CA1189234A - Solid epoxy resin systems - Google Patents

Abstract

Abstract of the Disclosure Solid epoxy resin systems comprising the reaction products of a polyepoxide compound with a functionality greater than two, a diglycidyl ether of a polyhydric phenol and a polyhydric phenol;
said systems being applicable for use in a variety of applications and particularly in combination with phenolic novolac hardeners for molding applications.

Description

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Various solid epoxy resins have been developed which can be made to satisfy a wide range of properties, such as softening point and melt viscosity, in order to improve the selection and augment the capabili-ties of epoxy resins available to molding formulations and end users.
Among the solid epoxy resins used in the manufacture of molding grade compounds are included difunctional resins based on advancement products of bisphenol A diglycidyl ethers, or various multifunctional resins such as epoxy novolacs, epoxy cresol novolacs, tri-glycidyl isocyanurate and tetra-[p-glycidyloxyphenyl]ethane.

Resin choice depends partly upon several processing considerations amongst which are ease of handlingg amount and type of flow during molding and cure rate. Cured properties such as glass transition temperature, moisture absorption and resistance to thermal and mechanical stress also affect resin choice. It has been determined that the multifunctional resins are superior to -the difunctional resins in molding applications both in terms of pre- and post-cured properties. Functionalities greater than two are desirable since they enhance the formation of a crosslink network during curing.
Such superiority is primarily evidenced in thermal properties and electrical properties at elevated temperatures. Correspondingly, physical blends of multiEunctional and difunctional resins exhibit performance characteristics which are inferior to those of the pure multifunctional resin, such differences being once again primarily observed in thermal performance charac-teristics.

Although it may thus be reasoned that multifunctional resins are the logical choice for such areas of application, there are a number of instances where this reasoning does not follow. For example, solid multifunctional resins in many cases provide performance ~L8~2~9~

characteristics well in excess of that which is required for a given application. Since these resins are expensive in comparison to solid bisphenol A based epoxies, their use in such instances is uneconomical.
Accordingly, the beneficial properties that could be provided by such resins are sacrificed by practitioners who may opt not to use the resins in view of the unfavorable cost factors.

It is also to be noted that the multifunctional resins exhibit various disadvantages. Thus, they exhibit restricted flow and vis-cosity characteristics. Subsequent to curing, these resin-based formulations exhibit extensive brittleness as evidenced by reduced tensile elongation and higher flexural and tensile moduli. Such brittleness is a distinct detriment when, for example, the resins are utilized as encapsulants. Finally, these resins exhibit moisture absorption characteristics which still could be improved upon. The water absorption of an encapsulant, for example, is a most important characteristic since it is known that device failure by corrosion can be caused by the reaction of various ionic species, hydrolyzable chlorine, and other substances present in the molding compound with small amounts of water.

Accordingly, it is the primary object of this invention to provide modified solid epoxy resin systems having processing characte-ristics and cured properties at least comparable to those of pure m~llti-functional resins. It is a further object to reduce the level of multifunctional resin in these systems without adversely effecting the performance characteristics thereof. It is another ob;ect to provide solid epoxy reaction products which improve upon the pro-cessing characteristics and flexibility of multifunctional resins.

It has now been surprisingly discovered that by reacting a poly-epoxide compound having a functionality greater than two with a diglycidyl ether of a polyhydric phenol and a polyhydric phenol, it 3~

is possible to retain most and improve upon other properties of the multifunctional resin while still being able to reduce the content of said multifunctional resin in the system by about 10-40%. These systems facilitate great flexibility in terms of achieving optimum softening points and melt viscosities or the desired end use. Corre-spondingly, the degree of grind ability of the resin system con be readily adjusted to meee the practi~ioneris specific needs. These properties thus enable the resin systems Jo be tailored for speciEic applications.

Therefore the present invention relates to a solid advanced epoxy resin comprising the reaction product resulting from a cataly7ed advancement reaction of (a) a polyepoxide resin having a functionality greater than two said resin corresponding to the formula J i9~
CH2~ !I c~l2~ 1!

wherein R i6 H or CH3 and n is about 0.2-6.09 or being the tetr~-glycidyl ether of tetra-[p-hydroxyphenyl]ethane;

(b) a diglycidyl ether of a polyhydric phenol or the alkyl or halogen derivatives thereof; and (c) a polyhydric phenol or the alkyl or halogen derivatives ther~o;

components (a) and (b) being present in concentration ranges of rom 60-90% by weight, and 10-40%! by weight respectivelyg and component a being present in a concentration range of from 2 to 23%, based on the total weight o components (a) and (b).

