MULTI-COMPONENT MISCIBLE BLENDS OF NYLONS WITH IMPROVED PROPERTIES

Abstract: A method for forming extremely uniform, melt blended mixtures of semi-crystalline nylon homopolymers with semi-crystalline nylon copolymers. The blends have a single significant melting point rather than maintaining the melting points of the individual nylon component parts. In one embodiment, the blend has a larger difference between its melting temperature and its crystallization temperature than each of the semi-crystalline nylon homopolymer and semi-crystalline nylon copolymer components. In another embodiment, the blend has a melting temperature that is about equal to that of the semi-crystalline nylon homopolymer.

Description: MULTI-COMPONENT MISCIBLE BLENDS OF NYLONS WITH IMPROVED PROPERTIES 5 BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to nylon blends or more particularly to a method for forming extremely uniform, melt blended mixtures of semi- l o crystalline nylon homopolymers with semi-crystalline nylon copolymers The blends are so uniform that they have essentially a single melting point rather than maintaining the melting points of the individual nylon component parts In one embodiment, the blend has a larger difference between its melting temperature and its crystallization temperature than each of the semi- 15 crystalline nylon homopolymer and semi-crystalline nylon copolymer components. In another embodiment, the blend has a melting temperature approximately equal to that of the semi-crystalline nylon homopolymer component. 20 DESCRIPTION OF THE PRIOR ART It is known in the art to prepare blends of nylon homopolymers and copolymers. However, polyamides such as nylon 6 (N6) and nylon 66 (N66), due to their relatively high crystallization rate develop sufficient crystallinity upon melt extrusion, which in turn, interferes with their 25 orientation process. Therefore, it has always been of interest to reduce the crystallization rates of nylons such as N6 and N66 Melt blending of N6 and N66 under commercial processing conditions leads to non- homogenous products with two separate phases as indicated by their characteristic melting points. A common approach, if not the only one, to 3 o reduce the crystallization rate of nylons is to use random copolymers There is an abundant literature on the preparation of copolyamides (copolymers) of N6 with other polyamides such as nylon 66, nylon 11, nylon 12, nylon 6T, nylon 46, etc. Such copolymers, classified as random copolymers are characterized by depressed melting temperature (T m ) and large super-cooling (i.e., the difference between melting and crystallization temperatures, AT = T m - T cc , in °C ) in relation to either of the two homopolymers. A larger ΔT, which is reflective of slower crystallization rate yields lower crystallinity in the copolymer, thereby, improving properties such as orientability. See, for example, Y.P. Khanna, Polym. Eng. and Sci., 30(4), 1615, 1990. It has now been unexpectedly found that when blends are formed from semi-crystalline nylon homopolymers with semi-crystalline random copolymers containing the same nylon as the homopolymer, in certain proportions, that a homogenous, super-miscible blend is formed having improved properties. U.S. patent 5,206,309 teaches heat stable films based on melt blends of N6 and N6 / N66, where N66 can be 0.1-99.9%. This patent does not describe the random copolymers in the proportions required to achieve a homogenous, miscible phase according to this invention. U.S. patents 5,053259 and 5,344679 teach blends of an amorphous nylon, a copolyamide of Tm > 145 °C, and optionally 10-30 weight % of a polyamide homopolymer. U.S. patent 4,877,684 claims films based on mixtures of nylon 6 and N6/N66. EP Patent 408,390 discloses the use of any polyamide, any copolyamide, or a mixture of polyamides along with amorphous polyamide or a copolyamide. Japanese patent 115,4752 discloses films based on mixtures of an aliphatic polyamide and a partially aromatic amorphous polyamide along with EVOH. AU Patent 8825700 discloses an aliphatic polyamide, e.g., nylon 6 or N6/66 copolymer and an amorphous polyamide. All of these likewise do not teach random copolymers of nylons in certain proportions to form a homogenous, miscible phase composition according to the invention. U.S. patents 4,647483; 4,665135 and 4,683170, show blends ofN6 plus a copolymer of N6/N66 or N6/N12 rich in N6 such that the overall blend contains 2.5- 10%, of N66 or N12. The present invention is more effective than the blends of these patents, since more N66 can be incorporated without adverse effects on homogeneity. It would be desirable to provide super-miscible uniform blends of semi- crystalline nylon homopolymers with semi-crystalline copolymers containing the same semi-crystalline nylon as the homopolymer having improved properties, a single melting point, a large difference between its melting temperature and its crystallization temperature and about the same melting temperature as that of the semi-crystalline nylon homopolymer. SUMMARY OF THE INVENTION The invention provides method for producing a uniformly blended semi- crystalline nylon composition which comprises: (a) forming a mixture of solid particles of a semi-crystalline nylon homopolymer A in an amount of from about 30 % to about 99 % based on the weight of the blended nylon composition; and a random semi- crystalline copolymer of nylon A with at least one different nylon B in an amount of from about 1 % to about 70 % based on the weight of the blended nylon composition; wherein the amount of nylon A in the copolymer ranges from about 70 % to about 95 % based on the weight of the copolymer and wherein the amount of nylon B in the copolymer ranges from about 5% to about 30 % based on the weight of the copolymer; and (b) melt blending the mixture at a temperature of at least the melting point of nylon homopolymer A; wherein the nylon composition has only a single significant