JP4227051B2 - Sound absorbing material and manufacturing method thereof - Google Patents

Description

The present invention relates to a sound absorbing material used for reducing noise generated from a hard disk of a computer, for example, and a method for manufacturing the same.

In hard disk drives used in personal computers (personal computers), etc., noise is generated by driving motor noise and disk wind noise, which occurs when a sound-absorbing material is sandwiched between the hard disk drive body and the board. Reduction of sound is achieved (for example, refer to Patent Document 1 and Patent Document 2). These sound absorbing materials are made of, for example, flexible polyurethane foam, and the physical properties such as density, rebound resilience, and air flow rate are set in a range suitable for sound absorption. Moreover, what is comprised from the organic foam containing the powder of specific gravity 2-10 is known as a sound-absorbing material used for a partition wall with good soundproof performance (refer patent document 3).
JP 10-254454 A (2nd page) JP-A-10-83667 (2nd, 5th and 6th pages) JP-A-9-13528 (pages 2 to 4)

  By the way, sound propagation includes air propagation sound in which sound propagates in the air and vibration propagation sound generated by vibration caused by sound. Since the sound absorbing material sandwiched between the main body of the hard disk drive and the substrate is normally used in a compressed state, it is presumed that the ratio of vibration propagation sound is larger than that of air propagation sound. For this reason, it is necessary to aim at comprehensive sound absorption with emphasis on reducing vibration propagation sound over air propagation sound. In recent years, hard disk drives have become smaller and require thinner sound absorbing materials, and sound has been increasing due to higher drive speeds. Further measures for sound absorption are required in response to these market changes. .

  Under such circumstances, the sound absorbing materials described in Patent Document 1 and Patent Document 2 described above have only improved the physical properties of the flexible polyurethane foam itself, and thus the sound absorbing performance has not been sufficiently improved. The sound absorbing material described in Patent Document 3 is specifically a polyurethane foam containing 10% by weight of iron powder (specific gravity 7.86) and a polystyrene foam containing 20% by weight of silica sand (specific gravity 2.3). In the former, since the specific gravity of the iron powder is too large compared to the specific gravity of the polyurethane foam itself, the iron powder tends to precipitate, and the dispersibility is also poor, so that sufficient improvement in sound absorption performance cannot be expected. In the latter case, since the polystyrene foam is generally hard, the viscoelastic properties are poor and the sound absorption performance cannot be sufficiently improved.

The present invention has been made paying attention to such problems existing in the prior art. An object of the present invention is to provide a sound absorbing material capable of effectively reducing vibration propagating sound and reliably improving sound absorbing performance, and a method for manufacturing the same.

In order to achieve the above object, the sound-absorbing material according to the first aspect of the present invention is used by being sandwiched between the main body of the hard disk drive and the substrate, and comprises a polyol, a polyisocyanate compound, a catalyst, and a foaming agent. A sound-absorbing material obtained by forming an open-cell type flexible polyurethane foam obtained by reacting raw materials into a sheet, the thickness thereof is 1 to 5 mm, and the raw material has an average particle diameter of 20 to 200 μm, A powder having a specific gravity of 2 to 4 is contained in an amount of 3 to 70 parts by mass with respect to 100 parts by mass of polyols, and a film made of a cured product formed by curing the surface of the flexible polyurethane foam is formed on the surface. The flexible polyurethane foam has a low-density layer at the center and a high-density layer having a higher density between the center and the surface or the film than the low-density layer at the center. And it is characterized in that it is foamed formed.

According to a second aspect of the present invention, in the sound absorbing material according to the first aspect, the powder is aluminum hydroxide .
According to a third aspect of the present invention, there is provided a method for producing a sound-absorbing material , comprising: forming an open-celled flexible polyurethane foam obtained by reacting raw materials comprising a polyol, a polyisocyanate compound, a catalyst and a foaming agent into a sheet. The raw material is a method for producing a sound-absorbing material in which a powder having an average particle diameter of 20 to 200 μm and a specific gravity of 2 to 4 is contained, and a polyol, a polyisocyanate compound, Supplying raw material of flexible polyurethane foam consisting of catalyst and foaming agent, placing a release film on it, reacting polyols and polyisocyanate compound in the presence of catalyst and foaming agent, and spontaneously foaming, then heating Cured and then peeled off both release films to produce an open-celled flexible polyurethane foam in the form of a sheet And it is characterized in and.

