Applications of Polyurethane Dispersions
Environmental advantages coupled with increasing solvent price and the excellent physical properties of these adhesives have steadily expanded their use in textile coatings, fiber sizing, and adhesives for a number of substrates. One of the most important applications of aqueous polyurethane adhesive is as a heat activated adhesive.
Important industrial applications for polyurethane dispersion based adhesives include the following:
- Automotive (generally 2K) - Dashboards (foam to TPO/PVC, door panels (textile / wood / ABS) carpets, headliners). Requirements are good initial bond strength under low pressure and / or low activation temperature.
- Furniture (generally 2K) - Kitchens (decorative PVC foil to wood or MDF-formed door panels). High tack and long life is necessary.
- Footwear - Polyurethane dispersions are higher priced and less forgiving than solvent borne adhesive. Requirements are very high initial tack at low pressure and temperature, excellent water and plasticizer resistance and good adhesion to PVC / rubber /leather.
Polyurethane dispersion adhesives are also finding their way into food packaging applications. Table below shows a starting formulation for a waterborne polyurethane that is used as a heat sealing adhesive. It can be formulated as a thermoplastic or thermosetting system with the addition of isocyanate.
|
Component
|
Ingredients
|
Parts by Weight
|
Polyol
|
Sulfonated polyester polyol, 0.65 hydroxyl equivalents (Rucoflex XS-5570-55, Ruco Polymer Corp.)
|
667.8
|
|
Isocyanate
|
Hexamethyl diisocyanate (0.8 isocyanate equivalents)
|
54.9
|
Isophorone diisocyanate (0.327 isocyanate equivalents)
|
36.3
|
Waterborne Polyurethane Heat Sealable Coating4
The polyol and isocyanate mixture was heated to 80°C for 2.5 hrs. When the isocyanate content reached approximately 2.6%, the NCO-terminated sulfonated polyurethane pre-polymers were dispersed in 1138gm of deionized water. The water temperature before dispersing was 40°C. The resulting dispersion had a pH of 6.5.
Properties
|
Value
|
Dispersion
|
No VOCs, free of solvent, catalyst, and other additives
|
|
Peel strength
(g/cm)
|
After aging
|
PET / PP
|
PET / Foil
|
24 hrs
|
236
|
200
|
192 hrs
|
293
|
Substrate failure
|
|
Peel strength
(g/cm)
after addition of 2% crosslinker*
|
After aging
|
PET / PP
|
PET / Foil
|
24 hrs
|
Substrate failure
|
Substrate failure
|
192 hrs
|
260
|
Substrate failure
|
| *WD-6314 from H.B. Fuller Co. |
Table below shows polyurethane dispersion adhesive requirements for common substrates and applications.
The application will decide the following characteristics of the adhesives film.
- Hardness
- Flexibility
- Abrasion resistance
- Chemical resistance and more
| Substrate |
Application Area |
Product |
| Wood |
- Parquet flooring
- Industrial wood finishes
- Cork tiles
|
- Hard
- Flexible grades
- High abrasion resistance
- High chemical and solvent resistance
- Good acrylic compatibility
|
| Plastics |
- uPVC and pPVC flooring
- Laminates and films
- ABS, PC, Nylon and PS automotive parts
- TV/Hi-fi housings
|
- Hard and soft types
- Good adhesion to difficult substrates
- Scratch resistance
- Good acrylic compatibility
|
| Textiles |
- Weatherproof clothing
- Synthetic leather
- Glass fibre sizes
|
- Hard and soft types
- Good adhesion
- High degree of flexibility / elasticity
- Low cost
|
| Masonry |
- Architectural coatings
- Interior concrete floors
- Tiles and Walls
|
- Mainly hard types to improve flexibility
- Low temperature properties of acrylics
- Good acrylic compatibility
|
| Graphic arts |
- Overprint varnishes
- Pigment binders
- Laminating adhesives
|
- Hard and soft types
- Good adhesion and scuff resistance
- Good chemical resistance
|
Polyurethane Dispersion Adhesive Applications5
Market Applications of Thermoplastic Polyurethanes
TPUs are the ideal adhesives in a wide range of markets, such as footwear, transportation, furniture or textile.
Transportation
This market requires adhesives that have good hot green strength and an excellent
final bond in order to meet the specific automotive specifications.
Thanks to the good performances obtained with the TPU-based adhesives, they are
successfully used in this market, for a series of applications.
Use of Thermoplastic Polyurethanes in Transportation
TPUs are raw materials offering an ever-increasing number of solutions to
these requirements.
- Automotive interior parts (door panel, instrument panel, attachment clip,
bonding of components)
- Heat sealable fabrics (soft trim, foam lamination)
Furniture
In the furniture industry TPU-based adhesives are widely used in
lamination of plastic
films onto applications in kitchen or bathroom furniture:
TPU adhesives provide very good bonding to wood like MDF and to plastics
such as PVC.
Use of Thermoplastic Polyurethanes in Furniture
There are applications (profile wrapping, edge banding, lamination), that
need the use Reactive Hot Melt adhesives. The presence of TPUs in the formulations
allows to improve the final performance of these adhesives.
Textile
TPU Hot Melt adhesives with different melt and viscosity characteristics are capable
of providing solutions to most of the laminating combinations of textile substrates.
Use of Thermoplastic Polyurethanes in Textile Industry
TPU Hot Melts are mainly used for making
heat sealable fabrics obtained by
coating processes such as scattering or dot-coating (powder or paste). TPU Hot Melts are
Oeko-Tex Class I compliant.
Footwear
There is a wide variety of bondings in shoe production. Several factors are involved, such as: technological development, requested performances, shoe design and, most of all, an extraordinary variety of materials.
As a result, a very wide range of adhesives is needed for each specific part of the article.
Use of Thermoplastic Polyurethanes in Footwear Industry
The main feature of footwear industrial production is its high productivity, which implies ever-shorter production cycles. TPUs are raw materials offering an ever-increasing number of solutions to these requirements.