melting temperature, and which has a larger difference between its melting temperature and its crystallization temperature than each of nylon homopolymer A and the copolymer of nylon A with at least one different nylon B. The invention also provides a method for producing a uniformly blended semi-crystalline nylon composition which comprises: (a) forming a mixture of solid particles of a semi-crystalline nylon homopolymer A in an amount of from about 30 % to about 99 % based on the weight of the blended nylon composition; and a random semi- crystalline copolymer of nylon A with at least one different nylon B in an amount of from about 1 % to about 70 % based on the weight of the blended nylon composition; wherein the amount of nylon A in the copolymer ranges from about 5 % to about 95 % based on the weight of the copolymer and wherein the amount of nylon B in the copolymer ranges from about 5 % to about 95 % based on the weight of the copolymer; and (b) melt blending the mixture at a temperature of at least the melting point of nylon homopolymer A; wherein the nylon composition has only a single significant melting temperature which is about equal to the melting temperature of the nylon homopolymer A. The above compositions optionally further comprises a non-crystalline amorphous nylon component. These compositions are useful in producing films by casting or blowing and optionally rhonoaxially or biaxially stretching the nylon compositions. According to this invention, a minor nylon component can be incorporated into a major component (e.g., N66 in N6 or N6 in N66 ) in such a way that the resulting product is a one-component, homogenous material as determined by Differential Scanning Calorimetry (DSC). The products of this invention are different from conventional blends in view of having only one melting point T m ( as opposed to two T m 's ) and reduced crystallizability at a particular chemical composition. The products of this invention are also different from conventional random 5 copolymers in view of a much higher T m and reduced crystallizability for a particular chemical composition of nylon. The invention, in addition, allows one to incorporate multi-component polyamides, e.g., N66, N12, and amorphous nylons into N6, without observing non-homogeneity in either crystalline or amorphous phase as determined by DSC. Miscibility 0 in blends traditionally has implied one homogenous amorphous phase but the crystalline phases always reveal their characteristic T m 's. In contrast, this invention provides multi-component miscible blends with just one amorphous phase and just one crystalline phase, as determined by DSC. 5 BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a graph of the melting pattern of melt blended nylon films. Figure 2 shows a graph of the melting pattern of nylon 6/nylon 66 random o copolymer films. Figure 3 shows a graph of the melting pattern of nylon films based on nylon 6 homopolymer plus nylon 6/nylon 66 (84/16) random copolymer blends. 5 Figure 4 shows a graph of melting temperature vs. % nylon 66 in nylon 6 films. Figure 5 shows a graph of super-cooling vs. % nylon 66 in nylon 6 films. o Figure 6 shows a graph of the melting pattern of nylon films based on nylon 6 homopolymer plus nylon 6/nylon 66 (75/25) random copolymer blends. Figure 7 shows a graph of the melting pattern of nylon films. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the practice of the present invention, a composition is prepared by melt blending a semi-crystalline homopolymer of a nylon A with a semi-crystalline nylon which is a copolymer of nylon A plus at least one different nylon B. The composition optionally also comprises a non-crystalline amorphous nylon copolymer C. The formed composition is determined to have a single significant melting point. For purposes of this invention, having only a single significant point means that a second melting point, if one is observed, is no more than 35% of the main melting peak, more preferably no more than 20% of the main melting peak and most preferably no more than 10% of the main melting peak. The intensity of the second melting peak, if observed, is determined by known DSC methods. Such methods include analyzing a film to be tested after drying at 25 °C - 45 °C under vacuum for several hours. The intensity of the major and any minor peaks in DSC are determined by heat of fusion integrated over the melting ranges of the individual peaks. Preferably the composition has only one melting point and no other melting point at all. In one embodiment, when the nylon components are blended in a first proportion, the composition has a larger difference between its melting temperature and its crystallization temperature than each of nylon homopolymer A and the copolymer. In another embodiment, when the nylon components are blended in a second proportion, the nylon composition has a melting temperature which is about equal to the melting temperature of the nylon homopolymer A. Within the context of this invention, a melting temperature which is about equal to the melting temperature of the nylon homopolymer A means within about + 5 °C of the melting temperature of the nylon homopolymer A. The first component of the inventive composition is a semi-crystalline homopolymer of nylon A which may be comprised of any semicrystalline polyamide homopolymer. Polyamides suitable for use in this invention as semi-crystalline homopolymer of nylon A include aliphatic polyamides or aliphatic/aromatic polyamides. As used herein, "aliphatic polyamides" are polyamides characterized by the presence of recurring carbonamide groups as an integral part of the polymer chain which are separated from one another by at least two aliphatic carbon atoms. Illustrative of these polyamides are those having recurring monomeric units represented by the general formula: O O O il II II -NHCRCNHR 1 - or -NH-R-C- or a combination thereof in which R and R 1 are the same or different