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Advanced soft coverpad made of non-woven fabric
JSAE Review 20 (1999) 109—115
Advanced soft coverpad made of non-woven fabric Toru Hayakawa , Kazuhito Kamezaki , Tomoyuki Tokida , Yoshio Yamada, Hideki Ono, Osamu Araki Takashimaya Nippatsu Kogyo, Development Divison, 1-1 Maehata, Oosima-cho, Toyota, Aichi, Japan Toyota Motor Corporation, 1 Toyota-cho, Toyota, Aichi, Japan Received 30 March 1998
Abstract The advancement of touching and fitting feeling of the seat are expected to be important factors to enhance the product-value of the automobile. For this purpose, we have noted the softening of the seat cover and carried out development of a cover pad made of non-woven fabric. As a result, we could achieve the quality required for the material with soft feeling and durability for use as a seat cover pad. 1999 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved.
1. Introduction To improve the marketability of an automobile, it is naturally important to improve the primary function of the automobile such as running, turning and stopping, but it is equally important to improve the so-called secondary functions that appeal to the senses of the vehicle occupants, such as seeing, hearing and touching. Among the interior parts that dress up the inside of the passenger compartment, the car seat can be described as one of the most familiar parts for the occupants because the seat is constantly in contact with the occupant’s body. Therefore, a considerably higher value will be created by offering the secondary function of the car seat in addition to the primary function such as safely holding the occupant’s body and the comfort of cushioning. In the pursuit of various secondary functions of the car seat, we took note of the “feel” of the seat. Considering this element as an important secondary function, we addressed ourselves to the development of a technology to make the car seat feel softer. It is quite appropriate that the car seat and a luxury sofa in the living room should have different feel and seating comfort, because they are designed for different purposes. However, most people will be satisfied with the softness they only feel when sitting on a luxury sofa. We focused our attention on the seat component and especially the cover pad (Fig. 1) in order to achieve the softer “feel” of the seat. The conventional slab poly-
urethane (PUR) was re-evaluated as the raw material, and a soft non-woven pad was later developed as the new raw material to achieve both softness and durability at the same time This paper will cover the process of our R&D effort.
2. Setting of development target for “softness feel” In order to investigate the relationship between the feel and compressive characteristics of the cover pad, the typically-used slab PUR at three levels of hardness (A—C) was tested (Fig. 2). Sample A, the general-purpose type, felt hard because of the heavy initial peak load exclusive to polyurethane. Sample B which was softer than Sample A still felt hard even though the initial peak load was lighter than Sample A. Sample C, which was the softest of all the samples, did not have a satisfactory feel because the load rapidly increased at the deflection of 70% to create bottoming even though the initial peak load was extremely light. Therefore, the characteristics that would produce the satisfactory softness feel were defined as light load over the entire deflection range, no peak load in the initial phase of deflection, and an increase in the load at a moderate slope angle in the second phase of deflection. Based on this definition, the target range in compressive characteristics was specified as the shaded area in Fig. 2.
0389-4304/99/$19.00 1999 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved. PII: S 0 3 8 9 - 4 3 0 4 ( 9 8 ) 0 0 0 4 5 - 9
JSAE9930090
110
T. Hayakawa et al. / JSAE Review 20 (1999) 109—115
Fig. 1. General components of the car seat.
Fig. 2. Compressive characteristics of slab PUR.
3. Selection of material for cover pad Since it was found impossible to achieve the desired properties with slab PUR, various materials for the cover pad were re-evaluated. Candidate-materials for the cover pad included non-woven fabric and feather laminate in addition to slab PUR, and these materials underwent the matrix test on four items including compressive characteristics and durability. It was determined that non-woven fabric had excellent properties (Table 1). However, there was concern over durability of nonwoven fabric used as the cover pad of a car seat. Thus, it became necessary to develop a soft non-woven fabric with the durability sufficient for automotive applications. Consequently, the effort to develop such fabric was started.
4. Durability test method and setting of target values In the development of soft non-woven fabric, it was necessary to determine the minimum requirement in durability for the cover pad application. Our past experience and knowledge, and the characteristics of nonwoven fabric, were taken into consideration to establish the test method and target values as shown in Table 2. Since polyurethane and non-woven fabric had widely different material characteristics, the test conditions for evaluation of compression set (or permanent set in fatigue)
was changed from the current compression deflection of 50% constant to constant compressive load that simulates the load of the hip (or the hip load of 0.1 kgf/cm) where the heaviest load is applied. As a result, the test conditions were much closer to the actual mode.
