- Email: [email protected]
Fulfilling composite's performance goals
Fulfilling composites’ performance goals.Fillers play an important role in composites and their vital contribution to the performance of these materials places an increasing demand on filler technology. The Fillers and Reinforcing Agents section of the British Plastics Federation looks at the role of fillers in composites.
hermosets have traditionally contained fillers and/or reinforcements mainly to improve impact performance which is the converse of thermoplastics which, in the main, contain fillers and reinforcements to improve flexural modulus or rigidity. Unsaturated polyester resins form the largest volume of thermosetting plastics used in the UK and account for the majority of the glass reinforced plastics (GRP) industry. Let us first consider the moulding of thermosets at elevated temperature as this process is by far the most important for fillers. The first process is to convert the unsaturated polyester resin into a sheet or dough moulding compound (SMC or DMC) . Fillers are by far the least expensive component of the compound, although they are essential to obtain the right consistency and have to be selected on technical merit. In the manufacture of SMC for example, the moisture content is critical as this affects the thickening rate and any variation can cause severe production problems. The choice of filler will depend upon the end application, although the effect on the viscosity of the filled resin mixture will also be a consideration, particularly when producing SMC. Calcium carbonate and dolomite are by far the most popular fillers for SMC and DMC and can be surface treated to reduce
T
REINFORCED
PLASTICS
APRIL
1992
viscosity and improve dispersion. In the case of SMC, a period of maturation is required followed by compression moulding in a heated tool at temperatures of the order of 140°C. Automotive components with a grade A surface finish can be produced and, as thermoset products have a high heat distortion temperature, it is possible to apply a paint finish in conventional ovens used for metal parts. Usually, the finer the filler the better the surface finish. Fibrous reinforcement is essential in order to achieve the desired mechanical properties and glass fibre is commonly used. In SMC, 50 mm fibre strands are incorporated whilst in DMC must shorter 6 mm strands are used. Because of the longer strands in SMC, higher
FIGURE 1: Chopped glass fibre being deposited onto filled resin paste during the manufacture of SMC
0034-3617/92/$3.50
Q
1992,
Elsevier
Science
Publishers
Ltd.
mechanical strengths can be obtained, therefore much larger mouldings are produced e.g. car bumpers, bonnets and boot lids. The shorter fibre length in DMC allows for easier flow, compared to SMC, therefore smaller more intricate mouldings are produced. These include electrical components, small domestic appliance units and, more recently, under the bonnet components for automotive use. Injection moulding of DMC under the right conditions produces mouldings with an excellent surface finish which require no subsequent surface treatment before being assembled. A good example is the production of domestic irons and toasters, which also need the high temperature resistance of filled thermosets. Other fibrous reinforcements are being evaluated, such as wollastonite which produces mouldings with excellent surfacefinish, particularly in the injection moulding of DMC. Cellulose fillers are also used in the production of thermosetting moulding compounds. The addition of cellulose fillers allows for higher strength, increased threedimensional stability, reduced density together wit.h a reduction in wear rate during processing. Fillers are also used with thermoset resins in the low temperature, low pressure resin transfer moulding process which has an advantage over compression moulding due to the lower capital costs of the equipment and the ability to use continuous glass fibre reinforcement which can be preformed to ensure the levels of reinforcement are appropriate to the required performance in each area of a particular moulding. The availability of fast-curing modified acrylic resins means this process is capable of producing components with cycle times similar to those possible with the higher capital cost compression moulding process. Calcium carbonate and dolomite are commonly used as fillers to reduce cost and increase modulus of glass fibre reinforced composit,es. Alumina trihydrate is also very effective, when combined with modified acrylic resins, for production of fire retarded composites which generate low smoke when combusted. These composites are typically produced by resin transfer moulding or pultrusion t,hrough a heated die. Alumina trihydrate dispersed in acrylic resin is also used in a casting process to produce refurbishable cladding and work surface materials for use in the building industry and kitchens. Harder fillers, such as
silica, when dispersed in acrylic resinfind large volume outlets for the manufacture of kitchen sinks in the UK and Europe and baths in Japan, and provide for excellent stain resistance and hard-wearing properties. In this case the hard filler produces stiffness in the product and resistance to scratching of the glossy surface. As unsaturated polyester resins can t akr high filler loadings, alumina trihydrate (ATH) is used in fire retardant SMC’ applications. As with calcium carbonate. coatings can be applied to reduce viscosity. or blending of two or more ATH grades with different particle size distributions can achieve similar results. A unique and rather unusual application for alumina trihydratc is in the manufacture of synthetic marble or onyx. As alumina trihydrate has similar refractive index compared to unsaturatrd polyester resin, when the two are mixed a translucent appearance is produced. This effect can be used to produce swthrtic marble by a casting process which is t hett used in the production of bathroom furnit urc’ such as vanity units.
MIGHW Supplying
minerals
HIGH QUALITY
industry.
In addition
MICRO TALC, SIL-CELL’
TALCMAN to the plastics
to our well known MICRODOL.
MICRO
low density
MICA ranges mineral
we also supply
additives.
Available now: MICRODOL Available
CT
soon :
Low oil absorption svstems,
surface treated white dolomite granular ,
putties. New white micronised Ultrafine calcium
talc
precipitated carbonate
Norwegian
2% Cotton
Talc (UK) Ltd.
Exchange BulldIng Old Hall Street, LIverpool L3 9LA Tel 051 236 6435 Telex 627012 Fax 051 227 5903 -
talc for liquid polymer
DMC. SMC oolvester
Members of the Fillers and Reinforcing Agents section of the BPF are organizing the Filplas Conference which takes place 19-20 May 1992 in Manchester, UK.
When discussing fillers, most people immediately think of relatively high density materials and little thought is given to tillers which exhibit densities less than that of the resin. Light weight fillers referred to as ‘cenospheres’ are produced as a by-product by coal burning power stations and are deposited on the surface of large lagoons, These are ‘harvested’ by companies which dry and refine the cenospheres making them suitable for use in plastics. Typical applications for cenospheres include polyvinyl chloride (PVC) floor tiles and light weight sheet moulding compounds. Cenospheres are relatively low priced materials unlike manufactured light weight fillers which are produced from glass. Specific gravities as low as 0.2 are possible and when these synthetic fillers are added to liquid resin systems a composite is formed with a specific gravity less than that of 1.0, i.e., the material will float. These composites are sometimes referred to as syntactic foams and due to their extremely high compressive strength to weight ratio, they are used in deep water
applications such as undersea robots, which are used for inspecting the structural work of deep sea oil rigs. They can also be used as insulation materials for underwater pipe lines and provide buoyancy when oil needs to be transported from the sea bed to the surface, in which case the application is known as ‘risers’. Mica has a long history of usage in thermosetting resins, particularly in phenolies. Mica is used for mechanical reinforcement, giving flexural strength similar to asbestos filled phenolic resins but with higher flexural modulus and improved dimensional control. Both warpage and thermal expansion are reduced. The main areas of application for mica in phenolics and epoxy resins is in electrical applications where mechanical reinforcement is necessary, combined with high electrical resistivity. Various types of mica are employed, ranging from micronized powder, through coarse flakes to large sheets and splittings.
PRODUCTS Follow Honda Marlboro McLaren’s lead, specify Frekote, the unique semi-permanent, multi-release formula. First choice release products for GRP / Composites 1, Elastomers / Thermoplastics / Thermosets / Rubber. CFC-free products available. FOI-technlcal assistance and data contact DEXTERA.S.M.Staglndustr~al Estate, AtlantlcStrert. Telephone OhI-929 0424 Telex 668926 FREKOT C THE DEXTER CORPORATION
REINFORCED
PLASTICS
APRIL
1992
Altrlncham,CheshlreWA145DW&$and Fax 061-929 0425
hermosets have traditionally contained fillers and/or reinforcements mainly to improve impact performance which is the converse of thermoplastics which, in the main, contain fillers and reinforcements to improve flexural modulus or rigidity. Unsaturated polyester resins form the largest volume of thermosetting plastics used in the UK and account for the majority of the glass reinforced plastics (GRP) industry. Let us first consider the moulding of thermosets at elevated temperature as this process is by far the most important for fillers. The first process is to convert the unsaturated polyester resin into a sheet or dough moulding compound (SMC or DMC) . Fillers are by far the least expensive component of the compound, although they are essential to obtain the right consistency and have to be selected on technical merit. In the manufacture of SMC for example, the moisture content is critical as this affects the thickening rate and any variation can cause severe production problems. The choice of filler will depend upon the end application, although the effect on the viscosity of the filled resin mixture will also be a consideration, particularly when producing SMC. Calcium carbonate and dolomite are by far the most popular fillers for SMC and DMC and can be surface treated to reduce
T
REINFORCED
PLASTICS
APRIL
1992
viscosity and improve dispersion. In the case of SMC, a period of maturation is required followed by compression moulding in a heated tool at temperatures of the order of 140°C. Automotive components with a grade A surface finish can be produced and, as thermoset products have a high heat distortion temperature, it is possible to apply a paint finish in conventional ovens used for metal parts. Usually, the finer the filler the better the surface finish. Fibrous reinforcement is essential in order to achieve the desired mechanical properties and glass fibre is commonly used. In SMC, 50 mm fibre strands are incorporated whilst in DMC must shorter 6 mm strands are used. Because of the longer strands in SMC, higher
FIGURE 1: Chopped glass fibre being deposited onto filled resin paste during the manufacture of SMC
0034-3617/92/$3.50
Q
1992,
Elsevier
Science
Publishers
Ltd.
mechanical strengths can be obtained, therefore much larger mouldings are produced e.g. car bumpers, bonnets and boot lids. The shorter fibre length in DMC allows for easier flow, compared to SMC, therefore smaller more intricate mouldings are produced. These include electrical components, small domestic appliance units and, more recently, under the bonnet components for automotive use. Injection moulding of DMC under the right conditions produces mouldings with an excellent surface finish which require no subsequent surface treatment before being assembled. A good example is the production of domestic irons and toasters, which also need the high temperature resistance of filled thermosets. Other fibrous reinforcements are being evaluated, such as wollastonite which produces mouldings with excellent surfacefinish, particularly in the injection moulding of DMC. Cellulose fillers are also used in the production of thermosetting moulding compounds. The addition of cellulose fillers allows for higher strength, increased threedimensional stability, reduced density together wit.h a reduction in wear rate during processing. Fillers are also used with thermoset resins in the low temperature, low pressure resin transfer moulding process which has an advantage over compression moulding due to the lower capital costs of the equipment and the ability to use continuous glass fibre reinforcement which can be preformed to ensure the levels of reinforcement are appropriate to the required performance in each area of a particular moulding. The availability of fast-curing modified acrylic resins means this process is capable of producing components with cycle times similar to those possible with the higher capital cost compression moulding process. Calcium carbonate and dolomite are commonly used as fillers to reduce cost and increase modulus of glass fibre reinforced composit,es. Alumina trihydrate is also very effective, when combined with modified acrylic resins, for production of fire retarded composites which generate low smoke when combusted. These composites are typically produced by resin transfer moulding or pultrusion t,hrough a heated die. Alumina trihydrate dispersed in acrylic resin is also used in a casting process to produce refurbishable cladding and work surface materials for use in the building industry and kitchens. Harder fillers, such as
silica, when dispersed in acrylic resinfind large volume outlets for the manufacture of kitchen sinks in the UK and Europe and baths in Japan, and provide for excellent stain resistance and hard-wearing properties. In this case the hard filler produces stiffness in the product and resistance to scratching of the glossy surface. As unsaturated polyester resins can t akr high filler loadings, alumina trihydrate (ATH) is used in fire retardant SMC’ applications. As with calcium carbonate. coatings can be applied to reduce viscosity. or blending of two or more ATH grades with different particle size distributions can achieve similar results. A unique and rather unusual application for alumina trihydratc is in the manufacture of synthetic marble or onyx. As alumina trihydrate has similar refractive index compared to unsaturatrd polyester resin, when the two are mixed a translucent appearance is produced. This effect can be used to produce swthrtic marble by a casting process which is t hett used in the production of bathroom furnit urc’ such as vanity units.
MIGHW Supplying
minerals
HIGH QUALITY
industry.
In addition
MICRO TALC, SIL-CELL’
TALCMAN to the plastics
to our well known MICRODOL.
MICRO
low density
MICA ranges mineral
we also supply
additives.
Available now: MICRODOL Available
CT
soon :
Low oil absorption svstems,
surface treated white dolomite granular ,
putties. New white micronised Ultrafine calcium
talc
precipitated carbonate
Norwegian
2% Cotton
Talc (UK) Ltd.
Exchange BulldIng Old Hall Street, LIverpool L3 9LA Tel 051 236 6435 Telex 627012 Fax 051 227 5903 -
talc for liquid polymer
DMC. SMC oolvester
Members of the Fillers and Reinforcing Agents section of the BPF are organizing the Filplas Conference which takes place 19-20 May 1992 in Manchester, UK.
When discussing fillers, most people immediately think of relatively high density materials and little thought is given to tillers which exhibit densities less than that of the resin. Light weight fillers referred to as ‘cenospheres’ are produced as a by-product by coal burning power stations and are deposited on the surface of large lagoons, These are ‘harvested’ by companies which dry and refine the cenospheres making them suitable for use in plastics. Typical applications for cenospheres include polyvinyl chloride (PVC) floor tiles and light weight sheet moulding compounds. Cenospheres are relatively low priced materials unlike manufactured light weight fillers which are produced from glass. Specific gravities as low as 0.2 are possible and when these synthetic fillers are added to liquid resin systems a composite is formed with a specific gravity less than that of 1.0, i.e., the material will float. These composites are sometimes referred to as syntactic foams and due to their extremely high compressive strength to weight ratio, they are used in deep water
applications such as undersea robots, which are used for inspecting the structural work of deep sea oil rigs. They can also be used as insulation materials for underwater pipe lines and provide buoyancy when oil needs to be transported from the sea bed to the surface, in which case the application is known as ‘risers’. Mica has a long history of usage in thermosetting resins, particularly in phenolies. Mica is used for mechanical reinforcement, giving flexural strength similar to asbestos filled phenolic resins but with higher flexural modulus and improved dimensional control. Both warpage and thermal expansion are reduced. The main areas of application for mica in phenolics and epoxy resins is in electrical applications where mechanical reinforcement is necessary, combined with high electrical resistivity. Various types of mica are employed, ranging from micronized powder, through coarse flakes to large sheets and splittings.
PRODUCTS Follow Honda Marlboro McLaren’s lead, specify Frekote, the unique semi-permanent, multi-release formula. First choice release products for GRP / Composites 1, Elastomers / Thermoplastics / Thermosets / Rubber. CFC-free products available. FOI-technlcal assistance and data contact DEXTERA.S.M.Staglndustr~al Estate, AtlantlcStrert. Telephone OhI-929 0424 Telex 668926 FREKOT C THE DEXTER CORPORATION
REINFORCED
PLASTICS
APRIL
1992
Altrlncham,CheshlreWA145DW&$and Fax 061-929 0425