1、10-109SSPC-TU 8February 1, 2001Editorial Revisions November 1, 2004SSPC: The Society for Protective Coatings TECHNOLOGY UPDATE No. 8The Use of Isocyanate-Containing Paints as Industrial Maintenance Coatings 1. Background Information Isocyanates are chemicals that contain at least one isocyanate (-NC
2、O) group. Depending on the number of iso-cyanate groups, one can distinguish among monoisocyanates (1 group), diisocyanates (2 groups), or polyisocyanates (3 or more groups). Monoisocyanates are of no value in coatings because they cannot build the polymeric structure needed for a coating raw materi
3、al. Nevertheless, diisocyanates, often called monomers, are important building blocks for coating raw materials. Commonly used diisocyanates are MDI (diphenylmethane diisocyanate),TDI (toluene diisocyanate), IPDI (isophorone diisocyanate), HDI (hexamethylene diisocyan-ate), HMDI (bis(4-isocyanatocyc
4、lohexyl)methane), and TMXDI (tetrameth-ylxylene diisocyanate). Evaporation rates determine how quickly a material is vaporized and dispersed into the atmosphere. High evapora-tion rates cause faster dispersion and more vapor exposure than lower evaporation rates. Diisocyanates have varying evaporati
5、on rates. For example, the evaporation rates of TDI and HDI are considerably higher than that of MDI. In order to make TDI and HDI safer to use as coatings raw materials, they are further reacted to make slightly larger polyisocyanates that may contain from 3 to 7 units of the starting diisocyanate
6、monomer. These polyisocyanates do not evaporate and can become airborne only during spray appli-cation. However, the polyisocyanates do contain a very small amount (0.15% to 1.6%) of residual free HDI and unreacted TDI monomer that can still evaporate. TDI, MDI and their polyisocyanates are known as
7、 aromatic isocyanates. These materials absorb ultraviolet light (UV) from the sun and therefore become dull due to a chalky layer that forms on the paint surface. Therefore, paints based on these materials are not typically used as topcoats in outdoor applica-tions. On the other hand, HDI, IPDI, HMD
8、I and TMXDI are called aliphatic isocyanates. These do not absorb much UV light and therefore can be used in formulating outdoor topcoats. “Polyurethane” (PU) is the name of the material formed by the chemical reaction of an alcohol and an isocyanate or, more precisely, polyalcohols and polyisocyana
9、tes. Polyurethane coatings can be of several types. In a one-component or moisture-cure polyurethane, the polyisocyanate reacts with water in the atmosphere. In a two-component system, the polyisocyanate reacts with a resin having reactive hydrogen, which can be acrylic, polyester, polyether, vinyl,
10、 castor oil, etc. The paint fi lm resulting from this chemical reaction is the foundation of the performance properties of polyurethanes: durability, corrosion and chemical resistance, and color and gloss retention. These properties have resulted in the use of polyurethanes in a wide range of indust
11、ry segments. In 1998, 13.3 million gallons of PU coatings were used in transportation, 12.7 million gallons in industrial maintenance, 28.8 million gallons in architectural, and 53 million gallons in product fi nishing applications. Some typical industrial mainte-nance applications are bridges, chem
12、ical plants, tank farms, power plants, and municipal structures (e.g. as anti-graffi ti coatings). High performance paints can contain diisocyanates, poly-isocyanates, solvents, pigments, additives, and other resins. All these ingredients can present certain potential health hazards if one is expose
13、d to a suffi ciently high dosage. This is why the applicator and any other workers in the application area must be properly protected. All coatings, including those containing isocyanates, can be applied safely when proper personal protective equipment (PPE) is worn and safe work practices are obser
14、ved. This technology update focuses on the isocyanates in industrial maintenance coatings. Exposure to polyisocyanates in excess of recommended limits can irritate the eyes, nose, throat, skin, and lungs. An overexposed person may develop skin sensitization and/or respiratory sensitization resulting
15、 in asthmatic symptoms that could be permanent. Exposure in excess of recommended limits may also result in a reduction in lung function and possible permanent lung damage. Symptoms of overexposure can include fl u-like symptoms such as fever, chills, or an achy feeling. There is no evidence that is
16、ocyanate exposure causes human cancer, birth defects, nerve damage, or reproductive effects. 2. Worker Exposure 2.1 RECOGNITION OF HAZARD: In order to determine whether a particular coating contains isocyanates, one should refer to the paint can label and the material safety data sheet (MSDS). If a
17、coating is referred to as a polyurethane or a polyurea, it may contain isocyanates. However, some polyure-thane coatings are fully reacted. That is, all of the isocyanate groups are chemically changed to polyurethane groups prior to packaging for shipment. Examples of such coatings would be most one
