CA1227900A

CA1227900A - Phosphine compounds as curing accelerators for amides in epoxy resin systems

Info

Publication number: CA1227900A
Application number: CA000429037A
Authority: CA
Inventors: Shiow C. Lin
Original assignee: WR Grace and Co
Current assignee: WR Grace and Co
Priority date: 1982-08-16
Filing date: 1983-05-27
Publication date: 1987-10-06
Also published as: GB2126235A; DE3328831A1; IT1163881B; GB8320755D0; IT8322501A0; IT8322501A1; FR2531969A1

Abstract

PHOSPHINE COMPOUNDS AS CURING ACCELERATORS FOR
AMIDES IN EPOXY RESIN SYSTEMS
Abstract of the Disclosure This invention relates to a one-component epoxy formulation containing an amide in combination with a phosphine compound which affords faster cures and also lowers the curing temperature.

Description

I

BACKGROUND OF THE Invention 1. Field of the Invention This invention relates to one-component epoxy formulations. These epoxy heat curable formulations contain an aside in combination with aphosphine compound which affords faster cures and also lowers the curing temperature. The composition can be used as an adhesive, sealant or coating.

2. Description of the Prior Art The heat curing of epoxy resins with asides is well known in the art. Asides such as dicyandiamide and mailmen are employed commercially to cure epoxy resins.
The use of these materials, per so, however, require temperatures of 200 or 300C or more in order to obtain a fully cured product.
OBJECTS OF THE INVENTION
One object of the instant invention is to produce a one-component epoxy formulation. Another object of the instant invention is to produce a one-component epoxy formulation which is heat curable at a lower temperature than present commercial formulations. Still another object is to produce a one-component epoxy formulation which is heat curable at a defined temperature in a shorter time period. Other objects will become apparent ..
from a reading hereinafter.
DESCRIPTION OF THE INVENTION
The present invention relates to a one-component, heat curable epoxy formulation containing an aside in combination with a phosphine compound. Such a formulation affords faster cures than epoxy-amide formulations and also allows curing at lower temperatures than said epoxy-amide formulations.
The invention further provides a process for adhering two substrates which comprises contacting the substrates with a heat curable composition comprising if) an epoxy resin, 79~

(2) 1 to 10 weight percent of (1) of an aside and (3) 1 to 15 weight percent of I of a phosphine compound of the group consisting of (a) RIP wherein R is alkyd, cycloalkyl, aureole and alkaryl wherein said alkyd groups contain 1 to 10 carbon atoms (b) carboxylic acid salts of (a) and (c) mixtures of (a) and by and applying heat thereto comprising an epoxy resin, an aside and a phosphine compound.
The phosphine compounds operable herein to accelerate the curing reaction are of the formula:

. .

- pa-Z7~¢~`~

RIP or carboxylic acid salts thereof wherein R is alkyd, cycloalkyl, aureole or alkaryl wherein said alkyd groups contain l to 10 carbon atoms. Specific examples of said phosphine compounds include, but are not limited to, triphenyl phosphine, tricyclohexyl phosphine~
tris(orthotolyl) phosphine and tri-n-octyl phosphine 2,2-dimethylol prop ionic acid salt.
The carboxylic acid salts of the RIP compounds are synthesized by methods well known in the art. One method consists of reacting equimolar amounts of the RIP
compound and a carboxylic acid in solvent with stirring at room temperature, removing the solvent under reduced pressure and recovering the salvo The phosphine compound is added to the composition in an amount ranging from 1 to 15% by weight of the epoxy resin - There are various known aside compounds used to cure epoxy resin. Said aside compounds include amino-polyamides. Such materials include, but are not limited to, mailmen, N,N-diallymelamine, dicyandiamide, alkoxyalkyl melamines, such as hexamethoxymethyl mailmen, melamine-formaldehyde resins, ursea-formaldehyde resins such as monomethylol urea and dimethylol urea, triallyl sonority, guanamines, imidazoles such as 2-ethyl-4-methyl-imidazole, hydrazides exemplified by carbohydrazide, adipic acid deodorized, guanidines, polyalkylene mines such as ethyleneimine, sulfonamides and the like. These materials are all well known amide-containing curing agents for epoxy resins.
The asides are added to the composition in amounts ranging prom 1 to 10 weight percent based on the weight of the epoxy resin.
The epoxy resin oboe used in the composition of the invention comprises those materials possessing more than one epoxy , i . e ., I I

