WO2000012434A1 - Carbonates for thermoplastic film and process of manufacture thereof - Google Patents

Carbonates for thermoplastic film and process of manufacture thereof Download PDF

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Publication number
WO2000012434A1
WO2000012434A1 PCT/GB1999/002614 GB9902614W WO0012434A1 WO 2000012434 A1 WO2000012434 A1 WO 2000012434A1 GB 9902614 W GB9902614 W GB 9902614W WO 0012434 A1 WO0012434 A1 WO 0012434A1
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Prior art keywords
weight
film
filler
inorganic particulate
particulate material
Prior art date
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PCT/GB1999/002614
Other languages
French (fr)
Inventor
Deeba Marjan Ansari
Original Assignee
Ecc International Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GBGB9818598.6A external-priority patent/GB9818598D0/en
Application filed by Ecc International Ltd. filed Critical Ecc International Ltd.
Priority to AU54303/99A priority Critical patent/AU5430399A/en
Publication of WO2000012434A1 publication Critical patent/WO2000012434A1/en

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/24—Acids; Salts thereof
    • C08K3/26—Carbonates; Bicarbonates
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/02—Compounds of alkaline earth metals or magnesium
    • C09C1/021—Calcium carbonates
    • C09C1/022—Treatment with inorganic compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/51—Particles with a specific particle size distribution
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C01P2004/84—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases one phase coated with the other
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/24—Acids; Salts thereof
    • C08K3/26—Carbonates; Bicarbonates
    • C08K2003/265—Calcium, strontium or barium carbonate

