WO2020084564A1

WO2020084564A1 - Method of molding a thermoplastic article and molded articles made by the method

Info

Publication number: WO2020084564A1
Application number: PCT/IB2019/059128
Authority: WO
Inventors: Brian Gray Price; Viswanathan Kalyanaraman; Cameron RoyAl YOUNGSTROM
Original assignee: Sabic Global Technologies B.V.
Priority date: 2018-10-25
Filing date: 2019-10-24
Publication date: 2020-04-30

Abstract

A method of molding a thermoplastic article includes filling a mold with a thermoplastic polymer composition comprising a plurality of thermoplastic polymer particles and exposing the mold to a first gas having a permeability in the thermoplastic composition relative to that of N₂ of at least 2.0; heating the mold to a temperature effective to cause the thermoplastic polymer composition to flow for a first time period; exposing the mold to a second gas after the first time period, wherein the second gas has a permeability in the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas; maintaining the mold at the temperature effective to cause the thermoplastic polymer composition to flow for a second time period; and cooling the mold at a temperature less than the temperature effective to cause the thermoplastic polymer composition to flow.

Description

METHOD OF MOLDING A THERMOPLASTIC ARTICLE AND MOLDED ARTICLES

MADE BY THE METHOD

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to European patent application No. 18202562.7, filed October 25, 2019, which incorporated herein by reference in its entirety.

BACKGROUND

[0001] Rotational molding (“rotomolding”) can allow for greater flexibility in end- product design, especially for hollow parts, beveled wall constructions and large sizes where conventional tooling would be cost prohibitive. A variety of products can be rotationally molded, including syringe bulbs, large storage tanks, shipping containers, bumpers, dolls, squeeze toys, basketballs, footballs, automotive armrests and headrests, and boat hulls.

[0002] In rotational molding, the product is formed inside a closed mold or cavity while the mold is rotating bi-axially in a heating chamber. Since the mold continues to rotate during heating, the rotomolding composition will gradually become distributed evenly on the mold walls. As the cycle continues, the composition melts completely, forming a homogeneous layer of thermoplastic material. A drawback to rotational molding can be excessive bubble formation, and long holding times in order to attempt to remove the bubbles. For some thermoplastic materials, bubble formation has been a significant technical limitation preventing their use to the extent that is desired.

[0003] Accordingly, there remains a need in the art for an improved rotational molding process that can advantageously reduce or eliminate the formation of bubbles in the

thermoplastic materials.

SUMMARY

[0004] A method of molding a thermoplastic article comprises: filling a mold with a thermoplastic polymer composition comprising a plurality of thermoplastic polymer particles and exposing the mold to a first gas, wherein the first gas has a permeability in the thermoplastic composition relative to that of N₂ of at least 2.0, preferably wherein exposing the mold to the first gas is prior to filling the mold with the thermoplastic polymer composition; heating the mold to a temperature effective to cause the thermoplastic polymer composition to flow for a first time period; exposing the mold to a second gas after the first time period, wherein the second gas has a permeability in the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1 times the permeability of the first gas, more preferably less than 0.05 times the permeability of the first gas; maintaining the mold at the temperature effective to cause the thermoplastic polymer composition to flow for a second time period; and cooling the mold at a temperature less than the temperature effective to cause the thermoplastic polymer composition to flow.

[0005] A molded article made by the method is also disclosed.

[0006] The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The following figures represent exemplary embodiments.

[0008] FIG. 1 is a photograph showing a molded part made according to the method of the present disclosure (left) and a comparative molded part not according to the present method (right).

[0009] FIG. 2 is a photograph showing a molded part made according to the method of the present disclosure (right) and a comparative molded part not according to the present method (left).

DET AIDED DESCRIPTION

[0010] The present inventors have advantageously discovered an improved process for molding thermoplastic articles, whereby bubble formation can be significantly reduced or eliminated. In particular, a method of molding a thermoplastic article includes filling a mold with a thermoplastic polymer composition comprising a plurality of thermoplastic polymer particles and exposing the mold to a first gas, wherein the first gas has a high permeability in the thermoplastic polymer composition; heating the mold to a temperature effective to melt the thermoplastic polymer composition for a first time period; maintaining the mold at the temperature effective to melt the thermoplastic polymer composition for a second time period; and cooling the mold at a temperature less than the temperature effective to melt the

thermoplastic polymer composition. In some embodiments, the method can optionally further comprise exposing the mold to a second gas after the first time period, wherein the second gas has a permeability in the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1, more preferably less than 0.05 relative to the permeability of the first gas. [0011] The present inventors have discovered a method that can advantageously be used to produce improved articles using open, powder-based molding techniques such as rotational molding (“rotomolding”). In an aspect, molding the thermoplastic article is preferably by rotational molding. Thus, the method can further comprise rotating the filled mold about at least two axes during the method. The method can also optionally further include continually rotating the mold about at least two axes during the cooling stage of the method.

[0012] The first gas can be introduced to the hollow mold prior to filling the mold with the thermoplastic composition (i.e., the mold can be purged with the first gas prior to

introducing the thermoplastic composition). Purging the mold with the first gas can comprise purging the entire mold of the system, or by a directed purging towards one or more

predetermined points within the mold. The purging prior can be for a length of time effective to provide an atmosphere suitable for forming the first layer (i.e., to provide an atmosphere which consists essentially of the first gas). For example, the purging can be conducted for 30 seconds to 30 minutes prior to filling the mold. Alternatively, the mold can be filled with the

thermoplastic composition and subsequently purged with the first gas. Preferably, exposing the mold to the first gas is prior to filling the mold with the thermoplastic polymer composition.

