Interior material for a vehicle and method for producing the same

Abstract

Disclosed is an interior material for a vehicle, including a hot melt sheet; a polyurethane foam attached to one surface of the hot melt sheet; and an interior sheet attached to the other surface of the hot melt sheet. The hot melt sheet has a structure in which a plurality of hot melt films are laminated. The hot melt film has a plurality of perforation patterns formed in a surface of the hot melt film.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2025-0052566, filed with the Korean Intellectual Property Office on April 22, 2025, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] This invention relates to an interior material for vehicles and a method for preparing the same, which exhibits excellent sound absorption and air permeability in response to noise generated by the motor of an electric vehicle. Background Technology

[0004] Efforts to improve vehicle noise, vibration, and harshness (NVH) performance—one of the five key performance indicators for vehicles—have been ongoing for many years. In recent years, the importance of NVH performance has increased significantly as vehicle architecture has shifted from internal combustion engines (ICE) to electric powertrains. Electric vehicles (EVs) typically produce less noise than conventional ICE vehicles, presenting new acoustic challenges. Specifically, road and wind noise, previously masked by engine noise in ICE vehicles, become more prominent in EVs. Therefore, there is a growing need to develop vehicle components and systems that address noise and vibration through approaches tailored to the unique characteristics of electric vehicles.

[0005] Various studies have been conducted to explore NVH-related technologies aimed at reducing noise and vibration. Among interior components, roof materials cover a large surface area and therefore contribute significantly to reducing interior noise. Notably, these materials inherently possess sound-absorbing capabilities related to NVH performance, eliminating the need for separate sound-absorbing elements. However, research and development efforts specifically focused on optimizing roof materials for the unique acoustic conditions of electric vehicles are relatively limited.

[0006] In conventional car roof materials, depending on the interior design, various fabrics are applied to the surface layer, while soft polyurethane foam serves as the backing layer to provide cushioning and tactile comfort. These two layers are typically combined using a flame lamination process, where the surface portion of the polyurethane foam is first melted by a flame and then pressed onto the fabric. After cooling, the layers bond together to form a composite structure. However, this process creates a uniformly thick cured foam layer between the surface layer and the foam layer, thus limiting sound absorption and breathability.

[0007] Therefore, there is a need for new roof materials that provide enhanced sound absorption and improved breathability, including roof materials tailored to address the unique noise characteristics of electric vehicles. Summary of the Invention

[0008] One aspect of the present invention provides an interior material for vehicles and a method for preparing the same, which can solve the above-mentioned problems.

[0009] More specifically, the present invention provides a novel interior material, particularly a roof material for vehicles, and a method for preparing the same, which exhibits excellent sound absorption performance over the noise frequency range generated by electric vehicles, while also exhibiting excellent air permeability.

[0010] The technical problems to be solved by the present invention are not limited to those described above. Those skilled in the art will clearly understand from the following description any other technical problems not mentioned herein.

[0011] More specifically, (1) the present invention provides an interior material for a vehicle, comprising a hot-melt sheet; a polyurethane foam attached to one surface of the hot-melt sheet; and an interior sheet attached to the other surface of the hot-melt sheet. The hot-melt sheet has a structure in which multiple layers of hot-melt film are laminated, and the hot-melt film has a plurality of perforated patterns formed in the surface of the hot-melt film.

[0012] (2) The present invention provides an interior material for a vehicle as in (1), wherein the hot melt film comprises at least one selected from polyolefins, thermoplastic polyurethanes, polyamides, polyesters, polyolefins comprising units derived from carboxylic acid monomers, or combinations thereof.

[0013] (3) The present invention provides an interior material for a vehicle as in (1) or (2), wherein the hot melt sheet has a structure in which three to five layers of hot melt film are laminated.

[0014] (4) The present invention provides an interior material for a vehicle as described in any one of (1) to (3), wherein the distance between the perforation centers of the hot melt film ranges from 2 mm to 20 mm.

[0015] (5) The present invention provides an interior material for a vehicle as described in any one of (1) to (4), wherein the perforation diameter of the hot melt film ranges from 0.3 mm to 1.5 mm.

[0016] (6) The present invention provides an interior material for a vehicle as described in any one of (1) to (5), wherein the weight per unit area of ​​the hot-melt sheet ranges from 18 g / m². 2 Up to 100 g / m 2 .

