3D printing method of flexible ultrasonic sensing material with multilayer structure

Abstract

The invention relates to the technical field of flexible ultrasonic sensing materials, in particular to a 3D printing method of a multi-layer structure flexible ultrasonic sensing material, which comprises the following steps: selecting a basic material, a function enhancing material and an interface combination regulating material, completing integrated forming of a multi-layer structure through layer-by-layer printing, and improving the performance by adopting a post-treatment process. By optimizing material distribution and interface bonding performance, adaptability and stability of the multi-layer structure in a dynamic environment can be remarkably improved, and the problem of insufficient integration of flexible materials in the prior art is solved. Free design of complex geometrical shapes is achieved through 3D printing, and the prepared sensing material has wide application potential in the fields of medical treatment, industrial detection, intelligent equipment and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of additive manufacturing, and relates to the preparation of ultrasonic sensing materials, in particular to a 3D printing method of a multi-layer structure flexible ultrasonic sensing material. BACKGROUND

[0002] With the continuous development of ultrasonic sensing technology, flexible ultrasonic sensing materials have gradually become a research hotspot due to their wide application prospects in the fields of medical treatment, industrial detection and intelligent devices. However, the existing ultrasonic sensors still have many deficiencies in the design of multi-layer structure, the selection of materials and the manufacturing process, which limit the further expansion of their performance optimization and application range.

[0003] Patent application CN104040619A discloses an ultrasonic sensor for transmitting and / or receiving ultrasonic signals, which improves the acoustic performance and anti-interference ability of the sensor through the design of decoupling ring and filling material between the diaphragm tank and the shell. However, in this technical solution, the structure of the diaphragm tank and the decoupling ring is complex, and it depends on traditional manufacturing process for assembly, which has certain limitations in realizing the integrated forming of high-precision multi-layer structure. In addition, the selection and distribution of its materials are less adaptable to application scenarios with high flexibility requirements, which affects its further application in the field of flexible sensing.

[0004] Patent application CN111796291A proposes an ultrasonic sensor design based on a semiconductor substrate, which forms a closed space as a resonance space between the shell side diaphragm and the element side diaphragm, improving the sensitivity and frequency response characteristics of the sensor. However, this technical solution mainly relies on traditional mechanical processing and assembly process, and there is room for improvement in realizing accurate control of multi-layer structure and free design of complex geometry. In addition, its material system mainly uses rigid materials, lacking effective integration of flexible materials, resulting in the need to improve the performance stability of the sensor in bending or dynamic environment.

[0005] The above problems show that the existing ultrasonic sensors still have certain limitations in the design of multi-layer structure, the application of flexible materials and the manufacturing process. Therefore, the present application provides a 3D printing method of a multi-layer structure flexible ultrasonic sensing material, which aims to realize the integrated forming of multi-layer structure through 3D printing technology, optimize the material distribution and interface bonding performance, and improve the adaptability and reliability of the sensor in flexible application scenarios, so as to meet the demand of modern ultrasonic sensing technology for high-performance, multi-functional flexible sensors. SUMMARY

[0006] Therefore, the purpose of the present application is to provide a 3D printing method of a multi-layer structure flexible ultrasonic sensing material, which optimizes the material distribution and interface bonding performance to improve the adaptability and stability of the multi-layer structure in dynamic environment.

[0007] To achieve the above object, the present application provides the following technical solutions:

[0008] A 3D printing method of a multi-layer structure flexible ultrasonic sensing material, comprising the following steps:

[0009] Step 1: mixing polydimethylsiloxane and thermoplastic polyurethane in the base material in proportion, then adding nano-sized silicon dioxide particles, stirring uniformly to form a first layer of printing paste;

[0010] Step 2: dispersing piezoelectric ceramic powder and conductive carbon nanotubes in the functional enhancement material in a solvent to form a second layer of printing paste;

[0011] Step 3: dissolving polyvinyl butyral and ethyl cellulose in the interface bonding regulation material in an organic solvent to form a third layer of printing paste;

[0012] Step 4: using an extrusion type 3D printing equipment to print the first layer of printing paste, the second layer of printing paste and the third layer of printing paste in turn, and performing solidification treatment after each layer of printing is completed during the printing process;

[0013] Step 5: performing hot pressing and surface modification treatment on the printed multi-layer structure.

