A fast-curing two-component silicone composition and its preparation method and application

Abstract

The present invention relates to a fast-curing two-component silicone composition and its preparation method and application, the silicone composition includes component A and component B; by weight, the raw materials of component A include 1 to 100 parts of hydroxyl-terminated polydimethylsiloxane, 0 to 5 parts of a first color paste, 0 to 10 parts of a cross-linking agent, 1 to 100 parts of a first filler, 0.1 to 5 parts of an α-aminosilane coupling agent, and 0 to 5 parts of a dewatering agent; the raw materials of component B include 1 to 100 parts of dimethyl silicone oil, 0 to 100 parts of a second filler, 0 to 5 parts of a second color paste, and 0 to 10 parts of a catalyst. The present invention designs a specific α-aminosilane coupling agent, which has good compatibility in the system, and due to the introduction of a large number of amino and alkoxy active groups, it can produce chemical bonds with the surface groups of the substrate. At the same time, the amino groups in the specific structure provide steric hindrance to the alkoxy groups at both ends, which is beneficial to the rapid curing and deep curing of the system, and improves the bonding effect of the two-component silicone composition product.

Description

Technical Field

[0001] The invention belongs to the technical field of silicone rubber, and particularly relates to a fast-curing two-component organosilicon composition and a preparation method and application thereof. Background Art

[0002] Condensation type room temperature vulcanization (RTV) silicone rubber can be divided into single component and two component according to product form. Two-component condensation type RTV silicone rubber is the most common RTV silicone rubber. Its main characteristics are that it does not release heat, does not absorb heat, does not expand, shrinks little, and can be vulcanized both internally and on the surface at the same time, and can be deeply vulcanized. Therefore, two-component condensation type RTV silicone rubber is widely used in the fields of construction, automobiles, electronic appliances, machinery, chemicals, light industry, etc.

[0003] In recent years, RTV silicone rubber has made great progress, but many types of RTV silicone rubber still have many problems when used, including weaker strength than epoxy and polyurethane adhesives, which limits its further application. Currently, the main way to improve the strength of silicone is to add gas silicon, but the increase in the amount of gas silicon added affects its process performance. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a fast-curing two-component silicone composition and its preparation method and application. By designing a specific α-aminosilane coupling agent, it has good compatibility in the system, and due to the introduction of a large number of amino and alkoxy active groups, it can produce chemical bonds with the surface groups of the substrate. At the same time, the amino groups in the specific structure provide steric hindrance to the alkoxy groups at both ends, which is beneficial to the rapid curing and deep curing of the system, and improves the bonding effect of the two-component silicone composition product.

[0005] The invention provides a fast-curing two-component silicone composition, which comprises a component A and a component B; in parts by weight, the raw materials of the component A comprise 1 to 100 parts of hydroxyl-terminated polydimethylsiloxane, 0 to 5 parts of a first color paste, 0 to 10 parts of a crosslinking agent, 1 to 100 parts of a first filler, 0.1 to 5 parts of an α-aminosilane coupling agent, and 0 to 5 parts of a dewatering agent; the raw materials of the component B comprise 1 to 100 parts of dimethyl silicone oil, 0 to 100 parts of a second filler, 0 to 5 parts of a second color paste, and 0 to 10 parts of a catalyst; wherein the structural formula of the α-aminosilane coupling agent is as follows: ; n≥4.

[0006] Preferably, the preparation method of the α-aminosilane coupling agent comprises the following steps:

[0007] (1) Add chloromethyldichloromethylsilane to anhydrous methanol, heat to 40-50° C. until no bubbles are generated, and distill under reduced pressure to obtain intermediate A; the structural formula of intermediate A is as follows:

[0008] ;

[0009] (2) Ethylenediamine and triethylamine are mixed, and the temperature is gradually raised to 80-100°C, and intermediate A is added to continue the reaction at the temperature, and the temperature is lowered to room temperature for liquid separation, and the upper liquid is taken and distilled under reduced pressure to obtain intermediate B; the structural formula of intermediate B is as follows:

[0010] ;

[0011] (3) N-(2-aminoethyl)-3-aminopropyltrimethoxysilane is mixed with water, and then MgO is added to stir and neutralize, and then anhydrous magnesium sulfate is added to stir and dry, and the material is discharged after reduced pressure distillation at 90-110° C. to obtain intermediate C; the structural formula of intermediate C is as follows:

[0012] , n≥4;

[0013] (4) Separately mix and stir intermediate C, ethylene glycol and isopropyl titanate, then add intermediate B to react, and perform vacuum distillation to obtain an α-aminosilane coupling agent.