5. Selection of fiber material for non-woven fabric Non-woven fabric is an aggregate of fibers, and selection of fiber material is important since the performance and the cost of non-woven fabric depend on the fiber material selected. Chemical fiber is generally composed of fused thermoplastic resin yarn, and is less thermally stable than polyurethane which is a thermosetting resin. Thus, the heat resistance performance needs to be emphasized when selecting chemical fiber material. The test was conducted on three types of chemical fiber materials and cotton and wool which are natural fibers [1,2]. After the test, polyester fiber was selected as the raw material for non-woven fabric (Table 3).
T. Hayakawa et al. / JSAE Review 20 (1999) 109—115
Fig. 3. Product method of non-woven fabric.
111
Fig. 4. Characteristics of thermal bond method.
Fig. 5. Enlarging photography of part of bound fiber.
6. Selection of product method for non-woven fabric 6.1. Product method for non-woven fabric To manufacture thick non-woven fabric for the cover pad, the best production method was selected. Among those dry methods shown in Fig. 3, the thermal bond method and the needle punch method are the only methods suitable for production of thick fabric. These methods are both designed to bond short fibers together. In the thermal bond method, a fibrous web is heated, and the fibers are melted and bonded together by melting and solidification of the portion of the binder fiber with low melting point. In the needle punch method, fibrous web is punched with a special needle with numerous projections called “barb” many times. As a result, the fibers are entangled and bonded together. There is yet another method in which these two methods are combined [3].
(or resistance to permanent set in fatigue) and compressive characteristics of the binder-fused non-woven fabric were tested (Fig. 4). The test showed that both repeated and wet heat static loads worsened as the binder fiber content was increased. This tendency can be attributed to the fact that repeated compression deformed or damaged the fused point of the fiber and impaired the restoration of fibers (Fig. 5). Deterioration of wet heat static load was probably caused by the fact that the portion of the binder fiber with low melting point was susceptible to heat. As for compressive characteristics, an increase in the binder fiber strengthened the crosslinking structure produced by the melt-bonding of fibers, and increased the compressive load. Based on the above test results, the needle punch method which can bond fibers together without binder fiber was selected as the product method for non-woven fabric, because softer feel and the resistance to permanent set in fatigue must be achieved at the same time.
6.2. Study of product methods for non-woven fabric
7. Study of fiber specifications
The thermal bond method was studied first. At different binder fiber content levels, the durability performance
Selection of the needle punch method succeeded in improving resistance to permanent set in fatigue, but
112
T. Hayakawa et al. / JSAE Review 20 (1999) 109—115
Fig. 6. Three-dimensional crimp fiber.
failed to achieve the target values. Thus, a study was conducted to determine the fiber specifications less susceptible to permanent set in fatigue. While fiber specifications included such items as thickness, length, the crosssectional shape, crimp and oil, our attention was focused on thickness and oil because the preliminary experiment showed that resistance to permanent set in fatigue depended heavily on thickness, oil and crimp. There are roughly three types of crimp: (i) straight, (ii) mechanically processed two dimensional crimp and (iii) three-dimensional crimp produced by thermal processing of two-component-formulated fiber (Fig. 6). The threedimensional crimp was selected because it had the highest degree of crystallinity and improved toughness. General specifications were used for length and crosssectional shape.
Fig. 7. Effect of fiber thickness.
