1、TAPPI/ANSI T 441 om-13 TENTATIVE STANDARD 1937 OFFICIAL STANDARD 1960 REVISED 1977 OFFICIAL TEST METHOD 1984 REVISED 1990 REVISED 1998 REVISED 2004 REVISED 2009 REVISED 2013 2013 TAPPI The information and data contained in this document were prepared by a technical committee of the Association. The
2、committee and the Association assume no liability or responsibility in connection with the use of such information or data, including but 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
3、published. Approved by the Standard Specific Interest Group for this Test Method TAPPI CAUTION: This Test Method may include safety precautions 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 relat
4、ed to such use. The user is responsible for determining that the safety precautions are complete and are appropriate to their use of the method, 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 ch
5、emicals which may present serious health hazards to humans. Procedures for the handling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of potentially haza
6、rdous chemicals. Prior to the use of this method, the user must determine whether any of the chemicals to be used or disposed of are potentially 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
7、 and disposal of these chemicals. Water absorptiveness of sized (non-bibulous) paper, paperboard, and corrugated fiberboard (Cobb test) 1. Scope 1.1 This method describes a procedure for determining the quantity of water absorbed by nonbibulous paper, paperboard, and corrugated fiberboard in a speci
8、fied time under standardized conditions. It is based on studies by Cobb and Lowe (1), Cobb (2) and other investigators (3, 4). 1.2 For testing unsized and absorbent paper or paperboard, see TAPPI T 432 “Water Absorbency of Bibulous Paper.” 2. Significance 2.1 Water absorptiveness is a function of va
9、rious characteristics of paper or board such as sizing, porosity, etc. This method is generally applicable to sized paper, paperboard and corrugated fiberboard, but it is not recommended as a sizing test for writing paper. 3. Definitions 3.1 Water absorptiveness (Cobb value), the mass of water absor
10、bed in a specific time by 1 square meter (10.76 square feet) of paper, board, or corrugated fiberboard under 1 cm of water. T 441 om-13 Water absorptiveness of sized (non-bibulous) paper, / 2 paperboard, and corrugated fiberboard (Cobb test) 4. Apparatus 4.1 Water absorption apparatus1, a device tha
11、t permits one side of the specimen to be wetted uniformly at the moment the soaking period begins, and to allow controlled rapid removal of the water from the specimen at the end of the test period. The specimen holder as shown in Fig. 1 comprises a metal ring with a machined lower face, 11.28 0.02
12、cm (4.44 in.) inside diameter (corresponding to a cross-sectional area of 100 cm2(15.5 in.2), 2.5 cm (1 in.) high and about 0.6 cm (0.24 in.) thick, clamped to a flat base plate of the same or bigger size. On the base plate is a rubber mat, larger than the outside dimensions of the ring, on which th
13、e specimen is clamped. NOTE 1: The metal parts should preferably be a brass or other corrosion-resistant material. NOTE 2: Several versions of the water absorption apparatus are now available. Some use different ring sizes that fit in the same clamping fixture and some use different clamping methods
14、. A change in clamping method may affect the speed at which the sample can be removed from the apparatus. It has been reported that spring loaded clamps may reduce leakage when testing corrugated fiberboard. 4.2 Metal roller, solid brass, stainless steel or other corrosion-resistant material, having
15、 a smooth face 20 cm wide and weighing 10.0 0.5 kg (22 1.1 lb). 4.3 Timer, stopwatch or electric timer reading in seconds. 4.4 Graduated cylinder, 100 mL. 4.5 Balance, with an accuracy of 0.001 g, or better. Fig. 1. Specimen holder. 1Names of suppliers of testing equipment and materials for this met
16、hod may be found on the Test Equipment Suppliers list, available as part of the CD or printed set of Standards, or on the TAPPI website general Standards page. 3 / Water absorptiveness of sized (non-bibulous) paper, T 441 om-13 paperboard, and corrugated fiberboard (Cobb test) 5. Materials 5.1 Blott
17、ing paper1, sheets of standard blotting paper, 200 mm square, weighing 250 10 g/m2 (AD) in accordance with TAPPI T 410, a thickness of 0.508 to 0.635 mm in accordance with TAPPI T 411, and having a minimum rate of absorbency of 25 s/1.0 mL of water when tested in accordance with TAPPI T 432 “Water A
18、bsorbency of Bibulous Paper.” The wet expansion shall not exceed 2.5% in the cross direction following the specification of TAPPI T 205. The blotters shall be white, produced from fully bleached chemical pulp free of any additives. They shall be flat, uniform, and free of wrinkles and dirt. 5.1.1 Bl
