FR2740463A1 - ORGANOSILICIC PASTES AND FATS - Google Patents

Abstract

Organosilicone pastes and greases including at least one oily diorganopolysiloxane polymer with a dynamic viscosity at 25 DEG C of at least 500 mPa.s, and at least one alkali-metal or alkaline-earth metal carbonate, but no actual thixotropic agent, wherein said carbonate has a particle size of at most 0.5 mu m and a high BET specific surface area of more than 5 m<2>/g, and is present in an amount of at least 20 wt % based on the total composition. The preparation method is carried out at a low temperature, e.g. 5-40 DEG C.

Description

ORGANOSILICIC PASTES AND FATS
The present invention relates to organosilicon pastes or fats having in particular a flow threshold and resistance to degradation in a basic, acidic and saline medium, their method of preparation and their use in particular in the food sector (lubrication, tap grease, etc.). etc.).

Silicone greases are usually used for the lubrication of parts working under low stress, such as valves. Silicone pastes are generally used as filling pastes, in particular for protecting electrical circuits, or as shock absorbers.

In the field of crosslinkable silicone elastomer compositions, in particular cold, it has already been proposed to incorporate precipitated carbonate into the compositions. The objective here is to give the composition a consistency in the cartridge and at the time of its application, before curing, and to increase the mechanical properties of the elastomer.

Moreover, the patent application JP-A-52/146505 of December 6, 1977 proposed a lubricating grease composed of a lubricating oil of low viscosity (in the examples between approximately 110 and 220 mPa.s at 37.8- C ), which can be a mineral oil, a di-ester oil, a silicone oil or a mixture of oils of different kinds, a rust inhibitor and calcium carbonate. The composition can comprise up to 50% by weight of calcium carbonate, but preferably between 20 and 30%. This document, which relates to various kinds of fats differing in the nature of the oil, primarily relates to mineral oils.

No example relates to the application to silicone oils.

Even today, silicone pastes and greases are generally composed of a diorganopolysiloxane oil free from aliphatic unsaturations, of combustion silica and of a thixotroping system which can be for example a combination of boric acid and polyols, polyethers , in particular polyoxyalkylated glycols, or else an α, -dihydroxylated silicone oil of low molecular weight. Silicone pastes and greases are generally prepared by a hot process, consisting of mixing the various constituents for several hours at approximately 120-C.

Operation at high temperature is necessary to give the dough the right rheology and to avoid an unfavorable development of this rheology over time, but in certain cases one may experience difficulties in obtaining a well reproducible rheology. In addition, combined with the complexity of thixotroping systems, this also results in high production costs, linked in particular to the use of temperature.

DE-A-2,535,304 has proposed incorporating 30 to 70% by weight of natural carbonates in a silicone resin associated with a curing agent. The natural calcium carbonate is preferably hydrophobic and has a particle size of less than 10 µm.

JP-A-4/307058 proposes a hydrophobic liquid based on oil or on silicone gum to which natural calcium carbonate is added, the particle size of which is of the order of 45 pn.

However, these ground natural carbonates having a particle size greater than Hm do not confer a flow threshold on the compositions to which they are added.

The main objective of the present invention is to provide new silicone pastes and greases which can exhibit a high yield point and which is stable over time even at high temperature and which can be prepared by a cold process and under price conditions of low cost and significantly lower than the cost price of silicone pastes and greases of the prior art.

Another essential objective of the invention is to provide such pastes and fats exhibiting improved resistance in a basic and acidic environment and in a marine environment.

Another essential objective of the invention is to provide such pastes and fats which can be used without risk in the food industry.

Yet another objective of the invention is to provide such pastes and fats, the yield point of which can be adjusted in a simple and reproducible manner to a value at least equal to 20 Pa, this property being measured according to the indications given in the detailed description.

