Plastics : How black plastic bags are made

Below is a simple explanation of how plastic black bags are made.

Main Ingredients:

• Clear plastic resin (LDPE/HDPE)
• Carbon black masterbatch (2-4%): Black coloring powder made from carbon particles and mixed into plastic

Masterbatch is a concentrated mixture of pigments and/or additives encapsulated in a carrier resin that is added to raw polymer materials to give them specific properties or colors during plastics manufacturing.

LDPE (Low-Density Polyethylene) and HDPE (High-Density Polyethylene) are two common types of polyethylene plastic with different molecular structures and properties.
LDPE is more flexible, softer and has a less crystalline structure. It is used in:

• plastic bags
• squeeze bottles
• flexible packaging.

HDPE is stiffer and stronger. Its common uses are: 

• milk jugs
• detergent bottles
• plastic lumber toys

LLDPE (Linear Low Density) is another type of PE  (Polyethylene) mainly used for stretch wrap and plastic films. Its more flexible than HDPE and stronger than LDPE. It has excellent stretch properties, good puncture resistance and it is easy to process

Its common are stretch films, food packaging, agricultural films, heavy-duty bags, industrial packaging and trash bags

Process:

• Clear plastic pellets are mixed with carbon black
• Both are heated together (160-220°C)
• The materials melt and blend completely
• They form a uniform black color
• We extrude them into film or bags

Extrusion is a manufacturing process where heated plastic material is forced through a die (shaped opening) to create a continuous product with a constant cross-section, like pipes, sheets, or profiles.

Key points:

Carbon black adds:

• Color to the plastic
• UV protection
• Strength
• Weather resistance
• Even mixing of carbon is crucial (Too little carbon = gray color , Too much carbon = brittle bags)

Quality control:

• We check color uniformity
• We test for UV resistance
• We ensure proper, even mixing
• We monitor the thickness of the bags

UV resistance is a material's ability to withstand exposure to ultraviolet light without degrading, fading, or losing its properties over time.

Carbon particles (Carbon Black):

What are carbon particles:

• It is a very fine black powder
• It is made by burning oil/gas with limited air
• Particles size: 10-500 nanometers
• It is pure carbon in particle form

Making process:

• Oil or natural gar is burned 
• We collect the soot (carbon particles)
• We process the soot into fine powder
• We package it for industrial use

Uses of carbon particles:

• They colors the plastic in black
• They adds UV protection
• They strengthens the materials
• They make rubber tougher
• They are used in tires, inks and plastics

Key Points:

• The carbon particles have a very strong black color
• Little quantity needed to produce the desired effects (2-4%)
• Improve material strength
• They provide UV protection
• They are a cost-effective colorant