JP2007308583A - Sound absorbing material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a clean sound absorbing material having sound absorbing properties in a low-frequency range, does not require a process of assembly, etc., has a product thickness not thicker than necessary and no problem of scattering of fine particles and fibers. <P>SOLUTION: The sound absorbing material (1) comprises: a matrix resin (2) constituting open cell foams made of a thermoplastic resin; and fibrous substances (3) that are incompatible with the matrix resin and dispersed in the matrix resin. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sound absorbing material having open cells, and also relates to a method for manufacturing the sound absorbing material and a method for manufacturing a sound absorbing sheet.

  Conventionally, urethane foam, glass wool, rock wool, and the like have been widely used as sound absorbing materials. Urethane foam, glass wool, rock wool have complex bubbles, pore channels, and cross-sectional shapes that communicate with each other, and the energy of sound waves incident on them collides with the surrounding walls in the process of propagating inside. Or by repeating friction, the wall surface is vibrated and absorbed as mechanical energy, and as a result, sound waves are absorbed. As described above, the above materials are excellent as a sound absorbing material, but they are not excellent for the entire wide frequency range, and are particularly excellent for the high frequency range of 4000 Hz or more. The performance is bad for 500-2000Hz.

  For absorption of sound waves in the low-frequency range, performance has been satisfied by providing structural considerations such as providing a space layer behind the sound absorbing material or installing a perforated gypsum plate in the space layer behind. I was letting. However, in the case of such a method, it is necessary to provide a large space layer on the back side, resulting in a disadvantage that the thickness of the product is increased and the assembling work is complicated.

  Therefore, as a sound absorbing material for improving the sound absorbing characteristics in the low frequency region, Patent Document 1 proposes a sound absorbing material in which fine particles such as silica and talc are enclosed in a breathable bag-like body. However, this exhibits sound absorption characteristics in a low frequency range, but its absorption band is very narrow, and there is a drawback that silica and talc in the bag-like body are dissipated or biased during use. As a countermeasure, Patent Document 2 proposes a sound absorbing material in which fine particles such as mica and talc are held in a gap between fibers with a resin binder. However, even by this method, it is difficult to firmly hold the fine particles in the gaps between the fibers, and the problem is not completely solved.

Further, in Patent Document 3, synthetic resin and glass fiber are mixed in the same ratio, and the resulting mixture is heated at 200 to 230 ° C. and expanded using the rebound resilience of glass fiber. A method of obtaining a body is described. However, in this method, depending on the porous state, particularly when the space is large and the wall is thick, a phenomenon occurs in which the energy of the sound wave cannot be vibrated or absorbed by the wall surface.
Japanese Patent Laid-Open No. 5-80775 JP-A-8-95576 Registered Utility Model Publication No. 3028639

  In view of the above circumstances, the present invention has an excellent sound absorption characteristic in a low frequency range, does not require a process such as assembly, the product thickness is not unnecessarily thick, and fine particles, fibers, etc. are dissipated. The purpose is to provide a clean sound absorbing material.

  In order to achieve the above object, a first sound-absorbing material according to the present invention comprises a matrix resin constituting an open-cell foam made of a thermoplastic resin, and is incompatible with the matrix resin and is contained in the matrix resin. It is characterized by comprising a fibrous substance dispersed in the.

  The second sound-absorbing material according to the present invention comprises a matrix resin constituting a thermoplastic resin foam, and a fibrous material that is incompatible with the matrix resin and dispersed in the matrix resin. Thus, since the fibrous material extends over a plurality of bubbles, these bubbles communicate with each other through the passage of the material.

  In the first and second sound absorbing materials, the thermoplastic resin is not particularly limited, but a polyolefin resin is preferably used. For example, a propylene homopolymer, an ethylene-propylene random copolymer, an ethylene-propylene block copolymer, Propylene-α-olefin copolymer, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polybutene, ethylene-α-olefin copolymer, or rubbers or thermoplastics that can be mixed with these polymers Mention may be made of polymer blends mixed with elastomers.

