Discussion on Plastic Formulation
Preface: Plastic products fill almost every aspect of our lives, and the pharmaceutical packaging we produce is only a small part of it. But it is not a simple matter to meet its special requirements for transparency, color, safety, airtightness, etc. In addition to studying the structural design and manufacturing process of the product, the formula design of the product is also a very important aspect. Take the white bottle we produce as an example. Although it is called PE bottle, it is not made of pure PE resin. Some blending materials and additives such as PP and color masterbatch are added to it. Modification, because the pure use of PE resin cannot meet our product requirements, and the process of finding some additives and additions that can modify the resin is called "recipe design". The key factor for the success of formula design is the selection of raw materials at first. According to data, for a plastic product, if the trial production of the product fails, errors in raw material selection account for about 23%. This requires us to understand the nature of the raw materials.
1. The most commonly used general-purpose thermoplastics are PE, PP, PVC, and PS.
1). Polyethylene (PE)
PE is one of the most produced plastic varieties, accounting for about 30% of the total plastic production. PE can be mainly divided into three types: low-density polyethylene (DPE), high-density polyethylene (HDPE), and linear low-density polyethylene (DPE). DPE-good processability, general mechanical properties, but good impact resistance; The heat is not good, but the embrittlement temperature is low; the environment resistance is good, and it can withstand various non-strong oxidizing acids at room temperature, and the electrical insulation is very good. DPE adhesives have poor printability. DPE is mainly used for agricultural greenhouse film, mulch film, light packaging film, and daily-use injection molding products. After cross-linking, it can be used as cable material. The mechanical properties and heat resistance of HDPE are slightly better than DPE, and other properties are basically the same, but the rigidity is greater than DPE. HDPE is mainly used for heavy packaging film, woven bag, tear film, packing tape, injection molding products, various hard tubes, hollow products, fishing wire nets, etc. In addition to the properties of DPE and HDPE, DPE has tensile strength, tear strength, ring stress cracking resistance, low temperature resistance, impact resistance, toughness, rigidity, heat resistance, oil resistance, puncture resistance and transparency. Better than DPE and HDPE. The melt viscosity of DPE is relatively high, and its processability is not as good as that of DPE and HDPE. DPE is mainly used to produce ultra-thin films. In addition, we can also produce woven bags, hollow products, injection molding products and pipes, etc.
2). Polyvinyl chloride (PVC)
Polyvinyl chloride is a polymer formed by the polymerization of vinyl chloride monomer, and its output is second only to PE, ranking second. The VC content of sanitary grade PVC is lower than 10×10, which can be used in food and medicine. Compared with PE, PVC has the advantages of high hardness, wear resistance, corrosion resistance, high strength, and natural resistance, and is widely used to replace metal and wood. PVC is difficult to process, and its melting temperature is close to the decomposition temperature. Therefore, plasticizers and stabilizers are often added during processing. Among them, about 7 parts of stabilizers are added to hard products, and about 2 to 4 parts are added to soft products. PVC resin is mainly used in the production of various films, various boards, sheets, pipes, hollow products, cables, various injection molding products, artificial leather, floor leather, Tang plastic toys, etc.
3). Polypropylene (PP)
PP has good electrical properties and chemical stability, and its mechanical properties and heat resistance are higher than PE. The reinforced PP can be used as engineering plastics. PP has good fiber-forming properties and fatigue resistance, and the hinges made of it last hundreds of thousands of times; PP has good low-temperature impact resistance, high molding shrinkage, and low product precision; but PP has the most balanced performance among general-purpose thermoplastic resins. good kind. PP is mainly used for film, PP film has good transparency, good gloss, better strength after two-way stretching, and strong sound when rubbed by hand. It is used for high-end moisture-proof packaging, such as clothing and cigarettes. PP can be used for plastic sheeting to produce beverage cups, ice cream boxes, etc.; PP can also be used to produce tear film, packing tape, braided tape and qualified wire. PP injection molding products are mainly auto parts, home appliance parts, daily products, and medical appliances.
4). Polystyrene (PS)
The main advantages of PS are good transparency, light transmittance up to 88%~92%, refractive index 1.59~1.60, PS has good electrical insulation, high dimensional stability, easy molding and coloring. PS has poor wear resistance, poor impact resistance, poor weather resistance, and low heat resistance, so it is rarely used in industry. PS foam plastic is the largest use of PS, its density is only 0.016g/cm, and it is the most commonly used in the packaging industry at present. PS injection molding products can be used to produce combs, children's toys, tape boxes, etc., as well as optical instrument accessories, optical glass, lampshades, electrical accessories, instrument parts, etc.
2. General engineering plastics
Engineering plastics refer to a type of resin that has high strength and can be used in engineering at high temperatures. There are ABS, PA, POM, PC, PET, PBT, etc.
<!--[if !supportLists]-->3. <!--[endif]-->General thermosetting material
Phenolic resin (PF), etc.
4. Other types of plastics and functional plastics
Polyurethane resin (PU), polysulfone (PSF), etc. Although there are many types of plastics with various properties, to meet the specific requirements of the product, it is necessary to modify the plastics, which requires adding suitable additives to the resin. Take the PE bottle as an example: the color masterbatch added in it is a kind of auxiliary agent, called colorant. There are many types of additives, which can be roughly divided into: plasticizers, stabilizers, colorants, flame retardants, tougheners, antioxidants, foaming agents, etc. The purpose of formulation design is to select suitable additives, improve resin processing performance, intrinsic performance and reduce cost. There are hundreds of additives that can be used in formulation design, and hundreds of resins that can be blended. It is impossible to find a needle in a haystack to choose the right one. Formula design must be carried out according to certain principles.
1. Design according to the purpose of the product
As far as HDPE bottles are concerned, oil resistance modification is required for oil filling; barrier modification is required for carbonated beverages; black coating is required for photosensitive drugs; PP injection chairs need low-temperature impact modification in the north for In underground mines, anti-static and flame-retardant modifications must be carried out.
2. Design according to the compatibility of additives and resin
3. Design according to the processing resistance of additives;
4. Design according to the processing method;
For example, in the manufacture of PVC film - the blow molding method often uses internal lubricants, and the calendering method uses external lubricants.
5. Design according to the source and cost of additives;
When it can be used instead, try to use auxiliaries with wide sources, convenient procurement and low cost.
6. Design according to the safety of additives;
For pharmaceutical packaging, it is necessary to choose safe and non-toxic (or low-toxic) additives. With these basic principles as a guide, we can do it in a targeted manner when designing formulas. For the formula design of but variable can be used - step-by-step method, golden section method, bisect method, batch experiment method, etc. For multi-variable formula design, the orthogonal method can be used.
Now list several examples of modified formulations for reference:
1. Pure PVC cannot be plasticized, and additives such as plasticizers and stabilizers must be added. Adding a plasticizer can weaken the force between molecules and increase the mobility between molecules, thereby reducing the processing melting temperature, which is lower than the decomposition temperature of PVC. Adding a heat stabilizer can inhibit the de-HC reaction of PVC, increase the thermal decomposition temperature of PVC, and make it higher than the melting processing temperature of PVC.
PVC general pipe formula:
PVC (SG-4) 100 Bast 0.8
Tribasic lead sulfate 4 Paraffin wax 1
Dibasic lead phosphite 0.8 CaCo3 5
PbSt 1.2 Carbon black 0.01
2. The impact strength of PS is the worst variety among plastics, and rubber is often used for impact modification, such as styrene-butadiene rubber, ethylene-propylene rubber, SBS and ABS.
PS 85%
Styrene Butadiene Rubber 15%
The impact strength of this formula is 8 times higher than that of pure PS.
3. PET can be blended with PBT, PA, PC, DPE, EVA, ethylene propylene rubber, chlorinated SBS, etc.
PET 100
PBT 15~20
Talc powder 0.5
The impact strength of this formula can be increased by 50%.
4. PE antistatic formula
PE 100
Glycerol monopalmitate 5
The surface resistivity of this formula is 9.55*1012Ω.
Summary:Plastic formula must be tested in practice to be successful.
