1、 FORD LABORATORY TEST METHOD AI 103-03 Date Action Revisions 2000 08 07 Editorial no technical change A. C ockman 2000 04 05 Editorial no technical change A. Cockman 1995 03 13 Printed copies are uncontrolled Page 1 of 5 Copyright 2000, Ford Global Technologies, Inc. Photooxidation and Film Loss in
2、Coatings Method A: Photooxidation and Film Loss of Coatings on Silicon Disks Application This test method determines the amount of photooxidation and film loss in coatings by measuring the changes in IR spectra after weat hering. Chemical changes occur in coatings during weathering and can be monito
3、red as a function of exposure time. This information provides a way to evaluate the durability of coatings and monitor film loss. Required Test Equipment IR Silicon Disks - 2 mm x 13 mm, available from Wilmad Glass Co., Inc., Rte. 40 and Oak Rd., Buena, NJ 08310 (609)697 - 3000. Catalog #100N9 - SP
4、- 1 (notched for alignment purposes) Glass Capillary Tubes - for applying coating on silicon disks Laboratory Oven - capable of curi ng coating Silicon Disk Holder - this will have to be custom made to align disk in IR beam Fourier Transform Infrared (FTIR) Spectrophotometer Materials and Solution R
5、equired Methylene Chloride - certified ACS grade or equivalent I. Preparation of Coating on Silicon Disks 1. For each clearcoat being studied, make free - standing coating films of varying thickness. Obtain an IR spectrum of each film and integrate the CH absorbance area (see Figure 1) to obtain the
6、 CH absorbance area/micrometer correla tion. 2. Acquire an IR background on a clean, uncoated silicon disk. Observe that the notched disk rests in the proper orientation. 3. Using a capillary tube, coat a silicon disk with a thin uniform film of coating. 4. Allow the solvent to evaporate fo r severa
7、l minutes at room temperature. FORD LABORATORY TEST METHOD AI 103-03 Page 2 of 5 Copyright 2000, Ford Global Technologies, Inc. 5. Display the IR spectrum of the coating in absorbance mode. Integrate the CH absorbance area. Convert the integrated area to film thickness in micrometers. a. If the film
8、 thickness is between 7 and 10 micromete rs, cure the coating on the silicon disk using the recommended temperature and time, unless stated otherwise in applicable Engineering Material Specification. b. If the film thickness is not between 7 and 10 micrometers, remove the uncured coating from th e s
9、ilicon disk by rinsing with methylene chloride. Repeat steps 2 4 until the film thickness is in the recommended range. 5. Obtain the IR spectrum of the coating before weathering has occurred. This will be called the “time 0“ value. II. Obtaining IR Spectra 1. Remove the silicon disks from weathering
10、 at intervals suggested by the ongoing results. Record the hours of exposure upon removal. Exposure samples from Florida should be tested at least at six month intervals, or more often if suggested by the ongoing data. 2. Obtain the IR spectra of the coatings using a clean, uncoated silicon disk as
11、an IR background. (Place the silicon disks back in the weatherometer as soon as possible to continue weathering. Silicon disks from Florida exposure need not be sent back.) Note: Absorbed water might contribute strongly to the OH, NH area resulting in a false measure of polymer - based OH, NH photoo
12、xidation products. Therefore, it is important to remove samples at the end of the dry, light cycle of the weat herometer. Alternatively you can dry samples for 15 minutes at 104 C. III. Photooxidation Rate by Monitoring OH, NH Products One way to access the photooxidation rate of a coating is to mon
13、itor the concentration of - OH (hydroxy) and - NH (amine) produc ts as weathering occurs. The concentration is expressed as the amount of - OH and - NH products per amount of film remaining. The concentration is calculated by ratioing the OH, NH area to the CH area of the FTIR spectrum. 1. Integrate
14、 the entire OH, NH, C H stretch area. (See Figure 1.) 2. Integrate the CH stretch area centered around 2900 cm - 1 . 3. Subtract the CH stretch area from the total area to obtain the OH, NH area at time t. 4. Divide the OH, NH stretch area by the CH area to obtain the concentra tion of hydroxy and a
15、mine functional groups present in the coating. FORD LABORATORY TEST METHOD AI 103-03 Page 3 of 5 Copyright 2000, Ford Global Technologies, Inc. 5. Subtract the OH, NH/CH ratio at time 0 from subsequent OH, NH/CH ratios at time t to obtain the concentration of OH, NH/CH due to photooxidation products
