Richard Harper Sales Manager Lilly Industries Westlake, Ohio

Transcription

1 IN-MOLD COATING OF RIM INJECTED POLYURETHANES - A SENSIBLE ALTERNATIVE TO POST FINISHING Richard Harper Sales Manager Lilly Industries Westlake, Ohio Presented at: FINISHING '95 CONFERENCE AND EXPOSITION September 18-21, 1995 Cincinnati, Ohio 269

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3 r d. Introduction IN-MOLD COATING OF RIM INJECTED POLYURETHANES A SENSIBLE ALTERNATIVE TO POST FINISHING The traditional method for coating RIM injected polyurethanes and polyureas involves several steps: Line Loading Pretreatment Paint Application Curing Unloading Additional stepti may alm be required before finiehing. IS the RIM Injected plastic contains an internal mold release, post curing may be required to drive the internal mold release to the surface so that it can be removed during the pretreatment process. Post curing before painting may also be required on some RIM injected plastics to prevent gassing during the post finishing process. Depending upon the type of RIM (ie; structural foam, elastomeric, structural RIM, etc.) more than one paint application may be required to produce the desired coating appearance. Best results are usually obtained with two component urethane 27 1

4 finishes whether for interior or exterior application, although many coaters are now using water reducible finishes for interior applications. Post finishing requires large capital expenditures for pretreatment systems, spray booths, application equipment, and ovens (pretreatment dry-off, paint curing and post curing of the RIM substrate, if required). In addition, there is considerable labor expense in the form of personnel for loading and unloading, application, and line supervision. There is also the expense involved in the operation and maintenance of this post finishing system. In-Mold Coating of RIM Injected polyurethanes, polyureas, and polyisocyanurates is a relatively new method for finishing such plastics. There are three main types of in-mold coatings: In-mold Lacquers Urethane Lacquers Two Component Polyurethanes Water Reducible Systems In-mold lacquers were the first in-mold coatings developed for use with polyurethanes. They are used mainly for interior and primer applications, although they have been used for some exterior applications. Advantages include: single component composition, rapid set-up time, works well with a variety of RIM injected polyurethane plastics, and its functionality promotes chemical bonding between the RIM system and the in-mold coating. Disadvantages include: low solids, high VOC, and fair to poor exterior durability. They also tend to be soluble in strong solvents such as ketones (of concern if used as a primer). Two Component Polyurethane In-mold Coatings... The next generation of in-mold coatings to be developed were two component polyurethane coatings. These coatings provided a new level of performance for in-mold coatings and are still considered to be the in-mold coating benchmark for quality. These in-mold coatings exhibit two component urethane type exterior durability and, as such, are the best choice for high performance exterior applications. In addition, two-component urethane in-mold coatings provide a strong chemical bond to the RIM substrate, excellent abrasion resistance, and hot and cold cycle resistance. They also exhibit resistance to solvents, making them a better choice as an in-mold primer than in-mold lacquers. Disadvantages include the need for two component spray equipment, monitoring of isocyanate levels, and medium to high VOC. Lower VOC ( ) in-mold coatings are now under development and should be commercial within months. 272

5 d. 0 Current uses for two component polyurethane in-mold coatings are: encapsulated windows for cars and trucks, implement parts such as fenders for tractors and backhoes, bumpers for trucks, steering wheels, airbag covers, and other assorted interior automotive applications. The newest innovation has been the development of water reducible in-mold coatings for automotive and non-automotive interior applications. They are also being touted as exterior durable finishes. The advantages of water reducible technology are: single component (no need for two component spray equipment), generally lower cost than two component urethanes, and low VOC. While this in-mold coating offers cost and environmental advantages, they generally do not offer the same level of exterior performance, solvent resistance, or the abrasion resistance of two component urethane in-mold coatings. Current environmental legislation, which requires further reductions in VOC and HAPS levels, will result in increased demand for water reducible in-mold coatings. In-mold Coating Application... Whether your choice of in-mold coating is lacquer, two component or water, the press must have adequate ventilation to remove solvent fumes and overspray from the work environment. While adequate ventilation is required for any type of spray application it is especially important when using two component polyurethane in-mold coatings. Worker exposure to isocyanates must be kept within recommended guidelines and periodic monitoring of isocyanate levels ia advised. Applicators should also wear the proper respirator for the type of in-mold coating being applied. Thia may be a charcoal filter mask or fresh air respirator. In-mold coatings are applied to heated molds (usually llof - 190F) juat prior to the RIM injection cycle. Most manufacturers of in-mold coatings recommend the use of HVLP air atomized spray equipment in order to reduce the amount of overspray. Some inmold coating applicators, who had previously post finished RIM injected parts, have reported greater transfer efficiency for inmold coating; since most molde are female and spray patterns and delivery rates can be fine tuned to the specific mold configuration. In-mold coating lends itself extremely well to robotic application, as the same mold configuration is coated each cycle. Even though most in-mold applications are spray-close-inject, there will be some increase in cycle time as a result of in-mold 273

