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IMPROVEMENTS IN OR RELATING TO STRUCTURAL ADHESIVES

20170240774 · 2017-08-24

    Inventors

    Cpc classification

    International classification

    Abstract

    The invention relates to structural adhesives and in particular to structural adhesives which are heat activated and which can be used for the bonding of components, particularly metal components, employed in the automotive industry.

    Claims

    1. An adhesive for providing corrosion resistance to a substrate to which the adhesive is adhered, wherein the adhesive is reformable in the temperature range of from about 60° C. to about 120° C., and wherein the adhesive is curable in the temperature range of from about 130° C. to about 230° C.; and wherein in the temperature range G′>G.sup.II the storage modulus G.sup.I of the adhesive is higher than the loss modulus G.sup.II of the adhesive, wherein the temperature range G.sup.IG.sup.II is not narrower than of from about 10° C. to about 30° C.; and in the temperature range G.sup.II>G.sup.I the loss modulus G.sup.II of the adhesive is higher than the storage modulus of the adhesive, wherein the temperature range G.sup.II>G.sup.I is not narrower than of from about 110° C. to about 120° C.

    2. The adhesive according to claim 1, wherein the temperature range G.sup.I>G.sup.II is not narrower than of from about 10° C. to about 35° C.

    3. The adhesive according to claim 2, wherein the temperature range G.sup.I>G.sup.II is not narrower than of from about 10° C. to about 40° C.

    4. The adhesive according to claim 3, wherein the temperature range G.sup.I>G.sup.II is not narrower than of from about 10° C. to about 45° C.

    5. The adhesive according to claim 4, wherein the temperature range G′>G.sup.II is not narrower than of from about 10° C. about 50° C.

    6. The adhesive according to claim 1, wherein at least at one temperature within the temperature range G.sup.I>G.sup.II, the relative difference G.sup.I−G.sup.II of the storage modulus G.sup.I of the adhesive and the loss modulus G.sup.II of the adhesive is at least about 10,000 Pa.

    7. The adhesive according to claim 6, wherein the relative difference at least at one temperature within the temperature range G.sup.I>G.sup.II, the relative difference G.sup.I−G.sup.II of the storage modulus G of the adhesive and the loss modulus G.sup.II of the adhesive is at least about 30,000 Pa.

    8. The adhesive according to claim 7, wherein the temperature range G.sup.II>G.sup.I is not narrower than of from about 105° C. to about 120° C.

    9. The adhesive according to claim 8, wherein the temperature range G.sup.II>G.sup.I is not narrower than of from about 100° C. to about 120° C.

    10. The adhesive according to claim 9, wherein the temperature range G.sup.II>G.sup.I is not narrower than of from about 95° C. to about 120° C.

    11. The adhesive according to claim 10, wherein the temperature range G.sup.II>G.sup.I is not narrower than of from about 90° C. to about 120° C.

    12. The adhesive according to claim 11, wherein the temperature range G.sup.II>G.sup.I is not narrower than of from about 85° C. to about 120° C.

    13. The adhesive according to claim 12, wherein the temperature range G.sup.II>G.sup.I is not narrower than of from about 80° C. to about 120° C.

    14. The adhesive according to claim 1, wherein at least at one temperature within the temperature range G.sup.II>G.sup.I, the relative difference G.sup.II−G.sup.I of the loss modulus G.sup.II of the adhesive and the storage modulus G.sup.I of the adhesive is at least about 3000 Pa.

    15. The adhesive according to any of the preceding claims, wherein at least at one temperature within the temperature range G.sup.II≧G.sup.I, the relative difference G.sup.II−G.sup.I of the loss modulus G.sup.II of the adhesive and the storage modulus G.sup.I of the adhesive is at least about 6000 Pa.

    16. The adhesive according to claim 1, wherein the storage modulus G.sup.I of the adhesive is equal to the loss modulus G.sup.II of the adhesive at a crossover temperature which is within the temperature range of from about 30° C. to about 110° C.

    17-22. (canceled)

    23. The adhesive according to claim 1, wherein the adhesive starts to cure at about 125° C., leading to a thermoset structural adhesive.

    24. (canceled)

    25. The adhesive according to claim 1, wherein the adhesive is used for forming bonds on a substrate that are not susceptible to cause corrosion on the substrate along the length of the bond, wherein the adhesive is: heat activated at a temperature in the range of from about 130° C. to about 230° C.; reformable in the temperature range of from about 60° C. to about 120° C.; curable in the temperature range of from about 130° C. to about 230° C.; and wherein the adhesive; has a storage modulus G.sup.I higher than its loss modulus G.sup.II for temperatures up to about 50° C.; has a loss modulus G.sup.II higher than its storage modulus G.sup.I in the temperature range of from about 60° C. to about 120° C.; and starts to cure at about 130° C., leading to a thermoset structural adhesive.

