WO1996025445A1

WO1996025445A1 - Process for producing a siloxane group-containing epoxy resin

Info

Publication number: WO1996025445A1
Application number: PCT/DE1996/000152
Authority: WO
Inventors: Klaus Höhn; Ernst Wipfelder
Original assignee: Siemens Aktiengesellschaft
Priority date: 1995-02-13
Filing date: 1996-02-01
Publication date: 1996-08-22

Abstract

Siloxane group-containing epoxy resin components are obtained by reacting epoxy alkoxysilanes with silanols and hydroxy group-containing silsesquioxanes. The epoxide-containing transparent condensates are siloxane mixtures which can be used directly as resin components for mixing with epoxy resins for casting resin applications.

Description

description

Process for the preparation of an epoxy resin containing siloxane groups.

Silicones or siloxanes can be used to make reaction resins more flexible. In order to obtain a stable molding material, preference is given to those siloxanes which take part in the curing reaction of the reactive resin and are chemically incorporated into the molding material.

In order to be compared with epoxy resins, siloxanes containing epoxy groups are therefore sought, which can be incorporated into a molding material in a stable and hydrolysis-resistant manner with the epoxy group via SiC bonds.

Epoxysilanes with SiC-bonded epoxy groups are obtained by hydrosilylation of silane hydrogens with unsaturated epoxy compounds. Under technologically demanding conditions, reaction products can be obtained with exclusion of water in an absolute inert gas atmosphere, which have to be worked up in complex cleaning steps and freed from the required catalyst of the platinum metal group.

Epoxysilanes can also be made accessible by epoxidation of unsaturated silane compounds. This is also a complex synthesis that leads to inexpensive products.

It is therefore an object of the present invention to provide a simple process for the preparation of epoxy resins containing siloxane groups with epoxy groups bonded via SiC, which leads to a chemically and thermally stable product with a sufficient epoxy content, which is compatible with common epoxy resins. Zen is compatible for cast resin applications and can be cured together with them.

This object is achieved according to the invention by a method with the features of claim 1. Further embodiments of the invention, a finished epoxy resin formulation and their preferred use can be found in further claims.

The epoxy resin components containing siloxane groups are obtained by reacting epoxyalkoxysilanes with silanols and silsesquioxanes containing hydroxyl groups.

The process according to the invention can be carried out in a simple one-pot reaction under normal conditions with regard to atmosphere and pressure with minimal process expenditure in a short time. A mixture of different siloxane resins containing epoxy groups is obtained as the product. These are the condensation products from a silanol alkoxy condensation, which proceeds with the elimination of the corresponding alkyl alcohol. With constant reaction conditions, this can be done

Carry out procedures reproducibly. Transparent oils can be obtained.

The product is compatible with common epoxy resins and can be mixed in any ratio with these to form storage-stable resin components without further cleaning or working up.

The products can be mixed with preferably cycloaliphatic epoxides and other resin components and cured. Transparent molded materials are obtained from this.

The epoxy value of the epoxysiloxanes obtained, which is predetermined by the type and quantitative ratio of the starting substances, results in a product which is readily crosslinkable. This can be stored for several months at room temperature with only a slight increase in viscosity and only a slight reduction in the epoxy value. It shows a high thermal and thermal oxide tive stability that is also retained in the molding material that is obtained after hardening of a corresponding mixture with common epoxy resins.

In the condensation reaction from the alkoxy group of the epoxysilane i

and the OH groups of silanol 2 and silsesquioxane with elimination of the corresponding alkyl alcohol Si-O-Si bonds:

(R) ₃ Si-10R + Hj0-Si (R ') 3 → (R) ₃ Si-0-Si (R ¹ ) 3 + ROH

The epoxyalkoxysilane i used as the starting compound carries 1 to 3 condensable alkoxy groups. The radicals Rl to R4 independently of one another represent an alkyl radical having 1 to 6 carbon atoms, an aryl radical or an OH group, R5 is a glycidyloxyalkyl, epoxyalkyl or an epoxycycloalkyl radical, R6 represents an alkyl radical having 1 to 6 carbon atoms. Atoms, R7 and R8 independently represent R6, OR6 or an aryl radical and n is an integer with 1 <n <12.

The radical R6 is preferably a methyl radical, since the reactivity of the group to be split off during the condensation decreases as the chain length of the alkyl radical increases. Because of the harmlessness of the split-off ethyl alcohol, ethyl can also be preferred as alkyl group R6. Because of the easier availability, monomeric epoxyalkoxy silanes are _. preferred, but in principle the reaction is also possible with corresponding longer-chain alkoxysiloxanes.

