WO2024178570A1

WO2024178570A1 - Thermally conductive silicone rubber application

Info

Publication number: WO2024178570A1
Application number: PCT/CN2023/078566
Authority: WO
Inventors: Peng Wang; Rui Wang; Yusheng Chen; Qing Shi; Yi Guo
Original assignee: Dow Silicones Corp
Current assignee: Dow Silicones Corp
Priority date: 2023-02-28
Filing date: 2023-02-28
Publication date: 2024-09-06
Anticipated expiration: 2025-08-28
Also published as: CN120603707A; KR20250155031A

Abstract

A fabric reinforced thermally conductive silicone rubber tube comprising (A) a first inner layer being a thermally conductive silicone rubber tube in the form of an extruded cured product of a hydrosilylation (addition) curable thermally conductive silicone rubber composition; (B) a second middle layer of reinforcing fabric selected from glass-fiber fabric, polyester fiber fabric, polyamide fiber fabric, and/or polyaramid fiber fabric or a reinforcing fabric comprising a mixture of any two or more thereof covering tube (A); and (C) a third outer layer being a thermally conductive silicone rubber tube in the form of an extruded cured product of a hydrosilylation (addition) curable thermally conductive silicone rubber composition over the second middle layer (B); which first inner layer (A) and third outer layer (C) are both made from the cured product of a hydrosilylation (addition) curable thermally conductive silicone rubber composition.

Description

THERMALLY CONDUCTIVE SILICONE RUBBER APPLICATION

The present disclosure relates to fabric reinforced thermally conductive silicone rubber tube s suitable for liquid (e.g., water) cooling systems. They preferably have a thermal conductivity of at least 0.5 Watts per metre Kelvin (W/m. K. ) , whilst being able to withstand a fluid (e.g., water) pressure of greater than 1 MPa., The disclosure also relates to a method for the manufacture of said fabric reinforced thermally conductive silicone rubber tubes and extends to uses for such tubes.

The properties of cured silicone-based products including organosiloxane elastomers make them desirable for a variety of end use applications including in the field of electronics and other forms of electrical applications. Compositions which generate the cured silicone-based products may, for example, be used to coat and when cured encapsulate solid state electronic devices such as time transistors and integrated circuits and the circuit boards on which these devices are often mounted to protect them from contact with moisture, corrosive materials and other impurities present in the environment in which these devices operate. However, while the organosiloxane compositions and the resulting cured silicone-based products effectively protect solid state devices from materials that can adversely affect their operation, they typically do not possess the thermal conductivity required to dissipate the large amounts of heat generated during such uses.

One method for increasing heat dissipation is to increase the thermal conductivity of the materials used to coat or encapsulate the solid-state devices by addition of thermally conductive fillers (sometimes referred to as heat conductive fillers) such as metal powders e.g., silver, nickel and copper and carbonaceous powders such as carbon blacks, graphite powders and/or carbon fibres to the coating or encapsulating material. However, such compositions may suffer from a variety of problems not least because of the high levels of such fillers required in order to generate high thermal conductivities of e.g., at least 0.5 W/m. K. (measured in accordance with ASTM D7896 –hot disk method) . Such high thermal conductivities are achieved by increasing the amount of the thermally conductive fillers in the respective compositions, but the presence of such fillers in amounts of say greater than 70 or 75 weight % (wt. %) of the composition generally result in the pre-cured compositions having significantly increased viscosities causing impaired handling characteristics and additionally, upon cure, result in cured silicone-based products with poor physical properties as the vast majority of thermally conductive fillers are not reinforcing, i.e., their addition do not enhance mechanical properties in said cured silicone-based products. Whilst such cured silicone-based products may be acceptable for some applications, industry is increasingly demanding compositions for the generation of cured materials which have both

(i) desired high levels of thermal conductivity, and

(ii) required levels of physical properties,

whereas previously one might expect either one or the other. Solutions have been identified for (i) but at the expense of adequate physical properties. For example, the high viscosity of pre-cured compositions due to the level of thermally conductive filler present can be avoided by dilution of the compositions with non-reactive silicones or organic solvents, but this has been found to result in compatibility problems with the diluents bleeding out of the subsequently cured silicone-based products with time and furthermore, such products historically have not satisfied the physical property demands of the customer. Similarly the physical properties e.g., tensile strength and elasticity of cured materials with such high levels of the thermally conductive, non-reinforcing filler are relatively poor and/or inconsistent when compared with silicone elastomers containing optimised amounts of reinforcing fillers etc. consequently limiting their potential uses because without such physical properties the capability of the cured silicone material to perform over a long period of time in many preferred applications for such materials e.g., as gaskets, encapsulants or in shock isolation pads as such poor results can lead to failure thereof.

PCT/CN2022/114896 provided a thermally conductive high consistency silicone rubber (HCR) composition comprising thermally conductive filler having a volume median particle diameter of 0.1-100 micrometres (μm) measured by laser diffraction particle size analysis in an amount of from 80 to 95 wt. %of the composition, typically alumina (otherwise known as aluminium hydroxide) in an amount of from 85 to 90 wt. %of the composition. It was found that such a composition was particularly suited for molding heat conductive silicone rubber parts using a compression molding process. However, it was generally found to be unsuitable for extrusion applications because the composition was too soft and/or had too low a William’s plasticity resulting in an inability to form consistently acceptable extruded parts such as tubes (and/or pipes) for liquid cooling systems used in, for example, fast charging apparatus for electric vehicles.

The increasing popularity of electric vehicles (EVs) and hybrid electric vehicles (HEVs) is leading to a dramatic increase in research and development of EV charging infrastructure. Three of the biggest issues which remain problematic for the EV driver and which hamper the use of EV vehicles for long distance trips are:

(i) the lack of charging infrastructure,

(ii) the distance which can be travelled before the need to recharge and

(iii) the time required to recharge.

Whilst various methods for recharging EV batteries do exist, the development of the aforementioned “fast charging” technology has become increasingly important as it is increasing the speed by which vehicles are being charged. However, they generate a lot of heat which has led to problems dealing with how to extract heat generated in the charging cable from high voltages and/or currents utilised. A solution has been the use of liquid cooling systems designed to cool down charging apparatus and cables using low temperature liquids passing through liquid cooling tubes. The cooling tubes are positioned adjacent to the charging wire and low temperature liquid e.g., water is designed to flow through the cooling tubes enabling the charging cable to be cooled down and/or for the fast-charging apparatus to be maintained at a safe temperature with heat generated being transferred to the cooling liquid through the tube walls. Given the heat generated, the cooling liquid e.g., water is typically transported through said tubes at high pressure (e.g., greater than (>) 1MPa) , necessitating that the tubes need to be able to transfer the heat generated through the tube walls to the cooling liquid and be sufficiently structurally sound to avoid tube breakage due to the fluid pressure of the cooling liquid passing through the tube. However, the current commercialized materials used to form such tubes, e.g., cross-linked polyolefin (XLPO) for cooling tubes, are not suitable for long term durability and conformability under high temperature because it is believed tubes made with XLPO are much harder compared silicone elastomers and therefore far less flexible and furthermore, XLPO products such as tubes are not able to match the heat resistance properties of silicone elastomers at temperatures greater than (>) 150^o C for long-term applications.

There is provided herein a fabric reinforced thermally conductive silicone rubber tube comprising

(A) a first inner layer being a thermally conductive silicone rubber tube in the form of an extruded cured product of a hydrosilylation (addition) curable thermally conductive silicone rubber composition;

(B) a second middle layer of reinforcing fabric selected from glass-fiber fabric, polyester fiber fabric, polyamide fiber fabric, and/or polyaramid fiber fabric or a reinforcing fabric comprising a mixture of any two or more thereof covering tube (A) ; and

(C) a third outer layer being a thermally conductive silicone rubber tube in the form of an extruded cured product of a hydrosilylation (addition) curable thermally conductive silicone rubber composition over the second middle layer (B) ;

which first inner layer (A) and third outer layer (C) are both made from the cured product of a hydrosilylation (addition) curable thermally conductive silicone rubber composition comprising the following components:

a) a polydiorganosiloxane having a degree of polymerisation of at least 2,500 calculated from the number average molecular weight determined by gel permeation chromatography and at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl or alkynyl groups;

b) an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule,

c) an organopolysiloxane filler treating agent having a degree of polymerisation of between 4 to 500 calculated from the number average molecular weight determined by gel permeation chromatography and comprising

(i) at least one alkenyl group per molecule and

(ii) at least one hydroxy group or at least one alkoxy group or a mixture of hydroxy and alkoxy groups per molecule;

in an amount of from 0.1-10%wt. of the composition;

d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and either

(e) (i) at least one thermally conductive filler with a volume median particle diameter size 0.1-20 micrometres (μm) measured by laser diffraction particle size analysis in an amount of from 70 to 95 wt. %of the composition, alternatively in an amount of from 80 to 95 wt. %of the composition; or

a combination of (e) (ii) and (f) wherein

(e) (ii) is at least one thermally conductive filler with a volume median particle diameter size of greater than 20 to 100 micrometres (μm) measured by laser diffraction particle size analysis and

f) precipitated silica, fumed silica, colloidal silica or a mixture of any two or more of precipitated silica colloidal silica and fumed silica in an amount of from greater than zero to 5 wt. %of the composition;

wherein the combination of (e) (ii) + (f) is present in the composition in an amount of from 70 to 95 wt. %of the composition, alternatively in an amount of from 80 to 95 wt. %of the composition and wherein the total wt. %of the composition is 100 wt. %.

There is also provided herein a method for preparing a fabric reinforced thermally conductive silicone rubber tube comprising the steps of:

I) preparing a hydrosilylation (addition) curable thermally conductive silicone rubber composition comprising the following components:

(i) at least one alkenyl group per molecule and

in an amount of from 0.1-10%wt. of the composition;

a combination of (e) (ii) and (f) wherein

wherein the combination of (e) (ii) + (f) is present in the composition in an amount of from 70 to 95 wt. %of the composition, alternatively in an amount of from 80 to 95 wt. %of the composition and wherein the total wt. %of the composition is 100 wt. %;

II) introducing hydrosilylation (addition) curable thermally conductive silicone rubber composition onto an extruder, extruding said hydrosilylation (addition) curable thermally conductive silicone rubber composition from the extruder to form a thermally conductive silicone rubber tube (A) and cooling the tube;

III) covering the tube resulting from step (II) with a layer (B) of reinforcing fabric selected from glass-fiber fabric, polyester fiber fabric, polyamide fiber fabric, and/or polyaramid fiber fabric or a reinforcing fabric comprising a mixture of any two or more thereof to form a step (III) product;

IV) extruding an outer layer (C) of said hydrosilylation (addition) curable thermally conductive silicone rubber composition from the extruder around the step (III) product to form a fabric reinforced thermally conductive silicone rubber tube.

There is also provided herein a fabric reinforced thermally conductive silicone rubber tube made in accordance with the method described above.

