Photocurable epoxy resin systems

Abstract

The invention is directed to a photocurable epoxy resin composition that is tougher and more flexible and contains 30 to 90 wt % of at least one aromatic epoxy resin; 2 to 30 wt % of at least one core-shell rubber (CSR); up to 20 wt % of at least one flexibilizer comprising reactive functional groups selected from among epoxy groups, carboxylate groups, amino groups and/or hydroxyl groups; and 1 to 4 wt % of at least one cationic photoinitiator. Also disclosed are the use of said composition for sealing and/or coating materials as well as corresponding coating/sealing processes.

Claims

1. A photocurable epoxy resin composition comprising: (a) 30 to 90 wt % of at least one aromatic epoxy resin; (b) 2 to 30 wt % of at least one core-shell rubber as toughener; (c) 1 to 20 wt % of at least one flexibilizer comprising reactive functional groups selected from epoxy groups, carboxylate groups, amino groups and/or hydroxyl groups; (d) 1 to 4 wt % of at least one cationic photoinitiator; (e) a co-toughener in an amount of 0.1-10 wt %; and/or (f) a reactive diluent in an amount of 0.1-10 wt %; and/or (g) an adhesion promoter selected from chelate-modified epoxy resins and epoxy-modified silanes in an amount of 0.1-3 wt %, characterized in that the at least one flexibilizer comprises epoxy groups.

2. The photocurable epoxy resin composition as claimed in claim 1, characterized in that the core-shell rubbers are selected from those that have a core formed of polybutadiene and a shell formed of polybutadiene, polystyrene or a polybutadiene-polystyrene copolymer, wherein the core-shell rubbers are optionally dispersed in a matrix, wherein the matrix is selected from aromatic epoxy resins.

3. The photocurable epoxy resin composition as claimed in claim 1, characterized in that the at least one flexibilizer is a polymer or an oligomer having a glass transition temperature of less than 20 C.

4. The photocurable epoxy resin composition as claimed in claim 1, characterized in that the at least one flexibilizer is selected from the group consisting of polytetramethylene ether glycol, polycaprolactone diol or triol, cardanol glycidyl ethers and dicarboxylic acid bis((3,4-epoxycyclohexyl)methyl) esters.

5. A photocurable epoxy resin composition comprising: (a) 30 to 90 wt % of at least one aromatic epoxy resin; (b) 2 to 30 wt % of at least one core-shell rubber as toughener; (c) 1 to 20 wt % of at least one flexibilizer comprising reactive functional groups selected from epoxy groups, carboxylate groups, amino groups and/or hydroxyl groups; (d) 1 to 4 wt % of at least one cationic photoinitiator; (e) a co-toughener in an amount of 0.1-10 wt %; and/or (f) a reactive diluent in an amount of 0.1-10 wt %; and/or (g) an adhesion promoter selected from chelate-modified epoxy resins and epoxy-modified silanes in an amount of 0.1-3 wt %, characterized in that the photoinitiator is selected from sulfonium salts and iodonium salts, wherein the counterion is selected from hexafluoroantimonate, hexafluorophosphate and (tetrakis(pentafluoroaryl)borates.

6. A photocurable epoxy resin composition comprising: (a) 30 to 90 wt % of at least one aromatic epoxy resin; (b) 2 to 30 wt % of at least one core-shell rubber as toughener; (c) 1 to 20 wt % of at least one flexibilizer comprising reactive functional groups selected from epoxy groups, carboxylate groups, amino groups and/or hydroxyl groups; (d) 1 to 4 wt % of at least one cationic photoinitiator; (e) a co-toughener in an amount of 0.1-10 wt %; and/or (f) a reactive diluent in an amount of 0.1-10 wt %; and/or (g) an adhesion promoter selected from chelate-modified epoxy resins and epoxy-modified silanes in an amount of 0.1-3 wt %, , characterized in that the reactive diluent is selected from monoglycidyl ethers of aliphatic or aromatic alcohols.

7. The photocurable epoxy resin composition as claimed in claim 1, characterized in that the co-toughener is a polyether polyol.

8. A process for sealing metal-containing electrical lines or contacts for protection against electrochemical corrosion, comprising the steps of: (i) applying in the form of a film the photocurable epoxy resin composition as claimed in claim 1 to metal-containing electrical lines or contacts; and (ii) curing the film by exposure to light.

