Copyright B C Hymel Nov 2004 All rights reserved. Latex Rubber Bonding Introduction It should be noted that these tests were conducted prior to reading methods posted elsewhere on various sites, and that the many of the methods and techniques developed independently by me are similar to those described by others posting in several forum, further validating their effectiveness. I began by searching for contact and rubber cements and contacting manufacturers for recommendations. During this search I had the opportunity to speak with an adhesive chemist whose company did not have an appropriate product, but he was quite helpful anyway. I will not disclose the company, but the results of our conversations reflected here, so there is no need for everyone to bug him. I work in product development professionally and am in contact with adhesive and resin specialists on a regular basis identifying the best systems for product manufacturing. This report is an outline of what I would do for any application. While I did test some industrial materials the best performers were common rubber cements available at most art supply, auto parts and craft stores. For those not chemically minded the pronunciation of Isoprene is “latex” (Natural Rubber, NR) For those not chemically minded the pronunciation of chloroprene is “neoprene” (synthetic Rubber) Safety Before you begin read and follow all manufacturers safety precautions. (Material Safety Data Sheet, MSDS, most available on line). Work in a well ventilated area away from sparks flames fires etc. Solvent vapors are harmful!, and may cause permanent damage to lungs, liver, brain and other vital organs. Most adhesives contain volatile solvents including nitromethane which is explosive! (The MSDS is also a good source t o find out what is in a product) Copyright B C Hymel Nov 2004 All rights reserved. Adhesives Recommended /Tested: 1 Barge Cement Chloroprene 2 Master Cement Chloroprene 3 3M Scotchgrip 1357 Chloroprene 4 Bostik L2402AP/2402BX urethane? 5 Bostik L1096M/BOSC4 urethane? 6 Bestest White Latex Isoprene / heptane 7 NAPA Cam Cure (Camel) Chloroprene 8 Elmer’s Rubber Cement Isoprene / heptane 9 Tandy XXX contact cement Isoprene / heptane 10 Pliobond Chloroprene Not tested, see Barge 11 Henkel Copydex Isoprene/ammonia? Not available in US 12 Bostik 3851/6009 solvent Isoprene / Heptane Not available in US 13 Monkey Grip Universal Cement ?? suspect Chloroprene?? 14 Slime Rubber Cement ?? suspect Chloroprene?? 15 NAPA Balkamp Universal Cement ?? suspect Chloroprene?? 16 Camel #12-086 Universal Cement unable to locate sample Non Flammable Formulations Most of the non-flammable formulas fall into two categories. They are either ammonia dispersions, or contain chlorinated solvents, such as chloroform, methylene chloride, or trichloroethylene. These adhesives are compounded for the complex synthetic compounds used in tires and may adversely affect natural rubber. While many report they have had good results with ammonia type adhesives, there are several reports that they are less effective than the solvent based adhesives. I was not able to easily find and test these products. (I am still looking for a product called “Canvas Grip Cement” to test) Method The rubber (.012"/.33mm hygienic tm sheet) was prepared by backing the joints with masking tape to control curling, and limit the stretch of the substrates. The substrates were prepared by buffing with abrasive paper or Scotch Brite pad, followed by solvent cleaning or simply solvent cleaning alone. Solvents tested were MEK, naphtha, cyclohexane, lacquer thinner, Bestine cement thinner (heptane). I felt that the best solvent for cleaning the rubber prior to bonding was the Bestine Solvent.(once again heptane is also a good choice). The cleaned surfaces can be tested by pressing them together while the rubber is swollen, if the surfaces seem to be sticky and lightly adhering to each other they should be ready for adhesive. This preparation is probably the most critical phase of the process! The adhesive was thinned approximately 2:1 with recommended solvent for the initial tests Copyright B C Hymel Nov 2004 All rights reserved. and later higher dilutions of up to 5:1 or higher(see addendum, Dilution). All of the adhesives were thinned with the Bestine solvent since it was the only rubber cement solvent readily available, it seemed to work well with all latex / heptane ,as well as the universal and tire patch adhesives tested. The main and likely only ingredient in Bestine solvent is heptane. Heptane could be used for cleaning and thinning if it is available. Adhesive was applied in two* thin coats, and allowed to dry for about 5 minutes. The substrates were overlapped approximately 8mm,and pressed firmly together and the tape then burnished with a blunt object or rolled. Further tests at a later date seemed to indicate that highly diluted adhesive applied in a single coat might be best. Also