BACKGROUND

The present invention pertains in a general sense to a process for producing N,N'-bis-(tetrabromophthalimide) or N,N'-alkylene-bis-(tetrabro ophthalimide) compositions which are useful flame retardants. More particularly, the present invention relates to a unique processes conducted with high levels of solids in what are conventionally known and used as mixers/dryers for solid particulate materials.

Fire retardant compositions are performance chemicals that must meet exacting standards to gain acceptance and widespread use in industry. Among requirements for flame retardants, color and thermal stability are of great importance. For a majority of applications, it is desired that the flame retardant be as white as possible. This enables production of high quality white plastics, but is also important because polymer processors require that colors of end products result from the particular pigment utilized rather than its combination with the color of the

flame retardant. Of course, it is also desired that the flame retardant composition be thermally stable so as to withstand high temperature processing conditions during polymer formulation. N,N-bis-(tetrabromophthalimide) and

N,N'-alk lene-bis-(tetrabromophthalimide) compositions have been identified as useful flame retardants for incorporation into polymeric materials. As such, their large scale, economical manufacture while retaining acceptable product characteristics is of high interest.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a process for preparing an N,N'-bis-(tetrabromophthalimide) or N,N'-alkylene-bis-(tetrabromophthalimide) composition which employs a high level of reaction solids while nevertheless yielding quality product.

Another object of the invention is to provide a process for preparing an N,N'-bis-(tetrabromophthalimide) or N,N'-alkylene-bis-(tetrabromophthalimide) composition which can provide increased plant productivity as compared to prior known processes while still yielding quality product.

Another object of the invention is to provide a process for preparing an N,N'-bis-(tetrabromophthalimide) or N,N'-alkylene-bis-(tetrabromophthalimide) composition which is conducted in a high mass transfer mixed vessel (such as apparatuses conventionally used as dryers), and which can be operated from start -to finished, dried product in that same vessel. These and other objects of the invention are achieved by preferred embodiments of the present invention, one of which provides a high-solids process for preparing an N,N'-bis-(tetrabromophthalimide) or N,N'-alkylene-bis-(tetrabromophthaliπιide) composition. This process comprises charging, to a reactor equipped with a heat source and internal agitators effective to agitate particulate solids within the reactor, a solvent, tetrabromophthalic anhydride and a diamine of the formula H„N-R, _\ ^-NH _τ wherein R is a C, to C, _n alkylene radical and n is 0 or 1. The tetrabromophthalic anhydride, solvent and diamine are charged in amounts which provide a reaction mixture having about 25% to about 75% by weight solids. This high-solids mixture is heated at a temperature of about 100°C to about 200°C to react

the tetrabromophthalic anhydride and diamine, while being effectively agitated to maintain substantial homogeneity, so as to provide a product predominant in N,N*-bis-(tetrabromophthalimide) when n = 0 or in N,N'-alkylene-bis-(tetrabromophthalimide) when n = 1. In a preferred mode, this process is achieved by the steps of preparing a slurry of tetrabromophthalic anhydride in the solvent in the reactor, adding the diamine to the slurry at a temperature of at least about 80°C, and reacting the reaction mixture at a temperature of at least about 120°C to achieve at least 70% conversion to N,N'-ethylene-bis(tetrabromophthalimide) or N,N'-ethylene-bis(tetrabromophthalimide) .

Another preferred embodiment of the invention provides a process for preparing an in situ-dried N,N'-bis-(tetrabromophthalimide) or

N, '-alkylene-bis-(tetrabromophthalimide) composition. This process comprises charging, to a reactor equipped with a heat source and internal agitators effective to agitate particulate solids within the reactor, a liquid-solid containing reaction mixture. The reaction mixture is formed from a solvent, tetrabromophthalic anhydride and a diamine of the formula H 2_N-R(,n>)-NH2. wherein R is a C, to C, _n alkylene radical and n is O or 1, or is a prereacted mixture thereof. The reaction mixture is then heated at a temperature of about 100°C to about 200°C to react any unreacted tetrabromophthalic anhydride and diamine, while being effectively agitated to maintain substantial homogeneity, so as to provide a N,N'-bis-(tetrabromophthalimide) product when n = O or in N,N'-alkylene-bis-(tetrabromophthalimide) product when n = 1. The reaction mixture is subjected to continued heating and agitation within the reactor to remove the solvent and yield a dried particulate product predominant in N,N'-bis-(tetrabromophthalimide) when n = 0 or in

N,N'-alkylene-bis-(tetrabromophthalimide) when n = 1.