[0014] Further, the base material includes, by mass fraction: polydimethylsiloxane 70-80%, thermoplastic polyurethane 15-25%, and the balance is nano-sized silicon dioxide particles.

[0015] Further, the functional enhancement material includes, by mass fraction: piezoelectric ceramic powder 10-20%, conductive carbon nanotubes 2-5%.

[0016] Further, the interface bonding regulation material includes, by mass fraction: polyvinyl butyral 1-3%, ethyl cellulose 0.5-2%.

[0017] Further, the mixing process of the base material in step 1 uses a twin-screw extruder for blending, the extrusion temperature is 160-180℃, and the screw rotation speed is 100-150r / min.

[0018] Further, the dispersion process of the functional enhancement material in step 2 uses ultrasonic dispersion technology, the ultrasonic frequency is 20-40kHz, and the dispersion time is 30-60 minutes.

[0019] Further, the dissolution process of the interface bonding regulation material in step 3 is carried out in a constant temperature water bath, the water bath temperature is 50-70℃, and the stirring speed is 200-300r / min.

[0020] Further, the nozzle diameter of the extrusion 3D printing device in step 4 is 0.2-0.5 mm, the printing speed is 10-30 mm / s, the printing thickness of each layer is 0.1-0.3 mm, the curing treatment adopts ultraviolet light irradiation, the irradiation intensity is 100-200 mW / cm 2 , and the irradiation time is 5-10 seconds.

[0021] The application has the advantages that the application provides a 3D printing method of a multilayer structure flexible ultrasonic sensing material, through reasonable selection and proportioning of a base material, a function enhancing material and an interface combination regulating material, combined with layer-by-layer printing and post-processing technology, the integrated forming of the multilayer structure is realized. The method solves the problems of difficult accurate control of the multilayer structure and insufficient integration of the flexible material in the prior art, so that the prepared flexible ultrasonic sensing material has excellent performance stability in a bending or dynamic environment. At the same time, the application realizes free design of a complex geometric shape by using the 3D printing technology, which significantly improves the application potential of the sensor in the fields of medical treatment, industrial detection and intelligent equipment.

[0022] Other advantages, objects, and features of the application will be set forth in part in the following specification taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art from a consideration of the following specification and drawings, or can be learned from the practice of the application. The advantages and objects of the application can be realized and attained by means of the instrumentalities and combinations pointed out in the following specification. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to make the purposes, technical solutions and advantages of the application clearer, the preferred detailed description of the application will be combined with the drawings to describe the application, and the drawings are as follows:

[0024] Figure 1 It is a flowchart of the 3D printing method of the multilayer structure flexible ultrasonic sensing material in the embodiment of the application.

[0025] Figure 2 It is the minimum bending radius of the embodiments 1-3 of the application.

[0026] Figure 3 It is the sensitivity of the embodiments 1-3 of the application. DETAILED DESCRIPTION

[0027] The present application is further explained in the following detailed description with reference to the accompanying drawings, wherein:

[0028] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:

[0029] The same or similar components in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that if the terms "upper", "lower", "left", "right", "front", "back" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only for illustrative purposes, and cannot be understood as a limitation of the present application, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0030] The present application provides a 3D printing method of a multi-layer structure flexible ultrasonic sensing material, as shown in Figure 1 First, in the material preparation stage, the base material, functional enhancement material and interface bonding control material are selected as the main raw materials, and the quality fraction ratio is strictly matched.

[0031] The base material is composed of 70-80% of polydimethylsiloxane (PDMS), 15-25% of thermoplastic polyurethane (TPU) and nano-sized silicon dioxide particles, wherein the nano-sized silicon dioxide particles are the balance. The functional enhancement material includes 10-20% of piezoelectric ceramic powder (PZT) and 2-5% of conductive carbon nanotubes (CNTs), and the interface bonding control material is composed of 1-3% of polyvinyl butyral (PVB) and 0.5-2% of ethyl cellulose (EC). The selection of these materials is based on the synergistic effect of their flexibility, conductivity and interface bonding performance, to ensure the adaptability and stability of the multi-layer structure in dynamic environment.

