A thermally conductive polyester composite material, a preparation method and application thereof

Abstract

The application relates to a heat-conducting polyester composite material and a preparation method and application thereof. The heat-conducting polyester composite material comprises the following components in parts by weight: 28-66 parts of PCT resin, 8-42 parts of reinforcing material and 10-42 parts of modified spherical boron nitride; the modified spherical boron nitride is spherical boron nitride with isocyanurate alkoxysilane on the surface; and the PCT resin has a characteristic viscosity of 0.5-1.0 dl / g. The heat-conducting polyester composite material has good mechanical properties, high inter-plane thermal conductivity and thermal conductivity isotropy.

Description

Technical Field

[0001] This invention relates to the field of polyester thermally conductive materials technology, and more specifically, to a thermally conductive polyester composite material, its preparation method, and its application. Background Technology

[0002] In recent years, with the increasing density and miniaturization of electronic products, lead-free reflow surface mount technology (SMT) has become an important assembly method. Its applications require components to withstand high temperatures of 250-280℃, which traditional engineering plastics such as PA66 and PBT simply cannot meet. Therefore, high-temperature resistant engineering plastics have emerged. Among them, semi-aromatic polyamide (PPA) is widely used due to its many advantages such as high melting point, high heat distortion temperature, high strength, and high dimensional stability. However, in certain natural or light-colored applications, the material is required to have excellent resistance to photothermal and oxidative aging and discoloration under long-term high-temperature application conditions. In this case, PPA is prone to aging and discoloration due to the inherent molecular structure of polyamide. Conventional methods of adding color stabilizing agents can only improve the aging and discoloration resistance of PPA materials to a certain extent and cannot meet the needs of applications with high color requirements. Poly(1,4-cyclohexanedimethyl terephthalate) (PCT), as a typical representative of high-temperature resistant polyester materials, not only has many advantages of conventional PPA materials such as high melting point, high heat distortion temperature, and high strength, but also has excellent resistance to photothermal and oxidative aging and color change due to the introduction of cyclohexane structure into its molecular structure, making it suitable for applications with high requirements for color stability.

[0003] Furthermore, with the rapid development of microelectronics integration and assembly technologies, assembly density has increased dramatically, and the size of electronic components and logic circuits has shrunk by thousands of times. Electronic instruments are becoming increasingly thinner and smaller, while operating frequencies are increasing dramatically, and the semiconductor thermal environment is rapidly changing towards higher temperatures. At this point, the heat generated by electronic devices accumulates rapidly. To ensure that electronic components can still operate normally with high reliability and efficiency under ambient temperatures, the thermal conductivity of the material becomes a crucial limiting factor affecting its lifespan. In actual use, the heat generated internally must be dissipated to the external environment through the plastic casing. Therefore, the magnitude of the vertical thermal conductivity plays a vital role; that is, the magnitude of the interplane thermal conductivity plays a crucial role.

[0004] In summary, the research and development of high-temperature resistant polyester materials with good thermal conductivity is of urgent practical significance.

[0005] Current high-temperature resistant polyester materials use thermally conductive fillers such as calcium carbonate and magnesium hydroxide. For example, a patented thermally conductive and flame-retardant polyester composite material and heat dissipation device for LED lamps uses calcium carbonate filler, which has a low thermal conductivity, resulting in a low thermal conductivity of the polyester material. Furthermore, the patent does not address the interplanar thermal conductivity of the material. In addition, the addition of thermally conductive fillers often reduces the tensile strength of the polyester material, thus affecting its application.

[0006] Therefore, it is necessary to develop a polyester material with high interplanar thermal conductivity and good tensile strength. Summary of the Invention

[0007] The primary objective of this invention is to overcome the problems of poor interplanar thermal conductivity of current polyester materials and the negative impact of thermally conductive fillers on the tensile strength of polyester materials, and to provide a thermally conductive polyester composite material. This thermally conductive polyester composite material has good mechanical properties as well as high interplanar thermal conductivity and thermal isotropy.

[0008] A further object of the present invention is to provide a method for preparing the above-mentioned thermally conductive polyester composite material.

[0009] A further object of the present invention is to provide the application of the above-mentioned thermally conductive polyester composite material in the manufacture of electronic products.