The present invention therefore relates to an organosilicon paste or fat comprising at least one oily diorganopolysiloxane polymer having a dynamic viscosity at 25 ° C. at least equal to 500 mPa.s and at least one alkali or alkaline earth metal carbonate, in absence of a thixotroping agent proper, that is to say of an agent of purely thixotroping nature of the prior art, the carbonate having a particle size (average particle diameter) less than or equal to 0.5 Hm and a high BET specific surface area greater than 5 m2 / g, and being present in an amount of at least 20%, preferably more than 30%, preferably 30 to 70%, by weight relative to the total composition, and more preferably from 35 to 45% by weight.

Indeed, the Applicant has found that, under the conditions of the invention, it was possible to replace the usual fillers and thixotroping agents with a single compound which is a carbonate as defined above, and the use of which allows the once an implementation at low temperature and to ensure the mechanical properties of the pastes and fats thus prepared and to give them a high flow threshold that is stable over time even at high temperature. In addition, some of the carbonates according to the invention are perfectly suitable for use in the food industry. Another advantage results in the fact that the paste or fat obtained exhibits improved creaminess.

By implementation at low temperature, is meant in accordance with the invention that the implementation can be carried out between 5 and 40 ° C., advantageously at room temperature (between 20 and 25 ° C. approximately).

The oily polymer will preferably have a dynamic viscosity of between 800 and 30,000 mPa.s and more preferably still between 900 and 15,000 mPa.s.

The carbonate according to the invention will preferably have an average particle diameter or particle size less than or equal to 0.1 μm, more preferably between 0.01 and 0.1 μm, and preferably a BET specific surface area ranging from 10 to 70. m2 / g, preferably from 15 to 30 m2 / g.

It will preferably be an alkaline earth metal carbonate, preferably calcium.

As commercial product which is well suited to the implementation of the invention, mention may be made of precipitated carbonates.

By carbonate according to the invention is meant a carbonate which, as is the case with carbonates used in industry, contain a certain amount of residual hydration moisture, which is generally of the order of 0.1 at 0.5%.

In the present application, the viscosity of the oils is a Newtonian dynamic viscosity at 25 ° C. measured using a BROOKFIELD viscometer according to the indications of the AFNOR NFT 76102 standard of May 1982.

The BET specific surface is determined according to the BRUNAUER, EMMET, TELLER method described in "The Journal of
American Chemical Society, Vol. 80, page 309 (1938) "corresponding to the AFNOR NFT 45007 standard of November 1987.

Particularly preferably, as is known per se to improve the dispersibility of carbonates in a hydrophobic medium, the carbonates according to the invention are treated in particular with carboxylic fatty acids such as, for example, stearic acid.

It has been observed that, advantageously, for a given particle size and specific surface area, the yield point sees its value increase with the level of carbonate, so that a person skilled in the art can easily adapt the composition to the intended applications and to the desired flow thresholds and obtain very high flow thresholds. It is also possible, for a given carbonate, to play on the viscosity of the oily polymer.

The oily diorganopolysiloxane polymers, which are the basic constituents of the pastes, generally correspond to the following formula R3Si (OSiR2) nOSiR3 in which the symbols R, identical or different, represent hydrocarbon radicals not possessing aliphatic unsaturations and having at most 10 carbon atoms and the symbol n represents any number defined so as to obtain the viscosities defined above.

Apart from the terminal units, these linear polymers thus consist essentially of a succession of units of formula R2Sio; however, the presence of a small amount of other units, such as those of formulas SiO2 and RSiolt5 is not excluded, in particular at a rate of at most 1% relative to the number of R2Sio units.

The hydrocarbon radicals represented by the symbols R are chosen from - alkyl radicals having from 1 to 8 carbon atoms such as methyl, ethyl, propyl, butyl, pentyl, hexyl and 2-ethylhexyl radicals.

- aromatic radicals with a single benzene nucleus having from 6 to 10 carbon atoms such as phenyl, tolyl, xylyl, ethylphenyl, cumenyl and butylphenyl radicals.

However, for each molecule of the polymers, preferably at least 45%, and more preferably at least 80%, of all the hydrocarbon radicals R are methyl radicals. Most of them are manufactured industrially by silicone manufacturers.