7.1. Study of fiber thickness The needle punch non-woven fabric was tested for resistance to permanent set in fatigue and compressive characteristics at different fiber thickness levels. The test showed that the best resistance to permanent set in fatigue was achieved with a thin fiber with fiber thickness of 2d, and the resistance decreased as the thickness increased. As for compressive characteristics, the softness feel was enhanced as the fiber thickness decreased. Therefore, it was decided to decrease the thickness of the fiber in the production of non-woven fabric as long as no problem is observed (Fig. 7). Under the same load, thinner fiber tends to cause more deflection. An attempt was made to verify this tendency from the dynamics point of view (Fig. 8). When a thick fiber with the diameter D and a bundle of n thin fibers with the diameter of 1/n ) D were compared, the deflection rigidity of the bundle of thin fibers was 1/n times that of the thick fiber. In other words, if the weight and the thickness of non-woven fabric are the same, thinner fiber is more likely to deflect under the same load. 7.2. Study of oil (surface treatment) Oil is the surface-treatment agent applied to the fiber by dipping or spray coating. This treatment is designed to improve the unraveling and carding characteristics
Fig. 8. Comparison of rigidity.
during the non-woven fabric production process. Oil is available in many types according to the applications of the processed products including non-woven fabric. It was our assumption that permanent set in fatigue of the fiber would be improved by strengthening the restoring performance of the fiber. Then, it was presumed that minimizing the friction resistance of each fiber and providing sufficient sliding property to the fiber would improve the restoring performance. Therefore, a study of the silicon-added oil which is used for the above fiber surface treatment was conducted. The performance of non-woven fabric was tested at different ratios of added silicon in the base oil. It was confirmed that an increase in the ratio of added silicon would diminish the sliding stress of the fiber and at the same time improve the resistance to permanent set in fatigue. However, the ratio of added silicon was fixed at 60% because the carding performance showed a problem when the ratio was increased to 80% (Fig. 9).
T. Hayakawa et al. / JSAE Review 20 (1999) 109—115
113
Table 4 Durability of the developed product (density"0.03 g/cm) Compression set (%)
Target value
Developed product
Repeated
10
6.1
20 15 —
18.6 11.3 3.5
Resistance
Wet heat Dry heat Ordinary temp
Fig. 9. Effects of the addition of silicon to oil.
Fig. 10. Effect by density.
8. Durability performance of developed product The above study results indicated a direction in achieving the target values in resistance to permanent set in fatigue. Finally, to find out the optimum weight (apparent density) range which takes into consideration compressive characteristics, the relationship between apparent density and resistance to permanent set in fatigue and compressive characteristics was investigated (Fig. 10). It was shown that increasing the apparent density would improve the resistance to permanent set in fatigue but increase the hardness feel. However, target values in resistance to permanent set in fatigue and the feel were achieved at the same time by setting the apparent density within the 0.03—0.04 g/cm range. The durability performance of the developed product is shown in Table 4.
9. Durability test 9.1. Results of actual vehicle monitoring durability test The durability target for the individual non-woven fabric was achieved. As the next step, durability of non-woven fabric as the seat assembly was checked. Non-woven fabric passed a wet hot-cold environmental durability test, which was the severest of all durability tests, without causing a significant problem in such basic performance items as seating comfort and the appear-
Fig. 11. Monitoring.
ance of the seat. For further checking, a durability test based on monitoring of an actual vehicle was conducted. In the test, non-woven fabric showed slight permanent set in fatigue in the initial stage, but the permanent set in fatigue immediately subdued and stabilized. In addition, the softness feel did not change, and no abnormality was observed in the appearance of the seat. Based on these results, the permanent set in fatigue rate upon aging was estimated at about 10%, which confirmed that nonwoven fabric has a performance level sufficient for actual use (Fig. 11). 9.2. Discussion of the results of durability test This section is devoted to technical discussion of the results of the durability test. During the day, the temperature in the passenger compartment of the actual vehicle increases by solar radiation and the temperature at the surface of the seat increases to 60—70°c in summertime. Fig. 12 shows the results of the compression cyclic test on non-woven fabric and polyurethane that was conduced to simulate the temperature increase. When compared with polyurethane, non-woven fabric showed far greater restoring performance by heating after being compressed under the wet-hot condition. This phenomenon is presumably due to the bi-metallic characteristic of the fabric. In other words, it is presumed that the restoring performance of the fabric that constitutes the developed product is heavily dependent on the temperature, and the
114
T. Hayakawa et al. / JSAE Review 20 (1999) 109—115
fabric will return to the three-dimensional state by applying heat at a certain temperature level even when the three-dimensional crimp has been set and temporarily becomes a two-dimensional state. In this respect, the developed product can be described as a cover pad material with excellent softness and a special restoring performance which are vastly different from the characteristics of polyurethane.
