FORM-2
THE PATENT ACT, 1970
COMPLETE


Specification
SECTION-10

NON HALOGENATED FLAME RETARDANT NYLON-6 MOULDING COMPOUND
GUJARAT STATE FERTILIZERS & CHEMICALS LIMITED,
of P.O.Fertilizernagar 391 750, Dist. Vadodara.
Gujarat, India,
an Indian Company

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES AND
ASCERTAINS THE NATURE OF THIS INVENTION AND THE MANNER
IN WHICH IT IS TO BE PERFORMED :-

This invention relates to Nylon-6.
Particularly this invention relates to Flame Retardant Nylon-6.
Nylons are being used in a wide variety of applications and they now constitute a very important class of engineering plastics world-wide. Nylons play an important role in the electrical and electronic industry. For example, industrial switching systems and electrical installations as well as transformers and coil forms for electronics are equipped with Nylon-6.
Electronic components are always exposed to the risk of overheating and short circuit. These occurrences, of course, may cause a fire that might have disastrous consequences. This is a cause for concern behind regulations relating to the fire behaviour of plastics[synthetic polymers] used in this sector. Thus, for instance, parts used for industrial electrical applications are often rquired to comply with fire class V-0 of the UL-94 testing regulations. These standards essentially state that in case of ignition the components must be self-extinguishing within a prescribed short period of time and they must not set fire to any other parts, for example because of dripping of burning molten materials.
Flame resistant Nylon-6 has been on the market for many years. Until now, most of the flame retardant agents used in the manufacture or treatment of Nylon-6 were halogenated organic compounds which are not totally devoid of disadvantages. For example, plastics that have been made flame retardant with halogen compounds are difficult to process, have only a low tracking resistance and in case of fire, generate a large quantity of corrosive smoke. Moreover, recycling problems because of the
2

halogen at ed additives. Environmental issues associated with these flame retard ants necessitated the development of flame retard ant nylon 6 in accordance with this invention that does not contain halogenated additives.
It is an object of this invention to provide a flame retard ant commercially viable flame retard ant Nylon-6 that does not contain halogens.
It is a further object of this invention to provide a halogen free Nylon 6 that can be used for forming, shaping, moulding or otherwise making a variety of useful articles that have the critical property of being flame retard ant. As such, the Nylon-6 developed in accordance with this invention has excellent mechanical, electrical and flame resistant properties.
It is yet another object of this invention to provide a method of making halogen free flame retardant Nylon-6, and consequently articles made therefrom, which can be dyed in light pastel colors due to the inherent light colour of the base material.
It is yet another object of this invention to provide a method of making halogen free flame retardant Nylon-6, which has good flow behaviour and alow tendency towards discoloration during processing.
According to this invention there is provided a method of making flame retardant nylon-6 which comprises the steps of:
Preparing a first homogenous mixture A by intimately mixing 55 to 65 parts of thoroughly dried Nylon-6 with 0.10 to 0.30 parts of TNPP; 0.5 to 0.15 parts of silane and 0.5 to 0.15 parts of PEG;
3

Preparing a second homogeneous mixture B by intimately mixing 35 to 45
parts of thoroughly dried and finely ground melamine with 1.5 to 2.5 parts
of cyanuric acid; 0.01 to 0.03 parts of Potassium Iodide and 0.10 to 0.30
parts of kaolin;
Intimately blending Mixture A with approximately 25% of Mixture B to
form Mixture C;
Dispersively melt mixing Mixture C the remaining 75% of Mixture B in
a twin screw compounding extruder into which the two mixtures are fed at
predetermined rates to obtain pellets of composite mixture of Mixture C
and Mixture B referred to as the masterbatch;
Drying the masterbatch pellets to reduce the moisture content of the pellets
to below 0.25%;
Intimately mixing 40 tO 60 parts of masterbatch pellets with 60 to 40 parts
of virgin nylon-6; 4 to 10 parts of parts of Antimony oxide and 0 15 to
0.25 parts of TNPP to form Mixture D and extruding Mixture D at
temperatures between and 240 to 270 degrees Celsius to form pellets
of flame retardant nylon-6 after drying the pellets to reduce the moisture to
below 0.25%.
The invention will now be described with reference to the accompanying drawing which shows a block diagram of the process for the manufacture of flame retardant nylon 6 in accordance with this mvention.
Referring to the drawings a block diagram for manufacturing flame retardant Nylon 6 in accordance with this invention is indicated generally by the reference numeral 100.
4

The important steps for the lab scale process for the preparation of non halogenated flame retardant Nylon-6 are as follows:-
1. Process Steps:
Halogen free flame retardant grade Nylon-6 is prepared by alloying of virgin Nylon-6 with the masterbatch of Nylon-6 containing halogen free flame retardant additives.
It is a two steps compounding process. In the first step, masterbatch of Nylon-6 is prepared with a very high loading of flame retardant and other additives, on melt compounding extrusion system, whereas the second step in compounding extrusion of the masterbatch with virgin Nylon-6 and other additives. These two steps are elaborated separately as follows-
1. Step-1 Preparation of Masterbatch Formulation :
Physical Mix-A Physical Mix - B
Nylon-6 (E-35) 55 to 65 Parts Melamine 35 to 45 parts
TNPP 0.10-0.20 " Cyanuric 1.5-2.5 "
Acid
Silane 0.5-0.15 " KI 0.01-0.02
PEG 0.5-0.15 " Kaoline 0.10-0.30 "
Nylon-6 used for the blending purpose is first dried in vacuum oven at 80 deg. C. for 4 hours. Similarly, melamine of specific quality is also dried and finally ground in the grinder for specific period to attain specific particle size of around +36 um.
5

Melamine, a commerical grade of very high purity above 99.9% has been used as FR additive. To improve the dispersion of Melamine into the matrix of Nylon-6 which is a very vital factor for the success in achieving FR rating, melamine is dried thoroughly at 80 deg. C. for 3-4 hours in vacuum. Dried powder is pulverised for particle size reduction in a high speed grinder/ball mill for 30 mins. To achieve desired particle size of Melamine of + 36 um to when measured by wet screening analysis.
The additives such as TNPP, Silane, PEG, KI and Kaolin are used in the mixture for improving the dispersion, wettability, and processability of Nylon 6. These characteristics are required to be improved because Melamine and its derivatives are need to be introduced into the Nylon 6 matrix to achieve flame retardance properties and a intimate interphase is required to be achieved between the nylon 6 and the flame retarding additive compund.
Raw materials/ additives mentioned in the Mixture-A and B are mixed separately. 25% of the Mixture-B is removed and mixed with the Mixture -A to form Mixture C. Then both the Mixture C and the remaining portion of Mixture B are separately fed into the volumetric feeders simultaneously which are finally conveyed to the hopper of a twin screw compounding extruder EX1. EX1 is a Twin screw extruder is of corotating type where both the screws co-rotate in the same direction . This configuration of screws leads to uniform and desirable dispersive mixing of additives in the Nylon-6 melt.
In accordance with the preferred ombodiment of the process of this invention a twin screw extruder is used instead of a single screw to achieve
6

optimum levels of mixing between the ingredients of the mixtures. The dispersive and mixing effects including kneading are of much hugher magnitude in the twin screw extrusion process.
The processing conditions of this operation are maintained as follows:
Operating Conditions:
Temperature Profile :
Zone I II III to VIII
Temp. (deg.C.) 34 220 245 - 265 degree C.
2) Screw RPM 150-180rpm
3) Feeding Rate Mixture-C 40g/min.
Mixture - B 2.4g/min.
4) Melt Temp. deg.C: 270-290 degree C.
5) Cutter Speed. 50 rpm
Polymer melt is extruded in the form of two strands which are cooled in water to ambient temperature and finally cut into small pieces of size 2 mm X 2mm. The size of the pellets is adjusted with the speed of cutter.
Extruder pellets are dried under vacuum at 80 deg. C. till the moisture content is less than 0.25%. Generally this period is of 24 hours. Finally, dried pellets were packed and sealed in polyethylene bag till further use.
The resulting blend designated as the masterbatch has the composition :
Nylon-6-FR additives : 60 :40
And % yield : 96%
7

Step - II
Compounding of Nylon-6 with Masterbatch from step -I;
Compounding of Nylon-6 with above prepared masterbatch is carried out in co-rotating type twin screw system similar to the operation carried out in Step-I.
A typical batch taken up for blending will contain
Virgin - Nylon-6 (E-35) 35 to 65 parts
Masterbatch (60:40) from Step I : 65 to 35 parts
TNPP 0.10 to 0.30 parts
Sb203 4 to 8 parts
A typical formulation for 5 kg batch based on above stated masterbatch :

Virgin-Nylon-6 (E-35) 1936 g
Masterbatch (60:40) from Step I : 2814 g
TNPP 10 g
Sb203 250 g
Total 5010 g
All the raw materials and additives are mixed thoroughly in a high speed blender for 15 minutes and fed to a hopper of a volumetric feeder and extruded at following conditions in the extruder EX2:
8

1)

Operating Conditions:
Temperature Profile:
Zone : I II III to VI VII to VIII
Temp. (deg. C.) 34 220 245-265 255-270 degree C
2) Screw RPM 200-225 rpm
3) Feeding Rate 80-85 g/min.
4) Melt Temp. deg. C 275 -285 degree C.
5) Cutter Speed. 50-60 rpm

The extruded pellets are dried under vacuum at 80 degree C. till the moisture content less than 0.25% is attained. Thereafter, the pellets are packed and sealed in polyethylene bag till further use. The resulting halogen free, flame retardant Nylon-6 has 72.5% Nylon-6 and 27.5% FR additives. The yield of the product is 96%.
II. Physical Proerties of FR grade of Nylon-6 compared with base materials.
Typical Unit ASTM Test Nylon-6 FR grade
Properties Method Nylon-6
1. Sp. Gravity - D 792 1.12-1.3 1.22-1.25
2. Tensile Strength kg/cm2 D 683 700-50 575-50
3. Izod Impact kg.cm/cm D256 3-4.5 4-5 Strength
(notched)
4. HDT deg. C. D 648 60-2 60-1
5. Water Absorption % D 570 2.5-3 1.30-17.0
6. Melting Temp. deg. C. 220-2 220-2
7. FR rating - UL-94 V-2 V-0
(3.2 mm)
9

III. Processing conditions for injection moulding of components from Flame Retardant grade of Nylon-6 made in accordance with this invention;
1) Predrying at 80 degree C. for 2 hours.
2) Processing Temperature Range:
Rear to Front Zones 245-265 degree C.
Nozzle Temperature 290-295 degree C.
A typical Quantity of Raw materials needed for the manufacture of 1 Ton of FR grade Nylon-6 is as follows:
Raw Materials Qty in Kg.

1. Nylon-6 (E-35) 800.00
2. Melamine Grade-A 245.00
3. Cyanuric Acid. Technical grade 12.00
4. Trisnonyl Phenyl Phosphite tech. Grade (TNP) 3.50
5. Potassium Iodide. KI, tech. Grade 0.15
6. Kaoline, technical grade 1.35
7. T-Amino propyltrimethoxy silane (silane) 1.35
8. Antimony trioxide, Sb203 55.00
9. Poly (ethylene glycol) PEG-4000 1.35
Total 119.70
The usefulness of the present invention is highlighted by the following salient features:
10

1. This process is innovative as Melamine is used synergistic ally with antimony trioxide as a flame retardant and smoke suppressant. In absence of use of Sb203, the desired UL-94 rating of V - 0 is not achieved at such a loading level. This may be mainly due to intumescent effect of Sb203 with Melamine.
2. This process is innovative as expensive Melamine cyanurate is prepared in-Situ using Melamine and Cyan uric Acid. This resulting adduct has added advantages of better dispersion in the polymer matrix.
3. Components made from the flame retardant Nylon 6 in accordance with this invention exhibited excellent therm omech an ical properties.
4. Melamine, Cyan uric Acid and/or their derivatives can be used in the concentration of 10-30 parts with the synergistic additive like antimony trioxide, Sb203 in concentration of 5-10 parts, for preparing Flame Retardant Nylon-6 Compound with "V- 0" rating as per the UL-94 test standards with good therm omech an ical properties.
5. The Flame Retardant performance is achieved at comparatively lower concentration then commercial Melamine Cyanurate for preparation of Flame Retardant Nylon-6 Compounds with superior therm omech an ical properties with "VO" rating as per UL-94 test standards.
n

We Claim:
1. A method of making flame retardant nylon-6 which comprises the steps
of:
Preparing a first homogenous mixture A by intimately mixing 5 5 to 65
parts of thoroughly dried Nylon-6 with 0.10 to 0.30 parts of TNPP; 0.5 to
0.15 parts of silane and 0.5 to 0.15 parts of PEG;
Preparing a second homogeneous mixture B by intimately mixing 35 to 45
parts of thoroughly dried and finely ground melamine with 1.5 to 2.5 parts
of cyanuric acid; 0.01 to 0.03 parts of Potassium Iodide and 0.10 to 0.30
parts of kaolin;
Intimately blending Mixture A with approximately 25% of Mixture B to
form Mixture C;
Dispersively melt mixing Mixture C the remaining 75% of Mixture B in
a twin screw compounding extruder into which the two mixtures are fed at
predetermined rates to obtain pellets of composite mixture of Mixture C
and Mixture B referred to as the masterbatch;
Drying the masterbatch pellets to reduce the moisture content of the pellets
to below 0.25%;
Intimately mixing 40 tO 60 parts of masterbatch pellets with 60 to 40 parts
of virgin nylon-6; 4 to 10 parts of parts of Antimony oxide and 0.15 to
0.25 parts of TNPP to form Mixture D and extruding Mixture D at
temperatures between and 240 to 270 degrees Celsius to form pellets of
flame retardant nylon-6 after drying the pellets to reduce the moisture to
below 0.25%.
2. A method of making flame retardant nylon-6 as described herein with
reference to the accompanying drawing.
Dated this 28th day of March 2000.

Mohan Dewan OfRKDewan&Co Applicants' Patent Attorney.