Additional objects, features and advantages of the present invention will be apparent from the following description.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to certain embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations, further modifications and applications of the principles of the invention as described herein being contemplated as would normally occur to one skilled in the art to which the invention relates.

As indicated, a feature of this invention is the a high-solids production process for an N,N'-bis-(tetrabromophthalimide) or N,N'-alkylene-bis(tetrabromophthalimide) product

(hereinafter together referred to as "a bisi ide product".) The bisimide product is prepared by reacting tetrabromophthalic anhydride with-a diamine of the formula

H2.-.N-R(,n _λ )-NH2- wherein R is a C1, to about C1, ₀ 0 alkylene radical and n is zero (0) or one (1).

Tetrabromophthalic anhydride ("TBPA") suitable for use in the process of the invention is commercially available, such as from Great Lakes Chemical Corporation, West Lafayette, Indiana, USA. The TBPA may be used in either micronized or non-micronized form. Additionally, when contemplated for use in a non-aqueous process, the acid number of the TBPA is desirably less that about 0.2 mg/g to prevent formation of impurities, for example those which may be related to salts of the diamine employed in the synthesis or to side reactions of intermediates involved.

Diamines suitable for use in the reaction are readily available from commercial sources or via preparations known to the art. Representative suitable diamines include hydrazine (e.g. as hydrazine hydrate),

diaminomethane, 1,2-diaminoethane ("ethylene diamine" or "EDA"), 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, and 1,10-diaminodecane. Branched dia inoalkanes may also be used. It is preferred that the diamine used in the process of the invention assay at 99%+ purity. In particular, it is highly desirable that the diamine be free from water and carbonate. Among these diamines, EDA and hydrazine are preferred.

It will be understood that any suitable reaction solvent for the selected reactants may be employed. Preferred solvents are acidic in nature, such as a C, to about C carboxylic acid, which acid may be used neat or as an aqueous solution, generally at least about 3% aqueous solution. The acid used as or in the reaction medium is also preferably of high purity. For example, the use of acid of 99%+ purity is preferred, and such grades are commercially available ^~ fro many sources. Of course, when an aqueous carboxylic acid reaction medium is to be used, preferred carboxylic acid starting materials need not exclude the presence of water in the acid as an impurity. When using carboxylic acid in the reaction medium, it is desirable that it be essentially free of the corresponding anhydride, as the presence of anhydride in the carboxylic acid can lead to the formation of an impurity which adversely affects TGA's of the final product. It is thus highly advantageous to employ carboxylic acid having low anhydride content, such as less than about 0.1%.

Carboxylic acid, when used in the reaction medium, may be regenerated from the mother liquors of a previous synthesis, and re-used in a subsequent synthesis. If water removal from the recovered acid is desired, this can be accomplished by treatment with sufficient anhydride, preferably the corresponding anhydride (e.g. acetic

anhydride when acetic acid is used as or in the reaction medium) to remove the water present. This anhydride treatment is desirably conducted at a temperature of about 0-150°C. Further, after this treatment, the liquors can be distilled before use in the subsequent reaction, although this has not proven to be necessary.

An important aspect of the invention is the discovery that an apparatus conventionally known as a particulate solids dryer or mixer can be employed as a reaction vessel in which very high solids reactions can be conducted, while still achieving quality bisimide products. Particulate solids dryers or mixers include of course a heat source and internal mechanical agitators that are effectively located and sufficiently powered to agitate and provide substantial homogeneity to solid particulate matter, and in this respect are also effective to maintain substantial homogeneity of the high-solids reaction mass of the present invention. Maintenance of such homogeneity is vital to the successful production of quality bisimide products, as localized concentrations of reactants such as the diamine compound can cause the formation of deleterious impurities that may affect not only the thermal stability of the product but product color as well. Representative apparatuses that may be used for conducting processes of the invention include those having a heating/cooling jacketed housing within which is mounted a rotating horizontal shaft upon which are mounted agitators that serve to mix the reaction mass. The shaft and the agitators may be internally heated/cooled as well. Included within such apparatuses are those known as paddle dryers, ribbon mixers and Z-blade mixers. Additional suitable apparatuses house generally vertically mounted screws (vertical screw dryers or mixers) which may be used to transfer material vertically to achieve mixing and substantial homogeneity. Examples of a commercially available paddle dryers are the CHEMDRY-EO and STERIDRY-EO