According to the present invention, the following effects can be exhibited.
According to the sound absorbing material of the invention described in claim 1 and claim 2 , since the average particle diameter of the powder contained in the raw material of the flexible polyurethane foam is large at 20 to 200 μm, the dispersion state of the powder becomes rough. Thus, the sound absorbing material is suppressed from being hardened, and the viscoelastic properties are improved. Furthermore, since the specific gravity of the powder is 2 to 4, the mass can be increased while maintaining the dispersibility in the flexible polyurethane foam, which can contribute to the suppression of vibration propagation. As a result, vibration propagation sound can be effectively reduced and sound absorption performance can be reliably improved.

Moreover, the said effect can be exhibited, maintaining the performance as a flexible polyurethane foam.
In addition, the surface density can be increased by the film of the cured product of the flexible polyurethane foam, and the sound absorption performance can be further improved.

Further, the surface density can be further increased based on the high-density layer of the flexible polyurethane foam, and the sound absorption performance can be further improved.
According to the method for manufacturing a sound absorbing material of the third aspect, the sheet-shaped sound absorbing material can be easily manufactured. Moreover, a film and a high-density layer can be easily formed on the surface of the flexible polyurethane foam.

Hereinafter, embodiments of a sound absorbing material of the present invention will be described in detail with reference to the drawings.
The sound-absorbing material of the present embodiment is formed by molding an open-celled flexible polyurethane foam obtained by reacting raw materials comprising a polyol, a polyisocyanate compound, a catalyst, and a foaming agent into a sheet shape. The raw material contains a powder having a particle diameter of 20 to 200 μm and a specific gravity of 2 to 4. Polyurethane foam is manufactured by a complex reaction, but basically the following reaction is the main component. That is, an addition polymerization reaction (urethanization reaction) between polyols and a polyisocyanate compound, a foaming reaction between a polyisocyanate compound and a foaming agent, and a crosslinking reaction between these reaction products and the polyisocyanate compound.

  As shown in FIG. 1, the sound-absorbing material 11 is formed by forming films 14a and 14b made of a cured product of a flexible polyurethane foam 12 on both surfaces of a flexible polyurethane foam 12 having a sheet shape. The thickness of the films 14a and 14b is about 2 to 50 μm. Further, a low density layer 15 is formed at the center of the flexible polyurethane foam 12, and between the low density layer 15 and the coatings 14a and 14b, a high density layer 16a having a higher density than the center low density layer 15 is formed. 16b is formed. That is, since cells (bubbles) formed by foaming are large at the central portion of the flexible polyurethane foam 12 and small at the outside thereof, the density is small at the central portion, and the density is large at the outside.

  The presence of 4 to 5 cells in the thickness direction of the flexible polyurethane foam 12 is desirable from the viewpoint of exhibiting sound absorption performance. This flexible polyurethane foam 12 is an open-celled foam in which cells communicate. In addition, the flexible polyurethane foam 12 shown in FIG. 1 represents the structure typically, and does not represent the open cell structure. The thickness of the sound absorbing material 11 is preferably 5 mm or less and more preferably 1 to 5 mm in order to sandwich the sound absorbing material 11 between the main body of the hard disk drive and the substrate in the computer.

The sound absorbing material 11 is manufactured using a manufacturing apparatus shown below.
FIG. 2 is a schematic explanatory view showing a sound absorbing material manufacturing apparatus. As shown in FIG. 2, release films 13a and 13b are wound around a pair of upper and lower delivery rollers 17a and 17b, respectively. 13a and 13b are superposed and sent forward (rightward in the figure). In this case, the delivery roller 17b at the lower position rotates to the right, and the delivery roller 17a at the upper position rotates to the left. The release films 13a and 13b are formed of a fluorine resin, a silicone resin, or the like.

  A raw material supply device 20 that discharges the raw material 18 (liquid) of the flexible polyurethane foam 12 from a supply port 21 that is opened downward is disposed below the feed roller 17a at the upper position. And the raw material 18 discharged from the supply port 21 of the raw material supply apparatus 20 is supplied on the release film 13b sent out from the delivery roller 17b of the lower position, and supported by the support stand 19. A presser roller 22 is disposed at a front position of the raw material supply device 20, and the raw material 18 of the flexible polyurethane foam 12 is sandwiched between the release films 13a and 13b from the upper surfaces of the release films 13a and 13b. The thickness between the release films 13a and 13b is adjusted by pressing.