applying the thinned cement with an artist’s bristle brush using a scrubbing motion also proved effective. Joints were tested after 24 hours, and were considered successful if the rubber was tearing before the joint, although there was always some peeling at the interface. Findings: All of Isoprene (latex) / heptane formula’s created the good to excellent bonds overall. And all of the adhesives in this category performed similarly. The Elmer’s cement showed slightly better bond strength, but was thinned considerably more than the other adhesives, Bestine cement was tested under as the same conditions as the Elmer’s and performed similarly. This indicates that the tests should be rerun with different dilutions to find the optimum bond strength. Cleaning technique also played an important part in ultimate bond strength. Of the chloroprene (neoprene) adhesives the NAPA Cam-Cure (Camel), Monkey Grip Universal, and NAPA Balkamp Universal Rubber cement (tire patch cements) performed well. After a conversation with a rubberist who preferred Camel tire patch cement, I retested the Cam Cure form NAPA with my much improved techniques and got somewhat better results. I the course of looking for The camel products, which have yet to be found locally, I found the Monkey Grip product, which I found to work as well as the latex / heptane formula’s. The Barge and Master cements are compounded primarily for shoe repair and contain silica fillers and other solids. While they did bond the rubber, they did not work quite as well as the chloroprene based adhesives above, possibly due to the fillers. While not tested here, Pliobond is similar to these products. The Bostik products suggested by Bostik USA failed due to differential expansion characteristics when the latex substrates were stretched. Both product performed similarly. Copyright B C Hymel Nov 2004 All rights reserved. The Bostik 3851,and it’s solvent, recommended by 4d are not available in the US according to Bostik tech support, but seems to be a heptane based adhesive.(is the grass really greener..) The 3M product was not as good as the Barge or Master would be ok but not great. Henkel USA reports they have no solvent based products. Copydex, is not available in the US. It should be noted that my conversations with a chemist at a large adhesive company indicated that most of the solvent based latex products are not formulated for heat vulcanizing and suggested the addition of 1 to 3% elemental sulphur to facilitate heat vulcanization , this has not been tested at this time. In addition this method would require precisely heated fixtures to apply pressure and heat for a specified amount of time. It is not recommended to apply too much stress to bonded joints, so articles should be designed accordingly. Like wise additional gussets or reinforcement should be applied to high stress areas. Much of the success in the bonding of latex in the technique, also keep in mind that sheet latex and latex for dipped articles are compounded differently and results may vary. Tests conducted at the end of this cycle showed that one thin coat may achieve higher bond strength than two coats, Further testing is needed. Bonding Technique The success of latex bonding is a combination of the proper cement, and technique. You should determine the optimum dilution for the cement, as well as a joint preparation and cleaning method that will best suit your materials and needs, by first experimenting with scrap. It is important to work carefully and methodically, in a clean area with fresh materials until you are satisfied with your results. Start with simple strips 3 to 6 inches long by one to two inches wide, bond them together, and then take them apart after 24 hours or more to evaluate your success. Then proceed to easy projects straight seams, until you are comfortable with your skill development. (True for building any skill set). Try to visualize and rehearse your procedure in your head or do dry runs before applying cement and beginning assembly. As you develop your technique your bonds should improve. Materials Cement, Bestest white latex cement, heptane formula ( or your favorite) Bestine heptane solvent ( heptane, or recommended solvent for your favorite) Copyright B C Hymel Nov 2004 All rights reserved. Blue painters masking tape 3/4 wide. Cotton swabs lint free cloth sand paper, 220 and 320 wet/dry scotch brite pad ( abrasive paper) seam roller, patch stitcher, brayer or the like Theories 1 Thin adhesive boundary layers allow molecular exchange at the joint achieving the strongest joints. 2 Solvent cleaning removes oils and opens the molecular structure allowing the cement to penetrate This is evident by the curling (expansion) of the rubber. 3 Scuffing or buffing the surfaces breaks the glaze, removes surface oxidation ( old or dry rubber) aids adhesive penetration , increases bond surface area (somewhat) improving overall bond strength.