Glass adhesive: common problems and solutions for neutrality

Sealants are mostly classified as constituent adhesives, and their main body is polymers. Their properties can be divided into three categories: bulk properties, process properties, and application properties (commodity functions). The application nature (product function) clearly refers to the inductive function of the sealant from the formation of the bonding process to the formation of the bonding joint, which depends on the functional requirements of the sealant for the construction of the joint. Whether it is related to the construction of peripheral protection or indoor decoration; Whether it is window construction or other forms of enclosure and decoration construction, they can be regarded as unit components, and joints occur between each unit. The vast majority of construction requires sealing and filling with sealant. The reasonable design of joint construction, understanding and understanding of sealant construction, reasonable material selection, and accurate construction of sealing are essential throughout the entire process to ensure the success of joint sealing construction.

1. Analysis of Bubble Causes

The reasons for the foaming of silicone weather resistant adhesive during construction are multifaceted and complex, making it difficult to determine the cause of foaming using one method and one result. Silicone structural sealants are generally injected in factories, where the environment and operating conditions are relatively good, making it easy to meet the external conditions required for curing silicone structural sealants. Silicone weather resistant sealants are generally completed at the construction site for injection work. The construction site environment and working conditions are poor, and the external conditions required for the curing process of silicone weather resistant sealants are not easily met. The non human factors such as climate, environment, and operating conditions have a significant impact on the curing quality of silicone weather resistant adhesives. So the limitations of the environment and operating conditions in which silicone weather resistant adhesive is used determine the main reason for foaming. Below is an analysis of some specific situations.

(1) Air trapped during glue injection

Silicone weather resistant adhesive is generally completed at the construction site, resulting in poor working conditions. Workers stand on scaffolding to inject glue, but the uniformity of the glue injection is difficult to grasp, and air is easily trapped inside the glue joint. After the glue is applied, the surface of the glue seam is scraped and polished. The cushion rod inside the glue seam is generally closed polyethylene foam rod. The air wrapped in the glue seam is not easy to overflow. After the air for the glue seam trimming is compressed, it will produce outward uplift tension. The weather resistant glue seam is generally wide and thin. The weather resistant glue that provides high displacement capacity is low in hardness and very soft before the glue is cured. The high tension of compressed air slowly puffs up the adhesive seam. This phenomenon is more likely to occur in the application of weather resistant adhesive that can provide a displacement capacity of more than ± 25% of the adhesive seam. On the contrary, some weather resistant adhesives with lower allowable displacement have higher hardness and become thicker before curing. The tension of compressed air wrapped in the adhesive seam is not easy to support the adhesive and cause bubbles. So, the more weather resistant the adhesive can provide high displacement ability, the more attention should be paid to the uniformity of the adhesive during injection. Vertical adhesive joints can generally be glued from bottom to top, which can overcome some foaming phenomena. More importantly, the proficiency and sense of responsibility of the work operator.

(2) Wet interface during glue injection

When working outdoors, we often encounter rain, especially in summer in the south, it rains almost every day. If the interface is wet after rain, glue will be injected directly. When the sun shines on the bonding substrate and glue joints, the temperature inside the interface will rise, and the moisture inside the glue joints will evaporate, which will blister the uncured and soft glue joints. Sometimes the polyethylene foam cushion rod is wet, which will also cause the glue joints to blister. So during construction, it is not advisable to blindly pursue progress. Wait until the interface is dry before injecting glue to avoid the above situation.

(3) Foam rod deflation

Generally, the cushion rod in the glue seam is closed cell high foaming polyethylene foam rod. Due to improper extrusion during placement, the internal air bag will burst and release air. When the glue is just injected, there will be bubbles or bulges. The solution to this problem is to cut the foam rod and cut it to the inside. The second is to use open cell foam rod or foamed ethylene foam rod to overcome the above situation. On the other hand, methanol will be released from alcohol type weather proofing adhesive during curing, and methanol will react with some foam rods. In this case, the problem was solved by replacing the foam rod or ketoxime sealant.

(4) When the adhesive is not cured, it is exposed to the sun

Silicone adhesive should not be exposed to the sun before curing, especially when exposed to the sun just after injection, which can cause honeycomb like bubbles inside the adhesive joint and cause external protrusion. This situation is more obvious when using alcohol based silicone adhesive. This situation is difficult to overcome during construction in the hot summer. When using glue injection, avoiding direct sunlight can overcome some foaming phenomena. Specific method: inject glue on the west or north side of the building in the morning, and inject glue on the east or south side of the building in the afternoon. After injection, the adhesive has solidified for a period of time, and the surface has formed skin. When exposed to the sun again, it has a certain resistance and can overcome some foaming phenomena.

