The structures and production processes of natural leather, polyurethane (PU) microfiber synthetic leather and polyvinyl chloride (PVC) synthetic leather were compared, and the material properties were tested, compared and analyzed. The results show that in terms of mechanics, the comprehensive performance of PU microfiber synthetic leather is better than that of genuine leather and PVC synthetic leather; in terms of bending performance, the performance of PU microfiber synthetic leather and PVC synthetic leather is similar, and the bending performance is better than that of genuine leather after aging in wet heat, high temperature, climate alternation, and at low temperature; in terms of wear resistance, the wear and tear resistance of PU microfiber synthetic leather and PVC synthetic leather is better than that of genuine leather; in terms of other material properties, the water vapor permeability of genuine leather, PU microfiber synthetic leather and PVC synthetic leather decreases in turn, and the dimensional stability of PU microfiber synthetic leather and PVC synthetic leather after thermal aging is similar and better than that of genuine leather.
As an important part of car interior, car seat fabrics directly affect the user’s driving experience. Natural leather, polyurethane (PU) microfiber synthetic leather (hereinafter referred to as PU microfiber leather) and polyvinyl chloride (PVC) synthetic leather are all commonly used seat fabric materials.
Natural leather has a long history of application in human life. Due to the chemical properties and triple helix structure of collagen itself, it has the advantages of softness, wear resistance, high strength, high moisture absorption and water permeability. Natural leather is mostly used in the seat fabrics of mid-to-high-end models in the automotive industry (mostly cowhide), which can combine luxury and comfort.
With the development of human society, the supply of natural leather can hardly meet the growing demand of people. People began to use chemical raw materials and methods to make substitutes for natural leather, that is, artificial synthetic leather. The advent of PVC synthetic leather can be traced back to the 20th century. In the 1930s, it was the first generation of artificial leather products. Its material characteristics are high strength, wear resistance, folding resistance, acid and alkali resistance, etc., and it is low cost and easy to process. PU microfiber leather was successfully developed in the 1970s. After the progress and improvement of modern technology applications, as a new type of artificial synthetic leather material, it has been widely used in high-end clothing, furniture, balls, car interiors and other fields. The material characteristics of PU microfiber leather are that it truly simulates the internal structure and texture quality of natural leather, and has better durability than genuine leather, more material cost advantages and environmental friendliness.
PVC synthetic leather
The material structure of PVC synthetic leather is mainly divided into surface coating, PVC dense layer, PVC foam layer, PVC adhesive layer and polyester base fabric. In the release paper method (transfer coating method) process, the PVC slurry is first scraped for the first time to form a PVC dense layer (surface layer) on the release paper, and enters the first oven for gel plasticization and cooling; secondly, after the second scraping, a PVC foam layer is formed on the basis of the PVC dense layer, and then plasticized and cooled in the second oven; again, after the third scraping, a PVC adhesive layer (bottom layer) is formed, and it is bonded with the base fabric and enters the third oven for plasticization and foaming; finally, it is peeled off from the release paper after cooling and forming.
Natural leather and PU microfiber leather
Natural leather material structure The structure includes the grain layer, fiber structure and surface coating. The production process from raw leather to synthetic leather is generally divided into three stages: preparation, tanning and finishing. The original intention of the design of PU microfiber leather is to truly simulate natural leather in terms of material structure and appearance texture. The material structure of PU microfiber leather mainly includes PU layer, Base part and surface coating. Among them, the Base part uses bundled microfibers with similar structure and performance to the bundled collagen fibers in natural leather. Through special process treatment, a high-density non-woven fabric with a three-dimensional network structure is processed and synthesized, combined with PU filling materials with an open microporous structure.
Sample preparation
The samples are from the mainstream automotive seat fabric suppliers in the domestic market. Genuine leather, PU microfiber leather and PVC Two samples of each synthetic leather material were prepared from six different suppliers. The samples were named leather 1# and 2#, PU microfiber leather 1# and 2#, and PVC synthetic leather 1# and 2#. The sample colors were all black.
Testing and characterization
Combined with the requirements of vehicle applications for materials, the above samples were compared in terms of mechanical properties, folding resistance, wear resistance and other material properties. The specific test items and methods are shown in Table 1.
Analysis and discussion
Mechanical properties
Table 2 is the mechanical properties test data of leather, PU microfiber leather and PVC synthetic leather, where L represents the warp direction of the material and T represents the weft direction of the material. It can be seen from Table 2 that in terms of tensile strength and elongation at break, the tensile strength of natural leather in both the warp and weft directions is higher than that of PU microfiber leather. PU microfiber leather showed better strength, while PU microfiber leather had a higher elongation at break and better toughness; while the tensile strength and elongation at break of PVC synthetic leather were both lower than those of the other two materials. In terms of static elongation and permanent deformation, the permanent deformation of PU microfiber leather was the smallest in both the warp and weft directions (the average permanent deformation in the warp direction was 0.5%, and the average permanent deformation in the weft direction was 2.75%), indicating that the material had the best recovery performance after being subjected to tensile force, which was better than genuine leather and PVC synthetic leather. Static elongation refers to the degree of elongation deformation of the material under stress conditions during the assembly of the seat cover. There is no clear requirement in the standard and it is only used as a reference value. In terms of tearing force, the values of the three material samples are similar and can meet the standard requirements.
In general, the PU microfiber leather samples have good tensile strength, elongation at break, permanent deformation and tearing force, and the comprehensive mechanical properties are better than those of genuine leather and PVC synthetic leather samples.
