MINERAL FLAKY FILLER FOR COMPOSITES

Abstract: A mineral flaky filler for composites, produced by melting a starting mineral, shaping hard flaky vitreous particles from the melt, and subjecting such particles to thermochemical treatment in an oxidizing atmosphere until a crystal phase is developed. With an object of obtaining such a crystallinity-reactivity balance that would provide for quality consistant protective and ornamental coatings on large-size articles and structures preferably for use in the tropical climate and of producing a filler that would be commercially available at the step of the thermochemical treatment the flaky particles were treated at a temperature range of 680 to 850 DEG C until at least 12 % by weight of the crystal phase and at least 7x10<19>spin/cm<3> of reactive paramagnetic centers were developed, and followed by air cooling.

Description: MINERAL FLAKY FILLER FOR COMPOSITES Technical Field This invention relates to dispersible flaky materials of uncertain chemical composition, which can be prepared from the minerals containing lower oxides of iron (preferably basalt,- wind-blown sands, etc. ) by melting the minerals, breaking-up the melt to produce vitreous hard flakes followed by a chemical modification and incomplete crystallization of the flaky material by thermochemical treatment in an oxidizing atmosphere. It is well established that such flakes can be used as reactive fillers for various composites (preferably polymerizable composites) in preparing protective and both protective and ornamental coatings featuring high weather- and water resistance (in protecting metal tanks, bridges, offshore drilling platforms, etc. ) and/or abrasion resistance (e.g. sludge lines). Background Art As the description of the technical field suggests, the fillers of the type described are in great demand. Accordingly, such fillers must satisfy a number of requirements that are getting more exact and are not easily combinable. These fillers are desirable to be: as reactive as possible, the property being determined from at least the surface area and preferably by the presence of the active centers over the surface of such flakes. The active centers constitute a contributory factor in polymerization of oligomeric binders and in establishing chemical interconnection between macro- molecules and inorganic components; as mechanically strong as possible thus providing an appreciable reinforcement in prepared composites even with low concentrations of the flaky fillers; as chemically stable as possible (specifically corrosion resistant) to ease up storage and the use of the flakes in preparing many types of composites which usually contain corrosive ingredients while in a green - 2 - state; commercially available to a variety of customers as a result of large-scale production and low cost. These requirements taken separately are not too difficult to meet. US Patent No. 4,363,889 for one discloses a commercially available and somewhat reactive filler for polymerizable composites, prepared as glass flakes of a thickness ranging from 0.5 to 5.0 urn and from 100 to 400 urn in diameter or as a mixture of 10 to 70 parts by weight of such flakes and from 10 to 150 parts by weight of flaky metallic pigments. Glass flakes are extremely breakable and feature low surface reactivity unless subjected to an additional treatment (e.g. vacuum metallization), while metallic flakes of highly developed surface area are not corrosion stable. Also known in the art are flaky fillers such as micaceous iron oxide pigments (E. Carter, "Micaceous iron oxide pigments in high- performance coatings", Po lymer Paint Co lour Journal, 1986, vol.176, No.4164, pp.226, 228, 230, 232, 234). Compared to glass flakes, they are more durable and chemically stable. However, such fillers are costly, that is why their use is advisable in applying protective coatings only to such articles and structures where the costs of failure are substantially higher than those of protecting arrangements. It is, therefore, believed that one of the most preferable ways of providing flaky fillers intended mainly for use in polymer composites is to use flakes produced from natural minerals. And the present inventor has been involved as a joint originator in developing a technological package including: a process for the production of finely-dispersed flakes (USSR Pat. No. 1,831,856), an apparatus for producing finely-dispersed flakes - 3 - (USSR Pat. No. 1,823,293), a method of heat treatment of finely-dispersed flakes and an apparatus ' for carrying out the method (RU Pat. No. 2,036,748). USSR Pat. No. 1,831,856 discloses a mineral flaky filler produced by melting basalt and dispersing the melt to produce ellipsoidal flakes. Microscopically analyzed for their shape and dimensions, the flakes are characterized, in terms of the ratio between the minor and the major axes of an ellipse, by a distorsion from the circular shape within 0.80 and 0.95. Such flakes remain in the vitreous state and are chemically unstable specifically due to the presence of lower oxides of iron inherent in basalt (and wind-blown sands) used as a raw material. These flakes have low chemical activity as well. USSR Pat. No. 1,823,293 teaches the manufacture of a mineral flaky filler by ' substantially the same process and this filler compared with the above-described one is more acceptable as regards its particle size, namely, it contains up to 99% of flakes of substantially identical form and size. However, these flakes again remain in the vitreous state and are chemically unstable, and have low chemical activity. These disadvantages are noticeably eliminated in the mineral flaky filler bearing closely on the invention and disclosed in RU Pat. No. 2,036,748. This filler is produced by melting a starting mineral (basalt), shaping hard vitreous flaky particles from the melt and by subjecting such particles to thermo ¬ chemical treatment in an oxidizing atmosphere until a substantially crystal structure is developed. The thermochemical treatment includes heating vitreous particles at the rate of 40 to 190°C/min to a temperature of 600 to 950°C ' nd simultaneously air blowing for 5 to 30 min followed by induced cooling at the rate of at least 950°C/min. The mineral flaky filler treated as above contains substantially no FeO and exhibits high (at least - 4 - 3 g/cm 3 ) density which is higher than that of vitreous particles by the factor 1.5, higher percentage (up to 53% by weight) of a crystal phase (hereinafter "crystallinity") and noticeable amounts of chemically active paramagnetic centers (hereinafter PMC). These advantages have provided for an appreciable improvement in the properties of polymerizable composites reinforced with the described mineral flakes and of protective and ornamental coatings produced therefrom (Vesselovsky R.A. , V. V. Yefanova, I. P. Petukhov, "Study of physical, chemical, thermodynamic and mechanical properties of interface layers in cross-linked polymers", Mechanics of Composites, 1994, vol.30, No.5, pp.3-11; in Russian - BecejioBCKHii P. A., EφaHOBa B.B. , πeτyxoB 14. π. MccieflOBaHHe φH3Hκo-XHMHHecκHX, TepMOflHHaMHHecKHX H Mexa- HMπecKHx CBOHCTB rpaHHHHbix cjioeB ceτπaτbix πojiMepoB//Me- xaHHKa κoMπo3HTHbix MaTepπajoB, 1994, τ.30, N°5, c.3-11). Subsequently, it was however found that this filler has no more than 6xl0 19 spin/cm 3 of PMC that are active in the process of polymerizing mono- and oligomers (V.V. Yefanova, "Study of the properties of a new activated basalt filler for coating applications", Ecotechnology and Saving of Resources, 1993, No.5, pp.67-72; in Russian- EφaHOBa B. B. MccjieflOBaHHe CBOHCTB HOBOΓO aκτHB-- poBaHHoro 6a3ajibτoBoro HaπojHHTejiH nm πoκpbiτn-ι//3κoτex- HOJIOΠIH H pecypcocόepejκeffl-e, 1993, N°5, c.67-72). To put it otherwise, the cristallinity mentioned above and chemical activity of the prior art filler are not in balance. Moreower, the present inventor's unpublished experimental findings ' have proved that the quest for higher cristallinity of the mineral flaky filler is not justified on account of process efficiency as well. For example, the flakes subjected to thermochemical treatment for 30 minutes at temperatures close to the smallest value of the indicated temperature range, i.e. slightly higher than 600°C, show neither detectable cristallinity nor a detectable increase in chemical activity, while an - 5 - increase in the treatment time over 30 min results in a decrease in the product output. A change-over to a relatively short-run (about 5 to 10 min) thermochemical treatment at about 900° C or still higher has been surprisingly found open to uncontrolled revitrification and a decrease in the chemical activity of the particles to be more readily percieved the higher are both the temperature of heating the particles and the rate of cooling the heat-treated particles. And finally, the rate of heating vitrified particles, prior to exposure thereof to a gaseous oxidant such as air, has appeared to virtually have no effect on the progress and result of the treatment. Consequently, use of additional process instrumentation will unjustifiably increase the cost of the end product. Disclosure of Invention Therefore, the technical problem underlying the present invention is to provide a mineral flaky filler for composites wherein, by way of improving operating conditions of the thermochemical treatment of the vitreous particles and subsequent cooling thereof, cristallinity and chemical activity would be significantly closer to balance, compared with the prior-art fillers, could be commercially available and, as used in polymerizable composites, would provide for more durable protective and ornamental or abrasion- resistant coatings. To this end the invention consists in a mineral flaky filler for composites, produced by melting a starting mineral, shaping hard flaky vitreous particles from the melt, and subjecting such particles to thermochemical treatment in an oxidizing atmosphere until a crystal phase is developed, according to the invention at the step of the thermochemical treatment the flaky particles were treated at a temperature range of 680 to 850° C until at least 12% by weight of the crystal phase and at least 7xl0 19 spin/cm 3 of reactive PMC are developed, and followed by air cooling. - 6 - The filler thus produced is mechanically strong due to an adequate degree of crystallization and, owing to the congruity of the crystallinity with the chemical activity, it can be used as a highly effective means of upgrading the quality of mainly thick (>1, and typically >3 mm) protective, ornamental, and abrasion-resistant coatings by the use of preferably such binders that are produced under polymerization of mono- and/or oligomers. It should be mentioned here that production costs were reduced due to a reduction in an investment in the heating, cooling, and control equipment as well as in the costs of power for the- thermochemical treatment and for preparing and feeding the coolant. The end product is therefore commercially more readily available. The mineral flaky filler of the invention is further characterized by containing at least 30% of particles having a mean size of about 100 urn across to the total amount of the particles and at least 14xl0 19 spin/cm 3 of the PMC to thereby enable such filler to be preferred for use with polymerizable composites. Best Mode for Carrying out the Invention The invention is further explained by way of general description and specific data of the experimentation on the method of producing a mineral flaky filler for polymerizable composites, including the values of physical and chemical properties obtained, examples of how the filler is used in polymerizable composites for application as protective coatings, and results of comparative tests on the composites for applying such coatings. Generally, the method of producing the mineral flaky filler of the invention comprises the steps of: (1) obtaining hard vitreous particles (usually as flakes) by: crushing selected mineral to sizes suitable for charging a melting furnace, heating the charge to obtain a thin melt (specifically, to a temperature of 1400-1500° C for basalt - 7 - and above 1500°C for wind-blown sands), breaking up a stream of the melt flowing through a heated die into vitreous particles as by a whirler and/or an airstream); 05 (2) thermochemical treatment of the vitreous particles from step (1) in an oxidizing atmosphere (preferably in air) at temperatures from 680 to 850° C (preferably 680-780°C) until an incomplete crystallization, i.e. at least 12% by weight of the 10 crystal phase, and at least 7xl0 19 spin/cm 3 of reactive PMC are developed, and followed by air cooling; and, optionally, (3) mechanical treatment of the particles, e.g. fragmentation and separation according to size, until a 15 mineral flaky filler containing at least 30% of particles having a mean size of about 100 urn across to the total amount of the particles and at least 14xl0 19 spin/cm 3 of reactive PMC are obtained. In the production of hard vitreous flakes, use was 20 made of basalt containing about 10% FeO from the Kostopol deposits (Ukraine). The crushed stone of 5 to 40 mm in size was melted in a modified melting furnace similar to a quartz-glass furnace, in which heat is supplied by gas burners. The melt was heated to a temperature of 251400-1450° C to be extruded through a heated die of heat-resistant steel in a stream of 8 to 10 mm in diameter. The stream of the melt was broken up in a stream of cooling air by a whirler generally heated to about 1300°C. 30 The flakes obtained were colored gray, about 3 um thick and from 25 um to predominantly 3 mm in size across. The flakes were carefully (to avoid breaking up or compacting) poured over underpans of heat-resistant steel in loose layers from 80 to 100 mm thick, placed into 35 a muffle furnace, and subjected to thermochemical treatment in air at successive temperatures of 660, 680, 750, 850, and 875°C for 90, 60, 30, 20, and 15 minutes, respectively, and then removed from the furnace and cooled to room temperature in air. Samples of the flakes treated at above temperatures were analysed for crystallinity and the PMC by conventional methods. Crystallinity X was defined by the formula dtp-d X = vp #1 dcp- dv κ b where d is the density of the particles after treatment, v is the density of the vitreous particles, d is the density of the crystal phase, vb is the density of the vitreous body of the particles, substituting density values defined in xylene into the formula (G.A.Rashin, N.A.Polkovoi "Certain physico- technical properties of stoneware defined", Glass and Ceramics", No.10, 1963, pp.11-14 - in Russian: PaiMH r.A. , ΠOJIKOBOH H.A. "Oπpe^eieHHe Heκoτopbix ΦH3HKO-TΘXHH- πecKHX CBOHCTB KaMeHHoro JiHTbfl" B aypHaie "Cτeκjιo H Kepa- MHKa", 1963, N°10, c.11-14). The PMC were counted from electron paramagnetic resonance (EPR) spectra in a mineral filler and diphenyl- picrylhydrazine, the latter being a reference substance ("Electron Paramagnetic Resonance" An abridged Chemical Encyc lopedia, V, Moscow: Soviet Encyclopedia, pp.961-968 - in Russian: cτaτb5. "3jιeκτpoHHbiH πapaMaπMTHHH pe30HaHc" B "Kpaτκo-1 XMMHHecKO-i θHiiHKJioπeΛHH", τ.5, M: I43Λ-BO "Co- Beτcκai 3HUHKJioπeflH5.", c.961-968). The EPR-spectra were obtained from the model E/x-2547 radio spectrometer commercially available from RADIOPAN (Poland). The analysis findings are summarized in Table 1. Table 1 CRYSTALLINITY AND PARAMAGNETIC CENTERS VS. TREATMENT TEMPERATURE 1 Treatment temperatures,—C Indicators* 1 660 680 750 850 875 Crvstallinity,% bv wt. 1 5.8 14.8 35.2 52.3 49.8 PMC, lO 1 l^9 spin/cm^ I 5.8 16 18 19 17 - 9 - "Note: the respective indicators would constitute 0.0% and <2.0*10 19 spin/cm 3 for vitreous particles prior to the thermochemical treatment and 51.5% and about 6.0*10 9 spin/cm 3 for prior-art particles after thermochemical treatment at 900°C, when essentially all FeO has changed to Fe 0 . As will be seen from Table 1, thermochemical treatment of the vitreous particles at temperatures below 680°C is not practicable since both crystallinity and PMC increase but significantly, nor it is practicable at temperatures above 850° C because crystallinity and PMC begin, though insignificantly, to be adversely affected. Following thermochemical treatment, the mineral flaky filler was crushed and separated according to the particle size to thereby enchance reactivity of the filler. The experiments were performed on the particles treated at 750° C. Samples containing various proportions of particles with a mean size of about 100 um across were prepared and the number of PMC was determined. The results of the experiments are shown in Table 2. Table 2 PARAMAGNETIC CENTERS VS. MEAN PARTICLE SIZE ACROSS IN SAMPLES [Particles with mean size across <100 um. % I 5.0 10.0 20.0 30.0 40.0 80.0 PMC, 10— spin/cm-1 90 210 280 370 560 630 To assess the effect of the mineral flaky filler of the invention on the physicomechanical properties of polymerizable composites, standard samples were prepared. These were used in determining the adhesive strength (measured as a force required to separate a steel mushroom-like piece from the coating applied to a support also made of steel), the compressive strength, the tensile strength, the modulus of elasticity in lateral flexure, and the impact strength per unit area. Similar samples of the prior art filler were also prepared and used in concurrent tests (the methods and equipment for - 10 - running such tests are well known to those skilled in the art). In the above tests, the filler of the invention (hereinafter referred IF) was that as prepared by the thermochemical treatment at 680°C prior to crushing and classification and ■ therefore having the lowest crystallinity and PMC counts, while the prior art filler (hereinafter referred PF) was prepared at 900°C and had crystallinity and the PMC counts close to maximum. A relatively simple mixture of acrylic monomers containing polymeric additives and an initiator of polymerization, which are listed in the left column of Table 3, were used as a binder for experimental cold polymerizable composites. Table 3 COMPOSITION OF EXPERIMENTAL POLYMERIZABLE COMPOSITES Applicable standards Amount, Ingredients or specifications parts by wt. Methyl methacrylate GOST 20370-74 100 Polybutyl methacrylate TU 6-01-358-75 20 Polyvinyl chloride OST 6-01-37-88 20 Polyisocyanate TU 113-03-29-6-84 15 Benzoyl peroxide* GOST 2168-83 10 * Dimethyl anyline GOST 14888-78 3 IF, or 10 PF — 10 * Note: benzoyl peroxide is used in a paste form as a mixture with dimethyl phtalate in approximate ratio by weight of 1: 1. The ingredients were proportioned, methyl methacrylate, polybutyl methacrylate and polyvinyl chloride premixed, then one of the fillers was introduced, with stirring the mix, polyisocyanate and dimethyl anyline added (again with stirring), and lastly benzoyl peroxide was introduced. After a thorough mixing, the compositions were shaped in a conventional way into as many samples as required to obtain data on the - 11 - physicomechanical properties of the composites, the mean square deviation being +/-5%. The findings are summarized in Table 4. Table 4 COMPARISON OF SAMPLES TESTED Filler Properties IF I PF Adhesive strength, MPa 42 I 27 Compressive strength, MPa 92.0 I 72.0 Tensile strength, MPa 14.0 I 9.2 Modulus of elasticity in lateral flexure, MPa 36.4 I 28.5 Impact strength, kJ/m- 17.3 1 14.2 AAss ccaann bbee sseeeenn ffrroomm TTaabbllee 44 tthhee mmiinneerraall flaky filler according to invention is more efficient compared with the prior art filler. Industrial Applicability The industrial applicability of the mineral flaky filler stems from above-disclosed in connection with both possible large-scale production and wide application.

Claims: - 12 - C L A I M S 1. A mineral flaky filler for composites, produced by melting a starting mineral, shaping hard flaky vitreous particles from the melt, and subjecting such particles to thermochemical treatment in an oxidizing atmosphere until a crystal phase is developed characterized in that at the step of the thermochemical treatment the flaky particles were treated at a temperature range of 680 to 850° C until at least 12% by weight of the crystal phase and at least 7xl0 19 spin/cm 3 of reactive paramagnetic centers were developed, and followed by air cooling. 2. A mineral flaky filler of claim 1 characterized in that it contains at least 30% of particles having a mean size of about.100 um across to the total amount of the particles and at least 14xl0 19 spin/cm 3 of the paramagnetic centers.

Inventors: EFANOVA VERA VASILYEVNA, EFANOVA, VERA VASILYEVNA
Applicants: EFANOVA VERA VASILYEVNA, EFANOVA, VERA VASILYEVNA
Application year: 1998
Main classification: C03B37
IPC codes: C03B32, C03B37, C03C13, C04B35, C08K3