Patent Description:
Currently, a screen of an electronic device is bonded to a housing of the electronic device by using glue, for example, the screen is directly bonded to a battery cover by using battery cover glue, or the screen is bonded to a middle frame of the electronic device by using caulking glue. In this solution, good bonding performance between a touch screen and glue is required, and good bonding performance between the middle frame of the electronic device or the battery cover and glue is also required, so as to prevent the touch screen of the integrated device and a glue line from falling off.

As one of materials for preparing the middle frame of the electronic device and the battery cover, plastic can make the electronic device lighter and thinner. Currently, a spraying process is usually used to decorate appearance of the plastic middle frame or battery cover, so that an ink layer including a priming coat, an effect layer, and a finish coat layer is formed on a plastic substrate. As an outermost protective coating, the finish coat layer has a high crosslinking degree and non-recoatability, resulting in poor bonding performance between the finish coat layer of the plastic middle frame or battery cover and glue.

To solve the technical problem of poor bonding performance between a plastic middle frame or battery cover and glue in an electronic device, embodiment of this application provides a finish coat composition according to the enclosed claim <NUM>. Advantageous features of the present invention are defined in the corresponding subclaims.

In the following, parts of the description and drawings referring to embodiments, which are not covered by the claims, are not presented as embodiments of the invention but as examples useful for understanding the invention.

In the finish coat composition according to this application, one or more of the acrylic resins and the polyurethane acrylate resins used as a film-forming substance(s) is/are crosslinked and cured with the acrylic monomer under the action of ultraviolet light to form a finish coat having good reliability and bonding performance, which can be used as a finish coat layer of a middle frame of an electronic device and a battery cover of an electronic device, and can have good bonding performance with glue without etching off the finish coat layer, thereby preventing a screen of the electronic device from falling off. Experimental results show that a shear strength between the finish coat according to this application and a PUR adhesive can reach <NUM> MPa or more.

In a typical embodiment of this application, the finish coat composition includes:.

The film-forming resin is polyurethane acrylate EB600; the acrylate monomer is tripropylene glycol diacrylate and dodecyl acrylate at a mass ratio of <NUM>:<NUM>; the photoinitiator is TPO and <NUM> at a mass ratio of <NUM>:<NUM>; the leveling agent is BYK373 and TEGO900 at a mass ratio of <NUM>:<NUM>; the solvent is acetone and n-butanol at a volume ratio of <NUM>:<NUM>; and the matting powder is fumed silica or precipitated silica.

The finish coat composition in the foregoing embodiment has an excellent shear strength, can directly replace a finish coat used at a current ink layer, and can bond step glue to a middle frame or a battery cover without changing a process for producing the middle frame or the battery cover or etching off the ink layer, thereby preventing a touch screen of the integrated device and a glue line from falling off, and improving reliability of an electronic device.

According to another aspect, an embodiment of this application further provides a composite material, including:.

The foregoing composite material may be made into a middle frame of an electronic device or a battery cover of an electronic device. As an outermost layer of the middle frame or the battery cover, the finish coat layer can be bonded to a screen by using glue without etching, thereby preventing a touch screen of the integrated device and a glue line from falling off, and prolonging the service life of electronic device. In addition, as the outermost layer of the middle frame or the battery cover, the finish coat layer has good reliability.

To describe technical methods in embodiments of this application more clearly, the following briefly describes accompanying drawings required for describing embodiments.

The following clearly and completely describes technical solutions in embodiments of this application with reference to accompanying drawings in embodiments of this application. As used in the specification and the appended claims of this application, the terms "one", "a/an", "said", "the", and "this" of singular forms are also intended to include, for example, the form of "one or more", unless otherwise specified in the context clearly. It should be further understood that in embodiments of this application, "one or more" means one, two, or more than two; and the term "and/or" in this specification is only an associative relationship for describing associated objects, indicating that three relationships may exist. For example, A and/or B may represent the following three cases: Only A exists, both A and B exist, and only B exists, where A and B may be singular or plural. The character "/" generally indicates an "or" relationship between associated objects.

