[New Adhesive for Adhesive Binding—Reactive Polyurethane (PUR) Hot Melt Adhesive was first introduced at the Drupa Expo in the year 88. Experts at the time claimed that it was an irresistible adhesive product and was an innovation. Will exceed the traditional wireless glue binding process, so that the processing of difficult jobs to a new level.
After more than ten years of development, PUR adhesives have become more and more popular in UV coated papers and high-filled papers. It is also very suitable for bookbinding such as computer manuals that may require high-strength external forces, and some may Exposure to bookbinding areas with extreme temperature or temperature fluctuations, such as car manuals and maps.
What is PUR technology? Why is it so successful? This article will briefly introduce the development of PUR technology and its latest development trends.
What is PUR technology?
PUR hot melt adhesives are mass-produced PUR toppers with active terminal groups. Cross-linking reactions occur when the active terminal group is exposed to moist air or the moisture of the paper reaches a certain level. After the top polymer is wetted, it penetrates well into the paper, achieving a higher viscosity and a higher paper tension.
After cross-linking, the PUR film exhibits a higher intrinsic strength (cohesion) so that a very durable adhesive film can be formed. PUR film is not only insensitive to printing inks and solvents, but also has extremely strong durability.
If you use PUR hot melt binding book, you can use in ultra-cold or super hot environment. PUR wireless books can be safely stored in a 120°C environment without any loss of quality. In addition, they can maintain good plasticity even at minus 40 degrees.
Adhesive equipment
Despite so many advantages, by the end of 1988, only two German bookbinding companies were using PUR hot melt adhesive technology for wireless adhesive bonding. To be sure, performance is not a problem. PUR technology has been well validated in many market segments. One of the biggest obstacles to development is the need to transform the equipment, especially the system that reacts to this technology.
For example, the plastic box will be covered with thick adhesive after being used for a period of time, and can only be removed after cleaning. In addition, the pressure of the adhesive must be reduced, and the operating temperature must be optimized.
The two German book binding companies that first mentioned the use of PUR technology used the DIY method to modify the structure of the equipment themselves.
In addition to equipment issues, the need for new hot melt equipment has also hindered the growth of PUR technology. Since the PUR adhesive is a moisture-cured system, the adhesive must be isolated and kept absolutely dry. Therefore, the transportation and application of the adhesive must be done with care. This is why the PUR is always transported in full containers and applied by a dedicated melter. The dedicated melter always seals the seal of the tank, avoids contact between the glue and air, and conveniently provides PUR on-demand supply. Due to the need to take glue as needed, the pressure of the system temperature is avoided.
PUR is a perfect process
There are currently more than 150 bookbinding companies in Germany, and hundreds of binding companies worldwide have switched from traditional hot melt adhesives to PUR hot melt adhesives. The new binding device, combined with the latest PUR hot melt adhesive technology, ensures the smooth and complete binding process.
Users of PUR are no longer limited to traditional roller coating applications, but have introduced many new processes and technologies, such as the use of a nozzle system to effectively apply glue to the bottom of each book. With these nozzles, the binding plant can reduce the thickness of the coating to 0.3 mm, making the book unfolded very well.
The thickness of the PUR film can be reduced by 50% or less compared to the standard EVA hot melt adhesive. Although it is more expensive, it is relatively thin, so the two can be complementary.
Third generation PUR hot melt adhesive
The first generation of active PUR hot melt adhesives appeared in the late 1980s and early 1990s, and there has been a rapid increase in processing viscosity. In the beginning, these hot melt adhesives did not have a strong viscosity, and only after the reaction did they achieve strong strength, and the best binding properties were achieved within three to six days after gluing. Therefore, products bound with PUR glue cannot be transported immediately, and transportation can only be ensured without impairing the quality of the product after achieving the best performance.
The second-generation PUR hot melt adhesives appeared in the late 1990s and cured faster. Its curing time is shorter than three days, and the final strength and availability are guaranteed.
Today's third-generation PUR products have faster chemical reactivity, and its high-speed cross-linking properties can be cured in 6 to 16 hours.
This new product offers lower handling tack, as well as better initial strength and viscosity stability, which are required for the tank fuser.
Although manufacturers have made great advances in processing equipment and technology, PUR hot melt adhesives still require more attention than conventional products to determine every detail, especially during maintenance. Although users have certain restrictions on the cleaning of accessories produced by PUR chemical products, these removal products are very effective. Residual adhesive can be removed from dirty tanks, pumps, hoses, and nozzles and other related equipment. substance. Even the glue left in the cracks and crevices of the equipment can be removed.
Avoid environmental issues
Whichever new process is chosen, it needs to consider its environmental issues. Despite the need for extra care when using PUR hot melt adhesives, many users of PUR hot melt adhesives still face the problem of reducing the volatilization of the isocyanates. The "micro-irradiation" PUR hot melt adhesive system contains fewer monomeric iso-hydrogen salts than conventional systems. These products contain less than 0.1% of the monomeric iso-hydrogen acid salt, so it is set as a legal indicator in the European region. After melting, the MicroEmission (micro-radioactive) product is said to emit heat differently than the conventional PUR hot melt adhesive. The acid salt is less than 90%.
in conclusion
Since the late 1980s, PUR has evolved from an enthusiasm for technological innovation to advanced technology that has now been used by hundreds of postpress specialists.
The active PUR hot melt adhesive can meet all the requirements of the wireless glue binding, side coating and backing coating, and completes the saddle stitching and binding of the binding book. They can provide excellent stability, fast curing and other features.
PUR history
There are several types of adhesives that can be used in wireless glue, PUR, EVA hot melt and PVA cold emulsion adhesives or Smythe locks. PUR first appeared in 1989 and is now used to bind hardcover books, annual reports, catalogues, and magazines.
Since its emergence, PUR applications have grown rapidly. In 1995, there were only 28 PUR users. By the end of 2002, this figure had grown to 50 (in North America).
PUR has become the standard hot melt adhesive for a variety of reasons, the most important of which is the high degree of stickiness, and the stability of PUR-bound books, which can spread the book to a very flat nature.
PUR has excellent adhesion to some paints and UV-coated surfaces and has a good effect on film and paper. Due to the polar nature of the polyurethane molecules, this adhesive can also have good adhesion to highly coated paper.
The grammage of the paper, the coating and the ink all do not have a great influence on the bookbinding properties of the PUR. Page tension is 40%-60% higher than conventional adhesives. Moreover, the traditional method will have a certain impact on the quality of the binding because the ink gets into the paper, while the PUR glue will not have any effect on the ink transfer.
