L2: Packaging Materials and Substrates - Part B

Paperboard (Cont.) - Corrugated

Description: Corrugated paperboard is a versatile and widely used packaging material, particularly for shipping. It consists of multiple layers of paperboard, with a fluted layer sandwiched between two liner boards.

Key Points:

• Components:

  • Liner: The outer layers of the corrugated board, providing strength and surface for printing.

  • Corrugated Medium (Fluting): The fluted layer, providing cushioning and structural support.

  • Adhesive: Binds the layers together.

  
  

• Types:

  • Single Face: One liner + one medium.

  • Single Wall: Two liners + one medium.

  • Double Wall: Three liners + two mediums.

  • Triple Wall: Four liners + three mediums.

  
  

• Flutes: The shape and size of the corrugated medium, influencing the board's strength and stiffness.

• Grammage: The weight of the paperboard per square meter, expressed in grams per square meter (gsm).

• Corrugator: The machine used to manufacture corrugated paperboard.

• Directions:

  • Machine Direction (MD): The direction the paperboard travels through the corrugator.

  • Cross Machine Direction (CD): Perpendicular to the MD, often the direction of the flutes.

  • Thickness Direction (ZD): The direction of the board's thickness.

  
  

• ECT (Edgewise Crush Test): Measures the force required to crush a piece of board standing on its edge with flutes vertical. This test predicts the compression strength of a corrugated box. (Twede and Selke 2008)

Corrugated Paperboard Box

Description: Corrugated paperboard boxes are commonly used for packaging and shipping. They offer strength, durability, and protection for various products.

Key Points:

• Dimensions:

  • Length: The greater of the flap opening dimensions.

  • Depth (Height): The inside dimension between the top and bottom inner flaps.

  • Order of Dimensions: Indicates the location of the opening.

  
  

• Types:

  • Regular Slotted Containers (RSCs): The most common type, with varying flap styles for added strength. Can be used to make "box and lid" configurations.

  • Die-Cut Containers: Customized shapes, like pizza boxes.

  • Multi-Component Designs: Boxes with multiple parts, offering flexibility and functionality.

  
  

Print and Corrugated

Description: Corrugated paperboard can be printed using various methods to enhance its appearance and provide branding.

Key Points:

• Printing Methods:

  • Post Print: Printing after the corrugated board is formed.

  • Pre Print: Printing before the corrugated board is formed.

  • Litho Label or Lamination: Applying labels or laminates to the corrugated board.

  
  

Plastics

Description: Plastics are versatile materials derived from crude oil, offering lightweight, formability, and durability. They are widely used in packaging due to their diverse properties and applications.

Key Points:

• Monomers: Small molecular fragments that join together to form polymers.

• Polymers: Large molecules composed of repeating monomer units.

• Natural Polymers: Occur in nature and can be extracted, often water-based. Examples include silk, wool, DNA, cellulose, and proteins.

• Synthetic Polymers: Include plastics, commonly used in packaging and found in households. Examples include nylon, polyethylene, and polypropylene.

Two Classes of Plastic

Description: Plastics are categorized into two main classes based on their response to heat: thermosets and thermoplastics.

Key Points:

• Thermoset Plastics (Thermosetting Plastics):

  • Curing Process: Polymers cross-link during curing, forming irreversible chemical bonds.

  • Solid State: Remain permanently solid even when heated.

  • Examples: Epoxy, melamine formaldehyde, polyester.

  
  

• Thermoplastics:

  • Curing Process: Curing is reversible, with no chemical bonding.

  • Remeltable: Can be remelted into a liquid when heated.

  • Commonly Used for Packaging: Due to their versatility and recyclability.

  • Examples: Polyethylene, polypropylene, polystyrene, nylon.

  
  

Thermoset Plastic

Description: Thermoset plastics offer high temperature resistance, excellent aesthetics, and dimensional stability. However, they are not recyclable or remoldable.

Key Points:

• Pros:

  • High temperature resistance.

  • Excellent aesthetic appearance.

  • High levels of dimensional stability.

  • Cost-effective.

  
  

• Cons:

  • Cannot be recycled.

  • Cannot be remolded or reshaped.

  
  

Thermo Plastics

Description: Thermoplastics are highly recyclable, impact-resistant, and can be remolded or reshaped. They are generally more expensive than thermosets.

Key Points:

• Pros:

  • Highly recyclable.

  • High-impact resistance.

  • Remolding/reshaping capabilities.

