A high-efficiency defoaming and foam-suppressing agent for silicone rubber, its preparation method and application

Abstract

This invention discloses a high-efficiency defoamer and defoaming agent for silicone rubber, its preparation method, and its application. The defoamer is a polyether-polysiloxane block copolymer with an A-B-A structure, wherein the polysiloxane intermediate block provides low surface tension for rapid foam breaking, and a specific ratio of polyether end blocks promotes the migration of active ingredients to the bubble interface and achieves long-lasting foam suppression by adjusting the appropriate compatibility with the silicone rubber matrix. This invention also provides a hydrosilylation preparation method for this defoamer and its application in addition-type and condensation-type silicone rubbers. This defoamer has the advantages of fast defoaming speed, long foam suppression time, good compatibility with silicone rubber, and no impact on vulcanization or transparency.

Description

Technical Field

[0001] This invention relates to the field of silicone material processing aids, specifically to an antifoaming agent for addition-curing and condensation-curing silicone rubber systems. Particularly, it relates to a polyether-polysiloxane block copolymer with a special block structure that can simultaneously achieve rapid defoaming and long-term foam suppression, and its preparation method. Background Technology

[0002] Silicone rubber is highly susceptible to air entrapment and bubble formation during processing such as mixing, stirring, potting, or vacuum degassing. If these bubbles are not eliminated in time, they will form pores and surface defects after curing, severely affecting the product's appearance, electrical insulation, sealing properties, and mechanical strength. Therefore, high-efficiency defoamers are indispensable additives in silicone rubber processing.

[0003] Currently, the commonly used defoamers in silicone rubber systems are mainly polydimethylsiloxane (dimethyl silicone oil) and its simple modified products. However, these traditional defoamers have significant limitations in application: 1. The contradiction between defoaming and compatibility: Low-viscosity dimethyl silicone oil has high defoaming activity, but its compatibility with silicone rubber is too good. It is easily dissolved in the base rubber and cannot selectively accumulate at the bubble interface, resulting in extremely poor foam suppression (preventing the generation of new bubbles) performance. Moreover, it is prone to failure under high temperature or high shear. Some modified silicone oils developed to improve compatibility often sacrifice defoaming efficiency due to excessive compatibility.

[0004] 2. Impact on transparency and surface properties: Some defoamers have poor compatibility with the system, which can lead to micro-phase separation, resulting in increased haze and decreased transparency of the cured product, or migration to the surface causing oil spots and affecting subsequent bonding.

[0005] 3. May interfere with vulcanization: Defoamers containing special functional groups (such as amine groups) may poison platinum catalysts, delaying or inhibiting the addition curing reaction of silicone rubber.

[0006] 4. Lack of long-lasting effect: Traditional defoamers are mostly small molecules or straight-chain structures, which have poor stability in the system and cannot effectively suppress the generation of bubbles for a long operating window of several hours.

[0007] Therefore, developing a silicone rubber-specific defoamer that combines rapid defoaming, long-lasting foam suppression, excellent compatibility, and does not affect vulcanization is key to improving the quality and processing efficiency of silicone rubber products. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a polyether-polysiloxane block copolymer with a carefully designed molecular structure as a highly efficient defoaming and foam-suppressing agent. This design achieves a breakthrough in performance by balancing "interfacial migration ability" and "system compatibility".

[0009] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a highly efficient defoaming and defoaming agent for silicone rubber, which is a polyether-polysiloxane block copolymer having the structure shown in formula (I): ``` PEO / PPO - [Si(R)2O]_m - PEO / PPO ``` In formula (I): - `[Si(R)2O]_m` is a polysiloxane intermediate block (B-segment), where R is methyl and m is an integer, making the kinematic viscosity (25°C) of this block 100 - 10,000 cSt. This block provides low surface tension and hydrophobicity, and is the core of the defoaming function, responsible for inserting into and tearing the bubble liquid film.

[0010] - `PEO / PPO` is a polyether-terminated block (A-segment), which is a random or block copolymer of ethylene oxide (EO) and propylene oxide (PO), with a number-average molecular weight (Mn) of 500-3000 g / mol, and the molar content of ethylene oxide (EO) accounts for **10%-40%** of the polyether segment. This polyether segment plays a crucial dual role: a) Adjusting compatibility: By controlling the EO content to a low level, the polyether segments are kept "moderately compatible" with the silicone rubber matrix. This ensures that the defoamer is uniformly dispersed in the system, and due to the slight difference in polarity between the defoamer and silicone rubber, a slight "incompatibility driving force" is generated, which makes the middle polysiloxane block (B segment) more likely to migrate and accumulate at the bubble interface.

