Note: Descriptions are shown in the official language in which they were submitted.
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Product;on of sheet-like moldings of
f;ber reinf ~
The present invent;on relates to a process for
the production of sheet-like moldings from f;ber-re;n-
forced nylons by alkaline polymerization of a lactam ina closed mold which contains reinforcing f;bers in the
form of a textile fiber structure, eg. a glass fiber mat.
It is known that thermoplastics reinforced with
glass mats can be produced by impregnating glass fiber
mats continuously with a thermoplastic melt and compres-
sing the product. In the case of nylons~ their high vis-
cosity makes this process very difficult to carry out, and
their high melting point furthermore means that it is
very energy-consumptive.
Attempts have therefore been made to impregnate
glass mats cont;nuously with a lactam and to subject th;s
to alkaline polymer;zation. This process is carried out
on a double-belt press under an inert gas atmosphere and
therefore requires very expensive apparatus. Furthermore,
only flat sheets can be produced by th;s procedure.
In the convent;onal alkaline lactam polymeriza-
tion carried out by a batchwise procedure, the monomer ;s
poured into an open mold and is polymerized therein.
Var;ous publ;cat;ons ~eg~ U.Sc Patents 3,451,975 and
3,341,501) ment;on that the polymer;zat;on can also be
carr;ed out ;n the pressnce of additives, eg. glass fab-
rics~ some of which are introduced into the mold even
prior to polymerization. In order to achieve complete,
-~ bubble-free impregnation of the glass mats with the Liquid
monomer, relatively long cycle times are used, which means
that a process carr;ed out on an ;ndustr;al scale will
probably be uneconomical.
DE-A Z8 17 778 ind;cates that the lactam can also
be injected ;nto a mold conta;n;ng glass f;bers. However,
;n the process described there, the lactam ;s introduced
into a mold preheated to only 100C, and is heated to
175-220C in the mold itself, and polymerized. In this
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case, too, the cycle times are long because the mold has
to be heated to 175-~20C each time it has been charged
w;th lactam and then has to be cooled to 100C again.
Moreover, we have found that, at polymerization tempera-
tures above 170C, in part;cular above 180C, nylons
hav;ng a low molecular weight and a relatively high resi-
dual monomer content are formed, and the mechanical pro-
perties are thus adversely affected~ Furthermore, there
is a danger that the conventional activators will decom-
pose at such high polymerization temperatures, producing
bubbles at the surface of the mold.
It is an object of the present ;nvention to im-
prove the conventional process for the production, by al-
kaline lactam polymerization, of sheet-like moldings from
nylon reinforced with textile fiber structures, the ;m-
provement being such that moldings having good mechanical
properties and a satisfactory surface are obtained in
shor~ cycle times.
We have found that this object is achieved, in
accordance with the invention, if the lactam melt is for-
ced, in the course of from 2 to 50 sec, into a closed mold
heated at from 120 to 1~0C, and is polymerized in the
course of less than 3 min at from 120 to 180C to give
a nylon having a K value greater than 100.
It is surprising that satisfactory impregnation
of the textile sheet-like structure present in the mol~
takes place at all when liquid lactam is forced into the
mold under superatmospheric pressure. On the basis of
experience in polyurethane technology, it was to be ex-
pected that the sheet-like textile structu~e would be
swept away by the lactam melt forced in at high velocity,
resulting in non-uniform impregnation and a large number
of air bubbles.
The production of nylon moldings by activated al~
kaline lactam polymerization is known. It is described
in detail in, for example, Kunststoff-Handbuch, Volume VI,
Polyamide, Carl-Hanser-Verlag 1966, pages 46-49. In this
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procedure, the starting mater;als compr;se two components
A and a, component A being a catalyst-conta;ning lactam
melt, and component B be;ng an act;vator-conta;ning lac-
tam melt. The two components are mixed~ transported ;nto
a mold and polymer;zed there;n.
The preferred lactam ;s ~-caprolactam, but it is
also poss;ble to use pyrrol;done~ caprylolactam, lauro-
lactam, enanthlactam and the corresponding C-subst;tuted
lactams. The lactams may also be modified, for example
with polyetherols or isocyanate prepolymers, or with bis-
acyl lactams as described in U~S. Patent 4,031,164.