[0014] Preferably, the molar ratio of chloromethyldichloromethylsilane to anhydrous methanol in step (1) is 1:2-3.

[0015] Preferably, the reduced pressure distillation in step (1) collects a fraction with a temperature of 68-72°C / 10kpa.

[0016] Preferably, the molar ratio of ethylenediamine to triethylamine (excluding water) in step (2) is 0.5-1:1.

[0017] Preferably, the molar ratio of ethylenediamine to intermediate A in step (2) is 0.5-1:0.5.

[0018] Preferably, the insulation reaction time in step (2) is 3-4 hours.

[0019] Preferably, the reduced pressure distillation in step (2) collects a fraction at 128°C-135°C / 10kpa.

[0020] Preferably, the molar ratio of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, water and MgO in step (3) is 0.3:0.4-0.5:0.005-0.01.

[0021] Preferably, the neutralization time in step (3) is 3-4 hours, and the stirring and drying time is 1-2 hours.

[0022] Preferably, the mass ratio of intermediate C, ethylene glycol, isopropyl titanate and intermediate B in step (4) is 300-400:50-100:0.1-0.5.

[0023] Preferably, the reaction time in step (4) is 1-4 h.

[0024] Preferably, the reduced pressure distillation in step (4) collects a fraction at 140°C-142°C / 10 kpa.

[0025] Preferably, n in the structural formula of the α-aminosilane coupling agent is any integer of 4-8.

[0026] Preferably, the hydroxyl-terminated polydimethylsiloxane comprises two hydroxyl-terminated polydimethylsiloxanes with different viscosities, which are denoted as hydroxyl-terminated polydimethylsiloxane A and hydroxyl-terminated polydimethylsiloxane B.

[0027] Preferably, the viscosity of the hydroxyl-terminated polydimethylsiloxane A at 25° C. is 100 to 200,000 mPa•s; more preferably, it is 2,000 to 100,000 mPa•s; and even more preferably, it is 2,000 to 20,000 mPa•s.

[0028] Preferably, the viscosity of the hydroxyl-terminated polydimethylsiloxane B at 25° C. is 100 to 200,000 mPa•s; more preferably, it is 2,000 to 100,000 mPa•s; and even more preferably, it is 5,000 to 50,000 mPa•s.

[0029] Preferably, the crosslinking agent is an alkoxysilane, such as one or more of 1,2-bis(trimethoxysilyl)ethane and dimethyldimethoxysiloxane.

[0030] Preferably, the desiccant is vinyltrimethoxysilane.

[0031] Preferably, the dimethyl silicone oil is one or more of butadiene, polyether polyol, phthalate, aliphatic dibasic acid ester, trimellitate, polyol ester, citrate, phosphate, polyester, and epoxy fatty acid.

[0032] Preferably, the dimethyl silicone oil comprises two dimethyl silicone oils of different viscosities, which are denoted as dimethyl silicone oil A and dimethyl silicone oil B.

[0033] Preferably, the viscosity of the dimethyl silicone oil at 25° C. is 100 to 200,000 mPa·s; more preferably, it is 200 to 10,000 mPa·s; and even more preferably, it is 300 to 80,000 mPa·s.

[0034] Preferably, the catalyst is a tin-based catalyst. Further preferably, the catalyst is one or more of tributyltin oxide (TBTO), dibutyltin chloride (DBTC), di-n-octyl-bis(2-ethylhexylthioacetate)tin (DOTE), dibutyltin dilaurate, and dibutyltin diacetylacetonate.

[0035] Preferably, the first filler and the second filler are one or more of calcium carbonate, aluminum oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide and silicon dioxide.

