Multilayer structure and bulletproof plate

Abstract

To provide a multilayer structure and a bulletproof plate capable of exhibiting excellent impact resistance by increasing the ceramic crushing mass at the time of impact and softening the impact against high-speed flying objects.SOLUTION: A multilayer structure has, in this order, a first fiber-reinforced plastic layer 1, a ceramic layer 2, a second fiber-reinforced plastic layer 3, and a third fiber-reinforced plastic layer 4. The fibers used in the first fiber-reinforced plastic layer and the second fiber-reinforced plastic layer include carbon fibers, and the fibers used in the third fiber-reinforced plastic layer include aramid fibers and / or high-strength polyethylene fibers.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multilayer structure that can exhibit excellent impact resistance against high-speed flying objects. [Background technology]

[0002] As bullet-resistant materials for protecting the body from high-speed projectiles, bulletproof plates have been proposed that combine high-strength fiber plastics, which are made by reinforcing high-strength fiber fabrics with special resins, and even more rigid ceramics, to improve defensive performance against highly penetrating threats such as rifle bullets.

[0003] For example, Patent Document 1 discloses a three-layer bulletproof composite plate used for armor to stop bullets, which is made up of a ceramic first layer coated with polyurethane resin, a polyurethane resin second layer reinforced with aramid fiber, and a honeycomb sandwich panel made of metal, resin, fiber, or the like coated with polyurethane resin as a third layer.

[0004] Furthermore, Patent Document 2 describes a structure in which a ceramic layer, a first fiber layer (aramid fiber), and a second fiber layer (high molecular weight polyethylene fiber) are layered in that order, with glass fiber or graphite fiber wrapped around the outside of the ceramic layer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-39646 [Patent Document 2] International Publication No. 2008 / 014020 Summary of the Invention [Problem to be solved by the invention]

[0006] However, although the bulletproof composite plate described in Patent Document 1 has a lighter mass per unit area than conventional steel plates and has excellent bullet resistance against the first bullet, when the first bullet hits, the ceramic coated with the first layer of polyurethane resin shatters and the ceramic scatters, reducing the effectiveness of the bullet fragmentation when subsequent bullets hit. Furthermore, when the second bullet hits, the fragmentation mass of the ceramic also decreases, increasing the risk of bullet penetration, so there was a demand for improved impact resistance.

[0007] Similarly, the structure described in Patent Document 2 has a lighter mass per unit area than conventional steel plates and is excellent in bullet resistance against the initial bullet, but when the initial bullet hits, the ceramic layer wrapped around the outside with glass fiber or graphite fiber shatters, resulting in the same problem as Patent Document 1. Furthermore, in Patent Document 2, the outer surface of the ceramic layer is reinforced with glass fiber or graphite fiber, which prevents ceramic fragments from scattering when the bullet hits, but the inner surface of the ceramic layer is adjacent to the first fiber layer (aramid fiber) and is not reinforced with a reinforced plastic layer made of graphite fiber, which has high strength and a high elastic modulus, which results in the problem that ceramic fragmentation when the bullet hits is unlikely to be promoted.

[0008] In view of the above-described conventional technology, an object of the present invention is to provide a multilayer structure and a bulletproof plate that can exhibit excellent impact resistance by increasing the ceramic fragmentation mass upon impact and thereby softening the impact against high-speed flying objects. [Means for solving the problem]

[0009] As a result of extensive research into achieving the above-mentioned objectives, the inventors discovered that by sandwiching a ceramic layer between specific fiber-reinforced plastic layers, it is possible to promote the fragmentation of the ceramic and effectively absorb the energy of the bullet, thereby obtaining a multilayer structure with excellent impact resistance against high-speed, highly penetrating flying objects.

[0010] The present invention has been completed based on these findings, and provides the following inventions.

[0011] That is, in order to solve the above problems, the present invention has the following configuration. (1) A first fiber-reinforced plastic layer, a ceramic layer, a second fiber-reinforced plastic layer, and a third fiber-reinforced plastic layer in this order; the fibers used in the first fiber-reinforced plastic layer and the second fiber-reinforced plastic layer contain carbon fibers; A multilayer structure in which the fibers used in the third fiber-reinforced plastic layer include aramid fibers and / or high-strength polyethylene fibers. (2) The area density of the third fiber-reinforced plastic layer is 5000 g / m 2 The multilayer structure according to (1) above. (3) The multilayer structure according to (1) or (2), wherein the ceramic layer has a bending strength of 300 MPa or more and a Vickers hardness of 1000 or more. (4) The multilayer structure according to any one of (1) to (3), wherein the ceramic layer has an average thickness of 4 mm or more. (5) The multilayer structure according to any one of (1) to (4), wherein the ceramic used in the ceramic layer is alumina, silicon carbide, or boron carbide. (6) A bulletproof plate comprising the multilayer structure according to any one of (1) to (5) above. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a multilayer structure and a bulletproof plate that can exhibit excellent impact resistance compared to conventional structures by increasing the ceramic crushing mass at the time of impact and softening the impact against high-speed flying objects. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view showing an example of an embodiment of a multilayer structure according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below with reference to embodiments.

