Resin contents

Laminates. Laminate manufacture involves the impregnation of a web with a Hquid phenoHc resin in a dip-coating operation. Solvent type, resin concentration, and viscosity determine the degree of fiber penetration. The treated web is dried in an oven and the resin cures, sometimes to the B-stage (semicured). Final resin content is between 30 and 70%. The dry sheet is cut and stacked, ready for lamination. In the curing step, multilayers of laminate are stacked or laid up in a press and cured at 150—175°C for several hours. The resins are generally low molecular weight resoles, which have been neutralized with the salt removed. Common carrier solvents for the varnish include acetone, alcohol, and toluene. Alkylated phenols such as cresols improve flexibiUty and moisture resistance in the fused products. 

Cured amino resins are far too brittle to be used alone as surface coatings for metal or wood substrates, but in combination with other film formers (alkyds, polyesters, acryUcs, epoxies) a wide range of acceptable performance properties can be achieved. These combination binder coating formulations cure rapidly at slightly elevated temperatures, making them well suited for industrial baking appHcations. The amino resin content in the formulation is typically in the range of 10—50% of the total binder soHds. 

The specification requirements for electrode binder pitch, eg, high C/H ratio, high coking value, and high P-resin content, effectively ruled out pitches from gasworks or low temperature tars. The cmde tar is distilled to a medium-soft pitch residue and then hardened by heating for several hours at 385—400°C. This treatment increases the toluene-insoluble content and produces only a slight increase in the quinoline-insoluble (Ql) material, the latter by the formation of mesophase. 

Several factors were utilized in bringing formaldehyde release down. In particular, resin manufacturer executed more careful control of variables such as pH, formaldehyde content, and control of methylolation. There has also been a progressive decrease in the resin content of pad baths. The common practice of applying the same level of resin to a 50% cotton—50% polyester fabric as to a 100% cotton fabric was demonstrated to be unnecessary and counter productive (89). Smooth-dry performance can be enhanced by using additives such as polyacrylates, polyurethanes, or siUcones without affecting formaldehyde release. 

Adhesives (qv) used to make plywood are classified as either the exterior adhesive or the lesser quaHty interior adhesive. The terms relate to the abUity of the adhesive to survive exposure to moisture and weather. PhenoHc resins (qv) are commonly used as adhesives to make plywood. The difference between interior and exterior phenoHc resin adhesive is the filler level. Exterior rated plywood uses higher resin content adhesives. Interior rated plywood uses either highly extended (below 24% resin soHds) or protein-based adhesives. The adhesive is appHed to the veneer by roU coating, spraying, curtain coating, or foam extmsion. 

Properties measured using 1—1.5 mm laminates glass fabric U.S. 2116, resin content 45% by weight. 

Sticky waxes are generally composed of resins and wax. A high resin content gives viscosity to the melt, a long plastic range, and a brittle fracture when cooled. No modem formulas are available, but the older recipes usually had rosin, beeswax, and gum dammar as the essential constituents. 

Triglycerides are important constituents of resin. In softwood, the triglycerides account for 20—40% of total resin content, and in hardwood, 40—50%. The paper industry uses the term pitch for resins that create problems in paper machines. Traditionally, pitch is controlled or reduced by aging the wood, by use of chemicals to avoid deposits on the roUs, or by intensive washing of the pulp. AH these methods add to the cost of paper production. An alternative is to add a Upase to the pulp in a reaction lasting about one hour with the help of agitation. Results from Japanese paper mills show substantial... 

The properties of the varnish, such as the nature of the solvent and the viscosity and resin content of the varnish. 

Figures 23.21 and 23.22 show how two variables, moulding pressure and resin content, affect the mechanical properties of a laminate.

Figure 23.22. Effect of resin content on strength properties of a high-density Kraft paper laminate.

Because of the lack of solubility in the usual solvents, aniline-formaldehyde laminates are made by a pre-mix method. In this process the aniline hydrochloride-formaldehyde product is run into a bath of paper pulp rather than of caustic soda. Soda is then added to precipitate the resin on to the paper fibres. The pulp is then passed through a paper-making machine to give a paper with a 50% resin content. 

