WO2005026252A1

WO2005026252A1 - Surface-modified fillers for polymer resin compositions

Info

Publication number: WO2005026252A1
Application number: PCT/GB2004/003962
Authority: WO
Inventors: Howard Goodman
Original assignee: Imerys Minerals Ltd
Priority date: 2003-09-16
Filing date: 2004-09-16
Publication date: 2005-03-24
Also published as: GB0321703D0

Abstract

A surface-modified filler, comprising a particulate filler selected from alkaline earth metal carbonates and hydroxides of aluminiurn and magnesium or mixtures thereof, wherein the surfaces of the particles of the filler are modified with a plurality of amine, thiol or hydroxyl groups, or mixtures thereof, provided that the amine, thiol or hydroxyl groups are not provided solely by 11-aminoundecanoic acid or 6-aminocaproic acid.

Description

SURFACE-MODIFIED FILLERS FOR POLYMER RESIN COMPOSITIONS

Field of Invention

[0001] The present invention relates to certain particulate fillers, the surfaces of which have been modified in such a way that the filler is compatible with and therefore readily dispersible in polymer resin compositions which include a polar group in the polymer structure, such as polyamide resin compositions. The invention also relates to processes for the production of the surface-modified filler, to polymer resin compositions comprising the filler, methods for making the compositions, and to articles made from the polymer resin compositions. The invention is in particular concerned with surface coated alkaline earth metal carbonates, such as calcium carbonate, and surface coated hydroxides of aluminium and magnesium.

Background of the Invention

[0002] Clay mineral fillers which have been surface-modified using silanes are known as fillers for polyamides. One such material which is commercially available is Polarite 102A which is a calcined and silane-treated kaolin intended for polyamide applications. Compounding a polyamide with this surface-modified kaolin enhances the stiffness and high-temperature properties of the polymer without excessively affecting toughness or ductility.

[0003] As an alternative to clay minerals as particulate fillers in polymer resin compositions, it is also known to use particulate calcium carbonate, as well as other alkaline earth metal carbonates. These may be surface treated with stearic acid which results in the hydrophobicity of the surface increasing. Such stearate coated calcium carbonates are, however, not readily suitable for use in polar polymer resins such as polyamides. With a view to improving the compatibility of a range of fillers, including calcium carbonate fillers, in various polymer systems, it has been proposed in US-A- 4960816 (the content of which is hereby incorporated by reference in its entirety) to modify the surface of the filler by carrying out a polymerization in situ, whereby the polymer formed at the surface of the filler may be the same as the polymer into which the filler is to be dispersed. One example given is to modify the surfaces of particulate calcium carbonate to produce a polyamide coating which is compatible with a polyamide resin in which the filler is to be used. This process is however, complicated (requiring the use of a reactive gas to accomplish the polymerization) and is thus relatively expensive.

[0004] In general, calcium carbonate is a less expensive filler material than a clay mineral filler; it would therefore be desirable to be able to identify an alternative approach to that proposed in US-A-4960816, to enable a particulate calcium carbonate to be used effectively as the filler material in polymer resins such as polyamides, and to retain and even improve upon the advantageous properties provided by silane treated clay mineral fillers such as Polarite 102A. [0005] Hydroxides of aluminium and magnesium, for example alumina trihydrate (ATH; AI(OH)₃) and Mg(OH)₂ are well known fillers for fire retardant polymeric resin compositions. These fillers may be surface treated with, for example, organic acids such as stearic acid (US-4098762 and US 4420341 , the contents of which are hereby incorporated by reference in their entirety). [0006] The present invention is based on the finding that, when certain particulate filler materials or filler compositions comprising certain particulate filler materials, such as calcium carbonate, are treated with an agent which adheres to the surface of the particles and which additionally provides a plurality of free amine, hydroxyl or thiol groups, in particular the particles may be modified with an amino acid or an aminophosphate, the result is a surface-treated filler material which is compatible with polymer resin compositions having polar groups in the polymer structure, such as polyamide resins, and additionally provides articles which are formed from the filled polymer with good mechanical properties. Furthermore, such surface coated fillers give a lower viscosity melt which is expected to improve the injection moulding process and reduce gate marking (characterized as white rough marks on the surface of injection-moulded articles).

Summary of the Invention

[0007] Thus, according to a first aspect of the present invention there is provided a surface-modified filler, comprising a particulate filler selected from alkaline earth metal carbonates and hydroxides of aluminium and magnesium or mixtures thereof, wherein the surfaces of the particles of the filler are modified with a plurality of amine, thiol or hydroxyl groups, or mixtures thereof, provided that the amine, thiol or hydroxyl groups are not provided solely by 11-aminoundecanoic acid or 6-aminocaproic acid. In preferred embodiments, the surfaces of the particles are modified with a plurality of amine groups.

[0008] According to a second aspect of the present invention, there is provided a polymer resin composition comprising a polymer resin; and a surface-modified filler dispersed in the resin, wherein the surface-modified filler comprises a particulate filler selected from alkaline earth metal carbonates and hydroxides of aluminium and magnesium or mixtures thereof and wherein the surfaces of the particles of the filler are modified with a plurality of amine, thiol or hydroxyl groups, or mixtures thereof, and wherein the polymer is one which includes polar functional groups capable of hydrogen bonding with the amine, thiol or hydroxyl groups on the surface of the filler. [0009] According to a third aspect of the present invention, there is provided an article formed from the polymer resin composition of the second aspect of the present invention. For example, the polymer resin composition may be used to produce moulded automotive parts such as wheel discs and underbonnet components. The polymer resin may also be used to form articles which have fire retardant properties, particularly where the filler material is a hydroxide of aluminium or magnesium. [0010] The surface-treated filler of the first aspect of the present invention may be made by a method in which a particulate filler selected from alkaline earth metal carbonates and hydroxides of aluminium and magnesium or mixtures thereof is contacted with a coating agent which is capable of adhering to the particle surfaces and which additionally includes a plurality of amine, thiol or hydroxyl groups or groups convertible to amine, thiol or hydroxyl groups, provided that the coating agent is not solely 11-aminoundecanoic acid or 6-aminocaproic acid. In the case of embodiments in which the coating agent includes a plurality of groups convertible to amine, thiol or hydroxyl groups, the method includes the further step of converting said groups to amine, thiol or hydroxyl groups.

Detailed Description of the Invention

[0011] As described above, the present invention pertains to a surface-modified, filler, in which the surfaces of the particles of the filler are modified such that they are provided with a plurality of amine, thiol or hydroxyl groups, or mixtures of one or more of such groups. The filler comprises a particulate filler selected from alkaline earth metal carbonates and hydroxides of aluminium and magnesium or mixtures thereof. The preferred groups provided on the surface of the filler are amine groups, which may be primary, secondary or tertiary amine groups, or a mixture thereof.

[0012] Modification of the surface of the particulate filler may be suitably achieved by the use of a coating agent, sometimes referred to in the art as a coupling agent. Preferably the particles are coated with a coating agent wherein the coating agent comprises a first functional group capable of binding to cationic sites on the surface of the particulate filler and a second amine, thiol or hydroxyl group (or functional group convertible to an amine, thiol or hydroxyl group), an amine group being preferred. The resulting surface-modified filler material thus comprises the particulate filler, surfaces of which are coated or otherwise provided with said coating agent. Any further treatment of the surface-modified filler material to polymerise or otherwise cross-link the coating agent on the surface of the filler particles is to be avoided as this will eliminate the desired amine, thiol or hydroxy groups.

[0013] The first functional group of the coating agent may be chosen from carboxyl and phosphate groups, of which carboxyl groups are preferred. [0014] Preferably the coating or coupling agent is an amino acid. The amino acid may be naturally occurring or non-naturally occurring and the amino acid may therefore be selected from any of the known naturally occurring amino acids, namely: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, lysine, proline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine. [0015] In particular and most preferably, when the coating agent is chosen from a naturally occurring amino acid, it is glycine.

[0016] An example of an amino acid which does not occur naturally is GABA (gamma-aminobutyric acid). [0017] The coating agent used for preparing the surface-modified filler may be one which includes one or more functional group which is convertible to an amine, thiol or hydroxyl group. For example, the amine, thiol or hydroxyl groups of the coating agent may be protected with suitable protecting groups which are removed after coating of the particulate filler has been accomplished. Suitable protecting groups will be apparent to those skilled in the art. [0018] The amount of coating agent used may be such as to provide an amount of surface amine, thiol or hydroxyl groups in the range of 0.02 to 0.08 mmol of coating agent per square metre of the particulate material to be coated and preferably of about 0.025 to 0.075 mmol of coating agent per square metre of the particulate material to be coated. This corresponds to approximately mono-layer coverage of the surfaces of the particulate filler. The actual amount of coating agent required will vary depending upon the surface area of particulate material to be coated, the molecular weight and the number of amine/thiol or hydroxyl groups in the coating agent structure. However, for amino acids like glycine having a single carboxylic group and a single amine group an amount of about 0.05 mmol of glycine per square metre of the particulate material to be coated is suitable. The surface area of the filler may be determined by the BET N₂ method.

[0019] The surface-modified filler of the present invention may be prepared by contacting the untreated particulate filler with the coating agent which is in a suitable form to permit it to mix with the .r particles and adhere to the surfaces of the particles. Thus, where the coating agent is a fluid at normal ambient temperatures (or at a suitable coating temperature), the coating agent may be applied neat. However, the coating agent will typically be used as a solution in a suitable solvent, such as water. This approach is appropriate when the coating agent is an amino acid. The concentration of coating agent in the solvent will be apparent to one skilled in the art and will depend on the solubility characteristics of the coating agent in relation to the particular solvent and to what degree the particulate filler is to be coated. Typically, the amount of solute will lie in the range of 1%-60% by weight, preferably 5%-30% by weight and more preferably 10-20% by weight. The coating agent may be dissolved in the solvent in the presence of heat and/or stirring. The solution comprising the coating agent may then be combined, in portions if necessary, with the particulate filler and mixed in a standard mixer, for example a laboratory Steele and Cowlishaw mixer. The amount used may be such as to provide the amount of coating referred to above. The application of the solution of coating agent to the filler may be carried out in the presence of heat. The mixer may be operated at any stage, i.e. before and/or during and/or after the addition of the solution of coating agent to the particulate filler and optionally in the presence of heat. As an alternative to mixing a solution of the coating agent with the particulate filler, the solution may be applied to the particles by spraying, preferably whilst the particles are tumbled or otherwise moved to expose the whole of the bulk of the particles to the spray of coating agent.

[0020] After application of the solution of the coating agent is complete and the particulate filler has been sufficiently coated, the coated filler may be dried. Typically the drying stage will last from a few seconds to a number of hours.

[0021] As an alternative approach to the use of a solution of the coating agent, preparation of the surface-modified filler may be accomplished by melting the coating agent and combining it with the particulate filler.

The particulate filler

[0022] The particulate fillers used in the present invention may be obtained from natural sources by, for example, grinding and/or, in some cases, prepared synthetically or may be a combination of the two. [0023] Suitable sources of hydroxides of aluminium include natural AI(OH)₃ - containing materials such as hydrargillite or gibbsite or synthetic aluminium hydroxides. [0024] Suitable sources of hydroxides of magnesium are natural Mg(OH)₂ - containing materials such as brucite or synthetic magnesium hydroxides. [0025] Of the alkaline earth metal carbonates, calcium carbonate and magnesium carbonate are preferred. Calcium carbonate is particularly preferred. The alkaline earth metal carbonate may also be calcium-magnesium carbonate which may be obtained from the mineral source dolomite.

[0026] 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. [0027] 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. Preferably the grinding process is carried out in a dry state ("dry grinding"), in the absence of added hygroscopic or hydrophilic chemicals. This ensures that the surfaces of the ground particles are "clean", and do not have adhering to them any of the chemicals which may be used in a wet grinding process. The surfaces of the particles are therefore in a suitable state to be directly contacted with a coating agent for preparation of the surface-modified material. By "dry grinding" herein, we mean that the grinding process is carried out in the presence of 10% or less water. Grinding agents may be used in dry grinding, examples of which include propylene, ethylene glycol or triethanolamine, typically in an amount of less than 1%. 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. Further information regarding the dry grinding of calcium carbonate may be found in, for example the following patent specifications: GB-A-1310222, GB-A-2179268, GB-A- 2190016, and EP-A-00510890, the content of each of which is incorporated by reference in its entirety.

[0028] Less preferred than dry ground calcium carbonate is a wet ground material obtained by a process in which an aqueous suspension of the naturally occurring calcium carbonate is ground 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. Although the amount of dispersing agent used can be minimized, nevertheless such wet ground material is not well suited for direct use in the present invention, and will normally require further treatment in order to remove at least a portion of the dispersing agent on the particle surfaces.

[0029] When the fillers of the present invention are obtained from naturally occurring sources, it may be that some mineral impurities will inevitably contaminate the ground fillers (whether wet or dry ground); 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 together with the filler. 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. [0030] The particulate fillers used in the present invention both before and after modification may have a d₅₀ of at least 0.1 μm, and for example may have a d₅₀ which is greater than 0.5 μm. Preferably the particulate fillers used in the present invention have a d₅₀ of less than or equal to 5 μm.

[0031] All particle size values as specified herein are measured by the well known conventional 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.

[0032] 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 by-product 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.

[0033] 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.

The precipitated calcium carbonate filler used in the present invention may have a d50 as described for the ground fillers.

Polymer resin

[0034] In accordance with the invention, the surface-modified filler is combined with a polymer resin to form a polymer composition from which a shaped article is subsequently formed. "Polymer resin" is the general term used in the plastics art to denote a polymeric material (solid or liquid) prior to shaping into a plastic article. In the case of thermoplastic polymers, the polymer resin is melted (or otherwise softened) prior to formation of an article usually, by a moulding process, and the polymer will not normally be subjected to any further chemical transformations. After formation of the shaped article, the polymer resin is cooled and allowed to harden. In the case of thermosetting polymers, the polymer resin is in a precursor state which, after shaping, is cured to obtain the final polymeric article. In the curing stage, chemical crosslinks are formed. The present invention is suited for use with polymer resins which are thermoplastic in nature or to polymer resins in which the resin is thermosetting. [0035] The polymer resin for use in the present invention is one in which the polymer molecules include polar functional groups capable of hydrogen bonding with the amine, thiol or hydroxyl groups on the surface of the particulate calcium carbonate filler. Typically, the polymer comprises polar functional groups comprising O, N or halogen atoms which are capable of hydrogen bonding to at least one of the hydrogen atoms bound to the amine, thiol or hydroxyl group on the surface of the filler. [0036] Examples of polymers which may be used in the present invention include: polyamides (or nylons), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonates, acrylonitrile butadiene styrene (ABS), ethylene vinylacetate (EVA), polyesters, epoxy resins, acrylate resins and mixtures of polycarbonate and ABS. [0037] Examples of suitable polyamides which find use in the present invention are the aliphatic polyamides including nylon 6, nylon 11 , nylon 12, nylon 6/6 and nylon 6/12; preferred are nylon 6 and 6/6. In addition, the invention may be used with aromatic polyamides (or aramids).

Preparation of the Polymer Resin Compositions

[0038] The polymer resin composition of the present invention may be made by methods which are well known in the art generally in which the surface-treated filler and the polymer resin are mixed together in suitable ratios to form a blend (so-called "compounding"). In general, the polymer resin should be in a liquid form to enable the particles of the filler to be dispersed therein. Where the polymer resin is solid at ambient temperatures, therefore, the polymer resin will need to be melted before the compounding can be accomplished. In some embodiments, the surface-modified 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 an article from the melt, for example in an extruder itself.

[0039] In embodiments of the invention, the polymer resin and the surface-modified 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 together. Alternatively, separate inlets may be provided for the filler and the polymer resin. Suitable compounders are available commercially, for example from Werner & Pfleiderer. Examples of suitable additives include pigments, antioxidants, processing aids, light stabilisers and glass fibre.

Preparation of Articles

[0040] The polymer resin compositions according to the present invention can be processed to form, or to be incorporated in, articles of commerce in any suitable way. Such processing may include compression moulding, injection moulding, gas-assisted injection moulding, calendaring, vacuum forming, thermoforming, extrusion, blow moulding, drawing, spinning, film forming, laminating or any combination thereof. Any suitable apparatus may be used, as will be apparent to one of ordinary skill in this art. [0041] The articles which may be formed from the compositions are many and varied. Examples include so-called underbonnet applications in the automotive industry (e.g. engine covers, frames for cooling fans, manifold inlets and the like), gears, shafts, impellers, wheel discs, bearings, films for vacuum systems, cooking bags, drill cases and zip fasteners.

Examples

[0042] Embodiments of the present invention will now be described by way of example only, and with reference to the Examples. Preparation of test materials

[0043] The following Examples illustrate the preparation of the test materials embodying the present invention and the comparison and control materials.

Particulate calcium carbonate

[0044] A chemical-free, ground calcium carbonate (approximate median particle size of about 1 μm) was prepared by a wet grinding process in such a way that no residual dispersant remained on the calcium carbonate. The calcium carbonate was then dried using a flash dryer fired directly from a furnace and then indirectly heated.

Comparative materials

[0045] Polarite 102A (P102A) is a calcined and aminosilane-treated kaolin. Filmlink 400 is a stearate coated ground calcium carbonate. Carbitol 110 (C110) is an uncoated ground calcium carbonate. All of the comparative materials, P102A, Filmlink 400 and C110 are commercially available from Imerys, Cornwall, England.

Example 1 (Preparation of coated particulate calcium carbonate)

[0046] 15 g of glycine (Fluka chemical, commercially available from SIGMA- ALDRICH, assay > 99%) was dissolved, using a magnetic stirrer, in 85g of water to give a 15% Solution. 1.5kg of calcium carbonate was measured into a laboratory Steele and Cowlishaw mixer and the temperature set to 60°C. Approximately 11g of the required glycine solution was added to the mixer followed by mixing for 2 minutes. This step was repeated until all of the glycine solution had been added; 32.66g of glycine solution was needed to achieve monolayer coverage. Once all of the required glycine was added the materials were then mixed for 10 minutes. The resultant product was then dried in an oven overnight at 105°C. Example 1b

[0047] Gamma amino butyric acid (GABA, i.e. piperidinic acid), commercially available from SIGMA-ALDRICH, UK as a Fluka chemical (assay > 99%), was coated onto the particulate calcium carbonate following the procedure of Example 1.

Example 2 (Preparation of the polymer rer composition)

[0048] The coated particulate calcium carbonate filler obtained from Example 1 was oven dried at 80°C overnight prior to use and mixed with fresh polyamide

(Durethan B30S (ex Bayer) nylon 6 pellets). The composition contained 30 wt% of the filler. As polyamides are hygroscopic materials they require special handling in all aspects of processing and testing. For this reason, the bag of polyamide was opened just prior to use. Any material remaining at the end of the trial was either djsoosed of, or placed in a vacuum oven for use as a purge material in subsequent injeo., n moulding trials. The compounding of the calcium carbonate filler and nylon 6 was carried out in a Baker-Perkins twin screw co-rotating compounder. The conditions used in the production of compounded filled nylon 6 were as follows:

Compounder barrel temperature profile: 200, 250, 255, 260, 265, 270/°C. Devolatilising vacuum: 0.6-0.8 bar. Screw speed: 300rpm. Torque: 40-50%.

[0049] Once compounded and pelletised, the filled nylon samples were air dried at

50°C for 24 hours and then vacuum dried at 80°C for a further 24 hours prior to injection moulding.

[0050] The conditions used in the production of injection moulded test specimens were as follows:

Injector barrel temperature profile: 240, 250, 255, 265, 265/°C. Example C1 (Preparation of comparative examples)

Test Methods

[0051] The comparative filler materials were mixed with nylon 6 according to the experimental details of Example 2. The compositions contained 30 wt% of the fillers.

Mechanical Testing

[0052] The mechanical tests on the filled polymer resins were carried out in accordance with British Safety Standard (BSS) 2782 Part III. [0053] The specific mechanical tests were carried out according to the following:

Measurement BSS

Flexural Modulus and Strength 335A

Tensile Properties (including elongation) 320A-F

Izod Impact Strength 350

Falling Weight Impact Strength 353B

[0054] Tables 1 , 2, 3, 4 and 5 compare the tensile strength, toughness, stiffness, elongation and breaking point respectively of the various samples for two different conditions. Dry as moulded indicates that the samples were stored at room temperature for two or three days prior to testing and conditioned means that the samples were stored at 23°C/50% relative humidity (RH) for fourteen days prior to testing.

Table 1 (Tensile Strength)

Table 2 (Toughness)

Table 3 (Stiffness)

Table 4 (Elongation)

Table 5 (Break point)

[0055] Table 6 compares approximate stiffness and toughness measurements for a further range of fillers at 30 wt% filler loading in nylon 6. The comparative filler materials were mixed with nylon 6 according to the experimental details of Example 2. Comparable data for the materials of the present invention may be found in Tables 2 and 3.

Table 6

Discussion

[0056] Referring to the results shown in Tables 1 to 5 the surface-modified fillers according to the present invention compare well with Polarite 102A in terms of tensile strength, stiffness, elongation and break point, whilst maintaining an acceptable performance with regard to toughness. Comparison with Filmlink 400 indicates a significantly better tensile strength and stiffness. Filmlink 400 exhibited the type of behaviour expected from an unbonded filler, namely good toughness (sometimes referred to as impact strength) but low tensile strength. Comparison of the coated particulate calcium carbonate according to the present invention with C110 indicated a generally comparable tensile strength and stiffness whilst the toughness of the coated material was significantly better. [0057] With regard to the results in Table 6, the surface-modified fillers of the present invention exhibit generally improved impact strength whilst maintaining acceptable, and, in some cases improved stiffness. [0058] The surface-modified fillers are believed to be particularly useful in the present invention for various reasons. Without wishing to be bound by any particular theory, it is believed that the thiol, amine or hydroxyl group is effectively pointing outwards with respect to the filler to which it is bound, such that it may effectively hydrogen bond with the polymer structure. [0059] The use of a surface-modified filler in accordance with the present invention offers significant cost and technical advantages in the formulation of polymer resin compositions having generally acceptable and, optionally, improved tensile strength with good stiffness, elongation, break point and acceptable toughness.

Claims

1. A surface-modified filler, comprising a calcium carbonate particulate filler, wherein the surfaces of the particles of the calcium carbonate filler are modified with a coating agent selected from an amino acid or an aminophosphate or the coating agent comprises a functional group convertible to an amine group to form said amino acid or amino phosphate, provided that the amino acid is not solely 11- aminoundecanoic acid or 6-aminocaproic acid.

2. A surface-modified filler according to claim 1 , wherein the amino acid is selected from alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, lysine, proline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine and mixtures thereof.

3. A surface-modified filler according to claim 2, wherein the amino acid is glycine.

4. A surface-modified filler according to claim 1 , wherein the amino acid is gamma- amino butyric acid (GABA).

5. A surface-modified filler according to any one of the preceding claims, wherein the calcium carbonate filler is a ground calcium carbonate (GCC).

6. A surface-modified filler according to any one of claims 1 to 4, wherein the calcium carbonate filler is a precipitated calcium carbonate (PCC).

7. A surface-modified filler according to any one of the preceding claims, wherein the calcium carbonate filler has a d₅₀ of greater than 0.1 μm.

8. A surface-modified filler according to any one of the preceding claims, wherein the calcium carbonate filler has a d₅₀ of greater than 0.5μm.

9. A surface-modified filler according to any one of the preceding claims, wherein the calcium carbonate filler has a d₅₀ of 0.1 μm to 5μm.

10. A polymer resin composition comprising a polymer resin and a surface-modified filler dispersed in the resin, wherein the surface-modified filler comprises a calcium carbonate particulate filler and wherein the surfaces of the particles of the calcium carbonate filler are modified with a coating agent selected from an amino acid or an aminophosphate or the coating agent comprises a functional group convertible to an amine group to form said amino acid or aminophosphate and wherein the polymer is one which includes polar functional groups capable of hydrogen bonding with the amine groups of the coating agent.

11. A polymer resin composition according to claim 10, wherein the amino acid is selected from alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, lysine, proline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine and mixtures thereof.

12. A polymer resin composition according to claim 11 , wherein the amino acid is glycine.

13. A polymer resin composition according to claim 10, wherein the amino acid is gamma-amino butyric acid (GABA).

14. A polymer resin composition according to any one of claims 10 to 13, wherein the calcium carbonate filler is a ground calcium carbonate (GCC).

15. A polymer resin composition according to any one of claims 10 to 13, wherein the calcium carbonate filler is a precipitated calcium carbonate (PCC).

16. A polymer resin composition according to any one of claims 10 to 15, wherein the calcium carbonate filler has a d₅₀ of greater than 0.1 μm.

17. A polymer resin composition according to any one of claims 10 to 15, wherein the calcium carbonate filler has a d₅₀ of greater than 0.5μm.

18. A polymer resin composition according to any one of claims 10 to 15, wherein the calcium carbonate filler has a d₅₀ of 0.1 μm to 5μm.

19. A polymer resin composition according to any one of claims 10 to 18, wherein the polymer is selected from polyamides, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonates, acrylonitrile butadiene styrene (ABS), ethylene vinylacetate (EVA), polyesters, epoxy resins, acrylate resins and mixtures of polycarbonate and ABS.

20. A polymer resin composition according to claim 19, wherein the polymer is a polyamide and is selected from nylon 6 or nylon 6/6.

21. An article formed from a polymer composition as claimed in any one of claims 10 to 20.

22. A proot for preparing the surface-modified filler as claimed in any one of claims 1 to 9, which comprises contacting a calcium carbonate particulate filler with a coating agent which is capable of adhering to the particle surfaces and which is selected from an amino acid or an aminophosphate or the coating agent comprises a functional group convertible to an amine group to form said amino acid or amino phosphate

23. A process according to claim 22 wherein the coating agent includes a plurality of groups convertible to amine groups and the process comprises the further step of converting said groups to amine groups.

24. A process for preparing the polymer resin composition as claimed in any one of claims 10 to 20 which comprises combining the polymer resin with the surface- modified filler.

25. A process for preparing the polymer resin composition as claimed in any one of claims 10 to 20 which comprises preparing a surface-modified filler according to claim 22 or 23 and combining said filler with the polymer resin.

26. A surface-modified filler, comprising a particulate filler selected from alkaline earth metal carbonates or mixtures thereof, wherein the surfaces of the particles of the filler are modified with a coating agent which comprises glycine, gamma-amino butyric acid (GABA), or an aminophosphate or the coating agent comprises a functional group convertible to an amine group to form glycine, GABA or said aminophosphate.

27. A surface-modified filler according to claim 26, wherein the coating agent further comprises one or more of the amino acids alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, histidine, lysine, proline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine and mixtures thereof.

28. A surface-modified filler according to claim 26 or 27, wherein the coating agent is glycine.

29. A surface-modified filler according to any one of claims 26 to 28, wherein the alkaline earth metal carbonate filler is selected from magnesium carbonate, calcium carbonate or calcium-magnesium carbonate.

30. A surface-modified filler according to claim 29, wherein the alkaline earth metal carbonate filler is calcium carbonate.

31. A surface-modified filler according to claim 30, wherein the calcium carbonate filler is a ground calcium carbonate (GCC).

32. A surface-modified filler according to claim 30, wherein the calcium carbonate filler is a precipitated calcium carbonate (PCC).

33. A surface-modified filler according to any one of claims 26 to 32, wherein the particulate filler has a d₅₀ of greater than 0.1 μm.

34. A surface-modified filler according to any one of claims 26 to 32, wherein the particulate filler has a d₅₀ of greater than 0.5μm.

35. A surface-modified filler according to any one of claims 26 to 32, wherein the particulate filler has a d₅₀ of 0.1 μm to 5μm.

36. A polymer resin composition comprising a polymer resin and a surface-modified filler as claimed in any one of claims 26 to 35 dispersed in the resin and wherein the polymer is one which includes polar functional groups capable of hydrogen bonding with the amine groups of the coating agent.

37. A polymer resin composition according to claim 36, wherein the polymer is selected from polyamides, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonates, acrylonitrile butadiene styrene (ABS), ethylene vinylacetate (EVA), polyesters, epoxy resins, acrylate resins and mixtures of polycarbonate and ABS.

38. A polymer resin composition according to claim 37, wherein the polymer is a polyamide and is selected from nylon 6 or nylon 6/6.

39. An article formed from a polymer composition as claimed in any one of claims 36 to 38.

40. A process for preparing the surface-modified filler as claimed in any one of claims 26 to 35, which comprises contacting a particulate filler selected from alkaline earth metal carbonates with a coating agent which is capable of adhering to the particle surfaces and which is selected from glycine, gamma-amino butyric acid (GABA), or an aminophosphate or the coating agent comprises a functional group convertible to an amine group to form glycine, GABA or said aminophosphate.

41. A process according to claim 40 wherein the coating agent includes a plurality of groups convertible to amine groups and the process comprises the further step of converting said groups to amine groups.

42. A process for preparing the polymer resin composition as claimed in any one of claims 36 to 38 which comprises combining the polymer resin with the surface- modified filler.

43. A process for preparing the polymer resin composition as claimed in any one of claims 36 to 38 which comprises preparing a surface-modified filler according to claim 40 or 41 and combining said filler with the polymer resin.

44. A polymer resin composition comprising a polyamide resin and a surface-modified filler dispersed in the resin, wherein the surface-modified filler comprises a particulate filler selected from alkaline earth metal carbonates and wherein the surfaces of the particles of the alkaline earth metal carbonate filler are modified with a coating agent selected from an amino acid or an aminophosphate or the coating agent comprises a functional group convertible to an amine group to form said amino acid or aminophosphate.

45. A polymer resin composition according to claim 44, wherein the amino acid is selected from alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, lysine, proline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine and mixtures thereof.

46. A polymer resin composition according to claim 45, wherein the amino acid is glycine.

47. A polymer resin composition according to claim 44, wherein the amino acid is gamma-amino butyric acid (GABA).

48. A polymer resin composition according to any one of claims 44 to 47, wherein the alkaline earth metal carbonate filler is selected from magnesium carbonate, calcium carbonate or calcium-magnesium carbonate.

49. A polymer resin composition according to claim 48, wherein the alkaline earth metal carbonate filler is calcium carbonate.

50. A polymer resin composition according to claim 49, wherein the calcium carbonate filler is a ground calcium carbonate (GCC).

51. A polymer resin composition according to claim 49, wherein the calcium carbonate filler is a precipitated calcium carbonate (PCC).

52. A polymer resin composition according to any one of claims 44 to 51 , wherein the particulate filler has a d₅₀ of greater than 0.1 μm.

53. A polymer resin composition according to any one of claims 44 to 51 , wherein the particulate filler has a d₅₀ of greater than 0.5μm.

54. A polymer resin composition according to any one of claims 44 to 51 , wherein the particulate filler has a d₅₀ of 0.1 μm to 5μm.

55. A polymer resin composition according to any one of claims 44 to 54, wherein the polyamide is selected from nylon 6 or nylon 6/6.

56. An article formed from a polymer composition as claimed in any one of claims 44 to 55.

57. A process for preparing the polymer resin composition as claimed in any one of claims 44 to 55 which comprises combining the polyamide resin with the surface- modified filler.