Laminate High pressure

Phcnolics Good acid resistance, good electrical properties (except arc resistance), high heat resistance Compression molding, continuous lamination high pressure process... 

Cellulose acetate propionate Nitrocellulose resin, laminating high-pressure Epoxy-novolac resin, modifier adhesives M ethy Isty rene/vi ny Itol uene copolymer resin, nonyel./very resilient/soft Polyvinyl ethyl ether Polyvinyl isobutyl ether resin, nonyel./very resilient/soft flexographic inks... 

Laminate, high pressure Laminates molded and cured at pressures not lower than lOOOpsi, and commonly in the range of 1200-200 psi. 

See also continuous laminate decorative laminate high-pressure laminate electrical laminate. 

Table 8,2 AJi mative ways of constructing Laminated high pressure vessels...

Another widely used overlay adhesive is the contact type. These specialized adhesives, in the same group as mbber cement, may be of the solvent-base or water-base types. They are often used to bond overlays such as wood veneer, vinyl (poly(vinyl chloride)) films, or high pressure laminates such as countertop overlays. 

The most commonly used reinforcement for high pressure decorative and industrial laminates is paper (qv). The strong substrate layers, or filler, are kraft paper. Kraft is a brown paper made from a sulfate pulp process (8). It consists of both short cellulose fibers from hardwoods and long fibers from conifers. The long fibers impart most of the wet strength required for resin saturation processes. 

The quantity of resin appHed to the reinforcing ply to achieve a state of full densification varies inversely with the laminating pressure. Therefore, high pressure laminates pressed at about 7 MPa (1000 psi) need only about 25—30% phenoHc resin in kraft paper, whereas low pressure (1 MPa = 145 psi) laminates need 50—60% resin in the reinforcing ply if all voids are to be filled in the final product. 

In small pieces or as inserts, laminates may be used unsupported because they are quite stiff and strong. The modulus of a high pressure decorative laminate is about 7 GPa (106 psi) at room temperature. Thick laminates range up to 25 mm and are very strong, having flexual strength of 130 MPa (19,000 psi). These products are used unsupported as toilet partitions, laboratory tops, and so forth. 

The properties of standard grades of high pressure decorative laminates manufactured are shown in Table 1. Tables 2 and 3 show properties of industrial laminates (12,13). 

General-purpose type is a high pressure decorative laminate (HPDL) designed for both horizontal and vertical appHcations where appearance, durabiUty, resistance to stains, and resistance to heat up to 135°C (275°F) are requited. 

In the final product, the formaldehyde has completely reacted to form a very inert thermoset resin. Spontaneous emission of formaldehyde from high pressure laminates is measured at approximately the accepted background level of 0.035 ppm (15). Melamine surfaced laminates are tested and approved for food service equipment by the National Sanitation Foundation (16). 

Because of their favourable price, polyesters are preferred to epoxide and furane resins for general purpose laminates and account for at least 95% of the low-pressure laminates produced. The epoxide resins find specialised uses for chemical, electrical and heat-resistant applications and for optimum mechanical properties. The furane resins have a limited use in chemical plant. The use of high-pressure laminates from phenolic, aminoplastic and silicone resins is discussed elsewhere in this book. 

Solvent-borne CR adhesives allow almost any two substrates to stick together. The adhesives are extensively used in bonding high-pressure plastic laminates, automotive adhesives, adhesives for construction and shoe adhesives. 

High-pressure laminates. Solvent-borne CR adhesives are used for bonding foams to wood or fabric, and for bonding metal, fibreglass and plastics. 

Polychloroprene latices are mainly used for high-pressure lamination, for foam bonding and for vinyl adhesion [82]. Also they are used for foil lamination, carpet installation, and PVC floor tile bonding. 

High-pressure lamination constitutes a large market for water-borne polychloroprene adhesives. The choice of the polymer has a high impact on end-use properties. 

In high-pressure boilers, there are three types of on-load corrosion acidic chloride, neutral chloride/dissolved oxygen, and caustic attack. The first and second (once it becomes established) are brittle and thick-walled and are accompanied by hydrogen damage which can lead to failure within a few hundred hours. Caustic attack tends to produce a gouged appearance of the metal due to extensive wastage. The morphology is fairly characteristic of the failure type. Acidic chloride forms hard, laminated oxide, whilst, with caustic attack, the oxide is often soft, and, as it is easily removed, may be absent. 

In the past, the term high-pressure laminates was reserved for melamine and phenolic impregnated papers or fabrics compressed under high pressures (about 13.8 to 34.5 MPa, or 2,000 to 5,000 psi). They were heated to form either decorative laminates (for example Formica and Micarta) or industrial lami-... 

Amino (melamine and urea) Melamine formaldehyde (MF) have excellent electrical properties, heat and moisture resistance, abrasion resistance (good for dinnerware and buttons) in high-pressure laminates it is resistant to alkalies and detergents. They are used as the plastic for counter tops. Urea (urea formaldehyde) has properties similar to melamine and is used for wall switch plates, light-colored appliance hardware, buttons, toilet seats, and cosmetics containers. Unlike MFs they are translucent, giving them a brightness and depth of color somewhat similar to opal glass. 

Neutralizing or volatile amines such as morpholine and cyclohexy-lamine neutralize carbonic acid, which generally raises the condensate and FW pH levels in high-pressure units. 

Reinforced plastics differ from high-pressure laminates in that little or no pressure is employed. For instance, in making formed shapes, impregnated reinforcing material is cut to a desired shape, the various layers are added to a mold, which is then heated. This process is favored over the high-pressure process because of the use of a simpler, lower cost mold and production of strain-free products. 

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