ASTM D5235-2018 Standard Test Method for Microscopic Measurement of Dry Film Thickness of Coatings on Wood Products.pdf

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1、Designation: D5235 14D5235 18Standard Test Method forMicroscopic Measurement of Dry Film Thickness ofCoatings on Wood Products1This standard is issued under the fixed designation D5235; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio

2、n, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the measurement of dry film thickness of coatings applied to a smooth, textured

3、 or curved rigidsubstrate of wood or a wood-based productproduct.1.2 This test method covers the preparation of wood or wood-based specimens for the purpose of microscopic measurement ofdry film thickness.1.3 This test method suggests an analysis of dry film thickness of coatings on wood or wood-bas

4、ed products using a microscopicmeasurement.1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in eachsystem may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from thet

5、wo systems may result in non-conformance with the standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices

6、 and determine theapplicability of regulatory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recomme

7、ndations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test M

8、ethod3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 dry film thickness or DFT, nthe thickness of dried, cured coating film on the substrate surface which may includeattached fibers but excludes free fibers that are encapsulated in the layer itself.3.1.2 edge face, nthat part

9、of the specimen that is a plane perpendicular to the surface showing a cross section of the coatingand substrate.3.1.3 soak in, nrefers to a coating on a porous (wood) where the coating does not lie essentially on the surface of the woodor wood-based product, but has penetrated into the fiber struct

10、ure of the wood or wood-based material.3.1.3.1 DiscussionWood or wood-based products are generally of a porous nature; sometimes exhibiting uniform absorption of coatings. Frequently1 This test method is under the jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materials, and Appli

11、cations and is the direct responsibility ofSubcommittee D01.52 on Factory Coated Wood Products.Current edition approved Dec. 1, 2014Jan. 15, 2018. Published February 2015June 2018. Originally approved in 1992. Last previous edition approved in 20132014 asD5235 13.D5235 14. DOI: 10.1520/D5235-14.10.1

12、520/D5235-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is int

13、ended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the curr

14、ent versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1absorption of coatings is of a non-uniform nature and influenced by localized surface density di

15、fferences or wood pore size. Theseconditions of coating absorption are commonly referred to as soak in.4. Summary of Test Method4.1 A specimen of coated wood or wood-based product is cut to convenient size and edge face with the coating filmcross-section is prepared by polishing or cutting with a sh

16、arp blade.4.2 The prepared edge of the specimen is imaged by a calibrated imaging system with known magnification in order to measurethe dry film thickness using an image analysis computer program.4.3 Suggestions regarding interpretation of dry film thickness on porous wood or wood-based material ar

17、e offered.5. Significance and Use5.1 As a base for calibration adjustment or accuracy verification of dry film coating thickness measuring instruments.5.2 The dry film thickness of coatings on wood or wood-based products is specified in written product warranties for properdecorative and protective

18、performance of coatings on wood or wood-based products.5.3 The minimum and maximum dry film thickness of coatings is recommended by coating companies for satisfactorydecorative and protective performance on wood or wood-based products.5.4 The average dry film thickness of coatings on wood or wood-ba

19、sed material may be used by manufacturing companies toestimate the theoretical cost of applied coatings.5.5 The ratio of minimum to maximum dry film thickness on textured products is used as an indication of coating uniformity.5.6 Specific coated product requirements may dictate certain film thickne

20、ss determinations to be made. Agreement betweenbuyer and seller may be advisable to accommodate product needs relative to dry film thickness.6. Apparatus6.1 Microscope with Attached Digital Camera (see Note 1), providing sufficient magnification and image quality in the field ofview; generally 100 t

21、o 200 magnification is sufficient.NOTE 1Certain digital cameras can provided sufficient magnification and image quality of the coating cross-section without a microscope.6.2 Source of Oblique Illumination, for the microscope.6.3 Image Analysis Program, with capabilities for lines to be drawn along t