[0011] b) Anchoring and stabilization: The polyether segments act as "anchors," appropriately fixing the entire molecule within the silicone rubber matrix to prevent the defoaming active ingredient (B segment) from dissolving and becoming ineffective too quickly, thereby providing long-lasting defoaming ability.

[0012] Preferably, the kinematic viscosity (25°C) of the polysiloxane mesoblock is 350-2000 cSt.

[0013] Preferably, the molar content of ethylene oxide (EO) in the polyether end block is 15%-30%.

[0014] Preferably, the number-average molecular weight (Mn) of the copolymer is 3,000 - 15,000 g / mol.

[0015] Secondly, the present invention provides a method for preparing the above-mentioned defoaming and foam-suppressing agent, characterized in that it employs a hydrosilylation method, the specific steps of which are as follows: 1. Raw material preparation: a) Terminal allyl polyether: prepared by ring-opening polymerization of ethylene oxide and propylene oxide in the presence of an initiator (such as allyl alcohol) and a catalyst, with the EO / PO ratio and molecular weight controlled to meet design requirements.

[0016] b) Hydrogen-containing silicone oil: Polydimethylsiloxane with dimethylhydrosiloxy groups at both ends is selected, `(H)(CH3)2SiO-[Si(CH3)2O]_n-Si(CH3)2H`, whose molecular weight corresponds to the block viscosity of the target polysiloxane.

[0017] 2. Hydrosilylation reaction: Terminal allyl polyether and hydrogen-containing silicone oil are dissolved in an inert solvent (such as toluene or isopropanol) at a molar ratio of alkenyl to Si-H bond of (2.0 ~ 2.2): 1. A platinum-based catalyst (such as Karstedt catalyst) is added. Under nitrogen protection, the reaction is carried out at 80-110℃ for 4-8 hours. The endpoint of the reaction is determined by monitoring the disappearance of the Si-H characteristic peak near 2250 cm⁻¹ using infrared spectroscopy.

[0018] 3. Post-processing: After the reaction is complete, the solvent and low-boiling substances can be removed by vacuum distillation, and optionally by adsorption to reduce catalyst residue, to obtain a clear and transparent viscous liquid product.

[0019] Thirdly, the present invention provides the application of the above-mentioned defoaming and foam-suppressing agent in silicone rubber compositions. The silicone rubber compositions include addition-curing types (such as addition-curing liquid silicone rubber LSR) and condensation-curing types (such as room-temperature curing silicone rubber RTV).

[0020] Fourthly, the present invention provides a silicone rubber composition comprising: - Polyorganosiloxane raw rubber: 100 parts by weight; - Crosslinking agent, catalyst: appropriate amount; - The above defoaming and defoaming agent: 0.01 - 1.0 parts by weight, preferably 0.05 - 0.3 parts by weight.

[0021] The beneficial effects of this invention are: 1. Excellent defoaming and foam suppression performance: The unique "ABA" structure achieves a perfect balance of performance. The polysiloxane (B) segment efficiently breaks bubbles; the polyether (A) segment, by adjusting compatibility, both promotes the migration of the B segment to the interface and anchors it, providing long-lasting foam suppression capability. Even during prolonged stirring or vacuum degassing processes, it can continuously suppress the generation of new bubbles.

[0022] 2. Excellent compatibility with silicone rubber: By precisely controlling the EO content of the polyether segments, the defoamer achieves an ideal state of "microscopic incompatibility and macroscopic compatibility" with the silicone rubber matrix, which will not cause the system to become cloudy, oily, or migrate on the surface, and is fully applicable to high-transparency silicone rubber products.

[0023] 3. Does not affect the vulcanization process: The molecule does not contain active groups such as amines and tin that may interfere with vulcanization (especially platinum catalytic addition vulcanization), and has no negative impact on the curing speed and depth of silicone rubber.

[0024] 4. High stability: The polymer structure is stable and not easily hydrolyzed or degraded. Its performance does not decrease during long-term storage in the silicone rubber system.

[0025] 5. Low dosage, high efficiency: Significant effects can usually be achieved with very low dosage, making it highly economical. Detailed Implementation

[0026] The present invention will be further described below with reference to the embodiments.

[0027] Example 1: Synthesis of defoamer SP-1 (EO content ~20%) 1. Synthesis of allyl-terminated polyether (APEG): Using allyl alcohol as an initiator, under KOH catalysis, PO is first introduced for polymerization, followed by EO polymerization, to obtain an allyl-terminated polyether with Mn≈1000 and EO content of about 20%.

[0028] 2. Take 80g of the above APEG (containing about 0.16 mol of allyl groups), 40g of hydrogen-containing silicone oil (kinematic viscosity 500 cSt, Si-H content about 0.08 mol), and dissolve it in 200g of toluene.