18、-package, clear, polyurethane wood varnishes sold at retail home improvement stores. Polyurethane coatings used for industrial maintenance painting usually contain unreacted isocyanates at the time of application to the substrate. The two-package types have a “paint” side that needs to be mixed with
19、 a hardener, activator or “catalyst”, just before application. The hardener is the part that typically contains the unreacted 10-110SSPC-TU 8February 1, 2001Editorial Revisions November 1, 2004isocyanate. Because these two parts of the paint system are packaged and shipped separately, the supplier o
20、ften provides two different MSDSs, one for the “paint” side and one for the “catalyst” side. Both MSDSs must be reviewed in such a case because the “paint” side MSDS will typically not mention that “free” isocyanates may be present. Another type of polyurethane coating typically used in industrial m
21、aintenance is the one-package, moisture-cure system. This type does contain the isocyanate ingredient in the single can. This type of paint cures by reaction of the unreacted isocyanate with atmospheric moisture once the can has been opened to the ambient environment. Specifi c words and acronyms to
22、 look for on labels and MSDSs are: isocyanate, polyisocyanate, aliphatic isocyanate, aromatic isocyanate, hexamethylene diisocyanate (HDI), di-phenyl methane diisocyanate (MDI), isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), dicyclohexylmethane diiso-cyanate (HMDI), TMXDI (tetramethylxy
23、lene diisocyanate), HDI homopolymer, isocyanate prepolymer, isocyanate oligomer, isocyanate monomer, etc. If the applicator suspects that a particular coating contains isocyanates but cannot fi nd any mention of them on the label or MSDS, a second step would be to call the paint supplier and ask to
24、speak to a product safety specialist. Often the MSDS itself will list the name of the contact.2.2 EVALUATION: Once it has been established that a particular paint system does contain an isocyanate ingredi-ent, the workplace atmosphere should be characterized to determine the airborne concentration.
25、Most diisocyanate monomers have an OSHA(1)Permissible Exposure Limit (PEL), an ACGIH(2)Threshold Limit Value (TLV), a NIOSH(3)Recommended Exposure Limit (REL), or a Manufacturers Guideline Limit (MGL). Most commonly, the 8 hour Time Weighted Average (TWA) airborne concentration guideline or standard
26、 for diisocyanates is fi ve parts per billion parts of air (ppb). For HDI monomer, this is equal to 0.034 milligrams/per cubic meter of air (mg/m3). Polyisocyanates are less toxic and therefore can have a higher allowable TWA exposure. The MGL (and Oregon OSHA PEL) for HDI polyisocyanates is usually
27、 0.5 mg/m3as an 8-hour TWA and 1.0 mg/m3as a 15 minute Short Term Exposure Limit (STEL). MSDSs often list the ap-plicable airborne concentration guidelines/standards. Another source for diisocyanate monomer exposure standards is the ACGIH publication entitled “Guide to Occupational Exposure Values.”
28、 Monitoring of the workplace air to determine concentrations of isocyanates is a key step in determining the effectiveness of engineering controls as well as in determining the type of respiratory protection and other personal protective equipment which may be required. Specifi c sampling and analyt
29、ical tech-niques have been developed to determine these levels. At present, the recommended method for sampling and analysis of HDI, TDI, and IPDI polyisocyanates in spray ap-plications is Bayer Method 1.4.4.(4)Samples are collected using impingers containing 2 x 10-4M N-(4-nitrobenzyl)-propylamine
30、(nitroreagent) in toluene. Analysis is by high performance liquid chromatography (HPLC) and ultraviolet detection at 254 nanometers. Bayer has developed Method 1.4.4 independently and used it successfully for 20 years. In terms of current NIOSH methods, the one which is perhaps most similar is Metho
31、d 5521 which uses an impinger containing methoxyphenyl piperazine (MOPP) reagent in toluene.(5)This NIOSH method uses both electrochemical and ultraviolet (UV) detectors. However, if only the UV detector is used and the calibration curves are run using diisocyanate monomer and commercial polyisocyan
32、ate, the method would be quite similar to Bayer 1.4.4. In addition, OSHA Method 18(6)would be similar to Bayer 1.4.4 if an impinger jet inlet were used instead of the fritted glass bubbler inlet specifi ed in OSHA 18. For situations in which only HDI, TDI, IPDI, HMDI, TMXDI monomer vapors would be p
33、resent, such as in non-spray han-dling and use, Bayer Method 1.7.6 is recommended. Samples may be collected using a 1-(2-pyridyl) piperazine impregnated glass fi ber fi lter with analysis by HPLC. Bayer 1.7.6 is OSHA Method 42 modifi ed by coating the fi lter with 2 mg of derivatiz-ing reagent inste