Use of a thermally conductive silicone rubber composition, which comprises the following components:

(i) at least one alkenyl group per molecule and

in an amount of from 0.1-10%wt. of the composition; and

a combination of (e) (ii) and (f) wherein

in the manufacture of a fabric reinforced thermally conductive silicone rubber tube comprising

(A) a first inner layer being a thermally conductive silicone rubber tube in the form of an extruded cured product of said hydrosilylation (addition) curable thermally conductive silicone rubber composition;

(C) a third outer layer being a thermally conductive silicone rubber tube in the form of an extruded cured product of said hydrosilylation (addition) curable thermally conductive silicone rubber composition over the second middle layer (B) .

The fabric reinforced thermally conductive silicone rubber tube herein may have a circular, rectangular, i.e., square or oval cross-section determined by the desired end use but typically has a circular cross-section which may be of any suitable size typically with an inner diameter (ID) of the hollow interior of from 1.0 to 20.0mm, alternatively from 2mm to 15mm, alternatively from 2mm to 10mm, alternatively from 2mm to 8 mm, alternatively from 2mm to 6 mm.

Said tube may have any suitable wall thickness (WT) dependent on the thickness of the three layers thereof and an outside diameter (OD) which is consequently the sum of ID + 2WT.

The fabric reinforced thermally conductive silicone rubber tube must be strong enough to be able to withstand the (fluid) pressure on it from the liquid (s, ) e.g., water, passing through the hollow interior of said tube when in use, i.e., the fabric reinforced thermally conductive silicone rubber tube must not be subjected to a fluid pressure (i.e., water pressure) which exceeds a “breaking pressure” causing the tube to fracture. Typically, for example, in the case of using tubes herein to improve the safety for EV charging cable water-cooling systems such a fabric reinforced thermally conductive silicone rubber tube must be sufficiently flexible for use whilst being able to withstand a fluid pressure e.g., water pressure of greater than (>) 1.0MPa in accordance with Chinese National

Standard Test Method GB/T5563-2013. However, given the tube herein is a thermally conductive silicone rubber tube there is an additional requirement, in that it is important to ensure that the tube is sufficiently thermally conductive for purpose in the case of using tubes herein for EV charging cable water-cooling systems such a fabric reinforced thermally conductive silicone rubber tube the tube must also exceed a thermal conductivity is at least 0.5W/m. K. Typically, the fabric reinforced thermally conductive silicone rubber tubes described herein resulting from the thermally conductive silicone rubber composition comprising at least 70wt. %thermally conductive filler (e) (i) or (e)

(ii) (in combination with (f) ) described herein will have a high thermal conductivity of at least 0.5 W/m. K., measured in accordance with ASTM D7896 –hot disk method.

Furthermore, such fabric reinforced thermally conductive silicone rubber tube may have a wall thickness (WT) of from 0.5 to 10.0mm when utilised as EV charging cable water-cooling system tubes in order to be accommodated in a standard sized EV charging cable as a water-cooling system. For example, the first inner layer (A) of the fabric reinforced thermally conductive silicone rubber tube may have a wall thickness of from 0.25 to 7.5mm, alternatively from 0.50 to 5.0mm and the third outer layer (C) of the fabric reinforced thermally conductive silicone rubber tube may have a wall thickness of from 0.25 to 7.5mm, alternatively from 0.50 to 5.0mm. For the sake of charging example, in one embodiment, when the tube herein is used as a cooling tube for an 24mm (OD) EV charging cable water-cooling system the first inner layer (A) may have a wall thickness of from 0.6 and 0.8mm, and the third outer layer (C) may have a wall thickness of 0.4 to 0.6mm.

It was found that tubes prepared by extrusion of a single layer of the hydrosilylation (addition) curable thermally conductive silicone rubber composition described herein were, flexible enough and strong enough to be extruded into form tubes of only one layer having e.g., a WT of from 1 to 2mm. However, such tubes struggled in this form to withstand a fluid pressure e.g., water pressure of greater than (>) 1.0MPa in accordance with Chinese National Standard Test Method GB/T5563-2013 when water is directed through the tube during the water pressure resistance test.

This problem was surprisingly overcome by tubes described in the present disclosure by replacing the single layered tubes with fabric reinforced thermally conductive silicone rubber tubes as described herein and as prepared using the method described herein.

The fabric layer B provides the resulting cured fabric reinforced thermally conductive silicone rubber tubes with additional strength. The reinforcing fabric used in middle layer B may comprise any suitable fabric or combination of fabrics. The fabric layer may comprise one or more suitable synthetic fibres such as, for the sake of example, of glass-fiber fabric, polyester fiber fabric such as polyethylene terephthalate, polyamide fiber fabric, and/or polyaramid fiber fabric or any other suitable reinforcing fabric comprising two or more thereof. The fabric layer B may be provided and utilised in any suitable form. For example, it may be provided in any suitable woven, non-woven or knitted form. The fabric be used to cover the inner layer A in any suitable manner, for example this may include wrapping, or knitting or any other suitable methodology or indeed a combination of two or more processes, if desired. An optional example is preferably wrapped or knitted around the inner tube A, using any suitable net size, for example, 14*14meshes, 10*10meshes, 8*8meshes, 5*5meshes i.e., the number of grids per inch (2.54cm) in warp &weft.

Such a fabric reinforced thermally conductive silicone rubber tube was found to achieve and maintain all the required parameters described above and as such said fabric reinforced thermally conductive silicone rubber tubes were considered suitable as cooling tubes positioned alongside the charging wires in fast charging apparatus for EV applications. They are sufficiently strong to withstand higher fluid pressures of > 1.0MPa when cold water is directed through the tube during the hydrostatic testing in accordance with Chinese National Standard Test Method GB/T5563-2013 for rubber and plastic hoses and hose assemblies. to cool an EV charging cable. This is highly beneficial given it would seem that currently commercialized materials such as cross-linked polyolefins used for cooling tube have questionable long-term durability and conformability under high temperature issues. The fabric reinforced thermally conductive silicone rubber tubes as described herein and made by the process described herein have improved parameters with good flexibility, enough mechanical strength making them a potentially a better option in terms of heat resistance for cooling tubes.

The fabric reinforced thermally conductive silicone rubber tubes described herein and made by the process described herein utilise two layers of thermally conductive silicone rubber made by extruding and curing a hydrosilylation (addition) curable thermally conductive silicone rubber composition comprising the following components:

Component (a)

Component (a) of the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein is a polydiorganosiloxane having a degree of polymerisation of at least 2,500, and at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl and/or alkynyl groups.

Hence, each polydiorganosiloxane of component (a) has a degree of polymerisation of at least 2,500, alternatively at least 3,500, alternatively at least 4000, i.e., therefore has at least 2,500, alternatively at least 3,500, alternatively at least 4000, siloxy units, of formula (I) :

R’_aSiO _(4-a) /2 (I)

The subscript “a” is 0, 1, 2 or 3.

Siloxy units may be described by a shorthand (abbreviated) nomenclature, namely -"M, " "D, " "T, " and "Q" , when R’ is for example, an independently selected substituted or unsubstituted hydrocarbyl group having from 1 to 18 carbon atoms; , alternatively an alkyl group, typically a methyl group (further teaching on silicone nomenclature may be found in Walter Noll, Chemistry and Technology of Silicones, dated 1962, Chapter I, pages 1-9) . The M unit corresponds to a siloxy unit where a = 3, that is R’₃SiO_1/2; the D unit corresponds to a siloxy unit where a = 2, namely R’₂SiO_2/2; the T unit corresponds to a siloxy unit where a = 1, namely R’₁SiO_3/2; the Q unit corresponds to a siloxy unit where a = 0, namely SiO_4/2. The polyorganosiloxane such as a polydiorganosiloxane of component (a) is substantially linear but may contain a proportion of branching due to the presence of T units (as previously described) within the molecule, hence the average value of a in structure (I) is about 2. The unsaturated groups of component (a) may be positioned either terminally or pendently on the polydiorganosiloxane, or in both locations. The unsaturated groups of component (a) may be alkenyl groups or alkynyl groups as described above. Each alkenyl group, when present, may comprise for example from 2 to 30, alternatively 2 to 24, alternatively 2 to 20, alternatively 2 to 12, alternatively 2 to 10, and alternatively 2 to 6 carbon atoms. When present the alkenyl groups may be exemplified by, but not limited to, vinyl, allyl, methallyl, propenyl, and hexenyl and cyclohexenyl groups. Each alkynyl group, when present, may also have 2 to 30, alternatively 2 to 24, alternatively 2 to 20, alternatively 2 to 12, alternatively 2 to 10, and alternatively 2 to 6 carbon atoms. Examples of alkynyl groups may be exemplified by, but not limited to, ethynyl, propynyl, and butynyl groups. Preferred examples of the unsaturated groups of component (a) include vinyl, isopropenyl, allyl, and 5-hexenyl.

In formula (I) , each R’ , other than the unsaturated groups described above, is an independently selected substituted or unsubstituted hydrocarbyl group having from 1 to 18 carbon atoms. These may be individually selected from an aliphatic hydrocarbyl group, a substituted aliphatic hydrocarbyl group, an aromatic group or a substituted aromatic group. Each aliphatic hydrocarbyl group may be exemplified by, but not limited to, alkyl groups having from 1 to 20 carbons per group, alternatively 1 to 15 carbons per group, alternatively 1 to 12 carbons per group, alternatively 1 to 10 carbons per group, alternatively 1 to 6 carbons per group or cycloalkyl groups such as cyclohexyl.

Specific examples of alkyl groups may include methyl, ethyl, propyl, pentyl, octyl, undecyl, and octadecyl groups, alternatively methyl and ethyl groups. Substituted aliphatic hydrocarbyl group are preferably non-halogenated substituted alkyl groups.

The aliphatic non-halogenated organyl groups are exemplified by, but not limited to alkyl groups as described above with a substituted group such as suitable nitrogen containing groups such as amido groups, imido groups; oxygen containing groups such as polyoxyalkylene groups, carbonyl groups, alkoxy groups and hydroxyl groups. Further organyl groups may include sulfur containing groups, phosphorus containing groups, boron containing groups. Examples of aromatic groups or substituted aromatic groups are phenyl groups and substituted phenyl groups with substituted groups as described above.

Component (a) may, for example, be selected from polydimethylsiloxanes,alkylmethylpolysiloxanes, alkylarylpolysiloxanes or copolymers thereof (where reference to alkyl means any suitable alkyl group, alternatively an alkyl group having two or more carbons) providing each polymer contains at least two unsaturated groups, typically alkenyl groups as described above and has a degree of polymerisation of at least 2,500. They may for example be trialkyl terminated, alkenyldialkyl terminated alkynyldialkyl terminated or may be terminated with any other suitable terminal group combination providing each polymer contains the required at least two unsaturated groups per molecule and a degree of polymerisation of at least 2,500.

Hence component (a) may, for the sake of example, be:

a dialkylalkenyl terminated polydimethylsiloxane, e.g., dimethylvinyl terminated polydimethylsiloxane; a dialkylalkenyl terminated dimethylmethylphenylsiloxane, e.g., dimethylvinyl terminated dimethylmethylphenylsiloxane; a trialkyl terminated dimethylmethylvinyl polysiloxane; a dialkylvinyl terminated dimethylmethylvinyl polysiloxane copolymer; a dialkylvinyl terminated methylphenylpolysiloxane, a dialkylalkenyl terminated methylvinylmethylphenylsiloxane; a dialkylalkenyl terminated methylvinyldiphenylsiloxane; a dialkylalkenyl terminated methylvinyl methylphenyl dimethylsiloxane; a trimethyl terminated methylvinyl methylphenylsiloxane; a trimethyl terminated methylvinyl diphenylsiloxane; or a trimethyl terminated methylvinyl methylphenyl dimethylsiloxane.

