CN112480816A

CN112480816A - Room-temperature-curing solvent-free conformal coating and preparation method thereof

Info

Publication number: CN112480816A
Application number: CN202011374647.2A
Authority: CN
Inventors: 伊港; 张明; 刘海龙; 耿宁; 毛正楠; 石科飞; 肖月玲; 张学迪
Original assignee: Shandong Dongyue Organic Silicon Material Co Ltd
Current assignee: Shandong Dongyue Organic Silicon Material Co Ltd
Priority date: 2020-11-30
Filing date: 2020-11-30
Publication date: 2021-03-12
Anticipated expiration: 2040-11-30
Also published as: CN112480816B

Abstract

The invention provides a room-temperature curing solvent-free conformal coating and a preparation method thereof, wherein the conformal coating comprises the following raw materials in parts by weight: 90-110 parts of phenyl block copolymer, 5-20 parts of cross-linking agent and 0.1-2 parts of catalyst, wherein the phenyl block copolymer is prepared from phenyl trialkoxysilane and hydroxyl-terminated polysiloxane. The preparation process of the conformal coating does not need to add an organic solvent, the preparation method is simple and environment-friendly, and the coating obtained after curing has good hardness, plasticity and tensile strength.

Description

Room-temperature-curing solvent-free conformal coating and preparation method thereof

Technical Field

The invention relates to a room temperature curing solvent-free conformal coating and a preparation method thereof, in particular to a room temperature curing solvent-free conformal coating for coating the surface of a printed circuit, belonging to the technical field of coating preparation.

Background

With the development of science and technology, the requirements of electronic components such as PCB boards, sensitive circuits and the like on the indexes such as insulativity, moisture resistance, shock resistance and the like are more and more strict, the organic silicon conformal coating can provide lower modulus than other organic conformal coatings, and has the optimal performances of stress elimination, moisture resistance, dust resistance, shock resistance and the like in a harsh environment, so that the organic silicon conformal coating becomes an ideal choice for eliminating stress on tiny wires or sensitive welding spots. Silicones can be cured to form coatings comparable in hardness and toughness to acrylic resins, but silicones have better flexibility and function reliably at both higher and lower temperatures.

There are many patent documents reporting on silicone conformal coatings. Chinese patent document CN102304323A reports a room temperature curable phenyl silicone conformal coating, which is prepared by copolymerizing phenyl silicone or methyl phenyl silicone with hydroxyl-terminated linear polysiloxane in organic solvent such as toluene to obtain block copolymer, and finally adding cross-linking agent, catalyst and organic diluent. Chinese patent document CN101591504A provides a single-component organosilicon flame-retardant conformal coating, which is prepared by taking phenyl silicone resin and hydroxyl-terminated linear polysiloxane copolymer as a matrix, adding a cross-linking agent, a catalyst and a flame retardant, and taking toluene as an organic solvent. Chinese patent document CN108441115A provides a room temperature curing radiation-resistant silicon resin composition and a preparation method thereof, the silicon resin composition is prepared by taking hydroxyl-terminated phenyl silicon resin as a matrix and adding a radiation-resistant agent, a cross-linking agent, a catalyst and volatile organic siloxane as a diluent. However, in the preparation process of the conformal coating described in the above patent, a large amount of organic reagents such as toluene and volatile components are used, and serious harm is easily caused to human bodies and environment in the actual use process of the conformal coating; furthermore, the copolymerization of phenyl silicone with hydroxyl terminated linear polysiloxanes in the above patents is not easily controlled and gels are easily formed.

Therefore, there is a need to develop a room temperature curable organic solvent free silicone conformal coating. The invention is therefore proposed.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a room-temperature curing solvent-free conformal coating and a preparation method thereof. The preparation process of the conformal coating does not need to add an organic solvent, the preparation method is simple and environment-friendly, and the coating obtained after curing has good hardness, plasticity and tensile strength.

The technical scheme of the invention is as follows:

the room temperature curing solvent-free conformal coating comprises the following raw materials in parts by weight: 90-110 parts of phenyl block copolymer, 5-20 parts of cross-linking agent and 0.1-2 parts of catalyst.

Preferably according to the invention, the phenyl block copolymer is prepared from a phenyltrialkoxysilane and a hydroxyl-terminated polysiloxane;

further preferably, the phenyltrialkoxysilane is phenyltrimethoxysilane or phenyltriethoxysilane;

further preferably, the hydroxyl-terminated polysiloxane is a hydroxyl-terminated polydimethylsiloxane; the viscosity of the hydroxyl-terminated polysiloxane is 30-3000 mpa.s.

