Patent Application
20230287193
The present disclosure relates to foamable silicone compositions.
As a power source for electric vehicles, stable, safe and reliable battery packs are critical to the quality of vehicles. And consequently, higher requirements are placed on the performances of materials for sealing battery pack cases, such as hardness, resilience and mechanical properties.
Foamable silicone materials, particularly auto-dispensing foamable silicone compositions which are dispensed via an automatic dispenser and then cured into foam at room temperature or a high temperature followed by compression to achieve sealing, are new solutions for sealing battery pack cases. If the silicone foam has a too high hardness, compression will become difficult and the upper cover of the battery pack is likely to deform, leading to a sealing failure. If the foam has poor resilience, rebound force generated under pressure will be insufficient, which is likely to cause leakage due to deformation or displacement of the battery pack. Therefore, the resilience and hardness of the silicone foam are critical to ensure the safety.
CN1182187C discloses a silicone foam with a density of 0.29-0.35 g/cm3, and also discloses that the foam resilience can be improved by adding an organic sulfur compound such as 3-mercaptopropyltrimethoxysilane. However, compression set (CS) (50%, 24 hours, 100° C.) of the foam is still greater than 20%, which is not conducive to a good sealing performance. Besides mechanical properties of the foam are also poor, and not an ideal material for sealing battery pack cases.
CN110862693A discloses a silicone sponge with a density of 0.17-0.22 g/cm3 by using n-butanol as a porogenic agent. The CS (50%, 22 hours, 70° C.) of the sponge is less than 3%, however, it is not a suitable material for sealing battery pack case due to its ultra-low density, which sacrifices mechanical properties.
Moreover, further requirements on the flame retardancy of sealing materials exist due to the safety issue of battery packs. It has been reported that the addition of flame retardants can impart flame retardancy to foamable silicone materials. However, this is considered to be detrimental to e.g. resilience and hardness of foamable materials since the flame retardancy of V-0 grade is achieved usually with a high amount of flame retardants, which seriously affects the homogeneity of the material.
CN106589954A discloses in Example 1 that adding 26 wt % of flame retardant comprising modified aluminum hydroxide and expandable graphite to foamable silicone rubber can achieve V-0 flame retardancy. However, such foamed silicone rubber has poor resilience performance and mechanical properties and cannot be used as a sealing material for battery pack cases.
CN101845224B discloses in Example 4 that adding 22 wt % of flame retardant comprising aluminum hydroxide, expandable graphite, ammonium polyphosphate and pentaerythritol to silicone foam can achieve V-0 flame retardancy. However, the resilience performance and mechanical properties of the silicone foam are also unsatisfactory.
The foregoing deficiencies are solved by the use of a foamable silicon composition containing an alkenyl-functional organopolysiloxane, an Si—H functional organopolysiloxane, a hydroxy-containing porogenic, and a hydrosilyation catalyst where the molar ratio of Si—H groups to silicon alkenyl groups is form 5:1 to 15:1, and the molar ratio of Si—H groups to hydroxy groups is from 2:1 to 20:1.
The present disclosure provides a foamable silicone composition which balances two competing reactions, i.e. curing reactions between Si—H and alkenyl groups and foaming reactions between Si—H and hydroxyl groups, by the combination of specific molar ratios of Si—H to alkenyl and Si—H to hydroxyl. When the foaming reaction is too fast, the cured network is insufficient to support the cell structure, causing collapse of cells which affects the product performance. When the foaming reaction is too low, the cured network is too strong, making the product difficult to expand. However, the foamable silicone composition of the present disclosure overcomes such conventional defects and achieves at least one of the following goals with a good cell structure obtained.
Herein, term “foamable silicone material” refers to materials, based on organopolysiloxane, able to react to form porous structures in the presence of porogenic agent, crosslinker, catalyst and other additives. The materials with porous structures includes foams or sponges, but not limited thereto.
Herein, “sieve particle size” is determined by sieving granulometry, in μm.
The first aspect of the present disclosure provides a foamable silicone composition, comprising:
The organopolysiloxane (A) is typically of following formula:
Organopolysiloxane (A) of the following formula is particularly preferred:
Vi(Me2SiO)m(ViMeSiO)nVi
Component (A) of the present disclosure may be a single alkenyl group-containing organopolysiloxane, or may be a mixture of different alkenyl group-containing organopolysiloxanes which differ in molecular structure (for example type and number of substituents), vinyl content or viscosity. For a mixture of organopolysiloxanes, m and n represent average values, and the viscosity range met by m+n is relative to the viscosity of the mixture.
In order to increase crosslinking sites and crosslinking density, and improve the resilience performance and mechanical properties of the cured foam, Component (A) of the present disclosure may also contain a small amount of alkenyl group-containing organopolysiloxane with a low viscosity. In an embodiment herein, Component (A) comprises (A1) a first organopolysiloxane containing at least two alkenyl groups bonded to silicon per molecule with a dynamic viscosity at 25° C. of from 1,000 to 100,000 mPa·s, for example from 5,000 to 50,000 mPa·s, and (A2) a second organopolysiloxane containing at least two alkenyl groups bonded to silicon per molecule with a dynamic viscosity at 25° C. of from 10 to 1,000 mPa·s, for example from 50 to 500 mPa·s. In a more specific embodiment herein, Component (A) comprises (A1) a first organopolysiloxane containing at least two alkenyl groups bonded to silicon per molecule with a dynamic viscosity of from 10,000 to 30,000 mPa·s at 25° C., and (A2) a second organopolysiloxane containing at least two alkenyl groups bonded to silicon per molecule with a dynamic viscosity of from 100 to 300 mPa·s at 25° C. According to any of the above embodiments, organopolysiloxane (A2) is used in an amount of from 0.2 wt % to 10 wt %, for example from 1 wt % to 5 wt %, based on the total weight of Component (A).
In the present disclosure, Component (A) is suitably used in an amount of from 35 wt % to 95 wt %, for example from 50 wt % to 90 wt %, based on the total weight of the composition.
Component (B) acts as a crosslinker in the composition. Generally Component (B) has a hydrogen content of from 0.01 wt % to 1.7 wt %, preferably from 1.2 wt % to 1.7 wt %. The position of Si—H groups is not particularly limited, and they can be present only as side groups, or as both side and end groups.
Organopolysiloxane (B) may be linear, cyclic, branched or resinous. Linear or cyclic organopolysiloxane (B) is typically composed of units selected from R23SiO1/2, HR2SiO2/2, HR22SiO1/2 and R22SiO2/2 wherein R2 is as defined above, preferably methyl and phenyl, more preferably methyl. Branched or resinous organopolysiloxane (B) further comprises trifunctional units such as HSiO3/2 and R2SiO3/2, and/or tetrafunctional units such as SiO4/2. Linear or cyclic organopolysiloxane (B) composed of units selected from Me3SiO1/2, HMeSiO2/2, HMe2SiO1/2 and Me2SiO2/2 is particularly preferred.
In order to obtain a foam with high resilience, moderate hardness and good mechanical properties, the molar ratio of SiH groups from Component (B) to silicon-bonded alkenyl groups from Component (A) of the present disclosure is preferably from 5:1 to 12:1, particularly from 7:1 to 12:1.
Component (C) acts as a porogenic agent in the composition, which reacts with Si—H groups in Component (B) generating gaseous hydrogen to influence foaming behavior but does not contribute to crosslinking. Commonly used porogenic agents are at least one hydroxyl-group-containing compound including organopolysiloxane (C1) containing at least one hydroxyl group, alkanol and water.
The organopolysiloxane (C1) is typically of following formula:
Organopolysiloxane (C1) of the following formula is particularly preferred:
HO(Me2SiO)p(HOMeSiO)qOH
In a preferred embodiment herein, Component (C) is free of organopolysiloxane (C1). Herein “free of” refers to the content of a certain ingredient in the component is less than 1 wt %, less than 0.5 wt %, less than 0.1 wt %, or less than 0.05 wt %.
