EVA edge banding adhesive PK PUR edge banding adhesive

2,Strength 

The initial strength of PUR is usually lower than that of EVA, so in summer, there are often occurrences of PUR edge sealing falling off or inability to directly slot and punch holes after removal. Based on experience, a machine strength of 40-50N/18mm is sufficient to meet the requirements for subsequent slotting and punching. After the PUR reaction, the final strength is usually higher than that of EVA, otherwise there must be a major problem with the edge sealing process. The main factors affecting the final peel strength of edge banding include back coating of edge banding, board density, pre milling accuracy, preheating, adhesive amount, adhesive state, and roller pressure. The influence of several factors is similar to the barrel effect, and the final strength depends not only on the weakest factor, but also on the combination of several factors that go against each other. Therefore, in actual production, it is important not to focus solely on a few factors, but to achieve the goal of “not missing any”, identify shortcomings, and focus on “filling gaps” to comprehensively improve. For example, in winter, as the temperature decreases and the pulling force weakens, workers usually resort to rough methods such as increasing the temperature of the glue roller and increasing the thickness of the glue. In reality, the “short board” at this time is that the temperature of the board and edge banding is too low, and preheating is necessary to improve the wettability of the glue. Regarding the minefield of strength, firstly, the standard setting is too high, and it is used as the standard for selecting adhesive. In the group standard for edge banding, the visible surface particle board tensile force requirement is ≥ 4N/mm, that is, 72N/18mm; Secondly, when there are defects in the adhesive state, blindly increasing the adhesive thickness to increase the tensile strength is not only useless, but also prone to serious adhesive overflow and difficult cleaning of the board surface. Practical experience has proven that when there are certain process defects, PUR with higher viscosity can better ensure the stability of strength.

3,Water resistance 

The water resistance of PUR is much better than EVA, which is why the bathroom furniture industry has been using PUR edge sealing for a long time. But the water resistance of PUR is not equivalent to the water resistance of PUR edge sealed boards. The fact that PUR edge sealed boards swell after soaking in water but do not peel off precisely reflects the good water resistance of PUR. Each step of the edge sealing process will affect the quality of the board edge sealing, which in turn affects the water resistance. Therefore, the water immersion test is not testing the water resistance of the adhesive, but whether the edge sealing process is perfect. So using water immersion testing as the criterion for evaluating the quality of PUR is the biggest minefield here. The perfect process requires glue to fill the gap between the board and the edge banding, and the board must not have broken edges or white spots. Separating agent, pre milling, gluing, pressing, trimming, cleaning agent, each process is a necessary condition. From the perspective of the adhesive itself, good wettability and extensibility are more conducive to forming a continuous adhesive film. Generally speaking, less filler has better wettability, and the extensibility of the adhesive film is closely related to its thixotropy. So these two points can be considered as factors when choosing adhesive.

4.2 Board Cleaning
  PUR sticking to the board surface needs to be cleaned in a timely manner, otherwise it will be difficult to clean after curing. The positive significance of this feature is to urge users to solve problems from the source, rather than treating the head and feet. Therefore, the correct selection and use of separation and cleaning agents have become particularly important. The function of the separating agent is to form a continuous protective layer with demolding effect on the board surface, making it easier to clean the residual adhesive overflowing from the board surface. If selected properly, it can save manual cleaning in the backend, greatly improve efficiency, and reduce labor costs. The separating agent must be evenly dispersed within a range of about 1cm from the edge of the board, and should not be excessive to avoid penetrating into the edge and causing local gaps and delamination risks. This requires the nozzle to be adjusted to the appropriate position, usually with the center of the nozzle about 2-3cm above the plate and 0.5-1cm from the edge of the plate. If water-based separation agents are used, the nozzle pressure must be increased to 4-5 bar. The most common COSDINA nozzle on the market has a unique design that can achieve better dispersion and is less prone to clogging. If there are still residual adhesives according to the above process, it may be considered to replace the separating agent or PUR adhesive.
4.3 Cleaning of glue machine
      Glue will age after prolonged heating, ranging from thickening, discoloration, and difficulty in cleaning equipment components to clogging of the glue machine. This is mainly related to the thermal stability of PUR hot melt adhesive. PUR adhesive with good thermal stability does not require cleaning of the adhesive machine during short-term shutdowns. It is recommended to wash it once a year; But if the selected PUR has poor thermal stability, the glue machine needs to be cleaned regularly according to usage habits. From the user’s perspective, it is difficult to determine the thermal stability of PUR in a single adhesive test, although the appearance, strength, water resistance, efficiency, and cost all meet the requirements. This is also the biggest risk and minefield faced by procurement, as there may inevitably be prolonged standby heating in actual production.

5,Cost 

Low priced products are often tempting, but professional and rational users are concerned about the overall cost of use. There are reasons for high prices, and traps for low prices. Pursuing cheapness often results in higher adhesive costs and even damages to the glue machine, affecting production and order delivery time. So when choosing PUR, in addition to price, one also needs to consider the cost impact caused by the amount of glue applied, cleaning work, health intermediate products, and even energy consumption.
5.1 Glue application amount
  Glue is bought based on weight and used based on volume. The surface roughness and density of the material determine the required thickness of the glue. Therefore, in theory, the amount of adhesive required for edge sealing is determined by the surface roughness, board density, and adhesive density of the board after pre milling. The surface roughness mainly depends on the pre milling process. The sharp new milling cutter cuts a sufficiently flat surface, which can meet the requirements with a lower amount of adhesive coating; As the milling cutter gradually wears out during use, there is a certain degree of unevenness on the cutting surface, so more glue is needed to fill it to ensure continuous glue lines.   The density of the board cannot be changed. If a looser board is selected, more adhesive needs to penetrate into the interior of the board to improve the bonding strength.   The density of glue is most closely related to the amount of filler. Increasing the filler can reduce costs, but it will affect the low-temperature wettability of the formula. Usually, transparent PUR without fillers has a specific gravity of around 1.1, but roller coating is prone to wire drawing and contaminating the surface of the board. Practice has proven that PUR with a specific gravity of around 1.2 can improve drawing properties without affecting wetting.   However, in actual production, the various processes may not be ideal, so process factors can also affect the amount of glue applied. For example, the perpendicularity of the pre milling cutter and the glue roller will affect the uniformity of the glue coating, which will inevitably increase the amount of glue applied; The viscosity of the adhesive can affect the transfer rate from the glue roller to the board, so the amount of adhesive applied for adhesives with poor thermal stability may change at any time due to changes in viscosity; Whether the adjustment of the conical wheel is appropriate and whether the pressure is uniform. If the pressure is insufficient, the glue line will be thicker, the penetration will be insufficient, and it is more likely to cause pinholes, gaps, and low strength. Therefore, in order to achieve the theoretical minimum amount of glue, it is not enough to thin the glue on the glue roller. It is necessary to adjust every step of the process that affects the edge sealing effect in place.
5.2 Cleaning Work
  The overflow of glue in the edge sealing and pressing wheel composite process is inevitable, even for laser edge sealing. Therefore, separation agents and cleaning agents are standard equipment for edge banding machines. However, the difficulty of cleaning PUR varies greatly among different formulations. Although the adhesive line thickness of unfilled PUR can theoretically be very thin, the overflow of adhesive during roller coating is severe, and the subsequent process requires a large amount of manual cleaning. Generally speaking, adhesives with more fillers and shorter opening times are relatively easy to clean.
5.3 Health intermediate products
  Compared to EVA, the impact of PUR on efficiency is mainly reflected in low temperature environments in winter and high temperature environments in summer. Adhesives with poor low-temperature wetting cannot be processed immediately and require 1-2 days or longer for curing, even requiring a curing room; The initial strength increases slowly at high temperatures, and it needs to be left to rest for several hours before slotting and punching holes. Of course, PUR technology has been advancing, and winter and summer specific formulas can now achieve online slotting and punching at both 0 degrees and 40 degrees, greatly reducing intermediate inventory, thereby improving turnover and reducing costs.
      In summary, the edge banding process is a complex system engineering, with unique requirements for glue in each step of the process, and even some requirements are contradictory to each other. For example, it is necessary to have both high initial strength at high temperatures and good low-temperature wettability; Not only should it have a long opening time and good wetting properties, but also the surface of the board should be easy to clean; It requires both high initial adhesion and good extensibility of the adhesive film. Therefore, when designing the formula for effective PUR adhesive, it is necessary to make trade-offs and balance various performance indicators. Excessive pursuit of one aspect of performance will inevitably affect others, and universal glue does not exist. Therefore, choosing glue is also a technical task, and it is necessary to know oneself and others in order to select the most suitable product for oneself.