Urea-formaldehyde

Urea resins are amino resins in accordance with DIN 7728 ( plastic), which as the condensation products of urea (or urea derivatives ), and aldehydes ( especially formaldehyde ) were prepared and can be cured chemically and thermally.

Urea -formaldehyde resins are referred to simply as UF resins (of English. Urea = urea).

  • 2.1 Liquid resin
  • 2.2 Cured resin

Production

Technically, the production of UF resins in large reactors is done ( about 20 to 40 m³), which are equipped with a stirrer, heating and cooling coils and metering possibilities for the "big " raw materials, acids, alkalis and any additives.

The "traditional" production process for UF resins extends technically according to the following steps:

  • Methylolation: addition of urea to formaldehyde solution
  • Condensation: addition of acid or acid salts ( such as ammonium sulfate)
  • Terminating the condensation: by increasing the pH - value by means of water ( pH> 7)
  • Adjusting the right molar ratio of formaldehyde and urea
  • Setting the proper solids content (if necessary, by removing water by distillation )

For special applications, such as glues for joinery applications, find the largely dried Pulverleime use. These are prepared by spray drying the liquor in place of the UF- step distillation.

Methylolation

In an addition reaction of formaldehyde to urea are formed essentially methylolureas (see hydroxymethyl )

Condensation

By over time, temperature and pH controlled condensation reaction of methylol urea, or well with one another, the monomers combine to form larger molecules (oligomers and polymers). Here, methylene bridges and ether bridges form. The control of the degree of condensation is performed by measuring the degree of condensation - dependent parameters such as viscosity or water compatibility.

Recent addition of urea

The last urea addition is that a molar ratio of formaldehyde to urea ( F / U), which is needed for the application. This ether - bridges are broken down partially. Also terminal methylols ( - CH2 -OH) react even with the added urea.

Properties

Liquid resin

This is the product which is used as glue. The following parameters are used as criteria or as part of the quality assurance checks ( next to typical values):

  • Viscosity: ca 300 - 2000 mPa.s
  • Gelling time: depending on the curing agent, and temperature of less than 1 minute to hours
  • (Also known as hard resin ) Solid content: about 66 %

Cured resin

Urea resins form very lightfast, low flammability, mostly white masses, however, are not resistant to hydrolysis when cured. Particularly strong acids and alkalis, and boiling water they are attacked. Urea - Formaldehyde resins resists fading, hard, scratch-resistant and good sandable films.

Use

Because of the relatively low cost ( both the production as well as the raw materials ) and the rapid curing (= high reactivity) and good dry bond strength of the bulk of the UF resins used as adhesive for the production of (non- outwardly climaproof ) timber materials (eg Formica ). Under the brand names Pollopas household items were produced in the 1930s that had a wide range of colors in contrast to the widespread phenolics.

Other areas of use are:

  • Impregnating resins ( Resins )
  • Insulating resins
  • Finishing agent
  • Production of wet strength papers

Manufacturer

  • Sadepan chimica
  • BASF
  • Dynea Chemicals
Methylenes
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