Understanding water-based mold releasants.
In recent years, numerous articles have presented detailed and technical comparison# between water-based and solvent-based release agents, so, rather than repeat them, we'll simply summarize their conclusions: Laboratory research and practical user experience have shown that properly-formulated and applied water-based agents perform as well as or better than solvent-based releasants at comparable or lower overall cost. Most water-based agents are "environmentally friendly" in that they contain no ozone-depleting compounds. They are not flammable (though some may contain solvents which can create a combustible situation) or otherwise dangerous to handle or dispose of; they emit no strong odors; and have no threshold limit values.
So, our objective here is not to argue the case for water-based releasants, but to offer the information which processors need to select the best possible water-based release agents for their specific applications and get maximum efficiency and effectiveness from them.
A bit of history
Environmental restrictions on the use of ODS (ozone-depleting substances such as CFC and hydrocarbon solvents) spurred development of water-based releasants. Excise taxes on ODS added an economic incentive to finding alternatives. For example, excise taxes are primarily responsible for doubling or even tripling the pre-1990 cost per gallon of CFC-based releases. Several individual states have completely outlawed use of certain CFC products.
Research efforts continued in several areas, with water-based agents showing great promise. That is not to say their development was not without "teething pains" on the part of both suppliers and early users.
As a releasant carrier, water offered the advantages of meeting regulatory requirements regarding ODS, and lack of flammability, volatility and noxious odors. But it had its drawbacks. Water's surface tension is higher than that of most metals and other substrates used for molds. Its evaporation rate is slower than that of solvent-based releasants. And it had little or no solvency for the polymers then known and used for semi-permanent mold releasants.
Through extensive formulation efforts, supplier labs eventually solved the solvency problems. Field and laboratory testing showed that supplying water-based releasants to heated molds increased evaporation rates to perfectly acceptable levels and overcame most surface-tension problems as well. Difficulties remained, however, in using early water-based releasants in applications involving processing at ambient temperatures. If facilities were available, molds could be heated, the releasant applied and cured, and the mold cooled again before use. This process, however, results in a slowing of actual production.
A second alternative was to institute a system of fans or blowers to speed evaporation, but some users were reluctant to incur that additional expense.
A third alternative was to add non-ozone-depleting solvents such as alcohol or naphtha to the formulation. (In fact, water-based today doesn't necessarily mean solvent-free. Some formulations are 100 percent solvent-free. Others may be as much as 49% solvent.)
Initial water-based semi-permanent mold releases fell short in performance with natural rubber and most synthetic rubber compounds, including the typically-difficult fluorocarbons, ECOs and peroxide-cured EPDM. Superior water-based products for silicone and urethane came later.
Early problems in particular were exacerbated by the fact that most processors do not deal with a single material, or a single mold size and shape, but in several different ones, so a releasant found to be ideal for one material and mold might prove unsuitable for another (a problem not unique to solvent-based releasants). Finding a "workhorse" mold release that provides excellent or good performance on all their different compounds is the ultimate goal of most molders.
Some early users who experienced such teething pains (and/or who dealt with suppliers unwilling or unable to provide the technical support needed to overcome them) continue to resist use of water-based releasants, despite the fact that most of the early problems with most materials have now been resolved.
Types of release agents
There are two basic types of mold releasants: conventional (sometimes called sacrificial) and semi-permanent.
The most common conventional releasants are silicones, waxes and soaps, conveyed to the mold by water or solvents and applied by spraying, brushing or wiping. When the carrier has evaporated, the agent creates a weak barrier between mold and material. There is no crosslinking, and little or no bonding to the mold. These agents work by failing: release is achieved by a splitting of the agent, with a portion adhering to the mold and a portion to the item being molded.
Silicone releasants, by their very nature, require frequent reapplication, costly in terms of both releasant and increased cycle time. In some cases, sacrificial releasants must be reapplied after every cycle. Furthermore, since silicone slides rather than sticking, it can cause knit-lines on the molded product, it and the portion of silicone releasant that adheres to the product must be removed (a costly and time-consuming process) before painting or bonding.
Silicone also migrates into the air. Over time, particles build up on the tools, affecting release performance and cosmetics and potentially clogging vent holes.
Semi-permanent releasants are crosslinkable polymers carried to the mold via water and/or solvents by spray, brushing or wiping. A brief cure time (one to ten minutes at molding temperature is usually enough, depending on the agent) is required to bond the polymers to the mold and evaporate the carrier, forming a thin, uniform release film. The bonding which occurs between the polymers and the mold results in very little, if any, releasant transfer to the molded part. As a result, multiple releases can be achieved before reapplication is required. The lubricous surface deters buildup on the polymer being molded, reducing the frequency of mold cleaning, enhancing part cosmetics and lowering scrap rates.
Selecting the right releasant(s)
Given the wide range of water-based releasant formulations now available, it should be relatively easy to find the ideal release agent for processors who deal primarily in large production runs of one primary compound and molds of similar size, shape and construction. Unfortunately, most processors do not have that luxury. They process a variety of different compounds, using different molds for each customer. As a result, what is optimally right for one application may prove unsatisfactory for another. We know of processors who regularly use as many as ten different releasants for their various operations. Obviously, purchasing multiple formulations can be costly as well as an administrative headache, causing storage problems, and increasing the possibility that employee error could lead to selection of the wrong releasant for a particular application.
Ideally, one must find a release agent that works satisfactorily on most molds and compounds being processed. One technique for doing that is "most difficult first," the theory being that a releasant that performs well under the most difficult circumstances likely will do even better on less difficult applications. Of course, that does not hold true in all cases, but this approach has been proved successful in significantly reducing the need for multiple releasants for multiple applications.