Referring to "one embodiment" or "some embodiments" or the like described in this specification means that one or more embodiments of this application include a specific feature, structure, or characteristic described with reference to the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", and the like appearing at different locations in this specification do not mean that these embodiments are all necessarily referred to, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways.

"A plurality of' described in embodiments of this application means two or more. It should be noted that in the description of embodiments of this application, words such as "first" and "second" are merely used for distinguishing in the description, cannot be understood as indicating or implying relative importance, and cannot be understood as indicating or implying a sequence.

The orientation words such as "up", "down", "inner", and "outer" described in embodiments of this application are relative. It can be understood by a person skilled in the art that when the direction is changed, the orientation changes accordingly.

Reliability described in embodiments of this application includes tests of adhesion, RCA paper tape wear resistance, alcohol friction, rubber friction, vibration friction, pencil hardness, stain resistance, Newton hardness tester, micro Vickers hardness, cosmetic resistance, hand sweat resistance, low-temperature storage, high-temperature storage, alternating damp heat, temperature shock, solar radiation, salt spray, boiling, and the like.

Bonding performance described in embodiments of this application refers to bonding performance between bonding surfaces, which is indicated by a shear strength in this application.

This application is described by using a mobile phone as an example. <FIG> is a schematic diagram of a typical structure of a mobile phone, and <FIG> is a schematic diagram of a structure of a surface A-A of the mobile phone shown in <FIG>, where <NUM> indicates a middle frame, <NUM> indicates a display module, <NUM> indicates a touch/display module, and <NUM> indicates step glue.

The mobile phone <NUM> includes the middle frame <NUM>, where the middle frame <NUM> has a bottom surface and a side surface, so that the inside of the middle frame <NUM> forms an accommodating space for accommodating the display module <NUM> and the touch/display module <NUM>, and the touch/display module <NUM> is arranged above the display module <NUM>. The top of the middle frame <NUM> is provided with a groove, so that an inner side surface of the middle frame <NUM> forms a two-stage step structure; and the touch/display module <NUM> is bonded to the first-stage step of the middle frame <NUM> by using the step glue <NUM>, so that the touch/display module <NUM> and the middle frame <NUM> form a sealed space.

A laminated structure of the middle frame <NUM> includes a plastic substrate layer <NUM> and an ink layer <NUM>. The ink layer <NUM> usually has a laminated structure, and includes a base coat layer, an effect layer, and a finish coat layer that are in contact with the plastic substrate layer <NUM> and that are sequentially laminated. As an outermost layer of the middle frame <NUM>, the finish coat layer features a high crosslinking degree, non-recoatability, and the like. To increase an adhesive force between the step glue <NUM> and the plastic substrate layer <NUM>, the ink layer at a contact part between the step glue <NUM> and the plastic substrate layer <NUM> is usually etched off, but the plastic substrate layer has low surface affinity, which leads to poor bonding performance with the step glue.

Based on this, an embodiment of this application provides a finish coat composition. In addition to meeting performance such as wear resistance and stain resistance required by an outermost layer of a middle frame, the finish coat composition further has a certain adhesive force, so that good bonding performance between the step glue <NUM> and the ink layer <NUM> can be achieved without etching off the ink layer of the step glue <NUM>, thereby preventing the screen of the electronic device from falling off.

The finish coat composition according to this application includes:.

The finish coat composition according to this application includes the film-forming resin, where the film-forming resin is one or more selected from acrylic resins and the polyurethane acrylate. After the acrylic resin and the polyurethane acrylate as main film-forming substances in the finish coat composition are cured and crosslinked with the acrylic monomer, the obtained finish coat not only has good performance such as wear resistance, stain resistance, and cosmetic resistance, but also has good bonding performance. In an embodiment, the acrylic resin is at least one selected from tetrafunctional modified acrylic resins, and the tetrafunctional modified acrylic resin includes, but is not limited to, EB810, Changxing <NUM>, and the like. In an embodiment, the polyurethane acrylate is at least one selected from hexafunctional aliphatic polyurethane acrylates, and the hexafunctional aliphatic polyurethane acrylate includes, but is not limited to, models such as ST8106, EB600, EB145, EB524, and CN966J5. In an embodiment, the content of the film-forming resin is <NUM>~<NUM> parts by mass. In an embodiment, the content of the film-forming resin is <NUM>~<NUM> parts by mass.

