Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L77/00—Compositions of polyamides obtained by reactions forming a carboxylic amide link in the main chain; Compositions of derivatives of such polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/49—Phosphorus-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L77/00—Compositions of polyamides obtained by reactions forming a carboxylic amide link in the main chain; Compositions of derivatives of such polymers
  • C08L77/02—Polyamides derived from omega-amino carboxylic acids or from lactams thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L77/00—Compositions of polyamides obtained by reactions forming a carboxylic amide link in the main chain; Compositions of derivatives of such polymers
  • C08L77/06—Polyamides derived from polyamines and polycarboxylic acids

Definitions

• the present invention relates to polyamide blends. More specifically, it relates to polyamide resins that are translucent while retaining excellent mechanical and thermal properties.
• polyamides also known broadly as nylons
• nylons are excellent in toughness, heat resistance, oil resistance, and processability.
• examples of such polyamides include aliphatic polyamides such as those commonly denoted nylon 6, nylon 6,6, nylon 6,10, nylon 12, and the like. These polyamides are generally semi-crystalline.
• semi-crystalline polyamides are widely used for engineering plastics, fibers, etc., owing to the above mentioned excellent properties.
• engineering plastics they are widely used in various applications, such as electric and electronic parts and accessories for automobiles.
• a drawback of the above polyamides for many applications is that they are often opaque due to the presence in the polymers of spherulite crystals. The spherulite crystals are sufficiently large to interfere with and scatter visible light.
• US Patent No. 5,053,447 discloses a polyamide-based thermoplastic formulation having: a) at least 50 weight percent, based on the total weight of the formulation, unreinforced nylon selected from nylon 6,6, nylon 6, or mixtures thereof; b) about 5-50 weight percent fillers; and c) a sufficient amount of decabromodiphenyl ethane to provide a melt index value that is higher than the melt index value of the nylon alone.
• the fillers used are glass fibers.
• Glass fibers used as fillers are known to distort or interfere with the passage of light in plastics.
• US Patents Nos. 5, 149,897 and 4, 133,287 disclose the problem that when glass fibers are added to nylon as reinforcing or strengthening agents, they can interfere with the optical properties of the materials.
• compositions having a high degree of transparency that contain blends of select polyamide homopolymers or copolymers having balanced amino and acid terminal groups with further select polyamide homopolymers or copolymers having an excess of terminal amino groups.
• An optically translucent polyamide composition comprising: a) 59 to 96.99 weight percent of a miscible blend of at least two polyamides and wherein at least one of these polyamides is a semicrystalline polyamide; b) 3 to 40 weight percent of a glass filler; and c) 0.01 to 1 weight percent of a catalyst containing phosphorus in an oxidation state of +1 , +2, or +3.
• Another aspect of the invention is an improved process for the preparation of such compositions, comprising first providing the above-described miscible blend, and adding thereto the glass filler and catalyst mentioned above to form a blend mixture. The blend mixture is melt-blended to form a homogeneous blend. Further processing to shape the blend may include any of a variety of techniques as understood by those having skill in the art. These include without limitation injection molding, blow molding, extrusion, coextrusion, compression molding, or vacuum forming.
• Shaped articles of the invention may include, again without intending to limit the generality of the foregoing, bottles, sheets, films, packaging materials, pipes, rods, laminates, sacks, bags, molded goods, granules, or powders.
• Optical properties' means the ability of the material in question to transmit visible light. Materials can be 'transparent', in which case they will transmit visible light without significant scattering such that items lying beyond are completely visible. Materials can also be Opaque', in which case visible light will be blocked and one cannot see through an object made from those materials. In between are materials that transmit some visible light, such that items lying beyond can be seen, but perhaps not perfectly clearly or at a distance. Such materials are referred to as 'translucent'.
• compositions described herein are resin compositions that not only have excellent physical properties and processability, but are translucent.
• the compositions have three components: (A) a melt miscible/compatible blend of at least two polyamides, at least one of which is crystalline or semi-crystalline; (B) glass fibers, glass beads or other fillers that could improve heat transfer; and (C) a catalyst.
• the first component (A) is a blend of at least two miscible thermoplastic polyamides, at least one of which is a semi-crystalline polyamide. These resins can indude semi-crystalline homopolymers, and block and random copolyamides.
• a thermoplastic semi-crystalline polyamide has a distinct melting point with a measurable heat of fusion, whereas an amorphous polyamide generally has neither a distinct melting point nor a measurable heat of fusion.
