ISO 7783-2018 “Paints and varnishes — Determination of water vapor transmission characteristics cup method”

preface
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This document has been prepared by Technical Committee ISO/TC 35, Paints and Varnishes, Subcommittee SC 9, Common Test Methods for Paints and varnishes.

The second edition rescinded and replaced the first edition (ISO 7783:2011), in which it constituted a minor revision to correct the conversion factor in formula (3) and to add a reference to ISO 4618 paint and varnish terms in Article 3.

Any feedback or questions about this document should be directed to the user’s national standards body. A complete list of these institutions can be found at iso.org/members.html.

ISO 7783-2018 “Paints and varnishes — Determination of water vapor transmission characteristics cup method”

introduce
This document is one of a series of standards dealing with the sampling and testing of paints, varnishes and related products. It describes a method for determining the water vapor transmittance of self-supporting and non-self-supporting coatings.

Water vapor transmittance is not necessarily a linear function of film thickness, temperature, or relative humidity difference. Measurements made under one set of conditions are not necessarily comparable to those made under other conditions. Therefore, you must choose a test condition that is as close to the usage condition as possible.

Under conditions of high humidity, the propagation of water vapor is of greatest concern. Therefore, the wet cup method has been adopted as the reference method. Depending on the agreement, other procedures and conditions may be used, such as the Cheers method.

ISO 7783-2018 “Paints and varnishes — Determination of water vapor transmission characteristics cup method”

1 range
This document specifies the method for determining the water vapour permeability of paints, varnishes and coatings for related products.

It complements ISO 12572. Procedures, definitions, and calculations have been taken over from ISO 12572 as far as possible. If necessary, refer to ISO 12572 for a better understanding of the procedures specified in this document.

Vapor transmittance exceeding 680 g/ (m 2⋅d) (i.e., the vapor diffusion equivalent air layer thickness sd is less than 0.03 m) cannot be accurately quantified by the test method described in this document.

2 Normative references
The following files are referenced in the text in such a way that some or all of the content constitutes the requirements of this document. For dated references, citation-only versions apply. For undated references, the latest version of the reference (including any revisions) applies.

ISO 1513, Paints and varnishes – Examination and preparation of test samples

ISO 2808, Paints and varnishes – determination of film thickness

ISO 3233-1, Paints and varnishes – Determination of non-volatile substances as a percentage by volume – Part 1: Method for determination of non-volatile substances using a coating test panel and dry film density by Archimedean principle

ISO 3696, Analytical laboratory water – specifications and test methods

ISO 4618, Paints and varnishes — Terms and definitions

ISO 15528, Paints, varnishes and raw materials for paints and varnishes — Sampling

3 Terms and Definitions
For the purposes of this document, the terms and definitions given in ISO 4618 and the following articles apply.

3.1 Water vapor transmittance

The mass of water vapor transmitted over a given surface area of the sample under a specified constant relative humidity on each surface of the sample under test over a given period of time

Note 1: It is measured in grams/square meters per day [g/ (m2⋅d)].

Note 2 Water vapor transmittance p measured at atmospheric pressure can be converted to the equivalent value at standard atmospheric pressure p0 by multiplying p/p0. This allows for a linear correlation of 20,4, with the water vapor diffusion equivalent air layer thickness (sd) value (see 3.3).

Note 3: The term “water vapor transfer” is often incorrectly used for water vapor transfer rates.

3.2 Velocity G of steam flowing through the sample under test

The mass of constant water vapor passing through each surface of the sample under test at a specified constant relative humidity during a given period of time

Note 1: It is expressed in grams per hour.

3.3 Vapor diffusion equivalent air layer thickness SD

The thickness of a static air layer with the same water vapor transmittance as the test coating under the same measurement conditions

Note 1: It is measured in meters.

3.4 Water vapor drag coefficient M

A coefficient indicating how many times more resistant a material is to water vapor than a static air layer of the same thickness at the same temperature and pressure

Note 1: It is dimensionless.

Note 2 The calculation and use of the water vapor drag coefficient is meaningful only if the water vapor transmittance of a particular material is constant, that is, independent of thickness, which, however, is not usually the case for coatings.

ISO 7783-2018 “Paints and varnishes — Determination of water vapor transmission characteristics cup method”

3.5 Specimen

< Non-self-supporting coating > Coated supporting material

3.6 Specimen

< Self-supporting coating > Separate coating

3.7 Wet Cup Method

Method for measuring water vapor permeability in which the sample is sealed around the rim of a cup containing a saturated aqueous solution of ammonium dihydrogen phosphate

Note 1: This is the most convenient method for determining water vapor permeability at high relative humidity (between 93% and 50%).

3.8 Cheers

A method of measuring the permeability of water vapor in which a sample is sealed around the edge of a cup containing a desiccant

Note 1: This is the most convenient method for determining water vapor permeability at low relative humidity (between 50% and 3%).

3.9 Testing Components

An assembly consisting of a test cup sealed at the edge of a test cup containing a saturated ammonium dihydrogen phosphate solution in contact with an undissolved ammonium dihydrogen phosphate crystal (wet cup method) or containing a desiccant (cheers method)

3.10 Test Area

The surface area of the sample under test through which water vapor flows during the test

Note 1: It is measured in square metres.

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