CA1064644A - Polylauric lactam, method of making higher polylactams and their application - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention relates to higher polylactams, their method of manufacture and their use. The new polylactams have advantageous proper-ties over known polylactams and are prepared by a novel method based on the surprising discovery that the addition of an activator after the addition of a catalyst to a monomeric lactam melt produces a polymer having different properties from those of known polylactams. Heat generated during the novel process is greatly reduced resulting in a novel product free from stresses and one which is completely homogeneous.

Description

64~

The present invention relates to a new higher polylactam, a method of making higher polylactams and their application.
The well-known polyamides 6, 6.6, 6.10, 11 and 12 obtained by polymerization from the corresponding lactams and, respectively, by polycon-densation from the corresponding dicarbonic acids and diamines, while possess-; ing numerous good properties, are unsuitable for numerous applications, -~
particularly for processing by metal casting methods. ;~
In the production of polyamide 6 from E-caprolactam the melt is forced, under high pressure, into very costly injection moulding tools in injection moulding machines. The larges* moulds will at present hold 20 to 30 kgJ it being possible only to make components of uniform wall thicknesses according to this method. This method is furthermore suitable only for mass production since the costs of the injection moulding machines are very high.
In the application of the casting method to ~-caprolactam the great advantage must be accepted that, after melting the monomer at about 70C with the addition of catalysts and activators, the moulds must be brought `~
to a polymerization temperature of 175 to 178C and kept at that temperature ~ `~
for 2 to 10 hours depending on the desired wall thickness of the moulded body since no serviceable product will otherwise be obtained.
In particular in making large moulded bodies and, respectively, in making moulded bodies of great and/or varying wall thicknesses, this requires ~ -subs~antial invsstments in equipment and time owing to the relatively high , heat tone of the polymerization reaction of about 37 kcal/kg and o~ing to the inadequate thermal conductivity of the materials employed. In addition, it must be ensured in making moulded bodies according to casting methods that ~
ambient air is excluded whenever possible otherwise a homogeneous body is not ~;
obtained owing to the oxygen and water content of the air. In general it is `
found that the range of applications of the said method is comparatively limited, particularly in respect of the dimensions that can be obtained.
The polyamides 6, 6.6, 6.10 and -caprolactam monomer castings .:

3 064~ii44 display the serious disadvantage that they obtain their optimum properties only in the conditioned state, i.e. when a certain water content is homogen-eously distributed. In completely dry conditions the materials made of these products, while very hard, are brittle, in the case of water saturation, they do indeed become ductile but lose their hardness. Where the water content - varies between o% and 11%, the volume of the said materials undergoes a linear change by about 0.25% per percent water absorbed, i.e. dimensional ... ~ .
stability is not adequate for most applications, more particularly, the use in brackish and sea water is virtually excluded. In addition, all mechanical, chemical and physical properties of the said materials change very notably with theîr water content.
The polyamides 11 and 12 do not exhibit the disadvantage of high water absorption. However, the preparation of the polyamides 11 and 12 calls ~;
for many complex procedural steps. The the~moplastic polymerizates oannot be cast when in workable condition owing to their high viscosities. Process-ing therefore necessitates the same costly equipment as in the case of the ; polyamides 6, 6.6 and 6.10.
The present invention relates to a new polylactam which is devoid ~ of the abovementioned disad~antages and distinguishes itself favourably from known polyamides.
` According to the present invention, there is provided a method of making polylactams by polymerizing a monomeric higher lactam having 12 to 15 .~:
carbon atoms in the lactam ring~ which comprises fusing the monomeric higher lactam, mixing a catalyst with the higher lactam melt, and thereafter mixing an activator with the catalyst/higher lactam mix, the higher lactam melt being kept at a constant temperature during mixing with the catalyst, and during the subsequent addition of the activator and the consequent polymerization.
In another aspect the invention provides a polylauric lactam which is characterized in that it will not melt during heating hut disintegrates in ~ `
; d~ .. `. ...

