JPH10245258A - Sound absorbing material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a sound absorbing material having both high sound absorbing properties and a high strength and to provide a method for producing the sound absorbing material. SOLUTION: This method for producing a sound absorbing material comprises casting a slurry of (A) an expandable inorganic composition composed of an Al2 O3 -SiO2 -based inorganic powder, an alkali metallic silicate, a foaming agent, water and an anionic surfactant into a molding formwork and casting a slurry of (B) an expandable inorganic composition at a higher compounding ratio of the foaming agent than that of the expandable inorganic composition A onto the slurry cast layer, then expanding and thermally hardening the expandable inorganic composition containing superposed two layers comprising the expandable inorganic composition A and the expandable inorganic composition B. The surface skin layer of the resultant porous inorganic foam prepared by expanding and hardening the resultant expandable inorganic composition is subsequently excised.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound absorbing material and a method for producing the same, and more particularly to a sound absorbing material having excellent sound absorbing properties and having high strength, which is useful for non-combustible civil engineering and building materials, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, inorganic foams have been widely used as non-combustible civil engineering and building materials because of their excellent light weight and heat insulation. However, these inorganic foams generally consist of closed cells, and their performance as a sound absorbing material is low and small. As the inorganic sound absorbing material, for example, Japanese Unexamined Patent Publication No. 5-85858 discloses a main material comprising a water-soluble alkali metal silicate, an inorganic solid component, and a filler, and a foaming agent such as an anionic surfactant and hydrogen peroxide. There is disclosed an inorganic foam having open cells which can be foamed and cured using the composition for an inorganic foam to be used for a sound absorbing material, a filter and the like.

[0003] Further, as an attempt to achieve both the mechanical strength of the surface of the lightweight cellular concrete plate and various characteristics such as heat insulation and light weight, a lightweight cellular concrete plate having a specific gravity gradient in the thickness direction of the plate has been proposed. Manufacturing methods have been proposed. For example, Japanese Patent Application Laid-Open No. 8-208345 discloses a method for producing a lightweight cellular concrete plate having a specific gravity gradient by injecting a low specific gravity mortar slurry and a high specific gravity mortar slurry and performing form vibration.

However, according to the method disclosed in Japanese Patent Application Laid-Open No. 8-208345, bubbles generated during foaming are partially crushed by the vibration of the mold, so that the specific gravity of the high specific gravity layer is 0.7 to 0.7.
Adjusted to about 1.3, the resulting lightweight cellular concrete board has low sound absorbing properties, and a sound absorbing material cannot be manufactured by such a method.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts, and an object of the present invention is to provide a sound absorbing material having high sound absorbing properties and a method for manufacturing the same. .

[0006]

According to the first aspect of the present invention,
Two types of Al with different blending ratio of foaming agent_TwoO_Three-SiO _Two
Inorganic powder, alkali metal silicate, blowing agent, water and
Plate-like layer of foamable inorganic composition comprising a nonionic surfactant
The bulk density obtained by foaming and heat curing the state body is 0.15 to 0.1.
4g / cm^ThreeLow density continuous vent inorganic foam layer and bulky
Degree 0.20-0.5g / cm^ThreeHigh density continuous vent of inorganic
Sound absorbing material characterized by being laminated with a porous foam layer
Is the gist.

The curable inorganic material used in the present invention
The product is (A) Al_TwoO_Three-SiO _TwoInorganic powder,
(A) alkali metal silicate, (c) blowing agent, (d) water
And (e) a foamable inorganic composition comprising an anionic surfactant
Object is used. The above (A) Al_TwoO_Three-SiO_TwoKindness
Al powder as the material powder_TwoO_Three90 to 10% by weight, Si
O_TwoA powder having a composition of 10 to 90% by weight is used.
You. Al of the above composition_TwoO_Three-SiO_TwoBased inorganic powder
For example, when manufacturing alumina-based abrasives,
, Fly ash, fly ash classified products and crushing
Product, metakaolin and fly ash are sprayed into the air
Powder, Al _TwoO_Three-SiO_TwoSystem powder
Powder obtained by melting and spraying clay into the air_TwoO
_Three-SiO_TwoBy applying mechanical energy to the
Powders, clay minerals obtained by heating at 500-900 ° C
Powder obtained by applying mechanical energy to powder
Can be used, but limited to these if you select the composition and particle size
It is not something to be done.

The above (a) alkali metal silicates include:
General formula M ₂ O.nSiO ₂ (M = Li, K, Na or a mixture thereof, the value of n is preferably n = 0.05 to
8, more preferably n = 0.1 to 3). When the value of n of the alkali metal silicate exceeds 8, the alkali metal silicate aqueous solution is apt to gel,
Immediately the viscosity sharply rises, making it difficult to mix with other powders. If it is less than 0.05, the strength of the obtained open-cell foam decreases, so that the alkali metal silicate in the above range is used.

When the alkali metal silicate is mixed with other powder components to prepare a curable inorganic composition, it is preferably added and mixed as an aqueous solution. The aqueous solution concentration of the alkali metal silicate is not particularly limited, but if the concentration is high, a viscosity suitable for foaming cannot be obtained,
If the concentration is low, the curing shrinkage of the obtained open-cell foam may increase or the strength may decrease.
60% by weight is preferred.

The amount of the alkali metal silicate to be added depends on the amount of the hydraulic inorganic material 1 such as the Al ₂ O ₃ —SiO ₂ inorganic powder.
The amount is preferably 0.2 to 450 parts by weight, more preferably 10 to 350 parts by weight, per 100 parts by weight. When the addition amount of the alkali metal silicate is less than 0.2 parts by weight,
The resulting open-cell foam is poorly cured, and conversely, 45
If the amount exceeds 0 parts by weight, the water resistance of the obtained open-cell foam may be reduced.

The foaming agent (c) is not particularly limited, but examples thereof include peroxides and metal powders.

As the above-mentioned peroxide foaming agent, for example,
Examples include hydrogen peroxide, sodium peroxide, potassium peroxide, sodium perborate and the like. The addition amount of these peroxide-based foaming agents is preferably 0.01 to 10 parts by weight based on 100 parts by weight of the hydraulic inorganic substance of the curable inorganic composition. If the addition amount is less than 0.01 part by weight, bubbles are not sufficiently formed, and it is difficult to obtain a desired foam. There is.

When hydrogen peroxide is used as a foaming agent, it is preferable to use hydrogen peroxide in an aqueous solution. When the concentration of the aqueous solution is too high, foaming is severe and dangerous, and stable foaming is difficult, and when the solution is too thin. The viscosity is preferably 0.5 to 35% by weight, more preferably 1 to 25% by weight, since the viscosity of the curable inorganic composition decreases and stable foaming becomes difficult.

As the metal powder-based foaming agent, for example,
Mg, Ca, Cr, Mn, Fe, Co, Ni, Cu, Z
n, Al, Ga, Sn, Si, ferrosilicon and the like. If the average particle size of these metal powder-based foaming agents is too small, the dispersibility in the curable inorganic composition may be reduced, and if the dispersibility is good, the reactivity becomes high, and foaming may occur. Vigorous and stable foaming becomes difficult, and if it is too large, the reactivity decreases, and it may become difficult to obtain a desired foam.
It is. The addition amount of these metal powder-based foaming agents is based on 100 parts by weight of the hydraulic inorganic substance of the curable inorganic composition.
Preferably it is 0.01 to 5 parts by weight. If the addition amount is less than 0.01 part by weight, bubbles are not sufficiently formed, it is difficult to obtain a desired foam, and if it exceeds 5 parts by weight,
The foaming gas becomes excessive, and there is a possibility that a lot of foam breakage is generated.

The type and amount of these foaming agents are appropriately selected and set based on the specifications of the target product. However, cost, safety during use, easy availability, easy handling, and the like are comprehensive. In particular, hydrogen peroxide and aluminum powder are preferably used.

The water (d) contains the water component in the alkali metal silicate aqueous solution and contains the water component of the Al ₂ O ₃ —SiO ₂
Based on 100 parts by weight of curable inorganic powder such as system inorganic powder,
Preferably 35 to 1500 parts by weight, more preferably 45
１０００1000 parts by weight. When the water content increases, the viscosity of the curable inorganic composition decreases, the foaming process becomes unstable, and the strength of the obtained open-cell foam also decreases. Conversely, when the water content is low, the viscosity of the curable inorganic composition becomes too high, the foaming step becomes unstable, and a high-magnification foam and a low-density open-cell foam cannot be obtained.

The above (e) anionic surfactant is used to make the cell structure of the obtained foam into continuous pores. These anionic surfactants are not particularly limited. Alkali metal salts of fatty acids, alkyl sulfate salts, alkyl aryl sulfonate salts, etc., among which zinc stearate, calcium stearate, aluminum stearate, sodium oleate, potassium oleate, sodium palmitate, potassium palmitate, lauryl Sodium benzenesulfonate and sodium lauryl sulfate can be suitably used.

The amount of the anionic surfactant (e) is preferably 0.05 to 5 parts by weight based on 100 parts by weight of the hydraulic inorganic substance of the curable inorganic composition. When the addition amount is less than 0.05 part by weight, the cell diameter becomes smaller, the number of closed cells increases, and the airflow resistance increases,
If the amount exceeds 5 parts by weight, the strength of the obtained foam may decrease.
It is added in the range of parts by weight.

If necessary, the curable inorganic composition may contain an inorganic filler, a reinforcing fiber, a foaming aid, an inorganic foam, and the like. The inorganic filler is added for the purpose of improving the fluidity of the curable inorganic composition slurry, stabilizing bubbles during and after foaming, reducing shrinkage during curing of the obtained open-cell foam, and densifying cells. Is done.

Examples of the inorganic filler include porous inorganic materials such as silica sand, silica powder, fly ash, slag, silica fume, mica, talc, wollastonite, calcium carbonate, aerosil, silica gel, alumina gel, zeolite, and activated carbon. Powder.

The average particle size of the inorganic filler is preferably 0.01 μm to 1 mm. The average particle size is 0.0
If it is less than 1 μm, the viscosity of the curable inorganic composition increases due to an increase in the amount of adsorbed water, and there is a possibility that mixing workability may decrease or foaming may not be sufficiently performed. If it exceeds 1 mm, the stability of foaming will be impaired.

The amount of the inorganic filler to be added is preferably 20 to 600 parts by weight, more preferably 40 to 40 parts by weight, based on 100 parts by weight of the hydraulic inorganic substance of the curable inorganic composition.
0 parts by weight. If the amount is less than 20 parts by weight, a sufficient effect cannot be obtained. If the amount exceeds 600 parts by weight, the strength of the obtained open-cell foam may be reduced.

The reinforcing fibers are added for the purpose of improving the strength of the obtained open-cell foam and preventing cracks. Examples of the reinforcing fibers include vinylon fiber, polypropylene fiber, aramid fiber, acrylic fiber, rayon fiber,
Examples include carbon fiber, glass fiber, potassium titanate whisker, alumina fiber, steel wool, and slag wool.

The fiber length of the reinforcing fiber is preferably 1
１５15 mm. When the fiber length is less than 1 mm, the fibers are re-agglomerated at the time of mixing to form fiber balls, and the fiber length is 15 m.
If it exceeds m, the dispersibility will be reduced, and none of them may exhibit a sufficient reinforcing effect. The fiber diameter of the reinforcing fibers is preferably 1 to 500 μm. If the fiber diameter is out of the above range, there is a possibility that no sufficient reinforcing effect is exhibited.

The amount of the reinforcing fiber to be added is preferably 10 parts by weight or less based on 100 parts by weight of the hydraulic inorganic substance of the curable inorganic composition. If the addition amount exceeds 10 parts by weight, the dispersibility of the fiber is reduced, and the reinforcing effect may be impaired.

The foaming aid is added for the purpose of stabilizing bubbles during foaming. Examples of the foaming aid include porous inorganic powders such as silica gel, alumina gel, zeolite, and activated carbon.

The addition amount of the foaming aid composed of the porous inorganic powder is determined by the amount of the hydraulic inorganic material 100 of the curable inorganic composition.
It is preferably 5 parts by weight or less based on parts by weight. If the amount exceeds 5 parts by weight, the occurrence of foam breakage increases,
Foaming stability is impaired.