Silanols 2 which have OH groups in the α-position, α- and G5-position or in the chain as reactive groups are more readily available and less expensive. The selection of the further organic groups R 1 to R 4 bonded via SiC is not critical. Depending on the remaining radicals, however, with increasing chain length or larger n there can be an increasing incompatibility of the condensation products with epoxy resins, which can make their later desired use as a resin component in a mixture with these epoxy resins more difficult or impossible.

The epoxy group-containing radical R5 of the starting compound 1 is bonded to silicon via a carbon atom and is otherwise freely selectable. Depending on the availability of the corresponding epoxyalkoxysilane, R2 can be a glycidyloxyalkyl, an epoxyalkyl, epoxyaryl, an epoxyarylalkyl or an epoxycycloalkyl group. The corresponding glycidyloxy compounds which are obtained by reacting correspondingly reactive compounds with epichlorohydrin are readily available.

Depending on the reactivity of the starting materials, which can be electronically and sterically hindered, a condensation catalyst may be required to support the reaction. With regard to the implementation itself, there are no restrictions for the catalyst, so that any condensation catalyst is suitable. Taking into account the preferred or intended use of the product as a resin component for reactive resins, however, the catalyst is selected in such a way that the epoxy group is preserved as far as possible during the concentration. A catalyst which is ideal in this regard therefore does not react in a particularly basic manner extremely acidic, ideally neutral. Preferred catalysts are derived from the alkyl esters of titanium acid Ti.OH.4 or have tin as the central atom.

The starting materials can be reacted in suitable solvents, for example in alcohols, ethers, aromatic hydrocarbons or the like. The reaction is preferably carried out as a bulk reaction without a solvent.

The reaction can take place in an open reaction vessel and is carried out at elevated temperatures. Preferred reaction temperatures are between 80 and 150 ° C. Volatile reaction products are preferably driven off, for example by passing a dry inert gas (for example nitrogen) into the reaction mixture.

The composition of the product depends on the reaction conditions, in particular on the stoichiometry of the batch, the reaction temperature and the catalyst. A stoichiometric approach to the starting materials is designed so that a total of one OH group is available in the case of silanol 2 and silsesquioxane per alkoxy group which can be split off in the case of epoxysilane J_.

The product is a mostly colorless, transparent oil, which can be mixed with common reaction resins in any mixing ratio. With aromatic glycidyl ethers, in particular based on bisphenol A and F, with corresponding glycidyl esters, cycloaliphatic epoxides, or any other epoxides obtained, for example, by epoxidation of unsaturated compounds, new reaction resin mixtures can be obtained which are stable in storage for several months. The storage stability of the reaction resin mixture with the new epoxysiloxane can be increased by heating the reaction resin mixtures in an applied vacuum. The epoxysiloxanes, which are also compatible with the hardening process of the reaction resin, result in transparent molding materials in the corresponding reaction resin mixtures, the glass transition temperature of which is unusually high in comparison to other siloxane-containing molding materials. With the reaction resin mixture containing siloxane, only a slight decrease in the glass transition temperature of the molding material compared to the pure epoxy resin is observed. The thermal and thermal oxidative stability of the silsesquioxanes is retained in the molding material. This is attributed to their chemical integration, which results in silox-rich domains with a nanostructure.

In general, the siloxane condensates containing epoxy groups according to the invention show improved compatibility with the constituents of epoxy formulations compared to the conventionally produced epoxysiloxanes. The reactive behavior of the epoxy resin formulations is not impaired by admixing the epoxysiloxanes according to the invention. In general, the reactivity is increased. In the case of the cycloaliphatic epoxides, the light-off temperature is lowered by up to 20 ° C., so that curing can take place under milder conditions in these cases. All components are soluble in one another and the viscosities can be set within wide limits. Low and medium viscosity resins can be obtained which are particularly suitable for cast resin applications. Compared to epoxysiloxanes which are obtained by hydroεilylation, there is the further advantage of a greatly simplified and inexpensive preparation of different epoxysilanes. Of particular advantage is the fact that the product can be used directly as a resin component without further processing steps being necessary. In addition, hydrosilylated epoxysiloxanes are neither clear, transparent nor color-stable.

The invention is described in more detail below on the basis of an exemplary embodiment and the associated figure. The figure shows the thermomechanical properties of a cast resin molding material according to the invention using measurement curves.

