1、 T 578 sp-11 STANDARD PRACTICE 2011 2011 TAPPI The information and data contained in this document were prepared by a technical committee of the Association. The committee and the Association assume no liability or responsibility in connection with the use of such information or data, including but
2、not limited to any liability under patent, copyright, or trade secret laws. The user is responsible for determining that this document is the most recent edition published. Approved by the Standard Specific Interest Group for this Test Method TAPPI CAUTION: This Test Method may include safety precau
3、tions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the method to safety issues related to such use. The user is responsible for determining that the safety precautions are complete and are appropriate to their use of the m
4、ethod, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use, disposal, or both, of chemicals which may present serious health hazards to humans. Procedures for the handling of such substances are set forth on Material Safet
5、y Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of potentially hazardous chemicals. Prior to the use of this method, the user must determine whether any of the chemicals to be used or disposed of are poten
6、tially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal authorities for safe use and disposal of these chemicals. Accelerated light aging of printing and writing paper by xenon-arc exposure apparatus 1. Scope 1.1. This
7、 standard practice describes a laboratory procedure for the exposure of printing and writing paper to xenon-arc light at elevated levels of light flux to permit accelerated aging of that type of paper. 1.2. This standard practice specifies the sample preparation and conditions of exposure required t
8、o obtain information on the relative stability of paper with regard to change in optical properties brought about by exposure of such paper to light. 1.3. This standard practice provides qualitative guidelines regarding paper stability. It does not define the life expectancy for a given paper to rea
9、ch a specified set of optical properties. 1.4 This standard practice uses high-intensity broadband light sources that may not be suitable for the evaluation of light stability of papers that contain peroxide bleached mechanical pulp (1). 2. Summary 2.1. In this standard practice, light from a xenon-
10、arc lamp that makes use of filters to simulate natural daylight that has passed through window glass shines on a paper surface with light flux that is substantially greater than in normal indoor conditions of paper exposure. The light flux shines in a controlled manner and for a specified period of
11、time. The light flux causes photochemical reactions in the paper that may change its reflectance (brightness) and color. Comparing initial and final levels of these parameters against different criteria, provides a measure of optical stability. 3. Significance 3.1. This standard practice will find u
12、se by parties concerned with the relative optical stability of various printing and writing papers. 3.2. The practice will provide manufacturers, paper users and other interested parties with guidelines to determine quantified rankings of paper stability that identify papers that are stable, moderat
13、ely stable and unstable when exposed to light over periods of time. 3.3. The stability rankings may be used for definition of the stability of paper to light, but will not define specific periods of life expectancy of a given paper. T 578 sp-11 Accelerated light aging of printing and writing paper /
14、 2 by xenon-arc exposure apparatus 4. Applicable standards 4.1. TAPPI Test Methods: TAPPI T 400 “Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Product” TAPPI T 412 “Moisture in Pulp, Paper, and Paperboard”TAPPI T 402 “Standard Conditioning and Testing Atmospher
15、e for Paper, Board, Pulp Handsheets and Related Products” TAPPI T 452 “Brightness of pulp, paper, and paperboard (directional reflectance at 457 nm)” TAPPI T 254 “Cupriethylenediamene disperse viscosity of pulp (falling ball method)” TAPPI T 524 “Color of paper and paperboard (45/0 geometry)” TAPPI
16、T 1200 “Interlaboratory Evaluation of Test Methods to Determine TAPPI Repeatability and Reproducibility.” TAPPI T 1212 “Light sources for evaluating papers including those containing fluorescent whitening agents” TAPPI T 1213 “Optical measurement terminology (related to appearance evaluation of pape
17、r” 4.2. ASTM Standards: D 1968 “Standard Terminology Relating to Paper and Paper Products” G 113 “Terminology relating to natural and artificial weathering tests of nonmetallic materials” G 151 “Standard practice for exposing nonmetallic materials in accelerated test devices that use laboratory ligh