The inorganic foam is added for the purpose of reducing the weight of the obtained open-cell foam. Examples of the inorganic foam include a glass balloon, a shirasu balloon, a fly ash balloon, a silica balloon, a pearlite,
Hill stone, granular expanded silica, and the like. These may be used alone or in combination of two or more. When the apparent density of the inorganic foam is less than 0.01 g / cc, the mechanical strength of the obtained open-cell foam is reduced. When the apparent density is more than 1 g / cc, the purpose of reducing the weight is sufficiently achieved. Therefore, preferably 0.01 to 1 g / c
c, more preferably 0.03 to 0.7 g / cc.
The amount of the inorganic foam added is preferably 10 to 10 parts by weight of the hydraulic inorganic substance of the curable inorganic composition.
100 parts by weight, more preferably 30 to 80 parts by weight. If the amount is less than 10 parts by weight, the purpose of reducing the weight cannot be sufficiently achieved, and if it exceeds 100 parts by weight, the mechanical strength of the obtained open-cell foam may be reduced.

The continuous pores of the inorganic foam in the present invention are in contact with the individual cells in the closed cell foam in which small cells (cells) are gathered, adjacent to each other in the longitudinal direction of the closed cell foam. Refers to thin and long bubbles as if the open cells were broken one after another, and the continuous pore diameter indicates the diameter of the continuous pore. The average of the continuous pore diameter is preferably 10 to 5000 μm, more preferably 50 to 10 μm.
00 μm. The average value of the continuous pore diameter is 10 to 500.
When the thickness is outside the range of 0 μm, the sound absorbing property is reduced.

The open cell foam has an air permeability of 1 cm.
^Three・ Cm / cm^Two・ Sec ・ cmH _TwoIf less than O,
Decreased sound absorption, 40cm^Three・ Cm / cm^Two・ Sec ・
cmH_TwoIf it exceeds O, in addition to the decrease in sound absorption, open cells
Since the mechanical strength of the foam itself decreases, the continuous ventilation
The air permeability of the pore foam is preferably 1 to 40 cm^Three・ Cm
/ Cm^Two・ Sec ・ cmH_TwoO, more preferably 3 to 2
0cm^Three・ Cm / cm ^Two・ Sec ・ cmH_TwoO, best
Preferably 5-10cm^Three・ Cm / cm^Two・ Sec ・ cm
H_TwoO.

The sound-absorbing material of the present invention has a foaming property comprising two kinds of Al ₂ O ₃ —SiO ₂ inorganic powders having different mixing ratios of a foaming agent, an alkali metal silicate, a foaming agent, water and an anionic surfactant. An inorganic composition formed by foaming and curing a plate-like layered body, having a bulk density of 0.15 to 0.4 g / cm.
³ low density continuous vent inorganic foam layer and bulk density 0.20
It is composed of a high-density continuous pore inorganic foam layer of about 0.5 g / cm ³ , and is laminated at the interface between both layers with a specific gravity gradient in the thickness direction.

The low-density continuous-porous inorganic foam layer used toward the sound source side of the sound absorbing material has a bulk density of 0.15 g.
If it is less than / cm ³ , the mechanical strength decreases, handling becomes difficult, and in particular, the foam layer is damaged by high-pressure water washing, and may lose its performance in a short time. If it exceeds 0.4 g / cm ³ , the sound absorbing property may be reduced. When the bulk density of the high-density continuous pore inorganic foam layer is less than 0.2 g / cm ³ , the mechanical strength decreases, and when the bulk density exceeds 0.5 g / cm ³ , the sound absorbing property may decrease. There is.

[0033] The invention according to claim 2 is characterized in that Al ₂ O ₃ -Si
After casting a foamable inorganic composition (A) slurry comprising an O ₂ -based inorganic powder, an alkali metal silicate, a foaming agent, water and an anionic surfactant, the foamable inorganic composition (A)
A first step of casting a foamable inorganic composition (B) slurry having a higher mixing ratio of a foaming agent than the foamable inorganic composition (A) on the slurry casting layer, and the foamable inorganic composition (A) A second step of foaming and heat-curing the foamable inorganic composition obtained by laminating two layers of the foamable inorganic composition (B), and a continuous pore inorganic material obtained by foaming and curing the foamable inorganic composition. And a third step of cutting off a surface skin layer of the foam.