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Similar performance benefits are obtained when the resin system is formulated with a phenol novolac hardener and various other ingrP-dients to prepare molding compounds. Although 10-40% of extensive multifunctional resin is eliminated, the resulting system substan-tially maintains tha thermal and mechanical properties of molding systems based solely on multifunctional resinO The maintaince of such thermal properties, including thennal stability, heat deflec-tion, ehermal coefficient of expansion, retention of Plec~rical properties, and the like, is evidenced by glass transition tempera-tures comparable to those of the multifunctional resin systems.
Furthermore, performance improvements in the molding formulations are noted in properties such as flexibility, tensile elongation and moisture absorption. Thus, the instant systems provide great2r per-centages of tensile elongation and lower flexural and tensile moduli.
They demonstraee superior water moisture resistance which can be expected to minimize corrosion problems and the like which can be encountered.

Accordingly, it is seen that the instant systems provide the benefits of a pure multifunctional resin system without incurring the adverse economic factors associated therewith. These modified syste~ns are available for use in a broad range of molding applications such D for exa~nple, in the encapsulation of semi-conductor devices. They also find U9e in the manufacture of powder coatings, reinforcad articles, and the like.

Applicable ~ultirunctional resin of Eunctionality greater than two correspond to the formula I, 2 1 2 ~0/ 2 1 / 2 CH2t~ I' CH2~ i1 wherein R is hydrogen or methyl, and n is about 0.2~0.6. These com-ponents are exemplified by the epoxidation products of cresol novolacs and phenol novolacs of varying molecular weight with cresol novolacs being preferred. The preparation of such materials is well known in the art. Likewise, such materials are commercially available.

In addition, the tetra-glycidyl ether of tetra-[p-hydroxyphenyl]-ethane is applicable as the multifunctional resin to prepare appro-priate solid resins suitable for molding applications. This material i9 commercially available.

It is also to be noted that multifunctional resins such as tetra--glycidylated methylene dianiline, tri-glycidylated p-aminophenol, tri-glycidyl isocyanurate and tri-glycidyl ether of tris-(p-hydroxy-phenyl)methane may have corresponding applicability.

Among the applicable diglycidyl ethers of polyhydric phenols are included those corresponding to the formula _ H2C\ C/HCH2- o_-\ ox -OCH2CHCH2~ 0--~ ~--X- ~--OCH2C~H-,CH2 - OH J m wherein m is 0-50 and X is -CH -, -C- or -S- .

2 1 11 These represent, respectively, bisphenols F, A and S. Other appli-cable ethers include the diglycidyl ethers of resorcinol, catechol, hydroquinone, and the like. The various ethers may be substituted on the respectively phenyl rings by such non-reactive substituents as alkyl, halogen, and the like. The diglycidyl ether of bisphenol A and the tetra-brominated derivative thereoE are preferred for purposes of this invention.

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The polyhydric phenol functions primarily to adjust the softening point, melt viscosity and degree of grindability of the resin system.
Applicable phenols include the phenols noted in the above description of the diglycidylated ethers absent, of course, the glycidyl ether groups. ~isphenol A and the tetra-brominated derivative thereof are preferred for purposes of this invention.

The epoxy-containing components of the instant systems will generally be present in concentrations ranging from 60-90% of multifunctional resin and 10~40% of diglycidyl ether, and preferably 65-75% of multi-functional resin and 25-35% of diglycidyl ether. The polyhydric phenol will be present in concentrations ranging from 2 to 23%, based on the total weight of epoxy-containing components, and preferably 5 to 12%.
As previously noted, the amount of polyhydric phenol will help deter-mine the basic properties of the resin systems. It is essential that the selection of the specific amount of polyhydric phenol within the noted range for any particular system be based on the components of the system and on the need to avoid premature gelling of the resin components.

The reaction procedure, i.e. advancement reaction, is well known to those skilled in the art and generally involves the reaction of the multifunctional resin, diglycidyl ether and polyhydric phenol in the presence of an advancing catalyst or accelerator. Typical accelerators include alkali metal hydroxides, imidazoles, phosphonium compounds, and the like. The specific choice of catalyst will depend on the in-tended end use application. In order to facilitate the initial blending operation, it is preferred to warm the multifunctional resin and diglycidyl ether to about 80-100C and then to add the dihydric phenol. Stirring at this point provides a clear melt blend. The catalyst is then added and the temperature is raised to 140-180C to effect the advancement reaction. The progress of the reaction can be monitored by titration of the epoxide groups using samples taken during the reaction. Completion of the reaction will generally take

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1 to 6 hours to provide resin systems having epoxy values in the range of 0.2-0.5 epoxy equivalents per 100 grams of resin.

The resulting advanced resins are solid and will generally having a softening point range of 60-95C, a melt viscosity range ox 700-15,000 centipoises a 130C and, as previously noted, an epoxy value range of 0.2-0.5 epoxy equivalent pPr 100 gram of resin.

Depending upon the desired end use application, the r2sin Jill he fonmulated with the appropriate ingredient and combined with the appropriate hardener and accelera or components. For ehe pr;mary area of utility of the instant resin sys~em~ as molding compounds, no~olac hardeners art utilized. Suck hardener can include phenol or cresol novolacs as dçfined under the mNltifunc~ion~l re3ins absent the epoxy groups. Such n~v~lae~ are know ant are widely used in ehe manufacture of encapsulant 8y hems. The hardener is utilized in con-centration~ ranging from about 25 to 40%, by weight of the total advanced resin.

The resin-hardener system can furthermore be mixed, prior to cure, with usual modifiers such a extenders, fillers and reinforcing agents, pigments, dyeseuffs, plasticizers, diluents, accelerators, and thy like. As extender, reinforcing agent, fillers and pigment which can be employed in the curable system accorting to the invention where may be mentioned, for example: cowl jar, bitumen, glas3 fibers, carbon fiber, cellulose, polyethyle4e powder, polypropylene powder, mica, asbestos, Yarious quartz powder, fused silicas, silicate3) silanes, magnesium and calcium carbonates, gypsum, Bentone I, silica aerogen (Aerosil ) , lithopone, barite, titanium dioxide, carbon black, graphite, iron oxide, or metal powders such as aluminium powder or iron powder. Ie i5 also possible to add other usual addi-tives, for example, flameproofing agents such as antimony triox;de, agents for conferring thixo~ropy, flow control agents such as sili-cones, cellulose acetate butyrate, polyvinyl butyral, waxes, stearates, .,',~, .

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ant the like (which are in part also used as mold release agents) to the curable systems. The accelerators that are added may be iden-tical to the advancement catalysts or may additionally include boron trifluoride monoethylamine complexes, tertiary amines, and the like.

The end products can be manufactured in the usual manner with the aid of known mixing equipment (kneaders, extruders, rollers, and the like). For purposes of preparing molding compositions, one satis-factory approach involves utilizing heated two roll mills, wherein the resin system and the hardener system are separately combined with filler and milled and the resulting phases are ground to the desired size and then blended.

Curing will generally be conducted at temperatures ranging from 140 to 185C. The expression "cure", as used herein, denotes the con-version of the above systems into insoluble and infusible crosslinked products, with simultaneous shaping to give shaped articles such as moldings, pressings or laminates, or to give two-dimensional struc-tures such as coatings, enamels or adhesive bonds.

Although major emphasis has been placed on the use of the instant resin system for moLding compounds, it is to be noted that they Like-wise may be utilized for the preparation of powder coatings, rein-forced articles (substrates), and the like. In these other areas of use, it is possible to utilize additional hardeners such as dicyan-diamide, polyesters, enhydrides, aromatic amines, and the like. The benefits derived in powder coating Eormulations include chemical and thermal resistanceO Typical powder coating formulations include the resin, hardener, accelerator, pigment and flow agent. Preparation and application of such powder coatings are known to those skilled in the art.

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The following examples will further illustrate the embodiments of the instant invention. In these examples, all parts given are by weight unless otherwise noted.

Example I: This example illustrates the preparation of a typical resin system of this invention.

The following components were utilized:
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Formulation A Parts _ Epoxy cresol novolac l 70 Diglycidyl ether of bisphenol A (2) 30 Bisphenol A 11 l epoxy value = 0.44 equivalents/100 g, softening point = 82C and viscosity at 130C = 5,7 Paos (2) epoxy value = 0,52 equivalents/100 gg viscosity at 25C = 17 Paus The epoxy cresol novolac and the diglycidyl ether were blended and warmed to 80C to provide a uniform mixture. The bisphenol A was then admixed to form a clear melt blend. Thereafter, 40 ppm oE 2-phenyl imidazole catalyst were added, the temperature was raised to 160C and the advancement allowed to continue for a period oE 3 hours.
The resulting solid epoxy resin system was determined to have an epoxy value of 0.34 per 100 grams with a softening point of 80C and a melt viscosity of 10,7 Paos at 130C.

: The following resin systems were prepared according to the procedure of Example I.

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parts B C D E F G
Epoxy cresol novolac (1) -- 60 80 Epoxy cresol novolac (3) 70 -- -- -- -- --Epoxy cresol novolac (4) -- -- -- 75 -I ~~
Epoxy phenol novolac (5) -- -- -- -- 75 --Tetraglycidyl ether of tetra-[p-hydroxyphenyl]ethane (6) -- -- -- -- -- 70 Diglycidyl ether of bisphenolA (2) -- 40 20 25 25 30 Diglycidyl ether of bisphenol A (7~ 30 --Bisphenol A 9 15 8 22.3 22.3 8 (3) epoxy value = 0.46 equivalents/100 g, softening point = 73C, viscosity at 130C = 1,9 Paas

(4) epoxy value = 0.47 equivalents/100 g, viscous liquid at room temperature.

(5) epoxy value = 0.56 equivalents/100 g, viscous liquid at room temperature.

(6) epoxy value = 0.55 equivalents/100 g, softening point = 60C.

(7) DER 331 from Dow Chemical Corporation.

These resin systems exhibited the following characteristics:
Formulation Epoxy Value/100 g Softening point (C) B 0.37 75 C 0.30 91 D 0.35 90-91 E 0.24 83 F 0.30 85 G 0.41 72.5 2~

Example III: This example illustrates the preparation of molding compounds utilizing the resin systems of this invention.

The following formulations were prepared:
parts . . . _ Resin A 100 --- --- --- --- --- 100 ---Resin B --- 100 --- --- --- --I --I ~~~
Resin C --- --- 100 --- --- --- --- ---Resin D --- --- --- 100 --- --- -I
Resin E --- --- --- --- 100 --- --- ---Resln F --- --- --- --- --- 100 --- ---Resin G --- --- --- --- --- --- --- 100 Novolac hardener(8) 30 33 27.6 32.221.8 27.3 30.7 37.3 Wax (release agent) Imidazole (accelerator) Silica filler (9) 244249 241 2~9 230 240 2~6 260

(8) BRWE 5833 (solid phenol-novolac having 1 OH group/100 g) Erom Union Carbide Corporation,

(9) NOVACITE 325 from Malvern Minerals Corporation.

In each instance, the molding compounds were prepared by a two com-ponent hot two roll mill method. The first phase involved blending the resin components with 65 weight % of the Eiller and hot two rolling the blend at 85-100C. The second phase involved blending the remaining filler with accelerator, hardener and release agent and hot two rolling the blend at 95-100C. The phases were then separately subjected to size reduction by hammer milling and uniformly combined by ball milling in proper proportions at room temperature to form the complete molding compound formulation.

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Correspondingly, control systems reflecting pure multifunctional resin and physical blends of multifunctional resin and glycidylated dihydric phenol were prepared by grinding all the components and then combining them in the desired proportions using a ball mill. These control systems are as Eollows:

parts Epoxy cresol novolac (1) 100 75 50 25 --- ___ Tetraglycidyl ether(6) --- --- --- --- --- lOO
Diglycidylated ether of bisphenol A --- 25 50 75 100 ---Novolac hardener (40) 40 34.629.1 23.618.2 50.0 Imidazole Wax Filler (9) 264 254 243 233 223282.3 The instant systems and the control systems were then subjected to the varlous test procedures.

Glass Transition Temperature . . . _ .
Specimens for this test were prepared by transfer molding of the sample and then post-curing Eor 4 hours at 175C. The glass transi-tion determinations were made by thermo-mechanical analysis in the expansion mode and gave the following results:

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Glass Transition Temp. (C) _, It is seen that in most instances, the glass transition temperatures of the instant systems are comparable to those of the multifunctional resins (~8 and ~14) indicating a retention of the beneficial thermal characteristics of the multiftmctional resin despite a reduction in the concentration thereof. It is also important to note that sub stantially equal percentage of multifunctional resin gives a higher glass transltion temperature when used in the resin advancemen-t formulation l than when used in the resin blend (~10).

Physical/Mechanical Properties Flexural, tensile as well as tensile elongation data for the various systems were obtained at room temperature according to ASTM test methods D--790 and D-638, respectively. Heat deflection temperatures (HDT) were determined by ASTM - D-648.

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The results are noted hereinbelow:

l ~2 ~9 _,. .
Flexural Strength (psi)12,000 13,800 12,860 Flexural Modulus (psi)1.4xlO 1.6xlO 1.7xlO
Tensile Strength (psi)10,160 9,268 8,300 Tensile Modulus (psi?1.5xlO 1.5xlO 1.6xlO
Tensile Elongation (%)0.70 0.70 0.59 HDT (C) 201 201 203 The similarity in most values provides f~lrther indication that the resin systems bf the instant invention provide comparable mechanical properties to systems based on pure multifunctional resin. It is important to note, however, that the respective values for room temperature flexural modulus and room temperature % tensile elonga-tion provide a clear indication that the instant systems show im-proved flexibility and elongation characteristics.

Moisture Absorption Molded samples were weighed, subjected to the conditions noted in the following table and then reweighed in order to determine moisture absorption.

Percent l~eight Increase Test Condition l ~2 ~9 ~13 24 hr. complete immersion at R.T. 0.05 0.04 0.04 0.06 48 hr. complete immersion at50C0.27 0.29 0.32 0.33 24 hr. in steam at 121C and 1.42 1.31 1.52 1.51 15 pSig 923~

Once again, it is to be noted that the instant systems show improved performance characteristics in an important variable. Thus, the con-trols ~9 and ~13 exhibit increased moisture absorption, particularly at the more severe test conditions.

Summarizing, it is seen that this invention provides novel solid epoxy resin systems which exhibit excellent performance characteris-tics. Variations may be made in proportions, procedures and materials without departing from the scope of the invention as deEined by the following claims.

Claims (10)

WHAT IS CLAIMED IS:

1. A solid advanced epoxy resin comprising the reaction product resulting from a catalyzed advancement reaction of (a) a polyepoxide resin having a functionality greater than two said resin corresponding to the formula wherein R is H or CH3 and n is about 0.2-6.0, or being the tetra-glycidyl ether of tetra-[p-hydroxyphenyl]ethane;
(b) a diglycidyl ether of a polyhydric phenol or the alkyl or halogen derivatives thereof; and (c) a polyhydric phenol or the alkyl or halogen derivatives thereof;
components (a) and (b) being present in concentration ranges of from 60-90% by weight, and 10-40% by weight, respectively, and component (c) being present in a concentration range of from 2 to 23%, based on the total weight of components (a) and (b).

2. The resin product of claim 1, wherein component (a) is the epoxi-dation product of cresol novolacs.

3. The resin product of claim 1, wherein component (a) is the tetra-glycidyl ether of tetra-[p-hydroxyphenyl]ethane.

4. The resin product of claim 1, wherein component (b) is selected from the group consisting of diglycidyl ethers of bisphenols corre-sponding to the formula wherein m is 0-50 and X is -CH2,

5. The resin product of claims 2 or 3, wherein component (b) in the diglycidyl ether of bisphenol A.

6. The resin product of claim 1, wherein component (c) is bisphenol F, A or S.

7. The resin product of claim 1, wherein component (c) is bisphenol A.

8. The resin product of claim 13 wherein component (a) is present in a concentration of 65-75% by weight.

9. The resin product of claim 6, wherein component (c) is present in concentration of 5-12% based on the total weight of components (a) and (b).

10. A heat curable composition which comprises the resin product of claim 1 and a hardener for epoxy resins.