WO1997031061A1

WO1997031061A1 - Resin composition

Info

Publication number: WO1997031061A1
Application number: PCT/EP1997/000717
Authority: WO
Inventors: Barry James Hayes
Original assignee: Ciba Specialty Chemicals Holding Inc.
Priority date: 1996-02-23
Filing date: 1997-02-15
Publication date: 1997-08-28
Also published as: ID16029A; ZA971509B; AU1769997A; GB9603848D0

Abstract

The present invention concerns an epoxy resin composition which comprises an epoxy resin liquid, a sufficient amount of a thixotropic agent to induce thixotropic properties, and a monopolar compound in an amount sufficient to at least partially destroy the thixotropic properties.

Description

Resin Composition

In many applications there is a need for an epoxy composition which is easy to dispense from its container but which develops an almost instant increase in texture even up to the point of being totally non-slump or thixotropic on mixing with the hardener.

Such applications are widespread and include adhesives, sealants, mastics, stopping compounds, caulking materials, encapsulants and surface coatings amongst many others.

Dispensing of such epoxy compositions may be from bottles, cans, tubes, sachets and drums for instance and sometimes may be mixed with the hardener components via static or dynamic mixer heads.

There are some very demanding applications where epoxy/hardener compositions are required to exhibit no slump when mixed and laid horizontally oriented on a vertical surface in thicknesses up to 40mm and greater.

Historical attempts to produce a suitable product to satisfy these requirements have usually resulted in heavily thixotropic resins and hardeners which are difficult to handle.

We have now developed epoxy resin systems which are liquid or of low thixotropy and are easy to handle but which instantly develop flow reduction or complete thixotropy on blending with an amine hardener.

Accordingly the present invention provides an epoxy resin composition which comprises an epoxy resin liquid, a sufficient amount of a thixotropic agent to induce thixotropic properties, and a monopolar compound in an amount sufficient to at least partially destroy the thixotropic properties. The liquid epoxy resin may be a polyglycidyl ether of a polyhydric alcohol or phenol such as 2,2-bis(4-hydroxyphenyi)propane (Bisphenol A), bis(4-hydroxyphenyl)methane (Bisphenol F), a phenol-formaldehyde novolak or a cresol-formaldehyde novolak or mixtures thereof and contain epoxy functional diluents if required. The epoxy resin should not contain sufficient numbers of strongly polar groups such as hydroxyl groups to prevent the efficent accomplishment of this invention.

Suitable thixotropic agents are particularly those which largely rely on interparticle hydrogen bonding to achieve this effect and in this class especially the hydrophilic fumed silicas.

Sufficient thixotropic agent is used to achieve the claimed thickening of the epoxy resin liquid in the absence of the monopolar compound. Depending on the specific resin and thixotropic agent used, the amount of thixotropic agent may be from 1 to 20% by weight, based on the weight of epoxy resin, preferably 3 to 12% by weight.

Suitable monopolar compounds are those which do not react rapidly with the epoxy resin either to generate polyhydroxyl compounds or to cure the resin. Suitable compounds include aliphatic alcohols, cycloaliphatic alcohols, aralkyl alcohols, phenols, monoesters and mixtures thereof. Suitable specific compounds include cyclohexanol, cycloheptanol, cyclooctanol, cyclohexylmethanol, 2-cyclohexylethanol, 4-ethyl cyclohexanol, 3,5-dimethyl cyclohexanol, decahydro-2-naphthol, benzyl alcohol, butyl benzoate, and nonyl phenol.

The amount of monopolar compound should be sufficient to destroy as much of the thixotropic properties of the epoxy resin/thixotropic agent mixture as required. The actual amount needed varies according to the specific compounds used but in general at least about 30% by weight of monopolar compound, based on the weight of thixotropic agent is needed. Amounts of up to 100% or more may be used as required to either enhance the effect, reduce viscosity to below that of the epoxy resin itself or convey some other benefit. We find that cycloaliphatic alcohols are more effective than araliphatic alcohols which are more effective than aliphatic alcohols in suppressing thixotropy according to this invention. As stated above, when the composition of the invention is mixed with a hardener the resulting mixture should become more or less instantaneously of the desired final application texture or thixotropy.

