Application experience of PUR adhesive

PUR (PolyUrethaneReactive) is polyurethane, which is a polymer with recurring structural unit of urethane segment formed by the reaction of isocyanate and polyol. PUR products are divided into two categories of foamed products and non-foamed products. Foamed products include soft, hard, semi-rigid PUR foam plastics; non-foamed products include coatings, adhesives, synthetic leather, elastomers and elasticity Fiber etc. PUR materials have excellent performance, a wide range of applications, and a wide range of products. Among them, the outstanding representative-PUR adhesives are being more and more widely used in wireless binding products in the printing industry.

Development history of PUR adhesive

Since the development of PUR adhesives, it has been nearly 20 years of history, and its development has roughly experienced four stages.

PUR adhesive appeared in 1989, and was first tested and applied on a manual binding system in North America. At that time, the first generation of PUR adhesive required more than 24 hours of curing time to ensure the strength and appearance of books and periodicals.

The second-generation PUR adhesive was developed in 1994. It can already be cut online, the stack thickness has also increased, and it can be cut within 4 hours after binding.

The curing time of the third generation PUR adhesive is only 1 hour, even if there is still a considerable amount of moisture in the paper. After cutting, you can pack it, but it also has certain side effects. Because the PUR adhesive can quickly reach the relative strength, the PUR adhesive in the glue pot becomes very heavy. In a humid environment, this This situation is more obvious.

At present, the fourth-generation PUR that has been widely applied has been very mature, with a shorter curing time and a thinner adhesive layer than the third-generation, but it has the same strength and can be stored for a longer period of time. The current generation has largely replaced the second and third generation PUR adhesives. [next]

Application experience of PUR adhesive

Due to the development of PUR adhesives, the current market share is still low. According to the statistics of 2008, it is only 10% (weight ratio) in Europe, which is the most widely used, and lower in China. But precisely because of its advantages, it is currently growing at a rate of more than 20% per year, and the prospect is very broad, while ordinary hot-melt adhesives are declining at a rate of 5% per year.

The company where the author is located is a large-scale printing group mainly focusing on books and commercial printing. It has factories in Beijing, Shanghai and Guangdong. As one of the industry leaders, it is brave to pioneer the industry in terms of investment and application of new technologies. .

As early as 2005, we introduced the PUR technology. At that time in China, few dare to try. At that time, our equipment itself did not have the PUR binding function, but after more than 4 years of continuous improvement and application of the equipment, we have mastered the related technology of using PUR adhesive to produce beautiful books and periodicals.

Before the introduction of PUR glue binding technology, orders made by overseas customers that require the use of PUR glue can only be rejected. In addition, when encountering orders with large ink levels and surface coating varnishes in production, problems such as page breaks and misalignment often occur, which makes the production department very headache. After the introduction of PUR technology, these problems have been solved, which has provided us with a strong help in enhancing our competitiveness and product quality. [next]

1. PUR binding process implementation process and recommendations

For colleagues who intend to introduce PUR binding technology, combined with our experience, we give the following suggestions.

First of all, in terms of products, if the plastic products produced by the company have the following situations, you can consider introducing PUR technology: ①Customers require more orders to use PUR; ② often produce large ink level plastic books; ③ the text has been surface-treated (Coated with UV / varnish / adhesive layer) there are many bound books; ④Atlas, fine art albums, etc. need to spread out all the books; ⑤Wireless square back hardcover books.

Secondly, in terms of equipment, there are currently two types of PUR glue application systems, which are roll coating and spray coating. The principle of roller coating is similar to the packaging and decoration of ordinary EVA coating system. A thin layer of PUR adhesive is applied to the back of the book using an adhesive roller. However, it requires finer scratch marks than ordinary coating, which requires glue binding. A fine grinding system must be installed on the linkage line to lightly draw the fiber on the surface of the paper and cross-link with the PUR adhesive; the spraying method also needs to be processed by the fine grinding system, which is different from the roller coating method. Use a nozzle to spray PUR glue onto the spine.

2. Other considerations

(1) Some PUR adhesives contain trace amounts of organic substances, isocyanates (Isocyanates) before unreacted. If this chemical substance is exposed or inhaled for a long time, the human body may be allergic. Therefore, it is recommended not to work in confined spaces. It is used in a good environment or an environment equipped with appropriate exhaust equipment, and it is completely cured after it is used in the production of plastic binding, and there is no longer a safety problem;

(2) When storing, it should be placed in a confined space without light, and it is isolated from moisture to avoid irreversible curing reaction;

(3) Always wear gloves, goggles and other personal protective equipment during operation.