3.5.1.1.1 Silicone characteristics

provides a very high toughness to the assembly as a very high bond line stress is

Typical applications are galvanized steel bonding for construction to prevent corrosion bonding failure; school bus structure bonding for fire wall, side wall, and roof; marine yacht bonding for deck, stringer, hull, and gel coat; boom bonding for special vehicles; structure bonding with spot welding; office cubicle bonding; com-

These adhesives and sealants are polymerized by (in most cases) a condensation reaction which involves reaction with ambient moisture. Two general chemistry

Depending on the curing mechanism, it consists of one-component RTV silicone and two-component silicone. For one-component silicone, it vulcanizes at room temperature either by reaction with moisture in the air and substrates. It starts to cure from the surface and cures into depth. Depending on the type of formulation, it generates a by-product and evaporates. For two-component silicone, it vulcanizes at room temperature by part A and B reactions. Its curing starts from both surface and inside of mixed product. Therefore, its curing is not affected by the lack of

This is widely used in various industries. Depending on the type of formulation, a by-product is generated such as vinegar smell and non-vinegar smell. Acetic acid type has a pungent odor and is mainly used in the construction area and some machinery repair applications. Oxime type is the most popular in the assembly industry as it has no pungent odor and is regarded as non-acetic acid silicone. The cure speed of silicone primarily depends on the relative humidity which means it is

Because of the nature of the curing mechanism, silicones vulcanize from the outside to the inside of the bond line. Due to the necessary moisture migration to

posite structure bonding; and case bonding of hand-held display device.

types fall into two categories which are silicone and polyurethane.

fast in summer time and slow in winter time (see Figure 12) [15].

eliminated with this design (see Figure 11) [14].

Adhesives and Adhesive Joints in Industry Applications

3.5 Adhesives cured by ambient moisture

3.4.3.2 Typical applications

3.5.1 Silicone

moisture in the air.

Figure 12.

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RTV silicone curing mechanism.

3.5.1.1 One-component RTV silicone

One-component silicone characteristics are the following: excellent thermal resistance ("up to 270°C"), flexible, tough, high elongation, low to medium modulus, effective sealants for a variety of fluid types, and excellent gap filling.

### 3.5.1.1.2 Typical applications

One-component silicone applications are gasketing and sealing in automotive industry, sealing in high temperature applications, sealing and bonding for small parts, sealing and potting, and coating of PCBs.

### 3.5.1.2 Two-component silicone

When part A and part B are mixed in a proper mixing ratio, a chemical reaction occurs initiated by the catalyst reacting with water. This chemical reaction occurs not only at the surface but also inside the mixed product. Therefore, it has a very fast fixturing and curing time for faster fixture and assembly, and it allows a structural bonding assembly in more compact assembly line and automated assembly with less manpower. This technology can replace various assemblies that have used double-sided tape or RTV silicone that requires a manual and lengthy assembly line and time with much manpower. During the chemical reaction, moisture ("H2O") comes in and alcohol ("OH") that was generated during chemical reaction as a by-product comes out and evaporates (see Figure 13) [15].

## 3.5.1.2.1 Silicone characteristics

Two-component silicone characteristics are such as fast tack free time, fast fixture time and fast full curing time. Its curing speed is not affected by moisture and bond line thickness. It is flexible, tough, high modulus and UL 746C listed for high temperature applications. It also has an excellent gap filling capability and high temperature resistance up to 270C. Three colors such as black, gray and almond are available.

#### 3.5.1.2.2 Typical applications

Typical applications of two-component silicone are glass bonding for refrigerator, washing machine, microwave, cook top, dish washer, air conditioner and bridge structure bonding.

Figure 13. Two-component silicone curing mechanism.

### Adhesives and Adhesive Joints in Industry Applications

panel lamination bonding for recreational vehicle and mobile home; wind blade bonding (one-component, two-component); sport goods lamination bonding (twocomponent); and filter bonding or casting for water filter, air filter, mechanical

Major reactive functional adhesives and sealants have been described with conventional methods and benefits of adhesive and sealant solutions in this chapter. The assembly industry still has numerous area that can improve their assembly process with cost saving and increase reliability of their assembly. It would be worthwhile that all the information be thoroughly reviewed and studied, and with this material, it is hoped that ideas to improve a cost and to increase a reliability of various assemblies with such adhesives and sealants would be materialized as a

filter, and blood filter (two-component).

Functional Adhesive Trend for Assembly Industry DOI: http://dx.doi.org/10.5772/intechopen.84880

4. Conclusion

life time guide.

Author details

Henkel (China) Investment Co., Ltd, Shanghai, China

\*Address all correspondence to: cs.woo@henkel.com

provided the original work is properly cited.

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

ChulSoo Woo

87

Figure 14. Curing mechanism of two-component polyurethane.

Figure 15.

Open time versus ambient temperature of two-component polyurethane.

#### 3.5.2 Polyurethane

Polyurethane adhesives cure with polyol and isocyanate at room temperature. During the reaction, it generates some carbon dioxide (CO2). One unique feature of polyurethane adhesive is that its cure is sensitive to the moisture level. For some applications to achieve the best and most durable adhesion, the use of appropriate cleaners and primers (adhesion promoters) is recommended. Depending on the substrates, different primers are used. According to where it is used, they consist of one-component PU and two-component PU. PU has a different open time according to the ambient temperature and mixed amount. Figures 15 explains that the open time in high temperature environment such as summer time reacts fast and has a short open time while it does a long open time in cold environment such as winter time (see Figures 14 and 15) [16].

#### 3.5.2.1 Polyurethane characteristics

Polyurethane characteristics are excellent toughness and flexibility, high elongation, excellent gap filling, paintable when cured, and excellent chemical resistance.

#### 3.5.2.2 Typical applications

Typical applications of polyurethane are bonding/sealing of direct glazing window for automotive, railway, and earth movers (one-component, two-component); panel lamination bonding for recreational vehicle and mobile home; wind blade bonding (one-component, two-component); sport goods lamination bonding (twocomponent); and filter bonding or casting for water filter, air filter, mechanical filter, and blood filter (two-component).
