Laminated glass is a high-performance building material composed of glass and polymer interlayers, which are bonded together during heating and pressure. Laminated glass is usually subjected to performance tests to evaluate the ability of the material to resist damage or attack. Edge delamination is usually caused by damage or attack caused by the exposed edges of the interlayer of laminated glass. Edge delamination affects the beauty of laminated glass and can be described as a material characteristic called edge stability.
Determining the edge stability of the laminated glass structure is complicated, but it can be checked by various test methods. Exposing laminates to moisture and chemicals, especially at the edges, is the basis of various testing protocols that have led to the development of edge stability ratings.
This article will describe exposure protocols, including natural weathering, sealants, salt spray, and immersion used to determine the edge stability characteristics of laminated glass configurations. The rating process and results of various mezzanine will be discussed. Participants will be familiar with the test scope, purpose and result interpretation of the included tests. This information allows the designator to make informed choices when choosing installation methods, system designs, and laminated glass products.
Edge stability is a performance characteristic that indicates the ability of the intermediate layer to resist delamination when the exposed edge is in a high temperature and humid environment. For natural exposure, a commercial operation location near Miami, Florida (the United States) was selected for the exposure edge stability test. The edge stability defined here is a long-term test on samples exposed to the natural external environment.
The edges are not protected, so they are wet in the early morning (dew) and during fog or rain. It should be noted that Arizona is another natural exposure location for laminate durability testing. The purpose of this site is often to evaluate the comparison of polymer degradation and edge stability due to hot and dry weather. Therefore, during long-term natural exposure in Arizona, edge defects in PVB laminates are usually not noticed or analyzed.
The Edge Stability Number (ESN) is the weighted sum of "Defect Length Percentage", where the weight increases with the square of the depth (expressed in one-sixteenth of an inch-the circular measurement is for reference only). The maximum number of ESN is 2500, and the minimum number is zero, so the smaller the number, the better the edge stability in this environment. This means that any product with a 6 mm layered band around the sample will be rated 2500 (Figure 1). Any product with an ESN lower than 500 is considered a special product. The ESN number is the average rating of all samples in the sample set using the following calculation method:
PCT1 =% defect length, depth <1/16 inch (1.6 mm) PCT2 =% defect length, depth = 1/16 inch to <1/8 inch (1.6 mm to 3 mm) PCT3 =% defect length, depth = 1 /8 inch to <3/16 inch (3 mm to 5 mm) PCT4 = defect length percentage and depth = 3/16 inch to <1/4 inch (5 mm to <6 mm) PCT5 = defect length percentage and depth = ±1/4 inch (> 6 mm)
ESN = 1*PCT1 4*PCT2 9*PCT3 16*PCT4 25*PCT5
A set of samples usually consists of 10 laminates prepared using standard laboratory conditions. According to ASTM D1435, these samples are mounted on a south-facing shelf with exposed edges, with an inclination of 45 degrees. They are rated on site every 6 months and exposed within a set time.
Figure 2 shows the difference between traditional PVB and structural PVB interlayers, both of which are exposed for the corresponding duration in the above positions. Using an ESN of 500 is considered a special criterion, and the structural PVB performed very well in 52 months. The traditional PVB exposure is completed at 46 months, but the structural PVB intermediate layer is exposed for a longer time.
Figure 3 is an enlarged photo of a laminate without edge protection exposed in South Florida, USA, with an ESN of about 100.
Florida Exposure Program data continues to collect various interlayers, and it is impractical to expose laminates for more than 5 years without affecting edge cleanliness. Climate can cause mold and fungus to grow on the edges of laminates, as shown in Figure 3. In order to effectively clean the edges to obtain an appropriate rating, the edges can be changed to provide the wrong ESN.
Natural exposure is often the mainstream method for deriving ESN values, however, it takes at least one year of exposure to discern current or upcoming trends in product stability. The following sections describe alternative tests that are used as predictive indicators or alternative mechanisms for assessing the stability of laminated glass edges when exposed.
The salt spray test exposes the laminate to salt spray and is expected to simulate the environmental conditions in South Florida. The test protocol aims to determine the response of laminates to simulated humid and hot environments and draw conclusions about their long-term performance and use in similar marine climates. The salt spray test does not include intentional or concentrated solar radiation exposure.
