Plastic Modification Processing and Cost Analysis

  In the middle of the 18th century, people could already process natural resins such as asphalt and rosin into man-made plastics. In the following just over a hundred years, plastics moved from the initial natural polymer processing stage to the synthetic material stage, solving the fatal problem of scarcity of raw materials. Then it flourished in the 1970s and became an indispensable existence in modern industrial production and life. At present, modified plastics have replaced traditional plastics and have become the most widely used materials such as FR4 sheet, 3240 Epoxy Resin Sheet and 3026 Phenolic Cotton Cloth Laminated Sheet, while also reflecting the cutting-edge technological level of modern materials science.

1. What is plastic?

  Plastic is a very large concept. It generally refers to all high molecular polymers synthesized from monomer raw materials or formed through polymerization. It is the fourth largest industrial material after steel, wood and cement. Usually, the basic resin produced by chemical plants is called "non-modified plastic", or "pure resin".

  According to the physical and chemical properties of the material,

  Plastics can be divided into two categories: thermoplastic and thermosetting.

  Thermoplastic materials, there is no chemical change between molecules when heated, the material becomes soft with the increase of temperature, and becomes hard when the temperature decreases. This process is reversible repeatedly. Therefore, the impact resistance of such products is often better, and it is easier to process, which is very suitable for some complex design applications. Due to the properties of thermoplastic materials that can be heated repeatedly, they are recyclable materials, accounting for about 85% of the current industry applications.

  Thermosetting material, as the name implies, refers to a material that undergoes a chemical change after heating to a certain temperature, and a cross-linked network structure is formed between the molecular chains to solidify and can no longer be softened. Such materials generally have good mechanical strength and dimensional stability, and are also very good in heat resistance and insulation. They are usually used in scenes that require heat preservation, insulation, corrosion resistance, and high temperature resistance.

  Plastics can also be divided into crystalline plastics and non-crystalline plastics according to their crystallinity. There is no clear dividing line here.

  Generally, polymers with crystallinity above 80% are called crystalline plastics. It has a clear melting point and appears translucent or opaque. Because of its smooth surface, it is not easy to do surface treatment, such as baking varnish, chrome plating, etc. This type of plastic has high molding shrinkage, high strength, and strong chemical resistance, and is widely used in industrial fields.

  Amorphous plastic refers to polymers with crystallinity below 20%. It has no obvious melting point and is transparent. Its characteristics, advantages and disadvantages are just opposite to those of crystalline plastics, and are widely used in daily life.

2. Why should plastic be modified?

  Plastic has the advantages of low density, easy processing and forming, corrosion resistance, good insulation, good light transmission, and easy coloring, and the price is relatively low. However, compared with common metal materials, plastics have poor heat resistance and general mechanical strength, and their application in the engineering field has certain limitations.

  For example, the common polypropylene (PP), its excellent mechanical properties and good heat resistance make it widely used in automotive interiors and home appliances. However, this type of material has disadvantages such as low dimensional accuracy, poor weather resistance, insufficient rigidity, poor decoration and assembly, and difficulty in pasting and electroplating, which has a huge impact on the production and application of the product.

  For another example, nylon (PA6 / PA66) often used in life has the advantages of toughness, wear resistance, oil and water resistance, and is very suitable for the production of electronic components (connectors), auto parts (cooling fans), and pedals. However, due to its insufficient hardness and elastic modulus, there are certain safety hazards during use.

  At this time, modified plastics came into being. It is processed and modified on the basis of general plastics and engineering plastics through filling, blending, reinforcement and other methods to achieve various properties of plastic products. It can be said that for modified plastics, every plastic particle is advanced customization.

3. How to modify plastics?

  Let's understand what substances are made of modified plastics.

Resin

  Resin is the most important component of plastics. It refers to high molecular compounds that have not been mixed with various additives, mostly low-molecular carbon and hydrogen. From raw materials such as petroleum, natural gas, and coal decomposition products, high molecular polymers refined and synthesized by chemical methods are called synthetic resins, which often have better performance than natural resins.

Filler

  In order to improve the strength and heat resistance of the plastic, and improve its properties and formability, we usually add fillers to the plastic. Since these materials are generally cheaper than plastics, they can reduce the cost of modified plastics to a certain extent. Common organic fillers are wood flour, chips, paper, fabric fibers; and common inorganic fillers are glass fiber, carbon black, carbon fiber, and so on.

Other additives

  The parts of modified plastics other than resins and fillers are collectively referred to as other additives. Common ones include plasticizers, stabilizers, colorants, antioxidants, and so on.

  Take plasticizers as an example. Plasticizers are also called plasticizers, which can increase the plasticity and softness of plastics, reduce brittleness, and make products easy to shape. However, since the plasticizer is easy to precipitate during the production process, it will lead to an increase in the product defect rate, and it is not recommended to use it on a large scale.

  Stabilizers are well understood to prevent the resin from being destroyed or decomposed by light and heat during processing and use. The colorant is to increase the color masterbatch, so that the plastic has a variety of colors. The antioxidant is to prevent the plastic from being oxidized and yellowed by heating.

There are three common modification methods:

 Filling

 The method used to improve the rigidity, hardness, heat resistance and other properties of plastic materials by using different mineral powders in the filler is called filling. Common talc powder (TD) is used to increase the lubricity of the material, fire resistance, acid resistance and insulation. In addition, it has a high melting point, inactive chemical properties, good adsorption capacity, and easy surface treatment.

Enhance

 The method used to improve the rigidity, strength, hardness, and heat resistance of the material by adding fibrous substances to the filler is called reinforcement. Common ones such as glass fiber can increase the insulation and heat resistance of the material. At the same time, the corrosion resistance and mechanical strength of the material will also be significantly improved. It is worth mentioning that too much fiber will lead to poor surface and reduced elongation at break, therefore, it is necessary to control the proportion of its addition.

Blend

  The way to change the physical and mechanical properties and processing properties of the polymer by mixing different resins is called blending. For example, the elastic material EPDM, when it is blended with brittle materials, the elastomer particles in the material can effectively absorb part of the impact energy, thereby greatly improving the toughness of the polymer.

4. Modified plastic process and cost

  Take the PP material mentioned above as an example. Polypropylene (PP) has excellent mechanical properties, but lacks rigidity and is difficult to electroplating. Therefore, for car bumpers, heater grilles, and car interior door panels, both appearance and For products that require material toughness and stability, EPDM can be blended to increase their rigidity. In addition, 20% talcum powder (TD) is filled to improve the stability of the material and reduce the difficulty of surface treatment.

PP → PP+EPDM+TD20

  According to the previous introduction of modified plastics and modification methods, we can divide the cost of modified materials into four categories: mixed resin cost, filler cost, additive cost and processing cost. In general, resin accounts for more than 50% of the total weight of the plastic, fillers and blending materials account for less than 40% of the total weight, and additives account for less than 10% of the total weight. This will focus on processing costs.

  The processing process of modified plastics is relatively simple. First of all, the mixed resin (PP+EPDM), filler (TD) and the mixture required for the modified plastic are weighed and mixed. They are melted in a twin screw, extruded through a side feeder, and cooled to become a final product. The slender stick shape is cut into pellets and sieved. After passing the inspection, it can be packaged.

  Take the cost composition of PP modified plastics as an example:

  Material cost is the total cost of raw and auxiliary materials, and the total cost can be obtained by analyzing the proportion of each material and calculating the price. Here it is assumed to be 8.2 yuan/kg.

  Manufacturing expenses can be divided into direct costs and indirect costs.

Direct cost here refers to direct labor. For the convenience of calculation, the calculation of labor costs in the table below also includes indirect labor costs.

  Through the analysis of the technological process, it can be seen that about 0.5 operators are needed in the mixing, and an operator is also needed in the extrusion process. For other links such as inspection and packaging, an indirect operator is probably needed. Assuming that the production capacity of each line is 800 kg/hour, and the unit price of working hours in the following table is the calculation premise, the labor cost can be obtained as 0.084 yuan/kg.

  Indirect costs include indirect labor, fuel power, waste rate, packaging, transportation, and depreciation costs. The waste rate, packaging, and transportation vary according to product complexity, size, production area, and production line planning. Here is an example to analyze fuel power and depreciation.

Combustion power

  By reading the nameplate of the production line equipment and checking the electric meter, it can be known that the average power of the production line is 360kw. Taking Guangzhou as an example, the average industrial electricity price is 0.5 yuan/kwh, and for a production line with a capacity of 800 kg/hour, the unit energy consumption is 0.22 yuan/kg.

Depreciation

  Here we mainly consider two aspects of house depreciation and equipment depreciation. The depreciation period depends on the specific conditions of each enterprise. Generally, house depreciation is based on 20 years, and equipment depreciation fluctuates in 8-10 years. Through the following conventional values, you can get a depreciation fee of 0.056 yuan/kg.

Cost summary & price

  For conventional plastic companies, their gross profit margin can generally be around 15%. Therefore, the cost structure of one kilogram of PP modified plastics is roughly as shown in the table above.