Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-07-06
2002-09-03
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C429S407000, C429S901000
Reexamination Certificate
active
06444315
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for modifying the surface of flame retardants by encapsulating the particles with a silicon-containing coating agent, and to the corresponding flame retardants themselves and their use.
2. Discussion of the Background
It is known that ammonium phosphates, ammonium polyphosphates, melamine phosphates, melamine borates and melamine cyanurates can be used as halogen-free flame retardants, e.g. for plastics. EP 0 584 567 A1 discloses a flame-retardant plastic molding composition made from olefin polymers and from a flame-retardant system made from ammonium polyphosphate and from a polycondensate made from tris(2-hydroxyethyl) isocyanurate and from an aromatic polycarboxylic acid. DE-A 33 16 880 describes a process for preparing hydrolysis-stable, water-insoluble ammonium polyphosphates by coating with, respectively, melamine-formaldehyde resins and phenol-formaldehyde resins. EP 0 180 790 A1 moreover describes a coated, powder ammonium polyphosphate in which polyurea, i.e. a reaction product made from isocyanate and water, is used for the encapsulation procedure.
Although ammonium polyphosphates, for example, give such plastics good flame retardancy, a disadvantage is that they migrate out of the plastic during the course of its service life and are washed out by environmental agents, such as moisture, since in particular untreated ammonium polyphosphates, but also other phosphoric acid derivatives, have considerable solubility in water.
Cured silicone resins have also been described as a coating material. JP-A 3-131 508, for example, teaches the encapsulation of ammonium polyphosphate as a slurry in an organic solvent with a curable silicone resin, where small amounts of an aminotriethoxysilane are used as a curing agent. However, a joint feature of all of these processes is that the preparation of such surface-treated flame retardants is very complicated, and this noticeably increases the cost of the product. In addition, environmental problems are caused by the use of environmentally unfriendly solvents and by the resultant wastewater and residues.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a simple and environmentally friendly process for modifying the properties of flame retardants, such as ammonium polyphosphates.
According to the invention this object has been achieved as described in the claims.
Surprisingly, it has been found that surface-modified flame retardants can be obtained in a simple, cost-effective and at the same environmentally friendly manner by applying an organofunctional-silane or a mixture of organofunctional silanes or an oligomeric organosiloxane or a mixture of oligomeric organosiloxanes or a solvent-containing preparation based on monomeric organosilanes and/or on oligomeric organosiloxanes or a preparation based on water-soluble organopolysiloxanes to a powder flame retardant. The present invention also provides surface-modified flame retardants which are prepared by this process.
DETAILED DESCRIPTION OF THE INVENTION
As used hereinafter, the phrase “organic silicon composition” means an organofunctional-silane or a mixture of organofunctional silanes, an oligomeric organosiloxane or a mixture of oligomeric organosiloxanes, or a solvent-containing preparation based on monomeric organosilanes and/or on oligomeric organosiloxanes, or a preparation based on water-soluble organopolysiloxanes, or mixtures of any or all of these.
The phrase “solvent-containing preparation based on” means that the preparation referred to is prepared by mixing at least the compounds it is based on with a solvent.
A suitable method of applying here is direct dropwise addition, injection or spraying of the coating agent into a fluidized bed of the flame retardant to be treated, whereupon the coating agent generally reacts with the surface of the flame retardant and thus encapsulates the particles. Water of condensation, and also in some cases small amounts of alcohol, can be produced here by condensation or hydrolysis, and these are introduced with the exhausted process air in a manner known per se into an exhaust air purification procedure, e.g. a condensation or catalytic or thermal post-incineration procedure.
A cost-effective and environmentally friendly, and therefore particularly advantageous, method is to use an aqueous preparation based on water-soluble organopolysiloxanes, since virtually exclusively water escapes into the exhausted process air. An additional factor is that explosion protection of the plant is unnecessary. The method of operation described, furthermore, does not produce any filtration residues or wash water.
