RU2731623C1 - Fire-resistant polysiloxane rubber mixture - Google Patents

Abstract

FIELD: rubber industry.

SUBSTANCE: invention relates to rubber industry, in particular to elastomer organosilicon resilient rubber, which can be used in automotive industry, machine building, production of protective polymer shells of building structures, process equipment, etc. Fire-resistant polysiloxane rubber mixture contains, in pts. wt.: high-molecular weight siloxane rubber – 100, fine silica – 40, aluminum hydroxide – 50, antistructuring additive – 8, decabromodiphenyl oxide – 15, dicumyl peroxide – 1.7, organoclay – 5, zinc oxide – 5–10 and thermally expanding graphite – 2.5–5.

EFFECT: disclosed composition is fire-resistant and withstands exposed flame for 95–150 seconds, which is 1_5–2 times higher than that of the prototype, and has a level of physical and mechanical properties, which enables to use them as fire-resistant protective materials.

1 cl, 2 dwg

Description

The invention relates to the rubber industry, in particular to elastomeric organosilicon rubbers with increased fire resistance, which can be used in the automotive industry, mechanical engineering, the production of protective polymer shells for building structures, process equipment, etc.

Protective materials must meet the following requirements: a high level of physical and mechanical properties, a wide temperature range of performance, increased requirements for non-propagation of combustion in emergency situations. The most promising elastomeric materials are rubbers based on organosilicon polymers due to their universal properties (high thermal stability, performance in the temperature range from minus 90 to 250 ° C, weather resistance, radiation resistance, good electrical insulating properties). However, given the increasing requirements for these materials, such as resistance to the action of an open flame, there is a need to increase the resistance of compositions based on silicone rubbers to high temperatures and open flame. After exposure to elevated temperatures and open flame, products made from such compositions should retain their physical, mechanical and operational properties.

To increase the fire resistance of polymeric materials, as a rule, various flame retardants are used, for example, aluminum hydroxide, decabromodiphenyl oxide, antimony oxide, ammonium polyphosphate, etc.

Known ceramic-forming rubber mixture based on high molecular weight silicone rubber for the manufacture of protective polymer sheaths of power electrical cables (patent RU 2519379, C08L 83/04, C08L 19/00, C08K 3/22, C08K 3/36, C08K 5/14, publ. 10.06 .fourteen). The mixture contains silicone rubber, finely dispersed silicon dioxide, silica filler in combination with a platinum complex containing low molecular weight vinyl-containing organosiloxanes, and aluminum silicate with a particle size of no more than 0.14 mm, an anti-structuring additive and organic peroxide, with the following ratio of components, wt. including: silicone rubber 100, finely dispersed silicon dioxide 45-55, silica filler 50-80, aluminum silicate 10-30, platinum complex (in terms of platinum) 5.7⋅10 ^-3 -9.5⋅10 ^-3 , anti-structuring additive 8-11, organic peroxide 1.2-2.0.

Known rubber mixture for the manufacture of fire-resistant polymer shells of high-voltage electrical products, which has increased resistance to ignition (RU 2540597, C08L 83/04, C08K 3/22, C08K 3/36, C08K 5/14, C08K 5/3492, publ. 10.02. 2015). The fire-resistant rubber mixture contains, by weight: finely dispersed silicon dioxide and / or highly dispersed hydrophobic silica filler 45-60, possibly titanium dioxide 10-15, pulverized quartz 10-40 wt. including, α, ω-dihydroxydimethylsiloxane 6-12, organic peroxide 2.8-5.0, melamine cyanurate 55-65, aluminum hydroxide or magnesium hydroxide 0-80 and pigment 5-10 per 100 wt. including high molecular weight methylvinylsiloxane rubber.

The disadvantages of the known mixtures are low strength and fire resistance.

Known rubber compound according to patent RU 2608399, C08L 83/04, C08K 3/36, C08K 5/14, C09K 3/10, publ. 18.01.2017. The mixture contains organosilicon rubber, dicumil peroxide, anti-structuring additive, finely dispersed silicon dioxide, aluminum hydroxide with a particle size of not more than 10 microns or decabromodiphenyl oxide (DBDFO), pigment titanium dioxide, as well as carbon black or fine powdery ceramic pigments in the following ratio of components, wt. including: silicone rubber 100, dicumyl peroxide 1.0, anti-structuring additive 8.0, finely dispersed silicon dioxide 40.0, pigment titanium dioxide 10.0, aluminum hydroxide 60.0-90.0 or decabromodiphenyl oxide 15.0-25, 0, carbon black 0.1-2.5 or fine powdery ceramic pigments 0.1-5.0.

