Лако-красочные материалы — производство

As with almost all commercially available high performance products on the market today, there are many proprietary, highly formulated products described as ‘‘acrylic adhesives.’’ The formulations vary widely with different families and subfamilies of products constantly being introduced, each offering certain advantages over previous “generations.” In general, however, they can all be characterized as having a significant portion of the formulation composed of acrylic monomers, used in combination with various other polymers. They all contain ingredients to initiate hardening or curing of the adhesive. In addition, they contain various other organic and inorganic components designed to achieve desired handling properties, flexibility, specific adhesion, and shelf stability.

Methyl methacrylate and some of the other related monomers that are typically used in acrylic adhesives are shown in Fig. 2. These monomers vary in volatility with the lower molecular weight members of this family having a rather high odor and low flash point.

CHj 0

I II

HjC = с — с — о — сн, сн, сн3снэ
Butyl methacrylate

О CH3

II I

H;C = C — C — О — CH;“ CHj— 0 — CHj— CHj— О — C — C = CHj
Diethylene glycol dfrnet, riacrylate

CH3 0

I II

H, C — C — C — 0 — CH;~ CHj — CHj — CHj — CHj — CHj — CH; — CHj Octyl methacrylate

Figure 2 Reactive species (monomers) for acrylics.

Higher molecular weight members offer lower odor and higher flash point, and also impart greater flexibility in the finished adhesives. Additionally, the lower molecular variants tend to be lower in overall cost and result in somewhat better adhesion to some surfaces. Depending on which properties are of most importance in a particular application, the lower molecular weight, the higher molecular weight, or blends thereof can be employed.

The tendency of acrylic monomers to spontaneously and quickly polymerize makes it necessary for adhesive formulators to include various types of chemical stabilizers as part of the formulation to assure good shelf stability. These stabilizers are generally complex organic compounds that have a strong ability to react with free radicals (the cure chemistry most commonly employed with acrylics). These stabilizers stop unwanted side reactions and assure good shelf life of formulated adhesive products.

In addition to the methacrylate monomers that are responsible for adhesive hardening, and the initiators and stabilizers already mentioned, most acrylic adhesives also contain polymers of various types and molecular weight. These additional components are included by formulating chemists to control handling properties, cure rates, flexibility, strength, adhesion, and environmental resistance. The exact nature of specific components is held as a trade secret by companies. Some insight into the types of polymers used and their combinations and levels can be found by searching patent literature and various technical journals.

It should be noted that modifiers to improve flexibility are particularly important in systems based on the most common monomer, methyl methacrylate. Polymerized methyl methacrylate monomer is a hard brittle material, not very useful as an adhesive. Consequently, most companies have developed unique proprietary ways to add flexible polymers to acrylic adhesives to achieve desired flexibility.

In summary, in light of a broad spectrum of acrylic adhesive formulations, it can be assumed that any purchased acrylic adhesive on the market today will be a complex, highly formulated product having numerous ingredients to control cure, handling proper­ties, shelf life, physical properties, and adhesion.