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Common wooden floors include finger-joined wood flooring, glued integrated wood flooring, three-layer and multi-layer parquet, and cladding wood flooring (high-density fiberboard HDF-coated high-pressure veneer HPL or resin-impregnated paper with wear-resistant materials), bamboo and wood Floor, parquet floor, cork floor. Due to the variety of flooring and processing techniques, it is difficult to meet the needs of various processing techniques and performances with an adhesive. Commonly used floor glues include 3 types: aldehyde glue (UF, MF); polyvinyl acetate emulsion (PVAc); polyisocyanate glue (EPI). These three types of glue have different cost of use, adhesive process and environmental performance. As for the price, EPI has the highest price, aldehyde glue is the cheapest, PVAc is centered; bonding performance is the strongest in EPI. Environmentally friendly PVAc is the best, aldehyde rubber contains harmful components of formaldehyde, EPI glue must be mixed with toxic curing agent. However, modern gluing technology can reduce the harmful components of the rubber in the floor to a level that does not harm human health.
1 Flooring industry glue
1 . 1 UF glue
Aldehydes are thermosetting glues that are typically cured by heat to form a bond. Aldehydes can also be cold-cured at room temperature, but require a strong acid curing agent and require extended pressurization time, which is not suitable for large-scale production.
Aldehydes are used in liquid form, but they come in both liquid and solid form when the glue is shipped. The solid glue is further atomized and dried by liquid glue. The price is more expensive than liquid glue, but it is easy to transport, and the storage period can be up to 1 year at room temperature, and the liquid glue can be stored for up to 3 months.
UF is a commonly used aldehyde gum. Urea-formaldehyde glue for floor manufacturing usually contains 3 to 4 components: urea-formaldehyde resin, curing agent, modifier, and water repellent. Different ratios to suit different processing techniques, bonding properties and formaldehyde release levels. In the flooring industry, it is mainly used for interlayer lamination of three-layer solid wood composite flooring, HPL veneer for laminate flooring, and bonding of bamboo flooring. At present, the E1 grade urea-formaldehyde glue used in the domestic flooring industry is usually a solid powdered rubber imported from Europe, such as the Dynorit SPS series of the Nordic Group. Its characteristics are as follows: thermosetting adhesive; multi-component (main agent UF resin + modifier + curing agent) modulation; high solid content (65% ~ 70%), flexible formula; can adapt to the glue of different tree species Meet different bonding processes; high strength and high water resistance (according to Japan JAS, American ANSI and China GB (reported draft)); low formaldehyde emission (European standard pr EN71 7-1: E1 formaldehyde emission is 0 . 1 2 5mg/m3 air, or weight ratio with air 0. 1× 1 0 - 6 ); storage period at room temperature for one year. Formaldehyde emission control is an important indicator of flooring products. This is because the floor is laid indoors, free formaldehyde can be directly inhaled into the body, causing headaches, mucous membranes and skin allergies, and may cause cancer. Reducing the release of free formaldehyde involves many factors, including: formaldehyde (UF) itself formaldehyde content (ie using low molar ratio UF glue); effective modifiers and curing agents and their reasonable ratio; coating amount and wood Control of moisture content; appropriate hot pressing temperature and hot pressing time; effect of floor surface material and thickness on the release of formaldehyde.
The standard method for the detection of free formaldehyde is the incubator method, as specified by the European standard pr EN71 7-1. It is based on the furniture and decorative materials in the living space, including the average release area of ​​the floor, and the limits of the impact of formaldehyde on health. The amount of release refers to the amount of formaldehyde in the air, ie the weight of formaldehyde/air volume (mg / m3). Most countries in Europe accept E1 as an environmentally friendly product.
Standard test conditions:
Temperature / ° C 2 3
Relative humidity / % 45
Loading ratio / (m2 / m3) 1
Air replacement frequency / h 1
Since this detection method usually takes 2 to 5 weeks, it is difficult to apply in production. The quick and easy test method derived from this is usually used in production:
(1) Perforation extraction method (EN1 2 0 ): for MDF/PB production, E1: less than 9 mg / 100 g plate;
(2) Ampoule method (EN 71 7-3): Instead of perforation method, measure the formaldehyde content (mg/kg) per kg of dry sample;
(3) Gas analysis method (EN71 7-2): used for the determination of plywood, divided into A, B, C three-stage measurement of formaldehyde emission per m2 sample per mg [mg / (h · m2)];
(4) Dryer method: mainly used in the United States and Japan.
