Method for strengthening of metal structures using toughened 2C-epoxy adhesives

Abstract

A method for strengthening metal structure, including steps: i) mixing two-component epoxy resin composition; ii) applying composition to metal structure surface, or onto strengthening element, or both; iii) contacting applied epoxy resin composition with strengthening element surface and/or metal structure surface wherein composition forms interlayer between metal structure and strengthening element, and iv) curing epoxy resin composition at 100° C. or below; wherein two-component epoxy resin composition contains: first component between 10-50 wt.-% of at least one epoxy resin contains on average more than one epoxy group per molecule; second component between 5-30 wt.-% of hardener for epoxy resins; between 3-25 wt.-% of at least one impact strength modifier in one or both components; between 15-80 wt.-% of at least one filler in one or both components; and wherein two-component epoxy resin composition exhibits after curing Elastic Modulus at least 2500 MPa, and Impact Peel Strength at least 15 N/mm.

Claims

1. A method for strengthening a metal structure M, comprising the steps of i) mixing a two-component epoxy resin composition C; ii) applying the composition C onto a strengthening element S, or both onto the strengthening element S and to a surface of the metal structure M, wherein the strengthening element S is made of a composite material comprising glass fibers or carbon fibers; iii) contacting the applied epoxy resin composition with the surface of the strengthening element S and/or the surface of the metal structure M such that the composition forms an interlayer between the metal structure M and the strengthening element S, iv) optionally pre-stressing the strengthening element S, v) optionally pre-fixing the strengthening element S onto the metal structure M by mechanical fixation or spot welding so that the strengthening element S is held in place before the composition is cured, and vi) curing the epoxy resin composition at a temperature of or below 100° C.; wherein the two-component epoxy resin composition C contains a first component K1 comprising from 18.0 to 23.6 wt.-%, based on the total weight of composition C, of at least one epoxy resin A, comprising at least predominantly a bisphenol A diglycidyl ether; a second component K2 comprising 8.2 to 11 wt.-%, based on the total weight of composition C, of an amine-based hardener B for epoxy resins; 7.7 to 11.6 wt.-%, based on the total weight of composition C, of at least one impact strength modifier I in either one or both of components K1 and K2, the impact strength modifier I being selected from the group consisting of polyurethane-based modifiers and core-shell rubbers; 51.5 to 60 wt.-%, based on the total weight of composition C, of at least one filler F consisting of quartz and fumed silica, in either one or both of components K1 and K2; and wherein the two-component epoxy resin composition C exhibits after curing an Elastic Modulus of at least 2500 MPa, measured according to DIN EN ISO 527, and an Impact Peel Strength of at least 15 N/mm, measured according to ISO 11343.

2. The method according to claim 1, wherein the composite material comprises the carbon fibers.

3. The method according to claim 1, wherein the strengthening element S is selected from the group consisting of glass fiber reinforced plastic sheet, glass fiber reinforced lamella, carbon fiber reinforced plastic sheet, and carbon fiber reinforced lamella.

4. The method according to claim 1, wherein the two-component epoxy resin composition C contains in either one or both of components K1 and K2 an anti-corrosion agent with an amount of between 1 and 15 wt.-%, based on the total weight of composition C.

5. The method according to claim 4, wherein the two-component epoxy resin composition C contains the anti-corrosion agent with an amount of between 2 and 10 wt.-%, based on the total weight of composition C.

6. The method according to claim 1, wherein the filler F comprises particles with a mean particle size of at least 0.1 to at least 1 mm.

7. The method according to claim 1, wherein the weight ratio of all epoxy-functional compounds in the composition to pure impact strength modifier I in the composition is between 1 and 3.

8. The method according to claim 1, wherein the weight ratio of epoxy resin A, hardener B, impact strength modifier I, and filler F in composition C is in the range of A:B:I:F=1:(0.25-1):(0.25-1):(1-4).

