Hot Melt Ahesives InformationHot melt adhesives are solvent-free chemical compounds that are used to join materials.

 

They can be repeatedly softened by heat and hardened or set by cooling, allowing parts to be removed or repositioned during assembly.

 

Most hot melt adhesives solidify at temperatures below 180° F and become low viscosity fluids at temperatures above 180° F.

 

They form strong bonds, set rapidly upon cooling, and are relatively easy to handle. In general, hot melt adhesives store well and are less sensitive to water, moisture, and humidity than thermosetting or chemically curing adhesives.

 

Some products contain:

 

  • Acetals
  • Acrylics
  • Glues and gums
  • Natural or synthetic rubbers
  • Epoxy resins
  • Water-based resins
  • Wax-based binders
  • Styrene compounds
  • Vinyl esters

Commonly used chemical systems also include:

 

  • Polypropylene (PP)
  • Polysulphone
  • Polyurethane (PUR)
  • Polyetherimide
  • Polyolefin

Filled or reinforced compounds consist of resins with additional modifiers such as fillers, pigments, or chopped fibers.

 

Features

 

Hot melt adhesives vary in terms of material compatibility and features. Some products adhere to substrates made of:

 

  • Ceramics
  • Glass
  • Concrete
  • Masonry
  • Metal
  • Paper
  • Paperboard
  • Plastic

Hot Melt Adhesives Information Products that can bond dissimilar substrates such as metal to rubber are also available. In terms of features, hot melt adhesives that are designed for electrical and electronics applications often provide protection against the following:

 

  • Electrostatic discharge (ESD)
  • Electromagnetic interference (EMI)
  • Radio frequency interference (RFI)

Materials that are electrically conductive, resistive, insulating, or suitable for high voltage applications are also available.

 

Flame retardant materials reduce the spread of flames or resist ignition when exposed to high temperatures.

 

Dampening materials are used to form layers that can bend or flex without cracking or delaminating.

 

Thermal compounds and thermal interface materials absorb heat from electronic devices or electrical components. Threadlocking adhesives bind threads that are subject to transverse and axial loads against vibrational loosening.

 

Specifications

 

Selecting hot melt adhesives requires an analysis of mechanical, thermal, electrical and optical properties. Mechanical properties include:

 

  • Tensile strength (break)
  • Tensile modulus
  • Elongation

Thermal properties include:

 

  • Use temperature
  • Thermal conductivity
  • Coefficient of thermal expansion (CTE)

Thermal conductivity is the linear heat transfer per unit area for a specific temperature. CTE is the amount of linear expansion or shrinkage that occurs in a material with a change in temperature.

 

Resistivity, dielectric strength, and dielectric constant are important electrical properties for hot melt adhesives. Optical properties include index of refraction, a measure of the speed of light in a material.

 

Applications

 

Hot melt adhesives are used in many industries and applications. For example, some products are used in:

 

  • Aerospace
  • Automotive
  • Marine
  • Military
  • Photonics

    Hot Melt Adhesives Information

  • Optical applications
  • Tooling

Others are designed for use with:

 

  • Electronic devices
  • Electrical power products
  • High voltage applications
  • Semiconductors
  • Integrated circuit (IC) packaging

Materials that are suitable for medical, pharmaceutical and food processing applications meet requirements established by the Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA).

 

Original equipment manufacturers (OEMs) and repair, maintenance and overhaul (MRO) organizations also use hot melt adhesives.

 

Standards

 

9981252 - Adhesive, hot melt, polyamide, supported vinyl to hardboard. 

ASTM D1994 - Standard test method for determination of acid numbers of hot-meltadhesives. 

ASTM D4499 - Standard test method for heat stability of hot-melt adhesives. 

BS 5350-H3 - Methods of test for adhesives - part h3: determination of heat resistance of hot-melt adhesives.

DIN EN ISO 10363 - Determination of thermal stability of hot-melt adhesives. 

 

References

 

Image Credits:

 

Kanishaka Overseas | Tex Year | 3M Industrial Adhesives & Tapes

 

Read user Insights about Hot Melt Adhesives

Related Products & Services

  • Anaerobic Adhesives and Anaerobic Sealants

    Anaerobic adhesives and anaerobic sealants cure in the absence of air or oxygen.

  • Casting Resins

    Casting resins are pourable plastic or elastomer compounds that are used to cast parts, make molds, or form structures in place. They are mixed with a hardener, catalyst or activator and then poured into the sprue of open molds.

  • Cyanoacrylate Adhesives

    Cyanoacrylate adhesives are one-part acrylate adhesives that cure instantly on contact with mated surfaces through a reaction with surface moisture. Cyanoacrylates are often called super glues. 

  • Electrical and Electronic Resins

    Electrical and electronic resins includes adhesives, greases, pads, stock shapes, tapes, encapsulants, potting compounds, thermal interface materials, and electrically conductive substances used in electrical, electronics, and semiconductor applications.

  • Polymers and Plastic Resins

    Polymers and plastic materials are organic, synthetic or processed polymers that are supplied as raw materials. They typically consist of thermoplastic or thermosetting resins in the form of pellets, powders or liquid resins. These materials can then be molded into a variety of shapes for a wide range of uses.

  • Rubber Adhesives and Sealants

    Rubber adhesives and sealants are highly flexible, natural or synthetic materials that are used to join components or fill gaps between seams or on surfaces.

  • Thermal Compounds and Thermal Interface Materials

    Thermal compounds and thermal interface materials form a thermally conductive layer on a substrate, between components or within a finished product.