60% of the respondents felt that the developed product offered improved seating comfort. The survey showed that the softness of the surface contributes not only to better feel but also to seating comfort. It was confirmed that the developed product is sufficiently effective (Fig. 13).
10. Testing of actual seat made of non-woven fabric 10.1. Results of questionnaire on feel of the seat To verify the advantage of the developed product in terms of feel, two seats made of the developed product and the conventional slab PUR were produced and a survey based on the questionnaire on the feel and seating comfort was conducted. In this survey, about 70% of the respondents felt that the surface of the developed product was softer than the slab PUR-based product, and about
Fig. 12. Restoring performance of 3D crimp fiber.
Fig. 13. Results of the questionnaire.
Fig. 14. Load-deflection characterstics of the seat.
Fig. 15. Pressure distribution of the seat.
T. Hayakawa et al. / JSAE Review 20 (1999) 109—115
10.2. Effect on seating comfort Changes in the seat performance of the developed product were investigated. Static load deflection characteristics of the seat were first investigated. The investigation showed that the developed product-based seat had a larger amount of deflection under a given load, and a significant amount of deflection in the light load area, which corroborates the results of the above questionnaire (Fig. 14). Then, the seating pressure distribution of the seat was compared. The area in the maximum load part under the hip was decreased for the developed product. This means that the developed product has better load distribution than the conventional products. It was concluded that this feature contributed to improvement in the fitting feeling and the holding feeling of the seat (Fig. 15).
11. Conclusion Based on the studies described above, development of the non-woven fabric-based cover pad material with sof-
115
ter seat surface, improved seating comfort and the durability performance sufficient for actual use were carried out. From now on, we will continue with the effort to pursue possibilities for non-woven fabric as the cover pad, and actively participate in the effort to recycle nonwoven fabric to protect the global environment.
References [1] Nobuo Suzuki et al., Textile Handbook, 2nd edition, Maruzen (1994) (in Japanese). [2] Kinzo Ishikawa et al., Textile, Tokyo Denki University Press, Tokyo (1991) (in Japanese). [3] Non-Woven Fabric Study Group, Textile Machinery Society of Japan, Basics and Applications of Non-Woven Fabrics, Textile Machinery Society of Japan (1993).
Advanced soft coverpad made of non-woven fabric Toru Hayakawa , Kazuhito Kamezaki , Tomoyuki Tokida , Yoshio Yamada, Hideki Ono, Osamu Araki Takashimaya Nippatsu Kogyo, Development Divison, 1-1 Maehata, Oosima-cho, Toyota, Aichi, Japan Toyota Motor Corporation, 1 Toyota-cho, Toyota, Aichi, Japan Received 30 March 1998
Abstract The advancement of touching and fitting feeling of the seat are expected to be important factors to enhance the product-value of the automobile. For this purpose, we have noted the softening of the seat cover and carried out development of a cover pad made of non-woven fabric. As a result, we could achieve the quality required for the material with soft feeling and durability for use as a seat cover pad. 1999 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved.
1. Introduction To improve the marketability of an automobile, it is naturally important to improve the primary function of the automobile such as running, turning and stopping, but it is equally important to improve the so-called secondary functions that appeal to the senses of the vehicle occupants, such as seeing, hearing and touching. Among the interior parts that dress up the inside of the passenger compartment, the car seat can be described as one of the most familiar parts for the occupants because the seat is constantly in contact with the occupant’s body. Therefore, a considerably higher value will be created by offering the secondary function of the car seat in addition to the primary function such as safely holding the occupant’s body and the comfort of cushioning. In the pursuit of various secondary functions of the car seat, we took note of the “feel” of the seat. Considering this element as an important secondary function, we addressed ourselves to the development of a technology to make the car seat feel softer. It is quite appropriate that the car seat and a luxury sofa in the living room should have different feel and seating comfort, because they are designed for different purposes. However, most people will be satisfied with the softness they only feel when sitting on a luxury sofa. We focused our attention on the seat component and especially the cover pad (Fig. 1) in order to achieve the softer “feel” of the seat. The conventional slab poly-
urethane (PUR) was re-evaluated as the raw material, and a soft non-woven pad was later developed as the new raw material to achieve both softness and durability at the same time This paper will cover the process of our R&D effort.