[0034] In the first step of the sound-absorbing material production method of the present invention, as shown in FIG. _{1 (a), Al 2 O} 3 -SiO
Foamable inorganic composition (A) composed of ₂ type inorganic powder, alkali metal silicate, foaming agent, water and anionic surfactant
The slurry is cast into a mold 1 to form a foamable inorganic composition (A) plate-like casting layer. As shown in FIG. 1 (b), the foamable inorganic composition (A) A slurry of the foamable inorganic composition (B) having a higher mixing ratio of the foaming agent than the foamable inorganic composition (A) is immediately cast on the shape casting layer.

In the second step, as shown in FIG. 2, the foamable inorganic compositions (A) and (B), which are closed 2 on the molding frame 1 and laminated and cast into the plate-like layer, are foamed. It is cured by heating, but in the first step, as described above, the foamable inorganic composition (A)
Foamable inorganic composition (B) having a higher blending ratio of foaming agent
By casting after the slurry is cast, the boundary between the high bulk density layer and the low bulk density layer becomes a structure having a specific gravity gradient in the foaming stage. A beautiful laminated structure of the bulk density layer is formed.

The foamable inorganic compositions (A) and (B)
After the laminate is foamed, the temperature at which the foam is cured may be room temperature, but in the present invention, the temperature is 50 to
By heating to about 100 ° C., the curing reaction is accelerated, and therefore, the mechanical strength of both the high bulk density layer and the low bulk density layer of the obtained sound absorbing material can be enhanced.

The skin layer of the continuous-porous inorganic foam obtained by foaming and heat-curing the foamable inorganic composition is defined as a portion of the foam gas generated by the foaming agent in contact with the surface of the molding frame during foaming. It means an outer shell formed by evaporating from some cells in the foamable inorganic composition to the outside of the system, crushing some cells in the surface layer portion, and forming a very low degree of non-foaming or foaming in the portion. FIG. 3 (a) shows the detached continuous pore inorganic foam. In the above-mentioned continuous-porous inorganic foam, both the low bulk density layer 4 and the high bulk density layer 5 have a surface of about 0.1 to 0.5 mm.
The thickness is the skin layer 3.

In the third step, as shown in FIGS. 3 (a) and 3 (b), the foamed and cured continuous pore inorganic foam is released from the mold, and the skin layer 3 of the low bulk density layer 4 and the The skin layer 3 on the side surface of the high bulk density layer 5 connected thereto is cut off, and the cut skin layer 3 is a portion that is in contact with the upper surface and the side of the molding mold surface, and is formed by ordinary foam molding. Then, approximately 0.5 mm may be cut off from the surface layer. FIG. 3B shows the sound absorbing material of the present invention from which the skin layer 3 has been cut.

As described above, the sound-absorbing material according to the first aspect of the present invention comprises two types of Al ₂ O ₃ —S having different mixing ratios of the foaming agent.
Since a plate-like layered body of an expandable inorganic composition comprising an iO ₂ -based inorganic powder, an alkali metal silicate, a foaming agent, water and an anionic surfactant is foamed and heat-cured,
It belongs to an extremely low bulk density consisting of a continuous pore inorganic foam layer having a bulk density of 0.15 to 0.4 g / cm ^{3 and} a continuous pore inorganic foam layer having a bulk density of 0.2 to 0.5 g / cm ^3. The continuous pore inorganic foam has a bulk density of 0.15 to 0.4 g /
cm ³ continuous vent inorganic foam layer and bulk density 0.2 ~
A continuous pore inorganic foam layer of 0.5 g / cm ³ is laminated with a specific gravity gradient in the thickness direction at the interface between the two layers, and the top and side surfaces of the continuous pore inorganic foam on the sound source side Since it is a low-bulk-density continuous-porous inorganic foam layer from which the skin layer has been cut off, it can be used as a civil engineering / building material having high sound absorbing properties.

