2. Description of related prior art In the prior art film products, porous or non-porous, are manufactured for and widely used in a number of consumer applications such as backsheet 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 or more basic components; the first being a thermoplastic polymer, usually a predominantly linear polyolefin polymer or a blend of polyolefins, such as a linear low density polyethylene and a low density polyethylene, and the second being an inorganic particulate filler, such as calcium carbonate. Other components, especially heat stabilizers, and a bonding or tackifying agent, may also be present. These components are mixed and melt compounded together to form a compound or concentrate having the composition required of an end film product.

It is usual for the compound or concentrate to be produced as an intermediate product, e. g. as extruded pellets which are suitable for supply to a user, viz a film producer, at a later date in a different location. The compound or concentrate is formed into a film by the user using any one of a variety of film-producing processes known to those of ordinary skill in the film making art including

casting, blowing, or deposition on a substrate such as paper or board, the process being 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.

For breathable films, the 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 U. S. Patent Nos.

5,008,296 and 5,011,698, is very high, e. g. 60% to 75% by weight of the composition with the filler preferably being a calcium carbonate.

U. S. Patent No. 4,698,372 discloses a micro-porous 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.

U. S. Patent No. 3,903,234 discloses gas permeable biaxially orientated film prepared from compositions of

polyolefins containing 26% to 50% by weight of inorganic filler particles.

U. S. Patent No. 4,176,148 discloses microporous orientated films composed of polybutene containing 3% to 80% by weight of inorganic fillers.

U. S. 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.

There may be several drawbacks in the manufacture of films, especially porous, breathable films having a high filler loading, eg at least 40% by weight, in some instances much higher, when these films are made in a conventional manner as that described herein above which involves the use of a pre-formed compound or concentrate with a required film composition. For example, generally, the film producer uses the same composition to form a film as that produced by the compounder without adjusting the composition. It may not be evident that the composition produced by the compounder may successfully be formed into a film until this composition is later used by the film producer. Unsuitable compositions can lead to serious defects in the film produced, e. g. macroscopic voids or holes, or streaking, and such defects generally require discarding and/or rejection of the end film product. Other defects may be seen in the form of decomposition of the end film products due to poor thermal stability of the compound.

SUMMARY OF THE INVENTION According to the present invention, a method of manufacturing a film product comprising a thermoplastic

polymeric material and an inorganic particulate material comprises the following steps: (a) forming a molten, homogeneously blended composition by mixing and heating together Components 1 and 2 as follows: Component 1: a thermoplastic film-forming polymeric material; Component 2: granules or pellets of a filler-in-binder concentrate comprising inorganic particulate material (filler) particles bonded together by a thermoplastic polymeric binder, the inorganic particulate material forming at least 80% by weight of the concentrate; and (b) forming the molten composition directly into a film product by a process including shaping and stretching.

The polymeric material of Component 1 and the binder of Component 2 may be the same or different materials. In many cases, especially in preferred embodiments described later, these materials will be different since the purpose of the binder is to bind together the particles in the concentrate of Component 2 whereas the purpose of the polymeric material of Component 1 is to form the main stretchable matrix of the film product. However, both materials will contribute to the thermoplastic polymeric material of the melt to be formed into a film product. During the mixing and heating of Components 1 and 2 the inorganic particulate material or filler of Component 2 will become uniformly dispersed throughout the polymeric matrix comprising the blend of polymeric materials from Components 1 and 2.

Components 1 and 2 may both initially be in the form of granules or pellets. These Components 1 and 2 may be added together before being heated to melt and blend them. Other additives in pelletized form may also be added at this

point. Alternatively, one of these two Components 1 and 2 may be formed into a melt prior to addition thereto of the other Component. In either case, Components 1 and 2 are intimately mixed and the heating to form the melt may be applied in a known manner, e. g. in a compounder, blender, or extruder. Formation of a film product from the molten composition thereby produced may be carried out in a known manner, e. g. in one of the ways described herein below.

