In the production of flexible packaging, pre-press equipment, plastic film is the most commonly used packaging materials, including PP, PE, NY, PET, PVC, PVDC coating film. In order to improve the quality, characteristics or processing properties of the above packaging materials, and facilitate subsequent operations, some auxiliary chemicals, that is, plastic film additives, are often added in the actual production of the materials. Plastic film additives are one of the key factors to ensure smooth production and quality of flexible packaging products. This article will focus on the types, properties, and precautions for use of commonly used plastic film additives.
Common plastic film additives
Anti-caking agent
In the process of processing, using and storing plastic film, the adjacent film layers are bonded together under heat and pressure, and are not easy to separate. In order to solve such problems, it is necessary to add an anti-caking agent to make it easy to stratify and certify, and it is easy to open after bag making, so the anti-caking agent is also called an opening agent.
Anti-caking agents can be divided into inorganic and organic categories. The inorganic anti-caking agent is usually dispersed in the plastic film in the form of fine particles, so that the surface of the plastic film becomes rough, and the microscopic level of "bridge" is achieved, so that the adjacent film layers are filled with gas screen printing, thereby avoiding the interlayer between the film layers. Bonding. Commonly used inorganic anti-caking agents are mica, talc, diatomaceous earth, synthetic silicon, kaolin and calcium carbonate. Organic anti-caking agents are generally naturally mobile and can crystallize on the surface of plastic film to prevent bonding between adjacent film layers. Commonly used organic anti-caking agents are ammonia compounds, organic stearates, metal stearic acid compounds, silicone resins, and polytetrafluoroethylene (PTFE).
2. Slip agent
The slip agent reduces the friction between the plastic film, the plastic film and the device, and makes the film surface smoother, which makes the flexible packaging production and the operation on the packaging machine smoother.
There are many types of slip agents, including traditional ammonia slip agents and specialized non-migratory slip agents. Conventional ammonia slip agents are synthesized based on fatty acid amino compounds (primary amides, secondary amides, bisamides) and are not completely soluble in the polymer, so they gradually migrate to the surface of the plastic film and coat the plastic film. The surface, thereby reducing the coefficient of friction of the plastic film surface. Among them, the primary amide slip agent has a relatively small molecular weight packaging stream, which can rapidly migrate to the surface of the plastic film; the secondary amide and bisamide slip agent have a larger molecular weight than the primary amide slip agent. Lower volatility and better thermal stability.
Non-migratory slip agents such as siloxanes have very high molecular weights and are not able to diffuse and migrate in the polymer. Such slip agents reach the surface of the plastic film during the extrusion of the polymer, thereby reducing the coefficient of friction of the plastic film. Compared with the ammonia slip agent, the non-migratory slip agent does not migrate, so it is more stable, controllable, and the price is correspondingly higher.
In general, anti-adhesives can also act as a slip agent.
3. Plasticizer
Any substance added to a polymer that increases the plasticity of the polymer can be called a plasticizer. The main role of the plasticizer is to weaken the van der Waals force between the polymer molecules, thereby increasing the mobility of the polymer molecular chain. Lekai di-gel, reducing the crystallinity of the polymer molecular chain, manifested as polymer hardness, modulus, softening The decrease in temperature and embrittlement temperature, as well as the increase in elongation, flexibility and flexibility. In short, it is to increase the fluidity of the polymer during production and processing to improve the flexibility of the product.
Plasticizers are available in a wide variety of printers, with the largest use of phthalate plasticizers. In China, this type of plasticizer is mainly composed of dioctyl phthalate (DOP) and dibutyl phthalate (DBP). Relevant organizations in foreign countries have pointed out that phthalate plasticizers do not form chemical bonds with high-molecular substances such as plastics and rubber. They maintain their own independent chemical properties and have a certain active digital printing machine, so they are exposed to water. When it is fat, it will dissolve, and phthalates have reproductive toxicity, as well as mutagenic and carcinogenic effects, which can endanger the health of users. However, some experts pointed out that many of the tests are post-press equipment under certain conditions. The phthalate plasticizers are used under the existing specifications, and the harm to the human body is very weak. Despite this, many countries and organizations have strict requirements and control over the use of phthalate plasticizers.