dryers available from Cogeim USA of Charlotte, North Carolina. An example of a commercially available vertical screw dryer is the MIXODRY-EMV also available from Cogeim USA. These apparatuses may be internally coated with a protective coating such as glass, chromium or the like to assist in preventing contamination of the product.

As to specific synthesis details, it is preferred to first provide a slurry of tetrabromophthalic anhydride in the reaction solvent. This slurry may be formed in the reaction vessel, or may be formed and then provided to the reaction vessel. The slurry is preheated to a temperature generally between about 80° and about 160°C, preferably about 90° to about 120°C, with agitation. This preheating can be for several hours or more but is preferably for a period up to about 1 hour. Thereafter, the diamine is added while the agitated slurry remains at a temperature of about 80° to about 160°C, more preferably about 90° to about 120°C. The addition of the diamine can be carried out over 1-2 hours or more, but rs preferably carried out in less than about 10 minutes and more preferably less than about 5 minutes. The addition of the diamine is desirably achieved by blowing the diamine into the reaction vessel under pressure of an inert gas such as nitrogen to ensure a rapid addition and to ensure against hang-up in the lines. In this regard, it is of course important that the addition of diamine be carried out in such a manner that the momentary increase in pressure in the reaction vessel does not exceed the head pressure of the EDA addition system or the pressure limit of the particular operating system employed.

As will be understood, the diamine will be added in essentially stoichiometric amount (i.e. essentially a 1:2 molar ratio) with respect to the TBPA. That is, about 1 mole of EDA will be added for every 2 moles of TBPA in the

slurry. It is important that this stoichiometric ratio be maintained since variations from it can lead to discolored product. For this reason, it is most preferable that the molar ratio of diamine to TBPA be kept in the range of 1:1.9 to 1:2.1.

After the diamine addition, the reaction is conducted at a temperature generally between about 100° and about 250°C, more preferably about 100° to about 180°C. The reaction is continued at the reaction temperature preferably until at least about 70% conversion to the cyclized bisimide product is obtained. It is even more preferred that the reaction be continued until conversion to the bisimide product is essentially complete, e.g. at least 90% and more preferably at least 95% complete. Conversion to the cyclized bisimide product can be determined, for instance, by observing the water event (which occurs upon cyclization of the amidic acid intermediate to form the bisimide final product) by thermogravimetric analysis ("TGA" . The pressure of reacting has thus far been the autogenous pressure of the reaction mixture at the reaction temperature used, or slightly higher due to the pressurized nitrogen gas used during addition of the diamine.

After the reaction, the reaction mixture can be cooled to a temperature of about 20° to about 100°C, more typically 80° to about 100°C, and the solids, which in preferred processes comprise about 25-75%, more typically about 25-50%, of the completed reaction mixture, can be isolated, e.g. by conventional centrifugation. The isolated product may then be washed. The isolated solid bisimide composition is dried, preferably at elevated temperature, to remove any solvent present and to complete any residual cyclization to the bisimide product. The drying and residual cyclization can be conducted at any temperature, but at least one drying step is preferably

conducted at a temperature of at least about 175°C and more typically at least about 200°C. The duration of the drying will vary in accordance with many factors such as the particular drying temperature used and the qualities of the material being dried. The drying will in any event be of sufficient temperature and duration to essentially complete the residual cyclization to form a predominantly bisimide product, which can be monitored by TGA. Bromine contents of the bisimide products are usually at least about 65% and more usually about 65% to about 69%.

The bisimide product can be milled during and/or after the drying operations, for example as occurs in a Winkworth plough share type mixer. The dried product is then preferably micronized to provide an average particle diameter of about 5 microns or less, more preferably about 2 microns or less.