1.2 Polyvinyl acetate glue (PVAc)
Polyvinyl acetate (PVAc) latex, commonly known as white latex, is a thermoplastic water-based rubber that has been fully reacted at the factory and solidified by the evaporation of water and physical changes in p H during use. It can be cold pressed at room temperature or hot pressed, in order to accelerate the evaporation of moisture in the glue to cure the glue layer. PVAc is mainly used in the floor industry for panel panels of three-layer solid wood composite flooring; HPL veneer for laminate flooring; floor installation; finger joints for flooring. The glue is non-toxic, non-irritating, non-flammable, non-corrosive, environmentally friendly, can be used in one component, convenient in gluing operation, and long in storage period, up to 6 to 12 months at normal temperature, but at high temperature The PVAc adhesive layer has a softening phenomenon. Therefore, its products should not be placed in a high temperature environment for a long time. For example, when the temperature in the container reaches 70-80 °C during oceanic tropical transportation, the stress of the wooden floor will cause the glue layer to be displaced and damage the glue. In addition, PVAc glue is poor in water repellency. The waterproof properties of the adhesive can be tested in accordance with the European standard EN 2 0 4/205. The grade of this standard is divided into 4 levels, which are gradually increased by D1, D2, D3 to D4. Floor glue is usually above D3.
1.3 Polyisocyanate Emulsion (EPI)
EPI (Emulsion Polymer Isocynate) glue is a two-component glue. The main agent is an emulsion composed of several polymers and copolymers, and the curing agent is diphenylmethane isocyanate (MDI). The main agent itself is thermoplastic, but after mixing with the curing agent, a graft reaction can occur to form a thermosetting polymer. This polymer is used to bond wood and is highly water and solvent resistant.
Usually, the ratio of the main agent to the curing agent for the EPI glue for the floor is 100:15. When the tree species, the pressing temperature and other process conditions are different, it needs to be appropriately adjusted. EPI glue for floor can be used to refer to grounding plate and laminated timber floor. It has good water resistance and can meet the European D 2 standard of EN 2 0 4/ 2 5; good bonding strength; good solvent resistance; medium and low temperature hot pressing (90 °C), can also be cold pressed at room temperature (10 ~ 35 ° C) or high frequency pressure. It is best to use a quantitative blender for large-scale production to increase the mixing accuracy and reduce the waste of use.
2 Gluing process
2 . 1 three-layer parquet
2.1.1 Table splicing is usually spliced ​​with PVAc glue, which requires the process and strength requirements of the panel blank, and does not guarantee the glue line. Waterproof to D3 grade, heat resistant (WATT91), anti-solvent. When hand-brushing or machine-spraying, the viscosity of the glue is required to be in the range of 50 0 to 90 0 m Pa·s. Curing speed: 40 to 60 s / 75 ° C, or 5 to 10 min / room temperature.
2 . 1 . 2 Interlayer bonding UF resin, production standards: JAS in Japan, EN in Europe, ANSI in the US and GB in China. Applicable process: the table and the back board are separately coated, the core board is glued, the main agent is mixed with the curing agent or applied separately; after the blank is pre-pressed or not pre-pressed. When the tree species, wood density, water content and thickness of the upper, middle and lower layers of wood are different, the amount of glue applied is also different. The commonly used glue is powdered urea-formaldehyde resin glue. When using powdery urea-formaldehyde resin glue, it should be noted that the ratio of each component should be accurate; the glue should be uniform and no block; the amount of glue should be moderate and uniform, and when the surface processing precision is poor, the amount of glue should be appropriately increased to prevent Partially lacking glue; the moisture content of the substrate is moderate; the higher the processing precision of the substrate is better; when the substrate species are different, the parameters of the glue should be adjusted appropriately; the time of the release should not be too long to prevent excessive evaporation of water in the glue; , time, pressure: should be set according to the instructions for use, to ensure that the glue is fully cured. If the above factors are not properly controlled, it will affect the performance of formaldehyde emission and bonding strength of the floor. The factors affecting the cost of using the urea-formaldehyde resin adhesive are: the unit price of the glue, the mixing ratio, the amount of glue applied, the operating loss and the level of the adhesive supplier. Users should choose a supplier with research and development capabilities to obtain an effective and low-cost formula (reduced high-cost components such as modifiers, water repellents). Automatic mixing and dosing equipment should be used to ensure proper mixing ratio and reduce the quality problems and associated losses caused by human error.
