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With the intensification of competition, some companies have used inferior or unqualified raw materials to reduce costs, and lax controls on the process have not even met the most basic production conditions, causing unqualified hollow glass to flow into the market, which has seriously affected the healthy development of the insulating glass industry. .
This article briefly analyzes the selection of the raw materials affecting the quality of the insulating glass and the control of the production process, and clarifies its influence on the quality of the insulating glass.
Poor insulating glass can cause problems such as air layer dew point and glass burst.
The dew point of the dew point in the air layer refers to the temperature at which the humidity of air sealed in the air layer reaches saturation. Below this temperature, the water vapor in the air layer will condense into liquid or solid water. The dew point of the hollow glass is increased due to the external water entering the air layer and cannot be absorbed by the desiccant, which will seriously affect the use and energy saving effects.
Poor quality of raw materials, such as high air permeability of sealant, low adsorption capacity of desiccant and lax control of production process, such as poor glass cleaning, uneven coating of butyl rubber, poor seal at the corners, and insufficient thickness of glue. Humidity in the production environment can cause the dew point of the hollow glass to rise.
The explosion of glass caused by hollow glass has both production reasons, material selection and installation reasons. The greater the temperature difference between the temperature at which the insulating glass is produced and the use environment, the more pronounced the deflection of the glass. When the stress generated by this deformation exceeds the maximum stress that the glass can withstand, the explosion of the hollow glass occurs.
Hollow glass is made of endothermic glass and coated glass. Under the irradiation of sunlight, there is a large temperature difference at different points of the glass, thermal stress is generated, and the glass may also be damaged.
Hollow glass sealant is hard and has poor elasticity. It will restrict the deformation of glass caused by changes in the ambient temperature and increase the stress in the edge of the insulating glass. The volatile components in the insulating glass sealant will make the sealant shrink too much. In particular, it will increase the likelihood of the first winter burst. This article only discusses both materials and processes.
Reasonable selection of raw materials The original glass sheets used in the production of insulating glass can be ordinary float glass, coated glass, heat absorbing glass, tempered glass, laminated glass, etc. When used, they should meet the corresponding national standards. In particular, the coated glass and the heat-absorbing glass may cause burst due to the large temperature difference between the center and the edge of the glass after the glass absorbs heat.
Sealant Nowadays, people have realized the importance of sealing life for insulating glass. The sealing and structural stability of the insulating glass system is achieved by the insulating glass sealant. The traditional grooved aluminum hollow glass system should adopt the double channel sealing form, use the first sealant to prevent water vapor, and use the second sealant to maintain the structural stability. If the insulating glass system only uses a single-pass seal, the insulating glass sealant not only plays a sealing role but also has a structural role, but so far, there is no sealant that can simultaneously have excellent sealing properties and structural properties. . In general, in the double-seal system, the glue used for the first seal is high in water vapor transmission resistance, but structurally poor, while the second sealant has high structural performance and poor water vapor transmission resistance.
The first sealant for insulating glass. The first sealant is generally made of butyl rubber, which is familiar to everyone. Its role is to control and ensure the minimum infiltration of water vapor and solvents into the sealed space of the insulating glass. Another function of the sealant is to enable the insulating glass to adopt an aeration process. Effectively blocks the exudation of inert gas. Therefore, butyl rubber is required to have the following characteristics: (1) It must have good adhesion, and the continuous sealing between two glass and spacers is ensured by perfectly bonding the glass to the spacers. 2 should have a high water vapor permeability. 3 It should have a certain bond strength to prevent the glass displacement before the second seal, so as to reduce the occurrence of poor stacking of the insulating glass. In order to improve the service life of the insulating glass, the butyl rubber should have good weather resistance, aging resistance and durability in addition to the above performance.
Although the butyl rubber has strong water vapor permeability and anti-aging properties, it has poor structure, so the structural strength of the hollow glass is mainly achieved by the second sealant.
Hollow glass second sealant. The second sealant effectively bonds the various components that make up the insulating glass into a single unit, forming an insulating glass member. The second sealant should have the following characteristics.
1 should have strong bonding properties. By maintaining a certain strength, it avoids excessive displacement caused by the dynamic load or static load of the insulating glass, so that the first sealant can have the function of blocking moisture. Therefore, the second sealant must have good mechanical properties and good adhesion to glass and other components. It has tensile and shear strength to withstand all dynamic and static loads.
2 should have good flexibility. It is very important that the secondary sealant should be able to recover its initial mechanical properties after it has been deformed by a dynamic load. Because during use, due to the influence of temperature changes, the gas in the hollow glass is constantly shrinking or expanding, which will directly cause the premature failure of the hollow glass or the explosion of the glass.
The expansion and contraction of the air layer poses new problems for the performance of the sealant. Should the edge sealant be softer to accommodate the change in gas volume in the compartment? If this area of ​​moisture infiltration (MVT) may increase, affecting the service life of the insulating glass; if the water vapor infiltration area is kept basically constant, then should the sealant be harder? However, such results restrict the deformation of the glass and increase the stress on the edge of the hollow glass, which may cause the glass to burst. The insulating glass sealant should not only effectively resist the expansion of the water vapor permeability area of ​​the hollow glass, but also make the edge stress of the hollow glass lower than the stress that causes the glass to break.
3 should have strong weather resistance and aging resistance. The second glue must have a strong ability to adapt to climate change in order to ensure its use and longevity. These climate changes include factors such as temperature, water, and ultraviolet rays. Sealants should not lose their effectiveness prematurely due to changes in these climatic factors.
Polysulfide rubber, polyurethane rubber and silicone rubber are often used as secondary sealants for insulating glass. They all have good weather resistance, aging resistance and durability, and have good adhesion to glass and other components. Ability. Among them, polysulfide rubber has the longest history of use and the largest amount of use, accounting for approximately 76% of the global market share of insulating glass. Polysulfide sealants are highly resistant to many types of oils and solvents. At the same time, it is also very good in anti-aging, anti-ozone, antioxidant, anti-sunshine and anti-climate circulation. However, if exposed to air at 60°C, the adhesion between polysulfide rubber and glass will be weakened, and some polysulfide rubbers containing more plasticizers will decompose. Silicone rubber is characterized by good chemical and physical compatibility with the contact material; excellent fluidic properties make extrusion and coating very easy; high mechanical strength, able to withstand the various types of insulating glass Dynamic load. Based on these features, silicone adhesive has been widely used in curtain wall insulating glass. Polysulfide rubber and silicone rubber are familiar to us. Polyurethane sealant is a sealing material that has been rapidly developed in recent years. Its market share in insulating glass sealant market is continuously increasing.
Polyurethane adhesive has the characteristics of low viscosity, fast curing, and no solvent.
1 Low viscosity, good flow and falling resistance. The low viscosity means that it is easier to apply the sealant and the glass and spacers work better. No need to level or remove the sealant after coating. This is especially useful for automated production lines.
2 Curing is fast, and the curing state of the polyurethane sealant after 3 hours can reach the hardness of the handling of the hollow glass, compared to 5 hours for the polysulfide adhesive.
3 does not contain solvent, will not produce the glass stress caused by colloidal shrinkage, reduce the possibility of hollow glass first crack in the first winter. Solvent-Containing Sealant If the solvent evaporates from the side sealant, the sealant still retains full contact with the glass, but the stress caused by the colloid shrinkage becomes the stress applied to the edge of the glass. Because the insulating glass flexes inwards in winter, the spacer acts as a stress fulcrum. This stress increases the likelihood of the glass breaking in the first winter after installation.
Desiccant Hollow glass uses desiccant for the purpose of adsorbing the moisture and volatile organic solvent sealed in the spacer layer during the production of the insulating glass; secondly, it continuously adsorbs the moisture entering the spacer layer through the sealant during the use of the insulating glass. To keep the gas in the hollow glass dry. Correct selection of a suitable desiccant can improve the overall performance of the hollow glass, reduce the deflection of the hollow glass, and reduce the occurrence of bursting of the hollow glass.
Mainly used for the manufacture of hollow glass desiccants are silica gel, molecular sieves, mixtures of silica gel and molecular sieves, and new binders containing desiccants (for U-shaped spacers). The choice of desiccant should be determined according to its adsorption properties, mainly considering its ability to adsorb moisture, air, and solvents. The desiccant commonly used in domestic hollow glass is molecular sieve, and the size of molecular sieve according to its pore size is 3A, 4A, 13X and other types. 3A molecular sieve only absorbs moisture; 4A molecular sieve absorbs moisture, air, etc.; 13X absorbs moisture, air, SF6, organic solvents and so on. The performance of various types of desiccants is shown in Table 1.
Table 1 Comparison of Desiccant Adsorption Capacity In addition to the desorption capacity of the desiccant, it is necessary to consider whether there is solvent in the spacer frame of the insulating glass, and the desiccant's adsorption to the air is also a factor that must be considered. . Because the desiccant has the ability of low temperature gas adsorption and high temperature gas desorption, the adsorption and desorption of gas by the hollow glass desiccant directly affect the deflection of the glass.
In the process of using the hollow glass, the gas between the space layers will shrink or expand due to the influence of temperature change, which will cause the glass to bend inward or outward. If there is no organic solvent that needs to be adsorbed in the hollow glass, a large pore size (adsorption gas) molecular sieve is selected. When the ambient temperature is low, the air inside the hollow glass will be adsorbed, making the inward deflection of the hollow glass more obvious. At high temperatures, gas is released by the desorption of the molecular sieve, exacerbating outward deflection of the glass.
Finally, the choice of desiccant should also consider whether the hollow glass is inflated. Inflatable hollow glass cannot use large-pore molecular sieves capable of adsorbing inert gas and solvent. Otherwise, it will reduce the concentration of the gas-filled body and affect the aeration effect.
Therefore, the choice of insulating glass desiccant should also consider comprehensively what kind of sealing system is used in production and what other materials are used in the hollow glass.
Hot melt butyl rubber, polyurethane glue, silicone rubber and butyl rubber do not release organic solvents into the spacer even under very bad weather conditions. In this case, 3A molecular sieve is the best choice. Some polysulfide rubber single-channel sealing systems and polysulfide rubber, butyl rubber double-channel sealing systems may release organic solvents into the air layer, so it is recommended to use a mixture of 3A and 13X molecular sieves. Table 2 lists several situations where the desiccant and sealant are properly paired.
Table 2. Desiccant Selection Intervals The function of the hollow glass spacers is to separate the two glass sheets of the hollow glass to form a spacer layer so that the hollow glass forms a uniform cavity. The desiccant is stored inside the spacer for drying and adsorption of moisture and chemical volatiles in the spacer. In addition, the spacers and the gussets also have the effect of supporting and enhancing the product's tightness, forming a solid water vapor barrier that enhances the integrity and durability of the IG unit. The factors that need to be taken into consideration in selecting the spacer are the strength and appearance quality of the spacer; whether it is compatible with the sealant; whether there is a warm edge requirement. There are many types of spacers, such as conventional metal spacers, non-metallic spacers, and hybrid spacers. U-shaped metal bars and super spacers with the concept of warm edges are newly developed, and aluminum spacers are used most frequently. .
Insulating glass production process control The original glass cleaning glass is best selected for mechanical cleaning, especially large glass, cleaning agent can be added when the amount of cleaning agent, the last one should use deionized water rinse to ensure that the glass surface is clean and dirt, so that the seal Adhesive is firmly bonded.
Control points: Use deionized water to keep the cleaning water clean.
Metal spacers should be decontaminated or chemically treated with metal spacers. If an insulating glass made of stained spacers is installed on a window, the oil traces gradually evaporate after being exposed to sunlight for a long time and is adsorbed on the inner surface of the insulating glass to form an oil film, which affects the visual effect of the insulating glass. It will also cause the sealant to fail due to poor adhesion of the sealant to the spacer.
Control points: The use of the front aluminum spacers should be anodized or decontaminated.
Control of the humidity in the production environment The humidity in the production environment mainly influences the effective adsorption capacity and residual adsorption capacity of the desiccant. Residual adsorption capacity refers to that after the insulating glass is sealed, the desiccant absorbs the moisture of the spacer layer to make the initial dew point meet the requirements. In addition, the desiccant also has an adsorption capacity, and this part of the adsorption capacity is called the residual adsorption capacity. Quantitatively speaking, it is equal to the effective adsorption capacity minus the adsorption capacity of the desiccant adsorbed on the moisture sealed in the air in the spacer layer.
