Selection and use of edge sealing hot melt adhesive and summary of hot topics!

Edge sealing hot melt adhesive is a type of adhesive specifically used for pasting artificial boards. It is an environmentally friendly, solvent-free thermoplastic adhesive. When the hot melt adhesive is heated to a certain temperature, it transitions from a solid state to a molten state. After being coated on the surface of the artificial board substrate or edge sealing material, it cools down to a solid state, bonding the material to the substrate.

From the late 1970s, hot melt adhesive began to enter the wood industry, used for edge sealing, plywood core, panel splicing, furniture tenoning, etc. The early hot melt adhesive equipment mainly relied on equipment from countries such as the United States, West Germany, and Italy.

 

With the increasingly mature and stable hot melt adhesive equipment in China, selecting and using hot melt adhesive equipment suitable for the specific situation of various furniture factories can not only improve the quality and grade of furniture, but also improve production efficiency, reduce the difficulty of panel repair, and reduce labor intensity for workers.

Composition of hot melt adhesive

Hot melt adhesive is a 100% solid thermoplastic high molecular weight polymer that does not require solvents during processing and application. It is non-toxic and odorless, and its components are roughly divided into high polymers, tackifiers, viscosity control agents, antioxidants, heat stabilizers, and fillers.

Main material

The main material of edge sealing adhesive is thermoplastic resin or elastomer, which is the main component of hot melt adhesive. According to different usage intentions, the main materials used for hot melt adhesives include ethylene and its copolymers, polyurethane, polyamide, polyester, polyolefin, styrene and its copolymers, as well as polyvinyl alcohol, cellulose, polyvinyl butyral, etc.

Patch enhancer

Adhesive enhancers refer to a class of amorphous hot melt polymers with a relative molecular weight of several hundred to several thousand and a softening point of 60-150 degrees Celsius. Its main function is to reduce the melt viscosity of the hot melt adhesive, improve the wettability and initial resistance of the adhesive after melting, and achieve the intention of increasing bonding strength, improving operational performance, and reducing costs.

Wax

Wax is also one of the main components of hot melt adhesive. Its function is to reduce the melt viscosity of the adhesive, improve flowability, shorten exposure time, improve creep resistance, flexibility, and melting speed, reduce the appearance of wire drawing, and avoid self adhesion of the adhesive material; It can also reduce the cost of adhesives. But the addition of wax can also reduce the cohesive strength and bonding strength of the hot melt adhesive.

Filler

Fillers are often added in hot melt adhesives to reduce costs, reduce volume reduction and excessive permeability after curing, improve the heat resistance and thermal capacity of edge sealing adhesives, and extend the operating time of the adhesive. The amount of filler is generally below 15% (mass fraction), and adding too much will increase the viscosity of the adhesive too much, reducing adhesion and resistance.

plasticizer

Adding plasticizers to furniture edge sealing adhesive can reduce melt viscosity, accelerate melt speed, and improve flexibility and cold resistance; The dosage generally does not exceed 10% (mass fraction), and excessive dosage will reduce the heat resistance, cohesive strength, and bonding strength of the adhesive.

Antioxidants

The function of antioxidants is to avoid oxidation and differentiation of hot melt adhesives, as well as to avoid adhesive degradation and decrease in adhesive strength. It is generally believed that when hot melt adhesives are heated at 180 to 230 degrees Celsius for 10 hours or when the composition used has poor thermal stability (such as alkane wax, resin rosin, etc.), it is necessary to add antioxidants.

Selection of edge sealing hot melt adhesive

Base material for edge sealing hot melt adhesive

Edge sealing hot melt adhesive can be divided into three categories according to different base materials:

(1) EVA (ethylene vinyl acetate copolymer resin) based hot melt adhesives can be divided into two types: filled and unfilled.

(2) POL YAMIDE (polyamide) based hot melt adhesive has excellent heat resistance and rapid curing characteristics, with the main drawback being its high price.

