CN114132034A

CN114132034A - A kind of electronic grade flexible polytetrafluoroethylene thermal insulation film and preparation method thereof

Info

Publication number: CN114132034A
Application number: CN202111465485.8A
Authority: CN
Inventors: 肖超; 王艳艳; 丁欣; 郑康; 张献; 田兴友
Original assignee: Hefei Institutes of Physical Science of CAS
Current assignee: Hefei Institutes of Physical Science of CAS
Priority date: 2021-12-03
Filing date: 2021-12-03
Publication date: 2022-03-04

Abstract

The invention belongs to the technical field of electronic product materials, in particular to an electronic-grade flexible polytetrafluoroethylene heat insulating film and a preparation method thereof. The preparation method includes the following steps: performing hydrophilic modification on an expanded polytetrafluoroethylene film (ePTFE), mixing silica aerogel powder with deionized water, an emulsifier, a wetting agent, an aqueous adhesive, an infrared The sunscreen agent is mixed to obtain aerogel water-based slurry; the aerogel water-based slurry is coated on the modified expanded polytetrafluoroethylene film and dried to obtain a composite film; the multi-layer composite film is superimposed and covered with a modified layer. The flexible expanded polytetrafluoroethylene film is obtained after hot pressing to obtain an electronic-grade flexible polytetrafluoroethylene heat insulating film. The electronic-grade flexible polytetrafluoroethylene heat insulating film of the invention realizes the controllable preparation of heat insulating films of different thicknesses, avoids the problem of powder falling after bending, has the characteristics of light and thin thickness, good flexibility, good reflection and heat insulation performance, and has the advantages of thermal conductivity. The rate is as low as 0.020W/mK, which is suitable for the field of consumer electronics and batteries.

Description

Electronic-grade flexible polytetrafluoroethylene heat-insulating film and preparation method thereof

Technical Field

The invention belongs to the technical field of electronic product materials, and particularly relates to an organic/inorganic nano composite heat-insulating material for electronic products and a preparation method thereof.

Background

With the continuous development of integrated circuit technology, the functional requirements of intelligent electronic products are also continuously increased, which brings about significant problems of sudden increase of power density and heat accumulation. Particularly, under the influence of miniaturization, lightness, thinness and intensification of electronic products, the heat dissipation space is very limited, which puts higher requirements on the performance of the heat management material. The single pursuit of high thermal conductivity of the packaging material can cause the excessive heat emission of the device, and influence the performance of the peripheral weak heat-resistant device and the body feeling comfort of a user. Some devices adopt a scheme of reserving a gap to avoid the influence of heat flow crosstalk, but the further miniaturization of the equipment is limited. Therefore, the development of high-performance electronic-grade heat-insulating materials is increasingly urgent, and the materials can be used with heat-dissipating materials to realize controllable dredging of heat, and have important significance for improving the reliability of electronic devices.

Aerogel materials are recognized as the lowest thermal conductivity insulating materials. The abundant porosity and the tiny pore diameter can effectively restrict the thermal movement of air molecules and reduce the heat transfer efficiency. At present, two main processes are used for preparing the silicon dioxide aerogel composite heat insulation film: firstly, aerogel powder is mixed with an adhesive and then coated on a basement membrane. For example, in the CN 112341658A patent, a non-stick aerogel slurry is obtained by mixing aerogel powder, an aqueous adhesive and a resin emulsion, and then the mixture is knife-coated on a PET base film by using a coater to obtain a heat insulation film. Secondly, coating a precursor of silicon dioxide aerogel on the substrate and then drying to obtain a composite film; for example, patent CN 113527760a coats an aerogel precursor on the surface of expanded polytetrafluoroethylene (ePTFE), and dries to obtain the thermal insulation film material. The precursor coating mode can keep the good integrity of the aerogel layer, but the method has complex drying process and poor flexibility of the continuous aerogel layer, and still has the problem of easy crushing and powder falling. Therefore, the development of a powder-dropping-free high-performance electronic grade aerogel heat-insulating film is a technical problem to be solved urgently.

Disclosure of Invention

The invention aims to solve the technical problems of high thermal conductivity, large thickness, poor flexibility and powder falling of aerogel materials in the prior art, and provides a high-performance electronic grade flexible polytetrafluoroethylene heat insulation film without powder falling and a preparation method thereof.

