CN109575743B

CN109575743B - Color-changing coating of mobile phone shell and manufacturing process thereof

Info

Publication number: CN109575743B
Application number: CN201811614479.2A
Authority: CN
Inventors: 魏晓锋
Original assignee: Dongguan Hua Precision Technology Co Ltd
Current assignee: Dongguan Hua Precision Technology Co., Ltd
Priority date: 2018-12-27
Filing date: 2018-12-27
Publication date: 2021-08-10
Anticipated expiration: 2038-12-27
Also published as: CN109575743A

Abstract

The invention discloses a color-changing coating of a mobile phone shell and a manufacturing process thereof, and the color-changing coating comprises a shell substrate, wherein a light-emitting groove is formed on the surface of the shell substrate in a photoetching manner, and a color-changing fluorescent strip is filled in the light-emitting groove; the outer surface of the shell substrate is sprayed with a metal color primer, the upper surface of the metal color primer is sprayed with a non-crosslinked photochromic coating, and the outer surface of the non-crosslinked photochromic coating is sprayed with a wear-resistant UV protective coating. When the non-crosslinked photochromic coating is prepared, the photochromic compound and the high polymer material are compounded to prepare the microsphere, so that the thermal stability and the oxidation resistance of the coating are obviously improved on the basis of not influencing the photochromic effect, and the service life of the coating is prolonged; adopt cold spraying to reduce harmful gas etc. that produce when the operation during the preparation, it is safer high-efficient, when having increased the phosphor strip and improving ornamental performance, also be convenient for discover at night and use the cell-phone.

Description

Color-changing coating of mobile phone shell and manufacturing process thereof

Technical Field

The invention relates to the field of mobile phone accessories, in particular to a color-changing coating of a mobile phone shell and a manufacturing process thereof.

Background

The cell-phone casing is a very common cell-phone protection device, and the cell-phone shell among the prior art is mostly printed various patterns on its surface for the outward appearance of cell-phone shell looks very beautiful, but general cell-phone shell only single colour or pattern, wants to change pattern or colour and just need purchase again, the wasting of resources that causes, the cell-phone shell that discolours begins to appear on this market for this reason.

Materials that change color under the influence of external conditions are often referred to as color-changing materials. The color-changing materials are generally classified into 4 types of photochromic materials, thermochromic materials, electrochromic materials and solvent-based photochromic materials according to the stimulation mode; among them, the photochromic material is the most common one, and usually, the main component of the photochromic material is the spiropyran and the derivatives thereof, and the spiropyran and the derivatives thereof only absorb ultraviolet rays but not visible light, so that the photochromic material does not develop color; under the heating or ultraviolet irradiation, the carbon-oxygen bond in the spiropyran is heterolytic-cracked to generate isomer-isoquinoline with color; at the moment, a conjugation phenomenon is generated at the broken bond, and conjugated isoquinoline strongly absorbs visible light to develop color; the process is completely reversible, and under the condition of changing temperature, isoquinoline can be closed and re-closed to the colorless state of the spiropyran. The discoloration efficiency of the spiropyran compound depends on the structure of the heterocyclic compound, the type and the temperature of a medium, the rate of discoloration and the depth of discoloration of an ideal solid or liquid spiropyran derivative after being heated are quite different, and the biggest defect of the spiropyran derivative is that the spiropyran derivative is easy to fatigue and loses the discoloration characteristic when being subjected to strong light or strong heat.

For example, patent application No. 201310755647.0 entitled photochromic cell phone case invention: the photochromic mobile phone shell is added with photochromic compounds, can change into different colors under the irradiation of sunlight and generates novel and peculiar effects.