[0032] In the preparation of the first layer printing paste, the polydimethylsiloxane (PDMS) and thermoplastic polyurethane (TPU) in the base material are mixed in proportion, and then nano-sized silicon dioxide particles are added. The mixing process is completed using a twin-screw extruder. The extrusion temperature of the twin-screw extruder is set to 160-180°C, and the screw speed is 100-150 r / min. The key to this step is to ensure uniform distribution of the material and no air bubbles remaining, thereby forming the first layer printing paste. The preparation of the first layer printing paste is the first step of the entire process and is the basis for subsequent layer-by-layer printing.

[0033] Subsequently, the piezoelectric ceramic powder (PZT) and conductive carbon nanotubes (CNTs) in the functional enhancement material are dispersed in a solvent to form the second layer printing paste. The dispersion process uses ultrasonic dispersion technology with a frequency of 20-40 kHz and a dispersion time of 30-60 minutes to ensure uniform distribution of the piezoelectric ceramic powder and conductive carbon nanotubes in the solvent. The focus of this step is to improve the dispersibility of the material through ultrasonic dispersion to avoid agglomeration and ensure the stability of the performance of the second layer printing paste.

[0034] The preparation of the third layer printing paste involves the dissolution process of the interfacial bonding regulation material. Polyvinyl butyral (PVB) and ethyl cellulose (EC) are dissolved in an organic solvent. The dissolution process is carried out in a constant temperature water bath with a water bath temperature of 50-70°C and a stirring speed of 200-300 r / min until complete dissolution to form a uniform solution. The key to this step is to control the dissolution conditions to ensure that the interfacial bonding regulation material can be fully dissolved and form a stable third layer printing paste.

[0035] The first layer printing paste, the second layer printing paste, and the third layer printing paste are sequentially printed layer by layer through an extrusion type 3D printing device. The nozzle diameter of the extrusion type 3D printing device is 0.2-0.5 mm, the printing speed is 10-30 mm / s, and the printing thickness of each layer is 0.1-0.3 mm. After each layer is printed, the solidification treatment area needs to be irradiated with ultraviolet light with an intensity of 100-200 mW / cm 2 , and the irradiation time is 5-10 seconds to achieve layer-by-layer solidification.

[0036] After the layer-by-layer printing is completed, the multi-layer structure is post-processed to further improve its overall performance. The post-processing includes two steps of hot pressing and surface modification. The temperature of hot pressing is 120-150℃, the pressure is 5-10MPa, and the duration is 10-20 minutes. The main purpose of hot pressing is to tightly bond each layer of material through high temperature and high pressure, thereby improving the overall stability and mechanical properties of the multi-layer structure. The surface modification adopts plasma treatment, the power is 50-100W, and the treatment time is 5-15 minutes. Plasma treatment can improve the surface properties of the multi-layer structure, making it more suitable for subsequent application requirements.

[0037] The present application realizes free design of complex geometric shapes by using 3D printing technology, significantly improving the application potential of sensors in the fields of medical treatment, industrial detection and intelligent equipment. The present application solves the problems of difficult accurate control of multi-layer structure and insufficient integration of flexible material in the prior art by reasonable selection and proportioning of basic materials, functional enhancement materials and interface combination control materials, combined with layer-by-layer printing and post-processing process, so that the prepared flexible ultrasonic sensing material has excellent performance stability in bending or dynamic environment.

[0038] In order to better enable the relevant persons in the art to fully understand and implement the present application, the specific implementation principles of the present application are further supplemented by three embodiments.

[0039] Example 1

[0040] Firstly, in the material preparation stage, the raw materials are weighed according to strict quality proportion, wherein the basic material is composed of 75% of polydimethylsiloxane (PDMS), 20% of thermoplastic polyurethane (TPU) and 5% of nano-sized silicon dioxide particles. According to the calculation of the mass percentage of the basic material, the functional enhancement material includes 15% of piezoelectric ceramic powder (PZT) and 3% of conductive carbon nanotubes (CNTs), and the interface combination control material is composed of 2% of polyvinyl butyral (PVB) and 1.5% of ethyl cellulose (EC).