Definitions

  • the present invention relates to a particulate calcium carbonate, for use with a polymer composition for producing a polymer based end product, eg film product, which may have a high mineral film loading.
  • the present invention relates to a carbonate with an unusually low surface moisture level and the processing and use of this carbonate.
  • thermoplastic polymers such as film products.
  • films porous or non-porous, are manufactured for a number of consumer products such as garbage bags, backing materials or outer covers on diapers, bandages, training pants, sanitary napkins, surgical drapes, and surgical gowns.
  • the compositions from which these films are made may include two basic components, the first being a thermoplastic polymer, usually a predominantly linear polyolefin polymer such as a linear low density polyethylene and the second being an inorganic particulate filler such as calcium carbonate.
  • a third component, namely a bonding or tackifying agent may often be present.
  • a compound or concentrate which is formed (usually in a subsequent process) into a film layer using any one of a variety of film-producing processes known to those of ordinary skill in the film making art including casting, or blowing, or may be laid down on a substrate such as paper or board in a process known as extrusion coating.
  • the film After the film is fabricated into its desired form, and if the film is to be a porous breathable film, the film can then be stretched, uniaxially or biaxially, by any of the well-known techniques in the art including by hydraulics, by pinch rolls moving at different rates, or by tentering.
  • Filler loading levels determine to a great extent how far the precursor film must be stretched to attain a given degree of overall porosity. Below a lower end of the loading range, the pores are less numerous and less interconnected, and therefore, the film is less permeable at a given draw ratio than when a higher filler loading is employed. Above a higher end of the loading range, either the materials will not blend « uniformly or the sheet made from the composition will not stretch.
  • the preferred loading in some applications, such as that in manufacturing the microporous film of US Patent Nos 5,008,296 and 5,011,698, is very high, eg 60% to 75% by weight of the composition, with the filler preferably being a calcium carbonate.
  • US Patent No 4,698,372 discloses a microporous polymeric film having good water vapour transmission rates and hydrostatic resistance to water penetration thereof.
  • the film has a filler loading of 25-35 volume % of inorganic fillers such as calcium carbonate, among others, and uses an "antagonizer” such as stearic acid in order to reduce the effective surface tension of the filler to the approximate level of that of the matrix polymer.
  • US Patent No 3,903,234 discloses gas permeable biaxially oriented film prepared from compositions of polyolefins containing 26% to 50% by weight of inorganic filler particles.
  • US Patent No 4,176,148 discloses microporous oriented films composed of polybutene containing 3% to 80% by weight of inorganic fillers.
  • US Patent Nos 5,376,445, 5,695,868, and 5,733,628 disclose breathable film or film laminates or composites which may or may not consist of fillers. If the moisture level within the film forming composition becomes significant, it may be difficult to prepare a film compound and/or to form a film from the compound with a smooth surface which is free from voids. A smooth surface which is free from voids is necessary to enable the film to be stretched uniformly, a process which is generally employed in the production of breathable and other films.
  • the purpose of the present invention is to provide a mineral filler comprising calcium carbonate particulate material, which has properties allowing a film end product comprising a thermoplastic polymeric material together with the filler to be easily and successfully produced with filler loadings of at least 10 per cent by weight, preferably at least 20 per cent by weight, and, surprisingly, in some cases at least 40 per cent by weight and in some cases even up to 75% by weight.
  • Fillers produced in a conventional manner would in many cases be unsuccessful in producing such film products without the application of special time consuming and costly additional processing steps during or after the formation of the composition (compound, masterbatch or blend) of filler plus thermoplastic polymer to be employed to produce the film.
  • a moisture content above but not below a minimum level (which we have determined) associated with the calcium carbonate mineral filler used in the composition for manufacturing a polymer film product can result in unwanted macroscopic size voids or holes (ie several mm in length) forming in the film as a result of steam generation whilst the thermoplastic polymer of the film is in the plastic melt phase.
  • the moisture content of the filler should desirably be • limited to or preferably below the specified minimum level at all times before use in producing the composition with the polymer.
  • an inorganic particulate material containing at least 95% by weight of calcium carbonate suitable for use as a mineral filler in the manufacture of thermoplastic film products wherein the inorganic particulate material is in the form of a composition wherein the inorganic particulate material is mixed together with a desiccant additive which forms not more than 10% by weight, usually less than 5% by weight, eg 0.1% to 3% by weight based on the dry weight. of the inorganic particulate material.
  • the desiccant may itself comprise an inorganic particulate material, especially an oxide of one or more elements of Group II of the Periodic Table.
  • Preferred desiccants are calcium oxide and zinc oxide, especially calcium oxide.
  • a particulate material as a mineral filler in high filler loading applications in the preparation of a film product and which particulate material comprises the material according to the first aspect.
  • the material according to the first aspect of the present invention will be referred to herein as the* ⁇ instant filler' .
  • the total surface adhered moisture level of the instant filler is less than 0.1% by weight even after exposure to an atmosphere of 80% or more relative humidity for 40 hours at a temperature of 20°C.
  • a particulate material as a mineral filler in high filler loading applications in the preparation of a film product and which particulate material comprises particles of the instant filler.
  • the instant filler may comprise a calcium carbonate product obtained from a mineral source and processed by refining and treatment processes including grinding to obtain a suitable particle size distribution.
  • the calcium carbonate product may be chemically synthesised in a known way.
  • the desiccant additive may be added after processing including drying of the calcium carbonate product.
  • its particles may be essentially free of hygroscopic or hydrophilic chemicals used in the processing of the instant filler prior to addition of the desiccant additive.
  • the grinding process where employed may be carried out either in a dry state in the absence of added hygroscopic or hydrophilic chemicals or in a wet state in an aqueous medium in which hydrophilic additives, eg dispersing agents are either avoided or removed after use.
  • Wet ground material is subsequently dried to an extent such that the particulate material has and maintains an adsorbed moisture content not • greater than about 0.1% by weight, preferably less, based on the dry weight of the instant filler.
  • the particles of the calcium carbonate employed in the instant filler may be treated (coated) with one of the hydrophobising surface treatment agents conventionally employed in the art.
  • hydrophobising surface treatment agents conventionally employed in the art.
  • the desiccant additive may be added to the calcium carbonate product obtained in a substantially dry form after treatment with the surface treatment agent.
  • the present invention is directed to the use of the instant filler described earlier as a mineral filler in intermediate and end products containing thermoplastic polymers such as film, especially breathable film, and compositions for forming such products requiring filler loading levels greater than 10 percent by weight, and preferably more than 20 percent by weight, and more preferably at least 40 percent by weight and even up to about 75 per cent.
  • film' means a sheet or layer of material having an average thickness of not more than 250 ⁇ m. Typical thickness sizes and properties of films are described later.
  • the film may be a breathable film, ie having microscopic interconnecting pores not greater than about 30 ⁇ m in size (usually much less) . Such a film allows for example water vapour in the atmosphere on one side of the film to permeate to the atmosphere on the other side without liquid water being transmitted through the film.
  • the instant filler may comprise calcium carbonate obtained from a natural source, eg marble, chalk or limestone and subsequently processed, or may be prepared synthetically, eg by reaction of carbon dioxide with calcium hydroxide, or may be a combination of the two, ie naturally derived and synthetic material.
  • At least 95%, preferably at least 98%, by weight of the inorganic particulate material comprises calcium carbonate although minor amounts of other minerals, eg one or more of kaolin, calcined kaolin, wollastonite, bauxite, talc or mica, could also be present together with the calcium carbonate.
  • At least 95% to 99% by weight may be calcium carbonate which has been obtained in a well known way by processing naturally occurring calcium carbonate obtained from a mineral source or by chemical synthesis, eg from the reaction of carbon dioxide and lime (calcium hydroxide) .
  • the instant filler preferably has one or more of the following particle size properties which are suitable for its subsequent use in manufacture of compositions for conversion into films: (i) a mean particle size (approximately equal to the value d 50 defined below) of from 0.5 ⁇ m to lO ⁇ m, especially from 0.5 ⁇ m to 5 ⁇ m, eg from 0.8 ⁇ m to 3 ⁇ m; (ii) a particle size distribution steepness factor,- ie d 5 o ⁇ d 20 , where d 50 is the particle size value less than which there are 50% by weight of the particles, and d 2 o 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; (iii) 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 lO ⁇ m, desirably less than 8 ⁇ m;
  • Dispersibility in a hydrophobic polymeric medium may be measured in a manner well known to those skilled in the art using the standard procedure specified in 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. The following recipe is used for testing:
  • the above ingredients are weighed into a dispersion container with an inside diameter of 7.5cm and a height of 6.5cm.
