JP2006169673A - Method for producing felt with multilayer structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a felt with a multilayer structure by which the weight and density of each layer in the felt with the multilayer structure can be regulated easily, which has high productivity and by which the felt is produced at a low production cost. <P>SOLUTION: The method for producing the felt with the multilayer structure constituted of a plurality of the layers having different densities comprises a step (step 1) for forming a web 3 by mixing fibers with a binder resin, a step (step 2) for heating the whole of one sheet of the web 3 obtained at the step 1 to a temperature not lower than the melting point or the softening point of the binder resin, a step (step 3) for forming a temperature gradient in the thickness direction in the interior of the web 3 obtained at the step 2 so that both of a part at which the temperature is not lower than the melting point or the softening point of the binder resin, and a part at which the temperature is lower than the melting point or the softening point of the binder resin may be present, and a step (step 4) for compressing the web obtained at the step 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a multilayered felt composed of a plurality of layers having different densities. In particular, the present invention relates to a method for producing a multilayered felt, in which the basis weight and density of each layer in the multilayered felt are easily adjusted, the productivity is high, and the production cost is low.

  Multi-layered felts composed of a plurality of layers having different densities are used in various applications. For example, the multilayered felt is widely used as a sound-absorbing material having excellent sound-absorbing properties in a wide frequency range because the frequency range of sound absorbed by each layer having different densities is different. Until now, a method of laminating a plurality of layers by needling or adhesion has been adopted as a method for producing a multilayered felt. However, in addition to the need to form a plurality of webs in advance, these methods increase the equipment and processes required for laminating each layer by needling or bonding, resulting in low productivity and increased manufacturing costs. There was a problem.

  In Patent Literature 1, a low-melting point thermoplastic resin fiber and a fiber having a higher melting point than this are defibrated and mixed, and a mixed fiber web is put into a porous mold having a desired shape, After heating the defibrating web in this mold to a temperature higher than the melting point of the low melting point thermoplastic resin, the low melting point thermoplastic resin is melted and fused between the fibers of the mixed fiber web, A method for producing a fibrous silencer in which a mixed fiber web in a mold is compressed with a cooled upper mold is described. As a result, the portion close to the upper mold of the mixed fiber web can be cooled earlier than the portion close to the mold to weaken the degree of compression to have a different density structure, and can be molded into a desired shape. It is said that a silencer having a different density structure can be obtained in which the contacting surface is shaped along the floor panel. However, in the method of cooling the mixed fiber web simultaneously with compression as described above, it is not easy to adjust the basis weight and density of each layer of the obtained two-layered silencer.

  In Patent Document 2, two webs in which the main fiber and the adhesive fiber having a lower melting point than the main fiber are mixed at different ratios are laminated, and the laminate is made to have the softening point of the adhesive fiber and the main fiber. A method for producing an interior material for a vehicle is described in which a uniform heat treatment is performed at a temperature lower than the melting point, a non-uniform heat treatment is performed on the front and back of the laminate without pressure, and then a cold press is performed at a heat treatment temperature or lower. This gives the web that can be deep-drawn to one side of the web, and a flexible finish can be expected on the other side of the web, eliminating the need for finishing by attaching a film or fabric to the front side. Is supposed to be possible. In Example 1, after performing needle punching on two webs, uniform heat treatment is performed to form a plate-like material, and then the temperature of the core side surface of the plate-like material is heated to a temperature higher than the uniform heat treatment temperature by infrared rays. A method of performing press molding after non-uniform heat treatment is exemplified. However, in the above method, since it is necessary to form two types of webs having different compositions and then laminate them, the productivity is low and the manufacturing cost is high.

JP-A-9-711169 JP 60-155446 A

  The present invention has been made in order to solve the above-described problems, and provides a method for producing a multilayered felt that is easy to adjust the basis weight and density of each layer in the multilayered felt, has high productivity, and is low in production cost. It is intended to provide.

  The above-mentioned problem is a method for producing a multilayered felt composed of a plurality of layers having different densities, and includes a step of forming a web by mixing fibers and a binder resin (step 1), and the one obtained in step 1 A step of heating the entire sheet of web at a temperature equal to or higher than the melting point or softening point of the binder resin (step 2), a portion of the web obtained in step 2 that is equal to or higher than the melting point or softening point of the binder resin; A multilayer structure comprising a step of providing a temperature gradient in the thickness direction (step 3) and a step of compressing the web obtained in step 3 (step 4) so as to have a portion that is less than the melting point or softening point of the resin It is solved by providing a felt manufacturing method. At this time, it is preferable that the steps 1 to 4 are continuously performed.

