Silicone sealant and preparation method thereof

Abstract

The invention mainly relates to the technical field of adhesives, in particular to a silicone sealant. The flame-retardant silicone rubber is prepared from the following raw materials in parts by weight: 15 to 30 parts of hydroxyl-terminated polysiloxane, 10 to 15 parts of PET (Polyethylene Terephthalate) polyester, 5 to 10 parts of m-phthalic acid-5-sodium sulfonate, 2 to 5 parts of 3-sulfenyl-butantetraol, 5 to 8 parts of a cross-linking agent, 25 to 50 parts of a flame retardant, 10 to 30 parts of filler, 0.5 to 2 parts of a chain extender, 0.5 to 2 parts of a tackifier and 0.5 to 1 part of a catalyst. A-SOH sulfenyl group is introduced into 1, 3-sulfenyl-butantetraol, and a hydrophobic group is generated after the 1, 3-sulfenyl-butantetraol is combined with PET polyester, so that water is prevented from entering from fine holes in the surface of a product, better waterproof performance is obtained, silicon-containing components of the flame retardant are mutually crosslinked, a Si-O-Si network structure is formed in the sealant, and the flame retardant property is improved. And the decomposed product can help to prevent further occurrence of combustion, so that the flame-retardant effect is achieved. And the grafting of the silicon-containing group can greatly reduce the formation of tiny holes in the internal structure, so that the sealant has good waterproofness.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and in particular to a silicone sealant and a preparation method thereof. Background Art

[0002] Silicone sealant, a new type of silicone elastomer, crosslinks and cures at room temperature. Depending on the packaging format, silicone sealants can be divided into two categories: single-component and two-component. The operating temperature range for silicone sealants is -50°C to 180°C. Silicone sealants are widely used in industries such as aerospace, automotive, construction, and electronics due to their excellent adhesion to a variety of substrates, their ability to prevent dust and moisture from entering the product, and their superior electrical insulation, chemical stability, aging resistance, and physiological inertness. However, silicone sealants are inherently flammable and will burn when exposed to open flames. With the increasing use of sealants in construction in recent years, fires are bound to cause serious property damage and casualties. Therefore, research on the flame retardancy of sealants has become a key development trend. Flame-retardant silicone sealant is a new type of flame-retardant composite material. When exposed to high temperatures or flames, the flame retardant within the material activates, preventing the spread of fire. Flame-retardant silicone sealant provides a new approach to the fire prevention and flame retardancy of glass curtain walls and other facilities in high-rise buildings. It can ensure the sealing and safety of the building in the event of a fire, buying valuable time for the evacuation of personnel.

[0003] The combustion of silicone sealant can be divided into three stages according to the development of time: heat accumulation, thermal decomposition and ignition. (1) Heat accumulation: Silicone sealant will not soften and melt before reaching the thermal decomposition temperature, but as the heat continues to accumulate, some of the heat will increase the internal energy of the polymer and cause the temperature of the polymer to continue to rise, and some of the heat will induce the silicone sealant to produce free radical chain scission and accelerate the decomposition autocatalysis, thereby increasing the rate of thermal decomposition; (2) Thermal decomposition: The thermal decomposition process of silicone sealant can be divided into depolymerization reaction, elimination reaction, cyclization reaction and cross-linking reaction according to the structure and chemical composition. When silicone sealant decomposes, the thermal decomposition on the surface of the material is oxidative thermal decomposition, that is, the decomposition process involves oxygen, while non-oxidative thermal decomposition occurs inside the material, in which oxygen does not participate; (3) Ignition: Under the action of heat transfer, the large amount of heat released by the combustion of the silicone sealant surface accelerates the decomposition of the polymer. When the combustible substances produced by the decomposition mix with a certain proportion of air and reach the ignition point, they begin to burn. At the same time, the flame will spread and propagate along the surface of the silicone sealant, causing a larger fire. Therefore, for flame retardant materials, controlling the spread of flame is an important task in preventing fires and an important basis for the design of flame retardant silicone sealants.

[0004] Chinese Patent No. 201510524661.9 discloses a new environmentally friendly flame-retardant silicone sealant and its preparation method. The sealant comprises the following components by weight: 100 parts α,ω-dihydroxypolysiloxane, 1-50 parts polydimethylsiloxane, 5-150 parts filler, 1-10 parts phosphorus silicon flame retardant, 1-15 parts cross-linking agent, 0.1-3 parts catalyst, and 0.5-4 parts coupling agent. This invention utilizes a new environmentally friendly flame retardant to prepare a dealcoholized flame-retardant silicone sealant. This solves the problem of poor flame retardancy in dealcoholized sealants. The preparation process is simple, production losses are low, and the product has excellent processability.

