TECHNOLOGY PTS-MARKETING IRRADIATION CROSS-LINKING
IRRADIATION CROSS-LINKING
Contents
Page
1.) Cross-linking and irradiation cross-linking
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2.) Advantages of irradiation cross-linking
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3.) Irradiation cross-linked components for industrial control equipment
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4.) Polymers for control panels
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5.) Insulating materials
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6.) Advantages of irradiation cross-linking of V-PTS-CREAMID
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7.) Summary
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4 1.) CROSS-LINKING AND IRRADIATION CROSS-LINKING The cross-linking of rubbers and thermoplastic polymers is a well-proven process for the improvement of the thermal properties. Chemical cross-linking or vulcanization of rubber normally takes place through the effect of heating after processing. The cross-linking process for thermosets takes place in a similar way. In thermosets the plastic molecules are also chemically linked by heat after processing. Cross-linked rubbers have a wide-meshed molecular network that keeps them soft and their properties change only slightly over a wide temperature range. Thermosets on the other hand are characterized by a very narrow-meshed network. Due to this fact they hardly change their high level of stiffness over a wide temperature range. The irradiation cross-linking of thermoplastic materials via electron beam or cobalt 60 (gamma rays) takes place separately after the processing. The level of cross-linking can be adjusted with the irradiation dosage and in many cases with the help of a cross-linking booster which is offered by PTS under the trade name BETALINKÂŽ.
2.) ADVANTAGES OF IRRADIATION CROSS-LINKING The following properties can be improved by irradiation cross-linking: Dimensional stability: Irradiation cross-linked materials retain their dimensional stability when heated over their former melting point (under low mechanical load). u Strength: Irradiation cross-linking normally creates higher strength as well as reduced creep under load if the application temperature is above the glass transition temperature (Tg) and below the former melting point. u Chemical resistance: Irradiation cross-linking leads to a huge improvement in the resistance to most chemicals. u Wear properties: Irradiation cross-linking often leads to improvement in the wear behaviour. u Hard/soft combinations: If the raw materials are properly selected hard/soft injection moulded parts can also be cross-linked by irradiation. u
Irradiation cross-linking of Polyethylene:
The figure shows time-yield lines for a PE-LD as a function of the irradiation level. The tensile stress is 5,6 N/mm 2 and the surrounding medium is air (temperature approx. 25°C).
Fig.1: Tensile creep test
Thermal exposure over 140°C is normally too high for thermoplastic elastomers. Irradiation crosslinked PTS-GAMMAFLEX types on the other hand behave like vulcanized rubbers and have a virtually unchangeable compression set up to 160°C. not cross-linked
crosslinked
Fig.2: Thermo-mechanical analysis (TMA)
The results of a thermo-mechanical analysis demonstrate that above the melting point, e.g. in the case of Polyamide 6.6 at temperatures over 260°C, cross-linked polyamide does not melt. It is however not a true thermoset, in fact its properties are more logically classified as somewhere between a cross-linked rubber and a thermoset depending on its cross-linking density. The cross-linking density can be adjusted through the use of BETALINK® Master IC/W65PA6* and IC/W25PA6* cross-linking boosters.
PTS also supplies irradiation cross-linkable thermoplastic polyurethane as well as irradiation cross-linkable polyester elastomers.
3.) IRRADIATION CROSS-LINKED COMPONENTS FOR INDUSTRIAL CONTROL EQUIPMENT The regulations of the Underwriters Laboratories No. 508 are valid throughout the world for conducting (live) parts in the industrial control panel sector, for motor controllers as well as automatic electrical control devices. In the so-called „Yellow Card” the most important characteristic data such as fire retardancy, ageing behaviour, comparative tracking index (CTI) etc. are documented and included as basis for device safety. The following list defines accurately the application range of UL508 in the case of industrial control equipment. 1.1 The regulations listed are valid for industrial control devices, installations and accessories that are used to start, stop, control, regulate or to protect electric motors. In detail (original text):
Fig.3: Irradiation cross-linked PTS-GAMMAFLEX
PTS-GAMMAFLEX is a thermoplastic rubber, that can be injection moulded and used for example for seals under the bonnets of motor cars.
