Use of hydrotalcite as filler in polymer compositions

Details Use of hydrotalcite as filler in polymer compositions Use of hydrotalcite as filler in polymer compositions

2003-02-12

2004-09-14

Thexton, Matthew A. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

Reexamination Certificate

active

06790895

ABSTRACT:

The present invention relates to the use as filler, in polymer compositions, of calcined hydrotalcite and/or hydrotalcite intercalated using at least one anionic surface-active agent.
It also relates to the polymer compositions thus obtained.
Finally, it also relates to finished articles based on these compositions, in particular tire covers.
It is known to employ reinforcing white fillers in polymers, in particular elastomers, such as, for example, precipitated silica. However, the results are not always those hoped for.
The aim of the invention is to provide another filler for polymer compositions which provides them with a highly satisfactory compromise with regard to properties, namely, preferably:
good rheological properties and excellent suitability for vulcanization, at least comparable with those of highly dispersible precipitated silicas,
particularly advantageous dynamic properties, in particular a Payne effect of relatively low amplitude, resulting in a rather low resistance to rolling for tires based on these compositions, and/or a rather high tangent &dgr; at 0° C., resulting in an improved adhesion for tires based on these compositions,
good strengthening in terms of modulus,
a generally high resistance to thermal aging and to UV (ultraviolet radiation) aging.
With this aim, a subject matter of the present invention is the use as filler, in particular as reinforcing filler, in a composition comprising polymer(s), of at least one calcined hydrotalcite and/or hydrotalcite intercalated by at least one anionic surface-active agent.
The hydrotalcite used in the context of the invention is thus at least one of the following compounds:
(a) a calcined hydrotalcite,
(b) a hydrotalcite which is calcined and then intercalated using at least one anionic surface-active agent (intercalated calcined hydrotalcite),
(c) a hydrotalcite intercalated using at least one anionic surface-active agent (intercalated hydrotalcite).
Use is advantageously made, in the context of the invention, rather of a calcined hydrotalcite (a), optionally additionally intercalated (b).
Even if the hydrotalcite used as filler according to the invention can comprise at least one monovalent cation, such as, for example, Li, and at least one trivalent cation, it usually contains rather at least one divalent cation and at least one trivalent cation; the divalent cation to trivalent cation molar ratio is then generally between 1 and 8, and preferably between 2 and 6.
The divalent cation can be in particular Mg, Ni, Zn or Co.
The trivalent cation can be, for example, Al, Ga, Fe or Cr.
Advantageously, the divalent cation is Mg and the trivalent cation is Al (magnesium aluminum hydrotalcite); the Mg/Al molar ratio is then generally between 1.5 and 5, preferably between 2 and 4, particularly between 2 and 3.
The starting hydrotalcite (that is to say, noncalcined and nonintercalated) can be prepared by any process known to a person skilled in the art. Thus, it can, for example, be obtained by neutralizing, by addition of a sodium carbonate solution, a vessel heel comprising the two types of cations mentioned above, in this instance at least one divalent cation (or monovalent cation) and at least one trivalent cation; the temperature of the reaction medium can be maintained between 50 and 95° C., in particular between 60 and 90° C., the pH being, for example, between 10 and 12.
The starting hydrotalcite can be obtained by simultaneously adding, to a vessel heel formed of water, a solution comprising acid salts of the two cations (or two solutions each comprising an acid salt of one of the two cations), a sodium carbonate solution and a sodium hydroxide solution (the latter serving in particular to adjust the pH, in particular to a value of between 10 and 12, for example to 11); the duration of the simultaneous addition can vary between 30 and 90 minutes, for example between 45 and 60 minutes; the temperature of the reaction medium can be maintained between 25 and 95° C.; in particular, the temperature during the simultaneous addition can be maintained between 25 and 35° C., for example at 30° C. approximately; on conclusion of this simultaneous addition, the temperature can be brought and maintained between 85 and 95° C., for example at approximately 90° C., in particular for 1 to 3 hours, for example for 2 hours.
The starting hydrotalcite can be a basic magnesium aluminum carbonate, for example of formula MgCO
3
.5Mg(OH)
2
.2Al(OH)
3
.yH
2
O (in which y≧0, for example y=4).
The hydrotalcite used in the context of the invention, in particular the calcined hydrotalcite (a), optionally intercalated (b), preferably has a BET specific surface of between 100 and 300 m
2
/g, generally between 120 and 220 m
2
/g, in particular between 130 and 200 m
2
/g; it is, for example, between 150 and 180 m
2
/g. The BET surface is determined according to the method of Brunauer-Emmet-Teller described in The Journal of the American Society, Vol. 60, page 309, February 1938 and corresponding to Standard NF T 45007 (November 1987)
It generally has a CTAB specific surface of between 100 and 300 m
2
/g, in particular between 120 and 210 m
2
/g, especially between 130 and 190 m
2
/g; it can be between 150 and 180 m
2
/g. The CTAB surface is the external surface determined according to Standard NF T 45007 (November 1987-5.12).
The calcined hydrotalcite employed preferably results from a calcination treatment of a hydrotalcite (referred to as “starting hydrotalcite”) at a temperature of at least 250° C., in particular of at least 300° C.; the calcination temperature is preferably between 300 and 600° C. and more preferably still between 300 and 550° C.; it is, for example, between 300 and 500° C., in particular between 350 and 500° C.
Said calcined hydrotalcite is advantageously decarbonated. In fact, the decarbonation is generally obtained by the calcination treatment itself.
The calcined hydrotalcite used generally exhibits a carbonate anion/trivalent cation molar ratio of less than 0.3 (decarbonated hydrotalcite), preferably of less than 0.25; this ratio can, for example, be at most 0.15.
It should be noted that at least one anionic surfactant can be intercalated in the structure of the calcined hydrotalcite before it is used (intercalated calcined hydrotalcite).
For this to be done, the calcined hydrotalcite can thus be mixed with a solution of at least one anionic surface-active agent, in particular at a temperature of between 50 and 90° C., for, for example, 1 to 4 hours; the suspension obtained can then be centrifuged and the centrifugation cake dried, in particular in an oven, at a temperature which can vary in particular between 40 and 60° C. Advantageously, recourse to rigorous conditions, in particular to flushing with nitrogen, during the intercalation procedure is not necessary.
The calcined hydrotalcite can be stored for a long time in a dry atmosphere without recarbonating, which facilitates the intercalating stage.
Even though this does not constitute a preferred alternative form, a hydrotalcite intercalated by at least one anionic surface-active agent can also be used in the context of the invention.
Such an intercalated hydrotalcite can be obtained in particular by simultaneously adding, to a vessel heel formed of water, a solution comprising acid salts of the two cations (or two solutions each comprising an acid salt of one of the two cations), a solution of anionic surface-active agent and a sodium hydroxide solution (the latter serving in particular to adjust the pH, in particular to a value of between 10 and 12, for example to 11); the duration of the simultaneous addition can vary between 30 and 90 minutes, for example between 45 and 60 minutes; the temperature of the reaction medium can be maintained between 25 and 95° C.; in particular, the temperature during the simultaneous addition can be maintained between 25 and 35° C., for example at 30° C. approximately; on conclusion of this simultaneous addition, the temperature can be brought and maintained between 85 and 95° C., for example at approximately 90°

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