A high-performance halogen-free flame-retardant polycarbonate composition, laminated composite material and preparation method and application thereof

Abstract

This invention discloses a high-performance halogen-free flame-retardant polycarbonate composition, a laminated composite material, its preparation method, and its applications, belonging to the field of composite material technology. The composition is prepared by melt extrusion granulation of the following raw materials in parts by weight: 100 parts polycarbonate resin, 5-25 parts halogen-free flame retardant, 0.1-8 parts modified nano-layered silicate, and 0.1-5 parts additives. The modified nano-layered silicate is obtained by a combination of variable-speed ball milling exfoliation and in-situ silane modification. The laminated composite material has at least a three-layer sandwich structure, formed by hot-pressing a preform of flame-retardant polycarbonate film and reinforcing fiber cloth under heating and pressure. It possesses excellent halogen-free flame retardancy, high mechanical strength, good dielectric properties, and outstanding interfacial bonding strength, making it suitable for structural components of electronic and electrical devices with stringent performance requirements, insulating components of new energy vehicle battery packs, interior parts of transportation vehicles, and flexible circuit board substrates, with broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a high-performance halogen-free flame-retardant polycarbonate composition, laminated composite material, its preparation method and application. Background Technology

[0002] With the rapid development of electronics, electrical engineering, new energy vehicles, and 5G communication technologies, increasingly stringent performance requirements are being placed on the key basic materials used in these technologies. Ideal materials need to possess excellent flame retardancy and safety, high mechanical strength, outstanding dimensional stability, and good dielectric properties (low dielectric constant and low dielectric loss factor) to meet the needs of high-frequency and high-speed signal transmission, while also complying with halogen-free and environmentally friendly regulations.

[0003] Thermoplastic polycarbonate (PC) resin is widely used in the aforementioned fields due to its excellent impact resistance, high light transmittance, good insulation, and heat resistance. However, the flame retardant properties of pure PC resin are limited, and modification with flame retardants is usually required. Although traditional halogenated flame retardants are highly efficient, they produce a large amount of toxic and corrosive gases during combustion, and their use has been explicitly restricted by regulations such as the EU RoHS. Therefore, the development of halogen-free flame-retardant PC systems has become an inevitable trend. Currently, most mainstream halogen-free flame-retardant technologies use phosphorus-nitrogen synergistic flame retardants. However, these flame retardants often require high addition levels (usually >15%) to achieve the ideal flame retardant rating (such as UL94V-0). High addition levels can lead to a significant decrease in the mechanical properties of the PC matrix material (especially toughness and flowability), and may also degrade its dielectric properties.

[0004] To achieve high-efficiency flame retardancy while maintaining or enhancing matrix properties at low addition levels, nanofillers, especially layered silicates (such as montmorillonite, MMT), are considered highly promising flame retardant synergists. Nano-montmorillonite forms nanocomposite structures in polymers, significantly improving the thermal stability, barrier properties, and flame retardancy of materials. However, untreated nano-montmorillonite is hydrophilic and has poor compatibility with hydrophobic polymer matrices, easily agglomerating and dispersing unevenly, thus forming defects at the phase interface. This not only fails to provide reinforcement but also leads to a deterioration of the material's mechanical properties. Conventional mechanical blending methods are insufficient to effectively overcome the agglomeration problem of nanoparticles and cannot fully utilize their nano-effects. On the other hand, fiber-reinforced composites are often used in applications requiring higher mechanical properties and dimensional stability. Thermosetting resin (such as epoxy resin) matrix composites reinforced with glass fiber cloth or carbon fiber cloth are widely used, but they suffer from complex preparation processes (involving curing reactions), difficult recycling, and poor dielectric properties of some thermosetting resins. Although there are related technologies that use thermoplastic resins (such as PP and PA) to combine with fiber cloth, they generally suffer from problems such as high resin melt viscosity, poor fiber wettability, and weak interfacial bonding, resulting in low interlaminar shear strength of composite materials and easy delamination.