Laminated glass samples were produced using standard laboratory practices with traditional and structural PVB interlayers.
The samples were exposed to the salt spray cabinet for 12 weeks, and the edges were visually evaluated for whitening and delamination. The test is conducted in accordance with ASTM B117-11 Standard Practice for Operating Salt Spray (Fog) Equipment. The method involves placing the sample in a hot (35°C) environment where the entire sample (except for the part protected by the bracket/frame) is evenly surrounded by mist generated by a 5% saline solution (Figure 4).
The sample group consisted of 6 laminated samples for each sandwich type, which were continuously exposed to the environment for a selected duration (12 weeks). Table 1 includes the laminate characteristics in terms of initial adhesion, moisture, and thickness of the interlayer before the laminate is exposed to the salt spray cabinet. The exception is the time for grading samples and chamber maintenance outside the cabinet (approximately 1 hour per week).
The whiteness and delamination appearance of the edges of the samples were visually evaluated. The whitishness or delamination of the corner edge is recorded diagonally from the corner, while the whitishness or delamination depth of the straight edge is measured perpendicular to the edge. Measure the depth and length of any edge effects; the average area and maximum depth of the sample set are reported in Table 2.
The samples were kept under environmental conditions for 60 days and re-evaluated. The results are shown in Table 3. After reassessment, the edge whiteness is no longer visible. The study shows that the salt spray test according to ASTM B117 can produce edge whitening and delamination in laminated glass samples in 12 weeks or less, and can be used as an accelerated predictive test for ESN.
In this study, the structural PVB middle layer in the laminate performed better than the traditional PVB in the laminate in terms of edge whitening. As simulated by the salt spray test, both interlayers have good durability when exposed to a continuous climate similar to the ocean, as evidenced by the minimal and reversible edge whitening. The results of this test also show that structural PVB is not as prone to slight edge delamination after being removed from salt spray exposure like traditional PVB.
The interlayer can react with incompatible materials with which it may come into contact. Therefore, direct contact between the intermediate layer and the chemicals used in the sealant or adhesive should be carefully checked and avoided in some cases. When the sealant is in direct contact with the edge of the laminate, this test method is intended to provide guidance on the compatibility of the sealant. According to the product introduction, product modification or special project guarantee, the compatibility test between the commercially available sealant and the interlayer is carried out.
The results are based on the test report, but the intermediate layer manufacturer does not recommend the sealant because the sealant may change and modify from time to time. The test is carried out under a strict agreement, allowing comparisons between the tested products. The test results may not reflect the field performance. When testing in accordance with the prescribed protocol, commercially available sealants that are always compatible with laminated glass have not yet been determined. According to market trends, silicone sealants seem to be most commonly used for laminated glass.
The sealant may contain solvents that are harmful to the interlayer. In most of the cases investigated, in this compatibility assessment, sealants that were considered neutral in curing generally performed better than those that indicated acetoxy curing. In the silicone glass sealant series, the acetoxy-cured sealant has the highest probability of edge effect in laminated glass.
Sealants and other adhesives need to be in close contact with the edges of the laminate during the entire test process in order to evaluate edge effects. The procedure used for the test was recorded and published by Eastman and the North American Glass Association (GANA) as a standard test method for the edges of laminated glass when in contact with sealants and cellophane tape. Exposure requires an ultraviolet condensing chamber, where the irradiance of the UV313 bulb is set to 0.71 W/m2. The continuous exposure cycle is 16 hours of ultraviolet radiation at 66°C, followed by 8 hours of condensation at 60°C. The total exposure time is 3500 hours, and the rated interval is 500 hours.
Edge effects are usually seen as sharp, very small, 2 mm-3 mm (0.08 inch-0.12 inch), edge bubbles, sometimes appearing continuously along the edge, and sometimes very obvious and isolated. The degree of edge effect varies with the sealant or adhesive. The edge effect of sealants and adhesives seen in this test usually reaches a maximum at a depth of about 10 mm (0.39 inches) from the edge, and usually appears as a single bubble. Although sulfide-containing sealants and adhesives may be slightly discolored, they usually have a clear edge effect and will not cause a change in the color of the interlayer
Sometimes, the test cycle will result in minimal or no interaction between the laminated glass and the sealant or adhesive. This does not guarantee the same results in the field, because application, environment and material deviations will affect the response. Sealants, adhesives, gaskets and fixing blocks should first be selected according to their required properties (ie: compression, tensile strength, weather resistance, structure, appearance), and edge effects should be considered after determining the performance level or series. Although the gasket and the fixing block can and do come into contact with the edge of the laminate, the data obtained using this test method is only valid when it is in close contact with the edge of the laminated glass during the entire test.