  • the dispersion is effected by means of a rapidly operating stirrer at 5000rpm using a toothed dissolver disc with a diameter of 4.0cm. After a stirring time of 15 minutes the particle fineness obtained is determined by grindometer as specified in ISO 1524.
  • the instant filler has a total surface moisture content which is less than 0.1% by weight even after exposure for 40 hours at 20°C to a moist atmosphere having a relative humidity of 80%.
  • the surface moisture content is less than 0.1% by weight even after exposure for 40 hours at 20°C to an atmosphere having a relative humidity of 97%.
  • minimising the surface moisture content in this way especially the level of trapped moisture when the instant filler is surface coated, allows the instant filler to be used in compositions having high filler content loadings by compounding with a thermoplastic polymeric material and other optional ingredients even after storing in a moist atmosphere.
  • the instant filler may be obtained from a natural mineral source it may have been processed eg by known purification, comminution and particle size classification procedures to have a suitable form prior to use to form the instant filler, eg to have the particle size properties described earlier. However, in such processing the use of hygroscopic or hydrophilic additives is desirably avoided as described earlier.
  • the instant filler may be treated with a hydrophobising surface treatment agent prior to use by addition to thermoplastic polymeric material.
  • the hydrophobising agent sometimes * referred to as antagonising agent, may be added directly to the thermoplastic polymer with which the instant filler is to be compounded, before, during or after addition of the instant filler. Where a hydrophobising agent is to be added, we prefer, for maximising the effect of the hydrophobising agent, surface treatment of the instant filler prior to addition to the thermoplastic polymer.
  • Suitable surface treatment agents are known to include aliphatic carboxylic acids and salts and esters thereof, especially fatty acids having from 10 to 24 carbon atoms in their chain, eg stearic acid, palmitic acid, montanic acid and mixtures thereof, and coupling agents, eg organosilanes, organotitanates and zircoaluminates .
  • the production route employed for the inorganic particulate material to which the desiccant is to be added to produce the material according to the first aspect of the invention may be selected from the many procedures known to those skilled in the art to produce calcium carbonate.
  • the route selected may involve comminution of the calcium carbonate, by grinding and if so the grinding is preferably carried out without the use of hydrophilic chemical additives or if such additives are employed they are preferably subsequently removed, eg by washing.
  • grinding of the inorganic particulate material may be carried out in an aqueous medium.
  • the wet grinding of the carbonate, where employed, may be done either by autogenous grinding or by ball milling and/or by stirred media grinding. In autogenous grinding, the particles of the carbonate ore itself act as the grinding media.
  • the feed to the autogenous grinders is the various quarry run ore.
  • Stirred media grinding uses hard, eg ceramic or graded sand, media usually having particles larger than the particles to be ground.
  • stirred media grinding starts with a finer feed from a classification step. Grinding and optional particle size classification may for example be used to obtain the particle size properties described earlier.
  • the calcium carbonate from which the instant filler is to be produced may be washed, dewatered and dried to leave not more than about 0.10 per cent by weight surface moisture content associated with the material. This dewatering/drying procedure may be carried out using one or more known steps.
  • the calcium carbonate particles are to be surface treated with a hydrophobising surface treatment agent
  • the calcium carbonate particles preferably carry substantially no surface moisture, or at most 0.10% by weight, desirably at most 0.08% by weight, at the point the particles are contacted by the surface treatment agent.
  • Such surface moisture occupies particulate surface space which and therefore prevents a complete particulate coating by the surface treatment agent to be obtained.
  • the particles of the calcium carbonate are preferably coated by a substantially * complete chemisorbed monolayer coating of the surface treatment agent.
  • the surface treatment of the carbonate preferably is carried out in a substantially dry atmosphere, eg containing a surface treatment agent as a liquid (eg as droplets) in a vessel heated indirectly, eg by a heating jacket, eg containing a heating fluid, eg heating oil.
  • a substantially dry atmosphere eg containing a surface treatment agent as a liquid (eg as droplets) in a vessel heated indirectly, eg by a heating jacket, eg containing a heating fluid, eg heating oil.
  • the temperature of the atmosphere in the vessel in which surface treatment using a hydrophobising surface treatment agent is carried out is 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 exits from that region at about 80°C, desirably about 120°C, or more, eg 150°C or more.
  • the residence time of the calcium carbonate in the vessel may be greater than 2 seconds. The residence time may range from about 50 to about 1000 seconds, eg 50 seconds to 500 seconds.
  • the surface treatment agent is stearic acid or a mixture of fatty acids containing stearic acid, eg technical grade stearic acid which typically consists of about 65% by weight stearic acid and about 35% by weight palmitic acid.
  • Other unsaturated fatty acids which may be used to produce calcium carbonates which may be used in accordance with the invention may be selected from the group consisting of capric acid, lauric acid, montanic acid, myristic acid, isostearic acid and cerotic acid and mixtures of two or more of these acids and stearic acid and/or graded stearic acids.
  • the surface treatment agent preferably is a hydrophobising agent which becomes chemisorbed onto the carbonate particles in order to facilitate dispersion of the carbonate in the polymeric thermoplastic material.
  • the presence of a hydrophilic agent is undesirable and only very minute traces of a hydrophilic component are tolerable on the calcium carbonate to be treated with the surface treatment agent .
  • the amount of surface treatment agent which is present in the heated atmosphere in which the carbonate is to be contacted by and treated with the agent is not substantially greater than the maximum theoretical amount of the agent which can become bonded by chemisorption to the carbonate. This maximum theoretical amount is dependent on the surface area of the particles of the carbonate.
  • an appropriate weight of surface treatment agent applied is 1.5% by weight or less, based on the dry weight of the coated material.
  • a suitable amount of surface treatment agent is that required to coat or slightly undercoat or not substantially overcoat the carbonate.
  • the amount required depends on the surface treatment agent employed, as explained earlier.
  • the amount is preferably in the range of from about 1.0% to about 1.4% based on the dry weight of the carbonate.
  • the instant filler is dried to a total surface moisture level not exceeding 0.10 weight percent, and preferably less than 0.08 weight percent, based on the dry weight of the instant filler.
  • the surface moisture level is within these specified limits both immediately preceding and following surface coating.
  • the surface moisture level may be measured in a known manner by a Karl Fischer titration apparatus or by a microbalance.
  • the inorganic particulate material of the instant filler is a ground calcium carbonate product produced by either a dry grinding process or a wet grinding process as described hereinbefore, but it may also be a precipitated calcium carbonate product.
  • the calcium carbonate product optionally coated with a surface treatment agent is preferably substantially dry, eg has a surface adsorbed moisture content of less than 0.1% by weight, when it is added to the desiccant additive.
  • the inorganic particulate material and desiccant additive for use in producing the instant filler may be blended together, eg by intimate mixing, prior to use of the material as a filler together with a polymeric material, although it could alternatively be blended with the desiccant at the point of mixing filler with the polymeric material.
  • the polymeric material to which the instant filler is added to form a high loading (ie greater than 10%) composition may comprise, for example, a continuous thermoplastic polymer matrix when the carbonate filler is added therein or thereto, eg a film or coating.
  • the instant filler may be incorporated in an application composition (to form an intermediate or end product) together with a thermoplastic polymeric material and other optional conventional additives, eg a bonding or tackifying agent.
  • the process employed to form the product from the thermoplastic material and the instant filler may be one or more of the methods well known in the art as described later.
  • the instant filler has been found to work extremely well as a filler in producing intermediate product compositions together with thermoplastic polymers and other optional ingredients, especially products made from polyolefin based polymers and end products produced therefrom such as cast film, blown film, and extrusion coatings using the instant filler in such applications an especially superior dispersion and extrusion performance, particularly with respect to homogeneity of the film produced and beneficially and surprisingly freedom from voids even at high filler solids.
  • the low associated free moisture content of the instant filler allows the instant filler to be incorporated into film formulations 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 having other desirable properties as described later, using known processes, eg using cast or blown film, or extrusion coating processes.
  • 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 will form from 30% to 80% by weight of the composition, ie combination of the polymer plus filler.
  • the polymer preferably comprises more than 50 per cent by weight of olefin units and is referred to as polyolefin resin.
  • the resins which can be used to provide the polyolefin resin 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- ⁇ -olefin copolymer) , 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.
  • 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.
  • polyethylene resins are preferable, and linear low-density polyethylene (ethylene- ⁇ -olefin copolymer) and low-density polyethylene are most preferable.
  • the melt index of the polyolefin resin is preferably in the range of about 0.5 to 5g/10 min.
  • the filler includes at least 50% by weight, eg from 80% to 99% by weight of the instant filler, where one or more other fillers are employed together with the instant filler.
