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Environmentally sound releases.

Environmentally sound releases

Remember reading and hearing about all the problems with solvent emissions and chlorinated and fluorinated solvents? Well, it's probably going to get worse before it gets better.

Unfortunately, our industry is one which has grown accustomed to using a fair amount of these products in the manufacturing process. This includes base materials used for adhesives, lubricants, plasticizers and carriers for mold releases. George Mann & Co., Providence, RI, one of the companies that is involved in manufacturing of mold lubricants, has been making some changes. Now, we can talk about water-based mold lubricants.

The problem

By this time, everyone is aware of the concern over emissions of solvents and chlorofluorocarbons (CFC) into the atmosphere. And, whether you believe in all the media attention to global warming and the greenhouse effect, everyone has to agree that allowing these products to evaporate into our atmosphere is not good.

Mold releases in the last decade have moved from water-based soap systems and "paint-ons" to the use of a large number of products that are applied directly from a spray can. These include silicones, some fluorocarbon lubes and other release mixtures. Unfortunately, most of these are using products such as RF-11, RF-12, butane and propane to propel them from the can to the mold surface. While they have been effective in the application, they are coming under more and more scrutiny for their potential to cause environmental problems.

Currently, there is a federal excise tax imposed on all CFCs. Users of sprays containing these are paying approximately $1.50 in federal taxes for every 16 ounce can used. And, it's likely that this will increase in the days ahead.

In addition to the problem with environmental concerns and additional tax cost, there is growing concern about the atmosphere inside the plant. Release of these chemicals into the workplace is causing occupational health personnel to raise concerns over the effect on workers. All in all, something has to give.

A solution

With respect to mold release, there are a number of alternatives to the continued use of solvents and CFCs. These include the use of internal release agents (waxes, stearate blends, petroleum derivatives), use of semi-permanent mold coatings and use of water-based release agents.

Internal lubricants can be very effective. However, it is important to remember that mold release is a surface phenomenon. In order for an internal agent to work, it must migrate to the surface and provide a surface finish on the part that will prevent adhesion to the mold. The release properties that are so desirable in the mold may not be that desirable once the part is molded. In addition, internal agents that provide release from molds will also provide release from any inserts that are bonded into the part. For very short cycle parts (e.g. RIM molding, various thermoplastic materials) there may not be enough time for the internal lubricant to migrate and provide sufficient release.

Finally, care must be taken with internal lubricants that the quantity used is not so much that the properties of the compound are altered. In order to obtain sufficient release, it is possible that properties such as tensile, tear, elongation, set and other important performance properties are changed. Likewise, if the lubricant is fugitive, it may continue to bleed out of the part causing problems in use.

Semi-permanent mold coatings can be very effective. This would include spray-on polymer coatings as well as PFA or other fluorocarbon coatings. However, these also have their limitations.

Problems with migration of the release to unwanted surfaces are mitigated. Also, there are no problems with alteration of physical properties of the molding compound. However, typically they are much expensive. The process used to clean the tooling, apply the coating and cure it, along with the lost production time on the tool, have to be factored into the cost. Also, often when these coatings begin to lose effectiveness, they do so by flaking off here and there in the mold. The mold must then have the balance of the coating removed prior to re-application of the release. Care must be taken not to use a cleaning process or solvent that actually damages the mold itself.

Semi-permanent coatings can be a very cost effective method if the production from the tool between coatings justifies the cost and the downtime on the tool can be tolerated.

Another solution

A relatively older/newer approach to mold release is the use of aqueous release agents. Older, since for years soap solutions have been used in rubber molding to provide effective release using a water-based system. However, soap solutions are not adequate for many polymers. Also, they cause problems with mold build-up and discoloration of some parts. With the recent problems in the solvent-based agents, water as a media for release agents has become more popular. As a result, work has been done to re-examine use of other release agents using water as the media to carry the lubricant. As a result, there are now a variety of water-based release agents available that perform with virtually all elastomers and thermoplastics. Performance of these products is reported to be equivalent to or better than their solvent-based cousins.

How do the water-based systems perform?

According to a number of people who use them, as well as the manufacturer, these systems perform as well as or better than their solvent- and CFC-based relatives. In some cases, reduced need for the mold lubrication has been reported.

In addition, no special permits are required for using them. There are no organic solvents being emitted, as well as no CFCs. The only material being put in the air is water. Pure, clean, environmentally sound water. Another benefit that has been found is that the parts molded using these lubricants are easier to clean after molding. For many products, it is necessary to remove all traces of any mold lubricant after the part is molded and before shipping. While not initially designed that way, parts molded using the new water-based systems have been found to be much easier to clean up. This may have to do with small amounts of residual solvent in the lube solvating the surface layer of the part and allowing the lubricant (silicone, PTFE, etc.) to embed itself in the surface layer of the part.