[0017] (7) The present invention provides an interior material for a vehicle as described in any one of (1) to (6), wherein the polyurethane foam is a soft polyurethane foam.

[0018] (8) The present invention provides an interior material for a vehicle as described in any one of (1) to (7), wherein the density of the polyurethane foam is in the range of 20 kg / m³. 3 Up to 40 kg / m 3 .

[0019] (9) The present invention provides an interior material for a vehicle as described in any one of (1) to (8), wherein the interior sheet comprises a knitted fabric.

[0020] (10) The present invention provides an interior material for a vehicle as described in any one of (1) to (9), wherein the interior sheet comprises at least one selected from polyethylene terephthalate, polyamide, polyurethane, natural hemp fiber, or combinations thereof.

[0021] (11) The present invention provides an interior material for a vehicle as described in any one of (1) to (10), wherein the weight per unit area of ​​the interior sheet is in the range of 100 g / m². 2 Up to 280 g / m 2 .

[0022] (12) The present invention provides an interior material for a vehicle as described in any one of (1) to (11), further comprising a base adhesive film attached to the surface of an unattached hot melt sheet in an opposing surface of a polyurethane foam.

[0023] (13) The present invention provides an interior material for a vehicle as described in any one of (1) to (12), wherein the base adhesive film comprises at least one selected from polyolefins, thermoplastic polyurethanes, polyamides, polyesters, polyolefins comprising units derived from carboxylic acid monomers, or combinations thereof.

[0024] (14) The present invention provides an interior material for a vehicle as described in any one of (1) to (13), wherein the base adhesive film has a weight per unit area ranging from 20 g / m². 2 Up to 100 g / m 2 .

[0025] (15) The present invention provides an interior material for a vehicle as described in any one of (1) to (14), wherein the airflow resistance measured in accordance with ISO 9053 is at most 60 × 10⁻⁶. 3 .

[0026] (16) The present invention provides an interior material for a vehicle as described in any one of (1) to (15), wherein the sound absorption coefficient at 2,000 Hz is at least 0.23 as measured in accordance with ISO 10354-2:2023, and the sound absorption coefficient at 5,000 Hz is at least 0.54.

[0027] (17) The present invention provides a method for preparing internal materials, comprising the following steps:

[0028] A hot melt sheet having a structure in which multiple hot melt films are laminated is manufactured by extruding a resin composition comprising at least one selected from polyolefins, thermoplastic polyurethanes, polyamides, polyesters, polyolefins including units derived from carboxylic acid monomers, or combinations thereof; forming a plurality of perforated patterns in the surface of the hot melt sheet; and attaching polyurethane foam and an inner sheet to the opposite surfaces of the hot melt sheet, respectively. Attached Figure Description

[0029] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings:

[0030] Figure 1 This is a schematic diagram illustrating an interior material for a vehicle according to the present invention; and

[0031] Figure 2 This is a schematic diagram illustrating the use of interior materials for vehicles when a base adhesive film is also provided. Detailed Implementation

[0032] The present invention will be described in detail below.

[0033] In this context, the terms or words used in this specification and claims should not be limited to their common dictionary definitions, but should be interpreted in the best manner based on the inventor's ability to appropriately define the concepts of the terms, and should be interpreted in relation to the technical scope of the invention.

[0034] Interior materials for vehicles

[0035] The present invention provides an interior material for a vehicle, comprising a hot-melt sheet; a polyurethane foam attached to one surface of the hot-melt sheet; and an interior sheet attached to the other surface of the hot-melt sheet, wherein the hot-melt sheet has a structure in which multiple layers of hot-melt film are laminated, and the hot-melt film has a plurality of perforated patterns formed in the surface of the hot-melt film.

[0036] like Figure 1As shown, the interior material for vehicles according to the present invention has the following structure: an interior sheet 3, a hot-melt sheet 1, and a polyurethane foam 2 are sequentially laminated. The interior sheet is exposed inside the vehicle when installed. Noise can enter the interior sheet and is absorbed as it passes through the interior sheet and the hot-melt sheet.

[0037] According to the present invention, in the vehicle interior material, a hot-melt sheet can be attached to a polyurethane foam and can absorb noise generated inside the vehicle. The hot-melt sheet may have a structure in which multiple layers of hot-melt film are laminated. Because the hot-melt sheet has a laminated structure, it exhibits improved sound absorption performance. The hot-melt sheet may have a structure in which at least three layers of hot-melt film are laminated, more preferably, it may have a structure in which three to five layers of hot-melt film are laminated. When the number of hot-melt films is within the above range, the hot-melt sheet is easy to manufacture while achieving sufficient sound absorption performance.