  • Chemical resistant.

  • Eco-friendly manufacturing.

  
  

• Cons:

  • Generally more expensive than thermosets.

  
  

Plastic Properties

Description: The physical properties of plastics are influenced by their molecular structure, particularly crystallinity.

Key Points:

• Crystallinity: The relative amount of amorphous and crystalline areas in the polymer.

• Effect of Crystallinity:

  • Increased Crystallinity:

    • Increased density, tensile strength, and compression strength.

    • Decreased permeability and clarity.

    
    

  
  

• Properties:

  • Tensile Strength: Resistance to stretching.

  • Tear Strength: Resistance to tearing.

  • Impact Strength: Resistance to impact.

  • Chemical Stability: Resistance to chemical degradation.

  • Moisture and Gas Barrier Properties: Ability to prevent moisture and gas permeation.

  • Heat Sealability: Ability to be sealed using heat.

  
  

Polyethylene (PE)

Description: Polyethylene (PE) is a widely used thermoplastic, available in various densities, each with unique properties.

Key Points:

• Types:

  • Low-Density Polyethylene (LDPE): Flexible, translucent, commonly used for bags, shrink wrap, and coatings.

  • Linear-Low Density Polyethylene (LLDPE): Flexible, translucent, commonly used for stretch wrapping.

  • High-Density Polyethylene (HDPE): More opaque and rigid than LDPE/LLDPE, good barrier properties, commonly used for bottles, bags, and liners.

  
  

• Density: HDPE > LLDPE > LDPE.

• Properties:

  • Flexible.

  • Natural milky color, translucent.

  • Toughness, flexibility, and relative transparency.

  • Heat sealability.

  • Resistance to acids, bases, and vegetable oils.

  
  

Low-Density Polyethylene (LDPE)

Description: LDPE is a flexible, translucent polyethylene commonly used for various packaging applications.

Key Points:

• Common Packaging Applications:

  • Bags for dry cleaning, newspapers, bread, frozen foods, fresh produce, and household garbage.

  • Shrink wrap and stretch film.

  • Coatings for paper milk cartons and hot/cold beverage cups.

  • Container lids.

  • Squeezable bottles (e.g., honey and mustard).

  
  

Linear Low-Density Polyethylene (LLDPE)

Description: LLDPE is a flexible, translucent polyethylene with good barrier properties and stiffness. It is commonly used for stretch wrapping.

High-Density Polyethylene (HDPE)

Description: HDPE is a more opaque and rigid polyethylene with good barrier properties and strength. It is commonly used for bottles, bags, and liners.

Key Points:

• Flexible.

• Natural color is milky white, but more opaque/rigid than LDPE/LLDPE.

• Good barrier properties and stiffness.

• Well suited to packaging products with a short shelf life, such as milk.

• Higher tensile strength compared to other forms of polyethylene.

  
  

• Common Packaging Applications:

  • Bottles for milk, water, juice, cosmetics, shampoo, dish and laundry detergents, and household cleaners.

  • Bags for groceries and retail purchases.

  • Cereal box liners.

    
    

Polypropylene (PP)

• Good for hot-fill liquids

  • Good chemical resistance

  • Strong

  • Used as a film in snacks, cookies, cakes and right for thermoformed containers for things like yogurt (called thin wall packaging)

• Common packaging applications:

  • Containers for yogurt, margarine, takeout meals, and deli foods medicine bottle, bottle caps and closure

  • Bottles for ketchup and syrup

Polyethylene terephthalate (PET)

• Excellent barrier to oxygen, water, and carbon dioxide

• High impact capability

• Excellent resistance to most solvents

• Moving into cosmetics and even beer

• Safe, but this plastic is know to allow bacteria to accumulate (don’t reuse after use)

Polyvinyl chloride (PVC)

• High impact strength, brilliant clarity

• Excellent processing performance

• Good resistance to grease, oil and chemicals

• Today more popular in construction than in packaging

• Concerns about manufacturing and migration of chemicals into food

• Commonly used for blister packs and clamshells

Polystyrene (PS)

• Rigid container having very thin wall (yogurt)

• Excellent moisture barrier for short shelf life products

• Poses a health risk, leaching potentially toxic chemicals, especially when heated

• Common packaging applications

  • Food service items, such as cups, plates, bowls, cutlery, hinged takeout containers (clamshells), meat and poultry trays, and rigid food containers

Bio-based polymers

• Made from biomass like sugar cane or corn starch which are renewable resources

• Ex. polylactic acid (PLA)

• Generally expensive

Plastic Cushion Foams

Description: Plastic cushion foams are lightweight, flexible, and provide cushioning and shockproofing capabilities. They are commonly used for packaging and protection.