[0005] In the prior art, for example, Chinese patent application CN116512496A discloses a method for preparing prepregs using a composite of liquid crystal polymer (LCP) film and fiberglass cloth, intended for use in high-frequency circuits. While this method offers a novel technical approach, the extremely high cost of LCP raw materials and the narrow processing temperature window severely limit its large-scale application. Furthermore, this method fails to solve the common industry challenge of achieving uniform dispersion and strong interfacial bonding of nanofillers in a resin matrix at low cost and with high efficiency. Summary of the Invention

[0006] To overcome the aforementioned shortcomings of the prior art, the first objective of this invention is to provide a high-performance halogen-free flame-retardant polycarbonate composition. By modifying the functional filler nano-layered silicate, the composition overcomes the problems of easy agglomeration, uneven dispersion, and weak interfacial bonding between nano-layered silicate and the polymer matrix. While leveraging its nano-reinforcing effect and flame-retardant synergistic effect, the composition significantly improves the flame-retardant rating of the polycarbonate material (reaching halogen-free V-0 level), maximizing the preservation of its mechanical properties and excellent dielectric properties, and avoiding performance degradation caused by high amounts of flame retardant.

[0007] A second objective of this invention is to provide a laminated composite material comprising the above-mentioned high-performance halogen-free flame-retardant polycarbonate composition, which combines the advantages of excellent halogen-free flame retardancy, high mechanical strength, excellent dielectric properties, good dimensional stability, and easy recyclability.

[0008] The third objective of this invention is to provide a method for preparing the laminated composite material, which uses a surface-treated reinforcing fiber cloth as a skeleton and a halogen-free flame-retardant polycarbonate containing modified nanofillers as a matrix. This method is efficient, continuous, and cost-controllable, improves the wetting ability of molten thermoplastic resin on the reinforcing fiber cloth, establishes a strong interfacial bond, prevents delamination of the composite material during use, and achieves a high level of interlaminar shear strength and dimensional stability.

[0009] The fourth objective of this invention is to provide applications of the laminated composite material that are suitable for application scenarios with stringent requirements for lightweight, high reliability, high security, and high-frequency signal transmission performance, thereby meeting the urgent demand for high-performance materials in fields such as high-end electronics, new energy vehicles, and 5G communications.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a high-performance halogen-free flame-retardant polycarbonate composition, which, by weight, is made from raw materials comprising the following components by melt blending and extrusion granulation: 100 parts of polycarbonate resin, 5-25 parts of halogen-free flame retardant, 0.1-8 parts of modified nano-layered silicate, and 0.1-5 parts of additives.

[0012] The modified nanolayered silicate is prepared by a method comprising the following steps:

[0013] (a) Disperse nano-layered silicates in a solvent to form a suspension with a mass fraction of 1%-10%;

[0014] (b) The suspension was subjected to a stripping treatment using a variable-speed ball milling method;

[0015] (c) The silane coupling agent is dissolved in a mixed solvent of ethanol and water, and the pH is adjusted to 4-5 with acid for hydrolysis to obtain a silane hydrolysate;

[0016] (d) The silane hydrolysate is mixed with the suspension treated in step (b), and the mixture is stirred in a water bath at 60-85°C for 4-8 hours. The reaction products are separated, washed, and vacuum dried at 70-90°C for 12-24 hours to obtain modified nano-layered silicates.

[0017] The nanolayered silicate is selected from one of montmorillonite, vermiculite, and hydrotalcite.

[0018] Preferably, in step (b), the variable speed ball milling method includes: first running at 200-400 rpm for 0.5-1.5 hours, and then running at 500-800 rpm for 2-6 hours.

[0019] Preferably, in step (c), the silane coupling agent is one of aminosilane, epoxysilane, and methacryloxysilane, and the amount of the silane coupling agent is 5%-30% of the dry weight of the nanolayered silicate.

[0020] More preferably, the nanolayered silicate is sodium-based montmorillonite; and / or the silane coupling agent is γ-aminopropyltriethoxysilane (KH-550).

[0021] Preferably, the polycarbonate resin is a high-flow polycarbonate with a melt flow rate (MFR, 300℃ / 1.2kg) of not less than 15g / 10min.

