Laminate papers, additives

Colour-Matching. It is essential in producing all types of laminates to ensure tight control of colour (acceptable matching, sheet-to-sheet, should be possible even between batches made several years apart). It is not possible to match papers either before or after impregnation with the precision required and hence all plain colour and printed papers are colour-matched after lamination. In addition to visual judgment it is normal to use spectrophotometers and associated computers to decide colour acceptance (or otherwise). 

Rosin and its derivatives are frequently used as polymer additives in different capacities. Their role as plasticizers is illustratedby recent work related to the paper coating for foodpackaging with a 3-hydroxybutirate/3-hydroxy valerate copolymer (PHBW) [112, 113]. The addition of tall oil rosin to the copolymer was found to improve its water vapour barrier properties as well as to reduce the pinhole density of the corresponding laminated papers. 

Urea-formaldehyde (UF) resins are mainly used as adhesives for wood. Laminated sheets (tables and counter tops) are a major application for melamine resins, which stay in the outer decorative surface. Molding compounds, their first big application, is still a major market, taking advantage of their extreme hardness and heat resistance. Coatings, textile finishing, paper additives, leather tanning and foundry binders, for which methanol- or butanol-etherified resins are usually employed, are important markets discussed in Ref 203. 

Urea—formaldehyde resins are also used as mol ding compounds and as wet strength additives for paper products. Melamine—formaldehyde resins find use in decorative laminates, thermoset surface coatings, and mol ding compounds such as dinnerware. 

In the paste coating method, a PVC paste, which contains emulsion-polymerized PVC and additives, is appHed onto a substrate and heated to gelation before fusion to produce a coating layer. This method is employed for products with a thin layer, ie, of 0.007—0.05 mm thickness. For foamed vinyl-coated fabrics, a substrate is laminated onto a transfer paper on which a PVC paste containing a foam-blowing agent has been appHed and geUed. After removal of the transfer paper, the paste is blown. 

Some common flake-shaped LCMs consist of shredded cellophane and paper, mica (qv), rice hulls, cottonseed hulls, or laminated plastic. These materials He flat across the opening to be sealed or are wedged into an opening such as a fracture. Some are sufficiently strong to withstand considerable differential pressure, whereas others are weak and the seal may be broken easily. Weaker flake materials typically are used near the surface or in combination with fibrous or granular additives. 

Adhesives for paper tubes, paperboard, cormgated paperboard, and laminated fiber board are made from dispersions of clays suspended with fully hydrolyzed poly(vinyl alcohol). Addition of boric acid improves wet tack and reduces penetration into porous surfaces (312,313). The tackified grades have higher solution viscosity than unmodified PVA and must be maintained at pH 4.6—4.9 for optimum wet adhesion. 

Two classes of resol are generally distinguished, water-soluble resins prepared using caustic soda as catalyst, and spirit-soluble resins which are catalysed by addition of ammonia. The water-soluble resins are usually only partially dehydrated during manufacture to give an aqueous resin solution with a solids content of about 70%. The solution viscosity can critically affect the success in a given application. Water-soluble resols are used mainly for mechanical grade paper and cloth laminates and in decorative laminates. 

In their pioneering paper on laminated plates, Reissner and Stavsky investigated an approximate approach (in addition to their exact approach) to calculate deflections and stresses for antisymmetric angie-ply laminated plates [5-27]. Much later, Ashton extended their approach to structural response of more general unsymmetrically laminated plates and called it the reduced stiffness matrix method [5-28]. The attraction of what is now called the Reduced Bending Stiffness (RBS) method is that an unsymmetrically laminated plate can be treated as an orthotropic plate using only a modified D matrix in the solution, i.e.,... 

Paper laminates, TiCh pigments in, 25 28 Papermaking, 11 179, 287-288. See also Paper manufacture additives in, 15 98 amino resin applications, 2 644-648 asbestos applications, 3 311 calcium carbonate applications, 4 554-555... 

Subramaniam, 1988]. Hydrochlorination, usually carried out at about 10°C, proceeds by electrophilic addition to give the Markownikoff product with chlorine on the tertiary carbon (Eq. 9-33) [Golub and Heller, 1964 Tran and Prud homme, 1977]. Some cyclization of the intermediate carbocation (XXVI) also takes place (Sec. 9-7). The product, referred to as rubber hydrochloride, has low permeability to water vapor and is resistant to many aqueous solutions (hut not bases or oxidizing acids). Applications include packaging film laminates with metal foils, paper, and cellulose films, although it has been largely replaced by cheaper packaging materials such as polyethylene. 

Melamine and its polymers have uses in many industrial fields. The commercial importance of the compounds is shown by the fact that 34 x 106 kg of melamine was produced in the USA in 1970. The chemistry of the melamine resins has been discussed already (see Chapter 1.11). The major uses of the resins are in the formation of high-pressure laminates for home furniture, and as moldings for crockery. In addition the resins are used in finishing textiles, to improve crease resistance, and as coatings for wet strength paper. 

In F grade laminates fire properties are improved further by incorporating additives like inorganic phosphates in the core resin or paper. Thus, when... 

In the Library of Congress collections one can find good and bad examples of the two systems, silking and cellulose acetate lamination. One can only conclude, therefore, that in addition to adequate treatment of the papers before lamination, the craftsman s manipulative techniques of application, (and, with silking, pressing and drying) are fundamental to truly archival protection. 

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