RUBBER COMPOUNDING TECHNOLOGY
SUDHA.P DEPUTY DIRECTOR(RIDT) RUBBER TRAINING INSTITUTE DEPARTMENT OF TRAINING RUBBER BOARD KOTTAYAM-686 009
[email protected] Mob: 94964 13731
RUBBER COMPOUNDING
COMPOUND It is a homogenous mixture of ingredients used in a particular product manufacture such that the properties of most of the ingredients are unchanged in the final product whereby providing a defined set of mechanical properties. COMPOUNDING It is the science of selecting and combining elastomers and additives to obtain physical and chemical properties for a finished product.
RUBBER COMPOUNDING OBJECTIVE 1. To secure certain properties in the finished product to satisfy the service requirements. 2. To attain processing characteristics necessary for efficient utilization of available equipment. 3. To achieve desirable properties and processability at the lowest cost. The most important factor in compounding is to secure an acceptable balance among demands arising from the above three criteria.
MAJOR OBJECTIVES OF COMPOUND DEVELOPMENT PROCESS REQUIREMENT Proper mixing (Incorporation, dispersion, distribution and plasticization) Viscosity/process safety (ML1+4, MS) Stickiness and tackiness Shaping (Calendering, Extrusion, Assembling and Moulding) COMPOUND PROPERTY REQUIREMENT Hardness Stress-Strain properties (TS, EB, M-100, M-300, tear) Abrasion resistance Hysteresis & set properties Resistance to cut growth, fatigue, flex cracking
MAJOR OBJECTIVES OF COMPOUND DEVELOPMENT RESISTANCE TO DEGRADATION
Heat, Oxygen, Ozone Flame Liquids Light
MISCELLANEOUS PROPERTY REQUIREMENTS Low temperature flexibility Electrical properties Permeability Contact with food stuff and drugs Bonding to metal & textiles Swelling Other specific requirements
CLASSIFICATION OF COMPOUNDING INGREDIENTS 1. 2. 3. 4. 5.
6. 7. 8. 9. 10.
Elastomers Vulcanizing Agents (curatives) Accelerators Activators and Retarders Antidegradants (Anti-oxidants, Antiozonants, Protective waxes ) Processing aids (Peptisers, Lubricants, Release Agents) Fillers (carbon black, non-black materials) Plasticizers, Softeners and Tackifiers Colour pigments Special Purpose Materials (Blowing Agents, Deodorants, etc.)
COMPOUND DESIGN DESIGN REQUIREMENTS SERVICE REQUIREMENTS/VULCANISATE PROPERTIES PROCESSABILITY ECONOMICS DESIGN BASED ON CUSTOMER SPECIFICATION/REQUIREMENTS COMPETITOR'S SAMPLE DEVELOP A NEW PRODUCT
POLYMER SELECTION CRITERIA
Cost Ease of mixing Strength requirements Modulus or stiffness requirement Abrasion resistance requirement Elongation requirement Oil resistance requirement Low temperature requirement Fatigue requirement Tack Set of stress relaxation Service temperature Dynamic properties (hysteresis, damping resistance) Flammability Chemical resistance
POLYMER SELECTION
SHOULD HAVE THOROUGH KNOWLEDGE ABOUT POLYMER PROPERTIES REFER STANDARD SELECTION CHARTS/COMPARATIVE CHARTS BLENDS OF POLYMERS PROCESSABILITY FACTOR-suitability for the processes and methods adopted COST FACTOR AVAILABILITY OF DATA ON POLYMER GRADES, PROPERTIES, START UP FORMULATIONS ETC.
