Behind the Urethane

Learn the Testing and Processes that Go into Auto Glass Adhesives

Just getting into an adhesive testing lab is usually quite the process. You must be vetted, of course, and agree not to disclose anything proprietary that you see. Cell phones, cameras and tape recorders are usually verboten too. And you will be escorted at all times, although the areas through which you can travel are limited too. Yes, the art and science of adhesive development is usually quite the covert affair.

Why? Because the adhesives used by auto glass installers are an integral part of the installation process. Indeed, there is no bond and therefore no proper installation without them. Adhesive manufacturers spend months, years, and millions developing products that can be used for proper and complete installations. Is it any surprise they want to keep their competitive advantages confidential?

Such a closed system keeps those involved in replacement from truly understanding what goes on in the lab, and how it translates to real-world installations.

With an eye toward achieving that level of understanding, AGRR magazine worked with three top adhesive manufacturers to understand what goes on in the lab and why it’s important to those who choose adhesive brands. You will see a lot of common themes among the three— and you will see differences. But in each case, the manufacturers have provided this window into their lab, so we can better understand what they do and why.

DuPont: Safety and Testing at the Top of the List

DuPont points out that safety is a core value and engrained into its culture. When it launches products, it tests with great rigor in the lab and through real world testing and actual installations. The goal is to make sure that when a product goes to the field there are no safety concerns—and to ensure that customers have the information and understanding to use the products correctly.

Lab Testing

In order to test you have to have a plan. Most of DuPont’s test plans are built off of OEM specification testing, with the recognition that many aftermarket installations are different than ones done in the automotive plant environment. Because of that, test plans for aftermarket adhesives include some extra evaluations to ensure that our customers
won’t have issues. Such test plans are complex, but can be broken down into a few main categories:

1. Adhesion performance. Tests confirm that the adhesives will not only adhere to the substrates in the field but maintain a robust, durable bond over time. The company also communicates with frit, glass and paint suppliers so it can stay on top of the newest technology in the industry. Many OEMs are using composite substrates like carbon fiber to reduce the overall weight of the vehicle. DuPont’s work with such OEMs allows it to access to see industry trends and evaluate the performance of aftermarket products on these new substrates before they are released to the field.

2. Minimum Drive-Away Time (MDAT). DuPont uses proprietary lab tests that have been developed by its internal engineering team. These tests are meant to characterize how the adhesive cures, builds strength, and absorbs energy in high speed crash events. The data from these lab tests are used in crash simulations that are a result of working directly with OEMs. All of this lab work is meant to build confidence for the final MDAT validation step: a crash test performed at an independent test facility. All adhesive systems are crash tested prior to launch.

3. Application testing. Makes sure that the product can be used in conditions under which customers use and store the adhesives.

4. Shelf life/stability. This is critical to make sure that the performance doesn’t deteriorate over the shelf life of the product.


Depending on the complexity of the development, many people that work on testing, including those in R&D/technical service, but engineering, analytical, quality and  manufacturing. Part of the company’s test plan includes taking new products to customers to get feedback before they are launched to the broader market.


Development time varies. Some developments are built on OEM technology which is usually a faster route to market as a completely new product does not need to be designed. Other projects involve working directly with customers to develop a product to meet specific needs, or to develop innovative new technology, these type of projects usually require more time.

Sika Corp.: Experience and Knowledge

Sika says it calls upon decades of experience, and a vast knowledge of glass bonding applications in the transportation market, to develop tests necessary to support new product introductions. For new AGR adhesives, testing at the development stage is critical to ensure the required safety and performance properties are met. In particular, Minimum Drive-Away Time (MDAT) and crash testing are a critical part of the process to ensure the retention of the windshield in the event of a crash and the safety of the vehicles’ occupants.

Before they are released, new aftermarket glass bonding adhesives undergo rigorous testing that typically falls into three categories: uncured material testing, cured material testing, and MDAT determination.

