PUR binding

In the binding binding industry, EVA hot-melt adhesives (hereinafter referred to as EVA) have been used more frequently.
According to productivity, quality stability, cost, etc., its demand has increased. However, in order to meet various quality requirements, from a practical perspective, intact products are neither easy nor realistic.

However, in recent years, as an alternative to EVA adhesives, we have developed polyurethane reactive hot-melt adhesives (PURs).
Due to its superior performance, practical production lines are increasing and attract attention. This manuscript is centered on PUR, the new wireless binding production condition.

Binding quality required

The main binding quality should be:

1 For publications for the purpose of long-term preservation such as photo collections and illustrations, the required quality is durability.

2 Requirements for reference books, manuals, recipes, etc. are open.

3 When reusing waste paper, consider the environment where waste is reused.

4 have to be able to replace the flat binding force.

5 For the summer season, it is placed in a car or winter is placed in a cold area. The book or map placed in a cool environment requires heat resistance and cold resistance.

6 Due to the use of petroleum-based inks, it is necessary to prevent the decrease of adhesive strength over time.

7 pairs of reusable papers, etc., because of their short fibers, not easy to glue, try to maintain its adhesiveness.

With these PURs, these requirements can be improved and the benefits can be improved.

Features of PUR

The PUR was heated and melted at 90°C, and the cooling solidified. In addition, cross-linking reaction occurs due to moisture and moisture in the atmosphere and paper, and once the reaction is completed, the adhesive strength, heat resistance, cold resistance, solvent resistance, and recyclability are all superior to those of EVA. characteristic. However, compared with EVA,
In the early stage of adhesive efficiency, it takes a long time and contact with outdoor air causes a cross-linking reaction. Therefore, a special glue applicator that can block air is provided.

PUR is a macromolecular compound having a urethane bond (NH-CO-O), and its terminal is in the form of an isocyanate group. The basic composition consists of a polyol with an active hydrogen end (polyester, polyether, etc.) and a low molecular weight glycol (chain extender), and an isocyanate-based addition polymer. A hard segment formed by the reaction of a diol and an isocyanate group and a soft segment formed by the reaction of a polyol and an isocyanate group (soft segment, van der Waals attractive force) ) A balance can be obtained to obtain an adhesive with both toughness and softness. In addition, isocyanate groups can only produce water and irreversible cross-linking reactions (urea bonds, ureidoformate ester chains, titration bonds). To have characteristic performance.

Because PUR has strong and soft properties, it can meet all the quality requirements at the same time and become the glue that people pay attention to. The following table shows the main performance comparison between PUR and EVA.
Table: Performance Comparison of PUR and EVA






PUR
EVA


Staple strength (Note)
15N/cm or more
5N/cm or so


Durability
More than 100 years, generally 10 years, up and down


Openness is not ideal


Reusability is not easy to crack, and it is easy to split the filter, and the filterability is not good.


Heat resistance
9°C
40°C


Cold resistance -40°C
-5°C


Good solvent resistance is affected


Drying time Early strength 3 minutes Safety intensity 5 N/cm hour Maximum strength 15 N/cm 12 hours Early strength only a few seconds Final strength 5N 30 minutes


Note: The values in the table are representative values, not absolute values. The listed binding strength is tensile strength (9.80665N=1Kgf).

PUR binding production conditions

Since PUR does not immediately exhibit strength after being coated with an adhesive, it cannot be judged immediately, and the binding machine must be adjusted in advance in consideration of its properties. In particular, when the production conditions such as the coating roll pressure are out of the standard, it is recognized that it is impossible to obtain sufficient strength, and it is necessary to comply with the production standards.

The PUR coating method has been proposed by several companies, and there are many kinds of glue applicators, and here the general stick coating is described. In addition, a part of the manufacturers at the cover feeding site adopts a nozzle coating device.