2-;

~.~6~ 4 ~ ~
air within the range of approx. 2t7 and 271 C and cannot be regenerated.
A preferred polylauric lactam possesses~ besides the aforemention-ed properties~ a yield stress ~S of approx. 470 to approx. 520 kp/cm2 measured according to DIN 53 455, an elongation under yield stress ~S of approx. 17 to ~ -approx. 25% measured according to DIN 53 455, a tensile strength ~R of approx.
500 to approx. 630 kp/cm measured according to IS0 R 527, an elongation at yield ~R of approx, 200 to 350% measured accordir~ to IS0 R 527, a modulus '' ,' ''', ... .
` ' .'`.'` : ' ' ' . ~ ~

'' '.`''', . ~ , .. .
. - .
, -2a_ ~ ~i3 ' 1a)64~;44 .

of elasticity E of approx. 19,000 to approx. 22,000 kp/cm2 measured according to DIN 53 457, Sec. 2.3, an ultimate bending stress ~B of approx. 750 to approx. 1000 kp/cm2 measured according to ISO R 178, a notch impact strength ak of approx. 55 to approx. 65 kp/cm2 measured according to DIN 53 453, a ball-pressure hardness 10" of approx. 1000 to approx. 1050 kp/cm2 measured accor-ding to DIN 53 456, step C, an abrasion strength of approx. 158 to approx.
129 mm3/rpm measured according to Taber-Ab^~azer, a time yield stress ~l/lOOO
~23C/95%) of approx. 50 to approx. 60 kp/cm2 measured according to DIN
53 444, and a creep modulus EC/1000 (~ 20.0) of approx. 13,000 to approx.
14,000 kp/cm2 measured according to DIN 53 444. The above properties refer to a pot time of 60 seconds.
The new higher polylactam according to the invention, hereinafter referred to for simplicity as polylauric lactam~ while resembling polyamide 12 in some of its properties, differs fundamentally therefrom in that polylauric lactam does not fuse when heated but disintegrates into a crumbly substance in the range of approx. 217 and 271C without forming a liquid phase in the process. Once that polylauric lactam has disintegrated, it can no longer be regenerated. In contradistinction, polyamide 12 fuses at approx. 260C and can then be processed and repeatedly melted.
Against the kno~n polyamide 12, polylauric lac~am has a metallic sound. Polylauric lactam therefore significantly differs from the known poly- -amide 12. In addition, a further difference between polylauric lactam and ~-~
the known polyamides in particular resides in its high cold resisting property down to -60C, its extremely low water absorption and the high dimensional stability resulting therefrom of moulded bodies made of the product, and by the ready capacity of being processed by casting, it being possible easily and reliably to obtain cavity-free moulded bodies of a weight up to several thousand kilogrammes.
The invention furthermore relates to a method of making polylactams by polymerizing at least one monomerous higher lactam, particularly lauric 1~;4~4~

lactam, the monon~erous lactam being fused and at least one catalyst and at least one activator (initiator) being added to the melt, characterized in that the melt is first mixed with the catalyst and the mix so obtained mixed with the ac~ivator.
The term "higher lactams" in the present disclosure stands par-; ticularly for lactams with 12 to 15 carbon atoms, i.e. for the lactams of the lauric, n-tridecan, myristic and n-pentadecane acids.
It is well known that, in the polymerization of lactamsJ the mono- ~`~
merous lactam is melted and the melt mixed with at least one catalyst and at least one activator, whereupon the polymerization reaction occurs. It is also known from the Swiss Patent No. 479,654 and the German patent disclosure No.
2,108,759 that polymerization can be performed by mixing the catalyst into a portion of the lactam melt and the activator into the other portion of the said lactam melt. Polymerization occurs after mixing the part melts so ob- - -tained. "
The present invention is based on the surprising discovery that, when the sequence of adding the catalyst to ~he melt of the monomerous lauric ~`~
, . - . , lactam and the subsequent addition of the activator pursuant to the invention, a new polymerizate is obtained with properties which differ from the pro-~, .
perties of the known polymerizates and, more particularly, distinguish them-selves to their advantage from the properties of the known polyamide 12. ;~
The properties of the new polylauric lactam will now be explained `~
in greater detail and compared with the corresponding properties of known ` -~
polyamides.
~igure 1 shows the behavior in terms of tensile stress against ~ `
time of polylauric lactam in comparison with~polyamide 6.10, the polyamide with the best behavior in terms of time;
, Figure 2 shows the dependence on temperature of the yield po mt ? of polylauric lactam as per DIN 53 455;
, ~ - : " .,.
Figure 3 shows the notch impact strength of polylauric lactam in , ~ ~

