Claims:WE CLAIM:
1. A rubber composition comprising:
- a synthetic rubber;
- a non-staining antioxidant ranging from 0.5 to 2 phr;
- a fire-retardant filler ranging from 30 to 120 phr;
- a reinforcing filler ranging from 2 to 10 phr; and
- a curative agent ranging from 0.4 to 2.1 phr.

2. The rubber composition according to claim 1, further comprises a silicone oil ranging from 0.2 to 1.0 phr, the silicone oil helps in processing and homogenous dispersion of the fire-retardant filler in the rubber composition.

3. The rubber composition according to claim 1, further comprises a dispersion agent for the reinforcing filler ranging from 0.1 to 0.5 phr.

4. The rubber composition according to claim 3, wherein the dispersion agent for reinforcing filler is vinyl triethoxy silane.

5. The rubber composition according to claim 1, wherein the synthetic rubber is vinyl silicone rubber.

6. The rubber composition according to claim 5, wherein a vinyl content in the vinyl silicone rubber is 0.03 % to 0.18 % per mole.

7. The rubber composition according to claim 1, wherein the fire-retardant filler includes at least one of an Alumina trihydrate, a Magnesium hydroxide or a combination thereof.

8. The rubber composition according to claim 1, wherein the reinforcing filler is a Precipitated silica.

9. The rubber composition according to claim 1, wherein the curative agent includes a Dicumyl Proxide ranging from 0.3 to 1.5 phr and Triallyl cyanurate ranging from 0.1 to 0.6 phr.

10. The rubber composition according to claim 1, wherein the non-staining antioxidant is trimethyl dihydroquinoline.

11. The rubber composition according to claim 1, is a self-extinguishing flame-retardant material.

12. The rubber composition according to claim 1, is a low smoke flame retardant material.

13. The rubber composition according to claim 1, comprises:
- a vinyl silicone rubber 100 phr;
- a trimethyl dihydroquinoline 1 phr;
- a flame retardant filler 100 phr;
- a silicone oil 0.6 phr;
- a precipitated silica 5 phr;
- a vinyl triethoxy silane 0.2 phr; and
- a curative agent including including a Dicumyl Proxide 0.5 phr and Triallyl cyanurate 0.2 phr.

14. The rubber composition according to claim 1, is used for making an elastomeric sleeve.

15. The rubber composition according to claim 14, wherein the elastomeric sleeve is a shroud used with a cable gland.

16. The rubber composition according to claim 1, is adapted to sustain without deteriorating in a temperature range of -60 to 250 degree Celsius.

17. A method of preparing the rubber composition of claim 13, comprising the steps of:
- mixing the vinyl silicone rubber and the trimethyl dihydroquinoline at a temperature of 80 degree Celsius;
- adding the flame retardant, the reinforcing filler, the silicone oil and the vinyl triethoxy silane and processing the mixture by rotation at 60 rpm for about 4 minutes; and
- adding the curative agent and mixing for next 1 minute.

18. The method of preparing the rubber composition according to claim 17, wherein the rubber composition is prepared in a torque rheometer with two roller rotors rotated with a speed ratio of 2:3.
, Description:FIELD OF THE INVENTION

[001] The present invention relates in general to shroud and more particularly, to a rubber composition for improving the properties of a shroud.

BACKGROUND OF THE INVENTION

[002] Cable glands are defined as ‘mechanical cable entry devices’ which are used in conjunction with cable and wiring in lighting, power, data and telecommunication systems. The main function of the cable gland is to act as a sealing and terminating device to ensure the protection of electrical equipment and enclosures. Cable gland may be used on all types of electrical power, control, instrumentation, data and telecommunications cables. They are used as a sealing and termination device to ensure that the characteristics of the enclosure which the cable enters can be maintained adequately. Cable glands may be made from a variety of metallic and non-metallic materials. Typically, cable glands are manufactured from brass because of its superior machining characteristics or from a rigid plastics material because of its production mouldability.