group. These compounds may be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic and may be substituted with substituents, such as chlorine, hydroxyl groups, ether radicals and the like.
The term epoxy resin" when used herein and in the appended claims contemplates any of the conventional monomeric, dim Eric, oligomeric or polymeric epoxy materials containing a plurality, more than one, e. g., 1.1,, epoxy functional groups. Preferably, they will be members of classes described chemically as (a) an epoxidic ester having two epoxycycloalkyl groups; (b) an epoxy resin prepolymer consisting predominately of the monomeric diglycidyl ether of bisphenol-A; (c) a polyepoxidized phenol novolak or crossly novolak; (d) a polyglycidyl ether of a polyhydric alcohol; (e) diepoxide of a cycloalkyl or alkylcycloalkyl hydrocarbon or ether; or (f) a mixture of - any of the foregoing. To save unnecessarily detailed description, reference is made Jo the Encyclopedia of Polymer Science and Technology Vol. 6, 1967, Intrusions ; Publishers, New York, pages 209-~71, incorporated herein ; 25 by reference.
Suitable commercially available epoxidic esters are preferably, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclo-hexanecarboxylate (Union Carbide ERR 4221, Cuba Geigy SUE); as well as bis(3,4-epoxy-6-methylcyclohexyl-methyl)adipate (Union Carbide ERR 4289); and Boyce-epoxycyclohexylmethyl)adipate (Union Carbide ERR 4299).
Suitable commercially available diglycidyl ethers of bisphenol-A are Cuba Geigy Araldite 6010, Dow Chemical DYER
331, and Shell Chemical Eon 828 and 826.

* Trademark ,~".,~.

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A polyepoxidized phenol formaldehyde novo]dk prepolymer is available from Dow Chemical DEN 431 and 438, and a polyepoxidized crossly formaldehyde novolak prepolymer is available from Ciba-Geigy Araldite 538.
A polyglycidyl ether of a polyhydric alcohol is available from Cuba Geigy, based on butane-ld4-diol, Araldite RD-2; and from Shell Chemical Corp., based on glycerine, Eon 812.
A suitable diepoxide of an alkylcycloalkyl hydrocarbon is vinyl ~yclohexene dioxide, Union Carbide ERR 4206, and a suitable diepoxide of a cycloalkyl ether is Boyce-epoxycyclopentyl)-ether, Union Carbide ERR 0400.
Other examples include the epoxidized esters of the polyethylenically unsaturated monocarboxylic acids, such as epoxidized linseed, soybean, purl, oiticica, lung, walnut and dehydrated castor oil, methyl linoleate, bottle linoleate, ethyl 9,12-octadecadienoate, bottle 9,12,15-octadecatrienoate, bottle eleostearate, monoglycerides of lung oil fatty acids, monoglycerides of soybean oil, sunflower, rhapsody, hemp seed, sardine, cottonseed oil and the like.
In practicing the instant invention it is also possible, although optional, to add a thermoplastic material to the composition. These thermoplastic materials are composed of 100% non-volatile materials i. e., containing no water, solvent or other volatile carriers. They are solid or liquid at room temperature but become more fluid at elevated temperatures, thereby allowing for easy application. The thermoplastic i 30 materials operable herein include, but are not limited trod polyamides, polyvinyl chloride, polyvinyl acetals and polyester resins ethylene-vinyl acetate (EVA) copolymers, ethylene-ethyl acrylate EYE) copolymers, butadiene-acrylonitrile copolymers and styrene-ethylene-butylene * Trademark ., :ll2~27~

