Insulating film, preparation method thereof and application of insulating film in battery shell

Abstract

The invention relates to an insulating film, a preparation method thereof and an application of the insulating film in a battery shell. The insulating film comprises a first film layer and a second film layer which are stacked, the first film layer is obtained by photocuring first ink, and the second film layer is obtained by photocuring second ink; the first ink and the second ink both comprise photoinitiators, the photoinitiators comprise a long-wave photoinitiator and a short-wave photoinitiator, and the mass ratio of the long-wave photoinitiator in the first ink is larger than that of the long-wave photoinitiator in the second ink. The insulating film can be prepared by in-situ forming of the first ink and the second ink on the surfaces of to-be-protected objects with different sizes and shapes, the photocuring efficiency is high, the formed insulating film has high shear strength and better aging resistance, the thickness of the insulating protective film can be further improved, and the high-insulation application requirement is met.

Description

Technical Field

[0001] The present invention relates to the technical field of insulating films and batteries, and in particular to an insulating film and a preparation method thereof, and application thereof in a battery casing. Background Art

[0002] Lithium-ion batteries have the advantages of large specific capacity, high operating voltage, long cycle life, portability, safety, environmental protection, and low environmental pollution, and are widely used in various products. The surface of the conventional lithium-ion battery shell is covered with a layer of blue insulating protective film, which plays the role of insulating and protecting the battery cells, reducing the battery cells from bumps and scratches, and improving the impact buffering of the battery cells in the module. However, this type of blue film has poor shear force and insulation fireproofing effects, and its thermal conductivity is relatively low, which is not conducive to heat conduction on the surface of the battery cells. It is not conducive to cooling the battery cells during fast charging, and there are relatively large safety hazards. In addition, the blue film coating process is prone to poor coating phenomena such as bulging, which leads to a decrease in the yield rate. In addition, the blue film size and coating fixtures need to be redesigned for battery cells of different sizes. The process is cumbersome and costly.

[0003] Based on the defects of the existing blue film coating technology, a method of using UV printing ink to in-situ form an insulating film on the surface of the battery shell has been proposed. This method has no restrictions on the type and size of the battery shell, and can effectively improve production efficiency and reduce costs. The insulating film used for the battery shell has certain requirements for its thickness to ensure its buffering effect and insulation properties, that is, the thickness of the insulating film cannot be too thin. However, the coating formed by conventional UV printing ink cannot effectively promote the generation of free radicals by photoinitiators with a specific absorption wavelength range because the wavelength of ultraviolet light entering during the photocuring process will attenuate as the thickness of the coating increases. This leads to incomplete cross-linking reactions between the internal photocuring monomers, affecting the aging resistance of the printed insulating film. It is also impossible to improve the insulation performance of the insulating film by further increasing the thickness of the insulating film while ensuring the aging resistance of the insulating film. Summary of the Invention

[0004] To solve the above problems, the present invention provides an insulating film, a preparation method thereof, and an application in a battery casing. A first ink with a high content of long-wave photoinitiator is used to prepare the inner layer (first film layer) of the insulating film, and a second ink with a relatively low content of long-wave photoinitiator is used to prepare the outer layer (second film layer) of the insulating film. During the photocuring process, the attenuation of the light wavelength does not affect the curing effect of the inner layer, and is conducive to accelerating the photocuring efficiency. The formed insulating film not only has high shear strength and better anti-aging ability, but also can further increase the thickness of the insulating protective film to meet the application requirements of high insulation.

[0005] Specifically, the following technical solutions are provided:

[0006] A first aspect of the present invention provides an insulating film comprising a first film layer and a second film layer stacked together; the first film layer is obtained by photocuring a first ink, and the second film layer is obtained by photocuring a second ink;

[0007] The first ink and the second ink both contain photoinitiators, which include long-wave photoinitiators and short-wave photoinitiators. The mass proportion of the long-wave photoinitiator in the first ink is greater than the mass proportion of the long-wave photoinitiator in the second ink.

[0008] Furthermore, the thickness of the insulating film is preferably 50-500 μm, and the thickness of the first film layer is preferably 30%-55% of the total thickness of the insulating film; more preferably, the thickness of the insulating film is 60-500 μm, and the thickness of the first film layer is 30%-50% of the total thickness of the insulating film.

[0009] Furthermore, the maximum absorption wavelength of the long-wave photoinitiator is greater than the maximum absorption wavelength of the short-wave photoinitiator, wherein the absorption wavelength range of the long-wave photoinitiator is in the range of 260-480 nm, and the absorption wavelength range of the short-wave photoinitiator is in the range of 230-340 nm.