[003] Cable glands which are used with armoured cable are usually metallic as they are frequently required to be electrically conductive in order to ensure electrical continuity between the cable armouring and the apparatus to which the cable is attached. Cable glands are often installed in harsh environmental conditions which are subjected to dirt, dust and moisture ingress in the joint and which may eventually result in corrosion. It is important that neither the cable gland nor the cable armouring should corrode during its installed lifetime. Such corrosion is known to interfere with the electrical continuity between the cable armouring and apparatus to which it attaches by means of a cable gland.

[004] A shroud is a sleeve made of elastomeric material and which sealingly engages on the periphery of the gland and the outer surface of the outer sheath of the cable. This prevents moisture from entering to the position between the outer sheath and armor wires. The shroud is required to be used with all cables glands to provide additional ingress protection and to minimize the risk of dust or any other foreign substance to accumulate around cable gland body. The shroud is like a cylindrical sleeve with a conical portion forming an arrow shape. During installation of shroud, the arrow end of the sleeve is cut with a knife, enabling it to be slipped over a wide range of cable diameters and assists ease of installation.

[005] The shrouds are generally made from high grade Polyvinyl Chloride (PVC) . PVC contains chlorine, a halogen element in its structure. PVC on combustion produce lots of smoke containing HCl (hydrogen chloride). These gases are very toxic and corrosive. Further, as these shrouds produce lots of smoke, they obscure the visibility making it difficult to escape in case of fire. Hence, PVC or other polymers containing a halogen element are not safe to use where the shroud may be exposed to combustion and protection of people, equipment is critical. Apart from this, to achieve flame retardant properties in polymers halogen containing additives are frequently used as these are very cost-effective. However, halogens are highly reactive and harmful, as they can form toxic and corrosive gases.

[006] To overcome problems of halogen containing materials for making shroud, an alternative is to use Phosphorous containing additives e.g. phosphates as replacement of halogenated fire-retardant materials. This class covers a wide range of both inorganic and organic compounds e.g. phosphate esters and various phosphates. Toxicological studies have revealed potential neurological and carcinogenic effects of these compounds. Hence both halogenated and phosphorous containing flame-retardant polymers are toxic and not environment-friendly.

[007] Various shrouds are available in market, sold with different acronyms like low smoke and fume shroud (LSF), low smoke zero halogen shroud (LSZH, LS0H). However Low smoke and fume shrouds are mostly those which generate low smoke in comparison to the traditional PVC shrouds. These LSF shrouds are also PVC based which contain additives to suppress the smoke, and they are marketed under the name “low smoke & fume” PVC shroud (LSF). However, they still contain chlorine and generate toxic hydrogen chloride gas on combustion. Moreover, the smoke generation is only marginally suppressed with these kind of low smokes as observed in the case of low smoke zero halogen ones.

[008] LSZH shrouds are low smoke producing shrouds and they don’t contain halogen elements. However, there is no mention of whether they contain any phosphorous or not. Further, the smoke generation parameter (e.g. smoke density to quantify smoke produced during combustion) or Limiting oxygen index etc data are not available explicitly.

[009] In view of the limitations inherent in the available shroud materials, there exists a need for an improved rubber composition for making the shroud which is low smoke, halogen free, phosphorous free which overcomes the disadvantages of the prior art and can be made in a simple, cost effective, reliable, secure and environmentally friendly manner.

[0010] The present invention fulfils this need and provides further advantages as described in the following summary.

SUMMARY OF THE INVENTION

[0011] In view of the foregoing disadvantages inherent in the prior arts, the general purpose of the present invention is to provide an improved combination of convenience and utility, to include the advantages of the prior art, and to overcome the drawbacks inherent therein.

[0012] A primary objective of the present invention is to provide a halogen free, phosphorous free, low smoke fire retardant rubber composition used for shroud which is simple and cost effective.

[0013] In one aspect, the present invention provides a rubber composition including synthetic rubber, non-staining antioxidant ranging from 0.5 to 2 phr, a fire-retardant filler ranging from 30 to 120 phr, a reinforcing filler ranging from 2 to 10 phr and a curative agent ranging from 0.4 to 2.1 phr.