[0015] As shown in Figure 1, the multilayer structure of the present invention has a first fiber-reinforced plastic layer 1, a ceramic layer 2, a second fiber-reinforced plastic layer 3, and a third fiber-reinforced plastic layer 4, in this order. To prevent fragments from scattering when hit by a bullet, a covering material 5 is used to cover the multilayer structure as needed. Note that, for convenience, each component is shown separately in Figure 1.

[0016] By arranging the layers used in the multilayer structure in the above order, the fracture of the ceramic is promoted, thereby effectively absorbing the energy of the bullet and providing a multilayer structure with excellent impact resistance against high-speed, highly penetrating projectiles.

[0017] <First fiber-reinforced plastic layer> First, the multilayer structure has a first fiber-reinforced plastic layer. The first fiber-reinforced plastic layer has excellent strength, which prevents the ceramic used in the ceramic layer from scattering when a bullet hits it. It also keeps the ceramic pieces within the multilayer structure. This effectively absorbs the energy of the bullet, increases the fragmentation mass when the bullet hits, and softens the impact.

[0018] The fibers used in the first fiber-reinforced plastic layer include carbon fibers. The carbon fibers provide high strength and a high modulus of elasticity, which suppresses the expansion and deformation of the through-holes in the first fiber-reinforced plastic layer against the force of the ceramic pieces scattering upon impact. By retaining the ceramic pieces within the multilayer structure, the energy of the bullet can be effectively absorbed, increasing the fragmentation mass and softening the impact. Examples of fiber-reinforced plastics that include carbon fibers include "Torayca" (registered trademark) (manufactured by Toray Industries, Inc.).

[0019] The mass of the carbon fibers is preferably 71 to 100% of the total mass of the fibers used in the first fiber-reinforced plastic layer.

[0020] The carbon fiber preferably has a tensile strength of 17 cN / dtex or more, more preferably 17 to 45 cN / dtex, and even more preferably 19 to 40 cN / dtex, and the tensile modulus is preferably 300 to 3000 cN / dtex, and even more preferably 1000 to 2500 cN / dtex.

[0021] The fineness of the carbon fiber is preferably 100 to 7000 dtex, more preferably in the range of 200 to 3500 dtex, but is not particularly limited.

[0022] Carbon fiber is a PAN-based fiber made by carbonizing acrylic fiber at high temperatures.

[0023] The above-mentioned fibers can be used to form a fabric, which can then be incorporated into the first fiber-reinforced plastic layer. Examples of the fabric that can be preferably used include woven fabrics, knitted fabrics, nonwoven fabrics, felt, unidirectional sheets (UD (unidirectionally aligned)), UD laminates at a 0° / 90° angle, and three-dimensional structures. Woven fabrics and UD are more preferred in terms of dimensional stability and strength. In the case of woven fabrics, plain weave, twill weave, satin weave, rib weave, basket weave, herringbone weave, and double weave can be used. The above-mentioned fabrics can be used in layers. Furthermore, since the amount of bullet energy of a high-speed projectile varies depending on the material, speed, mass, etc., it is preferable to appropriately adjust the number of layers depending on the threat level of the target.

[0024] The mass of the carbon fibers is preferably 50 to 70% of the total mass of the first fiber-reinforced plastic layer.

[0025] Such fibers and fabrics may contain various additives that are commonly used to improve productivity or properties in the manufacturing process or processing of raw yarns, such as heat stabilizers, antioxidants, light stabilizers, smoothing agents, antistatic agents, plasticizers, thickeners, pigments, flame retardants, oils, etc.