The polymerization of the lactam ;s carried out
in the presence of from 10 to 75, preferably from 1û to
60, X by weight, based on the ready~prepared molding, of
a textile f;ber structure which is introduced into the
mold prior to polymerization. The fiber structure can be
in the form of a mat, a non-woven, a ~oven fabr;c or felt.
The fibers can consist of glass, carbon, aromatic nylon
or a natural mater;al, such as cotton.
2û 6lass mats having a weight per unit area of from
150 to 1200 g.m Z are preferred. The mats can be compac-
ted mechanically in a conventional manner by means of
needles, or can be bonded by means of conventional binders,
eg. polyurethanes. The diameter of the fibers is prefe-
rably from 7 to 20 ~m, and the glass fibers are advanta-
geously sized with a conventional size which does not
interfere with the polymerization, as described in, for
example, US-A 4 358 502.
~; Examples of suitable catalysts are alkali metal
3û compounds and alkaline earth metal compoun~s of lactams,
such as sodium -caprolactamate, or of short~chain ali-
phat;c carboxylic acids, such as sodium formate or potas-
sium formate, or of alcohols of 1 to 6 carbon atoms, such
as sodium methylate or potassium tert.-butylate. It is
also possible to use alkali metal or alkaline earth metal
hydrides, hydroxides or carbonates, as ~ell as Grignard
compounds. The catalysts are usually employed in amounts
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of from 0.1 to 10 mole X based on the total amount of lac-
tam.
Su;table act;vators are N-acyllactams, such as
N-acetylcaprolactam, b;sacyllactams, substituted triazines,
carbodiimides, ketenes, cyanam;des, mono- and polyiso-
cyanates and masked isocyanate compounds. They are pre-
ferably employed in amounts of from û.1 to 10 mole X.
The impact strength of the molding materials can
be increased by means of conventional additives, such as
polyalkylene glycol~ having molecular weights of from
2000 to 1ûO,OOO, or by adding reactive or non-reactive
rubbers, eg. graft polymers.
The polymerization of the lactam can be carried
out in the presence of a convent;onal stabilizern A com-
bination of CuI and KI ;n a molar ratio of 1:3 is par-
ticularly advantageous, this combination being added to
the activator-containing component B in amounts corres-
ponding to 50-100 ppm, based on the total amount of lac-
tam, of copper. Other suitable stabilizers are crypto-
phenols and aminesA
Other additives are inorganic f;llers which do notinterfere w;th the polymerizat;on, eg. metal powders,
powdered quartz~ metal oxides, graph;te, carbon black,
silica gel, pigments, wo~lastonite and chalk, which are
used in amounts of froM 10 to 60X by weight, based on the
molding. It ;s also poss;ble to add light stabilizers,
optical brighteners, flameproofing agents, crystallization
accelerators, eg. talc or nylon-Z,2, lubricants, such as
molybdenum sulfide, and shrinkage-reduc;ng substances.
It has proven particularly advantageous to add
antifoams in amounts of from O.û5 to 5, preferably from
0.1 to 1, X by weight, such substances preventing the in-
clusion of air bubbles in the molding. Preferred ant;~
foams are 5-ZOX strength by weight solutions of d;ene
polymers, in particular polybutadier,e, in organic solvents,
in particular aromatic solvents. Antifoams of this type
are supplied by Mallinckrodt and have the names R~YK A 50û
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~ 5 ~ O.Z.'OOSOt36622
and A 501~
It is also advantageous to add internal release
agents in amounts of from 0.05 to 2X by weight, eg. cal-
cium, sodium or potassium stearate, stearyl stearate or
octadecyl alcohol.
The procedure used in the novel process corres~
ponds to a modified reaction injection molding (RIM) tech-
nique described for polyurethanes, for example by Piechota
and R~ohr' in "Integralschaumstoffe, Carl~Hanser-Verlag,
197S, pages 34 to 37.
The two components A and ~ are heated separately
in kettles to a temperature above the melting point of
the lactam, preferably 80-140C, and are transported by
means of hydraulically driven, heated plunger pumps through
heated pipes to a mixing head which is Likewise heated.
