Gluing of plywood

Commonly used gluing theory

1. Mechanical gluing theory

Microscopically, the surface of the material is uneven and there are many gaps. Adhesive penetrates into it

The theory of connecting the glued objects together into many glue nails

2. Adsorption theory

That is, through the contact between the adhesive and the surface of the material to be glued, hydrogen bonds and molecular attraction are obtained between the molecules, and the two are closely connected.

3. Diffusion Theory

Some adhesives are polymers with a chain structure, such as glued polymers, which are polymer materials.

Under certain conditions, the two molecules gain heat movement or the segment heat gain movement, so that the two molecules diffuse each other and form a transition layer that fuses with each other, thereby connecting the glued objects together.

4. The theory of chemical bonding

A strong chemical bond is formed between the adhesive and the glued object, connecting the two together

5. Electric double layer theory

That is, two electric double layers are formed on the interface between the adhesive and the object to be glued to form a capacitor, and the two sides of the material phase are obtained.

Equivalent to two plates of a capacitor. When peeling off the adhesive layer from the surface of the glued object, it is equivalent to separation capacitors have two plates, to generate a potential difference.


Adhesive composition

Synthetic resin adhesives are mainly composed of resins, curing agents, fillers and modifiers.

1. Synthetic resin

She is a polymer material that acts as a glue

UF resin

UF resin is cheap, has good bonding strength, fast curing speed, and good water resistance, so it is widely used. More than 80% of plywood products use this adhesive.

The weather resistance and aging resistance of UF resin is not as good as that of PF resin, so it is mainly used for indoor plywood.

PF resin

PF resin is an outdoor adhesive with good weather resistance and high bonding strength

But the color is darker and the price is higher, which limits the scope of use.


Veneer sizing

veneer sizing is a process that applies a certain amount of adhesive evenly to the surface of the veneer

Requirements: The thickness of the adhesive layer is uniform and continuous, and it has good bonding strength after curing.


Common rubber types and applications

Adhesives for wood are mainly based on "trialdehyde" glue, accounting for 80% of the total wood and wood-based panel industrial adhesives, urea-formaldehyde resin glue

Due to the low price, the indoor environment does not require high water resistance and weather resistance. The urea-formaldehyde resin adhesive modified with melamine can also be used for paper impregnation, and its total amount accounts for more than 80% of the total amount of trialdehyde adhesives.


Phenolic resin glue

It has good gluing performance and is suitable for use in outdoor environments. It is mainly used for the production of plywood formwork for concrete, and part of it is used for impregnation of the bottom paper in the high-pressure decorative laminate.


Melamine formaldehyde resin glue

Basically used for impregnation of decorative paper for wood-based panel facing, such as particleboard facing paper and reinforced composite

Impregnated wood floor decorative paper, balance paper and abrasion resistant paper


Assembling and pre-pressing

After the veneer is glued, the slab is formed according to the composition principle of the plywood, the thickness of the product and the number of layers.

After aging, the slab is cold-pressed for a short time to make it preliminarily glued and formed to facilitate mechanized production

After pre-pressing, the slabs should be inspected one by one, and the defects should be repaired immediately to improve the first pass rate of plywood production.


1. Group blanks

The grades of the front and back panels of each plywood should meet the national standards for plywood, and the defects of the core board can be obtained as long as they cannot be reflected on the panel.


2. Compression rate of various plywood   %

ordinary plywood                                     5-15

Carriage plywood                                      8-16

Aviation plywood                                      20-25

marine plywood                                        30-35


Each layer of veneer that composes the slab can be made of equal thickness, or the surface plate can be changed to a thin and thick core board structure. The latter can use wood more rationally, which is beneficial to increase the thin board rate and the grade rate, which is an important sign of the development of plywood production technology. However, the equipment and process should be improved accordingly, and management should be strengthened at the same time.


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