Use the following criteria to visually rank the data in this test report (Figure 5):
Average depth edge effect: The visually determined average depth at which bubbles, discoloration or haze are observed. The reading is taken from the edge of the laminate to the center of the laminate, and is measured in millimeters (mm). This number is assessed during each exposure time interval
Maximum depth edge effect: The maximum depth of bubbles, discoloration or haze measured from the edge of the laminate to the center. This is the highest number recorded on any edge during any rating interval for laminates in this group. The maximum depth is reported in millimeters (mm) when the test is completed.
Affected length: The sum of the lengths of the edges of the laminate to which the sealant is applied, in millimeters. Bubbles, discoloration, or haze are observed during the exposure interval.
Percentage of length affected: The average length affected by the edge effect divided by the total length of the laminate coated with the sealant. The total length of the sealant-coated laminate is 580 mm.
Average affected area: the average depth of the observed edge effect multiplied by the average length.
Stratified plateau: The maximum and average depths of the last two rating periods are the same.
Edge effects can "move" throughout the test and may vary from interval to interval. The maximum depth seen at any time during the entire exposure procedure is the reported value and has nothing to do with the maximum depth at the end of the test.
The data in Figure 6 shows the data presented in a typical way for structural PVB and structural sealants. The summary data in Table 4 shows the comprehensive data of the general silicone product types and laminated glass compatibility of conventional PVB and structural PVB. The data shown should be used as a reference and guide for the selection of sealants, but should not be regarded as a guarantee of performance.
The immersion test protocol consists of immersing the laminate sample in various liquids for a total of 60 days, plus a control to keep the environment dry. Check the laminate at different time intervals to determine if any edge degradation has occurred.
The purpose of this test is to: 1.) Determine whether the contact of various liquids with the exposed edge of the laminate has an adverse effect on the visual appearance and edge quality of the laminate, 2.) Determine whether the cut edge and the polished edge are affected differently, 3.) Evaluate the laminate after long-term storage to determine the adverse effects of absorbed chemicals and 4.) determine the suitability of the test as an accelerated ESN predictor.
This test does not examine repeated immersion after prolonged drying. There is no known national consensus standard covering this type of testing, so the details of the testing are provided.
The sample structure consists of laminated annealed glass and traditional PVB interlayer. The sample size is nominally 10 cm x 10 cm. Standard assembly and autoclave techniques are used for lamination. Half of the samples were further manufactured by polishing the edges after autoclaving. A zero-time rating was made for visual haze and edge effects.
The samples are then separated so that two of each edge type can be placed in various liquids. The samples were stacked horizontally on a flat surface in a plastic container with enough undiluted liquid to cover the top of the laminate. The edges of the laminate are completely free of container edges to ensure maximum exposure to the cleaning agent (Figure 7).
The sample is covered with the corresponding liquid for a period of time at ambient temperature. The sample is briefly removed from the liquid, rinsed with water to remove any remaining detergent, and dried with a towel before inspection. The samples are rated in this way every day for a week, and then on 14, 21, 28, and 60 days.
The rating includes recording the ambient temperature, visually inspecting turbidity, haze, discoloration, and recording the maximum depth, average depth, and length of any edges. Any flaws are measured in millimeters. After grading the samples, immediately put them back in the liquid cleaner until the next grading interval. This technique is repeated at every interval until 60 days have passed.
In the final rating, the rinsed and dried laminates are stacked and placed horizontally on the top of the corresponding container and balanced with the ambient atmosphere. Except for the rinsing and drying steps, the samples were graded on Day 1 and Week 1 in the same manner as previously reported. The liquids used for exposure are: bleach, washing powder, glass cleaner, dishwashing detergent and water. Generally speaking, no defects of any kind were formed in the samples before 14 days of grading.