However, the existing photochromic mobile phone shell has the following defects:

(1) although the photochromic material used in the photochromic mobile phone shell is sensitive in color change and bright in color, the photochromic material is easily oxidized and deteriorated under the influence of environmental factors such as temperature, oxygen, pH value, illumination and the like, so that the photochromic mobile phone shell is low in fatigue resistance and short in service life;

(2) such printed patterns cannot be displayed at night, so that the use of the mobile phone shell at night is only limited to the protection of the mobile phone, and the mobile phone cannot be found in the dark and cannot meet the use requirement.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides the color-changing coating of the mobile phone shell and the manufacturing process thereof, which can effectively solve the problems in the background art.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a color-changing coating of a mobile phone shell comprises a shell substrate, wherein a light-emitting groove is formed in the surface of the shell substrate in a photoetching mode, and a color-changing fluorescent strip is filled in the light-emitting groove; a metal color primer layer is sprayed on the outer surface of the shell substrate, a non-crosslinked photochromic coating is sprayed on the upper surface of the metal color primer layer, and a wear-resistant UV protective coating is sprayed on the outer surface of the composite photochromic coating;

further, the coating of the non-crosslinked photochromic coating is prepared by carrying out non-crosslinking reaction on the polymer microspheres and the photochromic compound, and the ratio of the components is that the photochromic compound: dioctyl phthalate: 5% styrene-maleic anhydride resin solution: the melamine formaldehyde precondensation polymer is 1:4:4:4, the coating thickness is 8-15um, wherein the photochromic compound is prepared by mixing two color-changing raw materials of spirooxazine and naphthopyran according to the proportion of 1: 1.

Furthermore, the shell substrate is formed by compounding acrylonitrile-butadiene-styrene copolymer and thermoplastic polyurethane elastic plastic, and the thickness of the shell is 0.8mm-1.0 mm.

Furthermore, the metallic color primer layer is prepared by spraying and curing silver primer at 60-80 ℃, and the thickness of the metallic color primer layer is 3-5 um.

Further, the paint for wear-resistant protection of the UV coating adopts high-gloss UV: the matte UV-1: 2 material is mixed to form the coating with the thickness of about 8-10 um.

In addition, the invention also designs a manufacturing process of the mobile phone shell color-changing coating, and the spraying manufacturing of the color-changing coating on the mobile phone shell comprises the following steps:

s101, spraying metal primer, and uniformly spraying silver primer on a shell substrate at the temperature of 60-80 ℃ by using a manipulator-controlled spray gun;

s102, preparing color-changing coating powder: adding photochromic microsphere powder into a resin substrate material, grinding by adopting an electronic control type three-roller machine, adding a diluent, and uniformly stirring to obtain coating powder;

s103, ultrasonic rapid cold spraying treatment: heating the coating powder obtained in the step S102 to a molten state at a high temperature, accelerating the coating powder to a supersonic speed through compressed air, and controlling the confined high-temperature particle beam to impact the surface of the mobile phone shell to form a thin color-changing coating;

s104, spraying an abrasion-resistant protective UV coating: and after the color-changing coating is cooled and solidified, spraying the UV coating obtained by compounding on the upper surface of the non-crosslinked photochromic coating by adopting a spray gun to control so as to form a protective layer.

Further, step S102 further includes a preparation method of the photochromic microsphere powder, which specifically includes the following steps:

step S201, preparing O/W type emulsion: adding a photochromic compound into 250mL of DOP, stirring until the photochromic compound is completely dissolved, cooling, adding SMA, and emulsifying to obtain O/W type emulsion;

step S202, shell polymerization reaction: adding a mixed solution of melamine formaldehyde pre-condensation polymer and water into the O/W type emulsion by stirring, adjusting the pH value of the system to acidity by adopting acetic acid, heating for 2 hours, cooling to room temperature after heating is stopped, adjusting the pH value to 9 by using NaOH, and drying to obtain photochromic compound powder;

step S203, styrene St pretreatment: repeatedly washing St to neutrality by using NaOH solution and ultrapure water, dehydrating by using anhydrous sodium sulfate, refining by using a reduced pressure distillation method to obtain St monomer, and refrigerating at 4 ℃ for later use;

step S204, divinylbenzene DVB pretreatment: repeatedly washing DVB to neutrality with NaOH solution and ultrapure water, dehydrating with anhydrous calcium chloride, and refrigerating at 4 deg.C for storage;

step S205, preparation of non-crosslinked PS color-changing microspheres: adding ultrapure water into a 3% sodium dodecyl sulfate solution, stirring until the mixture is completely dissolved, rapidly stirring and fusing the photochromic compound, the initiator and the St monomer prepared in the step S102 and heating in a water bath for 1 h; slowly adding a certain amount of DVB, stirring uniformly, emulsifying at high speed, heating in water bath for reaction, cooling to room temperature after stirring reaction is complete, washing, filtering and drying for multiple times to obtain white solid powder, and preparing the non-crosslinked PS color-changing microsphere.