[0036] Preferably, the silicone composition comprises component A and component B; in parts by weight, the raw materials of component A comprise 20 to 80 parts of hydroxyl-terminated polydimethylsiloxane, 0 to 5 parts of a first color paste, 0 to 5 parts of a cross-linking agent, 20 to 80 parts of a first filler, 0.1 to 3 parts of an α-aminosilane coupling agent, and 0 to 3 parts of a dehydrating agent; the raw materials of component B comprise 20 to 80 parts of dimethyl silicone oil, 20 to 80 parts of a second filler, 0 to 3 parts of a second color paste, and 0 to 3 parts of a catalyst.

[0037] More preferably, the silicone composition comprises component A and component B; in parts by weight, the raw materials of component A comprise 20 to 80 parts of hydroxyl-terminated polydimethylsiloxane, 0.5 to 5 parts of a first color paste, 1 to 5 parts of a crosslinking agent, 20 to 80 parts of a first filler, 0.1 to 3 parts of an α-aminosilane coupling agent, and 0.5 to 3 parts of a dehydrating agent; the raw materials of component B comprise 20 to 80 parts of dimethyl silicone oil, 20 to 80 parts of a second filler, 0.01 to 3 parts of a second color paste, and 0.01 to 3 parts of a catalyst.

[0038] The present invention also provides a method for preparing a fast-curing two-component silicone composition, comprising the following steps:

[0039] (1) heating the first filler to 80-120° C. for vacuum dehydration for 2-3 hours, and cooling to room temperature in vacuum to obtain the pretreated first filler; stirring and dispersing the hydroxyl-terminated polydimethylsiloxane, the first color paste, the crosslinking agent, the first filler, the α-aminosilane coupling agent, and the dehydrating agent in vacuum to obtain component A;

[0040] (2) heating the second filler to 80-110° C. and vacuum dehydrating for 2-3 hours, and then vacuum cooling to room temperature to obtain a pretreated second filler; stirring and dispersing the dimethyl silicone oil, the second filler, the second color paste, and the catalyst in a vacuum condition to obtain component B;

[0041] (3) Component A and component B are mixed to obtain a fast-curing two-component silicone composition.

[0042] The present invention also provides an application of a fast-curing two-component organic silicon composition in a sealant.

[0043] Preferably, the application method is to uniformly mix the component A and the component B in a volume ratio of 10-20:1 and use the mixture as a sealant. The fast-curing two-component silicone composition has a curing depth of ≥5 mm after 2 hours and a tensile shear strength of ≥0.52 MPa after 4 hours.

[0044] Preferably, the application method is to uniformly mix component A and component B in a volume ratio of 10-20:1 and then use.

[0045] Beneficial Effects

[0046] (1) The present invention designs a specific α-aminosilane coupling agent, which has good compatibility in the system and can form chemical bonds with the surface groups of the substrate due to the introduction of a large number of amino and alkoxy active groups. At the same time, the amino groups in the specific structure provide steric hindrance to the alkoxy groups at both ends, which is beneficial to the rapid curing and deep curing of the system, thereby improving the bonding effect of the two-component silicone composition product.

[0047] (2) The present invention achieves a good balance between the fluidity and toughness of the silicone composition by compounding two hydroxyl-terminated polydimethylsiloxanes with different viscosities. The mechanical properties of the silicone composition can also be adjusted by selecting the mass ratio of the two silicones with different viscosities, thereby being able to meet the needs of different substrates and usage scenarios.

[0048] (3) The preparation of the organosilicon composition of the present invention is simple and requires mild conditions, and is suitable for large-scale industrial production. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0050] Hydroxyl-terminated polydimethylsiloxane (viscosity 20000 mPa·s, viscosity 5000 mPa·s) was purchased from Zaoyang Dekaiyuan Organic Silicone Co., Ltd.;

[0051] Dimethyl silicone oil (viscosity 60000 mPa·s, viscosity 100 mPa·s) was purchased from Hubei Xinhaihong Chemical Co., Ltd.;

[0052] Catalyst: dibutyltin dilaurate and dibutyltin diacetylacetonate, purchased from Nitto Chemical;

[0053] Water removal agent: vinyl trimethoxysilane, brand A-171, purchased from Zhejiang Woxingman New Material Technology Co., Ltd.