The method for producing a sound-absorbing material of the present invention comprises, in addition to the first step, foaming and heat-curing the foamable inorganic composition in which the above two layers are superimposed. Promotes the mechanical properties of the inter-porous inter-porous wall of the low-bulk-density continuous-porous inorganic foam layer, and improves the low-bulk-density continuous-porous inorganic foam layer and the high-bulk-density continuous-porous inorganic foam layer. Although the boundary portion has a structure having a bulk density gradient, it is a layered structure of a low bulk density continuous vent inorganic foam layer and a high bulk density continuous vent inorganic foam layer without remarkably mixing with each other. The high sound absorption is not impaired at all.

Further, the method for producing a sound-absorbing material of the present invention comprises:
In addition to the step and the second step, since the surface skin layer of the obtained continuous-porous inorganic foam is cut off, the sound-absorbing surface is a low-bulk-density continuous-porous inorganic foam surface having a uniform surface. Since the high-bulk-density continuous-porous inorganic foam layer is continuously laminated in the thickness direction on the bulk-density continuous-porous inorganic foam layer, a high sound-absorbing property is exhibited.

[0042]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Inorganic curable powder] Fly ash (manufactured by Kanden Kako Co., Ltd., average particle diameter 20 μm, JIS A6201)
Was classified using a classifier (Model: TC-15, manufactured by Nisshin Engineering Co., Ltd.) to obtain inorganic curable powder-1 having a particle size of 10 μm or less.

(Example) [Preparation of expandable inorganic composition (A)] 100 parts by weight of the above inorganic curable powder and a 40% by weight aqueous solution of sodium silicate (SiO ₂ / Na ₂ O having a molar ratio of 1.5) Thing) 125
The parts by weight were stirred and mixed with a hand mixer to obtain a uniform paste-like mixture. Subsequently, 15 parts by weight of a 10% by weight aqueous solution of hydrogen peroxide (diluted with a 35% by weight aqueous solution manufactured by Mitsubishi Gas Chemical Co., Ltd.), 30 parts by weight of talc (manufactured by Sanyo Clay Industry Co., Ltd., average particle size 5 μm), vinylon fiber (Kuraray) 1 part by weight, product name "RM 182-3", fiber length 3 mm), 1.5 parts by weight of sodium oleate (manufactured by Wako Pure Chemical Industries, Ltd.) and 25 parts by weight of viscosity-adjusted water were added to the paste-like mixture, Further, the mixture is stirred and mixed for about 10 seconds, and the foamable curable inorganic composition (A)
I got

[Preparation of expandable inorganic composition (B)] Hydrogen peroxide 10 used in the above expandable inorganic composition (A)
A foamable inorganic composition (B) was prepared in the same manner as the foamable inorganic composition (A), except that the amount of the aqueous solution by weight was increased to 25 parts by weight.

The obtained foamable curable inorganic composition (A)
As shown in FIG. 1- (a),
(kg × length 600 mm × depth 80 mm), and immediately thereafter, as shown in FIG. 1- (b), the foamable inorganic composition (B) is similarly poured into the molding form as shown in FIG. After pouring 3.5 kg, as shown in FIG. 2, the forming mold is closed 2 and heated at 85 ° C. for 3 minutes to foam at a predetermined magnification. And then cured by heating for another 10 hours, as shown in FIG. 3- (a), formed from the foamable inorganic composition (B) having the skin layer 3 on the surface and having a thickness of 30 mm and a bulk density of 0.1 mm. 2
Continuous pore foam layer 4 and foamable inorganic composition (A)
A cured inorganic porous foam having a thickness of 50 mm and a bulk density of 0.3 was laminated with a specific gravity gradient in the thickness direction.

As shown in FIG. 3B, the continuous pore foam layer 4 on the upper surface and the surface skin layer 3 of the continuous pore foam layer on the side face of the obtained inorganic cured continuous pore foam are cut off as shown in FIG. Thus, a sound absorbing material was produced.

The thickness and bulk density (g) of the obtained sound absorbing material were
/ Cm ³ ) was dried in a desiccator and measured according to a conventional method.

Comparative Example 1 A sound absorbing material was produced in the same manner as in Example 1 except that the order of casting the foamable inorganic compositions (A) and (B) of the sound absorbing material of Example 1 was reversed. did. However, the thickness structure of the obtained sound-absorbing material in the thickness direction is not uniform because the specific gravity gradient is partially reversed, and the thicknesses of the low bulk density foam layer and the high bulk density foam layer are also largely fluctuated. It did not result in a preferred inorganic cured continuous vent foam.

(Comparative Example 2) The foamable inorganic compositions (A) and (B) of Example 1 were prepared in different molding molds, respectively, and a high bulk formed from the foamable inorganic composition (A) was prepared. The density foam layer has only the top surface skin layer, and the low bulk density foam layer formed from the foamable inorganic composition (B) has a top surface and a bottom surface laminated with the high bulk density foam layer. The skin layer was cut off, and both were pasted together with a urethane-based adhesive to produce a sound absorbing material similar to the sound absorbing material of Example 1. In the above-mentioned manufacturing method, not only the number of steps was doubled or more (5 → 12) than in the examples, but a lot of waiting time was generated, and the productivity was extremely low as compared with the examples.

In order to evaluate the performance of the sound-absorbing materials of Examples and Comparative Examples 1 and 2, the average sound absorption coefficient at normal incidence and the high-pressure washing water test were tested by the following methods. Productivity was evaluated. The test and evaluation results are shown in Table 1.

1. Normal incidence average sound absorption coefficient: JIS A1
According to 405, the normal incidence sound absorption coefficient (aj) was measured.
The size of the test piece was 100 mm in diameter, the surface on the low bulk density foam layer 4 side was the sound source side, and the back surface of the test piece had a thickness of 2 mm.
The measurement was carried out in the absence of an air layer with a 5 mm iron plate adhered. The measurement of the normal incidence sound absorption coefficient (aj) is performed at a frequency of 40
The measurement is performed in the range of 0 to 4000 Hz, and the measured value for each frequency is weighted using the weight Kj defined in the Road Traffic Noise Measurement Guideline of the Ministry of Construction, and the normal incidence average sound absorption coefficient Σa
j · Kj / ΣKj was calculated. The normal incidence average sound absorption coefficient is
Although shown as a real number, the evaluation in the present invention was 0.9
The above was treated as good.

2. Productivity: Comprehensive evaluation of the performance of the obtained sound-absorbing material, the value of the manufacturing facility, the number of manufacturing steps, the working environment, etc., was evaluated in two stages: ○: good, ×: poor productivity.

[0054]

[Table 1]

[0055]

Since the sound absorbing material of the present invention is constituted as described above, it has both high sound absorbing properties and high strength.

[0056]

[Brief description of the drawings]

FIG. 1 shows casting 2 of the first step of the method for producing a sound absorbing material of the present invention.
It is explanatory drawing of operation | work (a) and (b).

FIG. 2 shows the foaming and foaming of the second step of the method for producing a sound absorbing material of the present invention.
It is explanatory drawing of a heat hardening operation.

FIG. 3 is an explanatory view of two operations (a) and (b) of demolding and skin layer cutting in a third step of the method for producing a sound absorbing material of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Forming mold 2 Lid 3 Skin layer 4 Low bulk density foam layer 5 High bulk density foam layer A Foamable inorganic composition (A) B Foamable inorganic composition (B)

Claims (2)

[Claims] 1. Two kinds of Al _{2 having} different mixing ratios of a foaming agent.
O ₃ -SiO ₂ based inorganic powder, alkali metal silicates, blowing agents, water and anionic bulk density plate layered body is formed by curing the foam and heating the surfactant foamable inorganic composition comprising 0.15 A low-density continuous pore inorganic foam layer having a density of 0.4 g / cm ^{3 and} a high-density continuous pore inorganic foam layer having a bulk density of 0.20 to 0.5 g / cm ³ are laminated. Sound absorbing material. 2. A foamable inorganic composition (A) slurry comprising an Al ₂ O ₃ —SiO ₂ -based inorganic powder, an alkali metal silicate, a foaming agent, water and an anionic surfactant, is cast,
A first step of casting a foamable inorganic composition (B) slurry having a higher mixing ratio of a foaming agent than the foamable inorganic composition (A) on the foamable inorganic composition (A) slurry casting layer; A second step of foaming and heat-curing the foamable inorganic composition obtained by laminating the two layers of the foamable inorganic composition (A) and the foamable inorganic composition (B), and the foamable inorganic composition comprises: Cutting off the surface skin layer of the foamed and cured continuous pore inorganic foam.