[0013] The first gas has a high permeability in the thermoplastic composition. For simplicity, the permeability of a gas can be expressed in terms of the permeability relative to nitrogen gas (N₂), notated as P_rei (i.e., wherein N₂ has a relative permeability of 1.0). For example, the first gas can have a permeability in the thermoplastic composition relative to that of N₂ of at least 2.0, or at least 4.5, or at least 20, or at least 30. It will be understood that the actual permeability value of the first gas will depend on the identity of the first gas and the

thermoplastic composition, and such values can be determined by one of skill in the art. In some embodiments, gases suitable for use as the first gas include, but are not limited to, helium (P_rei 33.0), hydrogen (P_rei40.0), oxygen (P_rei 4.67), argon (P_rei2.67), carbon dioxide (P_rei 26.67), water, or a combination thereof. In some embodiments, the first gas contains no more than 5 volume percent of an impurity (i.e., no more than 5 volume percent of any gas having a permeability in the thermoplastic composition relative to that of N₂ of less than 2.0, or less than 1.8; and preferably no more than 5 volume percent of any gas having a permeability in the thermoplastic composition less than that of the first gas). Thus, the first gas can have a purity of 95 volume percent or greater, or 98 volume percent or greater, or 99 volume percent or greater, or 99.9 volume percent or greater. For example, the first gas can have a purity of 95 volume percent, or 98 volume percent, or 99 volume percent, or 99.9 volume percent. In an aspect, the first gas is hydrogen, oxygen, argon, carbon dioxide, water, or a combination thereof, having a purity of 95 volume percent or greater, or 98 volume percent or greater, or 99 volume percent or greater, or 99.9 volume percent or greater. For example, the hydrogen or helium or a combination thereof can have a purity of 95 volume percent, or 98 volume percent, or 99 volume percent, or 99.9 volume percent.

[0014] After filling the mold with thermoplastic polymer composition, the mold can be heated to a temperature effective to allow the thermoplastic polymer composition to flow. The temperature effective to cause the thermoplastic polymer composition to flow can be selected based on the identity of the particular thermoplastic polymer composition. For example, the temperature effective to cause the thermoplastic polymer composition to flow can be greater than or equal to the melting temperature of a particular crystalline or semicrystalline

thermoplastic composition or greater than the glass transition temperature of an amorphous thermoplastic composition. In some embodiments, the thermoplastic composition can be heated to a temperature between the glass transition temperature of the thermoplastic composition and the melting temperature of the thermoplastic composition. Thus, the temperature can be selected based on the identity of the thermoplastic composition, such that the heating temperature is greater than or equal to the glass transition temperature of the thermoplastic polymer particles, or greater than or equal to the melting temperature of the thermoplastic polymer particles, or at least l0°C less than the decomposition temperature of the thermoplastic polymer particles. In some embodiments, the temperature effective to melt the thermoplastic composition can be at least 200°C, or at least 250°C, or at least 275°C, or at least 300°C. In some embodiments, the heating can be to a temperature of less than 500°C, or less than 400°C.

[0015] Heating the mold to cause the thermoplastic polymer composition to flow is for a first period of time. In some embodiments, the first time period can be at least 5 minutes, or 5 minutes to 1 hour, or 5 to 30 minutes, or 10 to 20 minutes.

[0016] Following the first time period, the mold can optionally be exposed to a second gas. The second gas has a permeability in the thermoplastic composition that is less than the permeability of the first gas in the thermoplastic composition. Thus, suitable second gases can be selected depending on the identity of the thermoplastic composition and the first gas.

Preferably, the second gas has a permeability of the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1 times the permeability of the first gas, more preferably less than 0.05 times the permeability of the first gas. For example, the second gas can have a permeability relative to nitrogen in the

thermoplastic composition of less than or equal to 1, or less than or equal to 0.75, or less than or equal to 0.5, or less than or equal to 0.25, provided that the permeability of the second gas is less than or equal to 0.25 times the permeability of the first gas. In some embodiments, gases suitable for use as the second gas include, but are not limited to, air, nitrogen, argon, or a combination thereof.

[0017] In some embodiments, the second gas contains no more than 5 volume percent of an impurity (i.e., no more than 5 volume percent of a gas having a permeability that is greater than the permeability of the first gas, preferably no more than 5 volume percent of a gas having a permeability that is greater than or equal to 0.25 times the permeability of the first gas). Thus, the second gas can have a purity of 95 volume percent or greater, or 98 volume percent or greater, or 99 volume percent or greater, or 99.9 volume percent or greater. For example, the second gas can have a purity of 95 volume percent, or 98 volume percent, or 99 volume percent, or 99.9 volume percent. In an aspect the second gas is nitrogen, argon, or a combination thereof, having a purity of 95 volume percent or greater, or 98 volume percent or greater, or 99 volume percent or greater, or 99.9 volume percent or greater

[0018] The mold is then maintained at the temperature effective to cause the

thermoplastic composition to flow for a second period of time. The second time period can be, for example, at least 5 minutes, or 5 minutes to 1 hour, or 5 to 30 minutes, or 10 to 20 minutes.

[0019] Subsequent to the second time period, the mold can be cooled by adjusting the temperature to a temperature that is less than the temperature effective to cause the composition to flow. For example, the mold can be adjusted to a temperature of less than 250°C.