According to a preferred embodiment of the present invention, the phenyl block copolymer is prepared by the following method:

adding phenyl trialkoxysilane into a reaction kettle, dropwise adding a hydrochloric acid aqueous solution, controlling the temperature in the kettle to be 5-10 ℃ in the dropwise adding process, and controlling the dropwise adding time to be 1-2 hours; after the dropwise adding is finished, carrying out a first reaction to obtain a prepolymer reaction liquid; then adding the hydroxyl-terminated polysiloxane into a reaction kettle for a second reaction; after the reaction is finished, the phenyl block copolymer is obtained through post-treatment.

Preferably, the mass concentration of the hydrochloric acid aqueous solution is 0.1-2%.

Preferably, the molar ratio of the phenyltrialkoxysilane to water in the aqueous hydrochloric acid solution is 1: 3.

Preferably, the first reaction temperature is 65-75 ℃, and the first reaction time is 2-3 hours; the pressure of the reaction kettle is controlled to be-0.01 to-0.03 MPa in the first reaction process. The hydrolysis reaction is carried out in a vacuum state, and the hydrolysis of the phenyltrialkoxysilane monomer is promoted, so that the hydrolysis reaction is promoted to be carried out rightward.

Preferably, the mass ratio of the hydroxyl-terminated polysiloxane to the phenyltrialkoxysilane is 1: 5-15.

Preferably, the second reaction temperature is 105-115 ℃, and the second reaction time is 2-3 hours; the second reaction adopts a condensation reflux mode to carry out polymerization reaction, can control the reaction degree of the hydroxyl-terminated polysiloxane and the prepolymer, controls the evaporation of water, and prevents the system from generating gel due to excessive reaction.

Preferably, the post-treatment step is: washing the reaction solution obtained after the reaction is finished to be neutral, and then distilling under reduced pressure to remove low-boiling-point substances to obtain a transparent phenyl block copolymer; the temperature of the reduced pressure distillation is 70-80 ℃, and the pressure is-0.05 to-0.1 MPa.

According to the invention, the low-boiling-point substance is water, unreacted small molecules and the like.

Preferably, according to the invention, the crosslinking agent is a methyl-containing trialkoxysilane or a phenyl-containing trialkoxysilane; further preferably, the crosslinking agent is methyltrimethoxysilane or methyltriethoxysilane.

According to the invention, the catalyst is preferably an organic titanium compound or an organic tin compound; further preferably, the catalyst is isopropyl titanate or butyl titanate.

According to the invention, the preparation method of the room temperature curing solvent-free conformal coating comprises the following steps:

the phenyl block copolymer and the cross-linking agent are mixed and stirred evenly, the catalyst is added drop by drop, and the mixture is stirred and mixed fully, thus obtaining the room temperature curing solvent-free conformal coating.

The invention has the technical characteristics that:

organic reagents such as toluene and the like are added in the preparation of the prior phenyl silicone resin, and the aim is to reduce the hydrolysis speed, reduce the probability of mutual contact reaction among active groups in the synthesis process and prevent the occurrence of violent polymerization to generate gel.

1. According to the preparation method of the phenyl block copolymer, a phenyl alkoxy silane monomer is firstly hydrolyzed under the action of an acid catalyst to form a low-molecular-weight prepolymer, and then the low-molecular-weight prepolymer is reacted with hydroxyl-terminated polysiloxane to form the block copolymer. The method controls the hydrolysis degree by controlling the water quantity; by slowing down the hydrolysis speed of the system at low temperature, a uniform and transparent synthetic product is obtained.

2. In the synthesis process of the phenyl block copolymer, hydrolysis reaction is firstly carried out in a vacuum-pumping state, and then polymerization reaction is carried out in a condensation reflux mode. The former aims to promote the hydrolysis of the phenyl trialkoxysilane monomer and promote the hydrolysis reaction to proceed rightwards; the latter aims to control the reaction degree of hydroxyl-terminated polysiloxane and prepolymer, control water evaporation and prevent the system from generating gel due to over reaction.

The invention has the following beneficial effects:

1. the raw materials of the room temperature curing solvent-free conformal coating are mainly prepared phenyl block copolymers, the phenyl block copolymers contain a hard segment structure of phenyl silicone prepolymer and a hydroxyl-terminated polysiloxane soft segment structure, and the conformal coating is endowed with certain flexibility while certain hardness and plasticity are ensured.

2. In the synthesis process of the raw material phenyl block copolymer, the addition of volatile organic reagents such as benzene, toluene, xylene, tetrahydrofuran, ethanol, methanol and the like is not needed in the whole process, so that the harm of the volatile organic reagents to the environment and human bodies is effectively reduced.

3. The room temperature curing solvent-free conformal coating obtained by the invention is directly obtained by taking the prepared phenyl block copolymer as a main raw material and adding a cross-linking agent and an initiator, organic solvents such as toluene and the like are not added in the preparation process, and the preparation method is simple and environment-friendly; the coating obtained after curing has good hardness, plasticity and tensile strength.