  The fibrous material is not particularly limited as long as a material incompatible with the matrix resin is selected, and may be a synthetic fiber or a natural fiber. Examples thereof include carbon fiber, glass fiber, cellulose fiber, aramid fiber, polyester fiber, nylon fiber, and polypropylene fiber. The shape of the fiber is not particularly limited, and the diameter is preferably about 1 to 60 μm, and the length is preferably about 0.05 to 1.0 mm.

  In the first and second sound-absorbing materials, the weight ratio of the thermoplastic resin and the fibrous material is preferably 25 to 85% by weight and 75 to 15% by weight (a total of 100% by weight of both). If the ratio of the fibrous substance is too high, the fibrous substance may fall off from the sound absorbing material, and the sound absorption coefficient on the high frequency side is remarkably lowered due to the low ratio of the thermoplastic resin foam, which is not preferable. If the ratio of the fibrous material is too low, the effects of the invention described later may be difficult to obtain.

In the first and second sound absorbing materials, the density of the foam layer in the foam is preferably 0.05 to 0.2 g / cm ³ . The foam may be composed of a foam layer and a non-foamed skin layer formed outside the foam layer. In that case, the skin layer functions as a sound insulation layer, and it becomes difficult to introduce the sound wave that has entered into the sound absorbing material to absorb the sound, so the skin layer is removed and the density of the foam layer alone is within the above range. It is preferable to be within. When the foam does not have a skin layer, the density of the foam in the foam layer is the density of the foam itself. If the density is not within the above range, the effects of the invention described later may not be obtained.

  In the first and second sound absorbing materials, the open cell ratio in the foam layer of the foam is preferably 45 to 90%. If a skin layer is formed, it is preferably removed, and the open cell ratio in the foam layer alone is preferably within the above range. When the foam does not have a skin layer, the open cell ratio in the foam layer of the foam is the open cell ratio of the foam itself. If the open cell ratio is not within the above range, the effects of the invention described below may be difficult to obtain.

  In the first and second sound absorbing materials, it is preferable that the normal incident sound absorption coefficient per 10 mm thickness in the frequency range of 1500 to 2000 Hz is 0.4 or more. If the normal incident sound absorption coefficient is too low, the effects of the invention described later may be difficult to obtain.

  The present invention also melts a mixture comprising a thermoplastic resin, a fibrous material (the former: the weight ratio of the latter 25:75 to 85:15), and an effective amount of a foaming agent, and the resulting molten mixture is formed into a sheet. A method for producing a sound-absorbing sheet having open cells, characterized in that it is heated and foamed simultaneously with extrusion or after extrusion.

  Examples of the blowing agent used in this method include pyrolytic chemical blowing agents such as azodicarbonamide (ADCA), benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, toluenesulfonyl hydrazide, 4,4-oxybis (benzenesulfonyl hydrazide). Etc.) are preferably used.

  The present invention further melts a mixture comprising a thermoplastic resin, a fibrous substance (the former: the weight ratio of the latter 25:75 to 85:15) and an effective amount of the foaming agent, and the obtained molten mixture is used as a stationary mold. There is provided a method for producing a sound-absorbing material having open cells, which is characterized by being injected into a movable mold and then foamed by moving the movable mold in the expansion direction.

  Examples of the foaming agent used in this method include physical foaming agents such as water, carbon dioxide, nitrogen, and organic solvents in addition to the chemical foaming agent.

  According to the first aspect of the present invention, since the fibrous substance is dispersed in the matrix resin constituting the open cell foam, the energy of the sound wave introduced into the sound absorbing material causes the sound wave to collide with the bubble wall surface. Or, it is converted into vibration energy by repeatedly rubbing and vibrating the wall surface, and the sound wave in the low frequency region is also converted into vibration energy by the fibrous material protruding into the bubble from the bubble wall surface. Thereby, the outstanding sound absorption characteristic is expressed in a low frequency region.

  According to the second aspect of the present invention, the fibrous substance is dispersed in the matrix resin constituting the foam, and the fibrous substance is spread over a plurality of bubbles, so that these bubbles communicate with each other through the passage of the substance. Therefore, the energy of the sound wave introduced into the sound absorbing material is converted into vibration energy when the sound wave repeatedly vibrates and rubs against the bubble wall surface and vibrates the wall surface, and protrudes into the bubble from the bubble wall surface. The sound wave in the low frequency range is efficiently converted into vibration energy in the process in which the sound wave propagates through the communication path by the fibrous substance and the fibrous substance existing in the communication path between the communicating bubbles. Thereby, the outstanding sound absorption characteristic is expressed in a low frequency region.

