Issue 4: April 2004 - POLYMER-SPECIFIC MASTERBATCH FOR RIGID PVC WILL CHANGE THE COLOURED PVC COMPOUND MARKET IN EUROPE

An innovative material believed to be the world's first polymer-specific colour masterbatch for rigid PVC is poised to change the PVC compound market in Europe.

Developed by Colour Tone Masterbatch in the UK, the PVCu masterbatch is based on patented PVC colouring technology that makes it as easy to colour PVC as any other plastic material. With these properties the masterbatch has the potential to turn the PVC processing market on its head by allowing processors to cash-in on the benefits of lower polymer costs, reduced stock holding and production flexibility.

Universal and polymer specific masterbatches for flexible PVC have been available for many years but they have never worked reliably in rigid PVC because of its inherent processing difficulties. PVC is an extremely versatile polymer but it is very heat sensitive and highly resistant to flow in its melt phase.

There are no processing and compatibility issues with Vynacol and it is available in granular form or as prill (spherical beads typically 1 to 1.4 mm diameter) – these characteristics make Vynacol unique and the only masterbatch suited to adding colour, as well as additives, to PVCu. This is especially true where high loadings are required - for example on thin wall packaging applications and co-extruded coloured capping layers – which were previously only achieved by employing dry colouring techniques or pre-coloured compounds. Dry blends are known to create dust, contamination and health issues within a manufacturing plant.

Vynacol delivers to PVCu hitherto unobtainable benefits in quality and intensity of colour via the masterbatch route. It is clean, reliable and gives consistent results even in the most sophisticated manufacturing environments with none of the disadvantages of using dry powder and other colouring techniques.

The simplicity and effectiveness Vynacol gives processors total control of the colouring method and so has opened up new avenues of opportunity by allowing them to use colour in any PVCu application. Moreover, they can now communicate colour preferences and solve related manufacturing issues directly with a colouring specialist.  

Masterbatch properties
Processors of the material have always had to find just the right grade for their particular plant and application. Consequently there are literally thousands of PVC formulations on the market with varying amounts of additives and different levels of compounding; all developed to meet specific performance and processing requirements, or both!

Generally masterbatches are made by subjecting relatively high loadings of pigments and polymer to high shear forces such as in a twin screw masterbatch extruder. When this polymer is PVCu it can easily overheat causing the polymer to thermally degrade and producing choking fumes of HCl (hydrochoric acid). Until now PVCu polymer specific masterbatches containing large quantities of pigment have not been available.

Conversely, polymer specific masterbatches for flexible PVC contain plasticisers. Although this does not present compatibility problems when used in rigid PVC, users are, in effect, adding plasticisers to a polymer chosen specifically for its unplasticised characteristics. This can lead to application failures due to plasticizer migration particularly in food packaging or changes in the physical properties of the final product. 

PVCu polymer specific masterbatch is different because it works well both in rigid and flexible grades without any compatibility or homogenisation problems. It overcomes all the traditional difficulties associated with adding colour to rigid PVC via the masterbatch route. The product is now available in Europe through Vynacol Limited in Tralee, Co Kerry Ireland.

Benefits
PVC masterbatch offers many benefits to processors including:

• Faster colour changes.
• No loss in production rates - colours run as fast as clear material.
• Better optical properties.
• No compatibility problems.
• No homogenisation problems.
• Reduced stockholding.
• Lower polymer costs.
• Enhanced physical properties including colour ageing.
• Easily dispersed at a dosage of 1-2% for unfilled and up to 5% for filled grades.  
• Overdosing up to 10% with no effect on material properties.
• Contains no plasticisers

Formulation
Not surprisingly the formulation and manufacturing techniques used to produce the masterbatch are closely guarded secrets but they are based on existing polymer technology and involve specially modified manufacturing plant. The basic ingredients have been selected for good weatherability and excellent colour ageing characteristics. Further enhancements to outdoor performance are possible by adding UV stabilisers and absorbers while suitable approved pigments allow the masterbatch to meet all European food contact (European Resolution AP (89) 1, packaging (EU directive 94/62/EG) and toy (EN71 Part 3) criteria.

Supplied in dust-free easy flowing granules or prill the rigid PVC masterbatch is suitable for manual mixing or automated dosing and formulated for ease of homogenisation. The polymer specific masterbatch differs from traditional thermoplastic masterbatches in that as well as combining and dispersing the active ingredients [usually coloured pigments] with the polymeric part of the masterbatch it is also compounded from basic ingredients at the same time. This construction of the carrier component is one of the great advantages of the material over other PVC colouring systems because it allows the masterbatch to be tailored precisely to the processors application.

Internal lubrication levels can be varied to take into account subsequent processing; external lubricant levels can be adjusted and reduced for example if surface adhesion is a factor. Ingredient types and levels can also be varied to meet a wide range of processes and applications. The carrier formulation is also varied depending on the type of functional additive [e.g. organic or inorganic pigments], the level of additive[s] or even the dosing level it is to be used at.

As compatibility is not an issue these masterbatches can be formulated for dosing at a level suitable for the process and application rather than using the minimum amount of colourant to avoid “contaminating” the PVC more than necessary. 

Generally the masterbatch is easily dispersed at a recommended dosage of 1-2% and can be used in filled as well as unfilled grades. Depending on thickness and opacity required dosing in of excess of 10% is possible with no affects on processing or physical properties. Indeed, the product contains additives that improve and enhance the characteristics of the base PVC, for example: ease of processing, improved weld strength, increased ductility, impact strength (especially at low temperatures), and high gloss finish.

Monopigment concentrates
Using raw pigment can be a messy operation and this is an important consideration on an in-line compounding operation producing food packaging products. In this situation cross-contamination is a possibility and the quality of pigment dispersion and development become factors in dry-blending and subsequent compounding. Also any colour modification requires revisiting the dry-blending stage and clean-downs are lengthy processes.

With monopigment concentrates of polymer specific masterbatch for PVCu, it is now possible to dose pre-dispersed pigments into PVCu without any of these concerns. Supplied in dust free pelletised format, formulated for optimum homogenisation, clean-down times are significantly reduced; cross contamination is eliminated and expensive dust control measures become unnecessary. These dispersions can be added to the dry-blend or dosed in-line to the polymer stream during the compounding process. Colour control becomes easier and colour modification is a relatively simple procedure.

All the pigments used in PVCu can be supplied in this format, pigment loadings reflecting the application and process being employed by the compounder. The carrier component of the concentrate is also formulated specifically for the subsequent processing. Lubrication levels are carefully controlled to ensure optimum processing characteristics in whatever the compounding process. There is no loss in production rate when processing compounds coloured with monopigment concentrates.

Applications
These masterbatches can be used in virtually any application from toys to tubing but they excel in food packaging and building products.

Formulated for optimum uv resistance the colours can be used in PVCu profiles for windows, underground and roofline extrusions. Grades of titanium dioxide are utilised that are not associated with the “pinking” phenomena that has caused so much concern in this industry. Coloured pigments are selected for their weathering resistance in PVC and can be successfully incorporated at the high levels required for optimum long term performance.

Similarly PVCu masterbatches are used to produce injection moulded accessories for window systems such as cill ends, drain point covers, vent covers, screw caps etc. Injection moulding types are colour matched to extrusion grades which allows small quantities of ancillary products, offering similar weathering performance, to be produced economically.

Food packaging films
In thin films the PVCu masterbatch has no rivals. Large quantities of pigment can preclude most  pre-dispersed products. When the quantity of colourant is high it impacts upon the properties and processing characteristics of PVCu. This can manifest itself in a number of ways: optical hazing or blooming, changes in the physical properties of the sheet/film, lamination, or processing difficulties e.g. screw slip plate out for example.

Current trends for pearlescent based colours - golds, silvers, coppers for example - require high levels of these relatively weak pigments to achieve the opacity and lustre required. These PVCu masterbatches can be incorporated at levels that simply cannot be contemplated with any other colour concentrate system without any of the associated compatibility issues mentioned earlier. Transparent colours are easily achieved and offer vibrant, bright colours with excellent clarity and no blooming.

As the masterbatch carrier can be tailored to suit the production process - calendering, extrusion etc. - optimum production rates are ensured. Additionally the compatibility of masterbatch to the base polymer reduces the likelihood of plate-out which again results in enhanced production efficiency and cost savings.