What is PUR technology and its latest development trend

A new type of adhesive for wireless binding-active polyurethane (PUR) hot melt adhesive was first introduced at the Drupa exhibition in 1988. At that time, experts all claimed that this was an irresistible adhesive product and an innovation that will surely Beyond the traditional wireless binding process, the production of difficult operations is raised to a new level.

After more than ten years of development, the application of PUR glue on UV-coated paper and high-fill paper has become more and more popular. It is also very suitable for book binding that needs to withstand high-strength external forces, such as computer manuals, and some may Book binding areas exposed to extreme temperature environments or large temperature fluctuations, such as car manuals and maps.

So what exactly is PUR technology? Why is it so successful? This article will briefly introduce the development process of PUR technology and its latest development trend.

What is PUR technology?

PUR hot melt adhesives are mass-produced PUR top polymers with active end groups. When the active end groups are exposed to humid air or the humidity of the paper reaches a certain level, a cross-linking reaction occurs. After the top polymer is wetted, it can penetrate into the paper well to achieve higher viscosity and higher paper tension.

After cross-linking, the PUR film shows a high inherent strength (cohesion), which can form a very durable adhesive film. PUR film is not only insensitive to printing inks and solvents, but also extremely durable.

If you use PUR hot-melt glue binding manual, it can be used in super cold or super hot environment. PUR wireless bound books can be safely stored at 120 ° C without any loss of quality. In addition, they can maintain good plasticity in minus 40 degrees.

Plastic equipment

Despite so many advantages, by the end of 1988, only two German bookbinding companies used PUR hot-melt adhesive technology for wireless glue binding. It is safe to say that performance is not a problem, PUR technology has been well verified in many market areas. One of the biggest obstacles hindering development is the need to transform equipment, especially the system that reacts to this technology.

For example, the glue 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 temperature and pressure of the adhesive need to be reduced, and the operating temperature must be optimized.

The two German book binding companies that first used PUR technology mentioned earlier adopted the DIY method and modified the structure of the equipment themselves.

In addition to equipment problems, the need for new hot-melt equipment has also hindered the growth of PUR technology. Since PUR adhesive is a system that cures when exposed to moisture, it is necessary to isolate the adhesive and keep it absolutely dry. Therefore, the transportation and application of the adhesive must be very careful. This is why PUR is always shipped in the form of a full box and applied through a dedicated melter. The special melter always seals the seal of the plastic box, avoiding the contact between the glue and the air, and conveniently provides PUR on-demand supply. Because the glue is taken on demand as needed, system temperature pressure is avoided.

PUR is a perfect craft

There are currently more than 150 bookbinding companies in Germany, and hundreds of bookbinding companies worldwide have switched from traditional hot-melt adhesives to PUR hot-melt adhesives. The new binding equipment, combined with the latest PUR hot melt adhesive process, ensures the smooth progress and completion of the binding process.

PUR users are no longer limited to traditional roll coating applications, but have introduced many new processes and technologies, such as the use of nozzle systems to effectively apply glue to the bottom of each book. Using these nozzles, the bookbinding factory can reduce the thickness of the coating to 0.3mm, so that the performance of book unfolding is very good.

Compared with standard EVA hot-melt adhesive, the thickness of PUR adhesive film can be reduced by 50% or thinner. Although its price is more expensive, because of its thinner thickness, the two can be complementary.

The third generation of PUR hot melt adhesive

The first generation of active PUR hot melt adhesives appeared in the late 1980s and early 1990s, and the processing viscosity has increased rapidly. At the beginning, these hot melt adhesives did not have a strong viscosity. Only after the reaction occurred, the strong strength was obtained, and the best binding properties were achieved within three to six days after the glue was applied. Therefore, the products bound with PUR glue cannot be transported immediately. Only after the best performance is achieved, the transportation can ensure that the quality of the product will not be damaged.

The second generation of PUR hot-melt adhesives appeared in the late 1990s, curing faster. Its curing time is shorter than three days, and the final strength and usability are guaranteed.

The current third-generation PUR products have faster chemical reactivity, and its high-speed cross-linking properties can be cured within 6 to 16 hours.

This new product provides lower handling viscosity, as well as better initial strength and viscosity stability, which are all necessary conditions for glue box hot melters.

Although manufacturers have made great improvements to processing equipment and technology, PUR hot melt adhesives still require more attention than traditional similar products to determine every detail, especially when performing maintenance. Although users have certain restrictions when cleaning the accessories produced by PUR chemical products, these cleaning products are very effective, and can remove the residue of adhesive from dirty rubber boxes, glue pumps, hoses, nozzles and other related equipment substance. Even the glue remaining in the gaps and gaps of the equipment can be removed. [next]

Avoid environmental problems

No matter which new process is selected, it is necessary to consider its environmental issues. Although extra care is required when using PUR hot melt adhesives, many users of PUR hot melt adhesives still face the problem of reducing the volatilization of isohydrogenates. The "microradiation" PUR hot melt adhesive system contains less monomeric isohydrogenate than traditional systems. These products contain less than 0.1% of monomeric isohydrogen salt, so it is set as a legal indicator in Europe. After melting, it is said that MicroEmission products are hotter than traditional PUR hot melt adhesives. 90% less salt.

in conclusion

Since the late 1980s, PUR has evolved from a very tempting technological innovation to advanced technology that hundreds of post-processing experts are happy to apply.

Reactive PUR hot-melt adhesive can meet all the requirements of wireless binding, side coating and backing coating, and it can complete the binding of saddle stitching and thread binding. They can provide excellent stability, fast curing and other characteristics.

PUR history

There are several types of adhesives for wireless binding, PUR, EVA hot melt and PVA cold emulsifying adhesive or Smythe lock thread. PUR first appeared in 1989 and has now been used to bind hardcover books, annual reports, catalogs, and magazines.

Since its emergence, the application of PUR has grown rapidly. In 1995, there were only 28 PUR users. By the end of 2002, this number had increased to 50 (in North America).

There are many reasons why PUR becomes a standard hot-melt adhesive, the most important of which is the high viscosity and the stability of PUR bound books and periodicals, which can spread the book to a very flat nature.

PUR has excellent adhesion to some lacquered and UV-coated surfaces, and has a good effect on films and paper. Due to the polar characteristics of polyurethane molecules, this adhesive can also have good adhesion to highly coated paper.

The weight of the paper, coating and ink will not have a great impact on the binding properties of PUR, the page pull is 40% -60% more than the traditional adhesive. Moreover, the traditional method will cause a certain impact on the binding quality because the ink enters the paper, and the PUR glue will not have any effect on the transfer of the ink.