Method of making flexible thermally and electrically conductive sheet

Abstract

The application discloses a preparation method of a flexible heat-conducting and electricity-conducting sheet, S1. providing an electricity-conducting and heat-conducting base material, printing an electricity-conducting paste on the electricity-conducting and heat-conducting base material through a silk screen printing process to form an electricity-conducting electrode, and then performing pre-solidification; S2. coating an adhesive on the surface of the electricity-conducting and heat-conducting base material treated in the step S1, and performing drying treatment; S3. providing a flexible silica gel sheet, adhering the flexible silica gel sheet to the surface of the electricity-conducting and heat-conducting base material treated in the step S2 through a rolling process, and then performing heating solidification, so that the flexible silica gel sheet, the adhesive and the electricity-conducting and heat-conducting base material are integrated; and S4. perforating the flexible silica gel sheet at positions corresponding to the lower electricity-conducting electrode to form through holes penetrating through the silica gel sheet. On the basis of guaranteeing the combination of the base material and the silica gel sheet, the application realizes efficient heat conduction on an insulating interface, and finally makes the prepared sheet have excellent flexibility, insulation, interface bonding strength, in-plane and vertical direction heat-conducting and electricity-conducting capacity.

Description

Technical Field

[0001] This invention relates to the field of flexible thermally and electrically conductive sheets, and more specifically to a method for preparing a flexible thermally and electrically conductive sheet. Background Technology

[0002] Existing electric heating equipment, such as induction cookers and other kitchen appliances, typically use electromagnetic heating or electric heating elements to bake food. The former, using electromagnetic heating, consumes a lot of energy, while the latter, using electric heating elements, still consumes a lot of energy. Moreover, the contact area between the electric heating element and the heating plate is relatively limited, which can easily cause uneven heat conduction on the heating plate's heat-conducting surface, resulting in insufficient baking of the food and thus reducing the baking effect. Existing technologies have achieved rapid heating of food by adding a graphene coating and utilizing the graphene heating block's characteristics of uniform heating. However, kitchen appliances produced using existing technologies still suffer from technical problems such as uneven heating structure and slow temperature rise and fall response. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a method for preparing a flexible thermally and electrically conductive sheet, comprising the following steps: S1. Providing a thermally and electrically conductive substrate, and printing a conductive paste onto the substrate using a screen printing process to form conductive electrodes, followed by pre-curing; S2. Coating an adhesive layer onto the surface of the thermally and electrically conductive substrate treated in step S1, and then drying it; S3. Providing a flexible silicone sheet, and bonding it to the adhesive-coated surface of the thermally and electrically conductive substrate treated in step S2 using a roll forming process, followed by heat curing to integrate the flexible silicone sheet, adhesive, and thermally and electrically conductive substrate into a single unit; S4. Drilling holes in the flexible silicone sheet corresponding to the positions of the lower conductive electrodes to form through-holes penetrating the silicone sheet.

[0004] Furthermore, before step S1, step S0 is included: surface cleaning and roughening treatment of the conductive and thermally conductive substrate; the conductive and thermally conductive substrate is a graphene film or glass fiber fabric with a thickness of 10μm-100μm; the conductive paste is copper paste or silver paste, and carbon nanotubes or graphene powder are added to the paste.

[0005] Furthermore, the screen printing in step S1 uses a mesh count of 200-350; the pre-curing conditions are: treatment in a tunnel oven at 80°C-120°C for 5-15 minutes.

[0006] Furthermore, in step S2, the adhesive is a silicone resin-based, acrylic, or polyurethane thermosetting adhesive; it is applied by spraying, and the dry film thickness is controlled to be 5μm-25μm; the drying conditions are a temperature of 70°C-100°C and a time of 3-8 minutes.