[0038] A hot-melt film is a single-layer film forming a laminated structure of a hot-melt sheet, which may have multiple perforated patterns formed on the surface of the film. The perforated patterns ensure that air permeability is at a certain level or higher and can improve sound absorption performance in the high-frequency range.

[0039] The distance between the centers of the perforations in the hot melt film can range from 2 mm to 20 mm. Preferably, this distance can be at least 2 mm, at least 3 mm, at least 4 mm, at least 5 mm, at least 6 mm, or at least 7 mm, and at most 20 mm, at most 19 mm, at most 18 mm, or at most 17 mm. Furthermore, the perforation diameter of the hot melt film can range from 0.3 mm to 1.5 mm. Preferably, the perforation diameter can be at least 0.4 mm, at least 0.5 mm, or at least 0.6 mm, and at most 1.5 mm, at most 1.4 mm, at most 1.3 mm, at most 1.2 mm, at most 1.1 mm, or at most 1.0 mm. The distance between the centers of the perforations refers to the spacing between the perforations. When the spacing between the perforations and the perforation diameter meet the above conditions, excellent sound absorption performance and excellent air permeability can be exhibited simultaneously.

[0040] The hot melt film comprises at least one selected from polyolefins, thermoplastic polyurethanes, polyamides, polyesters, polyolefins including units derived from carboxylic acid monomers, or combinations thereof, preferably including at least one of polyolefins or polyurethanes. Such resins are readily processed by extrusion, smoothly adhere to the inner sheet and polyurethane foam, and provide excellent sound absorption and excellent air permeability.

[0041] The weight per unit area of ​​hot melt sheet can range from 18 g / m². 2 Up to 100 g / m 2 Preferably, it can be at least 20 g / m 2Or at least 30 g / m 2 And at most 60 g / m 2 Or at most 50 g / m 2 When the weight per unit area is within the above range, it ensures that the durability of the interior materials used in the vehicle is at a specific level or higher.

[0042] Polyurethane foam provides cushioning for interior materials used in vehicles and can support hot-melt sheets and interior panels. Polyurethane foam can be flexible polyurethane foam to provide improved cushioning.

[0043] The density range of polyurethane foam can be 20 kg / m³. 3 Up to 40 kg / m 3 Preferably, it can be at least 22 kg / m 3 At least 24 kg / m 3 or at least 26 kg / m 3 And at most 36 kg / m 3 Or at most 34 kg / m 3 The density of polyurethane foam is preferably within the aforementioned range in terms of vehicle weight reduction and the durability of interior materials.

[0044] Interior sheets can be exposed inside a vehicle to provide an aesthetically pleasing appearance. Interior sheets encompass a variety of materials, depending on the vehicle specifications in which the interior material according to the invention is installed. More specifically, interior sheets can be knitted fabrics.

[0045] In addition, the inner sheet material includes at least one of polyethylene terephthalate, polyamide, polyurethane, natural hemp fiber, or combinations thereof. These materials provide an excellent and aesthetically pleasing appearance and a superior tactile feel.

[0046] The weight per unit area of ​​the internal sheet can range from 100 g / m². 2 Up to 280 g / m 2 Preferably, it can be at least 120 g / m 2 At least 130 g / m 2 or at least 150 g / m 2 And at most 250 g / m 2 Up to 230 g / m 2 or at most 200 g / m 2 When the weight per unit area of ​​the internal sheet meets the above conditions, the durability of interior materials used in vehicles can be improved.

[0047] like Figure 2As shown, the interior material for vehicles according to the present invention may further include a base adhesive film 4, which is attached to the surface of the polyurethane foam 2 on the surface of the unattached hot-melt sheet 1. The base adhesive film can attach the interior material for vehicles to the vehicle frame.

[0048] The base adhesive film comprises at least one selected from polyolefins, thermoplastic polyurethanes, polyamides, polyesters, polyolefins including units derived from carboxylic acid monomers, or combinations thereof, preferably comprising at least one selected from polyolefins, thermoplastic polyurethanes, and polyolefins including units derived from carboxylic acid monomers. This material exhibits excellent adhesion, allowing for long-term stable adhesion of interior materials used in vehicles.

