"Valuable information sharing!" How to solve the problem of bubbling or cracking when manually pasting wood veneer?

The use of wood veneer has a history of over four thousand years since it was recorded in history. As one of the most decorative wood products, it has now been applied to many products.

Although the application of wood veneer has greatly liberated the material limitations of wood, various defects often occur during the veneering process in factories. Among them, "wood veneer bubbling" is the most common and also the most intractable problem. Don't worry. The editor has sorted out some situations where hand-pasted wood veneer is prone to bubbling and their solutions for you below. Come and take a look! The veneering process of thin wood is generally divided into two types: machine hot-pressing veneering and manual veneering. Here, we mainly discuss some problem points of manual veneering.

Veneering process of thin wood

For most manufacturers, the most crucial issue with the hand-applied wood veneer process lies in the fact that the paint is prone to bubbling. The following mind map sorts out the possible reasons for the bubbling of the painted wood veneer in each link. We will analyze them one by one to help manufacturers identify their own problems.

Material factors

1 - Wood veneer

Wood veneer can be classified into two types based on its thickness: thin wood veneer is 0.1 to 0.3mm thick, while thick wood veneer is 0.3 to 0.5mm thick. This article mainly focuses on the manual application of thin wood veneer. The process of applying thick wood veneer will be continued in the following text. Stay tuned. Dry wood veneer is prone to bubbling: Dry wood veneer itself has a relatively large rebound force and requires a high initial adhesion of glue. During bonding, it is easy to form false adhesion. Once painted, due to the evaporation of thinner, a certain external force will be generated, causing bubbling. The best choice is moist wood veneer: (1) Wet wood veneer that has just been planed and placed in the refrigerator will have a more balanced moisture content. (2) For wood veneer that has been moistened on the spot, it is recommended to wrap it with plastic paper on the same day to wait for the internal moisture to be even, and then wrinkle the wood veneer the next day, as it is prone to bubbling.
During the production process of wood veneer, due to unevenness and uneven moisture content, some parts or sections of it will show wavy and uneven shapes after drying, which is commonly known as wrinkled wood veneer. Wrinkled wood veneer is prone to accumulation, rebound and bubbling. Even if the creased wood veneer is moist, it is prone to rebound after being ironed dry. The rebound reduces the adhesive force of the glue, and it will also bubble after being painted. Therefore, when factories purchase wood veneers, they should pay close attention to the flatness of the wood veneers.

2 - Substrate

In the process of manually pasting wood veneer, not only the quality of the wood veneer should be considered, but also the quality of the base material is an important factor. Small areas of adhesive spots, paraffin spots, oil stains and other impurities on the surface of the substrate can affect the penetration of the adhesive, making it difficult for the material to bond well and prone to problems such as delamination and bubbling.

The uneven thickness of the base material is also an important cause of wood veneer bubbling. The national standard for artificial boards stipulates that the thickness deviation should be within ± 0.2mm, but some boards on the market have a thickness deviation that exceeds the national standard. This can cause various quality problems for relatively thin surface materials. Therefore, for artificial boards, flat medium (high) density fiberboards should be selected. Solid wood edge banding must be sanded flat on both sides. The design of hollow slab gaskets should not omit or reduce the amount of materials.

2 - Adhesive

A glue with good initial adhesion can greatly improve the efficiency and quality of veneering. Unqualified glue has insufficient adhesion and dries when heated, which can easily lead to false adhesion and insufficient glue, directly causing bubbling. All-purpose glue and white latex glue are no longer suitable for processes with high quality requirements. Professional wood veneer adhesive with a solid content of over 50% should be selected. Fushen veneer Adhesive is recommended. Its unique repairability can effectively solve the problems of bubbling, glue penetration and edge lifting caused by environmental or process issues.

"Process factors

1 - Operation time

After visiting many factories, we found that the process of most workers applying wood veneer is as follows: after applying glue on the base material, they cover the wood veneer and gently press it with their hands. Then, they leave it for a period of time before ironing. The most crucial part of this method is the control of the placement time. If the storage time is short and the moisture content is high, it is easy to not heat firmly, it is prone to rebound and there will also be a phenomenon of glue overflow. If it is left for too long, the moisture will evaporate, the permeability of the glue will weaken, and it is also easy to not stick firmly. How long is the most appropriate time to place it? The following factors should be taken into account for judgment: (1) The dryness and humidity of the environment: Different dryness and humidity of the environment result in different storage times. (2) The dryness and humidity of the wood veneer: If the wood veneer is too wet, it should be stored for a longer time; if it is relatively dry, the storage time will be shorter. (3) The moisture content of the glue: If the moisture content of the glue is high, the storage time will be longer; if the moisture content is low, the storage time will be shorter. (4) Substrate selection: A looser substrate has a shorter storage time, while a denser substrate has a correspondingly longer storage time

2 - Ironing technique

Hand-pasting wood veneer tests the proficiency and experience of the operators even more. Inexperienced operators may lead to product quality defects or an increase in waste rate. This requires manufacturers to provide standardized and normalized training for the operation staff. Here we have the following three suggestions:

Iron and sandpaper used simultaneously

The most common ironing method at present is direct ironing. This is not a big problem for skilled workers, but for beginners, ironing with sandpaper and an iron is easier to handle, has a lower error rate, and is less likely to cause bubbles.

(2) Iron at an Angle when necessary

When ironing flat with an iron, due to the large heating area, the wood veneer shrinks differently, thus causing cracking. Moreover, due to the inconsistent shrinkage of the wood veneer, a rebound force is generated, which reduces the adhesive force of the glue, creating false adhesion and causing the paint to bubble. The oblique ironing technique can effectively avoid this problem. Left side flat ironing effect/right side oblique ironing effect
(3) Control the iron temperature properly

Ironing at too low a temperature can easily lead to false adhesion, while ironing at too high a temperature, too frequently, or with too short intervals can all cause the wood veneer to break. Therefore, an appropriate ironing temperature is particularly important. Both too high and too low temperatures can cause different problems. Suggested operating temperature: The temperature of the moist thin wood veneer iron should not exceed 220 degrees and should not be lower than 120 degrees

3 - Gluing method

Incorrect coating methods can lead to uneven application of glue, insufficient glue, and glue accumulation, which is also an important cause of bubbling. We suggest: 1. Use short-bristled rollers or curved line rollers as coating tools, and avoid using scrapers, brushes, etc. 2. Apply glue on the wood veneer using a wood veneer gluing machine (Benefits of gluing wood veneer: 1. Reduce the amount of glue applied, no glue overflow, and save costs; 2. The wood veneer is less likely to crack; 3. The glue penetrates more easily and is less likely to bubble; 4. Save labor and be more efficient)

The craftsmanship is influenced by various factors. Those who have the need should study more about glue, wood veneer, and the environment of veneering, and improve their work efficiency and optimize the craftsmanship products through systematic learning. Now is a good opportunity to learn!