~, ;, "~ , , - 4 - `~

,' 1~4644 dry conditi.on as per DIN 53 453 (hexane tempering liquid);
Figure 4 shows the dielectric loss factor tan ~ of polylauric lactam at 100 cycles in dependence on temperature;
Figure 5 shows the dielectric strength of polylauric lactam in dependence on temperature; :
Figure 6a and 6b show the water absorption of polylauric lactam : when stored in water of 20C;
Figure 7 shows the specific volume of polylauric lactam in depen-dence on temperature.
The Table 1 below represents the mechanical properties of poly- -lauric lactam as compared with the corresponding properties of polyamides 6, : ;
6.6, 11 and 12: ~ ~

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, o a~ :
.~ .
~ h ~ o\ L~ .
00 0 L~
O ~I h ~ ~ ~ N ~
U.l 3 V) ~ L~ O L~ 1~
.
O O O O O
Ul N L'~ N~1 0 N
~:) Vl ,q1~ L~ L~ L') L~ . .
~> h O o O o o : :. ' , ~ Vl X \~L" ~ ~ ~
" :
F3 ~!; O N ~J N
o ~ ~_t ~ o O .~' a) u~ o o o ~ ~ "
h Vl oo o o o L~
N N N OOQ O ',- . .
--I ~ h ~ O O o O o ~ ~
t~ h td ~, NL'~ O~ ~ O .. : .
,' ~ ": :' .
'''' ~ . ":
`; ~1 ~ gL~ O O ;~
:, . ,1 L" L~ ~ 00 :
v~ `I N~1~I N ~
j~ . ,~ N I I I I I "
o o ~ o c~

~` ~ .,~
~ ,D ~ ~
~ L~ 00 N L~) L~
~ ~ h ~I N L~ L~
~, Z ~ C ~ CO L~ L~

` ~ ~,o o O O 0 0 '`~' ~`''' tn N L~) O N 3 0 .~ ' ~
h ~ 0 o o o o : `'- ::
, ~ r; ID ~P`~ NL~ O O L~ i .

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Vl N N ~ t~
o oo ' o o ` ~ ' :' ~ 1~ ~ N : O

Vl N N N `D O
0 h ~ 0 o o o o `.- . ~ ~ -: ' . rl ~ ~ O NL~ O O ' ` ~ ; ' " . :-: .
r ~ N
~:)h h '~

O O O o otd ~ ~
i P~ :-, : . ' ',. r-l N ~ ~L"
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1~6~644 'I'able II reflects the elec~rical properties of polylauric lactam:

Table II ~ ;
;:~
. . . _ _ . _ . _ _ _ _ . _ _ _ _ _ Property Measuring method Dimension Value Dielectric factor DIN 53 483 3.6 (1) at 800 cycles VDE 0303 TI.4 4.2 (2) . 5.5 (3) :; Dielectric loss DIN 53 483 40-10 3 (1) factor tan ~ at VDE 0303 TI.4 90-10 3 (2) ` 800 cycles 140-10 (3) : Dielectric streng~h DIN 53 481 kV/mm 33 (1) VDE 0303 TI.4 31 (3) Specific volume DIN 53 482 Q.cm 10-10153 (1) resistivity VDE 0303 TI.3 10-1013 (2) 1-10 (3) . Surface DIN 53 483 Q 30-101 (1) : resistivity VDE 0303 TI.4 6-10 2 ~2) ~ o~4~1ol2 ~3) . .~
Leakage current DIN 53 480 stage T 5 ` resistance VDE 0303 TI.l (4) KA 3 B .

