The standard “ISO 15106-1 Plastics - Films and sheets - Determination of water vapor transmission rate - Part 1: Humidity detection sensor method” developed by the International Organization for Standardization (ISO) describes an instrumental test method for determining the water vapor transmission rate of multilayer structures, including plastic films, plastic sheets and plastics, using a humidity detection sensor.
For the purposes of this document, the following terms and definitions apply.
When testing, in principle, a dry room at a given relative humidity is separated from a wet room where the atmosphere is saturated with water vapor at a known temperature by a layer of the material to be tested. The change in humidity caused by the water vapor passing through the sample is detected by a humidity sensor that can provide an electrical output signal that is a measure of the relative humidity in the dry room. The time it takes for the humidity to increase by a given amount is measured and converted into a water vapor transmission rate.
The samples shall be representative of the material, free from wrinkles, creases and pinholes and of uniform thickness. Each sample shall have an area greater than the transmission area of the cell used for the test and shall be hermetically mounted. Three samples shall be used in the tests unless otherwise specified or agreed upon between the parties concerned. However, for some products, testing more than three samples will give a more representative result. Unless otherwise specified, the thickness of each sample shall be determined at three equally spaced points in accordance with ISO 4593. The samples shall be conditioned at a temperature of 23 degrees plus/minus 2 degrees and a relative humidity of 50 percent plus/minus 10 percent. The conditioning period shall be as specified in the relevant specification for the material.
The tests use an apparatus consisting of a two-chamber transmission cell, a chamber in which a sample is mounted between a lower (high humidity) chamber and an upper (low humidity) chamber, a humidity sensor to determine the relative humidity in the upper chamber, a pump to supply air to the upper chamber, a drying tube and a water chamber. The lower chamber is directly connected to the water chamber. The upper chamber is designed to collect water vapor passing through the high humidity side of the sample and the humidity sensor is mounted above this chamber. The transmission area should be between 5 cm2 and 100 cm2. The temperature of the transmission cell should be maintained within plus/minus 0,5 degrees of the test temperature by means of a temperature controller.
The humidity sensor must be able to detect changes in relative humidity of 0,05 percent and the response time must not exceed 1 second. For each type of humidity sensor, appropriate maintenance and calibration procedures specified by the manufacturer must be followed. In addition, the water tank must contain distilled or deionized water.
Test conditions should preferably be selected from the table given in the standard.
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