Stapled reaction time characteristics

It should be noted that the PUR should take a long time to reach the maximum intensity. The mastery of changes in its intensity is of great significance to the quality management of the product. The use of paper (coated paper, offset paper) according to the binding style (borderless, saw-stitching) has different strengths and time requirements. In either case, after the book is opened, the book is opened after about 1 hour. It takes about half a day to reach maximum strength. Therefore, it is necessary to test this point when processing and planning shipments such as seal paintings, and leave enough time for ripening.

Strength due to coating roller pressure

When the roller pressure is low, sufficient strength cannot be obtained even after the reaction, and the page break occurs. On the other hand, if the roller pressure is high, the adhesive penetrates into the space between the papers and the opening property is impaired. Therefore, sufficient attention is required.

Strength due to coating amount

Compared with EVA, the coating amount can be less. If the coating amount is increased, although the strength is increased, the openability is damaged. In order to reduce the amount of coating under the premise of no problem in terms of strength, it is possible to achieve excellent open binding.

Strength due to sawtooth depth

The sawtooth depth does not seem to have a significant effect on the use of EVA, but it cannot be ignored. Sawtooth too deep,
It will increase the amount of excess adhesive, which is related to reducing the degree of opening. Therefore, compared to the case of using EVA,
Hope to make the serrations lighter. In terms of shape, the shape of the mouth is better than the shape of △, and the shape of the mouth should be designed to include the strength, the amount of coating, and the degree of opening.

Staple strength changes with time due to ink solvents

EVA is easily affected by the petroleum solvent in the ink composition, and in a sealed storage state, a pattern in a lot of fields may cause softening of the EVA, and the strength of the EVA may decrease, and the sheet may fall off. In contrast to this, PUR is not affected by the solvent and it avoids the loss of the sheet. The printed surface of the entire surface was placed under conditions of high temperature and tight pressure to confirm its change over time. EVA decreased strength and dropped after about 2 hours. However, PUR showed no decrease in strength.

PUR binding equipment

The following equipment is required for the roll-coated PUR bookbinding equipment.

1 Pre-melter with sealing structure not affected by moisture

There are several commercially available products that do not require nitrogen filling. In addition, the pre-melter tank capacity is the use of small rakes or rakes, respectively 10kg, 20kg, 200kg load, a wide variety.

2 Coating device that can be easily cleaned at the end of the job

One-shot 2Ro11 is the mainstream with a roll coater. After the job is over,
The PUR residue after the reaction must be removed, the coating roll and the like must be easily detached, and the adhesive must be easily removed. For this purpose, Teflon is coated in various types, and the amount of waste at the end of the work is also reduced.
It is also possible to take measures such as reducing the tank capacity.

3 Local exhaust device

When PUR is overheated (above 140°C), isocyanate gas will occur, causing effects on the human body, such as irritating the mucous membranes of the eyes, nose, and throat, causing headaches and other symptoms when the amount of inhalation is large. According to experiments, commonly used The operating temperature must not exceed 120°C. However, from a safety point of view, it is advisable to set a temperature control device and a local exhaust device for the heating of the glue so as to promote the gas diffusion and the moisture in the atmosphere to react and lose its vitality (harmlessness). In the case of thicker binding, in order to prevent deformation of the spine and to prevent the adhesive from adhering to the cutting edge, a transfer line that guarantees the drying time still needs to be provided.

Conclusion

Because of the superiority of PUR's adhesive strength, durability, openability, and reusability,
From the production point of view, excellent quality binding can be obtained. However, due to its higher production costs than EVA,
In addition, due to considerations from the production plant, it still requires early equipment investment, as well as operational issues such as the reaction time and the completion of the operation and the need for clean-up operations, so it has not been widely popularized.

In short, we must first promote the understanding of PUR binding, reduce the unit price of adhesives, and create the same level of manufacturing costs as EVA binding, which is probably the key to popularity. There are also convenient conditions for improving the use of adhesives and reducing the cost of special adhesive applicators, which have become an important factor in popularization and promotion.