In each case component (a) has a degree of polymerisation (DP) of at least 2,500, alternatively at least 3,500, alternatively at least 4000. Polydiorganosiloxane polymers of this magnitude are generally referred to in the industry as polydiorganosiloxane gums, siloxane gums or silicone gums (hereafter referred to a silicone gum) because of their very high viscosity (at least 1,000,000 mPa. s at 25℃, often many millions mPa. s at 25℃) and high molecular weight, and as a consequence high degrees of polymerisation (DPs) of e.g., at least 2500 given the DP is calculated from the number average molecular weight of a polymer. Because of the difficulty in measuring the viscosity of highly viscous polymers such as silicone gums, the gums tend to be defined by way of their Williams plasticity values as opposed to viscosity. When component (a) is a silicone gum, said gum has a Williams’s plasticity of at least 30mm/100 measured in accordance with ASTM D-926-08, alternatively at least 50mm/100 measured in accordance with ASTM D-926-08, alternatively at least 100mm/100 measured in accordance with ASTM D-926-08. Typically, silicone gums have a Williams’s plasticity of from about 100mm/100 to 300mm/100 measured in accordance with ASTM D-926-08 but some may have a greater value.

Number average molecular weight and weight average molecular weights of such polymers are typically determined by gel permeation chromatography using polystyrene standards. In the present disclosure number average molecular weight and weight average molecular weight values of the silicone gums used as component (a) herein were determined using a Waters 2695 Separations Module equipped with a vacuum degasser, and a Waters 2414 refractive index detector (Waters Corporation of MA, USA) . The analyses were performed using certified grade toluene flowing at 1.0 mL/min as the eluent. Data collection and analyses were performed using Waters Empower GPC software.

The degree of polymerisation of the polymer was approximately the number average molecular weight of the polymer divided by 74 (the molecular weight of one component (I) depicted above) . Typically, the alkenyl and/or alkynyl content, e.g., vinyl content of the polymer is from 0.01 to 3 wt. %for each polydiorganosiloxane containing at least two silicon-bonded alkenyl groups per molecule of component (a) , alternatively from 0.01 to 2.5 wt. %of component (a) , alternatively from 0.001 to 2.0 wt. %, alternatively from 0.01 to 1.5 wt. %of component (a) of the or each polydiorganosiloxane containing at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl or alkynyl groups per molecule of component (a) . The alkenyl/alkynyl content of component (a) is determined using quantitative infra-red analysis in accordance with ASTM E168.

Component (a) may be present in the composition in an amount of from 4 wt. %to about 30 wt. %of the composition, alternatively from 6 to about 27 wt. %of the composition, alternatively from 8 to 24 wt. %of the composition, alternatively from 10 to 20 wt. %of the composition. Typically, component (a) is present in an amount which is the difference between 100 wt. %and the cumulative wt. %of the other components/ingredients of the composition.

Component (b)

Component (b) of the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein functions as a cross-linker and is provided in the form of an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule. Component (b) normally contains three or more silicon-bonded hydrogen atoms so that the hydrogen atoms can react with the unsaturated alkenyl and/or alkynyl groups of polymer (a) to form a network structure therewith and thereby cure the composition. Some or all of Component (b) may alternatively have two silicon bonded hydrogen atoms per molecule when polymer (a) has greater than two unsaturated groups per molecule.

The molecular configuration of the organosilicon compound having at least two, alternatively at least three Si-H groups per molecule (b) is not specifically restricted, and it can be a straight chain, branched (a straight chain with some branching through the presence of T groups) , cyclic or silicone resin based.

While the molecular weight of component (b) is not specifically restricted, the viscosity is typically from 5 to 50,000 mPa. s at 25℃ relying on either a Brookfield DV-III Ultra Programmable Rheometer for viscosities greater than or equal to 50,000 mPa. s, and a Brookfield DV 3T Rheometer for viscosities less than 50,000 mPa. s, in order to obtain a good miscibility with polymer (a) .

Silicon-bonded organic groups used in component (b) may be exemplified by alkyl groups such as methyl, ethyl, propyl, n-butyl, t-butyl, pentyl, hexyl; aryl groups such as phenyl tolyl, xylyl, or similar aryl groups; 3-chloropropyl, 3, 3, 3-trifluoropropyl, or similar halogenated alkyl group, preferred alkyl groups having from 1 to 6 carbons, especially methyl ethyl or propyl groups or phenyl groups. Preferably the silicon-bonded organic groups used in component (b) are alkyl groups, alternatively methyl, ethyl or propyl groups.

Examples of the organosilicon compound having at least two, alternatively at least three Si-H groups per molecule (b) include but are not limited to:

(a) trimethylsiloxy-terminated methylhydrogenpolysiloxane,

(b) trimethylsiloxy-terminated polydimethylsiloxane-methylhydrogensiloxane,

(c) dimethylhydrogensiloxy-terminated dimethylsiloxane-methylhydrogensiloxane copolymers,

(d) dimethylsiloxane-methylhydrogensiloxane cyclic copolymers,

(e) copolymers and/or silicon resins consisting of (CH₃) ₂HSiO_1/2 units, (CH₃) ₃SiO_1/2 units and SiO_4/2 units,

(f) copolymers and/or silicone resins consisting of (CH₃) ₂HSiO_1/2 units and SiO_4/2 units,

(g) Methylhydrogensiloxane cyclic homopolymers having between 3 and 10 silicon atoms per molecule; alternatively, component (b) , the cross-linker, may be a filler, e.g., silica treated with one of the above, and mixtures thereof.

In one embodiment the Component (b) is selected from a methylhydrogenpolysiloxane capped at both molecular terminals with trimethylsiloxy groups; a copolymer of a methylhydrogensiloxane and a dimethylsiloxane capped at both molecular terminals with trimethylsiloxy groups; dimethylsiloxane capped at both molecular terminals with dimethylhydrogensiloxy groups; a copolymer of a methylhydrogensiloxane and a dimethylsiloxane capped at both molecular terminals with dimethylhydrogensiloxy groups.

The cross-linker (b) is generally present in the thermally conductive silicone rubber composition such that the molar ratio of the total number of the silicon-bonded hydrogen atoms in component (b) to the total number of alkenyl and/or alkynyl groups in polymer (a) and in component (c) is from 0.5: 1 to 20: 1. When this ratio is less than 0.5: 1, a well-cured composition will not be obtained.

When the ratio exceeds 20: 1, there is a tendency for the hardness of the cured composition to increase when heated. Preferably in an amount such that the molar ratio of silicon-bonded hydrogen atoms of component (b) to alkenyl/alkynyl groups, alternatively alkenyl groups of component (a) and component (c) ranges from 0.7 : 1.0 to 5.0 : 1.0, preferably from 0.9 : 1.0 to 2.5 : 1.0, and most preferably from 0.9 : 1.0 to 2.0 : 1.0.

The silicon-bonded hydrogen (Si-H) content of component (b) is determined using quantitative infra-red analysis in accordance with ASTM E168. In the present instance the silicon-bonded hydrogen to alkenyl (vinyl) and/or alkynyl ratio is important when relying on a hydrosilylation cure process. Generally, this is determined by calculating the total weight %of alkenyl groups in the composition, e.g., vinyl [V] and the total weight %of silicon bonded hydrogen [H] in the composition and given the molecular weight of hydrogen is 1 and of vinyl is 27 the molar ratio of silicon bonded hydrogen to vinyl is 27 [H] / [V] .

Typically, dependent on the number of unsaturated groups in component (a) and component (c) as well as the number of Si-H groups in component (b) , component (b) will be present in an amount of from 0.1 to 10 wt. %of the thermally conductive silicone rubber composition, alternatively 0.1 to 7.5wt. %of the thermally conductive silicone rubber composition, alternatively 0.5 to 7.5wt. %, further alternatively from 0.5%to 5 wt. %of the thermally conductive silicone rubber composition.

Component (c)

Component (c) of the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein is utilised as a thermally conductive filler (e.g., (e) (i) or (e) (ii) ) treating agent comprising an organopolysiloxane having a degree of polymerisation of between 4 to 500 and comprising

(i) at least one alkenyl group per molecule and

(ii) at least one hydroxy group or at least one alkoxy group or a mixture of hydroxy and alkoxy groups per molecule.

Hence, each organopolysiloxane of component (c) has a degree of polymerisation of between 4 to 500, i.e., therefore has between 4 to 500 siloxy units of formula (I) as described with respect to component (a) :

R’_aSiO _(4-a) _/2 (I)

The subscript “a” is 0, 1, 2 or 3.

The unsaturated group (s) of component (c) may be positioned either terminally or pendently on the polydiorganosiloxane, or when greater than one (>1) ) is present in both locations. The unsaturated groups of component (c) may be the alkenyl groups or alkynyl groups as described above with respect to component (a) .

In component (c) there is/are also at least one hydroxy group or at least one alkoxy group or a mixture of hydroxy and alkoxy groups per molecule. When present the alkoxy groups may have from 1 to 20 carbons per group, alternatively 1 to 15 carbons per group, alternatively 1 to 12 carbons per group, alternatively 1 to 10 carbons per group, alternatively 1 to 6 carbons per group with methoxy groups ethoxy groups, propoxy groups butoxy groups, pentoxy groups and/or hexoxy groups preferred. The organopolysiloxane of component (c) may be linear or branched.

In component (c) referring again to formula (I) , each R’ , other than the unsaturated groups described above, and the at least one hydroxy group or at least one alkoxy group or a mixture of hydroxy and alkoxy groups per molecule, is independently selected from the same aliphatic hydrocarbyl groups, substituted aliphatic hydrocarbyl groups, aromatic groups or substituted aromatic groups described above with respect to component (a) .

Component (c) may be selected from polydimethylsiloxanes, alkylmethylpolysiloxanes, alkylarylpolysiloxanes or copolymers thereof (where reference to alkyl means any suitable alkyl group, alternatively an alkyl group having two or more carbons) providing they have a degree of polymerisation of between 4 to 500 and comprise

(i) at least one alkenyl group per molecule and

The said alkenyl groups, hydroxy group (s) and alkoxy group (s) may be pendent or terminal groups. In one preferred alternative the unsaturated groups, hydroxy group (s) and alkoxy group (s) are terminal groups.