9. The photocurable epoxy resin composition as claimed in claim 1, characterized in that the aromatic epoxy resin is selected from bisphenol A diglycidyl ethers and bisphenol F diglycidyl ethers.

10. The photocurable epoxy resin composition as claimed in claim 1, characterized in that the aromatic epoxy resin comprises diglycidyl ethers of bisphenol A, F and/or S, or epoxy novolacs.

11. A photocurable epoxy resin composition comprising: (a) 30 to 90 wt % of at least one aromatic epoxy resin; (b) 2 to 30 wt % of at least one core-shell rubber as toughener; (c) 1 to 20 wt % of at least one flexibilizer comprising reactive functional groups selected from epoxy groups, carboxylate groups, amino groups and/or hydroxyl groups; (d) 1 to 4 wt % of at least one cationic photoinitiator; (e) a co-toughener in an amount of 0.1-10 wt %; and/or (f) a reactive diluent in an amount of 0.1-10 wt %; and/or (g) an adhesion promoter selected from chelate-modified epoxy resins and epoxy-modified silanes in an amount of 0.1-3 wt %, characterized in that the reactive diluent is selected from monoglycidyl ethers of C12/C14 fatty alcohols and alkyl phenols.

12. A photocurable epoxy resin composition comprising: (a) 30 to 90 wt % of at least one aromatic epoxy resin; (b) 2 to 30 wt % of at least one core-shell rubber as toughener; (c) 1 to 20 wt % of at least one flexibilizer comprising reactive functional groups selected from epoxy groups, carboxylate groups, amino groups and/or hydroxyl groups; (d) 1 to 4 wt % of at least one cationic photoinitiator; (e) a co-toughener in an amount of 0.1-10 wt %; and/or (f) a reactive diluent in an amount of 0.1-10 wt %; and/or (g) an adhesion promoter selected from chelate-modified epoxy resins and epoxy-modified silanes in an amount of 0.1-3 wt %, characterized in that the reactive diluent is selected from monoglycidyl ethers of para-tert-butyl phenol.

Description

EXAMPLES

(1) Materials:

(2) Epoxy Base Resin:

(3) Aromatic epoxy resin aE1: Blend of BADGE (bisphenol A diglycidyl ether) and BFDGE (bisphenol F diglycidyl ether)

(4) Cycloaliphatic epoxy resin cE2: (3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate)

(5) ##STR00003##

(6) Core-Shell (CS) Materials:

(7) CS1: BFDGE+25% CS (polybutadiene)

(8) CS2: BADGE+25% CS (styrene-butadiene copolymer)

(9) CS3: cycloaliphatic epoxy resin (ERL 4221)+25% CS (styrene-butadiene copolymer)

(10) Above all, CS1 and CS2 lead to products having excellent flexibility and toughness.

(11) Co-toughener: Fortera 100 (polyol derivative). Concentration identified as ideal for good toughness and flexibility alongside high reactivity: 2%

(12) Flexibilizers:

(13) F1: monofunctional epoxy based on cardanol

(14) F2: caprolactone triol (Mw300 g/mol)

(15) F3: bis(3,4-epoxycyclohexyl)methyl)adipate

(16) F4: polytetramethylene ether glycol (Mw1400 g/mol)

(17) All flexibilizers F1 to F4 are suitable for production of flexible and suitably tough films. The best results with regard to flexibilization were obtained with use of flexibilizer F2; flexibilizer F4 also leads to significantly increased flexibility. Concentration identified as ideal with regard to F2:10%

(18) Reactive Diluent

(19) R1: monofunctional glycidyl ethers of para-tert-butyl phenol

(20) R2: aliphatic monoglycidyl ethers of C.sub.12/C.sub.14 fatty acid alcohol

(21) R3: trimethylolpropane oxetane (TMPO)

(22) A standard reactive diluent is R1. R2 was used because R2 has a lower viscosity compared with R1, however the resultant films are minimally more brittle. R3 was used to increase the reaction speed of the system (oxetane-reactive, OH group additionally accelerates polymerization); in addition it was found that flexibility and toughness are increased by use of R3.

