Thermosetting epoxy resin composition having low curing temperature and good storage stability

Patent metadata

Field	Value
Publication number	US-11891507-B2
Application number	US-201917287067-A
Country	US
Kind code	B2
Filing date	Dec 23, 2019
Priority date	Jan 3, 2019
Publication date	Feb 6, 2024
Grant date	Feb 6, 2024

Abstract

A thermosetting epoxy resin composition including, as curing agent, a dihydrazide selected from the group consisting of glutaric dihydrazide, adipic dihydrazide and pimelic dihydrazide, in combination with a specific urea accelerator, which features good storage stability and a low curing temperature. The epoxy resin composition is especially suitable for use as bodywork adhesive.

First claim

The invention claimed is:

1. A thermosetting epoxy resin composition comprising
a) at least one epoxy resin A having an average of more than one epoxy group per molecule;
b) at least one curing agent B for epoxy resins, where the curing agent B is a dihydrazide selected from the group consisting of glutaric dihydrazide, adipic dihydrazide and pimelic dihydrazide; and
c) at least one accelerator C of the formula (Ia) or (Ib)

where R 1 is H or an n-valent aliphatic, cycloaliphatic or araliphatic radical;
R 2 and R 3 are
either
each independently an alkyl group or aralkyl group;

or
together are a divalent aliphatic radical which has 3 to 20 carbon atoms and is part of an optionally substituted heterocyclic ring having 5 to 8 ring atoms;

R 1′ is an n′-valent aliphatic, cycloaliphatic or araliphatic radical;
R 2′ is an alkyl group or aralkyl group or alkylene group;
R 3′ is independently H or an alkyl group or aralkyl group; and
n and n′ each have a value of 1 to 4,
wherein when R 1 is not H, R 1 does not include an aromatic group bonded directly to a nitrogen atom of Formula (Ia),
wherein a ratio of a proportion of epoxy groups of the epoxy resin A in a mol/a proportion of dihydrazide in mol is 3-5,
wherein a ratio of a proportion of accelerator C in grams per mole of epoxy groups of the epoxy resin A is 0.08-0.15 g/mol of epoxy groups, and
wherein the epoxy resin composition has a viscosity at 25° C. of 500 to 3000 Pa*s.

2. The thermosetting epoxy resin composition as claimed in claim 1 , wherein R 1 is H, and R 2 and R 3 are each a methyl, ethyl or propyl group, and n=1.

3. The thermosetting epoxy resin composition as claimed in claim 1 , wherein R 1 is

and R 2 and R 3 are each a methyl, ethyl or propyl group, and n=2.

4. The thermosetting epoxy resin composition as claimed in claim 1 , wherein the dihydrazide has a median particle size D 50 of ≤100 μm.

5. The thermosetting epoxy resin composition as claimed in claim 1 , wherein the thermosetting epoxy resin composition includes less than 0.5% by weight, based on the total weight of the epoxy resin composition, of dicyandiamide.

6. The thermosetting epoxy resin composition as claimed in claim 1 , wherein the thermosetting epoxy resin composition additionally includes 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.

7. The thermosetting epoxy resin composition as claimed in claim 1 , wherein the proportion of the epoxy resin A is 10-60% by weight, based on the total weight of the epoxy resin composition.

8. The thermosetting epoxy resin composition as claimed in claim 1 , wherein the thermosetting epoxy resin composition is a one-component thermosetting adhesive.

9. A process for the adhesive bonding of heat-stable substrates, comprising the stages of:
i) applying a thermosetting epoxy resin composition as claimed in claim 1 to the surface of a heat-stable substrate S1;
ii) contacting the thermosetting epoxy resin composition applied with the surface of a further heat-stable substrate S2;
iii) heating the composition to a temperature of 100-220° C.;
in which the substrate S2 consists of the same material as or a different material from the substrate S1.

10. The process as claimed in claim 9 , wherein, in step iii) of heating the composition to a temperature of 100-220° C., the composition is left at the aforementioned temperature for 10 min-6 h.

11. An adhesive-bonded article obtained from a process as claimed in claim 9 .

12. The thermosetting epoxy resin composition as claimed in claim 1 , wherein the epoxy resin A is of formula (II):

wherein R′ and R″ are independently either H or CH 3 and s has a value of >1.5.

13. The thermosetting epoxy resin composition as claimed in claim 12 , wherein s has a value of 2 to 12.

14. The thermosetting epoxy resin composition as claimed in claim 1 , wherein a viscosity of the thermosetting epoxy resin composition measured at 25° C., after storage for 1 week at 60° C. starting after production, rises by less than 500%.

Assignees

• Sika Tech Ag

Inventors

• Munzinger Noah
• Gallo Dominique

Classifications

• C08L63/04 Primary

  Epoxynovolacs · CPC title

• C08F136/06

  Butadiene · CPC title

• C08G18/755

  and at least one isocyanate or isothiocyanate group linked to a secondary carbon atom of the cycloaliphatic ring, e.g. isophorone diisocyanate · CPC title

• C08G59/245

  aromatic · CPC title

• C08G59/4021

  Ureas; Thioureas; Guanidines; Dicyandiamides · CPC title