The finish coat composition according to this application includes an acrylate monomer, and the acrylate monomer is used to be cured and crosslinked with the acrylic resin or polyurethane acrylate to improve performance of the obtained finish coat. In an embodiment, the acrylate monomer is one or more selected from acrylate monomers or modified acrylate monomers, and the acrylate monomer include, but is not limited to, tripropylene glycol diacrylate (TPGDA), <NUM>,<NUM>-hexanediol diacrylate (HDDA), trimethylolpropane triacrylate (TMP-TA), hydroxypropyl acrylate, hydroxyethyl acrylate, dodecyl acrylate (LA), and the like. In an embodiment, the acrylic monomer is a mixture of tripropylene glycol diacrylate and dodecyl acrylate. In an embodiment, the tripropylene glycol diacrylate and the dodecyl acrylate are at a mass ratio of (<NUM>~<NUM>):(<NUM>~<NUM>). In an embodiment, the tripropylene glycol diacrylate and the dodecyl acrylate are at a mass ratio of <NUM>:<NUM>. In an embodiment, the content of the acrylate monomer is <NUM>~<NUM> parts by mass. In an embodiment, the content of the acrylate monomer is <NUM>~<NUM> parts by mass.

The finish coat composition according to this application includes a photoinitiator, and the photoinitiator is used to initiate curing and crosslinking of the film-forming resin and the acrylic monomer under the action of ultraviolet light (UV). The photoinitiator includes, but is not limited to, Darocur <NUM>, TPO, Irgacure <NUM>, Irgacure <NUM>, and the like. In an embodiment, the photoinitiator is one or more of Darocur <NUM>, TPO, Irgacure <NUM>, or Irgacure <NUM>. In an embodiment, the photoinitiator is a mixture of TPO and Irgacure <NUM>. In an embodiment, the TPO and the Irgacure <NUM> are at a mass ratio of (<NUM>~<NUM>):(<NUM>~<NUM>). In an embodiment, the TPO and the Irgacure <NUM> are at a mass ratio of <NUM>:<NUM>. In an embodiment, the content of the photoinitiator is <NUM>~<NUM> parts by mass. In an embodiment, the content of the photoinitiator is <NUM>~<NUM> parts by mass.

The finish coat composition according to this application includes a leveling agent, and the leveling agent is used to make the obtained finish coat flat, smooth, and uniform. In an embodiment, the leveling agent includes at least a silicone leveling agent. In an embodiment, the leveling agent includes a silicone leveling agent and a polyacrylate leveling agent, where the content of the silicone leveling agent is not less than <NUM>%. In an embodiment, the silicone leveling agent is selected from TEGO900, TEGO920, or BYK373. In an embodiment, the leveling agent is a mixture of BYK373 and TEGO900. In an embodiment, the BYK373 and the TEGO900 are at a mass ratio of (<NUM>~<NUM>):<NUM>. In an embodiment, the BYK373 and the TEGO900 are at a mass ratio of <NUM>:<NUM>. In an embodiment, a usage of the leveling agent is <NUM>~<NUM> parts by mass. In an embodiment, a usage of the leveling agent is <NUM>~<NUM> parts by mass.

As a solvent-based finish coat composition, the finish coat composition according to this application includes a solvent, and the solvent is used to dissolve each component as a medium and make the components cured and crosslinked under the action of ultraviolet light and the photoinitiator. In an embodiment, the solvent is a mixed solvent, which is any two or more selected from acetone, n-butanol, ethylene glycol-butadiene, and ethyl acetate. In an embodiment, the solvent is acetone and n-butanol. In an embodiment, the solvent is acetone and ethylene glycol-butadiene. In an embodiment, the solvent is acetone and ethyl acetate. In an embodiment, the solvent is n-butanol and ethylene glycol-butadiene. In an embodiment, the solvent is n-butanol and ethyl acetate. In an embodiment, the solvent is ethylene glycol-butadiene and ethyl acetate. In an embodiment, the solvent is acetone, n-butanol, and ethylene glycol-butadiene. In an embodiment, the solvent is acetone, n-butanol, and ethyl acetate. In an embodiment, the solvent is n-butanol, ethylene glycol-butadiene, and ethyl acetate. In an embodiment, the solvent is acetone, n-butanol, ethylene glycol-butadiene, and ethyl acetate. In this application, no special limitation is imposed on the usage of each component in the solvent. In a two-component solvent, a mass ratio of two components is (<NUM>~<NUM>):(<NUM>~<NUM>); in a three-component solvent, a mass ratio of three components is (<NUM>~<NUM>):(<NUM>~<NUM>):(<NUM>~<NUM>); and in a four-component solvent, a mass ratio of four components is (<NUM>~<NUM>):(<NUM>~<NUM>):(<NUM>~<NUM>):(<NUM>~<NUM>). In an embodiment, a usage of the solvent is <NUM>~<NUM> parts by mass.