22、he coating/substrate interface and the coating surfaceand for calculation of the average distance between these lines on the specimen image.6.4 Microscope Image Calibration Tool.6.5 Cutoff Saw.6.6 Belt or Disc Sander.6.7 C-Type Clamp.6.8 Sharp Utility Knife or Razor Blade.7. Materials7.1 200 and 600

23、-Grit Sand Paper.7.2 Mould, such as a paper cup, aluminum weighing dish, or a 50.8 mm 2 in. or larger diameter plastic pipe that is at least25.4 mm 1 in. high.7.3 Source of Sanding Adhesive, which is used as encapsulating medium such as:7.3.1 Hot Melt Glue,7.3.2 Fast-Cure Acrylic Mounting Kit, or7.3

24、.3 Epoxy.7.4 Solvent-borne Tint Dispersion, which is compatible with the sanding adhesive.7.5 Mineral Oil.7.6 Automotive Red Transmission Oil.7.7 Zinc Stearate Powder.8. Procedure8.1 Specimen PreparationSelect the area to be measured for coating thickness and remove it from the coated wood orwood-ba

25、sed material by a suitable method. Methods of sawing, core drilling, chiseling etc., can be used. Avoid collection ofD5235 182samples near the edges of sheeting material or the ends of boards, particularly those coated in vacuum coaters, unless defectivecoating application is being investigated. For

26、 textured surfaces, areas representative of varying degrees of texture (average,extreme, minimal or non-existent) should be selected. Take care that areas of interest are not damaged. Cutting across wood grainsis preferable in exposure of area of the interest and must be conducted when a coated roug

27、h wood surface is being tested. Inspectionof the surface of interest for excessive damage, as well as preliminary assessment of coating conditions and uniformity ofapplication should be conducted under a microscope. Appropriate areas for coating dry film thickness measurements should beselected base

28、d on testing purpose.8.1.1 Frequently the purpose of testing is the measurement of the average coating dry film thickness for coating spreadassessment or identification of areas with excessively thick or thin coating dry film thickness.8.2 Specimen Surface PreparationTwo methods are described for sp

29、ecimen surface preparation due to the variability in theproperties of wood coatings. Method A is recommended to be used for hard coatings, for example, melamine furniture coating orpolyester coating, which are brittle at room temperature and could shatter in contact with a sharp blade. Method B is r

30、ecommendedfor flexible, exterior finishes, which would smear in contact with sandpaper. Such smearing may mask the appearance of voids orfracture lines in the coating and substrate and may eliminate coating/wood substrate interface details, thereby increasingmeasurement error.8.3 Method A:8.3.1 Sele

31、ct the desired coated area of a wood or wood-based material that is to be measured for dry film thickness. With thecutoff saw, cut off a sample at least 38.1 mm 112 in. wide from this area for mounting and encapsulation in casting resin (Note2).NOTE 2Some specimens could be satisfactorily prepared a

32、nd tested without mounting. Mounting may be omitted, if careful microscopic inspectionof the sanded specimen does not show any damage to the area of interest or coating edge distortion.8.3.2 Cut this specimen to a length that is at least 12.7 mm 12 in. less than the inside diameter of the mold to be

33、 used.8.3.3 Place the specimen, with the sample edge to be measured, face down and approximately centered in the mold.8.3.4 Prepare the sanding adhesive according to the manufacturers directions for use.Adispersed pigment may be added to theadhesive for better microscopic contrast between the dry fi

34、lm and the adhesive.8.3.5 Pour the sanding adhesive around the sample in the mold and allow to harden according to the manufacturers directions.8.3.6 Remove the mold from the hardened and encapsulated specimen edge.8.3.7 Using a disc sander, belt sander or 200-grit sandpaper mounted on a glass plate

35、, sand the edge face of the encapsulatedspecimen until the edge face is relatively smooth. Maintain the edge face of the specimen as flat as possible during sanding.Avoidheat buildup of the sanding adhesive by intermittent sanding if necessary.8.3.8 Polish the edge face of the rough sanded specimen

