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EP-4735503-A1 - HEAT-CURABLE SEALING COMPOSITION

EP4735503A1EP 4735503 A1EP4735503 A1EP 4735503A1EP-4735503-A1

Abstract

The invention relates to a thermosetting one-component epoxy resin composition comprising at least one liquid aromatic epoxy resin A1, at least one liquid aliphatic epoxy resin A2, at least one curing agent B for epoxy resins, where the curing agent B is a dihydrazide and at least one at least one toughness improver D. The weight ratio of the at least one liquid epoxy resin A1 to the at least one liquid epoxy resin A2 (A1/A2) is from 0.25 – 5.0. The thermosetting one-component epoxy resin composition that can be used as a sealing composition which does not show bubble formation at curing temperatures at 210 °C and provides good mechanical and storage properties, especially with respect to elongation at break performance and storage at elevated temperature between 50 °C – 60 °C.

Inventors

  • BÖFER, Cornelia

Assignees

  • Sika Technology AG

Dates

Publication Date
20260506
Application Date
20240612

Claims (16)

  1. 1 . A thermosetting one-component epoxy resin composition comprising a) at least one liquid epoxy resin A1 having an average of more than one epoxy group per molecule, that is an aromatic liquid epoxy resin; b) at least one liquid epoxy resin A2 having an average of more than one epoxy group per molecule, that is selected from the group consisting of: - glycidyl ethers of difunctional saturated, branched or unbranched, cyclic or open-chain C2-C30 alcohols; - glycidyl ethers of tri- or polyfunctional, saturated, branched or unbranched, cyclic or open-chain alcohols; and - epoxidized di- or trifunctional polyether polyols; c) at least one curing agent B for epoxy resins, where the curing agent B is a dihydrazide, preferably selected from the group consisting of aromatic dicarboxylic dihydrazide B1 and aliphatic dicarboxylic dihydrazide B2; and d) at least one at least one toughness improver D selected from the group consisting of terminally blocked polyurethane polymers D1 , liquid rubbers D2 and core-shell polymers D3, preferably a terminally blocked polyurethane polymer D1 , wherein the weight ratio of the at least one liquid epoxy resin A1 to the at least one liquid epoxy resin A2 (A1/A2) is from 0.25 - 5.0, preferably 0.33 - 3.0, more preferably 0.5 - 2.0, most preferably 0.75 - 1 .5.
  2. 2. The thermosetting one-component epoxy resin composition as claimed in claim 1 , characterized in that the curing agent B is an aliphatic dicarboxylic dihydrazide B2, preferably selected from the group consisting of glutaric dihydrazide, adipic dihydrazide, pimelic dihydrazide, 8,12-eicosadienedioic acid 1 ,20-dihydrazide and 4-isopropyl-2,5-dioxoimidazolidine-1 ,3- di(propionohydrazide), especially adipic dihydrazide.
  3. 3. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the at least one liquid epoxy resin A1 has the formula (II) wherein the substituents R’” and R”” are each independently H or CH3, the index r has a value of 0 to 1 , preferably, r has a value of less than 0.2.
  4. 4. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that liquid epoxy resin A2 is selected from glycidyl ethers of difunctional saturated, branched or unbranched, cyclic or open-chain C2-C30 alcohols, in particular selected from the group consisting of ethylene glycol, butanediol, hexanediol, octanediol glycidyl ethers, cyclohexane dimethanol diglycidyl ether and neopentyl glycol diglycidyl ether, most preferably the liquid epoxy resin A2 is a glycidyl ether of hexanediol.
  5. 5. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the thermosetting one- component epoxy resin composition additionally includes at least one accelerator C selected from the list consisting of substituted ureas, imidazoles, imidazolines and blocked amines, especially substituted ureas.
  6. 6. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the weight ratio of the sum of the at least one liquid epoxy resin A1 and the at least one liquid epoxy resin A2 to the at least one toughness improver D ((A1 +A2)/D) is from 0.25 - 0.6, preferably 0.3 - 0.5, more preferably 0.35 - 0.55.
  7. 7. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the thermosetting one- component epoxy resin composition additionally includes at least one plasticizer PL, preferably selected from the list consisting of phthalic acid diesters; dialkyl terephthalates; aliphatic carboxylic diesters; polyester-type polymers; adipic polyesters; phosphate esters; trimellitate esters; benzoate and dibenzoate esters; citrate esters and alkyl sulphonic esters of phenol, preferably selected from trimellitate esters.
  8. 8. The thermosetting one-component epoxy resin composition according to claim 7, characterized in that if the weight ratio of the sum of the at least one liquid epoxy resin A1 and the at least one liquid epoxy resin A2 to the at least one plasticizer PL ((A1+A2)/PL) is from 1 - 10, preferably 1.25 - 5, more preferably 1 .5 - 3, even more preferably 1 .75 - 2.5, most preferably 1.8 - 2.2.
  9. 9. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the thermosetting one- component epoxy resin composition additionally includes at least one filler F, preferably selected from the group consisting of calcium carbonate, calcium oxide, talc, titanium oxide, and fumed silicas; preferably the total proportion of the filler F is 35-60% by weight preferably 45-55% by weight, more preferably 47.5-52.5% by weight, based on the total weight of the thermosetting one-component epoxy resin composition.
  10. 10. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the ratio of the proportion of the sum of the epoxy groups of the liquid epoxy resins A1 and A2 in mol / proportion of curing agent B in mol ((A1+A2)/B) is 3-8, preferably 4-7, more preferably 5-7, most preferably 5.5-6.5.
  11. 11. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the ratio of the proportion of accelerator C in grams per mole of the sum of the epoxy groups of the liquid epoxy resins A1 and A2 ((A1+A2)/C) is preferably 0.01 -0.5 g/mol of epoxy groups, especially 0.05-0.3 g/mol of epoxy groups, more preferably 0.075-0.2 g/mol of epoxy groups, most preferably 0.08-0.15 g/mol of epoxy groups.
  12. 12. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the proportion of the sum of the liquid epoxy resins A1 and A2 is 5-20% by weight, preferably 7.5-15% by weight, more preferably 10-12.5% by weight, based on the total weight of the one-component epoxy resin composition.
  13. 13. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the epoxy resin composition has a viscosity at 23°C of 150 - 900 Pa*s, especially 200 - 800 Pa*s, preferably 200 - 400 Pa*s, more preferably 250 - 350 Pa*s.
  14. 14. The use of a thermosetting one-component epoxy resin composition as claimed in any of claims 1 to 13 as sealing compounds in autobody work, in particular in the engine space or for doors, trunk lids, tailgates or hoods.
  15. 15. A method for sealing which comprises the following steps: i) Applying a thermosetting one-component epoxy resin composition according to any of the claims 1 - 13, to a substrate (S); ii) Heating the thermosetting one-component epoxy resin composition to a temperature above 120°C, in particular between 160°C and 220°C, to form a cured thermosetting one-component epoxy resin composition, preferably step ii) is preferably performed in a CDC oven.
  16. 16. The method according to claim 15, wherein the thermosetting one-component epoxy resin composition is to be applied in or to a gap in step i), said gap being bordered by two surfaces of the substrate (S) and a second substrate (S2), the second substrate (S2) being made of the same material as the substrate (S) or a different material.