VULCANIZING AGENTS TYPE
COMMON USE
Sulphur or Sulphur bearing materials
Natural Rubber, Isoprene, SBR, Butyl, Poly Butadiene, EPDM, Nitrile
Organic Peroxides
Urethane, Silicone, Chlorinated Polyethylene, PVC/Nitrile
Metallic Oxide
Polychloroprene, Chlorosulphonated Polyethylene, Polysulphide
Organic Amines
Acrylic, Fluorocarbon, Epichlorohydrin
Phenolic Resins
Butyl
CURING SYSTEM Selection of curing system is based on:
Base polymer Processing conditions Curing conditions Service requirement
Base polymer
Saturated rubber – peroxide e.g. EPR with DCP Unsaturated rubber-peroxide, sulphur/accelerator & resins, e.g. EPDM with DCP, NR with sulphur accelerator, IIR with Resin Special Polymers – Metal oxide, Dioxime, Resin e.g. CR with ZnO/MgO
ACCELERATORS An accelerator is usually a complex organic chemical which takes part in the vulcanization, thereby reducing the vulcanization time considerably- Organic amines & its derivatives . It also improves the properties. Its action may be: slow-
eg. Guanidines, Diphenyl guanidine (DPG) Di ortho tolyl guanidine(DOTG)
medium-
eg. Thiazoles,
Mercapto benzo thiazole (MBT) Di benzthiazyl di sulphide) (MBTS)
fast ( ultra)- eg. Thiurams, Tetramethyl thiuram monosulphide (TMTM) Tetramethyl thiuram di sulphide (TMT)
Dithiocarbamates, Zinc diethyl dithiocarbamate (ZDC) Zinc dibutyl dithiocarbomate(ZDBC)
Delayed-action fast- eg. Sulfenamides Cyclohexyl benzthiazyl sulfenamide (CBS) Dicyclohexyl benzthiazyl sulfenamide (DCBS) Morpholino thio benzthiazylsulfenamide (MOR) Tertiary butyl benzthiazyl sulfenamide (TBBS)
CURING SYSTEM (Contd..) Accelerator Activator
ZnO and Stearic acid for sulphur cure system TAC for peroxide cure system
Processing condition
Type of processing equipment used Temperature build up during processing Extent of rework usage Rheological property requirement
Curing conditions
Type of the product Method of curing employed Temperature of curing Flow requirement during curing
CURING SYSTEM (Contd..)
Service Requirements Service temperature Duration of exposure Mechanical property requirement. Dynamic property requirement Ageing behaviour and permanent set requirements. Special property requirement.
FILLERS •
Fillers are materials used to extent the range of physical properties, to reduce compound cost, modify the processing properties and to influence the chemical resistance of the compound. The effect of a filler on rubber depends on• structure • particle size • surface area • geometrical characteristics
FILLERS Reinforcing Type
Extending Type
Carbon Black (listed in order of increasing particle size)
N220 (ISAF) N330(HAF) N550 (FEF) N762 (SRF-LM) N990 (MT)
Non-black
Silica Zinc Oxide Magnesium Carbonate Aluminium Silicate Sodium Aluminosilicate Magnesium Silicate Calcium Carbonate Barium Sulfate Aluminium Trihydrate Talc and Soapstone
• • • • •
•
reinforcing carbon blacks non- reinforcing carbon blacks reinforcing non- black semi reinforcing non- black non- reinforcing non- black Reinforcing carbon blacks
Furnace black SAF – Super Abrasion Furnace ISAF – Intermediate Super Abrasion Furnace CF - Conductive Furnace SCF - Super Conductive Furnace
HAF
-
High Abrasion Furnace (Low structure and high structure)
FF
-
Fine Furnace
FEF -
Fine Extrusion Furnace
GPF -
General Purpose Furnace
SRF -
Semi Reinforcing Furnace
Thermal Black MT - Medium Thermal • • •
•
Channel black EPC Easy Processing Channel Reinforcing Non- black Precipitated silica and fumed silica Semi Reinforcing Non-black aluminium and calcium silicates high styrene resins phenolic resins
Fillers Selection is based on • Reinforcement • Cost • Processing requirement • Colour requirement • Service requirement • Any other special requirement
Compound Designing – Hardness phr required for 1 unit increase in Hardness
Polymer Hardness
NR
SBR
CR
NBR
37-40
39-41
41-43
42-44
2
1.6
1.5
Ppt. Silica
3
3.3
2.2
Calcium silicate
5
4.1
4.5
Hard clay
7.9
5.6
5.0
Soft clay
6.6
8.4
5.0
Whiting
Compound Designing – Hardness Contd.