4. Heat stabilizer
In order to maintain the intrinsic properties of the plastic film and prevent the aging decomposition of the plastic film at high temperatures, it is often necessary to add a heat stabilizer.
Because PVC monomer is unstable and easy to decompose in high temperature environment, heat stabilizer is mainly used in the processing of PVC and its copolymer. In the thermal processing of PVC, a small amount of molecular chain breaks and releases hydrogen chloride before the melt flow has been reached, and hydrogen chloride is a catalyst for accelerating the chain reaction of molecular chain rupture. If the ink balance is not eliminated in time, the polymer chain It will always crack into low molecular compounds, affecting the processing of PVC. Therefore, it is necessary to add a suitable alkaline substance to the PVC to immediately neutralize the decomposed hydrogen chloride, which is the principle of action of the heat stabilizer.
5. Antioxidants
In the process of manufacturing, processing, storing and applying plastic films, the oxygen infiltrated into the plastic film can react with most polymers, causing the polymer to degrade or crosslink, thereby changing the properties of the plastic film. Moreover, only a small amount of oxygen can make a significant change in the strength, appearance and performance of the plastic film. The oxidation reaction is faster under hot working and sunlight conditions.
Antioxidant is a substance that can effectively prevent or retard the oxidation of plastic film. It can decompose the substance produced in the oxidation process - hydroperoxide, generate stable inactive products, interrupt the chain reaction, or capture activity. Free radicals form inactive free radicals, thereby terminating the chain reaction. The role of antioxidants is to delay the current state of the oxidation process of plastic films and to ensure that they can be processed smoothly and extend their service life.
An antioxidant capable of decomposing a hydroperoxide is called a secondary antioxidant; an antioxidant capable of eliminating a reactive radical is called a primary antioxidant, and is mainly classified into an aromatic amine antioxidant and a hindered phenol antioxidant. The major category is the main body of antioxidants, accounting for more than 90% of the total. Aromatic amine antioxidants are inexpensive, and the anti-oxidation effect is significantly lithographic, but under the action of light and oxygen, it will cause different degrees of discoloration of the plastic film, which is more polluting, thus limiting its color in light or white plastic. The application in products is currently mainly used for high-fidelity printing of rubber products, and is rarely used in plastic films. The hindered phenolic antioxidant does not pollute the product, but the anti-oxidation effect is slightly poor, and the comprehensive effect is good, occupying a dominant position in the plastic film.
6. Antistatic agent
The plastic film itself is a good insulator activity, but in the process of production, circulation and use, due to friction will accumulate static charge, resulting in electrostatic adsorption and discharge, there are certain safety hazards. Therefore, an antistatic agent is generally added to a plastic film. In particular, food, medicine (such as milk powder, solid beverages, powders and other powders) and soft packaging of electronic products Huaguang Precision, this requirement is relatively high.
The antistatic agent can form a conductive layer on the surface of the plastic film, reduce the electric resistance, and transfer the static charge, thereby avoiding the formation of static electricity. On the other hand, the antistatic agent can also perform lubrication evaluation on the surface of the plastic film to reduce the friction coefficient, thereby suppressing and reducing the generation of static charges.
Currently used plastic film antistatic agents are mainly surfactants and hydrophilic polymers, the most commonly used of which are air moisture adsorbing surfactants. The lipophilic group of the air moisture adsorbing surfactant has a strong affinity with the resin and thus can penetrate or diffuse into the interior of the resin; and the hydrophilic group can form a conductive layer on the surface of the plastic film, or through hydrogen bonding The moisture in the air is combined with proofing to reduce the surface resistivity and accelerate the transfer of static charge. The antistatic agent can be further divided into an amine group and an amine group. Amine-based antistatic agents will produce some "micro-corrosion" on precision electronic products, and will be slightly greasy after precipitation. However, amine-free antistatic agents do not have these two types of problems, so they are widely used in food or Electronic product packaging. In actual production, a suitable antistatic agent should be selected according to the characteristics of the product.
