The "external blade scraping" and "internal blade scraping" refer to the two major categories of PVC coated cloth produced by the blade scraping coating process, and the accurate names should be "external blade scraping cloth" and "internal blade scraping cloth". The production process of the two is basically the same - both involve uniformly coating liquid PVC slurry on the surface of polyester base fabric through a scraper, and then shaping it through high-temperature plasticization. The difference lies not in the position of the scraper (all on the same machine and with the same scraper system), but in the different requirements for light transmittance of the finished product, resulting in completely different formulas and uses.

External lightknife-scrim fabric, commonly known as external knife scraping, designed for outdoor scenes without backlight. Its characteristic is that the surface is dense, opaque, and light cannot penetrate. In order to achieve opacity, high coverage fillers such as titanium dioxide and carbon black are added to the PVC slurry during production, and double-sided coating or multi pass coating processes are used. The main use of external light knife scraping cloth is for large outdoor billboards, building fences, truck tarpaulins, sunshades, etc. Because it requires long-term exposure to sunlight, wind, and rain, the formula also contains anti UV agents and antioxidants, with a weather resistance life of up to 3-5 years. Its surface flatness is moderate, which can meet the requirements of solvent based or weak solvent based inkjet printing, with bright colors and no darkening due to backlighting.

Internal light knife scraping cloth, commonly known as internal knife scraping, is designed for indoor lighting light box scenes. Its key characteristics are uniform and soft light transmission. During production, high coverage pigments are not added to the PVC slurry. Instead, a semi transparent state is maintained and the coating thickness is controlled between 0.3-0.5mm to ensure a light transmittance of 60% -80%. The surface flatness of the internal light knife scraping cloth requires extremely high standards - because any small bumps and depressions after lighting will be magnified by the light, affecting the quality of the image. Therefore, the internal light knife scraping cloth often uses high fineness base cloth (no mesh, high density) and precision scraping process, and the finished product is commonly known as "net free knife scraping cloth". Its softness is also higher than that of the external light knife scraping cloth, making it easy to install into the lightbox frame.

How to choose between external blade scraping or internal blade scraping? The answer depends entirely on the usage scenario:

1. If you need to create outdoor billboards, building enclosures, activity background panels, truck tarpaulins - these scenes do not have backlighting, or backlighting can interfere with visual effects, please choose external knife scraping cloth (external light cloth). Its opaque performance ensures that the image is clear and visible under natural light, and it has strong weather resistance.

2. If you need to create lightbox advertisements, subway lightboxes, bus stop lighting advertisements, and interior lighting displays in shopping malls - these scenes rely on backlighting to illuminate the image, please choose the inner knife scraping cloth (inner lighting cloth). Its transparency allows light to penetrate evenly and colors to be full and transparent, while the opaque outer blade will turn into a black cloth on the lightbox.

3. Note that the two cannot be used interchangeably: place the outer blade scraper into the lightbox, the image will be completely opaque, and the lightbox will become a dark box; Hanging the inner blade scraper cloth outdoors will cause the image to turn white and gray due to backlight penetration, resulting in color distortion and poor weather resistance, leading to rapid aging.