The invention relates to a polyvinyl chloride formulation
useful to insulate automotive primary cables, characterized in that it is lead free,
abrasion resistant for use in insulation and sheathing of thin-walled minimum thickness
automotive cables able to operate at working temperatures of 105°C.
Polyvinyl chloride, "PVC", is used extensively in electrical
cables isolation and sheathing because it is economical and easily available, because
of its mechanical properties, chemical and weather resistance as well as because
of its dielectric properties.
However, in order to obtain some specially required characteristics,
it is necessary to investigate new additives producing the desired effect.
With regard to the object of the instant invention PVC
is always used in formulations through the addition of plasticizers to remove its
natural stiffness and to give it flexibility as well as through the addition of
other additives such as thermal stabilizers, lubricants, pigments, loads, impact
modifiers as well as flame retardant agents that are added to the compound to obtain
the PVC with the desired properties.
PVC itself is a thermally unstable polymer, with decomposition
at a temperature of 150° C, releasing HCl, producing establishment sites in
the polymer which causes the chain crosslinking and its eventual rupture resulting
in the degradation of the polymer properties. As PVC decomposes, the resin changes
color and becomes stiff and fragile.
To obtain the thermal stability necessary for its processing,
PVC compounds always use stabilizers. The most common stabilizers are generally
metals salts of organic or inorganic acids and phenols, organometallics, epoxy compounds
and phosphites. In the case of compounds used for automotive primary cable insulation,
Volkswagen 603 06 specification (December 1999 draft) mentions that the compounds
used for thin-walled cable manufacturing should be lead free.
The automotive industry is and will be affected by the
- a).- environment regulation forcing companies manufacturing automobiles to diminish
the environmental impact of the vehicles both with regard to their emissions and
- b).- increase in economy, safety, luxury and comfort offered by the current
Said new requirements have forced vehicle manufacturers
to carry out modifications and/or reductions both with regard to fuel consumption
and the materials used in the manufacturing of the vehicles and their performance.
One of the modifications was reflected in automotive primary
cables insulation through the elimination of the noxious materials found in the
polymers, among them PVC, that have traditionally use lead because of electrical
and cost advantages.
Besides, smaller vehicles have been designed and thus space
in the different compartments has been reduced, providing less room for devices,
among them for electrical connection harnesses for the connection and signaling
of the equipment, said equipment being now more complex because of safety and luxury
development in the car industry. For this reason, auto manufacturers have modified
cable designs, diminishing the insulation wall thickness in order to reduce weight
and diameter without lowering their mechanical resistant, offering thus an alternative
for the numerical increase of the circuits currently required by automobiles.
Some isolated technologies are known which partially fulfill
the characteristics required, either in the insulation composition or in the way
the wires are manufactured or in the disposition of cable construction such as,
US Patent 5,326,638, issued to Mottlne, Jr et al relates
to the sheating of insulated communication cables with lead free PVC compositions
and a metal antioxidant deactivator system in order to prevent the formation of
calcium and zinc chloride affecting the electrical properties.
US Patent 5, 149, 917 issued to Sawada et al, protects
conductors for automotive harness in which the conductors are compressed to reduce
the total diameter of the cable, said cables are insulated with different vinyl
chloride, crosslinked vinyl or cmsslinked polyethylene compositions.
US Patent 4.734,545 issued to Susuki et al, protects compressed
conductors for automotive hamess insulated with thermoplastic polyurethane, providing
The first above mentioned invention relates to a communication
cable and the two other inventions relates to conductors used in the automotive
industry that include polyurethane which promotes abrasion strength but is expensive.
Specification No. US-A-5,492,949 disclose a stabilised
polyvinyl chloride using an inorganic or organic zinc compound, and a terminal epoxide,
optionally with chalk.
Specification No. EP-A-0916,485 discloses a heavy metal
free polyvinyl chloride compound formulation for insulating thin wall automotive
Specification No. US-A-4,584,241 discloses the stabilisation
of PVC bodies by the use of a complex ester of oleic acid and a diglycerol ester
of oleic acid In conjunction with a cadmium-zinc composition.
Specification No. EP-A-O531,023 discloses a transmission
medium covered with lead-free stabilised polyvinyl chloride.