.; : : . .
:. 10 ~1) dried for 14 days over phosphorus pentoxide (2) 14-day storage at 65 rel. air humidity and 20C .: :
~ (3) 7-day storage in water at 20C ::
: (4) Testing solution A ~-' '.'~ ': ~ ' : ;. ,.

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:, . .:

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~646~ :

Table III recites the thermal properties of polylauric lactam:
Table III
'.

'`;:
Property Measuring method Dimension Destruction tempera- depending on C 217 - 271 ~ :
ture in the atmos- formula --phere ~in air) . .
Destruction tempera- VICAT B DIN C 178 `. ~
ture in direct con- 53 460 :~ -tact with the heat source Linear coefficient at -60 to ~30C 10 / C 0.8 - 1.0 of expansion, ~ at +30 to + 100C 1.0 - 1.9 Coefficient of ther- kcal/ 0.3 mal conductivity A mhsrd ~ ;
Spec. thermal kcal/kg 0.45 capacity cp grd ~:
Temperature limits up to a few hours C 155 ~: :
in application up to 4 months C 120 - 130 -:
up to years C 100 - 120 :~
,`'~
t ` '' '' ,..
Table IV represents further properties and/or parameters of polylauric ~ :
lactam:

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)/' '.

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,,t .
. ' I : ' ' 1 :, ., j ~ ~, .

,t .',~ '~' ' ' ~, - 8 - ~
., , ,.i :..
:-::: . : : . :

1~i46~

Table IV

n n '' 5- ~3 ~ ~ 1~ L t` N
O ~ ~1 0 ~1 ~1 0 ~ h ~ ~ h t~ h h ~, h ~ ~ h 4, .,~
: ~ n .c ~ ~ ; .
~ , . o o '~
.: '~o o o n _I ~
N 1~ _I O O h h h .~: :. ~ O O00~) t~ Lr~N ~ ~ ~ .. : :
. .. . a.) o o o ~1 ~1 4-l i'~ ., oo z n ~ 1~ ~ o c~ ~ ~d .," ~ .

;: ~:
~' .
El ~ o\ o\ O~o 0\O o\

h ~ `~ ~
. ~ ~ h :~ :
, ~ bO a~ '' ~ ' ' ' ,1 Lo n O t~4 h ul .,.
. ~ `:: : ~ h ~ ~ h ~

~_~ ~ ~ O ~ N ~ ~ . . ` ~ .
s~ ~ o o o a ~3 ~ ~ ^ ~ , :~ n ~ ~o n ~ ~ cd ~ a ~ f~
:~ ~ Z z ~ h ~ h ~3 ;, a,) H ~ ~-- H O H Z ~'d ~rl O
~: ~ ~ ~da O O H ~ O 40~
,~ ~ O~ ) ~L, ~'' ' ':
~ ~0 '~, .''~''' ' ,, ~ S~ ,S~

C~ 30 ~,1 ~ O O ~ ~ ~ h u) i :
~>~ ~ ~` .rl C~ R a~ ~- ~h ~
.:~ ~ ~ aP~ o ~ ~ ~
.,1 u) h ,1 a~ 3 ~ ~rl R ni ~ O~J~ o\ h R h ,~ O~ ~ O ~ ~ ~
~ ~ t~ o ~ ~ O~ ~ ~0 O ~ .:
;' h u) .,1 ~r~ h ~ ~ h O ~ O ~ ~ R
P~ ~ h .~1 ~ a~ O a) ~h 3 H R~ O ~ o h O~ X ~: ~ , ~ O

:~ _ g _ ', "' ` , ' , .: : - , :: , 106~S44 Table V is a compilation of water absorption and length varia~
tion by water absorption according ~o DIN 50 014 of polylauric lactam as : :
compared with the corresponding values of polyamides 6, 6.6, ll and 12: ~-: ' : ~, :',' ' '' :' :
:'; . :~-.-~
`-:' ':
~,;'., .' ~ '', ., '~ ' `.:,~ ''. :' ' .,., ~ ~ , .
~: . : ` '`

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::

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,, . : .~

-.: ', ~ ': ' , :-, ,: :
.'.~. . ;: ,~
';~ : '~
: . ~ ',' ', . ~ ., , ,,.'~ ~ .