[0020] The thermoplastic polymer composition for use in the present method comprises a plurality of thermoplastic polymer particles. The thermoplastic polymer particles can have an average particle diameter of 10 nanometer to 1 millimeter, preferably 1 micrometer to 1 millimeter, more preferably 50 to 600 micrometers, even more preferably 100 to 500

micrometers, even more preferably still 200 to 400 micrometers. Particle size can be

determined, for example, using laser light scattering techniques. In some embodiments, the polymer particles can be spherical polymer particles.

[0021] The thermoplastic particles comprise a thermoplastic polymer. As used herein, the term "thermoplastic" refers to a material that is plastic or deformable, melts to a liquid when heated, and freezes to a brittle, glassy state when cooled sufficiently. Thermoplastics are typically high molecular weight polymers. The thermoplastic polymer can be crystalline, semi crystalline, or amorphous. The terms“amorphous” and“crystalline” as used herein have their usual meanings in the polymer art. For example, in an amorphous polymer the molecules can be oriented randomly and can be intertwined, and the polymer can have a glasslike, transparent appearance. In crystalline polymers, the polymer molecules can be aligned in ordered regions. In the polymer art, some types of crystalline polymers are sometimes referred to as semi crystalline polymers. The term“crystalline” as used herein refers to both crystalline and semi crystalline polymers. In some embodiments, a crystalline thermoplastic polymer can have a percent crystallinity of at least 20%, for example 20 to 80%, preferably, at least 25%, for example 25 to 60%, or 25 to 30%, more preferably at least 27%, for example 27 to 40%. The term“percent crystallinity” or“% crystallinity” as used herein, refers to the portion of the polymer that has a crystalline form. The percentage is based upon the total weight of the crystalline polymer. In some embodiments, the thermoplastic polymer is amorphous. In some embodiments, an amorphous thermoplastic polymer has less than 20% crystallinity, or less than 15% crystallinity, or less than 10% crystallinity, or less than 1% crystallinity, or 0%

crystallinity. In some embodiments, the thermoplastic polymer can be an amorphous polymer that does not exhibit a melting point.

[0022] Examples of thermoplastic polymers that can be used include polyacetals (e.g., polyoxyethylene and polyoxymethylene), poly(Ci-₆ alkyl)acrylates, polyacrylamides, polyamides, (e.g., aliphatic polyamides, polyphthalamides, and polyaramides),

polyamideimides, polyanhydrides, polyarylates, polyarylene ethers (e.g., polyphenylene ethers), polyarylene sulfides (e.g., polyphenylene sulfides), polyarylsulfones (e.g., polyphenyl sulfones), polybenzothiazoles, polybenzoxazoles, polycarbonates (including polycarbonate copolymers such as polycarbonate-siloxanes, polycarbonate-esters, and polycarbonate-ester-siloxanes), polyesters (e.g., polyethylene terephthalates, polybutylene terephthalates, polyarylates, and polyester copolymers such as polyester-ethers), polyetherimides (including copolymers such as polyetherimide-siloxane copolymers), polyarylether ketones (which is inclusive of

polyetheretherketones, polyetherketoneketones, and polyetherketones), polyethersulfones, polyimides (including copolymers such as polyimide-siloxane copolymers), poly(Ci-₆ alkyl)methacrylates, polymethacrylamides, polynorbomenes (including copolymers containing norbornenyl units), polyolefins (e.g., polyethylene s, polypropylenes, polytetrafluoroethylenes, and their copolymers, for example ethylene-alpha-olefin copolymers), polyoxadiazoles, polyoxymethylenes, polyphthalides, polysilazanes, polysiloxanes, polystyrenes (including copolymers such as acrylonitrile-butadiene-styrene (ABS) and methyl methacrylate-butadiene- styrene (MBS)), polysulfides, poly sulfonamides, polysulfonates, polysulfones, polythioesters, polytriazines, polyureas, polyurethanes, polyvinyl alcohols, polyvinyl esters, polyvinyl ethers, polyvinyl halides, polyvinyl ketones, polyvinyl thioethers, polyvinylidene fluorides, or the like, or a combination thereof. In an embodiment, the thermoplastic polymer particles can comprise polycarbonate, polyetherimide, polyamides, polyphenylene ethers, polyarylether ketone, nylon, acrylonitrile-butadiene-styrene, polyphenylsulfone, or a combination thereof. Polycarbonates, polyolefins (e.g., polyethylene), polyamides, polyphenylene ethers, and combinations thereof can be especially useful, and even more preferably polycarbonates and polyetherimides are used.

[0023] In some embodiments, the thermoplastic polymer particles comprise a

polycarbonate. “Polycarbonate” as used herein means a homopolymer or copolymer having repeating structural carbonate units of formula (1)

wherein at least 60 percent of the total number of R¹ groups are aromatic, or each R¹ contains at least one C6-30 aromatic group. Specifically, each R¹ can be derived from a dihydroxy compound such as an aromatic dihydroxy compound of formula (2) or a bisphenol of formula

(3).

In formula (2), each R^h is independently a halogen atom, for example bromine, a Ci-io hydrocarbyl group such as a Ci-io alkyl, a halogen-substituted Ci-io alkyl, a C₆-io aryl, or a halogen-substituted C6-10 aryl, and n is 0 to 4.

