Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1993-11-24
1995-11-28
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
528129, 528137, 528142, 528144, 528147, 528155, 528156, 528161, 528176, C08F 600
Patent
active
054709245
DESCRIPTION:
BRIEF SUMMARY
This invention relates to improved phenol formaldehyde resins which have superior qualities of fire resistance, mouldability, insulation, and stability when compared to conventional resins.
Conventional phenol formaldehyde resins may be formed from phenol and formaldehyde wherein formaldehyde may react with the aromatic ring at the ortho and/or para positions. This is assisted by heating but can be a slow process unless a basic or acid catalyst is included. The main reactions involve direct addition of phenol and formaldehyde yielding methylol derivatives as well as direct condensation of phenol and a methylol derivative with loss of water yielding methylene derivatives. The direct condensation reaction involving the formation of methylene groups between adjacent aromatic rings is catalysed by bases and is favoured by an excess of phenol ie. a deficiency of formaldehyde. In contrast the addition reaction yielding methylol derivatives is catalysed by strong bases and is favoured by an excess of formaldehyde.
If the above reactions are allowed to continue assisted by heating hydrophobic compounds eventually separate out as a lower or base layer. When this layer is freed from an aqueous layer and further volatiles are removed by distillation under reduced pressure there is produced a resinous product of moderate molecular weight known as a resol or novolac which can be made to yield a cross linked polymeric network.
Novolacs involve the initial formation of dehydroxyphenol methanes and on further condensation and methylene bridge formation form a fusible and soluble linear polymers of phenol groups separated by methylene bridges where ortho and para links occur at random.
In contrast resol polymers are formed by condensation of methylol phenols either through methylene linkages or through ether linkages. If these reactions are carried further large numbers of phenolic nuclei can condense to give a repeating network.
Thus in summary the four major reactions in phenolic resin chemistry are (i) addition to give methylol phenols; (ii) condensation of a methylol phenol and a phenol to give a methylene bridge; (iii) condensation of ether bridges of methylene bridges and formaldehyde, the latter reacting again in reaction (i).
Phenolic resins known as one stage resins may be produced by charging all reactants comprising phenol, formaldehyde, and alkaline catalyst into a resin kettle and reacted together. The ratio of formaldehyde to phenol is about 1'25:1. In contrast two stage resins are made with an acid catalyst and only part of the necessary formaldehyde is added to the kettle producing a mole ratio of about 0.8:1. The rest of the formaldehyde is added as hexamethylene tetramine or paraformaldehyde which decomposes in the final curing step with heat and moisture present to yield formaldehyde and ammonia which acts as the catalyst for curing.
The procedures for one and two stage resins are similar and the same equipment is used for both. The reaction is exothermic and cooling is required. The formation of a resol or novolac is evidenced by an increase in viscosity. Water is driven off under vacuum and a thermoplastic A-resin or resol, soluble in organic solvents remains. The material is dumped from the kettle, cooled and ground to a fine powder. At this point colorants, lubricants, fillers and if a two stage resin is required enough hexamethylene tetramine to give a final formaldehyde phenol mole ratio of 1'5:1 is added. The mixture is rolled on heated mixing rolls where the reactions are carried further to the point where the resin is in the B stage or resitol nearly insoluble in organic solvents but still fusible under heat and pressure. The resin is then cooled and cut into final form. The C stage or resite which is the final, infusible, cross linked polymer is reached on subsequent fabrication eg. by moulding.
The resins produced as described above are used in compression or transfer moulding yielding products that are heat resistant, stable and resistance to cold flow. They are also used as laminating resins
REFERENCES:
patent: 5075414 (1991-12-01), Dailey, Jr.
Foelak Morton
Jones Richard
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