As an indication can be cited as polymers which can be used those represented by the following formulas (CH3) 3Sio [Si (CH3) 2O] nl Si (CH3) 3 (CH3) 3SiO [Si (CH3) 2O] n2 [Si (C6H5) ( CH3) 0] n3 Si (CH3) 3 (CH3) 3SiO [Si (CH3) 2O] n4 [Si (C6H5) 2O] n5 Si (CH3) 3 where nl to n5 will be chosen to have the viscosities defined above. More precisely, nl, n2 + n3 and n4 + n5 will be between 200 and 1000.

The present invention makes it possible to obtain pastes or fats having a yield point greater than 20 Pa and capable of reaching and exceeding values as high as 500 mPa.s, and this in a reproducible manner. It also makes it possible to fulfill the other objectives stated above.

The pastes and fats according to the invention can also incorporate other mineral fillers or other customary additives depending on the final application.

A subject of the invention is also a process for preparing these pastes and fats, in which they are used at low temperature, preferably between 5 and 40 ° C. According to an advantageous embodiment of the invention, the mixture is gradually added. silicone oil carbonate with stirring and / or mixed at room temperature, in particular for a few hours, then, optionally, degassed under vacuum.

More generally, a subject of the invention is also the use of the carbonate according to the invention for loading a silicone paste or grease, in particular for food use, and for giving it a flow threshold, the carbonate being present in the quantities indicated above.

For food use, it is necessary to use oils and carbonates approved for food contact according to the legislation in force. With regard to oils, they are in particular completely methylated.

The invention will now be described in more detail with the aid of non-limiting exemplary embodiments of the invention and highlighting other features and advantages of the invention.

The level of calcium carbonate was varied between 20% and 40% by weight in the dough. Different viscosities of polydimethylsiloxane oil with terminal trimethylsilyl units were tested: between 1000 and 10,000 mPa.s. All the tests were carried out without adding any thixotroping agent or combustion silica. Each time, a white, creamy paste is obtained, exhibiting a flow threshold, the value of which increases with the rate of carbonate precipitation.

In parallel, a test was carried out with a ground natural calcium carbonate with a BET specific surface area of approximately 2 m2 / g and an average particle diameter of 5 μm.

With 40% by weight of natural carbonate, this paste has no yield point.

EXAMPLE 1:
Preparation of precipitating carbonate pastes
In a hand mixer (Meili), 2190 g of a polydimethylsiloxane silicone oil with terminal trimethylsilyl groups, with a viscosity of 10,000 mPa.s at 25 c, are introduced gradually and g39 g of precipitated calcium carbonate (Calofort Se de Rhône Poulenc). Mixing at room temperature (22nu) for 2 hours until a homogeneous white paste is obtained. Degassed in vacuo (30 mm Hg, 3990 Pa) for 5 minutes. The white paste thus prepared contains 30% (by weight) of precipitated carbonate.

Pasta containing 20% and 40% of Calofort S.

A paste is also prepared under the same conditions (always with the same oil) by replacing the
Calofort S by ground natural carbonate BLR3 from OMYA (average diameter 5 Hm and BET surface 2 m2 / g). The paste contains 40% BLR3 carbonate.

Analysis of pasta properties
Flow threshold measurement
The measurements are carried out with a Carri-med CS 100 imposed stress rheometer (sold by the company Carri-med) at 25 C, with a cone / plane geometry, diameter of the cone 2 cm, angle 1., according to the manufacturer's specifications in "Operations manual for the Carri-med CSL range of rheometers using version 5.0 software".

From the measurements, the threshold is calculated according to the Casson model according to the specifications of Carri-med.

Flow threshold (CASSON) in Pa paste with 20% Calofort S 57 paste with 30% Calofort S 300 paste with 40% Calofort S 1000 paste with 40% BLR3 0.1
It is observed that the yield point increases with the rate of carbonate precipitation. On the other hand, BLR3 natural carbonate paste does not have a yield point.

Evolution of rheology with temperature
The change in the flow threshold of the doughs according to the invention was studied between -10-C and +60 "C: the rheology of the dough with 40% of Calofort S does not vary over the temperature range tested.