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:j ~:
';,' '~. , ::' .' '' ~, ~, :;

- 1~646~ ~

_ ~ ~n l __ W [ 1 l _ 2 2~ l _ 2 2~ _ . ~
~~ i N ~n I r r~ o o D C I i

3 ~

, . - .
,.. ..
,.~ . . h h h h h ,,1 3 3 3 ': . g g o~ ~ ' o~ ~ g o~ ~ g ~ .' ~ :' .. 1 `D O 'h ~:: `D h ~rl ~I h ~rl ~I h rl h ~rl , ... :.
D :~ ~rl ~ D :~ ~rl ~ d o ~ O h R h h ~ . :
X h ~ ~ X h ~ o ~ 0 0 ~ a) t~4 0 ~ ~re) O l~i t-d O,D O t~ t~ O,D O t~l ~ 0,8 0 a ~ ~ ~d ~ ~ 3 ~ ~ ~ ~ 3 ~ ~d ~ ~ 3 ~ ~ ~ a ~' .. ..

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6~644 The transverse and longitudinal shrinkage of polylauric lactam is compared with the pertinent values for the polyamides 6, 6.6, 11 and 12 in Table VI: -~
Table VI

Transverse Longitudinal ~
shrinkage shrinkage - ~ -~: % % ,~
Polyamide 6 1.6 2.5 ` Polyamide 6.6 1.3 3.8 -Polyamide 11 1.4 3.1 Polyamide 12 1.4 3.0 Polylauric lactam 0.9 0.9 ;~

~ Polylauric lactam is inert to water, including brackish and q sea water, at temperatures up to 90C; it is resistant to weak acids and alkalis and to most organic solvents, possesses a high specific electric resis-::. :: :tance and dielectric strength, a high abrasion and wear resistance and a low ~;
specific weight of 1.02 g/cm3.
The extractable component in polylauric lactam is low owing ~o the small quantities of catalyst and activator added; it amounts to a maximum of 0.5%. Polylauric lactam therefore possesses high resistance to aging.
As shown in greater detail in the tables and drawings, poly- ;
.
lauric lactam possesses outstanding properties which are rarely inferior to, and frequently substantially better than, those of the known polyamides. By ~ ~;
~ . .. ..
way of example, the values of the ultimate bending stress, notch impact ~ -strength, modulus of elasticity, ball-pressure hardness, elongation at yield, ,~ length variation by water absorption and shrinkage are higher than those of :. .: : ~
the polyamides 6, 6.6, 11 and 12.

Further resùlts of material tests are recited below. They reflect the excellent properties, so far unequalled in their totality, of :: .
polylauric lactam as well: ;~

~, ,! :

