WO2009031146A1

WO2009031146A1 - High refractive index, low viscosity room temperature two-part epoxy resins

Info

Publication number: WO2009031146A1
Application number: PCT/IL2008/001194
Authority: WO
Inventors: Andrew Shipway
Original assignee: Mempile Inc.
Priority date: 2007-09-06
Filing date: 2008-09-04
Publication date: 2009-03-12

Abstract

The present invention describes high refractive index, low viscosity room temperature two-part epoxy resins and adhesive compositions comprising them.

Description

fflGH REFRACTIVE INDEX, LOW VISCOSITY ROOM TEMPERATURE

TWO-PART EPOXY RESINS

FIELD OF THE INVENTION

This invention relates to a high refractive index, low viscosity room temperature two-part epoxy resins and adhesive compositions comprising them.

BACKGROUND OF THE INVENTION

Room-temperature curing two-part epoxy resins are extensively used for adhesive and structural applications in the optics, electronics and engineering industries. They are based on a so-called "Part A" which is typically based on organic epoxides (which may include oligomers and polymers) and a "Part B" which is typically based on diamines, higher oligoamines or other reactive compounds. When the two so-called "Parts A" and "Part B" are mixed together giving a viscous mixture, they chemically react, with the epoxide rings being opened by the amines, polymerizing and crosslinking the material upon which it becomes hard. At ambient temperature, this process takes between several hours and a few days, depending on the composition. In many cases, the cured material is optically transparent as a result of homogeneity and being amorphous.

Typical epoxy resins are based on reaction products of bisphenol A with epichlorohydrin or of phenyl glycidyl ether with formaldehyde, with other components added to give a convenient viscosity of the uncured mixture as well as other properties. The cured resins have refractive indices in the region 1.53-1.58. Other formulations use aliphatic epoxides and have lower refractive indices. The refractive index of resins that have low viscosity in the uncured mixture tends to be lower, because the proportion of aliphatic components is lower (since the high-index components, such as bisphenol A diglycidyl ether, have very high viscosities in their pure form).

Low viscosity mixtures are required for many applications, for example, when small cracks need to be filled or when large areas need to be adhered with a minimum adhesive thickness. In general, when the term "viscosity" is used to refer to an epoxy resin, it relates to the uncured mixture of "Part A" and "Part B". Epoxy resin formulations are developed for specific purposes, and the properties of the cured resins reflect their formulation. For example, formulations containing inflexible and short-chain multifunctional components tend to provide stiff resins, and formulations that include long, flexible chains give rise to more flexible, less brittle resins. Formulations containing aromatic groups tend to give resins with low water absorption, while those containing polar groups give high water absorption.

For use in optical applications, it is often advantageous to match the refractive index of an adhesive or coupling material with the refractive index of the substrate to be bonded. This allows the full passage of light from one substance to the other without losses from reflection that take place at any interface between two materials with different refractive indices approximately according to the equation [(n₁-n₂)/(n₁+n₂)]², where n] and n₂ are the refractive indices of the materials. Therefore, existing epoxy adhesives are not ideal for making optical bonds, i.e., bonds with very high optical transmission, thus low reflection, between materials with refractive indices above 1.58.

Many optical interfaces can also be damaged easily by any absorption of adhesive components into the substrate or dissolution of the substrate into the adhesive. This can take place with relative ease when low molecular weight components are used in the epoxy formulation, when cure times are relatively long, and when the cured resin still contains free molecules (either unreacted species or molecules such as octylphenol that are used as fillers or solvents to alter resin properties or decrease the viscosity of the uncured mixture).

