Radiation-curable systems

An Electrocure radiation curing unit could cost up to 400,000 or a capital expenditure cost of 20/hr. Radiation curable systems also require more maintenance and an inert atmosphere (nitrogen blanket) to ensure efficient curing operations. 

The advancement of low viscosity, radiation curable systems in the last two years has for the first time made gravure application of these systems a reality. Since many Industrial web processes (coating paper or film, laminating, metal coating, etc.) already employ gravure equipment, the availability of these new systems (1) has had major impact on the interest in electroncuring technology. 

Figure 11. Effect of pigment level on skinniness ratings of polyester/cotton, 50/50 fabrics printed with radiation-curable system (2.5% Graphtol Blue 6825, 15% acrylo-urethane oligomer (MW 6000), 79% monomer mixture EP-4 (80%) and v-pyrol (20%), 3% Cab-O-Sil, and 3% vicure 10. Then required amount of...

The print quality of polyester/cotton, 50/50 fabrics printed with the radiation-curable system is very close to that using an all aqueous system (Figure 12) and presumably due to their similar rheological behavior. 

In order to improve performance and processing efficiency of radiation curable systems it has been proposed that curing should be monitored using a technique of mechanical spectroscopy SS and in relation to this other workers have found that the molecular weight and structure of the diol component of multifunctional acrylates influenced the mechanical properties of the UV cured films produced 52,193. urea group in the resin tended to enhance the modulus of the cured film whereas a vinyl caprolactam diluent reduced resin viscosity for ease of coating. 

Larmner . BA AG] Unsaturated acrylates reactive diluem or thinner fix radiation-curable systems, finishes. 

Monomers. In radiation-curable systems, the solvent is replaced by reactive diluents (monomers) which are incorporated in the network during cross-linking. These monomers have two important functions they reduce the viscosity of the mixture and they strongly influence the physical and chemical properties of the final coating. Monomers can be divided into three groups ... 

Uses Diluent for radiation-curable systems Features Reactive Laromer HDDA [BASF AG]... 

Uses Reactive diluent for radiation-curable systems (lacquers, printing inks) comonomer for crosslinked acrylic resins Trade Names Laromer DPGDA Photomer 4226... 

Rapl-Cure CVE Rapi-Cure DVE-2 Rapl-Cure EHVE diluent, radiation-curable systems... 

Photonol PHO-7149 Polyether tml leveling agent, radiation-curable systems BYK -UV3500... 

The contributions of physics to adhesion are further manifested by the extension of uv- and electron-beam curing of adhesives to low temperatures. Radiation-curable adhesives were originally intended to eliminate solvents in the systems. However, the use of certain toxic acrylate monomers presented some problems. So far, radiation-curable systems have become technologically challenging, but economically less attractive than most thermally cured systems. Since one of the earliest papers on photoadhesives by Nakano (35) many patents have been issued on this subject. Two reviews have been published by Stueben (36). ... 

Free-radical, radiation-curable systems generally consist of monomers, oligomers, photoactivators, other resins, and fillers or tackifiers. An ultraviolet source or electron-beam generator is used to cure the systems. As an illustration Stueben (37) describes a typical UV-cured PSA system containing acrylates and polyvinyl ether. McGinniss (38) discusses formulation design related to UV-curable systems. The cationic photoinitiators are shown in Fig. 1. 

V. D. McGinness, "Polymer and Formulation Design Characteristics for Developing Adhesive Bonding Radiation-Curable Systems," in Ref. 14. 

More commonly, acrylic polymers have been utilized as the sole or major components of radiation-curable adhesive systems. These acrylics have included a homopolymer and many examples of copolymers. One UV-cured acrylic ester copolymer system cited was claimed to have 180° peel strength of 4.8 to 5.5 pounds/inch. Radiation-curable systems based on copolymers of vinyl acetate and 2-ethylhexyl acrylate have been reported more frequently than other compositions and sometimes have been applied by hot melt techniques. These pressure-sensitive adhesives have displayed 180° peel strengths ranging from about 1.5 to 3 pounds/inch when cured by either UV or EB radiation. Not surprisingly, solutions of acrylic polymers in acrylic and vinyl monomers have also been used as radiation-curable pressure-sensitive adhesives. 

The use of elastomeric or flexibilizing modifiers occurred and grew with epoxy resins first. Various aspects of toughened epoxy adhesives have been covered in reviews by the present authors (2,3), where the elastomeric modifiers have essentially been carboxylic, liquid and solid butadiene/acrylonitrile polymers. There has not been a systematic review, however, of these and other reactive liquid polybutadiene/acrylonitriles in the burgeoning areas of acrylic, anaerobic and radiation-curable systems. Thus, this paper s intent. 

A key feature of radiation curable systems is that they are one-part systems with shelf lives ranging from several weeks to six months or more. They should be stored in the dark and away from heat if possible. Some of these adhesives... 

Another important class of modified epoxy resins, known as epoxy acrylates, are reaction products of a low MW epoxy resin and acrylic acid or methacrylic acid, which are used in radiation curable systems. The acrylate functionality is 2, but higher functionality variants can also be prepared by using epoxy phenol novolac in place of BPA epoxy resin. Radiation curable formulations from these oligomers provide a better balance of properties and cost compared to some of the alternative polymer systems. 

Pressure-sensitive adhesives based on acrylic polymers grew 3.5-fold in the last dozen years. The acrylics are mostly emulsions and solutions, plus small quantities of radiation-curable systems. In tapes, acrylic adhesives are applied mainly to non-paper substrates such as polypropylene, acetate, cellophane, and polyester. In labels, acrylics are used for making permanent paper labels and plastic labels. 

In order to take advantage of the new abrasive grit materials, new and improved bond systems had to be developed. Subsequently, adhesive systems have also come a long way, progressing from fish and animal hide glues to urea-formaldehyde resins, epoxies, phenolic, and radiation-curable systems. This evolution has placed a continuing demand on the adhesive systems used in the manufacturing of abrasive products. 

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