[0005] Commonly used flame retardants can be broadly divided into five categories: halogen flame retardants, organophosphorus flame retardants, intumescent flame retardants, inorganic flame retardants, and silicone flame retardants. Different types of flame retardants have varying advantages and disadvantages, and in practice, it's rare to use just one flame retardant. In practical applications, two or more flame retardants are often added to leverage the advantages of different flame retardants and exploit their synergistic effects, thereby enhancing flame retardant efficiency, reducing the total amount of flame retardant added, lowering costs, and minimizing the impact on the substrate's performance. Silicone sealants are inherently waterproof, but when flame retardants are added as additives, they form numerous micropores due to their poor compatibility with the sealant. These micropores compromise the sealant's waterproofness, causing water absorption and ultimately water seepage. Therefore, it's necessary to develop a flame retardant with improved compatibility and apply it to silicone sealants to achieve optimal waterproofing. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the present invention provides a silicone sealant and a preparation method thereof, which solves the problem of insufficient waterproofness of the sealant in the prior art.

[0007] In a first aspect, the present invention provides a silicone sealant composed of the following raw materials in parts by weight: 15-30 parts of terminal hydroxy polysiloxane, 10-15 parts of PET polyester, 5-10 parts of sodium 5-sulfonate isophthalic acid, 2-5 parts of 3-sulfenyl-butanetetrol, 5-8 parts of a crosslinking agent, 25-50 parts of a flame retardant, 10-30 parts of a filler, 0.5-2 parts of a chain extender, 0.5-2 parts of a tackifier, and 0.5-1 parts of a catalyst.

[0008] Preferably, the flame retardant comprises one of tri(2,3-dibromo)propyl borate or polyborosiloxane.

[0009] Preferably, the filler is one of white carbon black, quartz powder or nano calcium carbonate.

[0010] Preferably, the crosslinking agent is one of methyltriacetoxysilane, methyltributylidene oxime silane and methyltrimethoxysilane.

[0011] Preferably, the chain extender is one of dimethyldibutylketoxime silane, methylvinyldibutylketoxime silane or methylvinyldiacetoneoxime silane.

[0012] Preferably, the adhesion promoter is one of γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropyloxy)propyltrimethoxysilane.

[0013] Preferably, the catalyst is a platinum catalyst, a palladium catalyst or a tin catalyst.

[0014] In a second aspect, the present invention further provides a method for preparing a silicone sealant, comprising the following steps:

[0015] S1. Knead the formulated amount of terminal hydroxyl polysiloxane and flame retardant at room temperature, add filler, heat to 130-150° C., knead and stir under vacuum for 2-4 hours, remove moisture from the system, then cool to room temperature, grind evenly, and obtain a base rubber;

[0016] S2. The base rubber prepared in step S1 is drawn into a reactor, vacuum stirred to remove moisture in the air, and then PET polyester is added. Subsequently, sodium 5-sulfoisophthalate is added to the reactor, and the reaction is maintained at 240° C. for 2 hours. Then, 3-sulfonyl-butanetetrol is added, followed by a cross-linking agent, a chain extender, a tackifier, and a catalyst. After mixing evenly, bubbles are removed to obtain a silicone sealant product.

[0017] Furthermore, the sodium 5-sulfoisophthalate is first prepared into a 40% wt esterification liquid and then added into the reactor.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention introduces PET polyester modified with 5-sodium sulfoisophthalate into traditional sealant raw materials, thereby destroying the regular spatial configuration of the polymer molecules, thereby having better interfacial compatibility and allowing various flame retardants to be combined more evenly. At the same time, the raw materials of the present invention also contain 3-sulfenic acid-butanetetrol, thereby introducing -SOH sulfenic acid groups. After combining with PET polyester, hydrophobic groups are generated, making the product surface water-resistant, thereby preventing moisture from entering through small holes on the product surface and obtaining better waterproof performance.

[0020] 2. The silicon-containing components of the flame retardant crosslink with each other, forming a Si-O-Si network within the sealant. This prevents volatilization during heating, ultimately degrading to SiO2, which remains in the carbon residue. The OC bond of the BOC bond in the boron-containing component breaks, forming a borate structure. This heat dissipation effect promotes the generation of water vapor, ultimately degrading to B2O3, which remains in the carbon residue. These components help prevent further combustion, thereby achieving a flame retardant effect. The nitrogen-containing groups within the sealant emit non-combustible gases such as NH3, NO, and NO2 during combustion, which dilute the oxygen and heat on the sealant surface, preventing the combustion of other combustible substances. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described below with reference to the embodiments.

[0022] Example 1

[0023] A method for preparing a silicone sealant comprises the following steps:

[0024] S1. Knead 4 kg of α,ω-dihydroxypolydimethylsiloxane and 2.5 kg of tri(2,3-dibromo)propyl borate (a flame retardant) at room temperature, add 2 kg of nano-calcium carbonate, heat to 140°C, knead and stir under vacuum for 4 hours to remove moisture from the system, then cool to room temperature, grind evenly, and obtain a base rubber;

[0025] S2. The base glue in step S1 is vacuumed and stirred to remove moisture in the air, and then 1.5 kg of PET polyester is added, and then 0.5 kg of sodium 5-sulfoisophthalate is made into a 40% wt esterification liquid and added to the reactor. The reaction is maintained at 240° C. for 2 hours, and then 0.1 kg of 3-sulfenyl-butanetetrol is added, and then 1 kg of methyltriacetoxysilane is added and mixed evenly. Then, 0.1 kg of dimethyl dibutyl ketoxime silane, 0.1 kg of γ-aminopropyltrimethoxysilane, and 0.05 kg of stannous octoate are added, and after mixing evenly, bubbles are removed to obtain a silicone sealant product.