  In Step 3, it is preferable to cool a part of the web obtained in Step 2 so as to have a temperature gradient in the thickness direction so as to be partially below the melting point or softening point of the binder resin. At this time, it is preferable to cool a part of the web by allowing the cold air below the melting point or softening point of the binder resin to pass through the web in the vertical direction.

Among the plurality of layers constituting the multilayered felt, it is preferable that a density ratio of a layer having the highest density and a layer having the lowest density is 2.5 or more. It is preferable that the total thickness is 5 to 100 mm and the total basis weight is 250 to 6500 g / m ² . It is preferable that the blend ratio of the fiber and the binder resin is 95/5 to 50/50. It is also a preferred embodiment to provide a step of forming a resin layer on one side of the obtained multilayer structure felt after the step 4.

  According to the method for manufacturing a multilayer structure felt of the present invention, it is possible to provide a method for manufacturing a multilayer structure felt in which the basis weight and density of each layer in the multilayer structure felt can be easily adjusted, and the productivity is high and the manufacturing cost is low. it can.

  The method for producing a multilayered felt according to the present invention comprises four steps. Each process will be described in turn.

  Step 1 of the present invention is a step of forming a web by mixing fibers and a binder resin.

  The fiber used in the present invention is not particularly limited, and various natural fibers and chemical fibers are used. For example, cotton, hemp, silk, hair, or the like is used as the natural fiber, and polyester fiber, polyamide fiber, acrylic fiber, rayon fiber, glass fiber, or the like is used as the chemical fiber. Among these, cotton is preferably used because the fibers have bristle feet and the fibers are easily entangled with each other and a strong multilayered felt is obtained. From the economical point of view, it is more preferable to use a piece of cotton such as jeans, which is cut off from ends or used clothes. You may use the said fiber not only 1 type but 2 or more types. Moreover, the thickness and length of the said fiber are not specifically limited.

  The binder resin used in the present invention functions to adhere the fibers in the web to each other, and needs to be made of a thermoplastic resin having a melting point or a softening point lower than that of the fibers. The resin used as the binder resin is not particularly limited as long as it satisfies this, and for example, a resin made of polyolefin, polyester, polyamide or the like is used. It is also possible to use a binder resin composed of two or more kinds of resins.

  The form of the binder resin is not particularly limited, and for example, a chip shape, a powder shape, or a fiber shape is used. When mixed with the above fibers, a fibrous binder resin that is less scattered and has a good working environment and can be easily dispersed uniformly is preferably used.

  As the fibrous binder resin, fibers obtained by compounding two or more kinds of resins having different melting points or softening points (hereinafter sometimes abbreviated as composite fibers) can also be used. Of the two or more resins having different melting points or softening points constituting the composite fiber, all resins can be used as the binder resin, or only a part of the resins can be used as the binder resin. is there. It is preferable to use only a part of the resin as the binder resin because the fibers can be firmly bonded to each other. As the composite fiber, for example, a core-sheath fiber, a bimetallic fiber, a sea-island fiber, or the like is used. Especially, since a fiber can be adhere | attached more firmly, a core-sheath-like fiber is used preferably. Examples of the configuration of the core-sheath fiber (core / sheath) include, but are not limited to, polypropylene / polyethylene, polyester / polyethylene, and polyester / copolyester.

  The mixing ratio of the fiber and the binder resin is not particularly limited, but is preferably 95/5 to 50/50 (fiber / binder resin: weight ratio). When the ratio of the fibers is more than 95/5, the adhesion between the fibers becomes insufficient, and it may be difficult to form a plurality of layers having density differences. Moreover, the strength of the resulting multilayered felt may be reduced. Further, when the ratio of the binder resin is more than 50/50, the resulting multilayer structure felt may be insufficiently flexible or the material cost may increase. More preferably, it is 95 / 5-65 / 35, More preferably, it is 90 / 10-80 / 20. Here, when using the composite fiber, the resin other than the binder resin among the resins constituting the composite fiber is regarded as a fiber in the present invention.