[0029] 3. Add an appropriate amount of Karstedt platinum catalyst, heat to 90°C under N2 protection, and react for 6 hours until the Si-H peak disappears in the IR display.

[0030] 4. Remove toluene by vacuum distillation to obtain a clear, transparent, viscous liquid, SP-1.

[0031] Example 2: Synthesis of defoamer SP-2 (EO content ~30%) Referring to Example 1, the synthesis steps of the terminal allyl polyether were changed to obtain a polyether with Mn≈1500 and EO content of about 30%, which was then reacted with a hydrogen-containing silicone oil with a kinematic viscosity of 1000 cSt to obtain product SP-2.

[0032] Comparative Example DC-1: Ordinary dimethyl silicone oil (viscosity 100 cSt).

[0033] DC-2: Commercially available polyether-modified silicone oil (high EO content, commonly used in water-based systems).

[0034] Application test case: Base material: vinyl-terminated polydimethylsiloxane (100 parts), hydrogen-containing silicone oil crosslinking agent (2 parts), platinum catalyst (appropriate amount).

[0035] Test method: A. Defoaming speed test: Add 0.5% fumed silica and 1% test defoamer to the base material, stir at high speed (2000 rpm) for 2 minutes to introduce a large number of bubbles, and then stop. Immediately record the time required for the foam layer height to drop to half of the initial value (T50) and the time for complete defoaming (T100).

[0036] B. Foam suppression performance test: The above mixture was vacuumed (-0.095 MPa) in a vacuum degassing machine, and the maximum foam height (Hmax) of the system was continuously observed and recorded within 5 minutes.

[0037] C. Compatibility observation: After curing the transparent silicone rubber base material containing 0.2% defoamer, observe the transparency and surface condition of the sample.

[0038] sample Amount added (phr) T50 (seconds) T100 (seconds) Hmax (mm Compatibility / Transparency blank 0 >300 >600 25 transparent DC-1 0.2 45 180 18 Transparent, with a slightly oily surface DC-2 0.2 >300 Transparent, with a slightly oily surface 25 Turbid, poor compatibility SP-1 0.2 25 80 8 clear and transparent SP-2 0.2 30 95 10 clear and transparent Conclusion: The defoamers SP-1 and SP-2 of this invention are far superior to traditional dimethyl silicone oil (DC-1) and incompatible polyether silicone oil (DC-2) in terms of defoaming speed (T50, T100) and foam suppression ability (significantly reduced Hmax), while maintaining perfect compatibility with silicone rubber matrix.

Claims

1. An antifoam agent for silicone rubber, which is a polyether-polysiloxane block copolymer, characterized in that, It has the structure of formula (I): `PEO / PPO - [Si(CH3)2O]_m - PEO / PPO`, wherein the kinematic viscosity (25℃) of the `[Si(CH3)2O]_m` block is 100-10,000 cSt; the `PEO / PPO` block is a copolymer of ethylene oxide and propylene oxide with a number average molecular weight of 500-3000, and the molar content of ethylene oxide accounts for 10%-40% of the block.

2. The antifoam and foam suppressant of claim 1, wherein The molar content of ethylene oxide in the PEO / PPO block is 15%-30%.

3. The antifoam and foam suppressant according to claim 1 or 2, characterized in that The kinematic viscosity (25°C) of the `[Si(CH3)2O]_m` block is 350-2000 cSt.

4. A process for the preparation of the antifoam and foam suppressant agent according to any one of claims 1 to 3, characterized in that, include: A polyether with allyl groups at both ends and a polydimethylsiloxane with dimethylhydrosiloxy groups at both ends undergo a hydrosilylation reaction catalyzed by a platinum catalyst.

5. The method of claim 4, wherein, The polyether with allyl groups at both ends is a copolymer obtained by polymerizing ethylene oxide and propylene oxide under allyl alcohol initiation.

6. The method according to claim 4 or 5, characterized in that, In the hydrosilylation reaction, the molar ratio of allyl to Si-H bond is (2.0~2.2):

1.

7. The use of the defoamer and defoaming agent as described in any one of claims 1-3 in addition-curing or condensation-curing silicone rubber compositions as a defoamer and defoaming agent.

8. A silicone rubber composition comprising a polyorganosiloxane gum, a crosslinker and a catalyst, characterised in that, It also contains an effective amount of the defoaming and foam-suppressing agent as described in any one of claims 1-3.

9. The silicone rubber composition according to claim 8, characterized in that, Based on 100 parts by weight of the polyorganosiloxane raw rubber, the amount of defoamer and foam inhibitor added is 0.01-1.0 parts by weight.

10. The silicone rubber composition according to claim 9, characterized in that, The amount of the defoaming and foam-suppressing agent added is 0.05-0.3 parts by weight.