9. The method according to claim 1, wherein the metal structure is a building or a metal part of a vehicle.

10. The method according to claim 1, wherein the metal structure is a bridge.

11. The method according to claim 1, wherein the impact strength modifier I comprises a polymer of the formula (V), ##STR00007## where n and n′ independently of one another are each values of from 0 to 7 with the proviso that n+n′ is a value of from 1 to 8, R.sup.1 is a linear or branched polyurethane prepolymer terminated with n+n′ isocyanate groups, after removal of all terminal isocyanate groups, and R.sup.2 and R.sup.3 are, independently of one another, aliphatic, cycloaliphatic, aromatic, or arylaliphatic groups with 1 to 20 C atoms, which optionally contain heteroatoms selected from O, N, and S.

12. The method according to claim 11, wherein in the polymer of the formula (V), n+n′ is 1.

13. The method according to claim 11, wherein in the polymer of the formula (V), n+n′ is 2.

14. The method according to claim 11, wherein in the polymer of the formula (V), R.sup.2 and R.sup.3 are, independently of one another, the aliphatic groups with 1 to 20 C atoms, which optionally contain heteroatoms selected from O and N.

15. The method according to claim 11, wherein in the polymer of the formula (V), R.sup.2 and R.sup.3 are, independently of one another, the cycloaliphatic, aromatic, or arylaliphatic groups with 3 to 20 C atoms, which optionally contain heteroatoms selected from O and N.

Description

EXAMPLES

(1) Examples are given below which illustrate the invention further but do not limit the scope of the invention in any way and merely illustrate some of the possible embodiments. “Standard conditions” or “norm climate” (“NK”) refers to a temperature of 23° C. and 50% relative humidity (r.h.).

(2) Test Methods

(3) The following test methods were employed:

(4) Compressive Strength (CS) and Modulus of Compression (C-Mod) (ASTM D695)

(5) The compressive strength and modulus of compression were determined by applying the mixed adhesive in the standard climate in a silicone mold to cuboids of the dimensions 12.7×12.7×25.4 mm. These samples were cured under standard conditions. After 7 days, a plurality of such cuboids were in each case released from the mold and compressed to destruction according to ASTM D695 at a test speed of 1.3 mm/min, the value for the compressive strength in each case being read off at the maximum force.

(6) Tensile Strength (TS), Elongation at Break (EOB) and Elastic Modulus (E-Mod) (DIN EN ISO 527)

(7) These mechanical properties were determined by applying and curing the mixed adhesive in the standard climate into a silicone mold to form dumbbell-shaped bars having a thickness of 10 mm, a length of 150 mm, a land length of 80 mm and a land width of 10 mm. After 7 days curing time (NK) the test specimens were released from the mold. The specimens were measured under standard conditions at a pulling speed of 2 mm/min. The tensile strength, elongation at break and the modulus of elasticity 0.05-0.25% were determined according to DIN EN ISO 527.

(8) Lap Shear Strength (LSS) (DIN EN 1465)

(9) To measure the lap shear strength on steel (LSS steel) several adhesive bonds were made, by applying the mixed adhesive between two heptane-degreased steel sheets in a layer thickness of 0.5 mm with an overlapping adhesive area of 10×25 mm. After a storage period of 7 days under standard conditions, the tensile shear strength was determined according to DIN EN 1465 at a tensile speed of 10 mm/min.

(10) To measure the lap shear strength on carbon fiber composite (CFRP) (LSS CFK) several adhesive bonds were made by applying the mixed adhesive between two heptane degreased Sika® CarboDur® S512 fins in a layer thickness of 0.5 mm with an overlapping adhesive surface of 10×50. After a storage time of 7 days in the NK, the lap shear strength was determined as described.