The melt produced from Components 1 and 2 is formed directly into a film product. This means that the melt is not allowed to cool substantially to form an intermediate cooled, solid product having the same composition as that required of the final film product. Such an intermediate product is conventionally produced in the prior art as described herein above for use in another (user) plant at a later time.

The ratio by weight of Component 1 to Component 2 in the melt formed from these two components may be in the range of from about 15: 85 to about 85: 15, depending on the composition required for the end film product to be produced therefrom. The melt may incorporate one or more other optional components of the kind known for use in film forming compositions, eg as described herein below. Either or both of Components 1 and 2 may incorporate one or more of the optional additives required to be included in the melt composition. Desirably, Component 1 comprises at least 90% by weight, e. g. 95% to 100% by weight, thermoplastic polymeric material. Preferably, Component 2 comprises from 3% to 20%, e. g. 8% to 15k by weight, of the polymeric binder.

The method according to the present invention shows some benefits not obvious over conventional film producing methods employed in the prior art. These are: 1) formulation flexibility via rapid change in mineral content leading to various levels of micro-porosity; and 2) reduction in the need for pre-drying of the compound prior to extrusion which is carried out in order to eliminate a problem known as"lensing", and especially, a reduction in the cost of manufacturing such film since the cost of compounding pre-prepared compound or concentrate is reduced significantly.

DESCRIPTION OF THE INVENTION In the method according to the invention, Components 1 and 2, as defined herein above, are formed into a melt composition which is then formed directly into an end film product.

The use of granules comprising a concentrate of an inorganic particulate material, e. g. calcium carbonate, together with a polymeric thermoplastic binder, for incorporation into a base thermoplastic composition to produce a filled, thermoplastic end product is known, e. g. from CA-A-2,016,447, and improvements to such granules are described in W095/17441. The present invention takes advantage of such granules as a convenient medium, Component 2, for use by a film producer for producing a film forming composition by addition to the base thermoplastic polymer, Component 1 in a controlled, uniform manner.

The inorganic particulate material of Component 2 may comprise one or more of the materials well known for use as fillers or extenders in plastics materials. For example, it

may comprise a white inorganic particulate pigment or filler selected from alkaline earth metal carbonates, especially calcium carbonate, kaolin, calcined kaolin, wollastonite, bauxite, talc, and mica. The inorganic particulate material may contain a small amount, e. g. up to 10% by weight (based on the weight of the inorganic particulate material), of a coating material or additive, which is known to facilitate intimate mixing and contacting of the inorganic material with plastics materials. In this instance, the binder of the granule may be a latex or a surface treatment coating, such as a fatty acid or derivative thereof. Preferably, although not essentially, the inorganic particulate material comprises an alkaline earth metal carbonate, eg calcium carbonate, magnesium carbonate, calcium magnesium carbonate or barium carbonate. Such a carbonate may be obtained from a natural source, e. g. marble, chalk, limestone or dolomite and subsequently processed, or may be prepared synthetically, e. g. by reaction of carbon dioxide with an alkaline earth metal hydroxide, eg calcium hydroxide, or may be a combination of the two, i. e. a naturally derived material and synthetic material. Preferably, at least 95%, and more preferably, at least 99%, by weight of the inorganic particulate material comprises alkaline earth metal carbonate. At least 95% to 99W by weight may be calcium carbonate which may be obtained in a well known way by processing naturally occurring calcium carbonate obtained from a mineral source or by chemical synthesis, for example, from carbon dioxide and lime.

Where the inorganic particulate material has been obtained from a natural mineral source it may have been processed e. g. by known purification, comminution, and

particle size classification procedures to have a suitable form prior to use in the granule. For example, where the material comprises calcium carbonate, at least 30%, preferably, at least 40%, by weight of the particles of the material have a size (equivalent spherical diameter as measured by sedimentation in the manner described later) of less than 10ym, e. g. at least 40% by weight may be less than 7ym, especially less than 5ym.

Preferably, the inorganic particulate material of Component 2, especially if an alkaline earth metal carbonate, is treated with a hydrophobizing surface treatment agent prior to use in the production of the binder containing granules.

The use of surface treatment agents on inorganic particulate material in dry form is known to facilitate dispersion of the inorganic particulate material in hydrophobic polymeric material.

Suitable surface treatment agents include carboxylic acids, salts, and esters thereof, especially fatty acids having from 10 to 24 carbon atoms in their chain, e. g. stearic acid, behenic acid, palmitic acid, montanic acid and mixtures thereof, and coupling agents, e. g. organosilanes, organotitanates and zircoaluminates.

The amount of surface treatment agent present may be up to 2% by weight based on the dry weight of the inorganic particulate material present.

The term"granule"as used herein is intended to refer to the individual discrete components which in total comprise a particulate which as such is in use blended with the aforementioned base thermoplastic provided by Component 1. These discrete components can have irregular surface

characteristics as commonly results from granulation, or can have smooth continuous surfaces as a result of pelletization. Both of these discrete types of assemblages are intended to be encompassed herein by the term"granule".

In order to maximize the particle packing characteristics in the granules of Component 2, the particle size distribution (psd) of the filler incorporated into the granules of Component 2 may be in accordance with Equation 1 as follows: Cumulative per cent finer than D = (Dn D, n) x 100% Equation (1) D n _ D n L s where D = Particle size D. = Smallest particle size selected Dol = Largest particle size selected N = Distribution modulus; DL should be in the range of 100pm to 1.0pm; Ds in the range of 10pm to 0.01pm; and n is accorded a value appropriate for particles assumed to be approximately spherical. Preferably DL is in the range of 10ym to 2pm, Dg is in the range of 0.5ym to 0. 1pm, and n is about 0.37. The filler used in the granules or pellets may be an alkaline earth metal carbonate, such as a calcium carbonate, dolomite, magnesite or strontium carbonate, and is preferably a ground or chemically precipitated calcium carbonate, or a mixture of ground and precipitated calcium carbonates. In many applications a ground marble is found to be particularly advantageous.

The method of producing desired particle sizes may be by comminution and/or particle size classification of naturally occurring carbonate minerals by a dry or a wet process, or by precipitation from an aqueous medium. They may be produced by a blending of components each having a different psd or from a production process which generates them naturally.

The thermoplastic bonded granules of Component 2 are typically in the size range of from lmm to 10mm, and preferably from about 2mm to about 4mm. The base thermoplastic polymeric material of Component 1 with which the granules are to be blended to produce an end product may comprise granules in the same size range.

Additional chemical materials for the purpose of preparation of the granules of Component 2 or of re- dispersion of the granules in a thermoplastic composition are not necessarily required, and thus the granules of Component 2 are preferably substantially free of a dispersing or fluidifacient additive. The granules of Component 2 may, however, include any additional functional additives which may be desired in the final thermoplastic film forming formulation.

Binders for use in the granules of Component 2, preferably, comprise an amorphous polyolefin or a highly branched polyethylene wax. Typical binders of these kinds are polypropylene homopolymers and amorphous copolymers of propylene and/or ethylene and/or butylene.

The binder used for the granules of Component 2 should be chemically and physically compatible with the base or matrix thermoplastic polymeric material of Component 1 to be used to produce the resulting end film product so that the

end film product is not significantly weakened or discolored by the presence of the binder, and does not exhibit surface bloom from migration of the granule binder to the product surface.

Among the amorphous polyolefins utilizable as binders in the granules of Component 2 are amorphous polypropylene homopolymers. These differ from conventional polypropylenes which are highly crystalline.

Amorphous copolymers of propylene and/or ethylene and/or butylene, and mixtures of copolymer with homopolymer are also effective for use in the granules of Component 2.

Highly branched polyethylene waxes suitable for use in the granules of Component 2 include preferably saturated, non-polar, synthetic hydrocarbon waxes which have been chemically neutralized. The special HULS/VEBA modification of the Ziegler low pressure polymerization of ethylene is typically used to produce the unique characteristics of this group of materials. The process confers branched-chain isoparaffinic configurations.

The granules of Component 2 may themselves be prepared in a known manner, e. g. by mixing and kneading the inorganic particulate material with other optional additives and the binder for the granules in a heated mixer or compounder, eg which is part of a batch or continuous compounding machine.

The resultant homogeneous mixture, eg in the form of one or more elongate extrudate portions, may be formed into granules by passing the mixture into a pelletizer or granulator. The resultant granules may be sized, eg by passing the granules through appropriately sized sieves or screens, eg to produce granule sizes in the range 2mm to 4mm.

The present invention is directed to the use of the melt formed by blending of Components of 1 and 2 to form film products, especially breathable film. The compositions for forming such products require filler (inorganic particulate) 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 as high as about 75 per cent.

As used herein, the term"film"means a sheet or layer of material having an average thickness of not more than 250ym. Typical thickness sizes and properties of films are described herein below. The film may be a breathable film, i. e. having microscopic interconnecting pores not greater than about 30ym 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 any liquid water being transmitted through the film. The breathability of the film may be determined by measuring the water vapour transmission rate of the film.

The inorganic particulate material of Component 2 preferably has one or more of the following particle size properties: (i) a mean particle size (approximately equal to the value dso defined below) of from 0.5m to 10ym, especially from 0.5ym to 5ym, e. g. from 0.8ym to 3ym; (ii) a particle size distribution steepness factor, i. e. d50. d20, where d50 is the particle size value less than which there are 50% by weight of the particles, and d20 is the particle size less than which there are 20% by weight of the particles, of less than 2.2, and preferably, about 1.1 to about 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 10ym, preferably, less than 8pm; (iv) a specific surface area of from about 3g. m-2 to about 6g. m-2 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.

The thermoplastic polymeric material provided by blending of Component 1 and the binder of Component 2 may form from 10% to 70% by weight and the filler will form from 30% to 80% by weight of the composition, i. e. combination of the polymer plus filler.

The polymeric material of Component 1 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 of Component 1, 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-a-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 for Component 1, with linear low-density polyethylene (ethylene-a-olefin copolymer) and low-density polyethylene being most preferable. Furthermore, in view of the extrudability and the stretchability of the film to be formed, the Melt Index of the polyolefin resin of Component 1 is preferably in the range of about 0.5 g/10 min. to about 5g/10 min.

The composition ratio between the thermoplastic polymeric material, provided by Components 1 and 2, and the filler provided by Component 2 in the melted composition to produce the required film has an influence on the extrudability and the stretchability of the film, as well as on 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"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 sufficient stretching cannot be carried out. In view of these limiting factors, the composition ratio between the thermoplastic polymeric material and the inorganic filler may be from about 25 to about 70 parts by weight of the polymeric material with respect to from about 75 to about 30 parts by weight of the filler, e. g. from about 30 to about 60 parts by weight of the polymeric material with respect to about 70 to about 40 parts by weight of the filler.

The mixture of ingredients to be blended by compounding may include, in addition to the polymeric material and the filler provided by Components 1 and 2, other known optional ingredients employed in thermoplastic films, e. g. one or more bonding or tackifying agents, plasticisers, lubricants, anti-oxidants, ultraviolet absorbers, dyes and colorants. A bonding or tackifying agent may be employed to facilitate bonding of the film after formation to another member, e. g. a non-woven fibrous or non-porous layer.

Components 1 and 2, and if necessary, other optional additives, may be mixed by the use of a suitable blender/mixer e. g. a Henschel mixer, a super mixer, or tumbler type mixer, then kneaded and/or melted, and then moulded into a film by the use of a known moulding and film forming machine.

The film may be a blown film, a cast film, or an 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 thermoplastic polymer films. The film as initially formed may be generally thick and noisy and may tend to make a"rattling" sound when shaken. Such a film does not yet have a sufficient degree of breathability as measured by its water vapour transmission rate. Consequently, the film, preferably heated to a temperature between room temperature and at least about 5°C less than the melting point of the thermoplastic polymeric material, is stretched to at least about 1.2 times, preferably at least 2.5 times, its original length in order to make the film thinner and porous.

An additional feature of the thinning process is a 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, especially for personal care absorbent article applications, and more preferably, 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 is carried out by forming the composition produced by blending together Components 1 and 2 and other optional ingredients into the film without producing an intermediate product, eg by pelletizing of the final required film forming composition.

The film can be stretched in at least a uniaxial direction at a temperature of from room temperature to the softening point of the thermoplastic polymeric material 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; therefore, excessively high stretch

magnification and excessively low stretch magnification are desirably avoided. The stretch magnification is preferably in the range of about 1.2 to about 10 times, more preferably, about 1.2 to about 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 present invention.

After the stretching, a heat setting treatment may be carried out if required in order to stabilise the shape of obtained voids in the film product. 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 thermoplastic material to a temperature less than the melting point of that material for a period of 0.1 to 100 seconds.

No particular restriction is put on the thickness of the porous film which may be produced by the method according to the invention. The thickness should be such as to obtain film unlikely to tear or break and which, where appropriate, has appropriate softness and good feel.

Usually, the thickness of a porous film so produced is in the range of 5ym to 100pm, preferably 10ym to 70pm.

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. 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 present invention having such properties may have a suitable breathability, moisture vapour transmission and"hand", as well as good mechanical properties and long-term stability.

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 disposable diapers and body fluid absorbing pads. 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, e. g. a non-

woven fibrous layer or one or more non-porous polymeric layers, by an adhesive or bonding agent or by melt bonding.

ILLUSTRATIVE EMBODIMENT An embodiment of the present invention will now be described by way of example only with reference to the following Example 1.

Example 1 A ground calcium carbonate particulate product having a DL of 7ym and a Ds of 0.2ym (DL and Ds being as defined earlier) and a mean particle size of lym is treated with 1.2wt% by weight of fatty acid comprising technical grade stearic acid in a high speed mixer running at 4000rpm for 5 minutes at a temperature of 150°C. This product is then mixed using a two roll mill at a temperature of 162°C with an amorphous polypropylene wax with a melting point of 152°C in the weight ratio of 85: 15 of treated calcium carbonate: amorphous polypropylene to form a homogeneous mixture. The resultant mixture is formed into granules by passing through a granulator and screening the resultant granulate between 5 mesh and 10 mesh screens. The granulated product thus produced which provides a concentrate of the carbonate filler, Component 2, is employed to produce a breathable film in the following manner.

The filler concentrate granules and a high strength LLDPE resin in the form of granules, Component 1, are co-fed into the receiving cavity of a compounder-film extruder together with an antioxidant concentrate.

The relative proportions of the feed materials are: Filler concentrate granules: 100 parts by weight.

LLDPE resin granules: 82 parts by weight.

Antioxidant concentrate: 3 parts by weight.

The LLDPE resin may be, for example, a blend of Dowlex 2517 linear low density polyethylene and DowlexTM 2532 linear low density polyethylene blended in a weight _ ratio of 1: 4 such that the Melt Index of the blend was 10M. L/10 minutes at 88°C. The Dowlex polymers are available from Dow Chemical USA, Midland, Michigan, U. S. A.

The antioxidant concentrate may be selected from any of the materials known to the industry.

The components are blended together at a temperature of from 160°C to 320°C and the resultant melt composition is blown into a film having a thickness of from 50ym to 100ym at a temperature of 160°C-320°C. The film is then uniaxially stretched, e. g. on a machine direction orientation machine, at a stretch ratio of about 3: 1. A breathable film, as measured by its water vapour transmission rate, suitable for use in the various consumer applications described herein above is produced.