In selecting, the proper releasants, a number of factors must be considered:
* the chemical and physical properties of each stock to be molded:
* releasant chemistry and film properties;
* mold size, shape and material; and
* the time, temperature and other parameters of processing. Ideally, the process engineer works closely with the supplier's technical staff to select - or custom-formulate-releasants that meet all process applications. And, processors should understand that changing release agents may require changes/additions in equipment, personnel functions and/or the process itself if the new releasant is to perform to expectations.
Proper releasant application is
critical (more is not better)
For an mold releasant to work to maximum effectiveness, the mold must be properly prepared and the releasant properly applied.
Molds must be thoroughly cleaned to remove any traces of grease, dirt, previously-molded products and/or previously-used release agents. Typically, this process involves some form of abrasion or a specially-formulated cleaner.
Rubber molders typically require some form of barrier protection to prevent corrosion of their steel tool surfaces after cleaning, especially if taken out of production for storage purposes. Some water-based release agents, properly-applied, will both prevent corrosion and act to seal the tool surface, simplifying mold start-up. (Molders who use plastic-faced or composite tools usually require a separate mold sealer and release agent. Water-based mold sealers are available, and can be applied at ambient temperature provided the film is rapidly dried by blowing it with compressed air.)
Releasants may be applied by spraying, brushing, wiping or dipping, either manually or by automation. (Automation, though expensive, is superior in that it offers increased assurance of uniform coating.) Care must be taken to avoid over- or under-application. Under-application may result in unsatisfactory releases; over-application can cause buildup on the mold and/or undesirable transfer to the part being molded.
We recommend spraying from four different angles to assure proper coating of all mold surfaces. Once applied, adequate time must be allowed for the agent to cure, following the manufacturer's recommendations for the specific releasant involved. If multiple coats are recommended, a second coat applied before the first has completely cured may diminish release performance. Brand-new molds may require additional coats and may not achieve the optimum number of releases until the mold is fully seasoned.
What to look for in a releasant supplier
Processors need and deserve suppliers who can "go-to-bat" for them in tough situations. Immediately. Selecting a good mold release suppliers should at least include:
* Reliability and responsiveness. In addition to releasants that work well, suppliers must assure prompt and efficient delivery. Some offer expedited same-day or overnight delivery capabilities in emergency situations.
* Consistent product quality. Even minor variations between releasant batches can cause unsatisfactory results.
* Ongoing technical service capabilities - both in the laboratory and in the field. A new application may require an entirely new custom formulation. Or, a previously unresolved problem may need solving.
* Value for price. The inability of a supplier to provide consistent product quality and technical services can turn modest cost-per-releasant-gallon savings into financial disaster.
* Capability for a wide range of releasants, including custom formulations, since dealing with multiple suppliers can be burdensome.
The question of cost
The August, 1995 issue of Plastics Technology magazine asserted, "While (water-based and solvent-free releasants) are generally reported to provide acceptable performance, they are at least 25% more costly than ones based on methylene chloride or low-flashpoint solvents." That is no longer true. The water-based release agents now available to rubber and other molders cost no more per gallon than the solvent-based releasants they have superseded. Most users of water-based releasants enjoy the additional benefits of eliminating the hidden costs inherent in solvent-based agents worker safety and incidents of "molder's flu," flammability and the related shipping/handling/storage concerns associated with solvents.
Until continually-developing mold-release technology comes up with yet a better mousetrap, water-based mold release agents - which themselves are being continually developed and improved - offer better results than most currently-available alternatives.
To achieve maximum results for the minimum cost means selecting the best possible releasants for each application, applying them properly to molds, keeping molds clean, and dealing with capable and responsive suppliers.
We estimate that, at present, about 80% of all molders have already switched from solvent-based to water-based releasants. The remaining 20% undoubtedly will do so eventually, since the benefits of changing continue to increase.
Table 1 - troubleshooting guide
Problem Possible causes Solution
Release agent Overapplication of Clean mold and transfers to release agent reapply release molded part agent after checking spray gun or other application device for proper operation
Improperly cured Clean mold, reapply release agent and cure agent following supplier's recommendations for the specific agent used
Dirty mold surface Properly clean mold and reapply release agent
Release agent Consult supplier's not well-suited to technical service this material or department mold
Part shows non-uniform Improper spray Determine correct cosmetic finish gun/applicator or application apparatus; application technique assure that it is functioning properly; follow supplier's application recommendations
Improper release Consult your supplier chosen
Insufficiently Clean tool thoroughly cleaned mold surface and reapply release agent Inability to Poor base coat or Follow recommended achieve proper mold release procedures number agent for achieving releases proper base coat (typically 3-5 applications)
Poor adhesion of Clean tool surface mold release film properly and to tool surface reapply release agent
Lack of uniform Consult supplier's film across entire application technique tool surface recommendations (light but uniform application across entire tool surface will eliminate random sticking) Localized sticking The area that Apply mold sticks has been release properly poorly sprayed across affected area (may require cleaning of tool before reapplication if sticking has caused build-up)
Excessive abrasion Apply extra coats in high contact of release agent or high draft to these areas areas
[TABULAR DATA OMITTED]
Table 4 - suitability of water-based mold release agents for selected common rubber compounds.
Material Common name Suitability
Cis 1-4 Natural rubber Excellent Isoprene rubber
Isobutylene Butyl rubber Excellent Isoprene co-polymer
EPT rubber EPDM Excellent (Terpolymer of ethylene (sulfur cure) propylene diene)
EPT rubber EPDM Excellent (Terpolymer of ethylene (peroxide cure) propylene diene)
Modified butyl Bromobutyl Excellent Chlorobutyl
Copolymer of vinilyideneflouride Fluorocarbon rubber Excellent and hexafluoropropylene
Polydimethylsiloxanes Silicone rubber Excellent
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|Date:||Nov 1, 1995|
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