[0014] In another aspect of the present invention, the rubber composition further comprises a silicone oil ranging from 0.2 to 1.0 phr, the silicone oil helps in processing and homogenous dispersion of the fire-retardant filler in the rubber composition

[0015] In yet another aspect of the present invention, the rubber composition further includes a dispersion agent for the reinforcing filler ranging from 0.1 to 0.5 phr. The dispersion agent for reinforcing filler is vinyl triethoxy silane.

[0016] In a further aspect of the present invention, the synthetic rubber is vinyl silicone rubber with a vinyl content of 0.03 % to 0.18 % per mole.

[0017] In another aspect of the present invention, the fire-retardant filler includes at least one of an Alumina trihydrate, a Magnesium hydroxide or a combination of these two.

[0018] In yet another aspect of the present invention, the reinforcing filler is a Precipitated silica.

[0019] In a further aspect of the present invention, the curative agent includes a Dicumyl Proxide ranging from 0.3 to 1.5 phr and Triallyl cyanurate ranging from 0.1 to 0.6 phr.

[0020] In one aspect of the present invention, the non-staining antioxidant is trimethyl dihydroquinoline.

[0021] In another aspect of the present invention, the rubber composition is a self-extinguishing and low smoke flame-retardant material.

[0022] In yet another aspect of the present invention, the rubber composition includes vinyl silicone rubber, trimethyl dihydroquinoline 1 phr, flame retardant filler 100 phr, silicone oil 0.6 phr, precipitated silica 5 phr, vinyl triethoxy silane 0.2 phr and curative agent including including a Dicumyl Proxide 0.5 phr and Triallyl cyanurate 0.2 phr.

[0023] In a further aspect of the present invention, the rubber composition used for making an elastomeric sleeve such as a shroud used with a cable gland.

[0024] In another aspect of the present invention, the rubber composition is adapted to sustain without deteriorating in a temperature range of -60 to 250 degree Celsius.

[0025] In another aspect, the present invention provides a method of preparing the rubber composition of the present invention that comprises mixing the vinyl silicone rubber and the trimethyl dihydroquinoline at a temperature of 80 degree Celsius, adding the flame retardant, the reinforcing filler, the silicone oil and the vinyl triethoxy silane and processing the mixture by rotation at 60 rpm for about 4 minutes and adding the curative agent and mixing for next 1 minute.

[0026] In yet another aspect of the present invention, the rubber composition is prepared in a torque rheometer with two roller rotors rotated with a speed ratio of 2:3.

[0027] These together with other aspects of the invention, along with the various features of novelty that characterize the invention, are pointed out with particularity in the description annexed hereto and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated exemplary embodiments of the invention.

DETAILED DESCRIPTION

[0028] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details.

[0029] As used herein, the term ‘plurality’ refers to the presence of more than one of the referenced item and the terms ‘a’, ‘an’, and ‘at least’ do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

[0030] Reference herein to “one embodiment” or “another embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the diagrams representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention.

[0031] The rubber composition of the present invention is used to make a shroud used in cable gland. The rubber composition comprises synthetic rubber, a non-staining antioxidant ranging from 0.5 to 2 phr, a fire retardant ranging from 30 to 120 phr, a reinforcing filler ranging from 2 to 10 phr and a curative agent ranging from 0.4 to 2.1 phr.

[0032] Synthetic rubber is the base polymer with high molecular weight chains to polymerization of matrix for polymer backbone formations. In one embodiment of the present invention, the synthetic rubber used is vinyl silicone rubber. In one preferred embodiment of the present invention, the vinyl content in the vinyl silicone rubber is 0.03 % to 0.18 % per mole. Vinyl silicone rubber is a non-halogenated rubber and has typical working temperature range of -60°C to +250°C. It is low smoke and meets the criteria of zero halogen. In addition, the rubber composition does not contain any phosphorous and hence it is Low smoke zero halogen zero phosphorous (LSZHZP) material.

[0033] The function of protective agents such as antioxidant and antiozonants is to protect the polymeric from environmental Oxygen and Ozone attack on unsaturated double bonds or free radical/ free ions present into polymer matrix during service life as static/dynamic mode. Antioxidants are chemicals that are used to protect rubber articles against attack from oxygen (O2). The non-staining antioxidant offers long term protection to rubber against oxidative ageing at ambient as well as elevated temperatures. In one embodiment of the present invention, the non-staining antioxidant used is trimethyl dihydroquinoline (TDQ).

[0034] The fire-retardant filler used in the present composition is flame-retardant and smoke suppressant. In one embodiment of the present invention, the fire-retardant filler includes at least one of an Alumina trihydrate (ATH) or Magnesium hydroxide (MDH) or a combination which includes both. The decomposition temperature of ATH begins at 240°C, whereas MDH begins to decompose at 320°C. ATH provides a flame-retardant effect as it decomposes endothermically (?H -1171 kJ/kg) into aluminum oxide and water (about 35?wt%). MDH also decomposes endothermically (?H -1372kJ/kg) into magnesium oxide and water (about 31?wt%). These decomposition reactions absorb heat from the combustion zone and in addition, the resulting metallic oxide is left behind and provides a protective intumescent layer on the surface of the substrate. These two flame retardants promote charring and serve as a barrier to heat and mass transfer. This contributes to extinguishing a flame.

[0035] 30-120 phr of Aluminium hydroxide (ATH) or 30-120 phr of Magnesium hydroxide (MDH) or a combination of ATH and MDH with 30-120 parts by weight is used to make the rubber composition of the present invention.

[0036] A minimum 30 phr fire-retardant filler such as ATH is required to achieve a good Limiting oxygen index (LOI) value to satisfy the criteria of flame retardancy. Higher the amount of ATH, higher is the value of LOI obtained and better is the flame retardancy.

[0037] High quantity of the flame-retardant filler is desirable to achieve better flame-retardant characteristic. However, processing with more than 120 phr of fire-retardant filler is difficult and will compromise other mechanical properties in the rubber composition. High quantity of such fillers generally poses a practical problem in processing or mixing, and it is difficult to achieve a homogenous dispersion. This ultimately leads to poor properties of the final product. In one preferred embodiment, the rubber composition of the present invention further comprises silicone oil ranging from 0.2 to 1.0 phr. The silicone oil helps in processing and homogenous dispersion of the fire-retardant filler in the rubber composition. Silicone oil helps in ATH and/or MDH processing and homogenous dispersion in the rubber matrix.

[0038] Reinforcing filler is a particulate material that is able to increase the tensile strength, tear resistance and abrasion resistance of natural or synthetic rubber. The reinforcing filler is used to provided needed mechanical strength to the rubber composition. In one embodiment of the present invention, the reinforcing filler is Precipitated silica. Precipitated silica is manufactured by acid precipitation from silicate solution, silicate solution product by reactions of sodium silicate with acid or alkaline earth metal salts, it has average particle size (10 to 100) nm and water contains is (10-14%).

[0039] Filler dispersion characterizes the degree of incorporation and distribution of fillers in an elastomer matrix. Filler dispersion is known to influence rubber properties like tensile strength and abrasion resistance. So, it is important to disperse the precipitated silica in the rubber matrix. In one embodiment, the rubber composition of the present invention further includes a dispersion agent for the reinforcing filler ranging from 0.1 to 0.5 phr. In one preferred embodiment of the present invention, the dispersion agent for reinforcing filler is vinyl triethoxy silane.

[0040] Curative agents help in vulcanization of rubber. In one embodiment of the present invention, the curative agent includes a Dicumyl Proxide ranging from 0.3 to 1.5 phr and Triallyl cyanurate ranging from 0.1 to 0.6 phr. The curative used in the composition is peroxide based. Dicumyl peroxide, DCP is the curative and may be used. Since antioxidant is also present in this composition, they also act as scavenger for free radicals and thus, reduces the cure rate. A little more DCP with TAC is required to achieve a cure rate suitable for processing. Triallyl cyanurate, TAC is the coagent used in this peroxide based curative. It helps to promote the curing.

[0041] In one preferred embodiment of the present invention, the rubber composition includes vinyl silicone rubber, a trimethyl dihydroquinoline 1 phr, flame retardant filler 100 phr, silicone oil 0.6 phr, precipitated silica 5 phr, vinyl triethoxy silane 0.2 phr and a curative agent including including a Dicumyl Proxide 0.5 phr and Triallyl cyanurate 0.2 phr.

[0042] The rubber composition of the present invention is evaluated to satisfy the requirements of low smoke, fire retardant, halogen free and phosphorus free as per the standard tests known in in the art.

[0043] The rubber composition is evaluated for Limiting oxygen index test (as per ASTM D2863) and Smoke density test (as per ASTM D2843). Limiting Oxygen index (LOI) is the minimum concentration of oxygen in an oxygen/nitrogen mixture in which the material will burn. As air contains approximately 21% oxygen, it is known in literature that a material with an oxygen index greater than about 26% will be self-extinguishing. Hence the higher the LOI value, better will be flame retardancy. The rubber composition of the present inventions shows a LOI value of 43%, which infers a high flame-retardancy behavior. To evaluate the smoke produced during combustion, smoke density test was carried out. The maximum smoke density (%) and smoke density rating (%) were measured. For low smoke criteria, value of smoke density more than 60 % is not acceptable as it will obscure the visibility. The composition has maximum smoke density value 37% with smoke density rating of less than 20% is achieved with this formulation.

[0044] In one embodiment of the present invention, the rubber composition has below mentioned properties:
• It is a self-extinguishing flame-retardant material Limiting Oxygen index (LOI) of 43%
• It is a low smoke flame retardant material and has maximum smoke density value of 5.3% and smoke density rating of 2.1%
• It is a flame-retardant material with UL94-V0 and UL94-HB rating
• It is halogen free and complies to standard EN14582, IEC60754-1 and IEC-60754-2
• It is a highly insulating material and has a breakdown voltage of >32 kV/mm and arcing resistance of >270 seconds
• It is adapted to sustain without deteriorating a temperature range of -60 to 250 degree Celsius.

[0045] The present invention provides a halogen free, phosphorous free, low smoke fire retardant rubber composition. In one embodiment of the present invention, the rubber composition is used for making an elastomeric sleeve. In one preferred embodiment, the rubber composition of the present invention is used to make the shroud used with a cable gland. The rubber composition is used to make a fire-resistant, halogen free, phosphorus free, low smoke and flame-retardant shroud.

[0046] In another embodiment, the present invention provides a method of preparing the rubber composition of present invention. The method starts with mixing the vinyl silicone rubber and the trimethyl dihydroquinoline at a temperature of 80 degree Celsius. Now the flame retardant, reinforcing filler, silicone oil and vinyl triethoxy silane is added to above and the mixture is processed by rotating at 60 rpm for about 4 minutes. Next the curative agent is added and mixed for next 1 minute to form the rubber composition of the present invention.

[0047] In a preferred embodiment of the present invention, the rubber composition is prepared in a torque rheometer with two roller rotors rotated with a speed ratio of 2:3.

[0048] The rubber composition of the present invention provides advantages as below:
- Halogen Free: Since PVC is eliminated, the composition is halogen free
- Better flame-retardancy: The LOI of 42.5% makes it very good flame retardant
- Low smoke: Maximum smoke density value of 5.3% and smoke density rating of 2.1% makes it categorized as low smoke composition
- High Insulation: A breakdown voltage more than 32 kV/mm and arcing resistance more than 270 seconds makes it a very good insulating material

[0049] Although a particular exemplary embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized to those skilled in the art that variations or modifications of the disclosed invention, including the rearrangement in the configurations of the parts, changes in steps and their sequences may be possible. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as may fall within the spirit and scope of the present invention.

[0050] The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.

[0051] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.