Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-06-12
2002-02-26
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C523S223000
Reexamination Certificate
active
06350805
ABSTRACT:
The invention relates to a process for the preparation of a polyamide nanocomposite composition by mixing in the melt phase a polyamide, a solid substance composed of anisotropic particles with a high aspect ratio and a liquid.
In the context of the present application ‘a nanocomposite composition’ will be understood to be a mixture of two or more materials, the mixture at least comprising a first material being a polymer and a second material being anisotropic particles with a large aspect ratio having dimensions in the nanometre area, the second material being dispersed in the first material, and the mixture possessing excellent mechanical properties, in particular a higher heat deflection temperature, impact resistance, stiffness and tensile strength and very good gas-diffusion barrier properties, in comparison with a polyamide composition not comprising this second material.
Such a process is known from EP-A-398.551 (Ube/Toyota). The process according to EP-A-398.551 is used to successively (a) preswell a clay in the presence of water and 12-aminododecanoic acid, (b) further swell the preswollen clay in the presence of water and &egr;-caprolactam, (c) prepare a dispersion consisting of the swollen clay, water, &egr;-caprolactam and nylon-6 and (d) melting and kneading the dispersion.
The process described in EP-A-398.551 involves the drawback that it is time-consuming because the anisotropic particles with a high aspect ratio are introduced into the polyamide composition by first causing the solid substance composed of anisotropic particles with a high aspect ratio to swell before the mixture is melted and kneaded. According to EP-A-398.551 the swelling is thus carried out in two steps, in the presence of water and 12-aminododecanoic acid at 80° C. for 60 minutes, and in the presence of water and &egr;-caprolactam for an unspecified time with constant stirring, respectively. The aim of effecting the swelling is to increase the distance between the anisotropic particles with a high aspect ratio in the solid substance composed of these anisotropic particles so that the anisotropic particles are, during the mixing in the melt phase, released form the swellable solid substance and dispersed in the melt.
An additional drawback of the process described in EP-A-398.551 is that it is necessary to use specific swelling agents, in this case 12-aminododecanoic acid and &egr;-caprolactam, which may give rise to undesired side-reactions in the polymer melt, leading to, inter alia, an impure composition and consequently an inferior end product.
Another drawback of the process described in EP-A-398.551 is that liquids, more specifically dispersing agents and swelling agents, for example water, organic compounds or mixtures of water and organic compounds present in the mixture that is melted, escape as vapours during the melting, for example via the feed opening of an extruder, and consequently give rise to processing problems, for example in the melting and kneading of the melt, as a result of which a polyamide nanocomposite composition of inferior quality is obtained, in particular the composition is discoloured or it comprises gas pockets.
The invention's aim is to provide a process that comprises fewer steps and can hence be carried out more quickly, in which it is not necessary for the solid substance composed of anisotropic particles with a high aspect ratio to be swollen before the solid substance is mixed with a polyamide and in which no processing problems occur as a result of the presence of a liquid in the mixture that is melted.
This aim is achieved by adding the liquid to, and subsequently mixing it with a melt comprising at least the polyamide.
An additional advantage of the process according to the invention is that the melt, comprising at least the polyamide, the solid substance composed of anisotropic particles with a high aspect ratio and the liquid, can be kneaded and processed at a temperature lower than the polyamide's melting temperature. It was also found that the melt, consisting of at least the polyamide, the solid substance composed of anisotropic particles with a high aspect ratio and the liquid, has a viscosity that is lower than the viscosity of a melt of the polyamide alone, as a result of which less energy need to be supplied to the mixing apparatus during the kneading and less shear heat is developed in the melt. As a result of the lowering of both the melt's processing temperature and the melt's viscosity there is a smaller risk of gel formation or chain break-up during the mixing in the melt phase, as a result of which a better end product is obtained.
In principle, all the usual solvents or mixtures thereof can be used as the liquid. Preferably a compound or mixture of compounds is chosen which is at least partly miscible with the polyamide in the melt phase or which is capable of causing a solid substance composed of anisotropic particles with a high aspect ratio to swell. ‘Mixtures’ are in this context also understood to be mixtures comprising a compound that is a good swelling agent, but is poorly miscible with a polyamide melt, and a compound that is not a good swelling agent, but is well miscible with a polyamide melt. The liquid is for example chosen from the group comprising water; aliphatic and cycloaliphatic hydrocarbons which may optionally be substituted, for example heptane, cyclohexane or dichloromethane; aromatic hydrocarbons which may optionally be substituted, for example benzene, toluene, xylene, chlorobenzene, dichlorobenzene, trichlorobenzene or nitrobenzene; ethers, for example dioxane, diethyl ether or tetrahydrofuran; ketones, for example cyclohexanone or acetophenone; esters, for example ethyl acetate or propiolactone; nitrites, for example acetonitrile or benzonitrile; alcohols, for example methanol, ethanol, n-propanol or isopropanol; or mixtures thereof. Particularly suitable is water or an aqueous mixture of one or more of the aforementioned compounds. It has surprisingly been found that the process according to the invention using water as the liquid caused no substantial degradation of the polyamide, whereas it is nevertheless commonly known that a polyamide degrades at a temperature of more than 100° C. in the presence of water, i.e. that chain break-up takes place, for example in an extruder, at a normal residence time of 2 to 4 minutes. Water is also—from an environmental viewpoint—a better choice for the liquid than for example an aromatic hydrocarbon.
The amount of liquid that can be used is not critical. The amount of liquid is preferably 5-50% by weight, more preferably 10-40% by weight, relative to the weight of the polyamide.
As the polyamide any polymer can be chosen that comprises acid-amide bonds (—CONH—) between the repeating units, more in particular polyamides or copolyamides obtained from &egr;-caprolactam, 6-aminocaproic acid, &ohgr;-enantholactam, 7-aminoheptanoic acid, 11-aminodecanoic acid, 9-aminononanoic acid, &agr;-pyrrolidone or &agr;-piperidone; polymers or copolymers obtained through the polycondensation of diamines, for example hexamethylene diamine, nonamethylene diamine, undecamethylene diamine, dodecamethylene diamine or metaxylene diamine, with dicarboxylic acids, for example terephthalic acid, isophthalic acid, adipic acid or sebacic acid; blends of the aforementioned polymers and copolymers. Examples of such polymers are nylon-6, nylon-9, nylon-11, nylon-12, nylon-4,6 and nylon-6,6. Preferably nylon-6 is chosen.
The polyamide preferably has an average molecular weight of between 9,000 and 40,000.
As the solid substance composed of anisotropic particles with a high aspect ratio a solid substance is preferably chosen from the group comprising layered and fibrous inorganic materials.
A particle's ‘aspect ratio’ is in the context of this invention understood to be the ratio of an individual particle's largest and smallest dimension. More in particular the aspect ratio of a plate is the ratio of the plate's length and average thickness and the aspect ratio of a f
Korbee Roland A.
Van Geenen Albert A.
DSM N.V.
Pillsbury & Winthrop LLP
Sanders Kriellion A.
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