2. Setting of development target for “softness feel” In order to investigate the relationship between the feel and compressive characteristics of the cover pad, the typically-used slab PUR at three levels of hardness (A—C) was tested (Fig. 2). Sample A, the general-purpose type, felt hard because of the heavy initial peak load exclusive to polyurethane. Sample B which was softer than Sample A still felt hard even though the initial peak load was lighter than Sample A. Sample C, which was the softest of all the samples, did not have a satisfactory feel because the load rapidly increased at the deflection of 70% to create bottoming even though the initial peak load was extremely light. Therefore, the characteristics that would produce the satisfactory softness feel were defined as light load over the entire deflection range, no peak load in the initial phase of deflection, and an increase in the load at a moderate slope angle in the second phase of deflection. Based on this definition, the target range in compressive characteristics was specified as the shaded area in Fig. 2.
0389-4304/99/$19.00 1999 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved. PII: S 0 3 8 9 - 4 3 0 4 ( 9 8 ) 0 0 0 4 5 - 9
JSAE9930090
110
T. Hayakawa et al. / JSAE Review 20 (1999) 109—115
Fig. 1. General components of the car seat.
Fig. 2. Compressive characteristics of slab PUR.
3. Selection of material for cover pad Since it was found impossible to achieve the desired properties with slab PUR, various materials for the cover pad were re-evaluated. Candidate-materials for the cover pad included non-woven fabric and feather laminate in addition to slab PUR, and these materials underwent the matrix test on four items including compressive characteristics and durability. It was determined that non-woven fabric had excellent properties (Table 1). However, there was concern over durability of nonwoven fabric used as the cover pad of a car seat. Thus, it became necessary to develop a soft non-woven fabric with the durability sufficient for automotive applications. Consequently, the effort to develop such fabric was started.
4. Durability test method and setting of target values In the development of soft non-woven fabric, it was necessary to determine the minimum requirement in durability for the cover pad application. Our past experience and knowledge, and the characteristics of nonwoven fabric, were taken into consideration to establish the test method and target values as shown in Table 2. Since polyurethane and non-woven fabric had widely different material characteristics, the test conditions for evaluation of compression set (or permanent set in fatigue)
was changed from the current compression deflection of 50% constant to constant compressive load that simulates the load of the hip (or the hip load of 0.1 kgf/cm) where the heaviest load is applied. As a result, the test conditions were much closer to the actual mode.
5. Selection of fiber material for non-woven fabric Non-woven fabric is an aggregate of fibers, and selection of fiber material is important since the performance and the cost of non-woven fabric depend on the fiber material selected. Chemical fiber is generally composed of fused thermoplastic resin yarn, and is less thermally stable than polyurethane which is a thermosetting resin. Thus, the heat resistance performance needs to be emphasized when selecting chemical fiber material. The test was conducted on three types of chemical fiber materials and cotton and wool which are natural fibers [1,2]. After the test, polyester fiber was selected as the raw material for non-woven fabric (Table 3).
T. Hayakawa et al. / JSAE Review 20 (1999) 109—115
Fig. 3. Product method of non-woven fabric.
111
Fig. 4. Characteristics of thermal bond method.
Fig. 5. Enlarging photography of part of bound fiber.
6. Selection of product method for non-woven fabric 6.1. Product method for non-woven fabric To manufacture thick non-woven fabric for the cover pad, the best production method was selected. Among those dry methods shown in Fig. 3, the thermal bond method and the needle punch method are the only methods suitable for production of thick fabric. These methods are both designed to bond short fibers together. In the thermal bond method, a fibrous web is heated, and the fibers are melted and bonded together by melting and solidification of the portion of the binder fiber with low melting point. In the needle punch method, fibrous web is punched with a special needle with numerous projections called “barb” many times. As a result, the fibers are entangled and bonded together. There is yet another method in which these two methods are combined [3].
(or resistance to permanent set in fatigue) and compressive characteristics of the binder-fused non-woven fabric were tested (Fig. 4). The test showed that both repeated and wet heat static loads worsened as the binder fiber content was increased. This tendency can be attributed to the fact that repeated compression deformed or damaged the fused point of the fiber and impaired the restoration of fibers (Fig. 5). Deterioration of wet heat static load was probably caused by the fact that the portion of the binder fiber with low melting point was susceptible to heat. As for compressive characteristics, an increase in the binder fiber strengthened the crosslinking structure produced by the melt-bonding of fibers, and increased the compressive load. Based on the above test results, the needle punch method which can bond fibers together without binder fiber was selected as the product method for non-woven fabric, because softer feel and the resistance to permanent set in fatigue must be achieved at the same time.
