What to do if the white bags, light-colored sofas or even the walls at home are dirty. It can’t be washed with water. It’s easy to crack. So what should I do? It seems very troublesome to find someone to clean it. Don’t worry, just use a small eraser to clean it. Bags, sofas and other leather products can be wiped with an eraser. It will not damage the surface, and the phone case can also be wiped with an eraser. There are many, many places that can be wiped with an eraser.   Introduction   name   English-Chinese translation: 1. [rubber] The general name for vulcanized rubber . 2. [eraser] Stationery made of rubber, which can erase traces of graphite or ink. There are many types of erasers, with different shapes and colors. There are ordinary fragrant erasers, 2B , 4B, 6B and other special art erasers for painting, as well as plastic erasers , etc.   principle   Pencil lead is made of graphite plus clay. Graphite is soft, black in color, and easily adheres to paper, so it can be written. The eraser is very soft, has high friction, and is somewhat sticky. When rubbed on the paper, the written words will stick away without damaging the paper surface. Therefore, the eraser can erase the pencil writing. If you write with a ballpoint pen , the ink will penetrate into the paper and be difficult to erase.   Relevant information   use correctly   When primary school students erase typos, they want to wipe them quickly and cleanly. They often dip an eraser into their saliva and then wipe. On the contrary, the typos are erased and the notebook is ruined. Especially for painting students, the backlit part of the sketch is often overdrawn, tired of the drawing, and dirty. At this time, if you continue to wipe it repeatedly, or even dip it in saliva , it will be ruined! The correct method should be: first dry wipe repeatedly on an empty piece of paper to get a lot of “rubber surface”, then gently pour the dough onto the area to be wiped off, and then gently rub the surface with the eraser. , it will be clean after a while, and the paper will not be damaged at all!

Polyvinyl chloride, referred to as PVC in English, is the third most produced synthetic polymer plastic in the world (after polyethylene and polypropylene ), with approximately 40 million tons of PVC produced annually. PVC is a polymer formed by polymerizing vinyl chloride monomer (VCM) with initiators such as peroxides and azo compounds or under the action of light and heat according to a free radical polymerization reaction mechanism. Vinyl chloride homopolymer and vinyl chloride copolymer are collectively called vinyl chloride resin .   PVC was once the most widely produced general-purpose plastic in the world and was widely used. There are two types of PVC: rigid (sometimes abbreviated as RPVC) and soft. Rigid polyvinyl chloride is used in construction pipes, doors and windows. It is also used to make plastic bottles, packaging, bank or loyalty cards. Adding plasticizers makes PVC softer and more elastic. It can be used in pipes, cable insulation, flooring, signage, phonograph records, inflatable products and rubber substitutes.   On October 27, 2017, the World Health Organization’s International Agency for Research on Cancer published a preliminary reference list of carcinogens. Polyvinyl chloride is included in the list of Class 3 carcinogens.     Main categories   According to different application scopes, PVC can be divided into : general-purpose PVC resin, high-polymerization PVC resin, and cross-linked PVC resin. General-purpose PVC resin is formed by the polymerization of vinyl chloride monomer under the action of an initiator; high degree of polymerization PVC resin refers to a resin polymerized by adding a chain extender to the vinyl chloride monomer polymerization system; cross-linked PVC resin is A resin polymerized by adding a cross-linking agent containing diene and polyene to the vinyl chloride monomer polymerization system.   According to the method of obtaining vinyl chloride monomer , it can be divided into calcium carbide method, ethylene method and imported (EDC, VCM) monomer method (it is customary to refer to the ethylene method and imported monomer method as the ethylene method).   According to the polymerization method , polyvinyl chloride can be divided into four categories: suspension polyvinyl chloride, emulsion polyvinyl chloride, bulk polyvinyl chloride, and solution polyvinyl chloride. Suspension polyvinyl chloride is the largest variety in production, accounting for about 80% of the total PVC production. Suspension polyvinyl chloride is divided into six models according to absolute viscosity: XS-1, XS-2…XS-6; XJ-1, XJ-2…, XJ-6. The meaning of each letter in the model: X-suspension method; S-loose type; J-compact type.   According to the plasticizer content , PVC plastics are often divided into: unplasticized PVC, the plasticizer content is 0; rigid PVC, the plasticizer content is less than 10%; semi-rigid PVC, the plasticizer content 10-30%; soft PVC, plasticizer content is 30-70%; PVC paste plastic, plasticizer content is more than 80%. The difference in properties between hard PVC and soft.   Physical and chemical properties   PVC is slightly yellow, translucent and shiny. The transparency is better than polyethylene and polypropylene, but worse than polystyrene. Depending on the amount of additives, it is divided into soft and hard polyvinyl chloride. Soft products are flexible and tough and have a sticky feel. Hard products have a higher hardness than low-density polyethylene. And lower than polypropylene, whitening will occur at the inflection point. Stable; not easily corroded by acid and alkali; relatively resistant to heat.   PVC has flame retardancy (flame retardant value is above 40), high chemical resistance (resistant to concentrated hydrochloric acid, 90% sulfuric acid, 60% nitric acid and 20% sodium hydroxide), mechanical strength And the advantage of good electrical insulation.   