NL8006611A - THICKENER. - Google Patents

Description

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Thickener.

The invention relates to thickeners and to organic liquids thickened with such agents. The thickeners according to the invention more particularly comprise a mixture of a finely divided silica and a finely divided fibrous polyolefin.

A wide variety of finely divided inorganic and organic materials have been used to increase the viscosity of organic liquids for use in various applications, such as paints, coatings, lubricating oils and molding mixtures. Synthetic amorphous silicas, such as silica aerogels and pyrogenic silicas, have been widely used, for example, for thickening liquids, such as paraffin oils and polyester, alkyd and epoxy resins, in the preparation of greases from oils, resinous gel coatings and other analogous applications.

Relatively large amounts of many silica and other conventional thickeners have been required to provide an increase in the viscosity of organic liquids required for thixotropic gel formation and certain other applications. The use of such amounts may adversely affect the properties of the thickened organic liquid desirable for use, while the thickener cost may become too high from an economic point of view.

Thus, there is a need for materials with an improved thickening efficiency to provide a greater viscosity increase when using the same amounts or smaller amounts than the known thickeners.

Silica thickeners with improved thickening efficiency are described in U.S. Pat. Nos. 3,293,205 and 3,354,114. The thickener of U.S. Pat. No. 3,293,205 may comprise a mixture of finely divided polyoxymethylene fibers and small sized materials such as finely divided polyethylene, oxidized polyethylene, silica aerogels, or other synthetic and natural silicas.

8006611 * ~ 2

The thickener of U.S. Pat. No. 3,354,114 is an intimately mixed particulate fiber mixture of finely divided polystyrene and silica fibers which is of the airgel type.

According to the invention it has now been found that a product comprising a mixture of finely divided silica and finely divided polyolefin fibers surprisingly exhibits superior efficacy in the thixotropic thickening of a wide variety of organic liquids as compared to the thickener. action of the silica component when used alone and does not exhibit the agglomeration which can occur when the polyolefin component is used alone. The fibers have a fibrillar structure and an extremely large specific surface area.

The particulate silica used in the present invention is generally a substantially dehydrated synthetic amorphous silica. The water content is generally from about 1 to about 15% by weight, as measured by weight loss after heating at 955 ° C for 1 hour. These synthetic amorphous silicas generally have specific surfaces of more than about 50 m per gram and usually 2 more than about 150 m per gram. The specific surfaces are determined according to the nitrogen absorption method described by Brunauer, Emmett and Teller, J.Am.Chem.Soc. 60, 309 (1933).

The method is performed to a P / P ^ of 0.967 so that pores with a diameter of 14 to 600 Pounds are measured.

The synthetic amorphous silicas generally have an aggregate weight median particle diameter of less than about 50 microns, and preferably less than about 10 microns. This aggregate silica particle diameter is the size to which the final silica particles having an average size of about 10 to about 50 millimicrons grow together through a combination of chemical reaction, physical attraction and mechanical interaction.

35 Silica aerogels, pyrogenic silicas and mixtures thereof are the synthetic amorphous silicas, which are largely the 8% 6 6 1 1%. * 3 colors for use in the thickeners according to the invention because the mixtures thereof with a finely divided fibrous polyolefin exhibit a very superior thickening action. These amorphous silicas comprise chemically analog polymerized silica-5 molecules and have some different and some analog physical properties. Because of this basic chemical analogy, the method of synthesis has been accepted in the silica art as the primary means of distinguishing the varying types of synthetic amorphous silicas.

Silica aerogels are the particularly preferred synthetic amorphous silicas for use in the thickener of the invention. A silica airgel is prepared by mixing sodium silicate and sulfuric acid to form an acidic silica hydrosol, solidifying the hydrosol to form a hydrogel, treating the hydrogel with ammonium hydroxide, washing the hydrogel substantially free of sodium. and ammonium compounds and the washed hydrogel dries in such a way that there is practically no shrinkage of the silica structure. According to a useful drying technique, use is made of a fluid energy mill, which simultaneously effects drying and adjustment of the silica airgel to the desired particle size range. Silica aerogels can also be prepared without an ammonium hydroxide treatment by using a drying step, wherein the hydrosol or washed hydrogel is heated in the presence of an organic solvent, such as ethyl acetate, to at least the critical temperature of the solvent and then the solvent is slowly removed from the system. The silica airgel products have relatively low specific surfaces and large pore volumes and average pore diameters.