The finish coat composition according to this application may further include a matting agent, so that the finish coat formed after curing has a matte effect. In an embodiment, the matting agent is a silica matting agent, such as an organic modified chemically-precipitated silica or fumed silica matting agent, and no matting wax slurry can be used. In an embodiment, the matting agent has a particle size <NUM>~<NUM> micrometer (microns). In an embodiment, a usage of the matting agent is <NUM>~<NUM> parts by mass.

In an embodiment, the finish coat composition according to this application includes:.

The finish coat composition according to this application can be crosslinked and cured under an action of ultraviolet light to form a finish coat having good reliability and bonding performance, which can be used as a finish coat layer of a middle frame of an electronic device and a battery cover of an electronic device. Experimental results show that a shear strength between the finish coat according to this application and a PUR adhesive can reach <NUM> MPa or more.

This application further provides a composite material, including:.

<FIG> is a schematic diagram of a structure of a composite material according to an embodiment of this application, where <NUM> indicates a plastic substrate layer, and <NUM> indicates a finish coat layer.

In the composite material, as a supporting material, the plastic substrate layer <NUM> has performance such as high strength and high modulus. In an embodiment, the material of the plastic substrate layer <NUM> includes, but is not limited to, polycarbonate (PC), nylon (PA), glass fiber-modified nylon (PA+GF), glass fiber-modified polycarbonate (PC+GF), aramid fiber-modified polycarbonate (AF+PC), and the like.

The finish coat layer <NUM> is composited on the surface of the plastic substrate layer <NUM>, has good wear resistance, chemical resistance, stain resistance, and the like as an outer protective layer, and has good bonding performance as a bonding surface, thereby improving bonding performance of the composite material. The finish coat layer is obtained by crosslinking and curing the foregoing finish coat composition. Details are not described herein again in this application.

In another embodiment, the composite material further includes a base coat layer composited between the plastic substrate layer <NUM> and the finish coat layer <NUM>, and the base coat layer is used to improve a bonding strength between the plastic substrate layer <NUM> and the finish coat layer <NUM>. In this application, no special limitation is imposed on the components of the base coat layer and content thereof.

In another embodiment, the composite material further includes an effect layer composited between the base coat layer and the finish coat layer <NUM>, and the effect layer can be formed at the base coat layer by using a method such as coating, electroplating, laser etching, and chemical deposition, so that the composite material has special optical or other appearance effects, such as matte and glare effects. In this application, no special limitation is imposed on the components of the effect layer and content thereof, and a method for preparing the effect layer. For example, an effect layer may be formed through non conductive vacuum metallization (NCVM).

The composite material according to this application may be used to produce a middle frame, battery cover or another housing assembly of an electronic device, which is bonded to a touch screen by using glue. A good bonding capability of the finish coat layer <NUM> can improve a bonding capability between the touch screen and the finish coat layer, thereby preventing the touch screen or a glue line from falling off.

Based on this, this application further provides a middle frame of an electronic device, and a laminated structure of the middle frame includes:.

This application further provides a battery cover of an electronic device, and a laminated structure of the battery cover includes:.