a) Manual, magnetic and solid-state starters and controllers b) Thermal, magnetic and solid-state overload relays c) Pushbutton stations, including selector switches and pilot lights d) Control circuit switches and relays e) Float, flow, pressure and vacuum-operated switches
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6
f) g) h) i) j) k) l) m) n) o) p)
Resistors and rheostats Proximity switches Time-delay relays and switches Resistors and rheostats intended for industrial heating and lighting, including those for motor generator fields Control devices intended for industrial heating and lighting Solid-state time-delay relays Programmable controllers Numerical control systems Lighting dimmer systems and controls Mercury-tube switches Definite purpose controllers
CTI classification according to the UL-746A „Yellow Card”
Fig.4: Test table for CTI
1.2 These regulations concern devices up to 1500 V which are operated in ambient temperatures of from 0°C to 40°C. 1.3 The regulations also apply to industrial control panels which are installed in control devices for motor-operated industrial equipment. Examples are industrial switchgears, controllers, installations, interrupters, temperature monitors, motor protection devices and electrical instruments. A specification is established in UL508 for polymers in which the individual test criteria are accurately defined. Fig.5: Test set-up for CTI
4.) POLYMERS FOR CONTROL PANELS The Comparative Tracking Index measures the insulation safety of control panels under the influence of a damp environment. This is of great significance – especially for the use of polymeric components in washing machines and dishwashers. Polymeric materials for electrical housings must comply with UL-746C (CTI, HAI, HWI).
Fig.6: CTI according to ASTM D 3638-85 (IEC112)
HAI (High current Arc Ignition – UL-746A) HAI simulates the ignitability by means of an arc that is generated by the application of a high current [A]. Assessment is carried out according to the number of arcs which occur until the test material ignites.
HWI (Hot Wire Ignition – UL-746A) according to ASTM D3874-88 The HWI test simulates the ignitability of a plastic test sample by a glowing wire. The test criterion is the time until the sample ignites.
Fig.7: Test table for HAI Fig.9: Test table for HWI
Fig.10: Test set-up for HWI Fig.8: Test set-up for HAI
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RTI (Relative Thermal Index) according to UL-746B The RTI data provides information on long term material behaviour as a function of temperature. The UL temperature index specifies the temperature at which after 100,000 hours (11.4 years)
50 % of the original mechanical or electrical properties are retained. Determination of the long-term behaviour takes place by projection of the values using the Arrhenius equation.
TEMPERATURE-TIME DEPENDENCY ACCORDING TO ARRHENIUS Time (hrs) 100.000 9 8 7 6 5
(A) Control material
4 3 2
(B) Material under investigation
10.000 9 8 7 6 5 4 3 2
1.000 9 8 7 6 5 4 3 2
100 9 8 7 6 5 4 3 2
Impact Impact Strength Strength
Tensile Tensile Strength Strength
100% 100% 50% 50% 100% 100%
50% 50% Dielectric Dielectric Strength Strength 100% 100%
Time
155ϒ 145ϒ 135ϒ 125ϒ
Time
155ϒ 145ϒ 135ϒ
50% 50% Time
10
100 SB1213 Fig.11: Arrhenius diagram
120
155ϒ 145ϒ 135ϒ
140
160
180
200
250
300
5.) INSULATION MATERIALS Minimum requirements according to UL508 for live parts.
For particularly thin-walled parts the greatest success is achieved with PA6.6/GF materials with red phosphorus such as PTS-CREAMID-AG5FRPH1 (PA6.6 with 25% glass fibre V-0/0.8 mm) and PTS-CREAMID-AG5FRPH2 (PA6.6 with 25% glass fibre V-0/1.6 mm. These flame retardant types display maximum mechanical properties. However the applications are limited by colour configurations (natural = red-brown), contact safety, ageing behaviour (RTI) and processing properties.
This decision matrix specifies the material selection for live parts.
Due to irradiation cross-linking of PTS-CREAMID, which after the products are called V-PTS-CREAMID, the inflammability by means of hot wires (HWI test) is much improved. On the basis of those new properties according to the regulations in UL508 the usage of flame retardant additives is no longer necessary.
Because of its good performance in the HAI test Polyamide 6.6 with glass-fibre reinforcement (GF) is well known as an excellent material for circuit breakers, contact bridges, interrupters, contacts and similar applications.
Since the cross-linking booster is thermally the most sensitive component in the cross-linking formulation, it is added during injection moulding in the form of a masterbatch. This way an additional thermal load during compounding is avoided.