Another feature of the invention is that the production of the bisimide product from liquid reaction to dry product can be conducted in the same reactor. To achieve this process, the completed reaction mixture is not isolated from the reactor as such. Instead, agitation and heating is continued in the reactor, optionally under vacuum, until a dried particulate bisimide product is obtained. This product can then be removed from the reactor and further dried or otherwise processed if desired. This "one pot" process provides an effective and highly economical manner in which to produce the valuable bisimide products.

The bisimide products of the invention can be incorporated as flame retardants in virtually any flammable material, natural or man-made, but will usually be incorporated in flammable synthetic polymers using conventional compounding techniques. For instance, the EBT product may be incorporated into crosslinked or non-crosslinked polymers of olefinic monomers, for example

ethylene, propylene and butylene homopolymers or their copolymers with other polymerizable monomers; polymers of styrenic monomers, e.g. high-impact polystyrene and styrene copolymers; polyurethanes; polyamides; polyimides; polycarbonates; polyethers; acrylic resins; polyesters, e.g. poly(ethyleneterephthalate) and poly(butyleneterephthalate; epoxy resins; alkyd resins; phenolics; elastomers, for example butadiene/styrene copolymers and butadiene/acrylonitrile copolymers; terpolymers of acrylonitrile, butadiene and styrene; natural rubber; butyl rubber; polysiloxanes; wool; cellulose; polyvinylchlorides, etc.

As will be understood, the level of bisimide product incorporated into the flammable material will vary widely in accordance with many factors such as the particular flammable material used, the application contemplated, other additives present, etc. Typically, the bisimide will be incorporated at levels between about 1% and 50% of the total system weight, and more ^" commonly between about 5% and 30% of the total system weight.

It will be understood that other conventional additives may also be incorporated into the flammable material. For example, the bisimide product can be incorporated along with other flame retardant materials such as oxides of Group V elements, especially antimony oxides. Additional conventional additives may include antioxidants, antistatic agents, colorants, fibrous reinforcements, fillers, foaming/blowing agents, catalysts, heat stabilizers, impact modifiers, lubricants, plasticizers, processing aids, UV light stabilizers, crosslinking/curing agents, etc.

In order to promote a further appreciation and understanding of the present invention and its features and advantages, the following examples are provided. It will be understood that these examples are illustrative,

and not limiting, of the invention. Percentages given herein are percentages by weight unless indicated otherwise. Color analyses in the Examples were performed with a Minolta Tricolorstimulus colorometer in accordance with ASTM 1313.

EXAMPLE 1

A paddle dryer was used in this Example. The dryer is a horizontally-disposed paddle dryer having a housing provided with an outside heating/cooling jacket. The housing has a heated main shaft running horizontally therethrough, upon which heated paddles are fitted, to provide efficient heat transfer and discharge of the product. Steam or hot oil may be employed has the heating medium, and are provided to the jacket, shaft and paddles. Shaft sealing is achieved by either fitting a special stuffing box or a mechanical seal. The agitator has a gearbox coupled to a reversible/variable speed motor. A jacketed dust filter is provided, with either a mechanical shaker or a reverse jet cleaning system. This is fitted to prevent any fines being carried over into the vacuum system when the dryer is used to carry out a vacuum drying operation.

The dryer may be used either under vacuum or pressure, and is typically constructed of stainless steel, Hastelloy (nickel-based alloy) or glass lined steel.

To the dryer was charged TBPA (500 g) and acetic acid (2 liters) . The resulting slurry was agitated heated to 92°C and ethylenediamine (32.3 g) was added via a pressurized addition funnel, using nitrogen at 2 Bar, over 3 minutes. The resulting slurry was heated and vigorously agitated at 135°C for 18 hours. The product was isolated by filtration (at approx. 80 C) and dried on a fluid bed

dryer at 200°C for about 12 hours. A white product was obtained having the following characteristics.

