The first sealing method typically comes in two main types: one involves using a composite sealant strip to bond and seal the inner and outer glass panes. This composite sealant strip integrates a supporting frame (made of corrugated aluminum) with a sealing material (butyl胶). The other method uses a metal spacer frame, which is filled with desiccant molecular sieves for drying purposes. Butyl胶 is applied evenly onto the upper and lower surfaces of the metal spacer frame before the inner and outer glass panes are carefully bonded and sealed in place. Butyl胶, used in the first sealing step, serves as the most effective barrier against moisture penetration. Inspection of this initial seal primarily focuses on: the quality of butyl胶 application on the bonding surfaces of the metal spacer frame’s top and bottom edges, the overall appearance of the spacer strip itself, and the condition at corners and joints.
　　Whether it’s hollow glass with composite sealant strips or hollow glass featuring metal spacer frames, the primary location of seal failure is at the joints of the spacer frame. For hollow glass with composite sealant strips, the corners must be clearly defined, and there should be only a single joint—so inspect this joint carefully to ensure a tight, airtight seal. In contrast, for hollow glass with metal spacer frames, it’s best to opt for designs that use a continuous bending process with just one joint. If all four corners of the metal spacer frame are connected using continuous corner joints, the risk of seal failure becomes significantly higher compared to hollow glass with a single joint. To effectively verify the sealing performance at the joint, you can gently score the second layer of sealant at the corner junction with a blade, checking whether the continuous corner has been adequately wrapped with sufficient butyl胶. If the butyl胶 isn’t applied generously enough to fully encase the joint, it’s a clear indication that the hollow glass will have a much shorter lifespan.
           
　　The quality of the second sealing胶 directly impacts the service life of insulated glass. Key inspections for the second sealing胶 include: selecting the appropriate second-sealant type, assessing the visual quality of the sealant, ensuring the sealant is fully applied, checking for tiny air bubbles trapped within the sealant, verifying the adhesion strength between the sealant and the glass, confirming compatibility between the second and first sealing gels, and evaluating the thickness of the second-sealant application.
　　Currently, most hollow glass products on the market use a two-seal sealing process. For these double-sealed hollow glass units, the accompanying materials include: glass, metal spacers (or composite seals), the first-layer bonding sealant (butyl rubber), the second-layer bonding sealant (polysulfide, silicone, or polyurethane adhesive), desiccant (molecular sieve), and connecting components.
　　Process quality primarily includes: the quality of the first seal, the quality of the second seal, and the quality at corners and joints. When determining and evaluating process quality, we must start from the premise that a failure in any one of these sealing steps will ultimately lead to the failure of the insulated glass unit's overall seal.
　　To determine the quality of insulated glass units, we first need to carefully examine their overall visual appearance. This visual inspection primarily focuses on: the internal condition of the unit, the quality of the inner and outer panes, and whether there is any misalignment between the two glass layers.
　　Appearance quality of the spacer strips in the middle space:
　　1. Appearance quality inside the hollow glass
　　Place the insulated glass unit under good natural or daylight illumination and carefully inspect the interior for cleanliness—specifically, ensure it is free of any impurities. The interior of the insulated glass must remain clean, transparent, and free of contaminants. If the internal cleanliness is poor and dust or other impurities are present, the product should be classified as nonconforming.
　　2. Quality of inner and outer glass panels
　　First, inspect the edges of both the inner and outer glass panes. There should be no noticeable shell-like chipping (larger than a green bean) along either the inner or outer edge. If you want the glass to maintain strong structural integrity while ensuring safety, it’s best to opt for insulated glass where both the inner and outer panes have been tempered. Next, consider the thickness of the insulated glass units. The choice of thickness depends on the area and dimensions of the glass; for larger panes, it’s recommended to use thicker glass to enhance durability and performance.
　　3. Internal and External Film Quality
　　There is no misalignment occurring in the hollow inner and outer glass sheets; the edges must be neat, and no significant misalignment is permitted.