Design example:

The alkoxysilane 1 used is the 3-glycidyloxypropyltrimethoxysilane (GPT), which is already known as an adhesion promoter for epoxy resins. A commercially available α, ω polyphenylpropylsilanediol with a hydroxyl group content of 3.5-5.5% (SY308, Wacker) is selected as silanol 2.

The 3-dimensional, polyhedral silsesquioxane (PPSS, ABCR-Chemie) is substituted with phenyl and propyl groups (30% propyl groups), has a molecular weight Mf> of 1,600 g / mol and a hydroxyl group content of 4%. Tetraisopropyl orthotitanate (IPT, Hüls) serves as the condensation catalyst.

Equimolar amounts of methoxy and silanol functions are reacted at 120 ° C within 4 hours in a stream of nitrogen. For this purpose, 10.0 g GPT, 38.3 g SY308 and 10.2 g PPSS are reacted with each other both with 0.3 g IPT and without a catalyst. Volatile reaction products are driven off in a stream of nitrogen and later removed in vacuo.

Transparent, highly viscous products are obtained. For better handling, they are diluted with a cycloaliphatic epoxy (CY 179, from Ciba-Geigy) in a ratio of 1: 1.

CY 179

After mixing with CY 179, an epoxy resin is obtained which can be acid or neutral cured in a manner known for epoxy resins. In the exemplary embodiment, the epoxy resin is mixed with hexahydrophthalic anhydride (HT907, from Ciba-Geigy) and 2,4-ethylimidazole (EMI) as an accelerator for a ready-to-use formulation. For this purpose, 10.0 g of epoxy resin, 5.4 g of HT907 and 0.3 g of EMI are homogenized at room temperature and degassed with stirring at about 100 hPa within 20 minutes. Curing takes place in three stages: 1 h at 120 ° C, 5 h at 150 ° C and 1 h at 170 ° C.

The most important properties of the epoxy resins are shown in Table 1.

Table 1

Epoxy resin with epoxy resin with

Epoxysilane with IPT Epoxysilane without IPT

Epoxy value

EEW (ol / lOOg) 0.370 0.390 after 1 month at RT 0.301 0.389

Viscosity η at

60 ° C (mPas) 1050 280 after 3 months at RT 16000 480 after 9 months at RT 1100

Appearance transparent transparent It is important that the epoxy content remains virtually unchanged even after months and that the viscosities are in a range which is suitable for cast resin applications.

The reactivity of the formulations with CY 179 was determined on the basis of DSC spectra (DSC 2, Perkin-Elmer) between 320K and 570K at a heating rate of 5 and 10 K / min.

Table 2 provides information on the measured values obtained. A comparison test is carried out with a siloxane-free formulation based on CY 179.

Table 2:

It can be seen that the reactivity of the siloxane-containing formulations increases compared to the comparative test, the period of use is shortened and the onset temperatures are reduced. At the same time, the heat of reaction decreases.

The molded materials cured as stated are examined for their dynamic mechanical properties. It will be a DMTA device (Polymer Laboratories, MKII) used at a heating rate of 3 K / minute. The conditioned samples are preloaded with a static preload of 0.1 and 0.5 N. Table 3 provides information about the measured values obtained.

Table 3:

The glass transition temperatures of over 170 ° C and the E-moduli with values above 2100 N / mm ² at room temperature are in all cases high despite the high siloxane content of 50 percent. In addition to the alpha and beta transitions of the epoxy network, no further relaxation can be clearly resolved in the temperature range from - 100 to 250 ° C. This indicates that all components are reactively integrated in the network of the molding material and that this with is homogeneous. The hardness of the molded materials is above Shore Δ 80.

The expansion coefficient of the molding materials according to the invention move around 90 ppm K ^_1 and are approximately 20 ppm K ^-1 hö ^¬ ago than that produced in the comparative test molding material on the basis of CY 179. The entire, caused by changes in temperature .DELTA.T ther omechanische stress calculated from the product ΔE'αΔT (where ΔE 'stands for the decrease in the E-moduli between 20 and 100 ° C, α is the thermal linear expansion coefficient and ΔT is the measured temperature interval). Due to the pronounced T-dependence of the modulus of elasticity of the molding materials according to the invention, the increase in modulus of elasticity outweighs the higher expansion coefficients even in the glass-hard region when the temperature rises. For example, in the temperature range far below the glass transition temperature Tg between 20 ° C. and 100 ° C., the thermomechanical stresses decrease by up to 4.6 N / mm ² . In the molding material of the comparison test, only 1.8 N / mm ^{2 are} calculated. When manufacturing components using the SMT process, where temperatures of up to 260 ° C occur briefly, the mechanical stresses are significantly reduced due to the discontinuities in the physical properties at the TG.

