Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-06-12
2004-03-23
Sellers, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C528S112000
Reexamination Certificate
active
06710139
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to epoxy resins and phenolic curing agents with increased functionality and a process for making the same.
The average functionality of currently commercially available solid epoxy resins (SER) and phenolic curing agents (PCA) that are used in powder coatings is two or slightly less than two.
As used herein, the term SER or solid epoxy resin refers to a higher molecular weight polymer whose epoxy functionality is typically 2 or less than 2. The term PCA or phenolic curing agent refers to a polymer whose phenolic functionality is typically 2 or less than 2.
As used herein, the term “functionality” refers to the average number of epoxy groups per resin molecule for SER and the average number of phenolic groups per resin molecule for PCA.
Phenolic curing agents and solid epoxy resins have similar structures and are made from the same monomers. If the number of epoxy groups in the monomer change is greater than the number of phenolic groups, then an SER will result. If the number of phenolic groups is greater than the number of epoxy groups, then a PCA will result.
In many applications, especially those applications in which better high temperature performance is needed, it is often desirable to employ an epoxy resin or curing agent having an average functionality of greater than two.
Methods for increasing the epoxy functionality of epoxy resins are known. One method comprises adding an epoxy novolac to the SER to increase its functionality. This approach works well in most applications; however, the novolac adds cost and produces resins with undesirable color stability. Use of novolacs also produces low molecular weight fractions which can make the resins prone to sintering. In another method known as “bodying,” a liquid epoxy resin (LER) is heated with a bisphenol in the absence of a catalyst and this results in some branching via the epoxy-epoxy reaction. A catalyst is then added to the reaction mixture to form a higher molecular weight polymer (SER). In this method, it is difficult to control the degree of reaction.
Anhydrides are usually used as curing agents for epoxy resins. It is generally thought that anhydrides create branches by reacting with the secondary hydroxyl on the epoxy polymer backbone. Thus, attempts have been made to use anhydrides to branch epoxy resins. However, these attempts have always produced a gelled product which is a fully crosslinked epoxy resin. As used herein, the term “branch” or “branching” refers to the addition of epoxy functionality to epoxy resins by the epoxy-epoxy and/or epoxy-hydroxy reaction of different epoxy resin molecules.
Another method for increasing the functionality of an epoxy resin is to branch the resin in the presence of a Li or Cs catalyst as described in U.S. Pat. No. 4,722,990. In this example, the branching must be terminated by cooling the reaction mixture or by adding a deactivating agent. It is important to terminate the branching or gelation will result.
It would be desirable to provide a process for preparing epoxy resins having an average functionality of greater than two without the disadvantages of the prior art. It is important that the epoxy resins so formed are not crosslinked systems (gels) and that they can be used with curing agents to form a thermosetting composition for use in coating applications.
SUMMARY OF THE INVENTION
In one aspect, the present invention is an epoxy or phenolic functional polyester/polyether oligomer or polymer having an epoxy functionality of greater than 2 and comprising moieties derived from diglycidyl ethers or diglycidyl esters, anhydrides and dihydric phenols.
In a second aspect, the present invention is a process for preparing the epoxy or phenolic functional polyester/polyether oligomer or polymer of the first aspect which comprises branching an epoxy resin or phenolic curing agent by (1) reacting a liquid epoxy resin (LER), along with a dihydric phenol, with a cyclic anhydride, in the presence of a catalyst, the cyclic anhydride being employed in an effective amount to increase the epoxy functionality. This effective amount is sufficient to achieve the desired epoxy or phenolic functionality but insufficient to cause the formation of gel in the anhydride-modified epoxy resin. As used herein, the term “LER” refers to a liquid diglycidyl ether or ester.
DETAILED DESCRIPTION OF THE INVENTION
The incorporation of anhydrides onto the backbone of an epoxy or phenolic polymer results in branching, the extent of which can be controlled by the amount of anhydride added to the reaction mixture. Using the present process, epoxy or phenolic resins of various equivalent weights and various levels of branching can be made.
It has now been found that the formation of gel in an anhydride-modified epoxy resin can be avoided by the process of the present invention which comprises adding an effective amount of an anhydride to the epoxy or phenolic resin to increase its functionality. This effective amount is sufficient to achieve the desired functionality but insufficient to form gel in the anhydride-modified resin.
The present reaction can be done in one step wherein a mixture of a liquid epoxy resin, anhydride, dihydric phenol and catalyst are stirred and heated to yield the final product.
Alternatively, the liquid epoxy resin and the dihydric phenol are reacted first and then the anhydride is added or, the LER and anhydride are reacted first, and then the dihydric phenol is added to the reaction. The reaction can be done using a batch process or continuous process conducted in a reactive extruder, such as that described in European Patent No. EP 0193809.
The epoxy resins which can be employed in the practice of the present invention for preparing the anhydride-modified resin (epoxy or phenolic functional polyester/polyether oligomer or polymer) include the diglycidyl ethers of dihydric phenols, such as those described in U.S. Pat. Nos. 5,246,751; 5,115,075; 5,089,588; 4,480,082 and 4,438,254, all of which are incorporated herein by reference, or the diglycidyl esters of dicarboxylic acids such as those described in U.S. Pat. No. 5,171,820. Other suitable diepoxides include &agr;,{overscore (&ohgr;)}-diglycidyloxyisopropylidene-bisphenol-based epoxy resins (commercially known as D.E.R.™ 300 and 600 series epoxy resins), &agr;,{overscore (&ohgr;)}-diglycidyloxy tetrabromoisopropylidene-bisphenol-based phenoxy resins, such as Quatrex™ 6410, both are product of The Dow Chemical Company. Preferred epoxy resins are the epoxy resins having an epoxy equivalent weight of from about 100 to about 4000. Most preferred epoxy resins are the diglycidyl ethers of bisphenol A; 4,4′-sulfonyldiphenol; 4,4-oxydiphenol; 4,4′-dihydroxybenzophenone; resorcinol; hydroquinone; 9,9′-bis(4-hydroxyphenyl)fluorene; 4,4′-dihydroxybiphenyl or 4,4′-dihydroxy-alpha-methylstilbene and the diglycidyl esters of the dicarboxylic acids mentioned previously.
The amount of epoxy resin used depends on whether a phenolic functional or epoxy functional polymer is desired. It also depends on the targeted molecular weight and functionality. In general, the epoxy resin is used in an amount of from about 10 wt. % to about 80 wt. %, more preferably, from about 30 wt. % to about 75 wt. % and, most preferably, from about 35 wt. % to about 70 wt. %, based on the weight of reactants.
The anhydrides which can be employed in the practice of the present invention for preparing the anhydride-modified resin (epoxy or phenolic functional polyester/polyether oligomer or polymer) include diglycolic anhydride, dichloromaleic anhydride, maleic anhydride, succinic anhydride, glutaric anhydride, citraconic anhydride, itaconic anhydride, tetrabromophthalic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, 4-methylhexahydrophthalic anhydride, methyl-5-norbornene-2,3-dicarboxylic anhydride, 1,8-naphthalic anhydride, trimilletic anhydride and 1,2,4,5-benzenetetracarboxylic dianhydride.
Preferred anhydrides
Franca Marcos
Hoyles Stephen M.
Subramanian Ramki
Damocles Nemia C.
Dow Global Technologies Inc.
Sellers Robert
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