[0054] The preparation method of the α-aminosilane coupling agent in this embodiment comprises the following steps:

[0055] (1) Add 0.9 mol (147.2 g) of chloromethyldichloromethylsilane (CAS1558-33-4) to a 500 ml three-necked flask, add 1.8 mol (57.7 g) of anhydrous methanol to a constant pressure funnel, raise the temperature to 45°C, add dropwise until no bubbles (HCl) are generated, perform vacuum distillation, and collect the fraction at 68-72°C / 10 kPa to obtain intermediate A;

[0056] (2) Add 0.6 mol (36.6 g) of ethylenediamine and 1 mol (101.2 g) of triethylamine to a 500 ml three-necked flask, gradually raise the temperature to 90°C, reflux the mixture and slowly add 0.5 mol (77.3 g) of intermediate A at a uniform rate. After the addition is complete, continue to keep the temperature for 3 h, cool to room temperature, separate the liquid, take the upper layer, and collect the fraction at 128°C-135°C / 10 kPa by vacuum distillation to obtain a light yellow transparent liquid, namely intermediate B.

[0057] (3) Add 0.3 mol (66.71 g) of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to a 100 ml three-necked flask and stir. Use a constant pressure funnel to drop 0.48 mol (12.97 g) of water with a pH value of about 7 at a rate of 2 drops / s. After the water is added, add 0.005 mol (0.2 g) of MgO (CAS1309-48-4) and stir to neutralize for 4 h. Then add anhydrous magnesium sulfate and stir to dry for 2 h. Then, distill under reduced pressure at 100 °C for 30 min to obtain intermediate C.

[0058] (4) Take intermediate C (360 g), ethylene glycol (90 g), and isopropyl titanate (0.45 g) respectively, mix them, add them into 1 L of three-mouth biscuit, stir them at 40 ° C for 5 min under nitrogen atmosphere, add intermediate B (270 g) dropwise at a constant speed, react for 2 h after the addition is complete, and distill under reduced pressure at 140 ° C / 10 kPa. After no droplets are left for 10 min, stop heating to obtain α-aminosilane coupling agent, the structural formula of which is shown below:

[0059] ; n=4.

[0060] Example 1

[0061] This embodiment provides a two-component organosilicon composition, the raw materials of the A and B components are shown in Table 1, and are prepared by the following method:

[0062] Component A:

[0063] Dehydrate calcium carbonate with a D50 of 2 μm and silicon dioxide with a D50 of 0.1 μm at 110°C for 3 hours and cool to room temperature; disperse 40 parts of hydroxyl-terminated polydimethylsiloxane A with a viscosity of 20000 mPa•s and 24.5 parts of hydroxyl-terminated polydimethylsiloxane B with a viscosity of 5000 mPa•s in a high-speed dispersing planetary mixer; add 28 parts of the above-mentioned pretreated calcium carbonate, 3 parts of silicon dioxide, 0.5 parts of color paste and 2.5 parts of cross-linking agent into the planetary mixer and disperse; then add 0.5 parts of dehydrating agent into the planetary mixer and disperse, stir under vacuum and discharge evenly to obtain component A.

[0064] Component B:

[0065] Dehydrate calcium carbonate with a D50 of 2 μm and silicon dioxide with a D50 of 0.1 μm at 110°C for 3 h and cool to room temperature; disperse 60 parts of dimethyl silicone oil A with a viscosity of 60000 mPa•s and 10 parts of dimethyl silicone oil B with a viscosity of 100 mPa•s in a high-speed dispersing planetary mixer; add 24.95 parts of the above-mentioned pretreated calcium carbonate and 3 parts of silicon dioxide into the planetary mixer for dispersion; then add 0.05 parts of the catalyst dibutyltin disilicic acid (CAS77-58-7) into the planetary mixer for dispersion, and vacuum stir to evenly discharge the material to obtain component B.

[0066] Example 2

[0067] This embodiment provides a two-component silicone composition, the raw materials of the A and B components are shown in Table 1, and the implementation method is the same as that of Example 1, except that the catalyst in the B component is replaced with dibutyltin diacetylacetonate (CAS 22673-19-4) in an amount of 0.05 parts.

