SOUND ABSORBING MATERIAL

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 106129964, filed on Sep. 1, 2017. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

TECHNICAL FIELD

The disclosure relates to an open-cell sound absorbing material.

BACKGROUND

In order to improve the echo interferences in life, the sound absorbing material is generally installed on a wall or a vehicle body to absorb the sound waves and decrease the reflection amounts. However, the porous polymers are usually used as a sound absorbing material, but the pore structure of porous polymers formed by the traditional foaming technology is often closed-cell structure that the incident sound waves are difficult to produce many times internal reflections within the sound absorbing material. Hence, the sound absorbing effects are limited. In addition, the traditional foaming technology needs to use foaming agents or gases such as CO₂that could cause the environmental pollution.

Based on the above, the development of an open-cell sound absorbing material is urgent without delay.

SUMMARY

The present disclosure provides a sound absorbing material, which includes a polymeric body having a first end, a second end opposed to the first end, and a plurality of branched passages connected to the first end and extending toward a direction of the second end. The plurality of branched passages have an average spacing of 5 μm to 50 μm therebetween and an average width of 5 μm to 50 μm.

Several exemplary embodiments accompanied with figures are described in detail below to further describe the disclosure in details.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the disclosure.

FIG. 1 is a schematic diagram illustrating the sound absorbing material according to one embodiment of the present disclosure.

FIG. 2 is a schematic diagram illustrating the freeze casting system.

FIG. 3 is a sectional SEM view illustrating the sound absorbing material obtained in Example 1.

FIG. 4 is a partial enlarged view of FIG. 3.

DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

As used in the specification and claims, the singular forms “a”, “an” and “the” include plural references unless the context clearly dictates otherwise.

The present disclosure is a sound absorbing material with an open-cell structure. As compared with the traditional foaming process using the foaming agents or gases, the pores in the sound absorbing material of the present disclosure are formed by the freeze casting method in which the water in the polymeric slurry is cooled to form ice crystals at low temperature, and then the ice crystals are removed at sufficiently low temperature and reduced-pressure so as to form the sound absorbing material with continuous open-cell pores which can cause the incident sound waves to produce many times internal reflections within the sound absorbing material. Therefore, the sound absorbing material of the present disclosure can improve the sound absorbing effects.

FIG. 1 is a schematic diagram illustrating the sound absorbing material according to one embodiment of the present disclosure. Referring to FIG. 1, the present disclosure provides a sound absorbing material 10, which includes a polymeric body 100 having a first end 101, a second end 102 opposed to the first end 101 and a plurality of branched passages 103, 103′ and 103″. These branched passages 103, 103′ and 103″ are formed within the polymeric body 100, and are connected to the first end 101 and extend toward a direction of the second end 102 so as to form the continuous open-cell structure and have directionality one another. As used in the specification and claims, the term “a first end 101 of the polymeric body 100” means an incident end or an absorbing surface for entrance of sound wave; the term “a second end 102 of the polymeric body 100” means a surface having a certain distance from the first end 101 which would or would not be parallel to the first end 101; the term “these branched passages 103, 103′ and 103” are connected to the first end 101″ means a plurality of open pores formed on the first end 101 of the polymeric body 100 for entrance of sound wave.

In one embodiment, all or part of the branched passages 103, 103′ and 103″ may directly be connected between the first end 101 and the second end 102 of the polymeric body 100 (not shown); or part of the branched passages 103, 103′ and 103″ may be connected in series to form a longer branched passage between the first end 101 and the second end 102 of the polymeric body 100 (not shown). In one embodiment, the branched passages 103, 103′ and 103″ may pass through the first end 101 and the second end 102 of the polymeric body 100 to form a plurality of open pores thereon. In one embodiment, each of the branched passages 103, 103′ and 103″ has an extending direction approximately from the first end 101 to the second end 102 which has a bias angle of 45 degrees or less relative to a direction of the shortest distance between the first end 101 and the second end 102. As long as the incident sound waves can enter into these branched passages 103, 103′ and 103″ from the first end 101 of the polymeric body 100 to produce internal reflections, it is not limed thereto.