Typically, large refractive index increases in organic formulations are brought about by the use of halogenated materials (particularly brominated or iodinated), and by increasing the amount of conjugation and aromaticity in the components. For example, while the refractive index of cyclohexane is 1.426, that of cyclohexene is 1.446, of 1,3- cyclohexadiene is 1.474, of benzene is 1.501, of bromobenzene is 1.559, of 1,2- dibromobenzene is 1.611, of iodobenzene is 1.62, and of 1-iodonaphthalene is 1.701. As may be noted, this strategy while affording the increase in refractive index, also involves the increase of molecular weight and loss of molecular flexibility, leading to increased melting points and viscosity. For example, while benzene is a low viscosity liquid, naphthalene, tribromobenzene, and diiodobenzene are all solids at ambient temperature. SUMMARY OF THE INVENTION

As demonstrated above, it is not trivial to implement refractive index-raising formulation changes of organic formulations without causing a severe impact on viscosity. In addition, simple substitutions, e.g. of bisphenol A with brominated bisphenol A, also impacts other properties such as toughness and flexibility. As viscosity plays an important role hi the processing and application of such formulations, there remains a need hi the optics, electronics, and engineering industries for adhesive compositions with high refractive indices but with viscosity, transparency, mechanical properties and reactivity of the cured adhesive that are similar to those of existing low- index epoxy formulations.

The inventors of the present invention have recently formulated new high index epoxy formulations which are based on highly brominated bisphenol A monomers of the formula (I), particularly tetrabromobisphenol A diglycidyl ether, of the formula (I), where m is zero, and highly brominated bisphenol F monomers of formula (II).

The materials of formula (I) which originally were developed as fire-retardants are, in their pure states, transparent and colorless glassy materials.

Thus, in one aspect of the present invention, there is provided a curable epoxy resin formulation (herein referred to as "Part A" of the adhesive composition disclosed hereinbelow) comprising: (i) at least one epoxy resin of the formula (I) or (II), wherein each of n, k, j and p, independently of each other is an integer selected from 1 to 4, and m is an integer being greater or equal to 0;

(ii) at least one ether selected from resourcinol diglycidyl ether (w-bis(2,3- epoxypropoxy)benzene), phenyl glycidyl ether, divinylbenzene dioxide, styrene oxide, and any mixture thereof; and

(iii) optionally at least one additive.

In some embodiments, said at least one epoxy resin of the formula (I) or (II) is a reaction product (e.g., a single product or two or more products as a mixture) of epichlorohydrin and a brominated bisphenol A of formula (I) or a brominated bisphenol F of formula (II), wherein each of n, k, j and p, independently of each other is an integer selected from 1 to 4, and m is 0.

As a person skilled in the art would recognize, the product distribution resulting from the reaction between epichlorohydrin and a brominated bisphenol A of formula (I) such as tetrabromobisphenol A (each of n, k, j and p is 4 and m is 0) or of a brominated bisphenol F of formula (II), such as tetrabromobisphenol F, depends on the mole ratio of the brominated bisphenol derivative used to that of the epichlorohydrin and on the reaction conditions.

As shown above, the polybrominated bisphenol F of the formula (II) is an isomeric mixture of ortho and para bisphenol F diglycidylether isomers which result form the isomeric mixture of the bisphenol F building blocks shown below:

The at least one epoxy resin of formula (I) or (II), employed in the curable resin formulation of the invention may be a commercially available mixture of such compounds of formula (I) or (II) or a mixture prepared according to methods known in the literature.

In some embodiments of the invention, the at least one epoxy resin of formula (I) or (II) is commercially available. Non-limiting examples of such commercially available epoxy resins of formula (I) are: (i) CAS 40039-93-8, commercially available from Aldrich as product no. 430234, containing 350-450 g/mol epoxide and 48 wt% Br.; (ii) CAS 68928-70-1, commercially available from The Dead Sea Bromine Works as product no. F-2001, containing 485-545 g/mole epoxy and 49-51% Br. Other commercially available epoxy resins from both manufacturers/distributors are also useful.

In other embodiments, the at least one epoxy resin is a reaction product of a one- step addition of the epichlorohydrin to the brominated bisphenol A derivative or brominated bisphenol F derivative and the conversion of the intermediate chlorohydrin into the epoxide compound, e.g., at a molar ratio of at least 6 moles of epichlorohydrin to 1 mole of a brominated bisphenol A or F derivative. The reaction product mixture comprises a combination of compounds of formula (I) or (II) wherein each of n, k, j and p, independently of each other is an integer between 0 and 4 (depending on the brominated bisphenol A or F derivative used) and wherein m equals to 0, 1 and 2 in a ratio of about 2 : 0.2 : 0.02, respectively.

