Rubber sheets uncured

Uncured Tel-Tak specimens were prepared by cutting rubber sheeted out from a mill at about 1.4 mm (0.06 in) thick. They were then placed over a piece of square woven fabric and pressed between a sheet of mylar on the top and cellophane on the bottom in a mold for 5 minutes at 100 C. After cooling, specimens were cut from the fabric side to 0,25 in, X 2 in. Two rectangular specimens are required for each test. Each test piece is mounted in the Tel-Tak instrument perpendicular to the other in order to assure the same contact area for each test. 

Silica particles are embedded into the surface of polyethylene Him to improve the adhesion of coatings of thermoplastic polymers (595). A fluorocarbon polymer surface is made cementable by coating it with the mixture of dispersed polytetrafluo-roethylene and colloidal silica, and heating the surface to over 500°C for a few minutes (596). On glassine paper used to separate uncured sheets of rubber, adhesion is needed on one surface but not on the other. One side of the paper is treated with 0.04-0.6 lb of colloidal silica per 1000 ft so that rubber sheeting will stick only to the treated surface when stored as a roll (597). 

The non-vulcanized or imcured rubber sheets that are self-curing are gradually cured on the roof by heat from the sun. Once they are cured, their behavior is similar to that of cured elastomers. If they are not self-curing, they remain uncured and exhibit properties similar to thermoplastics during their service life. In general, elastomeric sheets have good... 

Tack is best thought of as the ability of two pieces of rubber to stick when pressed together and is sometimes called auto adhesion. Therefore, it is not quite the same as stickiness or adhesion, which generally involves sticking or adhering to a second material. High tack can be a nuisance when handling sheets of rubber but is very important in the manufacture of articles built up from separate pieces of uncured compound. 

Calendering. Rubber calenders consist of at least three rolls, which can be adjusted for gap, speed, and temperature. Calendering can be used for forming sheets of uncured... 

The uncured rubber stock is passed through a series of gaps of decreasing size made by a stand of rotating rolls, and the final roll gap determines the sheet thickness (Fig. 4.31). A variant of this is the use of a calendering process for the production of coated fabric for such applications as carcass plies in tires (Fig. 4.32). 

A further technique is to form an adhesive strip containing the metallic coagent. The adhesive strip may then be used to bond another rubber to a metal surface. When the adhesive strip approach is used, the metallic coagents are milled into the rubber compoimd. The uncured compound is then formed into sheets by calendaring and then cut into stable, thin strips that contain the metallic coagent, peroxide and other rubber additives. The rubber strip can then be applied between the uncured rubber compound and the... 

The dispersion of type N-330 carbon black and of type N-326 carbon black into natural rubber (SMR 5CV) was investigated. In each case, the freshly mixed composition was press cured, razor cut, and microscopically examined to visually estimate the degree of carbon black dispersion as expressed by a dispersion rating (DR). Cured sheets of each composition were also tested with respect to ultimate tensile strength and other performance-related properties. The test recipes are given in Table 1. We note here that the uncured compositions can also be examined for dispersion quality (discussed later). 

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