PA 6.6/GF, especially without flame retardants, is also characterized by its excellent Comparative Tracking Index.
The use of PTS-CREAMID grades with functional groups permits a further increase in the degree of cross-linking and better bonding of the crosslinking additive to the reactive polyamide groups.
a = RTI (elec.) see UL file no. E173999 Fig.12: Decision matrix
The risk of ignition due to high currents (High current Arc Ignition – HAI) is very low for Polyamide 6.6/GF. Even without flame retardant for example PTS-CREAMID-A3HG6* (PA6.6/GF ) achieves the best rating according to UL746A with the classification „0”. In general PA6.6/GF displays its technical performance limit in its hot wire flammability at thin wall thicknesses as well as in its ageing behaviour. PTS-CREAMID-A3HG6* with a 3 mm wall thickness still displays the best achievable HWI value of 0. With a wall thickness of 0.7 mm the HWI value is already 4 and, according to the decision matrix, V-0 materials must be used (see Fig. 12).
The diagram (see Fig. 13) shows the procedure of the addition of BETALINK® during injection moulding process. Detailed test series have shown that volumetric dosing units using screw conveyors should be avoided. Ready-mixed dry blends with BETALINK® are also available.
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The „Yellow Card” with the UL file number E173999 (see www.ul.com) is therefore only valid after irradiation cross-linking. Irradiation cross-linking must be carried out according to the strict rules of PTS since the company – as owner of the Yellow Card – is responsible for the final quality. The excellent thermal and mechanical properties will only be achieved through the combination of PTS-CREAMID, specially stabilized for irradiation cross-linking, BETALINK® and the subsequent irradiation cross-linking.
The following V-PTS-CREAMID types are UL-listed: V-PTS-CREAMID-A3H2G5 NC, BL, GY PA6.6 heat-stabilized 25 % glass fibre V-PTS-CREAMID-A3H2G7 NC, BL PA6.6 heat-stabilized 35 % glass fibre V-PTS-CREAMID-A3H2G10 NC, BK PA6.6 heat-stabilized 50 % glass fibre V-PTS-CREAMID-AG5FRPH1 NC, BK PA6.6 with flame retardant V-0/0.8 mm (red phosphorus), 25 % glass fibre V-PTS-CREAMID-AG7FRPH1 NC PA6.6 with flame retardant V-0/0.8 mm (red phosphorus), 35 % glass fibre V-PTS-CREAMID-AG10FRPH1 NC, BK PA6.6 with flame retardant V-0/0.8 mm (red phosphorus), 50 % glass fibre V-PTS-CREAMID-A3H2K8 NC PA6.6 heat-stabilized 40 % mineral, low-warpage The Relative Thermal Index RTI (electrical), also called the temperature index, describes the ageing behaviour of an insulating material. Non-cross-linked materials, which are normally used for live parts, lose their insulating properties at elevated temperatures (e.g. at 160°C), even after a very short time.
Fig.13: UL 94 - Procedur for V-PTS-CREAMID (irradiation cross-linked)
The approval procedure specifies that an existing, already-listed material should be submitted at the same time as the new material so that a comparison test can be carried out. As a reference material PTS selected the grade ULTRAMID A3X2G5 (PA6.6, 25 % GF, flameresistant with red phosphorus). After 787 hours of thermal ageing at 170°C this material had 50 % of its initial properties.
V-PTS-CREAMID-AG7FRPH1*
v/m
The materials of the V-PTS-CREAMID series demonstrate a considerably longer service life:
Just like the reference material ULTRAMID A3X2G5, V-PTS-CREAMID-AG7FRPH1* is also a PA6.6 with red phosphorus and special stabilization for the following irradiation cross-linking. However at 170°C the service life is already increased to 2,652 hours (50 % line). Because of the irradiation cross-linking the service life thus trebles in comparison with the reference product.
—— BASF ULTRAMID A3X2G5 —— V-PTS-CREAMID-A3H2G5
0
2.000
v/m
1.300 1.200 1.100 1.000 900 800 700 600 500 400 300 200 100 0
6.000
—— —— —— ——
0
2.000
8.000
10.000
4.000
6.000
V-PTS-CREAMID-AG7FRPH1 BASF ULTRAMID A3X2G5 V-PTS-CREAMID-A3H2G5 V-PTS-CREAMON-A3H2K8
8.000
10.000
Exposed Hrs
v/m
V-PTS-CREAMID-A3H2G5* This PA6.6 with 25 % glass fibre reinforcement (without flame retardant) including stabilization for irradiation cross-linking displays an electrical service life, which at 7,868 hours is ten times higher than the reference material.