Particularly preferred silica aerogels for use in the thickener of the invention have a weight median particle diameter of about 2 to about 10 microns, a specific surface area of about 2,300 to about 400 m per gram, a pore volume of at least - - about 1.2 cm per gram and an average pore diameter of 8006611 * * * 4 about 150 to about 250 1. The pore volume is determined by the same BET nitrogen absorption method as used for the determination of the specific surface. The average pore diameter 3 in Angstrom is calculated from the pore volume in cm per gram and the specific surface area in m per gram according to the equation. ,. . 4 x pore volume x 10 ^ - Average pore diameter «-r ·. · -. .-r-T— specific surface

The preferred pyrogenic silicas are sometimes also referred to as smoke silicas. Pyrogenic silicas are prepared by volatilization and recondensation of silica using high temperature arc or plasma blasting processes or by supplying vapors of a silicon compound, such as silicon tetrachloride, silicon tetrafluoride or silicon sulfide, to a hydrolyzing flame of high temperature.

The fibrous polyolefin used in the thickener of the invention may be a polymer of a wide variety of olefins and is generally a crystalline or partially crystalline high density polyolefin.

Fibrous polymers of lower aliphatic olefins containing about 2 to about 6 carbon atoms are generally used. Preferably, the polyolefin is selected from polyethylene, polypropylene and mixtures thereof. Fibrous polyethylene is particularly preferred. Other olefins that can be used include diolefins, such as butadiene and isoprene, and α-olefins, such as butene-1, pentene-1, dodecene-1, and 4-methylpentene-1. In addition to fibrous homopolymers of these olefins, fibrous copolymers and block copolymers formed by polymerization of olefin blends can be used.

Preferably, the fibrous polyolefin has a viscosity average molecular weight of greater than about 400,000 and more preferably greater than about 0.5 million darlon. These molecular weights correspond to a preferred intrinsic viscosity greater than about 4.0 dl / gram and an even more preferred intrinsic viscosity greater than about 5.0 dl / gram and a melt index of zero, as measured according to ASTM D-1238-62T. The preferred fibrous polyethylene softens 8006611 * h 5 at a temperature of about 120 to about 130 ° C and melts at a temperature of about 130 to about 135 ° C.

The fibers are composed at least in part of fibrils and thus have a fibrillary structure. Some of the fibers are composed of bundles of macrofibrils, which are generally greater than about 1 micron in diameter, and some of the macrofibrils have portions composed of microfibrils less than about 1 micron in diameter. Preferably, the polyolefin fibers 10 are highly fibrillated (i.e., branched) and have an extremely high specific surface area of greater than about 1 m per gram, and preferably greater than about 5 m per gram. The specific surface area of the fibers typically ranges from about 5 to about 15 m per gram. The specific surface area is measured using gas absorption techniques, such as the BET nitrogen method, which are performed on samples rinsed in isopropanol, dried in an oven at 45 ° C and dried in vacuo.

For example, suitable high surface area fibrous polyolefins can be prepared by direct conversion of an olefin monomer gas. In these processes, a monomeric olefin is polymerized at a relatively high reaction rate in a reaction medium in which the polyolefin to be formed is swellable or soluble to a significant measurable degree, in the presence of a coordination catalyst under high shear stress conditions. . Representative polymerization processes of this type are described in U.S. Pat. Nos. 3,891,610 and 3,849,387. The fibrous polyolefin can also be prepared by the method of U.S. Pat. No. 3,743,272, wherein a polyolefin is dispersed in a precipitant under shear stress conditions to form polyolefin fibers having a microfibrillary structure, high surface area. and a size and morphology analogous to that of natural cellulose fibers.

