The application of lubricants in plastic products

Lubricants are essential functional additives in plastic production. By reducing the friction inside the plastic melt and between the melt and processing equipment, they improve processing fluidity, avoid melt adhesion to equipment, and prevent surface defects (such as scratches and pitting) on the product. At the same time, they optimize the surface gloss and demolding properties of the product. In plastic processing (such as injection molding, extrusion, blow molding), lubricants can reduce processing temperature and energy consumption, improve production efficiency, and are suitable for almost all plastic categories such as PE, PP, PVC, PET, ABS, etc. According to their mode of action, they are divided into internal lubricants (improving the internal fluidity of the melt) and external lubricants (reducing the friction between the melt and equipment). Currently, they are developing towards high efficiency, low migration, environmental compatibility, and multifunctionality, which is the core support for balancing plastic processability and product quality.

1、 The core mechanism of lubricants: bidirectional optimization of processing and performance

1. Internal lubrication function: reduce melt viscosity and improve fluidity

Internal lubricants have good compatibility with plastic resins, can penetrate between molecular chains, weaken intermolecular forces, reduce segment friction, and lower melt viscosity:

Effect: Make plastic flow more easily during processing, fill molds more fully (such as for complex injection molded parts without missing materials), reduce extruder screw torque and injection pressure;

Representative products: butyl stearate, dioctyl adipate, polyethylene glycol;

Adaptation scenarios: PVC profile extrusion, PP thin-walled injection molding production, to avoid product deformation caused by poor melt flowability.

2. External lubrication function: forms an isolation film, improves demolding and surface

External lubricants have poor compatibility with plastics and migrate to the surface of the melt during processing, forming a lubricating film that isolates direct contact between the melt and equipment (screws, molds)

Effect: Prevent melt adhesion equipment (such as extrusion film sticking rollers, injection molded parts sticking molds), reduce surface scratches and burrs on products, and improve surface glossiness;

Representative products: stearic acid, calcium stearate, paraffin wax, microcrystalline paraffin wax;

Adaptation scenarios: PE blown film, ABS household appliance shell injection molding, PVC pipe extrusion, ensuring continuous and smooth processing and improving product appearance quality.

3. Collaborative Assistance: Balancing Multiple Needs

Some lubricants have other functions, such as calcium stearate and zinc stearate, which are both external lubricants and auxiliary components of PVC heat stabilizers; Polyethylene glycol based lubricants can enhance the anti-static properties of plastics, achieving a synergistic effect of "lubrication+stability/anti-static":

Typical application: In the production of PVC cable materials, calcium stearate simultaneously solves lubrication and thermal stability problems, simplifying the formula; Polyethylene glycol lubricant is used for PE food packaging film, balancing fluidity and anti-static requirements.

2、 Mainstream lubricant types and compatible plastics: precise matching of characteristics and scenarios

Different lubricants have significant differences in compatibility, heat resistance, and lubrication efficiency, and should be selected based on the type of plastic, processing technology, and product use:

1. Fatty acids and their derivatives (stearic acid, stearic acid salts): universal lubricants

Core advantages: low cost, balanced lubrication effect, with both internal and external lubrication functions, and some can assist in thermal stability;

Representative products: stearic acid (SA), calcium stearate (CaSt ₂), zinc stearate (ZnSt ₂), magnesium stearate (MgSt ₂);

Suitable for plastics: PE, PP, PVC, ABS;

Typical applications: PP injection molded lunch boxes (to improve demolding), PVC pipes (anti sticking mold+auxiliary thermal stability), ABS toys (to improve surface gloss), with a typical addition amount of 0.1% -1.0%.

2. Ester lubricants (butyl stearate, dioctyl adipate): the main internal lubricant

Core advantages: Good compatibility with resin, high internal lubrication efficiency, and no impact on product transparency;

Compatible plastics: PVC, PET, PC, transparent PP;

Typical applications: PVC transparent film, PET beverage bottle preforms, PC lamp covers, to avoid fogging caused by the precipitation of internal lubricants, with an added amount of 0.3% -2.0%.

3. Paraffin wax (paraffin wax, microcrystalline paraffin wax, polyethylene wax): the main lubricant for external lubrication

Core advantages: Strong external lubrication effect, moderate heat resistance (processing temperature ≤ 200 ℃), can significantly improve the surface gloss of products;

Representative products: fully refined paraffin wax, microcrystalline paraffin wax (MPW), polyethylene wax (PE wax);

Compatible plastics: PE, PP, ABS, PS;

Typical applications: PE shopping bag blown film (anti sticking roller), PP woven bag wire drawing (improves filamentability), ABS home appliance shell (enhances surface smoothness), with an addition amount of 0.2% -1.5%.

4. Polyether (polyethylene glycol PEG): Special functional type

Core advantages: Adjustable compatibility, combining lubrication and anti-static functions, low migration, environmentally friendly, in line with food contact standards;

Compatible plastics: PE, PP, PET, food grade PVC;

Typical applications: PE food wrap, PP microwave lunch boxes, PET food packaging bottles, to prevent lubricant migration and contamination of food, with an added amount of 0.2% -0.8%.

3、 Application Practice of Lubricants in Key Plastic Products: Scenario based Formula Design

1. Polyolefin products (PE, PP): Balancing processing efficiency and surface quality

PE and PP have good processing fluidity, but lubricants are needed to optimize demolding and surface gloss. The commonly used compound is "paraffin wax+stearate":

PE agricultural film blow molding:

Formula: PE raw material+0.3% microcrystalline paraffin+0.2% calcium stearate+0.15% antioxidant 1076;

Process: blown film temperature of 150-180 ℃, blowing ratio of 2.5-3.0;

Effect: The film has no adhesive roller phenomenon, the surface is smooth without scratches, the light transmittance is greater than 85%, and the winding is smooth without adhesion.