[0041] In the preparation process of the first layer of printing slurry, the polydimethylsiloxane (PDMS) and thermoplastic polyurethane (TPU) in the basic material are mixed in proportion, and then the nano-sized silicon dioxide particles are added. The mixing process needs to be completed by using a twin-screw extruder. The extrusion temperature of the twin-screw extruder is set to 180℃, and the screw rotation speed is 120r / min. The key of this step is to ensure that the material is uniformly distributed and no bubbles are left, so as to form the first layer of printing slurry. The preparation of the first layer of printing slurry is the first step of the whole process and the basis for subsequent layer-by-layer printing.

[0042] Subsequently, the piezoelectric ceramic powder (PZT) and conductive carbon nanotubes (CNTs) in the functional enhancement material are dispersed in a solvent to form a second layer of printing paste. The dispersion process adopts ultrasonic dispersion technology, with an ultrasonic frequency of 30 kHz and a dispersion time of 50 minutes to ensure uniform distribution of the piezoelectric ceramic powder and conductive carbon nanotubes in the solvent.

[0043] The preparation of the third layer of printing paste involves a dissolution process of the interfacial bonding regulation material. Polyvinyl butyral (PVB) and ethyl cellulose (EC) are dissolved in an organic solvent. The dissolution process needs to be carried out in a constant temperature water bath, with a water bath temperature of 60°C and a stirring speed of 250 r / min, until a uniform solution is formed. The first layer of printing paste, the second layer of printing paste, and the third layer of printing paste are sequentially printed layer by layer by an extrusion type 3D printing equipment. The nozzle diameter of the extrusion type 3D printing equipment is 0.3 mm, the printing speed is 20 mm / s, and the printing thickness of each layer is 0.2 mm. After each layer of printing is completed, the solidification treatment area 4 needs to be irradiated by ultraviolet light, with an irradiation intensity of 150 mW / cm 2 , and an irradiation time of 8 seconds to achieve layer-by-layer solidification.

[0044] After the layer-by-layer printing is completed, the multi-layer structure is post-processed to further improve its overall performance. The post-processing includes two steps of hot pressing and surface modification. The temperature of hot pressing is 140°C, the pressure is 8 MPa, and the duration is 15 minutes. The main purpose of hot pressing is to tightly bond the materials in each layer through high temperature and high pressure, thereby improving the overall stability and mechanical properties of the multi-layer structure. Surface modification adopts plasma treatment, with a power of 80 W and a treatment time of 8 minutes, to obtain Example 1.

[0045] Example 2

[0046] First, in the material preparation stage, the raw materials are weighed according to strict mass fraction ratios. The base material is composed of 80% polydimethylsiloxane (PDMS), 15% thermoplastic polyurethane (TPU), and 5% nano-sized silicon dioxide particles. According to the mass percentage of the base material, the functional enhancement material includes 18% piezoelectric ceramic powder (PZT) and 2% conductive carbon nanotubes (CNTs), and the interfacial bonding regulation material is composed of 3% polyvinyl butyral (PVB) and 2% ethyl cellulose (EC).

[0047] In the preparation of the first layer printing paste, the polydimethylsiloxane (PDMS) and thermoplastic polyurethane (TPU) in the base material are mixed in proportion, and then nano-sized silicon dioxide particles are added. The mixing process is completed using a twin-screw extruder. The extrusion temperature of the twin-screw extruder is set to 160°C, and the screw speed is 150 r / min. The key to this step is to ensure uniform distribution of the material and no air bubbles remaining, thereby forming the first layer printing paste. The preparation of the first layer printing paste is the first step of the entire process and is the basis for subsequent layer-by-layer printing.

[0048] Subsequently, the piezoelectric ceramic powder (PZT) and conductive carbon nanotubes (CNTs) in the functional enhancement material are dispersed in a solvent to form the second layer printing paste. The dispersion process uses ultrasonic dispersion technology with a frequency of 40 kHz and a dispersion time of 30 minutes to ensure uniform distribution of the piezoelectric ceramic powder and conductive carbon nanotubes in the solvent.