The fibers obtained by the polymerization tend to be interconnected or bundled together. The fibers can be refined or beaten to separate individual fibers from the bundles using conventional defibrillation or cutting techniques in a device, such as a disc refiner, a Claflin refiner, a Hollander percussion device, a Dyna- pulverizer and the like.

The fibrous polyolefin can be made fluffy by passing the fibers several times through a high speed material fan. The fluffing treatment per se does not effect drying of the fibers to any significant degree, but the fluffed fibers can be dried to a moisture content of less than about 2% by weight by varying hot air systems. The fluffed fiber-like polyolefin with a moisture content of about 45 to about 55% by weight is preferred in the preparation of the thickener of the invention because of its easy handling.

Generally, the finely divided polyolefin used in this invention has an average fiber length of less than about 900 microns and a diameter of less than about 10 microns. Average fiber length is the weight average, measured in a Bauer-McNett classifier according to the TAPPI Standard Test T-233 SU-64. The length to diameter ratio of the fibers is greater than about 1: 1, and this ratio is generally greater than about 5: 1.

Preferably, the size of the fibrous polyolefin is reduced for use in the thickener of the invention so that it has a predominant size of no greater than about SO microns and preferably less than about 10 microns. The smaller size of the preferred fibers ranges from less than about 5 to less than about 1 micron. The length to diameter ratio of the fiber aggregate particles is preferably greater than about 10: 1 and more preferably greater than about 50: 1. The fibrous polyolefin generally contains a major amount, for example, 8006611 X17 more than 90 wt%, fibers of lengths from about 5 to about 10 microns and diameters less than about 1 micron. Small amounts, for example less than about 10%, large fibers or agglomerates of the smaller fibers with large sizes of up to about 50 microns and small sizes of about 5 to about 10 microns can be observed on microscopic examination. The particulate silica used in the thickener of the invention generally has a weight median particle diameter of less than about 50 microns and preferably less than about 10 microns.

Any device suitable for comminuting the silica and fibrous polyolefin to the desired size can be used. The feed to the device can be a silica hydrogel or a silica airgel obtained by drying the hydrogel. The gel and polyolefin components are preferably broken, such as by cutting or shearing, into pieces about 1/8 inch in size or less in order to facilitate their supply to the device. The polyolefin fibers and the silica can be mixed in a conventional manner to form the thickeners of the invention. Preferably, the components are mixed before being incorporated into the organic liquid and mixing methods such as mixing or tumbling mixing are sufficient. Although less thickening results are obtained, the silica and poly-olefin components can be mixed in the liquid to be thickened if desired.

According to a preferred embodiment, the mixture of the thickener according to the invention is prepared by simultaneously decreasing the size of the silica and the polyolefin in the presence of the others by a crushing, grinding or rubbing treatment such that the particles are broken and fresh exposed surfaces are formed and an intimate mixture of the components is provided. Suitable devices for the simultaneous reduction of the size, whereby freshly formed surfaces are exposed, are for example ball mills, vibration mills, potting mills, hammer 8006611 3-v 8 mills, rotary crushers, pulverizers, "speedline" mills, sand grinders, colloid mills, micron mills and the like.

The preferred method of preparing the mixture 5 involves the simultaneous fluidization of the components.

In this method, the polyolefin and the silica are suspended in a moving gaseous medium, and further gas is continuously supplied in a plurality of high velocity streams directed inwardly into the mill, such that extremely strong turbulence and attrition and refraction of the suspended silica and polyolefin is accomplished. The comminuted fibrous polyolefin-silica mixture is continuously removed from the mill along with the gaseous medium and separated from the suspending gas. Air and steam are the preferred suspending gases, and they are also preferably used as the additionally supplied gas, which causes turbulence, because these gases are cheap and readily available.