Referring to FIG. 1, these branched passages 103, 103′ and 103″ have a spacing S therebetween, wherein each spacing S may independently be the same or different. The average spacing S may be 5 μm to 50 μm, such as 10 μm to 30 μm. When the spacing S is too far, the sound absorbing effects would weaken due to the reduction of porosity. When the spacing S is too close, it would result in the visual penetration and weaker structure strength. In one embodiment, each of these branched passages 103, 103′ and 103″ itself has a width W, wherein each width W may independently be the same or different. The average width W may be 5 μm to 50 μm, such as 10 μm to 30 μm. When the width W is too large, it would result in the visual penetration and weaker structure strength. When the width W is too small, the sound absorbing effects would weaken due to the reduction of porosity. As used in the specification and claims, the term “spacing S” means a wall thickness or a distance between the main passages 1031 of two adjacent branched passages; the term “width W” means a pore size or a diameter of each main passage 1031 of these branched passages 103, 103′ and 103″ in a direction perpendicular to central axis A of the main passage 1031.

Referring to FIG. 1, each of the branched passages 103, 103′ and 103″ includes a main passage 1031 and a plurality of side passages 1032. The main passage 1031 is connected to the first end 101 of the polymer body 100 and extends toward a direction of the second end 102, wherein each main passage 1031 approximately has an identical directionality and is parallel (i.e., bias angle less than 10 degrees) to the adjacent main passage 1031 (i.e., each main passage 1031 of the branched passages 103, 103′ and 103″ is parallel to that of the adjacent branched passages 103, 103′ and 103″). These side passages 1032 are formed around the main passage 1031 and connected to the main passage 1031, and the plurality of side passages 1032 extend from the main passage 1031 toward a direction of the second end 102. In one embodiment, each of these side passages 1032 has an angle θ with the main passage 1031, wherein each angle θ may independently be the same or different. The average angle θ may be 10 degrees to 90 degrees, such as 30 degrees to 80 degree. As used in the specification and claims, the term “angle θ” means an angle between a central axis A of the main passage 1031 and a central axis B of the side passages 1032, as shown in FIG. 1.

In one embodiment, these main passage 1031 have a spacing S therebetween, wherein each spacing S may independently be the same or different. The average spacing S may be 5 μm to 50 μm, such as 10 μm to 30 μm. In one embodiment, each of these main passage 1031 itself has a width W, wherein each width W may independently be the same or different. The average width W may be 5 μm to 50 μm, such as 10 μm to 30 μm. In one embodiment, each of the side passages 1032 may be a lamellar structure or a columnar structure, which has a thickness Y, wherein each thickness Y may independently be the same or different. The average thickness Y may be 3 μm to 20 μm, such as 5 μm to 10 μm. Generally, the thickness Y of the side passages 1032 is less than the width W of the main passage 1031. As used in the specification and claims, the term “thickness Y” means a height of a contact position which the side passages 1032 are connected to the main passages 1031, wherein the height is a distance in a direction parallel to the central axis A of the main passages 1031.

In one embodiment, each of the branched passages 103, 103′ and 103″ may be a lamellar structure, a columnar structure, or a combination thereof. As used in the specification and claims, the term “lamellar structure” or “columnar structure” means a structure formed by the ice crystals in the freeze casting process, which may be adjusted by controlling the cooling temperature or the cooling rate; the term “lamellar structure” means an object which the size of one dimension thereof is far less than the size of the other two dimensions, for example, less than 5 times, 10 times, or 50 times. In one embodiment, these branched passages 103, 103′ and 103″ may be made by the freeze casting method.

In one embodiment, the polymer body 100 may consist of a water-soluble polymer. In another embodiment, the polymeric body includes at least 90 wt % of a water-soluble polymer. In one embodiment, the water-soluble polymer can be exemplified by polyvinyl alcohol (PVA) or polyethylene glycol (PEG). The polyvinyl alcohol has a weight average molecular weight (Mw) of 3000 to 25000, and the polyethylene glycol has a weight average molecular weight (Mw) of 300 to 6000. As used in the specification and claims, the term “water-soluble polymer” means hydrophilic polymers that can dissolve, disperse, or swell in water, which have a large number of hydrophilic groups, such as cationic groups (tertiary amine group, quaternary amine group, etc.), anionic groups (carboxyl group, sulfonic acid group, phosphoric acid group, sulfuric acid group, etc.), or polar nonionic groups (hydroxyl group, ether group, amine group, amide group, etc.).