19、otting paper should not be used for more than one test, as the absorptive nature of the material changes once it has been exposed to water during the first use. 5.2 Water, distilled (pure) or deionized. 6. Sampling and test specimens 6.1 If a lot of paper is being tested to determine whether it meet
20、s specifications, obtain a sample of the paper in accordance with TAPPI T 400 “Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Product.” From each test unit, cut specimens to a size slightly greater than the outside dimensions of the ring of the apparatus, i.e.,
21、squares 12.5 12.5 cm (4.9 4.9 in.). The specimens should be free from folds, wrinkles, or other blemishes not commonly inherent in the paper. 6.1.1 The standard test area is 100 cm2. If the available specimens are too small, a proportionately smaller test area may be used providing that the volume o
22、f water is reduced to provide a pressure head of 1 0.1 cm. Other common test areas include 25 cm2and 10 cm2. A change in area from 100 cm2should be noted in the report. 6.2 While Cobb absorptivity is often considered a bulk property, some materials may have different absorptive properties from each
23、side (felt or wire). Sample enough material so that complete testing can be performed on one or both sides of the paper to be evaluated. Specimens tested on one side cannot be reused for evaluation of the properties of the other side. 6.2.1 For hard-sized papers (absorbing less than 100 g of water/m
24、2(0.22 lb/10.76 ft2), use 5 specimens per side. 6.2.2 For soft-sized papers, absorbing more than 100 g/m2(0.22 lb/10.76 ft2), use 10 specimens per side. 6.2.3 For corrugated fiberboard at least five tests should be carried out on the outside (double back) liner. 6.2.4 United Nations and United State
25、s D.O.T. regulations for the shipment of hazardous materials specify a 30-min Cobb test for the outer surface (double back liner) of corrugated board. Five tests are required on the outer surface. When testing for U.N./U.S. D.O.T. compliance for the shipment of hazardous materials the user is advise
26、d to refer to specific standards for additional information. 7. Procedure 7.1 Precondition and condition the specimens in an atmosphere in accordance with TAPPI T 402 “Standard Conditioning and Testing Atmospheres for Paper, Pulp Handsheets, and Related Products.” 7.2 Weigh each specimen to the near
27、est 0.01 g. 7.3 Place a dry rubber mat on the metal plate and lay a weighed specimen on it. After wiping the metal ring, dry (do not use heat), place it upon the specimen, and fasten it firmly enough in place with the crossbar (or other clamping mechanism) to prevent any leakage between the ring and
28、 the specimen. 7.3.1 For materials where leakage between the ring and the upper surface of the test specimen may occur during the test, a soft elastic non-absorbent gasket may be used. The gasket should have the same internal dimensions as the ring. NOTE 3: On corrugated fiberboard, some users have
29、overcome leakage by either removing the flutes from the back of a sample or by crushing the flutes prior to testing. The former approach has been shown in round robin studies to impact (reduce) test results and is not recommended. See 11.6. 7.4 Pour 100 mL of water (23 1C (73.4F) into the ring as ra
30、pidly as possible thus giving a head of 1.0 0.1 cm (0.39 in.). Start the stopwatch immediately. At 10 2 s before the expiration of the predetermined test period, usually 120 s for paper or 1800 s for combined board, pour the water quickly from the ring, taking great care not to drip T 441 om-13 Wate
31、r absorptiveness of sized (non-bibulous) paper, / 4 paperboard, and corrugated fiberboard (Cobb test) any of the water upon the outside portion of the specimen. Promptly loosen the wing nuts (or other applicable clamping mechanism), and swing the crossbar out of the way while holding the ring in pos
32、ition by pressing it down with one hand. Carefully, but quickly, remove the ring and place the specimen with its wetted side up on a sheet of blotting paper resting on a flat rigid surface. NOTE 4: When different areas are used (25 cm2and 10 cm2being typical), proportionally less water is used in or
33、der to maintain a depth of 1.0 0.1 cm (0.39 in.). 7.4.1 Reject samples that show signs of leakage or spillage around the clamping area. 7.4.2 If any liquid has passed through the sheet to the rubber mat, the test is not acceptable and should be rejected. When this occurs, either shorten the test tim
34、e or fasten two or more specimen sheets together in an area outside the test area. In such a case, the calculated test area remains that of the inside ring. 7.4.3 The standard test time is a period of 120 s on a single-sheet thickness using 100 mL of water to wet an area 1 cm deep. Such conditions a