Suitable hardeners which lead to this thixotropy include primary and secondary aliphatic, aromatic, araliphatic and heterocyclic amino compounds such as, for example, diethylene triamine, triethylene tetramine, 3,3'-dimethyl-4,4'-diamino dicyclohexyl methane, reaction products of aliphatic polyamines with dimerised fatty acids, 4,9-dioxa-1 ,12- dodecanediamine, dibutylamine, dioctylamine, benzylamine and furfurylamine. Tertiary amines do not give the desired effect.

The mixture is then cured at ambient temperature or by heating.

The composition of the invention may be made by mixing the ingredients in any order. For instance the thixotropic agent may be added to the epoxy resin followed by the monopolar compound. This method would normally be used when the exact amount of monopolar compound needed is not certain. However, when the amounts are known it is possible to first add the monopolar compound to the epoxy resin followed by the thixotropic agent.

Certain polypolar compounds such as glycerol, polyethylene oxides and lightly polar glycidyl ethers are known to improve thixotropy. In order to improve the thixotropic properties of the mixture containing hardener it is possible in some cases to add such as polypolar compound to the compositions of the invention. For example a mixture of epoxy resin, thixotropic agent and cyclohexanol may have glycerol added to it and still not be thixotropic until the hardener is added. However a similar mixture containing benzyl alcohol instead of the cyclohexanol becomes thixotropic on addition of glycerol. Whether or not it is possible to add a polypolar material without making the mixture too thixotropic can be readily determined by simple experiment. ln some cases it is advantageous to restore an element of the original thixotropy to a resin, thixotrope, monopolar compound mixture by the addition of controlled amounts of polypolar material. This is of special value where the mixture contains fillers of higher or lower density and thus prevents settling or flotation during storage. Such partially restored thixotropy systems still develop near instantaneous full texture on mixing with hardeners and are part of this invention.

The compositions of the invention can be easily made by simple mixing in production. They can be run out of vessels by gravity. The low viscosity makes them easy for customers to handle. Addition of the hardener makes them instantaneously fully textured so that they behave exactly as designed.

The compositions of the invention can be storage stable for several months. If they become thixotropic after storage, simply stirring the composition destroys the thixotropy and they revert to their original texture.

The invention is illustrated by the following Examples in which the figures given are parts by weight.

Examples

Formulations are made as in the Tables below using a bisphenol A epoxy resin, GY260, having an epoxy value of 5.3 g mols epoxy per kilogramme a thixotrope and monopolar compound.

Aerosil 380 is a hydrophilic fumed silica with a surface area of approximately 380m ^z/gm

A B C D E F

Epoxy resin GY260 100 100 100 100 100 100

Aerosil A380 8 8 20 8 6 8

Cyclohexanol - 8 20 10 - -

Benzyl Alcohol 8 - - - 20 -

Glycerol 2 2

Mixtures A, B, C and D are free flowing liquids which become immediately thixotropic on addition of the amine hardeners according to the invention.

Mix E is lightly thixotropic but becomes heavily so on addition of these amines.

Mix A remains free flowing after 8 months at ambient temperature.

Mix C slowly becomes thixotropic but is rendered flowing again by stirring.

Mix E is not rendered free flowing by stirring and hence is an excellent system for suspending fillers.

Mix F is a very viscous semi thixotropic paste.

TABLE 2 shows the effect on thixotropy of cyclic alcohols both at room temperature and on heating.

G H I J

GY 260 80 80 80 80

A 380 10 10 10 10

2-cyclohexylethanol 10 - - - cyclohexylmethanol - 10 - - cyclooctanol - - 10 - cycloheptanol - - - 10

Initial behaviour at 22°C FF FF FF FF

After heating at 60 °C FF FF FF FF

FF = Free flowing

TABLE 3 shows the effect of short term ageing on an epoxy resin containing large amounts of hydrophilic fumed silica (Cabot EH5) an araliphatic alcohol and cycloaliphatic alcohols.