In order to solve the technical problem, the technical scheme is that the preparation method of the electronic-grade flexible polytetrafluoroethylene heat-insulating film comprises the following steps:

s1, spraying a hydrophilic modifier on the surface of the expanded polytetrafluoroethylene film, and drying to obtain a modified expanded polytetrafluoroethylene film;

s2, dispersing silicon dioxide aerogel powder into deionized water, adding an emulsifier, a wetting agent, a water-based adhesive and an infrared opacifier, and then ball-milling and uniformly mixing to obtain aerogel water-based slurry with the solid content of 5-25 wt% and the adhesive content of 3-30 wt%;

s3, uniformly coating the aerogel aqueous slurry prepared in the step S2 on the upper surface of the modified expanded polytetrafluoroethylene film prepared in the step S1 to form a slurry layer, wherein the coating thickness is 50-1000 mu m, and then carrying out vacuum drying at the temperature of 110-400 ℃ for 10-60min to prepare ePTFE-SiO₂Compounding film;

s4, taking two or more layers of ePTFE-SiO₂Stacking the composite films, wherein the modified expanded polytetrafluoroethylene film and the slurry layer are alternately arranged during stacking, one surface of the modified expanded polytetrafluoroethylene film in the lowest composite film faces downwards, and then covering the uppermost composite film with a layer of step S1The modified expanded polytetrafluoroethylene film is prepared by placing the superposed composite film into a hot press, molding and hot-pressing at the temperature of 150-;

wherein, the steps S1 and S2 are not in sequence.

The preparation method of the electronic grade flexible polytetrafluoroethylene heat insulation film is further improved:

preferably, the expanded polytetrafluoroethylene film in step S1 is a porous polytetrafluoroethylene film that is uniaxially or biaxially stretched, and the film thickness is 5 to 50 μm.

Preferably, the model of the hydrophilic modifier in the step S1 is one of HS-220M, HS-830D, HS-130TS and X-70M.

Preferably, the mixing mass ratio of the silica aerogel powder, the deionized water, the emulsifier, the wetting agent, the water-based binder and the infrared opacifier in the step S2 is (10-100): 100-900): 0.5-5.5): 1-3): 5-30): 0.2-2.5.

Preferably, the silica aerogel powder is a hydrophobic silica aerogel powder.

Preferably, the emulsifier in step S2 is one or a combination of two or more of tween 80, span 80, OP10 and triton.

Preferably, the wetting agent in step S2 is one or a combination of two or more of polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, and polyoxyethylene polyoxypropylene block copolymer.

Preferably, the aqueous adhesive in step S2 is one or a combination of two or more of polyvinyl alcohol, aqueous acrylate, aqueous polyurethane, pure acrylic emulsion, aqueous perfluoroethylene-propylene copolymer, copolymer of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene, and ethylene-tetrafluoroethylene copolymer.

Preferably, in step S2, the infrared opacifier is one or a combination of two or more of carbon black, titanium dioxide, potassium hexatitanate whisker and silicon carbide.

In order to solve the technical problem, the other technical scheme is that the electronic grade flexible polytetrafluoroethylene heat insulation film prepared by any one of the preparation methods is adopted.

Compared with the prior art, the invention has the beneficial effects that:

in the prior art, silicon dioxide aerogel or a precursor thereof is coated on the surface of a matrix, and a heat insulation film is prepared by utilizing the low heat conductivity of the silicon dioxide aerogel; however, the strength of the silica aerogel is extremely poor, and the silica aerogel is easily broken by external force to cause the powder falling phenomenon. According to the invention, the silica aerogel is coated on the surface of the hydrophilic modified expanded polytetrafluoroethylene by a novel process, after the ePTFE is treated by a hydrophilic modifier, the hydrophilicity is obviously improved, the water-based slurry can be naturally leveled and infiltrated on the membrane surface and filled into the inner holes of the ePTFE, and the silica powder is firmly restrained by fibers to form a compact heat-insulating aerogel layer; the hydrophobic silica aerogel powder is preferred because the hydrophobic silica can avoid the problem of performance degradation caused by moisture during the use of the material. After drying treatment, ePTFE porous fiber shrinks to be able to react with SiO₂The powder generates effective restraint to avoid falling off, and the uniform dispersion and flexible connection of aerogel particles are effectively ensured by the aid of various addition auxiliaries. The multilayer heat insulation films are superposed and pressed, controllable preparation of the heat insulation films with different thicknesses is realized, and the problem of powder falling after bending is avoided. The compounded heat-insulating film has good flexibility and can be used for non-static application. The heat-insulating material has the characteristics of low heat conduction, high strength and no dust, almost no particles fall off after being bent for many times, the heat conductivity is as low as 0.020W/mK, and the heat-insulating use requirement of electronic devices is met.

