Addition-type liquid silicone rubber primer and method for preparing the same

Abstract

The application provides an addition type liquid silicone primer and belongs to the technical field of primers. According to the weight percentage, the primer comprises the following components: polydimethylsiloxane containing a vinyl group: 20-30%; white carbon black: 20-30%; methyl-terminated polymethylhydrogen siloxane: 2-5%; inhibitor: 0.01-0.04%; silane coupling agent: 1-5%; zirconate coupling agent: 1-3%; catalyst: 0.3-0.5%; petroleum ether: 30-60%. The zirconate coupling agent is used to promote the hydrolysis of the alkoxy group of the silane coupling agent and to promote the ring opening of the epoxy group, so that the crosslinking degree of the primer on the surface of the substrate is increased, and thus greater adhesion is obtained.

Description

Technical Field

[0001] This invention relates to the field of primer technology, and more particularly to an addition-type liquid silicone rubber primer and its preparation method. Background Technology

[0002] The main function of the primer is to increase the adhesion between addition-type liquid silicone rubber and the substrate; at the same time, it strengthens the fragile substrate surface and acts as a shield against components in the substrate that hinder vulcanization. Currently, addition-type liquid silicone rubber primer systems are mainly classified according to different film-forming agents, including polymethylhydrosiloxane; silicone resin; epoxy-modified silicone; and acrylic-modified silicone systems. To achieve adhesion between the primer and the substrate, tackifiers also need to be added. Tackifiers used for addition-type liquid silicone rubber are mostly silanes or silane oligomers containing alkoxy, silanol, and reactive organic groups. During vulcanization, they form a coupling bond between the sulfide and the substrate.

[0003] Existing addition-type liquid silicone rubber primer technologies are mostly only suitable for bonding materials such as metals, fillers, phenolic resins, epoxy resins, PA, and PC.

[0004] Addition-cure silicone rubber is a non-polar material, while TPU is a highly polar material with low surface energy. The significant difference in polarity between the two leads to poor adhesion, a persistent challenge in the adhesive industry. To improve adhesion to the substrate, a pre-coating is usually required. Addition-cure liquid silicone rubber primers primarily consist of film-forming agents, ring-opening accelerators, tackifiers, catalysts, and diluents. The key to adhesion between the primer and the substrate lies in the tackifier, which is typically a silane coupling agent or alkoxy oligomer free from N, P, and S, which can cause platinum poisoning. Existing ring-opening accelerators, such as titanate coupling agents, tripropyl borate coupling agents, and aluminate coupling agents, are prone to hydrolysis due to their self-coupling properties, resulting in weak adhesion to TPU. Summary of the Invention

[0005] In view of this, in order to solve the technical problem of poor adhesion performance of existing primers, on the one hand, the present invention provides an addition-type liquid silicone rubber primer, which utilizes a zirconate coupling agent to promote the hydrolysis of alkoxy groups in the silane coupling agent and promote the ring-opening of epoxy groups, thereby increasing the degree of crosslinking of the primer on the substrate surface and thus obtaining greater adhesion.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] An addition-type liquid silicone rubber primer, comprising the following components by weight percentage:

[0008] Vinyl-containing polydimethylsiloxane: 20%-30%; silica: 20-30%; methyl-terminated polymethylhydrosiloxane: 2-5%; inhibitor: 0.01-0.04%; silane coupling agent: 1%-5%; zirconate coupling agent: 1-3%; catalyst: 0.3%-0.5%; petroleum ether: 30%-60%.

[0009] Preferably, the product comprises the following components by weight percentage:

[0010] Vinyl-containing polydimethylsiloxane: 30%; silica: 20-25%; methyl-terminated polymethylhydrosiloxane: 5%; inhibitor: 0.01-0.04%; silane coupling agent: 4-5%; zirconate coupling agent: 1-3%; catalyst: 0.3-0.5%; petroleum ether: 32.45-38.67%.

[0011] Preferably, the silane coupling agent is a vinyltriethoxysilane coupling agent and a γ-glycidoxypropyltrimethoxysilane coupling agent.

[0012] Preferably, the weight ratio of the vinyltriethoxysilane coupling agent to the γ-glycidyl etheroxypropyltrimethoxysilane coupling agent is (1-2):(1-3).

[0013] Preferably, the zirconate coupling agent is a tetra-n-propyl zirconate coupling agent.