[0007] Furthermore, in step S3, the flexible silicone sheet is a silicone rubber sheet filled with thermally conductive ceramic powder, with a thermal conductivity of 1.0-6.0 W / (m·K) and a thickness of 0.1mm-2.0mm; the rolling process is carried out on a heated roller at a temperature of 60°C-80°C and a linear pressure of 0.3-0.8MPa; the heating curing is hot pressing curing at a temperature of 120°C-160°C, a pressure of 0.1-0.5MPa, and a time of 30-120 minutes.

[0008] Furthermore, in step S4, the drilling process employs CNC punching, laser ablation, or plasma etching; the diameter of the through hole is 0.1mm-1.0mm.

[0009] Furthermore, after drilling in step S4, step S5 is also included: cleaning the inner wall of the through hole.

[0010] Furthermore, after the cleaning process described in step S5, step S6 is also included: filling the cleaned through hole with conductive silver paste or implanting a metal connector.

[0011] Furthermore, in step S3, the roller pressing and heating curing are continuous processes. The flexible silicone sheet and the substrate coated with adhesive are fed together into one or more sets of heated rollers for continuous pressing and preliminary curing, and then enter the oven for final heat curing.

[0012] Furthermore, the adhesive has a viscosity of 500-3000 mPa·s and a solid content of 40%-70% before coating; the spraying method is ultrasonic spraying, pressure spraying or electrostatic spraying.

[0013] Compared with the prior art, the beneficial effects of the present invention are:

[0014] This application ensures the long-term reliability of the product while constructing an efficient thermally conductive network through the introduction of functional conductive paste and high thermal conductivity filler. In particular, the functional modification of the adhesive layer, while ensuring the bonding between the substrate and the silicone sheet, achieves efficient thermal conductivity at the insulating interface, ultimately giving the prepared sheet excellent flexibility, insulation, interfacial bonding strength, and in-plane and vertical thermal and electrical conductivity.

[0015] Additional aspects and advantages of the invention will be set forth in the description which follows, and in some respects will be obvious from the description or may be learned by practice of the invention. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a process flow diagram illustrating the preparation method of the thermally and electrically conductive sheet of the present invention. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] The present invention will now be described in more detail. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. It should be noted that when an element is described as being "fixed to" another element, it can be directly on the other element, or one or more intermediate elements may exist between them. When an element is described as being "connected to" another element, it can be directly connected to the other element, or one or more intermediate elements may exist between them.

[0020] In the description of this invention, it should be noted that directional terms such as "front," "rear," "up," "down," "left," "right," "horizontal," "vertical," "horizontal," and "top," "bottom," etc., indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner or outer contours of each component itself. In the description of this invention, it should be noted that the use of terms such as "first" and "second" to define components is merely for the convenience of distinguishing the corresponding components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0021] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0022] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0023] The preferred embodiments of the present invention will now be further described with reference to the accompanying drawings. Example 1: A method for preparing a flexible thermally and electrically conductive sheet, characterized by the following steps: Preparatory step S0: Substrate pretreatment. A graphene film with a roughness of approximately 0.3 μm and a thickness of 35 μm is selected as the conductive and thermally conductive substrate. It is continuously passed through an online plasma treatment device under an argon atmosphere and a power of 800W for 3 seconds to effectively remove surface organic contaminants and activate surface energy. Subsequently, it is immediately immersed in a micro-etching solution (mainly composed of sodium persulfate and sulfuric acid) and treated at 40°C for 30 seconds to form a micron-level rough structure on the surface. This pretreatment step can improve the adhesion between the substrate and subsequent functional layers by at least 50%, fundamentally preventing delamination or peeling failure during use, and is the cornerstone of ensuring the long-term reliability of the product.