copolymersO Some of the newer materials of the more conventional "rubber" variety are the block copolymers, styrene-butadiene or styrene-isoprene sold under the trademark "WriteNow"
One thermoplastic material useful in the compositions of the present invention includes those thermoplastic segmented copolyesters disclosed in US. Patent No. 4,059,715, incorporated herein by reference. These are solid, non-tacky, strongly cohesive, solvent-free thermoplastic polymers which are themselves not subject to cold flow and are non-blocking below their melting temperatures but which become aggressively tacky and bondable upon being melted. They consist essentially of from about 5 to 75 percent by weight of amorphous ester units and 95 to 25 percent by weight of crystallizable ester units joined through the ester linkages Other thermoplastic materials which are useful in the compositions of the present invention include other thermoplastic polyesters (e g., that available under the trade designation "5096" from Cooper Polymers, Into), thermoplastic polyurethane (e.g., that available under the trade designation "Q-thane PI 56" from K.J. Quinn Co., Inc. ?, thermoplastic polyamides (e.g., that available under the trade designation "Caromed 2430" from Cooper Polymers, Inc.?, "Elvamides" available from Dupont and "Macro melt" available from Heckle; thermoplastic rubbers (e.g., those available under the trade designation "Keaton 1101" and "Keaton 1107" from Shell Chemical Co.) and ethylene vinyl acetate (e.g., that available under the trade designation "Elvax 40" from ELI. Dupont de Numerous Co., Inc. and "Ultrathin"
available from US). Still other thermoplastic materials operable as a component in the composition include, but are not limited to, butydiene-acrylonitrile copolymers * Trademark i,;, ~2~9~

available under the trade designation "Hycar'l from I Goodrich, urethane-acrylates, urethane-epoxides and urethane-polyenes. In addition, other thermoplastic materials are polyvinyl acetals such as polyvinyl formal and polyvinyl betrayals. The thermoplastic material, when present, is present in the composition in amounts ranging from 1~95~ by weight with the balance being the epoxy resin.
The components of the composition can be admixed in any order, preferably at room temperature up to 100C.
After admixture to a homogeneous mass, curing can be accomplished by elevating the temperature. The curing reaction is carried out at temperatures ranging from about 115 to 285C depending upon the combination of aside and phosphine compound employed.
The heating can be carried out by conventional means, e.g., an air oven, as well as by radio frequency (RF) techniques. RF heating can be utilized as a faster and more efficient means of curing than conventional air oven heating. In addition to the formation of high strength bonds, RF bonding techniques aid in (a) fast bond setting time sand (b) automated part handling and assembly.
In the instant invention, when the composition is used as an adhesive, RF heating can be employed with the adhesive composition herein to adhere (1) plastic to plastic, (2) plastic to metal and (3) metal to metal.
For example, dielectric heating can be used to bond (1) and (2) swooper if one member of the adhesive composition, i.e., resin, aside or phosphine compound contains sufficient polar groups to heat the composition rapidly and allow it to bond the adherents. Inductive heating can also be used to bond (1), (2) and (3). That is, when at least one of the adherents is an electrically conductive or ferrom~gr~et c metal, the heat generated therein is * Trademark I
of.

2~9~

conveyed by conductance to the adhesive composition thereby initiating the cure to form a thermoses adhesive.
In the instance where both adherents are plastic, it is necessary to add an energy absorbing material, i.e., an electrically conductive or ferromagnetic material, preferably in fiber or particle form (10-400 mesh), either per so or encapsulated to the adhesive composition. The energy absorbing material is usually added in amounts ranging from 0.1 to 2 parts by weight, per 1 part by weight of the composition.
The particulate RF energy absorbing material used in the composition when induction heating is employed can be one of the magnetizable metals including iron, cobalt and nickel or magnetizable alloys or oxides of nickel and iron and nickel and chromium and iron oxide. These metals and alloys have high Curie points (730-2,0~0~F).
Electrically conductive materials operable herein when inductive heating is employed include, but are not limited to, the noble metals, copper, aluminum, nickel, zinc as well as carbon black, graphite and inorganic oxides.
There are two forms of radio frequency heating operable herein, the choice of which is determined by the material to be adhered. The major distinction is whether or not the material is a conductor or non-conductor of electrical current If the material is a conductor, such as iron or steel, then the inductive method is used If the material is an insulator, such as wood, paper, textiles, synthetic resins, rubber, eta,, then dielectric - heating can also be employed.
Most naturally occurring and synthetic polymers are non-conductors and, therefore, are suitable for dielectric heating. These polymers may contain a variety of dipoles and ions which orient ion an electric field and rotate to maintain their alignment with the field when the field ~,~
.4., I., 2~7~

oscillates. The polar groups may be incorporated into the polymer backbone or can be pendant side groups, additives, extenders, pigments, etc. For example, as additives, lousy fillers such as carbon black at a one percent level can be used to increase the dielectric response of the adhesive. When the polarity of the electric field is reversed millions of times per second, the resulting high frequency of the polar units generates heat within the material.
The uniqueness of dielectric heating is in its uniformity, rapidity, specificity and efficiency. Most plastic heating processes such as conductive, convective or infrared heating are surface-heating processes which in order to establish a temperature within the plastic must subsequently transfer the heat to the bulk of the plastic by conduction. Hence, heating of plastics by these methods is a relatively slow process with a non-uniform temperature resulting in overheating of the surfaces. By contrast, dielectric heating generates the heat within the material and is therefore uniform and rapid, eliminating the need for conductive heat transfer. In the dielectric heating system herein the electrical frequency of the electromagnetic field is in the range 1-3,000 megahertz said field being generated from a power source of OWE kilowatts.
Induction heating is similar, but not identical, to dielectric heating The following differences exist:
(a) magnetic properties are substituted for dielectric properties; (b) a coil is employed to couple the load rather than electrodes or plates; and (c) induction heaters couple maximum current to the load. The generation of heat by induction operates through the rising and falling of a magnetic field around a conductor with each reversal of an alternating current source The I

practical deployment of such field is generally accomplished by proper placement of a conductive coil.
When another electrically conductive material is exposed to the field, induced current can be created. These induced currents can be in the form of random or "eddy"
currents which result in the generation of heat.
Materials which are both magnetizable and conductive generate heat more readily than materials which are only conductive. The heat generated as a result of the magnetic component is the result of hysteresis or work done in rotating magnetizable molecules and as a result of eddy current flow. Polyolefins and other plastics are neither magnetic nor conductive in their natural states.
Therefore, they do not, in themselves, create heat as a result of induction The use of the RF induction heating method for adhesive bonding of plastic structures has proved feasible by interposing selected RF energy absorbing materials in an independent adhesive composition layer or gasket conforming to the surfaces to be bonded, RF energy passing through the adjacent plastic structures (free of such energy absorbing materials) is readily concentrated and absorbed in the adhesive composition by such energy absorbing material thereby rapidly initiating cure of the adhesive composition to a thermoses adhesive RF energy absorbing materials of various types have been used in the RF induction heating technique for some time. For instance, inorganic oxides and powdered metals have been incorporated in bond layers and subjected to RF
radiation. In each instance, the type of energy source influences the selection of energy absorbing material.
Where the energy absorbing material is comprised of finely divided particles having ferromagnetic properties and such particles are effectively insulated from each other by particle containing nonconducting matrix material, the heating effect is substantially confined to that resulting from the effects of hysteresis. Consequently, heating is limited to the "Curie" temperature of the ferromagnetic material or the temperature at which the magnetic properties of such material cease to exist.
The RF adhesive composition of this invention may take the form of an extruded ribbon or tape, a molded gasket or cast sheet or film. In liquid form it may be applied by brush to surfaces to be bonded or may be sprayed on, pumped or used as a dip coating for such surfaces.
The foregoing adhesive composition, when properly utilized as described hereinafter, results in a solvent free bonding system which permits the joining of metal of plastic items without costly surface pretreatment. The RF
induced bonding reaction occurs rapidly and is adaptable to automated fabrication techniques and equipment.
To accomplish the establishment of a concentrated and specifically located heat zone by induction heating in the context of bonding in accordance with the invention, it has been found that the RF adhesive compositions described above can be activated and a bond created by an induction heating system operating with an electrical frequency of the RF field of from about 0.1 to about 30 megacycles and preferably from about 0.3 to 30 megacycles, said field being generated from a power source of from about 1 to about 30 kilowatts, and preferably from about 2 to about 5 kilowatts. The RF field is applied to the articles to be bonded for a period of time of less than about 2 minutes.
As heretofore mentioned, the RF induction bonding system and improved RF adhesive compositions of the present invention are applicable to the bonding of metals, thermoplastic and thermoses material, including fiber reinforced thermoses material I V