6 coating application. If this is a new application for in-mold and no post finishing line exists, engineering must evaluate the cost of increased cycle time versus the cost of installing and operating a post finishing operation. In most new applications, in-mold coating is more economical than post finishing. Even molders with post finishing lines have found in-mold coating to be more economical in certain applications. In some cases the labor and material savings realized can more than offset the cost of letting post finishing equipment sit idle. Whether in-mold coating is more economical than'post finiehing must be evaluated on a case by case basis. In operations where post finishing systems are at capacity, in-mold coating of RIM injected parts can provide additional painting capacity at lower additional cost than paint line expansion. Mold Design In-mold coatings are suitable for use with most tooling materials, auch ea steel, aluminum, epoxy, etc. Silicone molds are not usually recommended for in-mold coating applications as some inmold coatings do not wet out the silicone mold surface well. If tooling is being built with in-mold coating in mind, care ahould be given to the location of parting lines. Tooling should be designed, if possible, so that the parting lines do not appear on the class A surface. If it is not feaaible to design the tooling in this manner touch-up of these areas may be necessary, especially if the part is to be exposed to UV. If the part is not to be subjected to UV it may be possible to tint the RIM resin to minimize any color difference once the flash is trimmed from the part. Mold Maintenance The condition of the mold surface ia critical to the success of any In-mold coating operation. In-mold coating is unique in that it will tend to duplicate the mold surface. If an in-mold coating is applied to a mold with a poor surface appearance, the in-mold coated part will mirror this poor appearance. A mold with excellent surface appearance, however, will produce an in-mold coated part with excellent surface appearance. Care must be taken to keep toola which may scar the mold surface away from the molding operation. Once the mold surface is scarred, in-mold coating quality will be affected. If the part requires a class A surface, the tool may have to be resurfaced or reworked.. Mold maintenance is especially important for gloss consistency. Many interior parts are extremely low gloss (2-6 degrees) and a change in gloss of 2 or 3 degrees can result in a significant shift in color. Successful molders cite mold maint.enance as one of the keys to a successful in-mold coating operation. 274

7 r 3, ' * The ability to mirror the mold surface does have advantages as the same coating can be used for high and low gloss applications. If the tool is textured, an in-mold coating can provide excellent texture reproduction. Post finishing, on the other hand, tends to fill in the texture. Internal Mold Releases... Some in-mold coatings contain an internal mold release which may build up after several press cycles. When this build-up starts to effect coating appearance or gloss, the mold must be cleaned in order to restore the mold surface to its original appearance and gloss. In-mold Coating Applications... Most current applications for in- old c ting ar in the automotive market. Examples of these applications are: steering wheels, airbag covers, engine box covers for heavy duty trucks, speaker boxes, truck bumpers, window encapsulation, and arm rests. There are also a number of non-automotive applications currently in production. In-mold coatings, both as finish coats and primers, are currently in use for the production of: parts for farm equipment, business equipment, and medical equipment. There are nulnerous markets where in-mold coating and RIM injection may have real value. One such market is the marine industry where RIM injection and in-mold coating could have real value in the production of hatch covers, steering wheels, instrument panels, radar arches, etc. There are also other potential applications for in-mold coating within the recreation industry, such as: snowmobiles, jet skis, ATVs, exercise equipment, etc. In the future, it is expected that in-mold coatings will play a major role in the expansion of Polyurethane RIM injection into merkets other than automotive. 27 5

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