[0010] Furthermore, in the first ink, the long-wavelength photoinitiator accounts for 30%-85% of the total mass of the photoinitiator, and in the second ink, the long-wavelength photoinitiator accounts for 10%-40% of the total mass of the photoinitiator.

[0011] Furthermore, the first ink and the second ink both contain the following components in parts by mass: 0.5-20 parts of acrylate soft monomers, 1-40 parts of acrylate monomers containing multiple carbon-carbon double bonds, 0.5-20 parts of epoxy acrylates, 0.5-20 parts of flame retardant monomers, 0.5-10 parts of photoinitiators, 0.5-20 parts of low molecular weight acrylates, 0.5-20 parts of thermal conductive fillers, and 0.5-5 parts of nano-color pastes; preferably, the molecular weight of the low molecular weight acrylate is less than 120.

[0012] Furthermore, the acrylic soft monomer includes one or more of butyl acrylate, isooctyl acrylate, isopentyl acrylate and octyl acrylate.

[0013] Furthermore, the acrylic ester monomer containing multiple carbon-carbon double bonds includes one or more of trimethylol triacrylate, triethylol triacrylate, tributylol triacrylate, dimethylol diacrylate, diethylol diacrylate and dibutylol diacrylate.

[0014] Furthermore, the epoxy acrylate includes one or more of methyl-modified epoxy acrylate, ethyl-modified epoxy acrylate and propyl-modified epoxy acrylate.

[0015] Furthermore, the flame retardant monomer includes at least one of methyl metaphosphate modified acrylate and ethyl metaphosphate modified acrylate; such flame retardant monomers can be dispersed uniformly and stably.

[0016] Furthermore, the long-wave photoinitiator includes one or more of 2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester (absorption peak of 270-370nm), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (absorption peak of 269-393nm), and dibenzoyl (absorption peak of 300-480nm); the short-wave photoinitiator includes one or more of 2-methyl-2(4-morpholinyl)-1(4-(methylthio)phenyl)-1-propanone (absorption peak of 232-307nm), 1-hydroxycyclohexylphenyl ketone (absorption peak of 244-326nm), and 2-hydroxy-2methyl-1-phenylpropanone (absorption peak of 244-331nm).

[0017] Furthermore, the low molecular weight acrylate includes one or more of methyl acrylate, ethyl acrylate, and methyl methacrylate.

[0018] Furthermore, the thermally conductive filler includes one or more of silicon nitride, zinc oxide, silicon powder, boron nitride, aluminum oxide and magnesium oxide.

[0019] Furthermore, the first ink and the second ink both contain the following components in parts by mass: 1-20 parts of butyl acrylate, 1-20 parts of trihydroxymethyl triacrylate, 1-20 parts of dihydroxymethyl diacrylate, 1-20 parts of epoxy acrylate, 1-20 parts of metaphosphate-modified acrylate, 1-10 parts of photoinitiator, 1-20 parts of methyl acrylate, 1-20 parts of thermal conductive filler, and 1-5 parts of nano-color paste; and the long-wave photoinitiator in the first ink accounts for 35%-85% of the total mass of the photoinitiator, and the long-wave photoinitiator in the second ink accounts for 10%-35% of the total mass of the photoinitiator.

[0020] A second aspect of the present invention provides a method for preparing the insulating film according to the first aspect, comprising the following steps:

[0021] (1) providing a first ink and a second ink, UV printing the first ink to form a first UV printing layer, and then UV printing the second ink on the first UV printing layer to form a second UV printing layer;

[0022] (2) Curing treatment is performed under ultraviolet light to obtain the insulating film.

[0023] Furthermore, in step (1), in the UV printing step: the energy density of the ultraviolet light is 190.4-238mJ / cm2 .

[0024] Furthermore, in step (2), the energy density of the ultraviolet light is 26400-34000 mJ / cm 2 The curing temperature is 30-50°C and the curing time is 2-10s.

[0025] The third aspect of the present invention provides a battery casing, comprising a shell and an insulating film coated on the surface of the shell, wherein the insulating film is the insulating film described in the first aspect or the insulating film prepared by the preparation method described in the second aspect; the insulating film comprises a first film layer and a second film layer stacked, wherein the side of the first film layer away from the second film layer is in contact with the surface of the shell.

[0026] Furthermore, the first film layer is obtained by photocuring the first ink on the surface of the shell.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention provides an insulating film, which can be prepared by in-situ molding of first and second inks on the surface of an object to be protected of different sizes and shapes, wherein the inner layer (first film layer) of the insulating film is obtained by photocuring the first ink with a high content of long-wave photoinitiator, and the outer layer (second film layer) is obtained by photocuring the second ink with a relatively low content of long-wave photoinitiator. By utilizing the different proportions of long-wave and short-wave photoinitiators in different inks, the first ink located in the inner layer can still be efficiently cured when the wavelength of light is attenuated, thereby effectively improving the crosslinking degree and photocuring efficiency of the inner layer of the insulating film (the first film layer adhered to the battery shell).