36、as follows:8.3.8.1 Mount a piece of 600-grit sandpaper on a flat glass plate. Rub the edge face of the rough sanded specimen over the600-grit sandpaper in one direction, then reverse direction by 180 for several more rubs. Zinc stearate powder can be sprinkledon the 600-grit sandpaper or the 600-gri

37、t sandpaper can be wetted with mineral oil to produce a highly polished edge face free ofscratches.8.3.8.2 Some laboratories find that a mold for the specimen encapsulation with sanding adhesive is not necessary. In this casetwo specimens are prepared with the cutoff saw. The sanding adhesive after

38、proper mixing is generously applied to the coated faceof each specimen, the specimens are placed together and a C-clamp is used to squeeze out some of the sanding adhesive. TheC-clamp is not removed until sanding adhesive has hardened.8.4 Method B:8.4.1 Select the desired area of coated wood or wood

39、-based material that is to be measured for dry film thickness and obtaina suitable sample using the cutoff saw or other appropriate tool cut off a suitable sample. There is a handling advantage if thesample to be tested has a rectangular shape.8.4.2 To aid in the preparation of the cross-section for

40、 testing, the sample must be additionally cut at an acute angle 70 to 85with respect to the coated surface (Fig. 1). Then, using a sharp blade in a slow continuous movement, make a shallow cut parallelto the edge face with the coating cross-section, cutting from the coating surface into the substrat

41、e to remove any loose wood fibersand/or damaged coating from the area of interest. Inspect the obtained cross-section under microscope for surface quality. A cleanview of the cellular wood structure and clear focus along the coating cross-section with well-visible interface details is a goodindicati

42、on of proper surface preparation. The cutting direction depends on the wood grains and coating properties.8.5 Dry Film Thickness Measurement From the Image of the Edge Face of the Specimen:8.5.1 Place the polished or clean cut edge face under the microscope lens.8.5.2 Adjust the illuminating light a

43、t a convenient oblique angle. Proper light angle adjustment is helpful in obtaining goodcontrast along the coating surface edge, inter-coat boundaries, and coating/wood interface. This is particularly important whenmeasuring transparent coating DFT.D5235 1838.5.3 Adjust magnification. Generally 100

44、magnification is sufficient for coating DFT above 50 m and 200 magnificationis sufficient for coating DFT above 25 m. Lower magnification allows for a larger field of view which is beneficial whenmeasuring a coating applied to rough wood containing peaks and valleys.8.5.4 Adjust contrast and lightin

45、g for best imaging of the coating surface edge and coating/wood interface.8.5.5 To improve contrast between wood and coating interface light coat of mineral oil or automotive red transmission fluid maybe applied.8.5.6 Capture image of the edge face of the specimen preferably with the coating film cr

46、oss-section in the centre of the fieldof view.8.5.7 Capture calibration image (Note 3) at the same magnification.NOTE 3A certified silicon test specimen, with a 10 micron grid and 1.9 micron dividing lines, for imaging system calibration could be used. Sucha specimen can be supplied by Agar Scientif

47、ic.3 Other objects with known dimensions measured with certified tools could also be used for imaging andcalibration.8.5.8 Enter the calibration data into the image analysis program according to the software manufacturers4 instruction.8.5.9 Determine the average coating DFT using the image analysis

48、program following software manufacturers instruction(Note 4).NOTE 4This analysis usually involves drawing two lines: one along the entire coating surface edge and another along the entire coating/woodinterface or interface of interest. Porous substrates tend to have the coating soaked into their ope

49、n cellular structure and fibers of the wood or wood-basedproduct. A clear demarcation line between substrate and coating may not be discernible. In this case, such a demarcation line should be drawn as shownin Figs. X1.1-X1.9.8.5.10 The average coating thickness for a tested group of samples is reported based on the average DFT calculated for all testedsamples. The minimum DFT of the coating is reported as the lowest average DFT found within the tested samples while themaximum DFT of the coating is reported as the largest average DFT found withi