In this application, the mobile phone is used as an example to describe the middle frame of an electronic device, the battery cover of an electronic device, and the electronic device in detail. However, it can be understood that the electronic device in this application may be any device with communication and storage functions, such as a smartphone, a cellular phone, a cordless phone, a session initiation protocol (Session Initiation Protocol, SIP) phone, a tablet computer, a personal digital assistant (Personal Digital Assistant, PAD), a notebook computer, a digital camera, an e-book reader, a portable multimedia player, a handheld device with a wireless communication function, a computing device or another processing device connected to a wireless modem, an in-vehicle device, a wearable device, and a <NUM> terminal device, which is not limited in embodiments of this application.

<FIG> are schematic diagrams of structures of a mobile phone and a cross section thereof according to Embodiment <NUM> of this application, where <FIG> is a schematic diagram of a structure of a mobile phone according to Embodiment <NUM> of this application, and <FIG> is a schematic diagram of a structure of a cross section A-A of the mobile phone shown in <FIG>. <NUM> indicates a middle frame, <NUM> indicates a display module, <NUM> indicates a touch/display module, and <NUM> indicates step glue.

The mobile phone <NUM> includes the middle frame <NUM>, where the middle frame <NUM> has a bottom surface and a side surface, so that the inside of the middle frame <NUM> forms an accommodating space for accommodating the display module <NUM> and the touch/display module <NUM>, and the touch/display module <NUM> is arranged above the display module <NUM>. The middle frame <NUM> is provided with a groove, so that an inner side surface forms a two-stage step structure, and the touch/display module <NUM> is bonded to the first-stage step of the middle frame <NUM> by using the step glue <NUM>, so that the touch/display module <NUM> and the middle frame <NUM> form a sealed space.

The middle frame <NUM> includes a plastic substrate layer <NUM> and an ink layer <NUM> disposed at the plastic substrate layer <NUM>. The ink layer <NUM> is disposed on an outer surface and an upper surface of the plastic substrate layer <NUM>, and a bottom surface and a side surface of the groove, or may be disposed on an inner bottom surface and an inner side surface of the middle frame <NUM>.

In this embodiment, a laminated structure of the middle frame <NUM> is shown in <FIG> is a schematic diagram of a laminated structure of a middle frame according to Embodiment <NUM> of this application. In <FIG>, <NUM> indicates a plastic substrate layer for forming the middle frame, <NUM> indicates a base coat layer formed on the plastic substrate <NUM>, <NUM> indicates an effect layer formed at the base coat layer <NUM>, and <NUM> indicates a finish coat layer formed at the effect layer <NUM>. The base coat layer <NUM>, the effect layer <NUM>, and the finish coat layer <NUM> are the ink layer <NUM>.

The plastic substrate layer <NUM> is a main material for forming the middle frame, features high modulus, high strength, and the like, and may be polycarbonate (PC), nylon (PA), glass fiber-modified nylon (PA+GF), glass fiber-modified polycarbonate (PC+GF), aramid fiber-modified polycarbonate (AF+PC), and the like.

The base coat layer <NUM> may be formed at the plastic substrate layer <NUM> through coating, and can form strong interface bonding with the plastic substrate layer <NUM>, thereby increasing reliability of a mobile phone. In this application, no special limitation is imposed on the components of the base coat layer <NUM> and content thereof.

The effect layer <NUM> can be formed at the base coat layer <NUM> by using a method such as coating, electroplating, laser etching, and chemical deposition, to achieve an effect required for the middle frame appearance, especially a frame, such as matte and glare. In this application, no special limitation is imposed on the components of the effect layer and content thereof, and a method for preparing the effect layer. For example, an effect layer may be formed through non conductive vacuum metallization (NCVM).

The finish coat layer <NUM> is formed at the effect layer <NUM> through coating, which can enhance performance such as wear resistance and hardness of the middle frame, and increase bonding performance of the middle frame, so that the middle frame can be closely bonded to step glue without other treatments, thereby reducing a risk of degumming and falling off of a display. The finish coat layer <NUM> is formed by curing and crosslinking the finish coat composition in the foregoing technical solution. Details are not described herein again in this application.

In another embodiment, the laminated structure of the middle frame <NUM> may be provided with no base coat layer, no effect layer, or neither the base coat layer nor the effect layer, which does not affect the finish coat layer of the middle frame <NUM> having high reliability and bonding capability.