  A foaming device 23 that blows 10 to 70 ° C. heated air onto the object is disposed at a front position of the presser roller 22, and a curing device 24 that blows 50 to 150 ° C. heated air onto the object at the front position. It is installed side by side. In this embodiment, the foaming device 23 is set to normal temperature (20 ° C.), and the curing device 24 is set to 70 ° C. In the foaming apparatus 23, in order to form the film | membrane 14 and the high-density layer 16 on the surface of the flexible polyurethane foam 12, it is preferable to hold | maintain and foam at the low temperature of 10-40 degreeC. In the present embodiment, the support base 19 and the foaming device 23 are integrally formed.

  Winding rollers 33a and 33b are arranged at the front upper and lower positions of the curing device 24, and the release films 13a and 13b fed from the curing device 24 are respectively wound. The raw material 18 of the flexible polyurethane foam 12 sandwiched between the release films 13a and 13b is naturally foamed in the foaming device 23 and then cured (crosslinked) in the curing device 24, and then the release film 13a, 13b is wound around the winding rollers 33a and 33b. As a result, the sound absorbing material 11 described above in which the films 14a and 14b and the high-density layers 16a and 16b are formed on both surfaces of the flexible polyurethane foam 12 is manufactured.

  The raw material 18 of the flexible polyurethane foam 12 is composed of polyols, polyisocyanate compounds, catalysts, foaming agents, foam stabilizers and the like. The polyol is preferably a polyether polyol or a polyester polyol having a hydroxyl value of 20 to 200 mg KOH / g. The polyether polyol and the polyester polyol can be used alone or in combination. When the hydroxyl value of the polyols is less than 20 mgKOH / g, the hydroxyl value becomes too small, the crosslink density of the flexible polyurethane foam 12 becomes small, and the shape retention is lowered. When the hydroxyl value exceeds 200 mgKOH / g, the hydroxyl value becomes too large, the crosslink density of the flexible polyurethane foam 12 becomes large and hard, and it tends to be a closed cell type.

  Polyester polyols include condensed polyester polyols obtained by reacting polycarboxylic acids such as adipic acid and phthalic acid with polyols such as ethylene glycol, diethylene glycol, propylene glycol and glycerin, as well as lactone polyester polyols and polycarbonate polyols. Is mentioned. Examples of the polyether polyol include polypropylene glycol, polytetramethylene glycol, and modified products thereof. These polyols can change the number of functional groups and the hydroxyl value of the hydroxyl group by adjusting the type, molecular weight, condensation degree, and the like of the raw material components.

  The polyisocyanate compound to be reacted with polyols is a compound having a plurality of isocyanate groups, specifically, tolylene diisocyanate (TDI), 4,4-diphenylmethane diisocyanate (MDI), 1,5-naphthalene diisocyanate (NDI), Triphenylmethane triisocyanate, xylylene diisocyanate (XDI), hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate, isophorone diisocyanate (IPDI) and the like are used.

  Here, it is preferable that the isocyanate index of a polyisocyanate compound is 80-130. Here, the isocyanate index represents the equivalent ratio of the isocyanate group of the polyisocyanate compound to the hydroxyl group of the polyol and the foaming agent (water) as a percentage. Therefore, when the value is less than 100, it means that the hydroxyl group is in excess of the isocyanate group, and when it exceeds 100, it means that the isocyanate group is in excess of the hydroxyl group. When the isocyanate index is less than 80, polyols cannot sufficiently react with the polyisocyanate compound, resulting in large flexibility and reduced shape retention. On the other hand, when the isocyanate index exceeds 130, the flexible polyurethane foam becomes hard and its physical properties are deteriorated.

  The catalyst is for accelerating the urethanization reaction between polyols and polyisocyanate compounds. As such a catalyst, N, N ′, N′-trimethylaminoethylpiperazine, tertiary amines such as triethylenediamine and dimethylethanolamine, organometallic compounds such as tin octylate, acetates, alkali metal alcoholates and the like are used. Among these, in order to obtain the flexible polyurethane foam 12, it is desirable to use an amine such as a tertiary amine or a metal-containing catalyst in combination.

  The foaming agent is for foaming polyurethane into the flexible polyurethane foam 12. As the foaming agent, pentane, cyclopentane, hexane, cyclohexane, dichloromethane, carbon dioxide, etc. are used in addition to water. As a raw material of the flexible polyurethane foam 12, a foam stabilizer such as a surfactant, a flame retardant such as a condensed phosphate ester, an antioxidant, a plasticizer, an ultraviolet absorber, a colorant and the like can be added.