[0024] In formula (3), R^a and R^b are each independently a halogen, Ci-i₂ alkoxy, or Ci-i₂ alkyl, and p and q are each independently integers of 0 to 4, such that when p or q is less than 4, the valence of each carbon of the ring is filled by hydrogen. In an embodiment, p and q is each 0, or p and q is each 1, and R^a and R^b are each a Ci_-3 alkyl group, specifically methyl, disposed meta to the hydroxy group on each arylene group. X^a is a bridging group connecting the two hydroxy-substituted aromatic groups, where the bridging group and the hydroxy substituent of each C₆ arylene group are disposed ortho, meta, or para (specifically para) to each other on the C₆ arylene group, for example, a single bond, -O-, -S-, -S(O)-, -S(0)₂-, -C(O)-, or a C_MS organic group, which can be cyclic or acyclic, aromatic or non-aromatic, and can further comprise heteroatoms such as halogens, oxygen, nitrogen, sulfur, silicon, or phosphorous. For example, X^a can be a substituted or unsubstituted C3-18 cycloalkylidene; a Ci_-25 alkylidene of the formula - C(R^c)(R^d) - wherein R^c and R^d are each independently hydrogen, Ci-i₂ alkyl, C1-12 cycloalkyl, C_7-i2 arylalkyl, Ci-i₂ heteroalkyl, or cyclic C_7-i2 heteroarylalkyl; or a group of the formula - C(=R^e)- wherein R^e is a divalent Ci-i₂ hydrocarbon group. [0025] Examples of bisphenol compounds include 4,4'-dihydroxybiphenyl, 1,6- dihydroxynaphthalene, 2,6-dihydroxynaphthalene, bis(4-hydroxyphenyl)methane, bis(4- hydroxyphenyl)diphenylmethane, bis(4-hydroxyphenyl)-l-naphthylmethane, l,2-bis(4- hydroxyphenyl)ethane, l,l-bis(4-hydroxyphenyl)-l-phenylethane, 2-(4-hydroxyphenyl)-2-(3- hydroxyphenyl)propane, bis(4-hydroxyphenyl)phenylmethane, 2,2-bis(4-hydroxy-3- bromophenyl)propane, 1,1 -bis (hydroxyphenyl)cyclopentane, l,l-bis(4- hydroxyphenyl)cyclohexane, 1 , 1 -bis(4-hydroxyphenyl)isobutene, 1 , 1 -bis(4- hydroxyphenyl)cyclododecane, trans-2,3-bis(4-hydroxyphenyl)-2-butene, 2,2-bis(4- hydroxyphenyl)adamantane, alpha, alpha'-bis(4-hydroxyphenyl)toluene, bis(4- hydroxyphenyl)acetonitrile, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(3-ethyl-4- hydroxyphenyl)propane, 2,2-bis(3-n-propyl-4-hydroxyphenyl)propane, 2,2-bis(3-isopropyl-4- hydroxyphenyl)propane, 2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane, 2,2-bis(3-t-butyl-4- hydroxyphenyl)propane, 2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane, 2,2-bis(3-allyl-4- hydroxyphenyl)propane, 2,2-bis(3-methoxy-4-hydroxyphenyl)propane, 2,2-bis(4- hydroxyphenyl)hexafluoropropane, 1 , 1 -dichloro-2,2-bis(4-hydroxyphenyl)ethylene, 1,1- dibromo-2,2-bis(4-hydroxyphenyl)ethylene, l,l-dichloro-2,2-bis(5-phenoxy-4- hydroxyphenyl)ethylene, 4,4'-dihydroxybenzophenone, 3,3-bis(4-hydroxyphenyl)-2-butanone,

1.6-bis(4-hydroxyphenyl)-l,6-hexanedione, ethylene glycol bis(4-hydroxyphenyl)ether, bis(4- hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfoxide, bis(4- hydroxyphenyl)sulfone, 9,9-bis(4-hydroxyphenyl)fluorene, 2,7-dihydroxypyrene, 6,6'- dihydroxy-3,3,3',3'- tetramethylspiro(bis)indane ("spirobiindane bisphenol"), 3,3-bis(4- hydroxyphenyl)phthalimide, 2,6-dihydroxydibenzo-p-dioxin, 2,6-dihydroxythianthrene, 2,7- dihydroxyphenoxathin, 2,7-dihydroxy-9, lO-dimethylphenazine, 3,6-dihydroxydibenzofuran,

3.6-dihydroxydibenzothiophene, and 2,7-dihydroxycarbazole; resorcinol, substituted resorcinol compounds such as 5-methyl resorcinol, 5-ethyl resorcinol, 5-propyl resorcinol, 5-butyl resorcinol, 5-t-butyl resorcinol, 5-phenyl resorcinol, 5-cumyl resorcinol, 2,4,5,6-tetrafluoro resorcinol, 2,4,5,6-tetrabromo resorcinol, or the like; catechol; hydroquinone; substituted hydroquinones such as 2-methyl hydroquinone, 2-ethyl hydroquinone, 2-propyl hydroquinone, 2-butyl hydroquinone, 2-t-butyl hydroquinone, 2-phenyl hydroquinone, 2-cumyl hydroquinone,

2.3.5.6-tetramethyl hydroquinone, 2,3,5,6-tetra-t-butyl hydroquinone, 2,3,5,6-tetrafluoro hydroquinone, 2,3,5,6-tetrabromo hydroquinone, or the like.