6.2. Study of product methods for non-woven fabric
7. Study of fiber specifications
The thermal bond method was studied first. At different binder fiber content levels, the durability performance
Selection of the needle punch method succeeded in improving resistance to permanent set in fatigue, but
112
T. Hayakawa et al. / JSAE Review 20 (1999) 109—115
Fig. 6. Three-dimensional crimp fiber.
failed to achieve the target values. Thus, a study was conducted to determine the fiber specifications less susceptible to permanent set in fatigue. While fiber specifications included such items as thickness, length, the crosssectional shape, crimp and oil, our attention was focused on thickness and oil because the preliminary experiment showed that resistance to permanent set in fatigue depended heavily on thickness, oil and crimp. There are roughly three types of crimp: (i) straight, (ii) mechanically processed two dimensional crimp and (iii) three-dimensional crimp produced by thermal processing of two-component-formulated fiber (Fig. 6). The threedimensional crimp was selected because it had the highest degree of crystallinity and improved toughness. General specifications were used for length and crosssectional shape.
Fig. 7. Effect of fiber thickness.
7.1. Study of fiber thickness The needle punch non-woven fabric was tested for resistance to permanent set in fatigue and compressive characteristics at different fiber thickness levels. The test showed that the best resistance to permanent set in fatigue was achieved with a thin fiber with fiber thickness of 2d, and the resistance decreased as the thickness increased. As for compressive characteristics, the softness feel was enhanced as the fiber thickness decreased. Therefore, it was decided to decrease the thickness of the fiber in the production of non-woven fabric as long as no problem is observed (Fig. 7). Under the same load, thinner fiber tends to cause more deflection. An attempt was made to verify this tendency from the dynamics point of view (Fig. 8). When a thick fiber with the diameter D and a bundle of n thin fibers with the diameter of 1/n ) D were compared, the deflection rigidity of the bundle of thin fibers was 1/n times that of the thick fiber. In other words, if the weight and the thickness of non-woven fabric are the same, thinner fiber is more likely to deflect under the same load. 7.2. Study of oil (surface treatment) Oil is the surface-treatment agent applied to the fiber by dipping or spray coating. This treatment is designed to improve the unraveling and carding characteristics
Fig. 8. Comparison of rigidity.
during the non-woven fabric production process. Oil is available in many types according to the applications of the processed products including non-woven fabric. It was our assumption that permanent set in fatigue of the fiber would be improved by strengthening the restoring performance of the fiber. Then, it was presumed that minimizing the friction resistance of each fiber and providing sufficient sliding property to the fiber would improve the restoring performance. Therefore, a study of the silicon-added oil which is used for the above fiber surface treatment was conducted. The performance of non-woven fabric was tested at different ratios of added silicon in the base oil. It was confirmed that an increase in the ratio of added silicon would diminish the sliding stress of the fiber and at the same time improve the resistance to permanent set in fatigue. However, the ratio of added silicon was fixed at 60% because the carding performance showed a problem when the ratio was increased to 80% (Fig. 9).
T. Hayakawa et al. / JSAE Review 20 (1999) 109—115
113
Table 4 Durability of the developed product (density"0.03 g/cm) Compression set (%)
Target value
Developed product
Repeated
10
6.1
20 15 —
18.6 11.3 3.5
Resistance
Wet heat Dry heat Ordinary temp
Fig. 9. Effects of the addition of silicon to oil.
Fig. 10. Effect by density.
8. Durability performance of developed product The above study results indicated a direction in achieving the target values in resistance to permanent set in fatigue. Finally, to find out the optimum weight (apparent density) range which takes into consideration compressive characteristics, the relationship between apparent density and resistance to permanent set in fatigue and compressive characteristics was investigated (Fig. 10). It was shown that increasing the apparent density would improve the resistance to permanent set in fatigue but increase the hardness feel. However, target values in resistance to permanent set in fatigue and the feel were achieved at the same time by setting the apparent density within the 0.03—0.04 g/cm range. The durability performance of the developed product is shown in Table 4.