When using the fluid energy mill using air as a gaseous grinding medium, the suitable pressures of the suspension air range from about 7 kg / cm to 2 about 35 kg / cm and preferably from about 7.7 to about 2 21 kg / cm. The additional air supplied, which causes the turbulence, can be injected into the swirling mass of polyolefin and silica at pressures, which can range from about 7 to about 35 kg / cm and are preferably between about 7.7 2 and about 17.5 kg / cm. The suspension air and the additional supplied air are at a sufficiently low temperature to prevent softening or melting of the polyolefin. Preferably, the air temperature is about 10-49 ° C. The average particle size of the product can be varied by controlling the air speed, the temperature and the feed rate. The product can be separated from the suspending air in any suitable manner, preferably using bag collectors, although cyclones and other types of separators can also be used.

8 00 6 6 1 1 9

The preferred fluid energy means is the micronizer, in which relatively large particles are suspended in a gaseous medium and vortexed around an enclosed base, while additional gases are supplied to the vortex, such that turbulence within this mass and crushing and refraction of the particles is accomplished.

Simultaneous grinding of the fibers and the silica simultaneously causes a reduction in the particle size of the silica, a defibrillation (opening or unwinding) of the fibers and the formation of an intimately mixed mixture.

In the intimately mixed mixture, the fibers and the silica particles are held together and cannot be separated using normal mechanical means, so that more than a mere electrostatic attraction or a mechanical combination is present. It is believed that grinding exposes active surfaces that effect the adhesion of the polyolefin and the silica. Varying methods can be used to obtain such an intimately mixed mixture, but the simultaneous fluid energy grinding is preferred.

The polyolefin must be present in the mixture in an amount sufficient to provide a significant increase in the thickening action of the silica. The blend generally contains about 95 to about 5 weight percent polyolefin and about 5 to about 95 percent silica. Preferably, the mixture contains about 25 to about 35 weight percent polyolefin and about 75 to about 65 weight percent silica.

A preferred application for the mixtures of the invention is as a thickening agent, ie forming thixotropic gels, and / or increasing the viscosity of organic liquids. The organic liquids which can be used in the products of the invention are, for example, organic solvents, liquid organic film-forming agents, liquid organic resins, oily liquids and mixture thereof. Such organic solvents can be solvents used in paints, varnishes or paint removers, and include aliphatic and aromatic alcohols, ketones and esters such as ethanol, acetone, methyl ethyl ketone, ethyl acetate or amyl acetate. The liquid organic film-forming agents generally comprise solutions of high molecular film-forming agents dissolved in organic. solvents, and are generally used as adhesives, films, films, paints, lacquers and dopes. Examples of such high molecular weight organic film-forming agents are nitrocellulose, cellulose acetate, chlorinated rubber polyvinyl acetate, polyvinyl chloride, polyacrylic acid esters, cellulose butyrate and cellulose propionate. When these liquid products are sprayed or spread on articles, the thickener according to the invention upon contact with the article will almost immediately effect the formation of a thixotropic gel and the gel will not drain or drip.

The liquid resin products that can be used with the thickener of silica and fibrous polyolefin include plastisol products, which include halogenated vinyl or vinylidene resins. The thickener of the invention is particularly useful for thickening thixotropic, polymerizable organic liquid resin products used in coating, filling, adhesion and lamination treatments. Such products contain liquid alkyd or epoxy resins or solutions of solid alkyd, epoxy or polyester resins dispersed in a solvent (eg styrene) usually copolymerizable with the polyester resin. The compositions of the invention are easily wetted and dispersed and effect a very strong increase in viscosity at generally lower concentrations in curable liquid resins, such as polyesters and polyepoxides, and resin latices, such as paints.

The oily liquids in which the thickener according to the invention can be used include oils of animal and vegetable origin, for example liver oil, olive oil, corn oil and lubricating oils, such as hydrocarbon engine oils and mixtures thereof. The lubricating oils can be thickened with the invention thickener of the invention to provide gel-like masses of a grease consistency.

The thickener of the invention can be incorporated into the organic liquid using any conventional dispersion method. Relatively low shear mixing methods, such as hand stirring, are often satisfactory, but high shear dispersion mixers, such as roll mills, high speed mixers or ultrasonic mixers, are preferably used for certain organic liquids,

The amount of the thickening product used in the liquid to be treated can vary greatly depending on the nature of the organic liquid, the dispersion method and the desired degree of thickening, and this amount is generally the smallest amount, which is sufficient is to increase the viscosity of the organic liquid in the desired manner. The amount of the thickener can generally range from about 0.05 to about 10 Z, but is usually about 1-5% by weight of the liquid to be thickened.

The invention is further illustrated but not limited by the following examples.

Example I

250 g of silica airgel and 200 g of cut polyethylene fiber with the properties shown in Table A were mixed and mixed at high speed for 1 minute.

This mixing treatment was repeated many times to obtain 15 pounds of the mixture.

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The product was a white, odorless, flocked powder and consisted of finely divided polyethylene fibers intimately mixed with finely divided silica. The microscopic examination of the powder showed that the fibers had a major size of less than 1 micron and a smaller size in a low millimicron range.

The mixed mixture, the mixed and ground mixture and a sample of the same silica airgel as such were used to thicken a liquid styrene unsaturated polyester resin. The resin contained about 45 parts by weight of styrene and about 55 parts by weight of the unsaturated polyester resin. The liquid resin product had a viscosity of 110 centipoises at 25 ° C as measured with a Brookfield viscometer using a No. 4 spindle at 20 rpm.

Varying weight concentrations of each of the thickeners were mixed with individual portions of the liquid resin for 5 minutes at 4000 rpm in an Epperibach homogenizer. The viscosity was then immediately measured in the same viscometer under the same conditions as the thickened resin. The viscosities of the different thickened samples were also determined at 20 rpm in the same apparatus at 25 ° C using a No. 4 spindle and the thixotropic index was calculated as the viscosity at 2 rpm divided by the viscosity at 20 revolutions per minute. The results obtained are shown in Table B below.

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It is clear from the results obtained that the use of the thickener according to the invention leads to a surprisingly higher increase in viscosity and thixotxopy when incorporated into organic liquids as compared to the incorporation of a silica airgel as such in such organic Liquids. The incorporation of the polyethylene fibers significantly reduces the amount of silica material needed to thicken the liquid.

A considerably higher viscosity and thixotropic index were obtained with the ground polyolefin-silica thickener compared to that of the purely mixed mixture. It was also found that the polyethylene fibers agglomerated and floated on the surface of the resin when used alone.

15 800 6 6 1 1

Claims (44)

A thickener comprising a mixture of about 5 to about 95 wt.% Finely divided silica and about 95 to about 5 wt.% Finely divided polyolefin fibers having a fibrillary structure. ________ Thickener according to claim 1, characterized in that the fibers have a specific surface area of more than about 1 m per gram. Thickener according to claim 1, characterized in that the fibers have a specific surface area of more than about 5 m per gram. __ Thickener according to claim 1, characterized in that the silica has a weight median particle diameter of less than about 50 microns. Thickener according to claim 1, characterized in that the silica has a weight median particle diameter of less than about 10 microns. Thickener according to claim 1, characterized in that the silica is selected from a silica airgel, a fumed silica and mixtures thereof. Thickener according to claim 1, characterized in that the silica is a silica airgel. Thickener according to claim 7, characterized in that the silica airgel has a weight median particle diameter of about 2 to about 10 microns, a specific surface area of about 300 to about 400 m per gram, a pore volume of at least about 1.2 cm per gram and has an average pore diameter of about 150 to about 250 X. Thickener according to claim 1, characterized in that it contains about 25 to about 35% by weight polyolefin fibers. Thickener according to claim 1, characterized in that the polyolefin is a high-density crystalline or partially crystalline polyolefin. Thickener according to claim 1, characterized in that the polyolefin is a polymer of a lower aliphatic 8006611 olefin having from about 2 to about 6 carbon atoms. Thickener according to claim 1, characterized in that the polyolefin is selected from polyethylene, polypropylene and mixtures thereof. Thickener according to claim 1, characterized in that the polyolefin is polyethylene. Thickener according to claim 1, characterized in that the fibers have a major size of less than about 50 microns and a major size of less than about 5 microns. Thickener according to claim 1, characterized in that the fibers have a major size of less than about 10 microns and a major size of less than about 1 micron. Thickener according to claim 1, characterized in that the polyolefin has a viscosity average molecular weight of greater than about 400,000. Thickener according to claim 1, characterized in that the polyolefin has a viscosity average molecular weight of greater than about 0.5 million. Thickener according to claim 1, characterized in that the fibers have a length to diameter ratio of greater than about 5: 1. 19. A thickener comprising an intimately mixed mixture of (a) about 75 to about 55 weight percent of a silica airgel with a weight median particle diameter of about 2 to about 10 microns and (b) about 25 to about 45% by weight of polyethylene fibers. 20. Thickener according to claim 19, characterized in that the fibers have a specific surface area of greater than about 1 m per gram, a predominant size of less than about 10 microns and an underweight size of less than about 1 micron. . 21. A product comprising a mixture of (a) an organic liquid and (b) a thickener, characterized in that the thickener comprises about 5 to about 95 wt% 8006611 finely divided silica and about 95 to about 5 wt. % finely divided polyolefin fibers with a fibrillary structure, the thickener being present in a small amount sufficient to increase the viscosity of the liquid. _______ A product according to claim 21, characterized in that the surface area fibers have greater than about 2 liters per gram. ____ A product according to claim 21, characterized in that the fibers have a specific surface area of greater than about 10 m per gram. The product according to claim 21, characterized in that the silica has a weight median particle diameter of less than about 50 microns. ___ ______ 25. A product according to claim 21, characterized in that the silica has a weight median particle diameter of less than about 10 microns. The product according to claim 21, characterized in that the silica is selected from a silica airgel, a fumed silica and mixtures thereof. The product according to claim 21, characterized in that the silica is a silica airgel. 28. The product of claim 27 wherein the silica airgel has a weight median particle diameter of about 2 to about 10 microns, a specific surface area of about 300 to about 400 m per gram, a pone. volume of at least about 1.2 cm per gram and an average pore diameter of about 150 to about 250 lb. 29. A product according to claim 21, characterized in that the thickener contains about 25 to about 35% by weight polyolefin fibers. The product according to claim 21, characterized in that the polyolefin is a crystalline or partially crystalline high-density polyolefin. 31. A product according to claim 21, characterized in that the polyolefin is a polymer of a lower aliphatic olefin having from about 2 to about 6 carbon atoms. 8 00 6 6 1 1 -> - k «> The product according to claim 21, characterized in that the polyolefin is selected from polyethylene, polypropylene and mixtures thereof. 33. A product according to claim 21, characterized in that the polyolefin is polyethylene. The product according to claim 21, characterized in that the fibers have a major size of less than about 50 microns and a major size of less than about 5 microns. The product according to claim 21, characterized in that the fibers have a major size of less than about 10 microns and a major size of less than about 1 micron. 36. The product of claim 21 wherein the polyolefin has a viscosity average molecular weight greater than about 400,000. The product according to claim 21, characterized in that the polyolefin has a viscosity average molecular weight of greater than about 0.5 million. The product according to claim 21, characterized in that the mixture is prepared by grinding the polyolefin and the silica together. 39. A product according to claim 21, characterized in that the thickener is present in an amount from about 0.05 to about 10%, based on the weight of the organic liquid. 40. A product according to claim 21, characterized in that the thickener is present in an amount from about 1 to about 5%, based on the weight of the organic liquid. A product according to claim 21, characterized in that the organic liquid comprises a polyester resin or a polyepoxide resin. 42. A product according to claim 21, characterized in that the organic liquid is a styrene-polyester resin. 43. Products and methods as described in the description and / or examples. 8 00 6 6 1 1 Η "τ * 44. Articles manufactured using the product according to claims 3-42. ^ \ 8 00 6 6 1 1 \