WO1997016480A1 - Organosilicone pastes and greases - Google Patents

Abstract

Organosilicone pastes and greases including at least one oily diorganopolysiloxane polymer with a dynamic viscosity at 25 °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 νm and a high BET specific surface area of more than 5 m2/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 °C.

Description

 ORGANOSILICON PASTES AND FATS

The present invention relates to organosilicon pastes or fats having in particular a flow threshold and a resistance to degradation in basic, acid and saline medium, to their preparation process and to their use in particular in the food sector (lubrication, grease tap, etc.).

Silicone greases are usually used for the lubrication of parts working under low stresses, such as valves. The silicone pastes also serve as filling pastes, in particular for protecting electrical circuits, or as a shock absorber.

In the field of silicone elastomer compositions which can be crosslinked, in particular cold, it has already been proposed to incorporate precipitation 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 hardening, and to increase the mechanical properties of the elastomer.

Furthermore, patent application JP-A-52/146405 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 natures, an antirust and calcium carbonate. The composition may contain up to 50% by weight of calcium carbonate, but preferably between 20 and 30%. This document, which targets different kinds of fats which differ in the nature of the oil, mainly targets 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 of aliphatic unsaturations, of combustion silica and of a thixotropic system which can be, for example, a combination of boric acid and polyols, polyethers, in particular polyoxyalkylated glycols, or also an α, ω-dihydroxylated silicone oil of low molecular weight. The silicone pastes and greases are generally prepared by a hot process, consisting in mixing the various constituents for several hours at approximately 120 ° C.

The implementation at high temperature is necessary to give the right rheology to the dough and to avoid an unfavorable development of this rheology over time, but in some cases it may be difficult to obtain a well reproducible rheology. In addition, combined with the complexity of thixotropic systems, it also results in high production costs, linked in particular to the use of temperature. Patent DE-A-2 535 304 proposed incorporating from 30 to 70% by weight of natural carbonates in a silicone resin associated with a curing agent. Natural calcium carbonate is preferably hydrophobic and of particle size less than 10 μm Patent JP-A-4/307058 proposes a hydrophobic liquid based on oil or silicone gum to which natural calcium carbonate is added, the particle size of which is around 45 μm

However, these ground natural carbonates having a particle size greater than μm do not confer a flow threshold to the compositions to which they are added The present invention has the essential objective of proposing new silicone pastes and greases which may have a high flow threshold and stable over time even at high temperature and which can be prepared by a cold process and under conditions of low cost price and clearly lower than the cost price of silicone pastes and greases of the prior art Another objective essential of the invention is to propose such pastes and fats having improved resistance in basic and acidic medium and in a marine environment. Another essential objective of the invention is to propose 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 whose flow threshold 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 carbonate of alkali or alkaline earth metal, in the absence of a thixotropic agent proper, that is to say of a purely thixotropic agent of the prior art, the carbonate having a particle size (mean particle diameter) less than or equal to 0.5 μm and a high BET specific surface area greater than 5 m ² / 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 thixotropic agents with a single compound which is a carbonate as defined above, and the use of which allows the Once implemented at low temperature and ensure the mechanical properties of the pasta and fat thus prepared and give them a high flow threshold and 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 sector. Another advantage results in the fact that the paste or fat obtained has an improved smoothness.

By implementation at low temperature, it is understood according to 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 ranging from 10 to 70 m ^ / g, preferably 15 to 30 m ² / 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 precipitation 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 moisture of hydration, which is generally of the order of 0.1 at 0.5%.

In the present application, the viscosity of the oils is a dynamic Newtonian viscosity at 25 ° C. measured using a BROOKFIELD viscometer according to the indications of standard AFNOR NFT 76102 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 standard AFNOR NFT 45007 of November 1987. In a particularly preferred manner, 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 found that, advantageously, for a given particle size and specific surface area, the flow threshold sees its value increase with the carbonate content, so that a person skilled in the art can easily adapt the composition to the intended applications and at the desired flow thresholds and obtain very high flow thresholds. One can also, for a given carbonate, play on the viscosity of the oily polymer. The oily diorganopolysiloxane polymers, which are the basic constituents of pasta, generally correspond to the following formula: R ₃ Si (OSiR2) _n OSiR ₃ in which the symbols R, identical or different, represent hydrocarbon radicals having no 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 end units, these linear polymers thus essentially consist of a succession of units of formula R2SiO, however, the presence of a small quantity of other units, such as those of formulas Siθ2 and RSiO _j 5, 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, pentyle, hexyl, 2-ethylhexyl radicals

- aromatic radicals with a single benzene ring having 6 to 10 carbon atoms such as phenyl, tolyl, xylyl, ethylphenyl, cumenyl, 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. They are for the most part manufactured industrially by the manufacturers of silicones