Third, there is a significantly lower exposure of workers to vapors that can be physically harmful. Again, if given the choice, I would much prefer to inhale water vapor than butane or RF-11. Our workforce is becoming much better educated and is very much aware of the potential dangers in the workplace. And we have both a moral and legal responsibility to ensure that their work environment is as safe as we can make it.

Fourth, handling of the water-based system is much easier and safer. There is no danger from toxic vapors. No potential for defatting if the material is spilled on the skin. There is no fire hazard. In short, handling is by definition, much safer. Another benefit that has largely been discovered in use relates to overspray and contamination of surrounding areas. Virtually all solvent- or CFC-based sprays have a large "plume" associated with them. This plume is related to the character of the carrier base and carries with it the mold lubricant. As a result, not only will the mold being sprayed have the lube on it, but also the parts being molded next to it. In some cases, even parts in the next room will be contaminated with the lubricant.

The water-based sprays do not have this plume associated with them. Users have reported that they also do not create the nearby contamination problems that the solvent-based systems do. This has been most noticeable with silicone lube systems since silicone release agents can be very difficult to contain and clean off coated parts.

What about problems?

In general, compressed air assistance is recommended for spraying the water-based systems onto the surface to be coated. Air pressure must be adequate to thoroughly atomize the lubricant. If the lubricant is not properly atomized, the surface will not be properly coated.

Since the container containing the lubricant is also pressurized, it is important that this container be maintained at the proper pressure. Too much pressure will result in delivery of too much lube to the mold, possibly causing puddling and coverage that is too heavy. Too little may cause too little to be delivered to the mold. Proper balance between the pressure in the lubricant container and the pressure at the spray head is important to avoid these problems and to ensure proper atomization of the spray.

Water-based mold releases also need to be applied to a warm mold. While this may seem foolish to most rubber molders, this is a significant consideration for persons molding some urethane products and a variety of thermoplastics. As long as the mold temperature is 120 [degrees] F or greater, the water will evaporate adequately and rapidly. Pre-warming the lube should also be considered.

Solvent- and CFC-based lubricants are more forgiving in this regard. They just spray better. Use of the water-based material requires more attention to the detail of spray quality and the parameters controlling the spray. Also, because of the highly volatile nature of them, solvent- and CFC-based systems are easier to apply on cold molds.

Another consideration for water-based systems not required for the others is freezing. Freezing of the water-based systems can be catastrophic in terms of equipment damage and use.

Companies that decide to make the change to water-based systems may be faced with some new capital requirements. This can include such things as improved spray equipment, improved storage containers, etc. When these water-based systems were first introduced, corrosion of equipment was a significant concern and problem. That has been overcome in the newest generation of lubricants through inclusion of effective corrosion inhibitors.

Summary

It would appear that water-based mold lube systems are beginning to come of age. Renewed interest in water as an alternative to solvent- and CFC-based spray systems has spurred development of newer, more advanced lubricants than were available just a short time in the past.

The problems with solvents and CFCs are not new and they are not going to go away. They probably will get worse. The sooner manufacturers change to alternative systems, the better off they will probably be in the future. While changing now is not mandatory in a legal sense, changing at this time will allow manufacturers to make the climb up the learning curve with the least disruption.

Water-based systems are not going to perform exactly like the current organic systems. However, all reports are that they perform just as well. Also, reports also indicate that the cost of using them is essentially equivalent to use of the organic system. Therefore, there is no cost penalty. Add to this the fact that any use of materials that emit solvents into the atmosphere, let alone CFCs, is coming under increased scrutiny by our government regulators. Anyone not being affected by organic emission controls need only talk to a manufacturer in Los Angeles or San Jose to find out how truly challenging it can be. In addition to all this, we can add the financial and health benefit of providing a workplace that is more healthy and better for our workers.

There are other systems in development. These include airless, 100% active ingredient delivery systems. Also, some systems are being developed that use cryogenic gases to deliver the lubricant. However, these systems are still highly developmental and require significantly greater investment in capital resources. They are also more complex.

Compressed air systems are well known. Their operation is readily understood and is fairly simple. When in doubt, keep it simple. In all, it would seem that now is a good time to begin making the change to water-based mold lubes.

Jon Menough, contributing technical service editor
COPYRIGHT 1991 Lippincott & Peto, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:water-based mold lubricants in the rubber industry
Author:Menough, Jon
Publication:Rubber World
Date:Feb 1, 1991
Words:1987
Previous Article:Custom mixing capacity growth slowed.
Next Article:Custom mixing of silicone rubber.
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