Further, the polymerization reaction temperature in step S202 needs to be subjected to two temperature raising operations: the temperature is kept at 60 ℃ in the first 1h, and the temperature is raised to 70 ℃ after 1h and is raised to 80 ℃ after 1.5 h.

Further, 1% of azobisisobutyronitrile is adopted as the initiator in the step S205, the emulsifying speed is 13500rpm, the stirring speed is 600rpm, the water bath heating temperature is 60 ℃, and N is introduced all the way through₂And (6) protecting.

Further, in step S103, the coating powder is heated to 2000 ℃ for pressurization, then cooled to 800 ℃ by water cooling, accelerated to 1000m/S supersonic speed by a laval nozzle, and then sprayed.

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

(1) the composite photochromic coating disclosed by the invention is formed by compounding the photochromic compound and the high polymer material into microspheres, so that the microspheres are isolated from chemical environments such as acid, alkali, air and the like on the basis of not influencing the photochromic effect, the thermal stability and the oxidation resistance of the composite photochromic coating can be obviously improved, the service life of the composite photochromic coating is prolonged, and the composite coating has very strong fatigue resistance and is bright in color and long in duration;

(2) according to the invention, two times of heating operation are adopted during polymerization reaction in the preparation process of the photochromic microspheres, so that the conversion rate is increased, the reaction time is reduced, and the selected azobisisobutyronitrile is used as an initiator, so that the efficiency is higher, and the microspheres obtained by polymerization have smaller diameters and are uniform and free from adhesion;

(3) according to the invention, the luminous grooves are formed on the shell substrate and the color-changing fluorescent strips are filled, so that the mobile phone shell can emit light in the dark while the ornamental performance is improved, a user can conveniently find and find the mobile phone in the dark, and the risk of losing the mobile phone can be reduced;

(4) the invention adopts the ultrasonic rapid cold spraying method when the color changing coating is carried out, so that the particles are always kept in a solid state and form the coating through pure plastic deformation polymerization, thereby effectively eliminating the harmful influence in the traditional thermal spraying method and being safer and healthier.

Drawings

FIG. 1 is a schematic view of the overall structure of the present invention;

FIG. 2 is a schematic side view of the present invention;

FIG. 3 is a flow chart of a method of the present invention;

FIG. 4 is a flow chart of the preparation of a non-crosslinked photochromic coating.

Reference numbers in the figures:

1-a housing base; 2-a metallic color primer layer; 3-composite photochromic coating; 4-wear resistant protective UV coating;

101-a light emitting groove; 102-color changing fluorescent strip.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, the invention provides a color-changing coating of a mobile phone shell, which comprises a shell substrate 1, wherein the shell substrate 1 is formed by compounding acrylonitrile-butadiene-styrene copolymer (ABS) and Thermoplastic Polyurethane (TPU), and the thickness of the shell is 0.8mm-1.0mm, so that the shell substrate 1 has good insulation shielding property and good soft extension, is very thin in thickness and light in weight, and can reduce the weight of the whole mobile phone while protecting internal devices of the mobile phone; a light emitting groove 101 is etched on the surface of the shell substrate 1, and a color-changing fluorescent strip 102 is filled in the light emitting groove 101; the luminous groove 101 can be designed into different patterns and shapes according to requirements, has very good decorative performance, can play decorative performance on the one hand through filling the color-changing fluorescent strip 102, and on the other hand, the color-changing fluorescent strip 102 can emit light at night by absorbing illumination in the daytime, so that the luminous groove is convenient to use at night.

As shown in fig. 2, a metallic primer layer 2 is sprayed on the outer surface of the case substrate 1, the metallic primer layer 2 is prepared by spraying and curing 3-5um silver primer at 60-80 ℃, and the metallic luster of the surface of the mobile phone case can be improved by spraying the metallic primer layer 2.