[0029] The insulating film preparation method provided by the present invention is simple and efficient. The insulating film not only has high shear strength and better anti-aging ability, but also can further increase the thickness of the insulating protective film (the maximum printing thickness can be increased by at least 70%), meeting the application requirements of high insulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic structural diagram of an insulating film provided by the present invention;

[0031] Figure 2 A schematic structural diagram of a battery housing provided by the present invention;

[0032] Icon: 01 is the first film layer, 02 is the second film layer, and 1 is the shell. DETAILED DESCRIPTION

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the relevant listed items. The term "includes" or "comprising" described in the present invention means that in addition to the components described, it may also include or contain other components. The term "includes" or "comprising" described in the present invention may also be replaced by the closed form "for" or "consisting of..."

[0034] As described in the background technology, when a single UV printing ink is used to prepare an insulating film on the surface of a battery casing, the wavelength of the entering ultraviolet light during the photocuring process will attenuate as the coating thickness increases, and it is impossible to effectively promote the photoinitiator with a specific absorption wavelength range to produce free radicals, thereby resulting in incomplete cross-linking reaction between the photocurable monomers located in the bottom layer, and worsening the aging resistance of the insulating film; it is impossible to improve the insulating performance of the insulating film by further increasing the thickness of the insulating film while ensuring the aging resistance of the insulating film.

[0035] To solve the above problems, embodiments of the present invention provide an insulating film comprising a first film layer and a second film layer stacked together, wherein the first film layer is obtained by photocuring a first ink, and the second film layer is obtained by photocuring a second ink;

[0036] Both the first ink and the second ink contain photoinitiators, which include long-wave photoinitiators and short-wave photoinitiators. The mass proportion of the long-wave photoinitiator in the first ink is greater than the mass proportion of the long-wave photoinitiator in the second ink.

[0037] In order to solve the problems of low cross-linking degree of the bottom layer and poor aging performance of the insulating film when using a single UV printing ink to prepare the insulating film, and because the difference in light curing effect increases with the increase of the thickness of the insulating film, it is impossible to further increase the thickness of the insulating film to obtain a high-insulation protective film. Based on this, the present invention provides an insulating film, which is prepared by in-situ molding of first and second inks on the surface of an object to be protected (such as the surface of a battery shell), wherein the first ink is used to prepare the inner layer of the insulating film (first film layer), and the second ink is used to prepare the outer layer of the insulating film (second film layer). By controlling the content of the long-wave photoinitiator in the first ink to be greater than the long-wave photoinitiator in the second ink, during the photocuring process of the insulating film, the second ink located on the outside can effectively absorb short-wave ultraviolet light, promote the cross-linking and curing of monomers in the second ink to form a second film layer, and at the same time, as the ultraviolet light diffuses and the wavelength becomes longer in the thickness direction, a large amount of long-wave photoinitiator in the first ink located on the inside can effectively absorb the long wavelength, thereby decomposing to produce free radicals and promoting the full cross-linking of the bottom monomers, so that both the inside and the outside of the insulating film can be fully cured and cross-linked, thereby improving the aging resistance of the insulating film; and there is no need for full curing by layering, which improves the photocuring efficiency while being beneficial to the improvement of the bonding force between different film layers, further improving the aging resistance and insulation performance of the insulating film.

[0038] In the present invention, the first film layer of the insulating film is the inner film layer of the insulating film, and the second film layer is the outer film layer of the insulating film, wherein the side of the first film layer away from the second film layer is in contact with the surface of the object to be protected.

[0039] In the present invention, the thickness of the insulating film is preferably 50-500μm, and the thickness of the first film layer is preferably 30%-55% of the total thickness of the insulating film; more preferably, the thickness of the insulating film is 60-500μm, for example, 60μm, 80μm, 100μm, 150μm, 200μm, 250μm, 300μm, 350μm, 400μm, 450μm, 500μm, etc., including but not limited to the thickness values ​​listed above, and the thickness of the first film layer is 30%-50% of the total thickness of the insulating film, for example, 30%, 35%, 40%, 45%, 50%, etc.

[0040] In the present invention, the maximum absorption wavelength of the above-mentioned long-wave photoinitiator is greater than the maximum absorption wavelength of the above-mentioned short-wave photoinitiator, wherein the absorption wavelength range of the long-wave photoinitiator is in the range of 260-480nm, and the absorption wavelength range of the short-wave photoinitiator is in the range of 230-340nm.

