Pilgard PVI is an ideal pre vulcanization (scorch) inhibitor for NR, IR, NR-BR blend, SBR, NR-SBR, SBR-BR blends, NBR, CR and other diene rubber based accelerated sulphur cured compounds. Only very small dosages (e.g. 0.05-0.15 phr) can improve the scorch safety of NR based sulphenamide accelerated rubber compound by 30% without affecting the rate or state of cure. Pilgard PVI does not deactivate PPD class antidegradants and eliminates porosity problems associated with the use of common acid retarders.
Pilgard PVI is an effective scorch inhibitor with almost all types of accelerators and in all types of sulphur cured diene rubber based compounds. Pilgard PVI offers linear and predictable response and is most sensitive to sulphenamide accelerated stocks and highly unsaturated rubbers. An approximate order of response offered by Pilgard PVI to various rubbers is as follows:
NR > NBR > SBR > EPDM > Butyl (IIR) > Polychloroprene (CR)
Pilgard PVI can be used effectively in compounds based on NBR/PVC blends, polyacrylic rubbers and sulphur cured polyurethanes.
Pilgard PVI is most effective at sulphur dosages between 1.5-3.0 phr. At lower dosages of sulphur, the response offered by Pilgard PVI depends on the type of accelerator used whereas at very high dosages of sulphur levels (e.g. ebonites) the response offered by Pilgard PVI is comparatively poor. Pilgard PVI is not effective with organic peroxide, PF resin and metal oxide cures.
It is very important to determine the accurate dosage of Pilgard PVI required for producing the desired level of scorch delay under factory operating conditions for each rubber compound. This dosage can be finalized by conducting laboratory experiments followed by factory trials and evaluation of the compound for scorch safety as well as other vulcanizate properties. Fine adjustments in the dosages of Pilgard PVI should be carried out to achieve the desired minimum scorch delay and excess dosage of Pilgard PVI (than the minimum required to prevent scorch) should be avoided. This is necessary since excess dosage of Pilgard PVI can delay the cure time / render the product under cured which can affect vulcanizate properties such as state of cure, resilience, compression set, etc.
Pilgard PVI does not cause any detrimental effect on the vulcanizate properties such as tensile strength, modulus values, and resilience / heat build up, compression set or permanent set, ozone resistance and hot air aged vulcanizate properties when used at optimum dosage. Pilgard PVI does not cause contact or migration staining but can slightly discolor bright white rubber products. When very high dosages of Pilgard PVI are used (e.g. over 0.4 phr), phthalimide bloom may appear on the surface and also slight reduction in the state of cure and related properties may be experienced. The state of cure can be adjusted by a very small (e.g. 0.07-0.1 phr) increase in accelerator or sulphur dosage. The phthalimide bloom is water soluble and can easily be washed.
Pilgard PVI is an effective tool to overcome various processing limitations.
For example:
- Incorporation of Pilgard PVI can permit addition of curatives at an early stage of mixing for better dispersion of curatives, reduced mixing cycle time, reduced power consumption, reduced labor and capital investment costs.
- Permit use of higher processing speeds and temperatures during mixing, calendaring, extrusion, etc. for increased productivity and reduced processing cost,
- Permit use of higher injection temperatures and shorter cure cycles for increased productivity.
- Permit recovery of rubber compounds with marginal processing safety and recovery of partially scorched compound for scrap elimination.
- Improve the storage stability of fully compounded stocks at ambient temperatures (particularly the fast curing compounds).
Pilgard PVI is generally incorporated along with accelerators and sulphur during internal mixing / mill mixing of the stocks. In case of fast curing / rework stocks; Pilgard PVI is added on cool mill.
Pilgard PVI is widely used in the manufacture of almost all rubber products based on sulphur curable rubbers. Pilgard PVI is not used in latex compounding and the rubber products intended for contact with food/drugs.
TYPICAL DOSAGES:
Typical dosages of Pilgard PVI required to produce the desired scorch delay depend on the type of rubber, loadings of reinforcing fillers, selection of accelerator type and dosage, sulphur dosage, etc. used in the compounding formulations and the processing operations required to be performed for the product manufacture under the existing processing conditions. Also as stated earlier, Pilgard PVI dosages have to be fine tuned to achieve only the desired level of processing safety and mould flow time and excess dosages of Pilgard PVI have to be avoided. Ambient temperatures, process water temperatures and modifications in processing machinery with respect to processing temperatures or speeds can influence Pilgard PVI dosages considerably.
Given below are the typical dosages of Pilgard PVI for various products.
