Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
1999-09-13
2001-01-09
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S170000, C528S322000, C528S330000, C528S332000, C528S335000, C528S346000, C528S349000, C525S432000, C525S435000, C525S436000, C428S411100, C428S474400
Reexamination Certificate
active
06172178
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to car parts made from a polyamide composition, the polyamide of which substantially consists of units derived from aliphatic dicarboxylic acids and diamines.
BACKGROUND OF THE INVENTION
In the automotive sector, metal parts are increasingly being replaced by polymeric materials for the purpose of, for example, reducing the car's weight and preventing corrosion. High requirements are however imposed on polymeric materials used in car parts. The polymeric materials must have excellent mechanical properties, for example high stiffness, fatigue resistance, tenacity and impact resistance and little creep. The materials must have a high heat deflection temperature. A high oxidative stability and chemical resistance to, for example oils and greases, are also requirements that the material employed must meet. Limited moisture absorption is important with respect to obtaining a high dimensional stability of the car part. Depending on the place in which the car part will ultimately be used, the polymer composition will have to exhibit some of the properties mentioned above to a greater extent than others and/or will have to possess additional properties. If the part is to be used in for example the bodywork (bumpers, wings, wheel housings, door panels, spoilers, etc.) a combination of sufficient stiffness and impact resistance and an excellent surface quality of the polymer composition will require special attention. The heat deflection temperature is an extremely important factor for both parts of the bodywork and for parts under the bonnet. Parts of the bodywork are exposed to high temperatures, for example during painting at high temperatures. Parts under the bonnet are constantly exposed to the high heat of the engine. Examples of such parts are air inlet manifolds and radiator end caps. The heat deflection temperature (HDT) is the temperature at which a rod made of the material in question shows a prescribed deflection when it is subjected to a certain flexural stress under three-point loading. Usually, a material cannot be used at temperatures above its heat deflection temperature because the material loses its strength and stiffness at this temperature.
Conventional polyamide materials, such as nylon 4.6 and nylon 6.6, which find wide application in car parts, do not satisfy all the aforementioned properties that are many times required for use in car parts. A drawback of nylon 6.6, for example, is that its heat deflection temperature is not high enough for many applications in car parts under the motorhood. The aliphatic nylon 4.6 does not show this limitation. A drawback of polyamide 4.6, however, is that it absorbs a relatively large amount of moisture, as a result of which its dimensional stability is in many cases insufficient.
SUMMARY OF THE INVENTION
The aim of the invention is a car part made from a polyamide composition that possesses a good balance of properties.
This aim is achieved in that 1 to approx. 40 wt. % of the chain units of the aliphatic polyamide of the composition is replaced by units derived from one or more cycloaliphatic dicarboxylic acids and an aliphatic diamine or one or more cycloaliphatic diamines and an aliphatic dicarboxylic acid.
It has been found that, as a result of the incorporation of the chain units based on cycloaliphatic dicarboxylic acids or cycloaliphatic diamines, the heat deflection temperature of, for example, nylon 6.6 is sufficiently increased and the moisture absorption of, for example, nylon 4.6 is sufficiently reduced without any concessions being made with respect to the mechanical and processing properties.
A most surprising advantage of the car parts according to the invention is that the incorporation of the chain units based on cycloaliphatic dicarboxylic acid or cycloaliphatic diamine in nylon 6.6 results in a considerable increase in tenacity. Another surprising advantage of the car parts according to the invention is that the incorporation of the chain units based on cycloaliphatic dicarboxylic acid or cycloaliphatic diamine results in a considerable improvement of the polymer composition's flow behaviour at a normal processing temperature. This makes it easier to incorporate a higher proportion of reinforcing materials, for example glass fibres, in the polyamide, and no thermal degradation of the polyamide takes place during the compounding and parts can be injection-moulded under less rigid conditions.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has surprisingly been found that reinforced, for example glass-fibre-reinforced, parts according to the invention show a much higher tenacity. A high tenacity, being the product of the tensile strength and the elongation at break, is advantageous because it substantially reduces the risk of the part breaking, for example during mounting in the vehicle.
The polyamide composition of the car parts according to the invention contains a polyamide whose main chain consists for 60-99 wt % of units derived from aliphatic dicarboxylic acids and diamines and is characterised in that the remaining chain units are derived from one or more cycloaliphatic dicarboxylic acids and an aliphatic diamine or one or more cycloaliphatic diamines and an aliphatic dicarboxylic acid.
The cycloaliphatic dicarboxylic acids are preferably cyclohexyl dicarboxylic acids. Suitable cyclohexyl dicarboxylic acids are for example 1,3-cyclohexyl dicarboxylic acid or 1,4-cyclohexyl dicarboxylic acid. Most preferable is 1,4-cyclohexyl dicarboxylic acid because then the invention is most effective.
The cycloaliphatic diamines are preferably cyclohexyl diamines. Suitable cyclohexyl diamines are for example 1,3-cyclohexyl diamine or 1,4-cyclohexyl diamine. Most preferable is 1,4-cyclohexyl diamine because the invention is then most effective.
Suitable aliphatic dicarboxylic acids are for example dicarboxylic acids with 1 to 16 methyl groups in their chain, more preferably 2 to 10 methyl groups. Most preferable is adipic acid. The alkyl groups are preferably linear; a small degree of branching, such that the crystallisation behaviour and other properties are not too adversely affected, is however allowed. The copolyamide of polyamide 6.6 and hexamethylene-1,4-cyclohexyl diamine is incidentally known from J. Pol. Sc. A-1, 8 3089-3111 (1970). The special possibilities and outstanding properties for use in car parts were however not noticed.
Suitable aliphatic diamines are for example diamines with 2 to 16 methyl groups in their chain. Diamines with 4 to 10 methyl groups in their chain are preferred. The most preferable are 2-methylpentane diamine, 1,4-tetramethylene diamine and 1,6-hexamethylene diamine.
The main chain preferably substantially consists of tetramethylene adipamide or hexamethylene adipamide units and combinations thereof.
The proportion of the chain units derived from a cycloaliphatic dicarboxylic acid and an aliphatic diamine or a cycloaliphatic diamine and an aliphatic dicarboxylic acid is at least 1 wt. % and at most 40 wt. %. In the case of less than 1 wt. % the invention has insufficient effect, in the case of more than 40 wt. % the crystallisation behaviour is so adversely affected and the melting point becomes so high that processing by means of for example injection-moulding becomes virtually impossible. The latter objection can incidentally be met by incorporating units of a third polyamide, generally with a lower melting point, for example units derived from an &agr;,&ohgr;-amino acid. The &agr;,&ohgr;-amino acid is preferably chosen from the group comprising 6-aminocaproic acid, 11-aminoundecanoic acid and 12-aminododecanoic acid or mixtures hereof.
What proportion is the most preferable will have to be determined for each individual case. In general, the preferred proportion of the units derived from the cycloaliphatic dicarboxylic acid or cycloaliphatic diamine will lie between 2 and 35 wt. %, most preferable will be 10 to 25 wt. %. The aliphatic diamine or dicarboxylic acid is generally the same as in the repeated units of which
Koning Cornelis E.
Tijssen Johannes
DSM N.V.
Hampton-Hightower P.
Pillsbury Madison & Sutro Intellectual Property Group
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