  When the urethanization reaction between the polyols and the polyisocyanate compound is performed, a one-shot method or a prepolymer method is employed. The one-shot method is a method in which a polyol and a polyisocyanate compound are directly reacted. The prepolymer method is a method in which a part of a polyol and a polyisocyanate compound are reacted in advance to obtain a prepolymer having an isocyanate group or a hydroxyl group at a terminal, and the polyol or the polyisocyanate compound is reacted therewith. The one-shot method is a preferable method because the manufacturing process is one step compared to the prepolymer method, and there are few restrictions on the manufacturing conditions, and the manufacturing cost can be reduced.

  The flexible polyurethane foam 12 thus obtained must have an open-cell structure in order to exhibit sound absorption performance for sucking sound into the cell. The sound energy is attenuated and absorbed by propagating through the open-cell type flexible polyurethane foam 12, but the closed-cell type flexible polyurethane foam is not open-celled, so that the sound is reflected without entering the inside. Does not function as a sound absorbing material. In order to obtain an open-cell structure, it is preferable to set the time for the raw material 18 to be in the form of cream in the natural foaming stage to 10 to 40 seconds, and then the time for the cell to form 1 to 6 minutes. .

  Next, the powder is intended to increase the viscoelastic properties and mass of the flexible polyurethane foam 12 to mainly suppress vibration propagation sound, and has an average particle diameter of 20 to 200 μm and a specific gravity of 2 to 4. It is. Such powders include aluminum hydroxide (specific gravity 2.4), calcium carbonate (specific gravity 2.6), aluminum oxide (specific gravity 3.99), magnesium oxide (specific gravity 3.65), magnesium carbonate (specific gravity 2.2). ), Silica sand (specific gravity 2.3) and the like are used. Of these powders, hydroxides such as aluminum hydroxide are preferable from the viewpoint of imparting flame retardancy.

  When the average particle diameter of the powder is less than 20 μm, the viscosity of the raw material of the flexible polyurethane foam 12 increases, and the resulting flexible polyurethane foam 12 becomes too hard, resulting in a decrease in viscoelastic properties. On the other hand, when the average particle diameter exceeds 200 μm, the dispersibility of the powder in the raw material 18 of the flexible polyurethane foam 12 becomes too coarse, and the viscoelastic characteristics cannot be improved. Moreover, when specific gravity is less than 2, mass and a viscoelastic characteristic cannot be improved, and a vibration propagation sound cannot be suppressed. On the other hand, when the specific gravity exceeds 4, it becomes easy to settle, and the hardness of the flexible polyurethane foam 12 increases and the viscoelastic properties decrease.

  When the sound absorbing material 11 is manufactured, as shown in FIG. 2, the release film 13b is sent out from the feed roller 17b at the lower position, and the flexible polyurethane foam 12 is fed from the raw material supply device 20 onto the release film 13b. The raw material 18 is supplied. Then, at the front position, the release film 13a is supplied from the feed roller 17a at the upper position so as to overlap the raw material 18, and the release films 13a and 13b in a state where the raw material 18 is sandwiched between the pressing rollers 22 are supplied. Adjust the thickness between. After that, the foam is formed by naturally foaming the raw material 18 by maintaining the foaming apparatus 23 at a normal temperature. Subsequently, after being cured by heating in a curing device 24 set at 70 ° C., the release film is wound around a winding roller, whereby the sound absorbing material 11 made of the flexible polyurethane foam 12 having the structure shown in FIG. Is manufactured.

  The obtained sheet-like sound absorbing material 11 is used by being inserted in a compressed state between the main body of the hard disk drive and the substrate, for example. At this time, since the sound absorbing material 11 is composed of the open cell type flexible polyurethane foam 12, the sound is effectively absorbed in the open cells compared to the closed cells, and the sound propagation is reduced. The flexible polyurethane foam 12 is improved in viscoelastic properties by a powder having an average particle diameter of 20 to 200 μm and a specific gravity of 2 to 4 blended in the raw material 18. By the way, it is known that the propagation of vibration is determined by three elements of mass, rigidity, and damping. Among them, the following formula is established for the attenuation.