  A conventionally known method can be used as a method of forming the web by mixing the fibers and the binder resin. For example, a fiber and binder resin web can be formed by defibrating a mixture of fibers and binder resin and depositing them on a carrier such as a conveyor belt by an air flow or a card machine. . The thickness of the web obtained here is preferably 10 to 300 mm. If it exceeds 300 mm, it may be difficult to heat the entire web in Step 2 so that the temperature is equal to or higher than the melting point or softening point of the binder resin. If it is less than 10 mm, a sufficient temperature gradient cannot be imparted in Step 3, and it may be difficult to form a plurality of layers having a difference in density.

  Next, the entire web obtained in step 1 is heated at a temperature equal to or higher than the melting point or softening point of the binder resin (step 2). By this step, the entire web is heated so as to have a temperature equal to or higher than the melting point or softening point of the binder resin, the binder resin in the web is melted or softened, and the fibers are temporarily bonded. Here, the softening point refers to a temperature at which the resin does not have crystallinity or becomes soft and can be bonded to each other in a low crystalline thermoplastic resin, and is usually a temperature near the glass transition point. .

The method for heating the web is not particularly limited, and examples thereof include a method in which hot air is passed in the vertical direction of the web and a method in which the surface of the web is irradiated with infrared rays. By adjusting the temperature of the hot air, the air flow rate, the air flow time, etc., it becomes possible to easily control the degree of heating of the web, and the web can be heated uniformly in a short time, so the hot air passes in the vertical direction of the web. Is preferably used. The density of the web during the heat treatment in step 2 is preferably 0.1 g / cm ³ or less, which facilitates the ventilation of hot air. The density is more preferably at 0.05 g / cm ³ or less, and even more preferably, it is 0.03 g / cm ³ or less. The density is usually 0.001 g / cm ³ or more, preferably 0.002 g / cm ³ or more. In addition, it is preferable that the web be lightly pressed to the extent that it prevents fuzz on the surface from the viewpoint that the density of the web that has undergone Step 2 can be kept low.

  When the web is heated, it is preferable to perform the heat treatment while moving the web by a carrier such as a caterpillar because the web can be continuously heat-treated. Moreover, it is preferable that the said conveyance body consists of a perforated board or a net-like board since a hot air can be passed through a perpendicular direction, moving a web within oven. Thereby, it becomes possible to perform the heat treatment continuously and in a short time without unevenness. Further, it is preferable to move the web between a pair of upper and lower caterpillars, etc., because it is possible to suppress the fluff of the web and make the thickness uniform. Moreover, it is also possible to use an oven that includes a plurality of rooms in which each chamber is partitioned except for a transport body such as a caterpillar, and can apply different heat treatments to the web in each chamber. Thereby, in each chamber, it becomes possible to allow hot air to pass from both directions in the vertical direction from the top to the bottom and from the bottom to the top, and the entire web can be heated evenly in a shorter time.

  Next, in the inside of the web heated at a temperature equal to or higher than the melting point or softening point of the binder resin, it has a portion that becomes higher than the melting point or softening point of the binder resin and a portion that becomes lower than the melting point or softening point of the binder resin. Is given a temperature gradient in the thickness direction (step 3). By this step, the part where the binder resin is melted or softened and the part which is not so can be formed in the web with the melting point or softening point of the binder resin as a boundary. By compressing this web in the next step, it is possible to produce a multilayered felt having a plurality of layers having different densities from a single web. The above process is very simple and the manufacturing cost is low.

  The method of giving the web a temperature gradient as described above is not particularly limited, but it is preferable to cool a part of the web heated at a temperature equal to or higher than the melting point or softening point of the binder resin. This makes it possible to give the web a temperature gradient in the thickness direction that is partially less than the melting point or softening point of the binder resin while minimizing the loss of thermal energy. On the other hand, it is possible to heat the entire web once and then heat a part of the web. As a method for cooling a part of the web, a method in which cold air having a temperature lower than the melting point or softening point of the binder resin is passed through the web in the vertical direction is preferable. The temperature gradient in the thickness direction can be easily adjusted by adjusting the temperature of the cold air, the amount of ventilation, the ventilation time, etc., and as a result, the basis weight of each layer of the resulting multilayered felt can be easily adjusted. Because it becomes. Here, the method in which the web is moved in the oven by a carrier such as a caterpillar made of a perforated plate or a net-like plate while allowing the cool air to flow vertically from top to bottom is a part of the web. It is preferable from the point that can be cooled.