In this embodiment, the middle frame <NUM> is bonded to the touch/display module <NUM> by using the step glue <NUM>, and the step glue <NUM> may be a moisture-curing polyurethane reactive hot melt adhesive (PUR adhesive) as an adhesive. A good bonding capability is achieved between the finish coat composition in the foregoing solution and the PUR adhesive, which can improve bonding performance between a screen and the middle frame.

In another embodiment, the middle frame may be bonded to the display module and the touch/display module by using side caulking glue. <FIG> are schematic diagrams of structures of a mobile phone and a cross section thereof according to Embodiment <NUM> of this application, where <FIG> is a schematic diagram of a structure of a mobile phone according to Embodiment <NUM> of this application, and <FIG> is a schematic diagram of a structure of a cross section B-B of the mobile phone shown in <FIG>. <NUM> indicates a middle frame, <NUM> indicates a display module, <NUM> indicates a touch/display module, <NUM> indicates a double-sided adhesive, <NUM> indicates side sealing glue, <NUM> indicates inner caulking glue, and <NUM> indicates side caulking glue.

The mobile phone <NUM> includes the middle frame <NUM>, where the middle frame <NUM> has a bottom surface and a side surface, so that the inside of the middle frame <NUM> forms an accommodating space for accommodating the display module <NUM> and the touch/display module <NUM>, and the touch/display module <NUM> is arranged above the display module <NUM>. The bottom of the display module <NUM> is bonded to an inner bottom surface of the middle frame <NUM> by using the double-sided adhesive <NUM>, and a side surface of the display module <NUM> and a side surface of the touch/display module <NUM> form a closed space with an inner side surface of the middle frame <NUM> by using the side sealing glue <NUM>, the inner caulking glue <NUM>, and the side caulking glue <NUM>.

The middle frame <NUM> includes a plastic substrate layer and an ink layer <NUM> disposed at the plastic substrate layer <NUM>. The ink layer <NUM> is disposed on an outer surface, an upper surface, and the inner side surface of the middle frame, and a part where the inner bottom surface is bonded to the inner caulking glue <NUM>, and may also be disposed at a part where the inner bottom surface of the middle frame is not bonded to the inner caulking glue <NUM>. The laminated structure of the middle frame <NUM> is the same as that of the middle frame <NUM> described above. Details are not described herein again in this application.

In Embodiment <NUM>, the double-sided adhesive <NUM> is used to increase the bonding capability between the middle frame <NUM> and the display module <NUM>, and may be a pressure-sensitive adhesive with a three-layer structure of acrylic adhesive/foam/acrylic adhesive.

The inner caulking glue <NUM> is used to fill a gap between the bottom of the display module <NUM> and the inner side surface of the middle frame <NUM>, the side caulking glue <NUM> is used to fill the side surface of the display module <NUM> to achieve the same width as the touch/display module <NUM>, and the side caulking glue <NUM> is used to fill a gap between the inner side surface of the middle frame <NUM> and both the touch/display module <NUM> and the side sealing glue <NUM>, thereby forming a closed space. In this embodiment, the side sealing glue <NUM>, the inner caulking glue <NUM>, and the side caulking glue <NUM> may be PUR adhesives. A good bonding capability is achieved between the finish coat composition in the foregoing solution and the PUR adhesive, which can improve bonding performance between a screen and the middle frame.

This application further provides a battery cover. <FIG> are schematic diagrams of structures of a mobile phone and a cross section thereof according to Embodiment <NUM> of this application, where <FIG> is a schematic diagram of a structure of a mobile phone according to Embodiment <NUM> of this application, and <FIG> is a schematic diagram of a structure of a cross section C-C of the mobile phone shown in <FIG>. <NUM> indicates a middle frame, <NUM> indicates a display module, <NUM> indicates a touch/display module, and <NUM> indicates battery cover glue.

The mobile phone <NUM> includes the battery cover <NUM>, where the battery cover <NUM> has a bottom surface and a side surface, so that the inside of the middle frame <NUM> forms an accommodating space for accommodating the display module <NUM> and the touch/display module <NUM>, and the touch/display module <NUM> is arranged above the display module <NUM>. The top of the battery cover <NUM> is provided with a groove, so that an inner side surface of the middle frame <NUM> forms a two-stage step structure; and the touch/display module <NUM> is bonded to the first-stage step of the battery cover <NUM> by using the battery cover glue <NUM>, so that the touch/display module <NUM> and the battery cover <NUM> form a sealed space.