(11) Maximum Bending Force (MBF)

(12) Maximum bending force was determined using the method according to the present invention and the inventive and non-inventive adhesives of Table 1, by applying the mixed adhesive on a heptane-degreased steel sheet in a layer thickness of 1 mm. This was then covered by a heptane degreased CFK lamella (Sika® CarboDur® S512), pressed together and left for curing in NK during 7 d. After that, a three-point bending test was performed with each specimen until either adhesive failure (AF) or substrate failure (SF) was observed. The maximum bending force that the reinforced steel test specimen had been bent into under this force was determined. This value gives a good quantitative indication on the strengthening of the steel by the method and the behavior under stress and displacement of the metal structure.

(13) Impact Peel Strength (IPS) (ISO 11343)

(14) The test specimens were prepared from the example compositions described and with electrogalvanized DC04 steel (eloZn) having dimensions 90×20×0.8 mm, where the adhesion surface area was 25×10 mm with a layer thickness of 0.3 mm. They were cured for 7 days at 23° C. The impact peel strength was measured at 23° C. according to ISO 11343 with an impact velocity of 2 m/s. The failure mode was also determined. “AF” means adhesive failure, “CF” means cohesive failure.

(15) Tested Two-Component Epoxy Resin Compositions

(16) The used two-component epoxy resin compositions are listed in Table 1.

(17) TABLE-US-00001 TABLE 1 Tested two-component epoxy resin adhesives. Adhesive (supplier) Description SikaDur ®-30 (“SD-30”) Non-toughened reference adhesive used for (Sika Schweiz AG) structural strengthening of concrete Compositions C1 to C8* According to the present invention; details see below SikaPower ®-1200 (“SP- Commercial adhesive for composite bonding 1200”) (Sika Schweiz AG) in industry applications Araldite ® 2015 Commercial toughened adhesive, tough and (“Aral 2015”) (Huntsman) elastic, for composite applications Araldite ® 420 Commercial toughened adhesive, extremely (“Aral 420”) (Huntsman) tough and resilient, for metal, composite, thermoplastics Scotch Weld DP 490 Commercial toughened adhesive, toughness (“SW 490”) (3M) and high strength for composite bonding *according to the invention
Example of Compositions According to Present Invention

(18) A series of two-component example compositions (Compositions C1 to C8) was prepared using the following constituents (all wt.-% (percent by weight) values refer to the total composition C) by mixing the constituents:

(19) Epoxy Resin

(20) TABLE-US-00002 Wt. -% C1 C2 C3 C4 C5 C6 C7 C8 D.E.R. ® 331 22.1 16.6 17.1 18.8 18.8 18.5 16.2 14.6 (Olin), Bisphenol A diglycidyl ether Araldite ® 1.5 1.7 1.8 1.8 1.8 1.7 1.8 1.8 DY-D (Huntsman), butanediol diglycidyl ether TOTAL epoxy 23.6 18.5 18.9 20.6 20.6 20.2 18.0 16.4 resin A
Hardener

(21) TABLE-US-00003 Wt. -% C1 C2 C3 C4 C5 C6 C7 C8 Jeffamine ® 5 4.2 4 4.1 4.1 4.2 3.9 4.2 D230 (Huntsman), polyether amine Ancamine ® 1 0.8 0.8 0.8 0.8 0.8 0.8 0.8 K54 (Evonik), 2,4,6- tris(dimethyl- aminomethyl) phenol Jeffamine ® 5 3.3 3.2 3.3 3.3 3.3 3.1 3.3 RFD-270 (Huntsman), aliphatic polyether amine with an acyclic alkoxylate segment and a cycloaliphatic segment TOTAL 11 8.3 8 8.2 8.2 8.3 7.8 8.3 hardener B
Filler

(22) TABLE-US-00004 Wt. -% C1 C2 C3 C4 C5 C6 C7 C8 Quartz filler 49.5 55.5 56 55.15 55.15 55.6 54.4 54.6 (maximum particle size: 0.3 mm) hydrophobic 2 2.6 2.6 2.6 2.6 2.6 2.6 2.6 fumed silica TOTAL filler F 51.5 58.1 58.6 57.75 57.75 58.2 57.0 57.2
Impact Strength Modifier