NR
SBR
IIR
CR
PBR
NBR
EPDM
Black
ASTM Dsgn
DBP
1.5
1.8
1.3
1.2
2.2
1.7
2.4
SAF
N110
113
1.7
2.0
1.5
1.3
2.5
1.9
2.7
ISAF
N220
114
1.9
2.3
1.7
1.5
2.8
2.1
3.0
HAF
N330
102
2.3
2.8
2.1
1.8
3.4
2.6
3.7
FEF
N550
119
2.5
3.1
2.3
2.0
3.8
2.9
4.1
GPF
N660
90
2.8
3.4
2.5
2.2
4.2
3.2
4.5
SRF
N774
70
2.1
2.6
1.9
1.7
3.2
2.4
3.4
HAFLS
N326
72
SOFTENERS
Processing aids A softener is an ingredient that : 1. speeds up the rate of polymer breakdown 2. helps to disperse the other compounding ingredients 3. helps to reduce nerve within the compound 4 can impart building tack 5. improves the processing properties and modify the final compound properties 6. adjusts the compound cost and reduce power consumption during processing
Mineral petroleum oils They are available from petroleum industry. paraffinic naphthenic aromatic Plasticizers They are of the synthetic type , used where mineral oils are not compatible with the rubber dibutyl phthalate -DBP di isobutyl phthalate-DIB di octyl phthalate - DOP *Factices They are vulcanized vegetable oils used as plasticizers to get smooth compound in extrusion (brown) & to reduce abrasion resistance in products like erasers (white)
PROCESSING AIDS COMPOSITION
EXAMPLE
FUNCTION
Activated Dithiobisbenzaldihide
Pepton 44
Peptizer for NR
Xylyl Mercaptans
RPA-3
Peptizer for NR,IR,SBR and NBR.
Low-molecular-weight polyethylene
A-C Polyethylene 617A
Release agent, Lubricant
Calcium Oxide
Desical P
Desiccant
Aliphatic-naphthenicaromatic resins
Strucktol 60NS
Homogenizing agent for all elastomers.
Paraffin wax
Release agent, lubricant
Polyethylene glycol
Carbowax PEG3350
Activator for silica, lubricant
Petroleum hydrocarbon
Petrolatum
Release agent, lubricant
PROCESSING AIDS
Selection is based on
Nature of polymer Solubility parameter Viscosity requirement Filler dispersion Processing requirement Any other special requirement
ANTI-DEGRADANTS- They are agents added to rubber to improve ageing properties, resistance to oxygen, ozone, alkali, acid, chemicals etc TYPE
EXAMPLE
STAINING
Hindered Phenol
2,6 Di-t butyl p-cresol
None to slight
Hindered Bis-phenols
Anti-oxidant 2246
None to slight
Hindered Thiobisphenols
Santowhite Crystals
Slight
Hydroquinones
2,5 di(tert-amyl) hydroquinone
None to slight
Phosphites
Tri(mixed mono and di-nonylphenyl) phosphite
None to slight
Diphenylamines
Octylated diphenylamine
Slight to moderate
Naphthylamines
Phenyl-alpha-naphthylamine
Moderate
Quinolines
Polymerized 2,2,4, tri-methyl 1,2-dihydroquinoline
Slight to moderate
Carbonyl-amines condensation product
Reaction product of diphenylamine and acetone
Considerable
Para-phenylene diamines
Mixed Diaryl-p-phenylene diamines
Considerable to severe
ANTI-DEGRADANTS Selection is based on
Type of protection desired Environment in which the product is exposed. Chemical activity Persistence (volatility and extractability) Nature of end use Discolouration and staining Toxicology Cost
OTHER MATERIALS
Peptizers : They speed up the rate of polymer break down and also control the speed of breakdown, decreasing nerve within the compound and shrinkage during subsequent processing. penta chloro thiophenol Renacit VII
Retarders : They help to increase the scorch time (premature vulcanization) but do not interfere with the vulcanization
cyclohexyl thiophthalimide (CTP) Santogard PVI
Stiffeners : Stiffeners are used to improve the plasticity of the compound in very small quantities. dihydrazine sulfate
Flame retardants Chemicals which can improve the flame retardency of the compound highly chlorinated paraffins and waxes, antimony oxide, aluminium oxide and selenium
Colors and pigments They provide esthetic look and appearance for the product [organic and inorganic] Tackifying agents
They are useful in providing tackiness to the compound. wood rosin, coumarone resins, pine tar.
