Plate curing accelerating

Transparent PVC plates were coated with a 70 pm thick film of an epoxy-acrylate resin containing 0.5 % of a benzotriazole UV absorber. They were first UV cured for one second and then exposed at 40°C to the low intensity radiations of a QUV accelerated weathering tester. The extent of the degradation was followed by Invisible spectroscopy, a very sensitive method that permits detec-... 

Use Rubber accelerator, component of a catalyst system for polymerization of vinyl monomers, curing agent for water-repellent silicone materials, agent for plating with zirconium. 

Zonal processes are slow processes. They are responsible for the long duration of plate formation. Hence, it is important to find methods to by-pass the zonal processes. In order to accelerate the formation of positive plates, some conductive additives have been added to the positive pastes [28]. These additives increase the conductivity of the cured paste and formation proceeds almost uniformly throughout the whole plate volume as the electric current flows along the conductive additive network. The additives should be chemically stable in H2SO4 solution. Data have been reported about successful attempts to reduce the duration of the formation procedure to 8 h. 

Resin II contains tetraglycidyl methylene dianiline (TGMDA) as the principal epoxide with small amounts of a cresol novolac and DGEBA. DICY as curing agent is present in an amount such that the amine epoxy ratio is 0.25. Diuron is the accelerator. The supplier s recommended standard cure is the same as for SP250. However, in this system approximately 20 percent of the epoxide remains unreacted following the cure cycle (1 ). Selected resin plates were subjected to additional cure at 170°C and 220°C. The samples post cured at 220 C for forty minutes showed no residual epoxide absorbance in the IR spectrum. 

Positive plates need much more time to form than negatives. The reason for this is the dielectric behaviour of the cured positive paste. Oxidation of the bivalent lead compounds in the paste and formation of the Pb02 positive active mass passes through a number of chemical reactions, some of which proceed at a low rate, which retards the technological process of formation of the positive plate. In an attempt to accelerate the formation process, additives to the positive paste have been looked for, which are characterised by electro-conductive properties and stability in sulfuric acid. These additives create an electro-conductive network in the paste and the process of oxidation proceeds simultaneously within a large paste volume, thus accelerating plate formation. 

DCBS is a commonly used sulfenamide accelerator that is selected when good scorch safety is needed combined with a relatively slow cure rate. The selection of DCBS is particularly useful when a slow cure rate is needed to optimize rubber adhesion to brass-plated steel tire cord. 

Figure 14.4 gives plots of viscosity (log ri) versus cure time for different shear rates (y) when a general-purpose unsaturated polyester (Aropol 7030, Ashland Chemical Company) was subjected to steady-state shear flow in a cone-and-plate rheometer under an isothermal condition at 60 C. The resin had been prepared by the reaction of propylene glycol with a mixture of maleic anhydride and isophthalic anhydride. The resin system used in Figure 14.4 was cured with BPO as initiator and a solution of 5 wt % A,A-dimethylaniline, diluted in styrene, as accelerator. The following observations are worth noting in Figure 14.4. At an early stage of curing, the rj increased slowly, but then...

Figure 14.4 Plots of log t) versus cure time with 3.16 wt % BPO as initiator and 1.9 wt % AtJV-dimethylaniline as accelerator, during isothermal cure in a cone-and-plate rheometer at 60 C, for Aropol 7030 subjected to different shear rates (s ) (O) 0.269, (A) 1.07,...

These types of adhesives remain fluid in the presence of oxygen but cure to solids in its absence. The simplest anaerobic adhesive consists of dimethyl acrylate ester with the peroxide catalyst system and accelerator. They cure by free-radical polymerization in the absence of oxygen. Anaerobic adhesives have strength characteristics equivalent to those of the structural adhesives. One-part anaerobic adhesives cure at room temperature in several hours, but their cure can be accelerated to minutes by high-temperature cure and by the use of certain primers/ accelerators. Such elevated temperature, primer/accelerator-assisted cure is especially recommended when anaerobic adhesives are used on inactive surfaces, such as unclean metals or plastics, or inhibiting surfaces such as plated surfaces, chromates, oxides, and anodized surfaces. 

A flip-chip technology developed by Toshiba Corporation utilized an ACF to attach bare umbumped chips (with A1 pads) onto a polychlorinated biphenyl (PCB) with bumps formed from a silver paste screen printed on the PCB [32]. After curing, Ag bumps were formed (70 pm diameter, 20 pm height), which were subsequently overplated with Ni/Au. It was determined that an ACF with a low CTE (28 ppm/°C), low water absorption rate (1.3%), and utiUzing a Au-plated plastic ball worked best. It was also found that Ni/Au-plated Ag paste-formed bumps exhibited a lower initial connection resistance and a lower connection resistance increase as compared to Ag paste-formed bumps that were not overplated with Ni/Au. The initial connection resistance for Ni/Au-plated Ag paste bumps and nonplated bumps was 22 and 48 pll, respectively, with a respective increase of 294 and 717 pO after 1000 hr of accelerated thermal cycling (ATC) testing. 

---