Wood glue

Wood glues are adhesives made ​​from natural or synthetic raw materials for bonding wood and wood materials.

Stress groups

The wood glues are divided into different stress groups, old designation to DIN 68602 (B1, B2, B3 and B4) new name DIN/EN204 (D1, D2, D3 and D4) The stress groups arrange the glues according to their minimum shear strength values ​​and their behavior under humidity and exposure to water:

  • B1 or D1: Suitable for indoor use, the moisture content must be below 15%.
  • B2 or D2: Suitable for indoor use with occasional short-term exposure to water or condensation, the moisture content may reach a maximum of 18 %.
  • B3 or D3: Suitable for indoor use with frequent short-term exposure to water or higher humidity. Suitable for outdoor use without exposure to direct weathering.
  • B4 or D4: Suitable for indoor use with frequent and prolonged exposure to flowing water or condensation. Outside and exposed to the elements with adequate surface protection.

Glues

There are different types of glue, which differ in their properties, their processing and their composition:

Animal glue

Animal glue is made from animal waste higher animals ( " gelatinous body " ) by boiling. This forms a jelly, which is referred to as and in the dried state as " glue ". The main ingredient of the animal glues, the gluten, a protein compound. According to their origin distinguishes different animal glues, such as bones, hides ( hide glue ), Hasenleim, isinglass or Hausenblasenleim.

Casein

This glue consists of casein and slaked lime. It is again a natural glue, which in contrast to animal glue but is completely waterproof and heat resistant. Nevertheless, it is used in modern times less and is, due to its properties almost exclusively in joinery his application. It is available in the stress groups D2 and D3. It is available as a powder mixture to be mixed with water or can by extensive mixing of low-fat quark with slaked lime (ratio about 4-5:1 ) are produced.

Urea Formaldehydharzleim (also Polykondensationsleim or UF glue )

This type of glue is made of synthetic resins in conjunction with formaldehyde. It is offered in three forms;

  • Component adhesive: hardener already mixed.
  • Zweikomponentenleim: glue and hardener available as a powder or liquid. Depending on the processing of the right hardener to be used.
  • Leimfolie: addition of extenders (eg rye flour to make the glue joint gap-filling ).

Striking is the unpleasant, stabbing and striking formaldehyde odor ( therefore a good ventilation of the room is a good idea ). It is available in the stress groups D3 to D4.

Phenol Formaldehydharzleim (also PF- glue )

Phenol Formaldehydharzleime are dark, weather-resistant, resistant to boiling and gap filling. Use in the Bautischlerbranche, manufacture of particle board and plywood.

Resorcinol - Formaldehydharzleim (also RF - glue )

Consists of liquid glue and powdered hardener. This glue is resistant to boiling, has very good weather and heat resistant properties and is mainly used in shipbuilding, in glider and used in the manufacture of water-resistant plate materials.

Low formaldehyde Polykondensationsleim

Formaldehyde is required to cure the adhesive resins. In most cases, the formaldehyde content is higher than that of the resins, so that a good cure is given. However, in this Polykondensationsleim the reduction of free formaldehyde by the addition of formaldehyde scavengers or reducing the formaldehyde component is reached. Thus, the adhesive has a lower bond strength.

Low formaldehyde dispersion glue

The famous white glue is a low-formaldehyde dispersion adhesive based on PVA ( polyvinyl acetate) as a binder, which is supplied ready for use in water dispersion and as cold glue, Quick fasteners, plywood adhesives, Härterleim, Lackleim and hot glue is available. It is available in the stress groups D2 - D4.

For D4- D3 gluing requires a glue, which before consumption isocyanate crosslinking agent ( generally an HDI) is added. Such two-component adhesives have a pot life of several hours. Furthermore, there are systems based on a D2- glue, which for cross-linking, a curing agent ( a Lewis acid such as aluminum chloride) is added. One advantage of this mixture is much longer pot life. Especially with this kind of glue spreaders D4 glue is often preferred.

Some data:

  • Base: Dispersion
  • Color: white, cured: transparent
  • Viscosity: 13.500 mPas
  • Storage: at 20 ° C for about 6-12 months
  • Cleaning: water and acetone

Especially for smaller quantities consumed there for some time one-component D4 glues on the market.

Some data:

  • Base: Dispersion
  • Color: white, cured: transparent
  • Viscosity: 6000 mPas
  • Storage: at 20 ° C for about 4-6 months

Polyurethane glues

The modern glues for the wood sector are the one-component Polyurethanleime today. They are usually referred to as PU glue or polyurethane glue. They are waterproof (D4 ) and glue not only wood, but almost all bondable materials. It is solvent-free reactive adhesives which cure with the help of moisture. This leads in many cases to a slight foaming, whereby excellent gap fill is achieved. When gluing large surfaces before water should be sprayed in order to guarantee a complete cure. Not yet hardened glue may be removed with acetone.

Disadvantage: PU glues are harmful ( in liquid state ) and should be handled only with gloves.

Processing

The processing is different depending on the manufacturer. The stress alone groups say nothing about the Leimbasis, so the Leimgrundstoff from.

White glue is applied on one or both sides depending on the absorbency of the surfaces to be sized, with heavily absorbent surfaces, a double glue with an evaporation time of ~ 10 minutes is necessary. White glue can be diluted with water when the operating time (the time until the glue the pieces together after assembly connects ) must be extended; this is required, for example Formverleimungen difficult or pressing situations. Because the base of the white glue ( PVAc) these thermoplastics. This is used eg in the edge coating by both contact surfaces wetted with white glue, dried and subsequently assembled hot.

Kauritleime ( Heißleime ) are used primarily for gluing of veneers. The Kauritleim is generally supplied as a powder containing both the actual size and a chemical curing agent component. The addition of water activates the Kauritleim, which is then applied to one side of the support surface; the surfaces are briefly, approximately 3-5 minutes at high pressure (0.5 N / mm ², corresponding to 50 T / m ) and pressed temperatures between 70 and 120 ° C. After pressing the ( steaming ) workpieces are aired standing.

Wood types with tannic acid, such as oak, or with the use of iron-containing applicators it can discolor the wood come. Kauritleime can cause adverse reactions with wood stains. Can not be combined with enough clamping pressure surfaces, adhesives are recommended as epoxy resin.

Space, material and glue temperature should be 18-20 ° C, relative humidity 50-70 % and the wood moisture amount to 8-10%.

White Point: 3 ° C to 8 ° C is the threshold temperature, below which form during drying glues not have a " film " and therefore dry to form a white, rubbery layer. Optimally, about 15 ° C.

Open time: min (at 200 g / m²) to bring together the joints 8-10 parts within the open time and press.

Pot Life: Shelf life or after addition of curing agent; This is the time, which can remain in the sizing vat, a glue from its shelf to the start of setting. At the end of the pot life of the glue is useless.

Leimauftragungsmenge: surface bonding at 80-140 g / m², when mounting 150-180 g / m

Press pressure: 0.1-0.5 N / mm ² (equivalent to 10-50 t / m²)

Pressing time: Surface bonding of laminates in short-cycle presses ( 70 ° C ) from 1 min, Montageverleimung 8-15 min, joints in boards and block gluing 20-40 min.

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