  For example, it is possible to provide a temperature gradient such that only the lower part of the web has a temperature equal to or higher than the melting point or softening point of the binder resin by aerating cool air from above the web, and from above and below the web. It is also possible to give a temperature gradient such that only the central part of the web has a temperature equal to or higher than the melting point or softening point of the binder resin by passing cold air. By compressing the web in the next step, in the former case, the lower layer has a two-layer felt with a higher density than the upper layer, and in the latter case, the middle layer has a three-layer structure with a higher density than the upper and lower layers. It becomes possible to manufacture felt.

  Next, the web having a temperature gradient in the thickness direction is compressed so as to have a portion that becomes higher than the melting point or softening point of the binder resin and a portion that becomes lower than the melting point or softening point of the binder resin (step 4). Through this step, a multilayered felt can be obtained from the web.

  The mechanism by which the multilayered felt is obtained in the above process is as follows. In the inside of the web that has undergone step 3, the binder resin is solidified again at a portion that is less than the melting point or softening point of the binder resin, and thus is easily restored when the pressure is released after compression. On the contrary, in the part which became more than melting | fusing point or softening point of binder resin, since binder resin is fuse | melted or softened, it is hard to restore | restore at the time of pressure release after compression. Thus, a multilayered felt having a plurality of layers having different densities is obtained from a single web with the melting point or softening point of the binder resin as a boundary. At this time, the density of each layer can be adjusted by adjusting the pressure applied to the web.

  Examples of the method of compressing the web include a method of passing the web between press rollers and a method of sequentially compressing with a press. Since the web can be continuously compressed and the productivity is excellent, a method of passing between the press rollers is preferably used. It is preferable that the thickness ratio of the web before being compressed by the press roller and the clearance ratio (compression ratio) between the press rollers is 5 times or more because a multilayer structure felt having a large density difference is obtained. More preferably, it is 10 times or more, and further preferably 15 times or more. By increasing the compression ratio, the density of the high-density layer can be increased. Usually, the compression ratio is 100 times or less, and preferably 50 times or less. The temperature of the press roller is preferably lower on the low density side than on the high density side. Thereby, a web can be compressed in the state which maintained the temperature gradient given in process 3 favorably.

  It is preferable that Step 1 to Step 4 described above are performed continuously. Thereby, a multilayered felt is manufactured with high productivity. The production speed of the multilayer structure felt is not particularly limited, and is appropriately selected according to the desired configuration of the multilayer structure felt, but is usually 1 m / min to 20 m / min. Moreover, although it is preferable from a viewpoint of productivity that the web to be processed is continuous, the cut web may be processed continuously.

  The multilayer structure felt obtained through the process 4 is then subjected to a process for adjusting the total thickness of the multilayer structure felt as necessary. Examples of the method for adjusting the total thickness of the multilayer structure felt include a method of cold pressing the multilayer structure felt, a method of passing the multilayer structure felt through a cooling conveyor, and the like. Since continuous adjustment is possible, a method of passing a multilayered felt through a cooling conveyor is preferably used.

  Although the total thickness of the multilayered felt obtained by the production method of the present invention is not particularly limited, it is preferably 5 to 100 mm. When the total thickness is less than 5 mm, the sound absorbing performance may be insufficient when used as a sound absorbing material. More preferably, it is 10 mm or more. Moreover, when total thickness exceeds 100 mm, there exists a possibility that the softness | flexibility of the multilayered felt obtained may become inadequate. More preferably, it is 70 mm or less, More preferably, it is 40 mm or less.

The total weight of the multilayer structure felt combined with the weight of each layer is not particularly limited, but is preferably 250 to 6500 g / m ² . If it is less than 250 g / m ² , the sound absorption characteristics may be insufficient when used as a sound absorbing material. More preferably, it is 500 g / m ² . Moreover, when exceeding 6500 g / m < ² >, when using it in a motor vehicle etc. as a sound-absorbing material, there exists a possibility that the total weight of a motor vehicle etc. may increase. More preferably, it is 4500 g / m < ² > or less, More preferably, it is 2600 g / m < ² > or less.

  Moreover, it is preferable that the density ratio of the layer having the highest density and the layer having the lowest density among the plurality of layers constituting the multilayered felt is 2.5 or more. By using the production method of the present invention, it is possible to produce a multilayer structure felt having a large density ratio with high productivity and at low cost. More preferably, it is 3.0 or more, More preferably, it is 3.5 or more. The ratio is usually 10 or less.