The battery cover <NUM> includes a plastic substrate layer <NUM> and an ink layer <NUM> disposed at the plastic substrate layer <NUM>. The ink layer <NUM> is disposed on an outer surface and an upper surface of the plastic substrate layer <NUM>, and a bottom surface and a side surface of the groove, or may be disposed on an inner bottom surface and an inner side surface of the battery cover <NUM>. The laminated structure of the battery cover <NUM> is the same as that of the middle frame <NUM> described above. Details are not described herein again in this application.

The finish coat composition according to this application can directly replace a finish coat used at a current ink layer, and there is no need to change a process for producing the middle frame or the battery cover, and there is no need to etch off the ink layer.

The finish coat composition, the composite material, the middle frame of an electronic device, the battery cover of an electronic device, the housing of an electronic device, and the electronic device according to this application are further described below with reference to embodiments.

In the following embodiments, polyurethane acrylate is EB600; an acrylate monomer is a mixture of tripropylene glycol diacrylate (TPGDA) and dodecyl acrylate (LA) at a ratio of <NUM>:<NUM>; a photoinitiator is a mixture of TPO and <NUM> at a ratio of <NUM>:<NUM>; a leveling agent is a mixture of acrylic polyester-modified polysiloxane BYK373 and TEGO900 at a ratio of <NUM>:<NUM>; a solvent is acetone and n-butanol at a volume ratio of <NUM>:<NUM>; and matting powder is fumed silica or precipitated silica.

A finish coat composition includes the following components:.

A middle frame prepared from glass fiber-modified nylon (PA) sequentially undergoes spraying to form a base coat, and electroplating of an NCVM layer to form an effect layer, then the foregoing finish coat composition is coated, and a finish coat is obtained after ultraviolet curing.

Reliability tests were performed on the finish coat compositions according to Embodiments <NUM>~<NUM>, with results shown in Table <NUM>. Table <NUM> shows the reliability test results of the finish coat compositions according to embodiments of this application.

In Table <NUM>, the performance test methods are as follows:.

<NUM>×<NUM> small grids with a size of <NUM>×<NUM> were scribed on a surface of each test sample, and each scribed line should be as deep as a bottom layer of a coating; an adhesive tape with an adhesive force of (<NUM>±<NUM>) N/<NUM> was used to firmly bond the tested small grids, and the tape was squeezed with nails (note that nails should not destroy the adhesive tape) to expel air bubbles between the adhesive tape and the coating, so as to increase a contact area and strength between the adhesive tape and a tested area. After the sample stood for (<NUM>±<NUM>)s, an end of the adhesive tape was grabbed by hand, to pull off the adhesive tape in a reverse direction of <NUM> within <NUM>~<NUM>, and the test was performed once. After the test, a 5x magnifying glass was used to check a falling off status of the paint coating.

To-be-tested samples were covered with alcohol with a concentration greater than <NUM>% for <NUM> minutes, and then stored at a laboratory temperature for <NUM> hours. Minimum quantity of samples: <NUM> pcs.

Glass: An eraser No. <NUM>/<NUM> was used, and a force of <NUM> was applied, with a speed of <NUM> cycles/min, and a test stroke of <NUM>.

Mylar: A wear-resistant test eraser FABER-CASTELL7017R was used, and a force of <NUM> was applied, with a speed of <NUM> cycles/minute, and a test stroke of <NUM>.

An R180/<NUM> TE-<NUM> vibration friction tester was used, and a single housing/card tray was tested for <NUM> hours.

CG class: A <NUM> test pencil lead was used, and <NUM> strokes were scribed at a to-be-tested position with a pressure of <NUM> gf and an angle between the pencil lead and a to-be-tested surface being <NUM>°, with each stroke <NUM> long.