~646~4 a) Organic plastics are considered to be unbreakable in practical ;~
use if possessing a notch impact strength of at least 5 kpcm/cm2; according to this definition, polylauric lactam is unbreakable down to -80C.
b) In determining stability in terms of time of pipes made of poly-; amide 6, 11 and 12 and, respectively, polylauric lactam in water of ~0C, it was found that polylauric lactam and polyamide 11 possess, in comparison with -the polyamides 6 and 12, a comparative bursting limit which is approx. 30%
higher and a life under the same stress which is longer by several decimal powers.
c) The electrical properties of polylauric lactam are less reduced by ambient humidity than the properties of the known polyamides. ~hile the polyamides 6, 6.6 and 6.10 are only rarely used as insulators, polylauric lactam and the polyamides 11 and 12 may still be used as insulating materials ~ `
at high ambien~ humidities and not excessively high voltages.
d) Polyamides are resistant to alkaline liquids but are attacked by . :, . . .
-` acids, particularly at high temperatures. The polyamides 6, 6.6 and 6.10 -`
:.:, .. . .
j~ will dissolve in concentrated formic acid while such is not the case with poly-: ~ ~... .. ..
lauric lactam and the polyamides 11 and 12. Nor do the polyamides 11 and 12 ~
` ..................................................................... . .. .
and polylauric lactam reveal an inclination to embrittlement. In 1 n-sulphuric acid of 80C polylauric lactam has a life more than ten times higher than the~
polyamides 6 and 6.6. The polyamides 11 and 12 behave similarly as the pro-; duct forming the subject-matter of this invention. -e) The resistance of polylauric lactam t polar solvents proved to be partly equal toj and partly substantially better thanj that of the known polyamides.
:~-~ ,... . .
f) Test specimens under mechanical stress and formed of the poly- ~ -amides 6, 6.6 and 6.10 break down in 70% zinc chloride solution at 70C after ~
., :-., ~,-, only a few hours or minutes while samples made of polylauric lactam have been - v tested for over 200 hours under the same conditions without the appearance of tension cracks. i-.:. ,,, ~ .
'~ ` ':'~., '`'' ',~ i,', ~L~64644 g) Polylauric lactam is superior to E-caprolactam monomer castings in decisive respects. By way of example, polylauric lactam at 60C absorbs a maximum of approx. 0.3 percent by weight of water, only a negligible '~
change of volume occurring and the other properties hardly changing. Poly- '~ -- lauric lactam preserves its ductility up to approx. 80C while ~-caprolactam ~
.~
' monomer castings embrittle at only 0 to -5C. '~
The method according to this invention will now be dsicussed in greater detail by the example of the polymerization of lauric lactam for the ~purpose of producing the new polylauric lactam. To this end the lauric lactam `' -is first fused and the catalyst mixed into this m01t. Following thorough `~
mixing, the activator is added to the mix. Addition of the catalyst to the ;~
' lauric lactam melt, the subsequent addition of the activator and polymeriza--' tion are preferably performed at constant temperature. The melt is expedient~
ly kept at temperatures in the range of 150 to 200C~ it having been found `~
that the best res'u~l'ts are obtained at about 160C.
The addition of the activator according to the method of this ' ;~
invention may be effected shortly after the addition of the catalyst to the lauric lactam melt, HoweverJ the activator may also be added substantially later, e.g. approx. 48 hours after the addition of the catalyst, no polymeriz- ~
ation occurring in the meantime provided that the temperature of the mix ~ ~ `
of the lauric lactam melt and the catalyst is kept at a suitable and advan~
tageously constant level. '~ -For the purpose of mixing the lauric lactam melt with the catalyst '`~
and the addition of the activator respectively a mixer is expediently employed I which ensures fast and homogeneous intermixing.
According to a further preferred embodiment of the method accor-ding to the invention, the catalyst is first added to the stream of the mono~
merous lactam while the activator is added at a point downstream of the point '~
' at which the catalyst was added. In this way the method according to this -~
invention can simply and safely be performed continuously.

'~ - 14 -

4 ~

The mix obtained after mixing the two additions into it in the ;~
order according to this invention is as yet highly fluid and easy to process.
It may therefore without any problem be cast into moulds to make moulded `
bodies or passed through nozzles virtually under no pressure. The disadvan-tages, described above~ in processing known viscous polyamides are thus effec- ~ -tively avoided.
It should be made sure that the lauric lactam used is perfectly free from water and that the method is performed while air is excluded to the moment of casting or otherwise applying the melt since the presence of oxygen - ~
and water prevents the formation of a flawless product. Fusing the lauric ~ -`' ! '.
; lactam and adding the catalyst and the activator are therefore preferably ~` performed in an air-tight container under impinging inert gas such as nitrogen. ;
Another inert gas which may be employed is carbon dioxide which - as explained below - at the same time serves as a catalyst.
All the catalysts known in the production of polyamides may be applied in the method according to this invention. Metallic sodium, sodium amide, alkali lactams, anhydrous ethanol and carbon dioxide have proved to be :. :
; excellent and are therefore preferred. `
Again, the compounds known as activators cinitiators) in the pro-duction of polyamides, such as isocyanates, e.g. phenyl isocyanate, substitut-ed lactams, e.g. N-acrylic lactams and N-cyanolactams, substituted ureas and reaction products of carbamic acid chloride with heterocyclical compounds such : ~ ~: ,-as imidazole, may be employed.~ It has been found that particularly good results are obtained with phenyl isocyanate, and for this reason this compound constitutes the activator preferred in the method according to this invention.
The catalystCs~ and the actîvatorCsl are added to the lactam melt in quantities of a total of 0.01 to S percent by weight and preferably of 0.1 -to 0.6 percent by weight each. If the catalyst employed is sodium amide~
metallic sodium or anhydrous ethanol~ additions of catalyst and activator of . j , : .
-~ 30 approx. 0.38 percent by weight each referred to the lactam melt have proved to ~ ~

:; .
,:-, . ,: ;:

", '"' ~-.