[0041] In the present invention, the long-wave photoinitiator in the first ink accounts for 30%-85% of the total mass of the photoinitiator, for example, 30%, 40%, 50%, 60%, 70%, 80%, 85%, etc., including but not limited to the mass proportions listed above; the long-wave photoinitiator in the second ink accounts for 10%-40% of the total mass of the photoinitiator, for example, 10%, 20%, 30%, 40%, etc., including but not limited to the mass proportions listed above.

[0042] In the present invention, the first ink and the second ink both contain the following components in parts by mass: 0.5-20 parts of an acrylic acid ester soft monomer (e.g., 0.5 parts, 2 parts, 4 parts, 6 parts, 8 parts, 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts, etc., including but not limited to the parts listed), 1-40 parts of an acrylic acid ester monomer containing multiple carbon-carbon double bonds (e.g., 1 part, 4 parts, 8 parts, 12 parts, 16 parts, 20 parts, 24 parts), , 28 parts, 32 parts, 36 parts, 40 parts, etc., including but not limited to the parts listed), epoxy acrylate 0.5-20 parts (for example, 0.5 parts, 2 parts, 4 parts, 6 parts, 8 parts, 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts, etc., including but not limited to the parts listed), flame retardant monomer 0.5-20 parts (for example, 0.5 parts, 2 parts, 4 parts, 6 parts, 8 parts, 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts, etc., including but not limited to the parts listed), photoinitiator 0.5-10 parts (for example, 0.5 parts, 1 parts, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, etc., including but not limited to the parts listed), low molecular weight acrylate 0.5-20 parts (for example, 0.5 parts, 2 parts, 4 parts, 6 parts, 8 parts, 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts, etc., including but not limited to the parts listed), The present invention also comprises the following components: 1) 0.5-20 parts of thermal conductive filler (for example, 0.5 parts, 2 parts, 4 parts, 6 parts, 8 parts, 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts, etc., including but not limited to the parts listed), and 0.5-5 parts of nano color paste (for example, 0.5 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, etc., including but not limited to the parts listed); preferably, the molecular weight of the low molecular weight acrylate is less than 120.

[0043] In the present invention, the first ink and the second ink are mainly prepared from acrylate monomers, wherein the acrylate monomer containing multiple carbon-carbon double bonds forms a first cross-linked network with a three-dimensional network structure through carbon-carbon double bond free radical polymerization, and the introduced epoxy acrylate can further form a second cross-linked network through epoxy ring-opening reaction. Under the synergistic effect of the first and second cross-linked networks, the insulating film with high cross-linking density exhibits better aging resistance and insulation. At the same time, the first and second inks are improved by introducing an appropriate amount of acrylate soft monomers to improve the flexibility of the insulating film, so that the insulating film can better resist external stress and improve the stability of the electrical properties of the insulating film under deformation. In addition, based on the fact that the fireproof and thermal conductivity effects of the insulating film currently used on the surface of the battery shell are poor and the safety hazards are greater, the present invention introduces flame retardant monomers and conductive fillers into the first and second inks to improve the fireproof and thermal conductivity of the insulating film, and in order to improve the dispersibility of the conductive filler in the ink and the processability of the ink, the viscosity of the ink is reduced by introducing an appropriate amount of low molecular weight acrylate. Under the synergistic effect of the above components, the insulating film formed by the photocuring of the first and second inks not only has excellent anti-aging performance and insulation, but also has better fire resistance and thermal conductivity, and is particularly suitable for the protective film of the battery shell.

[0044] In the present invention, the acrylic soft monomer includes but is not limited to one or more of butyl acrylate, isooctyl acrylate, isopentyl acrylate and octyl acrylate.

[0045] In the present invention, the acrylic ester monomer containing multiple carbon-carbon double bonds includes but is not limited to one or more of trihydroxymethyl triacrylate, trihydroxyethyl triacrylate, trihydroxybutyl triacrylate, dihydroxymethyl diacrylate, dihydroxyethyl diacrylate and dihydroxybutyl diacrylate.

[0046] In the present invention, epoxy acrylate includes but is not limited to one or more of methyl-modified epoxy acrylate, ethyl-modified epoxy acrylate and propyl-modified epoxy acrylate, such as methyl-modified epoxy acrylate, methyl-modified epoxy acrylate, and ethyl-modified epoxy acrylate.

[0047] In the present invention, the flame retardant monomer includes at least one of methyl metaphosphate modified acrylate and ethyl metaphosphate modified acrylate, such as methyl metaphosphate modified methyl acrylate, methyl metaphosphate modified ethyl acrylate, etc. This type of flame retardant monomer is stably present in the insulating film through the polymerization reaction of carbon-carbon double bonds, and can be decomposed at high temperature to produce a covering, isolating the air and achieving a flame retardant effect.

