An article to understand molecular sieves for insulating glass.

--The secret of durable insulating glass for glass building decoration

1. Insulating glass and molecular sieve

Insulating glass is composed of glass original sheet, aluminum spacer, molecular sieve, first butyl coating, and second sealant sealing(conventional insulating glass). One piece complies with regulations and can reach a reasonable and effective service life (15 years). Qualified raw materials, followed by good production (environment, automatic machine, process flow, operation specification, etc.).

^{Figure 1 The insulating glass desiccant sieves}

In the preparation, the first and second sealants are very critical, they can tightly connect the two single pieces of glass, and at the same time form a relatively airtight and dry space.

Insulating glass has the characteristics of energy saving:

A good conductor of glass heat, the thermal conductivity is 0.90 W / (m K), and the thermal resistance is small;Air is a poor conductor of heat, the thermal conductivity is 0.024 W / (m K), and the thermal resistance is large;

The heat transfer coefficient (K value) of glass with a thickness of 6 mm is about 5.8 W / (m²·K);

The heat transfer coefficient of 5 mm + 12 A + 5 mm insulating glass is about 2.72 W / (m²·K);

The heat transfer coefficient K value is one of the main parameters to measure the energy-saving performance of glass, reflecting the temperature difference heat transfer performance of the glass, the lower the K value, the better the performance.

The heat transfer coefficient of 6 mm + 12 A + 6 mm insulating glass is about 2.70 W / (m² K), and the heat transfer coefficient of 10 mm + 12 A + 10 mm insulating glass is about 2.65 W / (m² K);

The K value of insulating glass with different glass thicknesses is almost the same. It can be seen that the energy saving of insulating glass is not determined by the increase in glass thickness, but the K value of the insulating glass layer is greatly reduced.

^{Figure 2 The relationship between the K value of the insulating glass and the thickness of the glass}

Source: "Production and Selection of Insulating Glass";

The key to energy saving of insulating glass is that the gas in the insulating glass layer is sealed and dry.

According to relevant research, for a piece of insulating glass in "normal use", the relative humidity of the air in the hollow layer is about 0.5%RH, which is far lower than the relative humidity of 45%RH ~ 75%RH in our daily life (human body feels Humidity around 60% - 70% is most comfortable).

Although the first and second sealants of insulating glass play a vital role in sealing and isolating air and water vapor, the "glue" cannot directly reduce the air humidity in the hollow layer.

Even if the insulating glass is made in an extremely dry workshop, the "insulating glass sealant sealing" is not 100% "absolutely sealed", and the air drives water vapor to have a certain penetration. Over the years, the sealant is equivalent to undergoing gas exchange, which increases the air humidity in the insulating glass layer.

Table 1 The changes of humidity and dew point of insulating glass in different stages of production

(Dew point: the temperature at which the hollow layer of the insulating glass condenses, reflecting the quality of the glass; a high dew point temperature indicates that the quality of the insulating glass is not good or the quality is declining, and it will fail)

Therefore, molecular sieves are indispensable in the processing and production of insulating glass.

A molecular sieve is one of the types of "desiccant". Its purpose is to quickly absorb the water vapor in the air in the insulating glass layer after the insulating glass is made so that the relative humidity of the air in the insulating glass layer can be quickly reduced to about 0.5%RH;

And during the normal use period of the insulating glass for more than ten years or even longer, it absorbs the water vapor in the air that is "put" by the sealant, delays the dew condensation time of the glass, and avoids the failure of the insulating glass.

^{Figure 3 The insulating glass molecular sieve}

If there is no molecular sieve, the air humidity in the hollow layer will not be absorbed, which will bring about two effects.

The first is performance. The air humidity in the hollow layer is high or condensation occurs when the dew point is reached, which will increase the heat transfer coefficient of the air (the heat transfer coefficient of dry air is 0.021 kcal / (㎡·h·℃), and the heat transfer coefficient of water is 0.5 kcal/(㎡·h·℃)). The increase of the heat transfer coefficient of the air in the hollow layer leads to a decrease in its thermal resistance, which reduces the heat insulation performance of the insulating glass.

If the hollow layer has condensed, it also means that the insulating glass has reached the effective service life and no longer has the heat insulation performance it should have.
Second, long-term low air humidity or condensation will cause mildew, alkali analysis, white spots, spacer corrosion, and even glass bursting on the inner surface of the glass (expanded below).

^{Figure 4 The condensation on the inner surface of the insulating glass}

2. Two major problems with molecular sieves —- a variation of molecular sieve products

3 A molecular sieve should be selected

To make molecular sieves easy to use and durable, relevant specifications have made some restrictions and regulations on the selection and use of insulating glass molecular sieves.