In one embodiment, the polymeric body 100 further includes a 10 wt % or less of an inorganic material besides the water-soluble polymer, wherein the inorganic material may be exemplified by a porous material with high specific surface area such as diatomite or active carbon, producing more pores in order to further enhance the sound absorbing effects of the sound absorbing material of the present disclosure. When the weight ratio of the inorganic material is too large, the number of theses branched passages could reduce to result in lower open porosity and poor sound absorbing effects; when the weight ratio of the inorganic material is too less, the sound absorbing effects could not be further enhanced. In one embodiment, the polymeric body 100 may consist of at least 94 wt % of the water-soluble polymer and 6 wt % or less of the inorganic material. In one embodiment, the inorganic material has an average particle size of 5 μm to 40 μm. In one embodiment, the inorganic material may be exposed on surface of the branched passages in addition to existing within the polymeric body, thereby producing more pores.

In one embodiment, the sound absorbing material of the present disclosure has a density of 300 kg/m³to 400 kg/m³. When the density of the sound absorbing material is too high, the sound absorbing material would be overweight and have poor sound absorbing effects. When the density of the sound absorbing material is too low, the structure strength of the sound absorbing material would be insufficient. As used in the specification and claims, the term “density” means a bulk density of the polymeric body including the plurality of branched passages. In one embodiment, the sound absorbing material of the present disclosure has a porosity of 60% to 80%. When the porosity of the sound absorbing material is too much, it would result in the visual penetration and weaker structure strength. When the porosity of the sound absorbing material is too less, the sound absorbing effects would become poor. As used in the specification and claims, the term “porosity” means a porosity determined by a density difference ratio method.

In one embodiment, the sound absorbing material of the present disclosure has a sound absorbing coefficient of at least 0.6 at 500 Hz, at least 0.55 at 1000 Hz, and at least 0.5 at 2000 Hz, determined by the tube method as defined in JIS A1405. In another embodiment, the sound absorbing material of the present disclosure has a sound absorbing coefficient of at least 0.85 at 500 Hz, at least 0.8 at 1000 Hz, and at least 0.7 at 2000 Hz. As used in the specification and claims, the term “JIS A1405” means the measurement of the vertically incident sound waves entering into the sound absorbing material by the in-tube method.

The sound absorbing material of the present disclosure may be made by the freeze casting method. FIG. 2 is a schematic diagram illustrating the freeze casting system. Referring to FIG. 2, the freeze casting system 20 includes a PTFE mould 201, a copper cold finger 202, a liquid nitrogen bath 203, a temperature controller 205, and a heating coil 206. The PTFE mould 201 has a sample area 204 for placing the slurry of preparing the sound absorbing material of the present disclosure. The copper cold finger 202 is connected between the sample area 204 and the liquid nitrogen bath 203. The liquid nitrogen bath 203 in which the liquid nitrogen is placed may cool the slurry in the sample area 204 through the copper cold finger 202. The heating coil 206 surrounding the outer of the copper cold finger 202 is connected to the temperature controller 205 to control the cooling temperature and the cooling rate. In this embodiment, the freeze casting system 20 of the present disclosure belongs to the one-side temperature controlled system. On the other hand, the freeze casting system 20 may also employ the double-sided temperature controlled system.

The preparation method of the sound absorbing material of the present disclosure is provided as below. First, the slurry is put into the sample area 204, wherein the slurry at least includes a water-soluble polymer and water. In one embodiment, the slurry has 60 wt % to 80 wt % of water. In some embodiment, the slurry may further include an inorganic material, wherein the water-soluble polymer and the inorganic material are described in detail above. Then, the liquid nitrogen is added into the liquid nitrogen bath 203, and water in the slurry are cooled from the bottom of the sample area 204 under the cooling conditions controlled by the temperature controller 205 and the heating coil 206 so as to form the ice crystal structures with directionality. When the slurry in the sample area 204 is all solidified to form a green body, the ice crystals growing in the green body are vaporized and removed at rapidly reduced-pressure, and then the green body is dried to obtain the sound absorbing material with the continuous open-cell structure. In one embodiment, after dried, the mechanical strength of sound absorbing material may further be increased through cross-linking by means of directly heating or further adding a cross-linking agent to the slurry. In one embodiment, the manufactured sound absorbing material may further be cut into a plurality of the sound absorbing material, wherein the cut surface exposes the branched passages to form many openings, served as the incident end of the absorbing sound wave (i.e., the first end of the polymeric body). In one embodiment, the manufactured sound absorbing material may further be cut along the direction vertical to the extending direction of the branched passages. The above preparation method of sound absorbing material of the present disclosure is provided merely as an exemplary embodiment, but it is not limited thereto.