In other embodiments, the at least one epoxy resin of the curable resin formulation (employing either a compound or mixture of formula (I) or (H)) of the invention is a product of a reaction between epichlorohydrin and a brominated bisphenol A or F derivative under the Taffy Process conditions, in the presence of a base and excess epichlorohydrin. The reaction product is a product mixture containing compounds of formula (I) or (II) wherein m is equal to 0, 1, 2, 3, 4, 5, 6, and 7.

As used herein, the term "epoxy equivalent weight" or "epoxide content" refers to the weight (in grams) of the resin containing one mole of epoxide moieties. Thus, for example, for a compound of formula (I), wherein m is 0, the epoxy equivalent weight is the weight of the compound divided by two, the number of epoxide groups. In some embodiments of the invention, said reaction product is a mixture of compounds of formula (I) and/or (II), comprising compounds wherein each of n, k, j and p, independently of each other is an integer selected from 1 to 4 and m is 0 and/or 1 and/or 2 and/or 3 and/or 4 and/or 5 and/or 6 and/or 7 and/or 8 and/or 9 and/or 10, at any ratio. For example, where the bisphenol A derivative is a tetrabromobisphenol A, the reaction product may contain a mixture of compounds of formula (I) wherein:

1. each of n, k, j and p is 4 and m is 0;

2. each of n, k, j and p is 4 and m is 1 ; and

3. each of n, k, j and p is 4 and m is 2. hi other embodiments, the reaction product contains a mixture of compounds of formula (II) wherein:

1. each of n, k,j and p is 4 and m is 0;

2. each of n, k,j and p is 4 and m is 1;

3. each of n, k, j and p is 4 and m is 2;

4. each of n, k, j and p is 4 and m is 3;

5. each of n, k, j and p is 4 and m is 4; and

6. each of n, k,j and p is 4 and m is 5. hi other embodiments, said reaction product is a mixture of compounds of formula (I) or (II) having an epoxy equivalent weight of between 150 and 1000.

In still further embodiment, said reaction product is a single reaction product of epichlorohydrin and a brominated bisphenol A of formula (I) or brominated bisphenol F of formula (II), wherein each of n, k, j and p, independently of each other is an integer selected from 1 to 4, and m is 0, or 1, or 2, or 3, or 4, or 5, or 6, or 7, or 8, or 9, or 10.

In yet other embodiments, said reaction product is a compound of formula (I) or (II), wherein each of n, k, j and p, independently of each other is an integer selected from 1 to 4, and m is different from 0.

In still further embodiments, said reaction product is a compound of formula (I) or (II), wherein each of n, k, j and p is 4 and m is different from 0.

In additional embodiments, said reaction product has a bromine content of between 30 and 50% in weight (wt%), and in others the bromine content is between 40 and 55 wt%.

In still further embodiments, said reaction product has a bromine content of 3 to 7 bromine atoms per bisphenol moiety. In yet further embodiments, said at least one ether is resourcinol diglycidyl ether (τn-bis(2,3-epoxypropoxy)benzene).

The compound of formula (I) or (II) typically contributes at least 20% of the total epoxide moieties in the mixture, hi some embodiments, the compound of formula (I) contributes at most 50% of the total epoxide moieties in the mixture. In other embodiments, the compound of formula (I) or (II) contributes between 30 and 40% of the epoxide moieties in the mixture.

The at least one ether typically contributes at least 40% of the total epoxide moieties in the mixture, hi some embodiments, the at least one ether contributes at most 80% of the total epoxide moieties in the mixture. In other embodiments, the at least one ether contributes between 40 and 70% of the epoxide moieties in the mixture.

In some embodiments, said at least one ether is resourcinol diglycidyl ether, contributing between 40 and 70% of the epoxide moieties in the mixture.