[0024] Next, we proceed to step S1: formation of the conductive electrodes. A functional conductive paste is prepared: micron-sized flake silver powder (D50=2μm) is used as the main conductive phase, accounting for 85wt% of the paste's solid content; innovatively, 1.2wt% of multi-walled carbon nanotubes are added as a reinforcing network framework for conductivity and thermal conductivity; the remainder consists of an organic carrier (ethyl cellulose dissolved in terpineol) and additives such as leveling agents and defoamers. The paste is dispersed at high speed under vacuum for 60 minutes in a planetary mixer to obtain a printing paste with a viscosity of approximately 12,000 cps and good thixotropic properties. Using a 350-mesh polyester stainless steel screen with a wire diameter of 31μm, and with the screen tension controlled at 25N / cm, a semi-automatic precision screen printing machine is used at a squeegee speed of 80mm / s to print conductive electrodes with a linewidth of 0.3mm on the pretreated graphene film. Immediately after printing, the substrate is placed in a three-zone tunnel oven for stepped pre-curing: Zone 1 at 80℃ for 2 minutes (slow solvent evaporation), Zone 2 at 110℃ for 6 minutes (initial cross-linking), and Zone 3 at 90℃ for 3 minutes (stress release). This pre-curing process not only cures the conductive electrodes, stabilizing their sheet resistance at 15mΩ, but also avoids internal stress accumulation caused by excessively rapid curing, ensuring the smoothness of the pattern edges and a strong bond with the substrate.

[0025] The next step is step S2: adhesive coating. A two-component addition-type liquid silicone rubber was selected as the base resin for the adhesive (A:B=1:1). To impart initial tack and control rheological properties, 10wt% methylphenyl silicone resin was added as a tackifying resin, and an appropriate amount of xylene solvent was added to adjust the system viscosity to approximately 2000 mPa·s, with a solid content of approximately 60%. A high-precision slit-type extrusion coating head was used at a speed of 5 m / min to coat a highly uniform wet film on the surface of the graphene film with grid electrodes, with the wet film thickness controlled at 40 μm. The coated substrate was then placed in a segmented far-infrared drying oven: the first stage was 65℃ / 3 minutes to gently remove most of the solvent and prevent surface skinning; the second stage was 85℃ / 4 minutes to allow the tackifying resin in the system to fully migrate to the surface, while simultaneously causing the silicone rubber to undergo an initial condensation reaction, achieving a conversion rate of approximately 30%. After this drying process, the adhesive layer is not completely cured, but forms a "B-stage" semi-cured film with a dry film thickness of approximately 25μm, excellent pressure-sensitive adhesion (initial peel strength of approximately 2.0N / 25mm), and a certain degree of cohesive strength. This state is the core technical effect of this step: it allows the subsequent silicone sheet to be precisely positioned and temporarily fixed with only slight pressure without the need for additional adhesive, greatly simplifying the assembly process. At the same time, it provides sufficient reaction space for final thermal curing, ensuring a dense and gapless final interface layer.

[0026] The next step is step S3: lamination and final curing of the flexible silicone sheet. A thermally conductive silicone sheet with a 50μm thick PET release film on one side is prepared. The base adhesive is vinyl silicone oil, filled with 70wt% high-purity spherical alumina powder with a bimodal particle size distribution (70% 3μm and 30% 15μm) treated with a silane coupling agent. This results in a silicone sheet with a thermal conductivity of 3.2 W / (m·K), a hardness of Shore A 40, and a thickness of 0.5mm. Before lamination, the PET release film on the silicone sheet is peeled off. A precision two-roller hot press laminating machine with temperature and pressure feedback is used. The upper roller temperature is set to 75℃, and the lower roller is a room-temperature support roller. The inter-roller linear pressure is precisely controlled at 0.5MPa. A graphene film coated with a semi-cured adhesive (adhesive side up) and a silicone sheet after the release film has been peeled off are simultaneously fed into the roller gap. Under the combined action of heat and pressure, the silicone sheet is flatly pressed onto the semi-cured adhesive film. During this process, the venting design of the roller gap effectively removes air between the interfaces, achieving an initial bonding without bubbles. Subsequently, this temporary composite is transferred to a flat vulcanizing machine for final thermosetting. The curing conditions are: at a mold closing pressure of 0.4 MPa, the temperature is increased from room temperature to 145°C at a rate of 10°C / min, and held at 145°C for 60 minutes, followed by natural cooling to below 60°C before mold opening. This thermosetting curing process allows the "B-stage" adhesive film and the silicone sheet base adhesive to undergo a sufficient covalent cross-linking reaction, with a final conversion rate exceeding 98%. This forms a gradient transition layer from the graphene film substrate to the silicone body without a clear physical interface. The interface peel strength can reach more than 8.0 N / cm, and the interface layer itself also has a thermal conductivity of about 1.0 W / (m·K). The thermal resistance in the thickness direction of the overall composite structure is significantly reduced.

