Waterproofing Mini-Lesson | The Development History of Polyurethane

1. Early 20th Century

The 20th century was a century of rapid development in polymer chemistry, providing a theoretical foundation for the synthesis of polyurethane. In 1937, German chemists first achieved the laboratory synthesis of polyurethane. In the 1940s, polyurethane was first mass-produced industrially. Its excellent plasticity, wear resistance, and chemical stability make it an ideal carrier for spraying technology.

In 1937, Bayer discovered synthetic polyurethane in Frankfurt.

Following World War II, European and American countries made breakthroughs in high-pressure airless spraying and electrostatic spraying, which enabled polyurethane solutions to be applied to automotive parts coating for the first time, marking its official entry into the mass commercial world. By the mid-1950s, polyurethane spraying was widely used in the field of anti-corrosion coatings for furniture and machinery.

However, by 1963, the construction industry had already adopted polyurethane spraying for roof waterproofing. Since then, the evolution of polyurethane waterproof coatings has never stopped. Due to its characteristics such as good film elongation, high tensile strength, good adhesion, small volume shrinkage, seamless waterproofing, strong adaptability to base layer cracks and deformation, and convenient construction and maintenance, it has developed rapidly in the field of building waterproofing and leak sealing.

In the 1980s, the emergence of two-component spraying systems further improved coating strength and construction efficiency. This veteran from World War II finally joined the field of building waterproofing as a rising star in the industry.

2. 1970s-1990s: The World of Oil and Asphalt

China began to study the theory and application of polyurethane waterproof coatings in the 1970s. As the first generation of waterproof coatings, early oil-based polyurethane represented the high-performance benchmark of the old era . As the name suggests, this type of polyurethane waterproof coating contains a large amount of tar, which is an industrial byproduct of coking and coal gasification. It contains a large amount of naphthalene, phenol and other substances that are harmful to the body and the environment . Especially when used in interior decoration, it is more likely to cause harm to the human body.

However, thanks to the excellent elasticity, strength and durability of polyurethane itself, oil-based polyurethane still stands out and has become the dominant force in the high-performance waterproofing market. It contains a large amount of organic solvents, has extremely high VOC emissions (≥400g/L), has a pungent odor during construction, requires strict fire and explosion prevention, and is extremely harmful to human health and environmental pollution.

Asphalt-based polyurethane waterproof coatings are a transitional product after tar-based coatings were phased out. The core issue is that the asphalt used is mostly petroleum asphalt (though coal tar is sometimes used), but the compatibility between petroleum asphalt and polyurethane is not ideal. Furthermore, asphalt contains strong carcinogens such as polycyclic aromatic hydrocarbons (PAHs) , which can easily lead to problems during use. While its environmental friendliness is significantly improved compared to tar-based coatings, it still cannot meet the market's increasingly demanding requirements for environmental protection and health.

The emergence of oil-based polyurethane and asphalt-based polyurethane was of great significance to the development of the building waterproofing industry, but the pollution and health damage they brought were also a microcosm of that era of extensive development.

3. 1990 to 2010s: The Exploration and Rise of Waterborne Polyurethane

With the successive promulgation of environmental protection regulations (such as China's "Air Pollution Prevention and Control Law" promulgated in 1988), VOC emissions were strictly limited, the development of oil-based/asphalt-based products began to be restricted, JS coatings ushered in a period of development, and water-based polyurethane coatings began a difficult exploration and rise.

In 2000, China banned tar-based polyurethane, marking its complete demise. In 2008, the JC 1066-2008 standard, "Limits of Hazardous Substances in Building Waterproof Coatings," was implemented, imposing limits on VOCs, formaldehyde, benzene compounds, and other substances.

Waterborne polyurethane coatings use water as a solvent to effectively disperse polyurethane resin, forming an environmentally friendly coating. This coating system contains almost no or only a small amount of organic solvents, thus offering significant advantages such as low odor, environmental friendliness, energy saving, and convenient application. It perfectly aligns with China's growing environmental awareness and has therefore attracted considerable attention.

However, due to the immaturity of the initial technology, waterborne polyurethane also has problems such as poor water resistance, low hardness, poor film formation and high cost. The tensile strength of early polyurethane was only about 1.0-1.5 MPa; the elongation at break was about 200%-300%, and the overall performance was significantly different from that of oil-based products.

Meanwhile, because toluene diisocyanate, a raw material used in the production of polyurethane waterproof coatings, is a highly toxic raw material, the environmental friendliness of polyurethane has always been questioned by the industry. The GB/T 19250—2003 standard for polyurethane waterproof coatings did not specify environmental protection indicators.

Meanwhile, JS cement polymer mortar, with its natural advantages of being water-based and environmentally friendly (VOC < 50g/L), easy to apply, and cost-effective, rapidly gained popularity and became the mainstream in home waterproofing. Even today, some experienced waterproofing professionals may still confidently tell homeowners that JS cement mortar is more environmentally friendly than polyurethane coatings, partly because they are indeed very experienced professionals.

Therefore, our polyurethane coatings still need to continue to evolve in order to truly establish their dominant position and make everyone feel that "a person who has been away for three days should be looked at with new eyes".

4. 2010s - Present: Green Revolution and Performance Maturity

In the past decade or so, polyurethane waterproof coatings, having learned from their mistakes, have made great strides by applying technologies such as crosslinking (e.g., internal crosslinking, self-crosslinking), composite modification (e.g., epoxy resin, organosilicon, acrylate modification) and aliphatic isocyanates (e.g., IPDI, HDI). These technologies have perfectly solved the problems of poor water resistance and low strength in the early stages.