~', :. .
. . , ~

~ 6~644 be particularly effective. If carbon dioxide is used as a catalyst, the lactam melt is preferably saturated with the carbon dioxide; in this case an activator addition of less than approx. 0.2 percent by weight is adequate.
This invention furthermore relates to the use of polylauric lactam ;~
for the production of moulded bodies, particularly according to pouring -practice.
After the catalyst has been added to the melt of the monomerous lauric lactam, after the subsequent addition of the activator and thorough : . .
; mixing, the mix begins to solidify approximately one minute after the activator has been added. Solidification occurs homogeneously through the entire volume of the melt. The total thermal tone amounts to only approx. 6 kcal/kg while a heat tone of approx. 37 kcal/kg occurs in the solidification of e.g. -caprolactam monomer casting. The said low heat tone presents the advantage that setting is free from stresses caused by irregular heat dissipation as is frequently the case with some of the known polyamides.
.~ ..
Since the melt prepared according to this invention is highly .
` fluid and heat dissipation occurs without p:roblems, moulded bodies of very ~ ` ~
...;
:.
large dimensions and any wall thickness may be made, which has so far not been possible. In addition, for=ation of the moulded bodies can be effected, thanks to the highly fluid melt, virtually without the application of pres~
sure. The inherent stress in the moulded bodies made according to this inven-` tion is far below the critical limit owing to the low thermal tone in solidifi-cation. Owing to the high fluidity of ~he melt prior to homogeneous solidifi-cation no cavities are formed in the moulded bodies.
Using the melt prepared according to this invention enables, inter alia~ moulded bodles with a complex geometry, also with sand cores for undercuts, to be cast in a simple manner. `
The melt prepared according to this invention may be compared with castable metal melts in respect of its processing properties. In using the melt prepared according to this invention, the moulds employed need not ~

,,~ ':
~; - 16 -. ,.

~ .

be preheated or cooled. }lowever, it has been found that particularly smooth castings with a homogeneously coloured surface are obtained with moulds preheated to e.g. 90C. The strength of the moulded bodies after solidifica-tion first increases fast and then more slowly, and reaches its peak value after approx. 48 hours. The moment after casting at which the castings may be removed from the moulds depends on the sizeJ the shape and the weight of -the moulded bodies cast. Ligher components may be removed from their moulds immediately after the melt has solidified, i.e. approx. 1 minute-after casting;
heavier parts are left in their moulds correspondingly longer.
The high fluidity of the melt, its high degree of wettability and great adhesion to non-greasy surfaces of other materials make it furthermore possible to manufacture compound materials and compound bodies. By way of - example, nonporous compound bodies may be made which incorporate fine-meshed . , : , metal and glass-fibre fabrics. In addition, the moulded bodies may be provid-ed with metallic reinforcement and stiffenings of a variety of kinds which are placed in the polylauric lactam when it is being cast. ;~
By virtue of its outstanding properties, the polylauric lactam may be employed instead of metal in many fields of application.
` The following examples exemplify this invention:
Example 1 A 10 kg batch of lauric lactam is placed in an air-tight container provided with an agitator while nltrogen is added continuously as an inert gas.
The lauric lactam is melted under agitation and the interior temperature of the container is then fixed at 160C. 3.8 g sodium amide is then added to the container while the contents are agitated. The contents of the container are -, .
agitated for 5 minutes. 11.5 g phenyl isocyanate is then added to the mix -and the latter strongly agitated afterwards for 1 minute. The melt is subse- -; quently cast into a mould and allowed to solidify. After solidification the ~ ~
.. "~
~: moulded body obtained is removed from the mould. After 48 hours it will possess the properties indicated in the above disclosure and in the drawing.

