JP5675051B2 - Coating type sound absorbing material - Google Patents

Description

  The present invention relates to a coating type sound absorbing material made of a foam of an olefin resin. The coating type sound absorbing material of the present invention is particularly useful as a sound absorbing material for automobile interior materials.

  Conventionally, it is known that a foam of urethane resin or polyethylene resin can be used as a sound absorbing material for automobile interior materials (Patent Document 1).

  For example, a sound absorbing material made of a foamed material such as polyurethane resin exhibits high sound absorbing performance when foamed at a high magnification of 15 to 25 times. However, since foaming is performed at a high magnification, the dimensional stability is deteriorated, and in the case of a thin foam, it is difficult to control the dimensions.

  On the other hand, the gap between the members may be filled with a foam sealing material. In this case, the foaming ratio of the sealing material is as low as about 3 times, and the sound absorbing performance is not so high because of the independent bubbles.

JP 2006-88439 A

  The present invention has been made in view of the above-described problems of the prior art, and provides a coating-type sound-absorbing material made of a foam that exhibits good sound-absorbing performance even with a thin shape and has good dimensional stability. With the goal.

The present invention is an invention specified by the matters described in [1] to [3] below.
[1] A coating type sound-absorbing material comprising a foam of an olefin resin containing polypropylene, wherein the foam has a foaming ratio of 2.7 to 4.0 times, and is 70 of the total number of bubbles in the foam. % Is a coating type sound-absorbing material in which open cells are formed by having at least one opening.
[2] The coating type sound absorbing material according to the above [1], wherein the average diameter of the bubbles in the foam is 50 μm to 200 μm.
[3] The coating type sound absorbing material according to the above [1] or [2], which has an unfoamed skin layer on the surface of the foam.

  According to the present invention described in [1], it is possible to provide a coating type sound absorbing material made of a foam which exhibits good sound absorbing performance even in a thin shape and has good dimensional stability.

  According to the present invention described in the above [2], it is possible to provide a coating type sound absorbing material made of a foam exhibiting better sound absorbing performance.

  According to the present invention described in [3] above, it is possible to provide a coating type sound absorbing material made of a foam having both good sound absorbing performance and a waterproof effect.

2 is an electron microscope cross-sectional photograph (magnification 100 times) in the vicinity of the surface layer portion of the coating type sound absorbing material of Example 1. FIG. It is an electron microscope cross-sectional photograph (magnification 50 times) of the foam part of the coating type sound-absorbing material of Example 1. 2 is an electron microscopic cross-sectional photograph (magnification 100 times) of a foam portion of a coating type sound absorbing material of Example 1. FIG. 3 is a graph showing sound absorption performance of Example 1 and Comparative Example 1. It is a graph which shows the sound absorption performance of Examples 1-3. 6 is a graph showing sound absorption performance of Example 1 and Comparative Example 2. It is a graph which shows the relationship between an aperture ratio and sound absorption performance. It is a graph which shows the relationship between an expansion ratio and an aperture ratio. It is a graph which shows the relationship between the thickness of a skin layer, and sound absorption performance. It is a graph which shows the relationship between the average diameter of a bubble, and an aperture ratio. 4 is an electron microscope cross-sectional photograph (magnification 100 times) of a foam portion of a coating type sound absorbing material of Comparative Example 1. FIG.

  In the present invention, the olefin resin includes polypropylene. Specifically, the proportion of polypropylene is preferably 5 to 50% by mass and more preferably 10 to 40% by mass in 100% by mass of the olefin resin. 1000-8000 mPa * s is preferable at 190 degreeC, and, as for the viscosity of the olefin resin containing a polypropylene, 2000-4000 mPa * s is more preferable. The upper limit values of these ranges are significant in terms of resin fluidity and moldability, and when the upper limit values are exceeded, the fluidity and moldability deteriorate. Moreover, the lower limit value of each range is significant in terms of the mechanical strength of the foam, and the mechanical strength is insufficient when the lower limit value is not satisfied. The olefin-based resin appropriately includes, as components other than polypropylene, a styrene-based block copolymer, a tackifier, a wax, a liquid hydrocarbon plasticizer, a filler, an antioxidant, and the like.

  Such an olefin resin containing polypropylene is foamed at a low magnification of 2.7 to 4.0 times to obtain a foam in which 70% or more of the total number of bubbles has at least one opening. The body is an application type sound absorbing material. In the present invention, since this expansion ratio is 4.0 times or less, there is little bubble breakage (so-called bubble breakage) during foam molding, and as a result, good sound absorption performance can be maintained. Further, since the expansion ratio is 2.7 times or more, a sufficient aperture ratio (open cell ratio) is obtained, and as a result, the sound absorbing performance is improved.