[0048] In the present invention, the long-wave photoinitiator includes but is not limited to one or more of 2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester (absorption peak of 270-370nm), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (absorption peak of 269-393nm), and dibenzoyl (absorption peak of 300-480nm); the short-wave photoinitiator includes but is not limited to one or more of 2-methyl-2(4-morpholinyl)-1(4-(methylthio)phenyl)-1-propanone (absorption peak of 232-307nm), 1-hydroxycyclohexylphenyl ketone (absorption peak of 244-326nm), and 2-hydroxy-2methyl-1-phenylpropanone (absorption peak of 244-331nm).

[0049] In the present invention, the low molecular weight acrylate includes but is not limited to one or more of methyl acrylate, ethyl acrylate, and methyl methacrylate.

[0050] In the present invention, the thermally conductive filler includes, but is not limited to, one or more of silicon nitride, zinc oxide, silicon powder, boron nitride, aluminum oxide, and magnesium oxide.

[0051] In some preferred embodiments of the present invention, the first ink and the second ink both contain the following components in parts by mass: 1-20 parts of butyl acrylate, 1-20 parts of trimethylol triacrylate, 1-20 parts of dimethylol diacrylate, 1-20 parts of epoxy acrylate, 1-20 parts of metaphosphate-modified acrylate, 1-10 parts of photoinitiator, 1-20 parts of methyl acrylate, 1-20 parts of thermal conductive filler, and 1-5 parts of nano-color paste; and the long-wave photoinitiator in the first ink accounts for 35%-85% of the total mass of the photoinitiator, and the long-wave photoinitiator in the second ink accounts for 10%-35% of the total mass of the photoinitiator. For example, the long-wave photoinitiator is 2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester, the short-wave photoinitiator is 1-hydroxycyclohexyl phenyl ketone, the long-wave photoinitiator in the first ink accounts for 70% of the total mass of the photoinitiator, and the short-wave photoinitiator in the second ink accounts for 30% of the total mass of the photoinitiator.

[0052] The embodiments of the present invention further provide a method for preparing the above-mentioned insulating film, comprising the following steps:

[0053] (1) providing a first ink and a second ink, UV printing the first ink to form a first UV printing layer, and then UV printing the second ink on the first UV printing layer to form a second UV printing layer;

[0054] (2) Curing treatment is performed under ultraviolet light to obtain the insulating film.

[0055] In the present invention, during the UV printing process of step (1), the ink is printed while being irradiated with ultraviolet light for pre-curing to form a corresponding printed layer. In some preferred embodiments, during the UV printing step: the energy density of the ultraviolet light is 190.4-238 mJ / cm 2 .

[0056] In the present invention, in step (2), the energy density of the ultraviolet light is preferably 26400-34000 mJ / cm 2 The curing temperature is preferably 30-50°C, and the curing time is preferably 2-10s; depending on the thickness of the insulating film, the curing time can be appropriately adjusted to improve the degree of curing of the insulating film.

[0057] The embodiments of the present invention also provide a battery shell, including a shell and an insulating film coated on the surface of the shell. The insulating film is formed in situ on the surface of the battery shell by the above method, and includes a first film layer and a second film layer stacked together, wherein the side of the first film layer away from the second film layer is in contact with the surface of the shell.

[0058] The present invention will be further described below with reference to specific examples so that those skilled in the art can better understand the present invention and implement it, but the examples are not intended to limit the present invention.

[0059] Example 1

[0060] This embodiment relates to the preparation of an insulating film, and the specific operations are as follows:

[0061] Preparation of the first ink: 12 parts of butyl acrylate, 10 parts of trimethylol triacrylate, 12 parts of dimethylol diacrylate, 10 parts of methyl-modified epoxy acrylate, 15 parts of methyl metaphosphate-modified methyl acrylate, 4.2 parts of long-wave photoinitiator (ethyl 2,4,6-trimethylbenzoylphenylphosphonate), 1.8 parts of short-wave photoinitiator (1-hydroxycyclohexyl phenyl ketone), 16 parts of methyl acrylate, 16 parts of silicon nitride, and 3 parts of nano-color paste are added to a stirring tank and stirred for 45 minutes. After mixing evenly, the mixture is ball-milled for 2 hours in a ball mill, dispersed at high speed for 1 hour, and filtered through a 300-mesh filter to obtain the first ink.