[0049] The weight per unit area of ​​the substrate adhesive film ranges from 20 g / m². 2 Up to 100 g / m 2 Preferably 25 g / m 2 Up to 55g / m 2 Within the aforementioned range, the durability of interior materials used in vehicles, vehicle weight reduction, and adhesive strength can be well balanced.

[0050] The interior material for vehicles according to the present invention can demonstrate an airflow resistance of up to 60 × 10⁻⁶ as measured in accordance with ISO 9053. 3 Preferably, the airflow resistance can be at least 10 × 10⁻⁶. 3 At least 20×10 3 At least 30×10 3 At least 40×10 3 or at least 45×10 3 And at most 60×10 3 Or at most 58×10 3 The vehicle interior material according to the present invention can improve its breathability by satisfying the above conditions.

[0051] The interior materials for vehicles according to the present invention have a sound absorption coefficient of at least 0.23 at 2000 Hz, measured in accordance with ISO 10354-2:2023, and a sound absorption coefficient of at least 0.54 at 5000 Hz. More specifically, the interior materials for vehicles according to the present invention have a sound absorption coefficient of at least 0.23, at least 0.24, or at least 0.25 at 2000 Hz, and at most 0.40, at most 0.35, at most 0.33, at most 0.32, at most 0.31, or at most 0.30. Furthermore, the sound absorption coefficient at 5000 Hz can be at least 0.54, at least 0.55, or at least 0.56, and at most 0.95, at most 0.93, at most 0.90, at most 0.88, or at most 0.87. The vehicle interior material according to the present invention exhibits excellent sound absorption performance for high-frequency noise, especially motor noise of electric vehicles, by satisfying the above conditions.

[0052] Methods for preparing interior materials for vehicles

[0053] The present invention provides a method for preparing the above-mentioned interior material for vehicles.

[0054] More specifically, the present invention provides a method for preparing interior materials for vehicles, comprising the steps of: producing a hot melt sheet having a structure in which multiple hot melt films are laminated by extruding a resin composition comprising at least one selected from polyolefins, thermoplastic polyurethanes, polyamides, polyesters, polyolefins comprising units derived from carboxylic acid monomers, or combinations thereof; forming a plurality of perforated patterns in the surface of the hot melt sheet; and attaching polyurethane foam and an interior sheet to the opposite surfaces of the hot melt sheet, respectively.

[0055] The aforementioned hot melt sheet for vehicle interior materials can be manufactured using an extrusion process. The extrusion process can be performed by simultaneously extruding a hot melt film to be included in the hot melt sheet and simultaneously laminating the hot melt film; or by extruding and manufacturing each layer of the hot melt film separately, and then laminating the hot melt film to manufacture the hot melt sheet.

[0056] By forming a perforated pattern on the hot-melt sheet manufactured in the previous steps, a hot-melt sheet with excellent sound absorption and air permeability can be produced. The perforated pattern can be formed under the conditions described above and can be formed by various known methods.

[0057] After the hot-melt sheet is manufactured using the above process, the interior material for the vehicle can be manufactured by attaching polyurethane foam and an interior sheet to the hot-melt sheet. In this step, the attachment can be performed by attaching one of the polyurethane foam and the interior sheet to the hot-melt sheet, and then attaching the other of the polyurethane foam and the interior sheet to the other surface of the hot-melt sheet; or, placing the polyurethane foam and the interior sheet on opposite surfaces of the hot-melt sheet while simultaneously attaching these three layers together.

[0058] According to the method for preparing interior materials for vehicles according to the present invention, the bonding between the layers of sheets can be performed by heat lamination or flame lamination. Heat lamination refers to heating the hot-melt sheets to melt a portion of the hot-melt sheets, and then bonding the two layers together. Flame lamination refers to using a flame to burn foam to bond the two layers together. More specifically, the hot-melt sheets and the interior sheets can be bonded together by heat lamination, and the hot-melt sheets and polyurethane foam can be bonded together by flame lamination or heat lamination.

[0059] Embodiments of the present invention will be described in detail below. However, the following embodiments are not provided for illustrative purposes only, and the scope of the invention is not limited thereto.