Among them, the "Insulating Glass Production Regulations" clearly require that the insulating glass desiccant (molecular sieve) should use a molecular sieve with a pore size of 3 A, and comply with the current international industry standard of "3 A Molecular Sieve".
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Types of commercially available molecular sieves

There are many types of insulating glass "desiccant" currently on the market, including 3 A molecular sieve, 4 A molecular sieve, 5 A molecular sieve, calcium oxide desiccant, calcium chloride desiccant, and clay desiccant. Among them, 3A, 4A, and calcium chloride desiccants are the most common.

What are the 3A insulating glass molecular sieves?

3 A, 4 A, and 5 A are all made of a material called "alkali metal aluminosilicate". The main difference between them is the pore size. is around 0.4 nm, and so on.

Why should we use the 3A insulating glass molecular sieves?

The effective pore size of "Class A Molecular Sieve" has a great effect, representing the maximum value of molecular size that can be absorbed. The diameter of water molecules in the air is 2.8 nm, the diameter of oxygen molecules is 0.34 nm, and the diameter of nitrogen molecules is 0.36 nm, so only 3 A molecular sieves can only absorb water vapor in the air, and other A molecular sieves can absorb oxygen and nitrogen in the air.

If the molecular sieve can absorb gas, there may be another problem. It will inhale and degas due to temperature differences such as day and night and seasons. Release more than 700 ml of gas, 3 A is less than 50 ml, data source from LIJIANG Glass)

The problem of suction and deflation will cause the insulating glass to suck in and bulge out, which will easily accelerate the aging of the sealant, and in extreme cases, the problem of glass breakage will also occur.

^{Figure 5 The insulating glass molecular sieve absorbs water}

In addition to "A-type molecular sieves", commercially available molecular sieves also commonly include calcium oxide, calcium chloride, and clay desiccants. "Calcium-based" desiccants tend to corrode the aluminum spacer and destroy the butyl rubber, thus affecting the life of the sealant and the life of the insulating glass.

"Clay-based" desiccants have a very low water absorption rate, so the insulating glass can reach an effective service life in a very short time.

^{Figure 6 Insulating glass aluminum spacer corroded}

^{Figure 7 Insulating Glass aluminum spacer corrosion and alkali analysis}

To sum up, the selection of 3 A molecular sieve as a desiccant for insulating glass is the basic prerequisite for reliable quality assurance. Moreover, the market unit price of insulating glass for home improvement doors and windows on the market is no less than 100-200 yuan/㎡, which is enough to guarantee the cost of molecular sieves of tens/hundreds of grams of a piece of glass. To save money here, it is only worth the price of selling inferior glass.

3. Two common problems with molecular sieves - non-standard production

Taking the molecular sieve used in the production of insulating glass as an example, it will be helpful for the selection of insulating glass below:

1. The specification generally requires that a square of insulating glass should be filled with molecular sieves of about 50g - 200g (determined by the thickness of the insulating glass layer). Some merchants fill it manually, some save materials, and some fill it too full (molecular sieve filling should be reserved). There must be a certain gap, and it cannot be filled with 100%, to expand after absorbing water vapor).

2. Some insulating glass uses gusseted aluminum spacers, because the gussets are not connected, and only part of them are filled.

3. Molecular sieves will absorb water vapor as soon as the package is opened. In principle, open a package and use it as soon as possible to prevent excessive absorption of water vapor when exposed to the air. Some glass deep-processing standards for this are very low, which eventually affects the service life of the glass.

^{Figure 8 The insulating glass aluminum spacer insert corner}

4. Identify the quality of insulating glass by molecular sieve

To buy reliable insulating glass, LIJIANG Glass has prepared some common questions and tips for dealing with suppliers, for reference only:

1. Take the initiative to ask the merchants if they know about insulating glass molecular sieves? What molecular sieve is used in the product? Only choose insulating glass products that are 3 A molecular sieves, or chat with suppliers about various knowledge about molecular sieves.

2. Ask the merchant who is the glass deep processing company. Molecular sieves are hand filled/machine filled? or some other way? Are the aluminum spacers bent or angled? (There is a whole molecular sieve) Would you post some related videos for us.

By determining the name of the glass deep-processing manufacturer + filling method + aluminum spacer production method, the production strength of the company can be preliminarily judged, and the precise of Automatic Desiccant Filling Machine could avoid pits with a high probability.

^{Figure 9 The insulating glass desiccant sieves filling machine}

3. Ask about the service life of insulating glass. The supplier has been engaged in the production of molecular sieves for several years. Is there any problem with condensation inside the insulating glass? Generally, the effective service life of insulating glass under normal conditions (non-self-explosion) can reach several years. I heard that the standard requires insulating glass to be free of internal fog for 15 years. Can you promise a warranty or replacement for 5 years or even longer?

^{For more information about LIJIANG Glass insulating glass processing equipment and insulating glass processing accessories, please click here to learn more.}