TYPICAL DOSAGES OF PILGARD PVI
|
Products
|
Rubber
|
Accelerator / Pilgard PVI / S, phr
|
|
Primary
Accelerator
|
Secondary
Accelerator
|
Pilgard PVI
|
S
|
|
Truck & Bus Treads
Bias
Radial
Cap
Base
Truck Sidewall
Truck Carcass
Steel cord skim
|
NR
NR-BR
NR-BR
NR
NR-BR
NR
NR
|
MOR: 0.5-0.7
MOR: 1.1-1.5
MOR: 1.3-1.5
MOR: 0.5-0.7
MOR: 0.8-1.0
MOR: 0.7-0.8
DCBS: 2.0
|
-
-
-
-
-
-
TMTM: 0.1-0.12
|
0.10-0.15
0.10-0.20
0.10-0.20
0.10-0.15
0.10-0.15
0.10-0.20
0.10-0.15
|
2.3-2.7
1.2-1.5
1.2-1.5
2.2-2.5
2.0-2.2
Insol S: 2.5
Insol S: 4.5
|
|
Passenger Tyre Treads
Passenger Tyre Sidewall
Passenger Tyre Carcass
|
NR-BR
SBR-BR
NR-SBR
NR
|
CBS: 1.2
CBS: 1.5
CBS: 1.3
CBS: 1.0-1.2
|
TMTM: 0.10
TMTM: 0.20
TMTM: 0.10-0.15
TMTM: 0 - 0.10
|
0.10-0.15
0.10-0.15
0.10-0.15
0.10-0.20
|
2.0
1.8
1.8
Insol S: 2.2
|
|
Cycle Tyre Treads
Cycle Tyre Carcass
|
NR-RR
NR-BR
NR
|
CBS: 1.0
CBS: 1.2
CBS: 1.0
|
TMTD: 0.10-0.15
TMTD: 0.10-0.15
TMTD: 0.20-0.25
|
0.10-0.20
0.10-0.15
0.15-0.20
|
2.4
2.0
2.5
|
|
Retreads
Hot Cure
Precured
|
NR
NR-BR
NR-BR
|
MOR: 0.5
MOR: 0.8-1.0
MOR: 1.0-1.2
|
-
-
-
|
0.10-0.15
0.10-0.15
0 - 0.10
|
Insol S: 2.5
Insol S: 2.0
1.5-1.7
|
|
Conveyor Belt Cover
General purpose
Heat Resistant
|
NR
NR-SBR
|
MOR: 0.8
CBS: 1.2-1.4
|
MBTS: 0.2
-
|
0.10-0.20
0.15-0.20
|
2.2-2.4
1.5
|
|
V Belts
Base
Cushion
Friction
|
NR
NR
NR
|
CBS: 0.6-0.8
CBS: 0.7-0.8
CBS: 0.7-0.8
|
MBTS: 0.2
MBTS: 0.3
-
|
0.10-0.20
0.10-0.15
0.10-0.15
|
3.0
2.4
2.6
|
|
Footwear
DV Soles & Molded soles
/ Heels
|
NR-SBR
|
CBS: 0.8-1.0
|
TMTD: 0.10-0.20
|
0.10-0.15
|
2.0-2.2
|
|
Hoses
Tube
Cover
|
NR-SBR
NBR
NR
|
CBS: 0.7-1.0
CBS: 1.0-1.2
CBS: 0.7-1.0
|
MBTS: 0.3
TMTD: 0.10-0.20
TMTD: 0.0-0.20
|
0.15-0.20
0.15-0.20
0.15-0.20
|
2.0-2.4
1.5
2.2-2.5
|
|
Cables
|
NR
|
CBS: 1.0
|
TMTD: 0.3
|
0.10-0.20
|
1.2-1.3
|
|
Injection Moldings
|
NR
|
CBS: 0.8
|
-
|
0.20-0.30
|
2.2-2.4
|
|
Misc. Molded and Extruded
Goods
|
NR
NR-SEV
SBR
SBR-SEV
NBR
NBR-SEV
|
CBS: 0.7
CBS: 1.5
CBS: 1.2
CBS: 2.0
CBS: 1.0-1.2
CBS: 1.0
|
TMTD: 0.10-0.20
TMTD: 0.5
TMTD: 0.10-0.20
TMTD: 0.5
TMTD: 0.15
TMTD: 1.0
|
0.0-0.15
0.0-0.15
0.0-0.10
0.0-0.10
0.0-0.10
0.0-0.10
|
2.2
1.5
2.2
0.75
1.5
1.0
|