The different types of special powdered plastic Dynorit SPS series offered by Nordic Group:
(1) L50 5, A93 2 / A942, H2 3 2 / H2 3 1 , M765: Meets American Standard ANSI, European Standard pr EN 71 7-1 E1
(2) L50 5, A93 2 / A942, H40 7: glue/curing agent coating, high frequency heating, American standard ANSI, European standard pr EN71 7-1 E1
(3) L 50 5, A93 2 / A942, H2 40: Suitable for pre-pressing process, meeting Japanese standard JAS/national standard (approval draft), European standard pr EN 71 7-1 E1
(4) L780, A952, H2 3 0 : Meet Japanese standard JAS/national standard (approval draft), European standard pr EN 71 7-1 E1
2 . 2 HPL coated laminate flooring
2 . 2 . 1 HPL cladding is covered with two types of high temperature hot pressing and normal temperature cold pressing. Cold pressing process floor deformation is small, usually multi-layered, and room temperature is pressed for about 3 to 4 hours. The rubber used is:
(1) UF glue: two components containing a main agent and a curing agent, respectively, the main agent is applied to the surface of the substrate, and the curing agent is applied to the back surface of the HPL. When the HPL is in contact with the surface of the substrate, the glue begins to cure. If the floor is required to achieve low free aldehyde release, the modifier must also be added to the main agent.
(2) PVAc glue: The required glue has the European standard waterproof D3 grade, and requires high solid content (more than 50%) to reduce the water absorption expansion of the substrate HDF. The viscosity is as small as possible to ensure a high solids content for the coating operation.
The hot pressing process has high production efficiency and there are two kinds of adhesives used:
(1) UF glue, comprising a main component and a curing agent, the curing agent can be applied to the surface of the substrate after being mixed with the main agent, and the main agent is added with a modifier to produce a product with low free aldehyde release. Usually, the hot pressing temperature is 100 ° C, and the pressurizing time is 2 to 4 min.
(2) PVAc glue, the same as cold pressure glue. Hot pressing accelerates curing. The hot pressing temperature is slightly lower than the UF glue and should be lower than 90 °C to avoid overheating and softening of the rubber layer. The manufacturer can flexibly adjust the hot pressing temperature and the corresponding pressurizing time according to the production efficiency.
2 . 2 . 2 The installation of the floor coverings is an important operation before the floor finally becomes a usable finished product.
The processing quality of the floor itself and the quality of the assembled glue directly affect the use effect. Even if the precision of the floor joint is perfect, the floor may be deformed and warped due to the water swelling of the substrate. For this reason, in addition to requiring the water resistance of the substrate to be good, the waterproof performance of the glue is also important. Floor mounts typically use PVAc glue. It is required that the waterproof property of the glue reaches D3 grade; the solid content is 50% to 52%; and the storage period is at least one year at normal temperature. The commonly used test items for PVAc glue are: 1 glue performance standard (refer to EN 2 0 4/ 2 0 5D3); 2 solid content; 3 floor assembly glue performance test (there is no uniform standard at present, each manufacturer and supplier press Self-determined method detection. It is more common to detect the water absorption thickness expansion rate of the floor under different water immersion conditions).
2 . 3 bamboo flooring
The glue of bamboo flooring is different from the glue of wood. It is because the bamboo material is hard, the deformation is large, the processing is difficult, the precision is difficult to guarantee; the bamboo strip is small in size and must be hand-coated; the surface is transparent, the hot plate is easy to stick, and the carbon is high temperature. . For this reason, the viscosity of the glue is required to be low, the solid content is high, and it can be cured at a low temperature. At present, most of the large bamboo flooring production plants exported to Europe in China use UP41 1 6/ UP43 72 and A93 2 / A942+H2 40 of the Tano Group.
2 . 4 refers to the grounding plate
According to the gluing characteristics of the grounding plate: the adhesive is required to prevent rebound; rapid curing at room temperature; high water resistance (Japanese standard JAS, European standard EN4 0 4 D4); multi-tree species adaptability. Two-component EPI glue is usually used.
3 Conclusion
The development of adhesives for flooring is developing in the direction of environmental protection, high performance, low cost, multi-standard, multi-tree and multi-process adaptation. Different types of flooring require different adhesives. The main considerations for choosing an adhesive include:
1) Floor launching market and applicable product quality standards in the region;
2) the production process of the floor, the tree species used and the cost of using the adhesive;
3) The service level of the adhesive supplier (including the completeness of the product, the quality level and stability, the timeliness of supply, the service in place, the integration of supply and demand, and the provision of necessary facilities).
Application and development of adhesives in the wood flooring industry
Modern wood flooring is an industrial product that is the process of cutting, selecting and re-bonding wood and wood panels. For consumers, the floor is only semi-finished when it leaves the factory, and it becomes a product until it is installed. For most floors, the installation is also a gluing process to prevent cracking and shrinkage of the floor joints. Therefore, floor adhesives include adhesives for both manufacturing and installation.