(3) HMPU (polyurethane) based hot melt adhesive is the best type of hot melt adhesive in terms of performance, ensuring high-quality sheet edge sealing. It is expensive and requires special usage methods.

Viscosity of edge sealing hot melt adhesive

The viscosity of edge sealing hot melt adhesive cannot directly reflect the performance of the adhesive. In general, the higher the viscosity of edge sealing hot melt adhesive, the better its initial adhesion strength, but the worse its coating performance. Low viscosity hot melt adhesive has a smaller coating amount and better wetting performance.

Some hot melt adhesives with low viscosity and fast curing speed may also have high initial adhesion strength. For poor quality particleboard, high viscosity hot melt adhesive needs to be used for edge sealing. This is because high viscosity hot melt adhesive has poor flowability, and it is not as easy to enter the pores at the edges of the particleboard as low viscosity hot melt adhesive when applying, so that the hot melt adhesive can be fully applied to the edges of the board.

Density of edge sealing hot melt adhesive

The density of edge sealing hot melt adhesive is generally between 0.95-1.6g/cm3, and its density depends on the amount of filler (the more filler, the higher the density). Due to the requirement of reaching a certain adhesive area when sealing the edges of the board, the adhesive amount per unit length of unfilled hot melt adhesive with low density should be smaller than that of filled hot melt adhesive.

Moreover, due to the good bonding performance of unfilled hot melt adhesive and achieving the same edge sealing effect, it is possible to use less unfilled hot melt adhesive than filled hot melt adhesive. To reduce the amount of adhesive applied, the edge banding machine must have a good adhesive system.

The softening point and usage temperature of edge sealing hot melt adhesive

The softening point is an indicator of the heat resistance performance of the edge sealing hot melt adhesive. The higher the softening point, the less likely the edge sealing hot melt adhesive is to melt. At the same time, the softening point is also an important aspect of measuring the temperature resistance performance of panel furniture.

In Europe, there is already a set of testing methods for the heat resistance of panel edge sealing, and standards have been proposed for the heat resistance of panel furniture. France, Germany, Italy and other countries no longer produce low softening point edge sealing hot melt adhesives on a large scale, but domestic manufacturers (including Taiwanese manufacturers) still produce and provide them to the domestic market. The reason is that domestic furniture manufacturers and consumers currently do not pay enough attention to the heat resistance of panel furniture, especially kitchen furniture.

Opening time of edge sealing hot melt adhesive

The opening time of edge bonding hot melt adhesive refers to the period of time from the beginning of adhesive application to the time before pressing the edge bonding tape onto the substrate. The opening time varies with different types of adhesive. The feeding speed and opening time of the edge banding machine are closely related, and both are very important in the selection and use of hot melt adhesives. The edge banding machine with fast feeding must choose hot melt adhesive with short opening time, otherwise, choose hot melt adhesive with long opening time.

For most manual edge banding machines, due to manual operation by workers, it requires the opening time of the hot melt adhesive used to be long enough to facilitate edge banding of bent parts.

For automatic or semi-automatic edge banding machines, due to the fact that the substrate and edge banding strip are quickly cut off, trimmed up and down, and polished after being coated and pressed, the edge banding strip needs to withstand mechanical cutting forces during these processes. Therefore, it is required that the hot melt adhesive has a short opening time and high initial adhesion strength.

Use of edge sealing hot melt adhesive

Temperature during edge sealing

Due to the influence of temperature on the performance of edge sealing hot melt adhesive, temperature is a very important indicator to pay attention to during the edge sealing process. The temperature of the hot melt adhesive, substrate, edge sealing material, and working environment (in the workshop where the edge sealing machine is located) are all very important edge sealing parameters during edge sealing.

The working environment temperature of the edge banding machine can affect the curing speed of the adhesive. Factories often encounter edge sealing problems during low temperature seasons, due to the accelerated curing speed of hot melt adhesives at low temperatures and the shortened effective bonding time. If the feeding speed of the edge banding machine cannot be changed (in most cases), it is necessary to preheat the plates and edge banding materials to ensure edge banding quality.