PVC has poor stability to light and heat. The softening point is 80°C and begins to decompose at 130°C. Without heating the stabilizer, PVC begins to decompose at 100°C and decomposes faster above 130°C. When heated, it decomposes and releases hydrogen chloride gas (hydrogen chloride gas is a poisonous gas), causing it to change color from white to light yellow to red to brown to black. Ultraviolet rays and oxygen in sunlight will cause photo-oxidative decomposition of PVC, thus reducing the flexibility of PVC and eventually becoming brittle. This is why some PVC plastics turn yellow and become brittle over time.   It has stable physical and chemical properties, is insoluble in water, alcohol, and gasoline, and has low gas and water vapor leakage; it can withstand any concentration of hydrochloric acid, sulfuric acid below 90%, nitric acid below 50-60%, and nitric acid below 20% at normal temperature. Caustic soda solution has certain resistance to chemical corrosion; it is quite stable to salts, but can be dissolved in organic solvents such as ethers, ketones, chlorinated aliphatic hydrocarbons and aromatic hydrocarbons.   Industrial polyvinyl chloride resin is mainly amorphous structure, but also contains some crystalline areas (about 5%), so polyvinyl chloride has no obvious melting point and starts to soften at about 80°C. The heat deformation temperature (under 1.82MPa load) is 70-71℃, it starts to flow at 150℃ under pressure and begins to slowly release hydrogen chloride, causing the polyvinyl chloride to change color (from yellow to red, brown, or even black).   The weight average relative molecular mass of industrial polyvinyl chloride is in the range of 48,000-48,000, and the corresponding number average relative molecular mass is 20,000-19,500. The weight average relative molecular mass of most industrial resins is between 100,000 and 200,000, and the number average relative molecular mass is between 45,500 and 64,000. Rigid polyvinyl chloride (without plasticizer) has good mechanical strength, weather resistance and flame resistance. It can be used alone as a structural material and used in the chemical industry to manufacture pipes, plates and injection molded products. Rigid polyvinyl chloride can be reinforced with materials.   Material processing   Polyvinyl chloride plastics come in various forms, which vary greatly, and their processing methods are also diverse, including pressing, extrusion, injection, coating, etc. The particle size, fish eyes, bulk density, purity, foreign impurities, and porosity of PVC resin all have an impact on processability; for paste resin, the viscosity and gelling properties of the paste should be considered.   PVC is an amorphous polymer with small shrinkage. The powder should be preheated before processing to eliminate moisture, enhance the plasticizing effect and prevent bubbles. Moreover, PVC is very easy to decompose, especially when it comes into contact with steel and copper at high temperatures (decomposition temperature is 200 degrees). The molding temperature range is small and the material temperature must be strictly controlled. When using a screw injection machine and a straight-through nozzle, the hole diameter should be large to prevent material stagnation in dead corners. The mold pouring system should be thick, the gate cross-section should be large, the mold should be cooled, the mold temperature is 30-60 ℃, and the material temperature is 160-190 ℃.   Below the glass transition temperature (T g , 80 ℃), polyvinyl chloride is in a glassy state; at T g → viscous flow temperature (T f , about 160 ℃), it is highly elastic and rubbery, with plasticity; at T f → thermal decomposition Temperature (T d ) is a viscous flow state. The higher the temperature, the easier the flow. When the temperature exceeds T d , PVC decomposes a large amount of hydrogen chloride (HCl), and the material loses its chemical stability and physical properties. Therefore, T d is the upper limit temperature for processing and molding. Due to the large intermolecular forces of polyethylene, Tf is very high, even close to the decomposition temperature, so plasticizers need to be added to reduce Tf. On the other hand, stabilizers also need to be added to increase the T d of PVC before it can be processed and formed.   The glass transition temperature (T g ) is only related to the molecular chain segment structure and has little to do with the molecular weight, while the viscous flow temperature (T f ) is the temperature at which macromolecules begin to move and is related to the molecular weight. The larger the molecular weight, the higher the Tf . Therefore, for some processing molding (such as injection molding), it is necessary to appropriately reduce the molecular weight of the resin. According to different molecular weights, domestic suspended polyvinyl chloride resins are divided into grades 1-7. The larger the number, the smaller the molecular weight. XJ-4 (XS-4 ) to Plasticizers reduce T f , so they are often used in the manufacture of soft products. Polyvinyl chloride with an average degree of polymerization below 1,000 is called low-polymerization polyvinyl chloride, which has better processing properties. Less plasticizer can be added during the processing, so that the product will not be accelerated due to the migration of plasticizers. Ageing. Low-polymerization polyvinyl chloride products have good transparency and are widely used in building materials, food and drug packaging materials, and as replacements for organic glass products.   PVC melt is a non-Newtonian pseudo-fluid. The greater the shear speed, the smaller the apparent viscosity, and the change is quite sensitive. When the temperature is raised, the viscosity does not decrease much. Even if the plastic is below the decomposition temperature, it will generate heat and oxidative degradation due to being at a higher temperature for a long time, which will affect its performance. Therefore, improving the fluidity of PVC melt should mainly consider increasing the shear rate (increasing pressure). In fact, increasing the external force helps the movement of macromolecules, causing T f to decrease, and macromolecules can flow at a lower temperature.   The main purpose   Vinyl chloride profile Profiles and special-shaped profiles are the largest areas of PVC consumption in my country, accounting for about 25% of the total PVC consumption. They are mainly used to make doors, windows and energy-saving materials, and their application volume is still growing significantly across the country. In developed countries, the market share of plastic doors and windows also ranks first, such as 50% in Germany, 56% in France, and 45% in the United States.   PVC pipe Among the many PVC products, PVC pipes are the second largest consumer area, accounting for about 20% of its consumption. In our country, PVC pipes were developed earlier than PE pipes and PP pipes. They have many varieties, excellent performance, and wide range of uses, and occupy an important position in the market.   PVC film The consumption of PVC in the PVC film field ranks third, accounting for about 10%. After PVC is mixed with additives and plasticized, a three-roller or four-roller calender is used to form a transparent or colored film with a specified thickness. The film is processed in this way to become a calendered film. It can also be processed by cutting and heat sealing to process packaging bags, raincoats, tablecloths, curtains, inflatable toys, etc. The wide transparent film can be used in greenhouses, plastic greenhouses and mulch films. Biaxially stretched films can be used for shrink packaging due to their thermal shrinkage characteristics.   PVC hard materials and sheets Stabilizers, lubricants and fillers are added to PVC. After mixing, the extruder can be used to extrude hard pipes, special-shaped pipes and corrugated pipes of various diameters, which can be used as sewer pipes, drinking water pipes, wire casings or stair handrails. . By overlapping and hot-pressing the rolled sheets, hard plates of various thicknesses can be made. The plates can be cut into the required shapes, and then PVC welding rods and hot air are used to weld them into various chemically resistant storage tanks, air ducts and containers.   PVC general soft products The extruder can be used to extrude hoses, cables, wires, etc.; the injection molding machine can be used with various molds to make plastic sandals, soles, slippers, toys, auto parts, etc.   PVC packaging materials PVC products are mainly used for packaging various containers, films and hard sheets. PVC containers are mainly used to produce bottles for mineral water, beverages, and cosmetics, as well as for packaging refined oils. PVC films can be used to co-extrude with other polymers to produce low-cost laminates, as well as transparent products with good barrier properties. PVC film can also be used in stretch or shrink packaging for mattresses, cloth, toys and industrial goods.   PVC siding and flooring PVC siding is mainly used to replace aluminum siding. Except for part of the PVC resin, the remaining components of PVC floor tiles are recycled materials, adhesives, fillers and other components. They are mainly used on the hard floors of airport terminals and other places.   PVC daily necessities Luggage bags are traditional products made of polyvinyl chloride. PVC is used to make various imitation leathers for luggage bags and sports products such as basketballs, footballs and rugby balls. It can also be used to make belts for uniforms and special protective equipment. PVC fabrics for clothing are generally absorbent fabrics (no coating required), such as ponchos, baby pants, imitation leather jackets and various rain boots. Polyvinyl chloride is used in many sports and entertainment products, such as toys, records and sporting goods. PVC toys and sporting goods have grown rapidly and have advantages due to their low production cost and easy molding.   PVC coated products Artificial leather with a backing is made by applying PVC paste on cloth or paper and then plasticizing it at above 100°C. You can also calender PVC and additives into a film first, and then laminate it with the substrate. Artificial leather without a backing is directly rolled into a soft sheet of a certain thickness by a calender, and then patterns are embossed on it. Artificial leather can be used to make suitcases, bags, book covers, sofas and car seat cushions, as well as floor leather, which can be used as floor coverings in buildings.   PVC foam products When mixing soft PVC, add an appropriate amount of foaming agent to make a sheet, which is foamed and molded into foam plastic, which can be used as foam slippers, sandals, insoles, and shock-proof buffer packaging materials. It can also be made into low-foaming hard PVC sheets and special profiles using an extruder. It can be used as a substitute for wood and is a new type of building material.   PVC transparent sheet Impact modifiers and organic tin stabilizers are added to PVC, and then mixed, plasticized, and calendered to become transparent sheets. Thermoforming can be used to make thin-walled transparent containers or for vacuum blister packaging. It is an excellent packaging material and decorative material.   other Doors and windows are assembled from hard special-shaped materials. In some countries, it has occupied the door and window market together with wooden doors and windows, aluminum windows, etc.; imitation wood materials, steel-substitute building materials (in the north and seaside); and hollow containers. Virtual circuit is one of the services provided by the packet switching network (the other is datagram service). Simply put, it uses the internal control mechanism of the network to establish virtual logical connections between user hosts and ensure that information can be transmitted on them. The correctness and sequence of packets, virtual circuits must be established and dismantled before and after communication. A permanent virtual circuit is a virtual circuit that is established during network initialization and remains maintained. Both X.25 networks and B-ISDN provide PVC services. PVC plastic bags are generally prohibited.