Mold releases: cleaner & safer are the watchwords.

More environmentally friendly mold releases are becoming dominant, despite higher cost and other drawbacks. New spray systems automate the task of mold coating.

Water-based and solvent-free formulations are typical of the latest crop of mold releases, which are free of ozone-depleting compounds (ODCs) and have low VOC levels. An industry-wide transition to "zero ODC" will take place within the next year, as suppliers eliminate the first generation of CFC replacements such as 1,1,1-trichloroethane and HCFCs.

While the new release agents are generally reported to provide acceptable performance, there are also drawbacks. For one thing, they are generally at least 25% more costly than ones based on methylene chloride or low-flash-point solvents.

Water-based release agents may lead to changes in production cycles simply because water dries slower than the organic solvents it replaces. This is particularly an issue with thermoset resins processed at room temperature. (Many water-based formulations actually do contain a little alcohol or xylene solvent, though some newer products are said to be solvent-free.)

In urethane molding; some processors report that water-based releases may not be as effective as earlier products. Water-based products may also tend to cause build-up on the mold, owing to the surfactants and/or other emulsifying agents used in water-based products. Processors are also concerned that water can corrode mild-steel molds. And because water does not evaporate fast at lower temperatures, there can be "spotting" or large droplets on the mold, which typically results in a less glossy part finish.

"Technology is now there to overcome these limitations," says Craig Pierson, technical support manager at Chem-Trend Inc., adding that "the biggest incentive for water-based releases is no flammability." He says the only cost-effective alternative is to use solvents with low flash points - hydrocarbons such as naphtha or isopropyl alcohols - since the industry is moving away from chlorinated solvents like methylene chloride.

Getting away from solvents has the advantage of versatility. While older solvent-based releases cannot be used with some sensitive resins, such as SAN, ABS, or clear acrylics, newer "solvent-free" release agents can be used with just about everything, according to Jim Harms, president of Slide Products.

Be aware that so-called "solvent-free" aerosol formulations do use hydrocarbons (butane, propane, or dimethyl ether), mineral spirits, or fluorocarbons (HFC 134a or HCFC 141b) as the propellant. (Only the bulk liquid products can be truly solvent-free.) The hydrocarbon propellants have the drawback of flammability, while non-flammable fluorocarbons are the most expensive. In fact, "non-solvent" releases tend to be the most expensive category overall, costing roughly 15-20% more than most water-based formulations.

Although non-solvent releases are supplied mainly in aerosol form, Andy Peabody, director of sales for Zip-Chem Products, cautions that bulk-liquid, 100%-active types can be difficult to spray uniformly without the proper equipment.

Internal mold releases are yet another alternative that not only eliminates environmental and flammability problems, but also results in faster production cycles since there is no delay for spraying the mold and waiting for the release agent to dry. This is an especially good alternative for thermoplastics, according to Frank Axel, president of Axel Plastics Research Laboratories. Internal mold releases have also gained considerable acceptance in RIM urethane and FRP casting applications such as cultured marble. Pultrusion of thermoset polyesters is another area where internal releases are favored, according to technical manager Len Pulman of Lilly Industries.

Internal mold releases generally appear to be best suited to large-volume jobs, suppliers say. Custom molders with smaller volume jobs may not have the expertise to deal with the chemistry of these additives, some of which may affect resin mechanical properties, colorability, printability, or paintability. Internal releases also typically require heat activation (above 150 F), and their performance improves as the temperature goes up.

Suppliers such as Axel Plastics are coming up with products not based on traditional chemistry (such as waxes, metal stearates, or silicones) and which reportedly do not affect mechanical properties. They are also non-blooming so that they will not interfere with adhesion of paint, printing, or hot-stamp foils, suppliers say.

Two new products from Axel (see Table 1) illustrate another advantage commonly seen with internal releases: They can also act as lubricants and processing aids. In the case of these two grades, the releases are said to aid filling of large, deep cavities such as automotive bumper fascias and outdoor furniture. One of the two (Mold-Wiz INT-34 DLK) also reportedly has proven helpful in releasing parts with colors (green, purple, and blue) that tend to stick in molds.