[0026] Specific dihydroxy compounds include resorcinol, 2,2-bis(4-hydroxyphenyl) propane (“bisphenol A” or“BPA”), 3,3-bis(4-hydroxyphenyl) phthalimidine, 2-phenyl-3,3’- bis(4-hydroxyphenyl) phthalimidine (also known as N-phenyl phenolphthalein bisphenol, “PPPBP”, or 3,3-bis(4-hydroxyphenyl)-2-phenylisoindolin-l-one), l,l-bis(4-hydroxy-3- methylphenyl)cyclohexane, and l,l-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane

(isophorone bisphenol).

[0027] In some embodiments, the thermoplastic composition comprises polyethylene. Exemplary polyethylenes can include high density polyethylene (HDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), and linear low density polyethylene (LLDPE).

[0028] In some embodiments, the thermoplastic composition can comprise a polyamide. Polyamides, also known as nylons, are characterized by the presence of a plurality of amide (- C(O)NH-) groups and are described in U.S. Patent No. 4,970,272 to Gallucci. Suitable polyamides include, for example, polyamide-6, polyamide-6,6, polyamide-4,6, polyamide-l l, polyamide- 12, polyamide-6, 10, polyamide-6, 12, polyamide 6/6,6, polyamide-6/6, 12, polyamide MXD,6 (where MXD is m-xylylene diamine), polyamide-6, T, polyamide-6,1, poly amide- 6/6, T, polyamide- 6/6, 1, polyamide-6, 6/6, T, polyamide-6,6/6,1, polyamide-6/6, T/6, 1, polyamide- 6, 6/6, T/6, 1, polyamide-6/l2/6,T, polyamide-6, 6/12/6, T, polyamide-6/l2/6,I, polyamide- 6, 6/12/6, 1, or a combination thereof. In some embodiments, the polyamide comprises a polyamide-6,6. In some embodiments, the polyamide comprises a polyamide-6 and a polyamide-6,6. In some embodiments, the polyamide or combination of polyamides has a melting point (T_m) greater than or equal to l7l°C. Polyamides can be obtained by a number of well-known processes such as those described in U.S. Patent Nos. 2,071,250, 2,071,251, 2,130,523, and 2,130,948 to Carothers; 2,241,322 and 2,312,966 to Hanford; and 2,512,606 to Bolton et al. Polyamides are commercially available from a variety of sources.

[0029] In some embodiments, the thermoplastic composition can comprise a

polyphenylene ether. Suitable polyphenylene ethers can comprise repeating structural units having the formula

wherein each occurrence of Q¹ and Q² is independently halogen, unsubstituted or substituted Ci-i2 hydrocarbyl provided that the hydrocarbyl group is not tertiary hydrocarbyl, Ci-i₂ hydrocarbylthio, C1-12 hydrocarbyloxy, or C2- 12 halohydrocarbyloxy wherein at least two carbon atoms separate the halogen and oxygen atoms; and each occurrence of Q² is independently hydrogen, halogen, unsubstituted or substituted C1-12 hydrocarbyl provided that the hydrocarbyl group is not tertiary hydrocarbyl, C1-12 hydrocarbylthio, Ci-i₂ hydrocarbyloxy, or C2--12 halohydrocarbyloxy wherein at least two carbon atoms separate the halogen and oxygen atoms. In some embodiments, the poly(phenylene ether) starting material comprises a homopolymer or copolymer comprising repeating units derived from 2,6-dimethylphenol.

[0030] In addition to the thermoplastic polymer, the thermoplastic polymer particles can optionally further comprise an additive. An additive composition can be used, comprising one or more additives selected to achieve a desired property, with the proviso that the additive(s) are also selected so as to not significantly adversely affect a desired property of the thermoplastic composition. The additive composition or individual additives can be mixed at a suitable time during the mixing of the components for forming the composition. The additive composition can include an impact modifier, flow modifier, filler (e.g., a particulate polytetrafluoroethylene (PTFE), glass, carbon, mineral, or metal), reinforcing agent (e.g., glass fibers), antioxidant, heat stabilizer, light stabilizer, ultraviolet (UV) light stabilizer, UV absorbing additive, plasticizer, lubricant, release agent (such as a mold release agent), antistatic agent, anti-fog agent, antimicrobial agent, colorant (e.g., a dye or pigment), surface effect additive, radiation stabilizer, flame retardant, anti-drip agent (e.g., a PTFE-encapsulated styrene- acrylonitrile copolymer (TSAN)), or a combination thereof. For example, a combination of a heat stabilizer, mold release agent, and ultraviolet light stabilizer can be used. In general, the additives are used in the amounts generally known to be effective. For example, the total amount of the additive composition (other than any impact modifier, filler, or reinforcing agent) can be 0.001 to 10.0 wt%, or 0.01 to 5 wt%, each based on the total weight of the polymer in the composition. In some embodiments, the thermoplastic polymer particles preferably comprise a flow agent, a mold release agent, a pigment, a filler, a flame retardant, or a combination thereof.

[0031] The method provided herein can be used to provide molded articles, in particular, molded articles which advantageously are free or substantially free of bubbles. “Bubbles” as used herein can also refer to voids, microbubbles, pinholes, and other similar defects. As used herein, the molded articles are“substantially free” of bubbles when the molded articles contain, on average, fewer than 1 bubble per square centimeter, determined by optical microscopy at a magnification of 40 X. In some embodiments, the articles do not contain any bubbles that are detectable by optical microscopy. For example, the molded articles can be free of bubbles having an average radius of less than or equal to 50 micrometers, or less than or equal to 30 micrometers, or less than or equal to 25 micrometers. In some embodiments, fewer than one bubble per square centimeter (on average) is visually observed in the article, either by eye of by use of an optical microscope at a magnification of 40 X, and preferably no bubbles are visually observed in the molded article, either by eye or by use of an optical microscope.