The curable epoxy resin formulation, "Part A", may optionally comprise at least one additive which is added to adjust the refractive index of the cured product. In some embodiments, said at least one additive constitutes at most about 25% by weight of the total weight of the formulation. In other embodiments, said at least one additive constitutes at least 0.01% by weight and at most about 25% by weight of the total weight of the formulation. A person skilled in the art would appreciate that the exact amount of said at least one additive in the formulation of the invention, may be adjusted, on one hand to achieve the desired refractive index of the cured resin and on the other to adjust (e.g., lower, increase or maintain) the viscosity of the uncured mixture. hi certain embodiment, said at least one additive is selected from iodoform; 1- iodonaphthalene or 2-iodonphthalene or any mixture thereof; o-diiodobenzene, m- diiodobenze, p-diiodobenzen or any mixture thereof; and 1,2,3-tribromobenzene, 1,2,4- tribromobenzene, 1,3,5-tribromobenzene or any mixture thereof.

As is stated hereinabove, the curable resin formulation, "Part A", comprises the monomer of a brominated bisphenol A derivative (formula (I), m is 0) or a brominated bisphenol F derivative (formula (II), m is 0), as defined above, mixed with at least one ether being of specific low viscosity and high index and optionally with at least one additive (which may or may not be epoxy monomers), to adjust the refractive index to a specific value. In another aspect of the present invention, there is provided a method for the preparation of a curable epoxy resin formulation ("Part A") according to the invention.

In some embodiments, the formulation is prepared by admixing each of the three components (i), (ii) and (iii) above in the desired ratios prior to application. The three components may be pre-made and stored before combination or prepared in situ.

In certain embodiments, the epoxy resin of formula (I) or (II) is prepared according to one of the procedures disclosed herein, or according to any equivalent procedure which may be known to a person skilled in the art, and to the resulting reaction product are added the two additional components (ii) and (iii). Typically, the reaction product containing the at least one epoxy resin is not purified or separated into its various low and/or high molecular weight components prior to combination.

The curable epoxy resin formulation, "Part A", may require heating of the components to at least their melting temperatures so that their mixing is possible. In some embodiments, the method for the preparation of "Part A" involves the mixing of the components at a temperature higher than their melting temperatures. In other embodiments, the mixing is performed at temperatures above room temperature. Still further, the temperature may be above 50⁰C, above 70°C, or above 90°C.

In further embodiments, the mixing is performed at a temperature between 70 and 90⁰C.

A person versed in the art would realize that the mixing of at least a compound of formula (I) or (II) and an ether such as resorcinol diglycidyl ether, both being solids at room temperature may not at all be trivial, particularly when considering that the mixture of the two is a thick liquid at room temperature.

The components of the formulation may be added one after the other, in any order as solids, in a solution, as a suspension or as a paste. If, for reasons of formulation, any one component needs to be added dissolved or suspended in, e.g., a solvent which presence in the final adhesive formulation may disrupt the curing process or have an effect on one or more physical or chemical properties of the cured resin, e.g., transparency and/or refractive index, the method of preparing the curable resin formulation may also involve the evaporation or removal of said e.g., solvent.

Thus, the method of the invention may also include the formulating of the formulation for storage or application as may be necessitated by, e.g., the specification of the user. In order to achieve a cured end product, "Part A" must be mixed with at least one reactive component or a mixture capable of undergoing a chemical reaction with said at least one epoxy resin of formula (I) or (II) of "Part A". The at least one reactive component or a mixture is herein designated "Part B".

Thus, in another aspect of the present invention, there is provided an adhesive composition comprising:

(a) "Part A", as defined above; and

(b) at least one curing agent.

The at least one curing agent may be selected from an organic amine, an oligoamine, a polyamine and any mixture thereof, a phenol, a mercaptan, an acid anhydride, an ester and derivatives thereof.

In some embodiment, the at least one curing agent is at least one amine which may be selected from commercially available amines or any mixtures thereof, depending on the precise requirements of the cured resin. Non-limiting examples of such amines are ethylene diamine, diethylene triamine, dipropylenetriamine, diethylaminopropyleneamine, diaminodiphenylsulfone, N-aminoethylpiperazine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, 1,3- pentanediamine, trioxa tridecanediamine, trimethyl hexanediamine, isophorone diamine, diethylaminopropylamine, dipropylenediamnie, neopentanediamine, and polyetheramines.

Additives which are non-reactive with any one of the components of "Part A" and/or "Part B" may be added to either "Part A" or "Part B" in order to adjust the properties of the final resin. In particular, liquid or low meting point compounds with high refractive indices and low vapor pressures may be used to allow the production of high refractive index, low viscosity formulations.

In some embodiments, "Part A" and "Part B" are mixed in a stoichiometric ratio of epoxide to NH, namely one epoxide to any one amine group. However, in cases where a particularly high refractive index is required, the "Part A" component may be used in excess. In such cases, curing is completed by the attack of the epoxide rings by hydroxyls (rather than amines) moieties inherent to the compounds of formula (I).

The curing of the adhesive composition may be achieved at various temperatures. In some embodiments, curing is carried out at room temperature. In other embodiments, the curing is carried out at temperatures above 40⁰C, above 50⁰C, and in still other embodiments, above 7O⁰C.

In other embodiments, the curing of "Part A" in the presence of "Part B" is achieved in the presence of at least one accelerator and/or at least one initiators and/or catalyst, which presence in the formulation typically has no affect on the final characteristics of the cured resin, e.g., refractive index.

Non-limiting examples of such accelerators are metal salts such as cobalt salts in the form of naphthenates or octoates, sulphinic acids, mercaptans, aryl phosphinic acid esters, compounds derived from pyrrolidone-2, and systems modified with vanadium/hydroxycyclopentanone.

Non-limiting examples of initiators are organic peroxides such as cyclohexanone peroxide, methyl ethyl ketone peroxide, cumene peroxide and others, and photo- initiators.

According to some embodiments, the refractive index of the cured resin is between 1.50 and 1.70. In other embodiments, the refractive index is between 1.6 and 1.7.

In a further aspect of the present invention, a kit is provided for an adhesive composition comprising "Part A" and "Part B" according to the invention. In some embodiments, the mixture of "Part A" is contained separately from "Part B". A separation between the "Part A" and "Part B" may be achieved by placing each in separate containers or in separate compartments of the same container, and which may be opened prior to use.

The kit of the invention may also include other additives e.g., a solvent, a diluent, an additive as described above, a liquid medium, an initiator, a stabilizer, a filler, an accelerator, an adhesive material, a colorant, etc., for improving and/or adjusting the curing properties, adhesion properties and final properties of the cured resin, said additives may be contained in separate containers or mixed. The kit may also include at least one device or applicator for use in the application of the adhesive and instructions to use.

In some embodiments, the kit comprises:

(a) a first container filled with at least one of: (i) at least one expoxy resin of the formula (I) or (II), wherein each of n, k, j and p, independently of each other is an integer selected from 1 to 4, and m is an integer being greater or equal to 0;

(ii) at least one ether selected from resourcinol diglycidyl ether (m- bis(2,3-epoxypropoxy)benzene), phenyl glycidyl ether, divinylbenzene dioxide, styrene oxide, and any mixture thereof; and (iii) optionally at least one additive; where said first container is filled with only one of (i), (ii) or (iii), a second container is included for one or both of the other of (i), (ii) or (iii), and where said second container is filled with a second of (i), (ii) or (iii), a third container is included for the remaining of (i), (ii) or (iii);

(b) a further container filled with at least one curing agent as defined above. hi some embodiments, said at least one curing agent is an amine selected from organic amine, oligoamine, polyamine and any mixture thereof.

In other embodiments, the two components of said kit are not contained each in a separate container but rather co-located in a single package.

Within the scope of the present invention, the term "filled with" does not mean completely filled, but merely to the inclusion of the referred substance, in any amount and in any physical state (solid, liquid, suspension, solution, etc) in the container.