Uncured Material Testing

When testing uncured material, Sika seeks to define the following application characteristics and properties:
• Density;
• Viscosity;
• Decking behavior;
• Skin time/working time;
• Sag;
• Glass slip properties;
• Cure rate;
• Shelf life.

Cured Material Testing

Testing performed on cured material confirms that the product meets our requirements for strength and durability:
• Tensile strength and elongation;
• Lap shear strength;
• Modulus;
• Hardness;
• Volume resistivity;
• Adhesion to all relevant substrate materials:
• Fritted and non-fritted glass parts (from a wide variety of glass suppliers);
• Trimmed polyurethane;
• Encapsulated parts;
• Painted metal parts;
• PAAS parts.

MDAT Determination

With its Simulated Windshield Impact Force Tester (SWIFT), Sika says it can accurately reproduce the forces experienced by an adhesive in the event of a crash. This proprietary test is used to generate MDATs across the temperature and humidity range where the product will be used. Following SWIFT testing, an actual FMVSS 212 crash test is performed at a third-party facility to validate the product’s crash worthiness. Both SWIFT testing and real-life FMVSS 212 crash tests are vital to the company’s mission to
ensure vehicle occupant safety by providing the safest adhesive available.

The company also continues to perform adhesion tests on an ongoing basis to ensure its materials deliver optimal performance.

SRP Makes Research and Testing a Priority

As a trusted name in the industry and a leader in technology, SRP Products performs extensive research and testing in the development process of all its product offerings. SRP says its first-hand installation experience allows it to pinpoint specific needs not being met in the market.

SRP says its investment and expertise in the auto glass replacement industry helped in determining product solutions with support from its urethane manufacturer, NPT. A considerable amount of industry research along with installer feedback was put into the product development to ensure the formulation raised the standards in this segment.

The testing processes for auto glass adhesives are complex and extensive to ensure the products are the safest in the marketplace and will meet requirement of the Federal Motor Vehicle Safety Standard (FMVSS). A new adhesive undergoes a variety of testing procedures conducted inside and outside of the laboratory. The majority of testing and development takes place in the laboratory, however, it’s equally as important that the products undergo hands-on, field testing within its training department.

The initial laboratory phase of product development is to determine the structural properties through a series of synthesis activities. The compound characterization is evaluated on mechanical properties, rheological behavior, electrical resistivity, adhesion profile and thermal stability testing. A modified Impact Test Machine which can develop a high level of energy in a very short amount of time thus simulating the impact of the car is used to create accurate drive away times at various temperatures and humidity levels. This is all done to ensure product safety in the aftermarket.

Once the formulated product successfully passes all the in-laboratory tests, the second phase of testing begins. Extensive real-world testing is conducted within its network and training facilities. Installing wind-shields, running bead after bead and just making sure the products are installer tested and approved.

Products undergo lab testing including:
• Viscosity;
• Curing kinetic (tack-free time, open time, cure through volume, strength built up);
• Mechanical properties according to stress-strain test (tensile) and lab-shear tests;
• Rheological behaviour by rheometer tests and internal specifications (viscosity, sagging, thixotropy, green strength, output, tail:
• Electrical resistivity (non-conductive) with selection of the proper carbon black filler;
• Adhesion profile depending on the specific market OEM or aftermarket.
• Thermal stability;
• Cataplasma test (adhesion and mechanical properties under high temperature and high humidity stress)

SRP does laboratory and real-world testing as well to make sure the products are chemically sound, safe, and what installers. Once our product passes all the in-laboratory tests, it begins to undergo testing by installers.

A modified Impact Test Machine (which is able to develop a high level of energy in a very short time, simulating the impact of the car) is used to test minimum drive-away times.

New products take from 1-2 years from idea to the fine-tuning and final approval. Although the transformation of a concept into a final product requires a great deal of time, SRP takes great pride in bringing products to the market that are safe and effective every time.

To view the laid-in version of this article in our digital edition, CLICK HERE.

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