and are alkylene groups of at least about two carbon atoms, preferably alkylene groups having from about 2 to about 12 carbon atoms. As used herein, an "aliphatic/aromatic polyamide" is characterized by the presence of recurring carbonamide groups as an integral part of the polymer chain where the carbonyl moieties are separated by aliphatic moieties having at least two carbon atoms and where the nitrogen groups are separated by aromatic moieties. Illustrative of the aliphatic/aromatic polyamides are those having recurring units of the formula: O O II II NHCR 2 CNHR 3 - in which R 2 and R 3 are different and are alkylene groups having at least 2 carbon atoms, preferably having from 2 to about 12 carbon atoms, or arylene, preferably substituted or unsubstituted phenylene, 7 alkylenephenylene or dialkylenephenylene and wherein the aliphatic moieties have from 1 to about 7 carbon atoms wherein permissible substituents are alkyl, alkoxy or halo, with the proviso that when R 2 is arylene, R 3 is alkylene and when R 2 is alkylene, R 3 is arylene or dialkylene phenylene. Examples of suitable aliphatic polyamides are polyamide homopolymers formed by the reaction of diamines and diacids such as poly(hexamethylene adipamide) (nylon 6,6), poly(hexamethylene sebacamide) (nylon 6,10), poly(heptamethylene pimelamide) (nylon 7,7), poly(octamethylene suberamide) (nylon 8,8), poly(hexamethylene azelamide) (nylon 6,9), poly(nonamethylene azelamide) (nylon 9,9), poly(decamethylene azelamide) (nylon 10,9), and the like. Illustrative of useful aliphatic polyamides are those formed by polymerization of amino acids and derivatives thereof, as for example lactams. Useful polyamides include poly(4-aminobutyric acid) (nylon 4), poly(6-aminohexanoic acid) (nylon 6, also known as poly(caprolactam)), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminooctanoic acid)(nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), ρoly(l l- aminoundecanoic acid) (nylon 11), poly(12-aminododecanoic acid) (nylon 12), as well as nylon 46, nylon 66 and nylon 69 and the like. Blends of two or more aliphatic polyamides may also be employed. Preferred polyamides for use in the semi-crystalline nylon A are poly(caprolactam) and poly(hexamethylene adipamide), with poly(caprolactam) being the most preferred. Aliphatic polyamides used in the practice of this invention may be obtained from commercial sources or prepared in accordance with known preparatory techniques. For example, poly(caprolactam) can be obtained from AlliedSignal Inc., Morristown New Jersey under the tradename CAPRON®. Exemplary of aliphatic/aromatic polyamides are poly(hexamethylene isophthalamide), poly (2,2,2-trimethyl hexamethylene terephthalamide), poly(m-xylylene adipamide) (MXD6), poly(p-xylylene adipamide), poly(hexamethylene terephthalamide), poly(dodecamethylene terephthalamide), and the like. Blends of two or more aliphatic/aromatic polyamides can also be used. The most preferred aliphatic/aromatic polyamide is poly(m-xylyene 5 adipamide). Aliphatic/aromatic polyamides can be prepared by known preparative techniques or can be obtained from commercial sources. The second component of the inventive composition is a semi-crystalline nylon which is a copolymer of nylon A plus at least one different nylon B. o The semi-crystalline nylon which is a copolymer of nylon A plus at least one different nylon B may be formed by copolymerizing two different monomers as described above for nylon A. Copolymers formed from recurring units of the above referenced aliphatic polyamides can be used in the fabrication of the polyamide. By means of illustration and not 5 limitation, such aliphatic polyamide copolymers include caprolactam/hexamethylene adipamide copolymer (nylon 6,6/6), hexamethylene adipamide/caprolactam copolymer (nylon 6/6,6), trimethylene adipamide/hexamethylene azelaiamide copolymer (nylon trimethyl 6,2/6,2), hexamethylene o adipamide/hexamethyleneazelaiamide/caprolactam copolymer (nylon 6/6,6/9,6) and the like. The number average molecular weight of nylon A as well as the nylon A/nylon B copolymer may vary widely. Such are sufficiently high to 5 form a free standing film but sufficiently low to allow melt processing of the blend. Such number average molecular weights are well known to those of skill in the film forming art and are usually at least about 5,000 as determined by the formic acid viscosity (FAV) method (ASTM D- 789). In this method, a solution of 11 grams of aliphatic polyamide in 0 100 ml of 90% formic acid at 25°C is used. In the preferred embodiments of the invention, the number average molecular weight of nylon A as well as the nylon A/nylon B ranges from about 5,000 to about 100,000, preferable from about 10,000 to about 60,000 and more preferably from about 20,000 to about 40,000. The nylon composition may further contain an optional non-crystalline, non-crystallizable, amorphous nylon component C. Amorphous nylons are well known in the art and are available commercially. Amorphous nylons are typically prepared by the reaction of at least one diamine with at least two different diacids. The result is a non-crystallizable nylon having no determinable melting point. Amorphous nylons are available as Grivory 21 available from EMS of Switzerland and Zytel amorphous nylon from DuPont. In a first embodiment of the invention, one may produce a composition which has a single melting temperature and wherein there is a larger difference between its melting temperature and its crystallization temperature than each of nylon homopolymer A and the copolymer of nylon A with at least one different nylon B. To attain this result, the amount of nylon homopolymer A ranges from about 30 % to about 99 % based on the weight of the blended nylon composition, preferably from about 35 % to about 85 % and more preferably from about 40 % to about 60 % based on the weight of the blended nylon composition. In this embodiment, the amount of the copolymer of nylon A with