The upper surface of the metallic color primer layer 2 is sprayed with a non-crosslinked photochromic coating 3, the coating of the non-crosslinked photochromic coating 3 is prepared by non-crosslinking reaction of polymer microspheres and photochromic compounds, and the component proportion is that the photochromic compounds: dioctyl phthalate: 5% styrene-maleic anhydride resin solution: the melamine formaldehyde precondensation polymer is 1:4:4:4, the coating thickness is 8-15um, wherein the photochromic compound is prepared by mixing two color-changing raw materials of spirooxazine and naphthopyran according to the proportion of 1: 1.

It should be noted that the photochromic phenomenon is a phenomenon that when a compound a is irradiated by light with a certain wavelength, a specific chemical reaction occurs to generate a compound B with a structure and spectral properties different from those of a, and when B is irradiated by another wavelength or under a heating condition, a compound B reversibly generates a, and a material with such reversible photochromic properties is called a photochromic material; the spiropyran is one of the earliest and most extensive systems researched in organic photochromic materials, the photochromic process of the spiropyran is completed through heterolytic cleavage of bonds, the thermal stability of a spiropyran open ring body is better, spirooxazine and spiropyran belong to a spiro compound, and the photochromic process of the spiropyran is also completed through heterolytic cleavage of bonds.

It should be noted that although the organic photochromic compound is sensitive in color change and bright in color, it is easily affected by environmental factors such as temperature, oxygen, pH, illumination, etc. to cause oxidative deterioration, thereby resulting in low fatigue resistance and short service life, and the organic photochromic compound can only be dissolved in organic solvent or exist in the form of molecules in the polymer matrix to have obvious color change effect; although the microspheres can wrap the photochromic material, the volatilization of the organic solvent still causes harm to the environment and human bodies in the application process due to the existence of the organic solvent.

In the embodiment, the non-crosslinked photochromic coating layer 3 is preferably formed by compounding the photochromic compound and the high polymer material, so that the influence of the external environment on the physical and chemical properties of the photochromic compound can be reduced, and the application of the photochromic compound in the fields of films, sheets, plates, fibers, glass powder and the like can be realized; by combining the photochromic compound with the polymer microsphere, the photochromic compound is isolated from chemical environments such as acid, alkali, air and the like on the basis of not influencing the color change effect, so that the thermal stability and the oxidation resistance of the photochromic compound can be obviously improved, and the service life of the photochromic compound is prolonged.

Preferably, the outer surface of the non-crosslinked photochromic coating 3 is sprayed with an abrasion-resistant protective UV coating 4, the abrasion-resistant protective UV coating 4 consisting of a high light UV: the coating is made of mixed materials of 1:2 of matt UV, the thickness of the coating is about 8-10um, the gloss of the outer surface of the mobile phone shell is controlled by the ratio of the high-gloss UV coating to the low-gloss UV coating, and the wear resistance of the surface can be improved.

As shown in fig. 3, the invention also designs a spraying manufacturing process of the color-changing coating on the mobile phone shell, which comprises the following steps:

s102, preparing color-changing coating powder, adding photochromic microsphere powder into a resin substrate material, grinding by adopting an electronic control type three-roller machine, adding a diluent, and uniformly stirring to obtain coating powder;

s103, ultrasonic rapid cold spraying treatment, namely heating the coating powder obtained in the S102 to a molten state at a high temperature, and accelerating the coating powder by compressed air to enable the constrained particle beam to impact the surface of the substrate to form a thin color-changing coating;

and S104, spraying the wear-resistant UV protection coating, and after the color-changing coating is cooled and solidified, spraying the UV coating obtained by compounding on the upper surface of the non-crosslinked photochromic coating by adopting a spray gun to form a protection layer.

When the spraying operation is performed on the surface of the shell substrate, it is particularly noted that the spraying operation is automatically programmed and controlled by an electronic manipulator, so that the accuracy of the spraying operation is ensured, the thickness of the coating is controlled, and the appearance attractiveness of the mobile phone shell is ensured.

Preferably, in step S103, the coating powder is heated to 2000 ℃ for pressurization, then cooled to 800 ℃ with water, and then sprayed at a supersonic speed of 1000m/S with a laval nozzle, where the cooling with water can achieve the cold spraying operation, and the particles are always kept in a solid state during cold spraying and polymerized by pure plastic deformation to form a coating, so that the harmful effects in the conventional thermal spraying method, such as high-temperature oxidation, evaporation, dissolution, crystallization, residual stress, peeling, gas release, etc., can be minimized or even eliminated.