Drawings

FIG. 1 is a graph comparing the dispersion effect before and after the hydrophobic silica powder treatment;

FIG. 2 (a) shows the impregnation of an ePTFE membrane with SiO₂Surface SEM appearance behind the aqueous slurry; (b) is a partially enlarged view of fig. (a).

FIG. 3 (a) shows the cross-sectional SEM topography of example 1; (b) is the surface SEM topography of example 1.

FIG. 4 (a) is the cross-sectional SEM topography of example 2; (b) is the surface SEM topography of example 2.

FIG. 5 (a) is the cross-sectional SEM topography of example 3; (b) is the surface SEM topography of example 3.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to embodiments, and all other embodiments obtained by a person of ordinary skill in the art without any creative effort based on the embodiments of the present invention belong to the protection scope of the present invention.

The hydrophilic modifier in the following examples is a commercially available ethanol solution with the model of X-70M, the expanded polytetrafluoroethylene film is a biaxially oriented porous polytetrafluoroethylene film, and the thickness of the film layer is 5 μ M.

Example 1

S1, spreading an expanded polytetrafluoroethylene film (ePTFE film) on the surface of a glass plate, and spraying a hydrophilic modifier with the concentration of 1% on the ePTFE film surface by using a spray gun; putting the glass plate into an oven to dry for 2 hours at the temperature of 80 ℃ to obtain a modified ePTFE film;

s2, adding 50 parts by mass of hydrophobic silica aerogel powder into 100 parts by mass of deionized water, sequentially adding 5 parts by mass of an emulsifier OP10, 2 parts by mass of a wetting agent polyoxyethylene alkylphenol ether, 25 parts by mass of a water-based adhesive perfluoroethylene propylene copolymer and 2.5 parts by mass of an infrared opacifier titanium dioxide, putting into a ball milling tank, and carrying out ball milling at the speed of 300rpm for 2 hours to obtain uniformly dispersed aerogel water-based slurry;

s3, coating aerogel aqueous slurry with the thickness of 200 microns on the surface of the modified ePTFE film by using a coating machine, and putting the coated composite film into a vacuum oven to dry for 2 hours at the temperature of 120 ℃ to obtain filled ePTFE/SiO₂A composite film having a thickness of about 70 μm;

s4, mixing the above ePTFE/SiO₂Stacking 20 layers of composite membrane, covering with a layer of modified expanded polytetrafluoroethylene film, placing into a flat plate hot press, setting the temperature of upper and lower plates at 320 deg.C, hot pressing at 5Mpa for 10min, and shaping to obtain ePTFE/SiO₂A heat insulating film 1.

Comparing the hydrophilic performance tests before and after the hydrophilic modification of the expanded polytetrafluoroethylene film in the step S1, wherein the test results show that: the polytetrafluoroethylene has strong hydrophobicity, and can not be infiltrated by deionized water; after being treated by the self-made hydrophilic modifier, the ePTFE film can be fully wetted by water.

The dispersion effect performance before and after the hydrophobic silica powder treatment in step S2 was compared, and the results are shown in fig. 1. As can be seen from fig. 1, the hydrophobic silica powder has very poor compatibility with water and floats on the water surface; after being treated by the multi-component auxiliary agent, the uniformly dispersed silicon dioxide water-based slurry can be obtained.

Example 2

S1, spreading an expanded polytetrafluoroethylene film (ePTFE film) on the surface of a glass plate, and spraying a hydrophilic modifier with the concentration of 3% on the ePTFE film surface by using a spray gun; putting the glass plate into an oven to dry for 2 hours at the temperature of 80 ℃ to obtain a modified ePTFE film;

s2, adding 30 parts by mass of hydrophobic silica aerogel powder into 200 parts by mass of deionized water, sequentially adding 3 parts by mass of emulsifier Tween 80, 1.5 parts by mass of wetting agent polyoxyethylene fatty alcohol ether, 30 parts by mass of aqueous binder polyvinyl alcohol and 1.5 parts by mass of infrared opacifier silicon carbide, putting into a ball milling tank, and carrying out ball milling at the speed of 300rpm for 2 hours to obtain uniformly dispersed aerogel aqueous slurry;

s3, coating aerogel aqueous slurry with the thickness of 100 microns on the surface of the modified ePTFE film by using a coating machine, and drying the coated composite film in a vacuum oven at 80 ℃ for 2h to obtain filled ePTFE/SiO₂A composite film having a thickness of about 20 μm;

s4, mixing the above ePTFE/SiO₂Superposing 30 layers of the composite membrane, covering a layer of modified expanded polytetrafluoroethylene membrane, placing the composite membrane into a flat plate hot press, setting the temperature of an upper plate and a lower plate to be 250 ℃, and hot-pressing for 10min under the pressure of 5Mpa for shaping to obtain ePTFE/SiO₂A heat insulating film 2.