As an indication, there may be mentioned as usable polymers those represented by the following formulas (CH ₃ ) ₃ SiO [Si (CH3) ₂ O] _nl Si (CH ₃ ) ₃

(CH ₃ ) ₃ SiO [Si (CH ₃ ) ₂ O] _n2 [Si (C ₆ H ₅ ) (CH ₃ ) O] _n3 Si (CH ₃ ) ₃

(CH ₃ ) ₃ SiO [Si (CH ₃ ) ₂ O] _n4 [Si (C ₆ H ₅ ) 2θ] _{n 5} Si (CH ₃ ) ₃

where neither at n5 will be chosen to have the viscosities defined above More precisely, ni, n2 + n3 and n4 + n5 will be between 200 and 1000

The present invention makes it possible to obtain pasta or fat having a flow threshold greater than 20 Pa and capable of reaching and exceeding values as high as 500 Pa, and this in a reproducible manner It also makes it possible to fulfill the other stated objectives upper

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

The invention also relates to a process for the preparation of 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 carbonate is gradually added to the silicone oil with stirring and / or it is mixed at room temperature, in particular for a few hours, then, optionally, it is degassed under vacuum. More generally, the invention also relates to the use of carbonate according to the invention to charge a silicone paste or grease, in particular for food use, and to give it a flow threshold, the carbonate being present in the quantities indicated above. For food use, oils and carbonates approved for food contact must be used according to the legislation in force. As regards oils, they are in particular completely methylated.

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

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

In parallel, a test was carried out with a ground natural calcium carbonate with a BET specific surface of approximately 2 vcrlg and an average particle diameter of 5 μm. With 40% by weight of natural carbonate, this paste has no flow threshold.

EXAMPLE 1

Preparation of pasta with precipitation carbonate:

In an arm mixer (Meili), 2190 g of a polydimethylsiloxane silicone oil with terminal trimethylsilyl groups, of viscosity 10,000 mPa.s at 25 ° C. are introduced and gradually added 939 g of precipitation calcium carbonate (Calofort S ® by Rhône Poulenc; average diameter 0.07 μm and BET surface 23 m ^ / g). Mix at room temperature (22 ° C) for 2 hours until a homogeneous white paste is obtained. It is degassed under vacuum (30 mm Hg, 3990 Pa) for 5 minutes. The white paste thus prepared contains 30% (by weight) of precipitation carbonate. Pastes containing 20% and 40% Calofort S are prepared by the same process.

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

Analysis of pasta properties:

Flow threshold measurement:

The measurements are carried out using a Carri-med CS 100 constrained rheometer (sold by the company Carri-med) at 25 ° C, with a cone / plane geometry, diameter cone 2 cm, angle 1 °, according to the manufacturer's specifications in "Operations manual for the Carri-med CSL rande 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

dough with 20% Calofort S 57 dough with 30% Calofort S 300 dough with 40% Calofort S 1000 dough with 40% BLR3 0, 1

It can be seen that the flow threshold increases with the rate of precipitation carbonate. In contrast, BLR3 natural carbonate paste does not have a flow threshold.

Evolution of rheology with temperature:

The evolution of 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% 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, there is 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 heart of the dough.

EXAMPLE 2:

Preparation of a precipitation carbonate grease, with an oil as in Example 1 but with a viscosity of 1000 mPa.s:

In a hand mixer (Meili), this silicone oil is introduced and calcium precipitation carbonate (Calofort S® by Rhône Poulenc) is gradually added. The mixture is mixed for 3 hours until a homogeneous white paste is obtained. It is degassed under vacuum (30 mm of Hg) for 5 minutes. A fat containing 35% Calofort S is thus prepared. This grease has a Casson flow threshold at 25 ° C of 160 Pa.

This new grease can be used for the lubrication of drinking water taps.

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

Claims

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 the thixotropic agent proper , this carbonate having a particle size less than or equal to 0.5 μm and a high BET specific surface greater than 5 m ² / g and being present at a rate 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 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 A paste or fat according to any one of claims 1 to 8, characterized in that the carbonate has a BET specific surface ranging from 10 to 70 m ² / g 10 Paste or fat according to claim 9, characterized in that the carbonate has a BET specific surface ranging from 15 to 30 m ² / g 1 1 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 1 1, characterized in that the alkaline earth metal carbonate is a calcium carbonate. 13. A paste or fat according to any one of claims 1 to 12, characterized in that the carbonate is a precipitation 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: R ₃ Si (OSiR2) _n OSiR ₃ in which the symbols R, identical or different, represent hydrocarbon radicals having no 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 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 method of 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.