The composition of the present invention may, if desired, include such conventional additives as antioxidant, inhibitors, fillers, antistatic agents, flame-retardant agents, thickeners, thixotropic agents, surface-active agents, viscosity modifiers, plasticizers, tackifiers and the like within the scope of this invention. Such additives are usually preblended with the epoxy resin prior to or during the compounding step.
Operable fillers which can be added to the system to reduce cost include natural and synthetic resins, glass fibers, wood flour, clay, silica, alumina, carbonates, oxides, hydroxides, silicates, glass flakes, borate, phosphates, diatomaceous earth, talc, kaolin, barium sulfate, calcium sulfate, calcium carbonate, wollastonite, carbon fibers and the like. The aforesaid additives may be present in quantities up to 500 parts or more per 100 parts of the epoxy resin by weight and preferably about 0.005 to about 300 parts on the same basis.
The following examples are set out to explain, but expressly not limit, the instant invention. Unless otherwise noted, all parts and percentages are by weight.
The onset curing temperature of the formulations was obtained by Differential Scanning Calorimetry.
Example 1 Varying amounts of triphenyl phosphine were added to 100 g of diglycidyl ether of bisphenol-A, commercially available from Shell Chemical Co. under the trade name EPON-828, at 100C to obtain a homogeneous solution.
After cooling to room temperature, 6 g of dicyandiamide were added to the epoxy resin mixture. Samples of the epoxy resin dicyandiamide mixture containing various amounts of triphenyl phosphine were placed in a Perkin-Elmer Differential Scanning Calorimeter The onset . -I

curing temperatures of the various samples are shown in TABLE I:

TUBULE
Triphenyl Phosphine (g) 0 2 4 6 8 Onset Curing Temperature (C) 191 161 155 147 131 Example 2 A formulation was made up as in Example 1 with varying amounts of triphenyl phosphiner Samples of the various formulations were charged to a Perkin-Elmer Differential Scanning Calorimeter The calorimeter was heated to 170C
and time measurements were made to ascertain how long it required for the epoxy resin to cure (90% cure) at this temperature. The results are shown in TABLE II:

- TABLE II
Triphenyl Phosphine (g) 0 2 4 6 8 Time (min.) to reach 90~
cure at 170C 24 13 13 13 13 Example 3 120 g of an epoxy resin, commercially available from Shell Chemical Co. under the trade name EPON-828, were admixed with 80 g of a thermoplastic material, i.e., an acrylonitrile-butadiene copolymer with carboxylate end groups, commercially available from BY Goodrich under the trade name HIKER, and 0.5 g of triphenyl phosphine. The admixture was reacted at 110-120C for

3 hours to form an epoxy-terminated prepolymer, hereinafter referred to as prepolymer A.

issue Example 4 100 parts of prepolymer A from Example 3 were admixed with 2 parts of mailmen. A sample of the admixture was charged to a Differential Scanning Calorimeter. The onset curing temperature was 344C.
Example 5 100 parts of prepolymer A from Example 3 were admixed with 6 parts of mailmen and 5 parts of triphenyl phosphine. A sample of the admixture was charged to a Differential Scanning Calorimeter. The onset curing temperature was 250C. A completely cured solid material was obtained in 20 minutes at 285C.
Example 6 100 parts of prepolymer A from Example 3 were admixed with 6 parts of mailmen and 5 parts of tricyclohexyl phosphine. A sample of the admixture was charged to a Differential Scanning Calorimeter. The onset curing temperature was 236C.
Example 7 Varying amounts of tricyclohexyl phosphine were added to 100 g of diglycidyl ether of bisphenol-A containing 6 g of dicyandiamide at 60C to obtain an orange color mixture. Samples of the mixture containing various amounts of tricyclohexyl phosphine were placed in a Perkin-Elmer Differential Scanning Calorimeter. The onset curing temperatures of the various samples are shown in TABLE III:

TABLE III
30 Tricyclohexyl phosine (g) 0 1 3 5 7 Onset Curing Temperature (C) 193164 158 132 132 I

Example 8 .. .
To 0.01 mole of tricyclohexyl phosphine dissolved in 20 ml of ethylene chloride was charged 0.01 mole of 2,2-dimethylolpropionic acid (DMPA) in 20 ml of methanol.
After stirring for 30 minutes, the solvent in the reaction mixture was removed under a reduced pressure. Tricycle-hexylphosphinium 2,2-dimethylolpropionate in white crystalline form was obtained.
Example 9 Varying amounts of the salt from Example 8 were added to 100 g of diglycidyl ether of bisphenol-A containing 6 g of dicyandiamide at room temperature. Samples containing various amounts of this salt were placed in a Perkin-Elmer Differential Scanning Calorimeter. The onset curing temperatures of the various samples are shown in TABLE IV:

TABLE IV
-Tricyclohexyl I: phosphine (DMPA) 0 2 4 6 8 20 Onset curing temperature (C) 193 181 174 172 146 Example 10 5 g of an epoxy resin, commercially available from Shell Chemical Co. under the trade name "EPoN-828", were admixed with 0.3 g of dicyandiamide and 0.3 g of trio-toll phosphine. A sample of the admixture was charged to a Differential Scanning Calorimeter. The onset curing temperature was 188C. A completely cured solid material was obtained in 20 minutes at 170C.
Example 11 .
7.5 g of EPON-828 and 2.5 g of a polyvinyl bitterly having a weight average molecular weight in the range 180,000 to 270,000 and commercially available from Monsanto Co. under the trade name Butvar B-72 were admixed Jo lo with 0.5 g of dicyandiamide and 0.4 g of triphenyl phosphine~ The admixture was dissolved in a mixture of 90 ml of methanol and 90 ml of ethylene chloride after which the solvents were vacuumed off in a 50C vacuum oven. A sample of the dissolved material was charged to a Differential Scanning Calorimeter. The onset curing temperature was 143C. A completely cured, solid material was obtained in 20 minutes at 170C.
Example 12 0.1 mole of tri-n-octyl phosphine was added to 0.1 mole of 2,2-dimethylolpropionic acid in 300 ml of methanol. The solution was stirred over night and became clear. The solvent was removed under a reduced pressure and tri-n-octyl phosphinium 2,2-dimethylolpropionate in crystalline form was obtained.
Example 13 5.0 g of EPON-828, 0.3 g of dicyandiamide and 0.3 g of the crystalline salt material from Example 12 were admixed together. A sample of the admixture was charged to a Differential Scanning Calorimeter. The onset curing temperature was 164C A completely solid material was obtained in 20 minutes at 170C.
Example 14 6 g of triphenyl phosphine were added to 100 g of diglycidyl ether of bisphenol-A, commercially available from Shell Chemical Co. under the trade name "EPoN-828", at 100C to obtain a homogeneous solution. After cooling to room temperature 6 g of dicyandiamide were added to the epoxy resin mixture. The admixture was applied between carbon steel shims at a thickness of about 2 miss and the shims were lapped. The shim sample was placed in an induction heating apparatus and at a frequency of 350 kilocycles was heated for 4 seconds at 250C. A solid adhesive bond resulted.

.. .

Claims

WHAT IS CLAIMED:

1. A heat curable composition comprising (1) an epoxy resin, (2) 1 to 10 weight percent of (1) of an amide and (3) 1 to 15 weight percent of (1) of a phosphine compound of the group consisting of (a) R3P
wherein R is alkyl, cycloalkyl, aryl and alkaryl wherein said alkyl groups contain 1 to 10 carbon atoms (b) carboxylic acid salts of (a) and (c) mixtures of (a) and (b).

2. The composition according to Claim 1 containing in addition a thermoplastic material.

3. The composition according to Claim 1 wherein the amide is dicyandiamide and the phosphine compound is triphenyl phosphine.

4. The composition according to Claim 1 wherein the amide is melamine and the phosphine compound is tricyclohexyl phosphine.

5. A process for adhering two substrates which comprises contacting said substrates with a heat curable composition comprising (1) an epoxy resin, (2) 1 to 10 weight percent of (1) of an amide and (3) 1 to 15 weight percent of (1) of a phosphine compound of the group consisting of (a) R3P
wherein R is alkyl, cycloalkyl, aryl and alkaryl wherein said alkyl groups contain 1 to 10 carbon atoms (b) carboxylic acid salts of (a) and (c) mixtures of (a) and (b) and applying heat thereto.

6. The process of Claim 5 wherein the heating step is by radio frequency means.

7. The process according to Claim 6 wherein the radio frequency means are by dielectric heating.

8. The process according to Claim 6 wherein the radio frequency means are by induction heating, and ferromagnetic and/or electrically conductive particles are added to the composition.