(5) The surface temperature of the substrate is too high

When silicone adhesive is cured, the temperature of the adhesive material cannot exceed 50 ℃, which has been recognized by most silicone adhesive manufacturers. When the surface temperature of the substrate exceeds 50 ℃, injecting adhesive can cause blistering of the adhesive joint, which can be encountered during weather resistant caulking of metal curtain walls. In hot weather, when the metal plate is exposed to sunlight, especially when the surface temperature of the aluminum plate reaches 80 ℃, the injection of glue can easily cause blistering of the adhesive seam. So you should choose the latter half of the afternoon or cloudy day to improve the above situation.

(6) Large temperature difference between day and night, large thermal expansion of interface

This situation is more likely to occur when injecting glue into aluminum curtain walls. Aluminum plate is a material with large linear expansion coefficient. In spring or autumn in northern China, the temperature difference between day and night is large, and when the sun directly shines on the aluminum plate at noon, the surface temperature of aluminum plate can be as high as 60 ℃ -70 ℃, and the temperature drops to about 10 ℃ at night. For large aluminum plates, thermal expansion are also large, and the interface displacement is large. After the weather resistant adhesive is caulked, the actual displacement of the interface is borne by the adhesive joint. During the curing process, excessive Repeated stretching and displacement can cause blistering in the adhesive seam, so avoid direct sunlight at noon during glue injection to improve some of the aforementioned blistering conditions.

(7) The climate in the northern region is dry in spring

Silicone sealant needs to use moisture in the air to chemically react to form an elastic sealing material. The magnitude of humidity in the air is closely related to the curing rate. The climate in the northern region of China is dry in spring, and the curing time of silicone sealant after injection is very long. Before curing, silicone sealant is easily affected by the external environment, providing opportunities for various foaming phenomena.

2. Why is the deep curing of sealant slow?

Firstly, the objective conditions of adhesive application have a significant impact on the deep curing speed. The construction environment, temperature, and humidity have a significant impact on the curing rate. Low temperature and high humidity can significantly slow down the deep curing process. In addition, there is also the ventilation situation at the construction site, and if the air circulation is not smooth, it will also affect the deep solidification. In addition, the design of the adhesive joint also has a significant impact on the deep solidification. When the width to depth ratio of the adhesive seam is not appropriate or the depth is too deep, deep curing will be slower; In general, deep curing is slightly slower and does not affect actual engineering use without quality issues such as foaming or internal failure to cure. The national standard stipulates a curing period of 21 days for specimens, while the thickness of the tested specimens is equivalent to that of the actual engineering application. That is to say, the national standard recognizes a complete curing time of 21 days, while our response to slow curing is far less than 21 days (generally exceeding 5-7 days is considered slow drying); In addition, we believe that curing the sealant too quickly is not good for long-term use, as it is not conducive to releasing the stress caused by temperature during the curing process and poses a hidden danger. If the curing time of concrete is limited, if it is too fast, it will lead to stress concentration and cracking.

Why does the sealant crack after curing?

There are very few cases of cracking in the middle of the real adhesive strip after curing, and due to the limited number of cases and unclear understanding of some objective situations, it is impossible to accurately determine the cause of the occurrence. The cracking here mainly refers to the phenomenon of delamination on one side of the substrate caused by poor adhesion to the substrate, also known as cracking.

The main reasons for this are as follows (excluding inferior glue):

1、 It is due to poor compatibility or no compatibility test conducted at all, that is, the incompatibility between the adhesive and the substrate leads to cracking.

2、 It is due to construction reasons, such as the substrate surface not being cleaned or improper construction, such as construction without drying the solvent or contamination after cleaning for too long.

Most of the reasons for the cracking of sealant after curing are due to improper construction.

4. Why is the surface of the adhesive strip wrinkled and uneven after curing?

This situation occurs more frequently when applying adhesive to vertical joints, and the reason for this analysis should be that in the early stage of adhesive application, the wetting speed of the adhesive on the surface of the substrate is slow, which means that the initial bonding force is poor, causing the sealant to sag due to its own weight and form wrinkling and unevenness; It is recommended to extend the trimming time as much as possible within the allowable range during construction, while changing the trimming operation and using a scraper to trim the edge from the bottom of the adhesive joint upwards; During trimming, attention shall be paid not to over squeeze, otherwise the cushion foam rod may be deformed, and then the foam rod will gradually recover, leading to the overall bulge of sealant.

Why does porcelain white sealant turn yellow or red?

Occasionally, this situation may occur with alcohol based adhesives. The analysis may be due to the unstable quality of the additives added, or it may be caused by contamination of accessories or other materials that come into contact with the cured adhesive strip.

Why does neutral transparent adhesive (ketoxime type) turn yellow or even red after curing?

Ketoxime transparent adhesive (including light colored adhesive) will experience varying degrees of yellowing after about 20 days of curing, and the yellowing trend will worsen over time. The yellowing of ketoneoxime transparent adhesive is not a problem for individual manufacturers, but a problem that exists throughout the entire industry of a product, including foreign manufacturers. After analysis, it may be due to the addition of coupling agents with amino groups.

Although yellowing is an inherent defect in current products, the curing environment has a significant impact on yellowing. Firstly, ketone oxime type transparent adhesive cannot coexist with acid adhesive and alcohol adhesive. If it is mixed with the other two types of adhesive for less than three days, ketone oxime type transparent adhesive will seriously turn yellow. In addition, placing the cured ketoxime type transparent adhesive in a dark and damp corner will also cause it to turn yellow until it turns red.

Why does sealant have poor adhesion to some building materials (such as aluminum, aluminum-plastic panels, steel, etc.)?

Firstly, let's talk about the diversity of building materials: There are a wide variety of building materials on the market, such as aluminum, which includes sprayed aluminum and anodized aluminum. Sprayed aluminum materials can be divided into various coatings such as electrophoresis and fluorocarbon, with different surface properties. Therefore, it is necessary to know the advantages and disadvantages of adhesion through experiments. Plastic steel profiles are generally made from PVC (polyvinyl chloride), and plasticizers and fillers are also added. However, there are many manufacturers now, and the materials used are not the same, so there is also great uncertainty.

Furthermore, the instability of sealant: As a chemical product, many factors that affect quality cannot be directly observed. Therefore, we suggest conducting compatibility tests before construction.

8. Why does weather resistant adhesive sometimes dry too quickly, resulting in insufficient repair time?

The surface drying time of weather resistant adhesive is between 30-40 minutes, which is not short for normal construction. However, when the construction environment changes significantly (such as high temperatures), the surface drying will become faster, resulting in insufficient repair. Similarly, when the temperature decreases, the surface drying time will be extended. Therefore, if the surface drying time is considered to be moderate during high temperatures, the surface drying time will be longer when the environmental temperature decreases, which will make the adhesive removal time longer, This will affect the acceptance of the project. So to reduce the impact of fast surface drying, it can be improved by adjusting the number of trimming times appropriately.

Why do uneven conditions such as mottled lines appear after the sealant is extruded?

The occurrence of such phenomena is mainly caused by pollution during the production or packaging process, and is a production quality control problem.

Why do I sometimes find a small amount of brittle solid near the bottom cover of sealant bottles?

This is a basic phenomenon in current products. The reason for the formation is that the bottom cover and bottle body are not tightly sealed, resulting in a small amount of adhesive curing nearby. When the adhesive solidifies, it will form a brittle and hard solid when in contact with plastic. This phenomenon does not occur when in contact with other materials, and there will be no quality issues.

11. Why are there particles inside the sealant?

If there are large particles or rubber sheets inside the sealant, it is a control problem in the production process and can be solved by strengthening management and control.

If there are small particles inside the sealant, they need to be treated differently, mainly in two situations:

One is the particles of powder, because all adhesives require the addition of reinforcing fillers, the most commonly used being calcium carbonate and white carbon black, which are solid substances. When solid and liquid are mixed, due to the small size of solid particles, the surface can easily form aggregates, making it difficult to completely disperse in the liquid and form some small particles. The basis for determining whether it is a powder particle is to pick out the small particles inside the adhesive and roll them with your hand to see if they are still present. If not, it indicates that it is a powder particle; Although small particles can be seen during actual application, the adhesive itself has a leveling property, and the surface can slowly flow flat to cover some small particles. Moreover, during application, it is an ultra close observation, and if viewed slightly from a distance of about one foot after construction, many particles are difficult to detect.

When the particles are still or become smaller after being crushed by hand, it is called skinning, which needs to be avoided in production, but there is also a probability problem of occurrence.