  • the other fillers include calcium carbonate, barium sulphate, calcium sulphate, barium carbonate, magnesium hydroxide, aluminium hydroxide, zinc oxide, magnesium oxide, titanium oxide, silica and talc.
  • the average particle diameter of the other filler is preferably 20 ⁇ m or less, more preferably lO ⁇ m or less, most preferably in the range of 0.5 to 5 ⁇ m.
  • the other filler may be subjected to a surface treatment and has minimal surface moisture.
  • a surface treatment agent having a function of covering the surfaces of the inorganic filler to render these surfaces hydrophobic, may be used.
  • the surface treatment agent include higher fatty acids such as stearic acid and lauric acid, and metallic salts thereof.
  • the composition ratio between the thermoplastic polymeric material, eg polyolefin resin and the filler has an influence on the mouldability and the stretchability of the film as well as the breathability and the moisture vapour transmission of the obtained film. If the amount of the filler is insufficient, adjacent micropores, which are required to be obtained by the interfacial separation of the polyolefin resin and the inorganic filler from each other, are not continuous, so that a porous film having the good gas breathability and moisture vapour transmission cannot be obtained. On the contrary, if the amount of the filler is excessive, defective moulding occurs during the film forming process and the stretchability deteriorates, so that the sufficient stretching cannot be carried out.
  • the amount of the filler is excessive, defective moulding occurs during the film forming process and the stretchability deteriorates, so that the sufficient stretching cannot be carried out.
  • the composition ratio between the polyolefin resin and the inorganic filler may be from 25 to 70 parts by weight of the polyolefin resin with respect to from 75 to 30 parts by weight of the filler, eg from 30 to 60 parts by weight of the polyolefin resin with respect to 70 to 40 parts by weight of the filler.
  • a blend or masterbatch of the thermoplastic polyolefin resin and the filler, including the instant filler may first be produced by mixing and compounding prior to the film production stages.
  • the mixture of ingredients to be blended by compounding may include in addition to the resin and the filler other known optional ingredients employed in thermoplastic films, eg one or more of bonding agents, plasticisers, lubricants, anti-oxidants, ultraviolet absorbers, dyes, colourants.
  • a bonding or tackifying agent where employed may facilitate bonding of the film after formation to another member, eg a non-woven fibrous layer, or one or more non-porous layers.
  • the polyolefin resin, the filler and if necessary, other optional additives may be mixed by the use of a suitable compounder/mixer eg a Henschel mixer, a super mixer, a tumbler type mixer or the like, and kneaded and may be pelletized, eg by the use of a single screw extruder or a twin-screw extruder which forms strands which may be cut or broken into pellets.
  • a suitable compounder/mixer eg a Henschel mixer, a super mixer, a tumbler type mixer or the like
  • kneaded and may be pelletized eg by the use of a single screw extruder or a twin-screw extruder which forms strands which may be cut or broken into pellets.
  • the masterbatch or blend eg in the form of pellets, is melted and moulded into a film by the use of a known moulding and film forming machine.
  • the film may be a blown film, cast film or extruded film.
  • Other types of films are also considered to be within the scope of the present invention provided the forming technique is compatible with filled films.
  • the film as initially formed may be generally too thick and too noisy as it tends to make a "rattling" sound when shaken and the film does not yet have a sufficient degree of breathability as measured by its water vapour transmission rate. Consequently, the film may be heated, eg to a temperature of about 5°C less than the melting point of the thermoplastic polymer or more, and then stretched to at least about 1.2 times, preferably at least 2.5 times, its original length to thin the film and make it porous.
  • An additional feature of the thinning process is the change in opacity of the film.
  • the film As formed, the film is relatively transparent but after stretching, it becomes opaque. In addition, while the film becomes orientated during the stretching process, it also becomes softer and it does not have the degree of "rattle" that it does prior to stretching. Taking all these factors into consideration, and the desire to have a water vapour transmission rate of at least 100 grams per square metre per 24 hours, the film should be thinned to such an extent that it has a weight per unit area of less than about 35 grams per square metre for personal care absorbent article applications and more desirable less than about 18 grams per square metre.
  • the moulding and film forming machine may for example comprise an extruder equipped with a T-die or the like or an inflation moulding machine equipped with a circular die.
  • the film production may be carried out at some time after the masterbatch production, possibly at a different manufacturing plant. In some cases, the masterbatch can directly be formed into the film without producing an intermediate product, eg by pelletizing.
  • the film can be stretched in at least a uniaxial direction at a temperature of from room temperature to the softening point of the resin in a known manner such as a roll method or a tenter method to bring about the interfacial separation of the polyolefin resin and the inorganic filler from each other, whereby a porous film can be prepared.
  • the stretching may be carried out by one step or by several steps.
  • Stretch magnification determines film breakage at high stretching as well as breathability and the moisture vapour transmission of the obtained film, and so excessively high stretch magnification and excessively low stretch magnification are desirably avoided.
  • the stretch magnification is preferably in the range of 1.2 to 5 times, more preferably 1.2 to 4 times in at least a uniaxial direction.
  • biaxial stretching it is possible that for example stretching in a first direction is applied in the machine direction or a direction perpendicular thereto, and stretching in a second direction is then applied at right angles to the first direction.
  • the biaxial stretching may be carried out simultaneously in the machine direction and the direction perpendicular thereto.
  • Either method can be applied in making the film in the method according to the third aspect of the present invention.
  • the heat setting treatment may be, for example, a heat setting treatment at a temperature in the range of from the softening point of the resin to a temperature less than the melting point of the resin for a period of 0.1 to 100 seconds.
  • the thickness of the porous film produced by the method according to the third aspect of the present invention should be such as to obtain film unlikely to tear or break and which has appropriate softness and good feel.
  • the thickness of the porous film is in the range of 5 ⁇ m to lOO ⁇ m, preferably lO ⁇ m to
  • a film is "breathable" if it has a water vapour transmission rate of at least 100g/m 2 /24 hours as calculated using the test method described in US-A-5695868. Generally, once the film is formed, it will have a weight per unit area of less than about 100 grams per square metre and after stretching and thinning its weight per unit area will be less than about 35 grams per square metre and more desirably less than about 18 grams per square metre.
  • the porous film can be suitably utilised in applications requiring softness, for example, as the backing sheet of disposable diapers. No particular restriction is put on the lower limit of the softness, but it is usually about 20mm.
  • the porous film prepared by the method according to the second aspect of the present invention having such properties may have a suitable breathability, moisture vapour transmission and feeling as well as excellent mechanical properties and long-term adhesives properties. Therefore, the porous film can be suitably used in products such as disposable diapers, body fluid absorbing pads and bed sheets; medical materials such as surgical gowns and base materials for hot compress; clothing materials such as jumpers, rainwear; building materials such as wallpapers and waterproof materials for roofs and house wraps; packaging materials for packaging desiccants, dehumidifying agents, deoxidizers, insecticides, disposable body warmers; packaging materials for keeping the freshness of various articles and foods; separators for the cells; and the like.
  • products such as disposable diapers, body fluid absorbing pads and bed sheets; medical materials such as surgical gowns and base materials for hot compress; clothing materials such as jumpers, rainwear; building materials such as wallpapers and waterproof materials for roofs and house wraps; packaging materials for packaging desiccants, dehumidifying agents, deoxidizers, insecticides
  • the porous film is particularly desirable as a material used in products such as the disposable diapers and body fluid absorbing pads which can for example be set and fixed by securing tapes (eg pressure-sensitive adhesive tape) .
  • the porous film may also be formed into a composite or laminate in one of the ways well known in the art with one or more other layers, eg a non-woven fibrous layer, by an adhesive or bonding agent.
  • a pre-blended mixture was formed of a ground calcium carbonate product and 2% by weight of calcium oxide.
  • a further mixture was then formed of the mixture together with a linear low density polyethylene in a compounder.
  • the mixture consisted of 50% by weight of the polyethylene and 50% of the calcium carbonate plus calcium oxide.
  • the calcium carbonate was a product produced by a wet grinding process and had the following properties:
  • CaC0 3 content 98.0% by weight of mineral MgC0 3 content 1.8% by weight of mineral stearic acid coating 1% by weight a particle size distribution as follows:
  • This product has a surface moisture content after exposure in an initially dry form to a moist atmosphere having a relative humidity of 50%, at a temperature of 20°C for a period of 1.5 hours, of 0.15% by weight (the change of weight being measured by a microbalance) .
  • the polyethylene was the product known by the trade designation STAMYLEX 1026F which is especially suitable for cast film production.
  • the carbonate/polyethylene blend was then formed into a masterbatch composition in the compounder using a die temperature of 220°C.
  • Samples of cast unstretched film were then produced from this masterbatch composition using a Betol BK32 Lab Scale Extruder plus three roll stack using a temperature of 265°C. Films having suitable physical properties and without undesirable macroscopic holes or voids were successfully produced. Such films could be uniaxially or biaxially stretched to produce breathable films.

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Abstract

An inorganic particulate material containing at least 95 % by weight calcium carbonate suitable for use as a mineral filler in the manufacture of thermoplastic film products which inorganic particulate material is in the form of a composition in which it is mixed together with a desiccant additive present in an amount which is not greater than 10 % by weight based on the weight of the inorganic particulate material.

Description

CARBONATES FOR THERMOPLASTIC FILM AND PROCESS OF MANUFACTURE THEREOF
BACKGROUND OF THE INVENTION 1. Field Of The Invention
The present invention relates to a particulate calcium carbonate, for use with a polymer composition for producing a polymer based end product, eg film product, which may have a high mineral film loading. In particular, the present invention relates to a carbonate with an unusually low surface moisture level and the processing and use of this carbonate.
2. Description Of Related Art Inorganic particulate materials are used as fillers in end products comprising compositions incorporating thermoplastic polymers, such as film products. Such films, porous or non-porous, are manufactured for a number of consumer products such as garbage bags, backing materials or outer covers on diapers, bandages, training pants, sanitary napkins, surgical drapes, and surgical gowns. The compositions from which these films are made may include two basic components, the first being a thermoplastic polymer, usually a predominantly linear polyolefin polymer such as a linear low density polyethylene and the second being an inorganic particulate filler such as calcium carbonate. A third component, namely a bonding or tackifying agent may often be present. These components are mixed and compounded together to form a compound or concentrate which is formed (usually in a subsequent process) into a film layer using any one of a variety of film-producing processes known to those of ordinary skill in the film making art including casting, or blowing, or may be laid down on a substrate such as paper or board in a process known as extrusion coating. After the film is fabricated into its desired form, and if the film is to be a porous breathable film, the film can then be stretched, uniaxially or biaxially, by any of the well-known techniques in the art including by hydraulics, by pinch rolls moving at different rates, or by tentering.
Filler loading levels determine to a great extent how far the precursor film must be stretched to attain a given degree of overall porosity. Below a lower end of the loading range, the pores are less numerous and less interconnected, and therefore, the film is less permeable at a given draw ratio than when a higher filler loading is employed. Above a higher end of the loading range, either the materials will not blend « uniformly or the sheet made from the composition will not stretch. The preferred loading in some applications, such as that in manufacturing the microporous film of US Patent Nos 5,008,296 and 5,011,698, is very high, eg 60% to 75% by weight of the composition, with the filler preferably being a calcium carbonate.
US Patent No 4,698,372 discloses a microporous polymeric film having good water vapour transmission rates and hydrostatic resistance to water penetration thereof. The film has a filler loading of 25-35 volume % of inorganic fillers such as calcium carbonate, among others, and uses an "antagonizer" such as stearic acid in order to reduce the effective surface tension of the filler to the approximate level of that of the matrix polymer.
US Patent No 3,903,234 discloses gas permeable biaxially oriented film prepared from compositions of polyolefins containing 26% to 50% by weight of inorganic filler particles.
US Patent No 4,176,148 discloses microporous oriented films composed of polybutene containing 3% to 80% by weight of inorganic fillers. US Patent Nos 5,376,445, 5,695,868, and 5,733,628 disclose breathable film or film laminates or composites which may or may not consist of fillers. If the moisture level within the film forming composition becomes significant, it may be difficult to prepare a film compound and/or to form a film from the compound with a smooth surface which is free from voids. A smooth surface which is free from voids is necessary to enable the film to be stretched uniformly, a process which is generally employed in the production of breathable and other films.
The aforesaid US Patent Nos 5,008,296 and 5,011,698 teach a method of maintaining the moisture level of a melt blended composition below 700 parts per million (ppm) and preferably below 300 ppm by cooling the extruded strands and/or pellets composed of polymer plus filler, which are used in the film composition using flowing air or employing vacuum-drying. However this additional processing step is time consuming and costly. Conventionally in the film making art, usage levels of a mineral filler, such as a ground calcium carbonate, in a host material have been less than 20% loading. In certain applications requiring higher loadings greater than 20%, we have found that conventional calcium carbonate filler materials are unlikely to provide a successful product if made in a conventional manner. Stated in another way, conventional filler products of calcium carbonate, have not been designed in the prior art to have a surface moisture level which facilitates moisture minimisation when used in thermoplastic polymer composition for film applications, especially for breathable films and for making compositions for preparing such films.
SUMMARY OF THE INVENTION
The purpose of the present invention is to provide a mineral filler comprising calcium carbonate particulate material, which has properties allowing a film end product comprising a thermoplastic polymeric material together with the filler to be easily and successfully produced with filler loadings of at least 10 per cent by weight, preferably at least 20 per cent by weight, and, surprisingly, in some cases at least 40 per cent by weight and in some cases even up to 75% by weight. Fillers produced in a conventional manner would in many cases be unsuccessful in producing such film products without the application of special time consuming and costly additional processing steps during or after the formation of the composition (compound, masterbatch or blend) of filler plus thermoplastic polymer to be employed to produce the film. We have found that the production and use of a calcium carbonate particulate mineral filler having a reduced moisture level and a low susceptibility to pick up surface moisture can surprisingly be achieved and improves the quality of the filler and the intermediate and final product in which it is used thereby enhancing the preparation of these products. Less processing is required or processing is facilitated in manufacturing the composition comprising the thermoplastic material plus filler and the final product, especially when a breathable film of high filler solids content is to be produced therefrom. We have found that a moisture content above but not below a minimum level (which we have determined) associated with the calcium carbonate mineral filler used in the composition for manufacturing a polymer film product can result in unwanted macroscopic size voids or holes (ie several mm in length) forming in the film as a result of steam generation whilst the thermoplastic polymer of the film is in the plastic melt phase. We have shown that in order to avoid such undesirable voids or holes the moisture content of the filler should desirably be • limited to or preferably below the specified minimum level at all times before use in producing the composition with the polymer. Although reducing the moisture content of particulate materials has been described previously, the minimisation of adhered surface moisture of a filler for use in producing a high filler loaded composition for fabrication into a breathable film has not previously been suggested in the film making art.
According to the present invention in a first aspect there is provided an inorganic particulate material containing at least 95% by weight of calcium carbonate suitable for use as a mineral filler in the manufacture of thermoplastic film products wherein the inorganic particulate material is in the form of a composition wherein the inorganic particulate material is mixed together with a desiccant additive which forms not more than 10% by weight, usually less than 5% by weight, eg 0.1% to 3% by weight based on the dry weight. of the inorganic particulate material. Conveniently, the desiccant may itself comprise an inorganic particulate material, especially an oxide of one or more elements of Group II of the Periodic Table. Preferred desiccants are calcium oxide and zinc oxide, especially calcium oxide.
According to the present invention in a second aspect, there is provided the use of a particulate material as a mineral filler in high filler loading applications in the preparation of a film product and which particulate material comprises the material according to the first aspect.
The material according to the first aspect of the present invention will be referred to herein as the* ^instant filler' . Desirably, the total surface adhered moisture level of the instant filler is less than 0.1% by weight even after exposure to an atmosphere of 80% or more relative humidity for 40 hours at a temperature of 20°C. According to the present invention in a third aspect, there is provided the use of a particulate material as a mineral filler in high filler loading applications in the preparation of a film product and which particulate material comprises particles of the instant filler.
The instant filler may comprise a calcium carbonate product obtained from a mineral source and processed by refining and treatment processes including grinding to obtain a suitable particle size distribution. Alternatively, the calcium carbonate product may be chemically synthesised in a known way. The desiccant additive may be added after processing including drying of the calcium carbonate product. In order to help to satisfy the requirement that the instant filler has a low surface moisture content its particles may be essentially free of hygroscopic or hydrophilic chemicals used in the processing of the instant filler prior to addition of the desiccant additive. The grinding process where employed may be carried out either in a dry state in the absence of added hygroscopic or hydrophilic chemicals or in a wet state in an aqueous medium in which hydrophilic additives, eg dispersing agents are either avoided or removed after use. Wet ground material is subsequently dried to an extent such that the particulate material has and maintains an adsorbed moisture content not • greater than about 0.1% by weight, preferably less, based on the dry weight of the instant filler.
The particles of the calcium carbonate employed in the instant filler may be treated (coated) with one of the hydrophobising surface treatment agents conventionally employed in the art. However, we have found that it is desirable to treat the material with the surface treatment agent in a manner in which the amount of surface moisture when the surface treatment agent is added and therefore can become entrapped is minimised and that a significant surface moisture is not introduced to the particulate material during treating, eg as described later. The desiccant additive may be added to the calcium carbonate product obtained in a substantially dry form after treatment with the surface treatment agent.
FURTHER DESCRIPTION OF THE INVENTION
The present invention is directed to the use of the instant filler described earlier as a mineral filler in intermediate and end products containing thermoplastic polymers such as film, especially breathable film, and compositions for forming such products requiring filler loading levels greater than 10 percent by weight, and preferably more than 20 percent by weight, and more preferably at least 40 percent by weight and even up to about 75 per cent. In this specification film' means a sheet or layer of material having an average thickness of not more than 250μm. Typical thickness sizes and properties of films are described later. The film may be a breathable film, ie having microscopic interconnecting pores not greater than about 30μm in size (usually much less) . Such a film allows for example water vapour in the atmosphere on one side of the film to permeate to the atmosphere on the other side without liquid water being transmitted through the film.
The instant filler may comprise calcium carbonate obtained from a natural source, eg marble, chalk or limestone and subsequently processed, or may be prepared synthetically, eg by reaction of carbon dioxide with calcium hydroxide, or may be a combination of the two, ie naturally derived and synthetic material. At least 95%, preferably at least 98%, by weight of the inorganic particulate material comprises calcium carbonate although minor amounts of other minerals, eg one or more of kaolin, calcined kaolin, wollastonite, bauxite, talc or mica, could also be present together with the calcium carbonate. At least 95% to 99% by weight may be calcium carbonate which has been obtained in a well known way by processing naturally occurring calcium carbonate obtained from a mineral source or by chemical synthesis, eg from the reaction of carbon dioxide and lime (calcium hydroxide) .
The instant filler preferably has one or more of the following particle size properties which are suitable for its subsequent use in manufacture of compositions for conversion into films: (i) a mean particle size (approximately equal to the value d50 defined below) of from 0.5μm to lOμm, especially from 0.5μm to 5μm, eg from 0.8μm to 3μm; (ii) a particle size distribution steepness factor,- ie d5o÷d20, where d50 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; (iii) 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 lOμm, desirably less than 8μm;
(iv) a dispersibility in hydrophobic polymeric media as measured by Hegman gauge value, of 20μm or less, desirably 13μm or less;
(v) a specific surface area of from 3g.rrf2 to δg.rrf2 as measured by the BET nitrogen absorption method. All particle size values as specified herein are measured 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 Micromeritics Corporation, USA.
Dispersibility in a hydrophobic polymeric medium may be measured in a manner well known to those skilled in the art using the standard procedure specified in 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. The following recipe is used for testing:
42.5 parts by weight alkyd resin with linoleic oil base with 68% oil content, 70% solution in white spirit;
12.0 parts by weight white spirit; 1.5 parts by weight Calcium Naphthenate (4 weight % calcium) ;
120.0 parts by weight particulate carbonate filler to be tested.
176.0 parts by weight
The above ingredients are weighed into a dispersion container with an inside diameter of 7.5cm and a height of 6.5cm. The dispersion is effected by means of a rapidly operating stirrer at 5000rpm using a toothed dissolver disc with a diameter of 4.0cm. After a stirring time of 15 minutes the particle fineness obtained is determined by grindometer as specified in ISO 1524. Desirably, the instant filler has a total surface moisture content which is less than 0.1% by weight even after exposure for 40 hours at 20°C to a moist atmosphere having a relative humidity of 80%.
Desirably, the surface moisture content is less than 0.1% by weight even after exposure for 40 hours at 20°C to an atmosphere having a relative humidity of 97%. We have found that minimising the surface moisture content in this way, especially the level of trapped moisture when the instant filler is surface coated, allows the instant filler to be used in compositions having high filler content loadings by compounding with a thermoplastic polymeric material and other optional ingredients even after storing in a moist atmosphere. We have found that although compounding may be carried out with prior art fillers having a higher surface moisture content use of the instant filler allows easier processing to take place which is not critically dependent on the design of the compounding apparatus employed, eg requiring an evacuation system associated with the compounder having a special efficiency to ensure extraction of moisture and other volatiles, especially when operating at high filler loadings. Furthermore, film products, especially breathable film products, can be successfully produced therefrom in a known manner with a low reject rate. In contrast, other fillers not having such a low surface moisture content may make processing to produce film products difficult to control and the reject rate is likely to be higher. Breathable film products will usually have to be rejected if they contain macroscopic voids or holes through which liquid water can pass. Such defects are usually caused by use of a conventional filler having a surface moisture content which has not been suitably controlled, especially a trapped surface moisture content which has not been suitably controlled and minimised during surface coating.
Where the instant filler has been obtained from a natural mineral source it may have been processed eg by known purification, comminution and particle size classification procedures to have a suitable form prior to use to form the instant filler, eg to have the particle size properties described earlier. However, in such processing the use of hygroscopic or hydrophilic additives is desirably avoided as described earlier. Desirably, the instant filler may be treated with a hydrophobising surface treatment agent prior to use by addition to thermoplastic polymeric material. Alternatively, the hydrophobising agent, sometimes * referred to as antagonising agent, may be added directly to the thermoplastic polymer with which the instant filler is to be compounded, before, during or after addition of the instant filler. Where a hydrophobising agent is to be added, we prefer, for maximising the effect of the hydrophobising agent, surface treatment of the instant filler prior to addition to the thermoplastic polymer.
Use of surface treatment agents, which, when added to the inorganic particulate material which is dry, facilitate dispersion of the inorganic particulate material in hydrophobic polymeric material are well known.
Suitable surface treatment agents are known to include aliphatic carboxylic acids and salts and esters thereof, especially fatty acids having from 10 to 24 carbon atoms in their chain, eg stearic acid, palmitic acid, montanic acid and mixtures thereof, and coupling agents, eg organosilanes, organotitanates and zircoaluminates .
The production route employed for the inorganic particulate material to which the desiccant is to be added to produce the material according to the first aspect of the invention may be selected from the many procedures known to those skilled in the art to produce calcium carbonate.
The route selected may involve comminution of the calcium carbonate, by grinding and if so the grinding is preferably carried out without the use of hydrophilic chemical additives or if such additives are employed they are preferably subsequently removed, eg by washing. For example, grinding of the inorganic particulate material may be carried out in an aqueous medium. The wet grinding of the carbonate, where employed, may be done either by autogenous grinding or by ball milling and/or by stirred media grinding. In autogenous grinding, the particles of the carbonate ore itself act as the grinding media. The feed to the autogenous grinders is the various quarry run ore.
Stirred media grinding uses hard, eg ceramic or graded sand, media usually having particles larger than the particles to be ground. Usually stirred media grinding starts with a finer feed from a classification step. Grinding and optional particle size classification may for example be used to obtain the particle size properties described earlier. Following such grinding, the calcium carbonate from which the instant filler is to be produced may be washed, dewatered and dried to leave not more than about 0.10 per cent by weight surface moisture content associated with the material. This dewatering/drying procedure may be carried out using one or more known steps.
Where the calcium carbonate particles are to be surface treated with a hydrophobising surface treatment agent, the calcium carbonate particles preferably carry substantially no surface moisture, or at most 0.10% by weight, desirably at most 0.08% by weight, at the point the particles are contacted by the surface treatment agent. Such surface moisture occupies particulate surface space which and therefore prevents a complete particulate coating by the surface treatment agent to be obtained. Desirably, the particles of the calcium carbonate are preferably coated by a substantially * complete chemisorbed monolayer coating of the surface treatment agent.
The surface treatment of the carbonate preferably is carried out in a substantially dry atmosphere, eg containing a surface treatment agent as a liquid (eg as droplets) in a vessel heated indirectly, eg by a heating jacket, eg containing a heating fluid, eg heating oil.
As described in our affiliate's WO 9928050, the temperature of the atmosphere in the vessel in which surface treatment using a hydrophobising surface treatment agent is carried out is 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 exits from that region at about 80°C, desirably about 120°C, or more, eg 150°C or more. The residence time of the calcium carbonate in the vessel may be greater than 2 seconds. The residence time may range from about 50 to about 1000 seconds, eg 50 seconds to 500 seconds.
Preferably, the surface treatment agent is stearic acid or a mixture of fatty acids containing stearic acid, eg technical grade stearic acid which typically consists of about 65% by weight stearic acid and about 35% by weight palmitic acid. Other unsaturated fatty acids which may be used to produce calcium carbonates which may be used in accordance with the invention may be selected from the group consisting of capric acid, lauric acid, montanic acid, myristic acid, isostearic acid and cerotic acid and mixtures of two or more of these acids and stearic acid and/or graded stearic acids.
The surface treatment agent preferably is a hydrophobising agent which becomes chemisorbed onto the carbonate particles in order to facilitate dispersion of the carbonate in the polymeric thermoplastic material. The presence of a hydrophilic agent is undesirable and only very minute traces of a hydrophilic component are tolerable on the calcium carbonate to be treated with the surface treatment agent . Desirably, as described in the Copending
Application, the amount of surface treatment agent which is present in the heated atmosphere in which the carbonate is to be contacted by and treated with the agent is not substantially greater than the maximum theoretical amount of the agent which can become bonded by chemisorption to the carbonate. This maximum theoretical amount is dependent on the surface area of the particles of the carbonate.
Typically, an appropriate weight of surface treatment agent applied is 1.5% by weight or less, based on the dry weight of the coated material.
It has been shown and described in the Copending Application that a suitable amount of surface treatment agent is that required to coat or slightly undercoat or not substantially overcoat the carbonate. The amount required depends on the surface treatment agent employed, as explained earlier. For an agent containing at least 60% by weight stearic acid, for example, the amount is preferably in the range of from about 1.0% to about 1.4% based on the dry weight of the carbonate.
The instant filler is dried to a total surface moisture level not exceeding 0.10 weight percent, and preferably less than 0.08 weight percent, based on the dry weight of the instant filler. Preferably, the surface moisture level is within these specified limits both immediately preceding and following surface coating. The surface moisture level may be measured in a known manner by a Karl Fischer titration apparatus or by a microbalance.
Preferably, the inorganic particulate material of the instant filler is a ground calcium carbonate product produced by either a dry grinding process or a wet grinding process as described hereinbefore, but it may also be a precipitated calcium carbonate product. The calcium carbonate product optionally coated with a surface treatment agent, is preferably substantially dry, eg has a surface adsorbed moisture content of less than 0.1% by weight, when it is added to the desiccant additive.
The inorganic particulate material and desiccant additive for use in producing the instant filler may be blended together, eg by intimate mixing, prior to use of the material as a filler together with a polymeric material, although it could alternatively be blended with the desiccant at the point of mixing filler with the polymeric material.
The polymeric material to which the instant filler is added to form a high loading (ie greater than 10%) composition may comprise, for example, a continuous thermoplastic polymer matrix when the carbonate filler is added therein or thereto, eg a film or coating.
The instant filler may be incorporated in an application composition (to form an intermediate or end product) together with a thermoplastic polymeric material and other optional conventional additives, eg a bonding or tackifying agent.
The process employed to form the product from the thermoplastic material and the instant filler may be one or more of the methods well known in the art as described later.
The instant filler has been found to work extremely well as a filler in producing intermediate product compositions together with thermoplastic polymers and other optional ingredients, especially products made from polyolefin based polymers and end products produced therefrom such as cast film, blown film, and extrusion coatings using the instant filler in such applications an especially superior dispersion and extrusion performance, particularly with respect to homogeneity of the film produced and beneficially and surprisingly freedom from voids even at high filler solids. The low associated free moisture content of the instant filler allows the instant filler to be incorporated into film formulations 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 having other desirable properties as described later, using known processes, eg using cast or blown film, or extrusion coating processes.
According to the present invention in a fourth aspect, 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 will form from 30% to 80% by weight of the composition, ie combination of the polymer plus filler. The polymer preferably comprises more than 50 per cent by weight of olefin units and is referred to as polyolefin resin.
The resins which can be used to provide the polyolefin resin, 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 copolymer) , 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 copolymer) 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. Desirably, the filler includes at least 50% by weight, eg from 80% to 99% by weight of the instant filler, where one or more other fillers are employed together with the instant filler. Examples of the other fillers include calcium carbonate, barium sulphate, calcium sulphate, barium carbonate, magnesium hydroxide, aluminium hydroxide, zinc oxide, magnesium oxide, titanium oxide, silica and talc. The average particle diameter of the other filler is preferably 20μm or less, more preferably lOμm or less, most preferably in the range of 0.5 to 5μm. In order to improve the dispersibility of the other filler in the polyolefin resin, the other filler may be subjected to a surface treatment and has minimal surface moisture. A surface treatment agent having a function of covering the surfaces of the inorganic filler to render these surfaces hydrophobic, may be used. Examples of the surface treatment agent include higher fatty acids such as stearic acid and lauric acid, and metallic salts thereof.
The composition ratio between the thermoplastic polymeric material, eg polyolefin resin and the filler has an influence on the mouldability and the stretchability of the film as well as the breathability and the moisture vapour transmission of the obtained film. If the amount of the filler is insufficient, adjacent micropores, which are required to be obtained by the interfacial separation of the polyolefin resin and the inorganic filler from each other, are not continuous, so that a porous film having the good gas breathability and moisture vapour transmission cannot be obtained. On the contrary, if the amount of the filler is excessive, defective moulding occurs during the film forming process and the stretchability deteriorates, so that the sufficient stretching cannot be carried out. In view of these limiting factors, "the composition ratio between the polyolefin resin and the inorganic filler may be from 25 to 70 parts by weight of the polyolefin resin with respect to from 75 to 30 parts by weight of the filler, eg from 30 to 60 parts by weight of the polyolefin resin with respect to 70 to 40 parts by weight of the filler. In the manufacture of a breathable film by the method according to the third aspect of the invention a blend or masterbatch of the thermoplastic polyolefin resin and the filler, including the instant filler, may first be produced by mixing and compounding prior to the film production stages.
The mixture of ingredients to be blended by compounding may include in addition to the resin and the filler other known optional ingredients employed in thermoplastic films, eg one or more of bonding agents, plasticisers, lubricants, anti-oxidants, ultraviolet absorbers, dyes, colourants. A bonding or tackifying agent where employed may facilitate bonding of the film after formation to another member, eg a non-woven fibrous layer, or one or more non-porous layers.
The polyolefin resin, the filler and if necessary, other optional additives, may be mixed by the use of a suitable compounder/mixer eg a Henschel mixer, a super mixer, a tumbler type mixer or the like, and kneaded and may be pelletized, eg by the use of a single screw extruder or a twin-screw extruder which forms strands which may be cut or broken into pellets.
The masterbatch or blend, eg in the form of pellets, is melted and moulded into a film by the use of a known moulding and film forming machine.
The film may be a blown film, cast film or extruded film. Other types of films are also considered to be within the scope of the present invention provided the forming technique is compatible with filled films. The film as initially formed may be generally too thick and too noisy as it tends to make a "rattling" sound when shaken and the film does not yet have a sufficient degree of breathability as measured by its water vapour transmission rate. Consequently, the film may be heated, eg to a temperature of about 5°C less than the melting point of the thermoplastic polymer or more, and then stretched to at least about 1.2 times, preferably at least 2.5 times, its original length to thin the film and make it porous.
An additional feature of the thinning process is the change in opacity of the film. As formed, the film is relatively transparent but after stretching, it becomes opaque. In addition, while the film becomes orientated during the stretching process, it also becomes softer and it does not have the degree of "rattle" that it does prior to stretching. Taking all these factors into consideration, and the desire to have a water vapour transmission rate of at least 100 grams per square metre per 24 hours, the film should be thinned to such an extent that it has a weight per unit area of less than about 35 grams per square metre for personal care absorbent article applications and more desirable less than about 18 grams per square metre.
The moulding and film forming machine may for example comprise an extruder equipped with a T-die or the like or an inflation moulding machine equipped with a circular die. The film production may be carried out at some time after the masterbatch production, possibly at a different manufacturing plant. In some cases, the masterbatch can directly be formed into the film without producing an intermediate product, eg by pelletizing.
The film can be stretched in at least a uniaxial direction at a temperature of from room temperature to the softening point of the resin in a known manner such as a roll method or a tenter method to bring about the interfacial separation of the polyolefin resin and the inorganic filler from each other, whereby a porous film can be prepared. The stretching may be carried out by one step or by several steps. Stretch magnification determines film breakage at high stretching as well as breathability and the moisture vapour transmission of the obtained film, and so excessively high stretch magnification and excessively low stretch magnification are desirably avoided. The stretch magnification is preferably in the range of 1.2 to 5 times, more preferably 1.2 to 4 times in at least a uniaxial direction. If biaxial stretching is carried out, it is possible that for example stretching in a first direction is applied in the machine direction or a direction perpendicular thereto, and stretching in a second direction is then applied at right angles to the first direction. Alternatively, the biaxial stretching may be carried out simultaneously in the machine direction and the direction perpendicular thereto.
Either method can be applied in making the film in the method according to the third aspect of the present invention.
After the stretching, a heat setting treatment may be carried out if required in order to stabilise the shape of obtained voids. The heat setting treatment may be, for example, a heat setting treatment at a temperature in the range of from the softening point of the resin to a temperature less than the melting point of the resin for a period of 0.1 to 100 seconds.
No particular restriction is put on the thickness of the porous film produced by the method according to the third aspect of the present invention. The thickness should be such as to obtain film unlikely to tear or break and which has appropriate softness and good feel. Usually, the thickness of the porous film is in the range of 5μm to lOOμm, preferably lOμm to
70μm.
For purposes of the present invention, a film is "breathable" if it has a water vapour transmission rate of at least 100g/m2/24 hours as calculated using the test method described in US-A-5695868. Generally, once the film is formed, it will have a weight per unit area of less than about 100 grams per square metre and after stretching and thinning its weight per unit area will be less than about 35 grams per square metre and more desirably less than about 18 grams per square metre. The porous film can be suitably utilised in applications requiring softness, for example, as the backing sheet of disposable diapers. No particular restriction is put on the lower limit of the softness, but it is usually about 20mm. The porous film prepared by the method according to the second aspect of the present invention having such properties may have a suitable breathability, moisture vapour transmission and feeling as well as excellent mechanical properties and long-term adhesives properties. Therefore, the porous film can be suitably used in products such as disposable diapers, body fluid absorbing pads and bed sheets; medical materials such as surgical gowns and base materials for hot compress; clothing materials such as jumpers, rainwear; building materials such as wallpapers and waterproof materials for roofs and house wraps; packaging materials for packaging desiccants, dehumidifying agents, deoxidizers, insecticides, disposable body warmers; packaging materials for keeping the freshness of various articles and foods; separators for the cells; and the like. The porous film is particularly desirable as a material used in products such as the disposable diapers and body fluid absorbing pads which can for example be set and fixed by securing tapes (eg pressure-sensitive adhesive tape) . In addition, the porous film may also be formed into a composite or laminate in one of the ways well known in the art with one or more other layers, eg a non-woven fibrous layer, by an adhesive or bonding agent.
Embodiments of the present invention will now be described by way of example only with reference to the following Example.
EXAMPLE 1
A pre-blended mixture was formed of a ground calcium carbonate product and 2% by weight of calcium oxide. A further mixture was then formed of the mixture together with a linear low density polyethylene in a compounder. The mixture consisted of 50% by weight of the polyethylene and 50% of the calcium carbonate plus calcium oxide. The calcium carbonate was a product produced by a wet grinding process and had the following properties:
CaC03 content 98.0% by weight of mineral MgC03 content 1.8% by weight of mineral stearic acid coating 1% by weight a particle size distribution as follows:
Figure imgf000027_0001
This product has a surface moisture content after exposure in an initially dry form to a moist atmosphere having a relative humidity of 50%, at a temperature of 20°C for a period of 1.5 hours, of 0.15% by weight (the change of weight being measured by a microbalance) . This represents a product having a medium moisture pick-up susceptibility. The polyethylene was the product known by the trade designation STAMYLEX 1026F which is especially suitable for cast film production.
The carbonate/polyethylene blend was then formed into a masterbatch composition in the compounder using a die temperature of 220°C.
Samples of cast unstretched film were then produced from this masterbatch composition using a Betol BK32 Lab Scale Extruder plus three roll stack using a temperature of 265°C. Films having suitable physical properties and without undesirable macroscopic holes or voids were successfully produced. Such films could be uniaxially or biaxially stretched to produce breathable films.
Similar processing of the same calcium carbonate product described above together with the same polyethylene was attempted several times without the presence of the CaO desiccant in the mixture used in the compounder which contained CaC03 and polyethylene mixed in a 50:50 weight ratio basis and it was not possible to produce suitable films from the compounded masterbatch composition thereby formed. The corresponding products produced in the same way as that using CaO together with the calcium carbonate contained numerous macroscopic holes or voids and were therefore not useful.
This demonstrates the benefit of using material embodying the first aspect of the invention in the compounding and film formation.

Claims

1. An inorganic particulate material containing at least 95% by weight calcium carbonate suitable for use as a mineral filler in the manufacture of thermoplastic film products which inorganic particulate material is in the form of a composition in which is it mixed together with a desiccant additive present in an amount which is not greater than 10% by weight based on the weight of the inorganic particulate material.
2. A material according to claim 1 and wherein the desiccant additive is present in the composition in an amount of from 0.1% to 3% by weight based on the weight of the inorganic particulate material.
3. A material according to claim 1 or claim 2 and wherein the desiccant additive is an inorganic particulate material.
4. A material according to claim 3 and wherein the desiccant additive comprises the oxide of one or more elements of Group II of the Periodic Table.
5. A material according to any one of the preceding claims and wherein the desiccant comprises calcium oxide or zinc oxide.
6. A material according to any one of the preceding claims and wherein the inorganic particulate material is coated with a hydrophobising surface treatment agent .
7. A method of preparing an inorganic particulate material according to any one of the preceding claims which includes mixing with a substantially dry, powdered inorganic particulate material containing at least 95% by weight of calcium carbonate a desiccant additive present in an amount of not more than 10% by weight based on the weight of the inorganic particulate material.
8. A method according to claim 7 and wherein the inorganic particulate material to which the desiccant is added has a coating of a hydrophobising surface treatment agent.
9. A method according to claim 7 and wherein the coating comprises less than 1.5% by weight, based on the dry weight of the coated material, of a fatty acid.
10. A method of use of the material according to any one of claims 1 to 6 which includes compounding the material together with a thermoplastic polymeric material.
11. A method as claimed in claim 10 and which includes forming the composition formed by the compounding into a film product.
12. A method as claimed in claim 11 and wherein the film product is a breathable film.
PCT/GB1999/002614 1998-08-27 1999-08-09 Carbonates for thermoplastic film and process of manufacture thereof WO2000012434A1 (en)

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Cited By (1)

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Publication number Priority date Publication date Assignee Title
EP3510120A4 (en) * 2016-09-12 2020-05-27 Imerys USA, Inc. Carbonate compositions and methods of use thereof

Citations (3)

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Publication number Priority date Publication date Assignee Title
JPS6179620A (en) * 1984-09-28 1986-04-23 Dainippon Printing Co Ltd Porous film
EP0352802A2 (en) * 1988-07-27 1990-01-31 Hercules Incorporated Breathable microporous film and method for making it
EP0854164A1 (en) * 1997-01-16 1998-07-22 Royal Packaging Industries Van Leer N.V. Polymeric microporous films and a method for their making

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JPS6179620A (en) * 1984-09-28 1986-04-23 Dainippon Printing Co Ltd Porous film
EP0352802A2 (en) * 1988-07-27 1990-01-31 Hercules Incorporated Breathable microporous film and method for making it
EP0854164A1 (en) * 1997-01-16 1998-07-22 Royal Packaging Industries Van Leer N.V. Polymeric microporous films and a method for their making

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Publication number Priority date Publication date Assignee Title
EP3510120A4 (en) * 2016-09-12 2020-05-27 Imerys USA, Inc. Carbonate compositions and methods of use thereof

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