[0026] The resin for forming the first fiber-reinforced plastic layer may be a thermosetting resin or a thermoplastic resin, but is not particularly limited thereto. Examples of thermosetting resins include phenolic resin, melamine resin, urea resin, unsaturated polyester resin, epoxy resin, polyurethane resin, diallyl phthalate resin, silicone resin, polyimide resin, vinyl ester resin, and modified resins thereof. Preferred examples of thermoplastic resins include polyvinyl butyral resin, vinyl chloride resin, polystyrene, ABS resin, polyethylene, polypropylene, fluororesin, polyamide resin, polyacetal resin, polycarbonate resin, polyester, and polyamide, as well as synthetic rubbers or elastomers such as thermoplastic polyurethane, butadiene rubber, nitrile rubber, neoprene, and polyester. Two or more of these resins may be mixed and used. Among these, mixed resins primarily composed of phenolic resin and polyvinyl butyral resin, unsaturated polyester resin, vinyl ester resin, polyethylene, polypropylene, and other polyolefin resins, and polyester resins are preferred due to their impact resistance, dimensional stability, strength, and cost. More preferably, the resin is a mixed resin containing a phenol resin and a polyvinyl butyral resin as main components.

[0027] Such resins may contain various additives that are commonly used industrially for their intended purpose, use, productivity in the manufacturing process, and processing steps, or to improve properties, such as modifiers, plasticizers, fillers, release agents, colorants, and diluents.

[0028] Furthermore, it is preferable that the resin is used in an amount of 30 to 50 parts by mass per 100 parts by mass of the fibers used in the first fiber-reinforced plastic layer.

[0029] <Ceramic layer> The multilayer structure of the present invention has a ceramic layer following the first fiber-reinforced plastic layer. The ceramic layer shatters high-speed projectiles, and the ceramic itself shatters into conical shapes, absorbing the kinetic energy of the bullet. This increases the impact resistance of the multilayer structure.

[0030] The ceramics used in the ceramic layer can be any fine ceramic. The ceramics are not particularly limited as long as they have, for example, a bending strength of 300 MPa or more and a Vickers hardness of 1000 or more. Examples of preferred ceramics include alumina, zirconia, silicon carbide, boron carbide, silicon nitride, and the like, as well as mixtures of these ceramics, ceramics reinforced with metal, ceramics reinforced with fiber, fiber-reinforced ceramics in which ceramics are toughened with heat-resistant fibers such as carbon fiber, and ceramic-based composite materials reinforced with ceramic particles, whiskers, short fibers, or continuous long fibers (e.g., silicon carbide fiber / silicon carbide matrix composites). Among these, alumina, silicon carbide, or boron carbide are more preferred due to their impact resistance, light weight, strength, and cost. Alumina with a purity of 85% or more is preferred. A purity of 85% or more further improves energy absorption during high-speed projectile impacts.

[0031] The bending strength of the ceramic layer is preferably 300 MPa or more. A bending strength of 300 MPa or more improves the crushing effect against high-speed projectiles and the ability to absorb the kinetic energy of bullets, further improving impact resistance. The bending strength is more preferably 500 MPa or more. The bending strength can be measured in accordance with JIS R1601:2008. The higher the bending strength, the better, but since this increases manufacturing costs, from the perspective of cost-effectiveness, a bending strength of 800 MPa or less is preferred.

[0032] The Vickers hardness of the ceramic layer is preferably 1000 or more. A Vickers hardness of 1000 or more improves the crushing effect against high-speed flying objects and the ability to absorb the kinetic energy of bullets, further improving impact resistance. The Vickers hardness is more preferably 2000 or more. The Vickers hardness can be measured in accordance with JIS R1600:2011. The higher the Vickers hardness, the better, but since this increases the unit price of the product, from the viewpoint of cost-effectiveness, a Vickers hardness of 3000 or less is preferable.

[0033] From the above viewpoint, it is preferable that the ceramic layer has a bending strength of 300 MPa or more and a Vickers hardness of 1000 or more.

[0034] The ceramic layer may have a polygonal shape such as a triangle, rectangle, square, trapezoid, or hexagon, and a plurality of small pieces may be arranged without gaps to form a single ceramic layer. By arranging a plurality of ceramic small pieces, for example, in a staggered pattern, a multilayer structure having excellent impact resistance against high-speed flying objects can be constructed. When the ceramic small pieces are square, the length of each side is preferably within the range of 3 to 10 cm, and more preferably within the range of 4 to 7 cm.

