Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-01-10
2003-03-04
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C023S3130FB, C023S29300R, C159S047200, C159S048100, C241S026000, C523S456000, C523S461000, C525S510000
Reexamination Certificate
active
06528594
ABSTRACT:
The present invention relates to a process for the manufacture of a flowable granulate and to a specific granulate manufactured from epoxy resins and substances having a high specific surface that are insoluble therein.
Polyglycidyl compounds are often used today as a reactive component of curable compositions, for example as hardeners or cross-linking agents in powder coating compositions based on polyesters. Many polyglycidyl compounds are liquid or semi-solid at room temperature or slightly elevated temperature and therefore have only a limited suitability for powder coating applications.
U.S. Pat. No. 5,525,685 describes solid compositions consisting of liquid or semi-solid epoxy resins and solid colloidal condensation polymers of urea or melamine and formaldehyde, which compositions are suitable as hardeners for powder coating compositions. The solidification of liquid epoxy resins requires, however, relatively high quantities of the inert condensation polymer, which results in a relatively low epoxy content in the powder coating composition hardener.
U.S. Pat. No. 5,294,683 describes the preparation of solid solutions by melting and subsequently cooling a mixture of at least one polyglycidyl compound that is solid at room temperature and at least 5% by weight of a polyglycidyl compound that is liquid at room temperature. The solid products so obtained are substantially free of inert components and have a high epoxy content. In that process, the solid products are obtained in the form of flakes that have a tendency to cake when stored for relatively long periods. Before being processed to form powder coating compositions, those flakes are ground to powders by various processes (e.g. by cryo-grinding), there being obtained, however, a material having a high dust content and a broad particle size distribution.
The problem of the present invention was to develop a process for the manufacture of free-flowing granulates of defined particle size and narrow particle size distribution that are stable to storage and have a low dust content.
Granulates having a narrow particle size distribution can generally be manufactured from liquid products, such as solutions or melts, by the process of continuous spray granulation which is described, for example, in U.S. Pat. No. 3,879,855. That process is problematical, however, where the solidification of epoxy resins is concerned. For example, in the case of spray granulation of the solid solutions described in U.S. Pat. No. 5,294,683, an agglomerating, poorly flowing, lumpy material is obtained.
It has now been found that waxy, semi-solid or cohesive (sticky) materials can be solidified by means of spray granulation without any problems to form free-flowing granulates having a low dust content and a narrow particle size distribution by the addition of a small quantity of a substance having a large surface area that is insoluble therein.
The problem of solidifying waxy or sticky substances or mixtures of substances arises especially in certain applications of polymeric or polymerisable substances. Use in powder coating compositions, for example, requires a high dispersibility; in addition, the substance should be in the form of a flowable solid that is stable to storage and has as low a proportion of fine dust as possible.
The present invention accordingly relates to a process for the manufacture of a flowable granulate by means of spray granulation, which process comprises using as starting material a formulation in liquid form comprising
(a) a substance or a mixture of substances that is in the form of a waxy or cohesive solid at room temperature, and
(b) up to 20% by weight, based on the amount of component (a), of a substance having a specific surface >3 m
2
/g that is insoluble in component (a).
The process of spray granulation is known to the person skilled in the art from numerous publications, for example from U.S. Pat. No. 3,879,855, European Patent Applications EP-A-0 087 039, EP-A-0 163 836, EP-A-0 332 929, EP-A-0 600 211 and EP-A-0 787 682, or German Offenlegungsschriften DE-A-29 41 637 and DE-A-43 04 809.
Preferably, the spray granulation is carried out as a fluidised-bed process.
In principle, spray granulation for the solidification of liquid or semi-solid epoxy resins can be carried out also as a batch process.
Preferably, however, the process is carried out continuously since, in the continuous process, the desired narrow particle size distribution can be set without any problems. Special preference is given to carrying out the spray granulation as a continuous process with sifting delivery.
By varying the process parameters (residence time, incoming air temperature, product temperature, spray pressure, spray rate, sifter air quantity) granulates having average particle diameters d
50
of from 0.1 to 10.0 mm can be produced.
Granulates having average particle diameters d
50
of from 0.3 to 5.0 mm, especially from 0.5 to 2.0 mm, are preferred.
The starting materials for the process of the invention are in liquid form, that is to say, they may be solutions, suspensions, emulsions or melts. The liquid products to be sprayed are produced according to customary methods by mixing the constituents and, where applicable, by subsequently heating the resulting mixtures.
When carrying out the process of the invention, the liquid product to be granulated is introduced into the fluidised bed through suitable spray nozzles. One-component nozzles, two-component nozzles or multiple-component nozzles can be used. The use of two-component nozzles, three-component nozzles or higher-multiple-component nozzles is advantageous. Two-component nozzles are especially preferred.
A preferred embodiment is the process of the invention wherein the liquid formulation is a suspension of component (b) in a melt or solution of component (a).
The substance (b) that is insoluble in component (a) can be in the form of a solid or in the form of a suspension in a solvent, for example in water.
When two-component nozzles are used, the liquid formulation to be granulated can be mixed in a pre-mixing zone immediately before being sprayed in. It is also possible for the melt or solution of component (a) and the suspension of component (b) to be supplied separately to a three-component nozzle. In that case, the two components do not mix until sprayed. Another preferred embodiment of the invention, therefore, is a process wherein product introduction is carried out via two-component nozzles with a pre-mixing zone or via three-component nozzles and the liquid formulation is produced immediately before being sprayed in by mixing a melt of the epoxy resin (a) and a suspension of component (b) in an inert solvent.
The process of the invention is used especially in the solidification of semi-solid and waxy or sticky synthetic polymers or corresponding monomers or oligomers, especially thermosetting resins, as component (a).
Examples of such thermosetting resins are phenolic resins, polyurethanes, unsaturated polyester resins and epoxy resins.
Preferably, an epoxy resin or a mixture of epoxy resins is used as component (a) in the process of the invention.
The epoxy resins that are customary in epoxy resin technology can be used as component (a). Examples of epoxy resins are:
I) Polyglycidyl and poly-(&bgr;-methylglycidyl) esters, obtainable by reacting a compound having at least two carboxyl groups in the molecule and epichlorohydrin or &bgr;-methylepichlorohydrin, respectively. The reaction is advantageously carried out in the presence of bases. Alternatively, such epoxy compounds can also be prepared by esterification with allyl halides and subsequent oxidation.
Aliphatic polycarboxylic acids can be used as the compound having at least two carboxyl groups in the molecule. Examples of such polycarboxylic acids are oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and dimerised or trimerised linoleic acid. It is also possible, however, to use cycloaliphatic polycarboxylic acids, such as, for example, tetrahydrophthalic aci
Bauer Michael
Rickert Christoph
Aylward D.
Dawson Robert
Esq. Kristin Neuman
Proskauer Rose LLP
Vantico Inc.
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