Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2002-01-22
2003-11-04
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C525S523000, C528S110000, C528S111000, C528S405000, C528S408000, C528S418000, C528S421000
Reexamination Certificate
active
06642344
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the curing of epoxy resins and more particularly to a new class of aliphatic secondary diamine curing agents for flexible epoxy resins which are less brittle but yet maintain high hardness and excellent chemical and wear resistance.
BACKGROUND OF THE INVENTION
Although epoxy resins have been found to be very useful in numerous applications relying on great strength, such as bonding agents, laminates and tooling, the cured unflexibilized epoxy resins are also quite brittle and tend to chip or fracture in applications requiring flexibility or impact. The present invention relates to cured epoxy resins used for protective surface coatings, such as paints, insulation, etc., where chipping and fracturing of the coating during flexure must be avoided. The cured epoxy resins of the present invention have decreased brittleness and improved impact resistance while maintaining the high hardness and the excellent chemical and wear resistance needed in, for example, coating applications.
Epoxy resins are formed by the reaction of a 1,2-epoxy compound and a polyol, including dihydric phenols or glycols. A commonly available epoxy resin, preferred for many applications, is prepared from epichlorohydrin and Bis-Phenol A (2,2-bis-(4-hydroxyphenol) propane). Other useful 1,2-epoxy compounds include 1,2-epoxy-4-chlorobutane, 1,2-epoxy-5-chloropentane, 1,2-epoxy-6-chlorohexane, dichlorohydrin, butadiene dioxide, polyglycidyl ethers of ethylene glycol, propylene glycol, trimethylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, glycerol, etc. Other dihydric phenols may be employed, including resorcinol, catechol, hydroquinone, 4,4′-dihydroxybenzophenone, 1,1-bis-(4-hydroxyphenyl)-ethane, 1,1-bis-(4-hydroxyphenyl)-butane, 2,2-bis-(4-hydroxyphenyl)-butane, (Bis-Phenol-B), 1,5-dihydroxynaphthylene, etc. Other polyols which may be reacted with a 1,2-epoxy compound include ethylene glycol, propylene glycol, trimethylene glycol, diethylene glycol, triethylene glycol, glycerol, erythritol, pentaerythritol, mannitol, sorbitol, polyallyl alcohol, polyvinyl alcohol, etc. Epoxy resins formed from combinations of the 1,2-epoxy compounds and polyols referred to above are not necessarily equivalent and furthermore, the composition of the epoxy resin is dependent upon the molecular proportions of the 1,2-epoxy compound and the polyol, as is well understood in the art.
In order to form the desired final product, the epoxy resin must be cured, during which a curing agent reacts with the epoxy resin to form a thermoset resin. The epoxy resin may be a viscous liquid, a semi-solid or solid, soluble in certain organic solvents or liquefiable on mild heating. The reaction may be catalyzed by an organic acid, an organic base such as tertiary amines, or a Lewis acid such as boron trifluoride and boron trifluoride ether complexes.
Various amine compounds have been suggested for use as curing agents for epoxy resins. For example, U.S. Pat. No. 3,280,043 B1 discloses that N
1
,N
3
-dialkyldiethylenetriamine is a curing agent for epoxy resins which will impart flexibility to the cured epoxy resin. Other curing agents having flexibilizing capability have been discussed in Lee, H.; Neville, K.
Handbook of Epoxy Resins
; McGraw-Hill: New York, 1982, 16-2 and 16-3, e.g., polyether diamines, fatty polyamides, amidopolyamines, polymeric acids, carboxyl-terminated polyesters, anhydrides and reactive modifiers, e.g., furfural-ketone reaction products. The secondary triamines of U.S. Pat. No. 3,280,043 B1 are mentioned in the Handbook of Epoxy Resins at page 9-7. Partially N-alkylated diphenylmethane bases are disclosed as epoxy curing agents in U.S. Pat. No. 3,634,275 B1. Japanese Kokai Patent Nos. 61-40318 and 63-37,117 disclose aromatic secondary diamines as curing agents for epoxy resins. The present invention avoids the drawbacks of the polyfunctional flexibilizers discussed above.
U.S. Pat. No. 4,709,003 B1 discloses alkylated triamines as curing agents for manufacturing polyurethanes. U.S. Pat. No. 3,752,768 B1 discloses a reaction mixture for producing a curing agent for epoxy resins, polyurethane foams and elastomers comprising a complex mixture of aniline and aniline derivatives and formaldehyde. U.S. Pat. No. 5,312,886 B1 discloses bis(N-alkylaminocyclohexyl)methanes as chain extenders in the formation of polyurethane and polyurea polymers.
SUMMARY OF THE INVENTION
The invention is an epoxy resin cured with an aliphatic secondary diamine curing agent having the structure of:
where R
1
and R
2
are each individually an alkyl, alkenyl, aryl, or arylalkyl group having from about 1 to about 20 carbon atoms, and R
3
and R
4
are each individually a hydrogen, an alkyl group having from 1-20 carbon atoms, or an alkenyl group having from 1-20 carbon atoms. Another embodiment of the invention is a method of curing an epoxy resin using at least one curing agent (I) or (II) above.
DESCRIPTION OF THE INVENTION
The flexible epoxy resins of the present invention are cured with a curing agent comprising at least one aliphatic secondary diamine curing agent having the structure of:
where R
1
and R
2
are each individually an alkyl, alkenyl, aryl, or arylalkyl group having from about 1 to about 20 carbon atoms, and R
3
and R
4
are each individually hydrogen, an alkyl group having from 1-20 carbon atoms, or an alkenyl group having from 1-20 carbon atoms. The flexibility of the cured resin would be enhanced when the curing agent of the present invention was used as compared to cured epoxy resins made with other similar curing agents.
The epoxy resins useful in the invention include the bis-phenol A-based epoxy resins as well as other polyol-based resins including novolac resins, etc., in which the phenol is reacted with a 1,2-epoxy compound, preferably epichlorohydrin. The resin may be a low or high viscosity liquid, a solid or a solution of a solid in an organic solvent. Suitable solvents include ketones, especially acetone, methyl ethyl ketone and methyl isobutyl ketone. Before curing the epoxy resin, additional materials may be added to fulfill certain functions, such as fillers, pigments and, even, additional flexibilizers or plasticizers.
As stated above, the curing agent of the present invention is an aliphatic secondary diamine having one of the following two general structures:
where R
1
and R
2
may be an alkyl, alkenyl, aryl, or arylalkyl, group and having from about 1 to about 20 carbon atoms. Although R
1
and R
2
need not be the same, in most cases they will be identical simply because of the convenience of their preparation. The alkyl groups may be linear, branched or cyclic. Representative alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, secondary butyl, tertiary butyl, and the various isomeric pentyl, hexyl, heptyl, octyl, nonyl, and decyl groups. The preferred R
1
and R
2
contain at least three carbon atoms with the sec-butyl group being particularly preferred. Representative aryl groups include phenyl and benzyl with representative arylalkyl groups including substituted phenyl and substituted benzyl. Examples of alkenyl groups are the unsaturated counterparts of the aforementioned alkyl groups. Secondary alkyl or alkenyl groups, i.e., those branched at the carbon atom bound to the nitrogen atom, and secondary alkyl groups in particular are preferred. Representative of such groups are 2-propyl, 2-butyl, 2-pentyl, 3-pentyl, 2-hexyl, and so forth. The groups R
3
and R
4
are each individually either an alkyl or an alkenyl group having from 1-20 carbon atoms, preferably from 1-8 carbon atoms or hydrogen. The alkyl or alkenyl group may be linear, cyclic or branched. Examples of alkyl groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, and eicosyl moieties. Examples of alkenyl groups are the unsaturated counterparts of the alkyl groups above. Secondary alkyl or alkenyl group
House David W.
Scott, Jr. Ray V.
Aylward D.
Dawson Robert
Dorf Ketal Chemicals, LLC
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