[0035] The average thickness of the ceramic layer is selected as appropriate depending on the structure, mass, speed, and safety factor of the high-speed projectile, but an average thickness of 4 mm or more is preferred. Furthermore, because an increase in the mass of the multilayer structure increases the product mass, which leads to reduced mobility, an average thickness of 15 mm or less is preferred. For example, if the high-speed projectile is a 30-06 M2AP bullet, the preferred thickness is 7 to 13 mm for alumina ceramics, 5 to 12 mm for silicon carbide, and 5 to 11 mm for boron carbide. Furthermore, if the high-speed projectile is a NATO M80 bullet, the preferred thickness is 5 to 11 mm for alumina ceramics, 4 to 10 mm for silicon carbide, and 4 to 9 mm for boron carbide. Furthermore, if the high-speed projectile is a NATO SS-109 bullet, the preferred thickness is 5 to 10 mm for alumina ceramics, 4 to 9 mm for silicon carbide, and 4 to 8 mm for boron carbide. If the average thickness is within the above range for each projectile, the finished product will be lighter, improving mobility and providing a multilayer structure with superior impact resistance. The shape is not limited to flat or curved plates, and can also be of uniform thickness, or a flat shape in which the edges are thicker than the center to improve the impact resistance of the joints. Among these, a uniform thickness is preferred from the perspective of lightweight construction. The thickness of the ceramic layer can be calculated by measuring the thickness of the center and edges of the ceramic at three points each using a micrometer or vernier caliper as specified in JIS B7502:2016 and B7507:2016, and averaging the measurements.

[0036] <Second fiber reinforced plastic layer> The multilayer structure of the present invention has a second fiber-reinforced plastic layer on the ceramic layer opposite the first fiber-reinforced plastic layer. The use of the second fiber-reinforced plastic layer increases the rigidity of the ceramic layer, inhibiting deformation and promoting conical fracture of the ceramic layer, while effectively absorbing the energy of the bullet and increasing the fracture mass of the ceramic layer, thereby softening the impact.

[0037] The second fiber-reinforced plastic layer contains carbon fiber, which can further increase the rigidity of the ceramic layer.

[0038] The resin used in the second fiber-reinforced plastic layer, including the type and content of the resin, can be the same as that described for the first fiber-reinforced plastic layer.

[0039] <Third fiber-reinforced plastic layer> The multilayer structure of the present invention has a third fiber-reinforced plastic layer next to the second fiber-reinforced plastic layer. The third fiber-reinforced plastic layer can capture fragmented bullets and ceramic fragments, protecting the user's body from bullets that are the target threat.

[0040] The fibers used in the third fiber-reinforced plastic layer include aramid fibers and / or high-strength polyethylene fibers, which can capture shattered bullets and ceramic fragments, thereby reducing damage to the wearer and increasing the impact resistance of the multilayer structure.

[0041] As the aramid fiber, a para-aramid fiber "Kevlar" (registered trademark) (manufactured by DuPont-Toray Co., Ltd.) or the like can be used.

[0042] As the high-strength polyethylene fiber, "Tensilon" (manufactured by DuPont Co., Ltd.) can be used. Here, "high-strength polyethylene fiber" refers to a high-density polyethylene fiber having a specific gravity of 0.94 or more.

[0043] The area density of the third fiber-reinforced plastic layer is 5000 g / m 2 It is preferable that the areal density is 5000 g / m or more. 2 By satisfying the above conditions, fragments of broken bullets and ceramics can be efficiently captured, and impact resistance can be further improved. The areal density is preferably 8000 g / m 2That's all. The areal density, or basis weight, can be measured based on JIS L1096:2010 8.3.2. The higher the areal density, the better. However, from the viewpoint of reducing the burden on the wearer, 10,000 g / m 2 The following is preferred:

[0044] When the third fiber-reinforced plastic layer contains aramid fibers, the aramid fibers preferably account for 45 to 90 mass% of the total mass of the third fiber-reinforced plastic layer. When the mass of the aramid fibers is 45 mass%, the heat resistance of the aramid fibers makes it possible to provide the multilayer structure with excellent shape retention in a high-temperature environment.

[0045] When the third fiber-reinforced plastic layer contains high-strength polyethylene fibers, the content of the high-strength polyethylene fibers is preferably 45 to 90 mass% of the total mass of the third fiber-reinforced plastic layer. When the mass of the high-strength polyethylene fibers is 45 mass% or more, the high strength properties of the high-strength polyethylene fibers enable an impact-resistant multilayer structure to be obtained.

[0046] The tensile modulus of the fibers used in the third fiber-reinforced plastic layer is preferably 300 to 3000 cN / dtex.

[0047] The resin used for the third fiber-reinforced plastic layer may be the same as the resin described for the first fiber-reinforced plastic layer.

[0048] <Multilayer structure> The shape of the multilayer structure can be appropriately selected depending on the purpose of use, such as a flat plate or a curved plate.