[0010] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0011] A thermally conductive polyester composite material comprises the following components in parts by weight:

[0012] 28-66 parts of PCT resin

[0013] 8-42 parts of reinforcing material

[0014] 10–42 parts of modified spherical boron nitride;

[0015] The modified spherical boron nitride is a spherical boron nitride with a surface modified isocyanurate alkoxysilane; the intrinsic viscosity of the PCT resin is 0.5 to 1.0 dl / g.

[0016] The inventors unexpectedly discovered that by modifying the surface of spherical boron nitride with isocyanurate alkoxysilane to obtain modified spherical boron nitride, and then adding this modified spherical boron nitride to PCT resin while controlling the intrinsic viscosity of the PCT resin, a thermally conductive polyester composite material with high interplanar thermal conductivity and isotropic thermal conductivity can be obtained. The reason is that isocyanurate alkoxysilane acts as a coupling agent, resulting in a tight bond between the two phases of spherical boron nitride and PCT resin. Furthermore, isocyanurate alkoxysilane possesses high reactivity and high heat resistance. Its high reactivity allows for a good chemical bonding force between it and the active functional groups of the matrix resin, while its high heat resistance ensures that it maintains good thermal stability and chemical activity at high temperatures (PCT resin has a high melting point, and the melting temperature must reach at least 300℃ during processing). This results in a strong interfacial bond and low interfacial thermal resistance between the modified spherical boron nitride and the PCT resin, thus achieving a high interplanar thermal conductivity. PCT resin with a specific intrinsic viscosity can exhibit high chemical reactivity. This high reactivity results in a strong chemical bond between the resin and modified spherical boron nitride, leading to strong interfacial bonding, low interfacial thermal resistance, and high interplanar thermal conductivity. Furthermore, by controlling the intrinsic viscosity of the PCT resin, the thermally conductive polyester composite material can maintain good tensile strength. If the intrinsic viscosity of the PCT resin is too high, its chemical reactivity is low. If the intrinsic viscosity of the PCT resin is too low, although it still exhibits high chemical reactivity, the physical and mechanical properties of the PCT bulk will be significantly reduced, resulting in a marked deterioration in the mechanical properties of the composition, ultimately causing the product to fail to meet basic usage requirements.

[0017] That is, the thermally conductive polyester composite material of the present invention has good mechanical properties (tensile strength) as well as high interplanar thermal conductivity and thermal isotropic conductivity.

[0018] The intrinsic viscosity of the PCT resin of the present invention can be measured according to the test standard GBT12006.1-2009. The specific process is as follows: 0.1250 g of PCT resin is dissolved in 25 ml of o-chlorophenol solution and measured in a constant temperature water bath at 25 ± 0.1 °C using an Ubbelohde viscometer.

[0019] Preferably, the thermally conductive polyester composite material comprises the following components in parts by weight:

[0020] 34-58 parts of PCT resin

[0021] 14-35 parts of reinforcing material,

[0022] 15-25 parts of modified spherical boron nitride;

[0023] Preferably, the average particle size of the spherical boron nitride is 15–130 μm.

[0024] More preferably, the average particle size of the spherical boron nitride is 15–75 μm.

[0025] Optionally, the isocyanurate alkoxysilane is at least one of isocyanurate trialkoxysilane or isocyanurate dialkoxysilane.

[0026] Preferably, the isocyanurate alkoxysilane is isocyanurate trialkoxysilane.

[0027] Compared to isocyanurate dialkoxysilanes (e.g., 1,3,5-tris(methyldimethoxysilylpropyl)isocyanurate), modifying with isocyanurate trimekoxysilanes (e.g., 1,3,5-tris(trimethoxysilylpropyl)isocyanurate, 1,3,5-tris(triethoxysilylpropyl)isocyanurate) results in thermally conductive polyester composites with higher thermal conductivity in both the in-plane and through-plane directions, as well as better tensile strength.

[0028] More preferably, the isocyanurate trialkoxysilane isocyanurate trimethoxysilane.

