Melamine-formaldehyde resins laminates

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. 

The decorative plastic laminates widely used for countertops and cabinets are based on melamine—formaldehyde resin (see Laminates). Several layers of phenohc-saturated kraft paper are placed in a press and a sheet of a-ceUulose paper printed with the desired design and impregnated with melamine—formaldehyde resin is placed over them. Then a clear a-ceUulose sheet, similarly impregnated with the resin, is placed on top to form a clear, protective surface over the decorative sheet. The assembly is cured under heat and pressure up to 138°C and 10 MPa (1450 psi). A similar process is used to make wall paneling, but because the surfaces need not be as resistant to abrasion and wear, laminates for wall panels are cured under lower pressure, about 2 MPa (290 psi). 

Amino resins are lighter in color and have better tensile strength and hardness than phenoHc resins their impact strength and heat and water resistance are less than those of phenoHcs. The melamine—formaldehyde resins are harder and have better heat and moisture resistance than the urea resins, but they are also more expensive. The physical properties of the melamine—formaldehyde laminates are Hsted in Table 1. 

Although phenolic resins are too dark for use in the surface layers of decorative laminates these resins are employed in impregnating the core paper. In the.se cases a melamine-formaldehyde resin is used for impregnating the top decorative layer. Phenolic laminates have also been used in aircraft construction and in chemical plant. 

Melamine (I,3,5-triamino-2,4,6-triazine) was first prepared by Liebig in 1835. For a hundred years the material remained no more than a laboratory curiosity until Henkel patented the production of resins by condensation with formaldehyde. Today large quantities of melamine-formaldehyde resins are used in the manufacture of moulding compositions, laminates, adhesives, surface coatings and other applications. Although in many respects superior in properties to the urea-based resins they are also significantly more expensive. 

In addition to their use in moulding powders and laminates, melamine-formaldehyde resins are widely used in many forms. 

At one time thiourea-urea-formaldehyde resins were of importance for moulding powders and laminating resins because of their improved water resistance. They have now been almost completely superseded by melamine-formaldehyde resins with their superior water resistance. It is, however, understood that a small amount of thiourea-containing resin is still used in the manufacture of decorative laminates. 

Another use of urea is for resins, which are used in numerous applications including plastics, adhesives, moldings, laminates, plywood, particleboard, textiles, and coatings. Resins are organic liquid substances exuded from plants that harden on exposure to air. The term now includes numerous synthetically produced resins. Urea resins are thermosetting, which means they harden when heated, often with the aid of a catalyst. The polymerization of urea and formaldehyde produces urea-formaldehyde resins, which is the second most abundant use of urea. Urea is dehydrated to melamine, which, when combined with formaldehyde, produces melamine-formaldehyde resins (Figure 96.2). Melamine resins tend to be harder and more heat-resistant than urea-formaldehyde resins. Melamine received widespread attention as the primary pet food and animal feed contaminant causing numerous cat and dog deaths in early... 

Melamine-formaldehyde resins are used in the surfaces of most decorative laminates and have excellent properties for this purpose in respects such as ... 

As with the melamine-formaldehyde resins, additives such as flame retardants (depending upon the type of laminate to be produced) can be added before... 

Overlay Paper. Overlay paper is a-cellulose paper of high purity, with substance weight in the range 20 to 80 g m-2. An essential feature is the refractive index, which is virtually identical with that of melamine-formaldehyde resin hence, after lamination—when all the fibres of the paper are wetted and consolidated with resin devoid of air—the overlay becomes transparent. It forms a durable, hard, clear layer to protect the decorative print layer below. 

Melamine-formaldehyde resins are inherently flame-retardant and normally, when bonded to chipboard, to plywood, or MDF, HGS and VGS laminates will achieve Class 2 in the spread of flame test (BS 476 Part 76). 

Straight melamine-formaldehyde resins are used primarily in the preparation of molding compounds, laminates, and textile finishes. Nearly 90% of these molding powders are used to make dinnerware. Melamine dinnerware can be made very decorative for popularity. This resin has better physical properties than phenolics and it can be very easily colored, which phenolics cannot. Methylolmelamine also is used as a synthetic tanning agent for white leather. 

Madurh. hoechst Celanese/Fine Chem.] Melamine-formaldehyde resins for laminates. 

Laminates. While phenol-formaldehyde-kraft-paper laminates are used for counters, cahinets, walls, and panels in puhUc transportation, the dark hrown-hlack color requires a decorative overlay to make it attractive. Colored and printed paper is impregnated with melamine-formaldehyde resin and applied as the surface layer to these laminates, providing decoration along with resistance to scratches, heat, ultraviolet, water, solvents, and stains. The laminating resin is made with melamine/formaldehyde ratios of 1/2 to 3 and press-cured at 125 to 150°C. This uses 14 percent of the melamine-formaldehyde market. 

Same as urea-formaldehyde resins, melamine-formaldehyde resins present a wide color range, are track and scratch resistant, possess good electrical properties and superior heat resistance and hardness. The resins excellent adhesive properties make them useful in the furniture industry. Due to fireedom fi-om color and the above mentioned properties, urea-formaldehyde resins are employed for laminating. Other applications depend on the nature of different fillers. Electrical applications demand mineral-filled urea-formaldehyde resins, whilst the cellulose-filled resins are used for manufacturing of clock cases and trays. Special applications include flame retardant agents [2]. 

The n-butanol is used as a latent solvent and coupling aid in nitrocellulose lacquer formulations to improve blush resistance, flow and leveling properties of the lacquers. The alcohol is also used for urea-formaldehyde and melamine-formaldehyde resins in surface coatings and in wood laminating adhesives. n-Butanol serves as an extraction solvent in the pharmaceutical industry. 

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