[0049] Furthermore, to further improve the impact resistance of high-speed flying objects, the entire multilayer structure can be further wrapped and coated with a high-strength fiber fabric, a thermoplastic resin, a two-component curing resin, or the like. This can prevent delamination between the second high-strength fiber layer and the third high-strength fiber layer when a high-speed flying object hits, further improving the crushing effect and impact resistance of high-speed flying objects. The resin contained in the first fiber-reinforced plastic layer, a heat-sealed film, or the like can be used as an adhesive material.

[0050] The multilayer structure of the present invention can be used in any application, without particular limitation. For example, it can be used in protective vests (protective materials inside vests), helmets and their mounting plates, bulletproof plates (plates inserted into protective vests), and additional armor for vehicles, ships, and aircraft. In such cases, the multilayer structure is manufactured and installed according to conventional methods in a state appropriate for the product shape and usage environment. In particular, by applying it to bulletproof plates, the mass per unit area can be lighter than that of conventional steel plates, resulting in a lighter product mass, reduced strain on the wearer, and improved mobility. Furthermore, while conventional steel bulletproof plates have the potential for secondary damage, such as bullets hitting the plate ricocheting and hitting nearby soldiers, bulletproof plates made from the multilayer structure of the present invention have the potential for greatly reduced risk of secondary damage due to ricochets, since the impacting bullets are captured by the third high-strength fiber layer.

[0051] For example, a protective vest is manufactured by cutting an outer garment and then sewing the multilayer structure in a conventional manner, or by creating sections that can be inserted into the protective vest. A helmet is manufactured by cutting the outer garment to the required shape and then molding the multilayer structure in a conventional manner. Alternatively, a multilayer structure of the required size can be added to a fiber-reinforced plastic helmet. Add-on armor for vehicles, ships, and aircraft is manufactured by molding the multilayer structure to a predetermined size in a conventional manner. The armor is then attached to the vehicle, ship, or aircraft by machine bolting or hook-and-loop fasteners.

[0052] <Covering material> The multilayer structure of the present invention may have a covering material that encases the entire multilayer structure. The covering material prevents the first fiber-reinforced plastic layer, the ceramic layer, the second fiber-reinforced plastic layer, and the third fiber-reinforced plastic layer from peeling off due to the impact of the bullet, and also prevents the scattering of crushed ceramic pieces. The fineness, tensile strength, and tensile modulus of the covering material can be the same as those of the fibers used in the third fiber-reinforced plastic layer.

[0053] <Method of manufacturing a multilayer structure> Next, an example of a method for producing the multilayer structure of the present invention will be described.

[0054] First, one example of a method for producing the third fiber-reinforced plastic layer is to laminate a predetermined number of prepreg materials, each made by adhering a thermosetting resin to a fabric, and then heat-pressure molding the laminate to obtain a fiber-reinforced plastic (hereinafter sometimes referred to as "FRP"). When a thermoplastic resin is used instead of a thermosetting resin, the FRP can be obtained by cooling the laminate to approximately room temperature after the heat-pressure molding described above and then releasing the pressure. The number of laminated prepreg materials is determined appropriately depending on the application and the basis weight of the fabric, but is usually around 40 to 120 sheets. Since laminating a large number of sheets complicates the molding process, a number of 100 sheets or less is preferred.

[0055] It is preferable to overlay the second fiber-reinforced plastic layer on the pressure-molded third fiber-reinforced plastic layer, the ceramic layer on top of that, and the first fiber-reinforced plastic layer on top of that, and then heat-pressure mold the layers together. To increase the adhesive strength of the layers in the multilayer structure, it is more preferable to bond the layers together with an adhesive material such as a resin used in producing prepregs, synthetic rubber, epoxy resin, urethane resin, or heat-sealing film.

[0056] It is preferable to apply, for example, a one-component curing adhesive to the entire surface of the multilayer structure obtained by integrating the first fiber-reinforced plastic layer / ceramic layer / second fiber-reinforced plastic layer / third fiber-reinforced plastic layer in this order and to one surface layer portion of the covering material, air-dry the surfaces until the tackiness disappears, and then overlap the adhesive-coated surfaces to encase the multilayer structure in the covering material. The surfaces of the covering material are preferably integrated by pressing while heated with an iron or by autoclave molding.

[0057] The multilayer structure obtained in this manner has the effect of suppressing the scattering of ceramic fragments when hit by a high-speed flying object, effectively absorbing the energy of the bullet and suppressing the occurrence of cracks, thereby providing excellent defensive performance. [Example]

[0058] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. The properties in the examples were measured using the following methods.

[0059] (Measurement and evaluation methods) 1. Tensile strength, tensile modulus Based on JIS L1013:2010 8.5, the tensile strength (cN / dtex) and tensile modulus were determined in a tensile test with a gripping distance of 25 cm, a tensile speed of 30±3 cm / min, and N=10 times, and the average values ​​were calculated.

