Note: Descriptions are shown in the official language in which they were submitted.
~OSl~
The present invention relate~ to polyamide film and to
a process for its manufacture
Polyamide film exhibit3 cxceptionally attractive
propertie , for example, outstanding machanic~l strength, e~cellent
toughne~, high perforation ro~istl~ce and high abra~ion resis_
tance. ~he ~urface of the film i9 brilliant and hard~ ~nd can be
printed. ~he film i~ highly tran~parent, and re~i~tant to fat~,
oil~ 2nd low temperature~. ~urthe~more, the film has a low
permeability to aromas and gase~, i8 vacuum-tight, ean be deep~
fro~en and i3 free from no2iou~ or potentially ha~ard~u3 forei~n
matter. ~ecause of these e-~:ceptionally advantageou~ propertie~ 9
polyamide film find~ diverse indu~trial use~ and i~, in particular,
a preferred packaging material.
However, for the economical manu~acture of thin poly-
amide film having ~upexior proces~ing and performance characte-
~istic~, it ha~ hitherto been nece~ary to use polyamides of fairlyhigh molecular weight, with relative Yiscosities of, a~ a rule,
~rom 3.8 to 4.5~ ~his i~adi~advantage becau~e the manufacture of
~uch polyamide~ of ~airly high mole¢ular weight i~ di~tinctly more
difficult and more time-con~u~ing than that of polyamides of lower
molecular weight. ~hu~S e.g., poly-~-caprolactam of relative
vi~cosity up to about 3.1 can be manufactured by a one~tep melt
polyconden~ation proce~ whil~t to achieve higher viscositie~ it
is nece~sary to work in two ~tep~, the melt polymerization boing
followed by a ~olid phaoe polymerisation. ~his requ~s ~pecial
and expen~ive production equipment and the conden.~ation time~
needed in the ~olid pha~e are se~eral times as long as the conde~-
sation times in the melt. A further disadvantage in the manufac-
ture of polyamide film i~ that b~cause, hitherto, high molecular
weight polyamides were needed, they had to be processed at high
melt temperature~.
z~
It i~ a~ ob~ect o~ the pre~ent invention to provide
thin polyamide fill~ h~ing excellent proces~ing and performance
charactari~tios.
W8 have found, IqurErisinglyy that thi~ obj~ct i~
achieved by a film web which oonsi~t of a polycaprolactam of
relative ViBCo~ity from 2.4 to 3.3, ~nd preferably from 2, 5 to
2.8, whi~h contain~ from 0.0005 to 0.5% by weight9 preferably
from 0.001 to 0.01~ by weight, of uniforml~ and finely di~tribut~d
~ry~tallin~ magne~ium silicate~ of p~rticle Bi~ le~ than 30 ~,
0 the film web b~ing le~ than 50 ~1 thick.
The invention Qlso r~lat~ to a proce~ for the manufac-
ture of the above film. In this proces~, ~ingle-lager or multl-
layer flat ~ilm of poly--caprolact~m or copolymer~ of~ caprolao-
tam whioh contaln more than 70% of caprolaotam unit~ i~ produced
by extruding the melt throu~h a ~lit die onto a chill roller ~nd
~ubseque~tl~ dra~ing off the film formed, the polycaprolactam
ha~ing a relati~e vi~co~ity of from 2.4 to 3.3, preferably ~rom
2.5 to 2.8 and containing from 0~0005 to Q.5% by weight,~pr~f~rably
from 0.001 to 0.0~%. of uniformly and fin~ly di~tributed naturally
20 occ~ring cry~talline magnesium silicate~ of parti~le si~e le~
tha~ 30,~, and th~ melt i~UiIlg Irom the slit die being dr~ oif
the chill roller at a ~p~ed greater tha~ 30 m/minute~ to give a
film le~ tha~ 50,~ thiok,
~he film manufactured in accordanoe with the proces~ :~
of the invent~on i8 di~tlnguished by e:~c~llent use ~d proce~ing
characteri~tic~, eOg. ~asy maohina running9 wh~ch oompri~e~
boththe behavior of the ~llm during manufacture ~nd th~ beha~ior
o~ the film un machine~ on which it i9 furth~r proces~ed. ~he
part~cular ~ui~t~bility of -th~ ~llm ~or coating, laminating and
30 printlng ~hould be ~ingled out. Particula~ ad~anta~es are ~Ouna~
in coating ~nd la~inating, becauæe o~ th~ high æpeed~ at which
the film ean be proce~ed ~nd its trouble-free running~ ~he
~ 5~24
high tra~sparency and glo~ of ~e film manufactured according to
the invention ~hou~ al~o be mentioned. Since the prooes~ of the
inv~ntion permitq the u~e of lower melt temperatures than with
conventional polyamides of f~irly high mnlecular weight, the
formation of degradation product~ i9 reduced and the interval~ at
which machine elementY coming into contact with the melt have to
be cleaned i~ longer.
The conventional ~crew extruder~ equipped with ~lit
d{~ may be u~ed to oarry out ~he proce~s of the invention. ~he
product temperature3 are a~ a rule from 200 to 300~C. The extruded
film i~ taken up on a chilled receiving roller, where it ~olidifies
and con~olidates, and i~ then conveyed, over guide roller~, to
the windup, or to a further proces~ing stage. The proces~ accor-
ding to the inventio~ is al~o exceptionally ~uitable for u~e on
tandem lines, where the thin polyamide film obtained can be
- combined with layers of other materials, e.g. polyethylene film.