(23) TABLE-US-00005 Wt. -% C1 C2 C3 C4 C5 C6 C7 C8 Impact strength 7.9 8.9 — — — — — — modifier I1 (see below) Impact strength — — 9.2 — — — — — modifier I2 (see below) Struktol ® XP — — — 7.05 — — — — 3570 (Schill + Seilacher), epoxy- funcitonal modifier Struktol ® XP — — — — 7.05 — — — 3571 (Schill + Seilacher), epoxy- funcitonal modifier Kane Ace ™ — — — — — 6.9 10.8 — MX-154 (Kaneka), core-shell rubber toughener based on SBR rubber Desmocap ® 11 — — — — — — — 12.2 (Covestro), branched endcapped polyurethane toughener ATBN ® 1 0.8 0.8 0.8 0.8 0.8 0.8 0.8 1300 × 16 (Emerald Materials), amine-terminated liquid rubber TOTAL impact 8.9 9.7 10.0 7.85 7.85 7.7 11.6 13.0 strength modifier I
Additives

(24) TABLE-US-00006 Wt. -% C1 C2 C3 C4 C5 C6 C7 C8 Additives (commercial 1 0.6 0.6 0.6 0.6 0.6 0.6 0.6 deaeration additive (Byk) and commercial adhesion promoter (silanes)) anti-corrosion additives (mixture of different 5 5 5 5 5 5 5 5 commercial products advertised for anti-corrosion properties (liquid or solid)). TOTAL additives 6.0 5.6 5.6 5.6 5.6 5.6 5.6 5.6

(25) For testing, a homogenous mixture of above constituents forming each composition C was prepared using a stirrer and directly applied to the substrate surfaces used for preparing the test pieces. The commercial reference samples were prepared according to the specifications for the tested commercial products. For each example, the resin component and the hardener component were then processed into a homogenous paste by means of the centrifugal mixer and tested immediately as detailed above.

(26) Synthesis of Exemplary Impact Strength Modifier 11

(27) 150 g of isocyanate-terminated prepolymer, produced from 60% by weight PolyTHF® 2000 (BASF), 40% by weight Poly BD® R45V (Cray Calley), Isophorone diisocyanate (Evonik) (0.75 equivalents) and dibutyl tin dilaurate catalyst, was treated with 1 equivalent of dry Epikote®828LVEL (Hexion). Next, 8.11 mmol phthalic anhydride (Sigma Aldrich) were added, the reaction mixture was mixed and then reacted at 110° C. under vacuum by adding catalyst.

(28) Synthesis of Impact Strength Modifier 12

(29) Under nitrogen atmosphere, 5687 g of Acclaim® 4200 polyol (Bayer MaterialScience) 712 g of MDI with the trade name Desmodur 44 MC L (Covestro) and 0.6 g catalyst DABCO 33 LV (Air Products) were heated with constant stirring to 80° C. and left at this temperature to produce an NCO-terminated prepolymer. After one hour of reaction time, a free NCO content was determined by titration. It had reached a content of isocyanate groups of 1.9 wt.-%. Subsequently, 910 g cardanol with the trade name Cardolite NC-700 (Cardolite) were added and stirring was continued for a further 2 hours at 80° C. The reaction was stopped as soon as free isocyanate was no longer detectable by IR spectroscopy (wavenumbers 2275-2230 cm.sup.−1).

(30) Mechanical Properties of Tested Two-Component Epoxy Resin Compositions

(31) The used two-component epoxy resin adhesives of Table 1 were tested according to the methods detailed above. The results are in Tables 2 and 4.