[0060] 2. Fineness Based on JIS L 1013:2010 8.3.1 Method A, five sets of 112.5m skeins were collected and left for 4 hours in an environment of 20℃ and 60% humidity, after which their mass (g) was measured and the value was multiplied by 10000 / 112.5 to determine the fineness (dtex) and the average value was calculated.

[0061] 3.Weight and area density Based on JIS L 1096:2010 8.3.2, measure the mass (g) of two test pieces of approximately 200 mm x 200 mm and measure the weight of the test piece. 2Mass per unit (g / m 2 ) was measured and the average value was calculated. In addition, multiple sheets of the above materials were stacked and molded into FRP, and the mass (g) was measured and 2 Mass per unit (g / m 2 ) is called the areal density.

[0062] 4. Fabric density Based on JIS L 1096:2010 8.6.1, the number of threads in a 25 mm section was counted at five locations in each of the warp and weft directions, the weave density per 25 mm (threads / 25 mm) was determined, and the average value was calculated.

[0063] 5. Thickness of fabric Based on JIS L 1096:2010 8.4, the thickness was measured at five points after applying pressure for 10 seconds using a dial thickness gauge (pressing pressure 23.5 kPa), and the average value was calculated.

[0064] 6. FRP bending stress and bending modulus Based on JIS K7017:1999 10.1, four test pieces measuring 60 mm in length and 20 mm in width were prepared, and bending stress (MPa) and bending modulus (GPa) were measured in a three-point bending test with a support distance of 40 mm and a test speed of 3 mm / min, and the average values ​​were calculated. The dimensions of the test pieces were measured using a vernier caliper. The thickness was also measured using a vernier caliper.

[0065] 7.Viscosity Based on JIS Z 8803:2011 9.4, the viscosity of the resin was measured using a B-type viscometer at a temperature of 20°C.

[0066] 8. Resin adhesion rate The basis weight before and after resin processing was calculated using the method described in Section 3, and the resin adhesion rate (mass%) was calculated using the following formula. Resin adhesion rate (mass%)=((basis weight after resin adhesion−basis weight before resin adhesion) / basis weight after resin adhesion)×100.

[0067] 9. Impact resistance (V0 test equivalent to level IV) A V0 test was conducted using a 7.62M2AP (10.8g) bullet in accordance with the NIJ-STD-0101.06 ballistic performance standard set by the U.S. Department of Justice (NIJ). Firing distance: 10m, test specimen dimensions: 20cm wide x 30cm long, number of shots: 2-3 per bullet, firing speed: 878±9m / s (bullet speed measured 2.5m in front of the test specimen), test room temperature: 21±2.9°C / 50±20%, and test specimen dent: the test specimen was fixed to a clay frame, and the clay dent after the 3-shot test was measured using a vernier caliper or ruler.

[0068] The clay frame material was heated to around 40°C 48 hours before the test, and the hardness of the clay was adjusted in advance so that the NIJ-specified iron ball test would result in a dent (19±2 mm) (the clay surface / internal temperatures were also measured before and after measuring the dent). Note that a new clay frame material was used for each shooting test of a test specimen. Used clay frames were used after repairing the dented areas and reheating (for 24 hours or more). Evaluation was based on the following evaluation criteria. [Judgment] No penetration and dent less than 30mm: ○, No penetration and dent more than 30mm: △, Penetration: ×

[0069] 10. Ceramic crushing mass The crushed mass of the ceramic was calculated using the following formula from the mass of the test specimen before the shooting test and the mass of the test specimen after removing the crushed ceramics after the test. Mass of crushed ceramics (g) = (mass of test specimen before shooting test) - (mass of test specimen after removing crushed ceramics after shooting test). The evaluation was based on the following criteria. [Judgment] Over 200g: Good, Under 200g but over 150g: Fair, Under 150g: Bad.

[0070] 11. Bending strength and Vickers hardness of ceramics The measured test data is listed based on JIS R1600:2011 and JIS R1601:2008.

[0071] 12. Average thickness of ceramic layer The thickness of the ceramics was measured at three points in the center and at the edges using a micrometer specified in JIS B7502:2016 and B7507:2016, and the average was calculated.

