Hot Melt Adhesives for Todays Applications

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Hot Melt Adhesives for Todays Applications

• H.B.Fuller

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Outline

• Introduction
• Typical Adhesive Properties
• Raw Materials

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Introduction

• Hot Melt Adhesive
• a thermoplastic, polymer based adhesive which
  is applied in the molten state at temperatures
  typically above 250F and which functions
  primarily by mechanical anchorage

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Introduction

• Benefits of Hot Melt Adhesives
• Fast Processing
• Environmentally Friendly
• Bond Impervious Surfaces
• Gap-filling
• Safe
• Efficient Shipment and Storage

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Comparison to Other Technologies
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Forms

• Pellets
• Pillow
• Bags
• Slats
• Cakes
• Bricks
• Bulk
• drum, pail, molten rail car

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bag
cake/brick
pillow
pellets
Some Hot Melt Forms
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Industries Served(need to change lists to
current website)

• Packaging
• Graphic Arts
• Nonwovens/Hygiene
• Tapes and Labels
• Product Assembly
• Automotive
• Textiles

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Equipment

• Application Methods
• Nozzle
• Slot Die
• Extrusion
• Wheel
• Screen Printing
• Melt Blown
• Spiral Spray

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Equipment

• Dispensing
• Drum unloaders
• Pail unloaders
• Melt reservoirs
• Pre-melters
• Vacuum Conveyance

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Typical Adhesive Properties

• Viscosity
• Color and Color Change
• Peel Adhesion Failure Temperature - Kraft paper
  (PAFT)
• Shear Adhesion Failure Temperature - Kraft paper
  (SAFT)
• Softening Point (Mettler)
• 180 Peel Adhesion (PSA)
• Shear Adhesion Failure Temperature - PSA (SAFT)
• Loop Tack

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Typical Adhesive Properties-continued

• Substrate Specific Adhesion
• -ambient
• -subambient
• -accelerated aging at elevated temperature
• Thermal Stability
• Mechanical Properties

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Typical Adhesive Properties

• Viscosity
• resistance to flow
• measured at relevant application temperature
  (250-
• 350F)
• knowledge of application conditions typical
• temperature
• shear rate
• Brookfield Thermosel (low shear)
• Dynamic Mechanical Analysis (low to high shear)
• Capillary Rheometer (high to very high shear)

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VISCOSITY

• Brookfield thermosel, measures the resistance to
  flow

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Typical Adhesive Properties

• Color and Color Change
• indicative of chemical purity, oxidation or
  oxidative tendencies
• subjective and quantitative
• measured before and after heat aging
• Several quantitative methods
• Gardner
• Saybolt
• Hunter

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Typical Adhesive Properties

• Peel Adhesion Failure Temperature (PAFT)
• -Non-PSA Hot Melts
• measures the resistance to deformation in a peel
  adhesion mode at elevated temperatures
• temperature ramped from 70 F at 1 F/min
• 100 gm weight, 1 x 1 specimen, Kraft paper
• run in triplicate

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Typical Adhesive Properties

• Shear Adhesion Failure Temperature for Packaging
  (SAFT)
• measures the resistance to deformation in a shear
  mode at an elevated temperature
• temperature ramped from 70 F at 1 F/min
• 500 gm weight, 1 x 1 specimen, Kraft paper
• run in triplicate

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Typical Adhesive Properties

• Softening Point
• measure of the temperature at which the adhesive
  begins to flow
• primarily influenced by melt point of wax or
  endblock Tg of Styrenic Block Copolymer
• Mettler, Ring and Ball methods most popular

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METTLER SOFTENING POINT

• Measures the temperature at which the hot melt
  begins to flow

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Typical Adhesive Properties

• 180 Peel Adhesion (PSAs)
• measures adhesion strength of PSA to Stainless
  Steel
• PSA is coated on film (1x 10strips)
• aged 24 hrs
• mated to SS with 4.5 lb roller
• bond separated at constant rate in a 180 peel
  mode
• data reported in Lbs./in

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Typical Adhesive Properties

• Loop Tack
• measures tack level of PSA to Stainless Steel
• PSA coated on film, cut into strips
• aged
• bent into loop, 1x 6
• mated to SS at constant rate (no pressure) 1x
  1
• removed at constant rate
• resistance to debonding is measured

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Typical Adhesive Properties

• Substrate Specific Adhesion
• unique to the application of interest
• use actual substrates
• bonds prepared in method to simulate actual
  production
• test at several different temperatures
• ambient
• subambient
• elevated
• test for bond strength, substrate destruction

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Typical Adhesive Properties

• Thermal Stability
• used to simulate pot stability of adhesive in
  melt
• age molten adhesive at typical pot temperature
• covered
• uncovered
• determine
• viscosity change
• color change
• formation of char, edge ring
• skin, gels

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Typical Adhesive Properties

• Mechanical Properties
• Ultimate Tensile - This is the maximum force
  needed to break a dogbone specimen
• Yield Point - This is the maximum stress a hot
  melt can withstand before undergoing perminant
  deformation

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Typical Adhesive Properties

• Mechanical Properties
• Elongation at Break- This is the distance a given
  length of sample will stretch before breaking
• Youngs Modulus - This is the ratio of stress over
  strain at very small stress values

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Typical Adhesive Properties

• Mechanical Properties
• Toughness- A combination of high tensile strength
  and high elongation
• Flexibility- A combination of low yield point,
  high elongation and low youngs modulus

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Raw Materials

• Polymer
• Tackifying Resins
• Diluents/Plasticizer
• Wax
• Antioxidants

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Raw Materials

• Role of Polymer
• Controls strength and flexibility
• Heat resistance, shear, impact resistance
• Dictated primarily by polymer type, molecular
  weight and amount

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Raw Materials- Polymer Content
Decreasing Increasing

• Higher Viscosity
• Increase Flexibility
• Increased Toughness
• Better Low Temperature
• Flexibility

• Lower Viscosity

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Raw Materials

• Role of Tackifying Resin
• Controls wetting
• Adhesion and tack
• Dictated by softening point (Tg) and
  compatibility with polymer

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Raw Materials- Tackifying Resin Content
Decreasing Increasing

• More Aggressive
• Increased Toughness

• Faster Speed
• Reduced Tack

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Raw Materials

• Role of Diluent/Plasticizer
• Controls wetting and flow
• Viscosity reduction, modulus and open time
  adjustment
• Dictated by MW and compatibility with polymer

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Raw Materials

• Role of Wax
• Controls set speed and open time
• Heat resistance and subambient adhesion
• Dictated primarily by crystallinity, melt
  point, and Mw/Mn

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Raw Materials-Wax Content
Decreasing Increasing

• Lower Viscosity
• Faster Rate of Set
• Less Aggressive Bonding

• Higher Viscosity
• Increased Flexibility
• More Aggressive Bonding