(23) Photoinitiators (PI):

(24) Cyracure UVI 9676: triarylsulfonium hexafluoroantimonate (50 wt % dissolved in propylene carbonate; Dow Chemicals):

(25) ##STR00004##
Irgacure 290: triarylsulfonium borate (100%; BASF):

(26) ##STR00005##
UV 1242: bis(dodecylphenyl)iodonium hexafluoroantimonate (50 wt % in C12/C14 glycidyl ether; Deuteron):

(27) ##STR00006##
UV 2257: bis(4-methylphenyl)iodonium hexafluorophosphate (50 wt % in propylene carbonate; Deuteron):

(28) ##STR00007##

(29) Flexible, tough systems can be obtained with all four used photoinitiators. The best results with regard to flexibility and toughness were attained for PI concentrations of 1% for undissolved PI (Irgacure 290) or 1.5%-2% for dissolved PI (Cyracure UVI 6976; UV 1242 and UV 2257).

(30) Adhesion Promoters:

(31) H1: chelate-modified epoxy resin

(32) H2: 3-glycidoxypropyl trimethoxysilane

Example 1

(33) In order to produce the compositions according to the invention, the base resin and the toughener were blended in an agitator under vacuum at room temperature. Flexibilizers and, as appropriate, reactive diluents were added to the mixture, which was stirred again under vacuum. The photoinitiator was then added and stirred under vacuum. If an adhesion promoter was added, this was added in a final step and the mixture was mixed again at room temperature under vacuum.

(34) To check flexibility and toughness, thin films were produced that were cured by means of UVA-LOC 1000 (30 s, 100 W, Fe-doped mercury lamp). To ensure complete curing, the films were then post-cured for 30 min at 100 C. The films were then tested by hand for flexibility and toughness.

(35) The following compositions were produced, which were characterized by particularly good results with regard to flexibility and toughness with good reactivity and adhesion:

(36) TABLE-US-00001 Sample 1 2 3 4 aromatic epoxy resin aE1 58.8 49 48 48.25 core-shell material CS1 29.4 29.4 28.8 28.95 co-toughener 2 2 flexibilizer F2 9.8 9.8 9.6 9.65 reactive diluent R1 9.8 reactive diluent R3 9.6 9.65 PI Cyracure UVI 9676 2 PI Irgacure 290 1 PI UV 2257 2 1.5 adhesion promoter H1 0.5

Example 2: Comparative Examples

(37) Procedure and test for checking flexibility and toughness: Production of thin films cured by means of UVA-LOC 1000 (30 s, 1000 W, Fe-doped mercury lamp). To examine the ageing behavior, the films were then stored for 1 h and 14 h at 130 C. in an oven and tested by hand for flexibility and toughness. Scoring scale: from 1 (very flexible/very high tensile strength) to 6 (very brittle, high crack growth).

(38) 1. Influence of Epoxy Resin

(39) As a comparison according to the invention, samples 1 and 3 from example 1 were used and the aromatic epoxy base resin was replaced by the same amount, in each case, of cycloaliphatic epoxy resin cE2.

Overview of the Flexibility and Toughness Test

(40) TABLE-US-00002 Base Flexibility Toughness epoxy before 1 h @ 14 h @ before 1 h @ 14 h @ Sample resin Photoinitiator ageing 130 C. 130 C. ageing 130 C. 130 C. 1 aE1 Cyracure 6976 1 2 2 1 2-3 2-3 CE1 cE2 Cyracure 6976 3 3-4 4 3 3-4 4 3 aE1 UV 2257 1 1 1 1 1-2 1-2 CE2 cE2 UV 2257 1 2 3 1 2 3

Composition of the Formulations (Values in %)

(41) TABLE-US-00003 Sample: 1 CE1 3 CE2 aromatic base resin aE1 58.8 48 cycloaliph. base resin cE2 58.8 48 toughener CS1 29.4 29.4 28.8 28.8 co-toughener 2.0 2.0 flexibilizer F2 9.8 9.8 9.60 9.60 reactive diluent R3 9.60 9.60 PI Cyracure 6976 2 2 PI UV 2257 2 2 Sum: 100 100 100 100

(42) The use of cycloaliphatic epoxy resin clearly leads to a less flexible system compared to formulations based on an aromatic epoxy resin.

(43) The results also show that the flexibility in cycloaliphatic system decreases with age; by contrast, flexibility and tensile strength decrease to a much lesser extent in the systems based on aromatic epoxy resin.