Key Points:

• Expanded Polyethylene (EPE): Made by expanding polyethylene beads with steam, pressure, and a blow agent. Light, flexible, and strong cushioning capabilities.

• Expanded Polystyrene (EPS): Made by expanding polystyrene beads with steam, pressure, and a blow agent. Low thermal conductivity, excellent insulation properties, light, rigid, and requires tooling (mold). Lower material cost than EPE, but recycling is a concern.

Labels

Description: Labels are essential for product identification, branding, and information. They have evolved from glue-applied labels to self-adhesive and in-mold labels.

Key Points:

• History:

  • 1900s: Glue-applied labels.

  • 1950s: Stephen Avery invents the self-adhesive (pressure-sensitive) label.

  • Today: In-mold labels and sleeves.

  
  

• Production:

  • Roll-to-roll webpress: Used to print labels.

  • Label Material: Paper or film, with adhesive on the back and a liner (silicone coating).

  • Label Finish: Plain, laminated, or varnished.

  
  

• Substrates:

  • Paper: The first and most common material.

  • Plastic Film: Provides a "no label" look, durability, versatility, and scuff resistance.

  
  

• Storage Requirements:

  • Use within 6 months.

  • Adhesive can bleed.

  • Stored on flat edge, not face.

  • Permanent curvature.

  
  

Wet Glue Labels

Description: Wet glue labels require adhesive to be applied before application. They are commonly used for beer and canned goods.

Key Points:

• AKA "gummed."

• Needs to have an adhesive applied before application.

• Beer, canned goods.

• Choose substrate based on application and storage.

In-Mold Labels

Description: In-mold labels are preprinted and precut, applied during manufacturing by placing them in the mold before molten plastic is injected.

Key Points:

• Provided preprinted and precut in stacks.

• Applied during manufacturing (placed in the mold).

• Molten plastic is then injected.

Sleeves

Description: Sleeves, also known as shrink sleeves, are labels that shrink around a container, providing tamper evidence and the ability to combine two packs into one.

Key Points:

• AKA Shrink Sleeves.

• Provides tamper evidence option.

• Can combine two packs into one.

• Reverse printing is possible.

Other Labels

Description: Other types of labels include UID (Unique Identifier) labels and NFC (Near Field Communication) labels, offering advanced features for product identification and communication.

Key Points:

• UID (Unique Identifier) Labels: Serials, barcodes, QR codes, only in silver and black.

• NFC (Near Field Communication) Labels: Smart tags equipped with wireless radio technology, emitting signals at a short distance. Most smartphones and devices can read them.

Aluminum Foil

Description: Aluminum foil is a thin, flexible material offering excellent barrier properties, corrosion resistance, and stability in cold conditions. It is commonly used in packaging for its protective qualities.

Key Points:

• Advantages:

  • Resistant to corrosion (oxidation).

  • Non-absorbent.

  • Stable in cold conditions.

  • Mostly no toxic residues or reaction.

  • Conductive.

  
  

• Disadvantages:

  • Loses strength above 150 degrees C.

  • Not ductile.

  • Prone to flex cracking.

  • Corrodes with strong acids, mild alkalines (soaps), and salts.

  
  

• Packaging Applications: Combined with coatings, inks, papers, paperboards, and plastic films. Example: Tetra Pak.

Multi-Layer Materials

Description: Multi-layer packaging materials are commonly used, particularly for food packaging, to enhance barrier properties, strength, and functionality.

Key Points:

• Multi-layers of packaging materials are commonly used (particularly for food packaging): typically 2~8 layers.

• Layers of different plastics.

• Combinations of plastics and paperboard or metal.

Key Points

Description: Packaging uses a wide range of materials and substrates, each with its own advantages and disadvantages. The ideal packaging material is flexible, resilient, environmentally friendly, and cost-effective, but achieving all these qualities is challenging.

Key Points:

• Packaging uses many complex materials and substrates.

• At the core of packaging, we have glass, metal, paperboard, corrugates, plastic, labels, and foil.

• We are constantly looking to work with substrates that are flexible, resilient to the environment, good for the environment, and cheap...an almost impossible dream.

• Mixing materials and substrates means difficulty recycling.

Table of Packaging Materials and Substrates