The 2013 national standard GB/T 19250-2013 "Polyurethane Waterproof Coatings" stipulates that polyurethane waterproof coatings should have a tensile strength ≥1.9 MPa, an elongation at break ≥400% , low-temperature resistance of -35℃ without cracking, and a VOC content ≤50g/L (JC 1066-2008). Manufacturers with sufficiently mature technology can already achieve below 30g/L. This makes JS waterproof coatings next door exclaim, "Wow, how are we supposed to compete?"

Fortunately, JS coatings themselves haven't given up on improving their internal capabilities, undergoing a glorious evolution: with the update of the national standard (GB/T 23445-2009) "Polymer Cement Waterproof Coatings," we see that the tensile strength specified in the standard has reached 1.5-2.0 MPa, and the elongation at break is ≥80% for JS-I type and ≥120% for JS-II type, somewhat salvaging their reputation. Through polymer emulsion modification (such as flexible acrylic emulsion) and cement system optimization, performance is also being improved, and their core advantages of bond strength (≥1.0 MPa) and breathability remain outstanding.

Even so, thanks to its environmental compliance and high flexibility, the new generation of water-based polyurethane waterproof coatings can become the preferred solution for "high deformation bathrooms" such as underfloor heating rooms and light steel structures, achieving differentiated advantages in the era of prefabricated construction and the "good housing" policy; its performance of being more resistant to chemical corrosion and less affected by chemicals such as acids and alkalis is also more in line with the needs of high-end transformation in high-end scenarios such as biology, medicine, and electronic technology.

In any case, in this green revolution that emphasizes both performance and health, the competition and optimization of materials is just a passing scene along the way. The real beneficiaries are the vast number of consumers involved in urban renewal and construction.

5. Embracing innovation and building on past achievements , Canlon elevates the polyurethane epic.

The story then moves to 2013. That year, a white polyurethane waterproof coating called MPU was selected for the National Construction Industry Science and Technology Achievement Promotion Project, and simultaneously obtained EU CE certification and CRCC railway product certification. This surprised many people at the time:

What kind of product is MPU?

What is its unique charm?

When was its manufacturer, Canlon, founded?

It turns out that although the state has explicitly prohibited the use of tar-based polyurethane waterproof coatings in residential buildings, it is an open secret in the building waterproofing industry to produce non-standard products. Many people add coal tar to the coatings to reduce costs. The cost of coal tar is only a few hundred yuan per ton. If coal tar is not added, many other plasticizers are required, and the cost of ten thousand yuan per ton is much higher than that of coal tar.

To differentiate itself from non-standard products and inferior polyurethane coatings, prevent counterfeiting, and eliminate harmful substances such as coal tar and liquid coumarone, Canlon adopts "visible honesty" as one of its business philosophies and proposes to use a "white strategy" to provide consumers with honesty and safety that can be seen with the naked eye.

Starting with white as the base color, Canlon has created a unique anti-sagging polyurethane waterproof coating. This coating has good thixotropic and anti-sagging properties, can be mechanically sprayed, and effectively solves the common quality problems of uneven coating and serious dripping when applying coatings on vertical surfaces.

It turns out that conventional polyurethane waterproof coatings suffer from a slow drying and film-forming time, making them unsuitable for application in harsh environments such as rainy seasons and winter. If they cannot dry quickly, it will delay the construction period, increase the difficulty of construction, and raise costs. Furthermore, for large-scale projects such as the South-to-North Water Diversion Project, large stadiums, high-speed railways, subways, tunnels, and civil defense projects, waterproofing needs to be applied to vertical or sloping surfaces. Conventional coatings tend to run when applied to vertical or sloping surfaces, resulting in a thinner top and thicker bottom, and uneven film thickness, significantly reducing efficiency and increasing construction costs. These hidden problems, often imperceptible to consumers, make it difficult to distinguish between good and bad products in the coating market.

Building on this foundation, Canlon seems to have sensed the pulse of the evolution of polyurethane waterproof coatings and has once again launched the innovative MPU-Pro. This new polyurethane waterproof coating, which adopts an advanced twin-screw extrusion automated and continuous production process, can achieve a 1mm thin coating at 50℃ , greatly saving construction labor costs and reducing material consumption. Compared with conventional products, it has stronger resistance to deformation, and the waterproof coating layer can not be torn when the "structural crack" reaches 20mm .

As a result, Canlon's patent for "A Single-Component Anti-Sagging Polyurethane Waterproof Coating" once again ignited the market, winning the Silver Award in the China Patent Award for Building Waterproofing Industry that year , and being selected for the 2022 Construction Industry Science and Technology Achievement Promotion Project (Waterproofing Special Project) and the 2023 Provincial Manufacturing Single Champion . On March 23, 2023, this material successfully obtained authorization from the Malaysian Patent Office , achieving success both domestically and internationally. On September 1, 2023, the CECS standard "Anti-Sagging Polyurethane Waterproof Coating," jointly drafted and edited by Canlon and China Building Materials Suzhou Waterproof Research Institute Co., Ltd., officially came into effect, marking the beginning of a new era for anti-sagging polyurethane waterproof coatings.

Currently, the building waterproof coating market maintains a steady growth momentum, with an annual growth rate of around 10%. Among them, polyurethane waterproof coatings account for 30.8% of the entire waterproof coating market, mainly used in Class I waterproof design projects, highlighting their unique and important position. MPU has also been applied in projects such as Chongqing West Railway Station, the expansion project of Xinghai Hospital in Suzhou Industrial Park, the industrial R&D building of Suzhou Health Industry Co., Ltd., the Party Political Life Experience Hall in Quanzhou City, and the warehouse construction project of Qiantang District Grain Reserve Center, winning high recognition from the market and customers.