[0014] Preferably, the catalyst is a rare metal catalyst.

[0015] Preferably, the rare metal catalyst is chloroplatinic acid.

[0016] Preferably, the inhibitor is ethynylcyclohexanol.

[0017] On the other hand, the present invention also provides a method for preparing the above-mentioned addition-type liquid silicone rubber primer, comprising the following steps:

[0018] Step (1), Group A allocation system

[0019] Vinyl-terminated polydimethylsiloxane, silica, chloroplatinic acid, and petroleum ether were mixed uniformly using a mixer according to the formula ratio to obtain primer component A.

[0020] Step (2), Group B allocation system

[0021] Polymethylhydrosiloxane, silane coupling agent, inhibitor, and zirconate coupling agent were mixed in a certain proportion and stirred until homogeneous to obtain component B of the primer.

[0022] Step (3): Preparation of addition-type liquid silicone rubber primer

[0023] Mixing component A and component B of the primer yields an addition-type liquid silicone rubber primer.

[0024] Preferably, in step (3), component A and component B are mixed in a ratio of 10:1.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The improvement of adhesion between addition-type liquid silicone rubber primers and substrates in existing technologies mainly relies on improving the compatibility between the film-forming agent and the substrate. For example, epoxy-modified or acrylic-modified silicone rubbers are used as film-forming agents to improve the adhesion between addition-type liquid silicone rubber and substrates. This invention utilizes silane or siloxane oligomers containing silanol, alkoxy, and reactive organic groups to achieve adhesion through vulcanization and coupling with the substrate. The combined use of silane coupling agents, through the interaction between the reactive R-termini, forms a more cross-linked adhesive surface, thereby improving adhesion to the substrate.

[0027] Existing technologies mostly utilize the hydrolysis of the alkoxy groups at the X-terminus of epoxy coupling agents for bonding, while rarely utilizing the ring-opening of the epoxy groups at the R-terminus. Due to the limitations of addition-cure liquid silicone rubber systems (the presence of substances such as N, P, and S deactivates the catalysts in addition-cure liquid silicone rubber), most acidic or basic coupling agents cannot be used in addition-cure liquid silicone rubber. This invention utilizes a zirconate ester coupling agent to promote the hydrolysis of the alkoxy groups in the silane coupling agent while simultaneously promoting the ring-opening of the epoxy groups, increasing the degree of cross-linking of the primer on the substrate surface, thereby obtaining greater adhesion. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and thoroughly described below with reference to specific embodiments.

[0029] Vinyl-terminated polydimethylsiloxane is selected from Jinsige T-2-2W;

[0030] The methyl-terminated polydimethylhydrosiloxane selected is Runhe RH-H512;

[0031] Choose Evonik A200 for silica;

[0032] The silane coupling agents selected are vinyltriethoxysilane coupling agent and γ-glycidyl etheroxypropyltrimethoxysilane coupling agent;

[0033] The titanate coupling agent selected is bis(ethyl acetoacetate) di-n-butoxy titanate.

[0034] The aluminate coupling agent selected is bis(acetylacetonyl)isopropyl aluminate;

[0035] Chloroplatinic acid was chosen as the rare metal catalyst.

[0036] The inhibitor chosen was etynylcyclohexanol;

[0037] The zirconate coupling agent selected is tetrapropyl zirconate coupling agent.

[0038] The formulations of the addition-type liquid silicone rubber primers prepared in Examples 1-6 are shown in Table 1.

[0039] Table 1. Formulation ratios of addition-type liquid silicone rubber primers in Examples 1-6

[0040]

[0041]

[0042] Following the above-described preparation method for addition-cure liquid silicone rubber primer, components A and B of the primer were prepared in a 10:1 ratio. Components A and B were stirred and mixed thoroughly, and a 0.01 mm thick layer was applied to a TPU substrate. The substrate was then baked at 100°C for 3 minutes. Addition-cure silicone rubber was then used to mold the primer, and after cooling, a sample sheet was obtained. The sample was then subjected to a 90°C peel strength test. The test results are shown in Table 2.

[0043] Table 2 Test results of Examples 1-6

[0044]

[0045] According to the test results, the addition-type liquid silicone rubber primer of the present invention can improve the adhesion between the molded addition-type liquid silicone rubber and the TPU substrate, and can achieve 90-100% cohesive failure and peel strength as high as 2.1-2.6KN / m.