[0049] The preparation of the third layer printing paste involves the dissolution process of the interfacial bonding regulation material. Polyvinyl butyral (PVB) and ethyl cellulose (EC) are dissolved in an organic solvent. The dissolution process is carried out in a constant temperature water bath with a water bath temperature of 70°C and a stirring speed of 200 r / min until a uniform solution is formed. The first layer printing paste, the second layer printing paste, and the third layer printing paste are sequentially printed layer by layer through an extrusion 3D printing device. The nozzle diameter of the extrusion 3D printing device is 0.2 mm, the printing speed is 15 mm / s, and the printing thickness of each layer is 0.3 mm. After each layer is printed, the solidification treatment area 4 needs to be irradiated with ultraviolet light with an intensity of 120 mW / cm 2 for 10 seconds to achieve layer-by-layer solidification.

[0050] After layer-by-layer printing, the multi-layer structure is post-processed to further improve its overall performance. The post-processing includes two steps of hot pressing and surface modification. The temperature of hot pressing is 120°C, the pressure is 10 MPa, and the duration is 13 minutes. The main purpose of hot pressing is to tightly bond the materials in each layer through high temperature and high pressure, thereby improving the overall stability and mechanical properties of the multi-layer structure. Surface modification uses plasma treatment with a power of 100 W and a treatment time of 7 minutes to obtain Example 2.

[0051] Example 3

[0052] Firstly, in the material preparation stage, the raw materials are weighed according to strict quality proportion, wherein the base material is composed of 72% of polydimethylsiloxane (PDMS), 15% of thermoplastic polyurethane (TPU) and 13% of nano-sized silicon dioxide particles. According to the mass percentage of the base material, the functional enhancement material includes 20% of piezoelectric ceramic powder (PZT) and 5% of conductive carbon nanotubes (CNTs), and the interface bonding regulation material is composed of 2% of polyvinyl butyral (PVB) and 1.5% of ethyl cellulose (EC).

[0053] In the preparation process of the first layer of printing slurry, the polydimethylsiloxane (PDMS) and thermoplastic polyurethane (TPU) in the base material are mixed in proportion, and then nano-sized silicon dioxide particles are added. The mixing process needs to be completed using a double screw extruder. The extrusion temperature of the double screw extruder is set to 170°C, and the screw rotation speed is 150 r / min. The key of this step is to ensure that the material is uniformly distributed and no bubbles are left, so as to form the first layer of printing slurry. The preparation of the first layer of printing slurry is the first step of the whole process and the basis for subsequent layer-by-layer printing.

[0054] Subsequently, the piezoelectric ceramic powder (PZT) and conductive carbon nanotubes (CNTs) in the functional enhancement material are dispersed in the solvent to form the second layer of printing slurry. The dispersion process adopts ultrasonic dispersion technology, the ultrasonic frequency is 40 kHz, and the dispersion time is 50 minutes to ensure the uniform distribution of the piezoelectric ceramic powder and the conductive carbon nanotubes in the solvent.

[0055] The preparation of the third layer of printing slurry involves the dissolution process of the interface bonding regulation material. Polyvinyl butyral (PVB) and ethyl cellulose (EC) are dissolved in an organic solvent. The dissolution process needs to be carried out in a constant temperature water bath, the water bath temperature is 50°C, the stirring speed is 300 r / min, and the uniform solution is formed until complete dissolution. The first layer of printing slurry, the second layer of printing slurry and the third layer of printing slurry are sequentially printed by the extrusion type 3D printing equipment. The nozzle diameter of the extrusion type 3D printing equipment is 0.5 mm, the printing speed is 10 mm / s, and the printing thickness of each layer is 0.3 mm. After each layer of printing is completed, the solidification treatment area 4 needs to be irradiated by ultraviolet light, the irradiation intensity is 180 mW / cm 2 , and the irradiation time is 7 seconds to realize layer-by-layer solidification.

