- Email: [email protected]
Technical briefs
January
1999
such as EPDM, but the low molecular weight and good flow and filling properties of the new copolymers help to bring high impact capability to high flow PP, giving more efficient processing and improved knit line strength.
Additives f;,r Polymers
The original concept was to mix on a continuous basis, but the production machine is designed to mix four shots at a time, to give adequate time for proper mixing.
DuPont Dow’s product line includes a wide range of TPO modifiers with various crystallinitics and molecular weights, the most efficient of which (Engage 8 180, 8 150 and 8 100) are available in pellet form for easy handling and increased productivity, giving better dispersibility in PP when compared with EPDM bales or crumbs.
Oima has experimented with a number of combinations of resin and reinforcement. At the recent K exhibition in Dusseldorf, the company demonstrated two possibilities: the door lock housing for an automobile, in polypropylene rcinforccd with long glass fibre, and a lightweight handle moulded in a thermoplastic elastomer filled with 85% (by volume) of ground natural cork.
Contact: DuPont Dow Elastomers, CH-1218 Le Grand-Saconnex. Switzerland; tel: +41-22 717 5111; fax: +41-22 717 5109
Contact: Oima SpA, Ma Feltrina Sud 172, 31044 Montehelluna/7T, Italy; tel: -+39-423 60054i;,fax: +39-423 24035
Compounding in the injection moulding machine
TECHNICAL
The trend among machinery manufacturers now is to bring technical compounding (or at least part of it) into the hands of moulders. After the launch by Krupp of a compounder to product long fibrc reinforced thermoplastics (Additives for Polymers, October 1998) comes the introduction by an Italian company of a direct compounding injection moulding system.
Influence of shrinkage compensators on SMC
Developed by Oima (and first unveiled at the Plast exhibition in Milan in 1997), the Integrated Material Mixer makes it possible for the moulder to incorporate particulate and/or fibrous rcinforcement within the moulding cycle. Precise details of the construction are not yet available, but it appears that Oima has taken the approach of diverting the plasticized melt into a mixing chamber, from which it is then fed back into the main line of injection into the mould. The additive is introduced downstream of the plasticizing screw, by means of a patented low pressure/low shear mixing stage placed after the screw and ahead of the mould sprue system. The vented mixing unit has a vertical three-stage mixing element, and hydraulic valves control admission and discharge of material. Gravimetric feed is used to meter the reinforcement into the mixer chamber and the design involves pressing the mix downwards to the bottom of the chamber, providing the pressure ncedcd to fill the injection chamber.
0 1999 Elsevier Science
BRIEFS
Sheet Moulding Compounds (SMCs) arc one of the most successful developments in reinforced thermosctting plastics, accounting for an estimated 40% of consumption. A key target of development has been the modification of SMCs to compensate for shrinkage which occurs during processing. Optimization of shrinkage compensators, development of special in-mould coatings and improvements in the compression moulding process have made great improvements in the quality and accuracy of mouldings. But the effect of shrinkage compensators on the dynamic properties of SMCs is at present insufficiently understood, and a useful paper in the German magazinc Gummi Fasern Kunststoffe attempts to remedy this. Unsaturated polyester resins can shrink by up to 6-9% in volume as a result of the chemical reaction during crosslinkage and thermal shrinkage as the moulding is cooled. This may create internal stress, causing war-page, cracking and voids, which will reduce the serviceability of the moulded parts and cause surface deterioration. Fillers and glass fibres can reduce the shrinkage of a standard resin to about 0.3% of volume, and a further reduction is possible by addition of lO40% by weight of thermoplastic additives dissolved or dispersed in styrene.
9
January I999
Additives for Polymers
Evaluation of SMC materials Component
Trade name
Raw material
Quantity
LS SMC
LP SMC
Parts by weight
100
60
60
Resin
UP resin
Palapreg
Shrinkage compensator
PVAC
H814 H870
Parts by weight Parts by weight
_
40
Filler
CaC03
Millicarb
Parts by weight’
150
150
150
Reinforcement
Glass fibre roving
Vetrotex
Parts by weight’ o/ov/v
25.5 14.6
27.4 15.8
26.8 14.8
Notes: ’ relative to resin + shrinkage Source: International
P 15-01
SMC
P280
compensator;
2 relative to the total quantity
40
of resin paste
Polymer Science and Technology
Tensile stress values of SMCs, with details of standard deviation Parameter Tensile
stress, Fe
Elongation Modulus
at break, IX, of elasticity,
Fibre content Source: International
E
Unit
SMC
LS SMC
LP SMC
N/mm2
90.5 f 6.9
83.6 f 3.0
91.8 f 2.8
%
1.543 f 0.06
1.65 f 0.09
1.43 f 0.08
N/mm2
16300 f 1400
o/ov/v
14.6
15.8
13600 f 310 14.8
Polymer Science and Technology
It is necessary to differentiate between systems for Low Shrinkage (LS = 0.06-0.14% by volume) and Low Profile (LP = -0.04-0.04% by volume). The exact mechanism by which they act is still disputed. The lower thermal contraction of LP systems can result in relative elongation, giving negative shrinkage on curing. Adding a thermoplastic dispersion, such as polystyrene or polyethylene, produces an LS system. The reduction of shrinkage appears to be based on the formation of cavities in the finelydistributed droplets. In an LP formulation with polymethyl methacrylate or polyvinyl acetate, the additive forms a second discontinuous phase in the network, compensating for stresses arising from shrinkage. The more compatible the LP additive the greater the reduction in shrinkage, but the mechanical properties are reduced. In tests for tensile properties, increasing load and fatigue, the LS formulation showed worse mechanical properties than the standard, while those of the LP formulation were slightly higher, but individual differences were not great. International Polymer Science and Technology, Vol 25, No 4, 1998, pp T/l-T/7 (tr. from Gummi Fasern Kunststoffe)
10
146OOk2800
LITERATURE Plastics, rubber, fi bres database now on Internet A database of plastics, rubbers and fibres is now offered on the Internet by the German Chemistry Information Ccntre, FIZ Chemie Berlin, via ChemWeb, the worldwide club for the chemical community. The first database to be launched, following an agreement between FIZ and ChemWeb, ‘Plastics Rubber Fibers’ is a large bibliographic database abstracting all important papers in the field of plastics since 1973. Sophisticated indexing and informative abstracts allow quick and easy access to all relevant publications worldwide. The first release of the system will cover the five most recent years of data. The next database will be ‘Cheminform’, an abstracting service covering synthetic organic and organometallic chemistry, handling some 17 000 original papers each year. The clear pictorial presentation of crucial results and complete schemes by structural formulae, that has been one of the most popular features of Cheminfomr, will also be available on the Web.
0 1999 Elsevier Science
1999
such as EPDM, but the low molecular weight and good flow and filling properties of the new copolymers help to bring high impact capability to high flow PP, giving more efficient processing and improved knit line strength.
Additives f;,r Polymers
The original concept was to mix on a continuous basis, but the production machine is designed to mix four shots at a time, to give adequate time for proper mixing.
DuPont Dow’s product line includes a wide range of TPO modifiers with various crystallinitics and molecular weights, the most efficient of which (Engage 8 180, 8 150 and 8 100) are available in pellet form for easy handling and increased productivity, giving better dispersibility in PP when compared with EPDM bales or crumbs.
Oima has experimented with a number of combinations of resin and reinforcement. At the recent K exhibition in Dusseldorf, the company demonstrated two possibilities: the door lock housing for an automobile, in polypropylene rcinforccd with long glass fibre, and a lightweight handle moulded in a thermoplastic elastomer filled with 85% (by volume) of ground natural cork.
Contact: DuPont Dow Elastomers, CH-1218 Le Grand-Saconnex. Switzerland; tel: +41-22 717 5111; fax: +41-22 717 5109
Contact: Oima SpA, Ma Feltrina Sud 172, 31044 Montehelluna/7T, Italy; tel: -+39-423 60054i;,fax: +39-423 24035
Compounding in the injection moulding machine
TECHNICAL
The trend among machinery manufacturers now is to bring technical compounding (or at least part of it) into the hands of moulders. After the launch by Krupp of a compounder to product long fibrc reinforced thermoplastics (Additives for Polymers, October 1998) comes the introduction by an Italian company of a direct compounding injection moulding system.
Influence of shrinkage compensators on SMC
Developed by Oima (and first unveiled at the Plast exhibition in Milan in 1997), the Integrated Material Mixer makes it possible for the moulder to incorporate particulate and/or fibrous rcinforcement within the moulding cycle. Precise details of the construction are not yet available, but it appears that Oima has taken the approach of diverting the plasticized melt into a mixing chamber, from which it is then fed back into the main line of injection into the mould. The additive is introduced downstream of the plasticizing screw, by means of a patented low pressure/low shear mixing stage placed after the screw and ahead of the mould sprue system. The vented mixing unit has a vertical three-stage mixing element, and hydraulic valves control admission and discharge of material. Gravimetric feed is used to meter the reinforcement into the mixer chamber and the design involves pressing the mix downwards to the bottom of the chamber, providing the pressure ncedcd to fill the injection chamber.
0 1999 Elsevier Science
BRIEFS
Sheet Moulding Compounds (SMCs) arc one of the most successful developments in reinforced thermosctting plastics, accounting for an estimated 40% of consumption. A key target of development has been the modification of SMCs to compensate for shrinkage which occurs during processing. Optimization of shrinkage compensators, development of special in-mould coatings and improvements in the compression moulding process have made great improvements in the quality and accuracy of mouldings. But the effect of shrinkage compensators on the dynamic properties of SMCs is at present insufficiently understood, and a useful paper in the German magazinc Gummi Fasern Kunststoffe attempts to remedy this. Unsaturated polyester resins can shrink by up to 6-9% in volume as a result of the chemical reaction during crosslinkage and thermal shrinkage as the moulding is cooled. This may create internal stress, causing war-page, cracking and voids, which will reduce the serviceability of the moulded parts and cause surface deterioration. Fillers and glass fibres can reduce the shrinkage of a standard resin to about 0.3% of volume, and a further reduction is possible by addition of lO40% by weight of thermoplastic additives dissolved or dispersed in styrene.
9
January I999
Additives for Polymers
Evaluation of SMC materials Component
Trade name
Raw material
Quantity
LS SMC
LP SMC
Parts by weight
100
60
60
Resin
UP resin
Palapreg
Shrinkage compensator
PVAC
H814 H870
Parts by weight Parts by weight
_
40
Filler
CaC03
Millicarb
Parts by weight’
150
150
150
Reinforcement
Glass fibre roving
Vetrotex
Parts by weight’ o/ov/v
25.5 14.6
27.4 15.8
26.8 14.8
Notes: ’ relative to resin + shrinkage Source: International
P 15-01
SMC
P280
compensator;
2 relative to the total quantity
40
of resin paste
Polymer Science and Technology
Tensile stress values of SMCs, with details of standard deviation Parameter Tensile
stress, Fe
Elongation Modulus
at break, IX, of elasticity,
Fibre content Source: International
E
Unit
SMC
LS SMC
LP SMC
N/mm2
90.5 f 6.9
83.6 f 3.0
91.8 f 2.8
%
1.543 f 0.06
1.65 f 0.09
1.43 f 0.08
N/mm2
16300 f 1400
o/ov/v
14.6
15.8
13600 f 310 14.8
Polymer Science and Technology
It is necessary to differentiate between systems for Low Shrinkage (LS = 0.06-0.14% by volume) and Low Profile (LP = -0.04-0.04% by volume). The exact mechanism by which they act is still disputed. The lower thermal contraction of LP systems can result in relative elongation, giving negative shrinkage on curing. Adding a thermoplastic dispersion, such as polystyrene or polyethylene, produces an LS system. The reduction of shrinkage appears to be based on the formation of cavities in the finelydistributed droplets. In an LP formulation with polymethyl methacrylate or polyvinyl acetate, the additive forms a second discontinuous phase in the network, compensating for stresses arising from shrinkage. The more compatible the LP additive the greater the reduction in shrinkage, but the mechanical properties are reduced. In tests for tensile properties, increasing load and fatigue, the LS formulation showed worse mechanical properties than the standard, while those of the LP formulation were slightly higher, but individual differences were not great. International Polymer Science and Technology, Vol 25, No 4, 1998, pp T/l-T/7 (tr. from Gummi Fasern Kunststoffe)
10
146OOk2800
LITERATURE Plastics, rubber, fi bres database now on Internet A database of plastics, rubbers and fibres is now offered on the Internet by the German Chemistry Information Ccntre, FIZ Chemie Berlin, via ChemWeb, the worldwide club for the chemical community. The first database to be launched, following an agreement between FIZ and ChemWeb, ‘Plastics Rubber Fibers’ is a large bibliographic database abstracting all important papers in the field of plastics since 1973. Sophisticated indexing and informative abstracts allow quick and easy access to all relevant publications worldwide. The first release of the system will cover the five most recent years of data. The next database will be ‘Cheminform’, an abstracting service covering synthetic organic and organometallic chemistry, handling some 17 000 original papers each year. The clear pictorial presentation of crucial results and complete schemes by structural formulae, that has been one of the most popular features of Cheminfomr, will also be available on the Web.
0 1999 Elsevier Science