The present invention provides a process for modifying the surface of flame retardants by encapsulating the particles with a silicon containing coating agent, by applying an organofunctional silane or a mixture of organo functional silanes or an oligomeric organosiloxane or a mixture of oligomeric organosiloxanes or a solvent-containing preparation based on monomeric organosilanes and/or on oligomeric organosiloxanes or a preparation based on water-soluble organopolysiloxanes to a powder flame retardant. The flame retardant is kept in motion during the coating procedure.
The novel process preferably uses from 0.05 to 10% by weight, particularly preferably from 0.1 to 3% by weight, very particularly preferably from 0.5 to 1.5% by weight, of silicon-containing coating agent, based on the amount of flame retardant. The coating agent may be applied over a period of from 10 seconds to 2 hours at a temperature of from 0 to 200° C., preferably over a period of from 30 seconds to 10 minutes at a temperature of from 20 to 100° C., particularly preferably over a period of from 1 to 3 minutes at a temperature of from 30 to 80° C.
The flame retardant encapsulated with coating agent may be post-treated by exposure to heat or to reduced pressure, or to reduced pressure together with heat. This post-treatment of the flame retardant encapsulated with coating agent preferably takes place at a temperature of from 0 to 200° C., particularly preferably at a temperature of from 80 to 150° C., very particularly preferably at a temperature of from 90 to 120° C.
The process may be carried out in a stream of air or of inert gas, such as nitrogen or carbon dioxide. The process may also be carried out by repeating the coating procedure, and if desired a subsequent drying of the encapsulated flame retardant, one or more times.
The flame retardants used in the novel process preferably have an average particle size (d
50
) of from 1 to 100 &mgr;m, particularly preferably from 2 to 25 &mgr;m, very particularly preferably from 5 to 15 &mgr;m. A suitable method is to use a powder flame retardant of this type in dry, i.e. free-flowing, form.
Flame retardants preferably used in the novel process are:
ammonium orthophosphates, e.g. NH
4
H
2
PO
4
, (NH
4
)
2
HPO
4
or mixtures of these (e.g. FR CROSS® 282, FABUTIT® 747 S), ammonium diphosphates, e.g. NH
4
H
3
P
2
O
7
, (NH
4
)
2
H
2
P
2
O
7
, (NH
4
)
3
HP
2
O
7
, (NH
4
)
4
P
2
O
7
or mixtures of these (e.g. FR CROS® 134), ammonium polyphosphates, in particular but not exclusively those found in J. Am. Chem. Soc. 91, 62 (1969), e.g. those with crystal structure phase 1 (e.g. FR CROS® 480), or with crystal structure phase 2 (e.g. FR CROS® 484) or mixtures of these (e.g. FR CROS® 485), melamine orthophosphates, e.g.
C
3
H
6
N
6
.H
3
PO
4
, 2C
3
H
6
N
6
.H
3
PO
4
, 3C
3
H
6
N
6
.2H
3
PO
4
, C
3
H
6
N
6
.H
3
PO
4
, melamine diphosphates, e.g. C
3
H
6
N
6
.H
4
P
2
O
7
, 2C
3
H
6
N
6
.H
4
P
2
O
7
, 3C
3
H
6
N
6
.H
4
P
2
O
7
or 4C
3
H
6
N
6
.H
4
P
2
O
7
, melamine polyphosphates, melamine borates, e.g. BUDIT® 313, melamine cyanurate, e.g. BUDIT® 315, melamine borophosphates, melamine 1,2-phthalates, melamine 1,3-phthalates, melamine 1,4-phthalates and melamine oxalates.
The organofunctional silanes used in the novel process are preferably alkoxysilanes with aminoalkyl or epoxyalkyl or acryloxyalkyl or methacrylox
Barfurth Dieter
Goetzmann Karl
Mack Helmut
Mans Vincente
Naegerl Hans-Dieter
Degussa - AG
Le Hoa T.
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