Blowing agents They are materials which provide either open or closed cell structure by producing CO2 or nitrous gases during vulcanization dinitroso pentamethylene tetramene (DNPT) azocarbonamide (ADC) baking soda (sod.bicarbonate)
Bonding agents They facilitate adhesion between rubbers, fibers, fabrics, metals chemlok, resorcinol – formaldehyde- latex for dipping of nylon cords in tyre manufacture Reordants They are basically perfumes added to mask odors of rubber during processing and service life of rubber. Bactericides / fungicides to resist microbial agents
STEPS OF COMPOUND DEVELOPMENT Modification of existing compound with respect to
Cost/price Processing Performance
New compound development
Set specific objectives (properties, processing, price etc) Select best polymer Study test data of existing compounds Survey compound formulations. Choose starting formulation. Develop compound in the laboratory to meet objectives. Estimate cost of the compound. Evaluate processability in factory Use compound to make a product sample. Test product sample against performance specification.
The mix
Rubber Vulcanizing agent Accelerator/s Activator Antidegradents Fillers Softner Other materials when necessary
100 0.3 - 3.5 0.5 – 1.5 2.5 – 5.0 1-2 As required
5 - 10 As required
STAGES OF PRODUCT DEVELOPMENT Compound Design, Lab Evaluation, Shop floor processing trials (mixing, moulding,extrusion, calendaring, fabrication of product, curing, etc ), Analysis of feedback , Compound Modification (if reqd.), Testing of processing properties and of finished product, Field trials, Validation of manufacturing process.
:
MIXING
Compound properties & batch to batch consistency depends on : Compounding formulation design, Raw materials Quality, Effects of Further Processing, Rework blending (Rework Quality & Quantity) Rubber processing equipments available & their condition. The knowledge of Raw Materials used & their behavior during mixing and further processing is essential
MIXING
Mixing Process is the base of Rubber Product Manufacturing Technology. The success of subsequent processing & finished product quality depends entirely on the quality & batch-to-batch consistency of the mixed compounds. ‘Mixing’ deals in deciding: What equipment to use (speeds, pressures, temperature, time cycles, procedures, etc. to blend the selected compounding ingredients into a properly mixed compound. How to achieve High Degree of Dispersion and batch to batch consistency.
MIXING • Mixing process can be sub-divided into three stages : 1) Feeding ingredients to mixer (correct quantities at correct times at correct temperature.), 2) Actual Mixing of the ingredients, 3) Discharge of mixed compound and its shaping, cooling, packaging and storage for the next process.
38
MIXING Five main steps involved in the Mixing Operations : 1.