As shown in fig. 4, in step 102, the non-crosslinked photochromic coating 3 powder on the surface of the housing substrate 1 is prepared by using non-crosslinked PS photochromic microspheres, and the preparation method of the photochromic microspheres includes the following steps:

s201, preparing O/W type emulsion, adding spirooxazine and naphthopyran photochromic compounds into 250mL of DOP, stirring until the spirooxazine and naphthopyran photochromic compounds are completely dissolved, cooling, adding SMA, and emulsifying to obtain O/W type emulsion;

step S202, shell polymerization reaction, namely adding a mixed solution of melamine formaldehyde pre-condensation polymer and water into an O/W type emulsion by stirring, adjusting the pH value of the system to acidity by adopting acetic acid, heating for 2 hours, cooling to room temperature after heating is stopped, adjusting the pH value to 9 by using NaOH, and drying to obtain photochromic compound powder;

s203, styrene (St) pretreatment, namely washing St to be neutral repeatedly by adopting NaOH solution and ultrapure water, dehydrating by adopting anhydrous sodium sulfate, refining by adopting a reduced pressure distillation method to obtain a St monomer, and refrigerating at 4 ℃ for later use;

step S204, carrying out divinyl benzene (DVB) pretreatment, repeatedly washing DVB to be neutral by adopting NaOH solution and ultrapure water, dehydrating by adopting anhydrous calcium chloride, and refrigerating for storage at 4 ℃;

s205, preparing non-crosslinked PS color-changing microspheres, namely adding ultrapure water into a 3% sodium dodecyl sulfate solution, stirring until the mixture is completely dissolved, rapidly stirring and fusing the photochromic compound in the S102 and the St monomer prepared in the S103, and heating in a water bath for 1 h; slowly adding a certain amount of DVB, stirring uniformly, emulsifying at a high speed, heating in a water bath for reaction, cooling to room temperature after complete stirring reaction, washing, filtering and drying for multiple times to obtain white solid powder.

It should be noted that the concentration of the photochromic solution in step S201 is an important influencing factor that influences the photochromic performance of the photochromic microspheres, and as the concentration of the photochromic solution increases, the microspheres have a reversible color change phenomenon, and when the concentration increases to a certain critical value, the color change effect of the microspheres is optimal, and the color contrast before and after color change is obvious, and when the concentration exceeds the critical value, the microspheres are illuminated, and then the reversible color change phenomenon does not occur.

Further, in step S202, the polymerization temperature needs to be increased twice: the temperature is kept at 60 ℃ in the first 1h, the temperature is raised to 70 ℃ after 1h, and the temperature is raised to 80 ℃ after 1.5h, because the polymerization temperature can directly influence the polymerization rate of the monomer, thereby influencing the particle size and the particle size distribution of the microspheres; for the non-crosslinked PS microspheres, when the polymerization temperature is 60 ℃, the obtained microspheres have small particle size and no adhesion phenomenon, and when the polymerization temperature is 80 ℃, the microspheres have small particle size but serious adhesion phenomenon; after polymerization is carried out at 60 ℃ for a certain time, the temperature is raised to 80 ℃ for polymerization in the later period, although the microspheres have no obvious adhesion phenomenon, the particle sizes of the microspheres are different, and the distribution is quite uneven; when the polymerization temperature of 60 ℃ is adopted for polymerization for a certain time, the polymerization temperature of 70 ℃ is adopted for polymerization for a certain time, and the polymerization is carried out at 80 ℃, the particle size of the obtained microspheres is less than 1um, and the distribution is narrowed, so that the temperature is increased twice in the later period of polymerization, the conversion rate of monomers is increased, and the whole polymerization time is obviously reduced.

The initiator in the step S205 is 1% of azobisisobutyronitrile, and the emulsifier can solve the problems of large particle size and uneven distribution of the formed microspheres due to the reduction of the initiator concentration, the reduction of the concentration of free radicals in a system, the reduction of polymerization centers and the polymerization growth of the microspheres caused by the decomposition of the initiator; simultaneously, the emulsifying speed is 13500rpm, the stirring speed is 600rpm, the water bath heating temperature is 60 ℃, and N is introduced in the whole process₂Protection is performed to prevent side reactions from occurring due to air influence.