[0068] Example 3

[0069] This embodiment provides a two-component silicone composition, the raw materials of its A and B components are shown in Table 1, and the implementation method is the same as that of Example 1, except that: the added amount of hydroxyl-terminated polydimethylsiloxane A with a viscosity of 20000mPa•s in component A is 24.5 parts, and the added amount of hydroxyl-terminated polydimethylsiloxane B with a viscosity of 20000mPa•s is 10 parts.

[0070] Comparative Example 1

[0071] This comparative example provides a two-component silicone composition, the raw materials of the A and B components are shown in Table 1, and the implementation method is the same as that of Example 2, except that the crosslinking agent in the A component is γ-aminopropyltriethoxysilane, the structural formula is .

[0072] Comparative Example 2

[0073] This comparative example provides a two-component silicone composition, the raw materials of its A and B components are shown in Table 1, and the implementation method is the same as Example 2, except that: the silane coupling agent in component A is γ-β-(aminoethyl)-γ-aminopropyltrimethoxysilane (CAS1760-24-3), and the structural formula is .

[0074] Comparative Example 3

[0075] This comparative example provides a two-component silicone composition, the raw materials of the A and B components are shown in Table 1, and the implementation method is the same as that of Example 3, except that the silane coupling agent in the A component is γ-aminopropyltrimethoxysilane (CAS No.: 13822-56-5), and the structural formula is .

[0076] Performance Testing

[0077] 1. Curing depth

[0078] Refer to the standard GB / T29595-2013-5.8 for the curing speed test method. Use acetone or other suitable solvents to clean the wedge-shaped groove and evaporate the solvent completely. You can also use a release agent. Start injecting the sealant from the lowest point of the groove, so that it completely fills the groove and has a little surplus to prevent air from entering and causing bubbles. Use a scraper to fill some of the remaining sealant into each gap along the groove wall, then scrape off the excess part, and check the curing condition after leaving it under standard test conditions for 2 hours. Start from the highest point of the groove, lift the sealant until you see the uncured sealant attached to the wedge-shaped groove, and stop the action, and measure the distance from the starting point of the groove to this point.

[0079] 2. Bonding strength

[0080] Between two cleaned aluminum die-casting plates, a composition of 1 mm thick, in which the A component and the B component obtained in the above-mentioned Examples 1-3 and Comparative Examples 1-3 were mixed uniformly in a volume ratio of 10:1, was sandwiched, and two groups of Al-Al were prepared according to the bonding size of 12.5×25×0.2 mm, and cured for 4 hours at room temperature of 25°C and 50% humidity. The tensile shear bonding strength of the bonding test body was measured according to the method specified in GB-T7124-2008 "Determination of tensile shear strength of adhesives (rigid material to rigid material)".

[0081] Referring to the curing test results in Table 3, compared with the comparative example, Examples 1-3 have significant improvements in key curing test indicators such as 2h curing depth and 4h tensile shear bond strength, achieving rapid curing and deep curing, which is crucial to reducing production costs.

[0082] Table 1A Components (parts by weight)

[0083]

[0084] Table 2B Components (parts by weight)

[0085]

[0086] Table 3 Test results

[0087] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 2h curing depth (mm) 6.79 8.78 5 1.32 3.33 2.94 4h bonding strength (MPa) 0.66 0.81 0.52 0.07 0.14 0.12