The alkanol may be an organic alcohol containing at least one hydroxyl group, but is not an alcohol acting as a hydrosilylation inhibitor for example alkynol, including monohydric alcohols with 1-12 carbon atoms such as ethanol, n-propanol, isopropanol, n-butanol, n-hexanol, n-octanol, cyclopentanol, cyclohexanol, or cycloheptanol, and polyols with 2-12 carbon atoms such as ethylene glycol, propylene glycol, glycerin, butylene glycol, pentanol glycol, or heptane. In a preferred embodiment herein, Component (C) is free of alkanol.
When water is used as a porogenic agent, it may be introduced in the form of an aqueous emulsion, such as an aqueous silicone emulsion including an oil-in-water silicone emulsion or a water-in-oil silicone reverse emulsion, to promote the dispersion of water in the composition. The aqueous silicone emulsion contains a polysiloxane oil phase, a water phase and an emulsifier. The emulsifier may be a nonionic emulsifier, an anionic surfactant, a cationic surfactant or a zwitterionic surfactant, preferably a nonionic surfactant. The aqueous silicone emulsion can be obtained by an emulsification process well known to those skilled in the art. The viscosity of the aqueous silicone emulsion is not particularly limited. In a preferred embodiment herein, Component (C) is an aqueous emulsion of polysiloxane with a dynamic viscosity of from 1,000 to 30,000 mPa·s at 25° C.
In order to obtain a foam with moderate density and hardness, good resilience and mechanical properties, the molar ratio of SiH groups from Component (B) to hydroxy groups from Component (C) of the present disclosure is from 3.5:1 to 12.5:1.
Component (D) can be a variety of hydrosilylation catalysts conventionally used for addition-crosslinking silicone rubbers, preferably a platinum-based catalyst, for example chloroplatinic acid, chloroplatinates, olefin complexes of platinum, and alkenylsiloxane complexes of platinum. The platinum-based catalyst can be used in an amount subject to the desired curing rate and economic consideration, which is usually a minimum level required to ensure an effective hydrosilylation reaction. Generally, the weight of platinum metal in the foamable silicone composition is from 0.1 to 500 ppm, for example from 1 to 100 ppm.
The foamable silicone composition can further comprise inhibitor (E) to control the pot life and curing rate of the composition. The inhibitor can be a variety of inhibitors used in the art, for example alkynol such as 1-ethynyl-1-cyclohexanol, 2-methyl-3-butyn-2-ol; or polymethylvinylcyclosiloxanes, such as 1,3,5,7-tetravinyltetramethyltetracyclo-siloxane, alkyl maleate. The amount of the inhibitor can be selected according to its chemical structure and the desired curing rate. Generally, the weight of inhibitor in the composition is from 1 to 50,000 ppm, for example from 10 to 10,000 ppm.
In order to obtain a cured foam with good mechanical properties, it is preferred to incorporate reinforcing filler (F) into the foamable silicone composition. Examples of reinforcing filler (F) are calcium carbonate, silica, silica fine powder, diatomaceous earth, organic montmorillonite, titanium dioxide, but are not limited thereto. And silica is particularly preferred. The silica includes fumed silica, precipitated silica, and mixtures thereof. The specific surface area of the silica is suitably at least 50 m2/g, preferably in the range from 100 to 400 m2/g for example 150 to 350 m2/g as determined by BET method. The silica can either be hydrophilic or hydrophobic.
The reinforcing filler (F) is suitably used in an amount of from 0 wt % to 30 wt %, for example from 5 wt % to 25 wt %, preferably from 15 wt % to 20 wt %, based on the total weight of the composition.
The foamable silicone composition can further comprise an appropriate amount of additives, as long as such additives do not impair the effects of the present invention. Examples of such additives are compression set assistants (G), halogen-free flame retardants (H), diluents (I), thixotropic agents (J), pigments (K), but are not limited thereto.
Examples of the compression set assistants (G) to be mentioned are organic sulfur compounds, including mercaptans for example alkylthiols, arylthiols, mercaptoheterocycles such as mercaptoimidazoles and mercaptobenzimidazoles, silanes with sulfur-containing functional groups for example mercaptoalkylalkylalkoxysilane, bis(trialkoxysilylalkyl) mono-, di- or polysulfane, thiocyanatoalkyltrialkoxysilane, and thiofunctional siloxanes for example a polydimethylsiloxane-co-mercaptoalkyl compound. Preferences are given to 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, a polydimethylsiloxane-co-mercaptoalkyl compound.