[0056] After the layer-by-layer printing is completed, the multi-layer structure is post-processed to further improve its overall performance. The post-processing includes two steps of hot pressing and surface modification. The temperature of hot pressing is 150℃, the pressure is 6MPa, and the duration is 15 minutes. The main purpose of hot pressing is to tightly combine each layer of material through high temperature and high pressure, so as to improve the overall stability and mechanical properties of the multi-layer structure. The surface modification adopts plasma treatment, the power is 85W, and the treatment time is 8 minutes, so as to obtain example 3.

[0057] Figure 2 The minimum bending radius of the three prepared examples is shown, it can be seen that the minimum radius of the three examples is less than 30mm, indicating that the ultrasonic sensing material prepared by the method of the application has good flexible bending performance. Figure 3 It is shown that the sensitivity of examples 1-3 is greater than 15, indicating that the ultrasonic sensing material prepared by the method of the application has good sensing performance.

[0058] In summary, the application realizes the integrated forming of the multi-layer structure by the above specific implementation steps combined with the 3D printing technology, solves the problem of insufficient integration of flexible materials in the prior art. In the medical application scene, the flexible ultrasonic sensing material prepared by the method not only has good flexibility, but also can maintain stable signal output in a dynamic environment, meeting the demand of high-performance flexible sensors.

[0059] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the application and are not limiting. Although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should be covered in the scope of the claims of the application.

Claims

1. A 3D printing method for a multilayer flexible ultrasonic sensing material, characterized in that, Includes the following steps: Step 1: Mix polydimethylsiloxane and thermoplastic polyurethane in the base material in a certain proportion, then add nano-sized silica particles and stir evenly to form the first layer of printing paste. Step 2: Disperse the piezoelectric ceramic powder and conductive carbon nanotubes in the functional enhancement material in a solvent to form a second layer of printing paste; Step 3: Dissolve the polyvinyl butyral and ethyl cellulose in the interface bonding control material in an organic solvent to form the third layer of printing paste; Step 4: Use an extrusion 3D printing device to print the first layer of printing paste, the second layer of printing paste, and the third layer of printing paste in sequence. During the printing process, a curing process is performed after each layer is printed. Step 5: Perform hot pressing and surface finishing on the printed multi-layer structure.

2. The 3D printing method for the multilayer flexible ultrasonic sensing material according to claim 1, characterized in that, The base materials, by mass fraction, include: 70-80% polydimethylsiloxane, 15-25% thermoplastic polyurethane, and the remainder being nano-sized silica particles.

3. The 3D printing method for the multilayer flexible ultrasonic sensing material according to claim 1, characterized in that, The functional enhancement materials, by mass fraction, include: 10-20% piezoelectric ceramic powder and 2-5% conductive carbon nanotubes.

4. The 3D printing method for the multilayer flexible ultrasonic sensing material according to claim 1, characterized in that, The interface bonding control materials, by mass fraction, include: 1-3% polyvinyl butyral and 0.5-2% ethyl cellulose.

5. The 3D printing method for the multilayer flexible ultrasonic sensing material according to claim 1, characterized in that, In step 1, the mixing process of the base materials is carried out using a twin-screw extruder with an extrusion temperature of 160–180°C and a screw speed of 100–150 r / min.

6. The 3D printing method for the multilayer flexible ultrasonic sensing material according to claim 1, characterized in that, In step 2, the dispersion process of the functional enhancement material adopts ultrasonic dispersion technology with an ultrasonic frequency of 20-40 kHz and a dispersion time of 30-60 minutes.

7. The 3D printing method for the multilayer flexible ultrasonic sensing material according to claim 1, characterized in that, In step 3, the dissolution process of the interface-controlled material is carried out in a constant temperature water bath at a temperature of 50–70°C and a stirring speed of 200–300 r / min.

8. The 3D printing method for the multilayer flexible ultrasonic sensing material according to claim 1, characterized in that, In step 4, the nozzle diameter of the extrusion 3D printing equipment is 0.2–0.5 mm, the printing speed is 10–30 mm / s, the thickness of each layer is 0.1–0.3 mm, and the curing process uses ultraviolet light irradiation with an intensity of 100–200 mW / cm². 2 The irradiation time is 5 to 10 seconds.

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