34、ad of 0.1 mg and by loading the fi lter in the cassette with a stainless-steel backup screen in place of the mixed-cellulose ester back-up pad. Both of these modifi ca-tions are designed to prevent the loss of derivatizing reagent. Such a depletion of reagent can result in under-estimation of airbor
35、ne isocyanate concentrations. Air monitoring for MDI can be performed using Bayer Method 1.7.7. This method is similar to Method 1.7.6 above but uses a 13 millimeter (mm) diameter glass fi ber fi lter instead of a 37 mm fi lter. (1)US Dept. of Labor, OSHA, Offi ce of Public Affairs - Room N3647, 200
36、 Constitution Ave., Washington DC 20210, or contact via internet at http:/www.osha.gov/readingroom/html(2)American Conference of Governmental Industrial Hygienists, 1330 Kemper Meadow Drive, Suite 600, Cincinnati OH 45240 (http:/www.acgih.org).(3)National Institute for Occupational Safety and Health
37、, 200 Independence Avenue, SW, Washington, DC 20201. (http:/www.cdc.gov/niosh).(4)Bayer Product Safety Department at Bayer Corporation, 100 Bayer Road, Pittsburgh, PA 15205-9741, Phone: (412) 777-2867. (Contact for information on the Bayer methods mentioned in this report.)(5)NIOSH Publications, 467
38、6 Columbia Parkway, Mail Stop C-13, Cincinnati, OH 45226-1998. May be downloaded from NIOSH web page at http:/www.cdc.gov/niosh/nmam/nmammenu.html(6)Method 18 from US Dept. of Labor, OSHA, Offi ce of Public Affairs, Room N3647, 200 Constitution Ave., Washington DC 20210, (http:/www.osha.gov/readingr
39、oom/html)(10-111SSPC-TU 8February 1, 2001Editorial Revisions November 1, 2004Continuous or direct reading monitors for diisocyanate monomer vapors have recently been developed. It must be pointed out, however, that these units may not be suitable for monitoring in spray application environments sinc
40、e the spray paint mist droplets can coat the optics and/or the treated paper tape and give erroneous readings. These instruments may provide information as to airborne diisocyanate monomer vapor concentrations during non-spray applications such as: mixing, repackaging, batchmaking, coil coating, and
41、 brush/roller/squeegee application. To date, no direct reading instru-ment has been developed which can be used to accurately determine airborne concentrations of polyisocyanates in spray application of coatings.(7,8)The technology for evaluating skin exposure to isocyanates is not as advanced as th
42、at for airborne monitoring. Check for any visual evidence of deposition of paint onto the skin. Usually, this is rather obvious because of the paint pigmentation and/or a feeling of stickiness on the skin. If the user wishes to check a surface to determine if isocyanate residue has been removed, suc
43、h as after a spill clean-up, he should consider purchase and use of SwypeTMTest kits which are manufactured by Colorimetric Laboratories, Inc.(9) 3. Control of Health Hazards 3.1 ENGINEERING CONTROLS: Ideally, hazard control of vapor or spray mist is accomplished through engineering controls. Effect
44、ive engineering controls should be used when-ever possible to reduce and/or eliminate worker exposure to all respiratory hazards. There are several engineering controls available to reduce exposure to vapors and mists generated by the use of these products. The most common is a properly designed and
45、 ventilated enclosure. General dilution ventilation, local exhaust ventilation, or isolation may prove adequate under certain conditions. “Adequate” generally means ventilation suf-fi cient to keep airborne concentrations of contaminants below their respective Threshold Limit Values (TLVs), Permissi
46、ble Exposure Limits (PELs) and Manufacturers Guideline Limits (MGLs). Whenever possible, local exhaust ventilation should be provided in accordance with the guidelines provided in Industrial Ventilation, A Manual of Recommended Practice. Use of alternative application equipment (e.g., airless, HVLP,
47、 or electrostatic spray equipment) may help reduce spray mist generation during spray painting. In addition, the use of spray gun extenders may help reduce the amount of spray mist in the breathing zone of the painter. The likelihood of overexposure in non-spray, non-heated applications of coatings
48、containing polyisocyanates is reduced due to the low volatility of these materials. Hence, the use of brush, roller, or squeegee for coating application reduces the likelihood of inhalation overexposure. 3.2 RESPIRATORY PROTECTION: One manufac-turer of polyisocyanates recommends air-supplied respira
49、tors for spray application if the airborne concentrations are unknown or if they exceed ten times the appropriate airborne concentration standards/guidelines.1However, the same manufacturer states that air-purifying respirators may be used under the following conditions: if airborne concentrations are known to be less than 10 times the standard/guideline concentration; if the spraying is not being done in a confi ned space; if pre-fi lters are changed as needed to prevent exces-sive breathing resistance; and if appropriate change schedules are implemented for the organic vapor car
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