WO2001032787A1

WO2001032787A1 - Treating particulate alkaline earth metal carbonates

Info

Publication number: WO2001032787A1
Application number: PCT/GB2000/004240
Authority: WO
Inventors: Howard Goodman
Original assignee: Imerys Minerals Limited
Priority date: 1999-11-03
Filing date: 2000-11-03
Publication date: 2001-05-10
Also published as: AU1160701A; GB9925927D0

Abstract

A particulate alkaline earth metal carbonate material product has on its particles a coating consisting of two components: 1) a first coating comprising an aliphatic fatty acid and; 2) a second coating comprising an ester or earth alkaline salt of an aliphatic fatty acid. The second component has a substantially higher carbonate release temperature than the first coating agent. The amount of the first component may be insufficient to produce more than a monolayer, but the total amount of the first and second coating agent may exceed the required amount. The first component comprises stearic acid and the second component may comprise calcium distearate.

Description

TITLE OF THE INVENTION

Treating particulate alkaline earth metal carbonates

BACKGROUND OF THE INVENTION (a) Field of the invention

The present invention relates to a method of treating a particulate material comprising an alkaline earth metal carbonate. In particular, the present invention relates to the treatment of such a material by application thereto of a hydrophobismg surface treatment agent comprising an aliphatic carboxylic acid and products produced thereby. (b) Known prior art

In the manufacture of particulate carbonate materials such as calcium carbonate for use in a variety of applications it is conventional to refine and treat the carbonate, e.g. obtained from a natural source such as marble, limestone or chalk, to provide suitable product properties by processing techniques such as milling, grinding and chemical treatments. Often aqueous processing media are employed. Where the carbonate material is to be employed in applications in which it is to be incorporated in an essentially hydrophobic host material, e.g. a hydrophobic polymeric binder, the treated carbonate is often coated with a surface treatment agent comprising a fatty acid or a salt or ester thereof which will render the surfaces of the particles of the material more suitable for incorporation in the hydrophobic host.

In the prior art various treatment methods have been employed to coat a particulate carbonate material with a hydrophobismg surface treatment agent, the method chosen depending on the nature of the agent employed. Thus, some methods have involved treating the particulate material with the agent contained in a liquid carrier medium. Such a medium may be an aqueous medium, especially where other processing steps applied to the material take place m an aqueous medium. Other methods have involved contacting the particulate material with the agent in a heated atmosphere, often whilst the particulate material is in a drying or dry form.

It is known from WO 99/28050 of our affiliate company Imerys Pigments Inc (previously ECC International Inc) that where the surface treatment agent is applied by conventional treatments, the amount of reaction between the surface treatment agent and the particulate carbonate material may not be ideal such as to render the particulate carbonate material fully or suitably hydrophobic. This can lead to various problems when the material is used in an application composition.

Alternatively, or in addition, where the treatment agent comprises one or more organic acids, the level of unreacted acid of the surface treatment agent associated with the carbonate material coated thereby can be unduly high and this also can cause problems when the carbonate material is subsequently used in an application composition , e.g. m which it is incorporated in a hydrophobic composition comprising a polymeric matrix material. Such a composition usually employs one or more various additives such as selected from lubricants, stabilising agents, colouring agents, plasticisers, antistatic agents, anti- oxidants and metal passivatmg agents. At the temperatures employed for processing, the unreacted excess free acid which is usually bound loosely by physisorption to the carbonate material can be released as a volatile impurity and migrate and produce unwanted chemical reactions with one or more of such additives and/or unwanted deposition of material on processing equipment leading to a degraded processing method or product properties or performance. In particular, the composition can be stained or degraded and the surface finish of the final product can be impaired.

WO 99/28050 describes how the amount of surface treatment agent applied to the particulate carbonate may be optimised by use of a higher than usual treatment temperature. However, we have found that application of an optimum coating is difficult to achieve in practice because process conditions can vary in practice, especially in continuous or semi-continuous processes. The amount of the agent may from time-to-time fluctuate causing the amount applied to be greater or less than the optimum amount. In both cases, i.e. where the amount is more than and less than the optimum amount, problems are caused, either by the presence of unreacted acid from the surface treatment agent or by the surface of the carbonate particles not being fully hydrophobic by incomplete reaction of its surfaces with the treatment agent.

The present invention is concerned with contacting the particulate carbonate material with a surface treatment agent by a novel treatment process to produce a novel product which reduces problems associated with the prior art .

Treatment using more than one component in the surface treatment agent has been described in various prior art references, e.g. WO 92/02587, US 5,135,967, US 4,151,136, JP 54162746 and JP 54162746, but none of these references suggests the problem and solution described herein. SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method of surface treating a particulate material comprising an alkaline earth metal carbonate with a surface treatment agent comprising an aliphatic saturated carboxylic acid, whereby the problems of the prior art caused by undercoatmg or overcoating of the particulate material with the acid-contammg surface treatment agent are reduced or eliminated without the need for applying a precise amount of the agent.

According to the present invention in a first aspect there is provided a particulate alkaline earth metal carbonate material product which has on its particles a coat g of hydrophobic material comprising a composition formed of: (a) a first component which comprises the reaction product of the alkaline earth metal carbonate and at least one aliphatic carboxylic acid which has a formula CH₃ (CH₂) _nCOOH where n is an integer equal to 8 or more; and (b) a second component which is an organic compound having a carbonate release temperature substantially higher than the carbonate release temperature of said acid, the second component comprising at least one compound having a formula CH₃ (CH₂) _mC00R, where m is zero or an integer equal to 1 or more and R is a Group II metal radical or a radical of formula CH₃(CH₂)_qO-, where q is zero or an integer equal to 1 or more, wherein at least one of m and q is equal to 8 or more, m being equal to 8 or more when R is a Group II metal radical, wherein the concentration of the first component in the coatmg composition is at least 0.5X, where X is the minimum concentration of the first component required to give a monolayer coatmg of the carbonate particles by the first component, and the coatmg composition also contains at least 10 per cent by weight of component B.