PP thin-walled injection molded parts (such as phone holder):

Formula: PP raw material+0.5% polyethylene wax+0.3% butyl stearate+0.2% antioxidant 168;

Process: Injection molding temperature 180-200 ℃, injection molding pressure 80-100MPa;

Effect: The melt filled mold is quickly and fully filled, with no shortage or shrinkage marks, smooth demolding, and the surface glossiness of the product is ≥ 90.

2. PVC products: lubrication and thermal stability in synergy

The processing temperature of PVC is close to the decomposition temperature, and a lubricant is needed to reduce the processing temperature. At the same time, a heat stabilizer is used, commonly using a combination of "ester internal lubrication+stearate external lubrication":

Extrusion of PVC door and window profiles:

Formula: PVC resin+0.8% butyl stearate (internal lubrication)+0.5% calcium stearate (external lubrication+auxiliary thermal stability)+2.0% calcium zinc composite thermal stabilizer;

Process: Extrusion temperature 150-170 ℃, traction speed 5-8m/min;

Effect: The surface of the profile is smooth and free of blemishes, the size is stable, the extruder screw has no material accumulation, and the production efficiency is increased by 15%.

PVC transparent hose extrusion:

Formula: PVC resin+1.0% dioctyl adipate (internal lubrication)+0.3% stearic acid (external lubrication)+1.5% epoxy soybean oil (plasticizing+lubrication synergy);

Process: Extrusion temperature of 140-160 ℃, cooling temperature of 40-50 ℃;

Effect: The hose is transparent and fog free, with a smooth surface, no creases or adhesions when bent.

3. Engineering plastic products (PET, PC, ABS): temperature resistance and precise surface control

The processing temperature of engineering plastics is high (PET: 260-280 ℃, PC: 280-320 ℃), requiring high-temperature resistant lubricants to avoid decomposition and affecting product performance:

PET beverage bottle preform injection molding:

Formula: PET raw material+0.4% polyethylene glycol (PEG-6000)+0.2% hypophosphite 168;

Process: drying temperature of 160 ℃, injection molding temperature of 270-280 ℃;

Effect: The surface of the bottle blank is smooth and free of sprue marks. After blow molding, the bottle body is transparent without yellowing or scratches, and the demolding efficiency is improved by 20%.

ABS Home Appliance Shell Injection Molding:

Formula: ABS resin+0.6% microcrystalline paraffin+0.4% zinc stearate+0.3% antioxidant 1010;

Process: Injection molding temperature 220-240 ℃, mold temperature 60-80 ℃;

Effect: The surface gloss of the shell is uniform, without scratches or burrs, and the retention rate of impact strength is greater than 95%, meeting the appearance and performance requirements of household appliances.

4. Food contact plastics: low migration, environmental priority

Food contact plastics have strict requirements for the toxicity and migration of lubricants, and products that comply with GB 9685 and EU No. 10/2011 standards must be selected

PP microwave lunch box injection molding:

Formula: PP raw material+0.3% polyethylene glycol (PEG-4000)+0.1% calcium stearate+0.1% antioxidant 1010;

Effect: The migration amount of lubricant is less than 0.01mg/kg, which meets food grade standards. The surface of the lunch box is smooth and easy to clean, and it can withstand microwave heating at 130 ℃ without any odor.

PE food preservation film blown film:

Formula: PE raw material+0.2% polyethylene glycol (PEG-2000)+0.15% butyl stearate;

Effect: The film has no adhesion, a smooth surface, and no risk of migration when in contact with food, ensuring the freshness of the food.

4、 Application Challenges and Development Trends

1. Existing challenges

Difficult compatibility balance: Excessive internal lubricant can easily precipitate and cause the product to become sticky, while excessive external lubricant can easily migrate and affect surface adhesion (such as printing and painting);

Processing temperature adaptation: Engineering plastics have high processing temperatures, and ordinary lubricants are prone to decomposition and failure, requiring specialized high-temperature resistant products;

Environmental compliance pressure: Some traditional lubricants (such as heavy metal stearate) do not comply with EU RoHS and food contact standards, limiting high-end scenarios.

2. Development Trends

Efficient and low migration: Develop high molecular weight lubricants (such as modified polyethylene wax), reduce migration through molecular chain entanglement, and adapt to food and pharmaceutical packaging;

Environmentally friendly and multifunctional: Developing bio based lubricants (such as castor oil derivatives and plant wax) that are non-toxic and biodegradable, while also possessing lubrication, antioxidant, and anti-static functions;

Precision adaptation: Develop specialized high-temperature resistant lubricants for specific plastics (such as PC and PET processed at high temperatures), and develop fog free lubricants for transparent products;

Composite integration: Develop "lubrication+thermal stability+antioxidant" composite additives, simplify formulas, reduce processing costs, such as complex products of stearic acid salts and antioxidants.

5、 Summary: Lubricants - the "balance link" between plastic processing and quality

From the smooth blow molding of PE film, to the stable extrusion of PVC profiles, to the exquisite appearance of ABS household appliance shells, lubricants have become the key to balancing efficiency and quality in plastic production by optimizing processing fluidity, improving demolding, and enhancing surface quality. It is not only a "processing aid", but also directly affects the qualification rate of plastic products (such as reducing surface defects), production costs (such as reducing energy consumption), and application scenarios (such as food contact compliance). In the future, with breakthroughs in the research and development of efficient, low migration, and environmentally friendly multifunctional lubricants, the plastic industry will be further promoted towards high-end and green development, providing support for the production of more high demand plastic products.