The invention has the advantages that the photochromic microspheres are used by spraying the non-crosslinked photochromic coating, so that the photochromic performance of the shell after being illuminated is ensured, the fatigue resistance of the material is improved, the appearance attractiveness of the mobile phone shell is ensured, and the service life is prolonged; two times of heating operation is adopted during the polymerization reaction in the preparation process of the photochromic microspheres, so that the conversion rate is increased, the reaction time is reduced, the efficiency is higher, and the microspheres obtained by polymerization have smaller diameter and are uniform without adhesion; the fluorescent strip is added, so that the lamp is convenient to use at night; and the whole mobile phone shell has metallic luster and good wear resistance.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Claims

1. A mobile phone casing discoloration coating, comprising a casing substrate (1), characterized in that: a light-emitting groove (101) is etched on the surface of the shell substrate (1), and a plurality of color-changing fluorescent strips (102) for emitting light under dark conditions are filled in the light-emitting groove (101); a metal color primer layer (2) is sprayed on the outer surface of the shell substrate (1), a non-crosslinked photochromic coating (3) is sprayed on the upper surface of the metal color primer layer (2), and a wear-resistant protective UV coating (4) is sprayed on the outer surface of the non-crosslinked photochromic coating (3); the coating of the non-crosslinked photochromic coating (3) is photochromic microsphere powder prepared by non-crosslinking reaction of polymer microspheres and photochromic compound powder, and the photochromic compound powder comprises the following components in percentage by weight: dioctyl phthalate: 5 wt% styrene-maleic anhydride resin solution: the melamine formaldehyde precondensation polymer is 1:4:4:4, the coating thickness is 8-15 μm, wherein the photochromic compound is prepared by mixing two color-changing raw materials of spirooxazine and naphthopyran according to the proportion of 1: 1.

2. A handset casing colour shifting coating according to claim 1, characterised in that: the shell substrate (1) is formed by compounding acrylonitrile-butadiene-styrene copolymer and thermoplastic polyurethane elastic plastic, and the thickness of the shell is 0.8mm-1.0 mm.

3. A handset casing colour shifting coating according to claim 1, characterised in that: the metallic primer layer (2) is prepared by spraying and curing silver primer at the temperature of 60-80 ℃, and the thickness of the metallic primer layer (2) is 3-5 mu m.

4. A handset casing colour shifting coating according to claim 1, characterised in that: the paint of the wear-resistant protective UV coating (4) adopts high-gloss UV: the matt UV-1: 2 material is mixed, and the coating thickness is 8-10 μm.

5. A process for making a discoloration coating for mobile phone housings in accordance with claim 1, wherein: the method comprises the following steps:

6. The process of claim 5, wherein the discoloration coating comprises: the step S102 further includes a preparation method of the photochromic microsphere powder, which specifically includes the steps of:

step S205, preparation of non-crosslinked PS color-changing microspheres: adding ultrapure water into a 3% sodium dodecyl sulfate solution, stirring until the mixture is completely dissolved, rapidly stirring and fusing the photochromic compound powder, the initiator and the St monomer prepared in the step S202 and heating in a water bath for 1 h; slowly adding a certain amount of DVB, stirring uniformly, emulsifying at high speed, heating in water bath for reaction, cooling to room temperature after stirring reaction is complete, washing, filtering and drying for multiple times to obtain white solid powder, and preparing the non-crosslinked PS color-changing microsphere.

7. The process of claim 6, wherein the discoloration coating comprises: the polymerization reaction temperature in step S202 needs to be increased twice: the temperature is kept at 60 ℃ in the first 1h, and the temperature is raised to 70 ℃ after 1h and is raised to 80 ℃ after 1.5 h.

8. The process of claim 5, wherein the discoloration coating comprises: in the step S103, the coating powder is heated to 2000 ℃ for pressurization, then is cooled to 800 ℃ by water cooling, and is accelerated to 1000m/S supersonic speed by a Laval nozzle for spraying.