Material data
Overview of amorphous thermoplastic injection
moulding materials
Max. service temperature in Deformation
air, without load
(glass
transition)
temperature
°C 2)
°C 3)
(°C)
50…70
60…80
90
50…70
60…80
85
85
95
100
7…8
8…10
(3)…6…8
75…85
85…100
105
(3)…8…11
70…90
55…65
70…80
80
6…8
3…o. Br.
30…40
50…55
55…65
55…75
18…21
2200
1000…1600
2…40
8…15
50…70
60…115
80…90
80…120
100
125
2700…3200
1.5…3
65…90
85…100
105
10…12
11…15
10…13
7…9
2500
8…15
90
130
120…130
(3)…6…10
PC
2100…2400
20…35
130
140
150
(2)…6…7
PAR 5)
PSU
PES
PEI
PAI
2300
2600…2750
2450
3000…4500
5000…7500
22
3…4
4…6
50…60
60…75
100
80…125
105…135
(160)
145…155
(160)
185
180…210
220…225
220 (235)
... 150
150
200
170…180
200…230
180
190
250
210
260
190
200
260
220…230
275
(3)…6…7
(3)…5…6
(3)…5…6
(1)…4…6
(2) …
Elasticity
Abbreviation
module E
(DIN 7728)
(N/mm²)
Notch impact
strength
(DIN 53453 1))
(Nmm/mm²)
Dimensional
stability (Vicat
method B
(°C)
PS
SB
SAN
3200
1800…2500
3600
1.5…3
5…20
2…3
ABS
1900…2700
7…25
75…100
75…95
100 (110)
85…105
(115)
1000…3500
2.5…50 4)
PVC rigid
PVC-U
PVC soft
PVC-P
CA
CAB
CP
PMMA
PPO mod.
PPE mod.
Linear
expansion
coefficient at
20 °C *)
The ranges given take into account the different materials and processing
conditions.
Values in brackets apply to fibre-glass reinforced materials.
Standard polystyrene (PS)
or
Typical characteristics
Typical applications
Identification features
Processing
♦
commodity plastic,
♦
hard, brittle, stiff, knock and notch-sensitive,
♦
transparent,
♦
very low dielectric losses,
♦
upper service temperature ≈ 70 °C max. 80 °C, depending on type.
♦
low-priced massed-produced items (housings, packaging, transparent
♦
toys, office equipment,
♦
components of HF-technology,
♦
household commodities.
♦
natural state: transparent,
♦
sound: sharp clink,
♦
flame: very smoky
♦
smell: has a typical, sweet smell.
♦
no particular problems,
♦
good to very good flow properties,
♦
primarily injection moulded,
♦
extrusion,
♦
bonding - welding,
♦
cutting methods,
♦
injection blow moulding.
Processing data
Pre-drying
Generally not necessary, only when high-quality surface is required:
recirculation dryer 2-3 hours at 70-80 °C is sufficient.
High surface moisture causes streak formation.
Melting temperature
160-250 °C, depending on type.
Mould temperatures
20 - 50 °C
Flow properties
good to very good
Injection speed
medium to high
Injection pressure
650 - 1550 bar
Holding pressure
300 - 700 bar
Max. cavity pressure
150 - 350 bar
Holding pressure must be low enough, 1 in order to prevent overcharging, in particular because of the tendency of PS to crack under
strain.
PS is therefore usually processed with reduced holding pressure
(declining pressure profile). Too high a holding pressure can cause
internal stress and the tendency to break during demoulding.
1
As an amorphous thermoplastic, PS has good elastic properties between the solidifying range and the glass transition temperature
ARB00145
Too low a melting temperature causes high internal stress. The onset of
decomposition, caused by too high a melting temperature, is noticeable
by sweet smell, yellow colouring and streak formation in the parts.
Back pressure
40 - 80 bar
Processing shrinkage
0.2 - 0.6 %
Subsequent shrinkage
practically = 0
Demoulding may be difficult if the outer contours taper less than 1.5°.
Special features
PS is suitable for injection with tab gating
SB
SAN
ABS
ASA
♦
Somewhat more resistant to impact but not as hard and rigid
as PS,
♦
usually not transparent (opaque) due to (too large)
butadiene particles,
♦
more sensitive to ageing than PS, due to butadiene content
♦
More rigid and harder than PS,
♦
relatively strong,
♦
impact resistance higher than PS, but lower than SB,
♦
transparent possible,
♦
lower risk of tension cracking than PS.
♦
Greater resistance to impact than PS and SB,
♦
not usually transparent due to (too large) butadiene particles
♦
more sensitive to ageing than PS due to butadiene content.
♦
Similar to ABS, however with better resistance to weathering
and ageing.
ABS/PC ♦ Greater resistance to impact even up to -50 °C and greater
thermal form stability.
blend
ABS/PUR ♦ High resistance to impact when cold,
blend
♦ good flow characteristics (thin-walled parts),
♦
PS-S
Typical applications
good resistance to abrasion.
Syndiotactic polystyrene (semi-crystalline material)
♦
high thermal form stability,
♦
crystal melting point 270 °C,
♦
good electric characteristics,
♦
not transparent (opaque).
SB
Housing and components for phono, electro, household and
refrigerator items, camping parts, impact-proof packaging.
SAN
Technical parts similar to SB, in particular when transparency is
required; lamp covers, scale indicators, battery housings, electro
housings, household goods.
ABS
Technical parts, similar to SB, however for higher strain
requirements.
ASA
Similar applications to ABS, however suitable for higher
requirements of resistance to light and weather, in particular for
outdoor applications.
PS-S
Technical parts in automobile branch and electro-technology.
ARB00145
Typical characteristics
Identifying features
SB
SAN
ABS
Appearance
usually not transparent
transparent
usually not transparent
Sound
somewhat duller than PS
not as dull as PS
duller than PS
Breakage
characteristics
low plastic deformation,
ruptured edges turn
slightly white
very low plastic
deformation, higher
resistance to deformation
than PS
strong plastic
deformation, higher
resistance to deformation,
ruptured edges white
Flame, odour
Similar to PS, B is noticeable (rubber-like smell).
Processing
Without any great problems. Pre-drying recommended, good flow
characteristics.
Processing data
Pre-drying
SB
As with PS, in general not necessary.
SAN,
Moisture causes streak formation on parts.
ABS, ASA Pre-drying is recommended to eliminate surface moisture,
recommendation: circulation dryer 2-3 h at 70-80 °C is
sufficient.
Melting temperature
Mould temperatures
SB
160-250 °C
SAN
200-260 °C
ABS
200-260 °C
ASA
220-280 °C
SB
50-70 °C
SAN
40-80 °C
ABS
50-85 °C
ASA
40-80 °C
Yellow colouring and streak formation
indicates the onset of decomposition
Upper values for better surface gloss
Flow characteristics
SB
somewhat poorer than PS
SAN
poorer than PS and SB
ABS
similar to SAN
ASA
similar to SAN
Injection speed
medium to high
Injection pressure
650 - 1500 bar
Holding pressure
350 - 900 bar
Max. cavity pressure
200 - 550 bar
Back pressure
40 - 80 bar
Processing shrinkage
SB
up to 0.7 %
SAN
0.5 - 0.6 %
ABS
0.4 - 0.7 %
ASA
0.4 - 0.7 %
Subsequent shrinkage
practically = 0
Sensitive to overloading, similar to PS
Polyvinyl chloride (PVC)
PVC rigid
PVC soft
Typical features
Typical applications
= PVC without plasticisers
= PVC with plasticisers
= PVC-U,
= PVC-P.
♦
Bulk plastic similar to PS, however more suitable for semi-processed
materials by extrusion rather than for moulded parts by injection
moulding, as there is a narrower tolerance in the processing
temperatures and because aggressive HCI is emitted on thermal
decomposition.
♦
High chlorine content.
Rigid PVC:
hard and stiff, similar to PS, less brittle.
Soft PVC:
degree of stiffness in relation to content and type of
plasticizer, at low temperatures often brittle.
♦
not even rigid PVC can be used at over 60 °C.
♦
low tendency to tension cracking.
♦
transparency possible,
♦
flexible.
Components required to have low-flammable and self-extinguishing
properties, or to be resistant to chemicals (salt solutions, many types of
acid, brines, petroleum, mineral oils, types of grease and alcohol), for the
building industry, electr. packaging (on the decline), mechanical
engineering.
Identifying features
PVC hard (PVC-U)
PVC soft (PVC-P)
Processing properties
Appearance
crystal clear, transparent, can be slightly opaque
Sound
clinking, duller than PS
Flame
very smoky,
Odour
strong smell of chlorine.
Appearance
Transparency is possible, also depending on type and
quantity of plasticizer, semi-hard to soft, rubber-like
Flame
very smoky, generally self-extinguishing, depending on
type of plasticizer; if with high plasticizer content
continues to burn after flame removed.
Aroma
strong smell of chlorine.
Thermally very sensitive, in particular hard PVC. Only suitable for
processing on reciprocating screw-type of injection moulding machine,
highly viscous melt, process with low screw rotational speed, low back
pressure and low injection speed.
Processing data
Pre-drying
generally not required
Melting temperature
PVC hard: 160 - 180 °C (200 °C)
PVC soft: 150 - 170 °C
depending on type and stabilisers
added
Short temperature load, i.e. short
dwell time in cylinder reduces the
risk of decomposition. Correct
temperature setting is important.
Decomposition is noticeable by
brown or black marks on moulded
parts and strong smell of
hydrochloric acid (HCl).
Mould temperatures
PVC hard: 20 - 60 °C
PVC soft: 20 - 40 °C
Upper values recommended to
improve flow quality
Flow characteristics
PVC hard: melt is highly viscous
Sprue runners and gates to be as
large and short as possible, avoiding
sharp deflections
Injection speed
not too high
in order to avoid overheating due to
a too high shear rate
Injection pressure
PVC hard: 1000 - 1550 bar
PVC soft: 400 - 1550 bar
Holding pressure
PVC hard: 500 - 900 bar
PVC soft: 300 - 600 bar
Maximum cavity pressure
PVC hard: 250 - 500 bar
PVC soft: 150 - 300 bar
Back pressure
40 - 80 bar
Screw circumferential speed
low, max. 4.8 - 6 m/min
(0.08 - 0.1 m/s)
Processing shrinkage
PVC hard: 0.2 - 0.5 %
PVC soft: 1 - 2.5 %
Subsequent shrinkage
with hard PVC practically 0
to avoid overheating due to friction
in cylinder
Other features
Use only types suitable for injection moulding.
To keep the dwell times in the cylinder short the shot volume per part
should not be less than 20 % of the maximum injection volume of the
machine.
Trapping corners in the flow of material are to be avoided, therefore
working with open nozzles is recommended (with hard PVC and soft PVC
from 85 Shore A onwards). If possible also without check valve.
Use special screws with low compression.
Signs of decomposition are not always avoidable, even under normal
processing conditions. Very aggressive hydrochloric acid (HCI) forms.
Cylinder assembly and mould must therefore be protected against
corrosion (mould chrome-plated or of corrosion-resistant steel (type
18.8).
Cellulose ester
Processing
♦
Pre-drying required,
♦
when overheated acid splitting occurs (acetic acid, etc.) risk of
corrosion,
♦
good flow properties.
Pre-drying
For water content of over 0.2 %:
No other material must be
circulation dryer 3 h at ca. 80 °C. Water included in dryer (due to risk of
absorption up to 3 %
plasticising agent drifting). Too
high a drying temperature can
lead to plasticiser drifting and/or
acetic acid splitting off (which
may cause corrosion).
Melting temperature
CA: 185 - 225 °C
CAB: 160 - 190 °C
CP: 160 - 190 °C
Mould temperatures
30 - 60 °C
Flow properties
good
Injection speed
medium to high
Injection pressure
650 - 1350 bar
Holding pressure
300 - 650 bar for CA,
300 - 900 bar for CAB,
400 - 700 bar for CP
Maximum cavity pressure
250 - 450 bar for CA and CAB
200 - 350 bar for CP
Back pressure
40 - 80 bar
as low as possible due to thermal
sensitivity of the melt.
Processing shrinkage
0.2 … 0.4 … 0.7 %
lower values for thin walled parts
Subsequent shrinkage
practically no subsequent shrinkage but moisture absorption can cause
dimensional instability
-2-
ARB00145
Processing data
2.1.4
..\ENGL_UK\ARB00145\EN02AD.FM 2013.09.04 01
Higher melting temperature for
higher stability. During initial
trials, start with lower marginal
values due to risk of
decomposition and plasticiser
drifting.
Polymethylmethacrylate (PMMA)
Copolymers
PMMA blends
AMMA =
Acrylonitril methylmethacrylate has a higher chemical
resistance than PMMA, available as semi-processed product.
MBS =
Methacrylate butadiene styrene has a higher impact
resistance than PMMA, without any substantial loss of
transparency.
e.g.
PMMA + PVC
PMMA + PC.
improve the characteristics
Typical characteristics of pure
PMMA
Typical applications
Surface treatment
♦
higher impact resistance,
♦
better resistance to tension cracking,
♦
lower notch sensitivity.
♦
brittle, rigid, stiff,
♦
breaks without plastic deformation, but does not splinter,
♦
good translucency and non-ageing,
♦
high static charging,
♦
good dielectric and electric characteristics,
♦
risk of tension cracking.
♦
high-quality optical components (lenses, prisms, etc),
♦
weathering resistant mechanical building components such as lamp
cover plates, back lights (reflectors), light windows, advertising signs,
photovoltaic elements, demonstration models,
♦
wide application areas in nearly all sectors.
Suitable for printing, hot foil stamping, varnishing.
Maximum cavity pressure
350 - 550 bar
Back pressure
80 - 120 bar (200 bar)
Screw circumferential speed
Medium to low screw speeds
Too high a circumferential speed
are recommended. Circumferential leads to overheating caused by
speed max. 0.3 m/s, i.e.
friction.
300 rpm with 20 mm screw,
200 rpm with 30 mm and
130 rpm with 45 mm screw.
Processing shrinkage
0.3 - 0.8 %
Subsequent shrinkage
Practically none
Other features
If the component has to fulfil high optical requirements, the screw,
cylinder etc. must be kept absolutely clean.
The back pressure is to be selected
high enough to ensure that no gas
pockets can form in the moulded
part. Also possible to check by
extrusion: in the melt emerging
from the nozzle there must be no
gas pockets (bubbles) visible.
Water-based temperature control devices are preferable to oil-based ones
(due to oil fumes).
The granules must be kept dust-free (otherwise dust may be attracted by
electrostatic charging). On moulded parts which may subsequently come
into contact with media that could cause tension cracking, or are to be
glued or varnished, subsequent tempering is recommended at a
temperature of 5 °C under the temperature at which deformation starts
(ca. 60 - 90 °C depending on type), followed by slow cooling.
Polycarbonate (PC)
Typical characteristics
♦
Hard and stiff and highly resistant to impact at temperatures between
-100°C and +135 °C (briefly),
♦
low creep tendency,
♦
low thermal expansion,
♦
low water absorption (max. 0.5 %) thus dimensionally stable parts,
♦
high electric volume resistance,
♦
low dielectric losses up to 103 Hz.
♦
Transparency (often with slight tinge of yellow or blue) possible.
♦
Resistant to:
♦
♦
♦
PC blends
♦
oil, grease, alcohol,
♦
aliphatic (linear) carbon hydride,
♦
carbon tetrachloride.
Also resistant to:
♦
weather influences,
♦
UV rays.
Not resistant to:
♦
aromatic (cyclic) carbon hydrides (e.g. benzene),
♦
cyclic ether,
♦
ketone, ester
♦
chlorinated carbon hydrides.
Hydrolytic decomposition occurs due to reaction with:
♦
hot water (over 60 °C) and steam,
♦
alkali,
♦
diluted acids.
♦
Tension cracking sensitivity with certain chemicals.
♦
PC + ABS, PC + ASA, PC + PET, PC + PBT,
new PC + LCP; improve the characteristics:
♦
greater rigidity,
♦
higher chemical resistance,
♦
higher resistance to thermal forming.
Typical applications
Identifying features
Processing characteristics
♦
Strong, impact-resistant (transparent) constructive components,
♦
Casings and protective covers, in particular for electric devices and
systems,
♦
Spools, plug connector strips, precision parts,
♦
Medical implements,
♦
Eating utensils,
♦
Compact discs etc. (of special material types),
♦
Automobile branch, e.g. headlamps,
♦
Optical applications.
Appearance:
transparent, with yellow or blue tinge
Sound:
dull
Flame:
low flammable properties, smoky, extinguishes
outside the flame
Odour:
like phenole.
♦
Pre-drying absolutely necessary (moisture content must be below
0.02 %).
♦
Medium (mostly) to high melt viscosity,
♦
Solidified melt tends to stick to cylinder,
♦
Moulded parts tend to stick in mould.
IMPORTANT
Tempering the moulded parts can help to reduce internal tension and
decrease the sensitivity towards tension cracking (thick-walled parts
should be cured for several hours).
Processing data
Pre-drying
Absolutely necessary
Circulation dryer:
6 - 12 h at 1 120 - 130°C
dry-air dryer: 4-6 h at 120 - 130 °C
PC only absorbs a small amount
of moisture (max. 0.5 %) but this
happens very quickly. For
processing, the moisture content
must not exceed 0.02 %. Higher
Important to keep granulate absolutely rates reduce the form filling
dry until it reaches the feed opening in capacity and cause streak
the screw.
formation in the moulded part.
Injecting with pre-heated granulate
improves the surface quality. Working
with heated feed hoppers or
drying/conveying appliances is
therefore recommended.
Melting temperature
250 - 330 °C
Thermal damage starts above
340 °C (discolouring). Reduction
of impact resistance
Mould temperatures
80 - 120 °C
Higher temperatures improve the
flow characteristics and reduce
the risk of internal tensions.
Flow characteristics
Highly viscous melt.
Raising the temperature has a stronger
influence on the mould filling than
increasing the pressure.
Sprue runners and gates should
have a suitably large crosssection and be as short as
possible.
Injection speed
Must not be selected too high to avoid Too low an injection speed
shear stress.
impairs the surface quality.
Injection pressure
1000 - 1600 bar
Holding pressure
600 - 1300 bar
Maximum cavity pressure
350 - 650 bar
Back pressure
80 - 120 bar
Processing shrinkage
0.7 - 0.8 %
Subsequent shrinkage
Practically none.
Almost the same in and across
the direction of flow (low
orientation tendency).
During production breaks, the cylinder temperatures must not be allowed
to drop below 160 - 170 °C, because solidified PC adheres strongly to the
cylinder walls.
Otherwise when restarting, dark particles may separate from the
thermally damaged outer layer and impair the quality of the part.
When changing the compound, the cylinder, screw and nozzle must be
thoroughly cleaned.
When processing transparent PC we recommend you use a nozzle which
is only used for this material.
It is imperative to work with an open nozzle with an outlet bore of at
least 3.0 mm.
ARB00145
Other features
Overview of semi-crystalline thermoplastic
injection moulding compounds
Abbreviation Elasticity
acc. to
modulus E
DIN 7728
(N/mm²)
( EN_TB00205A )
PE soft
PE-LD
PE rigid
PE-HD
Dimensional
Notch impact
stability acc.
strength acc.
1 to Vicat
to DIN 53453
method B
(Nmm/mm²)
(°C)
Max. service temperature in Crystallite
air, without load
melting
temperature
°C 3
°C 2
(°C)
Coefficient of
longitudinal
expansion at
20 °C *)
200 … 500
18 …w/o fract.
45 … 60 60 … 75
80 … 90
105 … 115
... 25
700 … 1400
4 … w/o fract.
55 … 80 70 … 80
90 … 120
125 … 140
13 … 20
PP
1100 … 1300
4 … 18
100 … 110
130 … 140
148 … 168
(6) … 10 … 18
PA 4.6
1500 … 4500
6 … 33
110 … 140
... 200
295
(3) … 7,5
PA 6
600 … 3200
3 … w/o fract.
80 … 100
140 … 180
215 … 225
(2) … 7 … 11
PA 6.6
1200 … 3500
5 … w/o fract.
80 … 120
170 … 200
250 … 265
(2) … 6 … 10
PA 6.10
... 2000
7 … 10
80 … 100
150
210 … 225
... 7 …
PA 11
800 … 1200
30 … 40
70 … 80
140 … 150
180 … 190
(2) … 9 … 13
PA 12
1200 … 1500
10 … 20
70 … 80
140 … 150
175 … 185
(3) … 13 … 15
130 … 140
150 … 160
6…8
90 … 110
110 … 140
165 … 175
(3) … 11 … 13
100
200
255 … 258
(2) … 7 … 8
100
165
220 … 225
(3) … 5 … 7
200
205
150
300
250
220
280 … 288
285 … 295
270
(4) … 7,5
8 … 10
... 9
... 230
... 280
... 300
235 … 240
310
225 … 370
(2) … 5
270 … 380
0…5
60 … 100
(... 110)
... 280
(… 290)
180 … 220
(... 230)
195 … 205
(… 250)
190 … 195
180 … 190
(... 240)
120 … 160
(... 170)
PA amorph.
PA 6-3-T
POM
2000
13
2800 … 3200
5 … 10
PET
3100
3…6
PBT
2000
3…6
PPS
FEP
ETFE
3400
350 … 650
1100
3…6
w/o fract.
w/o fract.
PAA
PPA
PAEK
11300 … 17700 5 7 … 27
6300 … 14500 5
4000
w/o fract.
115 … 145
... 185
250 …
LCP
10000 … 35000 4 20 … 70 4
120 … 140
145 80 … 100
150 … 170
160 … 190
(... 240)
165 … 180
(... 220)
200
The specified ranges cover different types of compound and processing
conditions.
Values in brackets apply to glass-fibre reinforced types.
Polyethylene (PE)
Soft PE
(LD-PE);  = 0.91 - 0.94 g/cm³
LD = low density = due to strongly branching molecules
Rigid PE
(HD-PE);  = 0.94 - 0.96 g/cm³
HD = high density = due to only slightly branching
molecules.
Service properties and processing characteristics depend strongly on the
density (molecular form) and on the degree of polymerisation (molecular
length or weight).
With increasing density and increasing degree of polymerisation
(decreasing melt flow index):
Typical characteristics
♦
the following also increase: e.g. hardness, rigidity and upper service
temperature (from 80 °C to 105 °C, briefly 120 °C),
♦
the following decrease: e.g. embrittlement temperature, tendency to
form tension cracks,
♦
the processability in injection moulding is impaired because the
viscosity is higher.
♦
Mass-production plastic,
♦
flexible (LD) to tough-hard (HD),
♦
tough at sub-zero temperatures up to -50 °C and lower,
♦
practically unbreakable,
♦
however embrittlement occurs under UV influence (stabilisation
against UV possible with carbon black).
♦
good electric insulating properties,
♦
no water absorption,
♦
very low dielectric losses,
♦
high chemical resistance (to nearly all common solvents),
♦
gas permeability is higher than with many other types of plastic but
water permeability very low,
♦
not crystal clear (semi-crystalline).
Typical applications
♦
sealing plugs,
♦
covers,
♦
containers,
♦
bottle crates,
♦
household goods,
♦
toys,
♦
foils.
Not suitable for precision parts due to high shrinkage and subsequent
shrinkage and their effect on the tendency of deformation.
Identifying characteristics
Processing
Appearance:
not crystal clear, transparent (opaque), because it is
semi-crystalline
Sound:
dull
Floating test:
lighter than water
Flame:
fluorescent with blue core, not smoky, melt drips
Odour:
like paraffin
♦
no particular problems,
♦
high to medium fluidity,
♦
wide processing temperature range.
Processing data
Pre-drying
Generally not required (no water
absorption)
Brief pre-drying only required
when surface moisture has
formed after a longer period of
open storage.
Melting temperature
210 - 250 °C for LD-PE
250 - 300 °C for HD-PE
In the lower temperature range,
dull spots can occur on the
moulded part.
Mould temperatures
20 - 40 °C for LD-PE
20 - 60 °C for HD-PE
In the upper temperature range a
better surface gloss, higher
degree of crystallisation and thus
less subsequent shrinkage. At
even higher temperatures:
demoulding difficulties caused
by sticking to the mould.
Flow characteristics
Good to medium, depending on density
and molecular weight.
Injection speed
Medium to high
Injection pressure
600 - 1350 bar
Holding pressure
300 - 800 bar
Maximum cavity pressure
200 - 600 bar
Back pressure
40 - 80 bar with LD-PE
60 - 90 bar with HD-PE
Processing shrinkage
1.5 - 3.5 % with LD-PE
2 - 5 % with HD-PE
Subsequent shrinkage
is always higher, the lower
the mould temperature
Other features
PE is non-sensitive in injection moulding (wide processing temperature
range). It is therefore suitable as a sandwich component between two
materials whose processing temperature ranges do not overlap.
Compared to other plastics PE
has a very high thermal capacity
(cools more slowly). This means
the holding pressure time should
be selected sufficiently long
(check this by weighing the
moulded parts or read off cavity
pressure measurement). If the
holding pressure time ends
before the gate has solidified,
sink spots are formed due to
high shrinkage.
Subsequent shrinkage is not
always avoidable because even
at a mould temperature of 70 °C
the cooling rate is still so high
that the crystallisation process is
not completed in the mould.
PE is suitable for tab-gating injection methods.
Gluing, printing, varnishing etc. is only possible after preliminary
treatment, due to the high chemical resistance. The chemical resistance
increases with the density. HD-PE better than LD-PE.
In foil production, PE-LLD (linear PE, low density) is more frequently used
because it has better mechanical characteristics which means the
thickness of the foil can be reduced.
Polypropylene (PP)
The commercially available type is isotactic PP (methyl groups arranged in
the same direction) with 0.90 g/cm³ (atactic PP with irregularly arranged
methyl groups has 0.84 g/cm³). Also available are copolymers containing
ethylene to increase the impact strength under 0 °C.
Typical characteristics
Typical applications
♦
Greater rigidity and hardness than PE (usually not possible to slit with
finger nail).
♦
However impact strength falls rapidly shortly below 0 °C.
♦
Upper service temperature 110 °C, can be higher with materials
containing stabilisers.
♦
Good electric characteristics, similar to PE.
♦
No tendency to tension cracking
♦
Lower chemical resistance than PE.
♦
Uncoloured more translucent than PE (less opaque).
♦
Fan blades,
♦
Heating ducts in vehicles,
♦
Internal parts of washing machines and dish washers,
♦
Transport crates,
♦
Containers with film hinges,
♦
Copolymer blends for high quality parts.
Not suitable for precision parts due to high shrinkage rates during and
after injection and their effect on the deformation tendency.
Characteristics of recognition
Processing
Similar to PE
Appearance:
more translucent (less opaque) than PE
Sound:
somewhat clearer than PE
Rigidity:
somewhat higher than PE
Scratch resistance:
greater than PE, cannot be slit with finger nail
Weight:
somewhat lower than PE
 PP = 0.9 g/cm³,  PE hard = 0.96 g/cm³
♦
High fluidity.
Processing data
Pre-drying
generally not necessary (similar to PE)
Melting temperature
220 - 290 °C
Mould temperatures
20 - 60 °C (80 °C)
Flow characteristics
Fluidity better than PE, in particular
Shut-off nozzles are usually
in lower processing temperature range. required, if processing without
decompression.
Injection pressure
800 - 1400 bar
injection speed
Medium to high
Holding pressure
500 - 1100 bar
Maximum cavity pressure
300 - 650 bar
Back pressure
60 - 90 bar
Processing shrinkage
In direction of flow 1.3 - 2.5 %,
across line of flow 0.8 -1.8 %
Subsequent shrinkage
Similar to PE
Upper temperatures provide
better surface gloss. In lower
temperature range parts are mat
in places and have higher rate of
subsequent shrinkage.
Select holding pressure time to
be sufficiently long (similar to PE)
Shrinkage is higher, the lower
the mould temperature.
Other features
PP is suitable for tab-gating injection moulding.
Due to its low density, the plasticising capacity of the machine is lower
(only ca. 70 % compared to polystyrene).
Cycle times can be reduced by adding an nucleating agent, both with PE
and PP. This produces a fine-structured texture which influences the
shrinkage characteristics accordingly.
Due to further developments such as CR-PP/PP-homo, PP-EPDM and PP
mass copolymers, these types of material are being increasingly used in
technical sectors (automobile branch).
Recognisable characteristics of plastics
A rough guide
Thermosets and elastomers
(network-like molecules)
Thermoplastics (thread-like molecules)
Amorphous
Semi-crystalline
Basically transparent, if not milky opaque, if not
coloured
strongly coloured.
Exception e.g. SB (mostly),
ABS through butadiene
Thermosets:
closely meshed
Elastomers:
widely meshed
Moulding compounds are mostly not transparent due
to fillers.
Resins (unfilled) are often transparent
Elastically deformable
Basically plastically deformable, if not at room
temperature then under sufficient heat
Usually very rubbery-elastic
shortly before melting
point (above solidifying
temperature).
Not plastically deformable
Only with some
thermosets: very rubberyelastic before
decomposition (above
solidifying temperature).
Basically meltable
Exception: thermoplastics with a very high degree of
polymerisation e.g. cast PMMA or PTFE
Not meltable
Become clear when
melted, if not strongly
coloured
Carbonise on burning
In moulded parts: tendency to flash formation
Smell test
Important information for smell tests:
♦
Take great care when sniffing!
♦
The characteristic smell is not generally apparent until after the flame
has been extinguished, in the fumes.
♦
Fumes can be toxic.
Recognition of amorphous thermoplastics
Plastic
PS
Polystyrene
SB
Styrene butadiene
SAN
Styrene acrylonitrile
ABS
Acrylonnitrile butadiene
styrene
PVC rigid
PVC-U
Polyvinyl chloride, rigid
Spec.
weight
g/cm³
Outer appearance 1
Crystal clear,
clear clinking sound,
1.05
no plastic deformation,
is not easily scratched
Mostly non-transparent,
stretched parts are
1.04
whitish,
low plastic deforming
No plastic deforming
1.08
is not easily scratched
Non-transparent,
stretched parts are
1.03
whitish
… 1.07
strong plastic
deformability
Crystal clear,
1.38
… 1.4 E-PVC slightly cloudy,
low plastic
deformability, is not
easily scratched
PVC, soft
PVC-P
Polyvinyl chloride, soft
1.2
Is easily scratched
… 1.35
CA
Cellulose acetate
1.26
Blunt sound
… 1.32 is not easily scratched
CAB
Cellulose acetobutyrate
1.16
Blunt sound
… 1.22
1
2
Scratching refers to scratching with finger nail
Colour of flame can be influenced by additives
Burning characteristics 2
Smell of fumes
Lively bright yellow flame
very smoky (smutty)
does not drip
Typical smell of PS
sweet
similar to lighting gas
Same as PS
Similar to PS
something like rubber
Same as PS
Similar to PS
Same as PS
flame resistance is possible
Similar to PS
something like rubber
Bright yellow flame, sometimes
with green edge, smoky, does
not drip and rarely selfextinguishing
chars
Similar to rigid PVC
stronger tendency to drip, often
not self-extinguishing
(plasticizers)
Bright, sparkling green-yellow
flame,
forms blisters,
drips
Bright yellow flame,
forms blisters,
drips heavily
Pungent smell of Cl
Similar to rigid PVC
Burnt paper, vinegar
Rancid butter
Plastic
CP
Cellulose propionate
PMMA
Polymethylmethacrylate
PPE (PPO) mod.
Polyphenylene ether
(oxide), modified
PC
Polycarbonate
PSU
Polysulfone
PES
Polyethersulfone
PA am.
PA 6-3-T
Polyamide, amorphous
1
2
Spec.
weight
Outer appearance 1
g/cm³
1.19
blunt sound
… 1.23
crystal clear
blunt sound,
1.18
no plastic
deformation, does not
scratch easily,
Burning characteristics 2
Smell of fumes
Bright greeny-yellow flame,
similar to CA
Similar to CA
Bright crackling flame with blue
Typical of PMMA
core,
fruity-sweet
forms blisters,
(acetic ether)
does not usually drip
Does not easily burn,
erratic flame,
not transparent
1.06
smoky,
does not scratch
… 1.1
does not drip,
easily
usually self-extinguishing
chars
pale yellow or blue
Does not easily burn,
transparency,
bright yellow flame
1.2
strong plastic
smoky,
… 1.24
deformation,
forms blisters
does not scratch easily often self-extinguishing
1.24
amber coloured
transparent,
Does not burn easily, smoky
1.27
does not scratch easily
… 1.37
1.06
crystal clear
… 1.08
Scratching refers to scratching with finger nail
Colour of flame can be influenced by additives
Bright smoky flame
Phenol
and
styrene
Phenol-like (less
characteristic)
Weak smell of bad eggs
(hydro-sulphide )
Sweet, scratchy
Recognition of semi-crystalline thermoplastics
Plastic
Spec.
weight
g/cm³
PE soft
PE-LD
Polyethylene soft
Burning characteristics 2
Smell of fumes
More translucent than
0.91
rigid PE,
… 0.94 flexible,
is easily scratched
Bluish flame with yellow border
not smoky,
drips while still burning
Paraffin
PE hard
PE-HD
Polyethylene hard
0.94
Opaque,
… 0.96 more rigid than soft PE
See PE soft
PP
Polypropylene
Still more translucent
0.9
than soft PE,
See PE soft
… 0.91 more rigid than hard PE,
is not easily scratched
PA
Polyamide
PA 6 and 6.6
PA 11 and 12
POM
Polyoximethylene ,
Polyacetal
PET
Polyethylene terephthalate
PBT
Polybutylene terephthalate
Outer appearance 1
1.1.2
Yellowish,
… 1.1.4 blunt sound,
is not easily scratched
1.04
… 1.01
1.41
Thick white/opaque,
… 1.43 is not easily scratched
1.37
1.39
Thick whitish-yellow
opaque,
is not easily scratched
Opaque,
dark,
is not easily scratched
PPS
Polyphenylene sulphide
1.34
PTFE
Polytretrafluor ethylene
2.14
Opaque, translucent
… 2.20
1
2
Scratching refers to scratching with finger nail
Colour of flame can be influenced by additives
Paraffin,
something like
petroleum
Paraffin,
more strongly of
petroleum,
somewhat soursmelling (of ester)
Does not burn easily, bluish
flame with yellow border,
sometimes formes blisters,
drips and crackles,
pulls threads,
partly self-extinguishing
Burnt horn,
stronger with P6 and
6.6
weaker with PA 11
and 12
Small blue flame, sometimes
hardly visible
Pungent smell of
formaldehyde
Bright very smoky flame
drips
Sweet and scratchy
Does not easily burn,
bright, smoky flame
expands,
does not drip,
self-extinguishing
Does not burn,
does not melt,
becomes clear at high
temperatures
Weak smell of styrene,
of bad eggs
(S, H2S)
Pungent
hydrofluoric acid (HF)
Quiz
1. What are plastic materials?
Materials with nitrogen as the main component.
Synthetically produced macro-molecular materials with carbon as the
main component.
Material with short molecules and with oxygen as the main
component.
2. What happens when a plastic melt is heated at very high
temperatures?
The melt will show a very dense structure after cooling.
The plastic molecules decompose.
3. Which characteristics are typical for thermoplastic?
It can only be melted down once.
At room temperature it is elastic, like rubber.
It can be melted down and solidify as often as required.
4. Plastics are won through the polymerisation of monomers to
polymeric macromolecules. Which form of production does not count
as a method of polymerisation in the production of plastics?
Polycondensation
Polyaddition
Polynitration
Quiz
5. Which elements form the basis of plastic?
Silicone
Carbon
Oxygen
6. Carbon is an …
… atom
… molecule with few atoms
… giant molecule with many atoms
7. There are thermoplastics and thermosets. Which group do the
following plastics belong …
PF
PS
POM
MF
PA
UF
PC
ABS
LCP
Thermoplastic
Thermoset
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
8. A sample of plastic burns with a bright flame and drips. Which type of
plastic is it?
Thermoplastic
Thermoset
Elastomer
Quiz
9. Which description fits the molecular structure of thermoplastics?
linear thread-like molecules
closely meshed net-like molecules
widely meshed net-like molecules
branched thread-like molecules
10. A plastic sample breaks without plastic deformation. What type of
plastic is it?
Thermoplastic
Thermoset
Elastomer
11.Which of the following is a standard material for galvanising?
PA
ABS
PE
POM
Quiz
12.What is the difference between classic and thermoplastic elastomers?
Thermoplastic elastomers can be melted down again, but classic
elastomers can not.
Classic elastomers can be melted down again but thermoplastic
elastomers can not.
Classic elastomers are physically cross-linked, thermoplastic
elastomers are chemically cross-linked.
Thermoplastic elastomers are physically cross-linked, classic
elastomers are chemically cross-linked
13.What influence does the reaction of formation of a plastic material
have during its processing?
The materials must be pre-dried, otherwise the moisture will form
streaks on the moulded parts.
The reaction of formation has no influence in the processing of
thermoplastics.
In thermoset processing, the reaction of formation must be taken into
consideration.
14.Which plastics are characterised by a high chemical resistance?
ABS
PE
PMMA
PTFE
PP
PA
PVC
PS
FEP
CA
ERFE
SAN