Claims

1. A fast-curing two-component silicone composition, characterized in that: The organic silicon composition comprises component A and component B; in terms of weight, the raw materials of component A comprise 1 to 100 parts of hydroxyl-terminated polydimethylsiloxane, 0 to 5 parts of a first color paste, 0 to 10 parts of a crosslinking agent, 1 to 100 parts of a first filler, 0.1 to 5 parts of an α-aminosilane coupling agent, and 0 to 5 parts of a dewatering agent; the raw materials of component B comprise 1 to 100 parts of dimethyl silicone oil, 0 to 100 parts of a second filler, 0 to 5 parts of a second color paste, and 0 to 10 parts of a catalyst; wherein the structural formula of the α-aminosilane coupling agent is as follows: ；n≥4。 2. A fast-curing two-component silicone composition according to claim 1, characterized in that: The preparation method of the α-aminosilane coupling agent comprises the following steps: (1) Add chloromethyldichloromethylsilane to anhydrous methanol, heat to 40-50° C. until no bubbles are generated, and distill under reduced pressure to obtain intermediate A; the structural formula of intermediate A is as follows: ； (2) Ethylenediamine and triethylamine are mixed, and the temperature is gradually raised to 80-100°C, and intermediate A is added to continue the reaction at the temperature, and the temperature is lowered to room temperature for liquid separation, and the upper liquid is taken and distilled under reduced pressure to obtain intermediate B; the structural formula of intermediate B is as follows: ； (3) N-(2-aminoethyl)-3-aminopropyltrimethoxysilane is mixed with water, and then MgO is added to stir and neutralize, and then anhydrous magnesium sulfate is added to stir and dry, and the material is discharged after reduced pressure distillation at 90-110° C. to obtain intermediate C; the structural formula of intermediate C is as follows: ，n≥4； (4) Separately mix and stir intermediate C, ethylene glycol and isopropyl titanate, then add intermediate B to react, and perform vacuum distillation to obtain an α-aminosilane coupling agent.

3. A fast-curing two-component silicone composition according to claim 1, characterized in that: The hydroxyl-terminated polydimethylsiloxane comprises two hydroxyl-terminated polydimethylsiloxanes with different viscosities.

4. A fast-curing two-component silicone composition according to claim 1, characterized in that: The cross-linking agent is alkoxysilane; and the dehydrating agent is vinyl trimethoxy silane.

5. A fast-curing two-component silicone composition according to claim 1, characterized in that: The dimethyl silicone oil is one or more of butadiene, polyether polyol, phthalate, aliphatic dibasic acid ester, trimellitate, polyol ester, citrate, phosphate, polyester, and epoxy fatty acid.

6. A fast-curing two-component silicone composition according to claim 1, characterized in that: The catalyst is a tin-based catalyst.

7. A fast-curing two-component silicone composition according to claim 1, characterized in that: The first filler and the second filler are one or more of calcium carbonate, aluminum oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide and silicon dioxide.

8. A fast-curing two-component silicone composition according to claim 1, characterized in that: The silicone composition comprises component A and component B; in parts by weight, the raw materials of component A comprise 20 to 80 parts of hydroxyl-terminated polydimethylsiloxane, 0 to 5 parts of a first color paste, 0 to 5 parts of a crosslinking agent, 20 to 80 parts of a first filler, 0.1 to 3 parts of an α-aminosilane coupling agent, and 0 to 3 parts of a dehydrating agent; the raw materials of component B comprise 20 to 80 parts of dimethyl silicone oil, 20 to 80 parts of a second filler, 0 to 3 parts of a second color paste, and 0 to 3 parts of a catalyst.

9. A method for preparing a fast-curing two-component silicone composition according to any one of claims 1 to 8, characterized in that: The steps include: (1) heating the first filler to 80-120° C. for vacuum dehydration for 2-3 hours, and cooling to room temperature in vacuum to obtain the pretreated first filler; stirring and dispersing the hydroxyl-terminated polydimethylsiloxane, the first color paste, the crosslinking agent, the first filler, the α-aminosilane coupling agent, and the dehydrating agent in vacuum to obtain component A; (2) heating the second filler to 80-110° C. and vacuum dehydrating for 2-3 hours, and then vacuum cooling to room temperature to obtain a pretreated second filler; stirring and dispersing the dimethyl silicone oil, the second filler, the second color paste, and the catalyst in a vacuum condition to obtain component B; (3) Component A and component B are mixed to obtain a fast-curing two-component silicone composition.

10. A use of the fast-curing two-component silicone composition according to any one of claims 1 to 8 or the fast-curing two-component silicone composition prepared by the preparation method according to claim 9, characterized in that: The component A and the component B are uniformly mixed in a volume ratio of 10-20:1 and used as a sealant.

11. The use of the fast-curing two-component silicone composition according to claim 10, characterized in that: The component A and the component B are mixed in a volume ratio of 10:

1. The fast-curing two-component silicone composition has a curing depth of ≥5 mm after 2 hours and a tensile shear strength of ≥0.52 MPa after 4 hours.

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