Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2002-01-02
2003-11-04
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S137000, C528S140000, C528S144000, C528S154000, C528S230000, C528S486000, C528S488000, C528S495000, C528S503000
Reexamination Certificate
active
06642345
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a novolak aralkyl resin having both structural units of low molecular weight novolak units and aralkyl group units together and a preparation process thereof, and composition containing the resin.
More in particular, it relates to a novolak aralkyl resin which is heightened its molecular weight while increasing the repeating structural units of low molecular weight novolak units and aralkyl group units by suppressing decomposition of low molecular weight novolak, makes its curing reaction with hexamethylenetetramine or the like progress uniformly and rapidly, provides excellent heat resistance to its cured products and suitable to application uses such as friction materials, sliding materials, molding materials and encapsulating materials, a preparation process thereof, a novolak aralkyl resin composition causing rapid curing reaction and providing excellent heat resistance to its cured products which is suitable to friction materials such as disk brake pads, brake linings and clutch facings for braking automobiles, railway vehicles and various industrial machines, to binders for molding materials such as electric and electronic equipment parts, communication equipment parts and mechanical parts and to sliding materials and so on.
In this invention, novolak means, resins having a repeating structure of phenol nuclear units and methylene group units obtained by reacting, for example, phenol and formaldehyde in the presence of an acidic catalyst. They are referred to bi-nuclear novolak, tri-nuclear novolak and the like depending on the number of phenol nuclear units. Further, low molecular weight novolak is a collective term for novolaks up to about penta-nuclear novolak.
2. Related Art Statement
A phenolic resin as a reaction product of a phenol compound and an aralkyl compound such as p-xylylene glycol dimethyl ether is generally referred to as a xylok resin which is a phenol aralkyl resin having a repeating structure of phenol nuclei and aralkyl group as described, for example, in Japanese Patent Publication No. 15111/1972 and Japanese Patent Publication No. 14280/1977. The phenol aralkyl resin has excellent characteristics for heat resistance, soft and flexibility and hygroscopic resistance compared with novolak type phenol resin and has been generally used for applications such as friction materials, molding materials and encapsulating materials. However, in the field where it is used by being cured with hexamethylenetetramine or the like, since the ratio of the phenol nuclei is small in the resin, the curing reaction is slow for which improvement has been desired.
For compensating the drawback, Japanese Patent Laid-Open No. 142324/1992 proposes a modified phenol aralkyl resin obtained by reacting phenols, an aralkyl compound and formaldehyde in the presence of an acidic catalyst at 100 to 150° C. Further, Japanese Patent Laid-Open No. 173834/1992 discloses a phenolic resin of using phenol and novolak resin together, which is reacted with p-xylylene glycol dimethyl ether. However, since phenol is used as the raw material in the both resins described above, they contain a phenol aralkyl resin portion causing slow curing reaction, their curing rate are insufficient. In addition, though a novolak resin portion is present during reaction in the method described in both of the publications, when the novolak resin has high molecular weight, it further is heightened molecular weight remarkably or gelled in the subsequent reaction, so that the amount of the aralkyl compound to be introduced can not be increased and, as a result, the amount of unreacted novolak resin increases to bring about a problem of lowering the heat resistance. Further, since the amount of the acidic catalyst used is large, it involves a problem that the catalyst remaining in the resin causes decomposing reaction, failing to obtain a resin of stable property.
In addition, there can be mentioned a method of increasing the velocity of curing reaction by mixing a novolak type phenol resin with the phenol aralkyl resin, but since the novolak type phenol resin reacts preferentially to hexamine or the like, this results in a problem of unevenness in the curing.
When novolak, particularly, a low molecular weight novolak and an acidic catalyst are brought into contact, it causes decomposition and re-bonding to form phenol and high molecular weight novolak. Accordingly, decomposition and re-bonding reaction are also caused in a case of reacting the low molecular weight novolak with the aralkyl compound in the presence of the acidic catalyst, so that it leads to a problem that a stable reaction product containing many repeating structural units of low molecular weight novolak and aralkyl groups can not be obtained.
DISCLOSURE OF THE INVENTION
This invention intends to provide a novolak aralkyl resin having both structures of bi-nuclear novolak units and aralkyl group units together and being capable of conducting the curing reaction with hexamethylenetetramine or the like rapidly and uniformly while maintaining the excellent heat resistance inherent to the phenol aralkyl resin, and a preparation process thereof, and a composition containing the novolak aralkyl resin described above.
An aimed novolak aralkyl resin can be obtained by increasing the repeating structural units of bi-nuclear novolak units and aralkyl group units and by increasing the molecular weight of the resin. In this case, it is important to suppress the decomposing reaction of the low molecular weight novolak. Novolak causes decomposition and re-bonding by being heated in the presence of an acidic substance to form phenol and high molecular weight novolak. For example, when a bi-nuclear novolak as a typical example of the low molecular weight novolak is heated for about one hour in the presence of the same acidic catalyst and at the same temperature as upon reaction with the aralkyl compound, about 8 mol % phenol is formed, and twice molar amount of bi-nuclear novolak is lost and tri-or higher poly-nuclear novolak is formed. On the other hand, when the reaction velocity with the aralkyl compounds is compared between the low molecular weight novolak and phenol, the reaction velocity is higher for the low molecular weight novolak. For example, when the mixture of bi-nuclear novolak and phenol containing each at an equal molar amount is reacted with the aralkyl compound, it results in more unreacted component for phenol.
Accordingly, even if the bi-nuclear novolak and the aralkyl compound are charged each by a predetermined amount for reaction into the reaction system, when the decomposition of the bi-nuclear novolak proceeds, reaction is taken place for three ingredients of novolak, phenol and aralkyl compound and the properties of the resultant resin is deviated from desired values depending on the extent of the decomposition. Further, after the completion of the reaction, in a case where the decomposition proceeds while liberating a phenol, the resultant resin becomes instable because of bonding of disconnected active residues with other molecules of bi-nuclear novolak or the like. Consequently, the molecular weight of the resultant resin becomes higher.
From the foregoings, as a means for obtaining a resin containing many repeating structural units of low molecular weight novolak and aralkyl groups, it is important to suppress the decomposing reaction of the low molecular weight novolak and to avoid the formation of the free phenol as an index of the decomposition of raw materials such as low molecular weight novolak as less as possible.
The present inventors have made an earnest study on the basis of the knowledge as described above, as a result, have found that the decomposition of the low molecular weight novolak during the reaction can be suppressed to obtain an aimed resin upon reacting low molecular weight novolak containing a bi-nuclear novolak at a specified amount or more and an aralkyl compound in the presence of an acidic catalyst by suppressing contact of the
Kaneko Masahiro
Narisawa Hiroaki
Yuasa Teruo
Mitsui Chemicals Inc.
Truong Duc
LandOfFree
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