  According to the third aspect of the present invention, the thermoplastic resin and the fibrous material are mixed at a ratio of 25 to 85% by weight and 75 to 15% by weight (both of which are 100% by weight in total). When the fibrous material protruding into the bubbles from the wall surface and the same wall surface vibrates, both the low-frequency side and the high-frequency side develop sound absorption properties. The fibrous material is not dissipated and a clean sound absorbing material can be provided.

According to the invention which concerns on Claim 4, the density in the foaming layer of a foam is 0.05-0.2 g / cm < ³ >. In the foam having such a density, the bubble wall becomes very thin, and the sound wave energy can be effectively converted into vibration energy. In addition, the fibrous substance enters the bubble from the wall surface into the bubble rather than the portion buried in the wall. Since the protruding part increases, the sound absorption coefficient on the low frequency side can be improved.

  According to the fifth aspect of the invention, since the open cell ratio in the foam layer of the foam is 45 to 90%, the sound wave energy is captured inside the sound absorbing material, and the sound wave energy is hardly leaked outside and efficiently vibrates. Can be converted into energy.

  According to the invention of claim 6, since the normal incident sound absorption coefficient per 10 mm thickness in the frequency range of 1500 to 2000 Hz is 0.4 or more, the normal incident sound absorption coefficient on the low frequency side is particularly high, and the sound absorbing material is It can be as thin as 10 mm or less, and it can deform and paste the sound absorbing material corresponding to the curved surface of products with complicated shapes, and it can also be inserted into narrow spaces become.

  According to the invention which concerns on Claim 7, there exists an above effect and it can manufacture the sound absorption sheet of a simple shape, the same thickness, and a big area.

  According to the invention which concerns on Claim 8, there exists an above effect and the sound-absorbing material which has a complicated shape and a three-dimensional free curved surface can be manufactured.

  Next, in order to specifically explain the present invention, examples of the present invention and comparative examples for showing comparison with the examples will be given.

  FIG. 1 schematically shows the structure of a sound absorbing material according to the present invention. The sound-absorbing material (1) according to the present invention comprises a matrix resin (2) constituting an open-cell foam made of a thermoplastic resin, and an incompatible with the matrix resin (2) and the matrix resin (2) It consists of fibrous material (3) dispersed in it. Some of the fibrous substances (3) are contained in the communicating path (4) of the open-cell foam, and some of the ends protrude from the bubble wall surface into the bubbles.

  The foam consists of a foam layer and a non-foamed very thin skin layer formed on the outside. The cross section of the foam is observed, the thickness of the skin layer is accurately grasped, and then the skin layer is cut and removed with an accuracy of several tens of μm.

Production Example 1
85 parts by weight of a polypropylene resin (grade: PF814) manufactured by Montel Co., Ltd. and 15 parts by weight of a cellulose fiber (fiber diameter: 10 μm, fiber length: 0.1 mm) are mixed, and a foaming agent (chemical foaming agent, grade by Eiwa Chemical Co., Ltd.) : EE275F) While mixing 10 parts by weight, the mixture was heated above the melting point of the resin. The obtained molten mixture was injected into a mold composed of a fixed mold and a movable mold, and then foam molded under atmospheric pressure by moving the movable mold in the expansion direction. Thereafter, the molded product was cooled and solidified. Thus, a sound-absorbing material having a thickness of 7 mm composed of the foamed layer and the non-foamed skin layer formed outside thereof was obtained. The skin layer was removed and only the foam layer was subjected to the test.

Production Example 2
The same as in Production Example 1 except that the proportion of the polypropylene resin (grade: PF814) manufactured by Montel was changed to 65 parts by weight and the proportion of the cellulose fibers (fiber diameter: 10 μm, fiber length: 0.1 mm) was changed to 35 parts by weight. By the operation, a sound absorbing material having a thickness of 7 mm was obtained. The skin layer was removed and only the foam layer was subjected to the test.