4.000
Exposed Hrs
V-PTS-CREAMON-A3H2K8* V-PTS-CREAMON-A3H2K8* is a 40% mineral filled PA 6.6 stabilized for the following irradiation cross-linking. The product does not reach the 50 % line until after 5,670 hours – a six times higher service life than the competitive material!
1.300 1.200 1.100 1.000 900 800 700 600 500 400 300 200 100 0
1.300 1.200 1.100 1.000 900 800 700 600 500 400 300 200 100 0
—— —— —— ——
0
2.000
4.000
6.000
Exposed Hrs
Fig.14: Comparison of insulation properties
V-PTS-CREAMID-AG7FRPH1 BASF ULTRAMID A3X2G5 V-PTS-CREAMID-A3H2G5 V-PTS-CREAMON-A3H2K8
8.000
10.000
11
12
Fig.15: QMFZ2.E173999 Plastics component
6.) ADVANTAGE OF IRRADIATION CROSS-LINKING 0F V-PTSCREAMID ULB 746B materials and F50 points (hours) Client name: PTS STR project no.: 14740-0002 UL file no.: E173999 UL project no.: 99ME46256
Fig.16: Comparative table
Significant improvement in ageing behaviour (RTI elec.). u Reference testing: Ten times the service life in comparison with ULTRAMID-A3X2G5 at 170°C (F50 point see document STR/UL746B). At the beginning of the thermal ageing test the dielectric strength increases by 20-25 % over the initial value. It only starts to degrade after 5000 hours. u Values established in the „Yellow Card”: - RTI (elec.): 150°C with V-PTS-CREAMID-GF and MF – RTI (elec.): 140°C with V-PTS-CREAMID- FRPH1 (with red phosphorus) – RTI (elec.): 115°C with ULTRAMID-A3X2G5 u No melting of the contacts at temperatures over 258°C. u Extremely inflammable (HWI = 0-1). Flame retardant can be avoided according to UL. u Highest contact safety since no red phosphorus and no halogens are used. u
No restrictions of colours Minimum smoke and low toxicity in the event of fire u Lead-free soldering technology with temperatures of up to 280°C can be used without problems. In many cases liquid-crystal polymers (LCP) and thermosets can be replaced. u u
Soldering using the high-temperature processes (0.5 sec. at 450-500°C) is possible, e.g. for the manufacture of small coils.
Diagram (Fig. 17) shows that optimum results can be achieved if an irradiation dosage of 100 kGy is applied and the degree of cross-linking is con-trolled by the dosing of the cross-linking booster. On the other hand irradiation over 100 kGy does not lead to higher degrees of cross-linking.
With a component wall thickness of 1.6 to 2 mm the hot wire test according to IEC 695-2-1 was successfully passed at 750, 850 and 960°C.
The gel content determination with solvent (formic acid) is preferentially used for Polyamide 6, Polyamide 6.6 and Polyamide 12 to document the significant improvement in chemical resistance. Polyamide dissolves up to 100 % in hot formic acid. The gel content, which is also called the degree
100
80 Gel content (%)
u
of cross-linking, in this case is „0”. The degree of cross-linking or gel content depends on the irradiation dosage and the amount of cross-linking booster used.
60
40
6% BETALINK ®-Master IC/W 65 PA6 4% BETALINK ®-Master C/W 65 PA6 3% BETALINK ®-Master C/W 65 PA6
20
0
0
50
100
150
200
250
300
Irradiation (kGy)
Fig.17: Gel content as a function of the irradiation dosage ( )
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PTS-CREAMID A3H2G6 (PA6.6 GF30) PTS-CREAMID B3H2G6 (PA6 GF30) PA12 GF30 V-PTS-CREAMID A3H2G6 (PA6.6 GF30) Cross-link. V-PTS-CREAMID B3H2G6 (PA6 GF30) Cross-linked PA12 GF30 Cross-linked
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Shear modulus MPa
10 4 10 3
High degree of cross-linking
10 2 10 1 10 0
Low degree of cross-linking -50
0
50
100
150
Fig.18: Comparison of the shear modulus of PA6/PA6.6/PA12, cross-linked and not cross-linked
200
250
300
350
400
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The shear modulus graph of V-PTS-CREAMIDA3H2G6 shows that at 258°C there is still sufficient residual rigidity, and this doesn’t change any more until the product is thermally decomposed. In the temperature range between 222°C and 260°C irradiation cross-linked V-PTS-CREAMID-A (PA6.6) has significantly higher strength compared to irradiation cross-linked V-PTS-CREAMID-B (PA6) and PA12. PTS cross-linking tester PTS has developed a simple thermo-mechanical device for testing the cross-linking level in seconds.