Loss coefficient (η) = C / (KM) ^1/2
However, C represents a viscous damping coefficient, K represents a spring constant, and M represents mass.
Since the powder has a large average particle size, it is considered that the dispersibility in the raw material 18 becomes coarse and the viscosity damping coefficient becomes large. For this reason, a loss coefficient becomes large and propagation of vibration is suppressed.

Further, coatings 14a and 14b are formed on both surfaces of the flexible polyurethane foam 12, and the surface density (kg / m ² ) of the portions is increased by the coatings 14a and 14b. As for the rigidity, the larger the Young's modulus (elastic coefficient) value, the more effective is the reduction of vibration propagation. The high surface density of the coatings 14a and 14b means that the Young's modulus is high, and the propagation of vibration is suppressed, and the vibration propagation sound can be effectively reduced.

  Furthermore, the high-density layers 16a and 16b are formed between the central portion of the flexible polyurethane foam 12 and the coatings 14a and 14b. The high-density layers 16a and 16b increase the surface density and increase the Young's modulus. Is suppressed. Therefore, the high-density layers 16a and 16b and the coatings 14a and 14b work synergistically to reduce vibration propagation sound.

The effects exhibited by the above embodiment will be described collectively below.
In the sound absorbing material 11 of the present embodiment, since the average particle diameter of the powder contained in the raw material 18 of the flexible polyurethane foam 12 is large at 20 to 200 μm, the dispersed state of the powder becomes coarse and the sound absorbing material 11 is hard. This is suppressed, and viscoelastic properties are improved. That is, the loss factor increases as the viscous damping coefficient increases.

  Furthermore, since the specific gravity of the powder is 2 to 4, the mass can be increased while maintaining the dispersibility in the flexible polyurethane foam 12, which can contribute to suppression of vibration propagation. As a result, vibration propagation sound can be effectively reduced and sound absorption performance can be reliably improved.

  -Moreover, content of the said powder is set to 3-70 mass parts with respect to 100 mass parts of polyols. For this reason, it is possible to improve the sound absorbing performance based on the reduction of vibration propagation sound while maintaining the performance as the flexible polyurethane foam 12.

  Furthermore, coatings 14 a and 14 b made of a cured product of the flexible polyurethane foam 12 are formed on the surface of the sound absorbing material 11. Therefore, the surface density of the surface of the sound absorbing material 11 can be increased by the coatings 14a and 14b, and the sound absorbing performance can be further improved.

In addition, the surface density can be further increased based on the high-density layers 16a and 16b of the flexible polyurethane foam 12, and the sound absorption performance can be further improved.
As described above, since the sound absorbing material 11 of the present embodiment is excellent in sound absorbing performance, a hard disk drive of a computer such as a personal computer, a video disk drive, a compact disk (CD) drive, a mini disk (MD) ) Can be suitably used for noise prevention such as drive.

Hereinafter, the embodiment will be described more specifically with reference to examples and comparative examples.
(Examples 1-9 and Comparative Examples 1-8)
Materials having the compositions shown in Tables 2 to 5 are prepared as raw materials for the flexible polyurethane foam 12, and the sheet-like sound absorbing material 11 made of the flexible polyurethane foam 12 is manufactured by the above-described manufacturing apparatus or by slicing the slab foam. did. The thickness of the sound absorbing material 11 was 2 mm. The meanings of the abbreviations in Tables 2 to 5 are as follows.

PML7001K: polyether polyol manufactured by Asahi Glass Co., Ltd., hydroxyl value 28 mgKOH / g
SBU0379: 4,4-diphenylmethane diisocyanate (MDI) prepolymer manufactured by Sumitomo Bayer Co., Ltd., 25% by mass of isocyanate groups
Water: hydroxyl group 6233mgKOH / g
LV33: catalyst composed of a mixture of triethylenediamine and propylene glycol in a mass ratio of 1: 2, flame retardant manufactured by Chukyo Yushi Co., Ltd .: 20 parts by mass of melamine powder manufactured by Mitsui Chemicals, Inc. and manufactured by Daihachi Chemical H10: Aluminum hydroxide with an average particle diameter of 55 μm and a specific gravity of 2.42 [Hijilite manufactured by Showa Denko KK]
H21: Aluminum hydroxide having an average particle size of 25 μm and a specific gravity of 2.42 [Hijilite manufactured by Showa Denko KK]
H31: Aluminum hydroxide having an average particle diameter of 18 μm and a specific gravity of 2.42 [Hijilite manufactured by Showa Denko KK]
H32: Aluminum hydroxide having an average particle diameter of 8 μm and a specific gravity of 2.42 [Hijilite manufactured by Showa Denko KK]
KS1300: Calcium carbonate having an average particle size of 1.77 μm and a specific gravity of 2.63 (manufactured by Dowa Calfine)
Charcoal Cal 2: Powdered from quick lime, calcium carbonate with an average particle size of 25 μm and a specific gravity of 2.63 PE powder: Polyethylene powder with an average particle size of 25 μm and a specific gravity of 0.93 (manufactured by Mitsui Chemicals, Inc.)
Iron powder: Iron powder with an average particle size of 100 μm (manufactured by Tokai Kogyo Co., Ltd.)
Silica sand: Silica sand with an average particle size of 35μm (Toho Zinc Co., Ltd.)
The EPDM foam is obtained by slicing an open-cell slab to a thickness of 2 mm.