• a polyamide homopolymer such as nylon 6,6, is a semi-crystalline polymer.
• Semi-crystalline polyamides are well-known in the art and widely available. They may be formed by condensation polymerization as well as addition polymerization, as discussed in The Encyclopedia of Polymer Science and Engineering, 2nd Edition, 1985, Wiley, Vol. 11, pages 318-360.
• the polyamides generally have molecular weights over 10,000 and can be produced by the condensation of equimolar amounts of a saturated aliphatic dicarboxylic acid containing from 4-12 carbon atoms and an aliphatic diamine containing 2-12 carbon atoms, in which the diamine can be employed, if desired, to provide an excess of amine end groups over carboxylic acid end groups in the polyamide.
• the diacid can be used to provide an excess of acid end groups.
• these polyamides may be made from acid-forming and amine- forming derivatives of said acids and amines such as esters, acid chlorides, amine salts, etc.
• Representative aliphatic dicarboxylic acids used to make the polyamides include adipic acid, pimelic add, azelaic acid, suberic acid, sebacic acid, and dodecanedioic acid, while representative aliphatic diamines include hexamethylenediamine and octamethylenediamine.
• these polyamides can also be prepared from the self-condensation of a lactam.
• suitable polyamides for use in the miscible blend making up component (A) include: polycaprolactam (nylon 6), polynonanolactam (nylon 9), polyundecaneolactam (nylon 1 1 ), polydodecanolactam (nylon 12), poly(tetramethylenediamine-co-adipic acid) (nylon 4,6), polyhexamethylene azelaiamide (nylon 6,9), polyhexamethylene sebacamide (nylon 6,10), polyhexamethylene isophthalamide (nylon 6, IP), polymetaxylylene adipamide (nylon MXD6), the polyamide of n-dodccanedioic acid and hexamethylenediamine (nylon 6,12), the polyamide of dodecamethylenediamine and n-dodecanedioic acid (nylon 12,12), as well as copolymers thereof.
• copolymers are the polyamide of hexamethylene adipamide and caprolactam (nylon 6,6/6), the polyamide of hexamethylene adipamide and hexamethylene-isophthalamide (nylon 6,6/6IP), the polyamide of hexamethylene adipamide and hexamethylene-terephthalamide (nylon 6,6/6T), the polyamide of hexamethyleneterephthalamide and (2-methyl)pentamethyleneterephthalamide (nylon 6T/DT), the polyamide of hexamethylene adipamide, hexamethylene azelaicamide, and caprolactam (nylon 6,6/6,9/6), the polyamide of hexamethylene terephthalamide and hexamethylene decanediamide (nylon 6T/6,10), and the polyamide of hexamethylene terephthalamide and hexamethylene dodecanediamide (nylon 6T/6,12), as well as others which are not particularly delineated here.
• Suitable polyamide copolymers could also be synthesized by condensation and ring opening polymerization, as will be understood by those skilled in the art.
• a copolymer will not necessarily be an amorphous material as many copolymers have distinctive melting points.
• the definition of copolymer here is a polymer synthesized by more than two kinds of monomer pair blocks (e.g., terephthalic acid, isophthalic acid, hexamethylenediamine, 1,12-diaminodedecane, caprolactam).
• monomer pair blocks e.g., terephthalic acid, isophthalic acid, hexamethylenediamine, 1,12-diaminodedecane, caprolactam.
• the addition of multi-monomer copolymers into polymer blends could also effectively reduce the size of sphemlites and even significantly reduce the degree of crystallization.
• Suitable amorphous polyamides will be copolymers that can include, but are not limited to, copolymers made from ingredients such as isophthalic acid, terephthalic acid, hexamethylenediamine, bis(/?-aminocyclohexyl)methane, 1 ,4- bis(aminomethyl)cyclohexane, or l-amino-3-aminomethyl-3,5,5- trimethylcyclohexane, as is understood by those skilled in the art.
• a blend be of at least two, but preferably more, miscible and compatible nylons, thus facilitating the reduction of the spherulite sizes in the crystalline regions of the semi-crystalline polymer components. Adding an amorphous polyamide could also facilitate a reduction in spherulite size. With optimally sized and dispersed phases and adequate interphase adhesion, the compatible polyamides provide a blend morphology conducive to useful mechanical properties.