[0046] Comparative Examples 1-3 were formed by replacing the zirconate coupling agents in Examples 3-5 with titanate coupling agents, aluminate coupling agents, and tripropyl borate coupling agents, respectively, and their proportions are shown in Table 3.

[0047] Table 3 shows the formulation ratios of addition-cured liquid silicone rubber primers for Comparative Examples 1-3.

[0048]

[0049] Using the same preparation method as in Examples 1-6 above, components A and B of the primer were formulated in a 10:1 ratio. Components A and B were stirred and mixed evenly, and a 0.01 mm thick layer was applied to a TPU substrate. The substrate was baked at 100°C for 3 minutes, and then addition-cure silicone rubber was used to mold the primer. After cooling, a sample sheet was obtained. The sample was then subjected to a 90°C peel strength test. The test results are shown in Table 4.

[0050] Table 4 Test results of Comparative Examples 1-3

[0051]

[0052] Based on the test results in Tables 2 and 4, the tetra-n-propylzirconate coupling agent selected as the ring-opening accelerator in Examples 1-6 of the present invention exhibits better peel strength and cohesive breakdown than commonly used titanate coupling agents, aluminate coupling agents, and tripropyl borate coupling agents in the prior art.

[0053] Comparative Example 4

[0054] Commercially available addition-cure liquid silicone rubber primer 429 hot vulcanizing adhesive was selected as Comparative Example 4. Its peel strength was 1.4 kN / m, and its cohesive failure rate was 40%.

[0055] The above are merely preferred embodiments of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solutions and improved concepts of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An addition-type liquid silicone rubber primer, characterized in that, By weight percentage, it includes the following components: Vinyl-containing polydimethylsiloxane: 20%-30%; silica: 20-30%; methyl-terminated polymethylhydrosiloxane: 2-5%; inhibitor: 0.01-0.04%; silane coupling agent: 1%-5%; zirconate coupling agent: 1-3%; Catalyst: 0.3%-0.5%; Petroleum ether: 30%-60%.

2. The addition-curing liquid silicone rubber primer according to claim 1, characterized in that, By weight percentage, it includes the following components: Vinyl-containing polydimethylsiloxane: 30%; silica: 20-25%; methyl-terminated polymethylhydrosiloxane: 5%; inhibitor: 0.01-0.04%; silane coupling agent: 4-5%; zirconate coupling agent: 1-3%; Catalyst: 0.3-0.5%; Petroleum ether: 32.45-38.67%.

3. The addition-curing liquid silicone rubber primer according to claim 1, characterized in that, The silane coupling agent is a vinyltriethoxysilane coupling agent and a γ-glycidoxypropyltrimethoxysilane coupling agent.

4. The addition-curing liquid silicone rubber primer according to claim 3, characterized in that, The weight ratio of the vinyltriethoxysilane coupling agent to the γ-glycidoxypropyltrimethoxysilane coupling agent is (1-2):(1-3).

5. The addition-curing liquid silicone rubber primer according to claim 1, characterized in that, The zirconate coupling agent is tetra-n-propyl zirconate coupling agent.

6. The addition-curing liquid silicone rubber primer according to claim 1, characterized in that, The catalyst is a rare metal catalyst.

7. The addition-curing liquid silicone rubber primer according to claim 6, characterized in that, The rare metal catalyst is chloroplatinic acid.

8. An addition-curing liquid silicone rubber primer according to any one of claims 1-7, characterized in that, The inhibitor is ethynylcyclohexanol.

9. A method for preparing an addition-type liquid silicone rubber primer according to any one of claims 1-8, characterized in that, Includes the following steps: Step (1), Group A allocation system Vinyl-terminated polydimethylsiloxane, silica, chloroplatinic acid, and petroleum ether were mixed uniformly using a mixer according to the formula ratio to obtain primer component A. Step (2), Group B allocation system Polymethylhydrosiloxane, silane coupling agent, inhibitor, and zirconate coupling agent were mixed in a certain proportion and stirred until homogeneous to obtain component B of the primer. Step (3): Preparation of addition-type liquid silicone rubber primer Mixing component A and component B of the primer yields an addition-type liquid silicone rubber primer.

10. The method for preparing an addition-type liquid silicone rubber primer according to claim 9, characterized in that, In step (3), component A and component B are mixed in a ratio of 10:1.

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