nylon B ranges from about 1 % to about 70 % based on the weight of the blended nylon composition, preferably from about 15 % to about 65 % and more preferably from about 40 % to about 60 % based on the weight of the blended nylon composition. In this first embodiment, the amount of nylon A in the copolymer ranges from about 70 % to about 95 % based on the weight of the copolymer, preferably from about 70 % to about 90 % based on the weight of the 10 copolymer, and more preferably from about 70 % to about 85 % based on the weight of the copolymer. The amount of nylon B in the copolymer ranges from about 5% to about 30 % based on the weight of the copolymer, preferably from about 10% to about 30 % and more preferably from about 15% to about 30 % based on the weight of the copolymer. When an amorphous nylon is included in the first embodiment of the invention, it is present in the overall composition an amount of from about 1 % to about 30 %, preferably from about 2 % to about 25 % and more preferably from about 5 % to about 20 % based on the weight of the blended nylon composition. In a second embodiment of the invention, the nylon composition also has a single melting temperature. The melting temperature is about equal to the melting temperature of nylon homopolymer A. To attain this result, the amount of nylon homopolymer A ranges from about 30 % to about 99 % based on the weight of the blended nylon composition, preferably about 35 % to about 85 % and more preferably ranges from about 40 % to about 60 % based on the weight of the blended nylon composition. The amount of the copolymer of nylon A with nylon B ranges from about 1 % to about 70 % based on the weight of the blended nylon composition, preferably from about 65 % to about 15 % and more preferably from about 60 % to about 40 % based on the weight of the blended nylon composition. In this second embodiment, the amount of nylon A in the copolymer ranges from about 5 % to about 95 % based on the weight of the copolymer, preferably from about 10 % to about 90 % and more preferably from about 15 % to about 85 % based on the weight of the copolymer. The amount of copolymer B in the copolymer ranges from 11 about 95 % to about 5 % based on the weight of the copolymer, preferably from about 90% to about 10 %, and more preferably from about 85% to about 15 % based on the weight of the copolymer. When an amorphous nylon is included in the second embodiment of the invention, it is present in the overall composition an amount of from about 1% to about 30 % based on the weight of the blended nylon composition, preferably from about 2 % to about 25 %, and more preferably from about 5% to about 20 % based on the weight of the blended nylon composition. Optionally the blend may contain additives which are conventionally used in nylon compositions. Examples of such additives are pigments, dyes, slip additives, fillers, nucleating agents, plasticizers, lubricants, reinforcing agents, antiblocking agents, stabilizers and inhibitors of oxidation, thermal stabilizers and ultraviolet light stabilizers. Preferably, such may be present in an amount of about 10% or less based on the weight of the composition. The composition may be formed by dry blending solid particles or pellets of each of the nylon components and then melt blending the mixture at a temperature of at least the melting point of the nylon A homopolymer. Typical melting temperatures range from about 175 °C to about 260 °C, preferably from about 215 °C to about 225 °C, and more preferably from about 220 °C to about 223 °C (for nylon 6). Blending may take place in any suitable vessel such as an extruder, a roll mixer, or the like. Blending is conducted for a period of time required to attain a substantially uniform blend. Such may easily be determined by those skilled in the art. If desired, the composition may be cooled and cut into pellets for further processing, or it may be formed into films and optionally uniaxially or biaxially stretched by means well known in the art. 12 Films of this invention may be produced by conventional methods useful in producing films, including extrusion techniques. Typically, a melted stream of the polyamide is fed through an extrusion die onto a casting roller or the polyamide may be introduced into a blown film apparatus. Optionally, the film may be stretched uniaxially in either the direction coincident with the direction of movement of the film being withdrawn from the film forming apparatus, also referred to in the art as the "machine direction", or in as direction which is perpendicular to the machine direction, and referred to in the art as the "transverse direction", or biaxially in both the machine direction and the transverse direction. The films of the present invention have sufficient dimensional stability to be stretched at least 1.5 and preferably more than three times and more preferably from more than three times to about ten times in either the machine direction or the transverse direction or both. Typically for use in the present invention, the oriented film formed from the composition of the invention are preferably produced at draw ratios of from about 1.5: 1 to about 6: 1, and preferably at a draw ratio of from about 3 : 1 to about 4: 1. The term "draw ratio" as used herein indicates the increase of dimension in the direction of the draw. Therefore, a film having a draw ratio of 2:1 has its length doubled during the drawing process. Generally, the film is drawn by passing it over a series of preheating and heating rolls. The heated film moves through a set of nip rolls downstream at a faster rate than the film entering the nip rolls at an upstream location. The change of rate is compensated for by stretching in the film. The film structure may have a thickness which preferably ranges from about 0.3 mils (7.6 μm) to about 5.0 mils (127.0 μm) and preferably from about 0.5 mils (12.7 μm) to about 1.5 mils (37.5 μm). While such thicknesses are