  In the sound absorbing material of Comparative Example 7, 150 parts by mass of KS1300 is added to EPDM resin / paraffin oil / azodicarbonamide (ADCA) organic foaming agent / sulfur = 100/50/15 / 2.5 (parts by mass). And formed into a sheet shape.

About the obtained sound-absorbing material, density, hardness, sound-absorbing performance (A characteristic value) and combustibility were measured by the following methods, and the results are shown in Tables 2 to 4.
Sound absorption performance (A characteristic): As shown in FIGS. 3A and 3B, the upper surface of the hard disk body 25 is provided with a housing recess 26 having a substantially U-shape in plan view. The substrate 27 is placed, and the accommodation recess 26 is disposed so as to contact the substrate 27 in a state where the sheet-like sound absorbing material 11 is compressed. As shown in FIG. 4, this hard disk body 25 is placed on a table 29 via a plate-like polyethylene foam 28 so that the hard disk body 25 can be driven. On the other hand, a microphone 30 is disposed above the hard disk main body 25, and the microphone 30 is connected to the analyzer 32 by a connection line 31. The sound generated from the hard disk main body 25 is collected by the microphone 30 and analyzed by the analyzer 32. The acoustic power level L _WA of the A characteristic is calculated by the following equation (1). In the example, when the sound absorbing material 11 was not used (blank), the acoustic power level of the A characteristic was 43.51 dB.

但し、Ｌ_WJは、ｊ番目の１／３オクターブバンドでの音響パワーレベル、Ａ_jはｊ番目の１／３オクターブバンドでの下記表１に示すＡ特性値を示す。

Where L _WJ is the sound power level in the _jth １ ／ octave band, and A _j is the A characteristic value shown in Table 1 below in the jth ３ octave band.

密度：ＪＩＳ Ｋ６４００に準じて測定した（kg／m³）。

Density: Measured according to JIS K6400 (kg / m ³ ).

Hardness: Compressive stress (kPa) when a sound absorbing material made of flexible polyurethane foam is compressed by 50%.
Flammability: Measured according to UL94HF1, with pass shown as ◯ and rejected as x.

表２及び表３に示すように、実施例１〜７ではブランクに比べて１．０ｄＢ以上の騒音レベルの低下が認められ、実施例８及び９ではブランクに比べて０．９ｄＢ以上の騒音レベルの低下が認められた。上記Ａ特性の吸音性能試験において、０．５ｄＢ以上の騒音レベルの低下は特にコンピュータのハードディスクドライブの吸音性能として効果的とされているレベルである。

As shown in Tables 2 and 3, in Examples 1 to 7, a noise level reduction of 1.0 dB or more was recognized compared to the blank, and in Examples 8 and 9, the noise level was 0.9 dB or more compared to the blank. Decrease was observed. In the sound absorption performance test of the A characteristic, a reduction in noise level of 0.5 dB or more is a level that is particularly effective as the sound absorption performance of a hard disk drive of a computer.