[0029] Compared to isocyanurate triethoxysilane (e.g., 1,3,5-tris(triethoxysilylpropyl)isocyanurate), the thermally conductive polyester composite material obtained by modification with isocyanurate trimethoxysilane (e.g., 1,3,5-tris(trimethoxysilylpropyl)isocyanurate) not only has higher thermal conductivity in both the in-plane and through-plane directions, but also better tensile strength.

[0030] In this invention, the mass ratio of isocyanurate alkoxysilane to spherical boron nitride in the modified spherical boron nitride is (0.2-4):100; it can be prepared by the following steps: 0.2-4 parts by weight of isocyanurate alkoxysilane and 100 parts by weight of spherical boron nitride are mixed at 40-80°C and 800-1200 rpm for 15-30 min.

[0031] Preferably, the mass ratio of isocyanurate alkoxysilane to spherical boron nitride in the modified spherical boron nitride is (0.2-1):100.

[0032] By adjusting the mass ratio of isocyanurate alkoxysilane to spherical boron nitride in modified spherical boron nitride, thermally conductive polyester composites can maintain good thermal conductivity (in the in-plane and through-plane directions) while exhibiting higher tensile strength.

[0033] Preferably, the intrinsic viscosity of the PCT resin is 0.6 to 0.8 dl / g.

[0034] Conventional reinforcing materials in this field can be used in this invention.

[0035] Preferably, the reinforcing material is at least one of glass fiber, carbon fiber, asbestos fiber, wollastonite fiber, ceramic fiber, potassium titanate whiskers, basic magnesium sulfate whiskers, silicon carbide whiskers, aluminum borate whiskers, silicon dioxide, aluminum silicate, silicon oxide, calcium carbonate, titanium dioxide, talc, wollastonite, diatomaceous earth, clay, kaolin, spherical glass, mica, or gypsum.

[0036] Applications of high-temperature resistant polyester materials often require them to have certain flame retardant properties; and organic phosphinate flame retardants, as halogen-free flame retardants, have excellent temperature resistance, so organic phosphinate flame retardants can be added as needed to give the thermally conductive polyester composite material of the present invention good flame retardant properties.

[0037] Preferably, the thermally conductive polyester composite material further includes 6-20 parts of organic phosphonate flame retardant, and the thermally conductive polyester composite material further includes 8-16 parts of organic phosphonate flame retardant.

[0038] More preferably, the organic phosphonate flame retardant includes at least one of aluminum diethylphosphonate, zinc diethylphosphonate, aluminum methyl ethylphosphonate, aluminum ethyl butylphosphonate, or aluminum ethylhexylphosphonate.

[0039] Preferably, the thermally conductive polyester composite material further includes 0.01 to 2 parts of other additives.

[0040] More preferably, the other additives are at least one of antioxidants, lubricants, or nucleating agents.

[0041] Optionally, the antioxidant is a hindered phenolic antioxidant or a phosphite antioxidant.

[0042] Optionally, the lubricant is a fluoropolymer, LLDPE, silicone oil, metal stearate, alkyl stearate, metal montanic acid, montanic ester wax, or polyethylene wax.

[0043] Optionally, the nucleating agent is talc, alumina, zirconium oxide, tin oxide, tin indium oxide, antimony tin oxide, calcium silicate, calcium carbonate, magnesium carbonate, or zeolite.

[0044] The preparation method of the above-mentioned thermally conductive polyester composite material includes the following steps: adding other components except for organic phosphonate flame retardant (if any), reinforcing material and modified spherical boron nitride from the main feed port of a twin-screw extruder, adding organic phosphonate flame retardant (if any), reinforcing material and modified spherical boron nitride from the side feed port of a twin-screw extruder, melting and blending at 250-300°C, granulating, and thus obtaining the thermally conductive polyester composite material.

[0045] The above-mentioned thermally conductive polyester composite material is used in the manufacture of electronic products.

[0046] Preferably, the electronic product is an electronic product that requires an SMT (Surface Mount Technology) process.

[0047] Optionally, the electronic products that need to undergo SMT processing include connectors, connector series components, optical cable connectors, plugs, USB series components, circuit breakers, winding elements, electric motor components, and electrical components.