[0022] Preferably, the halogen-free flame retardant is a compound system of phosphorus-based, nitrogen-based, and silicon-based flame retardants; the phosphorus-based flame retardant is bisphenol A-bis(diphenyl phosphate) (BDP) and / or resorcinol bis(diphenyl phosphate) (RDP); the nitrogen-based flame retardant is melamine cyanurate (MCA) and / or melamine polyphosphate (MPP); and the silicon-based flame retardant is polysiloxane and / or silicone powder.

[0023] Preferably, the halogen-free flame retardant is composed of BDP and MCA in a mass ratio of 3-5:1.

[0024] Preferably, the additives include one or more of antioxidants, lubricants, and light stabilizers.

[0025] A second aspect of the present invention provides a laminated composite material having a structure of at least three layers sandwiched together, comprising:

[0026] The upper layer is at least one flame-retardant polycarbonate film prepared from the high-performance halogen-free flame-retardant polycarbonate composition;

[0027] The middle layer consists of at least one layer of reinforcing fiber fabric;

[0028] The lower layer is at least one flame-retardant polycarbonate film prepared from the high-performance halogen-free flame-retardant polycarbonate composition;

[0029] The flame-retardant polycarbonate film has a thickness of 0.05-0.5 mm and is made from the high-performance halogen-free flame-retardant polycarbonate composition by a calendering process. The calendering temperature is 230-290℃ and the roller speed is 5-15 m / min.

[0030] Preferably, the reinforcing fiber cloth is a surface-treated glass fiber cloth or carbon fiber cloth, and the surface treatment includes impregnating and drying the reinforcing fiber cloth with a silane coupling agent solution; the silane coupling agent solution contains 0.5%-5.0% aminosilane.

[0031] A third aspect of the present invention provides a method for preparing the laminated composite material, comprising the following steps:

[0032] (1) Arrange at least one layer of the reinforcing fiber between at least two layers of the flame-retardant polycarbonate film to form a laminated preform;

[0033] (2) The laminated preform is fed into a calendering composite equipment and hot-pressed composite is carried out under heating and pressure conditions, wherein the temperature of the calendering roller is 220-280℃, the linear pressure is 30-250N / mm, and the production speed is 2-8m / min, so that the flame-retardant polycarbonate film melts into a viscous flow state, completely impregnates and covers the reinforcing fiber cloth, and is cooled, shaped and wound up to obtain the laminated composite material.

[0034] Preferably, the calendering and compounding equipment is a four-roll calender.

[0035] A fourth aspect of the present invention provides the application of the laminated composite material in the preparation of structural parts for electronic and electrical devices, insulating parts for battery packs of new energy vehicles, interior parts for transportation vehicles, and flexible circuit board substrates, wherein the laminated composite material is obtained by stamping, cutting, or in-mold injection molding processes.

[0036] Preferably, the new energy vehicle battery pack components include insulating separators, cover plates, or module end plates made of the laminated composite material.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] I. This invention modifies nano-layered silicates by combining variable-speed ball milling pretreatment with in-situ silanization modification. The mechanical shear force of ball milling effectively peels off silicate layers, increasing their specific surface area and reactive sites. The silanization reaction is carried out directly on the peeled fresh surface, allowing the silane coupling agent to be firmly grafted in the form of covalent bonds. The resulting modified nano-layered silicates exhibit nanoscale dispersion in the polymer matrix and have good interfacial compatibility with the PC matrix.

[0039] II. The laminated composite material of the present invention comprises a high-performance halogen-free flame-retardant polycarbonate composition, with surface-treated reinforcing fiber cloth as the skeleton and halogen-free flame-retardant polycarbonate containing modified nanofillers as the matrix. It has excellent flame retardancy, mechanical properties, dielectric properties and good flowability, achieving 1) efficient peeling and uniform dispersion of nanofillers in the resin matrix; 2) while significantly improving the flame retardant properties of the material, it maintains or even enhances its mechanical and dielectric properties to the maximum extent; 3) good wetting and firm bonding of thermoplastic resin to the reinforcing fiber cloth.