For the sake of example, component (c) herein may be a linear or branched polydimethylsiloxane having one dimethylalkenyl termination per molecule and one trialkoxy termination per molecule or a hydroxyldialkyl termination per molecule such as M^ViD_fSi (OMe) ₃ which may be alternatively written as

(CH₂=CH) (CH₃) ₂SiO [ (CH₃) ₂SiO] _fSi (OCH₃) ₃

Wherein f is an integer such that the degree of polymerisation is from 4 to 500, alternatively f is an integer such that the degree of polymerisation is from 4 to 250, f is an integer such that the degree of polymerisation is from 4 to 150, alternatively f is an integer such that the degree of polymerisation is from 4 to 100. An example thereof being when f is 25, i.e., M^ViD₂₅Si (OMe) ₃ otherwise written as

(CH₂=CH) (CH₃) ₂SiO [ (CH₃) ₂SiO] ₂₅SiO (CH₃) ₃

An alternative example of component (c) may be a polydimethylmethylvinylsiloxane polymer or a polymethylvinylsiloxane polymer having a degree of polymerisation of from 4 to 500 with dialkylhydroxy termination or dialkylmethoxy termination such as the following

R¹(CH₃) ₂SiO [ (CH₃) ₂SiO] _m [ (CH₂=CH) (CH₃) SiO] _nSiO (CH₃) ₃R¹

where R¹ is hydroxy or alkoxyl, m is zero or an integer and n is an integer such that the degree of polymerisation is from 4 to 500, alternatively such that the degree of polymerisation is from 4 to 250, alternatively such that the degree of polymerisation is from 4 to 150, alternatively such that the degree of polymerisation is from 4 to 100, alternatively such that the degree of polymerisation is from 4 to 50, for example where m + n= 4 to 17.

In each case component (c) has a degree of polymerisation of between 4 to 500 and comprising

(i) at least one alkenyl group per molecule and

A degree of polymerisation of between 4 to 500 which means the viscosity is going to be a minimum of about 20mPa. s at 25℃ and the number average molecular weight of the composition (Mw) is approximately at least about 300. Molecular weight values may again be determined by gel permeation chromatography but polymers at the lower end of the range e.g., having a DP of from about 4 to 20 can be analysed by gas chromatography –mass spectroscopy (GC-MS) .

Component (c) is present in the composition herein in an amount of 0.1-10 wt. %, alternatively in an amount of from 0.1-5 wt. %of the composition, alternatively in an amount of from 0.25-5 wt. %of the composition, alternatively in an amount of from 0.25-2.5 wt. %of the composition.

Component (d)

Component (d) of the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein, is a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof. These are usually selected from catalysts of the platinum group of metals (platinum, ruthenium, osmium, rhodium, iridium and palladium) , or a compound of one or more of such metals. Alternatively, platinum and rhodium compounds are preferred due to the high activity level of these catalysts in hydrosilylation reactions, with platinum compounds most preferred. In a hydrosilylation (or addition) reaction, a hydrosilylation catalyst such as component (d) herein catalyses the reaction between an unsaturated group, usually an alkenyl group e.g., vinyl with Si-H groups.

The hydrosilylation catalyst of component (d) can be a platinum group metal, a platinum group metal deposited on a carrier, such as activated carbon, metal oxides, such as aluminum oxide or silicon dioxide, silica gel or powdered charcoal, or a compound or complex of a platinum group metal.

Preferably the platinum group metal is platinum.

Examples of preferred hydrosilylation catalysts of component (d) are platinum based catalysts, for example, platinum black, platinum oxide (Adams catalyst) , platinum on various solid supports, chloroplatinic acids, e.g., hexachloroplatinic acid (Pt oxidation state IV) (Speier catalyst) , chloroplatinic acid in solutions of alcohols e.g., isooctanol or amyl alcohol (Lamoreaux catalyst) , and complexes of chloroplatinic acid with ethylenically unsaturated compounds such as olefins and organosiloxanes containing ethylenically unsaturated silicon-bonded hydrocarbon groups, e.g., tetra-vinyl-tetramethylcyclotetrasiloxane-platinum complex (Ashby catalyst) . Soluble platinum compounds that can be used include, for example, the platinum-olefin complexes of the formulae (PtCl₂. (olefin) ₂ and H (PtCl₃. olefin) , preference being given in this context to the use of alkenes having 2 to 8 carbon atoms, such as ethylene, propylene, isomers of butene and of octene, or cycloalkanes having 5 to 7 carbon atoms, such as cyclopentene, cyclohexene, and cycloheptene. Other soluble platinum catalysts are, for the sake of example a platinum-cyclopropane complex of the formula (PtCl₂C₃H₆) ₂, the reaction products of hexachloroplatinic acid with alcohols, ethers, and aldehydes or mixtures thereof, or the reaction product of hexachloroplatinic acid and/or its conversion products with vinyl-containing siloxanes such as methylvinylcyclotetrasiloxane in the presence of sodium bicarbonate in ethanolic solution –. Platinum catalysts with phosphorus, sulfur, and amine ligands can be used as well, e.g., (Ph₃P) ₂PtCl₂; and complexes of platinum with vinylsiloxanes, such as sym-divinyltetramethyldisiloxane.

Hence, specific examples of suitable platinum-based catalysts of component (d) include

(i) complexes of chloroplatinic acid with organosiloxanes containing ethylenically unsaturated hydrocarbon groups are described in US 3, 419, 593;

(ii) chloroplatinic acid, either in hexahydrate form or anhydrous form;

(iii) a platinum-containing catalyst which is obtained by a method comprising reacting chloroplatinic acid with an aliphatically unsaturated organosilicon compound, such as divinyltetramethyldisiloxane;

(iv) alkene-platinum-silyl complexes as described in US Pat. No. 6, 605, 734 such as (COD) Pt (SiMeCl₂) ₂ where “COD” is 1, 5-cyclooctadiene; and/or

(v) Karstedt's catalyst, a platinum divinyl tetramethyl disiloxane complex typically containing about 1 wt. %of platinum typically in a vinyl siloxane polymer. Solvents such as toluene and the like organic solvents have been used historically as alternatives but the use of vinyl siloxane polymers by far the preferred choice. These are described in US3,715,334 and US3,814,730. In one preferred embodiment component (d) may be selected from co-ordination compounds of platinum. In one embodiment hexachloroplatinic acid and its conversion products with vinyl-containing siloxanes, Karstedt's catalysts and Speier catalysts are preferred.

The catalytic amount of the hydrosilylation catalyst is generally between 0.01 ppm, and 10,000 parts by weight of platinum-group metal, per million parts (ppm) , based on the weight of the composition; alternatively, between 0.01 and 5000ppm; alternatively, between 0.01 and 3,000 ppm, and alternatively between 0.01 and 1,000 ppm. In specific embodiments, the catalytic amount of the catalyst may range from 0.01 to 1,000 ppm, alternatively 0.01 to 750 ppm, alternatively 0.01 to 500 ppm and alternatively 0.01 to 100 ppm of metal based on the weight of the composition. The ranges may relate solely to the metal content within the catalyst or to the catalyst altogether (including its ligands) as specified, but typically these ranges relate solely to the metal content within the catalyst. The catalyst may be added as a single species or as a mixture of two or more different species. Typically, dependent on the form/concentration in which the catalyst is provided e.g., in a polymer or solvent, the amount of component (d) present will be within the range of from 0.001 to 3.0 wt. %of the composition, alternatively from 0.001 to 1.5 wt. %of the composition, alternatively from 0.01–1.5 wt. %, alternatively 0.01 to 0.1.0 wt. %, of the thermally conductive silicone rubber composition.

Component (e) (i)

Component (e) (i) of the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein, when present, is at least one thermally conductive filler with a volume median particle diameter D (v, 0.5) of between 0.1-20 micrometres (μm) in an amount of from 70 to 95 wt. %of the composition, alternatively of from 80 to 95 wt. %of the composition.

The volume median particle diameter D (v, 0.5) is the particle diameter value for a D₅₀ particle size distribution (or median particle size distribution) where 50%of the distribution is above said value and 50%is below said value. The thermally conductive filler (e) (i) may be a single thermally conductive filler or a combination of two or more thermally conductive fillers that differ in at least one property such as particle shape, volume median particle diameter, particle size distribution, and type of filler. The volume median particle diameter D (v, 0.5) values herein were taken from supplier datasheets and/or were measured by laser diffraction particle size analysis using a Malvern

Mastersizer 2000 with Hydro 2000MU dispersion unit. The parameters relied upon were refractive index (R.I. ) of particle: 1.78/0.1; dispersant: water (1.33) ; obscuration: ～10%; inner stirring speed: 3000rpm.

Samples were prepared before analysis by mixing 0.5g fillers + 25ml water, shake and put into Hydro2000MU dispersion unit with 2min inner sonication.

Any suitable thermally conductive fillers may be utilised as component (e) (i) . Examples include: metals e.g., bismuth, lead, tin, antimony, indium, cadmium, zinc, silver, copper, nickel, aluminum, iron and silicon metal;

alloys e.g., alloys of one or more of bismuth, lead, tin, antimony, indium, cadmium, zinc, silver, aluminum, iron and/or silicon; for example, Fe-Si alloy, Fe-Al alloy, Fe-Si-Al alloy, Fe-Si-Cr alloy, Fe-Ni alloy, Fe-Ni-Co alloy, Fe-Ni-Mo alloy, Fe -Co alloy, Fe-Si-Al-Cr alloys, Fe-Si-B alloy and Fe-Si-Co-B alloy;

ferrites, Mn-Zn ferrite, Mn-Mg-Zn ferrite, Mg-Cu-Zn ferrite, Ni-Zn ferrite, and a Ni-Cu-Zn ferrite and Cu-Zn ferrite;

Metal oxides such as, aluminium oxide (alumina) , zinc oxide, silicon oxide, magnesium oxide, beryllium oxide, chromium oxide and titanium oxide;

metal hydroxides such as magnesium hydroxide, aluminum hydroxide, barium hydroxide and calcium hydroxide;

metal nitrides, such as boron nitride, aluminum nitride and silicon nitride;

metal carbides such as silicon carbide, include boron carbide and titanium carbide; and metal silicides such as magnesium silicide, titanium silicide, silicide, zirconium, tantalum silicide, niobium silicide, chromium silicide, and a tungsten silicide and molybdenum silicide.

The thermally conductive filler (e) (i) may be a mixture of two or more of the above. In some embodiments, combinations of metallic and inorganic fillers, may be used as thermally conductive filler (e) (i) , for example a combination of aluminium and aluminium oxide fillers; a combination of aluminium and zinc oxide fillers; or a combination of aluminium, aluminium oxide, and zinc oxide fillers.

Of the above, aluminium oxide, aluminum hydroxide, aluminium nitride, boron nitride and mixtures thereof are preferred.

The shape of the thermally conductive filler particles (e) (i) is not specifically restricted, e.g., they may be powders and/or fibers, however, rounded or spherical particles may prevent viscosity increase to an undesirable level upon high loading of the thermally conductive filler in the composition and as such are preferred. The volume median particle diameter and D₅₀ particle size distribution of the thermally conductive filler will depend on various factors including the type of thermally conductive filler selected and the exact amount added to the curable composition, as well as the bondline thickness of the device in which the cured silicone-based product of the composition will be used. In some particular instances, the thermally conductive filler (e) (i) may have a volume median particle diameter ranging from 0.1-20 micrometres (μm) measured by laser diffraction particle size analysis, alternatively 0.1 micrometre to 15 micrometres, alternatively 0.1 micrometre to 12.5 micrometres. When the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein comprises thermally conductive filler (e) (i) said compositions comprise from 70 wt. %to 95 wt. %, alternatively from e.g., 75 wt. %to 90 wt. %thermally conductive filler (e) (i) , alternatively from e.g., 80 wt. %to 90 wt. %thermally conductive filler (e) (i) .