16、. Plot the OH, NH/CH due t o photooxidation as a function of exposure time. The slope represents the photooxidation rate. IV. Monitoring Film Loss 1. Following steps 1 determine the decrease in absorbance by comparing “time t“ value to its respective “time 0“ value. 4. Using the correlation be tween
17、 CH absorbance area and film thickness obtained by making free -standing coating films (Section I) convert integrated area to film thickness in micrometers. 5. Plot the film thickness data as a function of exposure time. Method B: Photooxidation of Coatings on Painted Panels or Parts by Bulk Analysi
18、s Application This test method determines the amount of photooxidation in coatings by measuring the changes in IR spectra of coatings removed from painted panels and parts after weathering. Chemical cha nges occur in coatings during weathering and can be monitored as a function of exposure time. Thi
19、s information provides a way to evaluate the durability of coatings. If techniques such as photoacoustic IR are available, they may be used in place of the f ollowing potassium bromide (KBr) sample preparation procedure. Required Test Equipment Laboratory Oven - capable of curing coating Soft Foam P
20、ad - for cleaning exposure panels or parts Compressed Air Source - for drying panels or parts after washing Single Edged Razor Blades - for scraping coating off of panels or parts FORD LABORATORY TEST METHOD AI 103-03 Page 4 of 5 Copyright 2000, Ford Global Technologies, Inc. KBr Press and associate
21、d equipment - for preparing the sample for FTIR examination Fourier Transform Infrared (FTIR) Spectrophotometer Materials and Solution Required KBr Powder - FTIR Grade or equivalent Methylene Chloride - certified ACS grade or equivalent Mild Soap Solution - for washing Florida panels or parts I. Pre
22、paration of Photooxidation IR Samples (KBr) To allow for 12 data points of photooxidation growth versus h ours of weathering, spray up 12 panels for each type of coating using FLTM BI 103 -02 for each exposure condition (i.e., 12 panels for weatherometer and 12 panels for Florida). An appropriate nu
23、mber of retain panels shall be prepared to establish a reliabl e time 0 photooxidation determination. Prepare a KBr disk for each unexposed and weathered panel. Painted parts may be used instead of panels. 1. Cure the panels at the recommended time and temperature, or as indicated by the relevant en
24、gineering specif ication. Age fresh panels for 72 hours at 23 +/ - 2 C. 2. Returned, completed exposure panels from Florida only should be washed in entirety with a soft foam pad using mild soap solution. Next the panels are rinsed with tap water and blown dry using cle an compressed air. 3. The coa
25、ting is then scraped from the clean panels using a single edged razor blade. All of the coating in one area must be removed before moving onto a new area. Care must be taken not to scrape so far down as to remove the underla ying layer. 4. Enough coating is used to prepare a KBr IR disk. Proper spec
26、trographic techniques should be used to prepare the KBr disk. (Reference: Willard, H.H., Instrument Methods of Analysis , Lancaster Press, 1988.) Dry KBr disk in oven for 30 minu tes at 104 C to remove moisture. Absorbed water might contribute strongly to the OH, NH area resulting in a false measure
27、 of polymer - based OH, NH photooxidation products. II. Obtaining IR Spectra 1. Observe the IR spectrum for each KBr disk including t he unweathered sample. a. If the maximum absorbance is between 0.8 and 1.2, record the IR spectrum. b. If the maximum absorbance is not between 0.8 and 1.2, repeat st
28、eps 3 and 4 in section I. until the absorbance is in the recommended range. It is possi ble to estimate the amount of sample required from the first preparation and compensate accordingly. FORD LABORATORY TEST METHOD AI 103-03 Page 5 of 5 Copyright 2000, Ford Global Technologies, Inc. III. Photooxid
29、ation Rate by Monitoring OH, NH Products Use the same procedure as described under Method A, Section III. IV. Monitoring Film Loss Film loss can not be monitored by this method. Chemicals, materials, parts, and equipment referenced in this document must be used and handled properly. Each party is responsible for determining proper use and handling in its facilities.
