CA1041723A - Production of nylon 6-nylon 6,6 blended film - Google Patents

Abstract

INVENTION: PRODUCTION OF NYLON 6-NYLON 6,6 BLENDED FILM

INVENTORS: PAUL W. BERGER
PHILIP S. BOLLEN

ABSTRACT OF THE DISCLOSURE

In accordance with the present invention, films of a nylon 6-nylon 6,6 blend are produced by a process which comprises blending about 50 to about 80 percent by weight nylon 6 resin and correspondingly about 50 to about 20 percent by weight nylon 6,6 resin, extruding said blend at a temperature above its melting point onto a smooth moving support to form a coherent film; maintaining said support at a surface temperature in the range of about 230° to about 300°F, and collecting the resultant film. The resultant film has a haze value, as hereinafter defined, in the range of about 5 to about 20 percent, preferably about 8 to about 14 percent.
Film having the latter range of haze values is particularly suitable for the production of cooking bags.

Description

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PRODUCTION OF NY~ON 6-N~LON 6,6 BLENDED FILM
BACKGROUND OF THE INVENTION .
FIELD OF THE INVENTION :
This invention relates to a process for producing ; a blended film comprisin~ nylon 6 and nylon 6,6. ..
DE CRIPTION OF TEIE PRIOR ART
It has long been recognized that physical blends of nylon 6 and nylon 6,6 resins may be for~ed into ~ilms. For example, U.S. P. 2,123,529 to Co~man, issued in 1940, disclos~s ~
such blends. It has recently been discovered that ~ilms made : : .
: from ~ch blends containing at least about 50 percent by weight nylon 6 are particularly suitable ~or use in formin~ caoking . bags. However, to our knowledge, prior to ~he present invention, an efficient and reliable ~pocess ~or producing such blended .:. films having a homogeneous appearance, uniform and controllable optical proper~ies and good slip properties has not been known~
SUMMAR~ OF THE:INVENTION ..
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In acc~rdance.witA the present invention, ~ilms of a nylon 6-nylon 6,6 blend are produced by a process wh~ch comprises ..
b~ending about 50 to about.80 percent by weight nylon 6 resin and correspondingly about.50 to about 20 percent by weight nylon 6,6 resin, extruding said blend at a temperature above its melting point onto a smooth moving support ~o ~orm a coherent film;
maintaining said~support at a surface temperature in the ~ange :.
of a~out 230 to about 300F. and collecting the resultant film.
The resultant film has a haæe value, as hereina~ter defined, in ~
the range of about 5 to about 20 percent, pre~erably about 8 to about.l4 percent. Film having the latter range o~ haze values is particularly suitab].e for the production o~ cooking bags. ~.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The physical blend o~ resins from.which ~ilm is made in accordance with this invention comprises nylon 6 resin tpolyepsilon a.7;~
caprolactam~ and nylon 6,6 resin ~polyhexamethylene adipamide).
Preparation of these well-known polyamides is well understood by those skilled in the art and they may, for example, be prepared, respectively, from the intramolecular polymerization of the lactam of epsilon-aminoc~proic acid and the condensation of hexamethylen-ediamine and adipic acid. The nylon 6 and nylon 6,6 resins useful herein perferably have a viscosity average molecular weight of at least about 10,000, preferably between about 15,000 and about , ~0, 000. ~,.'- ,, The resins are intermixed to provide a blend compris-ing about 50 to about 80 weight percent nylon 6 resin and corres- ;
pondingly about 50 to about 20 weight percent nylon 6,6 resin; -~
preferably, ~he blend comprises about 60 to about 70 weight percent nylon 6 and correspondingly about 40 to about 30 weight percent . . , . ~
nylon 6,6. Blending may be accomplished by any suitable means ;
and although not required, the preparation o~ a homogeneous blend is definitely desirable. It is particularly preferred to blend the two resins at approximately room temperature, although the resins may alternatively be blended at elevated temperatures. -~
The blend is thereafter ~ed to an extrusion apparatus ~;~
to extrude the blend at a temperature generally above its melting point. Any standard extrusion apparatus may be employed for this purpose and as such are well known, they are not specifically described herein. In an alternate embodiment, the two resins may be ~ed unmixed to an extrusion apparatus and mixing be performed in the extruder. In such case, the extruder suitably is provided ~`
with a mixing section or sections in its screw. Extrusion is preferably conducted at a temperature o~ about 15~F. to about 200F. above the mel~ing point of the blend. Since the two resins have different mel~ing points, it will be understood by those skilled in the art that the melting point o a particular blend depends upon the relative amounts of each component res~n.

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For example, a blend of about 50 percent nylon 6 and 50 percent nylon 6,6 by weight, has a melting point in the range of about -242 to 245C., whereas a ~lend of about 75 percent nylon 6 and 25 percent nylon 6,6 by weight, has a melting point in the range of about 217 to 220C. The melting point o~ any particular blend can obviousl~ be determined.
The blended resin is extruded onto a smooth moving support or casting surface to form a coherent film. The rate of extrusion, the width of the extruder die ori~ice and the speed of the moving aupport may be varied widely and determine the thickness of the ~ilm. A casting dr~m, roll or continuous belt .
or similar means may be employed to serve as support. The pre~erred support is a casting ro~l, also known in the art as a chilled ro~l. Preferably, the rotating casting roll has a ;
polytetrafluoroethylene-impregnated chromium sur~ace to provide desired release-and anti-stick properties although it is understood that other surfaced rolls may be employed.
In accordance with the invention, the sur~ace tempera-ture of the casting roll is maintained in the range of about 230 to about 300F., pre~erably in the range o~ about 240 to ~ , about 280F., and more pre~erably in ~he range of 240 to 260F. ;~
The casting roll may be provided with any conventional means of maintaining the desired temperature. `-After passing about the casting roll, the 11m is wound and collected on suitable collecting means, such as a drum or roll. Additional moving supports, such as rolls, may be -employed~for controlled cooling of the film as is known in the art. ~or example, a three roll system can be employed, with the casting roll being the first r~ll. I~ this embodiment, the second roll ~cooling roll) may be maintained at a sur~ace temperature of about 215 to about 245F. and the third roll theat set roll~ may be maintained at the same temperature or hisher. The temperatures ,,.. . . .. , ~. . : . ,. .. . . . . ~ . .

~- i of such rolls may be varied to control the cooling of the film as desired. As is conventional, the edges of the fil~ may be slit to remove any distorted portions prior to winding. -~
` Film may be produced according to this invention at any convenient lineal speed, such as about 30 to about 350 feet per minutes and the film may be of any desired thickness, the preferred thickness being in the range of about 0.5 to about 2 mils. Conventional gauge monitoring systems may be employed to provide uniform thickness of the film.
The film may additionally comprise conventional additives such as heat stabilizers, fillers, lubricants, etc.
It is preferred that the film include a heat stabilizer for the nylon 6,6 resin and a combination o~ cuprous iodide and cuprous bromide may be employed for this purpose. The total amount of heat stabilizer may vary but desirably is below about 200 parts per million parts o~ nylon 6,6 resln. ; -The film-produced in accordance with the process of this invention has a haze ~alue, as determined by ASTM D-1003 ~`;
of about 5 to about 20 percent, preferably about 8 to!about 14 percent. Film o~ the latter haze range is especially suitable for use in the production of cooking bags, since the film has the requsisite clarity to be appealing to the consume~, the requisite blocking properties to pre~ent wrinkling when advanced '~
in a bag making machine and ~he requisite slip properties to be `;
readily openable for ~illing purposes. Furthermore, the film can be easily heat sealed and thermo~ormed. ~ilm having a haze value in the range o~ about 8 to about 14 percent may be prepared by maintaining the surface temperature of the casting roll in the range of about 240 to 280F.
The following examples illust~ate speci~ic applications of the above-described process~ It is to be understood that the examples are for the purpose o~ illustration only and that the .' . --4- ;~
`;"'''' ~V4:~7~3 invention is not to be regarded as limited in an~ manne~ to the -specific conditions or apparatus cited therein.

A blend of 65 weight percent nylon 6 ~viscosity average molecular w~ight of 25,000) and 35 weight percent nylon 6,6 Crelaiive viscosity of 150 cps~* is prepared by intimately mixing the resins in a drum tumbler at room temperatuxe for 30 minutes. The blend is fed into a standard screw extruder and is extruded at a temperature of 534F. through a die orifice o~-0.018 inch thickness. The molten resin blend is quenched to a coherent film by being drawn downward onto a rotating 18 inch diameter chromium plated steel drum having a polytetra-fluoroethylene-impregnated sur~ace. The surface o~ the drum is ~-maintained at 230~. The die orifice is located approxim~tely 1/4 inch above the rotating drum. The drum is rotated at a -perlipheral speed suf~icient to draw the melt to a thickness of 1 mil. The film is then passed about a cooling roll maintained at a sur~ace temperature o~ 236-240F., then about a heat set roll maintained at a surface temperature of 275-278F and is then.wound up. The extrusion rate and roll speeds are such that 204-208 pounds of film are produced per ~our. The-film has a haze o7~g~%as measured by the ASTM D-1003 haze test. The film is used in the manu~acture of coo~ing bags.
EXAMPLE 2 -' Example 1 is repeated using different casting roll temperatures. The results are shown in Table 1.

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* measured in formic acid :' Z3 ::
; ~ABLE l Casting Roll Temperature Hazel :
Sample ~. Percent 1 230 7.9

2 23~0 8.1 ;~

3 250 8.5

4 260 9.9 270 11.4 .
6 280 14.4 7 290 17.0 .:~
8 30~ 19.4 :

'. . ,' 1 = determined by ASTM D-1003 EXAMP~E 3 ~ ~
Film produced in accordance with a process similar to i~:-Example 1 and having certain haze values are tested ~or their slip :
properties in accordance with ASTM D-1894-61T. The results are ,;.
shown in Table 2. -.

Slip2, grams .:
20 Sample Hazel, % Static Kinetic i;;'.. ", ~ 4:-~ 5.3 225 148 ~.3: 1~0 122 11 11.7 194 127 .~
12 14.6 15~ 116 .: :
1 = determlned b~ AS~M D-1~03 2 = determined by ASTM D-1894-61T
As mentioned above, the film in this invention is particularly suited ~or ~orming cooking bags. It should be understood that the ~ilm may also be used ~or a variety of other ~ :
purposes, such as in the packaging and ~abricating ~ields, for example, as wrapping o~ ~ood, paper cartons, chemieal~, etc.
The film may also be lamintated to other plastic~ Csuch`as poly~
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olenfins) for easy seal~ng.
It is to be understood that variatmons a~d modifications of the present invention may be made without depa~ting from the :
scope of the in~ention~ It is also to be understood that the scope of the invention is not to be interpreted as limited to the specific embodiment disclosed herein, but only in accordance with the appended claims when read in light o~ the foregoing disclosure. .
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Claims (6)

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

1. A process for forming film comprising:
(a) blending nylon 6 and nylon 6,6 resins to form a blend comprising about 50 to about 80 weight percent nylon 6 and correspondingly about 50 to about 20 weight percent nylon 6,6;
(b) extruding said blend at a temperature above its melting point onto a smooth moving support to form a coherent film;
(c) mmaintaining said support at a surface temperature of about 230°F. to about 300°F.; and (d) collecting said film.

2. The process of claim 1 wherein said surface temperature is about 240°F. to 280°F.

3. The process of claim 2 wherein said blend comprises about 60 to about 70 weight percent nylon 6 and correspondingly about 40 to 30 weight percent nylon 6,6.

4. The process of claim 3 wherein said film has a haze value of about 8 to about 14 percent as measured by ASTM
D-1003.

5. The process of claim 1 wherein said blend comprises about 60 to about 70 weight percent cnylon 6 and correspondingly about 40 to about 30 weight percent nylon 6,6.

6. The process of claim 1 wherein said blend includes a heat stabilizer.