: ,....

1~)64~;44 ~

Example 2 , The procedure according to Example 1 is repeated with the excep-:
tion that the lauric lactam melt is saturated with carbon dioxide and only

5 g phenyl isocyanate added. ~In this case the carbon dioxide serves as both inert gas and catalyst.) The moulded body obtained possesses the same -properties as the product made according to Example 1. ; `~ -~
Example 3 Anhydrous ethanol is continuously added as a catalyst at a con-stant rate to a stream of lauric lactam melt constantly kept at a temperature ~
of 160C, air being excluded. At a point downstream of the point where the ~ -catalyst was added, phenyl isocyanate in a quantity corresponding to the ethanol quantity is continuously added to the melt. After mixing the stream, ,, ~;, constantly kept free from air, is poured into moulds. The moulded bodies obtained after solidification of the mix possess the same properties as the product obtained according to Example 1.

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Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of making polylactams by polymerizing a monomeric higher lactam having 12 to 15 carbon atoms in the lactam ring, which comprises fusing the monomeric higher lactam, mixing a catalyst with the higher lactam melt, and thereafter mixing an activator with the catalyst/higher lactam mix, the higher lactam melt being kept at a constant temperature during mixing with the catalyst, and during the subsequent addition of the activator and the consequent polymerization.

2. A method according to claim 1 characterized in that the melt is kept at a temperature in the range of approx. 150 to 200°C.

3. A method according to claim 2 wherein the melt is maintained at substantially 160°C.

4. A method according to claim 1 wherein the catalyst and the activator are added in quantities of approx. 0.01 to approx. 5 percent by weight of the lactam melt, approx. 0.1 to approx. 0.6 percent by weight referred to the lactam melt.

5. A method according to claim 4 wherein the catalyst and the activator are added in quantities of approx. 0.1 to 0.6 percent by weight of the lactam melt.

6. A method according to claim 1 characterized in that carbon dioxide is employed as the catalyst and that the melt of the monomeric lactam is saturated with carbon dioxide.

7. A method according to claim 1 characterized m that phenyl iso-cyanate is employed as the activator.

8. A method according to claim 1 characterized in that the catalyst is first added at a point in the stream of melt and that the activator is added downstream of said point where the catalyst was added.

9. A method according to claim 1 wherein said monomeric higher lactam is lauric lactam.

10. Polylauric lactam which is characterized in that it will not melt during heating but disintegrates in air within the range of approx. 217 and 271°C and cannot be regenerated.

11. A polylauric lactam according to claim 10 characterized in that it possesses a yield stress of .delta.S of approx. 470 to approx. 520 kp/cm2 measured according to DIN 53 455, an elongation under yield stress .epsilon.S of approx. 17 to approx. 25% measured according to DIN 53 455, a tensile strength .delta.R of approx.
500 to approx. 630 kp/cm2 measured according to ISO R 527, an elongation at yield .delta.R of approx. 200 to 350% measured according to IS0 R 527, a modulus of elasticity E of approx. 19,000 to 22,000 kp/cm2 measured according to DIN
53 455, Sec. 2.3, an ultimate bending stress .delta.B of approx. 750 to approx.
1000 kp/cm2 measured according to IS0 R 178, a notch impact strength aK of approx. 55 to 65 kp/cm2 measured according to DIN 53 455, a ball-pressure hardlless 10' ' of approx. 1000 to approx. 1050 kp/cm2 measured according to DIN 53 455 step C, an abrasion strength of approx. 158 to approx. 129 mm /rpm measured according to Table-Abrazer, a time yield stress .delta.1/1000 (23°C/95%) of approx. 50 to approx. 60 kp/cm2 measured according to DIN 53 444, and a creep modulus E/1000 (.delta. 20.0) of approx. 13,000 to 14,000 kp/cm2 measured according to DIN 53 444.

12. A method of forming a moulded body which comprises casting a melt including polylauric lactam as defined in claim 11 into a mould, permitting the melt to solidify and removing the moulded body product from the mould.