[0048] Compared with the prior art, the beneficial effects of the present invention are:

[0049] The thermally conductive polyester composite material of the present invention has good mechanical properties, as well as high interplanar thermal conductivity and thermal isotropic conductivity. Detailed Implementation

[0050] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0051] The reagents used in the various embodiments and comparative examples of this invention are described below:

[0052] PCT resin can be a commercially available product or can be obtained in-house. PCT resin is typically obtained by sequentially esterifying, prepolymerizing, and condensing terephthalic acid and 1,4-cyclohexanediethanol. The intrinsic viscosity of the PCT resin is controlled by adding different amounts of di(triisopropylamine)titanate catalyst and / or benzoic acid end-capping agent. The PCT resin of this invention is obtained in-house, and the preparation method is as follows:

[0053] Terephthalic acid and 1,4-cyclohexanediethanol were added to a reactor at a molar ratio of PTA:CHDM = 1.2. Based on the total molar content of terephthalic acid and 1,4-cyclohexane, 0.02% di(triisopropylamine)titanate catalyst and 0.2-1.2% benzoic acid end-capping agent were added. The system was stirred to carry out the esterification reaction. The esterification reaction temperature was 260℃, the reaction pressure was atmospheric pressure, and water generated during the reaction was separated by a distillation column. The reaction time was 60 min. After the esterification reaction, a prepolymerization reaction was carried out at a temperature of 290℃, with the pressure gradually reduced at the beginning until it reached 1000 Pa. The reaction time was 60 min. After the prepolymerization reaction, a polycondensation reaction was carried out at a temperature of 300℃, a reaction pressure of 100 Pa, and a reaction time of 150 min. After the reaction, the obtained PCT polymer was cast into tapes and granulated to obtain PCT resin (chips). The intrinsic viscosity of PCT resin can be controlled by adding different amounts of benzoic acid end-capping agent (based on the total molar content of terephthalic acid and 1,4-cyclohexane).

[0054] PCT resin #1: intrinsic viscosity is 0.65 dL / g, self-made, end-capping agent dosage is 0.8%.

[0055] PCT resin #2: intrinsic viscosity is 0.50 dL / g, self-made, end-capping agent dosage is 1.0%.

[0056] PCT resin #3: intrinsic viscosity is 1.0 dL / g, self-made, end-capping agent dosage is 0.40%.

[0057] PCT resin #4: intrinsic viscosity is 0.60 dL / g, self-made, end-capping agent dosage is 0.85%.

[0058] PCT resin #5: intrinsic viscosity is 0.80 dL / g, self-made, end-capping agent dosage is 0.65%.

[0059] PCT resin #6: intrinsic viscosity is 1.2 dL / g, self-made, end-capping agent dosage is 0.2%.

[0060] PCT resin #7: intrinsic viscosity 0.35 dL / g, self-made, end-capping agent dosage is 1.2%.

[0061] Organic phosphinate flame retardant: aluminum diethylphosphinate, commercially available;

[0062] Reinforcing material #1: Glass fiber, OCV995, Owens Corning Composites;

[0063] Reinforcing material #2: Wollastonite, HQ-1250, Dalian Huanqiu Minerals Co., Ltd.;

[0064] Other additives: lubricant, LLDPE, commercially available;

[0065] Spherical boron nitride 1#: CFA 50M, average particle size 15μm, Kunshan Libaodi Electronic Materials;

[0066] Spherical boron nitride 2#: SA75, average particle size 75μm, SAINT-GOBAIN, FRANCE;

[0067] Spherical boron nitride 3#: SA125, average particle size 130μm, SAINT-GOBAIN, FRANCE;

[0068] Spherical boron nitride 4#: SA300, average particle size 315μm, SAINT-GOBAIN, FRANCE;

[0069] Flaky boron nitride: SP16, average particle size 16 μm, SAINT-GOBAIN, FRANCE;

[0070] Isocyanurate alkoxysilane 1#: KH-597, 1,3,5-tris(trimethoxysilylpropyl)isocyanurate, Hangzhou Jessica Chemical;

[0071] Isocyanurate alkoxysilane 2#: SF-YQ42, 1,3,5-tris(triethoxysilylpropyl)isocyanurate, Tangshan Sanfu New Materials;

[0072] Isocyanurate alkoxysilane 3#: SF-YQ43, 1,3,5-tris(methyldimethoxysilylpropyl)isocyanurate, Tangshan Sanfu New Materials;

[0073] Conventional silane coupling agent: KH-901, 3-isocyanate-propyltrimethoxysilane, Hangzhou Jessica Chemical;

[0074] Modified spherical boron nitride: self-made, the preparation process is as follows: mix isocyanurate alkoxysilane or conventional silane coupling agent with spherical boron nitride according to the formulation in Table 1, mixing temperature: 60℃, mixing time: 15min, mixing speed: 1000rpm.

[0075] Table 1. Formulation of modified spherical boron nitride (parts by weight)

[0076]

[0077]

[0078] Modified plate-shaped boron nitride: self-made, the preparation process is as follows: mix 1 part by weight of conventional silane coupling agent and 100 parts by weight of plate-shaped boron nitride, mixing temperature: 60℃, mixing time: 15min, mixing speed: 1000rpm.

[0079] Unless otherwise specified, all components (e.g., organic phosphonate flame retardants, other additives) used in the parallel examples and comparative examples are the same commercially available products.

[0080] The thermally conductive polyester composite materials provided in the embodiments and comparative examples of this invention were subjected to performance testing according to the following test methods:

[0081] (1) Tensile strength test: Tested according to ISO527-1 / -2 standard, sample shape and size is Type 1B, tensile rate is 10mm / min.

[0082] (2) Flame retardant performance test: Tested according to UL 94 standard, with a sample thickness of 0.8 mm;

[0083] (3) Thermal conductivity test: Tested according to ASTM E1461 standard, using LFA467 HyperFlash thermal conductivity meter, test temperature: 23℃, sample size Φ10×1mm round disc, in plane and through plane directions.

[0084] The thermally conductive polyester composite materials of the various embodiments and comparative examples of the present invention are prepared by the following preparation method: According to the formula, the other components except for the organic phosphonate flame retardant (if any), the reinforcing material and the modified spherical boron nitride are mixed evenly, and then added from the main feed port of the twin-screw extruder. The reinforcing material is added from the first side feed port. The organic phosphonate flame retardant (if any) and the modified spherical boron nitride / modified flake boron nitride / spherical boron nitride are added from the side feed port of the twin-screw extruder. The mixture is melt-blended at 250-300°C and granulated to obtain the thermally conductive polyester composite material.

[0085] Examples 1-18

[0086] Examples 1-18 provide a series of thermally conductive polyester composite materials, the formulations of which are shown in Tables 2 and 3.

[0087] Table 2. Formulations (parts by weight) for Examples 1-11

[0088]

[0089] Table 3. Formulations (parts by weight) for Examples 12-18

[0090]

[0091] Comparative Example 1

[0092] This comparative example provides a thermally conductive polyester composite material whose formulation differs from that of Example 1 in that PCT resin 1# is replaced with PCT resin 6#.

[0093] Comparative Example 2

[0094] This comparative example provides a thermally conductive polyester composite material whose formulation differs from that of Example 1 in that modified spherical boron nitride 1# is replaced with modified spherical boron nitride 9#.

[0095] Comparative Example 3

[0096] This comparative example provides a thermally conductive polyester composite material whose formulation differs from that of Example 1 in that modified spherical boron nitride 1# is replaced with spherical boron nitride 1#.

[0097] Comparative Example 4

[0098] This comparative example provides a thermally conductive polyester composite material whose formulation differs from that of Example 1 in that modified spherical boron nitride 1 is not added.

[0099] Comparative Example 5

[0100] This comparative example provides a thermally conductive polyester composite material whose formulation differs from that of Example 1 in that the modified spherical boron nitride 1# is replaced with modified sheet-like boron nitride.

[0101] Comparative Example 6

[0102] This comparative example provides a thermally conductive polyester composite material whose formulation differs from that of Example 1 in that PCT resin 1# is replaced with PCT resin 7#.

[0103] The properties of the thermally conductive polyester composite materials of each embodiment and comparative example were determined according to the test methods mentioned above, and the test results are shown in Table 4.