[0062] Preparation of the second ink: 12 parts of butyl acrylate, 10 parts of trimethylol triacrylate, 12 parts of dimethylol diacrylate, 10 parts of methyl modified epoxy acrylate, 15 parts of methyl metaphosphate modified methyl acrylate, 1.8 parts of long-wave photoinitiator (2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester), 4.2 parts of short-wave photoinitiator (1-hydroxycyclohexyl phenyl ketone), 16 parts of methyl acrylate, 16 parts of silicon nitride, and 3 parts of nano-color paste are added to a stirring tank and stirred for 45 minutes. After mixing evenly, the mixture is ball-milled for 2 hours, dispersed at high speed for 1 hour, and filtered through a 300-mesh filter to obtain the second ink.

[0063] Preparation of insulating film:

[0064] The first UV printing layer is printed on the surface of the battery aluminum shell after laser cleaning using a UV printer. The printing thickness is 80 μm. Then, the second UV printing layer is printed on the first UV printing layer using a UV printer. The printing thickness is 120 μm. The thickness of the first UV printing layer accounts for 40% of the total printing layer thickness (during the UV printing process, ultraviolet rays will be used to pre-cure the two UV printing layers. The energy density of the ultraviolet light is 236.8 mJ / cm 2 ), and then irradiated with UV for 4s at 45°C for curing (the energy density of ultraviolet light is 28346mJ / cm 2 )

[0065] Example 2

[0066] This embodiment relates to the preparation of an insulating film, and the only difference from Example 1 is that the printing thickness of the first printed layer is 60 μm, the printing thickness of the second printed layer is 140 μm, and other operations are the same.

[0067] Example 3

[0068] This embodiment relates to the preparation of an insulating film, and the only difference from Example 1 is that the printing thickness of the first printed layer is 110 μm, the printing thickness of the second printed layer is 90 μm, and other operations are the same.

[0069] Example 4

[0070] This embodiment relates to the preparation of an insulating film, and the only difference from Example 1 is that the printing thickness of the first printed layer is 150 μm, the printing thickness of the second printed layer is 350 μm, the curing treatment time is increased to 6 s, and other operations are the same.

[0071] Example 5

[0072] This embodiment relates to the preparation of an insulating film. The only difference from Example 1 is that the long-wave photoinitiator (1.8 parts) in the first ink accounts for 30% of the total photoinitiator, and the long-wave photoinitiator (0.6 parts) in the second ink accounts for 10% of the total photoinitiator. Other operations are the same.

[0073] Example 6

[0074] This embodiment relates to the preparation of an insulating film. The only difference from Example 1 is that the long-wave photoinitiator (5.1 parts) in the first ink accounts for 85% of the total photoinitiator, and the long-wave photoinitiator (2.4 parts) in the second ink accounts for 40% of the total photoinitiator. Other operations are the same.

[0075] Comparative Example 1

[0076] This comparative example relates to the preparation of an insulating film. A UV printing layer is printed on the surface of a laser-cleaned battery aluminum shell using a commercially available UV printing ink (HP Colemans HSI-KL-04) using a UV printer. The printing thickness is 200 μm (during the UV printing process, ultraviolet light is used to pre-cure the two UV printing layers. The energy density of the ultraviolet light is 236.8 mJ / cm 2 ), and then irradiated with UV for 4s at 45°C for curing (the energy density of ultraviolet light is 28346mJ / cm 2 )

[0077] Comparative Example 2

[0078] This comparative example relates to the preparation of an insulating film, which differs from Example 1 only in that the printing thickness of the first printing layer is 20 μm, the printing thickness of the second printing layer is 180 μm, and other operations are the same.

[0079] Comparative Example 3

[0080] This comparative example relates to the preparation of an insulating film, which differs from Example 1 only in that the printing thickness of the first printing layer is 120 μm, the printing thickness of the second printing layer is 80 μm, and other operations are the same.

[0081] Comparative Example 4

[0082] This comparative example involves the preparation of an insulating film, and the only difference from Example 1 is that the long-wave photoinitiator (3 parts) in the first ink accounts for 50% of the total amount of the photoinitiator, and the long-wave photoinitiator (3 parts) in the second ink accounts for 50% of the total amount of the photoinitiator. Other operations are the same.

[0083] Comparative Example 5

[0084] This comparative example relates to the preparation of an insulating film, which differs from Example 1 only in that the first ink contains only long-wave photoinitiator (6 parts), and the second ink contains only short-wave photoinitiator (6 parts), and other operations are the same.

[0085] Performance Testing

[0086] The insulating films prepared in the above examples and comparative examples were subjected to shear strength, insulation performance, and aging resistance tests. The specific operations are as follows:

[0087] UV printed insulation film shear strength test: Cut the printed insulation cell shell into 25cm wide samples, gently peel off one end of the insulation film, and clamp it vertically on the tensile tester to test the shear strength between the insulation film and the aluminum shell at 180°. The shear strength test of UV printed insulation film is carried out according to GB / T 7124.