[0072] Example 1 [Fabrication of multilayer structure] High-strength polyethylene sheet "Tensilon" (manufactured by DuPont Co., Ltd.) 30A (weight: 110 g / m 2 , 0 / 90°UD. Equivalent to the third fiber-reinforced plastic layer.) were laminated (area density: 8360 g / m 2 Next, a thermoplastic resin film (olefin-based film) "Cranbetter" (registered trademark) (manufactured by Kurabo Industries, Ltd.) X4360 (thickness: 100 μm, adhesive material) was laminated on top of that, and a carbon fiber prepreg sheet "Torayca" (registered trademark) (manufactured by Toray Industries, Inc.) FK6241E-05K (basis weight: 667 g / m 2 , thickness: 0.44 mm, 2 / 2 twill weave. Corresponding to the second fiber-reinforced plastic layer. Epoxy resin was used as the resin.) was laminated on top of the above adhesive material. Next, the above adhesive material was laminated on top of that, and silicon carbide ceramics (thickness: 8 mm, 7 divided pieces: arranged in a staggered pattern while being shifted alternately up, down, left, and right. Corresponding to the ceramic layer) was laminated on top of that. Finally, the above adhesive material was laminated on top of that, and a carbon fiber prepreg sheet "TORAYCA" (registered trademark) (manufactured by Toray Industries, Inc.) FK6241E-05K (basis weight: 667 g / m 2 , thickness: 0.44 mm, 2 / 2 twill weave. Corresponding to the first fiber reinforced plastic layer.) was laminated.

[0073] This was covered with a release film (fluorine-based), a metal plate (shape: flat), a nonwoven fabric (polyester-based), and a bagging film (nylon-based), and the inside of the laminate was degassed to -0.1 MPa, and it was placed in an autoclave molding machine at room temperature and heated to 110°C at a rate of 2°C / min while being pressurized to 0.8 MPa. After holding at the specified temperature for 20 minutes, it was cooled at a rate of 2°C / min, and once the internal temperature of the laminate had dropped to 50°C or below, the pressure was released, yielding a multilayer structure.

[0074] [Covering material production] Next, a plain weave fabric (basis weight: 460 g / m) was used, using aramid fiber (total fineness: 3300 dtex) with a tensile strength of 20 cN / dtex and a tensile modulus of 500 cN / dtex. 2 A phenolic resin (main component: polyvinyl butyral) was coated onto a sheet of fabric (17.5 threads / 25 mm warp, 16.5 threads / 25 mm weft, 0.64 mm thick) and dried to obtain a prepreg (covering material) with a resin adhesion rate of 8.5% by mass.

[0075] A moisture-curing urethane-based one-component adhesive (No Tape Industrial Co., Ltd.) 5135SP was applied to the adhesive surface of one side of the covering material and the surface of the multilayer structure. The adhesive was then air-dried for 60 minutes, and the surface of the multilayer structure was then wrapped with the covering material. This was then covered with a release film (fluorine-based), a metal plate (shaped: flat), a nonwoven fabric (polyester-based), and a bagging film (nylon-based), and the interior of the laminate was degassed to -0.1 MPa. The laminate was then placed in an autoclave molding machine at room temperature and heated to 70°C at a rate of 2°C / min while pressurized to 0.4 MPa. After holding at the specified temperature for 30 minutes, the laminate was cooled at a rate of 2°C / min. Once the internal temperature of the laminate reached 50°C or below, the pressure was released, yielding a multilayer structure with a covering material. The evaluation results of the resulting multilayer structure with a covering material are shown in Table 1.

[0076] Example 2 As the second fiber-reinforced plastic layer, a carbon fiber prepreg sheet "TORAYCA" (registered trademark) (manufactured by Toray Industries, Inc.) FK6241E-05K (basis weight: 667 g / m 2 A multilayer structure with a covering material was obtained in the same manner as in Example 1, except that two sheets of a woven fabric (0.44 mm thick, 2 / 2 twill weave) were laminated together. The evaluation results of the resulting multilayer structure with a covering material are shown in Table 1.

[0077] Example 3 As the first fiber-reinforced plastic layer, a carbon fiber prepreg sheet "TORAYCA" (registered trademark) (manufactured by Toray Industries, Inc.) FK6241E-05K (basis weight: 667 g / m 2A multilayer structure with a covering material was obtained in the same manner as in Example 1, except that two sheets of a woven fabric (0.44 mm thick, 2 / 2 twill weave) were laminated together. The evaluation results of the resulting multilayer structure with a covering material are shown in Table 1.