During the 14-day rating period, very slight edge whitening (white "fog") was seen on the bleach, glass cleaner, and water samples. The maximum depth of this flaw with bleach and water is 1 mm, and the maximum depth of glass cleaner is 2 mm. By the 21-day grading period, all samples except the dry control showed some form of edge whitening. During the entire 60 days of the submerged part of the test, no edge loosening was seen. Over time, the edge whitening continued to penetrate the laminate, but during this test, the edge whitening never exceeded 4 mm (as seen on the glass cleaner sample). The average depth of the blush is 2mm.
After removing the sample from the submerged part of the test, it was noticed that in the grading on day 1, most of the edge whitening had been greatly reduced or completely disappeared. There is still no edge delamination. On day 7, at the dry level, slight edge turbidity was observed on the glass cleaner sample and the water control. Let's continue. All specimens are also confined to the edges, in some cases they are too small to be seen.
The only exception is sample number 9, glass cleaner, cut/autoclaved samples, which have obvious delamination in the lower right corner of the sample. The layers are in the shape of amoeba, located 15 mm from each edge, and the front of the layer is 20 mm diagonally from the corner. The diameter of the stratification is approximately 3 mm.
All samples except the dry control showed some form of edge whitening during the exposure. In most samples, this whitening of the edges basically disappeared within one day after being taken out of the liquid. Most specimens showed slight edge loosening (release) after being placed in ambient conditions for 1 week after being immersed. There does not seem to be a significant difference between cut edges and polished edges, although some polished edges have less loose edges after drying. During the test and subsequent drying process, it became clear that window cleaners are the most harsh liquid for laminates.
Laminates placed six (6) years later in an unlit environment require re-evaluation of laminates. All signs of blushing on each laminate disappeared. In the case of chlorine bleach, water, and untreated edges, all samples showed no delamination or whitish defects—even edge delamination was recorded during the test. Other samples are usually loosened evenly around the edges, and no sample has a delamination depth of more than 4 mm. The sample does not form a deeper layered area penetration, but the layered area becomes uniform around the edge in most cases, if it exists.
There is no significant difference between the cut/autoclaved edge and polished edge samples. However, the overall edge effect number is very small, and it is difficult to determine whether there are any improvements or disadvantages to the polished edges in this test. From the survey of the tested products, from the perspective of edge blush and layering, glass cleaner seems to be the most demanding cleaner. It is not known whether repeated immersion and drying will change these results, or whether exposure to other solvents or exposure to temperatures higher than ambient will have any effect. Please note that these samples have not yet completed adhesion or other mechanical tests.
Based on the results of this test, it can be determined that the limited (incidental) contact with the test liquid will not have a significant adverse effect on the visible acceptability of laminated glass made from traditional PVB interlayers. This test can also be used as a predictor of ESN performance.
Obviously, the four tests described have different transfer mechanisms to inject moisture or chemicals into the interlayer, which may react in turn and cause edge delamination. Laminated glass is a high-performance building material composed of glass and polymer interlayers, which are bonded together during heating and pressure.
Although this article focuses on test methods for evaluating edge stability, it should be noted that the cause of delamination in the edge or body of the laminate may be caused by many variables, and usually exists in a combination rather than a single factor. If the design and Improper lamination, laminated products with PVB and non-PVB intermediate layers may easily delaminate.
The causes of delamination can be the type and thickness of the interlayer, glass warping, kinking of glass edges, contamination, improper processing, storage and handling, or improper installation, and many other variables. Low ESN itself does not guarantee that there will be no delamination, just as the hot dip test cannot guarantee that the tempered glass will not spontaneously crack.
ESN is a rating that allows users to make decisions about the basic acceptability of a product for a given application. Edge delamination will affect the beauty of laminated glass, while center delamination will affect the impact characteristics and safety performance of the glass during or after impact. If the interlayer does not retain glass fragments. Determining the edge stability of laminated glass structures is complicated, but as demonstrated, it can be checked by various test methods.
For each project, an overall evaluation of the performance of laminated and laminated glass should be completed to ensure that the material can meet the required characteristics in situ. Laminated glass provides many benefits in terms of safety and security through UV shielding, acoustic damping, structure, and vibrant design options. This information allows the designator to make informed choices when choosing installation methods, system designs, and laminated glass products.
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