When the thermally conductive filler in the of the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein is component (e) (i) there is preferably no precipitated silica or fumed silica present in the composition. In one embodiment there is no precipitated silica or fumed silica present in the composition described herein (other than trace levels) when the at least one thermally conductive filler is component (e) (i) .

As discussed above component (e) (i) may be replaced in the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein by a combination of components (e) (ii) and (f) .

Component (e) (ii)

When present, component (e) (ii) of the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein, when present, is at least one thermally conductive filler with a volume median particle diameter D (v, 0.5) of from more than 20 -100 micrometres (μm) . Any suitable thermally conductive fillers as identified for component (e) (i) may be utilised for component (e) (ii) other than requiring with a volume median particle diameter D (v, 0.5) of from more than 20 -100 micrometres (μm) (determined in the same manner as discussed above) .

Excepting having a volume median particle diameter D (v, 0.5) of from more than 20 -100 micrometres (μm) component (e) (ii) is the same as component (e) (i) and as such the description is not repeated here. The volume median particle diameter and D₅₀ particle size distribution of the thermally conductive filler will also depend on various factors including the type of thermally conductive filler selected and the exact amount added to the curable composition, as well as the bond line thickness of the device in which the cured silicone-based product of the composition will be used. In some particular instances, the thermally conductive filler (e) (ii) may have a volume median particle diameter ranging from above 20.0 to 100 micrometres (μm) measured by laser diffraction particle size analysis, alternatively from 25 micrometre to 90 micrometres, alternatively from 30 micrometre to 75 micrometres.

In combination component (e) (ii) and component (f) are present in an amount of from 70 to 95 wt. %of the composition.

Component (f)

Precipitated silica, fumed silica, colloidal silica or a mixture of any two or more of precipitated silica colloidal silica and fumed silica in an amount of from greater than zero to 5 wt. %of the composition

As previously indicated, when the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein, is component (e) (i) there is preferably no precipitated silica, fumed silica or colloidal silica (component (f) ) present in said composition.

When the thermally conductive filler in the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein, is component (e) (ii) there is also present in the composition component (f) comprising precipitated silica, fumed silica, colloidal silica or a mixture of any two or more of precipitated silica colloidal silica and fumed silica in an amount of from greater than zero to 5 wt. %of the composition.

When present, the precipitated silica, fumed silica and/or colloidal silicas function is to reinforce the composition. Such silicas are preferably finely divided. Precipitated silica, fumed silica and/or colloidal silicas are particularly chosen because of their relatively high surface area, which is typically at least 50 m²/g (BET method in accordance with ISO 9277: 2010) ; alternatively, having surface areas of from 50 to at least 450 m²/g (BET method in accordance with ISO 9277: 2010) , alternatively having surface areas of from 50 to 300 m²/g (BET method in accordance with ISO 9277: 2010) , are typically used. All these types of silica are commercially available.

Typically, the fabric reinforced thermally conductive silicone rubber tubes described herein resulting from the thermally conductive silicone rubber composition comprising at least 70wt. %thermally conductive filler (e) (i) or (e) (ii) (in combination with (f) ) described herein will have a high thermal conductivity of at least 0.5W/m. K., measured in accordance with ASTM D7896 –hot disk method. The thermal conductivity of the fabric reinforced thermally conductive silicone rubber tubes will depend on the thermally conductive filler (s) (e) (i) or (e) (ii) utilised. In the case of less conductive thermally conductive fillers (e) (i) or (e) (ii) such as aluminium oxide and aluminium hydroxide when present in an amount of 70wt. %of the composition thermal conductivity of the product will be typically between 0.5W/m. K. and 1.0W/m. K., (ASTM D7896 –hot disk method) and as such the composition may require up to about 85wt. %of these thermally conductive fillers, for the cured silicone-based products to have a thermal conductivity of at least 2.0W/m. K. (ASTM D7896 –hot disk method) .

However, fabric reinforced thermally conductive silicone rubber tubes from the thermally conductive silicone rubber composition described above will have a greater thermal conductivity when the thermally conductive fillers (e) (i) or (e) (ii) are nitrides such as aluminum nitride, silicon nitride and/or boron nitride. In this case they may have significantly higher thermal conductivities e.g., at least 2.0 W/m. K. (ASTM D7896 –hot disk method) .

As previously discussed, when the thermally conductive filler (e) (i) is present, the thermally conductive silicone rubber compositions as described herein comprise from 70 wt. %to 95 wt. %, alternatively from e.g., 75 wt. %to 90 wt. %of thermally conductive filler (e) (i) . When there is both thermally conductive filler (e) (ii) at least 80 wt. %of the composition is thermally conductive filler (e) (ii) and component (f) present in the composition at least 75 wt. %of the composition is thermally conductive filler (e) (ii) at least 70 wt. %of the composition is thermally conductive filler (e) (ii) and the cumulative amount of thermally conductive filler and reinforcing filler when the latter is present is a maximum of 95 wt. %.

Additional optional components

Additional optional components may be present in the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein depending on the intended final use thereof.

Examples of such optional components include cure inhibitors, hydrophobic treating agent (s) (for the avoidance of doubt excluding component (c) herein) , compression set additives, pigments and/or coloring agents, and other additional additives such as metal deactivators, mold release agents, UV light stabilizers, bactericides, and mixtures thereof.

Optional hydrosilylation reaction inhibitors

The hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein, may also comprise one or more optional hydrosilylation reaction inhibitors. Hydrosilylation reaction inhibitors are used, when required, to prevent or delay the hydrosilylation reaction inhibitors curing process especially during storage. The optional hydrosilylation reaction inhibitors of platinum-based catalysts are well known in the art and include hydrazines, triazoles, phosphines, mercaptans, organic nitrogen compounds, acetylenic alcohols, silylated acetylenic alcohols, maleates, fumarates, ethylenically or aromatically unsaturated amides, ethylenically unsaturated isocyanates, olefinic siloxanes, unsaturated hydrocarbon monoesters and diesters, conjugated ene-ynes, hydroperoxides, nitriles, and diaziridines. Alkenyl-substituted siloxanes as described in US3989667 may be used, of which cyclic methylvinylsiloxanes are preferred.

One class of known hydrosilylation reaction inhibitors are the acetylenic compounds disclosed in US3445420. Acetylenic alcohols such as 2-methyl-3-butyn-2-ol constitute a preferred class of inhibitors that will suppress the activity of a platinum-containing catalyst at 25 ℃. Compositions containing these inhibitors typically require heating at temperature of 70 ℃ or above to cure at a practical rate.

Examples of acetylenic alcohols and their derivatives include 1-ethynyl-1-cyclohexanol (ETCH) , 2-methyl-3-butyn-2-ol, 3-butyn-1-ol, 3-butyn-2-ol, propargyl alcohol, 1-phenyl-2-propyn-1-ol, 3, 5-dimethyl-1-hexyn-3-ol, 1-ethynylcyclopentanol, 3-methyl-1-penten-4-yn-3-ol, and mixtures thereof. Derivatives of acetylenic alcohol may include those compounds having at least one silicon atom. When present, hydrosilylation reaction inhibitor concentrations may be as low as 1 mole of hydrosilylation reaction inhibitor per mole of the metal of catalyst (d) will, in some instances, still impart satisfactory storage stability and cure rate. In other instances, hydrosilylation reaction inhibitor concentrations of up to 500 moles of inhibitor per mole of the metal of catalyst are required. The optimum concentration for a given hydrosilylation reaction inhibitor in a given composition is readily determined by routine experimentation. Dependent on the concentration and form in which the hydrosilylation reaction inhibitor selected is provided/available commercially, when present in the composition, the inhibitor is typically present in an amount of from 0.0125 to 10wt. %of the composition.

In one embodiment the inhibitor, when present, is selected from 1-ethynyl-1-cyclohexanol (ETCH) and/or 2-methyl-3-butyn-2-ol and is present in an amount of greater than zero to 0.1 wt. %of the composition.

Hydrophobic Treating Agent for treating component (f) when present

When component (f) is present in combination with the thermally conductive fillers (e) (ii) in the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein, said component (f) the precipitated silica, fumed silica and/or colloidal silicas are (s) are naturally hydrophilic and therefore may be treated with a treating agent to render them hydrophobic.

Component (f) may be treated together with component (e) (ii) using component (c) or may be treated separately with an alternative hydrophobic treating agent. In such as case component (f) may be surface treated with any suitable hydrophobic treating agent other than component (c) disclosed in the art. For example, low molecular weight organosilicon compounds such as organosilanes, polydiorganosiloxanes, or organosilazanes e.g., hexaalkyl disilazane and short chain siloxane diols. Specific examples include, but are not restricted to, silanol terminated trifluoropropylmethylsiloxane, silanol terminated vinyl methyl (ViMe) siloxane, silanol terminated methyl phenyl (MePh) siloxane, liquid hydroxyldimethyl-terminated polydiorganosiloxane containing an average from 2 to 20 repeating units of diorganosiloxane in each molecule, hydroxyldimethyl terminated phenylmethyl Siloxane, hexaorganodisiloxanes, such as hexamethyldisiloxane, divinyltetramethyldisiloxane; hexaorganodisilazanes, such as hexamethyldisilazane (HMDZ) , divinyltetramethyldisilazane and tetramethyldi (trifluoropropyl) disilazane; hydroxyldimethyl terminated polydimethylmethylvinyl siloxane, octamethyl cyclotetrasiloxane, and silanes including but not limited to methyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, chlrotrimethyl silane, dichlrodimethyl silane, trichloromethyl silane.

In one embodiment, the treating agent may be selected from silanol terminated vinyl methyl (ViMe) siloxane, liquid hydroxyldimethyl-terminated polydiorganosiloxane containing an average from 2 to 20 repeating units of diorganosiloxane in each molecule, hexaorganodisiloxanes, such as hexamethyldisiloxane, divinyltetramethyldisiloxane; hexaorganodisilazanes, such as hexamethyldisilazane (HMDZ) , divinyltetramethyldisilazane and; hydroxyldimethyl terminated polydimethylmethylvinyl siloxane, octamethyl cyclotetrasiloxane, and silanes including but not limited to methyltriethoxysilane, dimethyldiethoxysilane and/or vinyltriethoxysilane. A small amount of water can be added together with the silica treating agent (s) as processing aid.

The surface treatment of untreated component (f) may be undertaken prior to introduction in the composition or in situ, i.e., in the presence of at least a portion of the other components of the composition herein by blending these components together at room temperature or above until the filler is completely treated. If the treating agent being used is component (c) described above, the reinforcing filler and the thermally conductive filler (component (e) (ii) ) are treated simultaneously. If separate filler treating agents are being used for component (f) and component (e) (ii) respectively they will need to be treated separately or sequentially.

Typically, any untreated component (f) is preferably treated in situ with a treating agent in the presence of polydiorganosiloxane polymer (a) which results in the preparation of a silicone rubber base material which can subsequently be mixed with other components.