  On the other hand, as shown in Table 4 and Table 5, when the raw material of the flexible polyurethane foam 12 does not contain powder (Comparative Example 1), the sound absorption performance based on the powder is not exhibited, and the blank Compared with the noise level, the reduction in the noise level was only 0.5 dB. When aluminum hydroxide having an average particle diameter of less than 20 μm is included (Comparative Examples 2 and 3) and when calcium carbonate having an average particle diameter of less than 20 μm is included (Comparative Example 4), there is almost no difference from Comparative Example 1. It was. When polyethylene powder having a specific gravity of less than 2 was used (Comparative Example 5), the noise level was reduced by 0.5 dB or less compared to the blank. Furthermore, in Comparative Example 6, the EPDM foam slab was cut out, and the noise level was reduced by 0.5 dB or less compared to the blank. The sound absorbing material of Comparative Example 7 was formed into a sheet shape by adding calcium carbonate which is generally added to the blend described in Patent Document 1, but almost no improvement in sound absorbing effect was observed. The sound absorbing material of Comparative Example 8 is obtained by molding a slab-like foam from the blend described in Patent Document 3, but the iron powder settles and the dispersibility is low, so the sound absorbing effect is not sufficient. There wasn't.

In addition, this embodiment can also be changed and embodied as follows.
-As shown to Fig.5 (a), the thickness of the high-density layers 16a and 16b formed in the both surfaces side of the flexible polyurethane foam 12 can be made thicker, and a vibration propagation sound can also be reduced further. As shown in FIG. 5B, vibration propagation sound can be further reduced by increasing the thickness of the coatings 14a and 14b provided on both surfaces of the flexible polyurethane foam 12.

-At least one or both of the films 14a and 14b and the high-density layers 16a and 16b can be omitted.
In the foaming device 23, the temperature can be changed below and above the release films 13a and 13b sandwiching the raw material 18, and the presence or absence of the coatings 14a and 14b and the high-density layers 16a and 16b or their thickness can be changed.

The viscoelastic properties of the flexible polyurethane foam 12 can be changed by combining a plurality of powders having different average particle diameters and specific gravity.
The flexible polyurethane foam 12 can be obtained by a molding method, an on-site construction spray molding method, or the like.

  A soft slab polyurethane foam can be used as the flexible polyurethane foam 12 and cut into a sheet shape to produce a sound absorbing material. The flexible slab polyurethane foam is obtained by discharging a raw material onto a belt conveyor, and spontaneously foaming the raw material at normal temperature and atmospheric pressure while the belt conveyor moves, and then curing (curing) in a drying furnace.

Sectional drawing which shows the sound-absorbing material in embodiment. Schematic explanatory drawing which shows the manufacturing apparatus of a sound-absorbing material. (A) is a top view which shows the hard disk in the state which mounted | wore with the sound absorption material in the Example, (b) is sectional drawing in the 3b-3b line | wire of (a). Schematic explanatory drawing which shows the apparatus for measuring a noise level about the hard disk in the state which mounted | wore with the sound-absorbing material. (A) And (b) is sectional drawing which shows another example of a sound-absorbing material.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Sound absorption material, 12 ... Soft polyurethane foam, 14, 14a, 14b ... Film | membrane, 15 ... Low density layer, 16, 16a, 16b ... High density layer, 18 ... Raw material.

Claims (3)

An open-celled flexible polyurethane foam obtained by reacting raw materials consisting of polyols, polyisocyanate compounds, catalysts, and foaming agents is formed into a sheet by being sandwiched between the main body of the hard disk drive and the substrate. A sound absorbing material
Its thickness is 1-5mm,
The raw material contains 3 to 70 parts by mass of a powder having an average particle diameter of 20 to 200 μm and a specific gravity of 2 to 4 with respect to 100 parts by mass of polyols ,
On the surface, a film is formed by a cured product formed by curing the surface of the flexible polyurethane foam,
The flexible polyurethane foam is foam-formed so that the center part is a low-density layer and the space between the center part and the surface or the film is a high-density layer having a higher density than the center low-density layer. Characteristic sound absorbing material. The sound absorbing material according to claim 1, wherein the powder is aluminum hydroxide . An open-celled flexible polyurethane foam obtained by reacting a raw material comprising a polyol, a polyisocyanate compound, a catalyst and a foaming agent is formed into a sheet shape. The raw material has an average particle diameter of 20 to 200 μm and a specific gravity. Is a method for producing a sound-absorbing material containing a powder of 2 to 4,
  On the release film, a raw material for a flexible polyurethane foam comprising a polyol, a polyisocyanate compound, a catalyst and a foaming agent is supplied, and a release film is placed on the raw material, and the polyol and the polyisocyanate are present in the presence of the catalyst and the foaming agent. Production of a sound-absorbing material characterized by producing an open-celled flexible polyurethane foam that forms a sheet by reacting with a compound and spontaneously foaming, followed by heat-curing and then peeling off both release films. Method.

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