preferred as providing a readily flexible film, it is to be 13 understood that other film thicknesses may be produced to satisfy a particular need and yet fall within the scope of the present invention. The composition produced according to the present invention are found to form extremely uniform films. The following non-limiting examples serve to illustrate the invention. EXAMPLES The starting polymers used were analyzed by Gas Chromatography (GC) using standard procedures. The precision of these measurements is ± 2%. The films were analyzed by Differential Scanning Calorimetry (DSC) using a Seiko RDC-220 thermal analyzer, equipped with a robotics system. About 7.5 (± 0.5) mg of the film sample was crimped in an aluminum pan, heated from room temperature to about 280 °C at a heating rate of 10 °C / min., and held there to erase crystalline memory. Subsequently, the sample was cooled from 280 °C to room temperature at a cooling rate of 10 °C and then reheated at the same rate. For film compositions using nylon 66 homopolymer, the upper temperature in DSC was changed to about 300 °C. The T m reported in the examples is the one obtained upon initial heating cycle, i.e., corresponding to the "as received films" cast under the same conditions. Super-cooling is reported as the difference between the reheat cycle T m and T cc ,i.e., corresponding to the heat history imposed prior to the cooling cycle. The T cc cooling curve, representing the crystallizability of a particular sample during the 10 °C / minute cooling cycle, was integrated to obtain the heat of crystallization (DH f , J/g ). For nylon 6 rich samples, a DH f = 230 J/g for 100% crystalline nylon 6, was used to calculate the crystallinity developed (Close , % ) during the 10 °C / minute cooling scan. For nylon 66 rich samples, DHf = 188 J/g, was used. The temperature and DHf calibrations, were assured through a two-point calibration using indium 14 and tin metal standards. Commercially available grades of nylons used in this study are listed with their nominal compositions as follows : nylon 6 [8207, AlliedSignal], nylon 6(95)/nylon 66(5) [AlliedSignal], nylon 6 (85)/nylon 66(15) [AlliedSignal], nylon 6(80)/nylon 66(20) [AlliedSignal], nylon 6 (70)/nylon 66 (30) [AlliedSignal], nylon 6 (21)/nylon 66 (79) [Monsanto], nylon 66 [Zytel 101L, DuPont], nylon 6 (83)/nylon 12 (17) [Ube], and amorphous nylon [Zytel 330, DuPont]. EXAMPLE If COMPARATIVES Modification of Nylon 6 Homopolymer by Blending Nylon 66 Homopolymer. This example prepares physical blends of nylon homopolymers, namely nylon 6 and nylon 66 in varying proportions. Dried pellets of nylon 6 and nylon 66 were physically mixed in the weight percents indicated in Table 1. The compositions were dried at 82 °C for about 18 hours and then extruded through a Killion single screw extruder (D = 1.5 in; L/D = 24 / 1) equipped with three heating zones (232 °C , 257 °C and 260 °C ) and two adapters (260 °C). The melt temperature was measured as 267 °C. After passing through an extrusion film die maintained at 260 °C, the extrudate was cast on a roll maintained at 82 °C followed by a cooling roll maintained at 43 °C. The resultant film had a total thickness of about 2 mil. For the film composition using nylon 66 homopolymer, the extrusion temperature was raised by about 30 °C. 15 TABLE 1 Film Film Description N66 Tm, °C DT = # % wt Tm - Tec °C 1 N6 (100) control 0 221.6 37.4 2 N6(93) / N66(7) 7 221.5 + 257.2 31.7 3 N6(88) / N66(12) 12 221.1 + 258.7 30.2 4 N6(76) / N66(24) 24 221.7 + 259.8 16.4 5 N6(61) / N66(39) 39 223.9 + 261.3 7.2 6 N66 (100) control 100 262.8 31.0 The melting patterns of each film are plotted in Figure 1. These data show that physical mixtures of two nylon homopolymers yield a composition having two distinct melting points. The control polymers have only one melting point. In addition, for such physical mixtures of homopolymers, the amount of supercooling DT is reduced and so the crystallization rate is increased. Figure 1 exhibits the DSC thermograms of N6 ( T m @ 222 °C ), N66 ( T m @ 262 °C ), and their melt-blended films. It is clear that the blends are non-homogenous and immiscible in the crystalline phase, as evident by two T m s. Example 1 shows that the super-cooling of nylon 6 decreases, i.e., the crystallization rate increases, by melt blending it with nylon 66 homopolymer. For purposes of reducing the crystallization rate of nylon 6, blending nylon 66 homopolymer by common processing techniques is, therefore, not a desired route. EXAMPLE 2 f COMPARATIVE) Modification of Nylon 6 with Nylon 66 by Copolymerization - Reaction of Comonomers. The procedure of example 1 is repeated except using commercially available random copolymers of nylon 6/nylon 66 in the proportions indicated in Table 2. These are produced by copolymerizing the nylon 6 and nylon 66 monomeric starting materials. A well known, if not the only 16 practical approach, to reducing the crystallization rate ( i.e., larger supercooling, DT, ) of nylon 6, is to make random copolymers with other polyamides such as nylon 66, nylon 12, nylon 46, nylon 69, etc. TABLE 2 Film Film Description N66 Tm DT = CI DSC # % wt °C Tm - Tec °C 1 N6 (100) control 0 222.8 38.3 29.1 222.3 37.9 29.4 222.3 37.8 28.3 222.7 38.9 28.9 223.1 39.0 28.2 222.6 38.4 28.6 2 N6(93) /N66(7) 7 212.9 41.8 22.2 213.2 41.4 23.3 3 N6(84) / 16 196.2 40.1 19.2 N66(16) 195.7 40.2 18.2 196.2 41.1 18.4 196.3 39.9 17.9 196.2 39.6 19.0 4 N6(82) / 18 196.9 42.8 19.6 N66(18) 197.1 44.3 19.8 5 N6(75) / 25 193.0 46.4 18.8 N66(25) 193.0 46.9 18.5 6 N6(21) / 79 214.9 39.3 22.9 N66(79) 216.2 40.2 23.6 7 N66 (100) 100 262.6 30.5 28.9 control 262.8 31.0 29.1 The temperature data are plotted in Figure 2 and show that these copolymers have a single melting temperature, but the melting l o temperature is depressed as the amount of diluent nylon component increases. This is evident as N6 increases in N66 rich copolymers and as N66 increases in N6 rich copolymers. Such random copolymers, characterized by a depressed T m relative to that of the homopolymer, are manufactured by a polycondensation reaction of the starting comonomer 17 mixtures. For example, a nylon 6/nylon 66 (50/50) copolymer would be made by a polymerization reaction of caprolactam (i.e., monomer for nylon 6) and hexamethylenediamine-adipic acid salt (i.e., monomer for nylon 66 ) in a 50 : 50 proportion. This example shows that such an approach, does enhance the super-cooling. For instance, the DT for nylon 6 is 38.4 °C ( ± 0.4 ) and this gradually increases to 46.6 °C ( ± 0.3 ) with the addition of 25%> of nylon 66 component. Similarly, the DT for nylon 66 is 30.8 °C ( ± 0.3 ) which increases to 39.8 °C ( ± 0.5 ) with the addition of 21% of nylon 6. Such copolymers, due to their lower crystallization rate ( i.e., larger DT ), develop lower crystallinity than their homopolymer counterparts during fast cooling rate melt processing, and therefore, are better materials for orientation / drawing applications. EXAMPLE 3 Modification of Nylon 6 Homopolymer by Blending with Nylon 6/Nylon 66 (84/16) Random Copolymer. Example 1 is repeated except the compositions are physical mixtures of commercially available nylon 6 homopolymer and commercially available random N6/N66 copolymers (84/16). Table 3 gives the proportion of each polymer component as well as the proportion of N66 in the overall composition. TABLE 3 Film Film Description N66 Tm DT = CI DSC # % wt °C Tm - Tec °C 1 N6 (100) control 0 222.8 38.3 29.1 222.3 37.9 29.4 222.3 37.8 28.3 222.7 38.9 28.9 223.1 39.0 28.2 222.6 38.4 28.6 2 N6(65) / N6-66(35) 6 220.8 41.8 25.5 220.9 41.3 24.9 3 N6(50) / N6-66(50) 8 219.0 47.3 25.0 4 N6(35) / N6-66(65)* 10 218.1 45.6 21.8 218.2 46.4 23.0 5 N6(20) / N6- 13 202 + 45.7 20.3 66(80)** 215.1 43.7 20.0 202 + 214.7 6 N6(10) / N6- 14 199.3 + 39.7 19.4 66(90)** 210 41.4 18.3 198.8 + 210 7 N66(100) control 16 196.2 40.1 19.2 195.7 40.2 18.2 196.2 41.1 18.4 196.3 39.9 17.9 196.2 39.6 19.0 * Possible phase-separation ** Two Tm's, indicative of phase-separation The data plotted in Figure 3 shows that samples 2, 3 and 4 according to the invention have a single melting point. Sample 4 may possibly have a second melting point but, if one is present, it is insignificant. Samples 5 and 6 which are outside the scope of the invention due to a low homopolymer content, have dual melting points. Comparing the data for nylon 6 content from samples 2, 3 and 4 from Figure 3 with similar nylon 6 content compositions from Figures 1 and 2 show that the compositions 19 of this invention have a single melting point which is not depressed. Example 3 and Figure 3 show that up to 50% of N6(84) / N66(16) copolymer can be melt blended into N6 homopolymer while retaining a single T m , indicative of a totally homogenous blend. When the amount of copolymer exceeds about 65%, the composition tends to become non- homogeneous. Note that a maximum DT @ 47 °C is observed for this blend system which is much higher than that for either of the two blend constituents, i.e., a case of synergistic interaction between the N6 homopolymer and the N6(84) / N66(16) copolymer (Example 3). The superiority of these miscible blends relative to that of the conventional random copolymers of the same N6 : N66 ratio, is exhibited in Figures 4 -5 in terms of higher Tm and larger DT; physical blends of N6 and N66 being inferior in terms of non-homogeneity as well as smaller DT (Figure 1 & Example 1). EXAMPLE 4 Modification of Nylon 6 Homopolymer by Blending with Nylon 6 / Nylon 66 (75/25) Random Copolymer. The melting temperature of conventional copolymers of nylon 6/nylon 66 are compared to the blends of this invention. 20 TABLE 4 Film Film Description N66 Tm, °C DT = CI DSC # % Tm - Tec wt °C 1 N6 (100) control 0 222.8 38.3 29.1 222.3 37.9 29.4 222.3 37.8 28.3 222.7 38.9 28.9 223.1 39.0 28.2 222.6 38.4 28.6 2 N6(83) / N6- 4 221.1 39.1 26.6 66(17) 221.2 39.5 27.5 3 N6(68) / N6- 8 221.2 41.6 24.9 66(32) 220.8 41.5 25.3 4 N6(50) / N6- 13 219.5 46.1 22.2 66(50) 219.4 45.0 23.1 5 N6(20) / N6- 20 185 + 51.7 20.7 66(80)* 215.1 51.7 20.6 185 + 215.5 6 N6-66(100) 25 193.0 46.4 18.8 control 193.0 46.9 18.5 * Two Tm's, indicative of phase-separation This example and Figure 6 show that up to 50% of N6(75) / N66(25) copolymer can be melt blended into N6 homopolymer while retaining a single T m , indicative of a totally homogenous blend. When the amount of copolymer is somewhere between 50 and 80%, the composition tends to become non-homogenous. Note that a maximum DT at 52 °C is observed for this blend system which is much higher than that for either of the two blend constituents, i.e., a case of synergistic interaction between the N6 homopolymer and the N6(75) / N66(25) copolymer (Example 4 ). The superiority of these miscible blends relative to that of the conventional random copolymers of the same N6 : N66 ratio, is exhibited in Figures 4 -5 in terms of higher Tm and larger DT; physical 21 blends of N6 and N66 being inferior in terms of non-homogeneity as well as smaller DT (Figure 1 and Example 1). EXAMPLE 5 Modification of Nylon 6 Homopolymer by Blending with Nylon 6 / Nylon 66 ( 21 / 79 ) Random Copolymer. This example demonstrates that the N6(21) / N66(79) copolymer when blended into N6, does not offer any advantages in terms of larger DT. Figure 7 shows that N66 homopolymer can similarly be modified by melt blending with a N6(84) / N66(16) copolymer. For example, a blend of 75% N66 homopolymer and 25% N6(84) / N66(16) copolymer, appears identical to the N66 homopolymer in terms of melting pattern. Such a miscible blend, containing 21% N6, has a 47 °C higher T m than a conventional random copolymer containing 21% N6 ( Figures 4 & 7 ) and much different from a blend of 79 % N66 and 21% N6 which would be expected to exhibit two Tm's ( Figure 1 ). In terms of super-cooling, the copolymer rich in N66, i.e., N6(21) / N66(79) is more effective in enhancing the DT of N66, as opposed to the N6(84) / N66(16) copolymer ( Figure 5 ). 