The single-layer ePTFE/SiO dried in the step S3₂SEM test of the composite membrane, in FIG. 2 (a) is ePTFE membrane surface soaked with SiO₂Surface SEM appearance behind the aqueous slurry; (b) is a partially enlarged view of fig. (a). As shown in FIG. (a), SiO₂The particles are fully filled into the pores inside the ePTFE, and the membrane surface is flat and compact. Can find after partial amplificationPolytetrafluoroethylene fiber and SiO₂An interpenetrating structure is formed, the fiber framework plays a role in restraining the aerogel, and the phenomenon of powder falling can be effectively avoided after the multiple layers are stacked.

Example 3

S1, spreading an expanded polytetrafluoroethylene film (ePTFE film) on the surface of a glass plate, and spraying a hydrophilic modifier with the concentration of 5% on the ePTFE film surface by using a spray gun; putting the glass plate into an oven to dry for 2 hours at the temperature of 80 ℃ to obtain a modified ePTFE film;

s2, adding 30 parts by mass of hydrophobic silica aerogel powder into 300 parts by mass of deionized water, sequentially adding 5 parts by mass of span 80 as an emulsifier, 2 parts by mass of polyoxyethylene fatty alcohol ether as a wetting agent, 15 parts by mass of a copolymer of perfluoropropyl perfluorovinyl ether as a water-based adhesive and polytetrafluoroethylene and 1.5 parts by mass of silicon carbide as an infrared opacifier, putting the mixture into a ball milling tank, and carrying out ball milling at the speed of 300rpm for 5 hours to obtain uniformly dispersed aerogel water-based slurry;

s3, coating a 50-micron thick aerogel aqueous slurry wet film on the surface of the modified ePTFE film by using a coating machine, and drying the coated composite film in a vacuum oven at 80 ℃ for 2h to obtain filled ePTFE/SiO₂A composite film having a thickness of about 10 μm;

s4, mixing the above ePTFE/SiO₂Superposing 50 layers of the composite membrane, covering a layer of modified expanded polytetrafluoroethylene film, placing into a flat plate hot press, setting the temperature of the upper plate and the lower plate to 380 ℃, and hot-pressing under the pressure of 5Mpa for 10min for shaping to obtain ePTFE/SiO₂A heat insulating film 3.

ePTFE/SiO prepared in examples 1-3₂The heat insulation films 1 to 3 were subjected to film thickness, thermal conductivity and bending test tests, respectively, and the results are shown in table 1 below:

TABLE 1 thermal conductivity and dusting for the examples

Examples	Coefficient of thermal conductivity (W/mK)	100 times of bending
			1	0.026	Slight dusting
2	0.022	Does not fall off powder
			3	0.020	Does not fall off powder

As can be seen from the test results in Table 1, the SiO coating₂The heat conductivity coefficient of the aerogel rear composite film is obviously reduced and is lower than 0.03W/mK. Among them, example 1 is due to SiO₂The slurry solids content was too high (above 25 wt%), the coating was thick when coated, the ePTFE fibers and the binder did not completely fix all SiO₂The particles still have the phenomenon of bending and powder falling after the multiple layers are overlapped. SiO in example 2 and example 3₂Low slurry solid content, thin coating thickness, pore pair SiO in ePTFE membrane₂Has good adsorption effect, and can not fall off after being repeatedly bent. Although SiO in examples 1 to 3₂The solid content and the coating thickness are different, and the total thickness of the ePTFE/SiO film can be approximate even if the number of the layers is different₂A thermal barrier film. Under the condition that the thickness is close to each other, the number of the superposed layers is more in the embodiment 3, the better constraint effect on air thermal motion is achieved, and the heat insulation effect is better.

ePTFE/SiO prepared in examples 1-3₂SEM electron microscope tests are respectively carried out on the heat insulation films 1-3, and the structures are respectively shown in figures 3-5, wherein (a) is an SEM topographic map of the cross section of the film, and (b) is an SEM topographic map of the surface of the film. As can be seen from FIGS. 3 to 5, SiO₂Slurry materialWhen the solid content is too high and the coating thickness is too thick, the ePTFE membrane surface is loaded with excessive SiO₂Aerogel granule, particle size is great moreover, leads to the multilayer stack back interlamellar spacing too big, and the flexible variation of complex film, and buckle the back granule and easily drop. SiO 2₂The lower the solid content of the slurry, the lower the SiO₂The better the particle dispersion effect; pore pair SiO in ePTFE membrane with thinner coating thickness₂The better the adsorption effect, the smaller the interlayer spacing, so the multilayer film of the invention has better flexibility and avoids the phenomenon of powder falling.

