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An alternative quality control procedure for the testing of insulating glass in compliance with EN 1279-2

Dr Kerstin Dreblow, Berghof Products + Instruments GmbH, 72800 Eningen u.A., tel. +49 (0)7121-894-0
Thomas Fiedler, UNIGLAS GmbH & Co KG, 56410 Montabaur, tel. +49 (0) 2602 – 94929-0

Insulating glass is employed not only for its thermal insulation and sound-proofing properties but also as a sun screen. It contributes to improved air conditioning and actively promotes environmental protection.

Figure 1: Schematic design of insulating glass

As a general rule commercially available insulating glass consists of at least two panes which are connected to each other by a hermetically sealed cavity (Figure 1). Selective functional layers are applied to one or several panes so as to achieve maximum thermal insulation. The cavity is filled with an inert gas (Ar or Kr) which, as a result of its molecular size, leads to improved inertness and thus to reduced thermal conductivity where there are temperature differences between the external and internal surfaces. At the core are the edge seals, which determine the long-term reliability of the insulating glass.  In order to prevent gas escaping and moisture penetrating from outside the edge seal must form a largely gas-tight barrier.

In addition the panes need to be connected mechanically. The pressure of the gas in the hermetically sealed cavities between the panes corresponds more or less to the atmospheric pressure during production. The edge seal must be designed in such a way that pressure variations caused by the permanently changing atmospheric pressure and meteorological effects are equalized. High summer temperatures and low pressure constitutes one extreme, with low winter temperatures and high pressure representing the other.

In modern insulated glazing stainless steel and plastic composite profiles or flexible spacer systems made of thermoplastics with an integrated desiccant (UNIGLAS® STARTPS) or silicone foam with a high barrier film applied to the back (UNIGLAS® STARFLS) are used. The natural lifetime of insulated glazing largely depends on the technology used to manufacture it. Diffusion of gases from the cavity between the panes cannot be entirely prevented. In addition to this, in time ambient moisture penetrates, which is adsorbed by the desiccant (molecular sieve). Once this becomes saturated the side of the glass facing the cavity between the panes mists over. Depending on the method of manufacture it can be presumed that modern insulated glazing will last at least 25 to 35 years.

DIN EN 1279-6 – Short-term climate test in factory production control

Periodic production tests must be carried out by the manufacturer in accordance with EN 1279-6 in order to ensure long service life on the part of the insulating glass. Up to now UNIGLAS GmbH & Co. KG has not been in a position to determine in its own laboratory the water content of the desiccant after climate storage in the case of insulated glazing with flexible spacing systems where the desiccant is embedded in the spacing material. The analytic work was awarded to other laboratories.

EN 1279-2, Attachment C, describes the measurement of the charge of desiccant with water after determining with thermo-coulometric Karl Fischer titration. Here the insulating glass is opened in the climatic chamber after treatment and samples of the sealing compound containing the desiccant retrieved at defined points. No more than fifteen minutes may pass between the selection of samples and the start of the measuring procedure.

In order that the proprietors of UNIGLAS GmbH & Co. KG continue to maintain a high standard of quality and are able to conduct production tests in their own laboratory the question must be asked as to suitable alternative techniques. The requirement here is for an uncomplicated and robust method that delivers results comparable to those obtained from Karl Fischer titration, but makes simple handling possible so that the production system can be implemented and used by anyone.

Figure 2: The measuring principle of the easyH2O

EasyH2O as an alternative procedure to classical Karl Fischer titration

EasyH2O combines the thermal evaporation of water with a selective, electrochemical water sensor made of hygroscopic phosphorus pentoxide (P2O5). The sample is weighed directly in the sample boat, inserted in the furnace chamber and measured immediately. Additional steps in sample preparation are not necessary. In the process the water is evaporated from the probe in the programmable oven and a stream of carrier gas is passed over the sensor (Figure 2). The transported water molecules are completely absorbed by the hygroscopic P2O5. The water is broken down into hydrogen (H2) and oxygen (O2) by electrolysis and then discharged from the system with the stream of carrier gas.

The amount of water is proportional to the electrical charge required for electrolysis and can be determined using Faraday’s Law. Therefore, measurement is an absolute measurement which can be carried out without calibration.

A further advantage is that the sensor is self-regenerating, in that the P2O5 layer is reformed in each case. The device remains operational at all times. All technical measurement processes, calculations and evaluations are conducted independently and once measurements are completed deliver a quantitative and graphic representation of the water content of the sample substance.

Ambient air is sucked in as carrier gas and dried, thus dispensing with special chemicals. So as to eliminate any disruptive reactions with oxygen in the air as an alternative hydrogen or argon can be used as the carrier gas. The entire process is controlled automatically by software.

Determination of water content by thermoplastic spacers (TPS)

The service life of panes of insulating glass depends on the effectiveness of the desiccant used in the edge seal. For manufacturers of insulated glazing the water content is therefore an important quality criterion. Attachment C of DIN EN 1279-2 was used as a basis for the comparative measurements that were carried out, and the determination conducted on the UNIGLAS® STARTPS spacer. Spacer samples were treated in a climatic chamber at 23°C and 30% RH. In each case ten identical conditioned samples were extracted at defined intervals (0h, 1h, 2h) for both Karl Fischer titration and for determination with the easyH2O. The analysis (n=5) was made at 160°C for 60min (Table 1). Karl Fischer titration and measurement using the easyH2O were conducted at the same time. This meant that any errors caused by storing for different lengths of time or by weather-related influences can be ruled out.

Storage in climatic chamber

EW 1 water content [%]

Karl Fischer water content [%]

0h

0.18 ± 0.02

0.15 ± 0.02

1h

0.17 ± 0.03

0.18 ± 0.04

2h

0.20 ± 0.01

0.17 ± 0.01

Table 1: Ascertaining the charge of UNIGLAS® STARTPS

The results of the measurements obtained with the easyH2O are comparable with those using the Karl Fischer technique. The easyH2O thus represents a practical alternative method for the prescribed short-term climate test in isolating glass systems within the framework of factory production checks.

Reliable results in a short time

With the easyH2O water determination unit the charge of sealant for spacers in which the deseccant is easily introduced can be ascertained easily and in a short measurement period. By using comparative measurements with the thermo-coulometric Karl Fischer technique in accordance with DIN EN 1279-2 it was possible to demonstrate the comparability and reproducibility of the method. The UNIGLAS GmbH & Co. KG proprietors now have to hand a device that is an aid to their own factory tests involved in the manufacture of insulated glazing without great effort or expense. In addition, system variants can be tried out beforehand and be assessed in compliance with DIN EN 1279-2 without processing by external laboratories being required. UNIGLAS GmbH & Co. KG profits from the use of the easyH2O as a result of low operational and waste disposal costs and possesses a measuring instrument which can also guarantee the high standard of product quality in the future.

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