Sub Division Of larger lumps & aggregates,
2. Incorporation Of powders or liquids 3. Dispersion Involves reduction of the size of agglomerates, 4. Simple Mixing Involves moving particles from one point to another. 5. Viscosity Reduction By breakdown of the polymer and transforming it to desired viscosity. 39
MIXING • A good Dispersion rating requires : High Shear Stress (i.e. High mix viscosity), High Filler Loading, Polymers of not too low viscosity, Low Mixing temperatures, Charging oils at the end of mixing cycle. • During Dispersive mixing, the carbon black agglomerates are broken down to less than 1 micron size. • Dispersion largely depends on shear stress ( a critical value of shear stress is necessary to breakdown the agglomerates below which no dispersion action will take place). 40
Two-Stage Mixing in Internal Mixers • To avoid scorching of compound; a two stage mixing procedure is used. • Stage 1 - carbon black and other non vulcanizing additives are combined with the raw rubber and Higher mixing temperatures up to 160°C are used. [The term Master Batch is used for first stage mixture] • Stage 2 - After stage 1 mixing has been completed, and time for cooling has been allowed; stage 2 mixing is carried out in which vulcanizing agents are added. Lower mixing temperatures 90-100 °C are used. [The term Final Batch is used for second stage mixture]
41
MIXING
42
NR Mastication & Blending NR+SR • Mastication of NR to Optimum Degree and proper blending of Synthetic Rubbers with NR is Very Important . • Ingredients which are difficult to disperse (e.g. hard carbon blacks, Ppt. silica, ZnO, etc) require Higher stock viscosity to disperse well.
Stock Viscosity Control is achieved through:
Compounding formulation design,
Close temperature control during mixing operations,
Use of specific sequence for addition of ingredients ,
Remixing of the stock after cooling. 43
• Raw NR is dry & tough (Mooney Viscosity at 100°C > 80) and has to be masticated to a Workable Level of Mooney Viscosity of 50 to 60. • Most Synthetic Rubbers are produced to a tailored Mooney viscosity (range 50 – 60) and hence ‘Mastication’ is not necessary. •
Keep Lower Mastication Temperatures when a Two-Roll mill is used (say, 60-70°C).
• Viscosity of Masticated NR should be closer to the Synthetic Rubber to be blended with it. • NR-BR blends require higher shear rates for proper blending and hence Banbury / Intermix are more suitable than a mixing mill. 44
EFFECT OF MASTICATION TEMPERATURE ON MOONEY VISCOSITY OF NR MILLING TIME, MIN
MOONEY VISCOSITY (ML1+4 @ 100°C, UNITS) WITHOUT PEPTIZER
WITH PEPTIZER (DBD=0.5 PHR)
@ 70°C
@ 100°C
@ 70°C
@ 100°C
0
95
95
95
95
3
76
85
58
56
6
57
83
40
40
9
47
68
33
28
12 45 START TEMPERATURE, OPEN MILL (TIME = 8 MIN) 70 °C 100 °C INTERNAL MIXER (TIME 4 MIN) 150 °C 160 °C
65 30 24 MOONEY VISCOSITY (ML1+4 AT 100°C), UNITS PEPTIZER = 0 55 75
PEPTIZER = 0.25 42 42
PEPTIZER = 0.5 36 37
90 88
54 48
42 36 45
Mixing Time, Min
Mixer Speed 25 rpm
Mixer Speed 50 rpm
No Peptizer
0.1 Phr PCTP
No Peptizer
0.1 Phr PCTP
ML1+4@100°C
ML1+4@100°C
ML1+4@100°C
ML1+4@100°C
0
90
90
90
90
2
74
69
69
52
4
68.5
60
50
37
6
67
56
42
29
8
65
53
34
-
Note of Mooney viscosity at 10the rapid reduction 61 50 - higher rotor speeds in the presence of chemical Peptizer at a very small dosage.
46
Effects of “Under Mastication” of NR • Lower Mixing Cycles, • High heat build up during mixing and subsequent steps, • Poor extrudability / calendaring properties of the stock, • Excessive shrinkage & dimensional control problems with extrudates / calendared stocks. • Scorchy compounds. • Excessive porosity in extrudates, • Difficulties with ‘Rework’ blending,
47
Effects of “Over Mastication” of NR Lower shrinkage of extrudates / calendared sheets, • Lower die swell & loss of dimensional control, • Increased curing defects in finished products due to excessive flow and air entrapment, • Compounded sheets stick to each other during storage and sagging of sheets, • Excessive surface tack due to poor green compound strength, • Loss of dynamic, tensile & tear strength properties of the vulcanizate, • Changes in the viscosity of solvent based solutions & loss of surface tack. 48
MIXING
PROBLEMS & REASONS
PROBLEMS
Poor Dispersion
REASONS Batch size not optimized, mixing time is lower, filler addition time not proper, insufficient ram pressure, poor temp. control, poor / inconsistent raw material quality, excessive moisture content in polymer and fillers, under / over mastication of NR.