• miscible blends it is meant that the blends of two or more melt compatible polyamides, at least one of which is semi-crystalline, of the present invention behave as a single homogeneous polyamide, exhibit a single T g , and give a single-phase composition in which the stratification of the polymeric components during or after processing is generally avoided. Since immiscible blends are phase separated, they suffer from delamination at the phase boundaries because of the weak bonding between the phases. This leads to light scattering, which negatively affects the optical properties of the molded articles. Since this miscibility is crucial for translucency, the selection of nylons used for the blends will depend on their mutual compatibility.
• nylons 6 and 6,6 are fully miscible and form a transparent melt.
• nylons 6,6 and 12 are not miscible and form a cloudy melt.
• a cloudy melt is one in which the material contains inhomogeneous regions that scatter light to the point where objects behind the melt are not fully and clearly visible at a distance.
• Preferred blends making up component (A) include: a blend of (i) nylon 6,6 and (ii) nylon 6; a blend of (i) nylon 6,6, (ii) nylon 6, and (iii) an amorphous nylon; and a blend of (i) nylon 6,6 and (ii) nylon 6, and (iii) nylon 6T/DT.
• the blend (A) is preferably present in an amount of from 69.5 to 95.9 weight percent, and with a most preferred range of 74.6 to 95.3 weight percent.
• the glass fillers when used in the form of glass fibers or glass beads are obtained from an inorganic glass composed of oxides, e.g., SiO 2 , B 2 O 3 , A- 2 O 3 , CaO, Na 2 O, and K 2 O. Preferred amounts of these and other fillers are in the range of 4 to 30 weight percent, with a most preferred range of 4.5 to 25 weight percent.
• Glass-based fillers were used not only to improve the physical properties of the final materials, but also to improve heat transfer from within the material during crystal formation period. Since crystallization is a thermodynamic process, a rapid cooling will tend to both reduce the rate of crystallization and the size of the resulting crystalline domains. Anything that enhances the rate of heat transfer from within the material would also be expected to reduce the degree of crystallization.
• Alkali-free glass and alkali-containing glass are useful in the instant invention (for example, E glass.C glass and A glass) with E glass being particularly preferred since it is most commonly used to reinforce engineering resins.
• Preferred glass fiber is in the form of glass rovings, glass chopped strands, and glass yarn made of continuous glass filaments 3-20 micron meters in diameter, commercially available as PPG 3531 , PPG3660 and PPG 3540 from Pittsburgh Plate Glass Company.
• the refractive index of E-glass fiber is 1.554 as measured by white light and index matching fluids (Composites, Part A (1998), Volume Date 1999, 30A(2), 139-145). To keep the blends translucent, the glass refractive index has to be fairly closely matched to that of the polymer matrix.
• the refractive index of nylon 6 and nylon 6,6 is 1.53 (ref. V-8, Polymer Handbook Second Ed., Brandrup, Wiley Interscience Publication). Catalyst (C).
• the third component (C) is a phosphorous catalyst, which promotes transamidation between the different semi-crystalline nylons.
• Useful catalytic oxidation states of phosphorus compounds are +1 , +2, and +3. (see Phosphorus: an Outline of its Chemistiy, Biochemistiy, and Technology, Fifth Ed., D. E. C Corbridge, Elsevier, 1995 p. 25,).
• phosphites and hypophosphites of Group I, Group II, zinc, manganese, and aluminum salts can be used.
• Phosphite and hypophosphite esters are also included.
• Preferred catalysts are sodium hypophosphite, potassium hypophosphite, and manganese hypophosphite,
• the amount of the catalyst to be added will vary depending on the blend, the amount of glass fiber, and other factors known to those skilled in art. However, it is effective in a surprisingly small amount, preferably ranging from 0.1 to 0.5 weight percent and most preferably from 0.2 to 0.4 weight percent.
• pigments, dyes, anti-oxidizing agents, or weathering agents may be incorporated into the polyamide resin composition in the present invention in so far as they do not affect the optical properties, moldability, and physical properties thereof.
• conventional additives are added to the composition in a mixing step and are included in an extrudate of the composition.
• Blending or mixing of the constituents that comprise the composition may be by any effective means that will effect their uniform dispersion. All of the constituents may be mixed simultaneously or separately by a mixer, blender, kneader, roll mixer, extruder, or the like in order to assure a uniform blend of the constituents.