[0026] Example 2

[0027] A method for preparing a silicone sealant comprises the following steps:

[0028] S1. Knead 4 kg of α,ω-dihydroxypolydimethylsiloxane and 2.5 kg of polyborosiloxane at room temperature, add 2 kg of nano calcium carbonate, heat up and knead under vacuum at 140°C for 4 hours to remove moisture from the system, then cool to room temperature, grind evenly, and obtain a base rubber;

[0029] S2. The base glue in step S1 is vacuumed and stirred to remove moisture in the air, and then 1.5 kg of PET polyester is added, and then 0.5 kg of sodium 5-sulfoisophthalate is made into a 40% wt esterification liquid and added to the reactor. The reaction is maintained at 240° C. for 2 hours, and then 0.1 kg of 3-sulfenyl-butanetetrol is added, and then 1 kg of methyltriacetoxysilane is added and mixed evenly. Then, 0.1 kg of dimethyl dibutyl ketoxime silane, 0.1 kg of γ-aminopropyltrimethoxysilane, and 0.05 kg of stannous octoate are added, and after mixing evenly, bubbles are removed to obtain a silicone sealant product.

[0030] Example 3

[0031] A method for preparing a silicone sealant comprises the following steps:

[0032] S1. Knead 4 kg of α,ω-dihydroxypolydimethylsiloxane and 2.5 kg of polyborosiloxane at room temperature, add 2 kg of nano calcium carbonate, heat up and knead under vacuum at 140°C for 4 hours to remove moisture from the system, then cool to room temperature, grind evenly, and obtain a base rubber;

[0033] S2. The base glue in step S1 is vacuumed and stirred to remove moisture in the air, and then 1.5 kg of PET polyester is added, and then 0.5 kg of sodium 5-sulfoisophthalate is made into a 40% wt esterification liquid and added to the reactor. The reaction is maintained at 240° C. for 2 hours, and then 0.1 kg of 3-sulfenyl-butanetetrol is added, and then 1 kg of methyltriacetoxysilane is added and mixed evenly. Then, 0.1 kg of dimethyl dibutyl ketoxime silane, 0.1 kg of γ-aminopropyltrimethoxysilane, and 0.05 kg of stannous octoate are added, and after mixing evenly, bubbles are removed to obtain a silicone sealant product.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A silicone sealant, characterized in that: The invention is composed of the following raw materials in parts by weight: 15-30 parts of terminal hydroxyl polysiloxane, 10-15 parts of PET polyester, 5-10 parts of 5-sulfoisophthalic acid sodium salt, 2-5 parts of 3-sulfenyl-butanetetrol, 5-8 parts of crosslinking agent, 25-50 parts of flame retardant, 10-30 parts of filler, 0.5-2 parts of chain extender, 0.5-2 parts of tackifier and 0.5-1 parts of catalyst.

2. The silicone sealant according to claim 1, wherein The flame retardant includes one of tri(2,3-dibromo)propyl borate or polyborosiloxane.

3. The silicone sealant according to claim 1, wherein: The filler is one of white carbon black, quartz powder or nano calcium carbonate.

4. The silicone sealant according to claim 1, wherein: The crosslinking agent is one of methyltriacetoxysilane, methyltributylanoximesilane and methyltrimethoxysilane.

5. The silicone sealant according to claim 1, wherein: The chain extender is one of dimethyl dibutyl ketoxime silane, methyl vinyl dibutyl ketoxime silane or methyl vinyl diacetone oxime silane.

6. The silicone sealant according to claim 1, wherein: The tackifier is one of γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

7. The silicone sealant according to claim 1, wherein: The catalyst is one of a platinum catalyst, a palladium catalyst or a tin catalyst.

8. A method for preparing the silicone sealant according to any one of claims 1 to 7, characterized in that: The steps include: S1. Knead the formulated amount of terminal hydroxyl polysiloxane and flame retardant at room temperature, add filler, heat to 130-150° C., knead and stir under vacuum for 2-4 hours, remove moisture from the system, then cool to room temperature, grind evenly, and obtain a base rubber; S2. The base rubber prepared in step S1 is drawn into a reactor, vacuum stirred to remove moisture in the air, and then PET polyester is added. Subsequently, sodium 5-sulfoisophthalate is added to the reactor, and the reaction is maintained at 240° C. for 2 hours. Subsequently, a cross-linking agent, a chain extender, a tackifier, and a catalyst are added. After mixing evenly, bubbles are removed to obtain a silicone sealant product.

9. The method for preparing a silicone sealant according to claim 8, wherein: The 5-sodium sulfoisophthalate is first prepared into a 40% wt esterification liquid and then added into the reaction kettle.