This invention relates to masterbatch compositions and in particular to compositions comprising an organic resin, and a zeolite.

Plastics masterbatch compositions are well known. They comprise resin and pigment compositions suitable for use as pigment concentrate for dilution or "let down" into various non-pigmented plastics. The masterbatch or pigment concentrate is designed to be diluted and added to non-pigmented plastics to add opacity and, if necessary, colour and/or other functional additives. It is therefore necessary to include a relatively high level of pigmentation to achieve satisfactory opacity. The most common opacifiying pigment used in plastic masterbatch compositions is titanium dioxide, but this is expensive. In view of the high level of pigmentation, it is necessary to use pigments with a low oil absorption, in order to minimise any deleterious effects on the properties of the masterbatch and its manufacture. Hence, it is difficult to reduce the cost of the masterbatch composition by adding materials such as calcium carbonate etc. to extend the titanium dioxide, since such materials generally have a high oil absorption. One type of material which has been used to extend titanium dioxide in plastic masterbatches is Lithopone (BaSO4ZZnS) or barium sulphate but these are a relatively ineffective extenders.

One object of this invention is to provide a masterbatch composition (alternatively known as a plastic pigment concentrate) with desirable properties and which is less expensive than compositions based on non-extended titanium dioxide.

According to a first aspect of the invention, a masterbatch composition comprises a mixture, in particulate form, of a zeolite and an organic resin, said zeolite containing less than 7 per cent water by weight as determined by heating at 800° C for 1 hour. In general, the empirical formula of a zeolite is

M2/nO . AI2O3. XSiO2. yH2O

wherein M represents a metallic cation having a valency of n, x/2 indicates the ratio of atoms of silicon to atoms of aluminium and y/2 indicates the ratio of molecules of water to atoms of aluminium. Many different types of zeolite, with varying ratios of silica to alumina, are known. Commonly, however, M is an alkali metal and a preferred alkali metal is sodium, for economic reasons.

The zeolites used in this invention may have the structure of any of the known zeolites. The structure and characteristics of many zeolites are described in the standard work "Zeolite Molecular Sieves" by Donald W. Breck, published by Robert E. Krieger Publishing Company. Usually, the value of x in the above empirical formula is in the range 1.5 to 10. The value of y, which represents the amount of water contained in the voids of the zeolite, can vary widely. In anhydrous material y = 0 and, in fully hydrated zeolites, y may be up to 5. However, for zeolites which are useful in the current invention, the value of y is such that the water content of the zeolite is less than 7 per cent by weight, as determined by heating at 800° C.

Zeolites useful in this invention may be based on naturally-occurring or synthetic aluminosilicates and the preferred forms of zeolite have the structure known as zeolite P or zeolite A. Particularly preferred forms of zeolite are those disclosed in EP-A-O 384 070, EP- A-O 565 364, EP-A-O 697 010, EP-A-O 742 780, WO-A-96/14270, WO-A-96/34828 and WO- A- 97/06102, the entire contents of which are incorporated herein by this reference. The zeolite P described in EP-A-O 384 070 has the empirical formula given above in which M represents an alkali metal and x has a value up to 2.66, preferably in the range 1.8 to 2.66, and which is particularly useful in the present invention.

The amount of water, determined by heating at 800° C for 1 hour, ("total water") present in the zeolite used in the invention is preferably less than 6.5 per cent by weight. More preferably, the total water in the zeolite is less than 6 per cent by weight.

The water present in the zeolite can produce undesirable effects if it is released during the incorporation of a masterbatch into a non-pigmented plastic. An estimate of water which may be released during the incorporation of the masterbatch into a non-pigmented plastic can be obtained by heating the zeolite at 105° C for 4 hours. The water loss under these conditions ("moisture content") should preferably be below 1 per cent by weight. More preferably, the moisture content of the zeolite is below 0.8 per cent by weight. The zeolite preferably has a weight mean particle size as determined by Malvern Mastersizer™ in the range 0.5 μm to 6.0 μm. Preferably, the weight mean particle size is in the range LOμrn to 3.0 μm.

The organic resin which is present in the masterbatch composition can be any organic resin which is suitable for let-down to non-pigmented plastics. It may be a thermoplastic resin or a thermosetting resin as will be familiar to those familiar with the prior art.

Suitable thermoplastic resins include polyvinyl chloride) and co-polymers thereof, polyamides and co-polymers thereof, polyolefins and co-polymers thereof, polystyrenes and co-polymers thereof, poly(vinylidene fluoride) and co-polymers thereof, acrylonitrile- butadiene-styrene, polyoxymethylene and acetal derivatives, polybutylene terephthalate and glycolised derivatives, polyethylene terephthalate and glycolised derivatives, polyacrylamide nylon (preferably nylon 11 or 12), polyacrylonitrile and co-polymers thereof, polycarbonate and co-polymers thereof. Polyethylene and polypropylene, which may be modified by grafting of carboxylic acid or anhydride groups onto the polymer backbone, are suitable polyolefins. Low density polyethylene may be used. A poly( vinyl chloride) may be plasticised, and preferably is a homopolymer of vinyl chloride.

Examples of thermosetting resins which may be used are epoxy resins, polyester resins, hybrid epoxy-polyester resins, urethane resins and acrylic resins.

The masterbatch compositions of the invention may additionally comprise a pigment. When masterbatches compositions according to the invention additionally contain pigmentary titanium dioxide, the zeolite acts as an extender or partial replacement for the titanium dioxide. A preferred masterbatch according to the invention comprises a mixture, in particulate form, of a zeolite, an organic resin and pigmentary titanium dioxide, said zeolite containing less than 7 per cent water by weight determined by heating at 800° C for 1 hour.

When the finished masterbatch is white, the masterbatch according to the invention usually contains from 10 to 80 per cent by weight pigmentary titanium dioxide. Preferably, the amount of titanium dioxide present is from 30 to 70 per cent by weight of the masterbatch, and may be present from 40 to 70 per cent by weight of the masterbatch. Masterbatches pigmented with colours other than white often contain pigmentary titanium dioxide in addition to at least one coloured pigment. In such systems, the amount of pigmentary titanium dioxide is frequently in the range 5 to 75 weight per cent of the composition, commonly in the range 10 to 65 weight per cent of the composition, and may be in the range 10 to 55 weight per cent of the composition.

The amount of zeolite in white or coloured compositions is usually up to 50 per cent of the combined weight of zeolite and pigmentary titanium dioxide. Preferably, the amount of zeolite is up to 30 per cent of the combined weight of zeolite and pigmentary titanium dioxide in the composition. For optimum properties (i.e. good opacity at an economical cost) the amount of zeolite is usually from 5 to 25 per cent of the combined weight of zeolite and titanium dioxide.

Thus, a typical white masterbatch according to the invention comprises up to 20 weight per cent zeolite, and preferably greater than 1 weight per cent zeolite. More commonly, a white masterbatch composition comprises from 1 to 15 weight per cent zeolite. A typical coloured masterbatch composition comprises up to 20 weight per cent of zeolite and preferably greater than 1 weight per cent zeolite. More commonly, a coloured masterbatch composition comprises from 1 to 15 per cent by weight zeolite.

In addition to the zeolite and titanium dioxide, coloured masterbatch compositions according to the invention also comprise at least one coloured pigment. Suitable pigments may be organic or inorganic pigments, as conventionally used in masterbatch compositions. In view of the fact that the masterbatches are heated during manufacture and use, suitable pigments usually need to be stable up to a temperature of at least 100° C and preferably up to 250° C.

The masterbatch compositions of the invention frequently contain additional components often used in such compositions, such as catalysts and curing accelerators, UV stabilisers, flow control additives, antifoams and matting agents.

It is generally necessary to mix intimately the ingredients of the masterbatch compositions of the invention in order to achieve a satisfactorily homogeneous finished pigment concentrate. Commonly used methods of producing an intimate mixture include melt-mixing and dry blending. Accordingly, in a second aspect of the invention there is provided a method of preparing a masterbatch comprising the step of forming an intimate mixture of an organic resin and a zeolite, in which the zeolite contains less than 7 per cent water by weight as determined by heating at 8000C for 1 hour.

In the melt-mixing process, dry ingredients (zeolite, organic resin and any other components, such as titanium dioxide) are weighed into a batch mixer such as a high intensity impeller mixer, a medium intensity plough-share mixer or a tumble mixer. Mixing times depend upon the equipment used. For high intensity mixers, the mixing time is usually in the range 1 to 5 minutes and the mixing time in a tumble mixer is frequently in the range 30 to 60 minutes. The premix thus formed is then compounded together with any liquid ingredients in a high shear extruder such as a single screw extruder (e.g. Buss Ko-kneader [RTM]) or a twin screw extruder. It is particularly important to ensure that the combination of temperature of the mixture and residence time for thermosetting compositions is such that little or no curing takes place in the extruder, although the temperature is usually slightly above the melting point of the organic resin. The appropriate processing temperature is chosen to suit the resin present in the composition, but is usually in the range 60 to 3000C. Residence time in the extruder is usually in the range 0.5 to 2 minutes. The resultant mixture is then typically extruded through a strand die. The extruded material is usually cooled rapidly by water cooling, such as in a water trough, and broken into pellets or chips with a size of about 5 to 10 mm. These pellets or chips can then be dried and ground further to an appropriate particle size using conventional techniques as necessary. Frequently, thermoplastic resins need to be ground using cryogenic techniques.

Masterbatch compositions can also be prepared by dry blending and this technique is particularly suitable where the organic resin is plasticised polyvinyl chloride). All the ingredients are agitated in a high speed mixer at an elevated temperature in order to achieve intimate mixing.

According to a third aspect of the invention there is provided a method of pigmenting an organic resin comprising the steps of: providing a masterbatch composition comprising a mixture, in particulate form, of a zeolite and a first organic resin, said zeolite containing less than 7 per cent water by weight as determined by heating at 8000C for 1 hour; and

mixing the masterbatch composition with a second organic resin.

The masterbatch composition provided is in accordance with the first aspect of the invention.

Generally, the first organic resin is the same as the second organic resin. However, this is not necessarily the case, and it is possible that the first organic resin may be different to the second organic resin.

The masterbatch compositions according to the invention are suitable for let down into a substrate using any method normally used for pigmenting substrates with masterbatches. The precise nature of the second organic resin to be pigmented will often determine the optimum conditions for application. The appropriate temperature for let down and application depends principally upon the actual resin or resins used, and is readily determined by a person skilled in the art. The second organic resin may be a thermoplastic resin. Suitable second organic resins in which masterbatches are used include polyvinyl chloride) and co-polymers thereof, polyamides and co-polymers thereof, polyolefins and co¬ polymers thereof, polystyrenes and co-polymers thereof, poly(vinylidene fluoride) and co¬ polymers thereof, acrylonitrile-butadiene-styrene, polyoxymethylene and acetal derivatives, polybutylene terephthalate and glycolised derivatives, polyethylene terephthalate and glycolised derivatives, polyacrylamide nylon (preferable nylon 11 or 12), polyacrylonitrile and co-polymers thereof, polycarbonate and co-polymers thereof. Polyethylene and polypropylene, which may be modified by grafting a carboxylic acid or anhydride groups onto the polymer backbone, are suitable polyolefins. Low density polyethylene may be used. A polyvinyl chloride) may be plasticised, and preferably is a homopolymer of vinyl chloride.

Let down of the masterbatch compositions to give the desired zeolite and titanium dioxide concentrations in the final application may be achieved by tumble mixing the masterbatch composition with a quantity of a compatible diluent second organic resin in order to achieve the correct concentration of the additives in the final application. The mixture is then fed to a single or twin-screw compounding extruder and processed as described earlier (in the context of the preparation of a masterbatch composition) to produce a fully compounded resin with additives present at the concentrations required in the final application or is fed to a profile or sheet extrusion, blown or cast polymer foil or film unit for conversion into the desired product form.

Alternatively the masterbatch and compatible diluent second organic resin can fed by an automatic metering system of a type common within the industry to a single or twin-screw compounding extruder and processed as described earlier to produce a fully compounded resin with additives present at the concentrations required in the final application or is fed to a profile or sheet extrusion, blown or cast polymer foil or film unit for conversion into the desired product form.

It is desirable that the masterbatch produced according to the invention is free of holes or voids resulting from incorporation of moisture or volatiles in the masterbatch during compounding. Methods of prevention of such (venting of compounding extruder barrels via vacuum etc) are well known in the art.

According to a fourth aspect of the invention there is provided the use, as a pigment extender in a masterbatch composition, of a zeolite. The zeolite may be used as a pigmentary titanium dioxide extender. Preferably, the zeolite contains less than 7 per cent water by weight as determined by heating at 8000C for one hour. A zeolite as defined with respect to the first aspect of the invention may be used.

Masterbatch Preparation and Let Down

Data obtained by an analysis of a successfully extended masterbatch show values for opacity, L*, a*, b*, gloss (60° and 20°) and other mechanical data that are either sufficiently similar to the masterbatch without extender or of sufficient value in their own right as to be commercially applicable. Typical masterbatch formulations are developed so as to be manufactured by an economical route, thus it is desirable that the use of zeolite extenders provided by the present invention affects such processes as little as possible. This is typically assessed by measuring the power consumption of blender/extruder unit and production rate. Finally, the application of the masterbatch in the let-down of a plastic needs to produce a material that is neither economically deleterious to processing efficiency or quality of the final product. The quality of the let down product is measured as for the masterbatch itself (opacity, L*, a*, b*, gloss (60° and 20°) and other mechanical data). The efficiency of the manufacture of the let down product is measured as per masterbatch formulation (power consumption and rate) but also by a key extrusion function, well known in the art, called "die lip" build up. Excessive moisture in the let-down plastic can be forcefully released from a let down system at the point where the molten plastic is forced from the dye during extrusion through pressure drop effects. This produces a plastic build up on the lip of the die itself which when large enough can cause surface imperfections and even breakage in the production line manifested through breaks in the continuously extruded let-down product. The dye lip test is used to evaluate formulation performance when a masterbatch is to be used to manufacture economically important products that are continuously extruded, such as plastic bags.

The following tests have been used to measure the parameters which characterise this invention.

Total Water Content Determination of % Dry Solids of Zeolite via Muffle Furnace (8000C)

1.0 Principle A sample of Zeolite is quantitatively transferred into a muffle furnace set at a temperature of 8000C. The sample is maintained at 80O0C for a period of one hour. After this time, the loss in mass is determined and calculated as a percentage of the original mass. 2.0 Apparatus 2.1 Silica crucible 2.2 Muffle Furnace capable of maintaining a temperature of 8000C 2.3 Analytical balance (Accurate to 4 d.p.) 2.4 Glass desiccator 2.5 Muffle tongues 3.0 Procedure 3.1 Before the analysis is carried out, a silica crucible should be heated to a constant weight in the 8000C muffle furnace. 3.2 Cool the silica crucible in a glass desiccator and record it's mass accurately. (W1) 3.3 Accurately weigh approx 2.5g of Zeolite into the silica crucible and record the combined weight. (W2) 3.4 Place the crucible in the muffle furnace set at 8000C and maintain this temperature for a period of one hour. 3.5 After one hour, remove the silica crucible from the muffle furnace and place it directly into a glass desiccator. Allow the crucible to cool. 3.6 When cool, accurately re-weigh the crucible and record the total mass. (W3) Calculation The following calculation is used: - % Dry Solids = 100 - [(W2 - W3) / (W2 -W1)] x100

Moisture Content Determination of the Percentage Moisture loss at 105°C.

1. Principle The zeolite is dried at 1050C for 4 hours and the loss in weight is expressed as a percentage. 2. Apparatus 2.1 Weighing dish 2.2 Oven maintained at 1050C 2.3 Desiccator 2.4 Analytical balance 3. Procedure 3.1 Accurately weigh a clean dry weighing dish. Record the weight - W1. 3.2 Into the crucible weigh approximately 3g of sample. Record the total weight - W2. 3.3 Place the oven set at 1050C for 4 hours. 3.4 Remove from the oven, cool to room temperature in a desiccator, reweigh and record the final weight - W3. Calculation The percentage moisture loss is calculate as % loss at 105°C = (W2 - W3) x 100% (W2 - W1) Weight Mean Particle Size The weight mean particle size is determined using a Malvern Mastersizer™ model X, with a lens range up to 300 mm RF and MS17 sample presentation unit. This instrument, made by Malvern Instruments, Malvern, Worcestershire, uses the principle of Mie scattering, utilising a low power He/Ne laser. Before measurement the sample is dispersed ultrasonically in water for 7 minutes to form an aqueous suspension. This suspension is stirred before it is subjected to the measurement procedure outlined in the instruction manual for the instrument, utilising the 300 mm RF lens range in the detector system. The Malvern Mastersizer™ measures the weight particle size distribution of the inorganic material or reference material. The weight mean particle size (d50) or 50 percentile is readily obtained from the data generated by the instrument.

Oil Absorption The oil absorption is determined by the ASTM spatula rub-out method (American Society of Test Material Standards D 281). The test is based on the principle of mixing linseed oil with the zeolite by rubbing with a spatula on a smooth surface until a stiff putty-like paste is formed which will not break or separate when it is cut with a spatula. The oil absorption is then calculated from the volume of oil (V cm3) used to achieve this condition and the weight, W, in grams, of zeolite by means of the equation: Oil absorption = (V x 100)/W, i.e. expressed in terms of cm3 oil/100 g zeolite.

Gloss and Sheen The gloss and sheen (60° and 20°) values of the cured coatings are measured using a Sheen Tri-rnicrogloss 20-60-85 (160) unit. Gloss is a measurement of the intensity of a reflected incident beam, where the incident beam is projected at 60° to the perpendicular of the coating plane as described in ASTM D 523. Sheen is a measurement of the intensity of a reflected incident beam, where the incident beam is projected at 85° to the perpendicular of the coating plane as described in ASTM D 523

Colour Colour is determined using an X-rite 938 Spectrodensiometer. This unit measures the L*, a*, b* tristimulus values as described under CIE 1976 L*, a*, b* (CIELAB) Space where the L* axis describes lightness, a* describes the axis from redness (positive a* values) to greeness (negative) and b* describes the axis from yellowness (positive b* values) to blueness (negative). It is standard practice to compare L*, a*, b* values of samples with a reference of known L*, a*, b* values. Analytical data is typically reported either as absolute data (L*, a*, or b*) or as differential values (dL*, da* and db* using the greek letter delta to denote differential). For instance if the std L* value is 90.00 and a comparative sample has an L* value of 89.00, this is typically shown dL* = -1.00 for the comparative sample. The term dE is used to denote the arithmetic mean of dL*, da* and db* for a given sample. By definition, E = 0.00 for the reference sample thus allowing a ready comparison of overall colour between various samples.

Opacity or Contrast Ratio The opacity or contrast ratio (CR) is measured using an X-rite 938 Spectrodensiometer. The opacity or contrast ratio is the extent to which a coating hides or obscures the contrasting features of a test substrate. In this instance, CR is expressed photometrically as the ratio of the luminous (CIE-Y) reflection of the coating measured over a black substrate and the luminous (CIE-Y) reflection of the same coating measured over a white substrate.

Examples A reference masterbatch sample A was prepared by combining 80Og pelletised polyethylene (Sabic PLLM2024P) and 120Og powdered titanium dioxide (DuPont TR92) in a plastic sack followed by agitation (by hand) to give a homogenous mixture. This mixture was then added to a Thermo Prism 16mm twin screw extruder operated in the temperature range of 1000C to 12O0C. The extruded masterbatch was continuously produced at a rate of 3 kg per hr and the 16mm diameter masterbatch extrudate immediately was cooled in a water trough at room temperature. The extruded masterbatch sample was then processed (chopped up) further to reduce the average extrudate length to around 5mm. This gave a final reference masterbatch sample whose composition was 40% polyethylene and 60% pigment/extender as necessary. Further masterbatch samples B and C were prepared using low moisture zeolite (Zeocros E300) as extender. Zeocros E300 is a zeolite sold by INEOS Silicas Limited, Warrington, England. This is a zeolite MAP (maximum aluminium P-type) with a weight mean particle size of 1.8 micron by Malvern Mastersizer, a Total Water Content of 6.0 per cent by weight and an oil absorption of 40 cm3/100 g. Preparation of masterbatch samples B and C was carried out in the same way as described above for reference sample A but employing different ratios of polymer, titanium dioxide and zeolite. In addition, a comparative sample D was prepared in the same way as reference sample A but using 90% of the amount of TiO2 used in reference sample A.

% polyethylene % TiO2 % Zeocros E300 A) Reference 40 60 0 B) 5% extension 40 57 3 C) 10% extension 40 54 6 D) 90% of reference A 46 54 0

Each of the above masterbatch samples was then let down into polyethylene as follows to give film samples E to Q containing 5% masterbatch at several thicknesses, 40 microns, 80 microns and 500 microns. The polyethylene used was LDPE lpethene 213. In all cases of let down, 190Og of polyethylene pellets were dry blended by hand with 100g of the masterbatch sample A to D in a plastic sack. A reference R was also prepared with a film thickness of 40 microns using polyethylene only.

% polyethylene % masterbatch Thickness (w/w) (w/w) (microns) E) prepared using A 95 5 40 F) prepared using A 95 5 80 G) prepared using 95 5 500 H) prepared using 95 5 40 I) prepared using 95 5 80 J) prepared using 95 5 500 K) prepared using 95 5 40 L) prepared using 95 5 80 M) prepared using 95 5 500 N) prepared using 95 5 40 P) prepared using 95 5 80 Q) prepared using 95 5 500 R) polyethylene only 100 40 To prepare the films, the homogenous let down mixture was added into a Secor 25mm single screw extruder fitted with three phase pre-die heating (B1 , B2 and B3, with B1 closest to the film die) and three phase die heating (Die 1 , Die 2 and Die 3) with adjustable film die 50mm outside diameter and 49.5mm internal diameter. Processing was carried out using the conditions given below to give pigment polyethylene films of 40 and 80 microns thickness. The film was collected via a conventional film tower with collapsing boards and nip rolls. The film samples were collected on cardboard spools by hand and immediately stored in polythene bags, to avoid static dust contamination. Extrusion temperatures and screw speed were constant for all batches and nip roll speed was varied for film thickness.

Processing Parameters B1 B2 B3 Die 1 Die 2 Die 3 Screw RPM 16O0C 17O0C 1800C 180' 3C 180c 1C 185( 3C 50

Samples of 500 micron thickness were prepared by stacking samples of 80um film (F, I, K, or P as appropriate) in a 0.5 x 150 x 150um frame mould between aluminium sheets coated with a P. ET film to give a final moulding thickness of approx. 500um. The film stack was then pressed in a high temperature, high pressure press as follows: press plates temp 18O0C; warm-up time 2 mins at nip pressure; samples pressed for 1 min at 10,000kg on a 10.16cm ram and water cooled.

Table 1 gives data for masterbatch compositions A to D while Table 2 gives data for the film samples E to R obtained following let down of the samples, where applicable, into polyethylene. When extending a masterbatch using any material, it is essential that the extended and therefore cheaper product shows physical characteristics which closely approximate those of original formulation. The data given in Tables 1 and 2 is notable as there is little variation in the colour and surface analyses both for the masterbatch samples and let down films, therefore demonstrating that the low moisture content zeolite is a very effective extender for TiO2. TABLE 1

dL* da* db* dE Gloss Sheen Sample Composition (60°) (85°)

A 60% TiO2, 40% PE 98.46 -0.48 1.85 0.00 45 66 3% E300, 57% TiO2, B 0.03 -0.01 -0.22 0.22 38 67 40% PE 6% E300, 54% TiO2, C -0.58 0.04 -0.01 0.58 28 66 40% PE D 54% TiO2, 46% PE -0.01 -0.05 -0.18 0.19 46 75 TABLE 2