The “opening ratio” is a ratio [(W / N) × 100 (%)] of the number W of bubbles having at least one opening to the total number N of bubbles in the foam. In the present invention, the opening ratio of the foam is 70% or more, whereby open cells are formed, and good sound absorbing performance is exhibited. Furthermore, an aperture ratio of 80% or more is preferable because it shows better sound absorption performance for frequencies of 2000 Hz or more. In addition, the density of a general conventional sound-absorbing material (rebounded felt 5 mm) is approximately 0.04 to 0.1 kg / m ³ .

  In this invention, it is preferable that the average diameter of the bubble in a foam is 50 micrometers-200 micrometers. By setting the average diameter of the bubbles within this range, it becomes easy to obtain the above aperture ratio. Moreover, by making this into 200 micrometers or less, the bubble breakage in the case of foam molding decreases, and favorable sound absorption performance can be maintained.

The average diameter of the bubbles in the foam is an average value of the diameters of all the bubbles in an arbitrary cross section parallel to the thickness direction of the sound absorbing material. That is, when the total number of bubbles in the cross section is N and the diameter of each bubble is represented by L ₁ , L ₂ ..., The average diameter of the bubbles is [(L ₁ + L ₂ +...) / N]. expressed.

  Similarly, the aperture ratio is the ratio (%) of bubbles having an opening in the total number of bubbles in an arbitrary cross section parallel to the thickness direction of the sound absorbing material. That is, when the total number of bubbles in the cross section is represented by N and the number of bubbles having openings is represented by W, the aperture ratio is represented by [(W / N) × 100 (%)] as described above.

  The sound absorbing material of the present invention is an application type sound absorbing material, and is formed by applying a resin material to a desired position. The coating type sound absorbing material is usually formed as a thin coating film on a substrate. Moreover, when the non-foamed skin layer is also formed in the surface of the coating film, since the foam part which shows a sound absorption performance is protected by a skin layer and waterproofing is provided, it is preferable. This skin layer is particularly preferably formed on the entire surface of the coating film. Moreover, it is preferable that the thickness of a skin layer is 10-60 micrometers. When the thickness is 10 μm or more, the skin layer has sufficient mechanical strength, can prevent damage to the entire coating film, and can maintain good sound absorption performance. On the other hand, when the thickness is 60 μm or less, particularly good sound absorption performance for a frequency of 2500 Hz or more is exhibited.

  Moreover, 2-50 mm is preferable and, as for the thickness of the coating type sound-absorbing material of this invention, 4-10 mm is more preferable.

  Next, a method for coating and forming the coating type sound absorbing material of the present invention at a desired position will be described.

  Since the coating type sound absorbing material of the present invention is made of a foam of an olefin resin, it is preferably foamed in the step of applying the olefin resin to a desired position.

  Therefore, in order to foam this olefin resin, extrusion processing is preferably used. Specifically, for example, the olefin resin in a molten state is stored in a tank or the like, and the inert gas serving as a blowing agent is stirred and mixed while blowing into the tank to dissolve the inert gas in the olefin resin. There is a method in which the olefin resin is foamed by releasing the pressure from the nozzle. Then, if the olefin resin is discharged from the nozzle to the position where the sound absorbing material is to be formed, the olefin resin in the tank is foamed due to a pressure change when discharged from the nozzle through the hose, Since it is simultaneously applied to the above position, the application type sound absorbing material of the present invention can be easily formed.

  In this foam molding, the olefin resin in the tank is preferably maintained at a constant temperature and a constant pressure. Although it depends on the characteristics of the olefin resin used, it is particularly desirable to maintain the pressure and temperature in the tank at a pressure and temperature at which the olefin resin does not foam. The temperature is preferably 150 ° C to 200 ° C, more preferably 160 ° C to 180 ° C.

  Examples of the inert gas (foaming agent) that is blown into the tank include dry air, carbon dioxide, nitrogen, and argon. Nitrogen, argon, and carbon dioxide are particularly preferable in view of cost, environmental impact, fire risk, and the like. Moreover, it is preferable that an inert gas exists in a supercritical state, and thereby melt | dissolution of the gas in an olefin resin is accelerated | stimulated. The dissolved amount of the inert gas is preferably 0.1 to 2.0% by mass in the resin.

As an apparatus used for this foam molding, an apparatus having the following structure can be preferably used.
(1) A resin tank that contains an olefin resin and maintains a constant temperature and pressure.
(2) A gas supply unit (gas cylinder or the like) for supplying an inert gas into the resin tank.
(3) Dissolution means (mixer, etc.) for dissolving inert gas and olefin resin,
(4) Discharge means (nozzle or the like) that is connected from the resin tank with a hose and discharges the foamed olefin resin to a desired position.

  Furthermore, it is efficient if the apparatus can automatically control the amount of dissolved inert gas and the stirring speed of the olefin resin.

  The application of the coating type sound absorbing material of the present invention is not particularly limited, and can be applied to various members that require a sound absorbing material. In particular, it is useful as a sound absorbing material for automobile interior materials. For example, it is a very preferable aspect that the sound absorbing material of the present invention is applied and formed between the attachment portion and the lip of a weather strip attached to the edge of the door opening of an automobile.

  Examples of the present invention will be given below.

<Example 1>
As an apparatus used for foam molding, a foam melt applicator manufactured by Nordson was prepared. This apparatus is an apparatus having each structure described above.

An olefin resin containing polypropylene (polypropylene content: 17% by mass, melt viscosity at 190 ° C .: 2400 mPa · s) was stored in the tank of this apparatus. Thereafter, the tank was maintained at a temperature (160 ° C.) at which the olefin resin did not foam, and the resin was melted. Then, nitrogen gas was dissolved in the resin by stirring with a mixer while blowing nitrogen gas into the resin tank at a pressure of 0.4 to 0.5 kgf / cm ² .

  Next, the resin in which nitrogen gas is dissolved is pressurized and sent to the hose, and the resin is foamed by discharging to the outside from the nozzle at the tip of the hose (foaming ratio: 3.3 times). A 5 mm thick coating film (coating type sound absorbing material) made of foam was formed.

  The cross section of the coating type sound absorbing material was observed with an electron microscope. FIG. 1 is an electron microscope cross-sectional photograph (magnification 100 times) near the surface layer portion of the coating type sound absorbing material of this example. Moreover, FIG.2 and FIG.3 is the electron microscope cross-sectional photograph (50 times of magnification, 100 times) of the foam part of the coating type sound-absorbing material of a present Example. From these cross-sectional photographs, it can be seen that the skin layer is present in the surface layer portion of the coating type sound-absorbing material, and that many bubbles having openings are present. Specifically, the average diameter of the bubbles of the coating type sound absorbing material of this example is in the range of 50 μm to 200 μm, the aperture ratio (open cell ratio) is 80%, and the thickness of the skin layer is in the range of 10 μm to 60 μm. there were.

<Adhesion test of Example 1>
The adhesion test for the coating type sound absorbing material of Example 1 was performed using an electrodynamic vibration tester manufactured by IMV, with a total amplitude of 2 to 2.5 mm, vibration acceleration: 34.3 m / s ² , and vibration frequency of 1.5 million times. Performed under conditions. It was found that the sound absorbing material did not peel off even after the test and had good adhesiveness.

  This test assumes the vibration situation of rough road driving in the lifetime of a car. From this result, it can be seen that the coating-type sound absorbing material of the present invention does not cause problems such as peeling even when used as an automobile interior part.

<Comparative Example 1>
A coating film (coating type sound absorbing material) having a thickness of 5 mm was formed in the same manner as in Example 1 except that the expansion ratio was 30 times, and the cross section was observed with an electron microscope. FIG. 11 is an electron microscope cross-sectional photograph (magnification 100 times) of the foam portion of the coating type sound absorbing material of this comparative example. From this cross-sectional photograph, it can be seen that the bubbles in the coating type sound absorbing material are independent bubbles, that is, bubbles having no opening. Specifically, the aperture ratio of the coating type sound absorbing material of this comparative example was 30%.

<Comparison of sound absorption performance between Example 1 and Comparative Example 1>
The normal incident sound absorption coefficient of the coating type sound absorbing material of Example 1 and Comparative Example 1 is set in accordance with the method described in JIS A1405 “Sound absorption coefficient and impedance measurement using impedance tube—standing wave ratio method”. The measurement was evaluated by contacting the back plate. The measurement results are shown in FIG.

  As is clear from FIG. 4, the sound absorption performance is the same between Example 1 and Comparative Example 1 at frequencies below about 1250 Hz, but there is a large difference at frequencies exceeding about 1250 Hz. Although the sound absorption rate of Comparative Example 1 does not change near 0.1 even if it exceeds around 1250 Hz, the sound absorption rate of Example 1 increases as the frequency increases. For example, it becomes about 0.4 around 5000 Hz. Therefore, it can be seen that the sound absorbing material comprising the foaming agent of the present invention has better sound absorbing performance than the conventional independent foamed foam material.

<Examples 2 and 3>
A 5 mm thick coating film (coating type sound absorbing material) in the same manner as in Example 1 except that the temperature in the resin tank during foam molding was changed to 170 ° C. (Example 2) and 180 ° C. (Example 3). ) And the sound absorption performance was measured and evaluated. The measurement results are shown in FIG. 5 together with the measurement results of Example 1.

  As is clear from FIG. 5, all of Examples 1 to 3 show good sound absorption performance, but in particular, Example 1 in which the temperature in the resin tank is as low as 160 ° C. shows optimum sound absorption performance. I understand.

<Comparative example 2>
The sound absorbing performance was measured and evaluated in the same manner for a conventional felt-made sound absorbing material (anti-wool felt) having a thickness of 5 mm. The measurement results are shown in FIG. 6 together with the measurement results of Example 1. This anti-felt felt is a conventional product often used as a sound absorbing material, and its density is 0.055 kg / m ³ .

  As is apparent from FIG. 6, the sound absorption performance is the same in Example 1 and Comparative Example 1 at frequencies below about 1250 Hz, but a large difference occurs at frequencies exceeding about 1500 Hz. For example, in the vicinity of 3000 Hz, the sound absorption coefficient of Example 1 is 0.25, but the sound absorption coefficient of Comparative Example 1 is slightly over 0.1. Therefore, it can be seen that the sound absorbing material comprising the foaming agent of the present invention has better sound absorbing performance than the conventional felt sound absorbing material. Moreover, since the frequency range when a person talks is 200 to 6300 Hz, it can be said that Example 1 has the effect of improving the clarity of a person's conversation.

<Relationship between aperture ratio and sound absorption performance>
A coating film (coating type sound absorbing material) was formed in the same manner as in Example 1 except that the expansion ratio was changed so that the opening ratio was 30 to 90%, and the sound absorbing performance was measured and evaluated. The measurement results are shown in FIG. 7 together with the measurement results of Comparative Example 2. FIG. 8 shows the relationship between the expansion ratio and the aperture ratio. As can be seen from FIG. 7, when the aperture ratio is 70%, a good sound absorption rate is obtained, when 80%, a better sound absorption performance is obtained at a frequency of 2000 Hz or higher, and when it is 90%, the best sound absorption performance is obtained. Show performance. Moreover, it turns out that the foam with an aperture ratio of 70% or more is obtained by setting it as the foaming ratio in the range of 2.7-4.0 times from the result of FIG.

<Relationship between skin layer thickness and sound absorption performance>
A coating film (coating type sound absorbing material) was formed in the same manner as in Example 1 except that the foaming ratio was changed so that the thickness of the skin layer was 10 to 100 μm, and the sound absorbing performance was measured and evaluated. . The measurement results are shown in FIG. As is apparent from FIG. 9, it can be seen that when the thickness of the skin layer is 10 to 60 μm, it is easy to exhibit good sound absorption performance particularly for a frequency of 2500 Hz or more.

<Relationship between average bubble diameter and aperture ratio>
A coating film (coating type sound absorbing material) was formed in the same manner as in Example 1 except that the average diameter of the bubbles was changed to 10 to 200 μm, and the aperture ratio was measured and evaluated. The measurement results are shown in FIG. As is apparent from FIG. 10, it can be seen that if the average diameter is 50 μm to 200 μm, the aperture ratio tends to be 70% or more.

Claims (5)

It is a coating type sound absorbing material formed by applying on a base material while foaming an olefin resin containing polypropylene,
The foaming ratio of the foam is 2.7 to 4.0 times,
An application type sound-absorbing material, wherein open cells are formed by 70% or more of the total number of bubbles in the foam having at least one opening.   The coating type sound-absorbing material according to claim 1, wherein the average diameter of the bubbles in the foam is from 50 µm to 200 µm.   The coating type sound-absorbing material according to claim 1, further comprising an unfoamed skin layer on the surface. The coating type sound absorbing material according to claim 3, wherein the skin layer has a thickness of 10 to 60 μm. The coating type sound absorbing material according to any one of claims 1 to 4, wherein the coating type sound absorbing material has a thickness of 2 to 50 mm.