The temperature dependency of the dynamic modulus of elasticity and the tangent δ of a molding material according to the invention in comparison to the corresponding siloxane-free comparison test is also illustrated on the basis of the measured curves and the figure.

The resistance to hydrolysis of the molded materials is determined, among other things, from the water absorption over seven days at 23 ° C. The molding material according to the invention shows a water absorption of 0.80%, while the corresponding siloxane-free molding material has a water absorption of 1.30%. This indicates a high resistance to hydrolysis, which in addition to the thermal and thermal oxidative resistance leads to high weather resistance. The invention With 160 ° C temperature aging within 3 d, molding materials show only slightly higher mass losses than the reference molding materials on 179 bases. There is also a high UV resistance because the tendency towards yellowing of the molding materials can be reduced by incorporating siloxane.

Compared to the comparison test, it is also shown that curing begins at a lower temperature and that complete curing is achieved with the molding material according to the invention under the same curing conditions. The siloxane-free molding material, on the other hand, only shows incomplete curing when cured up to a maximum of 170 ° C. Thus, the ready-to-use formulations according to the invention have a slightly reduced shelf life, but an increased reactivity and can be cured completely at moderate temperatures. In the glass transition area, the erfm-. Molding materials according to the invention greatly reduced thermomechanical property changes with reduced thermal stress. The reactive resins according to the invention are therefore particularly suitable for covering and encasing stress-sensitive parts. They are advantageously used for wrapping and covering electrical and electronic components.

Claims

claims

1. Process for the preparation of an epoxy resin component containing siloxane groups by reaction in bulk or solution of an epoxyalkoxysilane of the general structure with a hydroxyl-containing silsesquioxane and a silanol of the general structure 2. with the elimination of ROH,

R ⁸

1 λ where

Rl to R4 independently of one another represent an alkyl radical having 1 to 6 carbon atoms, an aryl radical or a hydroxyl group,

R5 is a glycidyloxyalkyl, epoxyalkyl or an epoxycycloalkyl radical,

R6 represents an alkyl radical with 1 to 6 carbon atoms,

R7 and R8 independently of one another represent R6, OR6 or an aryl radical, and n is an integer with 1 <n <12.

2. The method of claim 1, wherein the reaction in the presence of a neutral condensation catalyst is preferably carried out between pH 5 to 8.

3. The method according to claim 1 or 2, wherein the reaction is carried out at a temperature of 80 to 150 ° C.

4. The method according to any one of claims 1 to 3, in which the reaction (condensation) is carried out so that a total of at least one OH group of silanol 2 and silsesquioxane is available per condensable OR group.

5. The method according to any one of claims 1 to 4, in which a cluster-shaped or polyhedral silsesquioxane with condensable silanol groups is used.

6. The method according to any one of claims 1 to 5, in which a silsesquioxane is used which has 1 to 8% by weight OH groups.

7. The method as claimed in one of claims 1 to 6, in which volatile products are blown during the reaction in an inert gas stream.

8. The method according to any one of claims 2 to 7, in which a condensation catalyst with tin or titanium as

Central atom is used.

9. Epoxy resin comprising

- a cycloaliphatic epoxy and

The condensation product of an epoxyalkoxysilane of the general structure 1 with a hydroxyl-containing silsesquioxane and a silanol of the general structure 2 with elimination of ROH,

R ⁵ R ⁱ R3

I I

R ⁸ - -Si-OR ⁶ HO -Si-O- -Si-Ri

R4

in which Rl to R4 independently of one another represent an alkyl radical having 1 to 6 carbon atoms, an aryl radical or a hydroxyl group,

R5 is a glycidyloxyalkyl, epoxyalkyl or an epoxycycloalkyl radical,

R6 represents an alkyl radical with 1 to 6 carbon atoms,

10. The epoxy resin according to claim 9, wherein the mixing ratio of cycloaliphatic epoxy and condensation product is between 1: 1 and 5: 1.

11. Epoxy resin according to claim 9 or 10, which contains further additives common for epoxy resins, which are selected from reaction accelerators, reactive thinners, fillers, flow control agents, adhesion promoters, thixotropic agents, dyes and pigments.

12. Use of the product from the process according to one of the

Claims 1 to 8 as a resin component for blending with common epoxy resins.

13. Use of an epoxy resin according to any one of claims 9 to 11 in a reactive resin with anhydride, acidic or katio¬ African curing to cover or encapsulate electrical and electronic components.