The container to be used in the kit of the invention may be of any size, shape, material, color and transparency provided that its size, shape, material, color or transparency does not have a short or long term effect on the stability or reactivity of the substance contained therein. The container may also be constructed to only hold the substance therein for, e.g., storage, or may be constructed, for example, with an opening or a nozzle to permit full or partial delivery of any amount of the substance out of the container.

In still another aspect of the present invention, there is provided the use of a compound of formula (I) or (II), as defined above, for the preparation of a curable epoxy resin composition according to the invention and an adhesive composition according to the invention.

In yet another aspect of the present invention there is provided the use of a compound of formula (I) or (II), as defined above, as adhesive or adhesive filler. The compound of formula (I) or (II) or the curing composition containing it ("Part A), may also be used as a potting compound for molded objects for optical applications. In one embodiment, the compound of formula (I) or (II) or the curing mixture containing it ("Part A"), may be used for creating optical refractive index-matched bonds. The epoxy resin formulation of the invention may be further formulated in an existing commercial or non-commercial formulation so as to provide a final formulation with tailored properties suitable for a specific application.

In another aspect of the present invention, there is provided a structure of at least two substrates, each of said at least two substrates being bonded to the other with the adhesive composition of the invention. The structure may be any construction, e.g., device, having at least two components being bonded to each other. The two substrates or components may be bonded to each other as demonstrated herein in the Examples.

In yet another aspect of the present invention, there are provided epoxy resin formulations, adhesive compositions and cured products according to Table 1.

Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases "ranging/ranges between" a first indicate number and a second indicate number and "ranging/ranges from" a first indicate number "to" a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

It should also be noted that where various embodiments are described by using a given range, the range is given as such merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, "between 40 and 70%" should be considered to have specifically disclosed sub-ranges such as from 40 to 69, from 40 to 68, from 40 to 67,... etc., as well as from 41 to 70, from 71 to 69, from 41 to 68, from 41 to 67,... etc., as well as from 42 to 70, from 42 to 69,... etc., as well as individual values within that range, in this example, 40, 41, 42, 43...50, 51, 52, 53...60, 61, 62, 63, as well as 40.1, 40.2, 40.3...50.1, 50.2, 50.3, etc. Further, it is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

DETAILED DESCRIPTION OF EMBODIMENTS

Brominated bisphenol A-based epoxy compounds of the formula (I) or brominated bisphenol F- based epoxy compounds of formula (II) have refractive indices in the range 1.6-1.7, depending on the level of bromination. In order to maintain a high- index formulation, the primary thinning compound must have a relatively high refractive index, yet should also have a low viscosity (so that a minimum quantity is required). In addition, bifunctionality is preferred (since it leads to a more crosslinked epoxy resin, which generally means faster cure times and greater strength), as is cheap, bulk-scale availability. Therefore, primary thinning compounds are resorcinol diglyidyl ether, divinyl benzene dioxide, styrene oxide, and phenyl glycidyl ether.

In some embodiments, the primary thinning compound is resorcinol diglycidyl ether.

These primary thinning compounds are used either alone or as a mixture in a total of up to 4 epoxide equivalents as compared to the brominated bisphenol -based material (formula (I) or (H)).

The high index nonreactive species added to "Part A" may also serve to decrease viscosity. If such materials are used, it is usually possible to decrease the amount of the primary thinning compound (which also helps increase the refractive index). In general, nonreactive species are better used with bifunctional primary thinning agents since otherwise weak cured resins are produced. Suitable materials for this purpose include: iodoform, iodonaphthalene, diiodobenzene, and tribromobenzene. However, the use of such measures to raise the refractive index must be balanced against the fact that it results in a cured resin that contains molecules that are not covalently linked to the polymer matrix Curing of the resin is achieved at ambient temperature or elevated temperature after mixing the epoxide-containing "Part A" with the amine-containing "Part B" as demonstrated hereinnext.

In some embodiments, the curing is performed at room temperature (25°C). hi some other embodiments, the curing is performed at temperatures above room temperature, above 30°C, above 50°C, or above 8O⁰C. In still other embodiments, the curing is expedited by microwave radiation.

Example 1

The reaction product (or mixture thereof) of a brominated bisphenol A and epichlorohydrin, as defined above, and styrene oxide were mixed in a 1 :1 ratio of epoxide moieties. This "Part A" mixture was mixed thoroughly with diethylene triamine ("Part B") in a 1 : 1 ratio of NH:epoxide. The resulting mixture was free-flowing. At ambient temperature, it cured to the point of non-stickiness in —10 hours. After 2 days, it had fully cured to give a transparent resin with 4H hardness (pencil scale) and a refractive index of 1.62.

An analogous resin cured instead by trimethyl hexanediamine had IH hardness and a refractive index of 1.61.

Example 2

The reaction product (or mixture thereof) of a brominated bisphenol A and epichlorohydrin, as defined above, and resorcinol diglycidyl ether were mixed in a 1 :2 ratio of epoxide groups. This "Part A" mixture was mixed thoroughly (at a 1:1 reactivity ratio) with a "Part B" mixture consisting of diethylene triamine and trioxatridecane diamine in a 1 :1 ratio of NH groups. The resulting mixture was free-flowing. At ambient temperature, it cured to the point of non-stickiness in —3.5 hours. After 1 day, it had fully cured to give a transparent resin with 3 H hardness (pencil scale) and a refractive index of 1.60. An analogous resin cured instead by pure trimethyl hexanediamine had 3H hardness and a refractive index of 1.59. An analogous resin cured by pure trioxatridecane diamine in a 3:2 ratio of epoxide:NH had IH hardness and a refractive index of 1.59.

Example 3 The following Table 1 shows the properties of 22 different epoxy resin formulations according to the invention. As a key to the column titles:

A: Number of adhesive composition and corresponding cured end-product

B: YDB-400 (brominated bisphenol A diglycidyl ether mixture, Dead Sea Bromine, Israel), having 48 wt% bromine content.

C: Phenyl glycidyl ether

D: Butanediol diglycidyl ether

E: Resorcinol diglycidyl ether

F: Styrene oxide

G: Bisphenol F diglycidyl ether

H: diethylene triamine

I: trioxa tridecanediamine

J: trimethyl hexanediamine

K: Refractive index of cured resin at 589 nm

L: Time (hours) from mixing until mixture is hard and no longer sticky

M: Estimated strength, where l=very brittle and 5=very difficult to break 1 mm thickness sample by hand.

N: Estimated flexibility, where l=breaks before visibly flexing at all and 5=1 mm-thickness sample may be bent to a right angle without breaking.

O: Pencil hardness (hardest pencil that does not mark the cured resin).

Table 1 : Epoxy resin compositions according to the invention.

Example 4

Two blank DVD substrates (0.6 mm thick polycarbonate) were glued together using formulation 1 of Table 1. In order to achieve a bond with a very thin (10s of microns) adhesive thickness, the resin application was performed on a spin stage as follows: The first disc was put on the stage, and a small circle of uncured adhesive was applied at a small radius. The second disc was then placed on top of the first, and the whole was spun at a gradually increasing speed until 2000 rpm was achieved. The construction was then removed and allowed to cure under ambient conditions. After curing, the bond was found to be of excellent optical quality, and it was not possible to separate the two discs without breaking them. This final point is in contrast to standard DVD adhesives, which are generally not strong enough to prevent separation of the two parts without breakage.

Claims

CLAIMS:

1. A curable epoxy resin formulation comprising:

(i) at least one epoxy resin of the formula (I) or (II),

wherein each of n, k, j and p, independently of each other is an integer selected from 1 to 4, and m is an integer being greater or equal to 0;

(ii) at least one ether selected from resourcinol diglycidyl ether (τw-bis(2,3- epoxypropoxy)benzene), phenyl glycidyl ether, divinylbenzene dioxide, styrene oxide, and any mixture thereof; and

(iii) optionally at least one additive.

2. The formulation according to claim 1 , wherein said at least one epoxy resin of the formula (I) or (II) is the reaction product of a reaction between epichlorohydrin and a polybrominated bisphenol A of formula (I) or a polybrominated bisphenol F of formula (II), wherein each of n, k, j and p, independently of each other is an integer selected from 1 to 4, and m is 0.

3. The formulation according to claim 2, wherein said reaction product is a mixture of compounds of formula (I) or (II), comprising compounds wherein each of n, k, j and p, independently of each other is an integer selected from 1 to 4 and m is an integer selected from 0 to 10.

4. The formulation according to any one of the preceding claims, wherein said at least one epoxy resin of the formula (I) or (II) has an epoxy equivalent weight of between 150 and 1000.

5. The formulation according to any one of the preceding claims, wherein said at least one epoxy resin of the formula (I) or (II) has a bromine content of between 30 and 55 wt%.

6. The formulation according to any one of the preceding claims, wherein said at least one epoxy resin of the formula (I) or (II) has an average bromine content of 3 to 7 bromine atoms per bisphenol moiety.

7. The formulation according to claim 1, wherein said at least one ether is resourcinol diglycidyl ether (/w-bis(2,3-epoxypropoxy)benzene).

8. The formulation according to claim 1 , wherein said at least one epoxy resin of the formula (I) or (II) contributes at least 20% of the total epoxide moieties in the formulation.

9. The formulation according to claim 1 , wherein said at least one ether contributes at least 40% of the total epoxide moieties in the formulation.

10. The formulation according to claim 1 comprising at least one additive selected from iodoform; 1-iodonaphthalene or 2-iodonphthalene or any mixture thereof; o- diiodobenzene, m-diiodobenze, p-diiodobenzen or any mixture thereof; and 1,2,3- tribromobenzene, 1,2,4-tribromobenzene, 1,3,5-tribromobenzene or any mixture thereof.

11. Use of a compound of the formula (I) or (II) for the preparation of an adhesive composition.

12. Use of a compound of formula (I) or (II) in the preparation of an epoxy resin formulation.

13. Use of a compound of formula (I) or (II) in the preparation of a cured epoxy resin for bonding at least two surfaces.

14. An adhesive composition comprising:

(a) a formulation according to any one of claims 1 to 10; and

(b) at least one curing agent.

15. The adhesive composition according to claim 14, wherein said at least one curing agent is selected from an organic amine, an oligoamine, a polyamine and any mixture thereof, a phenol, a mercaptan, an acid anhydride, an ester and derivatives thereof.

16. The adhesive composition according to claim 15, wherein said organic amine and oligoamine are selected from ethylene diamine, diethylene triamine, dipropylenetriamine, diethylaminopropyleneamine, diaminodiphenylsulfone, N- aminoethylpiperazine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, 1,3-pentanediamine, trioxa tridecanediamine, trimethyl hexanediamine, isophorone diamine, diethylaminopropylamine, dipropylenediamnie, neopentanediamine, and polyetheramines.

17. A cured resin manufactured by contacting at a temperature being equal to or greater than room temperature a formulation according to any one of claims 1 to 10 with at least one amine selected from organic amine, oligoamine, polyamine and mixtures thereof.

18. The cured resin according to claim 17, having a refractive index of between 1.50 and 1.70.

19. A kit for an adhesive composition comprising as Part A, a formulation according to any one of claims 1 to 10; and as Part B, at least one amine selected from organic amine, oligoamine, polyamine and mixtures thereof, said Part A and Part B are contained separately within said kit.

20. The kit according to claim 19, wherein said Part A and Part B are each in separate containers which may be opened prior to use or in separate compartments of the same container.

21. The kit according to claim 19, further comprising at least one additive, at least one applicator and instructions to use.

22. A structure having at least two substrates, each of said at least two substrates being bonded to the other with an adhesive composition according to claim 14 or 16.

23. A structure comprising a cured resin according to claim 17 or 18.

24. An epoxy resin formulation of Table 1.

25. An adhesive composition of Table 1.

26. A cured resin of Table 1.