[0088] Insulation performance test of UV printed insulation film: High insulation tester test, DC voltage 1000V test for 5s, insulation resistance ≥ 1GΩ;

[0089] UV printed insulation film anti-aging performance test: The battery casing with the insulation film on the surface is placed in a temperature of 85°C and a humidity of 85% for 1000 hours, and the shear strength and insulation resistance of the insulation film are tested after standing.

[0090] The test results are shown in Table 1 below:

[0091] Table 1

[0092]

[0093] It can be seen from Table 1 that, compared with Comparative Example 1, the insulating films prepared in Examples 1-6 have higher shear strength, insulation resistance and better anti-aging performance. This is because the inner layer of the insulating film prepared in Examples 1-6, which is close to the surface of the aluminum shell, adopts the first printing ink formula, wherein the first UV printing ink contains a higher proportion of components containing long-wave photoinitiators, thereby ensuring that the UV printing ink can still be cured better when the wavelength of the UV light curing light attenuates (when UV printing the insulating film, the wavelength of UV ultraviolet light will become longer as the light diffuses in the thickness direction, and the efficiency of initiating cross-linking of different initiators within a specific wavelength range varies greatly. When the printing thickness is large, the initiation efficiency of the short-wave initiator in the bottom layer is significantly deteriorated), while the outer layer of the insulating film away from the surface of the aluminum shell adopts the second UV printing ink formula, wherein the second UV printing ink contains a higher proportion of photoinitiators with shorter wavelengths. In this way, the cross-linking degree of the entire insulating layer is higher in the thickness direction, and a denser cross-linking network can more significantly improve the insulation resistance of the insulating layer, but has little effect on the shear strength. In addition, a higher cross-linking network is beneficial to improving aging resistance and blocking external water vapor, oxygen, etc. from entering the interior of the insulating film, thereby reducing the shear strength of the insulating film after aging.

[0094] As shown in Examples 1, 2, and 3, as well as Comparative Examples 2 and 3, increasing the thickness of the first film layer (the inner layer near the aluminum shell) of the insulating film increases, the corresponding inner cross-linked network layer thickness increases, which is beneficial for improving the insulation resistance, residual insulation resistance, and shear strength of the insulating film after aging. Furthermore, the insulating performance and aging resistance are significantly improved compared to the insulating film prepared in Comparative Example 1 (containing only a short-wave initiator). Comparative Example 2 shows that when the thickness of the first film layer is too small, the overall insulation resistance improvement effect of the insulating film is relatively poor. When the thickness of the first film layer is too large (such as in Comparative Example 3), while it is beneficial for increasing the cross-linking density and improving the insulating performance of the insulating film, it can also lead to reduced flexibility of the insulating film and a corresponding decrease in shear strength.

[0095] As shown in Examples 1 and 4, as the total thickness of the insulating film increases, its total insulation resistance, residual insulation resistance after aging, and shear strength all significantly improve, and the shear strength does not significantly decrease compared to the thinner insulating film (Example 1). This shows that the insulating film preparation method provided by the present invention can produce an insulating film with both high shear strength and high insulation properties, meeting the application requirements of high insulation.

[0096] As shown in Examples 1, 5, and 6, as the content of the long-wavelength initiator in the first film layer (the inner layer near the aluminum shell) and the second film layer (the outer layer away from the aluminum shell) of the insulating film decreases, the insulation resistance, residual insulation resistance after aging, and shear strength of the insulating film all decrease to a certain extent. Specifically, the insulating film prepared in Example 6 contains a higher content of long-wavelength initiator in the first film layer, resulting in a higher degree of crosslinking in the inner layer. While this helps improve the resistance of the insulating layer, the excessive crosslinking density reduces the flexibility of the insulating film and reduces its shear strength.

[0097] It can be seen from Example 1 and Comparative Example 4 that the long-wave initiator added in the first film layer (inner layer close to the aluminum shell) and the long-wave initiator added in the second film layer (outer layer away from the aluminum shell) of the insulating film prepared in Comparative Example 4 are the same, the shear strength does not increase significantly, and the insulation performance and anti-aging performance are significantly deteriorated.

[0098] In addition, it can be seen from Example 1 and Comparative Example 5 that the long-wave initiator content in the first film layer of the insulating film prepared in Comparative Example 5 (the inner layer close to the aluminum shell) is too high, and the cross-linking density of the corresponding inner layer is too high, resulting in more obvious deterioration of the overall flexibility of the insulating film and a significant reduction in shear strength.