~ he magne~ium 3~1icates u~ed are in the main naturally
occurring cry~talline magnesium silicates, e.g. minerals of the
~ ...
~erpentine group or fibrou~ chry~otile a~be~tos or talc. White or
very light mineral~, which only contain ~mall amount~ of impu--
ritie~, are preferred. Naturally occurring cry~talline magnesium
silicates, wherein th~ ratio of MgO to SiO2 i~ 1:1 to 1:3J and
which contain le~ than 20% by weight of water, le~ than 0.5~
by weight o~ A1203, le~s thQn 0.5% by weight of FeO and less than
5~ by weight of calcium carbonate, have proved particularly
advantageou3. The mineral additive~ ~hould be ~ery uniforml~
distributed in the polyamide and mu~t not fo~m agglomerate~O
The ~ize of the individual
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particles should be less than 30 ~l and this is to be understood
as meaning that at least 99% of all particles are less than this
size. In a particular embodimen-t of the process of the invention,
the particle size is less than 10/u. The concentrations required
are from 0.001 to 0.01 per cent by weight.
: The relative viscosi-ty of the polyamide used in the process
of the invention is less than 3.3. In a particularly advantageous
embodiment of the process of the invention, it is from 2.5 to 2.8.
The relative viscosity is the ratio of the flow timw of a 1 per cent
strength solution of the polyamide in 96 per cent strength sulfuric
acid to the flow time of pure 96 per cent strength sulfuric acid in a
capillary viscometer at 25C.
In a further particularly advantageous embodiment of the
process of the invention, poly- -caprolactam manufactured exclusive-
ly by melt polycondensation, without subsequent solid state condensa
tion, is used. Not only pure polycaprolactam but also polymers
containing up to 30% of other comonomers may be used. Surprisingly,
very high production speeds are achievable in spite of these low
viscosities. In the process of the invention, the film produced
is drawn off the chill roller at speeds of more than 30 m/minute.
In particularly preferred embodiment, this speed is more than
50 m/minute. The temperature of the chilled receiving roller should
be from 80 to 130C, and temperatures of from 90 to 100C have
proved particularl~ advantageous.
Other conventional additives for polyamides, which improve
the properties of the resulting film in conventional ways, may also
be used in the process of the invention. Thus, the polymers star-
ting materials used may contain, e.g., stabilizers, light stabilizers,
waxes, dyes and pigments, or alternatively these materials may be
admixed during manufacture of the film.
EXAMPLE 1
A Barmag extruder having a screw of 90 mm diameter and of
_ 4 _
length 25 D was u~ed to carry out the experiment. ~he extruder
was equipped with a three-zone ~crew divided in the ratio of
7 : 3 : 15 D. The oompression ratio wa~ 14 : 4.5. A commercial
John~on die 800 mm wide was used as the slit die. ~he temperatures
in the indlvidual heating zones of the barrel were - ~tarting
from the feed zone - 185C, 200~, 230C, 230C, 230C and 240C.
The adaptor and die were kept at 240C. ~he ~crew ~peed wa~ 45
rpm and the -temperature of the chill roller on which the ex-
truded polyamide film wa~ received wa~ ~5C. The ~crew wa~ red,~ 10 from ahopper, with granular poly-~-caprolaotam which had a relative
viscosity of 2.6 and contained 25 ppm of finely di3tributed talcum
of particle ~ize ~lO ,u. ~he ~ilm wa~ drawn off at ~ thickness of
25 ~. At an output of 83 kg/hour9 film take-of~ speed~ of 50
m/minute were ~chieved. At thi~ ~peed, the film could be drawn
o~f, and wound up, satis~actorily7 and wa~ highly transparent
and lay perfectly flat. The film preæented no problem~ on lamlna-
ting with a polyethylene film, an~ printing, at high speeds.
EXAMPIE 2 ~Comparative)
~he ~ame experimental ~quipment, and the same arrangement,
as in Example 1 was used. ~he temperatures in the individual
zones of the barrel were - starting from the feed zone - 205C9
220a C7 250C, 250C, 250aC and 260C. ~he adaptor and die were
kept at 260C. Poly-~-caprolactam of relative vi3c09ity 4.0 wa~ :
introduced through the hopper of the extruder. For a film thick-
ness of 25 ~, the maximum take-off ~peed of the film was 35
m/minute. ~he film presented no problem~ on lamin~ting with a
polyethylene ~ilm, and printing, at high ~peed~.
EXAMPIE 3(Comparative)
~he ~ame experimental equipment, and the same arrangem~nt,
as in Example 1 was used, ~he 3ame temperatures as in Example 1
were used in -the heating ~one~ of the barrel, o~ the adaptor and
of the die. Poly--caprolactam of relative vi~co~ity 2,75 wa~ fed
., . .. ., ... . ~
~516i~4
in through the hopper of the ex-truder. At a film thicl~ess
of 25 ~9 the maximum pos~ible take-of'f ~peed of the film was
?5 m/minute. At these take-off ~peeds, the film frenquently
gave trouble and did not give a sati~factory ~mooth roll~
It wa~ no longer pos~ible ~ati~factorilly to laminate
and print the film at conventional production ~peed~.