Optional Compression Set Additives

Whilst compression set is not usually deemed a critical performance for typical thermally conductive applications such as silicone grease, silicone gel and gap fillers, standard thermally conductive silicone rubber compositions usually show very high compression set due to high loading of thermally conductive filler (s) in the compositions to achieve thermal conductivity. As discussed elsewhere when a thermally conductive silicone rubber composition is designed to generate high thermal conductivities of e.g., at least 1.5 W/m. K., (measured in accordance with ASTM D7896 –hot disk method) , the level of thermally conductive filler required generally result in the pre-cured compositions having significantly increased viscosities causing impaired handling characteristics and additionally, upon cure, result in cured silicone-based products with poor physical properties. Whilst such products may be acceptable for some applications, industry is increasingly demanding compositions for the generation of cured materials which have both

(i) the desired high levels of thermal conductivity, and

(ii) required levels of physical properties,

whereas previously one might expect either one or the other. The high amount of thermally conductive filler present in a thermally conductive silicone rubber composition has in the past significantly decreased the elasticity/resiliency of silicone rubber but the composition provided herein appears to overcome this issue. However, it was identified that if desired the inclusion of certain compression set additives in the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein have a significant improving effect on compression set. The compression set is measured herein in accordance with ASTM D395 and is the permanent deformation remaining after removal of a force that was applied to it. The term is often a property of interest when using elastomers. Compression set occurs when a material is compressed to a specific deformation, for a specified time, at a specific temperature. Compression set testing measures the ability of rubber to return to its original thickness after prolonged compressive stresses at a given temperature and deflection. As a rubber material is compressed over time, it loses its ability to return to its original thickness. This loss of resiliency (memory) may reduce the capability of an elastomeric gasket, seal or cushioning pad to perform over a long period of time. The resulting permanent set that a gasket may take over time may cause a leak; or in the case of a shock isolation pad, the ability to protect an accidentally dropped unit may be compromised. Compression set results for a material are expressed as a percentage. The lower the percentage, the better the material resists permanent deformation under a given deflection and temperature range. The compression set additive use herein may be selected from, for example, Dodecanedioic acid, bis [2- (2-hydroxy benzoyl) hydrazide] , diphenyl sulfide, salicyloylaminotriazole, 1, 2-di [- (3, 5-di-tert-butyl-4-hydroxyp-henyl) propionyl] hydrazine, copper (II) phthalocyanine and mixtures thereof, such as Dodecanedioic acid, bis [2- (2-hydroxy benzoyl) hydrazide] and copper (II) phthalocyanine. The compression set additive, when present is added to the composition in an amount of from 0.01-5 wt. %of the composition, alternatively from 0.01-2 wt. %of the composition.

Optional Pigments/Colorants

The hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein, may further comprise one or more pigments and/or colorants which may be added if desired. The pigments and/or colorants may be coloured, white, black, metal effect, and luminescent e.g., fluorescent and phosphorescent.

Suitable white pigments and/or colorants include titanium dioxide, zinc oxide, lead oxide, zinc sulfide, lithophone, zirconium oxide, and antimony oxide.

Suitable non-white inorganic pigments and/or colorants include, but are not limited to, iron oxide pigments such as goethite, lepidocrocite, hematite, maghemite, and magnetite black iron oxide, yellow iron oxide, brown iron oxide, and red iron oxide; blue iron pigments; chromium oxide pigments; cadmium pigments such as cadmium yellow, cadmium red, and cadmium cinnabar; bismuth pigments such as bismuth vanadate and bismuth vanadate molybdate; mixed metal oxide pigments such as cobalt titanate green; chromate and molybdate pigments such as chromium yellow, molybdate red, and molybdate orange; ultramarine pigments; cobalt oxide pigments; nickel antimony titanates; lead chrome; carbon black; lampblack, and metal effect pigments such as aluminium, copper, copper oxide, bronze, stainless steel, nickel, zinc, and brass.

Suitable organic non-white pigments and/or colorants include phthalocyanine pigments, e.g., phthalocyanine blue and phthalocyanine green; monoarylide yellow, diarylide yellow, benzimidazolone yellow, heterocyclic yellow, DAN orange, quinacridone pigments, e.g., quinacridone magenta and quinacridone violet; organic reds, including metallized azo reds and nonmetallized azo reds and other azo pigments, monoazo pigments, diazo pigments, azo pigment lakes, β-naphthol pigments, naphthol AS pigments, benzimidazolone pigments, diazo condensation pigment, isoindolinone, and isoindoline pigments, polycyclic pigments, perylene and perinone pigments, thioindigo pigments, anthrapyrimidone pigments, flavanthrone pigments, anthanthrone pigments, dioxazine pigments, triarylcarbonium pigments, quinophthalone pigments, and diketopyrrolo pyrrole pigments.

The pigments and/or colorants, when present, are present in the range of from 2 wt. %, alternatively from 3 wt. %, alternatively from 5 wt. %of the composition to 15 wt. %of the composition, alternatively to 10 wt. %of the composition.

Other optional Additives

Other optional additives in the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein, herein may include metal deactivators i.e., fuel additives and oil additives used to stabilize liquids by deactivating (usually by sequestering) metal ions, mostly introduced by the action of naturally occurring acids in the fuel and acids generated in lubricants by oxidative processes with the metallic parts of the systems e.g., dodecanedioic acid, bis [2- (2-hydroxybenzoyl) hydrazide] .

Pot life extenders, such as triazole, may be used, if desired but are not considered necessary. The thermally conductive silicone rubber composition may thus be free of pot life extender.

Examples of flame retardants include aluminium trihydrate, chlorinated paraffins, hexabromocyclododecane, triphenyl phosphate, dimethyl methylphosphonate, tris (2, 3-dibromopropyl) phosphate (brominated tris) , and mixtures or derivatives thereof.

Hence, in one alternative, the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein, comprises:

a) a polydiorganosiloxane having a degree of polymerisation of at least 2,500 calculated from the number average molecular weight determined by gel permeation chromatography and at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl or alkynyl groups and which is present in the composition in an amount of from 4 wt. %to about 30 wt. %of the composition, alternatively from 6 to about 27 wt. %of the composition, alternatively from 8 to 24 wt. %of the composition, alternatively from 10 to 20 wt. %of the composition, alternatively the difference between 100wt. %and the cumulative amount of all other ingredients present in the composition;

b) an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule, component (b) present in an amount of from 0.1 to 10 wt. %the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes, alternatively 0.1 to 7.5wt. %of the hydrosilylation (addition) curable thermally conductive silicone rubber composition, alternatively 0.5 to 7.5wt. %, further alternatively from 0.5%to 5 wt. %of the hydrosilylation (addition) curable thermally conductive silicone rubber composition.

(i) at least one alkenyl group per molecule and

in an amount of from 0.1-10%wt. of the composition, alternatively in an amount of from 0.1-5 wt. %, alternatively in an amount of from 0.25-5 wt. %of the composition, alternatively in an amount of from 0.25-2.5 wt. %of the composition; and

d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof, in an amount dependent on the form/concentration in which the catalyst is provided, within the range of from 0.001 to 3.0 wt. %of the composition, alternatively from 0.001 to 1.5 wt. %of the composition, alternatively from 0.01–1.5 wt. %, alternatively 0.01 to 0.1.0 wt. %, of the thermally conductive silicone rubber composition, and either

a combination of (e) (ii) and (f) wherein

wherein the combination of (e) (ii) + (f) is present in the composition in an amount of from 70 to 95 wt. %of the composition, alternatively in an amount of from 80 to 95 wt. %of the composition providing the total wt. %of the composition is 100 wt. %.

The composition may also contain one or more of the above optional additives in amounts indicated again providing the total wt. %of the composition is 100 wt. %.

Prior to step (I) of the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein, mixtures of the aforementioned components (a) , (b) , and (d) from the hydrosilylation (addition) curable thermally conductive silicone rubber composition may begin to cure at ambient temperature or greater. Hence, if mixtures of multiple components and additives need to be stored between mixing and final use, the composition can be stored in multiple parts.

However, given component (a) in the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein is a high viscosity (> 1000,000mPa. s at 25℃) polymer often referred to in the industry as a silicone gum, the composition is preferably mixed together into a single part composition as an aspect of the process step in making the aforementioned tubes.

In the latter case when a one-part composition is prepared, the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein may be prepared by combining all of components together into a one-part composition. Typically, a base is prepared first to enable the thermally conductive fillers to be treated in-situ and then the remaining ingredients can be introduced into the mixture in any suitable order. Any mixing techniques and devices described in the prior art can be used in order to complete step (I) of the process. The particular device to be used will be determined by the viscosities of components and the final curable coating composition. Suitable mixers include but are not limited to paddle type mixers e.g., planetary mixers and kneader type mixers. However, when component (a) is a gum, mixing may be preferably undertaken using e.g., a two-roll mill or a kneader mixer. Cooling of components during mixing may be desirable to avoid premature curing of the composition.

However, such hydrosilylation (addition) curable thermally conductive silicone rubber composition may be stored in multiple parts, typically two parts, which are mixed together immediately before use when the composition is not prepared for immediate use. In such a case, the two parts are generally referred to as Part (A) and Part (B) and are designed to keep components (b) the cross-linker (s) and (d) the catalyst (s) apart to avoid premature cure.

Typically, in such cases a Part A composition will comprise components (a) polymer, (c) treating agent, (d) catalyst and (e) (i) or a combination of (e) (ii) and (f) and Part B will comprise components (a) polymer, (b) cross-linker, (c) treating agent and (e) (i) or a combination of (e) (ii) and (f) and when present, inhibitor. Other optional additives, when present in the composition, may be in either Part A or Part B providing they do not negatively affect the properties of any other component (e.g., catalyst inactivation) . Whilst use of a one-part composition is preferred, in the event the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein is stored in two parts, the part A and part B compositions are mixed together shortly prior to use to initiate cure of the full composition into a silicone elastomeric material. The compositions can be designed to be mixed in any suitable weight ratio. Typically, the part A and part B compositions are mixed together using a two-roll mill or kneader mixer.

Components in each of Part A and/or Part B may be mixed together individually or may be introduced into the composition in pre-prepared in combination for, e.g., ease of mixing the final composition. For example, components (a) and components (e) (i) or a combination of (e) (ii) and (f) may be mixed together to form a base composition. In such cases component (c) the treating agent is usually introduced into the mixture so that the thermally conductive filler (e) can be treated in-situ. Alternatively, components (e) (i) or a combination of (e) (ii) and (f) may be pre-treated with component (c) although this is not preferred. The resulting base material can be split into two or more parts, typically part A and part B and appropriate additional components and additives may be added, if and when required.

Once the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes has been prepared in step (I) of the process the resulting composition is introduced onto a suitable extruder and is extruded therefrom to form a thermally conductive silicone rubber tube (A) , after which the tube produced is cooled or allowed to cool, typically to room temperature or thereabouts. thermally conductive silicone rubber tube (A) functions as the inner layer of the final fabric reinforced thermally conductive silicone rubber tube products.

Any suitable extruder may be utilised. The extruder may be a single screw extruder or a twin screw extruder and may be in the form of a horizontal extruder optionally with a vertical extruder head. The extruder may have at least two heating tunnels, alternatively two heating tunnels. When the extruder has two heating tunnels the sequentially first heating tunnel, through which the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes is transported, is maintained at a higher temperature than the sequentially second heating tunnel, through which the said composition is transported. For example, the sequentially first heating tunnel temperature is maintained at a temperature of from 350℃ to 600℃, alternatively from 350℃ to 550℃, alternatively from 400℃ to 500℃; and the sequentially second heating tunnel temperature is maintained at a temperature of from 150℃ to 300℃, alternatively from 200 to 300℃, alternatively from 200℃ to 250℃.

However, the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber passes through the first heating tunnel within no more than about 20 seconds, for example from 5 and 15 seconds, alternatively from 5 to 10 seconds and said composition passes through the second heating tunnel in a period of between 60 and 420 seconds, alternatively 90 and 360 seconds, alternatively, from 100 to 300 seconds.

The above requirements enable the horizontal extruder with a vertical extruder head to control the tube outside diameter (OD) and layer thickness with the latter preferably being from 0.1 to 10.0mm, alternatively 0.25 to 7.5, alternatively 0.5 to 5.0.

Once step (II) above is completed and the resulting tubes (A) have sufficiently cooled then the fibre layer of is applied over the external surface of the step (II) tubes.

As previously indicated the fabric used is made from fabric selected from glass-fiber fabric, polyester fiber fabric, polyamide fiber fabric, and/or polyaramid fiber fabric or a reinforcing fabric comprising a mixture thereof covering tube (A) . Step (III) may be carried in any suitable manner, for example the fabric may be in the form of a sleeve which is slid over the top of pipe A produced in step (II) . Alternatively, a fibre may be woven or knitted onto inner pipe (A) and then fabric may be wrapped around the inner pipe A to form layer B.

In one embodiment, there may be an optional priming step between steps (III) and (IV) to enhance the interaction between reinforcing fabric and Si tube layers. This may be achieved by applying adhesion primer onto the fabric. Any suitable adhesion promoter may be used for example it may be one or more commercially available coupling agents dissolved in organic solvents, such as alkoxy silane, ethoxy silane as well as titanates.

Subsequent to the application of the fabric layer B, step (IV) is undertaken in which a top layer of said hydrosilylation (addition) curable thermally conductive silicone rubber composition is extruded on top of/over the fabric layer B using an analogous process as was used for the preparation of the inner tube A.

The same extruder as used in step (II) may be utilised for step (IV) with the exception of the extrusion head and as such the same temperature ranges may be utilised if desired, but the full details are not repeated here.

The layer thickness of outer layer C maybe also be designed to have a layer thickness with the latter preferably being from 0.1～10.0mm, alternatively 0.25 to 7.5mm, alternatively 0.5 to 5.0mm, alternatively 0.5 to 2.5mm, alternatively 0.5 to 2.0mm. When desired the fabric reinforced thermally conductive silicone rubber tubes may be post-cured.

Post curing would be carried out within a temperature range of from about 120℃ to about 200℃. The post curing step may be carried out for a period of from about 1 to about 8hrs as required or desired.

The overall wall thickness for the fabric reinforced thermally conductive silicone rubber tubes prepared by this process are designed to meet the practical requirements for the end use of the tubes themselves. For example, in the case of when the tubes are to be used as fabric reinforced thermally conductive silicone rubber cooling tubes positioned alongside the 24mm (OD) charging wires in fast charging apparatus for EV applications the outer diameter of the tubes will be between 6 and 7 mm with the wall thickness of the tubes being between 1 and 2mm.

The fabric reinforced thermally conductive silicone rubber tubes described herein may be used as a means of cooling in a wide variety of applications, including, for the sake of example, any cable/apparatus that require liquid cooling system, for example in automotive and electronics applications including EV super charging gun, high power cooling cables as well as any apparatus for heat dissipation parts for motor drive module and control module.

EXAMPLES

All viscosities were measured at 25℃ unless otherwise indicated. Viscosities of individual components in the following examples were measured using a Brookfield DV-III Ultra Programmable Rheometer for viscosities greater than or equal to 50,000 mPa. s, and a Brookfield DV 3T Rheometer for viscosities less than 50,000 mPa. s, unless otherwise indicated. The molar ratio of SiH : vinyl for all examples and comparatives was 1.5 : 1.

A series of compositions for formulation comparative Examples and formulation composition examples were prepared and are depicted in Tables 1a and 1b respectively.

Table 1a : Composition of Comparative Examples F. C. 1 to F. C. 4 (wt. %)

The above were also compared with F. C. 4 which is sold commercially as XIAMETER^TM RBB-2400-70 Silicone Rubber by Dow Silicones Corporation of Midland Michigan, USA.

Table 1b : Composition of Reference Examples F. Ex. 1 to F. Ex. 5 (wt. %)

The components identified in Tables 1a and 1b are as follows:

Silicone gum 1 was a dimethylvinyl terminated polydimethylsiloxane having a degree of polymerisation (DP) of 5840 and Williams plasticity of 150mm/100 in accordance with ASTM D-926-08.

Silicone Rubber base 1: is 70.56 wt. %of Silicone Gum 1 and 29.44 wt. %of fumed silica sold as HDK^TM T30P by Wacker AG;

Alumina 1 was ALM-41-01 sold by from Sumitomo Chemical Co. of Japan which has a particle size of between 1 and 2 μm (manufacturer’s information) .

Alumina 2 was the ADM-40K grade from Denka Company Limited with an average particles which is a spherical form of alumina with a volume median particle diameter size of 40 μm (manufacturer’s information) .

Treatment Agent 1 was (CH₂=CH) (CH₃) ₂SiO [ (CH₃) ₂SiO] ₂₅SiO (CH₃) ₃

Treatment Agent 2 dimethyl hydroxy terminated Dimethyl, methylvinyl siloxane having a DP of between 4-17.

Si-H cross-linker 1 was a trimethyl terminated Dimethyl, methylhydrogen siloxane having a viscosity of approximately 15 mPa. s at 25℃.

Si-H cross-linker 2 was a trimethyl terminated Dimethyl, methylhydrogen siloxane having a viscosity of approximately 5 mPa. s at 25℃.

The Si-H/vinyl molar ratio for formulation comparative Examples F. C. 1, F. C. 2 and F. C. 3 was 1.5 : 1.

ETCH is Ethynyl Cyclohexanol.

A series of tests were undertaken to assess the physical characteristics of each formulation reference example 1 to 5 and the comparatives in accordance with the ASTM International standard Test methods indicated in Tables 2a and 2b below.

Samples for this testing were prepared as follows:

The compositions were prepared by first preparing an intermediate base composition by loading silicone gum 1 (component (a) ) the silicone rubber base 1 starting material, when present, the thermally conductive filler and the filler treating agent into a 5L lab kneader mixer step by step and then mixing to homogeneity for about an hour at 120℃ for 1 hour. The resulting base was then allowed to cool to room temperature. Once cooled the Si-H cross-linker, Karstedt’s catalyst and hydrosilylation cure inhibitor were added and mixed into the composition on a two roll-mill. The resulting compositions were then compression molded by means of a press cure apparatus for 10 minutes at 120℃ for samples 2mm thick.

Thermal conductivity testing was undertaken using 6mm slabs which were in the press cure apparatus for and 20 minutes at 120℃. Thermal conductivity testing was also undertaken on 6mm thick slabs which had been post-cured at 200℃ for 4hours to assess any change in thermal conductivity properties.

Table 2a: Physical property/performance after cure at 120℃ for 10 minutes and thermal conductivity testing of comparatives F. C. 1 to F. C. 3 as well as F. C. 4 (XIAMETER^TM RBB-2400-70 Silicone Rubber.

Table 2b: Physical property/performance after cure at 120℃ for 10 minutes and thermal conductivity testing of F. Ex. 1 to 5

It was found that the physical properties of all comparative and reference examples were acceptable. In each example and comparative example had been filled with large amounts of alumina filler to achieve required levels of thermal conductivity, so the physical properties dropped obviously when compared to commercial product XIAMETER^TM RBB-2400-70 Silicone Rubber. It was found for the highly filled examples and comparatives that the examples as hereinbefore described had better thermal conductivity and extrusion processability.

Each composition described above was also then tested for their suitability for extrusion into e.g., tubes which would prove suitable as cooling tubes and plasticity and the results are provided in Tables 3a and 3b.

When assessing extrudability samples were prepared as follows:

All the ingredients of the relevant composition were mixed together on a 2-roll mill into a one-part composition. When mixing was completed, the composition was introduced onto a horizontal extruder with a vertical extruder head having a first and a second heating tunnel. The composition was present in the first heating tunnel, which was maintained in a temperature range of from 400℃ to 500℃, for between 6 and 10 seconds. It then passed into a second heating tunnel, held in a temperature range of from 200℃ to 250℃ for a period of between 100 and 300 seconds and the resulting extrusion passed out of the extrusion head.

The ability of the different comparative compositions and example composition were assessed for their suitability for extruding tubes.

It was found that F. Ex. 1 to 5 were suitable for extrusion for making the likes of cooling tubes etc. but it was found that given the very high proportion of heat conductive filler (alumina) present whilst tubes could easily be prepared but those generated were not considered sufficiently strong to confidently withstand liquid passing through the tubes at a fluid pressure of least 1MPa according to Chinese National Standard Test Method GB/T5563-2013 without fracturing.

However, it was determined that by providing reinforcement in the shape of the reinforcing fibre second layer in a composite tube as described herein, the resulting tubes both satisfied thermal conductivity values and were able to withstand at least liquid passing through the tubes at a fluid pressure of least 1MPa according to Chinese National Standard Test Method GB/T5563-2013 without fracturing.

Table 3a: Plasticity results for comparative compositions F. C. 1 to FC. 3 and suitability for extrusion

It was found that the comparative compositions had poor extrudability and also had plasticity values below 200mm/100. The plasticity of these materials is not high enough to make the material consistent during extrusion. That is to say the green strength of these material is not strong enough. These materials could not be conveyed by screw consistently. They will break and trap air during screw extrusion.

Table 3b: Plasticity results for comparative compositions F. Ex. 1 to 5 and suitability for extrusion

In contrast F. Ex. 1 to 5 all had higher plasticity results, notably > 200mm/100 and indeed greater than 225mm/100 and were considered to be suitable for extrusion. For the avoidance of doubt, all of F. Ex. 1 to 5 were considered suitable for use as the extrudable hydrosilylation (addition) curable thermally conductive silicone rubber compositions required to make the fabric reinforced thermally conductive silicone rubber tubes herein but were considered to require the fabric reinforcement as described herein to ensure the tubes prepared were able to withstand the fluid pressures necessary.

Good extrusion processability was deemed met for samples showing a consistently stable OD, a smooth surface, and no bubbles or other defects detected on the tube surface and/or cross-section of the tube.

As evidence a further series of examples were generated, mainly based of the composition of F. Ex. 5 as shown in Table1b and compared with single layer tubes of Ex. 1 and a comparison tube made from the composition identified as C. 4. The process utilised is described below and the results are shown in Table 4 below.

The process used to form single layer tubes in comparative examples C. 1 and C. 2 were carried out using the process described previously.