22 TABLE 5 Film Film Description N66 Tm, °C DT = CI DSC # % wt Tm - Tec °C 1 N6 (100) control 0 222.8 38.3 29.1 222.3 37.9 29.4 222.3 37.8 28.3 222.7 38.9 28.9 223.1 39.0 28.2 222.6 38.4 28.6 2 N6(94) / N666(6) 5 221.3 38.2 27.4 221.2 38.7 27.3 3 N6(87) / 10 220.3 38.8 26.3 N666(13) 220.2 38.2 27.3 4 N6(81) / 15 218.7 39.6 24.4 N666(19) 219.3 39.2 25.1 5 N6(75) / 20 218.1 39.4 27.7 N666(25) 218.4 40.4 24.2 6 N6(49) / 40 211.1 40.0 21.3 N666(51) 210.7 39.3 22.3 7 N6(35) / 51 208.8 41.8 24.2 N666(65)* 208.6 39.8 24.7 8 N6(20) / 63 211.9 42.3 23.9 N666(80)* 212.9 41.7 24.0 9 N666(100) 79 214.9 39.3 22.9 control 216.2 40.2 23.6 * Melting Transition is somewhat broader, implying a minor phase- separation. EXAMPLE 6 Modification of Nylon 6 Homopolymer by Blending with Nylon /Nylon 12 (83/17) Random Copolymer. This example demonstrates that the present invention is not just restricted to the N6 and N66 system. For example, N12 can be incorporated in N6 by melt blending N6 homopolymer and a random copolymer of N6(83)/N12(17). The resulting blend is totally homogeneous, characterized by just one T m . 23 TABLE 6 Film Film Description N12 Tm, °C DT = Cl ose # % wt Tm - Tec °C 1 N6 (100) control 0 222.8 38.3 29.1 222.3 37.9 29.4 222.3 37.8 28.3 222.7 38.9 28.9 223.1 39.0 28.2 222.6 38.4 28.6 2 N6(71)/N612(29) 5 221.2 38.9 27.2 221.2 39.0 25.9 3 N612(100) control 17 202.4 42.5 22.0 203.4 42.8 20.3 EXAMPLE 7 Nylon 6 Compositions of Reduced Crystallizability. This example shows that by blending 17% of an amorphous nylon into N6, the super-cooling is increased, ( i.e., crystallization rate reduced ) from 38.4 °C ( ± 0.4 ) to 43.8 °C ( ± 1.2 ) and the developable crystallinity decreases from 28.8 %( ± 0.5 ) to 23.2 % ( ± 0.8 ). However, by replacing part of the amorphous nylon by N66 through this invention, i.e., by blending-in a N6 / N66 random copolymer rich in N6, e.g., N6(84) / N66(16), these effects are more enhanced ( Example 7 ). It should be noted that the overall composition is still a homogenous, single, miscible phase. Also, Example 7 shows that N66 could be replaced with N12 by using a random copolymer of N6 / N12. 24 TABLE 7 Film Film Description N6 N- N66 N12 Tm DT = CI DSC # % Am % % °C Tm - Tec wt % wt wt °C wt 1 N6 control (100) 10 0 0 0 222.8 38.3 29.1 0 222.3 37.9 29.4 222.3 37.8 28.3 222.7 38.9 28.9 223.1 39.0 28.2 222.6 38.4 28.6 2 N6 (83) 83 17 0 0 220.9 44.8 22.3 N-Am (17) 220.9 44.9 22.9 221.2 42.6 23.3 221.2 42.8 24.3 3 N6 (40) 82 10 8 0 217.5 48.2 20.0 N6(84)/N66(16) 217.6 49.2 19.3 (50) N-Am (10) 4 N6 (40) 81 10 0 9 219.5 43.7 21.7 N6(83)/N12(17) 50) 219.5 44.2 21.2 N-Am (10) EXAMPLE 8 Nylon 6 Compositions of Reduced Crystallizability This example shows that by keeping the amount of amorphous nylon the same and replacing part of the N6 homopolymer by N6(84) / N66(16) copolymer, the super-cooling increases from 43.8 °C ( ± 1.2 ) to 48.3 °C ( ± 0.5 ) and the developable crystallinity decreases from 23.2 %( ± 0.8 ) to 17.8 %( ± 0.5 ), see for example, films 2 vs. 3 in Example 8. Comparing film # 2 with 4-7, it is shown that with under otherwise similar compositions, the amount of amorphous nylon can be reduced from 17 to 5% while lowering the developable crystallinity and enhancing the super-cooling. 25 TABLE 8 Film Film Description N6 N- N66 Tm, DT = CI DSC # % Am % °C Tm - Tec wt % wt °C wt 1 N6 control (100) 100 0 0 222.8 38.3 29.1 222.3 37.9 29.4 222.3 37.8 28.3 222.7 38.9 28.9 223.1 39.0 28.2 222.6 38.4 28.6 2 N6 (83) 83 17 0 220.9 44.8 22.3 N-Am (17) 220.9 44.9 22.9 221.2 42.6 23.3 221.2 42.8 24.3 3 N6 (29) 74 17 9 214.5 47.8 18.3 N6(84)/N66(16) (54) 214.2 48.7 17.3 N-Am (17) 4 N6 (32) 81 10 9 215.8 48.6 20.2 N6(84)/N66(16) (58) 215.1 47.9 21.2 N-Am (10) 5 N6 (37) 84 7 9 216.3 47.7 21.3 N6(84)/N66(16) (56) 216.7 48.6 20.3 N-Am (7) 6 N6 (39) 86 5 9 217.4 46.9 21.6 N6(84) N66(16) (56) 217.4 46.8 21.6 N-Am (5) 7 N6 (54) 81 10 9 218.6 47.9 20.5 N6(75)/N66(25) (36) 218.9 48.1 21.0 N-Am (10) Examples 7-8 demonstrate the versatility of this invention in terms of 5 incorporating multi-component polyamides into a single, homogenous, and miscible phase while improving properties such as higher melting temperature, reduced crystallization rate, and lower developable crystallinity. l o From these data it can be seen that the compositions of the present invention for nylon blends which are homogenous, have only a single significant 26 melting temperature, reduced crystallization rate, and lower developable crystallinity. 27

Claims: What is claimed is: 1. A method for producing a uniformly blended semi-crystalline nylon composition which comprises: (a) forming a mixture of solid particles of a semi-crystalline nylon homopolymer A in an amount of from about 30 % to about 99 % based on the weight of the blended nylon composition; and a random semi- crystalline copolymer of nylon A with at least one different nylon B in an amount of from about 1 % to about 70 % based on the weight of the blended nylon composition; wherein the amount of nylon A in the copolymer ranges from about 70 % to about 95 % based on the weight of the copolymer and wherein the amount of nylon B in the copolymer ranges from about 5% to about 30 % based on the weight of the copolymer; and (b) melt blending the mixture at a temperature of at least the melting point of the nylon homopolymer A; wherein the nylon composition has only a significant single melting temperature, and which has a larger difference between its melting temperature and its crystallization temperature than each of nylon homopolymer A and the copolymer of nylon A with at least one different nylon B. 2. The method of claim 1 wherein each of nylon A and nylon B are selected from the group consisting of nylon 4, nylon 6, nylon 9, nylon 11, nylon 12, nylon 46, nylon 66 and nylon 69. 3. The method of claim 1 wherein nylon A is nylon 6 and the copolymer of nylon A with at least one different nylon B is a copolymer of nylon 6 and nylon 66. 