Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
1999-01-13
2001-02-27
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S312000, C528S323000, C528S326000, C528S336000, C528S480000, C528S499000
Reexamination Certificate
active
06194537
ABSTRACT:
BACKGROUND OF THE INVENTION
Prior art for making nylon 6 on the basis of caprolactam is a process employing mono- or bifunctional carboxylic acids or amines as chain regulators. It has further been known for a long time to use chain regulators based on dicarboxylic acids (cf. U.S. Pat. No. 3,386,967 and DE Pat. No. 4,019,780).
In this known process, reaction partners are caprolactam, water as initiator and the abovementioned chain regulators. Additives such as, for example, pigments (TiO
2
or others), light stabilizers or heat stabilizers may be included for specific applications. A characteristic feature of caprolactam polymerization is the formation of a reaction equilibrium. As well as the polymer, the melt includes about 10% of monomer (caprolactam) and cyclic oligomers. These low molecular weight constituents are dissolved out during chipmaking by an extraction with hot water. The extract water, which has an extractables concentration of up to 16%, depending on process specification, is generally concentrated by evaporation and the lactam separated from the oligomers by distillation. The oligomers are either removed from the process or depolymerized back to lactam. Lactam distillation and depolymerization are extremely energy-intensive.
The direct recycling of the concentrated extract water into the polymerization stage has hitherto been avoided for high grade applications of nylon 6 chip such as textile yarn or industrial yarn of high strength or film. The reason for this is the reduced quality such as reduced strength in the case of yarn or defective areas in film. Moreover, the spinning process is adversely affected by more broken ends and shorter spinning filter surface lives.
The underlying cause of these problems is in particular that the concentration of the cyclic oligomers of polycaprolactam, especially cyclic dimer, increases in the nylon 6 chip compared with nylon 6 chip produced without recycling of the concentrated extract water. The cyclic diner is particularly disadvantageous, since it has a very high melting point of 348° C., which is far above the melting point of nylon 6 (220° C.), and since it is partly present in the polymer melt in the form of undissolved particles or will rise to the surface in this form in the course of the processing into film and yarn and so cause yarn breakages or film defects.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide nylon 6 chip which has been obtained by recycling the extract water and which makes it possible to produce products such as, for example, yarn or film without loss of quality.
This object is achieved with regard to nylon 6 chip by the defining features of claim
1
, with regard to yarn produced with this chip by the features of claim
9
and with regard to film by the features of claim
18
. The subclaims present advantageous further developments.
The nylon 6 chip of the invention is accordingly produced by the extract water being returned into the polymerization process only after admixing with fresh lactam and subsequent concentrating. It is a particularly favorable aspect of the product of the invention that the cyclic dimer content following the extraction with water is less than 0.1% by weight in the polycaprolactam.
It has been found that the addition of dicarboxylic acids is indispensible. This group of substances act as chain length stabilizers. However, compared with monocarboxylic acids which perform the same function, dicarboxylic acids have the advantage in the case of extract water recycling of leading to a lower level of cyclic oligomer in the chip after polymerization. This low level persists throughout the extraction and drying stage into the chip for further processing. In the case of nylon 6 chip produced with the addition of dicarboxylic acids in the polymerization, the problems hitherto observed in further processing or in the end product when recycling the extract water can accordingly be avoided.
An essential aspect of the nylon 6 chip of the invention is that the reaction components are selected and combined in a specific optimum manner for the production process.
The extract water, which leaves the extractor enriched with lactam and oligomer to a concentration of up to 16%, is according to the invention gently concentrated in an evaporator, preferably in a multistage evaporator under reduced pressure. After evaporation, the extract concentration should be 75 to 95% by weight. To prevent oligomer precipitating out of the solution during the evaporation process, fresh lactam is added to the extract water prior to evaporation. The mixing ratio selected for admixing to the extract water is such that there will be at least 1 kg of fresh lactam per 1 kg of water-free extract. The proportion of fresh lactam added thus corresponds to the dissolved extractables (lactam plus oligomer), in the range from 1.0 to 2.0. A further favorable measure to prevent the precipitation of cyclic oligomer from the extract water even better is to maintain a minimum temperature of 80° until the solution is mixed with fresh lactam. These conditions ensure that partial precipitation of cyclic oligomer is prevented and the solution is storable. It is important for optimal polymer quality that this precipitation is prevented.
The temperature during evaporation of the extract water should not be more than 120°. The reaction mixture for the polymerization can have a concentration of 0.1 to 3% by weight of cyclic dimer and a water content between 0.8 and 6.0% by weight.
In another embodiment to produce the nylon 6 chip of the invention, the concentrated extract water from a plurality of process lines is combined before or after admixture with fresh lactam and this mixture is fed into the polymerization stage of a single process line and in this case too the concentration of cyclic dimer is less than 1% by weight on completion of the polymerization. This allows a particularly economical form of processing.
Suitable dicarboxylic acids include C3 to C12 alkane-dicarboxylic acids, e.g., adipic acid, cycloaliphatic dicarboxylic acids having 5 to 14 carbon atoms and/or aromatic dicarboxylic acids having 8 to 14 carbon atoms, for example naphthalenedicarboxylic acids, terephthalic acid or isophthalic acid. Preference is given to using terephthalic acid as chain regulator in the range from 0.08 to 0.6% by weight depending on the desired intended purpose of the nylon 6.
The invention further provides nylon 6 yarn produced using a chip as described above.
In the process of the invention, dried chip is conventionally melted in an extruder and the melt is then forced through spinneret holes. The molten filaments are air quenched and solidified and specifically drawn and wound up by means of take-off elements. The chip of the invention makes it possible in principle to achieve yarn speeds within the range from 500 to 6,000 m/min, between spinneret and first take-off element. It is particularly preferable here to use the nylon 6 chip to produce textile yarn within the conventional spinning range from 600 to 1,200 m/min.
This invention, however, also includes speed ranges of high speed spinning (including the possibility of direct further processing in a process line) within the speed range from 3,500 to 6,000 m/min. Similarly, the chip of the invention permits the spinning of BCF yarn in the speed range from 600 to 2,000 m/min and the spinning of industrial yarn and of tire cord in the speed range from 500 to 1,200 m/min up to the first godet with direct further processing in one processing step. The process of the invention is thus particularly useful for the following yarn:
textile yarn in the conventional spinning process (up to 1,200 m/min),
textile yarn by the high speed spinning process (POY) and in combination with subsequent drawing in the same process (FDY),
industrial yarn and tire cord in the conventional process and in the spin-draw process, and
BCF yarn in the spin-draw-texturing process.
Nylon 6 chip of the invention makes it possible to produce not only nylon 6 filament but also film and o
Hagen Reiner
Raue Eberhard
Hampton-Hightower P.
Karl Fischer Industrieanlagen GmbH
Marshall & Melhorn
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