A method of molding a thermoplastic article, the method comprising: filling a rotational mold with a thermoplastic polymer composition comprising a plurality of thermoplastic polymer particles and exposing the mold to a first gas, wherein the first gas has a permeability in the thermoplastic composition relative to that of N₂ of at least 2.0, preferably wherein exposing the mold to the first gas is prior to filling the mold with the thermoplastic polymer composition, and preferably wherein the first gas is helium, hydrogen, oxygen, carbon dioxide, water, or a combination thereof; heating the mold to a temperature effective to cause the thermoplastic polymer composition to flow for a first time period, preferably wherein the temperature effective to cause the thermoplastic polymer composition to flow is greater than or equal to the glass transition temperature of the thermoplastic polymer particles, or greater than or equal to the melting temperature of the thermoplastic polymer particles, or at least 10°C less than the decomposition temperature of the thermoplastic polymer particles, preferably at least 200°C, or at least 250°C, or least 275°C, or at least 300°C; exposing the mold to a second gas after the first time period, wherein the second gas has a permeability in the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1 times the permeability of the first gas, more preferably less than 0.05 times the permeability of the first gas, preferably wherein the second gas is air, nitrogen, argon, or a combination thereof;

maintaining the mold at the temperature effective to cause the thermoplastic polymer

composition to flow for a second time period; rotating the mold about at least two axes during the first time period and the second time period and cooling the mold at a temperature less than the temperature effective to cause the thermoplastic polymer composition to flow, preferably wherein the mold is continually rotated about at least two axes during the cooling. In this embodiment, the thermoplastic polymer particles preferably comprise a polycarbonate, a polyolefin, a polyamide, a polyphenylene ether, or a combination thereof, more preferably a polycarbonate or a polyetherimide. A molded article made by the method of this embodiment can have fewer than one bubble per square centimeter (on average) is present in the article, as viewed by the eye or optical microscopy at a magnification of 40X. Preferably in this embodiment, the molded article is substantially free of bubbles, more preferably wherein the article is substantially free of bubbles having an average radius of less than or equal to 50 micrometers, or less than or equal to 30 micrometers, or less than or equal to 25 micrometers.

[0032] This disclosure is further illustrated by the following examples, which are non limiting. The method is further faster than those conducted in the presence of nitrogen, as the times for nitrogen dissolution are not practical, and can result in polycarbonate degradation. The method further does not require high pressure equipment, and obviates the safety concerns associated with use of high pressure.

EXAMPLES

[0033] Materials used for the following examples are summarized in Table 1.

Table 1

[0034] The PC particles were made by grinding pellets of 1300 grade PC from SABIC. The PE powder was obtained from Chevron Phillips Chemical Company as MARLEX HMN TR-935G. Both powders were passed through a 35 ETS mesh sieve, providing particles having a maximum particle size of about 500 micrometers.

[0035] In the present examples, a hotplate was used as the heat source and an aluminum pan was used as the mold. In the first example, PC powder was added to the pan, and then pan was placed in a closed container to control the atmosphere. The closed container was purged with helium for 10 minutes. Following the 10 minute purge, the entire container was placed on a hot plate preheated to 320°C for 30 minutes. After 15 minutes of heating, the container was opened to quickly switch the atmosphere to replace the helium with air. The container was closed again, and the heating was continued for 15 minutes. As a comparative example, the same procedure was carried out except that the system was not purged with helium. For each example, the formed part was removed from the aluminum pan and evaluated for the presence of bubbles and other artifacts. Photographs of each part are shown in FIG. 1. In the photograph of FIG. 1, the resulting part formed with the helium purge is shown on the left, and the comparative part without the helium purge is shown on the right. As can be seen from FIG. 1, the PC part formed in the comparative example was filled with bubbles, and the part has contracted slightly upon cooling, resulting in a concave lower surface (shown facing upward in the photograph).

The part formed with the helium purge, shown in the left, is observed to be bubble-free, and is also free of any contraction effects.

[0036] The same procedure described above was also tested using a PE powder. The results are shown in FIG. 2, where the part on the left is a comparative example formed without the helium purge, and can be seen to exhibit numerous bubbles within the part. The part shown on the right in FIG. 2 (formed with the helium purge step) is essentially bubble free. As PE crystallizes (upon cooling), it becomes opaque. The photographs in FIG. 2 were taken at the same time post-heating for each part.

[0037] This disclosure further encompasses the following aspects.

[0038] Aspect 1: A method of molding a thermoplastic article, the method comprising: filling a mold with a thermoplastic polymer composition comprising a plurality of thermoplastic polymer particles and exposing the mold to a first gas, wherein the first gas has a permeability in the thermoplastic composition relative to that of N₂ of at least 2.0, preferably wherein exposing the mold to the first gas is prior to filling the mold with the thermoplastic polymer composition; heating the mold to a temperature effective to cause the thermoplastic polymer composition to flow for a first time period; exposing the mold to a second gas after the first time period, wherein the second gas has a permeability in the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1 times the permeability of the first gas, more preferably less than 0.05 times the permeability of the first gas; maintaining the mold at the temperature effective to cause the thermoplastic polymer composition to flow for a second time period; and cooling the mold at a temperature less than the temperature effective to cause the thermoplastic polymer composition to flow.