The organic sulfur compound of the present disclosure may be used alone, or may be applied, reacted or blended onto the filler. In an embodiment herein, fumed silica onto which 3-mercaptopropyltrimethoxysilane or 3-mercaptopropyltriethoxysilane has been applied, reacted or blended is used as the compression set assistant. The organic sulfur compound of the present disclosure is used suitably in an amount of less than 2 wt %, for example less than 1 wt %, based on the total weight of the composition. In an embodiment herein, the organic sulfur compound accounts for from 0.2 wt % to 0.8 wt % of the total weight of the composition.
Examples of the halogen-free flame retardants (H) are aluminum-magnesium-based flame retardants such as aluminum hydroxide and magnesium hydroxide, phosphorus-based flame retardants such as ammonium polyphosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, magnesium phosphate, red phosphorus, tributyl phosphate, tris(2-ethylhexyl) phosphate, cresyl diphenyl phosphate, tricresyl phosphate, triphenyl phosphate and (2-ethylhexyl) phosphate-diphenyl ester, nitrogen-based flame retardants such as melamine and its derivatives, triazine and its derivatives, carbon-based flame retardants such as carbon black, expandable graphite, expanded graphite, carbon nanotubes, fullerene and graphene, silicone-based flame retardants such as polydimethylsiloxane, polysilsesquioxane and silicone resins, boron-based flame retardants such as zinc borate, but are not limited thereto. Preference is given to the carbon-based flame retardants. In an embodiment herein, the halogen-free flame retardant is expandable graphite, and may not contain any other halogen-free flame retardants.
Component (H) is used in at least an amount of minimum level required to ensure an effective flame retardancy. Generally, the higher the amount of component (H) is, the better the flame retardancy of the silicone foam is. However, in order not to significantly affect the homogeneity of the silicone foam, Component (H) is preferably used in an amount of less than 20 wt %, for example less than 15 wt %, more preferably less than 10 wt %, based on the total weight of the composition. In an embodiment herein, the halogen-free flame retardant is a carbon-based flame retardant that accounts for from 5 wt % to 15 wt % of the total weight of the composition. In a more specific embodiment herein, the halogen-free flame retardant is expandable graphite that accounts for from 5 wt % to 10 wt %, for example from 5 wt % to 8 wt %, of the total weight of the composition. The halogen-free flame retardant preferably has a sieve particle size of from 80 to 200 μm, for example from 80 to 150 μm, or from 80 to 120 μm. Surprisingly, the halogen-free flame retardant having a particle size within the above range can significantly reduce the amount of flame retardant added.
Examples of diluents (I) to be mentioned are dimethyl silicone oils having a dynamic viscosity of from 10 to 5,000 mPa·s at 25° C., MDT silicone oils having a dynamic viscosity of from 15 to 300 mPa·s at 25° C., mineral oils having a kinematic viscosity of from 10 to 100 mm2/s at 25° C. Generally, the addition of diluents could lower the viscosity of the composition and change the rheological properties thereof. Nevertheless, in view of the potential bleeding issue, the foamable silicone composition of the present disclosure can be free of diluents.
Examples of thixotropic agents (J) to be mentioned are polyethers such as polyethylene oxide, polypropylene oxide, copolymers of ethylene oxide and propylene oxide, and polyether-modified silicones such as DC 193 supplied by Dow Corning, TEGOPREN 3022, TEGOPREN 3070, TEGOPREN 5878, TEGOPREN 5847 supplied by Evonik Industries.
The foamable silicone composition of the present disclosure can be stored as two separate packages where Component (B) and (C) are not stored in the same package and Component (A), (B) and (D) are not stored in the same package.
The composition of the present disclosure, or each separate package as mentioned above has a viscosity suitably of from 50,000 to 500,000 mPa·s, for example from 100,000 to 300,000 mPa·s. Generally, the higher the viscosity of the composition is, the lower density of the obtained foam tends to be. The composition of the present disclosure with a high viscosity cures to form a medium-density foam, taking into account both foam density and mechanical properties.