Folding resistance
The states of the folding resistance test samples are specifically divided into 6 types, namely initial state (unaged state), damp heat aging state, low temperature state (-10℃), xenon light aging state (PV1303/3P), high temperature aging state (100℃/168h) and climate alternation aging state (PV12 00/20P). The folding method is to use a leather bending instrument to fix the two ends of the rectangular sample in the length direction on the upper and lower clamps of the instrument, so that the sample is 90°, and repeatedly bends at a certain speed and angle. The folding performance test results of genuine leather, PU microfiber leather and PVC synthetic leather are shown in Table 3. It can be seen from Table 3 that the genuine leather, PU microfiber leather and PVC synthetic leather samples are all folded after 100,000 times in the initial state and 10,000 times in the aging state under xenon light. It can maintain a good state without cracks or stress whitening. In other different aging states, namely, the wet heat aging state, high temperature aging state, and climate alternation aging state of PU microfiber leather and PVC synthetic leather, the samples can withstand 30,000 bending tests. After 7,500 to 8,500 bending tests, cracks or stress whitening began to appear in the wet heat aging state and high temperature aging state samples of genuine leather, and the severity of wet heat aging (168h/70℃/75%) is lower than that of PU microfiber leather. Fiber leather and PVC synthetic leather (240h/90℃/95%). Similarly, after 14,000~15,000 bending tests, cracks or stress whitening appear in the state of leather after climate alternation aging. This is because the bending resistance of leather mainly depends on the natural grain layer and fiber structure of the original leather, and its performance is not as good as that of chemical synthetic materials. Correspondingly, the material standard requirements for leather are also lower. This shows that the leather material is more “delicate” and users need to be more cautious or pay attention to maintenance during use.
In general, the folding performance of leather, PU microfiber leather and PVC synthetic leather samples is good in the initial state and xenon light aging state. In the wet heat aging state, low temperature state, high temperature aging state and climate change aging state, the folding performance of PU microfiber leather and PVC synthetic leather is similar, which is better than leather.
Abrasion resistance
The abrasion resistance test includes friction color fastness test and ball plate abrasion test. The wear resistance test results of leather, PU microfiber leather and PVC synthetic leather are shown in Table 4. Rubbing color fastness test results The results show that the color fastness of leather, PU microfiber leather and PVC synthetic leather samples after friction can be maintained above 4.0 in the initial state, deionized water soaked state, alkaline sweat soaked state and 96% ethanol soaked state. The color state of the samples is stable and will not fade due to surface friction. The results of the ball plate abrasion test show that after 1800-1900 times of wear, the leather samples have about 10 damaged holes, which is comparable to the wear resistance of PU microfiber leather and PVC synthetic leather samples (both There is no damage hole after 19,000 wears). The reason for the damage hole is that the grain layer of the leather is damaged after wear, and its wear resistance is quite different from that of chemical synthetic materials. Therefore, the weak wear resistance of leather also requires users to pay attention to maintenance during use.
In general, the leather, PU microfiber leather and PVC synthetic leather samples have good friction color fastness, and PU microfiber leather and PVC synthetic leather have better wear and tear resistance than leather, which can effectively prevent wear and tear holes.
Its Other material properties
The test results of water vapor permeability, horizontal flame retardancy, dimensional shrinkage and odor level of genuine leather, PU microfiber leather and PVC synthetic leather samples are shown in Table 5.
The difference in test data comparison is mainly in water vapor permeability and dimensional shrinkage. The water vapor permeability of genuine leather is nearly twice that of PU microfiber leather, while PVC synthetic leather has almost no water vapor permeability. This is because the three-dimensional network skeleton (non-woven fabric) in PU microfiber leather is similar to the natural bundle collagen fiber structure of genuine leather, both of which have microporous structure, making them have It has a certain degree of water and air permeability. Furthermore, the cross-sectional area of collagen fibers in genuine leather is larger and more evenly distributed, and the proportion of micropore space is greater than that of PU microfiber leather, so genuine leather has the best water and air permeability. In terms of dimensional shrinkage, the shrinkage rates of PU microfiber leather and PVC synthetic leather samples after heat aging (120℃/168h) are similar and significantly smaller than that of genuine leather, and their dimensional stability is better than that of genuine leather. In addition, the test results of horizontal flame retardancy and odor level show that genuine leather, PU microfiber leather and PVC synthetic leather samples can To achieve similar levels, both flame retardant and odor performance can meet the material standard requirements.
In general, the water vapor permeability of leather, PU microfiber leather and PVC synthetic leather samples decreases in turn. The shrinkage rate (dimensional stability) of PU microfiber leather and PVC synthetic leather after heat aging is similar and better than that of leather, and the horizontal flame retardant and odor performance are similar.
Conclusion
The material cross-sectional structure of PU microfiber leather is similar to that of natural leather. The PU layer and the PU microfiber leather base part of the former correspond to The grain layer and fiber tissue part of the latter. The material structure of the dense layer, foaming layer, adhesive layer and base fabric of PU microfiber leather and PVC synthetic leather is significantly different.
The material advantage of natural leather is that it has good mechanical properties (tensile strength ≥15MPa, elongation at break>50%) and water permeability. The material advantage of PVC synthetic leather is wear resistance (no damage after 19,000 times of ball board wear), good durability to different environmental conditions (including resistance to moisture and heat, high temperature, low temperature, and air PU microfiber leather has the advantages of both genuine leather and PVC synthetic leather. The test results of mechanical properties, folding performance, wear resistance, horizontal flame retardancy, dimensional stability, odor level, etc. can reach the best level of natural leather and PVC synthetic leather, and it also has certain water permeability. Therefore, PU microfiber leather can better meet the application requirements of car seats and has broad application prospects.
Post time: Nov-19-2024