The first component may form at least 20% by weight, especially at least 50% by weight, of the coatmg composition of the product according to the first aspect. According to the present invention in a second aspect there is provided a method of treating particles of an alkaline earth metal carbonate material to provide a coatmg of hydrophobic material on the particles which comprises applying to particles of the carbonate material a hydrophobismg surface treatment agent having at least two components comprising (a) a first component which comprises at least one aliphatic carboxylic acid which has a formula CH₃ (CH₂) _nCOOH where n is an integer equal to 8 or more and (b) a second component which is an organic compound having a carbonate release temperature substantially higher than the carbonate release temperature of said acid, the second component comprising at least one compound having a formula CH₃ (CH₂) _mCOOR, where m is zero or an integer equal to 1 or more and R is a Group II metal radical or a radical of formula CH₃(CH₂)_qO-, where q is zero or an integer equal to 1 or more, wherein at least one of m and q is equal to 8 or more, m being equal to 8 or more when R is a Group II metal radical, wherein the concentration of the first component in the surface treatment agent is such as to give on the carbonate particles an amount of the first component which is at least 0.5X, where X is the minimum concentration of the first component required to give a monolayer coatmg of the carbonate particles by the first component, and the coatmg composition also contains at least 10 per cent by weight of the second component. This method is referred to herein as the 'treatment method of the invention' . In this specification, the expression 'carbonate release temperature' of a substance which may be a component of a surface treatment agent for surface treating a particulate carbonate or a component of a coating composition on the carbonate material is the lowest temperature at which the substance when present on the carbonate particles is thermally volatilised and released from the carbonate in a substantial amount, which may be defined as an amount of at least 2% by weight of the amount of the component present. The carbonate release temperature may be determined in a known manner by heating calcium carbonate having a coating of the substance in question and measuring the temperature at which the substance is first detected to be released from the calcium carbonate in a substantial amount, e.g. as a rapid increase in the rate of weight loss of the coated calcium carbonate. The carbonate release temperature is therefore a measure of the point or region on the temperature scale at which the substance becomes a volatile, free, potentially contaminating agent when carbonate products coated with the substance are heated, e.g. in use in the preparation of application compositions. The coating required for test purposes may be produced in a known manner by contacting dry calcium carbonate particles with the substance in a heated, fluid state in an excess amount which gives a suitable coating.

The carbonate material product according to the first aspect of the invention may be employed by incorporation in one of a variety of hydrophobic polymeric media in a known manner as described later. In particular, the product may be used in media comprising thermosetting or thermoplastic organic polymers which are to be heated to elevated temperatures with the product. In particular, the carbonate material product of the first aspect of the invention may be suitable for providing mineral filled polymeric materials by melt compounding with suitable matrix polymeric materials, e.g. thermoplastic polymeric materials as described later.

According to the present invention in a third aspect there is provided a method of processing a composition comprising a polymeric material and a mineral filler, wherein the mineral filler comprises the carbonate material product according to the first aspect of the invention, wherein the processing includes heating the composition to temperatures above the carbonate release temperature of the acid employed to provide said first component of the coatmg composition. Preferably, the processing temperatures do not exceed the carbonate release temperature of the said second component of the composition of the hydrophobic coating composition of the carbonate material product. The first and second components in the method and product of the invention in combination can beneficially reduce or prevent release of volatile components of the coatmg composition at the processing temperatures in the method according to the third aspect. The processing may for example comprise melt compounding and/or extrusion. The temperatures employed m the said processing method will, as will be familiar to those skilled in polymer processing, depend on the type of polymer employed and the type of heat processing applied, e.g. in one of the ways described later. For example, for melt compounding of compositions of mineral filled thermoplastic polyethylenes temperatures of up to about 300°C are usually employed whereas for melt compounding of mineral filled compositions of PEEK, temperatures of up to about 450°C are usually employed.

DESCRIPTION OF THE INVENTION

The first component of the surface treatment agent in the treatment method of the invention may be a compound or mixture of compounds which, when in a free, unreacted state, is substantially volatile at the temperatures at which the carbonate material product is subsequently to be processed, e.g. by melt compounding and/or extrusion, the method according to the third aspect. In contrast, the second component of the surface treatment agent may beneficially be one which has a lesser volatility, preferably one which is substantially volatile, at the temperatures at which the carbonate material product is to be processed m the processing method of the third aspect. The presence of the second component can thereby reduce or prevent the release of volatile compounds from the first component when the surface treatment agent has been applied to the particulate carbonate to produce the coatmg composition of the first and second components in the product according to the first aspect.

The particles of the carbonate material product which has been treated by the treatment method of the invention may have a level of the first component coated thereon which will not produce an unacceptable amount of volatile compound(s), i.e. free carboxylic acid, e.g. stearic acid, at temperatures to be used in subsequent processing, e.g. compounding and/or extrusion, in the method according to the third aspect of the invention. We prefer that substantially all of the first component of the surface treatment agent chemically reacts with the carbonate material whereby none of the first component is physisorbed and available to be volatilised during subsequent processing. The second component may be chemisorbed and/or physisorbed by the carbonate particles. We have found surprisingly and beneficially that the invention solves the alternative serious problems of the prior art, namely either incomplete hydrophobismg of the carbonate material by application of too little hydrophobismg agent during coatmg or contamination during subsequent production of filled polymeric materials by the presence of substantial amounts of unreacted volatile hydrophobismg agent caused by application of too much of such agent during coatmg. As demonstrated later, we have shown that the product according to first aspect of the invention can be efficiently produced using hydrophobismg components in the surface treatment agent composition which may, if required, be relatively inexpensive and that an overall enhancement of resulting properties of the carbonate material product and compositions and products made therefrom may be achieved by use of the invention.

The first component of the surface treatment agent used m the treatment method of the invention may comprise one or more of the fatty acids employed m the prior art as surface treatment agents to treat alkaline earth metal carbonates. The said fatty acid may for example have from 10 to 26 chain carbon atoms. It may be selected from capric acid, lauric acid, montanic acid, myristic acid, palmitic acid, stearic acid, behenic acid and mixtures of two or more of these acids. Commercially available material may consist of mixtures. For example so called technical grade stearic acid consists of about 60%-65% by weight stearic acid and about 40%-35% by weight palmitic acid. Commercially available behenic acid may contain about 85%- 90% behenic acid and minor amounts of other acids such as stearic, arachidic, lignoceric and palmitic acids. At least 50% by weight, in many cases at least 90% or even 100% by weight, of the first component may be unsaturated fatty acid(s) of the formula given earlier for the acid which is the first component of the surface treatment agent.