Detailed Description

The present invention is further illustrated by, but is not limited to, the following examples.

Meanwhile, the experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents, materials and equipment are commercially available, unless otherwise specified.

Example 1

A method for preparing a solvent-free conformal coating cured at room temperature comprises the following steps:

(1) 594g of phenyltrimethoxysilane is added into a reaction kettle with a reflux device, a thermometer, a constant-pressure dropping funnel and a stirrer, and the temperature is controlled to be 5-10 ℃; slowly dripping 163.6g of 1% hydrochloric acid aqueous solution into the kettle by using a constant-pressure low-liquid funnel, controlling the temperature in the kettle to be 5-10 ℃ in the dripping process, and controlling the dripping time to be 1.5 hours; after the dropwise adding is finished, heating the reaction kettle to 70 ℃, controlling the pressure of the reaction kettle to be-0.01 MPa, and reacting for 2 hours to obtain a prepolymer reaction liquid; then 65g of hydroxyl-terminated polydimethylsiloxane with the viscosity of 50mpa.s is added into a reaction kettle, and the temperature is raised to 110 ℃ for reflux reaction for 2 hours; washing the reaction solution obtained after the reaction is finished to be neutral, and removing low-boiling-point substances by reduced pressure distillation to obtain a transparent phenyl block copolymer; the reduced pressure distillation conditions are as follows: the temperature is 75 ℃, and the pressure is-0.05 to-0.1 MPa.

(2) Adding 150g of the phenyl block copolymer obtained in the step (1) into a reaction bottle, adding 12g of methyltrimethoxysilane, fully stirring for 1h, dropwise adding 1.5g of isopropyl titanate by using a constant-pressure dropping funnel, and fully stirring to obtain a room-temperature-cured solvent-free conformal coating product.

Example 2

(1) 721g of phenyltriethoxysilane is added into a reaction kettle with a reflux device, a thermometer, a constant pressure dropping funnel and a stirrer, and the temperature is controlled to be 5-10 ℃; slowly dripping 163.6g of 1% hydrochloric acid aqueous solution into the kettle by using a constant-pressure low-liquid funnel, controlling the temperature in the kettle to be 5-10 ℃ in the dripping process, and controlling the dripping time to be 1.5 hours; after the dropwise adding is finished, heating the reaction kettle to 70 ℃, controlling the pressure of the reaction kettle to be-0.01 MPa, and reacting for 2 hours to obtain a prepolymer reaction liquid; then 65g of hydroxyl-terminated polydimethylsiloxane with the viscosity of 50mpa.s is added into a reaction kettle, and the temperature is raised to 110 ℃ for reflux reaction for 2 hours; washing the reaction solution obtained after the reaction is finished to be neutral, and removing low-boiling-point substances by reduced pressure distillation to obtain a transparent phenyl block copolymer; the reduced pressure distillation conditions are as follows: the temperature is 75 ℃, and the pressure is-0.05 to-0.1 MPa.

Example 3

A room temperature cure solventless conformal coating was prepared as described in example 1, except that the hydroxyl terminated polydimethylsiloxane had a viscosity of 300 mPa.s.

Example 4

A room temperature cure solventless conformal coating was prepared as described in example 1, except that the hydroxyl terminated polydimethylsiloxane had a viscosity of 2000 mPa.s.

Comparative example 1

A room temperature cure conforma coating was prepared as described in example 1, except that: and (2) controlling the temperature of the reaction kettle to be 20 ℃ when the hydrochloric acid aqueous solution is dropwise added in the step (1).

Comparative example 2

A room temperature cure conforma coating was prepared as described in example 1, except that: and (2) controlling the temperature of the reaction kettle to be 0 ℃ when the hydrochloric acid aqueous solution is dropwise added in the step (1).

Comparative example 3

A room temperature cure conforma coating was prepared as described in example 1, except that: the mass of the aqueous hydrochloric acid solution in the step (1) was 202 g.

Comparative example 4

A room temperature cure conforma coating was prepared as described in example 1, except that: the first reaction process in the step (1) is that the reaction kettle is heated to 70 ℃ and reacts for 2 hours under normal pressure.

Comparative example 5

A room temperature cure conforma coating was prepared as described in example 1, except that: the second reaction process in the step (1) is to increase the temperature to 110 ℃, change the reflux mode into a reduction device and remove the moisture.

Test examples

The examples and the comparative conforma coatings were tested for performance.

The tack-free time was tested with reference to the standard GB/T1728-1989.

The hardness was tested according to standard GB/T531.1-2008.

Tensile strength was tested with reference to standard GB/T528-.

The dielectric constant (100Hz) was tested with reference to the standard GB/T1409-2006.

The volume resistivity was tested with reference to the standard GB/T1410-2006.