[0040] Third, the high fluidity of the high-performance halogen-free flame-retardant polycarbonate composition results in lower viscosity after melting, making it easy to flow and spread. At the same time, the special silane treatment of the fiber cloth gives it excellent chemical compatibility with the PC matrix. The uniform linear pressure of the four-roll calender ensures that the molten PC can fully penetrate every gap of the fiber cloth and form a strong chemical bond and mechanical interlock with the fiber surface, resulting in a laminated composite material with extremely strong interfacial bonding and no risk of delamination. Its interlaminar shear strength (ILSS) is greatly improved.

[0041] Fourth, the calendering-film-four-roll calendering composite integrated process route provided by this invention is an efficient and continuous industrial production process that effectively ensures the uniformity and stability of product quality, and is particularly suitable for large-scale, high-standard production needs.

[0042] Fifth, the laminated composite material of the present invention not only has the characteristics of high heat resistance, high impact resistance and high rigidity, but also maintains excellent dielectric properties (low Dk / Df), which meets the requirements of 5G high-frequency signal transmission. At the same time, the material has low density and is recyclable, which is in line with the trend of lightweighting and sustainable development, and has broad application prospects in high-end electronic appliances, new energy vehicles, next-generation communication equipment and other fields. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and comparative examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0044] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0045] Example 1

[0046] 1. Preparation of modified nano-montmorillonite:

[0047] Weigh 100 g of sodium montmorillonite and disperse it in 2 L of deionized water. Stir mechanically for 2 hours to form a homogeneous suspension. Transfer the suspension to a 5 L planetary ball mill jar, add zirconia grinding balls (ball-to-material mass ratio of 15:1), and set the ball milling program: first run at 300 rpm for 50 minutes, then switch to 700 rpm for 4 hours. In a separate beaker, add 750 mL of ethanol and 250 mL of deionized water, and add 20 g of silane coupling agent KH-550 while stirring. Adjust the pH to 4.8 by adding glacial acetic acid dropwise, and continue stirring for 40 minutes to obtain a hydrolysate. Slowly add the hydrolysate to the ball-milled montmorillonite suspension, transfer to an 85℃ water bath reactor, and react mechanically for 6 hours. After the reaction, filter, and wash the filter cake three times with a 1:1 volume ratio of ethanol to water. The filter cake was dried in a vacuum drying oven at 85°C for 24 hours, then lightly ground and passed through a 400-mesh sieve to obtain a white powdery organic modified montmorillonite (OMMT-1).

[0048] 2. Preparation of flame-retardant PC composition:

[0049] Prepare the raw materials according to the following weight proportions:

[0050] High-flowability PC (melt index 22 g / 10min, 300℃ / 1.2kg): 100 parts;

[0051] Phosphorus-based flame retardant BDP: 12 parts;

[0052] Nitrogen-based flame retardant MCA: 3 parts;

[0053] The above-prepared OMMT-1: 1.5 parts;

[0054] Antioxidant 1010: 0.3 parts;

[0055] Lubricant PETS: 0.5 parts

[0056] All raw materials are placed in a high-speed mixer and mixed for 5 minutes. The mixed material is then fed into the main feed port of a twin-screw extruder for melt blending, extrusion, cooling, and pelletizing. The temperature of each zone of the extruder is 240-260℃, and the screw speed is 300rpm, to obtain flame-retardant PC masterbatch (FR-PC-1).

[0057] 3. Preparation of PC film:

[0058] FR-PC-1 granules are fed into the calender hopper and calendered into a film. The temperatures of each roller in the calender are: Roll I 255℃, Roll II 260℃, Roll III 265℃, Roll IV 260℃, and the roller speed is 10m / min. Finally, a flame-retardant PC film (F-PC-1) with a thickness of 0.2mm and a smooth surface is obtained.

[0059] 4. Preparation of surface-treated fiberglass cloth:

[0060] Prepare a 2.0 wt% KH-550 aqueous solution, adjust the pH to 5.0 with acetic acid, immerse 1080 type electronic grade glass fiber cloth in the above solution for 2 minutes, control the liquid content to 80% by the extrusion roller, dry the impregnated glass fiber cloth in the drying tunnel at 125℃ for 5 minutes, and then roll it up to obtain surface-treated glass fiber cloth (T-GF-1).

[0061] 5. Preparation of laminated composite materials:

[0062] Two layers of F-PC-1 film and one layer of T-GF-1 fiberglass cloth are stacked in the order of film-fiber cloth-film. The resulting laminate is fed into a four-roll calender for hot pressing and lamination. The roll temperatures of the four-roll calender are: Roll I 258℃, Roll II 262℃, Roll III 260℃, Roll IV 257℃, linear pressure is 100N / mm, and production speed is 5 m / min. The laminated material is cooled and shaped by a cooling roller group (20℃) and finally wound up to obtain the final three-layer structure laminated composite material Laminate-1.

[0063] Example 2

[0064] 1. Preparation of modified nano-montmorillonite:

[0065] The method is basically the same as in Example 1, except that the amount of silane coupling agent used is 15g, and the ball milling program is to first ball mill at 250rpm for 1 hour, and then ball mill at 650rpm for 4.5 hours to obtain OMMT-2.

[0066] 2. Preparation of flame-retardant PC composition:

[0067] High-liquidity PC: 100 units;

[0068] BDP: 15 servings;

[0069] MCA: 3.75 parts (maintain BDP:MCA = 4:1);

[0070] OMMT-2: 2.5 portions;

[0071] Antioxidant 1010: 0.5 parts;

[0072] Lubricant PETS: 0.7 parts;

[0073] The processing technology is the same as in Example 1, resulting in FR-PC-2.

[0074] 3. Preparation of PC film:

[0075] Using FR-PC-2, the temperature of each roll in the calender is increased to 265-270℃ to produce a 0.25mm thick F-PC-2 film.

[0076] 4. Preparation of laminated composite materials:

[0077] Using F-PC-2 film and T-GF-1 fiberglass cloth, the four-roll calendering process parameters are: roll temperature of 265℃, linear pressure of 120N / mm, and speed of 4m / min, to obtain the laminated composite material Laminate-2.

[0078] Example 3

[0079] 1. Preparation of modified nano-montmorillonite:

[0080] The method is basically the same as in Example 1, except that KH-560 is used as a silane coupling agent, and the amount is 25g, to obtain OMMT-3.

[0081] 2. Preparation of flame-retardant PC composition:

[0082] High-liquidity PC: 100 units;

[0083] BDP: 10 servings;

[0084] MCA: 2.5 parts (maintain BDP:MCA = 4:1);

[0085] OMMT-3: 0.8 parts;

[0086] Antioxidant 1010: 0.2 parts;

[0087] Lubricant PETS: 0.3 parts;

[0088] The processing technology is the same as in Example 1, resulting in FR-PC-3.

[0089] 3. Preparation of PC film:

[0090] Using FR-PC-3, with the temperature of each roll in the calender set at 250-255℃, a film of F-PC-3 with a thickness of 0.15mm is produced.

[0091] 4. Preparation of laminated composite materials:

[0092] Laminate-3 composite material was prepared using F-PC-3 film and T-GF-1 fiberglass cloth with four-roll calendering process parameters of 252℃ roll temperature, 80N / mm linear pressure, and 7m / min speed.

[0093] Comparative Example 1

[0094] Using the same PC raw materials, flame retardant BDP / MCA (15 parts total) and additives as in Example 1, but without adding any modified montmorillonite, PC films and laminated composites (Comp-Laminate) were prepared using the same process, as shown in Table 1.

[0095] Table 1

[0096]

[0097] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-performance halogen-free flame-retardant polycarbonate composition, characterized in that, It is made by melt blending and extrusion granulation of raw materials comprising the following components in parts by weight: 100 parts polycarbonate resin, 5-25 parts halogen-free flame retardant, 0.1-8 parts modified nano-layered silicate, and 0.1-5 parts additives. The modified nanolayered silicate is prepared by a method comprising the following steps: (a) Dispersing nano-layered silicates in a solvent to form a suspension with a mass fraction of 1%-10%; (b) The suspension was subjected to a stripping treatment using a variable-speed ball milling method; (c) The silane coupling agent is dissolved in a mixed solvent of ethanol and water, and the pH is adjusted to 4-5 with acid for hydrolysis to obtain a silane hydrolysate; (d) The silane hydrolysate is mixed with the suspension treated in step (b), and the mixture is stirred in a water bath at 60-85°C for 4-8 hours. The reaction product is separated, washed, and vacuum dried at 70-90°C for 12-24 hours to obtain modified nano-layered silicate.