18、t sources” G 155 “Standard practice for operating xenon arc light apparatus for exposure of nonmetallic materials.”5. Apparatus test chamber 5.1. Provide a test chamber that utilizes a sealed “long-arc” xenon lamp to illuminate the test samples. The lamp selection shall be according to ASTM Standard
19、 G 155, as per Table 2 of that document. 5.2. Use a glass filtration system in front of the lamp to simulate natural daylight that has passed through window glass. This is to cut off almost all of the very short wavelength (nominally that which is below 320 nm) that occurs when daylight passes throu
20、gh window glass. Provide the glass filtration system as defined in ASTM Standard G 155. 5.3 Provide a cooling system with the test chamber such that a temperature at the paper surface is maintained at greater than 20C and less than 30C for all paper types. Air may be used as a cooling medium, but is
21、 not mandated so long as humidity of about 0.007 kg water/kg of dry air is maintained in the atmosphere above the paper surface and that a supply of oxygen, approximately equivalent to that which is found in standard air, is present at the paper surface. Apart form the oxygen, the remainder of the g
22、as present shall be inert. 5.4 The test chamber shall be designed such that it can be operated with ventilation so as to assure that is it free of ozone gas. 6. Test chamber operation and calibration 6.1 Control the intensity irradiance (E) of the xenon arc lamp to 765 W/m2 75 W/m2as measured in the
23、 290-800 m wavelength range. 6.2 Recalibrate the instrument with sufficient frequency to ensure continual preservation of both the light spectrum and the light intensity. For recalibration frequency recommendations, refer to the manufacturers instructions of the particular instrument in use. 6.3 Arr
24、ange the configuration of the test chamber so as to assure uniformity of light intensity (irradiance) across the paper sample area in a way that provides 10% deviation from target intensity for the entire sample. 6.4 Check the temperature at the paper surface with sufficient frequency to ensure that
25、 it is between 20C and 30C throughout the test. Make these measurements with a properly calibrated optical pyrometer. 3 / Accelerated light aging of printing and writing paper T 578 sp-11 by xenon-arc exposure apparatus 7. Conditioning Condition all test specimens in the dark prior to and at complet
26、ion of the light aging exposure in accordance with TAPPI T 402. 8. Procedure 8.1 At all times throughout this procedure, handle paper specimens only with clean cotton gloves. This means that clean cotton gloves are required for handling of the paper both before and following the aging procedure. 8.2
27、 Divide the sample equally into two parts. Use one part for exposure in the chamber. Cut a test specimen from this part to the size specified for testing by the test chamber manufacturer. Use the other for optical property tests of the unexposed paper. This is necessary to allow for proper light exp
28、osure in the chamber and at the same time to provide enough paper in each part to be cut to the small specimen size required for performance of subsequent standard optical property tests. 8.3 Measure the initial desired physical and optical properties on both sides of the unexposed paper specimens a
29、fter conditioning and just prior to insertion in the test chamber. Alternately the unexposed paper specimens can be stored in a conditioning atmosphere in the dark and tested along side the light exposed samples. 8.4 Conduct the test in a temperature and humidity controlled room that is maintained a
30、t 23C and 50% relative humidity according to TAPPI T 402. 8.5 Cut test specimens to a size that is the maximum that will fit in the available space provided in the selected test chamber, taking care to insure that the specimen will be uniformly irradiated over its entire surface. 8.6 Mount the speci
31、mens on the appropriate surface of the test chamber with clamps provided with the device. Take care to mount specimens of both sides of the paper for exposure. 8.7 Expose three replicate specimens of each paper to be tested to light from a xenon arc lamp controlled to 765 W/m2 75 W/m2as measured in
32、the 290-800 nm wavelength range. 8.8 Expose the specimens for 48 hours 0.5 hours. Do not remove the specimen from the chamber during the period of exposure. Remove the specimens from the test chamber at the end of the exposure at the same time of day at which the test was initiated. 8.9 Immediately
33、upon removal from the test chamber, condition the exposed paper specimens in the dark for 24 hours according to TAPPI T 402. 8.10 Immediately upon removal from the conditioning process, measure the desired physical and optical properties of the exposed specimens once again, taking care to again meas
34、ure both sides of the paper sheets. Report any differences that exist between the two sides. 9. Suggested calculation and interpretation of results for white and near-white papers 9.1 The following sections are a guide to what properties could be evaluated and how to interpret results. 9.2 The perce
35、ntage change in reflectance at 457 nm (brightness) according to the following: Reflectance change, % = (Ri Rf) / Ri 100where Ri= Initial reflectance Rf= Final reflectance 9.3 The absolute change in yellowness according to the following formula: Change in yellowness, (b*) points = b*f b*i where b*f=
36、Final yellowness b*i= Initial yellowness T 578 sp-11 Accelerated light aging of printing and writing paper / 4 by xenon-arc exposure apparatus 9.4 With regard to paper brightness (reflectance at 457 nm) stability, the following classes are specified: Stable: less than5% reflectance loss Moderately s
37、table: greater than 5% to 20% reflectance loss Unstable: greater than 20% reflectance loss NOTE 1: Papers in the “moderately stable” range may be fully stable for some users. However, if a very high level of optical stability is required, papers should be selected that meet the “stable” criteria abo
38、ve. 9.5 With regard to change of paper yellowness, the following classes are specified: Stable: 3 points of absolute b* increase Moderately stable: 3 to 8 points of absolute b* increase Optically unstable: 8 points of absolute b* increase NOTE 2: If all that is desired is legibility of a printed tex
39、t, paper can become significantly yellowed and still meet the requirements of the end user, even though the changes in optical properties may position it in the “Unstable” category. 10. Report 10.1 Report the type and manufacturer of the device used for exposure. 10.2 Report the method utilized for
40、cooling the paper surface, the temperature measured at the surface, and the relative humidity of the air above the surface being tested. 11. Precision Precision information is not applicable to this standard practice. 12. Keywords Paper, Accelerated tests, Aging tests, Xenon lamps, Optical propertie
41、s, Light, Photochemistry, Chemical reactions, Durability, Stability, Radiation effects, Directional measurement, Reflectance, Yellowness coefficient, Kubelka-Munk equation. 13. Additional information 13.1 Effective date of issue: September 27, 2011. 13.2 Strength testing 13.2.1 Very long-term contin
42、uous exposure to natural daylight and to common artificial light has been shown to cause loss of strength in uncoated papers regardless of their fiber composition. 13.2.2 The most sensitive test by which to measure physical property loss is cellulose degree of polymerization (DP). This method has pr
43、oblems for use in a standard accelerated light aging test. DP can be approximated for lignin-free papers using the well-established CED (cupriethlyenediamene) test (TAPPI T 254). However, for lignin-containing papers, a special test that uses a process developed by the Canadian Conservation Institut
44、e is required. This procedure calls for partial removal of the lignin with a mild acid chlorite treatment and then uses cadoxen instead of CED. This procedure is required to provide a reliable approximation of loss of DP in lignin-containing papers. The cadoxen method is currently used in only a few
45、 laboratories and cannot be considered a “standard” method. 13.3 Post color number 13.3.1 Post color number (PC) change may be useful to track. PC is calculated from Kubelka-Munk theory according to the following equation: k/s = (1 R)2/ 2R and PC = 100 (k/s)final (k/s)initial 5 / Accelerated light a
46、ging of printing and writing paper T 578 sp-11 by xenon-arc exposure apparatus where k is an absorption coefficient, s is a scattering coefficient and Ris the reflectance at 457 nm for an “infinitely” thick pad of the material. (The pad must be thick enough so that light does not reach the back surf
47、ace.) 13.3.2 For calculation of PC number, the reflectance values at 457 nm are most often used. PC calculations based on reflectance measurements in the reflectance spectrum from 250 to 750 nm wavelength are also valid. 13.3.3 The absorption coefficient (k) is a linear parameter with respect to chr
48、omophore concentration, whereas the reflectance (brightness) is not. To calculate the values of k and s, the basis weight (W) of the paper and the results of two reflectance measurements are used. The measurements are the reflectance of a sheet of paper over a black (zero reflectance) backing of zer
49、o reflectance (R) and the reflectance of an “infinitely thick pad of paper sheets (R). If the reflectance measurements are made in the wavelength region 250-750 nm, informative absorption coefficient spectra (k-spectra) can be obtained which more closely characterize chromophores causing yellowing. NOTE 3: In the calculation of PC and k, R can be measured at 457 nm for an “infinitely” thick pad (R) or alternatively for one sheet backed with a white background (R). In both of these calculations, R0is obtained from the reflectance of on