The main disadvantage of the known rubber compound is low physical and mechanical properties due to the high content of aluminum hydroxide. As can be seen from the description of the patent, a significant increase in the fire resistance of siloxane rubbers is observed when the content of aluminum hydroxide is more than 60 wt. hours, while there is a significant decrease in physical and mechanical properties, on average by 30%. And also insufficiently high fire resistance.

The closest in technical essence and the achieved result to the claimed rubber mixture is a siloxane rubber mixture, which contains, by weight. including: high molecular weight silicone rubber 100, finely dispersed silicon dioxide (aerosil) 40, anti-structuring additive (ND-8) 8, aluminum hydroxide 50, decabromodiphenyl oxide 15, organobentonite (organoclay) 0-5, dicumyl peroxide 1.4 [Gadelshin R.N. ., Kurbangaleeva A.R., Tayorova V.I., Sabirov R.K., Wolfson S.I., Khakimullin Yu.N., Nefediev E.S. Siloxane rubbers with increased thermal and fire resistance / Rubber and rubber, 2018, vol. 77, No. 3, pp. 188-191].

The disadvantage of the prototype is the lack of fire resistance.

The technical problem is to increase the fire resistance while maintaining the physical and mechanical properties of the polysiloxane rubber compound.

The technical problem is solved by a fire-resistant polysiloxane rubber compound containing high-molecular-weight silicone rubber, finely dispersed silicon dioxide, an anti-structuring additive, aluminum hydroxide, decabromodiphenyl oxide, dicumyl peroxide, organoclay, zinc oxide, thermally expanding graphite in the following ratio of components. h .:

silicone rubber one hundred finely dispersed silicon dioxide 40 aluminum hydroxide 50 decabromodiphenyl oxide 15 anti-structuring additive 8 zinc oxide 5-10 organoclay five thermally expandable graphite 2.5-5 dicumyl peroxide 1.7

The inventive fire-resistant polysiloxane rubber compound is characterized by higher fire-resistance compared to the prototype and retains the same level of physical and mechanical properties.

In the proposed rubber mixture, in contrast to the prototype, to increase the fire resistance, a combination of zinc oxide, organoclay and thermally expanding graphite (TRG) is used, which is more effective than each separately taken ingredient as a result of a synergistic effect.

The structure of the TRG contains many ordered cavities, when heated as a result of the action of an open flame, the gas pressure in the cavities increases, as a result, the volume of the TRG particles increases significantly, a foamed coke layer is formed, which prevents the spread of fire and protects the material matrix. The introduction of TRG is less than 2.5 wt. including does not significantly increase the fire resistance of rubber compounds, and the introduction of more than 5 wt. including significantly reduces the level of physical and mechanical properties.

Organoclay is Na ⁺ -montmorillonite modified with quaternary ammonium salts. Montmorillonite nanoplates in materials create tortuous paths for oxygen diffusion, causing the so-called "labyrinth effect" and increased fire resistance as a result of the formation of carbonized nanocarbon structures (products of interaction of carbon with silicates) with low thermal and thermal diffusion, which screen oxygen diffusion at the initial stages of combustion. The optimum content of organoclay for polymers is 5 wt. h.

Zinc oxide increases the resistance of the main chain of the silicone rubber to thermal degradation; as a result, the degradation temperature of the polymer increases, which, in combination with the protective mechanisms of organoclay and TRG, leads to an increase in the fire resistance of the material. With a zinc oxide content of less than 2 wt. including the heat resistance of rubbers increases slightly, and with a zinc oxide content of more than 10 wt. including the deterioration of the physical and mechanical properties of rubbers.

Brief description of the components of the mixture.

High-molecular-weight silicone rubber SKTV-1 produced by OAO KZSK (TU 38.103675-89) was taken as the basis of the rubber mixture.

Aerosil A 300 (GOST 14922-77) is a finely dispersed silicon dioxide; it is a dispersed powder filler, the particles of which have a regular spherical shape and do not exceed 10 nm, the maximum specific surface area is 380 m ² / g.

Dicumyl peroxide 14-40V-RD-S (TU 38-40-255-83) - a vulcanizing agent, is a white crystals.