[0060] Material

[0061] The internal sheet material uses a weight range of 170 g / m² per unit area. 2 The fabric is knitted, with its surface layer made of 100% polyethylene terephthalate filaments bonded together. The polyurethane foam has a density of 26 kg / m³. 3 Soft polyurethane foam.

[0062] Implementation Method 1

[0063] The hot melt sheet has a structure in which three hot melt films are laminated, and is manufactured by simultaneously extruding polyolefin resin. Multiple perforation patterns are formed on the hot melt sheet, such that the distance between the centers of the perforations ranges from 11 mm to 17 mm, and the diameter of each perforation ranges from 0.6 mm to 1.0 mm.

[0064] Knitted fabric is heat-laminated onto one surface of a hot-melt sheet manufactured using the above process, and soft polyurethane foam is heat-laminated or flame-laminated onto the other surface of the hot-melt sheet to prepare an interior material for vehicles.

[0065] Implementation Method 2

[0066] The hot-melt sheet has a structure in which three layers of hot-melt film are laminated, and is manufactured by compressing thermoplastic polyurethane resin. Multiple perforation patterns are formed on the hot-melt sheet, such that the distance between the centers of the perforations ranges from 8 mm to 10 mm, and the diameter of each perforation ranges from 0.4 mm to 0.8 mm.

[0067] Using the same process as in Embodiment 1, knitted fabric and soft polyurethane foam are respectively attached to one surface of a hot melt sheet manufactured by the above process, thereby preparing an interior material for a vehicle.

[0068] Comparative Example 1

[0069] One surface of a flexible polyurethane foam comprising the above materials is heated and softened. A knitted fabric of the same material is then attached to the softened surface. The resulting material is then cooled to room temperature to allow the molten flexible polyurethane foam to solidify, forming a surface composite layer between the flexible polyurethane foam and the knitted fabric, thereby creating an interior material for vehicles.

[0070] Comparative Example 2

[0071] The hot-melt sheet, comprising a layer of hot-melt film, is manufactured by extruding polyolefin resin. Multiple perforation patterns are formed on the hot-melt sheet, such that the distance between the centers of the perforations ranges from 3 mm to 4 mm, and the diameter of each perforation ranges from 0.4 mm to 0.8 mm.

[0072] Using the same process as in Embodiment 1, knitted fabric and soft polyurethane foam are respectively attached to one surface of a hot melt sheet manufactured by the above process, thereby preparing an interior material for a vehicle.

[0073] Comparative Example 3

[0074] The hot-melt sheet, comprising a layer of hot-melt film, is manufactured by extruding polyolefin resin. Multiple perforation patterns are formed on the hot-melt sheet, such that the distance between the centers of the perforations ranges from 8 mm to 10 mm, and the diameter of each perforation ranges from 0.6 mm to 1.0 mm.

[0075] Using the same process as in Embodiment 1, knitted fabric and soft polyurethane foam are respectively attached to one surface of a hot melt sheet manufactured by the above process, thereby preparing an interior material for a vehicle.

[0076] Table 1 summarizes the hot-melt sheets used in vehicle interior materials manufactured according to the embodiments and comparative examples.

[0077] Table 1

[0078]

[0079] Implementation Method 1: Measuring the sound absorption properties and airflow resistance of interior materials used in vehicles

[0080] The sound absorption performance and airflow resistance of the sound-absorbing materials for vehicles prepared according to the embodiments and comparative examples were measured at various frequencies. The specific measurement methods are as follows.

[0081] 1) Sound absorption performance at various frequencies

[0082] The sound absorption performance at various frequencies was measured using a dual-microphone impedance measuring tube in accordance with ISO 10354-2:2023. The sound absorption performance was also measured for internal sheets used in vehicle interiors.

[0083] 2) Airflow resistance

[0084] Airflow resistance was measured in accordance with ISO 9053.

[0085] The measurement results are summarized in Table 2 below.

[0086] Table 2

[0087]

[0088] As can be seen from the results in Table 2, the interior material for vehicles according to the embodiments of the present invention exhibits low airflow resistance and excellent sound absorption performance.

[0089] Specifically, the interior materials for vehicles according to embodiments 1 and 2 exhibit excellent sound absorption performance in the noise frequency range of 2000 Hz to 5000 Hz, which corresponds to the noise range generated by the electric vehicle motor. Furthermore, the low airflow resistance demonstrates excellent air permeability.