[0104] Table 4 Performance test results of each embodiment and comparative example

[0105]

[0106]

[0107] As can be seen from Table 4:

[0108] The thermally conductive polyester composite materials of Examples 1-18 achieve a flame retardancy rating of V-0, a thermal conductivity of 1.74 W / m·K or higher in the in-plane direction, and a thermal conductivity of 1.72 W / m·K or higher in the through-plane direction, indicating that the thermally conductive polyester composite material of the present invention has good flame retardant properties, high interplanar thermal conductivity, and isotropic thermal conductivity. Furthermore, the tensile strength of the thermally conductive polyester composite material of the present invention is 52 MPa or higher, meeting the requirements for use.

[0109] Comparative Example 1 used PCT resin #6, which had a very high intrinsic viscosity, resulting in a thermally conductive polyester composite material with low thermal conductivity in both the in-plane and through-plane directions. Comparative Example 2 used modified spherical boron nitride #9, obtained by modifying spherical boron nitride with a conventional coupling agent. The resulting thermally conductive polyester composite material also had low thermal conductivity in both the in-plane and through-plane directions. Comparative Example 3 used unmodified spherical boron nitride #1, resulting in a thermally conductive polyester composite material with low thermal conductivity in both the in-plane and through-plane directions. Comparative Example 4 did not use modified spherical boron nitride #1, resulting in a thermally conductive polyester composite material with very low thermal conductivity in both the in-plane and through-plane directions. Comparative Example 5 used modified lamellar boron nitride, resulting in a thermally conductive polyester composite material with relatively low thermal conductivity in the in-plane direction and significantly low thermal conductivity in the through-plane direction.

[0110] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A thermally conductive polyester composite material, characterized in that, The components include the following parts by weight: 28-66 parts of PCT resin, 14-42 parts of reinforcing material 10-42 parts of modified spherical boron nitride; The modified spherical boron nitride is a spherical boron nitride with a surface modified isocyanurate alkoxysilane; the intrinsic viscosity of the PCT resin is 0.5~0.65 dl / g; The isocyanurate alkoxysilane is isocyanurate trialkoxysilane.

2. The thermally conductive polyester composite material according to claim 1, characterized in that, The average particle size of the spherical boron nitride is 15~130 μm.

3. The thermally conductive polyester composite material according to claim 1, characterized in that, The isocyanurate trialkoxysilane is isocyanurate trimethoxysilane.

4. The thermally conductive polyester composite material according to claim 1, characterized in that, The intrinsic viscosity of the PCT resin is 0.6~0.65 dl / g.

5. The thermally conductive polyester composite material according to claim 1, characterized in that, The thermally conductive polyester composite material further includes 6-20 parts of an organic phosphonate flame retardant, wherein the organic phosphonate flame retardant includes at least one of aluminum diethylphosphonate, zinc diethylphosphonate, aluminum methyl ethylphosphonate, aluminum ethyl butylphosphonate, or aluminum ethylhexylphosphonate.

6. The thermally conductive polyester composite material according to claim 1, characterized in that, The reinforcing material is at least one of glass fiber, carbon fiber, asbestos fiber, wollastonite fiber, ceramic fiber, potassium titanate whiskers, basic magnesium sulfate whiskers, silicon carbide whiskers, aluminum borate whiskers, silicon dioxide, aluminum silicate, silicon oxide, calcium carbonate, titanium dioxide, talc, wollastonite, diatomaceous earth, clay, kaolin, spherical glass, mica, or gypsum.

7. The thermally conductive polyester composite material according to claim 1, characterized in that, The thermally conductive polyester composite material comprises the following components in parts by weight: 34-58 parts of PCT resin 14-35 parts of reinforcing material, 15-25 parts of modified spherical boron nitride.

8. A method for preparing the thermally conductive polyester composite material according to any one of claims 1 to 7, characterized in that, The process includes the following steps: adding all components except the reinforcing material and modified spherical boron nitride from the main feed port of the screw extruder, adding the reinforcing material and modified spherical boron nitride from the side feed port of the screw extruder, melting and blending at 250~310℃, and granulating to obtain the thermally conductive polyester composite material.

9. The application of the thermally conductive polyester composite material according to any one of claims 1 to 7 or the thermally conductive polyester composite material prepared by the preparation method according to claim 8 in the preparation of electronic products.

Images