[0039] Aspect 2: A method of molding a thermoplastic article, the method comprising: filling a mold with a thermoplastic polymer composition comprising a plurality of thermoplastic polymer particles and exposing the mold to a first gas, wherein the first gas has a high permeability in the thermoplastic polymer composition, preferably wherein exposing the mold to the first gas is prior to filling the mold with the thermoplastic polymer composition; heating the mold to a temperature effective to cause the thermoplastic polymer composition to flow for a first time period; exposing the mold to a second gas after the first time period, wherein the second gas has a permeability in the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1 times the permeability of the first gas, more preferably less than 0.05 times the permeability of the first gas; maintaining the mold at the temperature effective to cause the thermoplastic polymer composition to flow for a second time period; and cooling the mold at a temperature less than the temperature effective to cause the thermoplastic polymer composition to flow.

[0040] Aspect 3: The method of aspect 1 to 2, wherein the molding is rotational molding.

[0041] Aspect 4: The method of aspect 3, wherein the method further comprises rotating the mold about at least two axes during the first time period and the second time period. [0042] Aspect 5: The method of any one of aspects 3 to 4, wherein the mold is continually rotated about at least two axes during the cooling.

[0043] Aspect 6: The method of any one of aspects 1 to 5, wherein the temperature effective to cause the thermoplastic polymer composition to flow is greater than or equal to the glass transition temperature of the thermoplastic polymer particles, or greater than or equal to the melting temperature of the thermoplastic polymer particles, or at least l0°C less than the decomposition temperature of the thermoplastic polymer particles, preferably at least 200°C, or at least 250°C, or least 275°C, or at least 300°C.

[0044] Aspect 7: The method of any one of aspects 1 to 6, wherein the first time period is 5 minutes to 1 hour, or 5 to 30 minutes, or 10 to 20 minutes.

[0045] Aspect 8: The method of any one of aspects 1 to 7, wherein the second time period is 5 minutes to 1 hour, or 5 to 30 minutes, or 10 to 20 minutes.

[0046] Aspect 9: The method of any one of aspects 1 to 8, wherein the first gas comprises helium, hydrogen, oxygen, carbon dioxide, water, or a combination thereof.

[0047] Aspect 10: The method of any one of aspects 1 to 9, wherein the second gas comprises air, nitrogen, argon, or a combination thereof.

[0048] Aspect 11: The method of any one of aspects 1 to 10, wherein the thermoplastic polymer particles comprise polycarbonate, polyolefin, polyamide, polyphenylene ether, polyetherimide, or a combination thereof, more preferably polycarbonate or polyetherimide.

[0049] Aspect 12: The method of any one of aspects 1 to 11, wherein the thermoplastic composition further comprises an additive.

[0050] Aspect 13: The method of aspect 12, wherein the additive comprises a flow agent, a mold release agent, a pigment, a filler, a flame retardant, or a combination thereof.

[0051] Aspect 14: A molded article made by the method of any one of aspects 1 to 13.

[0052] Aspect 15: The molded article of aspect 14, wherein fewer than one bubble having per square centimeter (on average) is present in the article, as viewed by the eye or optical microscopy at a magnification of 40X.

[0053] Aspect 16. The molded article of Aspect 15, wherein the article is article is substantially free of bubbles, more preferably wherein the article is substantially free of bubbles have an average radius of less than or equal to 50 micrometers, or less than or equal to 30 micrometers, or less than or equal to 25 micrometers.

[0054] The compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any appropriate materials, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any materials (or species), steps, or components, that are otherwise not necessary to the achievement of the function or objectives of the compositions, methods, and articles.

[0055] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. “Combinations” is inclusive of blends, mixtures, alloys, reaction products, and the like. The terms“first,”“second,” and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms“a” and“an” and“the” do not denote a limitation of quantity, and are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly

contradicted by context. “Or” means“and/or” unless clearly stated otherwise. Reference throughout the specification to“some embodiments,”“an embodiment,” and so forth, means that a particular element described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. The term “combination thereof’ as used herein includes one or more of the listed elements, and is open, allowing the presence of one or more like elements not named. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.

[0056] Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears.

[0057] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this application belongs. All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0058] Compounds are described using standard nomenclature. For example, any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom. A dash

that is not between two letters or symbols is used to indicate a point of attachment for a substituent. For example, -CHO is attached through carbon of the carbonyl group.

