process, one or another product line will be better, and no one better than us knows the best solution for each case. It is important to know well the aspects to take into account when choosing the type of release agent and choose the most appropriate product for our needs.
Concentrol also offers silicone stabilizers that improve foam stabilization during its formation; mold cleaners, from the most toxic but effective that contain NMP and NEP to cleaners without health risk and free of NMP. Finally, we also have adhesives suitable for bonding all types of fabrics and leathers in pre-sewing operations.