• the constituents making up the polyamide blend component may be blended or mixed first by a mixer, blender, kneader, roll mixer, extruder, or the like in order to assure a uniform blend of the polyamide blend and the resultant polyamide mixture is melt-kneaded together with the glass fibers, catalyst, and any additives in an extruder to make a uniform blend.
• the uniform composition is then extruded into strands, and subsequently chopped into pellets.
• the pellets may be subsequently provided to the feed hopper of a molding apparatus used for forming articles.
• the novel blend is useful for both molded and film applications.
• the shaped articles formed from the compositions of the present invention are generally formed by a known molding method for thermoplastic resins such injection molding, extrusion molding, blow molding, transfer molding, or vacuum molding.
• Nylon 6,6 Zytel®101 supplied by DuPont.
• Nylon 6 Ultramid® B3 supplied by BASF.
• Amorphous nylon Zytel® 330 supplied by DuPont
• PPG3540 Glass fibers supplied by the Pittsburgh Plate Glass Company.
• SHP sodium hypophosphite: Supplied by OxyChem as EN grade.
• Al distearate (aluminum distearate): Supplied by Shepherd Chemicals.
• Irganox® 1098 Supplied by Ciba.
• a 40 mm Werner & Pfleiderer twin-screw extruder was used to prepare thoroughly mixed blends of polymers, glass fibers, catalysts, and additives.
• the temperatures used were typically 270-300 °C and the resulting melt temperatures were typically 280-330 °C.
• the extruder and screw were set up to accommodate main feeding and side feeding. Polymers, catalysts, and additives were fed into the extruder through the main feed throat and glass fibers or beads were fed the extruder through the main feed throat and glass fibers or beads were fed through a side feeder.
• the melting zone has to be severe enough to obtain the intimate mixing that is required to achieve a thorough compatibilization of multiple polyamides at the molecular level. A less severe melting zone could lead to inadequate mixing, which could result, upon cooling, in the formation of undesirably large crystals that would decrease the translucency of the resulting material.
• DAM dry-as-molded
• Elongation at break (E@B) and tensile strength (TS) measurements were determined as described in ASTM D-638 or ISO 527. Flexural modulus (FM) measurements were determined as described in
• Notched Izod (NI) and unnotched (UNI) impact testing was done as described in ASTM D-256, ASTM D-4812, or ISO 180.
• Heat deflection temperatures were determined as described in ASTM D-648.
• DSC Differential scanning calorimetry
• Yellowness index (YI) measurements were determined as described in ASTM E313. Characterization of Translucency.
• Nylon 6,6 by itself has a 55% elongation at break.
• Nylon 6,12 alone has an 80% elongation at break.
• 20% nylon 6,12 is melt blended with 80% nylon 6,6, the elongation at break of the mixture is only 19%.
• the melt has a milky appearance, which indicates that nylon 6,6 and nylon 6,12 are not fully miscible and that this system would not be suitable for inclusion in transparent or translucent blends.
• the blends used in this group of examples were made by melt-blending two commonly used semi-crystalline polymers, nylon 6,6 and nylon 6. Together they formed a homogeneous melt that was totally clear, indicating that the two polymers were compatible. PPG3540 glass fibers, a catalyst and other ingredients were added to the mixture as indicated in Table 2. After the materials were prepared, each blend was molded into bars for physical testing and 1.6-mm-thick bars for translucency testing. The results are shown in Table 2.
• DSC analysis was used to characterize the effect of using a catalyst, which, in these examples, was SHP. Melting and freezing points (abbreviated MP and FP, respectively), and the corresponding heats of fusion and crystallization were determined for two successive cycles of heating and cooling.
• MP and FP Melting and freezing points
• Heats of fusion and crystallization are reflective of the degree of crystallinity possessed by a material. If, in the case of a blend, the melting point, freezing point, and associated heats have changed between the first and second heating and cooling cycles, that is a good indication that chemical reactions between the various components have occurred.
• the amo ⁇ hous polyamide which has a refractive index of 1.588, was synthesized by condensation polymerization.
• the diamines used are bis(p- aminooyclohexyl)methane, and hexamethylenediamine.
• the diacids used are isophthalic acid and terephthalic acid.
• the amo ⁇ hous polyamide is fully miscible with nylon 6 and nylon 6,6 at all concentrations and the ternary mixture forms a transparent melt.

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• Organic Chemistry (AREA)
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