DESCRIPTION OF THE INVENTION
According to this invention, there is provided use of tris
(2,4-di-tert-butylphenyl) phosphite as a chelating agent in a thin walled automotive
cable having a lead free polyvinyl chloride insulation and sheathing composition,
said insulation and sheathing composition comprising a blend of:
- a) 60 to 100 parts by weight of a polyvinyl chloride resin;
- b) 3 to 6 parts by weight of a zinc stabiliser;
- c) 15 to 40 parts by weight of a 9 to 11 carbon atom linear co-ester type plasticizer;
- d) 10 to 40 parts by weight of a 1 micrometer (1 micron) calcium carbonate load;
- e) 3 to 6 parts by weight of a phenol type antioxidant; and
- f) 1 to 4 parts by weight of an oxidised polyethylene type lubricant;
wherein the tris (2,4-di-tert-butylphenyl) phosphite acts as a costabiliser to regenerate
the stabiliser metal, thereby prolonging the stabilisation action of the stabiliser.
The object of the PVC formulation of the present invention
is to offer some characteristics that automotive cables should present, such as:
- Breaking tensile stress
- Breaking elongation
- Thermal resistance (oven aging)
- Resistance to different automobile fluids to which the cables are exposed (oil,
gasoline, brake liquids, etc).
- Abrasion strength gage 0.35 mm2 = 200 cycles
- Low temperature breaking strength
- Flame resistance
- Water-resistant during a long period of time
All the components constituting the formulation are quality
materials certified according to the following:
- a PVC RESIN
Homopolymer type PVC resin with "K" value = 70 corresponding to a medium molecular
weight and viscosity resin, PVC Chemical Abstracts Registry No. 9002-86-2
- b PALATINOL 119 P
Co-ester linear phthalic plasticizer containing from 11 to 9 carbon atoms, according
to Chemical Abstract Registry No. 111381-91-0
- c IRGANOX 1076
Antioxidant: Octadecyl-3,5-diterbutyl-4-hydroxyhydrocinnamate, according to Chemical
Abstract Registry No. 2082-79-3
- d TERM CHECK 1890
Zinc based stabilizer according to Ferro formula.
- E POLYETHYLENE WAX AC-629
Oxidized polyethylene homopolymer according to Chemical Abstract Registry No. 68441-17-8
- f MICRONIZED CALCIUM CARBONATE
Micronized calcium carbonate with stearic cover according to Chemical Abstract No.
- g MARK 2112
co-stabilizer and chelation phosphite according to Witco formula.
The polymer composition based on a PVC thermoplastic compound
and/or on a mixture with other polymers fulfill the standard requirements of the
European automobile industry such as Volkswagen 603.06 and BMW 600 14, with regard
to the design of thin-walled cables and sheath, according to the following thicknesses:
Wall thickness mm
Through these wall thicknesses and characteristics of PVC
and/or mixture of other polymers, abrasion strength at 105° and thermal grade
105° according to DIN are obtained.
This thermal grade consists in submitting the cable to
the operating temperature of 105° C during 3000 hours, at the end of such period
of time, the cable is submitted to the flexibility test through winding around a
mandrel and the cable must also maintain its flexibility at -40° C.
Throughout the elaboration of said composition, the use
of lead stabilisers has been eliminated according to the following description:
- Polymer composition in parts per weight
- The compound includes polyvinyl chloride, from 60 to 100 parts; a zinc stabilising
agent, from 3 to 6 parts;
- A plasticizer of the linear co-ester type with 9 to 11 carbon atoms, from 15
to 40 parts;
- A 1 micrometer (1 micron) calcium carbonate load, from 10 to 40 parts;
- At least one phenol type antioxidant agent, from 3 to 6 parts;
- And an oxidised polyethylene type lubricant compound, from 1 to 4 parts.
In order to obtain the 105° C operation temperature
and flexibility at -40° C, the use of a linear co-ester plasticizer with 9
to 11 carbon atom is required in the design of branched type compound formulation
such as TOTM (Triocytl trimellitate), TIOIM (Triisooctyl trimellitate), etc. However,
because of their high molecular weight, said plasticizers have a leakage temperate
of -20° C which limits their use in compounds where flexibility is required
at lower temperatures. Besides, in order to obtain an operation temperature of 105°
C and also a good electrical insulation both in dry environment and in water exposition
at 85° C during a period of 30 days with lead free stabilizers, the most adequate
stabilizer type has been found to meet the requirements of the specification.