Mylar coating class: Test method <NUM>: A <NUM> test pencil lead was used, and five strokes were scribed at a to-be-tested position with a pressure of <NUM> gf and an angle between the pencil lead and a to-be-tested surface being <NUM>°, with each stroke being <NUM> long; test method <NUM>: An HB test pencil lead was used, and five strokes were scribed at a to-be-tested position with a pressure of <NUM> gf and an angle between the pencil lead and a to-be-tested surface being <NUM>°, with each stroke being <NUM> long.

Vaseline special-effect moisturizing lotion (dry-skin moisturizing formula) was applied on a surface of each to-be-tested sample, and two alternating damp heat cycles was performed (<NUM> hours).

The surface of each sample was wiped gently for <NUM> minutes with a dust-free cloth soaked in sweat, and the sample stood at a normal temperature for <NUM> hours.

Samples were kept for <NUM> hours at a temperature of -<NUM> and an incubator temperature change rate of <NUM>/minute.

Samples were kept for <NUM> hours at a temperature of <NUM> and an incubator temperature change rate of <NUM>/minute.

Samples were tested at a temperature of <NUM>~<NUM> and a humidity of <NUM>%±<NUM>% for a total of <NUM> (<NUM> cycles), with each cycle lasting for <NUM> hours; and the samples were kept at <NUM> and <NUM>%RH for <NUM> hours.

At -<NUM>/<NUM>, samples were kept for <NUM> hour at each temperature point, and the temperature was quickly switched within <NUM> minutes, with a total of <NUM> cycles for <NUM> hours. After an environmental test was completed, the coating surface needed to undergo an adhesion test.

A test with one cycle lasting for <NUM> hours was performed. Specifically, samples were kept for <NUM> hours at dry heat of <NUM> and a solar radiation intensity of <NUM> W/m<NUM>, and then a solar radiation source was off for <NUM> hours, with one test cycle including <NUM> cycles.

Sample were boiled for <NUM> minutes with purified water at <NUM>±<NUM>. After being kept at normal temperature for <NUM>, the samples underwent the adhesion test.

It can be learned from Table <NUM> that the finish coat composition according to this application has relatively high reliability.

Bonding strength testing was performed on the finish coat compositions in Embodiments <NUM> to <NUM>, and a shear strength was tested based on a method provided in GB/T-<NUM>-<NUM>. The specific method is as follows:.

A testing device is shown in <FIG> shows a testing device according to an embodiment of this application. The testing device includes: a clamp <NUM> for fixing a first polycarbonate (PC) sheet <NUM>, where an end of the first PC sheet <NUM> far from the clamp <NUM> is coated with a cured finish coat <NUM> in each of Embodiments <NUM> to <NUM>; and a second PC sheet <NUM>, where one end of the second PC sheet <NUM> is bonded to the finish coat <NUM> on the first PC sheet <NUM> by using a PUR adhesive <NUM>, and the other end thereof is connected to a forcing device <NUM> by a flexible connecting device <NUM>. The flexible connecting device <NUM> can ensure coaxiality of a force, and the forcing device <NUM> applies a tension to the second PC sheet <NUM>.

Table <NUM> shows bonding strength test conditions and results of the finish coat compositions according to embodiments of this application.

Comparative example <NUM> is a Merlia finish coat purchased from the market.

Claim 1:
A finish coat composition, comprising:
<NUM>~<NUM> parts by mass of film-forming resin, wherein the film-forming resin comprises one or more of acrylic resins and polyurethane acrylate resins;
<NUM>~<NUM> parts by mass of acrylate monomer;
<NUM>~<NUM> parts by mass of photoinitiator;
<NUM>~<NUM> parts by mass of leveling agent;
<NUM>~<NUM> parts by mass of matting powder; and
<NUM>~<NUM> parts by mass of solvent;
wherein the film-forming resin comprises one or more of tetrafunctional modified acrylic resins or hexafunctional aliphatic polyurethane acrylates;
wherein the acrylic monomer comprises one or more of tripropylene glycol diacrylate, <NUM>,<NUM>-hexanediol diacrylate, trimethylolpropane triacrylate, hydroxypropyl acrylate, hydroxyethyl acrylate, and dodecyl acrylate;
wherein the leveling agent comprises a silicone leveling agent;
wherein the solvent comprises any two or more of acetone, n-butanol, ethylene glycol-butadiene, and ethyl acetate.