The role of the remaining adsorption capacity is to continuously adsorb moisture that diffuses from the periphery into the spacer layer. The size of the remaining adsorption determines the amount of water adsorption through the diffusion into the spacer layer during the use of the insulating glass, which determines the speed of the accumulation of moisture in the spacer layer, and determines the effective use time of the insulating glass. The length of time. When the humidity of the insulating glass production environment is large, the moisture in the space layer is first sealed, the desorption capacity of the desiccant is large, and the remaining adsorption capacity is reduced. Therefore, the influence of humidity on the effective use time of the insulating glass is very important. To prolong the effective use of insulating glass, the humidity of the production environment must be kept low. General requirements of the workshop environment humidity is not higher than 75%.
Control points: Add necessary dehumidification equipment or try to avoid rainy weather production.
Ambient temperature at the time of production During the production of insulating glass, the pressure sealed in the spacer layer is the pressure at the production environment temperature. In the process of use, it is often the difference between the use temperature and the production environment temperature. The thermal expansion and contraction of air will cause the pressure of the air to change. In summer, the ambient temperature is generally higher than the production environment. The air in the spacer layer expands to generate positive pressure, especially for insulating glass made of heat-absorbing glass. The heat absorption effect of glass is very strong, the air temperature in the spacer layer is higher, and the positive pressure generated is also greater. When the pressure due to air expansion of the spacer layer is higher than the breaking pressure of the glass, the glass will burst. Also in winter, when the production temperature is higher than the ambient temperature at the time of use, the air in the spacer layer shrinks to generate a negative pressure. When the glass area is large and the spacing frame is small, the center of the two glasses may be stuck together. Rainbow-like spots seriously affect the use of results. When combined with snow and snow loads, it is possible to break the glass. In addition, our country has a vast territory. If there is a large difference in pressure between supply and demand, the glass can also be deformed. The temperature is generally controlled at 23±2°C.
Control points: Operate the workshop to install air-conditioning, if necessary, install a breathing tube or capillary on the insulating glass.
The width of the first sealant (butyl rubber), butyl rubber, determines the service life of the insulating glass to a large extent. It requires uniform and uninterrupted width of 3 to 5 mm, and the thickness is controlled at 0.3 when the film is assembled. In the range of ~ 0.5 mm, gel breakage is particularly likely to occur at the corners.
Control points: timely clean up the plastic injection hole, so that butyl rubber heating evenly, the temperature is around 125 °C.
The thickness of the second sealant and the bonding of the second sealant are the key part of the insulating glass, so the national standard has special provisions for it: When using the double seal, the thickness of the adhesive layer is 5 to 7 mm. When the single sealant is used, the thickness of the adhesive layer is 8-12mm. Since the gas diffusion is inversely proportional to the thickness of the adhesive layer, the thicker the adhesive layer is, the longer the lifetime is.
Sealing and bonding should avoid inaccurate extrusion so that there are fine pores on the colloid, and the two-component sealant should be mixed evenly. Do not mix too much glue at one time during manual operation to avoid early curing and affect the bonding strength. When using a plating film as the original film, the defilming process should be added.
Control points: Develop a reasonable thickness of the adhesive layer and ensure its uniform thickness. When mixing the glue, adjust the proportion of the two components according to the temperature change.
Shortening the production process time of the hollow glass The shortening of the process time means minimizing the contact time between the desiccant and the air in the production of the hollow glass, so as to reduce the loss of the adsorption capacity and make the desiccant have a higher residual adsorption capacity. It usually takes no more than two hours from the molecular sieve to the final sealant. At the same time, the activity of the molecular sieve (ie adsorption capacity) should be checked before filling. The simplest method is to do a temperature increase experiment: after mixing the same weight of water (room temperature) and molecular sieve, if the water temperature rises above 30°C, the molecular sieve has no failure. Otherwise, the molecular sieve has been partially or partially deactivated and should be used after drying.
Control points: Reasonably arrange the production time for each process, reduce the waiting time after filling the molecular sieves, and conduct a temperature increase experiment before each filling.
Because the structural composition and production process of hollow glass are relatively simple, many people pay insufficient attention to their materials and process control, so that the service life of the hollow glass can not meet the design requirements. Only the rational selection of raw materials, strict quality control of the production process, and improvement of quality awareness can improve the overall level of China's insulating glass industry.
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Hollow glass has been widely used as an important material in contemporary architecture in China. At present, there are more than 1,000 hollow glass production enterprises in China, and there are also hundreds of raw material production companies supporting them.