There are many reasons to put additives in plywood glue. They can do a lot of favours to the product cost and quality.
1. Curing Agent
The curing agent is a catalyst that accelerates the curing of the glue. The curing agent used in the production of plywood can ionize H+, which reduces the pH of the glue. The urea-formaldehyde resin glue continues to react to form an insoluble and infusible resin with a body structure.
The most commonly used curing agent is ammonium chloride, which is cheap, has good water solubility, is non-toxic and tasteless, and is very convenient to use. In addition to this, some acids (hydrochloric acid, benzene sulfonic acid, etc.) and strong acid and weak base salts (ammonium sulfate, chloride) Zinc, etc.) can also be used as a curing agent for urea-formaldehyde glue, which can be used alone or in combination.
Research on low-toxicity urea-formaldehyde resin adhesives in the past year has shown that since the free formaldehyde content in the adhesive is very small, only ammonium chloride is used as the curing agent, and the curing time is long. Therefore, a multi-component curing meter is used to accelerate the curing of the adhesive. The mixed curing agent includes a mixed curing agent of ammonium chloride and oxalic acid.
When using the curing agent, both the active period and curing speed of the glue should be taken into consideration. The active period of the glue should not be less than three hours. Too short time is not good for production, but at the same time, the necessary curing speed should be ensured.
Phenolic resin glue has high resin activity and cures quickly after heating, so hot pressing glue generally does not add curing agent, but cold pressing glue needs to add curing agents such as benzenesulfonic acid and petroleum sulfonic acid.
2. Glue Filler
Filler added in the glue can reduce the use of resin, which is expensive. No than that, filler can increase the glue performance.
A lot of benefits of adding filler in the glue
- Increase the viscosity of the glue
- Prevent veneer penetration
- Improve the aging resistance of the adhesive layer
- Reduce formaldehyde emission
Organic fillers added in plywood glue production are: flour, soybean powder, coco, wood dust, etc.
Inorganic fillers: Kaolin, chalk, asbestos, gypsum, glass powder. Inorganic fillers won’t make the glue better, just for reduce cost.
Modifiers can modify UF and PF glue for plywood production. For example, melamine and Polyvinyl alcohol are modifiers for UF glue.
They can increase the waterproof capacity of the plywood board.
Buffer can delay the curing time of the glue and plywood factory can keep the glue longer. Common buffers are Urea and Urotropine.
5. Formaldehyde Trapping Agent
The formaldehyde capturer includes chemicals that can react with formaldehyde thus reducing its amount in the plywood board. A formaldehyde trap can be added in the glue, in the glue spreading process. It can even be sprayed on the finished plywood board to obtain the results.
Colors can be added in the glue to help workers evaluate the glue spreading results.