Preparation of the Sound Absorbing Material

Example 1 (100 wt % PVA)

2.4 g of PVA powders (purchased from Polysciences Incorporation, Mw=6000, 80% hydrolyzed) and 21.6 g of water were mixed to form a slurry with 90 wt % water. Next, the slurry was put into the PTFE mould (Diameter: 2 cm; Height: 2 cm) of the freeze casting system (Referring to FIG. 2). The bottom of the PTFE mould was cooled from 25° C. to −5° C. at a cooling rate of 10° C./min, and then maintained for 3 minutes to solidify the slurry to form a green body. Subsequently, the ice crystals grown in the green body were removed at low temperature and low pressure through the freeze drying method (Temperature: −80° C.; Pressure: 80 mTorr; Time: 5 minutes). Finally, the green body was cross-linked at 150° C. to obtain a sound absorbing material. The results indicate that the sound absorbing material obtained in Example 1 has a density of 380 kg/m³and a porosity of 70%.

FIG. 3 is a sectional SEM view illustrating the sound absorbing material obtained in Example 1. Referring to FIG. 3, the position E1 is adjacent to the first end of the polymeric body, and the position E2 is adjacent to the second end of the polymeric body. It is observed that these branched passages arrange in layered construction, wherein each of these branched passages has a pore-growth direction (i.e., extending direction) X from the position E1 to the position E2.

FIG. 4 is a partial enlarged view of FIG. 3. It is observed that each of these branched passages has a main passage and a plurality of side passages, wherein these main passages are parallel to the adjacent main passages and have an approximate pore-growth direction X. As shown in FIG. 4, these main passages have an average width W of 21 μm and an average spacing S of 9 μm.

Example 2 (95 wt % PVA/5 wt % Diatomite)

2.4 g of PVA powders (purchased from Polysciences Incorporation, Mw=6000, 80% hydrolyzed), 0.13 g of diatomite (DICALITE MINERALS CORP., DICALITE SPEEDPLUS), and 22.77 g of water were mixed to form a slurry with 90 wt % water. Next, the slurry was put into the PTFE mould (Diameter: 2 cm; Height: 2 cm) of the freeze casting system (Referring to FIG. 2). The bottom of the PTFE mould was cooled from 25° C. to −5° C. at a cooling rate of 10° C./min, and then maintained for 3 minutes to solidify the slurry to form a green body. Subsequently, the ice crystals grown in the green body were removed at low temperature and low pressure through the freeze drying method (Temperature: −80° C.; Pressure: 80 mTorr; Time: 5 minutes). Finally, the green body was cross-linked at 150° C. to obtain a sound absorbing material. The results indicate that the sound absorbing material obtained in Example 2 has a density of 320 kg/m³and a porosity of 75%.

Comparison Example 1

The sound absorbing material (PU) purchased from ADHsing Corporation (Taiwan) was provided.

Test Example of the Sound Absorbing Material

Measurement of the sound absorbing coefficient of the sound absorbing materials obtained in Example 1, Example 2, and Comparison Example 1 were performed in accordance with the sound absorbing coefficient measurement by the tube method as defined in JIS A1405 (Testing system: Brüel & Kjær Type 4206T-Impedance tube (small tube); four Type 4187-¼″ Microphones; Transmission Loss (TL) software). The sound waves scanned in the range of frequency of 300 Hz to 6000 Hz were emitted from the sound source (speaker), and the sound absorbing coefficients in various frequencies were measured by the TL software. The test results were shown in FIG. 5 and FIG. 6.

FIG. 5 is a comparison diagram of sound absorbing coefficient versus frequency of the sound absorbing material obtained in Comparison Example 1 and the sound absorbing material obtained in Example 1 according to the present disclosure. Referring to FIG. 5, compared to the absorbing material obtained in Comparison Example 1, it is observed that the sound absorbing material obtained in Example 1 have better sound absorbing effects at medium-high frequency (1000 Hz to 2000 Hz) and at low frequency (500 Hz to 1000 Hz).

FIG. 6 is a comparison diagram of sound absorbing coefficient versus frequency of the sound absorbing material obtained in Comparison Example 1 and the sound absorbing material obtained in Example 2 according to the present disclosure. Referring to FIG. 6, it is observed that the sound absorbing coefficient of the sound absorbing material obtained in Example 2 at all frequencies (500 Hz to 4000 Hz) is far higher than that of the sound absorbing material in Comparison Example 1. As a result, the sound absorbing material having a small amount of the inorganic material may further enhance the overall sound absorbing effects.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.

SOUND ABSORBING MATERIAL

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