WO2012052778A1

WO2012052778A1 - Film compositions

Info

Publication number: WO2012052778A1
Application number: PCT/GB2011/052049
Authority: WO
Inventors: John Slater
Original assignee: Imerys Minerals Limited
Priority date: 2010-10-22
Filing date: 2011-10-21
Publication date: 2012-04-26
Also published as: GB201017888D0

Abstract

The present invention describes tearable polymer films comprising a polyester and a filler, polymer compositions for making said films, methods of production and uses thereof.

Description

FILM COMPOSITIONS Field of the Invention The present invention relates to tearable polymer films, polymer compositions suitable for making said films and methods of production of said films and compositions. In particular, the tearable polymer film may be a polyester film. The present invention also relates to uses of said polymer compositions and films. Background of the Invention

Thin polymer films find utility in many different industries for the packaging of consumer products including, for example, the food packaging industry. The film needs to act as a hygienic barrier to prevent contamination of the foodstuff to be packaged, yet be amenable to processing in the food packaging plant and also easily removable by the end user.

Polymer films are also used in the production of blister packs of the type used in the packaging of pharmaceutical drugs, and are often formed as multilayer films with enhanced mechanical properties to prevent inadvertent release of the contents of the blister recess or to render the blister pack child-proof.

In such applications, the polymer film needs to be resilient enough to not be accidentally breached and yet be consumer-friendly enough that it can be easily torn or ruptured at the appropriate juncture.

Polyesters such as polyethylene terephthalate (PET) are widely used for packaging due to their gas impermeabilities, good moisture resistance and aroma retention, and general pliability, in addition to the fact that they are cheap to produce and can be recycled. However, films formed from polyesters such as PET are not easily torn, meaning that the end consumer may struggle to open the packaging. This may cause the packaging to be ripped in an uncontrolled manner thereby spilling the contents.

There is a continuing need to develop alternative, or preferably improved, polymer films, which are easily and cheaply produced, and retain the performance characteristics of existing films with regard to, for example, moisture resistance, yet are more easily torn such that packaging can be torn or opened in a more controlled manner.

Summary of the Invention

The present invention provides polymer films comprising a polyester and a filler. The polymer films are formable from polymer compositions comprising polyester resins and particulate filler. The filler may suitably be selected from inorganic fillers. Suitable fillers include, for example, mica, calcium carbonate and coated calcium carbonate. By incorporating the particulate filler, the polymer film is tearable. Typically, the particulate filler may be present in an amount from about 4wt% to about 40wt% based on the total weight of the filled film.

Accordingly, in one aspect, the present invention provides a tearable polymer film comprising a polyester and a particulate filler.

A tearable polymer film is one which may be torn by hand using reasonable force.

The filled polymer film may suitably have a trouser tear force of about 2N or less. As such, the present invention provides a tearable polymer film comprising a polyester and a particulate filler wherein the tearable polymer film has a trouser tear force of about 2N or less.

The tearable polymer film may have a maximum trouser tear force of about 3N or less, or about 2N or less, for example about 0.5 to about 3N or about 0.5 to about 2N. The tearable polymer film may have an average trouser tear force ranging from about 0.5 to about 2N. The tearable polymer film may have a median peak trouser tear force ranging from about 0.5 to about 2N. The tearable polymer film is formable from a polymer composition comprising a polyester resin and a particulate filler. As such, and in accordance with a further aspect of the present invention, there is provided a polymer composition for making the tearable polymer film in accordance with the present invention comprising a polyester resin and a particulate filler. The polymer composition may comprise a single kind of polymer resin, for example a single kind of polyester resin. The polyester resin may be a polyethylene terephthalate resin. Accordingly, the present invention also provides a tearable polyester film, for example a polyethylene terephthalate film comprising a particulate filler.

In further aspects of the present invention, there are provided methods of making the polymer films and compositions in accordance with the invention. According to a further aspect of the present invention, there is provided a production process for said polymer compositions comprising blending a polyester or precursor of polyester with a filler. The composition may then be formed into the polymer film. In addition, there is provided a method for improving the tearability of a polyester film comprising blending a polyester with a filler and forming said composition into a polymer film, wherein the trouser tear force is equal to or less than about 3N, for example equal to or less than about 2N. The term "precursor" as applied to a polymer component will be readily understood by one of ordinary skill in the art. For example, suitable precursors may include one or more of: monomers, cross-linking agents, curing systems comprising cross-linking agents and promoters, or any combination thereof. Where, according to the invention the filler is mixed with precursors of the polymer, the polymer composition may subsequently be formed by curing and/or polymerising the precursor components to form the desired polymer. The various values and ranges stated in connection with trouser tear force and/or tensile strength in the present invention are also applicable to the various methods and uses disclosed herein.

In accordance with yet a further aspect of the invention, there is provided the use of a particulate filler, for example calcium carbonate, coated calcium carbonate or mica, to reduce the trouser tear force of a polyester film.

The tearable polymer film can be suitably used in packaging products, including food packaging products and consumer packaging products. Suitable examples include cake dome bases, envelopes, pouch packages for items such as kitchen wipes and sachets such as single serving sachets.

The filler may comprise, consist of or consist essentially of mica, calcium carbonate, coated calcium carbonate, dolomite, hydrous kaolin, calcined kaolin, wollastonite, bauxite, talc, coated kaolin, for example hydrous or calcined kaolin coated with a silane, for example a vinyl silane, diatomaceous earth (DE), including combinations thereof. Hereafter, the invention may tend to be discussed in terms of calcium carbonate, and in relation to aspects where the calcium carbonate is processed and/or treated. The invention should not be construed as being limited to such embodiments.

The filler may be coated. For example, the filler may be coated with a hydrophobising surface treatment agent. In particular, the calcium carbonate may be coated. For example, the calcium carbonate may be coated with one or more aliphatic carboxylic acids having at least 10 chain carbon atoms. For example, the calcium carbonate may be coated with one or more fatty acids. The fatty acids may be selected from stearic acid, palmitic acid, behenic acid, montanic acid, capric acid, lauric acid, myristic acid, isostearic acid and cerotic acid. The coated calcium carbonate may be a stearate coated calcium carbonate.

The particulate filler may have a median equivalent particle diameter (d₅₀) ranging from about 0.5μιη to about 50pm for example about 5pm to about 40pm, for example about 10pm.

The tearable polymer film may have a machine direction maximum trouser tear force of about 3N or less, for example, about 2N or less. The tearable polymer film may have a machine direction maximum trouser tear force of about 0.5N to about 3N or for example, about 0.5N to about 2N. The tearable polymer film may have a machine direction median trouser tear force of from about 0.5N to about 2N. The tearable polymer film may have a machine direction average trouser tear force of from about 0.5N to about 2N. The polymer film may have a machine direction tensile break value of at least about 50MPa, for example at least about 55MPa. The polymer film may have a machine direction tensile break value of from about 10MPa to about 60MPa. The polymer film may have a machine direction tensile break value of at least about 50MPa, for example at least about 55MPa, when the filler comprises, consists of or consists essentially of stearate coated calcium carbonate. The polymer film may have a machine direction tensile break value of at least about 10MPa, for example at least about 10MPa or at least about 25MPa, when the filler comprises, consists of or consists essentially of mica. The tearable polymer film may have a transverse direction tensile break value of at least about 55MPa. The tearable polyester film may have a transverse direction tensile break value of from about 13MPa to about 65MPa. For example, the tearable polyester film may have a transverse direction tensile break value of at least about 55MPa when the filler comprises, consists of or consists essentially of stearate coated calcium carbonate. The tearable polymer film may have a transverse direction tensile break value of at least about 13MPa, for example at least about 13MPa or at least about 27MPa when the filler comprises, consists of or consists essentially of mica.

The polymer film may have a machine direction tensile maximum force of at least about 50N, for example at least about 70N. The polymer film may have a machine direction tensile maximum force of from about 28N to about 90N. The polymer film may have a machine direction tensile maximum force of at least about 70N, for example at least about 80N, when the filler comprises, consists of or consists essentially of stearate coated calcium carbonate. The polymer film may have a machine direction tensile maximum force of at least about 28N, for example at least about 28N or at least about 50N, when the filler comprises, consists of or consists essentially of mica.

The tearable polymer film may have a transverse direction tensile maximum force of at least about 70N. The tearable polyester film may have a transverse direction tensile maximum force of from about 27N to about 80N. For example, the tearable polyester film may have a transverse direction tensile maximum force of at least about 70N when the filler comprises, consists of or consists essentially of stearate coated calcium carbonate. The tearable polymer film may have a transverse direction tensile maximum force of at least about 27N, for example at least about 27N or at least about 50N when the filler comprises, consists of or consists essentially of mica.

The terms machine direction and transverse direction in connection with polymer films have well-understood meanings in the art. Reference to the machine direction of a film is to the (longitudinal) direction in which the film exits, for example, a casting machine or extruder. Reference to the transverse direction is to the direction perpendicular to the machine direction. Detaiied Description of the Invention

The polymer film The polymer film comprises a polyester and a particulate filler. The polymer film is formable from a polymer composition comprising polyester resin and a particulate filler. The particulate filler may be an inorganic particulate filler. The particulate filler may be a mineral filler. The polyester to be filled in accordance with the present invention may be a homopolymer or a copolymer. Polyethylene terephthalate (PET) is particularly suitable for use in accordance with the present invention. Other suitable resins include derivatives of PET, including amine, alcohol, acid, ketone, ester, fluorinated, and aromatic functionalized derivatives and physical blends and copolymers of the same.

Before use, the polyester resin may be dried until a required level of dryness is attained. For example, a polyester resin, such as a PET resin, may be dried under vacuum for about 3 days at 80°C.

The particulate filler Suitable fillers include particulate inorganic fillers. For example, mineral fillers such as calcium carbonate, mica, coated calcium carbonate, dolomite, hydrous kaolin, calcined kaolin, wollastonite, bauxite, talc, coated kaolin, for example hydrous or calcined kaolin coated with a silane, for example a vinyl silane, diatomaceous earth (DE). Other suitable fillers include those with a low moisture pick-up. The filler may be a single mineral filler or may be a blend of said mineral fillers. For example, the filler may be a blend of two or more of the mineral fillers listed herein.

The filler may be present in the polymer film in an amount from about 4wt% to about 40wt% based on the total weight of the filled film. For example, in an amount from about 4wt% to about 20wt% based on the total weight of the filled film, for example, in an amount from about 12wt% to about 20wt% based on the total weight of the filled film.

The particulate filler may have a median particle size (d₅₀) from about 0.5pm to about 50pm, for example about 5pm to about 40pm or about 0.5pm to about 5pm, for example about 0.5pm to about 2pm, e.g. about 1.5pm. For example, the particulate filler may have a d₅₀ of about 10pm.

The median equivalent particle diameter (d₅₀ value) and other particle size properties referred to herein for the particulate filler are as measured by laser light particle size analysis using a CILAS (Compagnie Industrielle des Lasers) 1064 instrument. The (CILAS) measurements use a particle size measurement as determined by laser light particle size analysis using a CILAS (Compagnie Industrielle des Lasers) 1064 instrument. In this technique, the size of particles in powders, suspensions and emulsions may be measured using the diffraction of a laser beam, based on application of the Fraunhofer theory. The term d₅₀ (CILAS) used herein is the value determined in this way of the particle diameter at which there are 50% by volume of the particles which have a diameter less than the d₅₀ value. The preferred sample formulation for measurement of particle sizes using the CILAS 1064 instrument is a suspension in a liquid. The CILAS 1064 instrument normally provides particle size data to two decimal places. Samples of the filler are dispersed in water with the aid of a sodium polyacrylate dispersant and an ultrasonic device fitted with the CILAS equipment.

The particulate calcium carbonate used in the present invention may be obtained from a natural source by grinding or may be prepared synthetically by precipitation (PCC), or may be a combination of the two, i.e. a mixture of the naturally derived ground material and the synthetic precipitated material. The PCC may also be ground.

Ground calcium carbonate (GCC) is typically obtained by grinding a mineral source such as chalk, marble or limestone, which may be followed by a particle size classification step, in order to obtain a product having the desired degree of fineness. The particulate solid material may be ground autogenously, i.e. by attrition between the particles of the solid material themselves, or alternatively, in the presence of a particulate grinding medium comprising particles of a different material from the calcium carbonate to be ground.

Wet grinding of calcium carbonate involves the formation of an aqueous suspension of the calcium carbonate which may then be ground, optionally in the presence of a suitable dispersing agent. Reference may be made to, for example, EP-A-614948 (the contents of which are incorporated by reference in their entirety) for more information regarding the wet grinding of calcium carbonate. When the filler is obtained from naturally occurring sources, it may be that some mineral impurities will inevitably contaminate the ground material. For example, naturally occurring calcium carbonate occurs in association with other minerals. Also, in some circumstances, minor additions of other minerals may be included, for example, one or more of kaolin, calcined kaolin, wollastonite, bauxite, talc or mica, could also be present. In general, however, the filler used in the invention will contain less than 5% by weight, preferably less than 1 % by weight of other mineral impurities.

PCC may be used as the source of particulate calcium carbonate in the present invention, and may be produced by any of the known methods available in the art. TAPPI Monograph Series No 30, "Paper Coating Pigments", pages 34-35 describes the three main commercial processes for preparing precipitated calcium carbonate which is suitable for use in preparing products for use in the paper industry, but may also be used in the practice of the present invention. In all three processes, limestone is first calcined to produce quicklime, and the quicklime is then slaked in water to yield calcium hydroxide or milk of lime. In the first process, the milk of lime is directly carbonated with carbon dioxide gas. This process has the advantage that no byproduct is formed, and it is relatively easy to control the properties and purity of the calcium carbonate product. In the second process, the milk of lime is contacted with soda ash to produce, by double decomposition, a precipitate of calcium carbonate and a solution of sodium hydroxide. The sodium hydroxide must be substantially completely separated from the calcium carbonate if this process is to be commercially attractive. In the third main commercial process, the milk of lime is first contacted with ammonium chloride to give a calcium chloride solution and ammonia gas. The calcium chloride solution is then contacted with soda ash to produce, by double decomposition, precipitated calcium carbonate and a solution of sodium chloride.

The process for making PCC results in very pure calcium carbonate crystals and water. The crystals can be produced in a variety of different shapes and sizes, depending on the specific reaction process that is used. The three main forms of PCC crystals are aragonite, rhombohedral and scalenohedral, all of which are suitable for use in the present invention, including mixtures thereof.

Following the grinding process, the particulate filler may have a d₅₀ in the range of about 0.5pm to about 50pm. The filler, following grinding may have a d₅₀ of less than or equal to about 50pm. The maximum size of the particles may also be dependent on the thickness of the film. The maximum size of the particles is typically less than the thickness of the film.

Optionally, the particulate filler may be coated. For example, the calcium carbonate may be coated with a hydropftobising surface treatment agent. For example, the calcium carbonate may be coated with one or more aliphatic carboxylic acids having at least 10 chain carbon atoms. For example, the calcium carbonate may be coated with one or more fatty acids. The fatty acids may be selected from stearic acid, palmitic acid, behenic acid, montanic acid, capric acid, lauric acid, myristic acid, isostearic acid and cerotic acid. The coated calcium carbonate may be a stearate coated calcium carbonate. The inventors of the present invention have found that stearate coated calcium carbonate is particularly effective at reducing the trouser tear force while maintaining tensile strength. The level of coating may be about 0.5wt% to about 1.5wt%, for example about 0.8wt% to about 1.3wt% based on the dry weight of the particulate filler.

Other suitable coated fillers include clays treated with silane. For example, the particulate filler may be a clay, such as a kaolin, which may be hydrous or calcined and which may be coated with a silane. The silane may be a vinyl silane.

The filler may be dried before being combined with the polyester resin. Typically, the filler may be dried in a conventional oven at about 80°C. The polyester may be dried in a vacuum oven at approximately 80°C. The particulate filler may be dried to an extent such that the particulate filler has and maintains an adsorbed water (or moisture) content not greater than about 0.5wt%, for example and particularly advantageously, not greater than about 0.1 wt% based on the dry weight of the particulate filler. This includes both uncoated and coated particulate fillers.

Desirably, the particulate filler, including when either coated or uncoated, is not susceptible to further substantial moisture pick-up. The particulate filler may for example have a moisture level not greater than about 0.5wt%, for example not greater than about 0.1 wt% after exposure to an atmosphere of 80% or more relative humidity for 40 hours at a temperature of 20°C. The particulate filler may be free or substantially free of hygroscopic or hydrophilic compounds. For example, during grinding of the particulate filler, the grinding may be carried out in the absence of added hygroscopic or hydrophilic compounds, or if wet ground, any dispersant employed may be minimised and/or subsequently removed from the filler in a known manner. For example, not greater than about 0.05wt% of a hydrophilic component may be present on the particulate filler based on the dry weight of the particulate filler. For example, not greater than about 0.05wt% of a dispersant, for example, a hydrophilic dispersant, may be present on the particulate filler based on the dry weight of the particulate filler. An example of such a dispersant is sodium polyacrylate. The moisture level may be measured in a known manner, e.g. by a Karl Fischer (KF) titration apparatus. In this method the water may be driven off from the sample by heating and then measured using the quantitative reaction of water with iodine. In coulometric KF titration, the sample is added to a pyridine-methanol solution (with iodine and sulphur dioxide as principal components). The iodine generated electrolytically at the anode, reacts with water. The amount of water can be directly determined from the quantity of electric charge required for electrolysis.

Additives

Optionally, the polyester film may further comprise one or more additives. Examples of useful additives include, but are not limited to, opacifying agents, pigments, colorants, slip agents, antioxidants, anti-fog agents, anti-static agents, anti-block agents, moisture barrier additives, gas barrier additives, hydrocarbon resins or hydrocarbon waxes.

Preparation of Polymer Compositions and Films The particulate filler, which may or may not have been surface treated, may be incorporated in polymer compositions and is typically present at a concentration of about 4 to 40wt% by weight of the final polymer film, for example, about 4 to 20wt%, for example, about 12 to 20wt%. The polymer composition comprises at least one polyester, which may be referred to as a polyester resin. The term resin means a polymeric material, either solid or liquid, prior to shaping into an article such as a polymer film. The polyester resin and filler material may be independently dried prior to mixing.

The polyester resin may be melted (or otherwise softened) prior to formation of the polymer film, and the polyester will not normally be subjected to any further chemical transformations. After formation of the polymer film, the polymer resin is cooled and allowed to harden.

The polymer composition may be made by methods which are well known in the art generally in which a particulate filler and a polymer resin are mixed together in suitable ratios to form a blend (so-called "compounding"). The polyester resin may be in a liquid form to enable the particles of the filler to be dispersed therein. Where the polymer resins are solid at ambient temperatures, the polymer resin may need to be melted before the compounding can be accomplished. In some embodiments, the particulate filler may be dry blended with particles of the polymer resin, dispersion of the particles in the resin then being accomplished when the melt is obtained prior to forming a film from the melt, for example in an extruder itself.

In embodiments of the invention, the polyester resin and the particulate filler and, if necessary, any other optional additives, may be formed into a suitable masterbatch by the use of a suitable compounder/mixer in a manner known per se, and may be pelletized, e.g. 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 compounder may have a single inlet for introducing the filler and the polymer resin together. Alternatively, separate inlets may be provided for the filler and the polymer resin. Suitable compounders are available commercially, for example from Coperion (formerly Werner & Pfleiderer).

The polymer compositions according to the present invention can be processed to form, or to be incorporated in, polymer films in any suitable way. Methods of making polymer films are well known to those of ordinary skill in the art and may be prepared in a conventional manner. Known methods include the use of casting, extruding and blowing processes. For example, extrusion blown film lines may be used. For those instances where combinations of polymers are used, then co-extrusion techniques may be used. Methods of co-extrusion are well known to the person of ordinary skill. Typically, two or more streams of molten polymer resin are joined into a single extrudate stream in such a way that the resins bond together but do not mix. Generally, a separate extruder is required for each stream and the extruders are linked so that the extrudates can flow together in an appropriate manner for the desired application. For making layered films, several extruders may be used in combination and fed together into a complex die that will merge each of the resin streams into a layered film or sandwich material.

The films made according to the present invention may be of a size and thickness appropriate to the final application. For example, the median thickness of the film may be about 25 to 250μηι, for example, about 50pm.

The trouser tear force is measured using a method based on Standard ISO 34. Test pieces measuring 100mm x 50mm were cut from the film by hand using a scalpel. A 65mm slit was cut along the centre line of the long axis. The films were all approximately 0.05mm thick. A Hounsfield tensile test machine was used to measure the maximum, average and median force required to tear the polymer film. The operating conditions for the tensometer are given below.

Hounsfield Tensometer Trouser Tear Test Conditions

The test gives three results: the maximum force, the average force and the median force. The maximum force is that which corresponds to the initiation of the tear, the median force is the 50^th percentile of the peak force measurements from the maximum force to the point of failure, and the average force is the arithmetic mean of the force measurements taken between the maximum force and the point of failure. In Figure 11 , the maximum force and point of failure are indicated for a cast filled PET film. The machine direction and transverse direction tensile strengths of the films are measured by cutting rectangular test pieces of thickness 0.05mm using a Messmer instruments cutter and then subjecting the test pieces to a tensile test on a Hounsfield Tensometer. The operating conditions for the tensometer are given in the table below. Both the maximum force and the tensile break value (or tensile break stress) were obtained (machine and transverse directions). The tensile break value (which may also be referred to as the tensile break stress) is the force at break divided by the unit area. The maximum force is the greatest value of force recorded in the force/extension curve. Machine direction tensile break stress is measured with the test pieces cut so that the long axis is parallel to the machine direction. Transverse direction tensile break stress is measured by testing samples that are cut so that the long axis is perpendicular to the machine direction.

Hounsfield Tensometer Tensile Strength Conditions

Brief Description of the Figures

The invention will now be described, by way of example only and without limitation, with reference to the following Figures and Examples, in which:

Figure 1 shows the effect of a stearate coated calcium carbonate filler (designated Filler A) on the trouser tear maximum force of a polyester film;

Figure 2 shows the effect of a stearate coated calcium carbonate filler (Filler A) on the median peak trouser tear force of a polyester film; Figure 3 shows the effect of a stearate coated calcium carbonate filler (Filler A) on the average trouser tear force of a polyester film;

Figure 4 shows the effect of a mica filler (designated Filler B) on the maximum trouser tear force of a polyester film;

Figure 5 shows the effect of a mica filler (Filler B) on the median peak trouser tear force of a polyester film;

Figure 6 shows the effect of a mica filler (Filler B) on the average trouser tear force of a polyester film;

Figure 7 shows the effect of a mineral filler on the machine direction tensile break value of a polyester film; Figure 8 shows the effect of a mineral filler on the machine direction tensile maximum force of a polyester film;

Figure 9 shows the effect of a mineral filler on the transverse direction break stress of a polyester film;

Figure 10 shows the effect of a mineral filler on the transverse direction tensile maximum force of a polyester film; and Figure 1 1 is a plot of force against extension (trouser tear force test) for a cast PET film including 12wt% Filler A and shows the maximum force and point of failure.

Examples Test Methods

Trouser tear force

The machine direction trouser tear force of prepared films was determined on test pieces measuring 100 x 50mm with a 65mm slit along the centre line and thickness 0.05mm. The tests were carried out on a Hounsfield Tensometer. The settings used were as follows:

Load Range = 2N;

Preload = ON;

Extension range = 200%;

Cross-head Speed = 25mm/min.

From each test piece, three measurements were made: the maximum force, the median force and the average force. The maximum force is that which corresponds to the initiation of the tear, the median force is the 50^th percentile of the peak force measurements from the maximum force to the point of failure, and the average force is the arithmetic mean of the force measurements taken between the maximum force and the point of failure. Tensile strength

The machine direction and transverse direction tensile strengths of the films were tested by cutting rectangular test pieces of thickness 0.05mm using a Messmer instruments cutter and then subjecting the test pieces to a tensile test on a Hounsfield Tensometer. The settings used were as follows:

Stress range = 200MPa;

Extension range = 200%;

Cross-head speed = 50mm/min.

Materials

Polyethylene terephthalate (PET) resin used in the preparation of the samples was a standard resin used for film production. The PET resin was dried under vacuum for 3 days at 80°C. Filler A is a stearate coated calcium carbonate with a d₅₀ (CILAS) of about 1.5pm, a moisture level of about 0.1 wt% and was obtained from Imerys Minerals Ltd. Filler B is a fine dry ground mica which was also obtained commercially from Imerys Minerals Limited (Kaolins de Bretagne). Filler B has a d₅₀ of about 50pm and a moisture level of about 0.5wt%. The fillers were dried in a conventional oven at 80°C overnight prior to being compounded into the PET.

Example 1

PET films were prepared in accordance with Table 1.

Sample Polyester Filler Loading (wt%)

Comparative PET None N/A

Sample 1 PET A 4

Sample 2 PET A 12

Sample 3 PET A 20

Sample 4 PET B 4

Sample 5 PET B 12

Sample 6 PET B 20

The filler was compounded with the polyester resin using a Baker Perkins MP 2030 twin screw compounder in accordance with Table 2. Following granulation, the filled resin was dried at 1 10°C for 2 days, after which films were cast using a Dr Collin film line fitted with a 150mm slot die under the conditions shown in Table 3. After casting, the films were conditioned for a minimum of 7 days at 23°C; 50% relative humidity (RH). The films were then subjected to the Trouser and Tensile tests.

Table 2. Baker Perkins MP 2030 twin screw compounder conditions

Table 3. Film casting conditions

Figures 1 to 3 show the results of the trouser tear tests on cast PET films comprising differing amounts of Filler A compared with an unfilled (U/F) PET film. Increasing amounts of the filler resulted in a reduced maximum trouser tear force of the film. When compared with the unfilled film, this ranged from an approximate 10% reduction in the maximum force for a 4wt% loading up to an approximate 70% reduction for the 20wt% loading. The results also indicated that the median peak trouser force and the average trouser test force decreased as the amounts of Filler A were increased.

Figures 4 to 6 show the results of the trouser tear tests on cast PET films comprising differing amounts of a mica filler (Filler B) compared with an unfilled PET film. Increasing amounts of the filler resulted in a reduced trouser tear force of the film. Figures 7 and 8 show the results of the machine direction tensile tests on cast PET films comprising differing amounts of either Filler A or Filler B. Addition of Filler A had no significant effect on the machine direction tensile strength of the PET film.

Figures 9 and 10 show the results of the transverse direction tensile tests on cast PET films comprising differing amounts of either Filler A or Filler B. Addition of Filler A had no significant effect on the transverse direction tensile strength of the PET film.

The results show that the use of Filler A in a polyester film provides reduced tear properties while retaining good tensile properties. The use of Filler B provides films with reduced tear properties and reduced tensile properties when compared with Filler A.

Claims

1. A tearable polymer film comprising a polyester and a particulate filler.

2. A tearable polymer film according to claim 1 , wherein the particulate filler is calcium carbonate or coated calcium carbonate, for example calcium carbonate coated with one or more fatty acids, wherein the fatty acids may, for example, be selected from stearic acid, palmitic acid, behenic acid, montanic acid, capric acid, lauric acid, myristic acid, isostearic acid and cerotic acid.

3. A tearable polymer film according to claim 1 , wherein the particulate filler is mica.

4. A tearable polymer film according to claim 1 or 2, wherein the particulate filler is calcium carbonate coated with stearic acid.

5. A tearable polymer film according to claim 1 , wherein the particulate filler is selected from dolomite, hydrous kaolin, calcined kaolin, wollastonite, bauxite, talc, coated kaolin, for example hydrous or calcined kaolin coated with a silane, for example vinyl silane.

6. A tearable polymer film, according to any one of claims 1 to 5, wherein the particulate filler is present in an amount of about 4wt% to about 40wt%.

7. A tearable polymer film according to claim 6, wherein the particulate filler is present in an amount of about 4wt% to about 20wt%.

8. A tearable polymer film according to any one of claims 1 to 7, wherein the particulate filler has a total moisture level of not greater than about 0.5wt%, for example not greater than about 0.1wt%, based on the dry weight of the particulate filler.

9. A tearable polymer film according to any one of claims 1 to 8, wherein the particulate filler has a moisture pick up susceptibility such that its total moisture level is not greater than about 0.5wt%, for example not greater than about 0.1wt%, after exposure to an atmosphere of 80% or more relative humidity for 40 hours at a temperature of 20°C.

10. A tearable polymer film according to any one of claims 1 to 9, wherein there is present on the particulate filler not greater than about 0.05wt% of a dispersant, for example a hydrophilic dispersant, based on the dry weight of the particulate filler.

1 1. A tearable polymer film according to any one of claims 1 to 10, wherein the polyester is polyethylene terephthalate.

12. A tearable polymer film according to any one of claims 1 to 11 , wherein the average trouser tear force is about 2N or less.

13. A tearable polymer film according to claim 12, wherein the average trouser tear force is about 0.5N to about 2N.

14. A tearable polymer film according to any one of claims 1 to 13, wherein the polymer film has a machine direction tensile break value of at least about 10MPa.

15. A tearable polymer film according to claim 14, wherein the polymer film has a machine direction tensile break value of at least about 50MPa.

16. A tearable polymer film according to any one of claims 1 to 15, wherein the polymer film has a transverse direction tensile break value of at least about 13MPa.

17. A tearable polymer film according to claim 16, wherein the polymer film has a transverse direction tensile break value of at least about 55MPa.

18. A polymer composition for making the polymer film according to any one of claims 1 to 17, wherein the composition comprises a polyester resin and a particulate filler.

19. A method for making a polymer composition according to claim 18 comprising blending a polyester or precursor of polyester with a filler.

20. A method according to claim 19, further comprising forming the polymer composition into a polymer film.

21. Use of a polymer film according to any one of claims 1 to 17 for packaging.

22. Use according to claim 21 for packaging food.