The second component of the surface treatment agent may comprise one or more aliphatic organic compounds of the formula given for the second component earlier. The second component may comprise a metal salt of a Group II metal such as calcium, magnesium or zinc or an ester containing at least one carbon chain having at least eight carbon atoms, in many cases at least ten carbon atoms, the other moeity of the ester being an alkyl group. For example the ester may be stearyl stearate.

The second component may in some cases have a melting point which is substantially above, e.g. at least 50 Celsius degrees above, the melting point of the first component. For example, the melting point of the first component may be less than 100°C and the melting point of the second component may be higher than 150°C. This may facilitate coating treatment using mixtures of such components as described later. However, it is not necessary that the melting point of the second component is substantially above that of the first component. In some cases, the melting points may be similar but the second component may have a substantially higher carbonate release temperature . We prefer to use for the surface treatment agent stearic acid or a composition of fatty acids containing at least 50% by weight of stearic acid as the first component and calcium stearate as the second component on account of the commercial availability and cheapness of these materials and the familiarity of those working m the art with the use of these materials.

It should be noted that commercially available calcium stearate is different from the substance which forms by reaction on the surface of calcium carbonate when it comes into contact with stearic acid. It can be shown by analysis that the latter is a form of a calcium monostearate whereas the commercially available compound normally referred to as calcium stearate is calcium distearate.

Stearic acid which is applied to surface coat particulate alkaline earth carbonate and is substantially in excess of a monolayer equivalent as described later is physisorbed to particles of alkaline earth metal carbonate such as calcium carbonate and such physisorbed stearic acid is volatilised and released from such carbonates at temperatures in the range of from about 150°C to about 250°C. In contrast, calcium stearate (calcium distearate) applied (and physisorbed) to particles of alkaline earth metal carbonate is volatilised and released from such carbonates at temperatures in the range of from about 250°C to about 400°C. Thus, the carbonate release temperatures (defined earlier) of stearic acid and calcium stearate are respectively about 150°C and 250°C and this difference is exploited in an embodiment of the invention especially where carbonates coated by a combination of these components are later to be thermally processed at temperatures between 150°C and 250°C. The particles of the carbonate material in the treatment method of the invention may be treated with an amount of the first component which preferably is not in excess of the monolayer equivalent amount of that component. The 'monolayer equivalent amount' of the first component (or any component) is the minimum amount, which can be determined from theory or practice, of that component required to cover with a single molecular layer coating all of the available surfaces of the particles of the particulate carbonate material. WO 99/28050, the contents of which are incorporated herein by reference, describes how the monolayer equivalent amount for a given particulate carbonate of known specific surface area may be determined. The molecules of fatty acids will normally react with the carbonate to which they are applied. Thus, the monolayer equivalent amount of the first component if of fatty acid(s) produces a monomolecular reacted or chemisorbed layer of the first component on all of the available surfaces of the carbonate particles with no physisorbed overcoating thereof.

The amount of the first component applied in the treatment method of the invention may, in some cases, exceed the amount required to produce a monolayer coating thereof provided that the excess will not subsequently lead to an unacceptable amount of unreacted volatile impurity m subsequent processing. What is an unacceptable amount will depend on subsequent processing conditions especially residence time of the coated carbonate material product at the highest processing temperatures subsequently employed. In the treatment method of the invention, especially where a continuous or semi-continuous process, the amount of

surface treatment agent available to contact the carbonate may fluctuate according to variable process conditions. For this reason, we prefer to ensure that the amount of the first component does not exceed the monolayer equivalent amount even if the amount of the first component fluctuates. The overall coating of the surface treatment agent on the particles is in any case preferably substantially more than a monolayer to ensure complete hydrophobicity, but the amount of the hydrophobic material in excess of a monolayer may be provided predominantly, in many cases exclusively, by the second component. The combined concentration of the first and second components of the surface treatment agent on an active basis m the presence of the carbonate material in the treatment method of the invention may be from X to 2.5X or higher, especially from X to 1.5X, where X is the concentration required to give a monolayer coatmg. The concentration of the first component may be in the range 0. IX to 1.2X, preferably from 0.2X to 1.0X, especially from 0.4X to 0.9X. The weight ratio of the first component to the second component may be from 10:80 to 90:10, especially from 1:4 to 4:1.

Where the first component is stearic acid or a composition containing at least 50% by weight of stearic acid, the amount of the first component applied to the carbonate material may be from 0.05A% to 0.3A% by weight, e.g. from 0.1A% to 0.25 A% by weight based on the dry weight of the carbonate for a carbonate specific surface area of Am². g^"1 . The first and second components of the surface treatment agent may be applied separately or together to the particles of the carbonate material. Where the first and second components are applied separately, the first component is usually applied before the second component.

The first and second components of the surface treatment agent may be applied to the particles of the particulate carbonate material by any of the procedures known in the art. The first and second components may be applied by the same procedure, either together or separately, or they may be applied separately by different procedures . Thus, either or both of the first and second components may be applied by contacting the particulate carbonate material with an emulsion of the component, e.g. in an organic or preferably an aqueous medium. In such a known procedure, the liquid is subsequently removed and the resulting carbonate product dried.

The first and second components are preferably applied to the particles of the carbonate material in the treatment method of the invention by exposure of the particles, preferably a substantially dry form, to an atmosphere containing either or both of the first and second components present m a fluid reactive form, e.g. hot liquid droplets.

In a preferred form of the treatment method of the invention, the first and second components are intimately mixed and melted together prior to application to the carbonate particles m a dry state. In this form, the melting point of the two component mixture formed will be between the respective individual melting points of the first and second components. The melting points of mixtures of the two components may show an approximately linear relationship when plotted against mixture composition. The melted mixture may be cooled before subsequent use on a later occasion as a surface treatment agent in the treatment method of the invention.

The alkaline earth metal carbonate employed in the treatment method of the invention may comprise a carbonate of calcium, magnesium, barium or strontium or a carbonate of two or more alkaline earth metals, e.g. obtained from dolomite. The treatment method of the invention is especially applicable to treat calcium carbonate-containing and magnesium carbonate-containing particulate materials. The calcium carbonate-containing material may have been produced in a known way from marble, chalk, limestone or dolomite. The magnesium carbonate may have been produced from magnesite.

The treatment method of the invention is also applicable to treat alkaline earth metal carbonates which have been produced synthetically, e.g. calcium carbonate produced as a precipitate by reaction of calcium hydroxide and carbon dioxide in a known way.

Desirably, at least 95%, preferably at least 99%, by weight of the inorganic particulate material to be treated by the method of the invention comprises alkaline earth metal carbonate. Minor amounts of other mineral particles usually associated with alkaline earth metal carbonates could also be present together with the carbonate. Preferably at least 95%, e.g. at least 99%, by weight of the alkaline earth metal carbonate present is calcium carbonate. The calcium carbonate may be obtained in a well known way by processing naturally occurring calcium carbonate obtained from a mineral source or by chemical synthesis, e.g. from the reaction of carbon dioxide and lime (calcium hydroxide) . The present invention is particularly suitable to treat ground and processed calcium carbonate obtained from a mineral source.

The particulate carbonate material to be treated by the treatment method of the invention may have one or more of the following particle size properties:

(1) a median particle size of less than lOμm, especially from 0.2μm to 5μm, e.g. from 0.5μm to 3μm; (n) a particle size distribution steepness factor, i.e. d₅o~d₂o, where dso is the particle size value less than which there are 50% by weight of the particles, and d₂o is the particle size less than which there are 20% by weight of the particles, of less than 2.2, desirably 1.1 to 2.2; (m) a top cut (the particle size value less than which at least 99% by weight of the particles of the material have a size) of less than 12μm, desirably less than lOμm;

(IV) a dispersibility as measured by Hegman gauge value, of

20μm or less, desirably 13μm or less;

(v) a specific surface area of greater than lm².g^_1, e.g. from 2m². g^""1 to 13m². g^"1, especially from about 4m². g^"1 to about 8m². g^"1, as measured by the BET nitrogen adsorption method.

All particle size values and particle size distribution measurements as specified herein are measured, unless stated otherwise, by the well known standard method employed in the art, of sedimentation of the particles in a fully dispersed state in an aqueous medium using a

SEDIGRAPH 5100 machine as supplied by Micromeπtics

Corporation, USA.

Dispersibility may be measured in a manner well known to those skilled m the art using the standard procedure specified ISO 1524 using as test medium a long-oil alkyd resin with a 68% oil content of vegetable fatty acids, SYNOLAC 60W made by Cray Valley Ltd.

In the treatment method of the invention the particulate carbonate material may comprise material which has been sub ected to wet or dry processing m one of various well known ways to process the particulate material, e.g. to convert coarse, unrefined carbonate material obtained from a mineral source to a suitably pure and refined state. The material resulting from this processing may for example have a particle size distribution such that at least 60 per cent by weight, eg at least 70 per cent by weight of the particles of the material have an esd (equivalent spherical diameter measured as described earlier) of less than 2μm. The particulate material treated in accordance with the present invention may have been subjected to the following treatment steps prior to treatment by exposure to the said surface treatment agent:

(a) preparation and/or processing of the particulate material m an aqueous medium;

(b) where the carbonate is to be treated in a dry form drying of the particulate material.

The processing of step (a) which may have been applied to the material may comprise one or more wet processing steps applied to refine and process the particulate material in a conventional manner. For example, the wet processing step may include grinding and/or milling and/or particle size classification.

The wet processed particulate material so treated may following such processing be washed and dewatered in a known way, eg by filtration or forced evaporation, prior to treatment in a wet state to apply the surface treatment agent components or prior to drying, step (b) as referred to earlier. The drying step (b) may be carried out by heating m a hot atmosphere or current of air.

Alternatively, the material may have been subjected to dry processing e.g. using milling followed by grinding in a dry grinding mill, e.g. of the kind described in EP-A- 681155, prior to treatment with the surface treatment agent .

The exposure of the carbonate particulate material to the surface treatment agent, e.g. a mixture of the first and second components, m the treatment method of the invention may be carried out m a treatment vessel containing a water dry treatment atmosphere containing the agent as a liquid (e.g. as droplets) and/or vapour. As noted earlier, the amount of the first component present m the treatment method of the invention preferably is not greater than the monolayer equivalent amount of that component. The composition of the first and second components m the surface treatment agent applied in this way is therefore selected to maintain the amount of volatile material which may be produced from the first component below acceptable limits. During application of the surface treatment agent it is possible that the amount of the agent and therefore the two components thereof may exceed a desired norm owing to variations which occur in process conditions in the treatment vessel. The composition and the amount of the treatment agent present should at the process condition limits produce at least, preferably more than, a monolayer total coatmg and preferably the amount of the first component thereof should not exceed the monolayer equivalent even during fluctuations in process conditions . Where the carbonate is contacted with a molten mixture of the components of the surface treatment agents in a treatment vessel, the vessel may be heated externally, e.g. by a heating jacket, e.g. containing a heating fluid, e.g. a heating oil. The treatment conditions are controlled so that the required amounts of the first and second components of the surface treatment agent are present in the atmosphere which contacts the particles of the carbonate material in the vessel. Desirably, as described in WO99/28050, the particulate carbonate material enters the treatment vessel in a dry state and preferably also in a pre-heated state, e.g. heated to a temperature of at least 80°C, preferably at least 90°C, immediately prior to entering the treatment vessel. Such a temperature may result from the temperature applied in a dryer prior to delivery of the particulate carbonate material to the treatment vessel, the material remaining at an elevated temperature between the dryer and the treatment vessel. Desirably, as described in WO99/28050, the temperature of the atmosphere in such a treatment vessel can be externally varied and controlled so that a selected atmosphere reaction temperature may be chosen and monitored. The vessel may comprise an elongated heated cylindrical structure. Desirably, the required temperature is maintained throughout the region where the surface treatment agent is applied and on exit from that region at a temperature of at least, preferably greater than, about 100°C. Particulate carbonate material may be delivered for treatment in the treatment vessel in a batch or continuous process. For example, the particulate material may be conveyed into and out of the vessel in a current of hot air or other gas inert to the reagents employed.

The particulate carbonate material may be exposed to the components of the surface treatment agent in the said vessel at a temperature at which both components or a mixture thereof (if employed) are in a fluid state. Generally, the temperature may be in the range 100°C to 300°C, especially 100°C to 150°C. The temperature selected in the atmosphere of the treatment vessel should provide sufficient heat to ensure melting and good mobility of the molecules of both components of the surface treatment agent and therefore good contacting of and reaction with the particles of the particulate material.

The particulate carbonate material may be exposed in the said treatment vessel to each of the first and/or second components of the surface treatment agent or a mixture thereof for more for a period greater than a minimum for effective treatment at a given feed rate of particulate material for the treatment equipment employed. For feed rates of between 2 tons per hour (1814 kg per hour) and 10 tons per hour (9070 kg per hour) the minimum residence time in a treatment vessel containing the surface treatment agent components may for example be between 500 seconds and 100 seconds. The treatment of the particulate carbonate material with the surface treatment agent is desirably carried out in a heated vessel in which a rapid agitation or stirring motion is applied to the atmosphere containing the particulate carbonate material and the surface treatment agent whilst in the vessel, whereby the surface treatment agent is well dispersed in the treatment atmosphere. Preferably, the agitation is not sufficient to alter the surface area of the particulate material since such an alteration changes the required surface treatment agent concentration as discussed earlier. The vessel may include for example one or more rotating paddles, comprising a rotating shaft having laterally extending blades comprising one or more propellers which ensure agitation and deagglomeration of the particles and intimate contacting of the particulate material with the components of the surface treatment agent. The residence time of the particulate material in the said treatment vessel is sufficient to give the required contact to give reaction between the first component of the surface treatment agent and particles being treated. This time may generally be greater than 2 seconds, e.g. at least 10 seconds. For example the residence time in many cases may be 50 seconds to 1000 seconds, eg 100 seconds to 500 seconds .

The surface treatment agent when added to the treatment vessel may comprise flakes or particles of a solid which becomes molten, fluid and well dispersed in the treatment atmosphere of the vessel through which the particulate material is passed as described above. For example, where stearic acid or a stearic acid containing composition is employed, this material as added to the inlet to the vessel may comprise irregular flat particles having sizes of from about 1mm to about 5mm.

Metered amounts of the surface treatment agent or one or both components thereof as solid material may be added to the vessel via one or more feed hoppers via one or more entries into the vessel different from the entry of the particulate material. In a continuous process, the required amount may be added continuously to give delivery of the optimum amount of surface treatment agent m the treatment vessel as determined in the manner described above .

Desirably, the surface treatment agent components do not contact the particulate carbonate material until the particulate carbonate material is in the treatment vessel whereby the particulate material can be suitably receptive to be coated by the surface treatment agent and the concentration of the surface treatment agent which the particulate carbonate material contacts can be suitably controlled.

The particulate carbonate material product according to the second aspect of the invention may optionally be further treated by one or more chemical or physical processes, for example with one or more additional surface treatment agents, e.g. a known hydrophobic coupling agent such as an organosilane, organotitanate or zircoalummate .

The carbonate material product according to the second aspect of the invention may be employed in a known manner as a pigment, filler, extender or property modifier m a composition (herein called an "application composition") comprising a hydrophobic or oleophilic material, eg comprising a resin or organic polymeric binder. The carbonate material product may be employed together with other inorganic particulate material selected from known pigment, filler, extender and property modifier materials conventionally employed as additives in compositions comprising hydrophobic or oleophilic compositions, for example, optionally pre-treated kaolmitic clay, calcined kaolmitic clay, mica, talc, aluminium silicate, including natural aluminium silicates such as feldspar and nephelme syenite, calcium silicate, including natural calcium silicates such as wollastonite, bauxite, alumina trihydrate, hydroxide of magnesium, calcium sulphate, titanium dioxide, or a mixture of any two or more of these. The polymeric material to which the carbonate material product according to the second aspect of the invention is added to form an application composition may be of any of the kinds of hydrophobic or oleophilic (substantially water insoluble) polymeric materials in which inorganic particulate materials are known to be incorporated, e.g. as pigment, filler, extender, property modifying, reinforcing or coating materials. Such material may comprise for example a continuous polymer matrix when the filler is added therein or thereto, e.g. a shaped article. Such material may comprise a thermoplastic material, a thermosetting material, a cold setting material or a non- water based resin or resinous composition. Such materials may be employed in a variety of well known applications, e.g. as moulded or extruded plastics products, elastomers, rubbers, sealants, adhesives, varnishes, paints and the like. The particulate carbonate material may be added to the polymeric material to be distributed throughout the bulk thereof in a known manner. Alternatively, it may be added to the polymeric material in only a region thereof, eg on a surface of the material, e.g. where the material comprises a body to be coated.

The treated particulate carbonate material may be incorporated directly into or added to a body of a polymeric material to form a product by one of the suitable product forming processes well known in the art. For use with thermosetting and thermoplastic polymers, heating of the polymer will generally be applied. Alternatively, the particulate material may be formed together with thermoplastic or thermoplastic forming material into an intermediate product, e.g. as described in US 4,803,231 or WO 95/17441, such as in a granular or pellet form, which may subsequently be added to a polymeric, eg thermoplastic material for the formation of a product. Any of the polymeric materials described in US 4,803,231 or WO 95/17441 may be employed for this purpose. In particular, the treated particulate carbonate material may be formed into an intermediate product together with polyolefm material, e.g. an amorphous or wax material, such as a polypropylene or a polypropylene/polyethylene co-polymer. Other known agents, e.g. lubricant, may be included in the intermediate product formation.

Examples of thermoplastic materials into which the particulate material treated by the method of the present invention may be incorporated with or without the formation of an intermediate product include polyolefm homopolymers or copolymers (eg low density or high density polyethylenes, linear polyethylenes, polypropylenes, ethylene-propylene copolymers, ethylene ( vinyl acetate) copolymers, and ethylene- (acrylic acid) copolymers, halogenated polyethylenes (such as chlorinated polyethylene) , polybutene, polymethylbutene, polyisobutylene, polystyrenes and polystyrene derivatives (eg SB, ABS, SA and SBS rubbers), PVCs, polycarbonates, polysulphones, polyether sulphones, PEEK, saturated polyesters (eg polyethylene terephthalates and/or polybutylene terephthalates), and polyphenylene oxides and blends, mixtures or copolymers containing these species. We have found that the treated carbonate material produced by the method according to the present invention is especially suitable for incorporation into thermoplastic polyolefin compositions, especially containing polyethylene and polypropylene homo- or co-polymers.

As demonstrated later, by producing a surface coated particulate carbonate material by the method of the invention improved properties are obtained for the surface coated material. For example, the material may surprisingly and beneficially comprise a free-flowing hydrophobic powder having low moisture pick up and low tendency to produce agglomerates as well as minimised free acid impurities which cause undesirable effects during processing with the polymer. It is very suitable to use as a mineral filler (or extender or property modifier) for use in thermoplastic, eg polyolefm or pvc resin compositions. As noted above, where the application composition comprises a thermoplastic material the product-forming process employed to form a product from the thermoplastic material and the particulate filler comprising coated particulate carbonate material added thereto either as a powder or in the form of a granular or pelletised intermediate product as referred to above may be one of the methods well known in the art. Examples include melt compounding followed by extrusion of films, tubes, shapes, strips and coatings onto other materials, eg paper, metal sheet foil, injection moulding, blow moulding, casting and thermoforming and formation of tubes or pipes (especially where the polymer is a pvc polymer) . The melt compounding may for example be carried out in a suitable compounder or screw extruder. The thermoplastic material to be compounded may suitably be in a granular or pelletised form. The temperature of the compounding and moulding, shaping or extrusion processes will depend upon the thermoplastic material being processed and materials incorporated therein. The temperature will be above the softening point of the thermoplastic material. Where the polymeric material comprises a non-thermoplastic material, eg thermosetting or cold setting resin it may be processed with incorporation of material according to the second aspect of the invention in a known way.

The application composition may include 1% or more, eg up to about 80% by weight, in particular usually from 10% up to 75% by weight, of the particulate carbonate product according to the second aspect of the present invention, the amount depending upon the materials involved and the application of the product.

The application composition may include one or more optional additives well known to those familiar in the art, eg processing agents, such as lubricants, thermal or photochemical stabilising agents, colouring agents, plasticisers, antistatic agents, fire retardants, anti- oxidants, metal passivating agents or other reinforcing or filling agents such as natural or artificial fibres, metal particles, strands or foils, glass beads or microspheres and the like or other mineral (inorganic) fillers.

The application composition may be formed into products either alone or together with other materials such as plastics, metals, refractories, wood, paper etc. in the form of laminates, coatings and the like.

The particulate carbonate material surface coated by the method of the invention will be referred to as the 'instant filler' . The instant filler has been found to work extremely well as a mineral filler in producing intermediate product so called 'masterbatch' compositions together with thermoplastic polymers and other optional ingredients, especially products made using polyolefin based polymers. End products produced from such compositions such as cast film, blown film, and extrusion coatings using the instant filler in such applications can show an especially superior dispersion and extrusion performance, particularly with respect to homogeneity and quality of the film produced. The instant filler may be incorporated into compositions for use in producing film products at filler solids loadings ranging from 10% to as high as 75% and higher (by weight) , while maintaining its ability to be processed into useful thin films, especially breathable films, using known processes, eg using cast or blown film, or extrusion coating processes. We have demonstrated later than suitably breathable films may be produced from the carbonate products of the invention. A method of producing a porous, breathable film includes use in the film forming process of a composition which includes a thermoplastic polymeric material together with a filler, wherein the filler comprises partly or wholly the instant filler defined earlier. The thermoplastic polymer may form from 10% to 70% by weight and the filler may form from 30% to 80% by weight of the composition, ie combination of the polymer plus filler. The polymer preferably comprises more than 50% by weight of olefin units and is therefore usually referred to as a polyolefm resin.

The resins which can be used to provide the polyolefin resin to produce a composition suitable for producing films, for example, include mono-olefin polymers of ethylene, propylene, butene or the like, or copolymers thereof as a main component. Typical examples of the polyolefin resin include polyethylene resins such as a low- density polyethylene, linear low-density polyethylene (ethylene-α-olefin) copolymers, middle-density polyethylene and high-density polyethylene; polypropylene resins such as polypropylene and ethylene-polypropylene copolymer; poly (4- methylpentene) ; polybutene; ethylene-vinyl acetate copolymer; and mixtures thereof. These polyolefin resins may be obtained by polymerisation in a known way, eg by the use of a Ziegler catalyst, or obtained by the use of a single site catalyst such as a metallocene catalyst. Above all, polyethylene resins are preferable, and linear low- density polyethylene (ethylene-α-olefin) copolymers and low-density polyethylene are most preferable. Furthermore, in view of the mouldability, the stretchability and the like of the film, the melt index of the polyolefin resin is preferably in the range of about 0.5 to 5g/10 min. Where one or more other fillers are employed together with the instant filler, the filler composition may include typically at least 50% by weight, e.g. from 80% to 99% by weight of the instant filler.

Application compositions made from the instant filler together with thermoplastic materials and which are to be fabricated into breathable films may incorporate at least 40% by weight, e.g. from 50% to 80% by weight of the instant filler.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments of the present invention will now be described by way of example only with reference to the following Examples (in which materials prepared as in the prior art are also included for the purpose of comparison) .

EXAMPLE 1 A ground natural calcium carbonate filler was selected having a particle size distribution, measured as described earlier, such that the median particle size was 1.4μm, and a specific surface area, as measured by the BET nitrogen adsorption method, of about 4m²g^_1.

Samples of this calcium carbonate filler in dry form were surface coated by a method embodying the invention with various two component mixtures of stearic acid and calcium stearate (calcium distearate) . The amount of each of the components present for each coating run is as given in Table 1 later. Comparative coated samples of the same calcium carbonate filler were prepared using only stearic acid as the treatment agent, the amount of stearic acid present for these samples being as given in Table 1 later. Where mixtures of stearic acid and calcium stearate were used, these two components were mixed together in required proportions and the resultant mixture was melted before being applied to the dry particulate calcium carbonate filler. The coating in all cases was applied in a known manner in a stirred heated vessel at a temperature of 110°C.

The hydrophobicity of each sample of coated calcium carbonate filler produced was determined by measuring for the sample the amount of water adsorbed after standing in an atmosphere maintained at 97% relative humidity (and a temperature of 20°C) for a period of 24 hours. The amount of water adsorbed was determined by comparing the weight of the coated calcium carbonate filler before and after exposure to the humid atmosphere. The moisture pick up results obtained for the various coated calcium carbonates are as given in Table 1 as follows: Table 1

% by weight % by % by of calcium weight of weight of stearate stearic water acid adsorbed

0 0 0.565

0 0.4 0.309

0 0.6 0.163

0 0.8 0.146

0 1.2 0.07

0 1.5 0.082

0 1.6 0.088

0 2 0.094

0 2.4 0.099

0 2.8 0.096

0.125 0.875 0.071

0.25 0.75 0.063

0.375 0.625 0.079

0.5 0.5 0.074

The percentages by weight given in Table 1 are based upon the dry weight of calcium carbonate present. The results given in Table 1 show that when the calcium carbonate filler was coated with a mixture of calcium stearate and stearic acid in accordance with an embodiment of the invention in a total mixture amount of 1.0% by weight, (based on the dry weight of the calcium carbonate), 'Samples A', the water adsorbency of the coated calcium carbonate was approximately the same as that of the calcium carbonate which had been coated with 1.2% by weight of stearic acid alone, 'Sample B' . However, unlike the Sample B, the Samples A were found not to release volatile material, e.g. stearic acid, at temperatures up to about

250C and could therefore be incorporated into thermoplastic compositions and heat compounded and fabricated into films and other products with no observable volatilisation of free acid from the surface treatment agent, and no staining of the composition or degradation of the thermoplastic polymer.

EXAMPLE 2

Coated calcium carbonate filler samples were produced in the manner described in Example 1 using 1% surface treatment agent which as explained earlier is close to the monolayer equivalent amount. Two samples, Carbonates A and

B, were produced using respectively (A) a mixture of stearic acid and calcium stearate containing 75% by weight stearic acid and 25% calcium stearate and (B) 100% stearic acid. These samples were m separate runs heat compounded with a commercially available linear low density polyethylene resin having a melt flow rate of 3 g/10 mm (Stamylex 1026F supplied by Exxon Chemical) . A high shear mixer (a Baker Perkins MP2030 machine from Baker Perkins, UK) was employed operating at a maximum temperature of 190

C. The concentration of the coated Carbonate each case was 50% (by weight, based on the total weight of the resin and coated Carbonate) . The resulting composition produced in each case was cast into samples of unstretched film using a Killion (US) 1.5 inches (3.8 cm) single screw extruder with a 14 inches (35.6 cm) die operating at a maximum temperature of 243 °C . The chill rolls employed to cool the extruding film operated at 40 °C . The unstretched films produced had a thickness of 45 microns. The film produced in each case was then stretched 3.5 times m a temperature-controlled environment (23°C, 50% RH) using a Monsanto Tensometer 10 machine. This produced evenly stretched film specimens having an average thickness of 18 microns. Each stretched film specimen was then tested for water vapour transmission rates (WVTR) which is a measure of breathability in a well known manner using the cup method (ASTM E96-80) . Circular samples measuring 3 inches (7.6 cm) in diameter were cut from each of the specimens. A piece of commercially available breathable film material (Nuclepore 3.0 micron hydrophobic membrane from Nuclepore Corporation of Pleasanton, California) was similarly formed into such a circular sample and used to give a breathability standard. The WVTR test in each case was conducted using an aluminium pan containing 100 mL of water. A sample of each test or standard material was placed across the open top of the pans. A seal was then formed along the edges of the pan, leaving the associated test material or control exposed to the ambient atmosphere over a 2.5 inch (cm) diameter circle having an exposed area of approximately 31.7 cm². The weight of the pan was recorded. The pan was then placed in a forced air oven at 37 C for 24 hours. The preliminary WVTR values were calculated according to the following equation: Test WVTR = (grams weight loss over 24 hours) x 315.8 g / ιτ / 24 hrs. Under these predetermined conditions the standard material gave a control WVTR of 4000 g/m²/24hrs. Accordingly, each sample was run with the standard test and the preliminary test values were corrected to set conditions using the following equation WVTR = (Test WVTR/standard WVTR) x (4000) g/m²/24hrs. The corrected WVTR values obtained using the various samples are as given in Table 2 as follows: TABLE 2

Sample Type No,

Corrected WVTR

(g/m²/24hrs)

1 (Standard)

4000

2

2280

3

1780

In Table 2, Sample Type Nos. 2 and 3 are breathable film samples incorporating respectively coated Carbonates A (invention) and B (comparative) described above. These results illustrate that films without deterioration in breathability could be prepared from Carbonate A prepared by an embodiment of the invention when processed into films with LLDPE in a 50:50 composition. The comparative result for stearic acid only coated carbonate, Carbonate B, processed into films in a similar manner is that shown for Sample Type No.3. The result for Sample Type No. 2 can be considered to be superior to that obtained for comparative Sample Type No .3.

Claims

1. A particulate alkaline earth metal carbonate material product which has on its particles a coating of hydrophobic material comprising a composition formed of (a) a first component which comprises the reaction product of the alkaline earth metal carbonate and at least one aliphatic carboxylic acid which has a formula CH₃ (CH₂) _nC00H where n is an integer equal to 8 or more and (b) a second component having a carbonate release temperature substantially higher than that of the first component, wherein the second component comprises a compound of formula CH₃ (CH₂) _mCOOR, where m is zero or an integer equal to 1 or more and R is a Group II metal radical or a radical of formula CH₃(CH₂)_qO-, where q is zero or an integer equal to 1 or more, wherein at least one of m and q is equal to 8 or more, m being equal to 8 or more when R is a Group II metal radical, wherein the concentration of the first component in the coating composition is at least 0.5X, where X is the minimum concentration of the first component required to give a monolayer coating of the carbonate particles by the first component, and the coating composition also contains at least 10 per cent by weight of component B, wherein the carbonate release temperature of a component is the lowest temperature at which the component is thermally volatilised and released from the carbonate in a substantial amount.

2. A product according to claim 1 wherein the second component forms from 10% to 80% of the coating composition.

3. A product according to claim 1 or claim 2 wherein the first component forms at least 20% by weight of the coating composition.

4. A product according to claim 3 wherein the first component forms at least 50% by weight of the coating composition.

5. A product according to claim 1, claim 2, claim 3 or claim 4 wherein the weight ratio of the first component to the second component is from 1:4 to 4:1.

6. A product according to any one of the preceding claims wherein the amount of the first component on the particles is from 0.5X to 1.0X, where X is the concentration required to give a monolayer coating by the first component.

7. A product according to any one of the preceding claims wherein the amount of the coating composition present is from 1. OX to 1.5X, where X is the concentration required to give a monolayer coating by the coating composition.

8. A product according to any one of the preceding claims wherein the first component comprises the reaction product of stearic acid and the alkaline earth metal carbonate.

9. A product according to any one of the preceding claims wherein the second component comprises calcium distearate which has been applied to the carbonate.

10. A product according to any one of the preceding claims wherein the second component comprises stearyl stearate.

11. A product according to any one of the preceding claims wherein the particulate carbonate material has a median particle size of from 0.5μm to 5μm.

12. A product according to any one of the preceding claims wherein at least 95% by weight of the particulate carbonate is calcium carbonate.

13. A method of treating particles of an alkaline earth metal carbonate material to provide a coatmg of hydrophobic material on the particles which comprises applying to particles of the carbonate material a hydrophobismg surface treatment agent having at least two components comprising (a) a first component which comprises at least one aliphatic carboxylic acid which has a formula CH₃ (CH₂) _nCOOH where n is an integer equal to 8 or more and (b) a second component having a carbonate release temperature substantially higher than that of the first component, wherein the second component comprises a compound of formula CH₃ (CH₂) _mCOOR, where m is zero or an integer equal to 1 or more and R is a Group II metal radical or a radical of formula CH₃(CH₂)_qO-, where q is zero or an integer equal to 1 or more, wherein at least one of m and q is equal to 8 or more m being equal to 8 or more when R is a Group II metal radical, wherein the concentration of the first component m the surface treatment agent is such as to give on the carbonate particles an amount of the first component which is at least 0.5X, where X is the minimum concentration of the first component required to give a monolayer coatmg of the carbonate particles by the first component, and the coatmg composition also contains at least 10 per cent by weight of the second component, wherein the carbonate release temperature of a component of the surface treatment agent is the lowest temperature at which the component is thermally volatilised and released from the carbonate in a substantial amount.

14. A method according to claim 13 wherein the amount of the first component present is not m excess of the monolayer equivalent amount of that component.

15. A method according to claim 13 or claim 14 wherein substantially all of the first component applied to the particulate carbonate material is chemisorbed thereby.

16. A method according to claim 13, claim 14 or claim 15 wherein the amount of the first component applied to the particulate carbonate material is less than the monolayer equivalent amount of that component and the amount of the second component applied is such that the amount of the first and second components applied to the particulate carbonate material is equal to or more than the monolayer equivalent amount of the surface treatment agent.

17. A method according to any one of the preceding claims 13 to 16 wherein the first component is applied first followed by the second component.

18. A method to any one of claims 13 to 17 wherein the first component and the second component are applied together.

19. A method according to any one of the preceding claims 13 to 18 wherein one or both of the first and second components is applied by contacting the carbonate material in a dry state with the first and/or second component in a heated atmosphere.

20. A method according to claim 19 wherein the second component has a melting point higher than that of the first component and the first and second components are applied together as a molten mixture.

21. A method according to claim 20 and wherein the first and second components have been melted together prior to use by application to the carbonate material

22. A method according to any one of claims 13 to 21 wherein the concentration of the surface treatment agent applied is such as to produce on the particulate carbonate material a coating of an amount which is in the range of from X to 1.5X, where X is the concentration required to give a monolayer equivalent amount.

23. A method according to any one of claims 13 to 22 wherein the first component forms from 10% to 80% by weight and the second component forms from 80% to 10% by weight of the surface treatment agent on an active basis.

24. A method according to claim 23 wherein the first component forms at least 50% by weight of the surface treatment agent on an active basis.

25. A method according to any one of the claims 13 to 24 wherein the method is carried out as a continuous or semi- continuous process.

26. A method according to any one of claims 13 to 25 wherein at least 95% by weight of the particulate carbonate material to be coated by the surface treatment agent is calcium carbonate.

27. A method according to any one of claims 13 to 26 wherein the particulate carbonate material has a median particle size of from 0.5μm to 5μm.

28. A method according to any one of claims 13 to 27 wherein the first component contains at least 50% by weight of stearic acid.

29. A method according to any one of the preceding claims wherein the second component comprises calcium distearate.

30. A method according to any one of claims 13 to 28 wherein the second component comprises stearyl stearate.

31. A method of processing a composition comprising a polymeric material and a mineral filler, wherein the mineral filler comprises the carbonate material product according to any one of claims 1 to 12, wherein the processing includes heating the composition to temperatures above the carbonate release temperature of the said first component .

32. A method according to claim 31 wherein the temperatures applied in the said processing do not exceed the carbonate release temperature of the second component of the coating composition.

33. A method according to claim 31 or 32 wherein the processing comprises melt compounding and/or extrusion.

34. A filled polymer composition comprising a polymeric material and the carbonate material product according to any one of claims 1 to 12.

35. A composition according to claim 34 wherein the polymeric material comprises a thermoplastic material.

36. A composition according to claim 35 which is in the form of a product which is a breathable film.