Fillers are used in tooling and casting application. Not only do they reduce cost but in diluting the resin content they also reduce curing shrinkage, lower the coefficient of expansion, reduce exotherms and may increase thermal conductivity. Sand is frequently used in inner cores whereas metal powders and metal oxide fillers are used in surface layers. Wire wool and asbestos are sometimes used to improve impact strength. 

The properties of the laminate are dependent on the resin and type of glass cloth used, the method of arranging the plies, the resin content and the curing schedule. Figure 29.4 shows how the flexural strength may be affected by the nature of the resin and by the resin content. 

Figure 29.4. Influence of resin content on the flexural strength of glass-cloth laminates made with two silicone resins A and B. (After Gale " )...

The dielectric constant is normally in the range 3.6-4.4 and decreases with an increase in resin content. 

Fig. 23. Evolution of the glass transition temperature of polychloroprene-aromatic hydrocarbon resin blends as a function of the resin content. values were obtained from DSC experiments.

Fig. 27. Tack of polychloroprene-hydrocarbon resin blends (33 wt% resin content) as a function of the nature of the hydrocarbon resin. Tack was obtained as the immediate T-peel strength of joints produced with 0.6 mm thick styrene-butadiene rubber strips placed in contact without application of pressure. Peeling rate = 10 cm/min.

Effect of the phenolic resin content in the mechanical properties of nitrile rubber... 

Terpene phenolic resins can also be added to polychloroprene latex without great reduction in hot strength as the resin content is increased, but contactability is reduced. However, an adhesion failure is obtained, even at the 50 phr level. Furthermore, terpene phenolic resins have relatively poor tack and impart the best... 

Using such PUF-resins, the resin content of the board should be calculated only based on the PF-resin solids in the PUF-resin. 

Adhesive bonding is an integral part of virtually all composite structure. Early composite matrix resins could in some cases act as an adhesive, such as with self-filleting systems used for honeycomb sandwich fabrication. As composite systems became more optimized for minimum resin content and limited flow, supplementary adhesives became more common. Modern-day composite structure relies on adhesives almost as much as bonded metallic structure. 

The experimental and theoretical results for E., are shown in Figure 3-41 for a resin content by weight ranging from 10% to 100%. Because E. is not a function of C, only k was varied — two values were chosen k = 1 and k =. 9. Some experimental results in Figure 3-41 lie above the curve for k=1 (i.e., above the upper bound ) some results lie below k =. 9. However, most results lie between k =. 9 and k = 1 with k =. 9 being a conservative estimate of the behavior. The actual specimens were handmade, so the resin content might not be precise, and fiber misalignment is not unexpected. Thus, the results above the upper bound are not unusual nor is the basic fact of variation in E. ... 

The theoretical and measured results for E, are shown in Figure 3-41 as a function of resin content by weight. Theoretical results from Equation (3.64) are shown for C = 0,. 2,. 4, and 1, and the data are bounded by the curves for C = 0 and C =. 4. The theoretical curve labeled glass-resin connected in series is a lower, lower bound than the C = 0 curve and is an overly conservative estimate of the stiffness. 

Figure 3-41 E, and Eg versus Resin Content (After Tsai [3-1])...

The experimental results for of a glass-epoxy composite material are shown along with the theoretical prediction from Equation (3.66) as a function of resin content by weight in Figure 3-44. Theoretical results are shown for contiguity factors of C = 0,. 2,. 4, and 1. Apparently, C = 0 is the upper limit of the data whereas C =. 4 is the lower limit. Thus, the concept of contiguity factor is further reinforced. 

Cork, a natural material - the bark of the Mediterranean cork oak tree. It is largely air cells and the fibrous cell walls have a high resin content. When baked, the resin softens and welds the pieces of bark into a comparatively homogeneous mass, which is sliced into blocks, commonly 50, 75 and 100 mm thick. 

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