Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-11-13
2004-12-14
Sellers, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S079000, C521S082000, C521S089000, C521S094000, C521S095000, C521S098000, C523S453000, C523S456000, C523S457000, C523S461000, C523S466000, C525S113000, C525S114000, C525S115000, C525S523000, C525S533000
Reexamination Certificate
active
06831113
ABSTRACT:
Hot melt one component thermosettable epoxy resin compositions are difficult and hazardous to manufacture and pack. These difficulties often give rise to variability in the product both from batch to batch, container to container and even within containers.
These problems arise because the compositions contain viscous or solid resins as well as hardeners and are mixed in the hot viscous molten state. This can result in the reaction fully or partially occurring during mixing, discharging, or even in the end container.
This invention relates to methods utilising a specific type of composition for the safe and consistent manufacture and where required the simple filling of end use containers of one component heat curable, solvent free, hot melt epoxy resin compositions which have a melting point less than 55° C.
Because of safety, cost and possible environmental pollution it is becoming increasingly important to avoid the use of volatile solvents in industrial processes. Because of the need to maintain a safe, clean and healthy workplace, as well as manufacturing convenience, contact with all liquid chemicals should be avoided wherever possible.
These needs favour the use of epoxy resin formulations in solvent free, flexible or solid form and account in part for the increasing popularity of preimpregnated fibres, or prepregs, for the manufacture of reinforced composites, adhesives in hot melt and flexible tape form for bonding and the use of powders for coatings.
It is very important that the physical nature of these epoxy formulations is very consistent during storage because this affects the ability to apply them reliably and produce consistent quality items with them.
Mixing of the epoxy formulation does not present manufacturing problems is made in solution, as the ingredients can be mixed at low temperatures to avoid dangerous reaction between the resins and hardeners present, due to the low mix viscosities achieved by the use of solvents, but the manufacture and packaging of solvent free individual batches of reactive hot melt epoxy resin and hardener is much more difficult and dangerous, especially when the final composition is required to cure at temperatures say up to 180° C., due to the risk of the curing reaction being initiated prematurely.
Alternatively, mixing of the ingredients can be carried out continuously, which usually avoids the danger of major heat or reaction being given out in the blending equipment, even if carried out at elevated temperatures because only small quantities are present in the mixer at any one time. But the danger remains of reaction in the containers the mixture is poured into.
The result of reaction may be very serious where it proceeds out of control, leading to large quantities of decomposition gases, burnt products, damaged equipment and harzards to personnel, the workplace and the environment in general. Where the reaction only partly proceeds it leads to an increase of average molecular weight, either in the whole batch, or variably within a batch, or a container, for example as the result of different heating times coming from the variation in run-out times from the mixing vessel or cooling within a container. Any such partial reaction is very bad as it results in changed application and uncured physical properties either of the whole batch or container or, more likely, variability within it.
Because of these difficulties the volumes of many hot melt epoxy compositions that can safely be mixed at one time or be put hot into a compact bulk in a container rarely exceed 100 liters. Where the final composition is required to cure at 130° C. or below even 25 liter mixes are potentially dangerous.
Whether mixed continuously or batchwise the filling of small containers with hot viscous reactive liquids present major problems, particularly so when the viscosities at the permitted filling temperatures are high.
So a new method was needed to manufacture these difficult and hazardous materials both safely and in reproducible quality, including their presentation in practical end use containers.
We have now discovered a surprisingly simple way to make these one component epoxy hot melts consistently and safely and supply them in a wide variety of containers and shapes suitable for later hot melt or other processing applications. This process uses very mild conditions and consists of making an epoxy formulation which is liquid at 80° C. or below, more usually at normal shop floor temperatures (15° C.-30° C.) and adding to it a chemical solidifying system which reacts very slowly at these temperatures with the epoxy materials present.
The solidifying system must be picked to give very little reaction during the time it is being mixed with the epoxy resin and hardeners, by whatever method this is done, so that there is very little viscosity rise or temperature rise during the blending operation and hence making the filling of large or small, simple or complicated containers a relatively easy task. Alternatively mixing may take place in the final container if required.
The solidifying reaction must be a simple amine addition reaction with the epoxy groups and must stop when the addition reaction stops. No tertiary amines may be present in the initial mixture or generated during the reaction which could significantly react under the conditions chosen for the solidification reaction. Such reactions severely compromise, safety during bulk mixing, the state of solidification once mixed and the melting point stability and shelf life of the resultant product. The solidifying system must be picked to satisfy these criteria.
The levels of solidifying system used have a major effect on the physical nature of the fully reacted, uncured product. With a liquid resin increasing amounts of solidifying systems take the product through the stages of high viscosity, high tack, low tack, zero tack, flexibility and brittleness respectively.
For convenience, most of the solidification reaction should take place in the final containers used to receive the mixture and this should take place slowly enough to ensure that, in the selected size and shape of the container, there is no temperature rise high enough to cause any significant reaction between the epoxy resins and their main curing systems, but fast enough to ensure usability in a sensible time.
The solidifying agent may be introduced into the mixture at any stage in the process provided the reaction basically proceeds as above.
As the necessary quantity of the solidification system reacts the viscosity and melting point of the formulation increases until the reaction approaches completion when the physical nature of the final formulation is close to the desired end use requirements.
The present invention provides for the manufacture of one component hot meltable thermosettable epoxy resin formulations in bulk form in batch or continuous mixes and their presentation in containers intended for further processing by melt, or other, application methods and includes their composition in hot meltable, molten, powdered, solid, semi solid, tacky, bulk and final cured forms. For example the method of this invention could be performed using the following classes of ingredients:
(A) epoxy resins or epoxy containing compounds
(B) a solidifying amine system which will react with (A) to give a product with a Kofler Heat Bank melting point of less than 55° C., but which is not present in sufficient quantities to allow or cause chemical gelation under the reaction conditions chosen for (A) and (B) and which essentially stops solidifying once its active epoxy additive hydrogen groups are consumed by the epoxy groups, optionally
(C) a hardener system for (A) and the reaction product of (A) and (B) which is different from (B) and which remains substantially unreacted under the conditions of reaction chosen for (A) and (B) with (A) and (B), optionally
(D) other additives that may be required to modify the physical properties of the cured or uncured composition, and optionally (E) an expanding agent.
The method is carried out by ble
Huntsman Advanced Materials Americas Inc.
Levato Tiffany A.
Neuman Kristin H.
Proskauer Rose LLP
Sellers Robert
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