7. Colorant
The coloring agent is also called color masterbatch Yachang, its role is to add color to the plastic film, ink-like coloring, can be divided into two major categories of pigments and dyes. The color masterbatch used for the flexible packaging plastic film is usually titanium dioxide, carbon black and calcium carbonate supported by a polyethylene resin. If it is a colorant used for food packaging, it should not contain fluorescent whitening agents in accordance with relevant regulations.
8. Processing aids
After melting, the polymer usually has a higher viscosity because of cohesion. In the processing of plastic film, as needed, the molten polymer will surely rub against the surface of the processing machine when passing through the narrow slit, gate, etc., but the friction is too great for the processing of the polymer. Especially in the case that the flow path is not smooth, it will reduce the fluidity of the molten polymer, and will also make the surface of the plastic film rough and lack luster, and at the same time cause the molten polymer to rupture or flow. Problems such as the road line. For this reason, it is necessary to add an auxiliary agent, that is, a processing aid, for the purpose of improving lubricity during processing, reducing friction, and reducing interface adhesion performance. The main components of processing aids are fluorine bombs, stearic acid and its salts. Processing aids have the functions of promoting melting, improving fluidity, anti-adhesion, anti-static and lubrication, which can improve processing efficiency, improve and stabilize the quality of plastic film, reduce energy consumption and extend equipment life.
Precautions for the use of plastic film additives
There are many types of plastic film additives. When selecting, it is necessary to consider the economy, compatibility, durability, processing suitability, synergy, weather resistance, toxicity, odor and migration.
In general, inkjet printing, plastic film additives do not undergo physicochemical changes during processing and use, and can be well retained inside or on the surface of the plastic film. However, since the additive is a monomer having a relatively small molecular weight and a high activity, under certain external conditions, these small molecule additives may migrate to the surface of the plastic film, undergo physical reactions such as friction, extraction, precipitation, thermal decomposition, oxidation, etc. After the chemical reaction, the digital printing machine will have a lower content, which will lead to the weakening or even disappearing of its function. Therefore, according to the actual production situation and the effect of use, the amount of additives used can be appropriately increased to compensate for the loss.
In addition, HP, some plastic film additives or their reaction products may enter the package through a poorly barrier plastic substrate, contaminating the packaged object, resulting in discoloration, odor, corruption, etc. of the packaged product. In terms of safety, the hazard is more serious. Therefore, when selecting a plastic film additive for soft packaging of food, the screen should first consider its safety and hygiene.
According to the provisions of GB9685-2008 "Sanitary Standards for the Use of Additives for Food Packaging Containers and Packaging Materials", additives for food packaging must meet the following conditions:
(1) At the time of contact with food, the level of additives that migrate to the food should not endanger human health under the recommended conditions of use;
(2) Ink supply when in contact with food, under the recommended conditions of use, the additives that migrate to the food should not cause changes in the properties of the food ingredient, structure or color and aroma;
(3) The additive used should be as low as possible in the packaging material on the premise of achieving the desired effect;
(4) The additives used should be produced under conditions of good production specifications, and the products must meet the corresponding quality specifications.
For flexible packaging manufacturers, in providing high-quality products to customers, the company should also play the role of “packaging consultant†and consider the most suitable plastic film additives for customers.
Concerned about surprises
Label: Types and applications of plastic film additives
Previous: Working principle and performance characteristics of ultra-fine grinding machine Next: Installation and commissioning of high-viscosity pump correctly
Hard Start Kits,Hard Start Capacitor,Ac Hard Start Kit,Hard Start Kit Air Conditioner
LONG TERM ELEC. CO., LTD , https://www.longterm-hvac.com