(44) 2. Influence of the Core-Shell (CS) Material (Toughener):

(45) Here, the use of core-shell materials based on cycloaliphatic epoxy resins (UVR 6110) in contrast to core-shell materials based on aromatic epoxy resin (BFDGE) was examined.

Overview of the Flexibility and Toughness Test

(46) TABLE-US-00004 Base Flexibility Toughness CS epoxy before 1 h @ 14 h @ before 1 h @ 14 h @ Sample material resin Photoinitiator ageing 130 C. 130 C. ageing 130 C. 130 C. 1 CS1 aE1 Cyracure 1 2 2 1 2-3 2-3 6976 5 CS3 aE1 Cyracure 3 3 3 3 3 4 6976 CE3 CS3 cE2 Cyracure 4 4 4 4 4 4 6976 3 CS1 aE1 UV 2257 1 1 1 1 1-2 1-2 6 CS3 aE1 UV 2257 1 1-2 3 1 1-2 2 CE4 CS3 cE2 UV 2257 1 2 3 1 2 2-3

Composition of the Formulations (Values in %)

(47) TABLE-US-00005 Sample: 1 5 CE3 3 6 CE4 aromatic base resin 58.8 58.8 48 48 aE1 cycloaliph. base resin 58.8 48 cE2 toughener CS1 29.4 28.8 toughener CS3 29.4 29.4 28.8 28.8 co-toughener 2.0 2.0 2.0 flexibilizer F2 9.8 9.8 9.8 9.60 9.60 9.60 reactive diluent R3 9.60 9.60 9.60 PI Cyracure 6976 2 2 2 PI UV 2257 2 2 2 Sum: 100 100 100 100 100 100

(48) As had already been found in the case of the examinations relating to the base epoxy resin, it was shown similarly that the use of CS rubber particles embedded in an aromatic epoxy resin matrix is particularly preferred with regard to flexibility and toughness, in particular after ageing. However, the combination of an aromatic epoxy base resin with CS materials having a cycloaliphatic epoxy resin matrix also results in functioning systems, particularly with use of the photoinitiator UV 2257. The combination of cycloaliphatic base epoxy resin and CS materials having a cycloaliphatic epoxy resin matrix leads to systems without aromatic epoxy resin and therefore to systems that have the lowest flexibility and toughness.

(49) 3. Influence of the Flexibilizer and Co-Toughener

(50) Here, it was examined to what extent the system must have flexibilizer and co-toughener in order to obtain flexible and tear-resistant films. For this purpose, formulations containing no flexibilizer and no co-toughener were produced for comparison, as well as formulations containing no flexibilizer, but containing co-toughener.

Overview of the Flexibility and Toughness Test

(51) TABLE-US-00006 Flexibilizer/ Base Flexibility Toughness co- epoxy Photo- before 1 h @ 14 h @ before 1 h @ 14 h @ Sample toughener resin initiator ageing 130 C. 130 C. ageing 130 C. 130 C. CE5 aE1 Cyracure 3 3 4 3 4 4 6976 1 F2 aE1 Cyracure 1 2 2 1 2-3 2-3 6976 CE6 2% Fortegra aE1 Cyracure 2 2 2-3 1 2-3 3 100 6976 CE7 aE1 UV 2257 2 2-3 3 2 2-3 3 7 F2 aE1 UV 2257 1 1 1 1 1-2 1-2 3 F2 aE1 UV 2257 1 1 1 1 1-2 1-2 2% Fortegra 100

Composition of the Formulations (Values in %)

(52) TABLE-US-00007 Function: CE5 1 CE6 CE7 7 3 base resin aE1 65.3 58.8 64 54.4 49 48 toughener CS1 32.7 29.4 32 32.7 29.4 28.8 co-toughener 2 2.0 flexibilizer F2 9.8 9.8 9.60 reactive diluent R3 10.9 9.8 9.60 PI Cyracure UVI 9676 2 2 2 PI UV 2257 2 2 2 Sum: 100 100 100 100 100 100

(53) The produced films show that, without the use of flexibilizer and co-toughener, the flexibility and toughness decrease. Here, a high flexibility and toughness can be attained under the influence of either flexibilizer or a combination of flexibilizer and co-toughener. The use of photoinitiator UV-2257 again leads to comparatively more flexible films having higher toughness.