Q&A

Although the adhesion of wood is a relatively simple process, if you do not understand the factors that affect the adhesion of wood, the finished product will be degummed and deformed. Therefore, it is very important to understand and master the factors that affect the adhesion of wood and the preventive measures. Listed below Several indicator influencing factors.

1. Relative density of wood: For wood with a relative density <0.8, the strength increases as the relative density increases; in terms of durability, the relative density is low and the stress concentration of the wood glue layer is small, which is prone to inlaying and peeling. Higher intensity.

2. Shrinkage and expansion rate of wood: Even wood with the same relative density often has different shrinkage and expansion rates, which causes greater internal stress when joining large-scale wood products and reduces the joining strength.

3. Moisture content of wood: The general requirement is that the moisture content of wood is 8~15%. If the moisture content of wood is too high or too low, it will affect the bonding strength of the glue. The wood will shrink when it loses water and expands when it absorbs water. During the process, it will expand inside the wood. Stress is generated in the wood. When the stress reaches a certain level, the wood adhesive joint will crack. The ideal moisture content is controlled at about 10% ± no more than 2%, which is the best state.

4. Fiber direction of wood: Wood is a three-dimensional (fiber direction, tangential direction, radial direction), three-section (cross-section, radial section, chord section) heterogeneous material. When the wood is processed, the fibers can They are perpendicular to each other, parallel to each other or at a certain angle to each other; generally speaking, the greater the angle in the direction of the fibers, the lower the strength.

5. PH value of wood: The PH value of wood is roughly slightly acidic, which is not a big factor affecting the adhesion. It also indirectly affects the hardening time of the adhesive after gluing.

6. Subsequent operation process: In the wood joining operation, the influencing factors include the amount of glue spread, the dryness of the material placement, the pressure and temperature of heating and curing, etc. In most cases, the amount of glue is 100~200g/㎡. The general judgment method is that when pressure is applied, there is a slight glue overflow at the bonding point, which means that the glue amount meets the requirements. During the hot pressing process, the pressure is to make the joint surfaces come into close contact and expel the gas; the heat is to evaporate the water in the glue and promote the cross-linking and solidification of the adhesive. The pressure required for hot pressing depends on the type of wood and the viscosity of the adhesive as well as the requirements for the product.

The type of material to be adhered has a great relationship with the choice of adhesive. The choice of adhesive when wood is bonded to various materials is as follows:

Material classification can be divided into softwood (masson pine, yellow pine, larch, red pine, etc.) and hardwood (birch, ash, boxwood, paulownia, etc.).
It can be divided into 4 categories based on water resistance performance

1. Type I plywood: Plywood with high water resistance. This type of plywood has good resistance to boiling water and is mainly used outdoors, such as shipbuilding, vehicle manufacturing and construction cement formwork. The adhesive used is mainly phenolic resin.

2. Type II plywood: Water-resistant and moisture-proof plywood. The adhesive used in this type of plywood is mainly melamine modified urea glue. It can be used under high humidity conditions, but cannot be used outdoors for a long time.

3. Class III plywood: Moisture-proof plywood. The adhesive used in this type of plywood is mainly urea glue. This type of plywood is mainly used indoors.

4. Class IV plywood: plywood that is not resistant to water or moisture. It has been produced less and less in recent years.

At present, the most commonly used glue type for plywood adhesives is urea glue as the main adhesive. However, urea glue has the problem of free formaldehyde. In recent years, the amount of free formaldehyde released by urea glue has attracted more and more attention. The following table is compiled according to different release amounts and testing methods.

Understand ultra-low formaldehyde building materials

Taiwan has officially announced the implementation since July 1, 2007, and requires that the formaldehyde emission of plywood must not exceed the average of 1.5PPM before it can be imported.

UV light-curing paint, also called UV light-curing paint, is a UV varnish used in the coating industry. The application range of UV wavelength is 200nm~420nm, and the process of hardening the paint by irradiating it with UV light is called UV curing. This technology originated from the international coatings market in the 1970s. Because UV coatings contain no volatile organic compounds (VOC), cause little environmental pollution, have fast curing speeds, save energy, have good performance after curing, and are suitable for high-speed automated production, etc. advantage. Traditional coatings are volatile, slow to cure, and are not conducive to environmental protection. Therefore, UV coatings are the main alternative to traditional coatings.

Compared with traditional heat-curing coatings, UV light-curing coatings have the following advantages in painting:

1. Fast curing speed and high production efficiency. The efficiency of using UV coating is more than 15 times that of traditional drying coating.

2. Save energy. UV coatings are cured by ultraviolet rays, and the energy consumption is 1/5 of traditional drying heat-curing coatings.

3. There is little environmental pollution and the content of volatile organic compounds (VOC) is very low.

4. Excellent coating performance. The cross-linking density of UV coating after curing is much higher than that of thermal baking coating. It has excellent hardness, wear resistance, gloss, acid and alkali resistance, solvent resistance and other aspects.

5. The failure rate of coating equipment is low. Since UV paint will not solidify without ultraviolet radiation, it will not block or corrode the equipment. The coating tools and pipelines are easy to clean, so the equipment failure rate is low.

The UV lamps in the UV drying equipment will gradually age over time, causing the surface hardening of the UV paint to be incompletely dried due to insufficient UV irradiation. Generally, the effective time of UV lamps is about 1,000 hours. Therefore, the energy of the lamps should be checked regularly during the production process to ensure that the coating is completely dry. A UV energy meter can be used to detect it.

1. Understand the types, properties, effects and changes of UV coatings when configured with other solvents.

2. Select UV glazing oil with suitable performance according to the substrate and ink surface properties of the substrate.

3. Pay attention to the drying performance of UV glazing oil, whether its drying temperature range and drying time have any impact on the substrate.

4. It is necessary to consider the suitability of processing after glazing, such as hot stamping, wear resistance, pressure resistance of indentation and die cutting, etc.

5. Choose a glazing oil with high transparency and low odor.

1. The viscosity of UV varnish is too high and the leveling property is poor. The viscosity of the varnish can be reduced or a small amount of leveling agent can be added.

2. The pressure is too small and uneven.

3. The coating amount is too much.

4. Due to the low temperature, the glazing oil is easier to solidify, which is not conducive to the normal flow of the glazing oil. The normal temperature should be controlled within 20 to 30 seconds.

There are three possibilities for re-gluing after glazing:

1. If the coating is too thick, the viscosity of the UV varnish can be reduced to reduce the coating thickness.

2. Check the UV lamp energy to see if it is insufficient or aging. If it is insufficient, replace the UV lamp.

3. There are quality issues with the glazing oil itself.

Whether or not to remove the waterproof layer depends on the site conditions. The best waterproof layer is applied on the RC layer, so it is better to completely remove the old waterproof layer.

Drilling holes in the roof, whether for new water pipes, electric wires or water tower supports, will damage the original waterproof layer. The waterproofing of the damaged areas should be strengthened to prevent water from leaking down from around the holes, causing damage to the downstairs. There were leaks and wall cancers on the ceilings and walls.

A waterproof layer has been made on the attic floor, but if there is no waterproof layer on the surrounding parapets and floor joints, water may seep in from that part. In addition, it must be done around the drain holes on the attic floor. to the PVC pipe inside the drain hole to ensure that water does not penetrate from the joint between the drain hole and the RC structural layer.