TABLE 1 test data for examples and comparative conforma coatings

As can be seen from Table 1, the conforma coatings prepared in the examples of the present invention have an excellent combination of properties in terms of hardness, open time, tensile strength, and the like. In the preparation of the phenyl block copolymer of comparative example 1, the dropping temperature of the hydrochloric acid aqueous solution is increased, the hydrolysis speed is high, so that the gel is generated due to the sudden polymerization, and the conformal coating cannot be prepared; in the preparation of the phenyl block copolymer in the comparative example 2, the dropping temperature of a hydrochloric acid aqueous solution is reduced, the hydrolysis speed is low, the first reaction is insufficient, the prepolymer lacks enough active reaction sites to participate in the second reaction, the surface drying time of the coating is prolonged, and the film hardness and the tensile strength are reduced compared with those in the example 1; in the preparation of the phenyl block copolymer in comparative example 3, the amount of water added was increased, the second reaction did not proceed normally to the right due to the excessive amount of water, the obtained phenyl block copolymer was a turbid liquid, and the conformal coating could not be cured normally; in the preparation of the phenyl block copolymer in comparative example 4, the first reaction was carried out at normal pressure, and the hydrolysis product could not be distilled out in time, resulting in insufficient hydrolysis reaction and further affecting the second reaction, so that the obtained phenyl block copolymer was a turbid liquid, and the resulting coating showed a significant decrease in surface drying time, film hardness, tensile strength and film flexibility as compared with example 1; in the preparation of the phenyl block copolymer in the comparative example 5, a reduction device is adopted in the second reaction process to continuously remove moisture, intermolecular and intramolecular reactions can occur between hydroxyl-terminated polydimethylsiloxane molecules and phenyl prepolymer molecules in the second reaction, molecular chains are intertwined with each other, the molecular weight of the block copolymer is continuously increased, and finally gel is generated, so that the conformal coating cannot be prepared. From the above, it can be seen that the hydrolysis temperature, the water addition amount and the reaction conditions have a great influence on the preparation of the phenyl block copolymer, thereby affecting the performance of the conformal coating obtained by preparation; moreover, as can be seen from the table above, the performance of the conformal coating prepared by the invention without adding the solvent is equivalent to that of the conformal coating prepared by adding the solvent in the prior art, but the preparation of the conformal coating is simpler and more environment-friendly.

Claims

1. The room-temperature curing solvent-free conformal coating is characterized by comprising the following raw materials in parts by weight: 90-110 parts of phenyl block copolymer, 5-20 parts of cross-linking agent and 0.1-2 parts of catalyst.

2. The room temperature curing solvent-free conformal coating of claim 1, wherein the phenyl block copolymer is prepared from a phenyl trialkoxysilane and a hydroxyl terminated polysiloxane; the phenyl trialkoxysilane is phenyl trimethoxysilane or phenyl triethoxysilane; the hydroxyl-terminated polysiloxane is hydroxyl-terminated polydimethylsiloxane; the viscosity of the hydroxyl-terminated polysiloxane is 30-3000 mpa.s.

3. The room temperature curing solventless conformal coating of claim 2, wherein said phenyl block copolymer is prepared by the following method:

4. The room temperature curing solvent-free conformal coating material according to claim 3, wherein the mass concentration of the hydrochloric acid aqueous solution is 0.1-2%; the molar ratio of the phenyl trialkoxysilane to water in the hydrochloric acid aqueous solution is 1: 3.

5. The room temperature curing solvent-free conformal coating of claim 3, wherein the first reaction temperature is 65-75 ℃ and the first reaction time is 2-3 hours; the pressure of the reaction kettle is controlled to be-0.01 to-0.03 MPa in the first reaction process.

6. The room temperature curing solvent-free conformal coating of claim 3, wherein the mass ratio of the hydroxyl-terminated polysiloxane to the phenyltrialkoxysilane is 1: 5-15; the second reaction temperature is 105-115 ℃, and the second reaction time is 2-3 hours.

7. The room temperature curing solvent-free conformal coating of claim 3, wherein the post-processing steps are: washing the reaction solution obtained after the reaction is finished to be neutral, and then distilling under reduced pressure to remove low-boiling-point substances to obtain a transparent phenyl block copolymer; the temperature of the reduced pressure distillation is 70-80 ℃, and the pressure is-0.05 to-0.1 MPa.

8. The room temperature curing solvent-free conformal coating of claim 1, wherein the cross-linking agent is a methyl-containing trialkoxysilane or a phenyl-containing trialkoxysilane; preferably, the crosslinking agent is methyltrimethoxysilane or methyltriethoxysilane.

9. The room temperature curing solvent-free conformal coating of claim 1, wherein the catalyst is an organotitanium compound or an organotin-based compound; preferably, the catalyst is isopropyl titanate or butyl titanate.

10. The method of preparing the room temperature curing solventless conformal coating of claim 1, comprising the steps of: