Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1997-07-28
2001-02-06
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C521S089000, C521S134000
Reexamination Certificate
active
06184293
ABSTRACT:
DESCRIPTION
Molding composition based on fluoropolymers and process for producing foam material therefrom
The invention relates to a molding composition based on fluoropolymers and a process for producing foam material by thermal treatment of the molding composition.
Foamed polymer compositions are well known. They are used, in particular, where low weight or a high strength/weight ratio is required. Foamed fluoropolymers can be used as chemical- or heat-resistant insulation material, e.g. in the construction of chemical apparatus. Foam material is customarily produced from polymer compositions by adding to the polymer composition a blowing agent which liberates gaseous dissociation products on heating. However, the residual products of these blowing agents can sometimes restrict and thus impair the later possible uses of the foam material.
It is an object of the present invention to develop a molding composition based on fluoropolymers and a foam material produced therefrom which does not require the addition of customary blowing agents to the polymer to be foamed, and also a process for producing such a foam material which makes possible strong foaming without addition of blowing agents.
It has surprisingly been found that a mixture of fluoropolymers with polymers containing sulfoxide groups in the polymer chain easily forms a foam material. The thermally unstable sulfoxide decomposes under the action of heat, with the sulfoxide groups being reduced to the sulfide. At the same time, oxygen or CO
2
and H
2
O are liberated, these acting as blowing agents.
For the purposes of the present invention, polymers containing sulfoxide groups are polymers which contain at least one arylene sulfoxide unit (—Ar—SO—; Ar=arylene). Arylenes are, for example, phenylene, biphenylene (—C
6
H
4
—C
6
H
4
—), naphthalene, anthracene or phenanthrene, which can in each case be monosubstituted or polysubstituted. Substituents are, for example, straight-chain, cyclic or branched C
1
-C
20
hydrocarbon radicals such as C
1
-C
10
-alkyl radicals, e.g. methyl, ethyl, n-propyl, iso-propyl, n-butyl, t-butyl, n-hexyl, or C
6
-C
14
-aryl radicals, e.g. phenyl or naphthyl, halogens, sulfonic acid groups, amino groups, nitro groups, cyano groups, hydroxy groups, alkyloxy groups or carboxyl groups.
A preferred polymer containing sulfoxide groups is polyphenylene sulfoxide which can, for example, easily be prepared by oxidation of polyphenylene sulfide with ozone or nitric acid.
The fluoropolymers used can be the following fluorothermoplastics comprising recurring units of the formulae (I) and (II):
where
R in (I) and (II) is a perfluorinated alkyl radical having from 1 to 8 carbon atoms, or a plurality of different radicals of this type; m and n are each numbers from 0.01 to 1 and the sum of n and m is always 1.
Further fluoropolymers which can be used are polymers comprising recurring units of the formulae (III)-(VII):
—(CF
2
—CF
2
)
m
—(CH
2
—CH
2
)
n
— (III)
—(CF
2
—C(Cl)F)
m
—(CH
2
—CH
2
)
n
— (IV)
—CF
2
—C(Cl)F— (V)
—CH
2
—CF
2
— (VI)
—CHF—CHF— (VII)
where n and m are as defined above.
Furthermore, the fluoropolymers used can be substances of the formula (II) or (II) in which fluorine is partially replaced by chlorine. The fluorothermoplastics of the formulae (I)-(VII) can be used individually or in mixtures with fluoropolymers.
The foaming effect achievable according to the invention depends on the type of polymer containing sulfoxide groups, in particular on the number of sulfoxide groups and on the proportion of the polymer containing sulfoxide groups in the fluoropolymer. In addition, the foaming effect depends on the melt viscosity of the fluoropolymer to be foamed.
According to the invention, the proportion of polymers containing sulfoxide groups in the total mixture is in the range from 1 to 50% by weight, preferably from 3 to 30% by weight, particularly 5 to 15% by weight, based on the total weight of the mixture.
The heating of the starting polymers can, according to the invention, be carried out in a temperature range from 240° C. to 360° C. The exact preferred temperature depends on the structure of the polymer containing sulfoxide groups which is used. Depending on the electronic structure on the sulfoxide (electron-withdrawing or electron-donating substituents), the sulfoxide group has a slightly different thermal stability. When using polyphenylene sulfoxide, the temperature is, for example, preferably in the range from 300° C. to 320° C. A polyphenylene sulfoxide brominated on the phenyl group is preferably found in the range from 260° C. to 300° C.
According to the invention, the fluoropolymers used can also be mixtures of various fluoropolymers and the polymers containing sulfoxide groups which are used can also be mixtures of various polymers containing sulfoxide groups. The addition of further polymers such as, for example, polyphenylene sulfide to the mixture to be foamed is also possible.
The molding composition comprising the fluoropolymer and the polymer containing sulfoxide groups can generally be used as unblended material. However, it is also possible to add further fillers such as chalk, talc, clay, mica and/or fibrous reinforcements such as glass and carbon fibers, whiskers, and also further additives and processing aids, e.g. lubricants, mold release agents, antioxidants, UV stabilizers, so that commercial, filled fluoropolymers can be used for foam production.
The fluoropolymers can be used, for example, as powder, compacts or films. The powders here possess commercial particle sizes, with granulated materials also being able to be used. It is also possible to use films or film scraps in a suitable form.
The polymers containing sulfoxide groups should be used in powder form to achieve a uniform foam. The mean particle size (D
50
) is in the range from 0.3×10
−6
to 500×10
−6
m, preferably from 0.5×10
−6
to 300×10
−6
m and in particular from 0.5×10
−6
to 200×10
−6
m.
The mean molecular weight of the polymers containing sulfoxide groups, expressed as the weight average M
w
, is, according to the invention, between 4,000 and 200,000 g/mol, preferably between 10,000 and 150,000 g/mol, particularly preferably between 25,000 and 100,000 g/mol.
The molding composition of the invention as such or likewise the foam material produced therefrom can be used for producing shaped parts. The shaped parts can be used as functional components capable of withstanding high stresses, for example in aircraft and automobile construction. Further possible uses of the shaped parts are in construction of chemical apparatus. The foam materials or shaped parts can serve as chemical- or heat-resistant insulation materials.
The materials can be free-foamed or foamed in pressing molds so that ready-finished components can be obtained.
Advantages of the process of the invention for producing foamed fluoropolymer structures are that
no addition of low molecular weight blowing agents is necessary,
the process can be carried out using simple technical means,
fluoropolymer foams having a particularly low density are possible
and the degree of foaming and the pore size can be set within a wide range.
REFERENCES:
patent: 5708089 (1998-01-01), Scheckenbach
patent: 5721282 (1998-02-01), Schonfeld
patent: 5750221 (1998-05-01), Scheckenbach
Frank Georg
Scheckenbach Helmut
Schleicher Andreas
Schonfeld Axel
Buttner David J.
Connolly Dove Lodge & Hutz LLP
Hoechst AG
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