　　The first-seal inspection
　　The first sealing method typically comes in two main types: one involves using a composite sealant strip to bond and seal the inner and outer glass panes. This composite sealant strip integrates a supporting frame (made of corrugated aluminum) with a sealing material (butyl胶). The other method uses a metal spacer frame, which is filled with desiccant molecular sieves for drying purposes. Butyl胶 is applied evenly onto the upper and lower surfaces of the metal spacer frame before the inner and outer glass panes are carefully bonded and sealed in place. Butyl胶, used in the first sealing step, serves as the most effective barrier against moisture penetration. Inspection of this initial seal primarily focuses on: the quality of butyl胶 application on the bonding surfaces of the metal spacer frame’s top and bottom edges, the overall appearance of the spacer strip itself, and the condition at corners and joints.
　　1. Quality of butyl sealant application on the upper and lower bonding surfaces of the metal spacer frame  
　　Butyl sealant plays a critical role in sealing insulated glass units. Known for its extremely low water vapor permeability and high bonding strength, butyl acts as the most effective barrier—both internally and externally—to prevent moisture infiltration while ensuring secure adhesion between the inner and outer panes of glass. Additionally, butyl sealant offers excellent resistance to heat, ozone exposure, and chemicals, as well as outstanding shock-absorbing and insulating properties. If metal spacers are used in the insulated glass unit, it’s essential to inspect the quality of the coating applied to the spacer’s bonding surface. Specifically, ensure that there are no discontinuities in the butyl sealant layer on the coated area. Any breaks or uneven application directly disqualify the insulated glass unit as non-compliant.
　　2. Appearance quality of spacer bars
　　For insulated glass units using metal spacers, the metal spacers must remain free from deformation or distortion; the straight sections should stay perfectly aligned, while the curved sections must transition smoothly and evenly. For insulated glass units with composite sealants as spacers, the sealant strips must be straight, uniform, and free from any creep or sagging.
　　3. Corners and interfaces
　　Whether it's hollow glass with composite sealant strips or hollow glass featuring metal spacer frames, the primary location of seal failure is at the joints of the spacer frame. For hollow glass with composite sealant strips, the corners must be clearly defined, and there should be only a single joint—so inspect this joint carefully to ensure a tight, airtight seal. In contrast, for hollow glass with metal spacer frames, it’s best to opt for designs that use a continuous bending process with just one joint. If all four corners of the metal spacer frame are connected using continuous corner joints, the risk of seal failure becomes significantly higher compared to hollow glass with a single joint. To effectively verify the sealing performance at the joint, you can gently score the second layer of sealant at the corner junction with a blade, checking whether the continuous corner has been adequately wrapped with sufficient butyl胶. If the butyl胶 isn’t applied generously enough to fully encase the joint, it’s a clear indication that the hollow glass will have a much shorter lifespan.
　　Second edge-sealing adhesive
　　The quality of the second sealing胶 directly affects the service life of insulated glass. Key inspections for the second sealing胶 include: the selection of the appropriate second-sealant type, the visual quality of the sealant, whether the sealant is fully filled, whether tiny air bubbles are trapped within the sealant, the adhesion strength between the sealant and the glass, the compatibility between the second and first sealing gels, and the thickness of the second-sealant application.
　　1. Selection of the second type of sealant
　　The second sealant serves to protect the first sealant, bond the inner and outer glass panes together, and also prevent moisture from entering.
　　Currently, there are three main types of sealants used for the second sealing edge in insulated glass units on the market: polysulfide sealant, silicone sealant, and polyurethane sealant. It’s best to choose based on the specific application area of the insulated glass unit.