WHAT'S NEW

The accompanying tables provide a quick glance at mold-release product introductions for the last year or so. Some additional notes on new products are provided below:

* For thermoplastics (Table 1): New from Chem-Trend is a quick-cure water-based Monocoat release that contains no solvent. It reportedly cures in seconds while competitive water-based products take 3-5 min.

A new name in plastics is Franklynn Industries, which recently launched a Diamondkote water-based, solvent-free product for rotational molding.

* For urethanes (Table 2): Franklynn Industries also offers a line of water-based mold releases for urethane molding under the trade name Aqua-lift.

Not mentioned in Table 2 is that Lilly Industries reports increased interest in internal release agents [TABULAR DATA FOR TABLE 1 OMITTED] for PUR-based in-mold coatings for RIM. The company is now working to adapt its Moldgard liquid resin solution for such applications.

* For other thermosets (Table 3): Three new products introduced by Axel Plastics are specifically designed for uv-cured resins. They are said to offer superior release properties and improved resin flow and filling of complex mold contours. They also reportedly eliminate mold fouling, resulting in finer surface details of molded parts. Their use does not affect physical properties, clarity, or secondary applications such as bonding, Axel says.

Also noted briefly in Table 3 are new Mono-Coat semi-permanent releases from Chem-Trend. These are aimed at FRP boat builders who are looking for [TABULAR DATA FOR TABLE 2 OMITTED] water-based products to replace waxes. These new clear-drying liquid products are applied to the mold in five coats in approximately one day, vs. 15 to 20 coats in three to four days for wax products.

Franklynn Industries has launched a Diamondkote release for unsaturated polyester resins and vinyl esters in FRP and cultured marble.

[TABULAR DATA FOR TABLE 3 OMITTED]

NEW APPLICATION TECHNIQUES

A new version of an automated mold-coating system from George Mann & Co., first launched two years ago for extrusion of cable and hose, is designed for cast urethane parts such as wheels for forklifts and in-line skates. The Actilease CFM-5 atomizer system uses 100%-active release agents based on wax, silicone, or blends of both. There is no need for solvents, propellants, or liquid carriers of any kind. Hot or cold molds pass through the chamber of the CFM-5 on a conveyor at an infinitely adjustable rate up to 6 ft/min.

Inside the chamber a series of nozzles atomize the Actilease release gel into a mist or cloud of user-selectable density, while supplemental compressed air nozzles can be aimed to ensure uniform coating of difficult-to-reach mold contours. Once the mold leaves the chamber, it proceeds immediately to the filling station.

The system filters and recirculates all overspray, resulting in release-agent utilization of better than 95%. Conventional spraying typically achieves only 10-30% utilization - the rest lost through overspray, the company says. The system costs in the range of $25,000-30,000 depending on options and conveyor belts required.

An upgraded version of another automated spray system is offered by IMS Co. Cost is about $700 for the sprayer and its microprocessor controller, which can be integrated with any spray sweep/robot (not included). IMS will have a spray sweep for sale by year's end, according to engineering manager Chris Oulton.

For now, IMS offers a spray nozzle that mounts magnetically on top of the mold or platen. The nozzle is adjustable so that spray can be directed to hard-to-reach areas. It is operated with either an automatic or manual controller.

Also new from the company is Econo-Cube, a hand-held compressed-air sprayer that delivers a very fine mist of silicone mold release drawn from a 1-qt collapsible plastic cube (equivalent to 88 12-oz aerosol cans). The plastic base that holds the cube, spray gun, and air regulator is mounted right on the injection molding machine and is priced at around $200. According to Oulton, the system pays for itself right away, since the total price is about the same as for just 66 aerosol cans of silicone mold release. (A quart refill container runs $28.)

Last year, Frekote was among the first to offer a water-based, semi-permanent release in a solvent-free aerosol package (see PT, April '94, p. 73). Its new generation of aerosol-type spray cans use a patented compressed-air propellant system. The spray cans are said to dispense the release agent at an even rate until they are empty, and they can also be sprayed from any orientation.