It should be understood by those skilled in the art that the foregoing is only illustrative of several embodiments of the invention, and not of all embodiments. It should be noted that many variations and modifications are possible to those skilled in the art, and all variations and modifications that do not depart from the gist of the invention are intended to be within the scope of the invention as defined in the appended claims.

Claims

1. a preparation method of electronic grade flexible polytetrafluoroethylene thermal insulation film, is characterized in that, comprises the following steps:

S1, spray hydrophilic modifier on the surface of the expanded polytetrafluoroethylene film, followed by drying to obtain a modified expanded polytetrafluoroethylene film;

S2. Disperse the silica aerogel powder into deionized water, add an emulsifier, a wetting agent, a water-based adhesive, and an infrared shading agent, and then ball-mill and mix evenly to obtain a solid content of 5wt%-25wt%. Aqueous aerogel slurry with agent content of 3wt%-30wt%;

S3. Evenly coat the aerogel aqueous slurry prepared in step S2 on the upper surface of the modified expanded polytetrafluoroethylene film in step S1 to form a slurry layer, with a coating thickness of 50-1000 μm, and then at 110°C- Vacuum drying at 400°C for 10-60min to obtain ePTFE-SiO ₂ composite membrane;

S4. Take two or more layers of ePTFE-SiO ₂ composite membranes and superimpose them. During stacking, the modified expanded polytetrafluoroethylene film and the slurry layer are alternately arranged, and the modified expanded polytetrafluoroethylene thin film in the lowermost composite membrane face down, then cover a layer of the modified expanded polytetrafluoroethylene film of step S1 on the uppermost composite film, put the superimposed composite film into a hot press, at a temperature of 150-380 ° C, a pressure of 1 - Forming and hot pressing under 20MPa for 5-30min, after cooling, electronic-grade flexible PTFE thermal insulation film with thickness of 100μm-1000μm is obtained;

Wherein, steps S1 and S2 are in no particular order.

2. The preparation method of electronic-grade flexible polytetrafluoroethylene thermal insulation film according to claim 1, wherein the expanded polytetrafluoroethylene film described in step S1 is uniaxially stretched or biaxially stretched Porous PTFE film with a film thickness of 5-50μm.

3. The preparation method of electronic-grade flexible polytetrafluoroethylene thermal insulation film according to claim 2, characterized in that, the models of the hydrophilic modifiers described in step S1 are HS-220M, HS-830D, HS- One of 130TS and X-70M.

4. The preparation method of electronic-grade flexible polytetrafluoroethylene thermal insulation film according to claim 1, wherein the silicon dioxide aerogel powder, deionized water, emulsifier, wetting agent described in step S2 The mixing mass ratio of water-based adhesive and infrared sunscreen agent is (10-100):(100-900):(0.5-5.5):(1-3):(5-30):(0.2-2.5).

5 . The preparation method of electronic grade flexible polytetrafluoroethylene thermal insulation film according to claim 1 or 4 , wherein the silica aerogel powder is hydrophobic silica aerogel powder. 6 .

6. The preparation method of electronic-grade flexible polytetrafluoroethylene thermal insulation film according to claim 1 or 4, wherein the emulsifier described in step S2 is Tween 80, Span 80, OP10, Triton One or a combination of two or more.

7. The preparation method of electronic grade flexible polytetrafluoroethylene thermal insulation film according to claim 1 or 4, wherein the wetting agent described in step S2 is polyoxyethylene alkyl phenol ether, polyoxyethylene fat One or a combination of two or more of alcohol ether and polyoxyethylene polyoxypropylene block copolymer.

8. The preparation method of electronic-grade flexible polytetrafluoroethylene thermal insulation film according to claim 1 or 4, wherein the water-based adhesive described in step S2 is polyvinyl alcohol, water-based acrylate, water-based polyurethane, One or both of pure acrylic emulsion, aqueous perfluoroethylene propylene copolymer, copolymer of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer and combination of the above.

9. The preparation method of electronic-grade flexible polytetrafluoroethylene heat insulating film according to claim 1 or 4, wherein the infrared light-shielding agent described in step S2 is carbon black, titanium dioxide, potassium hexatitanate whisker, One or a combination of two or more of silicon carbide.

10. An electronic-grade flexible polytetrafluoroethylene thermal insulation film prepared by the preparation method of any one of claims 1-9.