Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-01-11
2001-02-13
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C525S420000, C525S421000, C525S423000, C525S425000, C525S438000, C525S445000, C521S079000, C521S135000, C521S138000, C264S050000, C264S054000
Reexamination Certificate
active
06187830
ABSTRACT:
The present invention relates to a process for the preparation of foamed articles having a foam density of less than 180 kg/m
3
and an average cell diameter of less than 1.5 mm.
Conventional semi-crystalline thermoplastic resins such as aromatic polyester resins and polyamides are known to have poor melt strength. Hence, molten semi-crystalline thermoplastic resin tends to quickly collapse when foamed. Conventional foamed semi-crystalline thermoplastic resin generally also may have poor mechanical properties, due to broad differences in cell size, cell wall thickness, and the like. A method was developed which consists of saturating amorphous aromatic polyester resin at high pressure with CO
2
and subsequent foaming in the amorphous state. This method, however, is laborious and economically disadvantageous.
To overcome the above-mentioned disadvantages, several solutions have been proposed:
1. The use of anhydride-functional compounds such as described in JP-A-08-151470, WO 90/10667, EP-A-0 475 142, WO 94/17131, EP-A-0 442 759, EP-A-0 372 846, EP-A-0 719 626, WO 93/12164, and WO 97/11126.
2. The use of copolymers prepared from a monomer mixture comprising among others (meth)acrylic acid, alkyl (meth)acrylate and/or vinyl alcohol such as described in U.S. Pat. No. 5,482,977.
3. The use of epoxy-functional compounds such as described in EP-A-0 026 554, JP-A-62001732, and JP-A-63082955.
However, solutions 1 and 2 have to be carried out in at least two process steps. Solution 3 requires the addition of a compound of Group Ia, IIa, or IIIa of the Periodic Table in the extrusion process, such as LiCl.
The invention now provides a process for the preparation of foamed articles having a foam density of less than 180 kg/m
3
and an average cell diameter of less than 1.5 mm comprising the extrusion of a molten semi-crystalline thermoplastic resin composition in the presence of a foaming agent, with the semi-crystalline thermoplastic resin composition comprising a polymeric epoxide containing at least two epoxide groups and said polymeric epoxide being a copolymer of a monomer mixture comprising at least one C
10
to C
18
-olefin and at least one ethylenically unsaturated compound comprising an epoxide group.
It has been found that the addition of a polymeric epoxide according to the present invention to the semi-crystalline thermoplastic resin composition results in foamed articles having a regular and homogeneous structure with a low density. Another advantage of the present invention is that it is not necessary anymore to add a compound of Group Ia, IIa, or IIIa of the Periodic Table, such as LiCl, to the extrusion process.
EP-A-0 511 475 discloses a polyester resin composition comprising an olefinic copolymer composed of an olefinic monomer and an unsaturated acid alkyl ester monomer in a molar ratio of 5:1 to 1000:1. The monomers are preferably selected from ethene and glycidyl (meth)acrylate. The polymeric epoxide of the present invention is not disclosed. Furthermore, although a foaming agent may be introduced into the polyester resin composition, it is not disclosed or suggested anywhere that the use of the present polymeric epoxides would result in such good properties in foamed articles of semi-crystalline thermoplastic resin.
The polymeric epoxide may be prepared in any conventional way. The polymeric epoxide preferably has an epoxide content of 1 to 7 moles/kg, 1.5-5 moles/kg being particularly preferred.
Preferably, the olefin has 12 to 18 carbon atoms. More preferably, the olefin is a C
12
to C
18
&agr;-olefin, such as dodecene-1, tridecene-1, tetradecene-1, pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1, and mixtures thereof.
The ethylenically unsaturated compound comprising an epoxide group preferably is an ethylenically unsaturated glycidyl ester. More preferably, this compound is elected from the group of glycidyl (meth)acrylate, itaconic acid monoglycidyl ester, butene tricarboxylic acid mono-, di-, and triglycidyl esters, &agr;-chloroallyl glycidyl ester, maleic acid glycidyl ester, crotonic acid glycidyl ester, fumaric acid glycidyl ester, and mixtures thereof. Glycidyl (meth)acrylate is preferred.
The molar ratio between C
12
to C
18
-olefin and the ethylenically unsaturated compound comprising an epoxide group preferably is 0.1-5:1, more preferably 0.4-2:1.
Optionally, other monomers may be present, such as (meth)acrylic acid esters of methyl, ethyl, propyl, butyl, 2-ethylhexyl, cyclohexyl, dodecyl, and octadecyl; monoesters or diesters of maleic acid, itaconic acid, and fumaric acid; vinyl esters such as vinyl propionate, vinyl acetate, vinyl capronate, vinyl carpylate, vinyl laurate, vinyl stearate, and vinyl trifluoroacetate; and mixtures thereof. The copolymer may comprise about 0 to 40 mole % of these monomers.
About 0.1 to 10 wt. % of polymeric epoxide, preferably 0.5 to 9 wt. %, based on semi-crystalline thermoplastic resin, may be introduced into the semi-crystalline thermoplastic resin prior to or during extrusion. However, it has been found that there is an optimum amount for each polymeric epoxide used in the process of the present invention. As it is required that a foam having a foam density of less than 180 kg/m
3
and an average cell diameter of less than 1.5 mm is obtained, the person of ordinary skill in the art will be able within the teachings of the present invention to provide the optimum range of amounts for the polymeric epoxide to be used. Without wishing to be bound by the following theory, we believe that the beneficial effect of the polymeric epoxide can be attributed to the positive influence of the polymeric epoxide on the melt strength of the mixture with the semi-crystalline thermoplastic resin.
The semi-crystalline thermoplastic resin is selected from the group of polyester resins, polyamide resins, and mixtures thereof. Optionally, other homo- or copolymers may be present in the semi-crystalline thermoplastic resin composition, such as polyethylene, polypropylene, polycarbonates, and mixtures thereof, in an amount of up to 20 wt. %. The polyester resin is preferred.
The polyester resin is derived from a dicarboxylic acid and a diol. The dicarboxylic acid may be selected from aliphatic dicarboxylic acids, aromatic dicarboxylic acids, and mixtures thereof. Aliphatic dicarboxylic acids include succinic acid, adipic acid, sebacic acid, and mixtures thereof. Aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenylether dicarboxylic acid, diphenyl dicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, and mixtures thereof. Typical examples of the diol include polymethylene-&agr;,&ohgr;-diols, such as ethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, cyclohexane dimethylol, tricyclodecane dimethylol, 2,2-bis(4-&bgr;-hydroxyethoxyphenyl) propane, 4,4′-bis(&bgr;-hydroxyethoxy)diphenylsulfone, diethylene glycol, and mixtures thereof. Amide and carbonate compounds also may be used in the monomer mixture to prepare the polyester resin. Polyethylene terephthalate and polybutylene terephthalate are especially preferred.
The polyester resin may also include recycled polyester resin up to 100%. Industrial and/or post-consumer polyester recycled resins generally are in more than abundant supply. Accordingly, it is a further advantage of the present invention that recycled polyester resin can also be used in the present process. The melt strength and the viscosity of recycled polyester resin generally are too low to produce adequately foamed structures with practical density reductions using conventional foam technology. However, it has surprisingly been found that in the process of the present invention foamed articles can be made from recycled polyester resin without the disadvantages mentioned above.
Every conventional foaming agent may be used. Examples include inert gases such as CO
2
and nitrogen, hydrocarbons boil
Beijers Gerard Henk
Boven Geert
Jelenic Jernej
Acquah Samuel A.
Akzo Nobel nv
Fennelly Richard P.
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