Stability of the pasta according to the invention at high temperature
In steps of 25 C per 24 hours, the dough is brought from 100-C to 200 C in a ventilated oven. Up to 150-C, there are no differences in properties (appearance, consistency). At 175 ° C, we notice a change in surface appearance, but no change in consistency. After 24 hours at 200 C, the evolution is identical to that observed at 175-C; on the other hand, after 100 hours at 200 ° C., there is a very significant hardening on the surface and a thickening of the core of the paste.

EXAMPLE 2
Preparation of a precipitating carbonate fat, with an oil as in Example 1 but with a viscosity of 1000 mPa.s
This silicone oil is introduced into a hand mixer (Meili) and precipitated calcium carbonate (Calofort SD from Rhône Poulenc) is gradually added. Mix for 3 hours until a homogeneous white paste is obtained. Degassed under vacuum (30 mm Hg) for 5 minutes. A fat containing 35% of
Calofort S.

This grease has a Casson flow threshold at 25 C of 160 Pa.

This new grease can be used for lubricating drinking water taps.

The precipitated carbonates used in accordance with the invention make it possible to achieve the various objectives set by the invention. It goes without saying that for the adjustment of the flow thresholds for various applications, those skilled in the art could if necessary carry out simple routine tests on the basis of the data and results presented in the examples.

Claims (19)

1. Organosilicon paste or fat comprising at least one oily diorganopolysiloxane polymer having a dynamic viscosity at 25 C at least equal to 500 mPa.s and at least one alkali or alkaline earth metal carbonate, in the absence of a thixotroping agent properly said carbonate having a particle size less than or equal to 0.5 μm and a high BET specific surface area greater than 5 m2 / g and being present in an amount of at least 20% by weight relative to the total composition. 2. Paste or fat according to claim 1, characterized in that the carbonate is present in an amount of more than 30% by weight relative to the total composition. 3. Paste or fat according to claim 1, characterized in that the carbonate is present between 30 and 70% by weight relative to the total composition. 4. Paste or fat according to claim 3, characterized in that the carbonate is present between 35 and 45% by weight relative to the total composition. 5. Paste or fat according to any one of claims 1 to 4, characterized in that the oily polymer has a dynamic viscosity of between 800 and 30,000 mPa.s. 6. Paste or fat according to claim 5, characterized in that the oily polymer has a dynamic viscosity of between 900 and 15,000 mPa.s. 7. Paste or fat according to any one of claims 1 to 6, characterized in that the carbonate has a particle size less than or equal to 0.1 µm. 8. Paste or fat according to claim 7, characterized in that the carbonate has a particle size between 0.01 and 0.1 µm. 9. Paste or fat according to any one of claims 1 to 8, characterized in that the carbonate has a BET specific surface area ranging from 10 to 70 m2 / g. 10. Paste or fat according to claim 9, characterized in that the carbonate has a specific surface. BET ranging from 15 to 30 m2 / g. 11. Paste or fat according to any one of claims 1 to 10, characterized in that the carbonate is an alkaline earth metal carbonate. 12. Paste or fat according to claim 11, characterized in that the alkaline earth metal carbonate is a calcium carbonate. 13. Paste or fat according to any one of claims 1 to 12, characterized in that the carbonate is a precipitated carbonate. 14. Paste or fat according to any one of claims 1 to 13, characterized in that it is a carbonate treated with stearic acid. 15. Paste or fat according to any one of claims 1 to 14, characterized in that the oily diorganopolysiloxane polymer corresponds to the general formula. R3Si (OSiR2) nOSiR3 in which the symbols R, identical or different, represent hydrocarbon radicals not possessing aliphatic unsaturations and having at most 10 carbon atoms and the symbol n represents any number defined so as to obtain a viscosity at least equal to at 500 mPa.s. 16. Paste or fat according to claim 15, characterized in that the symbols R all represent methyl groups. 17. Paste or fat according to any one of claims 1 to 16, characterized in that it has a flow threshold greater than 20 Pa. 18. A process for preparing an organosilicon paste or fat according to any one of claims 1 to 17, characterized in that the paste or fat is used at low temperature. 19. Preparation process according to claim 18, characterized in that the paste or fat is used between 5 and 40 C.