CA1051624A - Polyamide film and process for its manufacture - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A process for the manufacture of flat film from poly-.epsilon.-caprolactam or its copolymers containing more than 70% of caprolactam units, wherein a melt of polycaprolactam of relative viscosity from 2.4 to 3.3, preferably from 2.5 to 2.8, which contains from 0.001 to 0.01%, of uniformly and finely distributed crystalline magnesium silicates of particle size less than 30 µ, is extruded through a slit die onto a chill roller and the melt issuing from the slit die is drawn off the chill roller at a speed greater than 30 m/minute, to give a film less than 50 µ thick.

Description

~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 '',''' "`' : .
.
., . ~ : .
.. . . . . . .. .
.. , ~5~
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.

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~.

Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A film web comprising a layer of an .epsilon.-caprolactam polymer which contains more than 70% by weight of .epsilon.-caprolactam, wherein the .epsilon.-caprolactam polymer has a relative viscosity of from 2.4 to 3.3 and contains from 0.001% to 0.01% by weight of uniformly and finely distributed crystalline magnesium silicate of particle size less than 30 µ, the layer of .epsilon.-caprolactam polymer being less than 50 µ thick.

2. A film web as claimed in claim 1, which in addition comprises one or more layers of other materials.

3. A process for the manufacture of a film web comprising a layer of an .epsilon.-caprolactam polymer, wherein an .epsilon.-caprolactam polymer of relative viscosity from 2.4 to 3.3 which contains from 0.001% to 0.01% by weight of uniformly and finely distributed crystalline magnesium silicate of particle size less than 30 µ, is extruded through a slit die onto a chill roller and the melt issuing from the slit die is drawn off the chill roller at a speed greater than 30 m/minute to give a film less than 50 µ thick.