Α, ω-dihydroxydimethylsiloxane (ND-8) with a mass fraction of OH-groups 8.5-13.5% (TU 2229-044-05766764-01), which is an oily liquid, was used as an anti-structuring additive. Provides the mixtures with stable technological and physical and mechanical properties during storage.

Zinc oxide (zinc white) - white powder (GOST 202-84) is used as a heat stabilizer. We took as fire retardants:

Finely dispersed aluminum hydroxide TS 305 is a white powder with a particle size of 4-10 microns (TU 1711-011-00658716-99) produced by OOO Functional Materials Russia.

Decabromodiphenyl oxide (CAS number 1163-19-5) - white powder, melting point 300-310 ° C; density - 3000 kg / m ³ .

Organoclay brand Cloisite 15A (Na + -montmorillonite modified with quaternary ammonium salts, modifier dimethyldialkylammonium chloride) produced by Southern Clay Products (USA) is a white powder.

Thermally expanding graphite (TU 5728-001-74206540-2005) is a silvery powder with a bulk density of 1.5-5.0 kg / m ³ , a specific surface area of up to 500 m ² / g.

The rubber mixture was made on a Brabender plasticorder at room temperature for 10 minutes at a rotor speed of 60 rpm. When preparing a rubber mixture, first, siloxane rubber was loaded into the mixing chamber, then finely dispersed silicon dioxide was added in portions together with an anti-structuring additive, then fire retardants were introduced, then a curing agent, dicumyl peroxide, was introduced a minute before the end of mixing. After the end of mixing, the mixture was unloaded and rolled on laboratory rollers for 2-3 minutes. After rolling, the mixture was kept for about a day. Then the mixture was placed in a mold heated to the vulcanization temperature and vulcanized at a temperature of 160 ° C for 20 minutes in a hydraulic press with electrically heated plates.

For a correct comparison of the results, a rubber compound was prepared according to the prototype. Additionally, samples of rubber compounds containing organoclay and / or TRG and / or zinc oxide were prepared.

The compositions of the fire-resistant polysiloxane rubber compounds are shown in Table 1.

For the obtained samples, the physical and mechanical properties were determined: conditional tensile strength, elongation at break and relative residual elongation at break according to GOST 270-75, Shore A hardness according to GOST 263-75.

The fire test was carried out by firing the samples on a MEGA 1 type burner with a Kovica KS-1005 Korea piezo igniter. Samples 2 × 4 cm in size and 2 mm thick were brought to the burner at an angle of 90 ° and ignited in the center. Fire resistance is the maximum time that a sample can withstand exposure to an open flame. During this time, if the sample is taken out of the flame, it self-extinguishes. When the sample is kept under the flame for a longer time, the sample, when removed from the flame, burns.

The experimental data are shown in Table 2.

As can be seen from table 2, vulcanizates of the inventive fire-resistant polysiloxane rubber mixture (examples 1-4) withstand a longer exposure to an open flame in comparison with the prototype. At the same time, the proposed samples have physical and mechanical properties at the prototype level.

In the absence of one or two of the components: organoclay (example 6), TRG (example 8), zinc oxide (example 7), organoclays and TRG (example 5), zinc oxide and organoclay (example 9), fire resistance is significantly reduced. The data obtained show that only the combined presence of the three components of zinc oxide, organoclay and TRH gives an increase in fire resistance as a result of a synergistic effect.

Thus, the proposed composition is fire-resistant and can withstand exposure to an open flame for 120-150 seconds, which is 1.5-2 times higher than that of the prototype, and has a level of physical and mechanical properties that allows them to be used as fire-resistant protective materials ...

Claims (3)

1. Fire-resistant polysiloxane rubber compound containing high molecular weight siloxane rubber, finely dispersed silicon dioxide, anti-structuring additive, aluminum hydroxide, decabromodiphenyl oxide, organoclay, dicumyl peroxide, characterized in that it additionally contains zinc oxide and thermally expanding graphite in the following ratio. h .: silicone rubber one hundred finely dispersed silicon dioxide 40 anti-structuring additive 8 aluminum hydroxide 50 decabromodiphenyl oxide 15 zinc oxide 5-10 organoclay five thermally expandable graphite 2.5-5 dicumyl peroxide 1.7 2. Fire-resistant polysiloxane rubber compound according to claim 1, characterized in that it contains ND-8 as an anti-structuring additive.