Curing schedules

For mass production purposes matched metal moulding techniques are employed. Here the preform or mat is placed in a heated mould and the resin poured on. The press is closed and light pressure ( 501bf/in ) applied. Curing schedules are usually about three minutes at 120°C. It is possible to produce laminates using less resin with pressure moulding than with hand lay-up techniques and this results in better mechanical properties. 

Many other amines are catalytic in their action. One of these, piperidine, has been in use since the early patents of Castan. 5-7 pts phr of piperidine are used to give a system with a pot life of about eight hours. A typical cure schedule is three hours at 100°C. Although it is a skin irritant it is still used for casting of larger masses than are possible with diethylenetriamine and diethylaminopropylamine. 

Hardener Parrs used per 100 pts resin Pot life (500 g batch) Typical cure schedule Skin irritant Max HOT cured resin rcj Features Applications... 

Anhydride hardener Parts used phr Typical cure schedule Physical form Max. HDT of cured resin °C Use... 

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. 

Good quality steel is used and electrozinc is preferred for washing machines. Steel is pretreated with iron phosphate for economy electrozinc with a fine crystal zinc phosphate. No primer is normally used 25-40/im of finish is applied direct to metal. The required properties are best obtained with a thermosetting acrylic or polyester/melamine-formaldehyde finish. Self-reactive acrylics are usually preferred these resins contain about 15 Vo 7V-butoxymethyl acrylamide (CH2=CH —CO —NH —CHj—O —C4H,) monomer and cure in a manner similar to butylated melamine-formaldehyde resins. Resistance or anti-corrosive properties may be upgraded by the inclusion of small amounts of epoxy resin. Application is usually by electrostatic spray application from disc or bell. Shapes are complex enough to require convected hot-air curing. Schedules of 20 min at 150-175°C are... 

In curing thick articles in open steam it is sometimes necessary to reduce the temperature of cure at the end of the hold period at a slow yet uniform rate. This part of the cure schedule is the drop . 

The part of a cure schedule during which the temperature is held at a specified figure. 

In the vulcanisation of thick rubber articles the temperature may be stepped up in stages to ensure adequate heat penetration to the interior before the external surface begins to cure. Such a cure schedule is termed a step cure. Step post cures are used with thick section rubber articles to ensure that volatiles are released gradually without causing damage, such as porosity, due to an over rapid release. 

Hay JN (1994) Processing and cure schedules for cyanate ester resins. In Hamerton I (ed) (1994) Chemistry and technology of cyanate ester resins. Chapman Hall, London, p 151... 

Table I. Stoichiometry and Curing Schedules for Matrix Resins...

To determine the effect of the curing schedule upon the thermal stress development, a 0% excess MDA sample was made by first B-stage curing (2 hrs at 80°C) the sample, cutting it into the beam dimensions and then placing it in the apparatus. The deflection of the beam was measured during the remainder of the curing schedule (2 hrs at 150°C and 2 hrs at 180°C). 

Figure 5. Curing schedule effect on zero stress temperature.

The curing schedule of the epoxy controls the temperature at which the epoxy-metal system is at zero stress. The controlling variables are the final Tg of the system and the time and temperature of each stage in the curing schedule. The variables determine the percent of crosslinks formed in an unstressed state at each temperature of the curing schedule. 

We have found that the MEK absorption for a linear epoxy resin containing 12% carboxyl- terminated rubber and cured with P-108 is very sensitive to cure conditions. The MEK absorption was measured in the standard manner for a 5 minute immersion as a function of several cure schedules. The results of these experiments are summarized in Table IV and Figure 3. 

Several epoxy powders were formulated in a homologous series where the EEW of the base resin changed from 858 8/eq. to 1487 8/eq. All formulations contained 10% carboxyl-terminated rubber, were extruded two times, and were cured with calculated amounts of P-108. The standard cure schedule of 200OC for 15 minutes was used. MEK absorptions were measured in the usual manner. A definite dependence of MEK absorption on EEW was found. Table V summarizes the data. 

Figure 2.2 An example of cure schedule—two steps with constant temperature and two different heating rates (dTJdt) for the curing stage one step with constant temperature and one heating rate for the postcure stage one step with one heating rate for the cooling stage...

An optimization of the cure schedules and processing parameters consists of exploring the most favorable conditions, judged under specified criteria, that will lead to a product... 

Table 3.1 Cure Schedule for the Curing of PEI/Thermoset Blend...

The advantage of using free radical inhibitors to facilitate the copolymerization of a bisbenzocyclobutene with a bismaleimide was first noted in a patent to Bartmann [78]. Subsequent to this, Corley in a series of patents described some detailed experiments on the copolymerization of bisbenzocyclobutenes with bismaleimides both with and without the addition of a free radical inhibitor [33, 34]. The structures of the bisbenzocyclobutenes used in this study are shown in Fig. 33. The bismaleimide component that was used was a mixture of three different bismaleimides in the molar ratio shown in Fig. 34. The individual bisbenzocyclobutenes were blended at elevated temperature with varying amounts of the bismaleimide composition. In some of the experiments, the free radical inhibitor phenothiazine was added at a 0.5 mole % level. The various monomer mixtures were then copolymerized using one of the cure schedules described in Table 14. The copolymers were then physically characterized using a variety of techniques. Table 14 shows the results obtained from copolymers... 

Fig, 3. FTIR spectra of Epon 828/PACM-20 before and after standard curing schedule. Taken on Nicolet MX-1 Spectrometer... 

The use of a timescale instead of a conversion one requires a previous definition of the cure schedule e.g., isothermal, constant heating rate, etc. Usually, isothermal conditions are selected to define the timescale i.e., only trajectories at constant temperature have a physical meaning. This leads to the TTT diagram. 

From Eqs (5.18) (5.21), it is obvious that for any couple of values of conversion and temperature, the rate of consumption of epoxy groups, (dx/ dt), will depend on the particular value of a . And this, in turn, depends on the particular cure schedule e.g., for a particular couple (x,T), a different value of a will result from isothermal runs or from runs at constant heating rate that intercept the particular point (x,T). Therefore, Eq. (5.1) has no general validity for this case. 

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