[0027] Finally, step S4: precision machining of the vias. An ultraviolet laser processing system (wavelength 355nm) was used to ablate the cured composite silicone surface according to a pre-imported digital file that perfectly corresponds to the coordinates of the underlying grid electrode nodes. Laser parameters were set as follows: pulse frequency 40kHz, scanning speed 800mm / s, and repeated scanning 3 times. This resulted in a micro-hole array with a diameter of 0.35mm, smooth and vertical hole walls (taper <5°), and a depth strictly controlled at 0.50±0.02mm (i.e., just completely penetrating the 0.5mm silicone layer). The bottom of the holes precisely exposed the underlying silver grid conductive electrodes, and the cold processing characteristics of the laser ensured minimal thermal impact on the graphene film substrate and conductive electrodes, with no slag or carbonization. These vias form vertical channels from the outer surface of the composite material directly to the internal conductive network. This allows the sheet to achieve insulation, buffering, and lateral heat dissipation through the silicone layer on the upper surface, while also enabling fixed-point, low-resistance electrical connections with external components and efficient vertical heat transfer through these vias. This perfectly solves the spatially conflicting requirements of insulation and conductivity / thermal conduction.

[0028] Example 2 aims to demonstrate an optimized preparation method for higher performance and higher integration applications. Based on Example 1, it synergistically enhances materials and processes in multiple steps and introduces subsequent processing steps.

[0029] In step S0, the substrate is upgraded to a 50μm thick glass fiber fabric with a 1μm thick surface coating to obtain better surface conductivity and oxidation resistance. The pretreatment adopts a more enhanced chemical roughening process: immersion in an alkaline degreasing agent for ultrasonic cleaning for 2 minutes, followed by immersion in a micro-etching solution and treatment at 45°C for 45 seconds, to form a uniform honeycomb-like micro-rough structure on the surface, which increases the specific surface area by about 30% compared to Example 1, providing stronger mechanical anchoring points for subsequent interlayer bonding.

[0030] In step S1, a highly conductive copper paste was selected. The paste formulation was as follows: 82 wt% flake copper powder (D50=5μm, treated with antioxidants), 1.5 wt% flake graphene (as an antioxidant barrier and supplement to the conductive network), and the remainder being an organic carrier. A three-roll mill was used for higher-precision dispersion to ensure that the graphene uniformly coated the copper powder. A finer electrode was printed using a 250-mesh screen, with a minimum linewidth of 0.15 mm. Pre-curing was carried out in a tunnel oven under a nitrogen protective atmosphere, with a temperature profile of 100℃ / 10 minutes. The resulting electrode sheet resistance was approximately 25 mΩ / □, and its resistance stability was significantly improved under high temperature and high humidity conditions.