　　The key differences between polysulfide and silicone sealants for secondary sealing lie in their performance characteristics. Generally speaking, silicone sealants offer superior resistance to aging, UV exposure, temperature extremes, and bonding strength. Thanks to these outstanding properties, silicone-sealed insulating glass units are particularly well-suited for applications in areas with intense sunlight and harsh environmental conditions. Over time, silicone sealants remain stable even under prolonged UV exposure, maintaining excellent adhesion and structural integrity despite repeated exposure to temperature fluctuations and moisture—making them ideal for outdoor applications like curtain walls. On the other hand, polysulfide sealants boast a significantly lower water vapor permeability compared to silicone, making secondary-sealed insulating glass units with polysulfide more appropriate for indoor window and door installations where moisture control is critical.
　　When installing insulated glass units, if polyurethane adhesive is used to fill the gap between the panes, the secondary seal must be made with polyurethane sealant applied around the edges. However, if polysulfide or silicone sealants are used for the secondary sealing of insulated glass units, issues such as poor adhesion at the interface between the filler and the secondary sealant, as well as cracking in the sealant joint, may occur.
　　2. Visual Quality of the Sealant
　　Observe the visual quality of the surrounding sealant application—specifically, the second layer of edge sealant should be applied evenly, with no gaps or interruptions, and the sealant surface must remain smooth, free of any unevenness or irregularities.
　　3. Is the sealant fully filled?
         
　　Use your hands to press firmly around the sealant, checking whether it’s fully filled in. If the sealant isn’t properly packed, it will sink inward when pressed.
　　4. Are small air bubbles trapped within the sealant?
　　The second sealant layer contains an excessive number of air bubbles, directly impacting the lifespan of the insulated glass. To check whether the second sealant has trapped tiny air bubbles, you can carefully cut a cross-section of the sealant using a blade and then examine the freshly exposed surface. If numerous small air pockets appear in the cross-section, it indicates that either low-quality sealant was used during the sealing process, or improper handling allowed too much air to be incorporated into the edges while applying the sealant.
　　5. Adhesion between Sealant and Glass
　　The second sealant must ensure strong adhesion to the glass. To test the bonding strength between the second sealing bead and the glass, use a blade to carefully cut small openings—about 1 cm—in both the sealed joint area and the glass interface. Then, gently pull the sealant outward with your hands. If, after peeling it off, the glass surface remains smooth and free of any residual adhesive, it indicates that the secondary sealant used in this insulated glass unit has poor sealing performance.
　　6. Compatibility between the second edge-sealing adhesive and the first edge-sealing adhesive
　　Using inferior sealant for the second edge sealing often leads to incompatibility between the second and first sealants. If the two sealants are incompatible, it can significantly reduce the lifespan of the insulated glass unit. To check whether the second and first sealants are compatible, carefully use a blade to cut through the second sealant, then peel back 5–6 cm of the second layer. Next, examine the contact area between the first and second sealants. If you notice any of the following signs, it confirms that the two sealants are indeed incompatible:
　　a) Oily substance is seeping out at the contact area between the first and second layers of adhesive.
　　b) In composite sealant-filled insulated glass, it was found that the hardness of the sealant's contact surface had changed;
　　c) The curing of the second adhesive contact area is inadequate;
　　d) The color of the area where the first coat of adhesive meets the second coat changes.
　　To verify whether the first sealant is compatible with the second sealant, it typically takes some time for this phenomenon to become apparent. As a general rule, after the insulated glass unit is manufactured, it should be left undisturbed for 20 to 30 days before verification can take place.
           
　　7. The thickness of the sealant applied in the second layer
　　To ensure that the second sealant achieves lower water vapor permeability and excellent sealing performance, the thickness of the second sealant layer must not be less than 5–6 mm. In particular, for insulated glass units using silicone sealant as the secondary sealant—since silicone sealant offers weaker resistance to gases and moisture compared to polysulfide or polyurethane sealants—it is even more critical to increase the amount of silicone sealant applied, thereby guaranteeing a reliable and effective seal.
　　In short, energy efficiency and durability are two essential aspects of high-quality insulated glass. When evaluating and selecting insulated glass, it’s crucial to focus on these two key performance characteristics.