    26-29. (canceled)

    30. The adhesive according to any of the preceding claims, wherein the adhesive provides a shear strength greater than about 10 Mpa, greater than about 15 Mpa, or even greater than about 20 Mpa after crosslinking and cooling to ambient temperature.

    31-34. (canceled)

    35. The adhesive according to claim 1, wherein the adhesive comprises an epoxy resin component within the range of from about 2 wt.-% to about 75 wt.-%, relative to the total weight of the adhesive.

    36-53. (canceled)

    Description

    EXAMPLE 1

    [0144] A structural adhesive formulation containing curable polymers and a curing agent that starts to cure at about 125° C. was prepared and its storage modulus G.sup.I and loss modulus G.sup.II was determined over the temperature range of about 30° C. to about 110° C. as is shown in FIG. 1.

    [0145] The storage modulus G.sup.I and the loss modulus G.sup.II was also determined over a time period of 3500 seconds during the heating of the adhesive from about 30° C. to about 110° C. and then looking down to about 40° C. The change in the storage modulus G.sup.I and loss modulus G.sup.II is shown in FIG. 2 indicating that at about 70° C. the product changes from a solid state to a viscous liquid and that up to the temperature of about 11° C. this is reversible.

    [0146] It was found that the adhesive could be applied to a metal surface at a temperature of about 10° C. to provide a continuous strip of adhesive which could be cured to obtain a well-defined structural bond which appeared to provide long term corrosion resistance to the control area of the metal surface.

    EXAMPLE 2

    [0147] In accordance with Example 1, a structural adhesive formulation containing curable polymers and a curing agent that starts to cure at about 125° C. was prepared from the following constituents in the following amounts:

    TABLE-US-00001 Constituent wt.-% CTBN modified epoxy resin (1600 g/Eq) 6.00 Solid epoxy resin (900 g/Eq) Molecular Weight > 1100 g/mol 5.00 Micronized grade of dicyandiamide (<50 μm) 5.00 Aromatic substituted urea (Methylene Diphenyl Bis 0.60 (Dimethyl Urea)) (latent accelerator for the dicyandiamide cure of epoxy resins) Calcium oxide (<70 μm) 5.00 Calcium carbonate (<70 μm) 18.40 Silane modified epoxy resin (200 g/Eq) 16.00 Methacrylate-butadiene-styrene (MBS) core/shell impact 16.00 modifier: cross-linked poly (butadiene/styrene) core with a grafted polymethyl methacrylate shell Epoxy Phenol Novolac Resin 8.00 Phenoxy Resin 15.00 Amorphous Silica (<50 nanometers: 40%) reinforced 5.00 bisphenol F based epoxy resin

    [0148] The storage modulus G.sup.I and loss modulus G.sup.II was determined over the temperature range of about 30° C. to about 110° C. as is shown in FIG. 3. The absolute value for the difference of G′ and G′ is also shown (y-axis to the right). The crossover temperature was observed at about 66.5° C.

    EXAMPLE 3

    [0149] In accordance with Example 1 and 2, a structural adhesive formulation containing curable polymers and a curing agent that starts to cure at about 125° C. was prepared from the following constituents in the following amounts:

    TABLE-US-00002 Constituent wt.-% Solid epoxy resin type I (EEW 450-530 g/eq) 4.00 Liquid epoxy resin (EEW 200 g/eq) 22.00 MBS based core shell impact modifier 13.40 Polyvinylbutyral 4.85 Phenoxy resin derived from Bisphenol A 16.95 Epoxy terminated CTBN adduct 20.00 Micronized Polyamide 6/12 (particle size 20 μm) 8.00 Talc 1.01 Calcium oxide 5.00 Thixotropic agent (Organo clay) 0.76 Pigment 0.05 Disubstituted urea 0.35 Dicyandiamide 3.00 Chemical blowing agent ADCA 0.63 TOTAL 100.00

    [0150] The storage modulus G.sup.I and loss modulus G.sup.II was determined over the temperature range of about 30° C. to about 120° C. as is shown in FIG. 4. The absolute value for the difference of G′ and G′ is also shown (y-axis to the right). The crossover temperature was observed at about 94° C.