  It is also a preferred embodiment to provide a step of forming a resin layer on one side of the obtained multilayer structure felt after the step 4. This makes it possible to improve the sound absorption characteristics in a wider frequency range. As a method of forming a resin layer on one side of the multilayer structure felt, after placing the resin film on one side of the multilayer structure felt, the method of heating the resin film above its melting point or softening point by hot pressing, the multilayer structure felt A method of extruding a molten resin directly from a T die on one side is exemplified. Since a resin layer can be formed continuously, a method of directly extruding a molten resin from a T die on one side of a multilayer structure felt is preferably used. For example, the resin layer can be continuously formed by providing a T die immediately after the press roller and extruding the resin directly on the upper surface of the multilayered felt that is placed on a conveyor belt or the like and moves. From the viewpoint of the adhesiveness of the resin layer to the multilayer structure felt, it is preferable to laminate on the high density side.

  The multilayered felt obtained by the production method of the present invention can be widely used as a sound absorbing material or the like in the fields of automobiles, electric machines, building materials and the like. Especially, since the sound-absorbing material for automobiles is particularly required to be low cost, the production method of the present invention is preferably used.

  Hereinafter, the present invention will be described more specifically with reference to examples. The ratio is based on weight unless otherwise specified.

Example 1
FIG. 1 is a schematic diagram showing an outline of the manufacturing apparatus used in this example. A two-layered felt was manufactured using the manufacturing apparatus shown in FIG. First of all, cotton (mainly cotton) mainly made of jeans and “ESC Sufu” (grade name: ESC023SDL) [polypropylene (core part, melting point 165 ° C.) / Polyethylene (sheath part, melting point 130) manufactured by Chisso Corporation ℃), 50/50 core-sheath fibers], and those blended so that the blending ratio thereof was 70/30 were introduced into the feeding device. Here, since only the polyethylene sheath in “ESC Sufu” is used as the binder resin, the blending ratio of the fiber and the binder resin is 85/15. The blended cotton product was supplied to the defibrating apparatus 1, and the blended cotton product was defibrated. Thereafter, the defibrated blended cotton product is placed on a conveyor and conveyed to the web forming apparatus 2 and is deposited on a mesh roll by an air flow. The width: 2.2 m, the thickness: 160 mm, the basis weight: 1300 g / m ^2, density: the web 3 of 0.0081 g / cm ³ was continuously formed (step 1).

  The web 3 obtained in step 1 was introduced into the oven 5 while being moved by the conveyor 4. Thereafter, the web 3 was sandwiched between a pair of upper and lower caterpillars 6 and 6 'each having a plurality of perforated stainless steel plates connected, and the web 3 was passed through the oven 5 for 4 minutes. The oven 5 includes four chambers each of which is partitioned except for the caterpillars 6 and 6 ′, and can apply different heat treatments to the web 3 in each chamber. Inside the first chamber 7 and the third chamber 9 of the oven, air heated by the burner is supplied from the intake ports 11 and 15 below the caterpillar 6 ′, and is sucked by the exhaust ports 12 and 16 above the caterpillar 6. . In this way, the web 3 was heated by ventilating hot air in the vertical direction from bottom to top. In the second chamber 8, the web 3 was heated by allowing hot air to flow in the vertical direction from the top to the bottom, contrary to the first chamber 7 and the third chamber 9. The temperature of the air heated by the burner and supplied to the first to third chambers of the oven 5 was 160 ° C., and the entire web 3 was heated by passing through each chamber (step 2).

In the fourth chamber 10, unlike the other chambers, the outside air is sucked from the intake port 17 above the caterpillar 6 by the exhaust port 18 below the caterpillar 6 ′, and the cool air is vertically vented from top to bottom. 3 was cooled from above (step 3). The web 3 immediately after exiting the oven has a thickness of 70 mm, a density of 0.0186 g / cm ³ , and a part of the upper side of the web 3 is a melting point of a binder resin (polyethylene sheath in a core-sheathed fiber, melting point 130 ° C.). It had a temperature gradient in the thickness direction that would be less. The clearance between the caterpillars 6 and 6 ′ in the oven 5 is gradually narrowed as the thickness of the web 3 is reduced by melting the binder resin, and 140 mm at the entrance of the first chamber 7. It was adjusted to 65 mm at 10 outlets. In this way, a web having a uniform thickness can be obtained by gradually reducing the clearance between the caterpillars 6 and 6 ′. In the first to fourth chambers, the web 3 was lightly pressed by the caterpillars 6 and 6 'to prevent fluffing on the surface.