1% weight loss 357°C

Impurity level n/d Whiteness index 73.9

Yellowness index 4.4

EXAMPLE 2

To the dryer was charged TBPA (lOOOg) and acetic acid (2 liters). The resulting mix was heated to 92°C and ethylene diamine (64.8 g) added via a pressurized nitrogen funnel as in Example 1. The resulting slurry was agitated and heated at 135°C for 18 hours. The product was isolated by filtration (at approx. 80 C) and dried on a fluid bed dryer at 200°C for about 12 hours. The dried product had the following characteristics. 1% weight loss 323°C

Impurity level _ 1.06%

Whiteness index 68.5

Yellowness index 8.3

EXAMPLE 3

To the dryer was charged TBPA (lOOOg) and acetic acid (2 liters). The resulting mix was heated to 95°C and ethylene diamine (66.0 g) added via a pressurized nitrogen funnel as in Example 1. The resulting slurry was agitated and heated at 135°C for 18 hours. The product was isolated by filtration (at approx. 80 C) and dried on a fluid bed dryer at 200°C for about 12 hours. The dried product had the following characteristics. 1% weight loss 332°C Impurity level 0.76%

Whiteness index 67.3

Yellowness index 7.5

EXAMPLE 4

To the dryer was charged TBPA (lOOOg) and acetic acid (2 liters). The (resulting mix was heated to 95°C and ethylene diamine (67.5 g) added via a pressurized nitrogen funnel as in Example 1. The resulting slurry was agitated and heated at 135°C for 18 hours. The product was isolated by filtration (at approx. 80 C) and dried on a fluid bed dryer at 200°C for about 12 hours. The dried product had the following characteristics. 1% weight loss 390°C

Impurity level n/d

Whiteness index 60.7

Yellowness index 7.8

EXAMPLE 5

To the dryer was charged TBPA (lOOOg) and acetic acid (2 liters). The resulting mix was heated to 97°C and ethylene diamine (70.0 g) added via a pressurized nitrogen funnel as in Example 1. The resulting slurry was agitated and heated at 135°C for 18 hours. The product was isolated by filtration (at approx. 80 C) and dried on a fluid bed dryer at 200°C for about 12 hours. The dried product had the following characteristics. 1% weight loss 327°C

Impurity level 1.24 Whiteness index 54.6

Yellowness index 10.2

EXAMPLE 6

To the dryer are charged TBPA (500g), water (60 mis) and acetic acid (2 liters) . The resulting mix is heated

to 92°C and ethylene diamine (70.0 g) added via a pressurized nitrogen funnel as in Example 1. The resulting slurry is agitated and heated at 135°C for 18 hours. The product is isolated by filtration (at approx. 80 C) and dried on a fluid bed dryer at 200°C for about 12 hours. The dried product has good TGA, impurity level and whiteness and yellowness values similar to those in the preceding Examples.

EXAMPLE 7 To the dryer are charged TBPA (lOOOg), water (60 mis) and acetic acid (2 liters). The resulting mix is heated to 92°C and ethylene diamine (70.0 g) added via a pressurized nitrogen funnel as in Example 1. The resulting slurry is agitated and heated at 135°C for 18 hours. The product is isolated by filtration (at approx. 80 C) and dried on a fluid bed dryer at 200°C for about 12 hours. The dried product has good TGA, impurity level and whiteness and yellowness values similar to those in the preceding Examples.

EXAMPLE 8

To the dryer are charged TBPA (500g) and acetic acid (2 liters) . The resulting mix is heated to 92°C and ethylene diamine (32.3 g) added via a pressurized nitrogen funnel as in Example 1. The resulting slurry is agitated and heated at 135°C for 18 hours. The solvent is removed and the product dried jji situ, at 200°C. The resulting

product shows good TGA, impurity level and whiteness and yellowness values.

EXAMPLE 9

To the dryer are charged TBPA (lOOOg) and acetic acid (2 liters). The resulting mix is heated to 92°C and ethylene diamine (64.8 g) added via a pressurized nitrogen funnel as in Example 1. The resulting slurry is agitated and heated at 135°C for 18 hours. The solvent is removed and the product dried jji situ at 200 C. The resulting product shows good TGA, impurity level and whiteness and yellowness values.

While the invention has been described in some detail, it will be understood that the same is to be considered as illustrative of the invention, and that all changes or modifications that come within the spirit of the invention are contemplated as being a part thereof.