1 kg can be applied. The temperature of the test mandrel can be set on the soldering unit. The construction simulates in a practice-orientated way the loading of an insulated body (switching bridges for contacts and relays) by means of a very hot metal contact. Typical testing of irradiation cross-linked polyamide components The 2 mm diameter test tip is selected as well as a 1 kg load and a testing temperature of 350°C. After applying the test load at 90°C over the former melting temperature no penetration into the sample surface will be seen if the cross-linking level is good (gel content > 65%). Typical testing of irradiation cross-linked components made of soft materials Materials such as PTS-GAMMAFLEX (EPDM), irradiation cross-linked PTS-UNIFLEX-E (polyester elastomer) or irradiation cross-linked TPU are tested at about 250°C with a test mandrel diameter of 6 mm. This simple thermo-mechanical testing device can even be used to check the cross-linking of classically vulcanized rubbers. A leading German electrical company presented its more than 15 years of experience in irradiation cross-linking in the area of contact housings during the PTS series of seminars held in 2001 on the subject of the irradiation cross-linking of components and materials for the electrical industry:
Fig.19: PTS cross-linking tester
The device consists of a precision soldering unit. The soldering tip has been replaced by an exchangeable cylindrical test mandrel (available diameters: 1, 2, 3, 4 and 6 mm). The moving test load weighs 1 kg. For rigid irradiation cross-linked materials an additional load of
Since the introduction of irradiation crosslinking, using PTS materials, the complaints rate for „melted contact bridges” has gone down to zero. u The use of irradiation cross-linked contact bridges results in a cost reduction of around 30% in comparison with the use of thermosets. u
In the past burr splinters of the thermoset contact bridges often caused failures in relays. u The wear resistance and the service life of the components has increased significantly. u
Although in comparison with 1987, components became smaller, ten years later the volume of irradiation cross-linked components has almost quadrupled at this company (see Figs. 20, 21).
7. ) SUM MA RY In the year 2001 BGS Beta Gamma Service irradiated around 50,000 t of materials, preformed parts and extruded products, around 30 % of this for the purpose of sterilization. 35,000 t plastic articles passed through this process for irradiation cross-linking and property modification. Cross-linking by electronic beam or gamma plants can no longer be regarded as niche technology.
Typical applications – electronic parts
Irradiation cross-linked components made from V-PTS-CREAMID for contact bridges, relays and switching parts are displaying a dynamic development with constantly increasing volume. Through the elimination of lead in the solder, the soldering temperatures will increase in coming years from 220-230°C to 270°C. In the area of SMD (surface mounted device) components further marketing opportunities are thus arising for V-PTS-CREAMID. In the meantime irradiation cross-linking has also established itself in other market segments. Thus for example more and more representatives of the automotive industry have discovered the potential of this innovative technology. Irradiation cross-linking is gaining in significance in the manufacture of petrol lines, plug connectors for starter cables, radiator parts and many other vehicle components.
We are grateful to BGS Beta-Gamma-Service for the generous support in the development of irradiation cross-linking technology.
Fig.20, 21: Comparison of range and part sizes between 1987 and 1997
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PTS Plastic Technologie Service Marketing- & Vertriebs-GmbH Hautschenm端hle 3 D-91587 Adelshofen Phone +49-(0)9865-821 Fax +49-(0)9865-720 info@pts-marketing.de www.pts-marketing.de
Rothenburg o.d.T.
Concept, editing, graphics and production: Pia Seifried, Hans-Peter Singer Printed by: Druck+Papier Meyer January 2003
MEDIUM OF THE PTS-GROUP: PTS-MARKETING, PTS-COMPOUND, CPP-CREATIVE-POLYMERS-PRODUKTION