  Immediately after leaving the oven 5, the web 3 was compressed by passing between the press rollers 21 adjusted so that the clearance between the rolls 19 and 20 was 3 mm (compression ratio: 23 times). At this time, the upper roll 19 was cooled by cold water, and the lower roll 20 was heated by the oil heat medium. The thickness of the web 3 after passing through the press roller 21 was 30 mm (step 4).

  Thereafter, the web 3 was fed to a cooling conveyor 23 having a pair of upper and lower conveyor belts 22 and 22 'maintained at a clearance of 20 mm, and passed between the conveyor belts 22 and 22' over 30 seconds. The cooling conveyer 23 cools the web 3 by supplying air to the web 3 from the blowing port 24 above the conveyer and sucking it by the lower suction device 25. Further, the conveyor belts 22 and 22 'were made of reticulated glass fibers coated with polytetrafluoroethylene.

Through the above steps, a two-layer felt having a total thickness of 20 mm and composed of two layers having different densities was obtained at a speed of 5 m / min. In the two-layer felt, the binder resin was once melted in both the upper layer and the lower layer, and the fibers were bonded to each other. In the two-layered felt, the upper layer had a thickness of 14 mm and a basis weight of 416 g / m ² , and the lower layer had a thickness of 6 mm and a basis weight of 884 g / m ² . Further, the upper layer of the density of 0.030 g / cm ^3, the lower density is 0.148 g / cm ^3, the density ratio of both layers was 4.9.

(Measurement of sound absorption rate)
The sound absorption coefficient of the two-layered felt obtained by the above manufacturing method was measured by measuring the normal incident sound absorption coefficient by the two-microphone method. As a device, a 2 microphone impedance measuring tube “4206” (manufactured by BRUEL CARE, conforming to ASTM E1050), a measuring instrument “3550” (manufactured by BRUEL CARE) and measurement software “BZ5050” (manufactured by BRUEL CARE) are used. did. As the impedance measuring tube, two types of large measuring tube (50 to 1600 Hz: diameter 100 mm) and small measuring tube (500 to 6400 Hz: diameter 29 mm) were used depending on the measurement frequency. Three layers of felt were cut into a circular shape with a diameter of 100 mm (used when the measurement frequency was 50 to 1600 Hz) and a circular shape with a diameter of 29 mm (used when the measurement frequency was 500 to 6400 Hz), and used as measurement samples. In accordance with the thickness of each sample, the position of the back plate was determined so that the distance from the sample to the microphone was constant, and the sample was inserted into the specimen holder so that the low density layer side of the sample was in close contact with the back plate. The sound absorption coefficient was measured in the 1/3 octave band, and the measurement results of three samples were arithmetically averaged to obtain the sound absorption coefficient. A graph in which the sound absorption coefficient is plotted with respect to frequency is shown in FIG. In addition, about 500-1600 Hz, the average value of the sound absorption rate by a large measuring tube and a small measuring tube was plotted.

Example 2
The two-layered felt produced in Example 1 was cut into 200 mm × 200 mm, and two polypropylene films having a thickness of 60 μm were stacked on the high-density side surface. The upper and lower sides are sandwiched between polytetrafluoroethylene (PTFE) sheets, the low density side is at room temperature, the resin film side is sandwiched between hot presses heated to 200 ° C., and the distance between the PTFE sheets is maintained at 15 mm. Heated for 1 minute. Thereafter, the resin film was cooled by placing it on a cooled iron plate with the surface of the resin film facing down. Thereby, the multilayer structure in which the polypropylene resin layer was formed on the surface on the high density side was obtained. The density of the two layers forming the felt was not substantially changed from Example 1. Next, the sound absorption coefficient of the multilayer structure was measured in the same manner as in Example 1. The measurement results are shown in FIG.

Comparative Example 1
A single layer structure felt was manufactured using the manufacturing apparatus shown in FIG. First, using mixed cotton (cotton is the main component) mainly made of jeans and “ESC Sufu” (grade name: ESC023SDL) manufactured by Chisso Corporation, blended so that the blending ratio becomes 70/30. Was introduced into the feeder. Here, since only the polyethylene sheath in “ESC Sufu” is used as the binder resin, the blending ratio of the fiber and the binder resin is 85/15. The mixed cotton product was supplied from the supply device to the defibrating device 1, and the mixed cotton product was defibrated. Thereafter, the defibrated blended cotton product is placed on a conveyor and conveyed to the web forming apparatus 2 and is deposited on a mesh roll by an air flow, width: 2.2 m, thickness: 130 mm, basis weight: 1000 g / m ^2, density: the web 3 of 0.0077 g / cm ³ was continuously formed.

  The web 3 was passed through the oven 5 in the same manner as in Example 1 except that the web 3 was heated in the same manner as the second chamber 8 in the fourth chamber 10.

  Immediately after leaving the oven, the web 3 was compressed by passing between press rollers 21 adjusted so that the clearance above and below the roll during compression was 6 mm. At this time, the upper roll 19 and the lower roll 20 were cooled by cold water. The thickness of the web 3 after passing through the press roller 21 was 25 mm.

Thereafter, the web 3 was passed through the cooling conveyor 23 in the same manner as in Example 1 to obtain 6.5 m / min of a single-layered felt composed of a single layer having a thickness of 20 mm and a uniform density. Obtained at the speed of. The single layer structure felt had a basis weight of 1060 g / m ² and a density of 0.053 g / cm ³ . Next, the sound absorption coefficient of the single layer felt was measured in the same manner as in Example 1. The measurement results are shown in FIG.

  As shown in FIG. 2, the two-layered felt obtained in Example 1 has a lower sound absorption in a frequency region of 2 kHz or higher than the single-layered felt obtained in Comparative Example 1, but 250 It was found that the sound absorption was improved in the frequency region of ˜1.6 kHz. Moreover, it turned out that the tendency for the multilayered structure in which the polypropylene resin layer obtained in Example 2 was formed in the surface of a high-density side became stronger compared with the said 2 layer structure felt.

FIG. 1 is a schematic diagram showing an outline of the manufacturing apparatus used in this example. FIG. 2 is a graph in which the sound absorption coefficient is plotted with respect to frequency for the sample obtained in this example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Defibration apparatus 2 Web formation apparatus 3 Web 4 Conveyor 5 Oven 6, 6 'Caterpillar 7 1st chamber 8 2nd chamber 9 3rd chamber 10 4th chamber 11, 13, 15, 17 Intake port 12, 14, 16, DESCRIPTION OF SYMBOLS 18 Exhaust port 19 Upper roll 20 Lower roll 21 Press roller 22, 22 'Conveyor belt 23 Cooling conveyor 24 Spraying port 25 Suction apparatus

Claims (8)

A method for producing a multilayered felt composed of a plurality of layers having different densities,
A step of mixing a fiber and a binder resin to form a web (step 1);
A step of heating the entire web obtained in step 1 at a temperature equal to or higher than the melting point or softening point of the binder resin (step 2);
A step of providing a temperature gradient in the thickness direction so as to have a portion that is equal to or higher than the melting point or softening point of the binder resin and a portion that is lower than the melting point or softening point of the binder resin inside the web obtained in step 2. (Process 3) and the manufacturing method of the multilayer structure felt which consists of the process (process 4) which compresses the web obtained at process 3.   The method for producing a multilayered felt according to claim 1, wherein steps 1 to 4 are continuously performed.   3. The multilayer structure according to claim 1, wherein in step 3, a part of the web obtained in step 2 is cooled to have a temperature gradient in the thickness direction so as to be partially below the melting point or softening point of the binder resin. Felt manufacturing method.   The method for producing a multilayered felt according to claim 3, wherein in step 3, a part of the web obtained in step 2 is cooled by causing the web to cool in the vertical direction with cold air having a temperature lower than the melting point or softening point of the binder resin.   5. The multilayer felt according to claim 1, wherein a density ratio between a layer having the highest density and a layer having the lowest density among the plurality of layers constituting the multilayer felt is 2.5 or more. Method. The multilayer structure is the total thickness 5~100mm felt, the total basis weight of 250~6500g / ^{m 2} any multilayer structure felting method according to claim 1 to 5,.   The method for producing a multilayered felt according to any one of claims 1 to 6, wherein the mixing ratio of the fiber and the binder resin is 95/5 to 50/50.   The method for producing a multilayered felt according to any one of claims 1 to 7, further comprising a step of forming a resin layer on one side of the obtained multilayered felt after the step 4.

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