The second aspect of the present disclosure provides a foam formed from the foamable silicone composition of the first aspect of the present disclosure.
It is obtained by crosslinking or curing the composition described in the first aspect of the present disclosure, or mixing the separate packages as described above followed by crosslinking or curing.
Generally, the crosslinking or curing is carried out at a temperature of 15-180° C. for 10 minutes-72 hours. A lower curing temperature and a short curing time are desired. Considering that the curing and foaming reactions occur simultaneously and both are very sensitive to temperature, curing at a temperature of 70-150° C. for 15-60 minutes is preferred so as to balance these two reactions and obtain a good cell structure.
The foam of the present disclosure has a density of from 0.4 to 0.6 g/cm3 and a closed cell ratio of greater than 90%. The determination of the foam density is carried out according to the GB/T 6343-2009 standard which is titled Cellular plastics and rubbers—Determination of apparent density. The determination of the closed cell ratio is carried out according to the GB/T 10799-2008 standard which is titled Rigid cellular plastics—Determination of the volume percentage of open cells and of closed cells.
The third aspect of the present disclosure provides use of the foamable silicone composition of the first aspect of the present disclosure for sealing battery pack cases, especially battery pack cases of electric vehicles.
The use comprises dispensing, particularly advantageously via an automatic dispenser, and curing of the composition described in the first aspect of the present disclosure, and afterwards compressing to achieve the sealing between the bottom plate and upper cover of the battery case. If the foam cured from the foamable silicone composition has a hardness that is too high, compression will become difficult and the upper cover of the case is likely to deform, causing difficulties in processing and sealing.
The present invention is further illustrated by the following examples, but is not limited to the scope thereof. Any experimental methods with no conditions specified in the following examples are selected according to the conventional methods and conditions, or product specifications.
It is carried out according to Method C in Section 7 of the GB/T 6669-2008 standard which is titled Flexible cellular polymeric materials.—Determination of compression set. Results are expressed in CS (%) (compression amount/%, compression time/hour, compression temperature/° C.), which is calculated by the formula as follows.
CS=(d0−dr)/d0×100%
The value of CS varies with test conditions. Generally, the smaller the compression amount, the shorter the compression time and the lower the compression temperature, the lower the CS value. CS (%) (50%, 22 h, 70° C.) is typically used to determine the compression set of flexible foam polymeric materials. However, a low CS value measured under such test condition does not mean the corresponding foam material is suitable for the sealing of battery pack cases with high sealing levels since the CS value measured at a temperature of 100° C. may obviously be greater, or even significantly greater than that measured at 70° C. A foam material with a low CS value at a high temperature, for example 110° C., is desired for sealing of battery pack cases due to the ease of heat accumulation inside the battery, therefore the present invention uses CS (%) (50%, 22 h, 110° C.) to evaluate the compression set of foam under high temperature conditions.
The requirements of device, measuring tool and samples conform to the GB/T 6669-2008 standard, and the test process is as follows. Samples to be tested are adjusted at a temperature of (23±2)° C. and a relative humidity of 50%±5% for 16 hours, then are placed between two plates of the device and compressed to a thickness of 50% of their initial thickness, which is measured according to the GB/T 6342 standard, then within 15 minutes these samples are placed, without changing their shape, in an oven with constant temperature 85° C. and relative humidity 85% for 1000 hours, during which on the 7th, 14th, 28th and 42th day samples are taken out of the oven and subjected to a temperature of (23±2)° C. and a relative humidity of 50%±5% to recover for 2 hours followed by measuring thickness, and CS values are calculated according to the aforesaid formula, and results are expressed as CSD85 (%) (compression amount/%, compression time/day).
The requirements of device, measuring tool and samples conform to the GB/T 6669-2008 standard, and the test process is as follows. Samples to be tested are adjusted at a temperature of (23±2)° C. and a relative humidity of 50%±5% for 16 hours, then are placed between two plates of the device and compressed to a thickness of 50% of their initial thickness, which is measured according to the GB/T 6342 standard, then within 15 minutes these samples are placed, without changing their shape, in a thermal shock box running 1000 cycles of −40° C. (30 minutes)˜85° C. (30 minutes), during which on the 7th, 14th, 28th and 42th day samples are taken out of the oven and subjected to a temperature of (23±2)° C. and a relative humidity of 50%±5% to recover for 2 hours followed by measuring thickness, and CS values are calculated according to the aforesaid formula, and results are expressed as CSshock (%) (compression amount/%, compression time/d).
LX-C microporous material hardness tester is used for measurement. Sample size: thickness 10±0.5 mm, width≥30 mm, length≥60 mm.
It is carried out according to the GB/T 6344-2008 standard which is titled Flexible cellular polymeric materials—Determination of tensile strength and elongation at break.
It is carried out according to the UL 94V standard using samples with a size of length 120 mm×width 13 mm×thickness 2 mm.
Results are rated according to the following grades.
Details of the raw materials used in the Examples and Comparative Examples are as follows.
A1: dimethylvinylsiloxy-terminated polydimethylsiloxane, with a dynamic viscosity of about 20,000 mPa·s at 25° C., supplied by Wacker Chemicals.
A2: dimethylvinylsiloxy-terminated polydimethylsiloxane, with a dynamic viscosity of about 190 mPa·s at 20° C. according to DIN 53019, supplied by Wacker Chemicals.
B: hydrogen-containing polydimethylsiloxane, with a hydrogen content of 1.63 wt %, supplied by Wacker Chemicals.
C1: water-based emulsion of polydimethylsiloxane, with a dynamic viscosity of 5,000-10,000 mPa·s at 25° C. and a hydroxyl content of 59.9 wt %, supplied by Wacker Chemicals.
C2: dimethylhydroxylsiloxy-terminated polydimethylsiloxane, with a hydroxyl content of 1.2 wt %, supplied by Wacker Chemicals.
D: platinum-based catalyst, WACKER® CATALYST EP, supplied by Wacker Chemicals.
E: inhibitor, WACKER® INHIBITOR PT 88, supplied by Wacker Chemicals.
F: fumed silica, with a BET surface area of 150-350 m2/g, supplied by Wacker Chemicals.
G: compression set assistant, prepared by the below process.
H1: expandable graphite, with a sieve particle size of 100 μm.
H2: expandable graphite, with a sieve particle size of 75 μm.
According to the formulas in Table 1, the ingredients in each Component A and Component B were mixed well respectively. Then Component A and B were mixed at a ratio of 1:1 and cured at 80° C. for 0.5 hours to give a silicone foam.
Table 2 lists the test results of the foams obtained in each Example and Comparative Example regarding density, compression set and hardness. It can be seen from Table 2 that the foams obtained in Examples 1-8 have a CS (50%, 22 h, 110° C.) of less than or equal to 10%, displaying an excellent resilience performance, and a moderate hardness, which is very conducive to the sealing of battery pack cases. The Si—H/OH molar ratio of the foamable composition in Comparative Example 1 is too low, leading to a significantly increased CS of the resulting foam, which is not conducive to the sealing effect. The Si—H/Si—Vi molar ratio of the foamable composition in Comparative Example 2 is too high, leading to an obviously increased CS of the resulting foam as well and a high foam hardness, which is likely to cause sealing failure of battery pack cases.
Table 3 shows the compression set of the foam obtained in Example 4, under either high temperature and humidity or thermal shock, is less than or equal to 10%, indicating a good aging resistance, which is also suitable for the sealing of battery pack cases with high sealing levels. Table 4 shows the foam obtained in Example 1 has excellent mechanical properties, and incorporating a certain amount of expandable graphite into its formula does not reduce the foam mechanical properties.
Table 5 shows the foamable composition in Example 4 comprising a certain amount of expandable graphite H1 such that it achieves excellent flame retardancy of V-0 grade, to be noted that such flame retardancy is not achieved at the cost of an increased foam CS and hardness. The foamable compositions in Examples 5-6 comprising a certain amount of expandable graphite H2 have poor flame retardancy of N.C. grade.
This application is the U.S. National Phase of PCT Application No. PCT/CN2020/099907 filed Jul. 2, 2020, the disclosure of which is incorporated in its entirety by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2020/099907 | 7/2/2020 | WO |