[0078] Example 4 A plain weave fabric (weight: 460 g / m) made from aramid fiber (total fineness: 3300 dtex) with a tensile strength of 20 cN / dtex and a tensile modulus of 500 cN / dtex. 2 , weave density 17 threads / 2.54 cm, thickness 0.64 mm) is coated with phenolic resin (main component polyvinyl butyral), and dried to a resin adhesion rate of 8.5 mass% (basis weight 484 g / m 2 A prepreg of 1000 sq m (corresponding to the third fiber reinforced plastic layer) was obtained. 29 sheets of the prepreg material were laminated. Further, a carbon fiber prepreg sheet "TORAYCA" (registered trademark) (manufactured by Toray Industries, Inc.) FK6241E-05K (basis weight: 667 g / m) was laminated on top of the prepreg material. 2 , thickness: 0.44 mm, 2 / 2 twill weave. Corresponds to the second fiber-reinforced plastic layer. Epoxy resin was used as the resin.) was laminated. Then, it was set in a compression molding machine and subjected to a molding temperature of 165°C, a press pressure of 18 tons, and hot press molding for 15 minutes to obtain a molded body.

[0079] Next, a mixture of two-component urethane adhesive "Mighty Grip" (registered trademark) (manufactured by E-Tech Co., Ltd.) #5000 and #5030 was applied to the surface of the second fiber-reinforced plastic layer of the obtained molded body. After that, the same ceramics as in Example 1 were arranged on top of it and set in a compression molding machine. After treatment at a pressure of 3 tons and a room temperature pressing time of 1 minute, the molded body was placed in a dryer and heat-treated at 60°C for 15 minutes.

[0080] Next, the ceramic surface and a carbon fiber prepreg sheet "TORAYCA" (registered trademark) (manufactured by Toray Industries, Inc.) FK6241E-05K (basis weight: 667 g / m 2A moisture-curing urethane-based one-component adhesive (5135SP, manufactured by No Tape Industrial Co., Ltd.) was applied to one side of the sheet (thickness: 0.44 mm, 2 / 2 twill weave, equivalent to the first fiber-reinforced plastic layer). After that, the sheet was air-dried for 60 minutes, and the coated surfaces were placed together and pressed together while being heated with an iron (temperature: approximately 130°C).

[0081] Thereafter, a covering material was prepared by the steps described in [Preparation of Covering Material] in Example 1, to obtain a multilayer structure with a covering material. The evaluation results of the obtained multilayer structure with a covering material are shown in Table 1.

[0082] (Comparative Example 1) A multilayer structure with a covering material was obtained in the same manner as in Example 1, except that the first fiber-reinforced plastic layer was not formed. The evaluation results of the obtained multilayer structure with a covering material are shown in Table 1.

[0083] (Comparative Example 2) Except for not forming the first fiber-reinforced plastic layer and the second fiber-reinforced plastic layer, a multilayer structure with a covering material was obtained in the same manner as in Example 1. The evaluation results of the obtained multilayer structure with a covering material are shown in Table 1.

[0084] The multilayer structures of Examples 1 to 4 had a large ceramic fragmentation mass, which promoted the absorption of bullet energy, reducing damage to the bulletproof plate and suppressing the occurrence of cracks in the separated ceramic tiles, demonstrating good impact resistance. On the other hand, in Comparative Examples 1 and 2, the ceramic fragmentation mass was smaller than in the Examples, and the bullet energy absorption was not promoted, which increased the damage to the bulletproof plate and increased the risk of cracks occurring in the separated ceramic tiles, resulting in inferior impact resistance performance compared to the Examples.

[0085] [Table 1] [Explanation of symbols]

[0086] 1. First fiber-reinforced plastic layer 2. Ceramic layer 3 Second fiber-reinforced plastic layer 4. Third fiber-reinforced plastic layer 5 Covering material

Claims

1. A first fiber-reinforced plastic layer, a ceramic layer, a second fiber-reinforced plastic layer, and a third fiber-reinforced plastic layer in this order, the fibers used in the first fiber-reinforced plastic layer and the second fiber-reinforced plastic layer contain carbon fibers; A multilayer structure in which the fibers used in the third fiber-reinforced plastic layer include aramid fibers and / or high-strength polyethylene fibers.

2. The area density of the third fiber reinforced plastic layer is 5000 g / m ２ The multilayer structure according to claim 1, wherein the multilayer structure is a multilayer structure having the above structure.

3. 3. The multilayer structure according to claim 1, wherein the ceramic layer has a bending strength of 300 MPa or more and a Vickers hardness of 1000 or more.

4. 3. The multilayer structure according to claim 1, wherein the ceramic layer has an average thickness of 4 mm or more.

5. 3. The multilayer structure according to claim 1, wherein the ceramic used in the ceramic layer is alumina, silicon carbide, or boron carbide.

6. A ballistic plate comprising the multilayer structure of claim 1 or 2.

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