K L M

GY 260 52.5 52.5 52.5 52.5

EH 5 7.7 7.7 7.7 7.7

Benzyl alcohol 10.0 10.0 10.0 10.0

2-cyclohexylethanol 10.0 - - - cyclohexylmethanol - 10.0 - - cyclooctanol - - 10.0 - cycloheptanol - - - 10.0

Initial behaviour at 22°C FF FF FF FF

After 16 hours ambient FF FF FF FF TABLE 4 shows the efficacy of cycloaliphatic alcohols in viscosity suppression and compares this with effect of a lightly polar impure C ₁₂-C₁₄ glycidyl ether diluent.

O P Q R S

GY 260 75 75 75 75 75

A 380 11 11 11 11 11

Benzyl Alcohol 14 14 14 14 14

C1₂-C14 glycidyl ether 14 - - - -

Cyclohexanol - 14 - - -

4 ethyl cyclohexanol - - 14 - -

3,5 dimethyl cyclohexanol - - - 14 - decahydro 2 naphthol - - - - 14

Initial behaviour FF FF FF FF FF

After 16 hours at ambient T FF FF FF FF temperature DOS

T = thixotropic

DOS = destroyed on stirring.

From the foregoing Examples it can be seen that it is possible to control the rheological properties of an epoxy liquid containing hydrophilic fumed thixotrope by the addition of mono polar materials. Most valuable materials to permit this control are cycloaliphatic, araliphatic and alicyclic mono alcohols. These may be used to suppress some or all the viscosity building or thixotropic effects of the fumed silica as required. The effects can be even further fine timed by the addition of small quantities of thixotropy enhancing materials such as polyols for example.

The net result of exercising this invention is that when the epoxy resin liquid plus thixotrope plus viscosity suppressants plus viscosity enhancer if used, is blended with a suitable amine hardener the viscosity or thixotropy builds almost instantly to the level designed in by the quantity of thixotrope used.

Thus in the extreme case the final mixed resin plus hardener may be a totally thixotropic hard wax yet the components before blending are free flowing liquids.

Claims

1. An epoxy resin composition which comprises an epoxy resin liquid, a sufficient amount of a thixotropic agent to induce thixotropic properties, and a monopolar compound in an amount sufficient to at least partially destroy the thixotropic properties.

2. A composition as claimed in claim 1 in which the epoxy resin is a polyglycidyl ether of a polyhydric alcohol or phenol.

3. A composition as claimed in claim 1 or 2 in which the thixotropic agent is a hydrophilic fumed silica.

4. A composition as claimed in any preceding claim in which the amount of thixotropic agent is from 1 to 20% by weight based on the weight of epoxy resin.

5. A composition as claimed in claim 4 in which the amount of thixotropic agent is from 3 to 12% by weight based on the weight of epoxy resin.

6. A composition as claimed in any preceding claim in which the monopolar compound is an aliphatic alcohol, cycloaliphatic alcohol, aralkyl alcohol, a phenol, a monoester, or mixtures thereof.

7. A composition as claimed in claim 6 in which the monopolar compound is cyclohexanol, cycoheptanol, cyclooctanol, cyclohexylmethanol, 2-cyclohexylethanol, 4-ethyl cyclohexanol, 3,5-dimethyl cyclohexanol, decahydro-2-naphthol, benzyl alcohol, butyl benzoate or nonyl phenol.

8. A composition as claimed in any preceding claim in which the amount of monopolar compound is at least 30% by weight based on the weight of thixotropic agent.

9. A composition as claimed in any preceding claim which also comprises a polypolar compound.

10. A composition as claimed in claim 9 in which the polypolar compound is glycerol, a polyethylene oxide, or a lightly polar glycidyl ether.

11. A process for making a cured composition which comprises mixing a composition as claimed in any preceding claim with a hardener and curing at ambient temperature or by heating.

12. A process as claimed in claim 1 1 in which the hardener is an aliphatic, aromatic, araliphatic or heterocyclic amine compound containing primary and/or secondary amine groups.