Лако-красочные материалы — производство

The mechanism of the initial stages of the reaction of melamine with formaldehyde leading to the formation of methylol melamines is very similar to that of urea. The reaction mechanism of the acid-catalyzed condensation reactions of methylol melamines to form polymers and resins has been elucidated by Sato and Naito [4]. Melamine and formalde­hyde react […]

A. Condensation Reactions formaldehyde addition to melamine occurs more easily and completely than does addition to urea. The amino group in melamine accepts easily up to two molecules of formalde­hyde. Thus complete methylolation of melamine is possible, which is not the case with urea [1]. Up to six molecules of formaldehyde can be attached to […]

Melamine-formaldehyde resins are used as adhesives for exterior — and semiexterior-grade plywood and particleboard. In this application their handling is very similar to that of UF resins for the same use, with the added advantage of their excellent water and weather resistance. MF resins are also used for the impregnation of paper sheets in the […]

A. Pizzi Ecole Nationale Superieure des Technologies et Industries du Bois, Universite de Nancy 1, Epinal, France I. INTRODUCTION Melamine-formaldehyde (MF) and melamine-urea-formaldehyde (MUF) resins are among the most used adhesives for exterior and semiexterior wood panels and for the preparation and bonding of both low — and high-pressure paper laminates and overlays. Their much […]

An introduction to the typical resin synthesis of a UF resin used as an adhesive for wood products and in industrial applications is given below. It constitutes a handy formulation for those who want to work in this field. It is not a low-formaldehyde-emission formula­tion. To 1000 parts by mass of 42% formaldehyde solution (methanol […]

The potential introduction of an intermediate reaction step at very acid pH inducing the formation of some uron in the preparation of UF resins of lower formaldehyde emission has caused some industrial interest [40], and today industrial UF resins manufactured with the introduction of a rapid, very acid step (pH 1-2) during preparation are available. […]

Methods of formaldehyde analysis include the iodometric, sulfite [31], and mercurimetric [32,33] methods. The sulfite method measures only the formaldehyde present, whereas the iodometric method can also estimate the methylol groups. Another method is based on the partition of formaldehyde between water and isoamyl alcohol [34]. Estimation of the formaldehyde in the alcohol phase of […]

Although particleboard and plywood are the major users of UF adhesives, two other applications, although consuming much lower proportions of these resins, are also worthy of note. The first is in the furniture and joinery industry, including the manufacture of hollow-core doors. While in the latter application thermosetting resins with character­istics and glue mixes similar […]

In their cured state UF resins are nontoxic. Urea itself is also harmless. However, free formaldehyde and formaldehyde generated by slow hydrolysis of the aminoplastic bond are highly reactive and combine easily with proteins in the human body. This may cause a painful inflammation of the mucous membranes of the eyes, nose, and mouth [25]. […]

A very important application for UF adhesives is in the manufacture of particleboard. The glue mix is generally composed of a liquid resin to which water has been added to decrease viscosity and to facilitate spraying, plus small amounts of ammonium chloride or sulfate and small amounts of ammonia solution. Small quantities of insecticides, wax […]