For C. 3 and Ex. 1 and Ex. 2 the following process was used to generate fabric reinforced thermally conductive silicone rubber tube:

The components of the composition were mixed together on a 2-roll mill with the catalyst added last. The resulting composition was introduced onto a suitable horizontal extruder with a vertical extruder head having first and second heating tunnels and the inner layer tubes of about 0.7mm wall thickness were extruded through the first heating tunnel, which was maintained in a temperature range of from 400℃ to 500℃, for between 6 and 10 seconds. It then was then extruded through the second heating tunnel, held in a temperature range of from 200℃ to 250℃ for a period of between 100 and 300 seconds and the resulting extrusion passed out of the extrusion head. Once the inner tube had been allowed to sufficiently cool a second layer of polyethylene terephthalate reinforcing fabric was knitted over said inner tube. After the fabric layer had been applied the top layer of approximately a 0.5mm wall thickness was extruded over the top of the knitted fabric middle layer using the same process as for the inner tube layer.

The water pressure test in Tables 4a and 4b was Chinese National Standard Test Method GB/T5563-2013 for rubber and plastic hoses and hose assemblies as discussed previously.

Table 4a: property/performance table for comparatives C. 1 to C. 3.

Table 4b: property/performance table for comparatives Ex. 1 to 6

It can be seen from C. 1 and C. 2 that using a tube having a wall thickness (WT) of 1.0 or 1.2mm made from the composition of Ex. 1 hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes described herein gave good thermal conductivity results but relatively poor GB/T5563-2013 results suggesting that such tubes will potentially fracture during use as e.g., a cooling tube for an EV fast charging system and therefore were not sufficiently reliable for such a purpose. In the case of C. 3, a standard silicone rubber composition was used to make the composite tube of three layers. In this case, as might be expected the tube provided excellent GB/T5563-201 results, no doubt partially assisted by the presence of the reinforcing layer. However, this tube had very poor thermal conductivity results (almost zero) . Ex. 1 and Ex. 2 provide a very good composite tube having both high resistance to the fluid (water) pressure and high thermal conductivity results.

Claims

A fabric reinforced thermally conductive silicone rubber tube comprising

(A) a first inner layer being a thermally conductive silicone rubber tube in the form of an extruded cured product of a hydrosilylation (addition) curable thermally conductive silicone rubber composition;

(B) a second middle layer of reinforcing fabric selected from glass-fiber fabric, polyester fiber fabric, polyamide fiber fabric, and/or polyaramid fiber fabric or a reinforcing fabric comprising a mixture of any two or more thereof covering tube (A) ; and

(C) a third outer layer being a thermally conductive silicone rubber tube in the form of an extruded cured product of a hydrosilylation (addition) curable thermally conductive silicone rubber composition over the second middle layer (B) ;

which first inner layer (A) and third outer layer (C) are both made from the cured product of a hydrosilylation (addition) curable thermally conductive silicone rubber composition comprising the following components:

a) a polydiorganosiloxane having a degree of polymerisation of at least 2,500 calculated from the number average molecular weight determined by gel permeation chromatography and at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl or alkynyl groups;

b) an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule,

c) an organopolysiloxane filler treating agent having a degree of polymerisation of between 4 to 500 calculated from the number average molecular weight determined by gel permeation chromatography and comprising

(i) at least one alkenyl group per molecule and

(ii) at least one hydroxy group or at least one alkoxy group or a mixture of hydroxy and alkoxy groups per molecule;

in an amount of from 0.1-10%wt. of the composition;

d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and either

(e) (i) at least one thermally conductive filler with a volume median particle diameter size 0.1-20 micrometres (μm) measured by laser diffraction particle size analysis in an amount of from 70 to 95 wt. %wt. %of the composition; or

a combination of (e) (ii) and (f) wherein

(e) (ii) is at least one thermally conductive filler with a volume median particle diameter size of greater than 20 to 100 micrometres (μm) measured by laser diffraction particle size analysis and

f) precipitated silica, fumed silica, colloidal silica or a mixture of any two or more of precipitated silica colloidal silica and fumed silica in an amount of from greater than zero to 5 wt.%of the composition;

wherein the combination of (e) (ii) + (f) is present in the composition in an amount of from 70 to 95 wt.%of the composition and wherein the total wt. %of the composition is 100 wt. %.
A fabric reinforced thermally conductive silicone rubber tube in accordance with claim 1 wherein component (a) has a degree of polymerisation of at least 4,000 determined by gel permeation chromatography.
A fabric reinforced thermally conductive silicone rubber tube in accordance with any preceding claim wherein said tube has a thermal conductivity of at least 0.5 W/m. K., measured in accordance with ASTM D7896 –hot disk method, whilst having whilst being able to withstand a fluid (e.g., water) pressure of greater than 1 MPa., in accordance with standard test method GB/T5563-201.
A fabric reinforced thermally conductive silicone rubber tube in accordance with any preceding claim wherein the fabric reinforced thermally conductive silicone rubber tube has a wall thickness of from 0.50 to 10mm.
A fabric reinforced thermally conductive silicone rubber tube in accordance with any preceding claim which is utilised as an electric vehicle charging cable water-cooling system tube.
A method for preparing a fabric reinforced thermally conductive silicone rubber tube comprising the steps of:

I) preparing a hydrosilylation (addition) curable thermally conductive silicone rubber composition comprising the following components:

a) a polydiorganosiloxane having a degree of polymerisation of at least 2, 500 calculated from the number average molecular weight determined by gel permeation chromatography and at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl or alkynyl groups;

b) an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule,

c) an organopolysiloxane filler treating agent having a degree of polymerisation of between 4 to 500 calculated from the number average molecular weight determined by gel permeation chromatography and comprising

(i) at least one alkenyl group per molecule and

(ii) at least one hydroxy group or at least one alkoxy group or a mixture of hydroxy and alkoxy groups per molecule;

in an amount of from 0.1-10%wt. of the composition;

d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and either

(e) (i) at least one thermally conductive filler with a volume median particle diameter size 0.1-20 micrometres (μm) measured by laser diffraction particle size analysis in an amount of from 70 to 95 wt. %of the composition; or

a combination of (e) (ii) and (f) wherein

(e) (ii) is at least one thermally conductive filler with a volume median particle diameter size of greater than 20 to 100 micrometres (μm) measured by laser diffraction particle size analysis and

f) precipitated silica, fumed silica, colloidal silica or a mixture of any two or more of precipitated silica colloidal silica and fumed silica in an amount of from greater than zero to 5 wt.%of the composition;

wherein the combination of (e) (ii) + (f) is present in the composition in an amount of from 70 to 95 of the composition and wherein the total wt. %of the composition is 100 wt. %;

II) introducing hydrosilylation (addition) curable thermally conductive silicone rubber composition onto an extruder, extruding said hydrosilylation (addition) curable thermally conductive silicone rubber composition from the extruder to form a thermally conductive silicone rubber tube (A) and cooling the tube;

III) covering the tube resulting from step (II) with a layer (B) of reinforcing fabric selected from glass-fiber fabric, polyester fiber fabric, polyamide fiber fabric, and/or polyaramid fiber fabric or a reinforcing fabric comprising a mixture of any two or more thereof to form a step (III) product;

IV) extruding an outer layer (C) of said hydrosilylation (addition) curable thermally conductive silicone rubber composition from the extruder around the step (III) product to form a fabric reinforced thermally conductive silicone rubber tube.
A method for preparing a fabric reinforced thermally conductive silicone rubber tube in accordance with claim 6 wherein the extruder is a horizontal extruder optionally with a vertical extruder head.
A method in accordance with claim 7 wherein the extruder has two heating tunnels the sequentially first heating tunnel, through which the hydrosilylation (addition) curable thermally conductive silicone rubber composition used in the preparation of the fabric reinforced thermally conductive silicone rubber tubes is transported, is maintained at a higher temperature than the sequentially second heating tunnel, through which the said composition is transported.
A method for preparing a fabric reinforced thermally conductive silicone rubber tube in accordance with claim 6, 7 or 8 wherein component (a) of the composition is a silicone gum, said gum has a Williams’s plasticity of at least 100mm/100 measured in accordance with ASTM D-926-08.
A method for preparing a fabric reinforced thermally conductive silicone rubber tube in accordance with claim 6, 7, 8 or 9 wherein layer (B) of reinforcing fabric is wrapped or knitted around inner layer (A) .
A fabric reinforced thermally conductive silicone rubber tube made in accordance with any one of claim 6 to 10.
An electric vehicle charging cable water-cooling system tube comprising or consisting of a fabric reinforced thermally conductive silicone rubber tube in accordance with claim 11.
Use of a thermally conductive silicone rubber composition, which comprises the following components:

a) a polydiorganosiloxane having a degree of polymerisation of at least 2, 500 calculated from the number average molecular weight determined by gel permeation chromatography and at least two unsaturated groups per molecule, which unsaturated groups are selected from alkenyl or alkynyl groups;

b) an organosilicon compound having at least two, alternatively at least three Si-H groups per molecule,

c) an organopolysiloxane filler treating agent having a degree of polymerisation of between 4 to 500 calculated from the number average molecular weight determined by gel permeation chromatography and comprising

(i) at least one alkenyl group per molecule and

(ii) at least one hydroxy group or at least one alkoxy group or a mixture of hydroxy and alkoxy groups per molecule;

in an amount of from 0.1-10%wt. of the composition; and

d) a hydrosilylation catalyst comprising or consisting of a platinum group metal or a compound thereof; and either

(e) (i) at least one thermally conductive filler with a volume median particle diameter size 0.1-20 micrometres (μm) measured by laser diffraction particle size analysis in an amount of from 70 to 90 wt. %of the composition; or

a combination of (e) (ii) and (f) wherein

(e) (ii) is at least one thermally conductive filler with a volume median particle diameter size of greater than 20 to 100 micrometres (μm) measured by laser diffraction particle size analysis and

f) precipitated silica, fumed silica, colloidal silica or a mixture of any two or more of precipitated silica colloidal silica and fumed silica in an amount of from greater than zero to 5 wt.%of the composition;

wherein the combination of (e) (ii) + (f) is present in the composition in an amount of from 70 to 90 wt.%of the composition and wherein the total wt. %of the composition is 100 wt. %;

in the manufacture of a fabric reinforced thermally conductive silicone rubber tube comprising

(A) a first inner layer being a thermally conductive silicone rubber tube in the form of an extruded cured product of said hydrosilylation (addition) curable thermally conductive silicone rubber composition;

(B) a second middle layer of reinforcing fabric selected from glass-fiber fabric, polyester fiber fabric, polyamide fiber fabric, and/or polyaramid fiber fabric or a reinforcing fabric comprising a mixture of any two or more thereof covering tube (A) ; and

(C) a third outer layer being a thermally conductive silicone rubber tube in the form of an extruded cured product of said hydrosilylation (addition) curable thermally conductive silicone rubber composition over the second middle layer (B) .
Use of a fabric reinforced thermally conductive silicone rubber tube in accordance any one of claims 1 to 5 in a cable and/or apparatus liquid cooling system.
Use of a fabric reinforced thermally conductive silicone rubber tube in accordance with claim 14 wherein the cable and/or apparatus liquid cooling system is in or for an electric vehicle charging cable means.