[0031] Step S2 focuses on the functional modification of the adhesive. A modified acrylate silicone resin with improved temperature resistance was selected as the base adhesive. To significantly improve vertical thermal conductivity, 25 wt% of functional thermally conductive fillers were uniformly dispersed within it: 15 wt% consisted of spherical boron nitride (BN) with an average particle size of 5 μm, whose ultra-high in-plane thermal conductivity (~300 W / (m·K)) can construct efficient thermal pathways in the planar direction; the other 10 wt% consisted of surface-hydroxylated zinc oxide (ZnO) whiskers, whose unique fibrous structure can act as a "thermal bridge" in the thickness direction. The addition of fillers increased the adhesive viscosity to approximately 2800 mPa·s. The coating process was upgraded to non-contact ultrasonic atomization spraying. By controlling the atomization frequency and carrier gas pressure, an extremely uniform adhesive layer with a thickness fluctuation of less than ±1.5 μm and a target dry film thickness of 10 μm was deposited on the substrate surface. The drying process used mid-infrared radiation heating, rapidly raising the temperature to 80°C and holding it for 6 minutes. This process is not only highly efficient and energy-saving, but also provides uniform heating, allowing the solvent to escape rapidly and the resin to partially cross-link. The resulting semi-cured adhesive film not only possesses pressure-sensitive adhesion, but more importantly, due to the directional arrangement of the high thermal conductivity filler (which undergoes a certain orientation due to leveling during spraying and drying), the in-plane thermal conductivity of the adhesive film layer is increased to 1.8 W / (m·K), and the thermal conductivity in the thickness direction also reaches 0.9 W / (m·K). This improvement transforms the adhesive layer from a simple bonding layer into a functional layer that actively participates in heat diffusion, which is crucial for rapidly diffusing heat from local hot spots laterally and transferring it to the underlying metal substrate.

[0032] Step S3 uses a flexible silicone sheet made of high tear strength addition-cure silicone rubber, filled with 80wt% aluminum nitride and alumina mixed filler, with a thickness of 1.0mm and a thermal conductivity as high as 4.8 W / (m·K). Lamination and curing are integrated into a continuous production line: First, the silicone sheet and the substrate coated with functionalized adhesive are initially bonded and aligned under ambient temperature rollers; then, the composite tape enters a multi-section hot-press conveyor belt curing oven. The first section is the "soft curing zone," with a conveyor belt temperature of 90℃, a pressure of 0.3MPa, and a time of 2 minutes, allowing the adhesive to further react and enhance cohesion; the second section is the "main curing zone," where the temperature rises to 160℃, the pressure increases to 0.6MPa, and the time is 5 minutes, achieving complete curing; the third section is the "annealing zone," where the temperature slowly decreases to 100℃, with no pressure, and the time is 3 minutes, releasing internal stress. The technical benefits of continuous production are that it ensures extreme consistency in product performance and high production efficiency. At the same time, the high-temperature, short-time curing process helps maintain the elasticity of the silicone sheet, and the final composite's interfacial peel strength exceeds 10 N / cm.

[0033] Step S4 employs high-precision CNC mechanical punching and drilling, with a die punch diameter of 0.20mm, a punching speed of 300 times / minute, and a punching position accuracy within ±15μm. Mechanical punching is extremely efficient, producing clean hole walls with no heat-affected zone.

[0034] Subsequently, this embodiment adds two post-processing steps. Step S5: Deep cleaning and activation of the vias. The perforated sheet is passed through a custom-designed cavity, where a uniform low-temperature oxygen plasma (500W power, 100sccm oxygen flow rate, 30 seconds processing time) is generated. Plasma bombardment thoroughly removes trace organic residues and adsorbed moisture that may be generated during punching within the vias. Simultaneously, it causes slight hydrophilic modification and micro-roughening of the silicone material surface on the via walls, significantly improving the wettability and adhesion of the filler to the via walls in subsequent steps. Step S6: Reinforcement of vertical interconnect channels. Using a precision screw dispensing machine with a vision positioning system, a fast-curing conductive silver paste with 85% silver content and a viscosity of approximately 20,000cps is filled into the plasma-treated vias at a precise dosage of approximately 5 nanoliters per via. After filling, it is immediately cured for 3 minutes under hot air at 120°C. The conductive silver paste not only perfectly fills the micropores but also forms ohmic contacts with the silicone walls of the pores and the silver-plated electrodes at the bottom of the pores. Through this step, the vertical on-resistance of a single via is reduced from tens of milliohms when relying solely on physical contact to below 5 milliohms. Simultaneously, due to the high thermal conductivity of the silver paste (approximately 25 W / (m·K)), the thermal resistance of the vertical channel is also reduced by approximately 60%. This allows the sheet material to provide both extremely low electrical grounding impedance and extremely high heat flow capability when used for heat dissipation and grounding of high-power-density chips, resulting in superior performance.

[0035] The details of the exemplary embodiments described above are provided, and the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention.

Claims

1. A method for preparing a flexible thermally and electrically conductive sheet, characterized in that, Includes the following steps: S1. Provide a conductive and thermally conductive substrate, and print conductive paste onto the conductive and thermally conductive substrate by screen printing process to form conductive electrodes, followed by pre-curing; S2. Apply an adhesive layer to the surface of the conductive and thermally conductive substrate treated in step S1, and then dry it. S3. A flexible silicone sheet is provided and bonded to the surface of the conductive and thermally conductive substrate coated with adhesive by a roll forming process. Then, it is heated and cured to make the flexible silicone sheet, adhesive and conductive and thermally conductive substrate integrated into one piece. S4. Drill holes in the flexible silicone sheet corresponding to the position of the lower conductive electrode to form a through hole penetrating the silicone sheet.

2. The method for preparing the flexible thermally and electrically conductive sheet according to claim 1, characterized in that, Before step S1, step S0 is also included: surface cleaning and roughening treatment of the conductive and thermally conductive substrate; the conductive and thermally conductive substrate is a graphene film or glass fiber fabric with a thickness of 10μm-100μm; the conductive paste is copper paste or silver paste, and carbon nanotubes or graphene powder are added to the paste.

3. The method for preparing the flexible thermally and electrically conductive sheet according to claim 1, characterized in that, The screen printing in step S1 uses a mesh size of 200-350; the pre-curing conditions are: treatment in a tunnel oven at 80°C-120°C for 5-15 minutes.

4. The method for preparing the flexible thermally and electrically conductive sheet according to claim 1, characterized in that, In step S2, the adhesive is a silicone resin, acrylic, or polyurethane thermosetting adhesive; it is applied by spraying, and the dry film thickness is controlled to be 5μm-25μm; the drying conditions are a temperature of 70°C-100°C and a time of 3-8 minutes.

5. The method for preparing the flexible thermally and electrically conductive sheet according to claim 1, characterized in that, In step S3, the flexible silicone sheet is a silicone rubber sheet filled with thermally conductive ceramic powder, with a thermal conductivity of 1.0-6.0 W / (m·K) and a thickness of 0.1mm-2.0mm; the rolling process is carried out on a heated roller with a roller temperature of 60°C-80°C and a linear pressure of 0.3-0.8MPa; the heating curing is hot pressing curing with a temperature of 120°C-160°C, a pressure of 0.1-0.5MPa, and a time of 30-120 minutes.

6. The method for preparing the flexible thermally and electrically conductive sheet according to claim 1, characterized in that, In step S4, the drilling process employs CNC punching, laser ablation, or plasma etching; the diameter of the through hole is 0.1mm-1.0mm.

7. The method for preparing the flexible thermally and electrically conductive sheet according to claim 1, characterized in that, After drilling in step S4, step S5 is also included: cleaning the inner wall of the through hole.

8. The method for preparing the flexible thermally and electrically conductive sheet according to claim 7, characterized in that, After the cleaning process described in step S5, the process further includes step S6: filling the cleaned through-hole with conductive silver paste or implanting a metal connector.

9. The method for preparing the flexible thermally and electrically conductive sheet according to claim 1, characterized in that, In step S3, the roller pressing and heating curing are continuous processes. The flexible silicone sheet and the substrate coated with adhesive are fed together into one or more sets of heated rollers for continuous pressing and preliminary curing, and then enter the oven for final heat curing.

10. The method for preparing the flexible thermally and electrically conductive sheet according to claim 4, characterized in that, The adhesive has a viscosity of 500-3000 mPa·s and a solid content of 40%-70% before coating; the spraying method is ultrasonic spraying, pressure spraying or electrostatic spraying.

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