Treatment of edge sealing adhesive line

The adhesive line between the board and the edge banding strip after edge banding can have a negative impact on the appearance of panel furniture. Excessive adhesive application will make the adhesive line obvious, and conversely, it will reduce the edge sealing strength. The causes of discontinuous or uneven adhesive lines are multifaceted, and the following factors should be comprehensively considered:

The cutting accuracy of the sheet metal must be maintained at a 90 ° angle between the edges of the sheet metal and its plane; Is the pressure distribution of the edge banding machine pressure roller uniform and appropriate, and the pressure direction should be at a 90 ° angle with the edge of the sheet metal; Whether the gluing roller is intact, whether the hot melt adhesive is evenly applied on it, and whether the amount of glue applied is appropriate; The sealed edges of the board should be stored in a relatively clean and dust-free area as much as possible. During the sorting process, avoid contact between dirty objects and the adhesive line.

Maintenance of edge banding machine and hot melt adhesive

Temperature of the rubber can

When the edge banding machine is not in operation, the temperature of the adhesive can should be reduced to around 150 ° C. On the one hand, it can avoid carbonization of the hot melt adhesive when it is used at a temperature for a long time, keep the adhesive can clean, and will not cause blockage of the adhesive supply system and reduce heating performance; On the other hand, when working again, it is possible to quickly raise the temperature of the rubber can to its operating temperature.

Cleaning of rubber cans

Regularly clean the glue cans and glue rollers. Excessive carbonization around the glue cans and residue on the glue rollers will reduce the performance of the heating system and glue supply system.

Removal of residual adhesive

If you want to remove the remaining glue in the glue can, before the edge banding machine stops working, when the glue is still in a molten state, place a T-shaped object into the glue. After the glue has completely cooled, reheat it. As the glue at the bottom and around the can is first melted by heat, most of the remaining glue can be removed using a T-shaped object.

Questions about hot melt adhesive

1. Is thermal adhesive hot melt adhesive?

Thermal adhesive is actually hot melt adhesive, perhaps a dialect term for "hot melt adhesive". The dialects in China are diverse, and the same word may come from different people's mouths and have different pronunciations. Moreover, the literal understanding of "hot melt adhesive" and "thermal adhesive" is quite similar, which is not difficult to understand why some people call hot melt adhesive thermal adhesive.

2. How long is the actual shelf life of furniture edge sealing hot melt adhesive?

As a consumable item, the shelf life of furniture edge sealing hot melt adhesive is related to the formula. Generally, manufacturers say it can be stored for two years, which is just a conservative statement. In fact, the shelf life of edge sealing hot melt adhesive can be more than two years.

Perhaps some people may question whether furniture edge sealing hot melt adhesive that has been stored for more than two years can still be used? Will it affect the edge sealing effect—— There is actually no exact explanation for such a problem. Because this is related to the storage cycle, the degree of sealing of packaging bags during storage, the dry and humid storage environment, and the acidity and alkalinity of the air. If the storage environment is good, even if a large amount of inventory is in the warehouse, there is no need to worry about the edge sealing adhesive not sticking after being left for a long time.

3. The softer the hot melt adhesive, the worse it will stick?

The softness and hardness of hot melt adhesive do not directly reflect its adhesive performance, let alone the statement that the softer the adhesive, the less it is to stick to things. Use hard glue in summer and soft glue in winter, which is probably known to every glue user. Whether the hot melt adhesive and the substrate adhere firmly has nothing to do with the softness of the former.

Generally speaking, the softer the hot melt adhesive, the faster it dries. This is to ensure that it dries quickly in hot weather without affecting production efficiency and bonding effect. The good adhesion is directly related to the formula of the substrate and the hot melt adhesive itself. Hot melt adhesives with high softness indeed have poor cohesion, but if they penetrate the substrate well, the poor cohesion will not have a significant impact. The most important thing is that the adhesive cannot damage the molecular structure of the surface material of the substrate. Even if it dries quickly, it is useless, and poor adhesion becomes a major problem.

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