Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2003-02-06
2004-06-01
Thexton, Matthew A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S215000, C523S438000, C523S468000, C524S847000
Reexamination Certificate
active
06743832
ABSTRACT:
The invention relates to a thermosetting resin composition containing a radically curable resin mixture as matrix, in which 2D-randomly distributed, discontinuous carbon fibres as well as other additives are present. Thermosetting resin compositions are also referred to as compounds. Such compounds can be prepared and processed for example in the form of sheets and are then also referred to as Sheet Moulding Compounds (SMCs). Bulk preparation and processing of the compounds is also possible. The invention also relates to a process for the preparation of a thermosetting resin composition, as well as to processes for the manufacture of 3D-moulded articles from this thermosetting resin composition and to 3D-moulded articles manufactured from a thermosetting resin composition.
Thermosetting resin compositions containing a radically curable resin mixture as matrix, 2D-randomly distributed, discontinuous carbon fibres as well as other additives are described in an article by N. Tsuchiyama, Progress in Science and Engineering of Composites, Proceedings of the ICCM-IV, Tokyo, (1982), volume 1, 497-503. This reference relates to thermosetting resin compositions that are mainly used in SMCs. The resin composition from the article by N. Tsuchiyama is obtained by adding 20-55% by volume of chopped carbon fibre bundles with a K value of between 1-30 to a radically curable resin mixture containing 100 parts by weight of a polyester resin, 1.5 parts by weight of magnesium oxide and 1 part by weight of t-butylperbenzoate. According to the author, SMCs are obtained that show good mechanical properties if the percentage by volume of carbon fibres is between 40 and 45 and the K value of the carbon fibre bundle is 6. When use is made of chopped carbon fibre bundles with a K value higher than 6, products with much poorer mechanical properties are obtained.
The K value of a fibre bundle means the number of filaments present in the fibre bundle divided by a factor of 1000.
A serious drawback of the resin compositions in the prior art is that in the production of good SMCs relatively large numbers of fibre bundles need to be introduced next to each other (or partly on top of each other) in a chopper in order to produce an SMC with a sufficiently homogeneously distributed and easily wettable fibre bed.
The present invention aims to provide a thermosetting resin composition containing a radically curable resin mixture as matrix, 2D-randomly distributed, discontinuous carbon fibres and other additives that does not present the aforementioned drawback.
The resin composition according to the invention is characterized in that the radically curable resin mixture consists of:
(a) 50-100 parts by weight of a radically curable resin that also contains a free monomer capable of copolymerising with it
(b) 0-50 parts by weight of a shrink-resistant compound that may also contain an amount of copolymerisable free monomer, the total of (a) and (b) adding up to 100,
and in that the 2D-randomly distributed, discontinuous carbon fibres are obtained by chopping split, continuous carbon fibre bundles, which carbon fibre bundles are provided with a sizing that is at least partially chemically bonded thereto and a binder whose solubility at room temperature in the copolymerisable free monomer present amounts to at least 10% by weight and in that the weight percentage of carbon fibres relative to the resin composition is between 5 and 65% by weight,
and in that optionally also a filler is present in the resin composition.
Surprisingly, a resin composition has now been obtained in which the carbon fibres are well impregnated and are completely 2D-randomly and homogeneously distributed throughout the resin composition.
A 2D-random distribution of fibre bundles means a distribution in which the direction of the fibre bundles in the plane in which the fibre bundles are distributed shows no regularity.
The chopped, split, continuous carbon fibre bundles with the sizings and binders specified above show an excellent falling behaviour. As a result, it is now very well possible to use significantly fewer bobbins than in the prior art to produce compounds, for example SMCs, with a 2D-randomly distributed and homogeneous and easily wettable fibre distribution. This is especially important in the manufacture of wide SMCs, for example wider than 70 cm, which are essential for the manufacture of very large moulded articles (e.g. car roofs etc.) with a minimum of weld lines, via the use of large inlay sheets.
A further advantage of the invention is that resin compositions with a relatively low density can be produced. Moreover they are particularly suitable for EMI shielding and parts with a Class-A surface can also be produced.
Another important advantage of the resin compositions according to the invention is that they are also eminently suitable for bulk processing, for example via processing by means of extrusion-compression (also referred to as “injection compression moulding” or “transfer-compression moulding”).
In the radically curable resin mixture use is made in the invention of a radically curable resin (a). In general, resins that contain an unsaturation are radically curable. Examples of such resins are: vinyl ester resins. unsaturated-polyester resins and hybrid resins.
Suitable vinyl ester resins, also known as epoxy (meth)acrylates, that may be employed in the resin composition according to the invention, are addition products of polyepoxides and unsaturated carboxylic acids, preferably acrylic acid and methacrylic acid. Suitable polyepoxides are epoxy novolac resins and in particular polyepoxides based on bisphenol-A. A similarly suitable class of vinyl ester resins are the esterification products of alkoxylated bisphenol-A with (meth)acrylic acid. Examples of these are the ATLAC™ resins of DSM Composite Resins, Zwolle, the Netherlands)
Suitable unsaturated polyester resins that may be employed in the resin composition according to the invention are polyesters obtained by reaction of organic compounds that contain carboxyl and/or alcohol groups. At least one of the starting compounds then contains unsaturated compounds. Examples of these are the PALATAL™ resins of DSM Composite Resins.
Suitable hybrid resins that may be used in the resin composition according to the invention are resins that form a polyester-urethane hybrid network by reacting low-molecular starting compounds with each other in situ. Examples of these are the DARON™ resins of DSM Composite Resins.
Preferably, use is made in the invention of vinyl ester resins or unsaturated polyester resins.
The free monomer that is copolymerisable with the radically curable resin in the resin mixture contains one or more vinyl groups, and usually fewer than 50 carbon atoms. Examples of suitable copolymerisable free monomers are of the vinyl aromatic, vinyl ether, vinyl ester, acrylate and/or allyl type. Preferably, the free monomer is vinyl aromatic. Suitable vinyl aromatic monomers are for example styrene, &agr;-methyl styrene, o-, m-, p-methyl styrene, p-chlorostyrene, t-butyl styrene, divinyl benzene, bromostyrene, vinyl naphthalene, &agr;-chlorostyrene and divinylnaphthalene. Preferably, styrene is used.
The suitable amount of radically curable resin and copolymerisable free monomer in the resin mixture according to the invention is usually between 50 and 100 parts by weight relative to the total of (a) and (b) being 100 parts by weight. It is to be noticed, however, that in such cases where the amount of (a) is closer to 100 and that of (b) is closer to 0, handling of the radically curable resin pastes tends to become more difficult because of low values of viscosity. In such cases, and particularly in combination with a low amount of filler (i.e. at about 0-10 parts by weight relative to the total of (a) and (b)), one skilled in the art will, if desired, use other additives such as thixotropic agents (viscosity modifiers) or other amounts of copolymerisable free monomer (styrene) in order to adjust the viscosity of the resin mixture to such a suitable value that
Hornman Hans Hubertus Henricus
Janse Gerardus Hubertus Anna
Van Der Ploeg Antonius Franciscus Maria Josephus
Van Dijk Hans Klaas
DSM IP Assets B.V.
Pillsbury & Winthrop LLP
Thexton Matthew A.
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