Thermally Conductive Polyurethane Adhesive with Exceptional Combination of Mechanical Properties

Abstract

The present invention relates to a thermally conductive adhesive composition having excellent mechanical properties and a method of manufacturing the same. Further, the present invention relates to method of manufacturing an article comprising the thermally conductive adhesive composition and articles obtainable by the described method.

Claims

1. A two component adhesive composition comprising a first component (A) and a separate second component (B), wherein component (A) comprises a-1) at least one polyol having a molecular weight M.sub.n of 700 to 12000 g/mol; a-2) chain extender having a molecular weight M.sub.n of 60 to 600 g/mol; a-3) at least one thermally conductive filler A1 exhibiting a thermal conductivity of no more than 50 W/mK, determined according to ISO 22007; and a-4) at least one thermally conductive filler A2 exhibiting a thermal conductivity of at least 80 W/mK, determined according to ISO 22007; and wherein component (B) comprises at least one NCO-terminated compound.

2. The adhesive composition according to claim 1, wherein the conductive filler A1 is selected from the group consisting of metal oxide, metal hydroxide, metal silicate, metal sulfide and combinations thereof.

3. The adhesive composition according to claim 1, wherein the conductive filler A2 is selected from the group of graphite, extended graphite, graphene, metal nitride, metal flake, metal oxide, carbon fiber, carbon nanotube and combinations thereof.

4. The adhesive composition according to claim 1, wherein the ratio by mass of components A and B is 10:1 to 1:5.

5. The adhesive composition according to claim 1, wherein the polyol is a polyether polyol.

6. The adhesive composition according to claim 1, wherein the polyol is a polyether polyol comprising a mixture of primary and secondary hydroxyl groups.

7. The adhesive composition according to claim 1, wherein the chain extender is a diol selected from the group consisting of 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-prentanediol, 1,6-hexanediol, 1,9-nonanediol, ethylene glycol, polyethylene glycol, neopentyl glycol, polybutylene glycol, cyclohexane-1,2-diol, cyclohexane-1,4-diol, 1,4-bis(hydroxymethyl)cyclohexane and mixtures thereof.

8. The adhesive composition according to claim 1, wherein component B comprises a mixture of aromatic (poly)isocyanates and/or aromatic (poly)isocyanate prepolymers.

9. The adhesive composition according to claim 1, wherein component B comprises an aliphatic or aromatic NCO-terminated compound.

10. The adhesive composition according to claim 1, wherein the filler A1 is present in an amount of 30 to 80 wt.-%, based in the total weight of component A.

11. The adhesive composition according to claim 1, wherein the filler A2 is present in an amount of at 0.5 wt.-%, 1 to 15 wt.-%, based on the total weight of component A.

12. Cured reaction products of the adhesive composition of claim 1.

13. Cured reaction products of the adhesive composition of claim 1, wherein the cured products exhibit a thermal conductivity of at least 1 W/mK, 1 to 3 W/mK, determined according to ISO 22007.

14. A method of manufacturing an article comprising at least two bonded substrates, the method comprising: providing first and second substrates, each substrate having a respective surface to be bonded; providing the component A and the component B of claim 1; mixing components A and B together to obtain a mixed adhesive composition; applying the mixed adhesive composition onto the first substrate surface to be bonded; and bringing the second substrate surface to be bonded into contact with the applied adhesive on the first substrate to be bonded.

15. An article comprising the bonded first and second substrates of claim 14.

16. An article selected from a pipe, cooling coil; electronic component, light emitting device, computer device, mobile phone, tablet, touch screen, automobile, Wi-Fi system, audio system; joint between heat pipes and water tanks in a solar heating system; fuel cell, wind turbine; computer chip; light device; battery; housings; cooler; heat exchanging device; wire; cable; heating wire; household appliance; air conditioner; accumulator; transformer; laser; functional clothing; car seat; medical device; fire protection; electric motor, plane and train; comprising the two component adhesive composition of claim 1.

Description

EXAMPLE 1

[0074] The following adhesive composition was prepared:

TABLE-US-00001 Component A Wt.-% Polyol (4000 g/mol) 23.9 3-Methyl-1,5-pentanediol 3.8 Graphite 2.0 Boron nitride 5.0 Aluminum oxide 60.3 Additives 5.0

[0075] Modified isocyanate based in 4,4-MDI was used as component B.

[0076] The composition showed a viscosity of 232 Pas, determined at 20 C. with Brookfield RVDV-II+P, spindle RV T-F, 10 rpm

The following properties were determined for the cured composition, determined at 23 C., respectively:

TABLE-US-00002 Tensile modulus E.sub.t [MPa] 51 Tensile strength max. .sub.m [MPa] 8.2 Tensile elongation mach. b [%] 68 Thermal conductivity [W/mK].sup.1 1.71 .sup.1determined via Hot Disc Method

[0077] The cured composition showed a volume resistivity of 1.4*10.sup.10 m, determined according to DIN EN 62631-3-1 at a temperature of 21.4 C. and a relative humidity of 46%.

[0078] Compositions comprising only one filler showed a decreased thermal conductivity, as apparent from the comparative examples shown below.

[0079] A composition according to Example 1 was prepared wherein graphite and boron nitride were omitted. The comparative composition contained 60.3 wt.-% of aluminum oxide as the filler in component A. The thermal conductivity of the composition after curing was determined to be 0.82 W/mK. Even increasing the amount of aluminum oxide to 67.3 wt.-% in component A only resulted in a slight increase in the thermal conductivity (0.97 W/mK).

[0080] Omitting the chain extender resulted in a composition which was not curable.

[0081] Comparative Examples wherein the filler A2 was omitted or substituted with the corresponding amount of filler A1 showed a remarkedly reduced thermal conductivity of the cured material. The thermal conductivity did not exceed 0.8 W/mK and 1.0 W/mK, respectively, compared to 1.7 W/mK of a corresponding inventive composition.

[0082] The same results were obtained when both fillers A1 and A2 were substituted by the corresponding amount of commonly used fillers such as CaCO.sub.3 or MgCO.sub.3. The thermal conductivity of the cured material in these cases was found to be only around 0.8 W/mK.

[0083] As can be seen, the present invention solves the assigned task as a good thermal conductivity can be achieved in combination with excellent mechanical properties.