Description

HEAT-CURABLE SEALING COMPOSITION Technical Field The invention relates to the field of a sealing composition for automotive body work in particular. Prior Art In automotive body work, individual metal plates are joined together. The metal plates that are used are oiled to reduce corrosion as much as possible. Furthermore, typically, the vehicle body will be passed through a CDC bath (CDC = cathodic dip coating) at the end of assembly of the body, so that the body is coated with a so-called CDC paint, which is then baked in a CDC oven. Good CDC coating over the full surface area forms the basis for long-term use of a vehicle because it makes a significant contribution toward corrosion resistance. Therefore, usually on these oiled metal plates like steel substrates are usually coated with a sealer which is required to adhere well to oil-coated sheet metal, need not be cured with heat or UV radiation before being immersed in a paint bath and nevertheless rapidly build up strength. WO 2012/084806 provides a heat-curable sealing compound compositions having a dual curing mechanism. On the one hand, there is rapid formation of a skin due to the reaction of polyisocyanates with polyaldimines in contact with air and/or atmospheric humidity; this ensures that the sealing compound can pass through the CDC bath undamaged. The paint may be deposited on the sealing compound in a high-quality application. In another step, the sealing compound cures due to heat such as that prevailing in the CDC oven. However, there is in some cases a bubble formation problem in these sealers. It is further important, that heat-curable sealing compositions have good mechanical and storage properties, especially with respect to elongation at break performance and storage at elevated temperature between 50 °C - 60 °C. Summary of the Invention The object of the present invention is therefore to make available a thermosetting one-component epoxy resin composition that can be used as a sealing composition which does not show bubble formation at curing temperatures at 210 °C and provides good mechanical and storage properties, especially with respect to elongation at break performance and storage at elevated temperature between 50 °C - 60 °C. It has surprisingly been found that the thermosetting one-component epoxy resin composition according to claim 1 achieve this object. The thermosetting one-component epoxy resin composition is therefore suitable for use as a sealing compound in automotive bodies in particular. Additional aspects of the invention are the subject matter of further independent claims. Especially preferred embodiments of the invention are the subject matter of the dependent claims. Methods of Implementing the Invention The present invention relates to a thermosetting one-component epoxy resin composition comprising a) at least one liquid epoxy resin A1 having an average of more than one epoxy group per molecule, that is an aromatic liquid epoxy resin; b) at least one liquid epoxy resin A2 having an average of more than one epoxy group per molecule, that is selected from the group consisting of: - glycidyl ethers of difunctional saturated, branched or unbranched, cyclic or open-chain C2-C30 alcohols; - glycidyl ethers of tri- or polyfunctional, saturated, branched or unbranched, cyclic or open-chain alcohols; and - epoxidized di- or trifunctional polyether polyols; c) at least one curing agent B for epoxy resins, where the curing agent B is a dihydrazide, preferably selected from the group consisting of aromatic dicarboxylic dihydrazide B1 and aliphatic dicarboxylic dihydrazide B2; and d) at least one at least one toughness improver D selected from the group consisting of terminally blocked polyurethane polymers D1 , liquid rubbers D2 and core-shell polymers D3, preferably a terminally blocked polyurethane polymer D1. The weight ratio of the at least one liquid epoxy resin A1 to the at least one liquid epoxy resin A2 (A1/A2) is from 0.25 - 5.0, preferably 0.33 - 3.0, more preferably 0.5 - 2.0, most preferably 0.75 - 1 .5. The term "polymer" in the present document refers on the one hand to a group of macromolecules that are chemically uniform but are different with respect to the degree of polymerization, the molecular weight and the chain length and are synthesized by a polyreaction (polymerization, polyaddition, polycondensation). On the other hand, this term also includes derivatives of such a group of macromolecules from polyreactions, i.e. , compounds obtained by reactions, for example, addition or substitution of functional groups on predetermined molecules and which may be chemically uniform or chemically heterogeneous. This term additionally also includes so-called prepolymers, i.e., reactive oligomeric precursors whose functional groups are involved in the structure of the macromolecules. Substance names that begin with "poly-" such as polyisocyanate, polyaldimine, polyamine, polyol, polymercaptans or polyglycidyl