Determining Volume Solids of Coatings - …

1 Copyright 1998, Technology Publishing CompanyJPCL / DECEMBER 1998 13 AnswerDr. Nigel Whitehouse,Paint Research Association,Teddington, UK:The Volume Solids of a coating is theratio of the Volume of its non-volatile components to its total wetvolume. The figure is usual-ly expressed as a , volumesolids were calculated fromthe formulation of a coat-ing. This theoretical ap-proach did not take accountof pigment packing, solventretention, and film contraction, andso calculated values did not alwaysrelate well to practical use. Subse-quently, Volume Solids calculatedfrom the formulation often resultedin an underestimation of coveragefor some generic paint types and anoverestimation for manufacturers of protectivecoatings now favor the followingmore practical method of measuringthe Volume Solids of a paint. Measure the dry film thickness(dft) obtained from a measured wetfilm thickness (wft).

2 Calculate Volume Solids as follows:(measured dft x 100) coating should be applied at awft, as recommended in the techni-cal data sheet, and allowed todry/cure as scheduled (typically 7days at 23 1 C [73 2F) before thedry film thickness is laboratory proce-dures are described in ASTM D2697-86 (Reapproved 1991), Stan-dard Test Method for Volume Non-volatile Matter in Clear or PigmentedCoatings, and reviewed critically inMonograph No. 4 of the Oil andColour Chemists Association(OCCA).For two-pack products, such aschemically cured epoxies, there aretwo options to determine the vol-ume Solids of the base and hardenerseparately or to mix the two compo-nents together and then determinethe Volume Solids of the Volume Solids of the mixedpaint has practical significance, sincethe solvent release characteristicswill be influenced by the curingmechanism.]

3 In addition, the volumeof the mixed paint may not be thesame as the sum of the individualvolumes. For these reasons, it ispreferable to determine the volumesolids of the mixed paint. Care mustbe taken to mix the two compo-nents together accurately and toapply the film before any pigmentcan settle. The density determinationis made on the mixed paints are highly pig-mented Coatings (pigmented abovethe critical pigment Volume concen-tration). The resulting dry films con-tain voids (regions not completelyfilled with the medium). The extentof these voids is affected by themethod of application, and theirpresence leads to a dft that is higherthan might be predicted from calcu-lations. The Volume of such dryfilms cannot be determined by waterdisplacement techniquesbecause the water willpenetrate the voidspaces to an indetermi-nate Solids of in-organic zinc-rich paintsare best determined bymeasuring wet and dryfilm thicknesses (not volumes).

4 Thewft is calculated from the weightsolids, the dry film weight of aknown coated area, and the densityof the wet paint. (Use of a densitycup is recommended.) To calculatewft from weight Solids , three hoursat 105 C (221 F) is used in Method Aof ASTM D 1644-88 (Reapproved1993), Standard Test Methods forNonvolatile Content of film thickness is best mea-sured using a sensitive stylus or lasersurface tracing technique. The coat-ing is applied to microscope slidesusing a cube applicator, allowed todry for seven days at 23 1 C(73 2F), and the thickness of the re-sulting dry film is then stylus (or laser) traverses un-coated and coated areas of the slideand the dft is obtained by the differ-ence in displacement (Z axis). Theprocedure is described in more de-tail in the OCCA Volume Solids of CoatingsPROBLEM SOLVING FORUMQ uestionWhat is the best method to determine volumesolids of Coatings such as chemically curingepoxies and inorganic zinc riches?

5 Copyright 1998, Technology Publishing CompanyAnswerS. Vonckx,CoRI,Limelette, Belgium:Following is an easy and representa-tive method to determine the vol-ume Solids of Coatings . Mix the components as described inthe technical data sheet of the product. Immediately after mixing, applythe paint on steel panels with differ-ent sizes of application knives ( , 150 m [6 mils], 250 m [10mils], etc.). Immediately after applying thepaint, measure the wet film thick-ness on the different panels. Cure the paint as described in thetechnical data sheets. After curing, measure the dry filmthickness. Calculate the relationship (in per-centage) of the dry film thickness tothe wet film thickness on the severalpanels. Calculate the mean of all these have already used this methodand have demonstrated that the re-sults are representative of those ob-tained with other method is found in ISO3233, Paints and Varnishes Determi-nation of Percentage Volume ofNon-Volatile Matter by Measuringthe Density of a Dried Coating.

6 According to this method, a disc iscoated with the paint to be testedafter mixing its components. Themass and Volume of the disc beforethe coating is applied and after thecoating is applied and dried are de-termined by weighing it in air and ina liquid of known density. Fromthese measurements, the Volume ofthe dried coating can be the density of the liquidcoating (as determined by themethod in ISO 2811, Paints and Var-nishes Determination of Density)and the percentage by mass of non-volatile matter (using the method inISO 3251, Paints and Varnishes De-termination of Non-volatile Matter ofPaints, Varnishes and Binders forPaints and Varnishes), the Volume ofthe liquid coating deposited on thedisc can be calculated. The volumeof the dried coating divided by thevolume of the liquid coating andmultiplied by 100 is the percentageby Volume of non-volatile matter inthe liquid SOLVING FORUM14 DECEMBER 1998 / JPCLSend Reader Responses to thismonth s question to Karen Kapsanis,Editor, JPCL, 2100 Wharton St.

7 , Suite310, Pittsburgh, PA 15203; fax:412/431-5128; e-mail: Copyright 1998, Technology Publishing CompanyJPCL / DECEMBER 1998 15 PROBLEM SOLVING FORUMU pcoming Problem Solving Forum Questions What are the detrimental effects of overly thick finish coats, (not primers) on a substrate; on the coating itself; on intercoat adhesion; and on the following: steel structures exposed to the environment: linings in immersion service; hot duty steel surfaces above 149 F (65 C). What is the best way to remedy over-thickness after the coating has dried or cured? Which preparation procedures and acceptance criteria can be used and applied for secondary surface preparation of shop primer? How is it possible to effectively remove soft coating materials and replace them with hard coating materials when ships are in service? Given the prevalent use of surface-tolerant epoxies on flash-rusted surfaces, is it time to reduce the Sa 2 1/2 (SSPC-SP 10) cleanliness standard for new dry-blasted?

8 Likewise, what about the requirements for a specific surface profile? What types of Coatings can be used on the inside of pipes used to supply potable water in high-temperature conditions? What differences in performance and speed of application exist among airless, HVLP, and conventional spray equipment for field painting of structural steel?Send answers to Karen Kapsanis, Editor, JPCL, 2100 Wharton St., Suite 310, Pittsburgh, PA 15203; fax: 1/412-431-5428; e-mail.