[0059] As used herein, the term“hydrocarbyl,” whether used by itself, or as a prefix, suffix, or fragment of another term, refers to a residue that contains only carbon and hydrogen. The residue can be aliphatic or aromatic, straight-chain, cyclic, bicyclic, branched, saturated, or unsaturated. It can also contain combinations of aliphatic, aromatic, straight chain, cyclic, bicyclic, branched, saturated, and unsaturated hydrocarbon moieties. However, when the hydrocarbyl residue is described as substituted, it may, optionally, contain heteroatoms over and above the carbon and hydrogen members of the substituent residue. Thus, when specifically described as substituted, the hydrocarbyl residue can also contain one or more carbonyl groups, amino groups, hydroxyl groups, or the like, or it can contain heteroatoms within the backbone of the hydrocarbyl residue. The term "alkyl" means a branched or straight chain, unsaturated aliphatic hydrocarbon group, e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, t-butyl, n- pentyl, s-pentyl, and n- and s-hexyl. “Alkenyl” means a straight or branched chain, monovalent hydrocarbon group having at least one carbon-carbon double bond (e.g., ethenyl (-HC=CH₂)). “Alkoxy” means an alkyl group that is linked via an oxygen (i.e., alkyl-O-), for example methoxy, ethoxy, and sec-butyloxy groups. "Alkylene" means a straight or branched chain, saturated, divalent aliphatic hydrocarbon group (e.g., methylene (-CH₂-) or, propylene (-(CH₂)₃- )).“Cycloalkylene” means a divalent cyclic alkylene group, -C_nH_2n-x, wherein x is the number of hydrogens replaced by cyclization(s). “Cycloalkenyl” means a monovalent group having one or more rings and one or more carbon-carbon double bonds in the ring, wherein all ring members are carbon (e.g., cyclopentyl and cyclohexyl). "Aryl" means an aromatic hydrocarbon group containing the specified number of carbon atoms, such as phenyl, tropone, indanyl, or naphthyl. “Arylene” means a divalent aryl group. “Alkylarylene” means an arylene group substituted with an alkyl group. “Arylalkylene” means an alkylene group substituted with an aryl group (e.g., benzyl). The prefix "halo" means a group or compound including one more of a fluoro, chloro, bromo, or iodo substituent. A combination of different halo groups (e.g., bromo and fluoro), or only chloro groups can be present. The prefix“hetero” means that the compound or group includes at least one ring member that is a heteroatom (e.g., 1, 2, or 3 heteroatom(s)), wherein the heteroatom(s) is each independently N, O, S, Si, or P. “Substituted” means that the compound or group is substituted with at least one (e.g., 1, 2, 3, or 4) substituents that can each independently be a Ci-9 alkoxy, a Ci-9 haloalkoxy, a nitro (-N0₂), a cyano (-CN), a Ci-₆ alkyl sulfonyl (-S(=0)₂-alkyl), a C₆-i₂ aryl sulfonyl (-S(=0)₂-aryl), a thiol (-SH), a thiocyano (-SCN), a tosyl (CH₃C₆H₄S0₂-), a C_3-i2 cycloalkyl, a C_2-i2 alkenyl, a C₅-i₂

cycloalkenyl, a C₆-i₂ aryl, a C_7-i3 arylalkylene, a C₄-i₂ heterocycloalkyl, and a C_3-i2 heteroaryl instead of hydrogen, provided that the substituted atom’s normal valence is not exceeded. The number of carbon atoms indicated in a group is exclusive of any substituents. For example - CH₂CH₂CN is a C₂ alkyl group substituted with a nitrile. [0060] While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.

Claims

CLAIMS What is claimed is:

1. A method of molding a thermoplastic article, the method comprising:

filling a mold with a thermoplastic polymer composition comprising a plurality of thermoplastic polymer particles and exposing the mold to a first gas, wherein the first gas has a permeability in the thermoplastic composition relative to that of N₂ of at least 2.0, preferably wherein exposing the mold to the first gas is prior to filling the mold with the thermoplastic polymer composition;

heating the mold to a temperature effective to cause the thermoplastic polymer composition to flow for a first time period;

exposing the mold to a second gas after the first time period, wherein the second gas has a permeability in the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1 times the permeability of the first gas, more preferably less than 0.05 times the permeability of the first gas;

maintaining the mold at the temperature effective to cause the thermoplastic polymer composition to flow for a second time period; and

cooling the mold at a temperature less than the temperature effective to cause the thermoplastic polymer composition to flow.

2. The method of claim 1, wherein the molding is rotational molding.

3. The method of claim 2, wherein the method further comprises rotating the mold about at least two axes during the first time period and the second time period.

4. The method of any one of claims 2 to 3, wherein the mold is continually rotated about at least two axes during the cooling.

5. The method of any one of claims 1 to 4, wherein the temperature effective to cause the thermoplastic polymer composition to flow is greater than or equal to the glass transition temperature of the thermoplastic polymer particles, or greater than or equal to the melting temperature of the thermoplastic polymer particles, or at least 10°C less than the decomposition temperature of the thermoplastic polymer particles, preferably at least 200°C, or at least 250°C, or least 275°C, or at least 300°C.

6. The method of any one of claims 1 to 5, wherein the first time period is 5 minutes to 1 hour, or 5 to 30 minutes, or 10 to 20 minutes.

7. The method of any one of claims 1 to 6, wherein the second time period is 5 minutes to 1 hour, or 5 to 30 minutes, or 10 to 20 minutes.

8. The method of any one of claims 1 to 7, wherein the first gas is helium, hydrogen, oxygen, carbon dioxide, water, or a combination thereof.

9. The method of any one of claims 1 to 8, wherein the second gas is air, nitrogen, argon, or a combination thereof.

10. The method of any one of claims 1 to 9, wherein the thermoplastic polymer particles comprise polycarbonate, polyolefin, polyamide, polyphenylene ether, or a combination thereof, more preferably polycarbonate or polyetherimide.

11. The method of any one of claims 1 to 10, wherein the thermoplastic composition further comprises an additive.

12. The method of claim 11, wherein the additive comprises a flow agent, a mold release agent, a pigment, a filler, a flame retardant, or a combination thereof.

13. A molded article made by the method of any one of claims 1 to 12.

14. The molded article of claim 13, wherein fewer than one bubble per square centimeter (on average) is present in the article, as viewed by the eye or optical microscopy at a magnification of 40X.

15. The molded article of claim 14, wherein the article is substantially free of bubbles, more preferably wherein the article is substantially free of bubbles having an average radius of less than or equal to 50 micrometers, or less than or equal to 30 micrometers, or less than or equal to 25 micrometers.