Variation of start temp., variation in dump time and / or temp. , poor dispersion, Batch to Batch variation in ram pressure, variation in Variations polymer / filler/ oil quality / rework quality, under / over mastication of NR Poor Processability
Compound viscosity not within controlled limits, under / over mastication of NR, Processing temp. not under control, poor
49
Manufacturing process
Unvulcanized rubber, whether natural or synthetic behaves as a viscoelastic fluid during mixing. It is the operation required to obtain a thorough and uniform dispersion of all ingredients called for by the formulae in the rubber
Machinery 2-roll mixing mill kneader internal mixers Continuous, automatic high speed mixing
2 –ROLL MIXING MILL
KNEADER
Two Roll Mill with stock blender & individual roll drives
53
F 270 Banbury Mixer
K 6A INTERMIX
54
Capacities: Banbury Mixers Torque rating kW / RPM
Banbury Mixer
Mixer Chamber Net Volume, ltr
Approx. Batch Wt * kg
Mixing Speed Range, RPM
Compact Drive
Uni Drive
F 50
50
50
40 - 120
2.2
4.6
13.2
F 80
80
60
30 - 105
3.7
6.3
16.1
F 120
120
90
30 - 90
5.6
9.0
19.5
F 160
160
120
20 - 80
7.5
12.0
30.2
F 200
200
165
20 - 60
8.9
12.7
30.5
F 270
270
202
20 - 60
13.1
24.6
43.0
F 370
414
310
20 - 60
-
37.3
54.0
F 440
438
330
20 - 60
-
-
-
F 620
672
500
20 - 50
-
52.2
110.5
Approx. Machine Weight, MT
( * Fill factor = 75% , S.G. = 1.0 ) 55
Capacities: Intermix Mixer Chamber Net Volume, ltr
Approx. Batch Wt kg
Single Speed
Two Speed
K0
1.8
1.26
76
75 / 150
5,
K1
5.5
3.9
40 / 145
Variable drive
50
K 2
20
14
30
22 / 44
50.
50 / 100
50
K 2A
49
34
33
22 / 44
150 ,
75 / 150
60
K4
91
64
33
22 / 44
220,
50 / 300
98
K5
143
100
33
22 / 443
300,
200 / 400
140
K6
206
144
33
22 / 44
475,
320 / 640
235
K 6A
257
180
33
22 / 44
500,
350 / 700
280
K7
310
217
33
22 / 44
750,
500/1000
310
K8
498
349
33
22 / 44
Intermix
Mixing Speed, RPM
Motor HP 1-Speed , 2-Speed
5 / 10
Machine Weight, MT 5.6 20
-
-
( * Fill factor = 70% , S.G. = 1.0 ) 56
Dry rubber based products Mix and Compound Design For manufacture of dry rubber products, the following minimum process steps are essential compounding shaping vulcanization
MIXING PROCEDURE Weighing compounding ingrediants as per formulation Mastication
Compounding And Homogenisation
Maturation
Prewarming
Blank preparation
DRY RUBBER PRODUCTS MANUFACTURE
RUBBER
COMPOUNDIN G
CHEMICALS
MATURATION
PREWARMING TESTING& QC
MOULDED GOODS
EXTRUDED GOODS
CALENDERED GOODS
MOULDED GOODS
EXTRUDED GOODS
AUTO CLAVE OR OVEN
BLANK PREPARATION
MOULDING (HYDRAULIC PRESS)
CALENDARED GOODS
VULCANISATION
FINISIHING OPERATION AND QUALITY CONTROL
PACKING AND DESPATCH
