Dispensable chemical composition with high amount of filler materials and low thixotropic index levels

Abstract

A dispensable chemical composition comprising a blend of siloxane polymeric components, with a low viscosity component in an amount greater than a high viscosity component, and suitable to integrate a high amount of filler materials while maintaining rheological features of thixotropic index and viscosity values at low and high shear rates proper for a dispensing paste.

Claims

1. A dispensable chemical composition comprising a blend of at least two siloxane components comprising a first siloxane component selected among siloxane having a molecular weight comprised between 35000 and 70000, and a second siloxane component selected among siloxane having a weight-average molecular weight comprised between 10000 and 30000; and at least a first filler material, wherein a weight ratio between said first siloxane component and said second siloxane component is comprised between 0.1 and 0.45 and said filler is present in an amount between 50 and 70% by weight with respect to a total weight of the composition, wherein the first siloxane component is selected from the group consisting of a dimethylsiloxane polymer, a diethylsiloxane-dimethylsiloxane copolymer, a vinylmethylsiloxane-dimethylsiloxane copolymer wherein the vinyl group is in a terminal position, a vinyl-terminated polydimethylsiloxane polymer, and wherein the second siloxane component is selected from the group consisting of a dimethylsiloxane polymer, a diethylsiloxane-dimethylsiloxane copolymer with diethylsiloxane unit content lower than 25%, and a vinyl-terminated diethylsiloxane-dimethylsiloxane copolymer.

2. The composition according to claim 1, wherein the first filler material is selected from the group consisting of alkaline earth metal oxides, lithium oxide, aluminosilicates, zeolites, metal organic framework, and organic acid.

3. The composition according to claim 1, wherein the weight ratio between the first siloxane component and the second siloxane component is comprised between 0.15 and 0.45.

4. The composition according to claim 1, wherein the blend has an average weight-average molecular weight comprised between 20000 and 40000 g/mol.

5. The composition according to claim 1, wherein the amount of the first filler is comprised between 55 and 65%.

6. The composition according to claim 1, wherein the first filler material has a shape factor, defined as the ratio between length and thickness, comprised between 1 and 5.

7. The composition according to claim 1, wherein the first filler material consists of powders and wherein a maximum of granulometric distribution is between 0.1 and 20 m.

8. The composition according to claim 1, wherein a second filler is added in an amount between 0 and 10% by weight, with respect to the total weight of the composition.

9. The composition according to claim 8, wherein the second filler material is selected from the group consisting of fumed silica, silica, graphene, graphene oxide, CNT, phyllosilicate, nanocrystalline cellulose, polymer fibers, and polymer particles.

Description

EXAMPLES

(1) Different samples are prepared mixing together single or blended dimethylsiloxane polymers with calcium oxide or LTA zeolites as first filler and graphene oxide as second filler.

(2) Sample compositions 1 to 4 are in accordance with the present invention and compared to sample 5, characterized by a different ratio between the two siloxane matrices, and sample 7 which was prepared according to EP 2550692.

(3) Viscosities for each sample have been measured for the blend of the polymeric components in the selected ratio at a shear rate of 5 s.sup.1 and compared to the final compositions containing the fillers. Viscosity (cP) at different shear rates (s1) has been measured by means of a rotational rheometer in flow curve test mode, with 20 mm cone/plate geometry and 0,052 mm gap.

(4) Test temperature is preserved by a Peltier cell and a thermostatic bath. Obtained values are the result of averaging over three analyses performed on fresh material amounts.

(5) Thixotropic indexes of both the blends and the compositions have been calculated as the ratio of viscosities measured at a shear rate of 5 s.sup.1 (low shear rate) to viscosity measured at a shear rate of 50 s.sup.1 (high shear rate).

(6) TABLE-US-00001 Sample 5 - Sample 6 - Sample 7 - Sample 1 Sample 2 Sample 3 Sample 4 comparative comparative comparative 1.sup.st siloxane matrix -dimethylvinyl terminated dimethylsiloxane polymer 1.sup.st siloxane MW 40000 [g/mol] 2.sup.nd siloxane matrix -vinyl terminated dimethylsiloxane polymer 2.sup.nd siloxane MW 27000 [g/mol] Ratio 1.sup.st matrix/2.sup.nd 0.21 0.33 0.21 0.43 0.67 0.50 matrix 1.sup.st filler CaO CaO CaO CaO CaO CaO CaO 1.sup.st filler content 60% 60% 60% 60% 60% 60% 60% 2.sup.nd filler no no 1% no no no no graphene oxide Viscosity at 5 s.sup.1 900 1100 900 1200 1400 1300 8600 [mPa] (blend matrix) Thixotropic index 1.1 1.2 1.1 1.2 1.3 1.2 2.2 (blend matrix) MW [g/mol] 29000 31500 29000 32500 34000 33000 40000 (blend matrix) Viscosity at 5 s.sup.1 70000 85000 113133 105000 131000 122500 930000 [mPa] (composition) Viscosity at 50 s.sup.1 35000 40476 45253 50000 54100 51000 232500 [mPa] (composition) Thixotropic index 2 2.1 2.5 2.1 2.4 2.4 4.0 (composition)

(7) The comparative examples 5 and 6 point out that, although the final molecular weight of the blend is similar to the values according to our invention (i.e. examples 2 and 4), a different ratio between the two siloxane matrices (higher than 0.45) brings to viscosity values not suitable for a dispensing paste.

(8) Moreover, sample 7 characterized by a single siloxane matrix according to EP 2550692, shows to have unsuitable rheological values, with both viscosities and thixotropic index values of the final composition outside from the typical range of a dispensing paste.