[0090] In contrast, the composite layer of the vehicle interior material according to Comparative Example 1, formed using conventional methods with flame-softened soft polyurethane foam, exhibits poorer sound absorption and airflow resistance compared to the embodiment. Furthermore, the hot-melt sheets of Comparative Examples 2 and 3 employ a single-layer structure instead of a multi-layer structure, which is also inferior to the embodiment.

[0091] Therefore, it can be seen that the interior material for vehicles according to the present invention is suitable for electric vehicles that generate noise in the high-frequency region.

[0092] According to the present invention, the interior material for vehicles exhibits excellent sound absorption performance and excellent air permeability to reduce noise generated by the electric vehicle motor, and is suitable as an interior material for electric vehicles.

[0093] In the foregoing, although the invention has been described with reference to exemplary embodiments and accompanying drawings, the invention is not limited thereto, and those skilled in the art can make various modifications and variations thereto without departing from the spirit and scope of the invention as claimed in the claims.

[0094] 1: Hot melt sheet

[0095] 2: Polyurethane foam

[0096] 3: Internal sheet

[0097] 4: Substrate adhesive film

Claims

1. An interior material for a vehicle, said interior material comprising: Hot melt sheet; Polyurethane foam, which is attached to one surface of the hot melt sheet; as well as An inner sheet, which is attached to the other surface of the hot-melt sheet. The hot-melt sheet has a structure in which multiple layers of hot-melt film are laminated, and The hot melt film has a plurality of perforated patterns formed on the surface of the hot melt film.

2. The internal material according to claim 1, wherein the hot melt film comprises: It is selected from at least one of polyolefins, thermoplastic polyurethanes, polyamides, polyesters, polyolefins including units derived from carboxylic acid monomers, or combinations thereof.

3. The internal material according to claim 1, wherein the hot melt sheet has a structure in which three to five layers of hot melt film are laminated.

4. The internal material according to claim 1, wherein the distance between the perforation centers of the hot melt film ranges from 2 mm to 20 mm.

5. The internal material according to claim 1, wherein the perforation diameter of the hot melt film ranges from 0.3 mm to 1.5 mm.

6. The internal material according to claim 1, wherein the weight per unit area of ​​the hot-melt sheet ranges from 18 g / m². 2 Up to 100 g / m 2 .

7. The internal material according to claim 1, wherein the polyurethane foam is a flexible polyurethane foam.

8. The internal material according to claim 1, wherein the density of the polyurethane foam is in the range of 20 kg / m³. 3 Up to 40kg / m 3 .

9. The internal material according to claim 1, wherein the internal sheet comprises a knitted fabric.

10. The internal material according to claim 1, wherein the internal sheet comprises: It is selected from at least one of polyethylene terephthalate, polyamide, polyurethane, natural hemp fiber, or combinations thereof.

11. The internal material according to claim 1, wherein the weight per unit area of ​​the internal sheet is in the range of 100 g / m². 2 Up to 280 g / m 2 .

12. The internal material according to claim 1, further comprising: A base adhesive film is attached to the opposite surface of the polyurethane foam on the surface not attached to the hot melt sheet.

13. The internal material of claim 12, wherein the substrate adhesive film comprises: It is selected from at least one of polyolefins, thermoplastic polyurethanes, polyamides, polyesters, polyolefins including units derived from carboxylic acid monomers, or combinations thereof.

14. The internal material according to claim 12, wherein the weight per unit area of ​​the substrate adhesive film is in the range of 20 g / m². 2 Up to 100 g / m 2 .

15. The internal material according to claim 1, wherein the airflow resistance, measured in accordance with ISO 9053, is at most 60 × 10⁻⁶. 3 .

16. The internal material according to claim 1, wherein the sound absorption coefficient at 2,000 Hz, measured in accordance with ISO 10354-2:2023, is at least 0.23, and wherein the sound absorption coefficient at 5,000 Hz is at least 0.

54.

17. A method for preparing an internal material, the method comprising the following steps: A hot melt sheet having a structure in which multiple hot melt films are laminated is manufactured by extruding a resin composition comprising at least one selected from polyolefins, thermoplastic polyurethanes, polyamides, polyesters, polyolefins comprising units derived from carboxylic acid monomers, or combinations thereof. Multiple perforation patterns are formed on the surface of the hot-melt sheet; as well as The polyurethane foam and the inner sheet are respectively attached to the opposite surfaces of the hot melt sheet.

Images