(32) TABLE-US-00007 TABLE 2 Mechanical properties of the tested two-component epoxy resin adhesives. SD-30 Comp. C1* SP-1200 Aral 2015 Aral 420 SW 490 LSS steel  13.1 ± 3  23.2 ± 0.4  23.5 ± 1  14.8 ± 0.6  20.8 ± 5   21 ± 2 [MPa] LSS CFK   9.0 ± 2.4  23.2 ± 1  24.7 ± 2.4  21.8 ± 1.7  26.8 ± 3  26.6 ± 1.7 [MPa] TS [MPa]  31.2 ± 1   35 ± 0.9  27.9 ± 1.1   23 ± 2   32 ± 7   32 ± 0.5 E-Mod   8670 ±  4500 ± 120  2400 ± 37  2000 ± 100  1800 ± 130  1490 ± 60 [MPa]   210 EOB [%]   0.5 ± 0  1.9 ± 0.9  2.4 ± 0.3   01.5 ± 0.3   5.6 ± 3.4  4.7 ± 0.3 C-Mod.  12580 ±  5000 ± 50  2400 ± 85  1900 ± 50  1940 ± 15  1580 ± 7.7 [MPa] 20 CS [MPa]  77.5 ± 1.5   75 ± 4   53 ± 5   40 ± 4   43 ± 1.7   40 ± 2.5 IPS[N/mm]   0.3 ± 4 AF   20 ± 2 CF   10 ± 1 CF   10 ± 1 CF    5 ± 0.4 AF    4 ± 2 CF *according to the invention
Structural Strengthening Behavior of Tested Two-Component Epoxy Resin Compositions

(33) Some of the used two-component epoxy resin adhesives of Table 1 were tested according to the three-point bending test method detailed above. The results are in Table 3.

(34) TABLE-US-00008 TABLE 3 Strengthening properties of the tested two-component epoxy resin adhesives. SD-30 Comp. C1* SP-1200 Aral 2015 Aral 420 SW 490 MBF [N] 3050 ± 160 3300 ± 150 2900 ± 100 2200 ± 250 1890 ± 100 2530 ± 120 Failure AF SF SF/AF AF SF SF “AF” means adhesive failure, “SF” means substrate failure of the CFK lamella. *according to the invention

(35) TABLE-US-00009 TABLE 4 Mechanical properties of the exemplary two-component epoxy resin adhesives according to the invention. C1 C2 C3 C4 C5 C6 C7 C8 LSS steel  23.2 ±  25.0 ±  15.0 ±  15.5 ±  18.3 ±  24.0 ±  23.0 ±  20.9 ± [MPa] 0.4 2 4 1 1 4 3 0.1 LSS CFK  23.2 ±  21.0 ±  25.0 ±  23.2 ±  26.4 ±  30.8 ±  28.9 ±  15.9 ± [MPa] 1 1 0.6 0.4 1 0.2 0.1 0.1 TS [MPa]   35 ±  27.0 ±  27.4 ±  29.5 ±  28.0 ±  33.0 ±  32.0 ±  24.4 ± 0.9 1 0.2 0.1 2 4 2 0.1 E-Mod  4500 ±  4100 ±  3500 ±  3200 ±  3900 ±  4500 ±  4600 ±  2550 ± [MPa] 120 300 100 200 30 120 100 120 EOB [%]  1.9 ±  3.0 ±  2.0 ±  2.0 ±  1.2 ±  0.8 ±  2.0 ± 1  2.8 ± 0.9 0.2 02 0.1 0.4 0.3 0.2 C-Mod.  5000 ±  4600 ±  4500 ±  4300 ±  2600 ±  6600 ±  5200 ±  3100 ± [MPa] 50 30 150 200 80 200 300 200 CS [MPa]   75 ± 4   70 ± 1  56.4 ±   66 ± 1   62 ± 1   64 ± 4   60 ± 2   56 ± 1 1.4 IPS   20 ± 2   16 ± 2   21 ± 5   15 ± 2   17 ± 1   15 ± 2   22 ± 1   15 ± 2 [N/mm] CF CF CF CF CF CF CF CF Epoxy: 2.7 1.9 1.9 2.6 2.6 2.6 1.6 1.3 Impact strength modifier** **weight/weight ratio of all epoxy-functional compounds to all impact strength modifiers.