Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2000-02-18
2001-04-10
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C521S181000, C528S137000, C528S142000, C528S143000, C528S144000, C528S147000
Reexamination Certificate
active
06214964
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to phenol formaldehyde resins and a process for making the resins. In particular, the present invention is directed towards phenol formaldehyde resin having a relatively high formaldehyde to phenol ratio when compared with conventional resins.
BACKGROUND ART
Phenol formaldehyde resins are known. These resins are typically made by condensing phenol with formaldehyde in the presence of a basic or acidic catalyst. The product resin comprises a crosslinked network of phenyl rings connected by methylene bridges. The molecular weight and degree of crosslinking of the resin may be increased by increasing the amount of formaldehyde. Molecular weight and degree of crosslinking can influence physical properties such as heat and flame resistance and mouldability. However, there is a practical limitation to the amount of formaldehyde which can be used. At a formaldehyde phenol ratio of above about 2:1, the rate of the crosslinking reaction is difficult to control and is considered too reactive for commercial resin production. For this reason, the maximum ratio of formaldehyde in conventional resins is about 1.5:1.
In an earlier patent application No. WO 92/1758 a phenol formaldehyde resin having a relatively high formaldehyde ratio is described. This resin is prepared by mixing two separate phenol formaldehyde mixtures. A first resole is prepared by mixing phenol and excess formaldehyde in the presence of a basic catalyst. After a period of time, a stabiliser comprising glycerol and a dicarboxylic acid is added to control further reaction. Water is then removed under vacuum and methanol as solvent is added. Water is generally present in the reactants and is also produced by the condensation reaction between phenol and formaldehyde. The second resole is prepared by mixing phenol and formaldehyde in the presence of an acidic catalyst. In this case, only a marginal excess of formaldehyde is used. After the phenol and formaldehyde have reacted, water is removed under vacuum and a solution comprising zinc chloride, an alpha hydroxy acid, p-toluene sulphonic acid and sulphuric acid in a non-aqueous solvent is then added. To produce the product resin, an excess of the first mixture is mixed with the second mixture and the final mixture is allowed to cure.
The above process is essentially a two pack method for preparing a phenol formaldehyde resin. This method requires the preparation of two different types of resole, each resole being prepared under different catalytic conditions. The method also requires separate storage of each component until use.
It is an object of the present invention to provide a one step method for the preparation of a phenol formaldehyde resin having formaldehyde in excess or to provide the public with a useful choice.
SUMMARY OF THE INVENTION
According to a broad form of the present invention there is provided a process for forming a phenol formaldehyde resin, the process comprising the steps of;
(i) reacting phenol with an excess of a formaldehyde material in the presence of an acid or base catalyst until water separates from the reactants as an immiscible layer,
(ii) adding a mixture comprising an excess polyhydric alcohol and an aromatic dicarboxylic or tricarboxylic acid, salt or anhydride thereof to the phenol and formaldehyde reaction mixture followed by addition of an alpha hydroxy acid,
(iii) adding a non-aqueous solvent, wherein at least some of said water is removed either before addition of the mixture prepared in step (ii) or after addition of the alpha hydroxy acid,
(iv) preparing a solution comprising a Lewis acid, a polyhydric alcohol, an alpha hydroxy acid, a non-aqueous solvent, an aromatic sulphonic acid and sulphuric or hydrochloric acid,
(v) adding the solution formed in step (iv) to the mixture formed in step (iii) and allowing the mixture to cure.
According to a second broad form of the invention there is provided a phenol formaldehyde resin prepared by the process of the first broad form.
The present invention is based upon the surprising and unexpected discovery that a phenol: formaldehyde resin containing a high formaldehyde ratio can be prepared in a one step method.
In the present specification and claims, the term formaldehyde material includes formaldehyde and formaldehyde precursors which generate free formaldehyde in situ. Examples of such formaldehyde precursors include paraformaldehyde and hexamethylene tetramine. Preferably a mixture of paraformaldehyde and formaldehyde is used.
In the present specification and claims, the term phenol includes phenol, phenol derivatives and mixtures thereof. Typical phenol derivatives include cresol, resorcinol, xylenol, bisphenol A and p-t-butylphenol.
In the method of the present invention phenol is reacted with an excess of a formaldehyde material. Preferably the formaldehyde phenol ratio is between about 2:1 to about 3:1. Preferably the ratio is about 2.5:1.
The phenol and formaldehyde material are reacted in the presence of an acid or base catalyst. Any suitable catalyst may be used and these are known in the art. Preferably a basic catalyst is used. Typical catalysts include sodium hydroxide, calcium hydroxide, potassium hydroxide, sodium carbonate or organic amines.
The phenol and formaldehyde reactants are initially soluble in water. As the condensation reaction proceeds, the product become less soluble in water. After a period of time, an immiscible aqueous layer is formed. The reaction between the phenol and formaldehyde is allowed to proceed until formation of a separate aqueous layer. When this occurs, a stabiliser comprising a polyhydric alcohol and an aromatic dicarboxylic or tricarboxylic acid salt or anhydride thereof is added. The polyhydric alcohol is preferably a lower alkyl diol or triol. Suitable alcohols include glycerol, 2,3 butanediol, 1,3 propanediol, meso-hydroxybenzoin, ethylene glycol, pinacol, pentaerthyritol and 1,3-butanediol. Glycerol is a particularly preferred alcohol.
The aromatic dicarboxylic or tricarboxylic acid may include phthalic acid, isophthalic acid, trimellitic acid or trimesic acid. Particularly preferred is phthalic acid. Anhydrides of these acids may also be used and are preferred. An especially preferred anhydride is phthalic anhydride.
The polyhydric alcohol and acid or anhydride are preferably mixed prior to addition to the phenol formaldehyde mixture. The mixture contains an excess of polyhydric alcohol and typically comprises an alcohol acid molar ratio of between about 9:1 to about 22:1 based on the hydroxyl groups. The polyhydric alcohol and acid or anhydride may react to form an ester having free hydroxyls. These hydroxyls are available when a basic catalyst has been used, the alcohol/dicarboxylic acid mixture may neutralise the base. The alcohol/anhydride mixture may also react with hydroxy or carboxyl groups in the reaction mixture to form a condensation product. An especially preferred alcohol/anhydride mixture is glycerol and phthalic anhydride. Preferably the glycerol/phthalic anhydride mixture is in a weight ratio of about 5:1. Preferably about 3.5 wt % to about 4 wt % of the glycerol/phthalic anhydride based on phenol is added to the phenol/formaldehyde mixture.
After addition of the stabiliser, an alpha hydroxy carboxylic acid is added. Examples of suitable alpha hydroxy acids include lactic acid, glycolic acid, citric acid, mandelic acid and malic acid. Lactic acid is particularly preferred. When the phenol and formaldehyde have been reacted in the presence of a basic catalyst, the acid may also neutralise the base. Typically, about 0.05 to about 3 wt % of acid is added. (Based on the total amount of phenol and formaldehyde). Preferably, about 1 to about 1.5% is added.
At least some of the water is removed from the reactant mixture either before or addition of the mixture formed in step (iii). Preferably substantially all the water is removed. The water may be removed by any suitable means. The reactants may be allowed to stand for a period of time to allow the layers to separate. The
Akin Gump Strauss Hauer & Feld L.L.P.
Foelak Morton
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