When the material is pressed into the mold, the plunger
of the m;xing head is drawn back, and the two accurately
.,
metered components enter the open mixing chamber, are
mixed intimately therein and are pressed into the mold
which is connected by means of a flange. This takes place
in general under a pressure of more than 1, preferably
from 1.1 to 300, in particular from 2 to 30, bar. How-
ever, it is also possibLe in principle to carry out the
procedure under atmospheric pressure if, by using special
apparatuses, care is taken to ensure that the melt is
sprayed sufficiently rapidly into the mold. Transfer of
the lactam melt from the mixing head into the mold is
complete in the sourse of from 2 to 50, preferably from 3
to 20~sec. The mold need not be flushed with nitrogen.
In accordance with the invention, the mold is pre-
heated to 120-180C, preferably 125-160C, in particular
130-150C. Since the textile fiber structure has been
introduced into the mold beforehand, it also assumes the
mold temperature. The lactam melt warms up rapidly in
the mold to reach the temperature of the latter, and poly-
merizes in the course of less than 3 min. In general~
the ready-prepared molding can be removed from the mold
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after as little as 1 to 2 minutes. At a polymerization
temperature of from 1Z0 to 180C, the resulting h;gh
molecular weight nylon has a K value (according to Fikent-
scher, Cellulosechemie 13, page 58) greater than 100,
preferably from 110 to 160, and contains less than 3X,
preferably less than 2%, of monomers and oligomers. The
K value can be controlled by adding convent;onal regula-
tors, for example long-cha;n al;phat;c monoamines, such
as stearylamine, or crossl;nking agents, such as methyl-
eneb;scaprolactam.
The process accord;ng to the ;nvent;on can be
used to produce large sheet-l;ke mold;ngs, for example
panels hav;ng a thickness of from 0.5 to 20 mm. These,
be;ng sheet-l;ke preshapes, can be processed further to
g;ve finished components by pressing at above the melting
point of the nylon. Ho~ever, if appropriately shaped
molds and contoured mats are used, it is also possible to
produce finished components directly.
The moldings produced using the novel process
possess good mechaniçal properties and a satisfactory sur-
faceO They are particularly useful as shaped articles
for the automotive and aircraft industries, for example
for bodywork co~ponents, such as fenders and doors, for
;ndustr;al housings and for the product;on of sandwich
components.
In the Example which follows~ percentages are by
~eight.
EXAMPLE
Formulation for Com onent A:
P
30 43.75 9 of caprolactam~
6.0 9 of a 17.5% strength solution of sodium lactamate
in caprolactam and
O.Z5 9 of a 14X solut;on of a modified polybutadiene in
a m;xture of aromat;c hydrocarbons (R8YK A 500
~- 35 from Mall;nckrodt).
Formulation for Comoonent B:
41.2S g of caprolactam,
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8.5 9 o~ a solution of 83.5% of caprolactam and 16.5%
of hexamethylene di;socyanate and
O.Z5 9 of BYK A 500.
Component A was preheated to 100C, while com-
S ponent B was preheated to 128C. The components were
m;xed, ;n a rat;o of 1:1, in a self-purging mixing head
w;th a plunger produced by Elastogran Masch;nenbau, Strass-
lach.
The mold cav;ty ~as a steel mold of ;nternal d;men-
s;ons 640 x 240 x 4 mm, ;n wh;ch three glass mats having
a we;ght per un;t area of 600 g.m 2 were placed one on top
of the other without being f;xed. The mold together w;th
the glass mats was preheated to 150C. The m;xture was
transferred from the mix;ng head ;nto the mold under
atmospher;c pressure ;n the course of 7 sec. Xt warmed up
rap;dly to 150C, and polymer;zed to give 3 nylon ha-
ving a K ~alue of 130. After 1.5 m;n~ ~he mold was opened
and the completed molding was removed. It contained 35X
of glass fibers and had a smooth, bubble-free surface.
For comparison, a mold;ng was produced us;ng the
sa0e apparatus and the method descr;bed in DE-A 28 17 778,
the mold being preheated to only 100C, and subsequen~ly
be;ng heated to 177C in the course of 15 min. After
2 hours, the mold;ng was removed. The nylon had a K
value of 94 and contained 4X of monomer, resulting in
poorer ~echanical properties, in particular poorer ten-
s;le strength. The molding had a very poor surface.
