Understanding water-based mold releasants.Water-based release agents began their rise to prominence less than a decade ago in response to environmental and safety concerns and regulations. Today, they're widely used in the processing of most rubber compounds, some polyurethanes polyurethanes (pŏl'ēy  r`əthānz), group of plastics that may be either thermosetting or thermoplastic. Polyurethane can be made into both flexible and rigid foams. , phenolic-based composites, epoxy epoxyAny of a class of thermosetting polymers, polyethers built up from monomers with an ether group that takes the form of a three-membered epoxide ring. The familiar two-part epoxy adhesives consist of a resin with epoxide rings at the ends of its molecules and a curing , polyethylene polyethylene (pŏl'ēĕth`əlēn), widely used plastic. It is a polymer of ethylene, CH2=CH2, having the formula (-CH2-CH2-)n , polyimide Pronounced "poly-ih-mid." A type of plastic (a synthetic polymeric resin) originally developed by DuPont that is very durable, easy to machine and can handle very high temperatures. Polyimide is also highly insulative and does not contaminate its surroundings (does not outgas). and other compounds that require an external mold release. 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 sum·ma·rize intr. & tr.v. sum·ma·rized, sum·ma·riz·ing, sum·ma·riz·es To make a summary or make a summary of. sum 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 Environmentally friendly, also referred to as nature friendly, is a term used to refer to goods and services considered to inflict minimal harm on the environment.[1] " in that they contain no ozone-depleting compounds. They are not flammable flam·ma·ble adj. Easily ignited and capable of burning rapidly; inflammable. [From Latin flamm (though some may contain solvents which can create a combustible com·bus·ti·ble adj. Capable of igniting and burning. n. A substance that ignites and burns readily. situation) or otherwise dangerous to handle or dispose of; they emit TO EMIT. To put out; to send forth, 2. The tenth section of the first article of the constitution, contains various prohibitions, among which is the following: No state shall emit bills of credit. no strong odors Odors anosmia Medicine. the absence of the sense of smell; olfactory anesthesia. Also called anosphrasia. — anosmic, adj. halitosis bad breath; an unpleasant odor emanating from the mouth. ; and have no threshold limit values threshold limit value n. Abbr. TLV The maximum concentration of a chemical allowable for repeated exposure without producing adverse health effects. . 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 (Operational Data Store) A database designed for queries on transactional data. An ODS is often an interim or staging area for a data warehouse, but differs in that its contents are updated in the course of business, whereas a data warehouse contains static data. (ozone-depleting substances such as CFC CFC See: Controlled foreign corporation and hydrocarbon hydrocarbon (hī'drōkär`bən), any organic compound composed solely of the elements hydrogen and carbon. The hydrocarbons differ both in the total number of carbon and hydrogen atoms in their molecules and in the proportion of hydrogen solvents) spurred development of water-based releasants. Excise taxes excise taxes, governmental levies on specific goods produced and consumed inside a country. They differ from tariffs, which usually apply only to foreign-made goods, and from sales taxes, which typically apply to all commodities other than those specifically exempted. 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 teething /teeth·ing/ (teth´ing) the entire process resulting in eruption of the teeth. teeth·ing n. The eruption or cutting of the teeth. pains" on the part of both suppliers and early users. As a releasant carrier, water offered the advantages of meeting regulatory requirements Regulatory requirements are part of the process of drug discovery and drug development. Regulatory requirements describe what is necessary for a new drug to be approved for marketing in any particular country. regarding ODS, and lack of flammability flam·ma·ble adj. Easily ignited and capable of burning rapidly; inflammable. [From Latin flamm , volatility and noxious noxious adj. harmful to health, often referring to nuisances. 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 evaporation, change of a liquid into vapor at any temperature below its boiling point. For example, water, when placed in a shallow open container exposed to air, gradually disappears, evaporating at a rate that depends on the amount of surface exposed, the humidity 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 Outside temperature at any given altitude, preferably expressed in degrees centigrade. . 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 naphtha (năp`thə, năf`–), term usually restricted to a class of colorless, volatile, flammable liquid hydrocarbon mixtures. 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 synthetic rubber: see rubber. compounds, including the typically-difficult fluorocarbons, ECOs and peroxide-cured EPDM EPDM Ethylene-Propylene-Diene-Monomer EPDM Enterprise Product Data Management EPDM Ethylene Propylene Dimonomer (industrial/commercial piping/plumbing components) EPDM Engineering Product Data Management . Superior water-based products for silicone silicone, polymer in which atoms of silicon and oxygen alternate in a chain; various organic radicals, such as the methyl group, CH3, are bound to the silicon atoms. and urethane urethane (yoor´ithān´), n ethyl carbamate used as an anesthetic agent for laboratory animals, formerly used as a hypnotic in humans. 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 work·horse n. 1. Something, such as a machine, that performs dependably under heavy or prolonged use: "the 50-year-old DC-3 ... " 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 sac·ri·fi·cial adj. Of, relating to, or concerned with a sacrifice: a sacrificial offering. sac ) 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 evaporated reduced in volume by evaporation; concentrated to a denser form. , 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 Re`ap`pli`ca´tion n. 1. The act of reapplying, or the state of being reapplied. , 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 e·vap·o·rate v. 1. To convert or change into a vapor; volatilize. 2. To produce vapor. 3. To draw or pass off in the form of vapor. 4. 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 lu·bri·cous adj. Variant of lubricious. surface deters buildup build·up also build-up n. 1. The act or process of amassing or increasing: a military buildup; a buildup of tension during the strike. 2. 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 grease, mixture of lubricant and thickener. It is used to reduce friction between surfaces from which oils would leak away or cause damage by dripping, or where lubrication must be assured for extended periods. Many greases are mixtures of mineral oil and soap. , dirt, previously-molded products and/or previously-used release agents. Typically, this process involves some form of abrasion abrasion /abra·sion/ (ah-bra´zhun) 1. a rubbing or scraping off through unusual or abnormal action; see also planing. 2. a rubbed or scraped area on skin or mucous membrane. 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 sealer, n a substance used to fill the space around silver or gutta-percha points in a pulp canal. Most contain some combination of zinc, barium, and bismuth salts and eugenol, Canadian balsam, and eucalyptol. 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 compressed air, air whose volume has been decreased by the application of pressure. Air is compressed by various devices, including the simple hand pump and the reciprocating, rotary, centrifugal, and axial-flow compressors. .) 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 Noun 1. methylene chloride - a nonflammable liquid used as a solvent and paint remover and refrigerant dichloromethane chloride - any compound containing a chlorine atom 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. Conclusions Until continually-developing mold-release technology comes up with yet a better mousetrap "A Better Mousetrap" is a first season episode of Beast Wars which first aired on October 8, 1996. Plot Sentinel, a new automated defense system for the Axalon, is under development by Rhinox, as the Maximals' best line of defense against a Predacon attack. , 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 tab·u·lar adj. 1. Having a plane surface; flat. 2. Organized as a table or list. 3. Calculated by means of a table. tabular resembling a table. 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 |
|
||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion