Table Of ContentFabricating
Plastics
Edited by John D Beadle
Macmillan Engineering
Evaluations
Student Edition
Macmillan Education
ISBN 978-0-333-13793-2 ISBN 978-1-349-01588-7 (eBook)
DOI 10.1007/978-1-349-01588-7
©The Macmillan Press Ltd 1971
Student Edition 1972
Reprint of the original edition 1972
All rights reserved. No part of this publication may be
reproduced or transmitted, in any form or by any means,
without permission.
Published by
THE MACMILLAN PRESS LTD
London and Basingstoke
Associated companies in New York Toronto
Dublin Melbourne Johannesburg and Madras
SBN 333 13793 0
Preface
Intended for the student of materials and engineering, this book presents a
concise survey of thermosetting plastics and thermoplastics, indicating the
more important techniques of plastics fabrication and component assembly.
Later chapters discuss reinforced plastics and different coating techniques for
plastics. In keeping too with the necessary attention now being paid to environ
mental problems, such as pollution, there is a chapter on the disposal of plastics,
which puts this problem into perspective and reviews the current practices
and lines of research.
Although the need for Sl metric units to be used has been borne in mind, the
specialist authors have resorted to non-preferred metric units on occasions in
the interest of flexibility, and British units also appear where this reflects
current practice.
A companion volume to this book (Processing Plastics) covers a wide range
of forming methods used currently in plastics engineering.
Contents Chapter Page
5 ASSEMBLY TECHNIQUES 30
F A Dixon FIWM
Creators Limited
Chapter Page
6 REIN FORCED PLASTICS 36
1 THERMOSETTING PLASTICS 1 D Pickthall
Fibreglass Ltd
G W Parry ARIC
BP Chemicals International Ltd
7 COATING TECHNIQUES 43
2 THERMOPLASTICS 11 G E Barrett BSc PhD
Plastic Coatings Ltd
C C Gosselin BSc
Shell International Chemical Company Limited
8 DISPOSAL OF PLASTICS 51
3 MACHINING PLASTICS 17 Professor G Scott BA BSc
The University of Aston in Birmingham
T Lawrence and R Godwin
Tufnol Ltd
9 DESIGNING FOR PLASTICS 57
4 WELDING PLASTICS 23 V E Yarsley MSc DSc(Tech) CEng FRIC
H R Stilton Yarsley Research Laboratories Ltd
General Industrial Plastics (Research &
Development) Limited GLOSSARY OF TERMS 62
Chapter 1
Thermosetting
Plastics
G W Parry AR/C
BP Chemicals International Ltd
Thermosetting plastics are materials which once set in their
final shape cannot be re-shaped by means of heat or pressure.
They are intractable materials in their processed state. This
intractability is due to their chemical structure which
consists of a chemically bound three dimensional network.
This network is the result of a chemical reaction during
processing which can be initiated either by thermal or
chemical means. These curing reactions wiii be discussed
in greater detail later in the chapter (see phenolics and
polyesters).
Thermosets differ from thermoplastics in their greater
resistance to temperature and creep. However, in many
cases they cannot be prepared in light colours or as trans
lucent materials and suffer from insufficient impact
resistance.
Due to their intractability they cannot be re-shaped like
thermoplastics nor recovered and reprocessed. It is there
fore necessary to ensure that the component being produced
is of the correct dimensions before commencing a produc
tion run.
Most thermosetting materials are available in two forms,
ie resins and moulding compounds. The resins may be
used alone as in encapsulation processes but they are
normally used in conjunction with other materials. The
resins may be used with reinforcement, eg polyester/glass
laminates, or with fillers and reinforcement, eg moulding
compounds. This differs from the thermoplastic field where,
generally, the polymeric material is used without fillers
and/or reinforcement.
Thermosetting materials are normally processed by com
pression. transfer or injection moulding. In some cases,
such as polyester, 'hand lay-up' techniques are applicable.
The choice of process wiii depend on the component design
and choice of material.
in
The most common classes of thermosetting materials are having good gloss retention. As this field is well documented
alkyds, aminos, epoxides, phenolics, polyesters and sili and not within the scope of this book it will not be discussed
cones. The approximate consumption of these materials further.
in the United Kingdom during 1970 was as follows1:
Certain alkyd resins are used for the production of moulding
Alkyds 63000000kg
powders. In this case the resin is formulated on an un
Aminos 140 000 000 kg
saturated acid and alcohol producing an unsaturated
Epoxides 13 500000kg
polyester (see polyester resins). This polyester is reacted
Phenolics 76000000kg
with a non-volatile monomer, usually diallyl phthalate, to
Polyester 42500000kg
give a hard cross-linked structure.
These figures include resins used in the production of
Alkyd moulding powders are supplied in four basic forms,
moulding powders. The two main moulding powders are
granules, putty, fibrous and rope. Typical properties of
those based on amino and phenolic resins, the consumption
these materials are given in Table 1.
of which in 1970 was 43 500 000 kg and 31 000 000 kg
respectively.
All four forms can be processed using conventional com
pression moulding and transfer moulding techniques. These
ALKYD RESINS materials can also be handled satisfactorily on reciprocating
screw injection moulding machines. However, it is necessary
These materials are a special type of polyester. They are
to modify the feed hopper in order to injection mould
normally prepared by reacting together an acid, an alcohol
successfully the rope and putty types.
and the fatty acids of certain oils giving a resin having the
following main structural unit:
As the curing rate is rapid and proceeds without evolution of
volatile matter it is possible to produce void free mouldings
using a short cycle time. The rapid drop in viscosity of the
material with temperature allows moulding to take place
under relatively low pressure (15.5 MN/m2 maximum,
see Table 1).
The main applications for alkyd moulding powders are in
the electrical field, where good insulation properties
coupled with strength and heat resistance are required, and
in the decorative field when mouldings in pastel shades
where R is a long chain containing unsaturated groups. The
with good heat resistance and surface hardness are required.
resin is hardened by reacting together the unsaturated
groups. This reaction being initiated by a drier, eg lead
soap. AMINO RESINS
The main use of these resins is in surface coating applica There are two types of resin which fall into this class, urea
tions. They provide relatively low cost, flexible coatings formaldehyde and melamine formaldehyde resins.
Table 1. Typical properties of alkyd moulding powdersl.
Property Granular Putty Fibrous Rope
Shrinkage m/m 0.005-0.007 0.008-0.01 0 0.002-0.004 0.003-0.005
Moulding pressure MocN /m2 6.9-10.35 2.76-5.52 10 .35-15.50 4.14-6.9
Moulding temperature 130-165 130-165 130-165 122-160
Specific gravity 2.1-2.2 2.13-2.17 2.2-2.2 2.1-2.2
*Water absorption mg 55-65 25 50 20
Impact strength J/m 5.9-8.0 6.4-8.0 160-320 106-160
Flexural strength MN/m2 48.5-69 52-76 104-208 104
Tensile strength MN/m2 21-27.5 21-35 35-69 35-48.5
**Youngs modulus in tension MN/m2 10350-11750 8250-9650 7600-8950
Youngs modulus in flexure MN/m2 13 800-17 000 13 000-15 000 13000-16000 11000-12500
Electric strength MV/m 10.25-11.8 9.45-11.0 7.8-9.85 9.05-11.8
Dielectric strength at 1 MHz pF/m 31-37 31-35 28-38 35-45
Power factor at 1 MHz 0.018-0.022 0.018-0.023 0.015-0.020 0.012-0.Q14
Surface resistivity ohm > 1013.0 > 1013o6 > 1Q12.S > 1014
Volume resistivity ohmm > 1Q14 > 1Q14 > 1013.5 > 1014.S
****Comparative tracking index 235 210 195
••• Arc resistance sec 190 182 185 180-200
• As per BS2782 except immersion in boiling water is 60 minutes.
•• ASTM D790/58T (G.1.)
* * * ASTM D495/58T
•••• BS2781
All other tests to BS2782
2
Urea formaldehyde resins
Application kg
The main outlet for urea formaldehyde resins is in adhesives
Moulding Powders 43 500000 for plywood and chipboard. The ratio of urea to formalde
Adhesives 45000000 hyde used wiii influence the properties of the adhesive.
Surface Coating 10000000 For example, a resin with a high formaldehyde to urea
Textile Treatment 5000000
Paper Treatment 8000000 ratio wiii give an adhesive having the best clarity, water
Laminating 4500000 resistance and mechanical properties. The main disad
Others. Foundry. Foam 8000000
vantage of this type of adhesive is its poor water resistance.
Table 2. Amino consumption in the UK during 19701•4 Hence, it cannot be used for exterior applications where it
is superseded by adhesives based on phenolic resins.
The first stage in the resin process is to produce long
unconnected chains which then react together on further Urea resins are also used to impart crease resistance to
heat treatment giving the intractable product. This harden fabrics, to improve the wet strength of paper and in paints.
ing process can also be carried out at room temperature For the paper application it is necessary to use an 'ionic'
using an acid hardener, eg phosphoric acid or an acid resin. These 'ionic' resins are produced in such a way that
donor such as ammonium chloride. Details of the mech the molecules carry an electrical charge. The resins can
anism of resin formation and cure are given below? also be processed to produce a foam having a very low K
value.
CO(NH2), + CH20 ---->(NH2·CON = CH2)
Urea Formaldehyde
Urea resin based moulding powders are used in the follow
ing applications: domestic electrical accessories (plugs and
/N'-.
3(NH2·CON = CH2) -- CI H2 CI H2 sockets); toilet seats; bottle caps and closures. When cured
these materials are very brittle and should not be used for
H2N·OC·N......_ CH2_ ......N·CO·NH2 load bearing applications. The major usage being in
/ electrical and closure applications. Physical properties of
these materials are given in Table 3.
NH-----CH2.--------NH
I I
Urea moulding powders have the advantage over phenolic
co co
I I materials in that they can be prepared in light colours and
N N as an almost translucent material with the correct choice
/'-... /'-.
CI H2 CIH 2 CIH 2 CIH 2 of fillers. The cured resin has a refractive index of 1.55 and
so inclusion of cellulose as a filler, refractive index 1.55-1.56,
... HN·CON N-CO CO-N N·CO·NH·CH2 •••
'cu;' ~" ~ "cu;' wiii produce nearly translucent materials.
I I
CH2 CH2 The moulding properties of the material can be altered by
I I
the choice of resin. For example, a high molecular weight
NH NH
CH2 1 I /CH2...,_ resin wiii produce a moulding powder having a stiff flow
... HN·OC·N/ 'N-CO CO-N N·CO·NH·CH2 ••• but relatively long cure. The cure rate can be improved by
I I I I
Cflz CH2 CH"2 CH2 leaving some lower molecular weight materials in the
'-... N / N / resin. Moulding powders based on high molecular weight
I I resins also have the least shrinkage and this can be main
CO·NH·CH2••. CO·NH·CH2 ... tained and the flow increased by additions of up to 1 % of
CROSS LINKED RESIN
a plasticiser.
As with other thermosets both these materials are supplied
as resins or coupled with fillers, etc, as moulding materials. In most cases there is an optimum temperature for cure as
Table 2 gives an estimate of the main areas of use of amino increasing the temperature wiii reduce the viscosity of the
resin in the UK for 1970. material but decrease the cure time. Therefore, if too high
a moulding temperature is used, the material wiii cure
From Table 2 it can be seen that in many instances these before it has had time to flow and fill the mould cavity.
resins are used for applications which cannot be considered
to be of an engineering nature, eg surface coating and
These materials are normally processed by compression
textile treatment. However, composite materials, eg ply
moulding at temperatures of 135-170°C with pressures
wood, laminates, prepared using these materials may
varying between 20 and 55 MN/m2• Cure times can be as
possibly be considered an engineering material. Moulding
short as 20 seconds with a fast cure material.
powders produced from these two resins are nearer true
engineering materials in so much as they could be moulded
into engineering shapes and components. Melamine formaldehyde resins
Two materials are available, riz. resin and moulding
The properties and applications of these two classes of powders. The resins tend to be used only for special appli
resin wiii be dealt with separately. cations because of their cost.
3
Urea Melamine
ASTM
Property
Test Method
Wood-Filled a-Cellulose-Filled Wood-Filled a-Cellulose-Filled Glass-Filled
Mould shrinkage m/m 0.006-0.01 0 0.005-{).01 0 0.007-0.008 0.004--0.009 0.002-0.005
Moulding temperature oc 13~165 135-175 140-170 140-170 14~160
Specific gravity 0792 1.4-1.5 1.~1.55 1.~1.55 1.~1.55 1.9-2.0
Water absorption mg 24 hrs at 20oc 50-130 40-130 30-40 10-40 0-10
Impact strength J/m 0256 12-15 13-16 14-20 13-17 19-27
Flexural strength MN/m2 0790 80-120 80-125 6~0 90-120 80-120
Tensile strength MN/m2 0638 40-55 50-75 40-60 50-85 42-70
Youngs modulus in tension MN/m2 0638 6900-9650 6900-9650 "=<7900 8300-11 000 14 000-28 000
Electric strength' MV/m 0149 12-17.5 12-16 14-16 12-16 6-10
Dielectric constant at 1 MHz pF/m 0150 53.~75.5 57.~2 49-52.5 62-80 49-66
Power factor at 1 MHz 0150 0.025-{).040 0.020-0.030 0.025-{).040 0.025-{).045 0.020-0.030
Volume resistivity ohm m 0257 1011-1014 1011-1014 10"-1013 1011-1013 1011-1014
Comparative tracking index IEC 121 >600 ---800 >600 >600 >600
Arc resistance sees 0495 80-130 90-130 70-110 120-130 170-200
• Short time at 25oC
Table 3. Typical properties of amino moulding powders2.
Melamine resins are used with various reinforcements to 0
/ '\
produce laminates for special electrical applications and
epoxide groups (-CH -CH-) or the hydroxyl groups
for decorative purposes. The main use being in the decora 2
(-CH-OH). Acids or amines may be used for the harden
tive field where the laminates are used for household
ing process 7 and the properties of the cured product will
working surfaces and wall cladding. In this decorative
depend, to a large extent, on the curing system used. Rela
application the resins are used in conjunction with a thin
tively flexible cured materials may be prepared using a
layer of a IX-cellulose surface paper to produce a hard,
curing system that produces a low cross-linked density.
scratch resistant, transparent coating. This coating acts as
a preservative for the decorative pattern used in the pre
Amine hardening systems are used at room temperature
paration of the laminate.
giving a fast cure rate and a product having good chemical
resistance. Care must be taken with this type of curing
As with resins, moulding powders based on melamine are
agent as many of them are skin sensitisers.
used for specialised applications. The two main areas of
application are tableware, where their improved water and
Cure at elevated temperatures is normally carried out with
scratch resistance compared to urea based materials makes
acids or acid anhydrides. The anhydrides are preferred
them ideally suitable for this purpose, and for high per
because they are more soluble in the resin and do not
formance electrical goods. Their electrical properties are
produce as much water as the acid during cure so that
superior to urea formaldehyde based materials under
there is less tendency for foam formation. The advantages of
conditions of high temperature and humidity. They can be
this curing system, over an amine system, are a lower
made in more attractive colours than phenolic moulding
exotherm, less skin irritation and with the correct choice
powders and have superior track resistance.
of acid a product with a higher heat distortion temperature.
They do, however, produce cured products which are less
In the UK these materials are processed mainly in the
resistant to alkalis.
same manner as urea materials (compression and transfer
moulding) although some grades can be injection moulded The main applications of these resins are surface coating
on suitable machines. Care must be taken to establish the and encapsulation. Other applications are in adhesives,
optimum moulding condition for each application as cure prototype tooling, flooring, laminating and, to a lesser
times can affect properties. 5 extent, in moulding materials.
Typical physical and electrical properties of melamine Apart from decorative coating, amine cured resins are used
moulding materials can be found in Table 3. for protective coatings in chemical plant and oil refineries.
Adequate chemical resistance is obtained by room tem
perature cure which obviates the necessity of heat treat
EPOXIDE RESINS
ment as is required in the case of phenolic resins.
The most important commercial resins of this type are t
those based on bisphenol A and epichlorhydrin. The Laminates prepared from these resins have improved
general structure of the uncured material is as follows6 : mechanical properties, heat resistance and chemical resis-
0
/ \ CI H3 OI H CI H3 I 0 "-
CH 2 • CH • CH 2--.---u.----,. I -0-o·cH2 · CH·CH2 o---0-l -Q-o·CH2·CH·CH2
CH n CH
3 3
The hardening of these resins may be effected through the
4
General Heat
Flexibilised
Purpose Resistant
Flexural strength MN/m2 95 71 71
Flexural modulus MN/m2 1 900-2800 2500-3400 1 000-2250
Tensile strength MN/m2 62 42 62
Compressive strength MN/m2 95 132 76
Elongation % 1.2-4.0 0.6--2.5 6.0
lzod impact strength J/m 10-26 10-24 42-80
The electrical properties of all three grades are very similar at room temperature
Electric strength MV/m 17.5
Dielectric constant at 1 MHz pF/m 26
Volume resistivity ohm m 1014
Surface resistivity ohm 10115
Power factor at 1 M Hz 0.015
Arc resistance sees 100
Table 4. Typical properties of cast epoxide resins2•
tance when compared with polyester materials, although a 3 mm section. Their main processing advantage is that
they are more expensive. due to their fluidity they can be moulded at relatively low
pressure 3.5-13.5 MN/m2, a characteristic which enables
When used for potting and prototype tooling, fillers can be them to be used to encapsulate delicate electronic com
added to reduce the exotherm and the thermal expansion. ponents. They would, however, only be used where high
The low exotherm and the correspondingly low shrinkage temperature electrical properties are of paramount im
makes these material very suitable for prototype tooling 7 •8•9. portance because of their high cost. The main application
Aluminium filled epoxy resin moulds can be used for of epoxy moulding powders is for specialised electronic
compression moulding at temperatures up to 200°C and components.
pressure of 14 MN/m2•
PHENOLIC RESINS
Moulding powders produced from epoxide resins can be
supplied in granular or powder form. Typical properties These are resins based on phenol, cresol or modified
are given in Table 6. phenols and formaldehyde. They can be supplied as solids,
liquids, or solutions. The hardening of these materials is
These materials can be processed in the same way as other
an example of a heat initiated process as opposed to a
thermoset materials. Moulding temperatures are normally
chemical initiated curing reaction.
higher, being in the range 250-350°C, in order to obtain
economical cycle times. If moulded at normal temperatures, A B heat
---+ A+B
150-165°C, a cure time of 3 minutes would be required for Hardener
Table 5. Typical properties of epoxyjglass laminate2• Resin +A --he-at+ Hardened infusible product.
Flexural strength MN/m2 531
Flexural modulus MN/m2 24000 There are two forms of phenolic resin, novolacs and resols.
Tensile strength MN/m2 345 A novo lac is a fusible resin incapable of hardening without
Compressive strength MN/m2 352 the addition of a hardening agent. A resol is a resin which
Specific gravity 1.85
Dielectric constant at 1 MHz pF/m 38 is capable of hardening under the influence of heat without
Dissipation factor 1 MHz 0.014 the addition of any other product.
Resin content % 35
A typical novolac structure11 being
Table 6. Typical properties of epoxy moulding materials10•
Glass-Fibre Mineral
Filled Filled
Tensile strength MN/m2 97-207 34.5-48.5 whereas a resol structure6 would be
Tensile modulus MN/~ 20700
Flexural strength MN/m2 138-180 70-105
OH OH
Compressive strength MN/m2 172.5-207 124-172.5
Impact strength J/m 850-1600 26.5-48.0
Specific gravity 1.8-2.0 1.8-2.06 HO·CH2-6-CH2---("'CH2-D-CH2--6-CH2·0H
Volume resistivity ohmm 1016 1016 "'("oH
Electric strength MV/m 14.2 13.0-15.7
Dielectric constant at 1 MHz pF/m 35.5-44.5 35.5-44.5 CH2·0H
Arc resistance sees 125-140 150-180 It is the presence of reactive methylol groups (-CH OH)
2
Water absorption % 0.05-0.095 0.1
in the resol molecule which make it unnecessary to add a
Mould shrinkage % 0.4-1.0
hardening agent in order to achieve a cured product.
5