Comparative Example 1
For comparison, a sound absorbing material made of a nonwoven fabric (density 0.036 g / cm ³ , thickness 7 mm) formed of a resin mixture composed of 65% by weight of polypropylene and 35% by weight of polyester was prepared.

Measurement of physical properties The sound absorption coefficient, density and open cell ratio of the sound absorbing material or foam layer obtained in Production Examples 1 and 2 and the nonwoven fabric of Comparative Example 1 were measured by the following methods.

a) Sound Absorption Rate About the sound absorption material obtained in Production Examples 1 and 2 and the sound absorption material of Comparative Example 1, the normal incident sound absorption rate in the frequency region of 500 to 6500 Hz was determined. The obtained results are shown in the graph of FIG. The sound absorbing materials obtained in Production Examples 1 and 2 exhibited a sound absorption coefficient of 0.4 or more per 10 mm thickness in the low frequency range, and exhibited excellent sound absorption characteristics.

b) Density The foam layer obtained in Production Examples 1 and 2 (excluding the skin layer from the foam) was submerged in water in a graduated cylinder, its volume (A) was measured, and an electronic balance was used. Its weight (M) was measured. The density of the foam layer is determined by dividing weight (M) by volume (A). Density of the obtained foamed layer in Production Example 1 and 2, respectively 0.128 g ^/ cm 3, was 0.08 g / cm ^3.

c) Open cell ratio In the same manner as described above, the density was determined from the volume and weight of the mixture before foaming. Let ρ be the density of the mixture before foaming. Furthermore, a dry automatic densimeter Accupic 1330 (manufactured by Shimadzu Corporation) was used to measure the volume (B) excluding the volume of open cells in the foam layer, that is, the volume of the foam layer containing closed cells.

  The closed cell ratio is calculated by the following formula.

Closed cell ratio (%) = (volume B−weight M ÷ foamed layer density ρ before foaming) / (volume A−weight M ÷ foamed layer density ρ before foaming)
Open cell ratio (%) = 100-closed cell ratio (%)
The open cell ratios of the foamed layers obtained in Production Examples 1 and 2 were 50% and 65%, respectively.

FIG. 1 is an explanatory view schematically showing a sound absorbing material according to the present invention. FIG. 2 is a graph showing the relationship between sound absorption rate and frequency.

Explanation of symbols

(1) Sound absorbing material
(2) Matrix resin
(3) Fibrous material
(4) Communication passage

Claims (8)

  A sound absorbing material comprising: a matrix resin constituting an open-cell foam made of a thermoplastic resin; and a fibrous material that is incompatible with the matrix resin and dispersed in the matrix resin. Wood.   A matrix resin constituting a foam made of a thermoplastic resin and a fibrous material that is incompatible with the matrix resin and dispersed in the matrix resin, and the fibrous material extends over a plurality of bubbles. A sound-absorbing material characterized in that these bubbles communicate with each other through a passage of the same substance.   The sound absorbing material according to claim 1 or 2, wherein the weight ratio of the thermoplastic resin and the fibrous material is 25:75 to 85:15. The sound absorbing material according to any one of claims 1 to ³ , wherein the density of the foam layer of the foam is 0.05 to 0.2 g / cm ³ .   The sound absorbing material according to any one of claims 1 to 4, wherein an open cell ratio in the foam layer of the foam is 45 to 90%.   The sound-absorbing material according to claim 1, wherein a normal incident sound absorption coefficient per 10 mm thickness in a frequency region of 1500 to 2000 Hz is 0.4 or more.   At the same time, a mixture comprising a thermoplastic resin and a fibrous substance (the former: the weight ratio of the latter 25:75 to 85:15) and an effective amount of the foaming agent is melted, and the obtained molten mixture is extruded into a sheet, Alternatively, a method for producing a sound-absorbing sheet having open cells, which is foamed by heating after extrusion. A mixture of a thermoplastic resin, a fibrous material (the former: the weight ratio of the latter 25:75 to 85:15) and an effective amount of the foaming agent is melted, and the resulting molten mixture is made of a fixed mold and a movable mold. A method for producing a sound-absorbing material having open cells, which is injected into a mold and then foamed by moving the movable mold in the expansion direction.

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