4. The method of claim 1 wherein the amount of nylon A in the mixture ranges from about 35 % to about 85 % based on the weight of the 28 blended nylon composition and the amount of the copolymer of nylon A with nylon B in the mixture ranges from about 15 % to about 65 % based on the weight of the blended nylon composition. 5. The method of claim 1 wherein the amount of nylon A in the mixture ranges from about 40 % to about 60 % based on the weight of the blended nylon composition and the amount of the copolymer of nylon A with nylon B in the mixture ranges from about 40 % to about 60 % based on the weight of the blended nylon composition. 6. The method of claim 1 wherein the amount of nylon A in the copolymer ranges from about 70 % to about 90 % based on the weight of the copolymer and wherein the amount of nylon B in the copolymer ranges from about 10% to about 30 % based on the weight of the copolymer. 7. The method of claim 1 wherein the amount of nylon A in the copolymer ranges from about 70 % to about 85 % based on the weight of the copolymer and wherein the amount of nylon B in the copolymer ranges from about 15% to about 30 % based on the weight of the copolymer. 8. The method of claim 1 wherein the mixture further comprises at least one amorphous nylon C which is the reaction product of at least one diamine with two or more diacids. 9. The method of claim 8 wherein the amount of nylon C in the mixture ranges from about 1 % to about 30 % based on the weight of the blended nylon composition. 29 10. The method of claim 8 wherein the amount of nylon C in the mixture ranges from about 2 % to about 25 % based on the weight of the blended nylon composition. 11. The method of claim 8 wherein the amount of nylon C in the mixture ranges from about 5 % to about 20 % based on the weight of the blended nylon composition. 12. The nylon composition formed by the method of claim 1. 13. The nylon composition formed by the method of claim 8. 14. A film produced by casting or blowing, and optionally monoaxially or biaxially stretching the nylon composition of claim 1. 15. A film produced by casting or blowing, and optionally monoaxially or biaxially stretching the nylon composition of claim 8. 16. A method for producing a uniformly blended semi-crystalline nylon composition which comprises: (a) forming a mixture of solid particles of a semi-crystalline nylon homopolymer A in an amount of from about 30 % to about 99 % based on the weight of the blended nylon composition; and a random semi- crystalline copolymer of nylon A with at least one different nylon B in an amount of from about 1 % to about 70 % based on the weight of the blended nylon composition; wherein the amount of nylon A in the copolymer ranges from about 5 % to about 95 % based on the weight of the copolymer and wherein the amount of nylon B in the copolymer ranges from about 95 % to about 5 % based on the weight of the copolymer; and 30 (b) melt blending the mixture at a temperature of about the melting point of the nylon homopolymer A; wherein the nylon composition has only a single significant melting temperature which is about equal to the melting temperature of nylon homopolymer A. 17. The method of claim 16 wherein each of nylon A and nylon B are selected from the group consisting of nylon 4, nylon 6, nylon 9, nylon 11, nylon 12, nylon 46, nylon 66 and nylon 69. 18. The method of claim 16 wherein nylon A is nylon 6 and the copolymer of nylon A with at least one different nylon B is a copolymer of nylon 6 and nylon 66. 19. The method of claim 16 wherein the amount of nylon A in the mixture ranges from about 35 % to about 85 % based on the weight of the blended nylon composition and the amount of the copolymer of nylon A with nylon B in the mixture ranges from about 65 % to about 15 % based on the weight of the blended nylon composition. 20. The method of claim 16 wherein the amount of nylon A in the mixture ranges from about 40 % to about 60 % based on the weight of the blended nylon composition and the amount of the copolymer of nylon A with nylon B in the mixture ranges from about 60 % to about 40 % based on the weight of the blended nylon composition. 21. The method of claim 16 wherein the amount of nylon A in the copolymer ranges from about 10 % to about 90 % based on the weight of the copolymer and wherein the amount of nylon B in the copolymer ranges from about 90% to about 10 % based on the weight of the copolymer. 31 22. The method of claim 16 wherein the amount of nylon A in the copolymer ranges from about 15 % to about 85 % based on the weight of the copolymer and wherein the amount of nylon B in the copolymer ranges from about 85% to about 15 % based on the weight of the copolymer. 23. The method of claim 16 wherein the mixture further comprises at least one amorphous nylon C which is the reaction product of at least one diamine with two or more diacids. 24. The method of claim 23 wherein the amount of nylon C in the mixture ranges from about 1 % to about 30 % based on the weight of the blended nylon composition. 25. The method of claim 23 wherein the amount of nylon C in the mixture ranges from about 2 % to about 25 % based on the weight of the blended nylon composition. 26. The method of claim 23 wherein the amount of nylon C in the mixture ranges from about 5 % to about 20 % based on the weight of the blended nylon composition. 27. The nylon composition formed by the method of claim 16. 28. The nylon composition formed by the method of claim 23. 29. A film produced by casting and optionally monoaxially or biaxially stretching the nylon composition of claim 16. 32 30. A film produced by casting and optionally monoaxially or biaxially stretching the nylon composition of claim 23. 33

Inventors: DAY ERIC D, KHANNA YASH P, DAY, ERIC, D., KHANNA, YASH, P.
Applicants: ALLIED SIGNAL INC, ALLIEDSIGNAL INC.
Application year: 1999
Main classification: C08L77
IPC codes: B29C55, C08J5, C08L77