35、re suitable for most well-sized papers. For combined board, the standard time is typically 1800 s. Testing times may be adjusted according to the water absorptiveness and special natures of the paper or board under consideration and by agreement of the interested parties. For times exceeding an hour
36、, the user may want to add a glass cover to minimize evaporation. In all cases, the difference in time between removing excess water and blotting shall be 10 2 s. 7.5 Exactly at the end of the predetermined test period, place a second sheet of blotting paper on top of the specimen and remove the sur
37、plus water by moving the hand roller once back and once forward over the pad without exerting any additional pressure on the roller. Specimens with excess water after blotting, as shown by glossy areas on the surface, must be rejected and the test repeated, using a shorter time frame. 7.5.1 On corru
38、gated fiberboard the roller should be applied with its axis parallel to the flutes. In the case of boards coated with a barrier material it is important that a water film does not remain on the surface of the board. 7.5.2 Where corrugated fiberboard is indented by the cylinder edge or which exhibits
39、 “washboarding,” it may not be possible for the blotting paper to contact the entire wet area of the test piece. In such cases it is recommended that instead of using the roller, the back of the blotting paper is gently rubbed by hand. 7.5.3 For some coated papers, the roller and blotter paper appro
40、ach may also not remove all the surface water. In this case, gently rubbing the surface of the blotter paper by hand may also serve to remove the surface water and avoid an erroneously high result. 7.6 Fold the specimen with the wetted area inside. Immediately reweigh it to the nearest 0.01 g. 7.6.1
41、 In the case of corrugated fiberboard it may not be possible to fold the test piece. In such cases, the second weighing must be carried out with the least possible delay. 7.7 For the standard test area of 100 cm2, Subtract the conditioned weight of the specimen from its final weight, and multiply th
42、e gain in weight in grams by 100 to obtain the weight of water absorbed in grams per square meter: Weight of water, g/m2= Final weight, g Conditioned weight, g 100 7.7.1 For smaller test areas of 25 cm2and 10 cm2, the multiplier is 400 and 1000 respectively. 8. Report 8.1 Report the absorptiveness,
43、calculated as the average weight of the water absorbed in grams per square meter, for the wire and the felt side of the paper separately. If desired, state also the maximum and minimum values for each side. Include the test duration in the report. Deviations from standard conditions due to shorter t
44、imes, smaller test specimens, or additional plies shall be included in the report. 9. Precision 9.1 The following estimates of repeatability and reproducibility are based on results from two studies. 9.1.1 The estimates for hard-sized printing papers were obtained from a limited study for means of f
45、ive specimens on the same side in a 120 s Cobb test. 5 / Water absorptiveness of sized (non-bibulous) paper, T 441 om-13 paperboard, and corrugated fiberboard (Cobb test) 9.1.2 The precision estimates for linerboard and corrugated boxes were obtained from a 2002 study that compared different methods
46、 of preparing corrugated board (crushing, separating one linerboard sample was natural kraft and the other a white-top linerboard. The precision estimates are based on 5 determinations per test result and 3 test results per lab, per sample, again in an 1800 s test. 9.2 Hard-sized, Printing Papers (1
47、20 s) Repeatability (within a lab) = 8 % Reproducibility (between laboratories) = 10 % Corrugated Boxes (1800 s) Repeatability (within a lab) = 5.5 % Reproducibility (between laboratories) = 18 % Linerboard (1800 s) Repeatability (within a lab) = 2.5 % Reproducibility (between laboratories) = 14.5 %
48、 2002 Study of 1800 s Cobb Mean r %r R %R Kraft Linerboard 115.3 2.1 1.9% 15.0 13.0% White top Liner 111.4 3.3 3.0% 17.3 15.6% Corrugated Box 1 134.3 7.6 5.6% 24.9 18.5% Corrugated Box 2 (WT) 124.7 6.4 5.1% 21.9 17.5% Repeatability and reproducibility are estimates of the maximum difference (at 95%)
49、 which should be expected when comparing test results for materials similar to those described above under similar test conditions. These estimates may not be valid for different materials or testing conditions. NOTE 5: Some users have noticed higher precision percentages when using smaller test areas compared to those using standard areas for similar samples. 10. Keywords Blotting papers, Absorptivity, Sized paper, Sizing, Cobb test, Paper, Paperboard, Corrugated boards, Fiberboards 11. Additional info