2. The high-performance halogen-free flame-retardant polycarbonate composition according to claim 1, characterized in that, The nano-layered silicate is selected from one of montmorillonite, vermiculite, and hydrotalcite; And / or the variable speed ball milling method includes: first running at 200-400 rpm for 0.5-1.5 hours, and then running at 500-800 rpm for 2-6 hours; And / or the silane coupling agent is one of aminosilane, epoxysilane, or methacryloxysilane, and the amount of the silane coupling agent is 5%-30% of the dry weight of the nanolayered silicate.

3. The high-performance halogen-free flame-retardant polycarbonate composition according to claim 2, characterized in that, The nanolayered silicate is sodium-based montmorillonite, and the silane coupling agent is γ-aminopropyltriethoxysilane.

4. The high-performance halogen-free flame-retardant polycarbonate composition according to claim 1, characterized in that, The polycarbonate resin is a high-flow polycarbonate with a melt flow rate (MFR, 300℃ / 1.2kg) of not less than 15g / 10min; And / or the additives include one or more of antioxidants, lubricants, and light stabilizers.

5. The high-performance halogen-free flame-retardant polycarbonate composition according to claim 1, characterized in that, The halogen-free flame retardant is a compound system of phosphorus-based, nitrogen-based, and silicon-based flame retardants. The phosphorus-based flame retardant is bisphenol A-bis(diphenyl phosphate) and / or resorcinol bis(diphenyl phosphate). The nitrogen-based flame retardant is melamine cyanurate and / or melamine polyphosphate. The silicon-based flame retardant is polysiloxane and / or silicone powder.

6. The high-performance halogen-free flame-retardant polycarbonate composition according to claim 5, characterized in that, The halogen-free flame retardant is composed of bisphenol A-bis(diphenyl phosphate) and melamine cyanurate in a mass ratio of 3-5:

1.

7. A laminated composite material, characterized in that, Its structure is a sandwich structure with at least three layers, including: The upper layer is at least one flame-retardant polycarbonate film prepared from the high-performance halogen-free flame-retardant polycarbonate composition according to any one of claims 1 to 6; The middle layer consists of at least one layer of reinforcing fiber fabric; The lower layer is at least one flame-retardant polycarbonate film prepared from the high-performance halogen-free flame-retardant polycarbonate composition; The flame-retardant polycarbonate film has a thickness of 0.05-0.5 mm and is made from the high-performance halogen-free flame-retardant polycarbonate composition by a calendering process. The calendering temperature is 230-290℃ and the roller speed is 5-15 m / min.

8. The laminated composite material according to claim 7, characterized in that, The reinforcing fiber cloth is a surface-treated glass fiber cloth or carbon fiber cloth. The surface treatment includes impregnating and drying the reinforcing fiber cloth with a silane coupling agent solution. The silane coupling agent solution contains 0.5%-5.0% aminosilane.

9. The method for preparing the laminated composite material according to claim 7 or 8, characterized in that, Includes the following steps: (1) Arrange at least one layer of the reinforcing fiber between at least two layers of the flame-retardant polycarbonate film to form a laminated preform; (2) The laminated preform is fed into a calendering composite equipment and hot-pressed composite is carried out under heating and pressure conditions, wherein the temperature of the calendering roller is 220-280℃, the linear pressure is 30-250N / mm, and the production speed is 2-8m / min, so that the flame-retardant polycarbonate film melts into a viscous flow state, completely impregnates and covers the reinforcing fiber cloth, and is cooled, shaped and wound up to obtain the laminated composite material.

10. The application of the laminated composite material of claim 7 or 8 in the preparation of structural parts for electronic and electrical devices, insulating parts for battery packs of new energy vehicles, interior parts for transportation vehicles, and flexible circuit board substrates, wherein the laminated composite material is obtained by stamping, cutting, or in-mold injection molding.

11. The application according to claim 10, characterized in that, The new energy vehicle battery pack components include insulating separators, cover plates, or module end plates made of the laminated composite material.

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