[0099] The above-described embodiments are merely preferred examples for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. An insulating film, characterized in that: The insulating film comprises a first film layer and a second film layer which are stacked; The first film layer is obtained by photocuring a first ink, and the second film layer is obtained by photocuring a second ink; the first ink and the second ink both contain photoinitiators, and the photoinitiators contain long-wave photoinitiators and short-wave photoinitiators, and the mass proportion of the long-wave photoinitiator in the first ink is greater than the mass proportion of the long-wave photoinitiator in the second ink.

2. The insulating film according to claim 1, wherein The thickness of the insulating film is 50-500 μm; The thickness of the first film layer is 30%-55% of the total thickness of the insulating film.

3. The insulating film according to claim 1, wherein The absorption wavelength range of the long-wave photoinitiator is within the range of 260-480 nm, and the absorption wavelength range of the short-wave photoinitiator is within the range of 230-340 nm.

4. The insulating film according to claim 1, wherein The long-wavelength photoinitiator in the first ink accounts for 30%-85% of the total mass of the photoinitiator, and the long-wavelength photoinitiator in the second ink accounts for 10%-40% of the total mass of the photoinitiator.

5. The insulating film according to claim 1 or 4, characterized in that Both the first ink and the second ink contain the following components in parts by mass: 0.5-20 parts of acrylate soft monomers, 1-40 parts of acrylate monomers containing multiple carbon-carbon double bonds, 0.5-20 parts of epoxy acrylates, 0.5-20 parts of flame retardant monomers, 0.5-10 parts of photoinitiators, 0.5-20 parts of low molecular weight acrylates, 0.5-20 parts of thermal conductive fillers, and 0.5-5 parts of nano-color pastes; the molecular weight of the low molecular weight acrylate is less than 120.

6. The insulating film according to claim 5, wherein The acrylic soft monomer includes one or more of butyl acrylate, isooctyl acrylate, isopentyl acrylate and octyl acrylate; The acrylic acid ester monomer containing multiple carbon-carbon double bonds includes one or more of trimethylol triacrylate, triethylol triacrylate, tributylol triacrylate, dimethylol diacrylate, diethylol diacrylate and dibutylol diacrylate; The epoxy acrylate includes one or more of methyl-modified epoxy acrylate, ethyl-modified epoxy acrylate and propyl-modified epoxy acrylate; The flame retardant monomer includes at least one of methyl metaphosphate modified acrylate and ethyl metaphosphate modified acrylate; The long-wavelength photoinitiator includes one or more of 2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and dibenzoyl; The short-wavelength photoinitiator includes one or more of 2-methyl-2(4-morpholinyl)-1(4-(methylthio)phenyl)-1-propanone, 1-hydroxycyclohexylphenyl ketone, and 2-hydroxy-2methyl-1-phenylpropanone; The low molecular weight acrylate includes one or more of methyl acrylate, ethyl acrylate, and methyl methacrylate; The thermally conductive filler includes one or more of silicon nitride, zinc oxide, silicon powder, boron nitride, aluminum oxide and magnesium oxide.

7. The insulating film according to claim 6, wherein The first ink and the second ink each contain the following components in parts by mass: 1-20 parts of butyl acrylate, 1-20 parts of trimethylol triacrylate, 1-20 parts of dimethylol diacrylate, 1-20 parts of epoxy acrylate, 1-20 parts of metaphosphate modified acrylate, 1-10 parts of photoinitiator, 1-20 parts of methyl acrylate, 1-20 parts of thermal conductive filler, and 1-5 parts of nano color paste; The long-wavelength photoinitiator in the first ink accounts for 35%-85% of the total mass of the photoinitiator, and the long-wavelength photoinitiator in the second ink accounts for 10%-35% of the total mass of the photoinitiator.

8. A method for preparing an insulating film according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) providing a first ink and a second ink, UV printing the first ink to form a first UV printing layer, and then UV printing the second ink on the first UV printing layer to form a second UV printing layer; (2) Curing treatment is performed under ultraviolet light to obtain the insulating film.

9. The preparation method according to claim 8, characterized in that In step (1), in the UV printing step: the energy density of the ultraviolet light is 190.4-238mJ / cm 2 ; In step (2), the energy density of the ultraviolet light is 26400-34000 mJ / cm 2 The curing temperature is 30-50°C and the curing time is 2-10s.

10. A battery casing, comprising a shell and an insulating film covering the surface of the shell, characterized in that: The insulating film is the insulating film according to any one of claims 1 to 7 or the insulating film prepared by the preparation method according to claim 8 or 9; The insulating film includes a first film layer and a second film layer which are stacked, wherein the side of the first film layer away from the second film layer is in contact with the surface of the housing.

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