9. Durability test 9.1. Results of actual vehicle monitoring durability test The durability target for the individual non-woven fabric was achieved. As the next step, durability of non-woven fabric as the seat assembly was checked. Non-woven fabric passed a wet hot-cold environmental durability test, which was the severest of all durability tests, without causing a significant problem in such basic performance items as seating comfort and the appear-
Fig. 11. Monitoring.
ance of the seat. For further checking, a durability test based on monitoring of an actual vehicle was conducted. In the test, non-woven fabric showed slight permanent set in fatigue in the initial stage, but the permanent set in fatigue immediately subdued and stabilized. In addition, the softness feel did not change, and no abnormality was observed in the appearance of the seat. Based on these results, the permanent set in fatigue rate upon aging was estimated at about 10%, which confirmed that nonwoven fabric has a performance level sufficient for actual use (Fig. 11). 9.2. Discussion of the results of durability test This section is devoted to technical discussion of the results of the durability test. During the day, the temperature in the passenger compartment of the actual vehicle increases by solar radiation and the temperature at the surface of the seat increases to 60—70°c in summertime. Fig. 12 shows the results of the compression cyclic test on non-woven fabric and polyurethane that was conduced to simulate the temperature increase. When compared with polyurethane, non-woven fabric showed far greater restoring performance by heating after being compressed under the wet-hot condition. This phenomenon is presumably due to the bi-metallic characteristic of the fabric. In other words, it is presumed that the restoring performance of the fabric that constitutes the developed product is heavily dependent on the temperature, and the
114
T. Hayakawa et al. / JSAE Review 20 (1999) 109—115
fabric will return to the three-dimensional state by applying heat at a certain temperature level even when the three-dimensional crimp has been set and temporarily becomes a two-dimensional state. In this respect, the developed product can be described as a cover pad material with excellent softness and a special restoring performance which are vastly different from the characteristics of polyurethane.
60% of the respondents felt that the developed product offered improved seating comfort. The survey showed that the softness of the surface contributes not only to better feel but also to seating comfort. It was confirmed that the developed product is sufficiently effective (Fig. 13).
10. Testing of actual seat made of non-woven fabric 10.1. Results of questionnaire on feel of the seat To verify the advantage of the developed product in terms of feel, two seats made of the developed product and the conventional slab PUR were produced and a survey based on the questionnaire on the feel and seating comfort was conducted. In this survey, about 70% of the respondents felt that the surface of the developed product was softer than the slab PUR-based product, and about
Fig. 12. Restoring performance of 3D crimp fiber.
Fig. 13. Results of the questionnaire.
Fig. 14. Load-deflection characterstics of the seat.
Fig. 15. Pressure distribution of the seat.
T. Hayakawa et al. / JSAE Review 20 (1999) 109—115
10.2. Effect on seating comfort Changes in the seat performance of the developed product were investigated. Static load deflection characteristics of the seat were first investigated. The investigation showed that the developed product-based seat had a larger amount of deflection under a given load, and a significant amount of deflection in the light load area, which corroborates the results of the above questionnaire (Fig. 14). Then, the seating pressure distribution of the seat was compared. The area in the maximum load part under the hip was decreased for the developed product. This means that the developed product has better load distribution than the conventional products. It was concluded that this feature contributed to improvement in the fitting feeling and the holding feeling of the seat (Fig. 15).
11. Conclusion Based on the studies described above, development of the non-woven fabric-based cover pad material with sof-
115
ter seat surface, improved seating comfort and the durability performance sufficient for actual use were carried out. From now on, we will continue with the effort to pursue possibilities for non-woven fabric as the cover pad, and actively participate in the effort to recycle nonwoven fabric to protect the global environment.
References [1] Nobuo Suzuki et al., Textile Handbook, 2nd edition, Maruzen (1994) (in Japanese). [2] Kinzo Ishikawa et al., Textile, Tokyo Denki University Press, Tokyo (1991) (in Japanese). [3] Non-Woven Fabric Study Group, Textile Machinery Society of Japan, Basics and Applications of Non-Woven Fabrics, Textile Machinery Society of Japan (1993).